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Schistosomiasis in China has been substantially reduced due to an effective control programme employing various measures including bovine and human chemotherapy, and the removal of bovines from endemic areas. To fulfil elimination targets, it will be necessary to identify other possible reservoir hosts for Schistosoma japonicum and include them in future control efforts. This study determined the infection prevalence of S. japonicum in rodents (0–9·21%), dogs (0–18·37%) and goats (6·9–46·4%) from the Dongting Lake area of Hunan province, using a combination of traditional coproparasitological techniques (miracidial hatching technique and Kato-Katz thick smear technique) and molecular methods [quantitative real-time PCR (qPCR) and droplet digital PCR (ddPCR)]. We found a much higher prevalence in goats than previously recorded in this setting. Cattle and water buffalo were also examined using the same procedures and all were found to be infected, emphasising the occurrence of active transmission. qPCR and ddPCR were much more sensitive than the coproparasitological procedures with both KK and MHT considerably underestimating the true prevalence in all animals surveyed. The high level of S. japonicum prevalence in goats indicates that they are likely important reservoirs in schistosomiasis transmission, necessitating their inclusion as targets of control, if the goal of elimination is to be achieved in China.
We present the estimates of the black hole spins of five quasars. The peaks of the spectra of the accretion discs surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disc corona model, the soft photons from the disc are Comptonized to high energy in the hot corona, and the hard X-ray spectra (luminosity and spectral shape) contain the information of the incident spectra from the disc. The values of black hole spin parameter a are inferred from the spectral fitting, which spread over a large range, ~ −0.94 to 0.998.
The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing-array projects being carried out worldwide is to detect ultra-low frequency gravitational waves (f ∼ 10−9–10−8 Hz). Such waves are expected to be caused by coalescing supermassive binary black holes in the cores of merged galaxies. It is also possible that a detectable signal could have been produced in the inflationary era or by cosmic strings. In this paper, we review the current status of the Parkes Pulsar Timing Array project (the only such project in the Southern hemisphere) and compare the pulsar timing technique with other forms of gravitational-wave detection such as ground- and space-based interferometer systems.
A ‘pulsar timing array’ (PTA), in which observations of a large sample of pulsars spread across the celestial sphere are combined, allows investigation of ‘global’ phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A sample of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (~700 MHz), 20 cm (~1400 MHz), and 10 cm (~3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant ‘red’ timing noise is detected in about half of the sample. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an ‘extended PPTA’ data set that combines PPTA data with earlier Parkes timing data for these pulsars.
Undoped 69GaAs/71GaAs isotope superlattice structures grown by MBE on n-type GaAs substrates, doped by Si to ∼3×1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960°C, the SIMS measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and Al-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. SIMS, CV, and TEM characterizations showed that the as-grown superlattice layers were intrinsic which became p-type with hole concentrations up to ∼2×1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ∼106-107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si outdiffusion from the substrate, which was determined using CV measurements. Outdiffusion of Si decreases the n value in the substrate which causes the release of excess Ga vacancies into the superlattice layers where the supersaturated Ga vacancies enhance Ga self-diffusion.
Mechanical cues in cellular microenvironment are central in directing a
class of cellular behaviors such as the dynamic of cell adhesion, migration,
and differentiation. Several advanced optical techniques, such as
structured-illumination nano-profilometry (SINAP), have been developed for a
better resolution of these dynamic processes. These techniques however
require culturing cells on materials of refractive index close to that of
glass, while most studies regarding the effects of mechanical cues on
cellular dynamics were conducted on hydrogel-based substrates. Here we
report the development of culturing substrates of tunable rigidity and
refractive index suitable for SINAP studies. Polyvinyl chloride (PVC)-based
substrates were mixed with a softener called Di(isononyl)
Cyclohexane-1,2-Dicarboxylate (DINCH) and cured by heating. The volume
ratios of PVC to DINCH were varied from 1:1 to 3:1. The Young’s modulus of
the resulting substrates ranged from 18 kPa to 40 kPa. The yielded
refractive indices of the composite substrates as measured by phase contrast
tomography ranged from 1.47 to 1.53. Human lung adenocarcinoma cells CL1-5
were cultured on the composite substrates and cell viability was examined
using the MTT assay. The dynamics of cell adhesion and filopodia activities
were examined using SINAP. Preliminary results suggest that PVC based
culturing substrates have a great potential in the application of SINAP
The future high density multilevel interconnection and packaging requires that the combination of the insulator and conductor layers has a low RC value. Thermal stress and diffusion during processing are issues of great concern in the high density multilevel structures. The problem can be alleviated by a proper choice of materials and processes that do not require high temperature. In this paper we propose to use parylene and its derivatives (dielectric constant 2.3–2.6) as the possible interlayer dielectrics and Cu (bulk resistivity ∼1.7 μ Ω-cm) as the conductor. Parylene can be vapor-deposited and cured at room temperature. The metallization of Cu has been achieved at room temperature using the newly developed partially ionized beam deposition technique. This technique has been shown to grow high quality metal films with low resistivity at low substrate temperatures. The interaction between Cu and parylene, including adhesion and diffusion, is also discussed.
