Synthesizing genetic sequential logic circuit with clock pulse generator.

PubMed

Chuang, Chia-Hua; Lin, Chun-Liang

2014-05-28

Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. For the different cell types, it is supplied with various rhythmic frequencies. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. A cascaded genetic logic circuit generating clock pulse signals is proposed. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal.

[Calculation and analysis of arc temperature field of pulsed TIG welding based on Fowler-Milne method].

PubMed

Xiao, Xiao; Hua, Xue-Ming; Wu, Yi-Xiong; Li, Fang

2012-09-01

Pulsed TIG welding is widely used in industry due to its superior properties, and the measurement of arc temperature is important to analysis of welding process. The relationship between particle densities of Ar and temperature was calculated based on the theory of spectrum, the relationship between emission coefficient of spectra line at 794.8 nm and temperature was calculated, arc image of spectra line at 794.8 nm was captured by high speed camera, and both the Abel inversion and Fowler-Milne method were used to calculate the temperature distribution of pulsed TIG welding.

Modeling T1 and T2 relaxation in bovine white matter

NASA Astrophysics Data System (ADS)

Barta, R.; Kalantari, S.; Laule, C.; Vavasour, I. M.; MacKay, A. L.; Michal, C. A.

2015-10-01

The fundamental basis of T1 and T2 contrast in brain MRI is not well understood; recent literature contains conflicting views on the nature of relaxation in white matter (WM). We investigated the effects of inversion pulse bandwidth on measurements of T1 and T2 in WM. Hybrid inversion-recovery/Carr-Purcell-Meiboom-Gill experiments with broad or narrow bandwidth inversion pulses were applied to bovine WM in vitro. Data were analysed with the commonly used 1D-non-negative least squares (NNLS) algorithm, a 2D-NNLS algorithm, and a four-pool model which was based upon microscopically distinguishable WM compartments (myelin non-aqueous protons, myelin water, non-myelin non-aqueous protons and intra/extracellular water) and incorporated magnetization exchange between adjacent compartments. 1D-NNLS showed that different T2 components had different T1 behaviours and yielded dissimilar results for the two inversion conditions. 2D-NNLS revealed significantly more complicated T1/T2 distributions for narrow bandwidth than for broad bandwidth inversion pulses. The four-pool model fits allow physical interpretation of the parameters, fit better than the NNLS techniques, and fits results from both inversion conditions using the same parameters. The results demonstrate that exchange cannot be neglected when analysing experimental inversion recovery data from WM, in part because it can introduce exponential components having negative amplitude coefficients that cannot be correctly modeled with nonnegative fitting techniques. While assignment of an individual T1 to one particular pool is not possible, the results suggest that under carefully controlled experimental conditions the amplitude of an apparent short T1 component might be used to quantify myelin water.

Gender recognition from vocal source

NASA Astrophysics Data System (ADS)

Sorokin, V. N.; Makarov, I. S.

2008-07-01

Efficiency of automatic recognition of male and female voices based on solving the inverse problem for glottis area dynamics and for waveform of the glottal airflow volume velocity pulse is studied. The inverse problem is regularized through the use of analytical models of the voice excitation pulse and of the dynamics of the glottis area, as well as the model of one-dimensional glottal airflow. Parameters of these models and spectral parameters of the volume velocity pulse are considered. The following parameters are found to be most promising: the instant of maximum glottis area, the maximum derivative of the area, the slope of the spectrum of the glottal airflow volume velocity pulse, the amplitude ratios of harmonics of this spectrum, and the pitch. On the plane of the first two main components in the space of these parameters, an almost twofold decrease in the classification error relative to that for the pitch alone is attained. The male voice recognition probability is found to be 94.7%, and the female voice recognition probability is 95.9%.

Inverse Planning Approach for 3-D MRI-Based Pulse-Dose Rate Intracavitary Brachytherapy in Cervix Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chajon, Enrique; Dumas, Isabelle; Touleimat, Mahmoud B.Sc.

2007-11-01

Purpose: The purpose of this study was to evaluate the inverse planning simulated annealing (IPSA) software for the optimization of dose distribution in patients with cervix carcinoma treated with MRI-based pulsed-dose rate intracavitary brachytherapy. Methods and Materials: Thirty patients treated with a technique using a customized vaginal mold were selected. Dose-volume parameters obtained using the IPSA method were compared with the classic manual optimization method (MOM). Target volumes and organs at risk were delineated according to the Gynecological Brachytherapy Group/European Society for Therapeutic Radiology and Oncology recommendations. Because the pulsed dose rate program was based on clinical experience with lowmore » dose rate, dwell time values were required to be as homogeneous as possible. To achieve this goal, different modifications of the IPSA program were applied. Results: The first dose distribution calculated by the IPSA algorithm proposed a heterogeneous distribution of dwell time positions. The mean D90, D100, and V100 calculated with both methods did not differ significantly when the constraints were applied. For the bladder, doses calculated at the ICRU reference point derived from the MOM differed significantly from the doses calculated by the IPSA method (mean, 58.4 vs. 55 Gy respectively; p = 0.0001). For the rectum, the doses calculated at the ICRU reference point were also significantly lower with the IPSA method. Conclusions: The inverse planning method provided fast and automatic solutions for the optimization of dose distribution. However, the straightforward use of IPSA generated significant heterogeneity in dwell time values. Caution is therefore recommended in the use of inverse optimization tools with clinical relevance study of new dosimetric rules.« less

Synthesizing genetic sequential logic circuit with clock pulse generator

PubMed Central

2014-01-01

Background Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. For the different cell types, it is supplied with various rhythmic frequencies. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. Results This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. Conclusions A cascaded genetic logic circuit generating clock pulse signals is proposed. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal. PMID:24884665

Pulse reflectometry as an acoustical inverse problem: Regularization of the bore reconstruction

NASA Astrophysics Data System (ADS)

Forbes, Barbara J.; Sharp, David B.; Kemp, Jonathan A.

2002-11-01

The theoretical basis of acoustic pulse reflectometry, a noninvasive method for the reconstruction of an acoustical duct from the reflections measured in response to an input pulse, is reviewed in terms of the inversion of the central Fredholm equation. It is known that this is an ill-posed problem in the context of finite-bandwidth experimental signals. Recent work by the authors has proposed the truncated singular value decomposition (TSVD) in the regularization of the transient input impulse response, a non-measurable quantity from which the spatial bore reconstruction is derived. In the present paper we further emphasize the relevance of the singular system framework to reflectometry applications, examining for the first time the transient bases of the system. In particular, by varying the truncation point for increasing condition numbers of the system matrix, it is found that the effects of out-of-bandwidth singular functions on the bore reconstruction can be systematically studied.

Jump-and-return sandwiches: A new family of binomial-like selective inversion sequences with improved performance

NASA Astrophysics Data System (ADS)

Brenner, Tom; Chen, Johnny; Stait-Gardner, Tim; Zheng, Gang; Matsukawa, Shingo; Price, William S.

2018-03-01

A new family of binomial-like inversion sequences, named jump-and-return sandwiches (JRS), has been developed by inserting a binomial-like sequence into a standard jump-and-return sequence, discovered through use of a stochastic Genetic Algorithm optimisation. Compared to currently used binomial-like inversion sequences (e.g., 3-9-19 and W5), the new sequences afford wider inversion bands and narrower non-inversion bands with an equal number of pulses. As an example, two jump-and-return sandwich 10-pulse sequences achieved 95% inversion at offsets corresponding to 9.4% and 10.3% of the non-inversion band spacing, compared to 14.7% for the binomial-like W5 inversion sequence, i.e., they afforded non-inversion bands about two thirds the width of the W5 non-inversion band.

In vivo lactate and beta-hydroxybutyrate editing using a pure-phase refocusing pulse train.

PubMed

Shen, J; Novotny, E J; Rothman, D L

1998-11-01

A refocusing pulse train consisting of a semiselective refocusing pulse and a selective inversion pulse to obtain a pure-phase refocusing at the frequency of maximal excitation of the semiselective refocusing pulse is proposed and applied to in vivo lactate and beta-hydroxybutyrate editing using difference spectroscopy. It is shown, using both rotation matrix theory and phantom experiments, that the soft inversion pulse has to be halved to flank the semiselective pulse to obtain perfect refocusing and cancellation of interfering resonances. The editing method is used to obtain lactate and beta-hydroxybutyrate spectra from the occipital cortex of juvenile epilepsy patients before and after ketogenic diet treatment.

Bubble-based acoustic radiation force using chirp insonation to reduce standing wave effects.

PubMed

Erpelding, Todd N; Hollman, Kyle W; O'Donnell, Matthew

2007-02-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young's modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200 and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size.

Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects

PubMed Central

Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

2007-01-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

Jump-and-return sandwiches: A new family of binomial-like selective inversion sequences with improved performance.

PubMed

Brenner, Tom; Chen, Johnny; Stait-Gardner, Tim; Zheng, Gang; Matsukawa, Shingo; Price, William S

2018-03-01

A new family of binomial-like inversion sequences, named jump-and-return sandwiches (JRS), has been developed by inserting a binomial-like sequence into a standard jump-and-return sequence, discovered through use of a stochastic Genetic Algorithm optimisation. Compared to currently used binomial-like inversion sequences (e.g., 3-9-19 and W5), the new sequences afford wider inversion bands and narrower non-inversion bands with an equal number of pulses. As an example, two jump-and-return sandwich 10-pulse sequences achieved 95% inversion at offsets corresponding to 9.4% and 10.3% of the non-inversion band spacing, compared to 14.7% for the binomial-like W5 inversion sequence, i.e., they afforded non-inversion bands about two thirds the width of the W5 non-inversion band. Copyright © 2018 Elsevier Inc. All rights reserved.

Quantum dynamics of a two-state system induced by a chirped zero-area pulse

NASA Astrophysics Data System (ADS)

Lee, Han-gyeol; Song, Yunheung; Kim, Hyosub; Jo, Hanlae; Ahn, Jaewook

2016-02-01

It is well known that area pulses make Rabi oscillation and chirped pulses in the adiabatic interaction regime induce complete population inversion of a two-state system. Here we show that chirped zero-area pulses could engineer an interplay between the adiabatic evolution and Rabi-like rotations. In a proof-of-principle experiment utilizing spectral chirping of femtosecond laser pulses with a resonant spectral hole, we demonstrate that the chirped zero-area pulses could induce, for example, complete population inversion and return of the cold rubidium atom two-state system. Experimental result agrees well with the theoretically considered overall dynamics, which could be approximately modeled to a Ramsey-like three-pulse interaction, where the x and z rotations are driven by the hole and the main pulse, respectively.

Diagnostics for the optimization of an 11 keV inverse Compton scattering x-ray source

NASA Astrophysics Data System (ADS)

Chauchat, A.-S.; Brasile, J.-P.; Le Flanchec, V.; Nègre, J.-P.; Binet, A.; Ortega, J.-M.

2013-04-01

In a scope of a collaboration between Thales Communications & Security and CEA DAM DIF, 11 keV Xrays were produced by inverse Compton scattering on the ELSA facility. In this type of experiment, X-ray observation lies in the use of accurate electron and laser beam interaction diagnostics and on fitted X-ray detectors. The low interaction probability between < 100 μm width, 12 ps [rms] length electron and photon pulses requires careful optimization of pulse spatial and temporal covering. Another issue was to observe 11 keV X-rays in the ambient radioactive noise of the linear accelerator. For that, we use a very sensitive detection scheme based on radio luminescent screens.

Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

DOE PAGES

Graves, W.  S.; Bessuille, J.; Brown, P.; ...

2014-12-01

A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standingwave linac and rf photoinjector powered by a single ultrastable rf transmitter at X-band rf frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. Themore » entire accelerator is approximately 1 meter long and produces hard x rays tunable over a wide range of photon energies. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is 5 × 10¹¹ photons/second in a 5% bandwidth and the brilliance is 2 × 10¹² photons/(sec mm² mrad² 0.1%) in pulses with rms pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.« less

Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, Southern Japan, based on finite difference calculations of complex traveltimes

USGS Publications Warehouse

Tomatsu, T.; Kumagai, H.; Dawson, P.B.

2001-01-01

We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200-250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex. We use first-arrival times for the shots, which were hand-measured interactively. The waveform data are Fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first-arrival phases. A non-linear inversion method is used to invert 893 first-arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex. Wavefronts for the inversion are calculated with a finite difference method based on the Eikonal equation, which is well suited to estimating the complex traveltimes for the structures of the Kirishima volcano complex, where large structural heterogeneities are expected. The attenuation structure is derived using ray paths derived from the velocity structure. We obtain 3-D velocity and attenuation structures down to 1.5 and 0.5 km below sea level, respectively. High-velocity pipe-like structures with correspondingly low attenuation are found under the summit craters. These pipe-like structures are interpreted as remnant conduits of solidified magma. No evidence of a shallow magma chamber is visible in the tomographic images.

Local T1-T2 distribution measurements in porous media

NASA Astrophysics Data System (ADS)

Vashaee, S.; Li, M.; Newling, B.; MacMillan, B.; Marica, F.; Kwak, H. T.; Gao, J.; Al-harbi, A. M.; Balcom, B. J.

2018-02-01

A novel slice-selective T1-T2 measurement is proposed to measure spatially resolved T1-T2 distributions. An adiabatic inversion pulse is employed for slice-selection. The slice-selective pulse is able to select a quasi-rectangular slice, on the order of 1 mm, at an arbitrary position within the sample. The method does not employ conventional selective excitation in which selective excitation is often accomplished by rotation of the longitudinal magnetization in the slice of interest into the transverse plane, but rather a subtraction based on CPMG data acquired with and without adiabatic inversion slice selection. T1 weighting is introduced during recovery from the inversion associated with slice selection. The local T1-T2 distributions measured are of similar quality to bulk T1-T2 measurements. The new method can be employed to characterize oil-water mixtures and other fluids in porous media. The method is beneficial when a coarse spatial distribution of the components is of interest.

Standoff Detection of Trace Molecules by Remote High Gain Backward Lasing in Air

DTIC Science & Technology

2016-09-17

vapor it is essential. Backward lasing from two simultaneously pumped, closely separated regions in the air provides a method for the reduction of pulse... inversion in an atomic species, leading to “cavityless” lasing. Lasing occurs from the population inversion that is created in the focal volume of...provide a reference that is capable of removing these pulse-to- pulse variations, a second, simultaneous backward lasing beam is generated using the same

Joint design of large-tip-angle parallel RF pulses and blipped gradient trajectories.

PubMed

Cao, Zhipeng; Donahue, Manus J; Ma, Jun; Grissom, William A

2016-03-01

To design multichannel large-tip-angle kT-points and spokes radiofrequency (RF) pulses and gradient waveforms for transmit field inhomogeneity compensation in high field magnetic resonance imaging. An algorithm to design RF subpulse weights and gradient blip areas is proposed to minimize a magnitude least-squares cost function that measures the difference between realized and desired state parameters in the spin domain, and penalizes integrated RF power. The minimization problem is solved iteratively with interleaved target phase updates, RF subpulse weights updates using the conjugate gradient method with optimal control-based derivatives, and gradient blip area updates using the conjugate gradient method. Two-channel parallel transmit simulations and experiments were conducted in phantoms and human subjects at 7 T to demonstrate the method and compare it to small-tip-angle-designed pulses and circularly polarized excitations. The proposed algorithm designed more homogeneous and accurate 180° inversion and refocusing pulses than other methods. It also designed large-tip-angle pulses on multiple frequency bands with independent and joint phase relaxation. Pulses designed by the method improved specificity and contrast-to-noise ratio in a finger-tapping spin echo blood oxygen level dependent functional magnetic resonance imaging study, compared with circularly polarized mode refocusing. A joint RF and gradient waveform design algorithm was proposed and validated to improve large-tip-angle inversion and refocusing at ultrahigh field. © 2015 Wiley Periodicals, Inc.

Electron energy and electron trajectories in an inverse free-electron laser accelerator based on a novel electrostatic wiggler

NASA Astrophysics Data System (ADS)

Nikrah, M.; Jafari, S.

2016-06-01

We expand here a theory of a high-gradient laser-excited electron accelerator based on an inverse free-electron laser (inverse-FEL), but with innovations in the structure and design. The electrostatic wiggler used in our scheme, namely termed the Paul wiggler, is generated by segmented cylindrical electrodes with applied oscillatory voltages {{V}\\text{osc}}(t) over {{90}\\circ} segments. The inverse-FEL interaction can be described by the equations that govern the electron motion in the combined fields of both the laser pulse and Paul wiggler field. A numerical study of electron energy and electron trajectories has been made using the fourth-order Runge-Kutta method. The results indicate that the electron attains a considerable energy at short distances in this device. It is found that if the electron has got sufficient suitable wiggler amplitude intensities, it can not only gain higher energy in longer distances, but also can retain it even after the passing of the laser pulse. In addition, the results reveal that the electron energy gains different peaks for different initial axial velocities, so that a suitable small initial axial velocity of e-beam produces substantially high energy gain. With regard to the transverse confinement of the electron beam in a Paul wiggler, there is no applied axial guide magnetic field in this device.

A simple device for long-term radar cross section recordings.

PubMed

Eskelinen, Pekka; Ruoskanen, Jukka; Peltonen, Jouni

2009-05-01

A sample and hold circuit with settable delay can be used for recording of radar echo amplitude variations having time scales up to 100 s at the selected range bin in systems utilizing short rf pulses. The design is based on two integrated circuits and gives 1% uncertainty for 70 ns pulses. The key benefit is a real-time display of lengthy amplitude variations because the sample rate is defined by the radar pulse repetition frequency. Additionally we get a reduction in file size at least by the inverse of the radar's duty cycle. Examples of 10 and 100 s recordings with a Ka-band short pulse radar are described.

Completely explosive ultracompact high-voltage nanosecond pulse-generating system

NASA Astrophysics Data System (ADS)

Shkuratov, Sergey I.; Talantsev, Evgueni F.; Baird, Jason; Rose, Millard F.; Shotts, Zachary; Altgilbers, Larry L.; Stults, Allen H.

2006-04-01

A conventional pulsed power technology has been combined with an explosive pulsed power technology to produce an autonomous high-voltage power supply. The power supply contained an explosive-driven high-voltage primary power source and a power-conditioning stage. The ultracompact explosive-driven primary power source was based on the physical effect of shock-wave depolarization of high-energy Pb (Zr52Ti48)O3 ferroelectric material. The volume of the energy-carrying ferroelectric elements in the shock-wave ferroelectric generators (SWFEGs) varied from 1.2 to 2.6cm3. The power-conditioning stage was based on the spiral vector inversion generator (VIG). The SWFEG-VIG system demonstrated successful operation and good performance. The amplitude of the output voltage pulse of the SWFEG-VIG system exceeded 90kV, with a rise time of 5.2ns.

Repetitive pulses and laser-induced retinal injury thresholds

NASA Astrophysics Data System (ADS)

Lund, David J.

2007-02-01

Experimental studies with repetitively pulsed lasers show that the ED 50, expressed as energy per pulse, varies as the inverse fourth power of the number of pulses in the exposure, relatively independently of the wavelength, pulse duration, or pulse repetition frequency of the laser. Models based on a thermal damage mechanism cannot readily explain this result. Menendez et al. proposed a probability-summation model for predicting the threshold for a train of pulses based on the probit statistics for a single pulse. The model assumed that each pulse is an independent trial, unaffected by any other pulse in the train of pulses and assumes that the probability of damage for a single pulse is adequately described by the logistic curve. The requirement that the effect of each pulse in the pulse train be unaffected by the effects of other pulses in the train is a showstopper when the end effect is viewed as a thermal effect with each pulse in the train contributing to the end temperature of the target tissue. There is evidence that the induction of cell death by microcavitation bubbles around melanin granules heated by incident laser irradiation can satisfy the condition of pulse independence as required by the probability summation model. This paper will summarize the experimental data and discuss the relevance of the probability summation model given microcavitation as a damage mechanism.

Sensitivity to envelope-based interaural delays at high frequencies: center frequency affects the envelope rate-limitation.

PubMed

Bernstein, Leslie R; Trahiotis, Constantine

2014-02-01

Sensitivity to ongoing interaural temporal disparities (ITDs) was measured using bandpass-filtered pulse trains centered at 4600, 6500, or 9200 Hz. Save for minor differences in the exact center frequencies, those target stimuli were those employed by Majdak and Laback [J. Acoust. Soc. Am. 125, 3903-3913 (2009)]. At each center frequency, threshold ITD was measured for pulse repetition rates ranging from 64 to 609 Hz. The results and quantitative predictions by a cross-correlation-based model indicated that (1) at most pulse repetition rates, threshold ITD increased with center frequency, (2) the cutoff frequency of the putative envelope low-pass filter that determines sensitivity to ITD at high envelope rates appears to be inversely related to center frequency, and (3) both outcomes were accounted for by assuming that, independent of the center frequency, the listeners' decision variable was a constant criterion change in interaural correlation of the stimuli as processed internally. The finding of an inverse relation between center frequency and the envelope rate limitation, while consistent with much prior literature, runs counter to the conclusion reached by Majdak and Laback.

Reconstructing surface wave profiles from reflected acoustic pulses using multiple receivers.

PubMed

Walstead, Sean P; Deane, Grant B

2014-08-01

Surface wave shapes are determined by analyzing underwater reflected acoustic signals collected at multiple receivers. The transmitted signals are of nominal frequency 300 kHz and are reflected off surface gravity waves that are paddle-generated in a wave tank. An inverse processing algorithm reconstructs 50 surface wave shapes over a length span of 2.10 m. The inverse scheme uses a broadband forward scattering model based on Kirchhoff's diffraction formula to determine wave shapes. The surface reconstruction algorithm is self-starting in that source and receiver geometry and initial estimates of wave shape are determined from the same acoustic signals used in the inverse processing. A high speed camera provides ground-truth measurements of the surface wave field for comparison with the acoustically derived surface waves. Within Fresnel zone regions the statistical confidence of the inversely optimized surface profile exceeds that of the camera profile. Reconstructed surfaces are accurate to a resolution of about a quarter-wavelength of the acoustic pulse only within Fresnel zones associated with each source and receiver pair. Multiple isolated Fresnel zones from multiple receivers extend the spatial extent of accurate surface reconstruction while overlapping Fresnel zones increase confidence in the optimized profiles there.

IV INTERNATIONAL CONFERENCE ON ATOM AND MOLECULAR PULSED LASERS (AMPL'99): Critical electron density in a self-contained copper vapour laser in the restricted pulse repetition rate

NASA Astrophysics Data System (ADS)

Yakovlenko, Sergei I.

2000-06-01

One of the mechanisms of the inversion breaking in copper vapour lasers caused by a high prepulse electron density is considered. Inversion breaking occurs at a critical electron density Ne cr. If the prepulse electron density exceeds Ne cr, the electron temperature Te cr cannot reach, during a plasma heating pulse, the temperature of ~2eV required for lasing. A simple estimate of Ne cr is made.

Application of partial inversion pulse to ultrasonic time-domain correlation method to measure the flow rate in a pipe

NASA Astrophysics Data System (ADS)

Wada, Sanehiro; Furuichi, Noriyuki; Shimada, Takashi

2017-11-01

This paper proposes the application of a novel ultrasonic pulse, called a partial inversion pulse (PIP), to the measurement of the velocity profile and flow rate in a pipe using the ultrasound time-domain correlation (UTDC) method. In general, the measured flow rate depends on the velocity profile in the pipe; thus, on-site calibration is the only method of checking the accuracy of on-site flow rate measurements. Flow rate calculation using UTDC is based on the integration of the measured velocity profile. The advantages of this method compared with the ultrasonic pulse Doppler method include the possibility of the velocity range having no limitation and its applicability to flow fields without a sufficient amount of reflectors. However, it has been previously reported that the measurable velocity range for UTDC is limited by false detections. Considering the application of this method to on-site flow fields, the issue of velocity range is important. To reduce the effect of false detections, a PIP signal, which is an ultrasound signal that contains a partially inverted region, was developed in this study. The advantages of the PIP signal are that it requires little additional hardware cost and no additional software cost in comparison with conventional methods. The effects of inversion on the characteristics of the ultrasound transmission were estimated through numerical calculation. Then, experimental measurements were performed at a national standard calibration facility for water flow rate in Japan. The experimental results demonstrate that measurements made using a PIP signal are more accurate and yield a higher detection ratio than measurements using a normal pulse signal.

Counting-loss correction for X-ray spectroscopy using unit impulse pulse shaping.

PubMed

Hong, Xu; Zhou, Jianbin; Ni, Shijun; Ma, Yingjie; Yao, Jianfeng; Zhou, Wei; Liu, Yi; Wang, Min

2018-03-01

High-precision measurement of X-ray spectra is affected by the statistical fluctuation of the X-ray beam under low-counting-rate conditions. It is also limited by counting loss resulting from the dead-time of the system and pile-up pulse effects, especially in a high-counting-rate environment. In this paper a detection system based on a FAST-SDD detector and a new kind of unit impulse pulse-shaping method is presented, for counting-loss correction in X-ray spectroscopy. The unit impulse pulse-shaping method is evolved by inverse deviation of the pulse from a reset-type preamplifier and a C-R shaper. It is applied to obtain the true incoming rate of the system based on a general fast-slow channel processing model. The pulses in the fast channel are shaped to unit impulse pulse shape which possesses small width and no undershoot. The counting rate in the fast channel is corrected by evaluating the dead-time of the fast channel before it is used to correct the counting loss in the slow channel.

Soft x-ray plasma-based seeded multistage amplification chain.

PubMed

Oliva, Eduardo; Fajardo, Marta; Li, Lu; Sebban, Stephane; Ros, David; Zeitoun, Philippe

2012-10-15

To date, plasma-based soft x-ray lasers have demonstrated experimentally 1 μJ, 1 ps (1 MW) pulses. This Letter reports extensive study using time-dependant Maxwell-Bloch code of seeding millimeter scale plasmas that store more than 100 mJ in population inversion. Direct seeding of these plasmas has to overcome very strong amplified spontaneous emission (ASE) as well as prevent wake-field amplification. Below 100 nJ injected energy, seed produces pulses with picosecond duration. To overcome this limitation, a new scheme has been studied, taking advantage of a plasma preamplifier that dramatically increases the seed energy prior to entering the main plasma amplifier leading to ASE and wake-free, fully coherent 21.6 μJ, 80 fs pulses (0.27 GW).

Role of third-order dispersion in chirped Airy pulse propagation in single-mode fibers

NASA Astrophysics Data System (ADS)

Cai, Wangyang; Wang, Lei; Wen, Shuangchun

2018-04-01

The dynamic propagation of the initial chirped Airy pulse in single-mode fibers is studied numerically, special attention being paid to the role of the third-order dispersion (TOD). It is shown that for the positive TOD, the Airy pulse experiences inversion irrespective of the sign of initial chirp. The role of TOD in the dynamic propagation of the initial chirped Airy pulse depends on the combined sign of the group-velocity dispersion (GVD) and the initial chirp. If the GVD and chirp have the opposite signs, the chirped Airy pulse compresses first and passes through a breakdown area, then reconstructs a new Airy pattern with opposite acceleration, with the breakdown area becoming small and the main peak of the new Airy pattern becoming asymmetric with an oscillatory structure due to the positive TOD. If the GVD and chirp have the same signs, the finite-energy Airy pulse compresses to a focal point and then inverses its acceleration, in the case of positive TOD, the distance to the focal point becoming smaller. At zero-dispersion point, the finite-energy Airy pulse inverses to the opposite acceleration at a focal point, with the tight-focusing effect being reduced by initial chirp. Under the effect of negative TOD, the initial chirped Airy pulse disperses and the lobes split. In addition, in the anomalous dispersion region, for strong nonlinearity, the initial chirped Airy pulse splits and enters a soliton shedding regime.

Picosecond pulses from wavelength-swept continuous-wave Fourier domain mode-locked lasers.

PubMed

Eigenwillig, Christoph M; Wieser, Wolfgang; Todor, Sebastian; Biedermann, Benjamin R; Klein, Thomas; Jirauschek, Christian; Huber, Robert

2013-01-01

Ultrafast lasers have a crucial function in many fields of science; however, up to now, high-energy pulses directly from compact, efficient and low-power semiconductor lasers are not available. Therefore, we introduce a new approach based on temporal compression of the continuous-wave, wavelength-swept output of Fourier domain mode-locked lasers, where a narrowband optical filter is tuned synchronously to the round-trip time of light in a kilometre-long laser cavity. So far, these rapidly swept lasers enabled orders-of-magnitude speed increase in optical coherence tomography. Here we report on the generation of ~60-70 ps pulses at 390 kHz repetition rate. As energy is stored optically in the long-fibre delay line and not as population inversion in the laser-gain medium, high-energy pulses can now be generated directly from a low-power, compact semiconductor-based oscillator. Our theory predicts subpicosecond pulses with this new technique in the future.

Picosecond pulses from wavelength-swept continuous-wave Fourier domain mode-locked lasers

NASA Astrophysics Data System (ADS)

Eigenwillig, Christoph M.; Wieser, Wolfgang; Todor, Sebastian; Biedermann, Benjamin R.; Klein, Thomas; Jirauschek, Christian; Huber, Robert

2013-05-01

Ultrafast lasers have a crucial function in many fields of science; however, up to now, high-energy pulses directly from compact, efficient and low-power semiconductor lasers are not available. Therefore, we introduce a new approach based on temporal compression of the continuous-wave, wavelength-swept output of Fourier domain mode-locked lasers, where a narrowband optical filter is tuned synchronously to the round-trip time of light in a kilometre-long laser cavity. So far, these rapidly swept lasers enabled orders-of-magnitude speed increase in optical coherence tomography. Here we report on the generation of ~60-70 ps pulses at 390 kHz repetition rate. As energy is stored optically in the long-fibre delay line and not as population inversion in the laser-gain medium, high-energy pulses can now be generated directly from a low-power, compact semiconductor-based oscillator. Our theory predicts subpicosecond pulses with this new technique in the future.

Using Poisson-regularized inversion of Bremsstrahlung emission to extract full electron energy distribution functions from x-ray pulse-height detector data

NASA Astrophysics Data System (ADS)

Swanson, C.; Jandovitz, P.; Cohen, S. A.

2018-02-01

We measured Electron Energy Distribution Functions (EEDFs) from below 200 eV to over 8 keV and spanning five orders-of-magnitude in intensity, produced in a low-power, RF-heated, tandem mirror discharge in the PFRC-II apparatus. The EEDF was obtained from the x-ray energy distribution function (XEDF) using a novel Poisson-regularized spectrum inversion algorithm applied to pulse-height spectra that included both Bremsstrahlung and line emissions. The XEDF was measured using a specially calibrated Amptek Silicon Drift Detector (SDD) pulse-height system with 125 eV FWHM at 5.9 keV. The algorithm is found to out-perform current leading x-ray inversion algorithms when the error due to counting statistics is high.

Numerical developments for short-pulsed Near Infra-Red laser spectroscopy. Part I: direct treatment

NASA Astrophysics Data System (ADS)

Boulanger, Joan; Charette, André

2005-03-01

This two part study is devoted to the numerical treatment of short-pulsed laser near infra-red spectroscopy. The overall goal is to address the possibility of numerical inverse treatment based on a recently developed direct model to solve the transient radiative transfer equation. This model has been constructed in order to incorporate the last improvements in short-pulsed laser interaction with semi-transparent media and combine a discrete ordinates computing of the implicit source term appearing in the radiative transfer equation with an explicit treatment of the transport of the light intensity using advection schemes, a method encountered in reactive flow dynamics. The incident collimated beam is analytically solved through Bouger Beer Lambert extinction law. In this first part, the direct model is extended to fully non-homogeneous materials and tested with two different spatial schemes in order to be adapted to the inversion methods presented in the following second part. As a first point, fundamental methods and schemes used in the direct model are presented. Then, tests are conducted by comparison with numerical simulations given as references. In a third and last part, multi-dimensional extensions of the code are provided. This allows presentation of numerical results of short pulses propagation in 1, 2 and 3D homogeneous and non-homogeneous materials given some parametrical studies on medium properties and pulse shape. For comparison, an integral method adapted to non-homogeneous media irradiated by a pulsed laser beam is also developed for the 3D case.

In vivo repeatability of the pulse wave inverse problem in human carotid arteries.

PubMed

McGarry, Matthew; Nauleau, Pierre; Apostolakis, Iason; Konofagou, Elisa

2017-11-07

Accurate arterial stiffness measurement would improve diagnosis and monitoring for many diseases. Atherosclerotic plaques and aneurysms are expected to involve focal changes in vessel wall properties; therefore, a method to image the stiffness variation would be a valuable clinical tool. The pulse wave inverse problem (PWIP) fits unknown parameters from a computational model of arterial pulse wave propagation to ultrasound-based measurements of vessel wall displacements by minimizing the difference between the model and measured displacements. The PWIP has been validated in phantoms, and this study presents the first in vivo demonstration. The common carotid arteries of five healthy volunteers were imaged five times in a single session with repositioning of the probe and subject between each scan. The 1D finite difference computational model used in the PWIP spanned from the start of the transducer to the carotid bifurcation, where a resistance outlet boundary condition was applied to approximately model the downstream reflection of the pulse wave. Unknown parameters that were estimated by the PWIP included a 10-segment linear piecewise compliance distribution and 16 discrete cosine transformation coefficients for each of the inlet boundary conditions. Input data was selected to include pulse waves resulting from the primary pulse and dicrotic notch. The recovered compliance maps indicate that the compliance increases close to the bifurcation, and the variability of the average pulse wave velocity estimated through the PWIP is on the order of 11%, which is similar to that of the conventional processing technique which tracks the wavefront arrival time (13%). Copyright © 2017 Elsevier Ltd. All rights reserved.

Dynamic chirp control of all-optical format-converted pulsed data from a multi-wavelength inverse-optical-comb injected semiconductor optical amplifier.

PubMed

Lin, Gong-Ru; Pan, Ci-Ling; Yu, Kun-Chieh

2007-10-01

By spectrally and temporally reshaping the gain-window of a traveling-wave semiconductor optical amplifier (TWSOA) with a backward injected multi- or single-wavelength inverse-optical-comb, we theoretically and experimentally investigate the dynamic frequency chirp of the all-optical 10GBit/s Return-to-Zero (RZ) data-stream format-converted from the TWSOA under strong cross-gain depletion scheme. The multi-wavelength inverse-optical-comb injection effectively depletes the TWSOA gain spectrally and temporally, remaining a narrow gain-window and a reduced spectral linewidth and provide a converted RZ data with a smaller peak-to-peak frequency chirp of 6.7 GHz. Even at high inverse-optical-comb injection power and highly biased current condition for improving the operational bit-rate, the chirp of the multi-wavelength-injection converted RZ pulse is still 2.1-GHz smaller than that obtained by using single-wavelength injection at a cost of slight pulse-width broadening by 1 ps.

Non-Contrast-Enhanced Renal Angiography Using Multiple Inversion Recovery and Alternating TR Balanced Steady State Free Precession

PubMed Central

Dong, Hattie Z.; Worters, Pauline W.; Wu, Holden H.; Ingle, R. Reeve; Vasanawala, Shreyas S.; Nishimura, Dwight G.

2014-01-01

Non-contrast enhanced renal angiography techniques based on balanced steady state free precession (SSFP) avoid external contrast agents, take advantage of high inherent blood signal from the T2/T1 contrast mechanism, and have short SSFP acquisition times. However, background suppression is limited; inflow times are inflexible; labeling region is difficult to define when tagging arterial flow; and scan times are long. To overcome these limitations, we propose the use of multiple inversion recovery (MIR) preparatory pulses combined with alternating TR balanced SSFP (ATR-SSFP) to produce renal angiograms. MIR uses selective spatial saturation followed by four global inversion recovery pulses to concurrently null a wide range of background T1 species while allowing for adjustable inflow times; ATR-SSFP maintains vessel contrast and provides added fat suppression. The high level of suppression enables imaging in 3D as well as projective 2D formats, the latter of which has a scan time down to one heartbeat. In vivo studies at 1.5 T demonstrate the superior vessel contrast of this technique. PMID:23172805

Amplifying modeling for broad bandwidth pulse in Nd:glass based on hybrid-broaden mechanism

NASA Astrophysics Data System (ADS)

Su, J.; Liu, L.; Luo, B.; Wang, W.; Jing, F.; Wei, X.; Zhang, X.

2008-05-01

In this paper, the cross relaxation time is proposed to combine the homogeneous and inhomogeneous broaden mechanism for broad bandwidth pulse amplification model. The corresponding velocity equation, which can describe the response of inverse population on upper and low energy level of gain media to different frequency of pulse, is also put forward. The gain saturation and energy relaxation effect are also included in the velocity equation. Code named CPAP has been developed to simulate the amplifying process of broad bandwidth pulse in multi-pass laser system. The amplifying capability of multi-pass laser system is evaluated and gain narrowing and temporal shape distortion are also investigated when bandwidth of pulse and cross relaxation time of gain media are different. Results can benefit the design of high-energy PW laser system in LFRC, CAEP.

DLTPulseGenerator: A library for the simulation of lifetime spectra based on detector-output pulses

NASA Astrophysics Data System (ADS)

Petschke, Danny; Staab, Torsten E. M.

2018-01-01

The quantitative analysis of lifetime spectra relevant in both life and materials sciences presents one of the ill-posed inverse problems and, hence, leads to most stringent requirements on the hardware specifications and the analysis algorithms. Here we present DLTPulseGenerator, a library written in native C++ 11, which provides a simulation of lifetime spectra according to the measurement setup. The simulation is based on pairs of non-TTL detector output-pulses. Those pulses require the Constant Fraction Principle (CFD) for the determination of the exact timing signal and, thus, the calculation of the time difference i.e. the lifetime. To verify the functionality, simulation results were compared to experimentally obtained data using Positron Annihilation Lifetime Spectroscopy (PALS) on pure tin.

Using Poisson-regularized inversion of Bremsstrahlung emission to extract full electron energy distribution functions from x-ray pulse-height detector data

DOE PAGES

Swanson, C.; Jandovitz, P.; Cohen, S. A.

2018-02-27

We measured Electron Energy Distribution Functions (EEDFs) from below 200 eV to over 8 keV and spanning five orders-of-magnitude in intensity, produced in a low-power, RF-heated, tandem mirror discharge in the PFRC-II apparatus. The EEDF was obtained from the x-ray energy distribution function (XEDF) using a novel Poisson-regularized spectrum inversion algorithm applied to pulse-height spectra that included both Bremsstrahlung and line emissions. The XEDF was measured using a specially calibrated Amptek Silicon Drift Detector (SDD) pulse-height system with 125 eV FWHM at 5.9 keV. Finally, the algorithm is found to out-perform current leading x-ray inversion algorithms when the error duemore » to counting statistics is high.« less

Using Poisson-regularized inversion of Bremsstrahlung emission to extract full electron energy distribution functions from x-ray pulse-height detector data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swanson, C.; Jandovitz, P.; Cohen, S. A.

We measured Electron Energy Distribution Functions (EEDFs) from below 200 eV to over 8 keV and spanning five orders-of-magnitude in intensity, produced in a low-power, RF-heated, tandem mirror discharge in the PFRC-II apparatus. The EEDF was obtained from the x-ray energy distribution function (XEDF) using a novel Poisson-regularized spectrum inversion algorithm applied to pulse-height spectra that included both Bremsstrahlung and line emissions. The XEDF was measured using a specially calibrated Amptek Silicon Drift Detector (SDD) pulse-height system with 125 eV FWHM at 5.9 keV. Finally, the algorithm is found to out-perform current leading x-ray inversion algorithms when the error duemore » to counting statistics is high.« less

Pulse-Inversion Subharmonic Ultrafast Active Cavitation Imaging in Tissue Using Fast Eigenspace-Based Adaptive Beamforming and Cavitation Deconvolution.

PubMed

Bai, Chen; Xu, Shanshan; Duan, Junbo; Jing, Bowen; Yang, Miao; Wan, Mingxi

2017-08-01

Pulse-inversion subharmonic (PISH) imaging can display information relating to pure cavitation bubbles while excluding that of tissue. Although plane-wave-based ultrafast active cavitation imaging (UACI) can monitor the transient activities of cavitation bubbles, its resolution and cavitation-to-tissue ratio (CTR) are barely satisfactory but can be significantly improved by introducing eigenspace-based (ESB) adaptive beamforming. PISH and UACI are a natural combination for imaging of pure cavitation activity in tissue; however, it raises two problems: 1) the ESB beamforming is hard to implement in real time due to the enormous amount of computation associated with the covariance matrix inversion and eigendecomposition and 2) the narrowband characteristic of the subharmonic filter will incur a drastic degradation in resolution. Thus, in order to jointly address these two problems, we propose a new PISH-UACI method using novel fast ESB (F-ESB) beamforming and cavitation deconvolution for nonlinear signals. This method greatly reduces the computational complexity by using F-ESB beamforming through dimensionality reduction based on principal component analysis, while maintaining the high quality of ESB beamforming. The degraded resolution is recovered using cavitation deconvolution through a modified convolution model and compressive deconvolution. Both simulations and in vitro experiments were performed to verify the effectiveness of the proposed method. Compared with the ESB-based PISH-UACI, the entire computation of our proposed approach was reduced by 99%, while the axial resolution gain and CTR were increased by 3 times and 2 dB, respectively, confirming that satisfactory performance can be obtained for monitoring pure cavitation bubbles in tissue erosion.

Sodium imaging of the human knee using soft inversion recovery fluid attenuation.

PubMed

Feldman, Rebecca E; Stobbe, Robert; Watts, Alexander; Beaulieu, Christian

2013-09-01

Sodium signal strength in MRI is low when compared with (1)H. Thus, image voxel volumes must be relatively large in order to produce a sufficient signal-to-noise ratio (SNR). The measurement of sodium in cartilage is hindered by conflation with signal from the adjacent fluid spaces. Inversion recovery can be used to null signal from fluid, but reduces SNR. The purpose of this work was to optimize inversion recovery sodium MRI to enhance cartilage SNR while nulling fluid. Sodium relaxation was first measured for knee cartilage (T1=21±1 ms, T(2 fast)(∗)=0.8±0.2 ms, T(2 slow)(∗)=19.7±0.5 ms) and fluid (T1=48±3 ms, T2(∗)=47±4 ms) in nine healthy subjects at 4.7 T. The rapid relaxation of cartilage in relation to fluid permits the use of a lengthened inversion pulse to preferentially invert the fluid components. Simulations of inversion pulse length were performed to yield a cartilage SNR enhancing combination of parameters that nulled fluid. The simulations were validated in a phantom and then in vivo. B0 inhomogeneity was measured and the effect of off-resonance during the soft inversion pulse was assessed with simulation. Soft inversion recovery yielded twice the SNR and much improved sodium images of cartilage in human knee with little confounding signal from fluid. Copyright © 2013 Elsevier Inc. All rights reserved.

In VivoLactate Editing with Simultaneous Detection of Choline, Creatine, NAA, and Lipid Singlets at 1.5 T Using PRESS Excitation with Applications to the Study of Brain and Head and Neck Tumors

NASA Astrophysics Data System (ADS)

Star-Lack, Josh; Spielman, Daniel; Adalsteinsson, Elfar; Kurhanewicz, John; Terris, David J.; Vigneron, Daniel B.

1998-08-01

Two T2-independentJ-difference lactate editing schemes for the PRESS magnetic resonance spectroscopy localization sequence are introduced. The techniques, which allow for simultaneous acquisition of the lactate doublet (1.3 ppm) and edited singlets upfield of and including choline (3.2 ppm), exploit the dependence of the in-phase intensity of the methyl doublet upon the time interval separating two inversion (BASING) pulses applied to its coupling partner after initial excitation. Editing method 1, which allows for echo times TE =n/J(n= 1, 2, 3, …), alters the BASING carrier frequency for each of two cycles so that, for one cycle, the quartet is inverted, whereas, for the other cycle, the quartet is unaffected. Method 2, which also provides water suppression, allows for editing for TE > 1/Jby alternating, between cycles, the time interval separating the inversion pulses. Experimental results were obtained at 1.5 T using a Shinnar Le-Roux-designed maximum phase inversion pulse with a filter transition bandwidth of 55 Hz. Spectra were acquired from phantoms andin vivofrom the human brain and neck. In a neck muscle study, the lipid suppression factor, achieved partly through the use of a novel phase regularization algorithm, was measured to be over 103. Spectra acquired from a primary brain and a metastatic neck tumor demonstrated the presence of lactate and choline signals consistent with abnormal spectral patterns. The advantages and limitations of the methods are analyzed theoretically and experimentally, and significance of the results is discussed.

Electromagnetic inverse scattering

NASA Technical Reports Server (NTRS)

Bojarski, N. N.

1972-01-01

A three-dimensional electromagnetic inverse scattering identity, based on the physical optics approximation, is developed for the monostatic scattered far field cross section of perfect conductors. Uniqueness of this inverse identity is proven. This identity requires complete scattering information for all frequencies and aspect angles. A nonsingular integral equation is developed for the arbitrary case of incomplete frequence and/or aspect angle scattering information. A general closed-form solution to this integral equation is developed, which yields the shape of the scatterer from such incomplete information. A specific practical radar solution is presented. The resolution of this solution is developed, yielding short-pulse target resolution radar system parameter equations. The special cases of two- and one-dimensional inverse scattering and the special case of a priori knowledge of scatterer symmetry are treated in some detail. The merits of this solution over the conventional radar imaging technique are discussed.

A posteriori error estimates in voice source recovery

NASA Astrophysics Data System (ADS)

Leonov, A. S.; Sorokin, V. N.

2017-12-01

The inverse problem of voice source pulse recovery from a segment of a speech signal is under consideration. A special mathematical model is used for the solution that relates these quantities. A variational method of solving inverse problem of voice source recovery for a new parametric class of sources, that is for piecewise-linear sources (PWL-sources), is proposed. Also, a technique for a posteriori numerical error estimation for obtained solutions is presented. A computer study of the adequacy of adopted speech production model with PWL-sources is performed in solving the inverse problems for various types of voice signals, as well as corresponding study of a posteriori error estimates. Numerical experiments for speech signals show satisfactory properties of proposed a posteriori error estimates, which represent the upper bounds of possible errors in solving the inverse problem. The estimate of the most probable error in determining the source-pulse shapes is about 7-8% for the investigated speech material. It is noted that a posteriori error estimates can be used as a criterion of the quality for obtained voice source pulses in application to speaker recognition.

Terahertz spin current pulses controlled by magnetic heterostructures

NASA Astrophysics Data System (ADS)

Kampfrath, T.; Battiato, M.; Maldonado, P.; Eilers, G.; Nötzold, J.; Mährlein, S.; Zbarsky, V.; Freimuth, F.; Mokrousov, Y.; Blügel, S.; Wolf, M.; Radu, I.; Oppeneer, P. M.; Münzenberg, M.

2013-04-01

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters.

Fear and C-reactive protein cosynergize annual pulse increases in healthy adults

PubMed Central

Shenhar-Tsarfaty, Shani; Yayon, Nadav; Waiskopf, Nir; Shapira, Itzhak; Toker, Sharon; Zaltser, David; Berliner, Shlomo; Ritov, Ya'acov; Soreq, Hermona

2015-01-01

Recent international terror outbreaks notably involve long-term mental health risks to the exposed population, but whether physical health risks are also anticipated has remained unknown. Here, we report fear of terror-induced annual increases in resting heart rate (pulse), a notable risk factor of all-cause mortality. Partial least squares analysis based on 325 measured parameters successfully predicted annual pulse increases, inverse to the expected age-related pulse decline, in approximately 4.1% of a cohort of 17,380 apparently healthy active Israeli adults. Nonbiased hierarchical regression analysis among 27 of those parameters identified pertinent fear of terror combined with the inflammatory biomarker C-reactive protein as prominent coregulators of the observed annual pulse increases. In comparison, basal pulse primarily depended on general physiological parameters and reduced cholinergic control over anxiety and inflammation, together indicating that consistent exposure to terror threats ignites fear-induced exacerbation of preexisting neuro-immune risks of all-cause mortality. PMID:25535364

Reaction time to changes in the tempo of acoustic pulse trains.

NASA Technical Reports Server (NTRS)

Smith, R. P.; Warm, J. S.; Westendorf, D. H.

1973-01-01

Investigation of the ability of human observers to detect accelerations and decelerations in the rate of presentation of pulsed stimuli, i.e., changes in the tempo of acoustic pulse trains. Response times to accelerations in tempo were faster than to decelerations. Overall speed of response was inversely related to the pulse repetition rate.

Development of a Watt-level gamma-ray source based on high-repetition-rate inverse Compton scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mihalcea, D.; Murokh, A.; Piot, P.

2017-07-01

A high-brilliance (~10 22 photon s -1 mm -2 mrad -2 /0.1%) gamma-ray source experiment is currently being planned at Fermilab (E γ≃1.1 MeV). The source implements a high-repetition-rate inverse Compton scattering by colliding electron bunches formed in a ~300-MeV superconducting linac with a high-intensity laser pulse. This paper describes the design rationale along with some of technical challenges associated to producing high-repetition-rate collision. The expected performances of the gamma-ray source are also presented.

Inverse problems in 1D hemodynamics on systemic networks: a sequential approach.

PubMed

Lombardi, D

2014-02-01

In this work, a sequential approach based on the unscented Kalman filter is applied to solve inverse problems in 1D hemodynamics, on a systemic network. For instance, the arterial stiffness is estimated by exploiting cross-sectional area and mean speed observations in several locations of the arteries. The results are compared with those ones obtained by estimating the pulse wave velocity and the Moens-Korteweg formula. In the last section, a perspective concerning the identification of the terminal models parameters and peripheral circulation (modeled by a Windkessel circuit) is presented. Copyright © 2013 John Wiley & Sons, Ltd.

Nonresonant interaction of ultrashort electromagnetic pulses with multilevel quantum systems

NASA Technical Reports Server (NTRS)

Belenov, E.; Isakov, V.; Nazarkin, A.

1994-01-01

Some features of the excitation of multilevel quantum systems under the action of electromagnetic pulses which are shorter than the inverse frequency of interlevel transitions are considered. It is shown that the interaction is characterized by a specific type of selectivity which is not connected with the resonant absorption of radiation. The simplest three-level model displays the inverse population of upper levels. The effect of an ultrashort laser pulse on a multilevel molecule was regarded as an instant reception of the oscillation velocity by the oscillator and this approach showed an effective excitation and dissociation of the molecule. The estimations testify to the fact that these effects can be observed using modern femtosecond lasers.

Excitability in semiconductor microring lasers: Experimental and theoretical pulse characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gelens, L.; Coomans, W.; Van der Sande, G.

2010-12-15

We characterize the operation of semiconductor microring lasers in an excitable regime. Our experiments reveal a statistical distribution of the characteristics of noise-triggered optical pulses that is not observed in other excitable systems. In particular, an inverse correlation exists between the pulse amplitude and duration. Numerical simulations and an interpretation in an asymptotic phase space confirm and explain these experimentally observed pulse characteristics.

Nonlinear pulse compression in pulse-inversion fundamental imaging.

PubMed

Cheng, Yun-Chien; Shen, Che-Chou; Li, Pai-Chi

2007-04-01

Coded excitation can be applied in ultrasound contrast agent imaging to enhance the signal-to-noise ratio with minimal destruction of the microbubbles. Although the axial resolution is usually compromised by the requirement for a long coded transmit waveforms, this can be restored by using a compression filter to compress the received echo. However, nonlinear responses from microbubbles may cause difficulties in pulse compression and result in severe range side-lobe artifacts, particularly in pulse-inversion-based (PI) fundamental imaging. The efficacy of pulse compression in nonlinear contrast imaging was evaluated by investigating several factors relevant to PI fundamental generation using both in-vitro experiments and simulations. The results indicate that the acoustic pressure and the bubble size can alter the nonlinear characteristics of microbubbles and change the performance of the compression filter. When nonlinear responses from contrast agents are enhanced by using a higher acoustic pressure or when more microbubbles are near the resonance size of the transmit frequency, higher range side lobes are produced in both linear imaging and PI fundamental imaging. On the other hand, contrast detection in PI fundamental imaging significantly depends on the magnitude of the nonlinear responses of the bubbles and thus the resultant contrast-to-tissue ratio (CTR) still increases with acoustic pressure and the nonlinear resonance of microbubbles. It should be noted, however, that the CTR in PI fundamental imaging after compression is consistently lower than that before compression due to obvious side-lobe artifacts. Therefore, the use of coded excitation is not beneficial in PI fundamental contrast detection.

Coexisting nanoscale inverse spinel and rock salt crystallographic phases in NiCo2O4 epitaxial thin films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Sharona, H.; Loukya, B.; Bhat, U.; Sahu, R.; Vishal, B.; Silwal, P.; Gupta, A.; Datta, R.

2017-12-01

The origin of alternating wavy dark-bright stripe-like contrast in strain contrast transmission electron microscopy images of NiCo2O4 (NCO) epitaxial thin films grown by pulsed laser deposition has been investigated. The nanoscale stripe-like pattern is determined to be associated with coexisting rock salt (RS) and inverse spinel crystal phases. The presence of two different phases, not addressed in previous reports, is experimentally confirmed by both electron diffraction and high resolution transmission electron microscopy imaging. First principles based calculations, together with compressive strain present in the films, support the formation of such coexisting crystallographic phases in NCO. Similar microstructural patterns and RS structure are not observed in epitaxial films of two other oxides of the spinel family, namely, NiFe2O4 and CoFe2O4. A correlation between the coexisting structures and the macroscopic physical properties of NCO is discussed.

Transmission loss measurement of acoustic material using time-domain pulse-separation method (L).

PubMed

Sun, Liang; Hou, Hong

2011-04-01

An alternative method for measuring the normal incidence sound transmission loss (nSTL) is presented in this paper based on the time-domain separation of so-called Butterworth pulse with a short-duration time about 1 ms in a standing wave tube. During the generation process of the pulse, inverse filter principle was adopted to compensate the loudspeaker response, besides this, the effect of the characteristics of tube termination can be eliminated through the generation process of the pulse so as to obtain a single plane pulse wave in the standing wave tube which makes the nSTL measurement very simple. A polyurethane foam material with low transmission loss and a kind of rubber material with relatively high transmission loss are used to verify the proposed method. When compared with the traditional two-load method, a relatively good agreement between these two methods can be observed. The main error of this method results from the measuring accuracy of the amplitude of transmission coefficient.

Bilateral transit time assessment of upper and lower limbs as a surrogate ankle brachial index marker.

PubMed

Foo, Jong Yong Abdiel

2008-01-01

Ankle brachial index is useful in monitoring the pathogenesis of peripheral arterial occlusive diseases. Sphygmomanometer is the standard instrument widely used but frequent prolonged monitoring can be less comfortable for patients. Pulse transit time is known to be inversely correlated with blood pressure and a ratio-based pulse transit time measurement has been proposed as a surrogate ankle brachial index marker. In this study, 17 normotensive adults (9 men; aged 25.4 +/- 3.9 years) were recruited. Two postural change test activities were performed to induce changes in the stiffness of the arterial wall of the moved periphery. Results showed that only readings from the limbs that adopted a new posture registered significant blood pressure and pulse transit time changes (P < .05). Furthermore, there was significant correlation between the ankle brachial index and pulse transit time ratio measure for both test activities (R(2) > or = 0.704). The findings herein suggest that pulse transit time ratio is a surrogate and accommodating ankle brachial index marker.

Highly Efficient Vector-Inversion Pulse Generators

NASA Technical Reports Server (NTRS)

Rose, Franklin

2004-01-01

Improved transmission-line pulse generators of the vector-inversion type are being developed as lightweight sources of pulsed high voltage for diverse applications, including spacecraft thrusters, portable x-ray imaging systems, impulse radar systems, and corona-discharge systems for sterilizing gases. In this development, more than the customary attention is paid to principles of operation and details of construction so as to the maximize the efficiency of the pulse-generation process while minimizing the sizes of components. An important element of this approach is segmenting a pulse generator in such a manner that the electric field in each segment is always below the threshold for electrical breakdown. One design of particular interest, a complete description of which was not available at the time of writing this article, involves two parallel-plate transmission lines that are wound on a mandrel, share a common conductor, and are switched in such a manner that the pulse generator is divided into a "fast" and a "slow" section. A major innovation in this design is the addition of ferrite to the "slow" section to reduce the size of the mandrel needed for a given efficiency.

High duty cycle inverse Compton scattering X-ray source

DOE PAGES

Ovodenko, A.; Agustsson, R.; Babzien, M.; ...

2016-12-22

Inverse Compton Scattering (ICS) is an emerging compact X-ray source technology, where the small source size and high spectral brightness are of interest for multitude of applications. However, to satisfy the practical flux requirements, a high-repetition-rate ICS system needs to be developed. To this end, this article reports the experimental demonstration of a high peak brightness ICS source operating in a burst mode at 40 MHz. A pulse train interaction has been achieved by recirculating a picosecond CO 2 laser pulse inside an active optical cavity synchronized to the electron beam. The pulse train ICS performance has been characterized atmore » 5- and 15- pulses per train and compared to a single pulse operation under the same operating conditions. Lastly, with the observed near-linear X-ray photon yield gain due to recirculation, as well as noticeably higher operational reliability, the burst-mode ICS offers a great potential for practical scalability towards high duty cycles.« less

Models of brachial to finger pulse wave distortion and pressure decrement.

PubMed

Gizdulich, P; Prentza, A; Wesseling, K H

1997-03-01

To model the pulse wave distortion and pressure decrement occurring between brachial and finger arteries. Distortion reversion and decrement correction were also our aims. Brachial artery pressure was recorded intra-arterially and finger pressure was recorded non-invasively by the Finapres technique in 53 adult human subjects. Mean pressure was subtracted from each pressure waveform and Fourier analysis applied to the pulsations. A distortion model was estimated for each subject and averaged over the group. The average inverse model was applied to the full finger pressure waveform. The pressure decrement was modelled by multiple regression on finger systolic and diastolic levels. Waveform distortion could be described by a general, frequency dependent model having a resonance at 7.3 Hz. The general inverse model has an anti-resonance at this frequency. It converts finger to brachial pulsations thereby reducing average waveform distortion from 9.7 (s.d. 3.2) mmHg per sample for the finger pulse to 3.7 (1.7) mmHg for the converted pulse. Systolic and diastolic level differences between finger and brachial arterial pressures changed from -4 (15) and -8 (11) to +8 (14) and +8 (12) mmHg, respectively, after inverse modelling, with pulse pressures correct on average. The pressure decrement model reduced both the mean and the standard deviation of systolic and diastolic level differences to 0 (13) and 0 (8) mmHg. Diastolic differences were thus reduced most. Brachial to finger pulse wave distortion due to wave reflection in arteries is almost identical in all subjects and can be modelled by a single resonance. The pressure decrement due to flow in arteries is greatest for high pulse pressures superimposed on low means.

Fast and error-resilient coherent control in an atomic vapor

NASA Astrophysics Data System (ADS)

He, Yizun; Wang, Mengbing; Zhao, Jian; Qiu, Liyang; Wang, Yuzhuo; Fang, Yami; Zhao, Kaifeng; Wu, Saijun

2017-04-01

Nanosecond chirped pulses from an optical arbitrary waveform generator is applied to both invert and coherently split the D1 line population of potassium vapor within a laser focal volume of 2X105 μ m3. The inversion fidelity of f>96%, mainly limited by spontaneous emission during the nanosecond pulse, is inferred from both probe light transmission and superfluorescence emission. The nearly perfect inversion is uniformly achieved for laser intensity varying over an order of magnitude, and is tolerant to detuning error of more than 1000 times the D1 transition linewidth. We further demonstrate enhanced intensity error resilience with multiple chirped pulses and ``universal composite pulses''. This fast and robust coherent control technique should find wide applications in the field of quantum optics, laser cooling, and atom interferometry. This work is supported by National Key Research Program of China under Grant No. 2016YFA0302000, and NNSFC under Grant No. 11574053.

Distance and Cable Length Measurement System

PubMed Central

Hernández, Sergio Elias; Acosta, Leopoldo; Toledo, Jonay

2009-01-01

A simple, economic and successful design for distance and cable length detection is presented. The measurement system is based on the continuous repetition of a pulse that endlessly travels along the distance to be detected. There is a pulse repeater at both ends of the distance or cable to be measured. The endless repetition of the pulse generates a frequency that varies almost inversely with the distance to be measured. The resolution and distance or cable length range could be adjusted by varying the repetition time delay introduced at both ends and the measurement time. With this design a distance can be measured with centimeter resolution using electronic system with microsecond resolution, simplifying classical time of flight designs which require electronics with picosecond resolution. This design was also applied to position measurement. PMID:22303169

A Solution of the System of Partial Differential Equations Which Describe the Propagation of Acoustic Pulses in Layered Fluid Media,

DTIC Science & Technology

transformed problem. Then using several changes of integration variables, the inverse transform is obtained by direct identification without recourse to the complex Laplace transform inversion integral. (Author)

Validation of the inverse pulse wave transit time series as surrogate of systolic blood pressure in MVAR modeling.

PubMed

Giassi, Pedro; Okida, Sergio; Oliveira, Maurício G; Moraes, Raimes

2013-11-01

Short-term cardiovascular regulation mediated by the sympathetic and parasympathetic branches of the autonomic nervous system has been investigated by multivariate autoregressive (MVAR) modeling, providing insightful analysis. MVAR models employ, as inputs, heart rate (HR), systolic blood pressure (SBP) and respiratory waveforms. ECG (from which HR series is obtained) and respiratory flow waveform (RFW) can be easily sampled from the patients. Nevertheless, the available methods for acquisition of beat-to-beat SBP measurements during exams hamper the wider use of MVAR models in clinical research. Recent studies show an inverse correlation between pulse wave transit time (PWTT) series and SBP fluctuations. PWTT is the time interval between the ECG R-wave peak and photoplethysmography waveform (PPG) base point within the same cardiac cycle. This study investigates the feasibility of using inverse PWTT (IPWTT) series as an alternative input to SBP for MVAR modeling of the cardiovascular regulation. For that, HR, RFW, and IPWTT series acquired from volunteers during postural changes and autonomic blockade were used as input of MVAR models. Obtained results show that IPWTT series can be used as input of MVAR models, replacing SBP measurements in order to overcome practical difficulties related to the continuous sampling of the SBP during clinical exams.

A two-dimensional analysis of the sensitivity of a pulse first break to wave speed contrast on a scale below the resolution length of ray tomography.

PubMed

Willey, Carson L; Simonetti, Francesco

2016-06-01

Mapping the speed of mechanical waves traveling inside a medium is a topic of great interest across many fields from geoscience to medical diagnostics. Much work has been done to characterize the fidelity with which the geometrical features of the medium can be reconstructed and multiple resolution criteria have been proposed depending on the wave-matter interaction model used to decode the wave speed map from scattering measurements. However, these criteria do not define the accuracy with which the wave speed values can be reconstructed. Using two-dimensional simulations, it is shown that the first-arrival traveltime predicted by ray theory can be an accurate representation of the arrival of a pulse first break even in the presence of diffraction and other phenomena that are not accounted for by ray theory. As a result, ray-based tomographic inversions can yield accurate wave speed estimations also when the size of a sound speed anomaly is smaller than the resolution length of the inversion method provided that traveltimes are estimated from the signal first break. This increased sensitivity however renders the inversion more susceptible to noise since the amplitude of the signal around the first break is typically low especially when three-dimensional anomalies are considered.

Error reduction and parameter optimization of the TAPIR method for fast T1 mapping.

PubMed

Zaitsev, M; Steinhoff, S; Shah, N J

2003-06-01

A methodology is presented for the reduction of both systematic and random errors in T(1) determination using TAPIR, a Look-Locker-based fast T(1) mapping technique. The relations between various sequence parameters were carefully investigated in order to develop recipes for choosing optimal sequence parameters. Theoretical predictions for the optimal flip angle were verified experimentally. Inversion pulse imperfections were identified as the main source of systematic errors in T(1) determination with TAPIR. An effective remedy is demonstrated which includes extension of the measurement protocol to include a special sequence for mapping the inversion efficiency itself. Copyright 2003 Wiley-Liss, Inc.

The use of Acoustic Radiation Force decorrelation-weighted pulse inversion (ADW-PI) for enhanced ultrasound contrast imaging

PubMed Central

Herbst, Elizabeth; Unnikrishnan, Sunil; Wang, Shiying; Klibanov, Alexander L.; Hossack, John A.; Mauldin, F. William

2016-01-01

Objectives The use of ultrasound imaging for cancer diagnosis and screening can be enhanced with the use of molecularly targeted microbubbles. Nonlinear imaging strategies such as pulse inversion (PI) and “contrast pulse sequences” (CPS) can be used to differentiate microbubble signal, but often fail to suppress highly echogenic tissue interfaces. This failure results in false positive detection and potential misdiagnosis. In this study, a novel Acoustic Radiation Force (ARF) based approach was developed for superior microbubble signal detection. The feasibility of this technique, termed ARF-decorrelation-weighted PI (ADW-PI), was demonstrated in vivo using a subcutaneous mouse tumor model. Materials and Methods Tumors were implanted in the hindlimb of C57BL/6 mice by subcutaneous injection of MC38 cells. Lipid-shelled microbubbles were conjugated to anti-VEGFR2 antibody and administered via bolus injection. An image sequence using ARF pulses to generate microbubble motion was combined with PI imaging on a Verasonics Vantage programmable scanner. ADW-PI images were generated by combining PI images with inter-frame signal decorrelation data. For comparison, CPS images of the same mouse tumor were acquired using a Siemens Sequoia clinical scanner. Results Microbubble-bound regions in the tumor interior exhibited significantly higher signal decorrelation than static tissue (n = 9, p < 0.001). The application of ARF significantly increased microbubble signal decorrelation (n = 9, p < 0.01). Using these decorrelation measurements, ADW-PI imaging demonstrated significantly improved microbubble contrast-to-tissue ratio (CTR) when compared to corresponding CPS or PI images (n = 9, p < 0.001). CTR improved with ADW-PI by approximately 3 dB compared to PI images and 2 dB compared to CPS images. Conclusions Acoustic radiation force can be used to generate adherent microbubble signal decorrelation without microbubble bursting. When combined with pulse inversion, measurements of the resulting microbubble signal decorrelation can be used to reconstruct images that exhibit superior suppression of highly echogenic tissue interfaces when compared to PI or CPS alone. PMID:27495188

Electromagnetic pulse propagation in dispersive planar dielectrics.

PubMed

Moten, K; Durney, C H; Stockham, T G

1989-01-01

The responses of a plane-wave pulse train irradiating a lossy dispersive dielectric half-space are investigated. The incident pulse train is expressed as a Fourier series with summing done by the inverse fast Fourier transform. The Fourier series technique is adopted to avoid the many difficulties often encountered in finding the inverse Fourier transform when transform analyses are used. Calculations are made for propagation in pure water, and typical waveforms inside the dielectric half-space are presented. Higher harmonics are strongly attenuated, resulting in a single continuous sinusoidal waveform at the frequency of the fundamental depth in the material. The time-averaged specific absorption rate (SAR) for pulse-train propagation is shown to be the sum of the time-averaged SARs of the individual harmonic components of the pulse train. For the same average power, calculated SARs reveal that pulse trains generally penetrate deeper than carrier-frequency continuous waves but not deeper than continuous waves at frequencies approaching the fundamental of the pulse train. The effects of rise time on the propagating pulse train in the dielectrics are shown and explained. Since most practical pulsed systems are very limited in bandwidth, no pronounced differences between their response and continuous wave (CW) response would be expected. Typical results for pulse-train propagation in arrays of dispersive planar dielectric slabs are presented. Expressing the pulse train as a Fourier series provides a practical way of interpreting the dispersion characteristics from the spectral point of view.

Broadband excitation in nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tycko, Robert

1984-10-01

Theoretical methods for designing sequences of radio frequency (rf) radiation pulses for broadband excitation of spin systems in nuclear magnetic resonance (NMR) are described. The sequences excite spins uniformly over large ranges of resonant frequencies arising from static magnetic field inhomogeneity, chemical shift differences, or spin couplings, or over large ranges of rf field amplitudes. Specific sequences for creating a population inversion or transverse magnetization are derived and demonstrated experimentally in liquid and solid state NMR. One approach to broadband excitation is based on principles of coherent averaging theory. A general formalism for deriving pulse sequences is given, along withmore » computational methods for specific cases. This approach leads to sequences that produce strictly constant transformations of a spin system. The importance of this feature in NMR applications is discussed. A second approach to broadband excitation makes use of iterative schemes, i.e. sets of operations that are applied repetitively to a given initial pulse sequences, generating a series of increasingly complex sequences with increasingly desirable properties. A general mathematical framework for analyzing iterative schemes is developed. An iterative scheme is treated as a function that acts on a space of operators corresponding to the transformations produced by all possible pulse sequences. The fixed points of the function and the stability of the fixed points are shown to determine the essential behavior of the scheme. Iterative schemes for broadband population inversion are treated in detail. Algebraic and numerical methods for performing the mathematical analysis are presented. Two additional topics are treated. The first is the construction of sequences for uniform excitation of double-quantum coherence and for uniform polarization transfer over a range of spin couplings. Double-quantum excitation sequences are demonstrated in a liquid crystal system. The second additional topic is the construction of iterative schemes for narrowband population inversion. The use of sequences that invert spin populations only over a narrow range of rf field amplitudes to spatially localize NMR signals in an rf field gradient is discussed.« less

Growth hormone-binding protein activity is inversely related to 24-hour growth hormone release in normal boys.

