193 research outputs found
Quantum Speed Limit and Optimal Control of Many-Boson Dynamics
We extend the concept of quantum speed limit -- the minimal time needed to
perform a driven evolution -- to complex interacting many-body systems. We
investigate a prototypical many-body system, a bosonic Josephson junction, at
increasing levels of complexity: (a) within the two-mode approximation
{corresponding to} a nonlinear two-level system, (b) at the mean-field level by
solving the nonlinear Gross-Pitaevskii equation in a double well potential, and
(c) at an exact many-body level by solving the time-dependent many-body
Schr\"odinger equation. We propose a control protocol to transfer atoms from
the ground state of a well to the ground state of the neighbouring well.
Furthermore, we show that the detrimental effects of the inter-particle
repulsion can be eliminated by means of a compensating control pulse, yielding,
quite surprisingly, an enhancement of the transfer speed because of the
particle interaction -- in contrast to the self-trapping scenario. Finally, we
perform numerical optimisations of both the nonlinear and the (exact) many-body
quantum dynamics in order to further enhance the transfer efficiency close to
the quantum speed limit.Comment: 5 pages, 3 figures, and supplemental material (4 pages 1 figure
Autonomous Calibration of Single Spin Qubit Operations
Fully autonomous precise control of qubits is crucial for quantum information
processing, quantum communication, and quantum sensing applications. It
requires minimal human intervention on the ability to model, to predict and to
anticipate the quantum dynamics [1,2], as well as to precisely control and
calibrate single qubit operations. Here, we demonstrate single qubit autonomous
calibrations via closed-loop optimisations of electron spin quantum operations
in diamond. The operations are examined by quantum state and process
tomographic measurements at room temperature, and their performances against
systematic errors are iteratively rectified by an optimal pulse engineering
algorithm. We achieve an autonomous calibrated fidelity up to 1.00 on a time
scale of minutes for a spin population inversion and up to 0.98 on a time scale
of hours for a Hadamard gate within the experimental error of 2%. These results
manifest a full potential for versatile quantum nanotechnologies.Comment: 9 pages, 5 figure
Precise ultra fast single qubit control using optimal control pulses
Ultra fast and accurate quantum operations are required in many modern
scientific areas - for instance quantum information, quantum metrology and
magnetometry. However the accuracy is limited if the Rabi frequency is
comparable with the transition frequency due to the breakdown of the rotating
wave approximation (RWA). Here we report the experimental implementation of a
method based on optimal control theory, which does not suffer these
restrictions. We realised the most commonly used quantum gates - the Hadamard
(\pi/2 pulse) and NOT (\pi pulse) gates with fidelities
( and
), in an excellent agreement with the
theoretical predictions ( and
). Moreover, we demonstrate magnetic
resonance experiments both in the rotating and lab frames and we can
deliberately "switch" between these two frames. Since our technique is general,
it could find a wide application in magnetic resonance, quantum computing,
quantum optics and broadband magnetometry.Comment: New, updated version of the manuscript with supplementary informatio
Дослідження впливу фосфатів на біопродуктивність Chlorella vulgaris
Підвищений вміст фосфору у водоймах є основною причиною їхньої евтрофікації.
Евтрофікація – процес зростання водної рослинності, який відбувається внаслідок
перевищення балансу поживних речовин. Він супроводжується надмірним розвитком
водоростей, особливо зелених, синьо-зелених і діатомових, переважанням небажаних видів
планктону, порушенням життєдіяльності риб. Продукти метаболізму водоростей дають воді
неприємний запах, можуть викликати шкірні алергічні реакції і шлунково-кишкові
захворювання у людей і тварин. Після відмирання водорості виділяють у воду поліпептиди,
аміак і проміжні продукти білкового розпаду. Це може призводити до підвищення вмісту
фенолів, які мають канцерогенні властивості
Perfil de lesões em atletas brasileiros de rugby em cadeira de rodas
O estudo objetivou verificar o perfil das lesões em atletas brasileiros praticantes de rugby em cadeira de rodas (RCR). Trata-se de pesquisa de corte transversal, com 72 atletas de RCR, distribuídos entre 8 equipes brasileiras. Os dados foram coletados por meio de questionário semiestruturado do tipo recordatório, contemplando caracterização demográfica, esportiva (time, tipo de cadeira para prática esportiva, tempo da prática esportiva, classificação funcional, frequência e duração de treinamento) e das lesões (tipo da lesão, local acometido, mecanismo e momento da lesão, tratamento e afastamento). Os resultados mostraram que 66,67% dos atletas apresentaram algum tipo de lesão durante a prática esportiva, sendo que a maioria (75,5%) ocorreu durante os treinos. Maior acometimento foi em membros superiores, sendo em sua maioria no sistema tegumentar (abrasão, bolha e calo). A tendinite apresentou maior frequência (9%) dentre as lesões que acometeram o sistema musculoesquelético, seguida por distensão (3,3%) e luxação (2,5%). Não houve correlação entre a quantidade das lesões e o tempo de prática e/ou classificação funcional. Portanto, nosso estudo revelou de alta incidência de lesões com a prática esportiva, sendo a maior parte delas sem gravidade tendo como agente causal a condução da cadeira de rodas. Assim, evidencia-se a necessidade de estratégias e profissionais habilitados atuando na promoção, prevenção e reabilitação; além do acompanhamento a longo prazo, uma vez que é um esporte considerado novo no cenário brasileiro e que envolve contato físico e níveis elevados de condicionamento físico
Diagnosis of obstructive coronary artery disease using computed tomography angiography in patients with stable chest pain depending on clinical probability and in clinically important subgroups: meta-analysis of individual patient data
OBJECTIVE:
To determine whether coronary computed tomography angiography (CTA) should be performed in patients with any clinical probability of coronary artery disease (CAD), and whether the diagnostic performance differs between subgroups of patients.
