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Presents a study that investigated magnetic fields produced in a gas-puff Z pinch. Description of the models; Experimental apparatus used in the study; Results; Discussion.

Introgression of sequences from crop species in wild relatives is of fundamental and practical concern. Here, we address gene flow between cultivated wheat and its widespread polyploid relative, Aegilops triuncialis, using 12 EST- SSR markers mapped on wheat chromosomes. The presence of wheat diagnostic alleles in natural populations of the barbed goatgrass growing in proximity to cultivated fields highlights that substantial gene flow occurred when both species coexisted. Furthermore, loci from the A subgenome of wheat were significantly less introgressed than sequences from other subgenomes, indicating differential introgression into Ae. triuncialis. Gene flow between such species sharing nonhomeologous chromosomes addresses the evolutionary outcomes of hybridization and may be important for efficient gene containment. [ABSTRACT FROM AUTHOR] more...

Mountain birch, Betula pubescens ssp. tortuosa, forms the treeline in northern Sweden. A recent shift in the range of the species associated with an elevation of the treeline is commonly attributed to climate warming. Using microsatellite markers, we explored the genetic structure of populations along an altitudinal gradient close to the treeline. Low genetic differentiation was found between populations, whereas high genetic diversity was maintained within populations. High level of gene flow compensated for possible losses of genetic diversity at higher elevations and dissipated the founding effect of newly established populations above the treeline. Spatial autocorrelation analysis showed low spatial genetic structure within populations because of extensive gene flow. At the treeline, significant genetic structure within the juvenile age class at small distances did not persist in the adult age class, indicating recent expansion of young recruits due to the warming of the climate. Finally, seedling performance above the treeline was positively correlated with parameters related to temperature. These data confirm the high migration potential of the species in response to fluctuating environmental conditions and indicate that it is now invading higher altitudes due to the recent warming of the climate. [ABSTRACT FROM AUTHOR] more...

Introgression from allohexaploid wheat ( Triticum aestivum L., AABBDD) to allotetraploid jointed goatgrass ( Aegilops cylindrica Host, CCDD) can take place in areas where the two species grow in sympatry and hybridize. Wheat and Ae. cylindrica share the D genome, issued from the common diploid ancestor Aegilops tauschii Coss. It has been proposed that the A and B genome of bread wheat are secure places to insert transgenes to avoid their introgression into Ae. cylindrica because during meiosis in pentaploid hybrids, A and B genome chromosomes form univalents and tend to be eliminated whereas recombination takes place only in D genome chromosomes. Wheat random amplified polymorphic DNA (RAPD) fragments, detected in intergeneric hybrids and introgressed to the first backcross generation with Ae. cylindrica as the recurrent parent and having a euploid Ae. cylindrica chromosome number or one supernumerary chromosome, were assigned to wheat chromosomes using Chinese Spring nulli-tetrasomic wheat lines. Introgressed fragments were not limited to the D genome of wheat, but specific fragments of A and B genomes were also present in the BC1. Their presence indicates that DNA from any of the wheat genomes can introgress into Ae. cylindrica. Successfully located RAPD fragments were then converted into highly specific and easy-to-use sequence characterised amplified regions (SCARs) through sequencing and primer design. Subsequently these markers were used to characterise introgression of wheat DNA into a BC1S1 family. Implications for risk assessment of genetically modified wheat are discussed. [ABSTRACT FROM AUTHOR] more...

Variability between and within spontaneous populations of Hordeum murinum in Switzerland was studied by enzyme electrophoresis. Most of the variation (61.5%) occurred within populations, while 38.5% occurred between populations. Absence of cleistogamy was observed. The results suggest evidence for a mixed mating system in H. murinum. Isozyme diagnostic bands for H. murinum and cultivated barley were established, allowing the detection of putative hybrids between them. No hybrids were obtained after performing experimental hybridization in the field and in the greenhouse. None was detected in the progeny of H. murinum growing in spontaneous contact zones either, confirming the existence of strong genetic barriers against hybridization. Our results are discussed in the context of the risk of transgene escape, associated with the cultivation of transgenic crops. [ABSTRACT FROM AUTHOR] more...

