3,461 research outputs found
The Galeleo spacecraft magnetometer boom
The Galileo spacecraft utilizes a deployable lattice boom to position three science instruments at remote distances from the spacecraft body. An improved structure and mechanism to precisely control deployment of the boom, and the unique deployment of an outer protective cover are described
Censusing manatees: a report on the feasibility of using aerial surveys and mark and recapture techniques to conduct a population survey of the West Indian Manatee
This report results from an invitation to review the needs and
prospects for capture-recapture and aerial census studies of the
manatee (Trichechus manatus) in Florida. Three aerial reconnaissance flights provided a
first hand view of manatee habitats, as follows: May 3, Suwannee
River to Kings Bay and Crystal River (Rathbun, Eberhardt), May 4,
Vero Beach to Ft. Lauderdale and Ft. Myers by way of Whitewater Bay
(Rose, Percival, Eberhardt), and May 5, Cape Canaveral to Jacksonville,
St. Johns River and Blue Spring (Rose, Kinnaird, Eberhardt). (24 page document
Agricultural development, labour migration, and the resurgence of malaria in Swaziland, 1950-1981
African Studies Seminar series. Paper presented July 1985The introduction of DDT and related pesticides in the war
against malaria in Asia, Africa and Latin America during the
1940s had a dramatic impact on anopheles mosquito populations and consequently on the worldwide incidence of malaria. The
initial success of pesticide spraying created immense optimism on the part of health officials and economic planners. For the
first time, it appeared that malaria, which had had such a
devastating impact on human populations and had retarded economic development in tropical and sub-tropical areas, could be controlled or even eradicated. Thirty years later, however,
malaria has made a major comeback. … The resurgence of malaria in many areas has been linked to the so-called "green-revolution", the development of large scale agricultural projects combined with the extensive use of fertilizers and pesticides to increase agricultural production. The heavy use of pesticides succeeded in controlling some crop destroying peats, however, it had the unforseen consequence of producing DDT resistant strains of anopheles mosquitoes, short circuiting vector control measures and making possible the
recommencement of malaria transmission in areas in which the
disease had been brought under control
Quantum whistling in superfluid 4He
Fundamental considerations predict that macroscopic quantum systems such as
superfluids and the electrons in superconductors will exhibit oscillatory
motion when pushed through a small constriction. Here we report the observation
of these oscillations between two reservoirs of superfluid 4He partitioned by
an array of nanometer-sized apertures. They obey the Josephson frequency
equation and are coherent amongst all the apertures. This discovery at the
relatively high temperature of 2K (2000 times higher than related phenomena in
3He) may pave the way for a new class of practical rotation sensors of
unprecedented precision.Comment: 6 pages, 3 figures, to be published in Natur
Free energy landscapes, dynamics and the edge of chaos in mean-field models of spin glasses
Metastable states in Ising spin-glass models are studied by finding iterative
solutions of mean-field equations for the local magnetizations. Two different
equations are studied: the TAP equations which are exact for the SK model, and
the simpler `naive-mean-field' (NMF) equations. The free-energy landscapes that
emerge are very different. For the TAP equations, the numerical studies confirm
the analytical results of Aspelmeier et al., which predict that TAP states
consist of close pairs of minima and index-one (one unstable direction) saddle
points, while for the NMF equations saddle points with large indices are found.
For TAP the barrier height between a minimum and its nearby saddle point scales
as (f-f_0)^{-1/3} where f is the free energy per spin of the solution and f_0
is the equilibrium free energy per spin. This means that for `pure states', for
which f-f_0 is of order 1/N, the barriers scale as N^{1/3}, but between states
for which f-f_0 is of order one the barriers are finite and also small so such
metastable states will be of limited physical significance. For the NMF
equations there are saddles of index K and we can demonstrate that their
complexity Sigma_K scales as a function of K/N. We have also employed an
iterative scheme with a free parameter that can be adjusted to bring the system
of equations close to the `edge of chaos'. Both for the TAP and NME equations
it is possible with this approach to find metastable states whose free energy
per spin is close to f_0. As N increases, it becomes harder and harder to find
solutions near the edge of chaos, but nevertheless the results which can be
obtained are competitive with those achieved by more time-consuming computing
methods and suggest that this method may be of general utility.Comment: 13 page
Living on the edge of chaos: minimally nonlinear models of genetic regulatory dynamics
Linearized catalytic reaction equations modeling e.g. the dynamics of genetic
regulatory networks under the constraint that expression levels, i.e. molecular
concentrations of nucleic material are positive, exhibit nontrivial dynamical
properties, which depend on the average connectivity of the reaction network.
