SwePub - search: WFRF:(Wark J S)

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1.	Abe, K., et al. (author) J-PARC Neutrino Beamline Upgrade Technical Design Report 2019 Reports (peer-reviewed)abstract In this document, technical details of the upgrade plan of the J-PARC neutrino beamline for the extension of the T2K experiment are described. T2K has proposed to accumulate data corresponding to 2×1022 protons-on-target in the next decade, aiming at an initial observation of CP violation with 3σ or higher significance in the case of maximal CP violation. Methods to increase the neutrino beam intensity, which are necessary to achieve the proposed data increase, are described.
2.	Abe, K., et al. (author) Neutron tagging following atmospheric neutrino events in a water Cherenkov detector 2022 In: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 17:10 Journal article (peer-reviewed)abstract We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 +/- 9 mu s.
3.	Vinko, S. M., et al. (author) Electronic Structure of an XUV Photogenerated Solid-Density Aluminum Plasma 2010 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:22, s. 225001- Journal article (peer-reviewed)abstract By use of high intensity XUV radiation from the FLASH free-electron laser at DESY, we have created highly excited exotic states of matter in solid-density aluminum samples. The XUV intensity is sufficiently high to excite an inner-shell electron from a large fraction of the atoms in the focal region. We show that soft-x-ray emission spectroscopy measurements reveal the electronic temperature and density of this highly excited system immediately after the excitation pulse, with detailed calculations of the electronic structure, based on finite-temperature density functional theory, in good agreement with the experimental results.
4.	Romaguera, D., et al. (author) Consumption of sweet beverages and type 2 diabetes incidence in European adults: results from EPIC-InterAct 2013 In: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 56:7, s. 1520-1530 Journal article (peer-reviewed)abstract Consumption of sugar-sweetened beverages has been shown, largely in American populations, to increase type 2 diabetes incidence. We aimed to evaluate the association of consumption of sweet beverages (juices and nectars, sugar-sweetened soft drinks and artificially sweetened soft drinks) with type 2 diabetes incidence in European adults. We established a case-cohort study including 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,154 participants selected from eight European cohorts participating in the European Prospective Investigation into Cancer and Nutrition (EPIC) study. After exclusions, the final sample size included 11,684 incident cases and a subcohort of 15,374 participants. Cox proportional hazards regression models (modified for the case-cohort design) and random-effects meta-analyses were used to estimate the association between sweet beverage consumption (obtained from validated dietary questionnaires) and type 2 diabetes incidence. In adjusted models, one 336 g (12 oz) daily increment in sugar-sweetened and artificially sweetened soft drink consumption was associated with HRs for type 2 diabetes of 1.22 (95% CI 1.09, 1.38) and 1.52 (95% CI 1.26, 1.83), respectively. After further adjustment for energy intake and BMI, the association of sugar-sweetened soft drinks with type 2 diabetes persisted (HR 1.18, 95% CI 1.06, 1.32), but the association of artificially sweetened soft drinks became statistically not significant (HR 1.11, 95% CI 0.95, 1.31). Juice and nectar consumption was not associated with type 2 diabetes incidence. This study corroborates the association between increased incidence of type 2 diabetes and high consumption of sugar-sweetened soft drinks in European adults.
5.	Hajkova, V., et al. (author) X-ray laser-induced ablation of lead compounds 2011 In: DAMAGE TO VUV, EUV, AND X-RAY OPTICS III. - : SPIE. Conference paper (peer-reviewed)abstract The recent commissioning of a X-ray free-electron laser triggered an extensive research in the area of X-ray ablation of high-Z, high-density materials. Such compounds should be used to shorten an effective attenuation length for obtaining clean ablation imprints required for the focused beam analysis. Compounds of lead (Z=82) represent the materials of first choice. In this contribution, single-shot ablation thresholds are reported for PbWO(4) and PbI(2) exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 J/cm(2) at 1.55 nm in lead tungstate although a value of 0.4 J/cm(2) is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm(2) at a FEL wavelength of 13.5 nm. Mechanisms of ablation processes are discussed to explain this discrepancy. Lead iodide shows at 1.55 nm significantly lower ablation threshold than tungstate although an attenuation length of the radiation is in both materials quite the same. Lower thermal and radiation stability of PbI(2) is responsible for this finding.
