Richard A. Davis - Jodrell Bank Centre for Astrophysics, University of Manchester

Richard A. Davis
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Name
Richard A. Davis
Affiliation
Jodrell Bank Centre for Astrophysics, University of Manchester
City
Manchester
Country
United Kingdom

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Mathematics - Statistics (14)
 
Statistics - Theory (14)
 
Cosmology and Nongalactic Astrophysics (10)
 
Astrophysics of Galaxies (8)
 
Statistics - Methodology (8)
 
Astrophysics (6)
 
Instrumentation and Methods for Astrophysics (5)
 
Statistics - Applications (4)
 
Mathematics - Probability (4)
 
Statistics - Computation (2)
 
Physics - Classical Physics (1)
 
High Energy Astrophysical Phenomena (1)
 
Physics - Instrumentation and Detectors (1)
 
Computer Science - Learning (1)

Publications Authored By Richard A. Davis

Preferential attachment is an appealing mechanism for modeling power-law behavior of the degree distributions in directed social networks. In this paper, we consider methods for fitting a 5-parameter linear preferential model to network data under two data scenarios. In the case where full history of the network formation is given, we derive the maximum likelihood estimator of the parameters and show that it is strongly consistent and asymptotically normal. Read More

The revised International System of Units (SI), expected to be approved late in 2018, has implications for physics pedagogy; the ampere definition which dates from 1948 will be replaced by a definition that fixes the numerical value of the elementary charge, e, in coulombs. The kilogram definition which dates from 1889 will be replaced by a definition that fixes the numerical value of the Planck constant, h, in joule seconds. Existing SI equations are completely unaffected. Read More

Max-stable space-time processes have been developed to study extremal dependence in space-time data. We propose a semiparametric estimation procedure based on a closed form expression of the extremogram to estimate the parameters in a max-stable space-time process. We establish the asymptotic properties of the resulting parameter estimates and propose subsampling procedures to obtain asymptotically correct confidence intervals. Read More

The use of empirical characteristic functions for inference problems, including estimation in some special parametric settings and testing for goodness of fit, has a long history dating back to the 70s (see for example, Feuerverger and Mureika (1977), Csorgo (1981a,1981b,1981c), Feuerverger (1993)). More recently, there has been renewed interest in using empirical characteristic functions in other inference settings. The distance covariance and correlation, developed by Szekely and Rizzo (2009) for measuring dependence and testing independence between two random vectors, are perhaps the best known illustrations of this. Read More

We provide some asymptotic theory for the largest eigenvalues of a sample covariance matrix of a p-dimensional time series where the dimension p = p_n converges to infinity when the sample size n increases. We give a short overview of the literature on the topic both in the light- and heavy-tailed cases when the data have finite (infinite) fourth moment, respectively. Our main focus is on the heavytailed case. Read More

Recent proposals to re-define some of the base units of the SI make use of definitions that refer to fixed numerical values of certain constants. We review these proposals in the context of the latest results of the least-squares adjustment of the fundamental constants and against the background of the difficulty experienced with communicating the changes. We show that the benefit of a definition of the kilogram made with respect to the atomic mass constant (mu) may now be significantly stronger than when the choice was first considered 10 years ago. Read More

We consider reduced-rank modeling of the white noise covariance matrix in a large dimensional vector autoregressive (VAR) model. We first propose the reduced-rank covariance estimator under the setting where independent observations are available. We derive the reduced-rank estimator based on a latent variable model for the vector observation and give the analytical form of its maximum likelihood estimate. Read More

We present a Radio Recombination Line (RRL) survey of the Galactic Plane from the HI Parkes All-sky Survey and associated Zone of Avoidance survey, which mapped the region l=196degr -- 0degr --52degr and |b| < 5degr at 1.4 GHz and 14.4 arcmin resolution. Read More

The extremogram, proposed by Davis and Mikosch (2008), is a useful tool for measuring extremal dependence and checking model adequacy in a time series. We define the extremogram in the spatial domain when the data is observed on a lattice or at locations distributed as a Poisson point process in d-dimensional space. Under mixing and other conditions, we establish a central limit theorem for the empirical spatial extremogram. Read More

