First Results from SPARO: Evidence for Large-Scale Toroidal Magnetic Fields in the Galactic Center

We have observed the linear polarization of 450 micron continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends ~ 170 pc along the Galactic plane and ~ 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model.Comment: 11 pages, 2 figures, 1 table, submitted to ApJ Let

First Results from Viper: Detection of Small-Scale Anisotropy at 40 GHZ

Results of a search for small-scale anisotropy in the cosmic microwave background (CMB) are presented. Observations were made at the South Pole using the Viper telescope, with a .26 degree (FWHM) beam and a passband centered at 40 GHz. Anisotropy band-power measurements in bands centered at l = 108, 173, 237, 263, 422 and 589 are reported. Statistically significant anisotropy is detected in all bands.Comment: 5 pages, 4 figures, uses emulateapj.sty, submitted to ApJ Letter

Anisotropy in the Cosmic Microwave Background at Degree Angular Scales: Python V Results

Observations of the microwave sky using the Python telescope in its fifth season of operation at the Amundsen-Scott South Pole Station in Antarctica are presented. The system consists of a 0.75 m off-axis telescope instrumented with a HEMT amplifier-based radiometer having continuum sensitivity from 37-45 GHz in two frequency bands. With a 0.91 deg x 1.02 deg beam the instrument fully sampled 598 deg^2 of sky, including fields measured during the previous four seasons of Python observations. Interpreting the observed fluctuations as anisotropy in the cosmic microwave background, we place constraints on the angular power spectrum of fluctuations in eight multipole bands up to l ~ 260. The observed spectrum is consistent with both the COBE experiment and previous Python results. There is no significant contamination from known foregrounds. The results show a discernible rise in the angular power spectrum from large (l ~ 40) to small (l ~ 200) angular scales. The shape of the observed power spectrum is not a simple linear rise but has a sharply increasing slope starting at l ~ 150.Comment: 5 page

A Joint Sunyaev-Zel'dovich Effect and X-ray Analysis of Abell 3667

We present a 40GHz (7.5 mm) raster scan image of a 3.6x2 degree region centered on the low redshift (z=0.055) cluster of galaxies Abell 3667. The cluster was observed during the Antarctic winter of 1999 using the Corona instrument (15.7' FWHM beam) on the Viper Telescope at the South Pole. The Corona image of A3667 is one of the first direct (i.e. rather than interferometer) thermal Sunyaev-Zel'dovich effect images of a low redshift cluster. The brightness temperature decrement at the X-ray centroid (20h 12m 28.9s, -56 49 51 J2000) was measured to be $\Delta T_{\rm CMB}=-154\mu K$. We have used the 40GHz map of A3667 in conjunction with a deep ROSAT PSPC (X-ray) image of the cluster, to make a measurement of the Hubble Constant. We find $H_0 = 64^{+96}_{-30}$ km s$^{-1}$ Mpc$^{-1}$ (68% confidence interval). Our $H_0$ calculation assumes that the cluster can be described using an isothermal, tri-axial ellipsoidal, $\beta$-model and includes several new analysis techniques including an automated method to remove point sources from X-ray images with variable point spread functions, and an efficient method for determining the errors in multi-parameter maximum likelihood analyzes. The large errors on the $H_0$ measurement are primarily due to the statistical noise in the Corona image. We plan to increase the precision of our measurement by including additional clusters in our analysis and by increasing the sensitivity of the Viper SZE maps.Comment: 15 pages, 4 figures, submitted to ApJ (count rate units corrected in Table 1 and Figure 4

Electrochemical pore formation on InP in alkaline solutions

The surface properties of InP electrodes were examined following anodization in (NH4)2S and KOH electrolytes. In both solutions, the observation of current peaks in the cyclic voltammetric curves was attributed to selective etching of the substrate and a film formation process. AFM images of samples anodized in the sulfide solution, revealed surface pitting and TEM micrographs revealed the porous nature of the film formed on top of the pitted substrate. After anodization in the KOH electrolyte, TEM images revealed that a porous layer extending 500 nm into the substrate had been formed. Analysis of the composition of the anodic products indicates the presence of In2S3 in films grown in (NH4)2S and an In2O3 phase within the porous network formed in KOH

