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Wilson, Kelly (2019). Do women reap the benefits? Exploring access and social exclusion among village chicken producers in Kenya. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohi...

When refugees arrive in their new resettlement country, they are designated to work with a caseworker employed with a resettlement agency who helps them acclimate to their new environment and break...

Relatively small-scale laser-driven sources of short wavelength radiation covering a range from the extreme ultraviolet to the hard X-ray regime are now available. Because the duration of the X-ray pulses is comparable to, or shorter than the laser pulse width, it is possible to carry out X-ray measurements with picosecond or femtosecond time resolution.

Three experiments were conducted to evaluate the effects of feeding 2-hydroxy-4- (methylthio)-butanoic acid (HMTBA) on performance and carcass characteristics of feedlot cattle and on microbial fermentation in a continuous-culture system. In Exp. 1, 160 crossbred steers (initial BW = 385 +/- 10.3 kg) were assigned to 4 treatments consisting of control (0% HMTBA) or 3 diets containing HMTBA (0.069, 0.137, and 0.204%; DM basis) in a randomized complete block design. As the percent of HMTBA increased in the diet, final BW (P = 0.069), final BW adjusted to a constant dressing percent (P = 0.063), and overall ADG (P = 0.099) tended to decrease linearly. Overall DMI decreased linearly (P or = 0.10) were noted for carcass characteristics, except for a tendency (P = 0.078) for a linear increase in the percentage of cattle grading USDA Choice with increasing HMTBA dose. In Exp. 2, 80 crossbred steers (initial BW = 450 +/- 17 kg) in a randomized complete block design were assigned to a control (0% HMTBA) diet or to a diet in which the concentrations of HMTBA were gradually increased from 0.036 to 0.212% of DM over a 50-d period. The HMTBA-containing diet tended to decrease DMI (P = 0.132), but G:F (P = 0.319) for the overall feeding period, carcass measurements, and USDA quality grade (P > or = 0.149) did not differ between treatments. In Exp. 3, continuous culture fermenters (n = 5/treatment) were used to determine the effects of HMTBA (control vs. 0.24% HMTBA) on microbial fermentation. No differences (P > or = 0.31) were detected between treatments in ruminal OM digestibility, microbial N synthesis, pH, ammonia, molar proportions of VFA, or effluent concentration of selected long-chain fatty acids. These results suggest that HMTBA decreased DMI by feedlot steers fed a steam-flaked corn-based diet in a dose-dependent manner; however, gradually increasing the dose over time seemed to moderate effects on DMI. No major changes in microbial fermentation in continuous culture were observed with HMTBA at 0.24% of dietary DM, suggesting effects of HMTBA on DMI were not likely associated with changes in ruminal digestion or fermentation.

Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer x d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P > 0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P 0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P < 0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer x d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer x d) over a 30-d period.

We report experimental results on the low-temperature uptake of HCl on H(2)O ice (ice). HCl was deposited on the surface at greater than monolayer amounts at 85 K, and the ice substrate was heated. The temperature dependence of the HCl vapor pressure from this phase was measured from 110 to 150 K, with the nucleation of a bulk hydrate phase observed at 150 K. Measurements were conducted in a closed system by simultaneous application of gas phase mass spectrometry and surface spectroscopy to characterize vapor/solid equilibrium and the nucleation of bulk hydrate phases. Combining the nucleation data reported here with data we reported previously (180 to 200 K) and data from two other laboratories (165 and 170 K), the thermodynamic boundaries for the nucleation of both the metastable bulk solution and bulk hydrate phases subsequent to monolayer adsorption of HCl have been determined. The nucleation of the metastable bulk solution phase occurs promptly at monolayer coverage at the ice/liquid coexistence boundary on the binary bulk phase diagram. The nucleation of the bulk hexahydrate occurs from this metastable solution along a locus of points defining a state of constant solution free energy. This measured free energy is -51.2 +/- 0.9 kJ/mol. Finally, the temperature dependence of the HCl vapor pressure from the low-temperature phase is reported here for the first time and is consistent with that of the metastable solution predicted by this thermodynamic model of uptake, extending the range of validity of this model of adsorption followed by bulk solution and hydrate nucleation to a lower bound in temperature of 110 K.