For the directed edge preferential attachment network growth model studied by Bollobas et al. (2003) and Krapivsky and Redner (2001), we prove that the joint distribution of in-degree and out-degree has jointly regularly varying tails. Typically the marginal tails of the in-degree distribution and the out-degree distribution have different regular variation indices and so the joint regular variation is non-standard. Read More

Herschel FIR continuum data obtained as part of the Hi-GAL survey have been used, together with the GLIMPSE 8 $\mu$m and MIPSGAL 24 $\mu$m data, to attempt the first 3D-decomposition of dust emission associated with atomic, molecular and ionized gas at 15 arcmin angular resolution. Our initial test case is a 2$\times$2 square degrees region centred on (l,b)=(30$^{\circ}$,0$^{\circ}$), a direction that encompasses the origin point of the Scutum-Crux Arm at the tip of the Galactic Bar. Coupling the IR maps with velocity maps specific for different gas phases (HI 21cm, $^{12}$CO and $^{13}$CO, and RRLs), we estimate the properties of dust blended with each of the gas components and at different Galactocentric distances along the LOS. Read More

In this article we propose feature graph architectures (FGA), which are deep learning systems employing a structured initialisation and training method based on a feature graph which facilitates improved generalisation performance compared with a standard shallow architecture. The goal is to explore alternative perspectives on the problem of deep network training. We evaluate FGA performance for deep SVMs on some experimental datasets, and show how generalisation and stability results may be derived for these models. Read More

2013Oct
Authors: PRISM Collaboration, Philippe André, Carlo Baccigalupi, Anthony Banday, Domingos Barbosa, Belen Barreiro, James Bartlett, Nicola Bartolo, Elia Battistelli, Richard Battye, George Bendo, Alain Benoît, Jean-Philippe Bernard, Marco Bersanelli, Matthieu Béthermin, Pawel Bielewicz, Anna Bonaldi, François Bouchet, François Boulanger, Jan Brand, Martin Bucher, Carlo Burigana, Zhen-Yi Cai, Philippe Camus, Francisco Casas, Viviana Casasola, Guillaume Castex, Anthony Challinor, Jens Chluba, Gayoung Chon, Sergio Colafrancesco, Barbara Comis, Francesco Cuttaia, Giuseppe D'Alessandro, Antonio Da Silva, Richard Davis, Miguel de Avillez, Paolo de Bernardis, Marco de Petris, Adriano de Rosa, Gianfranco de Zotti, Jacques Delabrouille, François-Xavier Désert, Clive Dickinson, Jose Maria Diego, Joanna Dunkley, Torsten Enßlin, Josquin Errard, Edith Falgarone, Pedro Ferreira, Katia Ferrière, Fabio Finelli, Andrew Fletcher, Pablo Fosalba, Gary Fuller, Silvia Galli, Ken Ganga, Juan García-Bellido, Adnan Ghribi, Martin Giard, Yannick Giraud-Héraud, Joaquin Gonzalez-Nuevo, Keith Grainge, Alessandro Gruppuso, Alex Hall, Jean-Christophe Hamilton, Marijke Haverkorn, Carlos Hernandez-Monte\-agudo, Diego Herranz, Mark Jackson, Andrew Jaffe, Rishi Khatri, Martin Kunz, Luca Lamagna, Massimiliano Lattanzi, Paddy Leahy, Julien Lesgourgues, Michele Liguori, Elisabetta Liuzzo, Marcos Lopez-Caniego, Juan Macias-Perez, Bruno Maffei, Davide Maino, Anna Mangilli, Enrique Martinez-Gonzalez, Carlos Martins, Silvia Masi, Marcella Massardi, Sabino Matarrese, Alessandro Melchiorri, Jean-Baptiste Melin, Aniello Mennella, Arturo Mignano, Marc-Antoine Miville-Deschênes, Alessandro Monfardini, Anthony Murphy, Pavel Naselsky, Federico Nati, Paolo Natoli, Mattia Negrello, Fabio Noviello, Créidhe O'Sullivan, Francesco Paci, Luca Pagano, Rosita Paladino, Nathalie Palanque-Delabrouille, Daniela Paoletti, Hiranya Peiris, Francesca Perrotta, Francesco Piacentini, Michel Piat, Lucio Piccirillo, Giampaolo Pisano, Gianluca Polenta, Agnieszka Pollo, Nicolas Ponthieu, Mathieu Remazeilles, Sara Ricciardi, Matthieu Roman, Cyrille Rosset, Jose-Alberto Rubino-Martin, Maria Salatino, Alessandro Schillaci, Paul Shellard, Joseph Silk, Alexei Starobinsky, Radek Stompor, Rashid Sunyaev, Andrea Tartari, Luca Terenzi, Luigi Toffolatti, Maurizio Tomasi, Neil Trappe, Matthieu Tristram, Tiziana Trombetti, Marco Tucci, Rien Van de Weijgaert, Bartjan Van Tent, Licia Verde, Patricio Vielva, Ben Wandelt, Robert Watson, Stafford Withington

