610 research outputs found
The SPAIR method: Isolating incident and reflected directional wave spectra in multidirectional wave basins
Wave tank tests aiming to reproduce realistic or site specific conditions will commonly involve using directionally spread, short-crested sea states. The measurement of these directional characteristics is required for the purposes of calibrating and validating the modelled sea state. Commonly used methods of directional spectrumreconstruction, based on directional spreading functions, have an inherent level of uncertainty associated with them. In this paper we aim to reduce the uncertainty in directional spectrum validation by introducing the SPAIR (Single-summation PTPD Approach with In-line Reflections) method, in combination with a directional wave gauge array. A variety of wave conditions were generated in the FloWave Ocean Energy Research Facility, Edinburgh, UK, to obtain a range of sea state and reflection scenarios. The presented approach is found to provide improved estimates of directional spectra over standardmethods, reducing the mean apparent directional deviation down to below 6% over the range of sea states. Additionally, the method isolates incident and reflected spectra in both the frequency and time domain, and can separate these wave systems over 360°. The accuracy of themethod is shown to be only slightly sensitive to the level of in-line reflectionpresent,but at present cannot dealwithoblique reflections. The SPAIRmethod, as presented or with slightmodification, will allow complex directional sea states to be validated more effectively, enabling multidirectional wave basins to simulate realistic wave scenarios with increased confidence
Two-body correlations and the superfluid fraction for nonuniform systems
We extend the one-body phase function upper bound on the superfluid fraction
in a periodic solid (a spatially ordered supersolid) to include two-body phase
correlations. The one-body current density is no longer proportional to the
gradient of the one-body phase times the one-body density, but rather it
depends also on two-body correlation functions. The equations that
simultaneously determine the one-body and two-body phase functions require a
knowledge of one-, two-, and three-body correlation functions. The approach can
also be extended to disordered solids. Fluids, with two-body densities and
two-body phase functions that are translationally invariant, cannot take
advantage of this additional degree of freedom to lower their energy.Comment: 13 page
Visible-light photoredox catalysis enables the biomimetic synthesis of nyingchinoids A, B, and D, and rasumatranin D
German editionThe total synthesis of nyingchinoids A and B has been achieved through successive rearrangements of a 1,2-dioxane intermediate that was assembled using a visible-light photoredox-catalysed aerobic [2+2+2] cycloaddition. Nyingchinoid D was synthesised with a competing [2+2] cycloaddition. Based on NMR data and biosynthetic speculation, we proposed a structure revision of the related natural product rasumatranin D, which was confirmed through total synthesis. Under photoredox conditions, we observed the conversion of a cyclobutane into a 1,2-dioxane through retro-[2+2] cycloaddition followed by aerobic [2+2+2] cycloaddition.Jacob D. Hart, Laura Burchill, Aaron J. Day, Christopher G. Newton, Christopher J. Sumby, David M. Huang, and Jonathan H. Georg
Physical restraint in residential child care : the experiences of young people and residential workers
There have long been concerns about the use of physical restraint in residential care. This paper presents the findings of a qualitative study which explores the experiences of children, young people and residential workers about physical restraint. The research identifies the dilemmas and ambiguities for both staff and young people, and participants discuss the situations where they feel physical restraint is appropriate as well as their concerns about unjustified or painful restraints. They describe the negative emotions involved in restraint but also those situations where, through positive relationships and trust, restraint can help young people through unsafe situations
Theory of Supersolidity
After reviewing some experimental facts, and early theories, I sketch the
Hartree-Fock description of Boson solids, emphasizing the contrast with the
Fermion case in that the natural solution is a product of local wave-functions.
I then investigate the Boson Hubbard model to demonstrate that the local
functions are not orthogonal and exemplify a novel state of matter which has
superflow but not ODLRO, below a cooperative thermal transition. I then discuss
whether or not these ideas actually apply to solid He
Entanglement, Bell Inequalities and Decoherence in Particle Physics
We demonstrate the relevance of entanglement, Bell inequalities and
decoherence in particle physics. In particular, we study in detail the features
of the ``strange'' system as an example of entangled
meson--antimeson systems. The analogies and differences to entangled spin--1/2
or photon systems are worked, the effects of a unitary time evolution of the
meson system is demonstrated explicitly. After an introduction we present
several types of Bell inequalities and show a remarkable connection to CP
violation. We investigate the stability of entangled quantum systems pursuing
the question how possible decoherence might arise due to the interaction of the
system with its ``environment''. The decoherence is strikingly connected to the
entanglement loss of common entanglement measures. Finally, some outlook of the
field is presented.Comment: Lectures given at Quantum Coherence in Matter: from Quarks to Solids,
42. Internationale Universit\"atswochen f\"ur Theoretische Physik,
Schladming, Austria, Feb. 28 -- March 6, 2004, submitted to Lecture Notes in
Physics, Springer Verlag, 45 page
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Neutron structure function and inclusive DIS from H-3 and He-3 at large Bjorken-x
A detailed study of inclusive deep inelastic scattering (DIS) from mirror A =
3 nuclei at large values of the Bjorken variable x is presented. The main
purpose is to estimate the theoretical uncertainties on the extraction of the
neutron DIS structure function from such nuclear measurements. On one hand,
within models in which no modification of the bound nucleon structure functions
is taken into account, we have investigated the possible uncertainties arising
from: i) charge symmetry breaking terms in the nucleon-nucleon interaction, ii)
finite Q**2 effects neglected in the Bjorken limit, iii) the role of different
prescriptions for the nucleon Spectral Function normalization providing baryon
number conservation, and iv) the differences between the virtual nucleon and
light cone formalisms. Although these effects have been not yet considered in
existing analyses, our conclusion is that all these effects cancel at the level
of ~ 1% for x < 0.75 in overall agreement with previous findings. On the other
hand we have considered several models in which the modification of the bound
nucleon structure functions is accounted for to describe the EMC effect in DIS
scattering from nuclei. It turns out that within these models the cancellation
of nuclear effects is expected to occur only at a level of ~ 3%, leading to an
accuracy of ~ 12 % in the extraction of the neutron to proton structure
function ratio at x ~ 0.7 -0.8$. Another consequence of considering a broad
range of models of the EMC effect is that the previously suggested iteration
procedure does not improve the accuracy of the extraction of the neutron to
proton structure function ratio.Comment: revised version to appear in Phys. Rev. C; main modifications in
Section 4; no change in the conclusion
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
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