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Direct observation of prompt pre-thermal laser ion sheath acceleration.

ABSTRACT: High-intensity laser plasma-based ion accelerators provide unsurpassed field gradients in the megavolt-per-micrometer range. They represent promising candidates for next-generation applications such as ion beam cancer therapy in compact facilities. The weak scaling of maximum ion energies with the square-root of the laser intensity, established for large sub-picosecond class laser systems, motivates the search for more efficient acceleration processes. Here we demonstrate that for ultrashort (pulse duration ~30 fs) highly relativistic (intensity ~10(21) W cm(-2)) laser pulses, the intra-pulse phase of the proton acceleration process becomes relevant, yielding maximum energies of around 20 MeV. Prominent non-target-normal emission of energetic protons, reflecting an engineered asymmetry in the field distribution of promptly accelerated electrons, is used to identify this pre-thermal phase of the acceleration. The relevant timescale reveals the underlying physics leading to the near-linear intensity scaling observed for 100 TW class table-top laser systems.

SUBMITTER: Zeil K

PROVIDER: S-EPMC3621399 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Direct observation of prompt pre-thermal laser ion sheath acceleration.

Zeil K K Metzkes J J Kluge T T Bussmann M M Cowan T E TE Kraft S D SD Sauerbrey R R Schramm U U

Nature communications 20120606

High-intensity laser plasma-based ion accelerators provide unsurpassed field gradients in the megavolt-per-micrometer range. They represent promising candidates for next-generation applications such as ion beam cancer therapy in compact facilities. The weak scaling of maximum ion energies with the square-root of the laser intensity, established for large sub-picosecond class laser systems, motivates the search for more efficient acceleration processes. Here we demonstrate that for ultrashort (pu ...[more]

PMID: 22673901

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Project description:ObjectiveEvaluate intravitreal 0.5 mg ranibizumab or 4 mg triamcinolone combined with focal/grid laser compared with focal/grid laser alone for treatment of diabetic macular edema (DME).DesignMulticenter, randomized clinical trial.ParticipantsA total of 854 study eyes of 691 participants with visual acuity (approximate Snellen equivalent) of 20/32 to 20/320 and DME involving the fovea.MethodsEyes were randomized to sham injection + prompt laser (n=293), 0.5 mg ranibizumab + prompt laser (n=187), 0.5 mg ranibizumab + deferred (> or =24 weeks) laser (n=188), or 4 mg triamcinolone + prompt laser (n=186). Retreatment followed an algorithm facilitated by a web-based, real-time data-entry system.Main outcome measuresBest-corrected visual acuity and safety at 1 year.ResultsThe 1-year mean change (+/-standard deviation) in the visual acuity letter score from baseline was significantly greater in the ranibizumab + prompt laser group (+9+/-11, P<0.001) and ranibizumab + deferred laser group (+9+/-12, P<0.001) but not in the triamcinolone + prompt laser group (+4+/-13, P=0.31) compared with the sham + prompt laser group (+3+/-13). Reduction in mean central subfield thickness in the triamcinolone + prompt laser group was similar to both ranibizumab groups and greater than in the sham + prompt laser group. In the subset of pseudophakic eyes at baseline (n=273), visual acuity improvement in the triamcinolone + prompt laser group appeared comparable to that in the ranibizumab groups. No systemic events attributable to study treatment were apparent. Three eyes (0.8%) had injection-related endophthalmitis in the ranibizumab groups, whereas elevated intraocular pressure and cataract surgery were more frequent in the triamcinolone + prompt laser group. Two-year visual acuity outcomes were similar to 1-year outcomes.ConclusionsIntravitreal ranibizumab with prompt or deferred laser is more effective through at least 1 year compared with prompt laser alone for the treatment of DME involving the central macula. Ranibizumab as applied in this study, although uncommonly associated with endophthalmitis, should be considered for patients with DME and characteristics similar to those in this clinical trial. In pseudophakic eyes, intravitreal triamcinolone + prompt laser seems more effective than laser alone but frequently increases the risk of intraocular pressure elevation.

