4,447 research outputs found
Molecular and phylogenetic characterization of honey bee viruses, Nosema microsporidia, protozoan parasites, and parasitic mites in China
China has the largest number of managed honey bee colonies, which produce the highest quantity of honey and royal jelly in the world; however, the presence of honey bee pathogens and parasites has never been rigorously identified in Chinese apiaries. We thus conducted a molecular survey of honey bee RNA viruses, Nosema microsporidia, protozoan parasites, and tracheal mites associated with nonnative Apis mellifera ligustica and native Apis cerana cerana colonies in China. We found the presence of black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), and sacbrood virus (SBV), but not that of acute bee paralysis virus (ABPV) or Kashmir bee virus (KBV). DWV was the most prevalent in the tested samples. Phylogenies of Chinese viral isolates demonstrated that genetically heterogeneous populations of BQCV, CBPV, DWV, and A. cerana-infecting SBV, and relatively homogenous populations of IAPV and A. meliifera-infecting new strain of SBV with single origins, are spread in Chinese apiaries. Similar to previous observations in many countries, Nosema ceranae, but not Nosema apis, was prevalent in the tested samples. Crithidia mellificae, but not Apicystis bombi was found in five samples, including one A. c. cerana colony, demonstrating that C. mellificae is capable of infecting multiple honey bee species. Based on kinetoplast-encoded cytochrome b sequences, the C. mellificae isolate from A. c. cerana represents a novel haplotype with 19 nucleotide differences from the Chinese and Japanese isolates from A. m. ligustica. This suggests that A. c. cerana is the native host for this specific haplotype. The tracheal mite, Acarapis woodi, was detected in one A. m. ligustica colony. Our results demonstrate that honey bee RNA viruses, N. ceranae, C. mellificae, and tracheal mites are present in Chinese apiaries, and some might be originated from native Asian honey bees
Cleaning up the cosmological constant
We present a novel idea for screening the vacuum energy contribution to the
overall value of the cosmological constant, thereby enabling us to choose the
bare value of the vacuum curvature empirically, without any need to worry about
the zero-point energy contributions of each particle. The trick is to couple
matter to a metric that is really a composite of other fields, with the
property that the square-root of its determinant is the integrand of a
topological invariant, and/or a total derivative. This ensures that the vacuum
energy contribution to the Lagrangian is non-dynamical. We then give an
explicit example of a theory with this property that is free from Ostrogradski
ghosts, and is consistent with solar system physics and cosmological tests.Comment: 8 pages, typos corrected and more text added, version accepted for
publication in JHE
FGF19 Regulates Cell Proliferation, Glucose and Bile Acid Metabolism via FGFR4-Dependent and Independent Pathways
Fibroblast growth factor 19 (FGF19) is a hormone-like protein that regulates carbohydrate, lipid and bile acid metabolism. At supra-physiological doses, FGF19 also increases hepatocyte proliferation and induces hepatocellular carcinogenesis in mice. Much of FGF19 activity is attributed to the activation of the liver enriched FGF Receptor 4 (FGFR4), although FGF19 can activate other FGFRs in vitro in the presence of the coreceptor βKlotho (KLB). In this report, we investigate the role of FGFR4 in mediating FGF19 activity by using Fgfr4 deficient mice as well as a variant of FGF19 protein (FGF19v) which is specifically impaired in activating FGFR4. Our results demonstrate that FGFR4 activation mediates the induction of hepatocyte proliferation and the suppression of bile acid biosynthesis by FGF19, but is not essential for FGF19 to improve glucose and lipid metabolism in high fat diet fed mice as well as in leptin-deficient ob/ob mice. Thus, FGF19 acts through multiple receptor pathways to elicit pleiotropic effects in regulating nutrient metabolism and cell proliferation
Ground-State Fidelity and Kosterlitz-Thouless Phase Transition for Spin 1/2 Heisenberg Chain with Next-to-the-Nearest-Neighbor Interaction
The Kosterlitz-Thouless transition for the spin 1/2 Heisenberg chain with the
next-to-the-nearest-neighbor interaction is investigated in the context of an
infinite matrix product state algorithm, which is a generalization of the
infinite time-evolving block decimation algorithm [G. Vidal, Phys. Rev. Lett.
