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Search Results: 1 - 10 of 461941 matches for " A.;Bowden "
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The Role of Altered Nucleotide Excision Repair and UVB-Induced DNA Damage in Melanomagenesis
Timothy Budden,Nikola A. Bowden
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms14011132
Abstract: UVB radiation is the most mutagenic component of the UV spectrum that reaches the earth’s surface and causes the development of DNA damage in the form of cyclobutane pyrimidine dimers and 6-4 photoproducts. UV radiation usually results in cellular death, but if left unchecked, it can affect DNA integrity, cell and tissue homeostasis and cause mutations in oncogenes and tumour-suppressor genes. These mutations, if unrepaired, can lead to abnormal cell growth, increasing the risk of cancer development. Epidemiological data strongly associates UV exposure as a major factor in melanoma development, but the exact biological mechanisms involved in this process are yet to be fully elucidated. The nucleotide excision repair (NER) pathway is responsible for the repair of UV-induced lesions. Patients with the genetic disorder Xeroderma Pigmentosum have a mutation in one of eight NER genes associated with the XP complementation groups XP-A to XP-G and XP variant (XP-V). XP is characterized by diminished repair capacity, as well as a 1000-fold increase in the incidence of skin cancers, including melanoma. This has suggested a significant role for NER in melanoma development as a result of UVB exposure. This review discusses the current research surrounding UVB radiation and NER capacity and how further investigation of NER could elucidate the role of NER in avoiding UV-induced cellular death resulting in melanomagenesis.
HANDMADE PAPER: A REVIEW OF ITS HISTORY, CRAFT, AND SCIENCE
Martin A. Hubbe,Cindy Bowden
BioResources , 2009,
Abstract: For over 2000 years the manual craft of papermaking has been practiced all over the world utilizing a variety of techniques. This review describes the evolution of hand papermaking and its cultural significance. Paper’s evolution has been shaped by the structure and chemical composition of the fibers. Almost every aspect of modern papermaking technology has been foreshadowed by traditional practices. Such practices were passed down for many generations within families of papermakers. The main sources of cellulosic fiber evolved as the ancient craft migrated from its birthplace in China to Korea and Japan, the Islamic world, and then to Europe and America. Though most paper made today comes from automated, continuous production systems, handmade paper has enjoyed a resurgence, both as a traditional craft and as an art-form. In addition, traditional papermaking methods can provide insights to help in modern applications involving cellulosic fibers.
Extremely Flat Haloes and the Shape of the Galaxy
N. W. Evans,A. Bowden
Physics , 2014, DOI: 10.1093/mnras/stu1113
Abstract: We present a set of highly flattened galaxy models with asymptotically constant rotation curves. The mass density in the equatorial plane falls like (distance)$^{-1}$ at large radii. Although the inner equidensity contours may be spherical, oblate or prolate, the outer parts are always severely flattened. The elongated shape is supported by rotation or tangential velocity anisotropy. The models are thickened Mestel discs, and form a previously undiscovered part of the Miyamoto & Nagai sequence of flattened galaxies. The properties of the models -- axis ratios, velocity dispersions, streaming velocities and distribution functions -- are all discussed in some detail. We pose the question: are extremely flattened or disk-like haloes possible for the Milky Way galaxy? This has never been examined before, as very flattened halo models were not available. We fit the rotation curve and the vertical kinematics of disc stars in the solar neighbourhood to constrain the overall shape of the Galaxy. Denoting the ratio of polar axis to major axis by $q$, we show that models with $q\lesssim 0.57$ cannot simultaneously reproduce the in-plane and out-of-plane constraints. The kinematics of the Sagittarius galaxy also strongly disfavour models with high flattening, as the orbital plane precession is too great and the height reached above the Galactic plane is too small. At least for our Galaxy, the dark halo cannot be flatter than E4 (or axis ratio $q \sim 0.57$) at the Solar circle. Models in which the dark matter is accounted for by a massive baryonic disc or by decaying neutrinos are therefore ruled out by constraints from the rotation curve and the vertical kinematics.
