2,798 research outputs found
Electronics systems test laboratory testing of shuttle communications systems
Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail
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Discharge-generated electrical fields and electrical tree structures
The discharge-avalanche (D-A) model for electrical tree propagation in polymers is founded entirely upon basic physical concepts. Electrical discharges in an existing tree structure are taken to raise the electrical field in the polymer both along the discharge path and particularly at the tree tips. As a result of the field increase, electron multiplication avalanches occur within the polymer causing damage, possibly through ionisation of polymer molecules, which is accumulated over a period of thousands (or more) cycles and eventually leads to a tree extension of limited size. The assumption that the damage produced in an avalanche is proportional to the number of ionisations allows the model to be expressed quantitatively in terms of material properties: such as the ionisation potential, I; the impact-ionisation length parameter λ; the critical number of ionisations for tree extension Nc; discharge features such as the number of 1-electron initiated avalanches per half cycle, Nb ; and the potential difference ÎV between the start and end of the avalanche over a distance Lb
Food Safety and Functionality Assessment of Kombucha Systems Through Bacillus cereus Spore and Probiotic Inoculations
Kombucha is a SCOBY-fermented tea beverage known for its taste, sensorial qualities, and high endogenous microbial load. In recent years, kombucha has become a popular functional food with a compound annual growth rate of 25% from 2015 to 2020 in American kombucha sales alone, and sales are predicted to keep increasing significantly over the next decade. However, kombucha is lacking in scientific research, and there is still much to be explored regarding its safety and native probiotic content. This research looked into the various routes of contamination of several kombucha systems as well as the feasibility of the producing a kombucha beverage with health-promoting characteristics derived from the inclusion of lactic probiotics.
Although bacterial spore contamination and survival in the kombucha SCOBY have been documented, it is unknown whether spores can survive in the liquid, or whether they can be transmitted to daughter SCOBYs. The foodborne pathogen and spore-former Bacillus cereus was inoculated into the SCOBY, unfermented liquid, and fermented liquid of three different kombucha systems. Data suggest that neither the route of contamination nor the kombucha system influenced the transmission or survival of B. cereus spores. The spread of the spores between culture and liquid across generation was shown to be sporadic but possible, so hygienic handling of kombucha cultures and raw materials throughout the entire production process is crucial to prevent uptake of pathogenic organisms. There was no survival of B. cereus spores after short-term storage or secondary fermentation, indicating that implementation of a holding step may mitigate potential food safety threats.
Kombucha is perceived to contain probiotics, but not all live cultures comprise probiotics. Some commercial kombucha products have validated probiotic strains added to them post-fermentation, but this can be costly. If probiotics, such as lactic acid bacteria, are inoculated into sweet tea prior to fermentation, they may be able to acidify the tea, replacing the need for utilizing previous kombucha or acetic acid, or survive and/or produce beneficial metabolites during fermentation in great enough amounts to convey a health benefit upon consumption. The survivability of six probiotic Lactobacillus sp. in acidified, sweetened tea at 25ÂșC during kombucha fermentation was established, and the medium (tea) and temperature (25ÂșC) were both revealed to affect the growth rates of the bacteria. Differences in pH indicated that the probiotics were unable to acidify the tea pre-fermentation. Although survival during fermentation was possible for four out of the six probiotics, it was concluded that probiotic Lactobacillus sp. are not well suited for a probiotic kombucha beverages, but out of the tested probiotics, Lactobacillus brevis and Lactobacillus fermentum were the most promising candidates
Convergence of CI single center calculations of positron-atom interactions
The Configuration Interaction (CI) method using orbitals centered on the
nucleus has recently been applied to calculate the interactions of positrons
interacting with atoms. Computational investigations of the convergence
properties of binding energy, phase shift and annihilation rate with respect to
the maximum angular momentum of the orbital basis for the e^+Cu and PsH bound
states, and the e^+-H scattering system were completed. The annihilation rates
converge very slowly with angular momentum, and moreover the convergence with
radial basis dimension appears to be slower for high angular momentum. A number
of methods of completing the partial wave sum are compared, an approach based
on a Delta X_J = a/(J + 1/2)^n + b/(J + 1/2)^(n+1) form (with n = 4 for phase
shift (or energy) and n = 2 for the annihilation rate) seems to be preferred on
