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Articles de revues sur le sujet « Intrinsic barriers »

Auteur : Grafiati
Publié le 4 juin 2021
Mis à jour le 16 février 2022

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1

Coughlan, Jenn M., et Daniel R. Matute. « The importance of intrinsic postzygotic barriers throughout the speciation process ». Philosophical Transactions of the Royal Society B : Biological Sciences 375, no 1806 (13 juillet 2020) : 20190533. http://dx.doi.org/10.1098/rstb.2019.0533.

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Intrinsic postzygotic barriers can play an important and multifaceted role in speciation, but their contribution is often thought to be reserved to the final stages of the speciation process. Here, we review how intrinsic postzygotic barriers can contribute to speciation, and how this role may change through time. We outline three major contributions of intrinsic postzygotic barriers to speciation. (i) reduction of gene flow : intrinsic postzygotic barriers can effectively reduce gene exchange between sympatric species pairs. We discuss the factors that influence how effective incompatibilities are in limiting gene flow. (ii) early onset of species boundaries via rapid evolution : intrinsic postzygotic barriers can evolve between recently diverged populations or incipient species, thereby influencing speciation relatively early in the process. We discuss why the early origination of incompatibilities is expected under some biological models, and detail how other (and often less obvious) incompatibilities may also serve as important barriers early on in speciation. (iii) reinforcement : intrinsic postzygotic barriers can promote the evolution of subsequent reproductive isolation through processes such as reinforcement, even between relatively recently diverged species pairs. We incorporate classic and recent empirical and theoretical work to explore these three facets of intrinsic postzygotic barriers, and provide our thoughts on recent challenges and areas in the field in which progress can be made. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.
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Stepien, Bogdan, Czeslaw Jedrzejek et Roland E. Allen. « Dangling-bond resonances and intrinsic Schottky barriers ». Solid State Communications 69, no 6 (février 1989) : 647–50. http://dx.doi.org/10.1016/0038-1098(89)90053-7.

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Mitchell, David John, H. Bernhard Schlegel, Sason S. Shaik et Saul Wolfe. « Relationships between geometries and energies of identity SN2 transition states : the dominant role of the distortion energy and its origin ». Canadian Journal of Chemistry 63, no 7 (1 juillet 1985) : 1642–48. http://dx.doi.org/10.1139/v85-276.

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At the 4-31G computational level, the intrinsic barriers of eight identity SN2 reactions X− + CH3X → XCH3 + X− are less than the energies required to distort CH3X from its ground state geometry to its transition state geometry by a constant 25 kcal/mol. The distortion energy and its C—X stretching and H—C—X bending components can be calculated directly, or, alternatively, estimated from the force constants and bond dissociation energies of CH3X. Regardless of the mode of computation, the distortion energies are found to be dominated by the C—X stretching deformations, and these are linearly correlated with the intrinsic barriers. The total deformation energies are also linearly correlated with the intrinsic barriers. The transition vectors of the eight identity reactions have been calculated; each is dominated by the C—X stretch. The percentage of C—X stretching at the transition state, here termed the Distortion Index (DI), reflects the "tightness" or "looseness" of this structure. The intrinsic barrier increases as the DI increases, i.e., as the transition state becomes more "exploded". This result does not agree with the predictions of a More O'Ferrall–Jencks potential energy surface diagram. However, as shown in some detail, all of the computational results of the present work are in harmony with the surface crossing diagram model of the barrier. The essential feature of this model is the notion that the activation process in an identity SN2 reaction is a result of the distortion that is required to transfer one electron from X− to CH3X.
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Ghoneim, Hazem E., Anthony E. Zamora, Paul G. Thomas et Ben A. Youngblood. « Cell-Intrinsic Barriers of T Cell-Based Immunotherapy ». Trends in Molecular Medicine 22, no 12 (décembre 2016) : 1000–1011. http://dx.doi.org/10.1016/j.molmed.2016.10.002.

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Lee, Ikchoon, Chan Kyung Kim et Chang Kon Kim. « Intrinsic barriers for imbalanced versus balanced transition structures ». Journal of Physical Organic Chemistry 12, no 3 (mars 1999) : 255–58. http://dx.doi.org/10.1002/(sici)1099-1395(199903)12:3<255 ::aid-poc150>3.0.co;2-1.

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Adachi-Mejia, Anna M., Keith M. Drake, Todd A. MacKenzie, Linda Titus-Ernstoff, Meghan R. Longacre, Kristy M. Hendricks, Michael L. Beach et Madeline A. Dalton. « Perceived Intrinsic Barriers to Physical Activity Among Rural Mothers ». Journal of Women's Health 19, no 12 (décembre 2010) : 2197–202. http://dx.doi.org/10.1089/jwh.2009.1879.

