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Generation of hard x rays by ultrafast terawatt lasers (2001)

Guo, T.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 72 (2001), S. 41-47

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: A compact, tabletop terawatt Ti:sapphire laser drive, ultrafast hard x-ray source for time-resolved x-ray diffraction studies is described. With a copper target the energy conversion efficiency from laser photons (800 nm) to copper K x-ray radiation (1.54 Å) is 0.008%. The optimal laser intensity for generating these x rays is 1018 W cm−2, lower than the highest laser intensity available (5×1018 W cm−2) from the laser system. These results are consistent with a theoretical model proposed on the basis that the x rays are produced as a result of laser driven electron ionization of core level electrons of Cu atoms near room temperature. This source also provides features such as ultrashort pulse duration, extremely small source size, variable wavelengths, high peak spectral brightness, and the potential for multiple beam line experiments. X-ray diffraction patterns from GaAs single crystals and amorphous Ni films recorded with this source are presented. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1327309

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Does previous infection protect against atopic eczema and recurrent wheeze ininfancy? (2004)

Kramer, M. S. ; Guo, T. ; Platt, R. W. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Clinical & experimental allergy 34 (2004), S. 0

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ISSN: 1365-2222

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: Background Frequent infection in infancy and early childhood has been hypothesized to explain the low prevalence of asthma and other atopic disease among children in developing countries (the so-called ‘hygiene hypothesis’), but the low prevalence in Eastern Europe remains unexplained.Objective To test the hygiene hypothesis in the Republic of Belarus by examining the relationship between gastrointestinal (GI) and respiratory infection and two potentially atopic outcomes in the first 12 months of life: atopic eczema and recurrent wheeze.Methods We carried out two case–control studies nested within a large (n=17 046) randomized trial in Belarus, with cases defined as (1) first occurrence of atopic eczema (n=819) and (2) second episode of wheezing (n=112). Incidence density sampling was used to select four matched controls born within 1 month at the same hospital as the case. Exposure was defined as one or more episodes of GI or respiratory infection (examined separately) with onset 〉7 days before onset of the case's atopic outcome. Analyses controlled for family atopic history, duration of exclusive breastfeeding, sex, birth weight, maternal education, and (for recurrent wheeze) maternal smoking.Results For atopic eczema, prior GI infection occurred in 7.4% of cases vs. 6.0% of controls [adjusted OR=1.27 (0.94–1.72)] and prior respiratory infection in 35.2% vs. 32.6% [adjusted OR=1.14 (95% CI=0.94–1.37)]. For recurrent wheeze, prior GI infection occurred in 9.8% of cases vs. 7.4% of controls [adjusted OR=1.30 (0.60–2.82)].Conclusion Our results do not support the hypothesis that infection protects against atopic eczema or recurrent wheezing in the first 12 months of life.