Energy conversion and high power pulse production using miniaturemagnetic flux compressors

The design, construction, and testing of miniature, high-power magnetic flux compressors are presented and discussed. The magnetic flux compressors are located inside high-speed, 30-mm projectiles that are launched with a high-pressure helium gun to velocities of approximately 300 m/s. The large deceleration force created when the projectile impacts the ground is used to power the magnetic flux compressor. Initial magnetic flux compressor currents of 200 mA are amplified up to 230 times to reach a peak current approaching 50 A. The output peak power is on the order of 3.5 kW into a 1-Ω load with a pulse length of 100 to 150 μs. Good agreement exists between the experimental results and the theoretical predictions for peak output current     

Effects of hepatic impairment on the metabolism of fructose and 5-fluorouracil, as studied in fatty liver models using in vivo 31P-MRS and 19F-MRS

The purpose of this study was to observe the effects of hepatic impairment on the metabolism of fructose and 5-fluorouracil (5-FU) in fatty liver models using in vivo 31P-MRS and 19F-MRS and to compare the results. In addition, we compared the results to those of other conventional tests such as laboratory examinations, imaging and pathology. Male SIc:Wistar rats were examined on BEM170/200 (4.7 T, Otsuka Electronics, USA) with 17-mm diameter surface coil. Fatty liver was induced by a choline deficient diet (CD diet) for 2 weeks. 31P-MRS were obtained for 90 min after intravenous (i.v.) injection of 1 g/kg of fructose and 19F-MRS were measured for 100 min after i.v. injection of 100 mg/kg of 5-FU. 1H-MRS and 1H-MRI were also performed. On 31P-MRS, there was no statistical difference in the time course of phosphomonoester (PME), adenosine triphosphate (ATP), and inorganic phosphate (Pi) between CD diet group and control group. On 19F-MRS, we detected high peak of fluoronucleotide (Fnct) and suppressed peak of alpha-fluoro-beta-alanine (FBAL) in CD diet group. We showed the metabolism of fructose and 5-FU by 31P-MRS and 19F-MRS, respectively. There was no difference in fructose metabolism but we observed increased fluoronucleotide and decreased a-fluoro-b-alanine in 5-FU metabolism of fatty liver. We speculate that the effects of hepatic impairment in fatty liver may be more severe on 5-FU metabolism and the increased fluoronucleotide may reflect cell proliferation.     

Distribution of Peak Temperature and Energy Flux on the Surface of the Anode in a Multi-Cathode Spot Pulsed Vacuum Arc

The distribution of the peak temperature and energy flux on the surface of a steel anode in a pulsed high-current vacuum arc was determined by studying the spatial location of the borderline separating the region of hardened steel, produced by the pulse of energy flux to the anode, and the region of the anode which did not undergo a phase transition. The arc was run between a 14-mm-diameter stainless steel cathode and a 25-mm 4340 steel anode, separated by a 4-mm gap, with peak currents up to 1000 A and 71 ms full-width half-amplitude (FWHA) duration. The phase transition of the steel occurs at 727°C and the above-mentioned borderline is thus the geometrical location of all points which reached a peak temperature of 727°C. The peak anode surface temperature was calculated from the borderline position by approximate solution of the three-dimensional heat conduction equation. The effect of an axial magnetic field on the anode surface temperature and energy flux distribution was also studied showing that with no magnetic field the distribution had a pronounced maximum on the axis of the arc, while with the presence of a magnetic field the distribution became annular with a maximum at about mid-radius. In comparison, the shape of the distribution of the cathode mass deposited by the arc on the anode was uniform without a magnetic field. The peak of the anode temperature and the energy flux amplitude also depended on the magnetic field, first decreasing and then increasing almost linearly with it.     