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Richard, J. P., T. L. Amyes et K. B. Williams. « Intrinsic barriers to the formation and reaction of carbocations ». Pure and Applied Chemistry 70, no 10 (30 octobre 1998) : 2007–14. http://dx.doi.org/10.1351/pac199870102007.

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Creasy, W. R., et J. M. Farrar. « Intrinsic barriers in gas-phase dehydration reactions : an experimental probe ». Journal of Physical Chemistry 89, no 19 (septembre 1985) : 3952–55. http://dx.doi.org/10.1021/j100265a003.

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Bernasconi, Claude F. « Intrinsic barriers of reactions and the principle of nonperfect synchronization ». Accounts of Chemical Research 20, no 8 (août 1987) : 301–8. http://dx.doi.org/10.1021/ar00140a006.

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Majumdar, Amlan. « Effects of intrinsic spin on electronic transport through magnetic barriers ». Physical Review B 54, no 17 (1 novembre 1996) : 11911–13. http://dx.doi.org/10.1103/physrevb.54.11911.

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Hoz, Shmaryahu, Harold Basch, Joel L. Wolk, Tova Hoz et Esther Rozental. « Intrinsic Barriers in Identity SN2 Reactions and the Periodic Table ». Journal of the American Chemical Society 121, no 33 (août 1999) : 7724–25. http://dx.doi.org/10.1021/ja984315e.

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Wolk, Joel L., Esther Rozental, Harold Basch et Shmaryahu Hoz. « Strain Energy Release and Intrinsic Barriers in Internal Nucleophilic Reactions ». Journal of Organic Chemistry 71, no 10 (mai 2006) : 3876–79. http://dx.doi.org/10.1021/jo060215c.

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Sun, Fang, et Zhigang He. « Neuronal intrinsic barriers for axon regeneration in the adult CNS ». Current Opinion in Neurobiology 20, no 4 (août 2010) : 510–18. http://dx.doi.org/10.1016/j.conb.2010.03.013.

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Cowtan, K. « Structural barriers to scientific progress ». Acta Crystallographica Section D Structural Biology 76, no 10 (22 septembre 2020) : 908–11. http://dx.doi.org/10.1107/s2059798320011201.

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Structural biases, which are intrinsic in the social structures in which we function, play a key role in maintaining boundaries between traditionally privileged and underprivileged groups; however, they are particularly difficult to identify from within those societies. Two instances are highlighted in which the social structures of science appear to have discouraged collaboration, to the disadvantage of software and data users. Possible links are suggested to the strongly hierarchical structure of science and other factors which may in turn also serve to maintain sex and/or gender disparities in participation in the scientific endeavour.
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Agrawal, Aneil F., Jeffrey L. Feder et Patrik Nosil. « Ecological Divergence and the Origins of Intrinsic Postmating Isolation with Gene Flow ». International Journal of Ecology 2011 (2011) : 1–15. http://dx.doi.org/10.1155/2011/435357.

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The evolution of intrinsic postmating isolation has received much attention, both historically and in recent studies of speciation genes. Intrinsic isolation often stems from between-locus genetic incompatibilities, where alleles that function well within species are incompatible with one another when brought together in the genome of a hybrid. It can be difficult for such incompatibilities to originate when populations diverge with gene flow, because deleterious genotypic combinations will be created and then purged by selection. However, it has been argued that if genes underlying incompatibilities are themselves subject to divergent selection, then they might overcome gene flow to diverge between populations, resulting in the origin of incompatibilities. Nonetheless, there has been little explicit mathematical exploration of such scenarios for the origin of intrinsic incompatibilities during ecological speciation with gene flow. Here we explore theoretical models for the origin of intrinsic isolation where genes subject to divergent natural selection also affect intrinsic isolation, either directly or via linkage disequilibrium with other loci. Such genes indeed overcome gene flow, diverge between populations, and thus result in the evolution of intrinsic isolation. We also examine barriers to neutral gene flow. Surprisingly, we find that intrinsic isolation sometimes weakens this barrier, by impeding differentiation via ecologically based divergent selection.
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Elliott, Rebekah Omarkhail, et Mei He. « Unlocking the Power of Exosomes for Crossing Biological Barriers in Drug Delivery ». Pharmaceutics 13, no 1 (19 janvier 2021) : 122. http://dx.doi.org/10.3390/pharmaceutics13010122.

