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1
Coolen-Schrijner, Pauline, Andrew Hart, and Phil Pollett. "Quasistationarity of continuous-time Markov chains with positive drift." Journal of the Australian Mathematical Society. Series B. Applied Mathematics 41, no. 4 (April 2000): 423–41. http://dx.doi.org/10.1017/s0334270000011735.
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AbstractWe shall study continuous-time Markov chains on the nonnegative integers which are both irreducible and transient, and which exhibit discernible stationarity before drift to infinity “sets in”. We will show how this ‘quasi’ stationary behaviour can be modelled using a limiting conditional distribution: specifically, the limiting state probabilities conditional on not having left 0 for the last time. By way of a dual chain, obtained by killing the original process on last exit from 0, we invoke the theory of quasistationarity for absorbing Markov chains. We prove that the conditioned state probabilities of the original chain are equal to the state probabilities of its dual conditioned on non-absorption, thus allowing to establish the simultaneous existence and then equivalence, of their limiting conditional distributions. Although a limiting conditional distribution for the dual chain is always quasistationary distribution in the usual sense, a similar statement is not possible for the original chain.
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Girtler, Jerzy. "Limiting Distribution of the Three-State Semi-Markov Model of Technical State Transitions of Ship Power Plant Machines and its Applicability in Operational Decision-Making." Polish Maritime Research 27, no. 2 (June 1, 2020): 136–44. http://dx.doi.org/10.2478/pomr-2020-0035.
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AbstractThe article presents the three-state semi-Markov model of the process {W(t): t ≥ 0} of state transitions of a ship power plant machine, with the following interpretation of these states: s1 – state of full serviceability, s2 – state of partial serviceability, and s3 – state of unserviceability. These states are precisely defined for the ship main engine (ME). A hypothesis is proposed which explains the possibility of application of this model to examine models of real state transitions of ship power plant machines. Empirical data concerning ME were used for calculating limiting probabilities for the process {W(t): t ≥ 0}. The applicability of these probabilities in decision making with the assistance of the Bayesian statistical theory is demonstrated. The probabilities were calculated using a procedure included in the computational software MATHEMATICA, taking into consideration the fact that the random variables representing state transition times of the process {W(t): t ≥ 0} have gamma distributions. The usefulness of the Bayesian statistical theory in operational decision-making concerning ship power plants is shown using a decision dendrite which maps ME states and consequences of particular decisions, thus making it possible to choose between the following two decisions: d1 – first perform a relevant preventive service of the engine to restore its state and then perform the commissioned task within the time limit determined by the customer, and d2 – omit the preventive service and start performing the commissioned task.
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Kulkarni, Vidyadhar, and Tomasz Rolski. "Fluid Model Driven by an Ornstein-Uhlenbeck Process." Probability in the Engineering and Informational Sciences 8, no. 3 (July 1994): 403–17. http://dx.doi.org/10.1017/s0269964800003491.
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In this paper we consider a fluid model of a single buffer in a random external environment modeled by an Ornstein-Uhlenbeck process. Such a model appears as the limiting case of the multiplexing model of Anick, Mitra, and Sondhi [2] in a heavy traffic environment. We use the change of measure technique to derive an exponential upper bound on the tail probabilities of the steady-state buffer content. We also establish an asymptotic upper and lower exponential bounds on the tail probabilities.
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Sarsour, Wajeeh Mustafa, and Shamsul Rijal Muhammad Sabri. "Forecasting the Long-Run Behavior of the Stock Price of Some Selected Companies in the Malaysian Construction Sector: A Markov Chain Approach." International Journal of Mathematical, Engineering and Management Sciences 5, no. 2 (April 1, 2020): 296–308. http://dx.doi.org/10.33889/ijmems.2020.5.2.024.
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The fluctuations in stock prices produce a high risk that makes investors uncertain about their investment decisions. The present paper provides a methodology to forecast the long-term behavior of five randomly selected equities operating in the Malaysian construction sector. The method used in this study involves Markov chains as a stochastic analysis, assuming that the price changes have the proparty of Markov dependency with their transition probabilities. We identified a three-state Markov model (i.e., increase, stable, fall) and a two-state Markov model (i.e., increase and fall). The findings suggested that the chains had limiting distributions. The mean return time was computed for respective equities as well as to determine the average duration to return to a stock price increase. The analysis might aid investors in improving their investment knowledge, and they will be able to make better decisions when an equity portfolio possesses higher transition probabilities, higher limiting distribution, and lowest mean return time in response to a price increase. Finally, our investigations suggest that investors are more likely to invest in the GKent based on the three-state model, while VIZIONE seems to be a better investment choice based on a two-state model.
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Pollett, P. K., and A. J. Roberts. "A description of the long-term behaviour of absorbing continuous-time Markov chains using a centre manifold." Advances in Applied Probability 22, no. 1 (March 1990): 111–28. http://dx.doi.org/10.2307/1427600.
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We use the notion of an invariant manifold to describe the long-term behaviour of absorbing continuous-time Markov processes with a denumerable infinity of states. We show that there exists an invariant manifold for the forward differential equations and we are able to describe the evolution of the state probabilities on this manifold. Our approach gives rise to a new method for calculating conditional limiting distributions, one which is also appropriate for dealing with processes whose transition probabilities satisfy a system of non-linear differential equations.
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Pollett, P. K., and A. J. Roberts. "A description of the long-term behaviour of absorbing continuous-time Markov chains using a centre manifold." Advances in Applied Probability 22, no. 01 (March 1990): 111–28. http://dx.doi.org/10.1017/s0001867800019364.
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We use the notion of an invariant manifold to describe the long-term behaviour of absorbing continuous-time Markov processes with a denumerable infinity of states. We show that there exists an invariant manifold for the forward differential equations and we are able to describe the evolution of the state probabilities on this manifold. Our approach gives rise to a new method for calculating conditional limiting distributions, one which is also appropriate for dealing with processes whose transition probabilities satisfy a system of non-linear differential equations.
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Rodriguez, Patricia J., Zachary J. Ward, Michael W. Long, S. Bryn Austin, and Davene R. Wright. "Applied Methods for Estimating Transition Probabilities from Electronic Health Record Data." Medical Decision Making 41, no. 2 (February 2021): 143–52. http://dx.doi.org/10.1177/0272989x20985752.
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Background Electronic health record (EHR) data contain longitudinal patient information and standardized diagnostic codes. EHR data may be useful for estimating transition probabilities for state-transition models, but no guidelines exist on appropriate methods. We applied 3 potential methods to estimate transition probabilities from EHR data, using pediatric eating disorders (EDs) as a case study. Methods We obtained EHR data from PEDsnet, which includes 8 US children’s hospitals. Data included inpatient, outpatient, and emergency department visits for all patients with an ED. We mapped diagnoses to 3 ED health states: anorexia nervosa, bulimia nervosa, and other specified feeding or eating disorder. We estimated 1-y transition probabilities for males and females using 3 approaches: simple first-last proportions, a multistate Markov (MSM) model, and independent survival models. Results Transition probability estimates varied widely between approaches. The first-last proportion approach estimated higher probabilities of remaining in the same health state, while the MSM and independent survival approaches estimated higher probabilities of transitioning to a different health state. All estimates differed substantially from published literature. Limitations As a source of health state information, EHR data are incomplete and sometimes inaccurate. EHR data were especially challenging for EDs, limiting the estimation and interpretation of transition probabilities. Conclusions The 3 approaches produced very different transition probability estimates. Estimates varied considerably from published literature and were rescaled and calibrated for use in a microsimulation model. Estimation of transition probabilities from EHR data may be more promising for diseases that are well documented in the EHR. Furthermore, clinicians and health systems should work to improve documentation of ED in the EHR. Further research is needed on methods for using EHR data to inform transition probabilities.
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Stadje, Wolfgang. "Stationarity of a stochastic population flow model." Journal of Applied Probability 36, no. 1 (March 1999): 291–94. http://dx.doi.org/10.1239/jap/1032374251.
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We consider a classical population flow model in which individuals pass through n strata with certain state-dependent probabilities and at every time t = 0,1,2,…, there is a stochastic inflow of new individuals to every stratum. For a stationary inflow process we prove the convergence of the joint distribution of group sizes and derive the limiting Laplace transform.
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Stadje, Wolfgang. "Stationarity of a stochastic population flow model." Journal of Applied Probability 36, no. 01 (March 1999): 291–94. http://dx.doi.org/10.1017/s002190020001706x.
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We consider a classical population flow model in which individuals pass through n strata with certain state-dependent probabilities and at every time t = 0,1,2,…, there is a stochastic inflow of new individuals to every stratum. For a stationary inflow process we prove the convergence of the joint distribution of group sizes and derive the limiting Laplace transform.
