Experimental study of EUV mirror radiation damage resistance under long term free electron laser exposures below the single shot damage threshold

The durability of grazing and normal incidence optical coatings has been experimentally assessed under free electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10 of the single shot damage threshold. The experiment was performed at FLASH, the Free electron LASer in Hamburg, using 13.5 nm extreme UV EUV radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20 and 10 grazing incidence, respectively. Mo Si periodical multilayer structures were tested in the Bragg reflection condition at 16 off normal angle of incidence. The exposed areas were analysed post mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X ray photoelectron spectroscopy. The analysis revealed that Ru and Mo Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV induced oxidation of the surfac

Mechanism of single shot damage of Ru thin films irradiated by femtosecond extreme UV free electron laser

Ruthenium is a perspective material to be used for XUV mirrors at free electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser matter interaction. In this work, we present single shot damage studies of thin Ru films irradiated by femtosecond XUV free electron laser pulses at FLASH. Ex situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte Carlo code XCASCADE 3D and the two temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologie

Comparing unilateral and bilateral upper limb training: The ULTRA-stroke program design

<p>Abstract</p> <p>Background</p> <p>About 80% of all stroke survivors have an upper limb paresis immediately after stroke, only about a third of whom (30 to 40%) regain some dexterity within six months following conventional treatment programs. Of late, however, two recently developed interventions - constraint-induced movement therapy (CIMT) and bilateral arm training with rhythmic auditory cueing (BATRAC) - have shown promising results in the treatment of upper limb paresis in chronic stroke patients. The ULTRA-stroke (acronym for Upper Limb TRaining After stroke) program was conceived to assess the effectiveness of these interventions in subacute stroke patients and to examine how the observed changes in sensori-motor functioning relate to changes in stroke recovery mechanisms associated with peripheral stiffness, interlimb interactions, and cortical inter- and intrahemispheric networks. The present paper describes the design of this single-blinded randomized clinical trial (RCT), which has recently started and will take several years to complete.</p> <p>Methods/Design</p> <p>Sixty patients with a first ever stroke will be recruited. Patients will be stratified in terms of their remaining motor ability at the distal part of the arm (i.e., wrist and finger movements) and randomized over three intervention groups receiving modified CIMT, modified BATRAC, or an equally intensive (i.e., dose-matched) conventional treatment program for 6 weeks. Primary outcome variable is the score on the Action Research Arm test (ARAT), which will be assessed before, directly after, and 6 weeks after the intervention. During those test sessions all patients will also undergo measurements aimed at investigating the associated recovery mechanisms using haptic robots and magneto-encephalography (MEG).</p> <p>Discussion</p> <p>ULTRA-stroke is a 3-year translational research program which aims (1) to assess the relative effectiveness of the three interventions, on a group level but also as a function of patient characteristics, and (2) to delineate the functional and neurophysiological changes that are induced by those interventions.</p> <p>The outcome on the ARAT together with information about changes in the associated mechanisms will provide a better understanding of how specific therapies influence neurobiological changes, and which post-stroke conditions lend themselves to specific treatments.</p> <p>Trial Registration</p> <p>The ULTRA-stroke program is registered at the Netherlands Trial Register (NTR, <url>http://www.trialregister.nl</url>, number NTR1665).</p

Critical bandwidth in the cat following the selective destruction of cochlear inner and outer hair cells [Abstract]

Twenty-ninth Meeting of Australian Physiological and Pharmacological Society, Canberra, 17-19 August 1978This is a publisher’s version of a paper from Twenty-ninth Meeting of Australian Physiological and Pharmacological Society, Canberra, 17-19 August 1978 published by Australian Physiological and Pharmacological Society. This version is reproduced with the permission of publisher.It is of interest to determine the significance of the inner and outer hair cells of the cochlea in critical bandwidth measurements, as there is evidence for a difference in their roles in frequency selectivity (Dallos et at., 1977) and in frequency discrimination (Nienhuys and Clark, 1978). The present study has been undertaken on-four monauralized cats which were trained to respond by a conditioned suppression technique. Behavioural auditory thresholds were measured by plotting suppression ratios for frequencies of 1kHz, 4kHz, 8kHz, 10kHz, 12kHz and 16kHz. Critical bands were measured at the same frequencies by recording the pure tone thresholds in the presence of a masking noise with six different bandwidths, a constant total power, and geometrically centred on the test tone (Greenwood, 1961). The cats were then given a series of intramuscular injections of kanamycin (200mg kg-l d- l ) for 10 days to selectively destroy the outer hair cells, and behavioural thresholds determined shortly afterwards. Critical bands were again measured at all the previous frequencies except 16kHz, where the auditory behavioural threshold was too high. At the completion of the experiments behavioural thresholds were re-determined, the animals were anaesthetized with pentobarbital sodium (40mg/kg, i.p.) and auditory nerve action potentials recorded.17-19 August 197

Frequency discrimination and critical bands following the selective destruction of cochlear inner and outer hair cells

This is a publisher’s version of an article published in IRCS Medical Research 1977. This version is reproduced with permission from Lippincott Williams & Wilkins.The role of the inner and outer hair cells of the cochlea in frequency discrimination and critical band measurements is not clearly understood. There is, however, evidence for an interaction between the hair cells in threshold determinations (1) and frequency selectivity (2). Furthermore, although there is increasing evidence that a place theory is more importance than a periodicity theory in frequency coding the situation is still not clear, and the role of the inner and outer hair cells in frequency discrimination and critical band measurements should provide additional evidence to help clarify the situation

Audiological assessment of profoundly hearing-impaired children

This is a publisher’s version of an article published in Annals of Otology, Rhinology & Laryngology published by Annals Publishing Company. This version is reproduced with permission from Annals Publishing Company. http://www.annals.com/The design of an audiological assessment protocol for profoundly hearing-impaired children may be divided into three areas. First, accurate estimation of hearing loss includes the behavioral measures of unaided and aided thresholds and the objective measures of electrocochleography and auditory brain stem response. The reliability of these measures for the accurate diagnosis of a profound to total hearing loss is discussed. Second, speech perception includes the measure of perception in the audition alone, vision alone, and audition plus vision conditions. Test material should include speech features, words, and sentences. Factors influencing the choice of material are the developmental age of the child, the method of educational instruction, speech and language skills, and vocabulary limits. Third, psychophysical properties of residual auditory skills include measures such as frequency, intensity, and duration difference limens. These skills may be compared to those elicited through other sensory channels, such as visual and tactile. Other important factors that should be considered are the psychological well-being of the child and family, family motivations and expectations, and educational requirements

Training and assessment of children using a multi-electrode cochlear implant [Abstract]

Abstract of a paper presented at the 1st Asian-Pacific Regional Conference on DeafnessA training and assessment protocol has been developed for a research study on deaf children using multi-electrode cochlear implants. The areas of assessment and training include speech perception and production, language and communication skills. Material which is appropriate for language-and developmental-age is selected from a large battery of: tests to ensure that the individual abilities of children are addressed. A single-subject, time-series design has been adopted for regular assessment of the child's performance. The participating child receives a minimum of six months' pre-operative training and assessment using high gain hearing aids or a tactile device. Also included are audiological and medical evaluations to determine the child's suitability for inclusion in the study. Approximately two months are allocated for pre-operative, operative and postoperative surgical management as well as fitting and setting the external speech processor. Post-operatively, the same training and assessment procedures continue for a number of years. Extensive psychophysical studies are also undertaken to measure the child's abilities to discriminate simple stimuli which differ in electrical stimulus parameter values.Dec-8