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 firstname.lastname@example.org
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.
We conduct numerical simulations to investigate the formation and evolution of drops and vortex rings of particle-laden fingers in double-diffusive convection in stably stratified environments. We show that the temporal evolution can be divided into double diffusion, acceleration and deceleration phases. The acceleration phase is a result of the vanishing temperature perturbation in the drop during the descent in the layer of uniform temperature. The drop decelerates because it transforms into a vortex ring. A theoretical drag model is presented to predict the speed of the spherical drop with the low drop Reynolds number. By formulating the boundary condition based on the vorticity, our drag model gives a more general form of the drag coefficient for small spherical drops and shows good agreement in predicting the drag coefficient. Drops with five particle sizes are compared, and it is found that although the greater vertical settling enhances vertical transport, the final state differs little among the various sizes. Comparison of our drag model with the simulation results under various bulk conditions and previous experimental results shows good model predictability. Finally, a comparison with the salt-finger case shows that the diffusive nature of the dissolved scalar field, along with the wake effect, can result in an apparent loss of mass from the drop and a permanent presence of the connection between the drop and its parent finger. This makes the observed detachment of the particle-laden drop much less likely in the salt-finger case.
Simultaneous localization and mapping (SLAM) is a well-known and fundamental topic for autonomous robot navigation. Existing solutions include the FastSLAM family-based approaches which are based on Rao–Blackwellized particle filter. The FastSLAM methods slow down greatly when the number of landmarks becomes large. Furthermore, the FastSLAM methods use a fixed number of particles, which may result in either not enough algorithms to find a solution in complex domains or too many particles and hence wasted computation for simple domains. These issues result in reduced performance of the FastSLAM algorithms, especially on embedded devices with limited computational capabilities, such as commonly used on mobile robots. To ease the computational burden, this paper proposes a modified version of FastSLAM called Adaptive Computation SLAM (ACSLAM), where particles are predicted only by odometry readings, and are updated only when an expected measurement has a maximum likelihood. As for the states of landmarks, they are also updated by the maximum likelihood. Furthermore, ACSLAM uses the effective sample size (ESS) to adapt the number of particles for the next generation. Experimental results demonstrated that the proposed ACSLAM performed 40% faster than FastSLAM 2.0 and also has higher accuracy.
In this paper, we propose an enhanced Monte Carlo localization (EMCL) algorithm for mobile robots, which deals with the premature convergence problem in global localization as well as the estimation error existing in pose tracking. By incorporating a mechanism for preventing premature convergence (MPPC), which uses a “reference relative vector” to modify the weight of each sample, exploration of a highly symmetrical environment can be improved. As a consequence, the proposed method has the ability to converge particles toward the global optimum, resulting in successful global localization. Furthermore, by applying the unscented Kalman Filter (UKF) to the prediction state and the previous state of particles in Monte Carlo Localization (MCL), an EMCL can be established for pose tracking, where the prediction state is modified by the Kalman gain derived from the modified prior error covariance. Hence, a better approximation that reduces the discrepancy between the state of the robot and the estimation can be obtained. Simulations and practical experiments confirmed that the proposed approach can improve the localization performance in both global localization and pose tracking.
Bacillus pasteurii was used as synthesis director for the formation of hollow cylinder and helical NiO micro/nanostructure under urea hydrolysis conditions. Bacteria were capable of precipitating nickel product from nickel solution by metabolic processes. An appropriate amount of both water and bacterial solution were required to precipitate the nickel product in good yield. The average crystallite size of NiO was 11.45 nm and lengths of the cylinder and helices were non-uniform (~2–7 µm) and were varied with bacterial body structure template. The present study demonstrates a feasibility of synthesizing bacteria-guided metal oxide crystals for various functional applications.
We report herein the crystal growth of ZnO nanoparticles by the foam fractionation method. In this study, the vertical column height of the foam was fixed and the velocity of the sparging air was varied, and the effect of foam flow rate on the synthesis of ZnO was investigated. The obtained ZnO consisted of aggregated platelets and had differing ultraviolet absorbances. The as-synthesized ZnO was hydrophobic because of the interaction between the anionic head groups of sodium dodecyl sulfate (SDS) and the ZnO under the precipitation conditions. The long chain of the SDS molecule was the cause of hydrophobicity. The contact angle of water was in the range of 95–105° for the obtained ZnO/SDS surface. The photocatalytic degradation efficiency of the as-synthesized (ZnO/SDS) and the calcined ZnO was investigated for methylene blue, and the calcined ZnO retained its activity even after three recycles.
