6,813 research outputs found

    General Form of the Color Potential Produced by Color Charges of the Quark

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    Constant electric charge ee satisfies the continuity equation μjμ(x)=0\partial_\mu j^{\mu}(x)= 0 where jμ(x)j^\mu(x) is the current density of the electron. However, the Yang-Mills color current density jμa(x)j^{\mu a}(x) of the quark satisfies the equation Dμ[A]jμa(x)=0D_\mu[A] j^{\mu a}(x)= 0 which is not a continuity equation (μjμa(x)0\partial_\mu j^{\mu a}(x)\neq 0) which implies that a color charge qa(t)q^a(t) of the quark is not constant but it is time dependent where a=1,2,...8a=1,2,...8 are color indices. In this paper we derive general form of color potential produced by color charges of the quark. We find that the general form of the color potential produced by the color charges of the quark at rest is given by \Phi^a(x) =A_0^a(t,{\bf x}) =\frac{q^b(t-\frac{r}{c})}{r}\[\frac{{\rm exp}[g\int dr \frac{Q(t-\frac{r}{c})}{r}] -1}{g \int dr \frac{Q(t-\frac{r}{c})}{r}}\]_{ab} where drdr integration is an indefinite integration, ~~ Qab(τ0)=fabdqd(τ0)Q_{ab}(\tau_0)=f^{abd}q^d(\tau_0), ~~r=xX(τ0)r=|{\vec x}-{\vec X}(\tau_0)|, ~~τ0=trc\tau_0=t-\frac{r}{c} is the retarded time, ~~cc is the speed of light, ~~X(τ0){\vec X}(\tau_0) is the position of the quark at the retarded time and the repeated color indices b,db,d(=1,2,...8) are summed. For constant color charge qaq^a we reproduce the Coulomb-like potential Φa(x)=qar\Phi^a(x)=\frac{q^a}{r} which is consistent with the Maxwell theory where constant electric charge ee produces the Coulomb potential Φ(x)=er\Phi(x)=\frac{e}{r}.Comment: Final version, two more sections added, 45 pages latex, accepted for publication in JHE

    Development and formative evaluation of the e-Health implementation toolkit

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    <b>Background</b> The use of Information and Communication Technology (ICT) or e-Health is seen as essential for a modern, cost-effective health service. However, there are well documented problems with implementation of e-Health initiatives, despite the existence of a great deal of research into how best to implement e-Health (an example of the gap between research and practice). This paper reports on the development and formative evaluation of an e-Health Implementation Toolkit (e-HIT) which aims to summarise and synthesise new and existing research on implementation of e-Health initiatives, and present it to senior managers in a user-friendly format.<p></p> <b>Results</b> The content of the e-HIT was derived by combining data from a systematic review of reviews of barriers and facilitators to implementation of e-Health initiatives with qualitative data derived from interviews of "implementers", that is people who had been charged with implementing an e-Health initiative. These data were summarised, synthesised and combined with the constructs from the Normalisation Process Model. The software for the toolkit was developed by a commercial company (RocketScience). Formative evaluation was undertaken by obtaining user feedback. There are three components to the toolkit - a section on background and instructions for use aimed at novice users; the toolkit itself; and the report generated by completing the toolkit. It is available to download from http://www.ucl.ac.uk/pcph/research/ehealth/documents/e-HIT.xls<p></p> <b>Conclusions</b> The e-HIT shows potential as a tool for enhancing future e-Health implementations. Further work is needed to make it fully web-enabled, and to determine its predictive potential for future implementations

    Cholesterol and the risk of grade-specific prostate cancer incidence: evidence from two large prospective cohort studies with up to 37 years' follow up

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    <b>Background</b> High cholesterol may be a modifiable risk factor for prostate cancer but results have been inconsistent and subject to potential "reverse causality" where undetected disease modifies cholesterol prior to diagnosis.<p></p> <b>Methods</b> We conducted a prospective cohort study of 12,926 men who were enrolled in the Midspan studies between 1970 and 1976 and followed up to 31st December 2007. We used Cox-Proportional Hazards Models to evaluate the association between baseline plasma cholesterol and Gleason grade-specific prostate cancer incidence. We excluded cancers detected within at least 5 years of cholesterol assay.<p></p> <b>Results</b> 650 men developed prostate cancer in up to 37 years' follow-up. Baseline plasma cholesterol was positively associated with hazard of high grade (Gleason score[greater than or equal to]8) prostate cancer incidence (n=119). The association was greatest among men in the 4th highest quintile for cholesterol, 6.1 to <6.69 mmol/l, Hazard Ratio 2.28, 95% CI 1.27 to 4.10, compared with the baseline of <5.05 mmol/l. This association remained significant after adjustment for body mass index, smoking and socioeconomic status.<p></p> <b>Conclusions</b> Men with higher cholesterol are at greater risk of developing high-grade prostate cancer but not overall risk of prostate cancer. Interventions to minimise metabolic risk factors may have a role in reducing incidence of aggressive prostate cancer

