Performance comparison of Yb:YAG ceramics and crystal gain material in a large-area, high-energy, high average-power diode-pumped laser.

We compare for the first time the influence of different Yb:YAG gain media on the performance of a large-area, high average-power laser system with an output energy of up to 6 J. Monocrystalline slabs grown by a new technique without central growth defect are compared with ceramics. Small signal gain, maximum output energy and thermal lensing are compared for ceramic slabs with co-sintered amplified spontaneous emission (ASE) absorber cladding, monocrystalline slab with and without optically bonded ASE absorber cladding, and surface structured monocrystalline slabs. We show that these large monocrystals with optically bonded absorber cladding have similar performance to cladded ceramics, so far the only material for high-energy Yb:YAG lasers.

Compact laser accelerators for X-ray phase-contrast imaging.

Advances in X-ray imaging techniques have been driven by advances in novel X-ray sources. The latest fourth-generation X-ray sources can boast large photon fluxes at unprecedented brightness. However, the large size of these facilities means that these sources are not available for everyday applications. With advances in laser plasma acceleration, electron beams can now be generated at energies comparable to those used in light sources, but in university-sized laboratories. By making use of the strong transverse focusing of plasma accelerators, bright sources of betatron radiation have been produced. Here, we demonstrate phase-contrast imaging of a biological sample for the first time by radiation generated by GeV electron beams produced by a laser accelerator. The work was performed using a greater than 300 TW laser, which allowed the energy of the synchrotron source to be extended to the 10-100 keV range.

High-energy, ceramic-disk Yb:LuAG laser amplifier.

We report the first short-pulse amplification results to several hundred millijoule energies in ceramic Yb:LuAG. We have demonstrated ns-pulse output from a diode-pumped Yb:LuAG amplifier at a maximum energy of 580 mJ and a peak optical-to-optical efficiency of 28% at 550 mJ. In cavity dumped operation of a nanosecond oscillator we obtained 1 mJ at up to 100 Hz repetition rate. A gain bandwidth of 5.4 nm was achieved at room temperature by measuring the small-signal single-pass gain. Furthermore, we compared our results with Yb:YAG within the same amplifier system.

Racial disparities in job strain among American and immigrant long-term care workers.

BACKGROUND: Nursing homes are occupational settings, with an increasing minority and immigrant workforce where several psychosocial stressors intersect. AIM: This study aimed to examine racial/ethnic differences in job strain between Black (n = 127) and White (n = 110) immigrant and American direct-care workers at nursing homes (total n = 237). METHODS: Cross-sectional study with data collected at four nursing homes in Massachusetts during 2006-2007. We contrasted Black and White workers within higher-skilled occupations such as registered nurses or licensed practical nurses (n = 82) and lower-skilled staff such as certified nursing assistants (CNAs, n = 155). RESULTS: Almost all Black workers (96%) were immigrants. After adjusting for demographic and occupational characteristics, Black employees were more likely to report job strain, compared with Whites [relative risk (RR): 2.9, 95% confidence interval (CI) 1.3 to 6.6]. Analyses stratified by occupation showed that Black CNAs were more likely to report job strain, compared with White CNAs (RR: 3.1, 95% CI: 1.0 to 9.4). Black workers were also more likely to report low control (RR: 2.1, 95% CI: 1.1 to 4.0). Additionally, Black workers earned $2.58 less per hour and worked 7.1 more hours per week on average, controlling for potential confounders. CONCLUSION: Black immigrant workers were 2.9 times more likely to report job strain than White workers, with greater differences among CNAs. These findings may reflect differential organizational or individual characteristics but also interpersonal or institutional racial/ethnic discrimination. Further research should consider the role of race/ethnicity in shaping patterns of occupational stress.

Maternal experiences of racial discrimination and child weight status in the first 3 years of life.