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Fuh, C. D. "Corrected Diffusion Approximations for Ruin Probabilities in a Markov Random Walk." Advances in Applied Probability 29, no. 3 (September 1997): 695–712. http://dx.doi.org/10.2307/1428082.
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Let (X, S) = {(Xn, Sn); n ≧0} be a Markov random walk with finite state space. For a ≦ 0 < b define the stopping times τ= inf {n:Sn > b} and T= inf{n:Sn∉(a, b)}. The diffusion approximations of a one-barrier probability P {τ < ∝ | Xo= i}, and a two-barrier probability P{ST ≧b | Xo = i} with correction terms are derived. Furthermore, to approximate the above ruin probabilities, the limiting distributions of overshoot for a driftless Markov random walk are involved.
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Fuh, C. D. "Corrected Diffusion Approximations for Ruin Probabilities in a Markov Random Walk." Advances in Applied Probability 29, no. 03 (September 1997): 695–712. http://dx.doi.org/10.1017/s0001867800028305.
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Let (X, S) = {(Xn , Sn ); n ≧0} be a Markov random walk with finite state space. For a ≦ 0 < b define the stopping times τ= inf {n:Sn > b} and T= inf{n:Sn ∉(a, b)}. The diffusion approximations of a one-barrier probability P {τ < ∝ | X o = i}, and a two-barrier probability P{ST ≧b | X o = i} with correction terms are derived. Furthermore, to approximate the above ruin probabilities, the limiting distributions of overshoot for a driftless Markov random walk are involved.
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Panorias, C., A. Papadopoulou, and T. Tsapanos. "ON THE EARTHQUAKE OCCURRENCES IN JAPAN AND THE SURROUNDING AREA VIA SEMI MARKOV MODELING." Bulletin of the Geological Society of Greece 50, no. 3 (July 27, 2017): 1535. http://dx.doi.org/10.12681/bgsg.11866.
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In the present paper, the earthquake occurrences in the area of Japan, are studied by a semi Markov model which is considered homogeneous in time. The data applied refer to earthquakes of large magnitude (Mw>6.0) during the period 1900-2012. We consider 9 seismic zones derived from the typical 11 zones for the area of Japan, due to the lack of data for 3 zones (9-th,10-th and 11-th). Also, we define 3 groups for the magnitudes, corresponding to 6-7,7.1-8 and M> 8.0. Thus, we consider for our semi Markov model a finite state space, S={ ( ,)j i ZR | i=1,...9, j=1,2,3}, where i Z defines the i-th seismic zone and j R states the j-th magnitude scale. We applied the data to describe the interval transition probabilities for the states and the model's limiting behaviour for which is sufficient an interval of time of seven years. The time unit of the model is considered to be one day. Some interesting results, concerning the interval transition probabilities and the limiting state vector, are derived.
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Beuerman, Steven L., and Edward J. Coyle. "State space expansions and the limiting behavior of quasi-birth-and-death processes." Advances in Applied Probability 21, no. 2 (June 1989): 284–314. http://dx.doi.org/10.2307/1427161.
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The notion of complete level crossing information, or LCI-completeness, is introduced for quasi-birth-death (QBD) processes. It is shown that state space expansions allow any QBD-process to be modified so that it is LCI-complete.For any LCI-complete, QBD-process, there exists a matrix W such that , where is the vector of limiting probabilities for all states on level n of the process. When W cannot be found in closed form, it can be found via an algorithm requiring fewer than m steps, where m is the number of states on each level of the process. The result of this algorithm is always a linear matrix equation for which W is the solution.In essentially all cases considered in this paper, the matrix W is a solution of the matrix quadraticX2A2 + XA1 + A0 = 0.Despite this fact, W is never equal to Neuts' rate matrix R, although the non-zero eigenvalues and the corresponding left eigenvectors of R are a subset of the eigenvalues and left eigenvectors of W. This fact leads to two methods for determining R from W.If the transition rates of the QBD-process are level-dependent, then it is also shown that matrices W(n) exist such that .
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Beuerman, Steven L., and Edward J. Coyle. "State space expansions and the limiting behavior of quasi-birth-and-death processes." Advances in Applied Probability 21, no. 02 (June 1989): 284–314. http://dx.doi.org/10.1017/s0001867800018553.
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The notion of complete level crossing information, or LCI-completeness, is introduced for quasi-birth-death (QBD) processes. It is shown that state space expansions allow any QBD-process to be modified so that it is LCI-complete. For any LCI-complete, QBD-process, there exists a matrix W such that , where is the vector of limiting probabilities for all states on level n of the process. When W cannot be found in closed form, it can be found via an algorithm requiring fewer than m steps, where m is the number of states on each level of the process. The result of this algorithm is always a linear matrix equation for which W is the solution. In essentially all cases considered in this paper, the matrix W is a solution of the matrix quadratic X 2 A 2 + XA 1 + A 0 = 0. Despite this fact, W is never equal to Neuts' rate matrix R , although the non-zero eigenvalues and the corresponding left eigenvectors of R are a subset of the eigenvalues and left eigenvectors of W . This fact leads to two methods for determining R from W . If the transition rates of the QBD-process are level-dependent, then it is also shown that matrices W(n) exist such that .
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Kuz’min, D. A., and A. Yu Kuz’michevskiy. "THE SAFETY FACTORS OF PROBABILITY REACHING LIMITING STATES OF NPP EQUIPMENTS AND PIPELINES DURING DIFFERENT OPERATING MODES." Spravochnik. Inzhenernyi zhurnal, no. 291 (June 2021): 18–23. http://dx.doi.org/10.14489/hb.2021.06.pp.018-023.
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Reliability theory makes it possible to determine the probabilities of destruction, reaching limit states, equipment and pipeline failures (E&P). Normative documents, as a rule, define requirements for integral indicators of reliability or safety of objects, but do not establish requirements for admissible values of probabilities for individual systems and data elements of objects. This article proposes the approach for determining the permissible values of the probabilities of reaching the yield stress or ultimate strength by operating stresses on the basis of design data on loads and data from certificates on the mechanical properties of metal. During operation, the achievement of the working stresses in metal of E&P value of the permissible stress values is a probabilistic event, in this fact, the probabilistic approach has been developed to obtain the safety factor of probability reaching limiting states. The developed approach is based on the methods of strength science, statistical analysis and probability theory. The object of application of the developed approach is thermal mechanical equipment used in different branches of technology. Using the example of the main circulation pipeline of the NPP with WWER-440, the presence of a reserve in the probability of reaching the limit state is shown and a relationship is established between the stress variation coefficient and the calculated probability for normal operation and abnormal operation. This approach determines the reserve for the probability of destruction, which will justify the extension of the resource or optimize the operating parameters of the objects under consideration.
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Schrijner, Pauline, and Erik A. Van Doorn. "Weak convergence of conditioned birth-death processes in discrete time." Journal of Applied Probability 34, no. 01 (March 1997): 46–53. http://dx.doi.org/10.1017/s0021900200100683.
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We consider a discrete-time birth-death process on the non-negative integers with −1 as an absorbing state and study the limiting behaviour asn →∞ of the process conditioned on non-absorption until timen.By proving that a condition recently proposed by Martinez and Vares is vacuously true, we establish that the conditioned process is always weakly convergent when all self-transition probabilities are zero. In the aperiodic case we obtain a necessary and sufficient condition for weak convergence.
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Schrijner, Pauline, and Erik A. Van Doorn. "Weak convergence of conditioned birth-death processes in discrete time." Journal of Applied Probability 34, no. 1 (March 1997): 46–53. http://dx.doi.org/10.2307/3215173.
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We consider a discrete-time birth-death process on the non-negative integers with −1 as an absorbing state and study the limiting behaviour as n → ∞ of the process conditioned on non-absorption until time n. By proving that a condition recently proposed by Martinez and Vares is vacuously true, we establish that the conditioned process is always weakly convergent when all self-transition probabilities are zero. In the aperiodic case we obtain a necessary and sufficient condition for weak convergence.
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Van Doorn, Erik A. "Quasi-stationary distributions and convergence to quasi-stationarity of birth-death processes." Advances in Applied Probability 23, no. 4 (December 1991): 683–700. http://dx.doi.org/10.2307/1427670.
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For a birth–death process (X(t), ) on the state space {−1, 0, 1, ·· ·}, where −1 is an absorbing state which is reached with certainty and {0, 1, ·· ·} is an irreducible class, we address and solve three problems. First, we determine the set of quasi-stationary distributions of the process, that is, the set of initial distributions which are such that the distribution of X(t), conditioned on non-absorption up to time t, is independent of t. Secondly, we determine the quasi-limiting distribution of X(t), that is, the limit as t→∞ of the distribution of X(t), conditioned on non-absorption up to time t, for any initial distribution with finite support. Thirdly, we determine the rate of convergence of the transition probabilities of X(t), conditioned on non-absorption up to time t, to their limits. Some examples conclude the paper. Our main tools are the spectral representation for the transition probabilities of a birth–death process and a duality concept for birth–death processes.
