679 research outputs found
The universal functorial equivariant Lefschetz invariant
We introduce the universal functorial equivariant Lefschetz invariant for
endomorphisms of finite proper G-CW-complexes, where G is a discrete group. We
use K_0 of the category of "phi-endomorphisms of finitely generated free
RPi(G,X)-modules". We derive results about fixed points of equivariant
endomorphisms of cocompact proper smooth G-manifolds.Comment: 33 pages; shortened version of the author's PhD thesis, supervised by
Wolfgang Lueck, Westfaelische Wilhelms-Universitaet Muenster, 200
Thermally activated escape rates of uniaxial spin systems with transverse field
Classical escape rates of uniaxial spin systems are characterized by a
prefactor differing from and much smaller than that of the particle problem,
since the maximum of the spin energy is attained everywhere on the line of
constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is
applied, a saddle point of the energy is formed, and high, moderate, and low
damping regimes (similar to those for particles) appear. Here we present the
first analytical and numerical study of crossovers between the uniaxial and
other regimes for spin systems. It is shown that there is one HD-Uniaxial
crossover, whereas at low damping the uniaxial and LD regimes are separated by
two crossovers.Comment: 4 PR pages, 3 figures, final published versio
Field dependence of the temperature at the peak of the ZFC magnetization
The effect of an applied magnetic field on the temperature at the maximum of
the ZFC magnetization, , is studied using the recently obtained
analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for
the prefactor of the N\'{e}el relaxation time which allow one to precisely
calculate the prefactor in the N\'{e}el-Brown model and thus the blocking
temperature as a function of the coefficients of the Taylor series expansion of
the magnetocrystalline anisotropy. The present calculations indicate that even
a precise determination of the prefactor in the N\'{e}el-Brown theory, which
always predicts a monotonic decrease of the relaxation time with increasing
field, is insufficient to explain the effect of an applied magnetic field on
the temperature at the maximum of the ZFC magnetization. On the other hand, we
find that the non linear field-dependence of the magnetization along with the
magnetocrystalline anisotropy appears to be of crucial importance to the
existence of this maximum.Comment: 14 LaTex209 pages, 6 EPS figures. To appear in J. Phys.: Condensed
Matte
Classical and quantum magnetisation reversal studied in single nanometer-sized particles and clusters using micro-SQUIDs
Recent progress in experiment on quantum tunnelling of the magnetic moment in
mesoscopic systems will be reviewed. The emphasis will be made on measurements
of individual nanoparticles. These nanomagnets allow one to test the border
between classical and quantum behaviour. Using the micro-SQUID magnetometer,
waiting time, switching field and telegraph noise measurements show
unambiguously that the magnetisation reversal of small enough single
crystalline nanoparticles is described by a model of thermal activation over a
single-energy barrier. Results on insulating BaFeO nanoparticles show strong
deviations from this model below 0.4 K which agree with the theory of
macroscopic quantum tunnelling in the low dissipation regime.Comment: 6 pages, 2 figures, conference proceedings of LT22-Helsink
Hexahalorhenate (iv) salts of metal oxazolidine nitroxides
Eight coordination compounds of formulae [FeII(L•)2][ReIVCl6] (1a), [FeII(L•)2][ReIVBr6] (1b), [CoII(L•)2][ReIVCl6]·CH3CN (2a), [CoII(L•)2][ReIVBr6] (2b), [NiII(L•)(CH3CN)3][ReIVCl6]·CH3CN (3a), [NiII(L•)(CH3CN)3][ReIVBr6]·3CH3CN (3b), [CuII(L•)2][ReIVCl6] (4a)and [CuII(L•)2][ReIVBr6] (4b), where L• is the aminoxyl radical chelating ligand, 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N- oxide, have been synthesised. Structural and magnetic studies reveal metal-radical intramolecular antiferromagnetic interactions in the [MII(L•)2]2+ cations in the iron, cobalt and copper based compounds (1a, 1b, 2a, 2b, 4a and 4b) with the central metal ion low-spin in the case of Fe (1a and 1b) and a gradual, cobalt based, spin-crossover transition present in 2a and 2b. The nickel based compounds, 3a and 3b, were analysed in the dried form (3a(dried) and 3b(dried)) and directly in acetonitrile (3a(solvated) and 3b(solvated)). Microanalysis and IR spectroscopy on 3a(dried) and 3b(dried) suggests the dried samples are best formulated as [NiII(L•)(H2O)3][ReIVX6], where X = Cl (3a(dried)) and Br (3b(dried)). All forms for 3a and 3b exhibit cationic metal-radical ferromagnetic interactions resulting in S = 3/2 ground states. In addition, 3a(dried) exhibits spin-canting behaviour with an ordering temperature of 2.7 K, an open hysteresis loop with a coercive field Hc, = 580 Oe, and a remanent magnetisation Mr = 0.21 μB, resulting in a canting angle of ~1.8°. In contrast 3b(dried) shows no spin-canting behaviour; a maximum in χM vs. T at T = 3 K suggesting long-range antiferromagnetic order. 3a(solvated) and 3b(solvated) show no indication of long-range magnetic ordering, unlike 4a and 4b where anomalies are evident in the low-temperature magnetic susceptibility measurements
