538 research outputs found
Bright solitons in non-equilibrium coherent quantum matter
We theoretically demonstrate a mechanism for bright soliton generation in
spinor non-equilibrium Bose-Einstein condensates made of atoms or
quasiparticles such as polaritons in semiconductor microcavities. We give
analytical expressions for bright (half) solitons as minimizing functions of a
generalized non-conservative Lagrangian elucidating the unique features of
inter and intra-competition in non-equilibrium systems. The analytical results
are supported by a detailed numerical analysis that further shows the rich
soliton dynamics inferred by their instability and mutual cross-interactions.Comment: Published 13 January 2016 in Proc. Roy. Soc. A, DOI:
10.1098/rspa.2015.059
Spatiotemporal Response of Crystals in X-ray Bragg Diffraction
The spatiotemporal response of crystals in x-ray Bragg diffraction resulting
from excitation by an ultra-short, laterally confined x-ray pulse is studied
theoretically. The theory presents an extension of the analysis in symmetric
reflection geometry [1] to the generic case, which includes Bragg diffraction
both in reflection (Bragg) and transmission (Laue) asymmetric scattering
geometries. The spatiotemporal response is presented as a product of a
crystal-intrinsic plane wave spatiotemporal response function and an envelope
function defined by the crystal-independent transverse profile of the incident
beam and the scattering geometry. The diffracted wavefields exhibit amplitude
modulation perpendicular to the propagation direction due to both angular
dispersion and the dispersion due to Bragg's law. The characteristic measure of
the spatiotemporal response is expressed in terms of a few parameters: the
extinction length, crystal thickness, Bragg angle, asymmetry angle, and the
speed of light. Applications to self-seeding of hard x-ray free electron lasers
are discussed, with particular emphasis on the relative advantages of using
either the Bragg or Laue scattering geometries. Intensity front inclination in
asymmetric diffraction can be used to make snapshots of ultra-fast processes
with femtosecond resolution
Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers
Free-electron lasers (FELs) can now generate temporally short, high power
x-ray pulses of unprecedented brightness, even though their longitudinal
coherence is relatively poor. The longitudinal coherence can be potentially
improved by employing narrow bandwidth x-ray crystal optics, in which case one
must also understand how the crystal affects the field profile in time and
space. We frame the dynamical theory of x-ray diffraction as a set of coupled
waves in order to derive analytic expressions for the spatiotemporal response
of Bragg scattering from temporally short incident pulses. We compute the
profiles of both the reflected and forward scattered x-ray pulses, showing that
the time delay of the wave is linked to its transverse spatial shift
through the simple relationship , where
is the grazing angle of incidence to the diffracting planes. Finally,
we apply our findings to obtain an analytic description of Bragg forward
scattering relevant to monochromatically seed hard x-ray FELs.Comment: 11 pages, 6 figure
Survivin a radiogenetic promoter for glioblastoma viral gene therapy independently from CArG motifs
BACKGROUND: Radiogenetic therapy is a novel approach in the treatment of cancer, which employs genetic modification to alter the sensitivity of tumor cells to the effect of applied radiation. AIM: To select a potent radiation inducible promoter in the context of brain tumors and to investigate if CArG radio responsive motifs or other elements in the promoter nucleotide sequences can correlate to its response to radiation. METHODS: To select initial candidates for promoter inducible elements, the levels of mRNA expression of six different promoters were assessed using Quantitative RTPCR in D54 MG cells before and after radiation exposure. Recombinant Ad/reporter genes driven by five different promoters; CMV, VEGF, FLT-1, DR5 and survivin were constructed. Glioma cell lines were infected with different multiplicity of infection of the (promoter) Ad or CMV Ad. Cells were then exposed to a range of radiation (0–12 Gy) at single fraction. Fluorescent microscopy, Luc assay and X-gal staining was used to detect the level of expression of related genes. Different glioma cell lines and normal astrocytes were infected with Ad survivin and exposed to radiation. The promoters were analyzed for presence of CArG radio-responsive motifs and CCAAT box consensus using NCBI blast bioinformatics software. RESULTS: Radiotherapy increases the expression of gene expression by 1.25–2.5 fold in different promoters other than survivin after 2 h of radiation. RNA analysis was done and has shown an increase in copy number of tenfold for survivin. Most importantly cells treated with RT and Ad Luc driven by survivin promoter showed a fivefold increase in expression after 2 Gy of radiation in comparison to non-irradiated cells. Presence or absence of CArG motifs did not correlate with promoter response to radiation. Survivin with the best response to radiation had the lowest number of CCAAT box. CONCLUSION: Survivin is a selective potent radiation inducible promoter for glioblastoma viral gene therapy and this response to radiation could be independent of CArG motifs
Ultimate Precision of Adaptive Noise Estimation
