31,226 research outputs found

    Phase Space Models for Stochastic Nonlinear Parabolic Waves: Wave Spread and Singularity

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    We derive several kinetic equations to model the large scale, low Fresnel number behavior of the nonlinear Schrodinger (NLS) equation with a rapidly fluctuating random potential. There are three types of kinetic equations the longitudinal, the transverse and the longitudinal with friction. For these nonlinear kinetic equations we address two problems: the rate of dispersion and the singularity formation. For the problem of dispersion, we show that the kinetic equations of the longitudinal type produce the cubic-in-time law, that the transverse type produce the quadratic-in-time law and that the one with friction produces the linear-in-time law for the variance prior to any singularity. For the problem of singularity, we show that the singularity and blow-up conditions in the transverse case remain the same as those for the homogeneous NLS equation with critical or supercritical self-focusing nonlinearity, but they have changed in the longitudinal case and in the frictional case due to the evolution of the Hamiltonian

    Oil and natural gas reserve prices : addendum to CEEPR WP 03-016 ; including results for 2003 revisions to 2001

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    Introduction. A working paper entitled "Oil and Natural Gas Reserve Prices 1982-2002: Implications for Depletion and Investment Cost" was published in October 2003 (cited hereafter as Adelman & Watkins [2003]). Since then we have obtained data for 2003 and estimated oil and natural gas reserve prices for that year. We have also revised our previous estimates of reserve prices for 2001. This addendum paper reports on the nature and significance of the results for 2003 and the revisions to 2001. We have also extended the analysis by adding two new features. First is the expression of reserve prices in real terms -- previously we had only reported nominal prices. Second, we have estimated levelized or constant field prices that appear to underlie reserve prices, for each year. We refer to these as planning prices. Previously we had only published estimated growth rates in field prices from levels prevailing for a given year, congruent with our estimates of reserve prices. Section 1 of this Addendum paper highlights the 2003 results. Section 2 discusses the revisions for year 2001. Section 3 outlines the nature of the analytical extensions, presents the results, and discusses what they show. Concluding remarks are in Section 4. Adelman & Watkins [2003] included an extensive set of tables in Appendices. The revisions to all these tables to include 2003 and revised 2001 data are attached here as Appendices. This paper is to be read in conjunction with, not as a substitute for, Adelman & Watkins [2003]: analysis and description in the 2003 paper is not repeated here

    Oil and natural gas reserve prices, 1982-2002 : implications for depletion and investment cost

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    A time series is estimated of in-ground prices - as distinct from wellhead prices ₆ of US oil and natural gas reserves for the period 1982-2002, using market purchase and sale transaction information. The prices are a measure of the unit investment cost (long-run marginal cost) of creating new oil and gas reserves. The data are also used to examine the impact of reserves status (producing or not), the rate of production (R/P ratios) and of wellhead prices on reserve prices, and to reveal oil and natural gas price expectations embedded in reserve prices. Noticeable differences are disclosed between oil price expectations (ambiguous) and natural gas (positive). Estimates are made of current market values of US oil and gas reserves. Over the 21 year time span studied the trend in oil reserve prices is zero to mildly negative, that in natural gas is zero to mildly positive. All of these results -- the reserve prices themselves, their trends, and estimates of one year returns on holding reserve assets-- are incompatible with Hotelling doctrines. All these estimates refute the assumption of a fixed stock of hydrocarbons whose incessant decrease by production makes the still unproduced remainder constantly more valuable. The results are compatible with a process whereby investment adds to reserves even as production depletes them

    The value of United States oil and gas reserves

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    The object of this research is to estimate a time series, starting in 1979, for the value of in-ground oil reserves and natural gas reserves in the United States. Relatively good statistics exist for the physical quantities. (Regrettably, they will now be compiled only in alternate years.) Our task is to estimate the unit values. We focus mainly on data from the mid 1980s to the end of 1994.Supported by the United States Department of Energy

