323 research outputs found
An Atom Faucet
We have constructed and modeled a simple and efficient source of slow atoms.
From a background vapour loaded magneto-optical trap, a thin laser beam
extracts a continuous jet of cold rubidium atoms. In this setup, the extraction
column that is typical to leaking MOT systems is created without any optical
parts placed inside the vacuum chamber. For detailed analysis, we present a
simple 3D numerical simulation of the atomic motion in the presence of multiple
saturating laser fields combined with an inhomogeneous magnetic field. At a
pressure of mbar, the moderate laser power of
10 mW per beam generates a jet of flux atoms/s with a
mean velocity of 14 m/s and a divergence of mrad.Comment: Submitted to EPJD. 1 TeX file (EPJ format), 7 picture
Vortex formation in a stirred Bose-Einstein condensate
Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb
confined in a magnetic trap and observe the formation of a vortex for a
stirring frequency exceeding a critical value. At larger rotation frequencies
we produce states of the condensate for which up to four vortices are
simultaneously present. We have also measured the lifetime of the single vortex
state after turning off the stirring laser beam.Comment: 4 pages, 3 figure
Mixture of ultracold lithium and cesium atoms in an optical dipole trap
We present the first simultaneous trapping of two different ultracold atomic
species in a conservative trap. Lithium and cesium atoms are stored in an
optical dipole trap formed by the focus of a CO laser. Techniques for
loading both species of atoms are discussed and observations of elastic and
inelastic collisions between the two species are presented. A model for
sympathetic cooling of two species with strongly different mass in the presence
of slow evaporation is developed. From the observed Cs-induced evaporation of
Li atoms we estimate a cross section for cold elastic Li-Cs collisions.Comment: 10 pages 9 figures, submitted to Appl. Phys. B; v2: Corrected
evaporation formulas and some postscript problem
Manipulating nonequilibrium magnetism through superconductors
Electrostatic control of the magnetization of a normal mesoscopic conductor
is analyzed in a hybrid superconductor-normal-superconductor system. This
effect stems from the interplay between the non-equilibrium condition in the
normal region and the Zeeman splitting of the quasiparticle density of states
of the superconductor subjected to a static in-plane magnetic field. Unexpected
spin-dependent effects such as magnetization suppression, diamagnetic-like
response of the susceptibility as well as spin-polarized current generation are
the most remarkable features presented. The impact of scattering events is
evaluated and let us show that this effect is compatible with realistic
material properties and fabrication techniques.Comment: 5 pages, 4 figure
Vortex lattices in a stirred Bose-Einstein condensate
We stir with a focused laser beam a Bose-Einstein condensate of Rb
atoms confined in a magnetic trap. We observe the formation of a single vortex
for a stirring frequency exceeding a critical value. At larger rotation
frequencies we produce states of the condensate for which up to eleven vortices
are simultaneously present. We present measurements of the decay of a vortex
array once the stirring laser beam is removed
Comment on "Experimental determination of superconducting parameters for the intermetallic perovskite superconductor MgCNi"
In a recent paper (Phys. Rev. {\bf B 67}, 094502 (2003)) Mao et al.
investigated the bias-dependent conductance of mechanical junctions between
superconducting MgCNi and a sharp W tip. They interpreted their results in
terms of 'single-particle tunneling'. We show it is more likely that current
transport through those junctions is determined by thermal effects due to the
huge normal-state resistivity of MgCNi. Therefore no conclusion can be
drawn about the possible unconventional pairing or strong-coupling
superconductivity in MgCNi.Comment: 2 pages, 1 Fig. Comment on Z. Q. Mao et al. (Phys. Rev. {\bf B 67},
094502 (2003)
Thermal expansion, heat capacity and magnetostriction of RAl (R = Tm, Yb, Lu) single crystals
We present thermal expansion and longitudinal magnetostriction data for cubic
RAl3 (R = Tm, Yb, Lu) single crystals. The thermal expansion coefficient for
YbAl3 is consistent with an intermediate valence of the Yb ion, whereas the
data for TmAl3 show crystal electric field contributions and have strong
magnetic field dependencies. de Haas-van Alphen-like oscillations were observed
in the magnetostriction data of YbAl3 and LuAl3, several new extreme orbits
were measured and their effective masses were estimated. Zero and 140 kOe
specific heat data taken on both LuAl3 and TmAl3 for T < 200 K allow for the
determination of a CEF splitting scheme for TmAl3
Infrared Laser Driven Double Proton Transfer. An Optimal Control Theory Study
Laser control of ultrafast double proton transfer is investigated for a
two-dimensional model system describing stepwise and concerted transfer
pathways. The pulse design has been done by employing optimal control theory in
combination with the multiconfiguration time-dependent Hartree wave packet
propagation. The obtained laser fields correspond to multiple pump-dump pulse
sequences. Special emphasis is paid to the relative importance of stepwise and
concerted transfer pathways for the driven wave packet and its dependence on
the parameters of the model Hamiltonian as well as on the propagation time.
While stepwise transfer is dominating in all cases considered, for high barrier
systems concerted transfer proceeding via tunneling can make a contribution.Comment: 9 figure
Valence Fluctuations Revealed by Magnetic Field Scan: Comparison with Experiments in YbXCu_4 (X=In, Ag, Cd) and CeYIn_5 (Y=Ir, Rh)
The mechanism of how critical end points of the first-order valence
transitions (FOVT) are controlled by a magnetic field is discussed. We
demonstrate that the critical temperature is suppressed to be a quantum
critical point (QCP) by a magnetic field. This results explain the field
dependence of the isostructural FOVT observed in Ce metal and YbInCu_4.
Magnetic field scan can lead to reenter in a critical valence fluctuation
region. Even in the intermediate-valence materials, the QCP is induced by
applying a magnetic field, at which the magnetic susceptibility also diverges.
The driving force of the field-induced QCP is shown to be a cooperative
phenomenon of the Zeeman effect and the Kondo effect, which creates a distinct
energy scale from the Kondo temperature. The key concept is that the closeness
to the QCP of the FOVT is capital in understanding Ce- and Yb-based heavy
fermions. It explains the peculiar magnetic and transport responses in CeYIn_5
(Y=Ir, Rh) and metamagnetic transition in YbXCu_4 for X=In as well as the sharp
contrast between X=Ag and Cd.Comment: 14 pages, 9 figures, OPEN SELECT in J. Phys. Soc. Jp
antiSMASH 3.0—a comprehensive resource for the genome mining of biosynthetic gene clusters
Microbial secondary metabolism constitutes a rich source of antibiotics, chemotherapeutics, insecticides and other high-value chemicals. Genome mining of gene clusters that encode the biosynthetic pathways for these metabolites has become a key methodology for novel compound discovery. In 2011, we introduced antiSMASH, a web server and stand-alone tool for the automatic genomic identification and analysis of biosynthetic gene clusters, available at http://antismash.secondarymetabolites.org. Here, we present version 3.0 of antiSMASH, which has undergone major improvements. A full integration of the recently published ClusterFinder algorithm now allows using this probabilistic algorithm to detect putative gene clusters of unknown types. Also, a new dereplication variant of the ClusterBlast module now identifies similarities of identified clusters to any of 1172 clusters with known end products. At the enzyme level, active sites of key biosynthetic enzymes are now pinpointed through a curated pattern-matching procedure and Enzyme Commission numbers are assigned to functionally classify all enzyme-coding genes. Additionally, chemical structure prediction has been improved by incorporating polyketide reduction states. Finally, in order for users to be able to organize and analyze multiple antiSMASH outputs in a private setting, a new XML output module allows offline editing of antiSMASH annotations within the Geneious software
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