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Van Doorn, Erik A. "Quasi-stationary distributions and convergence to quasi-stationarity of birth-death processes." Advances in Applied Probability 23, no. 04 (December 1991): 683–700. http://dx.doi.org/10.1017/s0001867800023880.
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For a birth–death process (X(t), ) on the state space {−1, 0, 1, ·· ·}, where −1 is an absorbing state which is reached with certainty and {0, 1, ·· ·} is an irreducible class, we address and solve three problems. First, we determine the set of quasi-stationary distributions of the process, that is, the set of initial distributions which are such that the distribution of X(t), conditioned on non-absorption up to time t, is independent of t. Secondly, we determine the quasi-limiting distribution of X(t), that is, the limit as t→∞ of the distribution of X(t), conditioned on non-absorption up to time t, for any initial distribution with finite support. Thirdly, we determine the rate of convergence of the transition probabilities of X(t), conditioned on non-absorption up to time t, to their limits. Some examples conclude the paper. Our main tools are the spectral representation for the transition probabilities of a birth–death process and a duality concept for birth–death processes.
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Khandakar, Mostafizar, and Kuldeep Kumar Kataria. "Some Compound Fractional Poisson Processes." Fractal and Fractional 7, no. 1 (December 25, 2022): 15. http://dx.doi.org/10.3390/fractalfract7010015.
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In this paper, we introduce and study fractional versions of the Bell–Touchard process, the Poisson-logarithmic process and the generalized Pólya–Aeppli process. The state probabilities of these compound fractional Poisson processes solve a system of fractional differential equations that involves the Caputo fractional derivative of order 0<β<1. It is shown that these processes are limiting cases of a recently introduced process, namely, the generalized counting process. We obtain the mean, variance, covariance, long-range dependence property, etc., for these processes. Further, we obtain several equivalent forms of the one-dimensional distribution of fractional versions of these processes.
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Aoki, Masanao, and Yoshimasa Shirai. "A NEW LOOK AT THE DIAMOND SEARCH MODEL: STOCHASTIC CYCLES AND EQUILIBRIUM SELECTION IN SEARCH EQUILIBRIUM." Macroeconomic Dynamics 4, no. 4 (December 2000): 487–505. http://dx.doi.org/10.1017/s1365100500017041.
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We recast Diamond's search equilibrium model into that with a finite number of agents. The state of the model is described by a jump-Markov process, the transition rates of which are functions of the reservation cost, which are endogenously determined by value maximization by rational agents. The existence of stochastic fluctuations causes the fraction of the employed to move from one basin of attraction to the other with positive probabilities when the dynamics have multiple equilibria. Stochastic asymmetric cycles that arise are quite different from the cycles of the set of Diamond–Fudenberg nonlinear deterministic differential equations. By taking the number of agents to infinity, we get a limiting probability distribution over the stationary state equilibria. This provides a natural basis for equilibrium selection in models with multiple equilibria, which is new in the economic literature.
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Yue, Dequan, Wuyi Yue, and Guoxi Zhao. "Analysis of an M/M/cQueueing System with Impatient Customers and Synchronous Vacations." Journal of Applied Mathematics 2014 (2014): 1–11. http://dx.doi.org/10.1155/2014/893094.
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We consider an M/M/cqueueing system with impatient customers and a synchronous vacation policy, where customer impatience is due to the servers’ vacation. Whenever a system becomes empty, all the servers take a vacation. If the system is still empty, when the vacation ends, all the servers take another vacation; otherwise, they return to serve the queue. We develop the balance equations for the steady-state probabilities and solve the equations by using the probability generating function method. We obtain explicit expressions of some important performance measures by means of the two indexes. Based on these, we obtain some results about limiting behavior for some performance measures. We derive closed-form expressions of some important performance measures for two special cases. Finally, some numerical results are also presented.
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Ayriyan, Alexander, David Alvarez-Castillo, David Blaschke, and Hovik Grigorian. "Bayesian Analysis for Extracting Properties of the Nuclear Equation of State from Observational Data Including Tidal Deformability from GW170817." Universe 5, no. 2 (February 14, 2019): 61. http://dx.doi.org/10.3390/universe5020061.
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We develop a Bayesian analysis method for selecting the most probable equation of state under a set of constraints from compact star physics, which now include the tidal deformability from GW170817. We apply this method for the first time to a two-parameter family of hybrid equations of state that is based on realistic models for the hadronic phase (KVORcut02) and the quark matter phase (SFM α ) which produce a third family of hybrid stars in the mass–radius diagram. One parameter ( α ) characterizes the screening of the string tension in the string-flip model of quark matter while the other ( Δ P ) belongs to the mixed phase construction that mimics the thermodynamics of pasta phases and includes the Maxwell construction as a limiting case for Δ P = 0 . We present the corresponding results for compact star properties like mass, radius and tidal deformabilities and use empirical data for them in the newly developed Bayesian analysis method to obtain the probabilities for the model parameters within their considered range.
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Teknomo, Kardi. "Ideal flow of Markov Chain." Discrete Mathematics, Algorithms and Applications 10, no. 06 (December 2018): 1850073. http://dx.doi.org/10.1142/s1793830918500738.
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Ideal flow network is a strongly connected network with flow, where the flows are in steady state and conserved. The matrix of ideal flow is premagic, where vector, the sum of rows, is equal to the transposed vector containing the sum of columns. The premagic property guarantees the flow conservation in all nodes. The scaling factor as the sum of node probabilities of all nodes is equal to the total flow of an ideal flow network. The same scaling factor can also be applied to create the identical ideal flow network, which has from the same transition probability matrix. Perturbation analysis of the elements of the stationary node probability vector shows an insight that the limiting distribution or the stationary distribution is also the flow-equilibrium distribution. The process is reversible that the Markov probability matrix can be obtained from the invariant state distribution through linear algebra of ideal flow matrix. Finally, we show that recursive transformation [Formula: see text] to represent [Formula: see text]-vertices path-tracing also preserved the properties of ideal flow, which is irreducible and premagic.
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Kurlov, V. V., A. V. Kurlov, A. G. Stepanov, and V. G. Farafonov. "CONSTRUCTION OF SYSTEM FOR ORGANIZATION OF PRODUCTION IN CONDITIONS OF TECHNICAL AND ECONOMIC RISKS OF INDUSTRIAL ENTERPRISES." Issues of radio electronics, no. 10 (October 20, 2018): 115–24. http://dx.doi.org/10.21778/2218-5453-2018-10-115-124.
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One of the key components of effective production organization at the enterprises of the radio electronic industry is the need to take into account the risk environment, and take measures to minimize the likelihood of risk occurrence. The main problem is the probabilistic nature of the manifestation of risk. The probability is manifested in the realization of the risk and its duration, which, in the final analysis, will lead to financial losses. The article proposes an approach to building the core of the system of technical and economic risks and their interrelationship in the organization of production at the enterprises of the radio electronic industry. In the article it is proposed to use basic modules for estimating the limiting probabilities of various states of technical and economic risks for which special systems of linear algebraic equations are developed. In this case, to determine (calculate) the estimate, we can use the results of solving a system of linear algebraic equations. In addition, these results allow for the assessment of the stationary state of the basic modules of the technical and risks system in the organization of production at the enterprises of the radio electronic industry. When solving a system of algebraic equations, it is suggested to use the standard approach, namely, the limit transformation of the system of Kolmogorov's differential equations for state probabilities. The article concludes that to assess the impact of technical and economic risks on the effectiveness of the organization of production of enterprises of the electronic industry, it is necessary to assess the likelihood of finding a system of technical and economic risks in the state of their implementation. The results of such an assessment will allow to determine two main components - the intensity of the events' flows associated with the emergence (implementation) of technical and economic risks and the time (duration) of their finding in the state of realization (negative state).
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Brooks, R. F., and P. N. Riddle. "The 3T3 cell cycle at low proliferation rates." Journal of Cell Science 90, no. 4 (August 1, 1988): 601–12. http://dx.doi.org/10.1242/jcs.90.4.601.
