2,187 research outputs found
From Ice to Ether: The Adoption of a Regime to Govern Resource Exploitation in Outer Space
It is clear that the world community in general, and the United States in particular, intends to move forward in the exploration of space and the commercial exploitation of lunar and other resources. It would seem equally clear that, without law in this area, no country, government, or commercial enterprise is likely to undertake the substantial risks and costs involved in such exploitation. Companies will not undertake these risks without a clear understanding of how the resulting rewards will be allocated. For the United States commercial space program to move forward, it must seek the adoption of a regime to govern such activities which will be accepted and recognized by the international community. The purpose of this Article is to provide a short description of why past efforts to adopt such an international regime have failed. The Article will contrast the currently successful efforts to adopt an international regime to regulate mineral resource activities in a similarly inhospitable environment -- Antarctica -- and to suggest terms of a regime that the international community might find acceptable
From Ice to Ether: The Adoption of a Regime to Govern Resource Exploitation in Outer Space
It is clear that the world community in general, and the United States in particular, intends to move forward in the exploration of space and the commercial exploitation of lunar and other resources. It would seem equally clear that, without law in this area, no country, government, or commercial enterprise is likely to undertake the substantial risks and costs involved in such exploitation. Companies will not undertake these risks without a clear understanding of how the resulting rewards will be allocated. For the United States commercial space program to move forward, it must seek the adoption of a regime to govern such activities which will be accepted and recognized by the international community. The purpose of this Article is to provide a short description of why past efforts to adopt such an international regime have failed. The Article will contrast the currently successful efforts to adopt an international regime to regulate mineral resource activities in a similarly inhospitable environment -- Antarctica -- and to suggest terms of a regime that the international community might find acceptable
Large space system: Charged particle environment interaction technology
Large, high voltage space power systems are proposed for future space missions. These systems must operate in the charged-particle environment of space and interactions between this environment and the high voltage surfaces are possible. Ground simulation testing indicated that dielectric surfaces that usually surround biased conductors can influence these interactions. For positive voltages greater than 100 volts, it has been found that the dielectrics contribute to the current collection area. For negative voltages greater than-500 volts, the data indicates that the dielectrics contribute to discharges. A large, high-voltage power system operating in geosynchronous orbit was analyzed. Results of this analysis indicate that very strong electric fields exist in these power systems
The Sloan Digital Sky Survey Reverberation Mapping Project: Initial C IV Lag Results from Four Years of Data
We present reverberation-mapping (RM) lags and black hole mass measurements using the C iv λ1549 broad emission line from a sample of 348 quasars monitored as a part of the Sloan Digital Sky Survey RM Project. Our data span four years of spectroscopic and photometric monitoring for a total baseline of 1300 days, allowing us to measure lags up to ~750 days in the observed frame (this corresponds to a rest-frame lag of ~300 days in a quasar at z = 1.5 and ~190 days at z = 3). We report significant time delays between the continuum and the C iv λ1549 emission line in 48 quasars, with an estimated false-positive detection rate of 10%. Our analysis of marginal lag measurements indicates that there are on the order of ~100 additional lags that should be recoverable by adding more years of data from the program. We use our measurements to calculate black hole masses and fit an updated C iv radius–luminosity relationship. Our results significantly increase the sample of quasars with C iv RM results, with the quasars spanning two orders of magnitude in luminosity toward the high-luminosity end of the C iv radius–luminosity relation. In addition, these quasars are located at some of the highest redshifts (z ≈ 1.4–2.8) of quasars with black hole masses measured with RM. This work constitutes the first large sample of C iv RM measurements in more than a dozen quasars, demonstrating the utility of multiobject RM campaigns
The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry
We present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the Sloan Digital Sky Survey Reverberation Mapping Project. We successfully recover reverberation time delays between the g+i band emission and the broad Hβemission line for a total of 44 quasars, and for the broad Hα emission line in 18 quasars. Time delays are computed using the JAVELIN and CREAM software and the traditional interpolated cross-correlation function (ICCF): using well-defined criteria, we report measurements of 32 Hβ and 13 Hα lags with JAVELIN, 42 Hβ and 17 Hα lags with CREAM, and 16 Hβ and eight Hα lags with the ICCF. Lag values are generally consistent among the three methods, though we typically measure smaller uncertainties with JAVELIN and CREAM than with the ICCF, given the more physically motivated light curve interpolation and more robust statistical modeling of the former two methods. The median redshift of our Hβ-detected sample of quasars is 0.53, significantly higher than that of the previous reverberation mapping sample. We find that in most objects, the time delay of the Hαemission is consistent with or slightly longer than that of Hβ. We measure black hole masses using our measured time delays and line widths for these quasars. These black hole mass measurements are mostly consistent with expectations based on the local M_(BH) - σ* relationship, and are also consistent with single-epoch black hole mass measurements. This work increases the current sample size of reverberation-mapped active galaxies by about two-thirds and represents the first large sample of reverberation mapping observations beyond the local universe (z < 0.3)
