Dataset Information

Establishing nonlinearity thresholds with ultraintense X-ray pulses.

ABSTRACT: X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.

SUBMITTER: Szlachetko J

PROVIDER: S-EPMC5020491 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Establishing nonlinearity thresholds with ultraintense X-ray pulses.

Szlachetko Jakub J Hoszowska Joanna J Dousse Jean-Claude JC Nachtegaal Maarten M Błachucki Wojciech W Kayser Yves Y Sà Jacinto J Messerschmidt Marc M Boutet Sebastien S Williams Garth J GJ David Christian C Smolentsev Grigory G van Bokhoven Jeroen A JA Patterson Bruce D BD Penfold Thomas J TJ Knopp Gregor G Pajek Marek M Abela Rafael R Milne Christopher J CJ

Scientific reports 20160913

X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in ...[more]

PMID: 27620067

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Project description:Context and objectiveStandards for clinical practice guidelines require explicit statements regarding how values and preferences influence recommendations. However, no cancer screening guideline has addressed the key question of what magnitude of benefit people require to undergo screening, given its harms and burdens. This article describes the development of a new method for guideline developers to address this key question in the absence of high-quality evidence from published literature.Summary of methodThe new method was developed and applied in the context of a recent BMJ Rapid Recommendation clinical practice guideline for colorectal cancer (CRC) screening. First, we presented the guideline panel with harms and burdens (derived from a systematic review) associated with the CRC screening tests under consideration. Second, each panel member completed surveys documenting their views of expected benefits on CRC incidence and mortality that people would require to accept the harms and burdens of screening. Third, the panel discussed results of the surveys and agreed on thresholds for benefits at which the majority of people would choose screening. During these three steps, the panel had no access to the actual benefits of the screening tests. In step four, the panel was presented with screening test benefits derived from a systematic review of clinical trials and microsimulation modelling. The thresholds derived through steps one to three were applied to these benefits, and directly informed the panel's recommendations.ConclusionWe present the development and application of a new, four-step method enabling incorporation of explicit and transparent judgements of values and preferences in a screening guideline. Guideline panels should establish their view regarding the magnitude of required benefit, given burdens and harms, before they review screening benefits and make their recommendations accordingly. Making informed screening decisions requires transparency in values and preferences judgements that our new method greatly facilitates.

Project description:BackgroundUnderstanding minimum clinically important differences (MCID) in patient-reported outcomes is essential in interpreting the magnitude of changes in these measures. No MCID from patients' perspectives has ever been published for peripheral artery disease-specific health status assessment tools. The Peripheral Artery Questionnaire (PAQ) is a commonly used, validated peripheral artery disease-specific health status instrument for which we sought to prospectively establish its MCID from patients' perspectives.Methods and resultsPatients presenting to vascular clinics with new or worsened claudication in the US cohort of the PORTRAIT (Patient-Centered Outcomes Related to Treatment Practices in Peripheral Arterial Disease: Investigating Trajectories) registry who completed baseline and follow-up PAQ assessments along with the Global Assessment of Functioning scale were included. Mean change in PAQ summary scores from 3- to 6-month follow-up was calculated according to Global Assessment of Functioning category. MCID was defined as the mean difference in scores between those with small improvement or deterioration and those with no change. Multivariable linear regression was used to provide an MCID estimate after adjusting for patients' 3-month PAQ score. Of the 483 patients who completed the Global Assessment of Functioning score at 6 months and who had available 3- and 6-month PAQ assessments, the mean age was 69 years, 42% were female, and 71% were White. The MCIDs for PAQ summary scale improvement and worsening were 8.7 (2.9-14.5) and -11.0 (-18.6 to -3.3), respectively. After multivariable adjustment, these were 8.9 (3.0-14.8) and -11.2 (-18.2 to -4.2), respectively. There was no significant interaction between treatment (invasive versus noninvasive) and Global Assessment of Functioning response (P=0.75).ConclusionsIn patients with new or worsened claudication, a 10-point change in PAQ summary score represents an MCID. This estimate needs external validation and may inform the interpretation of PAQ scores when used as outcomes in clinical trials or in routine clinical care. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01419080.

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Establishing nonlinearity thresholds with ultraintense X-ray pulses.

Publications

Establishing nonlinearity thresholds with ultraintense X-ray pulses.

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