4,170 research outputs found
Chemisorption and reactions on clusters of nickel atoms
The nucleation and growth of metallic clusters on a substantially amorphous substrate are discussed with emphasis on the geometrical and electronic structure of the clusters. Several clusters of different symmetry containing five to nine nickel atoms were studied. It was found that the energy range of primary d-like states is not significantly different from the width of the d-band states in nickel metal, as long as the interatomic distance is comparable to that in the bulk metal. The approach of one or more molecules to the cluster is examined using at the hydrogenation of acetylene and the dehydrogenation of ethylene as examples
Comparative study of hybrid functionals applied to structural and electronic properties of semiconductors and insulators
We present a systematic study that clarifies validity and limitation of
current hybrid functionals in density functional theory for structural and
electronic properties of various semiconductors and insulators. The three
hybrid functionals, PBE0 by Perdew, Ernzerhof, and Becke, HSE by Heyd,
Sucseria, and Ernzerhof, and a long-range corrected (LC) functional, are
implemented in a well-established plane-wave-basis-set scheme combined with
norm-conserving pseudopotentials, thus enabling us to assess applicability of
each functional on equal footing to the properties of the materials. The
materials we have examined in this paper range from covalent to ionic materials
as well as a rare-gas solid whose energy gaps determined by experiments are in
the range of 0.6 eV - 14.2 eV: i.e., Ge, Si, BaTiO, -GaN, diamond,
MgO, NaCl, LiCl, Kr, and LiF. We find that the calculated bulk moduli by the
hybrid functionals show better agreement with the experiments than the
generalized gradient approximation (GGA) provides, whereas the calculated
lattice constants by the hybrid functionals and GGA show comparable accuracy.
The calculated energy band gaps and the valence-band widths for the ten
prototype materials show substantial improvement using the hybrid functional
compared with GGA. In particular, it is found that the band gaps of the ionic
materials as well as the rare-gas solid are well reproduced by the LC-hybrid
functional, whereas those of covalent materials are well described by the HSE
functional. We also examine exchange effects due to short-range and long-range
components of the Coulomb interaction and propose an optimum recipe to the
short-range and long-range separation in treating the exchange energy.Comment: 13pages, 4 figures, 4 table
Charge excitations associated with charge stripe order in the 214-type nickelate and superconducting cuprate
Charge excitations were studied for stipe-ordered 214 compounds,
LaSrNiO and 1/8-doped La(Ba, Sr)CuO
using resonant inelastic x-ray scattering in hard x-ray regime. We have
observed charge excitations at the energy transfer of 1 eV with the momentum
transfer corresponding to the charge stripe spatial period both for the
diagonal (nikelate) and parallel (cuprates) stripes. These new excitations can
be interpreted as a collective stripe excitation or charge excitonic mode to a
stripe-related in-gap state.Comment: 5 pages, 4 figure
A virtual intersubband spin-flip spin-orbit coupling induced spin relaxation in GaAs (110) quantum wells
A spin relaxation mechanism is proposed based on a second-order spin-flip
intersubband spin-orbit coupling together with the spin-conserving scattering.
The corresponding spin relaxation time is calculated via the Fermi golden rule.
It is shown that this mechanism is important in symmetric GaAs (110) quantum
wells with high impurity density. The dependences of the spin relaxation time
on electron density, temperature and well width are studied with the underlying
physics analyzed.Comment: 4+ pages, 4 figures, to be published in Solid Stat. Commu
Mesoscopic nature of serration behavior in high-Mn austenitic steel
セレーション挙動の解明 --高強度・高延性を示す高Mn鋼の変形の本質に迫る--. 京都大学プレスリリース. 2020-12-25.We have thoroughly clarified the mesoscopic nature of serration behavior in a high-Mn austenitic steel in connection with its characteristic localized deformation. A typical high-Mn steel, Fe-22Mn-0.6C (wt. %), with a face centered cubic (FCC) single-phase structure was used in the present study. After 4 cycles of repeated cold-rolling and annealing process, a specimen with a fully recrystallized microstructure having a mean grain size of 2.0 μm was obtained. The specimen was tensile tested at room temperature at an initial strain rate of 8.3 × 10−4 s−1, during which the digital image correlation (DIC) technique was applied for analyzing local strain and strain-rate distributions in the specimen. Obtained results indicated that a unique strain localization behavior characterized by the formation, propagation and annihilation of deformation localized bands, so-called Portevin–Le Chatelier (PLC) bands, determined the global mechanical response appearing as serration on the stress-strain curve. In addition, the in-situ synchrotron XRD diffraction during the tensile test was utilized to understand what was happening in the material with respect to the PLC banding. Lattice strain of (200) plane nearly perpendicular to the tensile direction dropped when every PLC band passed through the beam position, which indicated a stress relaxation occurred inside the PLC band. At the same time, the dislocation density increased drastically when the PLC band passed the beam position, which described that the material was plastically deformed and work-hardened mostly within the PLC band. All the results obtained consistently explained the serration behavior in a mesoscopic scale. The serration behavior on the stress-strain curve totally corresponded to the formation, propagation and annihilation of the PLC band in the 22Mn-0.6C steel, and the localized deformation, i.e., the PLC banding, governed the characteristic strain hardening of the material