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in May 2013 as a large-class mission for investigating within the framework of the ESA Cosmic Vision program a set of important scientific questions that require high resolution, high sensitivity, full-sky observations of the sky emission at wavelengths ranging from millimeter-wave to the far-infrared. PRISM's main objective is to explore the distant universe, probing cosmic history from very early times until now as well as the structures, distribution of matter, and velocity flows throughout our Hubble volume. PRISM will survey the full sky in a large number of frequency bands in both intensity and polarization and will measure the absolute spectrum of sky emission more than three orders of magnitude better than COBE FIRAS. Read More

This paper studies theory and inference of an observation-driven model for time series of counts. It is assumed that the observations follow a Poisson distribution conditioned on an accompanying intensity process, which is equipped with a two-regime structure according to the magnitude of the lagged observations. The model remedies one of the drawbacks of the Poisson autoregression model by allowing possibly negative correlation in the observations. Read More

In this paper we discuss the Planck-LFI in-flight calibration campaign. After a brief overview of the ground test campaigns, we describe in detail the calibration and performance verification (CPV) phase, carried out in space during and just after the cool-down of LFI. We discuss in detail the functionality verification, the tuning of the front-end and warm electronics, the preliminary performance assessment and the thermal susceptibility tests. Read More

2013Jun
Authors: PRISM Collaboration, Philippe Andre, Carlo Baccigalupi, Domingos Barbosa, James Bartlett, Nicola Bartolo, Elia Battistelli, Richard Battye, George Bendo, Jean-Philippe Bernard, Marco Bersanelli, Matthieu Bethermin, Pawel Bielewicz, Anna Bonaldi, Francois Bouchet, Francois Boulanger, Jan Brand, Martin Bucher, Carlo Burigana, Zhen-Yi Cai, Viviana Casasola, Guillaume Castex, Anthony Challinor, Jens Chluba, Sergio Colafrancesco, Francesco Cuttaia, Giuseppe D'Alessandro, Richard Davis, Miguel de Avillez, Paolo de Bernardis, Marco de Petris, Adriano de Rosa, Gianfranco de Zotti, Jacques Delabrouille, Clive Dickinson, Jose Maria Diego, Edith Falgarone, Pedro Ferreira, Katia Ferriere, Fabio Finelli, Andrew Fletcher, Gary Fuller, Silvia Galli, Ken Ganga, Juan Garcia-Bellido, Adnan Ghribi, Joaquin Gonzalez-Nuevo, Keith Grainge, Alessandro Gruppuso, Alex Hall, Carlos Hernandez-Monteagudo, Mark Jackson, Andrew Jaffe, Rishi Khatri, Luca Lamagna, Massimiliano Lattanzi, Paddy Leahy, Michele Liguori, Elisabetta Liuzzo, Marcos Lopez-Caniego, Juan Macias-Perez, Bruno Maffei, Davide Maino, Silvia Masi, Anna Mangilli, Marcella Massardi, Sabino Matarrese, Alessandro Melchiorri, Jean-Baptiste Melin, Aniello Mennella, Arturo Mignano, Marc-Antoine Miville-Deschenes, Federico Nati, Paolo Natoli, Mattia Negrello, Fabio Noviello, Francesco Paci, Rosita Paladino, Daniela Paoletti, Francesca Perrotta, Francesco Piacentini, Michel Piat, Lucio Piccirillo, Giampaolo Pisano, Gianluca Polenta, Sara Ricciardi, Matthieu Roman, Jose-Alberto Rubino-Martin, Maria Salatino, Alessandro Schillaci, Paul Shellard, Joseph Silk, Radek Stompor, Rashid Sunyaev, Andrea Tartari, Luca Terenzi, Luigi Toffolatti, Maurizio Tomasi, Tiziana Trombetti, Marco Tucci, Bartjan Van Tent, Licia Verde, Ben Wandelt, Stafford Withington

