8,000 research outputs found
Ions in glass forming glycerol: Close correlation of alpha and fast beta relaxation
We provide broadband dielectric loss spectra of glass-forming glycerol with
varying additions of LiCl. The measurements covering frequencies up to 10 THz
extend well into the region of the fast beta process, commonly ascribed to
caged molecule dynamics. Aside of the known variation of the structural alpha
relaxation time and a modification of the excess wing with ion content, we also
find a clear influence on the shallow loss minimum arising from the fast beta
relaxation. Within the framework of mode-coupling theory, the detected
significant broadening of this minimum is in reasonable accord with the found
variation of the alpha-relaxation dynamics. A correlation between
alpha-relaxation rate and minimum position holds for all ion concentrations and
temperatures, even below the critical temperature defined by mode-coupling
theory.Comment: 5 pages, 5 figure
Magnetic field enhanced structural instability in EuTiO_{3}
EuTiO_{3} undergoes a structural phase transition from cubic to tetragonal at
T_S = 282 K which is not accompanied by any long range magnetic order. However,
it is related to the oxygen ocathedra rotation driven by a zone boundary
acoustic mode softening. Here we show that this displacive second order
structural phase transition can be shifted to higher temperatures by the
application of an external magnetic field (increased by 4 K for mu_{0}H = 9 T).
This observed field dependence is in agreement with theoretical predictions
based on a coupled spin-anharmonic-phonon interaction model.Comment: 4 pages, 4 figure
Design and Simulation of THz Quantum Cascade Lasers
Strategies and concepts for the design of THz emitters based on the quantum
cascade scheme are analyzed and modeled in terms of a fully three-dimensional
Monte Carlo approach; this allows for a proper inclusion of both
carrier-carrier and carrier-phonon scattering mechanisms. Starting from the
simulation of previously published far-infrared emitters, where no population
inversion is achieved, two innovative designs are proposed. The first one
follows the well-established chirped-superlattice scheme whereas the second one
employs a double-quantum well superlattice to allow energy relaxation through
optical phonon emission. For both cases a significant population inversion is
predicted at temperatures up to 80 K.Comment: 4 pages, 2 figures, 2 table
Glucose and pyruvate catabolism in Litomosoides carinii
The filarial worm Litomosoides carinii showed a rapid uptake of glucose during in vitro incubation. This uptake proceeded linearly with time, and was significantly higher under aerobic compared to anoxic conditions. Under an atmosphere of nitrogen the worms converted glucose almost quantitatively to lactate, whereas in the presence of oxygen appreciable quantities of acetate, acetoin and CO2, in addition to lactate, were formed. Although aerobically only 73% of the carbohydrate carbon could be accounted for by the latter products as well as by a net glycogen synthesis, attempts to identify other compounds presumed to be derived from glucose metabolism have been unsuccessful. The complete sequence of the glycolytic enzymes was detected in particulate-free cytosolic extracts of the filarial worm. With the exception of 6-phosphofructokinase, all glycolytic enzyme activities were considerably higher than those reported for rat liver. In addition, L. carinii possesses the entire set of enzymes catalysing the eight successive reaction steps of the tricarboxylic acid cycle. On a mitochondrial protein basis, the specific activities of these enzymes were similar to those present in rat liver. Various enzymatic activities of the mitochondrial respiratory chain were detected in the parasite. These include low levels of NADH and cytochrome c oxidases, but a high activity value for NADH dehydrogenase. Cell-free extracts and the mitochondrial fraction of the worms were found to exhibit an enzyme capable of catalysing the decarboxylation of pyruvate. Since this activity was stimulated 5- to 20-fold by the cofactors known to be required by the pyruvate dehydrogenase complex of other animal cells, pyruvate decarboxylation and thus acetate formation in the parasite may be mediated by an enzyme similar to, or identical with, the pyruvate dehydrogenase system. Isotopic carbon balance studies and experiments in which substrates specifically labelled with 14C were employed showed that substrate carbon can to some extent enter into respiratory CO2. From these and the enzymatic analyses it is suggested that complete oxidation of carbon substrate may be of relevance as an energy-conserving pathway in the filarial wor
Hardness of Exact Distance Queries in Sparse Graphs Through Hub Labeling
A distance labeling scheme is an assignment of bit-labels to the vertices of
an undirected, unweighted graph such that the distance between any pair of
vertices can be decoded solely from their labels. An important class of
distance labeling schemes is that of hub labelings, where a node
stores its distance to the so-called hubs , chosen so that for
any there is belonging to some shortest
path. Notice that for most existing graph classes, the best distance labelling
constructions existing use at some point a hub labeling scheme at least as a
key building block. Our interest lies in hub labelings of sparse graphs, i.e.,
those with , for which we show a lowerbound of
for the average size of the hubsets.
