Investigation Of Ferroelectric Perovskite Oxides For Photovoltaic Applications

Ferroelectric materials have been demonstrated to be promising in developing emerging photovoltaic technologies because of the various mechanisms that allow above-bandgap photovoltages and higher efficiencies. However, the wide bandgaps of conventional ferroelectric oxides limit their utilization of the solar spectrum. This thesis focused on the identification of chemical substituents capable of reducing the bandgap of ferroelectric perovskite oxides, while retaining a robust polarization. Building upon the discovery of (1−x)KNbO3-xBa(Ni1/2Nb1/2)O2.75 solid solutions which have bandgaps compatible with traditional semiconductors, new families of Ni- and Ni/Nb-substituted BaTiO3 were fabricated through solid state methods. The oxygen vacancies accompanying the Ni and Ni-Nb substitutions significantly lower the optical bandgap of BaTiO3 to ~1.5 eV. Although effective in reducing the bandgap, the loss of the ferroelectric polarization in KNbO3 and BaTiO3 at relatively small concentrations (≤ ~10%) of Ni and Ni/Nb prevent access to a wide range of polar solid solutions. To mitigate this issue, bandgap reduction was explored in systems with a more robust ferroelectric order, namely the tetragonally-enhanced PbTiO3-BiFeO3 system where the A site is completely occupied by ferroelectrically active Pb/Bi cations. A morphotropic-phase-boundary (MPB) additive, Bi(Ni1/2Ti1/2)O3, was found to simultaneously lower the bandgap and retain the ferroelectric order of a wide range of compositions in the PbTiO3-BiFeO3-Bi(Ni1/2Ti1/2)O3 ternary system. MPB compositions showed a switchable photovoltaic effect with an open-circuit voltage (Voc) of 6 V. Under AM1.5G illumination the short-circuit photocurrent (jsc) of these systems increased by an order of magnitude as Eg was lowered from 2.85 to 2.25 eV. The dependence of the photovoltaic response on the ferroelectric polarization, device configuration, temperature and defects were investigated in 0.5PbTiO3-0.5Bi(Ni1/2Ti1/2)O3, a tetragonal composition close to the MPB. A direct correlation between the polarization and the photovoltaic response was established. The PV properties of 0.5PbTiO3-0.5Bi(Ni1/2Ti1/2)O3 showed strong temperature dependence with Voc increasing and jsc decreasing at lower temperature; a Voc above 100 V was obtained for a 250 µm thick sample below 160 K. Temperature dependent measurements of dielectric and mechanical responses showed the photovoltaic properties are influenced by thermal depolarization and a re-entrant relaxor phase transition, and are also mediated by the polaron hopping mechanism. Post-annealing in atmospheres with different pO2’s allowed modification of the carrier concentration, which in turn was used to control the dielectric, mechanical and photovoltaic properties

Coherent Compensation based ISAC Signal Processing for Long-range Sensing

Integrated sensing and communication (ISAC) will greatly enhance the efficiency of physical resource utilization. The design of ISAC signal based on the orthogonal frequency division multiplex (OFDM) signal is the mainstream. However, when detecting the long-range target, the delay of echo signal exceeds CP duration, which will result in inter-symbol interference (ISI) and inter-carrier interference (ICI), limiting the sensing range. Facing the above problem, we propose to increase useful signal power through coherent compensation and improve the signal to interference plus noise power ratio (SINR) of each OFDM block. Compared with the traditional 2D-FFT algorithm, the improvement of SINR of range-doppler map (RDM) is verified by simulation, which will expand the sensing range

Experimental investigations on drag-reduction characteristics of bionic surface with water-trapping microstructures of fish scales

Biological surfaces with unique wettability in nature have provided an enormous innovation for scientists and engineers. More specifically, materials possessing various wetting properties have drawn considerable attention owing to their promising application prospects. Recently, great efforts have been concentrated on the researches on wetting-induced drag-reduction materials inspired by biology because of their ability to save energy. In this work, the drag-reduction characteristics of the bionic surface with delicate water-trapping microstructures of fish Ctenopharyngodon idellus scales were explored by experimental method. Firstly, the resistance of smooth surface and bionic surface experimental sample at different speeds was carefully tested through the testing system for operation resistance. Then, the contact angle (CA) of fish scale surface was measured by means of the contact angle measuring instrument. It was discovered that the bionic surface created a rewarding drag-reduction effect at a low speed, and the drag-reduction rate significantly displayed a downward trend with the increase in flow speed. Thus, when the rate was 0.66 m/s, the drag-reduction effect was at the optimum level, and the maximum drag reduction rate was 2.805%, which was in concordance with the simulated one. Furthermore, a contact angle (CA) of 11.5° appeared on the fish scale surface, exhibiting fine hydrophilic property. It further manifested the spreading-wetting phenomenon and the higher surface energy for the area of apical of fish scales, which played an important role in drag-reduction performance. This work will have a great potential in the engineering and transportation field