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in response to the Call for White Papers for the definition of the L2 and L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1) an imager with a 3.5m mirror (cooled to 4K for high performance in the far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and (2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS instrument but over three orders of magnitude more sensitive. Read More

The goal of this paper is two-fold: 1. We review classical and recent measures of serial extremal dependence in a strictly stationary time series as well as their estimation. 2. Read More

Phenomena such as air pollution levels are of greatest interest when observations are large, but standard prediction methods are not specifically designed for large observations. We propose a method, rooted in extreme value theory, which approximates the conditional distribution of an unobserved component of a random vector given large observed values. Specifically, for $\mathbf{Z}=(Z_1,. Read More

We study the $k$-largest eigenvalues of heavy-tailed sample covariance matrices of the form $\bX\bX^\T$ in an asymptotic framework, where the dimension of the data and the sample size tend to infinity. To this end, we assume that the rows of $\bX$ are given by independent copies of some stationary process with regularly varying marginals with index $\alpha\in(0,2)$ satisfying large deviation and mixing conditions. We apply these general results to stochastic volatility and GARCH processes. Read More

The Arcminute Microkelvin Imager (AMI) is a telescope specifically designed for high sensitivity measurements of low-surface-brightness features at cm-wavelength and has unique, important capabilities. It consists of two interferometer arrays operating over 13.5-18 GHz that image structures on scales of 0. Read More

The vector autoregressive (VAR) model has been widely used for modeling temporal dependence in a multivariate time series. For large (and even moderate) dimensions, the number of AR coefficients can be prohibitively large, resulting in noisy estimates, unstable predictions and difficult-to-interpret temporal dependence. To overcome such drawbacks, we propose a 2-stage approach for fitting sparse VAR (sVAR) models in which many of the AR coefficients are zero. Read More

Max-stable processes have proved to be useful for the statistical modelling of spatial extremes. Several representations of max-stable random fields have been proposed in the literature. One such representation is based on a limit of normalized and scaled pointwise maxima of stationary Gaussian processes that was first introduced by Kabluchko, Schlather and de Haan (2009). Read More

This paper studies theory and inference related to a class of time series models that incorporates nonlinear dynamics. It is assumed that the observations follow a one-parameter exponential family of distributions given an accompanying process that evolves as a function of lagged observations. We employ an iterated random function approach and a special coupling technique to show that, under suitable conditions on the parameter space, the conditional mean process is a geometric moment contracting Markov chain and that the observation process is absolutely regular with geometrically decaying coefficients. Read More

The asymptotic theory of various estimators based on Gaussian likelihood has been developed for the unit root and near unit root cases of a first-order moving average model. Previous studies of the MA(1) unit root problem rely on the special autocovariance structure of the MA(1) process, in which case, the eigenvalues and eigenvectors of the covariance matrix of the data vector have known analytical forms. In this paper, we take a different approach to first consider the joint likelihood by including an augmented initial value as a parameter and then recover the exact likelihood by integrating out the initial value. Read More

WMAP data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here we examine the sky variation at intermediate and high latitudes using a cross-correlation technique. In particular, we compare the observed emission in several large partitions of the sky plus 33 selected sky regions to three "standard" templates. Read More

We present the derivation of the free-free emission on the Galactic plane between l=20 and 44 degrees and |b| < 4 degrees, using Radio Recombination Line (RRL) data from the HI Parkes All-Sky Survey (HIPASS). Following an upgrade on the RRL data reduction technique, which improves significantly the quality of the final RRL spectra, we have extended the analysis to three times the area covered in Alves et al. (2010). Read More

