35,512 research outputs found
Bi(111) thin film with insulating interior but metallic surfaces
The electrical conductance of molecular beam epitaxial Bi on BaF2(111) was
measured as a function of both film thickness (4-540 nm) and temperature (5-300
K). Unlike bulk Bi as a prototype semimetal, the Bi thin films up to 90 nm are
found to be insulating in the interiors but metallic on the surfaces. This
result has not only resolved unambiguously the long controversy about the
existence of semimetal-semiconductor transition in Bi thin film but also
provided a straightforward interpretation for the long-puzzled temperature
dependence of the resistivity of Bi thin films, which in turn might suggest
some potential applications in spintronics
Heuristic parameter-choice rules for convex variational regularization based on error estimates
In this paper, we are interested in heuristic parameter choice rules for
general convex variational regularization which are based on error estimates.
Two such rules are derived and generalize those from quadratic regularization,
namely the Hanke-Raus rule and quasi-optimality criterion. A posteriori error
estimates are shown for the Hanke-Raus rule, and convergence for both rules is
also discussed. Numerical results for both rules are presented to illustrate
their applicability
Hierarchical Harmonization of Atom-Resolved Metabolic Reactions across Metabolic Databases
Metabolic models have been proven to be useful tools in system biology and have been successfully applied to various research fields in a wide range of organisms. A relatively complete metabolic network is a prerequisite for deriving reliable metabolic models. The first step in constructing metabolic network is to harmonize compounds and reactions across different metabolic databases. However, effectively integrating data from various sources still remains a big challenge. Incomplete and inconsistent atomistic details in compound representations across databases is a very important limiting factor. Here, we optimized a subgraph isomorphism detection algorithm to validate generic compound pairs. Moreover, we defined a set of harmonization relationship types between compounds to deal with inconsistent chemical details while successfully capturing atom-level characteristics, enabling a more complete enabling compound harmonization across metabolic databases. In total, 15,704 compound pairs across KEGG (Kyoto Encyclopedia of Genes and Genomes) and MetaCyc databases were detected. Furthermore, utilizing the classification of compound pairs and EC (Enzyme Commission) numbers of reactions, we established hierarchical relationships between metabolic reactions, enabling the harmonization of 3856 reaction pairs. In addition, we created and used atom-specific identifiers to evaluate the consistency of atom mappings within and between harmonized reactions, detecting some consistency issues between the reaction and compound descriptions in these metabolic databases
The vibrational dynamics of vitreous silica: Classical force fields vs. first-principles
We compare the vibrational properties of model SiO_2 glasses generated by
molecular-dynamics simulations using the effective force field of van Beest et
al. (BKS) with those obtained when the BKS structure is relaxed using an ab
initio calculation in the framework of the density functional theory. We find
that this relaxation significantly improves the agreement of the density of
states with the experimental result. For frequencies between 14 and 26 THz the
nature of the vibrational modes as determined from the BKS model is very
different from the one from the ab initio calculation, showing that the
interpretation of the vibrational spectra in terms of calculations using
effective potentials can be very misleading.Comment: 7 pages of Latex, 4 figure
GPS scintillations associated with cusp dynamics and polar cap patches
This paper investigates the relative scintillation level associated with cusp
dynamics (including precipitation, flow shears, etc.) with and without the
formation of polar cap patches around the cusp inflow region by the EISCAT
Svalbard radar (ESR) and two GPS scintillation receivers. A series of polar cap
patches were observed by the ESR between 8:40 and 10:20 UT on December 3, 2011.
