63 research outputs found
Multiscale dislocation dynamics simulations of shock-induced plasticity in small volumes
No full textMultiscale dislocation dynamics plasticity (MDDP) was used to investigate shock-induced deformation in monocrystalline copper. In order to enhance the numerical simulations, a periodic boundary condition was implemented in the continuum finite element (FE) scale so that the uniaxial compression of shocks could be attained. Additionally, lattice rotation was accounted for by modifying the dislocation dynamics (DD) code to update the dislocations slip systems. The dislocation microstructures were examined in detail and a mechanism of microband formation is proposed for single- and multiple-slip deformation. The simulation results show that lattice rotation enhances microband formation in single slip by locally reorienting the slip plane. It is also illustrated that both confined and periodic boundary conditions can be used to achieve uniaxial compression; however, a periodic boundary condition yields a disturbed wave profile due to edge effects. Moreover, the boundary conditions and the loading rise time show no significant effects on shock-dislocations interaction and the resulting microstructures. MDDP results of high strain rate calculations are also compared with the predictions of the Armstrong-Zerilli model of dislocation generation and movement. This work confirms that the effect of resident dislocations on the strain rate can be neglected when a homogeneous nucleation mechanism is included. © 2012 Copyright Taylor and Francis Group, LLC.Armstrong RW, 2010, J PHYS D APPL PHYS, V43, DOI 10.1088-0022-3727-43-49-492002; Armstrong R.W., 2009, P 16 APS TOP C SHOCK, P1195; Barabash RI, 2010, MAT SCI ENG A-STRUCT, V528, P52, DOI 10.1016-j.msea.2010.04.045; Barton NR, 2011, J APPL PHYS, V109, DOI 10.1063-1.3553718; Benson D.J., 1997, J MECH PHYS SOLIDS, V45, P955; Braisted W, 1999, INT J FATIGUE, V21, P719, DOI 10.1016-S0142-1123(99)00035-3; Bringa EM, 2003, NUCL INSTRUM METH B, V202, P56, DOI 10.1016-S0168-583X(02)01831-1; Bringa EM, 2004, J APPL PHYS, V96, P3793, DOI 10.1063-1.1789266; Chen H., 2007, J APPL MECH, V71, P714; Cheng GJ, 2005, SCRIPTA MATER, V53, P1013, DOI 10.1016-j.scriptamat.2005.07.014; Cheng GJ, 2006, INT J PLASTICITY, V22, P2171, DOI 10.1016-j.ijplas.2006.03.006; Deshpande V.S., 2004, MAT SCI ENG A-STRUCT, V400, P154; Deshpande VS, 2003, J MECH PHYS SOLIDS, V51, P2057, DOI 10.1016-j.jmps.2003.09.012; Devincre B, 2001, MAT SCI ENG A-STRUCT, V309, P211, DOI 10.1016-S0921-5093(00)01725-1; Fivel MC, 1998, ACTA MATER, V46, P6183, DOI 10.1016-S1359-6454(98)00278-X; Gao B., 2010, MAT SCI ENG A-STRUCT, V527, P424; Ghoniem NM, 1999, PHYS REV B, V60, P128, DOI 10.1103-PhysRevB.60.128; Hayes D., 1999, SHOCK COMPRESSION CO, P483; Hirth JP, 1998, MODEL SIMUL MATER SC, V6, P165, DOI 10.1088-0965-0393-6-2-006; Holian L., 1998, SCIENCE, V280, P2085; Joo H. 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Modeling Shock Induced Plasticity in Copper Single Crystal: Numerical and Strain Localization Issues
No full textMultiscale dislocation dynamics plasticity (MDDP) simulations are carried out to address the following issues in modeling shock-induced plasticity: 1- the effect of finite element (FE) boundary conditions on shock wave characteristics and wave-dislocation interaction, 2- the effect of the evolution of the dislocation microstructure on lattice rotation and strain localization. While uniaxial strain is achieved with high accuracy using confined boundary condition, periodic boundary condition yields a disturbed wave profile due the edge effect. Including lattice rotation in the analysis leads to higher dislocation density and more localized plastic strain.</jats:p
On the ultra-high-strain rate shock deformation in copper single crystals: Multiscale dislocation dynamics simulations
No full textMultiscale dislocation dynamics plasticity (MDDP) calculations are carried out to simulate the mechanical response of copper single crystals that have undergone shock loading at high strain rates ranging from 1 × 10 6 to 1 × 1010 s-1. Plasticity mechanisms associated with both the activation of pre-existing dislocation sources and homogeneous nucleation of glide loops are considered. Our results show that there is a threshold strain rate of 108 s-1 at which the deformation mechanism changes from source activation to homogeneous nucleation. It is also illustrated that the pressure dependence on strain rate follows a one-fourth power law up to 108 s-1 beyond which the relationship assumes a one-half power law. The MDDP computations are in good agreement with recent experimental findings and compare well with the predictions of several dislocation-based continuum models. © 2014 Taylor & Francis
Recommendations for improving clinical trial design to facilitate the study of youth-onset type 2 diabetes
No full textBackground The prevalence of type 2 diabetes is increasing in youths and differs from adult-onset type 2 diabetes in its characteristics and progression. Currently, only two drugs are approved for youth-onset type 2 diabetes and many patients are not meeting glycemic targets. Clearly, there is an urgent need to complete clinical trials in youths with type 2 diabetes to increase the therapeutic choice for these patients. However, factors such as limited patient numbers, unwillingness of patients to participate in trials, failure to meet strict inclusion and exclusion criteria, and poor clinic attendance have limited the size and number of trials in this complicated patient demographic. Recommendations This is a narrative opinion piece on the design of clinical trials in youth-onset type 2 diabetes prepared by researchers who undertake this type of study in different countries. The review addresses possible ways to enhance trial designs in youth-onset type 2 diabetes to meet regulatory requirements, while minimizing the barriers to patients' participation. The definition of adolescence, recruitment of sufficient patient numbers, increasing flexibility in selection criteria, improving convenience of trial visits, requirements of a control group, possible endpoints, and trial compliance are all considered. The authors recommend allowing extrapolation from adult data, using multiple interventional arms within future trials, broadening inclusion criteria, and focusing on endpoints beyond glucose control, among others, in order to improve the successful completion of more trials in this population. Conclusions Improvements in trial design will enable better recruitment and retention and thereby more evidence for treatment outcomes for youth-onset type 2 diabetes