The Importance of Broad Emission-Line Widths in Single Epoch Black Hole Mass Estimates
Estimates of the mass of super-massive black holes (BHs) in distant active
galactic nuclei (AGNs) can be obtained efficiently only through single-epoch
spectra, using a combination of their broad emission-line widths and continuum
luminosities. Yet the reliability and accuracy of the method, and the resulting
mass estimates, M_BH, remain uncertain. A recent study by Croom using a sample
of SDSS, 2QZ and 2SLAQ quasars suggests that line widths contribute little
information about the BH mass in these single-epoch estimates and can be
replaced by a constant value without significant loss of accuracy. In this
Letter, we use a sample of nearby reverberation-mapped AGNs to show that this
conclusion is not universally applicable. We use the bulge luminosity (L_Bulge)
of these local objects to test how well the known M_BH - L_Bulge correlation is
recovered when using randomly assigned line widths instead of the measured ones
to estimate M_BH. We find that line widths provide significant information
about M_BH, and that for this sample, the line width information is just as
significant as that provided by the continuum luminosities. We discuss the
effects of observational biases upon the analysis of Croom and suggest that the
results can probably be explained as a bias of flux-limited, shallow quasar
samples.Comment: 10 text pages + 4 Figures + 1 Table. Accepted for publication in ApJ
Letter
Multidimensional optical fractionation with holographic verification
The trajectories of colloidal particles driven through a periodic potential
energy landscape can become kinetically locked in to directions dictated by the
landscape's symmetries. When the landscape is realized with forces exerted by a
structured light field, the path a given particle follows has been predicted to
depend exquisitely sensitively on such properties as the particle's size and
refractive index These predictions, however, have not been tested
experimentally. Here, we describe measurements of colloidal silica spheres'
transport through arrays of holographic optical traps that use holographic
video microscopy to track individual spheres' motions in three dimensions and
simultaneously to measure each sphere's radius and refractive index with
part-per-thousand resolution. These measurements confirm previously untested
predictions for the threshold of kinetically locked-in transport, and
demonstrate the ability of optical fractionation to sort colloidal spheres with
part-per-thousand resolution on multiple characteristics simultaneously.Comment: 4 pages, 2 figures. Accepted for publication in Physical Review
Letter
Indoor Cats, Scratching, and the Debate over Declawing: When Normal Pet Behavior Becomes a Problem
When pet animals share our living spaces, their needs and natural behaviors sometimes are at odds with the varying standards for household appearance, sanitation, and polite social life that Americans have established over time. How pet owners have resolved these issues provides insight into their changing ideas about the role of animals in their households and suggests how much, or how little, people may actually know about the biological behaviors and psychological needs of the creatures they care for. This essay examines one particular issue associated with the problem of sharing spaces: declawing pet cats as a common solution to avoid destructive scratching. This is a volatile issue and has generated much emotional debate. It pits loving cat owners who see such surgery as an act that breaches the trust of responsible pet care for their feline companions against loving cat owners who see the surgery as an act that strengthens their bond with their feline companions. It divides those in the animal welfare and veterinary community as well, where many opinions are believed to be the right opinion. The authors wish to stress that they enjoy the companionship of pet animals in their homes; pointing out the complexities and contradictions in living with pet cats is intended to acknowledge the historical, socially constructed, and changeable character of pet keeping and to encourage people involved in companion animal welfare work to consider why some practices can be promoted or simply tolerated, while others are problematic
Indoor Cats, Scratching, and the Debate over Declawing: When Normal Pet Behavior Becomes a Problem
When pet animals share our living spaces, their needs and natural behaviors sometimes are at odds with the varying standards for household appearance, sanitation, and polite social life that Americans have established over time. How pet owners have resolved these issues provides insight into their changing ideas about the role of animals in their households and suggests how much, or how little, people may actually know about the biological behaviors and psychological needs of the creatures they care for. This essay examines one particular issue associated with the problem of sharing spaces: declawing pet cats as a common solution to avoid destructive scratching. This is a volatile issue and has generated much emotional debate. It pits loving cat owners who see such surgery as an act that breaches the trust of responsible pet care for their feline companions against loving cat owners who see the surgery as an act that strengthens their bond with their feline companions. It divides those in the animal welfare and veterinary community as well, where many opinions are believed to be the right opinion. The authors wish to stress that they enjoy the companionship of pet animals in their homes; pointing out the complexities and contradictions in living with pet cats is intended to acknowledge the historical, socially constructed, and changeable character of pet keeping and to encourage people involved in companion animal welfare work to consider why some practices can be promoted or simply tolerated, while others are problematic
Brownian Dynamics of a Sphere Between Parallel Walls
We describe direct imaging measurements of a colloidal sphere's diffusion
between two parallel surfaces. The dynamics of this deceptively simple
hydrodynamically coupled system have proved difficult to analyze. Comparison
with approximate formulations of a confined sphere's hydrodynamic mobility
reveals good agreement with both a leading-order superposition approximation as
well as a more general all-images stokeslet analysis.Comment: 4 pages, 3 figures, REVTeX with PostScript figure
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