778 research outputs found
Engineering the Frequency Spectrum of Bright Squeezed Vacuum via Group Velocity Dispersion in an SU(1,1) Interferometer
Bright squeezed vacuum, a promising tool for quantum information, can be
generated by high-gain parametric down-conversion. However, its frequency and
angular spectra are typically quite broad, which is undesirable for
applications requiring single-mode radiation. We tailor the frequency spectrum
of high-gain parametric down-conversion using an SU(1,1) interferometer
consisting of two nonlinear crystals with a dispersive medium separating them.
The dispersive medium allows us to select a narrow band of the frequency
spectrum to be exponentially amplified by high-gain parametric amplification.
The frequency spectrum is thereby narrowed from (56.5 +- 0.1) to (1.22 +- 0.02)
THz and, in doing so, the number of frequency modes is reduced from
approximately 50 to 1.82 +- 0.02. Moreover, this method provides control and
flexibility over the spectrum of the generated light through the timing of the
pump.Comment: 6 pages, 5 figure
Photon correlations for colloidal nanocrystals and their clusters
Images of semiconductor `dot in rods' and their small clusters are studied by
measuring the second-order correlation function with a spatially resolving ICCD
camera. This measurement allows one to distinguish between a single dot and a
cluster and, to a certain extent, to estimate the number of dots in a cluster.
A more advanced measurement is proposed, based on higher-order correlations,
enabling more accurate determination of the number of dots in a small cluster.
Nonclassical features of the light emitted by such a cluster are analyzed.Comment: 4 pages, 4 figure
Indefinite-mean Pareto photon distribution from amplified quantum noise
Extreme events appear in many physics phenomena, whenever the probability
distribution has a ''heavy tail'', differing very much from the equilibrium
one. Most unusual are the cases of power-law (Pareto) probability
distributions. Among their many manifestations in physics, from ''rogue waves''
in the ocean to L\'evy flights in random walks, Pareto dependences can follow
very different power laws. For some outstanding cases the power exponents are
less than 2, leading to indefinite mean values, let alone higher moments. Here
we present the first evidence of indefinite-mean Pareto distribution of photon
numbers at the output of nonlinear effects pumped by parametrically amplified
vacuum noise, known as bright squeezed vacuum (BSV). We observe a Pareto
distribution with power exponent 1.31 when BSV is used as a pump for
supercontinuum generation, and other heavy-tailed distributions (however with
definite moments) when it pumps optical harmonics generation. Unlike in other
fields, we can flexibly control the Pareto exponent by changing the
experimental parameters. This extremely fluctuating light is interesting for
ghost imaging and quantum thermodynamics as a resource to produce more
efficiently non-equilibrium states by single-photon subtraction, the latter we
demonstrate experimentally
Analysis of a spatio-temporal advection-diffusion model for human behaviors during a catastrophic event
In this work, using the theory of first-order macroscopic crowd models, we
introduce a compartmental advection-diffusion model, describing the
spatio-temporal dynamics of a population in different human behaviors (alert,
panic and control) during a catastrophic event. For this model, we prove the
local existence, uniqueness and regularity of a solution, as well as the
positivity and --boundedness of this solution. Then, in order to study the
spatio-temporal behavioral dynamics of a population during a catastrophic
event, we present several numerical simulations for different evacuation
scenarios.Comment: I will correct and modify some facts and I will submit again the new
versio
Coupled-cavity terahertz quantum cascade lasers for single mode operation
We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30-40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency
30-Day Postoperative Morbidity of Emergency Surgery for Obstructive Right- and Left-Sided Colon Cancer in Obese Patients: A Multicenter Cohort Study of the French Surgical Association
BACKGROUND: Emergency surgery impairs postoperative outcomes in colorectal cancer patients. No study has assessed the relationship between obesity and postoperative results in this setting.
OBJECTIVE: To compare the results of emergency surgery for obstructive colon cancer (OCC) in an obese patient population with those in overweight and normal weight patient groups.
METHODS: From 2000 to 2015, patients undergoing emergency surgery for OCC in French surgical centers members of the French National Surgical Association were included. Three groups were defined: normal weight (body mass index [BMI] < 25.0 kg/m2), overweight (BMI 25.0-29.9 kg/m2), and obese (BMI ≥30.0 kg/m2).
RESULTS: Of 1,241 patients, 329 (26.5%) were overweight and 143 (11.5%) were obese. Obese patients had significantly higher American society of anesthesiologists score, more cardiovascular comorbidity and more hemodynamic instability at presentation. Overall postoperative mortality and morbidity were 8 and 51%, respectively, with no difference between the 3 groups. For obese patients with left-sided OCC, stoma-related complications were significantly increased (8 vs. 5 vs. 15%, p = 0.02).
