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Sample records for lh pulse frequency

  1. Progesterone has rapid positive feedback actions on LH release but fails to reduce LH pulse frequency within 12 h in estradiol-pretreated women.

    PubMed

    Hutchens, Eleanor G; Ramsey, Katherine A; Howard, Louisa C; Abshire, Michelle Y; Patrie, James T; McCartney, Christopher R

    2016-08-01

    In women, progesterone suppresses luteinizing hormone (LH) (gonadotropin-releasing hormone) pulse frequency, but how rapidly this occurs is unknown. In estradiol-pretreated women in the late follicular phase, progesterone administration at 1800 did not slow sleep-associated LH pulse frequency. However, mechanisms controlling LH pulse frequency may differ according to sleep status; and we thus hypothesized that progesterone acutely suppresses waking LH pulse frequency. This was a randomized, double-blind, crossover study of LH secretory responses to progesterone versus placebo administered at 0600. We studied 12 normal women in the late follicular phase (cycle days 7-11), pretreated with 3 days of transdermal estradiol (0.2 mg/day). Subjects underwent a 24-h blood sampling protocol (starting at 2000) and received either 100 mg oral micronized progesterone or placebo at 0600. In a subsequent menstrual cycle, subjects underwent an identical protocol except that oral progesterone was exchanged for placebo or vice versa. Changes in 10-h LH pulse frequency were similar between progesterone and placebo. However, mean LH, LH pulse amplitude, and mean follicle-stimulating hormone exhibited significantly greater increases with progesterone. Compared to our previous study (progesterone administered at 1800), progesterone administration at 0600 was associated with a similar increase in mean LH, but a less pronounced increase in LH pulse amplitude. We conclude that, in estradiol-pretreated women in the late follicular phase, a single dose of progesterone does not suppress waking LH pulse frequency within 12 h, but it acutely amplifies mean LH and LH pulse amplitude - an effect that may be influenced by sleep status and/or time of day. PMID:27535481

  2. Effect of pulse frequency and amplitude of D-Trp6-luteinizing hormone-releasing hormone on the pulsatile secretion of prolactin and LH.

    PubMed

    Rodriguez, T; Bordiu, E; Rubio, J A; Duran, A; Charro, A L

    1993-09-01

    This work analyzes the effect of the pulse amplitude and frequency of a potent LHRH analog, D-Trp6-LHRH, in a perfusion system of isolated rat pituitary cells. To this purpose, we studied the LH and PRL secretion in different conditions: basal secretion, secretion after increasing concentrations of D-Trp6-LHRL (0.001, 0.01, 0.1 and 1 nM) secretion in function of the pulses frequency (2,3, and 4 pulses per h) and amplitude (0.1, 1 and 10 nM). The principal findings were: 1. The basal LH and PRL secretions was pulsatile; 2. The stimulation of LH by the analog was not dose-dependent; 3. When more than 2 pulses per h were administered, a rapid desensitization of gonadotroph to release LH (at 20-30 min) occurred; 4. There was a loss of pulsatility of PRL secretion with an increase in the pulse frequency and amplitude of the D-Trp6-LHRH, which was produced parallelly to the desensitization of the gonadotroph to release LH. In summary, these findings suggest that a rapid loss of pulsatility of the PRL when the D-Trp6-LHRH pulse frequency and amplitude is increased might be due to the early desensitization of the gonadotroph to the analog.

  3. Luteinizing hormone pulse frequency and in vitro bioactivity in male idiopathic infertility.

    PubMed

    Bennet, A; Bujan, L; Plantavid, M; Barbe, P; Caron, P; Louvet, J P

    1991-03-01

    We investigated 51 patients with idiopathic oligospermia and 10 control subjects. Blood samples were collected every 20 minutes from 10 P.M. to 10 A.M. and luteinizing hormone (LH) pulsatility was analyzed. A pool of all samples obtained from each subject was used to measure bioactive LH in an in vitro mouse Leydig cell bioassay and immunoactive LH in an immunoradiometric assay. Mean immunoactive LH pulse frequency was higher and mean bioactive to immunoactive LH ratio was lower in infertile men than in controls. There was a significant negative correlation between bioactive LH to immunoreactive LH ratio and LH pulse frequency. These data indicate that the defect in the gonadal axis in oligospermic men resides not in the hypothalamic-pituitary function but rather in the testis itself.

  4. DynPeak: An Algorithm for Pulse Detection and Frequency Analysis in Hormonal Time Series

    PubMed Central

    Vidal, Alexandre; Zhang, Qinghua; Médigue, Claire; Fabre, Stéphane; Clément, Frédérique

    2012-01-01

    The endocrine control of the reproductive function is often studied from the analysis of luteinizing hormone (LH) pulsatile secretion by the pituitary gland. Whereas measurements in the cavernous sinus cumulate anatomical and technical difficulties, LH levels can be easily assessed from jugular blood. However, plasma levels result from a convolution process due to clearance effects when LH enters the general circulation. Simultaneous measurements comparing LH levels in the cavernous sinus and jugular blood have revealed clear differences in the pulse shape, the amplitude and the baseline. Besides, experimental sampling occurs at a relatively low frequency (typically every 10 min) with respect to LH highest frequency release (one pulse per hour) and the resulting LH measurements are noised by both experimental and assay errors. As a result, the pattern of plasma LH may be not so clearly pulsatile. Yet, reliable information on the InterPulse Intervals (IPI) is a prerequisite to study precisely the steroid feedback exerted on the pituitary level. Hence, there is a real need for robust IPI detection algorithms. In this article, we present an algorithm for the monitoring of LH pulse frequency, basing ourselves both on the available endocrinological knowledge on LH pulse (shape and duration with respect to the frequency regime) and synthetic LH data generated by a simple model. We make use of synthetic data to make clear some basic notions underlying our algorithmic choices. We focus on explaining how the process of sampling affects drastically the original pattern of secretion, and especially the amplitude of the detectable pulses. We then describe the algorithm in details and perform it on different sets of both synthetic and experimental LH time series. We further comment on how to diagnose possible outliers from the series of IPIs which is the main output of the algorithm. PMID:22802933

  5. Pulsed optically pumped frequency standard

    SciTech Connect

    Godone, Aldo; Micalizio, Salvatore; Levi, Filippo

    2004-08-01

    We reconsider the idea of a pulsed optically pumped frequency standard conceived in the early 1960s to eliminate the light-shift effect. The development of semiconductor lasers and of pulsed electronic techniques for atomic fountains and new theoretical findings allow an implementation of this idea which may lead to a frequency standard whose frequency stability is limited only by the thermal noise in the short term and by the temperature drift in the long term. We shall also show both theoretically and experimentally the possibility of doubling the atomic quality factor with respect to the classical Ramsey technique approach.

  6. Assessment of the LH wave for demo in pulsed and steady state scenario

    SciTech Connect

    Cardinali, A.; Barbato, E.; Castaldo, C.; Cesario, R.; Marinucci, M.; Ravera, G. L.; Tuccillo, A. A.; Ceccuzzi, S.; Mirizzi, F.; Panaccione, L.; Santini, F.; Schettini, G.

    2014-02-12

    The Lower Hybrid Current Drive (LHCD) has been analysed in DEMO tokamak plasma in the 'pulsed and steady state regime' considering two plasma scenarios characterized, respectively, by flat density profile and peaked density profiles. We have obtained LH deposition profiles in cases of neglecting the effect of spectral broadening produced by PI at the edge. By comparing the Power Deposition Profiles for both DEMO scenarios ('flat' and 'peaked'), the SOL of DEMO does not play any role in the absorption of the LH wave. In all cases the deposition is localized inside the separatrix layer r/a≤1. By lowering the parallel wave-number peak of the power spectrum from 1.8 to 1.5, the accessibility condition in both case prevents the power from reaching the deposition layer apart from a small fraction which pertains to the higher n∥ of the power spectrum. The spectrum centred at 1.8 is suggested to be useful in DEMO. More realistically, as supported by available data of LHCD in a wide range of operating densities, the effect of parametric decay instability (PDI) can produce a spectral broadening which should be included in the simulations. Further studies would be necessary for assessing the temperature profiles in the SOL at reactor-graded conditions. This is because, if the SOL temperature is at least of the order of 50 to 100 eV, the effect of PDI broads the spectrum up to n∥≤10, and the deposition profile is slightly wider but not much shifted outwards.

  7. Defects in pulsatile LH release in normally menstruating runners.

    PubMed

    Cumming, D C; Vickovic, M M; Wall, S R; Fluker, M R

    1985-04-01

    Intense physical exercise has been associated with reproductive dysfunction and menstrual cycles may be abnormal in a majority of women with a heavy training load. To determine whether training influenced pulsatile LH release, we measured LH pulse frequency, LH pulse amplitude and area under the curve over six hours during the early follicular phase of the menstrual cycle in four sedentary women and six eumenorrheic women runners with a training volume of at least 32 km per week. All three LH variables were significantly lower in runners than in controls. These data suggest that there is a central inhibition of the hypothalamic-pituitary-gonadal axis in eumenorrheic runners.

  8. Frequency independent quenching of pulsed emission

    SciTech Connect

    Gajjar, Vishal; Joshi, Bhal Chandra; Kramer, Michael; Karuppusamy, Ramesh; Smits, Roy E-mail: bcj@ncra.tifr.res.in E-mail: ramesh@mpifr-bonn.mpg.de

    2014-12-10

    Simultaneous observations at four different frequencies, 313, 607, 1380, and 4850 MHz, for three pulsars, PSRs B0031–07, B0809+74, and B2319+60, are reported in this paper. Identified null and burst pulses are highly concurrent across more than a decade of frequency. A small fraction of non-concurrent pulses (≤3%) is observed, most of which occur at the transition instances. We report, with very high significance for the first time, the full broadband nature of the nulling phenomenon in these three pulsars. These results suggest that nulling invokes changes on the global magnetospheric scale.

  9. Adiabatic frequency conversion of ultrafast pulses

    NASA Astrophysics Data System (ADS)

    Suchowski, H.; Bruner, B. D.; Ganany-Padowicz, A.; Juwiler, I.; Arie, A.; Silberberg, Y.

    2011-12-01

    A new method for efficient, broadband sum and difference frequency generation of ultrafast pulses is demonstrated. The principles of the method follow from an analogy between frequency conversion and coherent optical excitation of a two-level system. For conversion of ultrafast pulses, the concepts of adiabatic conversion are developed further in order to account for dispersion and group velocity mismatch. The scheme was implemented using aperiodically poled nonlinear crystals and a single step nonlinear mixing process, leading to conversion of near-IR (˜790 nm) ultrafast pulses into the blue (˜450 nm) and mid-IR (˜3.15 μm) spectral regions. Conversion bandwidths up to 15 THz FWHM and efficiencies up to 50% are reported.

  10. Radio frequency CD by LH waves in the reversed field experiment

    SciTech Connect

    Bilato, R.; Brambilla, M.

    1999-09-20

    We present a feasibility study for the active control of the poloidal current density profile in the RFX (reversed field pinch) experiment using radio frequency in the range of lower hybrid waves. The main goal of the rf current drive is to reduce the magnetic fluctuations and the magnetic stochasticity, so as to improve the energy confinement. The compelling constraints of accessibility and damping of the slow waves due to the present and extrapolated RFX plasma parameters are investigated; they have been used to fix the frequency ({approx_equal}1.3 GHz) and the best n{sub parallel} values ({approx_equal}8), and therefore the antenna size (Grill). A modified version of the FELICE code, which takes into account the strong shear of the magnetic field of the RFP plasmas, has been developed and used to estimate the antenna-plasma coupling: the reflected power for the proposed antenna is found to be less than 30% for a quite wide range of plasma parameters. In order to estimate the current drive profile and efficiency a one dimensional Fokker-Planck code has been used: an additional crucial contribution to the driven current is due to the enhancement of the plasma conductivity as consequence of the suprathermal electron population increase. Although the total estimated CD efficiency is promising, the rf-power required to drive the current necessary to produce a significant reduction of the magnetic fluctuations is found to be in the MW range.

  11. Secretory pattern of leptin and LH during lactational amenorrhoea in breastfeeding normal and polycystic ovarian syndrome women.

    PubMed

    Sir-Petermann, T; Recabarren, S E; Lobos, A; Maliqueo, M; Wildt, L

    2001-02-01

    Several studies have suggested that leptin modulates hypothalamic-pituitary-gonadal axis function. A synchronicity of LH and leptin pulses has been described in healthy women and in patients with polycystic ovarian syndrome (PCOS), suggesting that leptin may modulate the episodic secretion of LH. The aim of the present investigation was to assess the episodic fluctuations of circulating LH and leptin during lactational amenorrhoea in fully breastfeeding normal and PCOS women at 4 and 8 weeks postpartum, in order to establish LH-leptin interactions in the reactivation of the gonadal axis during this period. Six lactating PCOS patients and six normal lactating women of similar age and body mass index were studied. During a 12 h period on the 4th and 8th weeks postpartum, blood samples were collected at 10 min intervals for 12 h (22:00-10:00). Serum LH and leptin concentrations were measured in all samples. For pulse analysis, the cluster algorithm was used. To detect an interaction between LH and leptin pulses, an analysis of co-pulsatility was employed. LH concentrations tended to increase in both groups between the 4th and 8th weeks postpartum; however, serum leptin concentrations were not modified. Leptin pulse frequencies were similar at the 4th and 8th weeks postpartum, and did not differ between groups. Moreover, leptin pulse frequency was higher than LH pulse frequency in both groups, and in the two study periods. There was no synchronicity between LH and leptin pulses, and there were no increments in leptin concentration during the night. The fact that leptin concentrations were not modified and no synchronicity between LH and leptin pulses was observed suggests that, during lactational amenorrhoea, circulating leptin is probably not involved as a primary signal in promoting the reactivation of pulsatile LH secretion.

  12. Frequency content of current pulses in slapper detonator bridges

    SciTech Connect

    Carpenter, K H

    2006-12-18

    DFT amplitudes are obtained for digital current pulse files. The frequency content of slapper detonator bridge current pulses is obtained. The frequencies are confined well within the passband of the CVR used to sample them.

  13. Missing pulse detector for a variable frequency source

    DOEpatents

    Ingram, Charles B.; Lawhorn, John H.

    1979-01-01

    A missing pulse detector is provided which has the capability of monitoring a varying frequency pulse source to detect the loss of a single pulse or total loss of signal from the source. A frequency-to-current converter is used to program the output pulse width of a variable period retriggerable one-shot to maintain a pulse width slightly longer than one-half the present monitored pulse period. The retriggerable one-shot is triggered at twice the input pulse rate by employing a frequency doubler circuit connected between the one-shot input and the variable frequency source being monitored. The one-shot remains in the triggered or unstable state under normal conditions even though the source period is varying. A loss of an input pulse or single period of a fluctuating signal input will cause the one-shot to revert to its stable state, changing the output signal level to indicate a missing pulse or signal.

  14. Ultrasound vibrometry using orthogonal- frequency-based vibration pulses.

    PubMed

    Zheng, Yi; Yao, Aiping; Chen, Shigao; Urban, Matthew W; Lin, Haoming; Chen, Xin; Guo, Yanrong; Chen, Ke; Wang, Tianfu; Chen, Siping

    2013-11-01

    New vibration pulses are developed for shear wave generation in a tissue region with preferred spectral distributions for ultrasound vibrometry applications. The primary objective of this work is to increase the frequency range of detectable harmonics of the shear wave. The secondary objective is to reduce the required peak intensity of transmitted pulses that induce the vibrations and shear waves. Unlike the periodic binary vibration pulses, the new vibration pulses have multiple pulses in one fundamental period of the vibration. The pulses are generated from an orthogonal-frequency wave composed of several sinusoidal signals, the amplitudes of which increase with frequency to compensate for higher loss at higher frequency in tissues. The new method has been evaluated by studying the shear wave propagation in in vitro chicken and swine liver. The experimental results show that the new vibration pulses significantly increase tissue vibration with a reduced peak ultrasound intensity, compared with the binary vibration pulses.

  15. Low Frequency Electromagnetic Pulse and Explosions

    SciTech Connect

    Sweeney, J J

    2011-02-01

    This paper reviews and summarizes prior work related to low frequency (< 100 Hz) EMP (ElectroMagnetic Pulse) observed from explosions. It focuses on how EMP signals might, or might not, be useful in monitoring underground nuclear tests, based on the limits of detection, and physical understanding of these signals. In summary: (1) Both chemical and nuclear explosions produce an EMP. (2) The amplitude of the EMP from underground explosions is at least two orders of magnitude lower than from above ground explosions and higher frequency components of the signal are rapidly attenuated due to ground conductivity. (3) In general, in the near field, that is distances (r) of less than 10s of kilometers from the source, the amplitude of the EMP decays approximately as 1/r{sup 3}, which practically limits EMP applications to very close (<{approx}1km) distances. (4) One computational model suggests that the EMP from a decoupled nuclear explosion may be enhanced over the fully coupled case. This has not been validated with laboratory or field data. (5) The magnitude of the EMP from an underground nuclear explosion is about two orders of magnitude larger than that from a chemical explosion, and has a larger component of higher frequencies. In principle these differences might be used to discriminate a nuclear from a chemical explosion using sensors at very close (<{approx}1 km) distances. (6) Arming and firing systems (e.g. detonators, exploding bridge wires) can also produce an EMP from any type of explosion. (7) To develop the understanding needed to apply low frequency EMP to nuclear explosion monitoring, it is recommended to carry out a series of controlled underground chemical explosions with a variety of sizes, emplacements (e.g. fully coupled and decoupled), and arming and firing systems.

  16. Pulsatile secretion of LH in relation to the resumption of ovarian activity post partum.

    PubMed

    Glasier, A; McNeilly, A S; Howie, P W

    1984-04-01

    Changes in the pulsatile pattern of LH secretion in relation to the resumption of ovarian activity post partum have been studied in breast feeding mothers. Basal concentrations of LH were significantly lower than normal both when ovarian activity was completely suppressed and when there was evidence of some follicular development prior to the resumption of menstruation. Once menstruation resumed basal concentrations of LH were unchanged whether ovulation occurred or not. No difference in the frequency or amplitude of pulses in LH secretion could be found at any stage post partum in either breast or bottle feeding women. FSH levels remained constant throughout the post partum period while mean concentrations of prolactin fell as ovarian activity returned to normal. However, during the period of complete suppression of ovarian activity in breast feeding women, two patterns of pulsatile secretion of LH were observed. In 76% of observation periods, basal levels of LH were lower than normal and were characterized by low frequency and low amplitude pulses of LH. In contrast, in the remaining 24% of observation periods, basal levels and pulse amplitude and frequency of LH were similar to those in the follicular phase of normal menstrual cycles in these women. Individual women showed either or both of these patterns of secretion during the period of ovarian suppression post partum. The data suggests that the failure to maintain ovarian follicular development post partum in breast feeding women may be due to: (1) a direct block of LH action at ovarian level, perhaps by the high levels of prolactin associated with lactation and/or (2) an inability of the hypothalamic-pituitary axis-as a result of the suckling stimulus and/or prolactin-to maintain pulsatile secretion of LH in the face of the negative feedback effects of the increased oestrogen secretion resulting from the initiation of follicular development.

  17. Pulsed addressing of a dual-frequency nematic liquid crystal.

    PubMed

    Mottram, N J; Brown, C V

    2006-09-01

    A continuum theory of dielectric relaxation within liquid crystal materials is described and used to model the response of dual frequency materials to single pulse voltage waveforms. The equations governing the anisotropic axis (director) angle, electric field, and induced polarizations are solved numerically to investigate pulsed addressing of a model zenithally bistable liquid crystal device. By suitably tailoring the voltage pulse, it is found to be possible to switch between both bistable states. For short pulses the high frequency components of the leading edge of the voltage pulse excites the perpendicular polarization and forces the director to lie parallel to the cell substrates. For longer voltage pulses the constant dc component of the voltage pulse excites the parallel polarization causing the director to lie perpendicular to the substrates. It is also found that reducing rotational viscosity and increasing the achievable dielectric anisotropies (particularly the high frequency value) can significantly reduce the operating voltages of such a device.

  18. Pulsed addressing of a dual-frequency nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Mottram, N. J.; Brown, C. V.

    2006-09-01

    A continuum theory of dielectric relaxation within liquid crystal materials is described and used to model the response of dual frequency materials to single pulse voltage waveforms. The equations governing the anisotropic axis (director) angle, electric field, and induced polarizations are solved numerically to investigate pulsed addressing of a model zenithally bistable liquid crystal device. By suitably tailoring the voltage pulse, it is found to be possible to switch between both bistable states. For short pulses the high frequency components of the leading edge of the voltage pulse excites the perpendicular polarization and forces the director to lie parallel to the cell substrates. For longer voltage pulses the constant dc component of the voltage pulse excites the parallel polarization causing the director to lie perpendicular to the substrates. It is also found that reducing rotational viscosity and increasing the achievable dielectric anisotropies (particularly the high frequency value) can significantly reduce the operating voltages of such a device.

  19. Pulsed addressing of a dual-frequency nematic liquid crystal.

    PubMed

    Mottram, N J; Brown, C V

    2006-09-01

    A continuum theory of dielectric relaxation within liquid crystal materials is described and used to model the response of dual frequency materials to single pulse voltage waveforms. The equations governing the anisotropic axis (director) angle, electric field, and induced polarizations are solved numerically to investigate pulsed addressing of a model zenithally bistable liquid crystal device. By suitably tailoring the voltage pulse, it is found to be possible to switch between both bistable states. For short pulses the high frequency components of the leading edge of the voltage pulse excites the perpendicular polarization and forces the director to lie parallel to the cell substrates. For longer voltage pulses the constant dc component of the voltage pulse excites the parallel polarization causing the director to lie perpendicular to the substrates. It is also found that reducing rotational viscosity and increasing the achievable dielectric anisotropies (particularly the high frequency value) can significantly reduce the operating voltages of such a device. PMID:17025650

  20. Toward a High-Frequency Pulsed-Detonation Actuator

    NASA Technical Reports Server (NTRS)

    Cutler, Andrew D.; Drummond, J. Philip

    2006-01-01

    This paper describes the continued development of an actuator, energized by pulsed detonations, that provides a pulsed jet suitable for flow control in high-speed applications. A high-speed valve, capable of delivering a pulsed stream of reactants a mixture of H2 and air at rates of up to 1500 pulses per second, has been constructed. The reactants burn in a resonant tube and the products exit the tube as a pulsed jet. High frequency pressure transducers have been used to monitor the pressure fluctuations in the device at various reactant injection frequencies, including both resonant and off-resonant conditions. Pulsed detonations have been demonstrated in the lambda/4 mode of an 8 inch long tube at approximately 600 Hz. The pulsed jet at the exit of the device has been observed using shadowgraph and an infrared camera.

  1. Toward a High-Frequency Pulsed-Detonation Actuator

    NASA Technical Reports Server (NTRS)

    Cutler, Andrew D.; Drummond, J. Philip

    2006-01-01

    This paper describes the continued development of an actuator, energized by pulsed detonations, that provides a pulsed jet suitable for flow control in high-speed applications. A high-speed valve, capable of delivering a pulsed stream of reactants a mixture of H2 and air at rates of up to 1500 pulses per second, has been constructed. The reactants burn in a resonant tube and the products exit the tube as a pulsed jet. High frequency pressure transducers have been used to monitor the pressure fluctuations in the device at various reactant injection frequencies, including both resonant and off-resonant conditions. Pulsed detonations have been demonstrated in the lambda/4 mode of an 8 inch long tube at approx. 600 Hz. The pulsed jet at the exit of the device has been observed using shadowgraph and an infrared camera.

  2. Assessment of pulse rate variability by the method of pulse frequency demodulation

    PubMed Central

    Hayano, Junichiro; Barros, Allan Kardec; Kamiya, Atsunori; Ohte, Nobuyuki; Yasuma, Fumihiko

    2005-01-01

    Background Due to its easy applicability, pulse wave has been proposed as a surrogate of electrocardiogram (ECG) for the analysis of heart rate variability (HRV). However, its smoother waveform precludes accurate measurement of pulse-to-pulse interval by fiducial-point algorithms. Here we report a pulse frequency demodulation (PFDM) technique as a method for extracting instantaneous pulse rate function directly from pulse wave signal and its usefulness for assessing pulse rate variability (PRV). Methods Simulated pulse wave signals with known pulse interval functions and actual pulse wave signals obtained from 30 subjects with a trans-dermal pulse wave device were analyzed by PFDM. The results were compared with heart rate and HRV assessed from simultaneously recorded ECG. Results Analysis of simulated data revealed that the PFDM faithfully demodulates source interval function with preserving the frequency characteristics of the function, even when the intervals fluctuate rapidly over a wide range and when the signals include fluctuations in pulse height and baseline. Analysis of actual data revealed that individual means of low and high frequency components of PRV showed good agreement with those of HRV (intraclass correlation coefficient, 0.997 and 0.981, respectively). Conclusion The PFDM of pulse wave signal provides a reliable assessment of PRV. Given the popularity of pulse wave equipments, PFDM may open new ways to the studies of long-term assessment of cardiovascular variability and dynamics. PMID:16259639

  3. The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep.

    PubMed

    Fabre-Nys, Claude; Chanvallon, Audrey; Dupont, Joëlle; Lardic, Lionel; Lomet, Didier; Martinet, Stéphanie; Scaramuzzi, Rex J

    2016-01-01

    During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. "Precocious" LH surges were not preceded by a large increase in E2 unlike "normal" surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the "precocious" LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the "ram effect". Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators. PMID:27384667

  4. The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep.

    PubMed

    Fabre-Nys, Claude; Chanvallon, Audrey; Dupont, Joëlle; Lardic, Lionel; Lomet, Didier; Martinet, Stéphanie; Scaramuzzi, Rex J

    2016-01-01

    During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. "Precocious" LH surges were not preceded by a large increase in E2 unlike "normal" surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the "precocious" LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the "ram effect". Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators.

  5. Giant Crab pulses at low frequency: statistics, scattering, polarization

    SciTech Connect

    Smirnova, T. V.

    2010-01-01

    We carried out observations of Crab giant pulses at frequency 112 MHz from 2005 till 2008 on the Large Phased Array of the Pushchino Radio Astronomy Observatory. The scattering of pulses observed in various series varies by a factor of 3: from 11 ms in November 2005 till 34 ms in September 2008. The cumulative probability distribution for the peak intensities of the giant pulses for each of these series shows that the distribution is stable and is a power law with a single slope (n = -2.3). This testifies to stability of the mechanism generating the giant pulses. The energy in the pulses is conserved; i.e., the increase in the pulse intensity is proportional to the decrease in the scattering. Refractive scintillations at low frequencies in measurements with large time separation lead to variations in the relative number of giant pulses exceeding a given amplitude, proportional to the ratio of the mean flux densities of the pulsar in the corresponding observational series. The maximum energy of the recorded giant pulses is 2.5x10{sup 7} Jy mus. Analysis of the giant pulses observed at other frequencies shows that the frequency dependence of the maximum energy of the giant pulses in the range of 23 MHz-9 GHz is a power-law with index -2.2+-0.2. We measured the rotation measure using GP which is RM (-47.5+-0.4) rad/m{sup 2}, and the degree of linear polarization for pulses with measured frequency modulation was 9% divide 17% for November 2005.

  6. Ultrasonic spectrum analysis using frequency-tracked gated RF pulses

    NASA Technical Reports Server (NTRS)

    Cantrell, J. H., Jr.; Heyman, J. S.

    1980-01-01

    A new method of ultrasonic frequency analysis is introduced which employs frequency-tracked gated RF drive pulses rather than shock-excited broadband spikes to generate the ultrasonic waveform. The new technique, a variation of the sampled-continuous wave technique, eliminates problems associated with finite pulse widths of conventional methods. It is shown to yield correct ultrasonic wave velocity measurements of the sample irrespective of receiver gate width or position provided any portions of two successive echoes are gated simultaneously into the spectrum analyzer. The experimental observations are substantiated by a theoretical model based on the time-frequency domain formulation of ultrasonic frequency analysis.

  7. Effects of alcohol on pulsatile luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion in the adult male rat

    SciTech Connect

    Badger, T.M.; Abdallah, M.M.; Hayden, J.B. )

    1989-02-09

    To determine possible hypothalamic actions of alcohol on hormone secretion, the effects of acute intragastric alcohol on plasma LH and FSH pulsations were studied. One jugular and one intragastric cannula were surgically implanted into adult male Sprague Dawley rats. Eight days later, rats were bilaterally castrated at 1400 h and infused intragastrically with either saline or 3 g/kg ethanol between 0700 h 0800 h the next days. Blood samples (300 microliters) were collected every 5 min for 3 h (starting at 0800 h), centrifuged and the plasma was frozen for LH and FSH radioimmunoassay. The blood cells were resuspended in saline and returned to the animal immediately following the next sample collection. While the mean plasma LH or FSH concentration did not vary significantly between the alcohol-treated and saline-treated rats, the mean LH (but not FSH) pulse frequency was lower in ethanol-treated rats (3.3 {plus minus} 0.25 pulses/3 h) than saline-treated controls (7.2 {plus minus} 0.3 pulses/3 h). In addition, mean area under the OH pulses were significantly greater in ethanol-treated than saline controls. These data suggest that: (1) ethanol acts to reduce the frequency of LHRH release for the hypothalamus and increase the area under each LH pulse; and (2) LH and FSH secretion are differentially regulated.

  8. The effects of acute exercise on pulsatile LH release in high-mileage male runners.

    PubMed

    McColl, E M; Wheeler, G D; Gomes, P; Bhambhani, Y; Cumming, D C

    1989-11-01

    Evidence suggests that acute exercise and endurance training has a suppressive effect on the hypothalamic-pituitary-gonadal (HPG) axis in men and women. To determine if training and acute exercise influence the neuroendocrine regulation of the HPG axis in men we examined pulsatile LH release in six male endurance runners with a training volume of at least 80 km per week, and compared this with values in six age-matched sedentary controls. Blood samples were obtained through an indwelling i.v. cannula from the subjects at 15-min intervals for 6 h following 24 h without significant physical activity and again in the runners, following 60 min of running at a speed equivalent to 5% below the anaerobic threshold. Mean LH pulse frequency and amplitude, as well as areas under the LH pulses and total LH curve, were calculated but only the mean post-exercise area under the total LH curve area was significantly lower than basal values (P less than 0.05) following exercise compared with the resting values in runners. Other measures of LH release did not change with acute exercise. Basal and pre-exercise testosterone levels were also measured and found to be at the lower end of normal men. The mean pre-exercise serum testosterone levels were significantly higher than basal levels. Mean testosterone levels, mean pulse amplitude, and mean area under the LH curve were significantly lower in resting runners than in the controls. The data suggest that exercise induces a general lowering of LH levels but does not inhibit LH pulsatile release. An anticipatory increase in serum testosterone occurred before exercise.

  9. Generation of frequency-chirped optical pulses with felix

    SciTech Connect

    Knippels, G.M.H.; Meer, A.F.G. van der; Mols, R.F.X.A.M.

    1995-12-31

    Frequency-chirped optical pulses have been produced in the picosecond regime by varying the energy of the electron beam on a microsecond time scale. These pulses were then compressed close to their bandwidth limit by an external pulse compressor. The amount of chirp can be controlled by varying the sweep rate on the electron beam energy and by cavity desynchronisation. To examine the generated chirp we used the following diagnostics: a pulse compressor, a crossed beam autocorrelator, a multichannel electron spectrometer and multichannel optical spectrometer. The compressor is build entirely using reflective optics to permit broad band operation. The autocorrelator is currently operating from 6 {mu}m to 30 {mu}m with one single crystal. It has been used to measure pulses as short as 500 fs. All diagnostics are evacuated to prevent pulse shape distortion or pulse lengthening caused by absorption in ambient water vapour. Pulse length measurements and optical spectra will be presented for different electron beam sweep rates, showing the presence of a frequency chirp. Results on the compression of the optical pulses to their bandwidth limit are given for different electron sweep rates. More experimental results showing the dependence of the amount of chirp on cavity desynchronisation will be presented.

  10. Linearly frequency-modulated pulsed single-frequency fiber laser at 1083 nm.

    PubMed

    Zhang, Yuanfei; Yang, Changsheng; Li, Can; Feng, Zhouming; Xu, Shanhui; Deng, Huaqiu; Yang, Zhongmin

    2016-02-22

    A linearly frequency-modulated, actively Q-switched, single-frequency ring fiber laser based on injection seeding from an ultra-short cavity is demonstrated at 1083 nm. A piezoelectric transducer is employed to obtain linearly frequency-modulating performance and over 1.05 GHz frequency-tuning range is achieved with a modulating frequency reaching tens of kilohertz. A maximum peak power of the stable output pulse is over 3.83 W during frequency-modulating process. This type of pulsed fiber laser provides a promising candidate for coherent LIDAR in the measurement of thermosphere.

  11. Parametric Study of High Frequency Pulse Detonation Tubes

    NASA Technical Reports Server (NTRS)

    Cutler, Anderw D.

    2008-01-01

    This paper describes development of high frequency pulse detonation tubes similar to a small pulse detonation engine (PDE). A high-speed valve injects a charge of a mixture of fuel and air at rates of up to 1000 Hz into a constant area tube closed at one end. The reactants detonate in the tube and the products exit as a pulsed jet. High frequency pressure transducers are used to monitor the pressure fluctuations in the device and thrust is measured with a balance. The effects of injection frequency, fuel and air flow rates, tube length, and injection location are considered. Both H2 and C2H4 fuels are considered. Optimum (maximum specific thrust) fuel-air compositions and resonant frequencies are identified. Results are compared to PDE calculations. Design rules are postulated and applications to aerodynamic flow control and propulsion are discussed.

  12. Light pressure acceleration with frequency-tripled laser pulse

    SciTech Connect

    Wang, Xiaofeng; Shen, Baifei E-mail: zhxm@siom.ac.cn; Zhang, Xiaomei E-mail: zhxm@siom.ac.cn; Ji, Liangliang; Wang, Wenpeng; Zhao, Xueyan; Xu, Jiancai; Yu, Yahong; Yi, Longqing; Shi, Yin; Xu, Tongjun; Zhang, Lingang

    2014-08-15

    Light pressure acceleration of ions in the interaction of the frequency-tripled (3ω) laser pulse and foil target is studied, and a promising method to increase accelerated ion energy is shown. Results show that at a constant laser energy, much higher ion energy peak value is obtained for 3ω laser compared with that using the fundamental frequency laser. The effect of energy loss during frequency conversion on ion acceleration is considered, which may slightly decrease the acceleration effect.

  13. Modeling the Male Reproductive Endocrine Axis: Potential Role for a Delay Mechanism in the Inhibitory Action of Gonadal Steroids on GnRH Pulse Frequency.

    PubMed

    Ferasyi, Teuku R; Barrett, P Hugh R; Blache, Dominique; Martin, Graeme B

    2016-05-01

    We developed a compartmental model so we could test mechanistic concepts in the control of the male reproductive endocrine axis. Using SAAM II computer software and a bank of experimental data from male sheep, we began by modeling GnRH-LH feed-forward and LH-T feedback. A key assumption was that the primary control signal comes from a hypothetical neural network (the PULSAR) that emits a digital (pulsatile) signal of variable frequency that drives GnRH secretion in square wave-like pulses. This model produced endocrine profiles that matched experimental observations for the testis-intact animal and for changes in GnRH pulse frequency after castration and T replacement. In the second stage of the model development, we introduced a delay in the negative feedback caused by the aromatization of T to estradiol at the brain level, a concept supported by empirical observations. The simulations showed how changes in the process of aromatization could affect the response of the pulsatile signal to inhibition by steroid feedback. The sensitivity of the PULSAR to estradiol was a critical factor, but the most striking observation was the effect of time delays. With longer delays, there was a reduction in the rate of aromatization and therefore a decrease in local estradiol concentrations, and the outcome was multiple-pulse events in the secretion of GnRH/LH, reflecting experimental observations. In conclusion, our model successfully emulates the GnRH-LH-T-GnRH loop, accommodates a pivotal role for central aromatization in negative feedback, and suggests that time delays in negative feedback are an important aspect of the control of GnRH pulse frequency. PMID:26910309

  14. FREQUENCY DEPENDENCE OF PULSE WIDTH FOR 150 RADIO NORMAL PULSARS

    SciTech Connect

    Chen, J. L.; Wang, H. G.

    2014-11-01

    The frequency dependence of the pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the 10% multifrequency pulse widths can be well fit with the Thorsett relationship W {sub 10} = Aν{sup μ} + W {sub 10,} {sub min}. The relative fraction of pulse width change between 0.4 GHz and 4.85 GHz, η = (W {sub 4.85} – W {sub 0.4})/W {sub 0.4}, is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54%) have η < –10% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27%) have –10% ≤η ≤ 10% (group B), meaning a marginal change in pulse width, and 29 pulsars (19%) have η > 10% (group C), showing a remarkable profile broadening at high frequencies. The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and spectrum steepening is tested but disfavored.

  15. The “Ram Effect”: A “Non-Classical” Mechanism for Inducing LH Surges in Sheep

    PubMed Central

    Fabre-Nys, Claude; Chanvallon, Audrey; Dupont, Joëlle; Lardic, Lionel; Lomet, Didier; Martinet, Stéphanie; Scaramuzzi, Rex J.

    2016-01-01

    During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the “ram effect” in ewes that had a “precocious” LH surge (starting within 6 hours), a “normal” surge (between 6 and 28h) and “late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. “Precocious” LH surges were not preceded by a large increase in E2 unlike “normal” surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the “precocious” LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the “ram effect”. Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators. PMID:27384667

  16. Why high-frequency pulse tubes can be tipped

    SciTech Connect

    Swift, Gregory W092710; Backhaus, Scott N

    2010-01-01

    The typical low-frequency pulse-tube refrigerator loses significant cooling power when it is tipped with the pulse tube's cold end above its hot end, because natural convection in the pulse tube loads the cold heat exchanger. Yet most high-frequency pulse-tube refrigerators work well in any orientation with respect to gravity. In such a refrigerator, natural convection is suppressed by sufficiently fast velocity oscil1ations, via a nonlinear hydrodynamic effect that tends to align the density gradients in the pulse tube parallel to the oscillation direction. Since gravity's tendency to cause convection is only linear in the pulse tube's end-to-end temperature difference while the oscillation's tendency to align density gradients with oscillating velocity is nonlinear, it is easiest to suppress convection when the end-to-end temperature difference is largest. Simple experiments demonstrate this temperature dependence, the strong dependence on the oscillating velocity, and little dependence on the magnitude or phase of the oscillating pressure. In some circumstances in this apparatus, the suppression of convection is a hysteretic function of oscillating velocity. In some other circumstances, a time-dependent convective state seems more difficult to suppress.

  17. Frequency-Domain Methods for Characterization of Pulsed Power Diagnostics

    SciTech Connect

    White, A D; Anderson, R A; Ferriera, T J; Goerz, D A

    2009-07-27

    This paper discusses methods of frequency-domain characterization of pulsed power sensors using vector network analyzer and spectrum analyzer techniques that offer significant simplification over time-domain methods, while mitigating or minimizing the effect of the difficulties present in time domain characterization. These methods are applicable to characterization of a wide variety of sensors.

  18. Nonselective excitation of pulsed ELDOR using multi-frequency microwaves

    NASA Astrophysics Data System (ADS)

    Asada, Yuki; Mutoh, Risa; Ishiura, Masahiro; Mino, Hiroyuki

    2011-12-01

    The use of a polychromatic microwave pulse to expand the pumping bandwidth in pulsed electron-electron double resonance (PELDOR) was investigated. The pumping pulse was applied in resonance with the broad (˜100 mT) electron paramagnetic resonance (EPR) signal of the manganese cluster of photosystem II in the S 2 state. The observation pulses were in resonance with the narrow EPR signal of the tyrosine radical, YDrad . It was found that in the case of the polychromatic pumping pulse containing five harmonics with the microwave frequencies between 8.5 and 10.5 GHz the PELDOR effect corresponding to the dipole interaction between the Mn cluster and YDrad was about 2.9 times larger than that achieved with a monochromatic pulse. In addition to the dipolar modulation, the nuclear modulation effects were observed. The effects could be suppressed by averaging the PELDOR trace over the time interval between the observation microwave pulses. The polychromatic excitation technique described will be useful for improving the PELDOR sensitivity in the measurements of long distances in biological samples, where the pair consists of a radical with a narrow EPR spectrum and slow phase relaxation, and a metal center that has a broad EPR spectrum and a short phase relaxation time.

  19. Nonselective excitation of pulsed ELDOR using multi-frequency microwaves.

    PubMed

    Asada, Yuki; Mutoh, Risa; Ishiura, Masahiro; Mino, Hiroyuki

    2011-12-01

    The use of a polychromatic microwave pulse to expand the pumping bandwidth in pulsed electron-electron double resonance (PELDOR) was investigated. The pumping pulse was applied in resonance with the broad (∼100 mT) electron paramagnetic resonance (EPR) signal of the manganese cluster of photosystem II in the S2 state. The observation pulses were in resonance with the narrow EPR signal of the tyrosine radical, YD·. It was found that in the case of the polychromatic pumping pulse containing five harmonics with the microwave frequencies between 8.5 and 10.5 GHz the PELDOR effect corresponding to the dipole interaction between the Mn cluster and YD· was about 2.9 times larger than that achieved with a monochromatic pulse. In addition to the dipolar modulation, the nuclear modulation effects were observed. The effects could be suppressed by averaging the PELDOR trace over the time interval between the observation microwave pulses. The polychromatic excitation technique described will be useful for improving the PELDOR sensitivity in the measurements of long distances in biological samples, where the pair consists of a radical with a narrow EPR spectrum and slow phase relaxation, and a metal center that has a broad EPR spectrum and a short phase relaxation time.

  20. Optimization of electric pulse amplitude and frequency in vitro for low voltage and high frequency electrochemotherapy.

    PubMed

    Shankayi, Zeinab; Firoozabadi, S M P; Hassan, Zohair Saraf

    2014-02-01

    During standard electrochemotherapy (ECT), using a train of 1,000 V/cm amplitude rectangular pulses with 1 Hz frequency, patients experience an unpleasant sensation and slight edema. According to the patients, muscle contractions provoked by high amplitude (about 1,000 V/cm) and low repetition frequency (1 Hz) pulses are the most unpleasant and painful sensations. Recently, ECT using low voltage and higher repetition frequency (LVHF) has been shown to be an effective tool for inhibiting tumor growth. The aim of the present study was to optimize electric pulse amplitude and repetition frequency for LVHF ECT by sampling the different sets of pulse parameters on cell viability and permeabilization. In ECT, a reversible effect based on high permeabilization is desirable. For this purpose, we used bleomycin to evaluate the permeabilization of K562 and MIA-PACA2 cells caused by low voltage (50-150 V/cm) and higher repetition frequency (4-6 kHz) electric pulses. We show that the reversible effect with electropermeabilization of the cells caused by LVHF ECT is accessible; this interaction is more effective for electric pulses with 70 V/cm amplitude. PMID:24271721

  1. Pulsed radio frequency energy (PRFE) use in human medical applications.

    PubMed

    Guo, Lifei; Kubat, Nicole J; Isenberg, Richard A

    2011-03-01

    A number of electromagnetic field-based technologies are available for therapeutic medical applications. These therapies can be broken down into different categories based on technical parameters employed and type of clinical application. Pulsed radio frequency energy (PRFE) therapy is a non invasive, electromagnetic field-based therapeutic that is based on delivery of pulsed, shortwave radio frequency energy in the 13-27.12 MHz carrier frequency range, and designed for local application to a target tissue without the intended generation of deep heat. It has been studied for use in a number of clinical applications, including as a palliative treatment for both postoperative and non postoperative pain and edema, as well as in wound healing applications. This review provides an introduction to the therapy, a summary of clinical efficacy studies using the therapy in specific applications, and an overview of treatment-related safety. PMID:21554100

  2. Vacuum electron acceleration by using two variable frequency laser pulses

    SciTech Connect

    Saberi, H.; Maraghechi, B.

    2013-12-15

    A method is proposed for producing a relativistic electron bunch in vacuum via direct acceleration by using two frequency-chirped laser pulses. We consider the linearly polarized frequency-chiped Hermit-Gaussian 0, 0 mode lasers with linear chirp in which the local frequency varies linearly in time and space. Electron motion is investigated through a numerical simulation using a three-dimensional particle trajectory code in which the relativistic Newton's equations of motion with corresponding Lorentz force are solved. Two oblique laser pulses with proper chirp parameters and propagation angles are used for the electron acceleration along the z-axis. In this way, an electron initially at rest located at the origin could achieve high energy, γ=319 with the scattering angle of 1.02{sup ∘} with respect to the z-axis. Moreover, the acceleration of an electron in different initial positions on each coordinate axis is investigated. It was found that this mechanism has the capability of producing high energy electron microbunches with low scattering angles. The energy gain of an electron initially located at some regions on each axis could be greatly enhanced compared to the single pulse acceleration. Furthermore, the scattering angle will be lowered compared to the acceleration by using laser pulses propagating along the z-axis.

  3. Low temperature high frequency coaxial pulse tube for space application

    SciTech Connect

    Charrier, Aurelia; Charles, Ivan; Rousset, Bernard; Duval, Jean-Marc

    2014-01-29

    The 4K stage is a critical step for space missions. The Hershel mission is using a helium bath, which is consumed day by day (after depletion, the space mission is over) while the Plank mission is equipped with one He4 Joule-Thomson cooler. Cryogenic chain without helium bath is a challenge for space missions and 4.2K Pulse-Tube working at high frequency (around 30Hz) is one option to take it up. A low temperature Pulse-Tube would be suitable for the ESA space mission EChO (Exoplanet Characterisation Observatory, expected launch in 2022), which requires around 30mW cooling power at 6K; and for the ESA space mission ATHENA (Advanced Telescope for High ENergy Astrophysics), to pre-cool the sub-kelvin cooler (few hundreds of mW at 15K). The test bench described in this paper combines a Gifford-McMahon with a coaxial Pulse-Tube. A thermal link is joining the intercept of the Pulse-Tube and the second stage of the Gifford-McMahon. This intercept is a separator between the hot and the cold regenerators of the Pulse-Tube. The work has been focused on the cold part of this cold finger. Coupled with an active phase shifter, this Pulse-Tube has been tested and optimized and temperatures as low as 6K have been obtained at 30Hz with an intercept temperature at 20K.

  4. Radio-Frequency Pulse Compression for Linear Accelerators.

    NASA Astrophysics Data System (ADS)

    Nantista, Christopher Dennis

    Recent efforts to develop plans for an electron -positron linear collider with center-of-mass energy approaching a TeV have highlighted the need for sources capable of delivering hundreds of megawatts of peak rf drive power at X-band frequencies. This need has driven work in the area of rf pulse compression, which enhances the peak power available from pulsed rf tubes by compressing their output pulses in time, accumulating the available energy into shorter pulses. The classic means of rf pulse compression for linear accelerators is SLED. This technique is described, and the problem it presents for multibunch acceleration explained. Other pulse compression schemes, capable of producing suitable output pulses are explored, both theoretically and experimentally, in particular Binary Pulse Compression and SLED-II. The merits of each are considered with regard to gain, efficiency, complexity, size and cost. The development of some novel system components, along with the theory behind their design, is also discussed. The need to minimize copper losses in long waveguide runs led to the use of the circular TE_{01} propagation mode in over-moded guide, requiring much attention to mechanisms of coupling power between modes. The construction and commissioning of complete, high-power pulse compression systems is reported on, as well as their use in the testing of X-band accelerating structures, which, along with the X-band klystrons used, were developed at SLAC in parallel with the pulse compression work. The focus of the dissertation is on SLED-II, the favored scheme in some current linear accelerator designs. In addition to our experimental results, practical implementation considerations and design improvements are presented. The work to date has led to detailed plans for SLED-II systems to be used in the Next Linear Collider Test Accelerator, now under construction at SLAC. The prototype of the upgraded system is near completion. Descriptions of various rf pulse

  5. Frequency conversion of high-intensity, femtosecond laser pulses

    SciTech Connect

    Banks, P S

    1997-06-01

    Almost since the invention of the laser, frequency conversion of optical pulses via non- linear processes has been an area of active interest. However, third harmonic generation using ~(~1 (THG) in solids is an area that has not received much attention because of ma- terial damage limits. Recently, the short, high-intensity pulses possible with chirped-pulse amplification (CPA) laser systems allow the use of intensities on the order of 1 TW/cm2 in thin solids without damage. As a light source to examine single-crystal THG in solids and other high field inter- actions, the design and construction of a Ti:sapphire-based CPA laser system capable of ultimately producing peak powers of 100 TW is presented. Of special interest is a novel, all-reflective pulse stretcher design which can stretch a pulse temporally by a factor of 20,000. The stretcher design can also compensate for the added material dispersion due to propagation through the amplifier chain and produce transform-limited 45 fs pulses upon compression. A series of laser-pumped amplifiers brings the peak power up to the terawatt level at 10 Hz, and the design calls for additional amplifiers to bring the power level to the 100 TW level for single shot operation. The theory for frequency conversion of these short pulses is presented, focusing on conversion to the third harmonic in single crystals of BBO, KD*P, and d-LAP (deuterated I-arginine phosphate). Conversion efficiencies of up to 6% are obtained with 500 fs pulses at 1053 nm in a 3 mm thick BBO crystal at 200 GW/cm 2. Contributions to this process by unphasematched, cascaded second harmonic generation and sum frequency generation are shown to be very significant. The angular relationship between the two orders is used to measure the tensor elements of C = xt3)/4 with Crs = -1.8 x 1O-23 m2/V2 and .15Cri + .54Crs = 4.0 x 1O-23 m2/V2. Conversion efficiency in d-LAP is about 20% that in BBO and conversion efficiency in KD*P is 1% that of BBO. It is calculated

  6. A high voltage nanosecond pulser with independently adjustable output voltage, pulse width, and pulse repetition frequency

    NASA Astrophysics Data System (ADS)

    Prager, James; Ziemba, Timothy; Miller, Kenneth; Carscadden, John; Slobodov, Ilia

    2014-10-01

    Eagle Harbor Technologies (EHT) is developing a high voltage nanosecond pulser capable of generating microwaves and non-equilibrium plasmas for plasma medicine, material science, enhanced combustion, drag reduction, and other research applications. The EHT nanosecond pulser technology is capable of producing high voltage (up to 60 kV) pulses (width 20-500 ns) with fast rise times (<10 ns) at high pulse repetition frequency (adjustable up to 100 kHz) for CW operation. The pulser does not require the use of saturable core magnetics, which allows for the output voltage, pulse width, and pulse repetition frequency to be fully adjustable, enabling researchers to explore non-equilibrium plasmas over a wide range of parameters. A magnetic compression stage can be added to improve the rise time and drive lower impedance loads without sacrificing high pulse repetition frequency operation. Work supported in part by the US Navy under Contract Number N00014-14-P-1055 and the US Air Force under Contract Number FA9550-14-C-0006.

  7. Fast Rise Time and High Voltage Nanosecond Pulses at High Pulse Repetition Frequency

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth E.; Ziemba, Timothy; Prager, James; Picard, Julian; Hashim, Akel

    2015-09-01

    Eagle Harbor Technologies (EHT), Inc. is conducting research to decrease the rise time and increase the output voltage of the EHT Nanosecond Pulser product line, which allows for independently, user-adjustable output voltage (0 - 20 kV), pulse width (20 - 500 ns), and pulse repetition frequency (0 - 100 kHz). The goals are to develop higher voltage pulses (50 - 60 kV), decrease the rise time from 20 to below 10 ns, and maintain the high pulse repetition capabilities. These new capabilities have applications to pseudospark generation, corona production, liquid discharges, and nonlinear transmission line driving for microwave production. This work is supported in part by the US Navy SBIR program.

  8. Terahertz metrology on power, frequency, spectroscopy, and pulse parameters

    NASA Astrophysics Data System (ADS)

    Wu, Bin; Ying, Cheng Ping; Wang, Heng Fei; Zhang, Peng; Liu, Hong Yuan; Jiang, Bin

    2015-11-01

    Terahertz metrology is becoming more and more important along with the fast development of terahertz technology. This paper reviews the research works of the groups from the physikalisch-technische bundesanstalt (PTB), National institute of standards and technology (NIST), National physical laboratory (NPL), National institute of metrology (NIM) and some other research institutes. The contents mainly focus on the metrology of parameters of power, frequency, spectrum and pulse. At the end of the paper, the prospect of terahertz metrology is predicted.

  9. The effect of androgen blockade on pulsatile gonadotrophin release and LH response to naloxone.

    PubMed

    Balzano, S; Migliari, R; Sica, V; Scarpa, R M; Pintus, C; Loviselli, A; Usai, E; Balestrieri, A

    1987-10-01

    In order to clarify the effects of androgen blockade on the hypothalamic-pituitary-testicular axis in man, four patients with advanced prostate cancer, not previously treated, were given oral flutamide, 250 mg three times daily for 9 days. Before, and 7, 8 and 9 days after starting flutamide treatment, on separate days, the following tests were performed: a gonadotrophin pulsatility study, with 20 min interval blood sampling for 12 h, a naloxone test and a GnRH test. Flutamide induced a significant increase in both LH and FSH pulse frequency, while pulse amplitudes and plasma integrated concentrations (IC) of LH and FSH were unaffected. Plasma integrated concentrations of testosterone and oestradiol rose significantly, while that of prolactin was unaffected. The increase in plasma LH concentration induced by naloxone injection was abolished by flutamide treatment. On the other hand, the small FSH response to naloxone was unaffected by flutamide treatment. Response to GnRH was unaffected by flutamide. These results suggest that flutamide exerts effective androgen blockade at the hypothalamic level, since, despite increased plasma testosterone concentrations, gonadotrophin pulse frequency increased and the LH response to naloxone was abolished.

  10. Effect of pulse frequency on the ion fluxes during pulsed dc magnetron sputtering

    SciTech Connect

    Rahamathunnisa, M.; Cameron, D. C.

    2009-03-15

    The ion fluxes and energies which impinge on the substrate during the deposition of chromium nitride by asymmetric bipolar pulsed dc reactive magnetron sputtering have been analyzed using energy resolved mass spectrometry. It has been found that there is a remarkable increase in ion flux at higher pulse frequencies and that the peak ion energy is directly related to the positive voltage overshoot of the target voltage. The magnitude of the metal flux depositing on the substrate is consistent with a 'dead time' of {approx}0.7 {mu}s at the start of the on period. The variation of the ion flux with pulse frequency has been explained by a simple model in which the ion density during the on period has a large peak which is slightly delayed from the large negative voltage overshoot which occurs at the start of the on pulse due to increased ionization at that time. This is consistent with the previously observed phenomena in pulsed sputtering.

  11. Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization.

    PubMed

    de Vries, Oliver; Saule, Tobias; Plötner, Marco; Lücking, Fabian; Eidam, Tino; Hoffmann, Armin; Klenke, Arno; Hädrich, Steffen; Limpert, Jens; Holzberger, Simon; Schreiber, Thomas; Eberhardt, Ramona; Pupeza, Ioachim; Tünnermann, Andreas

    2015-07-27

    We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing. PMID:26367616

  12. Single pulse frequency compounding protocol for superharmonic imaging

    NASA Astrophysics Data System (ADS)

    Danilouchkine, M. G.; van Neer, P. L. M. J.; Verweij, M. D.; Matte, G. M.; Vletter, W. B.; van der Steen, A. F. W.; de Jong, N.

    2013-07-01

    Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and

  13. 10 K high frequency pulse tube cryocooler with precooling

    NASA Astrophysics Data System (ADS)

    Liu, Sixue; Chen, Liubiao; Wu, Xianlin; Zhou, Yuan; Wang, Junjie

    2016-07-01

    A high frequency pulse tube cryocooler with precooling (HPTCP) has been developed and tested to meet the requirement of weak magnetic signals measurement, and the performance characteristics are presented in this article. The HPTCP is a two-stage pulse tube cryocooler with the precooling-stage replaced by liquid nitrogen. Two regenerators completely filled with stainless steel (SS) meshes are used in the cooler. Together with cold inertance tubes and cold gas reservoir, a cold double-inlet configuration is used to control the phase relationship of the HPTCP. The experimental result shows that the cold double-inlet configuration has improved the performance of the cooler obviously. The effects of operation parameters on the performance of the cooler are also studied. With a precooling temperature of 78.5 K, the maximum refrigeration capacity is 0.26 W at 15 K and 0.92 W at 20 K when the input electric power are 174 W and 248 W respectively, and the minimum no-load temperature obtained is 10.3 K, which is a new record on refrigeration temperature for high frequency pulse tube cryocooler reported with SS completely used as regenerative matrix.

  14. Development of A Pulse Radio-Frequency Plasma Jet

    NASA Astrophysics Data System (ADS)

    Wang, Shou-Guo; Zhao, Ling-Li; Yang, Jing-Hua

    2013-09-01

    A small pulse plasma jet was driven by new developed radio-frequency (RF) power supply of 6.78 MHz. In contrast to the conventional RF 13.56 MHz atmospheric pressure plasma jet (APPJ), the power supply was highly simplified by eliminating the matching unit of the RF power supply and using a new circuit, moreover, a pulse controller was added to the circuit to produce the pulse discharge. The plasma jet was operated in a capacitively coupled manner and exhibited low power requirement of 5 W at atmospheric pressure using argon as a carrier gas. The pulse plasma plume temperature remained at less than 45 °C for an extended period of operation without using water to cool the electrodes. Optical emission spectrum measured at a wide range of 200-1000 nm indicated various excited species which were helpful in applying the plasma jet for surface sterilization to human skin or other sensitive materials. Institude of Plasma Physics, Chinese Academy of Science, Hefei, China.

  15. Electron heating enhancement by frequency-chirped laser pulses

    SciTech Connect

    Yazdani, E.; Afarideh, H.; Sadighi-Bonabi, R.; Riazi, Z.; Hora, H.

    2014-09-14

    Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a₀=5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about n{sub e}≈6n{sub c}, where n{sub c} is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

  16. Photodetachment of H- from intense, short, high-frequency pulses

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Robicheaux, F.

    2016-05-01

    We study the photodetachment of an electron from the hydrogen anion due to short, high-frequency laser pulses by numerically solving the time-dependent Schrödinger equation. Simulations are performed to investigate the dependence of the photoelectron spectra on the duration, chirp, and intensity of the pulses. Specifically, we concentrate on the low-energy distributions in the spectra that result from the Raman transitions of the broadband pulses. Contrary to the one-photon ionization, the low-energy distribution maintains a similar width as the laser bandwidth is expanded by chirping the pulses. In addition, we study the transitions of the ionization dynamics from the perturbative to strong-field regime. At high intensities, the positions of the net one- and two-photon absorption peaks in the spectrum shifts and the peaks split to multiple subpeaks because of the multiphoton effects. Moreover, although the one- and two-photon peaks and low-energy distribution exhibit saturation of the ionization yields, the latter shows relatively mild saturation. This work has been supported by DOE under Award No. DE-SC0012193.

  17. Phase and intensity characterization of femtosecond pulses from a chirped-pulse amplifier by frequency-resolved optical gating

    SciTech Connect

    Kohler, B.; Yakovlev, V.V.; Wilson, K.R.; Squier, J.; DeLong, K.W.; Trebino, R.

    1995-03-01

    Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also used to measure the regenerative amplifier dispersion and to characterize an amplitude-shaped pulse. The data provide an experimental demonstration of the value of FROG for characterizing complex pulses, including tailored femtosecond pulses for quantum control.

  18. Frequency stabilization in injection controlled pulsed CO2 lasers

    NASA Technical Reports Server (NTRS)

    Menzies, Robert T.; Ancellet, Gerard M.

    1987-01-01

    Longitudinal mode selection by injection has been demonstrated as a viable technique for tailoring a TEA-CO2 laser with pulse energies of a Joule or greater to fit the requirements of a coherent lidar transmitter. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, one can study the intrapulse frequency variation and attempt to determine the sources of frequency sweeping, or chirp. These sources include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with transverse spatial dimensions of the order of centimeters to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are briefly discussed in the paper, and representative experimental examples are included.

  19. Multi-pulse frequency shifted (MPFS) multiple access modulation for ultra wideband

    DOEpatents

    Nekoogar, Faranak; Dowla, Farid U.

    2012-01-24

    The multi-pulse frequency shifted technique uses mutually orthogonal short duration pulses o transmit and receive information in a UWB multiuser communication system. The multiuser system uses the same pulse shape with different frequencies for the reference and data for each user. Different users have a different pulse shape (mutually orthogonal to each other) and different transmit and reference frequencies. At the receiver, the reference pulse is frequency shifted to match the data pulse and a correlation scheme followed by a hard decision block detects the data.

  20. Frequency doubling of ultrashort laser pulses in biological tissues

    SciTech Connect

    Kim, Beop-Min; Eichler, Juergen; Da Silva, Luiz B.

    1999-12-01

    Theoretical and experimental studies of second-harmonic generation (SHG) in biological tissues was performed by use of ultrashort laser pulses (<1 ps). A simplified one-dimensional model for the generation and the propagation of frequency-doubled light inside tissue was developed. This model was tested in vitro against measurements of pig and chicken tissue and human tooth. The experimental results indicate that the intensity of SHG varies significantly among tissues types and between test sites in individual tissue. Possibilities of using this nonlinear tissue property in imaging and diagnostics are discussed. (c) 1999 Optical Society of America.

  1. Pulse swallowing frequency divider with low power and compact structure

    NASA Astrophysics Data System (ADS)

    Haijun, Gao; Lingling, Sun; Chaobo, Cai; Haiting, Zhan

    2012-11-01

    A pulse swallowing frequency divider with low power and compact structure is presented. One of the DFFs in the divided by 2/3 prescaler is controlled by the modulus control signal, and automatically powered off when it has no contribution to the operation of the prescaler. The DFFs in the program counter and the swallow counter are shared to compose a compact structure, which reduces the power consumption further. The proposed multi-modulus frequency divider was implemented in a standard 65 nm CMOS process with an area of 28 × 22 μm2. The power consumption of the divider is 0.6 mW under 1.2 V supply voltage when operating at 988 MHz.

  2. Optical pulse compression reflectometry based on single-sideband modulator driven by electrical frequency-modulated pulse

    NASA Astrophysics Data System (ADS)

    Zou, Weiwen; Yu, Lei; Yang, Shuo; Chen, Jianping

    2016-05-01

    We propose a novel scheme to generate a linear frequency-modulated optical pulse with high extinction ratio based on an electrical frequency-modulated pulse and optical single-sideband modulator. This scheme is proved to improve the stability and accuracy of optical pulse compression reflectometry (OPCR). In the experiment, a high spatial resolution of 10 cm and a long measurement range of 10.8 km using a laser source with 2-km coherence length are demonstrated.

  3. Single pulse frequency compounding protocol for superharmonic imaging

    NASA Astrophysics Data System (ADS)

    Danilouchkine, Mikhail G.; van Neer, Paul L. M. J.; Matte, Guillaume M.; Verweij, Martin D.; de Jong, Nico

    2011-03-01

    Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations

  4. SAR imagery using chaotic carrier frequency agility pulses

    NASA Astrophysics Data System (ADS)

    Xu, Xiaojian; Feng, Xiangzhi

    2011-06-01

    Synthetic aperture radar (SAR) systems are getting more and more applications in both civilian and military remote sensing missions. With the increasing deployment of electronic countermeasures (ECM) on modern battlefields, SAR encounters more and more interference jamming signals. The ECM jamming signals cause the SAR system to receive and process erroneous information which results in severe degradations in the output SAR images and/or formation of phony images of nonexistent targets. As a consequence, development of the electronic counter-countermeasures (ECCM) capability becomes one of the key problems in SAR system design. This paper develops radar signaling strategies and algorithms that enhance the ability of synthetic aperture radar to image targets under conditions of electronic jamming. The concept of SAR using chaotic carrier frequency agility pulses (CCFAP-SAR) is first proposed. Then the imaging procedure for CCFAP-SAR is discussed in detail. The ECCM performance of CCFAP-SAR for both depressive noise jamming and deceptive repeat jamming is analyzed. The impact of the carrier frequency agility range on the image quality of CCFAP-SAR is also studied. Simulation results demonstrate that, with adequate agility range of the carrier frequency, the proposed CCFAP-SAR performs as well as conventional radar with linear frequency modulation (LFM) waveform in image quality and slightly better in anti-noise depressive jamming; while performs very well in anti-deception jamming which cannot be rejected by LFM-SAR.

  5. Sub-15fs ultraviolet pulses generated by achromatic phase-matching sum-frequency mixing.

    PubMed

    Zhao, Baozhen; Jiang, Yongliang; Sueda, Keiich; Miyanaga, Noriaki; Kobayashi, Takayoshi

    2009-09-28

    A broadband ultraviolet pulse with a spectral width of 44 nm was generated by achromatic sum-frequency mixing of an 805-nm pulse and ultrabroadband visible pulse. Angular dispersion was introduced to achieve broadband phase matching by a prism pair. The UV pulse was compressed to 13.2 fs with another prism pair, with energy of 600 nJ. PMID:19907556

  6. State dependent model predictive control for orbital rendezvous using pulse-width pulse-frequency modulated thrusters

    NASA Astrophysics Data System (ADS)

    Li, Peng; Zhu, Zheng H.; Meguid, S. A.

    2016-07-01

    This paper studies the pulse-width pulse-frequency modulation based trajectory planning for orbital rendezvous and proximity maneuvering near a non-cooperative spacecraft in an elliptical orbit. The problem is formulated by converting the continuous control input, output from the state dependent model predictive control, into a sequence of pulses of constant magnitude by controlling firing frequency and duration of constant-magnitude thrusters. The state dependent model predictive control is derived by minimizing the control error of states and control roughness of control input for a safe, smooth and fuel efficient approaching trajectory. The resulting nonlinear programming problem is converted into a series of quadratic programming problem and solved by numerical iteration using the receding horizon strategy. The numerical results show that the proposed state dependent model predictive control with the pulse-width pulse-frequency modulation is able to effectively generate optimized trajectories using equivalent control pulses for the proximity maneuvering with less energy consumption.

  7. Different pulse pattern generation by frequency detuning in pulse modulated actively mode-locked ytterbium doped fiber laser

    NASA Astrophysics Data System (ADS)

    Chen, He; Chen, Sheng-Ping; Si, Lei; Zhang, Bin; Jiang, Zong-Fu

    2015-10-01

    We report the results of our recent experimental investigation of the modulation frequency detuning effect on the output pulse dynamics in a pulse modulated actively mode-locked ytterbium doped fiber laser. The experimental study shows the existence of five different mode-locking states that mainly depend on the modulation frequency detuning, which are: (a) amplitude-even harmonic/fundamental mode-locking, (b) Q-switched harmonic/fundamental mode-locking, (c) sinusoidal wave modulation mode, (d) pulses bundle state, and (e) noise-like state. A detailed experimental characterization of the output pulses dynamics in each operating mode is presented.

