93,801 research outputs found
A Terradynamics of Legged Locomotion on Granular Media
The theories of aero- and hydrodynamics predict animal movement and device
design in air and water through the computation of lift, drag, and thrust
forces. Although models of terrestrial legged locomotion have focused on
interactions with solid ground, many animals move on substrates that flow in
response to intrusion. However, locomotor-ground interaction models on such
flowable ground are often unavailable. We developed a force model for
arbitrarily-shaped legs and bodies moving freely in granular media, and used
this "terradynamics" to predict a small legged robot's locomotion on granular
media using various leg shapes and stride frequencies. Our study reveals a
complex but generic dependence of stresses in granular media on intruder depth,
orientation, and movement direction and gives insight into the effects of leg
morphology and kinematics on movement
Q-operator and T-Q relation from the fusion hierarchy
We propose that the Baxter -operator for the spin-1/2 XXZ quantum spin
chain is given by the limit of the transfer matrix with spin-
(i.e., -dimensional) auxiliary space. Applying this observation to the
open chain with general (nondiagonal) integrable boundary terms, we obtain from
the fusion hierarchy the - relation for {\it generic} values (i.e. not
roots of unity) of the bulk anisotropy parameter. We use this relation to
determine the Bethe Ansatz solution of the eigenvalues of the fundamental
transfer matrix. This approach is complementary to the one used recently to
solve the same model for the roots of unity case.Comment: Latex file, 12 pages; V2, misprints corrected and references adde
Supersymmetric QCD corrections to single top quark production at hadron colliders
We present the calculations of the supersymmetric QCD corrections to the
total cross sections for single top production at the Fermilab Tevatron and the
CERN Large Hadron Collider in the minimal supersymmetric standard model. Our
results show that for the s-channel and t-channel, the supersymmetric QCD
corrections are at most about 1%, but for the associated production process,
the supersymmetric QCD corrections increase the total cross sections
significantly, which can reach about 6% for most values of the parameters, and
the supersymmetric QCD corrections should be taken into consideration in the
future high precision experimental analysis for top physics.Comment: 33 pages, 19 figures, version to appear in Phys.Rev.
Exciton condensation and fractional charge in a bilayer two-dimension electron gas adjacent to a superconductor film
We study the exciton condensate (EC) in a bilayer two-dimension-electron-gas
(2DEG) adjacent to a type-II superconductor thin film with an array of pinned
vortex lattices. By applying continuum low energy theory and carrying numerical
simulations of lattice model within mean-field approximation, we find that if
the order parameter of EC has a vortex profile, there are exact zero modes and
associated \emph{rational} fractional charge for zero pseudospin potential
() and average chemical potential (): =0 and =0; while for
and =0, intervalley mixing splits the zero energy
levels, and the system exhibits \emph{irrational} fractional \emph{axial}
charge.Comment: 4.6 pages, 3 figure
Stripe, checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices
We study instabilities of single-species fermionic atoms in the p-orbital
bands in two-dimensional optical lattices at noninteger filling against
interactions. Charge density wave and orbital density wave orders with stripe
or checkerboard patterns are found for attractive and repulsive interactions,
respectively. The superfluid phase, usually expected of attractively
interacting fermions, is strongly suppressed. We also use field theory to
analyze the possible phase-transitions from orbital stripe order to
liquid-crystal phases and obtain the phase diagram. The condition of
nearly-perfect Fermisurface nesting, which is key to the above results, is
shown robustly independent of fermion fillings in such p-orbital systems, and
the momentum of density wave oscillation is highly tunable.