    Costs of aggregate hydrocarbon reserve additions

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    In what follows, we highlight problems created by aggregation using fixed conversion coefficients (Section 1). We then offer an economic index approach as an alternative, one that recognizes changing relative values of oil and gas over time (Section 2). This aggregation technique - the Divisia index - is applied to US reserve and in situ price data from 1982 to year 2001 to derive implicit shifts in unit costs of aggregated oil and gas reserve additions; these results are compared with those from the traditional fixed coefficient measures (Section 3). Concluding remarks are in Section 4.Supported by the MIT Center for Energy and Environmental Policy Research

    Shuttle Integration Status

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    As the Space Shuttle nears its first flight, the systems activity is changing its emphasis to concentrate on certification of the flight system and potential growth into the future. In this paper I would like to explain how we have approached the certification of the Shuttle system and then later describe recent activities which will enhance the capability of the Shuttle during the operational time period

    The Stellar Populations of NGC 3109: Another Dwarf Irregular Galaxy with a Population II Stellar Halo

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    We have obtained V and I-band photometry for about 17500 stars in the field of the dwarf irregular galaxy NGC3109, located in the outskirts of the Local Group. The photometry allows us to study the stellar populations present inside and outside the disk of this galaxy. From the VI color-magnitude diagram we infer metallicities and ages for the stellar populations in the main body and in the halo of NGC3109. The stars in the disk of this galaxy have a wide variety of ages, including very young stars with approximately 10^7 yr. Our main result is to establish the presence of a halo consisting of population II stars, extending out to about 4.5 arcmin (or 1.8 kpc) above and below the plane of this galaxy. For these old stars we derive an age of > 10 Gyr and a metallicity of [Fe/H] = -1.8 +/- 0.2. We construct a deep luminosity function, obtaining an accurate distance modulus (m-M)_0 = 25.62 +/- 0.1 for this galaxy based on the I-magnitude of the red giant branch (RGB) tip and adopting E(V-I) = 0.05.Comment: Accepted for publication in the Astronomical Journal 23 pages, latex, 12 Figures (Fig 1 not available in electronic format

    The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream

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    We report the detection, from observations using the James Clerk Maxwell Telescope, of CO J == 3\to 2 transition lines in six carbon stars, selected as members of the Galactic Halo and having similar infrared colors. Just one Halo star had been detected in CO before this work. Infrared observations show that these stars are red (J-K >>3), due to the presence of large dusty circumstellar envelopes. Radiative transfer models indicates that these stars are losing mass with rather large dust mass-loss rates in the range 1--3.3 ×\times10810^{-8}M_{\odot}yr1^{-1}, similar to what can be observed in the Galactic disc. We show that two of these stars are effectively in the Halo, one is likely linked to the stream of the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph), and the other three stars certainly belong to the thick disc. The wind expansion velocities of the observed stars are low compared to carbon stars in the thin disc and are lower for the stars in the Halo and the Sgr dSph stream than in the thick disc. We discuss the possibility that the low expansion velocities result from the low metallicity of the Halo carbon stars. This implies that metal-poor carbon stars lose mass at a rate similar to metal-rich carbon stars, but with lower expansion velocities, as predicted by recent theoretical models. This result implies that the current estimates of mass-loss rates from carbon stars in Local Group galaxies will have to be reconsidered.Comment: 10 pages, 7 figures, accepted for publication in MNRA

    Implications of genotype and amino acid sup-ply on pork quality

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    An experiment was conducted to evaluate the effect of different feeding regimes and genotypes on growth performance, carcass characteristics, composition and eating quality of pork under organic framework conditions. 198 individually housed pigs of 4 genotypes were allocated to three dietary treatments. Feeding regimes differed in relation to the supply of limiting amino acids (AA). The genotypes used were Pi x (DL x DE); Du x DL, Pi x German Swabian Hall (Pi x SH) and pure SH breed. While Pi x (DL x DE) pigs showed the highest carcass yields, pigs of the genotype Du x DL achieved higher values in dlwg and in meat composition compared to the other genotypes. Performance traits were significantly influenced by the feeding regime. Lean meat percentage and area of M.l.d. were significantly lower when a diet reduced in limited amino acids compared to the control treat-ment was fed. Backfat thickness was not influenced by the feeding regime. However, intramuscular fat content clearly increased when a diet without AA supplementation was fed. The results indicate that the limited availability of high quality feedstuffs in organic farming does not impair but improve the preconditions to produce pork of high eating quality
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