27,072 research outputs found
Measurement techniques for cryogenic Ka-band microstrip antennas
The measurement of cryogenic antennas poses unique logistical problems since the antenna under test must be embedded in a cooling chamber. A method of measuring the performance of cryogenic microstrip antennas using a closed cycle gas cooled refrigerator in a far field range is described. Antenna patterns showing the performance of gold and superconducting Ka-band microstrip antennas at various temperatures are presented
Air Force Eastern Test Range Central Telemetry Station (TEL-IV)
We have had a vast increase in the amount and rate of data telemetered back to the Eastern Test Range from both missiles and manned and unmanned space vehicles over the past few years.
In 1961, as a major part of the Eastern Test Range Telemetry Modernization Program, development of a new Central Telemetry Station at Kennedy Space Center was initiated. It was designated Telemetry Station IV (TEL-IV), The objectives of the new Central Telemetry Station (TEL-IV) have been established as:
1. Provide simultaneous multiple mission capability for both pre-launch and launch support. 2. Serve as a central telemetry station for receiving , processing, and distributing the telemetered data from remote mobile and landbased stations. 3. Provide minimum turn around time between mission setups and permit rapid equipment changes in the event of failures. 4. Provide real time and non - real time capability to meet all program requirements.
In order to achieve these objectives, the integrated systems design departed from the traditional ground station concept of hard wire or manual patching. Instead, the station was designed .and based on a central control technique. The system setup and equipment assignment for a given mission\u27s support is accomplished automatically by a launch coordinator through a special purpose , wired-program digital data processor and a cross-bar switching network
Staying true with the help of others: doxastic self-control through interpersonal commitment
I explore the possibility and rationality of interpersonal mechanisms of doxastic self-control, that is, ways in which individuals can make use of other people in order to get themselves to stick to their beliefs. I look, in particular, at two ways in which people can make interpersonal epistemic commitments, and thereby willingly undertake accountability to others, in order to get themselves to maintain their beliefs in the face of anticipated “epistemic temptations”. The first way is through the avowal of belief, and the second is through the establishment of collective belief. I argue that both of these forms of interpersonal epistemic commitment can function as effective tools for doxastic self-control, and, moreover, that the control they facilitate should not be dismissed as irrational from an epistemic perspective
Weak ties: Subtle role of information diffusion in online social networks
As a social media, online social networks play a vital role in the social
information diffusion. However, due to its unique complexity, the mechanism of
the diffusion in online social networks is different from the ones in other
types of networks and remains unclear to us. Meanwhile, few works have been
done to reveal the coupled dynamics of both the structure and the diffusion of
online social networks. To this end, in this paper, we propose a model to
investigate how the structure is coupled with the diffusion in online social
networks from the view of weak ties. Through numerical experiments on
large-scale online social networks, we find that in contrast to some previous
research results, selecting weak ties preferentially to republish cannot make
the information diffuse quickly, while random selection can achieve this goal.
However, when we remove the weak ties gradually, the coverage of the
information will drop sharply even in the case of random selection. We also
give a reasonable explanation for this by extra analysis and experiments.
Finally, we conclude that weak ties play a subtle role in the information
diffusion in online social networks. On one hand, they act as bridges to
connect isolated local communities together and break through the local
trapping of the information. On the other hand, selecting them as preferential
paths to republish cannot help the information spread further in the network.
As a result, weak ties might be of use in the control of the virus spread and
the private information diffusion in real-world applications.Comment: Final version published in PR
Inverse Cascade Regime in Shell Models of 2-Dimensional Turbulence
We consider shell models that display an inverse energy cascade similar to
2-dimensional turbulence (together with a direct cascade of an enstrophy-like
invariant). Previous attempts to construct such models ended negatively,
stating that shell models give rise to a "quasi-equilibrium" situation with
equipartition of the energy among the shells. We show analytically that the
quasi-equilibrium state predicts its own disappearance upon changing the model
parameters in favor of the establishment of an inverse cascade regime with K41
scaling. The latter regime is found where predicted, offering a useful model to
study inverse cascades.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Low incidence of toxoplasma infection during pregnancy and in newborns in Sweden
To estimate the burden of disease due to congenital toxoplasmosis in Sweden the incidence of primary infections during pregnancy and birth prevalence of congenital toxoplasmosis in 40978 children born in two regions in Sweden was determined. Women possibly infected during pregnancy were identified based on: 1, detection of specific IgG based on neonatal screening of the phenylketonuria (PKU) card blood spot followed by retrospective testing of stored prenatal samples to detect women who acquired infection during pregnancy and follow up of their children to 12 months; 2, detection of specific IgM on the PKU blood spot. The birth prevalence of congenital toxoplasmosis was 0·73/10000 (95% CI 0·15–2·14) (3/40978). The incidence of primary infection during pregnancy was 5·1/10000 (95% CI 2·6–8·9) susceptible pregnant women. The seroprevalence in the southern part was 25·7% and in the Stockholm area 14·0%. The incidence of infection during pregnancy was low, as the birth prevalence of congenital toxoplasmosis. Neonatal screening warrants consideration in view of the low cost and feasibility
Densest Subgraph in Dynamic Graph Streams
In this paper, we consider the problem of approximating the densest subgraph
in the dynamic graph stream model. In this model of computation, the input
graph is defined by an arbitrary sequence of edge insertions and deletions and
the goal is to analyze properties of the resulting graph given memory that is
sub-linear in the size of the stream. We present a single-pass algorithm that
returns a approximation of the maximum density with high
probability; the algorithm uses O(\epsilon^{-2} n \polylog n) space,
processes each stream update in \polylog (n) time, and uses \poly(n)
post-processing time where is the number of nodes. The space used by our
algorithm matches the lower bound of Bahmani et al.~(PVLDB 2012) up to a
poly-logarithmic factor for constant . The best existing results for
this problem were established recently by Bhattacharya et al.~(STOC 2015). They
presented a approximation algorithm using similar space and
another algorithm that both processed each update and maintained a
approximation of the current maximum density in \polylog (n)
time per-update.Comment: To appear in MFCS 201
An Analytical Construction of the SRB Measures for Baker-type Maps
For a class of dynamical systems, called the axiom-A systems, Sinai, Ruelle
and Bowen showed the existence of an invariant measure (SRB measure) weakly
attracting the temporal average of any initial distribution that is absolutely
continuous with respect to the Lebesgue measure. Recently, the SRB measures
were found to be related to the nonequilibrium stationary state distribution
functions for thermostated or open systems. Inspite of the importance of these
SRB measures, it is difficult to handle them analytically because they are
often singular functions. In this article, for three kinds of Baker-type maps,
the SRB measures are analytically constructed with the aid of a functional
equation, which was proposed by de Rham in order to deal with a class of
singular functions. We first briefly review the properties of singular
functions including those of de Rham. Then, the Baker-type maps are described,
one of which is non-conservative but time reversible, the second has a
Cantor-like invariant set, and the third is a model of a simple chemical
reaction . For the second example, the
cases with and without escape are considered. For the last example, we consider
the reaction processes in a closed system and in an open system under a flux
boundary condition. In all cases, we show that the evolution equation of the
distribution functions partially integrated over the unstable direction is very
similar to de Rham's functional equation and, employing this analogy, we
explicitly construct the SRB measures.Comment: 53 pages, 10 figures, to appear in CHAO
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