  8. Low frequency acoustic pulse propagation in temperate forests.

    PubMed

    Albert, Donald G; Swearingen, Michelle E; Perron, Frank E; Carbee, David L

    2015-08-01

    Measurements of acoustic pulse propagation for a 30-m path were conducted in an open field and in seven different forest stands in the northeastern United States consisting of deciduous, evergreen, or mixed tree species. The waveforms recorded in forest generally show the pulse elongation characteristic of propagation over a highly porous ground surface, with high frequency scattered arrivals superimposed on the basic waveform shape. Waveform analysis conducted to determine ground properties resulted in acoustically determined layer thicknesses of 4-8 cm in summer, within 2 cm of the directly measured thickness of the litter layers. In winter the acoustic thicknesses correlated with the site-specific snow cover depths. Effective flow resistivity values of 50-88 kN s m(-4) were derived for the forest sites in summer, while lower values typical for snow were found in winter. Reverberation times (T60) were typically around 2 s, but two stands (deciduous and pruned spruce planted on a square grid) had lower values of about 1.2 s. One site with a very rough ground surface had very low summer flow resistivity value and also had the longest reverberation time of about 3 s. These measurements can provide parameters useful for theoretical predictions of acoustic propagation within forests. PMID:26328690

  9. Low frequency acoustic pulse propagation in temperate forests.

    PubMed

    Albert, Donald G; Swearingen, Michelle E; Perron, Frank E; Carbee, David L

    2015-08-01

    Measurements of acoustic pulse propagation for a 30-m path were conducted in an open field and in seven different forest stands in the northeastern United States consisting of deciduous, evergreen, or mixed tree species. The waveforms recorded in forest generally show the pulse elongation characteristic of propagation over a highly porous ground surface, with high frequency scattered arrivals superimposed on the basic waveform shape. Waveform analysis conducted to determine ground properties resulted in acoustically determined layer thicknesses of 4-8 cm in summer, within 2 cm of the directly measured thickness of the litter layers. In winter the acoustic thicknesses correlated with the site-specific snow cover depths. Effective flow resistivity values of 50-88 kN s m(-4) were derived for the forest sites in summer, while lower values typical for snow were found in winter. Reverberation times (T60) were typically around 2 s, but two stands (deciduous and pruned spruce planted on a square grid) had lower values of about 1.2 s. One site with a very rough ground surface had very low summer flow resistivity value and also had the longest reverberation time of about 3 s. These measurements can provide parameters useful for theoretical predictions of acoustic propagation within forests.

  10. Acute effects of nalmefene on LH, prolactin, and testosterone in male rhesus monkeys.

    PubMed

    Mello, N K; Mendelson, J H; Kelly, M

    2000-06-01

    The effects of the long-acting opioid antagonist, nalmefene [17-N-cyclopropylmethyl-3,14-beta-dihydroxy-4, 5-alpha-epoxy-6-methylene morphinan hydrochloride] on LH, T, and prolactin release in rhesus monkeys are unknown. The acute effects of nalmefene (0.01 and 0.10 mg/kg, IV) or placebo on LH, PRL, and T were studied, and samples were collected at 10-min intervals for 360 min to permit cluster analysis of pulsatile release patterns. LH increased significantly within 30 min after nalmefene, and remained significantly above baseline levels for 50 to 60 min (p < 0.05). Testosterone increased significantly within 70 to 80 min after nalmefene, and remained significantly above baseline for 60 min (p < 0.05). Although nalmefene antagonizes opioid agonists for 6-8 h, inhibitory feedback by testosterone appeared to limit the duration of its antagonism of endogenous opioid inhibition of LHRH and stimulation of LH. Nalmefene did not change LH or PRL pulse frequency or amplitude significantly in comparison to placebo administration. PMID:10880679

  11. Acute effects of nalmefene on LH, prolactin, and testosterone in male rhesus monkeys.

    PubMed

    Mello, N K; Mendelson, J H; Kelly, M

    2000-06-01

    The effects of the long-acting opioid antagonist, nalmefene [17-N-cyclopropylmethyl-3,14-beta-dihydroxy-4, 5-alpha-epoxy-6-methylene morphinan hydrochloride] on LH, T, and prolactin release in rhesus monkeys are unknown. The acute effects of nalmefene (0.01 and 0.10 mg/kg, IV) or placebo on LH, PRL, and T were studied, and samples were collected at 10-min intervals for 360 min to permit cluster analysis of pulsatile release patterns. LH increased significantly within 30 min after nalmefene, and remained significantly above baseline levels for 50 to 60 min (p < 0.05). Testosterone increased significantly within 70 to 80 min after nalmefene, and remained significantly above baseline for 60 min (p < 0.05). Although nalmefene antagonizes opioid agonists for 6-8 h, inhibitory feedback by testosterone appeared to limit the duration of its antagonism of endogenous opioid inhibition of LHRH and stimulation of LH. Nalmefene did not change LH or PRL pulse frequency or amplitude significantly in comparison to placebo administration.

  12. LH (Luteinizing Hormone) Test

    MedlinePlus

    ... LH and FSH may be ordered when a boy or girl does not appear to be entering puberty at ... pubic hair Growth of testicles and penis in boys Beginning of menstruation in girls ^ Back to top What does the test result ...

  13. Repetitively rated plasma relativistic microwave oscillator with a controllable frequency in every pulse

    SciTech Connect

    Bogdankevich, I. L.; Grishin, D. M.; Gunin, A. V.; Ivanov, I. E.; Korovin, S. D.; Loza, O. T.; Mesyats, G. A.; Pavlov, D. A.; Rostov, V. V.; Strelkov, P. S.; Ul'yanov, D. K.

    2008-10-15

    A repetitively rated microwave oscillator whose frequency can be varied electronically from pulse to pulse in a predetermined manner is created for the first time. The microwave oscillator has a power on the order of 10{sup 8} W and is based on the Cherenkov interaction of a high-current relativistic electron beam with a plasma preformed before each pulse. Electronic control over the plasma properties allows one to arbitrarily vary the microwave frequency from pulse to pulse at a pulse repetition rate of up to 50 Hz.

  14. Shifts in frequency-modulated pulses recorded during an encounter with Blainville's beaked whales (Mesoplodon densirostris).

    PubMed

    Keating, Jennifer L; Barlow, Jay; Rankin, Shannon

    2016-08-01

    Echolocation signals produced by beaked whales (family: Ziphiidae) include frequency-modulated (FM) pulses that appear to have species-specific characteristics. To date there has been no established evidence that a single species of beaked whale might produce more than one type of FM pulse. In 2014 a group of Blainville's beaked whales (Mesoplodon densirostris) were sighted off of Southern California; recordings included FM pulses with significant increases in peak frequency, center frequency, and -10 dB bandwidth relative to FM pulses previously attributed to this species. This research suggests there may be greater variation in received beaked whale FM pulses than previously understood. PMID:27586775

  15. Effect of transport on pulsatile and surge secretion of LH in ewes in the breeding season.

    PubMed

    Dobson, H; Tebble, J E; Phogat, J B; Smith, R F

    1999-05-01

    The aim of this study was to elucidate the mechanism(s) involved in stress-induced subfertility by examining the effect of 4 h transport on surge and pulsatile LH secretion in intact ewes and ovariectomized ewes treated with steroids to induce an artificial follicular phase (model ewes). Transport caused a greater delay in the onset of the LH surge in nine intact ewes than it did in ten ovariectomized ewes (intact: 41.0 +/- 0.9 h versus 48.3 +/- 0.8 h, P < 0.02; ovariectomized model: 40.8 +/- 0.6 h versus 42.6 +/- 0.5 h, P < 0.02). Disruption of the hypothalamus-pituitary endocrine balance in intact ewes may have reduced gonadotrophin stimulation of follicular oestradiol production which had an additional effect on the LH surge mechanism. In the ovariectomized model ewes, this effect was masked by the exogenous supply of oestradiol. However, in these model ewes, there was a greater suppression of maximum LH surge concentrations (intact controls: 29 +/- 4 ng ml-1 versus intact transported 22 +/- 5 ng ml-1, P < 0.02; ovariectomized model controls: 35 +/- 7 ng ml-1 versus model transported 15 +/- 2 ng ml-1, P < 0.02). Subsequent exposure to progesterone for 12 days resulted in the resumption of a normal LH profile in the next follicular phase, indicating that acute stress leads to a temporary endocrine lesion. In four intact ewes transported in the mid-follicular phase, there was a suppression of LH pulse amplitude (0.9 +/- 0.3 versus 0.3 +/- 0.02 ng ml-1, P < 0.05) but a statistically significant effect on pulse frequency was not observed (2.0 +/- 0.4 versus 1.7 +/- 0.6 pulses per 2 h). In conclusion, activation of the hypothalamus-pituitary-adrenal axis by transport in the follicular phase of intact ewes interrupts surge secretion of LH, possibly by interference with LH pulsatility and, hence, follicular oestradiol production. This disruption of gonadotrophin secretion will have a major impact on fertility.

  16. Ultrashort-pulse measurement using noninstantaneous nonlinearities: Raman effects in frequency-resolved optical gating

    SciTech Connect

    DeLong, K.W.; Ladera, C.L.; Trebino, R.; Kohler, B.; Wilson, K.R.

    1995-03-01

    Ultrashort-pulse-characterization techniques generally require instantaneously responding media. We show that this is not the case for frequency-resolved optical gating (FROG). We include, as an example, the noninstantaneous Raman response of fused silica, which can cause errors in the retrieved pulse width of as much as 8% for a 25-fs pulse in polarization-gate FROG. We present a modified pulse-retrieval algorithm that deconvolves such slow effects and use it to retrieve pulses of any width. In experiments with 45-fs pulses this algorithm achieved better convergence and yielded a shorter pulse than previous FROG algorithms.

  17. Interactions between nutritional and opioidergic pathways in the control of LH secretion in male sheep.

    PubMed

    Celi, Pietro; Miller, David W; Blache, Dominique; Martin, Graeme B

    2010-01-01

    Our aim was to determine the role of opioidergic processes in the effects of nutrition on the secretion of LH pulses in the mature male sheep. In the first of three experiments, adult Merino rams were acclimatised to a maintenance diet and then allocated to one of three dietary groups (n=5): continuation of the maintenance diet (Group M); reduction to half of the maintenance allocation (Group HM); or supplementation of the maintenance diet with lupin grain (Group HD). An initial administration of naloxone (2mg/kg body weight, i.v.) was followed at 40-min intervals by three further administrations (1mg/kg). Blood was sampled every 20 min for 12h before the initial naloxone administration and then for a further 6h. LH pulse frequency after naloxone treatment was significantly higher in Group HD than in Group HM (P<0.05). The second study tested whether the response to naloxone depended on calcium status. We used 22 adult Merino rams in two consecutive experiments, one in which the rams were fed a maintenance diet, and one in which the rams were fed with the maintenance diet plus 1 kg lupin grain for 5 weeks. In both experiments, rams were allocated to groups that received one of the following treatments: (a) 0.02 g/kg calcium borogluconate+0.2mg/kg naloxone hydrochloride (Nal+Ca(2+); n=6); (b) 0.2mg/kg naloxone hydrochloride (Nal; n=6); (c) 0.02 g/kg calcium borogluconate (Ca(2+); n=5); (d) 0.1 ml/kg NaCl 0.9% (Saline; n=5). All treatments were given as a single i.v. administration daily for 5 days. Blood was sampled every 20 min for 24 h during the acclimatization period (Day 0) and on the last day (Day 5) of treatment. In the first study (under maintenance), none of the treatments affected LH pulse frequency. In the second study (the lupin-supplemented rams), LH pulse frequency was significantly increased (P<0.05) by the administration of naloxone+Ca(2+), naloxone alone and Ca(2+) alone. Overall, rams on a low plane of nutrition showed the smallest response to

  18. Ultrashort pulse Cr4+:YAG laser for high precision infrared frequency interval measurements

    PubMed Central

    Alcock, A. J.; Ma, P.; Poole, P. J.; Chepurov, S.; Czajkowski, A.; Bernard, J. E.; Madej, A. A.; Fraser, J. M.; Mitchell, I. V.; Sorokina, I. T.; Sorokin, E.

    2010-01-01

    A cavity stabilized, SESAM mode-locked Cr4+:YAG laser capable of generating sub-100 fs pulses has been developed. Locking the 130-MHz pulse repetition frequency to that of a hydrogen maser-referenced frequency synthesizer provides a 30-nm wide frequency comb for the 1530-nm wavelength region. In conjunction with a pair of acetylene stabilized, external cavity diode lasers, this laser provides a high precision measurement tool for the determination of acetylene transition frequencies. PMID:19498916

  19. Pulsed radio frequency therapy of experimentally induced arthritis in ponies.

    PubMed Central

    Crawford, W H; Houge, J C; Neirby, D T; Di Mino, A; Di Mino, A A

    1991-01-01

    The effect of pulsed radio frequency therapy (PRFT) was evaluated on seven ponies with no arthritis and in 28 ponies in which arthritis was created using intra-articular amphotericin B to induce synovitis in the right middle carpal joint. The ponies were divided into five treatment and two control groups. Two levels of arthritis were created and two dosage levels of PRFT were evaluated. The effect of PRFT on arthritic and nonarthritic joints was measured by comparing synovial fluid parameters, the degree and duration of lameness, the range of carpal motion, and carpus circumference, for treated and untreated groups. Lesions seen radiographically, at gross pathology, and by histopathology were also compared between the treated and control groups. In the ponies with a mild form of induced arthritis, PRFT significantly (p less than 0.05) reduced the severity and duration of lameness, swelling of the carpus, and the severity of gross pathological and radiographic changes. In these ponies the synovial acid phosphatase levels were lower, the mucin clot quality was superior, and the synovial protein levels were lower for the ponies receiving PRFT as compared to the arthritic ponies receiving no treatment. A dose response effect was evident. In ponies with a slightly more severe form of arthritis, PRFT was evaluated at one dosage level. The treated ponies were significantly improved over the untreated ponies with respect to carpal range of motion, degree of lameness, carpus swelling, and radiographic lesions. No deleterious effects were noted when normal, PRFT treated, middle carpal joints were compared to contralateral untreated, normal joints. It was concluded that significant beneficial effects resulted when affected ponies were treated with PRFT. PMID:1884288

  20. Intracavity frequency doubling of {mu}s alexandrite laser pulses

    SciTech Connect

    Brinkmann, R.; Schoof, K.

    1994-12-31

    Intracavity second harmonic generation (SHG) with a three mirror folded cavity configuration was investigated with a flashlamp pumped, Q-switched Alexandrite laser. The authors therefore used different nonlinear optical crystals to convert the fundamental 750 nm radiation into the near UV spectral ,range (3 75 nm). The laser pulses were stretched into the {mu}s time domain by an electronic feedback system regulating the losses of the resonator. They investigated the conversion efficiency for different pulse lengths as well as the effect of pulse-lengthening due to the nonlinearity of the intracavity losses introduced by the optical crystal used. Working with BBO-crystals, they were able to achieve a second harmonic output of 25 mJ per pulse at 375 mn with a temporal rectangular pulse of 1 {mu}s in length and a stable nearly gaussian shaped beam profile.

  1. Nonlinear-optical frequency-doubling metareflector: pulsed regime

    NASA Astrophysics Data System (ADS)

    Popov, A. K.; Myslivets, S. A.

    2016-01-01

    The properties of backward-wave second-harmonic metareflector operating in pulse regime are investigated. It is made of metamaterial which enables phase matching of contra-propagating fundamental and second-harmonic waves. References are given to the works that prove such a possibility. Physical principles underlying differences in the proposed and standard settings as well as between continuous-wave and pulsed regimes are discussed. Pulsed regime is more practicable and has a broader scope of applications. A set of partial differential equations which describe such a reflector with the account for losses are solved numerically. It is shown that unlike second-harmonic generation in standard settings, contra-propagating pulse of second harmonic may become much longer than the incident fundamental one and the difference grows with decrease in the input pulse length as compared to thickness of the metaslab. The revealed properties are important for applications and may manifest themselves beyond the optical wavelength range.

  2. Difference-frequency generation of optical radiation from two-color x-ray pulses.

    PubMed

    Shwartz, E; Shwartz, S

    2015-03-23

    We describe the process of difference-frequency generation of short optical pulses from two-color X-ray pulses. By assuming 10¹¹ photons per X-ray pulse, we predict that the optical count rate can exceed 10⁷ photons per pulse. Similar to other effects involving nonlinear interactions of X-rays and optical radiation, the effect we describe can be used for microscopic studies of chemical bonds and as a probe for light-matter interactions on the atomic scale. Since the X-ray damage threshold is much higher than the optical damage threshold, the efficiency of difference-frequency generation from two X-ray pulses is expected to be orders of magnitude higher than the efficiency of effects such as sum/difference-frequency mixing between X-rays and optical intense short-pulse sources. PMID:25837087

  3. A Low frequency Survey of Giant Pulses from the Crab Pulsar

    NASA Astrophysics Data System (ADS)

    Eftekhari, T.; Stovall, K.; Dowell, J.; Schinzel, F. K.; Taylor, G. B.

    2016-10-01

    We present a large survey of giant pulses from the Crab Pulsar as observed with the first station of the Long Wavelength Array. Automated methods for detecting giant pulses at low frequencies where scattering becomes prevalent are also explored. More than 1400 pulses were detected across four frequency bands between 20 and 84 MHz over a seven-month period beginning in 2013, with additional followup observations in late 2014 and early 2015. A handful of these pulses were detected simultaneously across all four frequency bands. We examine pulse characteristics, including pulse broadening and power law indices for amplitude distributions. We find that the flux density increases toward shorter wavelengths, consistent with a spectral turnover at 100 MHz. Our observations uniquely span multiple scattering epochs, manifesting as a notable trend in the number of detections per observation. These results are characteristic of the variable interface between the synchrotron nebula and the surrounding interstellar medium.

  4. Characterization of Ultrafast Laser Pulses using a Low-dispersion Frequency Resolved Optical Grating Spectrometer

    NASA Astrophysics Data System (ADS)

    Whitelock, Hope; Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Berrah, Nora

    2016-05-01

    A low dispersion frequency-resolved optical gating (FROG) spectrometer was designed to characterize ultrashort (<50 femtosecond) laser pulses from a commercial regenerative amplifier, optical parametric amplifier, and a home-built non-colinear optical parametric amplifier. This instrument splits a laser pulse into two replicas with a 90:10 intensity ratio using a thin pellicle beam-splitter and then recombines the pulses in a birefringent medium. The instrument detects a wavelength-sensitive change in polarization of the weak probe pulse in the presence of the stronger pump pulse inside the birefringent medium. Scanning the time delay between the two pulses and acquiring spectra allows for characterization of the frequency and time content of ultrafast laser pulses, that is needed for interpretation of experimental results obtained from these ultrafast laser systems. Funded by the DoE-BES, Grant No. DE-SC0012376.

  5. Amplification of frequency-modulated soliton-like pulses in inhomogeneous optical waveguides with normal dispersion

    NASA Astrophysics Data System (ADS)

    Zolotovskii, I. O.; Novikov, S. G.; Okhotnikov, O. G.; Sementsov, D. I.; Yavtushenko, I. O.; Yavtushenko, M. S.

    2012-06-01

    The possibility of effective amplification of self-similar frequency-modulated pulses (FMPs) in longitudinally inhomogeneous active optical waveguides is studied. Peculiarities of the dynamics of parabolic pulses with a constant frequency modulation rate are considered. An optimal profile of variation of the group velocity dispersion was obtained in correspondence with optimal amplification of a similariton-like pulse. The use of FMPs in amplifying and longitudinally inhomogeneous optical waveguides with a correspondingly matched profile of normal dispersion of group velocities is shown to be capable of providing for an amplification of subpicosecond pulses up to energies above 1 nJ.

  6. Effects of pulsed electromagnetic field frequencies on the osteogenic differentiation of human mesenchymal stem cells.

    PubMed

    Luo, Fei; Hou, Tianyong; Zhang, Zehua; Xie, Zhao; Wu, Xuehui; Xu, Jianzhong

    2012-04-01

    The purpose of this study was to evaluate the effect of different frequencies of pulsed electromagnetic fields on the osteogenic differentiation of human mesenchymal stem cells. Third-generation human mesenchymal stem cells were irradiated with different frequencies of pulsed electromagnetic fields, including 5, 25, 50, 75, 100, and 150 Hz, with a field intensity of 1.1 mT, for 30 minutes per day for 21 days. Changes in human mesenchymal stem cell morphology were observed using phase contrast microscopy. Alkaline phosphatase activity and osteocalcin expression were also determined to evaluate human mesenchymal stem cell osteogenic differentiation.Different effects were observed on human mesenchymal stem cell osteoblast induction following exposure to different pulsed electromagnetic field frequencies. Levels of human mesenchymal stem cell differentiation increased when the pulsed electromagnetic field frequency was increased from 5 hz to 50 hz, but the effect was weaker when the pulsed electromagnetic field frequency was increased from 50 Hz to 150 hz. The most significant effect on human mesenchymal stem cell differentiation was observed at of 50 hz.The results of the current study show that pulsed electromagnetic field frequency is an important factor with regard to the induction of human mesenchymal stem cell differentiation. Furthermore, a pulsed electromagnetic field frequency of 50 Hz was the most effective at inducing human mesenchymal stem cell osteoblast differentiation in vitro.

  7. Frequency-encoded multiplexed CARS microscopy by rapid pulse shaping

    NASA Astrophysics Data System (ADS)

    Levitt, Jonathan M.; Katz, Ori; Silberberg, Yaron

    2014-06-01

    A new coherent anti-Stokes Raman spectroscopy (CARS) technique is reported for real-time detection and classification of several chemical constituents, utilizing a single detector and a single beam of shaped femtosecond pulses. The technique is based on rapidly switching between differently shaped pulses that either maximize or minimize the targeted vibrational lines excitation, thus creating temporally modulated 'bright' and 'dark' profiles in the total CARS signal that are measured by a single photomultiplier tube and demodulated by a multi-channel lock-in amplifier. Using a two-dimensional spatial light modulator displaying 24 different pulse shapes, we demonstrate pulse shaping at 80 kHz and chemically specific microscopy with pixel dwell times of less than 0.5 ms.

  8. Direct visualization of exciton reequilibration in the LH1 and LH2 complexes of Rhodobacter sphaeroides by multipulse spectroscopy.

    PubMed

    Cohen Stuart, Thomas A; Vengris, Mikas; Novoderezhkin, Vladimir I; Cogdell, Richard J; Hunter, C Neil; van Grondelle, Rienk

    2011-05-01

    The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas.

  9. Direct Visualization of Exciton Reequilibration in the LH1 and LH2 Complexes of Rhodobacter sphaeroides by Multipulse Spectroscopy

    PubMed Central

    Cohen Stuart, Thomas A.; Vengris, Mikas; Novoderezhkin, Vladimir I.; Cogdell, Richard J.; Hunter, C. Neil; van Grondelle, Rienk

    2011-01-01

    The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. PMID:21539791

  10. ADRF experiments using near n.pi pulse strings. [Adiabatic Demagnetization due to Radio Frequency pulses

    NASA Technical Reports Server (NTRS)

    Rhim, W. K.; Burum, D. P.; Elleman, D. D.

    1977-01-01

    Adiabatic demagnetization (ADRF) can be achieved in a dipolar coupled nuclear spin system in solids by applying a string of short RF pulses and gradually modulating the pulse amplitudes or pulse angles. This letter reports an adiabatic inverse polarization effect in solids and a rotary spin echo phenomenon observed in liquids when the pulse angle is gradually changed across integral multiples of pi during a string of RF pulses. The RF pulse sequence used is illustrated along with the NMR signal from a CaF2 single crystal as observed between the RF pulses and the rotary spin echo signal observed in liquid C6F6 for n = 2. The observed effects are explained qualitatively on the basis of average Hamiltonian theory.

  11. Pulsed infrared difference frequency generation in CdGeAs/sub 2/

    DOEpatents

    Piltch, M.S.; Rink, J.P.; Tallman, C.R.

    1975-11-26

    A laser apparatus for generating a line-tunable pulsed infrared difference frequency output is described. The apparatus comprises a CO/sub 2/ laser which produces a first frequency, a CO laser which produces a second frequency, and a mixer for combining the output of the CO/sub 2/ and CO lasers so as to produce a final output comprising a difference frequency from the first and second frequency outputs.

  12. Pulsed infrared difference frequency generation in CdGeAs.sub.2

    DOEpatents

    Piltch, Martin S.; Rink, John P.; Tallman, Charles R.

    1977-03-08

    The disclosure relates to a laser apparatus for generating a line-tunable pulsed infrared difference frequency output. The apparatus comprises a CO.sub.2 laser which produces a first frequency, a CO laser which produces a second frequency and a mixer for combining the output of the CO.sub.2 and CO lasers so as to produce a final output comprising a difference frequency from the first and second frequency outputs.

  13. A critical review of liquid helium temperature high frequency pulse tube cryocoolers for space applications

    NASA Astrophysics Data System (ADS)

    Wang, B.; Gan, Z. H.

    2013-08-01

    The importance of liquid helium temperature cooling technology in the aerospace field is discussed, and the results indicate that improving the efficiency of liquid helium cooling technologies, especially the liquid helium high frequency pulse tube cryocoolers, is the principal difficulty to be solved. The state of the art and recent developments of liquid helium high frequency pulse tube cryocoolers are summarized. The main scientific challenges for high frequency pulse tube cryocoolers to efficiently reach liquid helium temperatures are outlined, and the research progress addressing those challenges are reviewed. Additionally some possible solutions to the challenges are pointed out and discussed.

  14. Diversified pulse generation from frequency shifted feedback Tm-doped fibre lasers

    NASA Astrophysics Data System (ADS)

    Chen, He; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2016-05-01

    Pulsed fibre lasers operating in the eye-safe 2 μm spectral region have numerous potential applications in areas such as remote sensing, medicine, mid-infrared frequency conversion, and free-space communication. Here, for the first time, we demonstrate versatile 2 μm ps-ns pulses generation from Tm-based fibre lasers based on frequency shifted feedback and provide a comprehensive report of their special behaviors. The lasers are featured with elegant construction and the unparalleled capacity of generating versatile pulses. The self-starting mode-locking is initiated by an intra-cavity acousto-optical frequency shifter. Diversified mode-locked pulse dynamics were observed by altering the pump power, intra-cavity polarization state and cavity structure, including as short as 8 ps single pulse sequence, pulse bundle state and up to 12 nJ, 3 ns nanosecond rectangular pulse. A reflective nonlinear optical loop mirror was introduced to successfully shorten the pulses from 24 ps to 8 ps. Beside the mode-locking operation, flexible Q-switching and Q-switched mode-locking operation can also be readily achieved in the same cavity. Up to 78 μJ high energy nanosecond pulse can be generated in this regime. Several intriguing pulse dynamics are characterized and discussed.

  15. Diversified pulse generation from frequency shifted feedback Tm-doped fibre lasers

    PubMed Central

    Chen, He; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2016-01-01

    Pulsed fibre lasers operating in the eye-safe 2 μm spectral region have numerous potential applications in areas such as remote sensing, medicine, mid-infrared frequency conversion, and free-space communication. Here, for the first time, we demonstrate versatile 2 μm ps-ns pulses generation from Tm-based fibre lasers based on frequency shifted feedback and provide a comprehensive report of their special behaviors. The lasers are featured with elegant construction and the unparalleled capacity of generating versatile pulses. The self-starting mode-locking is initiated by an intra-cavity acousto-optical frequency shifter. Diversified mode-locked pulse dynamics were observed by altering the pump power, intra-cavity polarization state and cavity structure, including as short as 8 ps single pulse sequence, pulse bundle state and up to 12 nJ, 3 ns nanosecond rectangular pulse. A reflective nonlinear optical loop mirror was introduced to successfully shorten the pulses from 24 ps to 8 ps. Beside the mode-locking operation, flexible Q-switching and Q-switched mode-locking operation can also be readily achieved in the same cavity. Up to 78 μJ high energy nanosecond pulse can be generated in this regime. Several intriguing pulse dynamics are characterized and discussed. PMID:27193213

  16. Diversified pulse generation from frequency shifted feedback Tm-doped fibre lasers.

    PubMed

    Chen, He; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2016-01-01

    Pulsed fibre lasers operating in the eye-safe 2 μm spectral region have numerous potential applications in areas such as remote sensing, medicine, mid-infrared frequency conversion, and free-space communication. Here, for the first time, we demonstrate versatile 2 μm ps-ns pulses generation from Tm-based fibre lasers based on frequency shifted feedback and provide a comprehensive report of their special behaviors. The lasers are featured with elegant construction and the unparalleled capacity of generating versatile pulses. The self-starting mode-locking is initiated by an intra-cavity acousto-optical frequency shifter. Diversified mode-locked pulse dynamics were observed by altering the pump power, intra-cavity polarization state and cavity structure, including as short as 8 ps single pulse sequence, pulse bundle state and up to 12 nJ, 3 ns nanosecond rectangular pulse. A reflective nonlinear optical loop mirror was introduced to successfully shorten the pulses from 24 ps to 8 ps. Beside the mode-locking operation, flexible Q-switching and Q-switched mode-locking operation can also be readily achieved in the same cavity. Up to 78 μJ high energy nanosecond pulse can be generated in this regime. Several intriguing pulse dynamics are characterized and discussed. PMID:27193213

  17. Advantages of high-frequency Pulse-tube technology and its applications in infrared sensing

    NASA Astrophysics Data System (ADS)

    Arts, R.; Willems, D.; Mullié, J.; Benschop, T.

    2016-05-01

    The low-frequency pulse-tube cryocooler has been a workhorse for large heat lift applications. However, the highfrequency pulse tube has to date not seen the widespread use in tactical infrared applications that Stirling cryocoolers have had, despite significant advantages in terms of exported vibrations and lifetime. Thales Cryogenics has produced large series of high-frequency pulse-tube cryocoolers for non-infrared applications since 2005. However, the use of Thales pulse-tube cryocoolers for infrared sensing has to date largely been limited to high-end space applications. In this paper, the performances of existing available off-the-shelf pulse-tube cryocoolers are examined versus typical tactical infrared requirements. A comparison is made on efficiency, power density, reliability, and cost. An outlook is given on future developments that could bring the pulse-tube into the mainstream for tactical infrared applications.

  18. Condition for short pulse generation in ultrahigh frequency mode-locking of semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Lau, K. Y.; Paslaski, J.

    1991-11-01

    It is shown that although it is possible to obtain mode-locking without self-pulsation when certain criteria are satisfied, the shortest pulses are almost always generated at or close to the onset of self-pulsation. Thus, the amplitude of the optical pulse train is modulated by the (relatively) low-frequency envelop of a few gigahertz under this condition. This observation was obtained by simultaneously measuring the pulsewidth using an autocorrelator and monitoring the optical intensity using a high-speed photodiode and a microwave spectrum analyzer. It is concluded that while it is possible to generate picosecond optical pulses in ultrahigh-frequency mode-locking of quantum-well lasers, very short pulses (approaching 1 ps) are almost always accompanied by self-pulsation which is manifested as low-frequency (gigahertz) envelope modulation of the optical pulse train.

  19. Experimental studies of the overshoot and undershoot in pulse-modulated radio-frequency atmospheric discharge

    NASA Astrophysics Data System (ADS)

    Huo, W. G.; Li, R. M.; Shi, J. J.; Ding, Z. F.

    2016-08-01

    The overshoot and undershoot of the applied voltage on the electrodes, the discharge current, and radio frequency (RF) power were observed at the initial phase of pulse-modulated (PM) RF atmospheric pressure discharges, but factors influencing the overshoot and undershoot have not been fully elucidated. In this paper, the experimental studies were performed to seek the reasons for the overshoot and undershoot. The experimental results show that the overshoot and undershoot are associated with the pulse frequency, the rise time of pulse signal, and the series capacitor Cs in the inversely L-shaped matching network. In the case of a high RF power discharge, these overshoot and undershoot become serious when shortening the rise time of a pulse signal (5 ns) or operating at a moderate pulse frequency (500 Hz or 1 kHz).

  20. Investigation of the input signal frequency effect on the formed pulse of the hydraulic-powered pulse machine

    NASA Astrophysics Data System (ADS)

    Novoseltseva, M. V.; Masson, I. A.

    2016-04-01

    Nowadays, a special emphasis is placed on an output signal curve during the analysis of well drilling machines since these machines should have as high energy efficiency as it is possible. This work proposes factors that have an impact of input signal frequency on the formed pulse that are used to find the most efficient frequency for its further applying in the machine. Results of the conducted experiment are obtained by using a mathematical model that is created in Simulink Matlab.

  1. Measuring ultrashort pulses using frequency-resolved optical gating

    SciTech Connect

    Trebino, R.

    1993-12-01

    The purpose of this program is the development of techniques for the measurement of ultrafast events important in gas-phase combustion chemistry. Specifically, goals of this program include the development of fundamental concepts and spectroscopic techniques that will augment the information currently available with ultrafast laser techniques. Of equal importance is the development of technology for ultrafast spectroscopy. For example, methods for the production and measurement of ultrashort pulses at wavelengths important for these studies is an important goal. Because the specific vibrational motion excited in a molecule depends sensitively on the intensity, I(t), and the phase, {psi}(t), of the ultrashort pulse used to excite the motion, it is critical to measure both of these quantities for an individual pulse. Unfortunately, this has remained an unsolved problem for many years. Fortunately, this year, the authors present a technique that achieves this goal.

  2. Characteristics of pulsed dual frequency inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Seo, Jin Seok; Kim, Kyoung Nam; Kim, Ki Seok; Kim, Tae Hyung; Yeom, Geun Young

    2015-01-01

    To control the plasma characteristics more efficiently, a dual antenna inductively coupled plasma (DF-ICP) source composed of a 12-turn inner antenna operated at 2 MHz and a 3-turn outer antenna at 13.56 MHz was pulsed. The effects of pulsing to each antenna on the change of plasma characteristics and SiO2 etch characteristics using Ar/C4F8 gas mixtures were investigated. When the duty percentage was decreased from continuous wave (CW) mode to 30% for the inner or outer ICP antenna, decrease of the average electron temperature was observed for the pulsing of each antenna. Increase of the CF2/F ratio was also observed with decreasing duty percentage of each antenna, indicating decreased dissociation of the C4F8 gas due to the decreased average electron temperature. When SiO2 etching was investigated as a function of pulse duty percentage, increase of the etch selectivity of SiO2 over amorphous carbon layer (ACL) was observed while decreasing the SiO2 etch rate. The increase of etch selectivity was related to the change of gas dissociation characteristics, as observed by the decrease of average electron temperature and consequent increase of the CF2/F ratio. The decrease of the SiO2 etch rate could be compensated for by using the rf power compensated mode, that is, by maintaining the same time-average rf power during pulsing, instead of using the conventional pulsing mode. Through use of the power compensated mode, increased etch selectivity of SiO2/ACL similar to the conventional pulsing mode could be observed without significant decrease of the SiO2 etch rate. Finally, by using the rf power compensated mode while pulsing rf powers to both antennas, the plasma uniformity over the 300 mm diameter substrate could be improved from 7% for the CW conditions to about around 3.3% with the duty percentage of 30%.

  3. Overview of LH operation at JET

    NASA Astrophysics Data System (ADS)

    Kirov, K. K.; Ekedahl, A.; Bernardo, J.; Goniche, M.; Mailloux, J.; Nave, M. F. F.

    2015-12-01

    In this report key aspects of Lower Hybrid Current Drive (LHCD) operation at JET are presented. Amplitude and broadening of the Radio Frequency (RF) spectrum at about 3.7GHz and the frequency shift of the lower sideband were analyzed by means of new diagnostic utilizing RF spectra measurements. Dependencies on plasma density, LH power and the toroidal magnetic field were studied. Plasma rotation profiles with and without LH power were investigated. Power deposition and Current Drive (CD) profiles were assessed by means of a new Ray Tracing / Fokker Planck (RT/FP) code. Significant progress in a number of technological issues including the new supplementary arc protection system based on a visible camera imaging system and operation of the system with waveguides filled with N2 instead of greenhouse SF6 gas was achieved.

  4. Effect of noise on Frequency-Resolved Optical Gating measurements of ultrashort pulses

    SciTech Connect

    Fittinghoff, D.N.; DeLong, K.W.; Ladera, C.L.; Trebino, R.

    1995-02-01

    We study the effects of noise in Frequency-Resolved Optical Gating measurements of ultrashort pulses. We quantify the measurement accuracy in the presence of additive, muliplicative, and quantization noise, and discuss filtering and pre-processing of the data.

  5. A single-frequency double-pulse Ho:YLF laser for CO2-lidar

    NASA Astrophysics Data System (ADS)

    Kucirek, P.; Meissner, A.; Eiselt, P.; Höfer, M.; Hoffmann, D.

    2016-03-01

    A single-frequency q-switched Ho:YLF laser oscillator with a bow-tie ring resonator, specifically designed for highspectral stability, is reported. It is pumped with a dedicated Tm:YLF laser at 1.9 μm. The ramp-and-fire method with a DFB-diode laser as a reference is employed for generating single-frequency emission at 2051 nm. The laser is tested with different operating modes, including cw-pumping at different pulse repetition frequencies and gain-switched pumping. The standard deviation of the emission wavelength of the laser pulses is measured with the heterodyne technique at the different operating modes. Its dependence on the single-pass gain in the crystal and on the cavity finesse is investigated. At specific operating points the spectral stability of the laser pulses is 1.5 MHz (rms over 10 s). Under gain-switched pumping with 20% duty cycle and 2 W of average pump power, stable single-frequency pulse pairs with a temporal separation of 580 μs are produced at a repetition rate of 50 Hz. The measured pulse energy is 2 mJ (<2 % rms error on the pulse energy over 10 s) and the measured pulse duration is approx. 20 ns for each of the two pulses in the burst.

  6. Effect of laser pulse repetition frequency on the optical breakdown threshold of quartz glass

    SciTech Connect

    Kononenko, T V; Konov, V I; Schöneseiffen, S; Dausinger, F

    2013-08-31

    The thresholds of optical breakdown in the volume of quartz glass were measured in relation to the number of pulses under irradiation by ultrashort laser pulses with different pulse repetition frequencies (1 – 400 kHz). Increasing this frequency from 10 to 400 kHz was found to substantially lower the breakdown threshold for 500-fs long pulses (at a wavelength of 1030 nm) and to lower to a smaller degree for 5-ps long pulses (515 nm). A strong frequency dependence of the breakdown threshold is observed under the same conditions as a manifold decrease of the breakdown threshold with increase in the number of pulses in a pulse train. The dependence of the optical breakdown on the number of pulses is attributable to the accumulation of point defects under multiple subthreshold irradiation, which affects the mechanism of collisional ionisation. In this case, the frequency dependence of the breakdown threshold of quartz glass is determined by the engagement of shortlived defects in the ionisation mechanism. (interaction of laser radiation with matter)

  7. High pulse repetition frequency, multiple wavelength, pulsed CO2 lidar system for atmospheric transmission and target reflectance measurements

    NASA Astrophysics Data System (ADS)

    Ben-David, Avishai; Emery, Silvio L.; Gotoff, Steven W.; D'Amico, Francis M.

    1992-07-01

    A multiple wavelength, pulsed CO2 lidar system operating at a pulse repetition frequency of 200 Hz and permitting the random selection of CO2 laser wavelengths for each laser pulse is presented. This system was employed to measure target reflectance and atmospheric transmission by using laser pulse bursts consisting of groups with as many as 16 different wavelengths at a repetition rate of 12 Hz. The wavelength tuning mechanism of the transversely excited atmospheric laser consists of a stationary grating and a flat mirror controlled by a galvanometer. Multiple wavelength, differential absorption lidar (DIAL) measurements reduce the effects of differential target reflectance and molecular absorption interference. Examples of multiwavelength DIAL detection for ammonia and water vapor show the dynamic interaction between these two trace gases. Target reflectance measurements for maple trees in winter and autumn are presented.

  8. High pulse repetition frequency, multiple wavelength, pulsed CO(2) lidar system for atmospheric transmission and target reflectance measurements.

    PubMed

    Ben-David, A; Emery, S L; Gotoff, S W; D'Amico, F M

    1992-07-20

    A multiple wavelength, pulsed CO(2) lidar system operating at a pulse repetition frequency of 200 Hz and permitting the random selection of CO(2) laser wavelengths for each laser pulse is presented. This system was employed to measure target reflectance and atmospheric transmission by using laser pulse bursts consisting of groups with as many as 16 different wavelengths at a repetition rate of 12 Hz. The wavelength tuning mechanism of the transversely excited atmospheric laser consists of a stationary grating and a flat mirror controlled by a galvanometer. Multiple wavelength, differential absorption lidar (DIAL) measurements reduce the effects of differential target reflectance and molecular absorption interference. Examples of multiwavelength DIAL detection for ammonia and water vapor show the dynamic interaction between these two trace gases. Target reflectance measurements for maple trees in winter and autumn are presented. PMID:20725406

  9. Interaction between pulsed discharge and radio frequency discharge burst at atmospheric pressure

    SciTech Connect

    Zhang, Jie; Guo, Ying; Shi, Yuncheng; Zhang, Jing; Shi, J. J.

    2015-08-15

    The atmospheric pressure glow discharges (APGD) with dual excitations in terms of pulsed voltage and pulse-modulation radio frequency (rf) power are studied experimentally between two parallel plates electrodes. Pulse-modulation applied in rf APGD temporally separates the discharge into repetitive discharge bursts, between which the high voltage pulses are introduced to ignite sub-microsecond pulsed discharge. The discharge characteristics and spatio-temporal evolution are investigated by means of current voltage characteristics and time resolved imaging, which suggests that the introduced pulsed discharge assists the ignition of rf discharge burst and reduces the maintain voltage of rf discharge burst. Furtherly, the time instant of pulsed discharge between rf discharge bursts is manipulated to study the ignition dynamics of rf discharge burst.

  10. Experimental observation of short-pulse upshifted frequency microwaves from a laser-created overdense plasma.

    PubMed

    Yugami, Noboru; Niiyama, Toshihiko; Higashiguchi, Takeshi; Gao, Hong; Sasaki, Shigeo; Ito, Hiroaki; Nishida, Yasushi

    2002-03-01

    A short and frequency upshifted from a source microwave pulse is experimentally generated by the overdense plasma that is rapidly created by a laser. The source wave, whose frequency is 9 GHz, is propagating in the waveguide filled with tetrakis-dimethyl-amino-ethylene gas, which is to be converted to the overdense plasma by the laser. The detected frequency of the pulse is over 31.4 GHz and its duration is 10 ns. This technique has the potential for the generation of a tunable frequency source.

  11. Absolute frequency synthesis of pulsed coherent light waves through phase-modulation active optical feedback.

    PubMed

    Shimizu, K; Horiguchi, T; Koyamada, Y

    1996-11-15

    A novel method for the broadband absolute frequency synthesis of pulsed coherent lightwaves is demonstrated. It is based on pulse recirculation around an active optical feedback ring containing a delay-line fiber, an external phase modulator, an acousto-optic frequency shifter (AOFS), and a high-finesse Fabry-Perot étalon. The modulation frequency F(M) and the frequency shift F(AO) that are due to AOFS are designed so that their sum or difference equals the free-spectral range of the étalon and F(AO) is set at larger than the half-width at full maximum of its resonant peaks. If one of the peak frequencies is tuned to the frequency of the initial pulse, the frequency of the recirculating pulse jumps to the next peak for each round trip. In the experiment the absolute frequency is synthesized over a frequency span of 700 GHz around the initial stabilized frequency of the master laser.

  12. Pulse dynamics in a mode-locked fiber laser and its quantum limited comb frequency uncertainty.

    PubMed

    Bao, Chengying; Funk, Andrew C; Yang, Changxi; Cundiff, Steven T

    2014-06-01

    We present an experimental study of pulse dynamics in a mode-locked Er:fiber laser. By injecting a continuous wave laser with sinusoidal intensity modulation into the fiber laser, we are able to modulate the gain. Measuring the response of the pulse energy, central frequency, central pulse time, and phase to the gain modulation allows determination of the parameters that describe their coupling. Based on the experimentally derived parameters, we evaluate the free running comb linewidth and frequency uncertainty with feedback included, assuming quantum noise is the limiting factor. Optimization of fiber lasers is also discussed.

  13. A Low Frequency Survey of Giant Pulses from the Crab Pulsar

    NASA Astrophysics Data System (ADS)

    Eftekhari, Tarraneh; Taylor, Gregory B.; Stovall, Kevin

    2015-01-01

    We present a low frequency survey of giant pulses from the Crab Pulsar as observed with the first station of the Long Wavelength Array (LWA1). Over 2000 pulses have been detected between 20 - 84 MHz over a period of seven months. This is currently the largest sample of giant pulses below 100 MHz. We examine pulse characteristics, including width distributions, pulse shapes, and power law indices for amplitude distributions. These properties are compared to those derived at higher frequencies in an attempt to constrain emission mechanisms. Since low frequency pulses are particularly susceptible to pulse broadening, an analysis of the scattering tail probes the electron density of the interstellar medium, including line-of-sight crossings by ionized clouds and filaments within the nebula itself. We also discuss potential correlations with the gamma-ray emission during what appears to be a substantial increase in the occurrence of pulses over the seven month period. Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147. Support for operations and continuing development of the LWA1 is provided by the National Science Foundation under grants AST-1139963 and AST-1139974 of the University Radio Observatory program.

  14. Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating

    SciTech Connect

    Kane, D.J. ); Trebino, R. )

    1993-02-01

    The authors introduce a new technique, which they call frequency-resolved optical gating (FROG), for characterizing and displaying arbitrary femtosecond pulses. The method is simple, general, broad-band, and does not require a reference pulse. Using virtually any instantaneous nonlinear-optical effect, FROG involves measuring the spectrum of the signal pulse as a function of the delay between two input pulses. The resulting trace of intensity versus frequency and delay is related to the pulse's spectrogram, a visually intuitive transform containing both time and frequency information. They prove, using phase retrieval concepts, that the FROG trace yields the full intensity l(t) and phase [var phi](t) of an arbitrary ultrashort pulse with no physically significant ambiguities. They argue, in analogy with acoustics problems, that the FROG trace is in many ways as useful a representation of the pulse as the field itself. FROG appears to have temporal resolution limited only by the response of the nonlinear medium. They demonstrate the method using self-diffraction via the electronic Kerr effect in BK-7 glass and few [mu]J, 620 nm, linearly chirped, [approximately]200 fs pulses.

  15. Phase retrieval and time-frequency methods in the measurement of ultrashort laser pulses

    SciTech Connect

    DeLong, K.W.; Fittinghoff, D.N.; Ladera, C.L.; Trebino, R.

    1995-02-01

    Recently several techniques have become available to measure the time- (or frequency-) dependent intensity and phase of ultrashort laser pulses. One of these, Frequency-Resolved Optical Gating (FROG), is rigorous and has achieved single-laser-shot operation. FROG combines the concepts of time-frequency analysis in the form of spectrogram generation (in order to create a two-dimensional problem), and uses a phase-retrieval-based algorithm to invert the experimental data to yield the intensity and phase of the laboratory laser pulse. In FROG it is easy to generate a spectrogram of the unknown signal, and inversion of the spectrogram to recover the signal is the main goal. Because the temporal width of a femtosecond laser pulse is much shorter than anything achievable by electronics, FROG uses the pulse to measure itself. In FROG, the laser pulse is split into two replicas of itself by a partially reflecting beamsplitter, and the two replicas interact with each other in a medium with an instantaneous nonlinear-optical response. This interaction generates a signal field that is then frequency-resolved using a spectrometer. The spectrum of the signal field is measured for all relevant values of the temporal delay between the two pulses. Here, the authors employ FROG and FROG related techniques to measure the time-dependent intensity and phase of an ultrashort laser pulse.

  16. Role of PTHrP(1-34) Pulse Frequency Versus Pulse Duration to Enhance Mesenchymal Stromal Cell Chondrogenesis.

    PubMed

    Fischer, Jennifer; Ortel, Marlen; Hagmann, Sebastien; Hoeflich, Andreas; Richter, Wiltrud

    2016-12-01

    Generation of phenotypically stable, articular chondrocytes from mesenchymal stromal cells (MSCs) is still an unaccomplished task, with formation of abundant, hyaline extracellular matrix, and avoidance of hypertrophy being prime challenges. We recently demonstrated that parathyroid hormone-related protein (PTHrP) is a promising factor to direct chondrogenesis of MSCs towards an articular phenotype, since intermittent PTHrP application stimulated cartilage matrix production and reduced undesired hypertrophy. We here investigated the role of frequency, pulse duration, total exposure time, and underlying mechanisms in order to unlock the full potential of PTHrP actions. Human MSC subjected to in vitro chondrogenesis for six weeks were exposed to 2.5 nM PTHrP(1-34) pulses from days 7 to 42. Application frequency was increased from three times weekly (3 × 6 h/week) to daily maintaining either the duration of individual pulses (6 h/day) or total exposure time (18 h/week; 2.6 h/day). Daily PTHrP treatment significantly increased extracellular matrix deposition regardless of pulse duration and suppressed alkaline-phosphatase activity by 87%. High total exposure time significantly reduced cell proliferation at day 14. Pulse duration was critically important to significantly reduce IHH expression, but irrelevant for PTHrP-induced suppression of the hypertrophic markers MEF2C and IBSP. COL10A1, RUNX2, and MMP13 expression remained unaltered. Decreased IGFBP-2, -3, and -6 expression suggested modulated IGF-I availability in PTHrP groups, while drop of SOX9 protein levels during the PTHrP-pulse may delay chondroblast formation and hypertrophy. Overall, the significantly optimized timing of PTHrP-pulses demonstrated a vast potential to enhance chondrogenesis of MSC and suppress hypertrophy possibly via superior balancing of IGF- and SOX9-related mechanisms. J. Cell. Physiol. 231: 2673-2681, 2016. © 2016 Wiley Periodicals, Inc. PMID:27548511

  17. Excitation of low-frequency residual currents at combination frequencies of an ionising two-colour laser pulse

    NASA Astrophysics Data System (ADS)

    Vvedenskii, N. V.; Kostin, V. A.; Laryushin, I. D.; Silaev, A. A.

    2016-05-01

    We have studied the processes of excitation of low-frequency residual currents in a plasma produced through ionisation of gases by two-colour laser pulses in laser-plasma schemes for THz generation. We have developed an analytical approach that allows one to find residual currents in the case when one of the components of a two-colour pulse is weak enough. The derived analytical expressions show that the effective generation of the residual current (and hence the effective THz generation) is possible if the ratio of the frequencies in the two-colour laser pulse is close to a rational fraction with a not very big odd sum of the numerator and denominator. The results of numerical calculations (including those based on the solution of the three-dimensional time-dependent Schrödinger equation) agree well with the analytical results.

  18. Effect of saturated frequency chirping on mode-locked laser pulses.

    NASA Technical Reports Server (NTRS)

    Kim, D. M.; Tittel, F. K.; Rabson, T. A.

    1972-01-01

    A dye-induced nonlinear frequency chirping is analytically shown to have significant modifications on the nature of the output mode-locked lasers. It is shown that the saturated frequency sweeping is responsible for substantial pulse broadening as well as substructures.

  19. Comparison of ultrashort-pulse frequency-resolved-optical-gating traces for three common beam geometries

    SciTech Connect

    DeLong, K.W.; Trebino, R. ); Kane, D.J. )

    1994-09-01

    We recently introduced frequency-resolved optical gating (FROG), a technique for measuring the intensity and phase of an individual, arbitrary, ultrashort laser pulse. FROG can use almost any instantaneous optical nonlinearity, with the most common geometries being polarization gate, self-diffraction, and second-harmonic generation. The experimentally generated FROG trace is intuitive, visually appealing, and can yield quantitative information about the pulse parameters (such as temporal and spectral width and chirp). However, the qualitative and the quantitative features of the FROG trace depend strongly on the geometry used. We compare the FROG traces for several common ultrashort pulses for these three common geometries and, where possible, develop scaling rules that allow one to obtain quantitative information about the pulse directly from the experimental FROG trace. We illuminate the important features of the various FROG traces for transform-limited, linearly chirped, self-phase modulated, and nonlinearly chirped pulses, pulses with simultaneous linear chirp and self-phase modulation, and pulses with simultaneous linear chirp and cubic phase distortion, as well as double pulses, pulses with phase jumps, and pulses with complex intensity and phase substructure.

  20. Constant frequency pulsed phase-locked loop measuring device

    NASA Technical Reports Server (NTRS)

    Yost, William T. (Inventor); Kushnick, Peter W. (Inventor); Cantrell, John H. (Inventor)

    1993-01-01

    A measuring apparatus is presented that uses a fixed frequency oscillator to measure small changes in the phase velocity ultrasonic sound when a sample is exposed to environmental changes such as changes in pressure, temperature, etc. The invention automatically balances electrical phase shifts against the acoustical phase shifts in order to obtain an accurate measurement of electrical phase shifts.

  1. Green pulsed lidar-radar emitter based on a multipass frequency-shifting external cavity.

    PubMed

    Zhang, Haiyang; Brunel, Marc; Romanelli, Marco; Vallet, Marc

    2016-04-01

    This paper investigates the radio frequency (RF) up-conversion properties of a frequency-shifting external cavity on a laser beam. We consider an infrared passively Q-switched pulsed laser whose intensity modulation results from the multiple round-trips in the external cavity, which contains a frequency shifter. The output beam undergoes optical second-harmonic generation necessary to reach the green wavelength. We model the pulse train using a rate-equation model to simulate the laser pulses, together with a time-delayed interference calculation taking both the diffraction efficiency and the Gaussian beam propagation into account. The predictions are verified experimentally using a diode-pumped Nd:YAG laser passively Q-switched by Cr4+:YAG whose pulse train makes multiple round-trips in a mode-matched external cavity containing an acousto-optic frequency shifter driven at 85 MHz. Second-harmonic generation is realized in a KTP crystal, yielding RF-modulated pulses at 532 nm with a modulation contrast of almost 100%. RF harmonics up to the 6th order (1.020 GHz) are observed in the green output pulses. Such a RF-modulated green laser may find applications in underwater detection and ranging.

  2. Green pulsed lidar-radar emitter based on a multipass frequency-shifting external cavity.

    PubMed

    Zhang, Haiyang; Brunel, Marc; Romanelli, Marco; Vallet, Marc

    2016-04-01

    This paper investigates the radio frequency (RF) up-conversion properties of a frequency-shifting external cavity on a laser beam. We consider an infrared passively Q-switched pulsed laser whose intensity modulation results from the multiple round-trips in the external cavity, which contains a frequency shifter. The output beam undergoes optical second-harmonic generation necessary to reach the green wavelength. We model the pulse train using a rate-equation model to simulate the laser pulses, together with a time-delayed interference calculation taking both the diffraction efficiency and the Gaussian beam propagation into account. The predictions are verified experimentally using a diode-pumped Nd:YAG laser passively Q-switched by Cr4+:YAG whose pulse train makes multiple round-trips in a mode-matched external cavity containing an acousto-optic frequency shifter driven at 85 MHz. Second-harmonic generation is realized in a KTP crystal, yielding RF-modulated pulses at 532 nm with a modulation contrast of almost 100%. RF harmonics up to the 6th order (1.020 GHz) are observed in the green output pulses. Such a RF-modulated green laser may find applications in underwater detection and ranging. PMID:27139644

  3. LH2 airport requirements study

    NASA Technical Reports Server (NTRS)

    Brewer, G. D. (Editor)

    1976-01-01

    A preliminary assessment of the facilities and equipment which will be required at a representative airport is provided so liquid hydrogen LH2 can be used as fuel in long range transport aircraft in 1995-2000. A complete facility was conceptually designed, sized to meet the projected air traffic requirement. The facility includes the liquefaction plant, LH2, storage capability, and LH2 fuel handling system. The requirements for ground support and maintenance for the LH2 fueled aircraft were analyzed. An estimate was made of capital and operating costs which might be expected for the facility. Recommendations were made for design modifications to the reference aircraft, reflecting results of the analysis of airport fuel handling requirements, and for a program of additional technology development for air terminal related items.

  4. Compact frequency-quadrupled pulsed 1030nm fiber laser

    NASA Astrophysics Data System (ADS)

    McIntosh, Chris; Goldberg, Lew; Cole, Brian; DiLazaro, Tom; Hays, Alan D.

    2016-03-01

    A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a short length of highly-doped, large core (20μm), coiled polarization-maintaining ytterbium-doped double-clad fiber pumped by a wavelength-stabilized 975nm diode. It is passively Q-switched via a Cr4+:YAG saturable absorber and generates 2.4W at 1030nm in a 110μJ pulse train. Lithium triborate (LBO) and beta-barium borate (BBO) are used to achieve 325mW average power at the fourth harmonic. The laser's small form factor, narrow linewidth and modest power consumption are suitable for use in a man-portable ultraviolet Raman explosives detection system.

  5. Wafer-level pulsed-DC electromigration response at very high frequencies

    SciTech Connect

    Pierce, D.G.; Snyder, E.S.; Swanson, S.E.; Irwin, L.W.

    1994-03-01

    DC and pulsed-DC electromigration tests were performed at the Wafer-Level Pulsed-DC Electromigration Response and pulsed-DC electromigration tests were performed at the wafer level using standard and self-stressing test structures. DC characterization tests over a very large temperature range (180 to 560{degrees}C) were consistent with an interface diffusion mechanism in parallel with lattice diffusion. That data allowed for extraction of the respective activation energies and the diffusion coefficient of the rapid mechanism. The ability to extract simultaneously a defect-based diffusion coefficient and activation energy is significant given the extreme difficulty in making those measurements in aluminum. The pulsed-DC experiments were conducted over a range that includes the highest frequency to date, from DC to 500 MHz. Measurements were also made as a function of duty factor from 15% to 100% at selected frequencies. The data shows that the pulsed-DC lifetime is consistent with the average current density model at high (> 10 MHz) frequencies and showed no additional effects at the highest frequency tested (500 MHz). At low frequencies, we attribute the lessened enhancement to thermal effects rather than vacancy relaxation effects. Finally, the deviation in lifetime from the expected current density dependence, characterized over 1{1/2} orders of magnitude in current density, is explained in terms of a shift in the boundary condition for electromigration as the current density is decreased.

  6. SONOTECH, INC. FREQUENCY-TUNABLE PULSE COMBUSTION SYSTEM (CELLO PULSE BURNER) - INNOVATIVE TECHNOLOGY EVALUATION REPORT

    EPA Science Inventory

    Sonotech, Inc. (Sonotech) of Atlanta, Georgia, has developed a pulse combustion burner technology that claims to offer benefits when applied in a variety of combustion processes. The technology incorporates a combustor that can be tuned to induce large-amplitude acoustic or soni...

  7. System for adjusting frequency of electrical output pulses derived from an oscillator

    DOEpatents

    Bartholomew, David B.

    2006-11-14

    A system for setting and adjusting a frequency of electrical output pulses derived from an oscillator in a network is disclosed. The system comprises an accumulator module configured to receive pulses from an oscillator and to output an accumulated value. An adjustor module is configured to store an adjustor value used to correct local oscillator drift. A digital adder adds values from the accumulator module to values stored in the adjustor module and outputs their sums to the accumulator module, where they are stored. The digital adder also outputs an electrical pulse to a logic module. The logic module is in electrical communication with the adjustor module and the network. The logic module may change the value stored in the adjustor module to compensate for local oscillator drift or change the frequency of output pulses. The logic module may also keep time and calculate drift.

  8. Method and means for generating a synchronizing pulse from a repetitive wave of varying frequency

    DOEpatents

    DeVolpi, Alexander; Pecina, Ronald J.; Travis, Dale J.

    1976-01-01

    An event that occurs repetitively at continuously changing frequencies can be used to generate a triggering pulse which is used to synchronize or control. The triggering pulse is generated at a predetermined percentage of the period of the repetitive waveform without regard to frequency. Counts are accumulated in two counters, the first counting during the "on" fraction of the period, and the second counting during the "off" fraction. The counts accumulated during each cycle are compared. On equality the trigger pulse is generated. Count input rates to each counter are determined by the ratio of the on-off fractions of the event waveform and the desired phase relationship. This invention is of particular utility in providing a trigger or synchronizing pulse during the open period of the shutter of a high-speed framing camera during its acceleration as well as its period of substantially constant speed.

  9. Influences of impedance matching network on pulse-modulated radio frequency atmospheric pressure glow discharges

    SciTech Connect

    Huo, W. G.; Xu, K.; Sun, B.; Ding, Z. F.

    2012-08-15

    Pulse-modulated RF atmospheric pressure glow discharges (APDGs) were investigated in recent years to reduce the thermal accumulation and extend the operation region of the stable alpha glow mode. Different pulse-modulated voltage and current waveforms were acquired in previous experiments, but no attention was paid to the interpretation. We investigated this issue and associated phenomenon via positive and negative feedback effects derived from varying the series capacitor in the inversely L-shaped matching network used in our pulse-modulated RF APGD source. The evolutions of pulse-modulated RF waveforms were found to be associated with the feedback region and the pulsed plasma absorbed RF power. In the positive feedback region, pulse-modulated RF APGDs are relatively stable. In the negative feedback region, wide spikes as well as undershoots occur in RF voltage and current waveforms and the plasma absorbed RF power. In case of a high RF power discharge with a low modulation frequency, the pulse-modulated RF APGD is extinguished and re-ignited due to the enhanced undershoot during the initial pulse phase. The pulse-modulated RF APGD can transit from positive to negative feedback region in a range of series capacitance. Experimental results are discussed by the aid of equivalent circuit, negative and positive feedback effects.

  10. Coherent propagation effects and pulse self-compression under the conditions of two-photon resonant difference-frequency generation

    NASA Astrophysics Data System (ADS)

    Nazarkin, A.; Korn, G.

    1997-12-01

    We predict the possibility of using two-photon coherent propagation effects for generating pulses at the difference frequency with duration significantly shorter and intensity higher than those of the input pump and injection pulse.

  11. Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline.

    PubMed

    Hillier, David; Danson, Colin; Duffield, Stuart; Egan, David; Elsmere, Stephen; Girling, Mark; Harvey, Ewan; Hopps, Nicholas; Norman, Michael; Parker, Stefan; Treadwell, Paul; Winter, David; Bett, Thomas

    2013-06-20

    This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14). PMID:23842168

  12. Shaping pulses using frequency conversion with a modulated picosecond free electron laser

    SciTech Connect

    Hooper, B.A.; Madey, J.M.J.

    1995-12-31

    Computer simulations and experiments indicate that we can shape the infrared picosecond pulses of the Mark III FEL in amplitude, frequency, and phase. Strongly modulated fundamental and second harmonic pulses have been generated by operating the Mark III FEL in the regime of strong sideband growth. In this paper, we present the results of simulations and experiments for second harmonic generation with fundamental inputs from 2 to 3 {mu}m.

  13. Pulsed radio frequency interference effects on data communications via satellite transponder

    NASA Technical Reports Server (NTRS)

    Weinberg, A.; Hong, Y.

    1979-01-01

    Power-limited communication links may be susceptible to significant degradation if intentional or unintentional pulsed high level radio frequency interference (RFI) is present. Pulsed RFI is, in fact, of current interest to NASA in studies relating to its Tracking and Data Relay Satellite System (TDRSS). The present paper examines the impact of pulsed RFI on the error probability performance of a power-limited satellite communication link: the assumed modulation scheme is PN coded binary PSK. The composite effects of thermal noise, pulsed CW and pulsed Gaussian noise are analyzed, where RFI arrivals are assumed to follow Poisson statistics. Under the assumption that the satellite repeater is ideal and that integrate and dump filtering is employed at the ground receiver, an exact error probability expression and associated approximations are derived. Computed results are generated using an arbitrarily specified RFI model.

  14. Variable pulse repetition frequency output from an optically injected solid state laser.

    PubMed

    Kane, D M; Toomey, J P

    2011-02-28

    An optically injected solid state laser (OISSL) system is known to generate complex nonlinear dynamics within the parameter space of varying the injection strength of the master laser and the frequency detuning between the master and slave lasers. Here we show that within these complex nonlinear dynamics, a system which can be operated as a source of laser pulses with a pulse repetition frequency (prf) that can be continuously varied by a single control, is embedded. Generation of pulse repetition frequencies ranging from 200 kHz up to 4 MHz is shown to be achievable for an optically injected Nd:YVO4 solid state laser system from analysis of prior experimental and simulation results. Generalizing this to other optically injected solid state laser systems, the upper bound on the repetition frequency is of order the relaxation oscillation frequency for the lasers. The system is discussed in the context of prf versatile laser systems more generally. Proposals are made for the next generation of OISSLs that will increase understanding of the variable pulse repetition frequency operation, and determine its practical limitations. Such variable prf laser systems; both low powered, and, higher powered systems achieved using one or more optical power amplifier stages; have many potential applications from interrogating resonance behaviors in microscale structures, through sensing and diagnostics, to laser processing.

  15. Measurement of electron density transients in pulsed RF discharges using a frequency boxcar hairpin probe

    NASA Astrophysics Data System (ADS)

    Peterson, David; Coumou, David; Shannon, Steven

    2015-11-01

    Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of 10 microseconds has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and rectified to produce a DC signal read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating reflected signal dips. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. A dc sheath correction is applied for the grounded probe, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in both inductively and capacitively coupled systems, the latter driven by multiple frequencies where a subset of these frequencies are pulsed. Measurements are compared to previous published results, time resolved OES, and in-line measurement of plasma impedance. This work is supported by the NSF DOE partnership on plasma science, the NSF GOALI program, and MKS Instruments.

  16. Odors Pulsed at Wing Beat Frequencies are Tracked by Primary Olfactory Networks and Enhance Odor Detection

    PubMed Central

    Tripathy, Shreejoy J.; Peters, Oakland J.; Staudacher, Erich M.; Kalwar, Faizan R.; Hatfield, Mandy N.; Daly, Kevin C.

    2009-01-01

    Each down stroke of an insect's wings accelerates axial airflow over the antennae. Modeling studies suggest that this can greatly enhance penetration of air and air-born odorants through the antennal sensilla thereby periodically increasing odorant-receptor interactions. Do these periodic changes result in entrainment of neural responses in the antenna and antennal lobe (AL)? Does this entrainment affect olfactory acuity? To address these questions, we monitored antennal and AL responses in the moth Manduca sexta while odorants were pulsed at frequencies from 10–72 Hz, encompassing the natural wingbeat frequency. Power spectral density (PSD) analysis was used to identify entrainment of neural activity. Statistical analysis of PSDs indicates that the antennal nerve tracked pulsed odor up to 30 Hz. Furthermore, at least 50% of AL local field potentials (LFPs) and between 7–25% of unitary spiking responses also tracked pulsed odor up to 30 Hz in a frequency-locked manner. Application of bicuculline (200 μM) abolished pulse tracking in both LFP and unitary responses suggesting that GABAA receptor activation is necessary for pulse tracking within the AL. Finally, psychophysical measures of odor detection establish that detection thresholds are lowered when odor is pulsed at 20 Hz. These results suggest that AL networks can respond to the oscillatory dynamics of stimuli such as those imposed by the wing beat in a manner analogous to mammalian sniffing. PMID:20407584

  17. Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing

    NASA Astrophysics Data System (ADS)

    Mishra, Anurag; Yeom, Geun Young

    2016-09-01

    An electron emitting probe in saturated floating potential mode has been used to investigate the temporal evolution of plasma potential and the effect of substrate RF biasing on it for pulsed dual frequency (2 MHz/13.56 MHz) inductively coupled plasma (ICP) source. The low frequency power (P2MHz) has been pulsed at 1 KHz and a duty ratio of 50%, while high frequency power (P13.56MHz) has been used in continuous mode. The substrate has been biased with a separate bias power at (P12.56MHz) Argon has been used as a discharge gas. During the ICP power pulsing, three distinct regions in a typical plasma potential profile, have been identified as `initial overshoot', pulse `on-phase' and pulse `off-phase'. It has been found out that the RF biasing of the substrate significantly modulates the temporal evolution of the plasma potential. During the initial overshoot, plasma potential decreases with increasing RF biasing of the substrate, however it increases with increasing substrate biasing for pulse `on-phase' and `off-phase'. An interesting structure in plasma potential profile has also been observed when the substrate bias is applied and its evolution depends upon the magnitude of bias power. The reason of the evolution of this structure may be the ambipolar diffusion of electron and its dependence on bias power.