6.	Cavalieri, A L, et al. (author) Clocking femtosecond X rays. 2005 In: Phys Rev Lett. - 0031-9007. ; 94:11 Journal article (peer-reviewed)abstract Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of the x-ray pulse duration are hampered by the inability to precisely synchronize an external laser to the accelerator. At the Sub-Picosecond Pulse Source at the Stanford Linear-Accelerator Center we solved this problem by measuring the arrival time of each high energy electron bunch with electro-optic sampling. This measurement indirectly determined the arrival time of each x-ray pulse relative to an external pump laser pulse with a time resolution of better than 60 fs rms.
7.	Gaffney, K J, et al. (author) Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb 2005 In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 95:12 Journal article (peer-reviewed)abstract The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs. This structural anisotropy indicates that the initially generated fluid differs significantly from the equilibrium liquid.
8.	Scott, R. A., et al. (author) The link between family history and risk of type 2 diabetes is not explained by anthropometric, lifestyle or genetic risk factors : the EPIC-InterAct study 2013 In: Diabetologia. - : Springer. - 0012-186X .- 1432-0428. ; 56:1, s. 60-69 Journal article (peer-reviewed)abstract Aims/hypothesis: Although a family history of type 2 diabetes is a strong risk factor for the disease, the factors mediating this excess risk are poorly understood. In the InterAct case-cohort study, we investigated the association between a family history of diabetes among different family members and the incidence of type 2 diabetes, as well as the extent to which genetic, anthropometric and lifestyle risk factors mediated this association.Methods: A total of 13,869 individuals (including 6,168 incident cases of type 2 diabetes) had family history data available, and 6,887 individuals had complete data on all mediators. Country-specific Prentice-weighted Cox models were fitted within country, and HRs were combined using random effects meta-analysis. Lifestyle and anthropometric measurements were performed at baseline, and a genetic risk score comprising 35 polymorphisms associated with type 2 diabetes was created.Results: A family history of type 2 diabetes was associated with a higher incidence of the condition (HR 2.72, 95% CI 2.48, 2.99). Adjustment for established risk factors including BMI and waist circumference only modestly attenuated this association (HR 2.44, 95% CI 2.03, 2.95); the genetic score alone explained only 2% of the family history-associated risk of type 2 diabetes. The greatest risk of type 2 diabetes was observed in those with a biparental history of type 2 diabetes (HR 5.14, 95% CI 3.74, 7.07) and those whose parents had been diagnosed with diabetes at a younger age (<50 years; HR 4.69, 95% CI 3.35, 6.58), an effect largely confined to a maternal family history.Conclusions/interpretation: Prominent lifestyle, anthropometric and genetic risk factors explained only a marginal proportion of the excess risk associated with family history, highlighting the fact that family history remains a strong, independent and easily assessed risk factor for type 2 diabetes. Discovering factors that will explain the association of family history with type 2 diabetes risk will provide important insight into the aetiology of type 2 diabetes.
9.	Nelson, A. J., et al. (author) Soft x-ray free electron laser microfocus for exploring matter under extreme conditions 2009 In: Optics Express. - 1094-4087. ; 17:20, s. 18271-18278 Journal article (peer-reviewed)abstract We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 mu J, 5Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) -PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of <= 1 mu m. Observations were correlated with simulations of best focus to provide further relevant information.
10.	Vinko, S. M., et al. (author) Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum 2020 In: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 124:22 Journal article (peer-reviewed)abstract The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.
11.	Lindenberg, AM, et al. (author) Atomic-scale visualization of inertial dynamics 2005 In: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 308:5720, s. 392-395 Journal article (peer-reviewed)abstract The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids.