Among US racial/ethnic minority women, we examined associations between maternal experiences of racial discrimination and child growth in the first 3 years of life. We analyzed data from Project Viva, a pre-birth cohort study. We restricted analyses to 539 mother-infant pairs; 294 were Black, 127 Hispanic, 110 Asian and 8 from additional racial/ethnic groups. During pregnancy, mothers completed the Experiences of Discrimination survey that measured lifetime experiences of racial discrimination in diverse domains. We categorized responses as 0, 1-2 or ≥3 domains. Main outcomes were birth weight for gestational age z-score; weight for age (WFA) z-score at 6 months of age; and at 3 years of age, body mass index (BMI) z-score. In multivariable analyses, we adjusted for maternal race/ethnicity, nativity, education, age, pre-pregnancy BMI, household income and child sex and age. Among this cohort of mostly (58.2%) US-born and economically non-impoverished mothers, 33% reported 0 domains of discrimination, 33% reported discrimination in 1-2 domains and 35% reported discrimination in ≥3 domains. Compared with children whose mothers reported no discrimination, those whose mothers reported ≥3 domains had lower birth weight for gestational age z-score (ß -0.25; 95% CI: -0.45, -0.04), lower 6 month WFA z-score (ß -0.34; 95% CI: -0.65, -0.03) and lower 3-year BMI z-score (ß -0.33; 95% CI: -0.66, 0.00). In conclusion, we found that among this cohort of US racial/ethnic minority women, mothers' report of experiencing lifetime discrimination in ⩾ 3 domains was associated with lower fetal growth, weight at 6 months and 3-year BMI among their offspring.

Optimising the efficiency of pulsed diode pumped Yb:YAG laser amplifiers for ns pulse generation.

We present a numerical model of a pulsed, diode-pumped Yb:YAG laser amplifier for the generation of high energy ns-pulses. This model is used to explore how optical-to-optical efficiency depends on factors such as pump duration, pump spectrum, pump intensity, doping concentration, and operating temperature. We put special emphasis on finding ways to achieve high efficiency within the practical limitations imposed by real-world laser systems, such as limited pump brightness and limited damage fluence. We show that a particularly advantageous way of improving efficiency within those constraints is operation at cryogenic temperature. Based on the numerical findings we present a concept for a scalable amplifier based on an end-pumped, cryogenic, gas-cooled multi-slab architecture.

Electron bunch length measurements from laser-accelerated electrons using single-shot THz time-domain interferometry.

Laser-plasma wakefield-based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5 J, 45 fs, 800 nm laser and a ZnTe-based electro-optical setup, we demonstrate the duration of laser-accelerated, quasimonoenergetic electron bunches [best fit of 32 fs (FWHM) with a 90% upper confidence level of 38 fs] to be shorter than the drive laser pulse, but similar to the plasma period.

High-efficiency, room-temperature nanosecond Yb:YAG laser.

Yb(3+)-doped gain media offer favorable properties for diode-pumped laser amplifiers for high-energy ns-pulses. To reach high optical-to-optical conversion efficiencies at room temperature however, very high and often impractical fluences are required both for pumping and extraction. Low temperature operation offers a solution, but the required cryogenic cooling systems add considerable complexity, bulkiness and cost. Multi-passing both pump and extraction beams through the gain medium is an alternative approach to overcome efficiency limitations at room temperature. In this article we present numerical and experimental results to this effect.We demonstrated ns-pulse output from a diode-pumped Yb:YAG amplifier at an energy of 566 mJ and an optical-to-optical efficiency of 20%, which is almost a doubling of the efficiency achieved with ns-lasers employing Yb(3+)-doped gain media at this energy level.

Near-GeV acceleration of electrons by a nonlinear plasma wave driven by a self-guided laser pulse.

The acceleration of electrons to approximately 0.8 GeV has been observed in a self-injecting laser wakefield accelerator driven at a plasma density of 5.5x10(18) cm(-3) by a 10 J, 55 fs, 800 nm laser pulse in the blowout regime. The laser pulse is found to be self-guided for 1 cm (>10zR), by measurement of a single filament containing >30% of the initial laser energy at this distance. Three-dimensional particle in cell simulations show that the intensity within the guided filament is amplified beyond its initial focused value to a normalized vector potential of a0>6, thus driving a highly nonlinear plasma wave.

