7,514 research outputs found

    Linear Amplifier Breakdown and Concentration Properties of a Gaussian Field Given that its L2\bm{L^2}-Norm is Large

    Full text link
    In the context of linear amplification for systems driven by the square of a Gaussian noise, we investigate the realizations of a Gaussian field in the limit where its L2L^2-norm is large. Concentration onto the eigenspace associated with the largest eigenvalue of the covariance of the field is proved. When the covariance is trace class, the concentration is in probability for the L2L^2-norm. A stronger concentration, in mean for the sup-norm, is proved for a smaller class of Gaussian fields, and an example of a field belonging to that class is given. A possible connection with Bose-Einstein condensation is briefly discussed.Comment: REVTeX file, 11 pages, 1 added paragraph in the introduction, 2 added references, minor modifications in the text and abstract, submitted to J. Stat. Phy

    The comparative hemodynamic efficacy of lower limb muscles using transcutaneous electrical stimulation.

    Get PDF
    Circulation in the limbs can be augmented using transcutaneous electrical stimulation devices. The optimum muscle stimulation sites for enhancement of vascular hemodynamic parameters have not been identified.Seven suitable anatomic sites were identified within the right leg. Twelve healthy participants were recruited (mean age, 23.1 ± 3 years; body mass index, 23.1 ± 3 kg/m(2)). Muscles were stimulated by transcutaneous bipolar electrodes at a current twice their motor threshold, at 1 Hz, for 5 minutes. Hemodynamic ultrasound measurements were taken from the right femoral vein. Laser Doppler measurements from the feet of the stimulated and nonstimulated sides were obtained. Baseline measurements were compared with readings after 5 minutes of stimulation, with device active. Discomfort experienced for stimulation of each muscle was rated out of 100.Hemodynamic changes displayed large intersubject variation, with no muscle statistically superior to the others. All muscles increased peak velocity; contraction of medial gastrocnemius increased time-averaged maximum velocity and volume flow. All muscles increased foot fluximetry (P < .05). Discomfort correlated weakly with current applied. Tibialis anterior and vastus lateralis were most tenable.Transcutaneous stimulation increases hemodynamic parameters significantly, locally and systemically. No optimum stimulation site has been identified, and it is limited by comfort and variability in the subjects response. Gastrocnemius, tibialis anterior, and vastus lateralis all provoke large changes in hemodynamic parameters, but clinical efficacy in disease prevention and management has not been explored

    The comparative haemodynamic efficacy of lower limb muscles using transcutaneous electrical stimulation

    Get PDF
    BACKGROUND: Circulation in the limbs can be augmented using transcutaneous electrical stimulation devices. The optimum muscle stimulation sites for enhancement of vascular hemodynamic parameters have not been identified. METHODS: Seven suitable anatomic sites were identified within the right leg. Twelve healthy participants were recruited (mean age, 23.1 ± 3 years; body mass index, 23.1 ± 3 kg/m(2)). Muscles were stimulated by transcutaneous bipolar electrodes at a current twice their motor threshold, at 1 Hz, for 5 minutes. Hemodynamic ultrasound measurements were taken from the right femoral vein. Laser Doppler measurements from the feet of the stimulated and nonstimulated sides were obtained. Baseline measurements were compared with readings after 5 minutes of stimulation, with device active. Discomfort experienced for stimulation of each muscle was rated out of 100. RESULTS: Hemodynamic changes displayed large intersubject variation, with no muscle statistically superior to the others. All muscles increased peak velocity; contraction of medial gastrocnemius increased time-averaged maximum velocity and volume flow. All muscles increased foot fluximetry (P < .05). Discomfort correlated weakly with current applied. Tibialis anterior and vastus lateralis were most tenable. CONCLUSIONS: Transcutaneous stimulation increases hemodynamic parameters significantly, locally and systemically. No optimum stimulation site has been identified, and it is limited by comfort and variability in the subject's response. Gastrocnemius, tibialis anterior, and vastus lateralis all provoke large changes in hemodynamic parameters, but clinical efficacy in disease prevention and management has not been explored

    Continuity of care with doctors - A matter of life and death? A systematic review of continuity of care and mortality

    Get PDF
     This is the final version. Available from BMJ Publishing Group via the DOI in this record. Objective Continuity of care is a long-standing feature of healthcare, especially of general practice. It is associated with increased patient satisfaction, increased take-up of health promotion, greater adherence to medical advice and decreased use of hospital services. This review aims to examine whether there is a relationship between the receipt of continuity of doctor care and mortality. Design Systematic review without meta-analysis. Data sources MEDLINE, Embase and the Web of Science, from 1996 to 2017. Eligibility criteria for selecting studies Peer-reviewed primary research articles, published in English which reported measured continuity of care received by patients from any kind of doctor, in any setting, in any country, related to measured mortality of those patients. Results Of the 726 articles identified in searches, 22 fulfilled the eligibility criteria. The studies were all cohort or cross-sectional and most adjusted for multiple potential confounding factors. These studies came from nine countries with very different cultures and health systems. We found such heterogeneity of continuity and mortality measurement methods and time frames that it was not possible to combine the results of studies. However, 18 (81.8%) high-quality studies reported statistically significant reductions in mortality, with increased continuity of care. 16 of these were with all-cause mortality. Three others showed no association and one demonstrated mixed results. These significant protective effects occurred with both generalist and specialist doctors. Conclusions This first systematic review reveals that increased continuity of care by doctors is associated with lower mortality rates. Although all the evidence is observational, patients across cultural boundaries appear to benefit from continuity of care with both generalist and specialist doctors. Many of these articles called for continuity to be given a higher priority in healthcare planning. Despite substantial, successive, technical advances in medicine, interpersonal factors remain important. PROSPERO registration number CRD42016042091