PubMed

Martha, P M; Rogol, A D; Blizzard, R M; Shaw, M A; Baumann, G

1991-07-01

To investigate the physiological relationship between serum GH-binding proteins and 24-h GH release, we compared the 24-h GH pulse attributes in serum samples obtained at 20-min intervals to the serum GH-binding protein activity (GH-BP) from 38 normal boys between 7 5/12 and 18 4/12 yr of age. GH-BP was determined in a serum sample from each study (containing less than 1.0 micrograms/L GH) using a standardized GH-BP assay. GH-BP results are expressed as the percentage of [125I]human GH bound to the high affinity GH-BP complex (peak II) per 160 microL serum. There were significant inverse relationships between the high affinity (receptor-related) GH-BP and several characteristics of 24-h GH release. Specifically, GH-BP was significantly (P less than 0.005 for all), but negatively, correlated with mean 24-h GH concentration (r = -0.62), sum of the GH pulse amplitudes (r = -0.57), sum of the GH pulse areas (r = -0.55), interpulse mean GH concentration (r = -0.53), and number of GH pulses per 24 h (r = -0.53). In addition, GH-BP correlated positively with the mean time interval between pulses (r = 0.59). There was also a significant positive correlation (r = 0.75; P less than 0.001) between GH-BP and the subject's age-adjusted body mass index SD score (BMI-SDS). Each characteristic of 24-h GH release correlating inversely with GH-BP also correlated inversely with BMI-SDS (P less than 0.01 for all comparisons). GH-BP did not, however, correlate with plasma insulin-like growth factor-I levels, serum testosterone concentrations, or height SDS. Binding to the low affinity GH-BP (peak I) did not correlate significantly with any of the examined GH pulse attributes, BMI-SDS, or the degree of binding to the high affinity GH-BP (peak II). We conclude that an inverse relationship exists between the high affinity serum GH-BP and 24-h GH release in boys under normal physiological conditions. We speculate that abnormalities in this relationship probably also exist and may underlie some disorders of growth.

Nonlinear Stimulated Raman Exact Passage by Resonance-Locked Inverse Engineering

NASA Astrophysics Data System (ADS)

Dorier, V.; Gevorgyan, M.; Ishkhanyan, A.; Leroy, C.; Jauslin, H. R.; Guérin, S.

2017-12-01

We derive an exact and robust stimulated Raman process for nonlinear quantum systems driven by pulsed external fields. The external fields are designed with closed-form expressions from the inverse engineering of a given efficient and stable dynamics. This technique allows one to induce a controlled population inversion which surpasses the usual nonlinear stimulated Raman adiabatic passage efficiency.

UTE imaging with simultaneous water and fat signal suppression using a time-efficient multispoke inversion recovery pulse sequence.

PubMed

Carl, Michael; Bydder, Graeme M; Du, Jiang

2016-08-01

The long repetition time and inversion time with inversion recovery preparation ultrashort echo time (UTE) often causes prohibitively long scan times. We present an optimized method for long T2 signal suppression in which several k-space spokes are acquired after each inversion preparation. Using Bloch equations the sequence parameters such as TI and flip angle were optimized to suppress the long T2 water and fat signals and to maximize short T2 contrast. Volunteer imaging was performed on a healthy male volunteer. Inversion recovery preparation was performed using a Silver-Hoult adiabatic inversion pulse together with a three-dimensional (3D) UTE (3D Cones) acquisition. The theoretical signal curves generally agreed with the experimentally measured region of interest curves. The multispoke inversion recovery method showed good muscle and fatty bone marrow suppression, and highlighted short T2 signals such as these from the femoral and tibial cortex. Inversion recovery 3D UTE imaging with multiple spoke acquisitions can be used to effectively suppress long T2 signals and highlight short T2 signals within clinical scan times. Theoretical modeling can be used to determine sequence parameters to optimize long T2 signal suppression and maximize short T2 signals. Experimental results on a volunteer confirmed the theoretical predictions. Magn Reson Med 76:577-582, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Sodium inversion recovery MRI of the knee joint in vivo at 7T

NASA Astrophysics Data System (ADS)

Madelin, Guillaume; Lee, Jae-Seung; Inati, Souheil; Jerschow, Alexej; Regatte, Ravinder R.

2010-11-01

The loss of proteoglycans (PG) in the articular cartilage is an early signature of osteoarthritis (OA). The ensuing changes in the fixed charge density in the cartilage can be directly linked to sodium concentration via charge balance. Sodium ions in the knee joint appear in two pools: in the synovial fluids or joint effusion where the ions are in free motion and bound within the cartilage tissue where the Na+ ions have a restricted motion. The ions in these two compartments have therefore different T1 and T2 relaxation times. The purpose of this study is to demonstrate the feasibility of a fluid-suppressed 3D ultrashort TE radial sodium sequence by implementing an inversion recovery (IR) preparation of the magnetization at 7T. This method could allow a more accurate and more sensitive quantification of loss of PG in patients with OA. It is shown that adiabatic pulses offer significantly improved performance in terms of robustness to B1 and B0 inhomogeneities when compared to the hard pulse sequence. Power deposition considerations further pose a limit to the RF inversion power, and we demonstrate in simulations and experiments how a practical compromise can be struck between clean suppression of fluid signals and power deposition levels. Two IR sequences with different types of inversion pulses (a rectangular pulse and an adiabatic pulse) were tested on a liquid phantom, ex vivo on a human knee cadaver and then in vivo on five healthy volunteers, with a (Nyquist) resolution of ∼3.6 mm and a signal-to-noise ratio of ∼30 in cartilage without IR and ∼20 with IR. Due to specific absorption rate limitations, the total acquisition time was ∼17 min for the 3D radial sequence without inversion or with the rectangular IR, and 24:30 min for the adiabatic IR sequence. It is shown that the adiabatic IR sequence generates a more uniform fluid suppression over the whole sample than the rectangular IR sequence.

Sodium inversion recovery MRI of the knee joint in vivo at 7T.

PubMed

Madelin, Guillaume; Lee, Jae-Seung; Inati, Souheil; Jerschow, Alexej; Regatte, Ravinder R

2010-11-01

The loss of proteoglycans (PG) in the articular cartilage is an early signature of osteoarthritis (OA). The ensuing changes in the fixed charge density in the cartilage can be directly linked to sodium concentration via charge balance. Sodium ions in the knee joint appear in two pools: in the synovial fluids or joint effusion where the ions are in free motion and bound within the cartilage tissue where the Na(+) ions have a restricted motion. The ions in these two compartments have therefore different T₁ and T₂ relaxation times. The purpose of this study is to demonstrate the feasibility of a fluid-suppressed 3D ultrashort TE radial sodium sequence by implementing an inversion recovery (IR) preparation of the magnetization at 7T. This method could allow a more accurate and more sensitive quantification of loss of PG in patients with OA. It is shown that adiabatic pulses offer significantly improved performance in terms of robustness to B₁ and B₀ inhomogeneities when compared to the hard pulse sequence. Power deposition considerations further pose a limit to the RF inversion power, and we demonstrate in simulations and experiments how a practical compromise can be struck between clean suppression of fluid signals and power deposition levels. Two IR sequences with different types of inversion pulses (a rectangular pulse and an adiabatic pulse) were tested on a liquid phantom, ex vivo on a human knee cadaver and then in vivo on five healthy volunteers, with a (Nyquist) resolution of ∼3.6 mm and a signal-to-noise ratio of ∼30 in cartilage without IR and ∼20 with IR. Due to specific absorption rate limitations, the total acquisition time was ∼17 min for the 3D radial sequence without inversion or with the rectangular IR, and 24:30 min for the adiabatic IR sequence. It is shown that the adiabatic IR sequence generates a more uniform fluid suppression over the whole sample than the rectangular IR sequence. Copyright © 2010 Elsevier Inc. All rights reserved.

Age-related change in renal corticomedullary differentiation: evaluation with noncontrast-enhanced steady-state free precession (SSFP) MRI with spatially selective inversion pulse using variable inversion time.

PubMed

Noda, Yasufumi; Kanki, Akihiko; Yamamoto, Akira; Higashi, Hiroki; Tanimoto, Daigo; Sato, Tomohiro; Higaki, Atsushi; Tamada, Tsutomu; Ito, Katsuyoshi

2014-07-01

To evaluate age-related change in renal corticomedullary differentiation and renal cortical thickness by means of noncontrast-enhanced steady-state free precession (SSFP) magnetic resonance imaging (MRI) with spatially selective inversion recovery (IR) pulse. The Institutional Review Board of our hospital approved this retrospective study and patient informed consent was waived. This study included 48 patients without renal diseases who underwent noncontrast-enhanced SSFP MRI with spatially selective IR pulse using variable inversion times (TIs) (700-1500 msec). The signal intensity of renal cortex and medulla were measured to calculate renal corticomedullary contrast ratio. Additionally, renal cortical thickness was measured. The renal corticomedullary junction was clearly depicted in all patients. The mean cortical thickness was 3.9 ± 0.83 mm. The mean corticomedullary contrast ratio was 4.7 ± 1.4. There was a negative correlation between optimal TI for the best visualization of renal corticomedullary differentiation and age (r = -0.378; P = 0.001). However, there was no significant correlation between renal corticomedullary contrast ratio and age (r = 0.187; P = 0.20). Similarly, no significant correlation was observed between renal cortical thickness and age (r = 0.054; P = 0.712). In the normal kidney, noncontrast-enhanced SSFP MRI with spatially selective IR pulse can be used to assess renal corticomedullary differentiation and cortical thickness without the influence of aging, although optimal TI values for the best visualization of renal corticomedullary junction were shortened with aging. © 2013 Wiley Periodicals, Inc.

Subfemtosecond directional control of chemical processes in molecules

NASA Astrophysics Data System (ADS)

Alnaser, Ali S.; Litvinyuk, Igor V.

2017-02-01

Laser pulses with a waveform-controlled electric field and broken inversion symmetry establish the opportunity to achieve directional control of molecular processes on a subfemtosecond timescale. Several techniques could be used to break the inversion symmetry of an electric field. The most common ones include combining a fundamental laser frequency with its second harmonic or with higher -frequency pulses (or pulse trains) as well as using few-cycle pulses with known carrier-envelope phase (CEP). In the case of CEP, control over chemical transformations, typically occurring on a timescale of many femtoseconds, is driven by much faster sub-cycle processes of subfemtosecond to few-femtosecond duration. This is possible because electrons are much lighter than nuclei and fast electron motion is coupled to the much slower nuclear motion. The control originates from populating coherent superpositions of different electronic or vibrational states with relative phases that are dependent on the CEP or phase offset between components of a two-color pulse. In this paper, we review the recent progress made in the directional control over chemical processes, driven by intense few-cycle laser pulses a of waveform-tailored electric field, in different molecules.

High-pulse energy-stabilized passively mode-locked external cavity inverse bow-tie 980nm laser diode for space applications

NASA Astrophysics Data System (ADS)

Krakowski, M.; Resneau, P.; Garcia, M.; Vinet, E.; Robert, Y.; Lecomte, M.; Parillaud, O.; Gerard, B.; Kundermann, S.; Torcheboeuf, N.; Boiko, D. L.

2018-02-01

We report on multi-section inverse bow-tie laser producing mode-locked pulses of 90 pJ energy and 6.5 ps width (895 fs after compression) at 1.3 GHz pulse repetition frequency (PRF) and consuming 2.9 W of electric power. The laser operates in an 80 mm long external cavity. By translation of the output coupling mirror, the PRF was continuously tuned over 37 MHz range without additional adjustments. Active stabilization with a phase lock loop actuating on the driving current has allowed us to reach the PRF relative stability at a 2·10-10 level on 10 s intervals, as required by the European Space Agency (ESA) for inter-satellite long distance measurements.

Chirped pulse inverse free-electron laser vacuum accelerator

DOEpatents

Hartemann, Frederic V.; Baldis, Hector A.; Landahl, Eric C.

2002-01-01

A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

How short are ultra short light pulses? (looking back to the mid sixties)

NASA Astrophysics Data System (ADS)

Weber, H. P.; Dändliker, R.

2010-09-01

With the arrival of mode locking for Q-switched lasers to generate ultra short light pulses, a method to measure their expected time duration in the psec range was needed. A novel method, based on an intensity correlation measurement using optical second harmonic generation, was developed. Other reported approaches for the same purpose were critically analysed. Theoretical and subsequent experimental studies lead to surprising new insight into the ultra fast temporal behaviour of broadband laser radiation: Any non mode locked multimode emission of a laser consists of random intensity fluctuations with duration of the total inverse band width of emitted radiation. However, it was shown, that with mode locking isolated ultra short pulses of psec duration can be generated. This article summarizes activities performed in the mid sixties at the University of Berne, Switzerland.

Two-Port Representation of a Linear Transmission Line in the Time Domain.

DTIC Science & Technology

1980-01-01

which is a rational function. To use the Prony procedure it is necessary to inverse transform the admittance functions. For the transmission line, most...impulse is a constant, the inverse transform of Y0(s) contains an impulse of value ._ Therefore, if we were to numerically inverse transform Yo(s), we...would remove this im- pulse and inverse transform Y-(S) Y (S) 1’LR+C~ (23) The prony procedure would then be applied to the result. Of course, an impulse

Copper bromide vapour laser with an output pulse duration of up to 320 ns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubarev, F A; Fedorov, K V; Evtushenko, G S

We report the development of a copper bromide vapour laser with an output pulse duration of up to 320 ns. To lengthen the pulse, the discharge current was limited using a compound switch comprising a pulsed hydrogen thyratron and a tacitron. This technique permits limiting the excitation of the working levels at the initial stage of the discharge development to lengthen the inversion lifetime. The longest duration of a laser pulse was reached in tubes 25 and 50 mm in diameter for a pulse repetition rate of 2 – 4 kHz. (lasers and laser beams)

Forearm Vascular Reactivity and Arterial Stiffness in Asymptomatic Subjects from the Community

PubMed Central

Malik, A. Rauoof; Kondragunta, Venkateswarlu; Kullo, Iftikhar J.

2010-01-01

Vascular reactivity may affect the stiffness characteristics of the arterial wall. We investigated the association between forearm microcirculatory and conduit artery function and measures of arterial stiffness in 527 asymptomatic non-Hispanic white adults without known cardiovascular disease. High-resolution ultrasonography of the brachial artery (ba) was performed to assess forearm microcirculatory function (ba blood flow velocity, local shear stress, and forearm vascular resistance at rest and during reactive hyperemia) and conduit artery function (ba flow-mediated dilatation baFMD and ba nitroglycerin-mediated dilatation baNMD). Arterial stiffness was assessed by cuff-derived brachial pulse pressure and aortic pulse wave velocity (aPWV) measured by applanation tonometry. In regression analyses that adjusted for heart rate, mean arterial pressure, height, cardiovascular risk factors, and hypertension medication and statin use, higher baseline ba systolic velocity and systolic shear stress were associated with greater pulse pressure (P=0.0002 and P=0.006, respectively) and higher aPWV (each P<0.0001). During hyperemia, lower ba mean velocity and lower mean shear stress were associated with higher pulse pressure (P=0.045 and P=0.036, respectively) while both systolic and mean velocity (P<0.0001 and P=0.002, respectively) and systolic and mean shear stress (P<0.0001 and P=0.003, respectively) were inversely associated with aPWV. baFMD was not associated with pulse pressure but was inversely associated with aPWV (P=0.011). baNMD was inversely associated with pulse pressure (P=0.0002) and aPWV (P=0.008). Our findings demonstrate that impaired forearm microvascular function (in the form of elevated resting blood flow velocity and impaired flow reserve) and impaired brachial artery reactivity are associated with increased arterial stiffness. PMID:18426995

Studies of the Plasma Triggering Mechanism of Inverse Pinch Switch

DTIC Science & Technology

1993-11-10

plasma - focus driven plasma-puff was also discussed in comparison with the hypocycloidal pinch plasma-puff triggering. The main discharge of inverse pinch switch with plasma - focus driven plasma-puff trigger is found to be more azimuthally uniform than that with hypocycloidal pinch plasma-puff trigger in a gas pressure region between 80 mTorr and 1 Torr. A comparative study of the INPIStron and a spark gap also reveals that the INPIStron with a low impedance Z = 9 ohms can transfer a high voltage pulse with a superior pulse-shape fidelity over that with

Excitation of atoms and ions in plasmas by ultra-short electromagnetic pulses

NASA Astrophysics Data System (ADS)

Astapenko, V. A.; Sakhno, S. V.; Svita, S. Yu; Lisitsa, V. S.

2017-02-01

The problem of atoms and ions diagnostics in rarefied and dense plasmas by ultrashort laser pulses (USP) is under consideration. The application of USP provides: 1) excitation from ground states due to their carrier frequency high enough, 2) penetration into optically dense media due to short pulses duration. The excitation from ground atomic states increases sharply populations of excited atomic states in contrast with standard laser induced fluorescence spectroscopy based on radiative transitions between excited atomic states. New broadening parameter in radiation absorption, namely inverse pulse duration time 1/τ appears in addition to standard line-shape width in the profile G(ω). The Lyman-beta absorption spectra for USP are calculated for Holtsmark static broadening mechanism. Excitation of highly charged H-like ions in hot plasmas is described by both Gaussian shapes for Doppler broadening and pulse spectrum resulting in analytical absorption line-shape. USP penetration into optically thick media and corresponding excitation probability are calculated. It is shown a great effect of USP duration on excitation probabilities in optically thick media. The typical situations for plasma diagnostics by USP are discussed in details.

A data-driven wavelet-based approach for generating jumping loads

NASA Astrophysics Data System (ADS)

Chen, Jun; Li, Guo; Racic, Vitomir

2018-06-01

This paper suggests an approach to generate human jumping loads using wavelet transform and a database of individual jumping force records. A total of 970 individual jumping force records of various frequencies were first collected by three experiments from 147 test subjects. For each record, every jumping pulse was extracted and decomposed into seven levels by wavelet transform. All the decomposition coefficients were stored in an information database. Probability distributions of jumping cycle period, contact ratio and energy of the jumping pulse were statistically analyzed. Inspired by the theory of DNA recombination, an approach was developed by interchanging the wavelet coefficients between different jumping pulses. To generate a jumping force time history with N pulses, wavelet coefficients were first selected randomly from the database at each level. They were then used to reconstruct N pulses by the inverse wavelet transform. Jumping cycle periods and contract ratios were then generated randomly based on their probabilistic functions. These parameters were assigned to each of the N pulses which were in turn scaled by the amplitude factors βi to account for energy relationship between successive pulses. The final jumping force time history was obtained by linking all the N cycles end to end. This simulation approach can preserve the non-stationary features of the jumping load force in time-frequency domain. Application indicates that this approach can be used to generate jumping force time history due to single people jumping and also can be extended further to stochastic jumping loads due to groups and crowds.

Non-contrast-enhanced MR portography and hepatic venography with time-spatial labeling inversion pulses: comparison at 1.5 Tesla and 3 Tesla

PubMed Central

Isoda, Hiroyoshi; Furuta, Akihiro; Togashi, Kaori

2015-01-01

Background A 3 Tesla (3 T) magnetic resonance (MR) scanner is a promising tool for upper abdominal MR angiography. However, there is no report focused on the image quality of non-contrast-enhanced MR portography and hepatic venography at 3 T. Purpose To compare and evaluate images of non-contrast-enhanced MR portography and hepatic venography with time-spatial labeling inversion pulses (Time-SLIP) at 1.5 Tesla (1.5 T) and 3 T. Material and Methods Twenty-five healthy volunteers were examined using respiratory-triggered three-dimensional balanced steady-state free-precession (bSSFP) with Time-SLIP. For portography, we used one tagging pulse (selective inversion recovery) and one non-selective inversion recovery pulse; for venography, two tagging pulses were used. The relative signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were quantified, and the quality of visualization was evaluated. Results The CNRs of the main portal vein, right portal vein, and left portal vein at 3 T were better than at 1.5 T. The image quality scores for the portal branches of segment 4, 5, and 8 were significantly higher at 3 T than at 1.5 T. The CNR of the right hepatic vein (RHV) at 3 T was significantly lower than at 1.5 T. The image quality scores of RHV and the middle hepatic vein were higher at 1.5 T than at 3 T. For RHV visualization, the difference was statistically significant. Conclusion Non-contrast-enhanced MR portography with Time-SLIP at 3 T significantly improved visualization of the peripheral branch in healthy volunteers compared with1.5 T. Non-contrast-enhanced MR hepatic venography at 1.5 T was better than at 3 T. PMID:26019890

Comparison of pulse sequences for R1-based electron paramagnetic resonance oxygen imaging.

PubMed

Epel, Boris; Halpern, Howard J

2015-05-01

Electron paramagnetic resonance (EPR) spin-lattice relaxation (SLR) oxygen imaging has proven to be an indispensable tool for assessing oxygen partial pressure in live animals. EPR oxygen images show remarkable oxygen accuracy when combined with high precision and spatial resolution. Developing more effective means for obtaining SLR rates is of great practical, biological and medical importance. In this work we compared different pulse EPR imaging protocols and pulse sequences to establish advantages and areas of applicability for each method. Tests were performed using phantoms containing spin probes with oxygen concentrations relevant to in vivo oxymetry. We have found that for small animal size objects the inversion recovery sequence combined with the filtered backprojection reconstruction method delivers the best accuracy and precision. For large animals, in which large radio frequency energy deposition might be critical, free induction decay and three pulse stimulated echo sequences might find better practical usage. Copyright © 2015 Elsevier Inc. All rights reserved.

X-Ray Laser Program Final Report for FY92

DTIC Science & Technology

1993-07-01

also produced population inversion. Ultra- intense , femtosecond- pulsed laboratory lasers ranging from the ultraviolet to the infrared represent an...with pulse lengths of 650 femtoseconds normally Incident on a 2p. thick planar aluminum slab. Comparisons are made for two laser Intensities , two...prepulse is subsequently irradiated by the main high intensity pulse . The persistence of the heliumlike ground state raises the possibility that a photon

3D noninvasive ultrasound Joule heat tomography based on acousto-electric effect using unipolar pulses: a simulation study

PubMed Central

Yang, Renhuan; Li, Xu; Song, Aiguo; He, Bin; Yan, Ruqiang

2012-01-01

Electrical properties of biological tissues are highly sensitive to their physiological and pathological status. Thus it is of importance to image electrical properties of biological tissues. However, spatial resolution of conventional electrical impedance tomography (EIT) is generally poor. Recently, hybrid imaging modalities combining electric conductivity contrast and ultrasonic resolution based on acouto-electric effect has attracted considerable attention. In this study, we propose a novel three-dimensional (3D) noninvasive ultrasound Joule heat tomography (UJHT) approach based on acouto-electric effect using unipolar ultrasound pulses. As the Joule heat density distribution is highly dependent on the conductivity distribution, an accurate and high resolution mapping of the Joule heat density distribution is expected to give important information that is closely related to the conductivity contrast. The advantages of the proposed ultrasound Joule heat tomography using unipolar pulses include its simple inverse solution, better performance than UJHT using common bipolar pulses and its independence of any priori knowledge of the conductivity distribution of the imaging object. Computer simulation results show that using the proposed method, it is feasible to perform a high spatial resolution Joule heat imaging in an inhomogeneous conductive media. Application of this technique on tumor scanning is also investigated by a series of computer simulations. PMID:23123757

Accurate step-FMCW ultrasound ranging and comparison with pulse-echo signaling methods

NASA Astrophysics Data System (ADS)

Natarajan, Shyam; Singh, Rahul S.; Lee, Michael; Cox, Brian P.; Culjat, Martin O.; Grundfest, Warren S.; Lee, Hua

2010-03-01

This paper presents a method setup for high-frequency ultrasound ranging based on stepped frequency-modulated continuous waves (FMCW), potentially capable of producing a higher signal-to-noise ratio (SNR) compared to traditional pulse-echo signaling. In current ultrasound systems, the use of higher frequencies (10-20 MHz) to enhance resolution lowers signal quality due to frequency-dependent attenuation. The proposed ultrasound signaling format, step-FMCW, is well-known in the radar community, and features lower peak power, wider dynamic range, lower noise figure and simpler electronics in comparison to pulse-echo systems. In pulse-echo ultrasound ranging, distances are calculated using the transmit times between a pulse and its subsequent echoes. In step-FMCW ultrasonic ranging, the phase and magnitude differences at stepped frequencies are used to sample the frequency domain. Thus, by taking the inverse Fourier transform, a comprehensive range profile is recovered that has increased immunity to noise over conventional ranging methods. Step-FMCW and pulse-echo waveforms were created using custom-built hardware consisting of an arbitrary waveform generator and dual-channel super heterodyne receiver, providing high SNR and in turn, accuracy in detection.

The possible importance of synchrotron/inverse Compton losses to explain fast MM-wave and hard X-ray emission of a solar event

NASA Technical Reports Server (NTRS)

Correia, E.; Kaufmann, P.; Costa, J. E. R.; Vaz, A. M. Z.; Dennis, B. R.

1986-01-01

The solar burst of 21 May 1984 presented a number of unique features. The time profile consisted of seven major structures (seconds), with a turnover frequency or approx. 90 GHz, well correlated in time to hard X-ray emission. Each structure consisted of multiple fast pulses (.1 seconds), which were analyzed in detail. A proportionality between the repetition rate of the pulses and the burst fluxes at 90 GHz and or approx. 100 keV hard X-rays, and an inverse proportionality between repetition rates and hard X-rays power law indices have been found. A synchrotron/inverse Compton model has been applied to explain the emission of the fast burst structures, which appear to be possible for the first three or four structures.

The possible importance of synchrotron/inverse Compton losses to explain fast mm-wave and hard X-ray emission of a solar event

NASA Technical Reports Server (NTRS)

Correia, E.; Kaufmann, P.; Costa, J. E. R.; Zodivaz, A. M.; Dennis, B. R.

1986-01-01

The solar burst of 21 May 1984, presented a number of unique features. The time profile consisted of seven major structures (seconds), with a turnover frequency of greater than or approximately 90 GHz, well correlated in time to hard X-ray emission. Each structure consisted of multiple fast pulses (0.1 seconds), which were analyzed in detail. A proportionality between the repetition rate of the pulses and the burst fluxes at 90 GHz and greater than or approximately 100 keV hard X-rays, and an inverse proportionality between repetition rates and hard X-ray power law indices were found. A synchrotron/inverse Compton model was applied to explain the emission of the fast burst structures, which appear to be possible for the first three or four structures.

Enhanced proton acceleration by intense laser interaction with an inverse cone target

NASA Astrophysics Data System (ADS)

Bake, Muhammad Ali; Aimidula, Aimierding; Xiaerding, Fuerkaiti; Rashidin, Reyima

2016-08-01

The generation and control of high-quality proton bunches using focused intense laser pulse on an inverse cone target is investigated with a set of particle-in-cell simulations. The inverse cone is a high atomic number conical frustum with a thin solid top and open base, where the laser impinges onto the top surface directly, not down the open end of the cone. Results are compared with a simple planar target, where the proton angular distribution is very broad because of transverse divergence of the electromagnetic fields behind the target. For a conical target, hot electrons along the cone wall surface induce a transverse focusing sheath field. This field can effectively suppress the spatial spreading of the protons, resulting in a high-quality small-emittance, low-divergence proton beam. A slightly lower proton beam peak energy than that of a conventional planar target was also found.

Enhanced proton acceleration by intense laser interaction with an inverse cone target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bake, Muhammad Ali; Aimidula, Aimierding, E-mail: amir@mail.bnu.edu.cn; Xiaerding, Fuerkaiti

The generation and control of high-quality proton bunches using focused intense laser pulse on an inverse cone target is investigated with a set of particle-in-cell simulations. The inverse cone is a high atomic number conical frustum with a thin solid top and open base, where the laser impinges onto the top surface directly, not down the open end of the cone. Results are compared with a simple planar target, where the proton angular distribution is very broad because of transverse divergence of the electromagnetic fields behind the target. For a conical target, hot electrons along the cone wall surface inducemore » a transverse focusing sheath field. This field can effectively suppress the spatial spreading of the protons, resulting in a high-quality small-emittance, low-divergence proton beam. A slightly lower proton beam peak energy than that of a conventional planar target was also found.« less

Control of pulse format in high energy per pulse all-fiber erbium/ytterbium laser systems

NASA Astrophysics Data System (ADS)

Klopfer, Michael; Block, Matthew K.; Deffenbaugh, James; Fitzpatrick, Zak G.; Urioste, Michael T.; Henry, Leanne J.; Jain, Ravinder

2017-02-01

A multi-stage linearly polarized (PM) (15 dB) pulsed fiber laser system at 1550 nm capable of operating at repetition rates between 3 and 20 kHz was investigated. A narrow linewidth seed source was linewidth broadened to approximately 20 GHz and pulses were created and shaped via an electro-optic modulator (EOM) in conjunction with a home built arbitrary waveform generator. As expected, a high repetition rate pulse train with a near diffraction limited beam quality (M2 1.12) was achieved. However, the ability to store energy was limited by the number of active ions within the erbium/ytterbium doped gain fiber within the various stages. As a result, the maximum energy per pulse achievable from the system was approximately 0.3 and 0.38 mJ for 300 ns and 1 μs pulses, respectively, at 3 kHz. Because the system was operated at high inversion, the erbium/ytterbium doped optical fiber preferred to lase at 1535 nm versus 1550 nm resulting in amplified spontaneous emission (ASE) both intra- and inter-pulse. For the lower power stages, the ASE was controllable via a EOM whose function was to block the energy between pulses as well as ASE filters whose purpose was to block spectral components outside of the 1550 nm passband. For the higher power stages, the pump diodes were pulsed to enable strategic placement of an inversion resulting in higher intrapulse energies as well as an improved spectrum of the signal. When optimized, this system will be used to seed higher power solid state amplifier stages.

Lidar inversion of atmospheric backscatter and extinction-to-backscatter ratios by use of a Kalman filter.

PubMed

Rocadenbosch, F; Soriano, C; Comerón, A; Baldasano, J M

1999-05-20

A first inversion of the backscatter profile and extinction-to-backscatter ratio from pulsed elastic-backscatter lidar returns is treated by means of an extended Kalman filter (EKF). The EKF approach enables one to overcome the intrinsic limitations of standard straightforward nonmemory procedures such as the slope method, exponential curve fitting, and the backward inversion algorithm. Whereas those procedures are inherently not adaptable because independent inversions are performed for each return signal and neither the statistics of the signals nor a priori uncertainties (e.g., boundary calibrations) are taken into account, in the case of the Kalman filter the filter updates itself because it is weighted by the imbalance between the a priori estimates of the optical parameters (i.e., past inversions) and the new estimates based on a minimum-variance criterion, as long as there are different lidar returns. Calibration errors and initialization uncertainties can be assimilated also. The study begins with the formulation of the inversion problem and an appropriate atmospheric stochastic model. Based on extensive simulation and realistic conditions, it is shown that the EKF approach enables one to retrieve the optical parameters as time-range-dependent functions and hence to track the atmospheric evolution; the performance of this approach is limited only by the quality and availability of the a priori information and the accuracy of the atmospheric model used. The study ends with an encouraging practical inversion of a live scene measured at the Nd:YAG elastic-backscatter lidar station at our premises at the Polytechnic University of Catalonia, Barcelona.

Specific characteristics of negative corona currents generated in short point-plane gap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhen; Zhang, Bo; He, Jinliang

The Trichel pulse is a typical kind of negative corona current observed in electronegative gases with a highly regular form. The characteristics of the Trichel pulse, such as the repetition frequency, the amplitude of each pulse, and the mean current, are dependent on different discharge conditions. Quite many scholars have studied the mean current and the current-voltage characteristic of Trichel pulses, yet the specific characteristics of the pulses have barely been investigated. In this paper, a series of experiments were carried out in a short point-to-plane discharge gap to investigate the detailed characteristics of Trichel pulses. After numerical fitting ofmore » the experiment results was performed, a new set of empirical formulas were derived to predict the specific characteristics of the negative corona current under different conditions. Different from existing literature, this paper uses as variables the average electric field intensity and the corona inception field intensity which is independent of the gap spacing in the empirical formulas. In the experiments, an inverse correlation between amplitude and repetition frequency of the pulses was observed. Based on the investigation of the remaining space charge in the discharge gap, this correlation is theoretically proved to be caused by the influence of space charges.« less

Self similar solution of superradiant amplification of ultrashort laser pulses in plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moghadasin, H.; Niknam, A. R., E-mail: a-niknam@sbu.ac.ir; Shokri, B.

2015-05-15

Based on the self-similar method, superradiant amplification of ultrashort laser pulses by the counterpropagating pump in a plasma is investigated. Here, we present a governing system of partial differential equations for the signal pulse and the motion of the electrons. These equations are transformed to ordinary differential equations by the self-similar method and numerically solved. It is found that the increase of the signal intensity is proportional to the square of the propagation distance and the signal frequency has a red shift. Also, depending on the pulse width, the signal breaks up into a train of short pulses or itsmore » duration decreases with the inverse square root of the distance. Moreover, we identified two distinct categories of the electrons by the phase space analysis. In the beginning, one of them is trapped in the ponderomotive potential well and oscillates while the other is untrapped. Over time, electrons of the second kind also join to the trapped electrons. In the potential well, the electrons are bunched to form an electron density grating which reflects the pump pulse into the signal pulse. It is shown that the backscattered intensity is enhanced with the increase of the electron bunching parameter which leads to the enhanced efficiency of superradiant amplification.« less

Transmission of laser pulses with high output beam quality using step-index fibers having large cladding

DOEpatents

Yalin, Azer P; Joshi, Sachin

2014-06-03

An apparatus and method for transmission of laser pulses with high output beam quality using large core step-index silica optical fibers having thick cladding, are described. The thick cladding suppresses diffusion of modal power to higher order modes at the core-cladding interface, thereby enabling higher beam quality, M.sup.2, than are observed for large core, thin cladding optical fibers. For a given NA and core size, the thicker the cladding, the better the output beam quality. Mode coupling coefficients, D, has been found to scale approximately as the inverse square of the cladding dimension and the inverse square root of the wavelength. Output from a 2 m long silica optical fiber having a 100 .mu.m core and a 660 .mu.m cladding was found to be close to single mode, with an M.sup.2=1.6. Another thick cladding fiber (400 .mu.m core and 720 .mu.m clad) was used to transmit 1064 nm pulses of nanosecond duration with high beam quality to form gas sparks at the focused output (focused intensity of >100 GW/cm.sup.2), wherein the energy in the core was <6 mJ, and the duration of the laser pulses was about 6 ns. Extending the pulse duration provided the ability to increase the delivered pulse energy (>20 mJ delivered for 50 ns pulses) without damaging the silica fiber.

Study and Characterization of Subharmonic Emissions by Using Shaped Ultrasonic Driving Pulse

NASA Astrophysics Data System (ADS)

Masotti, L.; Biagi, E.; Breschi, L.; Vannacci, E.

Subharmonic emissions from Ultrasound Contrast Agents (UCAs) were studied by a Pulse Inversion method in order to assess the feasibility of implementation of this technique to subharmonic imaging. Interesting results concerning the dependence of the subharmonic emission with respect to initial pulse shape are presented. The experimentation was performed also by varying the acoustic pressure and concentration of the contrast agent (SonoVue®)

Nanosecond Plasma Enhanced H2/O2/N2 Premixed Flat Flames

DTIC Science & Technology

2014-01-01

Simulations are conducted with a one-dimensional, multi-scale, pulsed -discharge model with detailed plasma-combustion kinetics to develop additional insight... model framework. The reduced electric field, E/N, during each pulse varies inversely with number density. A significant portion of the input energy is...dimensional numerical model [4, 12] capable of resolving electric field transients over nanosecond timescales (during each discharge pulse ) and radical

SU-E-T-558: An Exploratory RF Pulse Sequence Technique Used to Induce Differential Heating in Tissues Containing Iron Oxide Nanoparticles for a Possible Hyperthermic Adjuvant Effect to Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yee, S; Ionascu, D; Wilson, G

2014-06-01

Purpose: In pre-clinical trials of cancer thermotherapy, hyperthermia can be induced by exposing localized super-paramagnetic iron oxide nanoparticles (SPION) to external alternating magnetic fields generated by a solenoid electrical circuit (Zhao et al., Theranostics 2012). Alternatively, an RF pulse technique implemented in a regular MRI system is explored as a possible hyperthermia induction technique . Methods: A new thermal RF pulse sequence was developed using the Philips pulse programming tool for the 3T Ingenia MRI system to provide a sinusoidal magnetic field alternating at the frequency of 1.43 kHz (multiples of sine waves of 0.7 ms period) before each excitationmore » RF pulse for imaging. The duration of each thermal RF pulse routine was approximately 3 min, and the thermal pulse was applied multiple times to a phantom that contains different concentrations (high, medium and low) of SPION samples. After applying the thermal pulse each time, the temperature change was estimated by measuring the phase changes in the T1-weighted inversion-prepared multi-shot turbo field echo (TFE) sequence (TR=5.5 ms, TE=2.7 ms, inversion time=200 ms). Results: The phase values and relative differences among them changed as the number of applied thermal RF pulses increased. After the 5th application of the thermal RF pulse, the relative phase differences increased significantly, suggesting the thermal activation of the SPION. The increase of the phase difference was approximately linear with the SPION concentration. Conclusion: A sinusoidal RF pulse from the MRI system may be utilized to selectively thermally activate tissues containing super-paramagnetic iron oxide nanoparticles.« less

Ultrafast optical pulse convertor caused by oscillations of the energy level structure in the conjugated polymer poly(p-phenylenevinylene).

PubMed

Zhang, Yusong; Chen, Weikang; Lin, Zhe; Li, Sheng; George, Thomas F

2017-08-21

For a conjugated polymer irradiated by two optical pulses, the whole process of excitation, involving lattice oscillations, oscillations of the energy level structure, and evolution of the electron cloud, is investigated. Localization of the electron cloud appears in the first 100 fs of irradiation, which in turn induces vibrations of lattice of the polymer chain as well as oscillations of the band gap. These oscillations filter the absorption of the external optical field inversely and convert the original optical field to an ultrafast light field whose intensity varies with a certain period. Based on the mechanism, oscillations of the energy level structure, induced by the external excitation, can be designed as an ultrafast response optical convertor that is able to change the external optical pulse into a new effective light field with a certain oscillation period. This helps provide new insight into designing nanostructures for polymeric optoelectronics.

Megavolt, Multigigawatt Pulsed Plasma Switch

NASA Technical Reports Server (NTRS)

Lee, Ja H.; Choi, Sang H.; Song, Kyo D.

1996-01-01

Plasma switch proposed for use in high-voltage, high-current pulse power system. Designed not only to out-perform conventional spark-gap switch but also relatively compact and lightweight. Features inverse-pinch configuration to prevent constriction of current sheets into filaments, plus multiple-ring-electrode structure to resist high-voltage breakdown.

Maximizing energy deposition by shaping few-cycle laser pulses

NASA Astrophysics Data System (ADS)

Gateau, Julien; Patas, Alexander; Matthews, Mary; Hermelin, Sylvain; Lindinger, Albrecht; Kasparian, Jérôme; Wolf, Jean-Pierre

2018-07-01

We experimentally investigate the impact of pulse shape on the dynamics of laser-generated plasma in rare gases. Fast-rising triangular pulses with a slower decay lead to early ionization of the gas and depose energy more efficiently than their temporally reversed counterparts. As a result, in both argon and krypton, the induced shockwave as well as the plasma luminescence are stronger. This is due to an earlier availability of free electrons to undergo inverse Bremsstrahlung on the pulse trailing edge. Our results illustrate the ability of adequately tailored pulse shapes to optimize the energy deposition in gas plasmas.

CO.sub.2 laser

DOEpatents

Rink, John P.

1977-01-01

The disclosure relates to a pulsed gas laser comprising an optical resonant cavity, a CO.sub.2 lasing medium, structure for containing the CO.sub.2 lasing medium within the optical cavity and a device for causing a population inversion in the lasing medium, with a novel improvement comprising structure for causing a laser pulse comprising a wavelength in the near 14 .mu.m and near 16 .mu.m range. The structure for cooling the CO.sub.2 lasing medium to less than about -40.degree. C as well is a structure for pumping the maximum inversion of CO.sub.2 molecules within the lasing medium by minimizing the population in the 010 level.

A 1.5 million–base pair inversion polymorphism in families with Williams-Beuren syndrome

PubMed Central

Osborne, Lucy R.; Li, Martin; Pober, Barbara; Chitayat, David; Bodurtha, Joann; Mandel, Ariane; Costa, Teresa; Grebe, Theresa; Cox, Sarah; Tsui, Lap-Chee; Scherer, Stephen W.

2010-01-01

Williams-Beuren syndrome (WBS) is most often caused by hemizygous deletion of a 1.5-Mb interval encompassing at least 17 genes at 7q11.23 (refs. 1, 2). As with many other haploinsufficiency diseases, the mechanism underlying the WBS deletion is thought to be unequal meiotic recombination, probably mediated by the highly homologous DNA that flanks the commonly deleted region3. Here, we report the use of interphase fluorescence in situ hybridization (FISH) and pulsed-field gel electrophoresis (PFGE) to identify a genomic polymorphism in families with WBS, consisting of an inversion of the WBS region. We have observed that the inversion is hemizygous in 3 of 11 (27%) atypical affected individuals who show a subset of the WBS phenotypic spectrum but do not carry the typical WBS microdeletion. Two of these individuals also have a parent who carries the inversion. In addition, in 4 of 12 (33%) families with a proband carrying the WBS deletion, we observed the inversion exclusively in the parent transmitting the disease-related chromosome. These results suggest the presence of a newly identified genomic variant within the population that may be associated with the disease. It may result in predisposition to primarily WBS-causing microdeletions, but may also cause translocations and inversions. PMID:11685205

Direct Estimation of Optical Parameters From Photoacoustic Time Series in Quantitative Photoacoustic Tomography.

PubMed

Pulkkinen, Aki; Cox, Ben T; Arridge, Simon R; Goh, Hwan; Kaipio, Jari P; Tarvainen, Tanja

2016-11-01

Estimation of optical absorption and scattering of a target is an inverse problem associated with quantitative photoacoustic tomography. Conventionally, the problem is expressed as two folded. First, images of initial pressure distribution created by absorption of a light pulse are formed based on acoustic boundary measurements. Then, the optical properties are determined based on these photoacoustic images. The optical stage of the inverse problem can thus suffer from, for example, artefacts caused by the acoustic stage. These could be caused by imperfections in the acoustic measurement setting, of which an example is a limited view acoustic measurement geometry. In this work, the forward model of quantitative photoacoustic tomography is treated as a coupled acoustic and optical model and the inverse problem is solved by using a Bayesian approach. Spatial distribution of the optical properties of the imaged target are estimated directly from the photoacoustic time series in varying acoustic detection and optical illumination configurations. It is numerically demonstrated, that estimation of optical properties of the imaged target is feasible in limited view acoustic detection setting.

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.

A New Active Cavitation Mapping Technique for Pulsed HIFU Applications – Bubble Doppler

PubMed Central

Li, Tong; Khokhlova, Tatiana; Sapozhnikov, Oleg; Hwang, Joo Ha; Sapozhnikov, Oleg; O’Donnell, Matthew

2015-01-01

In this work, a new active cavitation mapping technique for pulsed high-intensity focused ultrasound (pHIFU) applications termed bubble Doppler is proposed and its feasibility tested in tissue-mimicking gel phantoms. pHIFU therapy uses short pulses, delivered at low pulse repetition frequency, to cause transient bubble activity that has been shown to enhance drug and gene delivery to tissues. The current gold standard for detecting and monitoring cavitation activity during pHIFU treatments is passive cavitation detection (PCD), which provides minimal information on the spatial distribution of the bubbles. B-mode imaging can detect hyperecho formation, but has very limited sensitivity, especially to small, transient microbubbles. The bubble Doppler method proposed here is based on a fusion of the adaptations of three Doppler techniques that had been previously developed for imaging of ultrasound contrast agents – color Doppler, pulse inversion Doppler, and decorrelation Doppler. Doppler ensemble pulses were interleaved with therapeutic pHIFU pulses using three different pulse sequences and standard Doppler processing was applied to the received echoes. The information yielded by each of the techniques on the distribution and characteristics of pHIFU-induced cavitation bubbles was evaluated separately, and found to be complementary. The unified approach - bubble Doppler – was then proposed to both spatially map the presence of transient bubbles and to estimate their sizes and the degree of nonlinearity. PMID:25265178

Fast pulsed excitation wiggler or undulator

DOEpatents

van Steenbergen, Arie

1990-01-01

A fast pulsed excitation, electromagnetic undulator or wiggler, employing geometrically alternating substacks of thin laminations of ferromagnetic material, together with a single turn current loop excitation of the composite assembly, of such shape and configuration that intense, spatially alternating, magnetic fields are generated; for use as a pulsed mode undulator or wiggler radiator, for use in a Free Electron Laser (FEL) type radiation source or, for use in an Inverse Free Electron Laser (IFEL) charged particle accelerator.

Output Beam Polarisation of X-ray Lasers with Transient Inversion

NASA Astrophysics Data System (ADS)

Janulewicz, K. A.; Kim, C. M.; Matouš, B.; Stiel, H.; Nishikino, M.; Hasegawa, N.; Kawachi, T.

It is commonly accepted that X-ray lasers, as the devices based on amplified spontaneous emission (ASE), did not show any specific polarization in the output beam. The theoretical analysis within the uniform (single-mode) approximation suggested that the output radiation should show some defined polarization feature, but randomly changing from shot-to-shot. This hypothesis has been verified by experiment using traditional double-pulse scheme of transient inversion. Membrane beam-splitter was used as a polarization selector. It was found that the output radiation has a significant component of p-polarisation in each shot. To explain the effect and place it in the line with available, but scarce data, propagation and kinetic effects in the non-uniform plasma have been analysed.

Adiabatic sweep pulses for earth's field NMR with a surface coil

NASA Astrophysics Data System (ADS)

Conradi, Mark S.; Altobelli, Stephen A.; Sowko, Nicholas J.; Conradi, Susan H.; Fukushima, Eiichi

2018-03-01

Adiabatic NMR sweep pulses are described for inversion and excitation in very low magnetic fields B0 and with broad distribution of excitation field amplitude B1. Two aspects distinguish the low field case: (1) when B1 is comparable to or greater than B0, the rotating field approximation fails and (2) inversion sweeps cannot extend to values well below the Larmor frequency because they would approach or pass through zero frequency. Three approaches to inversion are described. The first is a conventional tangent frequency sweep down to the Larmor frequency, a 180° phase shift, and a sweep back up to the starting frequency. The other two are combined frequency and amplitude sweeps covering a narrower frequency range; one is a symmetric sweep from above to below the Larmor frequency and the other uses a smooth decrease of B1 immediately before and after the 180° phase shift. These two AM/FM sweeps show excellent inversion efficiencies over a wide range of B1, a factor of 30 or more. We also demonstrate an excitation sweep that works well in the presence of the same wide range of B1. We show that the primary effect of the counter-rotating field (i.e., at low B0) is that the magnetization suffers large, periodic deviations from where it would be at large B0. Thus, successful sweep pulses must avoid any sharp features in the amplitude, phase, or frequency.

Optimization of flow-sensitive alternating inversion recovery (FAIR) for perfusion functional MRI of rodent brain.

PubMed

Nasrallah, Fatima A; Lee, Eugene L Q; Chuang, Kai-Hsiang

2012-11-01

Arterial spin labeling (ASL) MRI provides a noninvasive method to image perfusion, and has been applied to map neural activation in the brain. Although pulsed labeling methods have been widely used in humans, continuous ASL with a dedicated neck labeling coil is still the preferred method in rodent brain functional MRI (fMRI) to maximize the sensitivity and allow multislice acquisition. However, the additional hardware is not readily available and hence its application is limited. In this study, flow-sensitive alternating inversion recovery (FAIR) pulsed ASL was optimized for fMRI of rat brain. A practical challenge of FAIR is the suboptimal global inversion by the transmit coil of limited dimensions, which results in low effective labeling. By using a large volume transmit coil and proper positioning to optimize the body coverage, the perfusion signal was increased by 38.3% compared with positioning the brain at the isocenter. An additional 53.3% gain in signal was achieved using optimized repetition and inversion times compared with a long TR. Under electrical stimulation to the forepaws, a perfusion activation signal change of 63.7 ± 6.3% can be reliably detected in the primary somatosensory cortices using single slice or multislice echo planar imaging at 9.4 T. This demonstrates the potential of using pulsed ASL for multislice perfusion fMRI in functional and pharmacological applications in rat brain. Copyright © 2012 John Wiley & Sons, Ltd.

Two-colour X-gamma ray inverse Compton back-scattering source

NASA Astrophysics Data System (ADS)

Drebot, I.; Petrillo, V.; Serafini, L.

2017-10-01

We present a simple and new scheme for producing two-colour Thomson/Compton radiation with the possibility of controlling separately the polarization of the two different colours, based on the interaction of one single electron beam with two light pulses that can come from the same laser setup or from two different lasers and that collide with the electrons at different angle. One of the most interesting cases for medical applications is to provide two X-ray pulses across the iodine K-edge at 33.2 keV. The iodine is used as contrast medium in various imaging techniques and the availability of two spectral lines accross the K-edge allows one to produce subtraction images with a great increase in accuracy.

"FLIPSY"—A New Solvent-Suppression Sequence for Nonexchanging Solutes Offering Improved Integral Accuracy Relative to 1D NOESY

NASA Astrophysics Data System (ADS)

Neuhaus, David; Ismail, Ismail M.; Chung, Chun-Wa

A new method of solvent suppression is described, based on presaturation in combination with volume selection; the name "FLIPSY" is proposed for this sequence. A low-flip-angle pulse is used for excitation, immediately followed by two 180° pulses, each of which is independently phase cycled through Exorcycle. The phase-cycled inversion pulses achieve volume selection in a way similar to the widely used 1D NOESY sequence, thereby largely eliminating any residual "hump" signal from the solvent. The two 180° pulses combine to produce a net 360° rotation for zmagnetization and either a 180° or a 360° rotation for transverse magnetization, depending on the step in the phase cycle. This allows the overall flip angle of the sequence to be controlled by adjusting the length of the initial excitation pulse. It is demonstrated that this property allows one to choose freely a suitable compromise between signal strength and integral accuracy when using FLIPSY, just as when using single-pulse excitation. Such a choice cannot be made when using 1D NOESY, since the effective flip angle in that experiment is always 90°. The application of FLIPSY to recording LC-NMR spectra is demonstrated.

Finite-fault source inversion using adjoint methods in 3D heterogeneous media

NASA Astrophysics Data System (ADS)

Somala, Surendra Nadh; Ampuero, Jean-Paul; Lapusta, Nadia

2018-04-01

Accounting for lateral heterogeneities in the 3D velocity structure of the crust is known to improve earthquake source inversion, compared to results based on 1D velocity models which are routinely assumed to derive finite-fault slip models. The conventional approach to include known 3D heterogeneity in source inversion involves pre-computing 3D Green's functions, which requires a number of 3D wave propagation simulations proportional to the number of stations or to the number of fault cells. The computational cost of such an approach is prohibitive for the dense datasets that could be provided by future earthquake observation systems. Here, we propose an adjoint-based optimization technique to invert for the spatio-temporal evolution of slip velocity. The approach does not require pre-computed Green's functions. The adjoint method provides the gradient of the cost function, which is used to improve the model iteratively employing an iterative gradient-based minimization method. The adjoint approach is shown to be computationally more efficient than the conventional approach based on pre-computed Green's functions in a broad range of situations. We consider data up to 1 Hz from a Haskell source scenario (a steady pulse-like rupture) on a vertical strike-slip fault embedded in an elastic 3D heterogeneous velocity model. The velocity model comprises a uniform background and a 3D stochastic perturbation with the von Karman correlation function. Source inversions based on the 3D velocity model are performed for two different station configurations, a dense and a sparse network with 1 km and 20 km station spacing, respectively. These reference inversions show that our inversion scheme adequately retrieves the rise time when the velocity model is exactly known, and illustrates how dense coverage improves the inference of peak slip velocities. We investigate the effects of uncertainties in the velocity model by performing source inversions based on an incorrect, homogeneous velocity model. We find that, for velocity uncertainties that have standard deviation and correlation length typical of available 3D crustal models, the inverted sources can be severely contaminated by spurious features even if the station density is high. When data from thousand or more receivers is used in source inversions in 3D heterogeneous media, the computational cost of the method proposed in this work is at least two orders of magnitude lower than source inversion based on pre-computed Green's functions.

Finite-fault source inversion using adjoint methods in 3-D heterogeneous media

NASA Astrophysics Data System (ADS)

Somala, Surendra Nadh; Ampuero, Jean-Paul; Lapusta, Nadia

2018-07-01

Accounting for lateral heterogeneities in the 3-D velocity structure of the crust is known to improve earthquake source inversion, compared to results based on 1-D velocity models which are routinely assumed to derive finite-fault slip models. The conventional approach to include known 3-D heterogeneity in source inversion involves pre-computing 3-D Green's functions, which requires a number of 3-D wave propagation simulations proportional to the number of stations or to the number of fault cells. The computational cost of such an approach is prohibitive for the dense data sets that could be provided by future earthquake observation systems. Here, we propose an adjoint-based optimization technique to invert for the spatio-temporal evolution of slip velocity. The approach does not require pre-computed Green's functions. The adjoint method provides the gradient of the cost function, which is used to improve the model iteratively employing an iterative gradient-based minimization method. The adjoint approach is shown to be computationally more efficient than the conventional approach based on pre-computed Green's functions in a broad range of situations. We consider data up to 1 Hz from a Haskell source scenario (a steady pulse-like rupture) on a vertical strike-slip fault embedded in an elastic 3-D heterogeneous velocity model. The velocity model comprises a uniform background and a 3-D stochastic perturbation with the von Karman correlation function. Source inversions based on the 3-D velocity model are performed for two different station configurations, a dense and a sparse network with 1 and 20 km station spacing, respectively. These reference inversions show that our inversion scheme adequately retrieves the rise time when the velocity model is exactly known, and illustrates how dense coverage improves the inference of peak-slip velocities. We investigate the effects of uncertainties in the velocity model by performing source inversions based on an incorrect, homogeneous velocity model. We find that, for velocity uncertainties that have standard deviation and correlation length typical of available 3-D crustal models, the inverted sources can be severely contaminated by spurious features even if the station density is high. When data from thousand or more receivers is used in source inversions in 3-D heterogeneous media, the computational cost of the method proposed in this work is at least two orders of magnitude lower than source inversion based on pre-computed Green's functions.

Identification of Scattering Mechanisms from Measured Impulse Response Signatures of Several Conducting Objects.

DTIC Science & Technology

1984-02-01

conducting sphere 35 compared to inverse transform of exact solution. 4-5. Measured impulse response of a conducting 2:1 right 37 circular cylinder with...frequency domain. This is equivalent to multiplication in the time domain by the inverse transform of w(n), which is shown in Figure 3-1 for N=15. The...equivalent pulse width from 0.066 T for the rectangular window to 0.10 T for the Hanning window. The inverse transform of the Hanning window is shown

Hadamard Transform Time-of-Flight Mass Spectrometry

DTIC Science & Technology

2004-11-30

computer. This rather slow process -. 12 allowed us to evaluate different methods of -M processing the data prior to performing the 4- - inverse transform . The...DSK6713 is capable of • o , , performing the inverse transform and this would 0 & 10 Time (ms,)’ 5 20 25 be the preferred mode of operation since...treating the raw data prior to performing the -20"d Loutled patern inverse transform . We expected that noise associated 0-with the pulsing of the Bradbury

Reference values and associated factors for Japanese newborns' blood pressure and pulse rate: the babies' and their parents' longitudinal observation in Suzuki Memorial Hospital on intrauterine period (BOSHI) study.

PubMed

Satoh, Michihiro; Inoue, Ryusuke; Tada, Hideko; Hosaka, Miki; Metoki, Hirohito; Asayama, Kei; Murakami, Takahisa; Mano, Nariyasu; Ohkubo, Takayoshi; Yagihashi, Katsuyo; Hoshi, Kazuhiko; Suzuki, Masakuni; Imai, Yutaka

2016-08-01

Currently, normative means and ranges of blood pressure (BP) and pulse rates in Japanese newborns are not available. The objective of the present study was to estimate BP, pulse rate, and their distribution among Japanese newborns. Using oscillometric devices, arm or calf BP and pulse rate levels were obtained from 3148 infants born between 2007 and 2014, consecutively at Suzuki Memorial Hospital, Iwanuma, Japan. Of those, data from 2628 full-term, singleton newborns with BP measured on day 3 after birth were analyzed. Arm SBP/DBP and pulse rate in the reference group (n = 2628) were 70.5 ± 7.4/44.3 ± 6.7 mmHg and 117.3 ± 16.6 bpm, respectively. The 5-95th percentiles were 58-83 mmHg for SBP, 35-57 mmHg for DBP, and 91-145 bpm for pulse rate. Similar values were obtained from calf measurements. In multiple regression analysis, birth weight and spontaneous cephalic delivery were positively and light/deep sleep was inversely associated with higher arm SBP/DBP (P ≤ 0.04), whereas sex, Apgar score, gestational age, and mother's age did not significantly affect BP levels (P ≥ 0.06). Male sex, gestational age, spontaneous cephalic delivery, and light/deep sleep were inversely associated with higher pulse rate (P ≤ 0.02). The present study is the first to show the distributions of Asian newborns' BP levels and pulse rate. The assessment of newborns' BP levels and pulse rate should consider birth weight, gestational age after birth, and actual condition at BP measurement.

The relationship between pulsatile GnRH secretion and cAMP production in immortalized GnRH neurons.

PubMed

Frattarelli, John L; Krsmanovic, Lazar Z; Catt, Kevin J

2011-06-01

In perifused immortalized GnRH neurons (GT1-7), simultaneous measurements of GnRH and cAMP revealed that the secretory profiles for both GnRH and cAMP are pulsatile. An analysis of GnRH and cAMP pulses in 16 independent experiments revealed that 25% of pulses coincide. Inversion of the peak and nadir levels was found in 33% and random relationship between GnRH and cAMP found in 42% of analyzed pulses. The random relation between GnRH and cAMP pulse resets to synchronous after an inverse relation between pulses occurred during the major GnRH release, indicating that GnRH acts as a switching mechanism to synchronize cAMP and GnRH release in perifused GT1-7 neurons. Activation of GnRH receptors with increasing agonist concentrations caused a biphasic change in cAMP levels. Low nanomolar concentrations increased cAMP production, but at high concentrations the initial increase was followed by a rapid decline to below the basal level. Blockade of the GnRH receptors by peptide and nonpeptide antagonists generated monotonic nonpulsatile increases in both GnRH and cAMP production. These findings indicate that cAMP positively regulates GnRH secretion but does not participate in the mechanism of pulsatile GnRH release.

Modified Wideband Three-Dimensional Late Gadolinium Enhancement MRI for Patients with Implantable Cardiac Devices

PubMed Central

Rashid, Shams; Rapacchi, Stanislas; Shivkumar, Kalyanam; Plotnik, Adam; Finn, J. Paul; Hu, Peng

2015-01-01

Purpose To study the effects of cardiac devices on three-dimensional (3D) late gadolinium enhancement (LGE) MRI and to develop a 3D LGE protocol for implantable cardioverter defibrillator (ICD) patients with reduced image artifacts. Theory and Methods The 3D LGE sequence was modified by implementing a wideband inversion pulse, which reduces hyperintensity artifacts, and by increasing bandwidth of the excitation pulse. The modified wideband 3D LGE sequence was tested in phantoms and evaluated in six volunteers and five patients with ICDs. Results Phantom and in vivo studies results demonstrated extended signal void and ripple artifacts in 3D LGE that were associated with ICDs. The reason for these artifacts was slab profile distortion and the subsequent aliasing in the slice-encoding direction. The modified wideband 3D LGE provided significantly reduced ripple artifacts than 3D LGE with wideband inversion only. Comparison of 3D and 2D LGE images demonstrated improved spatial resolution of the heart using 3D LGE. Conclusion Increased bandwidth of the inversion and excitation pulses can significantly reduce image artifacts associated with ICDs. Our modified wideband 3D LGE protocol can be readily used for imaging patients with ICDs given appropriate safety guidelines are followed. PMID:25772155

Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging with a Phased Array Transducer

PubMed Central

Song, Pengfei; Zhao, Heng; Urban, Matthew W.; Manduca, Armando; Pislaru, Sorin V.; Kinnick, Randall R.; Pislaru, Cristina; Greenleaf, James F.; Chen, Shigao

2013-01-01

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE. PMID:24021638

Combined chirp coded tissue harmonic and fundamental ultrasound imaging for intravascular ultrasound: 20–60 MHz phantom and ex vivo results

PubMed Central

Park, Jinhyoung; Li, Xiang; Zhou, Qifa; Shung, K. Kirk

2013-01-01

The application of chirp coded excitation to pulse inversion tissue harmonic imaging can increase signal to noise ratio. On the other hand, the elevation of range side lobe level, caused by leakages of the fundamental signal, has been problematic in mechanical scanners which are still the most prevalent in high frequency intravascular ultrasound imaging. Fundamental chirp coded excitation imaging can achieve range side lobe levels lower than –60 dB with Hanning window, but it yields higher side lobes level than pulse inversion chirp coded tissue harmonic imaging (PI-CTHI). Therefore, in this paper a combined pulse inversion chirp coded tissue harmonic and fundamental imaging mode (CPI-CTHI) is proposed to retain the advantages of both chirp coded harmonic and fundamental imaging modes by demonstrating 20–60 MHz phantom and ex vivo results. A simulation study shows that the range side lobe level of CPI-CTHI is 16 dB lower than PI-CTHI, assuming that the transducer translates incident positions by 50 μm when two beamlines of pulse inversion pair are acquired. CPI-CTHI is implemented for a proto-typed intravascular ultrasound scanner capable of combined data acquisition in real-time. A wire phantom study shows that CPI-CTHI has a 12 dB lower range side lobe level and a 7 dB higher echo signal to noise ratio than PI-CTHI, while the lateral resolution and side lobe level are 50 μm finer and –3 dB less than fundamental chirp coded excitation imaging respectively. Ex vivo scanning of a rabbit trachea demonstrates that CPI-CTHI is capable of visualizing blood vessels as small as 200 μm in diameter with 6 dB better tissue contrast than either PI-CTHI or fundamental chirp coded excitation imaging. These results clearly indicate that CPI-CTHI may enhance tissue contrast with less range side lobe level than PI-CTHI. PMID:22871273

Energy deposition dynamics of femtosecond pulses in water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minardi, Stefano, E-mail: stefano@stefanominardi.eu; Pertsch, Thomas; Milián, Carles

2014-12-01

We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.

Physics for clinicians: Fluid-attenuated inversion recovery (FLAIR) and double inversion recovery (DIR) Imaging.

PubMed

Saranathan, Manojkumar; Worters, Pauline W; Rettmann, Dan W; Winegar, Blair; Becker, Jennifer

2017-12-01

A pedagogical review of fluid-attenuated inversion recovery (FLAIR) and double inversion recovery (DIR) imaging is conducted in this article. The basics of the two pulse sequences are first described, including the details of the inversion preparation and imaging sequences with accompanying mathematical formulae for choosing the inversion time in a variety of scenarios for use on clinical MRI scanners. Magnetization preparation (or T2prep), a strategy for improving image signal-to-noise ratio and contrast and reducing T 1 weighting at high field strengths, is also described. Lastly, image artifacts commonly associated with FLAIR and DIR are described with clinical examples, to help avoid misdiagnosis. 5 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017;46:1590-1600. © 2017 International Society for Magnetic Resonance in Medicine.

Ultraviolet-infrared laser-induced domain inversion in MgO-doped congruent LiNbO3 and near stoichiometric LiTaO3 crystals

NASA Astrophysics Data System (ADS)

Zhi, Ya'nan; Qu, Weijuan; Liu, De'an; Sun, Jianfeng; Yan, Aimin; Liu, Liren

2008-08-01

Laser-induced domain inversion is a promising technique for domain engineering in LiNbO3 and LiTaO3. The ultraviolet-infrared laser induced domain inversions in MgO-doped congruent LiNbO3 and near stoichiometric LiTaO3 crystals are investigated for the first time here. Within the wavelength range from 351 to 799 nm, the different reductions of nucleation field induced by the focused continuous laser irradiation are systematically investigated in the MgO-doped congruent LiNbO3 crystals. The investigation of ultrashort-pulse laser-induced domain inversion in MgO-doped congruent LiNbO3 is performed with 800 nm wavelength irradiation. The focused continuous ultraviolet laser-induced ferroelectric domain inversion in the near stoichiometric LiTaO3 is also investigated. The different physical explanations, based on space charge field and defect formation, are presented for the laser-induced domain inversion, and the solid experimental proofs are also presented. The results provide the solid experimental proofs and feasible schemes for the further investigation of laser-induced domain engineering in MgO-doped LiNbO3 and near stoichiometric LiTaO3 crystals. The important characteristics of domain inversion, including domain wall and internal field, in LiNbO3 crystals are also investigated by the digital holographic interferometry with an improved reconstruction method, and some creative experimental results and conclusions are achieved.

A review on the structural styles of deformation during Late Cretaceous and Paleocene tectonic phases in the southern North Sea area

NASA Astrophysics Data System (ADS)

Deckers, Jef; van der Voet, Eva

2018-04-01

The Mesozoic rifts in the southern North Sea area were affected by Late Cretaceous to Paleocene inversion. Two main inversion phases were traditionally identified in this interval: the Sub-Hercynian and the Laramide phases. The Sub-Hercynian phase started in the early Late Cretaceous, peaked during the Campanian and ended in the late Maastrichtian, while the Laramide phase started in the late Danian and ended in the Thanetian. The Late Cretaceous Sub-Hercynian phase was strong and occurred in several pulses. These pulses led to basin-scale uplift by large reverse movements along basin-bounding faults and resulted in large amounts of erosion (up to 2 km) of Mesozoic and older sediments. The middle Paleocene Laramide phase on the other hand resulted in mild, domal uplift of some Late Cretaceous inverted basins and subsidence (into depocenters) of others. The subsequent Cenozoic inversion phases displayed similar or lower amplitudes and wavelengths of vertical surface movements as the Laramide phase. The transition from the Sub-Hercynian to the Laramide phase in the southern North Sea area therefore coincides with the overall transition from fault-controlled inversion to broad domal vertical surface movements.

The effect of Cr substitution on the structural, electronic and magnetic properties of pulsed laser deposited NiFe2O4 thin films

NASA Astrophysics Data System (ADS)

Panwar, Kalpana; Tiwari, Shailja; Bapna, Komal; Heda, N. L.; Choudhary, R. J.; Phase, D. M.; Ahuja, B. L.

2017-01-01

We have studied the structural, electronic and magnetic properties of pulsed laser deposited thin films of Ni1-xCrxFe2O4 (x=0.02 and 0.05) on Si (111) and Si (100) substrates. The films reveal single phase, polycrystalline structure with larger grain size on Si (111) substrate than that on Si (100) substrate. Contrary to the expected inverse spinel structure, x-ray photoemission (XPS) studies reveal the mixed spinel structure. XPS results suggest that Ni and Fe ions exist in 2+ and 3+ states, respectively, and they exist in tetrahedral as well as octahedral sites. The deviation from the inverse spinel leads to modified magnetic properties. It is observed that saturation magnetization drastically drops compared to the expected saturation value for inverse spinel structure. Strain in the films and lattice distortion produced by the Cr doping also appear to influence the magnetic properties.

H(C)P and H(P)C triple-resonance experiments at natural abundance employing long-range couplings.

PubMed

Malon, Michal; Koshino, Hiroyuki

2007-09-01

Modified two-dimensional (2D) triple-resonance H(C)P and H(P)C experiments based on INEPT/HMQC and double-INEPT schemes are applied to the study of organophosphorus compounds at natural abundances. The implementation of effective (1)H--(13)C gradient selection, additional purging pulsed field gradients, spinlock pulses, and improved phase cycling is demonstrated to allow weak correlation signals based on long-range couplings to be readily observed. Through the combination of two heteronuclear long-range coupling constants, (n)J(CH) and (n)J(PC) in H(C)P experiments or (n)J(PH) and (n)J(PC) in H(P)C experiments, protons can be correlated to a second heteronucleus through 4-7 chemical bonds. These experiments thus overcome the inherit limitations of classical (1)H-X HMBC experiments, which require a nonzero value of the heteronuclear coupling constant (n)J(XH). Ultra-broadband inversion composite pulses are successfully employed in the H(P)C INEPT/HMQC and H(P)C double-INEPT pulse sequences to increase the utility of the experiments and the quality of obtained spectra. This work extends and completes a set of 2D phase-sensitive triple-resonance experiments applicable at natural abundances, and also offers insight into the methodology of triple-resonance experiments and the application of pulsed field gradients. A one-dimensional triple-resonance experiment employing carbon detection is suggested for accurate determination of small (n)J(PC).

Ultrafast magnetization switching by spin-orbit torques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garello, Kevin, E-mail: kevin.garello@mat.ethz.ch; Avci, Can Onur; Baumgartner, Manuel

2014-11-24

Spin-orbit torques induced by spin Hall and interfacial effects in heavy metal/ferromagnetic bilayers allow for a switching geometry based on in-plane current injection. Using this geometry, we demonstrate deterministic magnetization reversal by current pulses ranging from 180 ps to ms in Pt/Co/AlO{sub x} dots with lateral dimensions of 90 nm. We characterize the switching probability and critical current I{sub c} as a function of pulse length, amplitude, and external field. Our data evidence two distinct regimes: a short-time intrinsic regime, where I{sub c} scales linearly with the inverse of the pulse length, and a long-time thermally assisted regime, where I{sub c} variesmore » weakly. Both regimes are consistent with magnetization reversal proceeding by nucleation and fast propagation of domains. We find that I{sub c} is a factor 3–4 smaller compared to a single domain model and that the incubation time is negligibly small, which is a hallmark feature of spin-orbit torques.« less

Local diffusion and diffusion-T2 distribution measurements in porous media

NASA Astrophysics Data System (ADS)

Vashaee, S.; Newling, B.; MacMillan, B.; Marica, F.; Li, M.; Balcom, B. J.

2017-05-01

Slice-selective pulsed field gradient (PFG) and PFG-T2 measurements are developed to measure spatially-resolved molecular diffusion and diffusion-T2 distributions. A spatially selective adiabatic inversion pulse was employed for slice-selection. The slice-selective pulse is able to select a coarse slice, on the order of 1 cm, at an arbitrary position in the sample. The new method can be employed to characterize oil-water mixtures in porous media. The new technique has an inherent sensitivity advantage over phase encoding imaging based methods due to signal being localized from a thick slice. The method will be advantageous for magnetic resonance of porous media at low field where sensitivity is problematic. Experimental CPMG data, following PFG diffusion measurement, were compromised by a transient ΔB0(t) field offset. The off resonance effects of ΔB0(t) were examined by simulation. The ΔB0 offset artifact in D-T2 distribution measurements may be avoided by employing real data, instead of magnitude data.

Open-cavity fiber laser with distributed feedback based on externally or self-induced dynamic gratings.