Additionally, we show a hub-labeling construction for sparse graphs of average
size for some , where is the
so-called Ruzsa-Szemer{\'e}di function, linked to structure of induced
matchings in dense graphs. This implies that further improving the lower bound
on hub labeling size to would require a
breakthrough in the study of lower bounds on , which have resisted
substantial improvement in the last 70 years. For general distance labeling of
sparse graphs, we show a lowerbound of , where is the communication complexity of the
Sum-Index problem over . Our results suggest that the best achievable
hub-label size and distance-label size in sparse graphs may be
for some
Shortest Path Computation with No Information Leakage
Shortest path computation is one of the most common queries in location-based
services (LBSs). Although particularly useful, such queries raise serious
privacy concerns. Exposing to a (potentially untrusted) LBS the client's
position and her destination may reveal personal information, such as social
habits, health condition, shopping preferences, lifestyle choices, etc. The
only existing method for privacy-preserving shortest path computation follows
the obfuscation paradigm; it prevents the LBS from inferring the source and
destination of the query with a probability higher than a threshold. This
implies, however, that the LBS still deduces some information (albeit not
exact) about the client's location and her destination. In this paper we aim at
strong privacy, where the adversary learns nothing about the shortest path
query. We achieve this via established private information retrieval
techniques, which we treat as black-box building blocks. Experiments on real,
large-scale road networks assess the practicality of our schemes.Comment: VLDB201
Is Switzerland an Interest Rate Island after all? Time Series and Non-Linear Switching Regime Evidence
Has the “Swiss interest rate anomaly” persisted after the financial crisis? Regarding the hypothesis that the Swiss interest rate anomaly results from systemic risk anticipation, we discuss whether Switzerland remains an interest rate island in the wake of the financial crisis. We find evidence for the demise of the interest rate bonus of the Swiss franc (CHF) vis-à-vis the Euro (EUR) after the Swiss National Bank (SNB) started to advocate an exchange rate floor with the Euro. After the compression of the bonus to insignificant levels, the uncovered interest parity (UIRP) holds again. We find evidence for a recent regime switch after the SNB has discontinued the exchange rate floor with the Euro
A linear method for the retrieval of sun-induced chlorophyll fluorescence from GOME-2 and SCIAMACHY data
Global retrievals of near-infrared sun-induced chlorophyll fluorescence (SIF)
have been achieved in the last few years by means of a number of space-borne
atmospheric spectrometers. Here, we present a new retrieval method for medium
spectral resolution instruments such as the Global Ozone Monitoring
Experiment-2 (GOME-2) and the SCanning Imaging Absorption SpectroMeter for
Atmospheric CHartographY (SCIAMACHY). Building upon the previous work by
Guanter et al. (2013) and Joiner et al. (2013), our approach provides a
solution for the selection of the number of free parameters. In particular, a
backward elimination algorithm is applied to optimize the number of
coefficients to fit, which reduces also the retrieval noise and selects the
number of state vector elements automatically. A sensitivity analysis with
simulated spectra has been utilized to evaluate the performance of our
retrieval approach. The method has also been applied to estimate SIF at 740 nm
from real spectra from GOME-2 and for the first time, from SCIAMACHY. We find
a good correspondence of the absolute SIF values and the spatial patterns from
the two sensors, which suggests the robustness of the proposed retrieval
method. In addition, we compare our results to existing SIF data sets, examine
uncertainties and use our GOME-2 retrievals to show empirically the relatively
low sensitivity of the SIF retrieval to cloud contamination
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