Search Results - (Author, Cooperation:M. Dickinson)

2018-02-28

Genetics Society of America (GSA)

0016-6731

Biology

2018-05-04

Institute of Physics (IOP)

1757-8981

1757-899X

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

2013-10-25

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2012-06-16

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-12-21

American Society of Hematology (ASH)

0006-4971

1528-0020

Biology

Medicine

Myeloid Neoplasia, Clinical Trials and Observations

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Vacuum arc ion sources provide a convenient tool for the production of intense beams of metal ions. The sources are relatively easy to construct and they can produce beams from all of the solid metals as well as from compounds, alloys, and mixtures. We have made a number of different kinds of such sources over the course of our development work at LBL in the past decade, from very small "thumb-size'' versions to a very large one with a 50 cm diameter extractor. Beam current ranges from a few milliamperes up to almost 10 A and extraction voltage from about 1 to 100 kV. Multicathode versions have been made so that one can switch between metal ion species simply and quickly. Most of the sources have been operated in a repetitively pulsed mode, and we've also tested a dc version. Here we outline some construction features of the array of vacuum arc ion sources that we've developed and used, and describe their performance and limitations. © 1996 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A simple and economical microwave plasma-assisted chemical vapor deposition facility has been developed and used for synthesis of diamond thin films. The system is similar to those developed by others but includes several unique features that make it particularly economical and safe, yet capable of producing high quality diamond films. A 2.45-GHz magnetron from a commercial microwave oven is used as the microwave power source. A conventional mixture of 0.2% methane in hydrogen is ionized in a bell jar reaction chamber located within a simple microwave cavity. By using a small hydrogen reservoir adjacent to the gas supply, an empty hydrogen tank can be replaced without interrupting film synthesis or causing any drift in plasma characteristics. Hence films can be deposited continuously for arbitrarily long periods while storing only a 24-h supply of explosive gases. System interlocks provide safe start-up and shut-down and allow unsupervised operation. Here we describe the electrical, microwave, and mechanical aspects of the system, and summarize the performance of the facility as used to reproducibly synthesize high quality diamond thin films.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Triggering systems for vacuum arc plasma sources and ion sources have been developed that make use of a gaseous trigger discharge in a strong magnetic field. Two kinds of trigger discharge configurations have been explored, a Penning discharge and a magnetron discharge. The approach works reliably for low gas pressure in the vacuum arc environment and for long periods of operation between required maintenance: pressures in the mid-10−6 Torr range and for (approximately-greater-than)106 pulses. © 1996 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A pulsed magnetic field of up to 10 kG was incorporated into a vacuum arc ion source. The field was established by a small coil surrounding the arc discharge region, powered by either an additional power supply (capacitor bank) or by the arc power supply (arc current and coil current in series). This addition has led to a number of improvements in source performance: The mean charge state of the metal ions produced was enhanced by a factor of up to 2, for 30 different cathode materials from carbon to bismuth; hybrid metal/gaseous ion beams could be generated when an additional gas (nitrogen, oxygen, or argon) was admitted into the source, with gaseous ion fraction as high as 50%; triggering of the source could be done by a very long lifetime gaseous predischarge technique. We also report on the use of a wire mesh to stabilize the plasma emission surface at the extractor as a means for achieving a flat beam current characteristic as a function of extraction voltage. © 1996 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have developed several different embodiments of repetitively pulsed vacuum arc metal plasma gun, including miniature versions, multicathode versions that can produce up to 18 different metal plasma species between which one can switch, and a compact high-duty cycle well-cooled version, as well as a larger dc gun. Plasma guns of this kind can be incorporated into a vacuum arc ion source for the production of high-energy metal ion beams, or used as a plasma source for thin film formation and for metal plasma immersion ion implantation and deposition. The source can also be viewed as a low-energy metal ion source with ion drift velocity in the range 20–200 eV depending on the metal species used. Here we describe the plasma sources that we have developed, the properties of the plasma generated, and summarize their performance and limitations. © 1998 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30–40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the "anode'' plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al2O3 at 600–800 °C. The films were investigated by photoluminescence, cathodoluminescence, x-ray diffraction, Rutherford backscattering, and particle-induced x-ray emission. The film with the highest structural quality had a rocking curve width of 5 arcmin, the lowest reported value for MBE growth to date. © 1996 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Conventional ion sources generate energetic ion beams by accelerating the plasma-produced ions through a voltage drop at the extractor, and since it is usual that the ion beam is to propagate in a space which is at ground potential, the plasma source is biased at extractor voltage. For high ion beam energy the plasma source and electrical systems need to be raised to high voltage, a task that adds considerable complexity and expense to the total ion source system. We have developed a system which though forming energetic ion beams at ground potential as usual, operates with the plasma source and electronics at ground potential also. Plasma produced by a nearby source streams into a gridded chamber that is repetitively pulsed from ground to high positive potential, sequentially accepting plasma into its interior region and ejecting it energetically. We call the device a peristaltic ion source. In preliminary tests we've produced nitrogen and titanium ion beams at energies from 1 to 40 keV. Here we describe the philosophy behind the approach, the test embodiment that we have made, and some preliminary results. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report on measurements of the charge state distributions of ions formed in a vacuum arc plasma in a magnetic field. A vacuum arc ion source was used for plasma formation and ion beam extraction, and the charge state spectra were investigated using both magnetic and time-of-flight charge state diagnostics. We find that the charge states of all of the metal species investigated are significantly increased by a magnetic field of up to 6 kG. New high ion charge states are created, and the mean of the charge state distribution is increased by about 30% at 3.75 kG and 50% at 6 kG. The results are important fundamentally as well as being of relevance to vacuum arc ion source applications such as ion implantation and accelerator injection. © 1995 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We are developing an embodiment of metal vapor vacuum arc (Mevva) ion source which will operate dc and have a very large area beam. In preliminary testing, a dc titanium ion beam was formed with a current of approximately 0.6 A at an extraction voltage of 9 kV (about 18 keV ion energy, by virtue of the ion-charge state distribution) using an 18-cm-diameter set of multiaperture extraction grids. Separately, we have tested and formed a beam from a 50-cm-diameter (2000 cm2) set of grids using a pulsed plasma gun. This configuration appears to be very efficient in terms of plasma utilization, and we have formed beams with a diameter of 33 cm (FWHM) and ion current up to 7 A at an extraction voltage of 50 kV (about 100 keV mean ion energy) and up to 20 A peak at the current overshoot part of the beam pulse. Here we describe this part of our Mevva development program and summarize the results obtained to date.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Since its initial detection in Australia in 1979, wheat yellow (stripe) rust (Puccinia striiformis f.sp. tritici) has evolved in Australia and New Zealand into more than 20 pathotypes with assorted virulence characteristics. This evolution is believed to have occurred in a stepwise fashion from an original single pathotype, with no subsequent new introductions. A combination of random amplified polymorphic DNA (RAPDs) and amplified fragment length polymorphisms (AFLPs) was used to examine the level of molecular variation in Australian and New Zealand isolates, and to compare this with variation amongst other isolates of P. striiformis. Using 60 RAPD primers on seven Australian isolates representing seven different pathotypes collected between 1979 and 1991, more than 300 potentially polymorphic loci were analysed and no polymorphisms were detected. Using the same primers on two UK isolates, 3% of loci showed a polymorphism. A similar level of polymorphism was found between UK isolates using AFLP primers, and between 5 and 15% of fragments were polymorphic between an isolate from the UK, an isolate from Denmark, and one from Colombia. However, no AFLP polymorphisms were found amongst 14 Australian and New Zealand isolates tested, at over 100 potentially polymorphic loci. The lack of molecular variation in the Australian and New Zealand collection is consistent with the stepwise mutation theory of pathotype evolution from a single introduction.

