ResearchPad - 122 https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Microstructure-sensitive critical plastic strain energy density criterion for fatigue life prediction across various loading regimes]]> https://www.researchpad.co/article/Nec259dea-eba2-4023-a087-8d1097f40458 In the present work, we postulate that a critical value of the stored plastic strain energy density (SPSED) is associated with fatigue failure in metals and is independent of the applied load. Unlike the classical approach of estimating the (homogenized) SPSED as the cumulative area enclosed within the macroscopic stress–strain hysteresis loops, we use crystal plasticity finite element simulations to compute the (local) SPSED at each material point within polycrystalline aggregates of a nickel-based superalloy. A Bayesian inference method is used to calibrate the critical SPSED, which is subsequently used to predict fatigue lives at nine different strain ranges, including strain ratios of 0.05 and −1, using nine statistically equivalent microstructures. For each strain range, the predicted lives from all simulated microstructures follow a lognormal distribution. Moreover, for a given strain ratio, the predicted scatter is seen to be increasing with decreasing strain amplitude; this is indicative of the scatter observed in the fatigue experiments. Finally, the lognormal mean lives at each strain range are in good agreement with the experimental evidence. Since the critical SPSED captures the experimental data with reasonable accuracy across various loading regimes, it is hypothesized to be a material property and sufficient to predict the fatigue life.

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<![CDATA[Moulding three-dimensional curved structures by selective heating]]> https://www.researchpad.co/article/N2da92343-9e26-4dba-8b67-a4f60d3c8a08

It is of interest to fabricate curved surfaces in three dimensions from homogeneous material in the form of flat sheets. The aim is not just to obtain a surface which has a desired intrinsic Riemannian metric, but to get the desired embedding in R3 up to translations and rotations. In this paper, we demonstrate three generic methods of moulding a flat sheet of thermo-responsive plastic by selective contraction induced by targeted heating. These methods do not involve any cutting and gluing, which is a property they share with origami. The first method is inspired by tailoring, which is the usual method for making garments out of plain pieces of cloth. Unlike usual tailoring, this method produces the desired embedding in R3. The second method just aims to bring about the desired new Riemannian metric via an appropriate pattern of local contractions, without directly controlling the embedding. The third method is based on triangulation, and seeks to induce the desired local distances. This results in getting the desired embedding in R3. The second and the third methods, and also the first method for the special case of surfaces of revolution, are algorithmic in nature. We explain these methods and show examples.

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<![CDATA[Cognition at age 70]]> https://www.researchpad.co/article/Nd27d6813-5240-40fa-aebc-105afba68a90

Objective

To investigate predictors of performance on a range of cognitive measures including the Preclinical Alzheimer Cognitive Composite (PACC) and test for associations between cognition and dementia biomarkers in Insight 46, a substudy of the Medical Research Council National Survey of Health and Development.

Methods

A total of 502 individuals born in the same week in 1946 underwent cognitive assessment at age 69–71 years, including an adapted version of the PACC and a test of nonverbal reasoning. Performance was characterized with respect to sex, childhood cognitive ability, education, and socioeconomic position (SEP). In a subsample of 406 cognitively normal participants, associations were investigated between cognition and β-amyloid (Aβ) positivity (determined from Aβ-PET imaging), whole brain volumes, white matter hyperintensity volumes (WMHV), and APOE ε4.

Results

Childhood cognitive ability was strongly associated with cognitive scores including the PACC more than 60 years later, and there were independent effects of education and SEP. Sex differences were observed on every PACC subtest. In cognitively normal participants, Aβ positivity and WMHV were independently associated with lower PACC scores, and Aβ positivity was associated with poorer nonverbal reasoning. Aβ positivity and WMHV were not associated with sex, childhood cognitive ability, education, or SEP. Normative data for 339 cognitively normal Aβ-negative participants are provided.

Conclusions

This study adds to emerging evidence that subtle cognitive differences associated with Aβ deposition are detectable in older adults, at an age when dementia prevalence is very low. The independent associations of childhood cognitive ability, education, and SEP with cognitive performance at age 70 have implications for interpretation of cognitive data in later life.

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<![CDATA[Amyloid- and tau-PET imaging in a familial prion kindred]]> https://www.researchpad.co/article/5c2a7772d5eed0c4842265bc

Objective

To study the in vivo binding properties of 18F-AV-1451 (tau-PET) and Pittsburgh compound B (PiB-PET) in a unique kindred with a familial prion disorder known to produce amyloid plaques composed of prion protein alongside Alzheimer disease (AD)–like tau tangles.

