1,575 research outputs found
Economic Evaluation of Water Supply Alternatives: A Mathematical Programming Approach
The main task of this paper is to propose a method for deriving regional water supply functions, taking into account a variety of supply alternatives and some engineering and environmental aspects of each. The purpose is to provide a framework for decisions about the efficient use of a region's water resources. The first section deals with distinctions between engineering and economics. The notion of supply-demand equilibrium and the economic efficiency properties of this equilibrium are reviewed. The second section surveys the "State-of-the-Art" in regional water supply, describing a number of alternative sources of supply. The third section considers how, for a region having just two inputs, each point on a supply curve can be derived as the solution to a nonlinear program to minimize the cost of obtaining a given quantity of water. The procedure is however perfectly general, and in the fourth section an application is made to a hypothetical region with several sources of supply, each having several inputs, with constraints on their use, and so on. An interesting feature of the model is that it can -- and does, in the application -- reflect environmental constraints as well. For ease in computation the production relations are linearized in order to use a linear programming solution algorithm. Based on the assumed production relations and resource constraints, a well behaved regional water supply function is derived
Fecundity compensation and tolerance to a sterilizing pathogen in <em>Daphnia</em>
Hosts are armed with several lines of defence in the battle against parasites: they may prevent the establishment of infection, reduce parasite growth once infected or persevere through mechanisms that reduce the damage caused by infection, called tolerance. Studies on tolerance in animals have focused on mortality, and sterility tolerance has not been investigated experimentally. Here, we tested for genetic variation in the multiple steps of defence when the invertebrate Daphnia magna is infected with the sterilizing bacterial pathogen Pasteuria ramosa: anti-infection resistance, anti-growth resistance and the ability to tolerate sterilization once infected. When exposed to nine doses of a genetically diverse pathogen inoculum, six host genotypes varied in their average susceptibility to infection and in their parasite loads once infected. How host fecundity changed with increasing parasite loads did not vary between genotypes, indicating that there was no genetic variation for this measure of fecundity tolerance. However, genotypes differed in their level of fecundity compensation under infection, and we discuss how, by increasing host fitness without targeting parasite densities, fecundity compensation is consistent with the functional definition of tolerance. Such infection-induced life-history shifts are not traditionally considered to be part of the immune response, but may crucially reduce harm (in terms of fitness loss) caused by disease, and are a distinct source of selection on pathogens
On Measures of Natural Resource Scarcity
Several questions concerning measures of natural resource scarcity are considered with the aid of optimal control models of exploration and extraction. It is shown that the unit cost of extraction is not a sufficient indicator of resource scarcity, because it neglects demand generally and the value of future output foregone in particular. Under plausible conditions, though, cost will rise as stock is depleted. Resource rent is also not fully satisfactory as an indicator of scarcity, since, contrary to recent suggestions, it may fall if cost rises as the stock is depleted. The best measure of scarcity is probably the market price of the resource. Introducing exploration into a model of optimal extraction leads to a practical proposal for estimating rent from exploration cost data
PCV117 Identification of Hospital Guidelines for Prevention of Venous Thromboembolism (VTE) in Hospitalized Non-Surgical Medically-Ill Patients in the United States
Logarithmic Corrections to Scaling in the --Model
We study the distribution of partition function zeroes for the --model in
two dimensions. In particular we find the scaling behaviour of the end of the
distribution of zeroes in the complex external magnetic field plane in the
thermodynamic limit (the Yang--Lee edge) and the form for the density of these
zeroes. Assuming that finite--size scaling holds, we show that there have to
exist logarithmic corrections to the leading scaling behaviour of thermodynamic
quantities in this model. These logarithmic corrections are also manifest in
the finite--size scaling formulae and we identify them numerically. The method
presented here can be used to check the compatibility of scaling behaviour of
odd and even thermodynamic functions in other models too.Comment: 3 pages, latex, 2 figure
Electron transport in the dye sensitized nanocrystalline cell
Dye sensitised nanocrystalline solar cells (Gr\"{a}tzel cells) have achieved
solar-to-electrical energy conversion efficiencies of 12% in diffuse daylight.
