5,406 research outputs found
A quasi-pure Bose-Einstein condensate immersed in a Fermi sea
We report the observation of co-existing Bose-Einstein condensate and Fermi
gas in a magnetic trap. With a very small fraction of thermal atoms, the 7Li
condensate is quasi-pure and in thermal contact with a 6Li Fermi gas. The
lowest common temperature is 0.28 muK = 0.2(1) T_C = 0.2(1) T_F where T_C is
the BEC critical temperature and T_F the Fermi temperature. Behaving as an
ideal gas in the radial trap dimension, the condensate is one-dimensional.Comment: 4 pages, 5 figure
Measurements and Simulation Studies of Piezoceramics for Acoustic Particle Detection
Calibration sources are an indispensable tool for all detectors. In acoustic
particle detection the goal of a calibration source is to mimic neutrino
signatures as expected from hadronic cascades. A simple and promising method
for the emulation of neutrino signals are piezo ceramics. We will present
results of measruements and simulations on these piezo ceramics.Comment: 5 pages, 5 figure
Collective Oscillations of an Imbalanced Fermi Gas: Axial Compression Modes and Polaron Effective Mass
We investigate the low-lying compression modes of a unitary Fermi gas with
imbalanced spin populations. For low polarization, the strong coupling between
the two spin components leads to a hydrodynamic behavior of the cloud. For
large population imbalance we observe a decoupling of the oscillations of the
two spin components, giving access to the effective mass of the Fermi polaron,
a quasi-particle composed of an impurity dressed by particle-hole pair
excitations in a surrounding Fermi sea. We find , in agreement
with the most recent theoretical predictions.Comment: 4 pages, 4 figures, submitted to PR
Multi-component gap solitons in spinor Bose-Einstein condensates
We model the nonlinear behaviour of spin-1 Bose-Einstein condensates (BECs)
with repulsive spin-independent interactions and either ferromagnetic or
anti-ferromagnetic (polar) spin-dependent interactions, loaded into a
one-dimensional optical lattice potential. We show that both types of BECs
exhibit dynamical instabilities and may form spatially localized
multi-component structures. The localized states of the spinor matter waves
take the form of vector gap solitons and self-trapped waves that exist only
within gaps of the linear Bloch-wave band-gap spectrum. Of special interest are
the nonlinear localized states that do not exhibit a common spatial density
profile shared by all condensate components, and consequently cannot be
described by the single mode approximation (SMA), frequently employed within
the framework of the mean-field treatment. We show that the non-SMA states can
exhibits Josephson-like internal oscillations and self-magnetisation, i.e.
intrinsic precession of the local spin. Finally, we demonstrate that
non-stationary states of a spinor BEC in a lattice exhibit coherent undamped
spin-mixing dynamics, and that their controlled conversion into a stationary
state can be achieved by the application of an external magnetic field.Comment: 12 pages, 13 figure
Konfliktmanagement durch ECOWAS und SADC – die Rolle Nigerias und Südafrikas in subregionalen Interventionen:ein Beitrag zum Frieden?
Die Arbeit widmet sich der Fragestellung, inwieweit die Southern African Development Community (SADC) und Südafrika sowie die Economic Community of West African States (ECOWAS) und Nigeria einen Beitrag zum Frieden in regionalen Konflikten leisten. Die Analyse zeigt, dass subregionale Organisationen auf dem Kontinent an Bedeutung gewonnen haben. Insbesondere ECOWAS fungiert für Afrika inzwischen als ein Modell einer eigenständig praktizierten Konfliktregulierung. Trotz dieser positiven Erfahrungen tragen die subregionalen Akteure allerdings nicht ausreichend zum Frieden bei. Zum einen fehlt der politische Wille, auch in der Sicherheitspolitik Kompetenzen an überstaatliche Instanzen abzugeben. Zum anderen fehlen Ressourcen. Daher definiert sich Kooperation in strukturschwachen Regionen stark über Schlüsselstaaten wie Nigeria und Südafrika, die meist größere Truppenkontingente zur Verfügung stellen. Zugleich löst ihre Dominanz intra-regionale Spannungen aus und behindert Kooperation. This book examines to what degree the Southern African Development
Community (SADC) and South Africa as well as the Economic Community of
West African States (ECOWAS) and Nigeria contribute to peace in
regional conflicts. The analysis shows that sub-regional organisations
play an important role on the continent. Particularly, ECOWAS seems to
be a model for an Africa-based conflict-resolution. Nevertheless,
neither organisation restores or keeps peace successfully. On the one
hand, their members lack political will to hand over competences to
