Suppression of hidden order in URu2Si2 under pressure and restoration in magnetic field

We describe here recent inelastic neutron scattering experiments on the heavy fermion compound URu2Si2 realized in order to clarify the nature of the hidden order (HO) phase which occurs below T_0 = 17.5 K at ambient pressure. The choice was to measure at a given pressure P where the system will go, by lowering the temperature, successively from paramagnetic (PM) to HO and then to antiferromagnetic phase (AF). Furthermore, in order to verify the selection of the pressure, a macroscopic detection of the phase transitions was also achieved in situ via its thermal expansion response detected by a strain gauge glued on the crystal. Just above P_x = 0.5 GPa, where the ground state switches from HO to AF, the Q_0 = (1, 0, 0) excitation disappears while the excitation at the incommensurate wavevector Q_1 = (1.4, 0, 0) remains. Thus, the Q_0 = (1, 0, 0) excitation is intrinsic only in the HO phase. This result is reinforced by studies where now pressure and magnetic field $H$ can be used as tuning variable. Above P_x, the AF phase at low temperature is destroyed by a magnetic field larger than H_AF (collapse of the AF Q_0 = (1, 0, 0) Bragg reflection). The field reentrance of the HO phase is demonstrated by the reappearance of its characteristic Q_0 = (1, 0, 0) excitation. The recovery of a PM phase will only be achieved far above H_AF at H_M approx 35 T. To determine the P-H-T phase diagram of URu2Si2, macroscopic measurements of the thermal expansion were realized with a strain gauge. The reentrant magnetic field increases strongly with pressure. Finally, to investigate the interplay between superconductivity (SC) and spin dynamics, new inelastic neutron scattering experiments are reported down to 0.4 K, far below the superconducting critical temperature T_SC approx 1.3 K as measured on our crystal by diamagnetic shielding.Comment: 5 pages, 7 figures, ICN 2009 conference proceeding

Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry

Modulated electroreflectance spectroscopy $\Delta R/R$ of semiconductor self-assembled quantum dots is investigated. The structure is modeled as dots with lens shape geometry and circular cross section. A microscopic description of the electroreflectance spectrum and optical response in terms of an external electric field (${\bf F}$) and lens geometry have been considered. The field and lens symmetry dependence of all experimental parameters involved in the $\Delta R/R$ spectrum have been considered. Using the effective mass formalism the energies and the electronic states as a function of ${\bf F}$ and dot parameters are calculated. Also, in the framework of the strongly confined regime general expressions for the excitonic binding energies are reported. Optical selection rules are derived in the cases of the light wave vector perpendicular and parallel to $$. Detailed calculation of the Seraphin coefficients and electroreflectance spectrum are performed for the InAs and CdSe nanostructures. Calculations show good agreement with measurements recently performed on CdSe/ZnSe when statistical distribution on size is considered, explaining the main observed characteristic in the electroreflectance spectra

Interactions of vortices with rarefaction solitary waves in a Bose-Einstein condensate and their role in the decay of superfluid turbulence

There are several ways to create the vorticity-free solitary waves -- rarefaction pulses -- in condensates: by the process of strongly nonequilibrium condensate formation in a weakly interacting Bose gas, by creating local depletion of the condensate density by a laser beam, and by moving a small object with supercritical velocities. Perturbations created by such waves colliding with vortices are studied in the context of the Gross-Pitaevskii model. We find that the effect of the interactions consists of two competing mechanisms: the creation of vortex line as rarefaction waves acquire circulation in a vicinity of a vortex core and the loss of the vortex line to sound due to Kelvin waves that are generated on vortex lines by rarefaction pulses. When a vortex ring collides with a rarefaction wave, the ring either stabilises to a smaller ring after emitting sound through Kelvin wave radiation or the entire energy of the vortex ring is lost to sound if the radius of the ring is of the order of the healing length. We show that during the time evolution of a tangle of vortices, the interactions with rarefaction pulses provide an important dissipation mechanism enhancing the decay of superfluid turbulence.Comment: Revised paper accepted by Phys. Rev.