Frailty modifies effectiveness of psychosocial intervention in recovery from stroke.

OBJECTIVE: To evaluate the impact of a psychosocial intervention on instrumental activities of daily living, physical performance, cognition and mortality after stroke. DESIGN: A randomized clinical trial. SETTING: Patients were recruited from hospitals and rehabilitation centres; the intervention took place in subjects' homes. SUBJECTS: Two-hundred and ninety-one stroke survivors over age 45. One-hundred and forty-six subjects were assigned to the intervention and 145 subjects were assigned to usual care. INTERVENTION: Up to 16 meetings conducted over six months in the patient's home (approximately weekly for 12 weeks, followed by tri-weekly sessions for another 12 weeks). Sessions lasted approximately 1 hour and included, when possible, the entire support system (stroke survivor, primary caregiver, additional family and friends, and professional caregivers). MAIN OUTCOME MEASURES: Instrumental activities of daily living, physical performance, and cognition were assessed six months post stroke; mortality was assessed at an average of 47 months post stroke. RESULTS: No significant differences in outcomes were observed between the intervention and usual care groups when analysing the total study population. Among non-frail participants (n = 156), subjects randomized to treatment had better scores on instrumental activities of daily living (mean score among treated = 12.4 (standard deviation (SD) = 2.1), mean score among usual care subjects = 11.3 (SD = 2.9), P-value for difference in means = 0.01) and reduced risk of mortality (P = 0.03) than subjects randomized to usual care. CONCLUSION: While there is evidence that the treatment benefited healthier subgroups, results also show evidence that the treatment was not effective, and possibly harmful, in frail subgroups.

Modern skin cleansers.

The course of development of skin cleansers has been one of continual improvement. Soap-based products, used since antiquity, offered improved cleansing over mechanical methods or water alone but could irritate and dry skin. Bars based on synthetic detergents that offer improved skin compatibility compared with soap have become available over the past several decades. Body washes have been growing in consumer popularity. Some of the first body washes introduced into the market offered a moisturization benefit in addition to mildness. Some second-generation body washes that are now on the market use even more sophisticated formulation schemes, such as coacervate technology, to deliver emulsified petrolatum to the skin during washing, providing mild cleansing and a significant dry skin improvement benefit. Consumer demand and the formulation possibilities provided by new product formats, new technologies, and new ingredients will undoubtedly lead to the delivery of even greater skin benefits in the future.

Leg wash protocol to assess the skin moisturization potential of personal cleansing products.

Many personal cleansers claim to provide a skin moisturization benefit, but there has been relatively little discussion in the scientific literature of the clinical methods that provide the basis for such claims. We have developed a leg wash method to assess the dry skin improvement potential of personal cleansing products. The protocol is performed on 'natural' dry leg skin to avoid potential confounds that may result from applying cleansers to soap-damaged skin. Washes are conducted over a period of days or weeks, with visual and instrumental assessments performed at various times throughout the period to characterize products' short-term and cumulative skin effects. Studies conducted with a variety of personal cleansing technologies demonstrate the method's ability to discriminate products on the basis of their dry skin improvement potential. Further, results from a series of eleven leg wash studies conducted with the same treatment pair under different test conditions (time of year, test facility, expert grader) demonstrate the protocol's robustness. The data generated under this protocol show that personal cleansing products differ widely in their ability to improve dry skin. Our results indicate that there is a wide range of efficacy among moisturizing personal cleansing products, with some products delivering a significant dry skin improvement benefit even for periods as long as 24 hours.

Safety assessment of enzyme-containing personal cleansing products: exposure characterization and development of IgE antibody to enzymes after a 6-month use test.