  18. Laser-induced resonance states as dynamic suppressors of ionization in high-frequency short pulses

    SciTech Connect

    Barash, Danny; Orel, Ann E.; Baer, Roi

    2000-01-01

    An adiabatic-Floquet formalism is used to study the suppression of ionization in short laser pulses. In the high-frequency limit the adiabatic equations involve only the pulse envelope where transitions are purely ramp effects. For a short-ranged potential having a single-bound state we show that ionization suppression is caused by the appearance of a laser-induced resonance state, which is coupled by the pulse ramp to the ground state and acts to trap ionizing flux. (c) 1999 The American Physical Society.

  19. Visualization and analysis of modulated pulses in magnetic resonance by joint time-frequency representations.

    PubMed

    Köcher, S S; Heydenreich, T; Glaser, S J

    2014-10-17

    We study the utility of joint time-frequency representations for the analysis of shaped or composite pulses for magnetic resonance. Such spectrograms are commonly used for the visualization of shaped laser pulses in optical spectroscopy. This intuitive representation provides additional insight compared to conventional approaches, which exclusively show either temporal or spectral information. We focus on the short-time Fourier transform, which provides not only amplitude but also phase information. The approach is illustrated for broadband inversion pulses, multiple quantum excitation and broadband heteronuclear decoupling. The physical interpretation and validity of the approach is discussed.

  20. Blind frequency-resolved optical-gating pulse characterization for quantitative differential multiphoton microscopy.

    PubMed

    Field, Jeffrey J; Durfee, Charles G; Squier, Jeff A

    2010-10-15

    We use a unique multifocal multiphoton microscope to directly characterize the pulse in the focal plane of a high-NA objective using second-harmonic generation frequency-resolved optical gating (FROG). Because of the nature of the optical setup, femtosecond laser pulses of orthogonal polarization states are generated in the focal plane, each acquiring a different spectral dispersion. By applying an additional constraint on the phase extraction algorithm, we simultaneously extract both the gate and probe pulses from a single spectrogram with a FROG error of 0.016. PMID:20967069

  1. Investigation of pulsed mode operation with the frequency tuned CAPRICE ECRIS

    NASA Astrophysics Data System (ADS)

    Maimone, F.; Tinschert, K.; Endermann, M.; Hollinger, R.; Kondrashev, S.; Lang, R.; Mäder, J.; Patchakui, P. T.; Spädtke, P.

    2016-02-01

    In order to increase the intensity of the highly charged ions produced by the Electron Cyclotron Resonance Ion Sources (ECRISs), techniques like the frequency tuning and the afterglow mode have been developed and in this paper the effect on the ion production is shown for the first time when combining both techniques. Recent experimental results proved that the tuning of the operating frequency of the ECRIS is a promising technique to achieve higher ion currents of higher charge states. On the other hand, it is well known that the afterglow mode of the ECRIS operation can provide more intense pulsed ion beams in comparison with the continuous wave (cw) operation. These two techniques can be combined by pulsing the variable frequency signal driving the traveling wave tube amplifier which provides the high microwave power to the ECRIS. In order to analyze the effect of these two combined techniques on the ion source performance, several experiments were carried out on the pulsed frequency tuned CAPRICE (Compacte source A Plusiers Résonances Ionisantes Cyclotron Electroniques)-type ECRIS. Different waveforms and pulse lengths have been investigated under different settings of the ion source. The results of the pulsed mode have been compared with those of cw operation.

  2. Ultrabroadband 50-130 THz pulses generated via phase-matcheddifference frequency mixing in LiIO3

    SciTech Connect

    Zentgraf, Thomas; Huber, Rupert; Nielsen, Nils C.; Chemla, DanielS.; Kaindl, Robert A.

    2006-10-10

    We report the generation of ultrabroadband pulses spanningthe 50-130 THz frequency range via phase-matched difference frequencymixing within the broad spectrum of sub-10 fs pulses in LiIO_3. Modelcalculations reproduce the octave-spanning spectra and predict few-cycleTHz pulse durations less than 20~;fs. The applicability of this scheme isdemonstrated with 9-fs pulses from a Ti:sapphire oscillator and with 7-fsamplified pulses from a hollow fiber compressor as pumpsources.

  3. Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap

    NASA Astrophysics Data System (ADS)

    Vicario, C.; Monoszlai, B.; Jazbinsek, M.; Lee, S.-H.; Kwon, O.-P.; Hauri, C. P.

    2015-09-01

    In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1-15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light.

  4. Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap

    PubMed Central

    Vicario, C.; Monoszlai, B.; Jazbinsek, M.; Lee, S. -H.; Kwon, O. -P.; Hauri, C. P.

    2015-01-01

    In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1–15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light. PMID:26400005

  5. 4.8GHz CMOS Frequency Multiplier Using Subharmonic Pulse-Injection Locking for Spurious Suppression

    NASA Astrophysics Data System (ADS)

    Takano, Kyoya; Motoyoshi, Mizuki; Fujishima, Minoru

    To realize low-power wireless transceivers, it is necessary to improve the performance of frequency synthesizers, which are typically frequency multipliers composed of a phase-locked loop (PLL). However, PLLs generally consume a large amount of power and occupy a large area. To improve the frequency multiplier, we propose a pulse-injection-locked frequency multiplier (PILFM), where a spurious signal is suppressed using a pulse input signal. An injection-locked oscillator (ILO) in a PILFM was fabricated by a 0.18µm 1P5M CMOS process. The core size is 10.8µm × 10.5µm. The power consumption of the ILO is 9.6µW at 250MHz, 255µW at 2.4GHz and 1.47mW at 4.8GHz. The phase noise is -105dBc/Hz at a 1MHz offset.

  6. Collisionless expansion of pulsed radio frequency plasmas. I. Front formation

    NASA Astrophysics Data System (ADS)

    Schröder, T.; Grulke, O.; Klinger, T.; Boswell, R. W.; Charles, C.

    2016-01-01

    The dynamics during plasma expansion are studied with the use of a versatile particle-in-cell simulation with a variable neutral gas density profile. The simulation is tailored to a radio frequency plasma expansion experiment [Schröder et al., J. Phys. D: Appl. Phys. 47(5), 055207 (2014)]. The experiment has shown the existence of a propagating ion front. The ion front features a strong electric field and features a sharp plasma potential drop similar to a double layer. However, the presented results of a first principle simulation show that, in general, the ion front does not have to be entangled with an electric field. The propagating electric field reflects the downstream ions, which stream with velocities up to twice as high as that of the ion front propagation. The observed ion density peak forms due to the accumulation of the reflected ions. The simulation shows that the ion front formation strongly depends on the initial ion density profile and is subject to a wave-breaking phenomenon. Virtual diagnostics in the code allow for a direct comparison with experimental results. Using this technique, the plateau forming in the wake of the plasma front could be indirectly verified in the expansion experiment. Although the simulation considers profiles only in one spatial dimensional, its results are qualitatively in a very good agreement with the laboratory experiment. It can successfully reproduce findings obtained by independent numerical models and simulations. This indicates that the effects of magnetic field structures and tangential inhomogeneities are not essential for the general expansion dynamic. The presented simulation will be used for a detailed parameter study dealt with in Paper II [Schröder et al., Phys. Plasma 23, 013512 (2016)] of this series.

  7. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire.

    PubMed

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping

    2016-01-01

    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication. PMID:27609521

  8. Pulsed Discharge Effects on Bacteria Inactivation in Low-Pressure Radio-Frequency Oxygen Plasma

    NASA Astrophysics Data System (ADS)

    Vicoveanu, Dragos; Ohtsu, Yasunori; Fujita, Hiroharu

    2008-02-01

    The sporicidal effects of low-pressure radio frequency (RF) discharges in oxygen, produced by the application of continuous and pulsed RF power, were evaluated. For all cases, the survival curves showed a biphasic evolution. The maximum efficiency for bacteria sterilization was obtained when the RF power was injected in the continuous wave mode, while in the pulsed mode the lowest treatment temperature was ensured. The inactivation rates were calculated from the microorganism survival curves and their dependencies on the pulse characteristics (i.e., pulse frequency and duty cycle) were compared with those of the plasma parameters. The results indicated that the inactivation rate corresponding to the first phase of the survival curves is related to the time-averaged intensity of the light emission by the excited neutral atoms in the pulsed plasma, whereas the inactivation rate calculated from the second slope of the survival curves and the time-averaged plasma density have similar behaviors, when the pulse parameters were modified.

  9. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire.

    PubMed

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping

    2016-01-01

    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication.

  10. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire

    PubMed Central

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping

    2016-01-01

    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication. PMID:27609521

  11. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire

    NASA Astrophysics Data System (ADS)

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping

    2016-09-01

    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication.

  12. Operation Mode on Pulse Modulation in Atmospheric Radio Frequency Glow Discharges

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Guo, Ying; Huang, Xiaojiang; Zhang, Jing; Shi, Jianjun

    2016-10-01

    The discharge operation regime of pulse modulated atmospheric radio frequency (RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha(α)-gamma(γ) mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge. supported by National Natural Science Foundation of China (Nos. 11475043 and 11375042)

  13. Multiple-frequency injection-seeded nanosecond pulsed laser without parasitic intensity modulation.

    PubMed

    Penninckx, D; Luce, J; Diaz, R; Bonville, O; Courchinoux, R; Lamaignère, L

    2016-07-15

    Thanks to a phase-modulated injection seeder, we report the operation of a nanosecond Nd:YAG Q-switched laser with pulses having both a large spectral bandwidth and a smooth temporal waveform. Because of the smooth temporal waveform, such pulses allow, for instance, reducing the impact of the Kerr effect and, because of the large spectral bandwidth, suppressing stimulated Brillouin scattering. We conducted a parametric study of the features of the generated pulses versus the injection conditions. We show that, as opposed to the central frequency (wavelength) of the seeder, the phase modulation frequency has to be carefully chosen, but it is not a critical parameter and does not require any particular feedback. PMID:27420504

  14. Single Frequency, Pulsed Laser Diode Transmitter for Dial Water Vapor Measurements at 935nm

    NASA Technical Reports Server (NTRS)

    Switzer, Gregg W.; Cornwell, Donald M., Jr.; Krainak, Michael A.; Abshire, James B.; Rall, Johnathan A. R.

    1998-01-01

    We report a tunable, single frequency, narrow linewidth, pulsed laser diode transmitter at 935.68nm for remote sensing of atmospheric water vapor. The transmitter consists of a CW, tunable, external cavity diode laser whose output is amplified 2OdB using a tapered diode amplifier. The output is pulsed for range resolved DIAL lidar by pulsing the drive current to the diode amplifier at 4kHz with a .5% duty cycle. The output from the transmitter is 36OnJ/pulse and is single spatial mode. It maintains a linewidth of less than 25MHz as its wavelength is tuned across the water vapor absorption line at 935.68nm. The transmitter design and its use in a water vapor measurement will be discussed.

  15. Compact gas sensor using a pulsed difference-frequency laser spectrometer.

    PubMed

    Seiter, M; Sigrist, M W

    1999-01-15

    We present a novel compact pulsed laser spectrometer based on difference-frequency mixing of a cw tunable external-cavity diode laser (795-825 nm) and a pulsed Nd:YAG laser (1064 nm) in bulk LiNbO(3) . The pulsed mid-IR source is continuously tunable from 3.16 to 3.67microm and exhibits a linewidth of only 154 MHz, a peak power of approximately 50microW , and a pulse duration of 6 ns at a 6.5-kHz repetition rate. Spectra of methane in room air and formaldehyde have been recorded at room-temperature operation in a multipass cell with deduced detection limits of 10 and 40 parts in 10(9) , respectively. PMID:18071424

  16. Mode selection and frequency tuning by injection in pulsed TEA-CO2 lasers

    NASA Technical Reports Server (NTRS)

    Flamant, P. H.; Menzies, R. T.

    1983-01-01

    An analytical model characterizing pulsed-TEA-CO2-laser injection locking by tunable CW-laser radiation is presented and used to explore the requirements for SLM pulse generation. Photon-density-rate equations describing the laser mechanism are analyzed in terms of the mode competition between photon densities emitted at two frequencies. The expression derived for pulsed dye lasers is extended to homogeneously broadened CO2 lasers, and locking time is defined as a function of laser parameters. The extent to which injected radiation can be detuned from the CO2 line center and continue to produce SLM pulses is investigated experimentally in terms of the analytical framework. The dependence of locking time on the detuning/pressure-broadened-halfwidth ratio is seen as important for spectroscopic applications requiring tuning within the TEA-laser line-gain bandwidth.

  17. Frequency-modulation spectroscopy with transform-limited nanosecond laser pulses.

    PubMed

    Eyler, E E; Gangopadhyay, S; Melikechi, N; Bloch, J C; Field, R W

    1996-02-01

    We demonstrate high-quality FM spectra with nanosecond laser pulses. Transform-limited pulses with FM sidebands are produced by pulsed amplification of a phase-modulated cw laser. The pulses can be shifted to the UV by nonlinear mixing. We report both initial experiments on I(2) and what is to our knowledge the first observation of a far-UV transition by FM spectroscopy, at 214.5 nm. Major advantages of this method include (1) spectral resolution of the order of 0.001 cm(-1), (2) better-defined optical phase, and (3) a much smaller and more easily detected modulation frequency, ~500 MHz. The absorption sensitivity is ~10(-4), and considerable further improvement is expected.

  18. Development of an Ultra High Frequency Gyrotron with a Pulsed Magnet

    SciTech Connect

    Idehara, T.; Kamada, M.; Tsuchiya, H.; Hayashi, T.; Agusu, La; Mitsudo, S.; Ogawa, I.; Manuilov, V. N.; Naito, K.; Yuyama, T.; Jiang, W.; Yatsui, K.

    2006-01-03

    An ultra-high frequency gyrotron is being developed as a THz radiation source by using a pulsed magnet. We have achieved the highest field intensity of 20.2 T. High frequency operation at the second harmonic will achieve 1.01 THz; the corresponding cavity mode is TE6,11,1. On the other hand, an ultra-high power gyrotron with a pulsed magnet is also being developed as a millimeter to submillimeter wave radiation source. The gyrotron is a large orbit gyrotron (LOG) using an intense relativistic electron beam (IREB). A pulsed power generator 'ETIGO-IV' is applied for generation of the IREB. A prototype relativistic LOG was constructed for fundamental operation. The output of the LOG will achieve 144 GHz and 9 MW; the corresponding cavity mode is TE1,4,1. Cavities for 2nd and 4th harmonic operations were designed by numerical simulation for achievement of higher frequency. The progress of development for prototype high frequency gyrotrons with pulsed magnets is presented.

  19. Variation in Cardiac Pulse Frequencies Modulates vSMC Phenotype Switching During Vascular Remodeling.

    PubMed

    Tosun, Zehra; McFetridge, Peter S

    2015-03-01

    In vitro perfusion systems have exposed vascular constructs to mechanical conditions that emulate physiological pulse pressure and found significant improvements in graft development. However, current models maintain constant, or set pulse/shear mechanics that do not account for the natural temporal variation in frequency. With an aim to develop clinically relevant small diameter vascular grafts, these investigations detail a perfusion culture model that incorporates temporal pulse pressure variation. Our objective was to test the hypothesis that short-term variation in heart rate, such as changes in respiratory activity, plays a significant role in vascular remodeling and graft development. The pulse rate of a healthy volunteer was logged to model the effect of daily activities on heart rate. Vascular bioreactors were used to deliver perfusion conditions based on modeled frequencies of temporal pulse variability, termed Physiologically Modeled Pulse Dynamics (PMPD). Acellular scaffolds derived from the human umbilical vein were seeded with human vascular smooth muscle cells and perfused under defined pulsatile conditions. vSMC exposed to constant pulse frequencies expressed a contractile phenotype, while exposure to PMPD drove cells to a synthetic state with continued cell proliferation, increased tensile strength and stiffness as well as diminished vasoactivity. Results show the temporal variation associated with normal heart physiology to have a profound effect on vascular remodeling and vasoactive function. While these models are representative of vascular regeneration further investigation is required to understanding these and other key regulators in vSMC phenotype switching in non-pathological or wound healing states. This understanding has important clinical implications that may lead to improved treatments that enhance vessel regeneration. PMID:26577103

  20. Measurement of complex ultrashort laser pulses using frequency-resolved optical gating

    NASA Astrophysics Data System (ADS)

    Xu, Lina

    This thesis contains three components of research: a detailed study of the performance of Frequency-Resolved Optical Gating (FROG) for measuring complex ultrashort laser pulses, a new method for measuring the arbitrary polarization state of an ultrashort laser pulse using Tomographic Ultrafast Retrieval of Transverse Light E-fields (TURTLE) technique, and new approach for measuring two complex pulses simultaneously using PG blind FROG. In recent decades, many techniques for measuring the full intensity and phase of ultrashort laser pulses have been proposed. These techniques include: Spectral Interferometry (SI)[1], Temporal Analysis by Dispersing a Pair of Light E-Field (TADPOLE)[2], Spectral Phase Interferometry for direct electric-field reconstruction (SPIDER)[3], and Frequency-Resolved Optical Gating (FROG)[4]. Each technique is actually a class of techniques that includes different variations on the original idea, such as SEA-SPIDER[5], ZAP SPIDER[6] are two variations of SPIDER. But most of these techniques for measuring ultrashort laser pulses either do not yield the complete time-dependent intensity and phase (e.g., autocorrelation), can at best only measure simple pulses (e.g., SPIDER), or need well characterized reference pulse. In this thesis, we compare the performance of three versions of FROG: second-harmonic-generation (SHG) FROG, polarization-gate (PG) FROG, and cross-correlation FROG (XFROG), the last of which requires a well-characterized reference pulse. We found that the XFROG algorithm converged in all cases and required only one initial guess. The PG FROG algorithm converged for 99% of the moderately complex pulses that we tried, and for over 95% of the most complex pulses (TBP ˜ 100). And the SHG FROG algorithm converged for 95% of the pulses that we tried and for over 80% of the most complex pulses. After some analysis, we found that noise filtering and adding more sampling points to the FROG trace solved the non-converging problems and we

  1. High frequency application of nanosecond pulsed electric fields alters cellular membrane disruption and fluorescent dye uptake

    NASA Astrophysics Data System (ADS)

    Steelman, Zachary A.; Tolstykh, Gleb P.; Beier, Hope T.; Ibey, Bennett L.

    2016-03-01

    Cells exposed to nanosecond-pulsed electric fields (nsPEF) exhibit a wide variety of nonspecific effects, including blebbing, swelling, intracellular calcium bursts, apoptotic and necrotic cell death, formation of nanopores, and depletion of phosphatidylinositol 4,5-biphosphate (PIP2) to induce activation of the inositol trisphosphate/diacylglycerol pathway. While several studies have taken place in which multiple pulses were delivered to cells, the effect of pulse repetition rate (PRR) is not well understood. To better understand the effects of PRR, a laser scanning confocal microscope was used to observe CHO-K1 cells exposed to ten 600ns, 200V pulses at varying repetition rates (5Hz up to 500KHz) in the presence of either FM 1-43, YO-PRO-1, or Propidium Iodide (PI) fluorescent dyes, probes frequently used to indicate nanoporation or permeabilization of the plasma membrane. Dye uptake was monitored for 30 seconds after pulse application at a rate of 1 image/second. In addition, a single long pulse of equivalent energy (200V, 6 μs duration) was applied to test the hypothesis that very fast PRR will approximate the biological effects of a single long pulse of equal energy. Upon examination of the data, we found strong variation in the relationship between PRR and uptake in each of the three dyes. In particular, PI uptake showed little frequency dependence, FM 1-43 showed a strong inverse relationship between frequency and internal cell fluorescence, and YO-PRO-1 exhibited a "threshold" point of around 50 KHz, after which the inverse trend observed in FM 1-43 was seen to reverse itself. Further, a very high PRR of 500 KHz only approximated the biological effects of a single 6 μs pulse in cells stained with YO-PRO-1, suggesting that uptake of different dyes may proceed by different physical mechanisms.

  2. Calcium homeostasis of isolated heart muscle cells exposed to pulsed high-frequency electromagnetic fields

    SciTech Connect

    Wolke, S.; Gollnick, F.; Meyer, R.; Neibig, U.; Elsner, R.

    1996-05-01

    The intracellular calcium concentration ([Ca{sup 2+}]{sub i}) of isolated ventricular cardiac myocytes of the guinea pig was measured during the application of pulsed high-frequency electromagnetic fields. The high-frequency fields were applied in a transverse electromagnetic cell designed to allow microscopic observation of the myocytes during the presence of the high-frequency fields. The [Ca{sup 2+}]{sub i} was measured as fura-2 fluorescence by means of digital image analysis. Both the carrier frequency and the square-wave pulse-modulation pattern were varied during the experiments (carrier frequencies: 900, 1,300, and 1,800 MHz pulse modulated at 217 Hz with 14% duty cycle; pulsation pattern at 900 MHz; continuous wave, 16 Hz,and 50 Hz modulation with 50% duty cycle and 30 kHz modulation with 80% duty cycle). The mean specific absorption rate (SAR) values in the solution were within one order of magnitude of 1 mW/kg. They varied depending on the applied carrier frequency and pulse pattern. The experiments were designed in three phases: 500 s of sham exposure, followed by 500 s of field exposure, then chemical stimulation without field. The chemical stimulation (K{sup +}-depolarization) indicated the viability of the cells. The K{sup +} depolarization yielded a significant increase in [Ca{sup 2+}]{sub i}. Significant differences between sham exposure and high-frequency field exposure were not found except when a very small but statistically significant difference was detected in the case of 900 MHz/50 Hz. However, this small difference was not regarded as a relevant effect of the exposure.

  3. Elimination of the light shift in rubidium gas cell frequency standards using pulsed optical pumping

    NASA Technical Reports Server (NTRS)

    English, T. C.; Jechart, E.; Kwon, T. M.

    1978-01-01

    Changes in the intensity of the light source in an optically pumped, rubidium, gas cell frequency standard can produce corresponding frequency shifts, with possible adverse effects on the long-term frequency stability. A pulsed optical pumping apparatus was constructed with the intent of investigating the frequency stability in the absence of light shifts. Contrary to original expectations, a small residual frequency shift due to changes in light intensity was experimentally observed. Evidence is given which indicates that this is not a true light-shift effect. Preliminary measurements of the frequency stability of this apparatus, with this small residual pseudo light shift present, are presented. It is shown that this pseudo light shift can be eliminated by using a more homogeneous C-field. This is consistent with the idea that the pseudo light shift is due to inhomogeneity in the physics package (position-shift effect).

  4. Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous, anomalous group velocity dispersion fibre amplifier

    SciTech Connect

    Zolotovskii, Igor' O; Korobko, D A; Okhotnikov, Oleg G; Sysolyatin, A A; Fotiadi, A A

    2012-09-30

    We examine conditions for the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous, anomalous group velocity dispersion fibres. The group velocity dispersion profiles necessary for the existence and amplification of such pulses in active fibres are identified and the pulse duration and chirp are determined as functions of propagation distance. (optical fibres, lasers and amplifiers. properties and applications)

  5. Plasma dynamics in a discharge produced by a pulsed dual frequency inductively coupled plasma source

    SciTech Connect

    Mishra, Anurag; Lee, Sehan; Yeom, Geun Y.

    2014-11-01

    Using a Langmuir probe, time resolved measurements of plasma parameters were carried out in a discharge produced by a pulsed dual frequency inductively coupled plasma source. The discharge was sustained in an argon gas environment at a pressure of 10 mTorr. The low frequency (P{sub 2} {sub MHz}) was pulsed at 1 kHz and a duty ratio of 50%, while high frequency (P{sub 13.56} {sub MHz}) was maintained in the CW mode. All measurements were carried out at the center of the discharge and 20 mm above the substrate. The results show that, at a particular condition (P{sub 2} {sub MHz} = 200 W and P{sub 13.56} {sub MHz }= 600 W), plasma density increases with time and stabilizes at up to ∼200 μs after the initiation of P{sub 2} {sub MHz} pulse at a plasma density of (2 × 10{sup 17} m{sup −3}) for the remaining duration of pulse “on.” This stabilization time for plasma density increases with increasing P{sub 2} {sub MHz} and becomes ∼300 μs when P{sub 2} {sub MHz} is 600 W; however, the growth rate of plasma density is almost independent of P{sub 2} {sub MHz}. Interestingly, the plasma density sharply increases as the pulse is switched off and reaches a peak value in ∼10 μs, then decreases for the remaining pulse “off-time.” This phenomenon is thought to be due to the sheath modulation during the transition from “pulse on” to “pulse off” and partly due to RF noise during the transition period. The magnitude of peak plasma density in off time increases with increasing P{sub 2} {sub MHz}. The plasma potential and electron temperature decrease as the pulse develops and shows similar behavior to that of the plasma density when the pulse is switched off.

  6. Radio-Frequency Pulses Emitted by Intracloud Lightning, as Observed From Space by the FORTE Satellite

    NASA Astrophysics Data System (ADS)

    Jacobson, A. R.

    2002-12-01

    The FORTE satellite has been used to trigger upon, and record, radio-frequency signals and optical signals from lightning. This talk will present recent results on the pulse characteristics, remote-sensing utility, and meteorological setting of two distinct types of radio-frequency impulses usually accompanying intracloud discharges. Emphasis will be given to implications of our recent FORTE results for future global lightning and severe-convective-storm monitoring, being proposed for the radio-frequency sensors on the Global Positioning System satellites.

  7. Pressure and Thrust Measurements of a High-Frequency Pulsed-Detonation Actuator

    NASA Technical Reports Server (NTRS)

    Nguyen, Namtran C.; Cutler, Andrew D.

    2008-01-01

    This paper describes the development of a small-scale, high-frequency pulsed detonation actuator. The device utilized a fuel mixture of H2 and air, which was injected into the device at frequencies of up to 1200 Hz. Pulsed detonations were demonstrated in an 8-inch long combustion volume, at approx.600 Hz, for the lambda/4 mode. The primary objective of this experiment was to measure the generated thrust. A mean value of thrust was measured up to 6.0 lb, corresponding to specific impulse of 2611 s. This value is comparable to other H2-fueled pulsed detonation engines (PDEs) experiments. The injection and detonation frequency for this new experimental case was approx.600 Hz, and was much higher than typical PDEs, where frequencies are usually less than 100 Hz. The compact size of the model and high frequency of detonation yields a thrust-per-unit-volume of approximately 2.0 lb/cu in, and compares favorably with other experiments, which typically have thrust-per-unit-volume values of approximately 0.01 lb/cu in.

  8. Pressure and Thrust Measurements of a High-Frequency Pulsed Detonation Tube

    NASA Technical Reports Server (NTRS)

    Nguyen, N.; Cutler, A. D.

    2008-01-01

    This paper describes measurements of a small-scale, high-frequency pulsed detonation tube. The device utilized a mixture of H2 fuel and air, which was injected into the device at frequencies of up to 1200 Hz. Pulsed detonations were demonstrated in an 8-inch long combustion volume, at about 600 Hz, for the quarter wave mode of resonance. The primary objective of this experiment was to measure the generated thrust. A mean value of thrust was measured up to 6.0 lb, corresponding to H2 flow based specific impulse of 2970 s. This value is comparable to measurements in H2-fueled pulsed detonation engines (PDEs). The injection and detonation frequency for this new experimental case was much higher than typical PDEs, where frequencies are usually less than 100 Hz. The compact size of the device and high frequency of detonation yields a thrust-per-unit-volume of approximately 2.0 pounds per cubic inch, and compares favorably with other experiments, which typically have thrust-per-unit-volume of order 0.01 pound per cubic inch. This much higher volumetric efficiency results in a potentially much more practical device than the typical PDE, for a wide range of potential applications, including high-speed boundary layer separation control, for example in hypersonic engine inlets, and propulsion for small aircraft and missiles.

  9. Transportation decreases the pulse frequency of growth hormone in the blood of prepubertal male calves.

    PubMed

    Kadokawa, Hiroya; Noguchi, Koutarou; Hajiri, Yuuki; Takeshita, Kazuhisa; Fujii, Youichi

    2013-01-01

    Both the mean concentration and the pulse pattern of growth hormone (GH) in the blood are important for the metabolism and body growth of calves. Transportation is reported to decrease blood GH concentrations in prepubertal male calves. However, the effect of transportation on GH pulsatility remains unknown. Because transportation is important in moving these calves from calf-production farms to markets or fattening farms, we tested whether transportation decreases their GH pulse frequency. Five calves were subjected to transportation by trucking (transport group), while five were left in their shed (non-transport group). Both groups were subsequently subjected to frequent blood sampling at 15-min intervals for 5 h. In the transport group, the cortisol concentrations increased in the first hour (P < 0.05) but significantly decreased thereafter (P < 0.05) to lower than those of the non-transport group. During the 5-hour study period, the transport group displayed a similar mean GH concentration relative to the non-transport group, but displayed a delayed first GH pulse, and a lower number of GH pulses than the non-transport group (P < 0.05). Hence, transportation is suggested to decrease GH pulse frequency under abnormal cortisol states, presumably suppressing metabolism and body growth in prepubertal male calves.

  10. Influence of phase mismatching on temporal waveform of pulse in the process of frequency conversion

    NASA Astrophysics Data System (ADS)

    Cui, Zijian; Liu, Dean; Liu, Yaqun; Miao, Jie; Zhou, Shenlei; Zhu, Baoqiang; Zhu, Jianqiang

    2015-08-01

    The influence of phase mismatching on output pulse temporal waveform in the process of second and third harmonic generation at various power densities with different detuning angles is studied based on nonlinear coupled-wave equations. The rules of different frequencies pulse width vary with the detuning angle have been analyzed quantitatively in potassium dihydrogen phosphate (KDP) crystals. The results of numerical simulation show that in high power laser frequency conversion system, the changes of fundamental pulse width are more sensitive to the detuning angle than second harmonic in the process of doubling, and the maximum variation of the full-width at half-maximum (FWHM) of fundamental at different detuning angles is about 19.0%. For tripling, the output pulse width changes of fundamental and second harmonic are sensitive to the detuning angle at high power density, and the maximum variation of their FWHM at different detuning angles are about 19.0% and 19.2%, respectively. However, the SH pulse width almost unchanged at low power density. The results of this study may provide a promising route to determine the best angle for phase matching in the angle adjusting process of experiment.

  11. Study on technology of high-frequency pulsed magnetic field strength measurement.

    PubMed

    Chen, Yi-Mei; Liu, Zhi-Peng; Yin, Tao

    2012-01-01

    High-frequency transient weak magnetic field is always involved in researches about biomedical engineering field while common magnetic-field sensors cannot work properly at frequencies as high as MHz. To measure the value of MHz-level weak pulsed magnetic-field strength accurately, this paper designs a measurement and calibration method for pulsed magnetic-field. In this paper, a device made of Nonferromagnetic material was independently designed and applied to pulsed magnetic field measurement. It held an accurately relative position between the magnetic field generating coil and the detecting coil. By applying a sinusoidal pulse to the generator, collecting the induced electromotive force of the detector, the final magnetic field strength was worked out through algorithms written in Matlab according to Faraday's Law. Experiments were carried out for measurement and calibration. Experiments showed that, under good stability and consistency, accurate measurement of magnetic-field strength of a sinepulse magnetic-field can be achieved, with frequency at 0.5, 1, 1.5 MHz and strength level at micro-Tesla. Calibration results carried out a measuring relative error about 2.5%.

  12. Phase and frequency structure of superradiance pulses generated by relativistic Ka-band backward-wave oscillator

    NASA Astrophysics Data System (ADS)

    Rostov, V. V.; Romanchenko, I. V.; Elchaninov, A. A.; Sharypov, K. A.; Shunailov, S. A.; Ul'masculov, M. R.; Yalandin, M. I.

    2016-08-01

    Phase and frequency stability of electromagnetic oscillations in sub-gigawatt superradiance (SR) pulses generated by an extensive slow-wave structure of a relativistic Ka-band backward-wave oscillator were experimentally investigated. Data on the frequency tuning and radiation phase stability of SR pulses with a variation of the energy and current of electron beam were obtained.

  13. In-vitro suppression of metabolic activity in malignant human glioblastomas due to pulsed - low frequency electric potential exposures

    NASA Astrophysics Data System (ADS)

    Schlichting, Abby; Waynant, Ronald W.; Tata, Darrell B.

    2010-02-01

    The role of pulsed - low repetition frequency electric potential was investigated in suppressing the metabolic activities of aggressive human brain cancer cells. Twenty four hours post exposure the glioblastomas were found to be significantly inhibited in their metabolic activity. The findings herein reveal a near complete inhibition of glioblastoma's metabolic activity through selective applications of low frequency pulsed electric potentials.

  14. Spectrographic phase-retrieval algorithm for femtosecond and attosecond pulses with frequency gaps

    NASA Astrophysics Data System (ADS)

    Seifert, B.; Wallentowitz, S.; Volkmann, U.; Hause, A.; Sperlich, K.; Stolz, H.

    2014-10-01

    We present a phase-reconstruction algorithm for a self-referenced spectrographic pulse characterization technique called “very advanced method for phase and intensity retrieval of e-fields” (VAMPIRE). This technique permits a spectral phase reconstruction of pulses with separated frequency components. The algorithm uses the particular characteristics of VAMPIRE spectrograms. It is a locally structured algorithm which is fast, robust, and it allows us to master stagnation problems. The algorithm is tested by use of both simulated and measured data.

  15. Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments.

    PubMed

    Benuzzi-Mounaix, A; Koenig, M; Boudenne, J M; Hall, T A; Batani, D; Scianitti, F; Masini, A; Di Santo, D

    1999-09-01

    We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. PMID:11970183

  16. Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments

    NASA Astrophysics Data System (ADS)

    Benuzzi-Mounaix, A.; Koenig, M.; Boudenne, J. M.; Hall, T. A.; Batani, D.; Scianitti, F.; Masini, A.; di Santo, D.

    1999-09-01

    We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target ~5×1013 W/cm2 to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps.

  17. Building a Pulse Detector using the Frequency Resolved Optical Gating Technique

    SciTech Connect

    Vallin, J

    2004-02-05

    We show how to construct a diagnostic optical layout known as Frequency Resolved Optical Gating (FROG) for an ir mode-locked laser by using the nonlinear effect known as second harmonic generation (SHG). In this paper, we explain the principle of operation and the theory upon which this diagnostic is based. Moreover, we described the procedure used to measure the duration and frequency components of a pulse. This process consists of calibrating the scales of a two-dimensional image, time delay vs. frequency, known as FROG spectrogram or FROG trace. This calibration of the time delay scale yields the correspondence between a pixel and time delay. Similarly, the calibration of the frequency scale yields the correspondence between a pixel, and frequency.

  18. Mitigation of impedance changes due to electroporation therapy using bursts of high-frequency bipolar pulses

    PubMed Central

    2015-01-01

    Background For electroporation-based therapies, accurate modeling of the electric field distribution within the target tissue is important for predicting the treatment volume. In response to conventional, unipolar pulses, the electrical impedance of a tissue varies as a function of the local electric field, leading to a redistribution of the field. These dynamic impedance changes, which depend on the tissue type and the applied electric field, need to be quantified a priori, making mathematical modeling complicated. Here, it is shown that the impedance changes during high-frequency, bipolar electroporation therapy are reduced, and the electric field distribution can be approximated using the analytical solution to Laplace's equation that is valid for a homogeneous medium of constant conductivity. Methods Two methods were used to examine the agreement between the analytical solution to Laplace's equation and the electric fields generated by 100 µs unipolar pulses and bursts of 1 µs bipolar pulses. First, pulses were applied to potato tuber tissue while an infrared camera was used to monitor the temperature distribution in real-time as a corollary to the electric field distribution. The analytical solution was overlaid on the thermal images for a qualitative assessment of the electric fields. Second, potato ablations were performed and the lesion size was measured along the x- and y-axes. These values were compared to the analytical solution to quantify its ability to predict treatment outcomes. To analyze the dynamic impedance changes due to electroporation at different frequencies, electrical impedance measurements (1 Hz to 1 MHz) were made before and after the treatment of potato tissue. Results For high-frequency bipolar burst treatment, the thermal images closely mirrored the constant electric field contours. The potato tissue lesions differed from the analytical solution by 39.7 ± 1.3 % (x-axis) and 6.87 ± 6.26 % (y-axis) for conventional unipolar pulses

  19. Increased efficiency of ion acceleration by using femtosecond laser pulses at higher harmonic frequency

    SciTech Connect

    Psikal, J.; Klimo, O.; Weber, S.; Margarone, D.

    2014-07-15

    The influence of laser frequency on laser-driven ion acceleration is investigated by means of two-dimensional particle-in-cell simulations. When ultrashort intense laser pulse at higher harmonic frequency irradiates a thin solid foil, the target may become re lativistically transparent for significantly lower laser pulse intensity compared with irradiation at fundamental laser frequency. The relativistically induced transparency results in an enhanced heating of hot electrons as well as increased maximum energies of accelerated ions and their numbers. Our simulation results have shown the increase in maximum proton energy and increase in the number of high-energy protons by a factor of 2 after the interaction of an ultrashort laser pulse of maximum intensity 7 × 10{sup 21 }W/cm{sup 2} with a fully ionized plastic foil of realistic density and of optimal thickness between 100 nm and 200 nm when switching from the fundamental frequency to the third harmonics.

  20. Noise sensitivity in frequency-resolved optical-gating measurements of ultrashort pulses

    SciTech Connect

    Fittinghoff, D.N.; DeLong, K.W.; Trebino, R.; Ladera, C.L.

    1995-10-01

    Frequency-resolved optical gating (FROG), a technique for measuring ultrashort laser pulses, involves producing a spectrogram of the pulse and then retrieving the pulse intensity and phase with an iterative algorithm. We study how several types of noise---multiplicative, additive, and quantization---affect pulse retrieval. We define a convergence criterion and find that the algorithm converges to a reasonable pulse field, even in the presence of 10% noise. Specifically, with appropriate filtering, 1% rms retrieval error is achieved for 10% multiplicative noise, 10% additive noise, and as few as 8 bits of resolution. For additive and multiplicative noise the retrieval errors decrease roughly as the square root of the amount of noise. In addition, the background induced in the wings of the pulse by additive noise is equal to the amount of additive noise on the trace. Thus the dynamic range of the measured intensity and phase is limited by a noise floor equal to the amount of additive noise on the trace. We also find that, for best results, a region of zero intensity should surround the nonzero region of the trace. Consequently, in the presence of additive noise, baseline subtraction is important. We also find that Fourier low-pass filtering improves pulse retrieval without introducing significant distortion, especially in high-noise cases. We show that the field errors in the temporal and the spectral domains are equal. Overall, the algorithm performs well because the measured trace contains {ital N}{sup 2} data points for a pulse that has only 2{ital N} degrees of freedom; FROG has built in redundancy. {copyright} {ital 1995} {ital Optical} {ital Society} {ital of} {ital America}.

  1. 1540-nm single frequency single-mode pulsed all fiber laser for coherent Doppler lidar

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Diao, Weifeng; Liu, Yuan; Liu, Jiqiao; Hou, Xia; Chen, Weibiao

    2015-02-01

    A single-mode single frequency eye-safe pulsed all fiber laser based on master oscillator power amplification structure is presented. This laser is composed of a narrow linewidth distributed laser diode seed laser and two-stage cascade amplifiers. 0.8 m longitudinally gradient strained erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber and two acoustic-optics modulators are adopted to enhance pulse extinction ratio. A peak power of 160 W and a pulse width of 200 ns at 10 kHz repetition rate are achieved with transform-limited linewidth and diffraction-limited beam quality. This laser will be employed in a compact short range coherent Doppler wind lidar.

  2. An overview of DREV's activities on pulsed CO2 laser transmitters: Frequency stability and lifetime aspects

    NASA Technical Reports Server (NTRS)

    Cruickshank, James; Pace, Paul; Mathieu, Pierre

    1987-01-01

    After introducing the desired features in a transmitter for laser radar applications, the output characteristics of several configurations of frequency-stable TEA-CO2 lasers are reviewed. Based on work carried out at the Defence Research Establishment Valcartier (DREV), output pulses are examined from short cavity lasers, CW-TEA hybrid lasers, and amplifiers for low power pulses. It is concluded that the technique of injecting a low-power laser beam into a TEA laser resonator with Gaussian reflectivity mirrors should be investigated because it appears well adapted to producing high energy, single mode, low chirp pulses. Finally, a brief report on tests carried out on catalysts composed of stannic oxide and noble metals demonstrates the potential of these catalysts, operating at close to room temperature, to provide complete closed-cycle laser operation.

  3. Efficient frequency doubling of femtosecond pulses with BIBO in an external synchronized cavity

    NASA Astrophysics Data System (ADS)

    Kanseri, Bhaskar; Bouillard, Martin; Tualle-Brouri, Rosa

    2016-12-01

    We experimentally demonstrate the second harmonic generation (SHG) of infrared femtosecond pulses using a BIBO crystal placed in an external ring cavity, synchronized with an input mode-locked laser at 78 MHz. A frequency doubling efficiency of 53% is achieved which is, to the best of our knowledge, the highest value ever reported for a low energy input beam of 1.4 nJ/pulse. Theoretical analysis of cavity related issues such as design, fundamental mode characteristics and fidelity against misalignments are also presented. The modeling of SHG cavity enables us to estimate the cavity losses and the mode matching visibility. Such synchronized SHG cavities in pulse domain, having higher SHG conversion efficiencies compared to their continuous wave counterparts, may find potential applications in scientific areas such as in photonics, and in quantum optics.

  4. Holographic frequency resolved optical gating for spatio-temporal characterization of ultrashort optical pulse

    NASA Astrophysics Data System (ADS)

    Mehta, Nikhil; Yang, Chuan; Xu, Yong; Liu, Zhiwen

    2014-09-01

    We introduce a novel method for characterizing the spatio-temporal evolution of ultrashort optical field by recording the spectral hologram of frequency resolved optical gating (FROG) trace. We show that FROG holography enables the measurement of phase (up to an overall constant) and group delay of the pulse which cannot be measured by conventional FROG method. To illustrate our method, we perform numerical simulation to generate holographic collinear FROG (cFROG) trace of a chirped optical pulse and retrieve its complex profile at multiple locations as it propagates through a hypothetical dispersive medium. Further, we experimentally demonstrate our method by retrieving a 67 fs pulse at three axial locations in the vicinity of focus of an objective lens and compute its group delay.

  5. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

    NASA Astrophysics Data System (ADS)

    Pilia, M.; Hessels, J. W. T.; Stappers, B. W.; Kondratiev, V. I.; Kramer, M.; van Leeuwen, J.; Weltevrede, P.; Lyne, A. G.; Zagkouris, K.; Hassall, T. E.; Bilous, A. V.; Breton, R. P.; Falcke, H.; Grießmeier, J.-M.; Keane, E.; Karastergiou, A.; Kuniyoshi, M.; Noutsos, A.; Osłowski, S.; Serylak, M.; Sobey, C.; ter Veen, S.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Bîrzan, L.; Bonafede, A.; Breitling, F.; Broderick, J. W.; Brüggen, M.; Ciardi, B.; Corbel, S.; de Geus, E.; de Jong, A.; Deller, A.; Duscha, S.; Eislöffel, J.; Fallows, R. A.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Gunst, A. W.; Hamaker, J. P.; Heald, G.; Horneffer, A.; Jonker, P.; Juette, E.; Kuper, G.; Maat, P.; Mann, G.; Markoff, S.; McFadden, R.; McKay-Bukowski, D.; Miller-Jones, J. C. A.; Nelles, A.; Paas, H.; Pandey-Pommier, M.; Pietka, M.; Pizzo, R.; Polatidis, A. G.; Reich, W.; Röttgering, H.; Rowlinson, A.; Schwarz, D.; Smirnov, O.; Steinmetz, M.; Stewart, A.; Swinbank, J. D.; Tagger, M.; Tang, Y.; Tasse, C.; Thoudam, S.; Toribio, M. C.; van der Horst, A. J.; Vermeulen, R.; Vocks, C.; van Weeren, R. J.; Wijers, R. A. M. J.; Wijnands, R.; Wijnholds, S. J.; Wucknitz, O.; Zarka, P.

    2016-02-01

    Context. LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. Aims: The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. Methods: We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120-167 MHz, 100 profiles) and low band (15-62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. Results: We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. We offer this catalogue of low-frequency pulsar profiles in a user friendly way via the EPN Database of Pulsar Profiles, http://www.epta.eu.org/epndb/

  6. Identification of High Frequency Pulses from Earthquake Asperities Along Chilean Subduction Zone Using Strong Motion

    NASA Astrophysics Data System (ADS)

    Ruiz, S.; Kausel, E.; Campos, J.; Saragoni, G. R.; Madariaga, R.

    2011-01-01

    The Chilean subduction zone is one of the most active of the world with M = 8 or larger interplate thrust earthquakes occurring every 10 years or so on the average. The identification and characterization of pulses propagated from dominant asperities that control the rupture of these earthquakes is an important problem for seismology and especially for seismic hazard assessment since it can reduce the earthquake destructiveness potential. A number of studies of large Chilean earthquakes have revealed that the source time functions of these events are composed of a number of distinct energy arrivals. In this paper, we identify and characterize the high frequency pulses of dominant asperities using near source strong motion records. Two very well recorded interplate earthquakes, the 1985 Central Chile (Ms = 7.8) and the 2007 Tocopilla (Mw = 7.7), are considered. In particular, the 2007 Tocopilla earthquake was recorded by a network with absolute time and continuos recording. From the study of these strong motion data it is possible to identify the arrival of large pulses coming from different dominant asperities. The recognition of the key role of dominant asperities in seismic hazard assessment can reduce overestimations due to scattering of attenuation formulas that consider epicentral distance or shortest distance to the fault rather than the asperity distance. The location and number of dominant asperities, their shape, the amplitude and arrival time of pulses can be one of the principal factors influencing Chilean seismic hazard assessment and seismic design. The high frequency pulses identified in this paper have permitted us to extend the range of frequency in which the 1985 Central Chile and 2007 Tocopilla earthquakes were studied. This should allow in the future the introduction of this seismological result in the seismic design of earthquake engineering.

  7. The influence of flight speed on the ranging performance of bats using frequency modulated echolocation pulses

    NASA Astrophysics Data System (ADS)

    Boonman, Arjan M.; Parsons, Stuart; Jones, Gareth

    2003-01-01

    Many species of bat use ultrasonic frequency modulated (FM) pulses to measure the distance to objects by timing the emission and reception of each pulse. Echolocation is mainly used in flight. Since the flight speed of bats often exceeds 1% of the speed of sound, Doppler effects will lead to compression of the time between emission and reception as well as an elevation of the echo frequencies, resulting in a distortion of the perceived range. This paper describes the consequences of these Doppler effects on the ranging performance of bats using different pulse designs. The consequences of Doppler effects on ranging performance described in this paper assume bats to have a very accurate ranging resolution, which is feasible with a filterbank receiver. By modeling two receiver types, it was first established that the effects of Doppler compression are virtually independent of the receiver type. Then, used a cross-correlation model was used to investigate the effect of flight speed on Doppler tolerance and range-Doppler coupling separately. This paper further shows how pulse duration, bandwidth, function type, and harmonics influence Doppler tolerance and range-Doppler coupling. The influence of each signal parameter is illustrated using calls of several bat species. It is argued that range-Doppler coupling is a significant source of error in bat echolocation, and various strategies bats could employ to deal with this problem, including the use of range rate information are discussed.

  8. Broadband short pulse measurement by autocorrelation with a sum-frequency generation set-up

    SciTech Connect

    Glotin, F.; Jaroszynski, D.; Marcouille, O.

    1995-12-31

    Previous spectral and laser pulse length measurements carried out on the CLIO FEL at wavelength {lambda}=8.5 {mu}m suggested that very short light pulses could be generated, about 500 fs wide (FWHM). For these measurements a Michelson interferometer with a Te crystal, as a non-linear detector, was used as a second order autocorrelation device. More recent measurements in similar conditions have confirmed that the laser pulses observed are indeed single: they are not followed by other pulses distant by the slippage length N{lambda}. As the single micropulse length is likely to depend on the slippage, more measurements at different wavelengths would be useful. This is not directly possible with our actual interferometer set-up, based on a phase-matched non-linear crystal. However, we can use the broadband non-linear medium provided by one of our users` experiments: Sum-Frequency Generation over surfaces. With such autocorrelation set-up, interference fringes are no more visible, but this is largely compensated by the frequency range provided. First tests at 8 {mu}m have already been performed to validate the technic, leading to results similar to those obtained with our previous Michelson set-up.

  9. LPS levels in root canals after the use of ozone gas and high frequency electrical pulses.

    PubMed

    Melo, Tiago André Fontoura de; Gründling, Grasiela Sabrina Longhi; Montagner, Francisco; Scur, Alcione Luiz; Steier, Liviu; Scarparo, Roberta Kochenborger; Figueiredo, José Antônio Poli de; Vier-Pelisser, Fabiana Vieira

    2016-01-01

    The present study aims to verify the effect of ozone gas (OZY® System) and high frequency electric pulse (Endox® System) systems on human root canals previously contaminated with Escherichia colilipopolysaccharide (LPS). Fifty single-rooted teeth had their dental crowns removed and root lengths standardized to 16 mm. The root canals were prepared up to #60 hand K-files and sterilized using gamma radiation with cobalt 60. The specimens were divided into the following five groups (n = 10) based on the disinfection protocol used: OZY® System, one 120-second-pulse (OZY 1p); OZY® System, four 24-second-pulses (OZY 4p); and Endox® System (ENDOX). Contaminated and non-contaminated canals were exposed only to apyrogenic water and used as positive (C+) and negative (C-) controls, respectively. LPS (O55:B55) was administered in all root canals except those belonging to group C-. After performing disinfection, LPS samples were collected from the canals using apyrogenic paper tips. Limulus Amoebocyte Lysate (LAL) was used to quantify the LPS levels, and the data obtained was analyzed using one-way ANOVA. The disinfection protocols used were unable to reduce the LPS levels significantly (p = 0.019). The use of ozone gas and high frequency electric pulses was not effective in eliminating LPS from the root canals. PMID:26981752

  10. Pulsing frequency induced change in optical constants and dispersion energy parameters of WO3 films grown by pulsed direct current magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Punitha, K.; Sivakumar, R.; Sanjeeviraja, C.

    2014-03-01

    In this work, we present the pulsing frequency induced change in the structural, optical, vibrational, and luminescence properties of tungsten oxide (WO3) thin films deposited on microscopic glass and fluorine doped tin oxide (SnO2:F) coated glass substrates by pulsed dc magnetron sputtering technique. The WO3 films deposited on SnO2:F substrate belongs to monoclinic phase. The pulsing frequency has a significant influence on the preferred orientation and crystallinity of WO3 film. The maximum optical transmittance of 85% was observed for the film and the slight shift in transmission threshold towards higher wavelength region with increasing pulsing frequency revealed the systematic reduction in optical energy band gap (3.78 to 3.13 eV) of the films. The refractive index (n) of films are found to decrease (1.832 to 1.333 at 550 nm) with increasing pulsing frequency and the average value of extinction coefficient (k) is in the order of 10-3. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (Ed) parameters, dielectric constants, plasma frequency, oscillator strength, and oscillator energy (Eo) of WO3 films were calculated and reported for the first time due to variation in pulsing frequency during deposition by pulsed dc magnetron sputtering. The Eo is change between 6.30 and 3.88 eV, while the Ed varies from 25.81 to 7.88 eV, with pulsing frequency. The Raman peak observed at 1095 cm-1 attributes the presence of W-O symmetric stretching vibration. The slight shift in photoluminescence band is attributed to the difference in excitons transition. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

  11. Frequency-resolved optical-gating measurements of ultrashort pulses using surface third-harmonic generation

    SciTech Connect

    Tsang, T.; Krumbuegel, M.A.; DeLong, K.W.; Fittinghoff, D.N.; Trebino, R.

    1996-09-01

    We demonstrate what is to our knowledge the first frequency-resolved optical gating (FROG) technique to measure ultrashort pulses from an unamplified Ti:sapphire laser oscillator without direction-of-time ambiguity. This technique utilizes surface third-harmonic generation as the nonlinear-optical effect and, surprisingly, is the most sensitive third-order FROG geometry yet. {copyright} {ital 1996 Optical Society of America.}

  12. High spatial frequency periodic structures induced on metal surface by femtosecond laser pulses.

    PubMed

    Yao, Jian-Wu; Zhang, Cheng-Yun; Liu, Hai-Ying; Dai, Qiao-Feng; Wu, Li-Jun; Lan, Sheng; Gopal, Achanta Venu; Trofimov, Vyacheslav A; Lysak, Tatiana M

    2012-01-16

    The high spatial frequency periodic structures induced on metal surface by femtosecond laser pulses was investigated experimentally and numerically. It is suggested that the redistribution of the electric field on metal surface caused by the initially formed low spatial frequency periodic structures plays a crucial role in the creation of high spatial frequency periodic structures. The field intensity which is initially localized in the grooves becomes concentrated on the ridges in between the grooves when the depth of the grooves exceeds a critical value, leading to the ablation of the ridges in between the grooves and the formation of high spatial frequency periodic structures. The proposed formation process is supported by both the numerical simulations based on the finite-difference time-domain technique and the experimental results obtained on some metals such as stainless steel and nickel.

  13. High efficiency, low frequency linear compressor proposed for Gifford-McMahon and pulse tube cryocoolers

    SciTech Connect

    Höhne, Jens

    2014-01-29

    In order to reduce the amount of greenhouse gas emissions, which are most likely the cause of substantial global warming, a reduction of overall energy consumption is crucial. Low frequency Gifford-McMahon and pulse tube cryocoolers are usually powered by a scroll compressor together with a rotary valve. It has been theoretically shown that the efficiency losses within the rotary valve can be close to 50%{sup 1}. In order to eliminate these losses we propose to use a low frequency linear compressor, which directly generates the pressure wave without using a rotary valve. First results of this development will be presented.

  14. COMPARISON OF RADIO-FREQUENCY INTERFERENCE MITIGATION STRATEGIES FOR DISPERSED PULSE DETECTION

    SciTech Connect

    Hogden, John; Vander Wiel, Scott; Michalak, Sarah; Bower, Geoffrey C.; Siemion, Andrew; Werthimer, Daniel

    2012-03-10

    Impulsive radio-frequency signals from astronomical sources are dispersed by the frequency-dependent index of refraction of the interstellar media and so appear as chirped signals when they reach Earth. Searches for dispersed impulses have been limited by false detections due to radio-frequency interference (RFI) and, in some cases, artifacts of the instrumentation. Many authors have discussed techniques to excise or mitigate RFI in searches for fast transients, but comparisons between different approaches are lacking. This work develops RFI mitigation techniques for use in searches for dispersed pulses, employing data recorded in a 'Fly's Eye' mode of the Allen Telescope Array as a test case. We gauge the performance of several RFI mitigation techniques by adding dispersed signals to data containing RFI and comparing false alarm rates at the observed signal-to-noise ratios of the added signals. We find that Huber filtering is most effective at removing broadband interferers, while frequency centering is most effective at removing narrow frequency interferers. Neither of these methods is effective over a broad range of interferers. A method that combines Huber filtering and adaptive interference cancelation provides the lowest number of false positives over the interferers considered here. The methods developed here have application to other searches for dispersed pulses in incoherent spectra, especially those involving multiple beam systems.

  15. Effect of master oscillator stability over pulse repetition frequency on hybrid semiconductor mode-locked laser

    NASA Astrophysics Data System (ADS)

    Castro Alves, D.; Abreu, Manuel; Cabral, Alexandre; Rebordão, J. M.

    2015-04-01

    Semiconductor mode-locked lasers are a very attractive laser pulse source for high accuracy length metrology. However, for some applications, this kind of device does not have the required frequency stability. Operating the laser in hybrid mode will increase the laser pulse repetition frequency (PRF) stability. In this study it is showed that the laser PRF is not only locked to the master oscillator but also maintains the same level of stability of the master oscillator. The device used in this work is a 10 mm long mode-locked asymmetrical cladding single section InAs/InP quantum dash diode laser emitting at 1580 nm with a pulse repetition frequency of ≈4.37 GHz. The laser nominal stability in passive mode (no external oscillator) shows direct dependence with the gain current and the stability range goes from 10-4 to 10-7. Several oscillators with different stabilities were used for the hybrid-mode operation (with external oscillator) and the resulting mode-locked laser stability compared. For low cost oscillators with low stability, the laser PRF stability achieves a value of 10-7 and for higher stable oscillation source (such as oven controlled quartz oscillators (OXCO)) the stability can reach values up to 10-12 (τ =1 s).

  16. Synthesis of Optical Frequencies and Ultrastable Femtosecond Pulse Trains from an Optical Reference Oscillator

    NASA Astrophysics Data System (ADS)

    Bartels, A.; Ramond, T. M.; Diddams, S. A.; Hollberg, L.

    Recently, atomic clocks based on optical frequency standards have been demonstrated [1,2]. A key element in these clocks is a femtosecond laser that downconverts the petahertz oscillation rate into countable ticks at 1 GHz. When compared to current microwave standards, these new optical clocks are expected to yield an improvement in stability and accuracy by roughly a factor of 1000. Furthermore, it is possible that the lowest noise microwave sources will soon be based on atomically-stabilized optical oscillators that have their frequency converted to the microwave domain via a femtosecond laser. Here, we present tests of the ability of femtosecond lasers to transfer stability from an optical oscillator to their repetition rates as well as to the associated broadband frequency comb. In a first experiment, we phase-lock two lasers to a stabilized laser diode and find that the relative timing jitter in their pulse trains can be on the order of 1 femtosecond in a 100 kHz bandwidth. It is important to distinguish this technique from previous work where a femtosecond laser has been stabilized to a microwave standard [3,4] or another femtosecond laser [5]. Furthermore, we extract highly stable microwave signals with a fractional frequency instability of 2×10-14 in 1 s by photodetection of the laser pulse trains. In a second experiment, we similarly phase-lock the femtosecond laser to an optical oscillator with linewidth less than 1 Hz [6]. The precision with which we can make the femtosecond frequency comb track this reference oscillator is then tested by a heterodyne measurement between a second stable optical oscillator and a mode of the frequency comb that is displaced 76 THz from the 1 Hz-wide reference. From this heterodyne signal we place an upper limit of 150 Hz on the linewidth of the elements of the frequency comb, limited by the noise in the measurement itself.

  17. Compact field programmable gate array-based pulse-sequencer and radio-frequency generator for experiments with trapped atoms

    SciTech Connect

    Pruttivarasin, Thaned; Katori, Hidetoshi

    2015-11-15

    We present a compact field-programmable gate array (FPGA) based pulse sequencer and radio-frequency (RF) generator suitable for experiments with cold trapped ions and atoms. The unit is capable of outputting a pulse sequence with at least 32 transistor-transistor logic (TTL) channels with a timing resolution of 40 ns and contains a built-in 100 MHz frequency counter for counting electrical pulses from a photo-multiplier tube. There are 16 independent direct-digital-synthesizers RF sources with fast (rise-time of ∼60 ns) amplitude switching and sub-mHz frequency tuning from 0 to 800 MHz.

  18. Compact field programmable gate array-based pulse-sequencer and radio-frequency generator for experiments with trapped atoms.

    PubMed

    Pruttivarasin, Thaned; Katori, Hidetoshi

    2015-11-01

    We present a compact field-programmable gate array (FPGA) based pulse sequencer and radio-frequency (RF) generator suitable for experiments with cold trapped ions and atoms. The unit is capable of outputting a pulse sequence with at least 32 transistor-transistor logic (TTL) channels with a timing resolution of 40 ns and contains a built-in 100 MHz frequency counter for counting electrical pulses from a photo-multiplier tube. There are 16 independent direct-digital-synthesizers RF sources with fast (rise-time of ∼60 ns) amplitude switching and sub-mHz frequency tuning from 0 to 800 MHz. PMID:26628171

  19. Detailed performance modeling of a pulsed high-power single-frequency Ti:sapphire laser.

    PubMed

    Wagner, Gerd; Wulfmeyer, Volker; Behrendt, Andreas

    2011-11-01

    Differential absorption lidar (DIAL) is a unique technique for profiling water vapor from the ground up to the lower stratosphere. For accurate measurements, the DIAL laser transmitter has to meet stringent requirements. These include high average power (up to 10 W) and high single-shot pulse energy, a spectral purity >99.9%, a frequency instability <60 MHz rms, and narrow spectral bandwidth (single-mode, <160 MHz). We describe extensive modeling efforts to optimize the resonator design of a Ti:sapphire ring laser in these respects. The simulations were made for the wavelength range of 820 nm, which is optimum for ground-based observations, and for both stable and unstable resonator configurations. The simulator consists of four modules: (1) a thermal module for determining the thermal lensing of the Brewster-cut Ti:sapphire crystal collinear pumped from both ends with a high-power, frequency-doubled Nd:YAG laser; (2) a module for calculating the in-cavity beam propagations for stable and unstable resonators; (3) a performance module for simulating the pumping efficiency and the laser pulse energy; and (4) a spectral module for simulating injection seeding and the spectral properties of the laser radiation including spectral impurity. Both a stable and an unstable Ti:sapphire laser resonator were designed for delivering an average power of 10 W at a pulse repetition frequency of 250 Hz with a pulse length of approximately 40 ns, satisfying all spectral requirements. Although the unstable resonator design is more complex to align and has a higher lasing threshold, it yields similar efficiency and higher spectral purity at higher overall mode volume, which is promising for long-term routine operations. PMID:22086016

  20. a Study of a High Frequency Miniature Reservoir-Less Pulse Tube

    NASA Astrophysics Data System (ADS)

    Garaway, I.; Grossman, G.

    2008-03-01

    A miniature high frequency reservoir-less pulse tube cryocooler has been designed and tested in our laboratory. The cryocooler having a regenerator length of 12.0 mm and an overall volume of 2.3cc (excluding the compressor) reached a low temperature of 146K and provided 100mW of cooling at 160K. This experimental study shows that it is possible to miniaturize a pulse tube cryocooler to very short regenerator lengths by implementing a few basic principles: Most importantly, high operating frequencies at small tidal displacements, a regenerator matrix with small hydraulic diameters, and increased helium fill pressures. This study also shows that as the operating frequency of a miniature cryocooler increases, the reservoir becomes less necessary as a phase shifting device. At higher frequencies and appropriate inertance tube geometries, the impedance and capacitance of the inertance tube itself takes over the phase shifting task. An outline of the design and modeling principles is presented along with some details of the experimental apparatus and testing procedures.

  1. Investigation of bed load sediment pulse sources and frequencies using spectral and wavelet analysis

    NASA Astrophysics Data System (ADS)

    Boyd, J. S.; Yager, E. M.

    2011-12-01

    analysis on the bedload transport data to determine if there are dominant frequencies in sediment pulses through space and time. Further spectral and wavelet analysis will reveal whether flow turbulence pulses correlate to instantaneous transport rates, rates shifted in time, or if no correlation exists. Preliminary results show little change in the power of transport from low to high sampling frequencies despite a decline in velocity power spectra with increasing sampling frequency. This decline is due to change in turbulent eddy size and strength at higher frequencies. The lack of change in the power of transport suggests that the more numerous small scale eddies provide nearly equal contribution to the overall bedload transport as less frequent, large scale eddies. Transport equality at all frequencies may also be due to the domino/cluster disintegration effect masking the changes in bedload transport power by frequency.

  2. Constant frequency pulsed phase-locked-loop instrument for measurement of ultrasonic velocity

    SciTech Connect

    Yost, William T; Cantrell, John H; Kushnick, Peter W

    1991-10-01

    A new instrument based on a constant frequency pulsed phase-locked-loop (CFPPLL) concept has been developed to accurately measure the ultrasonicwavevelocity in liquids and changes in ultrasonicwavevelocity in solids and liquids. An analysis of the system shows that it is immune to many of the frequency-dependent effects that plague other techniques including the constant phase shifts of reflectors placed in the path of the ultrasonicwave.Measurements of the sound velocity in ultrapure water are used to confirm the analysis. The results are in excellent agreement with values from the literature, and establish that the CFPPLL provides a reliable, accurate way to measurevelocities, as well as for monitoring small changes in velocity without the sensitivity to frequency-dependent phase shifts common to other measurement systems. The estimated sensitivity to phase changes is better than a few parts in 10{sup 7}.

  3. Constant frequency pulsed phase-locked-loop instrument for measurement of ultrasonic velocity

    NASA Technical Reports Server (NTRS)

    Yost, William T.; Cantrell, John H.; Kushnick, Peter W.

    1991-01-01

    A new instrument based on a constant-frequency pulsed phase-locked-loop (CFPPLL) concept has been developed to accurately measure the ultrasonic wave velocity in liquids and changes in ultrasonic wave velocity in solids and liquids. An analysis of the system shows that it is immune to many of the frequency-dependent effects that plague other techniques. Measurements of the sound velocity in ultrapure water are used to confirm the analysis. The results are in excellent agreement with values from the literature, and establish that the CFPPLL provides a reliable, accurate way to measure velocities, as well as for monitoring small changes in velocity without the sensitivity to frequency-dependent phase shifts common to other measurement systems. The estimated sensitivity to phase changes is better than a few parts in 10 to the 7th.

  4. Frequency dependent FMR studies on pulsed laser ablated YIG films deposited on (111) GGG substrate

    NASA Astrophysics Data System (ADS)

    Bhoi, B.; Venkataramani, N.; Aiyar, R. P. R. C.; Prasad, Shiva; Kostylev, Mikhail; Stamps, R. L.

    2013-02-01

    Ferromagnetic Resonance (FMR) studies were carried out as a function of frequency on ex-situ post-annealed (Ta: 700 °C and 850 °C) YIG films. The films were deposited at TS: 750 °C on polished single crystal (111) GGG substrate using pulsed laser deposition. Both the films (Ta: 700 °C, 850 °C) shows a in-plane FMR line-width (ΔH) of 40 Oe and 50 Oe respectively which remains constant over a broad frequency range (8 GHz-20 GHz). On the other hand, a linear increment in in-plane resonance field (HR) has been observed with the increase in frequency of RF signal. The effective saturation magnetization (4πMeff) has been estimated for both the films using Kittel's equations and is found as 90% of the bulk value for the film deposited at 750 °C, annealed at 700 °C.

  5. Effect of source frequency and pulsing on the SiO2 etching characteristics of dual-frequency capacitive coupled plasma

    NASA Astrophysics Data System (ADS)

    Kim, Hoe Jun; Jeon, Min Hwan; Mishra, Anurag Kumar; Kim, In Jun; Sin, Tae Ho; Yeom, Geun Young

    2015-01-01

    A SiO2 layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C4F8 gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56-60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO2 etch characteristics were investigated. By pulsing the rf power, an increased SiO2 etch selectivity was observed with decreasing SiO2 etch rate. However, when the rf power frequency was increased, not only a higher SiO2 etch rate but also higher SiO2 etch selectivity was observed for both CW and pulse modes. A higher CF2/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO2 surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C-Fx bonding on the SiO2 surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO2 etch selectivity over the ACL. The increase of the SiO2 etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF2/F ratio in the plasma. The SiO2 etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.

