Single ion implantation for single donor devices using Geiger mode detectors

Electronic devices that are designed to use the properties of single atoms such as donors or defects have become a reality with recent demonstrations of donor spectroscopy, single photon emission sources, and magnetic imaging using defect centers in diamond. Improving single ion detector sensitivity is linked to improving control over the straggle of the ion as well as providing more flexibility in lay-out integration with the active region of the single donor device construction zone by allowing ion sensing at potentially greater distances. Using a remotely located passively gated single ion Geiger mode avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency at a distance of >75 um from the center of the collecting junction. This detection efficiency is achieved with sensitivity to ~600 or fewer electron-hole pairs produced by the implanted ion. Ion detectors with this sensitivity and integrated with a thin dielectric, for example 5 nm gate oxide, using low energy Sb implantation would have an end of range straggle of <2.5 nm. Significant reduction in false count probability is achieved by modifying the ion beam set-up to allow for cryogenic operation of the SIGMA detector. Using a detection window of 230 ns at 1 Hz, the probability of a false count was measured as 1E-1 and 1E-4 for operation temperatures of 300K and 77K, respectively. Low temperature operation and reduced false, dark, counts are critical to achieving high confidence in single ion arrival. For the device performance in this work, the confidence is calculated as a probability of >98% for counting one and only one ion for a false count probability of 1E-4 at an average ion number per gated window of 0.015.Comment: 10 pages, 5 figures, submitted to Nanotechnolog

High-field fMRI reveals brain activation patterns underlying saccade execution in the human superior colliculus

Background The superior colliculus (SC) has been shown to play a crucial role in the initiation and coordination of eye- and head-movements. The knowledge about the function of this structure is mainly based on single-unit recordings in animals with relatively few neuroimaging studies investigating eye-movement related brain activity in humans. Methodology/Principal Findings The present study employed high-field (7 Tesla) functional magnetic resonance imaging (fMRI) to investigate SC responses during endogenously cued saccades in humans. In response to centrally presented instructional cues, subjects either performed saccades away from (centrifugal) or towards (centripetal) the center of straight gaze or maintained fixation at the center position. Compared to central fixation, the execution of saccades elicited hemodynamic activity within a network of cortical and subcortical areas that included the SC, lateral geniculate nucleus (LGN), occipital cortex, striatum, and the pulvinar. Conclusions/Significance Activity in the SC was enhanced contralateral to the direction of the saccade (i.e., greater activity in the right as compared to left SC during leftward saccades and vice versa) during both centrifugal and centripetal saccades, thereby demonstrating that the contralateral predominance for saccade execution that has been shown to exist in animals is also present in the human SC. In addition, centrifugal saccades elicited greater activity in the SC than did centripetal saccades, while also being accompanied by an enhanced deactivation within the prefrontal default-mode network. This pattern of brain activity might reflect the reduced processing effort required to move the eyes toward as compared to away from the center of straight gaze, a position that might serve as a spatial baseline in which the retinotopic and craniotopic reference frames are aligned

The general classical solution of the superparticle

The theory of vectors and spinors in 9+1 dimensional spacetime is introduced in a completely octonionic formalism based on an octonionic representation of the Clifford algebra \Cl(9,1). The general solution of the classical equations of motion of the CBS superparticle is given to all orders of the Grassmann hierarchy. A spinor and a vector are combined into a $3 \times 3$ Grassmann, octonionic, Jordan matrix in order to construct a superspace variable to describe the superparticle. The combined Lorentz and supersymmetry transformations of the fermionic and bosonic variables are expressed in terms of Jordan products.Comment: 11 pages, REVTe

Aquifer thermal energy storage : A well doublet experiment at increased temperatures

This is the published version. Copyright 1983 American Geophysical UnionThe two main objectives of this communication are to present a study of potential advantages and disadvantages of the doublet supply-injection well configuration in an aquifer thermal energy storage (ATES) system and to report on aquifer storage problems with injection temperatures in the 80°C range. A 3-month injection-storage-recovery cycle followed by a 7.3-month cycle constituted the main experiment. The injection volumes were 25,402 m3 and 58,063 m3 at average temperatures of 58.5°C and 81°C respectively. Unlikely previous experiments at the Mobile site, no clogging of the injection well due to clay particle swelling, dispersion, and migration was observed. This is attributed to the fact that the supply water used for injection contained a cation concentration equal to or slightly greater than that in the native groundwater. For cycles I and II, the fraction of injected energy recovered in a volume of water equal to the injection volume was 0.56 and 0.45 respectively. Both groundwater temperature and tracer data support the conclusion that this relatively low recovery was due to the detrimental effects of free thermal convection, possibly augmented by longitudinal zones of high permeability. Construction of a partially penetrating recovery well improved recovery efficiency but is not thought to be an adequate solution to thermal stratification. A maximum increase of 1.24 cm in relative land surface elevation was recorded near the end of second cycle injection. The engineering implications of such an elevation change would have to be considered, especially if an ATES system were being designed in an urban environment. A third cycle was started at the Mobile site on April 7, 1982. This final experiment contains a partially penetrating, dual-recovery well system which is expected to maximize energy recovery from a thermally stratified storage aquifer

