A Novel Admission Control Model in Cloud Computing

With the rapid development of Cloud computing technologies and wide adopt of Cloud services and applications, QoS provisioning in Clouds becomes an important research topic. In this paper, we propose an admission control mechanism for Cloud computing. In particular we consider the high volume of simultaneous requests for Cloud services and develop admission control for aggregated traffic flows to address this challenge. By employ network calculus, we determine effective bandwidth for aggregate flow, which is used for making admission control decision. In order to improve network resource allocation while achieving Cloud service QoS, we investigate the relationship between effective bandwidth and equivalent capacity. We have also conducted extensive experiments to evaluate performance of the proposed admission control mechanism

The shift of percent excess mortality from zero-COVID policy to living-with-COVID policy in Singapore, South Korea, Australia, New Zealand and Hong Kong SAR

IntroductionWith the economic recession and pandemic fatigue, milder viral variants and higher vaccine coverage along the time lay the basis for lifting anti-COVID policies to restore COVID-19 normalcy. However, when and how to adjust the anti-COVID policies remain under debate in many countries.MethodsIn this study, four countries (Singapore, South Korea, Australia, and New Zealand) and one region (Hong Kong SAR), that have shifted from the zero-COVID (ZC) policy to or close to the living-with-COVID (LWC) during or after the Omicron outbreak, were selected as research objects. All-cause mortality data were collected for these objects from 2009 to 2019. The expected mortality was estimated by a simple linear regression method. Excess mortality over time was calculated as the difference between the expected mortality and the observed mortality. Finally, percent excess mortality (PEM) was calculated as the excess mortality divided by the expected mortality.ResultsIn the examined four countries, PEM fluctuated around 0% and was lower than 10% most of the time under the ZC policy before 2022. After shifting to the LWC policy, all the examined countries increased the PEM. Briefly, countries with high population density (Singapore and South Korea) experienced an average PEM of 20–40% during the first half of 2022, and followed by a lower average PEM of 15–18% during the second half of 2022. For countries with low population density under the LWC policy, Australia experienced an average PEM of 39.85% during the first half of 2022, while New Zealand was the only country in our analysis that achieved no more than 10% in average PEM all the time. On the contrary, Hong Kong SAR under their ZC policy attained an average PEM of 71.14% during the first half of 2022, while its average PEM decreased to 9.19% in the second half of 2022 with LWC-like policy.ConclusionPEM under different policies within each country/region overtime demonstrated that the mortality burden caused by COVID-19 had been reduced overtime. Moreover, anti-COVID policies are suggested to control the excess mortality to achieve as low as 10% in PEM

A nonlinear triboelectric nanogenerator with a broadened bandwidth for effective harvesting of vibration energy

A narrow resonance bandwidth of an energy harvesters limits its response to the wide frequency spectrum in ambient environments. This work proposes an addition of a nonlinear restoring force applied to a triboelectric nanogenerator (TENG) to tune and broaden the resonance bandwidth. This restoring force is applied by permanent magnets at both sides of the slider and two external magnets. The noncontact strategy is adopted between the slider and the grating electrodes to avoid the wear of electrodes and energy loss caused by friction. The results show that compared with the linear system, the nonlinear noncontact TENG (NN-TENG) can increase the peak current from 6.3 μA to 7.89 μA, with an increment of about 25%, increase the peak power from 650 μW to 977 μW, increasing by about 50%, and increase the bandwidth from 0.5 Hz to 7.75 Hz, increasing by about1400%. This work may enable a new strategy to boost the bandwidth and output power of TENG through nonlinear oscillators