The South Asian genome
Genetics of disease
Microarrays
Variant genotypes
Population genetics
Sequence alignment
AllelesThe genetic sequence variation of people from the Indian subcontinent who comprise one-quarter of the world's population, is not well described. We carried out whole genome sequencing of 168 South Asians, along with whole-exome sequencing of 147 South Asians to provide deeper characterisation of coding regions. We identify 12,962,155 autosomal sequence variants, including 2,946,861 new SNPs and 312,738 novel indels. This catalogue of SNPs and indels amongst South Asians provides the first comprehensive map of genetic variation in this major human population, and reveals evidence for selective pressures on genes involved in skin biology, metabolism, infection and immunity. Our results will accelerate the search for the genetic variants underlying susceptibility to disorders such as type-2 diabetes and cardiovascular disease which are highly prevalent amongst South Asians.Whole genome sequencing to discover genetic variants underlying type-2 diabetes, coronary heart disease and related phenotypes amongst Indian Asians. Imperial College Healthcare NHS Trust cBRC 2011-13 (JS Kooner [PI], JC Chambers)
Public Benefits of Undeveloped Lands on Urban Outskirts: Non-Market Valuation Studies and their Role in Land Use Plans
Over the past three decades, the economics profession has developed methods for estimating the public benefits of green spaces, providing an opportunity to incorporate such information into land-use planning. While federal regulations routinely require such estimates for major regulations, the extent to which they are used in local land use plans is not clear. This paper reviews the literature on public values for lands on urban outskirts, not just to survey their methods or empirical findings, but to evaluate the role they have played--or have the potential to play-- in actual land use plans. Based on interviews with authors and representatives of funding agencies and local land trusts, it appears that academic work has had a mixed reception in the policy world. Reasons for this include a lack of interest in making academic work accessible to policy makers, emphasizing revealed preference methods which are inconsistent with policy priorities related to nonuse values, and emphasis on benefit-cost analyses. Nevertheless, there are examples of success stories that illustrate how such information can play a vital role in the design of conservation policies. Working Paper 07-2
A review of the imaging and intervention of liver transplant complications
Liver transplantation has become a successful surgical solution to a variety of medical and oncological parenchymal liver diseases. As a result, these patients are being encountered more frequently within diagnostic imaging departments which may be remote from the transplant centre. Radiologists must therefore be proficient in identifying normal post-transplant anatomy which involves the anastomosis of four structures between the donor and recipient, namely the hepatic artery, the main portal vein, the retro-hepatic inferior vena cava and the extra-hepatic bile ducts. A number of potential complications can arise involving any or all of these structures, which can be potentially devastating and lead to graft failure. Radiologists must familiarise themselves with the normal post-operative appearances of liver transplantation and become competent in diagnosing post-transplant complications. Where possible, complications should be treated using interventional radiological techniques, thus avoiding the need for repeat surgical intervention or retransplantation
Characterisation of GLUT4 trafficking in HeLa cells: comparable kinetics and orthologous trafficking mechanisms to 3T3-L1 adipocytes
Insulin-stimulated glucose transport is a characteristic property of adipocytes and muscle cells and involves the regulated delivery of glucose transporter (GLUT4)-containing vesicles from intracellular stores to the cell surface. Fusion of these vesicles results in increased numbers of GLUT4 molecules at the cell surface. In an attempt to overcome some of the limitations associated with both primary and cultured adipocytes, we expressed an epitope- and GFP-tagged version of GLUT4 (HA–GLUT4–GFP) in HeLa cells. Here we report the characterisation of this system compared to 3T3-L1 adipocytes. We show that insulin promotes translocation of HA–GLUT4–GFP to the surface of both cell types with similar kinetics using orthologous trafficking machinery. While the magnitude of the insulin-stimulated translocation of GLUT4 is smaller than mouse 3T3-L1 adipocytes, HeLa cells offer a useful, experimentally tractable, human model system. Here, we exemplify their utility through a small-scale siRNA screen to identify GOSR1 and YKT6 as potential novel regulators of GLUT4 trafficking in human cells
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