Existing research suggests that leaders/supervisors are the major persons in work organizations to promote employee perception of job significance, which is an intrinsic motivator for employee productivity. However, the literature remains unclear on the relationship between workplace friendship and perceived job significance. Results from a survey of 290 Taiwanese employees indicated that workplace friendship enhanced perceived job significance, and such enhancement did not vary across organizational levels. Our findings suggest intrinsically motivating employees through workplace friendship, which extends extant literature on work role of leaders/supervisors in employee motivation. Further, although lower organizational levels have a disadvantage of objectively less job significance in work organizations, our findings suggest workplace friendship is an effective factor in promoting employee perception of job significance. Thus, organizations can embed the mechanism of workplace friendship into the factors of job design to promote employees' intrinsic motivation and thus job and organizational productivity.
Three types of Ganium Nitride (GaN) transistors were studied in this work. The devices were fabricated and exhibited unique characteristics over on-state current and off-state blocking performances. We also compared the performance differences of devices fabricated by multiepitaxial GaN/AlGaN layers on different substrates (Sapphire and Si) and evaluated the correlations among starting substrate, device variation, and manufacturing uniformity. The first device is a normally-on device with Sapphire substrate which shows good drain saturation current (Idsat) and breakdown characteristics, but the gate leakage current is quite large. The second device is a normally-off GaN transistor named metal-insulate-semiconductor (MIS) heterojunction field-effect transistor (MIS-HFET) which exhibits good performance with threshold voltage (Vth) of 3V and breakdown voltage (Vbd) of over 1800V. However the third device is a normally-off GaN metal-oxide-semiconductor field-elect transistor (MOSFET) structure which is rather difficult to exhibit good blocking characteristic due to inadequate doping process control of the reduce-surface-field (RESURF) region.
Polyaniline nanofiber (PANF) was synthesized using interfacial polymerization and was mixed with aqueous solution of poly(vinyl alcohol) (PVA) to form PANF–PVA binaries. The PANF suspension in water could be stabilized by PVA for more than 3 months due to the hydrogen bonding interaction between PANF and PVA. The specific characteristics of PANF–PVA films was checked by scanning electron microscopy, conductivity measurement, thermogravimetric analysis, Fourier transform infrared spectroscopy, and cyclic voltammetry. The composite film contained 25 wt% PVA (PANF–PVA25) casting at 105 °C was found to have a porous structure and good conductivity. The presence of hydrogen bonding interaction between PANF and PVA improves the electroactivity and electroactive stability of PANF–PVA25 for electrochemical applications. However, an ether linkage between PANF and PVA polymer chain was also found as casting the PANF–PVA film at 200 °C, which is unfavorable for electrochemical applications.
Modulation of the cellular response by the administration of probiotic bacteria may be an effective strategy for preventing or inhibiting tumour growth. We orally pre-inoculated mice with probiotics Lactobacillus acidophilus NCFM (La) for 14 d. Subcutaneous dorsal-flank tumours and segmental orthotopic colon cancers were implanted into mice using CT-26 murine colon adenocarcinoma cells. On day 28 after tumour initiation, the lamina propria of the colon, mesenteric lymph nodes (MLN) and spleen were harvested and purified for flow cytometry and mRNA analyses. We demonstrated that La pre-inoculation reduced tumour volume growth by 50·3 %, compared with untreated mice at 28 d after tumour implants (2465·5 (sem 1290·4) v. 4950·9 (sem 1689·3) mm3, P < 0·001). Inoculation with La reduced the severity of colonic carcinogenesis caused by CT-26 cells, such as level of colonic involvement and structural abnormality of epithelial/crypt damage. Moreover, La enhanced apoptosis of CT-26 cells both in dorsal-flank tumour and segmental orthotopic colon cancer, and the mean counts of apoptotic body were higher in mice pre-inoculated with La (P < 0·05) compared with untreated mice. La pre-inoculation down-regulated the CXCR4 mRNA expressions in the colon, MLN and extra-intestinal tissue, compared with untreated mice (P < 0·05). In addition, La pre-inoculation reduced the mean fluorescence index of MHC class I (H-2Dd, -Kd and -Ld) in flow cytometry analysis. Taken together, these findings suggest that probiotics La may play a role in attenuating tumour growth during CT-26 cell carcinogenesis. The down-regulated expression of CXCR4 mRNA and MHC class I, as well as increasing apoptosis in tumour tissue, indicated that La may be associated with modulating the cellular response triggered by colon carcinogenesis.
Few studies have been conducted to investigate the influence of recombinant human erythropoietin (rhEPO) on the long-term prognosis of end-stage renal disease (ESRD).
A retrospective cohort study.
The largest regional hospital renowned for haemodialysis in northern Taiwan.
A total of 702 ESRD patients undergoing haemodialysis between 1993 and 2002 were evaluated.