Tunable coupling to a mechanical oscillator circuit using a coherent feedback network

We demonstrate a fully cryogenic microwave feedback network composed of modular superconducting devices connected by transmission lines and designed to control a mechanical oscillator coupled to one of the devices. The network features an electromechanical device and a tunable controller that coherently receives, processes and feeds back continuous microwave signals that modify the dynamics and readout of the mechanical state. While previous electromechanical systems represent some compromise between efficient control and efficient readout of the mechanical state, as set by the electromagnetic decay rate, the tunable controller produces a closed-loop network that can be dynamically and continuously tuned between both extremes much faster than the mechanical response time. We demonstrate that the microwave decay rate may be modulated by at least a factor of 10 at a rate greater than $10^4$ times the mechanical response rate. The system is easy to build and suggests that some useful functions may arise most naturally at the network-level of modular, quantum electromagnetic devices.Comment: 11 pages, 6 figures, final published versio

Estsitalopraami efektiivsus depressiooni ravis võrrelduna konventsionaalsete selektiivsete serotoniini tagasihaarde inhibiitorite ja venlafaksiin XRiga: metaanalüüs

Estsitalopraam on kõige selektiivsem selektiivsete serotoniini tagasihaarde inhibiitorite rühma kuuluv antidepressant. Varasemad uuringud on näidanud, et estsitalopraam on oma toimelt tõhusam kui tsitalopraam. Artiklis on antud ülevaade metaanalüüsi uuringutest, milles estsitalopraami võrreldi teiste antidepressantidega (tsitalopraam, fluoksetiin, paroksetiin, sertraliin ja venlafaksiin XR). Estsitalopraam oli efektiivsem kui kõik teised võrdlusravimid nii üldise raviefekti, ravile reageerimise määra kui ka remissiooni saavutamise määra poolest. Eri ravimirühmade analüüs näitas, et estsitalopraam oli oluliselt tõhusam kui konventsionaalsed SSRId ja võrdväärne venlafaksiiniga, ehkki uuringu üldised tulemused ei näita tingimata, et estsitalopraam oleks oluliselt efektiivsem kui iga SSRI eraldi. Sarnased tulemused leiti ka raske depressiooniga patsientide seas. Eesti Arst 2006; 85 (11): 739–75

Oscillating Neutrinos from the Galactic Center

It has recently been demonstrated that the $\gamma$-ray emission spectrum of the EGRET-identified, central Galactic source 2EG J1746-2852 can be well fitted by positing that these photons are generated by the decay of $\pi^0$'s produced in p-p scattering at or near an energizing shock. Such scattering also produces charged pions which decay leptonically.The ratio of $\gamma$-rays to neutrinos generated by the central Galactic source may be accurately determined and a well-defined and potentially-measurable high energy neutrino flux at Earth is unavoidable. An opportunity, therefore, to detect neutrino oscillations over an unprecedented scale is offered by this source. In this paper we assess the prospects for such an observation with the generation of neutrino \v{C}erenkov telescopes now in the planning stage. We determine that the next generation of detectors may find an oscillation signature in the Galactic Center (GC) signal.Comment: 45 pages, LaTeX, uses ApJ style, some minor revisions, this final version to be published in ApJ

Is there an intramolecular hydrogen bond in 2-halophenols? A theoretical and spectroscopic investigation

The Abraham solute hydrogen bond acidity parameter A can be derived both from physical methods, A(Gen) and NMR experiments, A(NMR) and results for a large number of hydroxylic solutes show that the two methods agreed very well. However for halophenols the values of A(NMR) were not consistent with the A(Gen) values. The values of A(NMR) suggest that there is no intra-molecular hydrogen bonding in any of the 2-halophenols. In contrast the values of A(Gen) indicate that there is no intra-molecular hydrogen bonding in 2-fluorophenol, but weak intra-molecular hydrogen bonding in 2-chloro, 2-bromo, and 2-iodo-phenol. In view of this uncertainty in the presence or absence of intra-molecular H-bonds in the 2-halophenols, a detailed investigation of the methods used in the literature is presented together with a novel NMR method to determine the ratio of cis and trans forms in these compounds. The experimental data is complemented by a detailed theoretical analysis of the structures and bonding in these molecules to assess the presence or absence of an intra-molecular H-bond. We conclude that there is weak hydrogen bonding in 2-chloro, 2-bromo and 2-iodophenol but very little in 2-fluorophenol.The Abraham solute hydrogen bond acidity parameter Acan be derived both from physical methods,A(Gen) and NMR experiments,A(NMR) and results for a large number of hydroxylic solutes show that the two methods agreed very well. However for halophenols the va17251512515