The combination of Cu and parylene (poly-p-xylylene) for metallization and insulator in integrated circuit or packaging multilayer interconnection systems gives one of the lowest resistance and capacitance values per unit length. In this paper we present a detailed study of the diffusion characteristics of Cu in parylene-n (PA-n) substrates. PA-n was vapor-deposited and Cu metallization performed at room temperature using the Partially Ionized Beam (PIB) technique. Rutherford Backscattering (RBS) technique has been used to study the diffusion of Cu in PA-n substrate after annealing the samples to elevated temperatures in vacuum. We found no sign of Cu diffusion after the Cu/PA-n sample was annealed at 300°C for 6 hours. Diffusion occurs at 350 °C. However, preannealed PA-n substrate prior to Cu deposition can prevent the diffusion even at a temperatures above 350°C. Also we found that amorphous carbon and chromium are good diffusion barriers of Cu on PA-n. The dry adhesion between PA-n deposited on Al, Cu and Ag was found to be good. The adhesion of these PIB deposited metals on PA-n in high vacuum was also very good.
A four-circle diffractometry technique is used to determine the heteroepitaxial relations of VO2 and TiO2 thin films grown by an MOCVD technique on sapphire (0001) and (1120) surfaces. The use of a reflective geometry eliminates special sample preparation of the sample for the x-ray diffraction measurements. The distribution of epitaxial domains is found to depend strongly on the symmetry of the underlying substrate.
Parylene films, depending on the type, are thermally stable up to 530°C and have low dielectric constants ranging from 2.35 to 3.15. One of the most interesting properties of this material is its vapor depositability. Conventional vapor deposition involves cracking the parylene dimers at temperatures from 600 to 730 °C and polymerizingthe monomers at - 35 °C to RT. We have developed a simpler and less expensive technique that directly uses the precursors from which the dimers are made. This method requires the use of metal catalysts to produce parylene films. We have used the precursors α,α'-dibromo-p-xylene and dibromotetrafluoro-p-xylene to produce N-type and F-type parylene films. FTIR, XPS, thermal stability, and electrical studies show that the F-type parylene films grown from the precursors are comparable to, or sometimes better than, the films grown from dimer, and have potential microelectronics applications.
We performed in-situ x-ray reflectivity measurements to study the growth dynamics of gold sputter deposited onto silicon using an x-ray scattering chamber equipped with a faced magnetron source where the substrate is held at a right angle relative to the sputtering guns. By operating the guns at low power (1 watt) and under 20 mTorr Ar, we could control the gold deposition rate to less than 1Å/sec. The observed x-ray reflectivity for gold deposited onto a silicon substrate at 300 K and 400 K is consistent with nucleated island growth for average gold particle sizes less than 50 Å. Above 50 Å, the reflectivity data indicates that the gold film uniformly covers the silicon surface, and that as the film thickness is increased the gold-vacuum interface gets progressively rougher. Detailed analysis of room temperature data is in progress, as is the temperature dependence on the roughness of the gold vacuum interface.
We studied the finite size effect on the metal-insulator phase transition and the accompanying tetragonal to monoclinic structural phase transition of VO2 films grown by MOCVD. X-ray diffraction measurements and electrical conductivity measurements were done as a function of temperature for VO2 films with out-of plane particle size ranging from 60–310Å. Each VO2 film was grown on a thin TiO2 buffer layer, which in turn was grown by MOCVD on a polished sapphire (1120) substrate. The transition was found to be first order. As the out-of plane particle size becomes larger, the transition temperature shifts and the transition width narrows. For the 60Å film the transition was observed at ∼61°C with a transition width of ∼10°C, while for the 310Å film the transition temperature was ∼59°C and the transition width ∼2°C. We also observed thermal hysteresis for each film, which became smaller with increasing particle size.
