168,832 research outputs found
An apertureless near-field microscope for fluorescence imaging
We describe an apertureless near field microscope for imaging fluorescent samples. Optical contrast is generated by exploiting fluorescent quenching near a metallized atomic force microscope tip. This microscope has been used to image fluorescent latex beads with subdiffraction limit resolution. The use of fluorescence allows us to prove that the contrast mechanism is indeed spectroscopic in origin
Phase Diagram of a 2D Vertex Model
Phase diagram of a symmetric vertex model which allows 7 vertex
configurations is obtained by use of the corner transfer matrix renormalization
group (CTMRG), which is a variant of the density matrix renormalization group
(DMRG). The critical indices of this model are identified as and
.Comment: 2 pages, 5 figures, short not
Fecal contamination of drinking-water in low- and middle-income countries: a systematic review and meta-analysis
Background: access to safe drinking-water is a fundamental requirement for good health and is also a human right. Global access to safe drinking-water is monitored by WHO and UNICEF using as an indicator “use of an improved source,” which does not account for water quality measurements. Our objectives were to determine whether water from “improved” sources is less likely to contain fecal contamination than “unimproved” sources and to assess the extent to which contamination varies by source type and setting.Methods and findings: studies in Chinese, English, French, Portuguese, and Spanish were identified from online databases, including PubMed and Web of Science, and grey literature. Studies in low- and middle-income countries published between 1990 and August 2013 that assessed drinking-water for the presence of Escherichia coli or thermotolerant coliforms (TTC) were included provided they associated results with a particular source type. In total 319 studies were included, reporting on 96,737 water samples. The odds of contamination within a given study were considerably lower for “improved” sources than “unimproved” sources (odds ratio [OR] = 0.15 [0.10–0.21], I2 = 80.3% [72.9–85.6]). However over a quarter of samples from improved sources contained fecal contamination in 38% of 191 studies. Water sources in low-income countries (OR = 2.37 [1.52–3.71]; p<0.001) and rural areas (OR = 2.37 [1.47–3.81] p<0.001) were more likely to be contaminated. Studies rarely reported stored water quality or sanitary risks and few achieved robust random selection. Safety may be overestimated due to infrequent water sampling and deterioration in quality prior to consumption.Conclusion: access to an “improved source” provides a measure of sanitary protection but does not ensure water is free of fecal contamination nor is it consistent between source types or settings. International estimates therefore greatly overstate use of safe drinking-water and do not fully reflect disparities in access. An enhanced monitoring strategy would combine indicators of sanitary protection with measures of water qualit
Global Hilbert Expansion for the Vlasov-Poisson-Boltzmann System
We study the Hilbert expansion for small Knudsen number for the
Vlasov-Boltzmann-Poisson system for an electron gas. The zeroth order term
takes the form of local Maxwellian: $ F_{0}(t,x,v)=\frac{\rho_{0}(t,x)}{(2\pi
\theta_{0}(t,x))^{3/2}} e^{-|v-u_{0}(t,x)|^{2}/2\theta_{0}(t,x)},\text{\
}\theta_{0}(t,x)=K\rho_{0}^{2/3}(t,x).t=0u_00\leq t\leq \varepsilon
^{-{1/2}\frac{2k-3}{2k-2}},\rho_{0}(t,x) u_{0}(t,x)\gamma=5/3$
350 Micron Observations of Ultraluminous Infrared Galaxies at Intermediate Redshifts
We present 350micron observations of 36 ultraluminous infrared galaxies
(ULIRGs) at intermediate redshifts (0.089 <= z <= 0.926) using the
Submillimeter High Angular Resolution Camera II (SHARC-II) on the Caltech
Submillimeter Observatory (CSO). In total, 28 sources are detected at S/N >= 3,
providing the first flux measurements longward of 100micron for a statistically
significant sample of ULIRGs in the redshift range of 0.1 < z < 1.0. Combining
our 350micron flux measurements with the existing IRAS 60 and 100micron data,
we fit a single-temperature model to the spectral energy distribution (SED),
and thereby estimate dust temperatures and far-IR luminosities. Assuming an
emissivity index of beta = 1.5, we find a median dust temperature and far-IR
luminosity of Td = 42.8+-7.1K and log(Lfir/Lsolar) = 12.2+-0.5, respectively.
The far-IR/radio correlation observed in local star-forming galaxies is found
to hold for ULIRGs in the redshift range 0.1 < z < 0.5, suggesting that the
dust in these sources is predominantly heated by starbursts. We compare the
far-IR luminosities and dust temperatures derived for dusty galaxy samples at
low and high redshifts with our sample of ULIRGs at intermediate redshift. A
general Lfir-Td relation is observed, albeit with significant scatter, due to
differing selection effects and variations in dust mass and grain properties.
The relatively high dust temperatures observed for our sample compared to that
of high-z submillimeter-selected starbursts with similar far-IR luminosities
suggest that the dominant star formation in ULIRGs at moderate redshifts takes
place on smaller spatial scales than at higher redshifts.Comment: (24 pages in preprint format, 1 table, 7 figures, accepted for
publication in ApJ
Quality assessment of two- and three-dimensional unstructured meshes and validation of an upwind Euler flow solver
Quality assessment procedures are described for two-dimensional and three-dimensional unstructured meshes. The procedures include measurement of minimum angles, element aspect ratios, stretching, and element skewness. Meshes about the ONERA M6 wing and the Boeing 747 transport configuration are generated using an advancing front method grid generation package of programs. Solutions of Euler's equations for these meshes are obtained at low angle-of-attack, transonic conditions. Results for these cases, obtained as part of a validation study demonstrate the accuracy of an implicit upwind Euler solution algorithm
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