arXiv subjects

C. Cooper

Publications and source records attributed to C. Cooper.

9 recordsLinked to original sources

arXiv2025

Understanding and Improving Data Repurposing

We live in an age of unprecedented opportunities to use existing data for tasks not anticipated when those data were collected, resulting in widespread data repurposing. This commentary defines and maps the scope of data repurposing to highlight its importance for organizations and society and the need to study data repurposing as a frontier of data management. We explain how repurposing differs from original data use and data reuse and then develop a framework for data repurposing consisting of concepts and activities for adapting existing data to new tasks. The framework and its implications are illustrated using two examples of repurposing, one in healthcare and one in citizen science. We conclude by suggesting opportunities for research to better understand data repurposing and enable more effective data repurposing practices.

cs.CY↗

arXiv2018

On the rank of a random binary matrix

We study the rank of the random $n\times m$ 0/1 matrix ${\bf A}_{n,m;k}$ where each column is chosen independently from the set $\Omega_{n,k}$ of 0/1 vectors with exactly $k$ 1's. Here 0/1 are the elements of the field $GF_2$. We obtain an asymptotically correct estimate for the rank in terms of $c,n,k$, assuming that $m=cn$. In addition, we assign i.i.d. $U[0,1]$ weights $X_{{\bf c}},{\bf c}\in\Omega_{n,k}$ and let the weight of a set of columns $C$ be $X(C)=\sum_{{\bf c}\in C}X_{{\bf c}}$. Let a basis be a set of $n-1_{k\text{even}}$ linearly independent columns. We obtain an asymptotically correct estimate for the minimum weight of a basis. This generalises the well-known result for $k=2$ viz. that the expected length of a minimum weight spanning tree tends to $\zeta(3)$.

math.CO↗

arXiv2016

Seeding the m = 0 instability in dense plasma focus Z-pinches with a hollow anode

The dense plasma focus (DPF) is a classic Z-pinch plasma device that has been studied for decades as a radiation source. The formation of the m = 0 plasma instability during the compression phase is linked to the generation of high-energy charged particle beams, which, when operated in deuterium, lead to beam-target fusion reactions and the generation of neutron yield. In this paper, we present a technique of seeding the m = 0 instability by employing a hollow in the anode. As the plasma sheath moves along the anode's hollow structure, a low density perturbation is formed and this creates a non-uniform plasma column which is highly unstable. Dynamics of the low density perturbation and preferential seeding of the m = 0 instability were studied in detail with fully kinetic plasma simulations performed in the Large Scale Plasma particle-in-cell code as well as with a simple snowplow model. The simulations showed that by employing an anode geometry with appropriate inner hollow radius, the neutron yield of the DPF is significantly improved and low-yield shots are eliminated.

physics.plasm-ph↗

arXiv2015

The Dark Energy Camera

The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2kx4k CCDs for imaging and 12 2kx2k CCDs for guiding and focus. The CCDs have 15 microns x15 microns pixels with a plate scale of 0.263 arc sec per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

astro-ph.IM↗

arXiv2013

Fermilab experience of post-annealing losses in SRF niobium cavities due to furnace contamination and the ways to its mitigation: a pathway to processing simplification and quality factor improvement

We investigate the effect of high temperature treatments followed by only high-pressure water rinse (HPR) of superconducting radio frequency (SRF) niobium cavities. The objective is to provide a cost effective alternative to the typical cavity processing sequence, by eliminating the material removal step post furnace treatment while preserving or improving the RF performance. The studies have been conducted in the temperature range 800-1000C for different conditions of the starting substrate: large grain and fine grain, electro-polished (EP) and centrifugal barrel polished (CBP) to mirror finish. An interesting effect of the grain size on the performances is found. Cavity results and samples characterization show that furnace contaminants cause poor cavity performance, and a practical solution is found to prevent surface contamination. Extraordinary values of residual resistances ~ 1 nOhm and below are then consistently achieved for the contamination-free cavities. These results lead to a more cost-effective processing and improved RF performance, and, in conjunction with CBP, open a potential pathway to acid-free processing.

physics.acc-ph↗

arXiv2012

Investigations of surface quality and SRF cavity performance

Magnetic field enhancement has been studied in the past through replica and cavity cutting. Considerable progress of niobium cavity manufacturing and processing has been made since then. Wide variety of single cell cavities has been analyzed through replica technique. Their RF performances were compared in corresponding to geometric RF surface quality. It is concluded that the surface roughness affects cavity performance mostly in secondary role. The other factors must have played primary role in cavity performance limitations.

physics.acc-ph↗

arXiv2010

Network science: a review focused on tourism

This paper presents a review of the methods of the science of networks with an application to the field of tourism studies. The basic definitions and computational techniques are described and a case study (Elba, Italy) used to illustrate the effect of network typology on information diffusion. A static structural characterization of the network formed by destination stakeholders is derived from stakeholder interviews and website link analysis. This is followed by a dynamic analysis of the information diffusion process within the destination demonstrating that stakeholder cohesion and adaptive capacity have a positive effect on information diffusion. The outcomes and the implications of this analysis for improving destination management are discussed.

physics.soc-ph↗

arXiv2009

Knowledge transfer in a tourism destination: the effects of a network structure

Tourism destinations have a necessity to innovate to remain competitive in an increasingly global environment. A pre-requisite for innovation is the understanding of how destinations source, share and use knowledge. This conceptual paper examines the nature of networks and how their analysis can shed light upon the processes of knowledge sharing in destinations as they strive to innovate. The paper conceptualizes destinations as networks of connected organizations, both public and private, each of which can be considered as a destination stakeholder. In network theory they represent the nodes within the system. The paper shows how epidemic diffusion models can act as an analogy for knowledge communication and transfer within a destination network. These models can be combined with other approaches to network analysis to shed light on how destination networks operate, and how they can be optimized with policy intervention to deliver innovative and competitive destinations. The paper closes with a practical tourism example taken from the Italian destination of Elba. Using numerical simulations the case demonstrates how the Elba network can be optimized. Overall this paper demonstrates the considerable utility of network analysis for tourism in delivering destination competitiveness.

physics.soc-ph↗

arXiv1998

Gamma-Ray Burst and Relativistic Shells: The Surface Filling Factor

The variability observed in many complex gamma-ray bursts (GRBs) is inconsistent with causally connected variations in a single, symmetric, relativistic shell interacting with the ambient material ("external shocks"). Rather, the symmetry of the shell must be broken on an angular scale much smaller than Gamma^{-1} where Gamma is the bulk Lorentz factor for the shell. The observed variability in the external shock models arises from the number of causally connected regions that (randomly) become active. We define the "surface filling factor" to be the ratio of the area of causally connected regions that become active to the observable area of the shell. From the observed variability in 52 BATSE bursts, we estimate the surface filling factor to be typically 0.005 although some values are near unity. We find that the surface filling factor is about 0.1 Delta T/T in both the constant Gamma phase (which probably produces the GRB) and the deaccelerating phase (which probably produces the x-ray afterglows). Here, ΔT is a typical time scale of variability and T is the time since the initial signal. We analyze the 2 hr flare seen by ASCA 36 hr after the GRB and conclude that the surface filling factor must be small (0.001) in the x-ray afterglow phase as well. Explanations for low surface filling factor can either require more or less energy (by a factor of about 1000) compared to that expected for a symmetric shell.

astro-ph↗