Organic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.
We report an investigation of optical-limiting behavior in two neutral nickel complexes with multi-sulfur 1,2 dithiolene ligands, [Ni(medt)2] I (medt = 5,6-dihydro-6-methyl-1,4-dithiin-2,3- dithiolate) and [Ni(phdt)2] 2 (phdt = 5,6-dihydro-5-phenyl-l,4-dithiin-2,3-dithiolate) in benzene solution. The fluence-dependent transmission of the complexes was observed with nanosecond and picosecond laser pulses at 532-nm wavelength. The limiting thresholds of the complexes were ˜0.3 J/cm2, when measured with the picosecond pulses. Both picosecond time-resolved pump-probe and Z-scan measurement revealed that the limiting effects should originate from excited-state absorption and refraction. The transparency window (400˜900 nm), observed in the linear absorption spectra of the complexes, indicated that their limiting response should cover a wider range than those of fullerenes and phthalocyanines.
A void free 3C-SiC film grown on Si(100) can be achieved by low pressure chemical vapor deposition using the modified four-step method. The diffusion step plays an important role to enhance the quality of the 3C-SiC buffer layer on Si(100). X-ray photoelectron spectroscopy was used to characterize the bonding characteristics of the 3C-SiC buffer layer of about 10 nm thick. The Si-C bonds are partially formed on the as-carburized Si(100) before the diffusion step. The ratio of C-C to Si-C bonds on the as-carburized Si(100) is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350 oC for 5 min or at 1300 oC for 7 min. According to XPS data and Fick's second law, the diffusivity of Si across the 3C-SiC interlayer are determined to be 2.2×10-16 cm2/s and 3.13×10-16 cm2/s at 1300°C and 1350°C, respectively. The derived activation energy is 1.6 eV for the diffusion of Si atoms in the 3C-SiC buffer layer.
Silica aerogels were synthesized via sol-gel processing followed by a two-step surface modification and ambient pressure drying, using methyltrimethoxysilane (MTMS) and trimethylchlorosilane (TMCS)/ethanol/n-hexane as surface modification agents. The transparent silica aerogels possessed the porosities, densities and specific surface areas in the range of 87.7–92.3%, 0.27–0.17 g·cm-3 and 852–1005 m2·g-1, respectively. The SEM and HRTEM analysis revealed the three-dimensional nanoporous structure of the silica aerogels. The presence of –CH3 functional groups on the surface of silica particles as indicated by the FTIR spectra was further confirmed by two visible exothermic peaks at 310 and 450–500 °C from the DTA curve. In addition, the silica aerogels were superhydrophobic with the contact angle as high as 160°.
The structure and magnetic properties of the nanoparticles of immiscible
system Co20Cu80 prepared by means of arc-discharge, have been
studied in detail. The diameters of the particles are about 20 ~ 30 nm
and a core/shell structure forms. The cores are Co-Cu solutions, which show
some small Co precipitates, encapsulated with a shell of cupper oxide or
cobalt oxide as observed by means of high-resolution transmission electron
microscope (HRTEM) and energy dispersive X-ray (EDS). The loop shift in the
hysteresis loop indicates the existence of the exchange bias between
ferromagnetic and antiferromagnetic components at low temperatures. A block
temperature about 180 K has been observed for as-deposited nanoparticles.
For the annealed nanoparticles, the thermal magnetization at low
temperatures is satisfied with Bloch's law.
Recombining plasmas produced by picosecond laser pulses are characterized by measuring ratio of intensities of resonance lines of H- and He-like ions in the plasmas. It is found that the rapidly recombining plasmas produced by picosecond laser pulses are suitable for highgain operation.
We study commutators in pseudo-orthogonal groups O2nR (including unitary, symplectic, and ordinary orthogonal groups) and in the conformal pseudo-orthogonal groups GO2nR. We estimate the number of commutators, c(O2nR) and c(GO2nR), needed to represent every element in the commutator subgroup. We show that c(O2nR) ≤ 4 if R satisfies the ∧-stable condition and either n ≥ 3 or n = 2 and 1 is the sum of two units in R, and that c(GO2nR) ≤ 3 when the involution is trivial and ∧ = R∈. We also show that c(O2nR) ≤ 3 and c(GO2nR) ≤ 2 for the ordinary orthogonal group O2nR over a commutative ring R of absolute stable rank 1 where either n ≥ 3 or n = 2 and 1 is the sum of two units in R.