Journal articles: 'Critical loads'

1

Lovett, G. M. "Critical issues for critical loads." Proceedings of the National Academy of Sciences 110, no. 3 (December 27, 2012): 808–9. http://dx.doi.org/10.1073/pnas.1219007110.

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Pardo, L. H., and C. T. Driscoll. "A critical review of mass balance methods for calculating critical loads of nitrogen for forested ecosystems." Environmental Reviews 1, no. 2 (July 1, 1993): 145–56. http://dx.doi.org/10.1139/a93-011.

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Critical loads are used in the assessment of air pollution and regulation of the causative emissions to prevent or mitigate ecological damage. We critically review four mass balance methods for calculating critical loads for nitrogen deposition: the steady-state water chemistry method, the nitrogen mass balance method, the basic cation mass balance method, and the steady-state mass balance method. The critical loads may be calculated with respect to effects of acidification associated with nitrate leaching or effects of elevated nitrogen such as eutrophication, excess nitrate loss, and nutrient imbalances. The most useful method for calculating the critical load for nitrogen with respect to effects of elevated atmospheric deposition of nitrogen is the nitrogen mass balance method. The steady-state water chemistry method can be readily applied for regional-scale calculations because it requires only water chemistry data from synoptic surveys of surface waters and does not explicitly consider biogeochemical processes. Both of the other approaches are severely limited by lack of quantitative information on rates of mineral weathering. If weathering data were available, the steady-state mass balance method could be more effectively used to assess critical loads with respect to acidification. Similarly, the basic cation mass balance method could be used to calculate critical loads for both acidity and elevated nitrogen effects. Because of the complexity of the nitrogen cycle, it is not possible to obtain a single critical load for the whole ecosystem. Rather, one should analyze and synthesize several values of critical loads that reflect different components of the ecosystem and different ecological effects of elevated nitrogen deposition (e.g., acidification and eutrophication effects).Key words: atmospheric deposition of nitrogen, acidification, critical loads, nitrogen cycling.

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Posch, Maximilian, Julian Aherne, and Jean-Paul Hettelingh. "Nitrogen critical loads using biodiversity-related critical limits." Environmental Pollution 159, no. 10 (October 2011): 2223–27. http://dx.doi.org/10.1016/j.envpol.2010.11.001.

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S, Ganesh, Chiranjit Ghosh T, Kokilasree R, Nandhakumar M, and Md Haroon Alim T. "DC UPS for Critical Loads." International Journal of Electrical and Computer Engineering (IJECE) 5, no. 2 (April 1, 2015): 231. http://dx.doi.org/10.11591/ijece.v5i2.pp231-242.

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<p>The usual way to avoid a computer shutdown during a mains failure is to connect an uninterruptible power supply system (UPS), which can be suitably modified and fitted inside the computer cabinet by the use of proposed methodology known as a dc UPS. Conventional desk top UPS systems store electricity in form of chemical energy in batteries and when ever mains fail the batteries provide DC power which is then converter to ac by inverter and then fed to the computer in order to save critical data. Thus power from mains or from UPS is fed to switched mode power supply unit which converts it to dc to supply the computer motherboard and accessories. Leaving the case of the computer powered by mains, duing power failure the dc power is unnecessarily converted to ac and then to dc again in SMPS hence high switching losses and heat is produced there by making the entire system very lowe efficient. In this work it is proposed to directly feed the dc power from the battery to the computer SMPS system by building a UPS arrangement within the computer system. This not noly saves space, it is highly efficient compared to the conventional ups system, easy to carry, low cost and reliable since there is no change over operation is required/. A complete design of an ac to dc power supply with an internal dc UPS is presented in this paper. . A prototype has been fully developed and tested as a PC power supply. Thus the result is achieved at full power about 6-8 minutes.</p>

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(Steve) Sheppard, S. C. "Critical Loads Changing with Time." Human and Ecological Risk Assessment: An International Journal 14, no. 3 (June 2, 2008): 439–54. http://dx.doi.org/10.1080/10807030802073701.

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6

DeWinkel, C., and J. D. Lamoree. "Storing power for critical loads." IEEE Spectrum 30, no. 6 (June 1993): 38–42. http://dx.doi.org/10.1109/6.214584.

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7

Bull, K. R. "Critical loads ? Possibilities and constraints." Water, Air, & Soil Pollution 85, no. 1 (1995): 201–12. http://dx.doi.org/10.1007/bf00483701.

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8

Bull, K. R. "An introduction to critical loads." Environmental Pollution 77, no. 2-3 (1992): 173–76. http://dx.doi.org/10.1016/0269-7491(92)90074-k.

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9

Hettelingh, Jean Paul, Harald Sverdrup, and Dianwu Zhao. "Deriving critical loads for Asia." Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2565–70. http://dx.doi.org/10.1007/bf01186220.

