33,465 research outputs found
Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects and Disorder
We consider dipole oscillations of a trapped dilute Bose-Einstein condensate
in the presence of a scattering potential consisting either in a localized
defect or in an extended disordered potential. In both cases the breaking of
superfluidity and the damping of the oscillations are shown to be related to
the appearance of a nonlinear dissipative flow. At supersonic velocities the
flow becomes asymptotically dissipationless.Comment: 4 pages, 4 figure
Mikrobiologische Qualität von Fleischerzeugnissen aus ökologischer Produktion
Gegenwärtig gibt es keine repräsentativen Daten zur mikrobiologischen Sicherheit und Qualität von Ökofleischerzeugnissen wie streichfähiger Rohwurst und vorverpackter Aufschnittware wie Brühwurst und Kochschinken, die im Einzelhandel mit Mindesthaltbarkeiten von 15-30 Tagen angeboten werden. Aufgrund des zunehmenden Marktanteils von Ökofleischerzeugnissen und weitreichender Abweichungen bei der Fleischerzeugung und –verarbeitung, mit teilweisem oder völligem Verzicht auf Nitrit und andere „chemische“ Zusatzstoffe, war es erforderlich, diese Wissenslücke zu füllen.
Von Oktober 2002 - Oktober 2003 untersuchten wir Erzeugnisse, die wir zum einen direkt von sechs kooperierenden Herstellern mit deutschlandweiter Vermarktung und zum anderen aus dem Naturkosthandel bezogen. Die Ergebnisse wurden mit aktuellen Befunden der amtlichen LebensmittelĂĽberwachung verglichen.
Es zeigte sich, dass Ökofleischerzeugnisse, die nach den Richtlinen anerkannter Verbände wie Demeter und Bioland hergestellt werden, kein erhöhtes Gesundheitsrisiko im Vergleich zu konventionellen Produkten aufweisen. Proben von streichfähiger Rohwurst enthielten weder Salmonellen noch enterohämorrhagische Escherichia coli. Keimzahlen von Listeria monocytogenes waren immer < 10 KBE/g, d.h. innerhalb der tolerierten Grenzen. Enterobacteriaceae sowie Koagulase-positive Staphylokokken wurden bis auf wenige Ausnahmen in gesundheitlich unbedenklichen Keimzahlen gefunden. Isolierte Enterokokken zeigten keine klinisch relevanten Antibiotikaresistenzen. Die Aufschnittwaren enthielten in keinem Fall, weder „frisch“ noch nach Ablauf des Haltbarkeitsdatums, mehr als 100 KBE/g Listeria monocytogenes. Die Keimzahlen der Milchsäurebakterien und Enterobacteriaceae waren ähnlich wie bei konventionellen Produkten. Es werden Vorschläge gemacht, wie die mikrobiologische Qualität der Erzeugnisse weiter verbessert werden kann
Predicting the hypervelocity star population in Gaia
Hypervelocity stars (HVSs) are amongst the fastest objects in our Milky Way.
These stars are predicted to come from the Galactic center (GC) and travel
along unbound orbits across the Galaxy. In the coming years, the ESA satellite
Gaia will provide the most complete and accurate catalogue of the Milky Way,
with full astrometric parameters for more than billion stars. In this
paper, we present the expected sample size and properties (mass, magnitude,
spatial, velocity distributions) of HVSs in the Gaia stellar catalogue. We
build three Gaia mock catalogues of HVSs anchored to current observations,
exploring different ejection mechanisms and GC stellar population properties.
In all cases, we predict hundreds to thousands of HVSs with precise proper
motion measurements within a few tens of kpc from us. For stars with a relative
error in total proper motion below , the mass range extends to ~ but peaks at ~ . The majority of Gaia HVSs will
therefore probe a different mass and distance range compared to the current
non-Gaia sample. In addition, a subset of a few hundreds to a few thousands of
HVSs with ~ will be bright enough to have a precise
measurement of the three-dimensional velocity from Gaia alone. Finally, we show
that Gaia will provide more precise proper motion measurements for the current
sample of HVS candidates. This will help identifying their birthplace narrowing
down their ejection location, and confirming or rejecting their nature as HVSs.
Overall, our forecasts are extremely encouraging in terms of quantity and
quality of HVS data that can be exploited to constrain both the Milky Way
potential and the GC properties.Comment: 17 pages, 18 figures, accepted for publication in MNRA
Search in weighted complex networks
We study trade-offs presented by local search algorithms in complex networks
which are heterogeneous in edge weights and node degree. We show that search
based on a network measure, local betweenness centrality (LBC), utilizes the
heterogeneity of both node degrees and edge weights to perform the best in
scale-free weighted networks. The search based on LBC is universal and performs
well in a large class of complex networks.Comment: 14 pages, 5 figures, 4 tables, minor changes, added a referenc
Factorizing twists and R-matrices for representations of the quantum affine algebra U_q(\hat sl_2)
We calculate factorizing twists in evaluation representations of the quantum
affine algebra U_q(\hat sl_2). From the factorizing twists we derive a
representation independent expression of the R-matrices of U_q(\hat sl_2).