12.	Moayyeri, Alireza, et al. (author) Genetic determinants of heel bone properties : genome-wide association meta-analysis and replication in the GEFOS/GENOMOS consortium 2014 In: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 23:11, s. 3054-3068 Journal article (peer-reviewed)abstract Quantitative ultrasound of the heel captures heel bone properties that independently predict fracture risk and, with bone mineral density (BMD) assessed by X-ray (DXA), may be convenient alternatives for evaluating osteoporosis and fracture risk. We performed a meta-analysis of genome-wide association (GWA) studies to assess the genetic determinants of heel broadband ultrasound attenuation (BUA; n = 14 260), velocity of sound (VOS; n = 15 514) and BMD (n = 4566) in 13 discovery cohorts. Independent replication involved seven cohorts with GWA data (in silico n = 11 452) and new genotyping in 15 cohorts (de novo n = 24 902). In combined random effects, meta-analysis of the discovery and replication cohorts, nine single nucleotide polymorphisms (SNPs) had genome-wide significant (P < 5 x 10(-8)) associations with heel bone properties. Alongside SNPs within or near previously identified osteoporosis susceptibility genes including ESR1 (6q25.1: rs4869739, rs3020331, rs2982552), SPTBN1 (2p16.2: rs11898505), RSPO3 (6q22.33: rs7741021), WNT16 (7q31.31: rs2908007), DKK1 (10q21.1: rs7902708) and GPATCH1 (19q13.11: rs10416265), we identified a new locus on chromosome 11q14.2 (rs597319 close to TMEM135, a gene recently linked to osteoblastogenesis and longevity) significantly associated with both BUA and VOS (P < 8.23 x 10(-14)). In meta-analyses involving 25 cohorts with up to 14 985 fracture cases, six of 10 SNPs associated with heel bone properties at P < 5 x 10(-6) also had the expected direction of association with any fracture (P < 0.05), including three SNPs with P < 0.005: 6q22.33 (rs7741021), 7q31.31 (rs2908007) and 10q21.1 (rs7902708). In conclusion, this GWA study reveals the effect of several genes common to central DXA-derived BMD and heel ultrasound/DXA measures and points to a new genetic locus with potential implications for better understanding of osteoporosis pathophysiology.
13.	Trigo, M., et al. (author) Fourier-transform inelastic X-ray scattering from time- and momentum-dependent phonon-phonon correlations 2013 In: Nature Physics. - 1745-2473. ; 9:12, s. 790-794 Journal article (peer-reviewed)abstract The macroscopic characteristics of a material are determined by its elementary excitations, which dictate the response of the system to external stimuli. The spectrum of excitations is related to fluctuations in the density-density correlations and is typically measured through frequency-domain neutron(1) or X-ray(2-4) scattering. Time-domain measurements of these correlations could yield a more direct way to investigate the excitations of solids and their couplings both near to and far from equilibrium. Here we show that we can access large portions of the phonon dispersion of germanium by measuring the diffuse scattering from femtosecond X-ray free-electron laser pulses. A femtosecond optical laser pulse slightly quenches the vibrational frequencies, producing pairs of high-wavevector phonons with opposite momenta. These phonons manifest themselves as time-dependent coherences in the displacement correlations(5) probed by the X-ray scattering. As the coherences are preferentially created in regions of strong electron-phonon coupling, the time-resolved approach is a natural spectroscopic tool for probing low-energy collective excitations in solids, and their microscopic interactions.
