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M. M. Hedman, University of Idaho Moscow, Idaho, USA,
F. Postberg, University of Heidelberg Heidelberg, GERMANY,
D. P. Hamilton, University of Maryland College Park, Maryland, USA,
S. Renner, University of Lille Lille, FRANCE,
H.-W. Hsu, University of Colorado Boulder, Colorado, USA
All of the giant planets in the outer Solar System possess rings composed primarily of particles less than 100 microns across. Such small particles are conventionally referred to as “dust grains” regardless of their composition, and so these rings are considered “dusty rings” (as opposed to the more famous main rings of Saturn and Uranus, whose particles are more than a millimeter across). Dusty rings are often very tenuous and so can be much more difficult to observe than Saturn's broad, bright, and dense main rings. Nevertheless, dusty rings are extremely interesting because they have very rich dynamics and are extremely sensitive probes of their environment.
The high surface-area-to-volume ratio of dust-sized grains makes them much more responsive to non-gravitational forces like solar radiation pressure, plasma drag, and torques from the planet's electromagnetic field. Furthermore, sub-millimeter particles can be lost from the ring system on relatively short timescales due to erosion via charged-particle and micrometeoroid bombardment or through ejection by the non-gravitational forces listed above. This means that small particles need to be constantly supplied to these rings from larger bodies, and indeed all of the known dusty rings are associated with larger objects that are the likely sources of dusty debris. The most dramatic example of this is Saturn's E ring, which is clearly supplied by material erupting from beneath the surface of the geologically active moon Enceladus. However, this is a special case, and most dusty rings are instead associated with denser rings (which are composed primarily of millimeter-to-metersized particles) or small moons. These objects can serve as dust sources because they are constantly being bombarded by micrometeoroids, and these impacts release fine debris that can escape the weak gravitational fields of these small bodies and go into orbit around the planet. Note that the amount of dust released by this process depends on the size, mass, and regolith properties of the source object, and calculations of the dust production rate based on simple estimates of impact ejecta velocity distributions suggest that source moons that are several kilometers across are the most efficient at producing dusty rings (Burns et al., 1999).
Prior to integrated circuit (IC) packaging, die performance must be verified using probe cards to screen for defective products. With the decrease in IC line width, the dimensions of the pads used for performance verification and the spacing between adjacent pads have also decreased. However, when the pad pitch is reduced to less than 30 μm, commonly used probe cards will face manufacturing problems in miniaturization. To resolve probe card manufacturing problems caused by the miniaturization of IC components, the use of an anisotropic conductive film (ACF) in probe cards was proposed in this study. Theoretical calculations and experimental testing of this probe structure were conducted to demonstrate the feasibility of this concept.
In theoretical calculations, composite material and buckling theory were utilized to evaluate the buckling behavior of the ACF. In experimental testing, photolithography and electroplating techniques were used to control the line width and spacing intervals of the micron-scale metal wires in the ACF. After the ACF was fabricated, the mechanical properties of the ACF during wafer testing were assessed. Theoretical analyses and experimental testing verified that ACFs can potentially be applied to the performance verification of IC products. In the ACF structure, multiple probes came into contact with each pad. Therefore, ACFs can potentially be applied to the performance verification of IC components with pad diameters of less than 20 μm. The results of this study directly benefit the miniaturization of ICs.
With good combustion characteristics, hydrogen has been developing as a clean alternative fuel of engines. This study is to develop a diesel/hydrogen dual fuel engine. The hydrogen was added at inlet port in a 4-cylinder direct injection turbocharged diesel engine with an EGR (Exhaust Gas Recirculation) system to investigate engine performance and exhaust pollutant. The measured items are composed of the gas pressure of cylinder, crank angle, consumption rate of diesel, consumption rate of hydrogen, air flow rate, emissions (HC, CO2, NOX, and Smoke), and so on. The authors analyze how the addition of hydrogen with EGR system influences the engine performance and emissions. The diesel/hydrogen dual fuel turbocharged engine can increase the brake thermal efficiency with a greater decrease in emissions compared with the turbocharged diesel engine. Furthermore, the authors little altered the engine structure to get the positive effect of energy saving and pollutant decreasing.
In this study, the properties of surface acoustic wave (SAW) filters, including phase velocity and electromechanical coupling coefficient (K2) are investigated. The effective surface permittivity (ESP) method was employed to estimate the K2 of bulk materials (single layer) and multi-layer (double-layer and trilayer) structures. In the cases of bulk materials, the calculation results agree with the experimental data, and the errors are less than 7% for quartz. In the cases of double-layer materials, the phase velocity and K2 of various materials, such as ZnO/Diamond and LiNbO3/Diamond, were acquired, and the results demonstrate that LiNbO3/diamond is the optimal choice for high-frequency SAW devices. For the cases of trilayer, the structure of ZnO/PZT/diamond has relatively high K2 and phase velocity. Therefore, this structure is the optimal trilayer structure for high-frequency SAW devices. The study demonstrates that ESP method can be successfully used for estimating SAW properties in piezoelectric multi-layer structures even though the structures contain nonpiezoelectric film (diamond). The proposed numerical computation has the potential to shorten the developing time of SAW device.
