Absence of strong localization at low conductivity in the topological surface state of low disorder Sb2Te3

We present low-temperature transport measurements of a gate-tunable thin film topological insulator system that features high mobility and low carrier density. Upon gate tuning to a regime around the charge neutrality point, we infer an absence of strong localization even at conductivities well below $e^2/h$, where two dimensional electron systems should conventionally scale to an insulating state. Oddly, in this regime the localization coherence peak lacks conventional temperature broadening, though its tails do change dramatically with temperature. Using a model with electron-impurity scattering, we extract values for the disorder potential and the hybridization of the top and bottom surface states.Comment: 6 pages, 4 figures, with 11 pages of supplementary informatio

Proton conductivity of columnar ceria thin-films grown by chemical vapor deposition

Columnar thin films of undoped ceria were grown by metal–organic chemical vapor deposition. The films, deposited on Pt-coated MgO(100) substrates, display a columnar microstructure with nanometer scale grain size and ~30% overall porosity. Through-plane (thickness mode) electrical conductivity was measured by AC impedance spectroscopy. Proton conduction is observed below 350–400 °C, with a magnitude that depends on gas-phase water vapor pressure. The overall behavior suggests proton transport that occurs along exposed grain surfaces and parallel grain boundaries. No impedance due to grain boundaries normal to the direction of transport is observed. The proton conductivity in the temperature range of 200–400 °C is approximately four times greater than that of nanograined bulk ceria, consistent with enhanced transport along aligned grain surfaces in the CVD films

Decreasing Herpes Simplex Viral Infectivity in Solution by Surface-Immobilized and Suspended N,N-Dodecyl,methyl-polyethylenimine

Purpose To explore surface-immobilized and suspended modalities of the hydrophobic polycation N,N-dodecyl,methyl-polyethylenimine (DMPEI) for the ability to reduce viral infectivity in aqueous solutions containing herpes simplex viruses (HSVs) 1 and 2. Methods Surface-immobilized (coated onto surfaces) and suspended DMPEI were incubated with aqueous solutions containing HSV-1 or -2 to measure the antiviral effect of the hydrophobic polycation’s formulations on HSVs. Results DMPEI coated on either polyethylene slides or male latex condoms dramatically decreases infectivity in solutions containing HSV-1 or -2. Moreover, DMPEI suspended in aqueous solution markedly reduces the infectious titer of these HSVs. Conclusion Our results suggest potential uses of DMPEI for both prophylaxis (in the form of coated condoms) and treatment (as a topical suspension) for HSV infections.Martin Family Graduate FellowshipNational Institutes of Health (U.S.) (Grant AI057552)United States. Army Research Office (Grant W911NF-07-D-0004

Effect of increased quadriceps tensile stiffness on peak anterior cruciate ligament strain during a simulated pivot landing

ACL injury prevention programs often involve strengthening the knee muscles. We posit that an unrecognized benefit of such training is the associated increase in the tensile stiffness of the hypertrophied muscle. We tested the hypothesis that an increased quadriceps tensile stiffness would reduce peak anteromedial bundle (AM‐)ACL relative strain in female knees. Twelve female cadaver knees were subjected to compound impulsive two‐times body weight loads in compression, flexion, and internal tibial torque beginning at 15° flexion. Knees were equipped with modifiable custom springs to represent the nonlinear rapid stretch behavior of a normal and increased stiffness female quadriceps (i.e., 33% greater stiffness). Peak AM‐ACL relative strain was measured using an in situ transducer while muscle forces and tibiofemoral kinematics and kinetics were recorded. A 3D ADAMS™ dynamic biomechanical knee model was used in silico to interpret the experimental results which were analyzed using a repeated‐measures Wilcoxon test. Female knees exhibited a 16% reduction in peak AM‐ACL relative strain and 21% reduction in change in flexion when quadriceps tensile stiffness was increased by 33% (mean (SD) difference: 0.97% (0.65%), p  = 0.003). We conclude that increased quadriceps tensile stiffness reduces peak ACL strain during a controlled study simulating a pivot landing. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:423–430, 2014.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102663/1/jor22531.pd

Overview of a Proposed Flight Validation of Aerocapture System Technology for Planetary Missions