supra-national bodies. On the other hand, resource constraints hinder
the implementation of an effective peacekeeping. This is the reason why
cooperation between states in economically and politically weak regions
depends on key states like Nigeria or South Africa. They provide the
interventions with significant contingents of troops. However, these
states often act in a dominant way that causes intra-regional tensions
and weakens cooperation
A smoothing monotonic convergent optimal control algorithm for NMR pulse sequence design
The past decade has demonstrated increasing interests in using optimal
control based methods within coherent quantum controllable systems. The
versatility of such methods has been demonstrated with particular elegance
within nuclear magnetic resonance (NMR) where natural separation between
coherent and dissipative spin dynamics processes has enabled coherent quantum
control over long periods of time to shape the experiment to almost ideal
adoption to the spin system and external manipulations. This has led to new
design principles as well as powerful new experimental methods within magnetic
resonance imaging, liquid-state and solid-state NMR spectroscopy. For this
development to continue and expand, it is crucially important to constantly
improve the underlying numerical algorithms to provide numerical solutions
which are optimally compatible with implementation on current instrumentation
and at same time are numerically stable and offer fast monotonic convergence
towards the target. Addressing such aims, we here present a smoothing
monotonically convergent algorithm for pulse sequence design in magnetic
resonance which with improved optimization stability lead to smooth pulse
sequence easier to implement experimentally and potentially understand within
the analytical framework of modern NMR spectroscopy
Expansion of a lithium gas in the BEC-BCS crossover
We report on experiments in Li Fermi gases near Feshbach resonances. A
broad s-wave resonance is used to form a Bose-Einstein condensate of weakly
bound Li molecules in a crossed optical trap. The measured
molecule-molecule scattering length of nm at 770 G is found
in good agreement with theory. The expansion energy of the cloud in the BEC-BCS
crossover region is measured. Finally we discuss the properties of p-wave
Feshbach resonances observed near 200 Gauss and new s-wave resonances in the
heteronuclear Li- Li mixture.Comment: 10 pages, 3 figures, Proceedings of ICAP 200
Preferences for health outcomes associated with Group A Streptococcal disease and vaccination
<p>Abstract</p> <p>Background</p> <p>A 26-valent Group A Streptococcus (GAS) vaccine candidate has been developed that may provide protection against pharyngitis, invasive disease and rheumatic fever. However, recommendations for the use of a new vaccine must be informed by a range of considerations, including parents' preferences for different relevant health outcomes. Our objectives were to: (1) describe parent preferences for GAS disease and vaccination using willingness-to-pay (WTP) and time trade-off (TTO) methods; and (2) understand how parents' implied WTP for a quality-adjusted life year (QALY) gained might vary depending on the particular health outcome considered (e.g. averted GAS disease vs. vaccine adverse events).</p> <p>Methods</p> <p>Telephone interviews were conducted with parents of children diagnosed with GAS pharyngitis at 2 pediatric practice sites in the Boston metropolitan area. WTP and TTO (trading parental longevity for child's health) questions for 2 vaccine and 4 disease-associated health states were asked using a randomly selected opening bid, followed by a 2<sup>nd </sup>bid and a final open-ended question about the amount willing to pay or trade. Descriptive analyses included medians and interquartile ranges for WTP and TTO estimates. The Wilcoxon signed-rank test was used to assess differences in WTP/QALY values for vaccine adverse events vs. disease states.</p> <p>Results</p> <p>Of 119 respondents, 100 (84%) and 96 (81%) provided a complete set of responses for WTP and TTO questions, respectively. The median WTP and discounted (at 3% per year) TTO values to avoid each health state were as follows: local reaction, 50, 0.22 days; impetigo, 75, 2.5 days; septic arthritis, 3,000, 31.0 days. The median WTP/QALY was significantly higher for vaccine adverse events (~18,000 to $36,000/QALY).</p> <p>Conclusions</p> <p>Parents strongly prefer to prevent GAS disease in children compared to vaccine adverse events. However, implied WTP/QALY ratios were higher for the prevention of vaccine adverse events. Regret for errors of commission vs. omission may differ and should be considered by vaccine policymakers.</p
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