Methods

A case series of 4 symptomatic family members with the 12-octapeptide repeat insertion in the PRNP gene were imaged with 3T MRI, PiB-PET, and tau-PET in their fourth decade of life.

Results

There was significant neocortical uptake of the tau-PET tracer in all 4 familial prion cases. However, PiB-PET images did not demonstrate abnormally elevated signal in neocortical or cerebellar regions for any of the patients.

Conclusions

In vivo detection of molecular hallmarks of neurodegenerative diseases will be a prerequisite to well-conducted therapeutic trials. Understanding the in vivo behavior of these PET biomarkers in the setting of various neurodegenerative processes is imperative to their proper use in such trials and for research studies focused on the basic neurobiology of neurodegeneration. This study supports the high specificity of neocortical 18F-AV-1451 binding to AD-like tau and the lack of PiB binding to PrP plaques. It is uncertain how early in the disease course tau pathology appears in the brains of individuals who carry this PRNP gene mutation or how it evolves throughout the disease course, but future longitudinal 18F-AV-1451 imaging of symptomatic and asymptomatic individuals in this kindred will help address these uncertainties.

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<![CDATA[GABA deficiency in NF1]]> https://www.researchpad.co/article/5bd027e240307c4fee35a858

Objective:

To provide a comprehensive investigation of the γ-aminobutyric acid (GABA) system in patients with neurofibromatosis type 1 (NF1) that allows understanding the nature of the GABA imbalance in humans at pre- and postsynaptic levels.

Methods:

In this cross-sectional study, we employed multimodal imaging and spectroscopy measures to investigate GABA type A (GABAA) receptor binding, using [11C]-flumazenil PET, and GABA concentration, using magnetic resonance spectroscopy (MRS). Fourteen adult patients with NF1 and 13 matched controls were included in the study. MRS was performed in the occipital cortex and in a frontal region centered in the functionally localized frontal eye fields. PET and MRS acquisitions were performed in the same day.

Results:

Patients with NF1 have reduced concentration of GABA+ in the occipital cortex (p = 0.004) and frontal eye fields (p = 0.026). PET results showed decreased binding of GABAA receptors in patients in the parieto-occipital cortex, midbrain, and thalamus, which are not explained by decreased gray matter levels.

Conclusions:

Abnormalities in the GABA system in NF1 involve both GABA concentration and GABAA receptor density suggestive of neurodevelopmental synaptopathy with both pre- and postsynaptic involvement.

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<![CDATA[Should Patients With Frozen Shoulder Be Screened for Diabetes Mellitus?]]> https://www.researchpad.co/article/5b41f53d463d7e0fad551d11

Background:

Idiopathic frozen shoulder (nontraumatic) is commonly encountered in patients between the ages of 35 and 60 years in general orthopaedic practice. While the prevalence of frozen shoulder among the general population is estimated to be between 2% and 4%, a significantly higher prevalence of 10% to 22% has been reported in patients with diabetes mellitus. Since diabetic patients are more prone to develop frozen shoulder than nondiabetics, the question arises as to whether patients diagnosed as having idiopathic frozen shoulder are at greater risk to develop diabetes mellitus and should be routinely screened for this condition.

Purpose:

To compare the prevalence of diabetes mellitus and prediabetes among patients diagnosed with idiopathic frozen shoulder who are not known to have either diabetes mellitus or prediabetic conditions with that of an age-matched group from the general population.

Study Design:

Case series; Level of evidence, 4.

Methods:

Patients at a shoulder clinic with a diagnosis of idiopathic frozen shoulder were asked to participate in the study if they were aged between 35 to 60 years and had no known previous diagnosis of diabetes mellitus or prediabetic conditions. These patients underwent a 2-hour oral glucose tolerance test. According to their fasting and 2-hour plasma glucose levels, patients were diagnosed as normal glucose tolerance, prediabetic, or diabetic. Findings were matched with the prevalence in an age-matched general population.

Results:

Fifty patients completed the test. Four patients with idiopathic frozen shoulder (8%) were found to be prediabetic. No patient was found to be diabetic. All 4 patients reported a history of diabetes in their parents or siblings.

Conclusion:

Patients diagnosed with idiopathic frozen shoulder who are 60 years or younger and are not known diabetics have a similar probability of having diabetes or prediabetes to an age-matched population. No routine diabetic workup is warranted specifically for these patients.

