Prime Candidate For Application Research Articles

Mechanical properties of hafnium tantalum carbides via field assisted sintering technology for hypersonic vehicles

Ultra-high temperature ceramics (UHTCs) are refractory transition-metal carbides, nitrides, and borides with the highest melting temperatures known materials, making them prime candidates for applications in aerospace and hypersonic vehicles. Of the UHTCs, tantalum carbide (TaC) and hafnium carbide (HfC) feature the highest melting temperatures. We investigated the binderless consolidation of HfC/TaC powder blends using Field Assisted Sintering Technology (FAST). Powders consisting of 90/10, 50/50, and 10/90 vol% HfC:TaC were sintered to high densities (>94 %). Bulk and nanomechanical, chemical, and microstructural characterization revealed substantially greater strength, hardness, and stiffness for ternary alloys. Mechanical properties correlated with physiochemical analysis indicated trace oxygen phases, solid-solution strengthening, and nonstoichiometric carbon were the key mechanisms driving the peak property enhancement of the 50 vol% solid-solution sample, despite lower densities. This study provides insight into optimizing the compositional design of HfC-TaC alloys by balancing influences from solid solution strengthening and the thermodynamic effects of oxygen/carbon stoichiometry.

Gigahertz-Clocked Teleportation of Time-Bin Qubits with a Quantum Dot in the Telecommunication C Band

Semiconductor quantum dots are prime candidates for applications in quantum networks, such as quantum relays, but their typical emission wavelength, polarization-based qubit encoding scheme, and low operating frequency are incompatible with existing technologies. This study shows that InAs/InP quantum dots driven with gigahertz-clocked pulses, in combination with qubit-transcoding interferometers, can bridge these gaps. The observed teleportation of time-bin qubits in the telecom $C$ band, even when repetition rates exceed the inverse lifetime of the dot, shows the potential for integrating such devices with long-distance quantum network technologies.

Mn-doped topological insulators: a review

Topological insulators (TIs) host robust edge or surface states protected by time-reversal symmetry (TRS), which makes them prime candidates for applications in spintronic devices. A promising avenue of research for the development of functional TI devices has involved doping of three-dimensional (3D) TI thin film and bulk materials with magnetic elements. This approach aims to break the TRS and open a surface band gap near the Dirac point. Utilizing this gapped surface state allows for a wide range of novel physical effects to be observed, paving a way for applications in spintronics and quantum computation. This review focuses on the research of 3D TIs doped with manganese (Mn). We summarize major progress in the study of Mn doped chalcogenide TIs, including Bi2Se3, Bi2Te3, and Bi2(Te,Se)3. The transport properties, in particular the anomalous Hall effect, of the Mn-doped Bi2Se3 are discussed in detail. Finally, we conclude with future prospects and challenges in further studies of Mn doped TIs.

Fabrication and properties of C/SiC porous ceramics by grinding-mould pressing-sintering process

High temperature resistant porous ceramics are considered to be prime candidates for applications in the transpiration cooling system of a hypersonic vehicle. This paper describes a new preparation process including grinding-mould pressing-sintering process, which is successfully used to fabricate C/SiC porous ceramics with high compressive strength and excellent permeability. The effects of carbon fiber content on the microstructure, mechanical property, pore size distribution and permeability of this porous ceramic are investigated in detail. The results indicate that this porous ceramic prepared in this study exhibits high compressive strength (∼270.82 MPa) and excellent permeability (∼3.937 × 10−8 mm2). The C/SiC porous ceramics fabricated in this study will have potential application in active thermal protection systems.

Resonance fluorescence from an atomic-quantum-memory compatible single photon source based on GaAs droplet quantum dots

Single photon sources, which are compatible with quantum memories, are important components of quantum networks. In this article, we show optical investigations on isolated GaAs/Al0.25Ga0.75As quantum dots grown via droplet epitaxy, which emit single photons on resonance with the Rb-87-D2 line (780 nm). Under continuous wave resonant excitation conditions, we observe bright, clean, and narrowband resonance fluorescence emission from such a droplet quantum dot. Furthermore, the second-order correlation measurement clearly demonstrates the single photon emission from this resonantly driven transition. Spectrally resolved resonance fluorescence of a similar quantum dot yields a linewidth as narrow as 660 MHz (2.7 μeV), which corresponds to a coherence time of 0.482 ns. The observed linewidth is the smallest reported so far for strain free GaAs quantum dots grown via the droplet method. We believe that this single photon source can be a prime candidate for applications in optical quantum networks.