Dipping Our Toes in the Water: First Models of GD-1 as a Stream
A. Bowden,V. Belokurov,N. W. Evans
Physics , 2015, DOI: 10.1093/mnras/stv285
Abstract: We present a model for producing tidal streams from disrupting progenitors in arbitrary potentials, utilizing the idea that the majority of stars escape from the progenitor's two Lagrange points. The method involves releasing test particles at the Lagrange points as the satellite orbits the host and dynamically evolving them in the potential of both host and progenitor. The method is sufficiently fast to allow large-dimensional parameter exploration using Monte Carlo methods. We provide the first direct modelling of 6-D stream observations -- assuming a stream rather than an orbit -- by applying our methods to GD-1. This is a kinematically cold stream spanning $60^{\circ}$ of the sky and residing in the outer Galaxy $\approx 15$ kpc distant from the centre. We assume the stream moves in a flattened logarithmic potential characterised by an asymptotic circular velocity $v_0$ and a flattening $q$. We recover values of normalisation $v_0$ = $227.2^{+15.6}_{-18.2}$ kms$^{-1}$ and flattening $q$ = $0.91^{+0.04}_{-0.1}$, if the stream is assumed to leading, and $v_0$ = $226.5^{+17.9}_{-17.0}$ kms$^{-1}$, $q$ = $0.90^{+0.05}_{-0.09}$, if it is assumed to be trailing. This can be compared to the values $v_0 = 224 \pm 13$ kms$^{-1}$ and $q= 0.87^{+0.07}_{-0.04}$ obtained by Koposov et al (2010) using the simpler technique of orbit fitting. Although there are differences between stream and orbit fitting, we conclude that orbit fitting can provide accurate results given the current quality of the data, at least for this kinematically cold stream in this logarithmic model of the Galaxy.
On Asymmetric Distributions of Satellite Galaxies
A. Bowden,N. W. Evans,V. Belokurov
Physics , 2014, DOI: 10.1088/2041-8205/793/2/L42
Abstract: We demonstrate that the asymmetric distribution of M31 satellites cannot be produced by tides from the Milky Way as such effects are too weak. However, loosely bound associations and groups of satellites can fall into larger haloes and give rise to asymmetries. We compute the survival times for such associations. We prove that the survival time is always shortest in Keplerian potentials, and can be ~ 3 times longer in logarithmic potentials. We provide an analytical formula for the dispersal time in terms of the size and velocity dispersion of the infalling structure. We show that, if an association of ~10 dwarfs fell into the M31 halo, its present aspect would be that of an asymmetric disk of satellites. We also discuss the case of cold substructure in the Andromeda II and Ursa Minor dwarfs.
Triaxial Cosmological Haloes and the Disc of Satellites
A. Bowden,N. W. Evans,V. Belokurov
Physics , 2013, DOI: 10.1093/mnras/stt1253
Abstract: We construct simple triaxial generalisations of Navarro-Frenk-White haloes. The models have elementary gravitational potentials, together with a density that is cusped like 1/r at small radii and falls off like 1/r^3 at large radii. The ellipticity varies with radius in a manner that can be tailored to the user's specification. The closed periodic orbits in the planes perpendicular to the short and long axes of the model are well-described by epicyclic theory, and can be used as building blocks for long-lived discs. As an application, we carry out the simulations of thin discs of satellites in triaxial dark halo potentials. This is motivated by the recent claims of an extended, thin disc of satellites around the M31 galaxy with a vertical rms scatter of ~12 kpc and a radial extent of ~ 300 kpc (Ibata et al. 2013). We show that a thin satellite disc can persist over cosmological times if and only if it lies in the planes perpendicular to the long or short axis of a triaxial halo, or in the equatorial or polar planes of a spheroidal halo. In any other orientation, then the disc thickness doubles on ~5 Gyr timescales and so must have been born with an implausibly small vertical scaleheight.
