24,028 research outputs found
Development of a digital electronic rebalance loop for a dry tuned-rotor two degree-of-freedom gyroscope
Digital electronic rebalance loops were designed and implemented in brassboard form to capture both X and Y axes of the Kearfott Gyroflex. The loops were width-modulated binary types using a 614.4 kHz keying signal and a 2.4 kHz sample frequency. The loops were designed for a torquing rate of 2 deg/sec (70.6 mA torquing current) and a data resolution of 23.4 milli-arc-sec per data pulse. Design considerations, implementation details, and preliminary experimental results are presented
Development of a Low-Noise High Common-Mode-Rejection Instrumentation Amplifier
Several previously used instrumentation amplifier circuits were examined to find limitations and possibilities for improvement. One general configuration is analyzed in detail, and methods for improvement are enumerated. An improved amplifier circuit is described and analyzed with respect to common mode rejection and noise. Experimental data are presented showing good agreement between calculated and measured common mode rejection ratio and equivalent noise resistance. The amplifier is shown to be capable of common mode rejection in excess of 140 db for a trimmed circuit at frequencies below 100 Hz and equivalent white noise below 3.0 nv/square root of Hz above 1000 Hz
Development and preliminary evaluation of a clinical guidance programme for the decision about prophylactic oophorectomy in women undergoing a hysterectomy
Objectives: To develop a decision analysis based and computerised clinical guidance programme
(CGP) that provides patient specific guidance on the decision whether or not to undergo a prophylactic
oophorectomy to reduce the risk of subsequent ovarian cancer and to undertake a preliminary pilot
and evaluation.
Subjects: Women who had already agreed to have a hysterectomy who otherwise had no ovarian
pathology.
Setting: Oophorectomy decision consultation at the outpatient or pre-admission clinic.
Methods: A CGP was developed with advice from gynaecologists and patient groups, incorporating
a set of Markov models within a decision analytical framework to evaluate the benefits of undergoing
a prophylactic oophorectomy or not on the basis of quality adjusted life expectancy, life expectancy,
and for varying durations of hormone replacement therapy. Sensitivity analysis and preliminary testing
of the CGP were undertaken to compare its overall performance with established guidelines and practice.
A small convenience sample of women invited to use the CGP were interviewed, the interviews
were taped and transcribed, and a thematic analysis was undertaken.
Results: The run time of the programme was 20 minutes, depending on the use of opt outs to default
values. The CGP functioned well in preliminary testing. Women were able to use the programme and
expressed overall satisfaction with it. Some had reservations about the computerised format and some
were surprised at the specificity of the guidance given.
Conclusions: A CGP can be developed for a complex healthcare decision. It can give evidence-based
health guidance which can be adjusted to account for individual risk factors and reflects a patient’s
own values and preferences concerning health outcomes. Future decision aids and support systems
need to be developed and evaluated in a way which takes account of the variation in patients’ preferences
for inclusion in the decision making process
Design of a Torque Current Generator for Strapdown Gyroscopes
The design, analysis, and experimental evaluation of an optimum performance torque current generator for use with strapdown gyroscopes, is presented. Among the criteria used to evaluate the design were the following: (1) steady-state accuracy; (2) margins of stability against self-oscillation; (3) temperature variations; (4) aging; (5) static errors drift errors, and transient errors, (6) classical frequency and time domain characteristics; and (7) the equivalent noise at the input of the comparater operational amplifier. The DC feedback loop of the torque current generator was approximated as a second-order system. Stability calculations for gain margins are discussed. Circuit diagrams are shown and block diagrams showing the implementation of the torque current generator are discussed
High-resolution width-modulated pulse rebalance electronics for strapdown gyroscopes and accelerometers
Three different rebalance electronic loops were designed, implemented, and evaluated. The loops were width-modulated binary types using a 614.4 kHz keying signal; they were developed to accommodate the following three inertial sensors with the indicated resolution values: (1) Kearfott 2412 accelerometer - resolution = 260 micro-g/data pulse, (2) Honeywell GG334 gyroscope - resolution = 3.9 milli-arc-sec/data pulse, (3) Kearfott 2401-009 accelerometer - resolution = 144 milli-g/data pulse. Design theory, details of the design implementation, and experimental results for each loop are presented
Wireless, in-vessel neutron monitor for initial core-loading of advanced breeder reactors
An experimental wireless, in-vessel neutron monitor was developed to measure the reactivity of an advanced breeder reactor as the core is loaded for the first time to preclude an accidental critically incident. The environment is liquid sodium at a temperature of approx. 220 C, with negligible gamma or neutron radiation. With ultrasonic transmission of neutron data, no fundamental limitation was observed after tests at 230 C for 2000 h. The neutron sensitivity was approx. 1 count/s-nv, and the potential data transmission rate was approx. 10,000 counts/s
Podocyte Injury Associated with Mutant α-Actinin-4
Focal segmental glomerulosclerosis (FSGS) is an important cause of proteinuria and nephrotic syndrome in humans. The pathogenesis of FSGS may be associated with glomerular visceral epithelial cell (GEC; podocyte) injury, leading to apoptosis, detachment, and “podocytopenia”, followed by glomerulosclerosis. Mutations in α-actinin-4 are associated with FSGS in humans. In cultured GECs, α-actinin-4 mediates adhesion and cytoskeletal dynamics. FSGS-associated α-actinin-4 mutants show increased binding to actin filaments, compared with the wild-type protein. Expression of an α-actinin-4 mutant in mouse podocytes in vivo resulted in proteinuric FSGS. GECs that express mutant α-actinin-4 show defective spreading and motility, and such abnormalities could alter the mechanical properties of the podocyte, contribute to cytoskeletal disruption, and lead to injury. The potential for mutant α-actinin-4 to injure podocytes is also suggested by the characteristics of this mutant protein to form microaggregates, undergo ubiquitination, impair the ubiquitin-proteasome system, enhance endoplasmic reticulum stress, and exacerbate apoptosis
Heat kernels on curved cones
A functorial derivation is presented of a heat-kernel expansion coefficient
on a manifold with a singular fixed point set of codimension two. The existence
of an extrinsic curvature term is pointed out.Comment: 4p.,sign errors corrected and a small addition,uses JyTeX,MUTP/94/0
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