Quantum-mechanical wavepacket transport in quantum cascade laser structures

We present a viewpoint of the transport process in quantum cascade laser structures in which spatial transport of charge through the structure is a property of coherent quantum-mechanical wavefunctions. In contrast, scattering processes redistribute particles in energy and momentum but do not directly cause spatial motion of charge.Comment: 6 pages, 5 figures included in tex, to appear in Physical Review

Ultrafast modulation of electronic structure by coherent phonon excitations

Femtosecond x-ray absorption spectroscopy with a laser-driven high-harmonic source is used to map ultrafast changes of x-ray absorption by femtometer- scale coherent phonon displacements. In LiBH4, displacements along an Ag phonon mode at 10 THz are induced by impulsive Raman excitation and give rise to oscillatory changes of x-ray absorption at the Li K edge. Electron density maps from femtosecond x-ray diffraction data show that the electric field of the pump pulse induces a charge transfer from the BH4− to neighboring Li+ ions, resulting in a differential Coulomb force that drives lattice vibrations in this virtual transition state

Extreme selective sweeps independently targeted the X chromosomes of the great apes

The unique inheritance pattern of the X chromosome exposes it to natural selection in a way that is different from that of the autosomes, potentially resulting in accelerated evolution. We perform a comparative analysis of X chromosome polymorphism in 10 great ape species, including humans. In most species, we identify striking megabase-wide regions, where nucleotide diversity is less than 20% of the chromosomal average. Such regions are found exclusively on the X chromosome. The regions overlap partially among species, suggesting that the underlying targets are partly shared among species. The regions have higher proportions of singleton SNPs, higher levels of population differentiation, and a higher nonsynonymous-to-synonymous substitution ratio than the rest of the X chromosome. We show that the extent to which diversity is reduced is incompatible with direct selection or the action of background selection and soft selective sweeps alone, and therefore, we suggest that very strong selective sweeps have independently targeted these specific regions in several species. The only genomic feature that we can identify as strongly associated with loss of diversity is the location of testis-expressed ampliconic genes, which also have reduced diversity around them. We hypothesize that these genes may be responsible for selective sweeps in the form of meiotic drive caused by an intragenomic conflict in male meiosis

Clinical course and therapeutic approach to varicella zoster virus infection in children with rheumatic autoimmune diseases under immunosuppression.

To analyze the clinical presentation and complications of varicella zoster virus (VZV) infection in children with rheumatic diseases treated with immunosuppressive medication such as biological disease-modifying antirheumatic drugs (bDMARDs) and/or conventional disease-modifying antirheumatic drugs (cDMARDs), and to analyze the therapeutic approach to VZV infections with respect to the concomitant immunosuppressive treatment. Retrospective multicenter study using the Swiss Pediatric Rheumatology registry. Children with rheumatic diseases followed in a Swiss center for pediatric rheumatology and treated with cDMARD and/or bDMARD with a clinical diagnosis of varicella or herpes zoster between January 2004 and December 2013 were included. Twenty-two patients were identified, of whom 20 were treated for juvenile idiopathic arthritis, 1 for a polyglandular autoimmune syndrome type III, and 1 for uveitis. Of these 22 patients, 16 had varicella and 6 had herpes zoster. Median age at VZV disease was 7.6 years (range 2 to 17 years), with 6.3 years (range 2 to 17 years) for those with varicella and 11.6 years (range 5 to 16 years) for those with herpes zoster. The median interval between start of immunosuppression and VZV disease was 14.1 months (range 1 to 63 months). Two patients had received varicella vaccine (1 dose each) prior to start of immunosuppression. Concomitant immunosuppressive therapy was methotrexate (MTX) monotherapy (n = 9) or bDMARD monotherapy (n = 2), or a combination of bDMARD with prednisone, MTX or Leflunomide (n = 11). Four patients experienced VZV related complications: cellulitis in 1 patient treated with MTX, and cellulitis, sepsis and cerebellitis in 3 patients treated with biological agents and MTX combination therapy. Six children were admitted to hospital (range of duration: 4 to 9 days) and 12 were treated with valaciclovir or aciclovir. The clinical course of varicella and herpes zoster in children under immunosuppression is variable, with 4 (18 %) of 22 children showing a complicated course. Thorough assessment of VZV disease and vaccination history and correct VZV vaccination according to national guidelines at diagnosis of a rheumatic autoimmune disease is essential to minimize VZV complications during a later immunosuppressive treatment