Control and understanding growth of III-V nanowires structures

Scaling down conventional field effect transistors (FET) has shown the limitation of the inverse subthreshold slope S\u3e=60 mV/dec, since the operation of the conventional FET is based on the gate modulation of the thermal emission of charge carriers. To overcome this limitation, the tunneling FET based on the modulation of carriers tunneling through bandgap barriers has been demonstrated to have S smaller than 60 mV/dec. With the low effective mass and the high mobility, III-V nanowires have been proven to be the perfect material to enhance the performance of the tunneling FET. Especially, the InAs/GaSb core/shell nanowire heterostructure with the broken bandgap alignment will yield the minimum tunneling barrier and high tunneling probability. To achieve that, synthesis of InAs, GaSb nanowires and core/shell nanowires have to be understood and well controlled. To do that, controlled nanowire growth in a simple vapor deposition system was demonstrated in several nanowire systems. Metal-organic chemical vapor deposition (MOCVD) was also utilized to perform the GaSb film growth. ^ Au-catalyzed InAs nanowires were synthesized in our home-built simple vapor deposition system. Free-standing and planar InAs nanowires were grown with the same catalytic interface of (111)B even though the growth directions are different. The different growth behaviors in the termination time were observed in the growth of these two nanowires. A model based on the revised Gibbs-Thomson equations for the growth of the both nanowires was developed, showing the difference in supersaturations. By using this model, we predicted and successfully confirmed through experiments that the free-standing InAs nanowire growth was expected to be promoted by higher arsenic vapor partial pressure. The difference in critical diameters of both the planar and free-standing nanowire growths was also predicted and demonstrated experimentally. ^ Self-catalyzed InAs nanowire growth on III-V substrates was also performed in our simple vapor deposition system. The growth direction was always along \u3c111\u3eB directions. The pits thermally created on the substrates\u27 surface were hypothesized to initiate the self-catalyzed nanowire growth. The selected area growth with pits created by thermal annealing on GaAs substrate was performed to demonstrate the hypothesis, with pits identified in prepared cross-sectional TEM sample. The pre-growth annealing step was demonstrated to promote the density of nanowire growth. ^ GaSb nanowires were grown in our simple vapor deposition system with Au particles as catalysts. The growth direction was found to be \u3c220\u3e. The grown GaSb nanowires were found to be highly p-type, which shows very few gate modulations in fabricated nanowire FET. In-situ doping method with Te as the doping element was developed to counter-dope GaSb nanowires. Results from TEM-EDX and electrical characterization of Te-doped GaSb nanowires show successful doping of Te in nanowires. ^ Au-catalyst-free InAs nanowires were preferred as core material for core/shell structure synthesis. In the simple vapor deposition system with solid GaSb powder as precursors, serrated GaSb shell with the thickness of about 6 nm was grown, as the core/shell structure identified by TEM and EDX. In the MOCVD system, GaSb thin film growth was performed on GaSb and InAs substrates. Further optimized recipe is still required to be developed to enhance the shell thickness and to achieve more uniform surface. ^ The outlook includes fabrication and characterization of the tunneling FET based on the core/shell heterostructure, the transfer-free self-aligned InAs nanowire FET fabrication based on planar nanowire growth, position-controlled self-catalyzed InAs nanowire arrays, and III-V nanowires with differently doped segments.

Understanding Self-Aligned Planar Growth of InAs Nanowires

Semiconducting nanowires have attracted lots of attention because of their potential applications. Compared with free-standing nanowires, self-aligned planar nanowires grown epitaxially on the substrate have shown advantageous properties such as being twin defect free and ready for device fabrication, opening potentials for the large-scale device applications. Understanding of planar nanowire growth, which is essential for selective growth of planar vs free-standing wires, is still limited. In this paper, we reported different growth behaviors for self-aligned planar and free-standing InAs nanowires under identical growth conditions. We present a new model based on a revised Gibbs-Thomson equation for the planar nanowires. Using this model, we predicted and successfully confirmed through experiments that higher arsenic vapor partial pressure promoted free-standing InAs nanowire growth. A smaller critical diameter for planar nanowire growth was predicted and achieved experimentally. Successful control and understanding of planar and free-standing nanowire growth established in our work opens up the potential of large-scale integration of self-aligned nanowires for practical device applications

Current and Noise Properties of InAs Nanowire Transistors With Asymmetric Contacts Induced by Gate Overlap

Nanowire transistors are typically fabricated as geometrically symmetrical devices, with metal/semiconductor source and drain contacts rather than a graduated doping profile. While the source and drain contacts are nominally identical, contact asymmetry can arise when the gate contact is not centered over the nanowire, leaving uneven access regions with no gate coverage on one or both sides of the channel. Measuring the characteristics of devices with symmetric and asymmetric contact geometries allows contact effects to be studied. In this paper, indium arsenide nanowire transistors were fabricated with symmetric and asymmetric gate coverage. It is shown that devices with highly asymmetric gate coverage can exhibit a factor of 10 change in current and a shift in threshold of up to 0.5 V upon reversing the source-drain orientation. Devices with highly asymmetric properties show nearly identical channel-generated noise yet a significant difference in contact-generated noise levels when the contact orientation is reversed. Fully symmetric devices show higher current levels, lower threshold voltages, and lower contact-generated noise than asymmetric devices with either source or drain gated, but channel-generated noise levels are similar

Aminophosphonic acid derivatized polyacrylonitrile fiber for rapid adsorption of Au(S2O3)23– from thiosulfate solution