Formation and evolution of black silicon microcolumns with array distribution after IR nanosecond-pulsed laser ablation

ABSTRACTThe combination of low reflectivity and the semi-conductive properties of silicon found in black silicon make it a prime candidate for application in photovoltaic solar cells by manipulating the surface microstructure of the silicon. The black silicon can be produced by a complex laser ablation process both temporally and spatially. In this study, in order to explore the formation mechanism of the silicon microcolumn, the ablation area morphology was analyzed four times for 2min, 5min,10min and 20min and the analysis was induced by a 1064 nm nanosecond-pulsed laser in 10−1 Pa of ambient pressure. The experimental results indicated that the black silicon microcolumns were formed through irradiation accumulation, not instantly and stood neatly at the spot center. With the energy coupling, an increased amount of silicon became vapor and was re-deposited back onto the surface.

Biocompatibility assessment of single-walled carbon nanotubes using Saccharomyces cerevisiae as a model organism

BackgroundSingle-walled carbon nanotubes (SWCNTs) have many potential applications in various fields. Especially, the unique physicochemical properties make them as the prime candidates for applications in biomedical fields. However, biocompatibility of SWCNTs has been a major concern for their applications. In the study, biocompatibility of oxidized SWCNTs (O-SWCNTs) was assessed using Saccharomyces cerevisiae (S. cerevisiae) as a model organism.ResultsCell proliferation and viability were significantly changed after exposure to O-SWCNTs (188.2 and 376.4 mg/L) for 24 h. O-SWCNTs were internalized in cells and distributed in cytoplasm, vesicles, lysosomes and cell nucleus. The average O-SWCNTs contents in S. cerevisiae were ranged from 0.18 to 4.82 mg/g during the exposure from 0 to 24 h, and the maximum content was reached at 18 h after exposure. Both penetration and endocytosis were involved in the internalization of O-SWCNTs in S. cerevisiae, and endocytosis was the main pathway. Cellular structures and morphology were changed after exposure to O-SWCNTs, such as undulating appearance at the membrane, shrinking of the cytosol, increased numbers of lipid droplets and disruption of vacuoles. ROS and antioxidant enzymes activities were observably changed following exposure. For the treatment at 376.4 mg/L, 20.8% of the total cells was undergone apoptosis. Decrease of mitochondrial transmembrane potential and leakage of cytochrome c from mitochondria were observed after exposure. Moreover, expression levels of apoptosis-related genes were significantly increased.ConclusionsO-SWCNTs can internalize in S. cerevisiae cells via direct penetration and endocytosis, and distribute in cytoplasm, vesicles, lysosomes and cell nucleus. Besides, O-SWCNTs (188.2 and 376.4 mg/L) can induce apoptosis in S. cerevisiae cells, and oxidative stress is involved in activation of the mitochondria-dependent apoptotic pathway.

Utilizing Retinotopic Mapping for a Multi-Target SSVEP BCI With a Single Flicker Frequency

In brain-computer interfaces (BCIs) that use the steady-state visual evoked response (SSVEP), the user selects a control command by directing attention overtly or covertly to one out of several flicker stimuli. The different control channels are encoded in the frequency, phase, or time domain of the flicker signals. Here, we present a new type of SSVEP BCI, which uses only a single flicker stimulus and yet affords controlling multiple channels. The approach rests on the observation that the relative position between the stimulus and the foci of overt attention result in distinct topographies of the SSVEP response on the scalp. By classifying these topographies, the computer can determine at which position the user is gazing. Offline data analysis in a study on 12 healthy volunteers revealed that 9 targets can be recognized with about 95±3% accuracy, corresponding to an information transfer rate (ITR) of 40.8 ± 3.3 b/min on average. We explored how the classification accuracy is affected by the number of control channels, the trial length, and the number of EEG channels. Our findings suggest that the EEG data from five channels over parieto-occipital brain areas are sufficient for reliably classifying the topographies and that there is a large potential to improve the ITR by optimizing the trial length. The robust performance and the simple stimulation setup suggest that this approach is a prime candidate for applications on desktop and tablet computers.

Visible quantum cutting in Tb3+ doped BaGdF5 phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb3+) doped BaGdF5 phosphor. This phosphor was synthesized by varying molar concentration of Tb3+ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF5:Tb3+ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb3+ and Tb3+ or Tb3+ and Gd3+ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.