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When the proliferation rate of Swiss 3T3 cells is decreased by limiting the availability of growth factors, cell cycle variability increases, as predicted by the transition probability model. Nevertheless, the transition probabilities would appear to play a relatively minor role in the regulation of proliferation rate. Instead, at least 40% of the increase in the average cycle time is brought about by an elongation of the minimum cycle time (i.e. the ‘deterministic’ part of the cycle). In addition, we have found that a substantial proportion of the cells (roughly 20%, in the present experiments, for doubling times of the order of 35–40 h) drop out of cycle in each generation, leading to a growth fraction of less than 1.0. The non-dividing cells, which we have previously shown to remain capable of division, would seem to support the existence of a Go state outside the normal cell cycle, and distinct from the indeterminate states postulated by the transition probability model. Because of the generation of nondividing cells at low proliferation rates, the log alpha and beta plots (distributions of cycle times, and sibling cycle time differences, respectively) are markedly concave, with a continuously decreasing slope. The transition probabilities cannot therefore be estimated directly and it is impossible to determine the extent to which they contribute to the regulation of proliferation rate. Rather, our data suggest that the transition probabilities are not uniform throughout the population under these conditions, but vary substantially from cell to cell. In addition to the changes in cell cycle kinetics, we also report an increased failure rate of cytokinesis, at low proliferation rates, leading initially to the appearance of binucleate cells. Such failures of cytokinesis may be responsible for the well-known rise in the incidence of binucleate and polyploid cells in the liver, with age.
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Lange, Marius, Volker Bergen, Michal Klein, Manu Setty, Bernhard Reuter, Mostafa Bakhti, Heiko Lickert, et al. "CellRank for directed single-cell fate mapping." Nature Methods 19, no. 2 (January 13, 2022): 159–70. http://dx.doi.org/10.1038/s41592-021-01346-6.
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AbstractComputational trajectory inference enables the reconstruction of cell state dynamics from single-cell RNA sequencing experiments. However, trajectory inference requires that the direction of a biological process is known, largely limiting its application to differentiating systems in normal development. Here, we present CellRank (https://cellrank.org) for single-cell fate mapping in diverse scenarios, including regeneration, reprogramming and disease, for which direction is unknown. Our approach combines the robustness of trajectory inference with directional information from RNA velocity, taking into account the gradual and stochastic nature of cellular fate decisions, as well as uncertainty in velocity vectors. On pancreas development data, CellRank automatically detects initial, intermediate and terminal populations, predicts fate potentials and visualizes continuous gene expression trends along individual lineages. Applied to lineage-traced cellular reprogramming data, predicted fate probabilities correctly recover reprogramming outcomes. CellRank also predicts a new dedifferentiation trajectory during postinjury lung regeneration, including previously unknown intermediate cell states, which we confirm experimentally.
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Lecarpentier, Y., D. Chemla, J. C. Pourny, F. X. Blanc, and C. Coirault. "Myosin cross bridges in skeletal muscles: “rower” molecular motors." Journal of Applied Physiology 91, no. 6 (December 1, 2001): 2479–86. http://dx.doi.org/10.1152/jappl.2001.91.6.2479.
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Different classes of molecular motors, “rowers” and “porters,” have been proposed to describe the chemomechanical transduction of energy. Rowers work in large assemblies and spend a large percentage of time detached from their lattice substrate. Porters behave in the opposite way. We calculated the number of myosin II cross bridges (CB) and the probabilities of attached and detached states in a minimal four-state model in slow (soleus) and fast (diaphragm) mouse skeletal muscles. In both muscles, we found that the probability of CB being detached was ∼98% and the number of working CB was higher than 109/mm2. We concluded that muscular myosin II motors were classified in the category of rowers. Moreover, attachment time was higher than time stroke and time for ADP release. The duration of the transition from detached to attached states represented the rate-limiting step of the overall attached time. Thus diaphragm and soleus myosins belong to subtype 1 rowers.
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Xiao, Shaoning, Long Chen, Songyang Zhang, Wei Ji, Jian Shao, Lu Ye, and Jun Xiao. "Boundary Proposal Network for Two-stage Natural Language Video Localization." Proceedings of the AAAI Conference on Artificial Intelligence 35, no. 4 (May 18, 2021): 2986–94. http://dx.doi.org/10.1609/aaai.v35i4.16406.
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We aim to address the problem of Natural Language Video Localization (NLVL) — localizing the video segment corresponding to a natural language description in a long and untrimmed video. State-of-the-art NLVL methods are almost in one-stage fashion, which can be typically grouped into two categories: 1) anchor-based approach: it first pre-defines a series of video segment candidates (e.g., by sliding window), and then does classification for each candidate; 2) anchor-free approach: it directly predicts the probabilities for each video frame as a boundary or intermediate frame inside the positive segment. However, both kinds of one-stage approaches have inherent drawbacks: the anchor-based approach is susceptible to the heuristic rules, further limiting the capability of handling videos with variant length. While the anchor-free approach fails to exploit the segment-level interaction thus achieving inferior results. In this paper, we propose a novel Boundary Proposal Network (BPNet), a universal two-stage framework that gets rid of the issues mentioned above. Specifically, in the first stage, BPNet utilizes an anchor-free model to generate a group of high-quality candidate video segments with their boundaries. In the second stage, a visual-language fusion layer is proposed to jointly model the multi-modal interaction between the candidate and the language query, followed by a matching score rating layer that outputs the alignment score for each candidate. We evaluate our BPNet on three challenging NLVL benchmarks (i.e., Charades-STA, TACoS and ActivityNet-Captions). Extensive experiments and ablative studies on these datasets demonstrate that the BPNet outperforms the state-of-the-art methods.
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van der Wel, Kjetil A., Espen Dahl, and Karsten Thielen. "Social Inequalities in “Sickness”: Does Welfare State Regime Type Make a Difference? A Multilevel Analysis of Men and Women in 26 European Countries." International Journal of Health Services 42, no. 2 (April 2012): 235–55. http://dx.doi.org/10.2190/hs.42.2.f.
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In comparative studies of health inequalities, public health researchers have usually studied only disease and illness. Recent studies have also examined the sickness dimension of health, that is, the extent to which ill health is accompanied by joblessness, and how this association varies by education within different welfare contexts. This research has used either a limited number of countries or quantitative welfare state measures in studies of many countries. In this study, the authors expand on this knowledge by investigating whether a regime approach to the welfare state produces consistent results. They analyze data from the European Union Statistics on Income and Living Conditions (EU-SILC); health was measured by limiting longstanding illness (LLSI). Results show that for both men and women reporting LLSI in combination with low educational level, the probabilities of non-employment were particularly high in the Anglo-Saxon and Eastern welfare regimes, and lowest in the Scandinavian regime. For men, absolute and relative social inequalities in sickness were lowest in the Southern regime; for women, inequalities were lowest in the Scandinavian regime. The authors conclude that the Scandinavian welfare regime is more able than other regimes to protect against non-employment in the face of illness, especially for individuals with low educational level.
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Wang, Bin, and Robert Brenner. "An S6 Mutation in BK Channels Reveals β1 Subunit Effects on Intrinsic and Voltage-dependent Gating." Journal of General Physiology 128, no. 6 (November 27, 2006): 731–44. http://dx.doi.org/10.1085/jgp.200609596.
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Large conductance, Ca2+- and voltage-activated K+ (BK) channels are exquisitely regulated to suit their diverse roles in a large variety of physiological processes. BK channels are composed of pore-forming α subunits and a family of tissue-specific accessory β subunits. The smooth muscle–specific β1 subunit has an essential role in regulating smooth muscle contraction and modulates BK channel steady-state open probability and gating kinetics. Effects of β1 on channel's gating energetics are not completely understood. One of the difficulties is that it has not yet been possible to measure the effects of β1 on channel's intrinsic closed-to-open transition (in the absence of voltage sensor activation and Ca2+ binding) due to the very low open probability in the presence of β1. In this study, we used a mutation of the α subunit (F315Y) that increases channel openings by greater than four orders of magnitude to directly compare channels' intrinsic open probabilities in the presence and absence of the β1 subunit. Effects of β1 on steady-state open probabilities of both wild-type α and the F315Y mutation were analyzed using the dual allosteric HA model. We found that mouse β1 has two major effects on channel's gating energetics. β1 reduces the intrinsic closed-to-open equilibrium that underlies the inhibition of BK channel opening seen in submicromolar Ca2+. Further, PO measurements at limiting slope allow us to infer that β1 shifts open channel voltage sensor activation to negative membrane potentials, which contributes to enhanced channel opening seen at micromolar Ca2+ concentrations. Using the F315Y α subunit with deletion mutants of β1, we also demonstrate that the small N- and C-terminal intracellular domains of β1 play important roles in altering channel's intrinsic opening and voltage sensor activation. In summary, these results demonstrate that β1 has distinct effects on BK channel intrinsic gating and voltage sensor activation that can be functionally uncoupled by mutations in the intracellular domains.
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Pang, Guodong, and David D. Yao. "Heavy-Traffic Limits for a Many-Server Queueing Network with Switchover." Advances in Applied Probability 45, no. 3 (September 2013): 645–72. http://dx.doi.org/10.1239/aap/1377868533.