We study the joint limit distribution of the $k$ largest eigenvalues of a $p\times p$ sample covariance matrix $XX^\T$ based on a large $p\times n$ matrix $X$. The rows of $X$ are given by independent copies of a linear process, $X_{it}=\sum_j c_j Z_{i,t-j}$, with regularly varying noise $(Z_{it})$ with tail index $\alpha\in(0,4)$. It is shown that a point process based on the eigenvalues of $XX^\T$ converges, as $n\to\infty$ and $p\to\infty$ at a suitable rate, in distribution to a Poisson point process with an intensity measure depending on $\alpha$ and $\sum c_j^2$. Read More

Davis and Mikosch [7] introduced the extremogram as a flexible quantitative tool for measuring various types of extremal dependence in a stationary time series. There we showed some standard statistical properties of the sample extremogram. A major difficulty was the construction of credible confidence bands for the extremogram. Read More

Max-stable processes have proved to be useful for the statistical modelling of spatial extremes. Several representations of max-stable random fields have been proposed in the literature. For statistical inference it is often assumed that there is no temporal dependence, i. Read More

Discussion of "A statistical analysis of multiple temperature proxies: Are reconstructions of surface temperatures over the last 1000 years reliable?" by B.B. McShane and A. Read More

An anomalous radio continuum component at cm-wavelengths has been observed in various sources, including dark clouds. This continuum component represents a new property of the ISM. In this work we focus on one particular dark cloud, the bright reflection nebula M 78. Read More

The C-Band All-Sky Survey (C-BASS) aims to produce sensitive, all-sky maps of diffuse Galactic emission at 5 GHz in total intensity and linear polarization. These maps will be used (with other surveys) to separate the several astrophysical components contributing to microwave emission, and in particular will allow an accurate map of synchrotron emission to be produced for the subtraction of foregrounds from measurements of the polarized Cosmic Microwave Background. We describe the design of the analog instrument, the optics of our 6. Read More

We consider a strictly stationary sequence of random vectors whose finite-dimensional distributions are jointly regularly varying with some positive index. This class of processes includes, among others, ARMA processes with regularly varying noise, GARCH processes with normally or Student-distributed noise and stochastic volatility models with regularly varying multiplicative noise. We define an analog of the autocorrelation function, the extremogram, which depends only on the extreme values in the sequence. Read More

Radio recombination lines (RRLs) can be used to determine the emission measure unambiguously along the Galactic plane. We use the deep (2100s per beam) HI Parkes Zone of Avoidance survey which includes 3 RRLs (H$166\alpha$, H$167\alpha$ and H$168\alpha$) within its bandwidth. The region $\ell = 36\degr$ to $44\degr$, $b = -4\degr$ to $+4\degr$ is chosen to include emission from the Local, Sagittarius and Scutum arms. Read More

On an exquisite March day in 2006, David Brillinger and Richard Davis sat down with Murray and Ady Rosenblatt at their home in La Jolla, California for an enjoyable day of reminiscences and conversation. Our mentor, Murray Rosenblatt, was born on September 7, 1926 in New York City and attended City College of New York before entering graduate school at Cornell University in 1946. After completing his Ph. Read More

2009Sep
Affiliations: 1Jodrell Bank Centre for Astrophysics, University of Manchester, 2Jodrell Bank Centre for Astrophysics, University of Manchester, 3Jodrell Bank Centre for Astrophysics, University of Manchester, 4Jodrell Bank Centre for Astrophysics, University of Manchester, 5Jodrell Bank Centre for Astrophysics, University of Manchester, 6Instituto de Astrofisica de Canarias, 7Cavendish Laboratory, Cambridge, 8Instituto de Astrofisica de Canarias, 9Cavendish Laboratory, Cambridge, 10Cavendish Laboratory, Cambridge, 11Instituto de Astrofisica de Canarias, 12Instituto de Astrofisica de Canarias, 13Instituto de Astrofisica de Canarias, 14Cavendish Laboratory, Cambridge, 15Cavendish Laboratory, Cambridge, 16Cavendish Laboratory, Cambridge

