Quantitative Analysis of the Efficiency of Clonal Deletion in the Thymus

One of the major mechanisms for establishing self-tolerance is the clonal deletion of self-reactive T cells during their development in the thymus. Using a TCR transgenic mouse model, we have established a quantitative ex vivo assay for examining the sensitivity and specificity of negative selection. Thymic organ cultures established from mice of varying MHC haplotypes were incubated with antigen, and the efficiency of clonal deletion assessed. We show here that clonal deletion of CD4+8+ thymocytes is sensitive to both the gene dosage and the allelic variation of MHC class II molecules expressed on thymic antigen-presenting cells. We also find that when epithelial cells in the thymic cortex are the only antigen-presenting cells expressing the appropriate MHC class II molecules, negative selection of CD4+8+ cells is as efficient as when antigen is presented on all thymic antigen-presenting cells. These studies demonstrate that the induction of self-tolerance via clonal deletion in the thymus is a function not only of antigen concentration, but also of MHC class II cell-surface density. In addition, together with the reports of others, these results confirm that cortical epithelial cells can mediate negative selection, and demonstrate that they do so in the intact thymic microenvironment

The application of active controls technology to a generic hypersonic aircraft configuration

Analytical methods are described for the prediction of aerothermoelastic stability of hypersonic aircraft including active control systems. Thermal loads due to aerodynamic heating were applied to the finite element model of the aircraft structure and the thermal effects on flutter were determined. An iterative static aeroelastic trim analysis procedure was developed including thermal effects. And active control technology was assessed for flutter suppression, ride quality improvement, and gust load alleviation to overcome any potential adverse aeroelastic stability or response problems due to aerodynamic heating. A generic hypersonic aircraft configuration was selected which incorporates wing flaps, ailerons, and all moveable fins to be used for active control purposes. The active control system would use onboard sensors in a feedback loop through the aircraft flight control computers to move the surfaces for improved structural dynamic response as the aircraft encounters atmospheric turbulence

Finite temperature bosonization

Finite temperature properties of a non-Fermi liquid system is one of the most challenging probelms in current understanding of strongly correlated electron systems. The paradigmatic arena for studying non-Fermi liquids is in one dimension, where the concept of a Luttinger liquid has arisen. The existence of a critical point at zero temperature in one dimensional systems, and the fact that experiments are all undertaken at finite temperature, implies a need for these one dimensional systems to be examined at finite temperature. Accordingly, we extended the well-known bosonization method of one dimensional electron systems to finite temperatures. We have used this new bosonization method to calculate finite temperature asymptotic correlation functions for linear fermions, the Tomonaga-Luttinger model, and the Hubbard model.Comment: REVTex, 48 page

Screening and interlayer coupling in multilayer graphene field-effect transistors

With the motivation of improving the performance and reliability of aggressively scaled nano-patterned graphene field-effect transistors, we present the first systematic experimental study on charge and current distribution in multilayer graphene field-effect transistors. We find a very particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and propose a resistor network model including screening and interlayer coupling to explain the experimental findings. In particular, our model does not invoke modification of the linear energy-band structure of graphene for the multilayer case. Noise reduction in nano-scale few-layer graphene transistors is experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference

EVALUATION OF RELATIONSHIPS BETWEEN REPORTED RESILIENCE AND SOLDIER OUTCOMES, Report #2: Positive Performance Outcomes in Officers (Promotions, Selections, & Professions)