Seeds of English and Austrian populations of bearded wheatgrass (Elymus caninus L.) and sea barley (Hordeum marinum Huds.) growing in the vicinity of wheat (Triticum aestivum L.) fields were collected in order to search for evidence of the introgression of wheat traits into these wild relatives. Seeds were sown and plants grown for subsequent analyses using morphological and genetic (isozymes, RAPD and wheat microsatellites) markers. No F1 hybrids were found within the individuals of the two species grown, neither with morphological nor with genetic markers. Also, no evidence of introgression of wheat traits into E. caninus was observed. However, in one individual of H. marinum which had the typical morphology of this species, numerous species-specific DNA markers of wheat were amplified, thereby demonstrating previous hybridization. Consequently, the hybridization between wheat and H. marinum under natural conditions and the introgression of wheat traits into this wild relative seems to be possible. Our results contribute to the risk assessment of transgenic wheat cultivation. [ABSTRACT FROM AUTHOR] more...

In order to estimate the potential of gene flow between wheat (Triticum æstivum L.) and jointed goatgrass (Aegilops cylindrica Host.), we carried out mixed pollinations in experimental and natural conditions. A set of species-specific RAPD (random amplified polymorphic DNA) and microsatellite markers were used to detect the presence of parental markers in the progeny of the plants used in these experiments. No hybrids were found within the offsprings of the plants used for the greenhouse experiments, while 85 Ae. cylindrica×T. æstivum hybrids were found within 2400 analyzed F1 plants resulting from the field pollinations. The hybridization rates for individuals of different populations of the wild species differed considerably: 1% for two populations known for more than 90 years versus 7% for a newly discovered population. Most of the hybrids were completely sterile, but five of them produced 13 seeds (BC1) by backcross with Ae. cylindrica. Twelve seeds germinated and generated viable and partly fertile plants. About 25% of the wheat specific RAPD markers were found in the BC1 plants, indicating that introgression of wheat DNA into Ae. cylindrica is possible. In addition, one microsatellite marker, known to be situated on the D genome (a genome shared by both species), was also found in the BC1 plants. [ABSTRACT FROM AUTHOR] more...

A magneto-optic Faraday rotation diagnostic was implemented on a Z-pinch driven flux-compression generator to measure line-averaged, megagauss, axial-magnetic fields up to 1.6 MG with rise times of 30 kG/ns. The axial-magnetic field rotated the plane of polarization of a 2-W argon laser beam in a 0.725-mm-diam, fused silica quartz fiber mounted coaxial with the Z pinch. The rapid rise time and the high radiation environment presented by the Z-pinch plasma caused a high-pressure impulse <100 kbar, to be coupled into the quartz-fiber probe disrupting the polarization-preserving properties of the fiber. The time scale for disruption was characteristic of a shock propagating radially through the fiber to its core. This paper will describe the response of the Faraday diagnostic under these conditions and present a simple model that describes the effects of fiber depolarization that is consistent with previous observations of stress-induced depolarization in optical fibers. [ABSTRACT FROM AUTHOR] more...

Linear growth of instabilities during implosion of annular and columnar plasma pinches having sharp outer boundaries is analyzed. The dominant modes of the Rayleigh-Taylor instability differ in time, radius, and growth rate from the dominant modes of the bulk convective instability. The spectra of growth rates of perturbations localized azimuthally or axially suggest explanations for filamentation and stratification of plasmas. Localized Rayleigh-Taylor modes grow fastest initially in an implosion. These modes can be suppressed completely, however, by a relatively modest axial magnetic field, which produces magnetic shear in a Z pinch. Similarly, bulk convective modes can be substantially reduced by magnetic shear. The "window of stability" produced by magnetic shear occurs for an axial field magnitude about equal to the azimuthal. Properly shaped current pulses in Z pinches with axial fields may therefore produce stable implosions to high compression ratios, in agreement with recent experiments. The most dangerous Rayleigh-Taylor modes for the symmetry of an annular pinch of initial aspect ratio R[sub o]/δ[sub o] are those with wavenumber k∼R[sub o]/δ²[sub o], where R[sub o] is the initial pinch radius. To suppress pinch instabilities optimally, both the liner thickness and axial magnetic field should be chosen properly. [ABSTRACT FROM AUTHOR] more...

