7,723 research outputs found
Heralded phase-contrast imaging using an orbital angular momentum phase-filter
We utilise the position and orbital angular momentum (OAM) correlations between the signal and idler photons generated in the down-conversion process to obtain ghost images of a phase object. By using an OAM phase filter, which is non-local with respect to the object, the images exhibit isotropic edge-enhancement. This imaging technique is the first demonstration of a full-field, phase-contrast imaging system with non-local edge enhancement, and enables imaging of phase objects using significantly fewer photons than standard phase-contrast imaging techniques
Imaging with a small number of photons
Low-light-level imaging techniques have application in many diverse fields,
ranging from biological sciences to security. We demonstrate a single-photon
imaging system based on a time-gated inten- sified CCD (ICCD) camera in which
the image of an object can be inferred from very few detected photons. We show
that a ghost-imaging configuration, where the image is obtained from photons
that have never interacted with the object, is a useful approach for obtaining
images with high signal-to-noise ratios. The use of heralded single-photons
ensures that the background counts can be virtually eliminated from the
recorded images. By applying techniques of compressed sensing and associated
image reconstruction, we obtain high-quality images of the object from raw data
comprised of fewer than one detected photon per image pixel.Comment: 9 pages, 4 figure
Symmetrical and asymmetrical outcomes of leader anger expression: a qualitative study of army personnel
Recent studies have highlighted the utility of anger at work, suggesting that anger can have positive outcomes. Using the Dual Threshold Model, we assess the positive and negative consequences of anger expressions at work and focus on the conditions under which expressions of anger crossing the impropriety threshold are perceived as productive or counterproductive by observers or targets of that anger. To explore this phenomenon, we conducted a phenomenological study (n = 20) to probe the lived experiences of followers (as observers and targets) associated with anger expressions by military leaders. The nature of task (e.g. the display rules prescribed for combat situations) emerged as one condition under which the crossing of the impropriety threshold leads to positive outcomes of anger expressions. Our data reveal tensions between emotional display rules and emotional display norms in the military, thereby fostering paradoxical attitudes toward anger expression and its consequences among followers. Within this paradoxical space, anger expressions have both positive (asymmetrical) and negative (symmetrical) consequences. We place our findings in the context of the Dual Threshold Model, discuss the practical implications of our research and offer avenues for future studies
Critical behavior of weakly interacting bosons: A functional renormalization group approach
We present a detailed investigation of the momentum-dependent self-energy
Sigma(k) at zero frequency of weakly interacting bosons at the critical
temperature T_c of Bose-Einstein condensation in dimensions 3<=D<4. Applying
the functional renormalization group, we calculate the universal scaling
function for the self-energy at zero frequency but at all wave vectors within
an approximation which truncates the flow equations of the irreducible vertices
at the four-point level. The self-energy interpolates between the critical
regime k > k_c, where k_c is the
crossover scale. In the critical regime, the self-energy correctly approaches
the asymptotic behavior Sigma(k) \propto k^{2 - eta}, and in the
short-wavelength regime the behavior is Sigma(k) \propto k^{2(D-3)} in D>3. In
D=3, we recover the logarithmic divergence Sigma(k) \propto ln(k/k_c)
encountered in perturbation theory. Our approach yields the crossover scale k_c
as well as a reasonable estimate for the critical exponent eta in D=3. From our
scaling function we find for the interaction-induced shift in T_c in three
dimensions, Delta T_c / T_c = 1.23 a n^{1/3}, where a is the s-wave scattering
length and n is the density, in excellent agreement with other approaches. We
also discuss the flow of marginal parameters in D=3 and extend our truncation
scheme of the renormalization group equations by including the six- and
eight-point vertex, which yields an improved estimate for the anomalous
dimension eta \approx 0.0513. We further calculate the constant lim_{k->0}
Sigma(k)/k^{2-eta} and find good agreement with recent Monte-Carlo data.Comment: 23 pages, 7 figure
Self-energy and critical temperature of weakly interacting bosons
Using the exact renormalization group we calculate the momentum-dependent
self-energy Sigma (k) at zero frequency of weakly interacting bosons at the
critical temperature T_c of Bose-Einstein condensation in dimensions 3 <= D <
4. We obtain the complete crossover function interpolating between the critical
regime k << k_c, where Sigma (k) propto k^{2 - eta}, and the short-wavelength
regime k >> k_c, where Sigma (k) propto k^{2 (D-3)} in D> 3 and Sigma (k)
\propto ln (k/k_c) in D=3. Our approach yields the crossover scale k_c on the
same footing with a reasonable estimate for the critical exponent eta in D=3.
From our Sigma (k) we find for the interaction-induced shift of T_c in three
dimensions Delta T_c / T_c approx 1.23 a n^{1/3}, where a is the s-wave
scattering length and n is the density.Comment: 4 pages,1 figur
Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy
ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to
provide estimates of its hot young star population. Our approach differs from
previous investigations in that we are able to distinguish between the regions
in which different infrared fine-structure lines form, using complementary
ground-based observations. The high excitation nebular [SIV] emission is formed
in a very compact region, which we attribute to the central super-star-nucleus,
and lower excitation [NeII] nebular emission originates in the galactic core.
