48 research outputs found
Action principle formulation for motion of extended bodies in General Relativity
We present an action principle formulation for the study of motion of an
extended body in General Relativity in the limit of weak gravitational field.
This gives the classical equations of motion for multipole moments of arbitrary
order coupling to the gravitational field. In particular, a new force due to
the octupole moment is obtained. The action also yields the gravitationally
induced phase shifts in quantum interference experiments due to the coupling of
all multipole moments.Comment: Revised version derives Octupole moment force. Some clarifications
and a reference added. To appear in Phys. Rev.
Why don't some men with banked sperm respond to letters about their stored samples?
Long-term storage of banked sperm, especially when it is not needed, for reproductive purposes, is costly and poses practical problems for sperm banks. For sperm banks to function efficiently, men must understand the implications of unnecessary storage, and make timely decisions about disposal of their own samples. Men who bank sperm prior to cancer treatment are routinely offered follow-up consultations to test their fertility, update consent and, where necessary, expedite referral for Assisted Conception. Yet sperm banks report that men do not respond to letters, suggesting samples are stored needlessly. We conducted semi-structured interviews with six men with a history of not responding to letters, to document reasons for non-response. Interviews were transcribed and analysed using Interpretive Phenomenological Analysis. Men's reasons for not responding are a complex interplay between past, present and future perspectives. In terms of their past, information is important on diagnosis, because men must understand that fertility can change after treatment. Present and future concerns focus on fears of being told fertility has not recovered and being pressured to dispose of banked sperm. The challenge is to devise invitation letters that address men's concerns while offering them tangible benefits and peace of mind
Estimating overdiagnosis in giant cell arteritis diagnostic pathways using genetic data: genetic association study
Objectives
GCA can be confirmed by temporal artery biopsy (TAB) but false negatives can occur. GCA may be overdiagnosed in TAB-negative cases, or if neither TAB nor imaging is done. We used HLA genetic association of TAB-positive GCA as an ‘unbiased umpire’ test to estimate historic overdiagnosis of GCA.
Methods
Patients diagnosed with GCA between 1990 and 2014 were genotyped. During this era, vascular imaging alone was rarely used to diagnose GCA. HLA region variants were jointly imputed from genome-wide genotypic data of cases and controls. Per-allele frequencies across all HLA variants with P < 1.0 × 10−5 were compared with population control data to estimate overdiagnosis rates in cases without a positive TAB.
Results
Genetic data from 663 GCA patients were compared with data from 2619 population controls. TAB-negative GCA (n = 147) and GCA without TAB result (n = 160) had variant frequencies intermediate between TAB-positive GCA (n = 356) and population controls. For example, the allele frequency of HLA-DRB1*04 was 32% for TAB-positive GCA, 29% for GCA without TAB result, 27% for TAB-negative GCA and 20% in population controls. Making several strong assumptions, we estimated that around two-thirds of TAB-negative cases and one-third of cases without TAB result may have been overdiagnosed. From these data, TAB sensitivity is estimated as 88%.
Conclusions
Conservatively assuming 95% specificity, TAB has a negative likelihood ratio of around 0.12. Our method for utilizing standard genotyping data as an ‘unbiased umpire’ might be used as a way of comparing the accuracy of different diagnostic pathways
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
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KINETIC EQUATIONS AND TYPE CURVES FOR PREDICTING THE PRECIPITATION OF AMORPHOUS SILICA FROM GEOTHERMAL BRINES
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Kinetic equations and type curves for predicting the precipitation of amorphous silica from geothermal brines
The kinetics of amorphous silica precipitation from aqueous solution up to 100/sup 0/C and containing up to 1M NaCl were studied experimentally. Empirical equations for the rate of molecular deposition on surfaces as a function of temperature, dissolved silica concentration, pH and salinity are presented. Empirical type curves which depict the decrease in dissolved silica concentration through homogeneous nucleation of colloidal silica are also presented. Two practical examples related to geothermal practice are given
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Hydrological and geochemical investigations of selenium behavior at Kesterson Reservoir
From 1985 to the present we have studied the behavior of selenium in various habitats and environments at Kesterson reservoir, shifting emphasis as remedial actions altered the physical setting. Investigations have evaluated the efficacy of several remedial alternatives, from innovative techniques relying on the complex geochemical behavior of selenium alternatives, from innovative techniques relying on the complex geochemical behavior of selenium in aquatic environments to conventional excavation schemes. Results of these studies supported two cost-effective remedial measures; drain water deliveries were terminated in 1986 and, in 1988, 1 million cubic yards of soil were imported and used to fill the low lying areas of the former Kesterson Reservoir. To date, these two actions appear to have eliminated the aquatic habitat that caused waterfowl death and deformity at Kesterson from the early 1980's to 1987. Biological, surface water and groundwater monitoring data collected by the USBR indicate that Kesterson is now a much safer environment than in past years when drainage water containing 300{mu}g/l of selenium was delivered to the Reservoir. The continued presence of a large inventory of selenium within the upper portions of unfilled areas of Kesterson Reservoir and immediately below the fill material requires that a continued awareness of the status of this inventory be maintained and improved upon. 83 refs., 130 figs., 19 tabs