Narrow Frequency Channels Research Articles

The MeerKAT Galaxy Cluster Legacy Survey

MeerKAT’s large number (64) of 13.5 m diameter antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900−1670 MHz) observations of 115 galaxy clusters, observed for ∼6−10 h each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at ∼8″ resolution, and enhanced spectral and polarisation image cubes at ∼8″ and 15″ resolutions. Typical sensitivities for the full-resolution MGCLS image products range from ∼3−5 μJy beam−1. The basic cubes are full-field and span 2° × 2°. The enhanced products consist of the inner 1.2° × 1.2° field of view, corrected for the primary beam. The survey is fully sensitive to structures up to ∼10′ scales, and the wide bandwidth allows spectral and Faraday rotation mapping. Relatively narrow frequency channels (209 kHz) are also used to provide H I mapping in windows of 0 < z < 0.09 and 0.19 < z < 0.48. In this paper, we provide an overview of the survey and the DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary-beam-corrected compact source catalogue of ∼626 000 sources for the full survey and an optical and infrared cross-matched catalogue for compact sources in the primary-beam-corrected areas of Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of cluster-centric radius in Abell 209, extending out to 3.5 R 200. We find no dependence of the star-formation rate on distance from the cluster centre, and we observe a small excess of the radio-to-100 μm flux ratio towards the centre of Abell 209 that may reflect a ram pressure enhancement in the denser environment. We detect diffuse cluster radio emission in 62 of the surveyed systems and present a catalogue of the 99 diffuse cluster emission structures, of which 56 are new. These include mini-halos, halos, relics, and other diffuse structures for which no suitable characterisation currently exists. We highlight some of the radio galaxies that challenge current paradigms, such as trident-shaped structures, jets that remain well collimated far beyond their bending radius, and filamentary features linked to radio galaxies that likely illuminate magnetic flux tubes in the intracluster medium. We also present early results from the H I analysis of four clusters, which show a wide variety of H I mass distributions that reflect both sensitivity and intrinsic cluster effects, and the serendipitous discovery of a group in the foreground of Abell 3365.

An 8 bits, RF UHF-Band DAC based on interleaved bandpass delta sigma modulator assisted by background digital calibration

A multimode 8 to 4 bits delta sigma digital-to-analog converter (DAC) comprises a digital band-pass time interleaved delta sigma modulator (BP-TIDSM) with 2 interleaved channels in 5 frequency modes accompanied by a 4-bit analog DAC with a large SVR bandgap presented. As this interleaved modulator operates in narrow frequency channels around Fs/5, it leads to a low DCE design and there is no severe compulsion to calibrate which it leads to save power, area and hardware. Fully digital modulator design is modelled in MATLAB®/SIMULINK® and results in SNDR = 57 dB in 380, 420, 440, 460 MHz and 55 dB in 400 MHz with 1v supply voltage. In order to verify the results, this BP-TIDSM is synthesized by a behavioral VHDL code in ISE software and also Design compiler. Results are shown and compared in both MATLAB and ISE software. After noise shaping through the modulation and before multiplexing, a digital background calibration by a digital FIR filter applied to the modulator and all of them implemented by Cadence Virtuoso tool. A 4-bit analog DAC assigned to the multiplexer output to deliver a smooth analog signal. BP-TIDSM and calibration filters and also DAC circuits are implemented using Cadence in 180 nm technology. The proposed design used 52 mW of power with 1.6v output voltage swing and occupied an area of 0.121 mm2.

Intracellular Correlates of Stimulus-Specific Adaptation

Stimulus-specific adaptation (SSA) is the reduction in response to a common stimulus that does not generalize, or only partially generalizes, to rare stimuli. SSA is strong and widespread in primary auditory cortex (A1) of rats, but is weak or absent in the main input station to A1, the ventral division of the medial geniculate body. To study SSA in A1, we recorded neural activity in A1 intracellularly using sharp electrodes. We studied the responses to tone pips of the same frequency in different contexts: as Standard and Deviants in Oddball sequences; in equiprobable sequences; in sequences consisting of rare tone presentations; and in sequences composed of many different frequencies, each of which was rare. SSA was found both in subthreshold membrane potential fluctuations and in spiking responses of A1 neurons. SSA for changes in frequency was large at a frequency difference of 44% between Standard and Deviant, and clearly present with tones separated by as little as 4%, near the behavioral frequency difference limen in rats. When using equivalent measures, SSA in spiking responses was generally larger than the SSA at the level of the membrane potential. This effect can be traced to the nonlinearity of the transformation between membrane potential to spikes. Using the responses to the same tone in different contexts made it possible to demonstrate that cortical SSA could not be fully explained by adaptation in narrow frequency channels, even at the level of the membrane potential. We conclude that local processing significantly contributes to the generation of cortical SSA.