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We study a multiclass Markovian queueing network with switchover across a set of many-server stations. New arrivals to each station follow a nonstationary Poisson process. Each job waiting in queue may, after some exponentially distributed patience time, switch over to another station or leave the network following a probabilistic and state-dependent mechanism. We analyze the performance of such networks under the many-server heavy-traffic limiting regimes, including the critically loaded quality-and-efficiency-driven (QED) regime, and the overloaded efficiency-driven (ED) regime. We also study the limits corresponding to mixing the underloaded quality-driven (QD) regime with the QED and ED regimes. We establish fluid and diffusion limits of the queue-length processes in all regimes. The fluid limits are characterized by ordinary differential equations. The diffusion limits are characterized by stochastic differential equations, with a piecewise-linear drift term and a constant (QED) or time-varying (ED) covariance matrix. We investigate the load balancing effect of switchover in the mixed regimes, demonstrating the migration of workload from overloaded stations to underloaded stations and quantifying the load balancing impact of switchover probabilities.
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Pang, Guodong, and David D. Yao. "Heavy-Traffic Limits for a Many-Server Queueing Network with Switchover." Advances in Applied Probability 45, no. 03 (September 2013): 645–72. http://dx.doi.org/10.1017/s0001867800006522.
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We study a multiclass Markovian queueing network with switchover across a set of many-server stations. New arrivals to each station follow a nonstationary Poisson process. Each job waiting in queue may, after some exponentially distributed patience time, switch over to another station or leave the network following a probabilistic and state-dependent mechanism. We analyze the performance of such networks under the many-server heavy-traffic limiting regimes, including the critically loaded quality-and-efficiency-driven (QED) regime, and the overloaded efficiency-driven (ED) regime. We also study the limits corresponding to mixing the underloaded quality-driven (QD) regime with the QED and ED regimes. We establish fluid and diffusion limits of the queue-length processes in all regimes. The fluid limits are characterized by ordinary differential equations. The diffusion limits are characterized by stochastic differential equations, with a piecewise-linear drift term and a constant (QED) or time-varying (ED) covariance matrix. We investigate the load balancing effect of switchover in the mixed regimes, demonstrating the migration of workload from overloaded stations to underloaded stations and quantifying the load balancing impact of switchover probabilities.
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Ozen, Merve, and Ananth Krishnamurthy. "Evaluating relief center designs for disaster relief distribution." Journal of Humanitarian Logistics and Supply Chain Management 8, no. 1 (April 3, 2018): 22–48. http://dx.doi.org/10.1108/jhlscm-03-2017-0012.
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Purpose Relief item distribution to victims is a key activity during disaster response. Currently many humanitarian organizations follow simple guidelines based on experience to assess need and distribute relief supplies. However, the interviews with practitioners suggest a problem in efficiency in relief distribution efforts. The purpose of this paper is to develop a model and solution methodology that can estimate relief center (RC) performance, measured by waiting time for victims and throughput, for any RC design and analyze the impact of key design decisions on these performance measures. Design/methodology/approach Interviews with practitioners and current practice guidelines are used to understand relief distribution and a queuing network model is used to represent the relief distribution. Finally, the model is applied to data from the 2015 Nepal earthquake. Findings The findings identify that dissipating congestion created by crowds, varying item assignment decisions to points of distribution, limiting the physical RC capacity to control congestion and using triage queue to balance distribution times, are effective strategies that can improve RC performance. Research limitations/implications This research bases the RC designs on Federal Emergency Management Agency guidelines and assumes a certain area and volunteer availability. Originality/value This paper contributes to humanitarian logistics by discussing useful insights that can impact how relief agencies set up and operate RCs. It also contributes to the queuing literature by deriving analytic solutions for the steady state probabilities of finite capacity, state dependent queues with blocking.
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Augustine, Keith. "How *Not* to Do Survival Research: Reflections on the Bigelow Institute Essay Competition." Journal of Scientific Exploration 36, no. 2 (August 20, 2022): 366–98. http://dx.doi.org/10.31275/20222581.
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The recent Bigelow Institute contest rewarding the “best” evidence for life after death epitomizes much of what’s wrong with the current state of survival research, its participants constituting a who’s who list of contemporary survival researchers. Cases that are regularly hyped as among the best evidence for an afterlife are all too often easily susceptible to normal explanations—if only survival researchers would give them a chance. The consistently negative results of 121 years of experimental survival research ought to have spurred soul-searching questions for survival researchers by now. And if we treat discarnate personal survival as a scientific hypothesis, then researchers are rationally obliged to seriously consider biological facts that tell against it, too. Limiting one’s inquiry to attempts to only collect data that might confirm survival is one of the chief hallmarks of pseudoscience, and it’s sadly a feature, not a bug, of the survival literature. This systematic review reveals that survival researchers would better serve science by setting aside their feelings and heeding what the data are telling them, for the probabilities should drive our beliefs, not the other way around. Is discarnate personal survival likely to occur in light of the total available evidence? The overall evidence doesn’t even make personal survival more probable than not.
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Abebe Abera, Eticha, and Ahmed Endris Mossa. "The food insecurity status of pastoral and agro-pastoral households in Ethiopia." Holistic approach to environment 10, no. 4 (September 14, 2020): 88–99. http://dx.doi.org/10.33765/thate.10.4.1.
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Understanding the major causes of food insecurity is important for interventions aiming at minimizing food insecurity. Therefore, this study was conducted to assess the status of food insecurity of pastoral and agro-pastoral households of Seba Boru Woreda Guji Zone, Oromia National Regional State, Ethiopia. In order to achieve these objectives, 112 respondents’ agro pastoralists were selected from 2 kebeles (the smallest administrative unit). To this end, both probabilities (stratified, systematic and random) and non-probability (purposive) sampling techniques were employed. Primary and secondary data were collected from various sources. The data were analysed using descriptive statistics like mean standard deviation, percentage and frequency distributions. Univariate analysis such as t-test and chi-square (χ2) were also used to describe the characteristics of food secured and food insecure groups. The survey result shows that about 60 (53.7 %) of sample respondents were food insecure while only 52 (46.3 %) were food secure. As per a binary logistic model regression, four variables such as family size, land, income, and extension service were significant at 10 % probability levels. Finally, limiting population size through integrated health and education service, intensification of agriculture through extension service by strengthening PTC (pastoral training center), are some to recommend to curb food insecurity in the area
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Deniz, Baris, Thierry Facon, Ian Singer, Paul Micallef-Eynaud, Ian Joseph, Arran Shearer, and J. Jaime Caro. "Economic Evaluation of Thalidomide Combined with Melphalan and Prednisone in Previously Untreated Multiple Myeloma in Scotland." Blood 112, no. 11 (November 16, 2008): 2395. http://dx.doi.org/10.1182/blood.v112.11.2395.2395.
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Abstract INTRODUCTION: Thalidomide (Thalomid®/Thalidomide Pharmion®) combined with melphalan and prednisone (MPT) yields improved progression-free and overall survival compared to MP alone (Facon et. al., Lancet2007; 370:1191). This study was designed to estimate the life-time health and cost consequences of MPT versus MP in Scottish patients with previously untreated multiple myeloma. METHODS: A Markov model was developed to determine cost and health outcomes for a cohort of patients receiving a course of MPT or MP. The disease course was conceptualized by 4 mutually exclusive health states: pre-progression without adverse events, pre-progression with adverse event, progressive disease, and death. Probabilities of moving between these states (i.e. natural progression plus efficacy and safety of the treatments) were derived from a long-term randomized clinical trial, IFM 99-06 (Facon et. al., Lancet2007; 370:1191). Both patient cohorts remained on the assigned treatment for a maximum of twelve 6-week cycles, until progression or treatment-limiting toxicity. Treatment duration and the average daily dose were modelled to match IFM 99-06. During treatment, each cohort was exposed to adverse event risks associated with therapy estimated from IFM 99-06. Health state utilities associated with adverse events and disease states were obtained from the literature. Thalidomide cost was set at UK list price; routine disease-management costs by disease-state (progressive disease and remission state) reflect clinical practice in Scotland. As recommended by the UK treasury, costs and health outcomes were discounted at 3.5% per annum to adjust to present values. Univariate and multivariate sensitivity analyses were performed around key model parameters. RESULTS: The model estimated improvements in health outcomes with MPT with a median time to progression of 25 months vs. 12 months with MP. Estimated median overall survivals were 4.03 years vs. 2.88 years with MP. These results translate to a gain of 0.91 (3.24 vs. 2.32) quality-adjusted life-years (QALYs). MPT is associated with higher overall costs (£25,199 per patient) compared with MP (£8,935), over the modeled life-time, leading to an incremental cost-effectiveness ratio of £17,847 per QALY and £14,803 per life-year gained. Sensitivity analyses showed that results remained consistent through broad changes in model parameters including the addition of thromboembolic prophylaxis. CONCLUSIONS: MPT delivers improvements in progression-free and overall survival in a life-limiting orphan disease compared to MP and economic results fall within a range considered cost-effective in Scotland.
