3,221 research outputs found
Dissipation effects in percolating quantum Ising magnets
We study the effects of dissipation on a randomly dilute transverse-field
Ising magnet at and close to the percolation threshold. For weak transverse
fields, a novel percolation quantum phase transition separates a
super-paramagnetic cluster phase from an inhomogeneously ordered ferromagnetic
phase. The properties of this transition are dominated by large frozen and
slowly fluctuating percolation clusters. Implementing numerically a
strong-disorder real space renormalization group technique, we compute the
low-energy density of states which is found to be in good agreement with the
analytical prediction.Comment: 2 pages, 1 eps figure, final version as publishe
Method and concept evaluation of relaying oysters from Chesapeake Bay to high salinity water as a post-harvest-process to reduce Vibrio vulnificus to undetectable levels: Final Report
Post-harvest processing (PHP) methods for reducing vibrio levels that have been developed thus far are either capital intensive, have limited throughput, are not readily available, and/or are generally very expensive. In the summer of 2010 we initiated a small-scale evaluation to assess the effectiveness of relay to elevated salinity as a PHP strategy to reduce levels of Vibrio vulnificus in Crassostrea virginica oysters
Adiabatic Landau-Zener-St\"uckelberg transition with or without dissipation in low spin molecular system V15
The spin one half molecular system V15 shows no barrier against spin
reversal. This makes possible direct phonon activation between the two levels.
By tuning the field sweeping rate and the thermal coupling between sample and
thermal reservoir we have control over the phonon-bottleneck phenomena
previously reported in this system. We demonstrate adiabatic motion of molecule
spins in time dependent magnetic fields and with different thermal coupling to
the cryostat bath. We also discuss the origin of the zero-field tunneling
splitting for a half-integer spin.Comment: to appear in Phys. Rev. B - Rapid Communication
Imaging of compartmentalised intracellular nitric oxide, induced during bacterial phagocytosis, using a metalloprotein–gold nanoparticle conjugate
Nitric oxide (NO) plays an essential role within the immune system since it is involved in the break-down of infectious agents such as viruses and bacteria. The ability to measure the presence of NO in the intracellular environment would provide a greater understanding of the pathophysiological mechanism of this important molecule. Here we report the detection of NO from the intracellular phagolysosome using a fluorescently tagged metalloprotein–gold nanoparticle conjugate. The metalloprotein cytochrome c, fluorescently tagged with an Alexa Fluor dye, was self-assembled onto gold nanoparticles to produce a NO specific nanobiosensor. Upon binding of NO, the cytochrome c protein changes conformation which induces an increase of fluorescence intensity of the tagged protein proportional to the NO concentration. The nanobiosensor was sensitive to NO in a reversible and selective manner, and exhibited a linear response at NO concentrations between 1 and 300 μM. In RAW264.7γ NO− macrophage cells, the nanobiosensor was used to detect the presence of NO that had been endogenously generated upon stimulation of the cells with interferon-γ and lipopolysaccharide, or spontaneously released following treatment of the cells with a NO donor. Significantly, the nanobiosensor was shown to be taken up by the macrophages within phagolysosomes, i.e., the precise location where the NO, together with other species, destroys bacterial infection. The nanobiosensor measured, for the first time, increasing concentrations of NO produced during combined stimulation and phagocytosis of Escherichia coli bacteria from within localised intracellular phagolysosomes, a key part of the immune system
Evaluating Recruitment Contribution Of A Selectively Bred Aquaculture Line Of The Oyster, Crassostrea Virginica Used In Restoration Efforts