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Since the 2013 Nobel Prize was awarded for the discovery of vesicle trafficking, a subgroup of nanovesicles called exosomes has been driving the research field to a new regime for understanding cellular communication. This exosome-dominated traffic control system has increased understanding of many diseases, including cancer metastasis, diabetes, and HIV. In addition to the important diagnostic role, exosomes are particularly attractive for drug delivery, due to their distinctive properties in cellular information transfer and uptake. Compared to viral and non-viral synthetic systems, the natural, cell-derived exosomes exhibit intrinsic payload and bioavailability. Most importantly, exosomes easily cross biological barriers, obstacles that continue to challenge other drug delivery nanoparticle systems. Recent emerging studies have shown numerous critical roles of exosomes in many biological barriers, including the blood–brain barrier (BBB), blood–cerebrospinal fluid barrier (BCSFB), blood–lymph barrier (BlyB), blood–air barrier (BAB), stromal barrier (SB), blood–labyrinth barrier (BLaB), blood–retinal barrier (BRB), and placental barrier (PB), which opens exciting new possibilities for using exosomes as the delivery platform. However, the systematic reviews summarizing such discoveries are still limited. This review covers state-of-the-art exosome research on crossing several important biological barriers with a focus on the current, accepted models used to explain the mechanisms of barrier crossing, including tight junctions. The potential to design and engineer exosomes to enhance delivery efficacy, leading to future applications in precision medicine and immunotherapy, is discussed.
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Pezacki, John Paul. « Normal acid/base behaviour in proton transfer reactions to alkoxy substituted carbenes : estimates for intrinsic barriers to reaction and pKa values ». Canadian Journal of Chemistry 77, no 7 (1 juillet 1999) : 1230–40. http://dx.doi.org/10.1139/v99-087.

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Theoretical Eigen curves can be drawn through Brønsted data for dimethoxycarbene (1), phenyltrimethyl-siloxycarbene (3a), 4-methylphenyl(trimethylsiloxy)carbene (3b), 4-methoxyphenyl(trimethylsiloxy)carbene (3c), and β-naphthyl(trimethylsiloxy)carbene (3d). The Brønsted plots for these data are clearly curved with α values near 1 when proton transfer is thermodynamically unfavourable and α values near 0 when proton transfer is thermodynamically favourable, suggesting that these carbenes behave as "normal" Brønsted bases. Estimates of the intrinsic barriers (ΔG0‡) for proton transfer reactions and of the pKa values for the conjugate acids of the carbenes, extracted from these theoretical curves, have been made. The magnitudes of the intrinsic barriers (ΔG0‡) for these proton transfer reactions determined by Eigen and Marcus theories are all 1-5 kcal mol-1, suggesting that these reactions are intrinsically fast. Small intrinsic barriers also imply "normal" acid/base behaviour. Extrapolated pKa values are also the first estimates for the pKa values of the conjugate acids of carbenes 1 and 3a-3d. Key words: carbenes, proton transfer reactions, carbocations, Marcus theory, Brønsted plots.
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PASSIK, STEVEN D., KAREN BYERS et KENNETH L. KIRSH. « Empathy and the failure to treat pain ». Palliative and Supportive Care 5, no 2 (22 mai 2007) : 167–72. http://dx.doi.org/10.1017/s1478951507070241.

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We set out to discuss the psychological barriers that exist in the treatment of pain. Specifically, we argue that clinicians have several innate mechanisms at play that can hinder their judgment and lead to erroneous assumptions about their patients. Issues are discussed from social psychological and psychodynamic perspectives. A focus is placed on the issue of empathy and how this, too, can act as a barrier to rational judgment when evaluating patients. In the face of growing scrutiny on pain management in the United States, it is important to understand the barriers to providing care that already exist on an intrinsic level. Through the exploration of these barriers, clinicians might be better able to reflect on their own practice. Ultimately, we hope to push forward an agenda of rational therapy in pain management that utilizes safeguards against abuse and addiction while also preserving treatment modalities for patients in need of services.
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19

Buehl, Michael, et Henry F. Schaefer. « SN2 reaction at neutral nitrogen : transition state geometries and intrinsic barriers. » Journal of the American Chemical Society 115, no 20 (octobre 1993) : 9143–47. http://dx.doi.org/10.1021/ja00073a033.

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Kähkönen, Anna-Leena, Antti Laherto et Anssi Lindell. « Intrinsic and Extrinsic Barriers to Teaching Nanoscale Science : Finnish Teachers' Perspectives ». Journal of Nano Education 3, no 1 (1 juin 2011) : 1–12. http://dx.doi.org/10.1166/jne.2011.1017.

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CREUTZ, C. « ChemInform Abstract : Intrinsic Barriers to Atom Transfer Between Transition-Metal Centers ». ChemInform 28, no 37 (3 août 2010) : no. http://dx.doi.org/10.1002/chin.199737397.

