Electron Cooling in a Magnetically Expanding Plasma.

Electron cooling in a magnetically expanding plasma, which is a fundamental process for plasma flow and detachment in magnetic nozzles, is experimentally investigated using a radio frequency plasma source and magnetic nozzle (MN). Probe measurements of the plasma density, potential, and electron temperature along the center line of the MN indicate that the expansion follows a polytropic law with exponent γ_{e}=1.15±0.03. This value contradicts isothermal electron expansion, γ_{e}=1, which is commonly assumed in MN models. The axial variation of the measured quantities can be described by a simple quasi-1D fluid model with classical electron thermal conduction, for which it has been previously shown that a value of γ_{e}≈1.19 is expected in the weakly collisional limit. A new criterion, derived from the model, ensures efficient ion acceleration when a critical value for the ratio of convected to conducted power is exceeded.

Stochastic threshold for ion heating with beating electrostatic waves.

The stochastic threshold for the heating of ions in a magnetized plasma with two electrostatic waves is experimentally characterized. Two obliquely propagating electrostatic modes are launched in a magnetized plasma with frequencies that differ by the ion cyclotron frequency. The values of the wave amplitudes where a rapid increase in the local ion temperature occurs is then parametrically investigated. It is found that the two threshold wave amplitudes are linearly related and that this dependence translates to a lower required energy density for the onset of heating when compared to the case of a single electrostatic wave. Agreement also is demonstrated between the experimentally observed threshold for stochastic heating and an analytical prediction [B. Jorns and E. Y. Choueiri, Phys. Rev. E 87, 013107 (2013)] for this threshold.

New Insights into Esca of Grapevine: The Development of Foliar Symptoms and Their Association with Xylem Discoloration.

A new study on the development of foliar symptoms of esca was carried out from 2004 to 2006 in five mature vineyards in Aquitaine, France. Symptoms were monitored for severity and changes over time. Initial foliar symptoms were characterized by the presence of drying zones or discolorations (reddening or yellowing), which are symptoms that have also been attributed to Black Dead Arm (BDA). Then, the less-severely affected leaves persisted throughout the summer and developed into typical "tiger-stripe" symptoms of esca. The most severely symptomatic leaves fell soon after symptoms appeared. Severely diseased vines showed typical apoplectic or acute forms of esca that did not differ from the severe BDA forms. The appearance of leafsymptomatic vines increased uniformly over time, reaching a maximum incidence by the end of July. A second survey in 41 European and Lebanese vineyards showed that longitudinal discolorations were visible under the bark of 95% of the vines showing foliar esca symptoms. These wood symptoms, also previously attributed to BDA, appeared as xylem orange-brown stripes. Thus, foliar symptoms of esca showed transitory phases which overlapped with some BDA descriptions. Most of these symptoms, in the west-palearctic regions that were investigated, were commonly associated with the presence of one or several xylem discolorations.

Ion heating with beating electrostatic waves.

The nonlinear interaction of a magnetized ion with two beating electrostatic waves (BEW) whose frequencies differ by a cyclotron harmonic can lead, under some conditions [Phys. Rev. E 69, 046402 (2004)], to vigorous acceleration for an ion with arbitrarily low initial velocity. When applied to an ensemble of ions, this mechanism promises enhanced heating over single electrostatic wave (SEW) heating for comparable wave energy densities. The extension of single ion acceleration to heating (SEWH and BEWH) of an ensemble of initially thermalized ions was carried out to compare the processes. Using a numerical solution of the Vlasov equation as a guideline, an analytical expression for the heating level was derived with Lie transforms and was used to show BEWH's superiority over all parameter space.

Occurrence of Grapevine Declines and First Report of Black Dead Arm Associated with Botryosphaeria obtusa in Lebanon.