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10

Lindberg, Herbert E. "Dynamic Pulse Buckling of Imperfection-Sensitive Shells." Journal of Applied Mechanics 58, no. 3 (September 1, 1991): 743–48. http://dx.doi.org/10.1115/1.2897258.

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The theoretical basis of two related but distinctly different dynamic buckling criteria are summarized with the objective of demonstrating the range of applicability of each, so that together they cover the entire range of dynamic pulse loads from nearly impulsive loads to step loads of infinite duration. The example chosen is a cylindrical shell under elastic axial loads but the approach is applicable more generally. A critical amplification-of-imperfections criterion with a linear shell theory is shown to be applicable for short duration loads, for which a threshold nonlinear divergence criterion gives loads an order of magnitude too conservative. Conversely, the linear theory is inapplicable for long duration loads, for which critical loads are lower than the linear static buckling load because of imperfection sensitivity. In this range the threshold nonlinear divergence criterion is used. For loads of intermediate duration, an extended critical amplification criterion is used with equations that conservatively assume zero static buckling load but give an unchanged formula for critical load amplitude-duration combinations.

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11

Skeffington, R. A., P. G. Whitehead, and J. Abbott. "Quantifying Uncertainty in Critical Loads: (B) Acidity Mass Balance Critical Loads on a Sensitive Site." Water, Air, and Soil Pollution 169, no. 1-4 (January 2006): 25–46. http://dx.doi.org/10.1007/s11270-006-2218-9.

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12

Hoenderkamp, J. C. D. "Critical loads of lateral load resisting structures for tall buildings." Structural Design of Tall Buildings 11, no. 3 (2002): 221–32. http://dx.doi.org/10.1002/tal.196.

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13

Ghasemi, Sasan, Mokhtar Mohammadi, and Jamal Moshtagh. "A new Look-ahead Restoration of Critical Loads in the Distribution Networks during Blackout with considering Load curve of Critical Loads." Electric Power Systems Research 191 (February 2021): 106873. http://dx.doi.org/10.1016/j.epsr.2020.106873.

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14

Bowman, W. D., J. L. Gartner, K. Holland, and M. Wiedermann. "NITROGEN CRITICAL LOADS AND ALPINE VEGETATION." Bulletin of the Ecological Society of America 87, no. 2 (April 2006): 108–9. http://dx.doi.org/10.1890/0012-9623(2006)87[108:nclaav]2.0.co;2.

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15

Wilby, Robert L. "Critical Loads' Sensitivity to Climate Change." Environmental Conservation 22, no. 4 (1995): 363–65. http://dx.doi.org/10.1017/s0376892900034962.

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16

Barkman, Andreas, Per Warfvinge, and Harald Sverdrup. "Regionalization of critical loads under uncertainty." Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2515–20. http://dx.doi.org/10.1007/bf01186212.

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17

Sánchez, Marcos, Sergio Cicero, Borja Arroyo, and José Alberto Álvarez. "Coupling Finite Element Analysis and the Theory of Critical Distances to Estimate Critical Loads in Al6060-T66 Tubular Beams Containing Notches." Metals 10, no. 10 (October 20, 2020): 1395. http://dx.doi.org/10.3390/met10101395.

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This paper validates a methodology for the estimation of critical loads in tubular beams containing notch-type defects. The methodology is particularized for the case of Al6060-T66 tubular cantilever beams containing U-shaped notches. It consists in obtaining the stress field at the notch tip using finite element analysis (FEA) and the subsequent application of the theory of critical distances (TCD) to derive the corresponding critical load (or load-bearing capacity). The results demonstrate that this methodology provides satisfactory predictions of fracture loads.

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18

Langan, S. J., J. Hall, B. Reynolds, M. Broadmeadow, M. Hornung, and M. S. Cresser. "The development of an approach to assess critical loads of acidity for woodland habitats in Great Britain." Hydrology and Earth System Sciences 8, no. 3 (June 30, 2004): 355–65. http://dx.doi.org/10.5194/hess-8-355-2004.

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Abstract. Alongside other countries that are signatories to the UNECE Convention Long Range Transboundary on Air Pollution, the UK is committed to reducing the impact of air pollution on the environment. To advise and guide this policy in relation to atmospheric emissions of sulphur and nitrogen, a critical load approach has been developed. To assess the potential impact of these pollutants on woodland habitats a steady state, simple mass balance model has been parameterised. For mineral soils, a Ca:Al ratio in soil solution has been used as the critical load indicator for potential damage. For peat and organic soils critical loads have been set according to a pH criterion. Together these approaches have been used with national datasets to examine the potential scale of acidification in woodland habitats across the UK. The results can be mapped to show the spatial variability in critical loads of the three principal woodland habitat types (managed coniferous, managed broadleaved/ mixed woodland and unmanaged woodland). The results suggest that there is a wide range of critical loads. The most sensitive (lowest) critical loads are associated with managed coniferous followed by unmanaged woodland on peat soils. Calculations indicate that at steady state, acid deposition inputs reported for 1995–1997 result in a large proportion of all the woodland habitats identified receiving deposition loads in excess of their critical load; i.e. critical loads are exceeded. These are discussed in relation to future modelled depositions for 2010. Whilst significant widespread negative impacts of such deposition on UK woodland habitats have not been reported, the work serves to illustrate that if acid deposition inputs were maintained and projected emissions reductions not achieved, the long-term sustainability of large areas of woodland in the UK could be compromised. Keywords: critical loads, acid deposition, acidification, woodland, simple mass balance model, sustainability