\textbf{98}, 070201 (2007)] to accommodate both the
next-to-the-nearest-neighbor interaction and spontaneous dimerization. It is
found that, in the critical regime, the algorithm automatically leads to
infinite degenerate ground-state wave functions, due to the finiteness of the
truncation dimension. This results in \textit{pseudo} symmetry spontaneous
breakdown, as reflected in a bifurcation in the ground-state fidelity per
lattice site. In addition, this allows to introduce a pseudo-order parameter to
characterize the Kosterlitz-Thouless transition.Comment: 4 pages, 4 figure
Sculpting oscillators with light within a nonlinear quantum fluid
Seeing macroscopic quantum states directly remains an elusive goal. Particles
with boson symmetry can condense into such quantum fluids producing rich
physical phenomena as well as proven potential for interferometric devices
[1-10]. However direct imaging of such quantum states is only fleetingly
possible in high-vacuum ultracold atomic condensates, and not in
superconductors. Recent condensation of solid state polariton quasiparticles,
built from mixing semiconductor excitons with microcavity photons, offers
monolithic devices capable of supporting room temperature quantum states
[11-14] that exhibit superfluid behaviour [15,16]. Here we use microcavities on
a semiconductor chip supporting two-dimensional polariton condensates to
directly visualise the formation of a spontaneously oscillating quantum fluid.
This system is created on the fly by injecting polaritons at two or more
spatially-separated pump spots. Although oscillating at tuneable THz-scale
frequencies, a simple optical microscope can be used to directly image their
stable archetypal quantum oscillator wavefunctions in real space. The
self-repulsion of polaritons provides a solid state quasiparticle that is so
nonlinear as to modify its own potential. Interference in time and space
reveals the condensate wavepackets arise from non-equilibrium solitons. Control
of such polariton condensate wavepackets demonstrates great potential for
integrated semiconductor-based condensate devices.Comment: accepted in Nature Physic
Measuring Lensing Magnification of Quasars by Large Scale Structure using the Variability-Luminosity Relation
We introduce a technique to measure gravitational lensing magnification using
the variability of type I quasars. Quasars' variability amplitudes and
luminosities are tightly correlated, on average. Magnification due to
gravitational lensing increases the quasars' apparent luminosity, while leaving
the variability amplitude unchanged. Therefore, the mean magnification of an
ensemble of quasars can be measured through the mean shift in the
variability-luminosity relation. As a proof of principle, we use this technique
to measure the magnification of quasars spectroscopically identified in the
Sloan Digital Sky Survey, due to gravitational lensing by galaxy clusters in
the SDSS MaxBCG catalog. The Palomar-QUEST Variability Survey, reduced using
the DeepSky pipeline, provides variability data for the sources. We measure the
average quasar magnification as a function of scaled distance (r/R200) from the
nearest cluster; our measurements are consistent with expectations assuming NFW
cluster profiles, particularly after accounting for the known uncertainty in
the clusters' centers. Variability-based lensing measurements are a valuable
complement to shape-based techniques because their systematic errors are very
different, and also because the variability measurements are amenable to
photometric errors of a few percent and to depths seen in current wide-field
surveys. Given the data volume expected from current and upcoming surveys, this
new technique has the potential to be competitive with weak lensing shear
measurements of large scale structure.Comment: Accepted for publication in Ap
Two Mode Photon Bunching Effect as Witness of Quantum Criticality in Circuit QED
We suggest a scheme to probe critical phenomena at a quantum phase transition
(QPT) using the quantum correlation of two photonic modes simultaneously
coupled to a critical system. As an experimentally accessible physical
implementation, a circuit QED system is formed by a capacitively coupled
Josephson junction qubit array interacting with one superconducting
transmission line resonator (TLR). It realizes an Ising chain in the transverse
field (ICTF) which interacts with the two magnetic modes propagating in the
TLR. We demonstrate that in the vicinity of criticality the originally
independent fields tend to display photon bunching effects due to their
