Growth and Electronic Properties of GaAsN and GaAsBi Alloys.

Dilute nitride and dilute bismuthide semiconductor alloys are of significant interest since their bandgap energies can be tuned dramatically without a substantial change in lattice parameter, making them promising for a wide variety of optoelectronic applications. We examine the role of N environment on persistent photoconductivity (PPC) in GaAsN films. For N fractions >0.006, significant PPC is observed at cryogenic temperatures, with the PPC magnitude increasing with increasing N fraction due to an increase in the density of N-induced levels. Interestingly, rapid-thermal annealing suppresses the PPC magnitude and reduces the N interstitial fraction; thus, the N-induced level is likely associated with N interstitials. PPC is attributed to the photogeneration of carriers from N-induced levels to the conduction-band edge, leading to a modified N molecular bond configuration. With the addition of thermal energy, the ground state configuration is restored; the N-induced level is then able to accept carriers and the conductivity decays to its preillumination value. Furthermore, we have used PPC to drive a metal-insulator transition in GaAsN, allowing us to extract the electron effective mass using the Mott criterion. Reports indicate that the effective mass of GaAsN is dopant-dependent. We find that the effective mass for Si-doped GaAsN is consistent with predictions considering N clustering. For molecular-beam epitaxy of GaAsBi, we show that Bi incorporation into GaAs is favorable over a wider range of growth conditions with As_4 in comparison with As_2, facilitating growth of smooth, droplet-free GaAsBi films. The preference for Bi incorporation with As_4 is associated with the differences in the likelihood for As_2 vs. As_4 to replace weakly bonded surface Bi_2. Then, we consider the role of the transition from Group-V-rich to Group-III-rich conditions (the stoichiometry threshold) on the negative or positive type conductivity induced by silicon incorporation. For As-rich GaAsBi growth, Si incorporation leads to n-type conductivity. For Ga-rich GaAsBi growth, GaAsBi:Si films are p-type, and free carrier concentrations in excess of 5x10^{18} cm^{-3} are achieved for Bi fractions ~0.05, making Si a promising acceptor dopant. We propose a dopant incorporation mechanism based upon the growth-rate dependence of the stoichiometry threshold for GaAsBi.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113468/1/fieldr_1.pd

CpG island methylation phenotype (CIMP) in oral cancer: associated with a marked inflammatory response and less aggressive tumour biology.

Studies in several tumour sites highlight the significance of the CpG island methylation phenotype (CIMP), with distinct features of histology, biological aggression and outcome. We utilise pyrosequencing techniques of quantitative methylation analysis to investigate the presence of CIMP in oral squamous cell carcinoma (OSCC) for the first time, and evaluate its correlation with allelic imbalance, pathology and clinical behaviour. Tumour tissue, control tissue and PBLs were obtained from 74 patients with oral squamous cell carcinoma. Pyrosequencing was used to analyse methylation patterns in 75-200 bp regions of the CpG rich gene promoters of 10 genes with a broad range of cellular functions. Allelic imbalance was investigated using a multiplexed panel of 11 microsatellite markers. Corresponding variables, histopathological staging and grading were correlated with these genetic and epigenetic aberrations. A cluster of tumours with a greater degree of promoter methylation than would be predicted by chance alone (P=0.001) were designated CIMP+ve. This group had less aggressive tumour biology in terms of tumour thickness (p=0.015) and nodal metastasis (P=0.012), this being apparently independent of tumour diameter. Further, it seems that these CIMP+ve tumours excited a greater host inflammatory response (P=0.019). The exact mechanisms underlying CIMP remain obscure but the association with a greater inflammatory host response supports existing theories relating these features in other tumour sites. As CIMP has significant associations with other well documented prognostic indicators, it may prove beneficial to include methylation analyses in molecular risk modelling of tumours

Utilizing Gauss-Hermite Quadrature to Evaluate Uncertainty in Dynamic System Response

Probabilistic uncertainty is a phenomenon that occurs to a certain degree in many engineering!~ applications. The effects that the uncertainty has upon a given system response is a matter of some concern. Techniques which provide insight to these effects will be required as modeling and prediction become a more vital tool in the engineering design process. As might be expected, this is a difficult proposition and the focus of many research efforts. The purpose of this paper is to outline a procedure to evaluate uncertainty in dynamic system response exploiting Gauss-Hermite numerical quadrature. Specifically numerical integration techniques are utilized in conjunction with the Advanced Mean Value method to efficiently and accurately estimate moments of the response process. A numerical example illustrating the use of this analytical tool in a practical framework is presented

Numerical Techniques to Evaluate Moments of Dynamic System Response

Probabilistic uncertainty is a phenomenon that occurs to a certain degree in many engineering applications. The effects that this uncertainty has upon a given system response are a matter of some concern. Techniques which provide insight to these effects will be required as modeling and prediction becomes a more vital tool in the engineering design process. The purpose of this paper is to outline a procedure to evaluate uncertainty in dynamic system response exploiting various numerical methods. Specifically, the goal is to attain the statistics of the response with minimal computational effort. Numerical interpolation and integration techniques are utilized in conjunction with the iterative form of the Advanced Mean Value (AMV+) method to efficiently and accurately estimate statistical moments of the response random process. A numerical example illustrating the use of this analytical tool in a practical framework is presented

Do people favour policies that protect future generations? Evidence from a British survey of adults

Long-range temporal choices are built into contemporary policy-making, with policy decisions having consequences that play out across generations. Decisions are made on behalf of the public who are assumed to give much greater weight to their welfare than to the welfare of future generations. The paper investigates this assumption. It briefly discusses evidence from sociological and economic studies before reporting the findings of a British survey of people's intergenerational time preferences based on a representative sample of nearly 10,000 respondents. Questions focused on two sets of policies: (i) health policies to save lives and (ii) environmental policies to protect against floods that would severely damage homes, businesses and other infrastructure. For both sets of policies, participants were offered a choice of three policy options, each bringing greater or lesser benefits to their, their children's and their grandchildren's generations. For both saving lives and protecting against floods, only a minority selected the policy that most benefited their generation; the majority selected policies bringing equal or greater benefits to future generations. Our study raises questions about a core assumption of standard economic evaluation, pointing instead to concern for future generations as a value that many people hold in common