6,645 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
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
Hybrid paramagnon phonon modes at elevated temperatures in EuTiO3
EuTiO3 (ETO) has recently experienced an enormous revival of interest because
of its possible multiferroic properties which are currently in the focus of
research. Unfortunately ETO is an unlikely candidate for enlarged
multifunctionality since the mode softening - typical for ferroelectrics -
remains incomplete, and the antiferromagnetic properties appear at 5.5K only.
However, a strong coupling between lattice and Eu spins exists and leads to the
appearance of a magnon-phonon-hybrid mode at elevated temperatures as evidenced
by electron paramagnetic resonance (EPR), muon spin rotation ({\mu}SR)
experiments and model predictions based on a coupled spin-polarizability
Hamiltonian. This novel finding supports the notion of strong
magneto-dielectric (MD) effects being realized in ETO and opens new strategies
in material design and technological applications.Comment: 9 pages, 4 figure
Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence
Global monitoring of sun-induced chlorophyll fluorescence (SIF) is improving our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675–775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km × 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor of 2 with respect to GOME-2, which comes together with an approximately 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to map other important vegetation parameters at a global scale with moderate spatial resolution and short revisit time. Those include leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning
SPIRE-FTS observations of RCW 120
The expansion of Galactic HII regions can trigger the formation of a new
generation of stars. However, little is know about the physical conditions that
prevail in these regions. We study the physical conditions that prevail in
specific zones towards expanding HII regions that trace representative media
such as the photodissociation region, the ionized region, and condensations
with and without ongoing star formation. We use the SPIRE Fourier Transform
Spectrometer (FTS) on board to observe the HII region RCW 120.
Continuum and lines are observed in the m range. Line intensities
and line ratios are obtained and used as physical diagnostics of the gas. We
used the Meudon PDR code and the RADEX code to derive the gas density and the
radiation field at nine distinct positions including the PDR surface and
regions with and without star-formation activity. For the different regions we
detect the atomic lines [NII] at m and [CI] at and m,
the ladder between the and levels and the
ladder between the and levels, as well as CH in absorption. We find gas temperatures in the range K for
densities of , and a high column density on the order
of that is in agreement with dust
analysis. The ubiquitousness of the atomic and CH emission suggests the
presence of a low-density PDR throughout RCW 120. High-excitation lines of CO
indicate the presence of irradiated dense structures or small dense clumps
containing young stellar objects, while we also find a less dense medium
() with high temperatures (K).Comment: 11 pages, 11 figures, accepted by A&
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
Full counting statistics of heteronuclear molecules from Feshbach-assisted photo association
We study the effects of quantum statistics on the counting statistics of
ultracold heteronuclear molecules formed by Feshbach-assisted photoassociation
[Phys. Rev. Lett. {\bf 93}, 140405 (2004)]. Exploiting the formal similarities
with sum frequency generation and using quantum optics methods we consider the
cases where the molecules are formed from atoms out of two Bose-Einstein
condensates, out of a Bose-Einstein condensate and a gas of degenerate
fermions, and out of two degenerate Fermi gases with and without superfluidity.
Bosons are treated in a single mode approximation and fermions in a degenerate
model. In these approximations we can numerically solve the master equations
describing the system's dynamics and thus we find the full counting statistics
of the molecular modes. The full quantum dynamics calculations are complemented
by mean field calculations and short time perturbative expansions. While the
molecule production rates are very similar in all three cases at this level of
approximation, differences show up in the counting statistics of the molecular
fields. The intermediate field of closed-channel molecules is for short times
second-order coherent if the molecules are formed from two Bose-Einstein
condensates or a Bose-Fermi mixture. They show counting statistics similar to a
thermal field if formed from two normal Fermi gases. The coherence properties
of molecule formation in two superfluid Fermi gases are intermediate between
the two previous cases. In all cases the final field of deeply-bound molecules
is found to be twice as noisy as that of the intermediate state. This is a
consequence of its coupling to the lossy optical cavity in our model, which
acts as an input port for quantum noise, much like the situation in an optical
beam splitter.Comment: replacement of earlier manuscript cond-mat/0508080
''Feshbach-assisted photoassociation of ultracold heteronuclear molecules''
with minor revision
Zur Zukunft der Ordnungsökonomik
In diesem Beitrag setzen wir uns mit der zukünftigen Positionierung der Ordnungsökonomik innerhalb der Wirtschaftswissenschaften in dem zuvor angelegten Spannungsfeld zwischen positiver Analyse und normativer, auf wirtschaftspolitische Beratung zielender Disziplin auseinander. Ausgangspunkt der Betrachtung ist ein streng normativ-individualistischer, gemäß welchem der Bürger als Individuum Legitimationsquelle für politische Handlungsempfehlungen ist. Ganz im Sinne des verfassungsökonomischen Forschungsansatzes von James Buchanan werden die Bürgerinteressen als Referenzkriterium herangezogen. Um eine dem normativen Individualismus entsprechende Referenzgröße zu finden, bieten sich das Legitimationskriterium der individuellen Zustimmung bzw. die Steuerungsideale der Bürger- und Konsumentensouveränität an. Unter dieser Zielstellung gehen wir wie folgt vor: Zunächst wird ein Überblick über den aktuellen Stand der wirtschaftswissenschaftlichen Reflexion - dem Methodenstreit - geliefert und eine kurze Einordnung vorgenommen (Abschnitt 2). Anschließend diskutieren wir jüngste Beiträge zur zukünftigen Ausrichtung der Ordnungsökonomik vor dem Hintergrund des verfassungsökonomischen Forschungsprogramms (Abschnitt 3). In einem dritten Schritt wird unsere Perspektive zur Weiterentwicklung des ordnungsökonomischen Forschungsansatzes dargestellt (Abschnitt 4). --
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