3,233 research outputs found
Coherent and Squeezed Vacuum Light Interferometry: Parity detection hits the Heisenberg limit
The interference between coherent and squeezed vacuum light can produce path
entangled states with very high fidelities. We show that the phase sensitivity
of the above interferometric scheme with parity detection saturates the quantum
Cramer-Rao bound, which reaches the Heisenberg-limit when the coherent and
squeezed vacuum light are mixed in roughly equal proportions. For the same
interferometric scheme, we draw a detailed comparison between parity detection
and a symmetric-logarithmic-derivative-based detection scheme suggested by Ono
and Hofmann.Comment: Change in the format from aps to iop since we decided to submit it to
NJP; Minor changes in tex
Tunnelling time and tunnelling dynamics
The concept of 'tunnelling time' in the context of quantum particle tunnelling is reviewed. Various suggestions of linking the tunnelling dynamics with a characteristic time (real or complex) like the phase time, barrier interaction time (bounce time), presence time, etc. are analysed. A simple but fully quantal method of defining and estimating a real tunnelling time is examined in a variety of situations. The recently proposed idea of interpreting 'tunnelling time' as the cavity lifetime of a particle is also explored. We emphasize that proton or H-atom transfer reactions in double or triple wells offer systems in which the signature of the tunnelling time should be recognizable not just indirectly through the tunnelling splitting of spectral lines, but by following the relaxation dynamics of the subsystem that the proton or H atom leaves by tunnelling
Description of Drip-Line Nuclei within Relativistic Mean-Field Plus BCS Approach
Recently it has been demonstrated, considering Ni and Ca isotopes as
prototypes, that the relativistic mean-field plus BCS (RMF+BCS) approach
wherein the single particle continuum corresponding to the RMF is replaced by a
set of discrete positive energy states for the calculation of pairing energy
provides a good approximation to the full relativistic Hartree-Bogoliubov (RHB)
description of the ground state properties of the drip-line neutron rich
nuclei. The applicability of RMF+BCS is essentially due to the fact that the
main contribution to the pairing correlations is provided by the low-lying
resonant states. General validity of this approach is demonstrated by the
detailed calculations for the ground state properties of the chains of isotopes
of O, Ca, Ni, Zr, Sn and Pb nuclei. The TMA and NL-SH force parameter sets have
been used for the effective mean-field Lagrangian. Comprehensive results for
the two neutron separation energy, rms radii, single particle pairing gaps and
pairing energies etc. are presented. The Ca isotopes are found to exhibit
distinct features near the neutron drip line whereby it is found that further
addition of neutrons causes a rapid increase in the neutron rms radius with
almost no increase in the binding energy, indicating the occurrence of halos. A
comparison of these results with the available experimental data and with the
recent continuum relativistic Hartree-Bogoliubov (RCHB) calculations amply
demonstrates the validity and usefulness of this fast RMF+BCS approach.Comment: 59 pages, 40 figure
Electron transport properties of sub-3-nm diameter copper nanowires
Density functional theory and density functional tight-binding are applied to
model electron transport in copper nanowires of approximately 1 nm and 3 nm
diameters with varying crystal orientation and surface termination. The copper
nanowires studied are found to be metallic irrespective of diameter, crystal
orientation and/or surface termination. Electron transmission is highly
dependent on crystal orientation and surface termination. Nanowires oriented
along the [110] crystallographic axis consistently exhibit the highest electron
transmission while surface oxidized nanowires show significantly reduced
electron transmission compared to unterminated nanowires. Transmission per unit
area is calculated in each case, for a given crystal orientation we find that
this value decreases with diameter for unterminated nanowires but is largely
unaffected by diameter in surface oxidized nanowires for the size regime
considered. Transmission pathway plots show that transmission is larger at the
surface of unterminated nanowires than inside the nanowire and that
transmission at the nanowire surface is significantly reduced by surface
oxidation. Finally, we present a simple model which explains the transport per
unit area dependence on diameter based on transmission pathways results
Structure-(in)dependent interpretation of phrases in humans and LSTMs
In this study, we compared the performance of a long short-term memory (LSTM) neural network to the behavior of human participants on a language task that requires hierarchically structured knowledge. We show that humans interpret ambiguous noun phrases, such as second blue ball, in line with their hierarchical constituent structure. LSTMs, instead, only do so after unambiguous training, and they do not systematically generalize to novel items. Overall, the results of our simulations indicate that a model can behave hierarchically without relying on hierarchical constituent structure
Hierarchy in language interpretation: Evidence from behavioural experiments and computational modelling
