1,164 research outputs found
Production of heralded pure single photons from imperfect sources using cross phase modulation
Realistic single-photon sources do not generate single photons with
certainty. Instead they produce statistical mixtures of photons in Fock states
and vacuum (noise). We describe how to eliminate the noise in the
output of the sources by means of another noisy source or a coherent state and
cross phase modulation (XPM). We present a scheme which announces the
production of pure single photons and thus eliminates the vacuum contribution.
This is done by verifying a XPM related phase shift with a Mach-Zehnder
interferometer.Comment: 8 pages, 8 EPS figures, RevTeX4. Following changes have been made in
v.3: Title and abstract slightly changed; numerous minor revisions and
clarifications within the text; an appendix with three new figures has been
added. In version v4 we have included a supplementary analysis of our scheme
that takes into account absorption losses. Our analysis is heuristic and
based on a phenomenological model, which is independent of the physical
realization of the proposed scheme. We have estimated upper bounds up to
which absorption losses can be tolerated, so as our scheme to improve the
efficiency of single photon sources still works. Accepted for publication in
Phys. Rev.
Microbiological quality of anti-tuberculosis drugs commonly used at dots centres and pharmacies within Kaduna Metropolis, Kaduna, Nigeria
Medicinal drugs of low-quality likely due to microbial contamination can result in increased morbidity and mortality thereby reducing the human population and may also result in emergence of resistant strain organisms in the environment. Studies suggest that there are a lot of counterfeit and substandard anti-tuberculosis drugs in circulation especially in Africa that are used for the treatment and control of tuberculosis whose damage on public health were mostly underestimated. Research on microbiological quality of anti-TB drugs is regrettably inadequate and scarce with most of the researches focused only on determining the active pharmaceutical ingredients of the drugs. This research aimed at assessing the microbiological quality of the anti-TB drugs used at DOTS Centres and Pharmacies within Kaduna metropolis, specifically to determine the total aerobic microbial count, total combined yeast and mould counts, the presence of indicator organisms; Escherichia coli, Salmonella species, Staphylococcus aureus and Pseudomonas aeruginosa as well as the susceptibility of the isolates to standard antibiotics. A stratified random sampling was used. A total of fifty-two (52) samples comprising of Rifampicin, Pyrazinamide, Isoniazid, Ethambutol and 4FDC were collected for the study. Methods specified in the United States Pharmacopoeia (USP, 2019) under the test for specified organisms and enumeration test were adopted for this research work. The study conducted established that the anti-TB drugs used at DOTS centres and Pharmacies within Kaduna metropolis, Kaduna, Nigeria do not contain any of the indicator organisms but some of the selected anti-TB drugs are contaminated with other strains of microorganisms with some not meeting the requirement for total aerobic microbial count and total yeast and mould count. The microbial contaminants found include species of; Bacillus, Klebsiella, Enterobacter, Penicillium, Fusarium, Alterneria, Curvularia, Aspergillus, Candida and Sporotricum. Some of the selected isolates obtained from the selected anti-TB drugs were not susceptible to the standard antibiotics used; Augmentin, Chloramphenicol, Ciprofloxacin, Gentamicin, Amoxicillin and Ofloxacin, with highest resistance recorded in Amoxicillin for all the bacterial isolates. However, all the Candida species were susceptible to the antifungal drugs; Ketoconazole, Fluconazole, Clotrimazole and Itraconazole
Heralded single-photon generation using imperfect single-photon sources and a two-photon-absorbing medium
We propose a setup for a heralded, i.e. announced generation of a pure
single-photon state given two imperfect sources whose outputs are represented
by mixtures of the single-photon Fock state with the vacuum
. Our purification scheme uses beam splitters, photodetection and a
two-photon-absorbing medium. The admixture of the vacuum is fully eliminated.