Emerging Paramyxoviruses: Receptor Tropism and Zoonotic Potential
Antra Zeltina?,Thomas A. Bowden,Benhur Lee
PLOS Pathogens , 2016, DOI: 10.1371/journal.ppat.1005390
Abstract:
The Doubloon Models of Dark Haloes
N. W. Evans,J. An,A. Bowden,A. A. Williams
Physics , 2015, DOI: 10.1093/mnras/stv621
Abstract: A family of spherical halo models with flat circular velocity curves is presented. This includes models in which the rotation curve has a finite central value but declines outwards (like the Jaffe model). It includes models in which the rotation curve is rising in the inner parts, but flattens asymptotically (like the Binney model). The family encompasses models with both finite and singular (cuspy) density profiles. The self-consistent distribution function depending on binding energy $E$ and angular momentum $L$ is derived and the kinematical properties of the models discussed. These really describe the properties of the total matter (both luminous and dark). For comparison with observations, it is better to consider tracer populations of stars. These can be used to represent elliptical galaxies or the spheroidal components of spiral galaxies. Accordingly, we study the properties of tracers with power-law or Einasto profiles moving in the doubloon potential. Under the assumption of spherical alignment, we provide a simple way to solve the Jeans equations for the velocity dispersions. This choice of alignment is supported by observations on the stellar halo of the Milky Way. Power-law tracers have prolate spheroidal velocity ellipsoids everywhere. However, this is not the case for Einasto tracers, for which the velocity ellipsoids change from prolate to oblate spheroidal near the pole. Asymptotic forms of the velocity distributions close to the escape speed are also derived, with an eye to application to the high velocity stars in the Milky Way. Power-law tracers have power-law or Maxwellian velocity distributions tails, whereas Einasto tracers have super-exponential cut-offs.
Hamiltonians of Spherically Symmetric, Scale-Free Galaxies in Action-Angle Coordinates
A. A. Williams,N. W. Evans,A. Bowden
Physics , 2014, DOI: 10.1093/mnras/stu892
Abstract: We present a simple formula for the Hamiltonian in terms of the actions for spherically symmetric, scale-free potentials. The Hamiltonian is a power-law or logarithmic function of a linear combination of the actions. Our expression reduces to the well-known results for the familiar cases of the harmonic oscillator and the Kepler potential. For other power-laws, as well as for the singular isothermal sphere, it is exact for the radial and circular orbits, and very accurate for general orbits. Numerical tests show that the errors are always small, with mean errors across a grid of actions always less than 1 % and maximum errors less than 2.5 %. Simple first-order corrections can reduce mean errors to less than 0.6 % and maximum errors to less than 1 %. We use our new result to show that :[1] the misalignment angle between debris in a stream and a progenitor is always very nearly zero in spherical scale-free potentials, demonstrating that streams can be sometimes well approximated by orbits, [2] the effects of an adiabatic change in the stellar density profile in the inner regions of a galaxy weaken any existing 1/r density cusp, which is reduced to $1/r^{1/3}$. More generally, we derive the full range of adiabatic cusp transformations and show how to relate the starting cusp index to the final cusp index. It follows that adiabatic transformations can never erase a dark matter cusp.
Altered gene expression in the superior temporal gyrus in schizophrenia
Nikola A Bowden, Rodney J Scott, Paul A Tooney
BMC Genomics , 2008, DOI: 10.1186/1471-2164-9-199
Abstract: To identify altered mRNA expression in the superior temporal gyrus (STG) in schizophrenia, oligonucleotide microarrays were used with RNA from postmortem STG tissue from 7 individuals with schizophrenia and 7 matched non-psychiatric controls. Overall, there was a trend towards down-regulation in gene expression, and altered expression of genes involved in neurotransmission, neurodevelopment, and presynaptic function was identified. To confirm altered expression identified by microarray analysis, the mRNA expression levels of four genes, IPLA2γ, PIK31R1, Lin-7b and ATBF1, were semi-quantitatively measured using relative real-time PCR. A number of genes with altered expression in the STG were also shown to have similar changes in expression as shown in our previous study of peripheral blood lymphocytes in schizophrenia.This study has identified altered expression of genes in the STG involved in neurotransmission and neurodevelopment, and to a lesser extent presynaptic function, which further support the notion of these functions playing an integral role in the development of schizophrenia.The introduction of cDNA microarrays has identified changes in the expression of hundreds of genes in post-mortem brain tissue from individuals with schizophrenia [1-14]. These studies have identified new genes with both altered expression in, and genetic association to schizophrenia. Many functional groups of genes have been reported to be altered in these studies including those involved in neurotransmission, presynaptic functioning, myelination, neurodevelopment and basic cellular processes such as cell-cycle regulation and intracellular signalling. The most studied region for gene expression analysis is the prefrontal cortex (PFC), with fewer comprehensive gene expression profiling studies reported for other cortical regions.The superior temporal gyrus (STG), which encompasses the primary auditory cortex and is believed to be a major anatomical substrate for speech, language and
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