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Benner, Michael, and Alfred Rieckers. "Spectral Properties Of Weakly Inhomogeneous Bcs-Models In Different Representations." Zeitschrift für Naturforschung A 60, no. 5 (May 1, 2005): 343–65. http://dx.doi.org/10.1515/zna-2005-0506.
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For a class of Bardeen-Cooper-Schrieffer (BCS)-models, with complex, weakly momentum dependent interaction coefficients, the representation dependent effective Hamiltonians and their spectra are reconsidered in order to obtain a consistent physical picture by means of operator algebraic methods. The starting point is the limiting dynamics, the existence of which had been proved in a previous work, in terms of a C*-dynamical system acting in a classically extended, electronic Canonical Anticommutation Relations (CAR)-algebra. The C*-algebraic KMS-theory, including the low temperature limit, specifies the order parameters. These appear as classical observables, which commute with all other observables, constituting elements of the center of the algebra. The algebraic spectral theory, in the sense of Arveson, is first applied to the dynamics in general pure energy state representations. The spectra of the finite temperature representations are analyzed, identifying the gap as the lowest of those energy values, which are stable under local perturbations. Further insights are obtained by decomposing the thermal dynamical systems into the pure energy state Heisenberg dynamics, after having first extended them to more comprehensive W*-dynamical systems. The decomposing orthogonal measure is transferred to the infinite product space of quasi-particle occupation numbers and its support is characterized in terms of 0-1-laws leading to an asymptotic ratio of quasi-particles and holes, which depends on the temperature. This ratio is connected with an algebraic invariant of the representation dependent observable algebra. Energy renormalization aspects and pair occupation probabilities are discussed. The latter reveal, beside other things, the difference between macroscopic term occupation and coherent macroscopic term occupation for a condensate.
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Yemshanov, Dennis, and Ajith H. Perera. "Synthesizing published knowledge of boreal forest cover change for large-scale landscape dynamics modelling." Forestry Chronicle 79, no. 1 (February 1, 2003): 132–46. http://dx.doi.org/10.5558/tfc79132-1.
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We reviewed the published knowledge on forest succession in the North American boreal biome for its applicability in modelling forest cover change over large extents. At broader scales, forest succession can be viewed as forest cover change over time. Quantitative case studies of forest succession in peer-reviewed literature are reliable sources of information about changes in forest canopy composition. We reviewed the following aspects of forest succession in literature: disturbances; pathways of post-disturbance forest cover change; timing of successional steps; probabilities of post-disturbance forest cover change, and effects of geographic location and ecological site conditions on forest cover change. The results from studies in the literature, which were mostly based on sample plot observations, appeared to be sufficient to describe boreal forest cover change as a generalized discrete-state transition process, with the discrete states denoted by tree species dominance. In this paper, we outline an approach for incorporating published knowledge on forest succession into stochastic simulation models of boreal forest cover change in a standardized manner. We found that the lack of details in the literature on long-term forest succession, particularly on the influence of pre-disturbance forest cover composition, may be limiting factors in parameterizing simulation models. We suggest that the simulation models based on published information can provide a good foundation as null models, which can be further calibrated as detailed quantitative information on forest cover change becomes available. Key words: probabilistic model, transition matrix, boreal biome, landscape ecology
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Zhu, Xiaoli, Xiaoyu Lai, Yi Luo, Jimin Shi, Yamin Tan, and He Huang. "Combination of Mycophenolate Mofetil with Cyclosporine A and Methotrexate as Gvhd Prophylaxis In Unrelated Donor Allogeneic Hematopoietic Stem Cell Transplantation." Blood 116, no. 21 (November 19, 2010): 1280. http://dx.doi.org/10.1182/blood.v116.21.1280.1280.
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Abstract Abstract 1280 Graft-versus-host disease (GVHD) is the dominant complication limiting the efficacy and safety of hematopoietic stem cell transplantation (HSCT), especially from unrelated donors. The most widely used regimen of prophylaxis is the combination of cyclosporine A (CSA)and a short-course of methotrexate (MTX). But the patients receiving grafts from matched unrelated donors still have a 50–80% risk of clinical significant GVHD. Thus, more effective prophylaxis is needed. In this study, we try to evaluate the efficacy and safety of the new GVHD prophylaxis regimen combining mycophenolate mofetil (MMF) with CSA and MTX in unrelated donor allogeneic stem cell transplantation. Between November 1998 and June 2008, 153 patients with a variety of hematologic malignancies were enrolled. There were 102 males and 51 females, median age 26 (range, 8–52) years. Diagnoses were acute myeloid leukemia (n=54), acute lymphoblastic leukemia (n=47),myelodysplastic syndrome (n=8), multiple myeloma (n=1) and chronic myeloid leukemia (n=53). One hundred and eight patients had HLA compatible unrelated donors, 37 patients had single locus-mismatched unrelated donors and 8 patients had 2 loci-mismatched unrelated donors. GVHD prophylaxis consisted of CSA,MTX and MMF. CSA was started on day -7 with the initial dosage of 2.5mg/kg daily, and the dose was adjusted to maintain a whole blood steady-state level of 200–400ng/ml. The dose was tapered during the second to third month post-transplant depending on GVHD status. MTX was given at a dosage of 10mg on days+1, +3 and +6. MMF was administered at an oral dose of 500mg daily from day 0 to day +100. The cumulative incidence of grades II-IV aGVHD and grades III-IV aGVHD for all patients were 43.9% and 17.9% respectively for entire group. The cumulative incidence of grades II-IV aGVHD for patients who had HLA-matched donors and mismatched donors were 40.2% and 51.9% respectively (P=0.079). The cumulative incidence of grades III-IV aGVHD for patients who had HLA-matched donors and mismatched donors were 14.0% and 26.9% respectively (P=0.026). The cumulative incidence of cGVHD was 41.4%, with 19.3% extensive cGVHD. At 3 years, the incidence of relapse for entire group was 24.0%. The cumulative incidence of transplant-related mortality at 100 days and 3 years were 12.5% and 34.9%, respectively. The probabilities of overall survival at 2 years and 5 years were 59.2% and 50.2%, respectively. The probabilities of disease-free survival at 2 years and 5 years were 56.3% and 46.7%, respectively. From these results, we conclude that the combination of MMF with CSA and MTX is an effective prophylaxis regimen for acute and chronic GVHD in unrelated donor allogeneic stem cell transplantation without increasing the risk of relapse. Disclosures: No relevant conflicts of interest to declare.
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Samulenkov, Yu I., Ya A. Filatova, and A. D. Gruzd. "Aircraft maintenance system simulation mathematical model construction." Civil Aviation High Technologies 24, no. 4 (August 27, 2021): 38–49. http://dx.doi.org/10.26467/2079-0619-2021-24-4-38-49.
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The development of the aviation transport system is characterized by sophistication of interacting objects, the multi-criteria nature of the tasks to be solved and difficulties in making management decisions. For example, modern medium haul aircraft are fitted with up to 25,000 sensors to monitor the performance capabilities of functional systems components. Numerous ground-based instrumental methods and means of diagnosing the technical condition are used. This requires the development of methods and algorithms for determining and monitoring the criteria of limiting state of the monitored components and functional systems of aeronautical equipment. In this regard, analytical models of predictive estimate for the technical condition of aeronautical equipment, determination of aircraft maintenance modes and provision of spare parts and materials become essential. The paper proposes a scheme of the aircraft fleet maintenance system modeling algorithm and deducing the mathematical model of the optimal number of aircraft states in order to exclude secondary and subjective factors. The method of statistical modeling based on Markov processes with discrete states and continuous time is the basis of the proposed analytical model. The proposed method is reduced to the synthesis of some modeling algorithm of the investigated process that simulates the complex system components behavior and interaction as well as random perturbing factors. A distinctive feature of the presented algorithm is determination of the predominant estimated dependences of transition probabilities and intensities taking into account the requirements of the modern regulatory framework in terms of reliability of equipment and diagnosing the technical condition. The analysis of the predominant estimated dependencies study results in the conditions of operation of the aircraft maintenance system confirmed a high degree of correlation of the time duration effect on the particular states in order to diagnose the technical condition depending on the diagnostic concept. The proposed simulation model can be used for the aircraft technical condition predictive estimate, aircraft gas turbine engines and functional systems.