Grapevine, cultivated mostly in the Bekaa Plain, is one of the most important fruit crops in Lebanon. During July 2004, a survey was made in 11 vineyards of local table or wine grapes to evaluate the sanitary status of the grapevine industry as far as wood declines are concerned. The most common grapevine decline was esca. The two forms of the disease (mild and severe) were observed. The mild form was characterized by leaf symptoms consisting of interveinal necrotic spots with yellow or red chlorotic blotches on white and red cultivars. The severe form was characterized by dieback of one or more shoots, leaf drop, shrivelling, and drying of fruit clusters. In west Bekaa, on cv. Cabernet Sauvignon, some vines showed symptoms identical to those of Eutypa dieback such as stunted chlorotic shoots with small, distorted leaves; moreover, symptoms corresponding to black dead arm (BDA) such as wine red spots on the margins of leaves and dry spots were seen as reported earlier (1). Diseased vines of various cultivars were collected: 10 Cabernet Sauvignon (7 esca, 3 BDA, and 1 Eutypa dieback), 4 Beitamouni, 3 Carignan, 2 Teifihi, 1 Zeitouni, 1 Mourverdre, 1 Caladoc, and 1 Merlot. In wood, cross sections through the trunk were made that showed mainly central necrosis, white heart rot, brown red wood, and black spotting. Wedge-shaped lesions were the least common. Particularly for BDA, peeling off the bark revealed a brown streaking of the external wood. Isolations were made on malt agar (MA) with wood chips cut from the different necroses described above. Fungal identifications were based on morphological characteristics in comparison with French isolates after subculturing at 20 to 22°C: Fomitiporia sp. (F85-1), Phaeomoniella chlamydospora (F85-2), Eutypa lata (BX1-10, 8D, and 8F), and Botryosphaeria obtusa (F99-1). The fungus most frequently isolated from central necrosis with white heart rot was the basidiomycete Fomitiporia sp. (35% of vines). Cultures of Fomitiporia sp. on MA reached 4 to 5 cm in diameter after 2 weeks and were yellowish to brownish without conidia. P. chlamydospora (associated with esca, black goo, or Petri disease) was isolated from only 9% of vines investigated. Cultures of P. chlamydospora on MA were slow growing and reached 7 to 8 mm in diameter in the dark after 8 days. Colonies were white but became light green and later became dark green. Sporulation was abundant. E. lata (causing Eutypa dieback) was isolated from the vine of cv. Cabernet Sauvignon showing typical symptoms and from two vines showing symptoms of esca only. Two strains produced characteristic pycniospores, and all strains were identified using polymerase chain reaction (Primer Scar 10A-10B) (2). Among the saprophytic fungi isolated from the different kinds of necroses, either central, wedge-shaped, or under the bark, B. obtusa associated with BDA was found most commonly (65% of vines). Cultures of B. obtusa were gray brown with dense aerial mycelium. Pycnidia started to form after 4 to 5 days and conidia (20 to 26 × 9 to 16 µm) were dark brown when mature. These results are consistent with previous descriptions. To our knowledge, this is the first report of black dead arm in Lebanon. References: (1) P. Larignon et al. Phytopathol. Mediterr. 40:S336, 2001. (2) P. Lecomte et al. Appl. Environ. Microbiol. 66:4475, 2000.

First Report of a 16SrII Group Phytoplasma Associated with Shoot Proliferation of a Cactus (Opuntia monacantha) in Lebanon.

In October 2003, during a survey to evaluate the incidence of phytoplasma diseases in Lebanon, symptoms suggestive of phytoplasma infection in Opuntia monacantha (Haworth) were observed in Saghbine, Bekaa Valley. Symptoms were excessive stem and shoot proliferation. Three symptomatic and as well as symptomless plants were collected and analyzed for the presence of phytoplasmas. Nucleic acids were extracted from 0.5 g of shoot tissue and tested using polymerase chain reaction (PCR) with universal phytoplasma primers (fU5rU3) for partial amplification of the ribosomal 16SrDNA (4). PCR resulted in amplification of an expected 881-bp rDNA fragment from the symptomatic but not from symptomless samples. For characterization, sequence of the amplified DNA was determined (Genbank Accession No. AY939815). The sequence showed a high similarity with several isolates of the 16srII group of phytoplasmas. The highest similarity has been oserved with 16S rDNA of two isolates of cactus witches'-broom phytoplasma found in China (1) and Mexico (3) (Genbank Accession Nos. AJ293216 and AF320575, respectively) (99.8%) as well as faba bean phyllody phytoplasma (Genbank Accession No. X83432) (99.7%) and "Candidatus Phytoplasma aurantifolia" (Genbank Accession No. U15442) (99.3%). The presence of phytoplasmas was confirmed using nested-PCR with primers R16mF2/R1 and R16F2n/R2 (2). The Tru9I digestion pattern of the amplified product R16F2n/F16R2 detected in O. monacantha was identical to the digestion pattern obtained from periwinkle infected by "Ca. P. aurantifolia" (subgroup 16SrII-B) and soybean phyllody phytoplasma (subgroup 16SrII-C), but different from the Tru9I digestion pattern observed for cleome phyllody phytoplasma (subgroup 16SrII-A) and tomato big bud phytoplasma (subgroup 16SrII-E). To our knowledge, this is the first report of an infection with a phytoplasma belonging to16SrII group in Lebanon. References: (1) H. Cai et al. Plant Pathol. 51:394, 2002. (2) D. E. Gundersen and I. M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) N. E. Leyva-Lopez et al. Phytopathology. (Abstr.) 89(suppl):S45, 1999. (4) B. Schneider et al. Pages 369-380 in: Molecular and Diagnostic Procedures in Mycoplasmology. Academic Press, NY, 1995.

A survey of propulsion options for cargo and piloted missions to Mars.

