In some emerging wireless applications, such as wearable communication and low-power sensor network applications, wireless devices or nodes not only require simple physical implementation approaches ...but also require certain reliable receiver techniques to overcome the effects of multipath or shadowed fading. Switched diversity combining (SDC) systems could be a simple and promising solution to the above requirements. Recently, a Fisher-Snedecor ℱ composited fading model has gained much interest because of its modeling accuracy and calculation tractability. However, the performance of SDC systems over ℱ fading channels has not yet been analyzed in the open literature. To this end, this paper presents a systematic analysis of SDC systems over ℱ fading channels, including dual-branch switch-and-stay combining (SSC), multibranch switch-and examine combining (SEC), and SEC with post-examining selection (SECps) systems. We first investigate the statistical characteristics of univariate and bivariate ℱ distributions. Then, these statistical expressions are introduced into the above SDC systems and the statistical metrics of the output signal-to-noise ratio (SNR) for these systems are deduced in different ℱ fading scenarios. Thirdly, certain exact and novel expressions of performance criteria, such as the outage probability, the average bit error probability and average symbol error probability, as well as the average channel capacity for SSC, SEC, and SECps are derived. To find the optimum performance, optimal analysis is performed for the independent and identically distributed cases. Finally, numerical evaluation and simulations are carried out to demonstrate the validity of the theoretical analysis under various ℱ fading scenarios. According to the obtained results, the multipath fading parameter has more influence on the performance of SDC systems than the shadowing parameter, the correlation coefficient, or the average SNR. Importantly, the SDC systems can provide switched diversity gains only when the switching threshold is not too large or too small compared to the average SNR.
Ce anomaly is an important indicator for many geochemical processes. Although the role of strong ligand such as siderophore desferrioxamine B (DFOB) in facilitating negative Ce anomaly formation on ...Mn (hydr)oxide has been well studied, the effect of ubiquitous weak ligands such as polysaccharides on the mobility of Ce have not been considered. Here, we investigated the effects of polysaccharides with different molecular weights on Mn (hydr)oxide formation as well as the distribution coefficients of rare-earth elements (REEs) at the solid–liquid interface. In coprecipitation experiments, REEs distribution coefficients between Mn (hydr)oxide and the solution showed a negative Ce anomaly during coprecipitation of Mn in the presence of dextran with molecular weight of 5000 Dalton (Dextran 5 k). The molecular size of the saccharides affected the crystal growth of Mn (hydr)oxide. Mn (hydr)oxide was deposited on a matrix of polysaccharide molecules to form a metal–organic framework in the presence of dextran. The crystal size decreased with an increase in the length of the saccharide molecular chain. As a control test, when well crystallized δ-MnO2 was used as an adsorbent, the distribution coefficients of the REEs showed a positive Ce anomaly in the presence of dextran 5 k. Based on the results, we suggest that the mechanism by which saccharides affect the sorption behavior of REEs on Mn (hydr)oxide is different from the reported mechanisms of strong metal-binding ligands such as DFOB. Saccharide-mediated electron transfer may occur between Mn (hydr)oxides and Ce(III), resulting in the formation of an organic-Ce(IV) complex in solution. Our results imply that ubiquitous weak ligands such as polysaccharides may significantly affect the mobility of Ce largely due to the association with Mn oxides, which are widespread natural electron acceptors.
In this paper, the ultrasonic vibration treatment was applied to the TiAl alloy melt during the solidification aiming at modifying the coarse microstructure and improving the mechanical properties. ...Effects of ultrasonic vibration on the microstructure and mechanical properties of TiAl are elaborately studied. The results show that the grain size was refined from 545μm to 96μm, the yield strength was improved from 419MPa to 854MPa, and the coarse dendrite structure was modified into fine non-dendrite grains after ultrasonic vibration. Given the high melt viscosity and narrow liquid–solid temperature range, the predominant refinement mechanism of ultrasonic vibration for TiAl is the cavitation-enhanced nucleation due to the nucleus activation and/or heightened supercooling.
