4,440 research outputs found
Beyond "the Relationship between the Individual and Society": broadening and deepening relational thinking in group analysis
The question of âthe relationship between the individual and societyâ has troubled group analysis since its inception. This paper offers a reading of Foulkes that highlights the emergent, yet evanescent, psychosocial ontology in his writings, and argues for the development of a truly psychosocial group analysis, which moves beyond the individual/society dualism. It argues for a shift towards a language of relationality, and proposes new theoretical resources for such a move from relational sociology, relational psychoanalysis and the âmatrixial thinkingâ of Bracha Ettinger which would broaden and deepen group analytic understandings of relationality
Terminal area guidance along curved paths: A stochastic control approach
Stochastic control theory is applied to the problem of designing a digital flight compensator for terminal guidance along a helical flight path as a prelude to landing. The development of aircraft, wind, and measurement models is discussed along with a control scheme consisting of feedback gains multiplying estimate of the aircraft and wind states obtained from a Kalman one step predictor. Preliminary results are presented which indicate that the compensator performs satisfactorily in the presence of both steady winds and gusts
Quantum Monte Carlo Analysis of Exchange and Correlation in the Strongly Inhomogeneous Electron Gas
We use variational quantum Monte Carlo to calculate the density-functional
exchange-correlation hole n_{xc}, the exchange-correlation energy density
e_{xc}, and the total exchange-correlation energy E_{xc}, of several electron
gas systems in which strong density inhomogeneities are induced by a
cosine-wave potential. We compare our results with the local density
approximation and the generalized gradient approximation. It is found that the
nonlocal contributions to e_{xc} contain an energetically significant
component, the magnitude, shape, and sign of which are controlled by the
Laplacian of the electron density.Comment: 4 pages, 3 figure
Dissociation of high-pressure solid molecular hydrogen: Quantum Monte Carlo and anharmonic vibrational study
A theoretical study is reported of the molecular-to-atomic transition in
solid hydrogen at high pressure. We use the diffusion quantum Monte Carlo
method to calculate the static lattice energies of the competing phases and a
density-functional-theory-based vibrational self-consistent field method to
calculate anharmonic vibrational properties. We find a small but significant
contribution to the vibrational energy from anharmonicity. A transition from
the molecular Cmca-12 direct to the atomic I4_1/amd phase is found at 374 GPa.
The vibrational contribution lowers the transition pressure by 91 GPa. The
dissociation pressure is not very sensitive to the isotopic composition. Our
results suggest that quantum melting occurs at finite temperature.Comment: Accepted for publication by Phys. Rev. Let
Drift and Meander of Spiral Waves
In this thesis, we are concerned with the dynamics of spiral wave solutions
to Reaction-Diffsion systems of equations, and how they behave when subject to
symmetry breaking perturbations. We present an asymptotic theory of the study
of meandering (quasiperiodic spiral wave solutions) spiral waves which are
drifting due to symmetry breaking perturbations. This theory is based on
earlier theories: the 1995 Biktashev et al theory of drift of rigidly rotating
spirals, and the 1996 Biktashev et al theory of meander of spirals in
unperturbed systems. We combine the two theories by first rewriting the 1995
drift theory using the symmetry quotient system method of the 1996 meander
theory, and then go on to extend the approach to meandering spirals by
considering Floquet theory and using a singular perturbation method. We
demonstrate the work of the newly developed theory on simple examples. We also
develop a numerical implementation of the quotient system method, demonstrate
its numerical convergence and its use in calculations which would be difficult
to do by the standard methods, and also link this study to the problem of
calculation of response functions of spiral waves.Comment: PhD Thesis, University of Liverpool, Finalised March 2009, 282 pages,
many figures, pdf file size 5M
Purification and characterization of a protein-tyrosine kinase encoded by the Abelson murine leukemia virus
