8,378 research outputs found
Updating Bounds on -Parity Violating Supersymmetry from Meson Oscillation Data
We update the bounds on -parity violating supersymmetry originating from
meson oscillations in the and systems. To this end, we
explicitly calculate all corresponding contributions from -parity violating
operators at the one-loop level, thereby completing and correcting existing
calculations. We apply our results to the derivation of bounds on -parity
violating couplings, based on up-to-date experimental measurements. In
addition, we consider the possibility of cancellations among flavor-changing
contributions of various origins, e.g. from multiple -parity violating
couplings or -parity conserving soft terms. Destructive interferences among
new-physics contributions could then open phenomenologically allowed regions,
for values of the parameters that are naively excluded when the parameters are
varied individually.Comment: 53 pages, 10 figures, 2 tables; final versio
Vehicle Routing under Consideration of Transhipment in Horizontal Coalitions of Freight Carriers
AbstractIn order to reduce operational costs related to transportation activities in road haulage, small and medium-sized freight carriers can establish horizontal coalitions and share their resources. Through exchange of customer requests with other members within the coalition, carriers can improve the operational efficiency of their transportation processes. In this paper, transhipment is integrated into the conventional pickup and delivery problem in the collaborative context. Specifically, vehicles involved in transferring the same request are synchronized at the transhipment points. A mixed-integer programming model is proposed for this problem. Based on this model the benefits of transhipment are analysed. Computational results show considerable cost-savings enabled by transhipment in the operational planning of carrier coalitions
Propagation model for the dynamics of gainâguided semiconductor laser arrays
A model is presented for the spatiotemporal dynamics of gainâguided semiconductor laser arrays. The model goes beyond coupled mode theory and treats the array as a single entity. Numerical simulations of twinâstripe gainâguided arrays yield stable or pulsing outputs, depending on array parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70023/2/JAPIAU-73-1-462-1.pd
Fractal Landscapes in Policy Optimization
Policy gradient lies at the core of deep reinforcement learning (RL) in
continuous domains. Despite much success, it is often observed in practice that
RL training with policy gradient can fail for many reasons, even on standard
control problems with known solutions. We propose a framework for understanding
one inherent limitation of the policy gradient approach: the optimization
landscape in the policy space can be extremely non-smooth or fractal for
certain classes of MDPs, such that there does not exist gradient to be
estimated in the first place. We draw on techniques from chaos theory and
non-smooth analysis, and analyze the maximal Lyapunov exponents and H\"older
exponents of the policy optimization objectives. Moreover, we develop a
practical method that can estimate the local smoothness of objective function
from samples to identify when the training process has encountered fractal
landscapes. We show experiments to illustrate how some failure cases of policy
optimization can be explained by such fractal landscapes.Comment: 18 pages and 28 figure
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The role of TMPRSS6/matriptase-2 in iron regulation and anemia
Matriptase-2, encoded by the TMPRSS6 gene, is a member of the type II transmembrane serine protease family. Matriptase-2 has structural and enzymatic similarities to matriptase-1, which has been implicated in cancer progression. Matriptase-2 was later established to be essential in iron homeostasis based on the phenotypes of iron-refractory iron deficiency anemia identified in mouse models as well as in human patients with TMPRSS6 mutations. TMPRSS6 is expressed mainly in the liver and negatively regulates the production of hepcidin, the systemic iron regulatory hormone. This review focuses on the current understanding of matriptase-2 biochemistry, and its role in iron metabolism and cancer progression. In light of recent investigations, the function of matriptase-2 in hepcidin regulation, how it is being regulated, as well as the therapeutic potential of matriptase-2 are also discussed
Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires
We report four probe measurements of the low field magnetoresistance in
single core/shell GaAs/MnAs nanowires synthesized by molecular beam epitaxy,
demonstrating clear signatures of anisotropic magnetoresistance that track the
field-dependent magnetization. A comparison with micromagnetic simulations
reveals that the principal characteristics of the magnetoresistance data can be
unambiguously attributed to the nanowire segments with a zinc blende GaAs core.
The direct correlation between magnetoresistance, magnetization and crystal
structure provides a powerful means of characterizing individual hybrid
ferromagnet/semiconductor nanostructures.Comment: Submitted to Applied Physics Letters; some typos corrected and a
defective figure replace
Relative reactivities of alkenes toward the diphenylmethyl cation
The relative reactivities of alkyl and phenyl substituted alkenes toward diphenylmethyl chloride/ZnCl2/Et2O in dichloromethane at â78°C have been determined by competition experiments. The transition state structure is discussed
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