Project description:ObjectivePerform a cost-effectiveness analysis of the treatment of diabetic macular edema (DME) with ranibizumab plus prompt or deferred laser versus triamcinolone plus prompt laser. Data for the analysis were drawn from reports of the Diabetic Retinopathy Clinical Research Network (DRCRnet) Protocol I.DesignComputer simulation based on Protocol I data. Analyses were conducted from the payor perspective.ParticipantsSimulated participants assigned characteristics reflecting those seen in Protocol I.MethodsMarkov models were constructed to replicate Protocol I's 104-week outcomes using a microsimulation approach to estimation. Baseline characteristics, visual acuity (VA), treatments, and complications were based on Protocol I data. Costs were identified by literature search. One-way sensitivity analysis was performed, and the results were validated against Protocol I data.Main outcome measuresDirect cost of care for 2 years, change in VA from baseline, and incremental cost-effectiveness ratio (ICER) measured as cost per additional letter gained from baseline (Early Treatment of Diabetic Retinopathy Study).ResultsFor sham plus laser (S+L), ranibizumab plus prompt laser (R+pL), ranibizumab plus deferred laser (R+dL), and triamcinolone plus laser (T+L), effectiveness through 104 weeks was predicted to be 3.46, 7.07, 8.63, and 2.40 letters correct, respectively. The ICER values in terms of dollars per VA letter were $393 (S+L vs. T+L), $5943 (R+pL vs. S+L), and $20 (R+dL vs. R+pL). For pseudophakics, the ICER value for comparison triamcinolone with laser versus ranibizumab with deferred laser was $14 690 per letter gained. No clinically relevant changes in model variables altered outcomes. Internal validation demonstrated good similarity to Protocol I treatment patterns.ConclusionsIn treatment of phakic patients with DME, ranibizumab with deferred laser provided an additional 6 letters correct compared with triamcinolone with laser at an additional cost of $19 216 over 2 years. That would indicate that if the gain in VA seen at 2 years is maintained in subsequent years, then the treatment of phakic patients with DME using ranibizumab may meet accepted standards of cost-effectiveness. For pseudophakic patients, first-line treatment with triamcinolone seems to be the most cost-effective option.

Project description:ObjectiveTo report expanded 2-year follow-up of a previously reported randomized trial evaluating intravitreal 0.5 mg ranibizumab or 4 mg triamcinolone combined with focal/grid laser compared with focal/grid laser alone for treatment of diabetic macular edema (DME).DesignMulticenter, randomized clinical trial.ParticipantsA total of 854 study eyes of 691 participants with visual acuity of 20/32 to 20/320 (approximate Snellen equivalent) and DME involving the fovea.MethodsContinuation of procedures previously reported for the randomized trial.Main outcome measuresBest-corrected visual acuity and safety at the 2-year visit.ResultsAt the 2-year visit, compared with the sham + prompt laser group, the mean change in the visual acuity letter score from baseline was 3.7 letters greater in the ranibizumab + prompt laser group (95% confidence interval adjusted for multiple comparisons [aCI], -0.4 to +7.7), 5.8 letters greater in the ranibizumab + deferred laser group (95% aCI, +1.9 to +9.8), and 1.5 letters worse in the triamcinolone + prompt laser group (95% aCI, -5.5 to +2.4). After the 1- to 2-year visit in the ranibizumab + prompt or deferred laser groups, the median numbers of injections were 2 and 3 (potential maximum of 13), respectively. At the 2-year visit, the percentages of eyes with central subfield thickness ?250 ?m were 59% in the sham + prompt laser group, 43% in the ranibizumab + prompt laser group, 42% in the ranibizumab + deferred laser group, and 52% in the triamcinolone + prompt laser group. No systemic events attributable to study treatment were apparent. Three eyes in 3 (0.8%) of 375 participants had injection-related endophthalmitis in the ranibizumab groups, whereas elevated intraocular pressure and cataract surgery were more frequent in the triamcinolone + prompt laser group.ConclusionsThe expanded 2-year results reported are similar to results published previously and reinforce the conclusions originally reported: Ranibizumab should be considered for patients with DME and characteristics similar to those of the cohort in this clinical trial, including vision impairment with DME involving the center of the macula.

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Direct observation of prompt pre-thermal laser ion sheath acceleration.

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Direct observation of prompt pre-thermal laser ion sheath acceleration.

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