Divergent architecture of the heterotrimeric NatC complex explains N-terminal acetylation of cognate substrates

The heterotrimeric NatC complex, comprising the catalytic Naa30 and the two auxiliary subunits Naa35 and Naa38, co-translationally acetylates the N-termini of numerous eukaryotic target proteins. Despite its unique subunit composition, its essential role for many aspects of cellular function and its suggested involvement in disease, structure and mechanism of NatC have remained unknown. Here, we present the crystal structure of the Saccharomyces cerevisiae NatC complex, which exhibits a strikingly different architecture compared to previously described N-terminal acetyltransferase (NAT) complexes. Cofactor and ligand-bound structures reveal how the first four amino acids of cognate substrates are recognized at the Naa30–Naa35 interface. A sequence-specific, ligand-induced conformational change in Naa30 enables efficient acetylation. Based on detailed structure–function studies, we suggest a catalytic mechanism and identify a ribosome-binding patch in an elongated tip region of NatC. Our study reveals how NAT machineries have divergently evolved to N-terminally acetylate specific subsets of target proteins

Metal and oxidative potential exposure through particle inhalation and oxidative stress biomarkers: a 2-week pilot prospective study among Parisian subway workers.

In this pilot study on subway workers, we explored the relationships between particle exposure and oxidative stress biomarkers in exhaled breath condensate (EBC) and urine to identify the most relevant biomarkers for a large-scale study in this field. We constructed a comprehensive occupational exposure assessment among subway workers in three distinct jobs over 10 working days, measuring daily concentrations of particulate matter (PM), their metal content and oxidative potential (OP). Individual pre- and post-shift EBC and urine samples were collected daily. Three oxidative stress biomarkers were measured in these matrices: malondialdehyde (MDA), 8-hydroxy-2'deoxyguanosine (8-OHdG) and 8-isoprostane. The association between each effect biomarker and exposure variables was estimated by multivariable multilevel mixed-effect models with and without lag times. The OP was positively associated with Fe and Mn, but not associated with any effect biomarkers. Concentration changes of effect biomarkers in EBC and urine were associated with transition metals in PM (Cu and Zn) and furthermore with specific metals in EBC (Ba, Co, Cr and Mn) and in urine (Ba, Cu, Co, Mo, Ni, Ti and Zn). The direction of these associations was both metal- and time-dependent. Associations between Cu or Zn and MDA &lt;sub&gt;EBC&lt;/sub&gt; generally reached statistical significance after a delayed time of 12 or 24 h after exposure. Changes in metal concentrations in EBC and urine were associated with MDA and 8-OHdG concentrations the same day. Associations between MDA in both EBC and urine gave opposite response for subway particles containing Zn versus Cu. This diverting Zn and Cu pattern was also observed for 8-OHdG and urinary concentrations of these two metals. Overall, MDA and 8-OHdG responses were sensitive for same-day metal exposures in both matrices. We recommend MDA and 8-OHdG in large field studies to account for oxidative stress originating from metals in inhaled particulate matter

Aspects of the Noisy Burgers Equation

The noisy Burgers equation describing for example the growth of an interface subject to noise is one of the simplest model governing an intrinsically nonequilibrium problem. In one dimension this equation is analyzed by means of the Martin-Siggia-Rose technique. In a canonical formulation the morphology and scaling behavior are accessed by a principle of least action in the weak noise limit. The growth morphology is characterized by a dilute gas of nonlinear soliton modes with gapless dispersion law with exponent z=3/2 and a superposed gas of diffusive modes with a gap. The scaling exponents and a heuristic expression for the scaling function follow from a spectral representation.Comment: 23 pages,LAMUPHYS LaTeX-file (Springer), 13 figures, and 1 table, to appear in the Proceedings of the XI Max Born Symposium on "Anomalous Diffusion: From Basics to Applications", May 20-24, 1998, Ladek Zdroj, Polan