Crystal spectroscopy of silicon aero-gel end-caps driven by a dynamic hohlraum on Z

We present results from crystal spectroscopic analysis of silicon aero-gel foams heated by dynamic hohlraums on Z. The dynamic hohlraum on Z creates a radiation source with a 230-eV average temperature over a 2.4-mm diameter. In these experiments silicon aero-gel foams with 10-mg/cm³ densities and 1.7-mm lengths were placed on both ends of the dynamic hohlraum. Several crystal spectrometers were placed both above and below the z-pinch to diagnose the temperature of the silicon aero-gel foam using the K-shell lines of silicon. The crystal spectrometers were (1) temporally integrated and spatially resolved, (2) temporally resolved and spatially integrated, and (3) both temporally and spatially resolved. The results indicate that the dynamic hohlraum heats the silicon aero-gel to approximately 150-eV at peak power. As the dynamic hohlraum source cools after peak power the silicon aero-gel continues to heat and jets axially at an average velocity of approximately 50-cm/μs. The spectroscopy has also shown that the reason for the up/down asymmetry in radiated power on Z is that tungsten enters the line-of-sight on the bottom of the machine much more than on the top.     

Vacuum-cored hollow waveguide for transmission of high-energy, nanosecond Nd:YAG laser pulses and its application to biological tissue ablation

A vacuum-cored hollow waveguide has been found to transmit 1064-nm, Q-switched Nd:YAG laser pulses. With this scheme, laser-induced air breakdown was completely suppressed, and the laser-induced damage threshold of the waveguide's inner coating was significantly increased. With a 1-m-long, 1-mm inner-diameter, cyclic olefin polymer-coated silver hollow waveguide, the maximum transmitted laser energy was as great as 158 mJ/pulse (20.1 J/cm(2)), at a repetition rate of 10 Hz in a 90 degrees -bent waveguide condition. The corresponding transmitted peak laser power was 17.6 MW. With the transmitted laser pulses, deep ablation of myocardium tissues was demonstrated in vitro.     

Energy conversion and high power pulse production using miniaturepiezoelectric compressors

The design, construction, and testing of miniature, high-power piezoelectric compression generators are presented and discussed. The piezoelectric compression generators are located inside high speed, 30-mm projectiles that are launched with a high pressure helium gun to velocities of approximately 300 m/s. The large deceleration force created when the projectile imparts the ground is used to power the piezoelectric compression generator. The peak output power is approximately 25 kW into a 10-Ω load with the output pulse length on the order of 1 μs. Good agreement is found between the experimental results and the theoretical predictions     

Effect of power densities and irradiation times on the degree of conversion and temperature increase of a microhybrid dental composite resin

The different parameters used for the photoactivation process provide changes in the degree of conversion (DC%) and temperature rise (TR) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and TR of the microhybrid composite resin photoactivated by a new generation LED. For the KBr pellet technique, the composite resin was placed into a metallic mould (1-mm thickness and 4-mm diameter) and photoactivated as follows: continuous LED LCU with different power density values (50–1000 mW/cm²). The measurements for the DC (%) were made in a FTIR Spectrometer Bomen (model MB-102, Quebec-Canada). The spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory for the diffuse reflectance. The measurements were recorded in the absorbance operating under the following conditions: 32 scans, 4-cm^?1 resolution, and a 300 to 4000-cm^?1 wavelength. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of the absorbance intensities of aliphatic C=C (peak at 1638 cm^?1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm^?1). For the TR, the samples were made in a metallic mould (2-mm thickness and 4-mm diameter) and photoactivated during 5, 10, and 20 s. The thermocouple was attached to the multimeter to allow the temperature readings. The DC (%) and TR were calculated by the standard technique and submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 (±1.3) to 45.0 (±2.4) for 5 s, 45.0 (±1.3) to 55.0 (±2.4) for 10 s, and 47.0 (±1.3) to 52.0 (±2.4) for 20 s. For the TR, the values ranged from 0.3 (±0.01) to 5.4 (±0.11)°C for 5 s, from 0.5 (±0.02) to 9.3 (±0.28)°C for 10 s, and from 1.0 (±0.06) to 15.0 (±0.95)°C for 20 s. The power densities and irradiation times showed a significant effect on the degree of conversion and temperature rise.     