Background: Physician-assisted dying at the end of life has become a significant issue of public discussion. While legally available in a number of countries and jurisdictions, it remains controversial and illegal in New Zealand. Aim: The study aimed to explore the reasons some healthy older New Zealanders oppose physician-assisted dying in order to inform current debate. Design: Recorded interviews were transcribed and analysed by the authors after some edits had been made by respondents. Setting/participants: In all, 11 older participants (over 65 years) who responded to advertisements placed in Grey Power magazines and a University of Auckland email list were interviewed for around 1 h and asked a number of open-ended questions. Results: Four central themes opposing physician-assisted dying were identified from the interviews: one’s personal experience with health care and dying and death, religious reasoning and beliefs, slippery slope worries and concern about potential abuses if physician-assisted dying were legalised. Conclusions: An important finding of the study suggests that how some older individuals think about physician-assisted dying is strongly influenced by their past experiences of dying and death. While some participants had witnessed good, well-managed dying and death experiences which confirmed for them the view that physician-assisted dying was unnecessary, those who had witnessed poor dying and death experiences opposed physician-assisted dying on the grounds that such practices could come to be abused by others.

The purpose of this study is to determine how children are transported to and from hospital, and to understand caregivers' car restraint knowledge base.A convenience sample of 200 inpatients in five wards at Starship Children's Hospital. Parents or caregivers underwent a short interview, asking: the usual restraint used by their child; how the child was transported to hospital; their plans for transporting the child home; their knowledge of current New Zealand legislation and best practice recommendations regarding child car restraints.In their normal car travel, 95% children younger than 5 years were reported to be using a car seat all the time, versus 34% children aged 5 to 9 years. In their journey to hospital, 8% (7/91) of children younger than 5 years were not in a child car seat; 27% (3/11) of children younger than 5 years transported to hospital in a taxi, were not in car seats (one was held in the parent's lap). Responses about the planned trip home showed nine children (7%) were at immediate risk of being transported in an unsafe way, without a child restraint. Questions about awareness of correct child restraint use showed 68% of the families with children aged 5 to 9 were unaware that it was important to continue to use a child restraint for their child.There is an opportunity for child health professionals to provide support to families with children in hospital by collaborating with established child restraint rental agencies and making best practice child restraint advice and products more readily available. New Zealand law should be updated to require the use of child car restraints beyond a child's fifth birthday.

We present a model of heterogeneous reactivity based on physical adsorption that describes the observed relative humidity dependence of the ClONO 2 reaction probability with H 2 O and HCl on sulfuric acid tetrahydrate ice surfaces (SAT) and with H 2 O on nitric acid trihydrate (NAT). The laboratory data are modeled using only two parameters for a given system, the measured reaction probability on a neat H 2 O ice surface, and a constant from the BET theory which describes the fraction of an acid hydrate surface covered by H 2 O as a function of relative humidity. The model indicates that ClONO 2 reactivity with both HCl and H 2 O on SAT and with H 2 O on NAT is controlled by the surface coverage of H 2 O. In contrast, the reaction of ClONO 2 + HCl on NAT is better described by an alternative model based on reactivity in solutions formed within a porous ice by capillary liquid absorption.