DESIGN:
Prospectively designed meta-analysis of individual patient data from prospective diagnostic accuracy studies.
DATA SOURCES:
Medline, Embase, and Web of Science for published studies. Unpublished studies were identified via direct contact with participating investigators.
ELIGIBILITY CRITERIA FOR SELECTING STUDIES:
Prospective diagnostic accuracy studies that compared coronary CTA with coronary angiography as the reference standard, using at least a 50% diameter reduction as a cutoff value for obstructive CAD. All patients needed to have a clinical indication for coronary angiography due to suspected CAD, and both tests had to be performed in all patients. Results had to be provided using 2×2 or 3×2 cross tabulations for the comparison of CTA with coronary angiography. Primary outcomes were the positive and negative predictive values of CTA as a function of clinical pretest probability of obstructive CAD, analysed by a generalised linear mixed model; calculations were performed including and excluding non-diagnostic CTA results. The no-treat/treat threshold model was used to determine the range of appropriate pretest probabilities for CTA. The threshold model was based on obtained post-test probabilities of less than 15% in case of negative CTA and above 50% in case of positive CTA. Sex, angina pectoris type, age, and number of computed tomography detector rows were used as clinical variables to analyse the diagnostic performance in relevant subgroups.
RESULTS:
Individual patient data from 5332 patients from 65 prospective diagnostic accuracy studies were retrieved. For a pretest probability range of 7-67%, the treat threshold of more than 50% and the no-treat threshold of less than 15% post-test probability were obtained using CTA. At a pretest probability of 7%, the positive predictive value of CTA was 50.9% (95% confidence interval 43.3% to 57.7%) and the negative predictive value of CTA was 97.8% (96.4% to 98.7%); corresponding values at a pretest probability of 67% were 82.7% (78.3% to 86.2%) and 85.0% (80.2% to 88.9%), respectively. The overall sensitivity of CTA was 95.2% (92.6% to 96.9%) and the specificity was 79.2% (74.9% to 82.9%). CTA using more than 64 detector rows was associated with a higher empirical sensitivity than CTA using up to 64 rows (93.4% v 86.5%, P=0.002) and specificity (84.4% v 72.6%, P<0.001). The area under the receiver-operating-characteristic curve for CTA was 0.897 (0.889 to 0.906), and the diagnostic performance of CTA was slightly lower in women than in with men (area under the curve 0.874 (0.858 to 0.890) v 0.907 (0.897 to 0.916), P<0.001). The diagnostic performance of CTA was slightly lower in patients older than 75 (0.864 (0.834 to 0.894), P=0.018 v all other age groups) and was not significantly influenced by angina pectoris type (typical angina 0.895 (0.873 to 0.917), atypical angina 0.898 (0.884 to 0.913), non-anginal chest pain 0.884 (0.870 to 0.899), other chest discomfort 0.915 (0.897 to 0.934)).
CONCLUSIONS:
In a no-treat/treat threshold model, the diagnosis of obstructive CAD using coronary CTA in patients with stable chest pain was most accurate when the clinical pretest probability was between 7% and 67%. Performance of CTA was not influenced by the angina pectoris type and was slightly higher in men and lower in older patients.
SYSTEMATIC REVIEW REGISTRATION:
PROSPERO CRD42012002780
Skin and Soft Tissue Infections Caused by Methicillin-Resistant Staphylococcus aureus USA300 Clone
An increase in SSTIs suggests that USA300 is becoming more virulent with a greater propensity to cause SSTIs
Urbanizing refuge: interrogating spaces of displacement
Refugee spaces are emerging as quintessential geographies of the modern, yet their intimate and everyday spatialities remain under-explored. Rendered largely through geopolitical discourses, they are seen as biopolitical spaces where the sovereign can reduce the subject to bare life. In conceptualizing refugee spaces some scholars have argued that, although many camps grow and develop over time, they evolve their own unique form of urbanism that is still un-urban. This article challenges this idea of the camp as space of pure biopolitics and explores the politics of space in the refugee camp using urban debates. Using case studies from the Middle East and South Asia, it looks at how the refugee spaces developed and became informalized, and how people recovered their agency through ‘producing spaces’ both physically and politically. In doing so, it draws connections between refugee camps and other spaces of urban marginality, and suggests that refugee spaces can be seen as important sites for articulating new politics
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