Lower Vf Research Articles

A 4H-SiC p-channel insulated gate bipolar transistor with higher breakdown voltage and superior V F·C res figure of merit

A silicon carbide p-channel insulated gate bipolar transistor (IGBT) with higher breakdown voltage (BV) and low V F·C res figure of merit (FOM) has been simulated, fabricated, and characterized successfully. The proposed IGBT adds two n-type implant regions in the junction FET (JFET) area and increases the gate oxide thickness above the JFET area to reduce the reverse transfer capacitance (C res) and gate oxide electric field (E ox). The proposed structure notably lowers E ox below 3 MV cm−1 while elevating the BV to 16.6 kV. A new FOM of V F·C res is defined to evaluate the trade-off between the on-state and the C res characteristics. The experimental results demonstrate that a lower V F·C res FOM of 0.369 V·pF is achieved from the proposed IGBT with a reduction of 66.4%, compared to the conventional current spreading layer IGBT. Meanwhile, the simulated turn-on and turn-off times of the proposed IGBT are reduced by 29.4% and 20%, respectively.

Morphometric analysis of the North Liuleng Shan Fault in the northern Shanxi Graben System, China: Insights into active deformation pattern and fault evolution

The North Liuleng Shan Fault (NLSF) is one of the major active faults in the northern Shanxi Graben System (SGS) in North China. Although the fault has been investigated extensively in terms of late Quaternary activity, its active deformation pattern is still poorly characterized. In this study, we conducted a morphometric analysis of the fault using various geomorphic indices to assess the along-strike relative uplift rates, which include basin relief, slope, mountain front sinuosity (Smf), hypsometric integral (HI) and curves, valley floor width-to-height ratio (Vf), asymmetry factor (Af), basin elongation ratio (Re), and normalized channel steepness indices (ksn). Our findings indicate that the central portion of the fault has experienced higher relative uplift rates than the southwestern and northeastern portions, as demonstrated by higher basin-averaged slopes and ksn values, and lower Vf, Re, and Smf values. This spatial distribution pattern of relative uplift rates appears to correlate well with along-strike changes in the fault geometry and kinematics of the NLSF. We interpret the EW-striking, central portion of the NLSF as a releasing bend formed by the NE-striking, right-stepping, en-echelon southwestern and northeastern portions of the fault system, which are characterized by right-lateral oblique slip. Furthermore, the northeastward increase in HI values along with the regional basin evolution history suggest that the NLSF likely propagated from southwest to northeast. We propose that the southwestern portion of the fault most probably initiated earlier and that the central and northeastern portions formed later as extensional structures at the termini of the fault zone. Our findings contribute to a better understanding of the tectonics and genesis of the basin-and-range geomorphology in the northern SGS.

Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities

BackgroundDifferences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences. MethodsUsing an adult N95 mask as a control and two different face velocities (vf) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 μm. ResultsAll three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower vf and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 μm. ConclusionsLower vf for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 μm was low (typically <50%) for both vf‘s studied.

Structural integrity evaluation of cyclic loading Glass Fibre Reinforced Polymer composite by acoustic emission and heat transfer

GFRP composites experience structural changes like matrix cracking, debonding, delamination, and fibre failure on static and dynamic loading. In this work, composites with varying fibre orientation interaction angle and volume fractions are prepared and exposed to cyclic load. The cyclic load (R = 0) is a constant amplitude flexural load imposed on the cantilever beam specimen with varying frequencies (2.6, 4.6, 8.6 Hz) and cycles (up to 44 × 103). The structural integrity of the specimens on loading is examined in terms of Flexural, modulus, Acoustic Emission (AE) and heat transfer changes. The drop in flexural modulus is minimum in higher Vf = 32% laminate (A1 = 7.01%, B1 = 1.86%) than the lower Vf = 25% (A2 = 19.86%, B2 = 8.6%). The observed AE peak frequency for the induced damages is in the range of 50–100, 110–230, 245–380 kHz. The drop-in fibre volume fraction has a significant role in laminate with lower fibre interaction (Type A) to offer minimum variation (5.25%) in AE activity count which is the opposite in laminates with higher fibre interaction angle (31.75%). The step heat thermography exhibits minimum temperature difference (∆T) for moderate loading frequency and in a few cases, ∆T drops well below the virgin, insisting on in situ thermography to study the dynamic changes in composites. A fibre dominant behaviour can be observed with minimum variation in AE activity in a lower fibre interaction angle. Thus, the fibre orientation angle and fibre volume fraction have a significant role in the retention of the structural integrity of composites in dynamic loading.