This annual report is prepared pursuant to the National Emission Standards for Hazardous Air Pollutants (NESHAPs; Title 40 Code of Federal Regulations [CFR] Part 61, Subpart H). Subpart H governs radionuclide emissions to air from U.S. Department of Energy (DOE) facilities. NESHAPs limits the emission of radionuclides to the ambient air from DOE facilities to levels resulting in an annual effective dose equivalent (EDE) of 10 mrem (100 {micro}Sv) to any member of the public. The EDEs for the Lawrence Livermore National Laboratory (LLNL) site-wide maximally exposed members of the public from operations in 2007 are summarized here. Livermore site: 0.0031 mrem (0.031 {micro}Sv) (42% from point source emissions, 58% from diffuse source emissions). The point source emissions include gaseous tritium modeled as tritiated water vapor as directed by the U.S. Environmental Protection Agency (EPA) Region IX; the resulting dose is used for compliance purposes. Site 300: 0.0035 mrem (0.035 {micro}Sv) (90% from point source emissions, 10% from diffuse source emissions). The EDEs were calculated using the U.S. EPA-approved CAP88-PC air dispersion/dose-assessment model, except for doses for two diffuse sources that were estimated using measured radionuclide concentrations and dose calculations. Specific inputs to CAP88-PC for the modeled sources included site-specificmore » meteorological data and source emissions data, the latter variously based on continuous stack effluent monitoring data, stack flow or other release-rate information, ambient air monitoring data, and facility knowledge.« less

Three experiments were conducted to evaluate the effects of feeding 2-hydroxy-4- (methylthio)-butanoic acid (HMTBA) on performance and carcass characteristics of feedlot cattle and on microbial fermentation in a continuous-culture system. In Exp. 1, 160 crossbred steers (initial BW = 385 +/- 10.3 kg) were assigned to 4 treatments consisting of control (0% HMTBA) or 3 diets containing HMTBA (0.069, 0.137, and 0.204%; DM basis) in a randomized complete block design. As the percent of HMTBA increased in the diet, final BW (P = 0.069), final BW adjusted to a constant dressing percent (P = 0.063), and overall ADG (P = 0.099) tended to decrease linearly. Overall DMI decreased linearly (Por = 0.006) with increasing HMTBA dose. No differences (Por = 0.10) were noted for carcass characteristics, except for a tendency (P = 0.078) for a linear increase in the percentage of cattle grading USDA Choice with increasing HMTBA dose. In Exp. 2, 80 crossbred steers (initial BW = 450 +/- 17 kg) in a randomized complete block design were assigned to a control (0% HMTBA) diet or to a diet in which the concentrations of HMTBA were gradually increased from 0.036 to 0.212% of DM over a 50-d period. The HMTBA-containing diet tended to decrease DMI (P = 0.132), but G:F (P = 0.319) for the overall feeding period, carcass measurements, and USDA quality grade (Por = 0.149) did not differ between treatments. In Exp. 3, continuous culture fermenters (n = 5/treatment) were used to determine the effects of HMTBA (control vs. 0.24% HMTBA) on microbial fermentation. No differences (Por = 0.31) were detected between treatments in ruminal OM digestibility, microbial N synthesis, pH, ammonia, molar proportions of VFA, or effluent concentration of selected long-chain fatty acids. These results suggest that HMTBA decreased DMI by feedlot steers fed a steam-flaked corn-based diet in a dose-dependent manner; however, gradually increasing the dose over time seemed to moderate effects on DMI. No major changes in microbial fermentation in continuous culture were observed with HMTBA at 0.24% of dietary DM, suggesting effects of HMTBA on DMI were not likely associated with changes in ruminal digestion or fermentation.

Even though there have been extensive investigations of the temporal integration limits of binocular vision in perceptual tasks, relatively little is known about temporal integration limits during the completion of visuomotor tasks. To assess the temporal integration limits of binocular disparity within the action domain, accuracy of reach kinematics in a reaching and grasping task under continuous binocular and monocular viewing conditions were compared with those obtained under alternating monocular viewing conditions with interocular delays ranging from 14 to 58 ms. Even the shortest of the interocular delays resulted in larger grip apertures than those in the continuous monocular and binocular viewing conditions. The short temporal integration interval of stereovision obtained in this study cannot be accounted for by differential visual feedback in the binocular and interocular delay conditions, nor is it likely to be a consequence of visual disruption due to the interocular delays. Our findings suggest that the visuomotor system has little tolerance to interocular delay.

Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer x d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P0.01), and G:F (P0.01) increased linearly. As duration of feeding increased, ADG increased quadratically (P = 0.04), with tendencies for quadratic effects for FBW (P = 0.06), DMI (P = 0.07), and G:F (P = 0.09). Hot carcass weight increased linearly (P = 0.02) as dose of RAC increased. Thus, increasing the dose of RAC from 0 to 200 mg/(steer x d) and the duration of feeding from 28 to 42 d improved feedlot performance, although quadratic responses for duration of feeding indicated little improvement as the duration was extended from 35 to 42 d. In Exp. 2, 12 crossbred beef steers (BW = 593 kg) were used in a completely random design to evaluate the effects of RAC [0 or 200 mg/(steer x d) for 30 d; 6 steers/treatment] on rate of intake, daily variation in intake patterns, and acid-base balance. To assess intake patterns, absolute values of daily deviations in feed delivered to each steer relative to the total quantity of feed delivered were analyzed as repeated measures. There were no differences (P0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer x d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer x d) over a 30-d period.

NESHAPs limits the emission of radionuclides to the ambient air from DOE facilities to levels resulting in an annual effective dose equivalent (EDE) of 10 mrem (100 {micro}Sv) to any member of the public. The EDEs for the Lawrence Livermore National Laboratory (LLNL) site-wide maximally exposed members of the public from operations in 2006 are summarized here. Livermore site: 0.0045 mrem (0.045 {micro}Sv) (36% from point source emissions, 64% from diffuse source emissions). The point source emissions include gaseous tritium modeled as tritiated water vapor as directed by the U.S. Environmental Protection Agency (EPA) Region IX; the resulting dose is used for compliance purposes. Site 300: 0.016 mrem (0.16 {micro}Sv) (87.5% from point source emissions, 12.5% from diffuse source emissions). The EDEs were calculated using the EPA-approved CAP88-PC air dispersion/dose-assessment model, except for doses for two diffuse sources that were estimated using measured radionuclide concentrations and dose coefficients. Specific inputs to CAP88-PC for the modeled sources included site-specific meteorological data and source emissions data, the latter variously based on continuous stack effluent monitoring data, stack flow or other release-rate information, ambient air monitoring data, and facility knowledge.

We prepared polarization-entangled photon pairs and sent one of the photons through a Mach-Zehnder interferometer. The apparatus was arranged so that when going through each arm of the interferometer the pairs were in a different Bell state. The distinguishability of the interferometer paths was determined by projecting the entangled state of the two photons with a polarizer placed in the path of the photon that does not go through the interferometer. As a consequence, actions on the remote photon determined nonlocally the visibility of the interference pattern. We present a full theoretical analysis and experimental results that confirm the theoretical predictions.

This annual report is prepared pursuant to the National Emission Standards for Hazardous Air Pollutants (NESHAPs; Title 40 Code of Federal Regulations [CFR] Part 61, Subpart H). Subpart H governs radionuclide emissions to air from Department of Energy (DOE) facilities.

[1] We present a fully thermodynamically constrained model to calculate the thickness of the quasiliquid layer on ice surfaces and apply this model to atmospherically relevant situations to calculate the quasiliquid thickness and volume for ice aerosols and snow pack. These volumes are comparable to the liquid volumes present in a representative liquid-droplet cloud. The pure water calculations represent conservative lower bounds to the volume possible from more complex solutions. Incorporation of solution chemistry into the model demonstrates both the effect played by impurities when studying this phenomenon and how the formation of the quasiliquid layer concentrates impurities on the ice surface.

