A proposal for the coherent propagation studies portion of the 10.6-micrometer laser communications experiment Advanced Technology Satellite-F technical proposal

Coherent propagation study proposal for ATS-F 10.6 micrometer laser communications experimen

Advanced dual-sided microstructured semiconductor neutron detectors and instrumentation

Doctor of PhilosophyDepartment of Mechanical and Nuclear EngineeringDouglas S. McGregorDual-Sided Microstructured Semiconductor Neutron Detectors (DS-MSNDs) have been developed as a viable alternative to expensive ³He for thermal-neutron detection. DS-MSNDs were designed as an advancement on single-sided MSNDs which comprise high-aspect ratio trenches backfilled with ⁶LiF neutron conversion material etched deep into silicon pvn-junction diodes. Neutrons react in the conversion material, which produces energetic charged-particle reaction products that are measured in the adjacent silicon microfeatures. Single-sided MSNDs have been produced with an intrinsic thermal-neutron detection efficiency of 30-35% for normally incident neutrons, and the key limiting factor in detection efficiency is neutron free streaming paths through the neutron insensitive silicon fins. The DS-MSND incorporates a second set of ⁶LiF-backfilled trenches etched on the back-side of a thicker silicon diode that are offset from the front-side trenches to eliminate the neutron free streaming paths. Monte Carlo simulations show DS-MSNDs only 1.5-mm thick are theoretically capable of 80% intrinsic thermal-neutron detection efficiency, which could directly match commonly available ³He detectors. This work describes the design of DS-MSNDs including electric field modeling and microfeature geometry optimization with MCNP simulations, and fabrication process improvements implemented that elevate the state-of-the-art. The previous world record for intrinsic thermal-neutron detection efficiency for semiconductor neutron detectors was 53.5 ± 0.6%. Advancements in deep-trench etching and ⁶LiF backfilling methods presented herein have increased the current record intrinsic-thermal neutron detection efficiency to 69.3 ± 1.5%. Several prototype detector systems were fabricated implementing DS-MSND and MSND technology to aid in search and localization of special nuclear material. Drop-in replacements for small-diameter, high-pressure ³He detectors, and the DS-MSND-based HeRep Mk IV measured 80% to 115% of the count rate of a similarly sized 10-atm ³He detector based on the detector and source moderation configuration. Additionally, modular neutron detectors were developed for use in a high-sensitivity, low profile, wearable neutron detector for covert or overt source detection missions by warfighters, first responders, or law enforcement personnel. Additionally, MCNP simulations show the wearable detectors have potential to as operate as high-accuracy, real-time, neutron dose meters. The DS-MSND-based detector systems with on-board electronics offer a low-cost, low-power, compact, high sensitivity, alternative to ³He neutron detection

Novel Scaling Behavior for the Multiplicity Distribution under Second-Order Quark-Hadron Phase Transition

Deviation of the multiplicity distribution $P_q$ in small bin from its Poisson counterpart $p_q$ is studied within the Ginzburg-Landau description for second-order quark-hadron phase transition. Dynamical factor $d_q\equiv P_q/p_q$ for the distribution and ratio $D_q\equiv d_q/d_1$ are defined, and novel scaling behaviors between $D_q$ are found which can be used to detect the formation of quark-gluon plasma. The study of $d_q$ and $D_q$ is also very interesting for other multiparticle production processes without phase transition.Comment: 4 pages in revtex, 5 figures in eps format, will be appeared in Phys. Rev.

On the high order multiplicity moments

The description of multiplicity distributions in terms of the ratios of cumulants to factorial moments is analyzed both for data and for the Monte Carlo generated events. For the PYTHIA generated events the moments are investigated for the restricted range of phase-space and for the jets reconstructed from single particle momenta. The results cast doubts on the validity of extended local parton-hadron duality and suggest the possibility of more effective experimental investigations concerning the origin of the observed structure in the dependence of moments on their order.Comment: 10 pages, 5 figures; corrected version to be published in JP

Relationship between adiposity and admixture in African-American and Hispanic-American women.

ObjectiveThe objective of this study was to investigate whether differences in admixture in African-American (AFA) and Hispanic-American (HA) adult women are associated with adiposity and adipose distribution.DesignThe proportion of European, sub-Saharan African and Amerindian admixture was estimated for AFA and HA women in the Women's Heath Initiative using 92 ancestry informative markers. Analyses assessed the relationship between admixture and adiposity indices.SubjectsThe subjects included 11 712 AFA and 5088 HA self-identified post-menopausal women.ResultsThere was a significant positive association between body mass index (BMI) and African admixture when BMI was considered as a continuous variable, and age, education, physical activity, parity, family income and smoking were included covariates (P<10(-4)). A dichotomous model (upper and lower BMI quartiles) showed that African admixture was associated with a high odds ratio (OR=3.27 (for 100% admixture compared with 0% admixture), 95% confidence interval 2.08-5.15). For HA, there was no association between BMI and admixture. In contrast, when waist-to-hip ratio (WHR) was used as a measure of adipose distribution, there was no significant association between WHR and admixture in AFA but there was a strong association in HA (P<10(-4); OR Amerindian admixture=5.93, confidence interval=3.52-9.97).ConclusionThese studies show that: (1) African admixture is associated with BMI in AFA women; (2) Amerindian admixture is associated with WHR but not BMI in HA women; and (3) it may be important to consider different measurements of adiposity and adipose distribution in different ethnic population groups