Sequences termed v-abl, which encode the protein-tyrosine kinase activity of Abelson murine leukemia virus, have been expressed in Escherichia coli as a fusion product (ptabl50 kinase). This fusion protein contains 80 amino acids of SV40 small t and the 403 amino acid protein kinase domain of v-abl. We report here the purification and characterization of this kinase. The purified material contains two proteins (Mr = 59,800 and 57,200), both of which possess sequences derived from v-abl. Overall purification was 3,750-fold, with a 31% yield, such that 117 micrograms of kinase could be obtained from 40 g of E. coli within 6-7 days. The specific kinase activity is over 170 mumol of phosphate min-1 mumol-1, comparable to the most active protein- serine kinases. Kinase activity is insensitive to K+, Na+, Ca2+, Ca2+- calmodulin, cAMP, or cAMP-dependent protein kinase inhibitor. The Km for ATP is dependent on the concentration of the second substrate. GTP can also be used as a phosphate donor. The enzyme can phosphorylate peptides consisting of as few as two amino acids and, at a very low rate, free tyrosine. Incubation of the kinase with [gamma-32P]ATP results in incorporation of 1.0 mol of phosphate/mol of protein. This reaction, however, cannot be blocked by prior incubation with unlabeled ATP. Incubation of 32P-labeled kinase with either ADP or ATP results in the synthesis of [32P]ATP. This suggests the phosphotyrosine residue on the Abelson kinase contains a high energy phosphate bond
Discovery of disc precession in the M31 dipping X-ray binary Bo 158
We present results from three XMM-Newton observations of the M31 low mass
X-ray binary XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004,
July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic
intensity dips were previously seen to occur on a 2.78-hr period, due to
absorption in material that is raised out of the plane of the accretion disc.
The report of these observations stated that the dip depth was anti-correlated
with source intensity. However, our new observations do not favour a strict
intensity dependance, but rather suggest that the dip variation is due to
precession of the accretion disc. This is to be expected in LMXBs with a mass
ratio <~ 0.3 (period <~ 4 hr), as the disc reaches the 3:1 resonance with the
binary companion, causing elongation and precession of the disc. A smoothed
particle hydrodynamics simulation of the disc in this system shows retrograde
rotation of a disc warp on a period of ~11 P_orb, and prograde disc precession
on a period of ~29 P_orb. This is consistent with the observed variation in the
depth of the dips. We find that the dipping behaviour is most likely to be
modified by the disc precession, hence we predict that the dipping behaviour
repeats on a 81+/-3 hr cycle.Comment: 9 pages, 6 figures, accepted for publication by MNRAS, changed
conten
Hydrodynamic modelling of accretion flows
In the proceedings of this, and of several recent close binary conferences,
there have been several contributions describing smoothed particle
hydrodynamics simulations of accretion disks. It is apposite therefore to
review the numerical scheme itself with emphasis on its advantages for disk
modelling, and the methods used for modelling viscous processes.Comment: 3 pages, to appear in proceedings of IAU Colloquium 194: Compact
binaries in the galaxy and beyon
The effect of quantization on the FCIQMC sign problem
The sign problem in Full Configuration Interaction Quantum Monte Carlo
(FCIQMC) without annihilation can be understood as an instability of the
psi-particle population to the ground state of the matrix obtained by making
all off-diagonal elements of the Hamiltonian negative. Such a matrix, and hence
the sign problem, is basis dependent. In this paper we discuss the properties
of a physically important basis choice: first versus second quantization. For a
given choice of single-particle orbitals, we identify the conditions under
which the fermion sign problem in the second quantized basis of antisymmetric
Slater determinants is identical to the sign problem in the first quantized
basis of unsymmetrized Hartree products. We also show that, when the two
differ, the fermion sign problem is always less severe in the second quantized
basis. This supports the idea that FCIQMC, even in the absence of annihilation,
improves the sign problem relative to first quantized methods. Finally, we
point out some theoretically interesting classes of Hamiltonians where first
and second quantized sign problems differ, and others where they do not.Comment: 4 pages w/ 2 page appendix, 2 figures, 1 tabl
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