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Chang, S. J. "Probability of Fracture and Life Extension Estimate of the High-Flux Isotope Reactor Vessel." Journal of Pressure Vessel Technology 120, no. 3 (August 1, 1998): 290–96. http://dx.doi.org/10.1115/1.2842060.
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The state of the vessel steel embrittlement as a result of neutron irradiation can be measured by its increase in ductile-brittle transition temperature (DBTT) for fracture, often denoted by RTNDT for carbon steel. This transition temperature can be calibrated by the drop-weight test and, sometimes, by the Charpy impact test. The life extension for the high-flux isotope reactor (HFIR) vessel is calculated by using the method of fracture mechanics that is incorporated with the effect of the DBTT change. The failure probability of the HFIR vessel is limited as the life of the vessel by the reactor core melt probability of 10−4. The operating safety of the reactor is ensured by periodic hydrostatic pressure test (hydrotest). The hydrotest is performed in order to determine a safe vessel static pressure. The fracture probability as a result of the hydrostatic pressure test is calculated and is used to determine the life of the vessel. Failure to perform hydrotest imposes the limit on the life of the vessel. The conventional method of fracture probability calculations such as that used by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this Laboratory are based on the Monte Carlo simulation. Heavy computations are required. An alternative method of fracture probability calculation by direct probability integration is developed in this paper. The present approach offers simple and expedient ways to obtain numerical results without losing any generality. This approach provides a clear analytical expression on the physical random variables to be integrated, yet requires much less computation time. In this paper, numerical results on 1) the probability of vessel fracture, 2) the hydrotest time interval, and 3) the hydrotest pressure as a result of the DBTT increase are obtained. Limiting the probabilities of the vessel fracture as a result of hydrotest to 10−4 implies that the reactor vessel life can be extended up to 50 EFPY (100 MW) with the minimum vessel operating temperature equal to 85°F.
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Łosiewicz, Zbigniew, Waldemar Mironiuk, Witold Cioch, Ewelina Sendek-Matysiak, and Wojciech Homik. "Application of Generator-Electric Motor System for Emergency Propulsion of a Vessel in the Event of Loss of the Full Serviceability of the Diesel Main Engine." Energies 15, no. 8 (April 13, 2022): 2833. http://dx.doi.org/10.3390/en15082833.
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Oil tanker disasters have been a cause of major environmental disasters, with multi-generational impacts. One of the greatest hazards is damage to the propulsion system that causes the ship to turn sideways to a wave and lose stability, which in storm conditions usually leads to capsizing and sinking Despite the perceived consequences of maritime disasters in the current solutions for the propulsion of oil tankers, there are no legal or real solutions for independent emergency main propulsion in this type of ship. Stressing that the reliability of the propulsion system has a significant impact on the ship’s safety at sea, the authors presented a new solution in the form of a power take-off/power take-in (PTO/PTI) system. This is the emergency use of a shaft generator as the main electric motor, operating in parallel in a situation when the main engine (ME), (the main engine of the ship’s direct high-power propulsion system that is slow-speed) loses the operational capability to propel the ship. Since one cause of wear, or failure, of the main engines is improper operational decisions, the paper shows the wear mechanism in relation to the accuracy of operational decisions. Using classical reliability theory, it also shows that the use of the proposed system results in an increase in the reliability of the propulsion system. The main topic of the paper was the use of an electrical system called PTO/PTI as an emergency propulsion system on the largest commercial vessels, such as bulk carriers and crude oil tankers, which has not been used before in maritime technical solutions. Semi-Markov processes, continuous in time, discrete in states, and which are used in technology, were also proposed as a tool describing the process of the operation of such a ship propulsion system, and they are useful to support operational decisions affecting the state of the technical condition of the engine. There are two ship operation strategies that can be adopted: the four-state model, for normal operation, and the three-state model, which operates with the occurrence of failure. For these types of models, their limiting distributions were defined in the form of probabilities. It was also demonstrated that faster than expected engine wear and the occurrence of inoperability of the main engine can be caused by wrong operational decisions made by the shipowner or crew. Using this type of main engine operating methodology, it is possible to support the decision of the engineer to stop the main engine and to subject it to the process of restoration to an acceptable state of technical condition (before the failure or during the failure in severe storm conditions), with the parallel use of the proposed electric propulsion (PTO/PTI) as an emergency propulsion, giving the crew a chance to maintain the steering necessary to maintain safe lateral stability.
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Joosten, Reinoud, and Llea Samuel. "On Finding Large Sets of Rewards in Two-Player ETP–ESP Games." International Game Theory Review 22, no. 02 (May 4, 2020): 2040002. http://dx.doi.org/10.1142/s0219198920400022.
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Games with endogenous transition probabilities and endogenous stage payoffs (or ETP–ESP games for short) are stochastic games in which both the transition probabilities and the payoffs at any stage are continuous functions of the relative frequencies of all past action combinations chosen. We present methods to compute large sets of jointly-convergent pure-strategy rewards in two-player ETP–ESP games with communicating states under the limiting average reward criterion. Such sets are useful in determining feasible rewards in a game, and instrumental in obtaining the set of (Nash) equilibrium rewards.
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Liu, Shuo Shuo, and Yeying Zhu. "Simultaneous Maximum Likelihood Estimation for Piecewise Linear Instrumental Variable Models." Entropy 24, no. 9 (September 2, 2022): 1235. http://dx.doi.org/10.3390/e24091235.
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Analysis of instrumental variables is an effective approach to dealing with endogenous variables and unmeasured confounding issue in causal inference. We propose using the piecewise linear model to fit the relationship between the continuous instrumental variable and the continuous explanatory variable, as well as the relationship between the continuous explanatory variable and the outcome variable, which generalizes the traditional linear instrumental variable models. The two-stage least square and limited information maximum likelihood methods are used for the simultaneous estimation of the regression coefficients and the threshold parameters. Furthermore, we study the limiting distribution of the estimators in the correctly specified and misspecified models and provide a robust estimation of the variance-covariance matrix. We illustrate the finite sample properties of the estimation in terms of the Monte Carlo biases, standard errors, and coverage probabilities via the simulated data. Our proposed model is applied to an education-salary data, which investigates the causal effect of children’s years of schooling on estimated hourly wage with father’s years of schooling as the instrumental variable.
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Welsh, Matthew B., Nigel Rees, Hugh Ringwood, and Stephen (Steve) H. Begg. "The planning fallacy in oil and gas decision-making." APPEA Journal 50, no. 1 (2010): 389. http://dx.doi.org/10.1071/aj09023.
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The ‘planning fallacy’ describes the tendency of people to underestimate costs and times required for the completion of complex projects. Psychological research has demonstrated that a key component of this results from the packing/unpacking bias—where options or problems that are not specifically stated tend to be ignored by people when making estimates or assigning probabilities to events. We have investigated this effect as it relates to oil and gas decision making, highlighted by experimental results comparing estimates of drilling times made by both student and industry participants. Specifically, participants were provided with a drilling scenario and asked to estimate the time required to drill the well—including drilling, tripping, rigging and all potential problems. In the packed condition the options were given as just stated while, in the unpacked condition the ‘all potential problems’ category was divided into a list of specific problems. The packing effect was shown to markedly alter the time estimates made by all groups of participants—altering estimates of problem times by more than 100 hours on average. Additional analyses assessed the interactions between the packing/unpacking effect and personal traits such as optimism, tendency to procrastinate and industry experience. These findings are discussed in terms of their import for oil and gas decision makers desiring to improve prediction accuracy and, thus, economic outcomes by avoiding, or limiting, the impact of the planning fallacy.
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Hildreth, Brianna A., Giovanna Panarello, Gennaro Martucci, Fabio Tuzzolino, Alberto Piacentini, Giovanna Occhipinti, Andrea Giunta, et al. "ECMO Retrieval over the Mediterranean Sea: Extending Hospital Arms." Membranes 11, no. 3 (March 17, 2021): 210. http://dx.doi.org/10.3390/membranes11030210.
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The retrieval and transport of patients from peripheral hospitals to high volume extracorporeal membrane oxygenation (ECMO) centers aims to reduce complications and improve survival. In Sicily (Italy), our institute houses a mobile ECMO team that serves a population of around 10 million people for a vast area in southern Italy and Malta. This observational, descriptive study includes all patients that required veno–venous (V-V) ECMO and transport by a mobile team between October 2009 and May 2020. Linear and multiple logistic regressions were applied to explore the risk factors for mortality in the ICU. Kaplan–Meier estimates were generated to predict the survival in patients transported by helicopter or ambulance, and the two cohorts were compared according to their baseline characteristics. Of 122 patients transported, 89 (73%) survived to ICU discharge (50 (41%) patients were transported by ambulance, and 72 (59%) were transported by helicopter). Independent predictive factors associated with mortality in a stepwise multiple regression model were prone positioning, acute kidney injury, and the number of days spent on mechanical ventilation (MV). Kaplan–Meier estimates for survival favored the helicopter cohort (79%) rather than the ambulance cohort (64%). Patients transported by helicopter had better pre-ECMO profiles, with shorter hospital and ICU stays, a shorter duration of MV use, and higher RESP scores, which indicate better survival probabilities. ECMO transport can be carried out safely over long distances; in rural areas with underdeveloped roads, transportation via helicopter or ambulance can extend the arm of the hospital to remote areas. Early ECMO initiation can be crucial in improving survival outcomes, and when transportation is the limiting factor to starting ECMO support, it should be attempted at the earliest logistical stage possible.
