7,530 research outputs found
Towards Measuring the Maxwell–Boltzmann Distribution of a Single Heated Particle
The Maxwell–Boltzmann distribution is a hallmark of statistical physics in thermodynamic
equilibrium linking the probability density of a particle’s kinetic energies to the temperature
of the system that also determines its configurational fluctuations. This unique relation is
lost for Hot Brownian Motion, e.g., when the Brownian particle is constantly heated to
create an inhomogeneous temperature in the surrounding liquid. While the fluctuations of
the particle in this case can be described with an effective temperature, it is not unique for
all degrees of freedom and suggested to be different at different timescales. In this work,
we report on our progress to measure the effective temperature of Hot Brownian Motion in
the ballistic regime. We have constructed an optical setup to measure the displacement of
a heated Brownian particle with a temporal resolution of 10 ns giving a corresponding
spatial resolution of about 23 pm for a 0.92 ÎĽm PMMA particle in water. Using a goldcoated
polystyrene (AuPS) particle of 2.15 ÎĽm diameter we determine the mean squared
displacement of the particle over more than six orders of magnitude in time. Our data
recovers the trends for the effective temperature at long timescales, yet shows also clear
effects in the region of hydrodynamic long time tails
Hydrological long-term dry and wet periods in the Xijiang River basin, South China
In this study, hydrological long-term dry and wet periods are analyzed for the Xijiang River basin in South China. Daily precipitation data of 118 stations and data on daily discharge at Gaoyao hydrological station at the mouth of the Xijiang River for the period 1961–2007 are used. At a 24-month timescale, the standardized precipitation index (SPI-24) for the six sub-basins of the Xijiang River and the standardized discharge index (SDI-24) for Gaoyao station are applied. The monthly values of the SPI-24 averaged for the Xijiang River basin correlate highly with the monthly values of the SDI-24. Distinct long-term dry and wet sequences can be detected. <br><br> The principal component analysis is applied and shows spatial disparities in dry and wet periods for the six sub-basins. The correlation between the SPI-24 of the six sub-basins and the first principal component score shows that 67% of the variability within the sub-basins can be explained by dry and wet periods in the east of the Xijiang River basin. The spatial dipole conditions (second and third principal component) explain spatiotemporal disparities in the variability of dry and wet periods. All sub-basins contribute to hydrological dry periods, while mainly the northeastern sub-basins cause wet periods in the Xijiang River. We can also conclude that long-term dry events are larger in spatial extent and cover all sub-basins while long-term wet events are regional phenomena. <br><br> A spectral analysis is applied for the SPI-24 and the SDI-24. The results show significant peaks in periodicities of 11–14.7 yr, 2.8 yr, 3.4–3.7 yr, and 6.3–7.3 yr. The same periodic cycles can be found in the SPI-24 of the six sub-basins but with some variability in the mean magnitude. A wavelet analysis shows that significant periodicities have been stable over time since the 1980s. Extrapolations of the reconstructed SPI-24 and SDI-24 represent the continuation of observed significant periodicities at given magnitudes until 2030. The projected hydrological long-term dry and wet periods can be used for planning purposes in water resources management. The applied methodologies prove to be able to identify spatial disparities, and to detect significant periodicities in hydrological long-term dry and wet periods in the Xijiang River basin
Wet-Chemical Preparation and Characterization of Nanocrystalline Thin Films of Sulfated Zirconia
A Spitzer IRS Study of Debris Disks Around Planet-Host Stars
Since giant planets scatter planetesimals within a few tidal radii of their
orbits, the locations of existing planetesimal belts indicate regions where
giant planet formation failed in bygone protostellar disks. Infrared
observations of circumstellar dust produced by colliding planetesimals are
therefore powerful probes of the formation histories of known planets. Here we
present new Spitzer IRS spectrophotometry of 111 Solar-type stars, including
105 planet hosts. Our observations reveal 11 debris disks, including two
previously undetected debris disks orbiting HD 108874 and HD 130322. Combining
our 32 micron spectrophotometry with previously published MIPS photometry, we
find that the majority of debris disks around planet hosts have temperatures in
the range 60 < T < 100 K. Assuming a dust temperature T = 70 K, which is
representative of the nine debris disks detected by both IRS and MIPS, we find
that debris rings surrounding Sunlike stars orbit between 15 and 240 AU,
depending on the mean particle size. Our observations imply that the planets
detected by radial-velocity searches formed within 240 AU of their parent
stars. If any of the debris disks studied here have mostly large, blackbody
emitting grains, their companion giant planets must have formed in a narrow
region between the ice line and 15 AU.Comment: Accepted for publication in the Astronomical Journal. 14 pages,
including five figures and two table
A recombinant Chlamydia trachomatis major outer membrane protein binds to heparan sulfate receptors on epithelial cells.
Modeling Planetary System Formation with N-Body Simulations: Role of Gas Disk and Statistics Comparing to Observations
During the late stage of planet formation when Mars-size cores appear,
interactions among planetary cores can excite their orbital eccentricities,
speed their merges and thus sculpture the final architecture of planet systems.
