3,181 research outputs found
Relevance of Chaos in Numerical Solutions of Quantum Billiards
In this paper we have tested several general numerical methods in solving the
quantum billiards, such as the boundary integral method (BIM) and the plane
wave decomposition method (PWDM). We performed extensive numerical
investigations of these two methods in a variety of quantum billiards:
integrable systens (circles, rectangles, and segments of circular annulus),
Kolmogorov-Armold-Moser (KAM) systems (Robnik billiards), and fully chaotic
systems (ergodic, such as Bunimovich stadium, Sinai billiard and cardiod
billiard). We have analyzed the scaling of the average absolute value of the
systematic error of the eigenenergy in units of the mean level
spacing with the density of discretization (which is number of numerical
nodes on the boundary within one de Broglie wavelength) and its relationship
with the geometry and the classical dynamics. In contradistinction to the BIM,
we find that in the PWDM the classical chaos is definitely relevant for the
numerical accuracy at a fixed density of discretization . We present
evidence that it is not only the ergodicity that matters, but also the Lyapunov
exponents and Kolmogorov entropy. We believe that this phenomenon is one
manifestation of quantum chaos.Comment: 20 Revtex pages, 10 Eps figure
The Effective Fragment Molecular Orbital Method for Fragments Connected by Covalent Bonds
We extend the effective fragment molecular orbital method (EFMO) into
treating fragments connected by covalent bonds. The accuracy of EFMO is
compared to FMO and conventional ab initio electronic structure methods for
polypeptides including proteins. Errors in energy for RHF and MP2 are within 2
kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides
similar to FMO but obtained two to five times faster. For proteins, the errors
are also within a few kcal/mol of the FMO results. We developed both the RHF
and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures
had an RMSD of 0.40 and 0.44 {\AA} for RHF and MP2, respectively.Comment: Revised manuscrip
Dynamical Aspects of Analogue Gravity: The Backreaction of Quantum Fluctuations in Dilute Bose-Einstein Condensates
We discuss the backreaction force exerted by quantum fluctuations in dilute
Bose-Einstein condensates onto the motion of the classical background, derived
by an ab initio approach from microscopic physics. It is shown that the
effective-action method, widely employed in semiclassical quantum gravity,
fails to give the full backreaction force. The failure of the effective-action
method is traced back, inter alia, to the problem of the correct choice of the
fundamental variables and the related operator ordering issues.Comment: 21+epsilon pages; has appeared in Springer Lecture Notes in Physic
Two-Loop Analysis of Non-abelian Chern-Simons Theory
Perturbative renormalization of a non-Abelian Chern-Simons gauge theory is
examined. It is demonstrated by explicit calculation that, in the pure
Chern-Simons theory, the beta-function for the coefficient of the Chern-Simons
term vanishes to three loop order. Both dimensional regularization and
regularization by introducing a conventional Yang-Mills component in the action
are used. It is shown that dimensional regularization is not gauge invariant at
two loops. A variant of this procedure, similar to regularization by
dimensional reduction used in supersymmetric field theories is shown to obey
the Slavnov-Taylor identity to two loops and gives no renormalization of the
Chern-Simons term. Regularization with Yang-Mills term yields a finite
integer-valued renormalization of the coefficient of the Chern-Simons term at
one loop, and we conjecture no renormalization at higher order. We also examine
the renormalization of Chern-Simons theory coupled to matter. We show that in
the non-abelian case the Chern-Simons gauge field as well as the matter fields
require infinite renormalization at two loops and therefore obtain nontrivial
anomalous dimensions. We show that the beta function for the gauge coupling
constant is zero to two-loop order, consistent with the topological
quantization condition for this constant.Comment: 48 pages, UU/HEP/91/12; file format changed to standard Latex to
solve the problem with printin
Verticalization of bacterial biofilms
Biofilms are communities of bacteria adhered to surfaces. Recently, biofilms
of rod-shaped bacteria were observed at single-cell resolution and shown to
develop from a disordered, two-dimensional layer of founder cells into a
three-dimensional structure with a vertically-aligned core. Here, we elucidate
the physical mechanism underpinning this transition using a combination of
agent-based and continuum modeling. We find that verticalization proceeds
through a series of localized mechanical instabilities on the cellular scale.
For short cells, these instabilities are primarily triggered by cell division,
whereas long cells are more likely to be peeled off the surface by nearby
vertical cells, creating an "inverse domino effect". The interplay between cell
growth and cell verticalization gives rise to an exotic mechanical state in
which the effective surface pressure becomes constant throughout the growing
core of the biofilm surface layer. This dynamical isobaricity determines the
expansion speed of a biofilm cluster and thereby governs how cells access the
third dimension. In particular, theory predicts that a longer average cell
length yields more rapidly expanding, flatter biofilms. We experimentally show
that such changes in biofilm development occur by exploiting chemicals that
modulate cell length.Comment: Main text 10 pages, 4 figures; Supplementary Information 35 pages, 15
figure
Local and systemic immunomodulatory mechanisms triggered by Human Papillomavirus transformed cells: a potential role for G-CSF and neutrophils
Cervical cancer is the last stage of a series of molecular and cellular alterations initiated with Human Papillomavirus (HPV) infection. The process involves immune responses and evasion mechanisms, which culminates with tolerance toward tumor antigens. Our objective was to understand local and systemic changes in the interactions between HPV associated cervical lesions and the immune system as lesions progress to cancer. Locally, we observed higher cervical leukocyte infiltrate, reflected by the increase in the frequency of T lymphocytes, neutrophils and M2 macrophages, in cancer patients. We observed a strong negative correlation between the frequency of neutrophils and T cells in precursor and cancer samples, but not cervicitis. In 3D tumor cell cultures, neutrophils inhibited T cell activity, displayed longer viability and longer CD16 expression half-life than neat neutrophil cultures. Systemically, we observed higher plasma G-CSF concentration, higher frequency of immature low density neutrophils, and tolerogenic monocyte derived dendritic cells, MoDCs, also in cancer patients. Interestingly, there was a negative correlation between T cell activation by MoDCs and G-CSF concentration in the plasma. Our results indicate that neutrophils and G-CSF may be part of the immune escape mechanisms triggered by cervical cancer cells, locally and systemically, respectively.Tis study was supported by Sao Paulo Research foundation: grants 2008/57889-1, 2010/20010-4, 2014/19326-6,
by the Brazilian National Counsel of Technological and Scientifc Development: grant 573799/2008-3. KLFA and
RAMR had PhD fellowships by Sao Paulo Research Foundation, CRSF has a Coordination for the Improvement
of Higher Education Personnel PhD fellowship. We thank the Pathology Department of the School of Medicine,
coordinated by Prof. VenĂąncio Avancini Ferreira Alves, Universidade de SĂŁo Paulo for the slides containing
histological samples from the biopsies used in this study. We thank Sandra Alexandre Alves for her technical
support.info:eu-repo/semantics/publishedVersio
On Slow Light as a Black Hole Analogue
Although slow light (electromagnetically induced transparency) would seem an
ideal medium in which to institute a ``dumb hole'' (black hole analog), it
suffers from a number of problems. We show that the high phase velocity in the
slow light regime ensures that the system cannot be used as an analog
displaying Hawking radiation. Even though an appropriately designed slow-light
set-up may simulate classical features of black holes -- such as horizon, mode
mixing, Bogoliubov coefficients, etc. -- it does not reproduce the related
quantum effects. PACS: 04.70.Dy, 04.80.-y, 42.50.Gy, 04.60.-m.Comment: 14 pages RevTeX, 5 figure
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
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