2,439 research outputs found
Concepts for manned lunar habitats
The design philosophy that will guide the design of early lunar habitats will be based on a compromise between the desired capabilities of the base and the economics of its development and implantation. Preferred design will be simple, make use of existing technologies, require the least amount of lunar surface preparation, and minimize crew activity. Three concepts for an initial habitat supporting a crew of four for 28 to 30 days are proposed. Two of these are based on using Space Station Freedom structural elements modified for use in a lunar-gravity environment. A third concept is proposed that is based on an earlier technology based on expandable modules. The expandable modules offer significant advantages in launch mass and packaged volume reductions. It appears feasible to design a transport spacecraft lander that, once landed, can serve as a habitat and a stand-off for supporting a regolith environmental shield. A permanent lunar base habitat supporting a crew of twelve for an indefinite period can be evolved by using multiple initial habitats. There appears to be no compelling need for an entirely different structure of larger volume and increased complexity of implantation
Median Statistics, H_0, and the Accelerating Universe
(Abridged) We develop median statistics that provide powerful alternatives to
chi-squared likelihood methods and require fewer assumptions about the data.
Applying median statistics to Huchra's compilation of nearly all estimates of
the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics
assume only that the measurements are independent and free of systematic
errors. This estimate is arguably the best summary of current knowledge because
it uses all available data and, unlike other estimates, makes no assumption
about the distribution of measurement errors. The 95% range of purely
statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result
leads us to analyze the range of possible systematic errors in the median,
which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over
the statistical errors. A Bayesian median statistics treatment of high-redshift
Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess
et al. yields a posterior probability that the cosmological constant Lambda > 0
of 70 or 89%, depending on the prior information used. The posterior
probability of an open universe is about 47%. Analysis of the Perlmutter et al.
high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the
best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al.
odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe
Ia data do not rule out a time-variable Lambda model, and may even favor it
over a time-independent Lambda and a Lambda = 0 open model.Comment: Significant revisions include discussion of systematic errors in the
median of H_0. Accepted for publication in The Astrophysical Journal, v548,
February 20, 2001 issue. 47 pages incl. figures and table
Metal Enrichment of the Intergalactic Medium in Cosmological Simulations
Observations have established that the diffuse intergalactic medium (IGM) at
z ~ 3 is enriched to ~0.1-1% solar metallicity and that the hot gas in large
clusters of galaxies (ICM) is enriched to 1/3-1/2 solar metallicity at z=0.
Metals in the IGM may have been removed from galaxies (in which they presumably
form) during dynamical encounters between galaxies, by ram-pressure stripping,
by supernova-driven winds, or as radiation-pressure driven dust efflux. This
study develops a method of investigating the chemical enrichment of the IGM and
of galaxies, using already completed cosmological simulations. To these
simulations, we add dust and (gaseous) metals, distributing the dust and metals
in the gas according to three simple parameterized prescriptions, one for each
enrichment mechanism. These prescriptions are formulated to capture the basic
ejection physics, and calibrated when possible with empirical data. Our results
indicate that dynamical removal of metals from >~ 3*10^8 solar mass galaxies
cannot account for the observed metallicity of low-column density Ly-alpha
absorbers, and that dynamical removal from >~ 3*10^10 solar mass galaxies
cannot account for the ICM metallicities. Dynamical removal also fails to
produce a strong enough mass-metallicity relation in galaxies. In contrast,
either wind or radiation-pressure ejection of metals from relatively large
galaxies can plausibly account for all three sets of observations (though it is
unclear whether metals can be distributed uniformly enough in the low-density
regions without overly disturbing the IGM, and whether clusters can be enriched
quite as much as observed). We investigate in detail how our results change
with variations in our assumed parameters, and how results for the different
ejection processes compare. (Abridged)Comment: Minor revision, 1 figure added addressing diffusion of metals after
their ejection. Accepted by ApJ. 31 EmulateApj Pages with 13 embedded
postscript figure
Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports
We demonstrate a new class of hollow-core Bragg fibers that are composed of
concentric cylindrical silica rings separated by nanoscale support bridges. We
theoretically predict and experimentally observe hollow-core confinement over
an octave frequency range. The bandwidth of bandgap guiding in this new class
of Bragg fibers exceeds that of other hollow-core fibers reported in the
literature. With only three rings of silica cladding layers, these Bragg fibers
achieve propagation loss of the order of 1 dB/m.Comment: 9 pages including 5 figure
Method of providing a lunar habitat from an external tank
A lunar habitat is provided by placing an external tank of an orbiter in a low Earth orbit where the hydrogen tank is separated from the intertank and oxygen tank which form a base structure. The base structure is then outfitted with an air lock, living quarters, a thermal control system, an environmental control and life support system, and a propulsion system. After the mounting of an outer sheath about the base structure to act as a micrometeoroid shield, the base structure is propelled to a soft landing on the moon. The sheath is mounted at a distance from the base structure to provide a space therebetween which is filled with regolith after landing. Conveniently, a space station is used to outfit the base structure. Various elements of the oxygen tank and intertank are used in outfitting
Individual and collective stock dynamics: intra-day seasonalities
We establish several new stylised facts concerning the intra-day
seasonalities of stock dynamics. Beyond the well known U-shaped pattern of the
volatility, we find that the average correlation between stocks increases
throughout the day, leading to a smaller relative dispersion between stocks.
