Negative Bias Temperature Instability And Charge Trapping Effects On Analog And Digital Circuit Reliability

Nanoscale p-channel transistors under negative gate bias at an elevated temperature show threshold voltage degradation after a short period of stress time. In addition, nanoscale (45 nm) n-channel transistors using high-k (HfO2) dielectrics to reduce gate leakage power for advanced microprocessors exhibit fast transient charge trapping effect leading to threshold voltage instability and mobility reduction. A simulation methodology to quantify the circuit level degradation subjected to negative bias temperature instability (NBTI) and fast transient charge trapping effect has been developed in this thesis work. Different current mirror and two-stage operation amplifier structures are studied to evaluate the impact of NBTI on CMOS analog circuit performances for nanoscale applications. Fundamental digital circuit such as an eleven-stage ring oscillator has also been evaluated to examine the fast transient charge transient effect of HfO2 high-k transistors on the propagation delay of ring oscillator performance. The preliminary results show that the negative bias temperature instability reduces the bandwidth of CMOS operating amplifiers, but increases the amplifier\u27s voltage gain at mid-frequency range. The transient charge trapping effect increases the propagation delay of ring oscillator. The evaluation methodology developed in this thesis could be extended to study other CMOS device and circuit reliability issues subjected to electrical and temperature stresses

Coherent Radio Pulses From GEANT Generated Electromagnetic Showers In Ice

Radio Cherenkov radiation is arguably the most efficient mechanism for detecting showers from ultra-high energy particles of 1 PeV and above. Showers occuring in Antarctic ice should be detectable at distances up to 1 km. We report on electromagnetic shower development in ice using a GEANT Monte Carlo simulation. We have studied energy deposition by shower particles and determined shower parameters for several different media, finding agreement with published results where available. We also report on radio pulse emission from the charged particles in the shower, focusing on coherent emission at the Cherenkov angle. Previous work has focused on frequencies in the 100 MHz to 1 GHz range. Surprisingly, we find that the coherence regime extends up to tens of Ghz. This may have substantial impact on future radio-based neutrino detection experiments as well as any test beam experiment which seeks to measure coherent Cherenkov radiation from an electromagnetic shower. Our study is particularly important for the RICE experiment at the South Pole.Comment: 44 pages, 29 figures. Minor changes made, reference added, accepted for publication in Phys. Rev.

Measurement of the pp Analyzing Power A_y in the Coulomb-Nuclear Interference Region

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Making geology relevant for infrastructure and planning

The urban population is projected to rise to 66% in 2050 to 7.6 billion. This has had, and will have, a profound effect on the geological and geomorphological character of the Earth’s shallow geosphere. It is important to know the character and geometries of the geological deposits so that infrastructure is planned sensibly and sustainably, and urban areas can be reused responsibly to ensure that they help facilitate economic and social development. This brings major challenges for our cities, where there is increased pressure on resources, space and services. The geosciences have an important part to play in securing sustainable global cities - they can support urban innovation and city performance, reduce our environmental footprint and ensure greater resilience to natural hazards such as flooding and ground instability. For more than 30 years the British Geological Survey has advanced the geoscientific understanding and 3D characterisation of urban environments, producing multi-themed spatial datasets for geohazards and ground investigation used across the environmental, planning and insurance sectors. The BGS have collaborated with the University of Cambridge to better integrate geological data with landuse and infrastructure to look at the long-term impact on these types of activities at surface and subsurface. A 3D GeoLanduse layer was produced from the geological framework model of London. This vector-based grid means that many soil and rock properties (e.g. foundation conditions, groundwater levels, volume change potential), can be represented alongside landuse statistics and infrastructure type and correlated in the XYZ domain. Focus has been at geothermal potential of the ground surrounding residential basements and the broader correlation between geology, energy consumption and landuse at city scale using principle component analysis and cluster recognition

Current-induced cooling phenomenon in a two-dimensional electron gas under a magnetic field

We investigate the spatial distribution of temperature induced by a dc current in a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We numerically calculate the distributions of the electrostatic potential phi and the temperature T in a 2DEG enclosed in a square area surrounded by insulated-adiabatic (top and bottom) and isopotential-isothermal (left and right) boundaries (with phi_{left} < phi_{right} and T_{left} =T_{right}), using a pair of nonlinear Poisson equations (for phi and T) that fully take into account thermoelectric and thermomagnetic phenomena, including the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. We find that, in the vicinity of the left-bottom corner, the temperature becomes lower than the fixed boundary temperature, contrary to the naive expectation that the temperature is raised by the prevalent Joule heating effect. The cooling is attributed to the Ettingshausen effect at the bottom adiabatic boundary, which pumps up the heat away from the bottom boundary. In order to keep the adiabatic condition, downward temperature gradient, hence the cooled area, is developed near the boundary, with the resulting thermal diffusion compensating the upward heat current due to the Ettingshausen effect.Comment: 25 pages, 7 figure

Should health care professionals encourage living kidney donation?

