268 research outputs found
Suppressed reflectivity due to spin-controlled localization in a magnetic semiconductor
The narrow gap semiconductor FeSi owes its strong paramagnetism to
electron-correlation effects. Partial Co substitution for Fe produces a
spin-polarized doped semiconductor. The spin-polarization causes suppression of
the metallic reflectivity and increased scattering of charge carriers, in
contrast to what happens in other magnetic semiconductors, where magnetic order
reduces the scattering. The loss of metallicity continues progressively even
into the fully polarized state, and entails as much as a 25% reduction in
average mean-free path. We attribute the observed effect to a deepening of the
potential wells presented by the randomly distributed Co atoms to the majority
spin carriers. This mechanism inverts the sequence of steps for dealing with
disorder and interactions from that in the classic Al'tshuler Aronov approach -
where disorder amplifies the Coulomb interaction between carriers - in that
here, the Coulomb interaction leads to spin polarization which in turn
amplifies the disorder-induced scattering.Comment: 6 figures Submitted to PR
Sand Foot: A Prosthesis for Walking on Sand
This critical design report describes the product development of a prosthesis for use on sand. Quality of Life Plus (QL+), a national non-profit organization aimed to develop prostheses for veterans and people with disabilities, introduced this project and its accompanying challenger, Sgt. Brady, to Cal Poly’s Interdisciplinary Senior Project class in September 2018. After consulting with Sgt. Brady and QL+ and performing extensive research, the Sand Foot team defined customer requirements and engineering specifications to meet these requirements. Comfortability, durability, and sandproof were key customer requirements. Several conceptual models were brainstormed and a final design was selected based on the best design concepts of all considered models. The first prototype was composed of aluminum, carbon fiber, and polyurethane rubber -- all waterproof, sandproof, and non-corrosive materials -- and includes a curved toe design and rubber block used to mimic a flexing ankle and thus improve comfortability and functionality and several drains to waterproof and sandproof the prosthesis. Manufacturing occurred on the Cal Poly campus utilizing the Mustang 60 machine shop, the Cal Poly Composites Lab, and the QL+ lab. Funds were available to outsource parts if needed. The Sand Foot team manufactured the first prototype and sent it to Sgt. Brady for product testing and feedback. Unfortunately, the carbon fiber sole broke in transit to Sgt. Brady, and a thorough investigation determined the break was caused by impact. Poor manufacturing practices and unfamiliar materials resulted in a brittle sole. The team quickly pivoted and redesigned the sole using aluminum tubes, aluminum fittings, and canvas. The new design featured a curved toe and fit with the intended flexing ankle mechanism. A local amputee tested the final design. The amputee positively comments on the prosthesis’ functionality and comfort, while weight, shape, and sand proofness were concerns. The feedback was helpful for the team as well as engineers and student who wish to adapt the design and improve others’ quality of life
Calculation of Optical Conductivity of YbB using Realistic Tight-Binding Model
Based on the previously reported tight-binding model fitted to the LDA+U band
calculation, optical conductivity of the prototypical Kondo insulator
YbB is calculated theoretically. Many-body effects are taken into
account by the self-consistent second order perturbation theory. The gross
shape of the optical conductivity observed in experiments are well described by
the present calculation, including their temperature-dependences.Comment: 6 pages, 7 figures, use jpsj2.cls, to appear in J. Phys. Soc. Jpn.
Vol.73, No.10 (2004
Thermal and Dynamical Properties of the Two-band Hubbard Model Compared with FeSi
We study the two-band Hubbard model introduced by Fu and Doniach as a model
for FeSi which is suggested to be a Kondo insulator. Using the self-consistent
second-order perturbation theory combined with the local approximation which
becomes exact in the limit of infinite dimensions, we calculate the specific
heat, the spin susceptibility and the dynamical conductivity and point out that
the reduction of the energy gap due to correlation is not significant in
contrast to the previous calculation. It is also demonstrated that the gap at
low temperatures in the optical conductivity is filled up at a rather low
temperature than the gap size, which is consistent with the experiment.Comment: 6 pages, LaTeX, 7 PS figures included, uses RevTe
Sox7 controls arterial specification in conjunction with hey2 and efnb2 function
Supramolecular & Biomaterials Chemistr
Correlation Effects on Optical Conductivity of FeSi
Effects of electron correlation in FeSi are studied in terms of the two-band
Hubbard model with the density of states obtained from the band calculation.