    Characteristics, management and outcome of a large necrotising otitis externa case series: need for standardised case definition

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    Background: Necrotising otitis externa (NOE) is a severe ear infection for which there are no established diagnostic or treatment guidelines. Objective: Describe clinical characteristics, management and outcomes for patients managed as NOE at a UK tertiary referral centre. Methods: Retrospective case series. Results: 58 (63%) patients were classified as definite NOE cases, 31 (34%) as probable and 3 (3%) as possible cases. Median duration of intravenous and oral antimicrobial therapy was 6.0 weeks (0.49-44.9). 6% of patients relapsed a median of 16.4 weeks (IQR 23-121) after stopping antimicrobials. 28% of cases had complex disease. These patients were older (p=0.042), had a longer duration of symptoms prior to imaging (p= 0.0001) and higher CRP at diagnosis (p=0.005). Despite longer courses of intravenous antimicrobials (23 days v 14 days; p=0.032), complex cases were more likely to relapse (p=0.016). Conclusion: A standardised case-definition of NOE is needed to optimise diagnosis, management and research

    Benchmark performance of low-cost Sb2Se3 photocathodes for unassisted solar overall water splitting

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    Determining cost-effective semiconductors exhibiting desirable properties for commercial photoelectrochemical water splitting remains a challenge. Herein, we report a Sb2Se3 semiconductor that satisfies most requirements for an ideal high-performance photoelectrode, including a small band gap and favourable cost, optoelectronic properties, processability, and photocorrosion stability. Strong anisotropy, a major issue for Sb2Se3, is resolved by suppressing growth kinetics via close space sublimation to obtain high-quality compact thin films with favourable crystallographic orientation. The Sb2Se3 photocathode exhibits a high photocurrent density of almost 30mAcm(-2) at 0V against the reversible hydrogen electrode, the highest value so far. We demonstrate unassisted solar overall water splitting by combining the optimised Sb2Se3 photocathode with a BiVO4 photoanode, achieving a solar-to-hydrogen efficiency of 1.5% with stability over 10h under simulated 1 sun conditions employing a broad range of solar fluxes. Low-cost Sb2Se3 can thus be an attractive breakthrough material for commercial solar fuel production. While photoelectrochemical water splitting offers an integrated means to convert sunlight to a renewable fuel, cost-effective light-absorbers are rare. Here, authors report Sb2Se3 photocathodes for high-performance photoelectrochemical water splitting devices

    An Integrated-Photonics Optical-Frequency Synthesizer

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    Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the 7.010137.0*10^{-13} reference-clock instability for a 1 second acquisition, and constrain any synthesis error to 7.710157.7*10^{-15} while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Comment: 10 pages, 6 figure

    Left ventricular assist device implantation in high risk destination therapy patients: an alternative surgical approach

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    Left Ventricular Assist Device (LVAD) for Destination Therapy (DT) is an established therapy for end stage heart failure patients who are not transplant candidates. Many DT patients requiring LVADs have had prior open heart surgery, the majority of whom had prior sternotomy. In addition, DT patients tend to be older and more likely to have more significant co-morbidities than their Bridge-To-Transplant (BTT) counterparts. As such, placement of an implantable LVAD in DT patients can be technically hazardous and potentially prone to more perioperative complications. The purpose of this report is to describe an alternative implantation approach for the implantation of the Heartmate II™ LVAD in high risk DT patients

    Chern-Simons black holes: scalar perturbations, mass and area spectrum and greybody factors

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    We study the Chern-Simons black holes in d-dimensions and we calculate analytically the quasi-normal modes of the scalar perturbations and we show that they depend on the highest power of curvature present in the Chern-Simons theory. We obtain the mass and area spectrum of these black holes and we show that they have a strong dependence on the topology of the transverse space and they are not evenly spaced. We also calculate analytically the reflection and transmission coefficients and the absorption cross section and we show that at low frequency limit there is a range of modes which contributes to the absorption cross section.Comment: 19 pages, 18 figures, the title has been changed to reflect the addition of an another section on the reflection, transmission coefficients and absorption cross sections of the Chern-Simons black holes. Version to be published in JHE
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