330 research outputs found
Ultrasound attenuation and a P-B-T phase diagram of superfluid 3He in 98% aerogel
Longitudinal sound attenuation measurements in superfluid 3He in 98% aerogel
were conducted at pressures between 14 and 33 bar and in magnetic fields up to
4.44 kG. The temperature dependence of the ultrasound attenuation in the A-like
phase was determined for the entire superfluid region exploiting the field
induced meta-stable A-like phase at the highest field. In the lower field, the
A-B transition in aerogel was identified by a smooth jump in attenuation on
both cooling and warming. Based on the transitions observed on warming, a phase
diagram as a function of pressure (P), temperature (T) and magnetic field (B)
is constructed. We find that the A-B phase boundary in aerogel recedes in a
drastically different manner than in bulk in response to an increasing magnetic
field. The implications of the observed phase diagram are discussed.Comment: 9 pages, 13 figures, accepted to PR
Atomic Bose Gas with Negative Scattering Length
We derive the equation of state of a dilute atomic Bose gas with an
interatomic interaction that has a negative scattering length and argue that
two continuous phase transitions, occuring in the gas due to quantum degeneracy
effects, are preempted by a first-order gas-liquid or gas-solid transition
depending on the details of the interaction potential. We also discuss the
consequences of this result for future experiments with magnetically trapped
spin-polarized atomic gasses such as lithium and cesium.Comment: 16 PAGES, REVTEX 3.0, ACCEPTED FOR PUBLICATION IN PHYS. REV.
Excitation-assisted inelastic processes in trapped Bose-Einstein condensates
We find that inelastic collisional processes in Bose-Einstein condensates
induce local variations of the mean-field interparticle interaction and are
accompanied by the creation/annihilation of elementary excitation. The physical
picture is demonstrated for the case of three body recombination in a trapped
condensate. For a high trap barrier the production of high energy trapped
single particle excitations results in a strong increase of the loss rate of
atoms from the condensate.Comment: 4 pages, no figure
Policy Brief: UNSCR 1325: The Challenges of Framing Women’s Rights as a Security Matter
While UN Security Council Resolution (UNSCR) 1325 has certainly increased awareness among international actors about women’s and gender issues in armed conflict, opened new spaces for dialogue and partnerships from global to local levels, and even created opportunities for new resources for women’s rights, successes remain limited and notably inconsistent. To understand some of these shortcomings and think creatively about how to move the women, peace and security agenda forward, it is essential to understand the conceptual assumptions underscoring UNSCR 1325
Exciting, Cooling And Vortex Trapping In A Bose-Condensed Gas
A straight forward numerical technique, based on the Gross-Pitaevskii
equation, is used to generate a self-consistent description of
thermally-excited states of a dilute boson gas. The process of evaporative
cooling is then modelled by following the time evolution of the system using
the same equation. It is shown that the subsequent rethermalisation of the
thermally-excited state produces a cooler coherent condensate. Other results
presented show that trapping vortex states with the ground state may be
possible in a two-dimensional experimental environment.Comment: 9 pages, 7 figures. It's worth the wait! To be published in Physical
Review A, 1st February 199
Fabrication of fluorescent nanoparticles of dendronized perylenediimide by laser ablation in water
Highly fluorescent organic nanoparticles with size of about 300 nm were prepared by nanosecond laser ablation of micrometer-sized powder of dendronized perylenediimide dispersed in water. The nanoparticle colloidal solution provided a fluorescence quantum yield of 0.58. The absorption and emission spectral studies demonstrated that the bulky dendron groups at the side bays of perylenediimide chromophore efficiently suppress the interchromophoric interactions in the nanoparticles. Fluorescence measurement on several single nanoparticles underlines that the prepared nanoparticles are bright and photo-stable enough to be a useful probe for single particle fluorescence investigation.</p
Control over phase separation and nucleation using a laser-tweezing potential
Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter
Dense Antihydrogen: Its Production and Storage to Envision Antimatter Propulsion
We discuss the possibility that dense antihydrogen could provide a path
towards a mechanism for a deep space propulsion system. We concentrate at
first, as an example, on Bose-Einstein Condensate (BEC) antihydrogen. In a
Bose-Einstein Condensate, matter (or antimatter) is in a coherent state
analogous to photons in a laser beam, and individual atoms lose their
independent identity. This allows many atoms to be stored in a small volume. In
the context of recent advances in producing and controlling BECs, as well as in
making antihydrogen, this could potentially provide a revolutionary path
towards the efficient storage of large quantities of antimatter, perhaps
eventually as a cluster or solid.Comment: 12 pages, 3 figure
High frequency sound in superfluid 3He-B
We present measurements of the absolute phase velocity of transverse and
longitudinal sound in superfluid 3He-B at low temperature, extending from the
imaginary squashing mode to near pair-breaking. Changes in the transverse phase
velocity near pair-breaking have been explained in terms of an order parameter
collective mode that arises from f-wave pairing interactions, the so-called
J=4- mode. Using these measurements, we establish lower bounds on the energy
gap in the B-phase. Measurement of attenuation of longitudinal sound at low
temperature and energies far above the pair-breaking threshold, are in
agreement with the lower bounds set on pair-breaking. Finally, we discuss our
estimations for the strength of the f-wave pairing interactions and the Fermi
liquid parameter, F4s.Comment: 15 pages, 8 figures, accepted to J. Low Temp. Phy
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