Real-time dynamic holographic image storage device

A real-time dynamic holographic image storage device uses four-wave mixing in a pair of photorefractive crystals. An oscillation is produced between the crystals which can be maintained indefinitely after the initial object beam is discontinued. The object beam produces an interference pattern in a first crystal to produce phase-conjugated object beam which is directed towards the second crystal. In the second crystal another interference pattern is created which produces a reconstructed object beam. The reconstructed object beam is directed back towards the first crystal. The interference patterns are produced by interaction of the object and phase-conjugated object beam with a read and write beam in each of the crystals. By manipulation of the ratio of the read and write beam intensities in at least one of the crystals, the phase-conjugate or reconstructed object beam output therefrom can be amplified to maintain stable oscillation between the two crystals

Plasma control by modification of helicon wave propagation in low magnetic fields

By making use of nonuniform magnetic fields, it is shown experimentally that control of helicon wave propagation can be achieved in a low pressure (0.08 Pa) expanding plasma. The m=1 helicon waves are formed during a direct capacitive to wave mode transition that occurs in a low diverging magnetic field(B₀<3 mT). In this initial configuration, waves are prevented from reaching the downstream region, but slight modifications to the magnetic field allows the axial distance over which waves can propagate to be controlled. By changing the effective propagation distance in this way, significant modification of the density and plasma potential profiles can be achieved, showing that the rf power deposition can be spatially controlled as well. Critical to the modification of the wave propagation behavior is the magnetic field strength (and geometry) near the exit of the plasma source region, which gives electron cyclotron frequencies close to the wave frequency of 13.56 MHz

Detailed plasma potential measurements in a radio-frequency expanding plasma obtained from various electrostatic probes

On-axis plasma potential measurements have been made with an emissive probe in a low pressure (0.044 Pa) rf expanding plasma containing an ion beam. The beam is detected with a retarding field energy analyzer (RFEA), and is seen to disappear at high pressure (0.39 Pa). The emissive probe measurements are in very good agreement with corresponding measurements made with two separate RFEAs, and the results indicate that the floating potential of the strongly emitting probe gives an accurate measure of the plasma potential under the present conditions

Comparison of show-rates for telephone and walk-in referrals for substance abuse services

The investigator attempted to determine if individuals who make in-person (walk-in) referrals would be more likely to keep their initial appointment with a substance abuse counselor at an outpatient mental health clinic than will individuals who refer themselves over the telephone. Participants were 40 adults who had been ordered to undergo a substance abuse evaluation by the legal system between July and December 2001. The walk-in group consisted of 18 males and 2 females (mean age 34.04). The telephone-in group consisted of 18 males and 2 females (mean age 35.67). The investigator saw all participants for the initial appointment. The list of walk-in referrals\u27 attendance was compared to records of attendance for phone-in referrals during the same time period. Chi-square analysis revealed that participants in the walk-in group were not more likely to show up for the initial appointment than participants in the telephone-in group (χ2 = .476, p = .490). The results indicate that meeting with the counselor prior to the initial appointment does not decrease no-show rates

Ion beam formation in a very low magnetic field expanding helicon discharge

An ion beam has been measured emerging from a low pressure (0.04 Pa) helicon plasma reactor over a narrow range of magnetic field values (1 mT<B0<3 mT). The presence of the ion beam occurs simultaneously with a large increase in the plasma density for the same applied magnetic field, produced using a single solenoid half the length of the m=1 rfantenna. The peak central plasma density of 1.5×10¹⁷ m⁻³ is measured to be almost 15 times larger than that occurring before or after the increase, and is associated with a steep axial density gradient which follows the gradient of the magnetic field. During this low magnetic field transition the antenna power transfer efficiency is measured to increase from less than 10% to 50%, suggesting some form of localized bulk electron heating in the source region associated with the helicon wave

Electron–cyclotron damping of helicon waves in low diverging magnetic fields

Particle-in-cell simulations are performed to investigate wave propagation and absorption behavior of low-field (B0<5 mT) helicon waves in the presence of a diverging magnetic field. The 1D electromagnetic simulations, which include experimental external magnetic field profiles, provide strong evidence for electron–cyclotron damping of helicon waves in the spatially decaying nonuniform magnetic field. For a dipole-type magnetic field configuration, the helicon waves are absence in the downstream (lower field) region of the plasma and are observed to be completely absorbed. As the magnetic field is changed slightly however, wave damping decreases, and waves are able to propagate freely downstream, confirming previous experimental measurements of this phenomenon

Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster

It is shown analytically that the thrust from a simple plasma thruster (in the absence of a magnetic field) is given by the maximum upstream electron pressure, even if the plasma diverges downstream. Direct thrust measurements of a thruster are then performed using a pendulum thrust balance and a laser displacement sensor. A maximum thrust of about 2 mN is obtained at 700 W for a thruster length of 17.5 cm and a flow rate of 0.9 mg s1, while a larger thrust of 4 mN is obtained at a similar power for a length of 9.5 cm and a flow rate of 1.65 mg s1. The measured thrusts are in good agreement with the maximum upstream electron pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster.Dr. K. Takahashi would like to thank the Faculty of Engineering at Iwate University (sabbatical year), the TEPCO Research Foundation in Japan, the MEXT in Japan (Grant-in-Aid for Young Scientists A 22684031), and the SP3 laboratory (Australian Research Council Discovery Grant No. DP 1096653) for financial support

Particle-in-cell simulations of a current-free double layer

Current-free double layers of the type reported in plasmas in the presence of an expanding magnetic field [C. Charles and R. W. Boswell, Appl. Phys. Lett. 82, 1356 (2003)] are modeled theoretically and with particle-in-cell/Monte Carlo simulations. Emphasis is placed on determining what mechanisms affect the electron velocity distribution function (EVDF) and how the EVDF influences the double layer. A theoretical model is developed based on depletion of electrons in certain velocity intervals due to wall losses and repletion of these intervals due to ionization and elastic electron scattering. This model is used to predict the range of neutral pressures over which a double layer can form and the electrostatic potential drop of the double layer. These predictions are shown to compare well with simulation results.This work was supported by the United States National Science Foundation and the Australian Academy of Sciences under East Asia and Pacific Summer Institute (EAPSI) award number 1015362

Influence of the nature of the sterol on the behavior of palmitic acid/sterol mixtures and their derived liposomes

AbstractThe phase behavior of mixtures formed with palmitic acid (PA) and one of the following sterols (dihydrocholesterol, ergosterol, 7-dehydrocholesterol, stigmasterol and stigmastanol), in a PA/sterol molar ratio of 3/7, has been characterized by IR and 2H NMR spectroscopy at different pH. Our study shows that it is possible to form liquid-ordered (lo) lamellar phases with these binary non-phospholipid mixtures. The characterization of alkyl chain dynamics of PA in these systems revealed the large ordering effect of the sterols. It was possible to extrude these systems, using standard extrusion techniques, to form large unilamellar vesicles (LUVs), except in the case of ergosterol-containing mixture. The resulting LUVs displayed a very limited passive permeability consistent with the high sterol concentration. In addition, the stability of these PA/sterol self-assembled bilayers was also found to be pH-sensitive, therefore, potentially useful as nanovectors. By examining different sterols, we could establish some correlations between the structure of these bilayers and their permeability properties. The structure of the side chain at C17 of the sterol appears to play a prime role in the mixing properties with fatty acid