Isotope Shift in the Atomic Spectrum of Germanium

The stable isotopes of naturally occurring Germanium may emit slightly different frequencies, resulting in a hyperfine structure of the spectrum lines. An investigation of the isotopes shifts in the spectra of Ge I and Ge II has been made, and the methods and results of this investigation are presented in this paper

Paedophile as Apartheid event: Genealogical lessons for working with the Apartheid Archive

The narratives that constitute the beginnings of an apartheid archive do well to illustrate the value of collecting, centralising and analysing everyday accounts of apartheid’s subjects. Developing an archive of narratives that give voice to the quotidian experiences of apartheid is a valuable historical strategy. This approach may be usefully mobilised to offset some of the totalising effects of conventional history writing. Notwithstanding this value, an unreflective turn to narrative as a means to reading the socio-historical and political contours of apartheid, risks reducing critique to a symbolic exercise that centres subjectivity and subject positions as the key analytic targets. Such readings may shift the analysis away from the various levels of materiality and power of which these subject positions are both instruments and effects. In an attempt to demonstrate the way that Foucault’s genealogical maxims may be used to counter the danger of centring the subject in history writing, we present some of the key analytic strategies undertaken in a previous study that produced an effective history of the South African paedophile. In so doing, we argue for a re-scoping of the apartheid archive project to include materials required for undertaking histories of the present. This extension would challenge many of the methodological and political constraints implied by limiting the archive to a corpus of memory narratives

Selfish Dark Matter

We present a mechanism where a particle asymmetry in one sector is used to generate an asymmetry in another sector. The two sectors are not coupled through particle number violating interactions and are not required to be in thermal contact with each other. When this mechanism is applied to baryogenesis in asymmetric dark matter models, we find that the dark matter particles can be extremely light, e.g. much lighter than an eV, and that in some cases there is no need to annihilate away the symmetric component of dark matter. We discuss a concrete realization of the mechanism with signals in direct detection, at the LHC, at $B$-factories or future beam dump experiments.Comment: 18+5 pages, 2 figures; Journal version: Added references, small changes to the free-streaming length estimate

Rapid synaptic vesicle endocytosis in cone photoreceptors of salamander retina.

Following synaptic vesicle exocytosis, neurons retrieve the fused membrane by a process of endocytosis to provide a supply of vesicles for subsequent release and maintain the presynaptic active zone. Rod and cone photoreceptors use a specialized structure called the synaptic ribbon that enables them to sustain high rates of neurotransmitter release. They must also employ mechanisms of synaptic vesicle endocytosis capable of keeping up with release. While much is known about endocytosis at another retinal ribbon synapse, that of the goldfish Mb1 bipolar cell, less is known about endocytosis in photoreceptors. We used capacitance recording techniques to measure vesicle membrane fusion and retrieval in photoreceptors from salamander retinal slices. We found that application of brief depolarizing steps (\u3c100 \u3ems) to cones evoked exocytosis followed by rapid endocytosis with a time constant ∼250 ms. In some cases, the capacitance trace overshot the baseline, indicating excess endocytosis. Calcium had no effect on the time constant, but enhanced excess endocytosis resulting in a faster rate of membrane retrieval. Surprisingly, endocytosis was unaffected by blockers of dynamin, suggesting that cone endocytosis is dynamin independent. This contrasts with synaptic vesicle endocytosis in rods, which was inhibited by the dynamin inhibitor dynasore and GTPγS introduced through the patch pipette, suggesting that the two photoreceptor types employ distinct pathways for vesicle retrieval. The fast kinetics of synaptic vesicle endocytosis in photoreceptors likely enables these cells to maintain a high rate of transmitter release, allowing them to faithfully signal changes in illumination to second-order neurons

The Effect of Variability on the Estimation of Quasar Black Hole Masses

We investigate the time-dependent variations of ultraviolet (UV) black hole mass estimates of quasars in the Sloan Digital Sky Survey (SDSS). From SDSS spectra of 615 high-redshift (1.69 < z < 4.75) quasars with spectra from two epochs, we estimate black hole masses, using a single-epoch technique which employs an additional, automated night-sky-line removal, and relies on UV continuum luminosity and CIV (1549A) emission line dispersion. Mass estimates show variations between epochs at about the 30% level for the sample as a whole. We determine that, for our full sample, measurement error in the line dispersion likely plays a larger role than the inherent variability, in terms of contributing to variations in mass estimates between epochs. However, we use the variations in quasars with r-band spectral signal-to-noise ratio greater than 15 to estimate that the contribution to these variations from inherent variability is roughly 20%. We conclude that these differences in black hole mass estimates between epochs indicate variability is not a large contributer to the current factor of two scatter between mass estimates derived from low- and high-ionization emission lines.Comment: 76 pages, 15 figures, 2 (long) tables; Accepted for publication in ApJ (November 10, 2007