Using the self-consistent second-order perturbation theory combined with the
local approximation, the correlation effects are investigated on the density of
states and the optical conductivity spectrum, which are found to reproduce the
experiments done by Damascelli et al. semiquantitatively. It is also found that
the peak at the gap edge shifts to lower energy region by correlation effects,
as is seen in the experiments.Comment: 4 pages, 3 figure
Formation Mechanism of Hybridization Gap in Kondo Insulators based on a Realistic Band Model and Application to YbB
A new LDA+U band calculation is performed on the Kondo insulator material
YbB and an energy gap of about 0.001Ryd is obtained. Based on this, a
simple tight-binding model with 5d and 4f orbitals on Yb
atoms and the nearest neighbor -bonds between them is constructed with
a good agreement to the above the LDA+U calculation near the gap. The density
of states is also calculated and the shape is found to be very asymmetric with
respect to the gap. A formation mechanism of the gap is clarified for the first
time in a realistic situation with the orbital degeneracies in both conduction
bands and the f states. This model can be a useful starting point for
incorporating the strong correlation effect, and for understanding all the
thermal, thermoelectric, transport and magnetic properties of YbB.Comment: 15 pages, 15 figures, to appear in J. Phys. Soc. Jpn. Vol. 72 No. 5
(2003
Coupling of Glucose Deprivation with Impaired Histone H2B Monoubiquitination in Tumors
Metabolic reprogramming is associated with tumorigenesis. However, glucose metabolism in tumors is poorly understood. Here, we report that glucose levels are significantly lower in bulk tumor specimens than those in normal tissues of the same tissue origins. We show that mono-ubiquitinated histone H2B (uH2B) is a semi-quantitative histone marker for glucose. We further show that loss of uH2B occurs specifically in cancer cells from a wide array of tumor specimens of breast, colon, lung and additional 23 anatomic sites. In contrast, uH2B levels remain high in stromal tissues or non-cancerous cells in the tumor specimens. Taken together, our data suggest that glucose deficiency and loss of uH2B are novel properties of cancer cells in vivo, which may represent important regulatory mechanisms of tumorigenesis
Metabolic determinants of cancer cell sensitivity to glucose limitation and biguanides
As the concentrations of highly consumed nutrients, particularly glucose, are generally lower in tumours than in normal tissues1,2, cancer cells must adapt their metabolism to the tumour microenvironment. A better understanding of these adaptations might reveal cancer cell liabilities that can be exploited for therapeutic benefit. Here, we developed a continuous flow culture apparatus (Nutrostat) for maintaining proliferating cells in low nutrient media for long periods of time and used it to undertake competitive proliferation assays on a pooled collection of barcoded cancer cell lines cultured in low glucose conditions. Sensitivity to low glucose varies amongst cell lines, and an RNAi screen pinpointed mitochondrial oxidative phosphorylation (OXPHOS) as the major pathway required for optimal proliferation in low glucose. We found that cell lines most sensitive to low glucose are defective in the upregulation of OXPHOS normally caused by glucose limitation as a result of either mtDNA mutations in Complex I genes or impaired glucose utilization. These defects predict sensitivity to biguanides, anti-diabetic drugs that inhibit OXPHOS3,4, when cancer cells are grown in low glucose or as tumour xenografts. Remarkably, the biguanide sensitivity of cancer cells with mtDNA mutations was reversed by ectopic expression of yeast NDI1, a ubiquinone oxidoreductase that allows bypass of Complex I function5. Thus, we conclude that mtDNA mutations and impaired glucose utilization are potential biomarkers for identifying tumours with increased sensitivity to OXPHOS inhibitors
Evaluation of Two Models for Human Topoisomerase I Interaction with dsDNA and Camptothecin Derivatives
Human topoisomerase I (Top1) relaxes supercoiled DNA during cell division. Camptothecin stabilizes Top1/dsDNA covalent complexes which ultimately results in cell death, and this makes Top1 an anti-cancer target. There are two current models for how camptothecin and derivatives bind to Top1/dsDNA covalent complexes (Staker, et al., 2002, Proc Natl Acad Sci USA 99: 15387–15392; and Laco, et al., 2004, Bioorg Med Chem 12: 5225–5235). The interaction energies between bound camptothecin, and derivatives, and Top1/dsDNA in the two models were calculated. The published structure-activity-relationships for camptothecin and derivatives correlated with the interaction energies for camptothecin and derivatives in the Laco et al. model, however, this was not the case for several camptothecin derivatives in the Stacker et al. model. By defining the binding orientation of camptothecin and derivatives in the Top1/dsDNA active-site these results allow for the rational design of potentially more efficacious camptothecin derivatives
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