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Schlutow, Angela, Winfried Schröder, and Stefan Nickel. "Atmospheric Deposition and Element Accumulation in Moss Sampled across Germany 1990–2015: Trends and Relevance for Ecological Integrity and Human Health." Atmosphere 12, no. 2 (January 31, 2021): 193. http://dx.doi.org/10.3390/atmos12020193.

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Deposition of N and heavy metals can impact ecological and human health. This state-of-the-art review addresses spatial and temporal trends of atmospheric deposition as monitored by element accumulation in moss and compares heavy metals Critical Loads for protecting human health and ecosystem’s integrity with modelled deposition. The element accumulation due to deposition was measured at up to 1026 sites collected across Germany 1990–2015. The deposition data were derived from chemical transport modelling and evaluated with regard to Critical Loads published in relevant legal regulations. The moss data indicate declining nitrogen and HM deposition. Ecosystem and human health Critical Loads for As, Ni, Zn, and Cr were not exceeded in Germany 2009–2011. Respective Critical Loads were exceeded by Hg and Pb inputs, especially in the low rainfall regions with forest coverage. The Critical Load for Cu was exceeded by atmospheric deposition in 2010 in two regions. Human health Critical Loads for Cd were not exceeded by atmospheric deposition in 2010. However, the maximum deposition in 2010 exceeded the lowest human health Critical Load. This impact assessment was based only on deposition but not on inputs from other sources such as fertilizers. Therefore, the assessment should be expanded with regard to other HM sources and specified for different ecosystem types.

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20

Langusch, J. J., and E. Matzner. "Long-term modelling of nitrogen turnover and critical loads in a forested catchment using the INCA model." Hydrology and Earth System Sciences 6, no. 3 (June 30, 2002): 395–402. http://dx.doi.org/10.5194/hess-6-395-2002.

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Abstract. Many forest ecosystems in Central Europe have reached the status of N saturation due to chronically high N deposition. In consequence, the NO3 leaching into ground- and surface waters is often substantial. Critical loads have been defined to abate the negative consequences of the NO3 leaching such as soil acidification and nutrient losses. The steady state mass balance method is normally used to calculate critical loads for N deposition in forest ecosystems. However, the steady state mass balance approach is limited because it does not take into account hydrology and the time until the steady state is reached. The aim of this study was to test the suitability of another approach: the dynamic model INCA (Integrated Nitrogen Model for European Catchments). Long-term effects of changing N deposition and critical loads for N were simulated using INCA for the Lehstenbach spruce catchment (Fichtelgebirge, NE Bavaria, Germany) under different hydrological conditions. Long-term scenarios of either increasing or decreasing N deposition indicated that, in this catchment, the response of nitrate concentrations in runoff to changing N deposition is buffered by a large groundwater reservoir. The critical load simulated by the INCA model with respect to a nitrate concentration of 0.4 mg N l–1 as threshold value in runoff was 9.7 kg N ha–1yr–1 compared to 10 kg ha–1yr–1 for the steady state model. Under conditions of lower precipitation (520 mm) the resulting critical load was 7.7 kg N ha–1yr–1 , suggesting the necessity to account for different hydrological conditions when calculating critical loads. The INCA model seems to be suitable to calculate critical loads for N in forested catchments under varying hydrological conditions e.g. as a consequence of climate change. Keywords: forest ecosystem, N saturation, critical load, modelling, long-term scenario, nitrate leaching, critical loads reduction, INCA

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21

Jenkins, A., S. Coric, B. Reynolds, C. Curtis, and M. Renshaw. "Critical loads for soils and freshwaters; a comparison methods at the Plynlimon catchments." Hydrology and Earth System Sciences 1, no. 3 (September 30, 1997): 729–41. http://dx.doi.org/10.5194/hess-1-729-1997.