Living kidney donation provides a promising opportunity in situations where the scarcity of cadaveric kidneys is widely acknowledged. While many patients and their relatives are willing to accept its benefits, others are concerned about living kidney programs; they appear to feel pressured into accepting living kidney transplantations as the only proper option for them. As we studied the attitudes and views of patients and their relatives, we considered just how actively health care professionals should encourage living donation. We argue that active interference in peoples’ personal lives is justified - if not obligatory. First, we address the ambiguous ideals of non-directivity and value neutrality in counselling. We describe the main pitfalls implied in these concepts, and conclude that these concepts cannot account for the complex reality of living donation and transplantation. We depict what is required instead as truthful information and context-relative counselling. We then consider professional interference into personal belief systems. We argue that individual convictions are not necessarily strong, stable, or deep. They may be flawed in many ways. In order to justify interference in peoples’ personal lives, it is crucial to understand the structure of these convictions. Evidence suggests that both patients and their relatives have attitudes towards living kidney donation that are often open to change and, accordingly, can be influenced. We show how ethical theories can account for this reality and can help us to discern between justified and unjustified interference. We refer to Stephen Toulmin’s model of the structure of logical argument, the Rawlsian model of reflective equilibrium, and Thomas Nagel’s representation of the particularistic position

Magnetic Field Amplification in Galaxy Clusters and its Simulation

We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure

The nature and distribution of flowing features in a weakly karstified porous limestone aquifer

The nature and distribution of flowing features in boreholes in an area of approximately 400 km2 in a weakly karstic porous limestone aquifer (the Chalk) was investigated using single borehole dilution tests (SBDTs) and borehole imaging. One-hundred and twenty flowing features identified from SBDTs in 24 boreholes have densities which decrease from ∼0.3 m−1 near the water table to ∼0.07 m−1 at depths of more than 40 m below the water table; the average density is 0.20 m−1. There is some evidence of regional lithological control and borehole imaging of three boreholes indicated that most flowing features are associated with marls, hardgrounds and flints that may be developed at a more local scale. Borehole imaging also demonstrated that many flowing features are solutionally enlarged fractures, suggesting that even in carbonate aquifers where surface karst is developed on only a small scale, groundwater flow is still strongly influenced by dissolution. Fully connected solutional pathways can occur over 100s, sometimes 1000s of metres. However, conduits, tubules and fissures may not always be individually persistent along a flowpath, instead being connected together and also connected to unmodified fractures to create a relatively dense network of voids with variable apertures (15 cm). Groundwater therefore moves along flowpaths made up of voids with varying shape and character. Local solutional development of fractures at significant depths below the surface suggests that mixing corrosion and in situ sources of acidity may contribute to solutional enhancement of fractures. The study demonstrates that single borehole dilution testing is a useful method of obtaining a large dataset of flowing features at catchment-regional scales. The Chalk is a carbonate aquifer with small-scale surface karst development and this study raises the question of whether other carbonate aquifers with small-scale surface karst have similar characteristics, and what hydrological role small-scale dissolutional features play in highly karstic aquifers

Adenovirus-mediated correction of the genetic defect in hepatocytes from patients with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an inherited deficiency of LDL receptors that has been an important model for liver-directed gene therapy. We are developing approaches for treating FH that are based on direct delivery of recombinant LDL receptor genes to liver in vivo. As a first step towards this goal, replication-defective recombinant adenoviruses were constructed which contained either the lacZ gene or the human LDL receptor cDNA expressed from a β-actin promoter. Primary cultures of hepatocytes were established from two patients with homozygous FH and one nonFH patient, and subsequently exposed to recombinant adenoviruses at MOIs ranging from 0.1 to 5. Essentially all of the cells expressed high levels of the transgene without demonstrable expression of an early or late adenoviral gene product; the level of recombinant-derived LDL receptor protein in transduced FH hepatocytes exceeded the endogenous levels by at least 20-fold. These studies support the utility of recombinant adenoviruses for efficient transduction of recombinant LDL receptor genes into human FH hepatocytes without expression of viral proteins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45545/1/11188_2005_Article_BF01233250.pd