1,915 research outputs found
Forecasting using relative entropy
The paper describes a relative entropy procedure for imposing moment restrictions on simulated forecast distributions from a variety of models. Starting from an empirical forecast distribution for some variables of interest, the technique generates a new empirical distribution that satisfies a set of moment restrictions. The new distribution is chosen to be as close as possible to the original in the sense of minimizing the associated Kullback-Leibler Information Criterion, or relative entropy. The authors illustrate the technique by using several examples that show how restrictions from other forecasts and from economic theory may be introduced into a model's forecasts.Forecasting
The Two-Tiered Market in Western Water
I. Introduction
II. Historical Development of the Project Market
III. Federal Conditions Limiting the Transferability of Water Reclamation Projects … A. The Environmentalists’ Use of the Secretary of the Interior’s Lack of Authority as a Shield … b. The Small Farmers’ Use of Existing Statutes as a Sword … 1. The National Land for People Litigation … 2. The Yellen Litigation … 3. State Conditions Limiting Transferability … C. State Statutory Provisions That Restrict the Transfer of Project Water Rights
IV. Impact of the Federal and State Conditions on the Market for Water Rights
V. Private or Native Water … A. Improving the Market Allocation of Native Water … B. Quantification … C. Reducing the Cost of Necessary Quantification … D. Return Flow—The Intractable Problem … E. Avoiding Return Flow Problem
The Two-Tiered Market in Western Water
I. Introduction
II. Historical Development of the Project Market
III. Federal Conditions Limiting the Transferability of Water Reclamation Projects … A. The Environmentalists’ Use of the Secretary of the Interior’s Lack of Authority as a Shield … b. The Small Farmers’ Use of Existing Statutes as a Sword … 1. The National Land for People Litigation … 2. The Yellen Litigation … 3. State Conditions Limiting Transferability … C. State Statutory Provisions That Restrict the Transfer of Project Water Rights
IV. Impact of the Federal and State Conditions on the Market for Water Rights
V. Private or Native Water … A. Improving the Market Allocation of Native Water … B. Quantification … C. Reducing the Cost of Necessary Quantification … D. Return Flow—The Intractable Problem … E. Avoiding Return Flow Problem
Obtaining the spacetime metric from cosmological observations
Recent galaxy redshift surveys have brought in a large amount of accurate
cosmological data out to redshift 0.3, and future surveys are expected to
achieve a high degree of completeness out to a redshift exceeding 1.
Consequently, a numerical programme for determining the metric of the universe
from observational data will soon become practical; and thereby realise the
ultimate application of Einstein's equations. Apart from detailing the cosmic
geometry, this would allow us to verify and quantify homogeneity, rather than
assuming it, as has been necessary up to now, and to do that on a metric level,
and not merely at the mass distribution level. This paper is the beginning of a
project aimed at such a numerical implementation. The primary observational
data from our past light cone consists of galaxy redshifts, apparent
luminosities, angular diameters and number densities, together with source
evolution functions, absolute luminosities, true diameters and masses of
sources. Here we start with the simplest case, that of spherical symmetry and a
dust equation of state, and execute an algorithm that determines the unknown
metric functions from this data. We discuss the challenges of turning the
theoretical algorithm into a workable numerical procedure, particularly
addressing the origin and the maximum in the area distance. Our numerical
method is tested with several artificial data sets for homogeneous and
inhomogeneous models, successfully reproducing the original models. This
demonstrates the basic viability of such a scheme. Although current surveys
don't have sufficient completeness or accuracy, we expect this situation to
change in the near future, and in the meantime there are many refinements and
generalisations to be added.Comment: 26 pages, 10 figures. Minor changes to match the published versio
BEHAVIOR OF SANDHILL CRANES HARNESSED WITH DIFFERENT SATELLITE TRANSMITTERS
The effectiveness of various attachment methods and designs of platform transmitting terminals (PIT\u27s) was tested on captive sandhill cranes (Grus canadensis) at the Patuxent Wildlife Research Center, Laurel, Maryland, during 1989-91. Combinations of attachment and transmitter designs included neoprene cord harness with batteries separate from the transmitter (2 harness designs), Teflon ribbon harness with batteries incorporated into the transmitter package (4 transmitter models), and a package attached directly to the bird with epoxy glue only. Physical effects seen on cranes wearing PTT\u27s ranged from skin lacerations (caused by rubbing of harness material) to no observed effects (other than feather wear). The most successful harness material and design utilized a Teflon ribbon harness with the 4 ribbon ends from the transmitter forming a neck loop and a body loop joined at the sternum. Time spent by sandhill cranes performing most activities did not change after transmitter attachment using this harness method
