Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies

We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness between 0-1200 \AA. A negative differential resistance (NDR) is observed for all DHETs with GaSb thickness $>$ 60 \AA below which a dramatic change in the shape of the I-V and a marked hysteresis is observed. The temperature dependence of the I-V is found to be very strong below this critical GaSb thickness. The I-V characteristics of selected DHETs are also presented under hydrostatic pressures up to 11 kbar. Finally, a mid infra-red electroluminescence is observed at 1 bar with a threshold at the NDR valley bias. The band profile calculations presented in the analysis are markedly different to those given in the literature, and arise due to the positive charge that it is argued will build up in the GaSb layer under bias. We conclude that the dominant conduction mechanism in DHETs is most likely to arise out of an inelastic electron-heavy-hole interaction similar to that observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding, and not out of resonant electron-light-hole tunnelling as proposed by Yu et al. A Zener tunnelling mechanism is shown to contribute to the background current beyond NDR.Comment: 8 pages 12 fig

How do full-service carriers and low-cost carriers passengers perceived service dimensions, passengers’ satisfaction, and loyalty differently? An empirical study

Purpose: In this study, group differences between full-service carriers (FSC) and low-cost carriers (LCC) in loyalty constructs are investigated, revealing the relationship between service quality and loyalty. This work focuses on five dimensions, including tangibility, empathy, assurance, responsiveness, and reliability, constitute service quality. Design/methodology/approach: 248 questionnaires were collected in the first half of 2019. The antecedents of customer loyalty are explored, and the group differences between FSC and LCC are analyzed. For assessing the path model with the consideration of group variance, the Partial Least Squares Multiple Group Analysis (PLS-MGA) was adopted to analyze the differences of the estimated inter-group coefficient. Findings: Our findings suggest that service assurance, service empathy, and service reliability positively impact the value perceived. The impact of service empathy on customer satisfaction in FSC is significantly diverse from LCC. Several suggestions are provided to FSC and LCC on improving their services in view of passengers’ wants and interests. Originality/value: With the data collected at the HKIA, this study examined the relationships among service quality, perceived value, customer satisfaction, and customer loyalty and divided service quality into five dimensions. The findings show that assurance, empathy, and reliability of service quality positively affect the value perceived, and the effects of responsiveness and tangibility of service quality on perceived value are insignificant. Among the five aspects of service quality, assurance, reliability, responsiveness, and tangibility of the service quality are the pre-conditions of customer satisfaction. However, only the reliability of service is the antecedent of customer loyalty. Besides, the value perceived positively affects customers to be satisfactory and loyal. Furthermore, satisfaction degree also significantly influences the degree of customers’ loyalty. As to the role of airline types, the sole effect is on customers' satisfaction is service empathy, with a significant difference between FSC and LCCPeer Reviewe

Controlling extended systems with spatially filtered, time-delayed feedback

We investigate a control technique for spatially extended systems combining spatial filtering with a previously studied form of time-delay feedback. The scheme is naturally suited to real-time control of optical systems. We apply the control scheme to a model of a transversely extended semiconductor laser in which a desirable, coherent traveling wave state exists, but is a member of a nowhere stable family. Our scheme stabilizes this state, and directs the system towards it from realistic, distant and noisy initial conditions. As confirmed by numerical simulation, a linear stability analysis about the controlled state accurately predicts when the scheme is successful, and illustrates some key features of the control including the individual merit of, and interplay between, the spatial and temporal degrees of freedom in the control.Comment: 9 pages REVTeX including 7 PostScript figures. To appear in Physical Review

