FASCIOLA-HEPATICA - THE EFFECT OF THE MICROFILAMENT INHIBITOR CYTOCHALASIN-B ON THE ULTRASTRUCTURE OF THE ADULT FLUKE

The effect of the microfilament inhibitor cytochalasin B (10 and 100-mu-g/ml) on the ultrastructure of adult Fasciola hepatica was determined in vitro by scanning and transmission electron microscopy (SEM, TEM) using both intact flukes and tissue-slice material. SEM revealed that initial swelling of the tegument led to surface blebbing and limited areas of sloughing after 24 h treatment at 100-mu-g/ml. In the tegumental syncytium, basal accumulations of secretory bodies (especially T2s) were evident in the earlier time periods but declined with longer incubations, until few secretory bodies remained in the syncytium overall. Blebbing of the apical plasma membrane and occasional areas of breakdown and sloughing of the tegument were observed over longer periods of treatment at 100-mu-g/ml. In the tegumental cell bodies, the Golgi complexes gradually decreased in size and activity, and few secretory bodies were produced. In the later time periods, the cells assumed abnormal shapes, the cytoplasm shrinking in towards the nucleus. In the vitelline follicles, a random dispersion of shell protein globules was evident within the intermediate-type cells, rather than their being organized into distinct shell globule clusters. Disruption of this process was more severe at the higher concentration of 100-mu-g/ml and again was more evident in tissue-slice material. In the latter, after prolonged (12 h) exposure to cytochalasin B, the intermediate and mature vitelline cells were filled with loosely packed and expanded shell globule clusters, containing few shell protein globules. The mature vitelline cells continued to lay down "yolk" globules and glycogen deposits. Disruption of the network of processes from the nurse cells was evident at the higher concentration of cytochalasin. Spaces began to appear between the vitelline cells and grew larger with progressively longer incubation periods, and the cells themselves assumed abnormal shapes. A number of binucleate stem cells were observed in tissue-slice material at the longest incubation period (12 h).

FASCIOLA-HEPATICA - DISRUPTION OF SPERMATOGENESIS BY THE MICROFILAMENT INHIBITOR CYTOCHALASIN-B

The distribution of actin filaments in the spermatogenic cells of Fasciola hepatica was determined using a fluorescent derivative of phalloidin. Actin was localised primarily in the region of separation of a secondary spermatogonium from a primary spermatogonium, in the inner faces at the centre of four-cell clusters of tertiary spermatogonia and in the cytophore region of spermatocyte and spermatid rosettes. The effect of the microfilament inhibitor cytochalasin B (100-mu-g/ml) on the ultrastructure of the spermatogenic cells was determined in vitro by transmission electron microscopy using tissue-slice material. Cytochalasin B treatment led to the formation of bi- and multinucleate cells, whose frequency increased with progressively longer incubation periods. Few typical rosettes of spermatocyte and spermatid cells were evident from 6 h onwards, being replaced by syncytial masses of cells. Spermatozoon formation became abnormal in the longer treatment periods, the spermatozoa containing variable numbers of axonemes and an altered distribution of cortical microtubules. Multiple axonemes were observed in the cytoplasm of spermatid cells. The results are discussed in relation to the established role of actin in the cytokinesis phase of cell division and to the effects of cytochalasin B on other tissues and organ systems within the fluke.

MEASUREMENT OF THE PHOTO-PUMP STRENGTH OF THE 3D-5F TRANSITIONS IN THE AUTOMATICALLY LINE MATCHED NI-LIKE SM PHOTOPUMPED X-RAY LASER

The photo-pump strengths of both the ((3 (d) over bar(4))(0)(3d(6))(0))(0)-(((3 (d) over bar(3))(3/2)(3d(6))(0))(3/2)(5 (f) over bar)(5/2))(1) and the ((3 (d) over bar(4))(0)(3d(6))0)0-(((3 (d) over bar(4))(0)(3d(5))(5/2))(5/2)(5f)(7/2))(1) transitions in Ni-like Sm34+ have been measured to be 2.0 x 10(-4) and 2.4 x 10(-4) photons/mode respectively. The implications of the measurement are briefly discussed in a comparison of the merits of automatically line matched photo-pump scheme to those of the collisional excitation Ni-like Sm+34 scheme.

Spectral Enhancement in the Double Pulse Regime of Laser Proton Acceleration

The use of two separate ultraintense laser pulses in laser-proton acceleration was compared to the single pulse case employing the same total laser energy. A double pulse profile, with the temporal separation of the pulses varied between 0.75-2.5 ps, was shown to result in an increased maximum proton energy and an increase in conversion efficiency to fast protons by up to a factor of 3.3. Particle-in-cell simulations indicate the existence of a two stage acceleration process. The second phase, induced by the main pulse preferentially accelerates slower protons located deeper in the plasma, in contrast to conventional target normal sheath acceleration.