Stimulus-Specific Adaptation and Deviance Detection in the Rat Auditory Cortex

Stimulus-specific adaptation (SSA) is the specific decrease in the response to a frequent (‘standard’) stimulus, which does not generalize, or generalizes only partially, to another, rare stimulus (‘deviant’). Stimulus-specific adaptation could result simply from the depression of the responses to the standard. Alternatively, there may be an increase in the responses to the deviant stimulus due to the violation of expectations set by the standard, indicating the presence of true deviance detection. We studied SSA in the auditory cortex of halothane-anesthetized rats, recording local field potentials and multi-unit activity. We tested the responses to pure tones of one frequency when embedded in sequences that differed from each other in the frequency and probability of the tones composing them. The responses to tones of the same frequency were larger when deviant than when standard, even with inter-stimulus time intervals of almost 2 seconds. Thus, SSA is present and strong in rat auditory cortex. SSA was present even when the frequency difference between deviants and standards was as small as 10%, substantially smaller than the typical width of cortical tuning curves, revealing hyper-resolution in frequency. Strong responses were evoked also by a rare tone presented by itself, and by rare tones presented as part of a sequence of many widely spaced frequencies. On the other hand, when presented within a sequence of narrowly spaced frequencies, the responses to a tone, even when rare, were smaller. A model of SSA that included only adaptation of the responses in narrow frequency channels predicted responses to the deviants that were substantially smaller than the observed ones. Thus, the response to a deviant is at least partially due to the change it represents relative to the regularity set by the standard tone, indicating the presence of true deviance detection in rat auditory cortex.

Spatial aspects of acoustic processing in complex environments.

From the perspective of acoustical signal processing, it is a challenge to analyze a complex sound environment and segregate the acoustic mixture into individual sources, each with its own spatial characteristics and reverberation pattern. However, auditory systems perform this perceptually critical task with impressive ease. This talk will review how acoustical array processors work to separate sound sources. We then consider what most vertebrates, who have two point receivers separated in space, can accomplish by combining the signals that reach their two ears. The nature of the information available to bird and mammalian auditory systems is briefly reviewed, and the computational approaches these systems take to separating sound sources is assessed, including the logic of processing sound within narrow frequency channels over brief time epochs (rather than, e.g., undertaking broadband analysis). Some observations about the ability of classical binaural processing models to implement earlier stages of processing for these complex environments will be discussed. Finally, performance of human and zebra‐finch subjects in tasks requiring judgments about individual sources embedded in complex sound mixtures will be considered in the context of physiologically motivated processing schemes. [Work supported by NIDCD: DC00100 (Colburn), DC05778 (Shinn‐Cunningham), and DC07610 (Sen).]

The coding of surprise in auditory cortex of rats

Event Abstract Back to Event The coding of surprise in auditory cortex of rats Israel Nelken1* and N. Ta’aseh1 1 Department of Neurobiology and the ICNC, Hebrew University of Jerusalem, Israel We studied the relationships between standards and deviants in the generation of stimulus-specific adaptation in rat auditory cortex. We show that the responses to a low-probability sound depend, although weakly, on the sequence in which it is embedded. When presented alone, deviants evoke somewhat larger responses than when presented in oddball sequences. The decrease in the deviant response in the presence of standards can be attributed to simple adaptation or refractoriness. When presented in the context of a sequence composed of many tones, each of which is rare, deviant responses are on average similar to the responses to deviants in oddball sequences. In about 1/3 of the local field potential recordings, and in more than half of the well-separated single neurons, the responses to deviants in oddball sequences were larger than the corresponding responses among many standards, showing evidence for true deviance detection. We tried to model these results by assuming that SSA is due to adaptation in narrow frequency channels. Such models predict consistently smaller responses to deviants in oddball sequences than to deviants among many standards. To fit our data, it is necessary to assume that in presence of oddball sequences, the adaptation channels become narrower than in other conditions. The narrowing of the adaptation channels for oddball sequences could be a basic mechanism underlying deviance detection. Conference: MMN 09 Fifth Conference on Mismatch Negativity (MMN) and its Clinical and Scientific Applications, Budapest, Hungary, 4 Apr - 7 Apr, 2009. Presentation Type: Oral Presentation Topic: Abstracts Citation: Nelken I and Ta’aseh N (2009). The coding of surprise in auditory cortex of rats. Conference Abstract: MMN 09 Fifth Conference on Mismatch Negativity (MMN) and its Clinical and Scientific Applications. doi: 10.3389/conf.neuro.09.2009.05.066 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Mar 2009; Published Online: 24 Mar 2009. * Correspondence: Israel Nelken, Department of Neurobiology and the ICNC, Hebrew University of Jerusalem, Jerusalem, Israel, israel.nelken@mail.huji.ac.il Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Israel Nelken N. Ta’aseh Google Israel Nelken N. Ta’aseh Google Scholar Israel Nelken N. Ta’aseh PubMed Israel Nelken N. Ta’aseh Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.