22,519 research outputs found
Similitude requirements and scaling relationships as applied to model testing
The similitude requirements for the most general test conditions are presented. These similitude requirements are considered in relation to the scaling relationships, test technique, test conditions (including supersonic flow), and test objectives. Particular emphasis is placed on satisfying the various similitude requirements for incompressible and compressible flow conditions. For free flying models tests, the test velocities for incompressible flow are scaled from Froude number similitude requirements and those for compressible flow are scaled from Mach number similitude requirements. The limitations of various test techniques are indicated, with emphasis on the free flying model
Thermodynamics of nuclei in thermal contact
The behaviour of a di-nuclear system in the regime of strong pairing
correlations is studied with the methods of statistical mechanics. It is shown
that the thermal averaging is strong enough to assure the application of
thermodynamical methods to the energy exchange between the two nuclei in
contact. In particular, thermal averaging justifies the definition of a nuclear
temperature.Comment: 9 pages, 1 figur
On the derivation of Fourier's law in stochastic energy exchange systems
We present a detailed derivation of Fourier's law in a class of stochastic
energy exchange systems that naturally characterize two-dimensional mechanical
systems of locally confined particles in interaction. The stochastic systems
consist of an array of energy variables which can be partially exchanged among
nearest neighbours at variable rates. We provide two independent derivations of
the thermal conductivity and prove this quantity is identical to the frequency
of energy exchanges. The first derivation relies on the diffusion of the
Helfand moment, which is determined solely by static averages. The second
approach relies on a gradient expansion of the probability measure around a
non-equilibrium stationary state. The linear part of the heat current is
determined by local thermal equilibrium distributions which solve a
Boltzmann-like equation. A numerical scheme is presented with computations of
the conductivity along our two methods. The results are in excellent agreement
with our theory.Comment: 19 pages, 5 figures, to appear in Journal of Statistical Mechanics
(JSTAT
An Unusual New Cheilanthoid Fern From California
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141956/1/ajb208258.pd
Integrated cost-benefit analysis of tsetse control and herd productivity to inform control programs for animal African trypanosomiasis
Animal African trypanosomiasis (AAT) and its tsetse vector are responsible for annual losses estimated in billions of US dollars ($). Recent years have seen the implementation of a series of multinational interventions. However, actors of AAT control face complex resource allocation decisions due to the geographical range of AAT, diversity of ecological and livestock systems, and range of control methods available. The study presented here integrates an existing tsetse abundance model with a bio-economic herd model that captures local production characteristics as well as heterogeneities in AAT incidence and breed. These models were used to predict the impact of tsetse elimination on the net value of cattle production in the districts of Mambwe, in Zambia, and Faro et DĆ©o in Cameroon. The net value of cattle production under the current situation was used as a baseline, and compared with alternative publicly funded control programmes. In Zambia, the current baseline is AAT control implemented privately by cattle owners (Scenario Z0). In Cameroon, the baseline (Scenario C0) is a small-scale publicly funded tsetse control programme and privately funded control at farm level. The model was run for 10 years, using a discount rate of 5%
Acetazolamide-based fungal chitinase inhibitors
Chitin is an essential structural component of the fungal cell wall. Chitinases are thought to be important for fungal cell wall remodelling, and inhibition of these enzymes has been proposed as a potential strategy for development of novel anti-fungals. The fungal pathogen Aspergillus fumigatus possesses two distinct multi-gene chitinase families. Here we explore acetazolamide as a chemical scaffold for the inhibition of an A. fumigatus āplant-typeā chitinase. A co-crystal structure of AfChiA1 with acetazolamide was used to guide synthesis and screening of acetazolamide analogues that yielded SAR in agreement with these structural data. Although acetazolamide and its analogues are weak inhibitors of the enzyme, they have a high ligand efficiency and as such are interesting leads for future inhibitor development
A model checking approach to the parameter estimation of biochemical pathways
Model checking has historically been an important tool to
verify models of a wide variety of systems. Typically a model has to exhibit
certain properties to be classed āacceptableā. In this work we use
model checking in a new setting; parameter estimation. We characterise
the desired behaviour of a model in a temporal logic property and alter
the model to make it conform to the property (determined through
model checking). We have implemented a computational system called
MC2(GA) which pairs a model checker with a genetic algorithm. To
drive parameter estimation, the fitness of set of parameters in a model is
the inverse of the distance between its actual behaviour and the desired
behaviour. The model checker used is the simulation-based Monte Carlo
Model Checker for Probabilistic Linear-time Temporal Logic with numerical
constraints, MC2(PLTLc). Numerical constraints as well as the
overall probability of the behaviour expressed in temporal logic are used
to minimise the behavioural distance. We define the theory underlying
our parameter estimation approach in both the stochastic and continuous
worlds. We apply our approach to biochemical systems and present
an illustrative example where we estimate the kinetic rate constants in
a continuous model of a signalling pathway
Enteric-Coated Fenoprofen in Large-Joint Osteoarthritis
Enteric-coated fenoprofen was compared with standard fenoprofen (Nalfon, Dista, Indianapolis, IN) in a randomized, double-blind, parallel, three-month trial of 113 outpatients (mean age, 64 years) with large-joint osteoarthritis. A previous study showed that enteric coating of fenoprofen reduces gastrointestinal microbleeding and may offer a safety advantage. Both treatments provided statistically significant improvement in pain measures (tenderness on pressure, pain at rest, pain with weight-bearing activity, and pain on passive motion). Adverse experiences were similar with both treatments and of an expected type, severity, and incidence for nonsteroidal anti-inflammatory drugs. Enteric-coated fenoprofen was found to be as effective and safe as standard fenoprofen for large-joint osteoarthritis
Detecting brute-force attacks on cryptocurrency wallets
Blockchain is a distributed ledger, which is protected against malicious
modifications by means of cryptographic tools, e.g. digital signatures and hash
functions. One of the most prominent applications of blockchains is
cryptocurrencies, such as Bitcoin. In this work, we consider a particular
attack on wallets for collecting assets in a cryptocurrency network based on
brute-force search attacks. Using Bitcoin as an example, we demonstrate that if
the attack is implemented successfully, a legitimate user is able to prove that
fact of this attack with a high probability. We also consider two options for
modification of existing cryptocurrency protocols for dealing with this type of
attacks. First, we discuss a modification that requires introducing changes in
the Bitcoin protocol and allows diminishing the motivation to attack wallets.
Second, an alternative option is the construction of special smart-contracts,
which reward the users for providing evidence of the brute-force attack. The
execution of this smart-contract can work as an automatic alarm that the
employed cryptographic mechanisms, and (particularly) hash functions, have an
evident vulnerability.Comment: 10 pages, 2 figures; published versio
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