136 research outputs found
High-fidelity simulations of CdTe vapor deposition from a new bond-order potential-based molecular dynamics method
CdTe has been a special semiconductor for constructing the lowest-cost solar
cells and the CdTe-based Cd1-xZnxTe alloy has been the leading semiconductor
for radiation detection applications. The performance currently achieved for
the materials, however, is still far below the theoretical expectations. This
is because the property-limiting nanoscale defects that are easily formed
during the growth of CdTe crystals are difficult to explore in experiments.
Here we demonstrate the capability of a bond order potential-based molecular
dynamics method for predicting the crystalline growth of CdTe films during
vapor deposition simulations. Such a method may begin to enable defects
generated during vapor deposition of CdTe crystals to be accurately explored
Yacimiento cerro Vanguardia, Santa Cruz
El yacimiento se encuentra ubicado a unos 110 km., en línea recta, al noroeste de Puerto de San Julián. Un punto aproximadamente centrado en el área de campamento y planta tiene como coordenadas 48º23'28" L.S. y 68º15'51" L.O. El campamento minero se halla en las inmediaciones del que antiguamente fuera el casco de la estancia Cerro Vanguardia y a 4 km al noreste del cerro que da nombre al área. La altura promedio del área es del orden de 200 m s.n.m., con un máximo de 359 m s.n.m. en el cerro Vanguardia. El relieve es suave y ondulado. El avenamiento local se encauza por cortos arroyos de carácter efímero con escurrimiento hacia numerosas pequeñas cuencas centrípetas. Un camino enripiado, perfectamente mantenido, de 42 km, une el yacimiento con la Ruta Nacional 3 (35 km al sur del paraje Tres Cerros), constituyéndose en la principal vía de acceso.Instituto de Geología y Recursos MineralesInstituto de Recursos Minerale
Defect formation dynamics during CdTe overlayer growth
The presence of atomic-scale defects at multilayer interfaces significantly
degrades performance in CdTe-based photovoltaic technologies. The ability to
accurately predict and understand defect formation mechanisms during overlayer
growth is, therefore, a rational approach for improving the efficiencies of
CdTe materials. In this work, we utilize a recently developed CdTe bond-order
potential (BOP) to enable accurate molecular dynamics (MD) simulations for
predicting defect formation during multilayer growth. A detailed comparison of
our MD simulations to high-resolution transmission electron microscopy
experiments verifies the accuracy and predictive power of our approach. Our
simulations further indicate that island growth can reduce the lattice mismatch
induced defects. These results highlight the use of predictive MD simulations
to gain new insight on defect reduction in CdTe overlayers, which directly
addresses efforts to improve these materials
Theory of Electronic Ferroelectricity
We present a theory of the linear and nonlinear optical characteristics of
the insulating phase of the Falicov-Kimball model within the self-consistent
mean-field approximation. The Coulomb attraction between the itinerant
d-electrons and the localized f-holes gives rise to a built-in coherence
between the d and f-states, which breaks the inversion symmetry of the
underlying crystal, leading to: (1) electronic ferroelectricity, (2)
ferroelectric resonance, and (3) a nonvanishing susceptibility for
second-harmonic generation. As experimental tests of such a built-in coherence
in mixed-valent compounds we propose measurements of the static dielectric
constant, the microwave absorption spectrum, and the dynamic second-order
susceptibility.Comment: 15 pages, 5 PostScript figures, submitted to Physical Review
Maternal deaths in Pakistan : intersection of gender, class and social exclusion.
Background: A key aim of countries with high maternal mortality rates is to increase availability of competent
maternal health care during pregnancy and childbirth. Yet, despite significant investment, countries with the
highest burdens have not reduced their rates to the expected levels. We argue, taking Pakistan as a case study,
that improving physical availability of services is necessary but not sufficient for reducing maternal mortality
because gender inequities interact with caste and poverty to socially exclude certain groups of women from
health services that are otherwise physically available.
Methods: Using a critical ethnographic approach, two case studies of women who died during childbirth were
pieced together from information gathered during the first six months of fieldwork in a village in Northern Punjab,
Pakistan.
Findings: Shida did not receive the necessary medical care because her heavily indebted family could not afford it.
Zainab, a victim of domestic violence, did not receive any medical care because her martial family could not afford
it, nor did they think she deserved it. Both women belonged to lower caste households, which are materially poor
households and socially constructed as inferior.