In these systems the inflation of the edge of chaos and multi-stability have
been demonstrated to exist. The positivity constraint introduces a nonlinearity
which makes chaotic dynamics possible. Despite the simplicity of such minimally
nonlinear systems, their basic properties allow to understand fundamental
dynamical properties of complex biological reaction networks. We analyze the
Lyapunov spectrum, determine the probability to find stationary oscillating
solutions, demonstrate the effect of the nonlinearity on the effective in- and
out-degree of the active interaction network and study how the frequency
distributions of oscillatory modes of such system depend on the average
connectivity.Comment: 11 pages, 5 figure
Genomic organization, expression analysis, and chromosomal localization of the mouse PEX3 gene encoding a peroxisomal assembly protein
The peroxin Pex3p has been identified as an integral peroxisomal membrane protein in yeast where pex3 mutants lack peroxisomal remnant structures. Although not proven in higher organisms, a role of this gene in the early peroxisome biogenesis is suggested, We report here the cDNA cloning and the genomic structure of the mouse PEX3 gene. The 2 kb cDNA encodes a polypeptide of 372 amino acids (42 kDa). The gene spans a region of 30 kb, contains 12 exons and 11 introns and is located on band A of chromosome 10, The putative promoter region exhibits characteristic housekeeping features. PEX3 expression was identified in all tissues analyzed, with the strongest signals in liver and in testis, and could not be induced by fenofibrate. The data presented may be useful for the generation of a mouse model defective in PEX3 in order to clarify the yet unknown functional impact of disturbances in early peroxisomal membrane assembly
POPULATION REGULATION IN WOLVES
The possibility of social regulation of wolf populations has been discussed in the literature for several years. Some of the first ecological studies of wolves indicated that their populations did not increase as rapidly as was theoretically possible, and that they reached a saturation point apparently not set by food. Subsequent captive studies demonstrated the existence of social mechanisms possibly capable of regulating population growth. However, the importance of these factors in wild populations has not been established. This paper has four objectives: (1) to evaluate the existing concept of intrinsic limitation, (2) to propose that wolf population dynamics may be better understood by considering feedback between the prey resource and the wolf population, (3) to evaluate group selection explanations regarding evolution of intrinsic limiting mechanisms, and (4) to propose an alternative explanation based on individual selection
Forecasting time series by means of evolutionary algorithms
Proceeding of: 8th International Conference in Parallel Problem Solving from Nature - PPSN VIII , Birmingham, UK, September 18-22, 2004.The time series forecast is a very complex problem, consisting in predicting the behaviour of a data series with only the information of the previous sequence. There is many physical and artificial phenomenon that can be described by time series. The prediction of such phenomenon could be very complex. For instance, in the case of tide forecast, unusually high tides, or sea surges, result from a combination of chaotic climatic elements in conjunction with the more normal, periodic, tidal systems associated with a particular area. Too much variables influence the behaviour of the water level. Our problem is not only to find prediction rules, we also need to discard the noise and select the representative data. Our objective is to generate a set of prediction rules. There are many methods tying to achieve good predictions. In most of the cases this methods look for general rules that are able to predict the whole series. The problem is that usually the time series has local behaviours that dont allow a good level of prediction when using general rules. In this work we present a method for finding local rules able to predict only some zones of the series but achieving better level prediction. This method is based on the evolution of set of rules genetically codified, and following the Michigan approach. For evaluating the proposal, two different domains have been used: an artificial domain widely use in the bibliography (Mackey-Glass series) and a time series corresponding to a natural phenomenon, the water level in Venice Lagoon.Investigation supported by the Spanish Ministry of Science and Technology through the TRACER project under contract TIC2002-04498-C05-
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