Degree of conversion and temperature increase of a composite resin light cured with an argon laser and blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature (T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (°C) of the microhybrid composite resin (Filtek? Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm² for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen (model MB 102, Quebec, Canada). Spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm^?1 resolution, 300 to 4000-cm^?1 wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1638 cm^?1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm^?1). For T (°C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (°C) were submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% (100 to 1000 mW/cm²) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm²) for an LED. The temperature change values varied from 1.1 to 13.1 °C (100 to 1000 mW/cm²) for an argon laser and from 1.9 to 15.0 °C (100 to 1000 mW/cm²) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both lightcuring units.     

Behavior of a High Current Vacuum Arc between Hollow Cylindrical Electrodes in a Radial Magnetic Field

Experimental observations were conducted on the behavior of a high current vacuum arc on cylindrical electrodes in a radial magnetic field. The arc was sustained between the ends of two cylindrical Cu electrodes, 54-mm diam and 1.5-mm wall thickness separated by 5 mm. Arc current pulses with peak values in the range 4-15 kA with a half amplitude full width (HAFW) duration of 8 ms were investigated with radial magnetic fields proportional to the instantaneous current with proportionality constants of 4.0 and 6.5 × 10-6 T/A. The arcs were photographed simultaneously with a streak camera and by a high speed framing camera and the arc voltage was recorded on a digitizing transient recorder. The results indicated that the arc in this geometry, both with and without an imposed radial magnetic field, can be characterized by three development stages: a) arc formation, b) diffuse arc along the electrode perimeter, and c) simultaneous existence of several concentrated arc columns. When a radial magnetic field was imposed two changes were noted: 1) the arc appeared somewhat more distributed in that a greater number of constricted columns were observed, and they were distributed more evenly; and 2) the constricted columns moved in the J? × B? direction with velocities in the range 5-35 m/s.     

Thermal Performance of a Capillary Pumped Loop for Automotive Cooling

The design and test results for a capillary pumped loop (CPL) for thermal management of up to 210 W at the source and heat transfer over a distance of 1 m are discussed. The design configuration of the CPL evaporator consists of an internally grooved aluminum evaporator, 31.70-mm outer diameter and 500-mm long, fitted with a porous ultra-high molecular weight polyethylene wick, 8- to 15-μm pore radius, and 38% porous volume. Heat was transferred using a stainless steel tube of 4.5-mm internal diameter for vapor and liquid lines. High-grade acetone (99.99% pure) was used as the heat transfer fluid inside the loop. In the tests, thermal characteristics of the CPL were specifically studied with respect to the temperature control capability using an active thermal device on the reservoir and to the start-up process through pressure priming of the capillary evaporator. The loop was able to start-up successfully at both low and high heat loads, although proper priming of the wick structure before start-up was necessary to attain low evaporator temperatures during steady-state operation. While maintaining constant reservoir temperature through active means, the loop was able to control evaporator temperature within 55 ± 3°C, even with changing input heat from 30 to 210 W. Total thermal resistance from the evaporator surface to the surroundings was 0.19° to 1.15° C/W with the minimum value achieved at the maximum heat load of 210 W. This study is intended to illustrate the thermal potential of the CPL as an effective temperature control device in automotive applications.     

Spin-echo fluorine magnetic resonance imaging at 2 T: in vivo spatial distribution of halothane in the rabbit head

Spin-echo 19F magnetic resonance imaging was performed at 2.0 T to explore the in vivo spatial distribution of halothane in the rabbit head. Because the halothane concentration is low in vivo, and because the measured relaxation times of the 19F resonance peak for halothane were T1 approximately equal to 1.0 sec and T2 approximately equal to 3.5-65 msec, 1-3-h imaging times were required (TR = 1 sec, TE = 9 msec) in order to obtain adequate images with a 64 X 256 raw data matrix and a 20-mm slice thickness. With this technique, halothane was primarily detected in lipophilic regions of the rabbit head, but little or no halothane was observed in brain tissue. Because T2 was shorter in brain tissue than in surrounding fat, a shorter TE than we could obtain is needed for optimal spin-echo imaging of brain halothane.     