Drag reduction mechanism of Paramisgurnus dabryanus loach with self-lubricating and flexible micro-morphology

Underwater machinery withstands great resistance in the water, which can result in consumption of a large amount of power. Inspired by the character that loach could move quickly in mud, the drag reduction mechanism of Paramisgurnus dabryanus loach is discussed in this paper. Subjected to the compression and scraping of water and sediments, a loach could not only secrete a lubricating mucus film, but also importantly, retain its mucus well from losing rapidly through its surface micro structure. In addition, it has been found that flexible deformations can maximize the drag reduction rate. This self-adaptation characteristic can keep the drag reduction rate always at high level in wider range of speeds. Therefore, even though the part of surface of underwater machinery cannot secrete mucus, it should be designed by imitating the bionic micro-morphology to absorb and store fluid, and eventually form a self-lubrication film to reduce the resistance. In the present study, the Paramisgurnus dabryanus loach is taken as the bionic prototype to learn how to avoid or slow down the mucus loss through its body surface. This combination of the flexible and micro morphology method provides a potential reference for drag reduction of underwater machinery

Joint Influence of Individual Choices, Parenting Practices, and Physician Advice on Adolescent Obesity, Nebraska, 2008

Introduction Reducing childhood obesity remains a public health priority given its high prevalence and its association with increased risk of adult obesity and chronic diseases. The objective of this study was to examine the joint influence of multiple risk factors on adolescent overweight status. Methods We conducted a random-digit-dialed telephone survey of adolescents aged 12 to 19 years in fall 2008 in a Midwestern city in Nebraska. On the basis of survey data for 791 youths aged 12 to 18 years, we conducted latent class analysis to group youths by the joint occurrence of dietary behavior, physical activity, parenting practices, and physician advice. We then examined the association between the groups and overweight status by using logistic regression, controlling for age, sex, race/ethnicity, and parent and family information. Results Youths were clustered into 3 groups. Group I (52%) were youths with healthy dietary behavior and physical activity, less permissive parenting practices, and physician advice; Group II (30%) were youths with moderately healthy dietary behavior and physical activity, less permissive parenting practices, and no physician advice; and Group III (18%) were youths with unhealthy dietary behavior and physical activity, permissive parenting practices, and physician advice. Youths in Groups I and II were less likely to be overweight than youths in Group III. Conclusions Youths with healthier behavior and less permissive parenting practices were less likely to be overweight. Study findings highlight the need to address obesity risk factors among youths with unhealthy dietary behavior, inadequate exercise, permissive parenting practices, and some physician advice. Tailored interventions should be used to target youths with different obesity risk factors

Growth Rate and Leaf Functional Traits of Four Broad-Leaved Species Underplanted in Chinese Fir Plantations with Different Tree Density Levels

The close-to-Nature management method of interplanting broad-leaved trees after thinning of monoculture plantations is an important mixed species restoration model to improve the ecological service and functions effectively as well as to reduce the productivity decline of the multi-generation continuous planting of monoculture. Thus, the selection of tree species for establishing mixed forest and its ecological adaptability are the key issues. In this study, we conducted thinning experiment in an 11-year-old Chinese fir plantation with retention density of 900 trees/ha, 1200 trees/ha and 1875 trees/ha, and then underplanted four broad-leaved species, Schima superba, Phoebe bournei, Tsoongiodendron odorum and Michelia macclurei. After three years, we analyzed the growth rate and leaf functional traits of the broad-leaved species and their correlations with stand characteristics. The results showed that growth rate of seedlings of the four broad-leaved species were significantly different (p < 0.05) among different tree density levels and species. Low tree density favored seedling growth compared with high tree density and seedlings of T. odorum and S. superba performed best. However, leaf functional traits varied significantly (p < 0.01) among species only, and T. odorum had the largest specific leaf area, the smallest leaf mass per unit area, the smallest leaf tissue density, relatively large leaf thickness, and relatively small dry matter content. The leaf C content varied significantly among tree density levels and species; leaf N content varied significantly among species only; and leaf p content varied among tree density levels only. Correlation analyses between growth characters and leaf functional traits showed that height growth was significantly correlated with leaf N content (r = 0.686; p = 0.041) and with C:N ratio (r = -0.682; p = 0.043). Root collar diameter growth was significantly correlated with specific leaf area (r = 0.820; p = 0.007), leaf N content (r = 0.685; p = 0.042), leaf thickness (r = -0.706; p = 0.034) and leaf mass per unit area (r = -0.812; p = 0.008). Thus, leaf functional traits possibly predict diameter growth better than height growth. As a whole, growth rate and leaf functional traits could be used as a guide for selection of species for under planting in thinned pure monoculture plantations to establish conifer-broadleaved mixed forests. Based on growth rate and leaf functional traits, T. odorum appeared to be suitable for planting under low tree density stands where the degree of shading is low

