58,506 research outputs found
The bioarchaeology of Anglo-Saxon Yorkshire: present and future perspectives
The Anglo-Saxon period in Yorkshire - in terms of our knowledge of those questions which bioarchaeological studies are conventionally used to address - remains very much an unknown quantity, We can hardly claim even to know whether these questions are indeed appropriate in the Anglo-Saxon period. To some extent this reflects the nature of the Anglo-Saxon deposits so far encountered, in which preservation of the less durable organic remains has been very limited. The nature of Anglo-Saxon occupation, with a bias towards rural settlements of a kind whicb have generally left only faint traces in the ground, means that there are no deeply stratified richly organic deposits of the kind revealed in some Roman and Viking Age phases in major urban centres, of which only York is weIl known in the region. The Anglo-Saxon period thus presents exceptional challenges to the environmental archaeologist, and ones which closely parallel those for the Iron Age. It is a period for which the kind of assemblages traditionally provided by bioarchaeologica1 studies are most urgently needed, to define environment and land use, resource exploitation, living conditions, trade and exchange, as well as aspects of craft-working and industrial activities. In addition, the period in Yorkshire presents special problems concerning the status of individual rural or ecclesiastical settlements, particularly the nature of York as a possible wic. For the purposes of this paper (and in view of the complexities of the archaeology of the 5th to 11th centuries), we have elected to discuss only such biological material as .falls after the end of the Roman period (as generally accepted) and before the first significant waves of Scandinavian invasion in the mid 9th century
Recirculation effects produced by a pair of heated jets impinging on a ground plane
Exhaust recirculation effects produced by two heated jets impinging on ground plan
Dynamical self-assembly of dipolar active Brownian particles in two dimensions
Based on Brownian Dynamics (BD) simulations, we study the dynamical self-assembly of active Brownian particles with dipole–dipole interactions, stemming from a permanent point dipole at the particle center. The propulsion direction of each particle is chosen to be parallel to its dipole moment. We explore a wide range of motilities and dipolar coupling strengths and characterize the corresponding behavior based on several order parameters. At low densities and low motilities, the most important structural phenomenon is the aggregation of the dipolar particles into chains. Upon increasing the particle motility, these chain-like structures break, and the system transforms into a weakly correlated isotropic fluid. At high densities, we observe that the motility-induced phase separation is strongly suppressed by the dipolar coupling. Once the dipolar coupling dominates the thermal energy, the phase separation disappears, and the system rather displays a flocking state, where particles form giant clusters and move collective along one direction. We provide arguments for the emergence of the flocking behavior, which is absent in the passive dipolar system.TU Berlin, Open-Access-Mittel - 2020DFG, 65143814, GRK 1524: Self-Assembled Soft-Matter Nanostructures at Interface
Decay of an isolated monopole into a Dirac monopole configuration
We study numerically the detailed structure and decay dynamics of isolated
monopoles in conditions similar to those of their recent experimental
discovery. We find that the core of a monopole in the polar phase of a spin-1
Bose-Einstein condensate contains a small half-quantum vortex ring. Well after
the creation of the monopole, we observe a dynamical quantum phase transition
that destroys the polar phase. Strikingly, the resulting ferromagnetic order
parameter exhibits a Dirac monopole in its synthetic magnetic field.Comment: 6 pages, 5 figure
Generic model for tunable colloidal aggregation in multidirectional fields
Based on Brownian Dynamics computer simulations in two dimensions we
investigate aggregation scenarios of colloidal particles with directional
interactions induced by multiple external fields. To this end we propose a
model which allows continuous change in the particle interactions from
point-dipole-like to patchy-like (with four patches). We show that, as a result
of this change, the non-equilibrium aggregation occurring at low densities and
temperatures transforms from conventional diffusion-limited cluster aggregation
(DLCA) to slippery DLCA involving rotating bonds; this is accompanied by a
pronounced change of the underlying lattice structure of the aggregates from
square-like to hexagonal ordering. Increasing the temperature we find a
transformation to a fluid phase, consistent with results of a simple mean-field
density functional theory
Mode-selective toroidal mirrors for unstable resonator planar waveguide and thin slab solid-state lasers
Coherent states on spheres
We describe a family of coherent states and an associated resolution of the
identity for a quantum particle whose classical configuration space is the
d-dimensional sphere S^d. The coherent states are labeled by points in the
associated phase space T*(S^d). These coherent states are NOT of Perelomov type
but rather are constructed as the eigenvectors of suitably defined annihilation
operators. We describe as well the Segal-Bargmann representation for the
system, the associated unitary Segal-Bargmann transform, and a natural
inversion formula. Although many of these results are in principle special
cases of the results of B. Hall and M. Stenzel, we give here a substantially
different description based on ideas of T. Thiemann and of K. Kowalski and J.
Rembielinski. All of these results can be generalized to a system whose
configuration space is an arbitrary compact symmetric space. We focus on the
sphere case in order to be able to carry out the calculations in a
self-contained and explicit way.Comment: Revised version. Submitted to J. Mathematical Physic
The School Improvement Partnership Programme: Using Collaboration and Enquiry to tackle Educational Inequity
No abstract available
On the Theory of Killing Orbits in Space-Time
This paper gives a theoretical discussion of the orbits and isotropies which
arise in a space-time which admits a Lie algebra of Killing vector fields. The
submanifold structure of the orbits is explored together with their induced
Killing vector structure. A general decomposition of a space-time in terms of
the nature and dimension of its orbits is given and the concept of stability
and instability for orbits introduced. A general relation is shown linking the
dimensions of the Killing algebra, the orbits and the isotropies. The
well-behaved nature of "stable" orbits and the possible miss-behaviour of the
"unstable" ones is pointed out and, in particular, the fact that independent
Killing vector fields in space-time may not induce independent such vector
fields on unstable orbits. Several examples are presented to exhibit these
features. Finally, an appendix is given which revisits and attempts to clarify
the well-known theorem of Fubini on the dimension of Killing orbits.Comment: Latex, 19 pages, no figur
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