PubMed

Lobach, Ivan A; Drobyshev, Roman V; Fotiadi, Andrei A; Podivilov, Evgeniy V; Kablukov, Sergey I; Babin, Sergey A

2017-10-15

Dynamic population inversion gratings induced in an active medium by counter-propagating optical fields may have a reverse effect on writing laser radiation via feedback they provide. In this Letter we report, to the best of our knowledge, on the first demonstration of an open-cavity fiber laser in which the distributed feedback is provided by a dynamic grating "written" in a Yb-doped active fiber, either by an external source or self-induced via a weak (∼0.1%) reflection from an angle-cleaved fiber end. It has been shown that meters-long dynamic grating is formed with a narrow bandwidth (<50  MHz) and a relatively high-reflection coefficient (>7%) securing single-frequency operation, but the subsequent hole-burning effects accompanied by new grating formation lead to the switching from one longitudinal mode to another. providing a regular pulse-mode dynamics. As a result, periodically generated pulse trains cover a spectrum range of several terahertz delivering millions of cavity modes in sequent pulses.

Joint synthetic aperture radar plus ground moving target indicator from single-channel radar using compressive sensing

DOEpatents

Thompson, Douglas; Hallquist, Aaron; Anderson, Hyrum

2017-10-17

The various embodiments presented herein relate to utilizing an operational single-channel radar to collect and process synthetic aperture radar (SAR) and ground moving target indicator (GMTI) imagery from a same set of radar returns. In an embodiment, data is collected by randomly staggering a slow-time pulse repetition interval (PRI) over a SAR aperture such that a number of transmitted pulses in the SAR aperture is preserved with respect to standard SAR, but many of the pulses are spaced very closely enabling movers (e.g., targets) to be resolved, wherein a relative velocity of the movers places them outside of the SAR ground patch. The various embodiments of image reconstruction can be based on compressed sensing inversion from undersampled data, which can be solved efficiently using such techniques as Bregman iteration. The various embodiments enable high-quality SAR reconstruction, and high-quality GMTI reconstruction from the same set of radar returns.

Inverse spin Hall effect from pulsed spin current in organic semiconductors with tunable spin-orbit coupling.

PubMed

Sun, Dali; van Schooten, Kipp J; Kavand, Marzieh; Malissa, Hans; Zhang, Chuang; Groesbeck, Matthew; Boehme, Christoph; Valy Vardeny, Z

2016-08-01

Exploration of spin currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates is appealing for potential spintronics applications. Owing to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals in OSECs using pulsed ferromagnetic resonance, where the ISHE is two to three orders of magnitude larger compared to cw excitation. This strong ISHE enables us to investigate a variety of OSECs ranging from π-conjugated polymers with strong SOC that contain intrachain platinum atoms, to weak SOC polymers, to C60 films, where the SOC is predominantly caused by the curvature of the molecule's surface. The pulsed-ISHE technique offers a robust route for efficient injection and detection schemes of spin currents at room temperature, and paves the way for spin orbitronics in plastic materials.

Neon-hydrogen penning plasma laser in a helical hallow-cathode discharge

NASA Astrophysics Data System (ADS)

Pramatarov, P. M.; Stefanova, M. S.; Ganciu, M.; Karelin, A. V.; Yancharina, A. M.; Ivanova, J. P.; Yakovlenko, S. I.

1991-07-01

A Penning plasma laser (PPL) operating at the NeI 585.3 nm and NeI 1.15 μm lines in Ne-H2 mixture has been realized. Helical configuration of the electrodes was used. The dependence of the laser-pulse shape and output power on current pulse duration and amplitude values were investigated. Peak output powers of 1.5 W for the yellow line and 1.2 W for the IR line have been measured. The population inversion mechanism for the 585.3 nm line is discussed in the frames of a model for PPL. The main factor maintaining the population inversion on both lines is depopulation of the Ne(1 s 2) level by Penning reactions with H2.

Neon-hydrogen Penning plasma laser in a helical hallow-cathode discharge

NASA Astrophysics Data System (ADS)

Pramatarov, P. M.; Stefanova, M. S.; Ivanova, J. P.; Ganciu, M.; Karelin, A. V.; Iakovlenko, S. I.; Iancharina, A. M.

1991-07-01

A Penning plasma laser (PPL) operating at the NeI 585.3 nm and NeI 1.15-micron lines in Ne-H2 mixture has been realized. Helical configuration of the electrodes was used. The dependence of the laser-pulse shape and output power on current pulse duration and amplitude values were investigated. Peak output powers of 1.5 W for the yellow line and 1.2 W for the IR line have been measured. The population inversion mechanism for the 585.3 nm line is discussed in the frames of a model for PPL. The main factor maintaining the population inversion on both lines is depopulation of the Ne(1S2) level by Penning reactions with H2.

Arbitrary waveform modulated pulse EPR at 200 GHz

NASA Astrophysics Data System (ADS)

Kaminker, Ilia; Barnes, Ryan; Han, Songi

2017-06-01

We report here on the implementation of arbitrary waveform generation (AWG) capabilities at ∼200 GHz into an Electron Paramagnetic Resonance (EPR) and Dynamic Nuclear Polarization (DNP) instrument platform operating at 7 T. This is achieved with the integration of a 1 GHz, 2 channel, digital to analog converter (DAC) board that enables the generation of coherent arbitrary waveforms at Ku-band frequencies with 1 ns resolution into an existing architecture of a solid state amplifier multiplier chain (AMC). This allows for the generation of arbitrary phase- and amplitude-modulated waveforms at 200 GHz with >150 mW power. We find that the non-linearity of the AMC poses significant difficulties in generating amplitude-modulated pulses at 200 GHz. We demonstrate that in the power-limited regime of ω1 < 1 MHz phase-modulated pulses were sufficient to achieve significant improvements in broadband (>10 MHz) spin manipulation in incoherent (inversion), as well as coherent (echo formation) experiments. Highlights include the improvement by one order of magnitude in inversion bandwidth compared to that of conventional rectangular pulses, as well as a factor of two in improvement in the refocused echo intensity at 200 GHz.

Fourier transformation microwave spectroscopy of the methyl glycolate-H2O complex

NASA Astrophysics Data System (ADS)

Fujitake, Masaharu; Tanaka, Toshihiro; Ohashi, Nobukimi

2018-01-01

The rotational spectrum of one conformer of the methyl glycolate-H2O complex has been measured by means of the pulsed jet Fourier transform microwave spectrometer. The observed a- and b-type transitions exhibit doublet splittings due to the internal rotation of the methyl group. On the other hand, most of the c-type transitions exhibit quartet splittings arising from the methyl internal rotation and the inversion motion between two equivalent conformations. The spectrum was analyzed using parameterized expressions of the Hamiltonian matrix elements derived by applying the tunneling matrix formalism. Based on the results obtained from ab initio calculation, the observed complex of methyl glycolate-H2O was assigned to the most stable conformer of the insertion complex, in which a non-planer seven membered-ring structure is formed by the intermolecular hydrogen bonds between methyl glycolate and H2O subunits. The inversion motion observed in the c-type transitions is therefore a kind of ring-inversion motion between two equivalent conformations. Conformational flexibility, which corresponds to the ring-inversion between two equivalent conformations and to the isomerization between two possible conformers of the insertion complex, was investigated with the help of the ab initio calculation.

Boosting sensitivity and suppressing artifacts via multi-acquisition in direct polarization NMR experiments with small flip-angle pulses.

PubMed

Fu, Riqiang; Hernández-Maldonado, Arturo J

2018-05-24

A small flip-angle pulse direct polarization is the simplest method commonly used to quantify various compositions in many materials applications. This method sacrifices the sensitivity per scan in exchange for rapid repeating of data acquisition for signal accumulation. In addition, the resulting spectrum often encounters artifacts from background signals from probe components and/or from acoustic rings leading to a distorted baseline, especially in low-γ nuclei and wideline NMR. In this work, a multi-acquisition scheme is proposed to boost the sensitivity per scan and at the same time effectively suppress these artifacts. Here, an adiabatic inversion pulse is first applied in order to bring the magnetization from the +z to -z axis and then a small flip-angle pulse excitation is used before the data acquisition. Right after the first acquisition, the adiabatic inversion pulse is applied again to flip the magnetization back to the +z axis. The second data acquisition takes place after another small flip-angle pulse excitation. The difference between the two consecutive acquisitions cancels out any artifacts, while the wanted signals are accumulated. This acquisition process can be repeated many times before going into next scan. Therefore, by acquiring the signals multiple times in a single scan the sensitivity is improved. A mixture sample of flufenamic acid and 3,5-difluorobenzoic acid and a titanium silicate sample have been used to demonstrate the advantages of this newly proposed method. Copyright © 2018 Elsevier Inc. All rights reserved.

Statistical Feature Extraction for Artifact Removal from Concurrent fMRI-EEG Recordings

PubMed Central

Liu, Zhongming; de Zwart, Jacco A.; van Gelderen, Peter; Kuo, Li-Wei; Duyn, Jeff H.

2011-01-01

We propose a set of algorithms for sequentially removing artifacts related to MRI gradient switching and cardiac pulsations from electroencephalography (EEG) data recorded during functional magnetic resonance imaging (fMRI). Special emphases are directed upon the use of statistical metrics and methods for the extraction and selection of features that characterize gradient and pulse artifacts. To remove gradient artifacts, we use a channel-wise filtering based on singular value decomposition (SVD). To remove pulse artifacts, we first decompose data into temporally independent components and then select a compact cluster of components that possess sustained high mutual information with the electrocardiogram (ECG). After the removal of these components, the time courses of remaining components are filtered by SVD to remove the temporal patterns phase-locked to the cardiac markers derived from the ECG. The filtered component time courses are then inversely transformed into multi-channel EEG time series free of pulse artifacts. Evaluation based on a large set of simultaneous EEG-fMRI data obtained during a variety of behavioral tasks, sensory stimulations and resting conditions showed excellent data quality and robust performance attainable by the proposed methods. These algorithms have been implemented as a Matlab-based toolbox made freely available for public access and research use. PMID:22036675

Statistical feature extraction for artifact removal from concurrent fMRI-EEG recordings.

PubMed

Liu, Zhongming; de Zwart, Jacco A; van Gelderen, Peter; Kuo, Li-Wei; Duyn, Jeff H

2012-02-01

We propose a set of algorithms for sequentially removing artifacts related to MRI gradient switching and cardiac pulsations from electroencephalography (EEG) data recorded during functional magnetic resonance imaging (fMRI). Special emphasis is directed upon the use of statistical metrics and methods for the extraction and selection of features that characterize gradient and pulse artifacts. To remove gradient artifacts, we use channel-wise filtering based on singular value decomposition (SVD). To remove pulse artifacts, we first decompose data into temporally independent components and then select a compact cluster of components that possess sustained high mutual information with the electrocardiogram (ECG). After the removal of these components, the time courses of remaining components are filtered by SVD to remove the temporal patterns phase-locked to the cardiac timing markers derived from the ECG. The filtered component time courses are then inversely transformed into multi-channel EEG time series free of pulse artifacts. Evaluation based on a large set of simultaneous EEG-fMRI data obtained during a variety of behavioral tasks, sensory stimulations and resting conditions showed excellent data quality and robust performance attainable with the proposed methods. These algorithms have been implemented as a Matlab-based toolbox made freely available for public access and research use. Published by Elsevier Inc.

Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators

NASA Astrophysics Data System (ADS)

Singh, Ashish; Little, Jesse

2016-11-01

A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).

THz-driven zero-slippage IFEL scheme for phase space manipulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Curry, E.; Fabbri, S.; Musumeci, P.

In this paper, we describe an inverse free electron laser (IFEL) interaction driven by a near single-cycle THz pulse that is group velocity-matched to an electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. We discuss the application of this guided-THz IFEL technique for compression of a relativistic electron bunch and synchronization with the external laser pulse used to generate the THz pulse via optical rectification, as well as a laser-driven THz streaking diagnostic with the potential for femtosecond scale temporal resolution. Initial measurements of the THz waveform via an electro-optic sampling based technique confirm the predicted reduction of the group velocity, using a curved parallel plate waveguide, as a function of the varying aperture size of the guide. We also present the design of a proof-of-principle experiment based on the bunch parameters available at the UCLA PEGASUS laboratory. With amore » $$10\\,\\mathrm{MV}\\,{{\\rm{m}}}^{-1}$$ THz peak field, our simulation model predicts compression of a $$6\\,\\mathrm{MeV}$$ $$100\\,\\mathrm{fs}$$ electron beam by nearly an order of magnitude and a significant reduction of its initial timing jitter.« less

THz-driven zero-slippage IFEL scheme for phase space manipulation

DOE PAGES

Curry, E.; Fabbri, S.; Musumeci, P.; ...

2016-11-24

In this paper, we describe an inverse free electron laser (IFEL) interaction driven by a near single-cycle THz pulse that is group velocity-matched to an electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. We discuss the application of this guided-THz IFEL technique for compression of a relativistic electron bunch and synchronization with the external laser pulse used to generate the THz pulse via optical rectification, as well as a laser-driven THz streaking diagnostic with the potential for femtosecond scale temporal resolution. Initial measurements of the THz waveform via an electro-optic sampling based technique confirm the predicted reduction of the group velocity, using a curved parallel plate waveguide, as a function of the varying aperture size of the guide. We also present the design of a proof-of-principle experiment based on the bunch parameters available at the UCLA PEGASUS laboratory. With amore » $$10\\,\\mathrm{MV}\\,{{\\rm{m}}}^{-1}$$ THz peak field, our simulation model predicts compression of a $$6\\,\\mathrm{MeV}$$ $$100\\,\\mathrm{fs}$$ electron beam by nearly an order of magnitude and a significant reduction of its initial timing jitter.« less

Refractory pulse counting processes in stochastic neural computers.

PubMed

McNeill, Dean K; Card, Howard C

2005-03-01

This letter quantitiatively investigates the effect of a temporary refractory period or dead time in the ability of a stochastic Bernoulli processor to record subsequent pulse events, following the arrival of a pulse. These effects can arise in either the input detectors of a stochastic neural network or in subsequent processing. A transient period is observed, which increases with both the dead time and the Bernoulli probability of the dead-time free system, during which the system reaches equilibrium. Unless the Bernoulli probability is small compared to the inverse of the dead time, the mean and variance of the pulse count distributions are both appreciably reduced.

The effect of excitation and preparation pulses on nonslice selective 2D UTE bicomponent analysis of bound and free water in cortical bone at 3T

PubMed Central

Li, Shihong; Chang, Eric Y.; Bae, Won C.; Chung, Christine B.; Hua, Yanqing; Zhou, Yi; Du, Jiang

2014-01-01

Purpose: The purpose of this study was to investigate the effect of excitation, fat saturation, long T2 saturation, and adiabatic inversion pulses on ultrashort echo time (UTE) imaging with bicomponent analysis of bound and free water in cortical bone for potential applications in osteoporosis. Methods: Six bovine cortical bones and six human tibial midshaft samples were harvested for this study. Each bone sample was imaged with eight sequences using 2D UTE imaging at 3T with half and hard excitation pulses, without and with fat saturation, long T2 saturation, and adiabatic inversion recovery (IR) preparation pulses. Single- and bicomponent signal models were utilized to calculate the T2*s and/or relative fractions of short and long T2*s. Results: For all bone samples UTE T2* signal decay showed bicomponent behavior. A higher short T2* fraction was observed on UTE images with hard pulse excitation compared with half pulse excitation (75.6% vs 68.8% in bovine bone, 79.9% vs 73.2% in human bone). Fat saturation pulses slightly reduced the short T2* fraction relative to regular UTE sequences (5.0% and 2.0% reduction, respectively, with half and hard excitation pulses for bovine bone, 6.3% and 8.2% reduction, respectively, with half and hard excitation pulses for human bone). Long T2 saturation pulses significantly reduced the long T2* fraction relative to regular UTE sequence (18.9% and 17.2% reduction, respectively, with half and hard excitation pulses for bovine bone, 26.4% and 27.7% reduction, respectively, with half and hard excitation pulses for human bone). With IR-UTE preparation the long T2* components were significantly reduced relative to regular UTE sequence (75.3% and 66.4% reduction, respectively, with half and hard excitation pulses for bovine bone, 87.7% and 90.3% reduction, respectively, with half and hard excitation pulses for human bone). Conclusions: Bound and free water T2*s and relative fractions can be assessed using UTE bicomponent analysis. Long T2* components are affected more by long T2 saturation and IR pulses, and short T2* components are affected more by fat saturation pulses. PMID:24506644

The effect of excitation and preparation pulses on nonslice selective 2D UTE bicomponent analysis of bound and free water in cortical bone at 3T

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shihong; Department of Radiology, Hua Dong Hospital, Fudan University, Shanghai 200040; Yancheng Medical College, Jiangsu

Purpose: The purpose of this study was to investigate the effect of excitation, fat saturation, long T2 saturation, and adiabatic inversion pulses on ultrashort echo time (UTE) imaging with bicomponent analysis of bound and free water in cortical bone for potential applications in osteoporosis. Methods: Six bovine cortical bones and six human tibial midshaft samples were harvested for this study. Each bone sample was imaged with eight sequences using 2D UTE imaging at 3T with half and hard excitation pulses, without and with fat saturation, long T2 saturation, and adiabatic inversion recovery (IR) preparation pulses. Single- and bicomponent signal modelsmore » were utilized to calculate the T2{sup *}s and/or relative fractions of short and long T2{sup *}s. Results: For all bone samples UTE T2{sup *} signal decay showed bicomponent behavior. A higher short T2{sup *} fraction was observed on UTE images with hard pulse excitation compared with half pulse excitation (75.6% vs 68.8% in bovine bone, 79.9% vs 73.2% in human bone). Fat saturation pulses slightly reduced the short T2{sup *} fraction relative to regular UTE sequences (5.0% and 2.0% reduction, respectively, with half and hard excitation pulses for bovine bone, 6.3% and 8.2% reduction, respectively, with half and hard excitation pulses for human bone). Long T2 saturation pulses significantly reduced the long T2{sup *} fraction relative to regular UTE sequence (18.9% and 17.2% reduction, respectively, with half and hard excitation pulses for bovine bone, 26.4% and 27.7% reduction, respectively, with half and hard excitation pulses for human bone). With IR-UTE preparation the long T2{sup *} components were significantly reduced relative to regular UTE sequence (75.3% and 66.4% reduction, respectively, with half and hard excitation pulses for bovine bone, 87.7% and 90.3% reduction, respectively, with half and hard excitation pulses for human bone). Conclusions: Bound and free water T2{sup *}s and relative fractions can be assessed using UTE bicomponent analysis. Long T2{sup *} components are affected more by long T2 saturation and IR pulses, and short T2{sup *} components are affected more by fat saturation pulses.« less

Normal saline as a natural intravascular contrast agent for dynamic perfusion-weighted MRI of the brain: Proof of concept at 1.5T.

PubMed

Jara, Hernán; Mian, Asim; Sakai, Osamu; Anderson, Stephan W; Horn, Mitchel J; Norbash, Alexander M; Soto, Jorge A

2016-12-01

Gadolinium-based contrast agents have associated risks. Normal saline (NS) is a nontoxic sodium chloride water solution that can significantly increase the magnetic resonance imaging (MRI) relaxation times of blood via transient hemodilution (THD). The purpose of this pilot study was to test in vivo in the head the potential of normal saline as a safer, exogenous perfusion contrast agent. This Health Insurance Portability and Accountability Act (HIPAA)-compliant prospective study was approved by the local Institutional Review Board (IRB): 12 patients were scanned with T 1 -weighted inversion recovery turbo spin echo pulse sequence at 1.5T. The dynamic inversion recovery pulse sequence was run before, during, and after the NS injection for up to 5 minutes: 100 ml of NS was power-injected via antecubital veins at 3-4 ml/s. Images were processed to map maximum enhancement area-under-the-curve, time-to-peak, and mean-transit-time. These maps were used to identify the areas showing significant NS injection-related signal and to generate enhancement time curves. Hardware and pulse sequence stability were studied via phantom experimentation. Main features of the time curves were tested against theoretical modeling of THD signal effects using inversion recovery pulse sequences. Pearson correlation coefficient (R) mapping was used to differentiate genuine THD effects from motion confounders and noise. The scans of 8 out of 12 patients showed NS injection-related effects that correlate in magnitude with tissue type (gray matter ∼15% and white matter ∼3%). Motion artifacts prevented ascertaining NS signal effects in the remaining four patients. Positive and negative time curves were observed in vivo and this dual THD signal polarity was also observed in the theoretical simulations. R-histograms that were approximately constant in the range 0.1 < |R| < 0.8 and leading to correlation fractions of F corr (|R| > 0.5) = 0.45 and 0.59 were found to represent scans with genuine THD signal effects. A measurable perfusion effect in brain tissue was demonstrated in vivo using NS as an injectable intravascular contrast agent. J. Magn. Reson. Imaging 2016;44:1580-1591. © 2016 International Society for Magnetic Resonance in Medicine.

Generation of double giant pulses in actively Q-switched lasers

NASA Astrophysics Data System (ADS)

Korobeynikova, A. P.; Shaikin, I. A.; Shaykin, A. A.; Koryukin, I. V.; Khazanov, E. A.

2018-04-01

Generation of a second giant pulse in a longitudinal mode neighbouring to the longitudinal mode possessing minimal losses is theoretically and experimentally studied in actively Q-switched lasers. A mathematical model is suggested for explaining the giant pulse generation in a laser with multiple longitudinal modes. The model makes allowance for not only a standing, but also a running wave for each cavity mode. Results of numerical simulation and data of experiments with a Nd : YLF laser explain the effect of second giant pulse generation in a neighbouring longitudinal mode. After a giant pulse in the mode with minimal losses is generated, the threshold for the neighbouring longitudinal mode is still exceeded due to the effect of burning holes in the population inversion spatial distribution.

Broadband optical frequency comb generator based on driving N-cascaded modulators by Gaussian-shaped waveform

NASA Astrophysics Data System (ADS)

Hmood, Jassim K.; Harun, Sulaiman W.

2018-05-01

A new approach for realizing a wideband optical frequency comb (OFC) generator based on driving cascaded modulators by a Gaussian-shaped waveform, is proposed and numerically demonstrated. The setup includes N-cascaded MZMs, a single Gaussian-shaped waveform generator, and N-1 electrical time delayer. The first MZM is driven directly by a Gaussian-shaped waveform, while delayed replicas of the Gaussian-shaped waveform drive the other MZMs. An analytical model that describes the proposed OFC generator is provided to study the effect of number and chirp factor of cascaded MZM as well as pulse width on output spectrum. Optical frequency combs at frequency spacing of 1 GHz are generated by applying Gaussian-shaped waveform at pulse widths ranging from 200 to 400 ps. Our results reveal that, the number of comb lines is inversely proportional to the pulse width and directly proportional to both number and chirp factor of cascaded MZMs. At pulse width of 200 ps and chirp factor of 4, 67 frequency lines can be measured at output spectrum of two-cascaded MZMs setup. Whereas, increasing the number of cascaded stages to 3, 4, and 5, the optical spectra counts 89, 109 and 123 frequency lines; respectively. When the delay time is optimized, 61 comb lines can be achieved with power fluctuations of less than 1 dB for five-cascaded MZMs setup.

Left Gastric Vein Visualization with Hepatopetal Flow Information in Healthy Subjects Using Non-Contrast-Enhanced Magnetic Resonance Angiography with Balanced Steady-State Free-Precession Sequence and Time-Spatial Labeling Inversion Pulse.

PubMed

Furuta, Akihiro; Isoda, Hiroyoshi; Ohno, Tsuyoshi; Ono, Ayako; Yamashita, Rikiya; Arizono, Shigeki; Kido, Aki; Sakashita, Naotaka; Togashi, Kaori

2018-01-01

To selectively visualize the left gastric vein (LGV) with hepatopetal flow information by non-contrast-enhanced magnetic resonance angiography under a hypothesis that change in the LGV flow direction can predict the development of esophageal varices; and to optimize the acquisition protocol in healthy subjects. Respiratory-gated three-dimensional balanced steady-state free-precession scans were conducted on 31 healthy subjects using two methods (A and B) for visualizing the LGV with hepatopetal flow. In method A, two time-spatial labeling inversion pulses (Time-SLIP) were placed on the whole abdomen and the area from the gastric fornix to the upper body, excluding the LGV area. In method B, nonselective inversion recovery pulse was used and one Time-SLIP was placed on the esophagogastric junction. The detectability and consistency of LGV were evaluated using the two methods and ultrasonography (US). Left gastric veins by method A, B, and US were detected in 30 (97%), 24 (77%), and 23 (74%) subjects, respectively. LGV flow by US was hepatopetal in 22 subjects and stagnant in one subject. All hepatopetal LGVs by US coincided with the visualized vessels in both methods. One subject with non-visualized LGV in method A showed stagnant LGV by US. Hepatopetal LGV could be selectively visualized by method A in healthy subjects.

Note: Voltage and intensity dependence of the saturation curves of free-air ionization chambers irradiated with chopped synchrotron radiation beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nariyama, Nobuteru

2012-01-15

Current saturation characteristics of free-air ionization chambers with electrode gaps of 4.2 and 8.4 mm were investigated using pulsed photon beam obtained by periodically interrupting synchrotron radiation beams with a chopper. Pulsed photon beams of 10 and 15 keV with pulse duration of 2.5 {mu}s and a frequency of 230 Hz were produced by chopping the beam. The measured recombination rate was found to be proportional to the intensity and inversely proportional to the applied voltage.

Inverse Doppler shift and control field as coherence generators for the stability in superluminal light

NASA Astrophysics Data System (ADS)

Ghafoor, Fazal; Bacha, Bakht Amin; Khan, Salman

2015-05-01

A gain-based four-level atomic medium for the stability in superluminal light propagation using control field and inverse Doppler shift as coherence generators is studied. In regimes of weak and strong control field, a broadband and multiple controllable transparency windows are, respectively, identified with significantly enhanced group indices. The observed Doppler effect for the class of high atomic velocity of the medium is counterintuitive in comparison to the effect of the class of low atomic velocity. The intensity of each of the two pump fields is kept less than the optimum limit reported in [M. D. Stenner and D. J. Gauthier, Phys. Rev. A 67, 063801 (2003), 10.1103/PhysRevA.67.063801] for stability in the superluminal light pulse. Consequently, superluminal stable domains with the generated coherence are explored.

A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance

PubMed Central

Li, Yong; Jing, Haoqing; Zainal Abidin, Ilham Mukriz; Yan, Bei

2017-01-01

Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy. PMID:28441328

A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance.

PubMed

Li, Yong; Jing, Haoqing; Zainal Abidin, Ilham Mukriz; Yan, Bei

2017-04-25

Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy.

Synthesis of monopolar ultrasound pulses for therapy: the frequency-compounding transducer.

PubMed

Lin, Kuang-Wei; Hall, Timothy L; McGough, Robert J; Xu, Zhen; Cain, Charles A

2014-07-01

In diagnostic ultrasound, broadband transducers capable of short acoustic pulse emission and reception can improve axial resolution and provide sufficient bandwidth for harmonic imaging and multi-frequency excitation techniques. In histotripsy, a cavitation-based ultrasound therapy, short acoustic pulses (<2 cycles) can produce precise tissue ablation wherein lesion formation only occurs when the applied peak negative pressure exceeds an intrinsic threshold of the medium. This paper investigates a frequency compounding technique to synthesize nearly monopolar (half-cycle) ultrasound pulses. More specifically, these pulses were generated using a custom transducer composed of 23 individual relatively-broadband piezoceramic elements with various resonant frequencies (0.5, 1, 1.5, 2, and 3 MHz). Each frequency component of the transducer was capable of generating 1.5-cycle pulses with only one high-amplitude negative half-cycle using a custom 23-channel high-voltage pulser. By varying time delays of individual frequency components to allow their principal peak negative peaks to arrive at the focus of the transducer constructively, destructive interference occurs elsewhere in time and space, resulting in a monopolar pulse approximation with a dominant negative phase (with measured peak negative pressure [P-]: peak positive pressure [P+] = 4.68: 1). By inverting the excitation pulses to individual elements, monopolar pulses with a dominant positive phase can also be generated (with measured P+: P- = 4.74: 1). Experiments in RBC phantoms indicated that monopolar pulses with a dominant negative phase were able to produce very precise histotripsy-type lesions using the intrinsic threshold mechanism. Monopolar pulses with a dominant negative phase can inhibit shock scattering during histotripsy, leading to more predictable lesion formation using the intrinsic threshold mechanism, while greatly reducing any constructive interference, and potential hot-spots elsewhere. Moreover, these monopolar pulses could have many potential benefits in ultrasound imaging, including axial resolution improvement, speckle reduction, and contrast enhancement in pulse inversion imaging.

Pulse-drought atop press-drought: unexpected plant responses and implications for dryland ecosystems.

PubMed

Hoover, David L; Duniway, Michael C; Belnap, Jayne

2015-12-01

In drylands, climate change is predicted to cause chronic reductions in water availability (press-droughts) through reduced precipitation and increased temperatures as well as increase the frequency and intensity of short-term extreme droughts (pulse-droughts). These changes in precipitation patterns may have profound ecosystem effects, depending on the sensitivities of the dominant plant functional types (PFTs). Here we present the responses of four Colorado Plateau PFTs to an experimentally imposed, 4-year, press-drought during which a natural pulse-drought occurred. Our objectives were to (1) identify the drought sensitivities of the PFTs, (2) assess the additive effects of the press- and pulse-drought, and (3) examine the interactive effects of soils and drought. Our results revealed that the C3 grasses were the most sensitive PFT to drought, the C3 shrubs were the most resistant, and the C4 grasses and shrubs had intermediate drought sensitivities. Although we expected the C3 grasses would have the greatest response to drought, the higher resistance of C3 shrubs relative to the C4 shrubs was contrary to our predictions based on the higher water use efficiency of C4 photosynthesis. Also, the additive effects of press- and pulse-droughts caused high morality in C3 grasses, which has large ecological and economic ramifications for this region. Furthermore, despite predictions based on the inverse texture hypothesis, we observed no interactive effects of soils with the drought treatment on cover or mortality. These results suggest that plant responses to droughts in drylands may differ from expectations and have large ecological effects if press- and pulse-droughts push species beyond physiological and mortality thresholds.

Pulse-drought atop press-drought: unexpected plant responses and implications for dryland ecosystems

USGS Publications Warehouse

Hoover, David L.; Duniway, Michael C.; Belnap, Jayne

2015-01-01

In drylands, climate change is predicted to cause chronic reductions in water availability (press-droughts) through reduced precipitation and increased temperatures as well as increase the frequency and intensity of short-term extreme droughts (pulse-droughts). These changes in precipitation patterns may have profound ecosystem effects, depending on the sensitivities of the dominant plant functional types (PFTs). Here we present the responses of four Colorado Plateau PFTs to an experimentally imposed, 4-year, press-drought during which a natural pulse-drought occurred. Our objectives were to (1) identify the drought sensitivities of the PFTs, (2) assess the additive effects of the press- and pulse-drought, and (3) examine the interactive effects of soils and drought. Our results revealed that the C3 grasses were the most sensitive PFT to drought, the C3shrubs were the most resistant, and the C4 grasses and shrubs had intermediate drought sensitivities. Although we expected the C3 grasses would have the greatest response to drought, the higher resistance of C3 shrubs relative to the C4 shrubs was contrary to our predictions based on the higher water use efficiency of C4 photosynthesis. Also, the additive effects of press- and pulse-droughts caused high morality in C3 grasses, which has large ecological and economic ramifications for this region. Furthermore, despite predictions based on the inverse texture hypothesis, we observed no interactive effects of soils with the drought treatment on cover or mortality. These results suggest that plant responses to droughts in drylands may differ from expectations and have large ecological effects if press- and pulse-droughts push species beyond physiological and mortality thresholds.

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.

Ferroelectric domain engineering by focused infrared femtosecond pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xin; Shvedov, Vladlen; Sheng, Yan, E-mail: yan.sheng@anu.edu.au

2015-10-05

We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO{sub 3}, LiTaO{sub 3}, and KTiOPO{sub 4} are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoringmore » the Čerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls.« less

Search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam

NASA Astrophysics Data System (ADS)

Haddock, Christopher C.; Oi, Noriko; Hirota, Katsuya; Ino, Takashi; Kitaguchi, Masaaki; Matsumoto, Satoru; Mishima, Kenji; Shima, Tatsushi; Shimizu, Hirohiko M.; Snow, W. Michael; Yoshioka, Tamaki

2018-03-01

We describe an experimental search for deviations from the inverse-square law of gravity at the nanometer length scale using neutron scattering from noble gases on a pulsed slow neutron beam line. By measuring the neutron momentum transfer (q ) dependence of the differential cross section for xenon and helium and comparing to their well-known analytical forms, we place an upper bound on the strength of a new interaction as a function of interaction length λ which improves upon previous results in the region λ <0.1 nm , and remains competitive in the larger-λ region. A pseudoexperimental simulation is developed for this experiment and its role in the data analysis is described. We conclude with plans for improving sensitivity in the larger-λ region.

Ultrashort-Pulse Child-Langmuir Law in the Quantum and Relativistic Regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ang, L. K.; Zhang, P.

This Letter presents a consistent quantum and relativistic model of short-pulse Child-Langmuir (CL) law, of which the pulse length {tau} is less than the electron transit time in a gap of spacing D and voltage V. The classical value of the short-pulse CL law is enhanced by a large factor due to quantum effects when the pulse length and the size of the beam are, respectively, in femtosecond duration and nanometer scale. At high voltage larger than the electron rest mass, relativistic effects will suppress the enhancement of short-pulse CL law, which is confirmed by particle-in-cell simulation. When the pulsemore » length is much shorter than the gap transit time, the current density is proportional to V, and to the inverse power of D and {tau}.« less

The Correlates of Body Composition with Heart Rate Recovery after Step Test: An Exploratory Study of Malaysian Adolescents

PubMed Central

Abu Hanifah, Redzal; Mohamed, Mohd. Nahar Azmi; Jaafar, Zulkarnain; Abdul Mohsein, Nabilla Al-Sadat; Jalaludin, Muhammad Yazid; Abdul Majid, Hazreen; Murray, Liam; Cantwell, Marie; Su, Tin Tin

2013-01-01

Background In adults, heart rate recovery is a predictor of mortality, while in adolescents it is associated with cardio-metabolic risk factors. The aim of this study was to examine the relationship between body composition measures and heart rate recovery (HRR) after step test in Malaysian secondary school students. Methods In the Malaysian Health and Adolescents Longitudinal Research Team (MyHEART) study, 1071 healthy secondary school students, aged 13 years old, participated in the step test. Parameters for body composition measures were body mass index z-score, body fat percentage, waist circumference, and waist height ratio. The step test was conducted by using a modified Harvard step test. Heart rate recovery of 1 minute (HRR1min) and heart rate recovery of 2 minutes (HRR2min) were calculated by the difference between the peak pulse rate during exercise and the resting pulse rate at 1 and 2 minutes, respectively. Analysis was done separately based on gender. Pearson correlation analysis was used to determine the association between the HRR parameters with body composition measures, while multiple regression analysis was used to determine which body composition measures was the strongest predictor for HRR. Results For both gender groups, all body composition measures were inversely correlated with HRR1min. In girls, all body composition measures were inversely correlated with HRR2min, while in boys all body composition measures, except BMI z-score, were associated with HRR2min. In multiple regression, only waist circumference was inversely associated with HRR2min (p=0.024) in boys, while in girls it was body fat percentage for HRR2min (p=0.008). Conclusion There was an inverse association between body composition measurements and HRR among apparently healthy adolescents. Therefore, it is important to identify cardio-metabolic risk factors in adolescent as an early prevention of consequent adulthood morbidity. This reiterates the importance of healthy living which should start from young. PMID:24349388

Anomalous domain inversion in LiNbO3 single crystals investigated by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Lilienblum, M.; Soergel, E.

2011-09-01

Ferroelectric domains were written in lithium niobate (LiNbO3) single crystals by applying voltage pulses to the tip of a scanning force microscope. The generated domains are subsequently imaged by piezoresponse force microscopy. As it has been previously observed not only full domains but also doughnut-shaped ones arise from tip-based domain formation. In this contribution, we present our experiments which were carried out with 10-20 μm thin LiNbO3 single crystals. We show that by choosing appropriate writing parameters, domains of predetermined shape (full or doughnut) can be reliably generated. In addition to the duration and the amplitude of the voltage pulse the moment of the retraction of the tip from the sample surface was found to be a crucial parameter for reproducible domain formation.

Combining Fourier phase encoding and broadband inversion toward J-edited spectra

NASA Astrophysics Data System (ADS)

Lin, Yulan; Guan, Quanshuai; Su, Jianwei; Chen, Zhong

2018-06-01

Nuclear magnetic resonance (NMR) spectra are often utilized for gathering accurate information relevant to molecular structures and composition assignments. In this study, we develop a homonuclear encoding approach based on imparting a discrete phase modulation of the targeted cross peaks, and combine it with a pure shift experiments (PSYCHE) based J-modulated scheme, providing simple 2D J-edited spectra for accurate measurement of scalar coupling networks. Chemical shifts and J coupling constants of protons coupled to the specific protons are demonstrated along the F2 and F1 dimensions, respectively. Polychromatic pulses by Fourier phase encoding were performed to simultaneously detect several coupling networks. Proton-proton scalar couplings are chosen by a polychromatic pulse and a PSYCHE element. Axis peaks and unwanted couplings are complete eradicated by incorporating a selective COSY block as a preparation period. The theoretical principles and the signal processing procedure are laid out, and experimental observations are rationalized on the basis of theoretical analyses.

Effects of RF pulse profile and intra-voxel phase dispersion on MR fingerprinting with balanced SSFP readout.

PubMed

Chiu, Su-Chin; Lin, Te-Ming; Lin, Jyh-Miin; Chung, Hsiao-Wen; Ko, Cheng-Wen; Büchert, Martin; Bock, Michael

2017-09-01

To investigate possible errors in T1 and T2 quantification via MR fingerprinting with balanced steady-state free precession readout in the presence of intra-voxel phase dispersion and RF pulse profile imperfections, using computer simulations based on Bloch equations. A pulse sequence with TR changing in a Perlin noise pattern and a nearly sinusoidal pattern of flip angle following an initial 180-degree inversion pulse was employed. Gaussian distributions of off-resonance frequency were assumed for intra-voxel phase dispersion effects. Slice profiles of sinc-shaped RF pulses were computed to investigate flip angle profile influences. Following identification of the best fit between the acquisition signals and those established in the dictionary based on known parameters, estimation errors were reported. In vivo experiments were performed at 3T to examine the results. Slight intra-voxel phase dispersion with standard deviations from 1 to 3Hz resulted in prominent T2 under-estimations, particularly at large T2 values. T1 and off-resonance frequencies were relatively unaffected. Slice profile imperfections led to under-estimations of T1, which became greater as regional off-resonance frequencies increased, but could be corrected by including slice profile effects in the dictionary. Results from brain imaging experiments in vivo agreed with the simulation results qualitatively. MR fingerprinting using balanced SSFP readout in the presence of intra-voxel phase dispersion and imperfect slice profile leads to inaccuracies in quantitative estimations of the relaxation times. Copyright © 2017 Elsevier Inc. All rights reserved.

Amplification of the effects of magnetization exchange by (31) P band inversion for measuring adenosine triphosphate synthesis rates in human skeletal muscle.

PubMed

Ren, Jimin; Sherry, A Dean; Malloy, Craig R

2015-12-01

The goal of this study was to amplify the effects of magnetization exchange between γ-adenosine triphosphate (ATP) and inorganic phosphate (Pi) for evaluation of ATP synthesis rates in human skeletal muscle. The strategy works by simultaneously inverting the (31) P resonances of phosphocreatine (PCr) and ATP using a wide bandwidth, adiabatic inversion radiofrequency pulse followed by observing dynamic changes in intensity of the noninverted Pi signal versus the delay time between the inversion and observation pulses. This band inversion technique significantly delays recovery of γ-ATP magnetization; consequently, the exchange reaction, Pi ↔ γ-ATP, is readily detected and easily analyzed. The ATP synthesis rate measured from high-quality spectral data using this method was 0.073 ± 0.011 s(-1) in resting human skeletal muscle (N = 10). The T1 of Pi was 6.93 ± 1.90 s, consistent with the intrinsic T1 of Pi at this field. The apparent T1 of γ-ATP was 4.07 ± 0.32 s, about two-fold longer than its intrinsic T1 due to storage of magnetization in PCr. Band inversion provides an effective method to amplify the effects of magnetization transfer between γ-ATP and Pi. The resulting data can be easily analyzed to obtain the ATP synthesis rate using a two-site exchange model. © 2014 Wiley Periodicals, Inc.

Hybrid quantitative MRI using chemical shift displacement and recovery-based simultaneous water and lipid imaging: A preliminary study.

PubMed

Ohno, Naoki; Miyati, Tosiaki; Suzuki, Shuto; Kan, Hirohito; Aoki, Toshitaka; Nakamura, Yoshitaka; Hiramatsu, Yuki; Kobayashi, Satoshi; Gabata, Toshifumi

2018-07-01

To suppress olefinic signals and enable simultaneous and quantitative estimation of multiple functional parameters associated with water and lipid, we investigated a modified method using chemical shift displacement and recovery-based separation of lipid tissue (SPLIT) involving acquisitions with different inversion times (TIs), echo times (TEs), and b-values. Single-shot diffusion echo-planar imaging (SSD-EPI) with multiple b-values (0-3000 s/mm 2 ) was performed without fat suppression to separate water and lipid images using the chemical shift displacement of lipid signals in the phase-encoding direction. An inversion pulse (TI = 292 ms) was applied to SSD-EPI to remove olefinic signals. Consecutively, SSD-EPI (b = 0 s/mm 2 ) was performed with TI = 0 ms and TE = 31.8 ms for T 1 and T 2 measurements, respectively. Under these conditions, transverse water and lipid images at the maximum diameter of the right calf were obtained in six healthy subjects. T 1 , T 2 , and the apparent diffusion coefficients (ADC) were then calculated for the tibialis anterior (TA), gastrocnemius (GM), and soleus (SL) muscles, tibialis bone marrow (TB), and subcutaneous fat (SF). Perfusion-related (D*) and restricted diffusion coefficients (D) were calculated for the muscles. Lastly, the lipid fractions (LF) of the muscles were determined after T 1 and T 2 corrections. The modified SPLIT method facilitated sufficient separation of water and lipid images of the calf, and the inversion pulse with TI of 292 ms effectively suppressed olefinic signals. All quantitative parameters obtained with the modified SPLIT method were found to be in general agreement with those previously reported in the literature. The modified SPLIT technique enabled sufficient suppression of olefinic signals and simultaneous acquisition of quantitative parameters including diffusion, perfusion, T 1 and T 2 relaxation times, and LF. Copyright © 2018. Published by Elsevier Inc.

The Use of Acoustic Radiation Force Decorrelation-Weighted Pulse Inversion for Enhanced Ultrasound Contrast Imaging.

PubMed

Herbst, Elizabeth B; Unnikrishnan, Sunil; Wang, Shiying; Klibanov, Alexander L; Hossack, John A; Mauldin, Frank William

2017-02-01

The use of ultrasound imaging for cancer diagnosis and screening can be enhanced with the use of molecularly targeted microbubbles. Nonlinear imaging strategies such as pulse inversion (PI) and "contrast pulse sequences" (CPS) can be used to differentiate microbubble signal, but often fail to suppress highly echogenic tissue interfaces. This failure results in false-positive detection and potential misdiagnosis. In this study, a novel acoustic radiation force (ARF)-based approach was developed for superior microbubble signal detection. The feasibility of this technique, termed ARF decorrelation-weighted PI (ADW-PI), was demonstrated in vivo using a subcutaneous mouse tumor model. Tumors were implanted in the hindlimb of C57BL/6 mice by subcutaneous injection of MC38 cells. Lipid-shelled microbubbles were conjugated to anti-VEGFR2 antibody and administered via bolus injection. An image sequence using ARF pulses to generate microbubble motion was combined with PI imaging on a Verasonics Vantage programmable scanner. ADW-PI images were generated by combining PI images with interframe signal decorrelation data. For comparison, CPS images of the same mouse tumor were acquired using a Siemens Sequoia clinical scanner. Microbubble-bound regions in the tumor interior exhibited significantly higher signal decorrelation than static tissue (n = 9, P < 0.001). The application of ARF significantly increased microbubble signal decorrelation (n = 9, P < 0.01). Using these decorrelation measurements, ADW-PI imaging demonstrated significantly improved microbubble contrast-to-tissue ratio when compared with corresponding CPS or PI images (n = 9, P < 0.001). Contrast-to-tissue ratio improved with ADW-PI by approximately 3 dB compared with PI images and 2 dB compared with CPS images. Acoustic radiation force can be used to generate adherent microbubble signal decorrelation without microbubble bursting. When combined with PI, measurements of the resulting microbubble signal decorrelation can be used to reconstruct images that exhibit superior suppression of highly echogenic tissue interfaces when compared with PI or CPS alone.

Inversion of atmospheric optical parameters from elastic-backscatter lidar returns using a Kalman filter

NASA Astrophysics Data System (ADS)

Rocadenbosch, Francesc; Comeron, Adolfo; Vazquez, Gregori; Rodriguez-Gomez, Alejandro; Soriano, Cecilia; Baldasano, Jose M.

1998-12-01

Up to now, retrieval of the atmospheric extinction and backscatter has mainly relied on standard straightforward non-memory procedures such as slope-method, exponential- curve fitting and Klett's method. Yet, their performance becomes ultimately limited by the inherent lack of adaptability as they only work with present returns and neither past estimations, nor the statistics of the signals or a prior uncertainties are taken into account. In this work, a first inversion of the backscatter and extinction- to-backscatter ratio from pulsed elastic-backscatter lidar returns is tackled by means of an extended Kalman filter (EKF), which overcomes these limitations. Thus, as long as different return signals income,the filter updates itself weighted by the unbalance between the a priori estimates of the optical parameters and the new ones based on a minimum variance criterion. Calibration errors or initialization uncertainties can be assimilated also. The study begins with the formulation of the inversion problem and an appropriate stochastic model. Based on extensive simulation and realistic conditions, it is shown that the EKF approach enables to retrieve the sought-after optical parameters as time-range-dependent functions and hence, to track the atmospheric evolution, its performance being only limited by the quality and availability of the 'a priori' information and the accuracy of the atmospheric model assumed. The study ends with an encouraging practical inversion of a live-scene measured with the Nd:YAG elastic-backscatter lidar station at our premises in Barcelona.

Saturation of subjective reward magnitude as a function of current and pulse frequency.

PubMed

Simmons, J M; Gallistel, C R

1994-02-01

In rats with electrodes in the medial forebrain bundle, the upper portion of the function relating the experienced magnitude of the reward to pulse frequency was determined at currents ranging from 100 to 1,000 microA. The pulse frequency required to produce an asymptotic level of reward was inversely proportional to current except at the lowest currents and highest pulse frequencies. At a given current, the subjective reward magnitude functions decelerated to an asymptote over an interval in which the pulse frequency doubled or tripled. The asymptotic level of reward was approximately constant for currents between 200 and 1,000 microA but declined substantially at currents at or below 100 microA and pulse frequencies at or above 250 to 400 pulses per second. The results are consistent with the hypothesis that the magnitude of the experienced reward depends only on the number of action potentials generated by the train of pulses in the bundle of reward-relevant axons.

Acute changes in arterial stiffness following exercise in people with metabolic syndrome.

PubMed

Radhakrishnan, Jeyasundar; Swaminathan, Narasimman; Pereira, Natasha M; Henderson, Keiran; Brodie, David A

This study aims to examine the changes in arterial stiffness immediately following sub-maximal exercise in people with metabolic syndrome. Ninety-four adult participants (19-80 years) with metabolic syndrome gave written consent and were measured for arterial stiffness using a SphygmoCor (SCOR-PVx, Version 8.0, Atcor Medical Private Ltd, USA) immediately before and within 5-10min after an incremental shuttle walk test. The arterial stiffness measures used were pulse wave velocity (PWV), aortic pulse pressure (PP), augmentation pressure, augmentation index (AI), subendocardial viability ratio (SEVR) and ejection duration (ED). There was a significant increase (p<0.05) in most of the arterial stiffness variables following exercise. Exercise capacity had a strong inverse correlation with arterial stiffness and age (p<0.01). Age influences arterial stiffness. Exercise capacity is inversely related to arterial stiffness and age in people with metabolic syndrome. Exercise induced changes in arterial stiffness measured using pulse wave analysis is an important tool that provides further evidence in studying cardiovascular risk in metabolic syndrome. Copyright © 2016 Diabetes India. Published by Elsevier Ltd. All rights reserved.

Accelerating non-contrast-enhanced MR angiography with inflow inversion recovery imaging by skipped phase encoding and edge deghosting (SPEED).

PubMed

Chang, Zheng; Xiang, Qing-San; Shen, Hao; Yin, Fang-Fang

2010-03-01

To accelerate non-contrast-enhanced MR angiography (MRA) with inflow inversion recovery (IFIR) with a fast imaging method, Skipped Phase Encoding and Edge Deghosting (SPEED). IFIR imaging uses a preparatory inversion pulse to reduce signals from static tissue, while leaving inflow arterial blood unaffected, resulting in sparse arterial vasculature on modest tissue background. By taking advantage of vascular sparsity, SPEED can be simplified with a single-layer model to achieve higher efficiency in both scan time reduction and image reconstruction. SPEED can also make use of information available in multiple coils for further acceleration. The techniques are demonstrated with a three-dimensional renal non-contrast-enhanced IFIR MRA study. Images are reconstructed by SPEED based on a single-layer model to achieve an undersampling factor of up to 2.5 using one skipped phase encoding direction. By making use of information available in multiple coils, SPEED can achieve an undersampling factor of up to 8.3 with four receiver coils. The reconstructed images generally have comparable quality as that of the reference images reconstructed from full k-space data. As demonstrated with a three-dimensional renal IFIR scan, SPEED based on a single-layer model is able to reduce scan time further and achieve higher computational efficiency than the original SPEED.

Hadamard-Encoded Multipulses for Contrast-Enhanced Ultrasound Imaging.

PubMed

Gong, Ping; Song, Pengfei; Chen, Shigao

2017-11-01

The development of contrast-enhanced ultrasound (CEUS) imaging offers great opportunities for new ultrasound clinical applications such as myocardial perfusion imaging and abdominal lesion characterization. In CEUS imaging, the contrast agents (i.e., microbubbles) are utilized to improve the contrast between blood and tissue based on their high nonlinearity under low ultrasound pressure. In this paper, we propose a new CEUS pulse sequence by combining Hadamard-encoded multipulses (HEM) with fundamental frequency bandpass filter (i.e., filter centered on transmit frequency). HEM consecutively emits multipulses encoded by a second-order Hadamard matrix in each of the two transmission events (i.e., pulse-echo events), as opposed to conventional CEUS methods which emit individual pulses in two separate transmission events (i.e., pulse inversion (PI), amplitude modulation (AM), and PIAM). In HEM imaging, the microbubble responses can be improved by the longer transmit pulse, and the tissue harmonics can be suppressed by the fundamental frequency filter, leading to significantly improved contrast-to-tissue ratio (CTR) and signal-to-noise ratio (SNR). In addition, the fast polarity change between consecutive coded pulse emissions excites strong nonlinear microbubble echoes, further enhancing the CEUS image quality. The spatial resolution of HEM image is compromised as compared to other microbubble imaging methods due to the longer transmit pulses and the lower imaging frequency (i.e., fundamental frequency). However, the resolution loss was shown to be negligible and could be offset by the significantly enhanced CTR, SNR, and penetration depth. These properties of HEM can potentially facilitate robust CEUS imaging for many clinical applications, especially for deep abdominal organs and heart.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huo, W. G.; Li, R. M.; Shi, J. J.

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 C{sub s} in the inversely L-shaped matching network. In the case of a highmore » 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).« less

Dynamic propagation of symmetric Airy pulses with initial chirps in an optical fiber

NASA Astrophysics Data System (ADS)

Shi, Xiaohui; Huang, Xianwei; Deng, Yangbao; Tan, Chao; Bai, Yanfeng; Fu, Xiquan

2017-09-01

We analytically and numerically investigate the propagation dynamics of initially chirped symmetric Airy pulses in an optical fiber. The results show that the positive chirps act to promote the interference in generating a focal point on the propagation axis, while the negative chirps tend to suppress the focusing effect, as compared to conventional unchirped symmetric Airy pulses. The numerical results demonstrate that the linear propagation of chirped symmetric Airy pulses depend considerably on the chirp parameter and the primary lobe position. In the anomalous dispersion region, positively chirped symmetric Airy pulses first undergo an initial compression, and reach a foci due to the opposite acceleration, and then experience a lossy inversion transformation, and come to the opposite facing focal position. The impact of truncation coefficient and Kerr nonlinearity on the chirped symmetric Airy pulses propagation is also disclosed separately.

Eye-Safe KGd(WO4)2:Nd Laser: Nano- and Subnanosecond Pulse Generation in Self-Frequency Raman Conversion Mode with Active Q-Switching

NASA Astrophysics Data System (ADS)

Dashkevich, V. I.; Orlovich, V. A.

2017-03-01

The shape of the multimode Stokes pulse generated by an eye-safe KGd(WO4)2:Nd laser with self-frequency Raman conversion and active Q-switching was shown to depend on the inhomogeneity of the active-medium pump. The laser generated a short and undistorted Stokes pulse of length 2.5 ns that increased with increasing laser cavity length for a moderately inhomogeneous pump characterized by a higher population inversion in the center of the active element. The energy of the Stokes pulse ( 11.5 mJ) varied little as the output-mirror reflectivity varied in the range 5-45%. The Raman pulse became distorted if the inhomogeneity of the pump was increased considerably. The degree of pump inhomogeneity was negligible with fundamental TEM00 mode selection. The laser generated subnanosecond Stokes pulses with peak power in the MW range.

Signal-domain optimization metrics for MPRAGE RF pulse design in parallel transmission at 7 tesla.

PubMed

Gras, V; Vignaud, A; Mauconduit, F; Luong, M; Amadon, A; Le Bihan, D; Boulant, N

2016-11-01

Standard radiofrequency pulse design strategies focus on minimizing the deviation of the flip angle from a target value, which is sufficient but not necessary for signal homogeneity. An alternative approach, based directly on the signal, here is proposed for the MPRAGE sequence, and is developed in the parallel transmission framework with the use of the k T -points parametrization. The flip angle-homogenizing and the proposed methods were investigated numerically under explicit power and specific absorption rate constraints and tested experimentally in vivo on a 7 T parallel transmission system enabling real time local specific absorption rate monitoring. Radiofrequency pulse performance was assessed by a careful analysis of the signal and contrast between white and gray matter. Despite a slight reduction of the flip angle uniformity, an improved signal and contrast homogeneity with a significant reduction of the specific absorption rate was achieved with the proposed metric in comparison with standard pulse designs. The proposed joint optimization of the inversion and excitation pulses enables significant reduction of the specific absorption rate in the MPRAGE sequence while preserving image quality. The work reported thus unveils a possible direction to increase the potential of ultra-high field MRI and parallel transmission. Magn Reson Med 76:1431-1442, 2016. © 2015 International Society for Magnetic Resonance in Medicine. © 2015 International Society for Magnetic Resonance in Medicine.

Genetic algorithm optimized triply compensated pulses in NMR spectroscopy

NASA Astrophysics Data System (ADS)

Manu, V. S.; Veglia, Gianluigi

2015-11-01

Sensitivity and resolution in NMR experiments are affected by magnetic field inhomogeneities (of both external and RF), errors in pulse calibration, and offset effects due to finite length of RF pulses. To remedy these problems, built-in compensation mechanisms for these experimental imperfections are often necessary. Here, we propose a new family of phase-modulated constant-amplitude broadband pulses with high compensation for RF inhomogeneity and heteronuclear coupling evolution. These pulses were optimized using a genetic algorithm (GA), which consists in a global optimization method inspired by Nature's evolutionary processes. The newly designed π and π / 2 pulses belong to the 'type A' (or general rotors) symmetric composite pulses. These GA-optimized pulses are relatively short compared to other general rotors and can be used for excitation and inversion, as well as refocusing pulses in spin-echo experiments. The performance of the GA-optimized pulses was assessed in Magic Angle Spinning (MAS) solid-state NMR experiments using a crystalline U-13C, 15N NAVL peptide as well as U-13C, 15N microcrystalline ubiquitin. GA optimization of NMR pulse sequences opens a window for improving current experiments and designing new robust pulse sequences.

A unified heteronuclear decoupling strategy for magic-angle-spinning solid-state NMR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Equbal, Asif; Bjerring, Morten; Nielsen, Niels Chr., E-mail: madhu@tifr.res.in, E-mail: ncn@inano.au.dk

2015-05-14

A unified strategy of two-pulse based heteronuclear decoupling for solid-state magic-angle spinning nuclear magnetic resonance is presented. The analysis presented here shows that different decoupling sequences like two-pulse phase-modulation (TPPM), X-inverse-X (XiX), and finite pulse refocused continuous wave (rCW{sup A}) are basically specific solutions of a more generalized decoupling scheme which incorporates the concept of time-modulation along with phase-modulation. A plethora of other good decoupling conditions apart from the standard, TPPM, XiX, and rCW{sup A} decoupling conditions are available from the unified decoupling approach. The importance of combined time- and phase-modulation in order to achieve the best decoupling conditions ismore » delineated. The consequences of different indirect dipolar interactions arising from cross terms comprising of heteronuclear and homonuclear dipolar coupling terms and also those between heteronuclear dipolar coupling and chemical-shift anisotropy terms are presented in order to unfold the effects of anisotropic interactions under different decoupling conditions. Extensive numerical simulation results are corroborated with experiments on standard amino acids.« less

In vivo measurement of the longitudinal relaxation time of arterial blood (T1a) in the mouse using a pulsed arterial spin labeling approach.

PubMed

Thomas, David L; Lythgoe, Mark F; Gadian, David G; Ordidge, Roger J

2006-04-01

A novel method for measuring the longitudinal relaxation time of arterial blood (T1a) is presented. Knowledge of T1a is essential for accurately quantifying cerebral perfusion using arterial spin labeling (ASL) techniques. The method is based on the flow-sensitive alternating inversion recovery (FAIR) pulsed ASL (PASL) approach. We modified the standard FAIR acquisition scheme by incorporating a global saturation pulse at the beginning of the recovery period. With this approach the FAIR tissue signal difference has a simple monoexponential dependence on the recovery time, with T1a as the time constant. Therefore, FAIR measurements performed over a range of recovery times can be fitted to a monoexponential recovery curve and T1a can be calculated directly. This eliminates many of the difficulties associated with the measurement of T1a. Experiments performed in vivo in the mouse at 2.35T produced a mean value of 1.51 s for T1a, consistent with previously published values. (c) 2006 Wiley-Liss, Inc.

Direct visualization of pancreatic juice flow using unenhanced MRI with spin labeling can be aid in diagnosing chronic pancreatitis.

PubMed

Sugita, Reiji; Furuta, Akemi; Yamazaki, Tetsuro; Itoh, Kei; Fujita, Naotaka; Takahashi, Shoki

2014-05-01

The purpose of this study is to prospectively assess whether direct visualization of pancreatic juice flow using an unenhanced MRI technique with spin labeling can aid in the diagnosis of chronic pancreatitis. Ten healthy volunteers and 50 patients who were categorized as having no chronic pancreatitis (n = 11), early chronic pancreatitis (n = 7), or established chronic pancreatitis (n = 32) underwent MRI, including direct pancreatic juice visualization using a flow-out technique with a time-spatial labeling inversion pulse, comprising a nonselective inversion recovery pulse immediately followed by a spatially selective inversion labeling pulse. The mean velocities and volumes of pancreatic juice excretion were also obtained. Variance tests were used to evaluate the clinical groups with respect to the appearance rate and mean velocity; the Kruskal-Wallis test was used for volume. There were no significant differences between healthy volunteers and patients with no chronic pancreatitis. The appearance rate, mean velocity, and volume of pancreatic juice excretion tended to decrease with the degree of chronic pancreatitis. Although the difference in these values was statistically significant between the healthy group and the established chronic pancreatitis group, the values of the early group and other groups were not statistically significant. There was a significant correlation between the appearance rate of pancreatic juice and the clinical groups (τ = -0.4376, p = 0.0015). The measurement of directly visualized pancreatic juice flow may aid in establishing the diagnosis of chronic pancreatitis.

A methodology for using borehole temperature-depth profiles under ambient, single and cross-borehole pumping conditions to estimate fracture hydraulic properties

NASA Astrophysics Data System (ADS)

Klepikova, Maria V.; Le Borgne, Tanguy; Bour, Olivier; Davy, Philippe

2011-09-01

SummaryTemperature profiles in the subsurface are known to be sensitive to groundwater flow. Here we show that they are also strongly related to vertical flow in the boreholes themselves. Based on a numerical model of flow and heat transfer at the borehole scale, we propose a method to invert temperature measurements to derive borehole flow velocities. This method is applied to an experimental site in fractured crystalline rocks. Vertical flow velocities deduced from the inversion of temperature measurements are compared with direct heat-pulse flowmeter measurements showing a good agreement over two orders of magnitudes. Applying this methodology under ambient, single and cross-borehole pumping conditions allows us to estimate fracture hydraulic head and local transmissivity, as well as inter-borehole fracture connectivity. Thus, these results provide new insights on how to include temperature profiles in inverse problems for estimating hydraulic fracture properties.

A New Class of Pulse Compression Codes and Techniques.

DTIC Science & Technology

1980-03-26

04 11 01 12 02 13 03 14 OA DIALFL I NOTE’ BO𔃾T TRANSFORM AND DIGITAL FILTER NETWORK INVERSE TRANSFORM DRIVE FRANK CODE SAME DIGITAL FILTER ; ! ! I I...function from circuit of Fig. I with N =9 TRANSFORM INVERSE TRANSFORM SINGLE _WORD S1A ~b,.ISR -.- ISR I- SR I--~ SR SIC-- I1GENERATOR 0 fJFJ $ J$ .. J...FOR I 1 1 13 11 12 13 FROM RECEIVER TRANSMIT Q- j ~ ~ 01 02 03 0, 02 03 11 01 12 02 13 03 4 1 1 ~ 4 NOTrE: BOTH TRANSFORM ANDI I I I INVERSE TRANSFORM DRIVE

Terahertz emission from ultrafast spin-charge current at a Rashba interface

NASA Astrophysics Data System (ADS)

Zhang, Qi; Jungfleisch, Matthias Benjamin; Zhang, Wei; Pearson, John E.; Wen, Haidan; Hoffmann, Axel

Ultrafast broadband terahertz (THz) radiation is highly desired in various fields from fundamental research in condensed matter physics to bio-chemical detection. Conventional ultrafast THz sources rely on either nonlinear optical effects or ultrafast charge currents in semiconductors. Recently, however, it was realized that ultrabroad-band THz radiation can be produced highly effectively by novel spintronics-based emitters that also make use of the electron's spin degree of freedom. Those THz-emitters convert a spin current flow into a terahertz electromagnetic pulse via the inverse spin-Hall effect. In contrast to this bulk conversion process, we demonstrate here that a femtosecond spin current pulse launched from a CoFeB layer can also generate terahertz transients efficiently at a two-dimensional Rashba interface between two non-magnetic materials, i.e., Ag/Bi. Those interfaces have been proven to be efficient means for spin- and charge current interconversion.

A novel improved method for analysis of 2D diffusion relaxation data—2D PARAFAC-Laplace decomposition

NASA Astrophysics Data System (ADS)

Tønning, Erik; Polders, Daniel; Callaghan, Paul T.; Engelsen, Søren B.

2007-09-01

This paper demonstrates how the multi-linear PARAFAC model can with advantage be used to decompose 2D diffusion-relaxation correlation NMR spectra prior to 2D-Laplace inversion to the T2- D domain. The decomposition is advantageous for better interpretation of the complex correlation maps as well as for the quantification of extracted T2- D components. To demonstrate the new method seventeen mixtures of wheat flour, starch, gluten, oil and water were prepared and measured with a 300 MHz nuclear magnetic resonance (NMR) spectrometer using a pulsed gradient stimulated echo (PGSTE) pulse sequence followed by a Carr-Purcell-Meiboom-Gill (CPMG) pulse echo train. By varying the gradient strength, 2D diffusion-relaxation data were recorded for each sample. From these double exponentially decaying relaxation data the PARAFAC algorithm extracted two unique diffusion-relaxation components, explaining 99.8% of the variation in the data set. These two components were subsequently transformed to the T2- D domain using 2D-inverse Laplace transformation and quantitatively assigned to the oil and water components of the samples. The oil component was one distinct distribution with peak intensity at D = 3 × 10 -12 m 2 s -1 and T2 = 180 ms. The water component consisted of two broad populations of water molecules with diffusion coefficients and relaxation times centered around correlation pairs: D = 10 -9 m 2 s -1, T2 = 10 ms and D = 3 × 10 -13 m 2 s -1, T2 = 13 ms. Small spurious peaks observed in the inverse Laplace transformation of original complex data were effectively filtered by the PARAFAC decomposition and thus considered artefacts from the complex Laplace transformation. The oil-to-water ratio determined by PARAFAC followed by 2D-Laplace inversion was perfectly correlated with known oil-to-water ratio of the samples. The new method of using PARAFAC prior to the 2D-Laplace inversion proved to have superior potential in analysis of diffusion-relaxation spectra, as it improves not only the interpretation, but also the quantification.

Potential Characteristics and Applications of X-Ray Lasers,

DTIC Science & Technology

1982-01-01

useful to determine X-ray laser action. It is also possible to employ spectroscopy of the relevant levels to determine a population inversion, even if...Double-pulse heating of KCI cryst:is with a Nd laser was employed at the Spectroscopy Institute in Mosco.,. Elton !n;J Dixon ascribed the erission of...inversions were attributed to charge exchange which o-tjrred when ions from laser -heated plasmas expanded into a low-pressure (1-10 Torr) ’ ffer gas in

Non-contrast-enhanced MR portography and hepatic venography with time-spatial labeling inversion pulses: comparison of imaging with the short tau inversion recovery method and the chemical shift selective method.

PubMed

Shimizu, Hironori; Isoda, Hiroyoshi; Ohno, Tsuyoshi; Yamashita, Rikiya; Kawahara, Seiya; Furuta, Akihiro; Fujimoto, Koji; Kido, Aki; Kusahara, Hiroshi; Togashi, Kaori

2015-01-01

To compare and evaluate images of non-contrast enhanced magnetic resonance (MR) portography and hepatic venography acquired with two different fat suppression methods, the chemical shift selective (CHESS) method and short tau inversion recovery (STIR) method. Twenty-two healthy volunteers were examined using respiratory-triggered three-dimensional true steady-state free-precession with two time-spatial labeling inversion pulses. The CHESS or STIR methods were used for fat suppression. The relative signal-to-noise ratio and contrast-to-noise ratio (CNR) were quantified, and the quality of visualization was scored. Image acquisition was successfully conducted in all volunteers. The STIR method significantly improved the CNRs of MR portography and hepatic venography. The image quality scores of main portal vein and right portal vein were higher with the STIR method, but there were no significant differences. The image quality scores of right hepatic vein, middle hepatic vein, and left hepatic vein (LHV) were all higher, and the visualization of LHV was significantly better (p<0.05). The STIR method contributes to further suppression of the background signal and improves visualization of the portal and hepatic veins. The results support using non-contrast-enhanced MR portography and hepatic venography in clinical practice. Copyright © 2014 Elsevier Inc. All rights reserved.

Alternating steady state free precession for estimation of current-induced magnetic flux density: A feasibility study.

PubMed

Lee, Hyunyeol; Jeong, Woo Chul; Kim, Hyung Joong; Woo, Eung Je; Park, Jaeseok

2016-05-01

To develop a novel, current-controlled alternating steady-state free precession (SSFP)-based conductivity imaging method and corresponding MR signal models to estimate current-induced magnetic flux density (Bz ) and conductivity distribution. In the proposed method, an SSFP pulse sequence, which is in sync with alternating current pulses, produces dual oscillating steady states while yielding nonlinear relation between signal phase and Bz . A ratiometric signal model between the states was analytically derived using the Bloch equation, wherein Bz was estimated by solving a nonlinear inverse problem for conductivity estimation. A theoretical analysis on the signal-to-noise ratio of Bz was given. Numerical and experimental studies were performed using SSFP-FID and SSFP-ECHO with current pulses positioned either before or after signal encoding to investigate the feasibility of the proposed method in conductivity estimation. Given all SSFP variants herein, SSFP-FID with alternating current pulses applied before signal encoding exhibits the highest Bz signal-to-noise ratio and conductivity contrast. Additionally, compared with conventional conductivity imaging, the proposed method benefits from rapid SSFP acquisition without apparent loss of conductivity contrast. We successfully demonstrated the feasibility of the proposed method in estimating current-induced Bz and conductivity distribution. It can be a promising, rapid imaging strategy for quantitative conductivity imaging. © 2015 Wiley Periodicals, Inc.

Kinematic source inversion of the 2017 Puebla-Morelos, Mexico earthquake (2017/09/19, Mw.7.1)

NASA Astrophysics Data System (ADS)

Iglesias, A.; Castro-Artola, O.; Hjorleifsdottir, V.; Singh, S. K.; Ji, C.; Franco-Sánchez, S. I.