14.	Zamora-Ros, R., et al. (author) Dietary intakes and food sources of phytoestrogens in the European Prospective Investigation into Cancer and Nutrition (EPIC) 24-hour dietary recall cohort 2012 In: European Journal of Clinical Nutrition. - : Springer Science and Business Media LLC. - 0954-3007 .- 1476-5640. ; 66:8, s. 932-941 Journal article (peer-reviewed)abstract BACKGROUND/OBJECTIVES: Phytoestrogens are estradiol-like natural compounds found in plants that have been associated with protective effects against chronic diseases, including some cancers, cardiovascular diseases and osteoporosis. The purpose of this study was to estimate the dietary intake of phytoestrogens, identify their food sources and their association with lifestyle factors in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. SUBJECTS/METHODS: Single 24-hour dietary recalls were collected from 36 037 individuals from 10 European countries, aged 35-74 years using a standardized computerized interview programe (EPIC-Soft). An ad hoc food composition database on phytoestrogens (isoflavones, lignans, coumestans, enterolignans and equol) was compiled using data from available databases, in order to obtain and describe phytoestrogen intakes and their food sources across 27 redefined EPIC centres. RESULTS: Mean total phytoestrogen intake was the highest in the UK health-conscious group (24.9 mg/day in men and 21.1 mg/day in women) whereas lowest in Greece (1.3 mg/day) in men and Spain-Granada (1.0 mg/day) in women. Northern European countries had higher intakes than southern countries. The main phytoestrogen contributors were isoflavones in both UK centres and lignans in the other EPIC cohorts. Age, body mass index, educational level, smoking status and physical activity were related to increased intakes of lignans, enterolignans and equol, but not to total phytoestrogen, isoflavone or coumestan intakes. In the UK cohorts, the major food sources of phytoestrogens were soy products. In the other EPIC cohorts the dietary sources were more distributed, among fruits, vegetables, soy products, cereal products, non-alcoholic and alcoholic beverages. CONCLUSIONS: There was a high variability in the dietary intake of total and phytoestrogen subclasses and their food sources across European regions.
15.	Elks, Cathy E., et al. (author) Age at Menarche and Type 2 Diabetes Risk The EPIC-InterAct study 2013 In: Diabetes Care. - : American Diabetes Association. - 1935-5548 .- 0149-5992. ; 36:11, s. 3526-3534 Journal article (peer-reviewed)abstract OBJECTIVEYounger age at menarche, a marker of pubertal timing in girls, is associated with higher risk of later type 2 diabetes. We aimed to confirm this association and to examine whether it is explained by adiposity.RESEARCH DESIGN AND METHODSThe prospective European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study consists of 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,154 individuals from 26 research centers across eight European countries. We tested the association between age at menarche and incident type 2 diabetes using Prentice-weighted Cox regression in 15,168 women (n = 5,995 cases). Models were adjusted in a sequential manner for potential confounding and mediating factors, including adult BMI.RESULTSMean menarcheal age ranged from 12.6 to 13.6 years across InterAct countries. Each year later menarche was associated with 0.32 kg/m(2) lower adult BMI. Women in the earliest menarche quintile (8-11 years, n = 2,418) had 70% higher incidence of type 2 diabetes compared with those in the middle quintile (13 years, n = 3,634), adjusting for age at recruitment, research center, and a range of lifestyle and reproductive factors (hazard ratio [HR], 1.70; 95% CI, 1.49-1.94; P < 0.001). Adjustment for BMI partially attenuated this association (HR, 1.42; 95% CI, 1.18-1.71; P < 0.001). Later menarche beyond the median age was not protective against type 2 diabetes.CONCLUSIONSWomen with history of early menarche have higher risk of type 2 diabetes in adulthood. Less than half of this association appears to be mediated by higher adult BMI, suggesting that early pubertal development also may directly increase type 2 diabetes risk.
16.	Kermani, NZ, et al. (author) Type 2-low asthma phenotypes by integration of sputum transcriptomics and serum proteomics 2021 In: Allergy. - : Wiley. - 1398-9995 .- 0105-4538. ; 76:1, s. 380-383 Journal article (peer-reviewed)
17.	Milathianaki, D., et al. (author) Femtosecond Visualization of Lattice Dynamics in Shock-Compressed Matter 2013 In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 342:6155, s. 220-223 Journal article (peer-reviewed)abstract The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate phenomena. However, the visualization of lattice dynamics at scales commensurate with those of atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction measurements unveiling the response of copper to laser shock-compression at peak normal elastic stresses of similar to 73 gigapascals (GPa) and strain rates of 10(9) per second. We capture the evolution of the lattice from a one-dimensional (1D) elastic to a 3D plastically relaxed state within a few tens of picoseconds, after reaching shear stresses of 18 GPa. Our in situ high-precision measurement of material strength at spatial (<1 micrometer) and temporal (<50 picoseconds) scales provides a direct comparison with multimillion-atom molecular dynamics simulations.
