Persistent photoconductivity and the metal-insulator transition in Cd(_1-x)Mn(_x)Te:In

The persistent photoconductivity (PPC) effect in the diluted magnetic semiconductor Cd(_1-x)Mn(_x)Te:In has been studied in detail. Electrical transport measurements have been made on a large number of samples to build up an understanding of the phototransport properties of this material. In particular, the compositional dependence of the phototransport parameters has been measured up to x ≈ 0.2. Several samples exhibit an elevated temperature PPC effect which has been interpreted in terms of the formation of multiple DX centres. These samples can have a quenching temperature of up to 190 K, suggestmg that Cd(_1-x)Mn(_x)Te:In could be an interesting material in terms of applications of room temperature persistent photoconductors. The low field magnetoresistance has been measured and analysed quantitatively in order to attempt to identify the origin of the magnetoresistive effects in insulating and metallic samples. The positive magnetoresistance has been found to be linked with the magnetization of the sample. An anomalous negative magnetoresistance has been observed tinder certain experimental conditions. This negative magnetoresistance has been interpreted in terms of the formation of bound magnetic polarons and their contribution to spin-disorder scattering. The main body of this thesis is concerned with the study of the Metal-Insulator Transition (MIT). The PPC effect allows us to study the MIT in a continuous fashion by fine timing the carrier density by illumuiation. In this way we have made the first zero magnetic field study of the MIT in a magnetic semiconductor. The critical behaviour has been found to be consistent with the scaling theory of electron localization, which predicts a critical form σ = σ(_0)(n/n(_c) – 1)(^v). The critical conductivity exponent, v was determined to be close to one, while the critical carrier density, n(_e), was found to be ~ 2 x 10(^17) cm(^-3), for x = 0.08. The temperature dependence of the conductivity has been quantitatively analysed m both the metallic and insulating phases. On the insulating side of the transition, variable range hopping (VRH) conduction has been observed at low temperatures (down to 300 mK). The temperature dependence is consistent with VRH conduction with electron-electron interaction effects taken into account. In the metallic phase the temperature dependence of the conductivity (up to ~ 1 K) is consistent with a model where the zero temperature value of the conductivity is corrected by electron-electroninteraction effects, and the effects of weak localization. The magnitudes of these corrections are found to be in reasonable agreement with theoretical predictions. The electrical transport has also been studied in the weakly localized regime in Cd(_1-x)Mn(_x)Te:In and Cd(_1-x)Mn(_x)Te:In, Al. A rapid decrease in the conductivity occurs at low temperatures ( < 1.5 K). This is interpreted in terms of the effect of the s-d exchange interaction, which leads to the formation of bound magnetic polarons. It is suggested that this drop in conductivity can only be observed in the paramagnetic phase, and that spinglassordering has a significant effect on the temperature dependence of the conductivity at low temperatures

Venture Communist: Gu Zhun in Shanghai, 1949-1952

When the Communists took Shanghai in 1949, they brought seasoned soldiers, but scarcely an accountant. The victory that they claimed in the city presented both resources and temptations, including riches to fund a fledgling regime but also the taint of capitalism. How would they fight their new battle to control and reform China’s financial heart? For help, they turned to Gu Zhun (1915-1974), an accounting wunderkind, native Shanghainese, and veteran member of the Chinese Communist Party (CCP). Over the next three years, he oversaw and overhauled the city’s financial structure from various perches in government, sometimes concurrently heading as many as three municipal bureaus. He thus shaped many of the dilemmas capitalists confront elsewhere in this volume. That he sometimes shared as much with them as with his superiors in the party perhaps only compounded their predicament