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Richard, John P., Kathleen B. Williams et Tina L. Amyes. « Intrinsic Barriers for the Reactions of an Oxocarbenium Ion in Water ». Journal of the American Chemical Society 121, no 36 (septembre 1999) : 8403–4. http://dx.doi.org/10.1021/ja9915293.

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Clarke, Dave. « Intrinsic and Extrinsic Barriers to Health Care : Implications for Problem Gambling ». International Journal of Mental Health and Addiction 5, no 4 (19 mai 2007) : 279–91. http://dx.doi.org/10.1007/s11469-007-9089-1.

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Shukla, Deepak, Guanghua Liu, Joseph P. Dinnocenzo et Samir Farid. « Controlling parameters for radical cation fragmentation reactions : Origin of the intrinsic barrier ». Canadian Journal of Chemistry 81, no 6 (1 juin 2003) : 744–57. http://dx.doi.org/10.1139/v03-078.

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C—C bond cleavages of radical cations of 2-substituted benzothiazoline derivatives were investigated to determine the parameters controlling the fragmentation rate constants. In spite of the low oxidation potentials of the compounds, fragmentation rate constants greater than 1 × 106 s–1 could be achieved through weakening of the fragmenting bond by substituents that stabilize the radical fragment and exert steric crowding. A quantitative assessment of the relative roles of radical stabilization vs. steric effects to weaken the fragmenting C—C bond was achieved through DFT calculations. The calculated activation enthalpies matched reasonably well with the experimentally determined values. A thermokinetic analysis revealed that the fragmentations of benzothiazoline radical cations have relatively large intrinsic kinetic barriers, ascribed to the delocalized nature of the product radical and cation fragments. Interestingly, the same factors that lead to the large intrinsic barriers led, simultaneously, to large thermodynamic driving forces for the fragmentations, which should lead to lower activation barriers. These effects oppose each other kinetically and provide important insight into the design of fast radical ion fragmentation reactions.Key words: benzothiazoline, radical cation, fragmentation, steric effects, DFT.
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Wada, Yuuki, Akira Matsumoto, Keisuke Asano et Seijiro Matsubara. « Enantioselective bromination of axially chiral cyanoarenes in the presence of bifunctional organocatalysts ». RSC Advances 9, no 54 (2019) : 31654–58. http://dx.doi.org/10.1039/c9ra05532k.

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Mahendra, Nidhi. « South Asian Stories : Firsthand Client Perspectives on Barriers to Accessing Speech-Language Pathology Services ». Perspectives on Communication Disorders and Sciences in Culturally and Linguistically Diverse (CLD) Populations 19, no 1 (mars 2012) : 29–36. http://dx.doi.org/10.1044/cds19.1.29.

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This article details the experience of two South Asian individuals with family members who had communication disorders. I provide information on intrinsic and extrinsic barriers reported by these clients in responses to a survey and during individual ethnographic interviews. These data are part of a larger study and provide empirical support of cultural and linguistic barriers that may impede timely access to and utilization of speech-language pathology (SLP) services. The purpose of this article is to shed light on barriers and facilitators that influence South Asian clients' access to SLP services. I provide and briefly analyze two case vignettes to provide readers a phenomenological perspective on client experiences. Data about barriers limiting access to SLP services were obtained via client surveys and individual interviews. These two clients' data were extracted from a larger study (Mahendra, Scullion, Hamerschlag, Cooper, & La, 2011) in which 52 racially/ethnically diverse clients participated. Survey items and interview questions were designed to elicit information about client experiences when accessing SLP services. Results reveal specific intrinsic and extrinsic barriers that affected two South Asian clients' access to SLP services and have important implications for all providers.
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Muldoon, Leslie L., Jorge I. Alvarez, David J. Begley, Ruben J. Boado, Gregory J. del Zoppo, Nancy D. Doolittle, Britta Engelhardt et al. « Immunologic Privilege in the Central Nervous System and the Blood–Brain Barrier ». Journal of Cerebral Blood Flow & ; Metabolism 33, no 1 (17 octobre 2012) : 13–21. http://dx.doi.org/10.1038/jcbfm.2012.153.

