3,304 research outputs found
Hysteresis effects in rotating Bose-Einstein condensates
We study the formation of vortices in a dilute Bose-Einstein condensate
confined in a rotating anisotropic trap. We find that the number of vortices
and angular momentum attained by the condensate depends upon the rotation
history of the trap and on the number of vortices present in the condensate
initially. A simplified model based on hydrodynamic equations is developed, and
used to explain this effect in terms of a shift in the resonance frequency of
the quadrupole mode of the condensate in the presence of a vortex lattice.
Differences between the spin-up and spin-down response of the condensate are
found, demonstrating hysteresis phenomena in this system.Comment: 16 pages, 7 figures; revised after referees' report
Spatially Resolved Magnetization in the Bose-Einstein Condensed State of BaCuSi2O6: Evidence for Imperfect Frustration
In order to understand the nature of the two-dimensional Bose-Einstein
condensed (BEC) phase in BaCuSi2O6, we performed detailed 63Cu and 29Si NMR
above the critical magnetic field, Hc1= 23.4 T. The two different alternating
layers present in the system have very different local magnetizations close to
Hc1; one is very weak, and its size and field dependence are highly sensitive
to the nature of inter-layer coupling. Its precise value could only be
determined by "on-site" 63Cu NMR, and the data are fully reproduced by a model
of interacting hard-core bosons in which the perfect frustration associated to
tetragonal symmetry is slightly lifted, leading to the conclusion that the
population of the less populated layers is not fully incoherent but must be
partially condensed
Production of J/psi Mesons at HERA
Inelastic and diffractive production of J/psi mesons at HERA is reviewed. The
data on inelastic photoproduction are described well within errors by the
Colour Singlet Model in next-to-leading order. A search for colour octet
processes predicted within the NRQCD/factorisation approach is conducted in
many regions of phase space. No unambiguous evidence has been found to date.
Diffractive elastic production of J/psi mesons has been measured in the limit
of photoproduction up to the highest photon proton center of mass energies. The
increase of the cross section is described by pQCD models. At larger Q^2, the W
dependence is found to be similar to that observed in photoproduction. First
analyses of data at high t yield a powerlike dependence on |t|. A LO BFKL
calculation gives a good description of the data.Comment: 14 pages, 12 figures, contribution to Ringberg 200
INVESTIGATION ON THE CERVICAL SPINE MOTION
Several investigations on the problem of cervical spine motion describe the difficulties of measuring the movement exactly. Those models had to deal with the difficulties in fixation of the human head and to track the range of motion in degrees with respect to the three directions of movement; flexionlextension, lateral bending and rotation. The only objective method of measuring cervical spine movement and COlC1 or C11C2 displacements is the functional computer tomogram as described by Dvorak et al. The aim of our survey has been to identify differences between the "normaln and pathologic cervical spine (after whip leash injuries, disc diseases or spondylarthrosis in sport) as it relates to the range of movement and angular velocity. Two groups of 15 probants have been tested by a new computer-controlled setup. By using a three-dimensional motion-analysis-system special rigid-body software has been developed to calculate the cervical spine motion in all three coordinate directions. This represents the first time that it has been possible to obtain results about the movement and their time-derivations. These angles and the angular velocities were traced for 15 normal individuals and for 15 persons suffering with cervical spine problems. The setup for testing patients was no more than a small frame like sunglasses which gave exact information about the movement in space. This information gave accurate data which permitted calculation of the amount of motion concerning the patient's personal orientation in space and was additionally used to compute the coupled motions to the probants reference coordinate system. The present investigation demonstrated significant differences in the range of motion between normal individuals and patients with cervical spine problems in all defined direction. Our first conclusion so far is, that there are possibilities to measure those differences in cervical spine motion by the presented biomechanical measurement setup very easily. Furthermore, the setup is capable of providing accurate results about the range of motion, coupled motion and their time-derivations rapidly without the use of x-ray technology and x-ray exposition for the patient. These possibility and the good results are very important to judge problems after "ship leash injuries" and other cervical spine diseases in sport. The positive results raise the possibility that the technique may be employed to judge problems and other cervical spine injuries associated with sport. We conclude that the biomechanical measurement-setup presented here provides an easy method to measure differences in cervical spine motion