interaction with the ICTF. Thus, the occurrence of the QPT is reflected by the
quantum characteristics of the photonic fields.Comment: 7 pages, 4 figure
Religious coping among African Americans, Caribbean Blacks and Non-Hispanic Whites
This study examined demographic predictors of attitudes regarding religious coping (i.e., prayer during stressful times and look to God for support, strength and guidance) within a national sample of African Americans, Caribbean Blacks, and non-Hispanic Whites (National Survey of American Life). The findings demonstrate significant Black-White differences in attitudes regarding religious coping with higher endorsements of religious coping among African Americans and Black Caribbeans (Caribbean Blacks). Comparisons of African Americans and Black Caribbeans revealed both similar and divergent patterns of demographic effects. For both African Americans and Black Caribbeans, women were more likely to utilize religious coping than men and married respondents were more likely than never married respondents to report utilizing prayer when dealing with a stressful situation. Further, for both groups, higher levels of education were associated with lower endorsements of the importance of prayer in dealing with stressful situations. Among African Americans only, Southerners were more likely than respondents who resided in other regions to endorse religious coping. Among Black Caribbeans, those who emigrated from Haiti were more likely than Jamaicans to utilize religious coping when dealing with a stressful episode. © 2008 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58064/1/20202_ftp.pd
Extremely long quasiparticle spin lifetimes in superconducting aluminium using MgO tunnel spin injectors
There has been an intense search in recent years for long-lived
spin-polarized carriers for spintronic and quantum-computing devices. Here we
report that spin polarized quasi-particles in superconducting aluminum layers
have surprisingly long spin-lifetimes, nearly a million times longer than in
their normal state. The lifetime is determined from the suppression of the
aluminum's superconductivity resulting from the accumulation of spin polarized
carriers in the aluminum layer using tunnel spin injectors. A Hanle effect,
observed in the presence of small in-plane orthogonal fields, is shown to be
quantitatively consistent with the presence of long-lived spin polarized
quasi-particles. Our experiments show that the superconducting state can be
significantly modified by small electric currents, much smaller than the
critical current, which is potentially useful for devices involving
superconducting qubits
Linear approaches to intramolecular Förster Resonance Energy Transfer probe measurements for quantitative modeling
Numerous unimolecular, genetically-encoded Forster Resonance Energy Transfer (FRET) probes for monitoring biochemical activities in live cells have been developed over the past decade. As these probes allow for collection of high frequency, spatially resolved data on signaling events in live cells and tissues, they are an attractive technology for obtaining data to develop quantitative, mathematical models of spatiotemporal signaling dynamics. However, to be useful for such purposes the observed FRET from such probes should be related to a biological quantity of interest through a defined mathematical relationship, which is straightforward when this relationship is linear, and can be difficult otherwise. First, we show that only in rare circumstances is the observed FRET linearly proportional to a biochemical activity. Therefore in most cases FRET measurements should only be compared either to explicitly modeled probes or to concentrations of products of the biochemical activity, but not to activities themselves. Importantly, we find that FRET measured by standard intensity-based, ratiometric methods is inherently non-linear with respect to the fraction of probes undergoing FRET. Alternatively, we find that quantifying FRET either via (1) fluorescence lifetime imaging (FLIM) or (2) ratiometric methods where the donor emission intensity is divided by the directly-excited acceptor emission intensity (denoted R<sub>alt</sub>) is linear with respect to the fraction of probes undergoing FRET. This linearity property allows one to calculate the fraction of active probes based on the FRET measurement. Thus, our results suggest that either FLIM or ratiometric methods based on R<sub>alt</sub> are the preferred techniques for obtaining quantitative data from FRET probe experiments for mathematical modeling purpose
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