Rapid progression of type 2 diabetes and related complications in children and young people-A literature review
No full textType 2 diabetes (T2D) is suggested to progress faster in children and young people vs type 1 diabetes (T1D) in the same age group and T2D in adults. We reviewed the evidence base for this. A literature search was performed of PubMed-indexed publications between 2000 and 2018, for the terms pediatric and T2D. Results were combined and filtered for those relating to progression. Searches of abstract books from Latin American and Asian congresses were performed to include these populations. Pediatric populations were defined as <25 completed years of age. Of the articles and congress abstracts found, 30 were deemed relevant. Dividing the studies into categories based on how T2D progresses, we found the following: (a) yearly beta-cell function deterioration was shown to be 20% to 35% in children with T2D compared with 7% to 11% in adults with T2D, despite similar disease durations; (b) retinopathy progression was likely dependent on diabetes duration rather than diabetes type; however, nephropathy, neuropathy and probably hypertension progressed faster in youth-onset T2D vs T1D. Nephropathy progression was similar to adults with T2D, allowing for disease duration. Youth with T2D had a worse cardiovascular (CV) risk profile than youth with T1D, and a faster progression to CV death. (c) Progression to treatment failure was faster in youth-onset T2D vs adult-onset T2D. Substantial evidence exists for faster progression of T2D in pediatric patients vs T1D or adult-onset T2D. New treatments targeting the pathology are needed urgently to address this issue
Incidence of glucocorticoid-induced hyperglycemia among hospitalized nondiabetic patients
No full textCultural and Digital Health Literacy Appropriateness of App- and Web-Based Systems Designed for Pregnant Women With Gestational Diabetes Mellitus: Scoping Review
No full textBACKGROUND: The prevalence of women diagnosed with gestational diabetes mellitus (GDM) is increasing dramatically. Mobile technologies to enhance patient self-management offer many advantages for women diagnosed with GDM. However, to our knowledge, although mobile health (mHealth) and telemedicine systems for GDM management exist, evidence on their cultural and digital health literacy appropriateness levels is limited. OBJECTIVE: This review aimed to search and assess the literature on mHealth and telemedicine systems designed for women diagnosed with GDM. Our assessment of these technologies focused on their cultural and digital health literacy appropriateness as well as the systems’ effectiveness in improving glycemic control and maternal and infant outcomes. METHODS: We conducted a scoping review using a framework adapted from Arksey and O’Malley. Four electronic databases were searched for relevant studies: PubMed, MEDLINE (EBSCO), Web of Science, and Scopus. The databases were searched between January 2010 and January 2022. The inclusion criteria were pregnant women diagnosed with GDM, use of telemedicine for monitoring and management, and vulnerable or disadvantaged patients. We used terms related to mobile apps and telemedicine: GDM, vulnerable populations, periphery, cultural appropriateness, and digital health literacy. Studies were screened and selected independently by 2 authors. We extracted the study data on a Microsoft Excel charting table and categorized them into final themes. The results were categorized according to the cultural and digital health literacy features presented. RESULTS: We identified 17 studies that reported on 12 telemedicine and mHealth app interventions. We assessed the studies in three domains: cultural appropriateness, digital health literacy, and maternal and infant outcomes. In the literature, we found that existing digital technologies may improve glycemic control and diabetes self-management. However, there is a lack of assessment of cultural and digital health literacy appropriateness for pregnant women diagnosed with GDM. Considerations in app design regarding cultural appropriateness were found in only 12% (2/17) of the studies, and only 25% (3/12) of the interventions scored ≥3 out of 5 in our assessment of digital health literacy. CONCLUSIONS: mHealth and telemedicine can be an effective platform to improve the clinical management of women with GDM. Although studies published on the use of mHealth and telemedicine systems exist, there is a limited body of knowledge on the digital health literacy and cultural appropriateness of the systems designed for women diagnosed with GDM. In addition, as our study was restricted to the English language, relevant studies may have been excluded. Further research is needed to evaluate, design, and implement better tailored apps regarding cultural and digital literacy appropriateness for enhancing pregnant women’s self-management as well as the effectiveness of these apps in improving maternal and infant health outcomes
Analyses of alpha-alpha elastic scattering data in the energy range 53.4-119.9 MeV
No full textThe differential and reaction cross sections for alpha-alpha elastic scattering at energies ranging from 50 MeV to 120 MeV (lab. system) have been clearly explained for the first time, by using a new optical potential type. This potential, which is different from all other proposed potentials, is composed of two real parts: one is an attractive squared Woods-Saxon and the other is a repulsive core of the Woods-Saxon form in addition to a surface Woods-Saxon form for the imaginary part. The nature of the real part has been determined from available phase shifts through using inverse scattering theory for the identical particles at a fixed energy, adopting the framework of Schrödinger equation. It is found that the repulsive real part is essential for improving the fit to the measured elastic differential cross sections, and in explaining the kink that appears at rThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
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