969 research outputs found
Background field method in the large expansion of scalar QED
Using the background field method, we, in the large approximation,
calculate the beta function of scalar quantum electrodynamics at the first
nontrivial order in by two different ways. In the first way, we get the
result by summing all the graphs contributing directly. In the second way, we
begin with the Borel transform of the related two point Green's function. The
main results are that the beta function is fully determined by a simple
function and can be expressed as an analytic expression with a finite radius of
convergence, and the scheme-dependent renormalized Borel transform of the two
point Green's function suffers from renormalons.Comment: 13 pages, 4 figures, 1 table, to appear in the European Physical
Journal
Self-assembly of Nanometer-scale Magnetic Dots with Narrow Size Distributions on an Insulating Substrate
The self-assembly of iron dots on the insulating surface of NaCl(001) is
investigated experimentally and theoretically. Under proper growth conditions,
nanometer-scale magnetic iron dots with remarkably narrow size distributions
can be achieved in the absence of a wetting layer Furthermore, both the
vertical and lateral sizes of the dots can be tuned with the iron dosage
without introducing apparent size broadening, even though the clustering is
clearly in the strong coarsening regime. These observations are interpreted
using a phenomenological mean-field theory, in which a coverage-dependent
optimal dot size is selected by strain-mediated dot-dot interactions.Comment: 5 pages, 4 figure
Shotgun proteomic analysis of mulberry dwarf phytoplasma
<p>Abstract</p> <p>Background</p> <p>Mulberry dwarf (MD), which is caused by phytoplasma, is one of the most serious infectious diseases of mulberry. Phytoplasmas have been associated with diseases in several hundred plant species. The inability to culture phytoplasmas <it>in vitro </it>has hindered their characterization at the molecular level. Though the complete genomes of two phytoplasmas have been published, little information has been obtained about the proteome of phytoplasma. Therefore, the proteomic information of phytoplasmas would be useful to elucidate the functional mechanisms of phytoplasma in many biological processes.</p> <p>Results</p> <p>MD phytoplasmas, which belong to the 16SrI-B subgroup based on the 16S DNA analysis, were purified from infected tissues using a combination of differential centrifugation and density gradient centrifugation. The expressed proteome of phytoplasma was surveyed by one-dimensional SDS-PAGE and nanocapillary liquid chromatography-tandem mass spectrometry. A total of 209 phytoplasma proteins were unambiguously assigned, including the proteins with the functions of amino acid biosynthesis, cell envelope, cellular processes, energy metabolism, nucleosides and nucleotide metabolism, replication, transcription, translation, transport and binding as well as the proteins with other functions. In addition to these known function proteins, 63 proteins were annotated as hypothetical or conserved hypothetical proteins.</p> <p>Conclusions</p> <p>Taken together, a total of 209 phytoplasma proteins have been experimentally verified, representing the most extensive survey of any phytoplasma proteome to date. This study provided a valuable dataset of phytoplasma proteins, and a better understanding of the energy metabolism and virulence mechanisms of MD phytoplasma.</p
Lifelong Sequential Modeling with Personalized Memorization for User Response Prediction
User response prediction, which models the user preference w.r.t. the
presented items, plays a key role in online services. With two-decade rapid
development, nowadays the cumulated user behavior sequences on mature Internet
service platforms have become extremely long since the user's first
registration. Each user not only has intrinsic tastes, but also keeps changing
her personal interests during lifetime. Hence, it is challenging to handle such
lifelong sequential modeling for each individual user. Existing methodologies
for sequential modeling are only capable of dealing with relatively recent user
behaviors, which leaves huge space for modeling long-term especially lifelong
sequential patterns to facilitate user modeling. Moreover, one user's behavior
may be accounted for various previous behaviors within her whole online
activity history, i.e., long-term dependency with multi-scale sequential
patterns. In order to tackle these challenges, in this paper, we propose a
Hierarchical Periodic Memory Network for lifelong sequential modeling with
personalized memorization of sequential patterns for each user. The model also
adopts a hierarchical and periodical updating mechanism to capture multi-scale
sequential patterns of user interests while supporting the evolving user
behavior logs. The experimental results over three large-scale real-world
datasets have demonstrated the advantages of our proposed model with
significant improvement in user response prediction performance against the
state-of-the-arts.Comment: SIGIR 2019. Reproducible codes and datasets:
https://github.com/alimamarankgroup/HPM
Growth diagram of La0.7Sr0.3MnO3 thin films using pulsed laser deposition
An experimental study was conducted on controlling the growth mode of
La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition
(PLD) by tuning growth temperature, pressure and laser fluence. Different thin
film morphology, crystallinity and stoichiometry have been observed depending
on growth parameters. To understand the microscopic origin, the adatom
nucleation, step advance processes and their relationship to film growth were
theoretically analyzed and a growth diagram was constructed. Three boundaries
between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric
and non-stoichiometric growth were identified in the growth diagram. A good fit
of our experimental observation with the growth diagram was found. This case
study demonstrates that a more comprehensive understanding of the growth mode
in PLD is possible
Overestimation of thermal emittance in solenoid scans due to coupled transverse motion
The solenoid scan is a widely used method for the in-situ measurement of the
thermal emittance in a photocathode gun. The popularity of this method is due
to its simplicity and convenience since all rf photocathode guns are equipped
with an emittance compensation solenoid. This paper shows that the solenoid
scan measurement overestimates the thermal emittance in the ordinary
measurement configuration due to a weak quadrupole field (present in either the
rf gun or gun solenoid) followed by a rotation in the solenoid. This coupled
transverse dynamics aberration introduces a correlation between the beam's
horizontal and vertical motion leading to an increase in the measured 2D
transverse emittance, thus the overestimation of the thermal emittance. This
effect was systematically studied using both analytic expressions and numerical
simulations. These studies were experimentally verified using an L-band
1.6-cell rf photocathode gun with a cesium telluride cathode, which shows a
thermal emittance overestimation of 35% with a rms laser spot size of 2.7 mm.
The paper concludes by showing that the accuracy of the solenoid scan can be
improved by using a quadrupole magnet corrector, consisting of a pair of normal
and skew quadrupole magnets.Comment: 12 pages, 13 figure
State Regularized Policy Optimization on Data with Dynamics Shift
In many real-world scenarios, Reinforcement Learning (RL) algorithms are
trained on data with dynamics shift, i.e., with different underlying
environment dynamics. A majority of current methods address such issue by
training context encoders to identify environment parameters. Data with
dynamics shift are separated according to their environment parameters to train
the corresponding policy. However, these methods can be sample inefficient as
data are used \textit{ad hoc}, and policies trained for one dynamics cannot
benefit from data collected in all other environments with different dynamics.
In this paper, we find that in many environments with similar structures and
different dynamics, optimal policies have similar stationary state
distributions. We exploit such property and learn the stationary state
distribution from data with dynamics shift for efficient data reuse. Such
distribution is used to regularize the policy trained in a new environment,
leading to the SRPO (\textbf{S}tate \textbf{R}egularized \textbf{P}olicy
\textbf{O}ptimization) algorithm. To conduct theoretical analyses, the
intuition of similar environment structures is characterized by the notion of
homomorphous MDPs. We then demonstrate a lower-bound performance guarantee on
policies regularized by the stationary state distribution. In practice, SRPO
can be an add-on module to context-based algorithms in both online and offline
RL settings. Experimental results show that SRPO can make several context-based
algorithms far more data efficient and significantly improve their overall
performance.Comment: Preprint. Under Revie
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