The Balancing Act: Economic Determinism and Humanism in Marxism

I argue that there are two interpretations of the Marxist dialectic, both of which examine how human beings interact with objects around them conceptually and how society evolves over time, from different points of view. In the present paper, I undertake three tasks. First, I demonstrate that there is a clear difference between these two strains of Marxist thought which I here call humanist and determinist. Second, I show how Marxist thought has evolved from Hegel and Marx to the present in light of these two different models. Last, I argue that the determinist model is flawed, and that the humanist model stands as a more solid logical and epistemological perspective for Marxist theory

Two-layer viscous instability in a rotating couette device

A novel experiment to study the interfacial shear instability between two liquids is described. Density-matched immiscible liquids are confined between concentric cylinders such that the interface is parallel to the cylinder walls. Interfacial waves that develop because of viscosity differences between the shearing fluids are studied as a function of rotation rate and depth ratio using optical techniques. Conditions neutral stability and the most unstable wavenumber agree reasonably well with predictions from linear stability analysis of the Navier-Stokes equations. Illumination using laser sheets allows precise measurement of the interface shape. Future experiments will verify the correctness of weakly nonlinear theories that describe energy transfer and saturation of wave growth by nonlinear effects. Measurements of solitary wave shapes, that occur far above neutral stability, will be compared to similar measurements for systems that have gravity as an important force to determine how gravity effects large disturbances. These results will be used to interpret slug and annular flow data that have been obtained in other mu g studies

Binary Oscillatory Crossflow Electrophoresis

Electrophoresis has long been recognized as an effective analytic technique for the separation of proteins and other charged species, however attempts at scaling up to accommodate commercial volumes have met with limited success. In this report we describe a novel electrophoretic separation technique - Binary Oscillatory Crossflow Electrophoresis (BOCE). Numerical simulations indicate that the technique has the potential for preparative scale throughputs with high resolution, while simultaneously avoiding many problems common to conventional electrophoresis. The technique utilizes the interaction of an oscillatory electric field and a transverse oscillatory shear flow to create an active binary filter for the separation of charged protein species. An oscillatory electric field is applied across the narrow gap of a rectangular channel inducing a periodic motion of charged protein species. The amplitude of this motion depends on the dimensionless electrophoretic mobility, alpha = E(sub o)mu/(omega)d, where E(sub o) is the amplitude of the electric field oscillations, mu is the dimensional mobility, omega is the angular frequency of oscillation and d is the channel gap width. An oscillatory shear flow is induced along the length of the channel resulting in the separation of species with different mobilities. We present a model that predicts the oscillatory behavior of charged species and allows estimation of both the magnitude of the induced convective velocity and the effective diffusivity as a function of a in infinitely long channels. Numerical results indicate that in addition to the mobility dependence, the steady state behavior of solute species may be strongly affected by oscillating fluid into and out of the active electric field region at the ends of the cell. The effect is most pronounced using time dependent shear flows of the same frequency (cos((omega)t)) flow mode) as the electric field oscillations. Under such conditions, experiments indicate that solute is drawn into the cell from reservoirs at both ends of the cell leading to a large mass build up. As a consequence, any initially induced mass flux will vanish after short times. This effect was not captured by the infinite channel model and hence numerical and experimental results deviated significantly. The revised model including finite cell lengths and reservoir volumes allowed quantitative predictions of the time history of the concentration profile throughout the system. This latter model accurately describes the fluxes observed for both oscillatory flow modes in experiments using single protein species. Based on the results obtained from research funded under NASA grant NAG-8-1080.S, we conclude that binary separations are not possible using purely oscillatory flow modes because of end effects associated with the cos((omega)t) mode. Our research shows, however, that a combination of cos(2(omega)t) and steady flow should lead to efficient separation free of end effects. This possibility is currently under investigation