The stability of diffuse, dynamic Z pinches and theta pinches is analyzed. Spectra of the growth rates of hydromagnetic instabilities of dynamic pinches are calculated. The acceleration of plasma pinches during compression and expansion strongly modifies the growth of bulk instabilities. Also, even a relatively weak axial magnetic field substantially suppresses instabilities in Z pinches, in agreement with recent experiments. The initial axial field Bz 0 needed for a stable implosion of a pinch of initial radius R0 and average current I is Bz 0 >=(10–30 kG) I (MA)/R0(cm). The approximate analytic solutions of the linearized equations are shown to agree well with the exact numerical solutions. The stability analysis demonstrated here for dynamic pinches is broadly applicable to the stability of dynamic plasmas in general. [ABSTRACT FROM AUTHOR] more...

New self-similar solutions describe the subsonic compression of a plasma with an entrained axial magnetic field by a thin cylindrical liner. Effects of Ohmic dissipation, thermal conductivity, and plasma turbulence are included. The self-similar solutions, obtained in an explicit analytic form, demonstrate that magnetic flux can be compressed by an externally driven annular plasma shell with small losses. [ABSTRACT FROM AUTHOR] more...

Supersonic cumulative compressions of axial magnetic fields in cylindrically symmetric plasmas are studied. New self-similar solutions of the ideal magnetohydrodynamic (MHD) equations are presented. The solutions describe cumulative compressions of radially imploding plasma with entrained magnetic fields, subsequent reflections of MHD shock waves from the axis, compressions of hollow plasma liners, and implosions of fast magnetosonic waves. [ABSTRACT FROM AUTHOR] more...

Evidence is presented that an axial magnetic field of 100 kG has been compressed to 42 MG by an imploding neon gas-puff Z pinch on a 800 kJ, 7.5 MA, 60 nsec pulsed power generator. Machine electrical diagnostics and x-ray pinhole photographs indicate that this 420-fold field compression was produced by imploding plasma at high magnetic Reynolds number. [ABSTRACT FROM AUTHOR] more...

The radio-frequency power radiated from laser-target plasmas in a vacuum can be orders of magnitude greater than expected from such sources that have a negligible electric dipole moment. A model combining the Tidman–Stamper circuit model of a laser-target plasma with the theory of radiation from currents immersed in plasmas, however, predicts scaling of electric-dipole power radiated from laser plasmas in agreement with experiments. [ABSTRACT FROM AUTHOR] more...

The mountain birch, Betula pubescens ssp. tortuosa is a tetraploid tree species which forms the tree limit in northern Fennoscandia. We identified nine polymorphic microsatellite loci in order to characterize the genetic structure of populations at different elevations close to the treeline. The microsatellite loci were highly polymorphic, with 14–42 alleles per locus and an average expected heterozygosity of 0.73 ± 0.25 under random chromosome segregation and 0.68 ± 0.23 under random chromatid segregation. [ABSTRACT FROM AUTHOR] more...

A general class of methods is suggested for producing controlled magnetic fields up to the order of 100 MG. The methods involve radially imploding plasmas in which longitudinal magnetic fields have been entrained. Specific methods of implosion suggested are (a) gas-puff Z pinch and (b) ablative implosion of a liner by a laser. Applications include reducing fusion ignition thresholds, producing beams of gamma radiation, accelerating particles, and producing high-energy densities under controlled conditions. [ABSTRACT FROM AUTHOR] more...

The imploding plasma column of a gas-puff Z pinch was used to compress an embedded axial magnetic field. Field compression ratios up to 180 times and peak compressed fields up to 1.6 MG were measured by Faraday rotation. Field compression by this method has the advantage of high repetition rate for applications in the controlled production of high-energy densities, solid-state studies, generation of short-wavelength radiation, reducing the ignition threshold for fusion, and particle acceleration. [ABSTRACT FROM AUTHOR] more...