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<![CDATA[Noether's symmetry and conserved quantity for a time-delayed Hamiltonian system of Herglotz type]]> https://www.researchpad.co/article/5c1522efd5eed0c4840bd764

The variational problem of Herglotz type and Noether's theorem for a time-delayed Hamiltonian system are studied. Firstly, the variational problem of Herglotz type with time delay in phase space is proposed, and the Hamilton canonical equations with time delay based on the Herglotz variational problem are derived. Secondly, by using the relationship between the non-isochronal variation and the isochronal variation, two basic formulae of variation of the Hamilton–Herglotz action with time delay in phase space are derived. Thirdly, the definition and criterion of the Noether symmetry for the time-delayed Hamiltonian system are established and the corresponding Noether's theorem is presented and proved. The theorem we obtained contains Noether's theorem of a time-delayed Hamiltonian system based on the classical variational problem and Noether's theorem of a Hamiltonian system based on the variational problem of Herglotz type as its special cases. At the end of the paper, an example is given to illustrate the application of the results.

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<![CDATA[Tau imaging detects distinctive distribution of tau pathology in ALS/PDC on the Kii Peninsula]]> https://www.researchpad.co/article/5c5f19e2d5eed0c484699dfd

Objective

To characterize the distribution of tau pathology in patients with amyotrophic lateral sclerosis/parkinsonism dementia complex on the Kii Peninsula (Kii ALS/PDC) by tau PET using [11C]PBB3 as ligand.

Methods

This is a cross-sectional study of 5 patients with ALS/PDC and one asymptomatic participant with a dense family history of ALS/PDC from the Kii Peninsula who took part in this study. All were men, and their age was 76 ± 8 (mean ± SD) years. Thirteen healthy men (69 ± 6 years) participated as healthy controls (HCs). Dynamic PET scans were performed following injection of [11C]PBB3, and parametric PET images were generated by voxel-by-voxel calculation of binding potential (BP*ND) using a multilinear reference tissue model. [11C] Pittsburgh compound B (PiB) PET, MRI, and cognitive tests were also performed.

Results

A voxel-based comparison of [11C]PBB3 BP*ND illustrated PET-detectable tau deposition in the cerebral cortex and white matter, and pontine basis including the corticospinal tract in Kii ALS/PDC patients compared with HCs (uncorrected p < 0.05). Group-wise volume of interest analysis of [11C]PBB3 BP*ND images showed increased BP*ND in the hippocampus and in frontal and parietal white matters of Kii ALS/PDC patients relative to HCs (p < 0.05, Holm-Sidak multiple comparisons test). BP*ND in frontal, temporal, and parietal gray matters correlated with Mini-Mental State Examination scores in Kii ALS/PDC patients (p < 0.05). All Kii ALS/PDC patients were negative for [11C]PiB (β-amyloid) except one with marginal positivity.

Conclusion

[11C]PBB3 PET visualized the characteristic topography of tau pathology in Kii ALS/PDC, corresponding to clinical phenotypes of this disease.

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<![CDATA[In vivo staging of regional amyloid deposition]]> https://www.researchpad.co/article/5b463780463d7e5a7e7af6c7

Objectives:

To estimate a regional progression pattern of amyloid deposition from cross-sectional amyloid-sensitive PET data and evaluate its potential for in vivo staging of an individual's amyloid pathology.

Methods:

Multiregional analysis of florbetapir (18F-AV45)–PET data was used to determine individual amyloid distribution profiles in a sample of 667 participants from the Alzheimer's Disease Neuroimaging Initiative cohort, including cognitively normal older individuals (CN) as well as patients with mild cognitive impairment and Alzheimer disease (AD) dementia. The frequency of regional amyloid positivity across CN individuals was used to construct a 4-stage model of progressing amyloid pathology, and individual distribution profiles were used to evaluate the consistency of this hierarchical stage model across the full cohort.

Results:

According to a 4-stage model, amyloid deposition begins in temporobasal and frontomedial areas, and successively affects the remaining associative neocortex, primary sensory-motor areas and the medial temporal lobe, and finally the striatum. Amyloid deposition in these brain regions showed a highly consistent hierarchical nesting across participants, where only 2% exhibited distribution profiles that deviated from the staging scheme. The earliest in vivo amyloid stages were mostly missed by conventional dichotomous classification approaches based on global florbetapir-PET signal, but were associated with significantly reduced CSF Aβ42 levels. Advanced in vivo amyloid stages were most frequent in patients with AD and correlated with cognitive impairment in individuals without dementia.

Conclusions:

The highly consistent regional hierarchy of PET-evidenced amyloid deposition across participants resembles neuropathologic observations and suggests a predictable regional sequence that may be used to stage an individual's progress of amyloid pathology in vivo.

