5,974 research outputs found
The density of mid-sized Kuiper belt objects from ALMA thermal observations
The densities of mid-sized Kuiper belt objects are a key constraint into
understanding the assembly of objects in the outer solar system. These objects
are critical for understanding the currently unexplained transition from the
smallest Kuiper belt objects with densities lower than that of water to the
largest objects with significant rock content. Mapping this transition is made
difficult by the uncertainties in the diameters of these objects, which maps
into an even larger uncertainty in volume and thus density. The substantial
collecting area of the Atacama Large Millimeter Array allows significantly more
precise measurements of thermal emission from outer solar system objects and
could potentially greatly improve the density measurements. Here we use new
thermal observations of four objects with satellites to explore the
improvements possible with millimeter data. We find that effects due to
effective emissivity at millimeter wavelengths make it difficult to use the
millimeter data directly to find diameters and thus volumes for these bodies.
In addition, we find that when including the effects of model uncertainty, the
true uncertainties on the sizes of outer solar system objects measured with
radiometry are likely larger than those previously published. Substantial
improvement in object sizes will likely require precise occultation
measurements.Comment: AJ, in pres
Median price changes: an alternative approach to measuring current monetary inflation
An analysis concluding that inflation measures based on median price changes are a better indicator than measures based on mean price changes.Inflation (Finance) ; Consumer price indexes
The business cycle, investment and a wayward M2: a midyear review
A summary of the June 12, 1992 meeting of the Fourth District Economists' Roundtable, at which 22 panelists concurred that steady and moderate growth in the economy can be expected through late 1993; includes discussions on business fixed investment, monetary growth, and business cycle theory.Economic conditions - United States
Evidence for the intense exchange of MazG in marine cyanophages by horizontal gene transfer
Background: S-PM2 is a phage capable of infecting strains of unicellular cyanobacteria belonging to the genus Synechococcus. S-PM2, like other myoviruses infecting marine cyanobacteria, encodes a number of bacterial-like genes. Amongst these genes is one encoding a MazG homologue that is hypothesized to be involved in the adaption of the infected host for production of progeny phage.
Methodology/Principal Findings: This study focuses on establishing the occurrence of mazG homologues in other cyanophages isolated from different oceanic locations. Degenerate PCR primers were designed using the mazG gene of S-PM2. The mazG gene was found to be widely distributed and highly conserved among Synechococcus myoviruses and podoviruses from diverse oceanic provinces.
Conclusions/Significance: This study provides evidence of a globally connected cyanophage gene pool, the cyanophage mazG gene having a small effective population size indicative of rapid lateral gene transfer despite being present in a substantial fraction of cyanophage. The Prochlorococcus and Synechococcus phage mazG genes do not cluster with the host mazG gene, suggesting that their primary hosts are not the source of the mazG gene
ALMA Thermal Observations of Europa
We present four daytime thermal images of Europa taken with the Atacama Large
Millimeter Array. Together, these images comprise the first spatially resolved
thermal dataset with complete coverage of Europa's surface. The resulting
brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a
typical linear resolution of roughly 200 km. At this resolution, the images
capture spatially localized thermal variations on the scale of geologic and
compositional units. We use a global thermal model of Europa to simulate the
ALMA observations in order to investigate the thermal structure visible in the
data. Comparisons between the data and model images suggest that the
large-scale daytime thermal structure on Europa largely results from bolometric
albedo variations across the surface. Using bolometric albedos extrapolated
from Voyager measurements, a homogenous model reproduces these patterns well,
but localized discrepancies exist. These discrepancies can be largely explained
by spatial inhomogeneity of the surface thermal properties. Thus, we use the
four ALMA images to create maps of the surface thermal inertia and emissivity
at our ALMA wavelength. From these maps, we identify a region of either
particularly high thermal inertia or low emissivity near 90 degrees West and 23
degrees North, which appears anomalously cold in two of our images.Comment: 9 pages, 3 figures, accepted for publication in the Astronomical
Journa
System Mass Variation and Entropy Generation in 100âkWe ClosedâBraytonâCycle Space Power Systems
Stateâofâtheâart closedâBraytonâcycle (CBC) space power systems were modeled to study performance trends in a trade space characteristic of interplanetary orbiters. For workingâfluid molar masses of 48.6, 39.9 and 11.9 kg/kmol, peak system pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated. System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values examined. Minimum mass point comparison between 72% He at 1.38 MPa peak and 94% He at 3.0 MPa peak showed an increase in system mass of 14%. Converter flow loop entropy generation rates were calculated for 1.38 and 3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASAâGlenn modeling code, Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and turbomachinery. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87575/2/445_1.pd
Oil, the economy, and monetary policy
An examination of the theoretical impact of an oil shortage on the U.S. economy and the problems that such shortages present for monetary policy.Power resources - Prices ; Monetary policy
Using annotated interface definitions to optimize RPC
Journal ArticleIn RPC-based communication, it is useful to distinguish the RPC interface, which is the "network contract" between the client and the server, from the presentation, which is the "programmer's contract" between the RPC stubs and the code that calls or is called by them. Presentation is usually a fixed function of the RPC interface, but some RPC systems, such as DCE and Concert, support the notion of a flexible presentation or endpoint modifier, allowing controlled modification of the behavior of the stubs on each side without affecting the contract between the client and the server. Up until now, the primary motivation for flexible presentation has been for programmer convenience and improved interoperability. However, we have found flexible presentation also to be useful for optimization of RPC, and in many cases necessary to achieving maximal performance without throwing out the RPC system and resorting to hand-coded stubs. In this paper we provide examples demonstrating this point for a number of different operating systems and IPC transport mechanisms, with RPC performance improvements ranging from 5% to an order of magnitude. In general, we observe that the more efficient the underlying IPC transport mechanism is, the more important it is for the RPC system to support flexible presentation, in order to avoid unnecessary user-space overhead?
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