2017-12-01

On September 19th 2017, an Mw 7.1 earthquake struck Central Mexico, causing severe damage in the epicentral region, especially in several small and medium size houses as well as historical buildings like churches and government offices. In Mexico City, at a distance of 100km from the epicenter, 38 buildings collapsed. Authorities reported that 369 persons were killed by the earthquake (> 60% in the Mexico City). We determined the hypocentral location (18.406N, 98.706W, d=57km), from regional data, situating this earthquake inside the subducted Cocos Plate, with a normal fault mechanism (Globalcmt: =300°, =44°, and =-82°). In this presentation we show the the slip on the fault plane, determined by 1) a frequency-domain inversion using local and regional acceleration records that have been numerically integrated twice and bandpass filtered between 2 and 30, and 2) a wavelet domain inversion using teleseismic body and surface-waves, filtered between 1-100 s and 50-150 s respectively, as well as static offsets. In both methods the fault plane is divided into subfaults, and for each subfault we invert for the average slip, and timing of initiation of slip. In the first method the slip direction is fixed to the ? direction and we invert for the rise time. In the second method the direction of slip is estimated, with values between -90 and +90 allowed, and the time history is an asymmetric cosine time function, for which we determine the "rise" and "fall" durations. For both methods, synthetic seismograms, based on the GlobalCMT focal mechanism, are computed for each subfault-station pair and for three components (Z, N-S, EW). Preliminary results, using local data, show some slip concentrated close to the hypocentral location and a large patch 20 km in NW direction far from the origin. Using teleseismic data, it is difficult to distinguish between the two fault planes, as the waveforms are equally well fit using either one of them. However, both are consistent with a simple rupture patch of 25x20 km and maximum slip of 2 m. Solutions based on both fault planes suggest directivity towards the NW. There is some evidence of two short pulses superimposed on a longer duration pulse in the body wave seismograms, but they are difficult to resolve with the inversion

Non-water-suppressed 1 H FID-MRSI at 3T and 9.4T.

PubMed

Chang, Paul; Nassirpour, Sahar; Avdievitch, Nikolai; Henning, Anke

2018-08-01

This study investigates metabolite concentrations using metabolite-cycled 1 H free induction decay (FID) magnetic resonance spectroscopic imaging (MRSI) at ultra-high fields. A non-lipid-suppressed and slice-selective ultra-short echo time (TE) 1 H FID MRSI sequence was combined with a low-specific absorption rate (SAR) asymmetric inversion adiabatic pulse to enable non-water-suppressed metabolite mapping using metabolite-cycling at 9.4T. The results were compared to a water-suppressed FID MRSI sequence, and the same study was performed at 3T for comparison. The scan times for performing single-slice metabolite mapping with a nominal voxel size of 0.4 mL were 14 and 17.5 min on 3T and 9.4T, respectively. The low-SAR asymmetric inversion adiabatic pulse enabled reliable non-water-suppressed metabolite mapping using metabolite cycling at both 3T and 9.4T. The spectra and maps showed good agreement with the water-suppressed FID MRSI ones at both field strengths. A quantitative analysis of metabolite ratios with respect to N-acetyl aspartate (NAA) was performed. The difference in Cre/NAA was statistically significant, ∼0.1 higher for the non-water-suppressed case than for water suppression (from 0.73 to 0.64 at 3T and from 0.69 to 0.59 at 9.4T). The difference is likely because of chemical exchange effects of the water suppression pulses. Small differences in mI/NAA were also statistically significant, however, are they are less reliable because the metabolite peaks are close to the water peak that may be affected by the water suppression pulses or metabolite-cycling inversion pulse. We showed the first implementation of non-water-suppressed metabolite-cycled 1 H FID MRSI at ultra-high fields. An increase in Cre/NAA was seen for the metabolite-cycled case. The same methodology was further applied at 3T and similar results were observed. Magn Reson Med 80:442-451, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

A Novel Application for the Detection of an Irregular Pulse using an iPhone 4S in Patients with Atrial Fibrillation

PubMed Central

McManus, David D.; Lee, Jinseok; Maitas, Oscar; Esa, Nada; Pidikiti, Rahul; Carlucci, Alex; Harrington, Josephine; Mick, Eric; Chon, Ki H.

2012-01-01

Background Atrial fibrillation (AF) is common and associated with adverse health outcomes. Timely detection of AF can be challenging using traditional diagnostic tools. Smartphone use is increasing and may provide an inexpensive and user-friendly means to diagnose AF. Objective To test the hypothesis that a smartphone-based application could detect an irregular pulse from AF. Methods 76 adults with persistent AF were consented for participation in our study. We obtained pulsatile time series recordings before and after cardioversion using an iPhone 4S camera. A novel smartphone application conducted real-time pulse analysis using 2 statistical methods [Root Mean Square of Successive RR Differences (RMSSD/mean); Shannon Entropy (ShE)]. We examined the sensitivity, specificity, and predictive accuracy of both algorithms using the 12-lead electrocardiogram as the gold standard. Results RMSDD/mean and ShE were higher in participants in AF compared with sinus rhythm. The 2 methods were inversely related to AF in regression models adjusting for key factors including heart rate and blood pressure (β coefficients per SD-increment in RMSDD/mean and ShE were −0.20 and −0.35; p<0.001). An algorithm combining the 2 statistical methods demonstrated excellent sensitivity (0.962), specificity (0.975), and accuracy (0.968) for beat-to-beat discrimination of an irregular pulse during AF from sinus rhythm. Conclusions In a prospectively recruited cohort of 76 participants undergoing cardioversion for AF, we found that a novel algorithm analyzing signals recorded using an iPhone 4S accurately distinguished pulse recordings during AF from sinus rhythm. Data are needed to explore the performance and acceptability of smartphone-based applications for AF detection. PMID:23220686

A novel application for the detection of an irregular pulse using an iPhone 4S in patients with atrial fibrillation.

PubMed

McManus, David D; Lee, Jinseok; Maitas, Oscar; Esa, Nada; Pidikiti, Rahul; Carlucci, Alex; Harrington, Josephine; Mick, Eric; Chon, Ki H

2013-03-01

Atrial fibrillation (AF) is common and associated with adverse health outcomes. Timely detection of AF can be challenging using traditional diagnostic tools. Smartphone use is increasing and may provide an inexpensive and user-friendly means to diagnoseAF. To test the hypothesis that a smartphone-based application could detect an irregular pulse fromAF. Seventy-six adults with persistent AF were consented for participation in our study. We obtained pulsatile time series recordings before and after cardioversion using an iPhone 4S camera. A novel smartphone application conducted real-time pulse analysis using 2 statistical methods: root mean square of successive RR difference (RMSSD/mean) and Shannon entropy (ShE). We examined the sensitivity, specificity, and predictive accuracy of both algorithms using the 12-lead electrocardiogram as the gold standard. RMSDD/mean and ShE were higher in participants in AF than in those with sinus rhythm. The 2 methods were inversely related to AF in regression models adjusting for key factors including heart rate and blood pressure (beta coefficients per SD increment in RMSDD/mean and ShE were-0.20 and-0.35; P<.001). An algorithm combining the 2 statistical methods demonstrated excellent sensitivity (0.962), specificity (0.975), and accuracy (0.968) for beat-to-beat discrimination of an irregular pulse during AF from sinus rhythm. In a prospectively recruited cohort of 76 participants undergoing cardioversion for AF, we found that a novel algorithm analyzing signals recorded using an iPhone 4S accurately distinguished pulse recordings during AF from sinus rhythm. Data are needed to explore the performance and acceptability of smartphone-based applications for AF detection. Copyright © 2013 Heart Rhythm Society. All rights reserved.

Surface heating of electrons in atomic clusters irradiated by ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Krainov, V. P.; Sofronov, A. V.

2014-04-01

We consider a mechanism for electron heating in atomic clusters at the reflections of free electrons from the cluster surface. Electrons acquire energy from the external laser field during these reflections. A simple analytical expression has been obtained for acquired electron kinetic energy during the laser pulse. We find conditions when this mechanism dominates compared to the electron heating due to the well-known induced inverse bremsstrahlung at the electron-ion collisions inside clusters.

MRI image plane nonuniformity in evaluation of ferrous sulphate dosimeter gel (FeGel) by means of T1-relaxation time.

PubMed

Magnusson, P; Bäck, S A; Olsson, L E

1999-11-01

MR image nonuniformity can vary significantly with the spin-echo pulse sequence repetition time. When MR images with different nonuniformity shapes are used in a T1-calculation the resulting T1-image becomes nonuniform. As shown in this work the uniformity TR-dependence of the spin-echo pulse sequence is a critical property for T1 measurements in general and for ferrous sulfate dosimeter gel (FeGel) applications in particular. The purpose was to study the characteristics of the MR image plane nonuniformity in FeGel evaluation. This included studies of the possibility of decreasing nonuniformities by selecting uniformity optimized repetition times, studies of the transmitted and received RF-fields and studies of the effectiveness of the correction methods background subtraction and quotient correction. A pronounced MR image nonuniformity variation with repetition and T1 relaxation time was observed, and was found to originate from nonuniform RF-transmission in combination with the inherent differences in T1 relaxation for different repetition times. The T1 calculation itself, the uniformity optimized repetition times, nor none of the correction methods studied could sufficiently correct the nonuniformities observed in the T1 images. The nonuniformities were found to vary considerably less with inversion time for the inversion-recovery pulse sequence, than with repetition time for the spin-echo pulse sequence, resulting in considerably lower T1 image nonuniformity levels.

Relaxation of water infiltration pulses observed with GPR

NASA Astrophysics Data System (ADS)

Hantschel, Lisa; Hemmer, Benedikt; Roth, Kurt

2017-04-01

We observe the relaxation of infiltration pulses in sandy soil with ground-penetrating radar (GPR). The spatial distribution of water in the infiltration area and its temporal evolution is represented by ordinary reflections at layer boundaries as well as multiple reflections at the wetting front and the pulse boundaries. The structure of these highly resolved signals are reproduced by numerical simulations of electromagnetic wave propagation. The temporally highly resolved electrical fields reveal the origin also of complex reflection signals. The usage of these more complex signals might allow a more detailed representation of the infiltration process by direct analysis as well as in combination with inversion techniques.

Source mechanism of very-long-period signals accompanying dome growth activity at Merapi volcano, Indonesia

USGS Publications Warehouse

Hidayat, D.; Chouet, B.; Voight, B.; Dawson, P.; Ratdomopurbo, Antonius

2002-01-01

Very-long-period (VLP) pulses with period of 6-7s, displaying similar waveforms, were identified in 1998 from broadband seismographs around the summit crater. These pulses accompanied most of multiphase (MP) earthquakes, a type of long-period event locally defined at Merapi Volcano. Source mechanisms for several VLP pulses were examined by applying moment tensor inversion to the waveform data. Solutions were consistent with a crack striking ???70?? and dipping ???50?? SW, 100m under the active dome, suggest pressurized gas transport involving accumulation and sudden release of 10-60 m3 of gas in the crack over a 6s interval.

Non-destructive testing of ceramic materials using mid-infrared ultrashort-pulse laser

NASA Astrophysics Data System (ADS)

Sun, S. C.; Qi, Hong; An, X. Y.; Ren, Y. T.; Qiao, Y. B.; Ruan, Liming M.

2018-04-01

The non-destructive testing (NDT) of ceramic materials using mid-infrared ultrashort-pulse laser is investigated in this study. The discrete ordinate method is applied to solve the transient radiative transfer equation in 2D semitransparent medium and the emerging radiative intensity on boundary serves as input for the inverse analysis. The sequential quadratic programming algorithm is employed as the inverse technique to optimize objective function, in which the gradient of objective function with respect to reconstruction parameters is calculated using the adjoint model. Two reticulated porous ceramics including partially stabilized zirconia and oxide-bonded silicon carbide are tested. The retrieval results show that the main characteristics of defects such as optical properties, geometric shapes and positions can be accurately reconstructed by the present model. The proposed technique is effective and robust in NDT of ceramics even with measurement errors.

All-optical switching in granular ferromagnets caused by magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Ellis, Matthew O. A.; Fullerton, Eric E.; Chantrell, Roy W.

2016-07-01

Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength.

A Cr4+:YAG passively Q-switched Nd:YVO4 microchip laser for controllable high-order Hermite-Gaussian modes

NASA Astrophysics Data System (ADS)

Dong, Jun; He, Yu; Bai, Sheng-Chuang; Ueda, Ken-ichi; Kaminskii, Alexander A.

2016-09-01

A nanosecond, high peak power, passively Q-switched laser for controllable Hermite-Gaussian (HG) modes has been achieved by manipulating the saturated inversion population inside the gain medium. The stable HG modes are generated in a Cr4+:YAG passively Q-switched Nd:YVO4 microchip laser by applying a tilted pump beam. The asymmetrical saturated inversion population distribution inside the Nd:YVO4 crystal for desirable HG modes is manipulated by choosing the proper pump beam diameter and varying pump power. A HG9,8 mode passively Q-switched Nd:YVO4 microchip laser with average output power of 265 mW has been obtained. Laser pulses with a pulse width of 7.3 ns and peak power of over 1.7 kW working at 21 kHz have been generated in the passively Q-switched Nd:YVO4 microchip laser.

Ultrashort electromagnetic pulse control of intersubband quantum well transitions

PubMed Central

2012-01-01

We study the creation of high-efficiency controlled population transfer in intersubband transitions of semiconductor quantum wells. We give emphasis to the case of interaction of the semiconductor quantum well with electromagnetic pulses with a duration of few cycles and even a single cycle. We numerically solve the effective nonlinear Bloch equations for a specific double GaAs/AlGaAs quantum well structure, taking into account the ultrashort nature of the applied field, and show that high-efficiency population inversion is possible for specific pulse areas. The dependence of the efficiency of population transfer on the electron sheet density and the carrier envelope phase of the pulse is also explored. For electromagnetic pulses with a duration of several cycles, we find that the change in the electron sheet density leads to a very different response of the population in the two subbands to pulse area. However, for pulses with a duration equal to or shorter than 3 cycles, we show that efficient population transfer between the two subbands is possible, independent of the value of electron sheet density, if the pulse area is Π. PMID:22916956

Ultrashort electromagnetic pulse control of intersubband quantum well transitions.

PubMed

Paspalakis, Emmanuel; Boviatsis, John

2012-08-23

: We study the creation of high-efficiency controlled population transfer in intersubband transitions of semiconductor quantum wells. We give emphasis to the case of interaction of the semiconductor quantum well with electromagnetic pulses with a duration of few cycles and even a single cycle. We numerically solve the effective nonlinear Bloch equations for a specific double GaAs/AlGaAs quantum well structure, taking into account the ultrashort nature of the applied field, and show that high-efficiency population inversion is possible for specific pulse areas. The dependence of the efficiency of population transfer on the electron sheet density and the carrier envelope phase of the pulse is also explored. For electromagnetic pulses with a duration of several cycles, we find that the change in the electron sheet density leads to a very different response of the population in the two subbands to pulse area. However, for pulses with a duration equal to or shorter than 3 cycles, we show that efficient population transfer between the two subbands is possible, independent of the value of electron sheet density, if the pulse area is Π.

Threshold Evolution as an Analysis of the Different Pulse Frequencies in Rechargeable Systems for Spinal Cord Stimulation.

PubMed

Abejón, David; Rueda, Pablo; Vallejo, Ricardo

2016-04-01

Pulse frequency (Fc) is one of the most important parameters in neurostimulation, with Pulse Amplitude (Pw) and Amplitude (I). Up to certain Fc, increasing the number of pulses will generate action potentials in neighboring neural structures and may facilitate deeper penetration of the electromagnetic fields. In addition, changes in frequency modify the patient's sensation with stimulation. Fifty patients previously implanted with rechargeable current control spinal cord stimulation. With pulse width fixed at 300 μsec, we stimulated at 26 different Fc values between 40 and 1200 Hz and determine the influence of these changes on different stimulation thresholds: perception threshold (Tp ), therapeutic perception (Tt), and discomfort threshold (Td). Simultaneously, paresthesia coverage of the painful area and patient's sensation and satisfaction related to the quality of stimulation were recorded. Pulse Fc is inversely proportional to stimulation thresholds and this influence is statistically significant (p < 0.05). As Pulse Fc increased from 40 to 1200 Hz, the mean threshold decreases from 7.25 to 1.38 mA (Tp ), 8.17 to 1.63 (Tt ), and 9.20 to 1.85 (Td). Significant differences for Tp and Tt began at 750 Hz (Tp , Tt ) and at 650 Hz for Td. No significant influence was found regarding paresthesia coverage. As expected, Fc affects significantly patient's sensation and satisfaction. Changes in Fc affect the quality of paresthesias. Within the evaluated parameters higher frequencies are inversely proportional to stimulation thresholds and Tt. It seems that Fc is a vital parameter to achieve therapeutic success. Changes in Fc is a useful parameter to modulate the patient's sensory perception. Fc can be successfully used to adjust the quality of the paresthesias and to modify patient's subjective sensation. We showed that as the frequency increases, the patient's satisfaction with the perceived sensation decreases, suggesting that higher Fc may need to be set up at subthreshold amplitude to achieve positive response. © 2016 International Neuromodulation Society.

Arterial stiffness is associated to cardiorespiratory fitness and body mass index in young Swedish adults: The Lifestyle, Biomarkers, and Atherosclerosis study.

PubMed

Fernberg, Ulrika; Fernström, Maria; Hurtig-Wennlöf, Anita

2017-11-01

Background Early changes in the large muscular arteries are already associated with risk factors as hypertension and obesity in adolescence and young adulthood. The present study examines the association between arterial stiffness measurements, pulse wave velocity and augmentation index and lifestyle-related factors, body composition and cardiorespiratory fitness, in young, healthy, Swedish adults. Design This study used a population-based cross-sectional sample. Methods The 834 participants in the study were self-reported healthy, non-smoking, age 18-25 years. Augmentation index and pulse wave velocity were measured with applanation tonometry. Cardiorespiratory fitness was measured by ergometer bike test to estimate maximal oxygen uptake. Body mass index (kg/m 2 ) was calculated and categorised according to classification by the World Health Organisation. Results Young Swedish adults with obesity and low cardiorespiratory fitness have significantly higher pulse wave velocity and augmentation index than non-obese young adults with medium or high cardiorespiratory fitness. The observed U-shaped association between pulse wave velocity and body mass index categories in women indicates that it might be more beneficial to be normal weight than underweight when assessing the arterial stiffness with pulse wave velocity. The highest mean pulse wave velocity was found in overweight/obese individuals with low cardiorespiratory fitness. The lowest mean pulse wave velocity was found in normal weight individuals with high cardiorespiratory fitness. Cardiorespiratory fitness had a stronger effect than body mass index on arterial stiffness in multiple regression analyses. Conclusions The inverse association between cardiorespiratory fitness and arterial stiffness is observed already in young adults. The study result highlights the importance of high cardiorespiratory fitness, but also that underweight individuals may be a possible risk group that needs to be further studied.

Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser

NASA Astrophysics Data System (ADS)

Sun, Mingying; Zhu, Jianqiang; Lin, Zunqi

2017-01-01

We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses.

Inverse Faraday effect driven by radiation friction

NASA Astrophysics Data System (ADS)

Liseykina, T. V.; Popruzhenko, S. V.; Macchi, A.

2016-07-01

A collective, macroscopic signature to detect radiation friction in laser-plasma experiments is proposed. In the interaction of superintense circularly polarized laser pulses with high density targets, the effective dissipation due to radiative losses allows the absorption of electromagnetic angular momentum, which in turn leads to the generation of a quasistatic axial magnetic field. This peculiar ‘inverse Faraday effect’ is investigated by analytical modeling and three-dimensional simulations, showing that multi-gigagauss magnetic fields may be generated at laser intensities \\gt {10}23 {{{W}}{{cm}}}-2.

Plasma Power Station with Quasi Spherical Direct Drive Capsule for Fusion Yield and Inverse Diode for Driver-Target Coupling

DOE PAGES

VanDevender, J. P.; Cuneo, M. E.; Slutz, S. A.; ...

2012-01-01

The Meier-Moir economic model for Pulsed Power Driven Inertial Fusion Energy shows at least two approaches for fusion energy at 7 to 8 cents/kw-hr: One with large yield at 0.1 Hz and presented by M. E. Cuneo at ICENES 2011 and one with smaller yield at 3 Hz presented in this paper. Both use very efficient and low cost Linear Transformer Drivers (LTDs) for the pulsed power. Here, we report the system configuration and end-to-end simulation for the latter option, which is called the Plasma Power Station (PPS), and report the first results on the two, least mature, enabling technologies:more » a magnetically driven Quasi Spherical Direct Drive (QSDD) capsule for the fusion yield and an Inverse Diode for coupling the driver to the target. In addition, we describe the issues and propose to address the issues with a prototype of the PPS on the Saturn accelerator and with experiments on a short pulse modification of the Z accelerator test the validity of simulations showing megajoule thermonuclear yield with DT on a modified Z.« less

Longitudinal stability of MRI for mapping brain change using tensor-based morphometry.

PubMed

Leow, Alex D; Klunder, Andrea D; Jack, Clifford R; Toga, Arthur W; Dale, Anders M; Bernstein, Matt A; Britson, Paula J; Gunter, Jeffrey L; Ward, Chadwick P; Whitwell, Jennifer L; Borowski, Bret J; Fleisher, Adam S; Fox, Nick C; Harvey, Danielle; Kornak, John; Schuff, Norbert; Studholme, Colin; Alexander, Gene E; Weiner, Michael W; Thompson, Paul M

2006-06-01

Measures of brain change can be computed from sequential MRI scans, providing valuable information on disease progression, e.g., for patient monitoring and drug trials. Tensor-based morphometry (TBM) creates maps of these brain changes, visualizing the 3D profile and rates of tissue growth or atrophy, but its sensitivity depends on the contrast and geometric stability of the images. As part of the Alzheimer's Disease Neuroimaging Initiative (ADNI), 17 normal elderly subjects were scanned twice (at a 2-week interval) with several 3D 1.5 T MRI pulse sequences: high and low flip angle SPGR/FLASH (from which Synthetic T1 images were generated), MP-RAGE, IR-SPGR (N = 10) and MEDIC (N = 7) scans. For each subject and scan type, a 3D deformation map aligned baseline and follow-up scans, computed with a nonlinear, inverse-consistent elastic registration algorithm. Voxelwise statistics, in ICBM stereotaxic space, visualized the profile of mean absolute change and its cross-subject variance; these maps were then compared using permutation testing. Image stability depended on: (1) the pulse sequence; (2) the transmit/receive coil type (birdcage versus phased array); (3) spatial distortion corrections (using MEDIC sequence information); (4) B1-field intensity inhomogeneity correction (using N3). SPGR/FLASH images acquired using a birdcage coil had least overall deviation. N3 correction reduced coil type and pulse sequence differences and improved scan reproducibility, except for Synthetic T1 images (which were intrinsically corrected for B1-inhomogeneity). No strong evidence favored B0 correction. Although SPGR/FLASH images showed least deviation here, pulse sequence selection for the ADNI project was based on multiple additional image analyses, to be reported elsewhere.

Longitudinal stability of MRI for mapping brain change using tensor-based morphometry

PubMed Central

Leow, Alex D.; Klunder, Andrea D.; Jack, Clifford R.; Toga, Arthur W.; Dale, Anders M.; Bernstein, Matt A.; Britson, Paula J.; Gunter, Jeffrey L.; Ward, Chadwick P.; Whitwell, Jennifer L.; Borowski, Bret J.; Fleisher, Adam S.; Fox, Nick C.; Harvey, Danielle; Kornak, John; Schuff, Norbert; Studholme, Colin; Alexander, Gene E.; Weiner, Michael W.; Thompson, Paul M.

2007-01-01

Measures of brain change can be computed from sequential MRI scans, providing valuable information on disease progression, e.g., for patient monitoring and drug trials. Tensor-based morphometry (TBM) creates maps of these brain changes, visualizing the 3D profile and rates of tissue growth or atrophy, but its sensitivity depends on the contrast and geometric stability of the images. A s part of the Alzheimer’s Disease Neuroimaging Initiative (ADNI), 17 normal elderly subjects were scanned twice (at a 2-week interval) with several 3D 1.5 T MRI pulse sequences: high and low flip angle SPGR/FLASH (from which Synthetic T1 images were generated), MP-RAGE, IR-SPGR (N = 10) and MEDIC (N = 7) scans. For each subject and scan type, a 3D deformation map aligned baseline and follow-up scans, computed with a nonlinear, inverse-consistent elastic registration algorithm. Voxelwise statistics, in ICBM stereotaxic space, visualized the profile of mean absolute change and its cross-subject variance; these maps were then compared using permutation testing. Image stability depended on: (1) the pulse sequence; (2) the transmit/receive coil type (birdcage versus phased array); (3) spatial distortion corrections (using MEDIC sequence information); (4) B1-field intensity inhomogeneity correction (using N3). SPGR/FLASH images acquired using a birdcage coil had least overall deviation. N3 correction reduced coil type and pulse sequence differences and improved scan reproducibility, except for Synthetic T1 images (which were intrinsically corrected for B1-inhomogeneity). No strong evidence favored B0 correction. Although SPGR/FLASH images showed least deviation here, pulse sequence selection for the ADNI project was based on multiple additional image analyses, to be reported elsewhere. PMID:16480900

An inverse approach to determining spatially varying arterial compliance using ultrasound imaging

NASA Astrophysics Data System (ADS)

Mcgarry, Matthew; Li, Ronny; Apostolakis, Iason; Nauleau, Pierre; Konofagou, Elisa E.

2016-08-01

The mechanical properties of arteries are implicated in a wide variety of cardiovascular diseases, many of which are expected to involve a strong spatial variation in properties that can be depicted by diagnostic imaging. A pulse wave inverse problem (PWIP) is presented, which can produce spatially resolved estimates of vessel compliance from ultrasound measurements of the vessel wall displacements. The 1D equations governing pulse wave propagation in a flexible tube are parameterized by the spatially varying properties, discrete cosine transform components of the inlet pressure boundary conditions, viscous loss constant and a resistance outlet boundary condition. Gradient descent optimization is used to fit displacements from the model to the measured data by updating the model parameters. Inversion of simulated data showed that the PWIP can accurately recover the correct compliance distribution and inlet pressure under realistic conditions, even under high simulated measurement noise conditions. Silicone phantoms with known compliance contrast were imaged with a clinical ultrasound system. The PWIP produced spatially and quantitatively accurate maps of the phantom compliance compared to independent static property estimates, and the known locations of stiff inclusions (which were as small as 7 mm). The PWIP is necessary for these phantom experiments as the spatiotemporal resolution, measurement noise and compliance contrast does not allow accurate tracking of the pulse wave velocity using traditional approaches (e.g. 50% upstroke markers). Results from simulations indicate reflections generated from material interfaces may negatively affect wave velocity estimates, whereas these reflections are accounted for in the PWIP and do not cause problems.

Resonant optical pulses on a continuous-wave background in two-level active media

NASA Astrophysics Data System (ADS)

Li, Sitai; Biondini, Gino; Kovačič, Gregor; Gabitov, Ildar

2018-01-01

We present exact N-soliton optical pulses riding on a continuous-wave (c.w.) beam that propagate through and interact with a two-level active optical medium. Their representation is derived via an appropriate generalization of the inverse scattering transform for the corresponding Maxwell-Bloch equations. We describe the single-soliton solutions in detail and classify them into several distinct families. In addition to the analogues of traveling-wave soliton pulses that arise in the absence of a c.w. beam, we obtain breather-like structures, periodic pulse-trains and rogue-wave-type (i.e., rational) pulses, whose existence is directly due to the presence of the c.w. beam. These soliton solutions are the analogues for Maxwell-Bloch systems of the four classical solution types of the focusing nonlinear Schrödinger equation with non-zero background, although the physical behavior of the corresponding solutions is quite different.

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.

Association between Frequency of Consumption of Fruit, Vegetables, Nuts and Pulses and BMI: Analyses of the International Study of Asthma and Allergies in Childhood (ISAAC).

PubMed

Wall, Clare R; Stewart, Alistair W; Hancox, Robert J; Murphy, Rinki; Braithwaite, Irene; Beasley, Richard; Mitchell, Edwin A

2018-03-07

Diets which emphasize intakes of plant-based foods are recommended to reduce disease risk and for promoting healthy weight. The aim of this study was to examine the association between fruit, vegetables, pulses and nut intake and body mass index (BMI) across countries in adolescents (13-14 years) and children (6-7 years). Data from the International Study of Asthma and Allergies in Childhood; 77,243 children's parents and 201,871 adolescents was used to examine the association between dietary intake (Food Frequency Questionnaire) and BMI using general linear models, adjusting for country gross national index. Adolescents who consumed fruit, vegetables, pulses and nuts three or more times a week had a lower BMI than the never or occasional group; eating nuts three or more times a week, was associated with a BMI value of 0.274 kg/m² lower than the never group ( p < 0.001). Compared to children who never or occasionally reported eating vegetables, those reporting that they ate vegetables three or more times per week had a lower BMI of -0.079 kg/m². In this large global study, an inverse association was observed between BMI and the reported increasing intake of vegetables in 6-7 years old and fruit, vegetables, pulses and nuts in adolescents. This study supports current dietary recommendations which emphasize the consumption of vegetables, nut and pulses, although the effect sizes were small.

Design of a Low-Energy FARAD Thruster

NASA Technical Reports Server (NTRS)

Polzin, K. A.; Rose, M. F.; Miller, R.; Best, S.; Owens, T.; Dankanich, J.

2007-01-01

The design of an electrodeless thruster that relies on a pulsed, rf-assisted discharge and electromagnetic acceleration using an inductive coil is presented. The thruster design is optimized using known performance,scaling parameters, and experimentally-determined design rules, with design targets for discharge energy, plasma exhaust velocity; and thrust efficiency of 100 J/pulse, 25 km/s, and 50%, respectively. Propellant is injected using a high-speed gas valve and preionized by a pulsed-RF signal supplied by a vector inversion generator, allowing for current sheet formation at lower discharge voltages and energies relative to pulsed inductive accelerators that do not employ preionization. The acceleration coil is designed to possess an inductance of at least 700 nH while the target stray (non-coil) inductance in the circuit is 70 nH. A Bernardes and Merryman pulsed power train or a pulse compression power train provide current to the acceleration coil and solid-state components are used to switch both powertrains.

Estimation of Dynamic Friction Process of the Akatani Landslide Based on the Waveform Inversion and Numerical Simulation

NASA Astrophysics Data System (ADS)

Yamada, M.; Mangeney, A.; Moretti, L.; Matsushi, Y.

2014-12-01

Understanding physical parameters, such as frictional coefficients, velocity change, and dynamic history, is important issue for assessing and managing the risks posed by deep-seated catastrophic landslides. Previously, landslide motion has been inferred qualitatively from topographic changes caused by the event, and occasionally from eyewitness reports. However, these conventional approaches are unable to evaluate source processes and dynamic parameters. In this study, we use broadband seismic recordings to trace the dynamic process of the deep-seated Akatani landslide that occurred on the Kii Peninsula, Japan, which is one of the best recorded large slope failures. Based on the previous results of waveform inversions and precise topographic surveys done before and after the event, we applied numerical simulations using the SHALTOP numerical model (Mangeney et al., 2007). This model describes homogeneous continuous granular flows on a 3D topography based on a depth averaged thin layer approximation. We assume a Coulomb's friction law with a constant friction coefficient, i. e. the friction is independent of the sliding velocity. We varied the friction coefficients in the simulation so that the resulting force acting on the surface agrees with the single force estimated from the seismic waveform inversion. Figure shows the force history of the east-west components after the band-pass filtering between 10-100 seconds. The force history of the simulation with frictional coefficient 0.27 (thin red line) the best agrees with the result of seismic waveform inversion (thick gray line). Although the amplitude is slightly different, phases are coherent for the main three pulses. This is an evidence that the point-source approximation works reasonably well for this particular event. The friction coefficient during the sliding was estimated to be 0.38 based on the seismic waveform inversion performed by the previous study and on the sliding block model (Yamada et al., 2013), whereas the frictional coefficient estimated from the numerical simulation was about 0.27. This discrepancy may be due to the digital elevation model, to the other forces such as pressure gradients and centrifugal acceleration included in the model. However, quantitative interpretation of this difference requires further investigation.

Predicting the effect of relaxation during frequency-selective adiabatic pulses

NASA Astrophysics Data System (ADS)

Pfaff, Annalise R.; McKee, Cailyn E.; Woelk, Klaus

2017-11-01

Adiabatic half and full passages are invaluable for achieving uniform, B1-insensitive excitation or inversion of macroscopic magnetization across a well-defined range of NMR frequencies. To accomplish narrow frequency ranges with adiabatic pulses (<100 Hz), long pulse durations at low RF power levels are necessary, and relaxation during these pulses may no longer be negligible. A numerical, discrete recursive combination of the Bloch equations for longitudinal and transverse relaxation with the optimized equation for adiabatic angular motion of magnetization is used to calculate the trajectory of magnetization including its relaxation during adiabatic hyperbolic secant pulses. The agreement of computer-calculated data with experimental results demonstrates that, in non-viscous, small-molecule fluids, it is possible to model magnetization and relaxation by considering standard T1 and T2 relaxation in the traditional rotating frame. The proposed model is aimed at performance optimizations of applications in which these pulses are employed. It differs from previous reports which focused on short high-power adiabatic pulses and relaxation that is governed by dipole-dipole interactions, cross polarization, or chemical exchange.

Broadband MAS NMR spectroscopy in the low-power limit

NASA Astrophysics Data System (ADS)

Sanders, Kevin J.; Pell, Andrew J.; Wegner, Sebastian; Grey, Clare P.; Pintacuda, Guido

2018-04-01

We investigate the performance of broadband adiabatic inversion pulses in the high-power (short high-powered adiabatic pulse, SHAP) and low-power (single-sideband-selective adiabatic pulse, S3AP) RF regimes on a spin system subjected to large anisotropic interactions. We show by combined experimental results and spin dynamics simulations that when the magic-angle spinning rate exceeds 100 kHz S3APs begin outperforming SHAPs. This is especially true for low-gamma nuclei, such as 6 Li in paramagnetic Li-ion battery materials. Finally, we show how S3APs can be improved by combining multiple waveforms sweeping over multiple sidebands simultaneously, in order to produce inverted sideband profiles free from intensity biasing.

Inverse simulation system for evaluating handling qualities during rendezvous and docking

NASA Astrophysics Data System (ADS)

Zhou, Wanmeng; Wang, Hua; Thomson, Douglas; Tang, Guojin; Zhang, Fan

2017-08-01

The traditional method used for handling qualities assessment of manned space vehicles is too time-consuming to meet the requirements of an increasingly fast design process. In this study, a rendezvous and docking inverse simulation system to assess the handling qualities of spacecraft is proposed using a previously developed model-predictive-control architecture. By considering the fixed discrete force of the thrusters of the system, the inverse model is constructed using the least squares estimation method with a hyper-ellipsoidal restriction, the continuous control outputs of which are subsequently dispersed by pulse width modulation with sensitivity factors introduced. The inputs in every step are deemed constant parameters, and the method could be considered as a general method for solving nominal, redundant, and insufficient inverse problems. The rendezvous and docking inverse simulation is applied to a nine-degrees-of-freedom platform, and a novel handling qualities evaluation scheme is established according to the operation precision and astronauts' workload. Finally, different nominal trajectories are scored by the inverse simulation and an established evaluation scheme. The scores can offer theoretical guidance for astronaut training and more complex operation missions.

Model selection and Bayesian inference for high-resolution seabed reflection inversion.

PubMed

Dettmer, Jan; Dosso, Stan E; Holland, Charles W

2009-02-01

This paper applies Bayesian inference, including model selection and posterior parameter inference, to inversion of seabed reflection data to resolve sediment structure at a spatial scale below the pulse length of the acoustic source. A practical approach to model selection is used, employing the Bayesian information criterion to decide on the number of sediment layers needed to sufficiently fit the data while satisfying parsimony to avoid overparametrization. Posterior parameter inference is carried out using an efficient Metropolis-Hastings algorithm for high-dimensional models, and results are presented as marginal-probability depth distributions for sound velocity, density, and attenuation. The approach is applied to plane-wave reflection-coefficient inversion of single-bounce data collected on the Malta Plateau, Mediterranean Sea, which indicate complex fine structure close to the water-sediment interface. This fine structure is resolved in the geoacoustic inversion results in terms of four layers within the upper meter of sediments. The inversion results are in good agreement with parameter estimates from a gravity core taken at the experiment site.

Characterisation of the current switch mechanism in two-stage wire array Z-pinches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burdiak, G. C.; Lebedev, S. V.; Harvey-Thompson, A. J.

2015-11-15

In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA, 240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inverse wire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wire array, before rapidly switching the majority of the generator current into the load after a 100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse is presented. Measurements of the load resistivity and energy deposition suggest significant bulk heating of the array mass occurs. Themore » ∼5 kA pre-pulse delivers ∼0.8 J of energy to the load, leaving it in a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse array begins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicate that the main current switch may evolve in part as a plasma flow switch, driven by the expansion of a magnetic cavity and plasma bubble along the length of the load array. Analysis of implosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, corresponding to a doubling of the generator dI/dt. Potential scaling of the device to higher current machines is discussed.« less

Application of INEPT nitrogen-15 and silicon-29 nuclear magnetic resonance spectrometry to derivatized fulvic acids

USGS Publications Warehouse

Thorn, K.A.; Folan, D.W.; Arterburn, J.B.; Mikita, M.A.; MacCarthy, P.

1989-01-01

Use of the INEPT experiment has been examined in two derivatization studies of the Suwannee River fulvic acid. In the first study, the fulvic acid was derivatized with 15N enriched hydroxylamine. The quantitative 15N NMR spectrum, acquired with a 45° pulse angle, 2.0 second pulse delay and inverse gated decoupling, showed that oximes (390-340 ppm) were the major derivatives, followed by nitriles (270-240 ppm), hydroxamic acids (170-160 ppm), secondary amides (150-115 ppm), and lactams (115-90 ppm). The INEPT 15N NMR spectrum was acquired using refocussing delays and polarization transfer times optimized for signal enhancement of singly protonated nitrogens. INEPT greatly enhanced the amide and lactam resonances, and showed that resonances downfield of 180 ppm in the quantitative spectrum represented nonprotonated nitrogens. In the second study, the fulvic acid was first methylated with diazomethane and then silylated with hexamethyldisilazane. The 29Si NMR spectra exhibited two major peaks, from approximately 33 to 22 ppm, representing silyl esters of carboxylic acids, and from 22 to 13 ppm, representing silyl ethers of alcohols and phenols. The INEPT 29Si NMR spectrum was virtually identical to the quantitative 29Si spectrum, acquired with a 90° pulse angle, 5.0 second pulse delay, inverse gated decoupling, and relaxation reagent. INEPT therefore can be used for quantitative analysis of trimethylsilyl derivatives of the fulvic acid, saving spectrometer time and eliminating the need for relaxation reagents.

Cold pulse and rotation reversals with turbulence spreading and residual stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hariri, F.; Naulin, V.; Juul Rasmussen, J.

2016-05-15

Transport modeling based on inclusion of turbulence spreading and residual stresses shows internal rotation reversals and polarity reversal of cold pulses, with a clear indication of nonlocal transport effects due to fast spreading in the turbulence intensity field. The effects of turbulence spreading and residual stress are calculated from the gradient of the turbulence intensity. In the model presented in this paper, the flux is carried by the turbulence intensity field, which in itself is subject to radial transport effects. The pulse polarity inversion and the rotation profile reversal positions are close to the radial location of the stable/unstable transition.more » Both effects have no direct explanation within the framework of classical transport modeling, where the fluxes are related directly to the linear growth rates, the turbulence intensity profile is not considered and the corresponding residual stress is absent. Our simulations are in qualitative agreement with measurements from ohmically heated plasmas. Rotation reversal at a finite radius is found in situations not displaying saturated confinement, which we identify as situations where the plasma is nearly everywhere unstable. As an additional and new effect, the model predicts a perturbation of the velocity profile following a cold pulse from the edge. This allows direct experimental confirmation of both the existence of residual stress caused by turbulence intensity profiles and fundamental ideas of transport modeling presented here.« less

Signal averaging limitations in heterodyne- and direct-detection laser remote sensing measurements

NASA Technical Reports Server (NTRS)

Menyuk, N.; Killinger, D. K.; Menyuk, C. R.

1983-01-01

The improvement in measurement uncertainty brought about by the averaging of increasing numbers of pulse return signals in both heterodyne- and direct-detection lidar systems is investigated. A theoretical analysis is presented which shows the standard deviation of the mean measurement to decrease as the inverse square root of the number of measurements, except in the presence of temporal correlation. Experimental measurements based on a dual-hybrid-TEA CO2 laser differential absorption lidar system are reported which demonstrate that the actual reduction in the standard deviation of the mean in both heterodyne- and direct-detection systems is much slower than the inverse square-root dependence predicted for uncorrelated signals, but is in agreement with predictions in the event of temporal correlation. Results thus favor the use of direct detection at relatively short range where the lower limit of the standard deviation of the mean is about 2 percent, but advantages of heterodyne detection at longer ranges are noted.

Robust Population Inversion by Polarization Selective Pulsed Excitation

PubMed Central

Mantei, D.; Förstner, J.; Gordon, S.; Leier, Y. A.; Rai, A. K.; Reuter, D.; Wieck, A. D.; Zrenner, A.

2015-01-01

The coherent state preparation and control of single quantum systems is an important prerequisite for the implementation of functional quantum devices. Prominent examples for such systems are semiconductor quantum dots, which exhibit a fine structure split single exciton state and a V-type three level structure, given by a common ground state and two distinguishable and separately excitable transitions. In this work we introduce a novel concept for the preparation of a robust inversion by the sequential excitation in a V-type system via distinguishable paths. PMID:26000910

Acute effects of ultrafiltration on aortic mechanical properties determined by measurement of pulse wave velocity and pulse propagation time in hemodialysis patients

PubMed Central

Yıldız, Banu Şahin; Şahin, Alparslan; Aladağ, Nazire Başkurt; Arslan, Gülgün; Kaptanoğulları, Hakan; Akın, İbrahim; Yıldız, Mustafa

2015-01-01

Objective: The effects of acute hemodialysis session on pulse wave velocity are conflicting. The aim of the current study was to assess the acute effects of ultrafiltration on the aortic mechanical properties using carotid-femoral (aortic) pulse wave velocity and pulse propagation time. Methods: A total of 26 (12 women, 14 men) consecutive patients on maintenance hemodialysis (mean dialysis duration: 40.7±25.6 (4-70) months) and 29 healthy subjects (13 women, 16 men) were included in this study. Baseline blood pressure, carotid-femoral (aortic) pulse wave velocity, and pulse propagation time were measured using a Complior Colson device (Createch Industrie, France) before and immediately after the end of the dialysis session. Results: While systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and pulse wave velocity were significantly higher in patients on hemodialysis than in healthy subjects, pulse propagation time was significantly higher in healthy subjects. Although body weight, systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and pulse wave velocity were significantly decreased, heart rate and pulse propagation time were significantly increased after ultrafiltration. There was a significant positive correlation between pulse wave velocity and age, body height, waist circumference, systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and heart rate. Conclusion: Although hemodialysis treatment may chronically worsen aortic mechanical properties, ultrafiltration during hemodialysis may significantly improve aortic pulse wave velocity, which is inversely related to aortic distensibility and pulse propagation time. PMID:25413228

Single shot, double differential spectral measurements of inverse Compton scattering in the nonlinear regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakai, Y.; Gadjev, I.; Hoang, P.

Inverse Compton scattering (ICS) is a unique mechanism for producing fast pulses$-$picosecond and below$-$of bright photons, ranging from x to γ rays. These nominally narrow spectral bandwidth electromagnetic radiation pulses are efficiently produced in the interaction between intense, well-focused electron and laser beams. The spectral characteristics of such sources are affected by many experimental parameters, with intense laser effects often dominant. A laser field capable of inducing relativistic oscillatory motion may give rise to harmonic generation and, importantly for the present work, nonlinear redshifting, both of which dilute the spectral brightness of the radiation. As the applications enabled by thismore » source often depend sensitively on its spectra, it is critical to resolve the details of the wavelength and angular distribution obtained from ICS collisions. With this motivation, we present an experimental study that greatly improves on previous spectral measurement methods based on x-ray K -edge filters, by implementing a multilayer bent-crystal x-ray spectrometer. In tandem with a collimating slit, this method reveals a projection of the double differential angular-wavelength spectrum of the ICS radiation in a single shot. The measurements enabled by this diagnostic illustrate the combined off-axis and nonlinear-field-induced redshifting in the ICS emission process. The spectra obtained illustrate in detail the strength of the normalized laser vector potential, and provide a nondestructive measure of the temporal and spatial electron-laser beam overlap.« less

Single shot, double differential spectral measurements of inverse Compton scattering in the nonlinear regime

DOE PAGES

Sakai, Y.; Gadjev, I.; Hoang, P.; ...

2017-06-05

Inverse Compton scattering (ICS) is a unique mechanism for producing fast pulses$-$picosecond and below$-$of bright photons, ranging from x to γ rays. These nominally narrow spectral bandwidth electromagnetic radiation pulses are efficiently produced in the interaction between intense, well-focused electron and laser beams. The spectral characteristics of such sources are affected by many experimental parameters, with intense laser effects often dominant. A laser field capable of inducing relativistic oscillatory motion may give rise to harmonic generation and, importantly for the present work, nonlinear redshifting, both of which dilute the spectral brightness of the radiation. As the applications enabled by thismore » source often depend sensitively on its spectra, it is critical to resolve the details of the wavelength and angular distribution obtained from ICS collisions. With this motivation, we present an experimental study that greatly improves on previous spectral measurement methods based on x-ray K -edge filters, by implementing a multilayer bent-crystal x-ray spectrometer. In tandem with a collimating slit, this method reveals a projection of the double differential angular-wavelength spectrum of the ICS radiation in a single shot. The measurements enabled by this diagnostic illustrate the combined off-axis and nonlinear-field-induced redshifting in the ICS emission process. The spectra obtained illustrate in detail the strength of the normalized laser vector potential, and provide a nondestructive measure of the temporal and spatial electron-laser beam overlap.« less

Electro-magneto interaction in fractional Green-Naghdi thermoelastic solid with a cylindrical cavity

NASA Astrophysics Data System (ADS)

Ezzat, M. A.; El-Bary, A. A.

2018-01-01

A unified mathematical model of Green-Naghdi's thermoelasticty theories (GN), based on fractional time-derivative of heat transfer is constructed. The model is applied to solve a one-dimensional problem of a perfect conducting unbounded body with a cylindrical cavity subjected to sinusoidal pulse heating in the presence of an axial uniform magnetic field. Laplace transform techniques are used to get the general analytical solutions in Laplace domain, and the inverse Laplace transforms based on Fourier expansion techniques are numerically implemented to obtain the numerical solutions in time domain. Comparisons are made with the results predicted by the two theories. The effects of the fractional derivative parameter on thermoelastic fields for different theories are discussed.

Modeling magnetization transfer effects of Q2TIPS bolus saturation in multi-TI pulsed arterial spin labeling.

PubMed

Petr, Jan; Schramm, Georg; Hofheinz, Frank; Langner, Jens; van den Hoff, Jörg

2014-10-01

To estimate the relaxation time changes during Q2TIPS bolus saturation caused by magnetization transfer effects and to propose and evaluate an extended model for perfusion quantification which takes this into account. Three multi inversion-time pulsed arterial spin labeling sequences with different bolus saturation duration were acquired for five healthy volunteers. Magnetization transfer exchange rates in tissue and blood were obtained from control image saturation recovery. Cerebral blood flow (CBF) obtained using the extended model and the standard model was compared. A decrease of obtained CBF of 6% (10%) was observed in grey matter when the duration of bolus saturation increased from 600 to 900 ms (1200 ms). This decrease was reduced to 1.6% (2.8%) when the extended quantification model was used. Compared with the extended model, the standard model underestimated CBF in grey matter by 9.7, 15.0, and 18.7% for saturation durations 600, 900, and 1200 ms, respectively. Results for simulated single inversion-time data showed 5-16% CBF underestimation depending on blood arrival time and bolus saturation duration. Magnetization transfer effects caused by bolus saturation pulses should not be ignored when performing quantification as they can cause appreciable underestimation of the CBF. Copyright © 2013 Wiley Periodicals, Inc.

Broad Band Intra-Cavity Total Reflection Chemical Sensor

DOEpatents

Pipino, Andrew C. R.

1998-11-10

A broadband, ultrahigh-sensitivity chemical sensor is provided that allows etection through utilization of a small, extremely low-loss, monolithic optical cavity. The cavity is fabricated from highly transparent optical material in the shape of a regular polygon with one or more convex facets to form a stable resonator for ray trajectories sustained by total internal reflection. Optical radiation enters and exits the monolithic cavity by photon tunneling in which two totally reflecting surfaces are brought into close proximity. In the presence of absorbing material, the loss per pass is increased since the evanescent waves that exist exterior to the cavity at points where the circulating pulse is totally reflected, are absorbed. The decay rate of an injected pulse is determined by coupling out an infinitesimal fraction of the pulse to produce an intensity-versus-time decay curve. Since the change in the decay rate resulting from absorption is inversely proportional to the magnitude of absorption, a quantitative sensor of concentration or absorption cross-section with 1 part-per-million/pass or better sensitivity is obtained. The broadband nature of total internal reflection permits a single device to be used over a broad wavelength range. The absorption spectrum of the surrounding medium can thereby be obtained as a measurement of inverse decay time as a function of wavelength.

Comparative study of INPIStron and spark gap

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Lee, Ja H.

1993-01-01

An inverse pinch plasma switch, INPIStron, was studied in comparison to a conventional spark gap. The INPIStron is under development for high power switching applications. The INPIStron has an inverse pinch dynamics, opposed to Z-pinch dynamics in the spark gap. The electrical, plasma dynamics and radiative properties of the closing plasmas have been studied. Recently the high-voltage pulse transfer capabilities or both the INPIStron and the spark gap were also compared. The INPIStron with a low impedance Z = 9 ohms transfers 87 percent of an input pulse with a halfwidth of 2 mu s. For the same input pulse the spark gap of Z = 100 ohms transfers 68 percent. Fast framing and streak photography, taken with an TRW image converter camera, was used to observe the discharge uniformity and closing plasma speed in both switches. In order to assess the effects of closing plasmas on erosion of electrode material, emission spectra of two switches were studied with a spectrometer-optical multi channel analyzer (OMA) system. The typical emission spectra of the closing plasmas in the INPIStron and the spark gap showed that there were comparatively weak carbon line emission in 658.7 nm and copper (electrode material) line emissions in the INPIStron, indicating low erosion of materials in the INPIStron.

High-quality beam generation using an RF gun and a 150 MeV microtron

NASA Astrophysics Data System (ADS)

Kuroda, R.; Washio, M.; Kashiwagi, S.; Kobuki, T.; Ben-Zvi, I.; Wang, X. J.; Hori, T.; Sakai, F.; Tsunemi, A.; Urakawa, J.; Hirose, T.

2000-11-01

Low-emittance sub-picosecond electron pulses are expected to be used in a wide field, such as free electron laser, laser acceleration, femtosecond X-ray generation by Inverse Compton scattering, pulse radiolysis, etc. In order to produce the low-emittance sub-picosecond electron pulse, we are developing a compact Racetrack Microtron (RTM) with a new 5 MeV injection system adopting a laser photo cathode RF gun (Washio et al., Seventh China-Japan Bilateral Symposium on Radiation Chemistry, October 28, Cengdu, China, 1996). The operation of RTM has been kept under a steady state of beam loading for long pulse mode so far (Washio et al., J. Surf. Sci. Soc. Jpn. 19 (2) (1998) 23). In earlier work (Washio et al., PAC99, March 31, New York, USA, 1999), we have succeeded in the numerical simulation for the case of single short pulse acceleration. Finally, the modified RTM was demonstrated as a useful accelerator for a picosecond electron pulse generation under a transient state of beam loading. In the simulation, a picosecond electron pulse was accelerated to 149.6 MeV in RTM for the injection of 5 MeV electron bunch with a pulse length of 10 ps (FWHM), a charge of 1 nC per pulse, and an emittance of 3 πmm mrad.

Adaptive sparse grid approach for the efficient simulation of pulsed eddy current testing inspections

NASA Astrophysics Data System (ADS)

Miorelli, Roberto; Reboud, Christophe

2018-04-01

Pulsed Eddy Current Testing (PECT) is a popular NonDestructive Testing (NDT) technique for some applications like corrosion monitoring in the oil and gas industry, or rivet inspection in the aeronautic area. Its particularity is to use a transient excitation, which allows to retrieve more information from the piece than conventional harmonic ECT, in a simpler and cheaper way than multi-frequency ECT setups. Efficient modeling tools prove, as usual, very useful to optimize experimental sensors and devices or evaluate their performance, for instance. This paper proposes an efficient simulation of PECT signals based on standard time harmonic solvers and use of an Adaptive Sparse Grid (ASG) algorithm. An adaptive sampling of the ECT signal spectrum is performed with this algorithm, then the complete spectrum is interpolated from this sparse representation and PECT signals are finally synthesized by means of inverse Fourier transform. Simulation results corresponding to existing industrial configurations are presented and the performance of the strategy is discussed by comparison to reference results.

Modified Polar-Format Software for Processing SAR Data

NASA Technical Reports Server (NTRS)

Chen, Curtis

2003-01-01

HMPF is a computer program that implements a modified polar-format algorithm for processing data from spaceborne synthetic-aperture radar (SAR) systems. Unlike prior polar-format processing algorithms, this algorithm is based on the assumption that the radar signal wavefronts are spherical rather than planar. The algorithm provides for resampling of SAR pulse data from slant range to radial distance from the center of a reference sphere that is nominally the local Earth surface. Then, invoking the projection-slice theorem, the resampled pulse data are Fourier-transformed over radial distance, arranged in the wavenumber domain according to the acquisition geometry, resampled to a Cartesian grid, and inverse-Fourier-transformed. The result of this process is the focused SAR image. HMPF, and perhaps other programs that implement variants of the algorithm, may give better accuracy than do prior algorithms for processing strip-map SAR data from high altitudes and may give better phase preservation relative to prior polar-format algorithms for processing spotlight-mode SAR data.

Electromagnetic pulse excitation of finite- and infinitely-long lossy conductors over a lossy ground plane

DOE PAGES

Campione, Salvatore; Warne, Larry K.; Basilio, Lorena I.; ...

2017-01-13

This study details a model for the response of a finite- or an infinite-length wire interacting with a conducting ground to an electromagnetic pulse excitation. We develop a frequency–domain method based on transmission line theory that we name ATLOG – Analytic Transmission Line Over Ground. This method is developed as an alternative to full-wave methods, as it delivers a fast and reliable solution. It allows for the treatment of finite or infinite lossy, coated wires, and lossy grounds. The cases of wire above ground, as well as resting on the ground and buried beneath the ground are treated. The reportedmore » method is general and the time response of the induced current is obtained using an inverse Fourier transform of the current in the frequency domain. The focus is on the characteristics and propagation of the transmission line mode. Comparisons with full-wave simulations strengthen the validity of the proposed method.« less

Electromagnetic pulse excitation of finite- and infinitely-long lossy conductors over a lossy ground plane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campione, Salvatore; Warne, Larry K.; Basilio, Lorena I.

This study details a model for the response of a finite- or an infinite-length wire interacting with a conducting ground to an electromagnetic pulse excitation. We develop a frequency–domain method based on transmission line theory that we name ATLOG – Analytic Transmission Line Over Ground. This method is developed as an alternative to full-wave methods, as it delivers a fast and reliable solution. It allows for the treatment of finite or infinite lossy, coated wires, and lossy grounds. The cases of wire above ground, as well as resting on the ground and buried beneath the ground are treated. The reportedmore » method is general and the time response of the induced current is obtained using an inverse Fourier transform of the current in the frequency domain. The focus is on the characteristics and propagation of the transmission line mode. Comparisons with full-wave simulations strengthen the validity of the proposed method.« less

Picosecond Thermal Dynamics in an Underdense Plasma Measured with Thomson Scattering

NASA Astrophysics Data System (ADS)

Haberberger, D.; Katz, J.; Bucht, S.; Davies, A.; Bromage, J.; Zuegel, J. D.; Froula, D. H.; Trines, R.; Bingham, R.; Sadler, J.; Norreys, P. A.

2017-10-01

Field-ionized underdense plasmas have many promising applications within the laser-plasma interaction field: nuclear fusion, particle accelerators, x-ray sources, and laser-plasma amplification. Having complete knowledge of the plasma dynamics is essential to establishing optimal parameters for a given application. Here picosecond-resolved Thomson scattering measurements have been used to determine the electron thermal dynamics of an underdense ( 1019/cm) H2 plasma irradiated by a 60-ps, 1053-nm laser pulse with an intensity of 2 × 1014 W/cm2. The picosecond-resolved spectra were obtained with a novel pulse-front tilt compensated streaked optical spectrometer. The electron temperature was observed to rise from an initial 5 eV to a density-dependent plateau in 23 ps. Simulation results indicate that inverse bremsstrahlung heating, radiative cooling, and radial conduction cooling all play an important role in modeling the thermal dynamics. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

ARPA/NRL X-Ray Laser Program - Semiannual Technical Report to Defense Advanced Research Projects Agency

DTIC Science & Technology

1975-03-01

10 J. The beam divergence was 8 mrad. A beam splitter and an S-l response photodlode were used to monitor the laser pulse signal shape and the...laser beams on a cylinder [231] to compress a material to the necessary inversion density will be plagued by the non -uniform gain that these focused...of 30 psec and a good beam divergence can emerge after the non -linear stages as a 1773, 1182, or 887 k pulse still possessing good beam quality

Amplified spontaneous emission in solar-pumped iodine laser

NASA Technical Reports Server (NTRS)

Cho, Yong S.; Hwang, In H.; Han, Kwang S.; Lee, Ja H.

1992-01-01

The amplified spontaneous emission (ASE) from a long pulse, solar-simulating radiation pumped iodine laser amplifier is studied. The ASE threshold pump intensity is almost proportional to the inverse of the laser gain length when the gas pressure is constant in the laser tube.

Mapping thunder sources by inverting acoustic and electromagnetic observations

NASA Astrophysics Data System (ADS)

Anderson, J. F.; Johnson, J. B.; Arechiga, R. O.; Thomas, R. J.

2014-12-01

We present a new method of locating current flow in lightning strikes by inversion of thunder recordings constrained by Lightning Mapping Array observations. First, radio frequency (RF) pulses are connected to reconstruct conductive channels created by leaders. Then, acoustic signals that would be produced by current flow through each channel are forward modeled. The recorded thunder is considered to consist of a weighted superposition of these acoustic signals. We calculate the posterior distribution of acoustic source energy for each channel with a Markov Chain Monte Carlo inversion that fits power envelopes of modeled and recorded thunder; these results show which parts of the flash carry current and produce thunder. We examine the effects of RF pulse location imprecision and atmospheric winds on quality of results and apply this method to several lightning flashes over the Magdalena Mountains in New Mexico, USA. This method will enable more detailed study of lightning phenomena by allowing researchers to map current flow in addition to leader propagation.

Accuracy improvement in measurement of arterial wall elasticity by applying pulse inversion to phased-tracking method

NASA Astrophysics Data System (ADS)

Miyachi, Yukiya; Arakawa, Mototaka; Kanai, Hiroshi

2018-07-01

In our studies on ultrasonic elasticity assessment, minute change in the thickness of the arterial wall was measured by the phased-tracking method. However, most images in carotid artery examinations contain multiple-reflection noise, making it difficult to evaluate arterial wall elasticity precisely. In the present study, a modified phased-tracking method using the pulse inversion method was examined to reduce the influence of the multiple-reflection noise. Moreover, aliasing in the harmonic components was corrected by the fundamental components. The conventional and proposed methods were applied to a pulsated tube phantom mimicking the arterial wall. For the conventional method, the elasticity was 298 kPa without multiple-reflection noise and 353 kPa with multiple-reflection noise on the posterior wall. That of the proposed method was 302 kPa without multiple-reflection noise and 297 kPa with multiple-reflection noise on the posterior wall. Therefore, the proposed method was very robust against multiple-reflection noise.

Relationship between objectively measured physical activity and vascular structure and function in adults.

PubMed

Gomez-Marcos, Manuel A; Recio-Rodríguez, José I; Patino-Alonso, Maria C; Agudo-Conde, Cristina; Lasaosa-Medina, Lourdes; Rodriguez-Sanchez, Emiliano; Maderuelo-Fernandez, José A; García-Ortiz, Luis

2014-06-01

To analyze the relationship between regular physical activity, as assessed by accelerometer and 7-day physical activity recall (PAR) with vascular structure and function based on carotid intima-media thickness, pulse wave velocity, central and peripheral augmentation index and the ambulatory arterial stiffness index in adults. This study analyzed 263 subjects who were included in the EVIDENT study (mean age 55.85 ± 12.21 years; 59.30% female). Physical activity was assessed during 7 days using the Actigraph GT3X accelerometer (counts/minute) and 7-day PAR (metabolic equivalents (METs)/hour/week). Carotid ultrasound was used to measure carotid intima media thickness (IMT). The SphygmoCor System was used to measure pulse wave velocity (PWV), and central and peripheral augmentation index (CAIx and PAIx). The B-pro device was used to measure ambulatory arterial stiffness index (AASI). Median counts/minute was 244.37 and mean METs/hour/week was 11.49. Physical activity showed an inverse correlation with PAIx (r = -0.179; p < 0.01) and vigorous activity day time with IMT (r = -0.174), CAIx (r = -0.217) and PAIx (r = -0.324) (p < 0.01, all). Sedentary activity day time was correlated positively with CAIx (r = 0.103; p < 0.05). In multiple regression analysis, after adjusting for confounding factors, the inverse association of CAIx with counts/minute and the time spent in moderate and vigorous activity were maintained as well as the positive association with sedentary activity day time (p < 0.05). Physical activity, assessed by counts/minute, and the amount of time spent in moderate, vigorous/very vigorous physical activity, showed an inverse association with CAIx. Likewise, the time spent in sedentary activity was positively associated with the CAIx. Clinical Trials.gov Identifier: NCT01083082. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Laser Powered Launch Vehicle Performance Analyses

NASA Technical Reports Server (NTRS)

Chen, Yen-Sen; Liu, Jiwen; Wang, Ten-See (Technical Monitor)

2001-01-01

The purpose of this study is to establish the technical ground for modeling the physics of laser powered pulse detonation phenomenon. Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Successful predictions of the performance of laser powered launch vehicle concepts depend on the sophisticate models that reflects the underlying flow physics including the laser ray tracing the focusing, inverse Bremsstrahlung (IB) effects, finite-rate air chemistry, thermal non-equilibrium, plasma radiation and detonation wave propagation, etc. The proposed work will extend the base-line numerical model to an efficient design analysis tool. The proposed model is suitable for 3-D analysis using parallel computing methods.

Compressed Sensing SEMAC: 8-fold Accelerated High Resolution Metal Artifact Reduction MRI of Cobalt-Chromium Knee Arthroplasty Implants.

PubMed

Fritz, Jan; Ahlawat, Shivani; Demehri, Shadpour; Thawait, Gaurav K; Raithel, Esther; Gilson, Wesley D; Nittka, Mathias

2016-10-01

The aim of this study was to prospectively test the hypothesis that a compressed sensing-based slice encoding for metal artifact correction (SEMAC) turbo spin echo (TSE) pulse sequence prototype facilitates high-resolution metal artifact reduction magnetic resonance imaging (MRI) of cobalt-chromium knee arthroplasty implants within acquisition times of less than 5 minutes, thereby yielding better image quality than high-bandwidth (BW) TSE of similar length and similar image quality than lengthier SEMAC standard of reference pulse sequences. This prospective study was approved by our institutional review board. Twenty asymptomatic subjects (12 men, 8 women; mean age, 56 years; age range, 44-82 years) with total knee arthroplasty implants underwent MRI of the knee using a commercially available, clinical 1.5 T MRI system. Two compressed sensing-accelerated SEMAC prototype pulse sequences with 8-fold undersampling and acquisition times of approximately 5 minutes each were compared with commercially available high-BW and SEMAC pulse sequences with acquisition times of approximately 5 minutes and 11 minutes, respectively. For each pulse sequence type, sagittal intermediate-weighted (TR, 3750-4120 milliseconds; TE, 26-28 milliseconds; voxel size, 0.5 × 0.5 × 3 mm) and short tau inversion recovery (TR, 4010 milliseconds; TE, 5.2-7.5 milliseconds; voxel size, 0.8 × 0.8 × 4 mm) were acquired. Outcome variables included image quality, display of the bone-implant interfaces and pertinent knee structures, artifact size, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Statistical analysis included Friedman, repeated measures analysis of variances, and Cohen weighted k tests. Bonferroni-corrected P values of 0.005 and less were considered statistically significant. Image quality, bone-implant interfaces, anatomic structures, artifact size, SNR, and CNR parameters were statistically similar between the compressed sensing-accelerated SEMAC prototype and SEMAC commercial pulse sequences. There was mild blur on images of both SEMAC sequences when compared with high-BW images (P < 0.001), which however did not impair the assessment of knee structures. Metal artifact reduction and visibility of central knee structures and bone-implant interfaces were good to very good and significantly better on both types of SEMAC than on high-BW images (P < 0.004). All 3 pulse sequences showed peripheral structures similarly well. The implant artifact size was 46% to 51% larger on high-BW images when compared with both types of SEMAC images (P < 0.0001). Signal-to-noise ratios and CNRs of fat tissue, tendon tissue, muscle tissue, and fluid were statistically similar on intermediate-weighted MR images of all 3 pulse sequence types. On short tau inversion recovery images, the SNRs of tendon tissue and the CNRs of fat and fluid, fluid and muscle, as well as fluid and tendon were significantly higher on SEMAC and compressed sensing SEMAC images (P < 0.005, respectively). We accept the hypothesis that prospective compressed sensing acceleration of SEMAC is feasible for high-quality metal artifact reduction MRI of cobalt-chromium knee arthroplasty implants in less than 5 minutes and yields better quality than high-BW TSE and similarly high quality than lengthier SEMAC pulse sequences.

Composite pulses for interferometry in a thermal cold atom cloud

NASA Astrophysics Data System (ADS)

Dunning, Alexander; Gregory, Rachel; Bateman, James; Cooper, Nathan; Himsworth, Matthew; Jones, Jonathan A.; Freegarde, Tim

2014-09-01

Atom interferometric sensors and quantum information processors must maintain coherence while the evolving quantum wave function is split, transformed, and recombined, but suffer from experimental inhomogeneities and uncertainties in the speeds and paths of these operations. Several error-correction techniques have been proposed to isolate the variable of interest. Here we apply composite pulse methods to velocity-sensitive Raman state manipulation in a freely expanding thermal atom cloud. We compare several established pulse sequences, and follow the state evolution within them. The agreement between measurements and simple predictions shows the underlying coherence of the atom ensemble, and the inversion infidelity in a ˜80μK atom cloud is halved. Composite pulse techniques, especially if tailored for atom interferometric applications, should allow greater interferometer areas, larger atomic samples, and longer interaction times, and hence improve the sensitivity of quantum technologies from inertial sensing and clocks to quantum information processors and tests of fundamental physics.

Nonthermal ultrafast optical control of the magnetization in garnet films

NASA Astrophysics Data System (ADS)

Hansteen, Fredrik; Kimel, Alexey; Kirilyuk, Andrei; Rasing, Theo

2006-01-01

We demonstrate coherent optical control of the magnetization in ferrimagnetic garnet films on the femtosecond time scale through a combination of two different ultrafast and nonthermal photomagnetic effects and by employing multiple pump pulses. Linearly polarized laser pulses are shown to create a long-lived modification of the magnetocrystalline anisotropy via optically induced electron transfer between nonequivalent ion sites while circularly polarized pulses additionally act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday effect. Due to the slow phonon-magnon interaction in these dielectrics, thermal effects of the laser excitation are clearly distinguished from the ultrafast nonthermal effects and can be seen only on the time scale of nanoseconds for sample temperatures near the Curie point. The reported effects open exciting possibilities for ultrafast manipulation of spins by light, and provide insight into the physics of magnetism on ultrafast time scales.

Ultra-bright pulsed electron beam with low longitudinal emittance

DOEpatents

Zolotorev, Max

2010-07-13

A high-brightness pulsed electron source, which has the potential for many useful applications in electron microscopy, inverse photo-emission, low energy electron scattering experiments, and electron holography has been described. The source makes use of Cs atoms in an atomic beam. The source is cycled beginning with a laser pulse that excites a single Cs atom on average to a band of high-lying Rydberg nP states. The resulting valence electron Rydberg wave packet evolves in a nearly classical Kepler orbit. When the electron reaches apogee, an electric field pulse is applied that ionizes the atom and accelerates the electron away from its parent ion. The collection of electron wave packets thus generated in a series of cycles can occupy a phase volume near the quantum limit and it can possess very high brightness. Each wave packet can exhibit a considerable degree of coherence.

Enabling surface nuclear magnetic resonance at high-noise environments using a pre-polarization pulse

NASA Astrophysics Data System (ADS)

Lin, Tingting; Yang, Yujing; Teng, Fei; Müller-Petke, Mike

2018-02-01

The technique of surface nuclear magnetic resonance (SNMR) has been widely used for hydrological investigations in recent years. Unfortunately, the detected SNMR signals are limited to tens of nanovolts and are thus susceptible to environmental noise. While pre-polarization pulses to enhance the detected signal amplitudes are common in laboratory applications, SNMR field testing has only utilized excitation pulses until now. In conducting measurements in China, we demonstrate that adding a pre-polarization field to the SNMR pulse sequence is feasible and allows for the reliable detection of SNMR signals in noisy scenarios that otherwise prohibit signal detection. We introduce a forward modelling for pre-polarization using SNMR and present a three-layer model obtained from inverse modelling that satisfies the observed data from the field experiment. We expect this development to open up new applications for SNMR technology, especially in high-noise level places, such as active mines.

Measurement of magnetocaloric effect in pulsed magnetic fields with the help of infrared fiber optical temperature sensor

NASA Astrophysics Data System (ADS)

Kamantsev, Alexander P.; Koledov, Victor V.; Mashirov, Alexey V.; Shavrov, Vladimir G.; Yen, N. H.; Thanh, P. T.; Quang, V. M.; Dan, N. H.; Los, Anton S.; Gilewski, Andrzej; Tereshina, Irina S.; Butvina, Leonid N.

2017-10-01

We present a new technique for experimental study of kinetics of phase transitions (PTs) and direct measurement of the magnetocaloric effect (MCE) in pulsed magnetic fields by using the fast response temperature probe with infrared fiber optical (IRFO) sensor. As demonstration of the new technique, the results are presented of MCE measurements for Gd near Curie point: ΔTad = 21.3 K under pulsed magnetic field μ0H = 12.7 T; and inverse MCE for Fe48Rh52 sample at initial temperature 305.1 K: ΔTad = -4.5 K under pulsed magnetic field μ0H = 8.5 T. Also, the energy losses on magnetization near the 1st order PT were calculated from the results of direct measurements of magnetization versus time for Fe48Rh52 sample: W = 45 J/kg.

In Vivo3D Localized 13C Spectroscopy Using Modified INEPT and DEPT

NASA Astrophysics Data System (ADS)

Watanabe, H.; Ishihara, Y.; Okamoto, K.; Oshio, K.; Kanamatsu, T.; Tsukada, Y.

1998-10-01

The 3D localized13C spectroscopy methods LINEPT and LODEPT, which are modifications of INEPT and DEPT, are proposed. As long as a13C inversion pulse (180-degree pulse) is applied at 1/(4J) before the proton echo time in LINEPT and a13C excitation pulse (90-degree pulse) is applied at 1/(2J) before the proton echo time in LODEPT, the proton echo time can be set to any value longer than 1/(2J) in LINEPT and longer than 1/Jin LODEPT. As a result, the proton and the13C pulses can be applied separately and these proton pulses can be made slice-selective pulses. These localization features of LINEPT and LODEPT were evaluated using a phantom consisting of a cylinder filled with ethanol placed inside another cylinder filled with oil, and localized ethanol spectra could be obtained.In vivo3D localized13C spectra from the brain of a monkey could be obtained using decoupled LINEPT, and glutamate C-4 appeared directly after the administration of glucose C-1, followed by the appearance of glutamate C-2, C-3 and glutamine C-2, C-3, C-4.

Optimization of a double inversion recovery sequence for noninvasive synovium imaging of joint effusion in the knee.

PubMed

Jahng, Geon-Ho; Jin, Wook; Yang, Dal Mo; Ryu, Kyung Nam

2011-05-01

We wanted to optimize a double inversion recovery (DIR) sequence to image joint effusion regions of the knee, especially intracapsular or intrasynovial imaging in the suprapatellar bursa and patellofemoral joint space. Computer simulations were performed to determine the optimum inversion times (TI) for suppressing both fat and water signals, and a DIR sequence was optimized based on the simulations for distinguishing synovitis from fluid. In vivo studies were also performed on individuals who showed joint effusion on routine knee MR images to demonstrate the feasibility of using the DIR sequence with a 3T whole-body MR scanner. To compare intracapsular or intrasynovial signals on the DIR images, intermediate density-weighted images and/or post-enhanced T1-weighted images were acquired. The timings to enhance the synovial contrast from the fluid components were TI1 = 2830 ms and TI2 = 254 ms for suppressing the water and fat signals, respectively. Improved contrast for the intrasynovial area in the knees was observed with the DIR turbo spin-echo pulse sequence compared to the intermediate density-weighted sequence. Imaging contrast obtained noninvasively with the DIR sequence was similar to that of the post-enhanced T1-weighted sequence. The DIR sequence may be useful for delineating synovium without using contrast materials.

Inversion of Acoustic and Electromagnetic Recordings for Mapping Current Flow in Lightning Strikes

NASA Astrophysics Data System (ADS)

Anderson, J.; Johnson, J.; Arechiga, R. O.; Thomas, R. J.

2012-12-01

Acoustic recordings can be used to map current-carrying conduits in lightning strikes. Unlike stepped leaders, whose very high frequency (VHF) radio emissions have short (meter-scale) wavelengths and can be located by lightning-mapping arrays, current pulses emit longer (kilometer-scale) waves and cannot be mapped precisely by electromagnetic observations alone. While current pulses are constrained to conductive channels created by stepped leaders, these leaders often branch as they propagate, and most branches fail to carry current. Here, we present a method to use thunder recordings to map current pulses, and we apply it to acoustic and VHF data recorded in 2009 in the Magdalena mountains in central New Mexico, USA. Thunder is produced by rapid heating and expansion of the atmosphere along conductive channels in response to current flow, and therefore can be used to recover the geometry of the current-carrying channel. Toward this goal, we use VHF pulse maps to identify candidate conductive channels where we treat each channel as a superposition of finely-spaced acoustic point sources. We apply ray tracing in variable atmospheric structures to forward model the thunder that our microphone network would record for each candidate channel. Because multiple channels could potentially carry current, a non-linear inversion is performed to determine the acoustic source strength of each channel. For each combination of acoustic source strengths, synthetic thunder is modeled as a superposition of thunder signals produced by each channel, and a power envelope of this stack is then calculated. The inversion iteratively minimizes the misfit between power envelopes of recorded and modeled thunder. Because the atmospheric sound speed structure through which the waves propagate during these events is unknown, we repeat the procedure on many plausible atmospheres to find an optimal fit. We then determine the candidate channel, or channels, that minimizes residuals between synthetic and acoustic recordings. We demonstrate the usefulness of this method on both intracloud and cloud-to-ground strikes, and discuss factors affecting our ability to replicate recorded thunder.

Initial Breakdown Pulse Parameters in Intracloud and Cloud-to-Ground Lightning Flashes

NASA Astrophysics Data System (ADS)

Smith, E. M.; Marshall, T. C.; Karunarathne, S.; Siedlecki, R.; Stolzenburg, M.

2018-02-01

This study analyzes the largest initial breakdown (IB) pulse in flashes from four storms in Florida; data from three sensor arrays are used. The range-normalized, zero-to-peak amplitude of the largest IB pulse was determined along with its altitude, duration, and timing within each flash. Appropriate data were available for 40 intracloud (IC) and 32 cloud-to-ground (CG) flashes. Histograms of amplitude of the largest IB pulse by flash type were similar, with mean (median) values of 1.49 (1.05) V/m for IC flashes and -1.35 (-0.87) V/m for CG flashes. The largest IB pulse in 30 IC flashes showed a weak inverse relation between pulse amplitude and altitude. Amplitude of the largest IB pulse for 25 CG flashes showed no altitude correlation. Duration of the largest IB pulse in ICs averaged twice as long as in CGs (96 μs versus 46 μs), and all of the CG durations were <100 μs. Among the ICs, there is a positive relation between largest IB pulse duration and amplitude; the linear correlation coefficient is 0.385 with outliers excluded. The largest IB pulse in IC flashes typically occurred at a longer time after the first IB pulse (average 4.1 ms) than was the case in CG flashes (average 0.6 ms). In both flash types, the largest IB pulse was the first IB pulse in about 30% of the cases. In one storm all 42 IC flashes with triggered data had IB pulses.

High-resolution myocardial T1 mapping using single-shot inversion recovery fast low-angle shot MRI with radial undersampling and iterative reconstruction

PubMed Central

Joseph, Arun A; Kalentev, Oleksandr; Merboldt, Klaus-Dietmar; Voit, Dirk; Roeloffs, Volkert B; van Zalk, Maaike; Frahm, Jens

2016-01-01

Objective: To develop a novel method for rapid myocardial T1 mapping at high spatial resolution. Methods: The proposed strategy represents a single-shot inversion recovery experiment triggered to early diastole during a brief breath-hold. The measurement combines an adiabatic inversion pulse with a real-time readout by highly undersampled radial FLASH, iterative image reconstruction and T1 fitting with automatic deletion of systolic frames. The method was implemented on a 3-T MRI system using a graphics processing unit-equipped bypass computer for online application. Validations employed a T1 reference phantom including analyses at simulated heart rates from 40 to 100 beats per minute. In vivo applications involved myocardial T1 mapping in short-axis views of healthy young volunteers. Results: At 1-mm in-plane resolution and 6-mm section thickness, the inversion recovery measurement could be shortened to 3 s without compromising T1 quantitation. Phantom studies demonstrated T1 accuracy and high precision for values ranging from 300 to 1500 ms and up to a heart rate of 100 beats per minute. Similar results were obtained in vivo yielding septal T1 values of 1246 ± 24 ms (base), 1256 ± 33 ms (mid-ventricular) and 1288 ± 30 ms (apex), respectively (mean ± standard deviation, n = 6). Conclusion: Diastolic myocardial T1 mapping with use of single-shot inversion recovery FLASH offers high spatial resolution, T1 accuracy and precision, and practical robustness and speed. Advances in knowledge: The proposed method will be beneficial for clinical applications relying on native and post-contrast T1 quantitation. PMID:27759423

Effects of fish size and temperature on weakfish disturbance calls: implications for the mechanism of sound generation.

PubMed

Connaughton, M A; Taylor, M H; Fine, M L

2000-05-01

To categorize variation in disturbance calls of the weakfish Cynoscion regalis and to understand their generation, we recorded sounds produced by different-sized fish, and by similar-sized fish at different temperatures, as well as muscle electromyograms. Single, simultaneous twitches of the bilateral sonic muscles produce a single sound pulse consisting of a two- to three-cycle acoustic waveform. Typical disturbance calls at 18 degrees C consist of trains of 2-15 pulses with a sound pressure level (SPL) of 74 dB re 20 microPa at 10 cm, a peak frequency of 540 Hz, a repetition rate of 20 Hz and a pulse duration of 3.5 ms. The pulse duration suggests an incredibly short twitch time. Sound pressure level (SPL) and pulse duration increase and dominant frequency decreases in larger fish, whereas SPL, repetition rate and dominant frequency increase and pulse duration decreases with increasing temperature. The dominant frequency is inversely related to pulse duration and appears to be determined by the duration of muscle contraction. We suggest that the lower dominant frequency of larger fish is caused by a longer pulse (=longer muscle twitch) and not by the lower resonant frequency of a larger swimbladder.

Initial Breakdown Pulse Amplitudes in Intracloud and Cloud-to-Ground Lightning Flashes

NASA Astrophysics Data System (ADS)

Marshall, T. C.; Smith, E. M.; Stolzenburg, M.; Karunarathne, S.; Siedlecki, R. D., II

2017-12-01

This study analyzes the largest initial breakdown (IB) pulse in flashes from three storms in Florida. The study was motivated in part by the possibility that IB pulses of IC flashes may cause of terrestrial gamma-ray flashes (TGFs). The range-normalized, zero-to-peak amplitude of the largest IB pulse within each flash was determined along with its altitude, duration, and occurrence time in the flash. Appropriate data were available for 40 intracloud (IC) and 32 cloud-to-ground (CG) flashes. Histograms of the magnitude of the largest IB pulse amplitude by flash type were similar, with mean (median) values of 1.49 (1.05) V/m for IC flashes and -1.35 (-0.87) V/m for CG flashes. The mean amplitude of the largest IC IB pulses are substantially smaller (roughly an order of magnitude smaller) than the few known pulse amplitudes of TGF events and TGF candidate events. The largest IB pulse in 30 IC flashes showed a weak inverse relation between pulse amplitude and altitude. Amplitude of the largest IB pulse for 25 CG flashes showed no altitude correlation. Duration of the largest IB pulse in ICs averaged twice as long as in CGs (96 μs versus 46 μs); all of the CG durations were <100 μs. Among the ICs, there is a positive relation between largest IB pulse duration and amplitude; the linear correlation coefficient is 0.385 with outliers excluded. The largest IB pulse in IC flashes typically occurred at a longer time after the first IB pulse (average 4.1 ms) than was the case in CG flashes (average 0.6 ms). In both flash types, the largest IB pulse was the first IB pulse in about 30% of the cases.

Energy stores and switches for rail-launcher systems

NASA Technical Reports Server (NTRS)

Weldon, W. F.; Zowarka, R. C.; Marshall, R. A.

1983-01-01

An overview of existing switch and power supply technology applicable to space launch, a new candidate pulsed power supply for Earth-to-space rail launcher duty, the inverse railgun flux compressor, and a set of switching experiments to study further the feasibility of Earth-to-space launch are discussed.

Energy stores and switches for rail-launcher systems

NASA Astrophysics Data System (ADS)

Weldon, W. F.; Zowarka, R. C.; Marshall, R. A.

An overview of existing switch and power supply technology applicable to space launch, a new candidate pulsed power supply for Earth-to-space rail launcher duty, the inverse railgun flux compressor, and a set of switching experiments to study further the feasibility of Earth-to-space launch are discussed.

Solid-state NMR adiabatic TOBSY sequences provide enhanced sensitivity for multidimensional high-resolution magic-angle-spinning 1H MR spectroscopy

NASA Astrophysics Data System (ADS)

Andronesi, Ovidiu C.; Mintzopoulos, Dionyssios; Struppe, Jochem; Black, Peter M.; Tzika, A. Aria

2008-08-01

We propose a solid-state NMR method that maximizes the advantages of high-resolution magic-angle-spinning (HRMAS) applied to intact biopsies when compared to more conventional liquid-state NMR approaches. Theoretical treatment, numerical simulations and experimental results on intact human brain biopsies are presented. Experimentally, it is proven that an optimized adiabatic TOBSY (TOtal through Bond correlation SpectroscopY) solid-state NMR pulse sequence for two-dimensional 1H- 1H homonuclear scalar-coupling longitudinal isotropic mixing provides a 20%-50% improvement in signal-to-noise ratio relative to its liquid-state analogue TOCSY (TOtal Correlation SpectroscopY). For this purpose we have refined the C9151 symmetry-based 13C TOBSY pulse sequence for 1H MRS use and compared it to MLEV-16 TOCSY sequence. Both sequences were rotor-synchronized and implemented using WURST-8 adiabatic inversion pulses. As discussed theoretically and shown in simulations, the improved magnetization-transfer comes from actively removing residual dipolar couplings from the average Hamiltonian. Importantly, the solid-state NMR techniques are tailored to perform measurements at low temperatures where sample degradation is reduced. This is the first demonstration of such a concept for HRMAS metabolic profiling of disease processes, including cancer, from biopsies requiring reduced sample degradation for further genomic analysis.

Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

PubMed

Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

2013-09-01

This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

A Stable High-Energy Electron Source from Laser Wakefield Acceleration

NASA Astrophysics Data System (ADS)

Zhang, Ping; Zhao, Baozhen; Liu, Cheng; Yan, Wenchao; Golovin, Grigory; Banerjee, Sudeep; Chen, Shouyuan; Haden, Daniel; Fruhling, Colton; Umstadter, Donald

2016-10-01

The stability of the electron source from laser wake-field acceleration (LWFA) is essential for applications, such as novel x-ray sources and fundamental experiments in high field physics. To obtain such a stable source, we used an optimal laser pulse and a novel gas nozzle. The high-power laser pulse on target was focused to a diffraction-limited spot by the use of adaptive wavefront correction and the pulse duration was transform limited by the use of spectral feedback control. An innovative design for the nozzle led to a stable, flat-top profile with diameters of 4 mm and 8 mm with a high Mach-number ( 6). In experiments to generate high-energy electron beams by LWFA, we were able to obtain reproducible results with beam energy of 800 MeV and charge >10 pC. Higher charge but broader energy spectrum resulted when the plasma density was increased. These developments have resulted in a laser-driven wakefield accelerator that is stable and robust. With this device, we show that narrowband high-energy x-rays beams can be generated by the inverse-Compton scattering process. This accelerator has also been used in recent experiments to study nonlinear effects in the interaction of high-energy electron beams with ultraintense laser pulses. This material is based upon work supported by NSF No. PHY-153700; US DOE, Office of Science, BES, # DE-FG02-05ER15663; AFOSR # FA9550-11-1-0157; and DHS DNDO # HSHQDC-13-C-B0036.

Arterial spin-labeling assessment of normalized vascular intratumoral signal intensity as a predictor of histologic grade of astrocytic neoplasms.

PubMed

Furtner, J; Schöpf, V; Schewzow, K; Kasprian, G; Weber, M; Woitek, R; Asenbaum, U; Preusser, M; Marosi, C; Hainfellner, J A; Widhalm, G; Wolfsberger, S; Prayer, D

2014-03-01

Pulsed arterial spin-labeling is a noninvasive MR imaging perfusion method performed with the use of water in the arterial blood as an endogenous contrast agent. The purpose of this study was to determine the inversion time with the largest difference in normalized intratumoral signal intensity between high-grade and low-grade astrocytomas. Thirty-three patients with gliomas, histologically classified as low-grade (n = 7) or high-grade astrocytomas (n = 26) according to the World Health Organization brain tumor classification, were included. A 3T MR scanner was used to perform pulsed arterial spin-labeling measurements at 8 different inversion times (370 ms, 614 ms, 864 ms, 1114 ms, 1364 ms, 1614 ms, 1864 ms, and 2114 ms). Normalized intratumoral signal intensity was calculated, which was defined by the signal intensity ratio of the tumor and the contralateral normal brain tissue for all fixed inversion times. A 3-way mixed ANOVA was used to reveal potential differences in the normalized vascular intratumoral signal intensity between high-grade and low-grade astrocytomas. The difference in normalized vascular intratumoral signal intensity between high-grade and low-grade astrocytomas obtained the most statistically significant results at 370 ms (P = .003, other P values ranged from .012-.955). The inversion time by which to differentiate high-grade and low-grade astrocytomas by use of normalized vascular intratumoral signal intensity was 370 ms in our study. The normalized vascular intratumoral signal intensity values at this inversion time mainly reflect the labeled intra-arterial blood bolus and therefore could be referred to as normalized vascular intratumoral signal intensity. Our data indicate that the use of normalized vascular intratumoral signal intensity values allows differentiation between low-grade and high-grade astrocytomas and thus may serve as a new, noninvasive marker for astrocytoma grading.

Nonlinear propagation of vector extremely short pulses in a medium of symmetric and asymmetric molecules

NASA Astrophysics Data System (ADS)

Sazonov, S. V.; Ustinov, N. V.

2017-02-01

The nonlinear propagation of extremely short electromagnetic pulses in a medium of symmetric and asymmetric molecules placed in static magnetic and electric fields is theoretically studied. Asymmetric molecules differ in that they have nonzero permanent dipole moments in stationary quantum states. A system of wave equations is derived for the ordinary and extraordinary components of pulses. It is shown that this system can be reduced in some cases to a system of coupled Ostrovsky equations and to the equation intagrable by the method for an inverse scattering transformation, including the vector version of the Ostrovsky-Vakhnenko equation. Different types of solutions of this system are considered. Only solutions representing the superposition of periodic solutions are single-valued, whereas soliton and breather solutions are multivalued.

Cardiovascular magnetic resonance of myocardial edema using a short inversion time inversion recovery (STIR) black-blood technique: Diagnostic accuracy of visual and semi-quantitative assessment

PubMed Central

2012-01-01

Background The short inversion time inversion recovery (STIR) black-blood technique has been used to visualize myocardial edema, and thus to differentiate acute from chronic myocardial lesions. However, some cardiovascular magnetic resonance (CMR) groups have reported variable image quality, and hence the diagnostic value of STIR in routine clinical practice has been put into question. The aim of our study was to analyze image quality and diagnostic performance of STIR using a set of pulse sequence parameters dedicated to edema detection, and to discuss possible factors that influence image quality. We hypothesized that STIR imaging is an accurate and robust way of detecting myocardial edema in non-selected patients with acute myocardial infarction. Methods Forty-six consecutive patients with acute myocardial infarction underwent CMR (day 4.5, +/- 1.6) including STIR for the assessment of myocardial edema and late gadolinium enhancement (LGE) for quantification of myocardial necrosis. Thirty of these patients underwent a follow-up CMR at approximately six months (195 +/- 39 days). Both STIR and LGE images were evaluated separately on a segmental basis for image quality as well as for presence and extent of myocardial hyper-intensity, with both visual and semi-quantitative (threshold-based) analysis. LGE was used as a reference standard for localization and extent of myocardial necrosis (acute) or scar (chronic). Results Image quality of STIR images was rated as diagnostic in 99.5% of cases. At the acute stage, the sensitivity and specificity of STIR to detect infarcted segments on visual assessment was 95% and 78% respectively, and on semi-quantitative assessment was 99% and 83%, respectively. STIR differentiated acutely from chronically infarcted segments with a sensitivity of 95% by both methods and with a specificity of 99% by visual assessment and 97% by semi-quantitative assessment. The extent of hyper-intense areas on acute STIR images was 85% larger than those on LGE images, with a larger myocardial salvage index in reperfused than in non-reperfused infarcts (p = 0.035). Conclusions STIR with appropriate pulse sequence settings is accurate in detecting acute myocardial infarction (MI) and distinguishing acute from chronic MI with both visual and semi-quantitative analysis. Due to its unique technical characteristics, STIR should be regarded as an edema-weighted rather than a purely T2-weighted technique. PMID:22455461

Saturation pulse design for quantitative myocardial T1 mapping.

PubMed

Chow, Kelvin; Kellman, Peter; Spottiswoode, Bruce S; Nielles-Vallespin, Sonia; Arai, Andrew E; Salerno, Michael; Thompson, Richard B

2015-10-01

Quantitative saturation-recovery based T1 mapping sequences are less sensitive to systematic errors than the Modified Look-Locker Inversion recovery (MOLLI) technique but require high performance saturation pulses. We propose to optimize adiabatic and pulse train saturation pulses for quantitative T1 mapping to have <1 % absolute residual longitudinal magnetization (|MZ/M0|) over ranges of B0 and [Formula: see text] (B1 scale factor) inhomogeneity found at 1.5 T and 3 T. Design parameters for an adiabatic BIR4-90 pulse were optimized for improved performance within 1.5 T B0 (±120 Hz) and [Formula: see text] (0.7-1.0) ranges. Flip angles in hard pulse trains of 3-6 pulses were optimized for 1.5 T and 3 T, with consideration of T1 values, field inhomogeneities (B0 = ±240 Hz and [Formula: see text]=0.4-1.2 at 3 T), and maximum achievable B1 field strength. Residual MZ/M0 was simulated and measured experimentally for current standard and optimized saturation pulses in phantoms and in-vivo human studies. T1 maps were acquired at 3 T in human subjects and a swine using a SAturation recovery single-SHot Acquisition (SASHA) technique with a standard 90°-90°-90° and an optimized 6-pulse train. Measured residual MZ/M0 in phantoms had excellent agreement with simulations over a wide range of B0 and [Formula: see text]. The optimized BIR4-90 reduced the maximum residual |MZ/M0| to <1 %, a 5.8× reduction compared to a reference BIR4-90. An optimized 3-pulse train achieved a maximum residual |MZ/M0| <1 % for the 1.5 T optimization range compared to 11.3 % for a standard 90°-90°-90° pulse train, while a 6-pulse train met this target for the wider 3 T ranges of B0 and [Formula: see text]. The 6-pulse train demonstrated more uniform saturation across both the myocardium and entire field of view than other saturation pulses in human studies. T1 maps were more spatially homogeneous with 6-pulse train SASHA than the reference 90°-90°-90° SASHA in both human and animal studies. Adiabatic and pulse train saturation pulses optimized for different constraints found at 1.5 T and 3 T achieved <1 % residual |MZ/M0| in phantom experiments, enabling greater accuracy in quantitative saturation recovery T1 imaging.

Multi-frequency inversion-charge pumping for charge separation and mobility analysis in high-k/InGaAs metal-oxide-semiconductor field-effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Djara, V.; Cherkaoui, K.; Negara, M. A.

2015-11-28

An alternative multi-frequency inversion-charge pumping (MFICP) technique was developed to directly separate the inversion charge density (N{sub inv}) from the trapped charge density in high-k/InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs). This approach relies on the fitting of the frequency response of border traps, obtained from inversion-charge pumping measurements performed over a wide range of frequencies at room temperature on a single MOSFET, using a modified charge trapping model. The obtained model yielded the capture time constant and density of border traps located at energy levels aligned with the InGaAs conduction band. Moreover, the combination of MFICP and pulsed I{sub d}-V{sub g}more » measurements enabled an accurate effective mobility vs N{sub inv} extraction and analysis. The data obtained using the MFICP approach are consistent with the most recent reports on high-k/InGaAs.« less

Pulse Consumption, Satiety, and Weight Management1

PubMed Central

McCrory, Megan A.; Hamaker, Bruce R.; Lovejoy, Jennifer C.; Eichelsdoerfer, Petra E.

2010-01-01

The prevalence of obesity has reached epidemic proportions, making finding effective solutions to reduce obesity a public health priority. One part of the solution could be for individuals to increase consumption of nonoilseed pulses (dry beans, peas, chickpeas, and lentils), because they have nutritional attributes thought to benefit weight control, including slowly digestible carbohydrates, high fiber and protein contents, and moderate energy density. Observational studies consistently show an inverse relationship between pulse consumption and BMI or risk for obesity, but many do not control for potentially confounding dietary and other lifestyle factors. Short-term (≤1 d) experimental studies using meals controlled for energy, but not those controlled for available carbohydrate, show that pulse consumption increases satiety over 2–4 h, suggesting that at least part of the effect of pulses on satiety is mediated by available carbohydrate amount or composition. Randomized controlled trials generally support a beneficial effect of pulses on weight loss when pulse consumption is coupled with energy restriction, but not without energy restriction. However, few randomized trials have been conducted and most were short term (3–8 wk for whole pulses and 4–12 wk for pulse extracts). Overall, there is some indication of a beneficial effect of pulses on short-term satiety and weight loss during intentional energy restriction, but more studies are needed in this area, particularly those that are longer term (≥1 y), investigate the optimal amount of pulses to consume for weight control, and include behavioral elements to help overcome barriers to pulse consumption. PMID:22043448

Vascularization of liver tumors - preliminary results with Coded Harmonic Angio (CHA), phase inversion imaging, 3D power Doppler and contrast medium-enhanced B-flow with second generation contrast agent (Optison).

PubMed

Jung, E M; Kubale, R; Jungius, K-P; Jung, W; Lenhart, M; Clevert, D-A

2006-01-01

To investigate the dynamic value of contrast medium-enhanced ultrasonography with Optison for appraisal of the vascularization of hepatic tumors using harmonic imaging, 3D-/power Doppler and B-flow. 60 patients with a mean age of 56 years (range 35-76 years) with 93 liver tumors, including histopathologically proven hepatocellular carcinoma (HCC) [15 cases with 20 lesions], liver metastases of colorectal tumors [17 cases with 33 lesions], metastases of breast cancer [10 cases with 21 lesions] and hemangiomas [10 cases with 19 lesions] were prospectively investigated by means of multislice CT as well as native and contrast medium-enhanced ultrasound using a multifrequency transducer (2.5-4 MHz, Logig 9, GE). B scan was performed with additional color and power Doppler, followed by a bolus injection of 0.5 ml Optison. Tumor vascularization was evaluated with coded harmonic angio (CHA), pulse inversion imaging with power Doppler, 3D power Doppler and in the late phase (>5 min) with B-flow. In 15 cases with HCC, i.a. DSA was performed in addition. The results were also correlated with MRT and histological findings. Compared to spiral-CT/MRT, only 72/93 (77%) of the lesions could be detected in the B scan, 75/93 (81%) with CHA and 93/93 (100%) in the pulse inversion mode. Tumor vascularization was detectable in 43/93 (46%) of lesions with native power Doppler, in 75/93 (81%) of lesions after administering contrast medium in the CHA mode, in 81/93 (87%) of lesions in the pulse inversion mode with power Doppler and in 77/93 (83%) of lesions with contrast-enhanced B-flow. Early arterial and capillary perfusion was best detected with CHA, particularly in 20/20 (100%) of the HCC lesions, allowing a 3D reconstruction. 3D power Doppler was especially useful in investigating the tumor margins. Up to 20 min after contrast medium injection, B-flow was capable of detecting increased metastatic tumor vascularization in 42/54 (78%) of cases and intratumoral perfusion in 17/20 (85%) of HCC cases. All 19 hemangiomas were correctly classified by phase inversion imaging. Contrast medium-enhanced ultrasound investigation of liver tumors with Optison allowed reliable detection of tumor foci and, in most cases, appraisal of tumor vascularization. The time available for evaluation of tumor margin vascularization was substantially longer in B-flow.

Ultrahigh-resolution spectroscopy with atomic or molecular dark resonances: Exact steady-state line shapes and asymptotic profiles in the adiabatic pulsed regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zanon-Willette, Thomas; Clercq, Emeric de; Arimondo, Ennio

2011-12-15

Exact and asymptotic line shape expressions are derived from the semiclassical density matrix representation describing a set of closed three-level {Lambda} atomic or molecular states including decoherences, relaxation rates, and light shifts. An accurate analysis of the exact steady-state dark-resonance profile describing the Autler-Townes doublet, the electromagnetically induced transparency or coherent population trapping resonance, and the Fano-Feshbach line shape leads to the linewidth expression of the two-photon Raman transition and frequency shifts associated to the clock transition. From an adiabatic analysis of the dynamical optical Bloch equations in the weak field limit, a pumping time required to efficiently trap amore » large number of atoms into a coherent superposition of long-lived states is established. For a highly asymmetrical configuration with different decay channels, a strong two-photon resonance based on a lower states population inversion is established when the driving continuous-wave laser fields are greatly unbalanced. When time separated resonant two-photon pulses are applied in the adiabatic pulsed regime for atomic or molecular clock engineering, where the first pulse is long enough to reach a coherent steady-state preparation and the second pulse is very short to avoid repumping into a new dark state, dark-resonance fringes mixing continuous-wave line shape properties and coherent Ramsey oscillations are created. Those fringes allow interrogation schemes bypassing the power broadening effect. Frequency shifts affecting the central clock fringe computed from asymptotic profiles and related to the Raman decoherence process exhibit nonlinear shapes with the three-level observable used for quantum measurement. We point out that different observables experience different shifts on the lower-state clock transition.« less

Two-dimensional Maxwell-Bloch simulation of quasi-π-pulse amplification in a seeded XUV laser

NASA Astrophysics Data System (ADS)

Larroche, O.; Klisnick, A.

2013-09-01

The amplification of high-order-harmonics (HOH) seed pulses in a swept-gain XUV laser is investigated through numerical simulations of the full set of Bloch and two-dimensional paraxial propagation equations with our code colax. The needed atomic data are taken from a hydrodynamics and collisional-radiative simulation in the case of a Ni-like Ag plasma created from the interaction of an infrared laser with a solid target and pumped in the transient regime. We show that the interplay of strong population inversion and diffraction or refraction due to the short transverse dimensions and steep density gradient of the active plasma can lead to the amplification of an intense, ultrashort, quasi-“π” pulse triggered by the incoming seed. By properly tuning the system geometry and HOH pulse parameters, we show that an ≃10 fs, 8×1012 W/cm2 amplified pulse can be achieved in a 3-mm-long Ni-like Ag plasma, with a factor of ≳10 intensity contrast with respect to the longer-lasting wake radiation and amplified spontaneous emission.

Predictions of Gamma-ray Emission from Globular Cluster Millisecond Pulsars Above 100 MeV

NASA Technical Reports Server (NTRS)

Venter, C.; de Jaker, O.C.; Clapson, A.C.

2009-01-01

The recent Fermi detection of the globular cluster (GC) 47 Tucanae highlighted the importance of modeling collective gamma-ray emission of millisecond pulsars (MSPs) in GCs. Steady flux from such populations is also expected in the very high energy (VHE) domain covered by ground-based Cherenkov telescopes. We present pulsed curvature radiation (CR) as well as unpulsed inverse Compton (IC) calculations for an ensemble of MSPs in the GCs 47 Tucanae and Terzan 5. We demonstrate that the CR from these GCs should be easily detectable for Fermi, while constraints on the total number of MSps and the nebular B-field may be derived using the IC flux components.

Method of controlling cyclic variation in engine combustion

DOEpatents

Davis, L.I. Jr.; Daw, C.S.; Feldkamp, L.A.; Hoard, J.W.; Yuan, F.; Connolly, F.T.

1999-07-13

Cyclic variation in combustion of a lean burning engine is reduced by detecting an engine combustion event output such as torsional acceleration in a cylinder (i) at a combustion event (k), using the detected acceleration to predict a target acceleration for the cylinder at the next combustion event (k+1), modifying the target output by a correction term that is inversely proportional to the average phase of the combustion event output of cylinder (i) and calculating a control output such as fuel pulse width or spark timing necessary to achieve the target acceleration for cylinder (i) at combustion event (k+1) based on anti-correlation with the detected acceleration and spill-over effects from fueling. 27 figs.

Method of controlling cyclic variation in engine combustion

DOEpatents

Davis, Jr., Leighton Ira; Daw, Charles Stuart; Feldkamp, Lee Albert; Hoard, John William; Yuan, Fumin; Connolly, Francis Thomas

1999-01-01

Cyclic variation in combustion of a lean burning engine is reduced by detecting an engine combustion event output such as torsional acceleration in a cylinder (i) at a combustion event (k), using the detected acceleration to predict a target acceleration for the cylinder at the next combustion event (k+1), modifying the target output by a correction term that is inversely proportional to the average phase of the combustion event output of cylinder (i) and calculating a control output such as fuel pulse width or spark timing necessary to achieve the target acceleration for cylinder (i) at combustion event (k+1) based on anti-correlation with the detected acceleration and spill-over effects from fueling.

Recrystallization and grain growth behavior of rolled tungsten under VDE-like short pulse high heat flux loads

NASA Astrophysics Data System (ADS)

Yuan, Y.; Greuner, H.; Böswirth, B.; Krieger, K.; Luo, G.-N.; Xu, H. Y.; Fu, B. Q.; Li, M.; Liu, W.

2013-02-01

Short pulse heat loads expected for vertical displacement events (VDEs) in ITER were applied in the high heat flux (HHF) test facility GLADIS at IPP-Garching onto samples of rolled W. Pulsed neutral beams with the central heat flux of 23 MW/m2 were applied for 0.5, 1.0 and 1.5 s, respectively. Rapid recrystallization of the adiabatically loaded 3 mm thick samples was observed when the pulse duration was up to 1.0 s. Grains grew markedly following recrystallization with increasing pulse length. The recrystallization temperature and temperature dependence of the recrystallized grain size were also investigated. The results showed that the recrystallization temperature of the W grade was around 2480 °C under the applied heat loading condition, which was nearly 1150 °C higher than the conventional recrystallization temperature, and the grains were much finer. A linear relationship between the logarithm of average grain size (ln d) and the inverse of maximum surface temperature (1/Tmax) was found and accordingly the activation energy for grain growth in temperature evolution up to Tmax in 1.5 s of the short pulse HHF load was deduced to be 4.1 eV. This provided an effective clue to predict the structure evolution under short pulse HHF loads.

Effect of a superconducting coil as a fault current limiter on current density distribution in BSCCO tape after an over-current pulse

NASA Astrophysics Data System (ADS)

Tallouli, M.; Shyshkin, O.; Yamaguchi, S.

2017-07-01

The development of power transmission lines based on long-length high temperature superconducting (HTS) tapes is complicated and technically challenging task. A serious problem for transmission line operation could become HTS power cable damage due to over-current pulse conditions. To avoid the cable damage in any urgent case the superconducting coil technology, i.e. superconductor fault current limiter (SFCL) is required. Comprehensive understanding of the current density characteristics of HTS tapes in both cases, either after pure over-current pulse or after over-current pulse limited by SFCL, is needed to restart or to continue the operation of the power transmission line. Moreover, current density distribution along and across the HTS tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present paper we examine BSCCO HTS tape under two current feeding regimes. The first one is 100A feeding preceded by 900A over-current pulse. In this case none of tape protection was used. The second scenario is similar to the fist one but SFCL is used to limit an over-current value. For both scenarios after the pulse is gone and the current feeding is set up at 100A we scan magnetic field above the tape by means of Hall probe sensor. Then the feeding is turned of and the magnetic field scanning is repeated. Using the inverse problem numerical solver we calculate the corresponding direct and permanent current density distributions during the feeding and after switch off. It is demonstrated that in the absence of SFCL the current distribution is highly peaked at the tape center. At the same time the current distribution in the experiment with SFCL is similar to that observed under normal current feeding condition. The current peaking in the first case is explained by the effect of an opposite electric field induced at the tape edges during the overcurrent pulse decay, and by degradation of superconductivity at the edges due to penetration of magnetic field in superconducting core during the pulse.

Identification of peripheral vessels in oral and maxillofacial regions on magnetic resonance angiography obtained using a balanced steady-state free-precession sequence with a time-spatial labeling inversion pulse and using fresh blood imaging.

PubMed

Oda, Masafumi; Tanaka, Tatsurou; Yamashita, Yoshihiro; Kito, Shinji; Wakasugi-Sato, Nao; Matsumoto-Takeda, Shinobu; Nishimura, Shun; Habu, Manabu; Kodama, Masaaki; Uehara, Masataka; Kaneuji, Tsuyoshi; Kokuryo, Shinya; Miyamoto, Ikuya; Yoshiga, Daigo; Seta, Yuji; Tominaga, Kazuhiro; Yoshioka, Izumi; Morimoto, Yasuhiro

2013-12-01

To elucidate the characteristics of visualizing thin main peripheral vessels in oral and maxillofacial regions of 3-dimensional magnetic resonance angiography (MRA) using a balanced steady-state free-precession (SSFP) sequence with a time-spatial labeling inversion pulse (time-SLIP) and using fresh blood imaging (FBI). The conspicuity of blood vessels and the characteristics on MRA using SSFP with a time-SLIP was compared with those on MRA using FBI in 20 healthy participants. The conspicuity of the main peripheral arteries was significantly higher on MRA using SSFP with a time-SLIP than on MRA using FBI. MRA scans using SSFP were obtained in all participants, and scans using FBI were obtained in 16 of 20 participants. An electrocardiogram was unnecessary when using SSFP but was necessary when using FBI. MRA obtained using SSFP with a time-SLIP is a useful technique to visualize thin main peripheral arteries in the oral and maxillofacial regions without contrast medium. Copyright © 2013 Elsevier Inc. All rights reserved.

Investigation of Dynamic Properties of Water-Saturated Sand by the Results of the Inverse Experiment Technique

NASA Astrophysics Data System (ADS)

Bragov, A. M.; Balandin, Vl. V.; Kotov, V. L.; Balandin, Vl. Vl.

2018-04-01

We present new experimental results on the investigation of the dynamic properties of sand soil on the basis of the inverse experiment technique using a measuring rod with a flat front-end face. A limited applicability has been shown of the method using the procedure for correcting the shape of the deformation pulse due to dispersion during its propagation in the measuring rod. Estimates of the pulse maximum have been obtained and the results of comparison of numerical calculations with experimental data are given. The sufficient accuracy in determining the drag force during the quasi-stationary stage of penetration has been established. The parameters of dynamic compressibility and resistance to shear of water-saturated sand have been determined in the course of the experimental-theoretical analysis of the maximum values of the drag force and its values at the quasi-stationary stage of penetration. It has been shown that with almost complete water saturation of sand its shear properties are reduced but remain significant in the practically important range of penetration rates.

Optimization of contrast-to-tissue ratio by adaptation of transmitted ternary signal in ultrasound pulse inversion imaging.

PubMed

Ménigot, Sébastien; Girault, Jean-Marc

2013-01-01

Ultrasound contrast imaging has provided more accurate medical diagnoses thanks to the development of innovating modalities like the pulse inversion imaging. However, this latter modality that improves the contrast-to-tissue ratio (CTR) is not optimal, since the frequency is manually chosen jointly with the probe. However, an optimal choice of this command is possible, but it requires precise information about the transducer and the medium which can be experimentally difficult to obtain, even inaccessible. It turns out that the optimization can become more complex by taking into account the kind of generators, since the generators of electrical signals in a conventional ultrasound scanner can be unipolar, bipolar, or tripolar. Our aim was to seek the ternary command which maximized the CTR. By combining a genetic algorithm and a closed loop, the system automatically proposed the optimal ternary command. In simulation, the gain compared with the usual ternary signal could reach about 3.9 dB. Another interesting finding was that, in contrast to what is generally accepted, the optimal command was not a fixed-frequency signal but had harmonic components.

Interactive neonatal gastrointestinal magnetic resonance imaging using fruit juice as an oral contrast media.

PubMed

Arthurs, Owen J; Graves, Martin J; Edwards, Andrea D; Joubert, Ilse; Set, Pat A K; Lomas, David J

2014-09-22

The objective was to evaluate the use of fruit juice with an interactive inversion recovery (IR) MR pulse sequence to visualise the gastrointestinal tract. We investigated the relaxation properties of 12 different natural fruit juices in vitro, to identify which could be used as oral contrast. We then describe our initial experience using an interactive MR pulse sequence to allow optimal visualisation after administering pineapple juice orally, and suppressing pre-existing bowel fluid contents, with variable TI in three adult and one child volunteer. Pineapple juice (PJ) had both the shortest T1 (243 ms) and shortest T2 (48 ms) of the fruit juices tested. Optimal signal differentiation between pre-existing bowel contents and oral PJ administration was obtained with TIs of between 900 and 1100 ms. The use of an inversion recovery preparation allowed long T1 pre-existing bowel contents to be suppressed whilst the short T1 of fruit juice acts as a positive contrast medium. Pineapple juice could be used as oral contrast agent for neonatal gastrointestinal magnetic resonance imaging.

Investigation on magnetoacoustic signal generation with magnetic induction and its application to electrical conductivity reconstruction.

PubMed

Ma, Qingyu; He, Bin

2007-08-21

A theoretical study on the magnetoacoustic signal generation with magnetic induction and its applications to electrical conductivity reconstruction is conducted. An object with a concentric cylindrical geometry is located in a static magnetic field and a pulsed magnetic field. Driven by Lorentz force generated by the static magnetic field, the magnetically induced eddy current produces acoustic vibration and the propagated sound wave is received by a transducer around the object to reconstruct the corresponding electrical conductivity distribution of the object. A theory on the magnetoacoustic waveform generation for a circular symmetric model is provided as a forward problem. The explicit formulae and quantitative algorithm for the electrical conductivity reconstruction are then presented as an inverse problem. Computer simulations were conducted to test the proposed theory and assess the performance of the inverse algorithms for a multi-layer cylindrical model. The present simulation results confirm the validity of the proposed theory and suggest the feasibility of reconstructing electrical conductivity distribution based on the proposed theory on the magnetoacoustic signal generation with magnetic induction.

Age-related change of the secretory flow of pancreatic juice in the main pancreatic duct: evaluation with cine-dynamic MRCP using spatially selective inversion recovery pulse.

PubMed

Torigoe, Teruyuki; Ito, Katsuyoshi; Yamamoto, Akira; Kanki, Akihiko; Yasokawa, Kazuya; Tamada, Tsutomu; Yoshida, Koji

2014-05-01

The purpose of this study is to evaluate age-related changes in the secretory flow of pancreatic juice in the main pancreatic duct noninvasively by means of nonpharmacologic cine-dynamic MRCP using spatially selective inversion recovery (IR) pulse. Fifty-three subjects without a history of pancreatic disease were included. Four-second breath-hold MRCP using spatially selective IR pulse was performed every 15 seconds during 5 minutes (acquiring a total of 20 images) in cine-dynamic fashion. The secretion grade was classified into five grades by the distance of pancreatic juice inflow within the tagged area. The mean secretion grade and the frequency of secretion in cine-dynamic MRCP were compared among three age-range groups (group 1, < 40 years; group 2, 40-70 years; and group 3, > 70 years). Statistical analysis was performed using Spearman rank correlation coefficient and Kruskal-Wallis and Mann-Whitney U tests. The secretion grade and the frequency of secretion were significantly reduced with aging (r = -0.77, p < 0.001; and r = -0.74, p < 0.001, respectively). The mean secretion grade and the frequency of secretion were significantly lower in group 3 than in group 2 (mean grade, 0.36 vs 1.48, p = 0.001; and 4.8 vs 11.9 times, p = 0.001) and were lower in group 2 than in group 1 (mean grade, 1.48 vs 2.48, p < 0.001; and 11.9 vs 16.2 times, p = 0.011). Cine-dynamic MRCP using spatially selective IR pulse was able to show the age-related decrease of the secretory flow of pancreatic juice in the main pancreatic duct visually and noninvasively.

The Dual-Angle Method for Fast, Sensitive T1 Measurement in Vivo with Low-Angle Adiabatic Pulses

NASA Astrophysics Data System (ADS)

Bottomley, P. A.; Ouwerkerk, R.

A new method for measuring T1 based on a measurement of the ratio, R, of the steady-state partially saturated NMR signals acquired at two fixed low flip angles (<90°) and a single sequence-repetition period, TR, is presented, The flip angles are chosen to optimize both the signal-to-noise ratio per unit time relative to the best possible Ernst-angle performance and the sensitivity with which a measurement of R can resolve differences in T1. A flip-angle pair at of around (60°, 15°) yields 70-79% of the maximum achievable Ernst-angle signal-to-noise ratio and a near-linear dependence of R on TR/ T1 with gradient of about 2:1 over the range 0.1 ≤ TR/ T1 ≤ 1. Errors in hip-angle and excitation-field ( B1) inhomogeneity result in roughly proportionate errors in the apparent T1. The method is best implemented with adiabatic low-angle pulses such as B1-independent rotation (BIR-4) or BIR-4 phase-cycled (BIRP) pulses, which permit measurements with surface coils. Experimental validation was obtained at 2 T by comparison of unlocalized inversion-recovery and dual-angle proton ( 1H) and phosphorus ( 31P) measurements from vials containing doped water with 0.04 ≤ T1 ≤ 2.8 s and from the metabolites in the calf muscles of eight human volunteers. Calf muscle values of 6 ± 0.5 s for phosphocreatine and around 3.7 ± 0.8 s for the adenosine triphosphates (ATP) were in good agreement with inversion-recovery T1 values and values from the literature. Use of the dual-angle method accelerated T1 measurement time by about fivefold over inversion recovery. The dual-angle method was implemented in a one-dimensional localized surface-coil 31P spectroscopy sequence, producing consistent T1 measurements from phantoms, the calf muscle, and the human liver. 31P T1 values of ATP in the livers of six volunteers were about 0.5 ± 0.1 to 0.6 ± 0.2 s: the total exam times were about 35 minutes per subject. The method is ideally suited to low-sensitivity and/or low-concentration moieties, such as in 31P NMR in vivo, where study-time limitations are critical, and for rapid 1H T1 imaging.

Laboratory-Model Integrated-System FARAD Thruster

NASA Technical Reports Server (NTRS)

Polzin, K.A.; Best, S.; Miller, R.; Rose, M.F.; Owens, T.

2008-01-01

Pulsed inductive plasma accelerators are spacecraft propulsion devices in which energy is stored in a capacitor and then discharged through an inductive coil. The device is electrodeless, inducing a plasma current sheet in propellant located near the face of the coil. The propellant is accelerated and expelled at a high exhaust velocity (order of 10 km/s) through the interaction of the plasma current with an induced magnetic field. The Faraday Accelerator with RF-Assisted Discharge (FARAD) thruster [1,2] is a type of pulsed inductive plasma accelerator in which the plasma is preionized by a mechanism separate from that used to form the current sheet and accelerate the gas. Employing a separate preionization mechanism in this manner allows for the formation of an inductive current sheet at much lower discharge energies and voltages than those found in previous pulsed inductive accelerators like the Pulsed Inductive Thruster (PIT). In a previous paper [3], the authors presented a basic design for a 100 J/pulse FARAD laboratory-version thruster. The design was based upon guidelines and performance scaling parameters presented in Refs. [4, 5]. In this paper, we expand upon the design presented in Ref. [3] by presenting a fully-assembled and operational FARAD laboratory-model thruster and addressing system and subsystem-integration issues (concerning mass injection, preionization, and acceleration) that arose during assembly. Experimental data quantifying the operation of this thruster, including detailed internal plasma measurements, are presented by the authors in a companion paper [6]. The thruster operates by first injecting neutral gas over the face of a flat, inductive acceleration coil and at some later time preionizing the gas. Once the gas is preionized current is passed through the acceleration coil, inducing a plasma current sheet in the propellant that is accelerated away from the coil through electromagnetic interaction with the time-varying magnetic field. Neutral gas is injected over the face of the acceleration coil through a fast-acting valve that feeds a central distribution manifold. The thruster is designed to preionize the gas using an RF-frequency ringing signal produced by a discharging Vector Inversion Generator (VIG). The acceleration stage consists of a multiple-turn, multiple-strand spiral induction coil (see Fig. 1, left panel) and is designed for operation at discharge energies on the order of 100 J/pulse. Several different pulsed power train modules can be used to drive current through the acceleration coil. One such power train is based upon the Bernardes and Merryman circuit topology, which restricts voltage reversal on the capacitor banks and can be clamped to eliminate current reversal in the coil. A second option is a pulse-compression-ring power train (see Fig. 1, right panel), which takesa temporally broad, low current pulse and transforms it into a short, high current pulse.

Role of nonlinear refraction in the generation of terahertz field pulses by light fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zabolotskii, A. A., E-mail: zabolotskii@iae.nsk.su

2013-07-15

The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equationsmore » is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.« less

Plasmon enhanced terahertz emission from single layer graphene.

PubMed

Bahk, Young-Mi; Ramakrishnan, Gopakumar; Choi, Jongho; Song, Hyelynn; Choi, Geunchang; Kim, Yong Hyup; Ahn, Kwang Jun; Kim, Dai-Sik; Planken, Paul C M

2014-09-23

We show that surface plasmons, excited with femtosecond laser pulses on continuous or discontinuous gold substrates, strongly enhance the generation and emission of ultrashort, broadband terahertz pulses from single layer graphene. Without surface plasmon excitation, for graphene on glass, 'nonresonant laser-pulse-induced photon drag currents' appear to be responsible for the relatively weak emission of both s- and p-polarized terahertz pulses. For graphene on a discontinuous layer of gold, only the emission of the p-polarized terahertz electric field is enhanced, whereas the s-polarized component remains largely unaffected, suggesting the presence of an additional terahertz generation mechanism. We argue that in the latter case, 'surface-plasmon-enhanced optical rectification', made possible by the lack of inversion symmetry at the graphene on gold surface, is responsible for the strongly enhanced emission. The enhancement occurs because the electric field of surface plasmons is localized and enhanced where the graphene is located: at the surface of the metal. We believe that our results point the way to small, thin, and more efficient terahertz photonic devices.

Inverse Modelling to Obtain Head Movement Controller Signal

NASA Technical Reports Server (NTRS)

Kim, W. S.; Lee, S. H.; Hannaford, B.; Stark, L.

1984-01-01

Experimentally obtained dynamics of time-optimal, horizontal head rotations have previously been simulated by a sixth order, nonlinear model driven by rectangular control signals. Electromyography (EMG) recordings have spects which differ in detail from the theoretical rectangular pulsed control signal. Control signals for time-optimal as well as sub-optimal horizontal head rotations were obtained by means of an inverse modelling procedures. With experimentally measured dynamical data serving as the input, this procedure inverts the model to produce the neurological control signals driving muscles and plant. The relationships between these controller signals, and EMG records should contribute to the understanding of the neurological control of movements.

Rayleigh lidar observation of tropical mesospheric inversion layer: a comparison between dynamics and chemistry

NASA Astrophysics Data System (ADS)

Ramesh, K.; Sridharan, S.; Raghunath, K.

2018-04-01

The Rayleigh lidar at National Atmospheric Research Laboratory, Gadanki (13.5°N, 79.2°E), India operates at 532 nm green laser with 600 mJ/pulse since 2007. The vertical temperature profiles are derived above 30 km by assuming the atmosphere is in hydrostatic equilibrium and obeys ideal gas law. A large mesospheric inversion layer (MIL) is observed at 77.4-84.6 km on the night of 22 March 2007 over Gadanki. Although dynamics and chemistry play vital role, both the mechanisms are compared for the occurrence of the MIL in the present study.

Control of Terahertz Emission by Ultrafast Spin-Charge Current Conversion at Rashba Interfaces

NASA Astrophysics Data System (ADS)

Jungfleisch, Matthias B.; Zhang, Qi; Zhang, Wei; Pearson, John E.; Schaller, Richard D.; Wen, Haidan; Hoffmann, Axel

2018-05-01

We show that a femtosecond spin-current pulse can generate terahertz (THz) transients at Rashba interfaces between two nonmagnetic materials. Our results unambiguously demonstrate the importance of the interface in this conversion process that we interpret in terms of the inverse Rashba Edelstein effect, in contrast to the THz emission in the bulk conversion process via the inverse spin-Hall effect. Furthermore, we show that at Rashba interfaces the THz-field amplitude can be controlled by the helicity of the light. The optical generation of electric photocurrents by these interfacial effects in the femtosecond regime will open up new opportunities in ultrafast spintronics.

Control of Terahertz Emission by Ultrafast Spin-Charge Current Conversion at Rashba Interfaces.

PubMed

Jungfleisch, Matthias B; Zhang, Qi; Zhang, Wei; Pearson, John E; Schaller, Richard D; Wen, Haidan; Hoffmann, Axel

2018-05-18

We show that a femtosecond spin-current pulse can generate terahertz (THz) transients at Rashba interfaces between two nonmagnetic materials. Our results unambiguously demonstrate the importance of the interface in this conversion process that we interpret in terms of the inverse Rashba Edelstein effect, in contrast to the THz emission in the bulk conversion process via the inverse spin-Hall effect. Furthermore, we show that at Rashba interfaces the THz-field amplitude can be controlled by the helicity of the light. The optical generation of electric photocurrents by these interfacial effects in the femtosecond regime will open up new opportunities in ultrafast spintronics.

A laboratory validation study of the time-lapse oscillatory pumping test concept for leakage detection in geological repositories

NASA Astrophysics Data System (ADS)

Sun, A. Y.; Islam, A.; Lu, J.

2017-12-01

Time-lapse oscillatory pumping test (OPT) has been introduced recently as a pressure-based monitoring technique for detecting potential leakage in geologic repositories. By routinely conducting OPT at a number of pulsing frequencies, a site operator may identify the potential anomalies in the frequency domain, alleviating the ambiguity caused by reservoir noise and improving the signal-to-noise ratio. Building on previous theoretical and field studies, this work performed a series of laboratory experiments to validate the concept of time-lapse OPT using a custom made, stainless steel tank under relatively high pressures ( 120psi). The experimental configuration simulates a miniature geologic storage repository consisting of three layers (i.e., injection zone, caprock, and above-zone aquifer). Results show that leakage in the injection zone led to deviations in the power spectrum of observed pressure data, and the amplitude of which also increases with decreasing pulsing frequencies. The experimental results were further analyzed by developing a 3D flow model, using which the model parameters were estimated through frequency domain inversion.

The Effect of Ionospheric Models on Electromagnetic Pulse Locations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fenimore, Edward E.; Triplett, Laurie A.

2014-07-01

Locations of electromagnetic pulses (EMPs) determined by time-of-arrival (TOA) often have outliers with significantly larger errors than expected. In the past, these errors were thought to arise from high order terms in the Appleton-Hartree equation. We simulated 1000 events randomly spread around the Earth into a constellation of 22 GPS satellites. We used four different ionospheres: “simple” where the time delay goes as the inverse of the frequency-squared, “full Appleton-Hartree”, the “BobRD integrals” and a full raytracing code. The simple and full Appleton-Hartree ionospheres do not show outliers whereas the BobRD and raytracing do. This strongly suggests that the causemore » of the outliers is not additional terms in the Appleton-Hartree equation, but rather is due to the additional path length due to refraction. A method to fix the outliers is suggested based on fitting a time to the delays calculated at the 5 GPS frequencies with BobRD and simple ionospheres. The difference in time is used as a correction to the TOAs.« less

Determination of the rCBF in the Amygdala and Rhinal Cortex Using a FAIR-TrueFISP Sequence

PubMed Central

Martirosian, Petros; Klose, Uwe; Nägele, Thomas; Schick, Fritz; Ernemann, Ulrike

2011-01-01

Objective Brain perfusion can be assessed non-invasively by modern arterial spin labeling MRI. The FAIR (flow-sensitive alternating inversion recovery)-TrueFISP (true fast imaging in steady precession) technique was applied for regional assessment of cerebral blood flow in brain areas close to the skull base, since this approach provides low sensitivity to magnetic susceptibility effects. The investigation of the rhinal cortex and the amygdala is a potentially important feature for the diagnosis and research on dementia in its early stages. Materials and Methods Twenty-three subjects with no structural or psychological impairment were investigated. FAIR-True-FISP quantitative perfusion data were evaluated in the amygdala on both sides and in the pons. A preparation of the radiofrequency FOCI (frequency offset corrected inversion) pulse was used for slice selective inversion. After a time delay of 1.2 sec, data acquisition began. Imaging slice thickness was 5 mm and inversion slab thickness for slice selective inversion was 12.5 mm. Image matrix size for perfusion images was 64 × 64 with a field of view of 256 × 256 mm, resulting in a spatial resolution of 4 × 4 × 5 mm. Repetition time was 4.8 ms; echo time was 2.4 ms. Acquisition time for the 50 sets of FAIR images was 6:56 min. Data were compared with perfusion data from the literature. Results Perfusion values in the right amygdala, left amygdala and pons were 65.2 (± 18.2) mL/100 g/minute, 64.6 (± 21.0) mL/100 g/minute, and 74.4 (± 19.3) mL/100 g/minute, respectively. These values were higher than formerly published data using continuous arterial spin labeling but similar to 15O-PET (oxygen-15 positron emission tomography) data. Conclusion The FAIR-TrueFISP approach is feasible for the quantitative assessment of perfusion in the amygdala. Data are comparable with formerly published data from the literature. The applied technique provided excellent image quality, even for brain regions located at the skull base in the vicinity of marked susceptibility steps. PMID:21927556

Increased operational temperature of Cr2O3-based spintronic devices

NASA Astrophysics Data System (ADS)

Street, Michael; Echtenkamp, Will; Komesu, Takashi; Cao, Shi; Wang, Jian; Dowben, Peter; Binek, Christian

Spintronic devices have been considered a promising path to revolutionizing the current data storage and memory technologies. This work is an effort to utilize voltage-controlled boundary magnetization of the magnetoelectric chromia (Cr2O3) to be implemented into a spintronic device. The electric switchable boundary magnetization of chromia can be used to voltage-control the magnetic states of an adjacent ferromagnetic layer. For this technique to be utilized in a spintronic device, the antiferromagnetic ordering temperature of chromia must be enhanced above the bulk value of TN = 307K. Previously, based on first principle calculations, boron doped chromia thin films were fabricated via pulsed laser deposition showing boundary magnetization at elevated temperatures. Measurements of the boundary magnetization were also corroborated by spin polarized inverse photoemission spectroscopy. Exchange bias of B-doped chromia was also investigated using magneto-optical Kerr effect, showing an increased blocking temperature from 307K. Further boundary magnetization measurements and spin polarized inverse photoemission measurements indicate the surface magnetization to an in-plane orientation from the standard perpendicular orientation. This project was supported by the SRC through CNFD, an SRC-NRI Center under Task ID (2398.001) and by C-SPIN, part of STARnet, sponsored by MARCO and DARPA (No. SRC 2381.001).

Nonlinear propagation of vector extremely short pulses in a medium of symmetric and asymmetric molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sazonov, S. V., E-mail: sazonov.sergey@gmail.com; Ustinov, N. V., E-mail: n-ustinov@mail.ru

The nonlinear propagation of extremely short electromagnetic pulses in a medium of symmetric and asymmetric molecules placed in static magnetic and electric fields is theoretically studied. Asymmetric molecules differ in that they have nonzero permanent dipole moments in stationary quantum states. A system of wave equations is derived for the ordinary and extraordinary components of pulses. It is shown that this system can be reduced in some cases to a system of coupled Ostrovsky equations and to the equation intagrable by the method for an inverse scattering transformation, including the vector version of the Ostrovsky–Vakhnenko equation. Different types of solutionsmore » of this system are considered. Only solutions representing the superposition of periodic solutions are single-valued, whereas soliton and breather solutions are multivalued.« less

Micro-Doppler Signal Time-Frequency Algorithm Based on STFRFT.

PubMed

Pang, Cunsuo; Han, Yan; Hou, Huiling; Liu, Shengheng; Zhang, Nan

2016-09-24

This paper proposes a time-frequency algorithm based on short-time fractional order Fourier transformation (STFRFT) for identification of a complicated movement targets. This algorithm, consisting of a STFRFT order-changing and quick selection method, is effective in reducing the computation load. A multi-order STFRFT time-frequency algorithm is also developed that makes use of the time-frequency feature of each micro-Doppler component signal. This algorithm improves the estimation accuracy of time-frequency curve fitting through multi-order matching. Finally, experiment data were used to demonstrate STFRFT's performance in micro-Doppler time-frequency analysis. The results validated the higher estimate accuracy of the proposed algorithm. It may be applied to an LFM (Linear frequency modulated) pulse radar, SAR (Synthetic aperture radar), or ISAR (Inverse synthetic aperture radar), for improving the probability of target recognition.

Regional atmospheric CO2 inversion reveals seasonal and geographic differences in Amazon net biome exchange.

PubMed

Alden, Caroline B; Miller, John B; Gatti, Luciana V; Gloor, Manuel M; Guan, Kaiyu; Michalak, Anna M; van der Laan-Luijkx, Ingrid T; Touma, Danielle; Andrews, Arlyn; Basso, Luana S; Correia, Caio S C; Domingues, Lucas G; Joiner, Joanna; Krol, Maarten C; Lyapustin, Alexei I; Peters, Wouter; Shiga, Yoichi P; Thoning, Kirk; van der Velde, Ivar R; van Leeuwen, Thijs T; Yadav, Vineet; Diffenbaugh, Noah S

2016-10-01

Understanding tropical rainforest carbon exchange and its response to heat and drought is critical for quantifying the effects of climate change on tropical ecosystems, including global climate-carbon feedbacks. Of particular importance for the global carbon budget is net biome exchange of CO2 with the atmosphere (NBE), which represents nonfire carbon fluxes into and out of biomass and soils. Subannual and sub-Basin Amazon NBE estimates have relied heavily on process-based biosphere models, despite lack of model agreement with plot-scale observations. We present a new analysis of airborne measurements that reveals monthly, regional-scale (~1-8 × 10(6)  km(2) ) NBE variations. We develop a regional atmospheric CO2 inversion that provides the first analysis of geographic and temporal variability in Amazon biosphere-atmosphere carbon exchange and that is minimally influenced by biosphere model-based first guesses of seasonal and annual mean fluxes. We find little evidence for a clear seasonal cycle in Amazon NBE but do find NBE sensitivity to aberrations from long-term mean climate. In particular, we observe increased NBE (more carbon emitted to the atmosphere) associated with heat and drought in 2010, and correlations between wet season NBE and precipitation (negative correlation) and temperature (positive correlation). In the eastern Amazon, pulses of increased NBE persisted through 2011, suggesting legacy effects of 2010 heat and drought. We also identify regional differences in postdrought NBE that appear related to long-term water availability. We examine satellite proxies and find evidence for higher gross primary productivity (GPP) during a pulse of increased carbon uptake in 2011, and lower GPP during a period of increased NBE in the 2010 dry season drought, but links between GPP and NBE changes are not conclusive. These results provide novel evidence of NBE sensitivity to short-term temperature and moisture extremes in the Amazon, where monthly and sub-Basin estimates have not been previously available. © 2016 John Wiley & Sons Ltd.

Regional Atmospheric CO2 Inversion Reveals Seasonal and Geographic Differences in Amazon Net Biome Exchange

NASA Technical Reports Server (NTRS)

Alden, Caroline B.; Miller, John B.; Gatti, Luciana V.; Gloor, Manuel M.; Guan, Kaiyu; Michalak, Anna M.; van der Laan-Luijkx, Ingrid; Touma, Danielle; Andrews, Arlyn; Basso, Luana G.;

Generalized Uncertainty Quantification for Linear Inverse Problems in X-ray Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fowler, Michael James

2014-04-25

In industrial and engineering applications, X-ray radiography has attained wide use as a data collection protocol for the assessment of material properties in cases where direct observation is not possible. The direct measurement of nuclear materials, particularly when they are under explosive or implosive loading, is not feasible, and radiography can serve as a useful tool for obtaining indirect measurements. In such experiments, high energy X-rays are pulsed through a scene containing material of interest, and a detector records a radiograph by measuring the radiation that is not attenuated in the scene. One approach to the analysis of these radiographsmore » is to model the imaging system as an operator that acts upon the object being imaged to produce a radiograph. In this model, the goal is to solve an inverse problem to reconstruct the values of interest in the object, which are typically material properties such as density or areal density. The primary objective in this work is to provide quantitative solutions with uncertainty estimates for three separate applications in X-ray radiography: deconvolution, Abel inversion, and radiation spot shape reconstruction. For each problem, we introduce a new hierarchical Bayesian model for determining a posterior distribution on the unknowns and develop efficient Markov chain Monte Carlo (MCMC) methods for sampling from the posterior. A Poisson likelihood, based on a noise model for photon counts at the detector, is combined with a prior tailored to each application: an edge-localizing prior for deconvolution; a smoothing prior with non-negativity constraints for spot reconstruction; and a full covariance sampling prior based on a Wishart hyperprior for Abel inversion. After developing our methods in a general setting, we demonstrate each model on both synthetically generated datasets, including those from a well known radiation transport code, and real high energy radiographs taken at two U. S. Department of Energy laboratories.« less

A physics based approach to the pulse wave velocity prediction in compliant arterial segments.

PubMed

Liberson, Alexander S; Lillie, Jeffrey S; Day, Steven W; Borkholder, David A

2016-10-03

Pulse wave velocity (PWV) quantification commonly serves as a highly robust prognostic parameter being used in a preventative cardiovascular therapy. Being dependent on arterial elastance, it can serve as a marker of cardiovascular risk. Since it is influenced by a blood pressure (BP), the pertaining theory can lay the foundation in developing a technique for noninvasive blood pressure measurement. Previous studies have reported application of PWV, measured noninvasively, for both the estimation of arterial compliance and blood pressure, based on simplified physical or statistical models. A new theoretical model for pulse wave propagation in a compliant arterial segment is presented within the framework of pseudo-elastic deformation of biological tissue undergoing finite deformation. An essential ingredient is the dependence of results on nonlinear aspects of the model: convective fluid phenomena, hyperelastic constitutive relation, large deformation and a longitudinal pre-stress load. An exact analytical solution for PWV is presented as a function of pressure, flow and pseudo-elastic orthotropic parameters. Results from our model are compared with published in-vivo PWV measurements under diverse physiological conditions. Contributions of each of the nonlinearities are analyzed. It was found that the totally nonlinear model achieves the best match with the experimental data. To retrieve individual vascular information of a patient, the inverse problem of hemodynamics is presented, calculating local orthotropic hyperelastic properties of the arterial wall. The proposed technique can be used for non-invasive assessment of arterial elastance, and blood pressure using direct measurement of PWV, with account of hyperelastic orthotropic properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

The short pulse equation by a Riemann-Hilbert approach

NASA Astrophysics Data System (ADS)

Boutet de Monvel, Anne; Shepelsky, Dmitry; Zielinski, Lech

2017-07-01

We develop a Riemann-Hilbert approach to the inverse scattering transform method for the short pulse (SP) equation u_{xt}=u+{1/6}(u^3)_{xx} with zero boundary conditions (as |x|→ ∞). This approach is directly applied to a Lax pair for the SP equation. It allows us to give a parametric representation of the solution to the Cauchy problem. This representation is then used for studying the longtime behavior of the solution as well as for retrieving the soliton solutions. Finally, the analysis of the longtime behavior allows us to formulate, in spectral terms, a sufficient condition for the wave breaking.

Light collection and pulse-shape discrimination in elongated scintillator cells for the PROSPECT reactor antineutrino experiment

NASA Astrophysics Data System (ADS)

Ashenfelter, J.; Balantekin, B.; Band, H. R.; Barclay, G.; Bass, C. D.; Berish, D.; Bowden, N. S.; Bowes, A.; Brodsky, J. P.; Bryan, C. D.; Cherwinka, J. J.; Chu, R.; Classen, T.; Commeford, K.; Davee, D.; Dean, D.; Deichert, G.; Diwan, M. V.; Dolinski, M. J.; Dolph, J.; Dwyer, D. A.; Gaison, J. K.; Galindo-Uribarri, A.; Gilje, K.; Glenn, A.; Goddard, B. W.; Green, M.; Han, K.; Hans, S.; Heeger, K. M.; Heffron, B.; Jaffe, D. E.; Langford, T. J.; Littlejohn, B. R.; Martinez Caicedo, D. A.; McKeown, R. D.; Mendenhall, M. P.; Mueller, P.; Mumm, H. P.; Napolitano, J.; Neilson, R.; Norcini, D.; Pushin, D.; Qian, X.; Romero, E.; Rosero, R.; Saldana, L.; Seilhan, B. S.; Sharma, R.; Sheets, S.; Stemen, N. T.; Surukuchi, P. T.; Varner, R. L.; Viren, B.; Wang, W.; White, B.; White, C.; Wilhelmi, J.; Williams, C.; Wise, T.; Yao, H.; Yeh, M.; Yen, Y. R.; Zangakis, G.; Zhang, C.; Zhang, X.

2015-11-01

A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron-gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. Key design features for optimizing MeV-scale response and background rejection capabilities are identified.

NASA Tech Briefs, August 2004

NASA Technical Reports Server (NTRS)

2004-01-01

Topics covered include: Data Relay Board with Protocol for High-Speed, Free-Space Optical Communications; Software and Algorithms for Biomedical Image Data Processing and Visualization; Rapid Chemometric Filtering of Spectral Data; Prioritizing Scientific Data for Transmission; Determining Sizes of Particles in a Flow from DPIV Data; Faster Processing for Inverting GPS Occultation Data; FPGA-Based, Self-Checking, Fault-Tolerant Computers; Ultralow-Power Digital Correlator for Microwave Polarimetry; Grounding Headphones for Protection Against ESD; Lightweight Stacks of Direct Methanol Fuel Cells; Highly Efficient Vector-Inversion Pulse Generators; Estimating Basic Preliminary Design Performances of Aerospace Vehicles; Framework for Development of Object-Oriented Software; Analyzing Spacecraft Telecommunication Systems; Collaborative Planning of Robotic Exploration; Tools for Administration of a UNIX-Based Network; Preparing and Analyzing Iced Airfoils; Evaluating Performance of Components; Fuels Containing Methane of Natural Gas in Solution; Direct Electrolytic Deposition of Mats of MnxOy Nanowires; Bubble Eliminator Based on Centrifugal Flow; Inflatable Emergency Atmospheric-Entry Vehicles; Lightweight Deployable Mirrors with Tensegrity Supports; Centrifugal Adsorption Cartridge System; Ultrasonic Apparatus for Pulverizing Brittle Material; Transplanting Retinal Cells using Bucky Paper for Support; Using an Ultrasonic Instrument to Size Extravascular Bubbles; Coronagraphic Notch Filter for Raman Spectroscopy; On-the-Fly Mapping for Calibrating Directional Antennas; Working Fluids for Increasing Capacities of Heat Pipes; Computationally-Efficient Minimum-Time Aircraft Routes in the Presence of Winds; Liquid-Metal-Fed Pulsed Plasma Thrusters; Personal Radiation Protection System; and Attitude Control for a Solar-Sail Spacecraft.

Acoustic Network Localization and Interpretation of Infrasonic Pulses from Lightning

NASA Astrophysics Data System (ADS)

Arechiga, R. O.; Johnson, J. B.; Badillo, E.; Michnovicz, J. C.; Thomas, R. J.; Edens, H. E.; Rison, W.

2011-12-01

We improve on the localization accuracy of thunder sources and identify infrasonic pulses that are correlated across a network of acoustic arrays. We attribute these pulses to electrostatic charge relaxation (collapse of the electric field) and attempt to model their spatial extent and acoustic source strength. Toward this objective we have developed a single audio range (20-15,000 Hz) acoustic array and a 4-station network of broadband (0.01-500 Hz) microphone arrays with aperture of ~45 m. The network has an aperture of 1700 m and was installed during the summers of 2009-2011 in the Magdalena mountains of New Mexico, an area that is subject to frequent lightning activity. We are exploring a new technique based on inverse theory that integrates information from the audio range and the network of broadband acoustic arrays to locate thunder sources more accurately than can be achieved with a single array. We evaluate the performance of the technique by comparing the location of thunder sources with RF sources located by the lightning mapping array (LMA) of Langmuir Laboratory at New Mexico Tech. We will show results of this technique for lightning flashes that occurred in the vicinity of our network of acoustic arrays and over the LMA. We will use acoustic network detection of infrasonic pulses together with LMA data and electric field measurements to estimate the spatial distribution of the charge (within the cloud) that is used to produce a lightning flash, and will try to quantify volumetric charges (charge magnitude) within clouds.

Non-contrast-enhanced MR portography with balanced steady-state free-precession sequence and time-spatial labeling inversion pulses: comparison of imaging with flow-in and flow-out methods.

PubMed

Furuta, Akihiro; Isoda, Hiroyoshi; Yamashita, Rikiya; Ohno, Tsuyoshi; Kawahara, Seiya; Shimizu, Hironori; Fujimoto, Koji; Kido, Aki; Kusahara, Hiroshi; Togashi, Kaori

2014-09-01

To compare and evaluate images of non-contrast-enhanced MR portography acquired with two different methods, the flow-in and flow-out methods. Twenty-five healthy volunteers were examined using respiratory-triggered three-dimensional balanced steady-state free-precession (SSFP) with two selective inversion recovery pulses (flow-in method) and one tagging pulse and one nonselective inversion recovery pulse (flow-out method). For quantitative analysis, vessel-to-liver contrast (Cv-l) ratios of the main portal vein (MPV), right portal vein (RPV), and left portal vein (LPV) were measured. The quality of portal vein visualization was scored using a four-point scale. The Cv-ls of the MPV, RPV, and LPV were all significantly higher with the flow-out than flow-in method (MPV = 0.834 ± 0.06 versus 0.711 ± 0.10; RPV = 0.861 ± 0.04 versus 0.729 ± 0.11; LPV = 0.786 ± 0.08 versus 0.545 ± 0.22; P < 0.0001). In all analyses of vessel visibility, non-contrast-enhanced MR portography with the flow-out method showed higher scores than with the flow-in method. With the flow-out method, visual scores of the MPV, RPV, portal vein branches of segments 4 (P4), and 8 (P8) were significantly better than with the flow-in method (MPV = 3.4 ± 0.7 versus 2.6 ± 0.9; RPV = 4.0 ± 0.0 versus 3.5 ± 0.9; P4 = 2.8 ± 1.3 versus 1.6 ± 1.0; P8 = 4.0 ± 0.0 versus 2.9 ± 1.1; P < 0.05). Non-contrast-enhanced MR portography with the flow-out method improves the visualization of the intrahepatic portal vein in comparison with the flow-in method. J. Magn. Reson. Imaging 2014;40:583-587. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.

Reproducibility study of whole-brain 1H spectroscopic imaging with automated quantification.

PubMed

Gu, Meng; Kim, Dong-Hyun; Mayer, Dirk; Sullivan, Edith V; Pfefferbaum, Adolf; Spielman, Daniel M

2008-09-01

A reproducibility study of proton MR spectroscopic imaging ((1)H-MRSI) of the human brain was conducted to evaluate the reliability of an automated 3D in vivo spectroscopic imaging acquisition and associated quantification algorithm. A PRESS-based pulse sequence was implemented using dualband spectral-spatial RF pulses designed to fully excite the singlet resonances of choline (Cho), creatine (Cre), and N-acetyl aspartate (NAA) while simultaneously suppressing water and lipids; 1% of the water signal was left to be used as a reference signal for robust data processing, and additional lipid suppression was obtained using adiabatic inversion recovery. Spiral k-space trajectories were used for fast spectral and spatial encoding yielding high-quality spectra from 1 cc voxels throughout the brain with a 13-min acquisition time. Data were acquired with an 8-channel phased-array coil and optimal signal-to-noise ratio (SNR) for the combined signals was achieved using a weighting based on the residual water signal. Automated quantification of the spectrum of each voxel was performed using LCModel. The complete study consisted of eight healthy adult subjects to assess intersubject variations and two subjects scanned six times each to assess intrasubject variations. The results demonstrate that reproducible whole-brain (1)H-MRSI data can be robustly obtained with the proposed methods.

Effects of important parameters variations on computing eigenspace-based minimum variance weights for ultrasound tissue harmonic imaging

NASA Astrophysics Data System (ADS)

Haji Heidari, Mehdi; Mozaffarzadeh, Moein; Manwar, Rayyan; Nasiriavanaki, Mohammadreza

2018-02-01

In recent years, the minimum variance (MV) beamforming has been widely studied due to its high resolution and contrast in B-mode Ultrasound imaging (USI). However, the performance of the MV beamformer is degraded at the presence of noise, as a result of the inaccurate covariance matrix estimation which leads to a low quality image. Second harmonic imaging (SHI) provides many advantages over the conventional pulse-echo USI, such as enhanced axial and lateral resolutions. However, the low signal-to-noise ratio (SNR) is a major problem in SHI. In this paper, Eigenspace-based minimum variance (EIBMV) beamformer has been employed for second harmonic USI. The Tissue Harmonic Imaging (THI) is achieved by Pulse Inversion (PI) technique. Using the EIBMV weights, instead of the MV ones, would lead to reduced sidelobes and improved contrast, without compromising the high resolution of the MV beamformer (even at the presence of a strong noise). In addition, we have investigated the effects of variations of the important parameters in computing EIBMV weights, i.e., K, L, and δ, on the resolution and contrast obtained in SHI. The results are evaluated using numerical data (using point target and cyst phantoms), and the proper parameters of EIBMV are indicated for THI.

Enhanced photoelectrochemical and photocatalytic activity in visible-light-driven Ag/BiVO{sub 4} inverse opals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Liang, E-mail: lfang@suda.edu.cn, E-mail: dawei.cao@tu-ilmenau.de; Nan, Feng; Yang, Ying

2016-02-29

BiVO{sub 4} photonic crystal inverse opals (io-BiVO{sub 4}) with highly dispersed Ag nanoparticles (NPs) were prepared by the nanosphere lithography method combining the pulsed current deposition method. The incorporation of the Ag NPs can significantly improve the photoelectrochemical and photocatalytic activity of BiVO{sub 4} inverse opals in the visible light region. The photocurrent density of the Ag/io-BiVO{sub 4} sample is 4.7 times higher than that of the disordered sample without the Ag NPs, while the enhancement factor of the corresponding kinetic constant in photocatalytic experiment is approximately 3. The improved photoelectrochemical and photocatalytic activity is benefited from two reasons: onemore » is the enhanced light harvesting owing to the coupling between the slow light and localized surface plasmon resonance effect; the other is the efficient separation of charge carriers due to the Schottky barriers.« less

Thermonuclear targets for direct-drive ignition by a megajoule laser pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bel’kov, S. A.; Bondarenko, S. V.; Vergunova, G. A.

2015-10-15

Central ignition of a thin two-layer-shell fusion target that is directly driven by a 2-MJ profiled pulse of Nd laser second-harmonic radiation has been studied. The parameters of the target were selected so as to provide effective acceleration of the shell toward the center, which was sufficient for the onset of ignition under conditions of increased hydrodynamic stability of the ablator acceleration and compression. The aspect ratio of the inner deuterium-tritium layer of the shell does not exceed 15, provided that a major part (above 75%) of the outer layer (plastic ablator) is evaporated by the instant of maximum compression.more » The investigation is based on two series of numerical calculations that were performed using one-dimensional (1D) hydrodynamic codes. The first 1D code was used to calculate the absorption of the profiled laser-radiation pulse (including calculation of the total absorption coefficient with allowance for the inverse bremsstrahlung and resonance mechanisms) and the spatial distribution of target heating for a real geometry of irradiation using 192 laser beams in a scheme of focusing with a cubo-octahedral symmetry. The second 1D code was used for simulating the total cycle of target evolution under the action of absorbed laser radiation and for determining the thermonuclear gain that was achieved with a given target.« less

Resonant Inverse Compton Scattering Spectra from Highly Magnetized Neutron Stars

NASA Astrophysics Data System (ADS)

Wadiasingh, Zorawar; Baring, Matthew G.; Gonthier, Peter L.; Harding, Alice K.

2018-02-01

Hard, nonthermal, persistent pulsed X-ray emission extending between 10 and ∼150 keV has been observed in nearly 10 magnetars. For inner-magnetospheric models of such emission, resonant inverse Compton scattering of soft thermal photons by ultrarelativistic charges is the most efficient production mechanism. We present angle-dependent upscattering spectra and pulsed intensity maps for uncooled, relativistic electrons injected in inner regions of magnetar magnetospheres, calculated using collisional integrals over field loops. Our computations employ a new formulation of the QED Compton scattering cross section in strong magnetic fields that is physically correct for treating important spin-dependent effects in the cyclotron resonance, thereby producing correct photon spectra. The spectral cutoff energies are sensitive to the choices of observer viewing geometry, electron Lorentz factor, and scattering kinematics. We find that electrons with energies ≲15 MeV will emit most of their radiation below 250 keV, consistent with inferred turnovers for magnetar hard X-ray tails. More energetic electrons still emit mostly below 1 MeV, except for viewing perspectives sampling field-line tangents. Pulse profiles may be singly or doubly peaked dependent on viewing geometry, emission locale, and observed energy band. Magnetic pair production and photon splitting will attenuate spectra to hard X-ray energies, suppressing signals in the Fermi-LAT band. The resonant Compton spectra are strongly polarized, suggesting that hard X-ray polarimetry instruments such as X-Calibur, or a future Compton telescope, can prove central to constraining model geometry and physics.

Lipid suppression via double inversion recovery with symmetric frequency sweep for robust 2D‐GRAPPA‐accelerated MRSI of the brain at 7 T

PubMed Central

Hangel, Gilbert; Strasser, Bernhard; Považan, Michal; Gruber, Stephan; Chmelík, Marek; Gajdošík, Martin; Trattnig, Siegfried

2015-01-01

This work presents a new approach for high‐resolution MRSI of the brain at 7 T in clinically feasible measurement times. Two major problems of MRSI are the long scan times for large matrix sizes and the possible spectral contamination by the transcranial lipid signal. We propose a combination of free induction decay (FID)‐MRSI with a short acquisition delay and acceleration via in‐plane two‐dimensional generalised autocalibrating partially parallel acquisition (2D‐GRAPPA) with adiabatic double inversion recovery (IR)‐based lipid suppression to allow robust high‐resolution MRSI. We performed Bloch simulations to evaluate the magnetisation pathways of lipids and metabolites, and compared the results with phantom measurements. Acceleration factors in the range 2–25 were tested in a phantom. Five volunteers were scanned to verify the value of our MRSI method in vivo. GRAPPA artefacts that cause fold‐in of transcranial lipids were suppressed via double IR, with a non‐selective symmetric frequency sweep. The use of long, low‐power inversion pulses (100 ms) reduced specific absorption rate requirements. The symmetric frequency sweep over both pulses provided good lipid suppression (>90%), in addition to a reduced loss in metabolite signal‐to‐noise ratio (SNR), compared with conventional IR suppression (52–70%). The metabolic mapping over the whole brain slice was not limited to a rectangular region of interest. 2D‐GRAPPA provided acceleration up to a factor of nine for in vivo FID‐MRSI without a substantial increase in g‐factors (<1.1). A 64 × 64 matrix can be acquired with a common repetition time of ~1.3 s in only 8 min without lipid artefacts caused by acceleration. Overall, we present a fast and robust MRSI method, using combined double IR fat suppression and 2D‐GRAPPA acceleration, which may be used in (pre)clinical studies of the brain at 7 T. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd. PMID:26370781

Lipid suppression via double inversion recovery with symmetric frequency sweep for robust 2D-GRAPPA-accelerated MRSI of the brain at 7 T.

PubMed

Hangel, Gilbert; Strasser, Bernhard; Považan, Michal; Gruber, Stephan; Chmelík, Marek; Gajdošík, Martin; Trattnig, Siegfried; Bogner, Wolfgang

2015-11-01

This work presents a new approach for high-resolution MRSI of the brain at 7 T in clinically feasible measurement times. Two major problems of MRSI are the long scan times for large matrix sizes and the possible spectral contamination by the transcranial lipid signal. We propose a combination of free induction decay (FID)-MRSI with a short acquisition delay and acceleration via in-plane two-dimensional generalised autocalibrating partially parallel acquisition (2D-GRAPPA) with adiabatic double inversion recovery (IR)-based lipid suppression to allow robust high-resolution MRSI. We performed Bloch simulations to evaluate the magnetisation pathways of lipids and metabolites, and compared the results with phantom measurements. Acceleration factors in the range 2-25 were tested in a phantom. Five volunteers were scanned to verify the value of our MRSI method in vivo. GRAPPA artefacts that cause fold-in of transcranial lipids were suppressed via double IR, with a non-selective symmetric frequency sweep. The use of long, low-power inversion pulses (100 ms) reduced specific absorption rate requirements. The symmetric frequency sweep over both pulses provided good lipid suppression (>90%), in addition to a reduced loss in metabolite signal-to-noise ratio (SNR), compared with conventional IR suppression (52-70%). The metabolic mapping over the whole brain slice was not limited to a rectangular region of interest. 2D-GRAPPA provided acceleration up to a factor of nine for in vivo FID-MRSI without a substantial increase in g-factors (<1.1). A 64 × 64 matrix can be acquired with a common repetition time of ~1.3 s in only 8 min without lipid artefacts caused by acceleration. Overall, we present a fast and robust MRSI method, using combined double IR fat suppression and 2D-GRAPPA acceleration, which may be used in (pre)clinical studies of the brain at 7 T. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

Left ventricular ejection time, not heart rate, is an independent correlate of aortic pulse wave velocity.

PubMed

Salvi, Paolo; Palombo, Carlo; Salvi, Giovanni Matteo; Labat, Carlos; Parati, Gianfranco; Benetos, Athanase

2013-12-01

Several studies showed a positive association between heart rate and pulse wave velocity, a sensitive marker of arterial stiffness. However, no study involving a large population has specifically addressed the dependence of pulse wave velocity on different components of the cardiac cycle. The aim of this study was to explore in subjects of different age the link between pulse wave velocity with heart period (the reciprocal of heart rate) and the temporal components of the cardiac cycle such as left ventricular ejection time and diastolic time. Carotid-femoral pulse wave velocity was assessed in 3,020 untreated subjects (1,107 men). Heart period, left ventricular ejection time, diastolic time, and early-systolic dP/dt were determined by carotid pulse wave analysis with high-fidelity applanation tonometry. An inverse association was found between pulse wave velocity and left ventricular ejection time at all ages (<25 years, r(2) = 0.043; 25-44 years, r(2) = 0.103; 45-64 years, r(2) = 0.079; 65-84 years, r(2) = 0.044; ≥ 85 years, r(2) = 0.022; P < 0.0001 for all). A significant (P < 0.0001) negative but always weaker correlation between pulse wave velocity and heart period was also found, with the exception of the youngest subjects (P = 0.20). A significant positive correlation was also found between pulse wave velocity and dP/dt (P < 0.0001). With multiple stepwise regression analysis, left ventricular ejection time and dP/dt remained the only determinant of pulse wave velocity at all ages, whereas the contribution of heart period no longer became significant. Our data demonstrate that pulse wave velocity is more closely related to left ventricular systolic function than to heart period. This may have methodological and pathophysiological implications.

Wideband Arrhythmia-Insensitive-Rapid (AIR) Pulse Sequence for Cardiac T1 mapping without Image Artifacts induced by ICD

PubMed Central

Hong, KyungPyo; Jeong, Eun-Kee; Wall, T. Scott; Drakos, Stavros G.; Kim, Daniel

2015-01-01

Purpose To develop and evaluate a wideband arrhythmia-insensitive-rapid (AIR) pulse sequence for cardiac T1 mapping without image artifacts induced by implantable-cardioverter-defibrillator (ICD). Methods We developed a wideband AIR pulse sequence by incorporating a saturation pulse with wide frequency bandwidth (8.9 kHz), in order to achieve uniform T1 weighting in the heart with ICD. We tested the performance of original and “wideband” AIR cardiac T1 mapping pulse sequences in phantom and human experiments at 1.5T. Results In 5 phantoms representing native myocardium and blood and post-contrast blood/tissue T1 values, compared with the control T1 values measured with an inversion-recovery pulse sequence without ICD, T1 values measured with original AIR with ICD were considerably lower (absolute percent error >29%), whereas T1 values measured with wideband AIR with ICD were similar (absolute percent error <5%). Similarly, in 11 human subjects, compared with the control T1 values measured with original AIR without ICD, T1 measured with original AIR with ICD was significantly lower (absolute percent error >10.1%), whereas T1 measured with wideband AIR with ICD was similar (absolute percent error <2.0%). Conclusion This study demonstrates the feasibility of a wideband pulse sequence for cardiac T1 mapping without significant image artifacts induced by ICD. PMID:25975192

IV INTERNATIONAL CONFERENCE ON ATOM AND MOLECULAR PULSED LASERS (AMPL'99): Efficiency of an H2—SF6 laser with electron-beam initiation of chemical reactions

NASA Astrophysics Data System (ADS)

Erofeev, M. V.; Orlovskii, Viktor M.; Skakun, V. S.; Sosnin, E. A.; Tarasenko, Viktor F.

2000-06-01

The spectral and amplitude—time characteristics of HF lasers pumped by a nonchain chemical reaction and initiated by radially convergent and planar electron beams were investigated. The principal channels leading to the formation of vibrationally excited HF molecules were analysed. It was confirmed that high efficiencies (~10%) of a nonchain HF laser may be attained only as a result of the simultaneous formation of atomic and molecular fluorine when the active mixture is acted upon by an electron beam and of the participation of molecular fluorine in population inversion. It was shown that a laser pulse has a complex spectral—temporal profile caused by the successive generation of P-lines and the overlap during the radiation pulse of both the rotational lines of the same vibrational band and of individual vibrational bands.

Polarization transfer NMR imaging

DOEpatents

Sillerud, Laurel O.; van Hulsteyn, David B.

1990-01-01

A nuclear magnetic resonance (NMR) image is obtained with spatial information modulated by chemical information. The modulation is obtained through polarization transfer from a first element representing the desired chemical, or functional, information, which is covalently bonded and spin-spin coupled with a second element effective to provide the imaging data. First and second rf pulses are provided at first and second frequencies for exciting the imaging and functional elements, with imaging gradients applied therebetween to spatially separate the nuclei response for imaging. The second rf pulse is applied at a time after the first pulse which is the inverse of the spin coupling constant to select the transfer element nuclei which are spin coupled to the functional element nuclei for imaging. In a particular application, compounds such as glucose, lactate, or lactose, can be labeled with .sup.13 C and metabolic processes involving the compounds can be imaged with the sensitivity of .sup.1 H and the selectivity of .sup.13 C.

New integrable model of propagation of the few-cycle pulses in an anisotropic microdispersed medium

NASA Astrophysics Data System (ADS)

Sazonov, S. V.; Ustinov, N. V.

2018-03-01

We investigate the propagation of the few-cycle electromagnetic pulses in the anisotropic microdispersed medium. The effects of the anisotropy and spatial dispersion of the medium are created by the two sorts of the two-level atoms. The system of the material equations describing an evolution of the states of the atoms and the wave equations for the ordinary and extraordinary components of the pulses is derived. By applying the approximation of the sudden excitation to exclude the material variables, we reduce this system to the single nonlinear wave equation that generalizes the modified sine-Gordon equation and the Rabelo-Fokas equation. It is shown that this equation is integrable by means of the inverse scattering transformation method if an additional restriction on the parameters is imposed. The multisoliton solutions of this integrable generalization are constructed and investigated.

Fields of an ultrashort tightly focused radially polarized laser pulse in a linear response plasma

NASA Astrophysics Data System (ADS)

Salamin, Yousef I.

2017-10-01

Analytical expressions for the fields of a radially polarized, ultrashort, and tightly focused laser pulse propagating in a linear-response plasma are derived and discussed. The fields are obtained from solving the inhomogeneous wave equations for the vector and scalar potentials, linked by the Lorenz gauge, in a plasma background. First, the scalar potential is eliminated using the gauge condition, then the vector potential is synthesized from Fourier components of an initial uniform distribution of wavenumbers, and the inverse Fourier transformation is carried out term-by-term in a truncated series (finite sum). The zeroth-order term in, for example, the axial electric field component is shown to model a pulse much better than its widely used paraxial approximation counterpart. Some of the propagation characteristics of the fields are discussed and all fields are shown to have manifested the expected limits for propagation in a vacuum.

Control of Terahertz Emission by Ultrafast Spin-Charge Current Conversion at Rashba Interfaces

DOE PAGES

Jungfleisch, Matthias B.; Zhang, Qi; Zhang, Wei; ...

2018-05-18

Here, we show that a femtosecond spin-current pulse can generate terahertz (THz) transients at Rashba interfaces between two nonmagnetic materials. Our results unambiguously demonstrate the importance of the interface in this conversion process that we interpret in terms of the inverse Rashba Edelstein effect, in contrast to the THz emission in the bulk conversion process via the inverse spin-Hall effect. Furthermore, we show that at Rashba interfaces the THz-field amplitude can be controlled by the helicity of the light. The optical generation of electric photocurrents by these interfacial effects in the femtosecond regime will open up new opportunities in ultrafastmore » spintronics.« less

Control of Terahertz Emission by Ultrafast Spin-Charge Current Conversion at Rashba Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, Matthias B.; Zhang, Qi; Zhang, Wei

Here, we show that a femtosecond spin-current pulse can generate terahertz (THz) transients at Rashba interfaces between two nonmagnetic materials. Our results unambiguously demonstrate the importance of the interface in this conversion process that we interpret in terms of the inverse Rashba Edelstein effect, in contrast to the THz emission in the bulk conversion process via the inverse spin-Hall effect. Furthermore, we show that at Rashba interfaces the THz-field amplitude can be controlled by the helicity of the light. The optical generation of electric photocurrents by these interfacial effects in the femtosecond regime will open up new opportunities in ultrafastmore » spintronics.« less

Temperature measurements of inverse micelles coated in gold nanoparticles using fluorescence

NASA Astrophysics Data System (ADS)

Daley, Chad; Forrest, James A.; Speller, Ryan; William, Toews; McVeigh, Patrick; Emrick, Todd

2009-03-01

When nanoparticles are subject to laser radiation they have the ability to efficiently absorb energy from the beam and transform this energy into heat. Photothermal therapy uses this phenomenon to irreparably damage tissue surrounding nanoparticle conjugates. Despite the promise of this technique, there is no concensus on the damage mechanism or even the local heating. Here we present an experiment designed to measure local temperatures achieved in such processes. Ligand covered Gold nanoparticles are used to stabalize inverse micelles containing fluorescence dye in the water component. The fluorescence intensity being temperature dependent provides us with a means of measuring the temperature of the micelles as a function of time immediately following a laser pulse.

[Investigation of renal corticomedullary differentiation with age-related change on non-contrast-enhanced MRI].

PubMed

Shang, J N; Ren, K; Wu, W S; Lu, T; Sun, W G; Zhang, H G; Li, X D; Liu, Y

2016-05-24

To evaluate the relationship between renal corticomedullary differentiation, renal cortical thickness and age-related changes with non-contrast-enhanced steady-state free precession(SSFP) magnetic resonance imaging (MRI) and spatially selective inversion recovery(IR) pulse technology as well as its applied value . A total of 76 healthy volunteers had been recruited from August 2014 to June 2015 in First Hospital of China Medical University.All volunteers were divided into three groups: 2-40 years old, 41-60 years old, 61-80 years old. All 76 volunteers underwent non-contrast-enhanced steady-state free precession(SSFP) 3.0 T MRI scan using variable inversion times (TIs)(TI=1 000, 1 100, 1 200, 1 300, 1 400, 1 500, 1 600, 1 700 ms). The renal corticomedullary differentiation was observed and the signal intensity of renal cortex and medulla were measured respectively as well in order to calculate renal corticomedullary contrast ratio. Besides, renal cortical thickness and renal size were measured. All 76 volunteers were successfully performed all the sequences of MRI scan, including 152 useful imaging of kidney in total. The renal corticomedullary differentiation was clearly shown in all subjects. There was negative correlation between the optimal inversion time(TI) and age(r=-0.65, P<0.01). Similarly, negative correlation was observed between renal corticomedullary contrast ratio and age(r=-0.35, P<0.01). The mean renal cortical thickness of all subjects was (5.33±0.71)mm and there were statistically significant difference among those different groups, which was negative-related with age(r=-0.79, P<0.01). There was no statistically significant difference between sexuality and renal cortical thickness.Additionally, renal cortical thickness had no statistically significant difference in both sides of kidneys. The renal corticomedullary differentiation is depicted clearly by means of non-contrast-enhanced steady-state free precession MRI with spatially selective inversion recovery pulse technology. The optimal inversion time decreases along with the increase of age. In the meanwhile, the renal cortical thickness could be measured truthfully and accurately.

Range side lobe inversion for chirp-encoded dual-band tissue harmonic imaging.

PubMed

Shen, Che-Chou; Peng, Jun-Kai; Wu, Chi

2014-02-01

Dual-band (DB) harmonic imaging is performed by transmitting and receiving at both fundamental band (f0) and second-harmonic band (2f0). In our previous work, particular chirp excitation has been developed to increase the signal- to-noise ratio in DB harmonic imaging. However, spectral overlap between the second-order DB harmonic signals results in range side lobes in the pulse compression. In this study, a novel range side lobe inversion (RSI) method is developed to alleviate the level of range side lobes from spectral overlap. The method is implemented by firing an auxiliary chirp to change the polarity of the range side lobes so that the range side lobes can be suppressed in the combination of the original chirp and the auxiliary chirp. Hydrophone measurements show that the RSI method reduces the range side lobe level (RSLL) and thus increases the quality of pulse compression in DB harmonic imaging. With the signal bandwidth of 60%, the RSLL decreases from -23 dB to -36 dB and the corresponding compression quality improves from 78% to 94%. B-mode images also indicate that the magnitude of range side lobe is suppressed by 7 dB when the RSI method is applied.

Polarity inversion of AlN film grown on nitrided a-plane sapphire substrate with pulsed DC reactive sputtering

NASA Astrophysics Data System (ADS)

Noorprajuda, Marsetio; Ohtsuka, Makoto; Fukuyama, Hiroyuki

2018-04-01

The effect of oxygen partial pressure (PO2) on polarity and crystalline quality of AlN films grown on nitrided a-plane sapphire substrates by pulsed direct current (DC) reactive sputtering was investigated as a fundamental study. The polarity inversion of AlN from nitrogen (-c)-polarity to aluminum (+c)-polarity occurred during growth at a high PO2 of 9.4×103 Pa owing to Al-O octahedral formation at the interface of nitrided layer and AlN sputtered film which reset the polarity of AlN. The top part of the 1300 nm-thick AlN film sputtered at the high PO2 was polycrystallized. The crystalline quality was improved owing to the high kinetic energy of Al sputtered atom in the sputtering phenomena. Thinner AlN films were also fabricated at the high PO2 to eliminate the polycrystallization. For the 200 nm-thick AlN film sputtered at the high PO2, the full width at half-maximum values of the AlN (0002) and (10-12) X-ray diffraction rocking curves were 47 and 637 arcsec, respectively.

Optimization of contrast resolution by genetic algorithm in ultrasound tissue harmonic imaging.

PubMed

Ménigot, Sébastien; Girault, Jean-Marc

2016-09-01

The development of ultrasound imaging techniques such as pulse inversion has improved tissue harmonic imaging. Nevertheless, no recommendation has been made to date for the design of the waveform transmitted through the medium being explored. Our aim was therefore to find automatically the optimal "imaging" wave which maximized the contrast resolution without a priori information. To overcome assumption regarding the waveform, a genetic algorithm investigated the medium thanks to the transmission of stochastic "explorer" waves. Moreover, these stochastic signals could be constrained by the type of generator available (bipolar or arbitrary). To implement it, we changed the current pulse inversion imaging system by including feedback. Thus the method optimized the contrast resolution by adaptively selecting the samples of the excitation. In simulation, we benchmarked the contrast effectiveness of the best found transmitted stochastic commands and the usual fixed-frequency command. The optimization method converged quickly after around 300 iterations in the same optimal area. These results were confirmed experimentally. In the experimental case, the contrast resolution measured on a radiofrequency line could be improved by 6% with a bipolar generator and it could still increase by 15% with an arbitrary waveform generator. Copyright © 2016 Elsevier B.V. All rights reserved.

Support Minimized Inversion of Acoustic and Elastic Wave Scattering

NASA Astrophysics Data System (ADS)

Safaeinili, Ali

Inversion of limited data is common in many areas of NDE such as X-ray Computed Tomography (CT), Ultrasonic and eddy current flaw characterization and imaging. In many applications, it is common to have a bias toward a solution with minimum (L^2)^2 norm without any physical justification. When it is a priori known that objects are compact as, say, with cracks and voids, by choosing "Minimum Support" functional instead of the minimum (L^2)^2 norm, an image can be obtained that is equally in agreement with the available data, while it is more consistent with what is most probably seen in the real world. We have utilized a minimum support functional to find a solution with the smallest volume. This inversion algorithm is most successful in reconstructing objects that are compact like voids and cracks. To verify this idea, we first performed a variational nonlinear inversion of acoustic backscatter data using minimum support objective function. A full nonlinear forward model was used to accurately study the effectiveness of the minimized support inversion without error due to the linear (Born) approximation. After successful inversions using a full nonlinear forward model, a linearized acoustic inversion was developed to increase speed and efficiency in imaging process. The results indicate that by using minimum support functional, we can accurately size and characterize voids and/or cracks which otherwise might be uncharacterizable. An extremely important feature of support minimized inversion is its ability to compensate for unknown absolute phase (zero-of-time). Zero-of-time ambiguity is a serious problem in the inversion of the pulse-echo data. The minimum support inversion was successfully used for the inversion of acoustic backscatter data due to compact scatterers without the knowledge of the zero-of-time. The main drawback to this type of inversion is its computer intensiveness. In order to make this type of constrained inversion available for common use, work needs to be performed in three areas: (1) exploitation of state-of-the-art parallel computation, (2) improvement of theoretical formulation of the scattering process for better computation efficiency, and (3) development of better methods for guiding the non-linear inversion. (Abstract shortened by UMI.).

Conformal drug delivery and instantaneous monitoring based on an inverse synthesis method at a diagnostic ultrasound platform

NASA Astrophysics Data System (ADS)

Xu, Shanshan; Zong, Yujin; Liu, Xiaodong; Lu, Mingzhu; Wan, Mingxi

2017-03-01

In this paper, based on a programmable diagnostic ultrasound scanner, a combined approach was proposed, in which a variable-sized focal region wherein the acoustic pressure is above the ultrasound contrast agents (UCA) fragmentation threshold is synthesized by reasonably matching the excitation voltage and the transmit aperture of the linear array at 5MHz, the UCAs' temporal and spatial distribution before and after the microbubbles fragmentation is monitored using the plane-wave transmission and reception at 400Hz and, simultaneously, the broadband noise emission during the microbubbles fragmentation is extracted using the backscattering of focused release bursts (destruction pulse) themselves on the linear array. Then, acquired radio frequency (RF) data are processed to draw parameters which can be correlated with the indicator of broadband noise emission level, namely inertial cavitation dose (ICD) and microbubble fragmentation efficiency, namely decay rate of microbubbles.

PANDORA, a large volume low-energy neutron detector with real-time neutron-gamma discrimination

NASA Astrophysics Data System (ADS)

Stuhl, L.; Sasano, M.; Yako, K.; Yasuda, J.; Baba, H.; Ota, S.; Uesaka, T.

2017-09-01

The PANDORA (Particle Analyzer Neutron Detector Of Real-time Acquisition) system, which was developed for use in inverse kinematics experiments with unstable isotope beams, is a neutron detector based on a plastic scintillator coupled to a digital readout. PANDORA can be used for any reaction study involving the emission of low energy neutrons (100 keV-10 MeV) where background suppression and an increased signal-to-noise ratio are crucial. The digital readout system provides an opportunity for pulse shape discrimination (PSD) of the detected particles as well as intelligent triggering based on PSD. The figure of merit results of PANDORA are compared to the data in literature. Using PANDORA, 91 ± 1% of all detected neutrons can be separated, while 91 ± 1% of the detected gamma rays can be excluded, reducing the gamma ray background by one order of magnitude.

Light collection and pulse-shape discrimination in elongated scintillator cells for the PROSPECT reactor antineutrino experiment

DOE PAGES

Ashenfelter, J.; Jaffe, D.; Diwan, M. V.; ...

2015-11-06

A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron-gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. As a result, key design features for optimizing MeV-scale response and background rejection capabilities are identified.

UV laser interaction with a fluorescent dye solution studied using pulsed digital holography.

PubMed

Amer, Eynas; Gren, Per; Sjödahl, Mikael

2013-10-21

A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promising technique for quantitative study of fluorescent species.

Microbubble responses to a similar mechanical index with different real-time perfusion imaging techniques.

PubMed

Porter, Thomas R; Oberdorfer, Joseph; Rafter, Patrick; Lof, John; Xie, Feng

2003-08-01

The purpose of this study was to determine differences in contrast enhancement and microbubble destruction rates with current commercially available low-mechanical index (MI) real-time perfusion imaging modalities. A tissue-mimicking phantom was developed that had vessels at 3 cm (near field) and 9 cm (far field) from a real-time transducer. Perfluorocarbon-exposed sonicated dextrose albumin microbubbles (PESDA) were injected proximal to a mixing chamber, and then passed through these vessels while the region was insonified with either pulses of alternating polarity with pulse inversion Doppler (PID) or pulses of alternating amplitude by power modulation (PM) at MIs of 0.1, 0.2 and 0.3. Effluent microbubble concentration, contrast intensity and the slope of digital contrast intensity vs. time were measured. Our results demonstrated that microbubble destruction already occurs with PID at an MI of 0.1. Contrast intensity seen with PID was less than with PM. Therefore, differences in contrast enhancement and microbubble destruction rates occur at a similar MI setting when using different real-time pulse sequence schemes.

Suppression of Protonated Organic Solvents in NMR Spectroscopy Using a Perfect Echo Low-Pass Filtration Pulse Sequence.

PubMed

Howe, Peter W A

2018-04-03

Proton NMR spectra are usually acquired using deuterated solvents, but in many cases it is necessary to obtain spectra on samples in protonated solvents. In these cases, the intense resonances of the protonated solvents need to be suppressed to maximize sensitivity and spectral quality. A wide range of highly effective solvent suppression methods have been developed, but additional measures are needed to suppress the 13 C satellites of the solvent. Because the satellites represent 1.1% of the original solvent signal, they remain problematic if unsuppressed. The recently proposed DISPEL pulse sequences suppress 13 C satellites extremely effectively, and this Technical Note demonstrates that combining DISPEL and presaturation results in exceptionally effective solvent suppression. An important element in the effectiveness is volume selection, which is inherent within the DISPEL sequence. Spectra acquired in protonated dimethlysulfoxide and tetrahydrofuran show that optimum results are obtained by modifying the phase cycle, cycling the pulse-field gradients, and using broadband 13 C inversion pulses to reduce the effects of radiofrequency offset and inhomogeneity.

Kinetic model of stimulated emission created by resonance pumping of aluminum laser-induced plasma

NASA Astrophysics Data System (ADS)

Gornushkin, I. B.; Kazakov, A. Ya.

2017-06-01

Stimulated emission observed experimentally in an aluminum laser induced plasma is modeled via a kinetic approach. The simulated emission at several cascade transitions is created by a pump laser guided through the plasma at several microseconds after its creation and tuned in resonance with the strong 3s23p-3s24s transition at 266 nm. A two-dimensional space-time collisional radiative plasma model explains the creation of the population inversion and lasing at wavelengths of 2100 n m and 396.1 nm. The population inversion for lasing at 2100 n m is created by depopulation of the ground 3s23p state and population of the 3s25s state via the absorption of the resonant radiation at 266 nm. The population inversion for lasing at 396.1 nm occurs during the laser pulse via the decay of the population of the pumped 3s25s state to the excited 3s24s state via cascade transitions driven optically and by collisions. In particular, efficient are the mixing transitions between neighboring states separated by small gaps on the order of k T at plasma temperatures of 5000-10 000 K. The model predicts that the population inversion and corresponding gain may reach high values even at very moderate pump energy of several μJ per pulse. The efficiency of lasing at 2100 n m and 396.1 nm is estimated to be ˜3% and 0.05%, correspondingly with respect to the pump laser intensity. The gain for lasing at 396.1 nm can reach as high as ˜40 cm-1. The polarization effect that the pump radiation at 266 nm imposes on the stimulated emission at 396.1 nm is discussed. The calculated results are favorably compared to experimental data.

Direct and accelerated parameter mapping using the unscented Kalman filter.

PubMed

Zhao, Li; Feng, Xue; Meyer, Craig H

2016-05-01

To accelerate parameter mapping using a new paradigm that combines image reconstruction and model regression as a parameter state-tracking problem. In T2 mapping, the T2 map is first encoded in parameter space by multi-TE measurements and then encoded by Fourier transformation with readout/phase encoding gradients. Using a state transition function and a measurement function, the unscented Kalman filter can describe T2 mapping as a dynamic system and directly estimate the T2 map from the k-space data. The proposed method was validated with a numerical brain phantom and volunteer experiments with a multiple-contrast spin echo sequence. Its performance was compared with a conjugate-gradient nonlinear inversion method at undersampling factors of 2 to 8. An accelerated pulse sequence was developed based on this method to achieve prospective undersampling. Compared with the nonlinear inversion reconstruction, the proposed method had higher precision, improved structural similarity and reduced normalized root mean squared error, with acceleration factors up to 8 in numerical phantom and volunteer studies. This work describes a new perspective on parameter mapping by state tracking. The unscented Kalman filter provides a highly accelerated and efficient paradigm for T2 mapping. © 2015 Wiley Periodicals, Inc.

Location of acoustic radiators and inversion for energy density using radio-frequency sources and thunder recordings

NASA Astrophysics Data System (ADS)

Anderson, J.; Johnson, J. B.; Arechiga, R. O.; Edens, H. E.; Thomas, R. J.

2011-12-01

We use radio frequency (VHF) pulse locations mapped with the New Mexico Tech Lightning Mapping Array (LMA) to study the distribution of thunder sources in lightning channels. A least squares inversion is used to fit channel acoustic energy radiation with broadband (0.01 to 500 Hz) acoustic recordings using microphones deployed local (< 10 km) to the lightning. We model the thunder (acoustic) source as a superposition of line segments connecting the LMA VHF pulses. An optimum branching algorithm is used to reconstruct conductive channels delineated by VHF sources, which we discretize as a superposition of finely-spaced (0.25 m) acoustic point sources. We consider total radiated thunder as a weighted superposition of acoustic waves from individual channels, each with a constant current along its length that is presumed to be proportional to acoustic energy density radiated per unit length. Merged channels are considered as a linear sum of current-carrying branches and radiate proportionally greater acoustic energy. Synthetic energy time series for a given microphone location are calculated for each independent channel. We then use a non-negative least squares inversion to solve for channel energy densities to match the energy time series determined from broadband acoustic recordings across a 4-station microphone network. Events analyzed by this method have so far included 300-1000 VHF sources, and correlations as high as 0.5 between synthetic and recorded thunder energy were obtained, despite the presence of wind noise and 10-30 m uncertainty in VHF source locations.

Two collateral problems in the framework of ground-penetrating radar data inversion: influence of the emitted waveform outline and radargram comparison.

NASA Astrophysics Data System (ADS)

Oliveira, Rui Jorge; Caldeira, Bento; Borges, José Fernando

2017-04-01

Obtain three-dimensional models of the physical properties of buried structures in the subsurface by inversion of GPR data is an appeal to Archaeology and a challenge to Geophysics. Along the research of solutions to resolve this issue stand out two major problems that need to be solved: 1) Establishment the basis of the computation that allows assign numerically in the synthetic radargrams, the physical conditions at which the GPR wave were generated; and 2) automatic comparison of the computed synthetic radargrams with the correspondent observed ones. The influence of the pulse shape in GPR data processing was a studied topic. The pulse outline emitted by GPR antennas was experimentally acquired and this information has been used in the deconvolution operation, carried out by iterative process, similarly the approach used in seismology to obtain the receiver functions. In order to establish the comparison between real and synthetic radargrams, were tested automatic image adjustment algorithms, which search the best fit between two radargramas and quantify their differences through the calculation of Normalized Root Mean Square Deviation (NRMSD). After the implementation of the last tests, the NRMSD between the synthetic and real data is about 19% (initially it was 29%). These procedures are essential to be able to perform an inversion of GPR data obtained in the field. Acknowledgment: This work is co-funded by the European Union through the European Regional Development Fund, included in the COMPETE 2020 (Operational Program Competitiveness and Internationalization) through the ICT project (UID/GEO/04683/2013) with the reference POCI-01-0145-FEDER-007690.

Arterial stiffness and wave reflection: sex differences and relationship with left ventricular diastolic function.

PubMed

Russo, Cesare; Jin, Zhezhen; Palmieri, Vittorio; Homma, Shunichi; Rundek, Tatjana; Elkind, Mitchell S V; Sacco, Ralph L; Di Tullio, Marco R

2012-08-01

Increased arterial stiffness and wave reflection have been reported in heart failure with normal ejection fraction (HFNEF) and in asymptomatic left ventricular (LV) diastolic dysfunction, a precursor of HFNEF. It is unclear whether women, who have higher frequency of HFNEF, are more vulnerable than men to the deleterious effects of arterial stiffness on LV diastolic function. We investigated, in a large community-based cohort, whether sex differences exist in the relationship among arterial stiffness, wave reflection, and LV diastolic function. Arterial stiffness and wave reflection were assessed in 983 participants from the Cardiovascular Abnormalities and Brain Lesions study using applanation tonometry. The central pulse pressure/stroke volume index, total arterial compliance, pulse pressure amplification, and augmentation index were used as parameters of arterial stiffness and wave reflection. LV diastolic function was evaluated by 2-dimensional echocardiography and tissue-Doppler imaging. Arterial stiffness and wave reflection were greater in women compared with men, independent of body size and heart rate (all P<0.01), and showed inverse relationships with parameters of diastolic function in both sexes. Further adjustment for cardiovascular risk factors attenuated these relationships; however, a higher central pulse pressure/stroke volume index predicted LV diastolic dysfunction in women (odds ratio, 1.54; 95% confidence intervals, 1.03 to 2.30) and men (odds ratio, 2.09; 95% confidence interval, 1.30 to 3.39), independent of other risk factors. In conclusion, in our community-based cohort study, higher arterial stiffness was associated with worse LV diastolic function in men and women. Women's higher arterial stiffness, independent of body size, may contribute to their greater susceptibility to develop HFNEF.

Full analytical solution of the bloch equation when using a hyperbolic-secant driving function.

PubMed

Zhang, Jinjin; Garwood, Michael; Park, Jang-Yeon

2017-04-01

The frequency-swept pulse known as the hyperbolic-secant (HS) pulse is popular in NMR for achieving adiabatic spin inversion. The HS pulse has also shown utility for achieving excitation and refocusing in gradient-echo and spin-echo sequences, including new ultrashort echo-time imaging (e.g., Sweep Imaging with Fourier Transform, SWIFT) and B 1 mapping techniques. To facilitate the analysis of these techniques, the complete theoretical solution of the Bloch equation, as driven by the HS pulse, was derived for an arbitrary state of initial magnetization. The solution of the Bloch-Riccati equation for transverse and longitudinal magnetization for an arbitrary initial state was derived analytically in terms of HS pulse parameters. The analytical solution was compared with the solutions using both the Runge-Kutta method and the small-tip approximation. The analytical solution was demonstrated on different initial states at different frequency offsets with/without a combination of HS pulses. Evolution of the transverse magnetization was influenced significantly by the choice of HS pulse parameters. The deviation of the magnitude of the transverse magnetization, as obtained by comparing the small-tip approximation to the analytical solution, was < 5% for flip angles < 30 °, but > 10% for the flip angles > 40 °. The derived analytical solution provides insights into the influence of HS pulse parameters on the magnetization evolution. Magn Reson Med 77:1630-1638, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Circuit for monitoring temperature of high-voltage equipment

DOEpatents

Jacobs, Martin E.

1976-01-01

This invention relates to an improved circuit for measuring temperature in a region at high electric potential and generating a read-out of the same in a region at lower potential. The circuit is specially designed to combine high sensitivity, stability, and accuracy. A major portion of the circuit situated in the high-potential region can take the form of an integrated circuit. The preferred form of the circuit includes an input section which is situated in the high-potential region and comprises a temperature-compensated thermocouple circuit for sensing temperature, an oscillator circuit for generating a train of ramp voltages whose rise time varies inversely with the thermocouple output, a comparator and switching circuit for converting the oscillator output to pulses whose frequency is proportional to the thermocouple output, and a light-emitting diode which is energized by these pulses. An optical coupling transmits the light pulses generated by the diode to an output section of the circuit, situated in a region at ground. The output section comprises means for converting the transmitted pulses to electrical pulses of corresponding frequency, means for amplifying the electrical pulses, and means for displaying the frequency of the same. The preferred embodiment of the overall circuit is designed so that the frequency of the output signal in hertz and tenths of hertz is equal to the sensed temperature in degrees and tenths of degrees.

Inverse Analysis of Irradiated NuclearMaterial Gamma Spectra via Nonlinear Optimization

NASA Astrophysics Data System (ADS)

Dean, Garrett James

Nuclear forensics is the collection of technical methods used to identify the provenance of nuclear material interdicted outside of regulatory control. Techniques employed in nuclear forensics include optical microscopy, gas chromatography, mass spectrometry, and alpha, beta, and gamma spectrometry. This dissertation focuses on the application of inverse analysis to gamma spectroscopy to estimate the history of pulse irradiated nuclear material. Previous work in this area has (1) utilized destructive analysis techniques to supplement the nondestructive gamma measurements, and (2) been applied to samples composed of spent nuclear fuel with long irradiation and cooling times. Previous analyses have employed local nonlinear solvers, simple empirical models of gamma spectral features, and simple detector models of gamma spectral features. The algorithm described in this dissertation uses a forward model of the irradiation and measurement process within a global nonlinear optimizer to estimate the unknown irradiation history of pulse irradiated nuclear material. The forward model includes a detector response function for photopeaks only. The algorithm uses a novel hybrid global and local search algorithm to quickly estimate the irradiation parameters, including neutron fluence, cooling time and original composition. Sequential, time correlated series of measurements are used to reduce the uncertainty in the estimated irradiation parameters. This algorithm allows for in situ measurements of interdicted irradiated material. The increase in analysis speed comes with a decrease in information that can be determined, but the sample fluence, cooling time, and composition can be determined within minutes of a measurement. Furthermore, pulse irradiated nuclear material has a characteristic feature that irradiation time and flux cannot be independently estimated. The algorithm has been tested against pulse irradiated samples of pure special nuclear material with cooling times of four minutes to seven hours. The algorithm described is capable of determining the cooling time and fluence the sample was exposed to within 10% as well as roughly estimating the relative concentrations of nuclides present in the original composition.

A laboratory validation study of the time-lapse oscillatory pumping test for leakage detection in geological repositories

NASA Astrophysics Data System (ADS)

Sun, Alexander Y.; Lu, Jiemin; Islam, Akand

2017-05-01

Geologic repositories are extensively used for disposing byproducts in mineral and energy industries. The safety and reliability of these repositories are a primary concern to environmental regulators and the public. Time-lapse oscillatory pumping test (OPT) has been introduced recently as a pressure-based technique for detecting potential leakage in geologic repositories. By routinely conducting OPT at a number of pulsing frequencies, an operator may identify the potential repository anomalies in the frequency domain, alleviating the ambiguity caused by reservoir noise and improving the signal-to-noise ratio. Building on previous theoretical and field studies, this work performed a series of laboratory experiments to validate the concept of time-lapse OPT using a custom made, stainless steel tank under relatively high pressures. The experimental configuration simulates a miniature geologic storage repository consisting of three layers (i.e., injection zone, caprock, and above-zone aquifer). Results show that leakage in the injection zone led to deviations in the power spectrum of observed pressure data, and the amplitude of which also increases with decreasing pulsing frequencies. The experimental results are further analyzed by developing a 3D flow model, using which the model parameters are estimated through frequency domain inversion.

Development and investigation of a magnetic resonance imaging-compatible microlens-based optical detector

NASA Astrophysics Data System (ADS)

Paar, Steffen; Umathum, Reiner; Jiang, Xiaoming; Majer, Charles L.; Peter, Jörg

2015-09-01

A noncontact optical detector for in vivo imaging has been developed that is compatible with magnetic resonance imaging (MRI). The optical detector employs microlens arrays and might be classified as a plenoptic camera. As a resulting of its design, the detector possesses a slim thickness and is self-shielding against radio frequency (RF) pulses. For experimental investigation, a total of six optical detectors were arranged in a cylindrical fashion, with the imaged object positioned in the center of this assembly. A purposely designed RF volume resonator coil has been developed and is incorporated within the optical imaging system. The whole assembly was placed into the bore of a 1.5 T patient-sized MRI scanner. Simple-geometry phantom studies were performed to assess compatibility and performance characteristics regarding both optical and MR imaging systems. A bimodal ex vivo nude mouse measurement was conducted. From the MRI data, the subject surface was extracted. Optical images were projected on this surface by means of an inverse mapping algorithm. Simultaneous measurements did not reveal influences from the magnetic field and RF pulses onto optical detector performance (spatial resolution, sensitivity). No significant influence of the optical imaging system onto MRI performance was detectable.

Development and investigation of a magnetic resonance imaging-compatible microlens-based optical detector.

PubMed

Paar, Steffen; Umathum, Reiner; Jiang, Xiaoming; Majer, Charles L; Peter, Jörg

2015-09-01

A noncontact optical detector for in vivo imaging has been developed that is compatible with magnetic resonance imaging (MRI). The optical detector employs microlens arrays and might be classified as a plenoptic camera. As a resulting of its design, the detector possesses a slim thickness and is self-shielding against radio frequency (RF) pulses. For experimental investigation, a total of six optical detectors were arranged in a cylindrical fashion, with the imaged object positioned in the center of this assembly. A purposely designed RF volume resonator coil has been developed and is incorporated within the optical imaging system. The whole assembly was placed into the bore of a 1.5 T patient-sized MRI scanner. Simple-geometry phantom studies were performed to assess compatibility and performance characteristics regarding both optical and MR imaging systems. A bimodal ex vivo nude mouse measurement was conducted. From the MRI data, the subject surface was extracted. Optical images were projected on this surface by means of an inverse mapping algorithm. Simultaneous measurements did not reveal influences from the magnetic field and RF pulses onto optical detector performance (spatial resolution, sensitivity). No significant influence of the optical imaging system onto MRI performance was detectable.

Cardiac cell: a biological laser?

PubMed

Chorvat, D; Chorvatova, A

2008-04-01

We present a new concept of cardiac cells based on an analogy with lasers, practical implementations of quantum resonators. In this concept, each cardiac cell comprises a network of independent nodes, characterised by a set of discrete energy levels and certain transition probabilities between them. Interaction between the nodes is given by threshold-limited energy transfer, leading to quantum-like behaviour of the whole network. We propose that in cardiomyocytes, during each excitation-contraction coupling cycle, stochastic calcium release and the unitary properties of ionic channels constitute an analogue to laser active medium prone to "population inversion" and "spontaneous emission" phenomena. This medium, when powered by an incoming threshold-reaching voltage discharge in the form of an action potential, responds to the calcium influx through L-type calcium channels by stimulated emission of Ca2+ ions in a coherent, synchronised and amplified release process known as calcium-induced calcium release. In parallel, phosphorylation-stimulated molecular amplification in protein cascades adds tuneable features to the cells. In this framework, the heart can be viewed as a coherent network of synchronously firing cardiomyocytes behaving as pulsed laser-like amplifiers, coupled to pulse-generating pacemaker master-oscillators. The concept brings a new viewpoint on cardiac diseases as possible alterations of "cell lasing" properties.

Headspace solid-phase microextraction and gas chromatographic analysis of low-molecular-weight sulfur volatiles with pulsed flame photometric detection and quantification by a stable isotope dilution assay.

PubMed

Ullrich, Sebastian; Neef, Sylvia K; Schmarr, Hans-Georg

2018-02-01

Low-molecular-weight volatile sulfur compounds such as thiols, sulfides, disulfides as well as thioacetates cause a sulfidic off-flavor in wines even at low concentration levels. The proposed analytical method for quantification of these compounds in wine is based on headspace solid-phase microextraction, followed by gas chromatographic analysis with sulfur-specific detection using a pulsed flame photometric detector. Robust quantification was achieved via a stable isotope dilution assay using commercial and synthesized deuterated isotopic standards. The necessary chromatographic separation of analytes and isotopic standards benefits from the inverse isotope effect realized on an apolar polydimethylsiloxane stationary phase of increased film thickness. Interferences with sulfur-specific detection in wine caused by sulfur dioxide were minimized by addition of propanal. The method provides adequate validation data, with good repeatability and limits of detection and quantification. It suits the requirements of wine quality management, allowing the control of oenological treatments to counteract an eventual formation of excessively high concentration of such malodorous compounds. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shear wave elastography using amplitude-modulated acoustic radiation force and phase-sensitive optical coherence tomography

NASA Astrophysics Data System (ADS)

Nguyen, Thu-Mai; Arnal, Bastien; Song, Shaozhen; Huang, Zhihong; Wang, Ruikang K.; O'Donnell, Matthew

2015-01-01

Investigating the elasticity of ocular tissue (cornea and intraocular lens) could help the understanding and management of pathologies related to biomechanical deficiency. In previous studies, we introduced a setup based on optical coherence tomography for shear wave elastography (SWE) with high resolution and high sensitivity. SWE determines tissue stiffness from the propagation speed of shear waves launched within tissue. We proposed acoustic radiation force to remotely induce shear waves by focusing an ultrasound (US) beam in tissue, similar to several elastography techniques. Minimizing the maximum US pressure is essential in ophthalmology for safety reasons. For this purpose, we propose a pulse compression approach. It utilizes coded US emissions to generate shear waves where the energy is spread over a long emission, and then numerically compressed into a short, localized, and high-energy pulse. We used a 7.5-MHz single-element focused transducer driven by coded excitations where the amplitude is modulated by a linear frequency-swept square wave (1 to 7 kHz). An inverse filter approach was used for compression. We demonstrate the feasibility of performing shear wave elastography measurements in tissue-mimicking phantoms at low US pressures (mechanical index <0.6).

Shear wave elastography using amplitude-modulated acoustic radiation force and phase-sensitive optical coherence tomography

PubMed Central

Nguyen, Thu-Mai; Arnal, Bastien; Song, Shaozhen; Huang, Zhihong; Wang, Ruikang K.; O’Donnell, Matthew

2015-01-01

Abstract. Investigating the elasticity of ocular tissue (cornea and intraocular lens) could help the understanding and management of pathologies related to biomechanical deficiency. In previous studies, we introduced a setup based on optical coherence tomography for shear wave elastography (SWE) with high resolution and high sensitivity. SWE determines tissue stiffness from the propagation speed of shear waves launched within tissue. We proposed acoustic radiation force to remotely induce shear waves by focusing an ultrasound (US) beam in tissue, similar to several elastography techniques. Minimizing the maximum US pressure is essential in ophthalmology for safety reasons. For this purpose, we propose a pulse compression approach. It utilizes coded US emissions to generate shear waves where the energy is spread over a long emission, and then numerically compressed into a short, localized, and high-energy pulse. We used a 7.5-MHz single-element focused transducer driven by coded excitations where the amplitude is modulated by a linear frequency-swept square wave (1 to 7 kHz). An inverse filter approach was used for compression. We demonstrate the feasibility of performing shear wave elastography measurements in tissue-mimicking phantoms at low US pressures (mechanical index <0.6). PMID:25554970

Multinuclear NMR Study of the Pressure Dependence for Carbonate Exchange in the UO 2(CO 3) 3 4-(aq) Ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Rene L.; Harley, Stephen J.; Ohlin, C. André

2011-09-16

Rates of carbonate exchange by two pH-sensitive pathways between aqueous carbonate ion and UO 2(CO 3) 3 4-(aq) (see picture) are measured by high-pressure NMR. To accomplish this, a custom pulse sequence is employed to achieve selective inversion. Rates of chemical exchange are determined by modeling the return to equilibrium.

Multinuclear NMR study of the pressure dependence for carbonate exchange in the [UO2(CO3)3]4- (aq) ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Rene L.; Harley, S. J.; Ohlin, C. A.

2011-09-16

Rates of carbonate exchange by two pH-sensitive pathways between aqueous carbonate ion and UO₂(CO₃)₃⁴⁻(aq) are measured by high-pressure NMR. To accomplish this, a custom pulse sequence is employed to achieve selective inversion. Rates of chemical exchange are determined by modeling the return to equilibrium.

23RD International Conference on Phenomena in Ionized Gases, Volume 3

DTIC Science & Technology

1998-12-01

discharges, and high pressure glows; arcs; high frequency discharges; ionospheric magnetospheric, and astrophysical plasmas; plasma diagnostic methods ...kf) in pulse reflectometry. Second, it different frequencies , and an Abel inversion is gives a quantitative model of the behaviour of the wave... design V method in the case of narrow mutual pitch of surface electrodes for high concentration ozone generation. 2. Experimental setup 20 The electrode

High-resolution maps of magnetization transfer with inherent correction for RF inhomogeneity and T1 relaxation obtained from 3D FLASH MRI.

PubMed

Helms, Gunther; Dathe, Henning; Kallenberg, Kai; Dechent, Peter

2008-12-01

An empirical equation for the magnetization transfer (MT) FLASH signal is derived by analogy to dual-excitation FLASH, introducing a novel semiquantitative parameter for MT, the percentage saturation imposed by one MT pulse during TR. This parameter is obtained by a linear transformation of the inverse signal, using two reference experiments of proton density and T(1) weighting. The influence of sequence parameters on the MT saturation was studied. An 8.5-min protocol for brain imaging at 3 T was based on nonselective sagittal 3D-FLASH at 1.25 mm isotropic resolution using partial acquisition techniques (TR/TE/alpha = 25ms/4.9ms/5 degrees or 11ms/4.9ms/15 degrees for the T(1) reference). A 12.8 ms Gaussian MT pulse was applied 2.2 kHz off-resonance with 540 degrees flip angle. The MT saturation maps showed an excellent contrast in the brain due to clearly separated distributions for white and gray matter and cerebrospinal fluid. Within the limits of the approximation (excitation <15 degrees , TR/T(1) less sign 1) the MT term depends mainly on TR, the energy and offset of the MT pulse, but hardly on excitation and T(1) relaxation. It is inherently compensated for inhomogeneities of receive and transmit RF fields. The MT saturation appeared to be a sensitive parameter to depict MS lesions and alterations of normal-appearing white matter. (c) 2008 Wiley-Liss, Inc.

Beam engineering for zero conicity cutting and drilling with ultra fast laser (Conference Presentation)

NASA Astrophysics Data System (ADS)

Letan, Amelie; Mishchik, Konstantin; Audouard, Eric; Hoenninger, Clemens; Mottay, Eric P.

2017-03-01

With the development of high average power, high repetition rate, industrial ultrafast lasers, it is now possible to achieve a high throughput with femtosecond laser processing, providing that the operating parameters are finely tuned to the application. Femtosecond lasers play a key role in these processes, due to their ability to high quality micro processing. They are able to drill high thickness holes (up to 1 mm) with arbitrary shapes, such as zero-conicity or even inversed taper, but can also perform zero-taper cutting. A clear understanding of all the processing steps necessary to optimize the processing speed is a main challenge for industrial developments. Indeed, the laser parameters are not independent of the beam steering devices. Pulses energy and repetition rate have to be precisely adjusted to the beam angle with the sample, and to the temporal and spatial sequences of pulses superposition. The purpose of the present work is to identify the role of these parameters for high aspect ratio drilling and cutting not only with experimental trials, but also with numerical estimations, using a simple engineering model based on the two temperature description of ultra-fast ablation. Assuming a nonlinear logarithmic response of the materials to ultrafast pulses, each material can be described by only two adjustable parameters. Simple assumptions allow to predict the effect of beam velocity and non-normal incident beams to estimate profile shapes and processing time.

Method and apparatus for generating coherent near 14 and near 16 micron radiation

DOEpatents

Krupke, William F.

1977-01-01

A method and apparatus for producing coherent radiation in CO.sub.2 vibrational-rotational transitions at wavelengths near 14 and 16 microns. This is accomplished by passing a mixture of N.sub.2 and Ar through a glow discharge producing a high vibrational temperature in the N.sub.2, passing the excited N.sub.2 through a nozzle bank creating a supersonic flow thereof, injecting the CO.sub.2 in the supersonic flow creating a population inversion in the CO.sub.2, and directing the saturating pulse of radiation near 10.6 or 9.6 microns into the excited CO.sub.2 creating a population inversion producing coherent radiation at 14 or 16 microns, respectively.

Theoretical and experimental investigations on the cooling capacity distributions at the stages in the thermally-coupled two-stage Stirling-type pulse tube cryocooler without external precooling

NASA Astrophysics Data System (ADS)

Tan, Jun; Dang, Haizheng

2017-03-01

The two-stage Stirling-type pulse tube cryocooler (SPTC) has advantages in simultaneously providing the cooling powers at two different temperatures, and the capacity in distributing these cooling capacities between the stages is significant to its practical applications. In this paper, a theoretical model of the thermally-coupled two-stage SPTC without external precooling is established based on the electric circuit analogy with considering real gas effects, and the simulations of both the cooling performances and PV power distribution between stages are conducted. The results indicate that the PV power is inversely proportional to the acoustic impedance of each stage, and the cooling capacity distribution is determined by the cold finger cooling efficiency and the PV power into each stage together. The design methods of the cold fingers to achieve both the desired PV power and the cooling capacity distribution between the stages are summarized. The two-stage SPTC is developed and tested based on the above theoretical investigations, and the experimental results show that it can simultaneously achieve 0.69 W at 30 K and 3.1 W at 85 K with an electric input power of 330 W and a reject temperature of 300 K. The consistency between the simulated and the experimental results is observed and the theoretical investigations are experimentally verified.

Modeling of nanosecond pulsed laser processing of polymers in air and water

NASA Astrophysics Data System (ADS)

Marla, Deepak; Zhang, Yang; Hattel, Jesper H.; Spangenberg, Jon

2018-07-01

Laser ablation of polymers in water is known to generate distinct surface characteristics as compared to that in air. In order to understand the role of ambient media during laser ablation of polymers, this paper aims to develop a physics-based model of the process considering the effect of ambient media. Therefore, in the present work, models are developed for laser ablation of polymers in air and water considering all the relevant physical phenomena such as laser–polymer interaction, plasma generation, plasma expansion and plasma shielding. The current work focuses on near-infrared laser radiation (λ = 1064 nm) of nanosecond pulse duration. The laser–polymer interaction at such wavelengths is purely photo-thermal in nature and the laser–plasma interaction is assumed to occur mainly by inverse-bremsstrahlung photon absorption. The computational model is based on the finite volume method using the Crank‑Nicholson scheme. The model predicts that underwater laser ablation results in subsurface heating effect in the polymer and confinement of the laser generated plasma, which makes it different from laser ablation in air. Plasma expansion velocities are much lower in water than in air. This results in an enhanced plasma shielding effect in the case of water. The predicted results of ablation depth versus fluence from the model are in qualitative agreement with those observed in experiments.

Ultrasonic Method for Measuring Internal Temperature Profile in Heated Materials

NASA Astrophysics Data System (ADS)

Ihara, I.; Takahashi, M.

2008-02-01

A new ultrasonic method for internal temperature measurement is presented. The principle of the method is based on temperature dependence of the velocity of the ultrasonic wave propagating through the material. An inverse analysis to determine the temperature profile in a heated material is developed and an experiment is carried out to verify the validity of the developed method. A single side of a silicone rubber plate of 30 mm thickness is heated and ultrasonic pulse-echo measurements are then performed during heating. A change in transit time of ultrasonic wave in the heated rubber plate is monitored and used to determine the transient variation in internal temperature distribution of the rubber. The internal temperature distribution determined ultrasonically agrees well with both obtained using commercial thermocouples installed in the rubber and estimated theoretically.

Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

DOE PAGES

Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

2015-12-28

For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current—this is the chiral magnetic effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity toward the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electricmore » and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. In conclusion, we devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.« less

Ferroelectric domain inversion and its stability in lithium niobate thin film on insulator with different thicknesses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Guang-hao; Bai, Yu-hang; Cui, Guo-xin

2016-07-15

Ferroelectric domain inversion and its effect on the stability of lithium niobate thin films on insulator (LNOI) are experimentally characterized. Two sets of specimens with different thicknesses varying from submicron to microns are selected. For micron thick samples (∼28 μm), domain structures are achieved by pulsed electric field poling with electrodes patterned via photolithography. No domain structure deterioration has been observed for a month as inspected using polarizing optical microscopy and etching. As for submicron (540 nm) films, large-area domain inversion is realized by scanning a biased conductive tip in a piezoelectric force microscope. A graphic processing method is takenmore » to evaluate the domain retention. A domain life time of 25.0 h is obtained and possible mechanisms are discussed. Our study gives a direct reference for domain structure-related applications of LNOI, including guiding wave nonlinear frequency conversion, nonlinear wavefront tailoring, electro-optic modulation, and piezoelectric devices.« less

Case study of psychophysiological diary: infradian rhythms.

PubMed

Slover, G P; Morris, R W; Stroebel, C F; Patel, M K

1987-01-01

A 4-year case study was made of a 42-year-old white woman as seen through the psychophysiological diary. There was an awakening diary and a bedtime diary composed of 125 variables. The data are divided into two series: series I containing a manic episode, and series II as a control. Spectral analysis shows infradian rhythms in hypoglycemia and fear (11 days) and time to fall asleep (5 days). Depressed feelings showed a circatrigintan (28-day) rhythm, which was not correlated with menses. Mania had an annual rhythm (spring) but no circatrigintan or less rhythm. The following correlations have a P value less than or equal to 0.01: mania was directly correlated with number of sleeping pills, time to really wake up, need for rest, moodiness, and helplessness, and indirectly with expectations, pressure at work, sense of time, and emotional state. Interestingly, awakening pulse is directly correlated with awakening temperature, number of sleeping pills, bedtime pulse, tiredness at bedtime, hypoglycemia, and fear. Bedtime pulse is directly correlated with awakening pulse and awakening temperature. Both pulse and temperature at bedtime are directly correlated with negative variables such as tiredness, moodiness, helplessness, and depression, and inversely correlated with positive variables such as happiness, loving, performance at work, and thinking efficiency. This study demonstrates a significant correlation between physiological variables.

Single-mode single-frequency high peak power all-fiber MOPA at 1550 nm

NASA Astrophysics Data System (ADS)

Kotov, L. V.; Likhachev, M. E.; Bubnov, M. M.; Paramonov, V. M.; Belovolov, M. I.; Lipatov, D. S.; Guryanov, A. N.

2014-10-01

In this Report, we present a record-high-peak-power single-frequency master oscillator power amplifier (MOPA) system based on a newly developed double-clad large-mode-area Yb-free Er-doped fiber (DC-LMA-EDF). A fiber Bragg grating wavelength-stabilized fiber-coupled diode laser at λ=1551 nm with ~2 MHz spectral width was used as the master oscillator. Its radiation was externally modulated with a 5 kHz repetition rate and 92 ns pulse duration and then amplified in a core-pumped Er-doped fiber amplifier up to an average power of 4 mW. The amplified spontaneous emission (ASE) generated at the last preamplifier stage was suppressed by a narrow-band (0.7 nm) DWDM filter. The last MOPA stage was based on the recently developed single-mode DC-LMA-EDF with a mode field diameter of 25 microns and pump clad-absorption of 3 dB/m at λ=980 nm. The pump and the signal were launched into this fiber through a commercial pump combiner in a co-propagating amplifier scheme. At first, we used a 3-m long DC-LMAEDF. In such configuration, a peak power of 800 W was achieved at the output of the amplifier together with a ~ 12 % pump conversion slope efficiency. Further power scaling was limited by SBS. After that we shortened the fiber length to 1 m. As a result, owing to large unabsorbed pump power, the efficiency decreased to ~5 %. However, a peak power of more than 3.5 kW was obtained before the SBS threshold. In this case, the pulse shape changed and its duration decreased to ~60 ns owing to inversion depletion after propagation of the forward front of the pulse. To the best of our knowledge, the peak power of more than 3.5 kW reported here is the highest value ever published for a single-frequency single-mode silica-based fiber laser system operating near λ=1550 nm.

Sub-Fourier characteristics of a δ-kicked-rotor resonance.

PubMed

Talukdar, I; Shrestha, R; Summy, G S

2010-07-30

We experimentally investigate the sub-Fourier behavior of a δ-kicked-rotor resonance by performing a measurement of the fidelity or overlap of a Bose-Einstein condensate exposed to a periodically pulsed standing wave. The temporal width of the fidelity resonance peak centered at the Talbot time and zero initial momentum exhibits an inverse cube pulse number (1/N3)-dependent scaling compared to a 1/N2 dependence for the mean energy width at the same resonance. A theoretical analysis shows that for an accelerating potential the width of the resonance in acceleration space depends on 1/N3, a property which we also verify experimentally. Such a sub-Fourier effect could be useful for high precision gravity measurements.

Observation of emission process in hydrogen-like nitrogen Z-pinch discharge with time integrated soft X-ray spectrum pinhole image

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakai, Y.; Kumai, H.; Nakanishi, Y.

2013-02-15

The emission spectra of hydrogen-like nitrogen Balmer at the wavelength of 13.4 nm in capillary Z-pinch discharge plasma are experimentally examined. Ionization to fully strip nitrogen at the pinch maximum, and subsequent rapid expansion cooling are required to establish the population inversion between the principal quantum number of n = 2 and n = 3. The ionization and recombination processes with estimated plasma parameters are evaluated by utilizing a time integrated spectrum pinhole image containing radial spatial information. A cylindrical capillary plasma is pinched by a triangular pulsed current with peak amplitude of 50 kA and pulse width of 50more » ns.« less

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshimine, Isao; Iida, Ryugo; Shimura, Tsutomu

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed formore » excitation fluences higher than 100 mJ/cm{sup 2}.« less

Modeling plasma heating by ns laser pulse

NASA Astrophysics Data System (ADS)

Colonna, Gianpiero; Laricchiuta, Annarita; Pietanza, Lucia Daniela

2018-03-01

The transition to breakdown of a weakly ionized gas, considering inverse bremsstrahlung, has been investigated using a state-to-state self-consistent model for gas discharges, mimicking a ns laser pulse. The paper is focused on the role of the initial ionization on the plasma formation. The results give the hint that some anomalous behaviors, such as signal enhancement by metal nanoparticles, can be attributed to this feature. This approach has been applied to hydrogen gas regarded as a simplified model for LIBS plasmas, as a full kinetic scheme is available, including the collisional-radiative model for atoms and molecules. The model allows the influence of different parameters to be investigated, such as the initial electron molar fraction, on the ionization growth.

Analysis of hemodynamics in human skin using photothermal radiometry and diffuse reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Verdel, Nina; Marin, Ana; Vidovič, Luka; Milanič, Matija; Majaron, Boris

2017-07-01

We present a novel methodology for quantitative analysis of hemodynamics in human skin in vivo. Our approach combines pulsed photothermal radiometry (i.e., time-resolved measurements of midinfrared emission from sample surface after exposure to a short light pulse) and diffuse reflectance spectroscopy in visible part of the spectrum. Experimental data are fitted with predictions of a numerical model of light transport in a four-layer skin model (i.e., inverse Monte Carlo), which allows assessment of the layer thicknesses, chromophore contents (e.g., melanin, oxy- and deoxy-hemoglobin), as well as scattering properties. The performance is tested in comparison analysis of healthy skin before and during application of a blood pressure cuff (at 200 mm Hg) for 5 minutes.

Studies in electron phenomena in MOS structures: The pulsed C-V method. M.S. Thesis. Abstract Only

NASA Technical Reports Server (NTRS)

Kaplan, G.

1983-01-01

The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

Multi-color γ-rays from comb-like electron beams driven by incoherent stacks of laser pulses

NASA Astrophysics Data System (ADS)

Kalmykov, S. Y.; Davoine, X.; Ghebregziabher, I.; Shadwick, B. A.

2017-03-01

Trains of fs-length, GeV-scale electron bunches with controlled energy spacing and a 5-D brightness up to 1017 A/m2 may be produced in a mm-scale uniform plasma. The main element of the scheme is an incoherent stack of 10-TW-scale laser pulses of different colors, with mismatched focal spots, with the highest-frequency pulse advanced in time. While driving an electron density bubble, this stack remains almost proof against nonlinear red-shift and self-compression. As a consequence, the unwanted continuous injection of background electrons is minimized. Weak focusing of the trailing (lower-frequency) component of the stack enforces expansions and contractions of the bubble, inducing controlled periodic injection. The resulting train of electron bunches maintains exceptional quality while being accelerated beyond the energy limits predicted by accepted scalings. Inverse Thomson scattering from this comb-like beam generates a sequence of quasi-monochromatic, fs-length γ-ray beams, an asset for nuclear forensics and pump-probe experiments in dense plasmas.

Optimizing Variational Quantum Algorithms Using Pontryagin’s Minimum Principle

DOE PAGES

Yang, Zhi -Cheng; Rahmani, Armin; Shabani, Alireza; ...

2017-05-18

We use Pontryagin’s minimum principle to optimize variational quantum algorithms. We show that for a fixed computation time, the optimal evolution has a bang-bang (square pulse) form, both for closed and open quantum systems with Markovian decoherence. Our findings support the choice of evolution ansatz in the recently proposed quantum approximate optimization algorithm. Focusing on the Sherrington-Kirkpatrick spin glass as an example, we find a system-size independent distribution of the duration of pulses, with characteristic time scale set by the inverse of the coupling constants in the Hamiltonian. The optimality of the bang-bang protocols and the characteristic time scale ofmore » the pulses provide an efficient parametrization of the protocol and inform the search for effective hybrid (classical and quantum) schemes for tackling combinatorial optimization problems. Moreover, we find that the success rates of our optimal bang-bang protocols remain high even in the presence of weak external noise and coupling to a thermal bath.« less

Optimizing Variational Quantum Algorithms Using Pontryagin’s Minimum Principle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhi -Cheng; Rahmani, Armin; Shabani, Alireza

We use Pontryagin’s minimum principle to optimize variational quantum algorithms. We show that for a fixed computation time, the optimal evolution has a bang-bang (square pulse) form, both for closed and open quantum systems with Markovian decoherence. Our findings support the choice of evolution ansatz in the recently proposed quantum approximate optimization algorithm. Focusing on the Sherrington-Kirkpatrick spin glass as an example, we find a system-size independent distribution of the duration of pulses, with characteristic time scale set by the inverse of the coupling constants in the Hamiltonian. The optimality of the bang-bang protocols and the characteristic time scale ofmore » the pulses provide an efficient parametrization of the protocol and inform the search for effective hybrid (classical and quantum) schemes for tackling combinatorial optimization problems. Moreover, we find that the success rates of our optimal bang-bang protocols remain high even in the presence of weak external noise and coupling to a thermal bath.« less

The optical pumping of alkali atoms using coherent radiation from semi-conductor injection lasers and incoherent radiation from resonance lamps

NASA Technical Reports Server (NTRS)

Singh, G.

1973-01-01

An experimental study for creating population differences in the ground states of alkali atoms (Cesium 133) is presented. Studies made on GaAs-junction lasers and the achievement of population inversions among the hyperfine levels in the ground state of Cs 133 by optically pumping it with radiation from a GaAs diode laser. Laser output was used to monitor the populations in the ground state hyperfine levels as well as to perform the hyperfine pumping. A GaAs laser operated at about 77 K was used to scan the 8521 A line of Cs 133. Experiments were performed both with neon-filled and with paraflint-coated cells containing the cesium vapor. Investigations were also made for the development of the triple resonance coherent pulse technique and for the detection of microwave induced hyperfine trasistions by destroying the phase relationships produced by a radio frequency pulse. A pulsed cesium resonance lamp developed, and the lamp showed clean and reproducible switching characteristics.

Selective detection of cavitation bubbles by triplet pulse sequence in high-intensity focused ultrasound treatment

NASA Astrophysics Data System (ADS)

Iwasaki, Ryosuke; Nagaoka, Ryo; Yoshizawa, Shin; Umemura, Shin-ichiro

2018-07-01

Acoustic cavitation bubbles are known to enhance the heating effect in high-intensity focused ultrasound (HIFU) treatment. The detection of cavitation bubbles with high sensitivity and selectivity is required to predict the therapeutic and side effects of cavitation, and ensure the efficacy and safety of the treatment. A pulse inversion (PI) technique has been widely used for imaging microbubbles through enhancing the second-harmonic component of echo signals. However, it has difficulty in separating the nonlinear response of microbubbles from that due to nonlinear propagation. In this study, a triplet pulse (3P) method was investigated to specifically image cavitation bubbles by extracting the 1.5th fractional harmonic component. The proposed 3P method depicted cavitation bubbles with a contrast ratio significantly higher than those in conventional imaging methods with and without PI. The results suggest that the 3P method is effective for specifically detecting microbubbles in cavitation-enhanced HIFU treatment.

Industrial realization of a direct Fourier transform in automated experimental data processing systems

NASA Technical Reports Server (NTRS)

Lyubashevskiy, G. S.

1973-01-01

Fourier processing of automatic signals transforms direct current voltage into a numerical form through bandpass filtration in time-pulse multiplying devices. It is shown that the ratio of the interference energy to the useful signal energy is inversely proportional to the square of the product of the depth of the width modulation and the ratio of the time constant averaging to the cross-multiplied signals.

Gain measurements in stimulated rotational Raman scattering in para hydrogen

NASA Astrophysics Data System (ADS)

Corat, E. J.; Airoldi, V. J. T.; Scolari, S. L.; Ghizoni, C. C.

1986-06-01

The dependence on CO2-laser pump energy of the output Stokes radiation obtained through stimulated rotational Raman scattering in parahydrogen is studied experimentally. The effective plane-wave gain for this process was determined as a function of the scattered wavelength by using a theoretical expression for the scattered pulse energy. Experimental values for the gain follow an inverse-wavelength law and are in close agreement with theory.

TACS Central Control Facility.

DTIC Science & Technology

1981-02-12

PULSE RTC REAL TIME CLOCK -{> I . SIGNAL INVERSION UASC UNIVERSAL ASYNCHRONOUS SERIAL - ---- 4w SPECIAL INTERFACE CONTROLLER Fiq. 2-1. MAC hardware...34 Universal Asynchronous Serial Controller" (UASC) cards. The cards implement an RS-232 standard interface. All controllers are set to operate at a data...Bridwell and I. Richer, "A Preliminary Design of a TDMA System for FLEETSAT," Technical Note 1975-5, Lincoln Laboratory, M.I.T. (12 March 1975), DDC

Electrophoretic ratcheting of spherical particles in a simple microfluidic device: making particles move against the direction of the net electric field

NASA Astrophysics Data System (ADS)

Wang, Hanyang; Slater, Gary; Haan, Hendrick

We examine the electrophoresis of spherical particles in microfluidic devices made of alternating wells and narrow channels a type of system previously used to separate DNA molecules. Using computer simulations, we first show why it should be possible to separate particles having the same free-solution mobility using these systems in DC fields. Interestingly, in some of the systems we studied, the mobility shows an inversion as the field intensity is increased: while small particles have higher mobilities at low fields, the situation is reversed at high fields with the larger particles then moving faster. The resulting nonlinearity allows us to use asymmetric AC electric fields to build a ratchet in which particles have a net size-dependent velocity in the presence of an unbiased (zero-mean) AC field. Exploiting the inversion mentioned above, we show how to build pulsed field sequences that make particles move against the net field (an example of negative mobility). Finally, we demonstrate that it is possible to use these pulsed fields to make particles of different sizes move in opposite directions even though their charge have the same sign. Potential uses of these idea are discussed. Gary is my supervisor in my Master program.

Lack of RAAS inhibition by high-salt intake is associated with arterial stiffness in hypertensive patients.

PubMed

Kotliar, Carol; Kempny, Pablo; Gonzalez, Sergio; Castellaro, Carlos; Forcada, Pedro; Obregon, Sebastián; Cavanagh, Elena; Chiabaut Svane, Jorge; Casarini, Maria Jesus; Rojas, Mercedes; Inserra, Felipe

2014-12-01

The relationship between salt intake, blood pressure and RAAS activation is still controversial, being that both high- and low-salt intakes are associated with cardiovascular events in a J-shaped curve pattern. We hypothesized that different patterns of RAAS response to dietary salt intake among hypertensives could be identified, while vascular damage would be related to high-salt intake plus absence of expected RAAS inhibition. We aim to assess the relationship between sodium intake, RAAS and vascular stiffness in hypertension. We screened 681 hypertensive patients for urinary/plasma electrolytes, renin, aldosterone and pulse wave velocity (PWV) under their usual salt intake level. After applying exclusion criteria, an inverse relation between urinary sodium and RAAS was observed in the 300 remaining subjects. Additionally, four types of response were identified: 1) Low (L) sodium (S)-Low RAAS, 2) LS-High (H) SRAAS, 3) HS-Low RAAS, 4) HS-High RAAS. We found no differences in age/BP among groups, but type 4 response individuals included more females and a higher pulse wave velocity. We showed a) an inverse salt-RAAS relation, b) an association between HS plus high RAAS with increased PWV that could identify a higher-risk hypertensive condition. © The Author(s) 2014.

Association between heart rate variability and manual pulse rate.

PubMed

Hart, John

2013-09-01

One model for neurological assessment in chiropractic pertains to autonomic variability, tested commonly with heart rate variability (HRV). Since HRV may not be convenient to use on all patient visits, more user-friendly methods may help fill-in the gaps. Accordingly, this study tests the association between manual pulse rate and heart rate variability. The manual rates were also compared to the heart rate derived from HRV. Forty-eight chiropractic students were examined with heart rate variability (SDNN and mean heart rate) and two manual radial pulse rate measurements. Inclusion criteria consisted of participants being chiropractic students. Exclusion criteria for 46 of the participants consisted of a body mass index being greater than 30, age greater than 35, and history of: a) dizziness upon standing, b) treatment of psychiatric disorders, and c) diabetes. No exclusion criteria were applied to the remaining two participants who were also convenience sample volunteers. Linear associations between the manual pulse rate methods and the two heart rate variability measures (SDNN and mean heart) were tested with Pearson's correlation and simple linear regression. Moderate strength inverse (expected) correlations were observed between both manual pulse rate methods and SDNN (r = -0.640, 95% CI -0.781, -0.435; r = -0.632, 95% CI -0.776, -0.425). Strong direct (expected) relationships were observed between the manual pulse rate methods and heart rate derived from HRV technology (r = 0.934, 95% CI 0.885, 0.962; r = 0.941, 95% CI 0.897, 0.966). Manual pulse rates may be a useful option for assessing autonomic variability. Furthermore, this study showed a strong relationship between manual pulse rates and heart rate derived from HRV technology.

Food web flows through a sub-arctic deep-sea benthic community

NASA Astrophysics Data System (ADS)

Gontikaki, E.; van Oevelen, D.; Soetaert, K.; Witte, U.

2011-11-01

The benthic food web of the deep Faroe-Shetland Channel (FSC) was modelled by using the linear inverse modelling methodology. The reconstruction of carbon pathways by inverse analysis was based on benthic oxygen uptake rates, biomass data and transfer of labile carbon through the food web as revealed by a pulse-chase experiment. Carbon deposition was estimated at 2.2 mmol C m -2 d -1. Approximately 69% of the deposited carbon was respired by the benthic community with bacteria being responsible for 70% of the total respiration. The major fraction of the labile detritus flux was recycled within the microbial loop leaving merely 2% of the deposited labile phytodetritus available for metazoan consumption. Bacteria assimilated carbon at high efficiency (0.55) but only 24% of bacterial production was grazed by metazoans; the remaining returned to the dissolved organic matter pool due to viral lysis. Refractory detritus was the basal food resource for nematodes covering ∼99% of their carbon requirements. On the contrary, macrofauna seemed to obtain the major part of their metabolic needs from bacteria (49% of macrofaunal consumption). Labile detritus transfer was well-constrained, based on the data from the pulse-chase experiment, but appeared to be of limited importance to the diet of the examined benthic organisms (<1% and 5% of carbon requirements of nematodes and macrofauna respectively). Predation on nematodes was generally low with the exception of sub-surface deposit-feeding polychaetes that obtained 35% of their energy requirements from nematode ingestion. Carnivorous polychaetes also covered 35% of their carbon demand through predation although the preferred prey, in this case, was other macrofaunal animals rather than nematodes. Bacteria and detritus contributed 53% and 12% to the total carbon ingestion of carnivorous polychaetes suggesting a high degree of omnivory among higher consumers in the FSC benthic food web. Overall, this study provided a unique insight into the functioning of a deep-sea benthic community and demonstrated how conventional data can be exploited further when combined with state-of-the-art modelling approaches.

Optical field ionization of atoms and ions using ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Fittinghoff, D. N.

1993-12-01

This dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-run laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He(+2), Ne(+2), and Ar(+2). The ion yields for He(+1), Ne(sup +1) and Ar(sup +1) agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of the ionization indicates that the enhancements are consistent with a nonsequential ionization mechanism in which the linearly polarized field drives the electron wavefunction back toward the ion core and causes double ionization through inelastic e-2e scattering. These investigations have initiated a number of other studies by other groups and are of current scientific interest in the fields of high-irradiance laser-matter interactions and production of high-density plasmas. This work involved the following: (1) Understanding the characteristic nature of the ion yields produced by tunneling ionization through investigation of analytic solutions for tunneling at optical frequencies. (2) Extensive characterization of the pulses produced by 614-nm and 800-ran ultrashort pulse lasers. Absolute calibration of the irradiance scale produced shows the practicality of the inverse problem--measuring peak laser irradiance using ion yields. (3) Measuring the ion yields for three noble gases using linear, circular and elliptical polarizations of laser pulses at 614-nm and 800-nm. The measurements are some of the first measurements for pulse widths as low as 120-fs.

Pulsed arterial spin labeling using TurboFLASH with suppression of intravascular signal.

PubMed

Pell, Gaby S; Lewis, David P; Branch, Craig A

2003-02-01

Accurate quantification of perfusion with the ADC techniques requires the suppression of the majority of the intravascular signal. This is normally achieved with the use of diffusion gradients. The TurboFLASH sequence with its ultrashort repetition times is not readily amenable to this scheme. This report demonstrates the implementation of a modified TurboFLASH sequence for FAIR imaging. Intravascular suppression is achieved with a modified preparation period that includes a driven equilibrium Fourier transform (DEFT) combination of 90 degrees-180 degrees-90 degrees hard RF pulses subsequent to the inversion delay. These pulses rotate the perfusion-prepared magnetization into the transverse plane where it can experience the suitably placed diffusion gradients before being returned to the longitudinal direction by the second 90 degrees pulse. A value of b = 20-30 s/mm(2) was thereby found to suppress the majority of the intravascular signal. For single-slice perfusion imaging, quantification is only slightly modified. The technique can be readily extended to multislice acquisition if the evolving flow signal after the DEFT preparation is considered. An advantage of the modified preparation scheme is evident in the multislice FAIR images by the preservation of the sign of the magnetization difference. Copyright 2003 Wiley-Liss, Inc.

Quantitative two-dimensional HSQC experiment for high magnetic field NMR spectrometers

NASA Astrophysics Data System (ADS)

Koskela, Harri; Heikkilä, Outi; Kilpeläinen, Ilkka; Heikkinen, Sami

2010-01-01

The finite RF power available on carbon channel in proton-carbon correlation experiments leads to non-uniform cross peak intensity response across carbon chemical shift range. Several classes of broadband pulses are available that alleviate this problem. Adiabatic pulses provide an excellent magnetization inversion over a large bandwidth, and very recently, novel phase-modulated pulses have been proposed that perform 90° and 180° magnetization rotations with good offset tolerance. Here, we present a study how these broadband pulses (adiabatic and phase-modulated) can improve quantitative application of the heteronuclear single quantum coherence (HSQC) experiment on high magnetic field strength NMR spectrometers. Theoretical and experimental examinations of the quantitative, offset-compensated, CPMG-adjusted HSQC (Q-OCCAHSQC) experiment are presented. The proposed experiment offers a formidable improvement to the offset performance; 13C offset-dependent standard deviation of the peak intensity was below 6% in range of ±20 kHz. This covers the carbon chemical shift range of 150 ppm, which contains the protonated carbons excluding the aldehydes, for 22.3 T NMR magnets. A demonstration of the quantitative analysis of a fasting blood plasma sample obtained from a healthy volunteer is given.

Inversion climatology at San Jose, California

NASA Technical Reports Server (NTRS)

Morgan, T.; Bornstein, R. D.

1977-01-01

Month-to-month variations in the early morning surface-based and near-noon elevated inversions at San Jose, Calif., were determined from slow rise radiosondes launched during a four-year period. A high frequency of shallow, radiative, surface-based inversions were found in winter during the early morning hours, while during the same period in summer, a low frequency of deeper based inversions arose from a combination of radiative and subsidence processes. The frequency of elevated inversions in the hours near noon was lowest during fall and spring, while inversion bases were highest and thicknesses least during these periods.

Articular Cartilage: Evaluation with Fluid-suppressed 7.0-T Sodium MR Imaging in Subjects with and Subjects without Osteoarthritis

PubMed Central

Babb, James; Xia, Ding; Chang, Gregory; Krasnokutsky, Svetlana; Abramson, Steven B.; Jerschow, Alexej; Regatte, Ravinder R.

2013-01-01

Purpose: To assess the potential use of sodium magnetic resonance (MR) imaging of cartilage, with and without fluid suppression by using an adiabatic pulse, for classifying subjects with versus subjects without osteoarthritis at 7.0 T. Materials and Methods: The study was approved by the institutional review board and was compliant with HIPAA. The knee cartilage of 19 asymptomatic (control subjects) and 28 symptomatic (osteoarthritis patients) subjects underwent 7.0-T sodium MR imaging with use of two different sequences: one without fluid suppression (radial three-dimensional sequence) and one with fluid suppression (inversion recovery [IR] wideband uniform rate and smooth truncation [WURST]). Fluid suppression was obtained by using IR with an adiabatic inversion pulse (WURST pulse). Mean sodium concentrations and their standard deviations were measured in the patellar, femorotibial medial, and lateral cartilage regions over four consecutive sections for each subject. The minimum, maximum, median, and average means and standard deviations were calculated over all measurements for each subject. The utility of these measures in the detection of osteoarthritis was evaluated by using logistic regression and the area under the receiver operating characteristic curve (AUC). Bonferroni correction was applied to the P values obtained with logistic regression. Results: Measurements from IR WURST were found to be significant predicators of all osteoarthritis (Kellgren-Lawrence score of 1–4) and early osteoarthritis (Kellgren-Lawrence score of 1 or 2). The minimum standard deviation provided the highest AUC (0.83) with the highest accuracy (>78%), sensitivity (>82%), and specificity (>74%) for both all osteoarthritis and early osteoarthritis groups. Conclusion: Quantitative sodium MR imaging at 7.0 T with fluid suppression by using adiabatic IR is a potential biomarker for osteoarthritis. © RSNA, 2013 PMID:23468572

Enhanced tunability of the composition in silicon oxynitride thin films by the reactive gas pulsing process

NASA Astrophysics Data System (ADS)

Aubry, Eric; Weber, Sylvain; Billard, Alain; Martin, Nicolas

2014-01-01

Silicon oxynitride thin films were sputter deposited by the reactive gas pulsing process. Pure silicon target was sputtered in Ar, N2 and O2 mixture atmosphere. Oxygen gas was periodically and solely introduced using exponential signals. In order to vary the injected O2 quantity in the deposition chamber during one pulse at constant injection time (TON), the tau mounting time τmou of the exponential signals was systematically changed for each deposition. Taking into account the real-time measurements of the discharge voltage and the I(O*)/I(Ar*) emission lines ratio, it is shown that the oscillations of the discharge voltage during the TON and TOFF times (injection of O2 stopped) are attributed to the preferential adsorption of the oxygen compared to that of the nitrogen. The sputtering mode alternates from a fully nitrided mode (TOFF time) to a mixed mode (nitrided and oxidized mode) during the TON time. For the highest injected O2 quantities, the mixed mode tends toward a fully oxidized mode due to an increase of the trapped oxygen on the target. The oxygen (nitrogen) concentration in the SiOxNy films similarly (inversely) varies as the oxygen is trapped. Moreover, measurements of the contamination speed of the Si target surface are connected to different behaviors of the process. At low injected O2 quantities, the nitrided mode predominates over the oxidized one during the TON time. It leads to the formation of Si3N4-yOy-like films. Inversely, the mixed mode takes place for high injected O2 quantities and the oxidized mode prevails against the nitrided one producing SiO2-xNx-like films.

Bayesian Abel Inversion in Quantitative X-Ray Radiography

DOE PAGES

Howard, Marylesa; Fowler, Michael; Luttman, Aaron; ...

2016-05-19

A common image formation process in high-energy X-ray radiography is to have a pulsed power source that emits X-rays through a scene, a scintillator that absorbs X-rays and uoresces in the visible spectrum in response to the absorbed photons, and a CCD camera that images the visible light emitted from the scintillator. The intensity image is related to areal density, and, for an object that is radially symmetric about a central axis, the Abel transform then gives the object's volumetric density. Two of the primary drawbacks to classical variational methods for Abel inversion are their sensitivity to the type andmore » scale of regularization chosen and the lack of natural methods for quantifying the uncertainties associated with the reconstructions. In this work we cast the Abel inversion problem within a statistical framework in order to compute volumetric object densities from X-ray radiographs and to quantify uncertainties in the reconstruction. A hierarchical Bayesian model is developed with a likelihood based on a Gaussian noise model and with priors placed on the unknown density pro le, the data precision matrix, and two scale parameters. This allows the data to drive the localization of features in the reconstruction and results in a joint posterior distribution for the unknown density pro le, the prior parameters, and the spatial structure of the precision matrix. Results of the density reconstructions and pointwise uncertainty estimates are presented for both synthetic signals and real data from a U.S. Department of Energy X-ray imaging facility.« less

On the correlation between ‘non-local’ effects and intrinsic rotation reversals in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Rodriguez-Fernandez, P.; Rice, J. E.; Cao, N. M.; Creely, A. J.; Howard, N. T.; Hubbard, A. E.; Irby, J. H.; White, A. E.

2017-07-01

Contemporary predictive models for heat and particle transport in tokamak plasmas are based on the assumption that local fluxes can be described in terms of local plasma parameters, where electromagnetic drift-wave-type turbulence is driven by local gradients and results in cross-field transport. The question of whether or not transport could be dominated by non-local terms in certain circumstances is essential for our understanding of transport in magnetically confined plasmas, and critical for developing predictive models for future tokamaks, such as ITER. Perturbative transport experiments using cold-pulse injections at low density seem to challenge the local closure of anomalous transport: a rapid temperature increase in the core of the plasma following a sharp edge cooling is widely observed in tokamaks and helical devices. Past work in Ohmic plasmas in Alcator C-Mod and in ECH plasmas in KSTAR found that the temperature inversions disappear at higher densities, above the intrinsic toroidal rotation reversal density. These observations suggested that the so-called ‘non-local’ heat transport effects were related to the intrinsic rotation reversal, and therefore to changes in momentum transport. In this work, new experiments and analysis at Alcator C-Mod show that intrinsic rotation reversals and disappearance of temperature inversions are not concomitant in Ohmic plasmas at high plasma current and in ICRH L-modes. This new data set shows that the correlation between transient temperature inversions and intrinsic rotation reversals is not universal, suggesting that ‘non-local’ heat transport and momentum transport effects may be affected by different physical mechanisms.

Role of the inversion layer on the charge injection in silicon nanocrystal multilayered light emitting devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tondini, S.; Dipartimento di Fisica, Informatica e Matematica, Università di Modena e Reggio Emilia, Via Campi 213/a, 41125 Modena; Pucker, G.

2016-09-07

The role of the inversion layer on injection and recombination phenomena in light emitting diodes (LEDs) is here studied on a multilayer (ML) structure of silicon nanocrystals (Si-NCs) embedded in SiO{sub 2}. Two Si-NC LEDs, which are similar for the active material but different in the fabrication process, elucidate the role of the non-radiative recombination rates at the ML/substrate interface. By studying current- and capacitance-voltage characteristics as well as electroluminescence spectra and time-resolved electroluminescence under pulsed and alternating bias pumping scheme in both the devices, we are able to ascribe the different experimental results to an efficient or inefficient minoritymore » carrier (electron) supply by the p-type substrate in the metal oxide semiconductor LEDs.« less

Analysis of impulse signals with Hylaty ELF station

NASA Astrophysics Data System (ADS)

Kulak, A.; Mlynarczyk, J.; Ostrowski, M.; Kubisz, J.; Michalec, A.

2012-04-01

Lighting discharges generate electromagnetic field pulses that propagate in the Earth-ionosphere waveguide. The attenuation in the ELF range is so small that the pulses originating from strong atmospheric discharges can be observed even several thousand kilometers away from the individual discharge. The recorded waveform depends on the discharge process, the Earth-ionosphere waveguide properties on the source-receiver path, and the transfer function of the receiver. If the distance from the source is known, an inverse method can be used for reconstructing the current moment waveform and the charge moment of the discharge. In order to reconstruct the source parameters from the recorded signal a reliable model of the radio wave propagation in the Earth-ionosphere waveguide as well as practical signal processing techniques are necessary. We present two methods, both based on analytical formulas. The first method allows for fast calculation of the charge moment of relatively short atmospheric discharges. It is based on peak amplitude measurement of the recorded magnetic component of the ELF EM field and it takes into account the receiver characteristics. The second method, called "inverse channel method" allows reconstructing the complete current moment waveform of strong atmospheric discharges that exhibit the continuing current phase, such as Gigantic Jets and Sprites. The method makes it possible to fully remove from the observed waveform the distortions related to the receiver's impulse response as well as the influence of the Earth-ionosphere propagation channel. Our ELF station is equipped with two magnetic antennas for Bx and By components measurement in the 0.03 to 55 Hz frequency range. ELF Data recording is carried out since 1993, with continuous data acquisition since 2005. The station features low noise level and precise timing. It is battery powered and located in the sparsely populated area, far from major electric power lines, which results in high quality signal recordings and allows for precise calculations of the charge moments of upward discharges and strong cloud-to-ground discharges originating from distant sources. The same data is used for Schumann resonance observation. We demonstrate the use of our methods based on recent recordings from the Hylaty ELF station. We include examples of GJ (Gigantic Jet) and TGF (Terrestrial Gamma-ray Flash) related discharges.

Full wave two-dimensional modeling of scattering and inverse scattering for layered rough surfaces with buried objects

NASA Astrophysics Data System (ADS)

Kuo, Chih-Hao

Efficient and accurate modeling of electromagnetic scattering from layered rough surfaces with buried objects finds applications ranging from detection of landmines to remote sensing of subsurface soil moisture. The formulation of a hybrid numerical/analytical solution to electromagnetic scattering from layered rough surfaces is first presented in this dissertation. The solution to scattering from each rough interface is sought independently based on the extended boundary condition method (EBCM), where the scattered fields of each rough interface are expressed as a summation of plane waves and then cast into reflection/transmission matrices. To account for interactions between multiple rough boundaries, the scattering matrix method (SMM) is applied to recursively cascade reflection and transmission matrices of each rough interface and obtain the composite reflection matrix from the overall scattering medium. The validation of this method against the Method of Moments (MoM) and Small Perturbation Method (SPM) is addressed and the numerical results which investigate the potential of low frequency radar systems in estimating deep soil moisture are presented. Computational efficiency of the proposed method is also discussed. In order to demonstrate the capability of this method in modeling coherent multiple scattering phenomena, the proposed method has been employed to analyze backscattering enhancement and satellite peaks due to surface plasmon waves from layered rough surfaces. Numerical results which show the appearance of enhanced backscattered peaks and satellite peaks are presented. Following the development of the EBCM/SMM technique, a technique which incorporates a buried object in layered rough surfaces by employing the T-matrix method and the cylindrical-to-spatial harmonics transformation is proposed. Validation and numerical results are provided. Finally, a multi-frequency polarimetric inversion algorithm for the retrieval of subsurface soil properties using VHF/UHF band radar measurements is devised. The top soil dielectric constant is first determined using an L-band inversion algorithm. For the retrieval of subsurface properties, a time-domain inversion technique is employed together with a parameter optimization for the pulse shape of time delay echoes from VHF/UHF band radar observations. Numerical studies to investigate the accuracy of the proposed inversion technique in presence of errors are addressed.

Multi-focus image fusion algorithm using NSCT and MPCNN

NASA Astrophysics Data System (ADS)

Liu, Kang; Wang, Lianli

2018-04-01

Based on nonsubsampled contourlet transform (NSCT) and modified pulse coupled neural network (MPCNN), the paper proposes an effective method of image fusion. Firstly, the paper decomposes the source image into the low-frequency components and high-frequency components using NSCT, and then processes the low-frequency components by regional statistical fusion rules. For high-frequency components, the paper calculates the spatial frequency (SF), which is input into MPCNN model to get relevant coefficients according to the fire-mapping image of MPCNN. At last, the paper restructures the final image by inverse transformation of low-frequency and high-frequency components. Compared with the wavelet transformation (WT) and the traditional NSCT algorithm, experimental results indicate that the method proposed in this paper achieves an improvement both in human visual perception and objective evaluation. It indicates that the method is effective, practical and good performance.

Recovery of the parameters of cancellous bone by inversion of effective velocities, and transmission and reflection coefficients

NASA Astrophysics Data System (ADS)

Buchanan, James L.; Gilbert, Robert P.; Ou, Miao-jung Y.

2011-12-01

Estimating the parameters of an elastic or poroelastic medium from reflected or transmitted acoustic data is an important but difficult problem. Use of the Nelder-Mead simplex method to minimize an objective function measuring the discrepancy between some observable and its value calculated from a model for a trial set of parameters has been tried by several authors. In this paper, the difficulty with this direct approach, which is the existence of numerous local minima of the objective function, is documented for the in vitro experiment in which a specimen in a water tank is subject to an ultrasonic pulse. An indirect approach, based on the numerical solution of the equations for a set of ‘effective’ velocities and transmission coefficients, is then observed empirically to ameliorate the difficulties posed by the direct approach.

Real-time dynamics of Auger wave packets and decays in ultrafast charge migration processes

NASA Astrophysics Data System (ADS)

Covito, F.; Perfetto, E.; Rubio, A.; Stefanucci, G.

2018-06-01

The Auger decay is a relevant recombination channel during the first few femtoseconds of molecular targets impinged by attosecond XUV or soft x-ray pulses. Including this mechanism in time-dependent simulations of charge-migration processes is a difficult task, and Auger scatterings are often ignored altogether. In this work we present an advance of the current state-of-the-art by putting forward a real-time approach based on nonequilibrium Green's functions suitable for first-principles calculations of molecules with tens of active electrons. To demonstrate the accuracy of the method we report comparisons against accurate grid simulations of one-dimensional systems. We also predict a highly asymmetric profile of the Auger wave packet, with a long tail exhibiting ripples temporally spaced by the inverse of the Auger energy.

On-line depth measurement for laser-drilled holes based on the intensity of plasma emission

NASA Astrophysics Data System (ADS)

Ho, Chao-Ching; Chiu, Chih-Mu; Chang, Yuan-Jen; Hsu, Jin-Chen; Kuo, Chia-Lung

2014-09-01

The direct time-resolved depth measurement of blind holes is extremely difficult due to the short time interval and the limited space inside the hole. This work presents a method that involves on-line plasma emission acquisition and analysis to obtain correlations between the machining processes and the optical signal output. Given that the depths of laser-machined holes can be estimated on-line using a coaxial photodiode, this was employed in our inspection system. Our experiments were conducted in air under normal atmospheric conditions without gas assist. The intensity of radiation emitted from the vaporized material was found to correlate with the depth of the hole. The results indicate that the estimated depths of the laser-drilled holes were inversely proportional to the maximum plasma light emission measured for a given laser pulse number.

Ultrafast all-optical control of the magnetization in magnetic dielectrics

NASA Astrophysics Data System (ADS)

Kirilyuk, Andrei; Kimel, Alexey; Hansteen, Fredrik; Rasing, Theo; Pisarev, Roman V.

2006-08-01

The purpose of this review is to summarize the recent progress on laser-induced magnetization dynamics in magnetic dielectrics. Due to the slow phonon-magnon interaction in these materials, direct thermal effects of the laser excitation can only be seen on the time scale of almost a nanosecond and thus are clearly distinguished from the ultrafast nonthermal effects. However, laser pulses are shown to indirectly modify the magnetic anisotropy in rare-earth orthoferrites via the crystal field, and to bring about spin reorientation within a few picoseconds. More interesting, however, are the direct nonthermal effects of light on spin systems. We demonstrate coherent optical control of the magnetization in ferrimagnetic garnet films on a femtosecond time scale through a combination of two different ultrafast and nonthermal photomagnetic effects and by employing multiple pump pulses. Linearly polarized laser pulses are shown to create a long-lived modification of the magnetocrystalline anisotropy via optically induced electron transfer between nonequivalent ion sites. In addition, circularly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday effect. An all-optical scheme of excitation and detection of different antiferromagnetic resonance modes with frequencies of up to 500GHz will be discussed as well. The reported effects open new and exciting possibilities for ultrafast manipulation of spins by light and provide new insight into the physics of magnetism on ultrafast time scales.

Research on fission fragment excitation of gases and nuclear pumping of lasers

NASA Technical Reports Server (NTRS)

Schneider, R. T.; Davie, R. N.; Davis, J. F.; Fuller, J. L.; Paternoster, R. R.; Shipman, G. R.; Sterritt, D. E.; Helmick, H. H.

1974-01-01

Experimental investigations of fission fragment excited gases are reported along with a theoretical analysis of population inversions in fission fragment excited helium. Other studies reported include: nuclear augmentation of gas lasers, direct nuclear pumping of a helium-xenon laser, measurements of a repetitively pulsed high-power CO2 laser, thermodynamic properties of UF6 and UF6/He mixtures, and nuclear waste disposal utilizing a gaseous core reactor.

An Expendable Source for Measuring Shallow Water Acoustic Propagation and Geo-Acoustic Bottom Properties

DTIC Science & Technology

2015-09-30

Propagation and Geo -Acoustic Bottom Properties Harry A DeFerrari RSMAS – University of Miami 4600 Rickenbacker Causeway Miami FL. 33149...limited information about the ocean acoustic environment and the geo -acoustic properties of the bottom. The objective here is to measure the pulse...models and estimate the geo -acoustic properties of the bottom by inversion. APPROACH M-sequences have long been the workhorse of basic research

Three Dimensional Inverse Synthetic Aperture Radar Imaging

DTIC Science & Technology

1995-12-01

unfortunately produces a blurred image. To correct this problem, a deblurring filter must be applied to the data. It is preferred in some applications to...when the pulse is an impulse in time. So in order to get a high degree of downrange resolution directly it would be necessary to transmit the entire...bandwidth of frequencies simultaneously such as in an Impulse Radar. This would prove to be extremely difficult if not impossible. Luckily, the same

Laser-induced spin protection and switching in a specially designed magnetic dot: A theoretical investigation

NASA Astrophysics Data System (ADS)

Zhang, G. P.; Si, M. S.; George, T. F.

2011-04-01

Most laser-induced femtosecond magnetism investigations are done in magnetic thin films. Nanostructured magnetic dots, with their reduced dimensionality, present new opportunities for spin manipulation. Here we predict that if a magnetic dot has a dipole-forbidden transition between the lowest occupied molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO), but a dipole-allowed transition between LUMO+1 and HOMO, electromagnetically induced transparency can be used to prevent ultrafast laser-induced spin momentum reduction, or spin protection. This is realized through a strong dump pulse to funnel the population into LUMO+1. If the time delay between the pump and dump pulses is longer than 60 fs, a population inversion starts and spin switching is achieved. These predictions are detectable experimentally.

Short-lived solar burst spectral component at f approximately 100 GHz

NASA Technical Reports Server (NTRS)

Kaufmann, P.; Correia, E.; Costa, J. E. R.; Vaz, A. M. Z.

1986-01-01

A new kind of burst emission component was discovered, exhibiting fast and distinct pulses (approx. 60 ms durations), with spectral peak emission at f approx. 100 GHz, and onset time coincident to hard X-rays to within approx. 128 ms. These features pose serious constraints for the interpretation using current models. One suggestion assumes the f approx. 100 GHz pulses emission by synchrotron mechanism of electrons accelerated to ultrarelativistic energies. The hard X-rays originate from inverse Compton scattering of the electrons on the synchrotron photons. Several crucial observational tests are needed for the understanding of the phenomenon, requiring high sensitivity and high time resolution (approx. 1 ms) simultaneous to high spatial resolution (0.1 arcsec) at f approx. 110 GHz and hard X-rays.

Pulsed-discharge carbon dioxide lasers

NASA Technical Reports Server (NTRS)

Willetts, David V.

1990-01-01

The purpose is to attempt a general introduction to pulsed carbon dioxide lasers of the kind used or proposed for laser radar applications. Laser physics is an excellent example of a cross-disciplinary topic, and the molecular spectroscopy, energy transfer, and plasma kinetics of the devices are explored. The concept of stimulated emission and population inversions is introduced, leading on to the molecular spectroscopy of the CO2 molecule. This is followed by a consideration of electron-impact pumping, and the pertinent energy transfer and relaxation processes which go on. Since the devices are plasma pumped, it is necessary to introduce a complex subject, but this is restricted to appropriate physics of glow discharges. Examples of representative devices are shown. The implications of the foregoing to plasma chemistry and gas life are discussed.

Metabolite-cycled STEAM and semi-LASER localization for MR spectroscopy of the human brain at 9.4T.

PubMed

Giapitzakis, Ioannis-Angelos; Shao, Tingting; Avdievich, Nikolai; Mekle, Ralf; Kreis, Roland; Henning, Anke

2018-04-01

Metabolite cycling (MC) is an MRS technique for the simultaneous acquisition of water and metabolite spectra that avoids chemical exchange saturation transfer effects and for which water may serve as a reference signal or contain additional information in functional or diffusion studies. Here, MC was developed for human investigations at ultrahigh field. MC-STEAM and MC-semi-LASER are introduced at 9.4T with an optimized inversion pulse and elaborate coil setup. Experimental and simulation results are given for the implementation of adiabatic inversion pulses for MC. The two techniques are compared, and the effect of frequency and phase correction based on the MC water spectra is evaluated. Finally, absolute quantification of metabolites is performed. The proposed coil configuration results in a maximum B1 + of 48 μΤ in a voxel within the occipital lobe. Frequency and phase correction of single acquisitions improve signal-to-noise ratio (SNR) and linewidth, leading to high-resolution spectra. The improvement of SNR of N-acetylaspartate (SNR NAA ) for frequency aligned data, acquired with MC-STEAM and MC-semi-LASER, are 37% and 30%, respectively (P < 0.05). Moreover, a doubling of the SNR NAA for MC-semi-LASER in comparison with MC-STEAM is observed (P < 0.05). Concentration levels for 18 metabolites from the human occipital lobe are reported, as acquired with both MC-STEAM and MC-semi-LASER. This work introduces a novel methodology for single-voxel MRS on a 9.4T whole-body scanner and highlights the advantages of semi-LASER compared to STEAM in terms of excitation profile. In comparison with MC-STEAM, MC-semi-LASER yields spectra with higher SNR. Magn Reson Med 79:1841-1850, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

PubMed Central

Hoff, Daniel E.M.; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Choi, Eric J.; Mardini, Michael; Barnes, Alexander B.

2015-01-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198 GHz MAS DNP probe. Our calculations show that a microwave power input of 17 W is required to generate an average EPR nutation frequency of 0.84 MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5 kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. PMID:26482131

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization.

PubMed

Hoff, Daniel E M; Albert, Brice J; Saliba, Edward P; Scott, Faith J; Choi, Eric J; Mardini, Michael; Barnes, Alexander B

2015-11-01

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions. Copyright © 2015 Elsevier Inc. All rights reserved.

Computationally effective solution of the inverse problem in time-of-flight spectroscopy.

PubMed

Kamran, Faisal; Abildgaard, Otto H A; Subash, Arman A; Andersen, Peter E; Andersson-Engels, Stefan; Khoptyar, Dmitry

2015-03-09

Photon time-of-flight (PTOF) spectroscopy enables the estimation of absorption and reduced scattering coefficients of turbid media by measuring the propagation time of short light pulses through turbid medium. The present investigation provides a comparison of the assessed absorption and reduced scattering coefficients from PTOF measurements of intralipid 20% and India ink-based optical phantoms covering a wide range of optical properties relevant for biological tissues and dairy products. Three different models are used to obtain the optical properties by fitting to measured temporal profiles: the Liemert-Kienle model (LKM), the diffusion model (DM) and a white Monte-Carlo (WMC) simulation-based algorithm. For the infinite space geometry, a very good agreement is found between the LKM and WMC, while the results obtained by the DM differ, indicating that the LKM can provide accurate estimation of the optical parameters beyond the limits of the diffusion approximation in a computational effective and accurate manner. This result increases the potential range of applications for PTOF spectroscopy within industrial and biomedical applications.

Design of an Integrated-System FARAD Thruster

NASA Technical Reports Server (NTRS)

Polzin, K.A.; Rose, R.F.; Miller, R.; Owens, T.

2007-01-01

Pulsed inductive plasma accelerators are spacecraft propulsion devices in which energy is stored in a capacitor and then discharged through an inductive coil. The device is electrodeless, inducing a current s heet in a plasma located near the face of the coil. The propellant is accelerated and expelled at a high exhaust velocity (order of 10 km/s) through the interaction of the plasma current and the induced magne tic field, The Faraday Accelerator with RF-Assisted Discharge (FARAD) thruster is a type of pulsed inductive plasma accelerator in which t he plasma is preionized by a mechanism separate from that used to for m the current sheet and accelerate the gas. Employing a separate preionization mechanism allows for the formation of an inductive current s heet at much lower discharge energies and voltages than those used in previous pulsed inductive accelerators like the Pulsed Inductive Thr uster (PIT). In this paper, we present the design of a benchtop FARAD thruster with all the subsystems (mass injection, preionization, and acceleration) integrated into a single unit. Design of the thruster follows the guidelines and similarity performance parameters presented elsewhere. The system is designed to use the ringing, RF-frequency s ignal produced by a discharging Vector Inversion Generator (VIG) to p reionize the gas. The acceleration stage operates on the order of 100 J/pulse and can be driven by several different pulsed powertrains. These include a simple capacitor coupled to the system, a Bernardes and Merryman configuration, and a pulsecompression circuit that takes a temporally broad, low current pulse and transforms it into a short, h igh current pulse. A set of applied magnetic field coils are integrated into the system to guide the preionized propellant as it spreads ov er the face of the inductive acceleration coil. The coils are operate d in a pulsed mode, and the thruster can be operated without using the coils to determine if there is a performance improvement gain realiz ed when an applied field is present.

Scaling the Shear-flow Stabilized Z-pinch to Reactor Conditions

NASA Astrophysics Data System (ADS)

McLean, H. S.; Schmidt, A.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Cleveau, E.

2015-11-01

We present a conceptual design along with scaling calculations for a pulsed fusion reactor based on the shear-flow-stabilized Z-pinch device. Experiments performed on the ZaP device, at the University of Washington, have demonstrated stable operation for durations of 20 usec at ~100kA discharge current for pinches that are ~1 cm in diameter and 100 cm long. The inverse of the pinch diameter and plasma energy density scale strongly with pinch current and calculations show that maintaining stabilization durations of ~7 usec for increased discharge current (~15x) in a shortened pinch (10 cm) results in a pinch diameter of ~200 um and plasma conditions that approach those needed to support significant fusion burn and energy gain (Ti ~ 30keV, density ~ 3e26/m3, ntau ~1.4e20 sec/m3). Compelling features of the concept include operation at modest discharge current (1.5 MA) and voltage (40kV) along with direct adoption of liquid metals for at least one electrode--technological capabilities that have been proven in existing, commercial, pulse power devices such as large ignitrons. LLNL-ABS-674920. This work performed under the auspices of the U.S. Department of Energy ARPAe ALPHA Program by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Cloud Radiative Effect to Downward Longwave Radiation in the Polar Regions

NASA Astrophysics Data System (ADS)

Yamada, K.; Hayasaka, T.

2014-12-01

Downward longwave radiation is important factor to affect climate change. In polar regions, estimation of the radiative effect of cloud on the downward longwave radiation has large uncertainty. Relatively large cloud effect to the radiation occurs there due to low temperature, small amount of water vapor, and strong inversion layer. The cloud effect is, however, not evaluated sufficiently because the long term polar night and high surface albedo make satellite retrieval difficult. The intent of the present study is to quantify cloud radiative effect for downward longwave radiation in the polar regions by in-situ observation and radiative transfer calculation. The observation sites in this study are Ny-Ålesund (NYA), Syowa (SYO), and South Pole (SPO). These stations belong to the Baseline Surface Radiation Network. The period of data analysis is from 2003 to 2012. The effect of cloud on the downward longwave radiation is evaluated by subtraction of calculated downward longwave radiation under clear-sky condition from observed value under all-sky condition. Radiative transfer model was used for the evaluation of clear sky radiation with vertical temperature and humidity profile obtained by radiosonde observations. Calculated result shows good correlation with observation under clear-sky condition. The RMSE is +0.83±5.0. The cloud effect varied from -10 - +110 W/m2 (-10 - +40 %). Cloud effect increased with increasing of cloud fraction and decreasing of cloud base height and precipitable water. In SYO negative effects were sometimes obtained. The negative cloud effect emerged under dry and temperature inversion condition lower than 2 km. One of reasons of negative effect is considered to be existence of cloud at temperature inversion altitude. When the cloud effect is smaller than -5 W/m2 (standard deviation between calculation and observation), 50 % of them have a condition with cloud base height estimated by micro pulse lidar lower than 2 km.

Impact evaluation of conducted UWB transients on loads in power-line networks

NASA Astrophysics Data System (ADS)

Li, Bing; Månsson, Daniel

2017-09-01

Nowadays, faced with the ever-increasing dependence on diverse electronic devices and systems, the proliferation of potential electromagnetic interference (EMI) becomes a critical threat for reliable operation. A typical issue is the electronics working reliably in power-line networks when exposed to electromagnetic environment. In this paper, we consider a conducted ultra-wideband (UWB) disturbance, as an example of intentional electromagnetic interference (IEMI) source, and perform the impact evaluation at the loads in a network. With the aid of fast Fourier transform (FFT), the UWB transient is characterized in the frequency domain. Based on a modified Baum-Liu-Tesche (BLT) method, the EMI received at the loads, with complex impedance, is computed. Through inverse FFT (IFFT), we obtain time-domain responses of the loads. To evaluate the impact on loads, we employ five common, but important quantifiers, i.e., time-domain peak, total signal energy, peak signal power, peak time rate of change and peak time integral of the pulse. Moreover, to perform a comprehensive analysis, we also investigate the effects of the attributes (capacitive, resistive, or inductive) of other loads connected to the network, the rise time and pulse width of the UWB transient, and the lengths of power lines. It is seen that, for the loads distributed in a network, the impact evaluation of IEMI should be based on the characteristics of the IEMI source, and the network features, such as load impedances, layout, and characteristics of cables.

Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer.

PubMed

Svanström, Erika; Linder, Tomas; Löfqvist, Torbjörn

2014-03-01

Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials. Copyright © 2013 Elsevier B.V. All rights reserved.

Inverse Faraday Effect Revisited

NASA Astrophysics Data System (ADS)

Mendonça, J. T.; Ali, S.; Davies, J. R.

2010-11-01

The inverse Faraday effect is usually associated with circularly polarized laser beams. However, it was recently shown that it can also occur for linearly polarized radiation [1]. The quasi-static axial magnetic field by a laser beam propagating in plasma can be calculated by considering both the spin and the orbital angular momenta of the laser pulse. A net spin is present when the radiation is circularly polarized and a net orbital angular momentum is present if there is any deviation from perfect rotational symmetry. This orbital angular momentum has recently been discussed in the plasma context [2], and can give an additional contribution to the axial magnetic field, thus enhancing or reducing the inverse Faraday effect. As a result, this effect that is usually attributed to circular polarization can also be excited by linearly polarized radiation, if the incident laser propagates in a Laguerre-Gauss mode carrying a finite amount of orbital angular momentum.[4pt] [1] S. ALi, J.R. Davies and J.T. Mendonca, Phys. Rev. Lett., 105, 035001 (2010).[0pt] [2] J. T. Mendonca, B. Thidé, and H. Then, Phys. Rev. Lett. 102, 185005 (2009).

Metamodel-based inverse method for parameter identification: elastic-plastic damage model

NASA Astrophysics Data System (ADS)

Huang, Changwu; El Hami, Abdelkhalak; Radi, Bouchaïb

2017-04-01

This article proposed a metamodel-based inverse method for material parameter identification and applies it to elastic-plastic damage model parameter identification. An elastic-plastic damage model is presented and implemented in numerical simulation. The metamodel-based inverse method is proposed in order to overcome the disadvantage in computational cost of the inverse method. In the metamodel-based inverse method, a Kriging metamodel is constructed based on the experimental design in order to model the relationship between material parameters and the objective function values in the inverse problem, and then the optimization procedure is executed by the use of a metamodel. The applications of the presented material model and proposed parameter identification method in the standard A 2017-T4 tensile test prove that the presented elastic-plastic damage model is adequate to describe the material's mechanical behaviour and that the proposed metamodel-based inverse method not only enhances the efficiency of parameter identification but also gives reliable results.

Arterial stiffness in normotensive and hypertensive subjects: Frequency in community pharmacies.

PubMed

Rodilla Sala, Enrique; Adell Alegre, Manuel; Giner Galvañ, Vicente; Perseguer Torregrosa, Zeneida; Pascual Izuel, Jose Maria; Climent Catalá, María Teresa

2017-12-07

Arterial stiffness (AS) is a well-recognized target organ lesion. This study aims to determine: 1) the frequency of AS in community pharmacies; 2) if stiffened subjects identified by brachial oscillometry have more CV risk factors than normal subjects, and 3) the dependence of stiffness on using either age-adjusted values or a fixed threshold. Observational, cross-sectional study in 32 community pharmacies of the Valencia Community, between November/2015 and April/2016. Stiffness was as pulse wave velocity (PWV) measured with a semi-automatic, validated device (Mobil-O-Graph ® , IEM), followed by a 10-item questionnaire. Mean age of the 1,427 consecutive recruited patients was 56.6 years. Overall proportion of patients with AS was 17.4% with age-adjusted PWV (9.4% in normotensives, 28.3% in hypertensives). Multivariate logistic regression showed independent association of stiffness in normotensives with male gender, obesity, higher pulse pressure and heart rate, in hypertensives, with higher pulse pressure and lower age. AS was globally found in 20.5% of subjects, defining stiffness by PWV>10m/s (6.2% in normotensives, 40.2% in hypertensives). It was associated with higher age and pulse pressure in both groups. Concordance in classifying stiffness was 74.6%. Frequency of AS varied between 17.4-20.5%. Age-adjusted stiffness is associated in normotensives with male gender, pulse pressure, obesity and heart rate, in hypertensives with pulse pressure and inversely to age. Stiffness by 10m/s is determined by higher pulse pressure and higher age. Both definitions of PWV are not interchangeable. Copyright © 2017 Elsevier España, S.L.U. All rights reserved.

Fat suppression with short inversion time inversion-recovery and chemical-shift selective saturation: a dual STIR-CHESS combination prepulse for turbo spin echo pulse sequences.

PubMed

Tanabe, Koji; Nishikawa, Keiichi; Sano, Tsukasa; Sakai, Osamu; Jara, Hernán

2010-05-01

To test a newly developed fat suppression magnetic resonance imaging (MRI) prepulse that synergistically uses the principles of fat suppression via inversion recovery (STIR) and spectral fat saturation (CHESS), relative to pure CHESS and STIR. This new technique is termed dual fat suppression (Dual-FS). To determine if Dual-FS could be chemically specific for fat, the phantom consisted of the fat-mimicking NiCl(2) aqueous solution, porcine fat, porcine muscle, and water was imaged with the three fat-suppression techniques. For Dual-FS and STIR, several inversion times were used. Signal intensities of each image obtained with each technique were compared. To determine if Dual-FS could be robust to magnetic field inhomogeneities, the phantom consisting of different NiCl(2) aqueous solutions, porcine fat, porcine muscle, and water was imaged with Dual-FS and CHESS at the several off-resonance frequencies. To compare fat suppression efficiency in vivo, 10 volunteer subjects were also imaged with the three fat-suppression techniques. Dual-FS could suppress fat sufficiently within the inversion time of 110-140 msec, thus enabling differentiation between fat and fat-mimicking aqueous structures. Dual-FS was as robust to magnetic field inhomogeneities as STIR and less vulnerable than CHESS. The same results for fat suppression were obtained in volunteers. The Dual-FS-STIR-CHESS is an alternative and promising fat suppression technique for turbo spin echo MRI. Copyright 2010 Wiley-Liss, Inc.

Bayesian parameter estimation in spectral quantitative photoacoustic tomography

NASA Astrophysics Data System (ADS)

Pulkkinen, Aki; Cox, Ben T.; Arridge, Simon R.; Kaipio, Jari P.; Tarvainen, Tanja

2016-03-01

Photoacoustic tomography (PAT) is an imaging technique combining strong contrast of optical imaging to high spatial resolution of ultrasound imaging. These strengths are achieved via photoacoustic effect, where a spatial absorption of light pulse is converted into a measurable propagating ultrasound wave. The method is seen as a potential tool for small animal imaging, pre-clinical investigations, study of blood vessels and vasculature, as well as for cancer imaging. The goal in PAT is to form an image of the absorbed optical energy density field via acoustic inverse problem approaches from the measured ultrasound data. Quantitative PAT (QPAT) proceeds from these images and forms quantitative estimates of the optical properties of the target. This optical inverse problem of QPAT is illposed. To alleviate the issue, spectral QPAT (SQPAT) utilizes PAT data formed at multiple optical wavelengths simultaneously with optical parameter models of tissue to form quantitative estimates of the parameters of interest. In this work, the inverse problem of SQPAT is investigated. Light propagation is modelled using the diffusion equation. Optical absorption is described with chromophore concentration weighted sum of known chromophore absorption spectra. Scattering is described by Mie scattering theory with an exponential power law. In the inverse problem, the spatially varying unknown parameters of interest are the chromophore concentrations, the Mie scattering parameters (power law factor and the exponent), and Gruneisen parameter. The inverse problem is approached with a Bayesian method. It is numerically demonstrated, that estimation of all parameters of interest is possible with the approach.

Saturation capability of short phase modulated pulses facilitates the measurement of longitudinal relaxation times of quadrupolar nuclei.

PubMed

Makrinich, Maria; Gupta, Rupal; Polenova, Tatyana; Goldbourt, Amir

The ability of various pulse types, which are commonly applied for distance measurements, to saturate or invert quadrupolar spin polarization has been compared by observing their effect on magnetization recovery curves under magic-angle spinning. A selective central transition inversion pulse yields a bi-exponential recovery for a diamagnetic sample with a spin-3/2, consistent with the existence of two processes: the fluctuations of the electric field gradients with identical single (W 1 ) and double (W 2 ) quantum quadrupolar-driven relaxation rates, and spin exchange between the central transition of one spin and satellite transitions of a dipolar-coupled similar spin. Using a phase modulated pulse, developed for distance measurements in quadrupolar spins (Nimerovsky et al., JMR 244, 2014, 107-113) and suggested for achieving the complete saturation of all quadrupolar spin energy levels, a mono-exponential relaxation model fits the data, compatible with elimination of the spin exchange processes. Other pulses such as an adiabatic pulse lasting one-third of a rotor period, and a two-rotor-period long continuous-wave pulse, both used for distance measurements under special experimental conditions, yield good fits to bi-exponential functions with varying coefficients and time constants due to variations in initial conditions. Those values are a measure of the extent of saturation obtained from these pulses. An empirical fit of the recovery curves to a stretched exponential function can provide general recovery times. A stretching parameter very close to unity, as obtained for a phase modulated pulse but not for other cases, suggests that in this case recovery times and longitudinal relaxation times are similar. The results are experimentally demonstrated for compounds containing 11 B (spin-3/2) and 51 V (spin-7/2). We propose that accurate spin lattice relaxation rates can be measured by a short phase modulated pulse (<1-2ms), similarly to the "true T 1 " measured by saturation with an asynchronous pulse train (Yesinowski, JMR 252, 2015, 135-144). Copyright © 2017 Elsevier Inc. All rights reserved.

Comparison of (31)P saturation and inversion magnetization transfer in human liver and skeletal muscle using a clinical MR system and surface coils.

PubMed

Buehler, Tania; Kreis, Roland; Boesch, Chris

2015-02-01

(31)P MRS magnetization transfer ((31)P-MT) experiments allow the estimation of exchange rates of biochemical reactions, such as the creatine kinase equilibrium and adenosine triphosphate (ATP) synthesis. Although various (31)P-MT methods have been successfully used on isolated organs or animals, their application on humans in clinical scanners poses specific challenges. This study compared two major (31)P-MT methods on a clinical MR system using heteronuclear surface coils. Although saturation transfer (ST) is the most commonly used (31)P-MT method, sequences such as inversion transfer (IT) with short pulses might be better suited for the specific hardware and software limitations of a clinical scanner. In addition, small NMR-undetectable metabolite pools can transfer MT to NMR-visible pools during long saturation pulses, which is prevented with short pulses. (31)P-MT sequences were adapted for limited pulse length, for heteronuclear transmit-receive surface coils with inhomogeneous B1 , for the need for volume selection and for the inherently low signal-to-noise ratio (SNR) on a clinical 3-T MR system. The ST and IT sequences were applied to skeletal muscle and liver in 10 healthy volunteers. Monte-Carlo simulations were used to evaluate the behavior of the IT measurements with increasing imperfections. In skeletal muscle of the thigh, ATP synthesis resulted in forward reaction constants (k) of 0.074 ± 0.022 s(-1) (ST) and 0.137 ± 0.042 s(-1) (IT), whereas the creatine kinase reaction yielded 0.459 ± 0.089 s(-1) (IT). In the liver, ATP synthesis resulted in k = 0.267 ± 0.106 s(-1) (ST), whereas the IT experiment yielded no consistent results. ST results were close to literature values; however, the IT results were either much larger than the corresponding ST values and/or were widely scattered. To summarize, ST and IT experiments can both be implemented on a clinical body scanner with heteronuclear transmit-receive surface coils; however, ST results are much more robust against experimental imperfections than the current implementation of IT. Copyright © 2014 John Wiley & Sons, Ltd.

Nonlinear reflection of a spherically divergent N-wave from a plane surface: Optical interferometry measurements in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karzova, M., E-mail: masha@acs366.phys.msu.ru; Physics Faculty, Moscow State University, Leninskie Gory, 119991 Moscow; Yuldashev, P.

2015-10-28

Mach stem is a well-known structure typically observed in the process of strong (acoustic Mach numbers greater than 0.4) step-shock waves reflection from a rigid boundary. However, this phenomenon has been much less studied for weak shocks in nonlinear acoustic fields where Mach numbers are in the range from 0.001 to 0.01 and pressure waveforms have more complicated waveforms than step shocks. The goal of this work was to demonstrate experimentally how nonlinear reflection occurs in air for very weak spherically divergent acoustic spark-generated pulses resembling an N-wave. Measurements of reflection patterns were performed using a Mach-Zehnder interferometer. A thinmore » laser beam with sub-millimeter cross-section was used to obtain the time resolution of 0.4 µs, which is 6 times higher than the time resolution of the condenser microphones. Pressure waveforms were reconstructed using the inverse Abel transform applied to the phase of the signal measured by the interferometer. The Mach stem formation was observed experimentally as a result of collision of the incident and reflected shock pulses. It was shown that irregular reflection of the pulse occurred in a dynamic way and the length of the Mach stem increased linearly while the pulse propagated along the surface. Since the front shock of the spark-generated pulse was steeper than the rear shock, irregular type of reflection was observed only for the front shock of the pulse while the rear shock reflection occurred in a regular regime.« less

INPIStron switched pulsed power for dense plasma pinches

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Lee, Ja H.

1993-01-01

The inverse plasma switch INPIStron was employed for 10kJ/40kV capacitor bank discharge system to produce focused dense plasmas in hypocycloidal-pinch (HCP) devices. A single unit and an array of multiple HCP's were coupled as the load of the pulsed power circuit. The geometry and switching plasma dynamics were found advantageous and convenient for commutating the large current pulse from the low impedance transmission line to the low impedance plasma load. The pulse power system with a single unit HCP, the system A, was used for production of high temperature plasma focus and its diagnostics. The radially running down plasma dynamics, revealed in image converter photographs, could be simulated by a simple snow-plow model with a correction for plasma resistivity. The system B with an array of 8-HCP units which forms a long coaxial discharge chamber was used for pumping a Ti-sapphire laser. The intense UV emission from the plasma was frequency shifted with dye-solution jacket to match the absorption band of the Ti crystal laser near 500 nm. An untuned laser pulse energy of 0.6 J/pulse was obtained for 6.4 kJ/40 kV discharge, or near 103 times of the explosion limit of conventional flash lamps. For both systems the advantages of the INPIStron were well demonstrated: a single unit is sufficient for a large current (greater than 50 kA) without increasing the system impedance, highly reliable and long life operation and implied scalability for the high power ranges above I(sub peak) = 1 MA and V(sub hold) = 100 kV.

Sparsity-based acoustic inversion in cross-sectional multiscale optoacoustic imaging.

PubMed

Han, Yiyong; Tzoumas, Stratis; Nunes, Antonio; Ntziachristos, Vasilis; Rosenthal, Amir

2015-09-01

With recent advancement in hardware of optoacoustic imaging systems, highly detailed cross-sectional images may be acquired at a single laser shot, thus eliminating motion artifacts. Nonetheless, other sources of artifacts remain due to signal distortion or out-of-plane signals. The purpose of image reconstruction algorithms is to obtain the most accurate images from noisy, distorted projection data. In this paper, the authors use the model-based approach for acoustic inversion, combined with a sparsity-based inversion procedure. Specifically, a cost function is used that includes the L1 norm of the image in sparse representation and a total variation (TV) term. The optimization problem is solved by a numerically efficient implementation of a nonlinear gradient descent algorithm. TV-L1 model-based inversion is tested in the cross section geometry for numerically generated data as well as for in vivo experimental data from an adult mouse. In all cases, model-based TV-L1 inversion showed a better performance over the conventional Tikhonov regularization, TV inversion, and L1 inversion. In the numerical examples, the images reconstructed with TV-L1 inversion were quantitatively more similar to the originating images. In the experimental examples, TV-L1 inversion yielded sharper images and weaker streak artifact. The results herein show that TV-L1 inversion is capable of improving the quality of highly detailed, multiscale optoacoustic images obtained in vivo using cross-sectional imaging systems. As a result of its high fidelity, model-based TV-L1 inversion may be considered as the new standard for image reconstruction in cross-sectional imaging.

Kinetics of the Active Medium of a Copper Vapor Brightness Amplifier

NASA Astrophysics Data System (ADS)

Kulagin, A. E.; Torgaev, S. N.; Evtushenko, G. S.; Trigub, M. V.

2018-03-01

A spatiotemporal kinetics of the active medium of a copper vapor brightness amplifier is described that allows gain characteristics to be investigated during the pump pulse. Model calculations show that changing the discharge parameters allows the radial gain profiles to be improved significantly, as well as the gain and the inversion duration to be increased. The data obtained will be used to choose the operating conditions for the active medium in the brightness amplifier mode.

Diode Laser Pumped Alkali Vapor Lasers with Exciplex-Assisted Absorption

DTIC Science & Technology

2013-05-14

transfer agent that established the population inversion. The excitation source used in these initial studies was a pulsed optical parametric oscillator ...parametric oscillator . The lasers operated at 703.2 (Ne*), 912.5 (Ar*), 893.1 (Kr*) and 980.2 run (Xe*). Peak powers as high as 27kW/cm2 were observed...Larissa Glebova and Leonid B. Glebov. Ultra-low absorption and laser-induced heating of volume Bragg combiners recorded in photo-thermo- refractive

Assessment of alveolar bone marrow fat content using 15 T MRI.

PubMed

Cortes, Arthur Rodriguez Gonzalez; Cohen, Ouri; Zhao, Ming; Aoki, Eduardo Massaharu; Ribeiro, Rodrigo Alves; Abu Nada, Lina; Costa, Claudio; Arita, Emiko Saito; Tamimi, Faleh; Ackerman, Jerome L

2018-03-01

Bone marrow fat is inversely correlated with bone mineral density. The aim of this study is to present a method to quantify alveolar bone marrow fat content using a 15 T magnetic resonance imaging (MRI) scanner. A 15 T MRI scanner with a 13-mm inner diameter loop-gap radiofrequency coil was used to scan seven 3-mm diameter alveolar bone biopsy specimens. A 3-D gradient-echo relaxation time (T1)-weighted pulse sequence was chosen to obtain images. All images were obtained with a voxel size (58 µm 3 ) sufficient to resolve trabecular spaces. Automated volume of the bone marrow fat content and derived bone volume fraction (BV/TV) were calculated. Results were compared with actual BV/TV obtained from micro-computed tomography (CT) scans. Mean fat tissue volume was 20.1 ± 11%. There was a significantly strong inverse correlation between fat tissue volume and BV/TV (r = -0.68; P = .045). Furthermore, there was a strong agreement between BV/TV derived from MRI and obtained with micro-CT (interclass correlation coefficient = 0.92; P = .001). Bone marrow fat of small alveolar bone biopsy specimens can be quantified with sufficient spatial resolution using an ultra-high-field MRI scanner and a T1-weighted pulse sequence. Copyright © 2017 Elsevier Inc. All rights reserved.

Associations of Dairy Intake with Arterial Stiffness in Brazilian Adults: The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

PubMed

Ribeiro, Amanda Gomes; Mill, José Geraldo; Cade, Nágela Valadão; Velasquez-Melendez, Gustavo; Matos, Sheila Maria Alvim; Molina, Maria Del Carmen Bisi

2018-05-31

Recent studies have suggested the possible effect of dairy product intake on cardiovascular risk markers, including arterial stiffness. Our aim was to investigate whether dairy food intake is associated with arterial stiffness, which we assessed by carotid-femoral pulse wave velocity (cfPWV) and pulse pressure (PP) in a cross-sectional analysis of baseline data (2008⁻2010; n = 12,892) of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Dairy consumption was evaluated with a validated food-frequency questionnaire (FFQ) by computing servings per day for total and subgroups of dairy products. Dairy consumption was described in four categories (≤1 serving/day to >4 servings/day). Covariance analysis (ANCOVA) was used to compare cfPWV across increasing intake of dairy food, adjusting for confounding factors, including non-dairy food groups. The intake of total dairy was inversely associated with cfPWV and PP (-0.13 m/s and -1.3 mmHg, from the lowest and to the highest category of dairy intake). Low-fat dairy, fermented dairy and cheese showed an inverse relationship with cfPWV and PP. These findings suggest a beneficial effect of dairy consumption to reduce arterial stiffness. However, further evidence from longitudinal studies or long-term intervention is needed to support reduction of cfPWV and PP mediating the beneficial effects of dairy products on cardiovascular health.

Pump-induced phase aberrations in Yb3+-doped materials(Conference Presentation)

NASA Astrophysics Data System (ADS)

Keppler, Sebastian; Tamer, Issa; Hornung, Marco; Körner, Jörg; Liebetrau, Hartmut; Hein, Joachim; Kaluza, Malte C.

2017-05-01

Optical pumping of laser materials is an effective way to create a population inversion necessary for laser operation. However, a fraction of the pump energy is always transfered as heat into the laser material, which is mainly caused by the quantum defect. For Yb3+-doped materials, the small energy difference between the pump level and the laser level and the pumping with narrowband high-power laser diodes result in a quantum defect of approx. 9%, which is significantly lower compared to other dopants e.g. Ti3+ (33%) or Nd3+ (24%). Due to the low heat introduction, high optical-to-optical efficiency and high repetition rate laser systems based on diode-pumping are well-suited for a number of applications. Here, however, laser beam quality is of crucial importance. Phase distortions and beam profile modulations can lead to optical damages as well as a significant reduction of the focal spot intensity. Pump-induced phase aberrations are the main cause for phase distortions of the amplified laser beam. The heat transferred to the material causes a change of the refractive index (dn/dT), thermal expansion and stress within the laser material, eventually leading to spatial phase aberrations (also called `thermal lens'). However, the spatially dependent distribution of the population inversion itself also leads to spatial phase aberrations. Since electron excitation directly leads to a change in the charge distribution of the laser active ions, the dynamic response of the material to external fields changes. These electronic phase aberrations (also called `population lens') are described by a change in the polarizability of the material. Due to the low quantum defect of Yb3+-doped materials, this effect becomes more important. We show the first comprehensive spatio-temporal characterization of the pump-induced phase aberration including both effects. A high-resolution interference measurement was carried out with time steps of 50µs for times during the pump period and the cooling period between subsequent pump pulses. We found that both phase effects significantly contribute to the overall phase distortions. Since the temporal characteristic of the electronic phase depends on the fluorescence lifetime and the thermal phase on the thermal diffusivity, both phase effects could be distinguished by their different lifetimes. The measurements were carried out for Yb:YAG, Yb:CaF2 and Yb:glass, and are in excellent agreement to our detailed, COMSOL-based, spatio-temporal phase simulations. Since Yb:CaF2 and Yb:glass provide a negative dn/dT, the electronic phase change becomes even more important and, in case of Yb:CaF2, almost completely compensates the thermal phase imprint of a pump pulse during the time frame of laser pulse amplification.

Design and performance of a pulse transformer based on Fe-based nanocrystalline core.

PubMed

Yi, Liu; Xibo, Feng; Lin, Fuchang

2011-08-01

A dry-type pulse transformer based on Fe-based nanocrystalline core with a load of 0.88 nF, output voltage of more than 65 kV, and winding ratio of 46 is designed and constructed. The dynamic characteristics of Fe-based nanocrystalline core under the impulse with the pulse width of several microseconds were studied. The pulse width and incremental flux density have an important effect on the pulse permeability, so the pulse permeability is measured under a certain pulse width and incremental flux density. The minimal volume of the toroidal pulse transformer core is determined by the coupling coefficient, the capacitors of the resonant charging circuit, incremental flux density, and pulse permeability. The factors of the charging time, ratio, and energy transmission efficiency in the resonant charging circuit based on magnetic core-type pulse transformer are analyzed. Experimental results of the pulse transformer are in good agreement with the theoretical calculation. When the primary capacitor is 3.17 μF and charge voltage is 1.8 kV, a voltage across the secondary capacitor of 0.88 nF with peak value of 68.5 kV, rise time (10%-90%) of 1.80 μs is obtained.

Children with a history of prematurity presenting with snoring and sleep-disordered breathing: a cross-sectional study.

PubMed

Manuel, Anura; Witmans, Manisha; El-Hakim, Hamdy

2013-08-01

To report on the prevalence of premature (PM) birth in a consecutive series of children treated for snoring and sleep-disordered breathing (S/SDB), the parameters specific to their management and variables predictive of disease severity. A retrospective study was undertaken at a tertiary pediatric hospital. Children with history of PM and presenting with S/SDB were identified from a prospectively kept surgical database. We set out to determine the prevalence of PM among the patients presenting with S/SDB who required airway evaluations and surgery. Pulse oximetry is overnight recordable oxygen saturation and heart rate tracing that provides information about hypoxemia during sleep. This was performed on all children preoperatively. The pulse oximetry findings were used to plan for perioperative monitoring and care. A multivariable analysis was used to identify factors predictive of abnormal pulse oximetry studies. We evaluated the associated diagnoses, surgical procedures required, and response to treatment in these selected children. Fifty-seven out of 1,038 patients were PM (33 males; mean age, 62.09 ± 34.91 months; range, 4-190 months). The mean gestational age was 30.3 ± 4.0 weeks. The prevalence rate of PM among patients treated surgically for SDB is 5.5% (95% CI 5.2-5.8) at our center. Comorbid pulmonary and gastrointestinal disorders were encountered on 23 (40%) and 17 (29.8%) occasions, respectively, and were the most commonly encountered comorbid diagnostic categories. Large airway abnormalities were encountered in 11 (19.3%) children, and the most common were subglottic stenosis (four) and laryngeal paralysis (four). Comorbid respiratory disease was negatively predictive of abnormal pulse oximetry (coefficient -0.35, P<.05). Postoperative respiratory outcomes correlated with abnormal pulse oximetry (coefficient 0.3; P<.05). Our findings suggest children with PM presenting to pediatric otolaryngology require a comprehensive evaluation for S/SDB. A significant proportion of children with S/SDB and a history of PM frequently had pulmonary and gastrointestinal comorbidities in our cohort. One-half required admission postoperatively, and these were predictable based on preoperative pulse oximetry. Respiratory comorbidity was negatively predictive of severity of SDB. Inversely, children with untreated pulmonary comorbidities are more likely to have postoperative complications. © 2013 The American Laryngological, Rhinological and Otological Society, Inc.

Estimation of biological parameters of marine organisms using linear and nonlinear acoustic scattering model-based inversion methods.

PubMed

Chu, Dezhang; Lawson, Gareth L; Wiebe, Peter H

2016-05-01

The linear inversion commonly used in fisheries and zooplankton acoustics assumes a constant inversion kernel and ignores the uncertainties associated with the shape and behavior of the scattering targets, as well as other relevant animal parameters. Here, errors of the linear inversion due to uncertainty associated with the inversion kernel are quantified. A scattering model-based nonlinear inversion method is presented that takes into account the nonlinearity of the inverse problem and is able to estimate simultaneously animal abundance and the parameters associated with the scattering model inherent to the kernel. It uses sophisticated scattering models to estimate first, the abundance, and second, the relevant shape and behavioral parameters of the target organisms. Numerical simulations demonstrate that the abundance, size, and behavior (tilt angle) parameters of marine animals (fish or zooplankton) can be accurately inferred from the inversion by using multi-frequency acoustic data. The influence of the singularity and uncertainty in the inversion kernel on the inversion results can be mitigated by examining the singular values for linear inverse problems and employing a non-linear inversion involving a scattering model-based kernel.

The attitude inversion method of geostationary satellites based on unscented particle filter

NASA Astrophysics Data System (ADS)

Du, Xiaoping; Wang, Yang; Hu, Heng; Gou, Ruixin; Liu, Hao

2018-04-01

The attitude information of geostationary satellites is difficult to be obtained since they are presented in non-resolved images on the ground observation equipment in space object surveillance. In this paper, an attitude inversion method for geostationary satellite based on Unscented Particle Filter (UPF) and ground photometric data is presented. The inversion algorithm based on UPF is proposed aiming at the strong non-linear feature in the photometric data inversion for satellite attitude, which combines the advantage of Unscented Kalman Filter (UKF) and Particle Filter (PF). This update method improves the particle selection based on the idea of UKF to redesign the importance density function. Moreover, it uses the RMS-UKF to partially correct the prediction covariance matrix, which improves the applicability of the attitude inversion method in view of UKF and the particle degradation and dilution of the attitude inversion method based on PF. This paper describes the main principles and steps of algorithm in detail, correctness, accuracy, stability and applicability of the method are verified by simulation experiment and scaling experiment in the end. The results show that the proposed method can effectively solve the problem of particle degradation and depletion in the attitude inversion method on account of PF, and the problem that UKF is not suitable for the strong non-linear attitude inversion. However, the inversion accuracy is obviously superior to UKF and PF, in addition, in the case of the inversion with large attitude error that can inverse the attitude with small particles and high precision.

High frequency pressure oscillator for microcryocoolers.

PubMed

Vanapalli, S; ter Brake, H J M; Jansen, H V; Zhao, Y; Holland, H J; Burger, J F; Elwenspoek, M C

2008-04-01

Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80 K, delivering a cooling power of 10 mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5 MPa and compression volume of about 22.6 mm(3) when operating the actuator with a peak-to-peak sinusoidal voltage of 100 V at a frequency of 1 kHz. The electrical power input was 2.73 W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.

High frequency pressure oscillator for microcryocoolers

NASA Astrophysics Data System (ADS)

Vanapalli, S.; ter Brake, H. J. M.; Jansen, H. V.; Zhao, Y.; Holland, H. J.; Burger, J. F.; Elwenspoek, M. C.

2008-04-01

Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80K, delivering a cooling power of 10mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5MPa and compression volume of about 22.6mm3 when operating the actuator with a peak-to-peak sinusoidal voltage of 100V at a frequency of 1kHz. The electrical power input was 2.73W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.

Coherent pulses in the diffusive transport of charged particles`

NASA Technical Reports Server (NTRS)

Kota, J.

1994-01-01

We present exact solutions to the diffusive transport of charged particles following impulsive injection for a simple model of scattering. A modified, two-parameter relaxation-time model is considered that simulates the low rate of scattering through perpendicular pitch-angle. Scattering is taken to be isotropic within each of the foward- and backward-pointing hemispheres, respectively, but, at the same time, a reduced rate of sccattering is assumed from one hemisphere to the other one. By applying a technique of Fourier- and Laplace-transform, the inverse transformation can be performed and exact solutions can be reached. By contrast with the first, and so far only exact solutions of Federov and Shakov, this wider class of solutions gives rise to coherent pulses to appear. The present work addresses omnidirectional densities for isotropic injection from an instantaneous and localized source. The dispersion relations are briefly discussed. We find, for this particular model, two diffusive models to exist up to a certain limiting wavenumber. The corresponding eigenvalues are real at the lowest wavenumbers. Complex eigenvalues, which are responsible for coherent pulses, appear at higher wavenumbers.

Wave propagation in pulsar magnetospheres - Refraction of rays in the open flux zone

NASA Technical Reports Server (NTRS)

Barnard, J. J.; Arons, J.

1986-01-01

The propagation of waves through a relativistically outflowing electron-positron plasma in a very strong dipolar magnetic field, conditions expected in pulsar magnetospheres, is investigated. Halmilton's equations is derived for the propagation of rays through a plasma which is inhomogeneous in density, magnetic field directions, and Lorentz factor. These equations are solved for rays propagating through the plasmas outflowing along the 'open' dipolar field lines in which the density decreases inversely as the radius cubed and in the case where gradients transverse to the radial direction exist. In the radial case, the effects of refraction on pulse profiles, spectrum, and polarization are examined, and the effects of a transverse gradient are indicated. Attention is given to models in which the observed broad bandwidth in the radio emission has its origin in a radius to frequency map. Models with broad-band emission at a single radius are also studied. These are compared to observations of pulse width and pulse component separation as a function of frequency. The origin of 'orthogonal modes' is discussed.

Back-bombardment compensation in microwave thermionic electron guns

NASA Astrophysics Data System (ADS)

Kowalczyk, Jeremy M. D.; Madey, John M. J.

2014-12-01

The development of capable, reliable, and cost-effective compact electron beam sources remains a long-standing objective of the efforts to develop the accelerator systems needed for on-site research and industrial applications ranging from electron beam welding to high performance x-ray and gamma ray light sources for element-resolved microanalysis and national security. The need in these applications for simplicity, reliability, and low cost has emphasized solutions compatible with the use of the long established and commercially available pulsed microwave rf sources and L-, S- or X-band linear accelerators. Thermionic microwave electron guns have proven to be one successful approach to the development of the electron sources for these systems providing high macropulse average current beams with picosecond pulse lengths and good emittance out to macropulse lengths of 4-5 microseconds. But longer macropulse lengths are now needed for use in inverse-Compton x-ray sources and other emerging applications. We describe in this paper our approach to extending the usable macropulse current and pulse length of these guns through the use of thermal diffusion to compensate for the increase in cathode surface temperature due to back-bombardment.

Study of the intensity noise and intensity modulation in a of hybrid soliton pulsed source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dogru, Nuran; Oziazisi, M Sadetin

2005-10-31

The relative intensity noise (RIN) and small-signal intensity modulation (IM) of a hybrid soliton pulsed source (HSPS) with a linearly chirped Gaussian apodised fibre Bragg grating (FBG) are considered in the electric-field approximation. The HSPS is described by solving the dynamic coupled-mode equations. It is shown that consideration of the carrier density noise in the HSPS in addition to the spontaneous noise is necessary to analyse accurately noise in the mode-locked HSPS. It is also shown that the resonance peak spectral splitting (RPSS) of the IM near the frequency inverse to the round-trip time of light in the external cavitymore » can be eliminated by selecting an appropriate linear chirp rate in the Gaussian apodised FBG. (laser applications and other topics in quantum electronics)« less

Theoretical and experimental study of a laser-diode-pumped actively Q-switched Yb:NaY(WO4)2 laser with acoustic-optic modulator

NASA Astrophysics Data System (ADS)

Zhang, Haikun; Xia, Wei; Song, Peng; Wang, Jing; Li, Xin

2018-03-01

A laser-diode-pumped actively Q-switched Yb:NaY(WO4)2 laser operating at around 1040 nm is presented for the first time with acoustic-optic modulator. The dependence of pulse width on incident pump power for different pulse repetition rates is measured. By considering the Guassian spatial distribution of the intracavity photon density and the initial population-inversion density as well as the longitudinal distribution of the photon density along the cavity axis and the turn off time of the acoustic-optic Q-switch, the coupled equations of the actively Q-switched Yb:NaY(WO4)2 laser are given. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.

What is the surface temperature of a solid irradiated by a Petawatt laser?

NASA Astrophysics Data System (ADS)

Kemp, A. J.; Divol, L.

2016-09-01

When a solid target is irradiated by a Petawatt laser pulse, its surface is heated to tens of millions of degrees within a few femtoseconds, facilitating a diffusive heat wave and the acceleration of electrons to MeV energies into the target. Using numerically converged collisional particle-in-cell simulations, we observe a competition between two surface heating mechanisms-inverse bremsstrahlung in solid density on the one hand and electron scattering on turbulent electric fields on the other. Collisionless heating effectively dominates above the relativistic intensity threshold. Our numerical results show that a high-contrast 40 fs, f/5 laser pulse with 1 J energy will heat the skin layer to 5 keV, and the inside of the target over several microns deep to bulk temperatures in the range of 10-100 eV at solid density.

Circulating Adipokines and Vascular Function: Cross-Sectional Associations in a Community-Based Cohort.

PubMed

Zachariah, Justin P; Hwang, Susan; Hamburg, Naomi M; Benjamin, Emelia J; Larson, Martin G; Levy, Daniel; Vita, Joseph A; Sullivan, Lisa M; Mitchell, Gary F; Vasan, Ramachandran S

2016-02-01

Adipokines may be potential mediators of the association between excess adiposity and vascular dysfunction. We assessed the cross-sectional associations of circulating adipokines with vascular stiffness in a community-based cohort of younger adults. We related circulating concentrations of leptin and leptin receptor, adiponectin, retinol-binding protein 4, and fatty acid-binding protein 4 to vascular stiffness measured by arterial tonometry in 3505 Framingham Third Generation cohort participants free of cardiovascular disease (mean age 40 years, 53% women). Separate regression models estimated the relations of each adipokine to mean arterial pressure and aortic stiffness, as carotid femoral pulse wave velocity, adjusting for age, sex, smoking, heart rate, height, antihypertensive treatment, total and high-density lipoprotein cholesterol, diabetes mellitus, alcohol consumption, estimated glomerular filtration rate, glucose, and C-reactive protein. Models evaluating aortic stiffness also were adjusted for mean arterial pressure. Mean arterial pressure was positively associated with blood retinol-binding protein 4, fatty acid-binding protein 4, and leptin concentrations (all P<0.001) and inversely with adiponectin (P=0.002). In fully adjusted models, mean arterial pressure was positively associated with retinol-binding protein 4 and leptin receptor levels (P<0.002 both). In fully adjusted models, aortic stiffness was positively associated with fatty acid-binding protein 4 concentrations (P=0.02), but inversely with leptin and leptin receptor levels (P≤0.03 both). In our large community-based sample, circulating concentrations of select adipokines were associated with vascular stiffness measures, consistent with the hypothesis that adipokines may influence vascular function and may contribute to the relation between obesity and hypertension. © 2015 American Heart Association, Inc.

Sparsity-based acoustic inversion in cross-sectional multiscale optoacoustic imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yiyong; Tzoumas, Stratis; Nunes, Antonio

2015-09-15

Purpose: With recent advancement in hardware of optoacoustic imaging systems, highly detailed cross-sectional images may be acquired at a single laser shot, thus eliminating motion artifacts. Nonetheless, other sources of artifacts remain due to signal distortion or out-of-plane signals. The purpose of image reconstruction algorithms is to obtain the most accurate images from noisy, distorted projection data. Methods: In this paper, the authors use the model-based approach for acoustic inversion, combined with a sparsity-based inversion procedure. Specifically, a cost function is used that includes the L1 norm of the image in sparse representation and a total variation (TV) term. Themore » optimization problem is solved by a numerically efficient implementation of a nonlinear gradient descent algorithm. TV–L1 model-based inversion is tested in the cross section geometry for numerically generated data as well as for in vivo experimental data from an adult mouse. Results: In all cases, model-based TV–L1 inversion showed a better performance over the conventional Tikhonov regularization, TV inversion, and L1 inversion. In the numerical examples, the images reconstructed with TV–L1 inversion were quantitatively more similar to the originating images. In the experimental examples, TV–L1 inversion yielded sharper images and weaker streak artifact. Conclusions: The results herein show that TV–L1 inversion is capable of improving the quality of highly detailed, multiscale optoacoustic images obtained in vivo using cross-sectional imaging systems. As a result of its high fidelity, model-based TV–L1 inversion may be considered as the new standard for image reconstruction in cross-sectional imaging.« less

Interference of Overlapping Insect Vibratory Communication Signals: An Eushistus heros Model

PubMed Central

Čokl, Andrej; Laumann, Raul Alberto; Žunič Kosi, Alenka; Blassioli-Moraes, Maria Carolina; Virant-Doberlet, Meta; Borges, Miguel

2015-01-01

Plants limit the range of insect substrate-borne vibratory communication by their architecture and mechanical properties that change transmitted signal time, amplitude and frequency characteristics. Stinkbugs gain higher signal-to-noise ratio and increase communication distance by emitting narrowband low frequency vibratory signals that are tuned with transmission properties of plants. The objective of the present study was to investigate hitherto overlooked consequences of duetting with mutually overlapped narrowband vibratory signals. The overlapped vibrations of the model stinkbug species Eushistus heros, produced naturally or induced artificially on different plants, have been analysed. They represent female and male strategies to preserve information within a complex masked signal. The brown stinkbugs E. heros communicate with species and gender specific vibratory signals that constitute characteristic duets in the calling, courtship and rivalry phases of mating behaviour. The calling female pulse overlaps the male vibratory response when the latency of the latter is shorter than the duration of the female triggering signal or when the male response does not inhibit the following female pulse. Overlapping of signals induces interference that changes their amplitude pattern to a sequence of regularly repeated pulses in which their duration and the difference between frequencies of overlapped vibrations are related inversely. Interference does not occur in overlapped narrow band female calling pulses and broadband male courtship pulse trains. In a duet with overlapped signals females and males change time parameters and increase the frequency difference between signals by changing the frequency level and frequency modulation pattern of their calls. PMID:26098637

Reflexion measurements for inverse characterization of steel diffusion bond mechanical properties

NASA Astrophysics Data System (ADS)

Le Bourdais, Florian; Cachon, Lionel; Rigal, Emmanuel

2017-02-01

The present work describes a non-destructive testing method aimed at securing high manufacturing quality of the innovative compact heat exchanger developed under the framework of the CEA R&D program dedicated to the Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID). The heat exchanger assembly procedure currently proposed involves high temperature and high pressure diffusion welding of stainless steel plates. The aim of the non-destructive method presented herein is to characterize the quality of the welds obtained through this assembly process. Based on a low-frequency model developed by Baik and Thompson [1], pulse-echo normal incidence measurements are calibrated according to a specific procedure and allow the determination of the welding interface stiffness using a nonlinear fitting procedure in the frequency domain. Performing the characterization of plates after diffusion welding using this method allows a useful assessment of the material state as a function of the diffusion bonding process.

Ultrasound Contrast Agents

NASA Astrophysics Data System (ADS)

Cachard, Christian; Basset, Olivier

While the use of contrast agents in other imaging modalities (X ray, MRI, PET, …) has been routinely accepted for many years, the development and commercialization of contrast agents designed specifically for ultrasound imaging has occurred only very recently. As in the other imaging modalities, the injection of contrast agents during an ultrasound examination is intended to facilitate the detection and diagnosis of specific pathologies. Contrast agents efficiency is based on the backscattering of ultrasound by microbubbles. These microparticules are intravenously injected in the blood flow. After an introduction and generalities on ultrasound contrast agents (UCA) the microbubble physics in an acoustic field will be developed. Second, physics characteristics of contrast agents will be compared (bubbles with or without shell, gas nature, size distribution). Influence of acoustic pressure on the behaviour of the microparticules (linear, non linear and destruction) will be discussed. Finally, a review of specific imaging adapted to contrast agent properties as harmonic imaging, pulse inversion imaging will be presented.

Effect of substrate temperature on magnetic properties of MnFe2O4 thin films

NASA Astrophysics Data System (ADS)

Rajagiri, Prabhu; Sahu, B. N.; Venkataramani, N.; Prasad, Shiva; Krishnan, R.

2018-05-01

MnFe2O4 thin films were pulsed laser deposited on to quartz substrate from room temperature (RT) to 650 °C in a pure argon environment. Temperature dependence of spontaneous magnetization (4πMS) was measured on these films from 10 K to 350 K using a vibrating sample magnetometer. Ferromagnetic resonance (FMR) study was also carried out at 300 K. The exchange stiffness constant (D) values were obtained by fitting the 4πMS data to the Bloch's equation. The D values of the films thus found decreases while the 4πMS value increases, though non-monotonically, with the increase in TS and tend to reach bulk values at TS = 650 °C. The variation in D and 4πMS values of the films are explained based on the degree of inversion and oxidation state of cations in thin films.

Multi-mJ energy extraction using Yb-fiber based coherent pulse stacking amplification of fs pulses (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ruppe, John M.; Pei, Hanzhang; Chen, Siyun; Sheikhsofla, Morteza; Wilcox, Russell B.; Nees, John A.; Galvanauskas, Almantas

2017-03-01

We report multi-mJ energy (>5mJ) extraction from femtosecond-pulse Yb-doped fiber CPA using coherent pulse stacking amplification (CPSA) technique. This high energy extraction has been enabled by amplifying 10's of nanosecond long pulse sequence, and by using 85-µm core Yb-doped CCC fiber based power amplification stage. The CPSA system consists of 1-GHz repetition rate mode-locked fiber oscillator, followed by a pair of fast phase and amplitude electro-optic modulators, a diffraction-grating based pulse stretcher, a fiber amplifier chain, a GTI-cavity based pulse stacker, and a diffraction grating pulse compressor. Electro-optic modulators are used to carve out from the 1-GHz mode-locked pulse train an amplitude and phase modulated pulse burst, which after stretching and amplification, becomes equal-amplitude pulse burst consisting of 27 stretched pulses, each approximately 1-ns long. Initial pulse-burst shaping accounts for the strong amplifier saturation effects, so that it is compensated at the power amplifier output. This 27-pulse burst is then coherently stacked into a single pulse using a multiplexed sequence of 5 GTI cavities. The compact-footprint 4+1 multiplexed pulse stacker consists of 4 cavities having rountrip of 1 ns, and one Herriott-cell folded cavity - with 9ns roundtrip. After stacking, stretched pulses are compressed down to the bandwidth-limited 300 fs duration using a standard diffraction-grating pulse compressor.

Terahertz reflection imaging using Kirchhoff migration.

PubMed

Dorney, T D; Johnson, J L; Van Rudd, J; Baraniuk, R G; Symes, W W; Mittleman, D M

2001-10-01

We describe a new imaging method that uses single-cycle pulses of terahertz (THz) radiation. This technique emulates data-collection and image-processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a simple migration procedure to solve the inverse problem; this permits us to reconstruct the location and shape of targets. These results demonstrate the feasibility of the THz system as a test-bed for the exploration of new seismic processing methods involving complex model systems.

VESUVIO-the double difference inverse geometry spectrometer at ISIS

NASA Astrophysics Data System (ADS)

Mayers, J.; Tomkinson, J.; Abdul-Redah, T.; Stirling, W. G.; Andreani, C.; Senesi, R.; Nardone, M.; Colognesi, D.; Degiorgi, E.

2004-07-01

The VESUVIO spectrometer at the ISIS pulsed neutron source performs inelastic neutron scattering at high-energy and wave vector transfers, employing gold and uranium resonant foils. A factor of two improvement in the instrumental resolution has been achieved by making use of the double filter difference method. Experimental results are presented for measurements on polycrystalline Pb, which indicate that accurate measurements of single-particle momentum distribution n(p) in quantum fluids are now possible at eV energy transfers.

Energy spectra unfolding of fast neutron sources using the group method of data handling and decision tree algorithms

NASA Astrophysics Data System (ADS)

Hosseini, Seyed Abolfazl; Afrakoti, Iman Esmaili Paeen

2017-04-01

Accurate unfolding of the energy spectrum of a neutron source gives important information about unknown neutron sources. The obtained information is useful in many areas like nuclear safeguards, nuclear nonproliferation, and homeland security. In the present study, the energy spectrum of a poly-energetic fast neutron source is reconstructed using the developed computational codes based on the Group Method of Data Handling (GMDH) and Decision Tree (DT) algorithms. The neutron pulse height distribution (neutron response function) in the considered NE-213 liquid organic scintillator has been simulated using the developed MCNPX-ESUT computational code (MCNPX-Energy engineering of Sharif University of Technology). The developed computational codes based on the GMDH and DT algorithms use some data for training, testing and validation steps. In order to prepare the required data, 4000 randomly generated energy spectra distributed over 52 bins are used. The randomly generated energy spectra and the simulated neutron pulse height distributions by MCNPX-ESUT for each energy spectrum are used as the output and input data. Since there is no need to solve the inverse problem with an ill-conditioned response matrix, the unfolded energy spectrum has the highest accuracy. The 241Am-9Be and 252Cf neutron sources are used in the validation step of the calculation. The unfolded energy spectra for the used fast neutron sources have an excellent agreement with the reference ones. Also, the accuracy of the unfolded energy spectra obtained using the GMDH is slightly better than those obtained from the DT. The results obtained in the present study have good accuracy in comparison with the previously published paper based on the logsig and tansig transfer functions.

Optical Diagnostics for Plasma-based Particle Accelerators

NASA Astrophysics Data System (ADS)

Muggli, Patric

2009-05-01

One of the challenges for plasma-based particle accelerators is to measure the spatio-temporal characteristics of the accelerated particle bunch. ``Optical'' diagnostics are particularly interesting and useful because of the large number of techniques that exits to determine the properties of photon pulses. The accelerated bunch can produce photons pulses that carry information about its characteristics for example through synchrotron radiation in a magnet, Cherenkov radiation in a gas, and transition radiation (TR) at the boundary between two media with different dielectric constants. Depending on the wavelength of the emission when compared to the particle bunch length, the radiation can be incoherent or coherent. Incoherent TR in the optical range (or OTR) is useful to measure the transverse spatial characteristics of the beam, such as charge distribution and size. Coherent TR (or CTR) carries information about the bunch length that can in principle be retrieved by standard auto-correlation or interferometric techniques, as well as by spectral measurements. A measurement of the total CTR energy emitted by bunches with constant charge can also be used as a shot-to-shot measurement for the relative bunch length as the CTR energy is proportional to the square of the bunch population and inversely proportional to its length (for a fixed distribution). Spectral interferometry can also yield the spacing between bunches in the case where multiple bunches are trapped in subsequent buckets of the plasma wave. Cherenkov radiation can be used as an energy threshold diagnostic for low energy particles. Cherenkov, synchrotron and transition radiation can be used in a dispersive section of the beam line to measure the bunch energy spectrum. The application of these diagnostics to plasma-based particle accelerators, with emphasis on the beam-driven, plasma wakefield accelerator (PWFA) at the SLAC National Accelerator Laboratory will be discussed.

Two Dimensional Finite Element Based Magnetotelluric Inversion using Singular Value Decomposition Method on Transverse Electric Mode

NASA Astrophysics Data System (ADS)

Tjong, Tiffany; Yihaa’ Roodhiyah, Lisa; Nurhasan; Sutarno, Doddy

2018-04-01

In this work, an inversion scheme was performed using a vector finite element (VFE) based 2-D magnetotelluric (MT) forward modelling. We use an inversion scheme with Singular value decomposition (SVD) method toimprove the accuracy of MT inversion.The inversion scheme was applied to transverse electric (TE) mode of MT. SVD method was used in this inversion to decompose the Jacobian matrices. Singular values which obtained from the decomposition process were analyzed. This enabled us to determine the importance of data and therefore to define a threshold for truncation process. The truncation of singular value in inversion processcould improve the resulted model.

Improving the Automatic Inversion of Digital Alouette/ISIS Ionogram Reflection Traces into Topside Electron Density Profiles

NASA Technical Reports Server (NTRS)

Benson, Robert F.; Truhlik, Vladimir; Huang, Xueqin; Wang, Yongli; Bilitza, Dieter

2012-01-01

The topside sounders of the International Satellites for Ionospheric Studies (ISIS) program were designed as analog systems. The resulting ionograms were displayed on 35 mm film for analysis by visual inspection. Each of these satellites, launched between 1962 and 1971, produced data for 10 to 20 years. A number of the original telemetry tapes from this large data set have been converted directly into digital records. Software, known as the Topside Ionogram Scalar With True-Height (TOPIST) algorithm, has been produced and used for the automatic inversion of the ionogram reflection traces on more than 100,000 ISIS-2 digital topside ionograms into topside vertical electron density profiles Ne(h). Here we present some topside ionospheric solar cycle variations deduced from the TOPIST database to illustrate the scientific benefit of improving and expanding the topside ionospheric Ne(h) database. The profile improvements will be based on improvements in the TOPIST software motivated by direct comparisons between TOPIST profiles and profiles produced by manual scaling in the early days of the ISIS program. The database expansion will be based on new software designed to overcome limitations in the original digital topside ionogram database caused by difficulties encountered during the analog-to-digital conversion process in the detection of the ionogram frame sync pulse and/or the frequency markers. This improved and expanded TOPIST topside Ne(h) database will greatly enhance investigations into both short- and long-term ionospheric changes, e.g., the observed topside ionospheric responses to magnetic storms, induced by interplanetary magnetic clouds, and solar cycle variations, respectively.

Time stretch dispersive Fourier transform based single-shot pulse-by-pulse spectrum measurement using a pulse-repetition-frequency-variable gain-switched laser

NASA Astrophysics Data System (ADS)

Furukawa, Hideaki; Makino, Takeshi; Wang, Xiaomin; Kobayashi, Tetsuya; Asghari, Mohammad H.; Trinh, Paul; Jalali, Bahram; Man, Wai Sing; Tsang, Kwong Shing; Wada, Naoya

2018-02-01

The time stretch dispersive Fourier Transform (TS-DFT) technique based on a fiber chromatic dispersion is a powerful tool for pulse-by-pulse single-shot spectrum measurement for highrepetition rate optical pulses. The distributed feedback laser diode (DFB-LD) with the gain switch operation can flexibly change the pulse repetition frequency (PRF). In this paper, we newly introduce a semiconductor gain-switched DFB-LD operating from 1 MHz up to 1 GHz PRF into the TS-DFT based spectrum measurement system to improve the flexibility and the operability. The pulse width can be below 2 ps with a pulse compression technique. We successfully measure the spectrum of each optical pulse at 1 GHz, 100 MHz, and 10 MHz PRF, and demonstrate the flexibility of the measurement system.

ICPP: Relativistic Plasma Physics with Ultra-Short High-Intensity Laser Pulses

NASA Astrophysics Data System (ADS)

Meyer-Ter-Vehn, Juergen

2000-10-01

Recent progress in generating ultra-short high-intensity laser pulses has opened a new branch of relativistic plasma physics, which is discussed in this talk in terms of particle-in-cell (PIC) simulations. These pulses create small plasma volumes of high-density plasma with plasma fields above 10^12 V/m and 10^8 Gauss. At intensities beyond 10^18 W/cm^2, now available from table-top systems, they drive relativistic electron currents in self-focussing plasma channels. These currents are close to the Alfven limit and allow to study relativistic current filamentation. A most remarkable feature is the generation of well collimated relativistic electron beams emerging from the channels with energies up to GeV. In dense matter they trigger cascades of gamma-rays, e^+e^- pairs, and a host of nuclear and particle processes. One of the applications may be fast ignition of compressed inertial fusion targets. Above 10^23 W/cm^2, expected to be achieved in the future, solid-density matter becomes relativistically transparent for optical light, and the acceleration of protons to multi-GeV energies is predicted in plasma layers less than 1 mm thick. These results open completely new perspectives for plasma-based accelerator schemes. Three-dimensional PIC simulations turn out to be the superior tool to explore the relativistic plasma kinetics at such intensities. Results obtained with the VLPL code [1] are presented. Different mechanisms of particle acceleration are discussed. Both laser wakefield and direct laser acceleration in plasma channels (by a mechanism similar to inverse free electron lasers) have been identified. The latter describes recent MPQ experimental results. [1] A. Pukhov, J. Plasma Physics 61, 425 - 433 (1999): Three-dimensional electromagnetic relativistic particle-in-cell code VLPL (Virtual Laser Plasma Laboratory).

Wavelet-based 3-D inversion for frequency-domain airborne EM data

NASA Astrophysics Data System (ADS)

Liu, Yunhe; Farquharson, Colin G.; Yin, Changchun; Baranwal, Vikas C.

2018-04-01

In this paper, we propose a new wavelet-based 3-D inversion method for frequency-domain airborne electromagnetic (FDAEM) data. Instead of inverting the model in the space domain using a smoothing constraint, this new method recovers the model in the wavelet domain based on a sparsity constraint. In the wavelet domain, the model is represented by two types of coefficients, which contain both large- and fine-scale informations of the model, meaning the wavelet-domain inversion has inherent multiresolution. In order to accomplish a sparsity constraint, we minimize an L1-norm measure in the wavelet domain that mostly gives a sparse solution. The final inversion system is solved by an iteratively reweighted least-squares method. We investigate different orders of Daubechies wavelets to accomplish our inversion algorithm, and test them on synthetic frequency-domain AEM data set. The results show that higher order wavelets having larger vanishing moments and regularity can deliver a more stable inversion process and give better local resolution, while the lower order wavelets are simpler and less smooth, and thus capable of recovering sharp discontinuities if the model is simple. At last, we test this new inversion algorithm on a frequency-domain helicopter EM (HEM) field data set acquired in Byneset, Norway. Wavelet-based 3-D inversion of HEM data is compared to L2-norm-based 3-D inversion's result to further investigate the features of the new method.

The Association Between Fog and Temperature Inversions from Ground and Radiosonde Observations in East Greenland

NASA Astrophysics Data System (ADS)

Gilson, G.; Jiskoot, H.

2016-12-01

Many Arctic glaciers terminate along coasts where temperature inversions and sea fog are frequent during summer. Both can influence glacier ablation, but the effects of fog may be complex. To understand fog's physical and radiative properties and its association to temperature inversions it is important to determine accurate Arctic coastal fog climatologies In previous research we determined that fog in East Greenland peaks in the melt season and can be spatially extensive over glacierized terrain. In this study we aim to understand which environmental factors influence fog occurrence in East Greenland; understand the association between fog and temperature inversions; and quantify fog height. We analyzed fog observations and other weather data from coastal synoptic weather stations, and extracted temperature inversions from the Integrated Global Radiosonde Archive radiosonde profiles. Fog height was calculated from radiosonde profiles, based on a method developed for radiation fog which we expanded to include advection and steam fog. Our results show that Arctic coastal fog requires sea ice breakup and a sea breeze with wind speed between 1-4 m/s. Fog is mostly advective, occurring under stable synoptic conditions characterized by deep and strong low-level temperature inversions. Steam fog may occur 5-30% of the time. Fog can occur under near-surface subsidence, with a subsaturated inversion base, or a saturated inversion base. We classified five types of fog based on their vertical sounding characteristics: only at the surface, below an inversion, capped by an inversion, inside a surface-based inversion, or inside a low-level inversion. Fog is commonly 100-400 m thick, often reaching the top of the boundary layer. Fog height is greater at northern stations, where daily fog duration is longer and relative humidity lower. Our results will be included in glacier energy-balance models to account for the influence of fog and temperature inversions on glacier melt.

Plasma-puff initiation of high Coulomb transfer switches

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Venable, Demetrius D.; Lee, Ja H.; Choi, Eun H.; Kim, Y. K.; Kim, J. H.; Nguyen, D. X.

1993-01-01

The plasma-puff triggering mechanism based on a hypocycloidal pinch geometry was investigated to determine the optimal operating conditions for an azimuthally uniform surface flashover which initiates plasma-puff under wide ranges of fill gas pressures of Ar, He and N2. The optimal fill gas pressures for the azimuthally uniform plasma-puff were about 120 mTorr less than P(sub opt) less than 450 Torr for He and N2. For Argon 20 mTorr is less than P(sub opt) is less than 5 Torr. The inverse pinch switch was triggered with the plasma-puff and the switching capability under various electrical parameters and working gas pressures of Ar, He and N2 was determined. It was also shown that the azimuthally uniform switching discharges were dependent on the type of fill gas and its fill pressure. A new concept of plasma-focus driven plasma-puff was also discussed in comparison with hypocycloidal pinch plasma-puff triggering. The main discharge of the inverse pinch switch with the plasma-focus driven plasma-puff trigger is found to be more azimuthally uniform than that with the hypocycloidal pinch plasma-puff trigger in a gas pressure region between 80 mTorr and 1 Torr. In order to assess the effects of plasma current density on material erosion of electrodes, emissions from both an inverse-pinch plasma switch (INPIStron) and from a spark gap switch under test were studied with an optical multichannel analyzer (OMA). The color temperature of the argon plasma was approximately 4,000 K which corresponded with the peak continuum emission near 750 nm. There are the strong line emissions of argon in the 650 - 800 nm range and a lack of line emissions of copper and other solid material used in the switch. This indicates that the plasma current density during closing is low and the hot spot or hot filament in the switch is negligible. This result also indicates considerable reduction of line emission with the INPIStron switch over that of a spark-gap switch. However, a strong carbon line emission exists due to vaporization of the plastic insulator used. In order to reduce the vaporization of the insulator, the plexiglass insulating material of INPIStron was replaced with Z-9 material. A comparative study of the INPIStron and a spark gap also reveals that the INPIStron, with a low impedance of Z = 9 ohms, can transfer a high voltage pulse with a superior pulse-shape fidelity over that of a spark gap with Z = 100 ohms.

Plasma-puff initiation of high Coulomb transfer switches

NASA Technical Reports Server (NTRS)

Venable, D. D.; Han, K. S.

1993-01-01

The plasma-puff triggering mechanism based on a hypocycloidal pinch geometry was investigated to determine the optimal operating conditions for an azimuthally uniform surface flashover which initiates plasma-puff under wide ranges of fill gas pressures of Ar, He and N2. The optimal fill gas pressures for the azimuthally uniform plasma-puff were about 120 mTorr less than P(opt) less than 450 Torr for He and N2. For Argon 120 mTorr less than P(opt) less than 5 Torr for argon. The inverse pinch switch was triggered with the plasma-puff and the switching capability under various electrical parameters and working gas pressures of Ar, He and N2 was determined. It was also shown that the azimuthally uniform switching discharges were dependent on the type of fill gas and its fill pressure. A new concept of plasma-focus driven plasma-puff was also discussed in comparison with hypocycloidal pinch plasma-puff triggering. The main discharge of the inverse pinch switch with the plasma-focus driven plasma-puff trigger is found to be more azimuthally uniform than that with the hypocycloidal pinch plasma-puff trigger in a gas pressure region between 80 mTorr and 1 Torr. In order to assess the effects of plasma current density on material erosion of electrodes, emissions from both an inverse-pinch plasma switch (INPIStron) and from a spark gap switch under test were studied with an optical multichannel analyzer (OMA). The color temperature of the argon plasma was approximately 4,000 K which corresponded with the peak continuum emission near 750 nm. There are the strong line emissions of argon in the 650 - 800 nm range and a lack of line emissions of copper and other solid material used in the switch. This indicates that the plasma current density during closing is low and the hot spot or hot filament in the switch is negligible. This result also indicates considerable reduction of line emission with the INPIStron switch over that of a spark-gap switch. However, a strong carbon line emission exists due to vaporization of the plastic insulator used. In order to reduce the vaporization of the insulator, the plexiglass insulating material of INPIStron was replaced with Z-9 material. A comparative study of the INPIStron and a spark gap also reveals that the INPIStron, with a low impedance of Z equals 9 ohms, can transfer a high voltage pulse with a superior pulse-shape fidelity over that of a spark gap with Z equals 100 ohms.

Inversion of the resonance line of Sr/+/ produced by optically pumping Sr atoms

NASA Technical Reports Server (NTRS)

Green, W. R.; Falcone, R. W.

1978-01-01

A description is presented of an experiment which demonstrates the selective production of excited-state ions by an optical absorption from neutrals. An inversion on the resonance line of Sr(+) was produced by laser excitation of a two-electron transition, followed by ionization of one of the excited electrons by the same laser. A pulsed, mode-locked laser operating at 2680 A was used to excite atoms from the Sr ground level. The same laser then ionized the excited atoms. The 2680-A pump beam was generated by frequency doubling the output of a synchronously pumped mode-locked dye laser in a KDP crystal. It is pointed out that the reported results are significant for the construction of vacuum-ultraviolet and X-ray lasers. Many of the proposed methods for making such lasers depend on the selective production of excited-state ions.

Long T2 suppression in native lung 3-D imaging using k-space reordered inversion recovery dual-echo ultrashort echo time MRI.

PubMed

Gai, Neville D; Malayeri, Ashkan A; Bluemke, David A

2017-08-01

Long T2 species can interfere with visualization of short T2 tissue imaging. For example, visualization of lung parenchyma can be hindered by breathing artifacts primarily from fat in the chest wall. The purpose of this work was to design and evaluate a scheme for long T2 species suppression in lung parenchyma imaging using 3-D inversion recovery double-echo ultrashort echo time imaging with a k-space reordering scheme for artifact suppression. A hyperbolic secant (HS) pulse was evaluated for different tissues (T1/T2). Bloch simulations were performed with the inversion pulse followed by segmented UTE acquisition. Point spread function (PSF) was simulated for a standard interleaved acquisition order and a modulo 2 forward-reverse acquisition order. Phantom and in vivo images (eight volunteers) were acquired with both acquisition orders. Contrast to noise ratio (CNR) was evaluated in in vivo images prior to and after introduction of the long T2 suppression scheme. The PSF as well as phantom and in vivo images demonstrated reduction in artifacts arising from k-space modulation after using the reordering scheme. CNR measured between lung and fat and lung and muscle increased from -114 and -148.5 to +12.5 and 2.8 after use of the IR-DUTE sequence. Paired t test between the CNRs obtained from UTE and IR-DUTE showed significant positive change (p < 0.001 for lung-fat CNR and p = 0.03 for lung-muscle CNR). Full 3-D lung parenchyma imaging with improved positive contrast between lung and other long T2 tissue types can be achieved robustly in a clinically feasible time using IR-DUTE with image subtraction when segmented radial acquisition with k-space reordering is employed.

Release of endothelial microparticles in patients with arterial hypertension, hypertensive emergencies and catheter-related injury.

PubMed

Sansone, Roberto; Baaken, Maximilian; Horn, Patrick; Schuler, Dominik; Westenfeld, Ralf; Amabile, Nicolas; Kelm, Malte; Heiss, Christian

2018-06-01

Circulating endothelial microparticles (EMPs) are increased in arterial hypertension. The role of physicomechanical factors that may induce EMP release in vivo is still unknown. We studied the relationship of EMPs and physicomechanical factors in stable arterial hypertension and hypertensive emergencies, and investigated the pattern of EMP release after mechanical endothelial injury. In a pilot study, 41 subjects (50% hypertensives) were recruited. EMPs were discriminated by flow-cytometry (CD31 + /41 - , CD62e + , CD144 + ). Besides blood pressure measurements, pulse-wave-analysis was performed. Flow-mediated dilation (FMD), nitroglycerin-mediated dilation (NMD), and wall-shear-stress (WSS) were measured ultrasonographically in the brachial artery; microvascular perfusion by laser-Doppler (Clinicaltrials.gov: NCT02795377). We studied patients with hypertensive emergencies before and 4 h after BP lowering by urapidil (n = 12) and studied the release of EMPs due to mechanical endothelial injury after coronary angiography (n = 10). Hypertensives exhibited increased EMPs (CD31 + /41 - , CD144 + , CD62e + ) as compared to normotensives and EMPs univariately correlated with systolic BP (SBP), augmentation index, and pulse wave velocity and inversely with FMD. CD31 + /41 - -EMPs correlated with diameter and inversely with WSS and NMD. CD62e + and CD144 + -EMPs inversely correlated with microvascular function. During hypertensive emergency, only CD62e + and CD144 + -EMPs were further elevated and FMD was decreased compared to stable hypertensives. Blood pressure lowering decreased CD62e + and CD144 + -EMPs and increased FMD. CD31 + /41 - EMPs, diameter, and WSS remained unaffected. Similar to hypertensive emergency, catheter-related endothelial injury increased only CD144 + and CD62e + -EMPs. EMP release in hypertension is complex and may involve both physicomechanical endothelial injury and activation (CD144 + , CD62e + ) and decreased wall shear stress (CD31 + /41 - ). Copyright © 2018 Elsevier B.V. All rights reserved.

Stability analysis of ELMs in long-pulse discharges with ELITE code on EAST tokamak

NASA Astrophysics Data System (ADS)

Wang, Y. F.; Xu, G. S.; Wan, B. N.; Li, G. Q.; Yan, N.; Li, Y. L.; Wang, H. Q.; Peng, Y.-K. Martin; Xia, T. Y.; Ding, S. Y.; Chen, R.; Yang, Q. Q.; Liu, H. Q.; Zang, Q.; Zhang, T.; Lyu, B.; Xu, J. C.; Feng, W.; Wang, L.; Chen, Y. J.; Luo, Z. P.; Hu, G. H.; Zhang, W.; Shao, L. M.; Ye, Y.; Lan, H.; Chen, L.; Li, J.; Zhao, N.; Wang, Q.; Snyder, P. B.; Liang, Y.; Qian, J. P.; Gong, X. Z.; EAST team

2018-05-01

One challenge in long-pulse and high performance tokamak operation is to control the edge localized modes (ELMs) to reduce the transient heat load on plasma facing components. Minute-scale discharges in H-mode have been achieved repeatedly on Experimental Advanced Superconducting Tokamak (EAST) since the 2016 campaign and understanding the characteristics of the ELMs in these discharges can be helpful for effective ELM control in long-pulse discharges. The kinetic profile diagnostics recently developed on EAST make it possible to perform the pedestal stability analysis quantitatively. Pedestal stability calculation of a typical long-pulse discharge with ELITE code is presented. The ideal linear stability results show that the ELM is dominated by toroidal mode number n around 10–15 and the most unstable mode structure is mainly localized in the steep pressure gradient region, which is consistent with experimental results. Compared with a typical type-I ELM discharge with larger total plasma current (I p = 600 kA), pedestal in the long-pulse H-mode discharge (I p = 450 kA) is more stable in peeling-ballooning instability and its critical peak pressure gradient is evaluated to be 65% of the former. Two important features of EAST tokamak in the long-pulse discharge are presented by comparison with other tokamaks, including a wider pedestal correlated with the poloidal pedestal beta and a smaller inverse aspect ratio and their effects on the pedestal stability are discussed. The effects of uncertainties in measurements on the linear stability results are also analyzed, including the edge electron density profile position, the separatrix position and the line-averaged effective ion charge {Z}{{e}{{f}}{{f}}} value.

Aortic Blood Flow Reversal Determines Renal Function: Potential Explanation for Renal Dysfunction Caused by Aortic Stiffening in Hypertension.

PubMed

Hashimoto, Junichiro; Ito, Sadayoshi

2015-07-01

Aortic stiffness determines the glomerular filtration rate (GFR) and predicts the progressive decline of the GFR. However, the underlying pathophysiological mechanism remains obscure. Recent evidence has shown a close link between aortic stiffness and the bidirectional (systolic forward and early diastolic reverse) flow characteristics. We hypothesized that the aortic stiffening-induced renal dysfunction is attributable to altered central flow dynamics. In 222 patients with hypertension, Doppler velocity waveforms were recorded at the proximal descending aorta to calculate the reverse/forward flow ratio. Tonometric waveforms were recorded to measure the carotid-femoral (aortic) and carotid-radial (peripheral) pulse wave velocities, to estimate the aortic pressure from the radial waveforms, and to compute the aortic characteristic impedance. In addition, renal hemodynamics was evaluated by duplex ultrasound. The estimated GFR was inversely correlated with the aortic pulse wave velocity, reverse/forward flow ratio, pulse pressure, and characteristic impedance, whereas it was not correlated with the peripheral pulse wave velocity or mean arterial pressure. The association between aortic pulse wave velocity and estimated GFR was independent of age, diabetes mellitus, hypercholesterolemia, and antihypertensive medication. However, further adjustment for the aortic reverse/forward flow ratio and pulse pressure substantially weakened this association, and instead, the reverse/forward flow ratio emerged as the strongest determinant of estimated GFR (P=0.001). A higher aortic reverse/forward flow ratio was also associated with lower intrarenal forward flow velocities. These results suggest that an increase in aortic flow reversal (ie, retrograde flow from the descending thoracic aorta toward the aortic arch), caused by aortic stiffening and impedance mismatch, reduces antegrade flow into the kidney and thereby deteriorates renal function. © 2015 American Heart Association, Inc.

Double difference method in deep inelastic neutron scattering on the VESUVIO spectrometer

NASA Astrophysics Data System (ADS)

Andreani, C.; Colognesi, D.; Degiorgi, E.; Filabozzi, A.; Nardone, M.; Pace, E.; Pietropaolo, A.; Senesi, R.

2003-02-01

The principles of the Double Difference (DD) method, applied to the neutron spectrometer VESUVIO, are discussed. VESUVIO, an inverse geometry spectrometer operating at the ISIS pulsed neutron source in the eV energy region, has been specifically designed to measure the single particle dynamical properties in condensed matter. The width of the nuclear resonance of the absorbing filter, used for the neutron energy analysis, provides the most important contribution to the energy resolution of the inverse geometry instruments. In this paper, the DD method, which is based on a linear combination of two measurements recorded with filter foils of the same resonance material but of different thickness, is shown to improve significantly the instrumental energy resolution, as compared with the Single Difference (SD) method. The asymptotic response functions, derived through Monte-Carlo simulations for polycrystalline Pb and ZrH 2 samples, are analysed in both DD and SD methods, and compared with the experimental ones for Pb sample. The response functions have been modelled for two distinct experimental configurations of the VESUVIO spectrometer, employing 6Li-glass neutron detectors and NaI γ detectors revealing the γ-ray cascade from the ( n,γ) reaction, respectively. The DD method appears to be an effective experimental procedure for Deep Inelastic Neutron Scattering measurements on VESUVIO spectrometer, since it reduces the experimental resolution of the instrument in both 6Li-glass neutron detector and γ detector configurations.

An inverse problem strategy based on forward model evaluations: Gradient-based optimization without adjoint solves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguilo Valentin, Miguel Alejandro

2016-07-01

This study presents a new nonlinear programming formulation for the solution of inverse problems. First, a general inverse problem formulation based on the compliance error functional is presented. The proposed error functional enables the computation of the Lagrange multipliers, and thus the first order derivative information, at the expense of just one model evaluation. Therefore, the calculation of the Lagrange multipliers does not require the solution of the computationally intensive adjoint problem. This leads to significant speedups for large-scale, gradient-based inverse problems.

Single-shot, high-resolution, fiber-based phase-diversity photodetection of optical pulses

NASA Astrophysics Data System (ADS)

Dorrer, C.; Waxer, L. J.; Kalb, A.; Hill, E. M.; Bromage, J.

2016-03-01

Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with high-bandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources. Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of nonrepetitive events. A temporal diagnostic based on phase diversity is demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results. A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and processed to reconstruct the input pulse shape. This high-sensitivity (~50-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling. Experimental data obtained with a high-bandwidth real-time oscilloscope demonstrate accurate characterization of pulses from a high-energy chirped-pulse amplification system, even for pulses shorter than the photodetection impulse response.

Physics-based Inverse Problem to Deduce Marine Atmospheric Boundary Layer Parameters

DTIC Science & Technology

2017-03-07

please find the Final Technical Report with SF 298 for Dr. Erin E. Hackett’s ONR grant entitled Physics-based Inverse Problem to Deduce Marine...From- To) 07/03/2017 Final Technica l Dec 2012- Dec 2016 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Physics-based Inverse Problem to Deduce Marine...SUPPLEMENTARY NOTES 14. ABSTRACT This report describes research results related to the development and implementation of an inverse problem approach for

Diffraction leveraged modulation of X-ray pulses using MEMS-based X-ray optics

DOEpatents

Lopez, Daniel; Shenoy, Gopal; Wang, Jin; Walko, Donald A.; Jung, Il-Woong; Mukhopadhyay, Deepkishore

2016-08-09

A method and apparatus are provided for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based diffractive optics. An oscillating crystalline MEMS device generates a controllable time-window for diffraction of the incident X-ray radiation. The Bragg-diffraction leveraged modulation of X-ray pulses includes isolating a particular pulse, spatially separating individual pulses, and spreading a single pulse from an X-ray pulse-train.

Overview on the diversity of sounds produced by clownfishes (Pomacentridae): importance of acoustic signals in their peculiar way of life.

PubMed

Colleye, Orphal; Parmentier, Eric

2012-01-01

Clownfishes (Pomacentridae) are brightly colored coral reef fishes well known for their mutualistic symbiosis with tropical sea anemones. These fishes live in social groups in which there is a size-based dominance hierarchy. In this structure where sex is socially controlled, agonistic interactions are numerous and serve to maintain size differences between individuals adjacent in rank. Clownfishes are also prolific callers whose sounds seem to play an important role in the social hierarchy. Here, we aim to review and to synthesize the diversity of sounds produced by clownfishes in order to emphasize the importance of acoustic signals in their way of life. Recording the different acoustic behaviors indicated that sounds are divided into two main categories: aggressive sounds produced in conjunction with threat postures (charge and chase), and submissive sounds always emitted when fish exhibited head shaking movements (i.e. a submissive posture). Both types of sounds showed size-related intraspecific variation in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger ones, and inversely. Consequently, these sonic features might be useful cues for individual recognition within the group. This observation is of significant importance due to the size-based hierarchy in clownfish group. On the other hand, no acoustic signal was associated with the different reproductive activities. Unlike other pomacentrids, sounds are not produced for mate attraction in clownfishes but to reach and to defend the competition for breeding status, which explains why constraints are not important enough for promoting call diversification in this group.

A Codimension-2 Bifurcation Controlling Endogenous Bursting Activity and Pulse-Triggered Responses of a Neuron Model

PubMed Central

Barnett, William H.; Cymbalyuk, Gennady S.

2014-01-01

The dynamics of individual neurons are crucial for producing functional activity in neuronal networks. An open question is how temporal characteristics can be controlled in bursting activity and in transient neuronal responses to synaptic input. Bifurcation theory provides a framework to discover generic mechanisms addressing this question. We present a family of mechanisms organized around a global codimension-2 bifurcation. The cornerstone bifurcation is located at the intersection of the border between bursting and spiking and the border between bursting and silence. These borders correspond to the blue sky catastrophe bifurcation and the saddle-node bifurcation on an invariant circle (SNIC) curves, respectively. The cornerstone bifurcation satisfies the conditions for both the blue sky catastrophe and SNIC. The burst duration and interburst interval increase as the inverse of the square root of the difference between the corresponding bifurcation parameter and its bifurcation value. For a given set of burst duration and interburst interval, one can find the parameter values supporting these temporal characteristics. The cornerstone bifurcation also determines the responses of silent and spiking neurons. In a silent neuron with parameters close to the SNIC, a pulse of current triggers a single burst. In a spiking neuron with parameters close to the blue sky catastrophe, a pulse of current temporarily silences the neuron. These responses are stereotypical: the durations of the transient intervals–the duration of the burst and the duration of latency to spiking–are governed by the inverse-square-root laws. The mechanisms described here could be used to coordinate neuromuscular control in central pattern generators. As proof of principle, we construct small networks that control metachronal-wave motor pattern exhibited in locomotion. This pattern is determined by the phase relations of bursting neurons in a simple central pattern generator modeled by a chain of oscillators. PMID:24497927

Central hemodynamics could explain the inverse association between height and cardiovascular mortality.

PubMed

Reeve, Jake C; Abhayaratna, Walter P; Davies, Justin E; Sharman, James E

2014-03-01

Mechanisms underlying the inverse relationship between height and cardiovascular mortality are unknown but could relate to central hemodynamics. We sought to determine the relation of height to central and peripheral hemodynamics, as well as clinical characteristics. The study population was comprised of 1,152 randomly selected community-dwelling adults (aged 67.7 ± 12.3 years; 48% men). Brachial blood pressure (BP) was recorded by sphygmomanometry; central BP and aortic pulse wave velocity were estimated by applanation tonometry. Stepwise multiple regression analysis was used to determine associations between height and central and peripheral hemodynamics. Height was not significantly associated with aortic pulse wave velocity in men or women. The relationship with height and brachial systolic BP was borderline in women (β = -0.115; P = 0.051) but not significant in men (β = -0.096; P = 0.09). Conversely, central systolic BP, estimated by transfer function (β = -0.139 for men [βM]; β = -0.172 for women [βW]) or radial second systolic peak (β M = -0.239; β W = -0.281), augmentation index at 75 bpm (β M = -0.189; β W = -0.224), and aortic pulse wave timing (β M = 0.224; β W = 0.262) were independently associated with height in both sexes (P < 0.003 for all). Both men and women of greater than median height were less likely to have coronary artery disease (P < 0.05), to have systemic hypertension (P < 0.01), or to be taking vasoactive medication (P < 0.001) compared with participants of less than median height. Even after correcting for conventional cardiovascular risk factors, taller individuals have more favorable central hemodynamics and reduced evidence of coronary artery disease compared with shorter individuals. These findings may help explain the decreased cardiovascular risk associated with being taller and also have important clinical consequences regarding therapy.

Improved Performance of an Optically Pumped Mid-Infrared Acetylene-Filled Hollow-Core Fiber Laser

NASA Astrophysics Data System (ADS)

Dadashzadeh, Neda

The focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 mum and 3.17 mum lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 mum using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 microm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 muJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M2 measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M2 was investigated at several input pump powers in addition to the reproducibility checks. M 2 of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 muJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers.

A novel femtosecond-gated, high-resolution, frequency-shifted shearing interferometry technique for probing pre-plasma expansion in ultra-intense laser experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feister, S., E-mail: feister.7@osu.edu; Orban, C.; Innovative Scientific Solutions, Inc., Dayton, Ohio 45459

Ultra-intense laser-matter interaction experiments (>10{sup 18} W/cm{sup 2}) with dense targets are highly sensitive to the effect of laser “noise” (in the form of pre-pulses) preceding the main ultra-intense pulse. These system-dependent pre-pulses in the nanosecond and/or picosecond regimes are often intense enough to modify the target significantly by ionizing and forming a plasma layer in front of the target before the arrival of the main pulse. Time resolved interferometry offers a robust way to characterize the expanding plasma during this period. We have developed a novel pump-probe interferometry system for an ultra-intense laser experiment that uses two short-pulse amplifiersmore » synchronized by one ultra-fast seed oscillator to achieve 40-fs time resolution over hundreds of nanoseconds, using a variable delay line and other techniques. The first of these amplifiers acts as the pump and delivers maximal energy to the interaction region. The second amplifier is frequency shifted and then frequency doubled to generate the femtosecond probe pulse. After passing through the laser-target interaction region, the probe pulse is split and recombined in a laterally sheared Michelson interferometer. Importantly, the frequency shift in the probe allows strong plasma self-emission at the second harmonic of the pump to be filtered out, allowing plasma expansion near the critical surface and elsewhere to be clearly visible in the interferograms. To aid in the reconstruction of phase dependent imagery from fringe shifts, three separate 120° phase-shifted (temporally sheared) interferograms are acquired for each probe delay. Three-phase reconstructions of the electron densities are then inferred by Abel inversion. This interferometric system delivers precise measurements of pre-plasma expansion that can identify the condition of the target at the moment that the ultra-intense pulse arrives. Such measurements are indispensable for correlating laser pre-pulse measurements with instantaneous plasma profiles and for enabling realistic Particle-in-Cell simulations of the ultra-intense laser-matter interaction.« less

Elemental analysis using temporal gating of a pulsed neutron generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitra, Sudeep

Technologies related to determining elemental composition of a sample that comprises fissile material are described herein. In a general embodiment, a pulsed neutron generator periodically emits bursts of neutrons, and is synchronized with an analyzer circuit. The bursts of neutrons are used to interrogate the sample, and the sample outputs gamma rays based upon the neutrons impacting the sample. A detector outputs pulses based upon the gamma rays impinging upon the material of the detector, and the analyzer circuit assigns the pulses to temporally-based bins based upon the analyzer circuit being synchronized with the pulsed neutron generator. A computing devicemore » outputs data that is indicative of elemental composition of the sample based upon the binned pulses.« less

Design of a finger base-type pulse oximeter

NASA Astrophysics Data System (ADS)

Lin, Bor-Shyh; Huang, Cheng-Yang; Chen, Chien-Yue; Lin, Jiun-Hung

2016-01-01

A pulse oximeter is a common medical instrument used for noninvasively monitoring arterial oxygen saturation (SpO2). Currently, the fingertip-type pulse oximeter is the prevalent type of pulse oximeter used. However, it is inconvenient for long-term monitoring, such as that under motion. In this study, a wearable and wireless finger base-type pulse oximeter was designed and implemented using the tissue optical simulation technique and the Monte Carlo method. The results revealed that a design involving placing the light source at 135°-165° and placing the detector at 75°-90° or 90°-105° yields the optimal conditions for measuring SpO2. Finally, the wearable and wireless finger base-type pulse oximeter was implemented and compared with the commercial fingertip-type pulse oximeter. The experimental results showed that the proposed optimal finger base-type pulse oximeter design can facilitate precise SpO2 measurement.

Design of a finger base-type pulse oximeter.

PubMed

Lin, Bor-Shyh; Huang, Cheng-Yang; Chen, Chien-Yue; Lin, Jiun-Hung

2016-01-01

A pulse oximeter is a common medical instrument used for noninvasively monitoring arterial oxygen saturation (SpO2). Currently, the fingertip-type pulse oximeter is the prevalent type of pulse oximeter used. However, it is inconvenient for long-term monitoring, such as that under motion. In this study, a wearable and wireless finger base-type pulse oximeter was designed and implemented using the tissue optical simulation technique and the Monte Carlo method. The results revealed that a design involving placing the light source at 135°-165° and placing the detector at 75°-90° or 90°-105° yields the optimal conditions for measuring SpO2. Finally, the wearable and wireless finger base-type pulse oximeter was implemented and compared with the commercial fingertip-type pulse oximeter. The experimental results showed that the proposed optimal finger base-type pulse oximeter design can facilitate precise SpO2 measurement.

Ultrafast optical modification of exchange interactions in iron oxides

NASA Astrophysics Data System (ADS)

Mikhaylovskiy, R. V.; Hendry, E.; Secchi, A.; Mentink, J. H.; Eckstein, M.; Wu, A.; Pisarev, R. V.; Kruglyak, V. V.; Katsnelson, M. I.; Rasing, Th.; Kimel, A. V.

2015-09-01

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 103 Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of terahertz emission by spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond modification of the exchange interaction by laser pulses with fluence of about 1 mJ cm-2 acts as a pulsed effective magnetic field of 0.01 Tesla.

Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam

NASA Astrophysics Data System (ADS)

Cole, J. M.; Behm, K. T.; Gerstmayr, E.; Blackburn, T. G.; Wood, J. C.; Baird, C. D.; Duff, M. J.; Harvey, C.; Ilderton, A.; Joglekar, A. S.; Krushelnick, K.; Kuschel, S.; Marklund, M.; McKenna, P.; Murphy, C. D.; Poder, K.; Ridgers, C. P.; Samarin, G. M.; Sarri, G.; Symes, D. R.; Thomas, A. G. R.; Warwick, J.; Zepf, M.; Najmudin, Z.; Mangles, S. P. D.

2018-02-01

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (ɛ >500 MeV ) with an intense laser pulse (a0>10 ). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy ɛcrit>30 MeV .

Ellipticity-dependent of multiple ionisation methyl iodide cluster using 532 nm nanosecond laser

NASA Astrophysics Data System (ADS)

Tang, Bin; Zhao, Wuduo; Wang, Weiguo; Hua, Lei; Chen, Ping; Hou, Keyong; Huang, Yunguang; Li, Haiyang

2016-03-01

The dependence of multiply charged ions on laser ellipticity in methyl iodide clusters with 532 nm nanosecond laser was measured using a time-of-flight mass spectrometer. The intensities of multiply charged ions Iq+(q = 2-4) with circularly polarised laser pulse were clearly higher than those with linearly polarised laser pulse but the intensity of single charged ions I+ was inverse. And the dependences of ions on the optical polarisation state were investigated and a flower petal and square distribution for single charged ions (I+, C+) and multiply charged ions (I2+, I3+, I4+, C2+) were observed, respectively. A theoretical calculation was also proposed to simulate the distributions of ions and theoretical results fitted well with the experimental ones. It indicated that the high multiphoton ionisation probability in the initial stage would result in the disintegration of big clusters into small ones and suppress the production of multiply charged ions.

Intermittent inflations recorded by broadband seismometers prior to caldera formation at Miyake-jima volcano in 2000

NASA Astrophysics Data System (ADS)

Kobayashi, Tomokazu; Ohminato, Takao; Ida, Yoshiaki; Fujita, Eisuke

2012-12-01

Very-long-period (VLP) pulses with widths of 20 s on velocity seismograms were observed during volcanic activity at Miyake-jima Volcano, Japan in 2000. The VLP events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse. Waveform inversions of the pulse-like signals point to a source offset 3.5 km beneath and 1 km south of the summit. A candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20-30° from vertical and major axis of the elliptical cross section oriented northeast-southwest. The inferred mechanism appears consistent with a step-like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability. The repeated occurrences of the rock collapses lead to the caldera formation at Miyake-jima.

Octave-spanning supercontinuum generation at telecommunications wavelengths in a precisely dispersion- and length-controlled silicon-wire waveguide with a double taper structure

NASA Astrophysics Data System (ADS)

Ishizawa, Atsushi; Goto, Takahiro; Kou, Rai; Tsuchizawa, Tai; Matsuda, Nobuyuki; Hitachi, Kenichi; Nishikawa, Tadashi; Yamada, Koji; Sogawa, Tetsuomi; Gotoh, Hideki

2017-07-01

We demonstrate on-chip octave-spanning supercontinuum (SC) generation with a Si-wire waveguide (SWG). We precisely controlled the SWG width so that the group velocity becomes flat over a wide wavelength range. By adjusting the SWG length, we could reduce the optical losses due to two-photon absorption and pulse propagation. In addition, for efficient coupling between the laser pulse and waveguide, we fabricated a two-step inverse taper at both ends of the SWG. Using a 600-nm-wide SWG, we were able to generate a broadband SC spectrum at wavelengths from 1060 to 2200 nm at a -40 dB level with only 50-pJ laser energy from an Er-doped fiber laser oscillator. We found that we can generate an on-chip broadband SC spectrum with an SWG with a length even as small as 1.7 mm.

Development of very compact soft X-ray lasers

NASA Astrophysics Data System (ADS)

Korobkin, Dmitriy Vladlenovich

1999-10-01

A powerful subpicosecond laser system, based on solid state (Ti:Al 2O3) front end and gas excimer (KrF*) amplifiers, has been developed. It is capable of producing 40-50 mJ pulses at 248 nm (285 fs pulse duration) with 2 Hz repetition rate. That radiation can be focused to intensities greater than 1017 W/cm2 and cause the optical field ionization of lithium. The system was used in experiments on gain generation in hydrogen-like Li III. Lasing action in hydrogen-like Li III 2-1 transition to ground state (13.5 nm) has been demonstrated for the first time. Gain G = 11 cm-1 in 5-mm long plasma column, created in LiF microcapillary, was measured. The observed gain-length product was GL = 5.5. In another set of experiments an inversion population between levels n = 3 and n = 2 in hydrogen-like BV was created using a low-energy compact laser system at 1 Hz repetition rate. Gain G = 17 cm-1 at 26.2 nm was measured in 3 mm long B2O3 microcapillary, which corresponds to GL = 5.1. The entire experimental setup can be fit on a single medium size optical table. Also propagation of laser radiation through plasma, created in microcapillaries has been investigated at various experimental conditions. Real-time plasma probing with low intensity HeNe laser beam has been performed.