The rate of overall use of rhEPO, vitamin D3 or Fe therapy was 62 %. The 10-year survival rate in patients with rhEPO supplementation was statistically more favourable than that in patients without rhEPO (hazard ratio (HR) = 0·38, 95 % CI 0·30, 0·47, P < 0·0001). Similar findings were noted for patients receiving vitamin D3 (HR = 0·36, 95 % CI 0·21, 0·64, P = 0.0004) and Fe (HR = 0·45, 95 % CI 0·33, 0·61, P < 0·0001). After adjusting for age, education and aetiology, the administration of rhEPO resulted in statistically significant improvements in long-term survival rate either with (HR = 0·30, 95 % CI 0·22, 0·42) or without (HR = 0·48, 95 % CI 0·38, 0·61) combined use of Fe or vitamin D3.
We demonstrated a reduction in long-term mortality related to supplementation therapy with rhEPO, vitamin D3 and Fe. The findings provide a justification for the administration of combined supplement therapy in patients undergoing haemodialysis.
We applied the deactivation treatments to p-type single crystalline silicon solar cells for deactivating the recombination-active boron-oxygen complex. The methods we used include thermal annealing treatment, capacitively couple plasma (CCP) treatment, and plasma immersion ion implantation (PIII) treatment. The results showed that all the deactivation treatments were working and the energy transfer efficiency (Eff) was thereby increased by more than 1% absolute compared to the degraded state base on the increasing of the open-circular voltage (Voc) and short-current density (Jsc). The CCP deactivated treatment got better efficiencies than PIII treatment because the PIII treatment damaged the surface of solar cells. After the forming gas treatment, the samples could be improved to close to the PIII samples due to the surface damage repairing. However, the increased efficiency could not be kept and would be degraded again after illumination.
To rapidly establish a temporary isolation ward to handle an unexpected sudden outbreak of severe acute respiratory syndrome (SARS) and to evaluate the implementation of exposure control measures by healthcare workers (HCWs) for SARS patients.
Rapid creation of 60 relatively negative pressure isolation rooms for 196 suspected SARS patients transferred from 19 hospitals and daily temperature recordings of 180 volunteer HCWs from 6 medical centers.
A military hospital.
Of the 196 patients, 34 (17.3%) met the World Health Organization criteria for probable SARS with positive results of serologic testing for SARS-associated coronavirus (SARS-CoV), reverse transcriptase polymerase chain reaction (RT-PCR) from nasopharyngeal or throat swabs for SARS-CoV, or both. Seventy-four patients had suspected SARS based on unprotected exposure to SARS patients; three of them had positive results on RT-PCR but negative serologic results. The remaining 88 patients did not meet the criteria for a probable or suspected SARS diagnosis. Of the 34 patients with probable SARS, 13 were transferred to medical centers to receive mechanical ventilation due to rapid deterioration of chest x-ray results, and three patients died of SARS despite intensive therapy in medical centers. During the study period, one nurse developed probable SARS due to violation of infection control measures, but there was no evidence of cross-transmission to other HCWs.
Despite the use of full personal protection equipment, the facility failed to totally prevent exposures of HCWs to SARS but minimized the risk of nosocomial transmission. Better training and improvements in infection control infrastructure may limit the impact of SARS.
Breakdown characteristics of ultra-thin gate oxides caused by plasma charging were studied in this work. It is observed that as oxide thickness is scaled down to 4 nm, some traditional monitor parameters may lose their sensitivity for detecting oxide degradation induced by plasma charging damage, due to insignificant trap generation. Even the gate leakage current, although sensitive for 4 nm oxide, may no longer be sensitive enough for even thinner oxide (e.g., 2.6 nm), due to the existence of large tunneling current. Moreover, several soft-breakdown events were found to occur in ultrathin oxide before the final onset of a catastrophic hard-breakdown. Finally, an equivalent local oxide thickness is calculated using local oxide thinning model to estimate the stepwise increase of gate current after soft-breakdown event.
The room temperature fracture behavior for in situ reinforced (ISR) silicon nitride is correlated to its microstructure and R-curve behavior. The relation of strength to fracture origin suggests that stable growth of the intrinsic flaw precedes catastrophic fracture. Grainbridging that generates a rising bridging stress behind the crack-tip has been proposed as the cause for stable crack growth, which in turn reduces the strength dependency on initial flaw size. As a result of strong bridging by the acicular β-Si3N4 grains, ISR Si3N4 is characterized for high Weibull modulus. At elevated temperatures, the material's tensile creep rupture behavior follows the Monkman-Grant type plot. A tensile creep rate of -10−9s−1 at 1260°C/250 MPa, 1300°C/180 MPa, and 1350°C/90 MPa has been recorded. This relatively strong creep resistance is related to the sliding-resistance of the acicular grains and the properties of the amorphous film between the grains in ISR Si3N4.
Email your librarian or administrator to recommend adding this to your organisation's collection.