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Search Results: 1 - 10 of 18394 matches for " Mark Sutherland "
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On measuring the absolute scale of baryon acoustic oscillations
Will Sutherland
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21666.x
Abstract: The baryon acoustic oscillation (BAO) feature in the distribution of galaxies provides a fundamental standard ruler which is widely used to constrain cosmological parameters. In most analyses, the comoving length of the ruler is inferred from a combination of CMB observations and theory. However, this inferred length may be biased by various non-standard effects in early universe physics; this can lead to biased inferences of cosmological parameters such as H_0, \Omega_m and w, so it would be valuable to measure the absolute BAO length by combining a galaxy redshift survey and a suitable direct low-z distance measurement. One obstacle is that low-redshift BAO surveys mainly constrain the ratio r_S / D_V(z), where D_V is a dilation scale which is not directly observable by standard candles. Here, we find a new approximation D_V(z) \simeq (3/4) D_L(4z/3) (1+ 4z/3)^{-1} (1 - 0.02455 z^3 + 0.0105 z^4) which connects D_V to the standard luminosity distance D_L at a somewhat higher redshift; this is shown to be very accurate (relative error < 0.2 percent) for all WMAP-compatible Friedmann models at z < 0.4, with very weak dependence on cosmological parameters H_0, \Omega_m, \Omega_k, w. This provides a route to measure the absolute BAO length using only observations at z < 0.3, including type-Ia supernovae, and potentially future H_0-free physical distance indicators such as gravitational lenses or gravitational wave standard sirens. This would provide a zero-parameter check of the standard cosmology at 10^3 < z < 10^5, and can constrain the number of relativistic species N_{eff} with fewer degeneracies than the CMB.
Gravitational Microlensing - A Report on the MACHO Project
Will Sutherland
Physics , 1998, DOI: 10.1103/RevModPhys.71.421
Abstract: There is abundant evidence that the mass of the Universe is dominated by dark matter of unknown form. The MACHO project is one of several teams searching for the dark matter around our Galaxy in the form of Massive Compact Halo Objects (MACHOs). If a compact object passes very close to the line of sight to a background star, the gravitational deflection of light causes an apparent brightening of the star, i.e. a gravitational `microlensing' event. Such events will be very rare, so millions of stars must be monitored for many years. We describe our search for microlensing using a very large CCD camera on the dedicated 1.27m telescope at Mt. Stromlo, Australia: currently some 14 events have been discovered towards the Large Magellanic Cloud. The lack of short-timescale events excludes planetary mass MACHOs as a major contributor to the dark matter, but the observed long events (durations 1--6 months) suggest that a major fraction may be in fairly massive objects $\sim 0.5 \Msun$. It is currently difficult but not impossible to explain these events by other lens populations; we discuss some prospects for clarifying the nature of the lenses.
A cosmic speed-trap: a gravity-independent test of cosmic acceleration using baryon acoustic oscillations
Will Sutherland
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.20176.x
Abstract: We propose a new and highly model-independent test of cosmic acceleration by comparing observations of the baryon acoustic oscillation (BAO) scale at low and intermediate redshifts: we derive a new inequality relating BAO observables at two distinct redshifts, which must be satisfied for any reasonable homogeneous non-accelerating model, but is violated by models similar to LambdaCDM, due to acceleration in the recent past. This test is fully independent of the theory of gravity (GR or otherwise), the Friedmann equations, CMB and supernova observations: the test assumes only the Cosmological Principle, and that the length-scale of the BAO feature is fixed in comoving coordinates. Given realistic medium-term observations from BOSS, this test is expected to exclude all homogeneous non-accelerating models at ~ 4\sigma significance, and can reach ~ 7\sigma with next-generation surveys.
Isomorphy Classes of Finite Order Automorphisms of SL(2, k)
Robert W. Benim,Mark Hunnell,Amanda K. Sutherland
Mathematics , 2015,
Abstract: In this paper, we consider the order m k-automorphisms of SL(2,k). We first characterize the forms that order m k-automorphisms of SL(2,k) take and then we simple conditions on matrices A and B, involving eigenvalues and the field that the entries of A and B lie in, that are equivalent to isomorphy between the order m k-automorphisms Inn_A and Inn_B. We examine the number of isomorphy classes and conclude with examples for selected fields.
RGD-Binding Integrins in Prostate Cancer: Expression Patterns and Therapeutic Prospects against Bone Metastasis
Mark Sutherland,Andrew Gordon,Steven D. Shnyder,Laurence H. Patterson,Helen M. Sheldrake
Cancers , 2012, DOI: 10.3390/cancers4041106
Abstract: Prostate cancer is the third leading cause of male cancer deaths in the developed world. The current lack of highly specific detection methods and efficient therapeutic agents for advanced disease have been identified as problems requiring further research. The integrins play a vital role in the cross-talk between the cell and extracellular matrix, enhancing the growth, migration, invasion and metastasis of cancer cells. Progression and metastasis of prostate adenocarcinoma is strongly associated with changes in integrin expression, notably abnormal expression and activation of the β 3 integrins in tumour cells, which promotes haematogenous spread and tumour growth in bone. As such, influencing integrin cell expression and function using targeted therapeutics represents a potential treatment for bone metastasis, the most common and debilitating complication of advanced prostate cancer. In this review, we highlight the multiple ways in which RGD-binding integrins contribute to prostate cancer progression and metastasis, and identify the rationale for development of multi-integrin antagonists targeting the RGD-binding subfamily as molecularly targeted agents for its treatment.