Surveillance is integral for the monitoring and control of infectious diseases. We conducted prospective laboratory surveillance of methicillin-resistant Staphylococcus aureus (MRSA) in five Singaporean public-sector hospitals from 2006 to 2010, using WHONET 5.6 for data compilation and analysis. Molecular profiling using multilocus variable-number tandem-repeat analysis, staphylococcal cassette chromosome mec classification and multilocus sequence typing was performed for a random selection of isolates. Our results showed overall stable rates of infection and bacteraemia, although there was significant variance among the individual hospitals, with MRSA rates increasing in two smaller hospitals and showing a trend towards decreasing in the two largest hospitals. The proportion of blood isolates that are EMRSA-15 (ST22-IV) continued to increase over time, slowly replacing the multi-resistant ST239-III. A new MRSA clone – ST45-IV – is now responsible for a small subset of hospital infections locally. More effort is required in Singaporean hospitals in order to reduce the rates of MRSA infection significantly.
In this paper, analytical particular solutions of the augmented polyharmonic spline (APS) associated with Reissner plate model are explicitly derived in order to apply the dual reciprocity method. In the derivations of the particular solutions, a coupled system of three second-ordered partial differential equations (PDEs), which governs problems of Reissner plates, is initially transformed into a single six-ordered PDE by the Hörmander operator decomposition technique. Then the particular solutions of the coupled system can be found by using the particular solution of the six-ordered PDE derived in the first author's previous study. These formulas are further implemented for solving problems of Reissner plates under arbitrary loadings. In the solution procedure, an arbitrary loading measured at some scattered points is first interpolated by the APS and a corresponding particular solution can then be approximated by using the prescribed formulas. After that the complementary homogeneous problem is formally solved by the method of fundamental solutions (MFS). Numerical experiments are carried out to validate these particular solutions.
Stair locomotion is an important but challenging functional activity for people with lower limb pathology. This study aimed to investigate the bilateral changes in force-bearing on lower limbs during stair locomotion in patients with unilateral ACL deficiency. The ground reaction forces (GRF) were collected from three force platforms: One at ground level in front of a 5-step stair and two on the first two steps respectively. Parameters in vertical and anterior-posterior GRF were extracted and compared between the ACL-deficient (ACLD) and control groups. The ACLD group showed significantly slower stepping cadences in both stair ascent and stepping down to the ground (p < 0.05). The vertical GRF in the ACLD group demonstrated smaller peak forces but larger minimum forces between the two peaks than those in the control group during both stair ascent and descent. Significantly reduced anterior propulsive forces and push-off rates in the late stance were also found in both limbs of the ACLD group (p < 0.05). The slower cadences and reduced force-bearing on the affected limb suggested a protective strategy was adopted. However, the anterior loading parameters in the early stance on the unaffected limb demonstrated different adaptations with significantly larger magnitudes during stair ascent but reduced magnitudes during stair descent (p < 0.05). Similar results were also found in the weight- transferring strategies between legs in consecutive steps with a significantly larger percentage of lift-up forces but a smaller percentage of impact forces on the leading unaffected limb. The results of this study indicated a cautious force-bearing strategy and bilateral adaptation were apparent in the patients with unilateral ACL deficiency. This information may provide a safety guideline for the patients and be helpful for a better use of the stair tasks as part of a rehabilitation program.
A multi-cross-correlation method (MCCM) was developed in a particle image velocimetry (PIV) auto-processing system to reduce spurious vectors and improve accuracy of measurements. This technique is an improvement based on conventional cross-correlation method (CCM). Four typical neighboring interrogation windows were specified to be overlapped and calculated by MCCM. A high cross-correlation value is obtained in which many particle images match up with their corresponding spatially shifted partners, and small cross-correlation peaks due to interference of noises during experiments are reduced. Several parameters such as out-of-plane motions, particle size, and seeding density are considered for checking both MCCM and conventional PIV algorithms. The examination gives authenticity to the merits of MCCM for avoiding particles loss or mistaken velocity vectors.
The hydrogenated amorphous silicon (a-Si:H) single-junction thin-film solar cells were fabricated on SnO2:F-coated glasses by plasma-enhanced chemical vapor deposition (PECVD) system. The boron-doped amorphous silicon carbide (a-SiC:H) was served as the window layer (p-layer) and the undoped a-SiC:H was used as a buffer layer (b-layer). The optimization of the p/b/i/n thin-films in a-Si:H solar cells have been carried out and discussed. Considering the effects of light absorption, electron-hole extraction and light-induced degradation, the thicknesses of p, b, n and i layers have been optimized. The optimal a-Si:H thin-film solar cell having an efficiency of 9.46% was achieved, with VOC=906 mV, JSC=14.42 mA/cm2 and FF=72.36%.