Recent Work on the Design and Construction of Air Inflated Structures

AbstractOver the last few years our practice has been responsible for the structural design of a number of lightweight structures that achieve their structural stability by inflating elements of fabric structure. The paper will explain the design rationale of key examples; describing the structural forms, methods of analysis and design, and the detailing, materials, and methods of fabrication. The largest and most complex of these structures to date is a demountable stage set structure for the Cirque du Soleil “Toruk: First Flight” show, comprising two 15 metre high and 20 metre wide structures. The stage set structures form ‘trees’ on which acrobats climb and perform. Each structure incorporates a high level access gantry with acrobat suspension and counterweight systems, as well as a secondary inflatable skin cladding. The entire primary structure and cladding system is constructed from inflated fabric elements using internal pressures ranging from 0.5 KN/m2 up to 90 KN/m2, and are deflated down to less than 5% of their erected volume for transport between venues. Other examples of our work described will include temporary pavilions with clear spans of up to 25 metres, using a combination of air tight and air permeable elements. Also a range of wide span structures that we describe as “semi-permanent” that are capable of resisting full environmental wind and snow loading, and that are fully demountable but that can also be erected for extended periods of time in a single location

Dynamics of Social Balance on Networks

We study the evolution of social networks that contain both friendly and unfriendly pairwise links between individual nodes. The network is endowed with dynamics in which the sense of a link in an imbalanced triad--a triangular loop with 1 or 3 unfriendly links--is reversed to make the triad balanced. With this dynamics, an infinite network undergoes a dynamic phase transition from a steady state to "paradise"--all links are friendly--as the propensity p for friendly links in an update event passes through 1/2. A finite network always falls into a socially-balanced absorbing state where no imbalanced triads remain. If the additional constraint that the number of imbalanced triads in the network does not increase in an update is imposed, then the network quickly reaches a balanced final state.Comment: 10 pages, 7 figures, 2-column revtex4 forma

Structural and electrical analysis of the atomic layer deposition of HfO2/n-In0.53Ga0.47As capacitors with and without an Al2O3 interface control layer

High mobility III-V substrates with high-k oxides are required for device scaling without loss of channel mobility. Interest has focused on the self-cleaning effect on selected III-V substrates during atomic layer deposition of Al2O3. A thin (similar to 1 nm) Al2O3 interface control layer is deposited on In0.53Ga0.47As prior to HfO2 growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by similar to 50% while maintaining scaling trends. Significant reductions in leakage current density and increased breakdown voltage are found, indicative of a band structure improvement due to the reduction/removal of the In0.53Ga0.47As native oxides. (C) 2010 American Institute of Physics. (doi: 10.1063/1.3473773

Energy barriers at interfaces between (100) InxGa1-xAs (0 <= x <= 0.53) and atomic-layer deposited Al2O3 and HfO2

The electron energy band alignment at interfaces of InxGa1-xAs (0 <= x <= 0.53) with atomic-layer deposited insulators Al2O3 and HfO2 is characterized using internal photoemission and photoconductivity experiments. The energy of the InxGa1-xAs valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the known bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. It finds support from both electron and hole photoemission data. Similarly to the GaAs case, electron states originating from the interfacial oxidation of InxGa1-xAs lead to reduction in the electron barrier at the semiconductor/oxide interface. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3137187

Observation of peripheral charge induced low frequency capacitance-voltage behaviour in metal-oxide-semiconductor capacitors on Si and GaAs substrates

We report on experimental observations of room temperature low frequency capacitance-voltage (CV) behaviour in metal oxide semiconductor (MOS) capacitors incorporating high dielectric constant (high-k) gate oxides, measured at ac signal frequencies (2 kHz to 1 MHz), where a low frequency response is not typically expected for Si or GaAs MOS devices. An analysis of the inversion regions of the CV characteristics as a function of area and ac signal frequency for both n and p doped Si and GaAs substrates indicates that the source of the low frequency CV response is an inversion of the semiconductor/high-k interface in the peripheral regions outside the area defined by the metal gate electrode, which is caused by charge in the high-k oxide and/or residual charge on the high-k oxide surface. This effect is reported for MOS capacitors incorporating either MgO or GdSiOx as the high-k layers on Si and also for Al2O3 layers on GaAs(111B). In the case of NiSi/MgO/Si structures, a low frequency CV response is observed on the p-type devices, but is absent in the n-type devices, consistent with positive charge (>8 x 10(10) cm(-2)) on the MgO oxide surface. In the case of the TiN/GdSiOx/Si structures, the peripheral inversion effect is observed for n-type devices, in this case confirmed by the absence of such effects on the p-type devices. Finally, for the case of Au/Ni/Al2O3/GaAs(111B) structures, a low-frequency CV response is observed for n-type devices only, indicating that negative charge (> 3 x 10(12) cm(-2)) on the surface or in the bulk of the oxide is responsible for the peripheral inversion effect. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729331