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Abstract. International agreements aimed at reducing sulphur deposition from the atmosphere are now focused on the "critical loads" concept. This provides a distributed link between sources and receptors of acidic oxides and also links the level of reduction with biological recovery. Methods for calculating critical loads include simple classification (Level 0), mass-balance equilibrium models (Level 1) and dynamic hydrochemical models (Level 2). Here, examples of each method are applied to headwater catchments in Plynlimon, mid-Wales. The critical loads derived are compared and the utility of the critical loads concept as a tool for local pollution control and land management is assessed. Differences in critical load methods for soils result from assumptions regarding biological receptors. Surface water critical loads are generally similar under all methods. As a local management tool, the dynamic model is most appropriate although it has a high data requirement. The utility of other methods depends upon detailed maps of soil and vegetation being available at an appropriate scale.

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22

Chen, Zhenlei, Jiancheng Li, and Longfei Sun. "Calculation of Critical Lateral-Torsional Buckling Loads of Beams Subjected to Arbitrarily Transverse Loads." International Journal of Structural Stability and Dynamics 19, no. 03 (March 2019): 1950031. http://dx.doi.org/10.1142/s0219455419500317.

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This paper presents a novel approach for determining the critical lateral-torsional buckling loads of beams subjected to arbitrarily transverse loads. This new method is developed based on the classical energy method. However, the difference of the present method from the traditional energy methods is the formulation of potential energy of external loads, which is expressed in terms of the internal bending moment and internal shear force in the pre-buckling stage regardless of the type of loading. Compared to the traditional formulations of the potential energy of external loads, not only is the present formula simple in the form, easy and convenient in the calculation, but it also provides a unified form for calculating accurate critical load of lateral-torsional buckling of the beams.

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Khazaeinejad, P., and M. M. Najafizadeh. "Mechanical buckling of cylindrical shells with varying material properties." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, no. 8 (January 12, 2010): 1551–57. http://dx.doi.org/10.1243/09544062jmes1978.

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The analytical solutions of the first-order shear deformation theory are developed to study the buckling behaviour of functionally graded (FG) cylindrical shells under three types of mechanical loads. The Poisson's ratios of the FG cylindrical shells are assumed to be constant, while the Young's moduli vary continuously throughout the thickness direction according to the volume fraction of constituents given by power-law or exponential function. The stability equations are employed to obtain the closed-form solutions for critical buckling loads of each loading case. The dependence of the critical buckling loads on the variations of the material properties with a power-law or exponential function is studied. It is observed that these effects change appreciably the critical buckling loads. Results for critical loads are tabulated for thin and moderately thick shells. Although the critical buckling load of FG cylindrical shells decreases as the circumferential wave numbers increase, it rises for axially compressed long shells as the longitudinal wave numbers increase.

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Aware, M. V., and D. Sutanto. "SMES for Protection of Distributed Critical Loads." IEEE Transactions on Power Delivery 19, no. 3 (July 2004): 1267–75. http://dx.doi.org/10.1109/tpwrd.2003.823176.

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Rapp, L., and K. Bishop. "Modeling Surface Water Critical Loads with PROFILE." Journal of Environmental Quality 32, no. 6 (November 2003): 2290–300. http://dx.doi.org/10.2134/jeq2003.2290.

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Aherne, Julian, and Chris J. Curtis. "Critical loads of acidity for Irish lakes." Aquatic Sciences - Research Across Boundaries 65, no. 1 (March 1, 2003): 21–35. http://dx.doi.org/10.1007/s000270300002.

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27

Mill, W. "Critical loads mapping in Poland: Lessons learned." Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2547–52. http://dx.doi.org/10.1007/bf01186217.

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Henriksen, A., M. Posch, H. Hultberg, and L. Lien. "Critical loads of acidity for surface waters." Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2419–24. http://dx.doi.org/10.1007/bf01186196.

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Tervet, D. J., D. A. Rendall, and A. B. Stephen. "Critical loads ? A valuable catchment management tool?" Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2485–90. http://dx.doi.org/10.1007/bf01186207.

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Henriksen, A. "Critical loads of acidity to surface waters." Water, Air, & Soil Pollution 85, no. 4 (December 1995): 2437–41. http://dx.doi.org/10.1007/bf01186199.

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31

Mosello, R., B. M. Wathne, L. Lien, and H. J. B. Birks. "Al:Pe projects: Water chemistry and critical loads." Water, Air, & Soil Pollution 85, no. 2 (1995): 493–98. http://dx.doi.org/10.1007/bf00476877.

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32

Holdren, George R., Timothy C. Strickland, Bernard J. Cosby, David Marmorek, David Bernard, Robert Santore, Charles T. Driscoll, et al. "A national critical loads framework for atmospheric deposition effects assessment: IV. Model selection, applications, and critical loads mapping." Environmental Management 17, no. 3 (May 1993): 355–63. http://dx.doi.org/10.1007/bf02394678.

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Onyeka, Festus C., and Thompson E. Okeke. "Analysis of critical imposed load of plate using variational calculus." Journal of Advances in Science and Engineering 4, no. 1 (January 2, 2021): 13–23. http://dx.doi.org/10.37121/jase.v4i1.125.