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The brain is in many ways an immunologically and pharmacologically privileged site. The blood–brain barrier (BBB) of the cerebrovascular endothelium and its participation in the complex structure of the neurovascular unit (NVU) restrict access of immune cells and immune mediators to the central nervous system (CNS). In pathologic conditions, very well-organized immunologic responses can develop within the CNS, raising important questions about the real nature and the intrinsic and extrinsic regulation of this immune privilege. We assess the interactions of immune cells and immune mediators with the BBB and NVU in neurologic disease, cerebrovascular disease, and intracerebral tumors. The goals of this review are to outline key scientific advances and the status of the science central to both the neuroinflammation and CNS barriers fields, and highlight the opportunities and priorities in advancing brain barriers research in the context of the larger immunology and neuroscience disciplines. This review article was developed from reports presented at the 2011 Annual Blood-Brain Barrier Consortium Meeting.
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Clairbois, Jean-Pierre, Massimo Garai, Wolfram Bartolomaeus, Michael Chudalla, Fabio Strigari, Marco Conter et Andreas Fuchs. « Characterizing noise barriers : SOPRANOISE half-term progress report ». INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no 3 (1 août 2021) : 3663–74. http://dx.doi.org/10.3397/in-2021-2485.

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SOPRANOISE targets simplified assessment of the in-situ intrinsic acoustic performances of road / railway noise barriers. This paper presents its half-term progress. The research is divided in 5 Work Packages, the scientific ones being WP2 to WP5.WP2 is about establishing a state of art (SoA) of the intrinsic performances characterization: it is now finished and presented in 2 other papers by Conter and Fuchs. WP3 is about in-situ inspection tools: based on a review / questionnaire, an inspection protocol has been developed allowing simplified assessments mainly based on visual inspections and characterization of possible defects; WP3 is now in its final testing phase. WP4 is about designing a brand new "quick and safe methods" that could take place "in between" the inspection tools and the standardized EN1793-5 and 6; the research and development phases of WP4 are now finished, while its validation along highways is now scheduled. Finally, WP5 is about the use of noise barriers in the European market and the final report: a synthesis on the physical behavior of noise barriers and the physical significance of the test methods has been done, as well a SoA on the effective use of noise barriers; the results will be presented.
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Zhang, Jiajun, Beatriz Fidalgo, Athanasios Kolios, Dekui Shen et Sai Gu. « The mechanism of transmethylation in anisole decomposition over Brønsted acid sites : density functional theory (DFT) study ». Sustainable Energy & ; Fuels 1, no 8 (2017) : 1788–94. http://dx.doi.org/10.1039/c7se00280g.

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Würthwein, Ernst-Ulrich, Gabriele Lang, Ludwig H. Schappele et Herbert Mayr. « Rate-Equilibrium Relationships in Hydride Transfer Reactions : The Role of Intrinsic Barriers ». Journal of the American Chemical Society 124, no 15 (avril 2002) : 4084–92. http://dx.doi.org/10.1021/ja0121540.

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Jeamton, Wattana, Sudarat Dulsawat, Morakot Tanticharoen, Avigad Vonshak et Supapon Cheevadhanarak. « Overcoming Intrinsic Restriction Enzyme Barriers Enhances Transformation Efficiency in Arthrospira platensis C1 ». Plant and Cell Physiology 58, no 4 (1 février 2017) : 822–30. http://dx.doi.org/10.1093/pcp/pcx016.

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Kim, S. S., Hogun Jhang, P. H. Diamond, L. Terzolo, S. Yi et T. S. Hahm. « Intrinsic rotation, hysteresis and back transition in reversed shear internal transport barriers ». Nuclear Fusion 51, no 7 (2 juin 2011) : 073021. http://dx.doi.org/10.1088/0029-5515/51/7/073021.

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Zhao, Larry, Melina Lofrano, Kristof Croes, Els Van Besien, Zsolt Tőkei, Christopher J. Wilson, Robin Degraeve, Thomas Kauerauf, Gerald P. Beyer et Cor Claeys. « Evaluations of intrinsic time dependent dielectric breakdown of dielectric copper diffusion barriers ». Thin Solid Films 520, no 1 (octobre 2011) : 662–66. http://dx.doi.org/10.1016/j.tsf.2011.08.073.

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Stock, Philipp, Tomasz Pędziński, Nicole Spintig, Andreas Grohmann et Gerald Hörner. « High Intrinsic Barriers against Spin-State Relaxation in Iron(II)-Complex Solutions ». Chemistry - A European Journal 19, no 3 (11 décembre 2012) : 839–42. http://dx.doi.org/10.1002/chem.201203784.

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Ancheta Jr., Rosein, Roberto Padua, Shirley Ann A. Caballes, Dharyll Prince M. Abellana, Custer C. Deocaris, Celbert M. Himang, Lanndon A. Ocampo, Miriam F. Bongo et Jun Jun A. Obiso. « Management of Industry 4.0 – reviewing intrinsic and extrinsic adoption drivers and barriers ». International Journal of Technology Management 81, no 3/4 (2019) : 210. http://dx.doi.org/10.1504/ijtm.2019.10027028.