This annual report is prepared pursuant to the National Emission Standards for Hazardous Air Pollutants (NESHAPs; Title 40 Code of Federal Regulations [CFR] Part 61, Subpart H). Subpart H governs radionuclide emissions to air from Department of Energy (DOE) facilities. NESHAPs limits the emission of radionuclides to the ambient air from DOE facilities to levels resulting in an annual effective dose equivalent (EDE) of 10 mrem (100 {micro}Sv) to any member of the public. The EDEs for the Lawrence Livermore National Laboratory (LLNL) site-wide maximally exposed members of the public from operations in 2003 are summarized here. Livermore site: 0.044 mrem (0.44 {micro}Sv) (55% from point-source emissions, 45% from diffuse-source emissions). The point-source emissions include gaseous tritium modeled as tritiated water vapor as directed by EPA Region IX; the resulting dose is used for compliance purposes. Site 300: 0.017 mrem (0.17 {micro}Sv) (98% from point-source emissions, 2% from diffuse-source emissions). The EDEs were calculated using the EPA-approved CAP88-PC air dispersion/dose-assessment model, except for doses for two diffuse sources that were estimated using measured concentrations and dose coefficients. Site specific meteorological data, stack flow data, and emissions estimates based on radionuclide usage inventory data or continuous stack monitoring data were themore » specific inputs to CAP88-PC for each modeled source.« less

Summary form only given. Solid-target illumination with multi-terawatt ultrashort pulses can generate, through relativistic laser driven electron interactions, ultrafast pulses of 10 keV-range X-ray line radiation and 100 keV-range continuum emission with very high flux. Such pulses can be used to study a number of phenomena occurring on time scales which are to date inaccessible with synchrotron radiation and on internuclear length-scales which are difficult or impossible to access with conventional visible spectroscopy. Beyond the number of fundamental physical questions underlying relativistically driven X-ray sources, the high efficiency and comparatively low cost of this emerging technology will enable table-top time-resolved studies of atomic-scale motion during chemical reactions. In this contribution we present a detailed characterization and optimization of the experimental conditions for efficient production of short pulse X-rays to be used in time-resolved experiments. We present experimental evidence indicating that the production of K-shell holes generating line radiation arises from collisions with non-thermal electrons, and that the size of this source is on the order of the laser spot size. The combination of extremely small source size, high flux, and short time duration are ideal for time resolved pump-probe X-ray diffraction and spectroscopic studies of crystalline and molecular dynamics.

Summary form only given. Lasers for the next generation of laboratory-scale, high-field scientific research achieve multi-terawatt peak powers with pulse durations in the range of 20 to 40 fs. We report on a chirped-pulse-amplification system producing 60/spl plusmn/8 TW peak power, 23.5/spl plusmn/1.5 fs FWHM duration pulses and its use in a peak-field, atomic photoionization measurement.

Summary form only given. Recently Barad et al. (1997) showed that the third harmonic generated at the interface of a transparent sample can be used to map the surface of optical glass fibers in an index matching fluid. In the paper, we extend the technique and produce three-dimensional, third harmonic volume images of live biological specimens. Third-harmonic generation (THG) imaging has several advantages for biological imaging: (1) it is a background-free imaging technique requiring no additional staining, (2) it is non-fading in nature, and (3), it can be used with low phase contrast specimens. Because the third harmonic production is localized at interfaces, where there is a change in refractive index or nonlinear susceptibility, the technique as applied to microscopy inherently produces optically sectioned data sets. This allows three-dimensional reconstruction as in traditional confocal microscopy. We present a three dimensional image of a spiral algae formation taken using THG in this manner. In the paper, we demonstrate for the first time to our knowledge, dynamic imaging of live specimens, under moderate NA (0.6) and high NA (1.3) conditions. While significant work remains to fully develop THG microscopy for biological systems, this first demonstration is critical in that it establishes the relevance of the technique to living specimens.

