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The responses of canine middle cerebral arteries to changes in pCO2 and pO2 were tested in vitro. It was found that there was no response to changes in pCO2 from 38.1 mm. Hg to 26.6 mm. Hg. but there was some constriction of the vessels with lowering of the pCO2 below 26.6 mm. Hg and there was minimal dilatation of the vessels when the pCO2 was increased from 38.1 nan. Hg to 87.2 mm. Hg. There was no reresponse to changes in pO2 from more than 500 mm. Hg to 59.6 mm. Hg, but when pO2 was lowered below 50 mm. Hg there was a sudden, massive constriction of the arteries tested. It is postulated that this constriction is due to build-up of a substance (substances) during a period of hypoxia (pO2 < 50 mm. Hg). The significance of the results obtained are discussed.
High-intensity lasers are an effective source for the acceleration of high-energy particles. Using different interaction configurations, such facilities can be optimized for the acceleration of electrons, protons, heavy ions, high-energy photons, or neutrons. The shielding of these facilities to ensure the safety of personnel has always been a critical requirement and is a fundamental step within the design phase. The knowledge of radiation source terms through both experiments and modelling is now well understood and for the most part can be dealt with through the use of shielding and specialized beam dumps. Unlike most other particle accelerators most high-power laser facilities are still accessed by personnel post shot with little or no remote handling capabilities. As a result, the secondary activation and control of components that lie around the interaction is of great importance to safety. In this paper, we present a 10 year history of activation data on the Vulcan petawatt facility and discuss the primary sources of activation and the potential impact on future laser facilities.
We present a new simulation method to predict the maximum possible yield of X-rays produced by electron beams accelerated by petawatt lasers irradiating thick solid targets. The novelty of the method lies in the simulation of the electron refiluxing inside the target implemented with the Monte Carlo code Fluka. The mechanism uses initial theoretical electron spectra, cold targets and refiluxing electrons forced to re-enter the target iteratively. Collective beam plasma effects are not implemented in the simulation. Considering the maximum X-ray yield obtained for a given target thickness and material, the relationship between the irradiated target mass thickness and the initial electron temperature is determined, as well as the effect of the refiluxing on X-ray yield. The presented study helps to understand which electron temperature should be produced in order to generate a particular X-ray beam. Several applications, including medical and security imaging, could benefit from laser generated X-ray beams, so an understanding of the material and the thickness maximizing the yields or producing particular spectral characteristics is necessary. On the other more immediate hand, if this study is experimentally reproduced at the beginning of an experiment in which there is an interest in laser-driven electron and/or photon beams, it can be used to check that the electron temperature is as expected according to the laser parameters.
Over 250 durum wheats, Triticum durum Desf., and close relatives were screened for resistance to the wheat midge, Sitodiplosis mosellana (Géhin). Less than 2% showed consistently reduced egg and larval densities in field and laboratory trials. Two related accessions named ’Kahla’ had stable, low larval infestation levels, which were about 30% of those in commercial durum wheat cultivars. No antibiosis was detected in durum wheats. The reduction in infestation by larvae was associated with a similar reduction in oviposition. The resistance reduced egg densities by 80% or more in choice and no-choice laboratory tests and by about 70% in the field. Egg group size was not affected, and therefore reduced oviposition must have resulted from the number of egg groups deposited by females. The resistance was not associated with any of 12 morphological traits that were quantified for spikes. ’Kahla’ is the first durum wheat identified to have resistance against the wheat midge.
The presence and concentrations of each of the three subtypes of opioid receptors (mu, kappa, and delta) has been studied in the accessory optic nuclei (dorsal, lateral, and medial terminal nuclei and the interstitial nucleus of the superior fasciculus, posterior fibers: DTN, LTN, MTN, and inSFp) in normal young rats with radioligands directed towards each opioid receptor subtype. The changes in mu opioid receptors have also been investigated in monocularly enucleated rats in which one eye was removed and the rats sacrificed at postoperative day (PO) 2, 3, 5, 7, 14, and 30. As the MTN is the only accessory optic nucleus of the rat large enough for semiquantitative evaluation, the mu receptor population of the MTN has been subjected to optical microdensitometric analysis.