Baseline CD4 Cell Counts of Newly Diagnosed HIV Cases in China: 2006–2012

Background: Late diagnosis of HIV infection is common. We aim to assess the proportion of newly diagnosed HIV cases receiving timely baseline CD4 count testing and the associated factors in China. Methods: Data were extracted from the Chinese HIV/AIDS Comprehensive Response Information Management System. Adult patients over 15 years old who had been newly diagnosed with HIV infection in China between 2006 and 2012 were identified. The study cohort comprised individuals who had a measured baseline CD4 count. Results: Among 388,496 newly identified HIV cases, the median baseline CD4 count was 294 cells/µl (IQR: 130–454), and over half (N = 130,442, 58.8%) were less than 350 cells/µl. The median baseline CD4 count increased from 221 (IQR: 63–410) in 2006 to 314 (IQR: 159–460) in 2012. A slight majority of patients (N = 221,980, 57.1%) received baseline CD4 count testing within 6 months of diagnosis. The proportion of individuals who received timely baseline CD4 count testing increased significantly from 20.0% in 2006 to 76.9% in 2012. Factors associated with failing to receiving timely CD4 count testing were: being male (OR: 1.17, 95% CI: 1.15–1.19), age 55 years or older (OR:1.03, 95% CI: 1.00–1.06), educational attainment of primary school education or below (OR: 1.30, 95% CI: 1.28–1.32), infection with HIV through injection drug use (OR: 2.07, 95% CI: 2.02–2.12) or sexual contact and injection drug use (OR: 1.87, 95% CI: 1.76–1.99), diagnosis in a hospital (OR: 1.91, 95% CI: 1.88–1.95) or in a detention center (OR: 1.75, 95% CI: 1.70–1.80), and employment as a migrant worker (OR:1.55, 95% CI:1.53–1.58). Conclusion: The proportion of newly identified HIV patients receiving timely baseline CD4 testing has increased significantly in China from 2006–2012. Continued effort is needed for further promotion of early HIV diagnosis and timely baseline CD4 cell count testing

Expression of GCRG213p, LINE-1 endonuclease variant, significantly different in gastric complete and incomplete intestinal metaplasia.

BACKGROUND: Intestinal metaplasia (IM) of the gastric mucosa is classified as complete (Type I) and incomplete IM (Type II and III) subtypes, which showed significantly different risk for developing to gastric adenocarcinoma (GAC). GCRG213, a variant of L1-endonuclease (L1-EN), first identified in our lab, was upregulated in GAC tissue. However, the relationship between GCRG213 and IM subtypes is not clear. Our study explored the association of GCRG213 protein (GCRG213p) with IM subtypes. METHODS: Gastric cancer and/or para-tumor tissue samples were collected from 123 patients who underwent gastrectomy for intestinal type gastric adenocarcinoma. The subtypes of IM were characterized with Alcian blue-periodic acid-Schiff and High Iron Diamine-Alcian blue staining methods. Immunohistochemistry of GCRG213p was performed, and its expression in gastric adenocarcinoma and para-tumor tissue including dysplasia, IM, and normal mucosa were analyzed. RESULTS: GCRG213p was expressed in 48.94% IM, 57.14% dysplasia and 55.32% GAC, respectively. GCRG213p expression was higher in well and moderately differentiated adenocarcinoma (P = 0.037). In IM glands, GCRG213p expressed mainly in the cytoplasm of absorptive enterocytes with defined brush borders, but not in goblet cells. The expression of GCRG213p in type I IM (90.00%) was significantly higher than that in type II (36.36%) and type III (25.00%) (P \u3c 0.001). In normal gastric mucosa, GCRG213p was exclusively positive in the cytoplasm of gastric chief cells. CONCLUSIONS: The expression of GCRG213p in complete IM was significantly higher than in incomplete IM, which implies that GCRG213p may play a role on the developing of IM to adenocarcinoma. GCRG213p was exclusively expressed in chief cells, suggesting that it might be involved in cell differentiation from the chief cells to IM