Enhanced proton flux in the MeV range by defocused laser irradiation

Thin Al foils (50 nm and 6 mu m) were irradiated at intensities of up to 2x10(19) W cm(-2) using high contrast (10(8)) laser pulses. Ion emission from the rear of the targets was measured using a scintillator-based Thomson parabola and beam sampling 'footprint' monitor. The variation of the ion spectra and beam profile with focal spot size was systematically studied. The results show that while the maximum proton energy is achieved around tight focus for both target thicknesses, as the spot size increases the ion flux at lower energies is seen to peak at significantly increased spot sizes. Measurements of the proton footprint, however, show that the off-axis proton flux is highest at tight focus, indicating that a previously identified proton deflection mechanism may alter the on-axis spectrum. One-dimensional particle-in-cell modelling of the experiment supports our hypothesis that the observed change in spectra with focal spot size is due to the competition of two effects: decrease in laser intensity and an increase in proton emission area.

Spectral modification of laser-accelerated proton beams by self-generated magnetic fields

Target normal measurements of proton energy spectra from ultrathin (50-200 nm) planar foil targets irradiated by 10(19) W cm(-2) 40 fs laser pulses exhibit broad maxima that are not present in the energy spectra from micron thickness targets (6 mu m). The proton flux in the peak is considerably greater than the proton flux observed in the same energy range in thicker targets. Numerical modelling of the experiment indicates that this spectral modification in thin targets is caused by magnetic fields that grow at the rear of the target during the laser-target interaction.

Effects of front surface plasma expansion on proton acceleration in ultraintense laser irradiation of foil targets

The properties of beams of high energy protons accelerated during ultraintense, picosecond laser-irradiation of thin foil targets are investigated as a function of preplasma expansion at the target front surface. Significant enhancement in the maximum proton energy and laser-to-proton energy conversion efficiency is observed at optimum preplasma density gradients due, to self-focusing Of the incident laser pulse. For very long preplasma expansion, the propagating laser pulse is observed to filament, resulting in highly uniform proton beams, but with reduced flux and maximum energy.

Scaling of proton acceleration driven by petawatt-laser-plasma interactions

The possibility of using high-power lasers to generate high-quality beams of energetic ions is attracting large global interest. The prospect of using laser-accelerated protons in medicine attracts particular interest, as these schemes may lead to compact and relatively low-cost sources. Among the challenges remaining before these sources can be used in medicine is to increase the numbers and energies of the ions accelerated. Here, we extend the energy and intensity range over which proton scaling is experimentally investigated, up to 400 J and 6 x 10(20) W cm(-2) respectively, and find a slower proton scaling than previously predicted. With the aid of plasma-expansion simulation tools, our results suggest the importance of time-dependent and multidimensional effects in predicting the maximum proton energy in this ultrahigh-intensity regime. The implications of our new understanding of proton scaling for potential medical applications are discussed.

Measurements of energetic proton transport through magnetized plasma from intense laser interactions with solids

Protons with energies up to 18 MeV have been measured from high density laser-plasma interactions at incident laser intensities of 5 X 10(19) W/cm(2). Up to 10(12) protons with energies greater than 2 MeV were observed to propagate through a 125 mu m thick aluminum target and measurements of their angular deflection were made. It is likely that the protons originate from the front surface of the target and are bent by large magnetic fields which exist in the target interior. To agree with our measurements these fields would be in excess of 30 MG and would be generated by the beam of fast electrons which is also observed.

Active manipulation of the spatial energy distribution of laser-accelerated proton beams

The spatial energy distributions of beams of protons accelerated by ultrahigh intensity (> 10(19) W/cm(2)) picosecond laser pulse interactions with thin foil targets are investigated. Using separate, low intensity (

Reduction of proton acceleration in high-intensity laser interaction with solid two-layer targets

Reduction of proton acceleration in the interaction of a high-intensity, picosecond laser with a 50-mu m aluminum target was observed when 0.1-6 mu m of plastic was deposited on the back surface (opposite side of the laser). The maximum energy and number of energetic protons observed at the back of the target were greatly reduced in comparison to pure aluminum and plastic targets of the same thickness. This is attributed to the effect of the interface between the layers. Modeling of the electron propagation in the targets using a hybrid code showed strong magnetic-field generation at the interface and rapid surface heating of the aluminum layer, which may account for the results. (c) 2006 American Institute of Physics.

Tree-code simulations of proton acceleration from laser-irradiated wire targets

Recent experiments using Terawatt lasers to accelerate protons deposited on thin wire targets are modeled with a new type of gridless plasma simulation code. In contrast to conventional mesh-based methods, this technique offers a unique capability in emulating the complex geometry and open-ended boundary conditions characteristic of contemporary experimental conditions. Comparisons of ion acceleration are made between the tree code and standard particle-in-cell simulations for a typical collisionless