288 research outputs found
A simple formula for pooling knowledge about a quantum system
When various observers obtain information in an independent fashion about a
classical system, there is a simple rule which allows them to pool their
knowledge, and this requires only the states-of-knowledge of the respective
observers. Here we derive an equivalent quantum formula. While its realm of
applicability is necessarily more limited, it does apply to a large class of
measurements, and we show explicitly for a single qubit that it satisfies the
intuitive notions of what it means to pool knowledge about a quantum system.
This analysis also provides a physical interpretation for the trace of the
product of two density matrices.Comment: 5 pages, Revtex
Adaptive Resolution Simulation of Liquid Water
We present a multiscale simulation of liquid water where a spatially adaptive
molecular resolution procedure allows for changing on-the-fly from a
coarse-grained to an all-atom representation. We show that this approach leads
to the correct description of all essential thermodynamic and structural
properties of liquid water.Comment: 4 pages, 3 figures; changed figure
Detection of Strongylus vulgaris in equine faecal samples by real-time PCR and larval culture - method comparison and occurrence assessment
BACKGROUND: Strongylus vulgaris has become a rare parasite in Germany during the past 50 years due to the practice of frequent prophylactic anthelmintic therapy. To date, the emerging development of resistance in Cyathostominae and Parascaris spp. to numerous equine anthelmintics has changed deworming management and the frequency of anthelmintic usage. In this regard, reliable detection of parasitic infections, especially of the highly pathogenic S. vulgaris is essential. In the current study, two diagnostic methods for the detection of infections with S. vulgaris were compared and information on the occurrence of this parasite in German horses was gained. For this purpose, faecal samples of 501 horses were screened for S. vulgaris with real-time PCR and an additional larval culture was performed in samples of 278 horses. A subset of 26 horses underwent multiple follow-up examinations with both methods in order to evaluate both the persistence of S. vulgaris infections and the reproducibility of each diagnostic method.
RESULTS: The real-time PCR revealed S. vulgaris-DNA in ten of 501 investigated equine samples (1.9%). The larval culture demonstrated larvae of S. vulgaris in three of the 278 samples (1.1%). A direct comparison of the two methods was possible in 321 samples including 43 follow-up examinations with the result of 11 S. vulgaris-positive samples by real-time PCR and 4 S. vulgaris-positive samples by larval culture. The McNemar's test (p-value = 0.016) revealed a significant difference and the kappa values (0.525) showed a moderate agreement between real-time PCR and larval culture.
CONCLUSIONS: The real-time PCR detected a significantly higher proportion of positives of S. vulgaris compared to larval culture and should thus be considered as a routine diagnostic method for the detection of S. vulgaris in equine samples
Rapid state purification protocols for a Cooper pair box
We propose techniques for implementing two different rapid state purification
schemes, within the constraints present in a superconducting charge qubit
system. Both schemes use a continuous measurement of charge (z) measurements,
and seek to minimize the time required to purify the conditional state. Our
methods are designed to make the purification process relatively insensitive to
rotations about the x-axis, due to the Josephson tunnelling Hamiltonian. The
first proposed method, based on the scheme of Jacobs [Phys. Rev. A 67,
030301(R) (2003)] uses the measurement results to control bias (z) pulses so as
to rotate the Bloch vector onto the x-axis of the Bloch sphere. The second
proposed method, based on the scheme of Wiseman and Ralph [New J. Phys. 8, 90
(2006)] uses a simple feedback protocol which tightly rotates the Bloch vector
about an axis almost parallel with the measurement axis. We compare the
performance of these and other techniques by a number of different measures.Comment: 14 pages, 14 figures. v2: Revised version after referee comments.
Accepted for publication by Physical Review
A Straightforward Introduction to Continuous Quantum Measurement
We present a pedagogical treatment of the formalism of continuous quantum
measurement. Our aim is to show the reader how the equations describing such
measurements are derived and manipulated in a direct manner. We also give
elementary background material for those new to measurement theory, and
describe further various aspects of continuous measurements that should be
helpful to those wanting to use such measurements in applications.