We consider the estimation of noise parameters in a quantum channel, assuming the most general strategy allowed by quantum mechanics. This is based on the exploitation of unlimited entanglement and arbitrary quantum operations, so that the channel inputs may be interactively updated. In this general scenario, we draw a novel connection between quantum metrology and teleportation. In fact, for any teleportation-covariant channel (e.g., Pauli, erasure, or Gaussian channel), we find that adaptive noise estimation cannot beat the standard quantum limit, with the quantum Fisher information being determined by the channel’s Choi matrix. As an example, we establish the ultimate precision for estimating excess noise in a thermal-loss channel, which is crucial for quantum cryptography. Because our general methodology applies to any functional that is monotonic under trace-preserving maps, it can be applied to simplify other adaptive protocols, including those for quantum channel discrimination. Setting the ultimate limits for noise estimation and discrimination paves the way for exploring the boundaries of quantum sensing, imaging, and tomography
Chromatophore motor fields in the squid, Lolliguncula brevis
Chromatophore motoneurones in Lolliguncula brevis are known to originate in the suboesophageal lobes of the brain and to project directly to the mantle and fin through bilateral stellate ganglia and fin nerves. The chromatophore motor fields of stellar and fin nerves were investigated by stimulation of the cut end of individual nerves in a semi-intact preparation. This elicited expansion of yellow and brown chromatophores in distinct motor fields. Brown chromatophores extended over the entire mantle, whereas yellow chromatophores were limited to the dorsal and lateral mantle areas. Combined nerve stimulation and lesions demonstrated substantial overlap between adjacent chromatophore motor fields and innervation of individual chromatophores by different stellar nerves
Spontaneous spin bifurcations and ferromagnetic phase transitions in a spinor exciton-polariton condensate
We observe a spontaneous parity breaking bifurcation to a ferromagnetic state
in a spatially trapped exciton-polariton condensate. At a critical bifurcation
density under nonresonant excitation, the whole condensate spontaneously
magnetizes and randomly adopts one of two elliptically polarized (up to 95%
circularly-polarized) states with opposite handedness of polarization. The
magnetized condensate remains stable for many seconds at 5 K, but at higher
temperatures it can flip from one magnetic orientation to another. We optically
address these states and demonstrate the inversion of the magnetic state by
resonantly injecting 100-fold weaker pulses of opposite spin. Theoretically,
these phenomena can be well described as spontaneous symmetry breaking of the
spin degree of freedom induced by different loss rates of the linear
polarizations.This work was supported by Grants EPSRC No. EP/G060649/1, EU No. CLERMONT4 235114, EU No. INDEX 289968, Spanish MEC (MAT2008-01555), Greek GSRT ARISTEIA Apollo program and Fundación La Caixa, and Mexican CONACYT No. 251808. FP acknowledges financial support through an EPSRC doctoral prize fellowship at the University of Cambridge and a Schrödinger fellowship at the University of Oxford.This is the final version of the article. It first appeared from the American Physical Society via http://dx.doi.org/10.1103/PhysRevX.5.03100
Critical Rotational Speeds for Superfluids in Homogeneous Traps
We present an asymptotic analysis of the effects of rapid rotation on the
ground state properties of a superfluid confined in a two-dimensional trap. The
trapping potential is assumed to be radial and homogeneous of degree larger
than two in addition to a quadratic term. Three critical rotational velocities
are identified, marking respectively the first appearance of vortices, the
creation of a `hole' of low density within a vortex lattice, and the emergence
of a giant vortex state free of vortices in the bulk. These phenomena have
previously been established rigorously for a `flat' trap with fixed boundary
but the `soft' traps considered in the present paper exhibit some significant
differences, in particular the giant vortex regime, that necessitate a new
approach. These differences concern both the shape of the bulk profile and the
size of vortices relative to the width of the annulus where the bulk of the
superfluid resides. Close to the giant vortex transition the profile is of
Thomas-Fermi type in `flat' traps, whereas it is gaussian for soft traps, and
the `last' vortices to survive in the bulk before the giant vortex transition
are small relative to the width of the annulus in the former case but of
comparable size in the latter.Comment: To appear in J. Math. Phys, published versio
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Plasma mass density, species mix and fluctuation diagnostics using fast Alfven wave
The authors propose to employ a fast Alfven wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D-T species mix profile, and density fluctuations. Utilize the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfven speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion-ion hybrid cut-off in tokamaks is uniquely determined by the species mix ratio and the wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile
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