To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
A compact hybrid rocket motor design that incorporates a dual-vortical-flow (DVF) concept is proposed. The oxidizer (nitrous oxide, N2O) is injected circumferentially into various sections of the rocket motor, which are sectored by several solid fuel “rings” (made of hydroxyl-terminated polybutadiene, HTPB) that are installed along the central axis of the motor. The proposed configuration not only increases the residence time of the oxidizer flow, it also implies an inherent “roll control” capability of the motor. Based on a DVF motor geometry with a designed thrust level of 11.6 kN, the characteristics of the turbulent reacting flow within the motor and its rocket performance were analyzed with a comprehensive numerical model that implements both real-fluid properties and finite-rate chemistry. Data indicate that the vacuum specific impulse (Isp) of the DVF motor could reach 278 s. The result from a preliminary ground test of a lab-scale DVF hybrid rocket motor (with a designed thrust level of 3,000 N) also shows promising performance. The proposed DVF concept is expected to partly resolve the issue of scalability, which remains challenging for hybrid rocket motors development.
A new approach is proposed to analyze Bremsstrahlung X-rays that are emitted from laser-produced plasmas (LPP) and are measured by a stack type spectrometer. This new method is based on a spectral tomographic reconstruction concept with the variational principle for optimization, without referring to the electron energy distribution of a plasma. This approach is applied to the analysis of some experimental data obtained at a few major laser facilities to demonstrate the applicability of the method. Slope temperatures of X-rays from LPP are determined with a two-temperature model, showing different spectral characteristics of X-rays depending on laser properties used in the experiments.
An excellent candidate for an earth abundant absorber material is WSe2 which can be directly grown as a p-type semiconductor with a band gap near 1.4 eV. In this work we present the structural, optical, and electrical properties of thin film WSe2 grown via the selenization of sputter deposited tungsten films. We will show that highly textured films with an optical band gap in range of 1.4 eV, and absorption coefficients greater than 105/cm across the visible spectrum can be easily achieved. In addition we will present Hall Effect and carrier density measurements as well, where will show densities in the 1017cm-3 range and p-type Hall mobilities greater than 10 cm2/V-s range can be obtained. We employ these results to numerically simulate solar cells based on this material, where we will show efficiencies greater than 20% are possible.
We analyze photoluminescence (PL) and electroluminescence (EL) using a hyperspectral imager that records spectrally resolved luminescence images of solar cell absorbers. The system is calibrated to yield the luminescence flux in absolute values. This system enables to quantitatively image physical parameters such as the photovoltage with an uncertainty of less than 30mV. The wide field illumination, low power excitation and fast acquisition brings new insights compared to classical setups such as confocal microscope. Several types of absorbers have been analyzed. For instance, we can investigate spatial fluctuations of the Quasi Fermi Levels splitting in CIGS polycristalline absorbers and link those fluctuations to transport properties. The method is general to the point that third generation PV cells absorbers can also be evaluated. We illustrate the great potential of our setup by imaging carrier temperature in Hot Carriers Solar cells absorbers and quasi Fermi levels splitting in Intermediate Band Solar cells.
The impurity effects on the creation of vacancies in GaAs and in ZnSe were investigated by monoenergetic positron beam measurements. In the case of the Si-doped MBE grown GaAs, the doping of Si atoms was found to enhance the creation of Ga site vacancies. The concentration of Ga vacancies was found to be proportional to the doped Si concentration. The observed linear relation between both concentrations supports the theoretical prediction on the creation of Ga vacancies in terms of the change in the Fermi-level position by the Si doping into GaAs and also suggests that Si atoms diffuse in GaAs as a neutral complex of Ga vacancy-Si pair rather than that of Si-Si pair. In the case of the Ga-doped MBE grown ZnSe, Zn vacancies were found to be generated in proportion to the concentration of doped Ga atoms. The observed similarity of the vacancy creation in the Si-doped GaAs and in the Ga-doped ZnSe can be well explained by the consideration of the charge neutrality condition around impurities.
In Western countries, a history of major depression (MD) is associated with reports of received parenting that is low in warmth and caring and high in control and authoritarianism. Does a similar pattern exist in women in China?