Identifying Multiple Personalities in Large Language Models with External Evaluation
As Large Language Models (LLMs) are integrated with human daily applications
rapidly, many societal and ethical concerns are raised regarding the behavior
of LLMs. One of the ways to comprehend LLMs' behavior is to analyze their
personalities. Many recent studies quantify LLMs' personalities using
self-assessment tests that are created for humans. Yet many critiques question
the applicability and reliability of these self-assessment tests when applied
to LLMs. In this paper, we investigate LLM personalities using an alternate
personality measurement method, which we refer to as the external evaluation
method, where instead of prompting LLMs with multiple-choice questions in the
Likert scale, we evaluate LLMs' personalities by analyzing their responses
toward open-ended situational questions using an external machine learning
model. We first fine-tuned a Llama2-7B model as the MBTI personality predictor
that outperforms the state-of-the-art models as the tool to analyze LLMs'
responses. Then, we prompt the LLMs with situational questions and ask them to
generate Twitter posts and comments, respectively, in order to assess their
personalities when playing two different roles. Using the external personality
evaluation method, we identify that the obtained personality types for LLMs are
significantly different when generating posts versus comments, whereas humans
show a consistent personality profile in these two different situations. This
shows that LLMs can exhibit different personalities based on different
scenarios, thus highlighting a fundamental difference between personality in
LLMs and humans. With our work, we call for a re-evaluation of personality
definition and measurement in LLMs
Precision determination of band offsets in strained InGaAs/GaAs quantum wells by C-V-profiling and Schroedinger-Poisson self-consistent simulation
The results of measurements and numerical simulation of charge carrier
distribution and energy states in strained quantum wells In_xGa_{1-x}As/GaAs
(0.06 < x < 0.29) by C-V-profiling are presented. Precise values of conduction
band offsets for these pseudomorphic QWs have been obtained by means of
self-consistent solution of Schroedinger and Poisson equations and following
fitting to experimental data. For the conduction band offsets in strained
In_xGa_{1-x}As/GaAs - QWs the expression DE_C(x) = 0.814x - 0.21x^2 has been
obtained.Comment: 9 pages, 12 figures, RevTeX
Macroautophagy Is Regulated by the UPR–Mediator CHOP and Accentuates the Phenotype of SBMA Mice
Altered protein homeostasis underlies degenerative diseases triggered by misfolded proteins, including spinal and bulbar muscular atrophy (SBMA), a neuromuscular disorder caused by a CAG/glutamine expansion in the androgen receptor. Here we show that the unfolded protein response (UPR), an ER protein quality control pathway, is induced in skeletal muscle from SBMA patients, AR113Q knock-in male mice, and surgically denervated wild-type mice. To probe the consequence of UPR induction, we deleted CHOP (C/EBP homologous protein), a transcription factor induced following ER stress. CHOP deficiency accentuated atrophy in both AR113Q and surgically denervated muscle through activation of macroautophagy, a lysosomal protein quality control pathway. Conversely, impaired autophagy due to Beclin-1 haploinsufficiency decreased muscle wasting and extended lifespan of AR113Q males, producing a significant and unexpected amelioration of the disease phenotype. Our findings highlight critical cross-talk between the UPR and macroautophagy, and they indicate that autophagy activation accentuates aspects of the SBMA phenotype
Phylogeny of Prokaryotes and Chloroplasts Revealed by a Simple Composition Approach on All Protein Sequences from Complete Genomes Without Sequence Alignment
The complete genomes of living organisms have provided much information on their phylogenetic relationships. Similarly, the complete genomes of chloroplasts have helped to resolve the evolution of this organelle in photosynthetic eukaryotes. In this paper we propose an alternative method of phylogenetic analysis using compositional statistics for all protein sequences from complete genomes. This new method is conceptually simpler than and computationally as fast as the one proposed by Qi et al. (2004b) and Chu et al. (2004). The same data sets used in Qi et al. (2004b) and Chu et al. (2004) are analyzed using the new method. Our distance-based phylogenic tree of the 109 prokaryotes and eukaryotes agrees with the biologists tree of life based on 16S rRNA comparison in a predominant majority of basic branching and most lower taxa. Our phylogenetic analysis also shows that the chloroplast genomes are separated to two major clades corresponding to chlorophytes s.l. and rhodophytes s.l. The interrelationships among the chloroplasts are largely in agreement with the current understanding on chloroplast evolution
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