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This work studied the critical load analysis of rectangular plates, carrying uniformly distributed loads utilizing direct variational energy calculus. The aim of this study is to establish the techniques for calculating the critical lateral imposed loads of the plate before deflection attains the specified maximum threshold, qiw as well as its corresponding critical lateral imposed load before the plate reaches an elastic yield point. The formulated potential energy by the static elastic theory of the plate was minimized to get the shear deformation and coefficient of deflection. The plates under consideration are clamped at the first and second edges, free of support at the third edge and simply supported at the fourth edge (CCFS). From the numerical analysis obtained, it is found that the critical lateral imposed loads (qiw and qip) increase as the thickness (t) of plate increases, and decrease as the length to width ratio increases. This suggests that as the thickness increases, the allowable deflection improves the safety of the plate, whereas an increase in the span (length) of the plate increases the failure tendency of the plate structure.

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Kim, Boksun, Long-Yuan Li, and Ashley Edmonds. "Analytical Solutions of Lateral–Torsional Buckling of Castellated Beams." International Journal of Structural Stability and Dynamics 16, no. 08 (August 25, 2016): 1550044. http://dx.doi.org/10.1142/s0219455415500443.

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The majority of the existing literature on the lateral stability of castellated beams deals with experimental and/or numerical studies. This paper presents a comprehensive analytical study of the lateral–torsional buckling of simply supported castellated beams subject to pure bending and/or a uniformly distributed load. Using the principle of total potential energy, analytical expressions for the critical buckling moments and loads are derived and applied for various beam lengths. The three different locations of the applied load are used: At the top flange, shear center and bottom flange. The results show that the influence of web openings on the critical buckling moments and loads are mainly due to the reduction of the torsional constant caused by the web openings. Web shear effects and web shear buckling become important only when the beam is short and the flange is wide. The critical moments and loads will be overestimated or underestimated if the full or reduced section properties are used. The accurate critical moment or load should be calculated based on the average torsional constant of the full and reduced sections rather than simply taking the average of the critical moments or loads calculated from the full and reduced section properties. The present analytical solutions are verified using 3D finite element analysis results.

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Başbük, Musa, Aytekin Eryılmaz, and M. Tarık Atay. "On Critical Buckling Loads of Columns under End Load Dependent on Direction." International Scholarly Research Notices 2014 (October 29, 2014): 1–6. http://dx.doi.org/10.1155/2014/531438.

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Most of the phenomena of various fields of applied sciences are nonlinear problems. Recently, various types of analytical approximate solution techniques were introduced and successfully applied to the nonlinear differential equations. One of the aforementioned techniques is the Homotopy analysis method (HAM). In this study, we applied HAM to find critical buckling load of a column under end load dependent on direction. We obtained the critical buckling loads and compared them with the exact analytic solutions in the literature.

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Shah, Kirti, Mateo San Miguel, Rick Hofstetter, and Mark Tiffany. "Load preservation systems - Real-time cogeneration source protection of critical utility loads." IEEE Industry Applications Magazine 13, no. 5 (September 2007): 31–37. http://dx.doi.org/10.1109/mia.2007.901384.

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Bannerman, R. T., D. W. Owens, R. B. Dodds, and N. J. Hornewer. "Sources of Pollutants in Wisconsin Stormwater." Water Science and Technology 28, no. 3-5 (August 1, 1993): 241–59. http://dx.doi.org/10.2166/wst.1993.0426.

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Rainfall runoff samples were collected from streets, parking lots, roofs, driveways, and lawns. These five source areas are located in residential, commercial, and industrial land uses in Madison, Wisconsin. Solids, phosphorus, and heavy metals loads were determined for all the source areas using measured concentrations and runoff volumes estimated by the Source Load and Management Model. Source areas with relatively large contaminant loads were identified as critical source areas for each land use. Streets are critical source areas for most contaminants in all the land uses. Parking lots are critical in the commercial and industrial land uses. Lawns and driveways contribute large phosphorus loads in the residential land use. Roofs produce significant zinc loads in the commercial and industrial land uses. Identification of critical source areas could reduce the amount of area needing best-management practices in two areas of Madison, Wisconsin. Targeting best-management practices to 14% of the residential area and 40% of the industrial area could significantly reduce contaminant loads by up to 75%.

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Wang, Dong, and Mao See Wu. "Elastic buckling analysis of an embedded infinitely long rod under combined axial and torsional loads." Mathematics and Mechanics of Solids 24, no. 12 (June 24, 2019): 3779–94. http://dx.doi.org/10.1177/1081286519856062.