Crystalline Cd3As2

Thermo-electric generators (TEGs) directly convert thermal into electrical energy and are the prime candidates for application in low-grade thermal energy/heat waste recovery. TEGs possess several critical advantages as they remain silent, highly reliable and lightweight, which make them uniquely suited for niche deployments in transportation, space satellites, electronics cooling and thermo-voltaic cells. With the efficiency in a few percent range, the efficiency-to-cost ratio remains poor, with the bottleneck traced back to the thermo-electric (TE) materials. PbTe and Bi2Te3, two key TE materials that are in commercial operation, have room temperature ZT of less than 1, whereas ZT exceeding 3 is required for a TEG to be economically viable. Until recently, the enhancement of ZT was mainly attained by introducing phonon scattering interfaces and rattling centers to slow heat transport. With thermal conductivity already approaching the fundamental limit of amorphous materials, further gain in ZT can be only realized by improving the thermo-electric power factor, S2, typically via costly band structure engineering or by means of quantum confinement. In this work, we instead focus on Cd3As2, a high performance 3D Dirac semimetal. Compared to other semimetals, Cd3As2 possess Dirac fermions that disperse linearly in k3-space and in turn, one of the largest electron mobilities known for crystalline materials, i.e. ~104-105cm2V-1s-1. The carrier back-scattering remains suppressed and the electrical transport is dominated by high-energy carriers that favorably affect the thermopower of Cd3As2. Since the power factor scales with the carrier mobility, μ, and weighted density-of-states effective mass, i.e. S2 ~ μ, and the lattice thermal conductivity is within amorphous limit for this material, Cd3As2 shows a strong potential for demonstrating high, device-favorable S and in turn ZT. A reduced temperature vapor-based crystallization pathway was developed to produce free standing, stochiometric 2D cm-size crystals in Cd3As2. In contrast to previous findings, the Seebeck coefficient is seen to initially rise linearly with T to reach a peak within ~ 300-400 K range which is followed by a decline with the shift in the trend attributed to the increase in the role of the ambipolar heat transfer as temperature increases.The primary mechanism of the minority carrier generation in our samples is attributed to phonon-assisted interband electronic transitions involving E and A1 bands. Possessing a very high room-temperature thermopowers of ~613 uV/K and amorphous limit thermal conductivity, bulk Cd3As2 is identified as another high promise phonon-glass electron-crystal TE material for development of next generation a high efficiency thermo-electric generators and refrigerators operating under normal conditions. Figure 1

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries.

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ X-ray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SS-NMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na0.66Ni0.33Mn0.67O2. Zinc doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni(4+)/Ni(3+)/Ni(2+) redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.

Enhanced real-time performance using a secondary bus for cache write-backs

In spite of advances to improve cache efficiency, memory access bottlenecks still prevent processors from executing at full speed. This paper introduces the concept of using a secondary bus, connecting the level-2 cache to memory, for retiring cache write-backs. Simulations, using the sim-alpha version of the SimpleScalar tool set, demonstrate the feasibility and possible advantages of such a secondary bus. Based on simulation results, the added secondary bus can decrease queuing delays on the system bus by 75–90% when sufficient write-backs are present. Such reduction in queuing delays offers superior temporal determinacy in real-time environments. Real-time and near real-time embedded applications that depend on intense graphics processing and movement of large blocks of data, such as printer controllers and medical imaging, are prime candidates for applications of the secondary bus. The feasibility of implementing such a secondary bus using a serial line or wireless technology is also discussed.

Electron beam controlled restructuring of luminescence centers in polycrystalline diamond.

Color centers in diamond are becoming prime candidates for applications in photonics and sensing. In this work we study the time evolution of cathodoluminescence (CL) emissions from color centers in a polycrystalline diamond film under electron irradiation. We demonstrate room-temperature activation of several luminescence centers through a thermal mechanism that is catalyzed by an electron beam. CL activation kinetics were measured in realtime and are discussed in the context of electron induced dehydrogenation of nitrogen-vacancy-hydrogen clusters and dislocation defects. Our results also show that (unintentional) electron beam induced chemical etching can take place during CL analysis of diamond. The etching is caused by residual H2O molecules present in high vacuum CL systems.

Design and Experimental Study on the Controllable High-Speed Spiral Groove Face Seals

The spiral groove face seal is a prime candidate for application of the liquid oxygen and liquid hydrogen turbopump. The study investigated the designs of the electro-magnetic loading device (EMLD) and friction torque testing device (FTTD), and their application in the interface experiments of face seals with spiral grooves which used water as the sealing fluid. The seal performance parameters, including face temperature, face friction torque, film pressure at the seal dam, were measured under the static balance position, and the effects of the face closing force, which varied with the axial load generated from the EMLD, on the seal performance were tested under a specific controlled mode. The result indicated that both the pressure at the seal dam and face temperature increased with the rotating speed and that small friction was obtained when the face seal was fully film-lubricated. The separation speed of the controllable seal could also be controlled, which helped seal faces lift off and met the conditions of the face noncontact status. Additionally, with the application of the EMLD and FTTD, seal operation monitoring was rendered possible and a controllable face seal with desirable performance was achieved. The findings of the current study lend great insights into engineering seal design and its applications.