BACKGROUND: Enzyme-containing personal cleansing products were being considered for the consumer market. Although enzymes have been marketed safely for many years as ingredients in laundry products, their use in a personal cleansing application represented a new type of exposure for consumers that was not supported by the historical safety data. An exposure assessment and additional safety data would be needed before marketing to ensure consumer safety. OBJECTIVE: The work in this paper was designed to evaluate the potential for inhalation exposure to the enzyme during use of this new product while showering. Then a clinical trial was conducted to determine whether or not the level, duration, and routes of exposure encountered during use of this product would induce a Type I sensitization response to the enzyme. METHODS: Exposure was assessed during normal showering activities by collecting air samples with both high volume and personal samplers and quantitating enzyme levels with an ELISA. To assess the potential for sensitization, panelists were asked to use a prototype protease-containing bar product for all personal cleansing tasks and to keep a use diary reporting any associated symptoms. Physical and dermatologic examinations and skin prick tests with enzyme were conducted before the test commenced and at 2-month intervals. RESULTS: Exposure assessment results showed that airborne enzyme levels were primarily dependent on the concentration of the enzyme in the personal cleansing product. Mean values for total airborne enzyme protein ranged from 5.7 to 11.8 ng/m3 when enzyme concentration, time of use, and measurement technique remained constant. After 6 months of at-home product use, four of 61 test subjects using the enzyme-containing bar had positive skin prick test responses when tested with the enzyme. The skin prick test data were supplemented with serologic analyses, which detected IgE specific for the protease enzyme. None of these subjects showed any clinical symptoms indicative of allergic reaction. CONCLUSION: The ability of enzymes to induce development of allergic antibodies in this study led to the conclusion that this prototype enzyme-containing personal cleansing bar would represent an inappropriate use of enzymes in a consumer product application. The likelihood of both induction of an immunologic response and subsequent elicitation of allergy symptoms in a small but significant fraction of the user population was high. This finding resulted in the decision to halt further development of this prototype.

The influence of hard water (calcium) and surfactants on irritant contact dermatitis.

Although the induction of irritant contact dermatitis has been extensively studied for surfactants, the role of the environmental factor water hardness (i.e., calcium content) on the induction process has not received attention. Our objective was to investigate differences in surfactant-induced irritant skin reactions from cumulative exposure to 3 different personal cleansing agents and determine whether the irritation potential can be affected by the hardness of the water. 2 commonly used exaggerated washing procedures were variously employed to evaluate representative sodium soap, triethanolamine-soap, or synthetic detergent cleansers under conditions where the water hardness varied from 0-grain to 11-grain (gr). Subjects were clinically evaluated for skin dryness, skin redness, and instrumentally for hydration. Soap binding to skin was quantified using Fourier transform infrared reflectance spectroscopy. Using the more mild wash procedure, skin sites treated under conditions of hard, 11 gr water were significantly drier, had more erythema, and were less hydrated than corresponding sites treated with deionized 0 gr water. All 3 surfactant cleanser behaved similarly. We also found the hardness of the rinse water to be the more significant factor versus that of the wash water. Effect of water hardness on soap binding to skin revealed a similar outcome. Under a more exaggerated wash condition the relationship between water hardness and irritation broke down.

Statistical approaches to stability protocol design.

In stability protocols, data are usually visualized as being generated, and stability evaluation is accomplished at a point in time when sufficient data have been accumulated. Often, data are simply treated by the "statistically best fit" and, as a consequence, statements describing some batches as being first order and some being zero order are frequently used. From a scientific point of view, it is more advantageous at the preformulation stage to ascertain what the stability profile should be (i.e., what the mechanism is) and then apply the statistics to this format. Examples are given of pH profiles, Arrhenius plotting, and dissolution data. In the first case, the use of fractional factorials (a matrix approach) is suggested.

Chemical, physical, and lubricant properties of magnesium stearate.

Three batches of commercial magnesium stearate were characterized in terms of their fatty acid composition, moisture content, and specific surface area. None of these variables appeared to have any effect on the lubricant activity of the samples. The lubricant properties of the compound were further examined using three hydrates of laboratory-prepared (pure) magnesium stearate. Based on the results obtained from the pure samples, it appears that differences in the lubricant properties of magnesium stearate are correlated with differences in moisture content and crystalline structure.