Summary form only given. To date, the primary laser variables in ultrashort pulse excitation microscopy which are used to optimize efficiency have been wavelength, average power and peak power. In this paper we introduce two more parameters: pulse shape and phase (or chirp). Normally the pulse shape is usually assumed to be a simple analytical form, such as a Gaussian, and the pulse is assumed to be transform limited (no chirp). However, this also means that the peak power, and consequently intensity at focus have also contained certain assumptions. Thus, knowledge of these parameters is not only useful for maximizing the efficiency of the excitation, but it is also necessary for an exact description of the fields generated at focus. The effects of spectral shape on two-photon fluorescence efficiency were investigated using an acousto-optic pulse shaper to modify femtosecond pulses from a Ti:sapphire laser. By using different shapes, we find that the measured two-photon efficiency can vary by a factor of 2 for differently shaped spectra with the same full-width-half-maximum. We find that these effects are well described by a simple model assuming transform-limited pulses. The fact that even small changes in the spectral wings can significantly affect the efficiency of nonlinear processes has implications for biological multiphoton imaging, where it is desirable to minimize sample exposure to radiation and maximize fluorescence efficiency. In the case of single photon excitation of a fluorophore at high energy densities the fluorescence shows a strong chirp or phase dependence. The method is quite robust and applicable to very large molecules in room temperature liquid.

Summary form only given, as follow. Ultrafast optical-pump, X-ray diffraction probe experiments are providing new ways to study transient processes including the direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place. Current table-top-terawatt femtosecond laser systems provide an attractive source of few-hundred femtosecond duration bursts of angstrom-scale X-ray radiation with fluxes comparable to standard rotating anode sources. Their compact size enables time resolved structural dynamics to be studied in the small laboratory with temporal resolution better than typical molecular vibrational periods. Ultrafast structural dynamics in crystalline samples are readily studied with such systems and experiments to be discussed in this talk include ultrafast non-thermal solid-to-liquid transition in thin single-crystal Ge-111 films grown on Si-111 substrates; ultrafast non-thermal solid-to-solid transitions in bulk vanadium dioxide from a low temperature insulating phase to a high temperature metallic phase; and harmonic and anharmonic coherent acoustic dynamics in layered Ge-111/Si-111 and bulk GaAs-111 samples. Future improvements in high-average power short-pulse lasers will enable the study of a wider class of materials such as amorphous solids or liquid-phase dynamics of simple molecules, while proposed 4th generation light sources based upon single-pass X-ray free-electron lasers will permit singleshot structural determination of complex biomolecules.

Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed.

The melanocortin system consists of five seven-transmembrane spanning G-protein coupled (GPCRs) receptors (MC1R-MC5R), the endogenous agonists a-, B- and melanocyte stimulating hormone (MSH), adrenocorticotropic hormone (ACTH), and the endogenous antagonists Agouti and Agouti-related protein (AGRP). Melanocortin agonists are involved in the regulation of feeding behavior and weight omeostasis in mammals. Structure-activity relationships (SAR) have been performed on the endogenous melanocortin receptor agonists and antagonists that have identified ligand amino acid residues implicated as important for receptor binding and stimulation. Knowledge of putative ligand-receptor interactions may help to design molecules as therapeutic agents for the treatment of physiological diseases.

Summary form only given. 85% of biochemical reactions within cells occur at membrane surfaces. Indirect experimental evidence suggests that many of these biochemical processes are regulated through cellular control of the transport properties and oligomerization state of proteins within the membranes. Consequently, our being able to visualize and measure protein motions and aggregation state on living cells would tremendously enhance our understanding of cell function. The spatial and temporal scales that govern the biochemical reactions make measuring these membrane phenomena on living cells experimentally challenging. We use the image correlation spectroscopy (ICS) technique to obtain such information from measurements on living cells. To achieve the necessary spatial resolution we use two-photon fluorescence microscopy. This also has the additional advantage that the imaging process does not bleach non-imaged membranes contained within the cell volume. The image field can be acquired at rates up to video rate, which makes it possible to measure dynamic events occurring over a range of time scales.