Received parenting was assessed by a shortened version of the Parental Bonding Instrument (PBI) in two groups of Han Chinese women: 1970 clinically ascertained cases with recurrent MD and 2597 matched controls. MD was assessed at personal interview.
Factor analysis of the PBI revealed three factors for both mothers and fathers: warmth, protectiveness, and authoritarianism. Lower warmth and protectiveness and higher authoritarianism from both mother and father were significantly associated with risk for recurrent MD. Parental warmth was positively correlated with parental protectiveness and negatively correlated with parental authoritarianism. When examined together, paternal warmth was more strongly associated with lowered risk for MD than maternal warmth. Furthermore, paternal protectiveness was negatively and maternal protectiveness positively associated with risk for MD.
Although the structure of received parenting is very similar in China and Western countries, the association with MD is not. High parental protectiveness is generally pathogenic in Western countries but protective in China, especially when received from the father. Our results suggest that cultural factors impact on patterns of parenting and their association with MD.
In members of the Bocavirus genus, that contain three open reading frames (ORFs) of the Parvovirinae subfamily, porcine bocaviruses (PoBoVs) exhibit the most genetic diversity. Based on the ORF2-encoded viral protein (VP1) classification, the six reported porcine bocaviruses were grouped into four species: PoBoV1 (porcine boca-like virus or PBoLV), PoBoV2 (porcine parvovirus 4 or PPV4), PoBoV3 (PBoV1/PBoV2) and PoBoV4 (6V/7V), with PoBoV3 and PoBoV4 each having two genotype viruses. All four PoBoV species were detected in the 166 samples collected in 2010 from swine herds located in ten provinces of China. The detection rates for PoBoV1-4 were 28·9%, 6·6%, 19·3% and 39·7%, respectively. The co-infection combinations involving these six porcine bocaviruses in the collected samples were very complex. Furthermore, mixed infections with viruses from other families (porcine reproductive and respiratory syndrome virus, classic swine fever virus and porcine circovirus type 2) were also detected.
In previous studies, low-k carbon-doped silicon oxide (SiOC) films were deposited using organosilicon precursor: (CH3)xSiH4−x. In this paper, we present the properties of PECVD low-k SiOC films produced by using conventional SiH4 based gas precursors. The SiH4 based SiOC films have similar gross physical and electrical characteristics to those of (CH3)xSiH4−x based SiOC. Since the precursors are inexpensive, commercially available and convenient to operate for existing tools, the process should not require additional cost as compared with that of PECVD silicon dioxide. We demonstrate the feasibility of integrating Cu with SiOC on damascene interconnection. The evaluation on electrical performance of the Cu/SiOC based damascene structure will be discussed.
The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (CMR) is investigated by comparing the physical properties of magnetoresistive manganites and cobaltites. The samples studied in this work include epitaxial films and ceramics of manganites with both A- and B-site substitution, (La0.7Ca0.3MnO3, LaMn0.7 Ni0.3O3, LaMnO.5Ni0.5O3), as well as epitaxial films and ceramics of cobaltites (La0.5Ca0.5CoO3). The structural, chemical, electrical transport, magnetic, optical properties and tunneling spectroscopy are studied. Based on our experimental results, we conclude that both double-exchange interaction and strong electron-phonon coupling due to the Jahn-Teller effect are essential to the occurrence of CMR.
A single-step, low temperature self-aligned CoSi2 process using Ti/Co source material has been developed for use in extreme submicrometer MOSFET applications. Ultra-thin CoSi2 films (∼ 20 nm) were obtained from a single-step RTA anneal at 550°C for 30 sec using Ti/Co source material on patterned n+ implanted (100) Si. X-ray diffraction was used to verify CoSi2 formation. Highresolution SEM and TEM examination showed the silicide to be microstructurally smooth and the devices showed no lateral growth of the silicide at the polysilicon spacer edge. Some voiding and lateral overgrowth was observed at the LOCOS isolation edge and this effect was exacerbated at higher anneal temperatures. This single-step low temperature CoSi2 process is a promising technology for deep-submicron MOSFET applications.