Severe over-fishing, habitat degradation, and recent disease impacts have devastated the eastern oyster (Crassostrea virginica) fisherey in the Chesapeake Bay. Several restoration efforts are in progress, including the unconventional approach of seeding reefs with an aquaculture strain selected for disease resistance and fast growth in hopes of mitigating the negative effects of diseases and low census numbers. Supplementation of four sites (The Great Wicomico, Lynnhaven, York and Elizabeth Rivers) examined in this study totaled approximatedly 18,500,000 aquaculture oysters from 2002 to 2006. We collected locally recruited offspring (n = 6517) from 2002 to 2006 at these sites to determine if reproduction by the transplanted oysters produced detectable contributions to recruitment by examining the frequency of a composite mitochondrial haplotype that occurs at high frequencies in this aquaculture strain but is rare in wild Chesapeake Bay oysters. The estimated frequency of this haplotype in locally recruited oysters (average 1.4%, SD = 0.9) was compared with the average frequencies found in the hatchery produced (35%, SD = 12.8) and wild (1.2%, SD = 0.9) oysters, but we were unable to refute the null-hypothesis that population supplementation made no contribution to recruitment. We discuss five nonmutually exclusive explanations for the limited impact of supplementation, including unequal sex-ratio, predation, flushing, relative scale, and aquaculture selection. We argue that predation, relative scale and aquaculture selection are the likely reasons for the limited contribution made by aquaculture oysters used for population supplementation
Moderate Resolution Spitzer Infrared Spectrograph (IRS) Observations of M, L, and T Dwarfs
We present 10 - 19 um moderate resolution spectra of ten M dwarfs, one L
dwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS)
onboard the Spitzer Space Telescope. The IRS allows us to examine molecular
spectroscopic features/lines at moderate spectral resolution in a heretofore
untapped wavelength regime. These R~600 spectra allow for a more detailed
examination of clouds, non-equilibrium chemistry, as well as the molecular
features of H2O, NH3, and other trace molecular species that are the hallmarks
of these objects. A cloud-free model best fits our mid-infrared spectrum of the
T1 dwarf epsilon Indi Ba, and we find that the NH3 feature in epsilon Indi Bb
is best explained by a non-equilibrium abundance due to vertical transport in
its atmosphere. We examined a set of objects (mostly M dwarfs) in multiple
systems to look for evidence of emission features, which might indicate an
atmospheric temperature inversion, as well as trace molecular species; however,
we found no evidence of either.Comment: 19 pages, 7 figures, accepted ApJ 1/12/0
Quantum Coherence Oscillations in Antiferromagnetic Chains
Macroscopic quantum coherence oscillations in mesoscopic antiferromagnets may
appear when the anisotropy potential creates a barrier between the
antiferromagnetic states with opposite orientations of the Neel vector. This
phenomenon is studied for the physical situation of the nuclear spin system of
eight Xe atoms arranged on a magnetic surface along a chain. The oscillation
period is calculated as a function of the chain constant. The environmental
decoherence effects at finite temperature are accounted assuming a dipole
coupling between the spin chain and the fluctuating magnetic field of the
surface. The numerical calculations indicate that the oscillations are damped
by a rate , where is the number of spins and is
the relaxation time of a single spin.Comment: 10 pages, Latex, two postscript figures; submitted to Phys. Rev.
Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
We present the first mid-infrared spectra of brown dwarfs, together with
observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the
L8 dwarf DENIS-P J0255-4700, and the T1/T6 binary system epsilon Indi Ba/Bb. As
expected, the mid-infrared spectral morphology of these objects changes rapidly
with spectral class due to the changes in atmospheric chemistry resulting from
their differing effective temperatures and atmospheric structures. By taking
advantage of the unprecedented sensitivity of the Infrared Spectrograph on the
Spitzer Space Telescope we have detected the 7.8 micron methane and 10 micron
ammonia bands for the first time in brown dwarf spectra.Comment: 4 pages, 2 figure
Dynamic and spectral mixing in nanosystems
In the framework of simple spin-boson Hamiltonian we study an interplay
between dynamic and spectral roots to stochastic-like behavior. The Hamiltonian
describes an initial vibrational state coupled to discrete dense spectrum
reservoir. The reservoir states are formed by three sequences with rationally
independent periodicities typical for vibrational states in many nanosize
systems. We show that quantum evolution of the system is determined by a
dimensionless parameter which is characteristic number of the reservoir states
relevant for the initial vibrational level dynamics. Our semi-quantitative
analytic results are confirmed by numerical solution of the equation of motion.
We anticipate that predicted in the paper both kinds of stochastic-like
behavior (namely, due to spectral mixing and recurrence cycle dynamic mixing)
can be observed by femtosecond spectroscopy methods in nanosystems.Comment: 6 pages, 4 figure
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