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Obiso, Jun Jun A., Celbert M. Himang, Lanndon A. Ocampo, Miriam F. Bongo, Shirley Ann A. Caballes, Dharyll Prince M. Abellana, Custer C. Deocaris, Roberto Padua et Rosein Ancheta Jr. « Management of Industry 4.0 – reviewing intrinsic and extrinsic adoption drivers and barriers ». International Journal of Technology Management 81, no 3/4 (2019) : 210. http://dx.doi.org/10.1504/ijtm.2019.105310.

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Lee, Ikchoon. « Natural bond orbital analysis of the intrinsic reaction barriers in nucleophilic displacements ». International Reviews in Physical Chemistry 22, no 2 (avril 2003) : 263–83. http://dx.doi.org/10.1080/0144235031000086058.

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Christmas, Matthew J., Julia C. Jones, Anna Olsson, Ola Wallerman, Ignas Bunikis, Marcin Kierczak, Valentina Peona et al. « Genetic Barriers to Historical Gene Flow between Cryptic Species of Alpine Bumblebees Revealed by Comparative Population Genomics ». Molecular Biology and Evolution 38, no 8 (6 avril 2021) : 3126–43. http://dx.doi.org/10.1093/molbev/msab086.

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Abstract Evidence is accumulating that gene flow commonly occurs between recently diverged species, despite the existence of barriers to gene flow in their genomes. However, we still know little about what regions of the genome become barriers to gene flow and how such barriers form. Here, we compare genetic differentiation across the genomes of bumblebee species living in sympatry and allopatry to reveal the potential impact of gene flow during species divergence and uncover genetic barrier loci. We first compared the genomes of the alpine bumblebee Bombus sylvicola and a previously unidentified sister species living in sympatry in the Rocky Mountains, revealing prominent islands of elevated genetic divergence in the genome that colocalize with centromeres and regions of low recombination. This same pattern is observed between the genomes of another pair of closely related species living in allopatry (B. bifarius and B. vancouverensis). Strikingly however, the genomic islands exhibit significantly elevated absolute divergence (dXY) in the sympatric, but not the allopatric, comparison indicating that they contain loci that have acted as barriers to historical gene flow in sympatry. Our results suggest that intrinsic barriers to gene flow between species may often accumulate in regions of low recombination and near centromeres through processes such as genetic hitchhiking, and that divergence in these regions is accentuated in the presence of gene flow.
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Harris, Brigitte, Kwan Fan Cheng et Charlotte Gorley. « Benefits and Barriers ». Journal of Workplace Learning 27, no 3 (13 avril 2015) : 193–206. http://dx.doi.org/10.1108/jwl-07-2014-0053.

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Purpose – This study aims to describe the design of a provincial government ministry group mentoring program and examine mentees’ and mentors’ experiences in the program. Design/methodology/approach – A total of 151 mentees rated their satisfaction in a post-program survey. The survey was followed by in-depth, semi-structured interviews with 10 mentees and 11 mentors. Findings – In all, 87 per cent of mentees rated their learning as effective. Benefits to mentees were relevance of the learning, and senior leader/mentors use of current issues, events and personal stories. Delivery through a combination of Web conferencing and collaboration technologies was most effective. Mentors learned from mentees and other mentors. Regular and full mentee participation was an identified issue. In addition, not all mentoring teams worked well together. Research limitations/implications – The selection criteria favored participants who had a positive experience. Including more participants who were disengaged or less active may have revealed what inhibited full engagement. Complex underlying systemic and cultural issues negatively affected mentee participation and mentoring team effectiveness. It is unclear whether this was caused by intrinsic or extrinsic barriers. Further study could shed light on how to address participation issues. Practical implications – Selection criteria favored highly active participants who had a positive experience. Including more disengaged or less active participants may have revealed barriers to full engagement. Social implications – Despite a context of extreme organizational churn, this program delivered cost-effective and engaging learning to a large number of employees. Recommendations are made to further strengthen the program. Originality/value – This contextually grounded case study will be useful to those who plan to implement a group mentoring program.
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Wong, S. Y. W., Izzah A., N. A. Mahyudin, J. A. Ho et Ungku Fatimah U.Z.A. « Insight into food handlers’ perceived barriers and motivators to perform food temperature control practices in Malaysian public schools ». Food Research 4, no 3 (14 janvier 2020) : 793–804. http://dx.doi.org/10.26656/fr.2017.4(3).347.

