4,724 research outputs found
Baryon Spectroscopy in Lattice QCD
We review recent developments in the study of excited baryon spectroscopy in
lattice QCD. After introducing the basic methods used to extract masses from
correlation functions, we discuss various interpolating fields and lattice
actions commonly used in the literature. We present a survey of results of
recent calculations of excited baryons in quenched QCD, and outline possible
future directions in the study of baryon spectra.Comment: Contribution to Lecture Notes in Physics on Lattice Hadron Physics,
43 pages, 11 figures, 3 table
Bioinspired materials for underwater adhesion with pathways to switchability
Strong adherence to underwater or wet surfaces for applications like tissue adhesion and underwater robotics is a significant challenge. This is especially apparent when switchable adhesion is required that demands rapid attachment, high adhesive capacity, and easy release. Nature displays a spectrum of permanent to reversible attachment from organisms ranging from the mussel to the octopus, providing inspiration for underwater adhesion design that has yet to be fully leveraged in synthetic systems. Here, we review the challenges and opportunities for creating underwater adhesives with a pathway to switchability. We discuss key material, geometric, modeling, and design tools necessary to achieve underwater adhesion similar to the adhesion control demonstrated in nature. Through these interdisciplinary efforts, we envision that bioinspired adhesives can rise to or even surpass the extraordinary capabilities found in biological systems
Pyrochlore Photons: The U(1) Spin Liquid in a S=1/2 Three-Dimensional Frustrated Magnet
We study the S=1/2 Heisenberg antiferromagnet on the pyrochlore lattice in
the limit of strong easy-axis exchange anisotropy. We find, using only standard
techniques of degenerate perturbation theory, that the model has a U(1) gauge
symmetry generated by certain local rotations about the z-axis in spin space.
Upon addition of an extra local interaction in this and a related model with
spins on a three-dimensional network of corner-sharing octahedra, we can write
down the exact ground state wavefunction with no further approximations. Using
the properties of the soluble point we show that these models enter the U(1)
spin liquid phase, a novel fractionalized spin liquid with an emergent U(1)
gauge structure. This phase supports gapped S^z = 1/2 spinons carrying the U(1)
``electric'' gauge charge, a gapped topological point defect or ``magnetic''
monopole, and a gapless ``photon,'' which in spin language is a gapless,
linearly dispersing S^z = 0 collective mode. There are power-law spin
correlations with a nontrivial angular dependence, as well as novel U(1)
topological order. This state is stable to ALL zero-temperature perturbations
and exists over a finite extent of the phase diagram. Using a convenient
lattice version of electric-magnetic duality, we develop the effective
description of the U(1) spin liquid and the adjacent soluble point in terms of
Gaussian quantum electrodynamics and calculate a few of the universal
properties. The resulting picture is confirmed by our numerical analysis of the
soluble point wavefunction. Finally, we briefly discuss the prospects for
understanding this physics in a wider range of models and for making contact
with experiments.Comment: 22 pages, 14 figures. Further minor changes. To appear in Phys. Rev.
Reverse Shock Emission Revealed in Early Photometry in the Candidate Short GRB 180418A
We present observations of the possible short GRB 180418A in -rays,
X-rays, and in the optical. Early optical photometry with the TAROT and RATIR
instruments show a bright peak ( 14.2 AB mag) between and
seconds that we interpret as the signature of a reversal shock. Later
observations can be modeled by a standard forward shock model and show no
evidence of jet break, allowing us to constrain the jet collimation to
. Using deep late-time optical observations we place an
upper limit of AB mag on any underlying host galaxy. The detection of
the afterglow in the \textit{Swift} UV filters constrains the GRB redshift to
and places an upper bound on the -ray isotropic equivalent
energy erg.
The properties of this GRB (e.g. duration, hardness ratio, energetic, and
environment) lie at the intersection between short and long bursts, and we can
not conclusively identify its type. We estimate that the probability that it is
drawn from the population of short GRBs is 10\%-30\%.Comment: Accepted por publication in Ap
Construction of realistic hybrid computational fetal phantoms from radiological images in three gestational ages for radiation dosimetry applications
Radiation exposure and associated radiation risks are major concerns for fetal development for
pregnant patients who undergo radiation therapy or diagnostic imaging procedures. In order to
accurately estimate the radiation dose to the fetus and assess the uncertainty of fetal position and
rotation, three hybrid computational fetus phantoms were constructed using magnetic resonance
imaging (MRI) for each fetus model as a starting point to construct a complete anatomically accurate
fetus, gravid uterus, and placenta. A total of 27 fetal organs were outlined from radiological images
via the Velocity Treatment Planning System. The DICOM-Structure set was imported to Rhinoceros
software for further reconstruction of 3D fetus phantom model sets. All fetal organ masses were
compared with ICRP-89 reference data. Our fetal model series corresponds to 20, 31, and 35 weeks of
pregnancy, thus covering the second and third trimester. Fetal positions and locations were carefully
adapted to represent the real fetus locations inside the uterus for each trimester of pregnancy. The
new series of hybrid computational fetus models together with pregnant female models can be used
in evaluating fetal radiation doses in diagnostic imaging and radiotherapy procedures
Ginzburg Criterion for Coulombic Criticality
To understand the range of close-to-classical critical behavior seen in
various electrolytes, generalized Debye-Hueckel theories (that yield density
correlation functions) are applied to the restricted primitive model of
equisized hard spheres. The results yield a Landau-Ginzburg free-energy
functional for which the Ginzburg criterion can be explicitly evaluated. The
predicted scale of crossover from classical to Ising character is found to be
similar in magnitude to that derived for simple fluids in comparable fashion.
The consequences in relation to experiments are discussed briefly.Comment: 4 pages, revtex, 2 tables (latex2.09 required due to revtex's
incompatibility with latex2e tables
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