The Ageing Behavior of Titanium Alloy Ti-10V-2Fe-3Al

A good combination of high strength and hardenability makes the alloy Ti 10V-2Fe-3Al a prime candidate for applications in the aerospace arena. However, these properties are very dependent on a post-forming heat treatment. The overall objective of this work is to determine the effect of prior deformation on the aging behaviour. In this particular study, the influence of the heat treatment, either solution and/or aging, on the microstructures, and consequently on the mechanical properties, without introduced strain is reported. Various solution heat treatments have been conducted, either in the β phase or in the (α+β) phase field, followed by rapid quenching or slow cooling, and aging treatments at different temperatures (250, 350, 400, 500C°) above and below the ω-transus temperature. Vickers hardness indentations were used to follow the precipitation hardening behaviour, and mechanical properties were determined using a shear punch test. The aging response is dependent not only on the presence of the athermal ω phase but also on the proximity of the aging temperature to the ω-transus. Most treatments showed an unusual initial softening behaviour prior to age hardening, however this appears to be related again to the composition and fraction of the β phase retained after solution treatment.

Time-dependent failure of amorphous polylactides in static loading conditions

Polylactides are commonly praised for their excellent mechanical properties (e.g. a high modulus and yield strength). In combination with their bioresorbability and biocompatibility, they are considered prime candidates for application in load-bearing biomedical implants. Unfortunately, however, their long-term performance under static load is far from impressive. In a previous in vivo study on degradable polylactide spinal cages in a goat model it was observed that, although short-term mechanical and real-time degradation experiments predicted otherwise, the implants failed prematurely under the specified loads. In this study we demonstrate that this premature failure is attributed to the time-dependent character of the material used. The phenomenon is common to all polymers, and finds its origin in stress-activated segmental molecular mobility leading to a steady rate of plastic flow. The stress-dependence of this flow-rate is well captured by Eyring’s theory of absolute rates, as demonstrated on three amorphous polylactides of different stereoregularity. We show that the kinetics of the three materials are comparable and can be well described using the proposed modeling framework. The main conclusion is that knowledge of the instantaneous strength of a polymeric material is insufficient to predict its long-term performance.

The chemistry of the mechanical bond

The use of templation in the synthesis of unnatural products where two or more components are mechanically interlocked has not only raised the efficiency of their production to near quantitative levels in some instances, but the molecular recognition that aids and abets the templation is also part and parcel of the molecules after they have been prepared, purified and presented for investigation. The fact that the molecular recognition 'lives on' in mechanically interlocked molecules, following their templated formation, makes them prime candidates for applications that straddle the scientific and technical worlds from devices that could spawn new information technologies to integrated systems that could have fundamental applications in the health-care industries. The challenge to make more and more sophisticated compounds is predicated upon our fundamental understanding of the nature of the mechanical bond and how this associated knowledge base can be employed to do complex systems chemistry in very different environments where emergent phenomena become the order of the day (critical review, 104 references).

Charge Mobility in the Room‐Temperature Liquid‐Crystalline Semiconductor Poly(di‐n‐ butylstannane)

The mobility of charge along the σ-bonded backbone of tin atoms in poly(di-n-butylstannane) is ca. 0.1 cm2 V–1 s–1 in the crystalline phase. It decreases by only a factor of three in the liquid-crystalline mesophase, which is stable down to –25 °C on cooling from room temperature (see Figure). The high mobility and the ease with which the polymer chains can be aligned make it a prime candidate for applications in molecular electronic devices.

GaAs HBT's for microwave integrated circuits

The status of the microwave GaAs heterojunction bipolar transistor (HBT) technology is reviewed. Microwave circuits for advanced military and commercial systems continue to increase their dependence on the performance, functionality, and cost of active components fabricated using solid-state technology. The performance advantages provided by GaAs HBT's, for several critical circuit applications, have stimulated a worldwide development activity. Progress in HBT device technology and microwave circuit applications has been extremely rapid because of the broad availability of III-V compound semiconductor epitaxial materials and prior experience with GaAs field-effect transistors (FET's) and monolithic microwave integrated circuits (MMIC's). The great flexibility of HBT's in microwave circuits makes them prime candidates for applications in complex multifunctional microwave/digital IC's in next-generation systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>