TMDlib and TMDplotter: library and plotting tools for transverse-momentum-dependent parton distributions
Transverse-momentum-dependent distributions (TMDs) are central in high-energy
physics from both theoretical and phenomenological points of view. In this
manual we introduce the library, TMDlib, of fits and parameterisations for
transverse-momentum-dependent parton distribution functions (TMD PDFs) and
fragmentation functions (TMD FFs) together with an online plotting tool,
TMDplotter. We provide a description of the program components and of the
different physical frameworks the user can access via the available
parameterisations.Comment: version 2, referring to TMDlib 1.0.2 - comments and references adde
Incipient charge order observed by NMR in the normal state of YBa2Cu3Oy
The pseudogap regime of high-temperature cuprates harbours diverse
manifestations of electronic ordering whose exact nature and universality
remain debated. Here, we show that the short-ranged charge order recently
reported in the normal state of YBa2Cu3Oy corresponds to a truly static
modulation of the charge density. We also show that this modulation impacts on
most electronic properties, that it appears jointly with intra-unit-cell
nematic, but not magnetic, order, and that it exhibits differences with the
charge density wave observed at lower temperatures in high magnetic fields.
These observations prove mostly universal, they place new constraints on the
origin of the charge density wave and they reveal that the charge modulation is
pinned by native defects. Similarities with results in layered metals such as
NbSe2, in which defects nucleate halos of incipient charge density wave at
temperatures above the ordering transition, raise the possibility that
order-parameter fluctuations, but no static order, would be observed in the
normal state of most cuprates if disorder were absent.Comment: Updated version. Free download at Nature Comm. website (doi below
Spin susceptibility of charge ordered YBa2Cu3Oy across the upper critical field
The value of the upper critical field Hc2, a fundamental characteristic of
the superconducting state, has been subject to strong controversy in high-Tc
copper-oxides. Since the issue has been tackled almost exclusively by
macroscopic techniques so far, there is a clear need for local-probe
measurements. Here, we use 17O NMR to measure the spin susceptibility
of the CuO2 planes at low temperature in charge ordered
YBa2Cu3Oy. We find that increases (most likely linearly) with
magnetic field H and saturates above field values ranging from 20 to 40 T. This
result is consistent with Hc2 values claimed by G. Grissonnanche et al. [Nat.
Commun. 5, 3280 (2014)] and with the interpretation that the
charge-density-wave (CDW) reduces Hc2 in underdoped YBa2Cu3Oy. Furthermore, the
absence of marked deviation in at the onset of long-range CDW
order indicates that this Hc2 reduction and the Fermi-surface reconstruction
are primarily rooted in the short-range CDW order already present in zero
field, not in the field-induced long-range CDWorder. Above Hc2, the relatively
low values of at T=2 K show that the pseudogap is a ground-state
property, independent of the superconducting gap.Comment: To appea
The Structure of the Vortex Liquid at the Surface of a Layered Superconductor
A density-functional approach is used to calculate the inhomogeneous vortex
density distribution in the flux liquid phase at the planar surface of a
layered superconductor, where the external magnetic field is perpendicular to
the superconducting layers and parallel to the surface. The interactions with
image vortices are treated within a mean field approximation as a functional of
the vortex density. Near the freezing transition strong vortex density
fluctuations are found to persist far into the bulk liquid. We also calculate
the height of the Bean-Livingston surface barrier.Comment: 8 pages, RevTeX, 2 figure
Quantum transport and momentum conserving dephasing
We study numerically the influence of momentum-conserving dephasing on the
transport in a disordered chain of scatterers. Loss of phase memory is caused
by coupling the transport channels to dephasing reservoirs. In contrast to
previously used models, the dephasing reservoirs are linked to the transport
channels between the scatterers, and momentum conserving dephasing can be
investigated. Our setup provides a model for nanosystems exhibiting conductance
quantization at higher temperatures in spite of the presence of phononic
interaction. We are able to confirm numerically some theoretical predictions.Comment: 7 pages, 4 figure
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