Conclusions: The stories of Shida and Zainab illustrate how a rigidly structured caste hierarchy, the gendered
devaluing of females, and the reinforced lack of control that many impoverished women experience conspire to
keep women from lifesaving health services that are physically available and should be at their disposal
Didactical use of a remote lab: a qualitative reflection of a teacher
This work describes the teacher reflections about a didactical
implementation using a remote laboratory and their impact on his
practice. These reflections are analyzed from three different
perspectives: how the literature review influenced the design of
the didactical implementation (namely the first); how his
reflection upon his practice influenced its modifications; how his
research activity impacted and affected his teaching practices in
the subsequent implementations and guided the modifications
made. The remote lab was introduced in a Physics Course in an
Engineering degree and was intended to be a learning space where
students had the opportunity to practice before the lab class,
supporting the development of experimental competences,
fundamental in an engineer profile. After the first implementation
in 2016/17 academic year it has undergone two subsequent
editions with adjustments and modifications.
Some features previously reported in literature such as: teacher’s
experience with VISIR, the importance of an introductory activity
and defining VISIR tasks objectives, were corroborated by the
teacher during his practice and research. Others, such as the
difficulty some students have in understanding the difference
between simulation and remote labs appeared directly from his
practice and were pursued in his research in order to deeply
understand its implications
Antioxidant Activity of Hawaiian Marine Algae
Marine algae are known to contain a wide variety of bioactive compounds, many of which have commercial applications in pharmaceutical, medical, cosmetic, nutraceutical, food and agricultural industries. Natural antioxidants, found in many algae, are important bioactive compounds that play an important role against various diseases and ageing processes through protection of cells from oxidative damage. In this respect, relatively little is known about the bioactivity of Hawaiian algae that could be a potential natural source of such antioxidants. The total antioxidant activity of organic extracts of 37 algal samples, comprising of 30 species of Hawaiian algae from 27 different genera was determined. The activity was determined by employing the FRAP (Ferric Reducing Antioxidant Power) assays. Of the algae tested, the extract of Turbinaria ornata was found to be the most active. Bioassay-guided fractionation of this extract led to the isolation of a variety of different carotenoids as the active principles. The major bioactive antioxidant compound was identified as the carotenoid fucoxanthin. These results show, for the first time, that numerous Hawaiian algae exhibit significant antioxidant activity, a property that could lead to their application in one of many useful healthcare or related products as well as in chemoprevention of a variety of diseases including cancer
Coverage of private sector community midwife services in rural Punjab, Pakistan: development and demand
Antiferromagnetic metal phase in an electron-doped rare-earth nickelate
Long viewed as passive elements, antiferromagnetic materials have emerged as
promising candidates for spintronic devices due to their insensitivity to
external fields and potential for high-speed switching. Recent work exploiting
spin and orbital effects has identified ways to electrically control and probe
the spins in metallic antiferromagnets, especially in noncollinear or
noncentrosymmetric spin structures. The rare earth nickelate NdNiO3 is known to
be a noncollinear antiferromagnet where the onset of antiferromagnetic ordering
is concomitant with a transition to an insulating state. Here, we find that for
low electron doping, the magnetic order on the nickel site is preserved while
electronically a new metallic phase is induced. We show that this metallic
phase has a Fermi surface that is mostly gapped by an electronic reconstruction
driven by the bond disproportionation. Furthermore, we demonstrate the ability
to write to and read from the spin structure via a large zero-field planar Hall
effect. Our results expand the already rich phase diagram of the rare-earth
nickelates and may enable spintronics applications in this family of correlated
oxides.Comment: 25 pages, 4 figure
Antitumor activity of a small-molecule inhibitor of the histone kinase Haspin
The approval of histone deacetylase inhibitors for treatment of lymphoma subtypes has positioned histone modifications as potential targets for the development of new classes of anticancer drugs. Histones also undergo phosphorylation events, and Haspin is a protein kinase the only known target of which is phosphorylation of histone H3 at Thr3 residue (H3T3ph), which is necessary for mitosis progression. Mitotic kinases can be blocked by small drugs and several clinical trials are underway with these agents. As occurs with Aurora kinase inhibitors, Haspin might be an optimal candidate for the pharmacological development of these compounds. A high-throughput screening for Haspin inhibitors identified the CHR-6494 compound as being one promising such agent. We demonstrate that CHR-6494 reduces H3T3ph levels in a dose-dependent manner and causes a mitotic catastrophe characterized by metaphase misalignment, spindle abnormalities and centrosome amplification. From the cellular standpoint, the identified small-molecule Haspin inhibitor causes arrest in G2/M and subsequently apoptosis. Importantly, ex vivo assays also demonstrate its anti-angiogenetic features; in vivo, it shows antitumor potential in xenografted nude mice without any observed toxicity. Thus, CHR-6494 is a first-in-class Haspin inhibitor with a wide spectrum of anticancer effects that merits further preclinical research as a new member of the family of mitotic kinase inhibitors
- …