762 research outputs found
Antisymmetry and channel coupling contributions to the absorption for p + alpha/d + 3He
To understand recently established empirical p + alpha potentials, RGM
calculations followed by inversion are made to study contributions of the d +
3He reaction channels and deuteron distortion effects to the p + alpha
potential. An equivalent study of the d + 3He potential is also presented. The
contributions of exchange non-locality to the absorption are simulated by
including an phenomenological imaginary potential in the RGM. These effects
alone strongly influence the shape of the imaginary potentials for both p +
alpha and d + 3He. The potentials local-equivalent to the fully
antisymmetrised-coupled channels calculations have a significant
parity-dependence in both real and imaginary components, which for p + alpha is
qualitatively similar to that found empirically. The effects on the potentials
of the further inclusion of deuteron distortion are also presented. The
inclusion of a spin-orbit term in the RGM, adds additional terms to the
phase-equivalent potential, most notably the comparatively large imaginary
spin-orbit term found empirically.Comment: 17 pages, Latex, 8 postscript figs, submitted to Nucl. Phys.
Determination of Li-6 -- He-4 interaction from multi-energy scattering data
We present the first successful potential model description of Li-6 -- He-4
scattering. The differential cross-sections for three energies and the vector
analyzing powers for two energies were fitted by a single potential with energy
dependent imaginary components. An essential ingredient is a set of Majorana
terms in each component. The potential was determined using a recently
developed direct data-to-potential inversion method which is a generalisation
of the IP S-matrix-to-potential inversion algorithm. We discuss the problems
related to this phenomenological approach, and discuss the relationship of our
results to existing and future theories.Comment: 9 pages plain LaTeX, 6 postscript figue
The stratigraphy, correlation, provenance and palaeogeography of the Skiddaw Group (Ordovician) in the English Lake District
A new lithostratigraphy is presented for the Skiddaw Group (lower Ordovician) of the English Lake District. Two stratigraphical belts are described. Five formations are defined in the Northern Fells Belt, ranging in age from Tremadoc to early Llanvirn. They are all mudstone or sandstone dominated, of turbidite origin; in ascending order they are named the Bitter Beck, Watch Hill, Hope Beck, Loweswater and Kirk Stile formations. Two formations are defined in the Central Fells Belt, ranging in age from late Arenig to Llanvirn. These are the Buttermere Formation - a major olistostrome deposit - overlain by the Tarn Moor Formation, consisting of turbidite mudstones with volcaniclastic turbidite sandstone beds. A revised graptolite and new acritarch biostratigraphy for the Skiddaw Group is presented with eight graptolite biozones and thirteen acritarch assemblages and sub-assemblages. The provenance of the group is assessed from detailed petrographical and geochemical work. This suggests derivation, in the early Ordovician, largely from an old inactive continental arc terrane lying to the south-east, with the appearance of juvenile volcanic material in the Llanvirn. Comparisons and correlations of the Skiddaw Group are made with the Isle of Man and eastern Ireland
Deuteron -- interaction by inversion of RGM S-matrix: determination of spin-orbit potential for spin-1 projectile
The iterative-perturbative (IP) procedure for S-matrix to potential inversion
is applied to spin-one projectiles for the restricted case of vector spin-orbit
interaction only. In order to evaluate this extension of IP inversion we have
inverted the multi-channel RGM of Kanada et al for deuterons
scattering from He with deuteron distortion and then compared the central
components with those derived from RGM with spin set to zero. Attention is
given to the question of how well the resulting potentials are established.
