77 research outputs found
Analysis of defects on BN nano-structures using high-resolution electron microscopy and density-functional calculations
Cataloged from PDF version of article.Cubic boron nitride (c-BN) nucleation takes place on hexagonal boron nitride (h-BN) layers growing perpendicular to the substrate surface during thin film synthesis. Studies focused on the nucleation of the cubic phase suggest the possibility that transient phases and/or defects on these h-BN structures have a role in sp3-bonded cubic phase nucleation. In this study, we have investigated the nature, energetics, and structure of several possible defects on BN basal planes, including point defects, 4-, and 5-fold BN rings, that may possibly match the experimentally observed transient phase fine structure. TEM image observations are used to build approximate atomic models for the proposed structures, and DFT calculations are used to relax these structures while minimizing their respective total energies. These optimized atomic geometries are then used to simulate TEM images, which are compared to the experimentally observed structures. Data from DFT calculations and analysis of simulated images from the proposed atomic structures suggest that 4-fold BN rings are more likely to exist on the transient phase possibly leading to c-BN nucleation. © 2008 Elsevier B.V. All rights reserved.Cubic boron nitride (c-BN) nucleation takes place on hexagonal boron nitride (h-BN) layers growing
perpendicular to the substrate surface during thin film synthesis. Studies focused on the nucleation of
the cubic phase suggest the possibility that transient phases and/or defects on these h-BN structures
have a role in sp3-bonded cubic phase nucleation. In this study, we have investigated the nature,
energetics, and structure of several possible defects on BN basal planes, including point defects, 4-, and
5-fold BN rings, that may possibly match the experimentally observed transient phase fine structure.
TEM image observations are used to build approximate atomic models for the proposed structures, and
DFT calculations are used to relax these structures while minimizing their respective total energies.
These optimized atomic geometries are then used to simulate TEM images, which are compared to the
experimentally observed structures. Data from DFT calculations and analysis of simulated images from
the proposed atomic structures suggest that 4-fold BN rings are more likely to exist on the transient
phase possibly leading to c-BN nucleation
Magic structures of helical multi-shell zirconium nanowires
The structures of free-standing zirconium nanowires with 0.62.8 nm in
diameter are systematically studied by using genetic algorithm simulations with
a tight-binding many body potential. Several multi-shell growth sequences with
cylindrical structures are obtained. These multi-shell structures are composed
of coaxial atomic shells with the three- and four-strands helical, centered
pentagonal and hexagonal, and parallel double-chain-core curved surface
epitaxy. Under the same growth sequence, the numbers of atomic strands in
inner- and outer-shell show even-odd coupling and usually differ by five. The
size and structure dependence of angular correlation functions and vibrational
properties of zirconium nanowire are also discussed.Comment: 14 pages, 4 figure
Melting behavior of ultrathin titanium nanowires
The thermal stability and melting behavior of ultrathin titanium nanowires
with multi-shell cylindrical structures are studied using molecular dynamic
simulation. The melting temperatures of titanium nanowires show remarkable
dependence on wire sizes and structures. For the nanowire thinner than 1.2 nm,
there is no clear characteristic of first-order phase transition during the
melting, implying a coexistence of solid and liquid phases due to finite size
effect. An interesting structural transformation from helical multi-shell
cylindrical to bulk-like rectangular is observed in the melting process of a
thicker hexagonal nanowire with 1.7 nm diameter.Comment: 4 pages, 4 figure
Chirality in Bare and Passivated Gold Nanoclusters
Chiral structures have been found as the lowest-energy isomers of bare
(Au and Au_{28}(SCH_{16}_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in
the chiral clusters was calculated using the Hausdorff chirality measure. We
found that the index of chirality is higher in the passivated clusters and
decreases with the cluster size. These results are consistent with the observed
chiroptical activity recently reported for glutahione-passivated gold
nanoclusters, and provide theoretical support for the existence of chirality in
these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR
Structure of aluminum atomic chains
First-principles density functional calculations reveal that aluminum can
form planar chains in zigzag and ladder structures. The most stable one has
equilateral triangular geometry with four nearest neighbors; the other stable
zigzag structure has wide bond angle and allows for two nearest neighbors. An
intermediary structure has the ladder geometry and is formed by two strands.