18.	Molina-Montes, E., et al. (author) Dietary intake of iron, heme-iron and magnesium and pancreatic cancer risk in the European prospective investigation into cancer and nutrition cohort 2012 In: International Journal of Cancer. - : Wiley. - 0020-7136 .- 1097-0215. ; 131:7 Journal article (peer-reviewed)abstract Several studies support a protective effect of dietary magnesium against type 2 diabetes, but a harmful effect for iron. As diabetes has been linked to pancreatic cancer, intake of these nutrients may be also associated with this cancer. We examined the association between dietary intake of magnesium, total iron and heme-iron and pancreatic cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. In total, 142,203 men and 334,999 women, recruited between 1992 and 2000, were included. After an average follow-up of 11.3 years, 396 men and 469 women developed exocrine pancreatic cancer. Hazard ratios and 95% confidence intervals (CIs) were obtained using Cox regression stratified by age and center, and adjusted for energy intake, smoking status, height, weight, and self-reported diabetes status. Neither intake of magnesium, total iron nor heme-iron was associated with pancreatic cancer risk. In stratified analyses, a borderline inverse association was observed among overweight men (body mass index, =25 kg/m2) with magnesium (HRper 100 mg/day increase = 0.79, 95% CI = 0.631.01) although this was less apparent using calibrated intake. In female smokers, a higher intake of heme-iron was associated with a higher pancreatic cancer risk (HR per 1 mg/day increase = 1.38, 95% CI = 1.101.74). After calibration, this risk increased significantly to 2.5-fold (95% CI = 1.225.28). Overall, dietary magnesium, total iron and heme-iron were not associated with pancreatic cancer risk during the follow-up period. Our observation that heme-iron was associated with increased pancreatic cancer risk in female smokers warrants replication in additional study populations.
19.	Rehman, S, et al. (author) Role of dietary lipids in chronic obstructive pulmonary disease 2023 In: RESPIROLOGY. - 1323-7799. ; 28, s. 154-154 Conference paper (other academic/artistic)
20.	Zamora-Ros, R., et al. (author) Flavonoid and lignan intake in relation to bladder cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) study 2014 In: British Journal of Cancer. - : Springer Science and Business Media LLC. - 0007-0920 .- 1532-1827. ; 111:9, s. 1870-1880 Journal article (peer-reviewed)abstract Background: There is growing evidence of the protective role of dietary intake of flavonoids and lignans on cancer, but the association with bladder cancer has not been thoroughly investigated in epidemiological studies. We evaluated the association between dietary intakes of total and subclasses of flavonoids and lignans and risk of bladder cancer and its main morphological type, urothelial cell carcinoma (UCC), within the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Methods: A cohort of 477 312 men and women mostly aged 35-70 years, were recruited in 10 European countries. At baseline, dietary flavonoid and lignan intakes were estimated using centre-specific validated questionnaires and a food composition database based on the Phenol-Explorer, the UK Food Standards Agency and the US Department of Agriculture databases. Results: During an average of 11 years of follow-up, 1575 new cases of primary bladder cancer were identified, of which 1425 were UCC (classified into aggressive (n = 430) and non-aggressive (n = 413) UCC). No association was found between total flavonoid intake and bladder cancer risk. Among flavonoid subclasses, significant inverse associations with bladder cancer risk were found for intakes of flavonol (hazard ratio comparing fifth with first quintile (HRQ5-Q1) 0.74, 95% confidence interval (CI): 0.61-0.91; P-trend = 0.009) and lignans (HRQ5-Q 10.78, 95% CI: 0.62-0.96; P-trend = 0.046). Similar results were observed for overall UCC and aggressive UCC, but not for non-aggressive UCC. Conclusions: Our study suggests an inverse association between the dietary intakes of flavonols and lignans and risk of bladder cancer, particularly aggressive UCC.
21.	Lindenberg, A. M, et al. (author) Time-resolved X-ray diffraction from coherent phonons during a laser-induced phase transition 2000 In: Physical Review Letters. - 1079-7114. ; 84:1, s. 111-114 Journal article (peer-reviewed)abstract Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.