Human polyethylene granuloma tissues inhibit bone healing in a novel xenograft animal model

During revision of a conventional polyethylene joint replacement, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the polyethylene granuloma tissues. We developed a human/rat xenograft model to investigate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic nude rats. After 3 weeks in vivo, there was a significant difference in the bone volume fraction (Vf ) between empty, primary, and revision defects (p = 0.02), with a lower Vf in defects with revision granuloma tissues compared to defects with primary osteoarthritic tissues. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Therefore, debridement around a metal-on-polyethylene hip replacement may shorten the time it takes to achieve secondary stability around a revision hip replacement.

Validation of Next Generation Sequencing Cancer Panels for Clinical Somatic Mutation Profiling-- Identification of Source of Variations and Artifacts using FFPE Tissues

Use of a Next Generation Sequencing (NGS)-based test as a clinical trial assay requires that the test be analytically validated to CLIA/CAP regulations. During the course of analytically validating NGS cancer panels for use as patient enrollment assays, we assessed the repeatability, reproducibility and accuracy of commercially available Cancer Panels (Illumina TruSeq Cancer Panel on MiSeq and Life Technologies AmpliSeq v2 Cancer Panel on Ion Torrent PGM). We measured the repeatability and reproducibility by evaluating all variant calls among technical replicates and found in both platforms that variants with higher variant frequency (VF >30%) were called with much higher repeatability and reproducibility than those with lower VF (between 5 and 25%), a level at which many somatic mutations are found. Also, Illumina MiSeq run-to-run reproducibility was significantly higher than that of Ion Torrent PGM. However, Illumina TruSeq library preparation protocol resulted in much lower repeatability than those obtained from Ion Torrent AmpliSeq protocol at the low VF range. To determine the optimal variant call settings, we used different sets of more stringent filters (lower false positive rate, but higher false negative rate), each platform could achieve close to 95% reproducibility and repeatability. Sequenom MassArray was used as a tie-breaker assay for discordant calls between the two NGS platforms to establish the “truth”. Our data provide insight into the steps that contribute most to variability, such as the procedure of library preparation, the sequencingby- synthesis chemistry, the factors that impact mutation calls and sampling variation. We also found very high C to T mutation calls associated with Illumina Cancer Panel using TruSeq library preparation protocol (but not with Ion Torrent using AmpliSeq protocol) when a less stringent filter set was used. The C to T artifact mutation calls from formalin-fixed paraffin-embedded (FFPE) tissue samples observed in this study together with high C to A artifact mutation calls from acoustic shearing of intact DNA observed by others have the potential to negatively impact mutation profiling and mutation signature identification if not carefully addressed. Based on these results we conclude library preparation protocols that start with PCR amplification, such as the AmpliSeq protocol, provide higher repeatability on variant calls with low VF and therefore, are more suitable for mutation profiling and mutation signature studies where somatic mutations (including unknown mutations) are the focus and balanced false positive and false negative rates are critical to success.

Impact properties of injection molded glass fiber/polyamide-6 composites: effect of testing parameters

Reported data on impact properties show that wide discrepancies exist, although the same grade of materials was being used. In this article, we report some testing condition-property relationships of injection molded glass-fiber/polyamide-6 composites. It was found that an increase in specimen size/geometry leads to an increase in fracture energy and peak load; however, critical strain energy release rate and critical stress intensity factor decrease. Increase in impactor velocity, fracture energy, and peak load are all in mixed mode (increase and decrease). Similar to inconsistency obtained in fracture energy, critical strain energy release rate is also in mixed mode. However, critical stress intensity factor is marginally increased. Increases in impactor load weight and fracture energy at all notch to depth ratios are sensibly increased; however, critical strain energy release rate is marginally decreased at lower Vf and sensibly increased at higher fiber loading. With an increase in impactor load weight, changes in peak load are also in mixed mode, whereas critical stress intensity factor is marginally decreased.

