Radiation effects on silicon Fourth quarterly progress report, Sep. 25 - Dec. 31, 1965

Radiation effects in silicon solar cell

Single walled carbon nanotube channel flow electrode : hydrodynamic voltammetry at the nanomolar level

The use of single walled carbon nanotube (SWNT) band electrodes in a channel flow cell, for low concentration detection, with hydrodynamic voltammetry is reported. A two dimensional SWNT network electrode is combined with a one piece channel flow cell unit, fabricated by microstereolithography. This configuration provides well defined hydrodynamics over a wide range of volume flow rates (0.05–25 mL min− 1). Limiting current measurements, from linear sweep voltammograms, are in good agreement with the channel electrode Levich equation, for the one electron oxidation of ferrocenylmethyl trimethylammonium (FcTMA+), over a wide concentration range, 1 × 10− 8 M to 2.1 × 10− 5 M, with a detection limit of 5 nM. At the highest flow rates, some influence of the slightly recessed electrode geometry arising from the SWNT electrode fabrication is noted. However, this can be accounted for by a full simulation of the hydrodynamics and solution of the resulting convection–diffusion equation. Application of this hydrodynamic configuration to the voltammetric detection of dopamine is also demonstrated

Groups and the Entropy Floor- XMM-Newton Observations of Two Groups

Using XMM-Newton spatially resolved X-ray imaging spectroscopy we obtain the temperature, density, entropy, gas mass, and total mass profiles for two groups of galaxies out to ~0.3 Rvir (Rvir, the virial radius). Our density profiles agree well with those derived previously, and the temperature data are broadly consistent with previous results but are considerably more precise. Both of these groups are at the mass scale of 2x10^13 Msolar but have rather different properties. They have considerably lower gas mass fractions at r<0.3 Rvir than the rich clusters. NGC2563, one of the least luminous groups for its X-ray temperature, has a very low gas mass fraction of ~0.004 inside 0.1 Rvir, which rises with radius. NGC4325, one of the most luminous groups at the same average temperature, has a higher gas mass fraction of 0.02. The entropy profiles and the absolute values of the entropy as a function of virial radius also differ, with NGC4325 having a value of ~100 keV cm-2 and NGC2563 a value of ~300 keV cm-2 at r~0.1 Rvir. For both groups the profiles rise monotonically with radius and there is no sign of an entropy "floor". These results are inconsistent with pre-heating scenarios which have been developed to explain the entropy floor in groups but are broadly consistent with models of structure formation which include the effects of heating and/or the cooling of the gas. The total entropy in these systems provides a strong constraint on all models of galaxy and group formation, and on the poorly defined feedback process which controls the transformation of gas into stars and thus the formation of structure in the universe.Comment: 22 pages, 2 figure

Electroanalytical applications of carbon electrodes using novel hydrodynamic flow devices

Since the first reported use of carbon nanotubes (CNTs) as an electrode material in 1996 the use of CNTs within electrochemistry has grown rapidly. Single walled carbon nanotubes offer bio-compatibility combined with nano-scale dimensions and low background currents in the pristine state. Over the past decade the quantity of SWNTs synthesised globally has greatly increased making the material available for a variety of studies and potentially a feasible material for commercial electrodes. Despite this rise in popularity there is still an on going debate about the sites of electron transfer (ET) at a carbon nanotube. Some reports claim that the sidewall of the carbon nanotube exhibits sluggish ET rates with the majority of the ET occurring at defect sites and the end of the CNT. In contrast there is also evidence that suggests that ET at the sidewall is facile and not sluggish. The origin of ET is investigated using both theoretical and experimental data to probe the developing diffusion profiles to active ET sites. This is achieved on the timescale of a typical voltammetric experiment by significantly reducing the rate of diffusion to the electroactive sites using a NafionTM film. The reduced rate of diffusion allows the developing diffusion profiles to the individual sites to be decoupled. The use of convection and diffusion is a proven electrochemical technique to increase the sensitivity of analytical measurements and to probe reaction rates and mechanisms. The well-defined mass transport within a channel flow cell or an impinging jet electrode, combined with the continual replacement of solution, makes this geometry amenable to online studies, e.g. bedside or industrial monitoring, or a combination with chromatography. One draw back of conventional channel flow and impinging jet electrode set-ups is the need for specialist equipment or calibration steps each time the system is assembled. The use of microstereo lithography (MSL) to construct custom designed cells for use with a variety of planar electrodes is investigated. The hydrodynamics within the proposed designs are theoretically tested and verified experimentally. The devices constructed are easily assembled using a wide range of electrode materials and the computer aided manufacture provides flexibility in critical dimensions. Importantly, the devices only require a one-off determination of the height prior to assembly, removing the need for an electrochemical calibration step as the cells do not distort during assembly. Of particular interest for analytical studies is the greatly reduced background currents provided by a carbon nanotube network compared to an equivalent size carbon macroelectrode. The lower background signal allows small Faradaic currents to be observed experimentally, allowing lower concentrations to be distinguished. The enhanced sensitivity is combined with the increased mass transport of channel flow and impinging jet convective systems to determine the limit of detection for particular channel and impinging jet geometries under constant flow rates. This approach allows the successful detection of nano-molar concentrations under hydrodynamic control using standard voltammetric techniques