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In this paper, expressions for the critical axial–torsional loads are derived for the buckling of an elastic rod embedded in an elastic medium. The derivation is based on the assumption that the deforming rod encounters a response force from the surrounding medium, and a first-order perturbation analysis of the governing equilibrium equations. It is shown that a dimensionless universal buckling relationship, independent of material and geometry, exists between the critical axial load, both in compression and tension, and the critical torsional load. A reducing axial compression, or an increasing axial tension, enhances the critical torsional load. In addition, two different mode shapes are predicted for the same critical combined loads, and the buckled shapes are generally three-dimensional.

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Pinho, P., M. R. Theobald, T. Dias, Y. S. Tang, C. Cruz, M. A. Martins-Loução, C. Máguas, M. Sutton, and C. Branquinho. "Critical loads of nitrogen deposition and critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands." Biogeosciences 9, no. 3 (March 28, 2012): 1205–15. http://dx.doi.org/10.5194/bg-9-1205-2012.

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Abstract. Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds such as critical loads (deposition fluxes) and levels (concentrations) can be established. Few studies have assessed these thresholds for semi-natural Mediterranean ecosystems. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands. We have considered changes in epiphytic lichen communities, one of the most sensitive comunity indicators of excessive N in the atmosphere. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done for a Mediterranean climate in evergreen cork-oak woodlands, based on the relation between lichen functional diversity and modelled N deposition for critical loads and measured annual atmospheric ammonia concentrations for critical levels, evaluated downwind from a reduced N source (a cattle barn). Modelling the highly significant relationship between lichen functional groups and annual atmospheric ammonia concentration showed the critical level to be below 1.9 μg m−3, in agreement with recent studies for other ecosystems. Modelling the highly significant relationship between lichen functional groups and N deposition showed that the critical load was lower than 26 kg (N) ha−1 yr−1, which is within the upper range established for other semi-natural ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should aid development of policies to protect Mediterranean woodlands from the initial effects of excessive N.

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Long-yuan, Li. "Discussion of critical load in nonlinear stability analysis and suggestion of variational principle of solving critical loads." Applied Mathematics and Mechanics 11, no. 3 (March 1990): 293–95. http://dx.doi.org/10.1007/bf02015211.

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Choi, Dong Chul, and Tae Wan Kim. "Contact Analysis for the Critical Shoulder Height in Angular Contact Ball Bearing." Advanced Materials Research 433-440 (January 2012): 538–43. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.538.

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A numerical method to determine the shoulder height in the angular contact ball bearing using 3D contact analysis is proposed. The load analysis of a ball bearing was performed to calculate the distributions of internal loads and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between ball and inner/outer raceway, 3D contact analyses are conducted. The developed algorithm is applied to an angular contact ball bearing for the automotive wheel. The critical axial loads which are not affected by edge in the present shoulder height are calculated. The critical shoulder heights are also determined when the bearing is subjected to a practical load.

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Sarwar, Sohail, Hazlie Mokhlis, Mohamadariff Othman, Munir Azam Muhammad, J. A. Laghari, Nurulafiqah Nadzirah Mansor, Hasmaini Mohamad, and Alireza Pourdaryaei. "A Mixed Integer Linear Programming Based Load Shedding Technique for Improving the Sustainability of Islanded Distribution Systems." Sustainability 12, no. 15 (August 3, 2020): 6234. http://dx.doi.org/10.3390/su12156234.

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In recent years significant changes in climate have pivoted the distribution system towards renewable energy, particularly through distributed generators (DGs). Although DGs offer many benefits to the distribution system, their integration affects the stability of the system, which could lead to blackout when the grid is disconnected. The system frequency will drop drastically if DG generation capacity is less than the total load demand in the network. In order to sustain the system stability, under-frequency load shedding (UFLS) is inevitable. The common approach of load shedding sheds random loads until the system’s frequency is recovered. Random and sequential selection results in excessive load shedding, which in turn causes frequency overshoot. In this regard, this paper proposes an efficient load shedding technique for islanded distribution systems. This technique utilizes a voltage stability index to rank the unstable loads for load shedding. In the proposed method, the power imbalance is computed using the swing equation incorporating frequency value. Mixed integer linear programming (MILP) optimization produces optimal load shedding strategy based on the priority of the loads (i.e., non-critical, semi-critical, and critical) and the load ranking from the voltage stability index of loads. The effectiveness of the proposed scheme is tested on two test systems, i.e., a 28-bus system that is a part of the Malaysian distribution network and the IEEE 69-bus system, using PSCAD/EMTDC. Results obtained prove the effectiveness of the proposed technique in quickly stabilizing the system’s frequency without frequency overshoot by disconnecting unstable non-critical loads on priority. Furthermore, results show that the proposed technique is superior to other adaptive techniques because it increases the sustainability by reducing the load shed amount and avoiding overshoot in system frequency.

