1,428 research outputs found
Studies On The Lagoons Of East Centeral Florida
Detailed examination of the water quality parameters of the lagoons of East Central Florida were begun in 1969. This investigation was subsequently expanded to include other aspects of these waters. General trends and a statistical model are beginning to emerge for the water quality parameters. Man-made and natural effects have resulted in substantial alteration of water parameters since the study was initiated
An Ecological Study of the Lagoons Surrounding the John F. Kennedy Space Center, Brevard County, Florida
The studies reported here are the result of a three year effort to define the major biological, microbiological, chemical and geological characteristics of the water of the Indian River lagoon around the Kennedy Space Center and to determine the movements of those waters within and between the various basins. This work was the result of a jointly funded agreement between the Florida Institute of Technology and John F. Kennedy Space Center, NASA under NASA Grant NGR 10-015-008, dated April 11, 1972. This cost sharing grant was renewed for each of two successive years. Sampling operations were terminated August 31, 1975
Spectra and Light Curves of Failed Supernovae
Astronomers have proposed a number of mechanisms to produce supernova
explosions. Although many of these mechanisms are now not considered primary
engines behind supernovae, they do produce transients that will be observed by
upcoming ground-based surveys and NASA satellites. Here we present the first
radiation-hydrodynamics calculations of the spectra and light curves from three
of these "failed" supernovae: supernovae with considerable fallback, accretion
induced collapse of white dwarfs, and energetic helium flashes (also known as
type .Ia supernovae).Comment: 33 pages, 14 figure
A declining major merger fraction with redshift in the local Universe from the largest-yet catalog of major and minor mergers in SDSS
It is difficult to accurately identify galaxy mergers and it is an even
larger challenge to classify them by their mass ratio or merger stage. In
previous work we used a suite of simulated mergers to create a classification
technique that uses linear discriminant analysis (LDA) to identify major and
minor mergers. Here, we apply this technique to 1.3 million galaxies from the
SDSS DR16 photometric catalog and present the probability that each galaxy is a
major or minor merger, splitting the classifications by merger stages (early,
late, post-coalescence). We present publicly-available imaging predictor values
and all of the above classifications for one of the largest-yet samples of
galaxies. We measure the major and minor merger fraction ()
and build a mass-complete sample of galaxies, which we bin as a function of
stellar mass and redshift. For the major mergers, we find a positive slope of
with stellar mass and negative slope of
with redshift between stellar masses of
and redshifts of . We are able to reproduce an artificial
positive slope of the major merger fraction with redshift when we do not bin
for mass or craft a complete sample, demonstrating the importance of mass
completeness and mass binning. We determine that the positive trend of the
major merger fraction with stellar mass is consistent with a hierarchical
assembly scenario. The negative trend with redshift requires that an additional
assembly mechanism, such as baryonic feedback, dominates in the local Universe.Comment: 29 pages, 22 figures, see figures 16 and 17 for a summary of the
findings, accepted to MNRA
An ecological study of the KSC Turning Basin and adjacent waters
The conditions existing in the waters and bottoms of the Turning Basin, the borrow pit near Pad 39A, and the Barge Canal connecting them were investigated to determine the ecological significance of the chemical, biological, and microbiological parameters. The water quality, biological, microbiological findings are discussed. It is recommended that future dredging activities be limited in depth, and that fill materials should not be removed down to the clay strata
Antigen-Independent Maturation of CD2, CD11a/CD18, CD44, and CD58 Expression on Thymic Emigrants in Fetal and Postnatal Sheep
We have compared the expression of CD2, CD11a/CD18, CD44, and CD58 on αβ and γδ
T cells emigrating from the fetal and postnatal thymus. We report that both γδ and the
CD4+ CD8- and CD4-CD8+ subsets of αβ T cells express mature levels of the adhesion
molecules CD11a/CD18, CD44, and CD58 upon emigration from the thymus. Whereas
CD44 is up-regulated on γδ+ thymocytes prior to export, down-regulation of both
CD11a/CD18 and CD58 occurs prior to emigration from the thymus, suggesting that
down-regulation of these molecules may be a final maturational step taken by developing
γδ T cells before their export from the thymus. In contrast, there is continued up-regulation
of CD2 on αβ and γδ T cells upon emigration from the thymus and as they move into the
mature peripheral T-cell pool. There was also a marked reduction in the number of CD2+
γδ T cells exported during fetal development that was associated with a marked reduction
in the percentage of CD22+ γδ thymocytes exported. The postthymic maturation of CD2 and
the other changes in adhesion-molecule expression appear to be independent of extrinsic
antigen, as the same changes were observed in the antigen-free environment of the fetus
as in the postnatal lamb, which has been exposed to extrinsic antigen. It thus appears that
these changes in adhesion-molecule expression are as a result of the normal maturation