Welded structures are vulnerable to fracture due to cracks, especially at the welds. To investigate the safety of T-Shape welded structures used in some construction sites, a method is proposed in this paper to evaluate the crack occurrence probabilities of the structures. Three major factors that affect the crack occurrence are taken into consideration. They are residual stress, diffusible hydrogen content and chemical composition of the weld metal. In the analysis, finite element analysis is performed to find the residual stress distribution of the structures. The uncertainties of diffusible hydrogen content and chemical composition are treated as random variables. The critical cooling time is found and utilized for evaluating the crack occurrence probability of the welded structure. Numerical results indicate that T-shape welded joints lead to higher residual stresses and higher crack occurrence probabilities in comparison with the traditional butt joints. Therefore, more attention should be paid to this kind of welded joints when they are used.
The previous monolithic active grating bender design met some basic design requirements. However, after a real grating (BM-AGM) had been fabricated and installed for testing, the results showed that the usable length is a mere 60 mm because of the higher-order term error in the surface profile. A method was thus derived to eliminate the higher-order term error by modifying the width of the bender substrate through finite-element method simulation, reducing the residual error from about 100 nm to 6 nm. Owing to the closure of the grating department of Zeiss, ruling the monolithic bender is no longer available and the design has to be modified to a composite-type bender with Si substrate. A prototype was fabricated and assembled to examine all the design situations. The surface roughness of the width-modified Si substrate is around 30 nm before assembly. The residual error after assembly and bending is less than 10 nm. It proves that the design is feasible. However, due to the manufacturing capacity of the vendor, a short-length substrate is required and the design has to be modified. The detailed design modification and testing results are presented in this paper.
High‐T YBaCuO and BiSrCaCuO Superconducting wires have been fabricated by powder metallurgy technique. Copper and silver tubes were used as the external jackets. Thermal annealing treatments for all the wire‐type samples were performed between 773 K and 1223 K. Both electrical and magnetization studies show that the superconducting properties can be improved after properly thermal annealing these samples with silver jacket. Our experimental results show that proper thermal annealing treatment can enhance the intragrain critical current density more than 100 times; however, the intergrain critical current density improves only a few times.
The characteristics of YBa2Cu3O7−x (YBCO) thin films by laser ablation on MgO bicrystals have been investigated. The bicrystals were fabricated by hot pressing two single crystals with the configuration of  tilt boundaries. The YBCO films were epitaxial grown with C-axis normal to the both adjacent grains of bicrystals. The FWHM about (005) reflection was 0.4–0.5 degree, indicating the high degree of the oriention for the film with small mosaic spread. Our preliminary study showed that the typical value of Jc on either side of the bicrystal boundary was 0.4–10×106 A/cm2 at 15K, while that across the 10° tilt boundaries was 0.3–9×105 A/cm2 at 15K. These results implied that the artificial grain boundaries effectively weakened the supercurrent, and therefore, the weak-link properties of artificial boundaries were more easily controllable than those of naturally occuring grain boundaries.
Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been used to grow GexSi1−x/Si heteroepitaxial thin films at low temperatures (∼450°C). In situ RHEED has been used to confirm that smooth, single crystal heteroepitaxial films can be grown by RPCVD. Plan-view and cross-sectional TEM have been employed to study the microstructure of the heteroepitaxial films. Lattice imaging high resolution TEM (HRTEM) has shown perfect epitaxial lattice alignment at the heterojunction interfaces. GexSi1−x/Si films which exceed their CLT's appreciably show dense Moiré fringes under plan-view TEM. The spacings between the fringes have been used to estimate the relaxed lattice constants. In addition to the inhomogeneous strain observed in XTEM, Selected Area electron Diffraction (SAD) analysis of the interfaces displays two split patterns. The spacings between the diffraction spots have been used to calculate the lattice constants in the epitaxial films in different crystal directions, which agree very well with the prediction by Vegard's law as well as the estimate from planview TEM analysis. HRTEM analysis also reveals the crystallographic nature of the interfacial misfit dislocations in the relaxed films.
X-ray scattering has been used to study the interfacial structure of a dry oxide grown at room temperature on a system consisting of four layers of Si epitaxially grown on Ge(001). A 2x1 structure is seen at the interface, whose shape parallels the underlying terrace structure. The model producing the best fit to the specular reflectivity data consists of a Ge single crystal substrate, five intermediate ordered layers and an amorphous oxide layer. X-ray Photoelectron Spectroscopy (XPS) data is also presented, consistent with the specular model, which together indicate that not all of Si is oxidized and that there exists Ge in the SiOx amorphous layer.