Li+ ion emission from a hot-plate alumina-silicate source stimulated by flash heating with an infrared laser.

The Neutralized Drift Compression Experiment-II accelerator under construction at Lawrence Berkeley National Laboratory has been designed to employ a lithium-doped alumino-silicate (Al-Si) hot-plate surface-ionization ion source. In order to achieve the design 1 mA∕cm(2) current density, the emitter must be constantly kept at a high temperature, leading to the accelerated loss of Li material as ions or neutrals. As a result, the estimated lifetime of the source is 50 h. This lifetime can be extended if the source is kept at low temperature during standby, and pulse heated to the high temperature during the ion extraction phase only. A pulsed heating technique based on an infrared laser (CO(2) gas discharge, λ = 10.6 µm) is described in this paper. The feasibility of ion current emission stimulated by flash heating with an infrared (IR) laser was demonstrated. High repeatability of the laser-stimulated ion current was observed, creating an opportunity for modulation and gating of the ion current with a laser pulse. It was found that with the available low power (≈115 W∕cm(2)) IR laser, current densities as high as 0.8 mA∕cm(2) could be achieved with a 2.8 mm diameter source. Various approaches for scaling to a larger (10 cm diameter) source and the application of short pulse, high power lasers are discussed. The results and conclusions of this paper may apply to various species of hot-plate ion sources.

Radio frequency-driven proton source with a back-streaming electron dump.

This article describes an rf ion source with a back-streaming electron dump. A quartz tube, brazed to a metal plug at one end, is fused in the center of a flat quartz plate. rf power (at 13.6 MHz) is coupled to generate hydrogen plasma using a planar external antenna bonded to the window. Bonding the water-cooled rf antenna to the quartz window significantly lowers its temperature. The water-cooled metal plug serves as the back-streaming electron dump. At 1800 W, the current density of extracted hydrogen ions reaches approximately 125 mA/cm(2).

A tandem-based compact dual-energy gamma generator.

A dual-energy tandem-type gamma generator has been developed at E. O. Lawrence Berkeley National Laboratory and Sandia National Laboratories. The tandem accelerator geometry allows higher energy nuclear reactions to be reached, thereby allowing more flexible generation of MeV-energy gammas for active interrogation applications. Both positively charged ions and atoms of hydrogen are created from negative ions via a gas stripper. In this paper, we show first results of the working tandem-based gamma generator and that a gas stripper can be utilized in a compact source design. Preliminary results of monoenergetic gamma production are shown.

Sealed operation of a rf driven ion source for a compact neutron generator to be used for associated particle imaging.

We present the recent development of a prototype compact neutron generator to be used in conjunction with the method of associated particle imaging for the purpose of active neutron interrogation. In this paper, the performance and device specifications of these compact generators that employ rf driven ion sources will be discussed. Initial measurements of the generator performance include a beam spot size of 1 mm in diameter and a neutron yield of 2x10(5) n/s with air cooling.

Nonuniform distribution of cell proliferation in the adult teleost retina.

Teleost fish continue to grow throughout life, and their eyes enlarge correspondingly. Within the eye, the retina grows by stretching existing tissue and adding new cells. Cell addition occurs in two ways: First, all cell types except rod photoreceptors are added circumferentially at the edge of the eye where the retina meets the iris; second, rod photoreceptors are generated from a population of rod progenitor cells which divide throughout the outer nuclear layer (ONL). To determine the spatial distribution of rod progenitor cells across the teleost retina, we labeled dividing cells with an antibody to proliferating cell nuclear antigen (PCNA) throughout a 24 h period. We found a significantly higher density of dividing rod precursor cells at the nasal and temporal margins than in the central retina throughout the 24 h cycle. At night, the density of dividing cells is significantly greater at the nasal pole of the eye. The difference between cell division at the center and the margin was reduced at night when the density of cell division in the central retina increased significantly. Taken together, these data suggest that the eye grows asymmetrically, with more cells added at the nasal pole. Possible developmental causes and functional consequences of the reported distribution of cell divisions in time and location are presented.

High-technology i.v. infusion devices.

