430 research outputs found
Gallium transformation under femtosecond laser excitation: Phase coexistence and incomplete melting
The reversible phase transition induced by femtosecond laser excitation of
Gallium has been studied by measuring the dielectric function at 775 nm with ~
200 fs temporal resolution. The real and imaginary parts of the transient
dielectric function were calculated from absolute reflectivity of Gallium layer
measured at two different angles of incidence, using Fresnel formulas. The
time-dependent electron-phonon effective collision frequency, the heat
conduction coefficient and the volume fraction of a new phase were restored
directly from the experimental data, and the time and space dependent electron
and lattice temperatures in the layer undergoing phase transition were
reconstructed without ad hoc assumptions. We converted the temporal dependence
of the electron-phonon collision rate into the temperature dependence, and
demonstrated, for the first time, that the electron-phonon collision rate has a
non-linear character. This temperature dependence converges into the known
equilibrium function during the cooling stage. The maximum fraction of a new
phase in the laser-excited Gallium layer reached only 60% even when the
deposited energy was two times the equilibrium enthalpy of melting. We have
also demonstrated that the phase transition pace and a fraction of the
transformed material depended strongly on the thickness of the laser-excited
Gallium layer, which was of the order of several tens of nanometers for the
whole range of the pump laser fluencies up to the damage threshold. The
kinetics of the phase transformation after the laser excitation can be
understood on the basis of the classical theory of the first-order phase
transition while the duration of non-thermal stage appears to be comparable to
the sub-picosecond pulse length.Comment: 28 pages, including 9 figs. Submitted to Phys. Rev. B 14 March 200
Direct observation of spin-polarised bulk bands in an inversion-symmetric semiconductor
Methods to generate spin-polarised electronic states in non-magnetic solids
are strongly desired to enable all-electrical manipulation of electron spins
for new quantum devices. This is generally accepted to require breaking global
structural inversion symmetry. In contrast, here we present direct evidence
from spin- and angle-resolved photoemission spectroscopy for a strong spin
polarisation of bulk states in the centrosymmetric transition-metal
dichalcogenide WSe. We show how this arises due to a lack of inversion
symmetry in constituent structural units of the bulk crystal where the
electronic states are localised, leading to enormous spin splittings up to
eV, with a spin texture that is strongly modulated in both real and
momentum space. As well as providing the first experimental evidence for a
recently-predicted `hidden' spin polarisation in inversion-symmetric materials,
our study sheds new light on a putative spin-valley coupling in
transition-metal dichalcogenides, of key importance for using these compounds
in proposed valleytronic devices.Comment: 6 pages, 4 figure
Spectral Relationships Between Kicked Harper and On-Resonance Double Kicked Rotor Operators
Kicked Harper operators and on-resonance double kicked rotor operators model
quantum systems whose semiclassical limits exhibit chaotic dynamics. Recent
computational studies indicate a striking resemblance between the spectrums of
these operators. In this paper we apply C*-algebra methods to explain this
resemblance. We show that each pair of corresponding operators belong to a
common rotation C*-algebra B_\alpha, prove that their spectrums are equal if
\alpha is irrational, and prove that the Hausdorff distance between their
spectrums converges to zero as q increases if \alpha = p/q with p and q coprime
integers. Moreover, we show that corresponding operators in B_\alpha are
homomorphic images of mother operators in the universal rotation C*-algebra
A_\alpha that are unitarily equivalent and hence have identical spectrums.
These results extend analogous results for almost Mathieu operators. We also
utilize the C*-algebraic framework to develop efficient algorithms to compute
the spectrums of these mother operators for rational \alpha and present
preliminary numerical results that support the conjecture that their spectrums
are Cantor sets if \alpha is irrational. This conjecture for almost Mathieu
operators, called the Ten Martini Problem, was recently proved after intensive
efforts over several decades. This proof for the almost Mathieu operators
utilized transfer matrix methods, which do not exist for the kicked operators.