This series of work contributes to the final assembling of planet systems with
N-body simulations, including the type I and II migration of planets, gas
accretion of massive cores in a viscous disk. In this paper, the standard
formulations of type I and II migrations are adopted to investigate the
formation of planet systems around solar mass stars. Statistics on the final
distributions of planetary masses, semi-major axes and eccentricities are
derived, which are comparable to those of the observed systems. Our simulations
predict some orbital signatures of planet systems around solar mass stars: 36%
of the survival planets are giant planets (Mp>10Me). Most of the massive giant
planets (Mp>30Me) locate at 1-10AU. Terrestrial planets distribute more or less
evenly at <1-2 AU. Planets in inner orbits (<1 AU) may accumulate at the inner
edges of either the protostellar disk (3-5 days) or its MRI dead zone (30-50
days). There is a planet desert in the mass-eccecntricity diagram, i.e., lack
of planets with masses 0.005 - 0.08 MJ in highly eccentric orbits (e > 0.3 -
0.4). The average eccentricity (~ 0.15) of the giant planets (Mp>10Me) are
bigger than that (~ 0.05) of the terrestrial planets (Mp< 10Me). A planet
system with more planets tends to have smaller planet masses and orbital
eccentricities on average.Comment: receiveded by Ap
Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars
We present an analysis of ~5 years of Lick Observatory radial velocity
measurements targeting a uniform sample of 31 intermediate-mass subgiants (1.5
< M*/Msun < 2.0) with the goal of measuring the occurrence rate of Jovian
planets around (evolved) A-type stars and comparing the distributions of their
orbital and physical characteristics to those of planets around Sun-like stars.
We provide updated orbital solutions incorporating new radial velocity
measurements for five known planet-hosting stars in our sample; uncertainties
in the fitted parameters are assessed using a Markov Chain Monte Carlo method.
The frequency of Jovian planets interior to 3 AU is 26 (+9,-8)%, which is
significantly higher than the ~5-10% frequency observed around solar-mass
stars. The median detection threshold for our sample includes minimum masses
down to {0.2, 0.3, 0.5, 0.6, 1.3} MJup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To
compare the properties of planets around intermediate-mass stars to those
around solar-mass stars we synthesize a population of planets based on the
parametric relationship dN ~ M^{alpha}P^{beta} dlnM dlnP, the observed planet
frequency, and the detection limits we derived. We find that the values of
alpha and beta for planets around solar-type stars from Cumming et al. fail to
reproduce the observed properties of planets in our sample at the 4 sigma
level, even when accounting for the different planet occurrence rates. Thus,
the properties of planets around A stars are markedly different than those
around Sun-like stars, suggesting that only a small (~ 50%) increase in stellar
mass has a large influence on the formation and orbital evolution of planets.Comment: Accepted by the Astrophysical Journal; 15 pages, 15 figure
Burden of disease and circulating serotypes of rotavirus infection in sub-Saharan Africa: systematic review and meta-analysis.
Two new rotavirus vaccines have recently been licensed in many countries. However, their efficacy has only been shown against certain serotypes commonly circulating in Europe, North America, and Latin America, but thought to be globally important. To assess the potential impact of these vaccines in sub-Saharan Africa, where rotavirus mortality is high, knowledge of prevalent types is essential because an effective rotavirus vaccine is needed to protect against prevailing serotypes in the community. We did two systematic reviews and two meta-analyses of the most recent published data on the burden of rotavirus disease in children aged under 5 years and rotavirus serotypes circulating in countries in sub-Saharan Africa. Eligible studies were selected from PubMed/Medline, Cochrane Library, EmBase, LILACS, Academic Search Premier, Biological Abstracts, ISI Web of Science, and the African Index Medicus. Depending on the heterogeneity, DerSimonian-Laird random-effects or fixed-effects models were used for meta-analyses. Geographical variability in rotavirus burden within countries in sub-Saharan Africa is substantial, and most countries lack information on rotavirus epidemiology. We estimated that annual mortality for this region was 243.3 (95% CI 187.6-301.7) deaths per 100,000 under 5 years (ie, a total of 300,000 children die of rotavirus infection in this region each year). The most common G type detected was G1 (34.9%), followed by G2 (9.1%), and G3 (8.6%). The most common P types detected were P[8] (35.5%) and P[6] (27.5%). Accurate information should be collected from surveillance based on standardised methods in these countries to obtain comparable data on the burden of disease and the circulating strains to assess the potential impact of vaccine introduction
Varying Alpha
We review properties of cosmological theories for the variation of the fine
structure 'constant'. We highlight some general features of the cosmological
models that exist in these theories with reference to recent quasar data that
are consistent with time-variation in the fine structure 'constant' since a
redshift of 3.5.Comment: 9 pages, Paper for the Proceedings of the Grassmann Bicentennial
Conference, 'Grasscosmofun'09', Univ. Szczecin Sept. 14-19, 200
An Optical Wavefront Sensor Based on a Double Layer Microlens Array
In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA) to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS) above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin), the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution
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