7,335 research outputs found
Multigrid Monte Carlo in the Sine Gordon model
We pose two questions about the dynamical critical behavior of multigrid
Monte Carlo: Will a multigrid Monte Carlo simulation of the two dimensional
Sine Gordon model exhibit critical slowing down, as expected by a theoretical
analysis of Metropolis acceptance rates? Can we reduce critical slowing down
caused by decreasing acceptance rates on large blocks by performing more
updates on coarser lattices? To this end we simulate the model with a W-cycle
(gamma = 2) and a higher cycle with gamma = 4 using piecewise constant
interpolation. The answer to the first question is positive, the answer to the
second one is negative.Comment: 3 pages in ps-format, to appear in the Proceedings of LATTICE 93,
Dallas, USA, October 199
Nature vs naturalist : paths diverging and converging in Edmund Gosse's Father and son
I examine the impulses which drove Edmund Gosse to follow the formal biography of his father with Father and Son. Before looking for 'gay sensibility' in the text, I consider how scientific discourse in the late 19th century opened an understanding of homosexuality to Gosse, and consider how Father and Son preceded societal acceptance of Freudian analysis. Gosse's father was a naturalist, and I consider how Gosse eroticized childhood memory as 'natural' and 'intuitive'. I chart his attraction to a sub-culture of literature which expresses 'manly love', and track his expansion from the boyhood appreciation of Hero and Leander , which expelled him from the family home, to his devotional approaches to Whitman, the poet replacing the father as an eroticized father figure. Symonds presented himself as another older man, with explicit teachings about 'Greek love'. Gosse then became the older figure to Andre Gide, ultimately disturbed by the younger man's sexual explicitness. Ending this substitute father theme, I document how Gosse's 'true love' the sculptor Thornycroft removed himself to a 'father figure' role. The writing of Father and Son delivered child Edmund as the innocent companion the adult Edmund needed, and freed him from a disappointed paternal narrative
Holographic capture of femtosecond pulse propagation
We have implemented a holographic system to study the propagation of femtosecond laser pulses with high temporal (150 fs) and spatial resolutions (4 µm). The phase information in the holograms allows us to reconstruct both positive and negative index changes due to the Kerr nonlinearity (positive) and plasma formation (negative), and to reconstruct three-dimensional structure. Dramatic differences were observed in the interaction of focused femtosecond pulses with air, water, and carbon disulfide. The air becomes ionized in the focal region, while in water long plasma filaments appear before the light reaches a tight focus. In contrast, in carbon disulfide the optical beam breaks up into multiple filaments but no plasma is measured. We explain these different propagation regimes in terms of the different nonlinear material properties
A seminormal form for partition algebras
Using a new presentation for partition algebras (J. Algebraic Combin.
37(3):401-454, 2013), we derive explicit combinatorial formulae for the
seminormal representations of the partition algebras. These results generalise
to the partition algebras the classical formulae given by Young for the
symmetric group.Comment: Published version. 51 pages, includes figures and table
Enlarged symmetry algebras of spin chains, loop models, and S-matrices
The symmetry algebras of certain families of quantum spin chains are
considered in detail. The simplest examples possess m states per site (m\geq2),
with nearest-neighbor interactions with U(m) symmetry, under which the sites
transform alternately along the chain in the fundamental m and its conjugate
representation \bar{m}. We find that these spin chains, even with {\em
arbitrary} coefficients of these interactions, have a symmetry algebra A_m much
larger than U(m), which implies that the energy eigenstates fall into sectors
that for open chains (i.e., free boundary conditions) can be labeled by j=0, 1,
>..., L, for the 2L-site chain, such that the degeneracies of all eigenvalues
in the jth sector are generically the same and increase rapidly with j. For
large j, these degeneracies are much larger than those that would be expected
from the U(m) symmetry alone. The enlarged symmetry algebra A_m(2L) consists of
operators that commute in this space of states with the Temperley-Lieb algebra
that is generated by the set of nearest-neighbor interaction terms; A_m(2L) is
not a Yangian. There are similar results for supersymmetric chains with
gl(m+n|n) symmetry of nearest-neighbor interactions, and a richer
representation structure for closed chains (i.e., periodic boundary
conditions). The symmetries also apply to the loop models that can be obtained
from the spin chains in a spacetime or transfer matrix picture. In the loop
language, the symmetries arise because the loops cannot cross. We further
define tensor products of representations (for the open chains) by joining
chains end to end. The fusion rules for decomposing the tensor product of
representations labeled j_1 and j_2 take the same form as the Clebsch-Gordan
series for SU(2). This and other structures turn the symmetry algebra \cA_m