We outline a strategy, based on a special property of loop groups of semisimple
Lie groups, to prove this conjecture for the kicked operators.Comment: 26 pages, 8 figure
A new Rhodococcus aetherivorans strain isolated from lubricant-contaminated soil as a prospective phenol biodegrading agent
Time separation as a hidden variable to the Copenhagen school of quantum mechanics
The Bohr radius is a space-like separation between the proton and electron in
the hydrogen atom. According to the Copenhagen school of quantum mechanics, the
proton is sitting in the absolute Lorentz frame. If this hydrogen atom is
observed from a different Lorentz frame, there is a time-like separation
linearly mixed with the Bohr radius. Indeed, the time-separation is one of the
essential variables in high-energy hadronic physics where the hadron is a bound
state of the quarks, while thoroughly hidden in the present form of quantum
mechanics. It will be concluded that this variable is hidden in Feynman's rest
of the universe. It is noted first that Feynman's Lorentz-invariant
differential equation for the bound-state quarks has a set of solutions which
describe all essential features of hadronic physics. These solutions explicitly
depend on the time separation between the quarks. This set also forms the
mathematical basis for two-mode squeezed states in quantum optics, where both
photons are observable, but one of them can be treated a variable hidden in the
rest of the universe. The physics of this two-mode state can then be translated
into the time-separation variable in the quark model. As in the case of the
un-observed photon, the hidden time-separation variable manifests itself as an
increase in entropy and uncertainty.Comment: LaTex 10 pages with 5 figure. Invited paper presented at the
Conference on Advances in Quantum Theory (Vaxjo, Sweden, June 2010), to be
published in one of the AIP Conference Proceedings serie
Observation of the electromagnetic doubly OZI-suppressed decay
Using a sample of billion events accumulated with the BESIII
detector at the BEPCII collider, we report the observation of the decay , which is the first evidence for a doubly
Okubo-Zweig-Iizuka suppressed electromagnetic decay. A clear structure
is observed in the mass spectrum around 1.02 GeV/, which can
be attributed to interference between and
decays. Due to this interference, two
possible solutions are found. The corresponding measured values of the
branching fraction of are and .Comment: 7 pages, 4 figures, published in Phys. Rev.
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Expression in Antennae and Reproductive Organs Suggests a Dual Role of an Odorant-Binding Protein in Two Sibling Helicoverpa Species
Odorant-binding proteins (OBPs) mediate both perception and release of semiochemicals in insects. These proteins are the ideal targets for understanding the olfactory code of insects as well as for interfering with their communication system in order to control pest species. The two sibling Lepidopteran species Helicoverpa armigera and H. assulta are two major agricultural pests. As part of our aim to characterize the OBP repertoire of these two species, here we focus our attention on a member of this family, OBP10, particularly interesting for its expression pattern. The protein is specifically expressed in the antennae of both sexes, being absent from other sensory organs. However, it is highly abundant in seminal fluid, is transferred to females during mating and is eventually found on the surface of fertilised eggs. Among the several different volatile compounds present in reproductive organs, OBP10 binds 1-dodecene, a compound reported as an insect repellent. These results have been verified in both H. armigera and H. assulta with no apparent differences between the two species. The recombinant OBP10 binds, besides 1-dodecene, some linear alcohols and several aromatic compounds. The structural similarity of OBP10 with OBP1 of the mosquito Culex quinquefasciatus, a protein reported to bind an oviposition pheromone, and its affinity with 1-dodecene suggest that OBP10 could be a carrier for oviposition deterrents, favouring spreading of the eggs in these species where cannibalism is active among larvae
Development of a chimeric Zika vaccine using a licensed live-attenuated flavivirus vaccine as backbone
Given the recent Zika virus (ZIKV) epidemic, development of an effective vaccine is of high importance. Here, the authors use a licensed live-attenuated flavivirus vaccine backbone to develop a ZIKV vaccine and determine immunogenicity, safety and protection profiles in different animal models
CCR2 Acts as Scavenger for CCL2 during Monocyte Chemotaxis
<div><h3>Background</h3><p>Leukocyte migration is essential for effective host defense against invading pathogens and during immune homeostasis. A hallmark of the regulation of this process is the presentation of chemokines in gradients stimulating leukocyte chemotaxis via cognate chemokine receptors. For efficient migration, receptor responsiveness must be maintained whilst the cells crawl on cell surfaces or on matrices along the attracting gradient towards increasing concentrations of agonist. On the other hand agonist-induced desensitization and internalization is a general paradigm for chemokine receptors which is inconsistent with the prolonged migratory capacity.</p> <h3>Methodology/Principal Findings</h3><p>Chemotaxis of monocytes was monitored in response to fluorescent CCL2-mCherry by time-lapse video microscopy. Uptake of the fluorescent agonist was used as indirect measure to follow the endogenous receptor CCR2 expressed on primary human monocytes. During chemotaxis CCL2-mCherry becomes endocytosed as cargo of CCR2, however, the internalization of CCR2 is not accompanied by reduced responsiveness of the cells due to desensitization.</p> <h3>Conclusions/Significance</h3><p>During chemotaxis CCR2 expressed on monocytes internalizes with the bound chemoattractant, but cycles rapidly back to the plasma membrane to maintain high responsiveness. Moreover, following relocation of the source of attractant, monocytes can rapidly reverse their polarization axis organizing a new leading edge along the newly formed gradient, suggesting a uniform distribution of highly receptive CCR2 on the plasma membrane. The present observations further indicate that during chemotaxis CCR2 acts as scavenger consuming the chemokine forming the attracting cue.</p> </div
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