21 research outputs found
Magnetic field dependence of the critical current in stacked Josephson junctions. Evidence for fluxon modes in Bi2Sr2CaCu2O8+x mesas
Modulation of the critical current across layers, Ic(H), of stacked Josephson
junctions (SJJs) as a function of an applied magnetic field parallel to the
junction planes is studied theoretically and experimentally for different
junction lengths and coupling parameters. It is shown that the Ic(H) patterns
of long SJJs are very complicated without periodicity in H. This is due to
interaction between junctions in the stack. This, in turn, gives rise to the
existence of multiple quasi-equilibrium Josephson fluxon modes and submodes
which are different with respect to the symmetry of the phase and the fluxon
sequence in SJJs. The critical current of long SJJs is multiple valued and is
governed by switching between energetically close fluxon modes/submodes. Due to
this, the probability distribution of the critical current may become wide and
may consist of multiple maxima each representing a particular mode/submode.
Experimentally, multiple branched Ic(H) patterns and multiple maxima in the Ic
probability distribution were observed for Bi2Sr2CaCu2O8+x intrinsic SJJs,
which are in a good agreement with numerical simulations and support the idea
of having different quasi-equilibrium fluxon modes/submodes in intrinsic SJJs.Comment: 5 pages, 5 figure
The shape of a moving fluxon in stacked Josephson junctions
We study numerically and analytically the shape of a single fluxon moving in
a double stacked Josephson junctions (SJJ's) for various junction parameters.
We show that the fluxon in a double SJJ's consists of two components, which are
characterized by different Swihart velocities and Josephson penetration depths.
The weight coefficients of the two components depend on the parameters of the
junctions and the velocity of the fluxon. It is shown that the fluxon in SJJ's
may have an unusual shape with an inverted magnetic field in the second
junction when the velocity of the fluxon is approaching the lower Swihart
velocity. Finally, we study the influence of fluxon shape on flux-flow
current-voltage characteristics and analyze the spectrum of Cherenkov radiation
for fluxon velocity above the lower Swihart velocity. Analytic expression for
the wavelength of Cherenkov radiation is derived.Comment: 12 pages, 12 figure
In-plane fluxon in layered superconductors with arbitrary number of layers
I derive an approximate analytic solution for the in-plane vortex (fluxon) in
layered superconductors and stacked Josephson junctions (SJJ's) with arbitrary
number of layers. The validity of the solution is verified by numerical
simulation. It is shown that in SJJ's with large number of thin layers,
phase/current and magnetic field of the fluxon are decoupled from each other.
The variation of phase/current is confined within the Josephson penetration
depth, , along the layers, while magnetic field decays at the
effective London penetration depth, . For comparison
with real high- superconducting samples, large scale numerical simulations
with up to 600 SJJ's and with in-plane length up to 4000 %, are
presented. It is shown, that the most striking feature of the fluxon is a
Josephson core, manifesting itself as a sharp peak in magnetic induction at the
fluxon center.Comment: 4 pages, 4 figures. Was presented in part at the First Euroconference
on Vortex Matter in Superconductors (Crete, September 1999
Association of incident hip fracture with the estimated femoral strength by finite element analysis of DXA scans in the Osteoporotic Fractures in Men (MrOS) study
Finite element model can estimate bone strength better than BMD. This study used such a model to determine its association with hip fracture risk and found that the strength estimate provided limited improvement over the hip BMDs in predicting femoral neck (FN) fracture risk only. INTRODUCTION: Bone fractures occur only when it is loaded beyond its ultimate strength. The goal of this study was to determine the association of femoral strength, as estimated by finite element (FE) analysis of DXA scans, with incident hip fracture as a single condition or with femoral neck (FN) and trochanter (TR) fractures separately in older men. METHODS: This prospective case-cohort study included 91 FN and 64 TR fracture cases and a random sample of 500 men (14 had a hip fracture) from the Osteoporotic Fractures in Men study during a mean ± SD follow-up of 7.7 ± 2.2 years. We analysed the baseline DXA scans of the hip using a validated plane-stress, linear-elastic FE model of the proximal femur and estimated the femoral strength during a sideways fall. RESULTS: The estimated strength was significantly (P < 0.05) associated with hip fracture independent of the TR and total hip (TH) BMDs but not FN BMD, and combining the strength with BMD did not improve the hip fracture prediction. The strength estimate was associated with FN fractures independent of the FN, TR and TH BMDs; the age-BMI-BMD adjusted hazard ratio (95% CI) per SD decrease of the strength was 1.68 (1.07-2.64), 2.38 (1.57, 3.61) and 2.04 (1.34, 3.11), respectively. This association with FN fracture was as strong as FN BMD (Harrell's C index for the strength 0.81 vs. FN BMD 0.81) and stronger than TR and TH BMDs (0.8 vs. 0.78 and 0.81 vs. 0.79). The strength's association with TR fracture was not independent of hip BMD. CONCLUSIONS: Although the strength estimate provided additional information over the hip BMDs, its improvement in predictive ability over the hip BMDs was confined to FN fracture only and limited