Natural and anthropogenic lead in sediments of the Rotorua lakes, New Zealand

Global atmospheric sources of lead have increased more than 100-fold over the past century as a result of deforestation, coal combustion, ore smelting and leaded petroleum. Lead compounds generally accumulate in depositional areas across the globe where, due to low solubility and relative freedom from microbial degradation, the history of their inputs is preserved. In lakes there is rapid deposition and often little bioturbation of lead, resulting in an excellent depositional history of changes in both natural and anthropogenic sources. The objective of this study was to use sediments from a regionally bounded set of lakes to provide an indication of the rates of environmental inputs of lead whilst taking into account differences of trophic state and lead exposure between lakes. Intact sediment gravity cores were collected from 13 Rotorua lakes in North Island of New Zealand between March 2006 and January 2007. Cores penetrated sediments to a depth of 16–30 cm and contained volcanic tephra from the 1886 AD Tarawera eruption. The upper depth of the Tarawera tephra enabled prescription of a date for the associated depth in the core (120 years). Each core showed a sub-surface peak in lead concentration above the Tarawera tephra which was contemporaneous with the peak use of lead alkyl as a petroleum additive in New Zealand. An 8 m piston core was taken in the largest of the lakes, Lake Rotorua, in March 2007. The lake is antipodal to the pre-industrial sources of atmospheric lead but still shows increasing lead concentrations from <2 up to 3.5 μg g−1 between the Whakatane eruption (5530 ± 60 cal. yr BP) and the Tarawera eruption. Peaks in lead concentration in Lake Rotorua are associated with volcanic tephras, but are small compared with those arising from recent anthropogenic-derived lead deposition. Our results show that diagenetic processes associated with iron, manganese and sulfate oxidation-reduction, and sulfide precipitation, act to smooth distributions of lead from anthropogenic sources in the lake sediments. The extent of this smoothing can be related to changes in sulfate availability and reduction in sulfide driven by differences in trophic status amongst the lakes. Greatest lead mobilisation occurs in mesotrophic lakes during seasonal anoxia as iron and manganese are released to the porewater, allowing upward migration of lead towards the sediment–water interface. This lead mobilisation can only occur if sulfides are not present. The sub-surface peak in lead concentrations in lake sediments ascribed to lead alkyl in petroleum persists despite the diagenetic processes acting to disperse lead within the sediments and into the overlying water

Different types of visual cells in the photoreceptor layer of the retinae of the treeshrew (Tupaia belangeri chinensis) as revealed by scanning microscopy

The retinae of treeshrew have never been evaluated by scanning electron microscopic studies. This work described the visual cells in the photoreceptor layer of the retinae of treeshrew (Tupaia belangeri chinensis) living on the high plateau of Yunnan, China, via scanning electron microscopy. Results indicated five different types of cones morphologically, in which two of those have shown oil droplet like structures in their inner segments. To our knowledge, no prior studies have reported oil droplets in the visual cells of higher mammals, only in lower vertebrate and primitive mammals. In addition, this study revealed one type of degenerative visual cell without outer segments. The findings signal the needs for additional studies to understand the physiological functions and phylogenetic relationships of the diversity of visual cells in this group of mammal

Detection of severe acute respiratory syndrome-associated coronavirus in pneumocytes of the lung

Previous reports have indicated that patients with severe acute respiratory syndrome (SARS)-associated coronavirus infection could develop atypical pneumonia with fulminant pulmonary edema. However, the target cells of SARS viral infection have not been characterized in detail. We report the pathologic findings of the lung in 3 cases of SARS. Chest radiographs at 2 to 3 weeks of infection revealed an atypical pneumonia with pulmonary consolidation, a clinical characteristic of SARS infection. The presence of the SARS virus was determined by nested reverse transcription polymerase chain reaction (RT-PCR), and the infected cells were identified by in situ hybridization in open-lung biopsy and postmortem necropsy specimens. Expression of SARS virus-encoded RNA was detected in all 3 cases by RT-PCR, and the SARS viral signal was localized in pneumocytes by using in situ hybridization

Integrated motor drives: state of the art and future trends

With increased need for high power density, high efficiency and high temperature capabilities in Aerospace and Automotive applications, Integrated Motor Drives (IMD) offers a potential solution. However, close physical integration of the converter and the machine may also lead to an increase in components temperature. This requires careful mechanical, structural and thermal analysis; and design of the IMD system. This paper reviews existing IMD technologies and their thermal effects on the IMD system. The effects of the power electronics (PE) position on the IMD system and its respective thermal management concepts are also investigated. The challenges faced in designing and manufacturing of an IMD along with the mechanical and structural impacts of close physical integration is also discussed and potential solutions are provided. Potential converter topologies for an IMD like the Matrix converter, 2-level Bridge, 3-level NPC and Multiphase full bridge converters are also reviewed. Wide band gap devices like SiC and GaN and their packaging in power modules for IMDs are also discussed. Power modules components and packaging technologies are also presented