2,024 research outputs found
Multidimensional entropy landscape of quantum criticality
The Third Law of Thermodynamics states that the entropy of any system in
equilibrium has to vanish at absolute zero temperature. At nonzero
temperatures, on the other hand, matter is expected to accumulate entropy near
a quantum critical point (QCP), where it undergoes a continuous transition from
one ground state to another. Here, we determine, based on general thermodynamic
principles, the spatial-dimensional profile of the entropy S near a QCP and its
steepest descent in the corresponding multidimensional stress space. We
demonstrate this approach for the canonical quantum critical compound
CeCu6-xAux near its onset of antiferromagnetic order. We are able to link the
directional stress dependence of S to the previously determined geometry of
quantum critical fluctuations. Our demonstration of the multidimensional
entropy landscape provides the foundation to understand how quantum criticality
nucleates novel phases such as high-temperature superconductivity.Comment: 14 pages, 4 figure
Hadron Spectroscopy with COMPASS at CERN
The aim of the COMPASS hadron programme is to study the light-quark hadron
spectrum, and in particular, to search for evidence of hybrids and glueballs.
COMPASS is a fixed-target experiment at the CERN SPS and features a two-stage
spectrometer with high momentum resolution, large acceptance, particle
identification and calorimetry. A short pilot run in 2004 resulted in the
observation of a spin-exotic state with consistent with the
debated . In addition, Coulomb production at low momentum transfer
data provide a test of Chiral Perturbation Theory. During 2008 and 2009, a
world leading data set was collected with hadron beam which is currently being
analysed. The large statistics allows for a thorough decomposition of the data
into partial waves. The COMPASS hadron data span over a broad range of channels
and shed light on several different aspects of QCD.Comment: 4 pages, 5 figure
Fermi Surface of KFeAs from Quantum Oscillations in Magnetostriction
We present a study of the Fermi surface of KFeAs single crystals.
Quantum oscillations were observed in magnetostriction measured down to 50 mK
and in magnetic fields up to 14 T. For , the calculated
effective masses are in agreement with recent de Haas-van Alphen and ARPES
experiments, showing enhanced values with respect to the ones obtained from
previous band calculations. For , we observed a small orbit at a
cyclotron frequency of 64 T, characterized by an effective mass of , supporting the presence of a three-dimensional pocket at the Z-point.Comment: SCES Conference, Tokyo 201
An information theoretic characterisation of auditory encoding.
The entropy metric derived from information theory provides a means to quantify the amount of information transmitted in acoustic streams like speech or music. By systematically varying the entropy of pitch sequences, we sought brain areas where neural activity and energetic demands increase as a function of entropy. Such a relationship is predicted to occur in an efficient encoding mechanism that uses less computational resource when less information is present in the signal: we specifically tested the hypothesis that such a relationship is present in the planum temporale (PT). In two convergent functional MRI studies, we demonstrated this relationship in PT for encoding, while furthermore showing that a distributed fronto-parietal network for retrieval of acoustic information is independent of entropy. The results establish PT as an efficient neural engine that demands less computational resource to encode redundant signals than those with high information content
Haemoglobin and size dependent constraints on swimbladder inflation in fish larvae
In developmental studies of fish species (especially physostomians) it could be demonstrated,
that the lack of haemoglobin during larval and juvenile stages is a relatively common phenomenon.
Generally it is linked with body translucency. In representatives of the families Galaxiidae,
Osmeridae and Clupeidae, partly reared, partly observed immediately after being caught in the wild, it
turned out, that this condition coincides with a considerable delay in swimbladder inflation. To determine
the moment of its first inflation, larvae placed in a hermetic chamber were observed under a
dissecting microscope. While lowering the pressure, the expanding swimbladder showed whether or
not its content is really gaseous. The reason postulated to be responsible for the delayed inflation is
that larvae lacking haemoglobin do not have the possibility of oxygen transport to their buoyancy
organ by means of the blood. Apart of this, capillarity force calculations and body force estimations
show that with decreasing size the constraints linked with surface tension increase overproportionally.
While in larger sized larvae like trout we could demonstrate inflation by swallowing air, in species with
small larvae this was not the case. Below a certain size, even in physostomians, the ductus pneumaticus
is no alternative to the blood pathway for swimbladder inflation
Pressure Effect and Specific Heat of RBa2Cu3Ox at Distinct Charge Carrier Concentrations: Possible Influence of Stripes
In YBa2Cu3Ox, distinct features are found in the pressure dependence of the
transition temperature, dTc/dp, and in DeltaCp*Tc, where DeltaCp is the jump in
the specific heat at Tc: dTc/dp becomes zero when DeltaCp*Tc is maximal,
whereas dTc/dp has a peak at lower oxygen contents where DeltaCp*Tc vanishes.
Substituting Nd for Y and doping with Ca leads to a shift of these specific
oxygen contents, since oxygen order and hole doping by Ca influences the hole
content nh in the CuO2 planes. Calculating nh from the parabolic Tc(nh)
behavior, the features coalesce for all samples at nh=0.11 and nh=0.175,
irrespective of substitution and doping. Hence, this behavior seems to reflect
an intrinsic property of the CuO2 planes. Analyzing our results we obtain
different mechanisms in three doping regions: Tc changes in the optimally doped
and overdoped region are mainly caused by charge transfer. In the slightly
underdoped region an increasing contribution to dTc/dp is obtained when well
ordered CuO chain fragments serve as pinning centers for stripes. This behavior
is supported by our results on Zn doped NdBa2Cu3Ox and is responsible for the
well known dTc/dp peak observed in YBa2Cu3Ox at x=6.7. Going to a hole content
below nh=0.11 our results point to a crossover from an underdoped
superconductor to a doped antiferromagnet, changing completely the physics of
these materials.Comment: 6 pages, 5 figures Proccedings of the 'Stripes 2000' Conference, Rome
(2000
Changing preservice teacher students' stereotypes and attitudes and reducing judgment biases concerning students of different family backgrounds: effects of a short intervention
Numerous empirical findings have shown biased judgments of (future) teachers depending on studentsâ ethnic and social background. Furthermore, research has indicated that (future) teachersâ stereotypes and attitudes differ depending on studentsâ backgrounds and appear to influence (future) teachersâ judgments. Based on theories of stereotype change, attitude change, and judgment formation, a short intervention was developed to change stereotypes and attitudes and to reduce judgment biases. In an experimental study (within- and between-subject design) with Nâ=â215 preservice teacher students, the effectiveness of the intervention on stereotype change, attitude change, and reduction of judgment distortions was tested. The results showed hypothesized effects of the intervention on stereotypes and attitudes towards students with an immigration background and students with low social status. Furthermore, the intervention showed effects on preservice teacher studentsâ judgments, especially for low-status students
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