Thermal expansion behavior of LDEF metal matrix composites

The thermal expansion behavior of Long Duration Exposure Facility (LDEF) metal matrix composite materials was studied by (1) analyzing the flight data that was recorded on orbit to determine the effects of orbital time and heating/cooling rates on the performance of the composite materials, and (2) characterizing and comparing the thermal expansion behavior of post-flight LDEF and lab-control samples. The flight data revealed that structures in space are subjected to nonuniform temperature distributions, and thermal conductivity of a material is an important factor in establishing a uniform temperature distribution and avoiding thermal distortion. The flight and laboratory data showed that both Gr/Al and Gr/Mg composites were stabilized after prolonged thermal cycling on orbit. However, Gr/Al composites showed more stable thermal expansion behavior than Gr/Mg composites and offer advantages for space structures particularly where very tight thermal stability requirements in addition to high material performance must be met

Vietnamese Women and Domestic Violence: A Qualitative Examination

This grounded theory qualitative study investigated the major influencing factors in the United States that empowered six Vietnamese women who had been in abusive relationships to take actions, to make changes in their intimate relationships, unlike many of their abused counterparts in their homeland. Interviews of two focus group sessions, field-notes, and documentary evidence were used to obtain the results for this research study. Five major dominant influencing factors in the U.S. have helped these women to stand up to their abusers: 1) financial condition, 2) dominant U.S. cultures intolerance of domestic violence, 3) education, 4) support from other individuals, both genders, and 5) women role models in the community and from the media. These major determinant conditions of the theoretical model were identified and are illustrated by narrative data in this study

Evaluation of the Sustainability of an Intervention to Increase HIV Testing

BACKGROUND Sustainability—the routinization and institutionalization of processes that improve the quality of healthcare—is difficult to achieve and not often studied. OBJECTIVE To evaluate the sustainability of increased rates of HIV testing after implementation of a multi-component intervention in two Veterans Health Administration healthcare systems. DESIGN Quasi-experimental implementation study in which the effect of transferring responsibility to conduct the provider education component of the intervention from research to operational staff was assessed. PATIENTS Persons receiving healthcare between 2005 and 2006 (intervention year) and 2006 and 2007 (sustainability year). MEASUREMENTS Monthly HIV testing rate, stratified by frequency of clinic visits RESULTS The monthly adjusted testing rate increased from 2% at baseline to 6% at the end intervention year and then declined reaching 4% at the end of the sustainability year. However, the stratified, visit-specific testing rate for persons newly exposed to the intervention (i.e., having their first through third visits during the study period) increased throughout the intervention and sustainability years. Increases in the proportion of visits by patients who remained untested despite multiple, prior exposures to the intervention accounted for the aggregate attenuation of testing during the sustainability year. Overall, the percentage of patients who received an HIV test in the sustainability year was 11.6%, in the intervention year 11.1%, and in the pre-intervention year 5.0% CONCLUSIONS Provider education combined with informatics and organizational support had a sustainable effect on HIV testing rates. The effect was most pronounced during patients' early contacts with the healthcare system.Health Services Research & Development Service (SDP 06–001

The Current Adoption of Dry-Direct Seeding Rice (DDSR) in Thailand and Lessons Learned for Mekong River Delta of Vietnam

The paper documents the joint study trip, organized by CCAFS Southeast Asia for Vietnamese rice researchers, extension workers, as well as local decision makers, to visit Thailand in April 2018. The goal of the study trip was to observe and learn the experience of Thai farmers on the large-scale adoption process of dry-direct seeding rice (DDSR), a viable alternative to address regional scarcity of fresh water in irrigation caused by the drought and salinity intrusion in the Mekong River Delta

The impact of LDEF results on the space application of metal matrix composites

Over 200 graphite/aluminum and graphite/magnesium composites were flown on the leading and trailing edges of LDEF on the Advanced Composites Experiment. The performance of these composites was evaluated by performing scanning electron microscopy and x-ray photoelectron spectroscopy of exposed surfaces, optical microscopy of cross sections, and on-orbit and postflight thermal expansion measurements. Graphite/aluminum and graphite/magnesium were found to be superior to graphite/polymer matrix composites in that they are inherently resistant to atomic oxygen and are less susceptible to thermal cycling induced microcracking. The surface foils on graphite/aluminum and graphite/magnesium protect the graphite fibers from atomic oxygen and from impact damage from small micrometeoroid or space debris particles. However, the surface foils were found to be susceptible to thermal fatigue cracking arising from contamination embrittlement, surface oxidation, or stress risers. Thus, the experiment reinforced requirements for carefully protecting these composites from prelaunch oxidation or corrosion, avoiding spacecraft contamination, and designing composite structures to minimize stress concentrations. On-orbit strain measurements demonstrated the importance of through-thickness thermal conductivity in composites to minimize thermal distortions arising from thermal gradients. Because of the high thermal conductivity of aluminum, thermal distortions were greatly reduced in the LDEF thermal environment for graphite/aluminum as compared to graphite/magnesium and graphite/polymer composites. The thermal expansion behavior of graphite/aluminum and graphite/magnesium was stabilized by on-orbit thermal cycling in the same manner as observed in laboratory tests

