2,061 research outputs found
Targeted Excited State Algorithms
To overcome the limitations of the traditional state-averaging approaches in
excited state calculations, where one solves for and represents all states
between the ground state and excited state of interest, we have investigated a
number of new excited state algorithms. Building on the work of van der Vorst
and Sleijpen (SIAM J. Matrix Anal. Appl., 17, 401 (1996)), we have implemented
Harmonic Davidson and State-Averaged Harmonic Davidson algorithms within the
context of the Density Matrix Renormalization Group (DMRG). We have assessed
their accuracy and stability of convergence in complete active space DMRG
calculations on the low-lying excited states in the acenes ranging from
naphthalene to pentacene. We find that both algorithms offer increased accuracy
over the traditional State-Averaged Davidson approach, and in particular, the
State-Averaged Harmonic Davidson algorithm offers an optimal combination of
accuracy and stability in convergence
Seeing many-body effects in single- and few-layer graphene: Observation of two-dimensional saddle-point excitons
Significant excitonic effects were observed in graphene by measuring its
optical conductivity in a broad spectral range including the two-dimensional
{\pi}-band saddle-point singularities in the electronic structure. The strong
electron-hole interactions manifest themselves in an asymmetric resonance
peaked at 4.62 eV, which is red-shifted by nearly 600 meV from the value
predicted by ab-initio GW calculations for the band-to-band transitions. The
observed excitonic resonance is explained within a phenomenological model as a
Fano interference of a strongly coupled excitonic state and a band continuum.
Our experiment also showed a weak dependence of the excitonic resonance in
few-layer graphene on layer thickness. This result reflects the effective
cancellation of the increasingly screened repulsive electron-electron (e-e) and
attractive electron-hole (e-h) interactions.Comment: 9 pages, 3 figures, In PR
A network-based regression approach for identifying subject-specific driver mutations
In cancer genomics, it is of great importance to distinguish driver
mutations, which contribute to cancer progression, from causally neutral
passenger mutations. We propose a random-effect regression approach to estimate
the effects of mutations on the expressions of genes in tumor samples, where
the estimation is assisted by a prespecified gene network. The model allows the
mutation effects to vary across subjects. We develop a subject-specific
mutation score to quantify the effect of a mutation on the expressions of its
downstream genes, so mutations with large scores can be prioritized as drivers.
We demonstrate the usefulness of the proposed methods by simulation studies and
provide an application to a breast cancer genomics study.Comment: 23 pages; 9 figure
UTJECAJ RELIGIOZNOSTI I DUHOVNOSTI NA SVAKODNEVNU PRAKSU SOCIJALNIH RADNIKA
Although social work can trace the roots of its establishment as a profession to religion/spirituality, the relationship between social work and religion/spirituality has deteriorated due to the former’s professionalisation and secularisation. Nevertheless, religious/spiritual values are important for many social work services and for the practice of the profession. It is, hence, worth demarcating the role of religion/spirituality for frontline social workers. In the current qualitative study, repeated interviews were conducted with 11 Chinese social workers from diverse social work settings. It was noted that Eastern and Western religion/spirituality can instil meaning and value in the profession’s nature.Iako se uspostavljanje socijalnog rada kao profesije temelji na religIoznosti/duhovnosti, odnos između socijalnog rada i religioznosti/duhovnosti narušen je zbog profesionalizacije i sekularizacije socijalnog rada. Usprkos tome, religiozne/duhovne vrijednosti važne su za mnoge usluge socijalnog rada i za praksu socijalnog rada kao profesije. Stoga je važno utvrditi ulogu religioznosti/duhovnosti za najizloženije socijalne radnike. U ovom kvalitativnom istraživanju provedeni su ponovljeni razgovori s 11 kineskih socijalnih radnika iz različitih područja socijalnog rada. Uočeno je da istočnjačka i zapadnjačka religioznost/duhovnost mogu unijeti značenje i vrijednost u prirodu profesije
Can Strong Gravitational Lensing Constrain Dark Energy?
We discuss the ratio of the angular diameter distances from the source to the
lens, , and to the observer at present, , for various dark
energy models. It is well known that the difference of s between the
models is apparent and this quantity is used for the analysis of Type Ia
supernovae. However we investigate the difference between the ratio of the
angular diameter distances for a cosmological constant,
and that for other dark energy models,
in this paper. It has been known that there is
lens model degeneracy in using strong gravitational lensing. Thus, we
investigate the model independent observable quantity, Einstein radius
(), which is proportional to both and velocity
dispersion squared, . values depend on the parameters
of each dark energy model individually. However, for the various dark energy models, is well within
the error of for most of the parameter spaces of the dark energy
models. Thus, a single strong gravitational lensing by use of the Einstein
radius may not be a proper method to investigate the property of dark energy.
However, better understanding to the mass profile of clusters in the future or
other methods related to arc statistics rather than the distances may be used
for constraints on dark energy.Comment: 15 pages, 13 figures, Accepted in PR
Orbifold Family Unification
We study the possibility of complete family unification in higher-dimensional
space-time. Three families of matters in SU(5) grand unified theory are derived
from a single bulk multiplet of SU(N) gauge group (N >= 9) in the framework of
S^1/Z_2 orbifold models. In the case of the direct orbifold breaking down to
the standard model gauge group, there are models in which bulk fields from a
single multiplet and a few brane fields compose three families of quarks and
leptons.Comment: Comments added, version to appear in Physical Review D (v3);
References added (v2); 19 pages (v1
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