Such remarkable features show the promise of making those exotic orbital
phases, which are of broad interest in condensed-matter physics, experimentally
realizable with optical lattice gases.Comment: final version, 8 pages, 5 figure
Solar-type Stars Observed by LAMOST and Kepler
Obtaining measurements of chromospheric and photometric activity of stars
with near-solar fundamental parameters and rotation periods is important for a
better understanding of solar-stellar connection. We select a sample of 2603
stars with near-solar fundamental parameters from the Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST)-Kepler field and use LAMOST
spectra to measure their chromospheric activity and Kepler light curves to
measure their photospheric activity (i.e., the amplitude of the photometric
variability). While the rotation periods of 1556 of these stars could not be
measured due to the low amplitude of the photometric variability and highly
irregular temporal profile of light curves, 254 stars were further identified
as having near-solar rotation periods. We show that stars with near-solar
rotation periods have chromospheric activities that are systematically higher
than stars with undetected rotation periods. Furthermore, while the solar level
of photospheric and chromospheric activity appears to be typical for stars with
undetected rotation periods, the Sun appears to be less active than most stars
with near-solar rotation periods (both in terms of photospheric and
chromospheric activity).Comment: 7 pages, 6 figure
Full one-loop QCD and electroweak corrections to sfermion pair production in collisions
We have calculated the full one-loop electroweak (EW) and QCD corrections to
the third generation scalar-fermion pair production processes at an
electron-positron linear collider(LC) in the minimal supersymmetric standard
model (MSSM). We analyze the dependence of the radiative corrections on the
parameters such as the colliding energy and the SUSY
fundamental parameters , , , and so forth. The
numerical results show that the EW corrections to the squark-, stau-pair
production processes and QCD corrections to the squark-pair production
processes give substantial contributions in some parameter space. The EW
relative corrections to squark-pair production processes can be comparable with
QCD corrections at high energies. Therefore, these EW and QCD corrections
cannot be neglected in precise measurement of sfermion pair productions via
collision at future linear colliders.Comment: to be appeared in Phys. Rev.
Predicting drug response of tumors from integrated genomic profiles by deep neural networks
The study of high-throughput genomic profiles from a pharmacogenomics
viewpoint has provided unprecedented insights into the oncogenic features
modulating drug response. A recent screening of ~1,000 cancer cell lines to a
collection of anti-cancer drugs illuminated the link between genotypes and
vulnerability. However, due to essential differences between cell lines and
tumors, the translation into predicting drug response in tumors remains
challenging. Here we proposed a DNN model to predict drug response based on
mutation and expression profiles of a cancer cell or a tumor. The model
contains a mutation and an expression encoders pre-trained using a large
pan-cancer dataset to abstract core representations of high-dimension data,
followed by a drug response predictor network. Given a pair of mutation and
expression profiles, the model predicts IC50 values of 265 drugs. We trained
and tested the model on a dataset of 622 cancer cell lines and achieved an
overall prediction performance of mean squared error at 1.96 (log-scale IC50
values). The performance was superior in prediction error or stability than two
classical methods and four analog DNNs of our model. We then applied the model
to predict drug response of 9,059 tumors of 33 cancer types. The model
predicted both known, including EGFR inhibitors in non-small cell lung cancer
and tamoxifen in ER+ breast cancer, and novel drug targets. The comprehensive
analysis further revealed the molecular mechanisms underlying the resistance to
a chemotherapeutic drug docetaxel in a pan-cancer setting and the anti-cancer
potential of a novel agent, CX-5461, in treating gliomas and hematopoietic
malignancies. Overall, our model and findings improve the prediction of drug
response and the identification of novel therapeutic options.Comment: Accepted for presentation in the International Conference on
Intelligent Biology and Medicine (ICIBM 2018) at Los Angeles, CA, USA.
Currently under consideration for publication in a Supplement Issue of BMC
Genomic
Interaction between a fast rotating sunspot and ephemeral regions as the origin of the major solar event on 2006 December 13
The major solar event on 2006 December 13 is characterized by the
approximately simultaneous occurrence of a heap of hot ejecta, a great
two-ribbon flare and an extended Earth-directed coronal mass ejection. We
examine the magnetic field and sunspot evolution in active region NOAA AR
10930, the source region of the event, while it transited the solar disk centre
from Dec. 10 to Dec. 13. We find that the obvious changes in the active region
associated with the event are the development of magnetic shear, the appearance
of ephemeral regions and fast rotation of a smaller sunspot. Around the area of
the magnetic neutral line of the active region, interaction between the fast
rotating sunspot and the ephemeral regions triggers continual brightening and
finally the major flare. It is indicative that only after the sunspot rotates
up to 200 does the major event take place. The sunspot rotates at
least 240 about its centre, the largest sunspot rotation angle which
has been reported.Comment: 4 pages, 6 figures, ApJ Letters inpres
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