11,386 research outputs found
Estimating Refractive Index Spectra in Regions of Clear Air Turbulence
Estimation of refractive index spectra in regions of clear air turbulenc
Summary of photovoltaic system performance models
A detailed overview of photovoltaics (PV) performance modeling capabilities developed for analyzing PV system and component design and policy issues is provided. A set of 10 performance models are selected which span a representative range of capabilities from generalized first order calculations to highly specialized electrical network simulations. A set of performance modeling topics and characteristics is defined and used to examine some of the major issues associated with photovoltaic performance modeling. Each of the models is described in the context of these topics and characteristics to assess its purpose, approach, and level of detail. The issues are discussed in terms of the range of model capabilities available and summarized in tabular form for quick reference. The models are grouped into categories to illustrate their purposes and perspectives
Dissipative preparation of entanglement in optical cavities
We propose a novel scheme for the preparation of a maximally entangled state
of two atoms in an optical cavity. Starting from an arbitrary initial state, a
singlet state is prepared as the unique fixed point of a dissipative quantum
dynamical process. In our scheme, cavity decay is no longer undesirable, but
plays an integral part in the dynamics. As a result, we get a qualitative
improvement in the scaling of the fidelity with the cavity parameters. Our
analysis indicates that dissipative state preparation is more than just a new
conceptual approach, but can allow for significant improvement as compared to
preparation protocols based on coherent unitary dynamics.Comment: 4 pages, 2 figure
A Survey of Irradiated Pillars, Globules, and Jets in the Carina Nebul
We present wide-field, deep narrowband H, Br, H, [S II],
[O III], and broadband I and K-band images of the Carina star formation region.
The new images provide a large-scale overview of all the H and Br
emission present in over a square degree centered on this signature star
forming complex. By comparing these images with archival HST and Spitzer images
we observe how intense UV radiation from O and B stars affects star formation
in molecular clouds. We use the images to locate new candidate outflows and
identify the principal shock waves and irradiated interfaces within dozens of
distinct areas of star-forming activity. Shocked molecular gas in jets traces
the parts of the flow that are most shielded from the intense UV radiation.
Combining the H and optical images gives a more complete view of the jets,
which are sometimes only visible in H. The Carina region hosts several
compact young clusters, and the gas within these clusters is affected by
radiation from both the cluster stars and the massive stars nearby. The Carina
Nebula is ideal for studying the physics of young H II regions and PDR's, as it
contains multiple examples of walls and irradiated pillars at various stages of
development. Some of the pillars have detached from their host molecular clouds
to form proplyds. Fluorescent H outlines the interfaces between the ionized
and molecular gas, and after removing continuum, we detect spatial offsets
between the Br and H emission along the irradiated interfaces.
These spatial offsets can be used to test current models of PDRs once synthetic
maps of these lines become available.Comment: Accepted in the Astronomical Journa
Atmospheric variability and air-sea interaction
The topics studied include: (1) processing of Northern Hemispheric precipitation data, in order to fill in the transition seasons to provide a continuous 40 year data base on the variability of continental precipitation; (2) comparison of seasonally averaged fields of sea surface temperature obtained from ship observations in the North Atlantic and North Pacific in 1970 with the corresponding fields inferred from satellite observations; (3) estimation of seasonal average of total precipitable water at those admittedly few oceanic stations where repeated vertical soundings were made in 1970 and comparison with corresponding values inferred from satellite measurements; (4) comparison of seasonally averaged evaporation fields determined from ground based observations in 1970 with the field of divergence of the seasonal total horizontal water vapor flux inferred from satellite total water measurements and NMC wind data for the lower troposphere; (5) examination of meaning of convection-inversion index
Surface energy fluxes in complex terrain
The emphasis of the 1985 NASA project activity was on field measurements of wind data and heat balance data. Initiatives included a 19 station mountaintop monitoring program, testing and refining the surface flux monitoring systems and packing and shipping equipment to the People's Republic of China in preparation for the 1986 Tibet Experiment. Other work included more extensive analyses of the 1984 Gobi Desert and Rocky Mountain observations plus some preliminary analyses of the 1985 mountaintop network data. Details of our field efforts are summarized and results of our data analyses are presented
Entropy Production in Collisions of Relativistic Heavy Ions -- a signal for Quark-Gluon Plasma phase transition?
Entropy production in the compression stage of heavy ion collisions is
discussed within three distinct macroscopic models (i.e. generalized RHTA,
geometrical overlap model and three-fluid hydrodynamics). We find that within
these models \sim 80% or more of the experimentally observed final-state
entropy is created in the early stage. It is thus likely followed by a nearly
isentropic expansion. We employ an equation of state with a first-order phase
transition. For low net baryon density, the entropy density exhibits a jump at
the phase boundary. However, the excitation function of the specific entropy
per net baryon, S/A, does not reflect this jump. This is due to the fact that
for final states (of the compression) in the mixed phase, the baryon density
\rho_B increases with \sqrt{s}, but not the temperature T. Calculations within
the three-fluid model show that a large fraction of the entropy is produced by
nuclear shockwaves in the projectile and target. With increasing beam energy,
this fraction of S/A decreases. At \sqrt{s}=20 AGeV it is on the order of the
entropy of the newly produced particles around midrapidity. Hadron ratios are
calculated for the entropy values produced initially at beam energies from 2 to
200 AGeV.Comment: 17 pages, 8 figures, uses epsfig.sty; Submitted to Nucl.Phys.
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