Amyloid-like aggregates sequester numerous metastable proteins with essential cellular functions

Protein aggregation is linked with neurodegeneration and numerous other diseases by mechanisms that are not well understood. Here, we have analyzed the gain-of-function toxicity of artificial β sheet proteins that were designed to form amyloid-like fibrils. Using quantitative proteomics, we found that the toxicity of these proteins in human cells correlates with the capacity of their aggregates to promote aberrant protein interactions and to deregulate the cytosolic stress response. The endogenous proteins that are sequestered by the aggregates share distinct physicochemical properties: They are relatively large in size and significantly enriched in predicted unstructured regions, features that are strongly linked with multifunctionality. Many of the interacting proteins occupy essential hub positions in cellular protein networks, with key roles in chromatin organization, transcription, translation, maintenance of cell architecture and protein quality control. We suggest that amyloidogenic aggregation targets a metastable subproteome, thereby causing multifactorial toxicity and, eventually, the collapse of essential cellular functions. PaperFlick: © 2011 Elsevier Inc

Dynamic Power Convertor Development for Radioisotope Power Systems at NASA Glenn Research Center

The Thermal Energy Conversion Branch at NASA Glenn Research Center (GRC) is supporting the development of high-efficiency power convertors for use in Radioisotope Power Systems (RPS). Significant progress was made towards such a system that utilized Stirling conversion during the 2001 to 2015 timeframe. Flight development of the Advanced Stirling Radioisotope Generator (ASRG) was cancelled in 2013 by the Department of Energy (DOE) and NASA Headquarters primarily due to budget constraints, and the Advanced Stirling Convertor (ASC) technology contract was subsequently concluded in 2015. A new chapter of technology development has recently been initiated by the NASA RPS Program. This effort is considering all dynamic power convertor options, such as Stirling and Brayton cycles. Four convertor development contracts supporting this effort were awarded in 2017. The awarded contracts include two free-piston Stirling, one thermoacoustic Stirling, and one turbo-Brayton designs. The technology development contracts each consist of up to three phases: Design, Fabricate, and Test. As of May 2018, all contracts have completed the Design Phase, and each underwent a design review with an independent review board. Three of the contracts are planned to execute the Phase 2 option for fabrication. Convertors manifesting from these development efforts will then undergo independent validation and verification at NASA facilities, which will consist of convertor performance and RPS viability demonstrations. Example tests include launch vibration simulation, performance mapping over the environmental temperature range, and static acceleration exposure. In parallel with this renewed development effort, NASA GRC is still demonstrating free-piston Stirling convertor technology using assets from previous projects. The Stirling Research Laboratory (SRL) is still operating several convertors from previous development projects which have similarities and relevance to current contract designs. Four of which are flexure-bearing based, and another six are gas-bearing based. One of the flexure-bearing convertors has accumulated over 110,000 hours of operation, and holds the current record for maintenance-free heat-engine run-time. Another flexure-bearing convertor was recently manually shutdown after 105,620 hours of operation, then disassembled and inspected. This inspection produced a wealth of information about the effects of this amount of runtime on the technology's components. One of the engineering unit flexure-bearing convertors recently underwent launch simulation vibration test, a static acceleration exposure up to 20 g, and was then placed on extended operation. Amongst the gas-bearing convertors, the longest running unit has accumulated over 70,000 hours of operation. Four high-fidelity gas-bearing convertors from the ASRG project are still operating continuously, for which the longest runtime has reached 28,000 hours

Nighttime is the worst time: Parental fear of hypoglycemia in young children with type 1 diabetes

