4,298 research outputs found
Nucleon Structure from Lattice QCD
Recent advances in lattice field theory, in computer technology and in chiral
perturbation theory have enabled lattice QCD to emerge as a powerful
quantitative tool in understanding hadron structure. I describe recent progress
in the computation of the nucleon form factors and moments of parton
distribution functions, before proceeding to describe lattice studies of the
Generalized Parton Distributions (GPDs). In particular, I show how lattice
studies of GPDs contribute to building a three-dimensional picture of the
proton. I conclude by describing the prospects for studying the structure of
resonances from lattice QCD.Comment: 6 pages, invited plenary talk at NSTAR 2007, 5-8 September 2007,
Bonn, German
Overview of nucleon structure studies
A brief overview of the recent activity in the measurement of the elastic
electromagnetic proton and neutron form factors is presented. It is discussed
how the quality of the data has been greatly improved by performing double
polarization experiments, and the role of two-photon exchange processes will be
highlighted. The spatial information on the quark charge distribibutions in the
nucleon resulting from the form factors measurements will be discussed, as well
as the steady rate of improvements made in the lattice QCD calculations. It is
discussed how generalized parton distributions have emerged as a unifying theme
in hadron physics linking the spatial densities extracted from form factors
with the quark momentum distribution information residing in quark structure
functions. The recent progress in the electromagnetic excitation of the
resonance will also briefly be discussed.Comment: prepared for Proceedings of International Nuclear Physics Conference
(INPC07), typos corrected + references adde
Surface Polymer Network Model and Effective Membrane Curvature Elasticity
A microscopic model of a surface polymer network - membrane system is
introduced, with contact polymer surface interactions that can be either
repulsive or attractive and sliplinks of functionality four randomly
distributed over the supporting membrane surface anchoring the polymers to it.
For the supporting surface perturbed from a planar configuration and a small
relative number of surface sliplinks, we investigate an expansion of the free
energy in terms of the local curvatures of the surface and the surface density
of sliplinks, obtained through the application of the Balian - Bloch -
Duplantier multiple surface scattering method. As a result, the dependence of
the curvature elastic modulus, the Gaussian modulus as well as of the
spontaneous curvature of the "dressed" membrane, ~{\sl i.e.} polymer network
plus membrane matrix, is obtained on the mean polymer bulk end to end
separation and the surface density of sliplinks.Comment: 15 pages with one included compressed uuencoded figure
SynerGPT: In-Context Learning for Personalized Drug Synergy Prediction and Drug Design
Predicting synergistic drug combinations can help accelerate discovery of
cancer treatments, particularly therapies personalized to a patient's specific
tumor via biopsied cells. In this paper, we propose a novel setting and models
for in-context drug synergy learning. We are given a small "personalized
dataset" of 10-20 drug synergy relationships in the context of specific cancer
cell targets. Our goal is to predict additional drug synergy relationships in
that context. Inspired by recent work that pre-trains a GPT language model (LM)
to "in-context learn" common function classes, we devise novel pre-training
schemes that enable a GPT model to in-context learn "drug synergy functions".