Specifically, we use the simple and direct approach of generalized measurements
to derive the stochastic master equation describing the continuous measurements
of observables, give a tutorial on stochastic calculus, treat multiple
observers and inefficient detection, examine a general form of the measurement
master equation, and show how the master equation leads to information gain and
disturbance. To conclude, we give a detailed treatment of imaging the resonance
fluorescence from a single atom as a concrete example of how a continuous
position measurement arises in a physical system.Comment: 24 pages, 3 eps figues. To appear in Contemporary Physic
The non-Abelian dual Meissner effect as color-alignment in SU(2) lattice gauge theory
A new gauge (m-gauge) condition is proposed by means of a generalization of
the Maximal Abelian gauge (MAG). The new gauge admits a space time dependent
embedding of the residual U(1) into the SU(2) gauge group. This embedding is
characterized by a color vector . It turns out that this vector
only depends of gauge invariant parts of the link configurations. Our numerical
results show color ferromagnetic correlations of the field in
space-time. The correlation length scales towards the continuum limit. For
comparison with the MAG, we introduce a class of gauges which smoothly
interpolates between the MAG and the m-gauge. For a wide range of the gauge
parameter, the vacuum decomposes into regions of aligned vectors . The
''neutral particle problem'' of MAG is addressed in the context of the new
gauge class.Comment: 15 pages, 6 figures, LaTeX using eps
Studies of association of AGPAT6 variants with type 2 diabetes and related metabolic phenotypes in 12,068 Danes
BACKGROUND: Type 2 diabetes, obesity and insulin resistance are characterized by hypertriglyceridemia and ectopic accumulation of lipids in liver and skeletal muscle. AGPAT6 encodes a novel glycerol-3 phosphate acyltransferase, GPAT4, which catalyzes the first step in the de novo triglyceride synthesis. AGPAT6-deficient mice show lower weight and resistance to diet- and genetically induced obesity. Here, we examined whether common or low-frequency variants in AGPAT6 associate with type 2 diabetes or related metabolic traits in a Danish population. METHODS: Eleven variants selected by a candidate gene approach capturing the common and low-frequency variation of AGPAT6 were genotyped in 12,068 Danes from four study populations of middle-aged individuals. The case–control study involved 4,638 type 2 diabetic and 5,934 glucose-tolerant individuals, while studies of quantitative metabolic traits were performed in 5,645 non-diabetic participants of the Inter99 Study. RESULTS: None of the eleven AGPAT6 variants were robustly associated with type 2 diabetes in the Danish case–control study. Moreover, none of the AGPAT6 variants showed association with measures of obesity (waist circumference and BMI), serum lipid concentrations, fasting or 2-h post-glucose load levels of plasma glucose and serum insulin, or estimated indices of insulin secretion or insulin sensitivity. CONCLUSIONS: Common and low-frequency variants in AGPAT6 do not significantly associate with type 2 diabetes susceptibility, or influence related phenotypic traits such as obesity, dyslipidemia or indices of insulin sensitivity or insulin secretion in the population studied
Frequency dependent specific heat of viscous silica
We apply the Mori-Zwanzig projection operator formalism to obtain an
expression for the frequency dependent specific heat c(z) of a liquid. By using
an exact transformation formula due to Lebowitz et al., we derive a relation
between c(z) and K(t), the autocorrelation function of temperature fluctuations
in the microcanonical ensemble. This connection thus allows to determine c(z)
from computer simulations in equilibrium, i.e. without an external
perturbation. By considering the generalization of K(t) to finite wave-vectors,
we derive an expression to determine the thermal conductivity \lambda from such
simulations. We present the results of extensive computer simulations in which
we use the derived relations to determine c(z) over eight decades in frequency,
as well as \lambda. The system investigated is a simple but realistic model for
amorphous silica. We find that at high frequencies the real part of c(z) has
the value of an ideal gas. c'(\omega) increases quickly at those frequencies
which correspond to the vibrational excitations of the system. At low
temperatures c'(\omega) shows a second step. The frequency at which this step
is observed is comparable to the one at which the \alpha-relaxation peak is
observed in the intermediate scattering function. Also the temperature
dependence of the location of this second step is the same as the one of the
peak, thus showing that these quantities are intimately connected to
each other. From c'(\omega) we estimate the temperature dependence of the
vibrational and configurational part of the specific heat. We find that the
static value of c(z) as well as \lambda are in good agreement with experimental
data.Comment: 27 pages of Latex, 8 figure
Stool Microbiota Diversity Analysis of Blastocystis-Positive and Blastocystis-Negative Individuals
Blastocystis is a unicellular eukaryote found in the gastrointestinal tract of both human and other animal hosts. The clinical significance of colonic Blastocystis colonization remains obscure. In this study, we used metabarcoding and bioinformatics analyses to identify differences in stool microbiota diversity between Blastocystis-positive and Blastocystis-negative individuals (n = 1285). Alpha diversity was significantly higher in Blastocystis carriers. At phylum level, Firmicutes and Bacteroidetes were enriched in carriers, while Proteobacteria were enriched in non-carriers. The genera Prevotella, Faecalibacterium, Flavonifracter, Clostridium, Succinivibrio, and Oscillibacter were enriched in carriers, whereas Escherichia, Bacteroides, Klebsiella, and Pseudomonas were enriched in non-carriers. No difference in beta diversity was observed. Individuals with Blastocystis-positive stools appear to have gut microbiomes associated with eubiosis unlike those with Blastocystis-negative stools, whose gut microbiomes are similar to those associated with dysbiosis. The role of Blastocystis as an indicator organism and potential modulator of the gut microbiota warrants further scrutiny.publishedVersio
Recurring dynamically-induced thinning during 1985-2010 on Upernavik Isstrøm, West Greenland
This is the publisher's version, also available electronically from "http://onlinelibrary.wiley.com".1] Many glaciers along the southeast and northwest coasts of Greenland have accelerated, increasing the ice sheet's contribution to global sea-level rise. In this article, we map elevation changes on Upernavik Isstrøm (UI), West Greenland, during 2003to 2009 using high-resolution ice, cloud and land elevation satellite laser altimeter data supplemented with altimeter surveys from NASA's Airborne Topographic Mapper during 2002 to 2010. To assess thinning prior to 2002, we analyze aerial photographs from 1985. We document at least two distinct periods of dynamically induced ice loss during 1985 to 2010 characterized by a rapid retreat of the calving front, increased ice speed, and lowering of the ice surface. The first period occurred before 1991, whereas the latter occurred during 2005 to 2009. Analyses of air and sea-surface temperature suggest a combination of relatively warm air and ocean water as a potential trigger for the dynamically induced ice loss. We estimate a total catchment-wide ice-mass loss of UI caused by the two events of 72.3 ± 15.8 Gt during 1985 to 2010, whereas the total melt-induced ice-mass loss during this same period is 19.8 ± 2.8 Gt. Thus, 79% of the total ice-mass loss of the UI catchment was caused by ice dynamics, indicating the importance of including dynamically induced ice loss in the total mass change budget of the Greenland ice sheet
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