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<![CDATA[Regional amyloid accumulation and cognitive decline in initially amyloid-negative adults]]> https://www.researchpad.co/article/5c19b0ded5eed0c484c4b1a1

Objective

To assess whether global or regional changes in amyloid burden over 4 years predict early declines in episodic memory in initially amyloid-negative adults.

Methods

One hundred twenty-six initially amyloid-negative, cognitively normal participants (age 30–89 years) were included from the Dallas Lifespan Brain Study who completed florbetapir PET and a cognitive battery at baseline and 4-year follow-up. Standardized uptake value ratio (SUVR) change was computed across 8 bilateral regions of interest. Using general linear models, we examined the relationship between change in global and regional SUVR and change in episodic memory, controlling for baseline SUVR, baseline memory, age, sex, education, and APOE status.

Results

In initially amyloid-negative adults, we detected a regionally specific relationship between declining episodic memory and increasing amyloid accumulation across multiple posterior cortical regions. In addition, these amyloid-related changes in memory persisted when we focused on middle-aged adults only and after controlling for atrophy in global cortical, hippocampal, and Alzheimer disease signature cortical volume.

Conclusion

Our results indicate that assessing regional changes in amyloid, particularly in posterior cortical regions, can aid in the early detection of subclinical amyloid-related decline in episodic memory as early as middle age. Future research incorporating tau and other markers of neurodegeneration is needed to clarify the sequence of events that lead to this early, subclinical memory decline.

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<![CDATA[Concussions From Youth Football]]> https://www.researchpad.co/article/5af3631d463d7e5f595b1795

Background:

Youth football programs across the United States represent an at-risk population of approximately 3.5 million athletes for sports-related concussions. The frequency of concussions in this population is not known.

Study Design:

Descriptive epidemiology study.

Methods:

Over an 11-year span from January 2002 to December 2012, the authors reviewed the concussions sustained by athletes aged 5 to 13 years while playing football, as evaluated in emergency departments (EDs) in the United States and captured by the National Electronic Injury Surveillance System (NEISS) database of the US Consumer Product Safety Commission.

Results:

There were 2028 (national estimate, 49,185) young football players evaluated in NEISS EDs with concussion from 2002 to 2012. There were 1987 (97.9%) males and 41 (2.1%) females, with a mean age of 11.2 years. The total number of concussions reported increased with age and by year. The majority of concussions were treated in the outpatient setting, with 1878 (91.7%) being treated and released. The total number of head-to-head injury mechanisms mirrored the total number of concussions by year, which increased throughout the 11-year span. The total number of players experiencing a loss of consciousness increased throughout the study period but did not match the total number of concussions over the 11-year time period. Fractures occurred in 11 (0.5%) patients, with 2 being severe (1 skull fracture and 1 thoracic compression fracture).

Conclusion:

Within the 5- to 13-year age range, there were a significant number of young athletes who presented to EDs with concussion as a result of playing organized football. Older children may be at greater risk for sustaining concussions, fractures, and catastrophic injuries while playing football when compared with younger children.

Clinical Relevance:

Younger children are more susceptible to long-term sequelae from head injuries, and thus, improved monitoring systems for these athletes are needed to assist in monitoring patterns of injury, identifying risk factors, and driving the development of evidence-based prevention programs.

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<![CDATA[Forming three-dimensional closed shapes from two-dimensional soft ribbons by controlled buckling]]> https://www.researchpad.co/article/5b4ba49d463d7e7a50b84a4e

Conventional manufacturing techniques—moulding, machining and casting—exist to produce three-dimensional (3D) shapes. However, these industrial processes are typically geared for mass production and are not directly applicable to residential settings, where inexpensive and versatile tools are desirable. Moreover, those techniques are, in general, not adequate to process soft elastic materials. Here, we introduce a new concept of forming 3D closed hollow shapes from two-dimensional (2D) elastic ribbons by controlled buckling. We numerically and experimentally characterize how the profile and thickness of the ribbon determine its buckled shape. We find a 2D master profile with which various elliptical 3D shapes can be formed. More complex natural and artificial hollow shapes, such as strawberry, hourglass and wheel, can also be achieved via strategic design and pattern engraving on the ribbons. The nonlinear response of the post-buckling regime is rationalized through finite-element analysis, which shows good quantitative agreement with experiments. This robust fabrication should complement conventional techniques and provide a rich arena for future studies on the mechanics and new applications of elastic hollow structures.

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