The polar cap patches combined with the auroral dynamics were associated with a
significantly higher GPS phase scintillation level (up to 0.6 rad) than those
observed for the other two alternatives, i.e., cusp dynamics without polar cap
patches, and polar cap patches without cusp aurora. The cusp auroral dynamics
without plasma patches were indeed related to GPS phase scintillations at a
moderate level (up to 0.3 rad). The polar cap patches away from the active cusp
were associated with sporadic and moderate GPS phase scintillations (up to 0.2
rad). The main conclusion is that the worst global navigation satellite system
space weather events on the dayside occur when polar cap patches enter the
polar cap and are subject to particle precipitation and flow shears, which is
analogous to the nightside when polar cap patches exit the polar cap and enter
the auroral oval
Anomalous microwave conductivity coherence peak in c-axis MgB2 thin film
The temperature dependence of the real part of the microwave complex
conductivity at 17.9 GHz obtained from surface impedance measurements of two
c-axis oriented MgB2 thin films reveals a pronounced maximum at a temperature
around 0.6 times the critical temperature. Calculations in the frame of a
two-band model based on Bardeen-Cooper-Schrieffer (BCS) theory suggest that
this maximum corresponds to an anomalous coherence peak resembling the two-gap
nature of MgB2. Our model assumes there is no interband impurity scattering and
a weak interband pairing interaction, as suggested by bandstructure
calculations. In addition, the observation of a coherence peak indicates that
the pi-band is in the dirty limit and dominates the total conductivity of our
filmsComment: 10 pages, 4 figures, to be published in Phys. Rev. Let
Thermodynamics of lattice QCD with 2 sextet quarks on N_t=8 lattices
We continue our lattice simulations of QCD with 2 flavours of colour-sextet
quarks as a model for conformal or walking technicolor. A 2-loop perturbative
calculation of the -function which describes the evolution of this
theory's running coupling constant predicts that it has a second zero at a
finite coupling. This non-trivial zero would be an infrared stable fixed point,
in which case the theory with massless quarks would be a conformal field
theory. However, if the interaction between quarks and antiquarks becomes
strong enough that a chiral condensate forms before this IR fixed point is
reached, the theory is QCD-like with spontaneously broken chiral symmetry and
confinement. However, the presence of the nearby IR fixed point means that
there is a range of couplings for which the running coupling evolves very
slowly, i.e. it 'walks'. We are simulating the lattice version of this theory
with staggered quarks at finite temperature studying the changes in couplings
at the deconfinement and chiral-symmetry restoring transitions as the temporal
extent () of the lattice, measured in lattice units, is increased. Our
earlier results on lattices with show both transitions move to weaker
couplings as increases consistent with walking behaviour. In this paper
we extend these calculations to . Although both transition again move to
weaker couplings the change in the coupling at the chiral transition from
to is appreciably smaller than that from to .
This indicates that at we are seeing strong coupling effects and that
we will need results from to determine if the chiral-transition
coupling approaches zero as , as needed for the theory
to walk.Comment: 21 pages Latex(Revtex4) source with 4 postscript figures. v2: added 1
reference. V3: version accepted for publication, section 3 restructured and
interpretation clarified. Section 4 future plans for zero temperature
simulations clarifie
Comment on ''the controlled charge ordering and evidence of the metallic state in PrCaMnO films''
In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12}
L133) Lee \QTR{it}{et al.} have studied the transport properties of
PrCaMnO thin films. They claimed that they are able to
controlled the charge-ordered (CO) state by the lattice strains. We propose
herein another alternative since another indexation of the orientation of the
film can be found leading to almost no distortion of the cell, as compared to
the bulk compound.Comment: 2 page
Comparisons of students’ perceptions on BIM practice among Australia, China and UK
University students are the future driving forces in and leaders of the architectural, engineering and construction (AEC) industry advancement. Although BIM pedagogical studies have been performed in different institutions, there has not been sufficient research providing a global perspective of BIM education and students’ perceptions toward BIM practice and application following their learning progress. The purpose of this paper is to adopt student samples from Swinburne University of Technology (SUT, Australia), Wenzhou University (WZU, China) and University of Brighton (UK) as three case studies to investigate the BIM practice and application-related perceptions and motivations.
Design/methodology/approach
Based on the thorough understanding of the BIM pedagogical delivery including teaching contents and assessment methods among the three institutions, a questionnaire survey approach was adopted to collect AEC students’ perceptions of BIM. Within each selected case, statistical analysis was conducted to investigate both the overall sample and subgroup differences regarding students’ opinions on BIM’s functions (e.g. as a 3D visualization tool) and BIM usefulness in various industry professions, their motivation in BIM-related jobs and their perceptions of challenges encountered in BIM practice and application. Multiple factors influencing BIM learners’ perceptions were discussed, such as pedagogical assessment approach, and individual factors (e.g. disciplines).
Findings
The results showed that students were able to discern the latest industry practices and critical thinking in BIM movements. For example, SUT students perceived more challenges from the government legislation or incentive policies, which was consistent with Australia’s BIM policy movement. WZU students tended to have less positive views on BIM usefulness. The results also indicated fewer differences regarding perceived challenges among students from these three institutions.
Originality/value
This study contributed to the body of knowledge in managerial BIM by focusing on learners’ perceptions from the perspective of students’ understanding, motivation and individual views of BIM, which were insightful to both BIM educators and employers. By initiating the framework of BIM learning process and its influence factors, the current study serves as a point of reference to continue the future work in strengthening the connection between institutional BIM education and industry practical needs worldwide
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