5,843 research outputs found
Physisorption of Nucleobases on Graphene
We report the results of our first-principles investigation on the
interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine
(T), and uracil (U) with graphene, carried out within the density functional
theory framework, with additional calculations utilizing Hartree--Fock plus
second-order Moeller-Plesset perturbation theory. The calculated binding energy
of the nucleobases shows the following hierarchy: G > T ~ C ~ A > U, with the
equilibrium configuration being very similar for all five of them. Our results
clearly demonstrate that the nucleobases exhibit significantly different
interaction strengths when physisorbed on graphene. The stabilizing factor in
the interaction between the base molecule and graphene sheet is dominated by
the molecular polarizability that allows a weakly attractive dispersion force
to be induced between them. The present study represents a significant step
towards a first-principles understanding of how the base sequence of DNA can
affect its interaction with carbon nanotubes, as observed experimentally.Comment: 7 pages, 3 figure
Bogoliubov's Integrals of Motion in Quantum Cosmology and Gravity
Quantum Cosmology and Gravity are formulated here as the primary and
secondary quantizations of the energy constraints by analogy with the
historical formulation of quantum field theory. New fact is that both the
Universe and its matter are created from stable vacuum obtained by the
Bogoliubov-type transformation just as it is in the theory of quantum
superfluid liquid. Such the Quantum Gravity gives us possibility to explain
topical problems of cosmology by the cosmological creation of universes and
particles from vacuum.Comment: 12 pages, Proceedings of the II International Conference on
Superintegrable Systems in Classical and Quantum Mechanics, Dubna, Russia,
June 27 - July 1, 2005 (will be published in Yadernaya Fizika, 2006
Bounds on New Physics from B -> V1 V2 Decays
We consider the possibility that physics beyond the standard model
contributes to the decays B -> V1 V2, where V1 and V2 are vector mesons. We
show that a time-dependent angular analysis of B -> V1 V2 decays provides many
tests for this new physics (NP). Furthermore, although one cannot solve for the
NP parameters, we show that this angular analysis allows one to put bounds on
these parameters. This can be useful in estimating the scale of NP, and can
tell us whether any NP found directly at future high-energy colliders can be
responsible for effects seen in B -> V1 V2 decays.Comment: 23 pages, plain LaTeX, 5 figures (included
Bose-Einstein condensation of atomic gases in a harmonic oscillator confining potential trap
We present a model which predicts the temperature of Bose-Einstein
condensation in atomic alkali gases and find excellent agreement with recent
experimental observations. A system of bosons confined by a harmonic oscillator
potential is not characterized by a critical temperature in the same way as an
identical system which is not confined. We discuss the problem of Bose-Einstein
condensation in an isotropic harmonic oscillator potential analytically and
numerically for a range of parameters of relevance to the study of low
temperature gases of alkali metals.Comment: 11 pages latex with two postscript figure
Short-Wave Excitations in Non-Local Gross-Pitaevskii Model
It is shown, that a non-local form of the Gross-Pitaevskii equation allows to
describe not only the long-wave excitations, but also the short-wave ones in
the systems with Bose-condensate. At given parameter values, the excitation
spectrum mimics the Landau spectrum of quasi-particle excitations in superfluid
Helium with roton minimum. The excitation wavelength, at which the roton
minimum exists, is close to the inter-particle interaction range. It is shown,
that the existence domain of the spectrum with a roton minimum is reduced, if
one accounts for an inter-particle attraction.Comment: 5 pages, 5 figures, UJP style; presented at Bogolyubov Kyiv
Conference "Modern Problems of Theoretical and Mathematical Physics",
September 15-18, 200
Metformin Treatment Has No Beneficial Effect in a Dose-Response Survival Study in the SOD1G93A Mouse Model of ALS and Is Harmful in Female Mice
Background: Amyotrophic Lateral Sclerosis (ALS) is a devastating neurological disorder characterized by selective
degeneration of upper and lower motor neurons. The primary triggers for motor neuron degeneration are unknown but
inflammation, oxidative stress and mitochondrial defects have been identified as potential contributing factors. Metformin is
an anti-type II diabetes drug that has anti-inflammatory and anti-oxidant properties, can bring about mitochondrial
biogenesis and has been shown to attenuate pathology in mouse models of Huntington’s disease and multiple sclerosis. We
therefore hypothesized that it might increase survival in the SOD1G93A murine model of ALS.