BACKGROUND: Fear of hypoglycemia is common in parents of young children with type 1 diabetes (T1D), but little is known about the specific fears that parents most often experience. Hypoglycemia fear has been associated with poorer glycemic control in older children, though not yet studied in a large cohort of very young children. MATERIALS AND METHODS: Parents of 549 children <7 years (mean 5.2 ± 1.2 years [19% <3 years]) with a mean diabetes duration of 2.4 ± 1.0 years (range 1-6 years) and mean HbA1c 8.2% ± 1.1% (66 ± 12 mmol/mol) registered in the T1D Exchange completed the worry scale of the Hypoglycemia Fear Survey modified for parents (HFS-P). RESULTS: Mean parental fear of hypoglycemia worry score was 36.1 ± 23.1 (possible range 0-100), with most frequent worries related to the child having a low while asleep and the child not recognizing a low. The mean worry score was not associated with the child's age, glycemic control, or recent severe hypoglycemic event. Parental worries about lows while sleeping were significantly higher in pump users than non-users (61% vs. 45%; P < .001), and tended to be higher in CGM users than non-users (62% vs 51%; P = .02). CONCLUSIONS: The greatest worries of parents of young children with T1D were related to hypoglycemia during sleep and other times/circumstances during which it would be difficult to detect hypoglycemia. Using advanced diabetes technologies may be an effort to temper fears about hypoglycemia during sleep, though the directionality of this relationship is undetermined. Additional studies can clarify this association and leverage use of diabetes technologies to improve glycemic control

Simultaneous ultrafast probing of intramolecular vibrations and photoinduced charge carriers in rubrene using broadband time-domain THz spectroscopy

Mattijs Koeberg, Euan Hendry, Juleon M. Schins, Hendrik A. van Laarhoven, Cees F. J. Flipse, Klaus Reimann, Michael Woerner, Thomas Elsaesser, and Mischa Bonn, Physical Review B, Vol. 75, article 195216 (2007). "Copyright © 2007 by the American Physical Society."We determine the ultrafast frequency- and time-resolved complex dielectric responses of photoexcited, single-crystal rubrene in the frequency range of 10–30 THz (330–1000 cm−1) using ultrafast broadband THz spectroscopy. In this frequency range, we observe the response of both photogenerated mobile charges and intramolecular vibrational modes simultaneously, both of which vary with time after excitation. The data in conjunction with a theoretical model indicate a dynamic blueshift of the 15.5 THz phonon

Diamond Window Technology for Electron Cyclotron Heating and Current Drive: State of the Art

Nuclear fusion power plants require electron cyclotron (EC) heating and current drive (H&CD) systems for plasma heating and stabilization. High-power microwave beams between 1 and 2 MW generated by gyrotrons propagate in a dedicated waveguide transmission system to reach the plasma at specific locations. Key components in this transmission system are the chemical vapor deposition diamond windows on both the torus and gyrotron sides of the reactor as they allow transmission of high-power beams while acting as confinement and/or vacuum boundaries. Diamond windows consist of a polycrystalline diamond disk integrated in a metallic housing. In the conventional configuration, there is one disk perpendicular to the beam propagation direction. A steering mechanism is then used to deploy the fixed frequency beam at different locations in the plasma. This is, for instance, the configuration used in the ITER EC H&CD system. Movable parts close to the plasma will be problematic for the lifetime of launchers in future fusion reactors like the DEMOnstration nuclear fusion reactor (DEMO) because of the higher heat loads and neutron fluxes. Therefore, one of the alternative concepts is to deploy the beams directly at the desired resonant magnetic flux surface by frequency tuning gyrotrons. In this case, diamond windows able to work in a given frequency range, like the diamond Brewster-angle window, are required. It is an elegant and compact broadband window solution with the disk inclined at the Brewster angle with respect to the beam direction. This paper shows the development and the current state of different diamond window concepts including the design, the numerical analyses, and application of standard construction nuclear codes and of a specific qualification program