This technical report presents an analysis of reported resilience and psychological health among the U.S. Army’s Officer Corps. The focus of the current report is on linking resilience and psychological health (hereafter referred to as R/PH) to objective outcomes associated with high job performance. Specifically, this report examines the statistical relationships between officer R/PH - as measured by the Army’s Global Assessment Tool (GAT) - and promotions to Brigadier General, early (below zone) Field Grade Officer promotions, selections for command / key billet assignments, and officers who serve in career fields that require terminal professional degrees (e.g., medical doctors, dentists, lawyers, etc). Results show that officers who have been promoted to Brigadier General are more emotionally and socially fit than their peers who have not received a promotion to Brigadier General. These officers are more engaged with their work, have higher levels of organizational trust and friendship, report lower levels of loneliness, are more optimistic, and report higher levels of positive affect and lower levels of negative affect. Each of these findings is in line with our expectations regarding R/PH and job performance, and the findings comport with a substantial body of work in the academic literature. Additionally, analysis of R/PH for officers promoted early resulted in findings similar to above. In particular, those who have been promoted below zone report higher levels of work engagement, friendship, organizational trust, optimism, and coping abilities. In short, these officers score higher on the GAT dimensions of Emotional and Social Fitness than their peers who were not promoted early (“due course” officers). Similar results were found for officers selected for command for key billet assignments. They are also more emotionally and socially fit than their peers who were not selected for command (more engaged with their work, have higher levels of organizational trust and friendship, are less lonely, are more optimistic, and report higher levels of positive affect and lower levels of negative affect). There are no practical differences in R/PH between officers serving in career fields that require terminal professional degrees and other officers serving in “line” career fields (rank-matched analysis, Captain - Colonel). In light of academic literature on the subject, this finding is somewhat surprising as it suggests that advanced professional education / training alone may not influence (or be influenced by) R/PH. When taken together, the findings above strongly suggest there is a relationship between reported resilience and psychological health and outcomes associated with high job performance, but we are currently unable to determine causality. Stated differently, we do not know if the reported R/PH contributed to the performance outcomes, or if the high job performance outcomes contributed to the reported R/PH. Further data collection and analysis over the next 12-24 months will broaden our understanding of the relationships

Let the sun shine in: effects of ultraviolet radiation on invasive pneumococcal disease risk in Philadelphia, Pennsylvania

BACKGROUND: Streptococcus pneumoniae is a common cause of community acquired pneumonia and bacteremia. Excess wintertime mortality related to pneumonia has been noted for over a century, but the seasonality of invasive pneumococcal disease (IPD) has been described relatively recently and is poorly understood. Improved understanding of environmental influence on disease seasonality has taken on new urgency due to global climate change. METHODS: We evaluated 602 cases of IPD reported in Philadelphia County, Pennsylvania, from 2002 to 2007. Poisson regression models incorporating seasonal smoothers were used to identify associations between weekly weather patterns and case counts. Associations between acute (dayto- day) environmental fluctuations and IPD occurrence were evaluated using a case-crossover approach. Effect modification across age and sex strata was explored, and meta-regression models were created using stratum-specific estimates for effect. RESULTS: IPD incidence was greatest in the wintertime, and spectral decomposition revealed a peak at 51.0 weeks, consistent with annual periodicity. After adjustment for seasonality, yearly increases in reporting, and temperature, weekly incidence was found to be associated with clear-sky UV index (IRR per unit increase in index: 0.70 [95% CI 0.54-0.91]). The effect of UV index was highest among young strata and decreased with age. At shorter time scales, only an association with increases in ambient sulphur oxides was linked to disease risk (OR for highest tertile of exposure 0.75, 95% CI 0.60 to 0.93). CONCLUSION: We confirmed the wintertime predominance of IPD in a major urban center. The major predictor of IPD in Philadelphia is extended periods of low UV radiation, which may explain observed wintertime seasonality. The mechanism of action of diminished light exposure on disease occurrence may be due to direct effects on pathogen survival or host immune function via altered 1,25-(OH)2-vitamin-D metabolism. These findings may suggest less diminution in future IPD risk with climate change than would be expected if wintertime seasonality was driven by temperature

Compressibility of CeMIn5Ce M In_5 and Ce2MIn8Ce_2 M In_8 (M = Rh, Ir and Co) Compounds

The lattice parameters of the tetragonal compounds Ce$M$In$_{5}$ and Ce$_{2}M$In$_{8}$($M=$Rh, Ir and Co) have been studied as a function of pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and quasihydrostatic conditions at room temperature. The addition of $M$In$_{2}$ layers to the parent CeIn$_{3}$ compound is found to stiffen the lattice as the 2-layer systems (average of bulk modulus values $B_{0}$ is 70.4 GPa) have a larger $B_{0}$ than CeIn$_{3}$ (67 GPa), while the 1-layer systems with the are even stiffer (average of $B_{0}$ is 81.4 GPa). Estimating the hybridization using parameters from tight binding calculations shows that the dominant hybridization is $fp$ in nature between the Ce and In atoms. The values of $V_{pf}$ at the pressure where the superconducting transition temperature $T_{c}$ reaches a maximum is the same for all Ce$M$In$_{5}$ compounds. By plotting the maximum values of the superconducting transition temperature $T_{c}$ versus $c/a$ for the studied compounds and Pu-based superconductors, we find a universal $T_{c}$ versus $c/a$ behavior when these quantities are normalized appropriately. These results are consistent with magnetically mediated superconductivity.Comment: Updated version resubmitted to Phys. Rev.