The dust feature G159.6--18.5 in the Perseus region has previously been observed with the COSMOSOMAS experiment \citep{Watson:05} on angular scales of $\approx$ 1$^{\circ}$, and was found to exhibit anomalous microwave emission. Read More

We consider maximum likelihood estimation for both causal and noncausal autoregressive time series processes with non-Gaussian $\alpha$-stable noise. A nondegenerate limiting distribution is given for maximum likelihood estimators of the parameters of the autoregressive model equation and the parameters of the stable noise distribution. The estimators for the autoregressive parameters are $n^{1/\alpha}$-consistent and converge in distribution to the maximizer of a random function. Read More

Using the Arcminute Microkelvin Imager (AMI) at 16 GHz and the Very Small Array (VSA) at 33 GHz to make follow-up observations of sources in the New Extragalactic WMAP Point Source Catalogue, we have investigated the flux-density variability in a complete sample of 97 sources over timescales of a few months to approximately 1.5 years. We find that 53 per cent of the 93 sources, for which we have multiple observations, are variable, at the 99 per cent confidence level, above the flux density calibration uncertainties of approximately 4 per cent at 16 GHz; the fraction of sources having varied by more than 20 per cent is 15 per cent at 16 GHz and 20 per cent at 33 GHz. Read More

We present follow-up observations of 97 point sources from the Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data, contained within the New Extragalactic WMAP Point Source (NEWPS) catalogue between declinations of -4 and +60 degrees; the sources form a flux-density-limited sample complete to 1.1 Jy (approximately 5 sigma) at 33 GHz. Our observations were made at 16 GHz using the Arcminute Microkelvin Imager (AMI) and at 33 GHz with the Very Small Array (VSA). Read More

Accurate calibration of data is essential for the current generation of CMB experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 percent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. Read More

We present interferometric imaging at 33 GHz, with the new superextended configuration of the Very Small Array (VSA), of a very deep decrement in the cosmic microwave background (CMB) temperature. This decrement is located in the direction of the Corona Borealis supercluster, at a position with no known galaxy clusters, and was discovered by a previous VSA survey (Genova-Santos et al.). Read More

An autoregressive-moving average model in which all roots of the autoregressive polynomial are reciprocals of roots of the moving average polynomial and vice versa is called an all-pass time series model. All-pass models are useful for identifying and modeling noncausal and noninvertible autoregressive-moving average processes. We establish asymptotic normality and consistency for rank-based estimators of all-pass model parameters. Read More

The first-order moving average model or MA(1) is given by $X_t=Z_t-\theta_0Z_{t-1}$, with independent and identically distributed $\{Z_t\}$. This is arguably the simplest time series model that one can write down. The MA(1) with unit root ($\theta_0=1$) arises naturally in a variety of time series applications. Read More

We present results from observations made at 33 GHz with the Very Small Array (VSA) telescope towards potential candidates in the Galactic plane for spinning dust emission. In the cases of the diffuse HII regions LPH96 and NRAO591 we find no evidence for anomalous emission and, in combination with Effelsberg data at 1.4 and 2. Read More

(Abridged) We have used the Rayner & Best (1989) smooth tests of goodness-of-fit to study the Gaussianity of the Very Small Array (VSA) data. Out of the 41 published VSA individual pointings dedicated to cosmological observations, 37 are found to be consistent with Gaussianity, whereas four pointings show deviations from Gaussianity. In two of them, these deviations can be explained as residual systematic effects of a few visibility points which, when corrected, have a negligible impact on the angular power spectrum. Read More

We present interferometric imaging at 33 GHz of the Corona Borealis supercluster, using the extended configuration of the Very Small Array. A total area of 24 deg^2 has been imaged, with an angular resolution of 11 arcmin and a sensitivity of 12 mJy/beam. The aim of these observations is to search for Sunyaev-Zel'dovich (SZ) detections from known clusters of galaxies in this supercluster and for a possible extended SZ decrement due to diffuse warm/hot gas in the intercluster medium. Read More

We describe the source subtraction strategy and observations for the extended Very Small Array, a CMB interferometer operating at 33 GHz. A total of 453 sources were monitored at 33 GHz using a dedicated source subtraction baseline. 131 sources brighter than 20 mJy were directly subtracted from the VSA visibility data. Read More