An absorption tube for the investigation of gases in the photographic infrared

An absorption cell of novel design is described, which combines the advantages of long path and relatively small volume

Advances in Heat Transfer Through Coatings and Micro-scale Features

For most of the twentieth century, advanced heat transfer research was geared towards solving the two-phase flow and thermal problems of the nuclear, chemical, and materials processing industries that emerged near the start and middle of the century. These applications demanded relatively large scale systems, with scale up being the challenge of the day. At these power levels and length scales, understanding the interaction between the respective shear, momentum, and body forces of the vapor and liquid were of critical importance. Fast forward to the end of the twentieth century and start of the twenty-first century, and advanced thermal research has shifted towards solving the smaller problems of the electronics cooling industry with scale down being the challenge of the day. In large, many of the benefits associated with two-phase heat transfer at these smaller length scales are consistent with the high convection coefficients and lower flow rate requirements observed at larger length scales. Understanding two-phase heat transfer at these smaller length scales requires the understanding of the same macro-scale two-phase heat transfer physics along with additional physics such as capillary forces and wetting phenomenon. Perhaps this is most evident in heat pipes, where two-phase heat transfer in combination with capillary wick structures have emerged as a staple in the electronics cooling community. Increasing power density requirements have pushed the use of the monolithic hydrophilic wick structures used in commodity heat pipes to their limits, including their power transport capabilities and their convection thermal resistances. One way to improve upon traditional wick structures is to manipulate large droplets on hydrophobic surfaces in the condenser portion of heat pipes. Fluid can be circulated more readily as a droplet on a surface compared with fluid through small pores. Further, the convection resistance associated with dropwise condensation is an order of magnitude better than condensation on a hydrophilic wick structure. Surfaces with graded hydrophobicity have shown to be capable of passively moving condensing droplets while exhibiting the characteristic high heat transfer coefficient of dropwise condensation on hydrophobic surfaces. Vapor-liquid two-phase heat transfer alone cannot solve all modern thermal problems. The electronics community has pushed transistor sizes to the nano-scale feature size levels, where more complicated physics such as phonon-phonon and electron-phonon interactions are required to understand heat transfer physics and engineer solutions at these levels. For communications applications where the chips operate in pulsed modes, thermal storage through freeze-thaw cycles of a solid-liquid phase change material is an attractive solution. However, the thermal storage effect at high pulse frequencies is only warranted if the phase change material is located in close proximity, within a few microns, of the active transistors where electron-phonon and phonon-phonon interactions dominate conventional Fourier conduction thermal resistances. In high power density systems operating at 1,000\u27s of W/cm2 heat fluxes, such as high power laser diodes, compact micro-channel coolers using single phase coolants have emerged as a potentially viable cooling solution. The laminar flow and heat transfer physics involved in these devices are well understood. However, the compact nature of the micro-channel coolers along with the high flow rates needed to move the required power have lead to unavoidably high velocities. Copper is the only engineering material with thermal conductivities high enough to meet thermal performance requirements, but suffers from erosion at the high velocities required. Meanwhile, ceramic thin films have the necessary properties to limit erosion under the high velocities required. Although conventional fabrication techniques cannot be used to apply ceramic coatings within the small micro-channel features, nano-scale coating methodologies such as Atomic Layer Deposition may hold the key to meeting the application demands.Thermal testing at smaller length scales poses measurement challenges that are under development. One such challenge is encountered by CPU manufacturers during their development process, where optical inspection of active transistors is required while operating. The CPU dissipates heat at a rate equivalent to normal operation in these tests. The optical view requirement removes the possibility of using traditional heat sinks to remove this waste heat. The only way to remove heat and meet the optical view requirement is to use impingement cooling. The small sizes of the so called fireball processing cores push the limits of the measurement technology used to validate cooling solutions.Interdisciplinary research is the key to meeting many emerging research challenges, thermal management included. The twenty-first century has brought a new set of thermal challenges, pushed largely by the demands of the electronic industry. This thesis addresses several of those challenges, where interdisciplinary research involving heat transfer, surface engineering, and small length scales are a common theme

