6,429 research outputs found
Nonequilibrium dynamics in the O(N) model to next-to-next-to-leading order in the 1/N expansion
Nonequilibrium dynamics in quantum field theory has been studied extensively
using truncations of the 2PI effective action. Both 1/N and loop expansions
beyond leading order show remarkable improvement when compared to mean-field
approximations. However, in truncations used so far, only the leading-order
parts of the self energy responsible for memory loss, damping and equilibration
are included, which makes it difficult to discuss convergence systematically.
For that reason we derive the real and causal evolution equations for an O(N)
model to next-to-next-to-leading order in the 2PI-1/N expansion. Due to the
appearance of internal vertices the resulting equations appear intractable for
a full-fledged 3+1 dimensional field theory. Instead, we solve the closely
related three-loop approximation in the auxiliary-field formalism numerically
in 0+1 dimensions (quantum mechanics) and compare to previous approximations
and the exact numerical solution of the Schroedinger equation.Comment: 29 pages, minor changes, references added; to appear in PR
The effect of a seven-week exercise program on golf swing performance and musculoskeletal measures
As most golf exercise studies have shown improved golf performance as a result of two or three sessions per week, the present study investigated the effects of a supervised exercise session performed once a week for seven weeks on golf swing variables and musculoskeletal screening measures. Professional Golfers Association of Australia International Golf Institute student golfers (n ÂĽ 43) with a mean standard deviation handicap of 8.6 8.3 participated in the study. Each golfer performed 10 musculoskeletal tests and a standardised 60-shot golf performance test (TrackMan, Vedbaek, Denmark) on separate days before and after the seven-week program. Significant improvements in a number of musculoskeletal tests (i.e. left leg bridging (6.6%), thoracic extension (62.5%), right thoracic rotation (23.3%), and right (20.8%) and left single leg squat (29.1%)) were observed (all p 0.024); however, no significant differences were observed for any golf swing variables. Future research investigating different training protocols may help to determine whether the type or frequency of training has the greatest influence on golf swing performance
Long-lived domain wall plasmons in gapped bilayer graphene
Topological domain walls in dual-gated gapped bilayer graphene host edge
states that are gate- tunable and valley polarized. Here we predict that
plasmonic collective modes can propagate along these topological domain walls
even at zero bulk density, and possess a markedly different character from that
of bulk plasmons. Strikingly, domain wall plasmons are extremely long-lived,
with plasmon lifetimes that can be orders of magnitude larger than the
transport scattering time in the bulk. While most pronounced at low
temperatures, long domain wall plasmon lifetimes persist even at room
temperature with values up to a few picoseconds. Domain wall plasmons possess a
rich phenomenology including a wide range of frequencies (up to the
mid-infrared), tunable sub-wavelength electro-magnetic confinement lengths, as
well as a valley polarization for forward/backward propagating modes. Its
unusual features render them a new tool for realizing low-dissipation
plasmonics that transcend the restrictions of the bulk
Photo-excited Carrier Dynamics and Impact Excitation Cascade in Graphene
Photo-excitation in solids can trigger a cascade in which multiple
particle-hole excitations are generated. We analyze the carrier multiplication
cascade of impact excitation processes in graphene and show that the number of
pair excitations has a strong dependence on doping, which makes carrier
multiplication gate-tunable. We also predict that the number of excited pairs
as well as the characteristic time of the cascade scale linearly with
photo-excitation energy. These dependences, as well as sharply peaked angular
distribution of pair excitations, provide clear experimental signatures of
carrier multiplication
Exosomes released from breast cancer carcinomas stimulate cell movement
For metastasis to occur cells must communicate with to their local environment to initiate growth and invasion. Exosomes have emerged as an important mediator of cell-to-cell signalling through the transfer of molecules such as mRNAs, microRNAs, and proteins between cells. Exosomes have been proposed to act as regulators of cancer progression. Here, we study the effect of exosomes on cell migration, an important step in metastasis. We performed cell migration assays, endocytosis assays, and exosome proteomic profiling on exosomes released from three breast cancer cell lines that model progressive stages of metastasis. Results from these experiments suggest: (1) exosomes promote cell migration and (2) the signal is stronger from exosomes isolated from cells with higher metastatic potentials; (3) exosomes are endocytosed at the same rate regardless of the cell type; (4) exosomes released from cells show differential enrichment of proteins with unique protein signatures of both identity and abundance. We conclude that breast cancer cells of increasing metastatic potential secrete exosomes with distinct protein signatures that proportionally increase cell movement and suggest that released exosomes could play an active role in metastasis
Broken phase effective potential in the two-loop Phi-derivable approximation and nature of the phase transition in a scalar theory
We study the phase transition of a real scalar phi^4 theory in the two-loop
Phi-derivable approximation using the imaginary time formalism, extending our
previous (analytical) discussion of the Hartree approximation. We combine Fast
Fourier Transform algorithms and accelerated Matsubara sums in order to achieve
a high accuracy. Our results confirm and complete earlier ones obtained in the
real time formalism [1] but which were less accurate due to the integration in
Minkowski space and the discretization of the spectral density function. We
also provide a complete and explicit discussion of the renormalization of the
two-loop Phi-derivable approximation at finite temperature, both in the
symmetric and in the broken phase, which was already used in the real-time
approach, but never published. Our main result is that the two-loop
Phi-derivable approximation suffices to cure the problem of the Hartree
approximation regarding the order of the transition: the transition is of the
second order type, as expected on general grounds. The corresponding critical
exponents are, however, of the mean-field type. Using a "RG-improved" version
of the approximation, motivated by our renormalization procedure, we find that
the exponents are modified. In particular, the exponent delta, which relates
the field expectation value phi to an external field h, changes from 3 to 5,
getting then closer to its expected value 4.789, obtained from accurate
numerical estimates [2].Comment: 54 pages, 16 figure
Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high spectroscopic observations of a sample of six
suspected merger remnants, selected primarily on the basis of H{\sc i} tidal
debris detections. Single stellar population analysis of these galaxies
indicates that their ages, metallicities, and -enhancement ratios are
consistent with those of a representative sample of nearby elliptical galaxies.
The expected stellar population of a recent merger remnant, young age combined
with low [/Fe], is not seen in any H{\sc i}-selected galaxy. However,
one galaxy (NGC~2534), is found to deviate from the -plane in the sense
expected for a merger remnant. Another galaxy (NGC~7332), selected by other
criteria, best matches the merger remnant expectations.Comment: 12 pages, 10 figures, accepted by A
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