A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry

Aims: We describe a 6-12 GHz analogue correlator that has been developed for use in radio interferometers. Methods: We use a lag-correlator technique to synthesis eight complex spectral channels. Two schemes were considered for sampling the cross-correlation function, using either real or complex correlations, and we developed prototypes for both of them. We opted for the ``add and square'' detection scheme using Schottky diodes over the more commonly used active multipliers because the stability of the device is less critical. Results: We encountered an unexpected problem, in that there were errors in the lag spacings of up to ten percent of the unit spacing. To overcome this, we developed a calibration method using astronomical sources which corrects the effects of the non-uniform sampling as well as gain error and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&

A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry

Aims: We describe a 6-12 GHz analogue correlator that has been developed for use in radio interferometers. Methods: We use a lag-correlator technique to synthesis eight complex spectral channels. Two schemes were considered for sampling the cross-correlation function, using either real or complex correlations, and we developed prototypes for both of them. We opted for the ``add and square'' detection scheme using Schottky diodes over the more commonly used active multipliers because the stability of the device is less critical. Results: We encountered an unexpected problem, in that there were errors in the lag spacings of up to ten percent of the unit spacing. To overcome this, we developed a calibration method using astronomical sources which corrects the effects of the non-uniform sampling as well as gain error and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&

Observations of the Crab Nebula with H.E.S.S. Phase II

The High Energy Stereoscopic System (H.E.S.S.) phase I instrument was an array of four $100\,\mathrm{m}^2$ mirror area Imaging Atmospheric Cherenkov Telescopes (IACTs) that has very successfully mapped the sky at photon energies above $\sim 100\,$GeV. Recently, a $600\,\mathrm{m}^2$ telescope was added to the centre of the existing array, which can be operated either in standalone mode or jointly with the four smaller telescopes. The large telescope lowers the energy threshold for gamma-ray observations to several tens of GeV, making the array sensitive at energies where the Fermi-LAT instrument runs out of statistics. At the same time, the new telescope makes the H.E.S.S. phase II instrument. This is the first hybrid IACT array, as it operates telescopes of different size (and hence different trigger rates) and different field of view. In this contribution we present results of H.E.S.S. phase II observations of the Crab Nebula, compare them to earlier observations, and evaluate the performance of the new instrument with Monte Carlo simulations.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherland

Spectral signature of short attosecond pulse trains

We report experimental measurements of high-order harmonic spectra generated in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800nm laser field and a fraction (less than 10%) of its second harmonic. Additional spectral peaks are observed between the harmonic peaks, which are due to interferences between multiple pulses in the train. The position of these peaks varies with the CEO and their number is directly related to the number of pulses in the train. An analytical model, as well as numerical simulations, support our interpretation

Head-to-head comparison of length of stay, patients' outcome and satisfaction in Switzerland before and after SwissDRG-Implementation in 2012 in 2012: an observational study in two tertiary university centers.

On 1 January 2012 Swiss Diagnosis Related Groups (DRG), a new uniform payment system for in-patients was introduced in Switzerland with the intention to replace a "cost-based" with a "case-based" reimbursement system to increase efficiency. With the introduction of the new payment system we aim to answer questions raised regarding length of stay as well as patients' outcome and satisfaction. This is a prospective, two-centre observational cohort study with data from University Hospital Basel and the Cantonal Hospital Aarau, Switzerland, from January to June 2011 and 2012, respectively. Consecutive in-patients with the main diagnosis of either community-acquired pneumonia, exacerbation of COPD, acute heart failure or hip fracture were included. A questionnaire survey was sent out after discharge investigating changes before and after SwissDRG implementation. Our primary endpoint was LOS. Of 1,983 eligible patients 841 returned the questionnaire and were included into the analysis (429 in 2011, 412 in 2012). The median age was 76.7 years (50.8% male). Patients in the two years were well balanced in regard to main diagnoses and co-morbidities. Mean LOS in the overall patient population was 10.0 days and comparable between the 2011 cohort and the 2012 cohort (9.7 vs 10.3; p = 0.43). Overall satisfaction with care changed only slightly after introduction of SwissDRG and remained high (89.0% vs 87.8%; p = 0.429). Investigating the influence of the implementation of SwissDRG in 2012 regarding LOS patients' outcome and satisfaction, we found no significant changes. However, we observed some noteworthy trends, which should be monitored closely