An Investigation of Iris Recognition in Unconstrained Environments

Iris biometrics is widely regarded as a reliable and accurate method for personal identification and the continuing advancements in the field have resulted in the technology being widely adopted in recent years and implemented in many different scenarios. Current typical iris biometric deployments, while generally expected to perform well, require a considerable level of co-operation from the system user. Specifically, the physical positioning of the human eye in relation to the iris capture device is a critical factor, which can substantially affect the performance of the overall iris biometric system. The work reported in this study will explore some of the important issues relating to the capture and identification of iris images at varying positions with respect to the capture device, and in particular presents an investigation into the analysis of iris images captured when the gaze angle of a subject is not aligned with the axis of the camera lens. A reliable method of acquiring off-angle iris images will be implemented, together with a study of a database thereby compiled of such images captured methodically. A detailed analysis of these so-called “off-angle” characteristics will be presented, making possible the implementation of new methods whereby significant enhancement of system performance can be achieved. The research carried out in this study suggests that implementing carefully new training methodologies to improve the classification performance can compensate effectively for the problem of off-angle iris images. The research also suggests that acquiring off-angle iris samples during the enrolment process for an iris biometric system and the implementation of the developed training configurations provides an increase in classification performance

PON1 status does not influence cholinesterase activity in Egyptian agricultural workers exposed to chlorpyrifos.

Animal studies have shown that paraoxonase 1 (PON1) genotype can influence susceptibility to the organophosphorus pesticide chlorpyrifos (CPF). However, Monte Carlo analysis suggests that PON1 genotype may not affect CPF-related toxicity at low exposure conditions in humans. The current study sought to determine the influence of PON1 genotype on the activity of blood cholinesterase as well as the effect of CPF exposure on serum PON1 in workers occupationally exposed to CPF. Saliva, blood and urine were collected from agricultural workers (n=120) from Egypt's Menoufia Governorate to determine PON1 genotype, blood cholinesterase activity, serum PON1 activity towards chlorpyrifos-oxon (CPOase) and paraoxon (POase), and urinary levels of the CPF metabolite 3,5,6-trichloro-2-pyridinol (TCPy). The PON1 55 (P≤0.05) but not the PON1 192 genotype had a significant effect on CPOase activity. However, both the PON1 55 (P≤0.05) and PON1 192 (P≤0.001) genotypes had a significant effect on POase activity. Workers had significantly inhibited AChE and BuChE after CPF application; however, neither CPOase activity nor POase activity was associated with ChE depression when adjusted for CPF exposure (as determined by urinary TCPy levels) and stratified by PON1 genotype. CPOase and POase activity were also generally unaffected by CPF exposure although there were alterations in activity within specific genotype groups. Together, these results suggest that workers retained the capacity to detoxify chlorpyrifos-oxon under the exposure conditions experienced by this study population regardless of PON1 genotype and activity and that effects of CPF exposure on PON1 activity are minimal

Histone H2AX Is Phosphorylated at Sites of Retroviral DNA Integration but Is Dispensable for Postintegration Repair

The histone variant H2AX is rapidly phosphorylated (denoted {gamma}H2AX) in large chromatin domains (foci) flanking double strand DNA (dsDNA) breaks that are produced by ionizing radiation or genotoxic agents and during V(D)J recombination. H2AX-deficient cells and mice demonstrate increased sensitivity to dsDNA break damage, indicating an active role for {gamma}H2AX in DNA repair; however, {gamma}H2AX formation is not required for V(D)J recombination. The latter finding has suggested a greater dependence on {gamma}H2AX for anchoring free broken ends versus ends that are held together during programmed breakage-joining reactions. Retroviral DNA integration produces a unique intermediate in which a dsDNA break in host DNA is held together by the intervening viral DNA, and such a reaction provides a useful model to distinguish {gamma}H2AX functions. We found that integration promotes transient formation of {gamma}H2AX at retroviral integration sites as detected by both immunocytological and chromatin immunoprecipitation methods. These results provide the first direct evidence for the association of newly integrated viral DNA with a protein species that is an established marker for the onset of a DNA damage response. We also show that H2AX is not required for repair of the retroviral integration intermediate as determined by stable transduction. These observations provide independent support for an anchoring model for the function of {gamma}H2AX in chromatin repair