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Hoefel, Lauren, Annette M. O’Connor, Krystina B. Lewis, Laura Boland, Lindsey Sikora, Jiale Hu, and Dawn Stacey. "20th Anniversary Update of the Ottawa Decision Support Framework Part 1: A Systematic Review of the Decisional Needs of People Making Health or Social Decisions." Medical Decision Making 40, no. 5 (July 2020): 555–81. http://dx.doi.org/10.1177/0272989x20936209.
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Background. The Ottawa Decision Support Framework (ODSF) has been used for 20 years to assess and address people’s decisional needs. The evidence regarding ODSF decisional needs has not been synthesized. Objectives. To synthesize evidence from ODSF-based decisional needs studies, identify new decisional needs, and validate current ODSF decisional needs. Methods. A mixed-studies systematic review. Nine electronic databases were searched. Inclusion criteria: studies of people’s decisional needs when making health or social decisions for themselves, a child, or a mentally incapable person, as reported by themselves, families, or practitioners. Two independent authors screened eligibility, extracted data, and quality appraised studies using the Mixed Methods Appraisal Tool. Data were analyzed using narrative synthesis. Results. Of 4532 citations, 45 studies from 7 countries were eligible. People’s needs for 101 unique decisions (85 health, 16 social) were reported by 2857 patient decision makers ( n = 36 studies), 92 parent decision makers ( n = 6), 81 family members ( n = 5), and 523 practitioners ( n = 21). Current ODSF decisional needs were reported in 2 to 40 studies. For 6 decisional needs, there were 11 new (manifestations): 1) information (overload, inadequacy regarding others’ experiences with options), 2) difficult decisional roles (practitioner, family involvement, or deliberations), 3) unrealistic expectations (difficulty believing outcome probabilities apply to them), 4) personal needs (religion/spirituality), 5) difficult decision timing (unpredictable), and 6) unreceptive decisional stage (difficulty accepting condition/need for treatment, powerful emotions limiting information processing, lacking motivation to consider delayed/unpredictable decisions). Limitations. Possible publication bias (only peer-reviewed journals included). Possible missed needs (non-ODSF studies, patient decision aid development studies, 3 ODSF needs added in 2006). Conclusion. We validated current decisional needs, identified 11 new manifestations of 6 decisional needs, and recommended ODSF revisions.
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Hatzimichael, Eleftheria, Aggeliki Dasoula, Nelofer Syed, Peter Wojciech Szlosarek, George Dranitsaris, Tim Crook, and Evangelos C. Briasoulis. "Epigenetic inactivation to target the arginine biosynthetic pathway in multiple myeloma." Journal of Clinical Oncology 30, no. 15_suppl (May 20, 2012): e18567-e18567. http://dx.doi.org/10.1200/jco.2012.30.15_suppl.e18567.
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e18567 Background: Argininoosuccinate synthetase-1 (ASS1) catalyses the rate-limiting step in arginine biosynthesis, the conversion of citruline to arginine. Argininosuccinate lyase (ASL) is an enzyme that catalyses the reversible breakdown of arginosuccinate producing arginine and fumerate. Arginine deprivation using arginine deiminase (ADI-PEG20) is currently considered as a novel therapeutic intervention for cancer. In this perspective, we investigated the methylation status of the ASS1 and ASL CpG islands in multiple myeloma (MM) and analyzed for clinical relevance. Methods: Genomic DNA was extracted from bone marrow aspirate samples from 46 MM patients (28 male, 18 female, median age 64 years) obtained at diagnosis. Methylation-specific PCR was employed to study the methylation in the ASS1 and ASL CpG islands. DNA was isolated and bisulphite modified using commercially available kits. Logistic regression analyses were used to measure the association between gene methylation and sex, age>65, ISS stage, presence of extramedullary disease, renal failure and bone disease. Kaplan-Meier curves were used to estimate the probabilities of survival and the Log-rank test to assess the statistical significance of differences in event rates. Results: Methylation in the CpG island of ASS1 was detected in 71.7% patients and of ASL in 37% patients, while simultaneous methylation in both genes was present in 10 patients. None of the two genes was detectably methylated in the control group. Patients with ASS1 methylation were less likely to have bone disease (p=0.04, OR=0.22) and extramedullary disease (p=0.05, OR=0.22) and a trend was also noted that these patients were less likely to be >65 years of age (p=0.2, OR=0.37). We did not detect any statistically significant difference in overall survival by methylation status of the studied genes in this small study size. Conclusions: We demonstrate for the first time that arginine biosynthesis genes ASS1 and ASL are methylated in MM.Methylation of ASS1 was found to be more frequent and negatively associated with bone or extramedullary disease. Further evaluation of ASS1 and ASL is warranted in MM and supports the expansion of arginine deprivation trials in these patients
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Gladstone, Douglas Edward, Lode J. Swinnen, Christopher Gocke, Amanda Blackford, Constance A. Griffin, and Richard J. Jones. "IgVH Mutational Status Is Prognostic In 13q Deletion (del) Chronic Lymphocytic Leukemia (CLL)." Blood 116, no. 21 (November 19, 2010): 2419. http://dx.doi.org/10.1182/blood.v116.21.2419.2419.
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Abstract Abstract 2419 While the del (13q) is generally considered to portend an indolent course in CLL, there remains a subset of these patients who exhibit an aggressive clinical course. Although there is little published data on the clinical course of del (13q) CLL patients who also harbor unmutated IgVH, based on preliminary observations we hypothesized that IgVH mutational status may be prognostic in these patients. We screened 196 CLL patients seen at Johns Hopkins between January 2004 and June 2010 and identified 94 patients whose initial FISH evaluation revealed a del (13q); 79 of these also had an IgVH sequence analysis. Unmutated IgVH was found in 38/79 (48%) of the del (13q) CLL patients; baseline characteristics of age, stage of disease, prior therapy and time to first evaluation at Johns Hopkins were similar in these patients when compared to those with mutated IgVH. Accordingly, a Rai stage ≤2 was documented in 35 (92%) of the unmutated and 35 (85%) of the mutated patients at the time of their first evaluation at Johns Hopkins, and >75% in each group were treatment naïve at that time. Unmutated patients were more likely to have additional chromosomal aberrations as compared to mutated patients (66% versus 17%, p<0.001), respectively. During a median follow-up of 4.5 years for each group, unmutated del (13q) patients were also more likely to demonstrate Rai stage progression (72% versus 40%, p=0.01), with Rai stage 3/4 disease or Richter's transformation occurring more commonly in the unmutated group (57% versus 22%. p=0.002). The cumulative probabilities of receiving treatment and mortality were also higher in the unmutated group. The 5-year treatment-free actuarial survival for unmutated patients was 34% compared to 67% for the mutated group (p = 0.002). The 5 year overall actuarial survival estimate for the unmutated patients was 75% compared to 100% for the mutated group (p = 0.03). When limiting the analysis to the 46 patients with del (13q) as the sole chromosomal aberration, the incidence of unmutated disease is less common (28%) but, importantly, similar trends were seen. The 13 unmutated patients with del (13q) as the sole abnormality were also more likely to have Rai stage progression (67% versus 41%, p=0.18), with the Rai stage3/4 disease or Richter's transformation occurring more commonly in the unmutated group (50% versus 24%. p=0.14). Among those with (del)13q as the sole abnormality, the 5-year treatment-free and overall actuarial survivals for the unmutated group was 39% and 68% compared to 68% (p=0.03) and 100% (p=0.16) in the mutated group, respectively. These data confirm that del (13q) conveys an indolent course for CLL patients, but only in the setting of mutated IgVH. Although neither the mutated nor unmutated patients represented an advanced, chemotherapy-refractory group at initial presentation, we found that unmutated IgVH in patients with a del (13q)(as a sole abnormality or with other chromosomal aberrations) exhibited significantly more aggressive disease. Unmutated del (13q) CLL patients appear to have a prognosis similar to other CLL patients with unmutated IgVH. Disclosures: Swinnen: Genentech: Membership on an entity's Board of Directors or advisory committees, Research Funding.