    Probabilistic representation for solutions of an irregular porous media type equation: the degenerate case

    Get PDF
    We consider a possibly degenerate porous media type equation over all of Rd\R^d with d=1d = 1, with monotone discontinuous coefficients with linear growth and prove a probabilistic representation of its solution in terms of an associated microscopic diffusion. This equation is motivated by some singular behaviour arising in complex self-organized critical systems. The main idea consists in approximating the equation by equations with monotone non-degenerate coefficients and deriving some new analytical properties of the solution

    Density-potential mappings in quantum dynamics

    Full text link
    In a recent letter [Europhys. Lett. 95, 13001 (2011)] the question of whether the density of a time-dependent quantum system determines its external potential was reformulated as a fixed point problem. This idea was used to generalize the existence and uniqueness theorems underlying time-dependent density functional theory. In this work we extend this proof to allow for more general norms and provide a numerical implementation of the fixed-point iteration scheme. We focus on the one-dimensional case as it allows for a more in-depth analysis using singular Sturm-Liouville theory and at the same time provides an easy visualization of the numerical applications in space and time. We give an explicit relation between the boundary conditions on the density and the convergence properties of the fixed-point procedure via the spectral properties of the associated Sturm-Liouville operator. We show precisely under which conditions discrete and continuous spectra arise and give explicit examples. These conditions are then used to show that in the most physically relevant cases the fixed point procedure converges. This is further demonstrated with an example.Comment: 20 pages, 8 figures, 3 table

    Stratosphere-troposphere exchange: Chemical sensitivity to mixing

    Get PDF
    We present examples of how chemical evolution can exhibit sensitivity to mixing arising from stratosphere-troposphere exchange. A chemical transport model is used to survey the chemical contrasts on isentropic surfaces that intersect the tropopause. Significant cross-tropopause gradients in both ozone and water vapor are shown to exist between 300 and 340 K, Back trajectories are used to confirm that air parcels with widely varying chemical properties are rapidly brought together in a typical quasi-isentropic stratosphere-troposphere exchange event. A two-box model is used to investigate the chemical evolution of stratospheric and tropospheric air parcels and to determine the effect of mixing between them. Mixing of stratospheric ozone and tropospheric water vapor is shown to lead to enhanced hydroxyl (OH) radical concentrations compared with background tropospheric and stratospheric values. The oxidation of CO, methane, and higher hydrocarbons is correspondingly increased, and NOx is also lost more rapidly with faster mixing. Also, in low NOx conditions, the rate of O-3 loss is found to increase with faster mixing, The consequences of this anomalous chemistry for chemical transport in stratosphere-troposphere exchange events are discussed. It is also noted that if NOx levels in either parcel are very high initially, mixing of NOx can become more important than O-3 or H2O in determining OH levels

    Combining behavioural activation with physical activity promotion for adults with depression: findings of a parallel-group pilot randomised controlled trial (BAcPAc)

    Get PDF
    BACKGROUND: Depression is associated with physical inactivity, which may mediate the relationship between depression and a range of chronic physical health conditions. However, few interventions have combined a psychological intervention for depression with behaviour change techniques, such as behavioural activation (BA), to promote increased physical activity. METHODS: To determine procedural and clinical uncertainties to inform a definitive randomised controlled trial (RCT), a pilot parallel-group RCT was undertaken within two Improving Access to Psychological Therapies (IAPT) services in South West England. We aimed to recruit 80 adults with depression and randomise them to a supported, written self-help programme based on either BA or BA plus physical activity promotion (BAcPAc). Data were collected at baseline and 4 months post-randomisation to evaluate trial retention, intervention uptake and variance in outcomes to inform a sample size calculation. Qualitative data were collected from participants and psychological wellbeing practitioners (PWPs) to assess the acceptability and feasibility of the trial methods and the intervention. Routine data were collected to evaluate resource use and cost. RESULTS: Sixty people with depression were recruited, and a 73 % follow-up rate was achieved. Accelerometer physical activity data were collected for 64 % of those followed. Twenty participants (33 %) attended at least one treatment appointment. Interview data were analysed for 15 participants and 9 study PWPs. The study highlighted the challenges of conducting an RCT within existing IAPT services with high staff turnover and absences, participant scheduling issues, PWP and participant preferences for cognitive focussed treatment, and deviations from BA delivery protocols. The BAcPAc intervention was generally acceptable to patients and PWPs. CONCLUSIONS: Although recruitment procedures and data collection were challenging, participants generally engaged with the BAcPAc self-help booklets and reported willingness to increase their physical activity. A number of feasibility issues were identified, in particular the under-use of BA as a treatment for depression, the difficulty that PWPs had in adapting their existing procedures for study purposes and the instability of the IAPT PWP workforce. These problems would need to be better understood and resolved before proceeding to a full-scale RCT. TRIAL REGISTRATION: ISRCTN74390532 . Registered on 26 March 2013
    • …
    corecore