All four of the accessory optic nuclei (AOS nuclei) are found to contain exceedingly high levels of mu opioid receptor binding with the selective radioligand [3H]-[D-Ala, MePhe4, Gly-ol5] (DAGO), low levels of kappa opioid receptor binding using the radioligand [3H]-[ethylketocyclazocine] (EKC) together with the competing agents [D-Pro4]-morphiceptin and [D-Ser2, Thr6]-Leu-enkephalin, and an absence of delta opioid receptor binding with the radioligand [3H]-[D-A1a2, D-Leu5]-enkephalin (DADLE) combined with the competing agent [D-Pro4]-morphiceptin. Monocular enucleation, as studied on the mu opioid receptor population with this experimental approach, results in virtually a complete loss of mu opioid receptors throughout all four of the contralaterally located AOS nuclei, including both dorsal and ventral subdivisions of the medial terminal nucleus (MTNd, v). Kappa and delta receptors are very few (kappa receptors) or are lacking (delta receptors) in the AOS nuclei, and for this reason, the effects of monocular enucleation on these two opioid receptor subtypes have not been investigated. Monocular enucleation also produces a significant lowering in mu receptor binding in other primary optic nuclei (the lateral geniculate nuclei, nucleus of the optic tract, and superficial layers of the superior colliculus) and in the pars principalis of the medial geniculate nucleus (description of changes in mu receptors in non-accessory optic primary optic nuclei will be considered elsewhere).
Microdensitometric study of the MTNd, v shows that the decreased binding of mu receptors in this nucleus is barely detectable (about 6%) at PO2 and rises to 6–15% at PO3. At PO5 receptor loss reaches approximately 62%, whereas at PO7 it is about 81% complete. At PO14 and PO30, the mu receptor loss is nearly complete at around 93%. Mu receptor loss involves all of the AOS nuclei contralateral, but none ipsilateral, to ocular enucleation, an observation entirely consistent with the overwhelmingly crossed (about 97%) nature of the retinofugal projection to the rat accessory optic nuclei. These opioid receptors represent a prominent feature in the AOS and other primary optic nuclei of the rat. Their role in visuomotor control remains uncertain but probably involves the fine-tuning of information concerned with compensatory eye movements.
As the state of the art for high power laser systems increases from terawatt to petawatt level and beyond, a crucial parameter for routinely monitoring high intensity performance is laser spot size on a solid target during an intense interaction in the tight focus regime (<10 µm). Here we present a novel, simple technique for characterizing the spatial profile of such a laser focal spot by imaging the interaction region in third harmonic order (3ωlaser). Nearly linear intensity dependence of 3ωlaser generation for interactions >1019 Wcm−2 is demonstrated experimentally and shown to provide the basis for an effective focus diagnostic. Importantly, this technique is also shown to allow in-situ diagnosis of focal spot quality achieved after reflection from a double plasma mirror setup for very intense high contrast interactions (>1020 Wcm−2) an important application for the field of high laser contrast interaction science.
The Vulcan Nd:glass laser at the Central Laser Facility (CLF) is a
petawatt (1015 Watts) interaction facility, designed to deliver
irradiance on target of 1021W.cm−2 for the UK
and international user community. The facility came online to users in
2002 and considerable experience has been gained operating Vulcan in this
mode. The facility delivers a wide-ranging experimental program in
fundamental physics and advanced applications. This includes the
interaction of ultrahigh intensity light with matter, fast ignition fusion
research, photon induced nuclear reactions, electron and ion acceleration
by light waves, and the exploration of the exotic world of plasma physics
dominated by relativity. We report on the first year's operation of
the facility and the highlights of the experimental campaigns.
Due to an error, the published version of the paper differed from the final
version submitted by the authors. The section starting at page 271 with
“The beams are well collimated …” and finishing at the end
of the page, and the caption for figure 4 were to be replaced with an updated
version, submitted on 20 May 2002, which follows underneath.