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This study was conducted to identify the current temperature control practices and determine the perceived barriers and motivators of school food handlers during cooking and holding process. A total of seven focus group discussions (FGD) were carried out with 64 food handlers using purposive sampling method from selected school canteens in Klang Valley, Malaysia. Audio-recordings were transcribed into verbatim, and data were analyzed using Atlas.ti software. Data-driven coding was done and independently coded by a second researcher to obtain intercoder reliability. Findings reveal that the participants do not use thermometer during cooking. Hot holding equipment (i.e., bain-marie) were not commonly used for students’ food. For the perceived barriers of thermometer use during cooking, time constraint was the most frequently mentioned barrier reported. Other barriers identified were inadequate knowledge, no thermometer, not a requirement, and inconvenience. The perceived barriers for using hot holding equipment were inadequate resources and uncertainty of business contract renewal. On the other hand, motivators to perform overall temperature control practices were determined: 1) law and enforcement, 2) customer satisfaction, 3) resources, 4) intrinsic motivation, and 5) knowledge and training. Findings from this study can be applied in food safety intervention programs to increase food handlers' compliance with proper temperature control practices.
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Qu, Hong-jie, Lang Yuan, Cai-xin Jia, Hai-tao Yu et Hui Xu. « DFT Investigation of Hydrogen Atom Abstraction from NHC-Boranes by Methyl, Ethyl and Cyanomethyl Radicals—Composition and Correlation Analysis of Kinetic Barriers ». Molecules 25, no 19 (1 octobre 2020) : 4509. http://dx.doi.org/10.3390/molecules25194509.

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Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by •CH2CN, Me• and Et• radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans–Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.
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Schilling, Eva-Maria, Myriam Scherer et Thomas Stamminger. « Intrinsic Immune Mechanisms Restricting Human Cytomegalovirus Replication ». Viruses 13, no 2 (26 janvier 2021) : 179. http://dx.doi.org/10.3390/v13020179.

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Cellular restriction factors (RFs) act as important constitutive innate immune barriers against viruses. In 2006, the promyelocytic leukemia protein was described as the first RF against human cytomegalovirus (HCMV) infection which is antagonized by the viral immediate early protein IE1. Since then, at least 15 additional RFs against HCMV have been identified, including the chromatin regulatory protein SPOC1, the cytidine deaminase APOBEC3A and the dNTP triphosphohydrolase SAMHD1. These RFs affect distinct steps of the viral replication cycle such as viral entry, gene expression, the synthesis of progeny DNA or egress. This review summarizes our current knowledge on intrinsic immune mechanisms restricting HCMV replication as well as on the viral strategies to counteract the inhibitory effects of RFs. Detailed knowledge on the interplay between host RFs and antagonizing viral factors will be fundamental to develop new approaches to combat HCMV infection.
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Li, Honglin, Yuting Cui et Haijun Luo. « The modulation of Schottky contacts of p-type graphene-GeC/GeS heterointerface ». European Physical Journal Applied Physics 84, no 3 (décembre 2018) : 30101. http://dx.doi.org/10.1051/epjap/2018180279.

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n-Type contact of Schottky barriers at two-dimensional (2D) materials/metal interfaces is a usual formalization in the modern FETs applications. It is common to modulate it from n- to p-type through some specific methods. In this work, we came up with two new intrinsic p-type contacts of graphene-GeC/GeS and further tune them from p-type to n-type by external electric fields. It proved that the electronic properties of graphene and GeC/GeS can be roughly preserved for the weak van der Waals (vdW) interaction. p-Type contacts with relatively small barriers are formed at g-GeC/GeS heterointerfaces. After external electric field applied, the Schottky barrier can be effectively tuned by different external electric and the p-type contact further turns into n-type. Variation of the Schottky barriers indicated a partial pinning for interfaces of g-GeC/GeS. This is because the interfacial states between graphene and GeC/GeS hardly exists. The barrier height of g-GeC/GeS and the corresponding contact type can be flexibly tuned, which is of great importance in the design of novel transistors-based 2D materials. Searching for novel nanoscale electronic equipment based on 2D materials is a hot topic in the current study. This work would provide meaningful guidelines for nanoscale devices.
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Babbar, Priyanka, K. Vijaya Kumar, PT Abraham Joshua, M. Chakrapani et ZK Misri. « Adherence to Home-based Neuro-rehabilitation Exercise program in Stroke survivors ». Bangladesh Journal of Medical Science 20, no 1 (1 janvier 2021) : 145–53. http://dx.doi.org/10.3329/bjms.v20i1.50361.