A comparison was made of 6H-SiC surfaces etched with H2, C2H4/H2, and HCl/H2, and the resulting crystal quality of epitaxial GaN films deposited on these substrates. To remove the many fine scratches and to smooth the rough surfaces typical of commercial SiC substrates, the Si-face 6H-SiC substrates were etched in H2, C2H4/H2, and HCl/H2 at 1450°C. GaN was subsequently deposited on these etched surfaces after first depositing a low temperature GaN buffer layer via metalorganic chemical vapor deposition (MOCVD). The surface morphologies after etching and after GaN deposition were characterized by atomic force microscopy and Normaski differential interference contrast microscopy, while the crystal quality of the GaN films was assessed by double crystal x-ray rocking curves and x-ray topography. 6H-SiC substrate surfaces were improved in terms of the removal of scratches and the reduction of surface roughness, and both surface morphology and crystal quality of the subsequently deposited GaN films were enhanced. However, the dislocation density was not decreased by the surface etching. The best GaN film was produced by etching the substrate in pure H2 for 40 minutes before growth. Recommendations for the optimum substrate treatment are made.
Boron was incorporated into GaN in order to determine its limits of solubility, its ability of reducing the lattice constant mismatch with 6H-SiC, as well as its effects on the structural and optical properties of GaN epilayers. BxGal-xN films were deposited on 6H-SiC (0001) substrates at 950 °C by low pressure MOVPE using diborane, trimethylgallium, and ammonia as precursors. A single phase alloy with x=0.015 was successfully produced at a gas reactant B/Ga ratio of 0.005. Phase separation into pure GaN and BxGal-xN alloy with x=0.30 was deposited for a B/Ga reactant ratio of 0.01. This is the highest B fraction of the wurtzite structure alloy ever reported. For B/Ga ratio ≥ 0.02, no BxGal-xN was formed, and the solid solution contained two phases: wurtzite GaN and BN based on the results of Auger and x-ray diffraction. The band edge emission of BxGal-xN varied from 3.451 eV for x=0 with FWHM of 39.2 meV to 3.465 eV for x=0.015 with FWHM of 35.1 meV. The narrower FWHM indicated that the quality of GaN epilayer was improved with small amount of boron incorporation.
Tantallum silicide films were sputter deposited from targets with different Si/Ta stoichiometries. The films were then subjected to thermal treatments. Silicon precipitation was observed on films deposited from silicon rich targets. The effects of silicon precipitates on device characteristics was studied. A method to suppress silicon precipitation is reported.
Effects of the indent depth, the distance between the indent and the grain boundary, grain sizes, and crystallographic orientations on the microhardness of annealed coarse-grained polycrystalline α-brass were investigated using a Vickers indenter with indents much smaller than the α-brass grains (ranging from 80 μm to 550 μm). It is found that the microhardness of α-brass crystals shows a strong dependence on the indentation depth when it is smaller than 5 μm and a very weak dependence on both the distance between the indent and the grain boundary and the grain size when the indentation depth is about 5 μm and more. No significant dependence of the microhardness on the crystallographic orientations was observed in the fourteen grains of different orientations studied in this investigation.
A strong attenuation of surface acoustic waves in the range of 30 to 100 MHz by singlewalled carbon nanotube layers deposited on the surface of piezoelectric lithium niobate single crystal has been observed. The attenuation exhibits non-monotonous dependence on nanotube density. This attenuation is attributed to the acoustoelectronic interaction between electric fields of the SAW and charge carriers in the nanotubes. The experimental results are in the qualitative agreement with the theory of acoustoelectronic interaction in inhomogeneous structures.
In the present research, the adhesion properties and failure mechanisms for a ductile thin film on a silicon substrate (Ni/Si) are studied experimentally, and are simulated theoretically. In the experimental research, the relations of the horizontal driving force, vertical displacement and the frictional coefficients with horizontal displacement are measured. Furthermore, the variation of the total energy release rate and the frictional coefficient between contact surfaces are measured through obtaining a frictional effect law. The law displays that the frictional influences on the energy release rate of the total system weakly depend on the thin film thickness. This conclusion leads to that the frictional effect can be eliminated in the toughness ratio relation approximately. So that one can directly obtain the interfacial adhesion toughness from measurements in the micro-scratching test. In addition, the micro-scratching process for the ductile thin film/brittle substrate systems is simulated using the double cohesive zone model. Prediction results of the energy release rate are obtained, and are compared with the experimental results obtained in the present research.