2,347 research outputs found
Of NBOs and kHz QPOs: a low-frequency modulation in resonant oscillations of relativistic accretion disks
The origin of quasi periodic modulations of flux in the kilohertz range (kHz
QPOs), observed in low-mass X-ray binaries, is usually assumed to be physically
distinct from that of the ``normal branch oscillations'' (NBOs) in the
Z-sources. We show that a low-frequency modulation of the kHz QPOs is a natural
consequence of the non-linear relativistic resonance suggested previously to
explain the properties of the high-frequency twin peaks. The theoretical
results discussed here are reminiscent of the 6 Hz variations of frequency and
amplitude of the kHz QPOs reported by Yu, van der Klis and Jonker (2001).Comment: Accepted for publication in PASJ; 4 pages, 1 figur
Disorder-enhanced phase coherence in trapped bosons on optical lattices
The consequences of disorder on interacting bosons trapped in optical
lattices are investigated by quantum Monte Carlo simulations. At small to
moderate strengths of potential disorder a unique effect is observed: if there
is a Mott plateau at the center of the trap in the clean limit, phase coherence
{\it increases} as a result of disorder. The localization effects due to
correlation and disorder compete against each other, resulting in a partial
delocalization of the particles in the Mott region, which in turn leads to
increased phase coherence. In the absence of a Mott plateau, this effect is
absent. A detailed analysis of the uniform system without a trap shows that the
disordered states participate in a Bose glass phase.Comment: 4 pages, 4 figure
Collective Sideband Cooling in an Optical Ring Cavity
We propose a cavity based laser cooling and trapping scheme, providing tight
confinement and cooling to very low temperatures, without degradation at high
particle densities. A bidirectionally pumped ring cavity builds up a resonantly
enhanced optical standing wave which acts to confine polarizable particles in
deep potential wells. The particle localization yields a coupling of the
degenerate travelling wave modes via coherent photon redistribution. This
induces a splitting of the cavity resonances with a high frequency component,
that is tuned to the anti-Stokes Raman sideband of the particles oscillating in
the potential wells, yielding cooling due to excess anti-Stokes scattering.
Tight confinement in the optical lattice together with the prediction, that
more than 50% of the trapped particles can be cooled into the motional ground
state, promise high phase space densities.Comment: 4 pages, 1 figur
Scaling properties of cavity-enhanced atom cooling
We extend an earlier semiclassical model to describe the dissipative motion
of N atoms coupled to M modes inside a coherently driven high-finesse cavity.
The description includes momentum diffusion via spontaneous emission and cavity
decay. Simple analytical formulas for the steady-state temperature and the
cooling time for a single atom are derived and show surprisingly good agreement
with direct stochastic simulations of the semiclassical equations for N atoms
with properly scaled parameters. A thorough comparison with standard free-space
Doppler cooling is performed and yields a lower temperature and a cooling time
enhancement by a factor of M times the square of the ratio of the atom-field
coupling constant to the cavity decay rate. Finally it is shown that laser
cooling with negligible spontaneous emission should indeed be possible,
especially for relatively light particles in a strongly coupled field
configuration.Comment: 7 pages, 5 figure
Uber Terpene. LXXXIV.* Ober die Struktur des Arctiopikrin - des Sesquiterpenlactons aus Arctium minus B e r n h.
Es wurde die Struktur des friiher beschriebenen Lactons aus Arctium minus B er n h. studiert und bewiesen, dass dieser Stoff, welchem die Autoren die Bezeichnung Arctiopikrin gaben, die sumare Formel C19H28O6 hat. Weiter stellten sie fest, dass Arctiopikrin der Ester- der B-Hydroxyisobuttersaure und des monocyklischen Dihydroxylactons C15H22O4 (Arctiolid) ist, der einen zehngliedrigen Kohlenstoffcyklus mit zwei Doppelbindungen enthalt. Fiir Arctiopikrin wurden zwei alternative Formeln I oder II vorgeschlagen
Trapping and cooling single atoms with far-off resonance intracavity doughnut modes
We investigate cooling and trapping of single atoms inside an optical cavity
using a quasi-resonant field and a far-off resonant mode of the Laguerre-Gauss
type. The far-off resonant doughnut mode provides an efficient trapping in the
case when it shifts the atomic internal ground and excited state in the same
way, which is particularly useful for quantum information applications of
cavity quantum electrodynamics (QED) systems. Long trapping times can be
achieved, as shown by full 3-D simulations of the quasi-classical motion inside
the resonator.Comment: 18 pages, 18 figures, RevTe
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Thorium Energy Futures
The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options – liquid or solid, with or without an accelerator – can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice
A Pinned Polymer Model of Posture Control
A phenomenological model of human posture control is posited. The dynamics
are modelled as an elastically pinned polymer under the influence of noise. The
model accurately reproduces the two-point correlation functions of experimental
posture data and makes predictions for the response function of the postural
control system. The physiological and clinical significance of the model is
discussed.Comment: uuencoded post script file, 17 pages with 3 figure
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New York City Energy-Water Integrated Planning: A Pilot Study
The New York City Energy-Water Integrated Planning Pilot Study is one of several projects funded by Sandia National Laboratories under the U.S. Department of Energy Energy-Water Nexus Program. These projects are intended to clarify some key issues and research needs identified during the Energy-Water Nexus Roadmapping activities. The objectives of the New York City Pilot Project are twofold: to identify energy-water nexus issues in an established urban area in conjunction with a group of key stakeholders and to define and apply an integrated energy and water decision support tool, as proof-of-concept, to one or more of these issues. During the course of this study, the Brookhaven National Laboratory project team worked very closely with members of a Pilot Project Steering Committee. The Steering Committee members brought a breadth of experience across the energy, water and climate disciplines, and all are well versed in the particular issues faced by an urban environment, and by New York City in particular. The first task was to identify energy-water issues of importance to New York City. This exercise was followed by discussion of the qualities and capabilities that an ideal decision support tool should display to address these issues. The decision was made to start with an existing energy model, the New York City version of the MARKAL model, developed originally at BNL and now used globally by many groups for energy analysis. MARKAL has the virtue of being well-vetted, transparent, and capable of calculating 'material' flows, such as water use by the energy system and energy requirements of water technology. The Steering Committee members defined five scenarios of interest, representing a broad spectrum of New York City energy-water issues. Brookhaven National Laboratory researchers developed a model framework (Water-MARKAL) at the desired level of detail to address the scenarios, and then attempted to gather the New York City-specific information required to analyze the scenarios using Water-MARKAL. This report describes the successes and challenges of defining and demonstrating the decision tool, Water-MARKAL. The issues that the stakeholders perceive for New York City are listed and the difficulties in gathering required information for Water-MARKAL to analyze these issues at the desired level of detail are described
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