4,675 research outputs found
A two parameter ratio-product-ratio estimator using auxiliary information
We propose a two parameter ratio-product-ratio estimator for a finite
population mean in a simple random sample without replacement following the
methodology in Ray and Sahai (1980), Sahai and Ray (1980), Sahai and Sahai
(1985) and Singh and Ruiz Espejo (2003).
The bias and mean square error of our proposed estimator are obtained to the
first degree of approximation. We derive conditions for the parameters under
which the proposed estimator has smaller mean square error than the sample
mean, ratio and product estimators.
We carry out an application showing that the proposed estimator outperforms
the traditional estimators using groundwater data taken from a geological site
in the state of Florida.Comment: 13 pages, 2 figures, 4 table
What Factors are Responsible for Higher Prevalence of HIV Infection among Urban Women than Rural Women in Tanzania?
BACKGROUND: Tanzania is the country hit the hardest by the HIV epidemic in Sub-Saharan Africa. The present study was carried out to examine the factors of HIV infection among women who lived in an urban area in Tanzania.METHODS: The Tanzania HIV/AIDS and Malaria Indicator Survey (2011-12) data was used. The sample size for urban and rural women who had been tested for HIV and ever had sex was 2227 and 6210 respectively. Bivariate and multivariate logistic regression analyses were used.RESULTS: The present study found that rural women were significantly less likely to be HIV-infected compared to urban women (OR = 0.612, p<0.00). About 10% urban women were HIV-infected whereas 5.8% women in rural areas were HIV positive. Women who had more than five sex partners were significantly four times more likely to be HIV-infected as compared to women who had one sex partner (OR = 4.49, p<0.00).CONCLUSION: The results of this study suggest that less-educated women, women belonging to poor or poorer quintile, women spending nights outside and women having more than one sex partner were significantly more likely to have HIV infection among urban women as compared to rural women. There is an urgent need for a short and effective program to control the HIV epidemic in urban areas of Tanzania especially for less-educated urban women.KEYWORDS: Women, Urban, HIV/AIDS, Tanzania, Africa, Monitorin
The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations
The hot Jupiter HD189733b is the most extensively observed exoplanet. Its
atmosphere has been detected and characterised in transmission and eclipse
spectroscopy, and its phase curve measured at several wavelengths. This paper
brings together results of our campaign to obtain the complete transmission
spectrum of the atmosphere of this planet from UV to IR with HST, using STIS,
ACS and WFC3. We provide a new tabulation of the transmission spectrum across
the entire visible and IR range. The radius ratio in each wavelength band was
rederived to ensure a consistent treatment of the bulk transit parameters and
stellar limb-darkening. Special care was taken to correct for, and derive
realistic estimates of the uncertainties due to, both occulted and unocculted
star spots. The combined spectrum is very different from the predictions of
cloud-free models: it is dominated by Rayleigh scattering over the whole
visible and near infrared range, the only detected features being narrow Na and
K lines. We interpret this as the signature of a haze of condensate grains
extending over at least 5 scale heights. We show that a dust-dominated
atmosphere could also explain several puzzling features of the emission
spectrum and phase curves, including the large amplitude of the phase curve at
3.6um, the small hot-spot longitude shift and the hot mid-infrared emission
spectrum. We discuss possible compositions and derive some first-order
estimates for the properties of the putative condensate haze/clouds. We finish
by speculating that the dichotomy between the two observationally defined
classes of hot Jupiter atmospheres, of which HD189733b and HD209458b are the
prototypes, might not be whether they possess a temperature inversion, but
whether they are clear or dusty. We also consider the possibility of a
continuum of cloud properties between hot Jupiters, young Jupiters and L-type
brown dwarfs.Comment: Accepted for publication in MNRAS. 31 pages, 19 figures, 8 table
Seasonal variation of Pneumocystis jirovecii infection: analysis of underlying climatic factors
AbstractPneumocystis jirovecii causes severe pneumonia (PCP) in immunocompromised patients. Seasonal changes of PCP incidence may be associated with climate changes. In this first study using multiple linear regression statistics to assess monthly climatic data and Pneumocystis, PCP incidence was positively correlated with mean temperature, but not with rainfall or wind strength
Possible human-to-human transmission of toxigenic Corynebacterium ulcerans
AbstractToxigenic Corynebacterium ulcerans is an emerging cause of diphtheria. In contrast to the classical diphtheria pathogen C. diphtheriae, human-to-human transmission of this primarily zoonotic pathogen has not been clearly documented. Here we report on a two-person cluster suggesting an initial zoonotic and a subsequent human-to-human transmission event
Heat capacity of the quantum magnet TiOCl
Measurements of the heat capacity C(T,H) of the one-dimensional quantum
magnet TiOCl are presented for temperatures 2K < T < 300K and magnetic fields
up to 5T. Distinct anomalies at 91K and 67K signal two subsequent phase
transitions. The lower of these transitions clearly is of first order and seems
to be related to the spin degrees of freedom. The transition at 92K probably
involves the lattice and/or orbital moments. A detailed analysis of the data
reveals that the entropy change through both transitions is surprisingly small
(~ 0.1R), pointing to the existence strong fluctuations well into the
non-ordered high-temperature phase. No significant magnetic field dependence
was detected.Comment: 4 pages, 2 figure
Photoemission of a doped Mott insulator: spectral weight transfer and qualitative Mott-Hubbard description
The spectral weight evolution of the low-dimensional Mott insulator TiOCl
upon alkali-metal dosing has been studied by photoelectron spectroscopy. We
observe a spectral weight transfer between the lower Hubbard band and an
additional peak upon electron-doping, in line with quantitative expectations in
the atomic limit for changing the number of singly and doubly occupied sites.
This observation is an unconditional hallmark of correlated bands and has not
been reported before. In contrast, the absence of a metallic quasiparticle peak
can be traced back to a simple one-particle effect.Comment: 4 pages, 4 figures, related theoretical work can be found in
arXiv:0905.1276; shortene
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