11,739 research outputs found
Characterizing flows with an instrumented particle measuring Lagrangian accelerations
We present in this article a novel Lagrangian measurement technique: an
instrumented particle which continuously transmits the force/acceleration
acting on it as it is advected in a flow. We develop signal processing methods
to extract information on the flow from the acceleration signal transmitted by
the particle. Notably, we are able to characterize the force acting on the
particle and to identify the presence of a permanent large-scale vortex
structure. Our technique provides a fast, robust and efficient tool to
characterize flows, and it is particularly suited to obtain Lagrangian
statistics along long trajectories or in cases where optical measurement
techniques are not or hardly applicable.Comment: submitted to New Journal of Physic
183 GHz water line variation: An energetic outburst in orion KL
Observations of the 3(13)-2(20) transition of water vapor in the direction of Ori MC1 in 1980 February show a 50% flux increase and an apparent additional red shift of approximately 2 km/s relative to the line observed in 1977 December. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km/s with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MC1 can be due either to additional far-IR radiation to pump the 1983 GHz transition or to a change in the physical conditions in the gas. Statistical equilibrium calculations using the large-velocity-gradient formalism were carried out to develop a model for the emission. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHZ increase and the 22 GH1 water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions
Changes in alpine plant growth under future climate conditions
Alpine shrub- and grasslands are shaped by extreme climatic conditions such as a long-lasting snow cover and a short vegetation period. Such ecosystems are expected to be highly sensitive to global environmental change. Prolonged growing seasons and shifts in temperature and precipitation are likely to affect plant phenology and growth. In a unique experiment, climatology and plant growth was monitored for almost a decade at 17 snow meteorological stations in different alpine regions along the Swiss Alps. Regression analyses revealed highly significant correlations between mean air temperature in May/June and snow melt out, onset of plant growth, and plant height. These correlations were used to project plant growth phenology for future climate conditions based on the gridded output of a set of regional climate models runs. Melt out and onset of growth were projected to occur on average 17 days earlier by the end of the century than in the control period from 1971–2000 under the future climate conditions of the low resolution climate model ensemble. Plant height and biomass production were expected to increase by 77% and 45%, respectively. The earlier melt out and onset of growth will probably cause a considerable shift towards higher growing plants and thus increased biomass. Our results represent the first quantitative and spatially explicit estimates of climate change impacts on future growing season length and the respective productivity of alpine plant communities in the Swiss Alps
Competing charge, spin, and superconducting orders in underdoped YBa2Cu3Oy
To explore the doping dependence of the recently discovered charge density
wave (CDW) order in YBa2Cu3Oy, we present a bulk-sensitive high-energy x-ray
study for several oxygen concentrations, including strongly underdoped
YBa2Cu3O6.44. Combined with previous data around the so-called 1/8 doping, we
show that bulk CDW order exists at least for hole concentrations (p) in the
CuO2 planes of 0.078 <~ p <~ 0.132. This implies that CDW order exists in close
vicinity to the quantum critical point for spin density wave (SDW) order. In
contrast to the pseudogap temperature T*, the onset temperature of CDW order
decreases with underdoping to T_CDW ~ 90K in YBa2Cu3O6.44. Together with a
weakened order parameter this suggests a competition between CDW and SDW
orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of
competition with superconductivity as a function of temperature and magnetic
field as samples closer to p = 1/8. At low p the CDW incommensurability
continues the previously reported linear increasing trend with underdoping. In
the entire doping range the in-plane correlation length of the CDW order in
b-axis direction depends only very weakly on the hole concentration, and
appears independent of the type and correlation length of the oxygen-chain
order. The onset temperature of the CDW order is remarkably close to a
temperature T^\dagger that marks the maximum of 1/(T_1T) in planar 63^Cu
NQR/NMR experiments, potentially indicating a response of the spin dynamics to
the formation of the CDW. Our discussion of these findings includes a detailed
comparison to the charge stripe order in La2-xBaxCuO4.Comment: 11 pages, 5 figure
Game-theoretic analysis of pay-as-bid mechanisms
Enterprises are facing a challenging dilemma. In order to be able to accommodate peak loads on their IT systems, they must maintain large computing clusters, which lie idle most of the time. At the same time, IT departments are under constant pressure to cut down on hard- and software expenses. Grid technology offers a promising way out of this dilemma by allowing the dynamic sharing both within enterprises as well as across organizational boundaries. This sharing approach, however, requires proper economic incentives. This paper is concerned with the determination of dynamic market-based prices. Due to their simplicity, so-called pay-as-bid mechanisms have become popular. This paper is novel as we provide an in-depth analysis of two such pay-as-bid mechanisms – Proportional Share and a discriminatory pay-as-bid mechanism – for the case of three users, thus extending previous work by Sanghavi and Hajek (2004) and Stößer et al. (2008). This analysis is important as we show that the nice results for two users cannot be retained once three or more users are present. Even worse, we show that these results can even be reversed if we move to games with more than two players
Cooperative Scattering by Cold Atoms
We have studied the interplay between disorder and cooperative scattering for
single scattering limit in the presence of a driving laser. Analytical results
have been derived and we have observed cooperative scattering effects in a
variety of experiments, ranging from thermal atoms in an optical dipole trap,
atoms released from a dark MOT and atoms in a BEC, consistent with our
theoretical predictions.Comment: submitted for special issue of PQE 201
The nature of the charge density waves in under-doped YBaCuO revealed by X-ray measurements of the ionic displacements
All underdoped high-temperature cuprate superconductors appear to exhibit
charge density wave (CDW) order, but both the underlying symmetry breaking and
the origin of the CDW remain unclear. We use X-ray diffraction to determine the
microscopic structure of the CDW in an archetypical cuprate
YBaCuO at its superconducting transition temperature Tc ~ 60
K. We find that the CDWs present in this material break the mirror symmetry of
the CuO2 bilayers. The ionic displacements in a CDW have two components: one
perpendicular to the CuO planes, and another parallel to these planes,
which is out of phase with the first. The largest displacements are those of
the planar oxygen atoms and are perpendicular to the CuO planes. Our
results allow many electronic properties of the underdoped cuprates to be
understood. For instance, the CDW will lead to local variations in the doping
(or electronic structure) giving an explicit explanation of the appearance of
density-wave states with broken symmetry in scanning tunnelling microscopy
(STM) and soft X-ray measurements
Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II
The optical exciton Aharonov-Bohm effect, i. e. an oscillatory component in
the energy of optically active (bright) states, is investigated in nanorings.
It is shown that a small effective electron mass, strong confinement of the
electron, and high barrier for the hole, achieved e. g. by an InAs nanoring
embedded in an AlGaSb quantum well, are favorable for observing the optical
exciton Aharonov-Bohm effect. The second derivative of the exciton energy with
respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations
even for the lowest bright state unambiguously. A connection between the
theories for infinitesimal narrow and finite width rings is established.
Furthermore, the magnetization is compared to the persistent current, which
oscillates periodically with the magnetic field and confirms thus the
non-trivial (connected) topology of the wave function in the nanoring.Comment: 12 pages, 11 figure
Biosynthesis of Mitochondrial Porin and Insertion into the Outer Mitochondrial Membrane of Neuruspora crassa
Mitochondrial porin, the major protein of the outer mitochondrial membrane is synthesized by free cytoplasmic polysomes. The apparent molecular weight of the porin synthesized in homologous or heterologous cell-free systems is the same as that of the mature porin. Transfer in vitro of mitochondrial porin from the cytosolic fraction into the outer membrane of mitochondria could be demonstrated. Before membrane insertion, mitochondrial porin is highly sensitive to added proteinase; afterwards it is strongly protected. Binding of the precursor form to mitochondria occurs at 4°C and appears to precede insertion into the membrane. Unlike transfer of many precursor proteins into or across the inner mitochondrial membrane, assembly of the porin is not dependent on an electrical potential across the inner membrane
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