Associations of total and free 25OHD and 1,25(OH)2D with serum markers of inflammation in older men
UnlabelledVitamin D is hypothesized to suppress inflammation. We tested total and free vitamin D metabolites and their association with inflammatory markers. Interleukin-6 levels were lower with higher 25-hydroxyvitamin D. 1,25-dihydroxyvitamin D and free 25OHD associations mirrored those of 25OHD. However, associations for the two metabolites diverged for tumor necrosis factor alpha (TNF-α) soluble receptors.IntroductionVitamin D is hypothesized to suppress inflammation, and circulating 25-hydroxyvitamin D (25OHD) and inflammatory markers are inversely correlated. However, total serum 25OHD may not be the best indicator of biologically active vitamin D.MethodsWe tested serum total 25OHD, total 1,25(OH)2D, vitamin D binding protein (DBP), and estimated free 25OHD and free 1,25(OH)2D associations with inflammatory markers serum interleukin-6 (IL-6), TNF-α and their soluble receptors, interleukin-10 (IL-10), and C-reactive protein (CRP) as continuous outcomes and the presence of ≥2 inflammatory markers in the highest quartile as a dichotomous outcome, in a random subcohort of 679 men in the Osteoporotic Fractures in Men (MrOS) study.ResultsIL-6 was lower in men with higher 25OHD (-0.23 μg/mL per standard deviation (SD) increase in 25OHD, 95 % confidence intervals (CI) -0.07 to -0.38 μg/mL) and with higher 1,25(OH)2D (-0.20 μg/mL, 95 % CI -0.0004 to -0.39 μg/mL); free D associations were slightly stronger. 25OHD and DBP, but not 1,25(OH)2D, were independently associated with IL-6. TNF-α soluble receptors were inversely associated with 1,25(OH)2D but positively associated with 25OHD, and each had independent effects. The strongest association with ≥2 inflammatory markers in the highest quartile was for free 1,25(OH)2D (odds ratios (OR) 0.70, 95 % CI 0.54 to 0.89 per SD increase in free 1,25(OH)2D).ConclusionsAssociations of 1,25(OH)2D and free 25OHD with IL-6 mirrored those of 25OHD, suggesting that 1,25(OH)2D and free D do not improve upon 25OHD in population-based IL-6 studies. However, associations for the two metabolites diverged for TNF-α soluble receptor, warranting examination of both metabolites in studies of TNF-α and its antagonists
Reimplantation of an Extruded Femoral Segment After Gamma Sterilization in A Type IIIA Supracondylar Femur Fracture: A Case Report
Extruded bone is a rare complication of high energy open fractures, and there is only a handful of literature on reimplantation of the extruded segment. No clear guidelines exist regarding timing of reimplantation, stabilization of extruded bone segments, and also bone disinfection and sterilization techniques. Previous reports describe sterilization using thermal or chemical methods. We present a case of successful reimplantation of an extruded metaphyseal segment of femur after gamma sterilization in a fourteen- year old boy
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Association of incident hip fracture with the estimated femoral strength by finite element analysis of DXA scans in the Osteoporotic Fractures in Men (MrOS) study
Finite element model can estimate bone strength better than BMD. This study used such a model to determine its association with hip fracture risk and found that the strength estimate provided limited improvement over the hip BMDs in predicting femoral neck (FN) fracture risk only.IntroductionBone fractures occur only when it is loaded beyond its ultimate strength. The goal of this study was to determine the association of femoral strength, as estimated by finite element (FE) analysis of DXA scans, with incident hip fracture as a single condition or with femoral neck (FN) and trochanter (TR) fractures separately in older men.MethodsThis prospective case-cohort study included 91 FN and 64 TR fracture cases and a random sample of 500 men (14 had a hip fracture) from the Osteoporotic Fractures in Men study during a mean ± SD follow-up of 7.7 ± 2.2 years. We analysed the baseline DXA scans of the hip using a validated plane-stress, linear-elastic FE model of the proximal femur and estimated the femoral strength during a sideways fall.ResultsThe estimated strength was significantly (P < 0.05) associated with hip fracture independent of the TR and total hip (TH) BMDs but not FN BMD, and combining the strength with BMD did not improve the hip fracture prediction. The strength estimate was associated with FN fractures independent of the FN, TR and TH BMDs; the age-BMI-BMD adjusted hazard ratio (95% CI) per SD decrease of the strength was 1.68 (1.07-2.64), 2.38 (1.57, 3.61) and 2.04 (1.34, 3.11), respectively. This association with FN fracture was as strong as FN BMD (Harrell's C index for the strength 0.81 vs. FN BMD 0.81) and stronger than TR and TH BMDs (0.8 vs. 0.78 and 0.81 vs. 0.79). The strength's association with TR fracture was not independent of hip BMD.ConclusionsAlthough the strength estimate provided additional information over the hip BMDs, its improvement in predictive ability over the hip BMDs was confined to FN fracture only and limited
Hyperkyphosis and self-reported and objectively measured sleep quality in older men.