  6. Time resolved dosimetry of human brain exposed to low frequency pulsed magnetic fields

    NASA Astrophysics Data System (ADS)

    Paffi, Alessandra; Camera, Francesca; Lucano, Elena; Apollonio, Francesca; Liberti, Micaela

    2016-06-01

    An accurate dosimetry is a key issue to understanding brain stimulation and related interaction mechanisms with neuronal tissues at the basis of the increasing amount of literature revealing the effects on human brain induced by low-level, low frequency pulsed magnetic fields (PMFs). Most literature on brain dosimetry estimates the maximum E field value reached inside the tissue without considering its time pattern or tissue dispersivity. Nevertheless a time-resolved dosimetry, accounting for dispersive tissues behavior, becomes necessary considering that the threshold for an effect onset may vary depending on the pulse waveform and that tissues may filter the applied stimulatory fields altering the predicted stimulatory waveform’s size and shape. In this paper a time-resolved dosimetry has been applied on a realistic brain model exposed to the signal presented in Capone et al (2009 J. Neural Transm. 116 257-65), accounting for the broadband dispersivity of brain tissues up to several kHz, to accurately reconstruct electric field and current density waveforms inside different brain tissues. The results obtained by exposing the Duke’s brain model to this PMF signal show that the E peak in the brain is considerably underestimated if a simple monochromatic dosimetry is carried out at the pulse repetition frequency of 75 Hz.

  7. Time resolved dosimetry of human brain exposed to low frequency pulsed magnetic fields

    NASA Astrophysics Data System (ADS)

    Paffi, Alessandra; Camera, Francesca; Lucano, Elena; Apollonio, Francesca; Liberti, Micaela

    2016-06-01

    An accurate dosimetry is a key issue to understanding brain stimulation and related interaction mechanisms with neuronal tissues at the basis of the increasing amount of literature revealing the effects on human brain induced by low-level, low frequency pulsed magnetic fields (PMFs). Most literature on brain dosimetry estimates the maximum E field value reached inside the tissue without considering its time pattern or tissue dispersivity. Nevertheless a time-resolved dosimetry, accounting for dispersive tissues behavior, becomes necessary considering that the threshold for an effect onset may vary depending on the pulse waveform and that tissues may filter the applied stimulatory fields altering the predicted stimulatory waveform’s size and shape. In this paper a time-resolved dosimetry has been applied on a realistic brain model exposed to the signal presented in Capone et al (2009 J. Neural Transm. 116 257–65), accounting for the broadband dispersivity of brain tissues up to several kHz, to accurately reconstruct electric field and current density waveforms inside different brain tissues. The results obtained by exposing the Duke’s brain model to this PMF signal show that the E peak in the brain is considerably underestimated if a simple monochromatic dosimetry is carried out at the pulse repetition frequency of 75 Hz.

  8. Songbirds use pulse tone register in two voices to generate low-frequency sound.

    PubMed

    Jensen, Kenneth K; Cooper, Brenton G; Larsen, Ole N; Goller, Franz

    2007-11-01

    The principal physical mechanism of sound generation is similar in songbirds and humans, despite large differences in their vocal organs. Whereas vocal fold dynamics in the human larynx are well characterized, the vibratory behaviour of the sound-generating labia in the songbird vocal organ, the syrinx, is unknown. We present the first high-speed video records of the intact syrinx during induced phonation. The syrinx of anaesthetized crows shows a vibration pattern of the labia similar to that of the human vocal fry register. Acoustic pulses result from short opening of the labia, and pulse generation alternates between the left and right sound sources. Spontaneously calling crows can also generate similar pulse characteristics with only one sound generator. Airflow recordings in zebra finches and starlings show that pulse tone sounds can be generated unilaterally, synchronously or by alternating between the two sides. Vocal fry-like dynamics therefore represent a common production mechanism for low-frequency sounds in songbirds. These results also illustrate that complex vibration patterns can emerge from the mechanical properties of the coupled sound generators in the syrinx. The use of vocal fry-like dynamics in the songbird syrinx extends the similarity to this unusual vocal register with mammalian sound production mechanisms.

  9. Detection and Characterization of Flaws in Sprayed on Foam Insulation with Pulsed Terahertz Frequency Electromagnetic Waves

    NASA Technical Reports Server (NTRS)

    Winfree, William P.; Madaras, Eric I.

    2005-01-01

    The detection and repair of flaws such as voids and delaminations in the sprayed on foam insulation of the external tank reduces the probability of foam debris during shuttle ascent. The low density of sprayed on foam insulation along with it other physical properties makes detection of flaws difficult with conventional techniques. An emerging technology that has application for quantitative evaluation of flaws in the foam is pulsed electromagnetic waves at terahertz frequencies. The short wavelengths of these terahertz pulses make them ideal for imaging flaws in the foam. This paper examines the application of terahertz pulses for flaw detection in foam characteristic of the foam insulation of the external tank. Of particular interest is the detection of voids and delaminations, encapsulated in the foam or at the interface between the foam and a metal backing. The technique is shown to be capable of imaging small voids and delaminations through as much as 20 cm of foam. Methods for reducing the temporal responses of the terahertz pulses to improve flaw detection and yield quantitative characterizations of the size and location of the flaws are discussed.

  10. Generation of high-energy self-phase-stabilized pulses by difference-frequency generation followed by optical parametric amplification.

    PubMed

    Manzoni, C; Vozzi, C; Benedetti, E; Sansone, G; Stagira, S; Svelto, O; De Silvestri, S; Nisoli, M; Cerullo, G

    2006-04-01

    We produce ultrabroadband self-phase-stabilized near-IR pulses by a novel approach where a seed pulse, obtained by difference-frequency generation of a hollow-fiber broadened supercontinuum, is amplified by a two-stage optical parametric amplifier. Energies up to 20 microJ with a pulse spectrum extending from 1.2 to 1.6 microm are demonstrated, and a route for substantial energy scaling is indicated.

  11. Precipitation pulse size and frequency controls on dryland litter decomposition rates

    NASA Astrophysics Data System (ADS)

    Kurupas, K. L.; Throop, H.

    2014-12-01

    Drylands are an important component of the global carbon (C) cycle, accounting for 40% of the land area and 20% of the soil organic C globally. Litter decomposition is a key biogeochemical process, controlling C and nutrient cycling. While simple decomposition models successfully predict decomposition rates in many systems based on climate variables, there is a disconnect between the modeled and measured rates decomposition in drylands. This disconnect may stem from abiotic factors of importance in drylands, such as photodegradation and soil-litter mixing, not being taken into account. Soil-litter mixing can accelerate decomposition, but the underlying mechanisms are poorly understood. Potential mechanisms include microclimate buffering, physical abrasion, and enhanced microbial colonization. Recent work suggests that litter decomposition is remarkably insensitive to climate variables, at least when variables are presented as long temporal-scale values (e.g., annual precipitation). We hypothesized that decomposition would be more strongly affected by litter moisture content than total precipitation (PPT) alone. Thus, frequent, small PPT pulses would accelerate decomposition more than larger, but infrequent pulses. Furthermore, soil-litter mixing would enhance decomposition by buffering litter moisture content. To test the combined influence of soil-litter mixing and PPT pulses on decomposition, we incubated litter and soil in a semi-controlled greenhouse which simulated dryland summer temperatures. Two litter types (grass and shrub) were incubated under two levels of soil-litter mixing (no mixing and complete soil-litter mixing) and with 16 different PPT treatments (a factorial combination of four PPT pulses sizes and four PPT frequencies). We measured instantaneous CO2 flux throughout the 30 day incubation and mass loss at the end of the incubation. Shrub litter decomposed faster than grass litter. Flux rates generally peaked at day 8 and declined thereafter. CO2

  12. Electron acceleration in relativistic plasma waves generated by a single frequency short-pulse laser

    SciTech Connect

    Coverdale, C.A.; Darrow, C.B.; Decker, C.D.; Mori, W.B.; Tzeng, K.C., Clayton, C.E.; Marsh, K.A.; Joshi, C.

    1995-04-27

    Experimental evidence for the acceleration of electrons in a relativistic plasma wave generated by Raman forward scattering (SRS-F) of a single-frequency short pulse laser are presented. A 1.053 {mu}m, 600 fsec, 5 TW laser was focused into a gas jet with a peak intensity of 8{times}10{sup 17} W/cm{sup 2}. At a plasma density of 2{times}10{sup 19} cm{sup {minus}3}, 2 MeV electrons were detected and their appearance was correlated with the anti-Stokes laser sideband generated by SRS-F. The results are in good agreement with 2-D PIC simulations. The use of short pulse lasers for making ultra-high gradient accelerators is explored.

  13. Pulsed radio-frequency discharge inductively coupled plasma mass spectrometry for oxide analysis

    NASA Astrophysics Data System (ADS)

    Li, Weifeng; Yin, Zhibin; Hang, Wei; Li, Bin; Huang, Benli

    2016-08-01

    A direct solid sampling technique has been developed based on a pulsed radio-frequency discharge (RFD) in mixture of N2 and Ar environment at atmospheric pressure. With an averaged input power of 65 W, a crater with the diameter of 80 μm and depth of 50 μm can be formed on sample surface after discharge for 1 min, suggesting the feasibility of the pulsed RFD for sampling nonconductive solids. Combined with inductively coupled plasma mass spectrometry (ICPMS), this technique allows to measure elemental composition of solids directly with relative standard deviation (RSD) of ~ 20%. Capability of quantitative analysis was demonstrated by the use of soil standards and artificial standards. Good calibration linearity and limits of detection (LODs) in range of 10- 8-10- 9 g/g were achieved for most elements.

  14. Hypothyroidism affects pulsatile LH secretion in pubertal orchiectomized rats.

    PubMed

    Maia, A L; Favaretto, A L; Carvaho, T L; Rodrigues, J A; Iazigi, N

    1995-08-01

    The present study evaluated the effect of hypothyroidism on the pituitary-testicular axis in rats rendered hypothyroid on the beginning of puberty. Rats were treated with propylthiouracil for 8 weeks and killed for determination of hormonal status and body parameters. For determination of pulsatile LH secretion other animals were orchiectomized two weeks before sampling. Analysis of the results led us to conclude that although the absolute weight of sex organs tended to decrease in hypothyroid animals, the relative weights were equal or higher than control, suggesting that the development of these organs were not affected by hypothyroidism; the androgenic activity of hypothyroid rat testes were preserved; basal plasma levels of pituitary hormones were similar in control and hypothyroid groups; the pulsatile LH secretion showed a decrease in the number of pulses, nadir mean and total LH secretion in hypothyroid animals. Our results demonstrate that although hypothalamic-pituitary axis of hypothyroid pubertal rats displays an abnormal pulsation LH release, no evidences of abnormalities in the reproductive system functions were found.

  15. Correlation of hemodynamically significant internal carotid stenosis with pulsed Doppler frequency analysis.

    PubMed Central

    Blackshear, W M; Lamb, S L; Kollipara, V S; Anderson, J D; Murtagh, F R; Shah, C P; Farber, M S

    1984-01-01

    Systolic and mean pressure gradients across internal carotid stenoses were measured at the time of carotid endarterectomy in the arteries of 90 patients, all of whom underwent angiography. Eighty-two of these patients also had pulsed Doppler ultrasonic arteriography with real-time spectrum analysis. There were 71 (79%) high grade stenoses of greater than 50% diameter reduction by angiography. Significant systolic pressure gradients (greater than or equal to 10 mmHg) were identified in 41 patients (46%), 38 (46%) of whom underwent ultrasonic evaluation. A pulsed Doppler frequency measured within the stenosis equal to or greater than 6.5 kiloHertz had a sensitivity of 94.7% (36/38) in identifying pressure reducing lesions with a specificity of 47.7% (21/44). Positive predictive value was 61% (36/59). Angiographic criteria (50% diameter reduction) exhibited a sensitivity of 97.6% (40/41), a specificity of 36.7% (18/49) and a positive predictive value of 56.3% (40/71). Negative predictive value was 94.7% for angiography and 91.3% for ultrasonic arteriography. A pulsed Doppler frequency equal to or greater than 6.5 kiloHertz appears to accurately identify lesions that are at risk to reduce distal internal carotid pressure under operative conditions with a sensitivity similar to angiography. This criterion has a positive predictive value and specificity that is slightly superior to angiography and a high negative predictive value. Pulsed Doppler spectrum analysis provides physiologic information relative to blood flow velocity that is complimentary to the anatomic data provided by angiography for assessing the potential for hemodynamic significance of internal carotid stenoses. Images Fig. 1. PMID:6712324

  16. Assessment of non-sinusoidal, pulsed, or intermittent exposure to low frequency electric and magnetic fields.

    PubMed

    Heinrich, Hannah

    2007-06-01

    The correct assessment of non-sinusoidal, pulsed, or intermittent exposure to low frequency electric and magnetic fields already is a key issue in the occupational environment while becoming more and more important in the domain of the general public. The method presented provides a simple and safe solution for the assessment of arbitrary field types--including sinusoidal and continuous-wave signals--with frequencies up to several 100 kHz and has already proven its practicability and usefulness for more than 5 years. The concept is based on fundamental laws of physics and electrostimulation and well-established physiological data. It allows for a seamless and easy integration in any standard or guideline dealing with human safety in electric, magnetic, and electromagnetic fields. A very simple-to-use graphical version allows an easy and fast assessment of the exposure to non-sinusoidal, pulsed, or intermittent low-frequency magnetic fields without introducing a large overestimation of the exposure situation. A computer-based version makes a much more detailed signal analysis possible and can provide useful information for exposure reduction using modifications of the magnetic field's time parameters (e.g., rise/fall times). PMID:17495654

  17. Assessment of non-sinusoidal, pulsed, or intermittent exposure to low frequency electric and magnetic fields.

    PubMed

    Heinrich, Hannah

    2007-06-01

    The correct assessment of non-sinusoidal, pulsed, or intermittent exposure to low frequency electric and magnetic fields already is a key issue in the occupational environment while becoming more and more important in the domain of the general public. The method presented provides a simple and safe solution for the assessment of arbitrary field types--including sinusoidal and continuous-wave signals--with frequencies up to several 100 kHz and has already proven its practicability and usefulness for more than 5 years. The concept is based on fundamental laws of physics and electrostimulation and well-established physiological data. It allows for a seamless and easy integration in any standard or guideline dealing with human safety in electric, magnetic, and electromagnetic fields. A very simple-to-use graphical version allows an easy and fast assessment of the exposure to non-sinusoidal, pulsed, or intermittent low-frequency magnetic fields without introducing a large overestimation of the exposure situation. A computer-based version makes a much more detailed signal analysis possible and can provide useful information for exposure reduction using modifications of the magnetic field's time parameters (e.g., rise/fall times).

  18. Pulse sensitivity of the luteinizing hormone beta promoter is determined by a negative feedback loop Involving early growth response-1 and Ngfi-A binding protein 1 and 2.

    PubMed

    Lawson, Mark A; Tsutsumi, Rie; Zhang, Hao; Talukdar, Indrani; Butler, Brian K; Santos, Sharon J; Mellon, Pamela L; Webster, Nicholas J G

    2007-05-01

    The hypothalamic-pituitary-gonadal endocrine axis regulates reproduction through estrous phase-dependent release of the heterodimeric gonadotropic glycoprotein hormones, LH and FSH, from the gonadotropes of the anterior pituitary. Gonadotropin synthesis and release is dependent upon pulsatile stimulation by the hypothalamic neuropeptide GnRH. Alterations in pulse frequency and amplitude alter the relative levels of gonadotropin synthesis and release. The mechanism of interpretation of GnRH pulse frequency and amplitude by gonadotropes is not understood. We have examined gene expression in LbetaT2 gonadotropes under various pulse regimes in a cell perifusion system by microarray and identified 1127 genes activated by tonic or pulsatile GnRH. Distinct patterns of expression are associated with each pulse frequency, but the greatest changes occur at a 60-min or less interpulse interval. The immediate early gene mRNAs encoding early growth response (Egr)1 and Egr2, which activate the gonadotropin LH beta-subunit gene promoter, are stably induced at high pulse frequency. In contrast, mRNAs for the Egr corepressor genes Ngfi-A binding protein Nab1 and Nab2 are stably induced at low pulse frequency. We show that Ngfi-A binding protein members inhibit Egr-mediated frequency-dependent induction of the LH beta-subunit promoter. This pattern of expression suggests a model of pulse frequency detection that acts by suppressing activation by Egr family members at low frequency and allowing activation at sustained high-frequency pulses.

  19. Using phase retrieval to measure the intensity and phase of ultrashort pulses: Frequency-resolved optical gating

    SciTech Connect

    Trebino, R. ); Kane, D.J. )

    1993-05-01

    The authors recently introduced a new technique, frequency-resolved optical gating (FROG). For directly determining the full intensity I(t) and phase [var phi](t) of a single femtosecond pulse. By using almost any instantaneous nonlinear-optical interaction of two replicas of the ultrashort pulse to be measured, FROG involves measuring the spectrum of the signal pulse as a function of the delay between the replicas. The resulting trace of intensity versus frequency and delay yields an intuitive display of the pulse that is similar to the pulse spectrogram, except that the gate is a function of the pulse to be measured. The problem of inverting the FROG trace to obtain the pulse intensity and phase can also be considered a complex two-dimensional phase-retrieval problem. As a result, the FROG trace yields, in principle, an essentially unique pulse intensity and phase. It is shown that this is also the case in practice. An iterative-Fourier-transform algorithm is presented for inverting the FROG trace. The algorithm is unusual in its use of a novel constraint: the mathematical form of the signal field. Without the use of a support constraint, the algorithm performs quite well in practice, even for pulses with serious phase distortions and for experimental data with noise, although it occasionally stagnates when pulses with large intensity fluctuations are used. 49 refs., 15 figs.

  20. Spatially resolved frequency-dependent elasticity measured with pulsed force microscopy and nanoindentation.

    PubMed

    Sweers, Kim K M; van der Werf, Kees O; Bennink, Martin L; Subramaniam, Vinod

    2012-03-21

    Recently several atomic force microscopy (AFM)-based surface property mapping techniques like pulsed force microscopy (PFM), harmonic force microscopy or Peakforce QNM® have been introduced to measure the nano- and micro-mechanical properties of materials. These modes all work at different operating frequencies. However, complex materials are known to display viscoelastic behavior, a combination of solid and fluid-like responses, depending on the frequency at which the sample is probed. In this report, we show that the frequency-dependent mechanical behavior of complex materials, such as polymer blends that are frequently used as calibration samples, is clearly measurable with AFM. Although this frequency-dependent mechanical behavior is an established observation, we demonstrate that the new high frequency mapping techniques enable AFM-based rheology with nanoscale spatial resolution over a much broader frequency range compared to previous AFM-based studies. We further highlight that it is essential to account for the frequency-dependent variation in mechanical properties when using these thin polymer samples as calibration materials for elasticity measurements by high-frequency surface property mapping techniques. These results have significant implications for the accurate interpretation of the nanomechanical properties of polymers or complex biological samples. The calibration sample is composed of a blend of soft and hard polymers, consisting of low-density polyethylene (LDPE) islands in a polystyrene (PS) surrounding, with a stiffness of 0.2 GPa and 2 GPa respectively. The spring constant of the AFM cantilever was selected to match the stiffness of LDPE. From 260 Hz to 1100 Hz the sample was imaged with the PFM method. At low frequencies (0.5-35 Hz), single-point nanoindentation was performed. In addition to the material's stiffness, the relative heights of the LDPE islands (with respect to the PS) were determined as a function of the frequency. At the lower

  1. Pulse shape measurements using single shot-frequency resolved optical gating for high energy (80 J) short pulse (600 fs) laser

    SciTech Connect

    Palaniyappan, S.; Johnson, R.; Shimada, T.; Gautier, D. C.; Letzring, S.; Offermann, D. T.; Fernandez, J. C.; Shah, R. C.; Jung, D.; Hegelich, B. M.; Hoerlein, R.

    2010-10-15

    Relevant to laser based electron/ion accelerations, a single shot second harmonic generation frequency resolved optical gating (FROG) system has been developed to characterize laser pulses (80 J, {approx}600 fs) incident on and transmitted through nanofoil targets, employing relay imaging, spatial filter, and partially coated glass substrates to reduce spatial nonuniformity and B-integral. The device can be completely aligned without using a pulsed laser source. Variations of incident pulse shape were measured from durations of 613 fs (nearly symmetric shape) to 571 fs (asymmetric shape with pre- or postpulse). The FROG measurements are consistent with independent spectral and autocorrelation measurements.

  2. Neuroendocrine-gonadal axis in men: frequent sampling of LH, FSH, and testosterone.

    PubMed

    Spratt, D I; O'Dea, L S; Schoenfeld, D; Butler, J; Rao, P N; Crowley, W F

    1988-05-01

    Previous studies of episodic hormone secretion of the hypothalamic-pituitary-gonadal axis in normal men have produced conflicting results due to examinations of small cohorts of subjects or to limited sampling techniques. We evaluated gonadotropin and testosterone (T) secretory patterns in 20 normal men by sampling blood at 10-min intervals for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). T concentrations were also analyzed at 20-min intervals in 10 subjects. A previously unappreciated spectrum of gonadotropin and T secretory patterns was observed in normal men. Both mean LH concentrations and mean LH pulse amplitudes varied fourfold between individuals. LH interpulse intervals varied from 30 to 480 min (mean 119 +/- 32). Results also suggested a relative refractory period at the level of the hypothalamus or pituitary. In three subjects, a striking nighttime accentuation of LH pulsations was noted. Through use of Fourier analysis, a diurnal variation in LH was observed in the population (P less than 0.02). Mean FSH levels showed marked variation between individual subjects, with discrete pulses rarely observed. No diurnal variation in FSH secretion was noted. Serum T concentrations determined at 6-h intervals ranged from 105 to 1,316 ng/dl between subjects. When T was measured at 20-min intervals, marked intermittent declines in the T concentrations to levels well below the normal range were observed in 3 of 10 subjects. T secretion was found to lag behind LH secretion by approximately 40 min (P less than 0.02).

  3. Effects of low frequency pulsed electrical current on keratinocytes in vitro

    SciTech Connect

    Hinsenkamp, M.; Jercinovic, A.

    1997-05-01

    The effects of low frequency pulsed electrical current on epidermal repair in vitro were examined. Charge-balanced current stimuli proposed for chronic wound treatment were tested on skin keratinocytes cultured at an air-liquid interface on dead human dermis. Results imply that the balance between proliferation and differentiation in electrically treated samples is significantly modified in favor of differentiation. More advanced differentiation, shown through epidermal histology, was obtained in cultures exposed to electrical current, whereas the culture growth, the result of keratinocyte migration and proliferation, was greater in control samples.

  4. Self-focusing and frequency broadening of laser pulse in water

    SciTech Connect

    Sati, Priti; Tripathi, V. K.; Verma, Updesh

    2014-11-15

    An analytical model for the avalanche breakdown of water by an intense short laser pulse of finite spot size is developed. Initially, the laser undergoes self-focusing due to Kerr nonlinearity. As it acquires large intensity, it causes heating and avalanche breakdown of water. The plasma thus created on the laser axis causes nonlinear refraction induced defocusing of the laser. Thermal conduction tends to flatten the temperature profile and reduce the nonlinear refraction. The plasma density modification leads to frequency broadening of the laser.

  5. Dual Frequency Band Annular Probe for Volumetric Pulse-echo Optoacoustic Imaging

    NASA Astrophysics Data System (ADS)

    Kalkhoran, Mohammad Azizian; Varray, François; Vray, Didier

    Optoacoustic (OA) pulse echo (PE) imaging is a hybridized modality that is capable of providing physiological information on the basis of anatomical structure. In this work, we propose a dual frequency band annular probe for backward mode volumetric PE/OA imaging. The performance of this design is evaluated based on the spatio-temporal impulse response, three dimensional steerability of the transducer and point spread function. Optimum settings for number of elements in each ring and maximum steering are suggested. The transducer design and synthetic array beamforming simulation are presented. The resolution performance and reconstruction capabilities are shown with the in-silico measurements.

  6. Watermarking of linear frequency modulated pulses using chirplet graphs and stretch processing.

    PubMed

    Mobasseri, Bijan G; Nimbagal, Anirudh

    2015-12-01

    In many underwater acoustics problems such as search and rescue, it is desirable to establish the source of the sonar pings. In this paper a methodology is proposed to watermark sonar pulses prior to transmission by embedding them with a chain of low power chirplets represented by a graph. Watermark detection is formulated using stretch processing where chirplet energies are focused on a single beat frequency only if the graph is traversed along the same path used at the source. The algorithm is tested by simulation in shallow water at varying ranges.

  7. Watermarking of linear frequency modulated pulses using chirplet graphs and stretch processing.

    PubMed

    Mobasseri, Bijan G; Nimbagal, Anirudh

    2015-12-01

    In many underwater acoustics problems such as search and rescue, it is desirable to establish the source of the sonar pings. In this paper a methodology is proposed to watermark sonar pulses prior to transmission by embedding them with a chain of low power chirplets represented by a graph. Watermark detection is formulated using stretch processing where chirplet energies are focused on a single beat frequency only if the graph is traversed along the same path used at the source. The algorithm is tested by simulation in shallow water at varying ranges. PMID:26723363

  8. Pulse retrieval in frequency-resolved optical gating based on the method of generalized projections

    SciTech Connect

    DeLong, K.W.; Fittinghoff, D.N.; Trebino, R. ); Kohler, B.; Wilson, K. )

    1994-12-15

    We use the algorithmic method of generalized projections (GP's) to retrieve the intensity and phase of an ultrashort laser pulse from the experimental trace in frequency-resolved optical gating (FROG). Using simulations, we show that the use of GP's improves significantly the convergence properties of the algorithm over the basic FROG algorithm. In experimental measurements, the GP-based algorithm achieves significantly lower errors than previous algorithms. The use of GP's also permits the inclusion of an arbitrary material response function in the FROG problem.

  9. Highly efficient mid-infrared difference-frequency generation using synchronously pulsed fiber lasers.

    PubMed

    Murray, R T; Runcorn, T H; Kelleher, E J R; Taylor, J R

    2016-06-01

    We report the development of a high average power, picosecond-pulse, mid-infrared source based on difference-frequency generation (DFG) of two synchronous master oscillator power fiber amplifier systems. The generated idler can be tuned over the range 3.28-3.45 μm delivering greater than 3.4 W of average power, with a maximum pump to total DFG power conversion efficiency of 78%. The benefits of a synchronously pumped scheme, compared to CW seeding of DFG sources, are discussed. PMID:27244385

  10. Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

    PubMed

    Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

    2014-09-01

    The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber. PMID:25167146

  11. Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

    PubMed

    Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

    2014-09-01

    The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.

  12. Phase calibration of sonar systems using standard targets and dual-frequency transmission pulses.

    PubMed

    Islas-Cital, Alan; Atkins, Philip R; Foo, Kae Y; Picó, Ruben

    2011-10-01

    The phase angle component of the complex frequency response of a sonar system operating near transducer resonance is usually distorted. Interpretation and classification of the received sonar signal benefits from the preservation of waveform fidelity over the full bandwidth. A calibration process that measures the phase response in addition to the amplitude response is thus required. This paper describes an extension to the standard-target calibration method to include phase angle, without affecting the experimental apparatus, by using dual-frequency transmission pulses and frequency-domain data processing. This approach reduces the impact of unknown range and sound speed parameters upon phase calibration accuracy, as target phase is determined from the relationship of the two frequency components instead of relying on a local phase reference. Tungsten carbide spheres of various sizes were used to simultaneously calibrate the amplitude and phase response of an active sonar system in a laboratory tank. Experimental measurements of target phase spectra are in good agreement with values predicted from a theoretical model based upon full-wave analysis, over an operating frequency of 50-125 kHz.

  13. Fasting suppresses pulsatile luteinizing hormone (LH) secretion and enhances orderliness of LH release in young but not older men.

    PubMed

    Bergendahl, M; Aloi, J A; Iranmanesh, A; Mulligan, T M; Veldhuis, J D

    1998-06-01

    Pulsatile gonadotropin secretion and sex-steroid concentrations are suppressed reversibly in young fasted or malnourished human subjects. In this study, we investigated the impact of age on the dynamic neuroendocrine mechanisms underlying this stress response in healthy young (age, 28 +/- 3 yr, n = 8) vs. older (age 67 +/- 2 yr, n = 8) men with similar body mass indices (mean, 26 +/- 0.6 vs. 26 +/- 1.3 kg/m2, respectively). Serum LH concentrations were measured by immunoradiometric assay (IRMA) in blood collected at 10-min intervals over 27 h on a control (fed) day and on the third day of a 3.5-day fast (water only) assigned in randomized order. After 24 h of basal sampling, GnRH (10 micrograms i.v. bolus) was administered to test gonadotrope responsiveness. Cortisol, dehydroepiandrosterone sulfate, androstenedione, testosterone, FSH, GH, and PRL were measured in 24-h pooled serum as positive and negative control hormones. Approximate entropy was used to quantitate the orderliness of LH release over 24 h, and a multiple-parameter deconvolution method was applied to quantify pulsatile LH secretion and LH half-life. In the fed state, older men exhibited elevated mean (24-h pooled) serum FSH and cortisol concentrations compared with young controls but equivalent serum LH concentrations and reduced serum GH, free testosterone, androstenedione, and dehydroepiandrosterone sulfate concentrations. Fed older men also manifested a lower frequency and amplitude of 24-h pulsatile LH secretion, and, by approximate entropy calculations, a more disorderly pattern of basal LH release than younger individuals. Three- and one-half days of fasting evoked 40% and 47% increases in mean (24-h) serum cortisol concentrations in young and older men, respectively (P < 0.01 vs. fed, but P = not significant for percentage rise in older vs. young men). Concurrently, fasting induced a 2.1-fold fall in the 24-h endogenous LH production rate in young men (fed 36 +/- 9.7 vs. fasted 17 +/- 2.0 IU

  14. Cascade amplification of self-similar frequency-modulated pulses in normal group velocity dispersion active fibres

    SciTech Connect

    Zolotovskii, Igor' O; Okhotnikov, Oleg G; Sementsov, Dmitrii I; Sysolyatin, A A; Fotiadi, A A

    2012-09-30

    This paper examines the possibility of efficient amplification of self-similar frequency-modulated wave packets in longitudinally inhomogeneous active fibres. We analyse the dynamics of parabolic pulses with a constant frequency modulation rate and derive algorithms for optimising the group velocity dispersion profile in order to ensure self-similar propagation of such pulses. We demonstrate that the use of a cascade scheme can ensure efficient amplification of individual subpicosecond pulses of this type. (optical fibres, lasers and amplifiers. properties and applications)

  15. Copper bromide vapor brightness amplifiers with 100 kHz pulse repetition frequency

    NASA Astrophysics Data System (ADS)

    Trigub, M. V.; Evtushenko, G. S.; Torgaev, S. N.; Shiyanov, D. V.; Evtushenko, T. G.

    2016-10-01

    The paper presents a laser monitor with 10 μs time-resolution based on a high-frequency copper bromide vapor brightness amplifier. A sync circuit has been designed for single-pulse imaging. The analysis of amplifying characteristics of the active elements and active optical system (laser monitor) parameters allowed to determine the optimal concentration of HBr at which the images can be obtained with minimum distortions. For the active element operating at high frequencies (more than 50 kHz) as a brightness amplifier, the concentration of HBr must be lower than that needed for obtaining the maximum output power. The limiting brightness temperature of the background radiation which does not affect the image quality is determined. The potential feasibility of using a proposed brightness amplifier for visualizing processes blocked from viewing by the background radiation with the brightness temperature up to 8000 K is demonstrated.

  16. High Gain and Frequency Ultra-Stable Integrators for ICC and Long Pulse ITER Applications

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth; Ziemba, Timothy; Prager, James

    2012-10-01

    Eagle Harbor Technologies has developed a high gain and frequency ultra-stable integrator for small scale concept experiments and long pulse ITER applications. The Phase I integrator has a 10 μs RC time with a frequency response greater than 10 MHz. The device has been operated for the 3600 s with a drift error less than 600 μV, which exceeds the ITER specification. Longer period operation is also possible (> 30 hours). Additionally, this integrator has an extremely large dynamic range thereby increasing the effective bit depth of a digitizer. These integrators allow for both the fast and slow magnetic/plasma dynamics to be resolved with a single diagnostic. Data will be presented demonstrating the success of the Phase I program, and the Phase II work plan will be discussed. Work has begun to incorporate the integrators into legacy (CAMAC) and modern (National Instruments) DAQ systems.

  17. Generation of linear frequency modulation signal with reduced round-off error using pulse-output Direct Digital Synthesis technique.

    PubMed

    Peng, Cheng Y; Ma, Xiao C; Yan, She F; Yang, Li

    2014-02-01

    The pulse-output Direct Digital Synthesis (DDS), in which the overflow signal of the phase accumulator is used for the pulse output, can be easily implemented due to its simple hardware architecture and low algorithm complexity. This paper introduces the fundamentals for generating Linear Frequency Modulation (LFM) pulse using pulse-output DDS technique. Error introducing mechanisms that affect the accuracy of signal's duration, initial phase, and frequency are studied. Extensive analysis of round-off error is given. A modified hardware architecture for LFM pulse generation with reduced round-off error is proposed. Experiment results are given, which shows that the proposed generator is promising in applications such as sonar transmitters.

  18. Membrane Curvature Induced by Aggregates of LH2s and Monomeric LH1s

    PubMed Central

    Chandler, Danielle E.; Gumbart, James; Stack, John D.; Chipot, Christophe; Schulten, Klaus

    2009-01-01

    Abstract The photosynthetic apparatus of purple bacteria is contained within organelles called chromatophores, which form as extensions of the cytoplasmic membrane. The shape of these chromatophores can be spherical (as in Rhodobacter sphaeroides), lamellar (as in Rhodopseudomonas acidophila and Phaeospirillum molischianum), or tubular (as in certain Rb. sphaeroides mutants). Chromatophore shape is thought to be influenced by the integral membrane proteins Light Harvesting Complexes I and II (LH1 and LH2), which pack tightly together in the chromatophore. It has been suggested that the shape of LH2, together with its close packing in the membrane, induces membrane curvature. The mechanism of LH2-induced curvature is explored via molecular dynamics simulations of multiple LH2 complexes in a membrane patch. LH2s from three species—Rb. sphaeroides, Rps. acidophila, and Phsp. molischianum—were simulated in different packing arrangements. In each case, the LH2s pack together and tilt with respect to neighboring LH2s in a way that produces an overall curvature. This curvature appears to be driven by a combination of LH2's shape and electrostatic forces that are modulated by the presence of well-conserved cytoplasmic charged residues, the removal of which inhibits LH2 curvature. The interaction of LH2s and an LH1 monomer is also explored, and it suggests that curvature is diminished by the presence of LH1 monomers. The implications of our results for chromatophore shape are discussed. PMID:19948127

  19. Studies of Operating Frequency Effects On Ejector-based Thrust Augmentation in a Pulse Detonation Engine

    NASA Technical Reports Server (NTRS)

    Landry, K.

    2005-01-01

    Studies were performed in order to characterize the thrust augmentation potential of an ejector in a Pulse Detonation Engine application. A 49-mm diameter tube of 0.914-m length was constructed with one open end and one closed end. Ethylene, oxygen, and nitrogen were introduced into the tube at the closed end through the implementation of a fast mixing injector. The tube was completely filled with a stoichiometric mixture containing a one to one molar ratio of nitrogen to oxygen. Ethylene was selected as the fuel due to its detonation sensitivity and the molar ratio of the oxidizer was chosen for heat transfer purposes. Detonations were initiated in the tube through the use of a spark ignition system. The PDE was operated in a multi-cycle mode at frequencies ranging from 20-Hz to 50-Hz. Baseline thrust measurements with no ejector present were performed while operating the engine at various frequencies and compared to theoretical estimates. The baseline values were observed to agree with the theoretical model at low operating frequencies and proved to be increasingly lower than the predicted values as the operating frequency was increased. The baseline thrust measurements were observed to agree within 15 percent of the model for all operating frequencies. A straight 152-mm diameter ejector was installed and thrust augmentation percentages were measured. The length of the ejector was varied while the overlap percentage (percent of the ejector length which overlapped the tube) was maintained at 25 percent for all tests. In addition, the effect of ejector inlet geometry was investigated by comparing results with a straight inlet to those of a 38-mm inlet diameter. The thrust augmentation of the straight inlet ejector proved to be independent of engine operating frequency, augmenting thrust by 40 percent for the 0.914-m length ejector. In contrast, the rounded lip ejector of the same length seemed to be highly dependent on the engine operating frequency. An optimum

  20. a High Frequency Thermoacoustically-Driven Pulse Tube Cryocooler with Coaxial Resonator

    NASA Astrophysics Data System (ADS)

    Yu, G. Y.; Wang, X. T.; Dai, W.; Luo, E. C.

    2010-04-01

    High frequency thermoacoustically-driven pulse tube cryocoolers are quite promising due to their compact size and high reliability, which can find applications in space use. With continuous effort, a lowest cold head temperature of 68.3 K has been obtained on a 300 Hz pulse tube cryocooler driven by a standing-wave thermoacoustic heat engine with 4.0 MPa helium gas and 750 W heat input. To further reduce the size of the system, a coaxial resonator was designed and the two sub-systems, i.e., the pulse tube cryocooler and the standing-wave thermoacoustic heat engine were properly coupled through an acoustic amplifier tube, which leads to a system axial length of only about 0.7 m. The performance of the system with the coaxial resonator was tested, and shows moderate degradation compared to that with the in-line resonator, which might be attributed to the large flow loss of the 180 degree corner.

  1. Practical issues in ultrashort-laser-pulse measurement using frequency-resolved optical gating

    SciTech Connect

    DeLong, K.W.; Fittinghoff, D.N.; Trebino, R.

    1996-07-01

    The authors explore several practical experimental issues in measuring ultrashort laser pulses using the technique of frequency-resolved optical gating (FROG). They present a simple method for checking the consistency of experimentally measured FROG data with the independently measured spectrum and autocorrelation of the pulse. This method is a powerful way of discovering systematic errors in FROG experiments. They show how to determine the optimum sampling rate for FROG and show that this satisfies the Nyquist criterion for the laser pulse. They explore the low- and high-power limits to FROG and determine that femtojoule operation should be possible, while the effects of self-phase modulation limit the highest signal efficiency in FROG to 1%. They also show quantitatively that the temporal blurring due to a finite-thickness medium in single-shot geometries does not strongly limit the FROG technique. They explore the limiting time-bandwidth values that can be represented on a FROG trace of a given size. Finally, they report on a new measure of the FROG error that improves convergence in the presence of noise.

  2. Experimental investigation of a novel microchip laser producing synchronized dual-frequency laser pulse with an 85 GHz interval

    NASA Astrophysics Data System (ADS)

    Hu, M.; An, R. D.; Zhang, H.; Huang, Q. F.; Ge, J. H.

    2013-01-01

    A novel self-Q-switched microchip laser is introduced, which can produce synchronized dual-frequency laser pulse trains. By adopting a prepump mechanism, as well as shifting the gain curve and resonance wavelengths, the relative gains of π and σ polarization modes are adjusted, which offers an effective way to finely synchronize the laser pulses. By employing a 0.9 mm length monolithic cavity, a pair of synchronized pulse trains with a frequency separation of 85 GHz (0.32 nm) is achieved, which nearly approaches the gain bandwidth of the laser medium. Another separated cavity with a length of 2.8 mm operates in the same way for further investigation of microwave generation. A radiofrequency signal with frequency of 26.565 GHz is achieved by beat-noting of the synchronized laser pulse trains with 0.1 nm wavelength separation.

  3. Diagnostics and Optimization of a Miniature High Frequency Pulse Tube Cryocooler

    NASA Astrophysics Data System (ADS)

    Garaway, I.; Veprik, A.; Radebaugh, R.

    2010-04-01

    A miniature, high energy density, pulse tube cryocooler with an inertance tube and reservoir has been developed, tested, diagnosed and optimized to provide appropriate cooling for size-limited cryogenic applications demanding fast cool down. This cryocooler, originally designed using REGEN 3.2 for 80 K, an operating frequency of 150 Hz and an average pressure of 5.0 MPa, has regenerator dimensions of 4.4 mm inside diameter and 27 mm length and is filled with ♯635 mesh stainless steel screen. Various design features, such as the use of compact heat exchangers and a miniature linear compressor, resulted in a remarkably compact pulse tube cryocooler. In this report, we present the preliminary test results and the subsequent diagnostic and optimization sequence performed to improve the overall design and operation of the complete cryocooler. These experimentally determined optimal parameters, though slightly different from those proposed in the initial numerical model, yielded 530 mW of gross cooling power at 120 K with an input electrical power of only 25 W. This study highlights the need to further establish our understanding of miniature, high frequency, regenerative cryocoolers, not only as a collection of independent subcomponents, but as one single working unit. It has also led to a list of additional improvements that may yet be made to even further improve the operating characteristics of such a complete miniature cryocooler.

  4. Frequency doubled high-power disk lasers in pulsed and continuous-wave operation

    NASA Astrophysics Data System (ADS)

    Weiler, Sascha; Hangst, Alexander; Stolzenburg, Christian; Zawischa, Ivo; Sutter, Dirk; Killi, Alexander; Kalfhues, Steffen; Kriegshaeuser, Uwe; Holzer, Marco; Havrilla, David

    2012-03-01

    The disk laser with multi-kW output power in infrared cw operation is widely used in today's manufacturing, primarily in the automotive industry. The disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency and high reliability with low investment and operating costs. Additionally, the disk laser is ideally suited for frequency conversion due to its polarized output with negligible depolarization losses. Laser light in the green spectral range (~515 nm) can be created with a nonlinear crystal. Pulsed disk lasers with green output of well above 50 W (extracavity doubling) in the ps regime and several hundreds of Watts in the ns regime with intracavity doubling are already commercially available whereas intracavity doubled disk lasers in continuous wave operation with greater than 250 W output are in test phase. In both operating modes (pulsed and cw) the frequency doubled disk laser offers advantages in existing and new applications. Copper welding for example is said to show much higher process reliability with green laser light due to its higher absorption in comparison to the infrared. This improvement has the potential to be very beneficial for the automotive industry's move to electrical vehicles which requires reliable high-volume welding of copper as a major task for electro motors, batteries, etc.

  5. Pulsing frequency induced change in optical constants and dispersion energy parameters of WO{sub 3} films grown by pulsed direct current magnetron sputtering

    SciTech Connect

    Punitha, K.; Sivakumar, R.; Sanjeeviraja, C.

    2014-03-21

    In this work, we present the pulsing frequency induced change in the structural, optical, vibrational, and luminescence properties of tungsten oxide (WO{sub 3}) thin films deposited on microscopic glass and fluorine doped tin oxide (SnO{sub 2}:F) coated glass substrates by pulsed dc magnetron sputtering technique. The WO{sub 3} films deposited on SnO{sub 2}:F substrate belongs to monoclinic phase. The pulsing frequency has a significant influence on the preferred orientation and crystallinity of WO{sub 3} film. The maximum optical transmittance of 85% was observed for the film and the slight shift in transmission threshold towards higher wavelength region with increasing pulsing frequency revealed the systematic reduction in optical energy band gap (3.78 to 3.13 eV) of the films. The refractive index (n) of films are found to decrease (1.832 to 1.333 at 550 nm) with increasing pulsing frequency and the average value of extinction coefficient (k) is in the order of 10{sup −3}. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, oscillator strength, and oscillator energy (E{sub o}) of WO{sub 3} films were calculated and reported for the first time due to variation in pulsing frequency during deposition by pulsed dc magnetron sputtering. The E{sub o} is change between 6.30 and 3.88 eV, while the E{sub d} varies from 25.81 to 7.88 eV, with pulsing frequency. The Raman peak observed at 1095 cm{sup −1} attributes the presence of W-O symmetric stretching vibration. The slight shift in photoluminescence band is attributed to the difference in excitons transition. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

  6. The effect of applied electric field on pulsed radio frequency and pulsed direct current plasma jet array

    SciTech Connect

    Hu, J. T.; Liu, X. Y.; Liu, J. H.; Xiong, Z. L.; Liu, D. W.; Lu, X. P.; Iza, F.; Kong, M. G.

    2012-06-15

    Here we compare the plasma plume propagation characteristics of a 3-channel pulsed RF plasma jet array and those of the same device operated by a pulsed dc source. For the pulsed-RF jet array, numerous long life time ions and metastables accumulated in the plasma channel make the plasma plume respond quickly to applied electric field. Its structure similar as 'plasma bullet' is an anode glow indeed. For the pulsed dc plasma jet array, the strong electric field in the vicinity of the tube is the reason for the growing plasma bullet in the launching period. The repulsive forces between the growing plasma bullets result in the divergence of the pulsed dc plasma jet array. Finally, the comparison of 309 nm and 777 nm emissions between these two jet arrays suggests the high chemical activity of pulsed RF plasma jet array.

  7. 486nm blue laser operating at 500 kHz pulse repetition frequency

    NASA Astrophysics Data System (ADS)

    Creeden, Daniel; Blanchard, Jon; Pretorius, Herman; Limongelli, Julia; Setzler, Scott D.

    2016-03-01

    Compact, high power blue light in the 470-490nm region is difficult to generate due to the lack of laser sources which are easily convertible (through parametric processes) to those wavelengths. By using a pulsed Tm-doped fiber laser as a pump source for a 2-stage second harmonic generation (SHG) scheme, we have generated ~2W of 486.5nm light at 500kHz pulse repetition frequency (PRF). To our knowledge, this is the highest PRF and output power achieved in the blue region based on a frequency converted, monolithic fiber laser. This pump laser is a pulsed Tm-doped fiber laser/amplifier which generates 12.8W of 1946nm power at 500kHz PRF with diffraction-limited output from a purely single-mode fiber. The output from this laser is converted to 973nm through second harmonic generation (SHG). The 973nm is then converted to 486.5nm via another SHG stage. This architecture operates with very low peak power, which can be challenging from a nonlinear conversion standpoint. However, the low peak power enables the use of a single-mode monolithic fiber amplifier without undergoing nonlinear effects in the fiber. This also eliminates the need for novel fiber designs, large-mode area fiber, or free-space coupling to rod-type amplifiers, improving reliability and robustness of the laser source. Higher power and conversion efficiency are possible through the addition of Tm-doped fiber amplification stages as well as optimization of the nonlinear conversion process and nonlinear materials. In this paper, we discuss the laser layout, results, and challenges with generating blue light using a low peak power approach.

  8. Loss of echogenicity and onset of cavitation from echogenic liposomes: pulse repetition frequency independence

    PubMed Central

    Radhakrishnan, Kirthi; Haworth, Kevin J; Peng, Tao; McPherson, David D.; Holland, Christy K.

    2014-01-01

    Echogenic liposomes (ELIP) are being developed for the early detection and treatment of atherosclerotic lesions. An 80% loss of echogenicity of ELIP (Radhakrishnan et al. 2013) has been shown to be concomitant with the onset of stable and inertial cavitation. The ultrasound pressure amplitude at which this occurs is weakly dependent on pulse duration. Smith et al. (2007) have reported that the rapid fragmentation threshold of ELIP (based on changes in echogenicity) is dependent on the insonation pulse repetition frequency (PRF). The current study evaluates the relationship between loss of echogenicity and cavitation emissions from ELIP insonified by duplex Doppler pulses at four PRFs (1.25 kHz, 2.5 kHz, 5 kHz, and 8.33 kHz). Loss of echogenicity was evaluated on B-mode images of ELIP. Cavitation emissions from ELIP were recorded passively on a focused single-element transducer and a linear array. Emissions recorded by the linear array were beamformed and the spatial widths of stable and inertial cavitation emissions were compared to the calibrated azimuthal beamwidth of the Doppler pulse exceeding the stable and inertial cavitation thresholds. The inertial cavitation thresholds had a very weak dependence on PRF and stable cavitation thresholds were independent of PRF. The spatial widths of the cavitation emissions recorded by the passive cavitation imaging system agreed with the calibrated Doppler beamwidths. The results also show that 64%–79% loss of echogenicity can be used to classify the presence or absence of cavitation emissions with greater than 80% accuracy. PMID:25438849

  9. Simultaneous optimization of power and duration of radio-frequency pulse in PARACEST MRI.

    PubMed

    Rezaeian, Mohammad-Reza; Hossein-Zadeh, Gholam-Ali; Soltanian-Zadeh, Hamid

    2016-07-01

    Chemical exchange saturation transfer (CEST) MRI is increasingly used to probe mobile proteins and microenvironment properties, and shows great promise for tumor and stroke diagnosis. The CEST effect is complex and depends not only on the CEST agent concentration, exchange rates, the characteristic of the magnetization transfer (MT), and the relaxation properties of the tissue, but also varies with the experimental conditions such as radio-frequency (RF) pulse power and duration. The RF pulse is one of the most important factors that promote the CEST effect for biological properties such as pH, temperature and protein content, especially for contrast agents with intermediate to fast exchange rates. The CEST effect is susceptible to the RF duration and power. The present study aims at determining the optimal power and the corresponding optimal duration (that maximize the CEST effect) using an off-resonance scheme through a new definition of the CEST effect. This definition is formulated by solving the Bloch-McConnell equation through the R1ρ method (based on the eigenspace solution) for both of the MT and CEST effects as well as their interactions. The proposed formulations of the optimal RF pulse power and duration are the first formulations in which the MT effect is considered. The extracted optimal RF pulse duration and power are compared with those of the MTR asymmetry model in two- and three-pool systems, using synthetic data that are similar to the muscle tissue. To validate them further, the formulations are compared with the empirical formulation of the CEST effect and other findings of the previous researches. By extending our formulations, the optimal power and the corresponding optimal duration (in the biological systems with many chemical exchange sites) can be determined. PMID:26956610

  10. Two pulse-coupled non-identical, frequency-different BZ oscillators with time delay.

    PubMed

    Lavrova, Anastasia I; Vanag, Vladimir K

    2014-04-14

    Two non-identical, frequency-different pulse-coupled oscillators with time delay have been systematically studied using four-variable model of the Belousov-Zhabotinsky (BZ) reaction at mutual inhibitory, mutual excitatory, and mixed excitatory-inhibitory types of coupling. Different resonances like 1 : 2, 2 : 3, 1 : 3, etc., as well as complex rhythms and abrupt changes between them occur depending on the coupling strengths, time delay, and frequency ratio. Analogously to in-phase and anti-phase oscillations for 1 : 1 resonance, a similar phase locking exists for 1 : 2 resonance in the case of inhibitory coupling. For excitatory coupling, a bursting regime is found. The number of spikes in a single burst can be tuned by both the frequency ratio and time delay. For excitatory-inhibitory coupling, a region where one oscillator is suppressed (OS zone) has been found. Boundary of the OS zone depends on the frequency ratio. For weakly coupled oscillators, Farey sequence has been found for excitatory-inhibitory and mutual excitatory coupling.

  11. Cross-frequency coherence and pulse propagation in a turbulent atmosphere.

    PubMed

    Ostashev, Vladimir E; Wilson, D Keith; Collier, Sandra L; Cain, Jericho E; Cheinet, Sylvain

    2016-07-01

    Cross-frequency coherence of acoustic signals in a turbulent atmosphere is an important consideration for source localization with acoustic sensor arrays and for remote sensing of the atmosphere with sodars and tomography techniques. This paper takes as a starting point recently derived, closed-form equations for the spatial-temporal correlation function of a broadband acoustic signal propagating in a turbulent atmosphere with coupled spatial-temporal fluctuations in temperature and wind velocity. This theory is employed to calculate, based on the Rytov approximation, the two-point, two-time, two-frequency mutual coherence function of plane and spherical waves in the weak scattering regime. The cross-frequency coherence for these waveforms is then obtained and compared with that in the geometrical acoustics approximation. The coherence bandwidth is calculated and analyzed for typical meteorological regimes of the atmospheric surface layer and parameters of sound propagation. The results obtained are compared with available experimental data. The cross-frequency coherence is also used to study the effect of atmospheric turbulence on the mean intensity of an acoustic pulse propagating in a turbulent atmosphere. PMID:27475189

  12. Triangular pulse generation using a dual-parallel Mach-Zehnder modulator driven by a single-frequency radio frequency signal.

    PubMed

    Zhang, Fangzheng; Ge, Xiaozhong; Pan, Shilong

    2013-11-01

    A simple scheme for the generation of full-duty-cycle triangular pulses is proposed and experimentally demonstrated using a dual-parallel Mach-Zehnder modulator driven by a single-frequency RF signal. By properly setting the bias voltages and the RF power, even-order harmonics in the optical intensity are suppressed, and the amplitude of the first-order harmonic is 9 times of that of the third-order harmonic. A periodical triangular pulse train is obtained in the time domain. 2.5, 5, and 10 GHz triangular pulse trains are experimentally generated, which verifies the feasibility of the proposed scheme.

  13. Calcitonin gene-related peptide-induced suppression of luteinizing hormone pulses in the rat: the role of endogenous opioid peptides

    PubMed Central

    Bowe, JE; Li, XF; Kinsey-Jones, JS; Paterson, S; Brain, SD; Lightman, SL; O'Byrne, KT

    2005-01-01

    Calcitonin gene-related peptide (CGRP) is involved in a variety of stress responses in the rat. Central administration of CGRP activates the hypothalamo–pituitary–adrenal axis resulting in increased corticosterone secretion. We have previously shown that central CGRP suppresses the gonadotrophin-releasing hormone (GnRH) pulse generator, specifically LH pulses. Endogenous opioid peptides (EOPs) have been shown to play an important role in stress-induced suppression of the reproductive axis. The aim of the present study was to test the hypothesis that EOPs mediate CGRP-induced suppression of pulsatile LH secretion. Ovariectomized rats were implanted with intracerebroventricular (i.c.v.) and i.v. cannulae. Intravenous administration of the opioid antagonist naloxone (250 μg) completely blocked the suppression of LH pulses induced by 1.5 μg i.c.v. CGRP and significantly attenuated the suppression of pulsatile LH secretion induced by 5 μg i.c.v. CGRP. Furthermore, intravenous administration of naloxone was found to immediately restore normal LH pulse frequency in animals treated 90 min earlier with 1.5 μg i.c.v. CGRP. Co-administration (i.c.v.) of CGRP (1.5 μg) with the μ and κ opioid receptor-specific antagonists naloxone (10 μg) and norbinaltorphimine (5 μg), respectively, blocked the CGRP-induced suppression of LH pulses, whilst i.c.v. co-administration of CGRP (1.5 μg) with the δ opioid receptor-specific antagonist naltrindole (5 μg) did not. These data provide evidence that EOPs play a pivotal role in mediating the inhibitory effects of CGRP on pulsatile LH secretion in the rat. They also suggest that the μ and κ, but not the δ, opioid receptors may be responsible for mediating the effects of CGRP on LH pulses. PMID:15905218

  14. Theoretical and Experimental Study of Pulsed Optically Pumped Rubidium Frequency Standard

    NASA Astrophysics Data System (ADS)

    Du, Z. J.

    2013-09-01

    Atomic clocks have been recognized as the critical equipments for the global navigation satellite systems, and their performances determine the positioning accuracies and lifetimes of the satellite navigation systems. In order to ensure the reliability and technological diversity, it is of great importance to study new type atomic clocks with high precision. The advantages such as simple operation, compactness, and small size, make the Rb frequency standard preferred for satellite navigation systems. In order to reduce the light shift and cavity pulling shift, the Pulsed Optically Pumped (POP) Rb frequency standard has been theoretically and experimentally studied in this thesis, in which the pumping, interrogation, and detection phases are separated in time to avoid coupling between the microwave and optical field coherences. A laboratory POP ^{87}Rb frequency standard prototype has been realized. Meanwhile, the Autler-Townes splitting in electromagnetic induced transparency (EIT), which is induced by microwave, has been studied theoretically and experimentally. The main works and results are as follows: (1) In the formalism of the ensemble-averaged density matrix and in the rotating-wave approximation, a set of equations describing the POP clock dynamics with a three-level model has been obtained, and the optimum physical parameters are derived. When atoms are submitted to π/2 Ramsey pulses, it is indicated that: (a) With microwave detection, the full width at half maximum (FWHM) is 1/(4T) (T represents the Ramsey time), and the quality factor of the atomic line is increased by a factor of 2 with respect to the traditional approaches. (b) The light shift effect may be canceled, and cavity pulling effect may be strongly reduced. A better medium-, and long-term frequency stability is obtained. (2) The required characteristics of optics and physics packages have been analyzed. The instruments such as the laser system, microwave cavity, Rb vapor cell, quantization

  15. Optimization of Pulsed-DEER Measurements for Gd-Based Labels: Choice of Operational Frequencies, Pulse Durations and Positions, and Temperature

    SciTech Connect

    Raitsimring, A.; Astashkin, A. V.; Enemark, J. H.; Kaminker, I.; Goldfarb, D.; Walter, E. D.; Song, Y.; Meade, T. J.

    2012-12-29

    In this work, the experimental conditions and parameters necessary to optimize the long-distance (≥ 60 Å) Double Electron-Electron Resonance (DEER) measurements of biomacromolecules labeled with Gd(III) tags are analyzed. The specific parameters discussed are the temperature, microwave band, the separation between the pumping and observation frequencies, pulse train repetition rate, pulse durations and pulse positioning in the electron paramagnetic resonance spectrum. It was found that: (i) in optimized DEER measurements, the observation pulses have to be applied at the maximum of the EPR spectrum; (ii) the optimal temperature range for Ka-band measurements is 14-17 K, while in W-band the optimal temperatures are between 6-9 K; (iii) W-band is preferable to Ka-band for DEER measurements. Recent achievements and the conditions necessary for short-distance measurements (<15 Å) are also briefly discussed.

  16. Generation of third harmonic picosecond pulses at 355 nm by sum frequency mixing in periodically poled MgSLT crystal

    NASA Astrophysics Data System (ADS)

    Kaltenbach, André; Schönau, Thomas; Lauritsen, Kristian; Tränkle, Günther; Erdmann, Rainer

    2015-02-01

    Third harmonic 355nm picosecond pulses are generated by sum frequency mixing in a periodically poled magnesium doped stoichiometric lithium tantalate (PPMgSLT) crystal. The third harmonic generation is based on the 1064nm radiation of a gain-switched distributed feedback (DFB) diode laser which is amplified by a two-stage fiber amplifier. The diode laser is freely triggerable at variable repetition rates up to 80MHz and provides optical pulses of 65 ps FWHM duration and pulse energies in the range of 5 pJ. The 355nm third harmonic generation is realized in a two-step conversion process. First, the 1064nm fundamental radiation is frequency-doubled to 532 nm, afterwards both frequencies are mixed in the PPMgSLT crystal to 355 nm. The UV-radiation shows a pulse width of 60 ps, a good beam profile and stable pulse energy over a wide range of repetition rates by proprietary pump power management. At 355nm a pulse peak power of 5.3W was achieved with 192W pulse peak power of the fundamental radiation.

  17. Effects of pulse frequency of input power on the physical and chemical properties of pulsed streamer discharge plasmas in water

    NASA Astrophysics Data System (ADS)

    Ruma; Lukes, P.; Aoki, N.; Spetlikova, E.; Hosseini, S. H. R.; Sakugawa, T.; Akiyama, H.

    2013-03-01

    A repetitive pulsed-power modulator, which employs a magnetic pulse compression circuit with a high-speed thyristor switch, was used to study the effects of the pulse repetition rate of input power on the physical and chemical properties of pulsed discharges in water. Positive high-voltage pulses of 20 kV with repetition rates of up to 1 kHz were used to generate a discharge in water using the point-to-plane electrode geometry. By varying the pulse repetition rate, two distinct modes of the discharge plasma were formed in water. The first mode was characterized by the formation of a corona-like discharge propagating through water in the form of streamer channels. The second mode was formed typically above 500 Hz, when the formation of streamer channels in water was suppressed and all plasmas occurred inside a spheroidal aggregate of very fine gas bubbles surrounding the tip of the high-voltage electrode. The production of hydrogen peroxide, degradation of organic dye Acid Orange 7 (AO7) and inactivation of bacteria Escherichia coli by the discharge in water were studied under different discharge plasma modes in dependence on the pulse repetition rate of input power. The efficiency of both chemical and biocidal processes induced by the plasma in water decreased significantly with pulse repetition rates above 500 Hz.

  18. A pulse-frequency modulation sensor using memristive-based inhibitory interconnections.

    PubMed

    Kavehei, Omid; Lee, Sang-Jin; Cho, Kyoung-Rok; Al-Sarawi, Said; Abbott, Derek

    2013-05-01

    This paper proposes a programmable inhibitory interconnection network between pixels in an array of novel low-voltage Schmitt-trigger-based PFM sensors that will be of interest for future applications in memristor-based early vision processing. In addition, a new low-power inverter-based pulse-frequency modulation (PFM) design and its integration with the network is also presented. To ensure no change in the memristors conductance in the network, the CMOS imager was designed for low voltage operation. That has resulted in a significant power reduction, better than 60%, and a comparable linear dynamic range when compared to published designs in the literature. The design was performed using a 0.13 um Samsung Electronics standard CMOS process, using 0.75 V supply voltage. PMID:23858889

  19. Frequency-time coherence for all-optical sampling without optical pulse source

    PubMed Central

    Preußler, Stefan; Raoof Mehrpoor, Gilda; Schneider, Thomas

    2016-01-01

    Sampling is the first step to convert an analogue optical signal into a digital electrical signal. The latter can be further processed and analysed by well-known electrical signal processing methods. Optical pulse sources like mode-locked lasers are commonly incorporated for all-optical sampling, but have several drawbacks. A novel approach for a simple all-optical sampling is to utilise the frequency-time coherence of each signal. The method is based on only using two coupled modulators driven with an electrical sine wave. Since no optical source is required, a simple integration in appropriate platforms, such as Silicon Photonics might be possible. The presented method grants all-optical sampling with electrically tunable bandwidth, repetition rate and time shift. PMID:27687495

  20. On the passage of high-level pulsed radio frequency interference through a nonlinear satellite transponder

    NASA Technical Reports Server (NTRS)

    Weinberg, A.

    1984-01-01

    Attention is given to the uncoded bit error rate (BER) performance of a satellite communications system whose modulation scheme is binary PSK and whose transponder contains an arbitrary amplitude nonlinearity, all in the presence of high level pulsed radio frequency interference (RFI). A general approach is presented for direct BER evaluations, in contrast to other approaches which may employ SNR suppression factors. The computed results are based on arbitrarily specified RFI scenarios, in the presence of hard limiter, clipper, or blanker amplitude nonlinearities. Performance curves demonstrate the superiority of an appropriately chosen blanker when the RFI environment is most severe. The results obtained also pertain to the sensitivity of performance to the information bit rate, signal power variations, and the ratio of CW to noise content. The CW effects are found to be the most severe.

  1. Fixed lag smoothing target tracking in clutter for a high pulse repetition frequency radar

    NASA Astrophysics Data System (ADS)

    Khan, Uzair; Shi, Yi Fang; Song, Taek Lyul

    2015-12-01

    A new method to smooth the target hybrid state with Gaussian mixture measurement likelihood-integrated track splitting (GMM-ITS) in the presence of clutter for a high pulse repetition frequency (HPRF) radar is proposed. This method smooths the target state at fixed lag N and considers all feasible multi-scan target existence sequences in the temporal window of scans in order to smooth the target hybrid state. The smoothing window can be of any length N. The proposed method to smooth the target hybrid state at fixed lag is also applied to the enhanced multiple model (EMM) tracking algorithm. Simulation results indicate that the performance of fixed lag smoothing GMM-ITS significantly improves false track discrimination and root mean square errors (RMSEs).

  2. Effect of Finite Pulse Length and Laser Frequency Chirp on HGHG and EEHG Seeding

    SciTech Connect

    Stupakov, G.; /SLAC

    2011-11-18

    Theoretical studies of high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) often start from a simplified model in which the beam is assumed infinitely long and longitudinally uniform and the laser induced energy modulation is perfectly sinusoidal and of infinite duration. In such a model the resulting seed has a spectrum consisting of a collection of delta-functions (of zero width) located at the harmonics of the laser frequency. Being a useful tool for study of the seed bunching amplitudes, such a model cannot be used for realistic analysis the spectral properties of the seed. In this paper we take into account the finite duration of the laser pulse as well as some possible laser phase errors to study their effect on the spectrum of the seed.

  3. Frequency-time coherence for all-optical sampling without optical pulse source

    NASA Astrophysics Data System (ADS)

    Preußler, Stefan; Raoof Mehrpoor, Gilda; Schneider, Thomas

    2016-09-01

    Sampling is the first step to convert an analogue optical signal into a digital electrical signal. The latter can be further processed and analysed by well-known electrical signal processing methods. Optical pulse sources like mode-locked lasers are commonly incorporated for all-optical sampling, but have several drawbacks. A novel approach for a simple all-optical sampling is to utilise the frequency-time coherence of each signal. The method is based on only using two coupled modulators driven with an electrical sine wave. Since no optical source is required, a simple integration in appropriate platforms, such as Silicon Photonics might be possible. The presented method grants all-optical sampling with electrically tunable bandwidth, repetition rate and time shift.

  4. Measurement of the Optical Coherence of a Femtosecond Pulsed Laser by Shearing Interferometry with a Double-Frequency Grating

    NASA Astrophysics Data System (ADS)

    Ming, Hai; Qian, Jiang-yuan; Xie, Jian-ping; A, B. Fedotov; X, Xiao; M, M. T. Loy

    1998-01-01

    Shearing interferometry of an ion-etched holographic double-frequency grating is used to measure the optical coherence of femtosecond pulsed lasers. The experimental results show that the optical coherence of the femtosecond light beam is not only related to the spectral width and size of the light source but is also related to the pulse duration and mode-locked laser state. The results of theoretical analysis and numerical calculation are also given. Application of this research is also discussed.

  5. [Effects of low-frequency pulsed electromagnetic fields on the proliferation of chondrocytes].

    PubMed

    Indouraine, A; Petersen, J P; Pförringer, W

    2001-03-01

    Chondrocytes isolated from the human cartilage of 5 patients between the ages 23 and 56 were exposed to low frequency pulsed electromagnetic fields (9 mT; 3 Hz) for a daily period of 60 minutes on 5 consecutive days and then every 48 hours for the next 6 days (11 days in total). Cell viability was estimated using trypan blue exclusion and proliferation was estimated by counting the cells in a haemacytometer. Cell morphology was compared for control purposes by directly observing the cells under a light microscope after staining cells in a haematoxylin and eosin solution. The results were statistically analysed and compared to a control sample. Data revealed that exposing cells isolated from human cartilage to pulsed electromagnetic fields (9 mT; 3 Hz) led to a significantly higher number of cells in comparison to the control sample. Among the cells from the 5 patients, growth varied between 1.1 to 3.0 folds compared to the control sample. The difference in cell viability between the exposed cells and the control sample was, however, not significant. Some morphological variations were revealed when the cells were observed under a light microscope. The exposed cells were thinner and longer than the control cells which were large and flat. The exposed cells tended to grow in a more uniform direction while the control cells grew in all directions. These differences in morphology and growth may be related to the higher density of the exposed cells.

