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Takashi Sumigawa, Takahiro Shimada, Shuuhei Tanaka, Hiroki Unno, Naoki Ozaki, Shinsaku Ashida, Takayuki Kitamura
Brittle materials such as silicon fail via the crack nucleation and propagation, which is characterized by the singular stress field formed near the crack tip according to Griffith or fracture mechanics theory. The applicability of these continuum-based theories is, however, uncertain and questionable in nanoscale system due to its extremely small singular stress field of only a few nanometers. Here, we directly characterize the mechanical behavior of a nano-crack via the development of in situ nanomechanical testing using a transmission electron microscope, and demonstrate that Griffith or fracture mechanics theory can be applied to even 4-nm stress singularity despite their continuum-based concept...
May 26, 2017: ACS Nano
Péter Szövényi, Kristian K Ullrich, Stefan A Rensing, Daniel Lang, Nico van Gessel, Hans K Stenøien, Elena Conti, Ralf Reski
Long term reduction in effective population size will lead to major shift in genome evolution. In particular, when effective population size is small, genetic drift becomes dominant over natural selection. The onset of self-fertilization is one evolutionary event considerably reducing effective size of populations. Theory predicts that this reduction should be more dramatic in organisms capable for haploid than for diploid selfing. Although theoretically well-grounded, this assertion received mixed experimental support...
May 26, 2017: Genome Biology and Evolution
Jinhyuk Fred Chung, Sang Joon Lee, Anil K Sood
Risk factors of cardiovascular diseases have long been implicated as risk factors for carcinogenesis, but clear explanations for their association have not been presented. In this article, fundamental concepts from carcinogenesis, microvascular hemodynamics, and immunity are collectively reviewed and analyzed in context of the known features of vascular ageing effects, in formulating a theory that suggests reduced microvascular immunity as an important driving factor for carcinogenesis. Furthermore, scientific, preclinical, and clinical evidence that support this new theory are presented in an interdisciplinary manner, offering new explanations to previously unanswered factors that impact cancer risks and its treatment outcome such as chronic drug use, temperature, stress and exercise effects among others...
May 10, 2017: Oncotarget
Cleotilde Gonzalez, Pegah Fakhari, Jerome Busemeyer
OBJECTIVE: The aim of this manuscript is to provide a review of contemporary research and applications on dynamic decision making (DDM). BACKGROUND: Since early DDM studies, there has been little systematic progress in understanding decision making in complex, dynamic systems. Our review contributes to better understanding of decision making processes in dynamic tasks. METHOD: We discuss new research directions in DDM to highlight the value of simplification in the study of complex decision processes, divided into experimental and theoretical/computational approaches, and focus on problems involving control tasks and search-and-choice tasks...
May 1, 2017: Human Factors
Andrew R Motz, Andrew M Herring, Shubham Vyas, C Mark Maupin
Perfluorocyclobutyl polymers are thermally and chemically stable, may be produced without a catalyst via thermal 2π-2π cycloaddition, and can form block structures making them suitable for commercialization of specialty polymers. Thermal 2π-2π cycloaddition is a rare reaction that starts in the singlet state and proceeds through a triplet intermediate forming an energetically stable 4 membered ring in the singlet state. This reaction involves two changes in spin state and thus two spin-crossover transitions...
May 26, 2017: Journal of Organic Chemistry
Hugo Gattuso, Cristina García-Iriepa, Diego Sampedro, Antonio Monari, Marco Marazzi
Electronic circular dichroism (CD) spectroscopy of peptides is one of the most important experimental char-acterization tools to get insights regarding their structure. Nevertheless, even though highly useful, the reliable simulations of CD spectra result in a complex task. Here, we propose a combination of quantum mechanics/molecular mechanics (QM/MM) methods with a semi-empirical Hamiltonian based on the Frankel excitons theory to efficiently describe the behavior of a 27-amino acid α-helical peptide in water...