It has long been recognised that phrases and sentences are organised hierarchically, but many computational models of language treat them as sequences of words without computing constituent structure. Against this background, we conducted two experiments which showed that participants interpret ambiguous noun phrases, such as second blue ball, in terms of their abstract hierarchical structure rather than their linear surface order. When a neural network model was tested on this task, it could simulate such “hierarchical” behaviour. However, when we changed the training data such that they were not entirely unambiguous anymore, the model stopped generalising in a human-like way. It did not systematically generalise to novel items, and when it was trained on ambiguous trials, it strongly favoured the linear interpretation. We argue that these models should be endowed with a bias to make generalisations over hierarchical structure in order to be cognitively adequate models of human language
Impact Sensitivity of RDX and Viton Compositions Prepared by Co-precipitation Method
Desensitisation of explosive materials using polymers is an important area in safe utilisation of explosives in various applications. The RDX/viton composition has been developed using co-precipitation method with varying content of viton, ranging from 5 to 35 wt per cent. RDX and viton were dissolved in acetone which is a common solvent for RDX and viton, and then the acetone was extracted from the solution by distillation resulting in homogeneous RDX/viton composition. Infrared spectroscopy studies indicated presence of RDX and viton in the resulting compositions. Thermogravimetric and differential thermal analysis studies made on yielded compositions confirmed that RDX is present in the composition in desired content. The shift in exotherm of RDX/viton composition as compared to RDX showed that polymer-bonded RDX compositions are more stable. The impact sensitivity studies showed that sensitivity of RDX/viton composition decreased with increasing content of viton. The similar trend was observed for friction sensitivity. The co-precipitation method has been found to be advantages to obtain homogeneous composition of RDX and viton (with viton content up to 25 wt per cent) as revealed by linear trend in sensitivity data measurements. It has been demonstrated that the sensitivity of RDX can be tailored within a wide range using viton so as to suit in desired applications.Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 287-291, DOI: http://dx.doi.org/10.14429/dsj.65.864
Impact of COVID-19 pandemic on ophthalmic presentations to an Australian outer metropolitan and rural emergency department: a retrospective comparative study.
BACKGROUND: To analyse ophthalmic presentations to an outer metropolitan and a rural emergency department (ED) during the first wave of the COVID-19 pandemic in New South Wales (NSW), Australia. METHODS: A retrospective comparative study of ophthalmic emergency presentations to Campbelltown Hospital (fifth busiest NSW metropolitan ED; population 310,000) and Bowral and District Hospital (rural ED; population 48,000) before and during COVID-19 was conducted. Patient demographics, triage category, referral source, diagnosis, length of stay, departure status, and follow-up location were assessed from coding data between March 1st to May 31st in 2019 and 2020, corresponding to the peak case numbers and restrictions during the first wave of the COVID-19 pandemic in NSW. Differences before and during COVID-19 were analysed using chi-squared tests or independent sample t-tests. RESULTS: There was no change in ophthalmic presentations at Campbelltown (n = 228 in 2019 vs. n = 232 in 2020; + 1.75%, p = 0.12) and an increase at Bowral (n = 100 in 2019 vs. n = 111 in 2020; + 11%, p < 0.01) during COVID-19. Urgent ophthalmic presentations (Triage Category 3) decreased at Bowral (p = 0.0075), while non-urgent ophthalmic presentations (Triage Category 5) increased at both hospitals (Campbelltown p < 0.05, Bowral p < 0.01). CONCLUSIONS: There was no change in the total number of ophthalmic presentations to an outer metropolitan and an increase to a rural ED during the first wave of the COVID-19 pandemic in New South Wales, Australia. A change in the type of ophthalmic presentations at these peripheral EDs suggest that a high demand for ophthalmic services remained despite the pandemic and its associated gathering and movement restrictions. A flexible healthcare delivery strategy, such as tele-ophthalmology, may optimise patient care during and after COVID-19
Origin of magnetic moments and presence of a resonating valence bond state in BaYIrO
While it was speculated that 5 systems would possess non-magnetic
~=~0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems
have invariably shown presence of magnetic moments so far. A puzzling case is
that of BaYIrO, which in spite of having a perfectly cubic structure
with largely separated Ir () ions, has consistently shown presence
of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation
(SR) measurements that a change in the magnetic environment of the
implanted muons in BaYIrO occurs as temperature is lowered below 10~K.
This observation becomes counterintuitive, as the estimated value of SOC
obtained by fitting the RIXS spectrum of BaYIrO with an atomic
model is found to be as high as 0.39~eV, meaning that the system within this
model is neither expected to possess moments nor exhibit temperature dependent
magnetic response. Therefore we argue that the atomic coupling
description is not sufficient to explain the ground state of such systems,
where despite having strong SOC, presence of hopping triggers delocalisation of
holes, resulting in spontaneous generation of magnetic moments. Our theoretical
calculations further indicate that these moments favour formation of
spin-orbital singlets in the case of BaYIrO, which is manifested in
SR experiments measured down to 60~mK.Comment: 20 Pages, 7 Figure
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