22.	Sheppard, J M H, et al. (author) Simulations of the phonon Bragg switch in GaAs 2005 In: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 136:3, s. 181-185 Journal article (peer-reviewed)abstract It has recently been proposed that X-rays can be switched on sub-picosecond time-scales by using laser-generated coherent optical phonons: The so called phonon Bragg switch. We present here detailed simulations of the efficiency of such a switch by solving the time-dependent generalized Takagi-Taupin equations utilizing a perturbative approach. We explore the switching efficiency in diffraction from the (004) planes of GaAs as a function of both excited phonon wave vector and amplitude.
23.	Sondhauss, Peter, et al. (author) Time resolved X-ray diffraction and non-thermal inelastic X-ray scattering 2004 In: AIP Conference Proceedings. - 1551-7616 .- 0094-243X. ; 705, s. 1387-1390 Conference paper (peer-reviewed)abstract Atomic processes like e.g. molecular vibrations, chemical reactions or phase transitions happen on picosecond down to femtosecond time scales. Novel pulsed X-ray sources or alternatively ultrafast X-ray detectors allow the investigation of these processes in real time. A powerful tool for the investigation of the dynamics in crystalline materials is time resolved X-ray diffraction (TRXD). As an example the authors present the measurement of "phonon branch folding" in a GaSb/InAs superlattice by means of TRXD. In the second part we look forward to the near future of TRXD. X-ray scattering from coherent acoustic and optical phonons has recently become describable within the framework of dynamical diffraction theory. This theory provides the means for the detailed modeling of how various lattice dynamical processes manifest themselves in the diffracted X-ray signal. Simulations are presented showing the effects of coherent acoustic and optical phonons on the rocking curve of quartz (010)
24.	Enquist, Henrik, et al. (author) Large acoustic transients induced by non-thermal melting of InSb 2007 In: Physical Review Letters. - 1079-7114. ; 98 Journal article (peer-reviewed)abstract We have observed large-amplitude strain waves following a rapid change in density of InSb due to nonthermal melting. The strain has been measured in real time via time-resolved x-ray diffraction, with a temporal resolution better than 2 ps. The change from the solid to liquid density of the surface layer launches a high-amplitude strain wave into the crystalline material below. This induces an effective plane rotation in the asymmetrically cut crystal leading to deflection of the diffracted beam. The uniform strain in the layer below the molten layer is 2.0(±0.2)%. A strain of this magnitude develops within 5 ps of the incident pulse showing that the liquid has reached the equilibrium density within this time frame. Both the strain amplitude and the depth of the strained material in the solid can be explained by assuming a reduction in the speed of sound in the nonequilibrium liquid compared to measured equilibrium values.
25.	Reis, D. A, et al. (author) Probing impulsive strain propagation with x-ray pulses 2001 In: Physical Review Letters. - 1079-7114. ; 86:14, s. 3072-3075 Journal article (peer-reviewed)abstract Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden reflections in InSb is used to follow the propagation of a coherent acoustic pulse generated by ultrafast laser excitation. The surface and bulk components of the strain could be simultaneously measured due to the large x-ray penetration depth. Comparison of the experimental data with dynamical diffraction simulations suggests that the conventional model for impulsively generated strain underestimates the partitioning of energy into coherent modes.
26.	Sondhauss, Peter, et al. (author) Picosecond X-ray studies of coherent folded phonons in a multiple quantum well 2005 In: Physical Review Letters. - Lund Univ, Dept Phys, SE-22100 Lund, Sweden. European Synchrotron Radiat Facil, F-38043 Grenoble, France. Malmo Univ, Sch Technol & Soc, S-20506 Malmo, Sweden. Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England. : AMERICAN PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 94 Journal article (peer-reviewed)abstract Coherent folded acoustic phonons in a multilayered GaSb/InAs epitaxial heterostructure were generated by femtosecond laser pulses and studied by means of ultrafast x-ray diffraction. Coherent phonons excited simultaneously in the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the refractive index due to photogenerated free carriers.

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