May 26, 2017: Journal of Chemical Theory and Computation
Jing-Shuang Dang, Wei-Wei Wang, Jia-Jia Zheng, Xiang Zhao, Shigeru Nagase
We introduce monotitanium-based endohedral metallofullerenes (EMFs) using density functional theory calculations. Isomeric C64 fullerenes are initially employed as hosts, and Ti@C64 species show novel features on the electronic structures. Energetically, the preference of titanium residing on triple-fused-pentagon subunits is proposed in theory. More importantly, different from current knowledge on mono-EMFs, electron transfer between titanium and carbon cages is not unified but is essentially dependent on the pentagon distribution of the binding sites, giving rise to variations of the cationic titanium of Ti@C64...
May 26, 2017: Inorganic Chemistry
J W González, T Alonso-Lanza, F Delgado, F Aguilera-Granja, A Ayuela
Organometallic clusters based on transition metal atoms are interesting because of their possible applications in spintronics and quantum information processing. In addition to the enhanced magnetism at the nanoscale, the organic ligands may provide a natural shield against unwanted magnetic interactions with the matrices required for applications. Here we show that the organic ligands may lead to non-collinear magnetic order as well as the expected quenching of the magnetic moments. We use different density functional theory (DFT) methods to study the experimentally relevant three cobalt atoms surrounded by benzene rings (Co3Bz3)...
May 26, 2017: Physical Chemistry Chemical Physics: PCCP
Shui Hung Wong, Amy Yin Man Chow
The present study aimed at taking the first attempt in validating the measures generated based on the theory of reasoned action (TRA). A total of 211 university students participated in the study, 95 were included in the exploratory factor analysis and 116 were included in the confirmatory factor analysis. The TRA measurements were established with adequate psychometric properties, internal consistency and construct validity. Findings also suggested that attitude towards organ donation has both a cognitive and affective nature, while the subjective norm of the family seems to be important to students' views on organ donation...
May 26, 2017: Death Studies
Carlo Leget, Inge van Nistelrooij, Merel Visse
BACKGROUND: For many years the body of literature known as 'care ethics' or 'ethics of care' has been discussed as regards its status and nature. There is much confusion and little structured discussion. The paper of Klaver et al. (2014) was written as a discussion article to which we respond. OBJECTIVES: We aim to contribute to the ongoing discussion about the status and nature of care ethics. RESEARCH DESIGN: Responding to 'Demarcation of the ethics of care as a discipline' by Klaver et al...
January 1, 2017: Nursing Ethics
Alexander Pimenov, Svetlana Slepneva, Guillaume Huyet, Andrei G Vladimirov
We present a theoretical approach to investigate the effect of dispersion in dynamical systems commonly described by time-delay models. The introduction of a polarization equation provides a means to introduce dispersion as a distributed delay term. The expansion of this term in power series, as usually performed to study the propagation of waves in spatially extended systems, can lead to the appearance of spurious instabilities. This approach is illustrated using a long cavity laser, where in the normal dispersion regime both the experiment and theory show a stable operation, while a modulation instability, commonly referred as the Benjamin-Feir instability, is observed in the anomalous dispersion regime...
May 12, 2017: Physical Review Letters
Alex Monràs, Gael Sentís, Peter Wittek
In supervised learning, an inductive learning algorithm extracts general rules from observed training instances, then the rules are applied to test instances. We show that this splitting of training and application arises naturally, in the classical setting, from a simple independence requirement with a physical interpretation of being nonsignaling. Thus, two seemingly different definitions of inductive learning happen to coincide. This follows from the properties of classical information that break down in the quantum setup...
May 12, 2017: Physical Review Letters
Pablo Barcellona, Hassan Safari, A Salam, Stefan Yoshi Buhmann
We predict a discriminatory interaction between a chiral molecule and an achiral molecule which is mediated by a chiral body. To achieve this, we generalize the van der Waals interaction potential between two ground-state molecules with electric, magnetic, and chiral response to nontrivial environments. The force is evaluated using second-order perturbation theory with an effective Hamiltonian. Chiral media enhance or reduce the free interaction via many-body interactions, making it possible to measure the chiral contributions to the van der Waals force with current technology...
May 12, 2017: Physical Review Letters
Ben N Balz, Peter Reimann
We consider isolated many-body quantum systems which do not thermalize; i.e., expectation values approach an (approximately) steady longtime limit which disagrees with the microcanonical prediction of equilibrium statistical mechanics. A general analytical theory is worked out for the typical temporal relaxation behavior in such cases. The main prerequisites are initial conditions which appreciably populate many energy levels and do not give rise to significant spatial inhomogeneities on macroscopic scales...
