4,268 research outputs found
Dynamic Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions
Precisely engineered tunnel junctions exhibit a long sought effect that
occurs when the energy of the electron is comparable to the potential energy of
the tunneling barrier. The resistance of metal-insulator-metal tunnel junctions
oscillates with an applied voltage when electrons that tunnel directly into the
barrier's conduction band interfere upon reflection at the classical turning
points: the insulator-metal interface, and the dynamic point where the incident
electron energy equals the potential barrier inside the insulator. A model of
tunneling between free electron bands using the exact solution of the
Schroedinger equation for a trapezoidal tunnel barrier qualitatively agrees
with experiment.Comment: 4pgs, 3 fig
The Advantage of Increased Resolution in the Study of Quasar Absorption Systems
We compare a new R = 120,000 spectrum of PG1634+706 (z_QSO = 1.337,m_V =
14.9) obtained with the HDS instrument on Subaru to a R = 45, 000 spectrum
obtained previously with HIRES/Keck. In the strong MgII system at z = 0.9902
and the multiple cloud, weak MgII system at z = 1.0414, we find that at the
higher resolution, additional components are resolved in a blended profile. We
find that two single-cloud weak MgII absorbers were already resolved at R =
45,000, to have b = 2 - 4 km/s. The narrowest line that we measure in the R =
120, 000 spectrum is a component of the Galactic NaI absorption, with b =
0.90+/-0.20 km/s. We discuss expectations of similarly narrow lines in various
applications, including studies of DLAs, the MgI phases of strong MgII
absorbers, and high velocity clouds. By applying Voigt profile fitting to
synthetic lines, we compare the consistency with which line profile parameters
can be accurately recovered at R = 45,000 and R = 120,000. We estimate the
improvement gained from superhigh resolution in resolving narrowly separated
velocity components in absorption profiles. We also explore the influence of
isotope line shifts and hyperfine splitting in measurements of line profile
parameters, and the spectral resolution needed to identify these effects. Super
high resolution spectra of quasars, which will be routinely possible with
20-meter class telescopes, will lead to greater sensitivity for absorption line
surveys, and to determination of more accurate physical conditions for cold
phases of gas in various environments.Comment: To appear in AJ. Paper with better resolution images available at
http://www.astro.psu.edu/users/anand/superhigh.AJ.pd
PREPARATION OF CHITOSAN-TPP NANOPARTICLES: THE INFLUENCE OF CHITOSAN POLYMERIC PROPERTIES AND FORMULATION VARIABLES
Objective: The aim of this work was to prepare chitosan nanoparticles (CS NPs) using sodium tripolyphosphate (TPP) as crosslinker and to study the effect of chitosan polymeric properties and experimental conditions on the properties and stability of NPs.Methods: CS NPs were prepared by ionic gelation method, using TPP as a crosslinker. The particle size (PS), polydispersity index (PDI), zeta potential (ZP) and the morphologies of the NPs were studied. CS NPs prepared by varying the concentration of TPP, Chitosan molecular weight and its degree of deacetylation, the stirring speed, the rate of TPP addition and the freeze-drying method to study the effect of these variables on the NPs. The stability of the CS NPs was evaluated by storing aqueous suspensions of NPs and comparing the PS, PDI and ZP at the beginning and the end of the experiment.Results: This study shows that the PS, ZP and dispersity of the NPs depend on the chitosan polymeric properties and experimental conditions. The NPs sizes range between 145.73 and 724.23 nm. They all carried positive charges ranging between+4.32 and+43.67 mV. Most of the NPs have the same sizes after freeze-drying, but showed higher monodispersity and ZP, indicating higher stability. After twenty days of studying the stability, the NPs that had low ZP showed a large increment in size in comparison to the highly charged NPs.Conclusion: In conclusion, the polymeric properties and formulation variables in the ionic gelation method have a great influence on the CS NPs formed
Vaccine-preventable haemophilus influenza type B disease burden and cost-effectiveness of infant vaccination in Indonesia.