Fundamental Processes of Atomization in Fluid-Fluid Flows

This paper discusses our proposed experimental and theoretical study of atomization in gas-liquid and liquid-liquid flows. While atomization is a very important process in these flows, the fundamental mechanism is not understood and there is no predictive theory. Previous photographic studies in (turbulent) gas-liquid flows have shown that liquid is atomized when it is removed by the gas flow from the crest of large solitary or roll waves. Our preliminary studies in liquid-liquid laminar flows exhibit the same mechanism. The two-liquid system is easier to study than gas-liquid systems because the time scales are much slower, the length scales much larger, and there is no turbulence. The proposed work is intended to obtain information about the mechanism of formation, rate of occurrence and the evolving shape of solitary waves; and quantitative aspects of the detailed events of the liquid removal process that can be used to verify a general predictive theory

Timing recovery after the cretaceous/paleogene boundary: evidence from Brazos River, Texas

As part of an on-going re-assessment of the Cretaceous/ Paleogene boundary in the Brazos River area, Falls County, Texas, a number of new exposures have been described. One of these, at River Bank South, provides a near continuous record of the lowermost Paleocene. It is from this succession that stable isotope analysis of bulk organic matter (δ13C and C/N) and mono-specific samples of the benthic foraminifera Lenticulina rotulata Lamarck (δ18O and δ13C) yields an orbitally-tuned stable isotope record, which allows the timing of events adjacent to the Cretaceous/Paleogene boundary to be determined. Using this cyclicity, it is suggested that the on-set of biotic recovery began ∼40,000 years after the impact (near the base of Zone Pα) and that more significant recovery of planktic foraminifera and calcareous nannofossils began close to the base of Zone P1a, some 85,000–100,000 years post-impact. The data also appear to record the presence of the earliest Paleocene DAN-C2 and Lower C29n hyperthermal events and that these events appear to be an accentuated segment of this orbital cyclicity

Fighting Ebola with novel spore decontamination technologies for the military

AbstractRecently, global public health organizations such as Doctors without Borders (MSF), the World Health Organization (WHO), Public Health Canada, National Institutes of Health (NIH), and the U.S. government developed and deployed Field Decontamination Kits (FDKs), a novel, lightweight, compact, reusable decontamination technology to sterilize Ebola-contaminated medical devices at remote clinical sites lacking infra-structure in crisis-stricken regions of West Africa (medical waste materials are placed in bags and burned). The basis for effectuating sterilization with FDKs is chlorine dioxide (ClO2) produced from a patented invention developed by researchers at the US Army – Natick Soldier RD&E Center (NSRDEC) and commercialized as a dry mixed-chemical for bacterial spore decontamination. In fact, the NSRDEC research scientists developed an ensemble of ClO2 technologies designed for different applications in decontaminating fresh produce; food contact and handling surfaces; personal protective equipment; textiles used in clothing, uniforms, tents, and shelters; graywater recycling; airplanes; surgical instruments; and hard surfaces in latrines, laundries, and deployable medical facilities. These examples demonstrate the far-reaching impact, adaptability, and versatility of these innovative technologies. We present herein the unique attributes of NSRDEC’s novel decontamination technologies and a Case Study of the development of FDKs that were deployed in West Africa by international public health organizations to sterilize Ebola-contaminated medical equipment. FDKs use bacterial spores as indicators of sterility. We review the properties and structures of spores and the mechanisms of bacterial spore inactivation by ClO2. We also review mechanisms of bacterial spore inactivation by novel, emerging, and established nonthermal technologies for food preservation, such as high pressure processing, irradiation, cold plasma, and chemical sanitizers, using an array of

The Minority Spin Surface Bands of CoS2(001)

Angle-resolved photoemission was used to study the surface electronic band structure of high quality single crystals of ferromagnetic CoS2 (below 120 K). Strongly dispersing Co t2g bands are identified along the 100 k direction, the ¯–¯X line of the surface Brillouin zone, in agreement with model calculations. The calculated surface band structure includes corrections for the previously determined surface structure of CoS2(001) and is in general agreement with the experimental photoemission spectra in the region of the Fermi level. There is evidence of the existence of several minority spin surface states, falling into a gap of the projected minority spin bulk CoS2(001) band structure