Aiming at the problem of low efficiency of dicentric chromosome identification counting under the microscope, this paper presents a joint processing algorithm combining clustering and watershed. The ...method first uses clustering and watershed algorithm to segment the original chromosome image, and then identifies the individual chromosomes. The results show that when the equivalent width Y parameter is selected m = 1, n = 1, the true positive rate of dicentric chromosome identification is 76.6%, and positive predictive value is 76.6% in high dose, which is higher than the threshold algorithm for the true positive rate (63.9%) and positive predictive value (63.5%). The number of identified dicentric chromosomes can be used for dose estimation. When 500 cells are used for identification and dose estimation, the dose estimation pass rate can reach 80% in high dose. But for low dose, more cells should be used to identify to increase the dose estimation pass rate.
To modify the microstructure and enhance performances, the ultrasonic vibration is applied in the mould casting of TiAl alloy. The effects and mechanism of ultrasonic vibration on the solidifying ...microstructure and mechanical properties are investigated and the model for predicting lamellar colony size is established. After ultrasonic vibration, the coarse microstructure is well modified and lamellar colony is refined from 534 μm to 56 μm. Most of precipitated phases are dissolved into the lamellar colony leading to a homogenous element distribution. The phase ratio of α
-Ti
Al and γ-TiAl is increased, and the chemical composition is promoted to more close to equilibrium level by weakening the influence of β-alloying elements. The microhardness and yield strength are gradually improved by 23.72% and 181.88% due to the fine grain strengthening, while the compressive strength is enhanced by 24.47% through solution strengthening. The critical ultrasonic intensity (I
) for TiAl alloy is estimated at 220 W cm
and the model for average lamellar colony size is established as . The ultrasonic refinement efficiency exponentially increases as the ultrasonic vibration time with a theoretic limit maximum value of E
= 88% and the dominating refinement mechanism by ultrasonic vibration is the cavitation-enhanced nucleation rather than cavitation-induced dendrite fragmentation.
Terpenes have many applications and are widely found in nature, but recent progress in synthetic biology has enabled the use of microorganisms as chassis cells for the synthesis of these compounds.
...Candida glycerinogenes
(
C. glycerinogenes
) is an industrial strain that may be developed as a chassis for the synthesis of terpenes since it has a tolerance to hyperosmolality and high sugar, and has a complete mevalonate (MVA) pathway. However, monoterpenes such as pinene are highly toxic, and the tolerance of
C. glycerinogenes
to pinene was investigated. We also measured the content of mevalonate and squalene to evaluate the strength of the MVA pathway. To determine terpene synthesis capacity, a pathway for the synthesis of pinene was constructed in
C. glycerinogenes
. Pinene production was improved by overexpression, gene knockdown and antisense RNA inhibition. Pinene production was mainly enhanced by strengthening the upstream MVA pathway and inhibiting the production of by-products from the downstream pathway. With these strategies, yield could be increased by almost 16 times, to 6.0 mg/L. Overall, we successfully constructed a pinene synthesis pathway in
C. glycerinogenes
and enhanced pinene production through metabolic modification.
Thermal transport properties have attracted extensive research attentions over the past decades. First-principles-based approaches have proved to be very useful for predicting the thermal transport ...properties of materials and revealing the phonon and electron scattering or propagation mechanisms in materials and devices. In this review, we provide a concise but inclusive discussion on state-of-the-art first-principles thermal modeling methods and notable achievements by these methods over the last decade. A wide range of materials are covered in this review, including two-dimensional materials, superhard materials, metamaterials, and polymers. We also cover the very recent important findings on heat transfer mechanisms informed from first principles, including phonon–electron scattering, higher-order phonon–phonon scattering, and the effect of external electric field on thermal transport. Finally, we discuss the challenges and limitations of state-of-the-art approaches and provide an outlook toward future developments in this area.