Somewhat paradoxically, the kurtosis (a measure of volatility surprises)
reaches a minimum at the open of the market, when the volatility is at its
peak. We confirm that the dispersion kurtosis is a markedly decreasing function
of the index return. This means that during large market swings, the
idiosyncratic component of the stock dynamics becomes sub-dominant. In a
nutshell, early hours of trading are dominated by idiosyncratic or sector
specific effects with little surprises, whereas the influence of the market
factor increases throughout the day, and surprises become more frequent.Comment: 9 pages, 7 figure
Schistosoma haematobium and soil-transmitted Helminths in Tana Delta District of Kenya:infection and morbidity patterns in primary schoolchildren from two isolated villages
BACKGROUND: Schistosomes and soil-transmitted helminths (STH) (hookworm, Trichuris trichiura and Ascaris lumbricoides) are widely distributed in developing countries where they infect over 230 million and 1.5 billion people, respectively. The parasites are frequently co-endemic and many individuals are co-infected with two or more of the species, but information on how the parasites interact in co-infected individuals is scarce. The present study assessed Schistosoma haematobium and STH infection and morbidity patterns among school children in a hyper-endemic focus in the Tana River delta of coastal Kenya. METHODS: Two hundred and sixty-two children aged 5–12 years from two primary schools were enrolled in the study. For each child, urine was examined for S. haematobium eggs and haematuria, stool was examined for STH eggs, peripheral blood was examined for eosinophilia and haemoglobin level, the urinary tract was ultrasound-examined for S. haematobium-related pathology, and the height and weight was measured and used to calculate the body mass index (BMI). RESULTS: Prevalences of S. haematobium, hookworm, T. trichiura and A. lumbricoides infection were 94, 81, 88 and 46 %, respectively. There was no significant association between S. haematobium and STH infection but intensity of hookworm infection significantly increased with that of T. trichiura. Lower BMI scores were associated with high intensity of S. haematobium (difference =−0.48, p > 0.05) and A. lumbricoides (difference =−0.67, p < 0.05). Haematuria (both macro and micro) was common and associated with S. haematobium infection, while anaemia was associated with high intensity of S. haematobium (OR = 2.08, p < 0.05) and high hookworm infections OR = 4.75; p < 0.001). The majority of children had eosinophilia, which was significantly associated with high intensity of hookworm infection (OR = 5.34, p < 0.05). Overall 38 % of the children had ultrasound-detectable urinary tract morbidity, which was associated with high intensity of S. haematobium infection (OR = 3.13, p < 0.05). CONCLUSION: Prevalences of S. haematobium and STH infections among the primary school children were high and the parasites were responsible for significant morbidity. A clear synergistic interaction was observed between hookworm and T. trichiura infections. Increased coverage in administration of praziquantel and albendazole in the area is recommended to control morbidity due to these infections
Inclusão, democracia e novo-desenvolvimentismo : um balanço histórico
Este trabalho analisa o processo do desenvolvimentismo brasileiro compreendido entre a fase clássica dos anos 1950 até a perspectiva atual do novo-desenvolvimentismo, privilegiando o papel e a função desempenhadas pelo tema da democracia e da inclusão distributiva em cada arranjo. Na primeira seção, analisa-se a constelação semântica que envolve os termos progresso e desenvolvimento, procurando separá-los do processo/projeto denominado desenvolvimentismo. Na segunda seção, discutem-se as fases e características centrais do velho e do novo-desenvolvimentismo brasileiro e a perspectiva de sua subdivisão em três ondas históricas, separadas pelo aspecto político democrático e pelo tema da redistribuição. Por último, apresentam-se algumas considerações sobre o novo-desenvolvimentismo em seu arranjo democrático-inclusivo.This paper analyzes the process of the Brazilian developmentalism between the classical phase of the 1950s to the current perspective of new developmentalism, emphasizing the role and function played by the theme of democracy and distributive inclusion in every arrangement. In the first section, it is analyzed the semantic constellation involving the terms progress and development, seeking to separate them from the process / project called developmentalism. In the second section, it is discussed the phases and the central features of the old and the new Brazilian developmentalism and the prospect of their subdivision into three historical waves, separated by the political democratic aspect and by the theme of redistribution. Finally it presents some considerations about the new developmentalism in its democratic-inclusive arrangement
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