7,850 research outputs found
Chiral Symmetry Breaking out of QCD Effective Locality
The QCD non-perturbative property of Effective Locality whose essential
meaning has been disclosed recently, is here questioned about the chiral
symmetry breaking phenomenon, one of the two major issues of the
non-perturbative phase of QCD. As a first attempt, quenching and the eikonal
approximation are used so as to simplify calculations which are quite involved.
Chiral symmetry breaking appears to be realised in close connection to the
Effective Locality mass scale, , as could be expected.Comment: ICNAAM 2018, Analysis of Quantum Field Theory IV Conference extended
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SU(3) and SU(4) singlet quantum Hall states at
We report on an exact diagonalization study of fractional quantum Hall states
at filling factor in a system with a four-fold degenerate =0
Landau level and SU(4) symmetric Coulomb interactions. Our investigation
reveals previously unidentified SU(3) and SU(4) singlet ground states which
appear at flux quantum shift 2 when a spherical geometry is employed, and lie
outside the established composite-fermion or multicomponent Halperin state
patterns. We evaluate the two-particle correlation functions of these states,
and discuss quantum phase transitions in graphene between singlet states with
different number of components as magnetic field strength is increased.Comment: 5+2 pages, 3 figure
Measurement of thermal conductance of silicon nanowires at low temperature
We have performed thermal conductance measurements on individual single
crystalline silicon suspended nanowires. The nanowires (130 nm thick and 200 nm
wide) are fabricated by e-beam lithography and suspended between two separated
pads on Silicon On Insulator (SOI) substrate. We measure the thermal
conductance of the phonon wave guide by the 3 method. The cross-section
of the nanowire approaches the dominant phonon wavelength in silicon which is
of the order of 100 nm at 1K. Above 1.3K the conductance behaves as T3, but a
deviation is measured at the lowest temperature which can be attributed to the
reduced geometry
Generating Focussed Molecule Libraries for Drug Discovery with Recurrent Neural Networks
In de novo drug design, computational strategies are used to generate novel
molecules with good affinity to the desired biological target. In this work, we
show that recurrent neural networks can be trained as generative models for
molecular structures, similar to statistical language models in natural
language processing. We demonstrate that the properties of the generated
molecules correlate very well with the properties of the molecules used to
train the model. In order to enrich libraries with molecules active towards a
given biological target, we propose to fine-tune the model with small sets of
molecules, which are known to be active against that target.
Against Staphylococcus aureus, the model reproduced 14% of 6051 hold-out test
molecules that medicinal chemists designed, whereas against Plasmodium
falciparum (Malaria) it reproduced 28% of 1240 test molecules. When coupled
with a scoring function, our model can perform the complete de novo drug design
cycle to generate large sets of novel molecules for drug discovery.Comment: 17 pages, 17 figure
Dynamics and rheology of a dilute suspension of vesicles: higher order theory
Vesicles under shear flow exhibit various dynamics: tank-treading (),
tumbling () and vacillating-breathing (). A consistent higher order
theory reveals a direct bifurcation from to if is small enough (= vesicle relaxation time towards
equilibrium shape, =shear rate). At larger the is
preceded by the mode. For we recover the leading order original
calculation, where the mode coexists with . The consistent calculation
reveals several quantitative discrepancies with recent works, and points to new
features. We analyse rheology and find that the effective viscosity exhibits a
minimum at and bifurcation points.Comment: 4 pages, 5 figure
Prediction of anomalous diffusion and algebraic relaxations for long-range interacting systems, using classical statistical mechanics
We explain the ubiquity and extremely slow evolution of non gaussian
out-of-equilibrium distributions for the Hamiltonian Mean-Field model, by means
of traditional kinetic theory. Deriving the Fokker-Planck equation for a test
particle, one also unambiguously explains and predicts striking slow algebraic
relaxation of the momenta autocorrelation, previously found in numerical
simulations. Finally, angular anomalous diffusion are predicted for a large
class of initial distributions. Non Extensive Statistical Mechanics is shown to
be unnecessary for the interpretation of these phenomena
Measuring the eccentricity of the Earth orbit with a nail and a piece of plywood
I describe how to obtain a rather good experimental determination of the
eccentricity of the Earth orbit, as well as the obliquity of the Earth rotation
axis, by measuring, over the course of a year, the elevation of the Sun as a
function of time during a day. With a very simple "instrument" consisting of an
elementary sundial, first-year students can carry out an appealing measurement
programme, learn important concepts in experimental physics, see concrete
applications of kinematics and changes of reference frames, and benefit from a
hands-on introduction to astronomy.Comment: 12 pages, 6 figure
Unbiased mm-wave Line Surveys of TW Hya and V4046 Sgr: The Enhanced C2H and CN Abundances of Evolved Protoplanetary Disks
We have conducted the first comprehensive mm-wave molecular emission line
surveys of the evolved circumstellar disks orbiting the nearby T Tauri stars TW
Hya and V4046 Sgr AB. Both disks are known to retain significant residual
gaseous components, despite the advanced ages of their host stars. Our unbiased
broad-band radio spectral surveys of the TW Hya and V4046 Sgr disks were
performed with the Atacama Pathfinder Experiment (APEX) 12 meter telescope and
are intended to yield a complete census of bright molecular emission lines in
the range 275-357 GHz (1.1-0.85 mm). We find that lines of 12CO, 13CO, HCN, CN,
and C2H, all of which lie in the higher-frequency range, constitute the
strongest molecular emission from both disks in the spectral region surveyed.
The molecule C2H is detected here for the first time in both disks, as is CS in
the TW Hya disk. The survey results also include the first measurements of the
full suite of hyperfine transitions of CN N=3-2 and C2H N=4-3 in both disks.
Modeling of these CN and C2H hyperfine complexes in the spectrum of TW Hya
indicates that the emission from both species is optically thick and may
originate from very cold disk regions. It furthermore appears that the
fractional abundances of CN and C2H are significantly enhanced in these evolved
protoplanetary disks relative to the fractional abundances of the same
molecules in the environments of deeply embedded protostars.Comment: 29 pages, 6 figures; to appear in Vol. 791 of The Astrophysical
Journa
Energy spectrum and broken spin-surface locking in topological insulator quantum dots
We consider the energy spectrum and the spin-parity structure of the
eigenstates for a quantum dot made of a strong topological insulator. Using the
effective low-energy theory in a finite-length cylinder geometry, numerical
calculations show that even at the lowest energy scales, the spin direction in
a topologically protected surface mode is not locked to the surface. We find
"zero-momentum" modes, and subgap states localized near the "caps" of the dot.
Both the energy spectrum and the spin texture of the eigenstates are basically
reproduced from an analytical surface Dirac fermion description. Our results
are compared to microscopic calculations using a tight-binding model for a
strong topological insulator in a finite-length nanowire geometry.Comment: 11 pages, 12 figures, to appear in Physical Review B (2011
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