Some of the newer high-technology infusion devices commercially available or under development are described. The range of infusion devices includes both controllers and pumps; pumps can be classified by mechanism of operation (peristaltic, syringe, cassette, elastomeric reservoir), frequency or type of drug delivery (continuous or intermittent infusion, bolus dosing, single- or multiple-solution delivery), or therapeutic application (such as the patient-controlled analgesia, or PCA, pump). Advances in infusion technology and computer technology have led to the development of devices with extremely sophisticated drug-delivery capabilities (multiple-rate or multiple-solution programming, operation as pump or controller, or both, and interchangeable applications and settings). Current research in infusion-device technology is focusing on implantable pumps, pumps with chronobiological applications, osmotic-pressure devices, and open- and closed-loop systems. Pharmacists need to keep abreast of the rapidly changing intravenous device marketplace to provide clinical expertise and leadership in the review and evaluation of high-technology drug delivery systems.

Pharmacists' knowledge of infusion devices.

Results of a mail survey of pharmacists' knowledge of infusion-device technology are presented. In order to develop recommendations on how to prepare pharmacists to take responsible roles in the use of infusion devices, a survey was mailed to 576 directors of pharmacy in hospitals and home health-care companies, deans of pharmacy schools, and executives of state pharmaceutical associations. A total of 237 responses (41.2%) was received. Directors in both hospital and home health-care settings predicted increases in the use of infusion devices in their respective settings within the coming five years. Practitioners and deans concurred that pharmacy schools are not providing adequate instruction in the use of these devices. All four groups of respondents believed that the competencies most essential in the use of these devices are knowledge of therapeutic applications and the ability to select the most appropriate pump to meet clinical needs. Use of drug-infusion technology will increase in the coming five years, and undergraduate, postgraduate, and inservice pharmacy curricula must prepare pharmacists to use it appropriately.

Use of infusion devices for epidural or intrathecal administration of spinal opioids.

The use of infusion devices for epidural or intrathecal administration of spinal opioids is described. The risks of infection and mechanical catheter complications, the need for escalating doses, reservoir volume, drug stability, and cost are practical considerations associated with use of both external and internal infusion systems. Use of patient criteria to identify suitable candidates for intraspinal administration of pain medication helps ensure successful management. The criteria for intraspinal delivery pumps are safety, accuracy, reliability, ease of management by the patient and the health-care professional, and compatibility of the drug with the pump components. The primary factors to consider when comparing pumps to be used for intraspinal delivery of pain medication are the volume and flow rate requirements of the devices. External portable infusion devices are classified according to the mechanism of operation into three primary groups: syringe pumps, peristaltic mechanisms, and elastomeric reservoir pumps. Portable patient-controlled analgesia pumps that have syringes, flexible reservoir bags, and elastomeric reservoirs have been developed. Implanted systems with flow rates that are preset at the factory make pain management more difficult when the patient requires changes or escalations in doses over time. A programmable implanted pump is available. Two advantages of continuous epidural or intrathecal infusion are (1) the peaks and valleys of pain relief with bolus injections are eliminated and (2) the need for multiple injections is reduced. Patient-controlled analgesia (PCA) pumps enhance the efficacy of continuous infusions by allowing the patient to administer bolus doses to control acute pain.

High-technology i.v. infusion devices.

Some of the newer high-technology infusion devices commercially available or under development are described. The range of infusion devices includes both controllers and pumps; pumps can be classified by mechanism of operation (peristaltic, syringe, cassette, elastomeric reservoir), frequency or type of drug delivery (continuous or intermittent infusion, bolus dosing, single- or multiple-solution delivery), or therapeutic application (such as the patient-controlled analgesia, or PCA, pump). Advances in infusion technology and computer technology have led to the development of devices with extremely sophisticated drug-delivery capabilities (multiple-rate or multiple-solution programming, operation as pump or controller, or both, and interchangeable applications and settings). Current research in infusion-device technology is focusing on implantable pumps, pumps with chronobiological applications, osmotic-pressure devices, and open- and closed-loop systems. Pharmacists need to keep abreast of the rapidly changing intravenous device marketplace to provide clinical expertise and leadership in the review and evaluation of high-technology drug delivery systems.