In this paper, high-power electric propulsion options are surveyed in the context of cargo and piloted missions to Mars. A low-thrust trajectory optimization program (raptor) is utilized to analyze this mission. Candidate thrusters are chosen based upon demonstrated performance in the laboratory. Hall, self-field magnetoplasmadynamic (MPDT), self-field lithium Lorentz force accelerator (LiLFA), arcjet, and applied-field LiLFA systems are considered for this mission. In this first phase of the study, all thrusters are assumed to operate at a single power level (regardless of the efficiency-power curve), and the thruster specific mass and power plant specific mass are taken to be the same for all systems. Under these assumptions, for a 7.5 MW, 60 mT payload, piloted mission, the self-field LiLFA results in the shortest trip time (340 days) with a reasonable propellant mass fraction of 57% (129 mT). For a 150 kW, 9 mT payload, cargo mission, both the applied-field LiLFA and the Hall thruster seem reasonable choices with propellant mass fractions of 42 to 45%(7 to 8 mT). The Hall thrusters provide better trip times (530-570 days) compared to the applied-field LiLFA (710 days) for the relatively less demanding mission.

Instability of a current-carrying finite-beta collisional plasma.

The microinstability of a cross-field current-carrying plasma in which the electron collisions are important on the time scale of the oscillations and can be modeled with a Bhatnagar-Gross-Krook operator is studied using linearized kinetic theory under conditions of finite electron beta. The finiteness of beta allows for coupling between electrostatic and electromagnetic modes and necessitates dealing with the entire dispersion tensor. Fundamental features of the resulting instability are identified and contrasted with those found in previous studies of the lower hybrid current-driven instability in which either collisions or finite-beta effects were neglected. As beta increases, collisions play a more important role in destabilization, alter the character and extent of electromagnetic coupling, shift the instability to more perpendicular modes, and lead to a recapturing of some of the fluidlike properties the modes have in the electrostatic limit in contrast with their highly kinetic character in the collisionless limit.

Ion acceleration by beating electrostatic waves: domain of allowed acceleration.

The conditions under which a magnetized ion can be accelerated through a nonlinear interaction with a pair of beating electrostatic waves are explored. It has been shown [Benisti et al., Phys. Plasma 5, 3224 (1998)] that the electric field of the beating waves can, under some conditions, accelerate ions from arbitrarily low initial velocity in stark contrast with the well-known nonlinear threshold criteria for ion acceleration by a single wave. It is shown here that the previously found condition is necessary but not sufficient for acceleration to occur. The sufficient and necessary conditions are identified in terms of the location of the critical points of the motion on the Poincaré section. A second-order perturbation analysis was carried out to approximate the location of these critical points and define the domains of allowed and forbidden acceleration. It is shown that for an ion to be significantly energized, the Hamiltonian must be outside the energy barrier defined by the location of the elliptic and hyperbolic critical points. Despite the restriction on the Hamiltonian, an ion with arbitrarily low initial velocity may benefit from this acceleration mechanism.

Accidents in the U.S. and Europe: 1970-1980.

This study compares certain demographic and accident characteristics among Western European countries and between Western Europe and the United States. The specific objectives of the study were to: Identify various changes in fatalities and fatality rates experienced by each of eleven Western European Countries, by these countries as a whole, and by the United States from 1970 through 1980, with special attention given to the energy crisis and its aftermath from 1974 through 1980. Determine whether there were statistically significant changes during the 1970-1980 time period in the traffic accident characteristics studied. The findings of this study are as follows: During the decade studied, Western Europe as a whole experienced a fatality rate reduction per 10(9) vehicle-kilometers traveled of 45.8% while the U.S. experienced a 29.1% reduction during this same period. In Western Europe the age groups 0-14, 25-64 and over 64 and its road user groups pedestrians, bicyclists and motorcyclists and moped riders showed statistically significant improvements in the characteristics studied. The only U.S. group to experience a significant reduction in fatalities during this period was the age group 0-14; however the 1980 fatality rate per 10(9) vehicle-kilometers of travel of 21.0 for the U.S., versus 34.8 for Western Europe, indicates that driving in the U.S. is still much safer.

First Report of a Phytoplasma Disease of Almond (Prunus amygdalus) in Lebanon.