  6. Phase-locking and Pulse Generation in Multi-Frequency Brillouin Oscillator via Four Wave Mixing

    NASA Astrophysics Data System (ADS)

    Büttner, Thomas F. S.; Kabakova, Irina V.; Hudson, Darren D.; Pant, Ravi; Poulton, Christopher G.; Judge, Alexander C.; Eggleton, Benjamin J.

    2014-05-01

    There is an increasing demand for pulsed all-fibre lasers with gigahertz repetition rates for applications in telecommunications and metrology. The repetition rate of conventional passively mode-locked fibre lasers is fundamentally linked to the laser cavity length and is therefore typically ~10-100 MHz, which is orders of magnitude lower than required. Cascading stimulated Brillouin scattering (SBS) in nonlinear resonators, however, enables the formation of Brillouin frequency combs (BFCs) with GHz line spacing, which is determined by the acoustic properties of the medium and is independent of the resonator length. Phase-locking of such combs therefore holds a promise to achieve gigahertz repetition rate lasers. The interplay of SBS and Kerr-nonlinear four-wave mixing (FWM) in nonlinear resonators has been previously investigated, yet the phase relationship of the waves has not been considered. Here, we present for the first time experimental and numerical results that demonstrate phase-locking of BFCs generated in a nonlinear waveguide cavity. Using real-time measurements we demonstrate stable 40 ps pulse trains with 8 GHz repetition rate based on a chalcogenide fibre cavity, without the aid of any additional phase-locking element. Detailed numerical modelling, which is in agreement with the experimental results, highlight the essential role of FWM in phase-locking of the BFC.

  7. Gas breakdown mechanism in pulse-modulated asymmetric ratio frequency dielectric barrier discharges

    SciTech Connect

    Wang, Qi; Sun, Jizhong Ding, Zhenfeng; Ding, Hongbin; Wang, Dezhen; Nozaki, Tomohiro; Wang, Zhanhui

    2014-08-15

    The gas breakdown mechanisms, especially the roles of metastable species in atmospheric pressure pulse-modulated ratio frequency barrier discharges with co-axial cylindrical electrodes, were studied numerically using a one dimensional self-consistent fluid model. Simulation results showed that in low duty cycle cases, the electrons generated from the channels associated with metastable species played a more important role in initializing next breakdown than the direct ionization of helium atoms of electronic grounded states by electron-impact. In order to quantitatively evaluate the contribution to the discharge by the metastables, we defined a “characteristic time” and examined how the value varied with the gap distance and the electrode asymmetry. The results indicated that the lifetime of the metastable species (including He*and He{sub 2}{sup *}) was much longer than that of the pulse-on period and as effective sources of producing electrons they lasted over a period up to millisecond. When the ratio of the outer radius to the inner radius of the cylindrical electrodes was far bigger than one, it was found that the metastables distributed mainly in a cylindrical region around the inner electrode. When the ratio decreased as the inner electrode moved outward, the density of metastables in the discharge region near the outer electrode became gradually noticeable. As the discharging gap continued to decrease, the two hill-shaped distributions gradually merged to one big hill. When the discharge spacing was fixed, asymmetric electrodes facilitated the discharge.

  8. High-Frequency Pulsed-Electro-Acoustic (PEA) Measurements for Mapping Charge Distribution

    NASA Astrophysics Data System (ADS)

    Sorensen, Kristina; Pearson, Lee; Dennison, J. R.; Doyle, Timothy; Hartley, Kent

    2012-10-01

    High-frequency pulsed-electro-acoustic (PEA) measurements are a non-destructive method used to investigate internal charge distributions in dielectric materials. This presentation discusses the theory and signal processing of simple PEA experiments and shows results of PEA measurements. PEA experiments involve a thin dielectric positioned between two conducting electrodes. A voltage signal on the two electrodes generates an electric field across the dielectric, which stimulates embedded charge and creates a pressure wave that propagates within the capacitor. A coupled acoustic sensor then measures the ensuing pressure pulse response. Spatial distributions of the charge profile are obtained from the resultant pressure waveform. Gaussian filters and other signal processing methods are used to increase the signal-to-noise ratio in this waveform. Estimates of the charge distribution inside the dielectric are extracted from this analysis. Our ultimate objective is to develop high resolution PEA methods to investigate in vacuo charge deposition in thin film polymeric, ceramic, or glass dielectric materials using medium to high energy (approximately 103 to 107 eV) electron beams.

  9. [Evaluation of the Effect of Adiabatic Pulse and B1 Shim to the Radio Frequency Homogeneity in Chemical Shift Imaging].

    PubMed

    Kikuchi, Chie; Inoue, Mitsuhiro; Okawa, Kohei; Taguchi, Jyunichi; Hirota, Yoshifumi; Yanagiya, Yohei

    2016-04-01

    It is considered that the enhancement of chemical shift and the elevation of signal-to-noise ratio (SNR) induced by high magnetic fields are useful for the evaluation of metabolism using magnetic resonance spectroscopy (MRS). However, the reduction of the localization in MRS seems to be caused by the decreased homogeneity of radio frequency (RF) pulses, especially in chemical shift imaging (CSI). To search the influence of B1 shim mode and the significance of adiabatic pulses, we have examined the changes of RF homogeneity using 3 T magnetic resonance imaging (MRI) with the water phantom and the metabolites phantom (containing acetate and lactate) in CSI. The RF homogeneity and chemical shift artifact were obviously improved using the adiabatic pulses. Improvement of the homogeneity of RF pulses was observed when B1 shim was used. These results suggest the usefulness of CSI using adiabatic pulses and B1 shim when small amount of metabolites of target is measured in MRS. PMID:27097994

  10. A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements.

    PubMed

    Cho, F H; Stepanov, V; Takahashi, S

    2014-07-01

    We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107-120 GHz and 215-240 GHz and in the magnetic field range of 0-12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a (4)He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system. PMID:25085176

  11. A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements

    SciTech Connect

    Cho, F. H.; Stepanov, V.; Takahashi, S.

    2014-07-15

    We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107−120 GHz and 215−240 GHz and in the magnetic field range of 0−12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a {sup 4}He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system.

  12. Electron energy enhancement by frequency chirp of a radially polarized laser pulse during ionization of low-density gases

    NASA Astrophysics Data System (ADS)

    Pal Singh, Kunwar; Arya, Rashmi; Malik, Anil K.; Fisch, N. J.

    2016-11-01

    A scheme is proposed to enhance the energy of the electrons generated during the ionization of low-density krypton ions \\text{K}{{\\text{r}}32+} and argon ions \\text{A}{{\\text{r}}16+} by a radially polarized laser pulse using a negative frequency chirp. If a suitable frequency chirp is introduced then the energy of the electrons increases significantly and scattering decreases. The optimum value of the frequency chirp decreases with laser intensity and as well as spot size. The laser spot size also has an optimum value. The electron energy shows strong initial phase dependence. The scheme can be used to obtain quasi-monoenergetic collimated \\text{MeV}/\\text{GeV} electrons using the right choice of parameters. The chirped radially polarized laser pulse is more efficient than a chirped circularly polarized laser pulse to enhance energy and obtain quasi-monoenergetic electron beams.

  13. The pulse amplitude variation with QPO frequency in SAX J1808.4-3658: Resonances with the accretion disk

    NASA Astrophysics Data System (ADS)

    Caliskan, Sirin; Alpar, Mehmet Ali; Sasmaz Mus, Sinem

    2016-07-01

    SAX J1808.4-3658 is an accreting millisecond pulsar with a spin period of 401 Hz. The pulsed amplitudes of this source vary with its kHz QPO frequencies (Bult & van der Klis 2015). The pulsed amplitude peaks at certain upper kHz QPO frequencies which we associate with boundary layer modes of the viscous accretion disk (Erkut et al. 2008). We model this as peaks in the energy dissipation rate at the accretion caps due to resonances between the accretion column and the driving modes of the boundary layer.

  14. Pulse

    MedlinePlus

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... rate gives information about your fitness level and health.

  15. The effect of low frequency pulsing electromagnetic field in treatment of patients with knee joint osteoarthritis.

    PubMed

    Pavlović, Aleksandar S; Djurasić, Ljubomir M

    2012-01-01

    Pulsing electromagnetic field represents effective rocedure in treating of diverse diseases and p pathologic conditions, especially in rheumatology, orthopaedics and traumatology. The goal of this research is the objective evaluation of the treapeutic effect of low frequency pulsing electromagnetic field (LFEMF), in comparison with the effect of the other physical procedure: interfererence currents (IFC) and the medicamentous therapy, in treating of patients with knee joint osteoarthritis. This study was made as experimental, randomized, controlled clinical trial, opened type. The examination included 60 patients (40 females and 20 males) with osteoarthritis of the knee joint. All patients were divided in three groups. The first group of 20 persons, composed of patients treated with medicamentous therapy (Diklofenak of 100 mg, 2 tablets per day). The second group consisted of 20 patients treated by LFPEMF and the third group consisted of 20 patients treated by IFC. All procedures were implemented during 10 days All of patients had also the same duration therapeutic exercise. As observing parameter was used: Lattinen test for the evaluation of the pain sensitivity, before and after therapy. For the statistical analysis of the aquired data, was used Student's t-test. After therapy the pain was considerably reduced in each group, but this effect was the most significant in the II group of the examinees, treated by LFPEMF (p< 0.001), than the effects in other groups of patients: I group (p< 0.05) and III group (p< 0.01). According to the results of this study it can be concluded that LFPEMF is very effective therapeutic procedure in treatment of patients with knee joint osteoarthritis.

  16. Spectral Fraunhofer regime: time-to-frequency conversion by the action of a single time lens on an optical pulse.

    PubMed

    Azaña, José; Berger, Naum K; Levit, Boris; Fischer, Baruch

    2004-01-10

    We analyze a new regime in the interaction between an optical pulse and a time lens (spectral Fraunhofer regime), where the input pulse amplitude is mapped from the time domain into the frequency domain (time-to-frequency conversion). Here we derive in detail the conditions for achieving time-to-frequency conversion with a single time lens (i.e., for entering the spectral Fraunhofer regime) as well as the expressions governing this operation. Our theoretical findings are demonstrated both numerically and experimentally. A comparative study between the proposed single-time-lens configuration and the conventional dispersion + time-lens configuration for time-to-frequency conversion is also conducted. Time-to-frequency conversion with a single time lens can be used for applications similar to those previously proposed for the conventional time-to-frequency converters, e.g., high-resolution measurement of fast optical temporal waveforms. Moreover, our results also indicate that the spectral Fraunhofer regime provides additional capabilities for controlling and processing optical pulses.

  17. Instantaneous frequency time analysis of physiology signals: The application of pregnant women’s radial artery pulse signals

    NASA Astrophysics Data System (ADS)

    Su, Zhi-Yuan; Wang, Chuan-Chen; Wu, Tzuyin; Wang, Yeng-Tseng; Tang, Feng-Cheng

    2008-01-01

    This study used the Hilbert-Huang transform, a recently developed, instantaneous frequency-time analysis, to analyze radial artery pulse signals taken from women in their 36th week of pregnancy and after pregnancy. The acquired instantaneous frequency-time spectrum (Hilbert spectrum) is further compared with the Morlet wavelet spectrum. Results indicate that the Hilbert spectrum is especially suitable for analyzing the time series of non-stationary radial artery pulse signals since, in the Hilbert-Huang transform, signals are decomposed into different mode functions in accordance with signal’s local time scale. Therefore, the Hilbert spectrum contains more detailed information than the Morlet wavelet spectrum. From the Hilbert spectrum, we can see that radial artery pulse signals taken from women in their 36th week of pregnancy and after pregnancy have different patterns. This approach could be applied to facilitate non-invasive diagnosis of fetus’ physiological signals in the future.

  18. Efficient frequency doubling of a pulsed laser diode by use of a periodically poled KTP waveguide crystal with Bragg gratings

    NASA Astrophysics Data System (ADS)

    Rafailov, E. U.; Birkin, D. J. L.; Sibbett, W.; Battle, P.; Fry, T.; Mohatt, D.

    2001-12-01

    Blue light with an average power of as much as 7.5 mW in picosecond pulses has been generated at 486, 488, and 491 nm from a frequency-doubled, nonresonant injection seeded, gain-switched InGaAs/GaAs diode laser by use of a periodically poled KTP waveguide crystal that incorporates a Bragg grating section.

  19. Efficient frequency doubling of a pulsed laser diode by use of a periodically poled KTP waveguide crystal with Bragg gratings.

    PubMed

    Rafailov, E U; Birkin, D J; Sibbett, W; Battle, P; Fry, T; Mohatt, D

    2001-12-15

    Blue light with an average power of as much as 7.5 mW in picosecond pulses has been generated at 486, 488, and 491 nm from a frequency-doubled, nonresonant injection seeded, gain-switched InGaAs/GaAs diode laser by use of a periodically poled KTP waveguide crystal that incorporates a Bragg grating section. PMID:18059745

  20. The Effects of TM on Concurrent Heart Rate, Peripheral Blood Pulse Volume, and the Alpha Wave Frequency.

    ERIC Educational Resources Information Center

    Lukas, Jerome S.

    Through observation of 26 subjects over a 3 month period, this research project measured the effects of transcendental meditation (TM) on concurrent heart rate, peripheral blood pulse volume, and the alpha wave frequency. The subjects were assigned randomly to three groups. One group practiced TM as prescribed by the International Meditation…

  1. Spectral broadening measurement of the lower hybrid waves during long pulse operation in Tore Supra

    NASA Astrophysics Data System (ADS)

    Berger-By, G.; Decampy, J.; Antar, G. Y.; Goniche, M.; Ekedahl, A.; Delpech, L.; Leroux, F.; Tore Supra Team

    2014-02-01

    On many tokamaks (C-Mod, EAST, FTU, JET, HT-7, TS), a decrease in current drive efficiency of the Lower Hybrid (LH) waves is observed in high electron density plasmas. The cause of this behaviour is believed to be: Parametric Instabilities (PI) and Scattering from Density Fluctuations (SDF). For the ITER LH system, our knowledge must be improved to avoid such effects and to maintain the LH current drive efficiency at high density. The ITPA IOS group coordinates this effort [1] and all experimental data are essential to validate the numerical codes in progress. Usually the broadening of the LH wave frequency spectrum is measured by a probe located in the plasma edge. For this study, the frequency spectrum of a reflected power signal from the LH antenna was used. In addition, the spectrum measurements are compared with the density fluctuations observed on RF probes located at the antenna mouth. Several plasma currents (0.6 to 1.4 MA) and densities up to 5.2 × 1019 m-3 have been realised on Tore Supra (TS) long pulses and with high injected RF power, up to 5.4 MW-30s. This allowed using a spectrum analyser to make several measurements during the plasma pulse. The side lobe amplitude, shifted by 20-30MHz with respect to the main peak, grows with increasing density. Furthermore, for an increase of plasma current at the same density, the spectra broaden and become asymmetric. Some parametric dependencies are shown in this paper.

  2. Enhanced pulsar and single pulse detection via automated radio frequency interference detection in multipixel feeds

    NASA Astrophysics Data System (ADS)

    Kocz, J.; Bailes, M.; Barnes, D.; Burke-Spolaor, S.; Levin, L.

    2012-02-01

    Single pixel feeds on large aperture radio telescopes have the ability to detect weak (˜10 mJy) impulsive bursts of radio emission and sub-mJy radio pulsars. Unfortunately, in large-scale blind surveys, radio frequency interference (RFI) mimics both radio bursts and radio pulsars, greatly reducing the sensitivity to new discoveries as real signals of astronomical origin get lost among the millions of false candidates. In this paper a technique that takes advantage of multipixel feeds to use eigenvector decomposition of common signals is used to greatly facilitate radio burst and pulsar discovery. Since the majority of RFI occurs with zero dispersion, the method was tested on the total power present in the 13 beams of the Parkes multibeam receiver using data from archival intermediate-latitude surveys. The implementation of this method greatly reduced the number of false candidates and led to the discovery of one new rotating radio transient or RRAT, six new pulsars and five new pulses that shared the swept-frequency characteristics similar in nature to the `Lorimer burst'. These five new signals occurred within minutes of 11 previous detections of a similar type. When viewed together, they display temporal characteristics related to integer seconds, with non-random distributions and characteristic 'gaps' between them, suggesting they are not from a naturally occurring source. Despite the success in removing RFI, false candidates present in the data that are only visible after integrating in time or at non-zero dispersion remained. It is demonstrated that with some computational penalty, the method can be applied iteratively at all trial dispersions and time resolutions to remove the vast majority of spurious candidates.

  3. Space-time resolved density of helium metastable atoms in a nanosecond pulsed plasma jet: influence of high voltage and pulse frequency

    NASA Astrophysics Data System (ADS)

    Douat, Claire; Kacem, Issaad; Sadeghi, Nader; Bauville, Gérard; Fleury, Michel; Puech, Vincent

    2016-07-01

    Using tunable diode laser absorption spectroscopy, the spatio-temporal distributions of the helium He(23S1) metastable atoms’ density were measured in a plasma jet propagating in ambient air. The plasma jet was produced by applying short duration high voltage pulses on the electrodes of a DBD-like structure, at a repetition rate in the range 1–30 kHz. In addition to the metastable density, the spatial distribution of helium 587 nm emission intensity was also investigated to give insight into the excitation mechanisms of the He(33D) excited state inside the dielectric tube, in which no laser measurement can be performed. It is demonstrated that the shape of the radial distribution of helium He(23S1) metastable atoms strongly depends on the polarity of the applied voltage and on the repetition frequency. For positive applied voltages, a dramatic constriction of the excited species production is observed whenever the pulse repetition frequency is higher than 6 kHz, and the voltage higher than 5 kV. This shrinking of the jet structure induces an increase by one order of magnitude of the metastable atoms’ density in the jet centre which reaches values as high as 1014 cm‑3. Beyond a critical distance, associated to a transition between a positive streamer and a negative one, the distribution of the excited atoms gets back to an annular structure. For the negative polarity, no shrinking effect correlated to the pulse repetition frequency was observed. The on-axis constriction of the excited species for the high repetition rate and positive polarity is attributed to a memory effect induced by the negative ions, having a lifetime of hundreds of microseconds, left between successive pulses at the periphery of the helium gas flow.

  4. Space-time resolved density of helium metastable atoms in a nanosecond pulsed plasma jet: influence of high voltage and pulse frequency

    NASA Astrophysics Data System (ADS)

    Douat, Claire; Kacem, Issaad; Sadeghi, Nader; Bauville, Gérard; Fleury, Michel; Puech, Vincent

    2016-07-01

    Using tunable diode laser absorption spectroscopy, the spatio-temporal distributions of the helium He(23S1) metastable atoms’ density were measured in a plasma jet propagating in ambient air. The plasma jet was produced by applying short duration high voltage pulses on the electrodes of a DBD-like structure, at a repetition rate in the range 1-30 kHz. In addition to the metastable density, the spatial distribution of helium 587 nm emission intensity was also investigated to give insight into the excitation mechanisms of the He(33D) excited state inside the dielectric tube, in which no laser measurement can be performed. It is demonstrated that the shape of the radial distribution of helium He(23S1) metastable atoms strongly depends on the polarity of the applied voltage and on the repetition frequency. For positive applied voltages, a dramatic constriction of the excited species production is observed whenever the pulse repetition frequency is higher than 6 kHz, and the voltage higher than 5 kV. This shrinking of the jet structure induces an increase by one order of magnitude of the metastable atoms’ density in the jet centre which reaches values as high as 1014 cm-3. Beyond a critical distance, associated to a transition between a positive streamer and a negative one, the distribution of the excited atoms gets back to an annular structure. For the negative polarity, no shrinking effect correlated to the pulse repetition frequency was observed. The on-axis constriction of the excited species for the high repetition rate and positive polarity is attributed to a memory effect induced by the negative ions, having a lifetime of hundreds of microseconds, left between successive pulses at the periphery of the helium gas flow.

  5. Distortion cancellation of frequency converted pulses with simple linear signal processing and application to frequency modulation to amplitude modulation conversion in high power lasers.

    PubMed

    Vidal, Sébastien; Luce, Jacques; Hocquet, Steve; Gouédard, Claude; Calvet, Pierre; Penninckx, Denis

    2012-08-20

    It is known that a linear filter may be easily compensated with its inverse transfer function. However, it was shown that this approach could also be valid even for such a complex nonlinear system as frequency conversion. As a matter of fact, it is possible to at least partly precompensate for distortions occurring within, or even downstream from, frequency conversion crystals with a simple linear optical filter set upstream. In this paper, we give the theoretical background and derive the optimum precompensation filter from simple analytical formulas even in the case of saturation. We first show the relevance of our approach for Gaussian pulses: the pulse may be short or not and chirped or not, and the same linear precompensation filter may be used as long as saturation is not reached. We then study the case of phase-modulated pulses, as can be found on high power lasers such as lasers for fusion. We show that previous experimental results are in perfect agreement with these calculations. Finally, justified by our simple analytical formulas, we present a rigorous parametrical study giving the distortion reduction for any second and third harmonic generation system in the case of phase-modulated pulses. PMID:22907009

  6. A micropower supervisor for wireless nodes with a digital pulse frequency modulator battery monitor

    NASA Astrophysics Data System (ADS)

    Carloni, Mirko; d'Aparo, Rocco; Scorrano, Pierpaolo; Naticchia, Berardo; Conti, Massimo

    2013-05-01

    In the last few years the increased development of wireless technologies led to the development of micropower devices with power management and real time power control, aimed to maximize the battery life time.1 The main and simplest method to estimate residual battery life time is by voltage measurement. This kind of measurement is simple but is useless in many cases, especially when long term Lithium-Thionyl chloride batteries are used, since its voltage is flat for more than 90% of the battery discharge. In this case, a current control should be used. However, these kinds of devices have various problems as a limited range of measurement and not negligible quiescent current that may distort the measurements. In this work we developed a micropower supervisor for wireless sensor nodes with a charge battery monitor, whose features are aimed at solving the problems just described. The current measured by a sense resistor, is filtered by a super-capacitor, amplified by a current sense amplifier and then fed to a voltage to pulse frequency modulator. In this way, the charge consumption can be estimated without the saturation of the current sense amplifier, even if the wireless node consumes time limited high current spikes, for example during transmission.

  7. Dual Data Pulse Width Modulator for Radio Frequency Identification Biosensor Signal Modulation

    NASA Astrophysics Data System (ADS)

    Kim, Boram; Nakazato, Kazuo

    2013-04-01

    A dual data pulse width modulator is proposed and demonstrated for radio frequency identification (RFID) biosensor signal modulation. Simultaneous wireless measurement of two sensors can be carried out using this circuit, in which two analog signals are modulated and transmitted in a single clock cycle. The measured modulation sensitivity of the two input channels is 84.69 and 85.16 µs/V and the dynamic range is 55.6 and 63.5 dB, respectively. Here, redox potential and temperature are measured wirelessly using the proposed circuit. Temperature change measurement shows a sensitivity of 9.501 µs/°C in the range of 25-40 °C. The measured redox potential shows fairly good linearity for a concentration ratio of hexacyanoferrate (III) to (II) ranging from 10-2 to 102 and the slope is 58.0 mV/decade, almost the same as the theoretical value. The chip area and power consumption are 0.36 mm2 and 650 µW, respectively, using 1.2-µm, 2-metal, 2-poly CMOS technology.

  8. Reduction and degradation of amyloid aggregates by a pulsed radio-frequency cold atmospheric plasma jet

    NASA Astrophysics Data System (ADS)

    Bayliss, D. L.; Walsh, J. L.; Shama, G.; Iza, F.; Kong, M. G.

    2009-11-01

    Surface-borne amyloid aggregates with mature fibrils are used as a non-infectious prion model to evaluate cold atmospheric plasmas (CAPs) as a prion inactivation strategy. Using a helium-oxygen CAP jet with pulsed radio-frequency (RF) excitation, amyloid aggregates deposited on freshly cleaved mica discs are reduced substantially leaving only a few spherical fragments of sub-micrometer sizes in areas directly treated by the CAP jet. Outside the light-emitting part of the CAP jet, plasma treatment results in a 'skeleton' of much reduced amyloid stacks with clear evidence of fibril fragmentation. Analysis of possible plasma species and the physical configuration of the jet-sample interaction suggests that the skeleton structures observed are unlikely to have arisen as a result of physical forces of detachment, but instead by progressive diffusion of oxidizing plasma species into porous amyloid aggregates. Composition of chemical bonds of this reduced amyloid sample is very different from that of intact amyloid aggregates. These suggest the possibility of on-site degradation by CAP treatment with little possibility of spreading contamination elsewhere , thus offering a new reaction chemistry route to protein infectivity control with desirable implications for the practical implementation of CAP-based sterilization systems.

  9. A 0.9-V pulse frequency modulation photosensor based on capacitive feedback reset

    NASA Astrophysics Data System (ADS)

    Yasuoka, Koutaro; Kagawa, Keiichiro; Ohta, Jun; Nunoshita, Masahiro

    2005-03-01

    We are developing a retinal prosthesis vision chip based on a pulse-frequency-modulation (PFM) photosensor. Because the device is implanted in the eye ball and is powered by RF coil coupling with limited energy, low voltage and small current operation is required to achieve low power dissipation. We propose a capacitive-feedback-reset method for the PFM vision chip. The proposed method uses capacitive feed back through the junction capacitance of the photodiode and gate-source overlap capacitance of the reset transistor. In the proposed PFM circuit, the feed-through effect in resetting contributes to avoid current competition, so that the high dynamic range can be achieved even at the low voltage operation. We have fabricated a pixel TEG circuit in a 0.35-μm CMOS technology. The PFM photosensor circuit is composed of a four-stage inverter-chain. Dynamic range of 136dB has been achieved with 0.8-V power supply.

  10. Changes in peripheral blood levels and pulse frequencies of GnRH in patients with hypopituitarism.

    PubMed

    Hayashi, M; Takanashi, N; Yaoi, Y

    1998-09-01

    Pituitary dysfunction occasionally results from brain tumors or the surgical resection of brain tumors. The authors examined two patients with hypogonadotropic secondary amenorrhea, who had undergone surgical removal of brain tumors. Changes in immunoreactive gonadotropin-releasing hormone (GnRH) secretion are of interest in patients with a gonadotropin and gonadal steroid deficit, because both steroid and pituitary feedback systems are altered by tumors or tumor resection. The authors thus measured GnRH, luteinizing hormone, and follicle-stimulating hormone levels every 15 minutes for 4 hours by radioimmunoassay and investigated qualitative and quantitative changes in the pulsatile patterns of these hormones in two hypogonadotropic hypogonadism patients. They also performed similar multiple measurements of GnRH in two normal cycle women in follicular phase and two postmenopausal women. The concentration of plasma GnRH in two hypopituitarism patients was compared with that in two normal cycle women and two postmenopausal women. The study showed that the peripheral blood level of GnRH was significantly lower in two hypopituitarism patients than in both normal cycle and postmenopausal women, and that the pulsatile frequency was not different among these three groups. These findings suggest that alteration of feedback systems results in a decrease in the blood level of GnRH, and that pulses of GnRH maintain normal fluctuation despite the alteration of the hormonal circumstances in two hypogonadotropic hypogonadism patients. PMID:9749566

  11. Parallel electron force balance and the L-H transition

    NASA Astrophysics Data System (ADS)

    Stoltzfus-Dueck, T.

    2016-05-01

    In one popular paradigm for the L-H transition, energy transfer to the mean flows directly depletes turbulence fluctuation energy, resulting in suppression of the turbulence and a corresponding transport bifurcation. To quantitatively evaluate this mechanism, one must remember that electron parallel force balance couples nonzonal velocity fluctuations with electron pressure fluctuations on rapid timescales, comparable with the electron transit time. For this reason, energy in the nonzonal velocity stays in a fairly fixed ratio to the free energy in electron density fluctuations, at least for frequency scales much slower than electron transit. In order for direct depletion of the energy in turbulent fluctuations to cause the L-H transition, energy transfer via Reynolds stress must therefore drain enough energy to significantly reduce the sum of the free energy in nonzonal velocities and electron pressure fluctuations. At low k⊥ , the electron thermal free energy is much larger than the energy in nonzonal velocities, posing a stark challenge for this model of the L-H transition.

  12. Parallel electron force balance and the L-H transition

    DOE PAGESBeta

    Stoltzfus-Dueck, T.

    2016-05-23

    In one popular paradigm for the L-H transition, energy transfer to the mean flows directly depletes turbulence fluctuation energy, resulting in suppression of the turbulence and a corresponding transport bifurcation. To quantitatively evaluate this mechanism, one must remember that electron parallel force balance couples nonzonal velocity fluctuations with electron pressure fluctuations on rapid timescales, comparable with the electron transit time. For this reason, energy in the nonzonal velocity stays in a fairly fixed ratio to the free energy in electron density fluctuations, at least for frequency scales much slower than electron transit. Furthermore, in order for direct depletion of themore » energy in turbulent fluctuations to cause the L-H transition, energy transfer via Reynolds stress must therefore drain enough energy to significantly reduce the sum of the free energy in nonzonal velocities and electron pressure fluctuations. At low k⊥, the electron thermal free energy is much larger than the energy in nonzonal velocities, posing a stark challenge for this model of the L-H transition.« less

  13. Development of a high-speed impedance measurement system for dual-frequency capacitive-coupled pulsed-plasma.

    PubMed

    Lee, Hohyoung; Lee, Jeongbeom; Park, Gijung; Han, Yunseok; Lee, Youngwook; Cho, Gunhee; Kim, Hanam; Chang, Hongyoung; Min, Kyoungwook

    2015-08-01

    A high-speed impedance measurement system was developed, which enables the measurement of various characteristics of CW and pulsed plasmas with time resolution of less than a microsecond. For this system, a voltage and current sensor is implemented in a printed circuit board to sense the radio frequency signals. A digital board, which has a high-speed analog to digital converter and a field-programmable gate-array, is used to calculate the impedance of the signal. The final output of impedance is measured and stored with a maximum speed of 3 Msps. This sensor system was tested in a pulsed-plasma by applying it to the point between the matching box and the plasma chamber. The experimental equipment was constructed connecting the matching box, a 13.56 MHz generator, a 2 MHz generator that produced pulsed power, and a pulse-signal generator. From the temporal behavior of the measured impedance, we were able to determine the time intervals of transient states, especially of the initial active state. This information can be used to set the pulse frequency and duty for plasma processing. PMID:26329190

  14. Implementing fast sideband-modulated ``wah-wah'' pulses for driving transmon qubits with tight frequency separation

    NASA Astrophysics Data System (ADS)

    Vesterinen, V.; Saira, O.-P.; Bruno, A.; Egger, D. J.; Wilhelm, F. K.; Dicarlo, L.

    2014-03-01

    Packing multiple transmon qubits in a narrow frequency band is challenging due to the limited transmon anharmonicity: control drives targeting one qubit may drive the leakage transition of another. This cross-driving effect grows with decreasing gate time, potentially imposing a quantum speed limit. The widely used DRAG (derivative removal by adiabatic gate) technique only suppresses leakage in the targeted transmon. Adding a modulation tone to a Gaussian pulse envelope in one quadrature, and complementing with DRAG in the other, has been predicted [1] to reduce both intrinsic and cross-driving leakage. We have experimentally verified the performance of this new pulse-shaping method, termed ``wah-wah,'' with two transmons in a 2D circuit QED architecture. We optimize the modulation frequency and amplitude, and characterize the gate fidelity using randomized benchmarking (RB) and quantum process tomography. Pulses on the two qubits are characterized separately and simultaneously by interleaving the RB sequences. Wah-wah pulses show decoherence-limited fidelity at gate speeds where DRAG pulses add significant error. Research supported by NWO, EU projects SOLID and SCALEQIT, and the Research Foundation of Helsinki University of Technology.

  15. Studies on gas breakdown in pulsed radio frequency atmospheric pressure glow discharges

    SciTech Connect

    Huo, W. G.; Jian, S. J.; Yao, J.; Ding, Z. F.

    2014-05-15

    In pulsed RF atmospheric pressure glow discharges, the gas breakdown judged by the rapid drop in the amplitude of the pulsed RF voltage is no longer universally true. The steep increment of the plasma-absorbed RF power is proposed to determine the gas breakdown. The averaged plasma-absorbed RF power over a pulse period is used to evaluate effects of the preceding pulsed RF discharge on the breakdown voltage of the following one, finding that the breakdown voltage decreases with the increment in the averaged plasma-absorbed RF power under constant pulse duty ratio. Effects of the pulse off-time on the breakdown voltage and the breakdown delay time are also studied. The obtained dependence of the breakdown voltage on the pulse off-time is indicative of the transitional plasma diffusion processes in the afterglow. The breakdown voltage varies rapidly as the plasma diffuses fast in the region of moderate pulse off-time. The contribution of nitrogen atom recombination at the alumina surface is demonstrated in the prolonged memory effect on the breakdown delay time vs. the pulse off-time and experimentally validated by introducing a trace amount of nitrogen into argon at short and long pulse off-times.

  16. Study on the mode-transition of nanosecond-pulsed dielectric barrier discharge between uniform and filamentary by controlling pressures and pulse repetition frequencies

    NASA Astrophysics Data System (ADS)

    Yu, S.; Pei, X.; Hasnain, Q.; Nie, L.; Lu, X.

    2016-02-01

    In this paper, we investigate the temporally resolved evolution of the nanosecond pulsed dielectric barrier discharge (DBD) in a moderate 6 mm discharge gap under various pressures and pulse repetition frequencies (PRFs) by intensified charge-coupled device (ICCD) images, using dry air and its components oxygen and nitrogen. It is found that the pressures are very different when the mode transits between uniform and filamentary in air, oxygen, and nitrogen. The PRFs can also obviously affect the mode-transition. The transition mechanism in the pulsed DBD is not Townsend-to-Streamer, which is dominant in the traditional alternating-voltage DBD. The pulsed DBD in a uniform mode develops in the form of plane ionization wave due to overlap of primary avalanches, while the increase in pressure disturbs the overlap and discharge develops in streamer, corresponding to the filamentary mode. Increasing the initial electron density by pre-ionization may contribute to discharge uniformity at higher pressures. We also found that the dependence of homogeneity upon PRF is a non-monotonic one.

  17. Criteria for formation of low-frequency sound under wide-aperture repetitively pulsed laser irradiation of solids

    SciTech Connect

    Tishchenko, V N; Posukh, V G; Gulidov, A I; Zapryagaev, V I; Pavlov, A A; Boyarintsev, Ye L; Golubev, M P; Kavun, I N; Melekhov, A V; Golobokova, L S; Miroshnichenko, I B; Pavlov, Al A; Shmakov, A S

    2011-10-31

    The criteria for merging shock waves formed by optical breakdowns on the surface of solids have been investigated. Targets made of different materials were successively irradiated by two CO{sub 2}-laser pulses with energies up to 200 J and a duration of {approx}1 {mu}s. It is shown that the criteria under consideration can be applied to different targets and irradiation regimes and make it possible to calculate the parameters of repetitively pulsed laser radiation that are necessary to generate low-frequency sound and ultrasound in air.

  18. 3-D Surface Depression Profiling Using High Frequency Focused Air-Coupled Ultrasonic Pulses

    NASA Technical Reports Server (NTRS)

    Roth, Don J.; Kautz, Harold E.; Abel, Phillip B.; Whalen, Mike F.; Hendricks, J. Lynne; Bodis, James R.

    1999-01-01

    Surface topography is an important variable in the performance of many industrial components and is normally measured with diamond-tip profilometry over a small area or using optical scattering methods for larger area measurement. This article shows quantitative surface topography profiles as obtained using only high-frequency focused air-coupled ultrasonic pulses. The profiles were obtained using a profiling system developed by NASA Glenn Research Center and Sonix, Inc (via a formal cooperative agreement). (The air transducers are available as off-the-shelf items from several companies.) The method is simple and reproducible because it relies mainly on knowledge and constancy of the sound velocity through the air. The air transducer is scanned across the surface and sends pulses to the sample surface where they are reflected back from the surface along the same path as the incident wave. Time-of-flight images of the sample surface are acquired and converted to depth/surface profile images using the simple relation (d = V*t/2) between distance (d), time-of-flight (t), and the velocity of sound in air (V). The system has the ability to resolve surface depression variations as small as 25 microns, is useable over a 1.4 mm vertical depth range, and can profile large areas only limited by the scan limits of the particular ultrasonic system. (Best-case depth resolution is 0.25 microns which may be achievable with improved isolation from vibration and air currents.) The method using an optimized configuration is reasonably rapid and has all quantitative analysis facilities on-line including 2-D and 3-D visualization capability, extreme value filtering (for faulty data), and leveling capability. Air-coupled surface profilometry is applicable to plate-like and curved samples. In this article, results are shown for several proof-of-concept samples, plastic samples burned in microgravity on the STS-54 space shuttle mission, and a partially-coated cylindrical ceramic

  19. Ionization-Induced Multiwave Mixing: Terahertz Generation with Two-Color Laser Pulses of Various Frequency Ratios

    NASA Astrophysics Data System (ADS)

    Kostin, V. A.; Laryushin, I. D.; Silaev, A. A.; Vvedenskii, N. V.

    2016-07-01

    Ultrafast strong-field ionization is shown to be accompanied by atypical multiwave mixing with the number of mixed waves defined by the dependence of the ionization rate on the field strength. For two-color laser pulses of various frequency ratios, this results in the excitation of a free-electron current at laser combination frequencies and possibly in the excitation of the zero-frequency (residual) current responsible for terahertz (THz) generation in a formed plasma. The high-order nature of ionization-induced wave mixing may cause THz generation with uncommon laser frequency ratios (such as 2 : 3 and 3 : 4 ) to be virtually as effective as that with the commonly used frequency ratio of 1 : 2 .

  20. Time and Frequency Domain Analysis of Thunderstorm - Narrow Bipolar Electromagnetic Pulses and Cloud To-Ground Lightning Fields.

    NASA Astrophysics Data System (ADS)

    Medelius, Pedro Javier

    Single-station electric field (E) and electric field derivative (dE/dt) waveforms were recorded at digitization rates up to 400 MS/s during 1989 and 1990 at the Kennedy Space Center. Narrow bipolar pulses (NBP's) were found to occur separate from typical lightning events, but to be thunderstorm related. Frequency spectra for E obtained from NBP's dropped at a rate of close to 1/f up to 125 MHz. In comparison, the frequency spectra reported by Willett et al. (1989) for similar pulses dropped as 1/f up to about 20 MHz and became flat afterwards up to their 50 MHz Nyquist frequency. NBP's contained higher energy than return strokes above 10-20 MHz. NBP Spectra found from the output of digitally simulated narrowband receivers tended to underestimate the wideband frequency spectra by as much as 10 dB, indicating that the spectra obtained using narrowband receivers are unreliable. Initial E-field peaks of NBP's had a mean rise time of 1.38 mus. Large positive dE/dt pulses had a mean half width of 7 ns, much shorter than the 49 ns reported by Willett et al. (1989). The existence of a single process responsible for VHF radiation from lightning, such as that proposed by Labaune et al. (1990), was tested using deconvolution methods on the NBP waveforms. Our analysis failed to identify a single basic component in these pulses. Electric fields from lightning strikes at distances within 1-2 km consistently exhibited a chaotic behavior during the stepped leader, whereas distant stepped leaders did not. This "chaos" ranged from pulses occurring at rates close to one pulse per mus to a continuous noise-like high frequency signal with frequency components extending beyond 120 MHz. In agreement with other reports in the literature, we found that HF radiation following return strokes peaked 20-30 mus after the onset of the return stroke, and persisted for several tens of microseconds after the peak. However, the short propagation path (less than 7.5 km) over salt water does not

  1. Generation of optical frequency combs in fibres: an optical pulse analysis

    NASA Astrophysics Data System (ADS)

    Zajnulina, Marina; Böhm, Michael; Blow, Keith; Chavez Boggio, José M.; Rieznik, Andres A.; Haynes, Roger; Roth, Martin M.

    2014-07-01

    The innovation of optical frequency combs (OFCs) generated in passive mode-locked lasers has provided astronomy with unprecedented accuracy for wavelength calibration in high-resolution spectroscopy in research areas such as the discovery of exoplanets or the measurement of fundamental constants. The unique properties of OCFs, namely a highly dense spectrum of uniformly spaced emission lines of nearly equal intensity over the nominal wavelength range, is not only beneficial for high-resolution spectroscopy. Also in the low- to medium-resolution domain, the OFCs hold the promise to revolutionise the calibration techniques. Here, we present a novel method for generation of OFCs. As opposed to the mode-locked laser-based approach that can be complex, costly, and difficult to stabilise, we propose an all optical fibre-based system that is simple, compact, stable, and low-cost. Our system consists of three optical fibres where the first one is a conventional single-mode fibre, the second one is an erbium-doped fibre and the third one is a highly nonlinear low-dispersion fibre. The system is pumped by two equally intense continuous-wave (CW) lasers. To be able to control the quality and the bandwidth of the OFCs, it is crucial to understand how optical solitons arise out of the initial modulated CW field in the first fibre. Here, we numerically investigate the pulse evolution in the first fibre using the technique of the solitons radiation beat analysis. Having applied this technique, we realised that formation of higherorder solitons is supported in the low-energy region, whereas, in the high-energy region, Kuznetsov-Ma solitons appear.

  2. Efficacy of pulsed radio frequency energy therapy in temporomandibular joint pain and dysfunction.

    PubMed

    Al-Badawi, Emad A; Mehta, Noshir; Forgione, Albert G; Lobo, Silvia Lobo; Zawawi, Khalid H

    2004-01-01

    This randomized double-blind study evaluated the effectiveness of pulsed radio frequency energy therapy (PRFE) in patients with temporomandibular joint arthralgia. Forty subjects (age range 22 to 55 yrs.) were assigned randomly into two equal groups: (1) Experimental group received PRFE using the Energex unit (Energex, Inc. Emerson, New Jersey) and (2) Control group received PRFE placebo treatment using a sham device. Both groups received six applications to the TMJ area over two weeks. Data were analyzed for the following times: baseline, first and second follow-up visits. Numerical Rating Scale scores for TMJ pain showed a significant reduction over time for the experimental group (mean = 6.13 to 3.05, p < 0.001). There was also a significant effect for the controls (mean = 5.35 to 4.20, p = 0.01). The effect for experimental subjects was a mean reduction of 3.07 versus 1.15 for controls. The significant reduction in controls was attributed to the placebo effect. The experimental group showed a significant increase in mouth opening (mean = 34.95 to 41.70 mm, p = 0.002), right lateral movement (mean = 7.85 to 10.80 mm, p = 0.001) and left lateral movement (mean = 7.65 to 10.85 mm, p < 0.0001). No significant (p > 0.1) change in the control group occurred for mouth opening (mean = 38.50 to 39.65 mm), right lateral movement (mean = 8.60 to 8.75 mm) and left lateral movement (mean = 8.50 to 8.80 mm). No side effects were reported during the treatment and the two week follow-up. These results suggest strongly that PRFE is a safe and effective treatment for TMJ arthralgia as well as for increasing mandibular range of motion.

  3. Hydroxyapatite thin films grown by pulsed laser deposition and radio-frequency magnetron sputtering: comparative study

    NASA Astrophysics Data System (ADS)

    Nelea, V.; Morosanu, C.; Iliescu, M.; Mihailescu, I. N.

    2004-04-01

    Hydroxyapatite (HA) thin films for applications in the biomedical field were grown by pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RF-MS) techniques. The depositions were performed from pure hydroxyapatite targets on Ti-5Al-2.5Fe (TiAlFe) alloys substrates. In order to prevent the HA film penetration by Ti atoms or ions diffused from the Ti-based alloy during and after deposition, the substrates were pre-coated with a thin buffer layer of TiN. In both cases, TiN was introduced by reactive PLD from TiN targets in low-pressure N 2. The PLD films were grown in vacuum onto room temperature substrates. The RF-MS films were deposited in low-pressure argon on substrates heated at 550 °C. The initially amorphous PLD thin films were annealed at 550 °C for 1 h in ambient air in order to restore the initial crystalline structure of HA target. The thickness of the PLD and RF-MS films were ˜1 μm and ˜350 nm, respectively. All films were structurally studied by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS) and white light confocal microscopy (WLCM). The mechanical properties of the films were tested by Berkovich nano-indentation. Both PLD and RF-MS films mostly contain HA phase and exhibit good mechanical characteristics. Peaks of CaO were noticed as secondary phase in the GIXRD patterns only for RF-MS films. By its turn, the sputtered films were smoother as compared to the ones deposited by PLD (50 nm versus 250 nm average roughness). The RF-MS films were harder, more mechanically resistant and have a higher Young modulus.

  4. Definition of Shifts of Optical Transitions Frequencies due to Pulse Perturbation Action by the Photon Echo Signal Form

    NASA Astrophysics Data System (ADS)

    Lisin, V. N.; Shegeda, A. M.; Samartsev, V. V.

    2015-09-01

    A relative phase shift between the different groups of excited dipoles, which appears as result of its frequency splitting due to action of a pulse of electric or magnetic fields, depends on a time, if the pulse overlaps in time with echo-pulse. As а consequence, the echo waveform is changed. The echo time form is modulated. The inverse modulation period well enough approximates Zeeman and pseudo-Stark splitting in the cases of magnetic and, therefore, electrical fields. Thus the g-factors of ground 4I15/2 and excited 4F9/2 optical states of Er3+ ion in LuLiF4 and YLiF4 have been measured and pseudo-Stark shift of R1 line in ruby has been determined.

  5. Temporal characterization of mid-IR free-electron-laser pulses by frequency-resolved optical gating

    SciTech Connect

    Richman, B.A.; Krumbuegel, M.A.; Trebino, R.

    1997-05-01

    We performed what we believe are the first practical full-temporal-characterization measurements of ultrashort pulses from a free-electron laser (FEL). Second-harmonic-generation frequency-resolved optical gating (FROG) was used to measure a train of mid-IR pulses distorted by a saturated water-vapor absorption line and showing free-induction decay. The measured direction of time was unambiguous because of prior knowledge regarding free-induction decay. These measurements require only 10{percent} of the power of the laser beam and demonstrate that FROG can be implemented as a pulse diagnostic simultaneously with other experiments on a FEL. {copyright} {ital 1997} {ital Optical Society of America}

  6. Contrasting effects of different levels of food intake and adiposity on LH secretion and hypothalamic gene expression in sheep.

    PubMed

    Archer, Z A; Rhind, S M; Findlay, P A; Kyle, C E; Thomas, L; Marie, M; Adam, C L

    2002-11-01

    Body reserves (long-term) and food intake (short-term) both contribute nutritional feedback to the hypothalamus. Reproductive neuroendocrine output (GnRH/LH) is stimulated by increased food intake and not by high adiposity in sheep, but it is unknown whether appetite-regulating hypothalamic neurons show this differential response. Castrated male sheep (Scottish Blackface) with oestradiol implants were studied in two 4 week experiments. In Experiment 1, sheep were fed to maintain the initial body condition (BC) score of 2.0+/-0.00 (lower BC (LBC), n=7) or 2.9+/-0.09 (higher BC (HBC), n=9), and liveweight of 43+/-1.1 and 59+/-1.6 kg respectively. LBC and HBC sheep had similar mean plasma LH concentration, pulse frequency and amplitude, but HBC animals had higher mean plasma concentrations of insulin (P<0.01), leptin (P<0.01) and glucose (P<0.01). Gene expression (measured by in situ hybridisation) in the hypothalamic arcuate nucleus (ARC) was higher in LBC than HBC sheep for neuropeptide Y (NPY; 486% of HBC, P<0.01), agouti-related peptide (AGRP; 467%, P<0.05) and leptin receptor (OB-Rb; 141%, P<0.05), but lower for cocaine- and amphetamine-regulated transcript (CART; 92%, P<0.05) and similar between groups for pro-opiomelanocortin (POMC). In Experiment 2, sheep with initial mean BC score 2.4+/-0.03 and liveweight 55+/-0.8 kg were fed a liveweight-maintenance ration (low intake, LI, n=7) while sheep with initial mean BC score 2.0+/-0.03 and liveweight 43+/-1.4 kg were fed freely so that BC score increased to 2.5+/-0.00 and liveweight increased to 54+/-1.4 kg (high intake, HI, n=9). Compared with LI, HI sheep had higher mean plasma LH (P<0.05), baseline LH (P<0.01) and pulse amplitude (P<0.01) and showed a trend towards higher pulse frequency. Although there were no differences in final mean plasma concentrations, there were significant increases over time in mean concentrations of insulin (P<0.001), leptin (P<0.05) and glucose (P<0.001) in HI sheep. Gene expression

  7. Estimation of Arterial Stiffness by Time-Frequency Analysis of Pulse Wave

    NASA Astrophysics Data System (ADS)

    Saito, Masashi; Yamamoto, Yuya; Shibayama, Yuka; Matsukawa, Mami; Watanabe, Yoshiaki; Furuya, Mio; Asada, Takaaki

    2011-07-01

    Evaluation of a pulse wave is effective for the early diagnosis of arteriosclerosis because the pulse wave contains the reflected wave that is the age- and stiffness-dependent component. In this study, we attempted to extract the parameter reflecting the component by pulse wave analysis using continuous wavelet transform. The Morlet wavelet was used as the mother wavelet. We then investigated the relationship between the parameter and the reflected wave that was extracted from the pulse wave by our previously reported separation technique. Consequently, the result of wavelet transform of the differentiated pulse waveform changed markedly owing to age and had medium correlation with the peak of the reflected wave (R=0.68).

  8. Maternal postpartum learned helplessness (LH) affects maternal care by dams and responses to the LH test in adolescent offspring.

    PubMed

    Kurata, Akiko; Morinobu, Shigeru; Fuchikami, Manabu; Yamamoto, Shigeto; Yamawaki, Shigeto

    2009-06-01

    It is known that the early environment affects the mental development of rodent and human offspring. However, it is not known specifically whether a postpartum depressive state influences the depressive state in offspring. Using learned helplessness (LH) in rats as an animal model of depression, we examined the influence of maternal postpartum LH on responses to the LH test of offspring. Dam rats were judged as LH or non-helpless (nLH) on postnatal days (PN) 2-3, and maternal behavior was recorded during PN2-14. On PN 45-46, offspring were subjected to the LH test. Plasma corticosterone (CORT) levels, hippocampal levels of glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) mRNA were measured before and after the LH test in offspring. Active nursing in LH dams was significantly lower than that in nLH dams. Susceptibility to LH in the offspring of LH dams was significantly higher than in those of nLH dams, and was negatively correlated with active nursing by LH dams. The GR mRNA levels before and after the LH test were lower in the offspring of LH dams than in those of nLH dams, and the reduced basal GR mRNA and protein might have resulted in the higher CORT response after the LH test. There was no significant difference in BDNF mRNA in the offspring of LH and nLH dams. These findings suggest that early postpartum LH decreased active nursing and increased depression-like behavior in the adolescent offspring via dysfunction of the hypothalamic-pituitary-adrenal axis. PMID:19341740

  9. Comparison of Reconstruction Intervals in Routine ECG-Pulsed 64-Row-MSCT Coronary Angiography in Frequency Controlled Patients

    SciTech Connect

    Frydrychowicz, Alex Pache, Gregor; Saueressig, Ulrich; Foell, Daniela; Kotter, Elmar; Langer, Mathias; Bley, Thorsten A.

    2007-02-15

    Purpose. In light of the increasing use and acceptance of multislice computed tomography (MSCT) coronary angiography it was the purpose of this study to compare reconstruction intervals used in a routine ECG-pulsed MSCT coronary artery angiography setting with frequency controlled patients. Methods. Examinations were performed on a Siemens Somatom Sensation 64 scanner with a total of 110 ml of contrast agent and ECG pulsing (interval from 40% to 70%) after oral application of a {beta}-blocker if the heart rate was higher than 65 bpm. All human subjects were referred for the evaluation of suspected coronary artery disease. Coronary artery segments were evaluated by two experienced radiologists in a consensus reading. A ranking of diagnostic image quality (from 1 (no evaluation possible) to 5 (excellent image quality)) was statistically evaluated by Wilcoxon Signed Rank Test. Results. In 45 patients (30 male, 15 female, age 63.8 {+-} 12.1 years) we detected a significant advantage of the 60% reconstruction interval over 40%, 50%, and 70% (for each p < 0.05). In cases of sudden arrhythmia or movement during the scan, additional reconstruction intervals within the ECG-pulsed reconstruction intervals remained necessary for diagnosis. Conclusion. In a routine diagnostic setting with frequency controlled patients and ECG pulsing the 60% reconstruction interval can be considered superior for the initial diagnosis in 64-row multislice computed tomography coronary angiography. However, further information can be derived from various reconstruction intervals such as 40% and 70%.

  10. Concurrent effects of resource pulse amount, type, and frequency on community and population properties of consumers in detritus-based systems

    PubMed Central

    Juliano, Steven A.

    2012-01-01

    Episodic resource inputs (i.e., pulses) can affect food web properties and community dynamics, but detailed mechanistic understanding of such effects remain elusive. Natural aquatic microsystems (e.g., tree holes, human-made containers) are colonized by invertebrates that form complex food webs dependent on episodic and sometimes sizeable inputs of allochthonous detritus from adjacent terrestrial environments. We investigated how variation in pulse frequency, amount, and resource type interacted to affect richness, abundance, composition, and population sizes of colonizing invertebrates in water-filled tires and tree hole analogs in a forest habitat. Different container types were used to assess the generality of effects across two environmental contexts. Containers received large infrequent or small frequent pulses of animal or leaf detritus of different cumulative amounts distributed over the same period. Invertebrates were sampled in June and September when cumulative detritus input was equal for the two pulse frequencies. Pulse frequency and detritus type interacted to affect the responses of richness and abundance in both months; pulse frequency alone in June affected the relationship between richness and abundance. Richness and abundance were also greater with more detritus regardless of detritus type. One group, the filter feeders, were most important in driving the response of abundance and richness to pulses, especially in June. This work highlights the potential complex nature of responses of communities and populations to resource pulses and implicates the ability of certain groups to exploit pulses of detrital resources as a key to understanding community-level responses to pulses. PMID:22134863

  11. Frequency divide-and-conquer approach to producing octave-wide frequency combs and few-cycle pulses in the mid-IR

    NASA Astrophysics Data System (ADS)

    Vodopyanov, Konstantin

    2014-05-01

    I will present a new technique for extending frequency combs to the highly desirable yet difficult-to-achieve mid-IR spectral range. The technique is based on subharmonic optical parametric oscillation (OPO) that can be considered as a reverse of the second harmonic generation process. The frequency comb of a pump laser is transposed to half of its central frequency and simultaneously spectrally augmented, thanks to an enormous gain bandwidth of the OPO near degeneracy, as well as due to massive cross-coupling between the laser and the OPO frequency comb components. Using ultrafast erbium (1.56 microns) or thulium (2 microns)-based fiber lasers as a pump and using thin, sub-mm-long, quasi phase-matched lithium niobate or gallium arsenide crystals, we produce frequency combs centered correspondingly at 3.1 or 4 micron subharmonic of the pump frequency. With the properly managed OPO cavity group velocity dispersion, octave-wide frequency combs spanning 2.5 - 6 micron range were achieved. Due to the doubly-resonant operation, the threshold of such a system is low (typically 10 mW) and by several experiments including measuring frequency beats between the OPO comb teeth and a narrow-linewidth CW laser and by interfering the outputs of two identical but distinct OPOs pumped by the same laser, we established that the frequency comb from a subharmonic OPO is phase-locked to that of the pump laser. Pulse duration measurements show that for the optimal intracavity dispersion conditions, we generate sub 5-cycle pulses at the subharmonic of the pump. I will also talk about applications of our mid-IR frequency combs to trace gas detection, where part-per-billion sensitivity of molecular detection is achieved as well as about Fourier spectroscopy using a dual-comb system consisting of two phase-locked lasers. I thank NASA, Office of Naval Research, Air Force Office of Scientific Research, Agilent Technologies, Sanofi- Aventis, Stanford University Bio-X, Stanford Medical School

  12. Grism-based pulse shaper for line-by-line control of more than 600 optical frequency comb lines.

    PubMed

    Kirchner, M S; Diddams, S A

    2010-10-01

    We construct a line-by-line pulse shaper using a grism (grating plus prism) dispersive element, which provides constant angular dispersion over 13.4 THz centered at ~311 THz (965 nm). When combined with a dual-mask liquid crystal modulator, this grism-based shaper is capable of line-by-line amplitude and phase control of over 600 modes of a 21 GHz stabilized optical frequency comb.

  13. Grism-based pulse shaper for line-by-line control of more than 600 optical frequency comb lines.

    PubMed

    Kirchner, M S; Diddams, S A

    2010-10-01

    We construct a line-by-line pulse shaper using a grism (grating plus prism) dispersive element, which provides constant angular dispersion over 13.4 THz centered at ~311 THz (965 nm). When combined with a dual-mask liquid crystal modulator, this grism-based shaper is capable of line-by-line amplitude and phase control of over 600 modes of a 21 GHz stabilized optical frequency comb. PMID:20890354

  14. Generation of picosecond pulses and frequency combs in actively mode locked external ring cavity quantum cascade lasers

    SciTech Connect

    Wójcik, Aleksander K.; Belyanin, Alexey; Malara, Pietro; Blanchard, Romain; Mansuripur, Tobias S.; Capasso, Federico

    2013-12-02

    We propose a robust and reliable method of active mode locking of mid-infrared quantum cascade lasers and develop its theoretical description. Its key element is the use of an external ring cavity, which circumvents fundamental issues undermining the stability of mode locking in quantum cascade lasers. We show that active mode locking can give rise to the generation of picosecond pulses and phase-locked frequency combs containing thousands of the ring cavity modes.

  15. Plasma channel produced by femtosecond laser pulses as a medium for amplifying electromagnetic radiation of the subterahertz frequency range

    SciTech Connect

    Bogatskaya, A V; Volkova, E A; Popov, A M

    2013-12-31

    The electron energy distribution function in the plasma channel produced by a femtosecond laser pulse with a wavelength of 248 nm in atmospheric-pressure gases was considered. Conditions were determined whereby this channel may be employed for amplifying electromagnetic waves up to the terahertz frequency range over the energy spectrum relaxation time ∼10{sup -7} s. Gains were calculated as functions of time and radiation frequency. The effect of electron – electron collisions on the rate of relaxation processes in the plasma and on its ability to amplify the electromagnetic radiation was investigated. (interaction of laser radiation with matter)

  16. Anomalous enhancement and suppression of ionization induced by an effective few-cycle pulse in the frequency domain

    NASA Astrophysics Data System (ADS)

    Foote, David; Lin, Yingda; Hill, Wendell T., III

    2015-05-01

    In a recent set of coherent control experiments, an anomalous sinusoidal variation of the ionization yield was observed in Xe when ionized by a pairs of phase-locked, many-cycle 800 nm pulses. Compared with the signal of a single transform limited pulse, both enhancement and suppression was possible, which depended on the temporal separation and relative phase of the pulses. In the time domain, the control can be viewed as a temporal Young's double slit experiment - two coherent electron wavepackets interfering. In the frequency domain, the photoelectron spectrum is given by the modulus squared of the Fourier transform of the field, which is a few-cycle squared sinusodial function. In analogy to a few-cycle pulse where the carrier phase dictates the ejection direction of rescattered electrons, enhancement (suppression) occurs when the effective carrier waveform is cos[w-w0]2 (sin[w-w0]2). The contrast decreased with increasing pulse separation and decreasing multiphoton order. Detailed results and a model simulation will be presented.

  17. Hairpin resonator probes with frequency domain boxcar operation for time resolved density measurements in pulsed RF discharges

    NASA Astrophysics Data System (ADS)

    Peterson, David; Kummerer, Theresa; Coumou, David; Shannon, Steven

    2014-10-01

    In this work, microsecond time resolved electron density measurements in pulsed RF discharges are shown using an automated hairpin resonance probe using relatively low cost electronics, on par with normal Langmuir probe boxcar mode operation. A low cost signal generator is used to produce the applied microwave frequency and the reflected waveform is filtered to remove the RF component. The signal is then heterodyned with a simple frequency mixer to produce a dc signal read by an oscilloscope to determine the electron density. The applied microwave frequency is automatically shifted in small increments in a frequency boxcar routine through a Labview™program to determine the resonant frequency. A simple dc sheath correction is then easily applied since the probe is fully floating, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in a capacitively coupled, parallel plate configuration in a 13.56 MHz, 50--200 W RF discharge pulsed at 500 Hz, 200 W, 50% duty cycle. The gas input ranged from 50--100 mTorr pure Ar or with 5--10% O/He mixtures.

  18. Soft-Decision-Data Reshuffle to Mitigate Pulsed Radio Frequency Interference Impact on Low-Density-Parity-Check Code Performance

    NASA Technical Reports Server (NTRS)

    Ni, Jianjun David

    2011-01-01

    This presentation briefly discusses a research effort on mitigation techniques of pulsed radio frequency interference (RFI) on a Low-Density-Parity-Check (LDPC) code. This problem is of considerable interest in the context of providing reliable communications to the space vehicle which might suffer severe degradation due to pulsed RFI sources such as large radars. The LDPC code is one of modern forward-error-correction (FEC) codes which have the decoding performance to approach the Shannon Limit. The LDPC code studied here is the AR4JA (2048, 1024) code recommended by the Consultative Committee for Space Data Systems (CCSDS) and it has been chosen for some spacecraft design. Even though this code is designed as a powerful FEC code in the additive white Gaussian noise channel, simulation data and test results show that the performance of this LDPC decoder is severely degraded when exposed to the pulsed RFI specified in the spacecraft s transponder specifications. An analysis work (through modeling and simulation) has been conducted to evaluate the impact of the pulsed RFI and a few implemental techniques have been investigated to mitigate the pulsed RFI impact by reshuffling the soft-decision-data available at the input of the LDPC decoder. The simulation results show that the LDPC decoding performance of codeword error rate (CWER) under pulsed RFI can be improved up to four orders of magnitude through a simple soft-decision-data reshuffle scheme. This study reveals that an error floor of LDPC decoding performance appears around CWER=1E-4 when the proposed technique is applied to mitigate the pulsed RFI impact. The mechanism causing this error floor remains unknown, further investigation is necessary.

  19. Note: radio frequency inductance-capacitance band-stop filter circuit to perform contactless conductivity measurements in pulsed magnetic fields.

    PubMed

    Altarawneh, M M

    2012-09-01

    We present a new technique to perform radio frequency (rf) contactless conductivity measurements in pulsed magnetic fields to probe different ground states in condensed matter physics. The new method utilizes a simple analog band-stop filter circuit implemented in a radio frequency transmission setup to perform contactless conductivity measurements. The new method is more sensitive than the other methods (e.g., the tunnel diode oscillator and the proximity detector oscillator) due to more sensitive dependence of the circuit resonance frequency on the tank circuit inductance (not the transmission line). More important, the new method is more robust than other methods when used to perform measurements in very high magnetic fields, works for a wide range of temperatures (i.e., 300 K-1.4 K) and is less sensitive to noise and mechanical vibrations during pulse magnet operation. The new technique was successfully applied to measure the Shubnikov-de Haas effect in Bi(2)Se(3) in pulsed magnetic fields of up to 60 T.

  20. Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation.

    PubMed

    Naeem, Tariq Mahmood; Matsuta, Hideyuki; Wagatsuma, Kazuaki

    2004-05-01

    An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N(2)(+) 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed. PMID:15034707

  1. Influence of driving frequency on discharge modes in a dielectric-barrier discharge with multiple current pulses

    SciTech Connect

    Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

    2013-07-15

    A one-dimensional self-consistent fluid model was employed to investigate the effect of the driving frequency on the discharge modes in atmospheric-pressure argon discharge with multiple current pulses. The discharge mode was discussed in detail not only at current peaks but also between two adjacent peaks. The simulation results show that different transitions between the Townsend and glow modes during the discharge take place with the driving frequency increased. A complicated transition from the Townsend mode, through glow, Townsend, and glow, and finally back to the Townsend one is found in the discharge with the driving frequency of 8 kHz. There is a tendency of transition from the Townsend to glow mode for the discharge both at the current peaks and troughs with the increasing frequency. The discharge in the half period can all along operate in the glow mode with the driving frequency high enough. This is resulted from the preservation of more electrons in the gas gap and acquisition of more electron energy from the swiftly varying electric field with the increase in driving frequency. Comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increment of the driving frequency allows the plasma chemistry to be enhanced. This electrical characteristic is important for the applications, such as surface treatment and biomedical sterilization.

  2. Three-dimensional time and frequency-domain theory of femtosecond x-ray pulse generation through Thomson Scattering

    SciTech Connect

    Brown, W J; Hartemann, F V

    2004-01-27

    The generation of high intensity, ultra-short x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. Thomson backscattering of a high intensity laser pulse with a bright relativistic electron bunch is a promising method for producing such high brightness x-ray pulses in the 10-100 keV range within a compact facility. While a variety of methods for producing sub-picosecond x-ray bursts by Thomson scattering exist, including compression of the electron bunch to sub-picosecond bunch lengths and/or colliding a sub-picosecond laser pulse in a side-on geometry to minimize the interaction time, a promising alternative approach to achieving this goal while maintaining ultra-high brightness is the production of a time correlated (or chirped) x-ray pulse in conjunction with pulse slicing or compression. We present the results of a complete analysis of this process using a recently developed 3-D time and frequency-domain code for analyzing the spatial, temporal, and spectral properties an x-ray beam produced by relativistic Thomson scattering. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, laser focus, and the transverse and longitudinal phase space of the electron beam were examined. Simulations of chirped x-ray pulse production using both a chirped electron beam and a chirped laser pulse are presented. Required electron beam and laser parameters are summarized by investigating the effects of beam emittance, energy spread, and laser bandwidth on the scattered x-ray spectrum. It is shown that sufficient temporal correlation in the scattered x-ray spectrum

  3. Efficiency of non-linear frequency conversion of double-scale pico-femtosecond pulses of passively mode-locked fiber laser.

    PubMed

    Smirnov, Sergey V; Kobtsev, Sergey M; Kukarin, Sergey V

    2014-01-13

    For the first time we report the results of both numerical simulation and experimental observation of second-harmonic generation as an example of non-linear frequency conversion of pulses generated by passively mode-locked fiber master oscillator in different regimes including conventional (stable) and double-scale (partially coherent and noise-like) ones. We show that non-linear frequency conversion efficiency of double-scale pulses is slightly higher than that of conventional picosecond laser pulses with the same energy and duration despite strong phase fluctuations of double-scale pulses. PMID:24515065

  4. Effect of the stimulus frequency and pulse number of repetitive transcranial magnetic stimulation on the inter-reversal time of perceptual reversal on the right superior parietal lobule

    NASA Astrophysics Data System (ADS)

    Nojima, Kazuhisa; Ge, Sheng; Katayama, Yoshinori; Ueno, Shoogo; Iramina, Keiji

    2010-05-01

    The aim of this study is to investigate the effect of the stimulus frequency and pulses number of repetitive transcranial magnetic stimulation (rTMS) on the inter-reversal time (IRT) of perceptual reversal on the right superior parietal lobule (SPL). The spinning wheel illusion was used as the ambiguous figures stimulation in this study. To investigate the rTMS effect over the right SPL during perceptual reversal, 0.25 Hz 60 pulse, 1 Hz 60 pulse, 0.5 Hz 120 pulse, 1 Hz 120 pulse, and 1 Hz 240 pulse biphasic rTMS at 90% of resting motor threshold was applied over the right SPL and the right posterior temporal lobe (PTL), respectively. As a control, a no TMS was also conducted. It was found that rTMS on 0.25 Hz 60 pulse and 1 Hz 60 pulse applied over the right SPL caused shorter IRT. In contrast, it was found that rTMS on 1 Hz 240-pulse applied over the right SPL caused longer IRT. On the other hand, there is no significant difference between IRTs when the rTMS on 0.5 Hz 120 pulse and 1 Hz 120 pulse were applied over the right SPL. Therefore, the applying of rTMS over the right SPL suggests that the IRT of perceptual reversal is effected by the rTMS conditions such as the stimulus frequency and the number of pulses.