We use photo-ionization modelling coupled with the latest theoretical O-star
flux distributions to derive effective stellar temperatures and ionization
parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK,
logQ<8 for the larger core. Results are supported by more sophisticated
calculations using evolutionary synthesis models. We assess the contribution
that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]).
From our Br(alpha) flux, the 2" nucleus contains the equivalent of
approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old;
the 20" core contains about 2500 O7V star equivalents, with a representative
age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30
Doradus region. These quantities are in good agreement with the observed mid-IR
dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters
embedded in cooler emission may be common in dwarf starbursts, observing a
galaxy solely with a large aperture may result in confusion. Neglecting the
spatial distribution of nebular emission in NGC5253, implies `global' stellar
temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the
observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.Comment: 16 pages, 7 figures, uses mn.sty, to appear in MNRA
Neural network models for influenza forecasting with associated uncertainty using Web search activity trends
Influenza affects millions of people every year. It causes a considerable amount of medical visits and hospitalisations as well as hundreds of thousands of deaths. Forecasting influenza prevalence with good accuracy can significantly help public health agencies to timely react to seasonal or novel strain epidemics. Although significant progress has been made, influenza forecasting remains a challenging modelling task. In this paper, we propose a methodological framework that improves over the state-of-the-art forecasting accuracy of influenza-like illness (ILI) rates in the United States. We achieve this by using Web search activity time series in conjunction with historical ILI rates as observations for training neural network (NN) architectures. The proposed models incorporate Bayesian layers to produce associated uncertainty intervals to their forecast estimates, positioning themselves as legitimate complementary solutions to more conventional approaches. The best performing NN, referred to as the iterative recurrent neural network (IRNN) architecture, reduces mean absolute error by 10.3% and improves skill by 17.1% on average in nowcasting and forecasting tasks across 4 consecutive flu seasons
An analysis of the Research Fellowship Scheme of the Royal College of Surgeons of England.
BACKGROUND: The Research Fellowship Scheme of the Royal College of Surgeons of England commenced in 1993 with the aim of exposing selected surgical trainees to research techniques and methodology, with the hope of having an impact on surgical research and increasing the cadre of young surgeons who might decide to pursue an academic career in surgery. Over 11 million pounds sterling (approximately US 20 million dollars) has been invested in 264 fellowships. The College wished to evaluate the impact of the Scheme on the careers of research fellows, surgical research, and patient care. As the 10th anniversary of the Scheme approached. STUDY DESIGN: Two-hundred and sixty research fellows whose current addresses were available were sent a questionnaire. Two-hundred and thirty-eight (91.5%) responded. RESULTS: Three-quarters of the research fellows conducted laboratory-based research, with most of the remainder conducting patient-based clinical research. One-third of the fellows who have reached consultant status have an academic component to their post. The total number of publications based on fellowship projects was 531, with a median impact factor of 3.5. Almost all fellows had been awarded a higher degree or were working toward this. Half of the fellows received subsequent funding for research, mostly awarded by national or international funding bodies. CONCLUSIONS: The Research Fellowship Scheme of the Royal College of Surgeons of England has successfully supported many trainee surgeons in the initial phase of their research career. It has helped surgical research by increasing the pool of surgeons willing to embark on an academic career. Indirectly, patient care has benefited by promoting an evidence-based culture among young surgeons. Such schemes are relevant to surgical training programs elsewhere if more young surgeons are to be attracted into academic surgery
Impact of swimming on chronic suppurative otitis media in Aboriginal children: a randomised controlled trial
Objectives: To measure the impact of 4 weeks of daily swimming on rates of ear discharge among Aboriginal children with a tympanic membrane perforation (TMP) and on the microbiology of the nasopharynx and middle ear.Design, setting and participants: A randomised controlled trial involving 89 Aboriginal children (aged 5–12 years) with a TMP, conducted in two remote Northern Territory Aboriginal communities from August to December 2009.Intervention: 4 school weeks of daily swimming lessons (45 minutes) in a chlorinated pool.Main outcome measures: Proportions of children with ear discharge and respiratory and opportunistic bacteria in the nasopharynx and middle ear.Results: Of 89 children randomly assigned to the swimming or non-swimming groups, 58 (26/41 swimmers and 32/48 non-swimmers) had ear discharge at baseline. After 4 weeks, 24 of 41 swimmers had ear discharge compared with 32 of 48 non-swimmers (risk difference, − 8% (95% CI, − 28% to 12%). There were no statistically significant changes in the microbiology of the nasopharynx or middle ear in swimmers or non-swimmers. Streptococcus pneumoniae and non-typeable Haemophilus influenzae were the dominant organisms cultured from the nasopharynx, and H. influenzae, Staphylococcus aureus and Pseudomonas aeruginosa were the dominant organisms in the middle ear.Conclusions: Swimming lessons for Aboriginal children in remote communities should be supported, but it is unlikely that they will substantially reduce rates of chronic suppurative otitis media and associated bacteria in the nasopharynx and middle ear. However, swimming was not associated with increased risk of ear discharge and we found no reason to discourage it. 
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