considerations of utility and underlying physical justification.Comment: 23 pages preprint RevTeX, 11 figures, submitted to PR
The periodic standing-wave approximation: eigenspectral computations for linear gravity and nonlinear toy models
The periodic standing wave approach to binary inspiral assumes rigid rotation
of gravitational fields and hence helically symmetric solutions. To exploit the
symmetry, numerical computations must solve for ``helical scalars,'' fields
that are functions only of corotating coordinates, the labels on the helical
Killing trajectories. Here we present the formalism for describing linearized
general relativity in terms of helical scalars and we present solutions to the
mixed partial differential equations of the linearized gravity problem (and to
a toy nonlinear problem) using the adapted coordinates and numerical techniques
previously developed for scalar periodic standing wave computations. We argue
that the formalism developed may suffice for periodic standing wave
computations for post-Minkowskian computations and for full general relativity.Comment: 21 pages, 10 figures, RevTe
The periodic standing-wave approximation: post-Minkowski computation
The periodic standing wave method studies circular orbits of compact objects
coupled to helically symmetric standing wave gravitational fields. From this
solution an approximation is extracted for the strong field, slowly
inspiralling motion of black holes and binary stars. Previous work on this
model has dealt with nonlinear scalar models, and with linearized general
relativity. Here we present the results of the method for the post-Minkowski
(PM) approximation to general relativity, the first step beyond linearized
gravity. We compute the PM approximation in two ways: first, via the standard
approach of computing linearized gravitational fields and constructing from
them quadratic driving sources for second-order fields, and second, by solving
the second-order equations as an ``exact'' nonlinear system. The results of
these computations have two distinct applications: (i) The computational
infrastructure for the ``exact'' PM solution will be directly applicable to
full general relativity. (ii) The results will allow us to begin supplying
initial data to collaborators running general relativistic evolution codes.Comment: 19 pages, 3 figures, 1 table, RevTe
Observational evidence for stochastic biasing
We show that the galaxy density in the Las Campanas Redshift Survey (LCRS)
cannot be perfectly correlated with the underlying mass distribution since
various galaxy subpopulations are not perfectly correlated with each other,
even taking shot noise into account. This rules out the hypothesis of simple
linear biasing, and suggests that the recently proposed stochastic biasing
framework is necessary for modeling actual data.Comment: 4 pages, with 2 figures included. Minor revisions to match accepted
ApJL version. Links and color fig at
http://www.sns.ias.edu/~max/r_frames.html or from [email protected]
Models of helically symmetric binary systems
Results from helically symmetric scalar field models and first results from a
convergent helically symmetric binary neutron star code are reported here;
these are models stationary in the rotating frame of a source with constant
angular velocity omega. In the scalar field models and the neutron star code,
helical symmetry leads to a system of mixed elliptic-hyperbolic character. The
scalar field models involve nonlinear terms that mimic nonlinear terms of the
Einstein equation. Convergence is strikingly different for different signs of
each nonlinear term; it is typically insensitive to the iterative method used;
and it improves with an outer boundary in the near zone. In the neutron star
code, one has no control on the sign of the source, and convergence has been
achieved only for an outer boundary less than approximately 1 wavelength from
the source or for a code that imposes helical symmetry only inside a near zone
of that size. The inaccuracy of helically symmetric solutions with appropriate
boundary conditions should be comparable to the inaccuracy of a waveless
formalism that neglects gravitational waves; and the (near zone) solutions we
obtain for waveless and helically symmetric BNS codes with the same boundary
conditions nearly coincide.Comment: 19 pages, 7 figures. Expanded version of article to be published in
Class. Quantum Grav. special issue on Numerical Relativit
Planet formation around low mass stars: the moving snow line and super-Earths
We develop a semi-analytic model for planet formation during the pre-main
sequence contraction phase of a low mass star. During this evolution, the
stellar magnetosphere maintains a fixed ratio between the inner disk radius and
the stellar radius. As the star contracts at constant effective temperature,
the `snow line', which separates regions of rocky planet formation from regions
of icy planet formation, moves inward. This process enables rapid formation of
icy protoplanets that collide and merge into super-Earths before the star
reaches the main sequence. The masses and orbits of these super-Earths are
consistent with super-Earths detected in recent microlensing experiments.Comment: accepted by ApJ Letter
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