into a ribbon Hopf algebra, and we show that this is ``Morita equivalent'' to
the quantum group U_q(sl_2) for m=q+q^{-1}. The open-chain results are extended
to the cases |m|< 2 for which the algebras are no longer semisimple; these
possess continuum limits that are critical (conformal) field theories, or
massive perturbations thereof. Such models, for open and closed boundary
conditions, arise in connection with disordered fermions, percolation, and
polymers (self-avoiding walks), and certain non-linear sigma models, all in two
dimensions. A product operation is defined in a related way for the
Temperley-Lieb representations also, and the fusion rules for this are related
to those for A_m or U_q(sl_2) representations; this is useful for the continuum
limits also, as we discuss in a companion paper
Representation theory of towers of recollement: Theory, notes, and examples
We give an axiomatic framework for studying the representation theory of towers of algebras. We introduce a new class of algebras, contour algebras, generalising (and interpolating between) blob algebras and cyclotomic Temperley–Lieb algebras. We demonstrate the utility of our formalism by applying it to this class
Multigrid Monte Carlo with higher cycles in the Sine Gordon model
We study the dynamical critical behavior of multigrid Monte Carlo for the two
dimensional Sine Gordon model on lattices up to 128 x 128. Using piecewise
constant interpolation, we perform a W-cycle (gamma=2). We examine whether one
can reduce critical slowing down caused by decreasing acceptance rates on large
blocks by doing more work on coarser lattices. To this end, we choose a higher
cycle with gamma = 4. The results clearly demonstrate that critical slowing
down is not reduced in either case.Comment: 7 pages, 1 figure, whole paper including figure contained in ps-file,
DESY 93-00
Somerstown Stories and the benefits of using a design charette for community engagement
Somerstown Stories was a local heritage project supported by the Heritage Lottery Fund, collaborating initially with Somers Park Primary School in Somerstown, within the City of Portsmouth. The aim of the project was to enable people to reconnect with their locality by exploring local history. In addition, the project explored the question: does knowing more about where you live change how you feel about living there? At the time of the project, the area of Somerstown was at the beginning of a process of phased redevelopment, so it was timely for local groups and organizations as a whole to look back at their history and the shaping of the area, in order to prepare to look forward and plan for the future. As part of the larger Somerstown Stories project, the University of Portsmouth School of Architecture was invited to coordinate a design charette for Year 9 students from the local Charter Academy School. This paper explores the nature of the charette, and its value in engaging different stakeholders. The paper is written using commentaries, conclusions and reflections from the key people involved with this project, including Canon Nick Ralph from the Diocese of Portsmouth; Sharon Court, Creative Practitioner and Project Manager for the Somerstown Stories project; Martin Andrews, Architect and Principal Lecturer at the University of Portsmouth School of Architecture; and Andrew Joyce, a University of Portsmouth student at the time of the design charette and now a registered architect working at ArchitecturePLB in Winchester
Public Involvement in research within care homes: Benefits and challenges in the APPROACH Study
Public involvement in research (PIR) can improve research design and recruitment. Less is known about how PIR enhances the experience of participation and enriches the data collection process. In a study to evaluate how UK care homes and primary health care services achieve integrated working to promote older people’s health, PIR was integrated throughout the research processes. Objectives This paper aims to present one way in which PIR has been integrated into the design and delivery of a multi-site research study based in care homes. Design A prospective case study design, with an embedded qualitative evaluation of PIR activity. Setting and Participants Data collection was undertaken in six care homes in three sites in England. Six PIR members participated: all had prior personal or work experience in care homes. Data Collection Qualitative data collection involved discussion groups, and site-specific meetings to review experiences of participation, benefits and challenges, and completion of structured fieldwork notes after each care home visit. Results PIR members supported: recruitment, resident and staff interviews and participated in data interpretation. Benefits of PIR work were resident engagement that minimised distress and made best use of limited research resources. Challenges concerned communication and scheduling. Researcher support for PIR involvement was resource intensive. Discussion and Conclusions Clearly defined roles with identified training and support facilitated involvement in different aspectsPublic Involvement in Research members of the research team: Gail Capstick, Marion Cowie, Derek Hope, Rita Hewitt, Alex Mendoza, John Willmott. Also the involvement of Steven Iliffe and Heather Gag
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