`Spiking' radiation in the Columbia free electron laser

A report is presented on the observation of spikes of high-intensity radiation emitted from a 2-mm wavelength Raman free electron laser oscillator. The spikes are correlated with a well-developed sideband spectrum, including several sideband harmonics, together with the carrier. A pulse width ~150 ps is obtained from analysis of data obtained with a two-slit Young's experiment. An even shorter pulse width results from a numerical model. Using an elementary model of the spike, it is estimated that the peak spike pulse power is ~100 MW     

A 4-mm probe for (13)C CP/MAS NMR of solids at 21.15 T

The design of a broadband 4-mm magic-angle spinning (MAS) X-(1)H/(19)F double resonance probe for cross-polarization (CP)/MAS NMR studies at 21.15 T ((1)H at 900 MHz) is described. The high-frequency (1)H/(19)F channel employs a new and efficient transmission line tuning design. The first (13)C CP/MAS NMR spectra recorded at 21.15 T have been obtained with this probe and exhibit the best S/N per milligram sample of hexamethylbenzene achieved so far for a 4-mm rotor.     

High-peak power multi-wavelength picosecond pulses generated from a BaWO4 Raman-seeded optical parametric amplifier

We report the generation of high-peak power multi-wavelength picosecond laser pulses using optical parametric amplification (OPA) in BBO seeded with pulses generated in a 5-mm length BaWO₄ crystal by stimulated Raman scattering of 18-ps laser pulses at 532 nm. The maximum output energy of the amplified first-Stokes component at 559.7 nm was about 1.76 mJ. The corresponding maximum peak power, pulse duration and spectral line width were measured to be 117.3 MW, 15 ps and 18.0 cm⁻¹, respectively. The multi-wavelength picosecond laser pulses were in the visible and near infrared ranges. Using this Raman-seeded OPA technique, the beam quality of the stimulated Raman scattering pulses can be improved.     

Reducing inhomogeneity artifacts in functional MRI of human brain activation-thin sections vs gradient compensation

We evaluated two methods for correcting inhomogeneity-induced signal losses in magnetic resonance gradient-echo imaging that either use gradient compensation or simply acquire thin sections. The strategies were tested in the human brain in terms of achievable quality of T2*-weighted images at the level of the hippocampus and of functional activation maps of the visual cortex. Experiments were performed at 2.0 T and based on single-shot echo-planar imaging at 2. 0 x 2.0 mm(2) resolution, 4 mm section thickness, and 2.0 s temporal resolution. Gradient compensation involved a sequential 16-step variation of the refocusing lobe of the slice-selection gradient (TR/TE = 125/53 ms, flip angle 15 degrees ), whereas thin sections divided the 4-mm target plane into either four 1-mm or eight 0.5-mm interleaved multislice acquisitions (TR/TE = 2000/54 ms, flip angle 70 degrees ). Both approaches were capable of alleviating the inhomogeneity problem for structures in the base of the brain. When compared to standard 4-mm EPI, functional mapping in the visual cortex was partially compromised because of a lower signal-to-noise ratio of inhomogeneity-corrected images by either method. Relative to each other, consistently better results were obtained with the use of contiguous thin sections, in particular for a thickness of 1 mm. Multislice acquisitions of thin sections require minimal technical adjustments.     

Identification of a Suspicious Drug by Using Spectroscopic Techniques: A Forensic Analytical Chemistry Project

We identified a drug analog by using screening and confirmatory tests. Total ion chromatogram showed a major peak with a molecular ion of 190 m/z, but no mass spectrum match from the NIST library. A minor peak was identified as 1-benzylpiperazine (molecular ion = 176 m/z). Molecular ions of both peaks differed by 14 m/z units, suggesting a –CH₂ – group. Both peaks had the same base peak of 91 m/z. Derivatizing the drug analog with trifluoroacetic anhydride confirmed the presence of 1-benzylpiperazine. No reaction occurred with the major peak. We proposed a benzyl-4-methylpiperazine structure, which was confirmed by NMR studies.     