pathway from a developing thymocyte to a mature peripheral T cell
Nonlinear Saturation of g-modes in Proto-Neutron Stars: Quieting the Acoustic Engine
According to Burrows et al.'s acoustic mechanism for core-collapse supernova
explosions, the primary, l=1, g-mode in the core of the proto-neutron star is
excited to an energy of ~ 10^{50} ergs and damps by the emission of sound
waves. Here we calculate the damping of the primary mode by the parametric
instability, i.e., by nonlinear, 3-mode coupling between the low-order primary
mode and pairs of high-order g-modes. We show that the primary mode is strongly
coupled to highly resonant, neutrino damped pairs with n>10; such short
wavelength interactions cannot be resolved in the simulations. We find that the
parametric instability saturates the primary mode energy at ~10^{48} ergs, well
below the energy needed to drive an explosion. We therefore conclude that
acoustic power is unlikely to be energetically significant in core-collapse
supernova explosions.Comment: 6 pages, 3 figures, fixed minor typos, matches version published in
MNRAS Letter
Efficacy of an 8-Week Concurrent Strength and Endurance Training Programme on Hand Cycling Performance
The aim of the present study was to investigate the effects of an 8-week concurrent strength and endurance training programme in comparison to endurance training only on several key determinants of hand cycling performance. Five H4 and five H3 classified hand cyclists with at least one year’s hand cycling training history consented to participate in the study. Subjects underwent a battery of tests to establish body mass, body composition, VO2peak, maximum aerobic power, gross mechanical efficiency, maximal upper body strength, and 30 km time trial performance. Subjects were matched into pairs based upon 30 km time trial performance and randomly allocated to either a concurrent strength and endurance or endurance training only, intervention group. Following an 8-week training programme based upon a conjugated block periodisation model, subjects completed a second battery of tests. A mixed model, 2-way analysis of variance (ANOVA) revealed no significant changes between groups. However, the calculation of effect sizes (ES) revealed that both groups demonstrated a positive improvement in most physiological and performance measures with subjects in the concurrent group demonstrating a greater magnitude of improvement in body composition (ES -0.80 vs. -0.22) maximal aerobic power (ES 0.97 vs. 0.28), gross mechanical efficiency (ES 0.87 vs. 0.63), bench press 1 repetition maximum (ES 0.53 vs. 0.33), seated row 1 repetition maximum (ES 1.42 vs. 0.43), and 30 km time trial performance (ES -0.66 vs. -0.30). In comparison to endurance training only, an 8-week concurrent training intervention based upon a conjugated block periodisation model appears to be a more effective training regime for improving the performance capabilities of hand cyclists
Techniques for applying reinforcement learning to routing and wavelength assignment problems in optical fiber communication networks
We propose a novel application of reinforcement learning (RL) with invalid action masking and a novel training methodology for routing and wavelength assignment (RWA) in fixed-grid optical networks and demonstrate the generalizability of the learned policy to a realistic traffic matrix unseen during training. Through the introduction of invalid action masking and a new training method, the applicability of RL to RWA in fixed-grid networks is extended from considering connection requests between nodes to servicing demands of a given bit rate, such that lightpaths can be used to service multiple demands subject to capacity constraints. We outline the additional challenges involved for this RWA problem, for which we found that standard RL had low performance compared to that of baseline heuristics, in comparison with the connection requests RWA problem considered in the literature. Thus, we propose invalid action masking and a novel training method to improve the efficacy of the RL agent. With invalid action masking, domain knowledge is embedded in the RL model to constrain the action space of the RL agent to lightpaths that can support the current request, reducing the size of the action space and thus increasing the efficacy of the agent. In the proposed training method, the RL model is trained on a simplified version of the problem and evaluated on the target RWA problem, increasing the efficacy of the agent compared with training directly on the target problem. RL with invalid action masking and this training method outperforms standard RL and three state-of-the-art heuristics, namely, k shortest path first fit, first-fit k shortest path, and k shortest path most utilized, consistently across uniform and nonuniform traffic in terms of the number of accepted transmission requests for two real-world core topologies, NSFNET and COST - 239. The RWA runtime of the proposed RL model is comparable to that of these heuristic approaches, demonstrating the potential for real-world applicability. Moreover, we show that the RL agent trained on uniform traffic is able to generalize well to a realistic nonuniform traffic distribution not seen during training, thus outperforming the heuristics for this traffic. Visualization of the learned RWA policy reveals an RWA strategy that differs significantly from those of the heuristic baselines in terms of the distribution of services across channels and the distribution across links
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