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Ghasemi, Morteza, and Abdolrahman Jaamialahmadi. "Buckling analysis of orthotropic smart laminated nanoplates based on the nonlocal continuum mechanics using third-order shear and normal deformation theory." Journal of Thermoplastic Composite Materials 32, no. 5 (May 2, 2018): 593–618. http://dx.doi.org/10.1177/0892705718771114.

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In this article, the nonlocal buckling behavior of biaxially loaded graphene sheet with piezoelectric layers based on an orthotropic intelligent laminated nanoplate model is studied. The nonlocal elasticity theory is used in the buckling analysis to show the size scale effects on the critical buckling loads. The electric potential in piezoelectric layers satisfies Maxwell’s equation for either open- or closed-circuit boundary conditions. Based on the third-order shear and normal deformation theory, the nonlinear equilibrium equations are obtained. In order to obtain the linear nonlocal stability equations, the adjacent equilibrium criterion is used. The linear nonlocal governing stability equations are solved analytically, assuming simply supported boundary condition along all edges. To validate the results, the critical buckling loads are compared with those of molecular dynamics simulations. Finally, the effects of different parameters on the critical buckling loads are studied in detail. The results show that by increasing the nonlocal parameter, the critical buckling load decreases. The piezoelectric effect increases the critical buckling load for both open- and closed-circuit boundary conditions. For open-circuit boundary condition, the variation in the critical buckling load is due to the stiffness and piezoelectric effects, but for closed circuit, it is due to the stiffness effect only. Also, the critical buckling load for open circuit is bigger than that of closed one.

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Waddar, Sunil, P. Jeyaraj, and Mrityunjay Doddamani. "Influence of axial compressive loads on buckling and free vibration response of surface-modified fly ash cenosphere/epoxy syntactic foams." Journal of Composite Materials 52, no. 19 (January 8, 2018): 2621–30. http://dx.doi.org/10.1177/0021998317751284.

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This work deals with experimental buckling and free vibration behavior of silane-treated cenosphere/epoxy syntactic foams subjected to axial compression. Critical buckling loads are computed from compressive load–deflection plots deduced using universal testing machine. Further, compressive loads are applied in the fixed intervals until critical loading point on different set of samples having similar filler loadings to estimate natural frequency associated with the first three transverse bending modes. Increasing filler content increases critical buckling load and natural frequency of syntactic foam composites. Increasing axial compressive load reduce structural stiffness of all the samples under investigation. Syntactic foams registered higher stiffness compared to neat epoxy for all the test loads. Similar observations are noted in case of untreated cenosphere/epoxy foam composites. Silane-modified cenosphere embedded in epoxy matrix registered superior performance (rise in critical buckling load and natural frequencies to the tune of 23.75% and 11.46%, respectively) as compared to untreated ones. Experimental results are compared with the analytical solutions that are derived based on Euler–Bernoulli hypothesis and results are found to be in good agreement. Finally, property map of buckling load as a function of density is presented by extracting values from the available literature.

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Jeffries, D. S., and D. C. L. Lam. "Assessment of the Effect of Acidic Deposition on Canadian Lakes: Determination of Critical Loads for Sulphate Deposition." Water Science and Technology 28, no. 3-5 (August 1, 1993): 183–87. http://dx.doi.org/10.2166/wst.1993.0418.

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The operational definition of the “critical” load for wet SO4 deposition is that which does not increase the regional percent of lakes having pH≤6 for the portion of the population that historically had pH>6. Reviews of the effects of acidic deposition on aquatic biota show that the pH=6 threshold used to determine the critical load is sufficient to protect most organisms. It is inappropriate to specify a single critical load for the whole of eastern Canada due to variability in terrain sensitivity. The Atlantic provinces and easterr Quebec generally have very low critical loads (<8 kg. ha−1.yr−1). The terrain characteristics of this area dictate a critical load very close to background deposition. Lakes in southwestern Quebec and Ontario have critical loads of <8 to >20 kg.ha−1.yr−1 reflecting the wide range in terrain sensitivities that exist in each province.

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Henriksen, A., P. J. Dillon, and J. Aherne. "Critical loads of acidity for surface waters in south-central Ontario, Canada: regional application of the Steady-State Water Chemistry (SSWC) model." Canadian Journal of Fisheries and Aquatic Sciences 59, no. 8 (August 1, 2002): 1287–95. http://dx.doi.org/10.1139/f02-092.

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Critical loads of acidity and the amount by which these critical loads are exceeded by atmospheric deposition (termed "exceedances") were estimated for 1469 lakes from five regions in south-central Ontario, Canada, using single lake chemistry measurements and sulphur deposition data for the period 19761999. Based on the Steady-State Water Chemistry (SSWC) model, four of the five regions had low critical loads, which is consistent with the underlying geology (silicate bedrock) and the thin glacial soils in these regions. Sulphur deposition in the study area showed a clear downward trend over the time period, with a decrease of approximately 50% to current levels of approximately 44 meq·m2·year1. As a result of the declining deposition, the portion of lakes with critical load exceedances has dropped substantially, from 7482% in the four sensitive regions in 1976 to 1126% in 1999. The pentile critical load is typically used as a regional target to account for uncertainties, but also to ensure that a sufficient percentage of lakes are protected (95%). This suggests that further reductions in emissions are required to reduce depositions to approximately 34 meq·m2·year1 (11 kg S·ha1·year1) to prevent critical load exceedance.