Triaxial Modulation of the Acceleration Induced in the Lower Extremity During Whole-Body Vibration Training: A Pilot Study

The purpose of the present study was to quantify vibration transmissibility through the lower extremity during exercise on a whole-body vibration (WBV) platform. Six healthy adults completed 20 trials of 30-second static squat exercise at 30 or 40 degrees of knee flexion angle on a WBV platform working at combinations of 5 frequencies (VF: 20, 25, 30, 35, 40 Hz) and 2 amplitudes (VA: low, 1.5 mm or high, 3 mm). Accelerations induced by the platform were recorded simultaneously at the shank and the thigh using triaxial accelerometers positioned at the segmental center of mass. Root-mean-square (RMS) acceleration amplitude and transmission ratios between the platform and the leg segments were calculated and compared between the experimental conditions. An alpha level of 0.05 was set to establish significance. Shank vertical acceleration was greatest at the lower VF (p = 0.028), higher VA (p = 0.028), and deeper squat (p = 0.048). Thigh vertical acceleration was not affected by depth of squat (p = 0.25), but it was greatest at higher VA (p = 0.046) and lower VF (p = 0.028). Medial-lateral shank acceleration was greatest at higher VF and deeper squat (both p = 0.046) and at higher VA (p = 0.028). Medial-lateral thigh acceleration was positively related to both VF (p = 0.046) and VA (p = 0.028) but was not affected by knee angle (p = 0.46). Anterior-posterior shank acceleration was higher at deeper squat (p = 0.046) and at lower VF and higher VA (both p = 0.028). Anterior-posterior thigh acceleration was related positively to the VA (p = 0.028), inversely to the VF (p = 0.028), and not dependent on knee angle (p = 0.75). Identification of specific vibration parameters and posture, which underpin WBV training efficacy, will enable coaches and athletes to design WBV training programs to specifically target shank or thigh muscles for enhanced performance.

A Self-Correcting, Thermal-Curvature-Stable Bending Element

Under a through-thickness temperature variation, thin structural elements such as beams, plates, and shells tend to bend. This bending deformation can distort the elements of a structure and cause thermal stresses. In this paper, the requirements for a laminate which is "self-correcting" are given. These thermal-curvature-stable (TCS) laminates exhibit zero bending curvature under steady-state heat transfer conditions. The TCS effect is independent of the actual temperatures, within the context of linear theory. This effect is demonstrated for an aluminum/composite laminate, where the solution appears as the ratio of composite lamina to aluminum lamina thicknesses. The example laminated beams demonstrate a reduced net in-plane thermal expansion when compared to mono-lithic aluminum beams. The efficiency of the iCS laminate is shown to be more sensitive to lamina thickness than to lamina properties. An additional design parameter for TCS laminates is the fiber volume fraction (Vf), which affects the composite modulus, thermal expansion, and transverse thermal conductivity. It is shown that at higher Vf, the TCS effect is relatively insensitive to Vf. At lower Vf, the in-plane thermal expansion can be further reduced at the expense of increased composite layer thickness.

ＳｉＣウィスカ強化アルミニウム合金複合材料の機械的性質に及ぼすウィスカ体積率の影響

SiC whisker reinforced aluminum alloy composites with whisker volume fraction (Vf) ranging from 0 to 40% were fabricated by a powder metallurgical method. In a low Vf range, the ultimate tensile strength increases proportionally with the increase of Vf and agrees satisfactorily with the value calculated from Kelly and Tyson's equation. In a high Vf range, however, the increasing rate of strength becomes smaller than the theoretical value due to the decrease in ductility of composites. This deviation from the proportional line takes place at a lower Vf and the decrease in strength is also observed in higher strength aluminum alloy matrix composites. At elevated temperatures, the tensile strength follows the proportional relationship with the Vf to a higher Vf range due to the improvement in ductility. The elastic modulus increases as the Vf increases and is in good agreement with the value calculated from Cox's equation, assuming that the elastic modulus of whiskers is 43, 000kgf/mm2. The whisker orientation factors of three dimensional random array composites for the strength and the elastic modulus are determined experimentally as 0.38 and 0.68, respectively.

高温押出時の塑性流動がＡｌ２Ｏ３／Ａｌ複合材料の繊維配向性および繊維長に及ぼす影響

δ-Al2O3/Al composites were fabricated by high pressure infiltration and extruded at high temperatures. The plastic flow in extruded matrices is classified into two types, namely a laminar flow in the surface region and a turbulent flow in the core. The wider the laminar flow region, the better the fiber alignment obtained. The laminer flow region extends at lower Vf and lower extruding temperatures. Surface defects, fir-tree-type cracks, easily grow at high Vf. The δ-Al2O3/Al alloy has tensile strength twice as much as that the matrix alloy extruded in the same way.