313 research outputs found
Commitment to corporate, social, and environmental responsibilities: an insight into contrasting perspectives in China and the US
This cross-national study investigates antecedents and outcomes of corporate responsibility (CR) practices to stakeholders and the natural environment in the contrasting contexts of China and the US. In general, we found partial support for the proposition that the divergence of CR stakeholder practices across nations is dependent on the institutional environments of business. Whereas customer and community stakeholder practices were found to be more prevalent in US companies, there were no significant country differences in the prevalence of employee, investor, and environmental CR practices. In addition, we found that the relationship between the prevalence of CR practices and business outcomes (financial performance, corporate reputation, and employee commitment) varied depending on the type of CR practice and country
Finding list homomorphisms from bounded-treewidth graphs to reflexive graphs: A complete complexity characterization
In the list homomorphism problem, the input consists of two graphs G and H, together with a list L(v) subseteq V(H) for every vertex v in V(G). The task is to find a homomorphism phi:V(G) -> V(H) respecting the lists, that is, we have that phi(v) in L(v) for every v in V(H) and if u and v are adjacent in G, then phi(u) and phi(v) are adjacent in H. If H is a fixed graph, then the problem is denoted LHom(H). We consider the reflexive version of the problem, where we assume that every vertex
in H has a self-loop. If is known that reflexive LHom(H) is polynomial-time solvable if H is an interval graph and it is NP-complete otherwise [Feder and Hell, JCTB 1998].
We explore the complexity of the problem parameterized by the treewidth tw(G) of the input graph G. If a tree decomposition of G of width tw(G) is given in the input, then the problem can be solved in time |V(H)|^{tw(G)} n^{O(1)} by naive dynamic programming. Our main result completely reveals when and by exactly how much this naive algorithm can be improved. We introduce a simple combinatorial invariant i^*(H), which is based on the existence of decompositions and incomparable sets, and show that this number should appear as the base of the exponent in the best possible running time. Specifically, we prove for every fixed non-interval graph H that
* If a tree decomposition of width tw(G) is given in the input, then the problem can be solved in time i^*(H)^{tw(G)} n^{O(1)}.
* Assuming the Strong Exponential-Time Hypothesis (SETH), the probem cannot be solved in time (i^*(H)-epsilon)^{tw(G)} n^{O(1)} for any epsilon>0.
Thus by matching upper and lower bounds, our result exactly characterizes for every fixed H the complexity of reflexive LHom(H) parameterized by treewidth
Sorting signed circular permutations by super short reversals
We consider the problem of sorting a circular permutation by reversals of length at most 2, a problem that finds application in comparative genomics. Polynomial-time solutions for the unsigned version of this problem are known, but the signed version remained open. In this paper, we present the first polynomial-time solution for the signed version of this problem. Moreover, we perform an experiment for inferring distances and phylogenies for published Yersinia genomes and compare the results with the phylogenies presented in previous works.We consider the problem of sorting a circular permutation by reversals of length at most 2, a problem that finds application in comparative genomics. Polynomial-time solutions for the unsigned version of this problem are known, but the signed version rema9096272283FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCAPES - COORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO2013/08293-72014/04718-6306730/2012-0; 477692/2012-5; 483370/2013-411th International Symposium on Bioinformatics Research and Application
Absorption and wavepackets in optically excited semiconductor superlattices driven by dc-ac fields
Within the one-dimensional tight-binding minibands and on-site
Coloumbic interaction approximation, the absorption spectrum and coherent
wavepacket time evolution in an optically excited semiconductor superlattice
driven by dc-ac electric fields are investigated using the semiconductor Bloch
equations.