Shrinking II -- The Distortion of the Area Distance-Redshift Relation in Inhomogeneous Isotropic Universes
This paper and the others in the series challenge the standard model of the
effects of gravitational lensing on observations at large distances. We show
that due to the cumulative effect of lensing, areas corresponding to an
observed solid angle can be quite different than would be estimated from the
corresponding Friedmann-Lema\^{\i}tre model, even when averaged over large
angular scales. This paper concentrates on the specific example of spherically
symmetric but spatially inhomogeneous dust universes, the
Lema\^{\i}tre-Tolman-Bondi models, and shows that radial lensing significantly
distorts the area distance-redshift and density-redshift relations in these
exact solutions compared with the standard ones for Friedmann-Lema\^{\i}tre
models. Thus inhomogeneity may introduce significant errors into distance
estimates based on the standard FL relations, even after all-sky averaging. In
addition a useful new gauge choice is presented for these models, solving the
problem of locating the past null cone exactly.Comment: Minor technical refinement, 16 pages, RevTex, 8 eps figure
Entirely off-grid and solar-powered DNA sequencing of microbial communities during an ice cap traverse expedition
Microbial communities in remote locations remain under-studied. This is particularly true on glaciers and icecaps, which cover approximately 11% of the Earth’s surface. The principal reason for this is the inaccessibility of most of these areas due to their extreme isolation and challenging environmental conditions. While remote research stations have significantly lowered the barrier to studying the microbial communities on icecaps, their use has led to a bias for data collection in the near vicinity of these institutions. Here, miniaturisation of a DNA sequencing lab suitable for off-grid metagenomic studies is demonstrated. Using human power alone, this lab was transported across Europe’s largest ice cap (Vatnajökull, Iceland) by ski and sledge. After 11 days of unsupported polar-style travel, a metagenomic study of a geothermal hot spring gorge was conducted on the remote northern edge of the ice cap. This tent-based metagenomic study resulted in over 24 h of Nanopore sequencing, powered by solar power alone. This study demonstrates the ability to conduct DNA sequencing in remote locations, far from civilised resources (mechanised transport, external power supply, internet connection, etc.), whilst greatly reducing the time from sample collection to data acquisition
CT of mullerian adenosarcoma arising in endometriosis
Mullerian adenosarcoma is a rare tumor that usually arises in the uterus. Occasional cases arising in endometrial implants have been reported. We report the computed tomography (CT) findings of histologically proven mullerian adenosarcoma arising in perirectal endometriosis in a 46-year-old woman.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30705/1/0000351.pd
Clumps into Voids
We consider a spherically symmetric distribution of dust and show that it is
possible, under general physically reasonable conditions, for an overdensity to
evolve to an underdensity (and vice versa). We find the conditions under which
this occurs and illustrate it on a class of regular Lemaitre-Tolman-Bondi
solutions. The existence of this phenomenon, if verified, would have the result
that the topology of density contours, assumed fixed in standard structure
formation theories, would have to change and that luminous matter would not
trace the dark matter distribution so well.Comment: LaTeX, 17 pages, 4 figures. Submitted to GRG 20/4/200
Aspects of meson properties in dense nuclear matter
We investigate the modification of meson spectral densities in dense nuclear
matter at zero temperature. These effects are studied in a fully relativistic
mean field model which goes beyond the linear density approximation and also
includes baryon resonances. In particular, the role of N*(1520) and N*(1720) on
the rho meson spectral density is highlighted. Even though the nucleon-nucleon
loop and the nucleon-resonance loop contribute with the opposite sign, an
overall reduction of rho meson mass is still observed at high density.
Importantly, it is shown that the resonances cause substantial broadening of
the rho meson spectral density in matter and also induces non-trivial momentum
dependence. The spectral density of the a0 meson is also shown. We study the
dispersion relations and collective oscillations induced by the rho meson
propagation in nuclear matter together with the influence of the mixing of rho
with the a0 meson. The relevant expression for the plasma frequency is also
recovered analytically in the appropriate limit.Comment: 19 pages, 17 figure
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