  5. X-ray Spectra and Pulse Frequency Changes in SAX J2103.5+4545

    NASA Technical Reports Server (NTRS)

    Baykal, A.; Stark, M. J.; Swank, J. H.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    The November 1999 outburst of the transient pulsar SAX J2103.5+4545 was monitored with the large area detectors of the Rossi X-Ray Timing Explorer until the pulsar faded after a year. The 358 s pulsar was spun up for 150 days, at which point the flux dropped quickly by a factor of approximately 7, the frequency saturated and, as the flux continued to decline, a weak spin-down began. The pulses remained strong during the decay and the spin-up/flux correlation can be fit to the Ghosh and Lamb derivations for the spin-up caused by accretion from a thin, pressure-dominated disk, for a distance approximately 3.2 kpc and a surface magnetic field approximately 1.2 x 10(exp 13) Gauss. During the bright spin-up part of the outburst, the flux was subject to strong orbital modulation, peaking approximately 3 days after periastron of the eccentric 12.68 day orbit, while during the faint part, there was little orbital modulation. The X-ray spectra were typical of accreting pulsars, describable by a cut-off power-law, with an emission line near the 6.4 keV of Kappa(sub alpha) fluorescence from cool iron. The equivalent width of this emission did not share the orbital modulation, but nearly doubled during the faint phase, despite little change in the column density. The outburst could have been caused by an episode of increased wind from a Be star, such that a small accretion disk is formed during each periastron passage. A change in the wind and disk structure apparently occurred after 5 months such that the accretion rate was no longer modulated or the diffusion time was longer. The distance estimate implies the X-ray luminosity observed was between 1 X 10(exp 36) ergs s(exp -1) and 6 x 10(exp 34) ergs s(exp -1), with a small but definite correlation of the intrinsic power-law spectral index.

  6. Pulsatile LHRH therapy in patients with oligozoospermia and disturbed LH pulsatility.

    PubMed

    Aulitzky, W; Frick, J; Hadziselimovic, F

    1989-08-01

    Pulsatile administration of LHRH can drive the pituitary to secrete LH and FSH in a pattern that closely mimics the physiological pattern of the hypothalamic-pituitary-gonadal axis. As there is evidence that infertility in some men is due to dysfunction of this axis, 14 men with reported infertility of more than 2 years duration were treated by long-term pulsatile LHRH therapy. They were 24-42 years of age, with variable degrees of oligozoospermia, elevated FSH levels but normal LH and testosterone levels. The number of endogenous LH pulses/24 h was less than eight in all 14 subjects. The degree of testicular damage was assessed semi-thin sections prepared from biopsies of both testes. Scores for spermatogonia per seminiferous tubule (SPT) were calculated from the actual number of Ad-spermatogonia/tubule. Patients were grouped according to sperm density and SPT score (groups I-III). Pulsatile LHRH therapy was administered by means of a portable infusion pump; 4 micrograms LHRH were administered subcutaneously every 120 min for a period of 6 months. This treatment restored the normal pattern of LH secretion to 12 LH pulses/24 h in all patients. A statistically significant decrease of mean FSH levels to normal, and an increase of mean LH levels was observed in most of the 14 patients. Testosterone values did not change in any group. Marked improvement of the sperm count was observed in eight out of 14 patients (groups I and II) and three pregnancies were reported during the treatment periods. These results suggest that some states of male infertility are due to hormonal dysregulation and that these patients may benefit from pulsatile LHRH therapy.

  7. Effect of pulse frequency on microstructural, nanomechanical, and wear properties of electrodeposited Ni–TiN composite coatings

    SciTech Connect

    Xia, Fafeng; Tian, Jiyu; Ma, Chunyang Guo, Xue; Potts, Matt

    2014-12-21

    The current paper reports successful syntheses of Ni–TiN composite coatings by pulse electrodeposition. The effect of pulse frequency on the microstructures, nanomechanical, and wear properties of the coatings was investigated using transmission electron microscopy, X–ray diffraction, nanoindenter, scanning electron microscopy, and wear test instrument. The results showed that the Ni–TiN composite coating prepared at the pulse frequency of 100 Hz showed the presence of a less number of TiN particles and some degrees of aggregation in micro-regions. By contrast, in the Ni–TiN coating deposited at the pulse frequency of 500 Hz, the TiN particles were large in number and dispersed homogeneously, thereby, offering the coating a uniform and fine structure. The average grain diameters of Ni and TiN in the coating prepared at 100 Hz were 154.7 and 44.8 nm, respectively, whereas those for the coating prepared at 500 Hz were 67.3 and 25.9 nm, respectively. The maximum TiN content in the Ni-TiN coating deposited at 800 Hz was approximately 10.5 wt. %. The maximum microhardness and the Young's modulus values for the Ni–TiN composite coatings deposited at 800 Hz were 35.7 GPa and 167.4 GPa, respectively. Furthermore, the Ni–TiN composite coating prepared at 100 Hz had more severe damages, whereas the morphologies of worn surface of the coatings deposited at 500 Hz and 800 Hz were smooth and only a few small pits appeared on the surface.

  8. Pulse propagation and failure in the discrete FitzHugh-Nagumo model subject to high-frequency stimulation.

    PubMed

    Ratas, Irmantas; Pyragas, Kestutis

    2012-10-01

    We investigate the effect of a homogeneous high-frequency stimulation (HFS) on a one-dimensional chain of coupled excitable elements governed by the FitzHugh-Nagumo equations. We eliminate the high-frequency term by the method of averaging and show that the averaged dynamics depends on the parameter A=a/ω equal to the ratio of the amplitude a to the frequency ω of the stimulating signal, so that for large frequencies an appreciable effect from the HFS is attained only at sufficiently large amplitudes. The averaged equations are analyzed by an asymptotic theory based on the different time scales of the recovery and excitable variables. As a result, we obtain the main characteristics of a propagating pulse as functions of the parameter A and derive an analytical criterion for the propagation failure. We show that depending on the parameter A, the HFS can either enhance or suppress pulse propagation and reveal the mechanism underlying these effects. The theoretical results are confirmed by numerical simulations of the original system with and without noise.

  9. An analysis of short pulse and dual frequency radar techniques for measuring ocean wave spectra from satellites

    NASA Technical Reports Server (NTRS)

    Jackson, F. C.

    1980-01-01

    Scanning beam microwave radars were used to measure ocean wave directional spectra from satellites. In principle, surface wave spectral resolution in wave number can be obtained using either short pulse (SP) or dual frequency (DF) techniques; in either case, directional resolution obtains naturally as a consequence of a Bragg-like wave front matching. A four frequency moment characterization of backscatter from the near vertical using physical optics in the high frequency limit was applied to an analysis of the SP and DF measurement techniques. The intrinsic electromagnetic modulation spectrum was to the first order in wave steepness proportional to the large wave directional slope spectrum. Harmonic distortion was small and was a minimum near 10 deg incidence. NonGaussian wave statistics can have an effect comparable to that in the second order of scattering from a normally distributed sea surface. The SP technique is superior to the DF technique in terms of measurement signal to noise ratio and contrast ratio.

  10. Numerical solution to the Bloch equations: paramagnetic solutions under wideband continuous radio frequency irradiation in a pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Jun; Ma, Hong; Yu, De; Zeng, Xiao-Hu

    2016-08-01

    A novel nuclear magnetic resonance (NMR) experimental scheme, called wideband continuous wave NMR (WB-CW-NMR), is presented in this article. This experimental scheme has promising applications in pulsed magnetic fields, and can dramatically improve the utilization of the pulsed field. The feasibility of WB-CW-NMR scheme is verified by numerically solving modified Bloch equations. In the numerical simulation, the applied magnetic field is a pulsed magnetic field up to 80 T, and the wideband continuous radio frequency (RF) excitation is a band-limited (0.68–3.40 GHz) white noise. Furthermore, the influences of some experimental parameters, such as relaxation time, applied magnetic field strength and wideband continuous RF power, on the WB-CW-NMR signal are analyzed briefly. Finally, a multi-channel system framework for transmitting and receiving ultra wideband signals is proposed, and the basic requirements of this experimental system are discussed. Meanwhile, the amplitude of the NMR signal, the level of noise and RF interference in WB-CW-NMR experiments are estimated, and a preliminary adaptive cancellation plan is given for detecting WB-CW-NMR signal from large background interference. Supported by National Natural Science Foundation of China (11475067), the Innovative Research Foundation of Huazhong University of Science and Technology (2015 ZDTD017) and the Experimental Apparatus Research Project of Wuhan Pulsed High Magnetic Field Center (2015KF17)

  11. Numerical solution to the Bloch equations: paramagnetic solutions under wideband continuous radio frequency irradiation in a pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Jun; Ma, Hong; Yu, De; Zeng, Xiao-Hu

    2016-08-01

    A novel nuclear magnetic resonance (NMR) experimental scheme, called wideband continuous wave NMR (WB-CW-NMR), is presented in this article. This experimental scheme has promising applications in pulsed magnetic fields, and can dramatically improve the utilization of the pulsed field. The feasibility of WB-CW-NMR scheme is verified by numerically solving modified Bloch equations. In the numerical simulation, the applied magnetic field is a pulsed magnetic field up to 80 T, and the wideband continuous radio frequency (RF) excitation is a band-limited (0.68-3.40 GHz) white noise. Furthermore, the influences of some experimental parameters, such as relaxation time, applied magnetic field strength and wideband continuous RF power, on the WB-CW-NMR signal are analyzed briefly. Finally, a multi-channel system framework for transmitting and receiving ultra wideband signals is proposed, and the basic requirements of this experimental system are discussed. Meanwhile, the amplitude of the NMR signal, the level of noise and RF interference in WB-CW-NMR experiments are estimated, and a preliminary adaptive cancellation plan is given for detecting WB-CW-NMR signal from large background interference. Supported by National Natural Science Foundation of China (11475067), the Innovative Research Foundation of Huazhong University of Science and Technology (2015 ZDTD017) and the Experimental Apparatus Research Project of Wuhan Pulsed High Magnetic Field Center (2015KF17)

  12. Finite-pulse radio frequency driven recoupling with phase cycling for 2D 1H/1H correlation at ultrafast MAS frequencies

    NASA Astrophysics Data System (ADS)

    Nishiyama, Yusuke; Zhang, Rongchun; Ramamoorthy, Ayyalusamy

    2014-06-01

    The first-order recoupling sequence radio frequency driven dipolar recoupling (RFDR) is commonly used in single-quantum/single-quantum homonuclear correlation 2D experiments under magic angle spinning (MAS) to determine homonuclear proximities. From previously reported analysis of the use of XY-based super-cycling schemes to enhance the efficiency of the finite-pulse-RFDR (fp-RFDR) pulse sequence, XY814 phase cycling was found to provide the optimum performance for 2D correlation experiments on low-γ nuclei. In this study, we analyze the efficiency of different phase cycling schemes for proton-based fp-RFDR experiments. We demonstrate the advantages of using a short phase cycle, XY4, and its super-cycle XY414 that only recouples the zero-quantum homonuclear dipolar coupling, for the fp-RFDR sequence in 2D 1H/1H correlation experiments at ultrafast MAS frequencies. The dipolar recoupling efficiencies of XY4, XY414 and XY814 phase cycling schemes are compared based on results obtained from 2D 1H/1H correlation experiments, utilizing the fp-RFDR pulse sequence, on powder samples of U-13C,15N-L-alanine, N-acetyl-15N-L-valyl-15N-L-leucine, and glycine. Experimental results and spin dynamics simulations show that XY414 performs the best when a high RF power is used for the 180° pulse, whereas XY4 renders the best performance when a low RF power is used. The effects of RF field inhomogeneity and chemical shift offsets are also examined. Overall, our results suggest that a combination of fp-RFDR-XY414 employed in the recycle delay with a large RF-field to decrease the recycle delay, and fp-RFDR-XY4 in the mixing period with a moderate RF-field, is a robust and efficient method for 2D single-quantum/single-quantum 1H/1H correlation experiments at ultrafast MAS frequencies.

  13. High-frequency acousto-optic mode locker for picosecond pulse generation

    SciTech Connect

    Keller, U.; Li, K.D.; Khuri-Yakub, P.T.; Bloom, D. ); Gerstenberger, D.C.; Weingarten, K.J. )

    1990-01-01

    We modeled, designed, and built a 500-MHz acousto-optic mode locker with a diffraction efficiency of 28% per 1 W drive power. The transducer is zinc oxide sputtered onto a sapphire substrate. A new figure of merit is defined for the mode-locker design, which indicates that sapphire is a good substrate material. Pulse widths of less than 10 psec with an average power of 150 mW were achieved from a 500-MHz pulse-rate, diode-pumped, cw mode-locked Nd:YLF laser using a pump power of 700 mW.

  14. Comparison of pulse and SFCW GPR in time, frequency and wavelet domain

    NASA Astrophysics Data System (ADS)

    De Pue, Jan; Van De Vijver, Ellen; Cornelis, Wim; Van Meirvenne, Marc

    2014-05-01

    Ground penetrating radar (GPR) systems operating in the time- or frequency domain are two fundamentally different concepts, pursuing the same objective: non-invasive characterization of the subsurface. The aim of this study is to compare the performance of these two GPR systems in the time, frequency and wavelet domain. The time domain GPR investigated is the Utilityscan DF. This is a ground coupled GPR with a digital dual-frequency antenna (300 and 800 MHz). The Geoscope GS3F and VX1213 antenna array from 3DRadar is the frequency domain GPR used in this comparison. It is an air coupled stepped frequency continuous wave (SFCW) GPR with a frequency bandwidth from 200 MHz to 3000 MHz. Using data from several test sites of various soil types, the data is evaluated in the time domain, the frequency domain and the wavelet domain. Each of these domains contains specific information regarding the data quality. Presenting the data in the time domain, allows visualizing the subsurface reflections. This makes it visible how strong the data is affected by internal interference, ringing and other noise. To compensate for the attenuation of the signal in time, automatic gain control is applied. The maximum of this gain function indicates the time where the signal is attenuated completely and noise becomes more dominant, corresponding with the maximal penetration depth of the different GPR systems. In the frequency domain, the data allows to investigate which frequencies contain most valuable information and which ones are affected by noise. Finally, by performing a wavelet transformation the data is transformed to the time-frequency domain. Due to frequency dependent attenuation of electromagnetic signals in the soil, low frequencies will be more dominant in deeper layers, and high frequencies will not be present anymore. This is determining for the range resolution of the data throughout the traveltime of the signal. This work is a contribution to COST Action TU1208 "Civil

  15. High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis

    SciTech Connect

    Tosa, V.; Kim, H.T.; Kim, I.J.; Nam, C.H.

    2005-06-15

    We present a time-dependent analysis of high-order harmonics generated by a self-guided femtosecond laser pulse propagating through a long gas jet. A three-dimensional model is used to calculate the harmonic fields generated by laser pulses, which only differ by the sign of their initial chirp. The time-frequency distributions of the single-atom dipole and harmonic field reveal the dynamics of harmonic generation in the cutoff. A time-dependent phase-matching calculation was performed, taking into account the self-phase modulation of the laser field. Good phase matching holds for only few optical cycles, being dependent on the electron trajectory. When the cutoff trajectory is phase matched, emitted harmonics are locked in phase and the emission intensity is maximized.

  16. Generation of high-quality parabolic pulses with optimized duration and energy by use of dispersive frequency-to-time mapping.

    PubMed

    Huh, Jeonghyun; Azaña, José

    2015-10-19

    We propose and demonstrate a novel linear-optics method for high-fidelity parabolic pulse generation with durations ranging from the picosecond to the sub-nanosecond range. This method is based on dispersion-induced frequency-to-time mapping combined with spectral shaping in order to overcome constraints of previous linear shaping approaches. Temporal waveform distortions associated with the need to satisfy a far-field condition are eliminated by use of a virtual time-lens process, which is directly implemented in the linear spectral shaping stage. Using this approach, the generated parabolic pulses are able to maintain most energy spectrum available from the input pulse frequency bandwidth, regardless of the target pulse duration, which is not anymore limited by the finest spectral resolution of the optical pulse spectrum shaper. High-quality parabolic pulses, with durations from 25ps to 400ps and output powers exceeding 4dBm before amplification, have been experimentally synthesized from a picosecond mode-locked optical source using a commercial optical pulse shaper with a frequency resolution >10GHz. In particular, we report the synthesis of full-duty cycle parabolic pulses that match up almost exactly with an ideal fitting over the entire pulse period.

  17. Generation of surface waves and low-frequency radiation under exposure of a conductor to a laser pulse focused by a cylindrical lens

    SciTech Connect

    Uryupin, S A; Frolov, A A

    2014-09-30

    We have developed a theory of generation of low-frequency radiation and surface waves under the pondermotive action of a femtosecond laser pulse irradiating a conductor along the normal and focused by a cylindrical lens. It is shown that for the chosen focusing method and specified values of laser pulse duration and flux density it is possible to significantly increase the total energy of both surface waves and low-frequency radiation. (terahertz radiation)

  18. Inhibitory and excitatory pulse coupling of two frequency-different chemical oscillators with time delay.

    PubMed

    Proskurkin, Ivan S; Lavrova, Anastasia I; Vanag, Vladimir K

    2015-06-01

    Dynamical regimes of two pulse coupled non-identical Belousov-Zhabotinsky oscillators have been studied experimentally as well as theoretically with the aid of ordinary differential equations and phase response curves both for pure inhibitory and pure excitatory coupling. Time delay τ between a spike in one oscillator and perturbing pulse in the other oscillator plays a significant role for the phase relations of synchronous regimes of the 1:1 and 1:2 resonances. Birhythmicity between anti-phase and in-phase oscillations for inhibitory pulse coupling as well as between 1:2 and 1:1 resonances for excitatory pulse coupling have also been found. Depending on the ratio of native periods of oscillations T2/T1, coupling strength, and time delay τ, such resonances as 1:1 (with different phase locking), 2:3, 1:2, 2:5, 1:3, 1:4, as well as complex oscillations and oscillatory death are observed.

  19. High-voltage nanosecond pulses in a low-pressure radio-frequency discharge.

    PubMed

    Pustylnik, M Y; Hou, L; Ivlev, A V; Vasilyak, L M; Couëdel, L; Thomas, H M; Morfill, G E; Fortov, V E

    2013-06-01

    An influence of a high-voltage (3-17 kV) 20 ns pulse on a weakly-ionized low-pressure (0.1-10 Pa) capacitively coupled radiofrequency (RF) argon plasma is studied experimentally. The plasma evolution after pulse exhibits two characteristic regimes: a bright flash, occurring within 100 ns after the pulse (when the discharge emission increases by 2-3 orders of magnitude over the steady-state level), and a dark phase, lasting a few hundreds μs (when the intensity of the discharge emission drops significantly below the steady-state level). The electron density increases during the flash and remains very large at the dark phase. 1D3V particle-in-cell simulations qualitatively reproduce both regimes and allow for detailed analysis of the underlying mechanisms. It is found that the high-voltage nanosecond pulse is capable of removing a significant fraction of plasma electrons out of the discharge gap, and that the flash is the result of the excitation of gas atoms, triggered by residual electrons accelerated in the electric field of immobile bulk ions. The secondary emission from the electrodes due to vacuum UV radiation plays an important role at this stage. High-density plasma generated during the flash provides efficient screening of the RF field (which sustains the steady-state plasma). This leads to the electron cooling and, hence, onset of the dark phase.

  20. Lightweight, broadband, pulsed, frequency agile, self-screening jammer for airborne deployment

    NASA Astrophysics Data System (ADS)

    Gagliardi, Richard P.

    1989-12-01

    A broadband RF microwave source is used to generate a high-energy, narrow pulse which is used to provide the illuminating signal for an active radar system while simultaneously jamming other active radar systems. The generation of the RF microwave energy utilizes a spark gap generation systems. Jamming is accomplished by overload ringing of the receiver portion of the other radar system.

  1. Serum LH and FSH Responses to Synthetic LH-RH in Normal Infants, Children and Patients With Turner's Syndrome

    ERIC Educational Resources Information Center

    Suwa, Seizo; And Others

    1974-01-01

    Effects of luteinizing hormone-releasing hormone (LH-RH) on LH and follicle-stimulating hormone (FSH) release were studied in 26 normal children and six patients (from 1-to 14-years-old) with Turner's syndrome. (Author)

  2. Fracture Mechanics Analysis of LH2 Feed Line Flow Liners

    NASA Technical Reports Server (NTRS)

    James, Mark A.; Dawicke, David S.; Brzowski, Matthew B.; Raju, Ivatury S.; Elliott, Kenny B.; Harris, Charles E.

    2006-01-01

    Inspections of the Space Shuttle Main Engine revealed fatigue cracks growing from slots in the flow liner of the liquid hydrogen (LH2) feed lines. During flight, the flow liners experience complex loading induced by flow of LH2 and the resonance characteristics of the structure. The flow liners are made of Inconel 718 and had previously not been considered a fracture critical component. However, fatigue failure of a flow liner could have catastrophic effect on the Shuttle engines. A fracture mechanics study was performed to determine if a damage tolerance approach to life management was possible and to determine the sensitivity to the load spectra, material properties, and crack size. The load spectra were derived separately from ground tests and material properties were obtained from coupon tests. The stress-intensity factors for the fatigue cracks were determined from a shell-dynamics approach that simulated the dominant resonant frequencies. Life predictions were obtained using the NASGRO life prediction code. The results indicated that adequate life could not be demonstrated for initial crack lengths of the size that could be detected by traditional NDE techniques.

  3. The discharge mode transition and O(5p1) production mechanism of pulsed radio frequency capacitively coupled plasma

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.; Hu, J. T.; Liu, J. H.; Xiong, Z. L.; Liu, D. W.; Lu, X. P.; Shi, J. J.

    2012-07-01

    The discharge mode transition from uniform plasma across the gas gap to the α mode happens at the rising phase of the pulsed radio frequency capacitively coupled plasma (PRF CCP). This transition is attributed to the fast increasing stochastic heating at the edge of sheath. In the second stage with the stable current and voltage amplitude, the consistency between experimental and numerical spatial-temporal 777 nm emission profile suggests that He* and He2* dominate the production of O(5p1) through dissociation and excitation of O2. Finally, the sterilization efficiency of PRF CCP is found to be higher than that of plasma jet.

  4. Difference-frequency generation in the field of a few-cycle laser pulse propagating in a GaAs crystal with a domain structure

    SciTech Connect

    Oganesyan, David L; Vardanyan, Aleksandr O; Oganesyan, G D

    2013-06-30

    Difference-frequency generation in a GaAs crystal with a periodic domain structure in the field of a few-cycle laser pulse is considered for the case of weakly pronounced material dispersion. The straight-line method is used to solve numerically the system of coupled nonlinear partial differential equations describing the evolution of the electric field of this laser pulse in GaAs crystals with periodic and chirped domain structures. It is shown that application of a GaAs crystal with a chirped domain structure makes it possible to control the frequency-modulation law for a broadband differencefrequency pulse. (nonlinear optical phenomena)

  5. Frequency doubling and tripling of ultrashort laser pulses in biological tissues

    SciTech Connect

    Da Silva, L. B.; Eichler, J.; Joslin, E. J.; Kim, B.-M.

    1998-07-24

    Structural proteins such as collagen and elastin are known to generate second harmonic at high laser intensities. Second and third harmonic generations (SHG, THG) of 0.4 ps Ti-Sapphire laser radiation at 800 nm were observed in various biological tissues. Dependence of SHG on laser pulse energy and pulse width was investigated. Reflected second harmonic yield was measured for animal tissue in vitro and human skin in vivo. The yield varies about a factor of 20 for various areas of the skin while the scattered laser radiation (diffuse reflectance) varies only by a factor of 2. In some cases the THG efficiency was comparable to the SHG. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed.

  6. Effects of the frequency detuning in Raman backscattering of infinitely long laser pulses in plasmas

    SciTech Connect

    Hur, Min Sup; Hwang, Ilmoon; Jang, Hyo Jae; Suk, Hyyong

    2006-07-15

    Raman backscattering (RBS) in an infinite homogeneous laser-plasma system was investigated with the three-wave fluid model and averaged particle-in-cell (aPIC) simulations in the nonrelativistic and low temperature regime. It was found that the periodic boundary condition for the electrostatic potential, which is commonly used in an infinite homogeneous plasma, induces a numerical frequency shift of the plasma wave. The initial frequency detuning between the three waves is modified by the frequency shift, leading to a significantly wrong result in the RBS system. An alternative boundary condition based on the Maxwell equation is presented. The aPIC simulations with the modified boundary condition show that the pump depletion level depends sensitively on the frequency mismatch between the three waves. This sensitivity is closely related with the erroneous RBS: the numerical frequency shift is very minor (a few percent of the plasma frequency or less than that) but RBS can be greatly affected even by such a small frequency change. Analytic formulas for the pump depletion time and level is derived and compared to the aPIC simulations with the modified boundary condition, showing an excellent agreement.

  7. Marginal chimera state at cross-frequency locking of pulse-coupled neural networks

    NASA Astrophysics Data System (ADS)

    Bolotov, M. I.; Osipov, G. V.; Pikovsky, A.

    2016-03-01

    We consider two coupled populations of leaky integrate-and-fire neurons. Depending on the coupling strength, mean fields generated by these populations can have incommensurate frequencies or become frequency locked. In the observed 2:1 locking state of the mean fields, individual neurons in one population are asynchronous with the mean fields, while in another population they have the same frequency as the mean field. These synchronous neurons form a chimera state, where part of them build a fully synchronized cluster, while other remain scattered. We explain this chimera as a marginal one, caused by a self-organized neutral dynamics of the effective circle map.

  8. [Thermoelastic excitation of acoustic waves in biological models under the effect of the high peak-power pulsed electromagnetic radiation of extremely high frequency].

    PubMed

    Gapeev, A B; Rubanik, A V; Pashovkin, T N; Chemeris, N K

    2007-01-01

    The capability of high peak-power pulsed electromagnetic radiation of extremely high frequency (35,27 GHz, pulse widths of 100 and 600 ns, peak power of 20 kW) to excite acoustic waves in model water-containing objects and muscular tissue of animals has been experimentally shown for the first time. The amplitude and duration of excited acoustic pulses are within the limits of accuracy of theoretical assessments and have a complex nonlinear dependence on the energy input of electromagnetic radiation supplied. The velocity of propagation of acoustic pulses in water-containing models and isolated muscular tissue of animals was close to the reference data. The excitation of acoustic waves in biological systems under the action of high peak-power pulsed electromagnetic radiation of extremely high frequency is the important phenomenon, which essentially contributes to the understanding of the mechanisms of biological effects of these electromagnetic fields.

  9. Effect of combined high-frequency and pulse-dynamic impact on adhesive-joint strength

    NASA Astrophysics Data System (ADS)

    Gorbushin, N. A.; Petrov, Yu. V.

    2016-08-01

    The problem on exfoliation of a string on an elastic foundation under the application of external force is considered. The dependence of amplitude of the forced load, which causes the exfoliation of the string, on its frequency and application time is investigated. The exfoliation criterion under use is based on the concept of incubation time. It should be noted that, at certain values of the forced-vibration frequency, it is possible to decrease considerably the threshold-amplitude value.

  10. A Power-Efficient Multichannel Neural Stimulator Using High-Frequency Pulsed Excitation From an Unfiltered Dynamic Supply.

    PubMed

    van Dongen, Marijn N; Serdijn, Wouter A

    2016-02-01

    This paper presents a neural stimulator system that employs a fundamentally different way of stimulating neural tissue compared to classical constant current stimulation. A stimulation pulse is composed of a sequence of current pulses injected at a frequency of 1 MHz for which the duty cycle is used to control the stimulation intensity. The system features 8 independent channels that connect to any of the 16 electrodes at the output. A sophisticated control system allows for individual control of each channel's stimulation and timing parameters. This flexibility makes the system suitable for complex electrode configurations and current steering applications. Simultaneous multichannel stimulation is implemented using a high frequency alternating technique, which reduces the amount of electrode switches by a factor 8. The system has the advantage of requiring a single inductor as its only external component. Furthermore it offers a high power efficiency, which is nearly independent on both the voltage over the load as well as on the number of simultaneously operated channels. Measurements confirm this: in multichannel mode the power efficiency can be increased for specific cases to 40% compared to 20% that is achieved by state-of-the-art classical constant current stimulators with adaptive power supply. PMID:25438324

  11. Modeling of the nanoparticle coagulation in pulsed radio-frequency capacitively coupled C2H2 discharges

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-Mei; Li, Qi-Nan; Li, Rui

    2015-07-01

    The role of pulse parameters on nanoparticle property is investigated self-consistently based on a couple of fluid model and aerosol dynamics model in a capacitively coupled parallel-plate acetylene (C2H2) discharge. In this model, the mass continuity equation, momentum balance equation, and energy balance equation for neutral gas are taken into account. Thus, the thermophoretic force arises when a gas temperature gradient exists. The typical results of this model are positive and negative ion densities, electron impact collisions rates, nanoparticle density, and charge distributions. The simulation is performed for duty ratio 0.4/0.7/1.0, as well as pulse modulation frequency from 40 kHz to 2.7 MHz for pure C2H2 discharges at a pressure of 500 mTorr. We find that the pulse parameters, especially the duty ratio, have a great affect on the dissociative attachment coefficient and the negative density. More importantly, by decreasing the duty ratio, nanoparticles start to diffuse to the wall. Under the action of gas flow, nanoparticle density peak is created in front of the pulse electrode, where the gas temperature is smaller. Project supported by the Natural Science Foundation of Heilongjiang Province, China (Grant Nos. A2015011 and A2015010), the Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province, China (Grant No. LBH-Q14159), the National Natural Science Foundation of China (Grant No. 11404180), and the Program for Young Teachers Scientific Research in Qiqihar University, China (Grant No. 2014k-Z11).

  12. Detector response in time-of-flight mass spectrometry at high pulse repetition frequencies

    NASA Technical Reports Server (NTRS)

    Gulcicek, Erol E.; Boyle, James G.

    1993-01-01

    Dead time effects in chevron configured dual microchannel plates (MCPs) are investigated. Response times are determined experimentally for one chevron-configured dual MCP-type detector and two discrete dynode-type electron multipliers with 16 and 23 resistively divided stages. All of these detectors are found to be suitable for time-of-flight mass spectrometry (TOF MS), yielding 3-6-ns (FWHM) response times triggered on a single ion pulse. It is concluded that, unless there are viable solutions to overcome dead time disadvantages for continuous dynode detectors, suitable discrete dynode detectors for TOF MS appear to have a significant advantage for high repetition rate operation.

  13. A dual-wavelength amplifier that enables the simultaneous chirped-pulse amplification of femtosecond 1562 nm pulses and continuous wave 1064 nm radiation for applications in difference frequency generation

    NASA Astrophysics Data System (ADS)

    Krzempek, Karol; Sobon, Grzegorz; Sotor, Jaroslaw; Abramski, Krzysztof

    2016-10-01

    We present the first demonstration of a chirped-pulse amplification system that enables the simultaneous amplification of femtosecond pulses from the erbium band and continuous wave radiation centered at 1064 nm. The setup generated 470 fs laser pulses, centered at 1562 nm, with an average output power of 590 mW. By exploiting the unique dual-wavelength design an additional gain of 18.08 dB was achieved for the auxiliary 1064 nm seed signal required in the frequency conversion part of the setup. The usability of the constructed source was verified by setting up a difference frequency generation experiment in which the unique characteristics of the mode-locked laser pulses were transferred into the mid-infrared wavelength region.

  14. The Effect of Extremely Low Frequency Pulsed Electromagnetic Field on In Vitro Fertilization Success Rate in N MRI Mice

    PubMed Central

    Hafizi, Leili; Sazgarnia, Ameneh; Mousavifar, Nezhat; Karimi, Mohammad; Ghorbani, Saleh; Kazemi, Mohammad Reza; Emami Meibodi, Neda; Hosseini, Golkoo; Mostafavi Toroghi, Hesam

    2014-01-01

    Objective: The effects of exposure to electromagnetic fields (EMF) on reproduction systems have been widely debated. In this study, we aimed to investigate whether low frequency EMF could ameliorate the in vitro fertilization success rate in Naval medical research institute (NMRI) Mice. Materials and Methods: In this randomized comparative animal study, ten NMRI mice were randomly divided into 2 equal groups (control and experimental). 10 IU of human chorionic gonadotropin (hCG) was injected intraperitoneally to both groups in order to stimulate ovulating, and ovums were then aspirated and kept in KSOM (modified version of sequential simplex optimization medium with a higher K+ concentration) culture medium. Metaphase II ovums were separated, and sperms obtained by "swim out" method were added to metaphase II ovums in the culture medium. The experimental group was exposed to 1.3 millitesla pulsed electromagnetic field at 4 kilohertz frequency for 5 hours. To assess the efficacy, we considered the identification of two-pronuclear zygote (2PN) under microscope as fertilizing criterion. Results: Total number of collected ovums in the control and experimental groups was 191 and 173, respectively, from which 58 (30.05%) and 52 (30.36%) ovums were collected from metaphase II, respectively. In vitro fertilization (IVF) success rate was 77% in extremely low frequency- pulsed electromagnetic field (ELFPEMF) for exposed group (experimental), whereas the rate was 68% for control group. Conclusion: Despite increased percentile of IVF success rate in exposed group, there was no statistically significant difference between 2 groups, but this hypothesis has still been stated as a question. Further studies with larger sample sizes and different EMF designs are suggested. PMID:24381855

  15. Effects of Biphasic Current Pulse Frequency, Amplitude, Duration and Interphase Gap on Eye Movement Responses to Prosthetic Electrical Stimulation of the Vestibular Nerve

    PubMed Central

    Davidovics, Natan S.; Fridman, Gene Y.; Chiang, Bryce; Della Santina, Charles C.

    2011-01-01

    An implantable prosthesis that stimulates vestibular nerve branches to restore sensation of head rotation and vision-stabilizing reflexes could benefit individuals disabled by bilateral loss of vestibular (inner ear balance) function. We developed a prosthesis that partly restores normal function in animals by delivering pulse frequency modulated (PFM) biphasic current pulses via electrodes implanted in semicircular canals. Because the optimal stimulus encoding strategy is not yet known, we investigated effects of varying biphasic current pulse frequency, amplitude, duration and interphase gap on vestibulo-ocular reflex (VOR) eye movements in chinchillas. Increasing pulse frequency increased response amplitude while maintaining a relatively constant axis of rotation. Increasing pulse amplitude (range 0–325 μA) also increased response amplitude but spuriously shifted eye movement axis, probably due to current spread beyond the target nerve. Shorter pulse durations (range 28–340 μs) required less charge to elicit a given response amplitude and caused less axis shift than longer durations. Varying interphase gap (range 25–175 μs) had no significant effect. While specific values reported herein depend on microanatomy and electrode location in each case, we conclude that PFM with short duration biphasic pulses should form the foundation for further optimization of stimulus encoding strategies for vestibular prostheses intended to restore sensation of head rotation. PMID:20813652

  16. A high pulse repetition frequency ultrasound system for the ex vivo measurement of mechanical properties of crystalline lenses with laser-induced microbubbles interrogated by acoustic radiation force.

    PubMed

    Yoon, Sangpil; Aglyamov, Salavat; Karpiouk, Andrei; Emelianov, Stanislav

    2012-08-01

    A high pulse repetition frequency ultrasound system for an ex vivo measurement of mechanical properties of an animal crystalline lens was developed and validated. We measured the bulk displacement of laser-induced microbubbles created at different positions within the lens using nanosecond laser pulses. An impulsive acoustic radiation force was applied to the microbubble, and spatio-temporal measurements of the microbubble displacement were assessed using a custom-made high pulse repetition frequency ultrasound system consisting of two 25 MHz focused ultrasound transducers. One of these transducers was used to emit a train of ultrasound pulses and another transducer was used to receive the ultrasound echoes reflected from the microbubble. The developed system was operating at 1 MHz pulse repetition frequency. Based on the measured motion of the microbubble, Young's moduli of surrounding tissue were reconstructed and the values were compared with those measured using the indentation test. Measured values of Young's moduli of four bovine lenses ranged from 2.6 ± 0.1 to 26 ± 1.4 kPa, and there was good agreement between the two methods. Therefore, our studies, utilizing the high pulse repetition frequency ultrasound system, suggest that the developed approach can be used to assess the mechanical properties of ex vivo crystalline lenses. Furthermore, the potential of the presented approach for in vivo measurements is discussed.

  17. Carotenoid-bacteriochlorophyll energy transfer in LH2 complexes studied with 10-fs time resolution.

    PubMed

    Polli, Dario; Cerullo, Giulio; Lanzani, Guglielmo; De Silvestri, Sandro; Hashimoto, Hideki; Cogdell, Richard J

    2006-04-01

    In this report, we present a study of carotenoid-bacteriochlorophyll energy transfer processes in two peripheral light-harvesting complexes (known as LH2) from purple bacteria. We use transient absorption spectroscopy with approximately 10 fs temporal resolution, which is necessary to observe the very fast energy relaxation processes. By comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it has been possible to directly evaluate their energy transfer efficiency to the bacteriochlorophylls. In the case of okenone in the LH2 complex from Chromatium purpuratum, we obtained an energy transfer efficiency of etaET2=63+/-2.5% from the optically active excited state (S2) and etaET1=61+/-2% from the optically dark state (S1); for rhodopin glucoside contained in the LH2 complex from Rhodopseudomonas acidophila these values become etaET2=49.5+/-3.5% and etaET1=5.1+/-1%. The measurements also enabled us to observe vibrational energy relaxation in the carotenoids' S1 state and real-time collective vibrational coherence initiated by the ultrashort pump pulses. Our results are important for understanding the dynamics of early events of photosynthesis and relating it to the structural arrangement of the chromophores.

  18. Removal of ruminal contents followed by restricted feeding does not affect the frequency of luteinizing-hormone pulses in steers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this study was to determine the effects of removal of ruminal contents and reduced nutrient intake on concentrations of LH in serum of beef cattle. Gonadectomized, male, Angus x Hereford cattle (steers, 402 ± 17 kg) with rumen cannulae were randomly assigned to treatment. Control (C...

  19. Male goat vocalizations stimulate the estrous behavior and LH secretion in anestrous goats that have been previously exposed to bucks.

    PubMed

    Delgadillo, José Alberto; Vielma, Jesús; Hernandez, Horacio; Flores, José Alfredo; Duarte, Gerardo; Fernández, Ilda Graciela; Keller, Matthieu; Gelez, Hélène

    2012-09-01

    We investigated whether live vocalizations emitted by bucks interacting with anestrous females stimulate secretion of LH, estrous behavior and ovulation in anestrous goats. In experiment 1, bucks rendered sexually active by exposure to long days followed by natural photoperiod were exposed in a light-proof-building to five anestrous females. Buck vocalizations were reproduced through a microphone-amplifier-loudspeaker system to an open pen where one group of goats (n=6) was exposed for 10 days to these live vocalizations. Another group of females (n=6) was isolated from males and vocalizations. The proportion of goats displaying estrous behavior was significantly higher in females exposed to buck vocalizations than in females isolated from males. The proportion of goats that ovulated did not differ between the 2 groups (exposed to males versus isolated). In experiment 2, female goats that either had previous contact with males (n=7), or no previous contact with males (n=7) were exposed to live buck vocalizations, reproduced as described in experiment 1, for 5 days. The number and amplitude of LH pulses did not differ between groups before exposition to buck vocalizations. Five days of exposure to male vocalizations significantly increased LH pulsatility only in females that had previous contact with males, while LH pulse amplitude was not modified. We concluded that live buck vocalizations can stimulate estrous behavior and LH secretion in goats if they have had previous contact with bucks.

  20. Space-selective growth of frequency-conversion crystals in glasses with ultrashort infrared laser pulses.

    PubMed

    Miura, K; Qiu, J; Mitsuyu, T; Hirao, K

    2000-03-15

    We report on space-selective growth of a second-harmonic-generation beta-BaB(2)O(4) (BBO) crystal inside a BaO-Al(2)O(3)-B(2)O(3) glass sample at the focal point of an 800-nm femtosecond laser beam. A spherical heated region was formed during the focused laser irradiation through observation with an optical microscope. We moved the heated region by changing the position of the focal point of the laser beam relative to the glass sample. We grew BBO crystal continuously in the glass sample by adjusting the moving speed of the heated zone. Our results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.

  1. Laser ablation of single-crystalline silicon by radiation of pulsed frequency-selective fiber laser

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Skvortsov, A. M.; Huynh, C. T.; Petrov, A. A.

    2015-07-01

    We have studied the process of destruction of the surface of a single-crystalline silicon wafer scanned by the beam of a pulsed ytterbium-doped fiber laser radiation with a wavelength of λ = 1062 nm. It is established that the laser ablation can proceed without melting of silicon and the formation of a plasma plume. Under certain parameters of the process (radiation power, beam scan velocity, and beam overlap density), pronounced oxidation of silicon microparticles with the formation of a characteristic loose layer of fine powdered silicon dioxide has been observed for the first time. The range of lasing and beam scanning regimes in which the growth of SiO2 layer takes place is determined.

  2. High-Frequency, Low-Intensity Pulsed Ultrasound Enhances Alveolar Bone Healing of Extraction Sockets in Rats: A Pilot Study.

    PubMed

    Kang, Kyung Lhi; Kim, Eun-Cheol; Park, Joon Bong; Heo, Jung Sun; Choi, Yumi

    2016-02-01

    Most studies of the beneficial effects of low-intensity pulsed ultrasound (LIPUS) on bone healing have used frequencies between 1.0 and 1.5 MHz. However, after consideration of ultrasound wave characteristics and depth of target tissue, higher-frequency LIPUS may have been more effective on superficially positioned alveolar bone. We investigated this hypothesis by applying LIPUS (frequency, 3.0 MHz; intensity, 30 mW/cm(2)) on shaved right cheeks over alveolar bones of tooth extraction sockets in rats for 10 min/d for 2 wk after tooth extraction; the control group (left cheek of the same rats) did not receive LIPUS treatment. Compared with the control group, the LIPUS group manifested more new bone growth inside the sockets on histomorphometric analysis (maximal difference = 2.5-fold on the seventh day after extraction) and higher expressions of osteogenesis-related mRNAs and proteins than the control group did. These findings indicate that 3.0-MHz LIPUS could enhance alveolar bone formation and calcification in rats.

  3. Frequencies of virulence genes and pulse field gel electrophoresis fingerprints in Escherichia coli isolates from canine pyometra.

    PubMed

    Maluta, Renato P; Borges, Clarissa A; Beraldo, Lívia G; Cardozo, Marita V; Voorwald, Fabiana A; Santana, André M; Rigobelo, Everlon C; Toniollo, Gilson H; Avila, Fernando A

    2014-11-01

    Escherichia coli is the most common bacterial agent isolated from canine pyometra. The frequencies of 24 virulence genes and pulsed field gel electrophoresis (PFGE) profiles were determined for 23 E. coli isolates from cases of canine pyometra in Brazil. The frequencies of virulence genes were 91.3% fimH, 91.3% irp-2, 82.6% fyuA, 56.5% iroN, 47.8% traT, 39.1% usp, 34.8% sfaD/E, 34.8% tsh, 30.4% papC, 30.4% hlyA, 26.1% papGIII, 26.1% cnf-1, 21.7% papE/F, 21.7% iss, 17.4% iutA, 17.4% ompT, 17.4% cvaC, 17.4% hlyF, 17.4% iucD, 13.0% iucC, 13.0% astA, 4.3% papGII, 0% afaB/C and 0% papGI. The high frequency of yersiniabactin (fyuA and irp2) and salmochelin (iroN) genes suggests that iron uptake systems might be important in the pathogenesis of canine pyometra. PFGE profiles of 19 isolates were heterogeneous, confirming that E. coli isolates from canine pyometra are unlikely to be epidemic clones. PMID:25201253

  4. Influence of electromagnetic signal of antibiotics excited by low-frequency pulsed electromagnetic fields on growth of Escherichia coli.

    PubMed

    Ke, Yin-Lung; Chang, Fu-Yu; Chen, Ming-Kun; Li, Shun-Lai; Jang, Ling-Sheng

    2013-01-01

    Energy medicine (EM) provides a new medical choice for patients, and its advantages are the noninvasive detection and nondrug treatment. An electromagnetic signal, a kind of EM, induced from antibiotic coupling with weak, extremely low-frequency pulsed electromagnetic fields (PEMFs) is utilized for investigating the growth speed of Escherichia coli (E. coli). PEMFs are produced by solenoidal coils for coupling the electromagnetic signal of antibiotics (penicillin). The growth retardation rate (GRR) of E. coli is used to investigate the efficacy of the electromagnetic signal of antibiotics. The E. coli is cultivated in the exposure of PEMFs coupling with the electromagnetic signal of antibiotics. The maximum GRR of PEMFs with and without the electromagnetic signal of antibiotics on the growth of E. coli cells in the logarithmic is 17.4 and 9.08%, respectively. The electromagnetic signal of antibiotics is successfully coupled by the electromagnetic signal coupling instrument to affect the growth of E. coli. In addition, the retardation effect on E. coli growth can be improved of by changing the carrier frequency of PEMFs coupling with the electromagnetic signal of antibiotics. GRR caused by the electromagnetic signal of antibiotics can be fixed by a different carrier frequency in a different phase of E. coli growth.

  5. Low-frequency pulsed electromagnetic field exposure can alter neuroprocessing in humans

    PubMed Central

    Robertson, John A.; Théberge, Jean; Weller, Julie; Drost, Dick J.; Prato, Frank S.; Thomas, Alex W.

    2010-01-01

    Extremely low-frequency magnetic fields (from DC to 300 Hz) have been shown to affect pain sensitivity in snails, rodents and humans. Here, a functional magnetic resonance imaging study demonstrates how the neuromodulation effect of these magnetic fields influences the processing of acute thermal pain in normal volunteers. Significant interactions were found between pre- and post-exposure activation between the sham and exposed groups for the ipsilateral (right) insula, anterior cingulate and bilateral hippocampus/caudate areas. These results show, for the first time, that the neuromodulation induced by exposure to low-intensity low-frequency magnetic fields can be observed in humans using functional brain imaging and that the detection mechanism for these effects may be different from those used by animals for orientation and navigation. Magnetoreception may be more common than presently thought. PMID:19656823

  6. Comparison of medium frequency pulsed radar interferometer and correlation analysis winds, part 1

    NASA Technical Reports Server (NTRS)

    Meek, C. E.; Reid, I. M.; Manson, A. H.

    1986-01-01

    In principle, the interferometer analysis determines the radial velocity and direction of single scatterers provided that each has a sufficiently different Doppler frequency to permit separation by spectral analysis. In fact, scatterers will not have constant radial velocity, and their Doppler frequencies as well as their directions will be modulated by their horizontal motion. Thus, there is a tradeoff between the poorer resolution but less smeared scatterers on shorter records and the higher resolution (longer) records. Three or more non-collinear scatterers are sufficient to determine the wind. It appears that the velocity found from the combined interferometer peaks agrees well with the apparent velocity from correlation methods, but the true velocity is a factor of 2 smaller. This difference might be resolved by searching for scatters showing regular movement between adjacent records.

  7. Stationary and high-frequency pulsed electron paramagnetic resonance of a calcified atherosclerotic plaque

    NASA Astrophysics Data System (ADS)

    Abdul'Yanov, V. A.; Galiullina, L. F.; Galyavich, A. S.; Izotov, V. G.; Mamin, G. V.; Orlinskii, S. B.; Rodionov, A. A.; Salakhov, M. Kh.; Silkin, N. I.; Sitdikova, L. M.; Khairullin, R. N.; Chelyshev, Yu. A.

    2008-09-01

    New possibilities of applying high-frequency electron paramagnetic resonance in medicine are demonstrated on an example of the investigation of a calcified atherosclerotic plaque. After the irradiation of the atherosclerotic plaque by x rays, a new type of paramagnetic centers—organomineral radicals—is detected. The spectral and relaxation characteristics of these radicals depend on the calcification degree of the atherosclerotic plaque and can be used for diagnostics.

  8. Terahertz beam steering and frequency tuning by using the spatial dispersion of ultrafast laser pulses.

    PubMed

    Maki, Ken-ichiro; Otani, Chiko

    2008-07-01

    We demonstrate a terahertz (THz) beam steering method using difference frequency generation that is based on the principle of phased array antennas. A strip-line photoconductive antenna was illuminated by two spatially dispersed beams produced from an ultrafast laser. THz radiation with a bandwidth of 65 GHz was generated from the overlapping area of the two beams, between which the frequency difference was approximately constant. We confirmed that the THz beam can be steered by tilting one of the incident pump beams so as to change their relative phase relation. The steering range of the THz beam was 29 degrees when the angle between the incident pump beams was only varied within a range of 0.155 degrees, that is, 187 times less. In addition, by laterally shifting one of the pump beams, the frequency of the THz radiation could be tuned from 0.3 to 1.7 THz. This technique can be applied to high-speed terahertz imaging and spectroscopy systems. PMID:18607423

  9. Echo frequency selectivity of duration-tuned inferior collicular neurons of the big brown bat, Eptesicus fuscus, determined with pulse-echo pairs.

    PubMed

    Wu, C H; Jen, P H-S

    2008-10-28

    During hunting, insectivorous bats such as Eptesicus fuscus progressively vary the repetition rate, duration, frequency and amplitude of emitted pulses such that analysis of an echo parameter by bats would be inevitably affected by other co-varying echo parameters. The present study is to determine the variation of echo frequency selectivity of duration-tuned inferior collicular neurons during different phases of hunting using pulse-echo (P-E) pairs as stimuli. All collicular neurons discharge maximally to a tone at a particular frequency which is defined as the best frequency (BF). Most collicular neurons also discharge maximally to a BF pulse at a particular duration which is defined as the best duration (BD). A family of echo iso-level frequency tuning curves (iso-level FTC) of these duration-tuned collicular neurons is measured with the number of impulses in response to the echo pulse at selected frequencies when the P-E pairs are presented at varied P-E duration and gap. Our data show that these duration-tuned collicular neurons have narrower echo iso-level FTC when measured with BD than with non-BD echo pulses. Also, IC neurons with low BF and short BD have narrower echo iso-level FTC than IC neurons with high BF and long BD have. The bandwidth of echo iso-level FTC significantly decreases with shortening of P-E duration and P-E gap. These data suggest that duration-tuned collicular neurons not only can facilitate bat's echo recognition but also can enhance echo frequency selectivity for prey feature analysis throughout a target approaching sequence during hunting. These data also support previous behavior studies showing that bats prepare their auditory system to analyze expected returning echoes within a time window to extract target features after pulse emission.

  10. Theoretical investigation and computational modeling of the difference frequency generation by interaction of few cycle laser pulses in a GaAs crystal

    NASA Astrophysics Data System (ADS)

    Hovhannisyan, D. L.; Hakhoumian, A. A.; Martirosyan, R. M.; Nikoghosyan, A. S.; Laziev, E. M.; Hovhannisyan, G. D.

    2010-08-01

    We present the results of theoretical studies of the generation process of difference frequency radiation arising via interaction of mutually orthogonal linearly polarized few-cycle laser pulses propagating in an isotropic nonlinear medium. Numerical time-integration by the finite-difference method of nonlinear Maxwell-equation systems has been performed. We consider the interaction of pulses having the central wavelengths of 1.98 and 1.55 µm, duration of 30 fs with the corresponding electric field amplitudes of 295 × 106 and 463 × 106 V m-1, propagating along the normal to the ⟨110⟩ plane in 854 µm thickness of GaAs crystal. The process of difference frequency pulse formation arising via spectral filtration of a supercontinuum formed in the spectra of pump pulses at the output of a nonlinear crystal is studied.

  11. A New Possibility for Production of Sub-picosecond X-ray Pulses using a Time Dependent Radio Frequency Orbit Deflection

    SciTech Connect

    Zholents, A. A.

    2015-05-01

    It is shown that two radio frequency deflecting cavities with slightly different frequencies can be used to produce time-dependent orbit deflection to a few special electron bunches while keeping the majority of the electron bunches unaffected. These special bunches produce an x-ray pulse in which transverse position or angle, or both, are correlated with time. The x-ray pulses are then shortened, either with an asymmetrically cut crystal that acts as a pulse compressor, or with an angular aperture such as a narrow slit positioned downstream. The implementation of this technique creates a highly flexible environment for synchrotrons in which users of most beamlines will be able to easily select between the x-rays originated by the standard electron bunches and the short x-ray pulses originated by the special electron bunches carrying a time-dependent transverse correlation.

  12. Effect of pulse frequency on the microstructure, phase composition and corrosion performance of a phosphate-based plasma electrolytic oxidation coated AM50 magnesium alloy

    NASA Astrophysics Data System (ADS)

    Bala Srinivasan, P.; Liang, J.; Balajeee, R. G.; Blawert, C.; Störmer, M.; Dietzel, W.

    2010-04-01

    An AM50 magnesium alloy was plasma electrolytic oxidation treated using a pulsed DC power supply at three different pulse frequencies viz., 10 Hz, 100 Hz and 1000 Hz with a constant pulse ratio for 15 min in an alkaline phosphate electrolyte. The resultant coatings were characterized by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy for their phase composition and microstructural features. The 10 Hz condition yielded relatively thick and rough coatings, which was attributed to the higher energy input per individual pulse during the PEO processing. The phase composition was also found to be influenced by the processing frequency. Electrochemical impedance spectroscopy studies performed in 0.1 M NaCl solutions revealed that the coatings produced at 10 Hz condition had a better corrosion resistance, which was attributed to the higher thickness, more compact microstructural features and a relatively stable phase composition.

  13. Effect of norepinephrine dosage and calibration frequency on accuracy of pulse contour-derived cardiac output

    PubMed Central

    2011-01-01

    Introduction Continuous cardiac output monitoring is used for early detection of hemodynamic instability and guidance of therapy in critically ill patients. Recently, the accuracy of pulse contour-derived cardiac output (PCCO) has been questioned in different clinical situations. In this study, we examined agreement between PCCO and transcardiopulmonary thermodilution cardiac output (COTCP) in critically ill patients, with special emphasis on norepinephrine (NE) administration and the time interval between calibrations. Methods This prospective, observational study was performed with a sample of 73 patients (mean age, 63 ± 13 years) requiring invasive hemodynamic monitoring on a non-cardiac surgery intensive care unit. PCCO was recorded immediately before calibration by COTCP. Bland-Altman analysis was performed on data subsets comparing agreement between PCCO and COTCP according to NE dosage and the time interval between calibrations up to 24 hours. Further, central artery stiffness was calculated on the basis of the pulse pressure to stroke volume relationship. Results A total of 330 data pairs were analyzed. For all data pairs, the mean COTCP (±SD) was 8.2 ± 2.0 L/min. PCCO had a mean bias of 0.16 L/min with limits of agreement of -2.81 to 3.15 L/min (percentage error, 38%) when compared to COTCP. Whereas the bias between PCCO and COTCP was not significantly different between NE dosage categories or categories of time elapsed between calibrations, interchangeability (percentage error <30%) between methods was present only in the high NE dosage subgroup (≥0.1 μg/kg/min), as the percentage errors were 40%, 47% and 28% in the no NE, NE < 0.1 and NE ≥ 0.1 μg/kg/min subgroups, respectively. PCCO was not interchangeable with COTCP in subgroups of different calibration intervals. The high NE dosage group showed significantly increased central artery stiffness. Conclusions This study shows that NE dosage, but not the time interval between calibrations, has an

  14. Anomalous high-frequency oscillations in a field emission tube and their significance in pulsed field emission.

    PubMed

    Hagmann, M J; Christensen, D A; Mousa, M S; Baturin, A; Sheshin, E P

    2007-09-01

    Relaxation oscillations occur when a capacitor is inserted in series with a field emission tube, a DC high-voltage power supply, and a ballast resistor. The waveform of these oscillations is highly reproducible with a dominant frequency of 200 MHz and a decay time of 20 ns. The peak current as high as 320 mA has been observed although the tungsten emitter is only rated for 10 microA. We have shown that these oscillations are due to a displacement current, charging of the anode-tip capacitance, and are not of a field emission origin. We conclude that the effects of displacement current should be considered in measurements of field emission with microsecond pulses, where high-current densities can be observed. PMID:17485175

  15. Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses.

    PubMed

    Zhang, J Y; Xu, Z; Kong, Y; Yu, C; Wu, Y

    1998-05-20

    We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 microm with a maximum overall efficiency of approximately 25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system.

  16. Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses.

    PubMed

    Zhang, J Y; Xu, Z; Kong, Y; Yu, C; Wu, Y

    1998-05-20

    We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 microm with a maximum overall efficiency of approximately 25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system. PMID:18273287

  17. Effect of Embedded RF Pulsing for Selective Etching of SiO2 in the Dual-Frequency Capacitive Coupled Plasmas.

    PubMed

    Kim, Nam Hun; Jeon, Min Hwan; Kim, Tae Hyung; Yeom, Geun Young

    2015-11-01

    The characteristics of embedded pulse plasma using 60 MHz radio frequency as the source power and 2 MHz radio frequency as the bias power were investigated for the etching of SiO2 masked with an amorphous carbon layer (ACL) using an Ar/C4F8/O2 gas mixture. Especially, the effects of the different pulse duty ratio of the embedded dual-frequency pulsing between source power and bias power on the characteristics on the plasma and SiO2 etching were investigated. The experiment was conducted by varying the source duty percentage from 90 to 30% while bias duty percentage was fixed at 50%. Among the different duty ratios, the source duty percentage of 60% with the bias duty percentage of 50% exhibited the best results in terms of etch profile and etch selectivity. The change of the etch characteristics by varying the duty ratios between the source power and bias power was believed to be related to the different characteristics of gas dissociation, fluorocarbon passivation, and ion bombardment observed during the different source/bias pulse on/off combinations. In addition, the instantaneous high electron temperature peak observed during each initiation of the source pulse-on period appeared to affect the etch characteristics by significant gas dissociation. The optimum point for the SiO2 etching with the source/bias pulsed dual-frequency capacitively coupled plasma system was obtained by avoiding this instant high electron temperature peak while both the source power and bias power were pulsed almost together, therefore, by an embedded RF pulsing. PMID:26726572

  18. Frequency-Tunable Multigigawatt Sub-Half-Cycle Light Pulses from Coupled-State Dynamics of Optical Solitons and Impulsively Driven Molecular Vibrations

    NASA Astrophysics Data System (ADS)

    Zheltikov, A. M.; Voronin, A. A.; Kienberger, R.; Krausz, F.; Korn, G.

    2010-09-01

    Coupling ultrashort optical field waveforms to ultrafast molecular vibrations in an impulsively excited Raman medium is shown to enable the generation of frequency-tunable sub-half-cycle multigigawatt light pulses. In a gas-filled hollow waveguide, this coupled-state dynamics is strongly assisted by soliton effects, which help to suppress temporal stretching of subcycle optical pulses, providing efficient Raman-type impulsive excitation of ultrafast molecular vibrations over large propagation paths.

  19. Duration and frequency of a high temperature pulse affect survival of emergence-ready Megachile rotundata (Hymenoptera: Megachilidae) during low-temperature incubation.

    PubMed

    Yocum, George D; Rinehart, Joseph P; Kemp, William P

    2012-02-01

    Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge -2 wk before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by using a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 degrees C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (5-120 min) and the frequency of a pulse (twice daily to weekly) on the survival of developing M. rotundata was examined. A pulse as short as 5 min at 20 degrees C increased survival of the developing bees as compared with the constant 6 degrees C controls. Increasing the pulse duration induced a further increase in tolerance to 6 degrees C. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata. PMID:22420249

  20. Duration and frequency of a high temperature pulse affect survival of emergence-ready Megachile rotundata (Hymenoptera: Megachilidae) during low-temperature incubation.

    PubMed

    Yocum, George D; Rinehart, Joseph P; Kemp, William P

    2012-02-01

    Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge -2 wk before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by using a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 degrees C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (5-120 min) and the frequency of a pulse (twice daily to weekly) on the survival of developing M. rotundata was examined. A pulse as short as 5 min at 20 degrees C increased survival of the developing bees as compared with the constant 6 degrees C controls. Increasing the pulse duration induced a further increase in tolerance to 6 degrees C. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata.

  1. Ground Operations Demonstration Unit for Liquid Hydrogen (GODU LH2)

    NASA Technical Reports Server (NTRS)

    Notardonato, William U.

    2015-01-01

    When the technology associated with zero loss storage and transfer is implemented, NASA can reduce the LH2 losses and procurement costs by up to 30 compared to historical Shuttle numbers. This return on investment is based on the mission manifest and commodity use. LH2 densification can provide improved launch vehicle ascent performance by minimizing the size of the LH2 tanks or storing more mass of propellant in the given tank volume.

  2. Pulsed photoacoustic flow imaging of whole blood with low frequency detection

    NASA Astrophysics Data System (ADS)

    van den Berg, Pim J.; Daoudi, Khalid; Steenbergen, Wiendelt

    2016-03-01

    Ultrasound flow imaging is widely used for quantification of blood flow in vivo, but estimating low flow velocities remains challenging. Pulsed photoacoustic flowmetry could be an alternative - but has not been shown capable of deep in vivo imaging so far. A new photoacoustic system is proposed, that has more potential for deep in-vivo applications. In this work the system is tested in vitro. In contrast to earlier research, 1064 nm NIR laser irradiation is used, that would allow deeper in-vivo light penetration. For detection, a 15 MHz transducer with lower in-vivo tissue ultrasound attenuation is used. Both changes are not trivial, as they reduce the overall visibility of the photoacoustic signals from red blood cells. This work shows the flow estimation performance of this system in vitro, and aims to serve as a point of reference when moving to an in-vivo application. Using this 15 MHz transducer, 1D flow profiles of flowing blood were extracted. The jitter (standard error) in the velocity estimation over the profiles was 10% when estimating flow of particles and 20% with whole blood; the bias in flow estimation was roughly 30%.

  3. Improving Processes of Mechanized Pulsed Arc Welding of Low-Frequency Range Variation of Mode Parameters

    NASA Astrophysics Data System (ADS)

    Saraev, Yu N.; Solodskiy, S. A.; Ulyanova, O. V.

    2016-04-01

    A new technology of low-frequency modulation of the arc current in MAG and MIG welding is presented. The technology provides control of thermal and crystallization processes, stabilizes the time of formation and crystallization of the weld pool. Conducting theoretical studies allowed formulating the basic criteria for obtaining strong permanent joints for high-duty structures, providing conditions for more equilibrium structure of the deposited metal and the smaller width of the HAZ. The stabilization of time of the formation and crystallization of the weld pool improves the formation of the weld and increases productivity in welding thin sheet metal.

  4. Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei

    NASA Astrophysics Data System (ADS)

    Bräuniger, Thomas; Hempel, Günter; Madhu, P. K.

    2006-07-01

    In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403-410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW (1/τ)-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SW (τ)-FAM). For static spectra of 27Al (I = 5/2), better signal-enhancement performance is found for the SW (1/τ)-FAM sequence, as demonstrated both by experiments and numerical simulations.

  5. Modulation of the human vestibuloocular reflex during saccades: probing by high-frequency oscillation and torque pulses of the head.

    PubMed

    Tabak, S; Smeets, J B; Collewijn, H

    1996-11-01

    1. We probed the gain and phase of the vestibuloocular reflex (VOR) during the execution of voluntary gaze saccades, with continuous oscillation or acceleration pulses, applied through a torque helmet. 2. Small-amplitude (< 1 degree), high-frequency (10-14 Hz) head oscillations in the horizontal or vertical plane were superimposed on ongoing horizontal gaze saccades (40-100 degrees). Torque pulses to the head ("with" or "against" gaze) were superimposed on 40 degrees horizontal saccades. Eye and head movements were precisely measured with sensor coils in magnetic fields. 3. Techniques were developed to separate the oscillatory (horizontal or vertical) component from the gaze shift and obtain VOR gain and phase with Fourier techniques from the relation between eye-in-head and head oscillations. These involved either subtraction of exactly matching saccades with and without oscillation (drawback: low yield) or time shifting of successive trials to synchronize the oscillations (drawback: slight time blurring of saccades). 4. The results of these matching and synchronization methods were essentially identical and consistent. Presaccadic gain values of the horizontal VOR (typically about unity) were reduced by, on average, approximately 20 and 50% during horizontal saccades of 40 and 100 degrees, respectively. These percentages may be truncated because of methodological limitations, but even after taking these into account (on the basis of simulation experiments with 2 different, theoretical profiles of suppression) our results do not support a complete saccadic VOR suppression for any substantial fraction of saccadic duration. Qualitatively similar changes were found when the vertical VOR was probed during 100 degrees horizontal saccades. 5. Concomitantly with the reductions in gain, VOR phase was advanced by approximately 20 degrees during the saccade. 6. In the wake of gaze saccades, VOR gain was consistently elevated (to approximately 1.0) above the presaccadic

  6. Relative velocity measurement from the spectral phase of a match-filtered linear frequency modulated pulse.

    PubMed

    Pinson, Samuel; Holland, Charles W

    2016-08-01

    Linear frequency modulated signals are commonly used to perform underwater acoustic measurements since they can achieve high signal-to-noise ratios with relatively low source levels. However, such signals present a drawback if the source or receiver or target is moving. The Doppler effect affects signal amplitude, delay, and resolution. To perform a correct match filtering that includes the Doppler shift requires prior knowledge of the relative velocity. In this paper, the relative velocity is extracted directly from the Doppler cross-power spectrum. More precisely, the quadratic coefficient of the Doppler cross-power-spectrum phase is proportional to the relative velocity. The proposed method achieves velocity estimates that compare favorably with Global Positioning System ground truth and the ambiguity method. PMID:27586779

  7. Inertial cavitation in theranostic nanoemulsions with simultaneous pulsed laser and low frequency ultrasound excitation

    NASA Astrophysics Data System (ADS)

    Arnal, Bastien; Wei, Chen-Wei; Xia, Jinjun; Pelivanov, Ivan M.; Lombardo, Michael; Perez, Camilo; Matula, Thomas J.; Pozzo, Danilo; O'Donnell, Matthew

    2014-03-01

    Ultrasound-induced inertial cavitation is a mechanical process used for site-localized therapies such as non-invasive surgery. Initiating cavitation in tissue requires very high intensity focused ultrasound (HIFU) and low-frequencies. Hence, some applications like thrombolysis require targeted contrast agents to reduce peak intensities and the potential for secondary effects. A new type of theranostic nanoemulsion has been developed as a combined ultrasound (US)/photoacoustic(PA) agent for molecular imaging and therapy. It includes a nanoscale emulsion core encapsulated with a layer of gold nanospheres at the water/ oil interface. Its optical absorption exhibits a spectrum broadened up to 1100 nm, opening the possibility that 1064 nm light can excite cavitation nuclei. If optically-excited nuclei are produced at the same time that a low-frequency US wave is at peak negative pressure, then highly localized therapies based on acoustic cavitation may be enabled at very low US pressures. We have demonstrated this concept using a low-cost, low energy, portable 1064 nm fiber laser in conjunction with a 1.24 MHz US transducer for simultaneous laser/US excitation of nanoemulsions. Active cavitation detection from backscattered signals indicated that cavitation can be initiated at very low acoustic pressures (less than 1 MPa) when laser excitation coincides with the rarefaction phase of the acoustic wave, and that no cavitation is produced when light is delivered during the compressive phase. US can sustain cavitation activity during long acoustic bursts and stimulate diffusion of the emulsion, thus increasing treatment speed. An in vitro clot model has been used to demonstrate combined US and laser excitation of the nanoemulsion for efficient thrombolysis.