Comparing with the corresponding quantities for the Yangian Y(sl_2), it is
shown that the U_q(\hat sl_2) results can be obtained by `replacing numbers by
q-numbers'. Conversely, the limit q -> 1 exists in representations of U_q(\hat
sl_2) and both the factorizing twists and the R-matrices of the Yangian Y(sl_2)
are recovered in this limit.Comment: 19 pages, LaTe
The H.E.S.S. extragalactic sky
The H.E.S.S. Cherenkov telescope array, located on the southern hemisphere in
Namibia, studies very high energy (VHE; E>100 GeV) gamma-ray emission from
astrophysical objects. During its successful operations since 2002 more than 80
galactic and extra-galactic gamma-ray sources have been discovered. H.E.S.S.
devotes over 400 hours of observation time per year to the observation of
extra-galactic sources resulting in the discovery of several new sources,
mostly AGNs, and in exciting physics results e.g. the discovery of very rapid
variability during extreme flux outbursts of PKS 2155-304, stringent limits on
the density of the extragalactic background light (EBL) in the near-infrared
derived from the energy spectra of distant sources, or the discovery of
short-term variability in the VHE emission from the radio galaxy M 87. With the
recent launch of the Fermi satellite in 2008 new insights into the physics of
AGNs at GeV energies emerged, leading to the discovery of several new
extragalactic VHE sources. Multi-wavelength observations prove to be a powerful
tool to investigate the production mechanism for VHE emission in AGNs. Here,
new results from H.E.S.S. observations of extragalactic sources will be
presented and their implications for the physics of these sources will be
discussed.Comment: 8 pages, 6 figures, invited review talk, in the proceedings of the
"International Workshop on Beamed and Unbeamed Gamma-Rays from Galaxies"
11-15 April 2011, Lapland Hotel Olos, Muonio, Finland, Journal of Physics:
Conference Series Volume 355, 201
New class of quantum error-correcting codes for a bosonic mode
We construct a new class of quantum error-correcting codes for a bosonic mode
which are advantageous for applications in quantum memories, communication, and
scalable computation. These 'binomial quantum codes' are formed from a finite
superposition of Fock states weighted with binomial coefficients. The binomial
codes can exactly correct errors that are polynomial up to a specific degree in
bosonic creation and annihilation operators, including amplitude damping and
displacement noise as well as boson addition and dephasing errors. For
realistic continuous-time dissipative evolution, the codes can perform
approximate quantum error correction to any given order in the timestep between
error detection measurements. We present an explicit approximate quantum error
recovery operation based on projective measurements and unitary operations. The
binomial codes are tailored for detecting boson loss and gain errors by means
of measurements of the generalized number parity. We discuss optimization of
the binomial codes and demonstrate that by relaxing the parity structure, codes
with even lower unrecoverable error rates can be achieved. The binomial codes
are related to existing two-mode bosonic codes but offer the advantage of
requiring only a single bosonic mode to correct amplitude damping as well as
the ability to correct other errors. Our codes are similar in spirit to 'cat
codes' based on superpositions of the coherent states, but offer several
advantages such as smaller mean number, exact rather than approximate
orthonormality of the code words, and an explicit unitary operation for
repumping energy into the bosonic mode. The binomial quantum codes are
realizable with current superconducting circuit technology and they should
prove useful in other quantum technologies, including bosonic quantum memories,
photonic quantum communication, and optical-to-microwave up- and
down-conversion.Comment: Published versio
Ultra narrow AuPd and Al wires
In this letter we discuss a novel and versatile template technique aimed to
the fabrication of sub-10 nm wide wires. Using this technique, we have
successfully measured AuPd wires, 12 nm wide and as long as 20 m. Even
materials that form a strong superficial oxide, and thus not suited to be used
in combination with other techniques, can be successfully employed. In
particular we have measured Al wires, with lateral width smaller or comparable
to 10 nm, and length exceeding 10 m.Comment: 4 pages, 4 figures. Pubblished in APL 86, 172501 (2005). Added
erratum and revised Fig.
TAMEing ADPKD with metformin:safe and effective?
The biguanide metformin has been safely and widely used in the treatment of type 2 diabetes mellitus for decades. Preclinical studies have suggested that it may have a role in slowing disease progression in autosomal dominant polycystic kidney disease. In this issue, Perrone et al. report results from the Trial of Administration of Metformin in PKD (TAME PKD) study, a phase 2 randomized controlled trial investigating the safety and tolerability of metformin in patients in the early stages of autosomal dominant polycystic kidney disease. We discuss the implications of these findings and how they relate to a major phase 3 trial in autosomal dominant polycystic kidney disease that will start later in 2021
Lattice Gas Dynamics; Application to Driven Vortices in Two Dimensional Superconductors
A continuous time Monte Carlo lattice gas dynamics is developed to model
driven steady states of vortices in two dimensional superconducting networks.
Dramatic differences are found when compared to a simpler Metropolis dynamics.
Subtle finite size effects are found at low temperature, with a moving smectic
that becomes unstable to an anisotropic liquid on sufficiently large length
scales.Comment: 5 pages, 4 figure
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