Cratering in glasses impacted by debris or micrometeorites

Mechanical strength measurements on five glasses and one glass-ceramic exposed on LDEF revealed no damage exceeding experimental limits of error. The measurement technique subjected less than 5 percent of the sample surface area to stresses above 90 percent of the failure strength. Seven micrometeorite or space debris impacts occurred at locations which were not in that portion of the sample subjected to greater than 90 percent of the applied stress. As a result of this, the impact events on the sample were not detected in the mechanical strength measurements. The physical form and structure of the impact sites was carefully examined to determine the influence of those events upon stress concentration associated with the impact and the resulting mechanical strength. The size of the impact site, insofar as it determines flaw size for fracture purposes, was examined. Surface topography of the impacts reveals that six of the seven sites display impact melting. The classical melt crater structure is surrounded by a zone of fractured glass. Residual stresses arising from shock compression and from cooling of the fused zone cannot be included in the fracture mechanics analyses based on simple flaw size measurements. Strategies for refining estimates of mechanical strength degradation by impact events are presented

Holding On by Letting Go: Personal Agency as Maternal Activism

Despite the efforts of maternal advocates and feminists through 150 years or more, a great many mothers today feel dissatisfied, shortchanged, and/or inadequate in their own lives. Even those who have reckoned with the fact that standards for mothering are absurdly out of synch with the real lives that families are living in contemporary times, or have carved out comfortable personal and familial space for themselves just beyond, or far beyond, the margins of mainstream motherhood ideologies, often struggle nevertheless with a needling sense of unrest and lack of personal agency. Further, women who agree that maternal empowerment is an important point of focus for social justice may not feel positioned to organize on behalf of mother activism. This essay explores ways that mothers can hold on to the continued struggle for maternal empowerment by letting go of some of the psychological barriers to living fully and purposefully as mothers. Focusing on personal agency as a form of maternal activism, Kinser examines ways for forgiving and embracing the humanity of our own mothers or maternal figures, our selves, and our children that can serve as powerful catalysts for significant change on personal and political scales

Book Review of Mothers and Daughters: Complicated Connections Across Cultures

Excerpt: As both a daughter to a mother and a mother to a daughter, I have lived, and pushed against, and been formed by, the profound truth about mother-daughter relationships suggested by this book\u27s title: it\u27s complicated

Major Depressive Disorder and Measures of Cellular Aging: An Integrative Review

Major depressive disorder (MDD) affects millions of individuals and causes significant suffering worldwide. It has been speculated that MDD is associated with accelerated aging-related biological and functional decline. To examine the accelerated aging hypothesis, one of the biomarkers under study is leukocyte telomeres, and specifically the measure of telomere length and telomerase activity. This review integrates findings from eleven human studies which evaluated telomere length and telomerase activity, in order to synthesize the state of the current science and to inform the development of new knowledge and enhance nursing research of depression using appropriate biobehavioral measures. Although preliminary, the findings from this integrated review suggest that there is evidence to support a conceptualization of depression as a stress-related condition in which telomeres shorten over time in relation to cumulative exposure to the chronic stress of depression. For the purposes of testing in future nursing research, visual representations of the theoretical connection between stress vulnerabilities, depression, and health outcomes and key moderators and mediators involved in this conceptualization are provided. The findings from this review and the conceptual framework provided may be a useful step towards advancing therapeutic nursing interventions for this debilitating chronic condition

Elastic modulus measurements of LDEF glasses and glass-ceramics using a speckle technique

Elastic moduli of five glass types and the glass-ceramic Zerodur, exposed to a near-earth orbit environment on the Long Duration Exposure Facility (LDEF), were compared to that of unexposed samples. A double exposure speckle photography technique utilizing 633 nm laser light was used in the production of the speckle pattern. Subsequent illumination of a double exposed negative using the same wavelength radiation produces Young's fringes from which the in-plane displacements are measured. Stresses imposed by compressive loading produced measurable strains in the glasses and glass-ceramic

Mechanical failure probability of glasses in Earth orbit

Results of five years of earth-orbital exposure on mechanical properties of glasses indicate that radiation effects on mechanical properties of glasses, for the glasses examined, are less than the probable error of measurement. During the 5 year exposure, seven micrometeorite or space debris impacts occurred on the samples examined. These impacts were located in locations which were not subjected to effective mechanical testing, hence limited information on their influence upon mechanical strength was obtained. Combination of these results with micrometeorite and space debris impact frequency obtained by other experiments permits estimates of the failure probability of glasses exposed to mechanical loading under earth-orbit conditions. This probabilistic failure prediction is described and illustrated with examples

Analysis of Barkhausen effect signals in surface-modified magnetic materials using a hysteretic-stochastic model

The effects of microstructural variations with depth on Barkhausen effect (BE) signals in surface-modified ferrous materials have been studied through measurements and simulations based on a hysteretic-stochastic model. The BE signals measured from an unhardened sample show a peak near zero field. In contrast, the BE signals in surface-hardened samples with different case depths exhibit low-amplitude pulses near zero field and a peak at a high reverse field, which are attributed to irreversible magnetization processes in the soft core and the hardened surface layer, respectively. Theoretical analysis showed that the model parameters k and ξ, which describe the domain-wall pinning strength and the range of interaction of a domain wall with pinning sites, respectively, are related to each other as ξ=a ρ−1/2=b/k via the pinning site density ρ, where a and b are constants. The relationship was used to simulate BE signals of the surface-hardened samples as a sum of signals generated at different depths by taking into account signal attenuation due to eddy current shielding. The simulated results were found to exhibit the general features observed in the experimental results

Barriers to Family Cancer Communication in Southern Appalachia

This study examines cultural issues surrounding family cancer communication in Appalachia, providing insight into participants’ communication choices regarding their illness within their families. Stories of 29 female Appalachian cancer survivors from Northeast Tennessee and Southwest Virginia were collected via a mixed methods approach in either a day-long story circle (N=26) or an in-depth interview (N=3). Qualitative content analysis was used to identify unique barriers to family cancer communication in Appalachia. Two barriers emerged: 1) the health of other family members and 2) cancer in a “taboo” area. These findings suggest that Appalachian female cancer survivors struggle with similar issues as survivors outside of the region regarding family cancer communication. However, there appear to be additional barriers to family cancer communication for Appalachian women that may be a result of cultural norms of the region

The synthesis of a laminated plate for high temperature application

Synthesis of laminated plate for high temperature application - thermoelastic syste