BACKGROUND: Most of Asia, including Indonesia, does not use Haemophilus influenzae type b (Hib) conjugate vaccines. We estimated total vaccine-preventable disease burden and the cost-effectiveness of Hib conjugate vaccine in Indonesia. METHODS: Hib pneumonia and meningitis incidences for children with access to health care were derived from a randomized vaccine probe study on Lombok Island, Indonesia during 1998-2002. Incidences were adjusted for limited access to care. Health system and patient out-of-pocket treatment cost data were collected concurrent with the probe study. For Hib vaccine in monovalent and combined (with DTP-HepB) presentations, we used 2007 UNICEF vaccine prices of US3.75 per dose. RESULTS: For the 2007 Indonesian birth cohort, Hib vaccine would prevent meningitis in 1 of every 179 children, pneumonia in 1 of every 18 children, and 4.9% of mortality among those younger than 5 years. The total incremental societal costs of introducing Hib vaccine in monovalent and pentavalent presentations were, respectively, US8.93 per child vaccinated. Annual discounted treatment costs averted amounted to 20% of pentavalent vaccine costs. For the pentavalent vaccine, the incremental costs per discounted death and disability adjusted life-year averted amounted to US74, respectively, versus 102 for monovalent vaccine. CONCLUSIONS: Routine infant Hib vaccination would prevent a large burden of pediatric illness and death in Indonesia. Even without external funding support, Hib vaccine will be a highly cost-effective intervention in either a monovalent or pentavalent presentation based on commonly used benchmarks
A Cross-sectional study on Out-of-Pocket expenditure towards Immunization and its consequences faced by families with under-five Children Residing at one of the Cities of Western India
Background: When immunization of under-five children results in Out-of-Pocket Expenditure (OOPE), it affects motivation of parents for vaccination inversely. Objectives: To assess determinants affecting preference for specific/mixed type of health facilities and to estimate out-of-pocket expenditure towards immunization of under-five children. To assess opinion of participants for prevention/decreasing OOPE towards immunization. Methods: A community-based cross-sectional study was conducted at one of zones of Ahmedabad city, selected by simple random sampling. Following technique of “30×7 cluster survey” with necessary house-hold information received from Municipal Corporation, selection of 7 children was pursued from each cluster reaching to sample-size of 210 (30 X 7). Results: Of 211 children included in study, 124(58.77%), 68(32.23%) and 19(9%) had taken immunization services from government, private and mixed variety respectively. Majority of families (110, 88.71%) preferring government healthcare-facility for immunization incurred expenses <5000 INR/child as while in other two groups, all beneficiaries had expensed>5000 INR/child. Conclusions: Determinants like child’s gender, parents’ education, Type of family, Socio-economic status, delivery place of child and occupation of father had statistically significant association with preferred place of vaccination. Fixation of upper ceiling-limit of vaccines which are recommended by pediatricians but not covered in government run program was one of suggestions
Deriving a multivariate CO-to-H conversion function using the [CII]/CO(1-0) ratio and its application to molecular gas scaling relations
We present Herschel PACS observations of the [CII] 158 micron emission line
in a sample of 24 intermediate mass (9<logM/M<10) and low
metallicity (0.4< Z/Z<1.0) galaxies from the xCOLD GASS survey.
Combining them with IRAM CO(1-0) measurements, we establish scaling relations
between integrated and molecular region [CII]/CO(1-0) luminosity ratios as a
function of integrated galaxy properties. A Bayesian analysis reveals that only
two parameters, metallicity and offset from the star formation main sequence,
MS, are needed to quantify variations in the luminosity ratio;
metallicity describes the total dust content available to shield CO from UV
radiation, while MS describes the strength of this radiation field. We
connect the [CII]/CO luminosity ratio to the CO-to-H conversion factor and
find a multivariate conversion function , which can be used up to
z~2.5. This function depends primarily on metallicity, with a second order
dependence on MS. We apply this to the full xCOLD GASS and PHIBSS1
surveys and investigate molecular gas scaling relations. We find a flattening
of the relation between gas mass fraction and stellar mass at
logM/M<10. While the molecular gas depletion time varies with
sSFR, it is mostly independent of mass, indicating that the low L/SFR
ratios long observed in low mass galaxies are entirely due to photodissociation
of CO, and not to an enhanced star formation efficiency.Comment: Submitted to MNRAS, this version after referee comments. 21 page
The X-ray surface brightness distribution from diffuse gas
We use simulations to predict the X-ray surface brightness distribution
arising from hot, cosmologically distributed diffuse gas. The distribution is
computed for two bands: 0.5-2 keV and 0.1-0.4 keV, using a
cosmological-constant dominated cosmology that fits many other observations. We
examine a number of numerical issues such as resolution, simulation volume and
pixel size and show that the predicted mean background is sensitive to
resolution such that higher resolution systematically increases the mean
predicted background. Although this means that we can compute only lower bounds
to the predicted level, these bounds are already quite restrictive. Since the
observed extra-galactic X-ray background is mostly accounted for by compact
sources, the amount of the observed background attributable to diffuse gas is
tightly constrained. We show that without physical processes in addition to
those included in the simulations (such as radiative cooling or
non-gravitational heating), both bands exceed observational limits. In order to
examine the effect of non-gravitational heating we explore a simple modeling of
energy injection and show that substantial amounts of heating are required
(i.e. 5 keV per particle when averaged over all baryons). Finally, we also
compute the distribution of surface brightness on the sky and show that it has
a well-resolved characteristic shape. This shape is substantially modified by
non-gravitational heating and can be used as a probe of such energy injection.Comment: 11 pages, 11 figures, submitted to Ap
Optical fiber sensors and signal processing for intelligent structure monitoring
Few mode optical fibers have been shown to produce predictable interference patterns when placed under strain. The use is described of a modal domain sensor in a vibration control experiment. An optical fiber is bonded along the length of a flexible beam. Output from the modal domain sensor is used to suppress vibrations induced in the beam. A distributed effect model for the modal domain sensor is developed. This model is combined with the beam and actuator dynamics to produce a system suitable for control design. Computer simulations predict open and closed loop dynamic responses. An experimental apparatus is described and experimental results are presented
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