One of the most exciting results recently obtained in the
ultraintense interaction research area is the observation of
beams of protons with energies up to several tens of megaelectron
volts, generated during the interaction of ultraintense picosecond
pulses with solid targets. The particular properties of these
beams (high brilliance, small source size, high degree of
collimation, short duration) make them of exceptional interest
in view of diagnostic applications. In a series of experiments
carried out at the Rutherford Appleton Laboratory (RAL) and
at the Lawrence Livermore National Laboratory (LLNL), the
laser-produced proton beams have been characterized in view
of their application as a particle probe for high-density matter,
and applied to diagnose ultraintense laser–plasma
interactions. In general, the intensity cross section of a proton
beam traversing matter will be modified both by collisional
stopping/scattering, and deflections caused by electric/magnetic
fields. With a suitable choice of irradiation geometry and target
parameters, the proton probe can be made mainly sensitive to
the electric field distribution in the object probed. Therefore,
point projection proton imaging appears as a powerful and unique
technique for electric field detection in laser-irradiated targets
and plasmas. The first measurements of transient electric fields
in high-intensity laser-plasma interactions have been obtained
with this technique.
Jovian auroral emissions are observed at infrared, visible, ultraviolet, and x-ray wavelengths. As at Earth, pitch-angle scattering of energetic particles into the atmospheric loss cone and the acceleration of current-carrying electrons in field-aligned currents both play a role in exciting the auroral emissions. The x-ray aurora is believed to result principally from heavy ion precipitation, while the ultraviolet aurora is produced predominantly by precipitating energetic electrons. The magnetospheric processes responsible for the aurora are driven primarily by planetary rotation. Acceleration of Iogenic plasma by rotationally-induced electric fields results in both the formation of the energetic ions that are scattered and the formation of strong, field-aligned currents that communicate the torques from the ionosphere. In addition to rotation-driven processes, solar-wind-modulated processes in the outer magnetosphere may lead to highly, time-dependent acceleration and thus also contribute to jovian auroral activity. Observational evidence for both sources will be presented. See Waite et al. (2001, Nat., 410, 787).
Frequency doubling a 140 × 110 mm 40 J sub-ps
1054 nm beam for laser matter interaction studies was investigated
at the Central Laser Facility, with efficiencies greater
than 60% being achieved. The conversion characteristics
(efficiency, beam quality, focusability, and pulse length)
for two large 157 mm diameter aperture high quality KDP
crystals of thickness 2 mm and 4 mm were studied. Using
a fundamental drive beam of two times diffraction limited
quality, focal spots of four times the diffraction limit
in the frequency doubled beam were achieved and beam degradation
effects shown to be minimal.
The diacetylenic phosphocholine lipid 1,2-bis(10, 12-tricosadiyonol)-sn-glycerol- 3-phosphocholine forms, upon cooling below the chain melting temperature, hollow cylindrical structures known as ‘tubules’. These tubules are approximately one micron in diameter and may range from tens to hundreds of microns in length. We have carried out x-ray diffraction studies of tubules (1) in 75/25 ethanol/water by volume and (2) in a dessicated state. We present results which show marked differences in the nature of both the in-plane and inter-layer correlations associated with the wrapped multilayer structure of the tubules in the two states.
The infrared bolometric luminosity of the extended infrared emission from the L1551 flow is estimated as 19 (−4 +10) L⊙. Ultraviolet radiation from the shock associated with the flow appears to heat the surrounding dust. The extended infrared emission raises the total energy requirement for the flow over a 10^4 year lifetime to 10^46–47 ergs. If gravitational in origin, this energy likely originates from a region <10^13 cm. Infrared radiation offers a new probe for interstellar shocks by sampling the ultraviolet halo surrounding the shock.
Biometrical genetical techniques have been applied to the analysis of certain anthropometric characters measured in 134 pairs of adult twins. After allowing for assortative mating it appears that there is a family environment (E2) component for variation in height larger than previously reported. “Fatness” traits – weight, ponderal index, and skinfold thickness – all show higher heritabilities in males and substantial E2 components in females, and reasons for this are discussed. The same is true for cephalic index and forearm length but the reason for these differences is not so obvious. Head length shows a much higher heritability than head breadth. A larger sample of DZ opposite-sex pairs would allow more powerful discrimination, but the variety of patterns of variation revealed by the model-fitting approach used here justify its use over more traditional techniques.