Measurements of microwave transmission through a decaying plasmacolumn

We have studied the width and the amplitude of the transmitted radio frequency (RF) pulse, as a function of the afterglow time for argon and nitrogen plasmas. In our study, the neutral gas pressure for the case of argon was 2 torr and that for nitrogen was 0.5 torr. The RF energy of the transmitted pulse was found to reach half of its maximum value for afterglow times of about 0.1 s for argon and about 375 μs for nitrogen     

Dynamic small-angle scattering system for the study of materials deformation and relaxation

A dynamic small-angle x-ray scattering system (DSAXS) for the study of materials deformation and relaxation has been developed in the National Center for Small-Angle Scattering Research, Oak Ridge National Laboratory (NCSASR-ORNL), in collaboration with Polymer Research Institute of the University of Massachusetts. The principles of DSAXS are outlined, including experimental procedures such as π-sector and Fourier expansion techniques. A few important functions required for studies of crystalline polymers, namely, static and dynamic lamellar orientation, dynamic lamellar separation, dynamic invariant function, etc., are defined. The hardware and software of the DSAXS system are described. Some preliminary results obtained for a spherulitic high-density polyethylene by π-sector technique and for a row-nucleated polybutene-1 by Fourier expansion techniques are demonstrated to evaluate the performance of the system.     

Effect of crystallization time on the properties of melt-crystallized linear polyethylene

Linear polyethylene was crystallized isothermally from the melt. Specimens were removed at different crystallization times and quenched to room temperature. The density, static mechanical properties, and small-angle x-ray scattering (SAXS) behavior of these specimens were measured at room temperature. The density and Young's modulus increased with crystallization time, whereas the upper yield point decreased with crystallization time. SAXS data showed that a zero-angle peak gradually disappeared as crystallization time increased. Concurrently, the breadth of the SAXS peaks, the Bragg angle, and the integrated intensity decreased. Changes in the ratio of second- and first-order peak intensities were also noted. On the basis of the SAXS and density data, it was concluded that a competition exists between the thickening of existing crystals and the creation of new crystallites between the older ones. At relatively low crystallization times, numerous new crystals can form during quenching to room temperature, whereas quenching after prolonged crystallization primarily results in the additional thickening of existing crystals. No change in the density of the amorphous material is found. A model is given whereby the upper yield stress is coupled to these morphological changes through a stress concentration effect caused by a decreased population of chains connecting adjacent crystallites. The tie-chain population change occurs by their elimination as crystallites disappear.     

Significant pulse-lengthening in a multigigawatt magneticallyinsulated transmission line oscillator

The Air Force Research Laboratory/Phillips Laboratory magnetically insulated transmission line oscillator (MILO) is a gigawatt-class, L-band, high-power microwave tube driven by a 500-kV, 60-kA electron beam. A previous version of this tube generated 1.5 GW pulses, but with significant RF pulse shortening, The paper reports on improvements to the tube that have allowed us to increase the output power by 25% and to increase the RF pulse duration by a factor of two and a half     

Investigation of RF breakdowns on the MILO

Describes a series of experiments performed to isolate the RF breakdown mechanisms in the hard tube magnetically insulated transmission line oscillator (MILO) Experiment at the Air Force Phillips Laboratory, Albuquerque, NM. Specifically, several causes of RF breakdown in the region of the vacuum-air interface and the antenna region have been investigated. These causes are X-ray induced electron emission, VUV and visible photoemission of electrons, and breakdown due to large field stresses in the antenna. Each of these mechanisms has the effect of liberating electrons from a surface in a high field region which then are a seed for a breakdown. This paper discusses measurements in the X-ray, VUV, and visible regimes with support from computer simulation. Also, imagery results are shown, which in conjunction with the computer work, point to the presence of high electric field stresses in the antenna, which cause a subsequent breakdown. In particular, X-rays, VUV, visible light, and plasmas do not seem to be the major source of RF breakdown in this tube     

Solvent-assisted soft nanoimprint lithography for structured bilayer heterojunction organic solar cells

We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.     

Inorganic membranes based on zirconium phosphate for fuel cells

In this paper we report on zirconium phosphate based inorganic membrane preparation and electrochemical characterization. The zirconium oxide microporous membranes were impregnated with colloidal particles of zirconium phosphate and were designed for application in direct methanol fuel cells. Scanning electron microscopy, thermogravimetry and impedance spectroscopy was used for membrane characterization.     

First chemical on-line separation and detection of a subsecond α-decaying nuclide, 224Pa

Subsecond ²²⁴ Pa (T _1/2 = 0.85 s) was produced via the ²⁰⁹ Bi(¹⁸ O,3n)²²⁴ Pa reaction at the 88 inch cyclotron at the Lawrence Berkeley National Laboratory. After production it was transported via a gas-jet system to the centrifuge system SISAK 3. Following on-line extraction with trioctylamine/scintillation solutions from 1M lactic acid, ²²⁴ Pa was detected applying on-line -liquid scintillation counting. Unambiguous identification was achieved using time-correlated --decay chain analysis. This constitutes the first chemical on-line separation and detection of a subsecond -decaying nuclide, 0.85-s ²²⁴ Pa with the fast extraction system SISAK 3.