Our model -- which does not use any textual corpora, molecular fingerprints,
protein interaction or any other domain-specific knowledge -- is able to
achieve competitive results. We further integrate our in-context approach with
a genetic algorithm to optimize model prompts and select synergy candidates to
test after conducting a patient biopsy. Finally, we explore a novel task of
inverse drug design which can potentially enable the design of drugs that
synergize specifically to target a given patient's "personalized dataset". Our
findings can potentially have an important impact on precision cancer medicine,
and also raise intriguing questions on non-textual pre-training for LMs
Residual Chiral Symmetry Breaking in Domain-Wall Fermions
We study the effective quark mass induced by the finite separation of the
domain walls in the domain-wall formulation of chiral fermion as the function
of the size of the fifth dimension (), the gauge coupling and the
physical volume . We measure the mass by calculating the small eigenvalues
of the hermitian domain-wall Dirac operator ( in the
topologically-nontrivial quenched SU(3) gauge configurations. We find that the
induced quark mass is nearly independent of the physical volume, decays
exponentially as a function of , and has a strong dependence on the size
of quantum fluctuations controlled by . The effect of the choice of the
lattice gluon action is also studied.Comment: 12 pages, 7 figure
Remote driving as the Failsafe: Qualitative investigation of Usersā perceptions and requirements towards the 5G-enabled Level 4 automated vehicles
AbstractThe Level 4 Automated Vehicles (L4 AV) potentially deliver social, economic, safety and environmental benefits. A key feature for the L4 AV is the failsafe mechanism which ensures the safety of the vehicle without human driver input when reaching system limitations. An important solution for the failsafe is the 5G-enabled teleoperation system controlled by a remote driver. However, understanding end-usersā perception, needs and requirements towards the L4 AV is a significant under-researched area. To fill the research gap, this study conducted semi-structured interviews with 29 potential end-users to qualitatively explore the new driver-automation-remote driver interaction in the L4 AV. Results showed that end-users would like to understand how the remote driver operates the vehicle remotely and would not expect them to be multitasking or distracted. They also show that remote driversā sensing and information about the driving environment are important. Remote drivers should also be qualified and experienced drivers and must have undergone background security checks before teleoperating the L4 AV. They require remote drivers based in the same country as the L4 AV to prevent issues such as unfamiliar road layouts, different traffic rules, cultural driving style variations, liability concerns, and time differences from affecting performance. They require the remote drivers to clarify what had happened and explain how they will deal with the situation and operate the vehicle in the situation of failsafe in the L4 AV. Dedicated remote drivers are preferred over random ones. A review and feedback system is important for the end-users to evaluate the services and choose preferred remote drivers. Finally, end-users are concerned about the liability and legal implications of utilising a L4 AV, especially during the period that the L4 AV is being operated by the remote drivers
The spontaneous emergence of ordered phases in crumpled sheets
X-ray tomography is performed to acquire 3D images of crumpled aluminum
foils. We develop an algorithm to trace out the labyrinthian paths in the three
perpendicular cross sections of the data matrices. The tangent-tangent
correlation function along each path is found to decay exponentially with an
effective persistence length that shortens as the crumpled ball becomes more
compact. In the mean time, we observed ordered domains near the crust, similar
to the lamellae phase mixed by the amorphous portion in lyotropic liquid
crystals. The size and density of these domains grow with further compaction,
and their orientation favors either perpendicular or parallel to the radial
direction. Ordering is also identified near the core with an arbitrary
orientation, exemplary of the spontaneous symmetry breaking
Domain-Wall Induced Quark Masses in Topologically-Nontrivial Background
In the domain-wall formulation of chiral fermion, the finite separation
between domain-walls () induces an effective quark mass ()
which complicates the chiral limit. In this work, we study the size of the
effective mass as the function of and the domain-wall height by
calculating the smallest eigenvalue of the hermitian domain-wall Dirac operator
in the topologically-nontrivial background fields. We find that, just like in
the free case, decreases exponentially in with a rate
depending on . However, quantum fluctuations amplify the wall effects
significantly. Our numerical result is consistent with a previous study of the
effective mass from the Gell-Mann-Oakes-Renner relation.Comment: 10 pages, an appendix and minor changes adde
Marine plankton phenology and life history in a changing climate : current research and future directions
Ā© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial License. The definitive version was published in Journal of Plankton Research 32 (2010): 1355-1368, doi:10.1093/plankt/fbq062.Increasing availability and extent of biological ocean time series (from both in situ and satellite data) have helped reveal significant phenological variability of marine plankton. The extent to which the range of this variability is modified as a result of climate change is of obvious importance. Here we summarize recent research results on phenology of both phytoplankton and zooplankton. We suggest directions to better quantify and monitor future plankton phenology shifts, including (i) examining the main mode of expected future changes (ecological shifts in timing and spatial distribution to accommodate fixed environmental niches vs. evolutionary adaptation of timing controls to maintain fixed biogeography and seasonality), (ii) broader understanding of phenology at the species and community level (e.g. for zooplankton beyond Calanus and for phytoplankton beyond chlorophyll), (iii) improving and diversifying statistical metrics for indexing timing and trophic synchrony and (iv) improved consideration of spatio-temporal scales and the Lagrangian nature of plankton assemblages to separate time from space changes.This study was supported by NSF grants to R.J.: OCE-0727033, 0815838 and 0732152. NSF grants to A.C.T.: OCE-0535386, 0815051 and 0814413. NSF grant to J.A.R.: OCE 0815336
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