We discuss two potential realizations of the scheme.Comment: 22 pages, 8 figures (LaTeX). In version v2 we have slightly modified
our setup so as to increase the success probability of single-photon
generation by a factor of two. In addition, in an appendix we discuss
alternative realizations of single-photon generation without a Mach-Zehnder
interferometer. Three new figures have been added. Version v3 is a revised
version published in Phys. Rev. A. It contains numerous minor corrections and
clarifications. A new figure has been added in order to clarify our
convention regarding labelling the field modes. The action of the beam
splitters in the Schroedinger picture is introduced. A new reference has been
include
Recommended from our members
The U.S. Support Program to IAEA Safeguards - How It Works
The U.S. Support Program to International Atomic Energy Agency (IAEA) Safeguards (USSP) was established in 1977 to transfer US technology and expertise to assist the IAEA Department of Safeguards because its limited budget and scope would not allow for R&D activities and the procurement of specialized or customized equipment. Over the years, the USSP and the Department of Safeguards have worked together continuously to develop and improve processes for requesting, selecting, and managing projects that support the Safeguards verification mission. This paper will discuss the main USSP processes for accepting and processing Safeguards requests, and managing and reporting task progress
Recommended from our members
Effects of Intravenous Ketamine on Explicit and Implicit Measures of Suicidality in Treatment-Resistant Depression
Background
Intravenous ketamine has shown rapid antidepressant effects in early trials, making it a potentially attractive candidate for depressed patients at imminent risk of suicide. The Implicit Association Test (IAT), a performance-based measure of association between concepts, may have utility in suicide assessment.
Methods
Twenty-six patients with treatment-resistant depression were assessed using the suicidality item of the Montgomery-Asberg Depression Rating Scale (MADRS-SI) 2 hours before and 24 hours following a single subanesthetic dose of intravenous ketamine. Ten patients also completed IATs assessing implicit suicidal associations at comparable time points. In a second study, nine patients received thrice-weekly ketamine infusions over a 12-day period.
Results
Twenty-four hours after a single infusion, MADRS-SI scores were reduced on average by 2.08 points on a 0 to 6 scale (p < .001; d = 1.37), and 81% of patients received a rating of 0 or 1 postinfusion. Implicit suicidal associations were also reduced following ketamine (p = .003; d = 1.36), with reductions correlated across implicit and explicit measures. MADRS-SI reductions were sustained for 12 days by repeated-dose ketamine (p < .001; d = 2.42).
Conclusions
These preliminary findings support the premise that ketamine has rapid beneficial effects on suicidal cognition and warrants further study.Psycholog
Venus Interior Structure Mission (VISM): Establishing a Seismic Network on Venus
Magellan radar data show the surface of Venus to contain a wide range of geologic features (large volcanoes, extensive rift valleys, etc.). Although networks of interconnecting zones of deformation are identified, a system of spreading ridges and subduction zones like those that dominate the tectonic style of the Earth do not appear to be present. In addition, the absence of a mantle low-viscosity zone suggests a strong link between mantle dynamics and the surface. As a natural follow-on to the Magellan mission, establishing a network of seismometers on Venus will provide detailed quantitative information on the large scale interior structure of the planet. When analyzed in conjunction with image, gravity, and topography information, these data will aid in constraining mechanisms that drive surface deformation
Effects of Intravenous Ketamine on Explicit and Implicit Measures of Suicidality in Treatment-Resistant Depression
Background
Intravenous ketamine has shown rapid antidepressant effects in early trials, making it a potentially attractive candidate for depressed patients at imminent risk of suicide. The Implicit Association Test (IAT), a performance-based measure of association between concepts, may have utility in suicide assessment.
Methods
Twenty-six patients with treatment-resistant depression were assessed using the suicidality item of the Montgomery-Asberg Depression Rating Scale (MADRS-SI) 2 hours before and 24 hours following a single subanesthetic dose of intravenous ketamine. Ten patients also completed IATs assessing implicit suicidal associations at comparable time points. In a second study, nine patients received thrice-weekly ketamine infusions over a 12-day period.
Results
Twenty-four hours after a single infusion, MADRS-SI scores were reduced on average by 2.08 points on a 0 to 6 scale (p < .001; d = 1.37), and 81% of patients received a rating of 0 or 1 postinfusion. Implicit suicidal associations were also reduced following ketamine (p = .003; d = 1.36), with reductions correlated across implicit and explicit measures. MADRS-SI reductions were sustained for 12 days by repeated-dose ketamine (p < .001; d = 2.42).