All these planar geometries are, however, more favored energetically than the
linear chain. We found that by going from bulk to a chain the character of
bonding changes and acquires directionality. The conductance of zigzag and
linear chains is 4e^2/h under ideal ballistic conditions.Comment: modified detailed version, one new structure added, 4 figures,
modified figure1, 1 tabl
Effect of molecular and electronic structure on the light harvesting properties of dye sensitizers
The systematic trends in structural and electronic properties of perylene
diimide (PDI) derived dye molecules have been investigated by DFT calculations
based on projector augmented wave (PAW) method including gradient corrected
exchange-correlation effects. TDDFT calculations have been performed to study
the visible absorbance activity of these complexes. The effect of different
ligands and halogen atoms attached to PDI were studied to characterize the
light harvesting properties. The atomic size and electronegativity of the
halogen were observed to alter the relaxed molecular geometries which in turn
influenced the electronic behavior of the dye molecules. Ground state molecular
structure of isolated dye molecules studied in this work depends on both the
halogen atom and the carboxylic acid groups. DFT calculations revealed that the
carboxylic acid ligands did not play an important role in changing the
HOMO-LUMO gap of the sensitizer. However, they serve as anchor between the PDI
and substrate titania surface of the solar cell or photocatalyst. A
commercially available dye-sensitizer, ruthenium bipyridine (RuBpy), was also
studied for electronic and structural properties in order to make a comparison
with PDI derivatives for light harvesting properties. Results of this work
suggest that fluorinated, chlorinated, brominated, and iyodinated PDI compounds
can be useful as sensitizers in solar cells and in artificial photosynthesis.Comment: Single pdf file, 14 pages with 7 figures and 4 table
Prevalence and associated factors of depressive and anxiety symptoms during pregnancy: A population based study in rural Bangladesh
<p>Abstract</p> <p>Background</p> <p>Few studies have examined the associated factors of antepartum depressive and anxiety symptoms (ADS and AAS) in low-income countries, yet the World Health Organization identifies depressive disorders as the second leading cause of global disease burden by 2020. There is a paucity of research on mental disorders and their predictors among pregnant women in Bangladesh. This study aims to estimate the prevalence of depressive and anxiety symptoms and explore the associated factors in a cross-section of rural Bangladeshi pregnant women.</p> <p>Methods</p> <p>The study used cross-sectional data originating from a rural community-based prospective cohort study of 720 randomly selected women in their third trimester of pregnancy from a district of Bangladesh. The validated Bangla version of the Edinburgh Postnatal Depression Scale was used to measure ADS, and a trait anxiety inventory to assess general anxiety symptoms. Background information was collected using a structured questionnaire at the respondents' homes.</p> <p>Results</p> <p>Prevalence of ADS was 18% and AAS 29%. Women's literacy (OR 0.59, 95% CI 0.37-0.95), poor partner relationship (OR 2.23, 95% CI 3.37-3.62), forced sex (OR 1.95, 95% CI 1.01-3.75), physical violence by spouse (OR 1.69, 95% CI 1.02-2.80), and previous depression (OR 4.62 95% CI 2.72-7.85) were found to be associated with ADS. The associated factors of AAS were illiteracy, poor household economy, lack of practical support, physical partner violence, violence during pregnancy, and interaction between poor household economy and poor partner relationship.</p> <p>Conclusion</p> <p>Depressive and anxiety symptoms are found to occur commonly during pregnancy in Bangladesh, drawing attention to a need to screen for depression and anxiety during antenatal care. Policies aimed at encouraging practical support during pregnancy, reducing gender-based violence, supporting women with poor partner relationships, and identifying previous depression may ameliorate the potentially harmful consequences of antepartum depression and anxiety for the women and their family, particularly children.</p
Use of complementary and alternative medicines by a sample of Turkish women for infertility enhancement: a descriptive study
<p>Abstract</p> <p>Background</p> <p>Infertility patients are a vulnerable group that often seeks a non-medical solution for their failure to conceive. World-wide, women use CAM for productive health, but only a limited number of studies report on CAM use to enhance fertility. Little is known about traditional and religious forms of therapies that are used in relation to conventional medicine in Turkey. We investigated the prevalence and types of complementary and alternative medicine (CAM) used by infertile Turkish women for fertility enhancement.</p> <p>Methods</p> <p>A face-to-face questionnaire inquiring demographic information and types of CAM used for fertility enhancement were completed by hundred infertility patients admitted to a primary care family planning centre in Van, Turkey between January and July 2009.</p> <p>Results</p> <p>The vast majority of infertile women had used CAM at least once for infertility. CAM use included religious interventions, herbal products and recommendations of traditional "hodja's" (faith healers). Of these women, 87.8% were abused in the last 12 months, 36.6% felt not being supported by her partner and 80.5% had never spoken with a physician about CAM.</p> <p>Conclusions</p> <p>Infertile Turkish women use complementary medicine frequently for fertility enhancement and are in need of information about CAM. Religious and traditional therapies are used as an adjunct to, rather than a substitute for, conventional medical therapy. Physicians need to approach fertility patients with sensitivity and should be able to council their patients about CAM accordingly.</p
TURK PSIKIYATRI DERGISI
Objective: The present study aimed to investigate the perceived level of burden of care and its correlates in family members of schizophrenia patients. Method: The study included 239 schizophrenic patients that were followed-up at the psychiatric outpatient clinics of Izmir Ataturk Education and Research Hospital, and Celal Bayar University Medical School, and 239 of their primary caregivers. Patients were assessed using the Positive and Negative Syndrome Scale (PANNS), Global Assessment of Functioning Scale (GAF), Social Functioning Scale (SFS), Brief Cognitive State Examination (BCE), and UKU Side Effect Rating Scale. Their primary caregivers were assessed using the Perceived Family Burden Scale (PFBS), Beck Depression Inventory (BDI), and Beck Anxiety Inventory (BM). Results: Caregiver PFBS scores ere correlated with male patients, female caregivers, inadequate social support, economic difficulty, the presence of chronic physical disorder in the caregivers, patient violence toward the caregivers, total duration of illness, the number of patient hospitalizations, PANNS total and subscale scores, and SFS, BDI, and BAI scores. Perceived burden of care was Predicted by the severity of the patients' positive symptoms, SFS independence/competence and interpersonal functioning subscale scores, and caregivers' anxiety and depression levels. Conclusion: In order to decrease the burden of care in schizophrenia we recommend effective management of patient symptoms, enhancement of patient social functioning, interventions that target caregivers with high levels anxiety and depression, and social support provided by healthcare professionals
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