Physical Conditions in the Seyfert Galaxy NGC 2992
Mark G. Allen,Michael A. Dopita,Zlatan I. Tsvetanov,Ralph S. Sutherland
Physics , 1998, DOI: 10.1086/306718
Abstract: This paper presents long slit spectral maps of the bi-cone shaped extended narrow line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the physical properties of the ENLR via emission line diagnostics, and compare the observations to shock and photoionization models for the excitation mechanism of the gas. The line ratios vary as a function of position in the ENLR, and the loci of the observed points on line ratio diagrams are shown to be most consistent with shock+precursor model grids. We consider the energetics of a nuclear ionizing source for the ENLR, and perform the q-test in which the rate of ionizing photons from the nucleus is inferred from measurements of the density and ionization parameter. The q-test is shown to be invalid in the case of NGC 2992 because of the limitations of the [S II]6717/6731 density diagnostic. The excitation of the gas is shown to be broadly consistent with the kinematics, with higher [N II]6583/H-alpha present in the more dynamically active region. We also show that the pressure associated with the X-ray emitting plasma may provide a large fraction of the pressure required to power the ENLR via shocks.
Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor C$_6$Yb
Mike Sutherland,Nicolas Doiron-Leyraud,Louis Taillefer,Thomas Weller,Mark Ellerby,S. S. Saxena
Physics , 2006, DOI: 10.1103/PhysRevLett.98.067003
Abstract: We report measurements of the in-plane electrical resistivity $\rho$ and the thermal conductivity $\kappa$ of the intercalated graphite superconductor C$_6$Yb to temperatures as low as $T_c$/100. When a field is applied along the c-axis, the residual electronic linear term $\kappa_0/T$ evolves in an exponential manner for $H_{c1} < H < H_{c2}$. This activated behaviour establishes the order parameter as unambiguously s-wave, and rules out the possibility of multi-gap or unconventional superconductivity in this system.
The mathematics of Spinpossible
Alex Sutherland,Andrew Sutherland
Computer Science , 2011,
Abstract: Notes on the Spinpossible puzzle game. We give a mathematical description of the game, prove some elementary bounds on the length of optimal solutions, and consider variations of the game which place restrictions on the set of permitted moves. We conclude with a list of open questions.
What Are the bona fide GSK3 Substrates?
Calum Sutherland
International Journal of Alzheimer's Disease , 2011, DOI: 10.4061/2011/505607
Abstract: Nearly 100 proteins are proposed to be substrates for GSK3, suggesting that this enzyme is a fundamental regulator of almost every process in the cell, in every tissue in the body. However, it is not certain how many of these proposed substrates are regulated by GSK3 in vivo. Clearly, the identification of the physiological functions of GSK3 will be greatly aided by the identification of its bona fide substrates, and the development of GSK3 as a therapeutic target will be highly influenced by this range of actions, hence the need to accurately establish true GSK3 substrates in cells. In this paper the evidence that proposed GSK3 substrates are likely to be physiological targets is assessed, highlighting the key cellular processes that could be modulated by GSK3 activity and inhibition. 1. Introduction 1.1. Why Identify Substrates? Glycogen synthase kinase-3 (GSK3) was first reported as a glycogen synthase phosphorylating activity in rabbit skeletal muscle (the third to be found, hence GSK3) [1]. GSK3 was later identified as a major tau protein kinase [2]. These substrates immediately focused attention on the importance of GSK3 in glucose metabolism and neurodegeneration, and these remain major areas of GSK3 research. Indeed GSK3 inhibitors, which were initially developed for the treatment of diabetes, are now being investigated for the treatment of Alzheimer’s disease, as well as many other conditions [3–5]. These therapeutic programmes have arisen directly from substrate identification; however, more recently the multitude of GSK3 substrates proposed in the literature has lessened therapeutic interest in this enzyme. It is therefore of great importance to establish beyond doubt what the physiological targets of this enzyme are, not only to focus therapeutic potential but also establish actual side effects of manipulating GSK3 activity. 1.2. Problems with False Positives It is reasonably straightforward to implicate a protein as a substrate for a kinase, with evidence ranging from the existence of a consensus phosphorylation sequence in the primary structure of a protein through to regulation of phosphorylation by manipulation of the protein kinase in vivo. Unfortunately, the existence of a consensus sequence is rarely a good predictor of whether a protein will be a substrate of that kinase. Indeed GSK3 target consensus sequences occur in more than half of all known human proteins, most of which are clearly not regulated by GSK3. In addition, phosphorylation in vitro does not always correlate with phosphorylation in vivo, and great care has to be taken
Correction: A Challenge for the Development of Malaria Vaccines: Polymorphic Target Antigens
Colin Sutherland
PLOS Medicine , 2007, DOI: 10.1371/journal.pmed.0040175
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