Probing the structure of the cold dark matter halo with ancient mica

Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from WIMPs. Ancient mica is a directional detector despite the complex motions it makes with respect to the WIMP "wind". We can exploit the properties of directionality and long integration time to probe for structure in the dark matter halo of our galaxy. We compute a sample of possible signals in mica for a plausible model of halo structure.Comment: 7 pages, 2 figure

X-Ray Shadowing Experiments Toward Infrared Dark Clouds

We searched for X-ray shadowing toward two infrared dark clouds (IRDCs) using the MOS detectors on XMM-Newton to learn about the Galactic distribution of X-ray emitting plasma. IRDCs make ideal X-ray shadowing targets of 3/4 keY photons due to their high column densities, relatively large angular sizes, and known kinematic distances. Here we focus on two clouds near 30 deg Galactic longitude at distances of 2 and 5 kpc from the Sun. We derive the foreground and background column densities of molecular and atomic gas in the direction of the clouds. We find that the 3/4 ke V emission must be distributed throughout the Galactic disk. It is therefore linked to the structure of the cooler material of the ISM, and to the birth of stars

The DRIFT Project: Searching for WIMPS with a Directional Detector

A low pressure time projection chamber for the detection of WIMPs is discussed. Discrimination against Compton electron background in such a device should be very good, and directional information about the recoil atoms would be obtainable. If a full 3-D reconstruction of the recoil tracks can be achieved, Monte Carlo studies indicate that a WIMP signal could be identified with high confidence from as few as 30 detected WIMP-nucleus scattering events.Comment: 5 pages, 3 figures. Presented at Dark 98, Heidelberg, July 1998, and to appear in conference proceeding

Scanning electrochemical cell microscopy : a versatile technique for nanoscale electrochemistry and functional imaging

Scanning electrochemical cell microscopy (SECCM) is a new pipette-based imaging technique purposely designed to allow simultaneous electrochemical, conductance, and topographical visualization of surfaces and interfaces. SECCM uses a tiny meniscus or droplet, confined between the probe and the surface, for high-resolution functional imaging and nanoscale electrochemical measurements. Here we introduce this technique and provide an overview of its principles, instrumentation, and theory. We discuss the power of SECCM in resolving complex structure-activity problems and provide considerable new information on electrode processes by referring to key example systems, including graphene, graphite, carbon nanotubes, nanoparticles, and conducting diamond. The many longstanding questions that SECCM has been able to answer during its short existence demonstrate its potential to become a major technique in electrochemistry and interfacial science

Track Reconstruction and Performance of DRIFT Directional Dark Matter Detectors using Alpha Particles

First results are presented from an analysis of data from the DRIFT-IIa and DRIFT-IIb directional dark matter detectors at Boulby Mine in which alpha particle tracks were reconstructed and used to characterise detector performance--an important step towards optimising directional technology. The drift velocity in DRIFT-IIa was [59.3 +/- 0.2 (stat) +/- 7.5 (sys)] m/s based on an analysis of naturally-occurring alpha-emitting background. The drift velocity in DRIFT-IIb was [57 +/- 1 (stat) +/- 3 (sys)] m/s determined by the analysis of alpha particle tracks from a Po-210 source. 3D range reconstruction and energy spectra were used to identify alpha particles from the decay of Rn-222, Po-218, Rn-220 and Po-216. This study found that (22 +/- 2)% of Po-218 progeny (from Rn-222 decay) are produced with no net charge in 40 Torr CS2. For Po-216 progeny (from Rn-220 decay) the uncharged fraction is (100 +0 -35)%.Comment: 27 pages, 12 figures, 5 tables. Submitted to Nuclear Instruments and Methods in Physics Research, Section A. Subj-class: Instrumentation and Detector

Teacher Perceptions of the Flipped Classroom: Using Video Lectures Online to Replace Traditional In-class Lectures

Advancements in media technologies have resulted in increased student usage causing teachers to struggle to be able to engage and hold student’s interest in a typical classroom. As students’ needs change, the field of education changes. One strategy that is gaining in popularity among teachers is the implementation of the “flipped classroom” also known as the “inverted classroom” or “reverse instruction” - a method incorporates technology to “flip” or “reverse” what is typically done in class with what is typically done as homework. Through teacher interviews of eight core teachers, this study attempts to discover teacher perceptions of the use of this method. Results of the study reveal that perceptions of the method are more positive among teachers who typically use lecture as a primary mode of information dissemination