Reliable spin-1 inversion is demonstrated. Results relating to inversion, to
deuteron-nucleus interactions and to RGM are presented and suggest the range of
nuclear interaction information which the procedure makes possible. Unusual
non-locality and parity dependence effects are found; these are of possible
relevance to generic properties of nuclear potentials.Comment: 15 pages LaTeX plus 6 postscript figure
Introducing a novel mesh following technique for approximation-free robotic tool path trajectories
Modern tools for designing and manufacturing of large components with complex geometries allow more flexible production with reduced cycle times. This is achieved through a combination of traditional subtractive approaches and new additive manufacturing processes. The problem of generating optimum tool-paths to perform specific actions (e.g. part manufacturing or inspection) on curved surface samples, through numerical control machinery or robotic manipulators, will be increasingly encountered. Part variability often precludes using original design CAD data directly for toolpath generation (especially for composite materials), instead surface mapping software is often used to generate tessellated models. However, such models differ from precise analytical models and are often not suitable to be used in current commercially available path-planning software, since they require formats where the geometrical entities are mathematically represented thus introducing approximation errors which propagate into the generated toolpath. This work adopts a fundamentally different approach to such surface mapping and presents a novel Mesh Following Technique (MFT) for the generation of tool-paths directly from tessellated models. The technique does not introduce any approximation and allows smoother and more accurate surface following tool-paths to be generated. The background mathematics to the new MFT algorithm are introduced and the algorithm is validated by testing through an application example. Comparative metrology experiments were undertaken to assess the tracking performance of the MFT algorithms, compared to tool-paths generated through commercial software. It is shown that the MFT tool-paths produced 40% smaller errors and up to 66% lower dispersion around the mean values
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Application of reactors for testing neutron-induced upsets in commercial SRAMs
Reactor neutron environments can be used to test/screen the sensitivity of unhardened commercial SRAMs to low-LET neutron-induced upset. Tests indicate both thermal/epithermal (< 1 keV) and fast neutrons can cause upsets in unhardened parts. Measured upset rates in reactor environments can be used to model the upset rate for arbitrary neutron spectra
Far-from-equilibrium quantum many-body dynamics
The theory of real-time quantum many-body dynamics as put forward in Ref.
[arXiv:0710.4627] is evaluated in detail. The formulation is based on a
generating functional of correlation functions where the Keldysh contour is
closed at a given time. Extending the Keldysh contour from this time to a later
time leads to a dynamic flow of the generating functional. This flow describes
the dynamics of the system and has an explicit causal structure. In the present
work it is evaluated within a vertex expansion of the effective action leading
to time evolution equations for Green functions. These equations are applicable
for strongly interacting systems as well as for studying the late-time
behaviour of nonequilibrium time evolution. For the specific case of a bosonic
N-component phi^4 theory with contact interactions an s-channel truncation is
identified to yield equations identical to those derived from the 2PI effective
action in next-to-leading order of a 1/N expansion. The presented approach
allows to directly obtain non-perturbative dynamic equations beyond the widely
used 2PI approximations.Comment: 20 pp., 6 figs; submitted version with added references and typos
corrected
Fractional Quantum Hall Effect via Holography: Chern-Simons, Edge States, and Hierarchy
We present three holographic constructions of fractional quantum Hall effect
(FQHE) via string theory. The first model studies edge states in FQHE using
supersymmetric domain walls in N=6 Chern-Simons theory. We show that D4-branes
wrapped on CP^1 or D8-branes wrapped on CP^3 create edge states that shift the
rank or the level of the gauge group, respectively. These holographic edge
states correctly reproduce the Hall conductivity. The second model presents a
holographic dual to the pure U(N)_k (Yang-Mills-)Chern-Simons theory based on a
D3-D7 system. Its holography is equivalent to the level-rank duality, which
enables us to compute the Hall conductivity and the topological entanglement
entropy. The third model introduces the first string theory embedding of
hierarchical FQHEs, using IIA string on C^2/Z_n.Comment: 36 pages, 6 figures; v2: with an improved derivation of Hall
conductivity in section 3.2, typo corrections, and additional references; v3:
explanations and comments adde
Mixed-symmetry octupole and hexadecapole excitations in N=52 isotones
In addition to the well-established quadrupole mixed-symmetry states, octupole and hexadecapole excitations with mixed-symmetry character have been recently proposed for the N = 52 isotones 92Zr and 94Mo. We performed two inelastic proton-scattering experiments to study this kind of excitations in the heaviest stable N = 52 isotone 96Ru. From the combined experimental data of both experiments absolute transition strengths were extracted
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