The high field photoionization cross sections for the (n=2) shell of argon were measured with pulsed 800 nm radiation (27±5 fs duration) at an intensity of 1.5×1019 W/cm2±1×1019 W/cm2. The pondermotive energy for an electron at these field intensities is approximately 1 MeV. The best agreement with a calculated AC tunneling model was at an intensity of 0.6×1019 W/cm2. The difference between experimental and calculated relative charge state yields is less than an order of magnitude for Ar+9 to Ar+14 and Ar+16.

Fundamental processes on the molecular level, such as vibrations and rotations in single molecules, liquids or crystal lattices and the breaking and formation of chemical bonds, occur on timescales of femtoseconds to picoseconds. The electronic changes associated with such processes can be monitored in a time-resolved manner by ultrafast optical spectroscopic techniques1, but the accompanying structural rearrangements have proved more difficult to observe. Time-resolved X-ray diffraction has the potential to probe fast, atomic-scale motions2,3,4,5. This is made possible by the generation of ultrashort X-ray pulses6,7,8,9,10, and several X-ray studies of fast dynamics have been reported6,7,8,11,12,13,14,15. Here we report the direct observation of coherent acoustic phonon propagation in crystalline gallium arsenide using a non-thermal, ultrafast-laser-driven plasma — a high-brightness, laboratory-scale source of subpicosecond X-ray pulses16,17,18,19. We are able to follow a 100-ps coherent acoustic pulse, generated through optical excitation of the crystal surface, as it propagates through the X-ray penetration depth. The time-resolved diffraction data are in excellent agreement with theoretical predictions for coherent phonon excitation20 in solids, demonstrating that it is possible to obtain quantitative information on atomic motions in bulk media during picosecond-scale lattice dynamics.

Gas clusters irradiated with ultrashort, high intensity laser pulses can exhibit “ionization ignition” which leads to very high charge states that are significantly higher than those for equivalent laser pulses applied to atoms in the gas phase [1,2]. Moreover, such laser generated plasmas from clusters might serve as bright sources of ultrashort duration, hard x-rays [3-5]. Experimental shapes of the x-ray emission spectra are distinctly non-thermal and show evidence of multiple inner shell holes [6] and high electron kinetic energies [7].

We present initial results of picosecond time resolved diffraction from GaAs(111) crystals using plasma generated, ultrafast x-ray pulses. Laser excitation of the GaAs transfers electron population from the valence into the conduction band. Such an excitation typically produces a hot electron gas in the conduction band that thermalizes with the lattice via phonon emission with a time constant of about 2 ps.[1, 2] However, upon transfer of a few percent of all valence electrons, the cohesive energy binding the atoms in the crystal lattice changes, which can lead to a rapid modification of the crystal structure.[3-8] This process, which does not require the thermalization of electrons and phonons, can proceed on femtosecond timescales. Both effects, which substantially disturb the equilibrium crystal structure, are in principle detectable by ultrafast x-ray diffraction, as are other effects such as melting and shock wave propagation.

Techniques for the control of femtosecond resolution phase and amplitude distortions during the amplification of 10‐fs optical pulses to joule‐level energies are discussed.

Recent results of an 18 fs, multiterawatt system designed to produce >1 J pulses are discussed including its use in an ultrafast x-ray source.

Atomic clusters illuminated with ultrashort, high intensity lasers pulses might serve as bright sources of ultrashort duration, hard x-rays. Several experiments carried out by other authors indicate high conversion efficiencies of laser light into x-rays1-3. The shape of the spectra are distinctively non-thermal and show evidence of multiple inner shell holes4. Moreover, very high charge states were generated by irradiation of clusters with ultrashort laser pulses5. These charge states were found to be significantly higher than those for equivalent laser pulses applied to atoms in the gas phase.