Aerocapture System Technology for Planetary Missions is being proposed to NASA's New Millennium Program for flight aboard the Space Technology 9 (ST9) flight opportunity. The proposed ST9 aerocapture mission is a system-level flight validation of the aerocapture maneuver as performed by an instrumented, high-fidelity flight vehicle within a true in-space and atmospheric environment. Successful validation of the aerocapture maneuver will be enabled through the flight validation of an advanced guidance, navigation, and control system as developed by Ball Aerospace and two advanced Thermal Protection System (TPS) materials, Silicon Refined Ablative Material-20 (SRAM-20) and SRAM-14, as developed by Applied Research Associates (ARA) Ablatives Laboratory. The ST9 aerocapture flight validation will be sufficient for immediate infusion of these technologies into NASA science missions being proposed for flight to a variety of Solar System destinations possessing a significant planetary atmosphere

Literature Review: Comparison of the Effects of Cigarette Smoke on Mesenchymal Stem Cells and Dental Stem Cells

Stem cells are distinguished from other cell types due to two important defining characteristics. First, stem cells must exhibit selfrenewal potential, which is the ability to produce identical copies of themselves through mitotic divisions over time. Second, stem cells must exhibit multilineage differentiation potential – pluripotency, which is the ability to give rise to various specialized cell types and serves as the driving concept behind stem cell regeneration. They also possess migration potential in order to reach sites of injury. These abilities allow stem cells to participate in the body’s natural processes of wound healing and tissue generation and raise the potential of using stem cells in various applications in regenerative medicine. However, certain environmental predisposing conditions such as cigarette smoke can negatively impact these abilities and stem cell viability for transplantation and regeneration. Most of the research conducted on stem cells involves mesenchymal stem cells (MSCs), typically from the bone marrow. The substantial growth in this research has allowed further understanding of the deleterious effects of cigarette smoke on MSCs, as well as improved our knowledge on the therapeutic usage of MSCs for smoking patients. As of now, there is a considerable lack of research focused on dental stem cells. Given that the first exposure to smoke occurs in the oral cavity, and that the content of nicotine is estimated to be nearly 8 times higher in saliva than in blood plasma (8 hours following application of nicotine patch; saliva: 76.8 ng/ml, plasma: 10.0 ng/ml)1, the potentially more susceptible stem cell populations in the oral cavity deserve more attention. Dental stem cells share many properties with MSCs, and a disruption in their function by higher concentrations of a known inhibitor of stem cell function would create significant problems in the repair process

Literature Review: Comparison of the Effects of Cigarette Smoke on Mesenchymal Stem Cells and Dental Stem Cells

Stem cells are distinguished from other cell types due to two important defining characteristics. First, stem cells must exhibit selfrenewal potential, which is the ability to produce identical copies of themselves through mitotic divisions over time. Second, stem cells must exhibit multilineage differentiation potential – pluripotency, which is the ability to give rise to various specialized cell types and serves as the driving concept behind stem cell regeneration. They also possess migration potential in order to reach sites of injury. These abilities allow stem cells to participate in the body’s natural processes of wound healing and tissue generation and raise the potential of using stem cells in various applications in regenerative medicine. However, certain environmental predisposing conditions such as cigarette smoke can negatively impact these abilities and stem cell viability for transplantation and regeneration. Most of the research conducted on stem cells involves mesenchymal stem cells (MSCs), typically from the bone marrow. The substantial growth in this research has allowed further understanding of the deleterious effects of cigarette smoke on MSCs, as well as improved our knowledge on the therapeutic usage of MSCs for smoking patients. As of now, there is a considerable lack of research focused on dental stem cells. Given that the first exposure to smoke occurs in the oral cavity, and that the content of nicotine is estimated to be nearly 8 times higher in saliva than in blood plasma (8 hours following application of nicotine patch; saliva: 76.8 ng/ml, plasma: 10.0 ng/ml)1, the potentially more susceptible stem cell populations in the oral cavity deserve more attention. Dental stem cells share many properties with MSCs, and a disruption in their function by higher concentrations of a known inhibitor of stem cell function would create significant problems in the repair process

Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical/NIR pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by attosecond transient absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium M_{4,5}-edge (~30 eV). We decompose the ATAS spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8*10^{20}cm^{-3}. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first order electron and hole decay of ~1 ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous observation of electrons and holes with ATAS paves the way for investigating few to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.Comment: Includes Supplementary Informatio