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Abdi, R. El, and G. Gambart. "Sur les opérateurs différentiels symétrisants relatifs aux systèmes non-conservatifs." Canadian Journal of Physics 76, no. 5 (May 1, 1998): 403–20. http://dx.doi.org/10.1139/p98-008.

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For nonconservative systems, which we call systems with follower loads, a study is proposed concerning the differential operators which lead to a self-adjoint problem for a generalization of the Rayleigh quotient.In the case of punctual loads, we give the general expression for the identification of these operators. For some systems under follower loads, a new method is developed for the identification of the eigenvalues (critical load and critical frequency) when these operators do not exist. A numerical comparison is presented when the exact solutions do exist. PACS Nos. : 02.00 et 03.00

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Maslen, E. H., and P. E. Allaire. "Magnetic Bearing Sizing for Flexible Rotors." Journal of Tribology 114, no. 2 (April 1, 1992): 223–29. http://dx.doi.org/10.1115/1.2920877.

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Magnetic bearing load capacity in flexible rotor systems must be adequate to accommodate external loads acting on the rotor. The first part of this paper develops the theoretical basis for computing the bearing load capacity requirements of flexible rotors subject to bounded external harmonic loads and strict motion constraints. The second part of this work illustrates the application of the theory to a specific example: a fairly simple three disk flexible rotor subject to mass unbalance loads. Load capacity requirements are computed for the example shaft at its first three free-free forward whirl critical speeds. Based on the bounds obtained, two bearing design cases are examined: one with 45 N load capacity and the other with 223 N load capacity. The performance of the rotor is not improved with the higher capacity bearing and neither is capable of adequately constraining the rotor at its second critical speed. It is concluded that this shaft cannot be operated above its second free-free critical speed without a midspan bearing.

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Zhang, Lei, and Gengshu Tong. "Elastic Stability of Two-Span Continuous Beams under Moving Loads." Advances in Structural Engineering 8, no. 2 (April 2005): 157–72. http://dx.doi.org/10.1260/1369433054037994.

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The elastic stability of two span continuous beams has been studied using FEA methods. Two formulae for estimating the critical loads are proposed, one is suitable for two-span beams with one span loaded, while the other is suitable for two-span beams with both spans equally loaded. Two identical concentrated loads symmetrically located about the mid-span of each loaded span were considered in the derivation of both formulae, and the effect of the height of loaded points for doubly symmetric beams was included. The formulae presented are also accurate enough in calculating the critical loads for two-span continuous beams with the mono-symmetric sections used in practice if the point of load application is at or above the shear centre. A linear approximation is suggested for the interaction of two spans when the two spans of the beam are not equally loaded. For a two-span continuous runway girder supporting moving cranes, the minimum critical load and the maximum absolute moment were investigated, some possible combination of wheel forces on beams considered, and approaches to calculating the critical load for each load combination are suggested when the girder has either one or two cranes moving along it.

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Pinho, P., M. R. Theobald, T. Dias, Y. S. Tang, C. Cruz, M. A. Martins-Loução, C. Máguas, M. Sutton, and C. Branquinho. "Critical loads of nitrogen deposition and critical levels of atmospheric ammonia for mediterranean evergreen woodlands." Biogeosciences Discussions 8, no. 6 (November 21, 2011): 11139–63. http://dx.doi.org/10.5194/bgd-8-11139-2011.

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Abstract. Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds have been established, such as critical loads (deposition fluxes) and levels (concentrations). For Mediterranean ecosystems, few studies have been carried out to assess these parameters. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for Mediterranean evergreen woodlands. For that we have considered changes in epiphytic lichen communities, which have been shown to be one of the most sensitive to excessive N. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done under Mediterranean climate, in evergreen cork-oak woodlands, by sampling lichen functional diversity and annual atmospheric ammonia concentrations and modelling N deposition downwind from a reduced N source (a cattle barn). By modelling the highly significant relationship between lichen functional groups and N deposition, the critical load was estimated to be below 26 kg (N) ha−1 yr−1, which is within the upper range established for other semi-natural ecosystems. By modelling the highly significant relationship of lichen functional groups with annual atmospheric ammonia concentration, the critical level was estimated to be below 1.9 μg m−3, in agreement with recent studies for other ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should be taken into account in policies that aim at protecting Mediterranean woodlands from the initial effects of excessive N.

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Journal articles on the topic 'Critical loads'

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