1,427 research outputs found
The CARMA correlator
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) requires a flexible correlator to process the data from up to 23 telescopes and up to 8GHz of receiver bandwidth. The Caltech Owens Valley Broadband Reconfigurable Array (COBRA) correlator, developed for use at the Owens Valley millimeter-wave array and being used by the Sunyaev-Zeldovich Array (SZA), will be adapted for use by CARMA. The COBRA correlator system, a hybrid analog-digital design, consisting of downconverters, digitizers and correlators will be presented in this paper. The downconverters receive an input IF of 1-9GHz and produce a selectable output bandwidth of 62.5MHz, 125MHz, 250MHz, or 500MHz. The downconverter output is digitized at 1Gsample/s to 2-bits per sample. The digitized data is optionally digitally filtered to produce bands narrower than 62.5MHz (down to 2MHz). The digital correlator system is a lag- or XF-based system implemented using Field-Programmable Gate Arrays (FPGAs). The digital system implements delay lines, calculates the autocorrelations for each antenna, and the cross-correlations for each baseline. The number of lags, and hence spectral channels, produced by the system is a function of the input bandwidth; with the 500MHz band having the coarsest resolution, and the narrowest bandwidths having the finest resolution
Learning from M/EEG data with variable brain activation delays
International audienceMagneto- and electroencephalography (M/EEG) measure the electromagnetic signals produced by brain activity. In order to address the issue of limited signal-to-noise ratio (SNR) with raw data, acquisitions consist of multiple repetitions of the same experiment. An important challenge arising from such data is the variability of brain activations over the repetitions. It hinders statistical analysis such as prediction performance in a supervised learning setup. One such confounding variability is the time offset of the peak of the activation, which varies across repetitions. We propose to address this misalignment issue by explicitly modeling time shifts of different brain responses in a classification setup. To this end, we use the latent support vector machine (LSVM) formulation, where the latent shifts are inferred while learning the classifier parameters. The inferred shifts are further used to improve the SNR of the M/EEG data, and to infer the chronometry and the sequence of activations across the brain regions that are involved in the experimental task. Results are validated on a long term memory retrieval task, showing significant improvement using the proposed latent discriminative method
The CARMA correlator
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) requires a flexible correlator to process the data from up to 23 telescopes and up to 8GHz of receiver bandwidth. The Caltech Owens Valley Broadband Reconfigurable Array (COBRA) correlator, developed for use at the Owens Valley millimeter-wave array and being used by the Sunyaev-Zeldovich Array (SZA), will be adapted for use by CARMA. The COBRA correlator system, a hybrid analog-digital design, consisting of downconverters, digitizers and correlators will be presented in this paper. The downconverters receive an input IF of 1-9GHz and produce a selectable output bandwidth of 62.5MHz, 125MHz, 250MHz, or 500MHz. The downconverter output is digitized at 1Gsample/s to 2-bits per sample. The digitized data is optionally digitally filtered to produce bands narrower than 62.5MHz (down to 2MHz). The digital correlator system is a lag- or XF-based system implemented using Field-Programmable Gate Arrays (FPGAs). The digital system implements delay lines, calculates the autocorrelations for each antenna, and the cross-correlations for each baseline. The number of lags, and hence spectral channels, produced by the system is a function of the input bandwidth; with the 500MHz band having the coarsest resolution, and the narrowest bandwidths having the finest resolution
The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array
A host of new low-frequency radio telescopes seek to measure the 21-cm
transition of neutral hydrogen from the early universe. These telescopes have
the potential to directly probe star and galaxy formation at redshifts , but are limited by the dynamic range they can achieve
against foreground sources of low-frequency radio emission. Consequently, there
is a growing demand for modern, high-fidelity maps of the sky at frequencies
below 200 MHz for use in foreground modeling and removal. We describe a new
widefield imaging technique for drift-scanning interferometers,
Tikhonov-regularized -mode analysis imaging. This technique constructs
images of the entire sky in a single synthesis imaging step with exact
treatment of widefield effects. We describe how the CLEAN algorithm can be
adapted to deconvolve maps generated by -mode analysis imaging. We
demonstrate Tikhonov-regularized -mode analysis imaging using the Owens
Valley Long Wavelength Array (OVRO-LWA) by generating 8 new maps of the sky
north of with 15 arcmin angular resolution, at frequencies
evenly spaced between 36.528 MHz and 73.152 MHz, and 800 mJy/beam thermal
noise. These maps are a 10-fold improvement in angular resolution over existing
full-sky maps at comparable frequencies, which have angular resolutions . Each map is constructed exclusively from interferometric observations
and does not represent the globally averaged sky brightness. Future
improvements will incorporate total power radiometry, improved thermal noise,
and improved angular resolution -- due to the planned expansion of the OVRO-LWA
to 2.6 km baselines. These maps serve as a first step on the path to the use of
more sophisticated foreground filters in 21-cm cosmology incorporating the
measured angular and frequency structure of all foreground contaminants.Comment: 27 pages, 18 figure
A Hadron Blind Detector for the PHENIX Experiment
A novel Hadron Blind Detector (HBD) has been developed for an upgrade of the
PHENIX experiment at RHIC. The HBD will allow a precise measurement of
electron-positron pairs from the decay of the light vector mesons and the
low-mass pair continuum in heavy-ion collisions. The detector consists of a 50
cm long radiator filled with pure CF4 and directly coupled in a windowless
configuration to a triple Gas Electron Multiplier (GEM) detector with a CsI
photocathode evaporated on the top face of the first GEM foil.Comment: 4 pages, 3 figures, Quark Matter 2005 conference proceeding
Conformational effects on the Circular Dichroism of Human Carbonic Anhydrase II: a multilevel computational study
Circular Dichroism (CD) spectroscopy is a powerful method for investigating conformational changes in proteins and therefore has numerous applications in structural and molecular biology. Here a computational investigation of the CD spectrum of the Human Carbonic Anhydrase II (HCAII), with main focus on the near-UV CD spectra of the wild-type enzyme and it seven tryptophan mutant forms, is presented and compared to experimental studies. Multilevel computational methods (Molecular Dynamics, Semiempirical Quantum Mechanics, Time-Dependent Density Functional Theory) were applied in order to gain insight into the mechanisms of interaction between the aromatic chromophores within the protein environment and understand how the conformational flexibility of the protein influences these mechanisms. The analysis suggests that combining CD semi empirical calculations, crystal structures and molecular dynamics (MD) could help in achieving a better agreement between the computed and experimental protein spectra and provide some unique insight into the dynamic nature of the mechanisms of chromophore interactions
The Caltech Millimeter Wave Interferometer
The Caltech Millimeter-Wave Interferometer has recently begun observations at a wavelength of 2.6 mm. We describe the instrument and some of the first results from it
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