A temperature-dependent impact-ionization-initiated RF breakdown model in the 2DEG channel of AlGaN/GaN HFETs is reported. When operating these devices in RF power amplifier circuits, impact ...ionization in the channel has a significant effect upon gain saturation, power-added efficiency, and output power. An analytical physics-based model of channel breakdown is formulated based on TCAD investigations of the internal device behavior. This model is integrated with an existing physics-based HFET compact model and accurately predicts large-signal device performance. Values of thermal resistance and the breakdown temperature coefficient were extracted from simulations of an industrial HFET and are in agreement with the literature, thus validating that the model captures the dominant breakdown mechanism.
We report the direct measurement of the {sup 7}Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV ...{sup 7}Be neutrinos is 49{+-}3{sub stat}{+-}4{sub syst} counts/(day{center_dot}100 ton). The hypothesis of no oscillation for {sup 7}Be solar neutrinos is inconsistent with our measurement at the 4{sigma} C.L. Our result is the first direct measurement of the survival probability for solar {nu}{sub e} in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of {sup 7}Be, pp, and CNO solar {nu}{sub e}, and the limit on the effective neutrino magnetic moment using solar neutrinos.
The liquid handling systems for the Borexino solar neutrino detector Alimonti, G.; Avanzini, M.B.; Back, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2009, Letnik:
609, Številka:
1
Journal Article
Recenzirano
The successful deployment of the Borexino solar neutrino detector required assorted physical and chemical operations to produce exceptional pure fluids and fill multiple detector zones. The ...composition and flow rates of high purity gases and liquids had to be precisely controlled to maintain liquid levels and pressures. The system was required to meet exceptional requirements for cleanliness and leak-tightness. A large scale modular system connecting fluid receiving, purification and fluid delivery processes was developed for Borexino. At the core is a flow control system that delivers scintillator components to plants for purification, and then fills the Borexino detector volumes with ultrahigh purity buffer or ultrahigh purity scintillator. The liquid handling system maintains precise control over the liquid levels and differential pressures between the different volumes of the detectors that are separated by flexible nylon vessels. The preparation, commissioning and operation of the system for filling the Borexino detector with scintillator is described.
Purification of the 278 tons of liquid scintillator and 889
tons of buffer shielding for the Borexino solar neutrino detector is performed with a system that combines distillation, water extraction, ...gas stripping, and filtration. This paper describes the principles of operation, design, and construction of that purification system, and reviews the requirements and methods to achieve system cleanliness and leak-tightness.
Category:
Trauma; Ankle
Introduction/Purpose:
The native sagittal plane alignment of the distal tibia has not been well-described and has implications during the fixation of tibia fractures. ...Cavovarus foot alignment has been previously thought to influence gastrocsoleus tightness and the potential for anterior talar escape in the setting of an osseous injury in this region. However, the relationship between midfoot alignment and sagittal distal tibia morphology is undescribed. Characterization of this osseous anatomy may be helpful to achieve adequate sagittal alignment during the reduction of distal tibia fractures. The purpose of this study was primarily to characterize distal tibia sagittal morphology and ankle radiographic parameters, determine whether symmetry exists from side-to- side, and secondarily to identify any differences based on midfoot alignment.
Methods:
112 patients (60 females, mean age 45.8 years) with bilateral lateral weight-bearing ankle radiographs were retrospectively evaluated (224 ankles). Midfoot morphology was classified as normal, planus, or cavus using Meary's angle (MA) (Planus: MA <-4°, Normal: MA -4°≤x≤4°, Cavus: MA>4°). The angle between the proximal diaphyseal (Line 1) and distal tibia (Line 2) axes was measured, and the location of the center of rotation of angulation (CORA) relative to the plafond was recorded (Figure 1). The horizontal distance (via a line parallel to the floor) from the distal tibia axis (Line 2) to the lateral talar process was measured, as well as the anterior distal tibial angle, and the plafond radius of curvature (ROC). Bilateral ankles and midfoot morphologies were compared using a Mann-Whitney U test and ANOVA, respectively. Correlation was assessed using linear regression.
Results:
The average distal tibia had 2° of apex posterior angulation with the CORA located 8.0 cm proximal to the plafond. There was no difference by laterality in magnitude of the angulation (p=.358) or distance from the plafond to the CORA (p=.901). The angulation increased as foot alignment transitioned from cavus (1.25°), to normal (1.89°), to planus (3.05°) alignment (r=.32; R2=.102; p<.001). The angulation was larger in men (2.8°) than in women (1.4°) (p<.001) and decreased with increasing patient age (r=.279, R2=.078, p<.001). The lateral talar process was on average 5.9 mm anterior to the distal tibia axis (Line 2), more anterior with cavus versus planus alignment (6.7mm vs. 4.8mm) (p<.001). The average anterior distal tibial angle and plafond ROC were 83.6° and 22.9 mm, respectively, with no significant differences by laterality or midfoot morphology (p>.05 for both).