A fast and efficient Au (I) recovery adsorption method from an actual leaching solution of Cu2+-en-S2O32- is presented. Aminophosphonic acid derivatized polyacrylonitrile fibers (PAN-NP), prepared with triethylenetetramine and phosphoric acid by chemical grafting, were used as the adsorbent. The adsorbent was well characterized by FT-IR, SEM, TGA and XPS. The effects of contact time, pH, temperature, and Au (Ⅰ) concentration were also investigated. PAN-NP can rapidly capture Au(S2O3)23– (20 min) and has a maximum adsorption capacity of 14.68 kg/t. Compared with -SH modified, PAN-NP has better stability and without oxidized. The adsorption process was described based on the Langmuir isothermal model (R2 > 0.99). Thermodynamic parameters indicated that the adsorption of Au(S2O3)23– on PAN-NP was exothermic (ΔHθ = −9.906 kJ/mol) and adsorption mechanism involved a collective effect resulting the anion exchange of Au(S2O3)23– with –RNH3+H2PO3-, electrostatic attraction between –RNH3+ and Au(S2O3)23– and complexation of P = O with Au (Ⅰ). Besides, PAN-NP-Au can be effectively eluted by sodium sulfite. Importantly, in the Cu2+-en-S2O32- actual leaching solution, the PAN-NP can efficiently recover Au (I) with an adsorption percentage of up to 97 % at a the solid­liquid ratio of 1:50, thereby affording a satisfactory application result. This is a meaningful method for recovering Au (Ⅰ) from thiosulfate solution

Low-Frequency Noise Contributions from Channel and Contacts in InAs Nanowire Transistors

Nanowire transistors are promising candidates for future electronics applications; however, they generally exhibit higher levels of low-frequency noise compared with traditional MOSFETs. The physics of this noise generation in nanowires needs to be understood for improving the device performance. In this paper, the low-frequency noise in InAs nanowire transistors was studied at different gate voltages before and after passivation by a polymethyl methacrylate (PMMA) layer. Noise levels in nanowire devices can be separated into contributions from the channel and from the contacts by analyzing the noise behavior under different bias conditions for devices with varying channel lengths. It is shown that a noise component, which is independent of channel length, can be attributed to the contacts, and a length-dependent component is attributed to the channel. Applying the PMMA passivation layer over the entire device reduces the noise level generated by the channel, but does not change the noise level generated by the contacts. This paper provides a method to understand, and potentially improve, the noise performance. Operation in a channel-dominated bias regime allows extraction of a Hooge parameter specifically for the channel. PMMA passivation was effective in reducing this channel Hooge parameter from 1.4 x 10(-1) to 1.8 x 10(-3)

High-fidelity dynamics of piezoelectric covered metamaterial Timoshenko beams using the spectral element method

Piezoelectric metamaterial beams have received enormous research interest for the applications of vibration attenuation and/or energy harvesting in recent years. This paper presents a generic modelling approach for predicting the high-frequency dynamics of piezoelectric metamaterial beams. The spectral element method (SEM) is used to derive the dynamic stiffness matrix of a composite piezoelectric beam segment. Boundary condition implementations are demonstrated. Both band structure and transmittance analyses are realized. Several case studies for piezoelectric metamaterial beams configured in different geometric/electrical forms are carried out. The corresponding finite element (FE) models are built for verification, and a comparison study with the transfer matrix method (TMM) is conducted. For the uniform configurations, an almost indistinguishable difference is noted between the theoretical and FE results. For the stepped configurations, only minor discrepancies are observed in the high-frequency responses. The improved robustness and stability of the SEM method compared to the TMM method are demonstrated. A further discussion has been provided to explain the cause of the high-frequency discrepancies: sudden changes in the cross-section of the beam result in the stress concentration effect and reduce the bending stiffness at the junction connection. Finally, the value of the high-fidelity modelling approach is reflected through a parametric-based optimization study towards merging the Bragg scattering and locally resonant band gaps in an example piezoelectric metamaterial beam to achieve a wide band gap.This work was financially supported by the State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, China (GZ21114, S22311)

Understanding Self-Catalyzed Epitaxial Growth of III–V Nanowires toward Controlled Synthesis

The self-catalyzed growth of III–V nanowires has drawn plenty of attention due to the potential of integration in current Si-based technologies. The homoparticle-assisted vapor–liquid–solid growth mechanism has been demonstrated for self-catalyzed III–V nanowire growth. However, the understandings of the preferred growth sites of these nanowires are still limited, which obstructs the controlled synthesis and the applications of self-catalyzed nanowire arrays. Here, we experimentally demonstrated that thermally created pits could serve as the preferred sites for self-catalyzed InAs nanowire growth. On that basis, we performed a pregrowth annealing strategy to promote the nanowire density by enhancing the pits formation on the substrate surface and enable the nanowire growth on the substrate that was not capable to facilitate the growth. The discovery of the preferred self-catalyzed nanowire growth sites and the pregrowth annealing strategy have shown great potentials for controlled self-catalyzed III–V nanowire array growth with preferred locations and density