1,343 research outputs found
Cryogenic thermal control technology summaries
A summarization and categorization is presented of the pertinent literature associated with cryogenic thermal control technology having potential application to in-orbit fluid transfer systems and/or associated space storage. Initially, a literature search was conducted to obtain pertinent documents for review. Reports determined to be of primary significance were summarized in detail. Each summary, where applicable, consists of; (1) report identification, (2) objective(s) of the work, (3) description of pertinent work performed, (4)major results, and (5) comments of the reviewer (GD/C). Specific areas covered are; (1) multilayer insulation of storage tanks with and without vacuum jacketing, (2) other insulation such as foams, shadow shields, microspheres, honeycomb, vent cooling and composites, (3) vacuum jacketed and composite fluid lines, and (4) low conductive tank supports and insulation penetrations. Reports which were reviewed and not summarized, along with reasons for not summarizing, are also listed
Capturing Velocity Gradients and Particle Rotation Rates in Turbulence
Turbulent fluid flows exhibit a complex small-scale structure with frequently
occurring extreme velocity gradients. Particles probing such swirling and
straining regions respond with an intricate shape-dependent orientational
dynamics, which sensitively depends on the particle history. Here, we
systematically develop a reduced-order model for the small-scale dynamics of
turbulence, which captures the velocity gradient statistics along particle
paths. An analysis of the resulting stochastic dynamical system allows
pinpointing the emergence of non-Gaussian statistics and non-trivial temporal
correlations of vorticity and strain, as previously reported from experiments
and simulations. Based on these insights, we use our model to predict the
orientational statistics of anisotropic particles in turbulence, enabling a
host of modeling applications for complex particulate flows
Qubit-Initialisation and Readout with Finite Coherent Amplitudes in Cavity QED
We consider a unitary transfer of an arbitrary state of a two-level atomic
qubit in a cavity to the finite amplitude coherent state cavity field. Such
transfer can be used to either provide an effective readout measurement on the
atom by a subsequent measurement on the light field or as a method for
initializing a fixed atomic state - a so-called "attractor state", studied
previously for the case of an infinitely strong cavity field. We show that with
a suitable adjustment of the coherent amplitude and evolution time the qubit
transfers all its information to the field, attaining a selected state of high
purity irrespectively of the initial state.Comment: 6 pages, 4 figure
Supernova explosions and the birth of neutron stars
We report here on recent progress in understanding the birth conditions of
neutron stars and the way how supernovae explode. More sophisticated numerical
models have led to the discovery of new phenomena in the supernova core, for
example a generic hydrodynamic instability of the stagnant supernova shock
against low-mode nonradial deformation and the excitation of gravity-wave
activity in the surface and core of the nascent neutron star. Both can have
supportive or decisive influence on the inauguration of the explosion, the
former by improving the conditions for energy deposition by neutrino heating in
the postshock gas, the latter by supplying the developing blast with a flux of
acoustic power that adds to the energy transfer by neutrinos. While recent
two-dimensional models suggest that the neutrino-driven mechanism may be viable
for stars from about 8 solar masses to at least 15 solar masses, acoustic
energy input has been advocated as an alternative if neutrino heating fails.
Magnetohydrodynamic effects constitute another way to trigger explosions in
connection with the collapse of sufficiently rapidly rotating stellar cores,
perhaps linked to the birth of magnetars. The global explosion asymmetries seen
in the recent simulations offer an explanation of even the highest measured
kick velocities of young neutron stars.Comment: 10 pages, 8 figures, 19 ps files; to be published in Proc. of Conf.
"40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August
12-17, 2007, McGill Univ., Montreal, Canada; high-resolution images can be
obtained upon request; incorrect panel in fig.8 replace
Error assessment of biogeochemical models by lower bound methods (NOMMA-1.0)
Biogeochemical models, capturing the major feedbacks of the pelagic ecosystem of the world ocean, are today often embedded into Earth system models which are increasingly used for decision making regarding climate policies. These models contain poorly constrained parameters (e.g., maximum phytoplankton growth rate), which are typically adjusted until the model shows reasonable behavior. Systematic approaches determine these parameters by minimizing the misfit between the model and observational data. In most common model approaches, however, the underlying functions mimicking the biogeochemical processes are nonlinear and non-convex. Thus, systematic optimization algorithms are likely to get trapped in local minima and might lead to non-optimal results. To judge the quality of an obtained parameter estimate, we propose determining a preferably large lower bound for the global optimum that is relatively easy to obtain and that will help to assess the quality of an optimum, generated by an optimization algorithm. Due to the unavoidable noise component in all observations, such a lower bound is typically larger than zero. We suggest deriving such lower bounds based on typical properties of biogeochemical models (e.g., a limited number of extremes and a bounded time derivative). We illustrate the applicability of the method with two real-world examples. The first example uses real-world observations of the Baltic Sea in a box model setup. The second example considers a three-dimensional coupled ocean circulation model in combination with satellite chlorophyll a
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