  8. Spectral broadening measurement of the lower hybrid waves during long pulse operation in Tore Supra

    SciTech Connect

    Berger-By, G.; Decampy, J.; Goniche, M.; Ekedahl, A.; Delpech, L.; Leroux, F.; Antar, G. Y.; Collaboration: Tore Supra Team

    2014-02-12

    On many tokamaks (C-Mod, EAST, FTU, JET, HT-7, TS), a decrease in current drive efficiency of the Lower Hybrid (LH) waves is observed in high electron density plasmas. The cause of this behaviour is believed to be: Parametric Instabilities (PI) and Scattering from Density Fluctuations (SDF). For the ITER LH system, our knowledge must be improved to avoid such effects and to maintain the LH current drive efficiency at high density. The ITPA IOS group coordinates this effort [1] and all experimental data are essential to validate the numerical codes in progress. Usually the broadening of the LH wave frequency spectrum is measured by a probe located in the plasma edge. For this study, the frequency spectrum of a reflected power signal from the LH antenna was used. In addition, the spectrum measurements are compared with the density fluctuations observed on RF probes located at the antenna mouth. Several plasma currents (0.6 to 1.4 MA) and densities up to 5.2 × 10{sup 19} m−3 have been realised on Tore Supra (TS) long pulses and with high injected RF power, up to 5.4 MW-30s. This allowed using a spectrum analyser to make several measurements during the plasma pulse. The side lobe amplitude, shifted by 20-30MHz with respect to the main peak, grows with increasing density. Furthermore, for an increase of plasma current at the same density, the spectra broaden and become asymmetric. Some parametric dependencies are shown in this paper.

  9. PULSE AMPLITUDE DEPENDS ON kHz QPO FREQUENCY IN THE ACCRETING MILLISECOND PULSAR SAX J1808.4-3658

    SciTech Connect

    Bult, Peter; Van der Klis, Michiel

    2015-01-10

    We study the relation between the 300-700 Hz upper kHz quasi-periodic oscillation (QPO) and the 401 Hz coherent pulsations across all outbursts of the accreting millisecond X-ray pulsar SAX J1808.4-3658 observed with the Rossi X-ray Timing Explorer. We find that the pulse amplitude systematically changes by a factor of ∼2 when the upper kHz QPO frequency passes through 401 Hz: it halves when the QPO moves to above the spin frequency and doubles again on the way back. This establishes for the first time the existence of a direct effect of kHz QPOs on the millisecond pulsations and provides a new clue to the origin of the upper kHz QPO. We discuss several scenarios and conclude that while more complex explanations can not formally be excluded, our result strongly suggests that the QPO is produced by azimuthal motion at the inner edge of the accretion disk, most likely orbital motion. Depending on whether this azimuthal motion is faster or slower than the spin, the plasma then interacts differently with the neutron-star magnetic field. The most straightforward interpretation involves magnetospheric centrifugal inhibition of the accretion flow that sets in when the upper kHz QPO becomes slower than the spin.

  10. Non-Linear Effects on the LH Wave Coupling in Tore Supra and Impact on the LH Current Drive Efficiency

    SciTech Connect

    Ekedahl, A.; Frincu, B.; Goniche, M.; Hillairet, J.; Petrzilka, V.

    2009-11-26

    A strong, non-linear degradation of the Lower Hybrid (LH) wave coupling in Tore Supra can be observed when the LH launcher is screened on both sides by additional side limiters, such as side protections of adjacent Ion Cyclotron (IC) antennas. The power reflection coefficient (RC) at the LH grill mouth is estimated to increase from {approx}20% at low power density (<1 MW/m{sup 2}) up to >40% at high power density (>10 MW/m{sup 2}). Such large RC (>40%) is unacceptably high, in particular for long durations. The screening by the additional side limiters reduces the connection length in front of the LH grill, which results in lower {lambda}{sub n}, {lambda}{sub T}, n{sub e} and T{sub e} at the grill. However, the reduction in ne alone is not enough to explain the non-linear behaviour. Modelling with a code that takes into account a ponderomotive force potential [1], depleting the electron density in front of the grill, shows consistent results. In full non-inductive current drive scenarios, the observed degradation in LH coupling is measurable on the LH current drive efficiency, through the increase in coupled LH power required to maintain V{sub Loop} = 0. These results demonstrate thus the importance of being able to control the LH coupling conditions, in order to optimize the efficiency and power handling of LH systems.

  11. Effect of low frequency low energy pulsing electromagnetic field (PEMF) on X-ray-irradiated mice

    SciTech Connect

    Cadossi, R.; Hentz, V.R.; Kipp, J.; Eiverson, R.; Ceccherelli, G.; Zucchini, P.; Emilia, G.; Torelli, G.; Franceschi, C.; Cossarizza, A.

    1989-02-01

    C3H/Km flora-defined mice were used to investigate the effect of exposure to pulsing electromagnetic field (PEMF) after total body x-ray irradiation. Prolonged exposure to PEMF had no effect on normal nonirradiated mice. When mice irradiated with different doses of x-ray (8.5 Gy, 6.8 Gy, and 6.3 Gy) were exposed to PEMF 24 h a day, we observed a more rapid decline in white blood cells (WBC) in the peripheral blood of mice exposed to PEMF at all the x-ray dosages used. No effect of exposure to PEMF was observed on the survival of the mice irradiated with 6.3 Gy and 8.5 Gy; in mice irradiated with 6.8 Gy, 2 out of 12 survived when exposed to PEMF as compared to 10 out of 12 control mice that were irradiated only. At day 4 after irradiation autoradiographic studies performed on bone marrow and spleen of 8.5-Gy-irradiated mice showed no difference between controls and mice exposed to PEMF, whereas on 6.8-Gy mice the bone marrow labeling index was lower in mice exposed to PEMF. In mice irradiated to 6.3 Gy we observed that the recovery of WBC in the peripheral blood was slowed in mice exposed to PEMF and their body weight was significantly lower than in control mice that were irradiated only. The spleen and bone marrow of the mice irradiated to 6.3 Gy and sacrificed at days 4, 14, 20, and 25 after irradiation were analyzed by autoradiography to evaluate the labeling index. Half of the spleens from mice sacrificed at day 25 after irradiation were used to evaluate the RNA content. Autoradiography showed that in the spleen and bone marrow of control mice, there were more cells labeled with (3H)thymidine at days 4 and 14 and less at days 20 and 25 after irradiation in comparison with mice irradiated and exposed to PEMF.

  12. Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX

    SciTech Connect

    Zweben, S; Hager, R; Hallatschek, K; Kaye, S M; Munsat, T; Poli, F M; Roquemore, A L; Sechrest, Y

    2010-04-26

    This paper describes the first observations in NSTX of ‘quiet periods’ in the edge turbulence preceding the L-H transition, as diagnosed by the GPI diagnostic near the outer midplane separatrix. During these quiet periods the GPI Dα light emission pattern was transiently similar to that seen during Hmode, i.e. with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ~3 kHz for at least 30 msec before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also analyzed to obtain an estimate for the dimensionless poloidal shearing S =(dVp/dr)(Lr/Lp)τ. The values of S were strongly modulated by the quiet periods, but not otherwise varying for at least 30 msec preceding the L-H transition. Since neither the quiet periods nor the shear flow increased significantly immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX.

  13. β-Adrenergic response is counteracted by extremely-low-frequency pulsed electromagnetic fields in beating cardiomyocytes.

    PubMed

    Cornacchione, Marisa; Pellegrini, Manuela; Fassina, Lorenzo; Mognaschi, Maria Evelina; Di Siena, Sara; Gimmelli, Roberto; Ambrosino, Paolo; Soldovieri, Maria Virginia; Taglialatela, Maurizio; Gianfrilli, Daniele; Isidori, Andrea M; Lenzi, Andrea; Naro, Fabio

    2016-09-01

    Proper β-adrenergic signaling is indispensable for modulating heart frequency. Studies on extremely-low-frequency pulsed electromagnetic field (ELF-PEMF) effects in the heart beat function are contradictory and no definitive conclusions were obtained so far. To investigate the interplay between ELF-PEMF exposure and β-adrenergic signaling, cultures of primary murine neonatal cardiomyocytes and of sinoatrial node were exposed to ELF-PEMF and short and long-term effects were evaluated. The ELF-PEMF generated a variable magnetic induction field of 0-6mT at a frequency of 75Hz. Exposure to 3mT ELF-PEMF induced a decrease of contraction rate, Ca(2+) transients, contraction force, and energy consumption both under basal conditions and after β-adrenergic stimulation in neonatal cardiomyocytes. ELF-PEMF exposure inhibited β-adrenergic response in sinoatrial node (SAN) region. ELF-PEMF specifically modulated β2 adrenergic receptor response and the exposure did not modify the increase of contraction rate after adenylate cyclase stimulation by forskolin. In HEK293T cells transfected with β1 or β2 adrenergic receptors, ELF-PEMF exposure induced a rapid and selective internalization of β2 adrenergic receptor. The β-adrenergic signaling, was reduced trough Gi protein by ELF-PEMF exposure since the phosphorylation level of phospholamban and the PI3K pathway were impaired after isoproterenol stimulation in neonatal cardiomyocytes. Long term effects of ELF-PEMF exposure were assessed in cultures of isolated cardiomyocytes. ELF-PEMF counteracts cell size increase, the generation of binucleated of cardiomyocytes and prevents the up-regulation of hypertrophic markers after β-adrenergic stimulation, indicating an inhibition of cell growth and maturation. These data show that short and long term exposure to ELF-PEMF induces a reduction of cardiac β-adrenergic response at molecular, functional and adaptative levels.

  14. Extremely low frequency pulsed electromagnetic field designed for antinociception does not affect microvascular responsiveness to the vasodilator acetylcholine.

    PubMed

    McKay, Julia C; Corbacio, Michael; Tyml, Karel; Prato, Frank S; Thomas, Alex W

    2010-01-01

    A 225 microT, extremely low frequency, pulsed electromagnetic field (PEMF) that was designed for the induction of antinociception, was tested for its effectiveness to influence blood flow within the skeletal microvasculature of a male Sprague-Dawley rat model (n = 103). Acetylcholine (0.1, 1.0, or 10 mM) was used to perturb normal blood flow and to delineate differential effects of the PEMF, based on degree of vessel dilation. After both 30 and 60 min of PEMF exposure, we report no effects on peak perfusion response to acetylcholine (with only 0.2% of the group difference attributed to exposure). Spectral analysis of blood flow data was generated to obtain information related to myogenic activity (0.15-0.40 Hz), respiratory rate (0.4-2.0 Hz), and heart rate (2.0-7.0 Hz), including the peak frequency within each of the three frequency regions identified above, peak power, full width at half maximum (FWHM), and mean within band. No significant effects due to exposure were observed on myogenic activity of examined blood vessels, or on heart rate parameters. Anesthesia-induced respiratory depression was, however, significantly reduced following PEMF exposure compared to shams (although exposure only accounted for 9.4% of the group difference). This set of data suggest that there are no significant acute physiological effects of 225 microT PEMF after 30 and 60 min of exposure on peak blood flow, heart rate, and myogenic activity, but perhaps a small attenuation effect on anesthetic-induced respiratory depression. PMID:19644977

  15. β-Adrenergic response is counteracted by extremely-low-frequency pulsed electromagnetic fields in beating cardiomyocytes.

    PubMed

    Cornacchione, Marisa; Pellegrini, Manuela; Fassina, Lorenzo; Mognaschi, Maria Evelina; Di Siena, Sara; Gimmelli, Roberto; Ambrosino, Paolo; Soldovieri, Maria Virginia; Taglialatela, Maurizio; Gianfrilli, Daniele; Isidori, Andrea M; Lenzi, Andrea; Naro, Fabio

    2016-09-01

    Proper β-adrenergic signaling is indispensable for modulating heart frequency. Studies on extremely-low-frequency pulsed electromagnetic field (ELF-PEMF) effects in the heart beat function are contradictory and no definitive conclusions were obtained so far. To investigate the interplay between ELF-PEMF exposure and β-adrenergic signaling, cultures of primary murine neonatal cardiomyocytes and of sinoatrial node were exposed to ELF-PEMF and short and long-term effects were evaluated. The ELF-PEMF generated a variable magnetic induction field of 0-6mT at a frequency of 75Hz. Exposure to 3mT ELF-PEMF induced a decrease of contraction rate, Ca(2+) transients, contraction force, and energy consumption both under basal conditions and after β-adrenergic stimulation in neonatal cardiomyocytes. ELF-PEMF exposure inhibited β-adrenergic response in sinoatrial node (SAN) region. ELF-PEMF specifically modulated β2 adrenergic receptor response and the exposure did not modify the increase of contraction rate after adenylate cyclase stimulation by forskolin. In HEK293T cells transfected with β1 or β2 adrenergic receptors, ELF-PEMF exposure induced a rapid and selective internalization of β2 adrenergic receptor. The β-adrenergic signaling, was reduced trough Gi protein by ELF-PEMF exposure since the phosphorylation level of phospholamban and the PI3K pathway were impaired after isoproterenol stimulation in neonatal cardiomyocytes. Long term effects of ELF-PEMF exposure were assessed in cultures of isolated cardiomyocytes. ELF-PEMF counteracts cell size increase, the generation of binucleated of cardiomyocytes and prevents the up-regulation of hypertrophic markers after β-adrenergic stimulation, indicating an inhibition of cell growth and maturation. These data show that short and long term exposure to ELF-PEMF induces a reduction of cardiac β-adrenergic response at molecular, functional and adaptative levels. PMID:27418252

  16. Nonlinear frequency up-conversion of femtosecond pulses from an erbium fibre laser to the range of 0.8 - 1 {mu}m in silica fibres

    SciTech Connect

    Anashkina, E A; Andrianov, A V; Kim, A V

    2013-03-31

    We consider different mechanisms of nonlinear frequency up-conversion of femtosecond pulses emitted by an erbium fibre system ({lambda} = 1.5 {mu}m) to the range of 0.8 - 1.2 {mu}m in nonlinear silica fibres. The generation efficiency and the centre frequencies of dispersive waves are found as functions of the parameters of the fibre and the input pulse. Simple analytical estimates are obtained for the spectral distribution of the intensity and the frequency shift of a wave packet in the region of normal dispersion during the emission of a high-order soliton under phase matching conditions. In the geometrical optics approximation the frequency shifts are estimated in the interaction of dispersive waves with solitons in various regimes. (extreme light fields and their applications)

  17. Investigation of the lasing characteristics of a barium vapor laser with pulse repetition frequencies up to 320 kHz for navigation

    NASA Astrophysics Data System (ADS)

    Soldatov, A. N.; Polunin, Yu. P.

    2015-11-01

    Results of experimental investigations into the characteristics of a laser on self-terminating transitions of the barium atom with λ = 1499 nm are presented for high pulse repetition frequencies (PRF). The frequency-energy characteristics are investigated in the self-heating mode of laser operation. Record values of PRF for the barium vapor laser, equal to ~320 kHz, have been attained.

  18. Directional spectra of ocean waves from microwave backscatter: A physical optics solution with application to the short-pulse and two-frequency measurement techniques

    NASA Technical Reports Server (NTRS)

    Jackson, F. C.

    1979-01-01

    Two simple microwave radar techniques that are potentially capable of providing routine satellite measurements of the directional spectrum of ocean waves were developed. One technique, the short pulse technique, makes use of very short pulses to resolve ocean surface wave contrast features in the range direction; the other technique, the two frequency correlation technique makes use of coherency in the transmitted waveform to detect the large ocean wave contrast modulation as a beat or mixing frequency in the power backscattered at two closely separated microwave frequencies. A frequency domain analysis of the short pulse and two frequency systems shows that the two measurement systems are essentially duals; they each operate on the generalized (three frequency) fourth-order statistical moment of the surface transfer function in different, but symmetrical ways, and they both measure the same directional contrast modulation spectrum. A three dimensional physical optics solution for the fourth-order moment was obtained for backscatter in the near vertical, specular regime, assuming Gaussian surface statistics.

  19. [Pulse-modulated Electromagnetic Radiation of Extremely High Frequencies Protects Cellular DNA against Damaging Effect of Physico-Chemical Factors in vitro].

    PubMed

    Gapeyev, A B; Lukyanova, N A

    2015-01-01

    Using a comet assay technique, we investigated protective effects of. extremely high frequency electromagnetic radiation in combination with the damaging effect of X-ray irradiation, the effect of damaging agents hydrogen peroxide and methyl methanesulfonate on DNA in mouse whole blood leukocytes. It was shown that the preliminary exposure of the cells to low intensity pulse-modulated electromagnetic radiation (42.2 GHz, 0.1 mW/cm2, 20-min exposure, modulation frequencies of 1 and 16 Hz) caused protective effects decreasing the DNA damage by 20-45%. The efficacy of pulse-modulated electromagnetic radiation depended on the type of genotoxic agent and increased in a row methyl methanesulfonate--X-rays--hydrogen peroxide. Continuous electromagnetic radiation was ineffective. The mechanisms of protective effects may be connected with an induction of the adaptive response by nanomolar concentrations of reactive oxygen species formed by pulse-modulated electromagnetic radiation.

  20. [Pulse-modulated Electromagnetic Radiation of Extremely High Frequencies Protects Cellular DNA against Damaging Effect of Physico-Chemical Factors in vitro].

    PubMed

    Gapeyev, A B; Lukyanova, N A

    2015-01-01

    Using a comet assay technique, we investigated protective effects of. extremely high frequency electromagnetic radiation in combination with the damaging effect of X-ray irradiation, the effect of damaging agents hydrogen peroxide and methyl methanesulfonate on DNA in mouse whole blood leukocytes. It was shown that the preliminary exposure of the cells to low intensity pulse-modulated electromagnetic radiation (42.2 GHz, 0.1 mW/cm2, 20-min exposure, modulation frequencies of 1 and 16 Hz) caused protective effects decreasing the DNA damage by 20-45%. The efficacy of pulse-modulated electromagnetic radiation depended on the type of genotoxic agent and increased in a row methyl methanesulfonate--X-rays--hydrogen peroxide. Continuous electromagnetic radiation was ineffective. The mechanisms of protective effects may be connected with an induction of the adaptive response by nanomolar concentrations of reactive oxygen species formed by pulse-modulated electromagnetic radiation. PMID:26591599

  1. Dynamics of a one-dimensional model and a three-dimensional hydrogen atom in an intense high-frequency short-pulse laser

    SciTech Connect

    Tang, X. ); Basile, S. di Fisica Teorica dell'Universita, Casello Postale 50, 98166 Sant'Agata di Messina, Messina, Italy )

    1991-08-01

    We present nonperturbative calculations of ionizing and trapping probabilities for a one-dimensional model and a three-dimensional hydrogen atom in an intense high-frequency Gaussian-pulsed laser field. Investigating the dynamics of the ionization process (for one- and two-photon ionization), we find that only for extremely short pulses, especially for hydrogen, does the system have a significant probability of surviving at the end of the pulse, leading to the phenomenon of atomic stabilization with respect to ionization. We also find that a one-dimensional model has a higher survival probability at the end of a Gaussian pulse, as compared to the three-dimensional hydrogen atom.

  2. Pulsed 456 nm deep-blue light generation by acousto-optical Q-switching and intracavity frequency doubling of Nd:GdVO4

    NASA Astrophysics Data System (ADS)

    Gao, J.; Yu, X.; Chen, F.; Li, X. D.; Yan, R. P.; Zhang, Z.; Yu, J. H.; Wang, Y. Z.

    2008-08-01

    We present what is, to the best of our knowledge, the first pulsed deep-blue laser at 456 nm by acousto-optical Q-switching and intracavity frequency doubling of a diode-end-pumped Nd:GdVO4 laser on the 4F3/2 → 4I9/2 transition at 912 nm. When the incident pump power is 36 W, the maximum single pulse energy of 44.1 μJ, pulse duration of 140 ns and peak power of 315 W are achieved at 10 kHz; the maximum average power of 770 mW, pulse duration of 200 ns and peak power of 193 W are obtained at 20 kHz. The fluctuation of the blue output power is less than 2.4% within the given 20 min at the maximum blue output power.

  3. A pulse-frequency-modulation vision chip using a capacitive feedback reset with an in-pixel 1-bit image processor

    NASA Astrophysics Data System (ADS)

    Kagawa, Keiichiro; Yamamoto, Shinya; Furumiya, Tetsuo; Tokuda, Takashi; Nunoshita, Masahiro; Ohta, Jun

    2006-02-01

    We report a low-voltage digital vision chip based on a pulse-frequency-modulation (PFM) photosensor using capacitive feedback reset and pulse-domain digital image processing to explore its feasibility of low power consumption and high dynamic range even at a low power-supply voltage. An example of the applications of the vision chip is retinal prosthesis, in which supplied power is limited. The pixel is composed of a PFM photosensor with a dynamic pulse memory, pulse gates, and a 1-bit digital image processor. The binary value stored at the dynamic pulse memory is read to the 1-bit digital image processor. The image processor executes spatial filtering by mutual operations between the pulses from the pixel and those from the four neighboring pixels. The weights in image processing are controlled by pulse gates. We fabricated a test chip in a standard 0.35-μm CMOS technology. Pixel size and pixel counts were 100 μm sq. and 32 x 32, respectively. In the experiments, four neighboring pixels were considered in image processing. The test chip successfully operated at low power supply voltage around 1.25 V. The frame rate was 26 kfps. Low-pass filtering, edge enhancement, and edge detection have been demonstrated. Relationships between power supply voltages and characteristics of the vision chip are investigated.

  4. Tokamak L/H mode transition

    SciTech Connect

    Tsui, K. H.; Navia, C. E.

    2012-01-15

    Through the non field-aligned rotational tokamak equilibrium of a divergence-free plasma flow with a pair of transformed plasma variables w-vector{sub *}=({mu}{rho}){sup 1/2}{nu}-vector and {mu}p{sub *}=({mu}p+w{sub *}{sup 2}/2)[K. H. Tsui, Phys. Plasmas 18, 072502 (2011)], a preliminary understanding of the L/H equilibrium transition is proposed through a feedback cycle, where the higher plasma flux due to external drives enters the rotational Grad-Shafranov equation through the velocity dependent poloidal plasma {beta} to generate the H equilibrium. This H rotational mode has the characteristics of higher normal electric field and plasma pressure. Coupled to the transport properties of E-vector x B-vector drift transport barrier leading to a higher plasma pressure, this makes the H mode a self-sustained equilibrium. The higher plasma {beta} then feeds back to the equilibrium and completes the feedback loop.

  5. Modeling seismic stimulation: Enhanced non-aqueous fluid extraction from saturated porous media under pore-pressure pulsing at low frequencies

    NASA Astrophysics Data System (ADS)

    Lo, Wei-Cheng; Sposito, Garrison; Huang, Yu-Han

    2012-03-01

    Seismic stimulation, the application of low-frequency stress-pulsing to the boundary of a porous medium containing water and a non-aqueous fluid to enhance the removal of the latter, shows great promise for both contaminated groundwater remediation and enhanced oil recovery, but theory to elucidate the underlying mechanisms lag significantly behind the progress achieved in experimental research. We address this conceptual lacuna by formulating a boundary-value problem to describe pore-pressure pulsing at seismic frequencies that is based on the continuum theory of poroelasticity for an elastic porous medium permeated by two immiscible fluids. An exact analytical solution is presented that is applied numerically using elasticity parameters and hydraulic data relevant to recent proof-of-principle laboratory experiments investigating the stimulation-induced mobilization of trichloroethene (TCE) in water flowing through a compressed sand core. The numerical results indicated that significant stimulation-induced increases of the TCE concentration in effluent can be expected from pore-pressure pulsing in the frequency range of 25-100 Hz, which is in good agreement with what was observed in the laboratory experiments. Sensitivity analysis of our numerical results revealed that the TCE concentration in the effluent increases with the porous medium framework compressibility and the pulsing pressure. Increasing compressibility also leads to an optimal stimulation response at lower frequencies, whereas changing the pulsing pressure does not affect the optimal stimulation frequency. Within the context of our model, the dominant physical cause for enhancement of non-aqueous fluid mobility by seismic stimulation is the dilatory motion of the porous medium in which the solid and fluid phases undergo opposite displacements, resulting in stress-induced changes of the pore volume.

  6. Structure/property relationships in pulsed-laser-deposited ferroelectric thin films for frequency-agile microwave electronics

    NASA Astrophysics Data System (ADS)

    Horwitz, James S.; Carter, A. C.; Chang, Wontae; Pond, Jeffrey M.; Kirchoefer, Steven W.; Chrisey, Douglas B.; Levy, J.; Hubert, C.

    1998-06-01

    Low loss ferroelectric thin films deposited by pulsed laser deposition (PLD) are currently being used to develop a new class of tunable microwave circuits based on the electric field dependence of the dielectric constant. Single phase, (100) oriented Ba0.5Sr0.5TiO3 (BST) films have been deposited onto (100) LaAlO3, SrTiO3, and MgO substrates. Interdigitated capacitors have been used to measure the dielectric constant and dissipation factor of these films as a function of DC bias and temperature at 1 MHz and as a function of DC bias at 1 to 20 GHz at room temperature. A low phase noise voltage controlled oscillator is currently being developed for use at frequencies from 1 - 20 GHz. To achieve low phase noise in the oscillator will require the loss tangent in the ferroelectric to be frequencies (tan(delta) equals 0.01 at 1 - 10 GHz) has been in a post-deposition annealed Ba0.5Sr0.5TiO3 film doped with approximately 1 - 2 atomic % Mn.

  7. Characteristics of temperature rise in variable inductor employing magnetorheological fluid driven by a high-frequency pulsed voltage source

    NASA Astrophysics Data System (ADS)

    Lee, Ho-Young; Kang, In Man; Shon, Chae-Hwa; Lee, Se-Hee

    2015-05-01

    A variable inductor with magnetorheological (MR) fluid has been successfully applied to power electronics applications; however, its thermal characteristics have not been investigated. To evaluate the performance of the variable inductor with respect to temperature, we measured the characteristics of temperature rise and developed a numerical analysis technique. The characteristics of temperature rise were determined experimentally and verified numerically by adopting a multiphysics analysis technique. In order to accurately estimate the temperature distribution in a variable inductor with an MR fluid-gap, the thermal solver should import the heat source from the electromagnetic solver to solve the eddy current problem. To improve accuracy, the B-H curves of the MR fluid under operating temperature were obtained using the magnetic property measurement system. In addition, the Steinmetz equation was applied to evaluate the core loss in a ferrite core. The predicted temperature rise for a variable inductor showed good agreement with the experimental data and the developed numerical technique can be employed to design a variable inductor with a high-frequency pulsed voltage source.

  8. Geometry of hydrogen bonds formed by lipid bilayer nitroxide probes : A high frequency pulsed ENDOR/EPR study.

    SciTech Connect

    Smirnova, T. I.; Smirnov, A. I.; Pachtchenko, S.; Poluektov, O. G.; Chemistry; North Carolina State Univ.

    2007-01-01

    Solvent effects on magnetic parameters of nitroxide spin labels in combination with side-directed spin-labeling EPR methods provide very useful means for elucidating polarity profiles in lipid bilayers and mapping local electrostatic effects in complex biomolecular systems. One major contributor to these solvent effects is the hydrogen bonds that could be formed between the nitroxide moiety and water and/or the available hydroxyl groups. Here, formation of hydrogen bonds between a lipid bilayer spin probe 5-doxyl stearic acid, 5DSA and hydrogen-bond donors has been studied using high-frequency (HF) pulsed ENDOR and EPR. A hydrogen-bonded deuteron was directly detected in HF ENDOR (130 GHz) spectra of 5DSA dissolved in several deuterated alcohols, while the characteristic signal was absent in nonpolar toluene-d{sub 8}. The length of the hydrogen bond, 1.74 {+-} 0.06 {angstrom}, and its geometry were found to be essentially the same for all four alcohols studied, indicating that nearly identical hydrogen bonds have been formed regardless of the solvent dielectric constant. This strengthens a hypothesis that HF EPR spectra are exclusively sensitive to formation of hydrogen bonds and could be used for probing the hydrogen-bond network in complex biomolecular assemblies and lipid bilayers with site-directed spin-labeling methods.

  9. Study on Surface Depression of Ti-6Al-4V with Ultrahigh-Frequency Pulsed Gas Tungsten Arc Welding

    NASA Astrophysics Data System (ADS)

    Mingxuan, Yang; Zhou, Yang; Bojin, Qi

    2015-08-01

    Molten pool surface depression was observed with the arc welding process that was caused by arc pressure. It was supposed to have a significant effect on fluid in the molten pool that was important for the microstructure and joint properties. The impact of arc force was recognized as the reason for the surface depression during arc welding. The mathematical distribution of arc force was produced with the exponent and parabola models. Different models showed different concentrations and attenuations. The comparison between them was discussed with the simulation results. The volume of fluid method was picked up with the arc force distribution model. The surface depression was caused by the arc force. The geometry of the surface depression was discussed with liquid metal properties. The welding process was carried out with different pulsed frequencies. The results indicated the forced depression exists in molten pool and the geometry of depression was hugely due to the arc force distribution. The previous work calculated the depression in the center with force balance at one point. The other area of gas shielding was resistant by the reverse gravity from the feedback of liquid metal that was squeezed out. The article discusses the pressure effect with free deformation that allowed resistance of liquid and was easy to compare with different distributions. The curve profiles were studied with the arc force distributions, and exponent model was supposed to be more accurate to the as-weld condition.

  10. Characteristics of temperature rise in variable inductor employing magnetorheological fluid driven by a high-frequency pulsed voltage source

    SciTech Connect

    Lee, Ho-Young; Kang, In Man; Shon, Chae-Hwa; Lee, Se-Hee

    2015-05-07

    A variable inductor with magnetorheological (MR) fluid has been successfully applied to power electronics applications; however, its thermal characteristics have not been investigated. To evaluate the performance of the variable inductor with respect to temperature, we measured the characteristics of temperature rise and developed a numerical analysis technique. The characteristics of temperature rise were determined experimentally and verified numerically by adopting a multiphysics analysis technique. In order to accurately estimate the temperature distribution in a variable inductor with an MR fluid-gap, the thermal solver should import the heat source from the electromagnetic solver to solve the eddy current problem. To improve accuracy, the B–H curves of the MR fluid under operating temperature were obtained using the magnetic property measurement system. In addition, the Steinmetz equation was applied to evaluate the core loss in a ferrite core. The predicted temperature rise for a variable inductor showed good agreement with the experimental data and the developed numerical technique can be employed to design a variable inductor with a high-frequency pulsed voltage source.

  11. Dynamic interference in the photoionization of He by coherent intense high-frequency laser pulses: Direct propagation of the two-electron wave packets on large spatial grids

    NASA Astrophysics Data System (ADS)

    Artemyev, Anton N.; Müller, Anne D.; Hochstuhl, David; Cederbaum, Lorenz S.; Demekhin, Philipp V.

    2016-04-01

    The direct ionization of the helium atom by intense coherent high-frequency short laser pulses is investigated theoretically from first principles. To this end, we solve numerically the time-dependent Schrödinger equation for the two-electron wave packet and its interaction with the linearly polarized pulse by the efficient time-dependent restricted-active-space configuration-interaction method (TD-RASCI). In particular, we consider photon energies which are nearly resonant for the 1 s →2 p excitation in the He+ ion. Thereby, we investigate the dynamic interference of the photoelectrons of the same kinetic energy emitted at different times along the pulse in the two-electron system. In order to enable observation of the dynamic interference in the computed spectrum, the electron wave packets were propagated on large spatial grids over long times. The computed photoionization spectra of He exhibit pronounced interference patterns the complexity of which increases with the decrease of the photon energy detuning and with the increase of the pulse intensity. Our numerical results pave the way for experimental verification of the dynamic interference effect at presently available high-frequency laser pulse sources.

  12. Frequency- and time-domain analysis of the transient resonance scattering resulting from the interaction of a sound pulse with submerged elastic shells.

    PubMed

    Gaunaurd, G C; Strifors, H C

    1993-01-01

    The authors present a resonance scattering analysis of the echoes returned by a submerged, air-filled, elastic spherical shell, and also from a rigid sphere, when they are insonified by sound pulses. They consider arbitrary pulsed incidences of any duration, carrier frequency, envelope and shape. The approach is equally effective in the frequency and the time domains. They compare backscattered echoes returned by the structures under study in various instances, which are predicted by exact modal approaches, and by the approximate Kirchhoff method. The effects of pulse duration are examined, and so are the various kinds of resonances that develop when a shell is insonified by extremely narrowband pulses. Also examined is the concept of an impulse sonar, for incident pulses that are short- and broadbanded. An inverse scattering analysis shows how and how well physical target characteristics extracted in situ from the remotely sensed echoes can be used for target identification. Various sample cases are constructed and solved and the results interpreted.

  13. Studies on LH-generated Fast Electron Tail Using the Oblique ECE Diagnostic at JET

    SciTech Connect

    Sozzi, C.; Grossetti, G.; Farina, D.; Figini, L.; Garavaglia, S.; Nowak, S.; Baranov, Y.; Kirov, K.; Luna, E. de la

    2009-11-26

    The new Oblique ECE diagnostics of JET allows simultaneous measurement along three lines of sight at different toroidal angles. JET pulses, in which modulated LHCD power was applied, were analyzed by means of the SPECE emission code, which takes into account the fast electron tail generated by LH. The code results were compared to the ECE spectra from the oblique ECE diagnostic. The match between the computed and the experimental data from the three lines of sight provides an estimate of the density of superthermal electrons and of their maximum energy from which the fraction of the plasma current driven by LHCD is derived.

  14. Pain Control on Demand Based on Pulsed Radio-Frequency Stimulation of the Dorsal Root Ganglion Using a Batteryless Implantable CMOS SoC.

    PubMed

    Hung-Wei Chiu; Mu-Lien Lin; Chii-Wann Lin; I-Hsiu Ho; Wei-Tso Lin; Po-Hsiang Fang; Yi-Chin Lee; Yeong-Ray Wen; Shey-Shi Lu

    2010-12-01

    This paper presents the implementation of a batteryless CMOS SoC with low voltage pulsed radio-frequency (PRF) stimulation. This implantable SoC uses 402 MHz command signals following the medical implanted communication system (MICS) standard and a low frequency (1 MHz) for RF power transmission. A body floating type rectifier achieves 84% voltage conversion ratio. A bi-phasic pulse train of 1.4 V and 500 kHz is delivered by a PRF driver circuit. The PRF parameters include pulse duration, pulse frequency and repetition rate, which are controllable via 402 MHz RF receiver. The minimal required 3 V RF Vin and 2.2 V VDDr is achieved at 18 mm gap. The SoC chip is fabricated in a 0.35 μm CMOS process and mounted on a PCB with a flexible spiral antenna. The packaged PRF SoC was implanted into rats for the animal study. Von Frey was applied to test the mechanical allodynia in a blinded manner. This work has successfully demonstrated that implanted CMOS SoC stimulating DRG with 1.4 V, 500 kHz PRF could significantly reduce spinal nerve ligation (SNL) induced mechanical allodynia for 3-7 days. PMID:23850752

  15. Changes in LH and prolactin in arteriosclerotic femal breeder rats.

    PubMed

    Lewis, B K; Wexler, B C

    1975-01-01

    Serum levels of LH and prolactin were measured in repeatedly-bred, arteriosclerotic female rats. Serum LH was abnormally decreased on the afternoon of proestrus and estrus. The extent of the depression of circulating LH levels parallels the severity of the arteriosclerosis. Serum prolactin was significantly increased above normal at proestrus, and the degree of prolactin increase was also correlated with the degree of severity of arteriosclerosis. It is suggested that frequent and repeated pregnancies affect the hypothalamic-pituitary-adrenal-gonadal axis leading to hormonal and metabolic imbalance, which may play a causal role in the pathogenesis of the spontaneous arteriosclerosis which appears in repeatedly-bred rats.

  16. LH response to GnRH blood test

    MedlinePlus

    Luteinizing hormone response to gonadotropin-releasing hormone ... GnRH is a hormone made by the hypothalamus gland. LH is made by the pituitary gland. GnRH causes (stimulates) the pituitary gland to ...

  17. Estrogen positive feedback on LH secretion in transsexuality.

    PubMed

    Gooren, L J; Rao, B R; van Kessel, H; Harmsen-Louman, W

    1984-01-01

    In order to test the hypothesis whether there is variation in hormonal levels or response to hormonal manipulation that could permit a distinction between heterosexuals and transsexuals, we designed the following protocol: Six male-to-female (m-to-f) transsexuals, six heterosexual control females and six female-to-male (f-to-m) transsexuals were given estradiol benzoate (E2B) (4.5 micrograms/kg/12 hr) for five days. In the female population, E2B treatment was initiated on day 5 of the menstrual cycle. In all the subjects blood luteinizing hormone (LH) and follicle stimulating hormone (FSH), estradiol-17 beta (E2) and testosterone (T) levels were measured twice daily. Additionally, LH and FSH responses to LHRH (100 micrograms iv) stimulation prior to and on day 5 of the E2B treatment were evaluated. In the m-to-f transsexuals, T levels decreased sharply and progressively during estrogen treatment, along with a fall in LH and FSH levels. The magnitude of the LH and FSH responses to LHRH stimulation also decreased following estrogen administration. In the heterosexual female controls and in the f-to-m transsexuals, estrogen administration increased LH levels to a minimum of 100% above initial values from day 3 onwards. Interestingly, the magnitude of the LH increase in the f-to-m transsexuals was greater than that of the heterosexual female controls. In both groups, LHRH stimulation resulted in a greater LH response compared to that prior to estrogen treatment. Our present observations, based on blood hormonal levels and responses to hormonal manipulations do not permit a distinction between heterosexual females and f-to-m transsexuals. There was no convincing evidence for the existence of a positive estrogen feedback on LH secretion in m-to-f transsexuals. These results contradict some of the reported hypotheses concerning hormonal alterations in these individuals.

  18. A frequency and pulse-width co-modulation strategy for transcutaneous neuromuscular electrical stimulation based on sEMG time-domain features

    NASA Astrophysics Data System (ADS)

    Zhou, Yu-Xuan; Wang, Hai-Peng; Bao, Xue-Liang; Lü, Xiao-Ying; Wang, Zhi-Gong

    2016-02-01

    Objective. Surface electromyography (sEMG) is often used as a control signal in neuromuscular electrical stimulation (NMES) systems to enhance the voluntary control and proprioceptive sensory feedback of paralyzed patients. Most sEMG-controlled NMES systems use the envelope of the sEMG signal to modulate the stimulation intensity (current amplitude or pulse width) with a constant frequency. The aims of this study were to develop a strategy that co-modulates frequency and pulse width based on features of the sEMG signal and to investigate the torque-reproduction performance and the level of fatigue resistance achieved with our strategy. Approach. We examined the relationships between wrist torque and two stimulation parameters (frequency and pulse width) and between wrist torque and two sEMG time-domain features (mean absolute value (MAV) and number of slope sign changes (NSS)) in eight healthy volunteers. By using wrist torque as an intermediate variable, customized and generalized transfer functions were constructed to convert the two features of the sEMG signal into the two stimulation parameters, thereby establishing a MAV/NSS dual-coding (MNDC) algorithm. Wrist torque reproduction performance was assessed by comparing the torque generated by the algorithms with that originally recorded during voluntary contractions. Muscle fatigue was assessed by measuring the decline percentage of the peak torque and by comparing the torque time integral of the response to test stimulation trains before and after fatigue sessions. Main Results. The MNDC approach could produce a wrist torque that closely matched the voluntary wrist torque. In addition, a smaller decay in the wrist torque was observed after the MNDC-coded fatigue stimulation was applied than after stimulation using pulse-width modulation alone. Significance. Compared with pulse-width modulation stimulation strategies that are based on sEMG detection, the MNDC strategy is more effective for both voluntary muscle

  19. Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse

    NASA Astrophysics Data System (ADS)

    Stauffer, Hans U.; Miller, Joseph D.; Slipchenko, Mikhail N.; Meyer, Terrence R.; Prince, Benjamin D.; Roy, Sukesh; Gord, James R.

    2014-01-01

    The hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs/ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs/ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs/ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

  20. A study of the effects of flux density and frequency of pulsed electromagnetic field on neurite outgrowth in PC12 cells.

    PubMed

    Zhang, Yang; Ding, Jun; Duan, Wei

    2006-01-01

    The aim of this study was to investigate the influence of pulsed electromagnetic fields with various flux densities and frequencies on neurite outgrowth in PC12 rat pheochromocytoma cells. We have studied the percentage of neurite-bearing cells, average length of neurites and directivity of neurite outgrowth in PC12 cells cultured for 96 hours in the presence of nerve growth factor (NGF). PC12 cells were exposed to 50 Hz pulsed electromagnetic fields with a flux density of 1.37 mT, 0.19 mT and 0.016 mT respectively. The field was generated through a Helmholtz coil pair housed in one incubator and the control samples were placed in another identical incubator. It was found that exposure to both a relatively high flux density (1.37 mT) and a medium flux density (0.19 mT) inhibited the percentage of neurite-bearing cells and promoted neurite length significantly. Exposure to high flux density (1.37 mT) also resulted in nearly 20% enhancement of neurite directivity along the field direction. However, exposure to low flux density field (0.016 mT) had no detectable effect on neurite outgrowth. We also studied the effect of frequency at the constant flux density of 1.37 mT. In the range from 1 approximately 100 Hz, only 50 and 70 Hz pulse frequencies had significant effects on neurite outgrowth. Our study has shown that neurite outgrowth in PC12 cells is sensitive to flux density and frequency of pulsed electromagnetic field.

  1. Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse.

    PubMed

    Stauffer, Hans U; Miller, Joseph D; Slipchenko, Mikhail N; Meyer, Terrence R; Prince, Benjamin D; Roy, Sukesh; Gord, James R

    2014-01-14

    The hybrid femtosecond∕picosecond coherent anti-Stokes Raman scattering (fs∕ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs∕ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs∕ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs∕ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

  2. Generation of 30 fs pulses at 635 nm by frequency doubling of cavity-dumped chromium-doped forsterite laser, and its application to spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagasawa, Y.; Ando, Y.; Watanabe, A.; Okada, T.

    A cavity-dumped Kerr-lens mode-locked chro-mium-doped forsterite (Cr:F) laser was developed. The fundamental frequency of 1270 nm was converted into 635 nm by second-harmonic generation in an LBO crystal. A pulse duration of 30 fs was obtained at 635 nm with energy of 3.8 nJ. The developed laser was applied to single-wavelength pump-probe measurements of dyes, malachite green (MG) and phenol blue (PB).

  3. Ultra-low phase-noise microwave generation using a diode-pumped solid-state laser based frequency comb and a polarization-maintaining pulse interleaver.

    PubMed

    Portuondo-Campa, Erwin; Buchs, Gilles; Kundermann, Stefan; Balet, Laurent; Lecomte, Steve

    2015-12-14

    We report ultra-low phase-noise microwave generation at a 9.6 GHz carrier frequency from optical frequency combs based on diode-pumped solid-state lasers emitting at telecom wavelength and referenced to a common cavity-stabilized continuous-wave laser. Using a novel fibered polarization-maintaining pulse interleaver, a single-oscillator phase-noise floor of -171 dBc/Hz at 10 MHz offset frequency has been measured with commercial PIN InGaAs photodiodes, constituting a record for this type of detector. Also, a direct optical measurement of the stabilized frequency combs' timing jitter was performed using a balanced optical cross correlator, allowing for an identification of the origin of the phase-noise limitations in the system. PMID:26699033

  4. Domain self-organization in iron garnet films in pulsed magnetic fields with a frequency between 0.001 and 25 Hz

    NASA Astrophysics Data System (ADS)

    Osadchenko, V. Kh.; Kandaurova, G. S.; Pashko, A. G.

    2007-04-01

    The results of studying processes of self-organization in a domain structure of highly anisotropic iron garnet films with perpendicular anisotropy in an ac magnetic field of a symmetrical meander type (with rectangular pulses with a frequency of 0.001-25 Hz and an amplitude H 0 = 0-70 Oe are reported for the first time. In the frequency range from 0.01 to 25 Hz, there has been observed an anger (excited) state, which is characterized by the formation of a close packing of spiral dynamic domains.

  5. Ion energy distributions in a pulsed dual frequency inductively coupled discharge of Ar/CF{sub 4} and effect of duty ratio

    SciTech Connect

    Mishra, Anurag; Seo, Jin Seok; Kim, Tae Hyung; Yeom, Geun Young

    2015-08-15

    Controlling time averaged ion energy distribution (IED) is becoming increasingly important in many plasma material processing applications for plasma etching and deposition. The present study reports the evolution of ion energy distributions with radio frequency (RF) powers in a pulsed dual frequency inductively discharge and also investigates the effect of duty ratio. The discharge has been sustained using two radio frequency, low (P{sub 2 MHz} = 2 MHz) and high (P{sub 13.56 MHz} = 13.56 MHz) at a pressure of 10 mTorr in argon (90%) and CF{sub 4} (10%) environment. The low frequency RF powers have been varied from 100 to 600 W, whereas the high frequency powers from 200 to 1200 W. Typically, IEDs show bimodal structure and energy width (energy separation between the high and low energy peaks) increases with increasing P{sub 13.56 MHz}; however, it shows opposite trends with P{sub 2 MHz}. It has been observed that IEDs bimodal structure tends to mono-modal structure and energy peaks shift towards low energy side as duty ratio increases, keeping pulse power owing to mode transition (capacitive to inductive) constant.

  6. Ion energy distributions in a pulsed dual frequency inductively coupled discharge of Ar/CF4 and effect of duty ratio

    NASA Astrophysics Data System (ADS)

    Mishra, Anurag; Seo, Jin Seok; Kim, Tae Hyung; Yeom, Geun Young

    2015-08-01

    Controlling time averaged ion energy distribution (IED) is becoming increasingly important in many plasma material processing applications for plasma etching and deposition. The present study reports the evolution of ion energy distributions with radio frequency (RF) powers in a pulsed dual frequency inductively discharge and also investigates the effect of duty ratio. The discharge has been sustained using two radio frequency, low (P2 MHz = 2 MHz) and high (P13.56 MHz = 13.56 MHz) at a pressure of 10 mTorr in argon (90%) and CF4 (10%) environment. The low frequency RF powers have been varied from 100 to 600 W, whereas the high frequency powers from 200 to 1200 W. Typically, IEDs show bimodal structure and energy width (energy separation between the high and low energy peaks) increases with increasing P13.56 MHz; however, it shows opposite trends with P2 MHz. It has been observed that IEDs bimodal structure tends to mono-modal structure and energy peaks shift towards low energy side as duty ratio increases, keeping pulse power owing to mode transition (capacitive to inductive) constant.

  7. Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading.

    PubMed

    Andrew, Rex K; Ganse, Andrew; White, Andrew W; Mercer, James A; Dzieciuch, Matthew A; Worcester, Peter F; Colosi, John A

    2016-07-01

    Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points. PMID:27475148

  8. Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading.

    PubMed

    Andrew, Rex K; Ganse, Andrew; White, Andrew W; Mercer, James A; Dzieciuch, Matthew A; Worcester, Peter F; Colosi, John A

    2016-07-01

    Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points.

  9. Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Sano, Yuji; Kimura, Motohiko; Mukai, Naruhiko; Yoda, Masaki; Obata, Minoru; Ogisu, Tatsuki

    2000-02-01

    The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training

  10. Theory and computation of the attosecond dynamics of pairs of electrons excited by high-frequency short light pulses

    SciTech Connect

    Mercouris, Th.; Komninos, Y.; Nicolaides, C.A.

    2004-03-01

    By defining and solving from first principles, using the state-specific expansion approach, a time-dependent pump-probe problem with real atomic states, we show computationally that, if time resolution reaches the attosecond regime, strongly correlated electronic ''motion'' can be probed and can manifest itself in terms of time-dependent mixing of symmetry-adapted configurations. For the system that was chosen in this study, these configurations, the He 2s2p,2p3d, and 3s3p P{sup o1}, whose radials are computed by solving multiconfigurational Hartree-Fock equations, label doubly excited states (DES) of He inside the 1s{epsilon}p P{sup o1} scattering continuum and act as nonstationary states that mix, and simultaneously decay exponentially to 1s{epsilon}p P{sup o1} via the atomic Hamiltonian, H{sub A}. The herein presented theory and analysis permitted the computation of attosecond snapshots of pairs of electrons in terms of time-dependent probability distributions of the angle between the position vectors of the two electrons. The physical processes were determined by solving ab initio the time-dependent Schroedinger equation, using as initial states either the He 1s{sup 2} or the 1s2s S{sup 1} discrete states and two femtosecond Gaussian pulses of 86 fs full width at half-maximum, having frequencies in resonance with the energies of the correlated states represented by the 2s2p and 2p3d configurations. We calculated the probability of photoabsorption and of two-photon resonance ionization and of the simultaneous oscillatory mixing of the configurations 2s2p,2p3d,3s3p, and 1s{epsilon}p P{sup o1}, within the attosecond scale, via the interactions present in H{sub A}. Among the possible channels for observing the attosecond oscillations of the occupation probabilities of the DES, is the de-excitation path of the transition to the He 1s3d D{sup 1} discrete state, which emits at 6680 A.

  11. Longwave infrared, single-frequency, tunable, pulsed optical parametric oscillator based on orientation-patterned GaAs for gas sensing.

    PubMed

    Clément, Q; Melkonian, J-M; Dherbecourt, J-B; Raybaut, M; Grisard, A; Lallier, E; Gérard, B; Faure, B; Souhaité, G; Godard, A

    2015-06-15

    We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 μJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning covers the 10.3-10.9 μm range with a quasi-phase-matching period of 72.6 μm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 μm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

  12. Negative ion injection to a wafer in a pulsed two frequency CCP in CF_4/Ar for SiO2 etching*

    NASA Astrophysics Data System (ADS)

    Maeshige, K.; Yagisawa, T.; Makabe, T.

    2001-10-01

    A capacitively coupled plasma (CCP) with electrodes connected respectively to the rf sources for sustaining the plasma at VHF and for biasing the wafer at LF is a powerful tool for a high energy ion assisted SiO2 etching. A time modulation of the two frequency (2f-)CCP by a pulsed-power operation will be one of the practical solutions of the next generation of etcher with the active function of a charging free plasma process for a high aspect ratio hole or trench manufacturing. We have numerically predicted the structure and functions of a pulsed two frequency CCP in CF_4(5%)/Ar, under a consideration of the negative ion production from CF3 in a high density plasma with 10^11cm-3. The functional separation is investigated between a plasma production by VHF (100MHz) and a bias voltage application by LF (1MHz). Alternate injections of high energy positive and negative ions to a patterned wafer are predicted during the off-phase of the pulsed 2f-CCP. It will enable us to provide a function of a local charge neutralization in the bottom of a high aspect ratio hole/trench. [2mm] ^*Work supported by STARC and Selete.

  13. Diode-pumped passively Q-switched 912 nm Nd:GdVO 4 laser and pulsed deep-blue laser by intracavity frequency-doubling

    NASA Astrophysics Data System (ADS)

    Chen, Fei; Yu, Xin; Li, Xudong; Yan, Renpeng; Wang, Cheng; Luo, Ming; Zhang, Zhonghua; Yu, Junhua

    2010-10-01

    A diode-end-pumped passively Q-switched 912 nm Nd:GdVO 4/Cr 4+:YAG laser and its efficient intracavity frequency-doubling to 456 nm deep-blue laser were demonstrated in this paper. Using a simple V-type laser cavity, pulsed 912 nm laser characteristics were investigated with two kinds of Cr 4+:YAG crystal as the saturable absorbers, which have the different initial transmissivity ( TU) of 95% and 90% at 912 nm. When the TU = 95% Cr 4+:YAG was used, as much as an average output power of 2.8 W 912 nm laser was achieved at an absorbed pump power of 34.0 W, and the pulse width and the repetition rate were ˜ 40.5 ns and ˜ 76.6 kHz, respectively. To the best of our knowledge, this is the highest average output power of diode-pumped passively Q-switched Nd 3+-doped quasi-three-level laser. Employing a BiBO as the frequency-doubling crystal, 456 nm pulsed deep-blue laser was obtained with a maximum average output power of 1.2 W at a repetition rate ˜ 42.7 kHz.

  14. Optimization of A 2-Micron Laser Frequency Stabilization System for a Double-Pulse CO2 Differential Absorption Lidar

    NASA Technical Reports Server (NTRS)

    Chen, Songsheng; Yu, Jirong; Bai, Yingsin; Koch, Grady; Petros, Mulugeta; Trieu, Bo; Petzar, Paul; Singh, Upendra N.; Kavaya, Michael J.; Beyon, Jeffrey

    2010-01-01

    A carbon dioxide (CO2) Differential Absorption Lidar (DIAL) for accurate CO2 concentration measurement requires a frequency locking system to achieve high frequency locking precision and stability. We describe the frequency locking system utilizing Frequency Modulation (FM), Phase Sensitive Detection (PSD), and Proportional Integration Derivative (PID) feedback servo loop, and report the optimization of the sensitivity of the system for the feed back loop based on the characteristics of a variable path-length CO2 gas cell. The CO2 gas cell is characterized with HITRAN database (2004). The method can be applied for any other frequency locking systems referring to gas absorption line.

  15. Cryogenic foam insulation for LH2 fueled subsonic transports

    NASA Technical Reports Server (NTRS)

    Sharpe, E. L.; Helenbrook, R. G.

    1978-01-01

    Shortages of petroleum-based aircraft fuels are foreseen before the end of the century. To cope with such shortages, NASA is developing a commercial aircraft which can operate on liquid hydrogen. Various foam insulators for LH2 storage are considered in terms of thermal performance and service life. Of the cryogenic foams considered (plain foam, foam with flame retardants and fiberglass reinforcement, and foam with vapor barriers), polyurethane foams were found to be the best. Tests consisted of heating a 5 cm layer of insulation around an aluminum tank containing LH2 to 316 K, and then cooling it to 266 K, while the inner surface was maintained at LH2 temperature (20 K).

  16. Eye-safe single-frequency single-mode polarized all-fiber pulsed laser with peak power of 361  W.

    PubMed

    Zhang, Xin; Diao, Weifeng; Liu, Yuan; Zhu, Xiaopeng; Yang, Yan; Liu, Jiqiao; Hou, Xia; Chen, Weibiao

    2014-04-10

    An all-fiber, single-frequency, single-mode linearly polarized, high peak power pulsed laser at 1540 nm for coherent Doppler wind lidar is demonstrated. A narrow-linewidth seed laser is pulse modulated by an acousto-optic modulator and then amplified by two-stage cascade amplifiers. An 0.8 m long erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber of a power amplifier, and longitudinally varied strains are applied on the gain fiber to realize approximately 3.4 times enhancement of the stimulated Brillouin scattering threshold. Peak power of 361 W pulse width of 200 ns at 10 kHz repetition rate is achieved with transform-limited linewidth and diffraction-limited beam quality. To the best of our knowledge, it is the highest peak power of an eye-safe, single-mode narrow-linewidth pulsed fiber laser based on 10 μm core diameter silica fiber.

  17. Time dependent Doppler shifts in high-order harmonic generation in intense laser interactions with solid density plasma and frequency chirped pulses

    SciTech Connect

    Welch, E. C.; Zhang, P.; He, Z.-H.; Dollar, F.; Krushelnick, K.; Thomas, A. G. R.

    2015-05-15

    High order harmonic generation from solid targets is a compelling route to generating intense attosecond or even zeptosecond pulses. However, the effects of ion motion on the generation of harmonics have only recently started to be considered. Here, we study the effects of ion motion in harmonics production at ultrahigh laser intensities interacting with solid density plasma. Using particle-in-cell simulations, we find that there is an optimum density for harmonic production that depends on laser intensity, which scales linearly with a{sub 0} with no ion motion but with a reduced scaling if ion motion is included. We derive a scaling for this optimum density with ion motion and also find that the background ion motion induces Doppler red-shifts in the harmonic structures of the reflected pulse. The temporal structure of the Doppler shifts is correlated to the envelope of the incident laser pulse. We demonstrate that by introducing a frequency chirp in the incident pulse we are able to eliminate these Doppler shifts almost completely.

  18. Comparison of intensity-modulated continuous-wave lasers with a chirped modulation frequency to pulsed lasers for photoacoustic imaging applications

    PubMed Central

    Petschke, Adam; La Rivière, Patrick J.

    2010-01-01

    Using a Green’s function solution to the photoacoustic wave equation, we compare intensity-modulated continuous-wave (CW) lasers with a chirped modulation frequency to pulsed lasers for photoacoustic imaging applications. Assuming the same transducer is used in both cases, we show that the axial resolution is identical and is determined by the transducer and material properties of the object. We derive a simple formula relating the signal-to-noise ratios (SNRs) of the two imaging systems that only depends on the fluence of each pulse and the time-bandwidth product of the chirp pulse. We also compare the SNR of the two systems assuming the fluence is limited by the American National Standards Institute (ANSI) laser safety guidelines for skin. We find that the SNR is about 20 dB to 30 dB larger for pulsed laser systems for reasonable values of the parameters. However, CW diode lasers have the advantage of being compact and relatively inexpensive, which may outweigh the lower SNR in many applications. PMID:21258540

  19. Does ethanol inhibit LH secretion in the rat?

    PubMed

    Ellingboe, J; Shaw, D G; Skupny, A S; Sikorski, M A

    1987-01-01

    A prevailing view among those studying neuroendocrine effects of ethanol is that acute doses suppress luteinizing hormone releasing hormone (LHRH) secretion, and consequently inhibit luteinizing hormone (LH) release in the rat. This phenomenon has not been observed in primates, and has been thought to be a species difference. The experimental procedures, however, have involved ethanol administration by oral or intragastric (ig) routes in humans and monkeys, but intraperitoneal (ip) or carotid artery injection in rats. It has also been suggested that inhibition of LH secretion by ethanol in rats is mediated by endogenous opioid peptides (EOP), because the effect can be reversed by the opiate antagonist naloxone. An alternative explanation is that ip ethanol injection might stress rats sufficiently to activate hypothalamic-pituitary-adrenocortical (H-P-A) and EOP systems that are well known to inhibit hormonal activities of the hypothalamic-pituitary-gonadal (H-P-G) axis. Presented here are preliminary results from experiments with male rats. When ethanol is administered ig, under relatively stress-free conditions, it does not inhibit LH secretion in gonadally intact or castrated males. In contrast, ip injection of the same ethanol dose (2.0 g/kg body wt) causes pronounced inhibition of LH secretion and concomitant increases in plasma prolactin (PRL) and corticosterone--indicative of a stress response. Furthermore, when ip ethanol administration is preceded by intracerebroventricular (icv) injection of a corticotropin releasing factor (CRF) antagonist (alpha-helical ovine CRF residues 9 to 41), the effects of ethanol on LH and corticosterone are blocked. These results indicate that it may be stress, rather than ethanol per se, that inhibits LHRH and LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

  20. A photonic band-gap resonator to facilitate GHz-frequency conductivity experiments in pulsed magnetic fields

    NASA Astrophysics Data System (ADS)

    McDonald, R. D.; Singleton, J.; Goddard, P. A.; Harrison, N.; Mielke, C. H.

    2006-08-01

    We describe instrumentation designed to perform millimeter-wave conductivity measurements in pulsed high magnetic fields at low temperatures. The main component of this system is an entirely nonmetallic microwave resonator. The resonator utilizes periodic dielectric arrays (photonic band-gap structures) to confine the radiation, such that the resonant modes have a high Q factor, and the system possesses sufficient sensitivity to measure small samples within the duration of a magnet pulse. As well as measuring the sample conductivity to probe orbital physics in metallic systems, this technique can detect the sample permittivity and permeability allowing measurement of spin physics in insulating systems. We demonstrate the system performance in pulsed magnetic fields with both electron paramagnetic resonance experiments and conductivity measurements of correlated electron systems.

  1. Functional verification of pulse frequency modulation-based image sensor for retinal prosthesis by in vitro electrophysiological experiments using frog retina.

    PubMed

    Furumiya, Tetsuo; Ng, David C; Yasuoka, Koutaro; Kagawa, Keiichiro; Tokuda, Takashi; Nunoshita, Masahiro; Ohta, Jun

    2006-01-15

    The functioning of a 16 x 16 pixel pulse frequency modulation (PFM) image sensor for retinal prosthesis is verified through in vitro electrophysiological experiments using detached frog retinas. This image sensor is a prototype for demonstrating the application to in vitro electrophysiological experiments. Each pixel of the image sensor consists of a pulse generator (PFM photosensor), a stimulus circuit, and a stimulus electrode (Al bonding pad). The image sensor is fabricated using standard 0.6 microm CMOS technology. For in vitro electrophysiological experiments, a Pt/Au stacked electrode is formed on the Al bonding pad of each pixel and the entire sensor is fixed in epoxy resin. The PFM image sensor is confirmed experimentally to provide electrical stimulus to the retinal cells in a detached frog retina.

  2. Pulsed two-frequency capacitively coupled plasma simulation with H_2/N2 mixtures for the etching of low-k materials

    NASA Astrophysics Data System (ADS)

    Shon, C. H.; Makabe, T.

    2002-10-01

    As the critical dimension of integrated circuit is scaled down, the resistance-capacitance (RC) delay of signals through interconnection materials becomes important. As a solution, the new materials like Cu and low-k dielectric polymers have been used to reduce the signal delay in interconnect. As a result, low-k materials etching becomes a big issue in the plasma etching process. In this research, we present the simulation results of a pulsed two-frequency capacitively coupled plasma (2f-CCP)[1,2] based on relaxation continuum (RCT) model[3,4] in H_2/N2 mixtures. The electrons, ions of each gas and NHx radicals are followed in the model. The characteristics of a pulsed plasma are investigated. In addition, the flux of ions and radicals toward the biased substrate which has great importance in etching process is also discussed. sep = -1mm [[1

  3. Frequency-doubled DBR-tapered diode laser for direct pumping of Ti:sapphire lasers generating sub-20 fs pulses.

    PubMed

    Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika; Le, Tuan; Stingl, Andreas; Hasler, Karl-Heinz; Sumpf, Bernd; Erbert, Götz; Andersen, Peter E; Petersen, Paul Michael

    2011-06-20

    For the first time a single-pass frequency doubled DBR-tapered diode laser suitable for pumping Ti:sapphire lasers generating ultrashort pulses is demonstrated. The maximum output powers achieved when pumping the Ti:sapphire laser are 110 mW (CW) and 82 mW (mode-locked) respectively at 1.2 W of pump power. This corresponds to a reduction in optical conversion efficiencies to 75% of the values achieved with a commercial diode pumped solid-state laser. However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2. The optical spectrum emitted by the Ti:sapphire laser when pumped with our diode laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20 fs can therefore be expected.

  4. Modeling and design of lossy waveguide structures for generation of broadband terahertz pulses through difference frequency mixing

    NASA Astrophysics Data System (ADS)

    Vallejo Monsalve, Felipe Antonio

    We present an integral coupled mode theory (CMT), suited to account for high optical losses, to model ultra-broadband terahertz (THz) waveguide emitters (0.1- 20 THz) based on difference frequency generation (DFG) pumped by femtosecond infrared (IR) optical pulses. This integral model works even in the situation where the DFG occurs between several IR and THz modes. We also present a simplified CMT approximation that reproduces the results of the rigorous integral CMT for situations where the THz generation is mediated through single-IR-mode to single-THz-mode interactions. Using the simplified approach we derive a new expression that incorporates loss effects into the coherence length for optical rectification (OR). The expression that we derived for the coherence length can be adapted to describe other second order nonlinear processes such as second harmonic generation. We apply both models to study waveguide emitters whose nonlinear cores are composed of poled guest-host electro-optic (EO) polymer composites, which belong to the 1mm symmetry class and have high nonlinearities. We apply the models to a generic, symmetric, five-layer, metal/cladding/core waveguide structure and provide design strategies for efficient ultra-broadband THz emitters. Two different design strategies are analyzed, one in which the waveguides are designed to have a single-IR-mode and a single-THz-mode guided within the structure, and other where the waveguide is made with a single-THz-mode but admits several IR guided modes. In both strategies the waveguide geometric parameters are optimized to obtain the highest THz conversion efficiencies and broader output bandwidth. The simplified CMT approach is much faster to implement than the integral CMT. Thus, we use the simplified approach to perform a parametric study for different waveguide parameters and pumping wavelengths, in the telecom and short wavelength infrared region, to establish under what conditions the five-layered structure

  5. Ghrelin suppresses nocturnal secretion of luteinizing hormone (LH) and thyroid stimulating hormone (TSH) in patients with major depression.

    PubMed

    Kluge, Michael; Schmidt, Doreen; Uhr, Manfred; Steiger, Axel

    2013-09-01

    Major depression is associated with various endocrine disturbances. Apart from the well-known hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, also the function of the hypothalamic-pituitary-gonadal (HPG) axis and of the hypothalamic-pituitary-thyroid (HPT) axis may be altered compared to healthy subjects. The orexigenic hormone ghrelin is involved in mood regulation and may have antidepressant effects. In addition, it has been shown to suppress secretion of luteinizing hormone (LH) and thyroid stimulating hormone (TSH) in healthy subjects. Aim of this study was therefore to test the effect of ghrelin on the activity of the HPG and HPT axis in patients with major depression. Therefore, secretion profiles of LH and TSH were determined in 14 unmedicated patients with major depression (7 women) twice, receiving 50 μg ghrelin or placebo at 2200, 2300, 0000, and 0100 h. LH secretion after ghrelin injection as assessed by the AUC (4.05 ± 1.18 mlIU min/ml) was significantly (P = 0.049) lower than after placebo injection (4.75 ± 1.33 mlIU min/ml) during the predefined intervention period (2220-0200 h). In addition, LH pulses occurred significantly (P = 0.045) less frequently after ghrelin injection (3.2 ± 1.4) than after placebo injection (3.9 ± 1.7). Mean TSH plasma levels were significantly lower at 0240 h and from 0320 until 0420 h after ghrelin injection than after placebo injection. In conclusion, ghrelin suppressed nocturnal secretion of LH and TSH in patients with major depression. However, these effects were weaker than previously shown in healthy subjects.

  6. [The application of the pulsed low-frequency electrostatic field for the combined treatment of the children presenting with bronchial asthma].