Entanglement between a spin-wave qubit (memory qubit) and a photonic qubit is a basic building block for quantum repeaters. Duan-Lukin-Cirac-Zoller (DLCZ) scheme, which generates spin waves via ...spontaneous Raman scattering (SRS) of Stokes photons in atomic ensemble, provides a promising way to generate such entanglement. In a recent work arXiv: 2006.05631, accepted by communications physics, DLCZ-like quantum memory that generates long-lived atom-photon entanglement has been experimentally demonstrated, where magnetic-field-insensitive (MFI) coherence is used to store spin waves. For realizing such MFI spin-wave storage, the atoms have to be initially prepared in a specific Zeeman sublevel, which is achieved by applying optical pumping lasers. Here, we demonstrate the memory lifetimes for the cases that the atoms are perfectly and imperfectly prepared in the specific Zeeman level, respectively. The experimental results show that the spin waves associated with magnetic-field-sensitive (MFS) and MFI coherences will be simultaneously created for the case that the atoms are imperfectly prepared in the Zeeman sublevel. Thus, the read outs will experience decay oscillations due to interferences between the two spin waves and the memory lifetime will be shorten due to dephasing of MFS coherence. A detailed theoretical analysis has been developed for explaining the experimental results. The present work will help one to understand decoherence of spin waves (SWs) and then enable one to obtain optimal lifetime of the entanglement storage in the cold atoms.
•Ultrasonic irradiation was successfully conducted in binary TiAl alloys initially.•Ultrasonic irradiation induces α phase directly precipitating from the melt.•Coarse colony is refined to 52μm and ...102μm for Ti44Al and Ti48Al alloys.•Ultrasonic mechanism is the cavitation-enhanced nucleation for TiAl alloys.
In spite of their high temperature and reactivity, the binary TiAl alloys are successfully imposed by the ultrasonic irradiation and the microstructure evolution, solidification behaviors and mechanical properties are elaborately investigated. After ultrasonic irradiation, a high quality ingot without shrinkage defects and element segregation is obtained and the coarse dendrite structure is well modified into fine non-dendrite globular grains. The coarse lamellar colony and lamellar space of Ti44Al alloy is refined from 685μm to 52μm and 1185nm to 312nm, respectively (similarly, 819μm to 102μm and 2085nm to 565nm for Ti48Al alloy). For Ti48Al alloy, the α peritectic phase is simultaneously precipitated from the melt as well as the β primary phase before the peritectic reaction and the solidification is transformed into the mixed α-solidifying and β-solidifying. Ultrasonic irradiation promotes the peritectic reaction and phase transformation completely and the phase constituent becomes more close to the equilibrium level. The compressive strength of Ti44Al and Ti48Al alloys are increased from 623MPa to 1250MPa and 980MPa to 1295MPa, respectively. The grain refinement and dendrite transformation enhance the grain boundary sliding improving the plastic deformation ability. Ultrasonic irradiation significantly accelerates the melt flow and solute redistribution and the main grain refinement mechanism is the cavitation-enhanced nucleation by inclusion activation and heightened supercooling.
Silicon carbide (SiC) devices have become one of the key research directions in the field of power electronics. However, due to the limitation of the SiC wafer growth process and processing capacity, ...SiC devices, such as SiC MOSFET (Metal-oxide-semiconductor Field-effect Transistor), are facing the problems of high cost and unsatisfied performance. To improve the precise machinability of single-crystal SiC wafer, this paper proposed a new hybrid process. Firstly, we developed an ultrasonic vibration-assisted device, by which ultrasonic-assisted lapping and ultrasonic-assisted CMP (chemical mechanical polishing) for SiC wafer were fulfilled. Secondly, a novel three-step ultrasonic-assisted precise machining route was proposed. In the first step, ultrasonic lapping using a cast iron disc was conducted, which quickly removed large surface damages with a high MRR (material removal rate) of 10.93 μm/min. In the second step, ultrasonic lapping using a copper disc was conducted, which reduced the residual surface defects with a high MRR of 6.11 μm/min. In the third step, ultrasonic CMP using a polyurethane pad was conducted, which achieved a smooth and less damaged surface with an MRR of 1.44 μm/h. These results suggest that the ultrasonic-assisted hybrid process can improve the precise machinability of SiC, which will hopefully achieve high-efficiency and ultra-precision machining.
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