Conclusion:
The distal tibia has a consistent apex posterior bow that is symmetric from side-to-side, but variable from patient- to-patient. Distal tibia osseous morphology is related to midfoot alignment, sex, and age. Cavus alignment is additionally correlated with anterior translation of the lateral talar process relative to the distal tibia axis. Surgeons treating distal tibia fractures may consider the use of contralateral imaging as a reduction template to help restore patient-specific sagittal alignment. A tibial nail that ends anterior in the distal segment of a distal tibia fracture should prompt the surgeon to carefully evaluate whether sagittal alignment has been restored.
The fluid-filling system for the Borexino solar neutrino detector Benziger, J.; Cadonati, L.; Calaprice, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2009, Letnik:
608, Številka:
3
Journal Article
Recenzirano
The system for controlled filling of the nested flexible scintillator containment vessels in the Borexino solar neutrino detector is described. The design and operation principles of pressure and ...shape monitoring systems are presented for gas filling, gas displacement by water, and water displacement by scintillator. System specifications for safety against overstressing the flexible nylon vessels are defined as well as leak-tightness and cleanliness requirements. The fluid-filling system was a major engineering challenge for the Borexino detector.
Two independent problem areas in AlGaN/GaN HFETs that affect device performance and reliability are investigated. The first is an investigation into the nonlinear resistance phenomenon present in ...these devices under high current RF operation. High-voltage microwave AlGaN/GaN HFETs operating under high-power conditions suffer from degraded RF performance and linearity due to a nonlinear resistance effect in the gate-source region. During RF operation, the nonlinear resistance is due to the onset a of space-charge-limited current (SCLC) transport mechanism within the device channel. Under high current injection conditions, SCLC transport can set in and, consequently, the source resistance becomes a function of the injected charge resulting in a rapid increase and limiting device performance. The threshold for SCL current is dependent on the donor-like states on the AlGaN surface which are responsible for supplying electrons to the channel. To understand the effect of nonlinear source resistance we show on an un-gated HFET channel model that the critical current density of space-charge effects and thus the onset of nonlinear source resistance can be reduced or can be shifted above the normal operating current density of the device by modification of the charge on the AlGaN surface. Secondly, nonlinearities stemming from avalanche breakdown due to high electric field magnitudes in the device channel while operating under high voltage conditions is investigated. A temperature dependent, impact ionization initiated RF breakdown model in the 2DEG channel of AlGaN/GaN HFETs is reported. When operating these devices in RF power amplifier circuits, impact ionization in the channel has a significant effect upon gain saturation, power-added efficiency and output power. An analytical physics-based model of channel breakdown is formulated based on TCAD investigations of the internal device behavior. This model is integrated with an existing physics-based HFET compact model and accurately predicts large-signal device performance. Values of thermal resistance and the breakdown temperature coefficient were extracted from simulations of an industrial HFET and are in agreement with the published measurements as well as an independent model of thermal resistance in AlGaN/GaN HFETs thus validating that the model accurately captures the dominant breakdown mechanism.
Purpose The extensor digitorum communis (EDC) splitting approach is a direct lateral approach that can provide greater visualization of the proximal radius than the posterolateral approach to the ...elbow. The purposes of this study were to identify the anatomic relationships of the posterior interosseous nerve (PIN) during the EDC splitting approach to the proximal radius and to determine its safe zone. Methods A fellowship-trained attending hand surgeon performed the EDC splitting approach on 15 cadaveric arms, exposing the EDC origin from the lateral epicondyle and dissecting distally to expose the supinator muscle. Calipers were used to measure the distance from the PIN to the radiocapitellar joint and to the lateral epicondyle in neutral position, full supination, and full pronation. The depth of the nerve from the most superficial aspect of the EDC was recorded for each cadaver. Results The average distances from the radiocapitellar joint to the PIN in neutral, supination, and pronation were 44.5 ± 7.9, 40.8 ± 8.1, and 48.2 ± 7.9 mm, respectively. The average distances from the lateral epicondyle to the PIN in neutral, supination, and pronation were 61.7 ± 10.9, 57.6 ± 9.1, and 64.7 ± 11.5 mm, respectively. The shortest distance measured from the radiocapitellar joint to the PIN in pronation was 29 mm; the shortest distance measured from the lateral epicondyle to the nerve was 42 mm. The average depth of the nerve from the most superficial aspect of the EDC was 10.2 ± 2.4 mm. Conclusions The PIN is generally safe when dissecting up to 29 mm from the radiocapitellar joint and up to 42 mm from the lateral epicondyle with the forearm in pronation.
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