ObjectivesHyperkyphosis is associated with restricted pulmonary function and posture, potentially contributing to poor sleep. A previous study reported older women with hyperkyphosis had worse self-reported sleep quality, but it is less clear if this association exists in men. We examined the association between hyperkyphosis and subjective and objective sleep quality in a cohort of older men.DesignLongitudinal analysis of data from large cohort of older men participating in the Osteoporotic Fractures in Men Study (MrOS).SettingCommunity.ParticipantsWe studied 754 men participants in MrOS who had kyphosis measured during the 3rd clinic visit (2007-2009) and future subjective and objective sleep quality assessed between 2009-2012 (an average of 2.9 years later).InterventionN/A.MeasurementsTo measure kyphosis, 1.7 cm thick wooden blocks were placed under the participant's head to achieve a neutral spine position while lying supine on a DXA table. We collected data on both subjective (Pittsburgh Sleep Quality Index [PSQI], and Epworth Sleepiness Scale [ESS]) and objective (wrist actigraphy: Total Sleep Time [TST], Wake After Sleep Onset [WASO], Sleep Efficiency [SE], Sleep Onset Latency [SOL]; and polysomnography: Apnea Hypopnea Index [AHI]) sleep measurements. Those who required >3 blocks were considered hyperkyphotic (n = 145 or 19.2%).ResultsIn unadjusted and multivariable analyses, men with hyperkyphosis did not report having worse self-reported sleep characteristics based on PSQI and ESS. Similarly, there were no significant associations between hyperkyphosis and objective sleep measures. When examined as a continuous predictor (blocks ranging from 0-8), results were no different.ConclusionsAlthough we hypothesized that poor posture in those with hyperkyphosis would interfere with sleep, in this sample of older men, worse kyphosis was not associated with self-reported or objectively measured poor sleep quality
Association of Lower Urinary Tract Symptom Severity with Kidney Function among Community Dwelling Older Men.
PurposeMost international practice guidelines recommend screening for chronic kidney disease among older men with lower urinary tract symptoms. However, prior studies supporting these guidelines are insufficient due to incomplete assessments of kidney function and inadequate adjustment for confounding factors.Materials and methodsWe conducted a cross-sectional study among 5,530 American men older than 65 years in the multicenter Osteoporotic Fractures in Men Study. Chronic kidney disease was defined per international guidelines as estimated glomerular filtration rate less than 60 ml/minute/1.73 m2 based on serum creatinine or cystatin C, or urinary albumin-to-creatinine ratio 30 mg/gm or greater. Lower urinary tract symptoms were assessed with the American Urological Association Symptom Index. Associations were estimated using multivariable linear and modified Poisson regression models.ResultsChronic kidney disease prevalence was 16% among 5,530 men with serum creatinine, 24% among 1,504 men with serum cystatin C and 14% among 1,487 men with urinary albumin-to-creatinine measurements. Lower urinary tract symptoms were not associated with lower estimated glomerular filtration rate based on serum creatinine or cystatin C. Although symptom severity was modestly associated with a higher prevalence of chronic kidney disease in age/site adjusted analyses, confidence intervals were wide and associations using all 3 definitions were not statistically significant after adjustment for important confounders, including cardiovascular disease and analgesic use.ConclusionsLower urinary tract symptoms are not independently associated with multiple measures of kidney dysfunction or prevalence of chronic kidney disease among older community dwelling men. Our results do not support recommendations for kidney function testing among older men with lower urinary tract symptoms
Height Loss in Old Age and Fracture Risk Among Men in Late Life: A Prospective Cohort Study.
To assess the association of height loss in old age with subsequent risk of hip and any clinical fracture in men late in life while accounting for the competing risk of mortality, we used data from 3491 community-dwelling men (mean age 79.2 years). Height loss between baseline and follow-up (mean 7.0 years between examinations) was categorized as <1 cm (referent group), ≥1 to <2 cm, ≥2 to <3 cm, and ≥3 cm. Men were contacted every 4 months after the follow-up examination to ask about fractures (confirmed by radiographic reports) and ascertain vital status (deaths verified by death certificates). Competing risk methods were used to estimate absolute probabilities of fracture outcomes by height loss category and calculate adjusted risks of fracture outcomes by height loss. During an average of 7.8 years, 158 (4.5%) men experienced a hip fracture and 1414 (40.5%) died before experiencing this event. The absolute 10-year probability of fracture events accounting for the competing risk of death increased with greater height loss. For example, the hip fracture probability was 2.7% (95% confidence interval [CI] 1.9-3.8%) among men with height loss <1 cm increasing to 11.6% (95% CI 8.0-16.0%) among men with height loss ≥3 cm. After adjustment for demographics, fall history, multimorbidity, baseline height, weight change, and femoral neck bone mineral density and considering competing mortality risk, men with height loss ≥3 cm versus <1 cm had a nearly twofold (subdistribution hazard ratio [HR] = 1.94, 95% CI 1.06-3.55) higher risk of hip fracture and a 1.4-fold (subdistribution HR = 1.42, 95% CI 1.05-1.91) increased risk of any clinical fracture. Height loss ≥3 cm in men during old age was associated with higher subsequent risk of clinical fractures, especially hip fractures, even after accounting for the competing risk of death and traditional skeletal and non-skeletal risk factors. © 2021 American Society for Bone and Mineral Research (ASBMR)