The JPL Field Emission Spectrometer

The Jet Propulsion Laboratory (JPL) Field Emission Spectrometer (FES) was built by Designs and Prototypes based on a set of functional requirements supplied by JPL. The instrument has a spectral resolution of 6 wavenumbers (wn) and can acquire spectra from either the Mid Infrared (3-5 mu m) or the Thermal Infrared (8-12 pm) depending on whether the InSb or HgCdTe detector is installed respectively. The instrument consists of an optical head system unit and battery. The optical head which is tripod mounted includes the interferometer and detector dewar assembly. Wavelength calibration of the interferometer is achieved using a Helium-Neon laser diode. The dewar needs replenishing with liquid Nitrogen approximately every four hours. The system unit includes the controls for operation and the computer used for acquiring viewing and processing spectra. Radiometric calibration is achieved with an external temperature-controlled blackbody that mounts on the fore-optics of the instrument. The blackbody can be set at 5 C increments between 10 and 55 C. The instrument is compact and weighs about 33 kg. Both the wavelength calibration and radiometric calibration of the instrument have been evaluated. The wavelength calibration was checked by comparison of the position of water features in a spectrum of the sky with their position in the output from a high resolution atmospheric model. The results indicatethat the features in the sky spectrum are within 6-8 wn of their position ill the model spectrum. The radiometric calibration was checked by first calibrating the instrument using the external blackbody supplied with the instrument and then measuring the radiance from another external blackbody at a series of temperatures. The temperatures of these radiance spectra were then recovered by inventing Planck's law and the recovered temperatures compared lo the measured blackbody temperature. These results indicate that radiometric calibration is good to 0.5 C over the range of temperatures 10 to 55 C. The results also indicate that the instrument drifts slowly over time and should be recalibrated every 20 to 30 minutes in the field to ensure good radiometric fidelity. The instrument has now been extensively tested in the field in the United States and Australia. These in situ field measurements are being used to validate emissivity spectra recovered from the Thermal Infrared Multispectral Scanner (TIMS) and also the Australian CO2 Laser. The availability of in situ measurements is proving crucial to validation of the spectra derived from the airborne instruments since many natural surfaces cannot be easily transported back to the laboratory

A Synoptic, Multiwavelength Analysis of a Large Quasar Sample

We present variability and multi-wavelength photometric information for the 933 known quasars in the QUEST Variability Survey. These quasars are grouped into variable and non-variable populations based on measured variability confidence levels. In a time-limited synoptic survey, we detect an anti-correlation between redshift and the likelihood of variability. Our comparison of variability likelihood to radio, IR, and X-ray data is consistent with earlier quasar studies. Using already-known quasars as a template, we introduce a light curve morphology algorithm that provides an efficient method for discriminating variable quasars from periodic variable objects in the absence of spectroscopic information. The establishment of statistically robust trends and efficient, non-spectroscopic selection algorithms will aid in quasar identification and categorization in upcoming massive synoptic surveys. Finally, we report on three interesting variable quasars, including variability confirmation of the BL Lac candidate PKS 1222+037.Comment: AJ, accepted for publication 15 Dec 200

Spectral Variability of Quasars in the Sloan Digital Sky Survey. II: The C IV Line

We examine the variability of the high-ionizaton C IV line in a sample of 105 quasars observed at multiple epochs by the Sloan Digital Sky Survey. We find a strong correlation between the change in the C IV line flux and the change in the line width, but no correlations between the change in flux and changes in line center and skewness. The relation between line flux change and line width change is consistent with a model in which a broad line base varies with greater amplitude than the line core. The objects studied here are more luminous and at higher redshift than those normally studied for variability, ranging in redshift from 1.65 to 4.00 and in absolute r-band magnitude from roughly -24 to -28. Using moment analysis line-fitting techniques, we measure line fluxes, centers, widths and skewnesses for the C IV line at two epochs for each object. The well-known Baldwin Effect is seen for these objects, with a slope beta = -0.22. The sample has a median intrinsic Baldwin Effect slope of beta = -0.85; the C IV lines in these high-luminosity quasars appear to be less responsive to continuum variations than those in lower luminosity AGN. Additionally, we find no evidence for variability of the well known blueshift of the C IV line with respect to the low-ionization Mg II line in the highest flux objects, indicating that this blueshift might be useful as a measure of orientation.Comment: 52 pages, 14 figures, accepted for publication in Ap

The racist bodily imaginary: the image of the body-in-pieces in (post)apartheid culture

This paper outlines a reoccurring motif within the racist imaginary of (post)apartheid culture: the black body-in-pieces. This disturbing visual idiom is approached from three conceptual perspectives. By linking ideas prevalent in Frantz Fanon’s description of colonial racism with psychoanalytic concepts such as Lacan’s notion of the corps morcelé, the paper offers, firstly, an account of the black body-in-pieces as fantasmatic preoccupation of the (post)apartheid imaginary. The role of such images is approached, secondly, through the lens of affect theory which eschews a representational ‘reading’ of such images in favour of attention to their asignifying intensities and the role they play in effectively constituting such bodies. Lastly, Judith Butler’s discussion of war photography and the conditions of grievability introduces an ethical dimension to the discussion and helps draw attention to the unsavory relations of enjoyment occasioned by such images