Conclusions
These preliminary findings support the premise that ketamine has rapid beneficial effects on suicidal cognition and warrants further study.Psycholog
Why alternative teenagers self-harm: exploring the link between non-suicidal self-injury, attempted suicide and adolescent identity
Background:
The term âself-harmâ encompasses both attempted suicide and non-suicidal self-injury (NSSI). Specific adolescent subpopulations such as ethnic or sexual minorities, and more controversially, those who identify as âAlternativeâ (Goth, Emo) have been proposed as being more likely to self-harm, while other groups such as âJocksâ are linked with protective coping behaviours (for example exercise). NSSI has autonomic (it reduces negative emotions) and social (it communicates distress or facilitates group âbondingâ) functions. This study explores the links between such aspects of self-harm, primarily NSSI, and youth subculture.<p></p>
Methods:
An anonymous survey was carried out of 452 15 year old German school students. Measures included: identification with different youth cultures, i.e. Alternative (Goth, Emo, Punk), Nerd (academic) or Jock (athletic); social background, e.g. socioeconomic status; and experience of victimisation. Self-harm (suicide and NSSI) was assessed using Self-harm Behavior Questionnaire and the Functional Assessment of Self-Mutilation (FASM).<p></p>
Results:
An âAlternativeâ identity was directly (râââ0.3) and a âJockâ identity inversely (râââ-0.1) correlated with self-harm. âAlternativeâ teenagers self-injured more frequently (NSSI 45.5% vs. 18.8%), repeatedly self-injured, and were 4â8 times more likely to attempt suicide (even after adjusting for social background) than their non-Alternative peers. They were also more likely to self-injure for autonomic, communicative and social reasons than other adolescents.<p></p>
Conclusions:
About half of âAlternativeâ adolescentsâ self-injure, primarily to regulate emotions and communicate distress. However, a minority self-injure to reinforce their group identity, i.e. âTo feel more a part of a groupâ
Bregman Voronoi Diagrams: Properties, Algorithms and Applications
The Voronoi diagram of a finite set of objects is a fundamental geometric
structure that subdivides the embedding space into regions, each region
consisting of the points that are closer to a given object than to the others.
We may define many variants of Voronoi diagrams depending on the class of
objects, the distance functions and the embedding space. In this paper, we
investigate a framework for defining and building Voronoi diagrams for a broad
class of distance functions called Bregman divergences. Bregman divergences
include not only the traditional (squared) Euclidean distance but also various
divergence measures based on entropic functions. Accordingly, Bregman Voronoi
diagrams allow to define information-theoretic Voronoi diagrams in statistical
parametric spaces based on the relative entropy of distributions. We define
several types of Bregman diagrams, establish correspondences between those
diagrams (using the Legendre transformation), and show how to compute them
efficiently. We also introduce extensions of these diagrams, e.g. k-order and
k-bag Bregman Voronoi diagrams, and introduce Bregman triangulations of a set
of points and their connexion with Bregman Voronoi diagrams. We show that these
triangulations capture many of the properties of the celebrated Delaunay
triangulation. Finally, we give some applications of Bregman Voronoi diagrams
which are of interest in the context of computational geometry and machine
learning.Comment: Extend the proceedings abstract of SODA 2007 (46 pages, 15 figures
Experimental characterization of universal one-way quantum computing
We report the characterization of a universal set of logic gates for one-way quantum computing using a four-photon 'star' cluster state generated by fusing photons from two independent photonic crystal fibre sources. We obtain a fidelity for the cluster state of 0.66 ± 0.01 with respect to the ideal case. We perform quantum process tomography to completely characterize a controlled-NOT, Hadamard and T gate all on the same compact entangled resource. Together, these operations make up a universal set of gates such that arbitrary quantum logic can be efficiently constructed from combinations of them. We find process fidelities with respect to the ideal cases of 0.64 ± 0.01 for the CNOT, 0.67 ± 0.03 for the Hadamard and 0.76 ± 0.04 for the T gate. The characterization of these gates enables the simulation of larger protocols and algorithms. As a basic example, we simulate a Swap gate consisting of three concatenated CNOT gates. Our work provides some pragmatic insights into the prospects for building up to a fully scalable and fault-tolerant one-way quantum computer with photons in realistic conditions
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