May 12, 2017: Physical Review Letters
Jianyun Zhao, Manisha Thakurathi, Manish Jain, Diptiman Sen, J K Jain
A conceptual difficulty in formulating the density-functional theory of the fractional quantum Hall effect is that while in the standard approach the Kohn-Sham orbitals are either fully occupied or unoccupied, the physics of the fractional quantum Hall effect calls for fractionally occupied Kohn-Sham orbitals. This has necessitated averaging over an ensemble of Slater determinants to obtain meaningful results. We develop an alternative approach in which we express and minimize the grand canonical potential in terms of the composite fermion variables...
May 12, 2017: Physical Review Letters
Christian Scholz, Thorsten Pöschel
The theory of homogeneously driven granular gases of hard particles predicts that the stationary state is characterized by a velocity distribution function with overpopulated high-energy tails as compared to the exponential decay valid for molecular gases. While this fundamental theoretical result was confirmed by numerous numerical simulations, an experimental confirmation is still missing. Using self-rotating active granular particles, we find a power-law decay of the velocity distribution whose exponent agrees well with the theoretic prediction...
May 12, 2017: Physical Review Letters
Meydi Ferrier, Tomonori Arakawa, Tokuro Hata, Ryo Fujiwara, Raphaëlle Delagrange, Richard Deblock, Yoshimichi Teratani, Rui Sakano, Akira Oguri, Kensuke Kobayashi
Universal properties of entangled many-body states are controlled by their symmetry and quantum fluctuations. By the magnetic-field tuning of the spin-orbital degeneracy in a Kondo-correlated quantum dot, we have modified quantum fluctuations to directly measure their influence on the many-body properties along the crossover from SU(4) to SU(2) symmetry of the ground state. High-sensitive current noise measurements combined with the nonequilibrium Fermi liquid theory clarify that the Kondo resonance and electron correlations are enhanced as the fluctuations, measured by the Wilson ratio, increase along the symmetry crossover...
May 12, 2017: Physical Review Letters
Attilio Cucchieri, Tereza Mendes
By exploiting the similarity between Bloch's theorem for electrons in crystalline solids and the problem of Landau gauge fixing in Yang-Mills theory on a "replicated" lattice, we show that large-volume results can be reproduced by simulations performed on much smaller lattices. This approach, proposed by Zwanziger [Nucl. Phys. B412, 657 (1994)NUPBBO0550-321310.1016/0550-3213(94)90396-4], corresponds to taking the infinite-volume limit for Landau-gauge field configurations in two steps: first for the gauge transformation alone, while keeping the lattice volume finite, and second for the gauge-field configuration itself...
May 12, 2017: Physical Review Letters
Eduardo Mendive-Tapia, Julie B Staunton
We describe a disordered local moment theory for long-period magnetic phases and investigate the temperature and magnetic field dependence of the magnetic states in the heavy rare earth elements (HREs), namely, paramagnetic, conical and helical antiferromagnetic (HAFM), fan, and ferromagnetic (FM) states. We obtain a generic HRE magnetic phase diagram which is consequent on the response of the common HRE valence electronic structure to f-electron magnetic moment ordering. The theory directly links the first-order HAFM-FM transition to the loss of Fermi surface nesting, induced by this magnetic ordering, as well as provides a template for analyzing the other phases and exposing where f-electron correlation effects are particularly intricate...
May 12, 2017: Physical Review Letters
Bridget N Queenan, Tomás J Ryan, Michael S Gazzaniga, Charles R Gallistel
The search for memory is one of the oldest quests in written human history. For at least two millennia, we have tried to understand how we learn and remember. We have gradually converged on the brain and looked inside it to find the basis of knowledge, the trace of memory. The search for memory has been conducted on multiple levels, from the organ to the cell to the synapse, and has been distributed across disciplines with less chronological or intellectual overlap than one might hope. Frequently, the study of the mind and its memories has been severely restricted by technological or philosophical limitations...
May 2017: Annals of the New York Academy of Sciences
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