    PubMed

    Ivanova, D A; Khan, M A; Lyan, N A; Mikitchenko, N A

    2015-01-01

    The objective of the present study was to develop a scientifically sound rationale for the application of the pulsed low-frequency electrostatic fields (PLIESF) for the combined treatment of the children presenting with bronchial asthma and the comparative assessment of the effectiveness of the use of this method either as monotherapy or together with therapeutic physical exercises based on the immediate and long-term results of the treatment. The dynamic clinical observations and special investigations were carried out on 101 children at the age varying from 5 to 15 years who suffered from bronchial asthma. PLIESF were shown to produce the beneficial effect on dynamics of clinical symptoms in the children manifested as the disappearance or reduced frequency of episodes of laborious respiration and the improvement of sputum discharge, auscultation picture, bronchial patency, and respiratory excursions of the chest. The application of PLIESF significantly increased the level of the general physical performance in the children with bronchial asthma, improved the functional conditions of the cardiovascular system, normalized both the cardiac rhythm and the heart rate. It was shown based on the analysis of the short-term and long-term outcomes of the treatment that the combined therapy with the use of the two physical factors, i.e. the pulsed low-frequency electrostatic fields and therapeutic physical exercises, ensures the significantly higher effectiveness of the treatment than the separate application of either of them. PMID:26595966

  7. Generation of Shear Alfvén Waves by Repetitive High Power Microwave Pulses Near the Electron Plasma Frequency - A laboratory study of a ``Virtual Antenna''

    NASA Astrophysics Data System (ADS)

    Wang, Yuhou; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Papadopoulos, Konstantinos

    2015-11-01

    ELF / ULF waves are important in terrestrial radio communications but difficult to launch using ground-based structures due to their enormous wavelengths. In spite of this generation of such waves by field-aligned ionospheric heating modulation was first demonstrated using the HAARP facility. In the future heaters near the equator will be constructed and laboratory experiments on cross-field wave propagation could be key to the program's success. Here we report a detailed laboratory study conducted on the Large Plasma Device (LaPD) at UCLA. In this experiment, ten rapid pulses of high power microwaves (250 kW X-band) near the plasma frequency were launched transverse to the background field, and were modulated at a variable fraction (0.1-1.0) of fci. Along with bulk electron heating and density modification, the microwave pulses generated a population of fast electrons. The field-aligned current carried by the fast electrons acted as an antenna that radiated shear Alfvén waves. It was demonstrated that a controllable arbitrary frequency (f frequency variation and power dependence of the virtual antenna is also presented. This work is supported by an AFOSR MURI award, and conducted at the Basic Plasma Science Facility at UCLA funded by DoE and NSF.

  8. 10 aJ-level sensing of nanosecond pulse below 10 THz by frequency upconversion detection via DAST crystal: more than a 4 K bolometer.

    PubMed

    Qi, Feng; Fan, Shuzhen; Notake, Takashi; Nawata, Koji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

    2014-03-01

    By using frequency upconversion detection of terahertz (THz) waves via 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal with an optimized frequency conversion process, ultrahigh sensitivity has been achieved. Direct comparisons with a 4 K bolometer were implemented. By using a simple positive intrinsic negative (PIN) diode without either electrical amplification or optical amplification, frequency upconversion detection can compete with the commercial 4 K bolometer, while by replacing the PIN diode with an avalanche photo diode (APD), it performs more than three orders better than the 4 K bolometer. Based on power calibration, the minimum detectable THz pulse energy is in the order of 10 aJ (9-25 aJ) at 4.3 THz, with a pulse duration of 6 ns. Thus, the minimum number of THz photons that can be detected is down to the order of 10(3) at room temperature. The current THz detection system gives a noise equivalent power (NEP) in the order of 100  fW/Hz(1/2) (50-128  fW/Hz(1/2)). Moreover, by switching current optical detectors, the dynamic range is over six orders. PMID:24690730

  9. Thermal Spray Using a High-Frequency Pulse Detonation Combustor Operated in the Liquid-Purge Mode

    NASA Astrophysics Data System (ADS)

    Endo, T.; Obayashi, R.; Tajiri, T.; Kimura, K.; Morohashi, Y.; Johzaki, T.; Matsuoka, K.; Hanafusa, T.; Mizunari, S.

    2016-02-01

    Experiments on thermal spray by pulsed detonations at 150 Hz were conducted. Two types of pulse detonation combustors were used, one operated in the inert gas purge (GAP) mode and the other in the liquid-purge (LIP) mode. In both modes, all gases were supplied in the valveless mode. The GAP mode is free of moving components, although the explosive mixture is unavoidably diluted with the inert gas used for the purge of the hot burned gas. In the LIP mode, pure fuel-oxygen combustion can be realized, although a liquid-droplet injector must be actuated cyclically. The objective of this work was to demonstrate a higher spraying temperature in the LIP mode. First, the temperature of CoNiCrAlY particles heated by pulsed detonations was measured. As a result, the spraying temperature in the LIP mode was higher than that in the GAP mode by about 1000 K. Second, the temperature of yttria-stabilized zirconia (YSZ) particles, whose melting point was almost 2800 °C, heated by pulsed detonations in the LIP mode was measured. As a result, the YSZ particles were heated up to about 2500 °C. Finally, a thermal spray experiment using YSZ particles was conducted, and a coating with low porosity was successfully deposited.

  10. The doppler frequency shift caused by the inhomogeneities of a medium induced by pulses of intense laser radiation

    NASA Astrophysics Data System (ADS)

    Rozanov, N. N.; Kiselev, Al. S.; Kiselev, An. S.

    2008-08-01

    Self-reflection of pulses of intense laser radiation from an inhomogeneity induced by them in a medium with fast optical nonlinearity is analyzed. The reflected radiation is characterized by a considerable Doppler shift and by a signal magnitude that is sufficient for experimental detection.

  11. Clinical Assessment of the RHUMART System Based on the Use of Pulsed Electromagnetic Fields with Low Frequency.

    ERIC Educational Resources Information Center

    Begue-Simon, A-M.; Drolet, R. A.

    1993-01-01

    Difficulties in using the double-blind method of evaluation with use of Pulsed Electromagnetic Fields led to an open evaluation with 96 patients with musculoskeletal diseases, neurological disorders, circulatory diseases, or gastroenterological diseases. This paper reports the impact of use on dependency, pain, and patient satisfaction. (DB)

  12. High average power difference-frequency generation of picosecond mid-IR pulses at 80MHz using an Yb-fiber laser pumped optical parametric oscillator

    NASA Astrophysics Data System (ADS)

    Michel, Julia; Beutler, Marcus; Rimke, Ingo; Büttner, Edlef; Farinello, Paolo; Agnesi, Antonio; Petrov, Valentin P.

    2015-02-01

    We present an efficient coherent source widely tunable in the mid-infrared spectral range consisting of a commercial picosecond Yb-fiber laser operating at 80 MHz repetition rate, a synchronously-pumped OPO (SPOPO) and differencefrequency generation (DFG) in AgGaSe2. With an average input pump power of 7.8 W at 1032 nm and at 80 MHz, the SPOPO outputs are tunable from 1380 to 1980 nm (Signal) and from 2.1 to ~4 μm (Idler) with pulse durations between 2.1 and 2.6 ps over the entire tuning range. After temporally overlapping Signal and Idler through a delay line, the two beams are spatially recombined with a dichroic mirror (reflecting for the Signal in s-polarization and transmitting for the Idler in p-polarization), and focused by a 150 mm CaF2 lens to a common focus. For DFG we employ an AR-coated 10- mm thick AgGaSe2 nonlinear crystal cut for type-I interaction at θ =52°. The generated mid-infrared picosecond pulses are continuously tunable between 5 and 18 μm with average power up to 130 mW at 6 μm and more than 1 mW at 18 μm. Their spectra and autocorrelation traces are measured up to 15 μm and 11 μm, respectively, and indicate that the input spectral bandwidth and pulse duration are maintained to a great extent in the nonlinear frequency conversion processes. The pulse duration slightly decreases from 2.1 to 1.9 ps at 6.7 μm while the spectral bandwidth supports ~1.5 ps (~10 cm-1)durations across the entire mid-infrared tuning range. For the first time narrow-band mid-infrared pulses with energy exceeding 1 nJ are generated at such high repetition rates.

  13. Identification and Removal of High Frequency Temporal Noise in a Nd:YAG Macro-Pulse Laser Assisted with a Diagnostic Streak Camera

    SciTech Connect

    Kent Marlett, Bechtel Nevada; Ke-Xun Sun Bechtel Nevada

    2004-09-23

    This paper discusses the use of a reference streak camera (SC) to diagnose laser performance and guide modifications to remove high frequency noise from Bechtel Nevada's long-pulse laser. The upgraded laser exhibits less than 0.1% high frequency noise in cumulative spectra, exceeding National Ignition Facility (NIF) calibration specifications. Inertial Confinement Fusion (ICF) experiments require full characterization of streak cameras over a wide range of sweep speeds (10 ns to 480 ns). This paradigm of metrology poses stringent spectral requirements on the laser source for streak camera calibration. Recently, Bechtel Nevada worked with a laser vendor to develop a high performance, multi-wavelength Nd:YAG laser to meet NIF calibration requirements. For a typical NIF streak camera with a 4096 x 4096 pixel CCD, the flat field calibration at 30 ns requires a smooth laser spectrum over 33 MHz to 68 GHz. Streak cameras are the appropriate instrumentation for measuring laser amplitude noise at these very high frequencies since the upper end spectral content is beyond the frequency response of typical optoelectronic detectors for a single shot pulse. The SC was used to measure a similar laser at its second harmonic wavelength (532 nm), to establish baseline spectra for testing signal analysis algorithms. The SC was then used to measure the new custom calibration laser. In both spatial-temporal measurements and cumulative spectra, 6-8 GHz oscillations were identified. The oscillations were found to be caused by inter-surface reflections between amplifiers. Additional variations in the SC spectral data were found to result from temperature instabilities in the seeding laser. Based on these findings, laser upgrades were made to remove the high frequency noise from the laser output.

  14. Two-frequency mutual coherence function for Gaussian-beam pulses propagating along a horizontal path in weak anisotropic atmospheric turbulence.

    PubMed

    Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan

    2015-06-20

    A theoretical formulation of the spherical-wave two-frequency mutual coherence function (MCF) for a propagation path characterized by a complex ABCD matrix with anisotropic atmospheric turbulence existing somewhere is developed. A specialization of this formulation leads to an expression for the two-frequency MCF of an equivalent pulsed Gaussian beam propagating in weak anisotropic atmospheric turbulence along a horizontal line-of-sight path; relevant closed-form analytical solutions under both near- and far-field conditions are obtained. The small- and large-scale solutions for both the plane- and spherical-wave spatial-coherence radii in either horizontal or vertical direction are derived. Analysis shows that the formula for the on-axis two-frequency MCF of a pulsed Gaussian beam under the weak-turbulence condition in both the near- and far-field regions is distinguished from that applicable in the strong-turbulence limit only by whether the turbulence-induced beam broadening can be thought of as negligible. Under both the near- and far-field conditions, the turbulence-induced increment of the mean-square temporal-pulse half-width is proportional to the effective anisotropy factor of turbulence. The MCF becomes statistically anisotropic due to the anisotropy of turbulence. For the spatial coherence radius of either a plane or spherical wave propagating along a horizontal line-of-sight path in anisotropic atmospheric turbulence, the corresponding small-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient depending only on the effective anisotropy factor of turbulence. The corresponding large-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient that depends on both the effective anisotropy factor and spectral index of turbulence.

  15. Theory and Practice in ICRF Antennas for Long Pulse Operation

    SciTech Connect

    Colas, L.; Bremond, S.; Mitteau, R.; Chantant, M.; Goniche, M.; Basiuk, V.; Bosia, G.; Gunn, J.P.

    2005-09-26

    Long plasma discharges on the Tore Supra (TS) tokamak were extended in 2004 towards higher powers and plasma densities by combined Lower Hybrid (LH) and Ion Cyclotron Range of Frequencies (ICRF) waves. RF pulses of 20sx8MW and 60sx4MW were produced. TS is equipped with 3 ICRF antennas, whose front faces are ready for CW operation. This paper reports on their behaviour over high power long pulses, as observed with infrared (IR) thermography and calorimetric measurements. Edge parasitic losses, although modest, are concentrated on a small surface and can raise surface temperatures close to operational limits. A complex hot spot pattern was revealed with at least 3 physical processes involved : convected power, electron acceleration in the LH near field, and a RF-specific phenomenon compatible with RF sheaths. LH coupling was also perturbed in the antenna shadow. This was attributed to RF-induced DC ExB0 convection. This motivated sheath modelling in two directions. First, the 2D topology of RF potentials was investigated in relation with the RF current distribution over the antenna, via a Green's function formalism and full-wave calculation using the ICANT code. In front of phased arrays of straps, convective cells were interpreted using the RF current profiles of strip line theory. Another class of convective cells, specific to antenna box corners, was evidenced for the first time. Within 1D sheath models assuming independent flux tubes, RF and rectified DC potentials are proportional. 2D fluid models couple nearby flux tubes via transverse polarisation currents. Unexpectedly this does not necessarily smooth RF potential maps. Peak DC potentials can even be enhanced. The experience gained on TS and the numerical tools are valuable for designing steady state high power antennas for next step devices. General rules to reduce RF potentials as well as concrete design options are discussed.

  16. Cost Beneftt Analysts of LH2 PadB

    NASA Technical Reports Server (NTRS)

    Mott, Brittany

    2013-01-01

    This analysis is used to evaluate, from a cost and benefit perspective, potential outcomes when replacing the pressurization switches and the pressurization system to meet the needs of the LH2 storage system at Pad B. This also includes alternatives, tangible and intangible benefits, and the results of the analysis.

  17. Astronomy. ASASSN-15lh: A highly super-luminous supernova.

    PubMed

    Dong, Subo; Shappee, B J; Prieto, J L; Jha, S W; Stanek, K Z; Holoien, T W-S; Kochanek, C S; Thompson, T A; Morrell, N; Thompson, I B; Basu, U; Beacom, J F; Bersier, D; Brimacombe, J; Brown, J S; Bufano, F; Chen, Ping; Conseil, E; Danilet, A B; Falco, E; Grupe, D; Kiyota, S; Masi, G; Nicholls, B; Olivares E, F; Pignata, G; Pojmanski, G; Simonian, G V; Szczygiel, D M; Woźniak, P R

    2016-01-15

    We report the discovery of ASASSN-15lh (SN 2015L), which we interpret as the most luminous supernova yet found. At redshift z = 0.2326, ASASSN-15lh reached an absolute magnitude of Mu ,AB = -23.5 ± 0.1 and bolometric luminosity Lbol = (2.2 ± 0.2) × 10(45) ergs s(-1), which is more than twice as luminous as any previously known supernova. It has several major features characteristic of the hydrogen-poor super-luminous supernovae (SLSNe-I), whose energy sources and progenitors are currently poorly understood. In contrast to most previously known SLSNe-I that reside in star-forming dwarf galaxies, ASASSN-15lh appears to be hosted by a luminous galaxy (MK ≈ -25.5) with little star formation. In the 4 months since first detection, ASASSN-15lh radiated (1.1 ± 0.2) × 10(52) ergs, challenging the magnetar model for its engine.

  18. Risk Assessment and Scaling for the SLS LH2 ET

    NASA Technical Reports Server (NTRS)

    Hafiychuk, Halyna; Ponizovskaya-Devine, Ekaterina; Luchinsky, Dmitry; Khasin, Michael; Osipov, Viatcheslav V.; Smelyanskiy, Vadim N.

    2012-01-01

    In this report the main physics processes in LH2 tank during prepress and rocket flight are studied. The goal of this investigation is to analyze possible hazards and to make risk assessment in proposed LH2 tank designs for SLS with 5 engines (the situation with 4 engines is less critical). For analysis we use the multinode model (MNM) developed by us and presented in a separate report and also 3D ANSYS simulations. We carry out simulation and theoretical analysis the physics processes such as (i) accumulation of bubbles in LH2 during replenish stage and their collapsing in the liquid during the prepress; (ii) condensation-evaporation at the liquid-vapor interface and tank wall, (iv) heating the liquid near the interface and wall due to condensation and environment heat, (v) injection of hot He during prepress and of hot GH2 during flight, (vi) mixing and cooling of the injected gases due to heat transfer between the gases, liquid and the tank wall. We analyze the effects of these physical processes on the thermo- and fluid gas dynamics in the ullage and on the stratification of temperature in the liquid and assess the associated hazards. A special emphasize is put on the scaling predictions for the larger SLS LH2 tank.

  19. ASASSN-15lh: A highly super-luminous supernova

    NASA Astrophysics Data System (ADS)

    Dong, Subo; Shappee, B. J.; Prieto, J. L.; Jha, S. W.; Stanek, K. Z.; Holoien, T. W.-S.; Kochanek, C. S.; Thompson, T. A.; Morrell, N.; Thompson, I. B.; Basu, U.; Beacom, J. F.; Bersier, D.; Brimacombe, J.; Brown, J. S.; Bufano, F.; Chen, Ping; Conseil, E.; Danilet, A. B.; Falco, E.; Grupe, D.; Kiyota, S.; Masi, G.; Nicholls, B.; Olivares E., F.; Pignata, G.; Pojmanski, G.; Simonian, G. V.; Szczygiel, D. M.; Woźniak, P. R.

    2016-01-01

    We report the discovery of ASASSN-15lh (SN 2015L), which we interpret as the most luminous supernova yet found. At redshift z = 0.2326, ASASSN-15lh reached an absolute magnitude of Mu,AB = -23.5 ± 0.1 and bolometric luminosity Lbol = (2.2 ± 0.2) × 1045 ergs s-1, which is more than twice as luminous as any previously known supernova. It has several major features characteristic of the hydrogen-poor super-luminous supernovae (SLSNe-I), whose energy sources and progenitors are currently poorly understood. In contrast to most previously known SLSNe-I that reside in star-forming dwarf galaxies, ASASSN-15lh appears to be hosted by a luminous galaxy (MK ≈ -25.5) with little star formation. In the 4 months since first detection, ASASSN-15lh radiated (1.1 ± 0.2) × 1052 ergs, challenging the magnetar model for its engine.

  20. High Specific Power Motors in LN2 and LH2

    NASA Technical Reports Server (NTRS)

    Brown, Gerald V.; Jansen, Ralph H.; Trudell, Jeffrey J.

    2007-01-01

    A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/cm2, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2.

  1. High Specific Power Motors in LN2 and LH2

    NASA Technical Reports Server (NTRS)

    Brown, Gerald V.; Jansen, Ralph H.; Trudell, Jeffrey J.

    2007-01-01

    A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/sq cm, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2.

  2. Astronomy. ASASSN-15lh: A highly super-luminous supernova.

    PubMed

    Dong, Subo; Shappee, B J; Prieto, J L; Jha, S W; Stanek, K Z; Holoien, T W-S; Kochanek, C S; Thompson, T A; Morrell, N; Thompson, I B; Basu, U; Beacom, J F; Bersier, D; Brimacombe, J; Brown, J S; Bufano, F; Chen, Ping; Conseil, E; Danilet, A B; Falco, E; Grupe, D; Kiyota, S; Masi, G; Nicholls, B; Olivares E, F; Pignata, G; Pojmanski, G; Simonian, G V; Szczygiel, D M; Woźniak, P R

    2016-01-15

    We report the discovery of ASASSN-15lh (SN 2015L), which we interpret as the most luminous supernova yet found. At redshift z = 0.2326, ASASSN-15lh reached an absolute magnitude of Mu ,AB = -23.5 ± 0.1 and bolometric luminosity Lbol = (2.2 ± 0.2) × 10(45) ergs s(-1), which is more than twice as luminous as any previously known supernova. It has several major features characteristic of the hydrogen-poor super-luminous supernovae (SLSNe-I), whose energy sources and progenitors are currently poorly understood. In contrast to most previously known SLSNe-I that reside in star-forming dwarf galaxies, ASASSN-15lh appears to be hosted by a luminous galaxy (MK ≈ -25.5) with little star formation. In the 4 months since first detection, ASASSN-15lh radiated (1.1 ± 0.2) × 10(52) ergs, challenging the magnetar model for its engine. PMID:26816375

  3. Frequency spectrum of focused broadband pulses of electromagnetic radiation generated by polarization currents with superluminally rotating distribution patterns.

    PubMed

    Ardavan, Houshang; Ardavan, Arzhang; Singleton, John

    2003-11-01

    We investigate the spectral features of the emission from a superluminal polarization current whose distribution pattern rotates (with an angular frequency omega) and oscillates (with a frequency omega > omega differing from an integral multiple of omega) at the same time. This type of polarization current is found in recent practical machines designed to investigate superluminal emission. Although all of the processes involved are linear, we find that the broadband emission contains frequencies that are higher than omega by a factor of the order of (omega/omega)2. This generation of frequencies not required for the creation of the source stems from mathematically rigorous consequences of the familiar classical expression for the retarded potential. The results suggest practical applications for superluminal polarization currents as broadband radio-frequency and infrared sources.

  4. Synchronous Measurement of Ultrafast Anisotropy Decay of the B850 in Bacterial LH2 Complex

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Peng; Du, Lu-Chao; Zhu, Gang-Bei; Wang, Zhuan; Weng, Yu-Xiang

    2015-02-01

    Ultrafast anisotropic decay is a prominent parameter revealing ultrafast energy and electron transfer; however, it is difficult to be determined reliably owing to the requirement of a simultaneous availability of the parallel and perpendicular polarized decay kinetics. Nowadays, any measurement of anisotropic decay is a kind of approach to the exact simultaneity. Here we report a novel method for a synchronous ultrafast anisotropy decay measurement, which can well determine the anisotropy, even at a very early time, as the rising phase of the excitation laser pulse. The anisotropic decay of the B850 in bacterial light harvesting antenna complex LH2 of Rhodobacter sphaeroides in solution at room temperature with coherent excitation is detected by this method, which shows a polarization response time of 30 fs, and the energy transfer from the initial excitation to the bacteriochlorophylls in B850 ring takes about 70 fs. The anisotropic decay that is probed at the red side of the absorption spectrum, such as 880 nm, has an initial value of 0.4, corresponding to simulated emission, while the blue side with an anisotropy of 0.1 contributes to the ground-state bleaching. Our results show that the coherent excitation covering the whole ring might not be realized owing to the symmetry breaking of LH2: from C9 symmetry in membrane to C2 symmetry in solution.

  5. The possibility of geodesic acoustic mode-initiated LH-transition in the TUMAN-3M tokamak

    NASA Astrophysics Data System (ADS)

    Askinazi, L. G.; Belokurov, A. A.

    2015-11-01

    A simple numerical model is proposed for modeling the possibility of the LH-transition (transition to improved plasma confinement state) being triggered by a burst of radial electric field oscillations in a tokamak. One-dimensional density evolution is considered to be governed by an anomalous diffusion coefficient dependent on radial electric field shear (spatial inhomogeneity measure). The radial electric field is taken as the sum of oscillating term and quasi-stationary one determined by density and ion temperature gradients through neoclassical formula. If oscillating field parameters (amplitude, frequency etc) are properly adjusted, a transport barrier forms at the plasma periphery and sustains after oscillations are switched off, manifesting a transition into high confinement mode with strong inhomogeneous radial electric field and suppressed transport at the plasma edge. Electric field oscillation parameters required for LH-transition triggering are compared with geodesic acoustic mode parameters observed at the TUMAN-3N tokamak in the ohmic LH-transition discharges. It is concluded on the basis of this comparison that the geodesic acoustic mode may act as a trigger for the LH transition.

  6. Remote Water Temperature Measurements Based on Brillouin Scattering with a Frequency Doubled Pulsed Yb:doped Fiber Amplifier

    PubMed Central

    Schorstein, Kai; Popescu, Alexandru; Göbel, Marco; Walther, Thomas

    2008-01-01

    Temperature profiles of the ocean are of interest for weather forecasts, climate studies and oceanography in general. Currently, mostly in situ techniques such as fixed buoys or bathythermographs deliver oceanic temperature profiles. A LIDAR method based on Brillouin scattering is an attractive alternative for remote sensing of such water temperature profiles. It makes it possible to deliver cost-effective on-line data covering an extended region of the ocean. The temperature measurement is based on spontaneous Brillouin scattering in water. In this contribution, we present the first water temperature measurements using a Yb:doped pulsed fiber amplifier. The fiber amplifier is a custom designed device which can be operated in a vibrational environment while emitting narrow bandwidth laser pulses. The device shows promising performance and demonstrates the feasibility of this approach. Furthermore, the current status of the receiver is briefly discussed; it is based on an excited state Faraday anomalous dispersion optical filter.

  7. [LH excretion during the ovulatory cycle and during therapy with various estrogen-gestagen combinations].

    PubMed

    Göretzlehner, G; Wilken, H

    1972-11-01

    Immunochemical determination of urinary LH was carried out in 7 normally ovulating women and in 25 women treated with various combined, sequential, and depot hormonal contraceptives. In ovulatory cycles without hormone treatment an LH peak was always observed at midcycle. During treatment with Ovosiston, OZN, and Quinestrol-norethisterone acetate, no LH peak was seen. In women receiving sequential preparations (mestranol-chlormadinone acetate, estrone cyanate-chlormadinone acetate), elevated LH levels were observed during estrogen medication. LH excretion was suppressed after administration of chlormadinone acetate. LH levels were also slightly elevated before and after medication with Quinestrol-chlormadinone acatate (1 pill per month). PMID:4121480

  8. Growth hormone-releasing hormone stimulates GH release while inhibiting ghrelin- and sGnRH-induced LH release from goldfish pituitary cells.

    PubMed

    Grey, Caleb L; Chang, John P

    2013-06-01

    Goldfish GH-releasing hormone (gGHRH) has been recently identified and shown to stimulate GH release in goldfish. In goldfish, neuroendocrine regulation of GH release is multifactorial and known stimulators include goldfish ghrelin (gGRLN19) and salmon gonadotropin-releasing hormone (sGnRH), factors that also enhance LH secretion. To further understand the complex regulation of pituitary hormone release in goldfish, we examined the interactions between gGHRH, gGRLN19, and sGnRH on GH and LH release from primary cultures of goldfish pituitary cells in perifusion. Treatment with 100nM gGHRH for 55min stimulated GH release. A 5-min pulse of either 1nM gGRLN19 or 100nM sGnRH induced GH release in naïve cells, and these were just as effective in cells receiving gGHRH. Interestingly, gGHRH abolished both gGRLN19- and sGnRH-induced LH release and reduced basal LH secretion levels. These results suggest that gGHRH does not interfere with sGnRH or gGRLN19 actions in the goldfish somatotropes and further reveal, for the first time, that GHRH may act as an inhibitor of stimulated and basal LH release by actions at the level of pituitary cells.

  9. A 16 x 16-pixel retinal-prosthesis vision chip with in-pixel digital image processing in a frequency domain by use of a pulse-frequency-modulation photosensor

    NASA Astrophysics Data System (ADS)

    Kagawa, Keiichiro; Furumiya, Tetsuo; Ng, David C.; Uehara, Akihiro; Ohta, Jun; Nunoshita, Masahiro

    2004-06-01

    We are exploring the application of pulse-frequency-modulation (PFM) photosensor to retinal prosthesis for the blind because behavior of PFM photosensors is similar to retinal ganglion cells, from which visual data are transmitted from the retina toward the brain. We have developed retinal-prosthesis vision chips that reshape the output pulses of the PFM photosensor to biphasic current pulses suitable for electric stimulation of retinal cells. In this paper, we introduce image-processing functions to the pixel circuits. We have designed a 16x16-pixel retinal-prosthesis vision chip with several kinds of in-pixel digital image processing such as edge enhancement, edge detection, and low-pass filtering. This chip is a prototype demonstrator of the retinal prosthesis vision chip applicable to in-vitro experiments. By utilizing the feature of PFM photosensor, we propose a new scheme to implement the above image processing in a frequency domain by digital circuitry. Intensity of incident light is converted to a 1-bit data stream by a PFM photosensor, and then image processing is executed by a 1-bit image processor based on joint and annihilation of pulses. The retinal prosthesis vision chip is composed of four blocks: a pixels array block, a row-parallel stimulation current amplifiers array block, a decoder block, and a base current generators block. All blocks except PFM photosensors and stimulation current amplifiers are embodied as digital circuitry. This fact contributes to robustness against noises and fluctuation of power lines. With our vision chip, we can control photosensitivity and intensity and durations of stimulus biphasic currents, which are necessary for retinal prosthesis vision chip. The designed dynamic range is more than 100 dB. The amplitude of the stimulus current is given by a base current, which is common for all pixels, multiplied by a value in an amplitude memory of pixel. Base currents of the negative and positive pulses are common for the all

  10. Combined effect of constant high voltage electrostatic field and variable frequency pulsed electromagnetic field on the morphology of calcium carbonate scale in circulating cooling water systems.

    PubMed

    Zhao, Ju-Dong; Liu, Zhi-An; Zhao, Er-Jun

    2014-01-01

    Research on scale inhibition is of importance to improve the heat transfer efficiency of heat exchangers. The combined effect of high voltage electrostatic and variable frequency pulsed electromagnetic fields on calcium carbonate precipitation was investigated, both theoretically and experimentally. Using energy dispersive spectrum analysis, the predominant phase was found to be CaCO(3). The formed crystal phases mainly consist of calcite and aragonite, which is, in part, verified by theory. The results indicate that the setting of water flow velocity, and high voltage electrostatic and variable frequency pulsed electromagnetic fields is very important. Favorable values of these parameters can have a significant anti-scaling effect, with 68.95% of anti-scaling ratio for scale sample 13, while unfavorable values do not affect scale inhibition, but rather promoted fouling, such as scale sample 6. By using scanning electron microscopy analysis, when the anti-scaling ratio is positive, the particle size of scale was found to become smaller than that of untreated sample and the morphology became loose. The X-ray diffraction results verify that the good combined effect favors the appearance and growth of aragonite and restrains its transition to calcite. The mechanism for scale reduction is discussed. PMID:25259497

  11. Combined effect of constant high voltage electrostatic field and variable frequency pulsed electromagnetic field on the morphology of calcium carbonate scale in circulating cooling water systems.

    PubMed

    Zhao, Ju-Dong; Liu, Zhi-An; Zhao, Er-Jun

    2014-01-01

    Research on scale inhibition is of importance to improve the heat transfer efficiency of heat exchangers. The combined effect of high voltage electrostatic and variable frequency pulsed electromagnetic fields on calcium carbonate precipitation was investigated, both theoretically and experimentally. Using energy dispersive spectrum analysis, the predominant phase was found to be CaCO(3). The formed crystal phases mainly consist of calcite and aragonite, which is, in part, verified by theory. The results indicate that the setting of water flow velocity, and high voltage electrostatic and variable frequency pulsed electromagnetic fields is very important. Favorable values of these parameters can have a significant anti-scaling effect, with 68.95% of anti-scaling ratio for scale sample 13, while unfavorable values do not affect scale inhibition, but rather promoted fouling, such as scale sample 6. By using scanning electron microscopy analysis, when the anti-scaling ratio is positive, the particle size of scale was found to become smaller than that of untreated sample and the morphology became loose. The X-ray diffraction results verify that the good combined effect favors the appearance and growth of aragonite and restrains its transition to calcite. The mechanism for scale reduction is discussed.

  12. [The influence of low-frequency pulsed electric and magnetic signals or their combination on the normal and modified fibroblasts (an experimental study)].

    PubMed

    Ulitko, M V; Medvedeva, S Yu; Malakhov, V V

    2016-01-01

    The results of clinical studies give evidence of the beneficial preventive and therapeutic effects of the «Tiline-EM» physiotherapeutic device designed for the combined specific treatment of the skin regions onto which both discomfort and pain sensations are directly projected, reflectively active sites and zones, as well as trigger zones with the use of low-frequency pulsed electric current and magnetic field. The efficient application of the device requires the understanding of the general mechanisms underlying such action on the living systems including those operating at the cellular and subcellular levels. The objective of the present study was the investigation of the specific and complex effects produced by the low-frequency pulses of electric current and magnetic field generated in the physiotherapeutic device «Tiline-EM» on the viability, proliferative activity, and morphofunctional characteristics of normal skin fibroblasts and the transformed fibroblast line K-22. It has been demonstrated that the biological effects of the electric and magnetic signals vary depending on the type of the cell culture and the mode of impact. The transformed fibroblasts proved to be more sensitive to the specific and complex effects of electric and magnetic pulses than the normal skin fibroblasts. The combined action of the electric and magnetic signals was shown to have the greatest influence on both varieties of fibroblasts. It manifests itself in the form of enhanced viability, elevated proliferative and synthetic activity in the cultures of transformed fibroblasts and as the acceleration of cell differentiation in the cultures of normal fibroblasts. The effect of stimulation of dermal fibroblast differentiation in response to the combined treatment by the electric and magnetic signals is of interest from the standpoint of the physiotherapeutic use of the «Tiline-EM» device for the purpose of obtaining fibroblasts cultures to be employed in regenerative therapy and

  13. [The influence of low-frequency pulsed electric and magnetic signals or their combination on the normal and modified fibroblasts (an experimental study)].

    PubMed

    Ulitko, M V; Medvedeva, S Yu; Malakhov, V V

    2016-01-01

    The results of clinical studies give evidence of the beneficial preventive and therapeutic effects of the «Tiline-EM» physiotherapeutic device designed for the combined specific treatment of the skin regions onto which both discomfort and pain sensations are directly projected, reflectively active sites and zones, as well as trigger zones with the use of low-frequency pulsed electric current and magnetic field. The efficient application of the device requires the understanding of the general mechanisms underlying such action on the living systems including those operating at the cellular and subcellular levels. The objective of the present study was the investigation of the specific and complex effects produced by the low-frequency pulses of electric current and magnetic field generated in the physiotherapeutic device «Tiline-EM» on the viability, proliferative activity, and morphofunctional characteristics of normal skin fibroblasts and the transformed fibroblast line K-22. It has been demonstrated that the biological effects of the electric and magnetic signals vary depending on the type of the cell culture and the mode of impact. The transformed fibroblasts proved to be more sensitive to the specific and complex effects of electric and magnetic pulses than the normal skin fibroblasts. The combined action of the electric and magnetic signals was shown to have the greatest influence on both varieties of fibroblasts. It manifests itself in the form of enhanced viability, elevated proliferative and synthetic activity in the cultures of transformed fibroblasts and as the acceleration of cell differentiation in the cultures of normal fibroblasts. The effect of stimulation of dermal fibroblast differentiation in response to the combined treatment by the electric and magnetic signals is of interest from the standpoint of the physiotherapeutic use of the «Tiline-EM» device for the purpose of obtaining fibroblasts cultures to be employed in regenerative therapy and

  14. Measurement of coronary flow using high-frequency intravascular ultrasound imaging and pulsed Doppler velocimetry: in vitro feasibility studies.

    PubMed

    Grayburn, P A; Willard, J E; Haagen, D R; Brickner, M E; Alvarez, L G; Eichhorn, E J

    1992-01-01

    The recent development of intravascular ultrasound imaging offers the potential to measure blood flow as the product of vessel cross-sectional area and mean velocity derived from pulsed Doppler velocimetry. To determine the feasibility of this approach for measuring coronary artery flow, we constructed a flow model of the coronary circulation that allowed flow to be varied by adjusting downstream resistance and aortic driving pressure. Assessment of intracoronary flow velocity was accomplished using a commercially available end-mounted pulsed Doppler catheter. Cross-sectional area of the coronary artery was measured using a 20 MHz mechanical imaging transducer mounted on a 4.8 F catheter. The product of mean velocity and cross-sectional area was compared with coronary flow measured by timed collection in a graduated cylinder by linear regression analysis. Excellent correlations were obtained between coronary flow calculated by the ultrasound method and measured coronary flow at both ostial (r = 0.99, standard error of the estimate [SEE] = 13.9 ml/min) and distal (r = 0.98, SEE = 23.0 ml/min) vessel locations under steady flow conditions. During pulsatile flow, calculated and measured coronary flow also correlated well for ostial (r = 0.98, SEE = 12.7 ml/min) and downstream (r = 0.99, SEE = 9.3 ml/min) locations. That the SEE was lower for pulsatile as compared with steady flow may be explained by the blunting of the flow profile across the vessel lumen by the acceleration phase of pulsatile flow. These data establish the feasibility of measuring coronary artery blood flow using intravascular ultrasound imaging and pulsed Doppler techniques. PMID:1531416

  15. High-power radio frequency pulse generation and extration based on wakefield excited by an intense charged particle beam in dielectric-loaded waveguides.

    SciTech Connect

    Gao, F.; High Energy Physics; Illinois Inst. of Tech

    2009-07-24

    Power extraction using a dielectric-loaded (DL) waveguide is a way to generate high-power radio frequency (RF) waves for future particle accelerators, especially for two-beam-acceleration. In a two-beam-acceleration scheme, a low-energy, high-current particle beam is passed through a deceleration section of waveguide (decelerator), where the power from the beam is partially transferred to trailing electromagnetic waves (wakefields); then with a properly designed RF output coupler, the power generated in the decelerator is extracted to an output waveguide, where finally the power can be transmitted and used to accelerate another usually high-energy low-current beam. The decelerator, together with the RF output coupler, is called a power extractor. At Argonne Wakefield Accelerator (AWA), we designed a 7.8GHz power extractor with a circular DL waveguide and tested it with single electron bunches and bunch trains. The output RF frequency (7.8GHz) is the sixth harmonic of the operational frequency (1.3GHz) of the electron gun and the linac at AWA. In single bunch excitation, a 1.7ns RF pulse with 30MW of power was generated by a single 66nC electron bunch passing through the decelerator. In subsequent experiments, by employing different splitting-recombining optics for the photoinjector laser, electron bunch trains were generated and thus longer RF pulses could be successfully generated and extracted. In 16-bunch experiments, 10ns and 22ns RF pulses have been generated and extracted; and in 4-bunch experiments, the maximum power generated was 44MW with 40MW extracted. A 26GHz DL power extractor has also been designed to test this technique in the millimeter-wave range. A power level of 148MW is expected to be generated by a bunch train with a bunch spacing of 769ps and bunch charges of 20nC each. The arrangement for the experiment is illustrated in a diagram. Higher-order-mode (HOM) power extraction has also been explored in a dual-frequency design. By using a bunch

  16. A new time-frequency method to reveal quantum dynamics of atomic hydrogen in intense laser pulses: Synchrosqueezing transform

    SciTech Connect

    Sheu, Yae-lin; Hsu, Liang-Yan; Wu, Hau-tieng; Li, Peng-Cheng; Chu, Shih-I

    2014-11-15

    This study introduces a new adaptive time-frequency (TF) analysis technique, the synchrosqueezing transform (SST), to explore the dynamics of a laser-driven hydrogen atom at an ab initio level, upon which we have demonstrated its versatility as a new viable venue for further exploring quantum dynamics. For a signal composed of oscillatory components which can be characterized by instantaneous frequency, the SST enables rendering the decomposed signal based on the phase information inherited in the linear TF representation with mathematical support. Compared with the classical type of TF methods, the SST clearly depicts several intrinsic quantum dynamical processes such as selection rules, AC Stark effects, and high harmonic generation.

  17. Slip pulse characteristics, Kathmandu basin resonance and high-frequency waves radiation during unzipping of locked MHT by the 2015, Mw 7.8 Gorkha earthquake, Nepal.

    NASA Astrophysics Data System (ADS)

    Avouac, J. P.; Meng, L.; Melgar, D.; Wei, S.; Elliott, J. R.; Jolivet, R.; Wang, T.; Bock, Y.; Stevens, V.; Ampuero, J. P.; Galetzka, J.; Genrich, J. F.; Geng, J.; Owen, S. E.; Shrestha, P. L.; Moore, A. W.; Adhikari, L. B.; Hudnut, K. W.

    2015-12-01

    We use high-rate GPS, seismological and Synthetic Aperture Radar imagery (SAR) measurements to produce a detailed image of the seismic rupture during the 2015 Mw 7.8 Gorkha earthquake, Nepal. The earthquake ruptured a 150x50km elliptical patch striking parallel to the Himalayan front located north of Kathmandu. This asperity represents only a small fraction of the previous locked portion of the Main Himalayan Thrust (MHT) along which the Himalaya is thrust over India. The earthquake initiated at western end of the ruptured patch, 75km northwest of Kathmandu. It produced a slip pulse of ~20 km width, ~6 s duration with peak sliding velocity of ~1 m/s which propagated eastwards at ~2.8 km/s. High frequency seismic waves (~ 1 Hz) were radiated continuously as the earthquake unzipped the northern edge of the locked portion of the of the MHT, a zone of presumably high and heterogeneous pre-seismic stress. Most of the moment was actually released south, hence, updip, of the sources of high frequency seismic waves. The slip pulse there shows a remarkable smooth onset indicating a large effective slip-weakening distance of several meters. This smooth onset can explain the moderate ground shaking at high frequencies (>1Hz) and the limited damage to regular few-storey high dwellings within Kathmandu basin. By contrast, the entire basin resonated at ~4-5 s for 30s resulting in the collapse of some tall buildings. The study suggests a deterministic control, of probably structural origin, of the source characteristics and induced ground shaking.

  18. LH Power Losses In Front of the JET Launcher

    SciTech Connect

    Jacquet, P.; Arnoux, G.; Kirov, K.; Mailloux, J.; Mayoral, M.-L.; Ongena, J.

    2009-11-26

    In recent JET experiments, Lower Hybrid (LH) power losses in the Scrape-Off Layer (SOL) were characterized using infra-red (IR) thermography. Hot spots were observed on objects intercepting the field lines passing in front of the LH launcher, i.e. on poloidal limiters and on dumplates located at the top of the tokamak; their locations being in good agreement with magnetic field line tracing using the EFIT equilibrium code. The dumplate temperature was monitored while scanning the launcher position so that the radial distance between field lines intercepting the hot spots and the launcher was increased up to 3.5 cm. The dissipation layer in front of the launcher was estimated to be at least 3.5 cm wide, in agreement with recent measurements on Tore-Supra, but not with simple models that predict a dissipation layer in the mm range.

  19. A Derivation of the Long-Term Degradation of a Pulsed Atomic Frequency Standard from a Control-Loop Model

    NASA Technical Reports Server (NTRS)

    Greenhall, C. A.

    1996-01-01

    The phase of a frequency standard that uses periodic interrogation and control of a local oscillator (LO) is degraded by a long-term random-walk component induced by downconversion of LO noise into the loop passband. The Dick formula for the noise level of this degradation is derived from an explicit solution of an LO control-loop model.

  20. The LH surge in humans: its mechanism and sex difference.

    PubMed

    Goh, H H; Ratnam, S S

    1988-06-01

    There is a sex difference in the response to an estrogen challenge test in humans, but, unlike with rats, this sex difference is not permanently imprinted in the central nervous system. Estrogen is not only the important ovarian signal to trigger off the LH surge, but it also probably plays an important role in activating the positive estrogen feedback mechanism in humans. For an LH surge to occur, amplification of the hypothalamic signal (enhanced secretion of GnRH) as well as sensitization of the pituitary responsiveness to GnRH are required. It is unlikely that androgens per se are responsible for suppressing the positive estrogen feedback in humans and the possible role of another gonadal factor other than androgens remains speculative. The LH surge is a neuroendocrine phenomenon involved primarily in the process of ovulation and it is not correlated to sexual identity and orientation. Furthermore, how the hypothalamic-pituitary axis (HPA) responds to the estrogen challenge can be accounted for purely by its exposure to a different steroid milieu without reference to gender identity or sexual orientation of the subject.

  1. On the Use of EBG in ICRF and LH Launcher

    NASA Astrophysics Data System (ADS)

    Guadamuz, S.; Maggiora, R.; Vecchi, G.

    2009-11-01

    High impedance surfaces or electromagnetic band gap (EBG) surfaces have proved themselves to be useful in wireless communications applications due to their unique characteristics such as no propagating surface wave support, no conduction of RF current for a given bandwidth, in-phase electromagnetic reflection and non-inverted image of the electric charge in front of them [1]. These characteristics make possible to design compact antennas achieving better performance in terms of radiation and input impedance. ICRF and LH antennas in plasma experiments can take advantage of using EBG surfaces. One of the main issues in ICRF plasma heating is the low power coupling of the plasma facing antenna. The adoption of EBG surfaces in the ICRF antenna structure and the advantages offered by a predictive designing tool as TOPICA [2] offer the possibility to improve significantly the coupled power to plasma. The adoption of EBG surfaces in the LH waveguides permits to reduce the major dimension of waveguides not affecting drastically the propagation [3]. It is then possible to manufacture more compact LH arrays of waveguides.

  2. Differential actions of FSH and LH during folliculogenesis.

    PubMed

    Palermo, Roberto

    2007-09-01

    In the gonadotrophin-dependent stage of follicular development, FSH- and LH-signalling pathways play an obligatory role in follicle differentiation, selection and survival. Under the effect of LH the theca-interstitial cell layer acts as an androgen producer. Thus, androgen diffusing into the mural granulosa cell layer represents the substrate for FSH-induced aromatase for follicular oestradiol synthesis. This is the landmark 'two cell-two gonadotrophin' concept in the physiology of ovarian function in mammals. The increase in plasma FSH during luteo-follicular transition is the basis for follicle selection. The rise of FSH to the threshold concentration represents a critical condition for the growth of the most sensitive follicle in a given time frame of the last 14 days of the dominant follicle odyssey. The gonadotrophin-induced follicular oestradiol secretion inhibits pituitary secretion of FSH, which in turn causes the concentration of FSH in the developing cohort follicles to drop below threshold concentrations and the arrest of the development of the less FSH-sensitive follicle (FSH threshold and window concept). In the gonadotrophin-dependent phase of follicular development, LH also seems to acts within a critical window of the hormone concentration framed between the minimal threshold and a ceiling for the normal functions of the follicle unit.

  3. How much radioactive nickel does ASASSN-15lh require?

    NASA Astrophysics Data System (ADS)

    Kozyreva, Alexandra; Hirschi, Raphael; Blinnikov, Sergey; den Hartogh, Jacqueline

    2016-06-01

    The discovery of the most luminous supernova ASASSN-15lh triggered a shock-wave in the supernova community. The three possible mechanisms proposed for the majority of other superluminous supernovae do not produce a realistic physical model for this particular supernova. In this study, we show the limiting luminosity available from a nickel-powered pair-instability supernova. We computed a few exotic nickel-powered explosions with a total mass of nickel up to 1500 solar masses. We used the hydrostatic configurations prepared with the GENEVA and MESA codes, and the STELLA radiative-transfer code for following the explosion of these models. We show that 1500 solar masses of radioactive nickel is needed to power a luminosity of 2 × 10 45 erg s - 1. The resulting light curve is very broad and incompatible with the shorter ASASSN-15lh time-scale. This rules out a nickel-powered origin of ASASSN-15lh. In addition, we derive a simple peak luminosity-nickel mass relation from our data, which may serve to estimate of nickel mass from observed peak luminosities.

  4. Generation of two-cycle pulses and octave-spanning frequency combs in a dispersion-flattened micro-resonator.

    PubMed

    Zhang, Lin; Bao, Chengying; Singh, Vivek; Mu, Jianwei; Yang, Changxi; Agarwal, Anuradha M; Kimerling, Lionel C; Michel, Jurgen

    2013-12-01

    We show that octave-spanning Kerr frequency combs with improved spectral flatness of comb lines can be generated in dispersion-flattened microring resonators. The resonator is formed by a strip/slot hybrid waveguide, exhibiting a flat and low anomalous dispersion between two zero-dispersion wavelengths that are separated by one octave from near-infrared to mid-infrared. Such flattened dispersion profiles allow for the generation of mode-locked frequency combs, using relatively low pump power to obtain two-cycle cavity solitons on a chip, associated with the octave-spanning comb bandwidth. The wavelength dependence of the optical loss and of the coupling coefficient and thus wavelength dependent Q-factor are also considered.

  5. Generation and Quantitative Analysis of Pulsed Low Frequency Ultrasound to Determine the Sonic Sensitivity of Untreated and Treated Neoplastic Cells

    PubMed Central

    Trendowski, Matthew; Christen, Timothy D.; Zoino, Joseph N.; Acquafondata, Christopher; Fondy, Thomas P.

    2015-01-01

    Low frequency ultrasound in the 20 to 60 kHz range is a novel physical modality by which to induce selective cell lysis and death in neoplastic cells. In addition, this method can be used in combination with specialized agents known as sonosensitizers to increase the extent of preferential damage exerted by ultrasound against neoplastic cells, an approach referred to as sonodynamic therapy (SDT). The methodology for generating and applying low frequency ultrasound in a preclinical in vitro setting is presented to demonstrate that reproducible cell destruction can be attained in order to examine and compare the effects of sonication on neoplastic and normal cells. This offers a means by which to reliably sonicate neoplastic cells at a level of consistency required for preclinical therapeutic assessment. In addition, the effects of cholesterol-depleting and cytoskeletal-directed agents on potentiating ultrasonic sensitivity in neoplastic cells are discussed in order to elaborate on mechanisms of action conducive to sonochemotherapeutic approaches. PMID:26274053

  6. L-H power threshold studies with tungsten/carbon divertor on the EAST tokamak

    NASA Astrophysics Data System (ADS)

    Chen, L.; Xu, G. S.; Gao, W.; Zhang, L.; Nielsen, A. H.; Luo, Z. P.; Si, H.; Wang, Y. M.; Qu, H.; Sun, Z.; Duan, Y. M.; Liu, H. Q.; Wang, S. X.; Li, M. H.; Zhang, X. J.; Wu, B.; Chen, R.; Wang, L.; Wang, H. Q.; Ding, S. Y.; Yan, N.; Liu, S. C.; Shao, L. M.; Zhang, W.; Hu, G. H.; Li, J.; Li, Y. L.; Wu, X. Q.; Zhao, N.; Jia, M. N.

    2016-05-01

    The power threshold for low (L) to high (H) confinement mode transition achieved by radio-frequency heating and molybdenum first wall with lithium coating has been experimentally investigated on the EAST tokamak for two sets of divertor geometries and materials: tungsten/carbon divertor and full carbon divertor. For both sets of divertors, the power threshold was found to decrease with gradual accumulation of the lithium wall coating, suggesting the important role played by the low Z impurities and/or the edge neutral density on the L-H power threshold. When operating in the upper single null configuration, with the ion grad-B drift direction away from the primary X-point, a lower normalized power threshold is observed in EAST with the tungsten/carbon divertor, compared to the carbon divertor after intensive lithium wall coating. A newly installed cryopump increasing the pumping efficiency also plays an important part in the observed lower threshold. In addition, the H-mode in the Quasi-Snowflake divertor configuration has been obtained on EAST, exhibiting higher L-H power threshold compared to the lower single null configuration with similar IP/BT pairs.

  7. Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

    SciTech Connect

    Feng, L. W.; Lin, L.; Huang, S. L.; Quan, S. W.; Hao, J. K.; Zhu, F.; Wang, F.; Liu, K. X.; Jiang, T.; Zhu, P. F.; Fu, F.; Wang, R.; Zhao, L.; Xiang, D.

    2015-11-30

    We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

  8. Effect of pulse repetition frequency and scan step size on the dimensions of the lesions formed in agar by HIFU histotripsy.

    PubMed

    Xu, Jin; Bigelow, Timothy A; Lee, Hangil

    2013-04-01

    Histotripsy uses high-intensity focused ultrasound pulses at low duty cycle to generate energetic bubble clouds inside tissue to fractionate a region. As a potential tumor treatment modality, this cavitation-based non-invasive technique has the advantages of easy monitoring and sharp borders. Aiming at therapy efficiency, we experimentally investigated the effects of pulse repetition frequency (PRF) and lateral scan step size on the dimensions of lesions formed through HIFU histotripsy in agar mimicking tissue in terms of mechanical (not acoustical) properties. The single-element spherically focused source (1.1 MHz, 6.34 cm focal length, f/1) was excited to reach the peak compressional and rarefactional pressures of ~102 and 17 MPa, respectively. A targeted rectangular block of 4.5 mm wide (lateral) and 6mm deep (axial) was scanned in a raster pattern with a constant axial step size of 3mm. The lateral step size was varied between 375, 750, 1500, 2250 and 4500 μm. Pulses at each treatment location consisted of 5000 20-cycle sine wave tone bursts with the PRF of 167, 333 or 1000 Hz. Results suggested that the bubble activity region could extend beyond the -3 dB region and that refining the lateral scan mesh and/or increasing PRF enlarged the lesion extent. The 1500 μm-333 Hz and the 1500 μm-1 kHz conditions were in a more favorable position to be viewed as optimal with regard to lesion volume generation rate, bubble activity region width, and the potential for thermal damage.

  9. Titanium dioxide thin films deposited by pulsed laser deposition and integration in radio frequency devices: Study of structure, optical and dielectric properties

    NASA Astrophysics Data System (ADS)

    Orlianges, Jean-Christophe; Crunteanu, Aurelian; Pothier, Arnaud; Merle-Mejean, Therese; Blondy, Pierre; Champeaux, Corinne

    2012-12-01

    Titanium dioxide presents a wide range of technological application possibilities due to its dielectric, electrochemical, photocatalytic and optical properties. The three TiO2 allotropic forms: anatase, rutile and brookite are also interesting, since they exhibit different properties, stabilities and growth modes. For instance, rutile has a high dielectric permittivity, of particular interest for the integration as dielectric in components such as microelectromechanical systems (MEMS) for radio frequency (RF) devices. In this study, titanium dioxide thin films are deposited by pulsed laser deposition. Characterizations by Raman spectroscopy and X-ray diffraction show the evolution of the structural properties. Thin films optical properties are investigated using spectroscopic ellipsometry and transmission measurements from UV to IR range. Co-planar waveguide (CPW) devices are fabricated based on these films. Their performances are measured in the RF domain and compared to simulation, leading to relative permittivity values in the range 30-120, showing the potentialities of the deposited material for capacitive switches applications.

  10. The discharge mode transition and O({sup 5}p{sub 1}) production mechanism of pulsed radio frequency capacitively coupled plasma

    SciTech Connect

    Liu, X. Y.; Hu, J. T.; Liu, J. H.; Xiong, Z. L.; Liu, D. W.; Lu, X. P.; Shi, J. J.

    2012-07-23

    The discharge mode transition from uniform plasma across the gas gap to the {alpha} mode happens at the rising phase of the pulsed radio frequency capacitively coupled plasma (PRF CCP). This transition is attributed to the fast increasing stochastic heating at the edge of sheath. In the second stage with the stable current and voltage amplitude, the consistency between experimental and numerical spatial-temporal 777 nm emission profile suggests that He* and He{sub 2}* dominate the production of O({sup 5}p{sub 1}) through dissociation and excitation of O{sub 2}. Finally, the sterilization efficiency of PRF CCP is found to be higher than that of plasma jet.

  11. Fabrication, optimization, and characterization of monolithic semiconductor mode-locked lasers and colliding, pulse mode-locked lasers at millimeter-wave frequencies

    NASA Astrophysics Data System (ADS)

    Passerini, Marco; Sorel, Marc; Laybourn, Peter J.; Giuliani, Guido; Donati, Silvano

    2004-09-01

    This work reports on the fabrication, optimisation and characterisation of monolithic mode-locked lasers (MLLs) and colliding-pulse mode-locked (CPM) lasers with repetition rate in the range 10-60 GHz. The devices consist of double section split-contact ridge waveguide lasers fabricated in GaAs/AlGaAs double quantum well (DQW) material. For CPM devices, the saturable absorber section was fabricated with a coplanar ground-signal-ground (G-S-G) pad structure. The optimum saturable absorber size for efficient mode-locking is found experimentally. The fabricated devices are characterised in terms of operating regimes (Continuous Wave, Self-Pulsation, Mode-Locking) and the mode-locking signals were observed in the frequency domain using an external fast photodiode. In the case of CPM devices a mm-wave signal could also be extracted directly from the saturable absorber section of the laser using a microwave probe.

  12. Generation of high-energy sub-20 fs pulses tunable in the 250-310 nm region by frequency doubling of a high-power noncollinear optical parametric amplifier.

    PubMed

    Beutler, Marcus; Ghotbi, Masood; Noack, Frank; Brida, Daniele; Manzoni, Cristian; Cerullo, Giulio

    2009-03-15

    We report on the generation of powerful sub-20 fs deep UV pulses with 10 microJ level energy and broadly tunable in the 250-310 nm range. These pulses are produced by frequency doubling a high-power noncollinear optical parametric amplifier and compressed by a pair of MgF2 prisms to an almost transform-limited duration. Our results provide a power scaling by an order of magnitude with respect to previous works.

  13. Tunable error-free optical frequency conversion of a 4ps optical short pulse over 25 nm by four-wave mixing in a polarisation-maintaining optical fibre

    NASA Astrophysics Data System (ADS)

    Morioka, T.; Kawanishi, S.; Saruwatari, M.

    1994-05-01

    Error-free, tunable optical frequency conversion of a transform-limited 4.0 ps optical pulse signalis demonstrated at 6.3 Gbit/s using four-wave mixing in a polarization-maintaining optical fibre. The process generates 4.0-4.6 ps pulses over a 25nm range with time-bandwidth products of 0.31-0.43 and conversion power penalties of less than 1.5 dB.

  14. Effect of acupuncture at Hsien-Ku (St-43) on the pulse spectrum and a discussion of the evidence for the frequency structure of Chinese medicine.

    PubMed

    Wan, W K; Hsu, T L; Chang, H C; Wan, Y Y

    2000-01-01

    We investigated the pulse spectrum variation of the human radial artery when Hsien- Ku (St 43), an acupoint on the stomach meridian, was needled and compared the results with the acupuncture effects of two other acupoints, Tsu-San-Li (St-36) and Tai-Shih (K-3), reported previously. For Hsien-Ku, the harmonic proportions were redistributed: the second harmonic (C2) decreased, C3, C5, C6, C7, C8 and C9 increased, C3, C6 and C9 became the relative peaks to their neighboring harmonics and C2, C4 became the relative minimums. The phase angles of the 2nd harmonic (P2) and 5th harmonic (P5) decreased, propagating faster. These effects were similar to that of Tsu-San-Li which is also on the stomach meridian. A totally different pattern was found for Tai-Shih on the kidney meridian. These results strengthen the theory that a meridian can be classified according to its effects on the pulse spectrum, and that all the meridian related effects such as those caused by acupuncture or meridian specific herbs are frequency specific.

  15. First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

    SciTech Connect

    Petrov, V. G.; Malyshev, A. Yu.; Markov, V. K.; Petrov, A. A.; Avino, F.; Angelis, R. de; Tudisco, O.

    2012-04-15

    A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50-100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution {alpha} and correctly determine the linear density Left-Pointing-Angle-Bracket Nl Right-Pointing-Angle-Bracket , regardless of the density profile (assuming a smooth density profile of the form of N({rho}) = N(0)(1 - {rho}{sup 2}){sup {alpha}}, where N(0) is the central plasma density and {rho} = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of {approx}6 Multiplication-Sign 10{sup 19} m{sup -3} was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.

  16. High efficiency production of germ-line transgenic Japanese medaka (Oryzias latipes) by electroporation with direct current-shifted radio frequency pulses.

    PubMed

    Hostetler, Heather A; Peck, Stephanie L; Muir, William M

    2003-08-01

    Although there have been several studies showing the production of transgenic fish through electroporation techniques, success rates have been low and few studies show germ-line integration and expression. When electroporation has been successful, the device used is no longer commercially available. The goal of this experiment was to find an alternative efficient method of generating transgenic Japanese medaka (Oryzias latipes) using a commercially available electroporation device. The Gene Pulser II and RF module (Bio-Rad Laboratories, USA), along with two reporter gene constructs, were used. In contrast to other electroporation devices, which are based on a single pulse with exponential decay or square wave technology, the Gene Pulser II incorporates a direct current (DC)-shifted radio frequency (RF) signal. With this technique, over 1000 embryos can be electroporated in less than 30 min. The plasmid pCMV-SPORT-beta-gal (Invitrogen, USA) was used in the supercoiled form to optimize parameters for gene transfer into single-celled embryos, and resulted in up to 100% somatic gene transfer. Similar conditions were used to generate fish transgenic for both the pCMV-EGFP plasmid (Clontech, USA) and a cytomegalovirus (CMV) driven phytase-EGFP construct. The conditions used were a voltage of 25 V, a percent modulation of 100%, a radio frequency of 35 kHz, a burst duration of 10 ms, 3 bursts, and a burst interval of 1.0 s. Seventy percent of the embryos electroporated with the pCMV-EGFP construct survived to sexual maturity, and of those, 85% were capable of passing the transgene on to their offspring. Transgenic second generation back-crossed (BC2) fry were subjected to Southern blot analysis, which confirmed germ-line integration, and observation for green fluorescence protein, which confirmed protein expression. DC-shifted RF pulses are effective and efficient in the production of transgenic medaka, and germ-line integration and expression can be achieved without

  17. Low frequency and low intensity pulsed electromagnetic field exerts its antiinflammatory effect through restoration of plasma membrane calcium ATPase activity.

    PubMed

    Selvam, Ramasamy; Ganesan, Kalaivani; Narayana Raju, K V S; Gangadharan, Akkalayi Chandrapuram; Manohar, Bhakthavatchalam Murali; Puvanakrishnan, Rengarajulu

    2007-06-01

    Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting 1% of the population worldwide. Pulsed electromagnetic field (PEMF) has a number of well-documented physiological effects on cells and tissues including antiinflammatory effect. This study aims to explore the antiinflammatory effect of PEMF and its possible mechanism of action in amelioration of adjuvant induced arthritis (AIA). Arthritis was induced by a single intradermal injection of heat killed Mycobacterium tuberculosis at a concentration of 500 microg in 0.1 ml of paraffin oil into the right hind paw of rats. The arthritic animals showed a biphasic response regarding changes in the paw edema volume. During the chronic phase of the disease, arthritic animals showed an elevated level of lipid peroxides and depletion of antioxidant enzymes with significant radiological and histological changes. Besides, plasma membrane Ca(2+) ATPase (PMCA) activity was inhibited while intracellular Ca(2+) level as well as prostaglandin E(2) levels was noticed to be elevated in blood lymphocytes of arthritic rats. Exposure of arthritic rats to PEMF at 5 Hzx4 microT x 90 min, produced significant antiexudative effect resulting in the restoration of the altered parameters. The antiinflammatory effect could be partially mediated through the stabilizing action of PEMF on membranes as reflected by the restoration of PMCA and intracellular Ca(2+) levels in blood lymphocytes subsequently inhibiting PGE(2) biosynthesis. The results of this study indicated that PEMF could be developed as a potential therapy for RA in human beings.

  18. A two-dimensional model of chemical vapor infiltration with radio-frequency heating and spatio-temporal evolution of a pulsed chlorine plasma

    NASA Astrophysics Data System (ADS)

    Midha, Vikas

    The first part of this work focused on modeling radio- frequency assisted chemical vapor infiltration (CVI) for the fabrication of fiber-reinforced composite materials. CVI involves diffusion and chemical reaction of precursor gases in a fibrous preform to deposit solid material within the pores. A two-dimensional finite-element model was developed which included the solution of Maxwell's equations for electromagnetic fields, transport equations for multicomponent gas diffusion and chemical kinetics for the deposition of solid material. Simulation results showed that densification of long cylindrical preforms initially occurred radially around the central zone and then axially towards the ends of the preform. This densification pattern resulted in significant entrapment of porosity at the center of the preform and required a relatively long time for completion. Comparison of results with reported experimental data showed agreement of important trends which could not be predicted by existing one-dimensional models. Based on the geometry of the preform, novel schemes for improved radio-frequency assisted CVI were proposed which resulted in complete densification and reduced overall processing time significantly compared to conventional isothermal processes. The second part of this work focused on modeling of high- density, low-pressure chlorine discharges used for the fabrication of sub-micron devices in the semiconductor industry. Recent experiments showed that pulsing of input power can lead to significant improvement in the etching characteristics of electronegative gas discharges. A one- dimensional model was developed which captured the transition of an electron-ion plasma in the active glow to a negative-ion dominated or ion-ion plasma in the afterglow phase of a pulse. The spatial evolution of the negative-ion density showed formation of self-sharpening fronts during the active glow and subsequent back- propagation of the fronts during the afterglow. In the

  19. Frequency-Dependent Regulation of Follicle-Stimulating Hormone β by Pulsatile Gonadotropin-Releasing Hormone Is Mediated by Functional Antagonism of bZIP Transcription Factors ▿

    PubMed Central

    Ciccone, Nick A.; Xu, Shuyun; Lacza, Charlemagne T.; Carroll, Rona S.; Kaiser, Ursula B.

    2010-01-01

    Oscillatory synthesis and secretion of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), under the control of pulsatile hypothalamic gonadotropin-releasing hormone (GnRH), is essential for normal reproductive development and fertility. The molecular mechanisms by which various patterns of pulsatile GnRH regulate gonadotrope responsiveness remain poorly understood. In contrast to the α and LHβ subunit genes, FSHβ subunit transcription is preferentially stimulated at low rather than high frequencies of pulsatile GnRH. In this study, mutation of a cyclic AMP response element (CRE) within the FSHβ promoter resulted in the loss of preferential GnRH stimulation at low pulse frequencies. We hypothesized that high GnRH pulse frequencies might stimulate a transcriptional repressor(s) to attenuate the action of CRE binding protein (CREB) and show that inducible cAMP early repressor (ICER) fulfills such a role. ICER was not detected under basal conditions, but pulsatile GnRH stimulated ICER to a greater extent at high than at low pulse frequencies. ICER binds to the FSHβ CRE site to reduce CREB occupation and abrogates both maximal GnRH stimulation and GnRH pulse frequency-dependent effects on FSHβ transcription. These data suggest that ICER production antagonizes the stimulatory action of CREB to attenuate FSHβ transcription at high GnRH pulse frequencies, thereby playing a critical role in regulating cyclic reproductive function. PMID:20008557

  20. [Hypogonadotropic hypogonadism and delayed puberty: differential diagnosis using the LH-RH-infusion test].

    PubMed

    Vierhapper, H

    1983-08-26

    Serum concentrations of LH and FSH were determined during an intravenous infusion of LH-RH (200 micrograms, t = 4 hours) in 8 patients (age: 15 to 20 years) with delayed sexual maturation and retarded bone age. Four patients who by clinical criteria were later recognized as suffering from hypogonadotropic hypogonadism (HH) presented during the infusion of LH-RH with only a small response of LH (and, in three cases, of FSH). In 3 patients with HH a deficiency of endogenous LH-RH due to a hypothalamic defect was suggested by an enhanced secretion of LH and FSH during a second LH-RH infusion test performed after priming of the pituitary by pulsatile, subcutaneous infusions of LH-RH (50 micrograms/night for 9 consecutive nights). The fourth patient with HH, who suffered from a pituitary adenoma, failed to display this enhanced secretion of gonadotropins following pituitary priming by intermittent administration of LH-RH. As compared with the patients with HH, 4 patients in whom puberty, although delayed, later occurred spontaneously (pubertas tarda, PT), presented with a considerably more pronounced secretion of LH and FSH during the infusion of LH-RH, and priming by intermittent subcutaneous LH-RH failed to achieve further enhancement of the secretion of LH and FSH during a second infusion test in these patients. The intravenous infusion of LH-RH in combination with a protocol of pituitary priming offers a possibility of distinguishing patients with delayed puberty from those with various forms of hypogonadotropic hypogonadism. PMID:6417915