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Background:Post discharge, Home-based exercise program (HEP), prescribed by physiotherapistis an integral part, to plan effective stroke rehabilitation, with the intended goal of maintainingfunctional motor performance and enhancing functional progress.Earlier studies have shown thatmany factors attribute to adherence and barriers for structured group based exercise program. Objective: This study was designed to identify the factors in stroke subjects, which mayinfluence the adherence and barriers to individually tailored HEP post-discharge, in strokesubjects. Method: An analytical cross-sectional study, with non-random sampling, consistingof first onset stroke subjects who had received acute stroke rehabilitation from tertiary carehospitals. Post-discharge, seventy-four participants were followed up and their responses relatedto adherence and barriers to the prescribed HEP by administering a self-reported adherence to home exercise questionnaire. Results: 63.5% were adherent and 36.5% were non-adherent toHEP, among 74 subjects. The adherent group had performed exercises for at least 5-6 times in aweek, for 31-45 minutes each day. Intrinsic factors related to self-efficacy and perceived level ofanticipated recovery had found an association with adherent and non-adherent groups.The mostcommon barriers for adherence to HEP were fear of fall or injury and fatigue for both adherent and non-adherent subjects. Conclusion: This present study helped to put an insight, onto sociodemographicand intrinsic factors, with the level of adherence and to identify the barriers foradherence to individually tailored HEP. Bangladesh Journal of Medical Science Vol.20(1) 2021 p.145-153
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Ellis, Graham W. L., Donald F. Tavares et Arvi Rauk. « The mechanism of an intramolecular Michael addition : a MNDO study ». Canadian Journal of Chemistry 63, no 12 (1 décembre 1985) : 3510–15. http://dx.doi.org/10.1139/v85-575.

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The 5-endo-trig cyclization reactions of α′-hydroxy α,β-unsaturated carbonyl compounds to form the 3-furanone ring system has been investigated by means of MNDO calculations. In acid medium, the activation energy for ring formation is reduced by protonation of the carbonyl oxygen and by electron-releasing β-substituents, both of which facilitate torsion about the α,β-CC bond. Rotation about the α,β-CC bond is essentially complete when the transition structure is achieved. In reverse ring opening, heterolytic rupture of the C—O bond is aided by prior enolization since induced polarization of the enol π system acts to stabilize the developing cationic centre at the β-carbon. In basic medium, ring closure is hindered by the combined effects of the intrinsic barrier to cyclization and solvation of the intermediate alkoxide. Ring opening in basic medium is prevented by prohibitively high intrinsic barriers except when a strongly electron-releasing group such as p-O(−)-phenyl is at the β-carbon.
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Pinto, Nelangi, Xiaoming Sheng, Heather T. Keenan, Janice L. B. Byrne, Belva Stanton et Anita Y. Kinney. « Sonographer-Identified Barriers and Facilitators to Prenatal Screening for Congenital Heart Disease ». Journal of Diagnostic Medical Sonography 33, no 1 (11 novembre 2016) : 3–12. http://dx.doi.org/10.1177/8756479316677019.

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Background: Fetal ultrasound screening for congenital heart disease has high detection rates in efficacy studies but not in practice. We investigated sonographers’ perspectives on barriers to screening and their association with intermediate measures of cardiac imaging. Methods: Barriers to fetal heart screening were identified in focus groups with obstetric sonographers. A web-based survey measured reported barriers and sonographers’ ability to interpret fetal heart screening images. Generalized linear random effect models assessed associations between barriers and image interpretation. Results: Four themes were identified: intrinsic barriers (self-efficacy), external barriers (time), informational needs, and provider and patient expectations. Among 224 sonographers surveyed, an average of 77.6% of fetal heart images were interpreted correctly. Perceptions about self-efficacy ( P = .03) and ease of performing imaging ( P = .01) were associated with accuracy of image interpretation. Conclusions: Several sonographer-identified barriers associated with image interpretation may be novel targets for improving prenatal detection of congenital heart disease.
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Goll, James G., Wentian Liu et H. Holden Thorp. « Excited-state quenching through large intrinsic barriers : proton-transfer reactions of metal hydrides ». Journal of the American Chemical Society 115, no 23 (novembre 1993) : 11048–49. http://dx.doi.org/10.1021/ja00076a096.

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Shi, Zheng, et Russell J. Boyd. « Intrinsic barriers of some model SN2 reactions : second-order Moeller-Plesset perturbation calculations ». Journal of the American Chemical Society 113, no 7 (mars 1991) : 2434–39. http://dx.doi.org/10.1021/ja00007a013.

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Maslak, Przemyslaw, et Jay Theroff. « Intrinsic Barriers of the Alternative Modes of Mesolytic Fragmentations of C−S Bonds ». Journal of the American Chemical Society 118, no 30 (janvier 1996) : 7235–36. http://dx.doi.org/10.1021/ja960735x.

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Roth, Justine P., Scott Lovell et James M. Mayer. « Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes ». Journal of the American Chemical Society 122, no 23 (juin 2000) : 5486–98. http://dx.doi.org/10.1021/ja9941328.

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