The dominating roles of the ratios of dc-Stark to external ac frequency, as
well as ac-Stark to external ac frequency, is emphasized. If the former is an
integer , then also harmonics are present within one Stark
frequency, while the fractional case leads to the formation of excitonic
fractional ladders. The later ratio determines the size and profile of the
wavepacket. In the absence of excitonic interaction it controls the maximum
size wavepackets reach within one cycle, while the interaction produces a
strong anisotropy and tends to palliate the dynamic wavepacket localization.Comment: 14 pages, 7 postscript figure
The Effective Particle-Hole Interaction and the Optical Response of Simple Metal Clusters
Following Sham and Rice [L. J. Sham, T. M. Rice, Phys. Rev. 144 (1966) 708]
the correlated motion of particle-hole pairs is studied, starting from the
general two-particle Greens function. In this way we derive a matrix equation
for eigenvalues and wave functions, respectively, of the general type of
collective excitation of a N-particle system. The interplay between excitons
and plasmons is fully described by this new set of equations. As a by-product
we obtain - at least a-posteriori - a justification for the use of the TDLDA
for simple-metal clusters.Comment: RevTeX, 15 pages, 5 figures in uufiles format, 1 figure avaible from
[email protected]
Diagrammatic Quantum Monte Carlo for Two-Body Problem: Exciton
We present a novel method for precise numerical solution of the irreducible
two-body problem and apply it to excitons in solids. The approach is based on
the Monte Carlo simulation of the two-body Green function specified by
Feynman's diagrammatic expansion. Our method does not rely on the specific form
of the electron and hole dispersion laws and is valid for any attractive
electron-hole potential. We establish limits of validity of the Wannier (large
radius) and Frenkel (small radius) approximations, present accurate data for
the intermediate radius excitons, and give evidence for the charge transfer
nature of the monopolar exciton in mixed valence materials.Comment: 4 pages, 5 figure
Attitudes toward Corporate Responsibilities in Western Europe and in Central And East Europe
This study investigated the attitudes toward social, economic, and environmental corporate responsibilities of 3064 current managers and business students in 8 European countries. Participants in Western European countries had significantly different perspectives on the importance of these corporate responsibilities (CR) than those in Central and East European countries. Within each country, environmental CR is perceived as most important in both CEE and Western European countries. Across countries, Western European respondents accord more importance to social CR and less importance to economic CR. CEE countries are not homogenous, e.g., CR attitudes in the Czech Republic are closer to that of Western Europeans, possibly triggered by the accession to EU. Work experience (managers vs. business students) influences social and environmental orientations more than the economic orientation for only some countries. Generational differences were found as well: Business students attribute more importance to environmental CR and less importance to social CR than managers
Dispersion of the dielectric function of a charge-transfer insulator
We study the problem of dielectric response in the strong coupling regime of
a charge transfer insulator. The frequency and wave number dependence of the
dielectric function and its inverse is the main object of consideration. We show that the
problem, in general, cannot be reduced to a calculation within the Hubbard
model, which takes into account only a restricted number of electronic states
near the Fermi energy. The contribution of the rest of the system to the
longitudinal response (i.e. to ) is essential
for the whole frequency range. With the use of the spectral representation of
the two-particle Green's function we show that the problem may be divided into
two parts: into the contributions of the weakly correlated and the Hubbard
subsystems. For the latter we propose an approach that starts from the
correlated paramagnetic ground state with strong antiferromagnetic
fluctuations. We obtain a set of coupled equations of motion for the
two-particle Green's function that may be solved by means of the projection
technique. The solution is expressed by a two particle basis that includes the
excitonic states with electron and hole separated at various distances. We
apply our method to the multiband Hubbard (Emery) model that describes layered
cuprates. We show that strongly dispersive branches exist in the excitonic
spectrum of the 'minimal' Emery model () and consider the
dependence of the spectrum on finite oxygen hopping and on-site
repulsion . The relationship of our calculations to electron energy loss
spectroscopy is discussed.Comment: 22 pages, 5 figure
The QCD phase diagram at nonzero quark density
We determine the phase diagram of QCD on the \mu-T plane for small to
moderate chemical potentials. Two transition lines are defined with two
quantities, the chiral condensate and the strange quark number susceptibility.
The calculations are carried out on N_t =6,8 and 10 lattices generated with a
Symanzik improved gauge and stout-link improved 2+1 flavor staggered fermion
action using physical quark masses. After carrying out the continuum
extrapolation we find that both quantities result in a similar curvature of the
transition line. Furthermore, our results indicate that in leading order the
width of the transition region remains essentially the same as the chemical
potential is increased.Comment: 12 pages, 6 figure
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