During a survey conducted in October 1999 to establish the sanitary status of stone fruits in Lebanon, almond trees with symptoms of leaf yellowing, shoot proliferation, and dieback were observed in the Bekaa region. Because such symptoms are often associated with phytoplasma infections, samples were collected for analysis by PCR using universal primers for amplification of phytoplasma ribosomal RNA genes (2). DNA was extracted from the leaf midveins and/or bark phloem tissue from nine symptomatic trees and one symptomless tree in four different orchards as well as from healthy almond trees collected in France. PCR resulted in amplification of an expected 1.8 kbp rDNA fragment from all symptomatic samples but not from the healthy or symptomless samples. For characterization, the amplified DNA was analyzed by RFLP. Even though the restriction profiles were different from those published for other phytoplasmas and in particular from those infecting almond trees in Western Europe (1), sequence analysis of the amplified DNA revealed that it belongs to the pigeon pea witches' broom cluster (PPWB) (2). This is the first report of a phytoplasma infection in Lebanon and the first report for a PPWB group phytoplasma in almond trees. References: (1) W. Jarausch et al. J. Plant Pathol. 104:17-27, 1998. (2) B. Schneider et al. 1995. Molecular and diagnostic procedures in Mycoplasmology Vol. 1, 369-380, S. Razin and J. G. Tully, eds.

First Report of Grapevine "Bois Noir" Disease and a New Phytoplasma Infecting Solanaceous Plants in Lebanon.

During a 2001 survey to evaluate the incidence of phytoplasma diseases in Lebanon, samples were collected from plants showing symptoms suggestive of phytoplasmal infections. Samples were also collected from symptomless plants. Sampled hosts from the Bekaa Valley included: 3 samples of tomato (Lycopersicum esculentum), 4 samples of pepper (Capsicum annuum), 10 samples of grapevine (Vitis vinifera) cvs. Chardonnay and Alicante Bouschet; 7 samples of ornamental periwinkle (Catharantus roseus) from the Tyr area; and 4 samples of weeds (Lactucca serratia). DNA was extracted from leaf midveins of diseased and symptomless plants, and from healthy periwinkle, grapevine, tomato, and pepper plants grown in a greenhouse in France. Polymerase chain reaction (PCR) with universal primers for the amplification of phytoplasma ribosomal RNA genes (3) only produced a 1.8-kbp rDNA fragment from symptomatic samples. The amplified DNAs were analyzed by restriction fragment length polymorphism (RFLP) with several restriction enzymes and sequenced. The analysis showed extracts of diseased grapevines, and two periwinkle plants had identical rDNA sequences and restriction profiles of the stolbur cluster (4). The sequences had 98% identity with two European stolbur isolates from grapevine and periwinkle (GenBank Accession Nos. X76428 and AF248959, respectively). In grapevine, the disease induced by the stolbur phytoplasma is "bois noir." Bois noir is present in Europe where its incidence is predominant in northern vineyards and has been reported in Israel (2). To our knowledge, this is the first report of the stolbur/bois noir disease in Lebanon. In tomato and pepper, the restriction profiles and sequences of the phytoplasma rDNAs were identical. Sequencing and phylogenetic analysis indicated that the phytoplasma belonged to the clover proliferation (CP) cluster, as does the eggplant little leaf phytoplasma of solanaceous plants in Asia. They differed from the stolbur phytoplasma, known to infect solanaceaous plants in Europe. Lastly, a phytoplasma belonging to the pigeon pea witches' broom (PPWB) cluster was found in L. serratia and in some periwinkle plants. A phytoplasma of the PPWB cluster was recently shown to be responsible for an emerging lethal disease of almond trees in Lebanon (1). References: (1) E. Choueiri et al. Plant Dis. 85:802, 2001. (2) X. Daire et al. Vitis 36:53, 1997. (3) B. Schneider et al. Pages 369-380 in: Molecular and Diagnostic Procedures in Mycoplasmology. Academic Press, NY, 1995. (4) E. Seemüller et al. J. Plant Pathol. 80:3, 1998.

Stochastic ion acceleration by beating electrostatic waves.

A study is presented of the stochasticity in the orbit of a single, magnetized ion produced by the particle's interaction with two beating electrostatic waves whose frequencies differ by the ion cyclotron frequency. A second-order Lie transform perturbation theory is employed in conjunction with a numerical analysis of the maximum Lyapunov exponent to determine the velocity conditions under which stochasticity occurs in this dynamical system. Upper and lower bounds in ion velocity are found for stochastic orbits with the lower bound approximately equal to the phase velocity of the slower wave. A threshold condition for the onset of stochasticity that is linear with respect to the wave amplitudes is also derived. It is shown that the onset of stochasticity occurs for beating electrostatic waves at lower total wave energy densities than for the case of a single electrostatic wave or two nonbeating electrostatic waves.

Low genetic variability in the coat and movement proteins of American plum line pattern virus isolates from different geographic origins.

Until very recently isolates of American plum line pattern virus (APLPV) had not been reported from outside North America. The nucleotide sequences corresponding to the movement (MP) and coat (CP) proteins of eight APLPV isolates from five Mediterranean countries were determined. Sequence analysis showed that both MP and CP genes are highly conserved irrespective of geographic origin. The study of the distribution of synonymous and nonsynonymous changes along both open reading frames revealed that these proteins are under the effect of negative purifying selection. The MP and CP of APLPV possess most of the functional motifs described for other members of the genus Ilarvirus.