The cell is based on a thin film of dye-sensitised nanocrystalline TiO
interpenetrated by a redox electrolyte. The high surface area of the TiO
and the spectral characteristics of the dye allow the device to harvest 46% of
the solar energy flux. One of the puzzling features of dye-sensitised
nano-crystalline solar cells is the slow electron transport in the titanium
dioxide phase. The available experimental evidence as well as theoretical
considerations suggest that the driving force for electron collection at the
substrate contact arises primarily from the concentration gradient, ie the
contribution of drift is negligible. The transport of electrons has been
characterised by small amplitude pulse or intensity modulated illumination.
Here, we show how the transport of electrons in the Gr\"{a}tzel cell can be
described quantitatively using trap distributions obtained from a novel charge
extraction method with a one-dimensional model based on solving the continuity
equation for the electron density. For the first time in such a model, a back
reaction with the I ions in the electrolyte that is second order in the
electron density has been included.Comment: 6 pages, 5 figures, invited talk at the workshop 'Nanostructures in
Photovoltaics' to appear in Physica
Microwave conductivity of a d-wave superconductor disordered by extended impurities: a real-space renormalization group approach
Using a real-space renormalization group (RSRG) technique, we compute the
microwave conductivity of a d-wave superconductor disordered by extended
impurities. To do this, we invoke a semiclassical approximation which naturally
accesses the Andreev bound states localized near each impurity. Tunneling
corrections (which are captured using the RSRG) lead to a delocalization of
these quasiparticles and an associated contribution to the microwave
conductivity.Comment: 8 pages, 4 figures. 2 figures added to previous versio
Sequential drain amylase to guide drain removal following pancreatectomy
BACKGROUND:
Although used as criterion for early drain removal, postoperative day (POD) 1 drain fluid amylase (DFA) ≤ 5000 U/L has low negative predictive value for clinically relevant postoperative pancreatic fistula (CR-POPF). It was hypothesized that POD3 DFA ≤ 350 could provide further information to guide early drain removal.
METHODS:
Data from a pancreas surgery consortium database for pancreatoduodenectomy and distal pancreatectomy patients were analyzed retrospectively. Those patients without drains or POD 1 and 3 DFA data were excluded. Patients with POD1 DFA ≤ 5000 were divided into groups based on POD3 DFA: Group A (≤350) and Group B (>350). Operative characteristics and 60-day outcomes were compared using chi-square test.
RESULTS:
Among 687 patients in the database, all data were available for 380. Fifty-five (14.5%) had a POD1 DFA > 5000. Among 325 with POD1 DFA ≤ 5000, 254 (78.2%) were in Group A and 71 (21.8%) in Group B. Complications (35 (49.3%) vs 87 (34.4%); p = 0.021) and CR-POPF (13 (18.3%) vs 10 (3.9%); p < 0.001) were more frequent in Group B.
CONCLUSIONS:
In patients with POD1 DFA ≤ 5000, POD3 DFA ≤ 350 may be a practical test to guide safe early drain removal. Further prospective testing may be useful
Logarithmic Corrections to Scaling in the Two Dimensional --Model
By expressing thermodynamic functions in terms of the edge and density of
Lee--Yang zeroes, we relate the scaling behaviour of the specific heat to that
of the zero field magnetic susceptibility in the thermodynamic limit of the
--model in two dimensions. Assuming that finite--size scaling holds, we
show that the conventional Kosterlitz--Thouless scaling predictions for these
thermodynamic functions are not mutually compatable unless they are modified by
multiplicative logarithmic corrections. We identify these logarithmic
corrections analytically in the case of the specific heat and numerically in
the case of the susceptibility. The techniques presented here are general and
can be used to check the compatibility of scaling behaviour of odd and even
thermodynamic functions in other models too.Comment: 11 pages, latex, 4 figure
Four-nucleon system with -isobar excitation
The four-nucleon bound state and scattering below three-body breakup
threshold are described based on the realistic coupled-channel potential CD
Bonn + which allows the excitation of a single nucleon to a
isobar. The Coulomb repulsion between protons is included. In the four-nucleon
system the two-baryon coupled-channel potential yields effective two-, three-
and four-nucleon forces, mediated by the isobar and consistent with
each other and with the underlying two-nucleon force. The effect of the
four-nucleon force on the studied observables is much smaller than the effect
of the three-nucleon force. The inclusion of the isobar is unable to
resolve the existing discrepancies with the experimental data.Comment: 11 figures, to be published in Phys. Lett.
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