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

Non-equilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar coupled spin-glass LiHo0.5_{0.5}Er0.5_{0.5}F4_{4}

We present a study of the model spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_4$ using simultaneous AC susceptibility, magnetization and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when the field is applied along the crystallographic c axis. Furthermore avalanche-like relaxation is observed in a static field after ramping from the zero-field-cooled state up to $200 - 300$ Oe. SANS measurements are employed to track the microscopic spin reconfiguration throughout both the hysteresis loop and the related relaxation. Comparing the SANS data to inhomogeneous mean-field calculations performed on a box of one million unit cells provides a real-space picture of the spin configuration. We discover that the avalanche is being driven by released Zeeman energy, which heats the sample and creates positive feedback, continuing the avalanche. The combination of SANS and mean-field simulations reveal that the conventional distribution of cluster sizes is replaced by one with a depletion of intermediate cluster sizes for much of the hysteresis loop.Comment: 6 pages, 4 figure

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

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

Supersymmetric NLO QCD Corrections to Resonant Slepton Production and Signals at the Tevatron and the LHC

We compute the total cross section and the transverse momentum distribution for single charged slepton and sneutrino production at hadronic colliders including NLO supersymmetric and non-supersymmetric QCD corrections. The supersymmetric QCD corrections can be substantial. We also resum the gluon transverse momentum distribution and compare our results with two Monte Carlo generators. We compute branching ratios of the supersymmetric decays of the slepton and determine event rates for the like-sign dimuon final state at the Tevatron and at the LHC.Comment: 14 pages, LaTeX, 8 figures, uses REVTex

Dependence of the BEC transition temperature on interaction strength: a perturbative analysis

We compute the critical temperature T_c of a weakly interacting uniform Bose gas in the canonical ensemble, extending the criterion of condensation provided by the counting statistics for the uniform ideal gas. Using ordinary perturbation theory, we find in first order $(T_c-T_c^0)/T_c^0 = -0.93 a\rho^{1/3}$, where T_c^0 is the transition temperature of the corresponding ideal Bose gas, a is the scattering length, and $\rho$ is the particle number density.Comment: 14 pages (RevTeX

Free-electron Model for Mesoscopic Force Fluctuations in Nanowires

When two metal electrodes are separated, a nanometer sized wire (nanowire) is formed just before the contact breaks. The electrical conduction measured during this retraction process shows signs of quantized conductance in units of G_0=2e^2/h. Recent experiments show that the force acting on the wire during separation fluctuates, which has been interpreted as being due to atomic rearrangements. In this report we use a simple free electron model, for two simple geometries, and show that the electronic contribution to the force fluctuations is comparable to the experimentally found values, about 2 nN.Comment: 4 pages, 3 figures, reference correcte