Some interesting birational morphisms of smooth affine quadric 33-folds

We study a family of birational maps of smooth affine quadric 3-folds, {over the complex numbers}, of the form $x_1x_4-x_2x_3=$ constant, which seems to have some (among many others) interesting/unexpected characters: a) they are cohomologically hyperbolic, b) their second dynamical degree is an algebraic number but not an algebraic integer, and c) the logarithmic growth of their periodic points is strictly smaller than their algebraic entropy. These maps are restrictions of a polynomial map on $\mathbb{C}^4$ preserving each of the quadrics. The study in this paper is a mixture of rigorous and experimental ones, where for the experimental study we rely on Bertini which is a reliable and fast software for expensive numerical calculations in complex algebraic geometry.Comment: 30 pages. A revised versio

Diameter of Commuting Graphs of Lie Algebras

In this paper, we study the connectedness of the commuting graph of a general Lie algebra and provide a process to determine whether the commuting graph is connected or not, as well as to compute an upper bound for its diameter. In addition, we will examine the connectedness and diameter of the commuting graphs of some remarkable classes of Lie algebras, including: (1) a class of Lie algebras with one- or two-dimensional derived algebras; and (2) a class of solvable Lie algebras over the real field of dimension up to $4$.Comment: 21 page

Child stunting is associated with child, maternal, and environmental factors in Vietnam

Child stunting in Vietnam has reduced substantially since the turn of the century but has remained relatively high for several years. We analysed data on children 6–59 months (n = 85,932) from the Vietnam Nutritional Surveillance System, a nationally representative cross‐sectional survey. Multivariable Poisson regression models were used to estimate relative risk (RR) of stunting, stratified by child age and ecological region. Covariates at the child, maternal, household, and environmental levels were included based on available data and the World Health Organization conceptual framework on child stunting. Among children 6–23 months, the strongest associations with child stunting were child age in years (RR: 2.49; 95% CI [2.26, 2.73]), maternal height < 145 cm compared with ≥150 cm (RR: 2.04; 95% CI [1.85, 2.26]), living in the Northeast compared with the Southeast (RR: 2.01; 95% CI [1.69, 2.39]), no maternal education compared with a graduate education (RR: 1.77; 95% CI, [1.44, 2.16]), and birthweight < 2,500 g (RR: 1.75; 95% CI [1.55, 1.98]). For children 24–59 months, the strongest associations with child stunting were no maternal education compared with a graduate education (RR: 2.07; 95% CI [1.79, 2.40]), living in the Northeast compared with the Southeast (RR: 1.94; 95% CI [1.74, 2.16]), and maternal height < 145 cm compared with ≥150 cm (RR: 1.81; 95% CI [1.69, 1.94]). Targeted approaches that address the strongest stunting determinants among vulnerable populations are needed and discussed. Multifaceted approaches outside the health sector are also needed to reduce inequalities in socioeconomic status.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151838/1/mcn12826.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151838/2/mcn12826_am.pd

High Efficiency Dual-Bridge LLC Resonant Converter with Adaptive Frequency Control for On-Board Charger Applications

This paper proposes an adaptive frequency control strategy for the unidirectional DC/DC converter based on Dual-bridge LLC (DBLLC) resonant converter to eliminate the circulating interval (CI), which causes high conduction loss. The LLC resonant converters are the preferred choice to select of DC/DC converter topology for on-board charger (OBC) due to it provides many advantages such as high efficiency, high power density. The DBLLC resonant converter operating with variable frequency and the pulse width-modulated (PWM) control will be applied as an isolated stage (DC/DC converter) of 400V-7.4 kW to improve the power density and efficiency of the whole system. The advantage of operating at the adaptive frequency is that the conduction loss in all devices will be reduced, while the soft switching technique is still achieved over the full load range. Furthermore, the detailed CI characteristic along with losses analysis is presented. The topology is designed for 400 VDC input to 220-380VDC output conversion, in the power range from 3.3 kW to 7.4kW. All theoretical analysis and the experimental results on the proposed converter are provided to verify the system performance.journal articl