C-Band All-Sky Survey: A First Look at the Galaxy

We present an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane using two months of preliminary intensity data taken with the C-Band All Sky Survey (C-BASS) northern instrument at the Owens Valley Radio Observatory, California. Combining C-BASS maps with ancillary data to make temperature-temperature plots we find synchrotron spectral indices of $\beta = -2.65 \pm 0.05$ between 0.408 GHz and 5 GHz and $\beta = -2.72 \pm 0.09$ between 1.420 GHz and 5 GHz for $-10^{\circ} < |b| < -4^{\circ}$, $20^{\circ} < l < 40^{\circ}$. Through the subtraction of a radio recombination line (RRL) free-free template we determine the synchrotron spectral index in the Galactic plane ($|b| < 4^{\circ}$) to be $\beta = -2.56 \pm 0.07$ between 0.408 GHz and 5 GHz, with a contribution of $53 \pm 8$ per cent from free-free emission at 5\,GHz. These results are consistent with previous low frequency measurements in the Galactic plane. By including C-BASS data in spectral fits we demonstrate the presence of anomalous microwave emission (AME) associated with the HII complexes W43, W44 and W47 near 30 GHz, at 4.4 sigma, 3.1 sigma and 2.5 sigma respectively. The CORNISH VLA 5 GHz source catalogue rules out the possibility that the excess emission detected around 30\;GHz may be due to ultra-compact HII regions. Diffuse AME was also identified at a 4 sigma level within $30^{\circ} < l < 40^{\circ}$, $-2^{\circ} < b < 2^{\circ}$ between 5 GHz and 22.8 GHz.Comment: 16 pages, 9 figures, submitted to MNRAS, referee's corrections made, awaiting for final approval for publicatio

High harmonic generation in a gas-filled hollow-core photonic crystal fiber

High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31, 1988; McPherson et al., J. Opt. Soc. Am. B 4:595, 1987) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature 424:831, 2003; Südmeyer et al., Nat. Photonics 2:599, 2008; Röser et al., Opt. Lett. 30:2754, 2005; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, 2009) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times, and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies were developed: external build-up cavities (Gohle et al., Nature 436:234, 2005; Jones et al., Phys. Rev. Lett. 94:193, 2005) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, 2008). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality, and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, 2003; Ren et al., Opt. Express 16:17052, 2008; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, 2004; Serebryannikov et al., Opt. Lett. 33:977, 2008; Zhang et al., Nat. Phys. 3:270, 2007). The interaction between the laser pulses and the gas occurs in a Kagome-type Hollow-Core Photonic Crystal Fiber (HC-PCF) (Benabid et al., Science 298:399, 2002), which reduces the detection threshold for HHG to only 200nJ. This novel type of fiber guides nearly all of the light in the hollow core (Couny et al., Science 318:1118, 2007), preventing damage even at intensities required for HHG. Our fiber guided 30-fs pulses with a pulse energy of more than 10μJ, which is more than five times higher than for any other photonic crystal fiber (Hensley et al., Conference on Lasers and Electro-Optics (CLEO), IEEE Press, New York, 2008

A blind detection of a large, complex, Sunyaev--Zel'dovich structure

We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have been observed down to our target sensitivity of 100{\mu}Jy/beam. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than 8 \times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (\approx 10') and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical beta-model, which do not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as the true prior, the formal Bayesian probability ratio of detection is 2.1 \times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot. (c) Abandoning a physical model with num- -1.3 70 ber density prior and instead simply modelling the SZ decrement using a phenomenological {\beta}-model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295+36 {\mu}K - this allows for CMB primary anisotropies, receiver -15 noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters.Comment: accepted MNRAS. 12 pages, 9 figure

Understanding public speakers’ performance: first contributions to support a computational approach

Communication is part of our everyday life and our ability to communicate can have a significant role in a variety of contexts in our personal, academic, and professional lives. For long, the characterization of what is a good communicator has been subject to research and debate by several areas, particularly in Education, with a focus on improving the performance of teachers. In this context, the literature suggests that the ability to communicate is not only defined by the verbal component, but also by a plethora of non-verbal contributions providing redundant or complementary information, and, sometimes, being the message itself. However, even though we can recognize a good or bad communicator, objectively, little is known about what aspects – and to what extent—define the quality of a presentation. The goal of this work is to create the grounds to support the study of the defining characteristics of a good communicator in a more systematic and objective form. To this end, we conceptualize and provide a first prototype for a computational approach to characterize the different elements that are involved in communication, from audiovisual data, illustrating the outcomes and applicability of the proposed methods on a video database of public speakers.publishe

The Goldilocks Model for TCR—Too Much Attraction Might Not Be Best for Vaccine Design

Recent research on T cell-antigen interactions suggests that tighter binding is not always better at eliciting an effective immune response