CONCLUSION: Compared with lower BMI patients, obese patients with OCC had a more severe presentation at admission but similar surgical management. Obesity did not increase 30-day postoperative morbidity except stoma-related complications for those with left-sided OCC
Guidance on the environmental risk assessment of plant pests
The European Food Safety Authority (EFSA) requested the Panel on Plant Health to develop a methodology for assessing the environmental risks posed by harmful organisms that may enter, establish and spread in the European Union. To do so, the Panel first reviewed the methods for assessing the environmental risks of plant pests that have previously been used in pest risk assessment. The limitations identified by the review led the Panel to define the new methodology for environmental risk assessment which is described in this guidance document. The guidance is primarily addressed to the EFSA PLH Panel and has been conceived as an enhancement of the relevant parts of the “Guidance on a harmonised framework for pest risk assessment and the identification and evaluation of pest risk management options by EFSA”. Emphasizing the importance of assessing the consequences on both the structural (biodiversity) and the functional (ecosystem services) aspects of the environment, this new approach includes methods for assessing both aspects for the first time in a pest risk assessment scheme. A list of questions has been developed for the assessor to evaluate the consequences for structural biodiversity and for ecosystem services in the current area of invasion and in the risk assessment area. To ensure the consistency and transparency of the assessment, a rating system has also been developed based on a probabilistic approach with an evaluation of the degree of uncertainty. Finally, an overview of the available risk reduction options for pests in natural environments is presented, minimum data requirements are described, and a glossary to support the common understanding of the principles of this opinion is provided
Scientific opinion on a quantitative pathway analysis of the likelihood of Tilletia indica M. introduction into EU with importation of US wheat
The European Commission requested EFSA to provide a scientific opinion on the USDA APHIS quantitative
pathway analysis on likelihood of Karnal bunt introduction with importation of US wheat for grain into EU and
desert durum wheat for grain into Italy. EFSA was also requested to indicate whether the US bunted kernel
standard would provide equivalent protection against introduction of Tilletia indica into EU, compared to the
existing EU import requirement. The Panel on Plant Health reviewed pathway scenarios, model and parameters
and found several shortcomings regarding model equations and parameter values, particularly a lack of scientific
evidence for the infection threshold. Simulations were computed, for importations of US wheat into EU and
desert durum wheat into Italy, based on original model and an updated model with revised parameter values.
Model output was teliospores number per hectare on soil surface of each EU country. Simulated teliospores
numbers entering EU were lower with the updated than with the original model. These results showed a high
uncertainty, underestimated with the original model, over the number of teliospores entering each EU country.
Sensitivity analysis showed several key parameters (proportion of bunted kernels in Arizona regulated counties,
number of Arizona positive hectares and number of teliospores per bunted kernel) strongly influencing number
of teliospores entering the EU. In addition, high sensitivity indices were obtained with the updated wheat model
for several parameters related to EU country characteristics. Further research is needed to refine parameter
values, to reduce uncertainty and to determine relationship between teliospores number on soil surface and
number of bunted kernels resulting from infection of a wheat plant. The Panel concluded that the US bunted
kernel standard does not provide a level of protection equivalent to EU requirements and that such level of
protection could only be warranted by measures which include testing at harvest and before shipment to detect T.
indica teliospores
Statement on a heat treatment to control Agrilus planipennis
In 2011, the EFSA Panel on Plant Health was asked by the European Commission to provide an opinion on a technical file submitted by the US Authorities to support a request to list a new heat treatment (60 °C/60 min) among the EU import requirements for wood of Agrilus planipennis host plants. After a thorough analysis of the documents provided the Panel concluded that, with a low uncertainty, A. planipennis is likely to survive the proposed heat treatment of 60 °C/60 min, and that, to ensure a control level of 99 % the temperature of the heat treatment of 60 min should be higher than 70 °C. Following the publication of this scientific opinion, the US Authorities submitted a new proposal to the European Commission, consisting in a new heat treatment (71.1 °C/60 min). The EFSA Panel on Plant Health was asked to consider whether this new proposal was within the scope of the published opinion and, if not, to clarify its conclusion and indicate what data would be needed to assess the effectiveness of the new treatment. The Panel concluded that the new proposal is not within the scope of the opinion as the data provided by the US Authorities cannot be used to evaluate the effectiveness of the new proposed heat treatment. An accurate assessment of the new proposed heat treatment (71.1 °C/60 min) would require an experiment including several temperatures higher than 70 °C (one corresponding to the proposed treatment). Regarding the data requirements for assessing the effectiveness of the new treatment, the Panel lists the information required in the checklist presented in the Panel’s draft guidance document on methodology for evaluation of the effectiveness of options to reduce the risk of introduction and spread of organisms harmful to plant health in the EU territory, currently under public consultation on EFSA website
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