Methodology/Principal Findings: Treatment of male and female SOD1G93A mice (n = 14 per sex). Results for all groups were
compared using Kaplan-Meier time to event analyses. In this survival study, metformin was unable to reduce pathology at
any dose and had an unexpected dose-dependent negative effect on the onset of neurological symptoms (P = 0.0236) and
on disease progression (P = 0.0362) in female mice.
Conclusions/Significance: This study suggests that metformin is a poor candidate for clinical trial in ALS patients and that
the possibility of harmful effects of metformin in female ALS patients with type II diabetes should be investigated
’Team GB’ and London 2012: The Paradox of National and Global Identities
This article explores the problems associated with ’national identity’ in the UK and examines the tensions arising between the international and local dimensions of the games through examples of domestic (UK) and international (Brazil, Chicago) media coverage of the key debates relating to London’s period of preparation. The chapter proposes a conception of London 2012 as exemplar of an event poised to generate insights and experiences connected to a new politics of ’cosmopolitan’ identity; insights central to grasping the cultural politics of contemporary urban development-and the paradoxes of national identity in current discourses of Olympism. Properly speaking, cosmopolitanism suits those people who have no country, while internationalism should be the state of mind of those who love their country above all, who seek to draw to it the friendship of foreigners by professing for the countries of those foreigners an intelligent and enlightened sympathy. © 2010 Taylor & Francis
Quantum Equilibrium and the Origin of Absolute Uncertainty
The quantum formalism is a ``measurement'' formalism--a phenomenological
formalism describing certain macroscopic regularities. We argue that it can be
regarded, and best be understood, as arising from Bohmian mechanics, which is
what emerges from Schr\"odinger's equation for a system of particles when we
merely insist that ``particles'' means particles. While distinctly
non-Newtonian, Bohmian mechanics is a fully deterministic theory of particles
in motion, a motion choreographed by the wave function. We find that a Bohmian
universe, though deterministic, evolves in such a manner that an {\it
appearance} of randomness emerges, precisely as described by the quantum
formalism and given, for example, by ``\rho=|\psis|^2.'' A crucial ingredient
in our analysis of the origin of this randomness is the notion of the effective
wave function of a subsystem, a notion of interest in its own right and of
relevance to any discussion of quantum theory. When the quantum formalism is
regarded as arising in this way, the paradoxes and perplexities so often
associated with (nonrelativistic) quantum theory simply evaporate.Comment: 75 pages. This paper was published a long time ago, but was never
archived. We do so now because it is basic for our recent article
quant-ph/0308038, which can in fact be regarded as an appendix of the earlier
on
Magnetic Field-Induced Condensation of Triplons in Han Purple Pigment BaCuSiO
Besides being an ancient pigment, BaCuSiO is a quasi-2D magnetic
insulator with a gapped spin dimer ground state. The application of strong
magnetic fields closes this gap creating a gas of bosonic spin triplet
excitations called triplons. The topology of the spin lattice makes
BaCuSiO an ideal candidate for studying the Bose-Einstein condensation
of triplons as a function of the external magnetic field, which acts as a
chemical potential. In agreement with quantum Monte Carlo numerical
simulations, we observe a distinct lambda-anomaly in the specific heat together
with a maximum in the magnetic susceptibility upon cooling down to liquid
Helium temperatures.Comment: published on August 20, 200
New Physics in CP Asymmetries and Rare B Decays
We review and update the effects of physics beyond the standard model on CP
asymmetries in B decays. These asymmetries can be significantly altered if
there are important new-physics contributions to \bqbqbar mixing. This same new
physics will therefore also contribute to rare, flavor-changing B decays.
Through a study of such decays, we show that it is possible to partially
distinguish the different models of new physics.Comment: 42 pages, plain TeX (macros included), 1 figure (included). A few
sentences added, references updated. Present manuscript is now identical to
the version accepted for publication in Phys. Rev.
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