Validation and accuracy of software for peak synthesis in XPS

The development of a range of VAMAS format data files containing synthetic test spectra and their use in evaluating the peak fitting routines of three commercial XPS data analysis systems A, B and C, is reported. The synthetic spectra allow tests for: (1) acceptance of VAMAS formats with kinetic energy or binding energy scales that may have positive or negative abscissa increments; (2) Gaussian–Lorentzian sum or product function peaks; (3) effectiveness of Shirley background subtraction; (4) effectiveness of Tougaard background subtraction; (5) peak synthesis with partly resolved peaks with no background; and (6) peak synthesis with a Shirley background. The results show that all the data systems studied accept VAMAS format files but not all would accept both of the options of direction of scan. In addition, each data system had programming faults, some of which were later rectified.Synthetic spectra approximating the carbon 1s peaks for poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride) and poly(isobutylene) allow an analysis of accuracy of the fits in these tests. One full set of spectra is constructed with Gauss–Lorentz product function peaks and a second full set with Gauss–Lorentz sum function peaks since each software was designed for fitting only one of these options. The fitting of the individual peaks is only good for software using the same peak shapes as those of the data. The fit quality can deteriorate markedly for fitting to a peak shape different to that used in the peak fitting algorithm (ie fitting sum function peaks with product function software or vice versa). For unresolved peaks additional information is required to provide meaningful intensities. The three software systems studied all have different facilities but it is clear that the quality of convergence to the correct result gives a general order of preference in the fitting algorithm of B, A and C. Other aspects can favour software A which has more facilities.     

Relative hazard of weapons impulses

Arguments in favor of a theoretically based damage-risk criterion (DRC) for intense noise [G.R. Price, J. Acoust. Soc. Am. 69, 171-177 (1981); 66, 456-465 (1979); J. Acoust. Soc. Am. Suppl. 1 62, S95 (1977)] are further developed here to make a crucial prediction. Based on measured spectral differences, it was predicted that rifle impulses would cause permanent threshold shifts at approximately 9 dB lower peak pressures than cannon impulses. In contrast, DRCs in use in the world predict that the cannon would be more hazardous than the rifle by 7 to 10 dB. Electrophysiological measures of sensitivity were used in 38 cats (76 ears) which were exposed to 60 impulses, approximately 3 s apart, at various peak pressures, from either a rifle or a 105-mm Howitzer. Hearing changes were followed until recovery was complete (2 months). Permanent threshold shifts began at about 140 dB for rifle impulses and 150-155 dB for cannon impulses, confirming the prediction and supporting the contention that there is a spectrally dependent critical level for the ear at high intensities. Implications for present DRCs and future risk assessment schemes are discussed.     

High contrast air-coupled acoustic imaging with zero group velocity lamb modes

The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1 mode, a broad range of wavenumbers couple into the first-order symmetric mode at nearly a constant frequency, greatly enhancing transmission at that frequency. Coupled energy remains localized near the coupling point because the group velocity is zero. We excite the mode with a broadband, focussing, air-coupled transducer at the frequency of the zero group velocity point in the S1 mode. By exploiting the efficient coupling at the zero group velocity frequency, we have easily imaged a single layer of Scotch tape attached to a 6.4-mm thick Plexiglas plate and 3.2-mm Teflon inserts in a composite laminate.     

A longitudinal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single-crystal piezoelectric transformer

In present work, a simple longitudinal piezoelectric transformer with the size of 16-mm length, 2-mm width, and 2-mm thickness was designed and fabricated with relaxor ferroelectric single-crystal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃. Both the input and output parts utilized the ultrahigh longitudinal extensional electromechanical coupling coefficients. Compared to the Rosen-type transformer, this transformer has the advantages of smaller-size, simpler structure, no spurious vibration, and no acoustic mismatch between the input and output parts. The electrical measurement results indicated that under the resonance frequency of 114 kHz, a step-up voltage of about 30 can be obtained under a 10-MΩ load resistance, which agreed well with the calculated results. Besides, the frequency and load dependences of this transformer were also systematically studied and discussed. The results indicated that this transformer has potential applications in the small-size high-voltage amplifier and magnetoelectric/piezoelectric-transformer composite transducers.