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Comparisons were made between two breeding lines of faba bean (designated 224 and 335), following inoculation of leaf material with Botrytis cinerea and the more aggressive B. fabae. Line 335 exhibited greater initial resistance to infection, in terms of retarded lesion development and higher rates of phytoalexin production. However, in whole plant inoculation experiments line 335 abscinded its leaflets more readily after infection. The role of the gaseous plant hormone ethylene in this reaction was analysed. Both lines exhibited a similar abscission response to exogenous ethylene, applied at a concentration of 10 μL L−1. However, there were significant differences in the ability of the lines to produce ethylene. In response to inoculation with B. fabae, line 335 liberated ethylene at a higher concentration and for a longer period. These results suggest that the differential levels of abscission are a consequence of differences in the biosynthesis of ethylene in the two lines rather than in their responses to ethylene.

Electronic Resource

1365-3059

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Lethal disease (LD) is a lethal yellowing-type disease of coconuts associated with phytoplasmas in Tanzania, but the insect vector for it has not yet been identified. In this study, the auchenorrynchous insects in LD-infected coconut fields were surveyed to determine potential vectors for the disease. No significant correlation was found between disease incidence and numbers of insects collected from the field, possibly reflecting the unknown incubation period for the disease. However, analysis of more than 5000 individual insects by the polymerase chain reaction (PCR), using LD-specific primers derived from the phytoplasma 16S rRNA gene, revealed PCR products of the correct size from eight individuals of Diastrombus mkurangai and four of Meenoplus spp. When digested with restriction endonucleases, fragments of the same size as the LD phytoplasma were obtained. No PCR products were detected in any of the other insect species tested. These results implicate D. mkurangai and Meenoplus spp. as probable vectors of the LD phytoplasma.

Electronic Resource

0031-9163

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0031-9163

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource