Virtual Active Touch Using Randomly Patterned Intracortical Microstimulation

PubMed Central

O’Doherty, Joseph E.; Lebedev, Mikhail A.; Li, Zheng; Nicolelis, Miguel A.L.

2012-01-01

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices. PMID:22207642

Synaptic behaviors of thin-film transistor with a Pt/HfO x /n-type indium-gallium-zinc oxide gate stack.

PubMed

Yang, Paul; Park, Daehoon; Beom, Keonwon; Kim, Hyung Jun; Kang, Chi Jung; Yoon, Tae-Sik

2018-07-20

We report a variety of synaptic behaviors in a thin-film transistor (TFT) with a metal-oxide-semiconductor gate stack that has a Pt/HfO x /n-type indium-gallium-zinc oxide (n-IGZO) structure. The three-terminal synaptic TFT exhibits a tunable synaptic weight with a drain current modulation upon repeated application of gate and drain voltages. The synaptic weight modulation is analog, voltage-polarity dependent reversible, and strong with a dynamic range of multiple orders of magnitude (>10 4 ). This modulation process emulates biological synaptic potentiation, depression, excitatory-postsynaptic current, paired-pulse facilitation, and short-term to long-term memory transition behaviors as a result of repeated pulsing with respect to the pulse amplitude, width, repetition number, and the interval between pulses. These synaptic behaviors are interpreted based on the changes in the capacitance of the Pt/HfO x /n-IGZO gate stack, the channel mobility, and the threshold voltage that result from the redistribution of oxygen ions by the applied gate voltage. These results demonstrate the potential of this structure for three-terminal synaptic transistor using the gate stack composed of the HfO x gate insulator and the IGZO channel layer.

Synaptic behaviors of thin-film transistor with a Pt/HfO x /n-type indium–gallium–zinc oxide gate stack

NASA Astrophysics Data System (ADS)

Yang, Paul; Park, Daehoon; Beom, Keonwon; Kim, Hyung Jun; Kang, Chi Jung; Yoon, Tae-Sik

2018-07-01

We report a variety of synaptic behaviors in a thin-film transistor (TFT) with a metal-oxide-semiconductor gate stack that has a Pt/HfO x /n-type indium–gallium–zinc oxide (n-IGZO) structure. The three-terminal synaptic TFT exhibits a tunable synaptic weight with a drain current modulation upon repeated application of gate and drain voltages. The synaptic weight modulation is analog, voltage-polarity dependent reversible, and strong with a dynamic range of multiple orders of magnitude (>104). This modulation process emulates biological synaptic potentiation, depression, excitatory-postsynaptic current, paired-pulse facilitation, and short-term to long-term memory transition behaviors as a result of repeated pulsing with respect to the pulse amplitude, width, repetition number, and the interval between pulses. These synaptic behaviors are interpreted based on the changes in the capacitance of the Pt/HfO x /n-IGZO gate stack, the channel mobility, and the threshold voltage that result from the redistribution of oxygen ions by the applied gate voltage. These results demonstrate the potential of this structure for three-terminal synaptic transistor using the gate stack composed of the HfO x gate insulator and the IGZO channel layer.

Cortico-cortical and motor evoked potentials to single and paired-pulse stimuli: An exploratory transcranial magnetic and intracranial electric brain stimulation study.

PubMed

Boulogne, Sébastien; Andre-Obadia, Nathalie; Kimiskidis, Vasilios K; Ryvlin, Philippe; Rheims, Sylvain

2016-11-01

Paired-pulse (PP) paradigms are commonly employed to assess in vivo cortical excitability using transcranial magnetic stimulation (TMS) to stimulate the primary motor cortex and modulate the induced motor evoked potential (MEP). Single-pulse cortical direct electrical stimulation (DES) during intracerebral EEG monitoring allows the investigation of brain connectivity by eliciting cortico-cortical evoked potentials (CCEPs). However, PP paradigm using intracerebral DES has rarely been reported and has never been previously compared with TMS. The work was intended (i) to verify that the well-established modulations of MEPs following PP TMS remain similar using DES in the motor cortex, and (ii) to evaluate if a similar pattern could be observed in distant cortico-cortical connections through modulations of CCEP. Three patients undergoing intracerebral EEG monitoring with electrodes implanted in the central region were studied. Single-pulse DES (1-3 mA, 1 ms, 0.2 Hz) and PP DES using six interstimulus intervals (5, 15, 30, 50, 100, and 200 ms) in the motor cortex with concomitant recording of CCEPs and MEPs in contralateral muscles were performed. Finally, a navigated PP TMS session targeted the intracranial stimulation site to record TMS-induced MEPs in two patients. MEP modulations elicited by PP intracerebral DES proved similar among the three patients and to those obtained by PP TMS. CCEP modulations elicited by PP intracerebral DES usually showed a pattern comparable to that of MEP, although a different pattern could be observed occasionally. PP intracerebral DES seems to involve excitatory and inhibitory mechanisms similar to PP TMS and allows the recording of intracortical inhibition and facilitation modulation on cortico-cortical connections. Hum Brain Mapp 37:3767-3778, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Engineering information on an Analog Signal to Discrete Time Interval Converter (ASDT-IC)

NASA Technical Reports Server (NTRS)

Schwarz, F. C.

1974-01-01

An electronic control system for nondissipative dc power converters is presented which improves (1) the routinely attainable static output voltage accuracy to the order of + or - 1% for ambient temperatures from -55 to 100 C and (2) the dynamic stability by utilizing approximately one tenth of the feedback gain needed otherwise. Performance is due to a functional philosophy of deterministic pulse modulation based on pulse area control and to an autocompensated signal processing principle. The system can be implemented with commercially available unselected components.

A fatigue monitoring system based on time-domain and frequency-domain analysis of pulse data

NASA Astrophysics Data System (ADS)

Shen, Jiaai

2018-04-01

Fatigue is almost a problem that everyone would face, and a psychosis that everyone hates. If we can test people's fatigue condition and remind them of the tiredness, dangers in life, for instance, traffic accidents and sudden death will be effectively reduced, people's fatigued operations will be avoided. And people can be assisted to have access to their own and others' physical condition in time to alternate work with rest. The article develops a wearable bracelet based on FFT Pulse Frequency Spectrum Analysis and IBI's standard deviation and range calculation, according to people's heart rate (BPM) and inter-beat interval (IBI) while being tired and conscious. The hardware part is based on Arduino, pulse rate sensor, and Bluetooth module, and the software part is relied on network micro database and APP. By doing sample experiment to get more accurate standard value to judge tiredness, we prove that we can judge people's fatigue condition based on heart rate (BPM) and inter-beat interval (IBI).

Increased first and second pulse harmonics in Tai Chi Chuan practitioners.

PubMed

Lu, Wan-An; Chen, Yung-Sheng; Kuo, Cheng-Deng

2016-02-29

Tai Chi Chuan (TCC) is known to be a good calisthenics for people. This study examined the relationship between pulse harmonics and autonomic nervous modulation in TCC practitioners. Power spectral measures of right pulse wave and heart rate variability (HRV) measures were compared between TCC practitioners and control subjects. Correlation analyses between pulse harmonics and HRV measures were performed using linear regression analysis. At baseline, the total power of pulse (TPp), powers of all individual pulse harmonics, normalized power of the 1(st) harmonics (nPh1) of TCC practitioners were greater, while the normalized power of the 4(th) pulse harmonics (nPh4) of TCC practitioners was smaller, than those of the controls. Similarly, the baseline standard deviation (SD(RR)), coefficient of variation (CV(RR)), and normalized high-frequency power (nHFP) of RR intervals were smaller, while the normalized very low-frequency power (nVLFP) and low-/high- frequency power ratio (LHR) were larger in the TCC practitioners. The TCC age correlated significantly and negatively with nPh1, and nearly significantly and negatively with nPh2 in the TCC practitioners. Thirty min after TCC exercise, the percentage changes in mRRI, SDRR, TP, VLFP were decreased, while the percentage changes in HR, ULFP, nLFP, and Ph2 were increased, relative to the controls. Correlation analysis shows that the %Ph2 correlates significantly and negatively with %mRRI and significantly and positively with %HR. The TCC practitioners had increased baseline total power of pulse and the 1(st) and 2(nd) pulse harmonics, and decreased power of the 4(th) pulse harmonics, along with decreased vagal modulation and increased sympathetic modulation. After TCC exercise, the power of the 2(nd) harmonics of TCC practitioners was increased which might be related to the increase in HR due to decreased vascular resistance after TCC exercise.

Power supply and pulsing strategies for the future linear colliders

NASA Astrophysics Data System (ADS)

Brogna, A. S.; Göttlicher, P.; Weber, M.

2012-02-01

The concept of the power delivery systems of the future linear colliders exploits the pulsed bunch structure of the beam in order to minimize the average current in the cables and the electronics and thus to reduce the material budget and heat dissipation. Although modern integrated circuit technologies are already available to design a low-power system, the concepts on how to pulse the front-end electronics and further reduce the power are not yet well understood. We propose a possible implementation of a power pulsing system based on a DC/DC converter and we choose the Analog Hadron Calorimeter as a specific example. The model features large switching currents of electronic modules in short time intervals to stimulate the inductive components along the cables and interconnections.

Direct coupling of pulsed radio frequency and pulsed high power in novel pulsed power system for plasma immersion ion implantation.

PubMed

Gong, Chunzhi; Tian, Xiubo; Yang, Shiqin; Fu, Ricky K Y; Chu, Paul K

2008-04-01

A novel power supply system that directly couples pulsed high voltage (HV) pulses and pulsed 13.56 MHz radio frequency (rf) has been developed for plasma processes. In this system, the sample holder is connected to both the rf generator and HV modulator. The coupling circuit in the hybrid system is composed of individual matching units, low pass filters, and voltage clamping units. This ensures the safe operation of the rf system even when the HV is on. The PSPICE software is utilized to optimize the design of circuits. The system can be operated in two modes. The pulsed rf discharge may serve as either the seed plasma source for glow discharge or high-density plasma source for plasma immersion ion implantation (PIII). The pulsed high-voltage glow discharge is induced when a rf pulse with a short duration or a larger time interval between the rf and HV pulses is used. Conventional PIII can also be achieved. Experiments conducted on the new system confirm steady and safe operation.

Channel Equalization for Single Carrier MIMO Underwater Acoustic Communications

DTIC Science & Technology

2010-01-01

II Tx 1 Tx 2 Symbol mapping s1 s2 x1 x2 sa Figure 2: Signalling at the transmitter in Makai05 experiment. fc = 32 kHz and the symbol interval was...frequency was fc = 37.5 kHz and the symbol interval was 0.05ms. The occupied channel bandwidth was fb = 25 kHz due to a pulse shaping filter with roll...water. QPSK modulation was used with a symbol rate of 4 ksps. The carrier frequency was fc = 17 kHz. The structure of the transmission packet is

RXTE and BeppoSAX Observations of the Transient X-ray Pulsar XTE J 18591+083

NASA Technical Reports Server (NTRS)

Corbet, R. H. D.; intZand, J. J. M.; Levine, A. M.; Marshall, F. E.

2008-01-01

We present observations of the 9.8 s X-ray pulsar XTE J159+083 made with the All-Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer (RXTE), and the Wide Field Cameras (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD50, 250, and 50, 460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible 61 day modulation. Eighteen sets of PCA observations were obtained over an approx. one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease non-monotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give an error box which is consistent with a previously determined PCA error box but is significantly smaller. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutral star binary. The possible 61 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period.

Heart rate, multiple body temperature, long-range and long-life telemetry system for free-ranging animals

NASA Technical Reports Server (NTRS)

Lund, G. F.; Westbrook, R. M.; Fryer, T. B.

1980-01-01

The design details and rationale for a versatile, long-range, long-life telemetry data acquisition system for heart rates and body temperatures at multiple locations from free-ranging animals are presented. The design comprises an implantable transmitter for short to medium range transmission, a receiver retransmitter collar to be worn for long-range transmission, and a signal conditioner interface circuit to assist in signal discrimination and demodulation of receiver or tape-recorded audio outputs. Implanted electrodes are used to obtain an ECG, from which R-wave characteristics are selected to trigger a short RF pulse. Pulses carrying heart rate information are interrupted periodically by a series of pulse interval modulated RF pulses conveying temperature information sensed at desired locations by thermistors. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as radio frequency interference. The implanted transmitter may be used alone for medium and short-range tracking, or with a receiver-transmitter collar that employs commercial tracking equipment for transmissions of up to 12 km. A system prototype has been tested on a dog.

flexTMS--a novel repetitive transcranial magnetic stimulation device with freely programmable stimulus currents.

PubMed

Gattinger, Norbert; Moessnang, Georg; Gleich, Bernhard

2012-07-01

Transcranial magnetic stimulation (TMS) is able to noninvasively excite neuronal populations due to brief magnetic field pulses. The efficiency and the characteristics of stimulation pulse shapes influence the physiological effect of TMS. However, commercial devices allow only a minimum of control of different pulse shapes. Basically, just sinusoidal and monophasic pulse shapes with fixed pulse widths are available. Only few research groups work on TMS devices with controllable pulse parameters such as pulse shape or pulse width. We describe a novel TMS device with a full-bridge circuit topology incorporating four insulated-gate bipolar transistor (IGBT) modules and one energy storage capacitor to generate arbitrary waveforms. This flexible TMS (flexTMS ) device can generate magnetic pulses which can be adjusted with respect to pulse width, polarity, and intensity. Furthermore, the equipment allows us to set paired pulses with a variable interstimulus interval (ISI) from 0 to 20 ms with a step size of 10  μs. All user-defined pulses can be applied continually with repetition rates up to 30 pulses per second (pps) or, respectively, up to 100 pps in theta burst mode. Offering this variety of flexibility, flexTMS will allow the enhancement of existing TMS paradigms and novel research applications.

A pilot investigation of the effect of extremely low frequency pulsed electromagnetic fields on humans' heart rate variability.

PubMed

Baldi, Emilio; Baldi, Claudio; Lithgow, Brian J

2007-01-01

The question whether pulsed electromagnetic field (PEMF) can affect the heart rhythm is still controversial. This study investigates the effects on the cardiocirculatory system of ELF-PEMFs. It is a follow-up to an investigation made of the possible therapeutic effect ELF-PEMFs, using a commercially available magneto therapeutic unit, had on soft tissue injury repair in humans. Modulation of heart rate (HR) or heart rate variability (HRV) can be detected from changes in periodicity of the R-R interval and/or from changes in the numbers of heart-beat/min (bpm), however, R-R interval analysis gives only a quantitative insight into HRV. A qualitative understanding of HRV can be obtained considering the power spectral density (PSD) of the R-R intervals Fourier transform. In this study PSD is the investigative tool used, more specifically the low frequency (LF) PSD and high frequency (HF) PSD ratio (LF/HF) which is an indicator of sympatho-vagal balance. To obtain the PSD value, variations of the R-R time intervals were evaluated from a continuously recorded ECG. The results show a HR variation in all the subjects when they are exposed to the same ELF-PEMF. This variation can be detected by observing the change in the sympatho-vagal equilibrium, which is an indicator of modulation of heart activity. Variation of the LF/HF PSD ratio mainly occurs at transition times from exposure to nonexposure, or vice versa. Also of interest are the results obtained during the exposure of one subject to a range of different ELF-PEMFs. This pilot study suggests that a full investigation into the effect of ELF-PEMFs on the cardiovascular system is justified.

TIME-INTERVAL MEASURING DEVICE

DOEpatents

Gross, J.E.

1958-04-15

An electronic device for measuring the time interval between two control pulses is presented. The device incorporates part of a previous approach for time measurement, in that pulses from a constant-frequency oscillator are counted during the interval between the control pulses. To reduce the possible error in counting caused by the operation of the counter gating circuit at various points in the pulse cycle, the described device provides means for successively delaying the pulses for a fraction of the pulse period so that a final delay of one period is obtained and means for counting the pulses before and after each stage of delay during the time interval whereby a plurality of totals is obtained which may be averaged and multplied by the pulse period to obtain an accurate time- Interval measurement.

Cross-Phase Modulation: A New Technique for Controlling the Spectral, Temporal, and Spatial Properties of Ultrashort Pulses

NASA Astrophysics Data System (ADS)

Baldeck, P. L.; Ho, P. P.; Alfano, Robert R.

Self-phase modulation (SPM) is the principal mechanism responsible for the generation of picosecond and femtosecond white-light supercontinua. When an intense ultrashort pulse progagates through a medium, it distorts the atomic configuration of the material, which changes the refractive index. The pulse phase is time modulated, which causes the generation of new frequencies. This phase modulation originates from the pulse itself (self-phase modulation). It can also be generated by a copropagating pulse (cross-phase modulation).

Interference Resilient Sigma Delta-Based Pulse Oximeter.

PubMed

Shokouhian, Mohsen; Morling, Richard; Kale, Izzet

2016-06-01

Ambient light and optical interference can severely affect the performance of pulse oximeters. The deployment of a robust modulation technique to drive the pulse oximeter LEDs can reduce these unwanted effects and increases the resilient of the pulse oximeter against artificial ambient light. The time division modulation technique used in conventional pulse oximeters can not remove the effect of modulated light coming from surrounding environment and this may cause huge measurement error in pulse oximeter readings. This paper presents a novel cross-coupled sigma delta modulator which ensures that measurement accuracy will be more robust in comparison with conventional fixed-frequency oximeter modulation technique especially in the presence of pulsed artificial ambient light. Moreover, this novel modulator gives an extra control over the pulse oximeter power consumption leading to improved power management.

High-order UWB pulses scheme to generate multilevel modulation formats based on incoherent optical sources.

PubMed

Bolea, Mario; Mora, José; Ortega, Beatriz; Capmany, José

2013-11-18

We present a high-order UWB pulses generator based on a microwave photonic filter which provides a set of positive and negative samples by using the slicing of an incoherent optical source and the phase inversion in a Mach-Zehnder modulator. The simple scalability and high reconfigurability of the system permit a better accomplishment of the FCC requirements. Moreover, the proposed scheme permits an easy adaptation to pulse amplitude modulation, bi phase modulation, pulse shape modulation and pulse position modulation. The flexibility of the scheme for being adaptable to multilevel modulation formats permits to increase the transmission bit rate by using hybrid modulation formats.

Photonic ultra-wideband pulse generation, hybrid modulation and dispersion-compensation-free transmission in multi-access communication systems.

PubMed

Tan, Kang; Shao, Jing; Sun, Junqiang; Wang, Jian

2012-01-16

We propose and demonstrate a scheme for optical ultrawideband (UWB) pulse generation by exploiting a half-carrier-suppressed Mach-Zehnder modulator (MZM) and a delay-interferometer- and wavelength-division-multiplexer-based, reconfigurable and multi-channel differentiator (DWRMD). Multi-wavelength, polarity- and shape-switchable UWB pulses of monocycle, doublet, triplet, and quadruplet are experimentally generated simply by tuning two bias voltages to modify the carrier-suppression ratio of MZM and the differential order of DWRMD respectively. The pulse position modulation, pulse shape modulation, pulse amplitude modulation and binary phase-shift keying modulation of UWB pulses can also be conveniently realized with the same scheme structure, which indicates that the hybrid modulation of those four formats can be achieved. Consequently, the proposed approach has potential applications in multi-shape, multi-modulation and multi-access UWB-over-fiber communication systems.

Clicks, whistles and pulses: Passive and active signal use in dolphin communication

NASA Astrophysics Data System (ADS)

Herzing, Denise L.

2014-12-01

The search for signals out of noise is a problem not only with radio signals from the sky but in the study of animal communication. Dolphins use multiple modalities to communicate including body postures, touch, vision, and most elaborately sound. Like SETI radio signal searches, dolphin sound analysis includes the detection, recognition, analysis, and interpretation of signals. Dolphins use both passive listening and active production to communicate. Dolphins use three main types of acoustic signals: frequency modulated whistles (narrowband with harmonics), echolocation (broadband clicks) and burst pulsed sounds (packets of closely spaced broadband clicks). Dolphin sound analysis has focused on frequency-modulated whistles, yet the most commonly used signals are burst-pulsed sounds which, due to their graded and overlapping nature and bimodal inter-click interval (ICI) rates are hard to categorize. We will look at: 1) the mechanism of sound production and categories of sound types, 2) sound analysis techniques and information content, and 3) examples of lessons learned in the study of dolphin acoustics. The goal of this paper is to provide perspective on how animal communication studies might provide insight to both passive and active SETI in the larger context of searching for life signatures.

Hybrid simulation of electron energy distributions and plasma characteristics in pulsed RF CCP sustained in Ar and SiH4/Ar discharges

NASA Astrophysics Data System (ADS)

Wang, Xi-Feng; Jia, Wen-Zhu; Song, Yuan-Hong; Zhang, Ying-Ying; Dai, Zhong-Ling; Wang, You-Nian

2017-11-01

Pulsed-discharge plasmas offer great advantages in deposition of silicon-based films due to the fact that they can suppress cluster agglomeration, moderate the energy of bombarding ions, and prolong the species' diffusion time on the substrate. In this work, a one-dimensional fluid/Monte-Carlo hybrid model is applied to study pulse modulated radio-frequency (RF) plasmas sustained in capacitively coupled Ar and SiH4/Ar discharges. First, the electron energy distributions in pulsed Ar and SiH4/Ar plasmas have been investigated and compared under identical discharge-circuit conditions. The electron energy distribution function (EEDF) in Ar discharge exhibits a familiar bi-Maxwellian shape during the power-on phase of the pulse, while a more complex (resembling a multi-Maxwellian) distribution with extra inflection points at lower energies is observed in the case of the SiH4/Ar mixture. These features become more prominent with the increasing fraction of SiH4 in the gas mixture. The difference in the shape of the EEDF (which is pronounced inside the plasma but not in the RF sheath where electron heating occurs) is mainly attributed to the electron-impact excitations of SiH4. During the power-off phase of the pulse, the EEDFs in both Ar and SiH4/Ar discharges evolve into bi-Maxwellian shapes, with shrinking high energy tails. Furthermore, the parameter of ion species in the case of SiH4/Ar discharge is strongly modulated by pulsing. For positive ions, such as SiH3+ and Si2H4+ , the particle fluxes overshoot at the beginning of the power-on interval. Meanwhile, for negative ions such as SiH2- and SiH3- , density profiles observed between the electrodes are saddle-shaped due to the repulsion by the self-bias electric field as it builds up. During the power-off phase, the wall fluxes of SiH2- and SiH3- gradually increase, leading to a significant decrease in the net surface charge density on the driven electrode. Compared with ions, the density of SiH3 is poorly modulated by pulsed power and is nearly constant over the entire modulation period, but the density of SiH2 shows a detectable decline in the afterglow. However, because of a much smaller content of SiH2, the deposition rate hardly shows any variation under the selected waveform of the pulse.

Generation of ultra-wideband triplet pulses based on four-wave mixing and phase-to-intensity modulation conversion.

PubMed

Li, Wei; Wang, Li Xian; Hofmann, Werner; Zhu, Ning Hua; Bimberg, Dieter

2012-08-27

We propose and demonstrate a novel scheme to generate ultra-wideband (UWB) triplet pulses based on four-wave mixing and phase-to-intensity modulation conversion. First a phase-modulated Gaussian doublet pulse is generated by four-wave mixing in a highly nonlinear fiber. Then an UWB triplet pulse is generated by generating the first-order derivative of the phase-modulated Gaussian doublet pulse using an optical filter serving as a frequency discriminator. By locating the optical signal at the linear slope of the optical filter, the phase modulated Gaussian doublet pulse is converted to an intensity-modulated UWB triplet pulse which well satisfies the Federal Communications Commission spectral mask requirements, even in the extremely power-restricted global positioning system band.

Digital time delay

DOEpatents

Martin, A.D.

1986-05-09

Method and apparatus are provided for generating an output pulse following a trigger pulse at a time delay interval preset with a resolution which is high relative to a low resolution available from supplied clock pulses. A first lumped constant delay provides a first output signal at predetermined interpolation intervals corresponding to the desired high resolution time interval. Latching circuits latch the high resolution data to form a first synchronizing data set. A selected time interval has been preset to internal counters and corrected for circuit propagation delay times having the same order of magnitude as the desired high resolution. Internal system clock pulses count down the counters to generate an internal pulse delayed by an internal which is functionally related to the preset time interval. A second LCD corrects the internal signal with the high resolution time delay. A second internal pulse is then applied to a third LCD to generate a second set of synchronizing data which is complementary with the first set of synchronizing data for presentation to logic circuits. The logic circuits further delay the internal output signal with the internal pulses. The final delayed output signal thereafter enables the output pulse generator to produce the desired output pulse at the preset time delay interval following input of the trigger pulse.

Phase matching of high order harmonic generation using dynamic phase modulation caused by a non-collinear modulation pulse

DOEpatents

Cohen, Oren; Kapteyn, Henry C.; Mumane, Margaret M.

2010-02-16

Phase matching high harmonic generation (HHG) uses a single, long duration non-collinear modulating pulse intersecting the driving pulse. A femtosecond driving pulse is focused into an HHG medium (such as a noble gas) to cause high-harmonic generation (HHG), for example in the X-ray region of the spectrum, via electrons separating from and recombining with gas atoms. A non-collinear pulse intersects the driving pulse within the gas, and modulates the field seen by the electrons while separated from their atoms. The modulating pulse is low power and long duration, and its frequency and amplitude is chosen to improve HHG phase matching by increasing the areas of constructive interference between the driving pulse and the HHG, relative to the areas of destructive interference.

Harmonic generation with a dual frequency pulse.

PubMed

Keravnou, Christina P; Averkiou, Michalakis A

2014-05-01

Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components.

Temporal and spectral properties of the songs of the southern green stink bug Nezara viridula (L.) from Slovenia.

PubMed

Cokl, A; Virant-Doberlet, M; Stritih, N

2000-01-01

Substrate born songs of the southern green stinkbug Nezara viridula (L.) from Slovenia were recorded and analysed. The male calling song is composed of narrow-band regularly repeated single pulses and of broad-band frequency modulated pulses grouped into pulse trains. The female calling song is characterised by broad-band pulsed and narrow-band non-pulsed pulse trains. A frequency modulated pre-pulse precedes the narrow-band pulse train. A frequency-modulated post-pulse usually follows the pulse train of the male courtship song. The male calling song triggers broad-band pulse trains of the female courtship song. The female also produces a repelling low-frequency vibration that inhibits male calling and courtship. The male rival song is characterised by prolonged pulses with a typical frequency modulation.

Ultra-large optical modulation of electrochromic porous WO3 film and the local monitoring of redox activity† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc03727a

PubMed Central

Cai, Guofa; Cui, Mengqi; Kumar, Vipin; Darmawan, Peter; Wang, Jiangxin; Wang, Xu; Lee-Sie Eh, Alice; Qian, Kai

2016-01-01

Porous WO3 films with ultra-high transmittance modulation were successfully fabricated on different substrates by a novel, facile and economical pulsed electrochemical deposited method with 1.1 s interval time between each pulse. The near ideal optical modulation (97.7% at 633 nm), fast switching speed (6 and 2.7 s), high coloration efficiency (118.3 cm2 C–1), and excellent cycling stability are achieved by the porous WO3 on ITO-coated glass. The outstanding electrochromic performances of the porous WO3 film were mainly attributed to the porous structure, which facilitates the charge-transfer, promotes the electrolyte infiltration and alleviates the expansion of the WO3 during H+ insertion compared to that of the compact structure. In addition, the relationships between the structural and electrochemical activity of the electrochromic WO3 films were further explored by the scanning electrochemical microscopy. These results testify that the porous structure can promote the infiltration of electrolyte and reduce the diffusion path, which consequently enhance the electrochemical activity. PMID:29910894

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1985-07-29

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and sway from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch.

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1987-10-27

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal is disclosed. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch. 5 figs.

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

DOEpatents

Bartholomew, David B.

2006-11-14

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

High resolution digital delay timer

DOEpatents

Martin, Albert D.

1988-01-01

Method and apparatus are provided for generating an output pulse following a trigger pulse at a time delay interval preset with a resolution which is high relative to a low resolution available from supplied clock pulses. A first lumped constant delay (20) provides a first output signal (24) at predetermined interpolation intervals corresponding to the desired high resolution time interval. Latching circuits (26, 28) latch the high resolution data (24) to form a first synchronizing data set (60). A selected time interval has been preset to internal counters (142, 146, 154) and corrected for circuit propagation delay times having the same order of magnitude as the desired high resolution. Internal system clock pulses (32, 34) count down the counters to generate an internal pulse delayed by an interval which is functionally related to the preset time interval. A second LCD (184) corrects the internal signal with the high resolution time delay. A second internal pulse is then applied to a third LCD (74) to generate a second set of synchronizing data (76) which is complementary with the first set of synchronizing data (60) for presentation to logic circuits (64). The logic circuits (64) further delay the internal output signal (72) to obtain a proper phase relationship of an output signal (80) with the internal pulses (32, 34). The final delayed output signal (80) thereafter enables the output pulse generator (82) to produce the desired output pulse (84) at the preset time delay interval following input of the trigger pulse (10, 12).

47 CFR 2.201 - Emission, modulation, and transmission characteristics.

Code of Federal Regulations, 2014 CFR

2014-10-01

... carrier is amplitude-modulated (including cases where sub-carriers are angle-modulated): —Double-sideband... is amplitude and angle-modulated either simultaneously or in a pre-established sequence D (5) Emission of pulses: 1 —Sequence of unmodulated pulses P —A sequence of pulses: —Modulated in amplitude K...

47 CFR 2.201 - Emission, modulation, and transmission characteristics.

Code of Federal Regulations, 2013 CFR

2013-10-01

... carrier is amplitude-modulated (including cases where sub-carriers are angle-modulated): —Double-sideband... is amplitude and angle-modulated either simultaneously or in a pre-established sequence D (5) Emission of pulses: 1 —Sequence of unmodulated pulses P —A sequence of pulses: —Modulated in amplitude K...

47 CFR 2.201 - Emission, modulation, and transmission characteristics.

Code of Federal Regulations, 2012 CFR

2012-10-01

... carrier is amplitude-modulated (including cases where sub-carriers are angle-modulated): —Double-sideband... is amplitude and angle-modulated either simultaneously or in a pre-established sequence D (5) Emission of pulses: 1 —Sequence of unmodulated pulses P —A sequence of pulses: —Modulated in amplitude K...

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.

Physiological Parameter Monitoring from Optical Recordings with a Mobile Phone

PubMed Central

Scully, Christopher G.; Lee, Jinseok; Meyer, Joseph; Gorbach, Alexander M.; Granquist-Fraser, Domhnull; Mendelson, Yitzhak

2012-01-01

We show that a mobile phone can serve as an accurate monitor for several physiological variables, based on its ability to record and analyze the varying color signals of a fingertip placed in contact with its optical sensor. We confirm the accuracy of measurements of breathing rate, cardiac R-R intervals, and blood oxygen saturation, by comparisons to standard methods for making such measurements (respiration belts, ECGs, and pulse-oximeters, respectively). Measurement of respiratory rate uses a previously reported algorithm developed for use with a pulse-oximeter, based on amplitude and frequency modulation sequences within the light signal. We note that this technology can also be used with recently developed algorithms for detection of atrial fibrillation or blood loss. PMID:21803676

Evaluation of agreement between temporal series obtained from electrocardiogram and pulse wave.

NASA Astrophysics Data System (ADS)

Leikan, GM; Rossi, E.; Sanz, MCuadra; Delisle Rodríguez, D.; Mántaras, MC; Nicolet, J.; Zapata, D.; Lapyckyj, I.; Siri, L. Nicola; Perrone, MS

2016-04-01

Heart rate variability allows to study the cardiovascular autonomic nervous system modulation. Usually, this signal is obtained from the electrocardiogram (ECG). A simpler method for recording the pulse wave (PW) is by means of finger photoplethysmography (PPG), which also provides information about the duration of the cardiac cycle. In this study, the correlation and agreement between the time series of the intervals between heartbeats obtained from the ECG with those obtained from the PPG, were studied. Signals analyzed were obtained from young, healthy and resting subjects. For statistical analysis, the Pearson correlation coefficient and the Bland and Altman limits of agreement were used. Results show that the time series constructed from the PW would not replace the ones obtained from ECG.

Breaking through the bandwidth barrier in distributed fiber vibration sensing by sub-Nyquist randomized sampling

NASA Astrophysics Data System (ADS)

Zhang, Jingdong; Zhu, Tao; Zheng, Hua; Kuang, Yang; Liu, Min; Huang, Wei

2017-04-01

The round trip time of the light pulse limits the maximum detectable frequency response range of vibration in phase-sensitive optical time domain reflectometry (φ-OTDR). We propose a method to break the frequency response range restriction of φ-OTDR system by modulating the light pulse interval randomly which enables a random sampling for every vibration point in a long sensing fiber. This sub-Nyquist randomized sampling method is suits for detecting sparse-wideband- frequency vibration signals. Up to MHz resonance vibration signal with over dozens of frequency components and 1.153MHz single frequency vibration signal are clearly identified for a sensing range of 9.6km with 10kHz maximum sampling rate.

140 GHz pulsed fourier transform microwave spectrometer

DOEpatents

Kolbe, William F.; Leskovar, Branko

1987-01-01

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer (10), including means (11, 19) for generating a high frequency carrier signal, and means (12) for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator (20) and the modulating signal is fed through a pulse switch (23) to the modulator. When the pulse switch (23) is on, the modulator (20) will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device (31) is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device (31) is controlled by the pulse switch (23).

All-optical UWB generation and modulation using SOA-XPM effect and DWDM-based multi-channel frequency discrimination.

PubMed

Wang, Fei; Dong, Jianji; Xu, Enming; Zhang, Xinliang

2010-11-22

An all-optical UWB pulses generation and modulation scheme using cross phase modulation (XPM) effect of semiconductor optical amplifier (SOA) and DWDM-based multi-channel frequency discrimination is proposed and demonstrated, which has potential application in multiuser UWB-Over-Fiber communication systems. When a Gaussian pulse light and a wavelength-tunable CW probe light are together injected into the SOA, the probe light out from the SOA will have a temporal chirp due to SOA-XPM effect. When the chirped probe light is tuned to the slopes of single DWDM channel transmittance curve, the optical phase modulation to intensity modulation conversion is achieved at DWDM that serves as a multi-channel frequency discriminator, the inverted polarity Gaussian monocycle and doublet pulse is detected by a photodetector, respectively. If the probe lights are simultaneously aimed to different slopes of several DWDM channels, multi-channel or binary-phase-coded UWB signal generation can be acquired. Using proposed scheme, pulse amplitude modulation (PAM), pulse polarity modulation (PPM) and pulse shape modulation (PSM) to UWB pulses also can be conveniently realized.

Microscopy imaging system and method employing stimulated raman spectroscopy as a contrast mechanism

DOEpatents

Xie, Xiaoliang Sunney [Lexington, MA; Freudiger, Christian [Boston, MA; Min, Wei [Cambridge, MA

2011-09-27

A microscopy imaging system includes a first light source for providing a first train of pulses at a first center optical frequency .omega..sub.1, a second light source for providing a second train of pulses at a second center optical frequency .omega..sub.2, a modulator system, an optical detector, and a processor. The modulator system is for modulating a beam property of the second train of pulses at a modulation frequency f of at least 100 kHz. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of the first train of pulses from the common focal volume by blocking the second train of pulses being modulated. The processor is for detecting, a modulation at the modulation frequency f, of the integrated intensity of the optical frequency components of the first train of pulses to provide a pixel of an image for the microscopy imaging system.

Photonic ultrawideband impulse radio generation and modulation over a fiber link using a phase modulator and a delay interferometer.

PubMed

Shao, Jing; Sun, Junqiang

2012-08-15

We propose and experimentally demonstrate a simple and flexible photonic scheme for generation and modulation of ultrawideband (UWB) using a phase modulator and a fiber delay interferometer (DI)-based multichannel frequency discrimination. By introducing a Gaussian signal to the phase modulator, the UWB polarity-switchable doublet pulses can be achieved by combining the pair of UWB monocycle pulses with inverted polarities at the DI outputs under proper time delay. Furthermore, the pulse shape modulation, pulse position modulation, and on-off keying can be performed by coding the electrical data patterns and adjusting the time delay between the two monocycle pulses. Only a laser source introduced in the architecture guarantees the excellent dispersion tolerance over 75 km optical fiber link for UWB pulse sequence, which has potential application in future high-speed UWB impulse radio over optical fiber access networks.

Gaussian temporal modulation for the behavior of multi-sinc Schell-model pulses in dispersive media

NASA Astrophysics Data System (ADS)

Liu, Xiayin; Zhao, Daomu; Tian, Kehan; Pan, Weiqing; Zhang, Kouwen

2018-06-01

A new class of pulse source with correlation being modeled by the convolution operation of two legitimate temporal correlation function is proposed. Particularly, analytical formulas for the Gaussian temporally modulated multi-sinc Schell-model (MSSM) pulses generated by such pulse source propagating in dispersive media are derived. It is demonstrated that the average intensity of MSSM pulses on propagation are reshaped from flat profile or a train to a distribution with a Gaussian temporal envelope by adjusting the initial correlation width of the Gaussian pulse. The effects of the Gaussian temporal modulation on the temporal degree of coherence of the MSSM pulse are also analyzed. The results presented here show the potential of coherence modulation for pulse shaping and pulsed laser material processing.

Data acquisition system

DOEpatents

Phillips, David T.

1979-01-01

A data acquisition system capable of resolving transient pulses in the subnanosecond range. A pulse in an information carrying medium such as light is transmitted through means which disperse the pulse, such as a fiber optic light guide which time-stretches optical pulses by chromatic dispersion. This time-stretched pulse is used as a sampling pulse and is modulated by the signal to be recorded. The modulated pulse may be further time-stretched prior to being recorded. The recorded modulated pulse is unfolded to derive the transient signal by utilizing the relationship of the time-stretching that occurred in the original pulse.

Sensitivity to binaural timing in bilateral cochlear implant users.

PubMed

van Hoesel, Richard J M

2007-04-01

Various measures of binaural timing sensitivity were made in three bilateral cochlear implant users, who had demonstrated moderate-to-good interaural time delay (ITD) sensitivity at 100 pulses-per-second (pps). Overall, ITD thresholds increased at higher pulse rates, lower levels, and shorter durations, although intersubject differences were evident. Monaural rate-discrimination thresholds, using the same stimulation parameters, showed more substantial elevation than ITDs with increased rate. ITD sensitivity with 6000 pps stimuli, amplitude-modulated at 100 Hz, was similar to that with unmodulated pulse trains at 100 pps, but at 200 and 300 Hz performance was poorer than with unmodulated signals. Measures of sensitivity to binaural beats with unmodulated pulse-trains showed that all three subjects could use time-varying ITD cues at 100 pps, but not 300 pps, even though static ITD sensitivity was relatively unaffected over that range. The difference between static and dynamic ITD thresholds is discussed in terms of relative contributions from initial and later arriving cues, which was further examined in an experiment using two-pulse stimuli as a function of interpulse separation. In agreement with the binaural-beat data, findings from that experiment showed poor discrimination of ITDs on the second pulse when the interval between pulses was reduced to a few milliseconds.

Linear transformer driver for pulse generation with fifth harmonic

DOEpatents

Mazarakis, Michael G.; Kim, Alexander A.; Sinebryukhov, Vadim A.; Volkov, Sergey N.; Kondratiev, Sergey S.; Alexeenko, Vitaly M.; Bayol, Frederic; Demol, Gauthier; Stygar, William A.; Leckbee, Joshua; Oliver, Bryan V.; Kiefer, Mark L.

2017-03-21

A linear transformer driver includes at least one ferrite ring positioned to accept a load. The linear transformer driver also includes a first, second, and third power delivery module. The first power delivery module sends a first energy in the form of a first pulse to the load. The second power delivery module sends a second energy in the form of a second pulse to the load. The third power delivery module sends a third energy in the form of a third pulse to the load. The linear transformer driver is configured to form a flat-top pulse by the superposition of the first, second, and third pulses. The first, second, and third pulses have different frequencies.

Multiple polarization states of vector soliton in fiber laser

NASA Astrophysics Data System (ADS)

Chen, Weicheng; Xu, Wencheng; Cao, Hui; Han, Dingan

2007-11-01

Vector soliton is obtained in erbium-doped fiber laser via nonlinear polarization rotation techniques. In experiment, we observe the every 4- and 7-pulse sinusoidal peak modulation. Temporal pulse sinusoidal peak modulation owes to evolution behavior of vector solitons in multiple polarization states. The polarizer in the laser modulates the mode-locked pulses with different polarization states into periodical pulse train intensities modulation. Moreover, the increasing pumping power lead to the appearance of the harmonic pulses and change the equivalent beat length to accelerate the polarization rotation. When the laser cavity length is the n-th multiple ratios to the beat length to maintain the mode-locking, the mode-locked vector soliton is in n-th multiple polarization states, exhibiting every n-pulse sinusoidal peak modulation.

High resolution data acquisition

DOEpatents

Thornton, G.W.; Fuller, K.R.

1993-04-06

A high resolution event interval timing system measures short time intervals such as occur in high energy physics or laser ranging. Timing is provided from a clock, pulse train, and analog circuitry for generating a triangular wave synchronously with the pulse train (as seen in diagram on patent). The triangular wave has an amplitude and slope functionally related to the time elapsed during each clock pulse in the train. A converter forms a first digital value of the amplitude and slope of the triangle wave at the start of the event interval and a second digital value of the amplitude and slope of the triangle wave at the end of the event interval. A counter counts the clock pulse train during the interval to form a gross event interval time. A computer then combines the gross event interval time and the first and second digital values to output a high resolution value for the event interval.

High resolution data acquisition

DOEpatents

Thornton, Glenn W.; Fuller, Kenneth R.

1993-01-01

A high resolution event interval timing system measures short time intervals such as occur in high energy physics or laser ranging. Timing is provided from a clock (38) pulse train (37) and analog circuitry (44) for generating a triangular wave (46) synchronously with the pulse train (37). The triangular wave (46) has an amplitude and slope functionally related to the time elapsed during each clock pulse in the train. A converter (18, 32) forms a first digital value of the amplitude and slope of the triangle wave at the start of the event interval and a second digital value of the amplitude and slope of the triangle wave at the end of the event interval. A counter (26) counts the clock pulse train (37) during the interval to form a gross event interval time. A computer (52) then combines the gross event interval time and the first and second digital values to output a high resolution value for the event interval.

[Some Features of Sound Signal Envelope by the Frog's Cochlear Nucleus Neurons].

PubMed

Bibikov, N G

2015-01-01

The responses of single neurons in the medullar auditory center of the grass frog were recorded extracellularly under the action of long tonal signals of the characteristic frequency modulated by repeating fragments of low-frequency (0-15 Hz, 0-50 Hz or 0-150 Hz) noise. Correlation method was used for evaluating the efficacy of different envelope fragments to ensure generation of a neuron pulse discharge. Carrying out these evaluations at different time intervals between a signal and a response the maximum delays were assessed. Two important envelope fragments were revealed. In majority of units the most effective was the time interval of the amplitude rise from mean value to maximum, and the fragment where the amplitude fall from maximum to mean value was the second by the efficacy. This type of response was observed in the vast majority of cells in the range of the envelope frequency bands 0-150 and 0-50 Hz. These cells performed half-wave rectification of such type of the envelope. However, in some neurons we observed more strong preference toward a time interval with growing amplitude, including even those where the amplitude value was smaller than the mean one. These properties were observed mainly for low-frequency (0-15 Hz) modulated signals at high modulation depth. The data show that even in medulla oblongata specialization of neural elements of the auditory pathway occurs with respect to time interval features of sound stimulus. This diversity is most evident for signals with a relatively slowly varying amplitude.

Oscillations of absorption of a probe picosecond light pulse caused by its interaction with stimulated picosecond emission of GaAs

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

Ageeva, N. N.; Bronevoi, I. L., E-mail: bil@cplire.ru; Zabegaev, D. N.

2015-04-15

The self-modulation of absorption of a picosecond light pulse was observed earlier [1] in a thin (∼1-μm thick) GaAs layer pumped by a high-power picosecond pulse. Analysis of the characteristics of this self-modulation predicted [5] that the dependences of the probe pulse absorption on the pump pulse energy and picosecond delay between pump and probe pulses should be self-modulated by oscillations. Such self-modulation was experimentally observed in this work. Under certain conditions, absorption oscillations proved to be a function of part of the energy of picosecond stimulated emission of GaAs lying above a certain threshold in the region where themore » emission front overlapped the probe pulse front. Absorption oscillations are similar to self-modulation of the GaAs emission characteristics observed earlier [4]. This suggests that the self-modulation of absorption and emission is determined by the same type of interaction of light pulses in the active medium, the physical mechanism of which has yet to be determined.« less

Solid-state pulse modulator using Marx generator for a medical linac electron-gun

NASA Astrophysics Data System (ADS)

Lim, Heuijin; Hyeok Jeong, Dong; Lee, Manwoo; Lee, Mujin; Yi, Jungyu; Yang, Kwangmo; Ro, Sung Chae

2016-04-01

A medical linac is used for the cancer treatment and consists of an accelerating column, waveguide components, a magnetron, an electron-gun, a pulse modulator, and an irradiation system. The pulse modulator based on hydrogen thyratron-switched pulse-forming network is commonly used in linac. As the improvement of the high power semiconductors in switching speed, voltage rating, and current rating, an insulated gate bipolar transistor has become the more popular device used for pulsed power systems. We propose a solid-state pulse modulator to generator high voltage by multi-stacked storage-switch stages based on the Marx generator. The advantage of our modulator comes from the use of two semiconductors to control charging and discharging of the storage capacitor at each stage and it allows to generate the pulse with various amplitudes, widths, and shapes. In addition, a gate driver for two semiconductors is designed to reduce the control channels and to protect the circuits. It is developed for providing the pulsed power to a medical linac electron-gun that requires 25 kV and 1 A as the first application. In order to improve the power efficiency and achieve the compactness modulator, a capacitor charging power supply, a Marx pulse generator, and an electron-gun heater isolated transformer are constructed and integrated. This technology is also being developed to extend the high power pulsed system with > 1 MW and also other applications such as a plasma immersed ion implantation and a micro pulse electrostatic precipitator which especially require variable pulse shape and high repetition rate > 1 kHz. The paper describes the design features and the construction of this solid-state pulse modulator. Also shown are the performance results into the linac electron-gun.

Linear transformer driver for pulse generation

DOEpatents

Kim, Alexander A; Mazarakis, Michael G; Sinebryukhov, Vadim A; Volkov, Sergey N; Kondratiev, Sergey S; Alexeenko, Vitaly M; Bayol, Frederic; Demol, Gauthier; Stygar, William A

2015-04-07

A linear transformer driver includes at least one ferrite ring positioned to accept a load. The linear transformer driver also includes a first power delivery module that includes a first charge storage devices and a first switch. The first power delivery module sends a first energy in the form of a first pulse to the load. The linear transformer driver also includes a second power delivery module including a second charge storage device and a second switch. The second power delivery module sends a second energy in the form of a second pulse to the load. The second pulse has a frequency that is approximately three times the frequency of the first pulse. The at least one ferrite ring is positioned to force the first pulse and the second pulse to the load by temporarily isolating the first pulse and the second pulse from an electrical ground.

A Novel Approach to Photonic Generation and Modulation of Ultra-Wideband Pulses

NASA Astrophysics Data System (ADS)

Xiang, Peng; Guo, Hao; Chen, Dalei; Zhu, Huatao

2016-01-01

A novel approach to photonic generation of ultra-wideband (UWB) signals is proposed in this paper. The proposed signal generator is capable of generating UWB doublet pulses with flexible reconfigurability, and many different pulse modulation formats, including the commonly used pulse-position modulation (PPM) and bi-phase modulation (BPM) can be realized. Moreover, the photonic UWB pulse generator is capable of generating UWB signals with a tunable spectral notch-band, which is desirable to realize the interference avoidance between UWB and other narrow band systems, such as Wi-Fi. A mathematical model describing the proposed system is developed and the generation of UWB signals with different modulation formats is demonstrated via computer simulations.

Dual-pulse laser ignition of ethylene-air mixtures in a supersonic combustor.

PubMed

Yang, Leichao; An, Bin; Liang, Jianhan; Li, Xipeng; Wang, Zhenguo

2018-04-02

To reduce the energy of an individual laser pulse, dual-pulse laser ignitions (LIs) at various pulse intervals were investigated in a Mach 2.92 scramjet engine fueled with ethylene. For comparison, experiments on a single-pulse LI were also performed. Schlieren visualization and high-speed photography were employed to observe the ignition processes simultaneously. The results indicate that the energy of an individual laser pulse can be reduced by half via a dual-pulse LI method as compared with a single-pulse LI with the same total energy. The reduction of the individual laser pulse energy degrades the requirements on the laser source and the beam delivery system, which facilitates the practical application of LI in hypersonic vehicles. A pulse interval shorter than 40 μs is suggested for dual-pulse LI in the present study. Because of the intense heat loss and radical dissipation in high-speed flows, the pulse interval for dual-pulse LI should be short enough to narrow the spatial distribution of the initial flame kernel.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, Thomas E.

1996-01-01

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a "IF homodyne" receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, T.E.

1996-05-21

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a ``IF homodyne`` receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses. 5 figs.

Amplitude Modulator Chassis

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

Erbert, G

2009-09-01

The Amplitude Modulator Chassis (AMC) is the final component in the MOR system and connects directly to the PAM input through a 100-meter fiber. The 48 AMCs temporally shape the 48 outputs of the MOR using an arbitrary waveform generator coupled to an amplitude modulator. The amplitude modulation element is a two stage, Lithium Niobate waveguide device, where the intensity of the light passing through the device is a function of the electrical drive applied. The first stage of the modulator is connected to a programmable high performance Arbitrary Waveform Generator (AWG) consisting of 140 impulse generators space 250 psmore » apart. An arbitrary waveform is generated by independently varying the amplitude of each impulse generator and then summing the impulses together. In addition to the AWG a short pulse generator is also connected to the first stage of the modulator to provide a sub 100-ps pulse used for timing experiments. The second stage of the modulator is connect to a square pulse generator used to further attenuate any pre or post pulse light passing through the first stage of the modulator. The fast rise and fall time of the square pulse generator is also used to produce fast rise and fall times of the AWG by clipping the AWG pulse. For maximum extinction, a pulse bias voltage is applied to each stage of the modulator. A pulse voltage is applied as opposed to a DC voltage to prevent charge buildup on the modulator. Each bias voltage is adjustable to provide a minimum of 50-dB extinction. The AMC is controlled through ICCS to generate the desired temporal pulse shape. This process involves a closed-loop control algorithm, which compares the desired temporal waveform to the produced optical pulse, and iterates the programming of the AWG until the two waveforms agree within an allowable tolerance.« less

Overview of radar intra-pulse modulation recognition

NASA Astrophysics Data System (ADS)

Zang, Hanlin; Li, Yanling

2018-05-01

This paper introduces the current radar intra-pulse modulation method, describes the status quo and development direction of the intentional modulation and unintentional modulation in the pulse, and summarizes the existing problems and prospects for the future. Looking forward to the future, and providing a reference direction for the research on radar signal recognition in the next step.

Damping of collective modes and the echo effect in a confined Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Kuklov, A. B.; Chencinski, N.

1998-04-01

We discuss the reversible nature of two mechanisms of the apparent damping of the collective modes of a confined Bose-Einstein condensate -- Landau Damping (LD) and a dephasing caused by thermal fluctuations of the normal component. The reversibility of the damping in both cases can be tested by the echo effect, when two consecutive external pulses modulate the potential trapping the condensate and induce a third pulse -- the echo -- at the time approximately equal to twice the time interval between the first two pulses. This effect is similar to the phonon echo in powders (Koji Kajimura in Physical Acoustics), ed. W.P. Mason, V.XVI, Academic Press, NY, Toronto 1982.. Parameters of the echo for the isotropic condensate are calculated analytically in the adiabatic approximation for the case of the small external pulses. Numerical simulations for the arbitrary pulses are also presented. The echo in an anisotropic condensate, where the adaibatic approximation is not valid because of the LD, is described in terms of the model of a single oscillator interacting with a quasi-continuum of modes which constitutes the normal component. In both cases in the weak echo limit the echo amplitude turns out to be proportional to the amplitudes of the external pulses. We suggest to test these predictions experimentally.

Global synchronization of parallel processors using clock pulse width modulation

DOEpatents

Chen, Dong; Ellavsky, Matthew R.; Franke, Ross L.; Gara, Alan; Gooding, Thomas M.; Haring, Rudolf A.; Jeanson, Mark J.; Kopcsay, Gerard V.; Liebsch, Thomas A.; Littrell, Daniel; Ohmacht, Martin; Reed, Don D.; Schenck, Brandon E.; Swetz, Richard A.

2013-04-02

A circuit generates a global clock signal with a pulse width modification to synchronize processors in a parallel computing system. The circuit may include a hardware module and a clock splitter. The hardware module may generate a clock signal and performs a pulse width modification on the clock signal. The pulse width modification changes a pulse width within a clock period in the clock signal. The clock splitter may distribute the pulse width modified clock signal to a plurality of processors in the parallel computing system.

Time-reversing light pulses by adiabatic coupling modulation in coupled-resonator optical waveguides

NASA Astrophysics Data System (ADS)

Wang, Chao; Martini, Rainer; Search, Christopher P.

2012-12-01

We introduce a mechanism to time reverse short optical pulses in coupled resonator optical waveguides (CROWs) by direct modulation of the coupling coefficients between microresonators. The coupling modulation is achieved using phase modulation of a Mach-Zehnder interferometer coupler. We demonstrate that by adiabatic modulation of the coupling between resonators we can time reverse or store light pulses with bandwidths up to a few hundred GHz. The large pulse bandwidths, small device footprint, robustness with respect to resonator losses, and easy tuning process of the coupling coefficients make this method more practical than previous proposals.

Optical ultra-wide-band pulse bipolar and shape modulation based on a symmetric PM-IM conversion architecture.

PubMed

Wang, Shiguang; Chen, Hongwei; Xin, Ming; Chen, Minghua; Xie, Shizhong

2009-10-15

A simple and feasible technique for ultra-wide-band (UWB) pulse bipolar modulation (PBM) and pulse shape modulation (PSM) in the optical domain is proposed and demonstrated. The PBM and PSM are performed using a symmetric phase modulation to intensity modulation conversion architecture, including a couple of phase modulators and an optical bandpass filter (OBPF). Two optical carriers, which are separately phase modulated by two appropriate electrical pulse patterns, are at the long- and short-wavelength linear slopes of the OBPF spectrum, respectively. The high-speed PBM and PSM without limit of chip length, polarity, and shape are implemented in simulation and are also verified by experiment. (c) 2009 Optical Society of America.

Rise time analysis of pulsed klystron-modulator for efficiency improvement of linear colliders

NASA Astrophysics Data System (ADS)

Oh, J. S.; Cho, M. H.; Namkung, W.; Chung, K. H.; Shintake, T.; Matsumoto, H.

2000-04-01

In linear accelerators, the periods during the rise and fall of a klystron-modulator pulse cannot be used to generate RF power. Thus, these periods need to be minimized to get high efficiency, especially in large-scale machines. In this paper, we present a simplified and generalized voltage rise time function of a pulsed modulator with a high-power klystron load using the equivalent circuit analysis method. The optimum pulse waveform is generated when this pulsed power system is tuned with a damping factor of ˜0.85. The normalized rise time chart presented in this paper allows one to predict the rise time and pulse shape of the pulsed power system in general. The results can be summarized as follows: The large distributed capacitance in the pulse tank and operating parameters, Vs× Tp , where Vs is load voltage and Tp is the pulse width, are the main factors determining the pulse rise time in the high-power RF system. With an RF pulse compression scheme, up to ±3% ripple of the modulator voltage is allowed without serious loss of compressor efficiency, which allows the modulator efficiency to be improved as well. The wiring inductance should be minimized to get the fastest rise time.

Short optical pulse generation at 40 GHz with a bulk electro-absorption modulator packaged device

NASA Astrophysics Data System (ADS)

Langlois, Patrick; Moore, Ronald; Prosyk, Kelvin; O'Keefe, Sean; Oosterom, Jill A.; Betty, Ian; Foster, Robert; Greenspan, Jonathan; Singh, Priti

2003-12-01

Short optical pulse generation at 40GHz and 1540nm wavelength is achieved using fully packaged bulk quaternary electro-absorption modulator modules. Experimental results obtained with broadband and narrowband optimized packaged modules are presented and compared against empirical model predictions. Pulse duty cycle, extinction ratio and chirp are studied as a function of sinusoidal drive voltage and detuning between operating wavelength and modulator absorption band edge. Design rules and performance trade-offs are discussed. Low-chirp pulses with a FWHM of ~12ps and sub-4ps at a rate of 40GHz are demonstrated. Optical time-domain demultiplexing of a 40GHz to a 10GHz pulse train is also demonstrated with better than 20dB extinction ratio.

Multifunction audio digitizer. [producing direct delta and pulse code modulation

NASA Technical Reports Server (NTRS)

Monford, L. G., Jr. (Inventor)

1974-01-01

An illustrative embodiment of the invention includes apparatus which simultaneously produces both direct delta modulation and pulse code modulation. An input signal, after amplification, is supplied to a window comparator which supplies a polarity control signal to gate the output of a clock to the appropriate input of a binary up-down counter. The control signals provide direct delta modulation while the up-down counter output provides pulse code modulation.

Optical UWB pulse generator using an N tap microwave photonic filter and phase inversion adaptable to different pulse modulation formats.

PubMed

Bolea, Mario; Mora, José; Ortega, Beatriz; Capmany, José

2009-03-30

We propose theoretically and demonstrate experimentally an optical architecture for flexible Ultra-Wideband pulse generation. It is based on an N-tap reconfigurable microwave photonic filter fed by a laser array by using phase inversion in a Mach-Zehnder modulator. Since a large number of positive and negative coefficients can be easily implemented, UWB pulses fitted to the FCC mask requirements can be generated. As an example, a four tap pulse generator is experimentally demonstrated which complies with the FCC regulation. The proposed pulse generator allows different pulse modulation formats since the amplitude, polarity and time delay of generated pulse is controlled.

Dark solitons in erbium-doped fiber lasers based on indium tin oxide as saturable absorbers

NASA Astrophysics Data System (ADS)

Guo, Jia; Zhang, Huanian; Li, Zhen; Sheng, Yingqiang; Guo, Quanxin; Han, Xile; Liu, Yanjun; Man, Baoyuan; Ning, Tingyin; Jiang, Shouzhen

2018-04-01

Dark solitons, which have good stability, long transmission distance and strong anti-interference ability. By using a coprecipitation method, the high quality indium tin oxide (ITO) were prepared with an average diameter of 34.1 nm. We used a typical Z-scan scheme involving a balanced twin-detector measurement system to investigated nonlinear optical properties of the ITO nanoparticles. The saturation intensity and modulation depths are 13.21 MW/cm2 and 0.48%, respectively. In an erbium-doped fiber (EDF) lasers, we using the ITO nanoparticles as saturable absorber (SA), and the formation of dark soliton is experimentally demonstrated. The generated dark solitons are centered at the wavelength of 1561.1 nm with a repetition rate of 22.06 MHz. Besides, the pulse width and pulse-to-pulse interval of the dark solitons is ∼1.33ns and 45.11 ns, respectively. These results indicate that the ITO nanoparticles is a promising nanomaterial for ultrafast photonics.

Systems and methods for selective detection and imaging in coherent Raman microscopy by spectral excitation shaping

DOEpatents

Xie, Xiaoliang Sunney; Freudiger, Christian; Min, Wei

2016-03-15

A microscopy imaging system is disclosed that includes a light source system, a spectral shaper, a modulator system, an optics system, an optical detector and a processor. The light source system is for providing a first train of pulses and a second train of pulses. The spectral shaper is for spectrally modifying an optical property of at least some frequency components of the broadband range of frequency components such that the broadband range of frequency components is shaped producing a shaped first train of pulses to specifically probe a spectral feature of interest from a sample, and to reduce information from features that are not of interest from the sample. The modulator system is for modulating a property of at least one of the shaped first train of pulses and the second train of pulses at a modulation frequency. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of a train of pulses of interest transmitted or reflected through the common focal volume. The processor is for detecting a modulation at the modulation frequency of the integrated intensity of substantially all of the optical frequency components of the train of pulses of interest due to the non-linear interaction of the shaped first train of pulses with the second train of pulses as modulated in the common focal volume, and for providing an output signal for a pixel of an image for the microscopy imaging system.

High resolution time interval meter

DOEpatents

Martin, A.D.

1986-05-09

Method and apparatus are provided for measuring the time interval between two events to a higher resolution than reliability available from conventional circuits and component. An internal clock pulse is provided at a frequency compatible with conventional component operating frequencies for reliable operation. Lumped constant delay circuits are provided for generating outputs at delay intervals corresponding to the desired high resolution. An initiation START pulse is input to generate first high resolution data. A termination STOP pulse is input to generate second high resolution data. Internal counters count at the low frequency internal clock pulse rate between the START and STOP pulses. The first and second high resolution data are logically combined to directly provide high resolution data to one counter and correct the count in the low resolution counter to obtain a high resolution time interval measurement.

A coaxial-output capacitor-loaded annular pulse forming line.

PubMed

Li, Rui; Li, Yongdong; Su, Jiancang; Yu, Binxiong; Xu, Xiudong; Zhao, Liang; Cheng, Jie; Zeng, Bo

2018-04-01

A coaxial-output capacitor-loaded annular pulse forming line (PFL) is developed in order to reduce the flat top fluctuation amplitude of the forming quasi-square pulse and improve the quality of the pulse waveform produced by a Tesla-pulse forming network (PFN) type pulse generator. A single module composed of three involute dual-plate PFNs is designed, with a characteristic impedance of 2.44 Ω, an electrical length of 15 ns, and a sustaining voltage of 60 kV. The three involute dual-plate PFNs connected in parallel have the same impedance and electrical length. Due to the existed small inductance and capacitance per unit length in each involute dual-plate PFN, the upper cut-off frequency of the PFN is increased. As a result, the entire annular PFL has better high-frequency response capability. Meanwhile, the three dual-plate PFNs discharge in parallel, which is much closer to the coaxial output. The series connecting inductance between adjacent two modules is significantly reduced when the annular PFL modules are connected in series. The pulse waveform distortion is reduced when the pulse transfers along the modules. Finally, the shielding electrode structure is applied on both sides of the module. The electromagnetic field is restricted in the module when a single module discharges, and the electromagnetic coupling between the multi-stage annular PFLs is eliminated. Based on the principle of impedance matching between the multi-stage annular PFL and the coaxial PFL, the structural optimization design of a mixed PFL in a Tesla type pulse generator is completed with the transient field-circuit co-simulation method. The multi-stage annular PFL consists of 18 stage annular PFL modules in series, with the characteristic impedance of 44 Ω, the electrical length of 15 ns, and the sustaining voltage of 1 MV. The mixed PFL can generate quasi-square electrical pulses with a pulse width of 43 ns, and the fluctuation ratio of the pulse flat top is less than 8% when the pulse rise time is about 5 ns.

A coaxial-output capacitor-loaded annular pulse forming line

NASA Astrophysics Data System (ADS)

Li, Rui; Li, Yongdong; Su, Jiancang; Yu, Binxiong; Xu, Xiudong; Zhao, Liang; Cheng, Jie; Zeng, Bo

2018-04-01

A coaxial-output capacitor-loaded annular pulse forming line (PFL) is developed in order to reduce the flat top fluctuation amplitude of the forming quasi-square pulse and improve the quality of the pulse waveform produced by a Tesla-pulse forming network (PFN) type pulse generator. A single module composed of three involute dual-plate PFNs is designed, with a characteristic impedance of 2.44 Ω, an electrical length of 15 ns, and a sustaining voltage of 60 kV. The three involute dual-plate PFNs connected in parallel have the same impedance and electrical length. Due to the existed small inductance and capacitance per unit length in each involute dual-plate PFN, the upper cut-off frequency of the PFN is increased. As a result, the entire annular PFL has better high-frequency response capability. Meanwhile, the three dual-plate PFNs discharge in parallel, which is much closer to the coaxial output. The series connecting inductance between adjacent two modules is significantly reduced when the annular PFL modules are connected in series. The pulse waveform distortion is reduced when the pulse transfers along the modules. Finally, the shielding electrode structure is applied on both sides of the module. The electromagnetic field is restricted in the module when a single module discharges, and the electromagnetic coupling between the multi-stage annular PFLs is eliminated. Based on the principle of impedance matching between the multi-stage annular PFL and the coaxial PFL, the structural optimization design of a mixed PFL in a Tesla type pulse generator is completed with the transient field-circuit co-simulation method. The multi-stage annular PFL consists of 18 stage annular PFL modules in series, with the characteristic impedance of 44 Ω, the electrical length of 15 ns, and the sustaining voltage of 1 MV. The mixed PFL can generate quasi-square electrical pulses with a pulse width of 43 ns, and the fluctuation ratio of the pulse flat top is less than 8% when the pulse rise time is about 5 ns.

VARIABLE TIME-INTERVAL GENERATOR

DOEpatents

Gross, J.E.

1959-10-31

This patent relates to a pulse generator and more particularly to a time interval generator wherein the time interval between pulses is precisely determined. The variable time generator comprises two oscillators with one having a variable frequency output and the other a fixed frequency output. A frequency divider is connected to the variable oscillator for dividing its frequency by a selected factor and a counter is used for counting the periods of the fixed oscillator occurring during a cycle of the divided frequency of the variable oscillator. This defines the period of the variable oscillator in terms of that of the fixed oscillator. A circuit is provided for selecting as a time interval a predetermined number of periods of the variable oscillator. The output of the generator consists of a first pulse produced by a trigger circuit at the start of the time interval and a second pulse marking the end of the time interval produced by the same trigger circuit.

Design and implementation of the NaI(Tl)/CsI(Na) detectors output signal generator

NASA Astrophysics Data System (ADS)

Zhou, Xu; Liu, Cong-Zhan; Zhao, Jian-Ling; Zhang, Fei; Zhang, Yi-Fei; Li, Zheng-Wei; Zhang, Shuo; Li, Xu-Fang; Lu, Xue-Feng; Xu, Zhen-Ling; Lu, Fang-Jun

2014-02-01

We designed and implemented a signal generator that can simulate the output of the NaI(Tl)/CsI(Na) detectors' pre-amplifier onboard the Hard X-ray Modulation Telescope (HXMT). Using the development of the FPGA (Field Programmable Gate Array) with VHDL language and adding a random constituent, we have finally produced the double exponential random pulse signal generator. The statistical distribution of the signal amplitude is programmable. The occurrence time intervals of the adjacent signals contain negative exponential distribution statistically.

Modulation of somatosensory evoked potentials during wake-sleep states and spike-wave discharges in the rat.

PubMed

Shaw, Fu-Zen; Lee, Su-Ying; Chiu, Ted H

2006-03-01

To clarify the cortical evoked responses in the primary somatosensory cortex of the rat under states of waking, slow-wave sleep (SWS), paradoxical sleep (PS), and spike-wave discharges (SWDs), which are associated with absence seizure. Somatosensory evoked potentials (SEPs) in response to single- and paired-pulse stimulations under waking, SWS, PS, and SWDs were compared. SEPs to a single-pulse stimulus with regard to cortical spikes of sleep spindles and SWDs were also evaluated. Twenty Long Evans rats. Single- and paired-pulse innocuous electrical stimulations were applied to the tail of rats with chronically implanted electrodes in the primary somatosensory cortex and neck muscle under waking, SWS, PS, and SWDs. SEPs displayed distinct patterns under waking/PS and SWS/SWDs. The short-latency P1-N1 wave of the SEP was severely impeded during SWDs but not in other states. Reduction of the P1-N1 magnitude to the second stimulus of the paired-pulse stimulus for interstimulus intervals of < or = 300 milliseconds appeared in waking and PS states, but the decrease occurred only at particular interstimulus intervals under SWS. Interestingly, augmentation was found under SWDs. Moreover, cyclic augmentation of the P1-N1 magnitude was associated with spindle spikes, but cyclic reduction was observed with SWD spikes. Changes in SEPs are not only behavior dependent, but also phase locked onto ongoing brain activity. Distinct short-term plasticity of SEPs during sleep spindles or SWDs may merit further studies for seizure control and tactile information processing.

A Solid-State Modulator for High Speed Kickers

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

Watson, J A; Cook, E G; Chen, Y J

2001-06-11

An all solid-state modulator with multi-pulse burst capability, very fast rise and fall times, pulse width agility, and amplitude modulation capability for use with high-speed beam kickers has been designed and tested at LLNL. The modulator uses multiple solid-state modules stacked in an inductive-adder configuration. It provides a nominal 18kV pulse with {+-} 10% amplitude modulation on the order of several MHz, rise times on the order of 10nS, and can be configured for either positive or negative polarity. The presentation will include measured performance data.

Development of a wearable system module for monitoring physical and mental workload.

PubMed

Kim, Sinbae; Nakamura, Hiromi; Yoshida, Toshihiko; Kishimoto, Masamichi; Imai, Yohsuke; Matsuki, Noriaki; Ishikawa, Takuji; Yamaguchi, Takami

2008-11-01

The population of most developed countries is rapidly aging, which has created a growing demand for home care. A key issue in medicine is supporting the increasing number of elderly patients, both physically and mentally. In this study, we developed a wearable computer that contained modules for measuring electrocardiograms (ECGs) and femoral artery pulse waves using an accelerometer. This system has several benefits: (a) it can provide a database server in each patient's home; (b) its high extendibility and flexibility facilitate adaptation to a patient's needs; and (c) it allows patients to keep their own data, thus protecting the privacy of personal information. To clarify the capabilities and reliability of the system, we applied it to 8 healthy young volunteers during states of physical and mental work. This system successfully detected clear ECGs and femoral artery pulse waves to calculate important bioinformation, including heart rate, pulse wave velocity, and the power spectral density of spontaneous beat-to-beat oscillations in the R-R interval. In this study, we proposed the way to provide an assessment of the physical and mental condition of the subject using analysis of the bio-information with respect to the physical and mental workloads. The present study provides useful knowledge for the development of a wearable computer designed to monitor the physical and mental conditions of older persons and patients.

Multiple frequency optical mixer and demultiplexer and apparatus for remote sensing

NASA Technical Reports Server (NTRS)

Chen, Jeffrey R. (Inventor)

2010-01-01

A pulsed laser system includes a modulator module configured to provide pulsed electrical signals and a plurality of solid-state seed sources coupled to the modulator module and configured to operate, responsive to the pulsed electrical signals, in a pulse mode. Each of the plurality of solid-state seed sources is tuned to a different frequency channel separated from any adjacent frequency channel by a frequency offset. The pulsed laser system also includes a combiner that combines outputs from each of the solid state seed sources into a single optical path and an optical doubler and demultiplexer coupled to the single optical path and providing each doubled seed frequency on a separate output path.

Width-tunable pulse laser via optical injection induced gain modulation of semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Pan, Honggang; Zhang, Ailing; Tong, Zhengrong; Zhang, Yue; Song, Hongyun; Yao, Yuan

2018-03-01

A width-tunable pulse laser via an optical injection induced gain modulation of a semiconductor optical amplifier (SOA) is demonstrated. When the pump current of the SOA is 330 mA or 400 mA and a continuous wave is injected into the laser cavity with different powers, bright or dark pulses with different pulse widths and frequency repetition rates are obtained. The bright and dark pulses are formed by the effect of gain dispersion and cross-gain modulation of the SOA.

The impulse response of S-cone pathways in detection of increments and decrements

PubMed Central

Shinomori, Keizo; Werner, John S.

2008-01-01

Impulse response functions (IRFs) were obtained from two-pulse detection thresholds using isoluminant stimuli that produced increments or decrements in S-cone excitation. The pulses were chromatically modulated at constant luminance (based on 18 Hz heterochromatic flicker photometry). Chromatic stimuli were presented as a Gaussian patch (±1 SD = 2.3°) in one of four quadrants around a central fixation cross on a CRT screen. Each of the two pulses (6.67 ms) was separated by an inter-stimulus interval (ISI) from 20 to 360 ms. Chromaticity of the pulses was changed from the equal-energy white of the background to a bluish or yellowish color along individually determined tritan lines (based on color matching under strong S-cone adaptation from a 420 nm background superimposed in Maxwellian view). Chromatic detection thresholds were determined by a four-alternative forced-choice method with staircases for each ISI interleaved in each session. Measurements were repeated in at least four sessions for each observer. IRFs were calculated by varying four parameters of an exponentially-damped sinewave. Both S-cone increment and decrement IRFs are characterized by a single excitatory phase and a much longer time course compared with IRFs derived for luminance modulation using the same apparatus and observers. S-cone increment IRFs are faster than S-cone decrement IRFs; the time to peak amplitude of S-cone increment and decrement IRFs is 50–70 and 100–120 ms, respectively. These results were used to derive the temporal contrast sensitivity for human observers of putative ON- and OFF-channels carrying signals from S-cones. PMID:18321402

Self-synchronization of the modulation of energy-levels population with electrons in GaAs induced by picosecond pulses of probe radiation and intrinsic stimulated emission

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

Ageeva, N. N.; Bronevoi, I. L., E-mail: bil@cplire.ru; Zabegaev, D. N.

Picosecond optical pumping leads to the initiation of intrinsic picosecond stimulated emission in GaAs. As was established previously, due to the interaction of pulses of probe radiation with those of intrinsic emission, the dependence of the absorption α of the probe pulse on its delay τ with respect to the pump pulse is modulated with oscillations. It is found that the oscillatory dependences α(τ) have a similar shape only in the case of certain combinations of energies of the interacting pulses. As a result, it is assumed that the above interaction is, in fact, a synchronization of modulations (formed bymore » pulses) of charge-carrier populations at energy levels; this synchronization occurs in the direction of the reconstruction of detailed equilibrium. The real-time picosecond self-modulation of the absorption α is measured for the first time. The characteristics of this self-modulation as well as absorption α and intrinsic emission self-modulation characteristics measured previously by correlation methods are now accounted for by the concept of synchronization.« less

Wearable Sensing of In-Ear Pressure for Heart Rate Monitoring with a Piezoelectric Sensor

PubMed Central

Park, Jang-Ho; Jang, Dae-Geun; Park, Jung Wook; Youm, Se-Kyoung

2015-01-01

In this study, we developed a novel heart rate (HR) monitoring approach in which we measure the pressure variance of the surface of the ear canal. A scissor-shaped apparatus equipped with a piezoelectric film sensor and a hardware circuit module was designed for high wearability and to obtain stable measurement. In the proposed device, the film sensor converts in-ear pulse waves (EPW) into electrical current, and the circuit module enhances the EPW and suppresses noise. A real-time algorithm embedded in the circuit module performs morphological conversions to make the EPW more distinct and knowledge-based rules are used to detect EPW peaks. In a clinical experiment conducted using a reference electrocardiogram (ECG) device, EPW and ECG were concurrently recorded from 58 healthy subjects. The EPW intervals between successive peaks and their corresponding ECG intervals were then compared to each other. Promising results were obtained from the samples, specifically, a sensitivity of 97.25%, positive predictive value of 97.17%, and mean absolute difference of 0.62. Thus, highly accurate HR was obtained from in-ear pressure variance. Consequently, we believe that our proposed approach could be used to monitor vital signs and also utilized in diverse applications in the near future. PMID:26389912

Dynamic optical arbitrary waveform shaping based on cascaded optical modulators of single FBG.

PubMed

Chen, Jingyuan; Li, Peili

2015-08-10

A dynamic optical arbitrary waveform generation (O-AWG) with amplitude and phase independently controlled in optical modulators of single fiber Bragg Grating (FBG) has been proposed. This novel scheme consists of several optical modulators. In the optical modulator (O-MOD), a uniform FBG is used to filter spectral component of the input signal. The amplitude is controlled by fiber stretcher (FS) in Mach-Zehnder interference (MZI) structure through interference of two MZI arms. The phase is manipulated via the second FS in the optical modulator. This scheme is investigated by simulation. Consequently, optical pulse trains with different waveforms as well as pulse trains with nonuniform pulse intensity, pulse spacing and pulse width within each period are obtained through FSs adjustment to alter the phase shifts of signal in each O-MOD.

Losses analysis of soft magnetic ring core under sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) excitations

NASA Astrophysics Data System (ADS)

Gao, Hezhe; Li, Yongjian; Wang, Shanming; Zhu, Jianguo; Yang, Qingxin; Zhang, Changgeng; Li, Jingsong

2018-05-01

Practical core losses in electrical machines differ significantly from those experimental results using the standardized measurement method, i.e. Epstein Frame method. In order to obtain a better approximation of the losses in an electrical machine, a simulation method considering sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) waveforms is proposed. The influence of the pulse width modulation (PWM) parameters on the harmonic components in SPWM and SVPWM is discussed by fast Fourier transform (FFT). Three-level SPWM and SVPWM are analyzed and compared both by simulation and experiment. The core losses of several ring samples magnetized by SPWM, SVPWM and sinusoidal alternating current (AC) are obtained. In addition, the temperature rise of the samples under SPWM, sinusoidal excitation are analyzed and compared.

Improving the therapeutic window of retinal photocoagulation by spatial and temporal modulation of the laser beam

NASA Astrophysics Data System (ADS)

Sramek, Christopher; Leung, Loh-Shan; Leng, Theodore; Brown, Jefferson; Paulus, Yannis M.; Schuele, Georg; Palanker, Daniel

2011-02-01

Decreasing the pulse duration helps confine damage, shorten treatment time, and minimize pain during retinal photocoagulation. However, the safe therapeutic window (TW), the ratio of threshold powers for thermomechanical rupture of Bruch's membrane and mild coagulation, also decreases with shorter exposures. Two potential approaches toward increasing TW are investigated: (a) decreasing the central irradiance of the laser beam and (b) temporally modulating the pulse. An annular beam with adjustable central irradiance was created by coupling a 532-nm laser into a 200-μm core multimode optical fiber at a 4-7 deg angle to normal incidence. Pulse shapes were optimized using a computational model, and a waveform generator was used to drive a PASCAL photocoagulator (532 nm), producing modulated laser pulses. Acute thresholds for mild coagulation and rupture were measured in Dutch-Belted rabbit in vivo with an annular beam (154-163 μm retinal diameter) and modulated pulse (132 μm, uniform irradiance ``flat-top'' beam) with 2-50 ms pulse durations. Thresholds with conventional constant-power pulse and a flat-top beam were also determined. Both annular beam and modulated pulse provided a 28% increase in TW at 10-ms duration, affording the same TW as 20-ms pulses with conventional parameters.

Effect of Missing Inter-Beat Interval Data on Heart Rate Variability Analysis Using Wrist-Worn Wearables.

PubMed

Baek, Hyun Jae; Shin, JaeWook

2017-08-15

Most of the wrist-worn devices on the market provide a continuous heart rate measurement function using photoplethysmography, but have not yet provided a function to measure the continuous heart rate variability (HRV) using beat-to-beat pulse interval. The reason for such is the difficulty of measuring a continuous pulse interval during movement using a wearable device because of the nature of photoplethysmography, which is susceptible to motion noise. This study investigated the effect of missing heart beat interval data on the HRV analysis in cases where pulse interval cannot be measured because of movement noise. First, we performed simulations by randomly removing data from the RR interval of the electrocardiogram measured from 39 subjects and observed the changes of the relative and normalized errors for the HRV parameters according to the total length of the missing heart beat interval data. Second, we measured the pulse interval from 20 subjects using a wrist-worn device for 24 h and observed the error value for the missing pulse interval data caused by the movement during actual daily life. The experimental results showed that mean NN and RMSSD were the most robust for the missing heart beat interval data among all the parameters in the time and frequency domains. Most of the pulse interval data could not be obtained during daily life. In other words, the sample number was too small for spectral analysis because of the long missing duration. Therefore, the frequency domain parameters often could not be calculated, except for the sleep state with little motion. The errors of the HRV parameters were proportional to the missing data duration in the presence of missing heart beat interval data. Based on the results of this study, the maximum missing duration for acceptable errors for each parameter is recommended for use when the HRV analysis is performed on a wrist-worn device.

Chirped-pulse coherent-OTDR with predistortion

NASA Astrophysics Data System (ADS)

Xiong, Ji; Jiang, Jialin; Wu, Yue; Chen, Yongxiang; Xie, Lianlian; Fu, Yun; Wang, Zinan

2018-03-01

In this paper, a novel method for generating high-quality chirped pulses with IQ modulator is studied theoretically and experimentally, which is a crucial building block for high-performance coherent optical time-domain reflectometry (COTDR). In order to compensate the nonlinearity of the modulator transfer function, we present a predistortion technique for chirped-pulse coherent optical time-domain reflectometry (CP-COTDR), the arcsin predistortion method and the single sideband with a suppressed carrier analog modulation used to generate the high quality chirped optical pulse. The high order sidebands, due to the large amplitude of the modulation signal and the nonlinear transfer function of the IQ modulator, can be relieved by the predistortion process, which means the power and the quality of the generated chirped pulse has been improved. In the experiment, this method increases the peak power of the chirped pulse by 4.2 dB compared to the case without predistortion process, as for the CP-COTDR system, this method increases the signal-to-noise ratio of the demodulated phase variation by 6.3 dB.

An experimental vestibular neural prosthesis: design and preliminary results with rhesus monkeys stimulated with modulated pulses.

PubMed

Nie, Kaibao; Ling, Leo; Bierer, Steven M; Kaneko, Chris R S; Fuchs, Albert F; Oxford, Trey; Rubinstein, Jay T; Phillips, James O

2013-06-01

A vestibular neural prosthesis was designed on the basis of a cochlear implant for treatment of Meniere's disease and other vestibular disorders. Computer control software was developed to generate patterned pulse stimuli for exploring optimal parameters to activate the vestibular nerve. Two rhesus monkeys were implanted with the prototype vestibular prosthesis and they were behaviorally evaluated post implantation surgery. Horizontal and vertical eye movement responses to patterned electrical pulse stimulations were collected on both monkeys. Pulse amplitude modulated (PAM) and pulse rate modulated (PRM) trains were applied to the lateral canal of each implanted animal. Robust slow-phase nystagmus responses following the PAM or PRM modulation pattern were observed in both implanted monkeys in the direction consistent with the activation of the implanted canal. Both PAM and PRM pulse trains can elicit a significant amount of in-phase modulated eye velocity changes and they could potentially be used for efficiently coding head rotational signals in future vestibular neural prostheses.

XUV pulse effect on signal modulations of harmonic spectra from H2+ and T2+

NASA Astrophysics Data System (ADS)

Feng, Liqiang; Liu, Hang; Kapteyn, Henry J.; Feng, April Y.

2018-05-01

The effects of signal modulations on the molecular high-order harmonic generations in H2^{+ } and T2+ have been theoretically investigated. It is found that with the introduction of the XUV pulse, due to the absorption of the extra XUV photons in the recombination process, multiplateaus on the harmonic spectra, separated by the XUV photon energy can be found. Moreover, this multiplateau structure is insensitive to the wavelength of the XUV pulse. In shorter pulse duration, the intensities of the multiplateaus from H2+ are higher than those from T2+; while in longer pulse duration, the opposite results can be found. Finally, by changing the delay time of the XUV pulse, the signal modulations (including the amplitude and the frequency modulations) of the multiplateaus can be controlled.

Method for spatially modulating X-ray pulses using MEMS-based X-ray optics

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

Lopez, Daniel; Shenoy, Gopal; Wang, Jin

A method and apparatus are provided for spatially modulating X-rays or X-ray pulses using microelectromechanical systems (MEMS) based X-ray optics. A torsionally-oscillating MEMS micromirror and a method of leveraging the grazing-angle reflection property are provided to modulate X-ray pulses with a high-degree of controllability.

Pulse Shaped Constant Envelope 8-PSK Modulation Study

NASA Technical Reports Server (NTRS)

Tao, Jianping; Horan, Sheila

1997-01-01

This report provides simulation results for constant envelope pulse shaped 8 Level Phase Shift Keying (8 PSK) modulation for end to end system performance. In order to increase bandwidth utilization, pulse shaping is applied to signals before they are modulated. This report provides simulation results of power spectra and measurement of bit errors produced by pulse shaping in a non-linear channel with Additive White Gaussian Noise (AWGN). The pulse shaping filters can placed before (Type B) or after (Type A) signals are modulated. Three kinds of baseband filters, 5th order Butterworth, 3rd order Bessel and Square-Root Raised Cosine with different BTs or roll off factors, are utilized in the simulations. The simulations were performed on a Signal Processing Worksystem (SPW).

Active/passive mode-locked laser oscillator

DOEpatents

Fountain, William D.; Johnson, Bertram C.

1977-01-01

A Q-switched/mode-locked Nd:YAG laser oscillator employing simultaneous active (electro-optic) and passive (saturable absorber) loss modulation within the optical cavity is described. This "dual modulation" oscillator can produce transform-limited pulses of duration ranging from about 30 psec to about 5 nsec with greatly improved stability compared to other mode-locked systems. The pulses produced by this system lack intrapulse frequency or amplitude modulation, and hence are idealy suited for amplification to high energies and for other applications where well-defined pulses are required. Also, the pulses of this system have excellent interpulse characteristics, wherein the optical noise between the individual pulses of the pulse train has a power level well below the power of the peak pulse of the train.

FM-to-AM modulations induced by a weak residual reflection stack of sine-modulated pulses in inertial confinement fusion laser systems

NASA Astrophysics Data System (ADS)

Huang, Xiaoxia; Deng, Xuewei; Zhou, Wei; Hu, Dongxia; Guo, Huaiwen; Wang, Yuancheng; Zhao, Bowang; Zhong, Wei; Deng, Wu

2018-02-01

We report on frequency to amplitude modulation (FM-to-AM) conversion induced by a weak residual reflection stack of sine-modulated pulses in a complex laser system. Theoretical and experimental investigations reveal that when weak residual reflected pulses stack on the main pulse, the spectral intensity changes in the stacked region, which then converts to obvious AM. This kind of FM-to-AM effect often occurs in the tail of the pulse and cannot be eliminated by common compensation methods, which even enhance the modulation depth. Furthermore, the actual intensity modulation frequency and depth induced by the residual reflection stack are much higher and deeper than observed on the oscilloscope, which is harmful for safe operation of the laser facility and the driving power balance during inertial confinement fusion. To eliminate this kind of FM-to-AM effect, any possible on-axis and near-axis residual reflection in laser systems must be avoided.

The association between brain-derived neurotrophic factor and central pulse pressure after an oral glucose tolerance test.

PubMed

Lee, I-Te; Chen, Chen-Huan; Wang, Jun-Sing; Fu, Chia-Po; Lee, Wen-Jane; Liang, Kae-Woei; Lin, Shih-Yi; Sheu, Wayne Huey-Herng

2018-01-01

Arterial stiffening blunts postprandial vasodilatation. We hypothesized that brain-derived neurotrophic factor (BDNF) may modulate postprandial central pulse pressure, a surrogate marker for arterial stiffening. A total of 82 non-diabetic subjects received a 75-g oral glucose tolerance test (OGTT) after overnight fasting. Serum BDNF concentrations were determined at 0, 30, and 120min to calculate the area under the curve (AUC). Brachial and central blood pressures were measured using a noninvasive central blood pressure monitor before blood withdrawals at 0 and 120min. With the median AUC of BDNF of 45(ng/ml)∗h as the cutoff value, the central pulse pressure after glucose intake was significantly higher in the subjects with a low BDNF than in those with a high BDNF (63±16 vs. 53±11mmHg, P=0.003), while the brachial pulse pressure was not significantly different between the 2 groups (P=0.099). In a multivariate linear regression model, a lower AUC of BDNF was an independent predictor of a higher central pulse pressure after oral glucose intake (linear regression coefficient-0.202, 95% confidence interval-0.340 to -0.065, P=0.004). After oral glucose challenge, a lower serum BDNF response is significantly associated with a higher central pulse pressure. Copyright © 2017 Elsevier B.V. All rights reserved.

Automated pulse discrimination of two freely-swimming weakly electric fish and analysis of their electrical behavior during dominance contest.

PubMed

Guariento, Rafael T; Mosqueiro, Thiago S; Matias, Paulo; Cesarino, Vinicius B; Almeida, Lirio O B; Slaets, Jan F W; Maia, Leonardo P; Pinto, Reynaldo D

2016-10-01

Electric fishes modulate their electric organ discharges with a remarkable variability. Some patterns can be easily identified, such as pulse rate changes, offs and chirps, which are often associated with important behavioral contexts, including aggression, hiding and mating. However, these behaviors are only observed when at least two fish are freely interacting. Although their electrical pulses can be easily recorded by non-invasive techniques, discriminating the emitter of each pulse is challenging when physically similar fish are allowed to freely move and interact. Here we optimized a custom-made software recently designed to identify the emitter of pulses by using automated chirp detection, adaptive threshold for pulse detection and slightly changing how the recorded signals are integrated. With these optimizations, we performed a quantitative analysis of the statistical changes throughout the dominance contest with respect to Inter Pulse Intervals, Chirps and Offs dyads of freely moving Gymnotus carapo. In all dyads, chirps were signatures of subsequent submission, even when they occurred early in the contest. Although offs were observed in both dominant and submissive fish, they were substantially more frequent in submissive individuals, in agreement with the idea from previous studies that offs are electric cues of submission. In general, after the dominance is established the submissive fish significantly changes its average pulse rate, while the pulse rate of the dominant remained unchanged. Additionally, no chirps or offs were observed when two fish were manually kept in direct physical contact, suggesting that these electric behaviors are not automatic responses to physical contact. Copyright © 2017 Elsevier Ltd. All rights reserved.

Apparatus and method for compensating for clock drift in downhole drilling components

DOEpatents

Hall, David R [Provo, UT; Pixton, David S [Lehi, UT; Johnson, Monte L [Orem, UT; Bartholomew, David B [Springville, UT; Hall, Jr., H. Tracy

2007-08-07

A precise downhole clock that compensates for drift includes a prescaler configured to receive electrical pulses from an oscillator. The prescaler is configured to output a series of clock pulses. The prescaler outputs each clock pulse after counting a preloaded number of electrical pulses from the oscillator. The prescaler is operably connected to a compensator module for adjusting the number loaded into the prescaler. By adjusting the number that is loaded into the prescaler, the timing may be advanced or retarded to more accurately synchronize the clock pulses with a reference time source. The compensator module is controlled by a counter-based trigger module configured to trigger the compensator module to load a value into the prescaler. Finally, a time-base logic module is configured to calculate the drift of the downhole clock by comparing the time of the downhole clock with a reference time source.

Low-Frequency Repetitive Transcranial Magnetic Stimulation Targeted to Premotor Cortex Followed by Primary Motor Cortex Modulates Excitability Differently Than Premotor Cortex or Primary Motor Cortex Stimulation Alone.

PubMed

Chen, Mo; Deng, Huiqiong; Schmidt, Rebekah L; Kimberley, Teresa J

2015-12-01

The excitability of primary motor cortex (M1) can be modulated by applying low-frequency repetitive transcranial magnetic stimulation (rTMS) over M1 or premotor cortex (PMC). A comparison of inhibitory effect between the two locations has been reported with inconsistent results. This study compared the response secondary to rTMS applied over M1, PMC, and a combined PMC + M1 stimulation approach which first targets stimulation over PMC then M1. Ten healthy participants were recruited for a randomized, cross-over design with a one-week washout between visits. Each visit consisted of a pretest, an rTMS intervention, and a post-test. Outcome measures included short interval intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). Participants received one of the three interventions in random order at each visit including: 1-Hz rTMS at 90% of resting motor threshold to: M1 (1200 pulses), PMC (1200 pulses), and PMC + M1 (600 pulses each, 1200 total). PMC + M1 stimulation resulted in significantly greater inhibition than the other locations for ICF (P = 0.005) and CSP (P < 0.001); for SICI, increased inhibition (group effect) was not observed after any of the three interventions, and there was no significant difference between the three interventions. The results indicate that PMC + M1 stimulation may modulate brain excitability differently from PMC or M1 alone. CSP was the assessment measure most sensitive to changes in inhibition and was able to distinguish between different inhibitory protocols. This work presents a novel procedure that may have positive implications for therapeutic interventions. © 2015 International Neuromodulation Society.

Modeling and Simulation of the ITER First Wall/Blanket Primary Heat Transfer System

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

Ying, Alice; Popov, Emilian L

2011-01-01

ITER inductive power operation is modeled and simulated using a thermal-hydraulics system code (RELAP5) integrated with a 3-D CFD (SC-Tetra) code. The Primary Heat Transfer System (PHTS) functions are predicted together with the main parameters operational ranges. The control algorithm strategy and derivation are summarized as well. The First Wall and Blanket modules are the primary components of PHTS, used to remove the major part of the thermal heat from the plasma. The modules represent a set of flow channels in solid metal structure that serve to absorb the radiation heat and nuclear heating from the fusion reactions and tomore » provide shield for the vacuum vessel. The blanket modules are water cooled. The cooling is forced convective with constant blanket inlet temperature and mass flow rate. Three independent water loops supply coolant to the three blanket sectors. The main equipment of each loop consists of a pump, a steam pressurizer and a heat exchanger. A major feature of ITER is the pulsed operation. The plasma does not burn continuously, but on intervals with large periods of no power between them. This specific feature causes design challenges to accommodate the thermal expansion of the coolant during the pulse period and requires active temperature control to maintain a constant blanket inlet temperature.« less

Adenosine transiently modulates stimulated dopamine release in the caudate putamen via A1 receptors

PubMed Central

Ross, Ashley E.; Venton, B. Jill

2014-01-01

Adenosine modulates dopamine in the brain via A1 and A2A receptors, but that modulation has only been characterized on a slow time scale. Recent studies have characterized a rapid signaling mode of adenosine that suggests a possible rapid modulatory role. Here, fast-scan cyclic voltammetry was used to characterize the extent to which transient adenosine changes modulate stimulated dopamine release (5 pulses at 60 Hz) in rat caudate putamen brain slices. Exogenous adenosine was applied and dopamine concentration monitored. Adenosine only modulated dopamine when it was applied 2 or 5 s before stimulation. Longer time intervals and bath application of 5 µM adenosine did not decrease dopamine release. Mechanical stimulation of endogenous adenosine 2s before dopamine stimulation also decreased stimulated dopamine release by 41 ± 7 %, similar to the 54 ± 6 % decrease in dopamine after exogenous adenosine application. Dopamine inhibition by transient adenosine was recovered within 10 minutes. The A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) blocked the dopamine modulation, whereas dopamine modulation was unaffected by the A2A receptor antagonist SCH 442416. Thus, transient adenosine changes can transiently modulate phasic dopamine release via A1 receptors. These data demonstrate that adenosine has a rapid, but transient, modulatory role in the brain. PMID:25219576

Heterodimer Autorepression Loop: A Robust and Flexible Pulse-Generating Genetic Module

NASA Astrophysics Data System (ADS)

Lannoo, B.; Carlon, E.; Lefranc, M.

2016-07-01

We investigate the dynamics of the heterodimer autorepression loop (HAL), a small genetic module in which a protein A acts as an autorepressor and binds to a second protein B to form an A B dimer. For suitable values of the rate constants, the HAL produces pulses of A alternating with pulses of B . By means of analytical and numerical calculations, we show that the duration of A pulses is extremely robust against variation of the rate constants while the duration of the B pulses can be flexibly adjusted. The HAL is thus a minimal genetic module generating robust pulses with a tunable duration, an interesting property for cellular signaling.

Pulse transmission transceiver architecture for low power communications

DOEpatents

Dress, Jr., William B.; Smith, Stephen F.

2003-08-05

Systems and methods for pulse-transmission low-power communication modes are disclosed. A method of pulse transmission communications includes: generating a modulated pulse signal waveform; transforming said modulated pulse signal waveform into at least one higher-order derivative waveform; and transmitting said at least one higher-order derivative waveform as an emitted pulse. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

Optical generation of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system.

PubMed

Ye, Qing; Qu, Ronghui; Fang, Zujie

2007-04-10

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission.

A compact pulse shape discriminator module for large neutron detector arrays

NASA Astrophysics Data System (ADS)

Venkataramanan, S.; Gupta, Arti; Golda, K. S.; Singh, Hardev; Kumar, Rakesh; Singh, R. P.; Bhowmik, R. K.

2008-11-01

A cost-effective high-performance pulse shape discriminator module has been developed to process signals from organic liquid scintillator-based neutron detectors. This module is especially designed for the large neutron detector array used for studies of nuclear reaction dynamics at the Inter University Accelerator Center (IUAC). It incorporates all the necessary pulse processing circuits required for neutron spectroscopy in a novel fashion by adopting the zero crossover technique for neutron-gamma (n- γ) pulse shape discrimination. The detailed layout of the circuit and different features of the module are described in the present paper. The quality of n- γ separation obtained with this electronics is much better than that of commercial modules especially in the low-energy region. The results obtained with our module are compared with similar setups available in other laboratories.

Real-Time Optical Image Processing Techniques

DTIC Science & Technology

1988-10-31

pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the modification of micro-chan- nel spatial...required for non-linear operation. Real-time nonlinear processing was performed using the halftone screen and MSLM. The experiments showed the effectiveness...pulse frequency modulation has been pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the

Facilitation and refractoriness of the electrically evoked compound action potential.

PubMed

Hey, Matthias; Müller-Deile, Joachim; Hessel, Horst; Killian, Matthijs

2017-11-01

In this study we aim to resolve the contributions of facilitation and refractoriness at very short pulse intervals. Measurements of the refractory properties of the electrically evoked compound action potential (ECAP) of the auditory nerve in cochlear implant (CI) users at inter pulse intervals below 300 μs are influenced by facilitation and recovery effects. ECAPs were recorded using masker pulses with a wide range of current levels relative to the probe pulse levels, for three suprathreshold probe levels and pulse intervals from 13 to 200 μs. Evoked potentials were measured for 21 CI patients by using the masked response extraction artifact cancellation procedure. During analysis of the measurements the stimulation current was not used as absolute value, but in relation to the patient's individual ECAP threshold. This enabled a more general approach to describe facilitation as a probe level independent effect. Maximum facilitation was found for all tested inter pulse intervals at masker levels near patient's individual ECAP threshold, independent from probe level. For short inter pulse intervals an increased N 1 P 1 amplitude was measured for subthreshold masker levels down to 120 CL below patient's individual ECAP threshold in contrast to the recreated state. ECAPs recorded with inter pulse intervals up to 200 μs are influenced by facilitation and recovery. Facilitation effects are most pronounced for masker levels at or below ECAP threshold, while recovery effects increase with higher masker levels above ECAP threshold. The local maximum of the ECAP amplitude for masker levels around ECAP threshold can be explained by the mutual influence of maximum facilitation and minimal refractoriness. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Radar transponder operation with compensation for distortion due to amplitude modulation

DOEpatents

Ormesher, Richard C [Albuquerque, NM; Tise, Bertice L [Albuquerque, NM; Axline, Jr., Robert M.

2011-01-04

In radar transponder operation, a variably delayed gating signal is used to gate a received radar pulse and thereby produce a corresponding gated radar pulse for transmission back to the source of the received radar pulse. This compensates for signal distortion due to amplitude modulation on the retransmitted pulse.

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre

PubMed Central

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-01-01

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C2H2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C2H2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C2H2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy. PMID:28009011

Pulsed photothermal interferometry for spectroscopic gas detection with hollow-core optical fibre.

PubMed

Lin, Yuechuan; Jin, Wei; Yang, Fan; Ma, Jun; Wang, Chao; Ho, Hoi Lut; Liu, Yang

2016-12-23

Gas detection with hollow-core photonic bandgap fibre (HC-PBF) and pulsed photothermal (PT) interferometry spectroscopy are studied theoretically and experimentally. A theoretical model is developed and used to compute the gas-absorption-induced temperature and phase modulation in a HC-PBF filled with low-concentration of C 2 H 2 in nitrogen. The PT phase modulation dynamics for different pulse duration, peak power and energy of pump beam are numerically modelled, which are supported by the experimental results obtained around the P(9) absorption line of C 2 H 2 at 1530.371 nm. Thermal conduction is identified as the main process responsible for the phase modulation dynamics. For a constant peak pump power level, the phase modulation is found to increase with pulse duration up to ~1.2 μs, while it increases with decreasing pulse duration for a constant pulse energy. It is theoretically possible to achieve ppb level detection of C 2 H 2 with ~1 m length HC-PBF and a pump beam with ~10 ns pulse duration and ~100 nJ pulse energy.

Novel ultra-wideband (UWB) photonic generation through photodetection and cross-absorption modulation in a single electroabsorption modulator.

PubMed

Wu, Tsu-Hsiu; Wu, Jui-pin; Chiu, Yi-Jen

2010-02-15

We propose and demonstrate, by proof of concept, a novel method of ultra-wide band (UWB) photonic generation using photodetection and cross-absorption modulation (XAM) of multiple quantum wells (MQW) in a single short-terminated electroabsorption modulator (SEAM). As an optical pump pulse excite the MQWs of SEAM waveguide, the probe light pulse with the same polarity can be generated through XAM, simultaneously creating photocurrent pulse propagating along the waveguide. Using the short termination of SEAM accompanied by the delayed microwave line, the photocurrent pulse can be reversed in polarity and re-modulated the waveguide, forming a monocycle UWB optical pulse. An 89 ps cycle of monocycle pulse with 114% fractional bandwidth is obtained, where the electrical power spectrum centered at 4 GHz of frequency ranges from 0.1 GHz to 8 GHz for -10 dB drops. Meanwhile, the generation processing is also confirmed by observing the same cycle of monocycle electrical pulse from the photodetection of SEAM. The whole optical processing is performed inside a compact semiconductor device, suggesting the optoelectronic integration template has a potential for the application of UWB photonic generation.

Pulse width modulation inverter with battery charger

DOEpatents

Slicker, James M.

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Pulse width modulation inverter with battery charger

NASA Technical Reports Server (NTRS)

Slicker, James M. (Inventor)

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

Photonic generation of ultra-wideband doublet pulse using a semiconductor-optical-amplifier based polarization-diversified loop.

PubMed

Luo, Bowen; Dong, Jianji; Yu, Yuan; Yang, Ting; Zhang, Xinliang

2012-06-15

We propose and demonstrate a novel scheme of ultra-wideband (UWB) doublet pulse generation using a semiconductor optical amplifier (SOA) based polarization-diversified loop (PDL) without any assistant light. In our scheme, the incoming gaussian pulse is split into two parts by the PDL, and each of them is intensity modulated by the other due to cross-gain modulation (XGM) in the SOA. Then, both parts are recombined with incoherent summation to form a UWB doublet pulse. Bi-polar UWB doublet pulse generation is demonstrated using an inverted gaussian pulse injection. Moreover, pulse amplitude modulation of UWB doublet is also experimentally demonstrated. Our scheme shows some advantages, such as simple implementation without assistant light and single optical carrier operation with good fiber dispersion tolerance.

Generation of picosecond optical pulse based on chirp compensation

NASA Astrophysics Data System (ADS)

Sun, Xiaofeng; Yang, Jiaqian; Li, Shangyuan; Xue, Xiaoxiao; Zheng, Xiaoping; Zhou, Bingkun

2017-10-01

Picosecond optical pulses are widely used in optical communication systems, such as the optical time division multiplexing (OTDM) and photonic analog-to-digital converter (ADC). We have proposed and demonstrated a simple method to generate picosecond optical pulse using the mach-zehnder modulator (MZM), phase modulator (PM) and single model fiber (SMF). The phase modulator is used to generate a frequency chirp which varies periodically with time. The MZM is used to suppress the pedestal of the pulse and improve the performance of the pulse. The SMF is used to compensate the frequency chirp. We have carried out theoretical analysis and numerical simulation for the generation process of the picosecond optical pulse. The influence of phase shift between the modulation signals loaded on the MZM and PM is analyzed by numerical simulation and the conditions for the generation of picosecond optical pulse are given. The formula for calculating the optimum length of SMF which is used to compensate the linear chirp is given. The optical pulses with a repetition frequency of 10 GHz and a pulse width of 8.5 ps were obtained. The time-bandwidth product was as small as 1.09 and the timing jitter is as low as 83 fs.

Adjustable repetition-rate multiplication of optical pulses using fractional temporal Talbot effect with preceded binary intensity modulation

NASA Astrophysics Data System (ADS)

Xie, Qijie; Zheng, Bofang; Shu, Chester

2017-05-01

We demonstrate a simple approach for adjustable multiplication of optical pulses in a fiber using the temporal Talbot effect. Binary electrical patterns are used to control the multiplication factor in our approach. The input 10 GHz picosecond pulses are pedestal-free and are shaped directly from a CW laser. The pulses are then intensity modulated by different sets of binary patterns prior to entering a fiber of fixed dispersion. Tunable repetition-rate multiplication by different factors of 2, 4, and 8 have been achieved and up to 80 GHz pulse train has been experimentally generated. We also evaluate numerically the influence of the extinction ratio of the intensity modulator on the performance of the multiplied pulse train. In addition, the impact of the modulator bias on the uniformity of the output pulses has also been analyzed through simulation and experiment and a good agreement is reached. Last, we perform numerical simulation on the RF spectral characteristics of the output pulses. The insensitivity of the signal-to-subharmonic noise ratio (SSNR) to the laser linewidth shows that our multiplication scheme is highly tolerant to the incoherence of the input optical pulses.

Adaptive threshold hunting for the effects of transcranial direct current stimulation on primary motor cortex inhibition.

PubMed

Mooney, Ronan A; Cirillo, John; Byblow, Winston D

2018-06-01

Primary motor cortex excitability can be modulated by anodal and cathodal transcranial direct current stimulation (tDCS). These neuromodulatory effects may, in part, be dependent on modulation within gamma-aminobutyric acid (GABA)-mediated inhibitory networks. GABAergic function can be quantified non-invasively using adaptive threshold hunting paired-pulse transcranial magnetic stimulation (TMS). The previous studies have used TMS with posterior-anterior (PA) induced current to assess tDCS effects on inhibition. However, TMS with anterior-posterior (AP) induced current in the brain provides a more robust measure of GABA-mediated inhibition. The aim of the present study was to assess the modulation of corticomotor excitability and inhibition after anodal and cathodal tDCS using TMS with PA- and AP-induced current. In 16 young adults (26 ± 1 years), we investigated the response to anodal, cathodal, and sham tDCS in a repeated-measures double-blinded crossover design. Adaptive threshold hunting paired-pulse TMS with PA- and AP-induced current was used to examine separate interneuronal populations within M1 and their influence on corticomotor excitability and short- and long-interval inhibition (SICI and LICI) for up to 60 min after tDCS. Unexpectedly, cathodal tDCS increased corticomotor excitability assessed with AP (P = 0.047) but not PA stimulation (P = 0.74). SICI AP was reduced after anodal tDCS compared with sham (P = 0.040). Pearson's correlations indicated that SICI AP and LICI AP modulation was associated with corticomotor excitability after anodal (P = 0.027) and cathodal tDCS (P = 0.042). The after-effects of tDCS on corticomotor excitability may depend on the direction of the TMS-induced current used to make assessments, and on modulation within GABA-mediated inhibitory circuits.

Research on channel characteristics of differential multi pulse position modulation without background noise

NASA Astrophysics Data System (ADS)

Gao, Zhuo; Zhan, Weida; Sun, Quan; Hao, Ziqiang

2018-04-01

Differential multi-pulse position modulation (DMPPM) is a new type of modulation technology. There is a fast transmission rate, high bandwidth utilization, high modulation rate characteristics. The study of DMPPM modulation has important scientific value and practical significance. Channel capacity is one of the important indexes to measure the communication capability of communication system, and studying the channel capacity of DMPPM without background noise is the key to analyze the characteristics of DMPPM. The DMPPM theoretical model is established. The symbol structure of DMPPM with guard time slot is analyzed, and the channel capacity expression of DMPPM is deduced. Simulation analysis by MATLAB. The curves of unit channel capacity and capacity efficiency at different pulse and photon counting rates are analyzed. The results show that DMPPM is more advantageous than multi-pulse position modulation (MPPM), and is more suitable for future wireless optical communication system.

Development of a 33 kV, 20 A long pulse converter modulator for high average power klystron

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

Reghu, T.; Mandloi, V.; Shrivastava, Purushottam

Research, design, and development of high average power, long pulse modulators for the proposed Indian Spallation Neutron Source are underway at Raja Ramanna Centre for Advanced Technology. With this objective, a prototype of long pulse modulator capable of delivering 33 kV, 20 A at 5 Hz repetition rate has been designed and developed. Three Insulated Gate Bipolar Transistors (IGBT) based switching modules driving high frequency, high voltage transformers have been used to generate high voltage output. The IGBT based switching modules are shifted in phase by 120° with respect to each other. The switching frequency is 25 kHz. Pulses ofmore » 1.6 ms pulse width, 80 μs rise time, and 70 μs fall time have been achieved at the modulator output. A droop of ±0.6% is achieved using a simple segmented digital droop correction technique. The total fault energy transferred to the load during fault has been measured by conducting wire burn tests and is found to be within 3.5 J.« less

Development of a 33 kV, 20 A long pulse converter modulator for high average power klystron

NASA Astrophysics Data System (ADS)

Reghu, T.; Mandloi, V.; Shrivastava, Purushottam

2014-05-01

Research, design, and development of high average power, long pulse modulators for the proposed Indian Spallation Neutron Source are underway at Raja Ramanna Centre for Advanced Technology. With this objective, a prototype of long pulse modulator capable of delivering 33 kV, 20 A at 5 Hz repetition rate has been designed and developed. Three Insulated Gate Bipolar Transistors (IGBT) based switching modules driving high frequency, high voltage transformers have been used to generate high voltage output. The IGBT based switching modules are shifted in phase by 120° with respect to each other. The switching frequency is 25 kHz. Pulses of 1.6 ms pulse width, 80 μs rise time, and 70 μs fall time have been achieved at the modulator output. A droop of ±0.6% is achieved using a simple segmented digital droop correction technique. The total fault energy transferred to the load during fault has been measured by conducting wire burn tests and is found to be within 3.5 J.

High resolution time interval counter

DOEpatents

Condreva, Kenneth J.

1994-01-01

A high resolution counter circuit measures the time interval between the occurrence of an initial and a subsequent electrical pulse to two nanoseconds resolution using an eight megahertz clock. The circuit includes a main counter for receiving electrical pulses and generating a binary word--a measure of the number of eight megahertz clock pulses occurring between the signals. A pair of first and second pulse stretchers receive the signal and generate a pair of output signals whose widths are approximately sixty-four times the time between the receipt of the signals by the respective pulse stretchers and the receipt by the respective pulse stretchers of a second subsequent clock pulse. Output signals are thereafter supplied to a pair of start and stop counters operable to generate a pair of binary output words representative of the measure of the width of the pulses to a resolution of two nanoseconds. Errors associated with the pulse stretchers are corrected by providing calibration data to both stretcher circuits, and recording start and stop counter values. Stretched initial and subsequent signals are combined with autocalibration data and supplied to an arithmetic logic unit to determine the time interval in nanoseconds between the pair of electrical pulses being measured.

High resolution time interval counter

DOEpatents

Condreva, K.J.

1994-07-26

A high resolution counter circuit measures the time interval between the occurrence of an initial and a subsequent electrical pulse to two nanoseconds resolution using an eight megahertz clock. The circuit includes a main counter for receiving electrical pulses and generating a binary word--a measure of the number of eight megahertz clock pulses occurring between the signals. A pair of first and second pulse stretchers receive the signal and generate a pair of output signals whose widths are approximately sixty-four times the time between the receipt of the signals by the respective pulse stretchers and the receipt by the respective pulse stretchers of a second subsequent clock pulse. Output signals are thereafter supplied to a pair of start and stop counters operable to generate a pair of binary output words representative of the measure of the width of the pulses to a resolution of two nanoseconds. Errors associated with the pulse stretchers are corrected by providing calibration data to both stretcher circuits, and recording start and stop counter values. Stretched initial and subsequent signals are combined with autocalibration data and supplied to an arithmetic logic unit to determine the time interval in nanoseconds between the pair of electrical pulses being measured. 3 figs.

Comparative study of dual-pulsed 1064 nm Q-switched Nd:YAG laser and single-pulsed 1064 nm Q-switched Nd:YAG laser by using zebrafish model and prospective split-face analysis of facial melasma.

PubMed

Jang, Hee Won; Chun, Seung Hyun; Park, Hae Chul; Ryu, Hwa Jung; Kim, Il-Hwan

2017-04-01

Recently dual-pulsed low-fluence 1064-nm Q-switched Nd:YAG (QSNY) laser has been developed for reducing complication during melasma treatment. Comparison of the efficacy and safety between dual-pulsed mode and single-pulsed mode for the treatment of melasma. In preclinical study, adult zebrafish were irradiated with dual-pulsed and single-pulsed mode. Changes of melanophore and cell death were assessed. In split-face clinical study, dual-pulsed and single-pulsed mode were irradiated on the left and right side of the face, respectively. L* value, clinical digital photos, modified Melasma Area and Severity Index (MASI) scores, and side effects were measured. As compared to single-pulsed mode and dual-pulsed mode with longer intervals, zebrafish melanophore was cleared quickly at dual-pulsed mode with 80-μsec interval and 0.3 J/cm 2 fluence. Dual-pulsed mode showed the least regeneration of melanophore at 4 weeks after irradiation and no cell death was observed with 80-μsec interval. Both pulse modes improved melasma significantly but modified MASI score and L* value were not significantly different between each other. Lesser pain and shorter duration of post-laser erythema were observed with dual-pulsed mode. Dual-pulsed mode was as effective as single-pulsed mode for the treatment of melasma and revealed less side effects.

Plasma optical modulators for intense lasers

PubMed Central

Yu, Lu-Le; Zhao, Yao; Qian, Lie-Jia; Chen, Min; Weng, Su-Ming; Sheng, Zheng-Ming; Jaroszynski, D. A.; Mori, W. B.; Zhang, Jie

2016-01-01

Optical modulators can have high modulation speed and broad bandwidth, while being compact. However, these optical modulators usually work for low-intensity light beams. Here we present an ultrafast, plasma-based optical modulator, which can directly modulate high-power lasers with intensity up to 1016 W cm−2 to produce an extremely broad spectrum with a fractional bandwidth over 100%, extending to the mid-infrared regime in the low-frequency side. This concept relies on two co-propagating laser pulses in a sub-millimetre-scale underdense plasma, where a drive laser pulse first excites an electron plasma wave in its wake while a following carrier laser pulse is modulated by the plasma wave. The laser and plasma parameters suitable for the modulator to work are based on numerical simulations. PMID:27283369

Prototype Solid State Induction Modulator for SLAC NLC

NASA Astrophysics Data System (ADS)

Cassel, R. L.; DeLamare, J. E.; Nguyen, M. N.; Pappas, G. C.; Cook, E.

2002-08-01

The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed power modulator to drive the X band klystrons. The present NLC envisions a solid-state induction modulator design to drive up to 8 klystrons to 500kV for 3muS at 120 PPS with one modulator (>1,000 megawatt pulse, 500kW average). A prototype modulator is presently under construction, which well power 4 each 5045 SLAC klystron to greater than 380 kV for 3muS (>600 megawatt pulse, >300 kW Ave.). The modulator will be capable of driving the 8 each X band klystrons when they become available. The paper covers the design, construction, fabrication and preliminary testing of the prototype modulator.

Ethanol modulates cortical activity: direct evidence with combined TMS and EEG.

PubMed

Kähkönen, S; Kesäniemi, M; Nikouline, V V; Karhu, J; Ollikainen, M; Holi, M; Ilmoniemi, R J

2001-08-01

The motor cortex of 10 healthy subjects was stimulated by transcranial magnetic stimulation (TMS) before and after ethanol challenge (0.8 g/kg resulting in blood concentration of 0.77 +/- 0.14 ml/liter). The electrical brain activity resulting from the brief electromagnetic pulse was recorded with high-resolution electroencephalography (EEG) and located using inversion algorithms. Focal magnetic pulses to the left motor cortex were delivered with a figure-of-eight coil at the random interstimulus interval of 1.5-2.5 s. The stimulation intensity was adjusted to the motor threshold of abductor digiti minimi. Two conditions before and after ethanol ingestion (30 min) were applied: (1) real TMS, with the coil pressed against the scalp; and (2) control condition, with the coil separated from the scalp by a 2-cm-thick piece of plastic. A separate EMG control recording of one subject during TMS was made with two bipolar platinum needle electrodes inserted to the left temporal muscle. In each condition, 120 pulses were delivered. The EEG was recorded from 60 scalp electrodes. A peak in the EEG signals was observed at 43 ms after the TMS pulse in the real-TMS condition but not in the control condition or in the control scalp EMG. Potential maps before and after ethanol ingestion were significantly different from each other (P = 0.01), but no differences were found in the control condition. Ethanol changed the TMS-evoked potentials over right frontal and left parietal areas, the underlying effect appearing to be largest in the right prefrontal area. Our findings suggest that ethanol may have changed the functional connectivity between prefrontal and motor cortices. This new noninvasive method provides direct evidence about the modulation of cortical connectivity after ethanol challenge. Copyright 2001 Academic Press.

Multi-pulse multi-delay (MPMD) multiple access modulation for UWB

DOEpatents

Dowla, Farid U.; Nekoogar, Faranak

2007-03-20

A new modulation scheme in UWB communications is introduced. This modulation technique utilizes multiple orthogonal transmitted-reference pulses for UWB channelization. The proposed UWB receiver samples the second order statistical function at both zero and non-zero lags and matches the samples to stored second order statistical functions, thus sampling and matching the shape of second order statistical functions rather than just the shape of the received pulses.

Predictions of psychophysical measurements for sinusoidal amplitude modulated (SAM) pulse-train stimuli from a stochastic model.

PubMed

Xu, Yifang; Collins, Leslie M

2007-08-01

Two approaches have been proposed to reduce the synchrony of the neural response to electrical stimuli in cochlear implants. One approach involves adding noise to the pulse-train stimulus, and the other is based on using a high-rate pulse-train carrier. Hypotheses regarding the efficacy of the two approaches can be tested using computational models of neural responsiveness prior to time-intensive psychophysical studies. In our previous work, we have used such models to examine the effects of noise on several psychophysical measures important to speech recognition. However, to date there has been no parallel analytic solution investigating the neural response to the high-rate pulse-train stimuli and their effect on psychophysical measures. This work investigates the properties of the neural response to high-rate pulse-train stimuli with amplitude modulated envelopes using a stochastic auditory nerve model. The statistics governing the neural response to each pulse are derived using a recursive method. The agreement between the theoretical predictions and model simulations is demonstrated for sinusoidal amplitude modulated (SAM) high rate pulse-train stimuli. With our approach, predicting the neural response in modern implant devices becomes tractable. Psychophysical measurements are also predicted using the stochastic auditory nerve model for SAM high-rate pulse-train stimuli. Changes in dynamic range (DR) and intensity discrimination are compared with that observed for noise-modulated pulse-train stimuli. Modulation frequency discrimination is also studied as a function of stimulus level and pulse rate. Results suggest that high rate carriers may positively impact such psychophysical measures.

Cocaine effects on pulsatile secretion of anterior pituitary, gonadal, and adrenal hormones.

PubMed

Mendelson, J H; Mello, N K; Teoh, S K; Ellingboe, J; Cochin, J

1989-12-01

Pulse frequency analysis of LH, PRL, testosterone, and cortisol was carried out with the Cluster Analysis Program in eight male cocaine abusers and eight aged-matched normal men. Four of the eight cocaine abusers had hyperprolactinemia (range, 22.08-44.65 micrograms/L). Cocaine users as a group had significantly higher mean peak height (P less than 0.02) than control subjects. Cocaine users with hyperprolactinemia had higher mean peak height than control subjects or cocaine users with normal PRL levels (P less than 0.01). Cocaine users with hyperprolactinemia also had higher mean amplitude increments than control subjects (P less than 0.02). Cocaine users with hyperprolactinemia had a higher mean valley than controls (P less than 0.01) and cocaine users with normal PRL levels (P less than 0.03). However, there were no significant differences in PRL peak frequency, peak duration, or interpulse intervals between cocaine users with or without hyperprolactinemia and control subjects. There were minimal differences between cocaine users and control subjects in pulse frequency analysis of LH parameters; the small differences in mean LH levels and average interpulse interval were not in the abnormal range and were probably not biologically significant. No differences between cocaine users and controls were detected for pulse frequency analysis of testosterone or cortisol. Cocaine-induced hyperprolactinemia may contribute to disorders of sexual and reproductive function in men who abuse the drug, and recent reports that PRL modulates immune function suggest that cocaine-induced derangements of PRL secretion may also contribute to cocaine-related comorbidity in infectious disease. Since cocaine users with hyperprolactinemia had a higher mean valley as well as a higher peak pulse PRL height than control subjects, but did not have greater PRL pulse frequencies, we conclude that hyperprolactinemia in these men may be due to a cocaine-induced derangement of dopaminergic inhibition of basal PRL secretion.

Method and apparatus for pulse width modulation control of an AC induction motor

DOEpatents

Geppert, Steven; Slicker, James M.

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Method and apparatus for pulse width modulation control of an AC induction motor

NASA Technical Reports Server (NTRS)

Geppert, Steven (Inventor); Slicker, James M. (Inventor)

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

Optimal time-domain technique for pulse width modulation in power electronics

NASA Astrophysics Data System (ADS)

Mayergoyz, I.; Tyagi, S.

2018-05-01

Optimal time-domain technique for pulse width modulation is presented. It is based on exact and explicit analytical solutions for inverter circuits, obtained for any sequence of input voltage rectangular pulses. Two optimal criteria are discussed and illustrated by numerical examples.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, Daniel L.; Reginato, Louis L.

1988-01-01

An electron beam accelerator comprising an electron beam generator-injector to produce a focused beam of .gtoreq.0.1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electrons by about 0.1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially .gtoreq.0.1-1 MeV maximum energy over a time duration of .ltoreq.1 .mu.sec.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, Daniel L.; Reginato, Louis L.

1987-01-01

An electron beam accelerator comprising an electron beam generator-injector to produce a focused beam of .gtoreq.0.1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electrons by about 0.1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially 0.1-1 MeV maximum energy over a time duration of .ltoreq.1 .mu.sec.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, D.L.; Reginato, L.L.

1984-03-22

An electron beam accelerator is described comprising an electron beam generator-injector to produce a focused beam of greater than or equal to .1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electron by about .1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially .1-1 MeV maximum energy over a time duration of less than or equal to 1 ..mu..sec.

Echo tracker/range finder for radars and sonars

NASA Technical Reports Server (NTRS)

Constantinides, N. J. (Inventor)

1982-01-01

An echo tracker/range finder or altimeter is described. The pulse repetition frequency (PFR) of a predetermined plurality of transmitted pulses is adjusted so that echo pulses received from a reflecting object are positioned between transmitted pulses and divided their interpulse time interval into two time intervals having a predetermined ratio with respect to each other. The invention described provides a means whereby the arrival time of a plurality of echo pulses is defined as the time at which a composite echo pulse formed of a sum of the individual echo pulses has the highest amplitude. The invention is applicable to radar systems, sonar systems, or any other kind of system in which pulses are transmitted and echoes received therefrom.

Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

NASA Astrophysics Data System (ADS)

Furukawa, Yuki; Sakata, Ryoichi; Konishi, Kazuki; Ono, Koki; Matsuoka, Shusaku; Watanabe, Kota; Inoue, Shunsuke; Hashida, Masaki; Sakabe, Shuji

2016-06-01

By pairing femtosecond laser pulses (duration ˜40 fs and central wavelength ˜810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm2 and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm2, while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse.

Detailed characteristics of intermittent current pulses due to positive corona

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

Liu, Yang, E-mail: liuyangwuh520@sina.com; Cui, Xiang; Lu, Tiebing

In order to get detailed characteristics of intermittent current pulses due to positive corona such as the repetition rate of burst-pulse trains, the peak value ratio of the primary pulse to the secondary pulse, the number of pulses per burst, and the interval of the secondary pulses, a systematic study was carried out in a coaxial conductor-cylinder electrode system with the conductor electrode being set with a discharge point. Empirical formulae for the number of pulses per burst and the interval of the secondary pulses are first presented. A theoretical model based on the motion of the space-charge clouds ismore » proposed. Analysis with the model gives explanations to the experimental results and reveals some new insights into the physical mechanism of positive intermittent corona.« less

Vibrotactile sensory substitution for object manipulation: amplitude versus pulse train frequency modulation.

PubMed

Stepp, Cara E; Matsuoka, Yoky

2012-01-01

Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despite the potential pragmatic benefits associated with pulse train frequency modulated vibrotactile stimulation, comparison of the approach with amplitude modulation indicates that amplitude modulation vibrotactile stimulation provides superior feedback for object manipulation.

An Investigation of Fully Modulated, Turbulent Diffusion Flames in Reduced Gravity

NASA Technical Reports Server (NTRS)

Hermanson, J. C.; Johari, H.; Usowicz, J. E.; Sangras, R.; Stocker, D. P.; Hegde, U. G.; Nagashima, T.; Obata, S.

2001-01-01

Pulsed combustion appears to have the potential to provide for rapid fuel/air mixing, compact and economical combustors, and reduced exhaust emissions. The objective of this Flight-Definition experiment (PuFF, for Pulsed-Fully Flames) is to increase the fundamental understanding of the fuel/air mixing and combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. In this research the fuel jet is fully modulated (i.e., completely shut off between pulses) by an externally controlled valve system. This gives rise to drastic modification of the combustion and flow characteristics of flames, leading to enhanced fuel/air mixing mechanisms not operative for the case of acoustically excited or partially-modulated jets. The fully-modulated injection approach also simplifies the combustion process by avoiding the acoustic forcing generally present in pulsed combustors. Relatively little is known about the behavior of turbulent flames in reduced-gravity conditions, even in the absence of pulsing. Fundamental issues addressed in this experiment include the impact of buoyancy on the fuel/air mixing and combustion characteristics of fully-modulated flames. It is also important for the planned space experiments to establish the effects of confinement and oxidizer co-flow on these flames.

Pulsed ytterbium-doped fibre laser with a combined modulator based on single-wall carbon nanotubes

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

Khudyakov, D V; Borodkin, A A; Vartapetov, S K

2015-09-30

This paper describes an all-normal-dispersion pulsed ytterbium-doped fibre ring laser mode-locked by a nonlinear combined modulator based on single-wall carbon nanotubes. We have demonstrated 1.7-ps pulse generation at 1.04 μm with a repetition rate of 35.6 MHz. At the laser output, the pulses were compressed to 180 fs. We have examined an intracavity nonlinear modulator which utilises nonlinear polarisation ellipse rotation in conjunction with a saturable absorber in the form of a polymer-matrix composite film containing single-wall carbon nanotubes. (lasers)

Influence of the cubic spectral phase of high-power laser pulses on their self-phase modulation

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

Ginzburg, V N; Kochetkov, A A; Yakovlev, I V

2016-02-28

Spectral broadening of high-power transform-limited laser pulses under self-phase modulation in a medium with cubic nonlinearity is widely used to reduce pulse duration and to increase its power. It is shown that the cubic spectral phase of the initial pulse leads to a qualitatively different broadening of its spectrum: the spectrum has narrow peaks and broadening decreases. However, the use of chirped mirrors allows such pulses to be as effectively compressed as transform-limited pulses. (nonlinear optical phenomena)

Fiber Bragg grating Fabry-Perot cavity sensor based on pulse laser demodulation technique

NASA Astrophysics Data System (ADS)

Gao, Fangfang; Chen, Jianfeng; Liu, Yunqi; Wang, Tingyun

2011-12-01

We demonstrate a fiber laser sensing technique based on fiber Bragg grating Fabry-Perot (FBG-FP) cavity interrogated by pulsed laser, where short pulses generated from active mode-locked erbium-doped fiber ring laser and current modulated DFB laser are adopted. The modulated laser pulses launched into the FBG-FP cavity produce a group of reflected pulses. The optical loss in the cavity can be determined from the power ratio of the first two pulses reflected from the cavity. This technique does not require high reflectivity FBGs and is immune to the power fluctuation of the light source. Two short pulse laser sources were compared experimentally with each other on pulse width, pulse stability, pulse chirp and sensing efficiency.

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

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

Modulated heat pulse propagation and partial transport barriers in chaotic magnetic fields

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

Castillo-Negrete, Diego del; Blazevski, Daniel

2016-04-15

Direct numerical simulations of the time dependent parallel heat transport equation modeling heat pulses driven by power modulation in three-dimensional chaotic magnetic fields are presented. The numerical method is based on the Fourier formulation of a Lagrangian-Green's function method that provides an accurate and efficient technique for the solution of the parallel heat transport equation in the presence of harmonic power modulation. The numerical results presented provide conclusive evidence that even in the absence of magnetic flux surfaces, chaotic magnetic field configurations with intermediate levels of stochasticity exhibit transport barriers to modulated heat pulse propagation. In particular, high-order islands andmore » remnants of destroyed flux surfaces (Cantori) act as partial barriers that slow down or even stop the propagation of heat waves at places where the magnetic field connection length exhibits a strong gradient. Results on modulated heat pulse propagation in fully stochastic fields and across magnetic islands are also presented. In qualitative agreement with recent experiments in large helical device and DIII-D, it is shown that the elliptic (O) and hyperbolic (X) points of magnetic islands have a direct impact on the spatio-temporal dependence of the amplitude of modulated heat pulses.« less

Externally-Modulated Electro-Optically Coupled Detector Architecture for Nuclear Physics Instrumentation

NASA Astrophysics Data System (ADS)

Xi, Wenze; McKisson, J. E.; Weisenberger, Andrew G.; Zhang, Shukui; Zorn, Carl

2014-06-01

A new laser-based externally-modulated electro-optically coupled detector (EOCD) architecture is being developed to enable high-density readout for radiation detectors with accurate analog radiation pulse shape and timing preservation. Unlike digital conversion before electro-optical modulation, the EOCD implements complete analog optical signal modulation and multiplexing in its detector front-end. The result is a compact, high performance detector readout that can be both radiation tolerant and immune to magnetic fields. In this work, the feasibility of EOCD was explored by constructing a two-wavelength laser-based externally-modulated EOCD, and testing analog pulse shape preservation and wavelength-division multiplexing (WDM) crosstalk. Comparisons were first made between the corresponding initial pulses and the electro-optically coupled analog pulses. This confirmed an excellent analog pulse preservation over 29% of the modulator's switching voltage range. Optical spectrum analysis revealed less than -14 dB crosstalk with 1.2 nm WDM wavelength bandgap, and provided insight on experimental conditions that could lead to increased inter-wavelength crosstalk. Further discussions and previous research on the radiation tolerance and magnetic field immunity of the candidate materials were also given, and quantitative device testing is proposed in the future.

Experimental Observation of Thermal Self-Modulation in OPO

NASA Technical Reports Server (NTRS)

Gao, Jiangrui; Wang, Hai; Xie, Changde; Peng, Kunchi

1996-01-01

The thermal self-modulation has been observed experimentally via SHG in OPO. The threshold pump power for the thermal self- modulation is much smaller than that of the nonlinear self-pulsing. The thermal effect prevent from realizing the theoretical prediction for the self-pulsing.

[Pulse-modulated Electromagnetic Radiation of Extremely High Frequencies Protects Cellular DNA against Damaging Effect of Physico-Chemical Factors in vitro].

PubMed

Gapeyev, A B; Lukyanova, N A

2015-01-01

Using a comet assay technique, we investigated protective effects of. extremely high frequency electromagnetic radiation in combination with the damaging effect of X-ray irradiation, the effect of damaging agents hydrogen peroxide and methyl methanesulfonate on DNA in mouse whole blood leukocytes. It was shown that the preliminary exposure of the cells to low intensity pulse-modulated electromagnetic radiation (42.2 GHz, 0.1 mW/cm2, 20-min exposure, modulation frequencies of 1 and 16 Hz) caused protective effects decreasing the DNA damage by 20-45%. The efficacy of pulse-modulated electromagnetic radiation depended on the type of genotoxic agent and increased in a row methyl methanesulfonate--X-rays--hydrogen peroxide. Continuous electromagnetic radiation was ineffective. The mechanisms of protective effects may be connected with an induction of the adaptive response by nanomolar concentrations of reactive oxygen species formed by pulse-modulated electromagnetic radiation.

Integrable high order UWB pulse photonic generator based on cross phase modulation in a SOA-MZI.

PubMed

Moreno, Vanessa; Rius, Manuel; Mora, José; Muriel, Miguel A; Capmany, José

2013-09-23

We propose and experimentally demonstrate a potentially integrable optical scheme to generate high order UWB pulses. The technique is based on exploiting the cross phase modulation generated in an InGaAsP Mach-Zehnder interferometer containing integrated semiconductor optical amplifiers, and is also adaptable to different pulse modulation formats through an optical processing unit which allows to control of the amplitude, polarity and time delay of the generated taps.

Analytical treatment of self-phase-modulation beyond the slowly varying envelope approximation

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

Syrchin, M.S.; Zheltikov, A.M.; International Laser Center, M.V. Lomonosov Moscow State University, 119899 Moscow

Analytical treatment of the self-phase-modulation of an ultrashort light pulse is extended beyond the slowly varying envelope approximation. The resulting wave equation is modified to include corrections to self-phase-modulation due to higher-order spatial and temporal derivatives. Analytical solutions are found in the limiting regimes of high nonlinearities and very short pulses. Our results reveal features that can significantly impact both pulse shape and the evolution of the phase.

An Experiment Investigation of Fully-Modulated, Turbulent Diffusion Flames in Reduced Gravity

NASA Technical Reports Server (NTRS)

Hermanson, J. C.; Johari, H.; Usowicz, J. E.; Stocker, D. P.; Nagashima, T.; Obata, S.

1999-01-01

Pulsed combustion appears to have the potential to provide for rapid fuel/air mixing, compact and economical combustors, and reduced exhaust emissions. The ultimate objective of this program is to increase the fundamental understanding of the fuel/air mixing and combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. In this research the fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system. This can give rise to drastic modification of the combustion and flow characteristics of flames, leading to enhanced fuel/air mixing mechanisms not operative for the case of acoustically excited or partially-modulated jets. In addition, the fully-modulated injection approach avoids the strong acoustic forcing present in pulsed combustion devices, significantly simplifying the mixing and combustion processes. Relatively little is known of the behavior of turbulent flames in reduced-gravity conditions, even in the absence of pulsing. The goal of this Flight-Definition experiment (PUFF, for PUlsed-Fully Flames) is to establish the behavior of fully-modulated, turbulent diffusion flames under microgravity conditions. Fundamental issues to be addressed in this experiment include the mechanisms responsible for the flame length decrease for fully-modulated, turbulent diffusion flames compared with steady flames, the impact of buoyancy on the mixing and combustion characteristics of these flames, and the characteristics of turbulent flame puffs under fully momentum-dominated conditions.

Multi-Modulator for Bandwidth-Efficient Communication

NASA Technical Reports Server (NTRS)

Gray, Andrew; Lee, Dennis; Lay, Norman; Cheetham, Craig; Fong, Wai; Yeh, Pen-Shu; King, Robin; Ghuman, Parminder; Hoy, Scott; Fisher, Dave

2009-01-01

A modulator circuit board has recently been developed to be used in conjunction with a vector modulator to generate any of a large number of modulations for bandwidth-efficient radio transmission of digital data signals at rates than can exceed 100 Mb/s. The modulations include quadrature phaseshift keying (QPSK), offset quadrature phase-shift keying (OQPSK), Gaussian minimum-shift keying (GMSK), and octonary phase-shift keying (8PSK) with square-root raised-cosine pulse shaping. The figure is a greatly simplified block diagram showing the relationship between the modulator board and the rest of the transmitter. The role of the modulator board is to encode the incoming data stream and to shape the resulting pulses, which are fed as inputs to the vector modulator. The combination of encoding and pulse shaping in a given application is chosen to maximize the bandwidth efficiency. The modulator board includes gallium arsenide serial-to-parallel converters at its input end. A complementary metal oxide/semiconductor (CMOS) field-programmable gate array (FPGA) performs the coding and modulation computations and utilizes parallel processing in doing so. The results of the parallel computation are combined and converted to pulse waveforms by use of gallium arsenide parallel-to-serial converters integrated with digital-to-analog converters. Without changing the hardware, one can configure the modulator to produce any of the designed combinations of coding and modulation by loading the appropriate bit configuration file into the FPGA.

Three-Level 48-Pulse STATCOM with Pulse Width Modulation

NASA Astrophysics Data System (ADS)

Singh, Bhim; Srinivas, Kadagala Venkata

2016-03-01

In this paper, a new control strategy of a three-level 48-pulse static synchronous compensator (STATCOM) is proposed with a constant dc link voltage and pulse width modulation at fundamental frequency switching. The proposed STATCOM is realized using eight units of three-level voltage source converters (VSCs) to form a three-level 48-pulse STATCOM. The conduction angle of each three-level VSC is modulated to control the ac converter output voltage, which controls the reactive power of the STATCOM. A fuzzy logic controller is used to control the STATCOM. The dynamic performance of the STATCOM is studied for the control of the reference reactive power, the reference terminal voltage and under the switching of inductive and capacitive loads.

Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

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

Furukawa, Yuki; Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502; Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011

By pairing femtosecond laser pulses (duration ∼40 fs and central wavelength ∼810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm{sup 2} and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm{sup 2}, while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse.

Buoyancy Effects in Fully-Modulated, Turbulent Diffusion Flames

NASA Technical Reports Server (NTRS)

Hermanson, J. C.; Johari, H.; Ghaem-Maghami, E.; Stocker, D. P.; Hegde, U. G.; Page, K. L.

2003-01-01

Pulsed combustion appears to have the potential to provide for rapid fuel/air mixing, compact and economical combustors, and reduced exhaust emissions. The objective of this experiment (PuFF, for Pulsed-Fully Flames) is to increase the fundamental understanding of the fuel/air mixing and combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. In this research the fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system. This gives rise to drastic modification of the combustion and flow characteristics of flames, leading to enhanced fuel/air mixing compared to acoustically excited or partially-modulated jets. Normal-gravity experiments suggest that the fully-modulated technique also has the potential for producing turbulent jet flames significantly more compact than steady flames with no increase in exhaust emissions. The technique also simplifies the combustion process by avoiding the acoustic forcing generally present in pulsed combustors. Fundamental issues addressed in this experiment include the impact of buoyancy on the structure and flame length, temperatures, radiation, and emissions of fully-modulated flames.

Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels

PubMed Central

Tan, Chao; Wu, Xinghua; Wang, Qinkai; Tang, Pinghua; Shi, Xiaohui; Zhan, Shiping; Xi, Zaifang; Fu, Xiquan

2017-01-01

The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration. PMID:28772712

EFFECTS OF CONTINUOUS-WAVE, PULSED, AND SINUSOIDAL-AMPLITUDE-MODULATED MICROWAVES ON BRAIN ENERGY METABOLISM

EPA Science Inventory

A comparison of the effects of continuous wave, sinusoidal-amplitude modulated, and pulsed square-wave-modulated 591-MHz microwave exposures on brain energy metabolism was made in male Sprague Dawley rats (175-225g). Brain NADH fluorescence, adensine triphosphate (ATP) concentrat...

Method of high precision interval measurement in pulse laser ranging system

NASA Astrophysics Data System (ADS)

Wang, Zhen; Lv, Xin-yuan; Mao, Jin-jin; Liu, Wei; Yang, Dong

2013-09-01

Laser ranging is suitable for laser system, for it has the advantage of high measuring precision, fast measuring speed,no cooperative targets and strong resistance to electromagnetic interference,the measuremen of laser ranging is the key paremeters affecting the performance of the whole system.The precision of the pulsed laser ranging system was decided by the precision of the time interval measurement, the principle structure of laser ranging system was introduced, and a method of high precision time interval measurement in pulse laser ranging system was established in this paper.Based on the analysis of the factors which affected the precision of range measure,the pulse rising edges discriminator was adopted to produce timing mark for the start-stop time discrimination,and the TDC-GP2 high precision interval measurement system based on TMS320F2812 DSP was designed to improve the measurement precision.Experimental results indicate that the time interval measurement method in this paper can obtain higher range accuracy. Compared with the traditional time interval measurement system,the method simplifies the system design and reduce the influence of bad weather conditions,furthermore,it satisfies the requirements of low costs and miniaturization.

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.

Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors

NASA Astrophysics Data System (ADS)

Luo, X. L.; Modamio, V.; Nyberg, J.; Valiente-Dobón, J. J.; Nishada, Q.; de Angelis, G.; Agramunt, J.; Egea, F. J.; Erduran, M. N.; Ertürk, S.; de France, G.; Gadea, A.; González, V.; Goasduff, A.; Hüyük, T.; Jaworski, G.; Moszyński, M.; Di Nitto, A.; Palacz, M.; Söderström, P.-A.; Sanchis, E.; Triossi, A.; Wadsworth, R.

2018-07-01

The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and γ standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigated as a function of the time interval between two pulses constituting a pile-up event. The obtained results show that the method is capable of disentangling two pulses with a time interval among them down to 20 ns, as well as classifying them as neutrons or γ rays. Furthermore, the error of reconstructing pile-up pulses could be kept below 6% when successive peaks were separated by more than 50 ns. By applying the method in a high counting rate of pile-up events measurement of the NEutron Detector Array (NEDA), it was empirically found that this method can reconstruct the pile-up pulses and perform neutron- γ discrimination quite accurately. It can also significantly correct the distorted pulse height spectrum due to pile-up events.

Discharge conditions for CW and pulse-modulated surface-wave plasmas in low-temperature sterilization

NASA Astrophysics Data System (ADS)

Xu, L.; Terashita, F.; Nonaka, H.; Ogino, A.; Nagata, T.; Koide, Y.; Nanko, S.; Kurawaki, I.; Nagatsu, M.

2006-01-01

The discharge conditions required for low-temperature plasma sterilization were investigated using low-pressure surface-wave plasma (SWP). The discharge conditions for both continuous wave (CW) and pulse-modulated SWPs in low-temperature sterilization of Geobacillus stearothermophilus with a population of 1.5 × 106 and 3.0 × 106 were studied by varying the microwave input power from 500 W to 3 kW, and the effective plasma treatment time from 40 to 300 s. Results showed that sterilization was possible in a shorter treatment time using a higher microwave power for both CW and pulse-modulated SWPs. Pulse-modulated SWPs gave effective sterilization at a temperature roughly 10 to 20 °C below that of CW SWPs under the same average microwave power.

Method to generate a pulse train of few-cycle coherent radiation

DOE PAGES

Garcia, Bryant; Hemsing, Erik; Raubenheimer, Tor; ...

2016-09-06

We develop a method to generate a long pulse train of few-cycle coherent radiation by modulating an electron beam with a high power laser. The large energy modulation disperses the beam in a radiating undulator and leads to the production of phase-locked few-cycle coherent radiation pulses. These pulses are produced at a high harmonic of the modulating laser, and are longitudinally separated by the modulating laser wavelength. Here, we discuss an analytical model for this scheme and investigate the temporal and spectral properties of this radiation. This model is compared with numerical simulation results using the unaveraged code Puffin. Wemore » examine various harmful effects and how they might be avoided, as well as a possible experimental realization of this scheme.« less

Apollo 16/AS-511/LM-11 operational calibration curves. Volume 1: Calibration curves for command service module CSM 113

NASA Technical Reports Server (NTRS)

Demoss, J. F. (Compiler)

1971-01-01

Calibration curves for the Apollo 16 command service module pulse code modulation downlink and onboard display are presented. Subjects discussed are: (1) measurement calibration curve format, (2) measurement identification, (3) multi-mode calibration data summary, (4) pulse code modulation bilevel events listing, and (5) calibration curves for instrumentation downlink and meter link.

Modular compact solid-state modulators for particle accelerators

NASA Astrophysics Data System (ADS)

Zavadtsev, A. A.; Zavadtsev, D. A.; Churanov, D. V.

2017-12-01

The building of the radio frequency (RF) particle accelerator needs high-voltage pulsed modulator as a power supply for klystron or magnetron to feed the RF accelerating system. The development of a number of solid-state modulators for use in linear accelerators has allowed to develop a series of modular IGBT based compact solid-state modulators with different parameters. This series covers a wide range of needs in accelerator technology to feed a wide range of loads from the low power magnetrons to powerful klystrons. Each modulator of the series is built on base of a number of unified solid-state modules connected to the pulse transformer, and covers a wide range of modulators: voltage up to 250 kV, a peak current up to 250 A, average power up to 100 kW and the pulse duration up to 20 μsec. The parameters of the block with an overall dimensions 880×540×250 mm are: voltage 12 kV, peak current 1600 A, pulse duration 20 μsec, average power 10 kW with air-cooling and 40 kW with liquidcooling. These parameters do not represent a physical limit, and modulators to parameters outside these ranges can be created on request.

Light modulated switches and radio frequency emitters

DOEpatents

Wilson, Mahlon T.; Tallerico, Paul J.

1982-01-01

The disclosure relates to a light modulated electron beam driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

Light modulated electron beam driven radiofrequency emitter

DOEpatents

Wilson, M.T.; Tallerico, P.J.

1979-10-10

The disclosure relates to a light modulated electron beam-driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

180 MW/180 KW pulse modulator for S-band klystron of LUE-200 linac of IREN installation of JINR

NASA Astrophysics Data System (ADS)

Su, Kim Dong; Sumbaev, A. P.; Shvetsov, V. N.

2014-09-01

The offer on working out of the pulse modulator with 180 MW pulse power and 180 kW average power for pulse S-band klystrons of LUE-200 linac of IREN installation at the Laboratory of neutron physics (FLNP) at JINR is formulated. Main requirements, key parameters and element base of the modulator are presented. The variant of the basic scheme on the basis of 14 (or 11) stage 2 parallel PFN with the thyratron switchboard (TGI2-10K/50) and six parallel high voltage power supplies (CCPS Power Supply) is considered.

Changes in auditory nerve responses across the duration of sinusoidally amplitude-modulated electric pulse-train stimuli.

PubMed

Hu, Ning; Miller, Charles A; Abbas, Paul J; Robinson, Barbara K; Woo, Jihwan

2010-12-01

Response rates of auditory nerve fibers (ANFs) to electric pulse trains change over time, reflecting substantial spike-rate adaptation that depends on stimulus parameters. We hypothesize that adaptation affects the representation of amplitude-modulated pulse trains used by cochlear prostheses to transmit speech information to the auditory system. We recorded cat ANF responses to sinusoidally amplitude-modulated (SAM) trains with 5,000 pulse/s carriers. Stimuli delivered by a monopolar intracochlear electrode had fixed modulation frequency (100 Hz) and depth (10%). ANF responses were assessed by spike-rate measures, while representation of modulation was evaluated by vector strength (VS) and the fundamental component of the fast Fourier transform (F(0) amplitude). These measures were assessed across the 400 ms duration of pulse-train stimuli, a duration relevant to speech stimuli. Different stimulus levels were explored and responses were categorized into four spike-rate groups to assess level effects across ANFs. The temporal pattern of rate adaptation to modulated trains was similar to that of unmodulated trains, but with less rate adaptation. VS to the modulator increased over time and tended to saturate at lower spike rates, while F(0) amplitude typically decreased over time for low driven rates and increased for higher driven rates. VS at moderate and high spike rates and degree of F(0) amplitude temporal changes at low and moderate spike rates were positively correlated with the degree of rate adaptation. Thus, high-rate carriers will modify the ANF representation of the modulator over time. As the VS and F(0) measures were sensitive to adaptation-related changes over different spike-rate ranges, there is value in assessing both measures.

Dual-Pulse Pulse Position Modulation (DPPM) for Deep-Space Optical Communications: Performance and Practicality Analysis

NASA Technical Reports Server (NTRS)

Li, Jing; Hylton, Alan; Budinger, James; Nappier, Jennifer; Downey, Joseph; Raible, Daniel

2012-01-01

Due to its simplicity and robustness against wavefront distortion, pulse position modulation (PPM) with photon counting detector has been seriously considered for long-haul optical wireless systems. This paper evaluates the dual-pulse case and compares it with the conventional single-pulse case. Analytical expressions for symbol error rate and bit error rate are first derived and numerically evaluated, for the strong, negative-exponential turbulent atmosphere; and bandwidth efficiency and throughput are subsequently assessed. It is shown that, under a set of practical constraints including pulse width and pulse repetition frequency (PRF), dual-pulse PPM enables a better channel utilization and hence a higher throughput than it single-pulse counterpart. This result is new and different from the previous idealistic studies that showed multi-pulse PPM provided no essential information-theoretic gains than single-pulse PPM.

Gain-phase modulation in chirped-pulse amplification

NASA Astrophysics Data System (ADS)

Shen, Yijie; Gao, Gan; Meng, Yuan; Fu, Xing; Gong, Mali

2017-10-01

The cross-modulation between the gain and chirped phase in chirped-pulse amplification (CPA) is theoretically and experimentally demonstrated. We propose a gain-phase coupled nonlinear Schrödinger equation (GPC-NLSE) for solving chirped-pulse propagation in a nonlinear gain medium involved in the gain-phase modulation (GPM) process. With the GPC-NLSE, the space-time-frequency-dependent gain, chirped phase, pulse, and spectrum evolutions can be precisely calculated. Moreover, a short-length high-gain Yb-doped fiber CPA experiment is presented in which a self-steepening distortion of the seed pulse is automatically compensated after amplification. This phenomenon can be explained by the GPM theory whereas conventional models cannot. The experimental results for the temporal and spectral intensities show excellent agreement with our theory. Our GPM theory paves the way for further investigations of the finer structures of the pulse and spectrum in CPA systems.

Responses to amplitude modulated infrared stimuli in the guinea pig inferior colliculus

NASA Astrophysics Data System (ADS)

Richter, Claus-Peter; Young, Hunter

2013-03-01

Responses of units in the central nucleus of the inferior colliculus of the guinea pig were recorded with tungsten electrodes. The set of data presented here is limited to high stimulus levels. The effect of changing the modulation frequency and the modulation depth was explored for acoustic and laser stimuli. The selected units responded to sinusoidal amplitude modulated (AM) tones, AM trains of clicks, and AM trains of laser pulses with a modulation of their spike discharge. At modulation frequencies of 20 Hz, some units tended to respond with 40 Hz to the acoustic stimuli, but only at 20 Hz for the trains of laser pulses. For all modes of stimulation the responses revealed a dominant response to the first cycle of the modulation, with decreasing number of action potential during successive cycles. While amplitude modulated tone bursts and amplitude modulated trains of acoustic clicks showed similar patterns, the response to trains of laser pulses was different.

Tuning the frequency of ultrashort laser pulses by a cross-phase-modulation-induced shift in a photonic crystal fiber.

PubMed

Konorov, S O; Akimov, D A; Zheltikov, A M; Ivanov, A A; Alfimov, M V; Scalora, M

2005-06-15

Femtosecond pulses of fundamental Cr:forsterite laser radiation are used as a pump field to tune the frequency of copropagating second-harmonic pulses of the same laser through cross-phase modulation in a photonic crystal fiber. Sub-100-kW femtosecond pump pulses coupled into a photonic crystal fiber with an appropriate dispersion profile can shift the central frequency of the probe field by more than 100 nm, suggesting a convenient way to control propagation and spectral transformations of ultrashort laser pulses.

Self-pulsing in a 2 km single-mode fiber with the seed source broadened via WNS phase modulation

NASA Astrophysics Data System (ADS)

Zha, Congwen; Sun, Yinhong; Wang, Yanshan; Li, Tenglong; Peng, Wanjing; Ma, Yi; Zhang, Kai

2018-03-01

The seed source with spectral linewidth broadening via phase modulation is potential to achieve the higher output power with effective SBS suppression. However, self-pulsing from the amplifier output is harmful. In this work, we study the self-pulsing characteristics in a long single-mode fiber with lower self-pulsing threshold instead of the high power amplifier. We provide a powerful experimental support for the self-pulsing mechanism in high-power narrow-linewidth fiber lasers, which is important for further output power scaling.

Coherent control of acoustic vibrations in metal nanoparticles and thin films with sequences of femtosecond pulses: Harmonic-oscillator model

NASA Astrophysics Data System (ADS)

Zheltikov, A. M.

2002-08-01

A harmonic oscillator model is used to demonstrate the possibility of coherent control of acoustic vibrations of metal nanoparticles and thin films with sequences of femtosecond laser pulses. When the interval between the pulses in such a sequence is chosen equal to the oscillation period of the expansion mode of a nanoscale system, the relevant acoustic vibrations can be excited in a resonant and selective way. Sequences of femtosecond pulses with picosecond time intervals between the pulses are shown to be ideally suited for a resonant excitation and coherent control of acoustic modes of silver nanoparticles.

Temporal characteristic analysis of laser-modulated pulsed X-ray source for space X-ray communication

NASA Astrophysics Data System (ADS)

Hang, Shuang; Liu, Yunpeng; Li, Huan; Tang, Xiaobin; Chen, Da

2018-04-01

X-ray communication (XCOM) is a new communication type and is expected to realize high-speed data transmission in some special communication scenarios, such as deep space communication and blackout communication. This study proposes a high-speed modulated X-ray source scheme based on the laser-to-X-ray conversion. The temporal characteristics of the essential components of the proposed laser-modulated pulsed X-ray source (LMPXS) were analyzed to evaluate its pulse emission performance. Results show that the LMPXS can provide a maximum modulation rate up to 100 Mbps which is expected to significantly improve the data rate of XCOM.

[Comprehensive testing system for cardiorespiratory interaction research].

PubMed

Zhang, Zhengbo; Wang, Buqing; Wang, Weidong; Zheng, Jiewen; Liu, Hongyun; Li, Kaiyuan; Sun, Congcong; Wang, Guojing

2013-04-01

To investigate the modulation effects of breathing movement on cardiovascular system and to study the physiological coupling relationship between respiration and cardiovascular system, we designed a comprehensive testing system for cardiorespiratory interaction research. This system, comprising three parts, i. e. physiological signal conditioning unit, data acquisition and USB medical isolation unit, and a PC based program, can acquire multiple physiological data such as respiratory flow, rib cage and abdomen movement, electrocardiograph, artery pulse wave, cardiac sounds, skin temperature, and electromyography simultaneously under certain experimental protocols. Furthermore this system can be used in research on short-term cardiovascular variability by paced breathing. Preliminary experiments showed that this system could accurately record rib cage and abdomen movement under very low breathing rate, using respiratory inductive plethysmography to acquire respiration signal in direct-current coupling mode. After calibration, this system can be used to estimate ventilation non-intrusively and correctly. The PC based program can generate audio and visual biofeedback signal, and guide the volunteers to perform a slow and regular breathing. An experiment on healthy volunteers showed that this system was able to guide the volunteers to do slow breathing effectively and simultaneously record multiple physiological data during the experiments. Signal processing techniques were used for off-line data analysis, such as non-invasive ventilation calibration, QRS complex wave detection, and respiratory sinus arrhythmia and pulse wave transit time calculation. The experiment result showed that the modulation effect on RR interval, respiratory sinus arrhythmia (RSA), pulse wave transit time (PWTT) by respiration would get stronger with the going of the slow and regular breathing.

A SiGe Quadrature Pulse Modulator for Superconducting Qubit State Manipulation

NASA Astrophysics Data System (ADS)

Kwende, Randy; Bardin, Joseph

Manipulation of the quantum states of microwave superconducting qubits typically requires the generation of coherent modulated microwave pulses. While many off-the-shelf instruments are capable of generating such pulses, a more integrated approach is likely required if fault-tolerant quantum computing architectures are to be implemented. In this work, we present progress towards a pulse generator specifically designed to drive superconducing qubits. The device is implemented in a commercial silicon process and has been designed with energy-efficiency and scalability in mind. Pulse generation is carried out using a unique approach in which modulation is applied directly to the in-phase and quadrature components of a carrier signal in the 1-10 GHz frequency range through a unique digital-analog conversion process designed specifically for this application. The prototype pulse generator can be digitally programmed and supports sequencing of pulses with independent amplitude and phase waveforms. These amplitude and phase waveforms can be digitally programmed through a serial programming interface. Detailed performance of the pulse generator at room temperature and 4 K will be presented.

The optimal input optical pulse shape for the self-phase modulation based chirp generator

NASA Astrophysics Data System (ADS)

Zachinyaev, Yuriy; Rumyantsev, Konstantin

2018-04-01

The work is aimed to obtain the optimal shape of the input optical pulse for the proper functioning of the self-phase modulation based chirp generator allowing to achieve high values of chirp frequency deviation. During the research, the structure of the device based on self-phase modulation effect using has been analyzed. The influence of the input optical pulse shape of the transmitting optical module on the chirp frequency deviation has been studied. The relationship between the frequency deviation of the generated chirp and frequency linearity for the three options for implementation of the pulse shape has been also estimated. The results of research are related to the development of the theory of radio processors based on fiber-optic structures and can be used in radars, secure communications, geolocation and tomography.

Combinatorial pulse position modulation for power-efficient free-space laser communications

NASA Technical Reports Server (NTRS)

Budinger, James M.; Vanderaar, M.; Wagner, P.; Bibyk, Steven

1993-01-01

A new modulation technique called combinatorial pulse position modulation (CPPM) is presented as a power-efficient alternative to quaternary pulse position modulation (QPPM) for direct-detection, free-space laser communications. The special case of 16C4PPM is compared to QPPM in terms of data throughput and bit error rate (BER) performance for similar laser power and pulse duty cycle requirements. The increased throughput from CPPM enables the use of forward error corrective (FEC) encoding for a net decrease in the amount of laser power required for a given data throughput compared to uncoded QPPM. A specific, practical case of coded CPPM is shown to reduce the amount of power required to transmit and receive a given data sequence by at least 4.7 dB. Hardware techniques for maximum likelihood detection and symbol timing recovery are presented.

All-Fiber, Directly Chirped Laser Source for Chirped-Pulse-Amplification

NASA Astrophysics Data System (ADS)

Xin, Ran

Chirped-pulse-amplification (CPA) technology is widely used to produce ultra-short optical pulses (sub picosecond to femtoseconds) with high pulse energy. A chirped pulse laser source with flexible dispersion control is highly desirable as a CPA seed. This thesis presents an all-fiber, directly chirped laser source (DCLS) that produces nanosecond, linearly-chirped laser pulses at 1053 nm for seeding high energy CPA systems. DCLS produces a frequency chirp on an optical pulse through direct temporal phase modulation. DCLS provides programmable control for the temporal phase of the pulse, high pulse energy and diffraction-limited beam performance, which are beneficial for CPA systems. The DCLS concept is first described. Its key enabling technologies are identified and their experimental demonstration is presented. These include high-precision temporal phase control using an arbitrary waveform generator, multi-pass phase modulation to achieve high modulation depth, regenerative amplification in a fiber ring cavity and a negative feedback system that controls the amplifier cavity dynamics. A few technical challenges that arise from the multi-pass architecture are described and their solutions are presented, such as polarization management and gain-spectrum engineering in the DCLS fiber cavity. A DCLS has been built and its integration into a high energy OPCPA system is demonstrated. DCLS produces a 1-ns chirped pulse with a 3-nm bandwidth. The temporal phase and group delay dispersion on the DCLS output pulse is measured using temporal interferometry. The measured temporal phase has an ˜1000 rad amplitude and is close to a quadratic shape. The chirped pulse is amplified from 0.9 nJ to 76 mJ in an OPCPA system. The amplified pulse is compressed to close to its Fourier transform limit, producing an intensity autocorrelation trace with a 1.5-ps width. Direct compressed-pulse duration control by adjusting the phase modulation drive amplitude is demonstrated. Limitation to pulse compression is investigated using numerical simulation.

New hybrid reverse differential pulse position width modulation scheme for wireless optical communication

NASA Astrophysics Data System (ADS)

Liao, Renbo; Liu, Hongzhan; Qiao, Yaojun

2014-05-01

In order to improve the power efficiency and reduce the packet error rate of reverse differential pulse position modulation (RDPPM) for wireless optical communication (WOC), a hybrid reverse differential pulse position width modulation (RDPPWM) scheme is proposed, based on RDPPM and reverse pulse width modulation. Subsequently, the symbol structure of RDPPWM is briefly analyzed, and its performance is compared with that of other modulation schemes in terms of average transmitted power, bandwidth requirement, and packet error rate over ideal additive white Gaussian noise (AWGN) channels. Based on the given model, the simulation results show that the proposed modulation scheme has the advantages of improving the power efficiency and reducing the bandwidth requirement. Moreover, in terms of error probability performance, RDPPWM can achieve a much lower packet error rate than that of RDPPM. For example, at the same received signal power of -28 dBm, the packet error rate of RDPPWM can decrease to 2.6×10-12, while that of RDPPM is 2.2×10. Furthermore, RDPPWM does not need symbol synchronization at the receiving end. These considerations make RDPPWM a favorable candidate to select as the modulation scheme in the WOC systems.

Amplitude Control of Solid-State Modulators for Precision Fast Kicker Applications

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

Watson, J A; Anaya, R M; Caporaso, G C

2002-11-15

A solid-state modulator with very fast rise and fall times, pulse width agility, and multi-pulse burst and intra-pulse amplitude adjustment capability for use with high speed electron beam kickers has been designed and tested at LLNL. The modulator uses multiple solid-state modules stacked in an inductive-adder configuration. Amplitude adjustment is provided by controlling individual modules in the adder, and is used to compensate for transverse e-beam motion as well as the dynamic response and beam-induced steering effects associated with the kicker structure. A control algorithm calculates a voltage based on measured e-beam displacement and adjusts the modulator to regulate beammore » centroid position. This paper presents design details of amplitude control along with measured performance data from kicker operation on the ETA-II accelerator at LLNL.« less

Bunch modulation in LWFA blowout regime

NASA Astrophysics Data System (ADS)

Vyskočil, Jiří; Klimo, Ondřej; Vieira, Jorge; Korn, Georg

2015-05-01

Laser wakefield acceleration (LWFA) is able to produce high quality electron bunches interesting for many applications ranging from coherent light sources to high energy physics. The blow-out regime of LWFA provides excellent accelerating structure able to maintain small transverse emittance and energy spread of the accelerating electron beam if combined with localised injection. A modulation of the back of a self-injected electron bunch in the blowout regime of Laser Wakefield Acceleration appears 3D Particle-in-Cell simulations with the code OSIRIS. The shape of the modulation is connected to the polarization of the driving laser pulse, although the wavelength of the modulation is longer than that of the pulse. Nevertheless a circularly polarized laser pulse leads to a corkscrew-like modulation, while in the case of linear polarization, the modulation lies in the polarization plane.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

DOEpatents

Dowla, Farid U; Nekoogar, Faranak

2015-03-03

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications according to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

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

Dowla, Farid; Nekoogar, Faranak

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications accordingmore » to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.« less

Limiting of microjoule femtosecond pulses in air-guided modes of a hollow photonic-crystal fiber

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

Konorov, S.O.; Serebryannikov, E.E.; Sidorov-Biryukov, D.A.

Self-phase-modulation-induced spectral broadening of laser pulses in air-guided modes of hollow photonic-crystal fibers (PCFs) is shown to allow the creation of fiber-optic limiters for high-intensity ultrashort laser pulses. The performance of PCF limiters is analyzed in terms of elementary theory of self-phase modulation. Experiments performed with 100 fs microjoule pulses of 800 nm Ti:sapphire laser radiation demonstrate the potential of hollow PCFs as limiters for 10 MW ultrashort laser pulses and show the possibility to switch the limiting level of output radiation energy by guiding femtosecond pulses in different PCF modes.

Synaptic characteristics with strong analog potentiation, depression, and short-term to long-term memory transition in a Pt/CeO2/Pt crossbar array structure

NASA Astrophysics Data System (ADS)

Kim, Hyung Jun; Park, Daehoon; Yang, Paul; Beom, Keonwon; Kim, Min Ju; Shin, Chansun; Kang, Chi Jung; Yoon, Tae-Sik

2018-06-01

A crossbar array of Pt/CeO2/Pt memristors exhibited the synaptic characteristics such as analog, reversible, and strong resistance change with a ratio of ∼103, corresponding to wide dynamic range of synaptic weight modulation as potentiation and depression with respect to the voltage polarity. In addition, it presented timing-dependent responses such as paired-pulse facilitation and the short-term to long-term memory transition by increasing amplitude, width, and repetition number of voltage pulse and reducing the interval time between pulses. The memory loss with a time was fitted with a stretched exponential relaxation model, revealing the relation of memory stability with the input stimuli strength. The resistance change was further enhanced but its stability got worse as increasing measurement temperature, indicating that the resistance was changed as a result of voltage- and temperature-dependent electrical charging and discharging to alter the energy barrier for charge transport. These detailed synaptic characteristics demonstrated the potential of crossbar array of Pt/CeO2/Pt memristors as artificial synapses in highly connected neuron-synapse network.

Synaptic characteristics with strong analog potentiation, depression, and short-term to long-term memory transition in a Pt/CeO2/Pt crossbar array structure.

PubMed

Kim, Hyung Jun; Park, Daehoon; Yang, Paul; Beom, Keonwon; Kim, Min Ju; Shin, Chansun; Kang, Chi Jung; Yoon, Tae-Sik

2018-06-29

A crossbar array of Pt/CeO 2 /Pt memristors exhibited the synaptic characteristics such as analog, reversible, and strong resistance change with a ratio of ∼10 3 , corresponding to wide dynamic range of synaptic weight modulation as potentiation and depression with respect to the voltage polarity. In addition, it presented timing-dependent responses such as paired-pulse facilitation and the short-term to long-term memory transition by increasing amplitude, width, and repetition number of voltage pulse and reducing the interval time between pulses. The memory loss with a time was fitted with a stretched exponential relaxation model, revealing the relation of memory stability with the input stimuli strength. The resistance change was further enhanced but its stability got worse as increasing measurement temperature, indicating that the resistance was changed as a result of voltage- and temperature-dependent electrical charging and discharging to alter the energy barrier for charge transport. These detailed synaptic characteristics demonstrated the potential of crossbar array of Pt/CeO 2 /Pt memristors as artificial synapses in highly connected neuron-synapse network.

Signal recognition and parameter estimation of BPSK-LFM combined modulation

NASA Astrophysics Data System (ADS)

Long, Chao; Zhang, Lin; Liu, Yu

2015-07-01

Intra-pulse analysis plays an important role in electronic warfare. Intra-pulse feature abstraction focuses on primary parameters such as instantaneous frequency, modulation, and symbol rate. In this paper, automatic modulation recognition and feature extraction for combined BPSK-LFM modulation signals based on decision theoretic approach is studied. The simulation results show good recognition effect and high estimation precision, and the system is easy to be realized.

High aspect ratio nanoholes in glass generated by femtosecond laser pulses with picosecond intervals

NASA Astrophysics Data System (ADS)

Ahn, Sanghoon; Choi, Jiyeon; Noh, Jiwhan; Cho, Sung-Hak

2018-02-01

Because of its potential uses, high aspect ratio nanostructures have been interested for last few decades. In order to generate nanostructures, various techniques have been attempted. Femtosecond laser ablation is one of techniques for generating nanostructures inside a transparent material. For generating nanostructures by femtosecond laser ablation, previous studies have been attempted beam shaping such as Bessel beam and temporal tailored beam. Both methods suppress electron excitation at near surface and initiate interference of photons at certain depth. Recent researches indicate that shape of nanostructures is related with temporal change of electron density and number of self-trapped excitons. In this study, we try to use the temporal change of electron density induced by femtosecond laser pulse for generating high aspect ratio nanoholes. In order to reveal the effect of temporal change of electron density, secondary pulses are irradiated from 100 to 1000 ps after the irradiation of first pulse. Our result shows that diameter of nanoholes is increasing and depth of nanoholes is decreasing as pulse to pulse interval is getting longer. With manipulating of pulse to pulse interval, we could generate high aspect ratio nanoholes with diameter of 250-350 nm and depth of 4∼6 μm inside a glass.

Pulse-Width-Modulating Driver for Brushless dc Motor

NASA Technical Reports Server (NTRS)

Salomon, Phil M.

1991-01-01

High-current pulse-width-modulating driver for brushless dc motor features optical coupling of timing signals from low-current control circuitry to high-current motor-driving circuitry. Provides high electrical isolation of motor-power supply, helping to prevent fast, high-current motor-driving pulses from being coupled through power supplies into control circuitry, where they interfere with low-current control signals.

[An integral chip for the multiphase pulse-duration modulation used for voltage changer in biomedical microprocessor systems].

PubMed

Balashov, A M; Selishchev, S V

2004-01-01

An integral chip (IC) was designed for controlling the step-down pulse voltage converter, which is based on the multiphase pulse-duration modulation, for use in biomedical microprocessor systems. The CMOS technology was an optimal basis for the IC designing. An additional feedback circuit diminishes the output voltage dispersion at dynamically changing loads.

High-sensitivity observations of 28 pulsars

NASA Technical Reports Server (NTRS)

Weisberg, J. M.; Armstrong, B. K.; Backus, P. R.; Cordes, J. M.; Boriakoff, V.

1986-01-01

Average 430-MHz pulse profiles and, where possible, modulation indices and pulse-nulling fractions are computed for 28 pulsars. Morphological classifications are determined for most of the pulsars. It is found that core emission components tend to have lower modulation indices than conal components, and that pulsars having only a core component never exhibit pulse pulling. PSR 1612 + 07 is shown to undergo mode changes.

Effects of 900 MHz radiofrequency radiation on skin hydroxyproline contents.

PubMed

Çam, Semra Tepe; Seyhan, Nesrin; Kavaklı, Cengiz; Çelikbıçak, Ömür

2014-09-01

The present study aimed to investigate the possible effect of pulse-modulated radiofrequency radiation (RFR) on rat skin hydroxyproline content, since skin is the first target of external electromagnetic fields. Skin hydroxyproline content was measured using liquid chromatography mass spectrometer method. Two months old male wistar rats were exposed to a 900 MHz pulse-modulated RFR at an average whole body specific absorption rate (SAR) of 1.35 W/kg for 20 min/day for 3 weeks. The radiofrequency (RF) signals were pulse modulated by rectangular pulses with a repetition frequency of 217 Hz and a duty cycle of 1:8 (pulse width 0.576 ms). A skin biopsy was taken at the upper part of the abdominal costa after the exposure. The data indicated that whole body exposure to a pulse-modulated RF radiation that is similar to that emitted by the global system for mobile communications (GSM) mobile phones caused a statistically significant increase in the skin hydroxyproline level (p = 0.049, Mann-Whitney U test). Under our experimental conditions, at a SAR less than the International Commission on Non-Ionizing Radiation Protection safety limit recommendation, there was evidence that GSM signals could alter hydroxyproline concentration in the rat skin.

Slow-Frequency Pulsed Transcranial Electrical Stimulation for Modulation of Cortical Plasticity Based on Reciprocity Targeting with Precision Electrical Head Modeling

PubMed Central

Luu, Phan; Essaki Arumugam, Easwara Moorthy; Anderson, Erik; Gunn, Amanda; Rech, Dennis; Turovets, Sergei; Tucker, Don M.

2016-01-01

In pain management as well as other clinical applications of neuromodulation, it is important to consider the timing parameters influencing activity-dependent plasticity, including pulsed versus sustained currents, as well as the spatial action of electrical currents as they polarize the complex convolutions of the cortical mantle. These factors are of course related; studying temporal factors is not possible when the spatial resolution of current delivery to the cortex is so uncertain to make it unclear whether excitability is increased or decreased with anodal vs. cathodal current flow. In the present study we attempted to improve the targeting of specific cortical locations by applying current through flexible source-sink configurations of 256 electrodes in a geodesic array. We constructed a precision electric head model for 12 healthy individuals. Extraction of the individual’s cortical surface allowed computation of the component of the induced current that is normal to the target cortical surface. In an effort to replicate the long-term depression (LTD) induced with pulsed protocols in invasive animal research and transcranial magnetic stimulation studies, we applied 100 ms pulses at 1.9 s intervals either in cortical-surface-anodal or cortical-surface-cathodal directions, with a placebo (sham) control. The results showed significant LTD of the motor evoked potential as a result of the cortical-surface-cathodal pulses in contrast to the placebo control, with a smaller but similar LTD effect for anodal pulses. The cathodal LTD after-effect was sustained over 90 min following current injection. These results support the feasibility of pulsed protocols with low total charge in non-invasive neuromodulation when the precision of targeting is improved with a dense electrode array and accurate head modeling. PMID:27531976

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1994-02-15

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figures.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1996-01-23

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figs.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1996-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1994-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Baird's beaked whale echolocation signals.

PubMed

Baumann-Pickering, Simone; Yack, Tina M; Barlow, Jay; Wiggins, Sean M; Hildebrand, John A

2013-06-01

Echolocation signals from Baird's beaked whales were recorded during visual and acoustic shipboard surveys of cetaceans in the California Current ecosystem and with autonomous, long-term recorders in the Southern California Bight. The preliminary measurement of the visually validated Baird's beaked whale echolocation signals from towed array data were used as a basis for identifying Baird's signals in the autonomous recorder data. Two distinct signal types were found, one being a beaked whale-like frequency modulated (FM) pulse, the other being a dolphin-like broadband click. The median FM inter-pulse interval was 230 ms. Both signal types showed a consistent multi-peak structure in their spectra with peaks at ~9, 16, 25, and 40 kHz. Depending on signal type, as well as recording aspect and distance to the hydrophone, these peaks varied in relative amplitude. The description of Baird's echolocation signals will allow for studies of their distribution and abundance using towed array data without associated visual sightings and from autonomous seafloor hydrophones.

Artificial neuron synapse transistor based on silicon nanomembrane on plastic substrate

NASA Astrophysics Data System (ADS)

Liu, Minjie; Huang, Gaoshan; Feng, Ping; Guo, Qinglei; Shao, Feng; Tian, Ziao; Li, Gongjin; Wan, Qing; Mei, Yongfeng

2017-06-01

Silicon nanomembrane (SiNM) transistors gated by chitosan membrane were fabricated on plastic substrate to mimic synapse behaviors. The device has both a bottom proton gate (BG) and multiple side gates (SG). Electrical transfer properties of BG show hysteresis curves different from those of typical SiO2 gate dielectric. Synaptic behaviors and functions by linear accumulation and release of protons have been mimicked on this device: excitatory post-synaptic current (EPSC) and paired pulse facilitation behavior of biological synapses were mimicked and the paired-pulse facilitation index could be effectively tuned by the spike interval applied on the BG. Synaptic behaviors and functions, including short-term memory and long-term memory, were also experimentally demonstrated in BG mode. Meanwhile, spiking logic operation and logic modulation were realized in SG mode. Project supported by the National Natural Science Foundation of China (No. 51322201), the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20120071110025), and Science and Technology Commission of Shanghai Municipality (No. 14JC1400200).

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

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

Zhang, Jie; College of Science, Donghua University, Shanghai 201620; Guo, Ying

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

Changes in corticospinal excitability and the direction of evoked movements during motor preparation: A TMS study

PubMed Central

van Elswijk, Gijs; Schot, Willemijn D; Stegeman, Dick F; Overeem, Sebastiaan

2008-01-01

Background Preparation of the direction of a forthcoming movement has a particularly strong influence on both reaction times and neuronal activity in the primate motor cortex. Here, we aimed to find direct neurophysiologic evidence for the preparation of movement direction in humans. We used single-pulse transcranial magnetic stimulation (TMS) to evoke isolated thumb-movements, of which the direction can be modulated experimentally, for example by training or by motor tasks. Sixteen healthy subjects performed brisk concentric voluntary thumb movements during a reaction time task in which the required movement direction was precued. We assessed whether preparation for the thumb movement lead to changes in the direction of TMS-evoked movements and to changes in amplitudes of motor-evoked potentials (MEPs) from the hand muscles. Results When the required movement direction was precued early in the preparatory interval, reaction times were 50 ms faster than when precued at the end of the preparatory interval. Over time, the direction of the TMS-evoked thumb movements became increasingly variable, but it did not turn towards the precued direction. MEPs from the thumb muscle (agonist) were differentially modulated by the direction of the precue, but only in the late phase of the preparatory interval and thereafter. MEPs from the index finger muscle did not depend on the precued direction and progressively decreased during the preparatory interval. Conclusion Our data show that the human corticospinal movement representation undergoes progressive changes during motor preparation. These changes are accompanied by inhibitory changes in corticospinal excitability, which are muscle specific and depend on the prepared movement direction. This inhibition might indicate a corticospinal braking mechanism that counteracts any preparatory motor activation. PMID:18559096

Free electron laser with masked chicane

DOEpatents

Nguyen, Dinh C.; Carlsten, Bruce E.

1999-01-01

A free electron laser (FEL) is provided with an accelerator for outputting electron beam pulses; a buncher for modulating each one of the electron beam pulses to form each pulse into longitudinally dispersed bunches of electrons; and a wiggler for generating coherent light from the longitudinally dispersed bunches of electrons. The electron beam buncher is a chicane having a mask for physically modulating the electron beam pulses to form a series of electron beam bunches for input to the wiggler. In a preferred embodiment, the mask is located in the chicane at a position where each electron beam pulse has a maximum dispersion.

CIDME: Short distances measured with long chirp pulses.

PubMed

Doll, Andrin; Qi, Mian; Godt, Adelheid; Jeschke, Gunnar

2016-12-01

Frequency-swept pulses have recently been introduced as pump pulses into double electron-electron resonance (DEER) experiments. A limitation of this approach is that the pump pulses need to be short in comparison to dipolar evolution periods. The "chirp-induced dipolar modulation enhancement" (CIDME) pulse sequence introduced in this work circumvents this limitation by means of longitudinal storage during the application of one single or two consecutive pump pulses. The resulting six-pulse sequence is closely related to the five-pulse "relaxation-induced dipolar modulation enhancement" (RIDME) pulse sequence: While dipolar modulation in RIDME is due to stochastic spin flips during longitudinal storage, modulation in CIDME is due to the pump pulse during longitudinal storage. Experimentally, CIDME is examined for Gd-Gd and nitroxide-nitroxide distance determination using a high-power Q-band spectrometer. Since longitudinal storage results in a 50% signal loss, comparisons between DEER using short chirp pump pulses of 64ns duration and CIDME using longer pump pulses are in favor of DEER. While the lower sensitivity restrains the applicability of CIDME for routine distance determination on high-power spectrometers, this result is not to be generalized to spectrometers having lower power and to specialized "non-routine" applications or different types of spin labels. In particular, the advantage of prolonged CIDME pump pulses is demonstrated for experiments at large frequency offset between the pumped and observed spins. At a frequency separation of 1GHz, where broadening due to dipolar pseudo-secular contributions becomes largely suppressed, a Gd-Gd modulation depth larger than 10% is achieved. Moreover, a CIDME experiment at deliberately reduced power underlines the potential of the new technique for spectrometers with lower power, as often encountered at higher microwave frequencies. With longitudinal storage times T below 10μs, however, CIDME appears rather susceptible to artifacts. For nitroxide-nitroxide experiments, these currently inhibit a faithful data analysis. To facilitate further developments, the artifacts are characterized experimentally. In addition, effects that are specific to the high spin of S=7/2 Gd-centers are examined. Herein, population transfer within the observer spin's multiplet due to the pump pulse as well as excitation of dipolar harmonics are discussed. Copyright © 2016 Elsevier Inc. All rights reserved.

Use of biphase-coded pulses for wideband data storage in time-domain optical memories.

PubMed

Shen, X A; Kachru, R

1993-06-10

We demonstrate that temporally long laser pulses with appropriate phase modulation can replace either temporally brief or frequency-chirped pulses in a time-domain optical memory to store and retrieve information. A 1.65-µs-long write pulse was biphase modulated according to the 13-bit Barker code for storing multiple bits of optical data into a Pr(3+):YAlO(3) crystal, and the stored information was later recalled faithfully by using a read pulse that was identical to the write pulse. Our results further show that the stored data cannot be retrieved faithfully if mismatched write and read pulses are used. This finding opens up the possibility of designing encrypted optical memories for secure data storage.

Using a fast dual-wavelength imaging ellipsometric system to measure the flow thickness profile of an oil thin film

NASA Astrophysics Data System (ADS)

Kuo, Chih-Wei; Han, Chien-Yuan; Jhou, Jhe-Yi; Peng, Zeng-Yi

2017-11-01

Dual-wavelength light sources with stroboscopic illumination technique were applied in a process of photoelastic modulated ellipsometry to retrieve two-dimensional ellipsometric parameters of thin films on a silicon substrate. Two laser diodes were alternately switched on and modulated by a programmable pulse generator to generate four short pulses at specific temporal phase angles in a modulation cycle, and short pulses were used to freeze the intensity variation of the PEM modulated signal that allows ellipsometric images to be captured by a charge-coupled device. Although the phase retardation of a photoelastic modulator is related to the light wavelength, we employed an equivalent phase retardation technique to avoid any setting from the photoelastic modulator. As a result, the ellipsometric parameters of different wavelengths may be rapidly obtained using this dual-wavelength ellipsometric system every 4 s. Both static and dynamic experiments are demonstrated in this work.

Hybrid Simulation of Duty Cycle Influences on Pulse Modulated RF SiH4/Ar Discharge

NASA Astrophysics Data System (ADS)

Wang, Xifeng; Song, Yuanhong; Zhao, Shuxia; Dai, Zhongling; Wang, Younian

2016-04-01

A one-dimensional fluid/Monte-Carlo (MC) hybrid model is developed to describe capacitively coupled SiH4/Ar discharge, in which the lower electrode is applied by a RF source and pulse modulated by a square-wave, to investigate the modulation effects of the pulse duty cycle on the discharge mechanism. An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase. Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species, such as electrons, ions, and radicals. The simulation results show that, the electron energy distribution f(ɛ) is modulated evidently within a pulse cycle, with its tail extending to higher energies during the power-on period, while shrinking back promptly in the afterglow period. Thus, the rate coefficients could be controlled during the discharge, resulting in modulation of the species composition on the substrate compared with continuous excitation. Meanwhile, more negative ions, like SiH-3 and SiH-2, may escape to the electrodes owing to the collapse of ambipolar electric fields, which is beneficial to films deposition. Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components. supported by National Natural Science Foundation of China (No. 11275038)

Attosecond control of electrons emitted from a nanoscale metal tip.

PubMed

Krüger, Michael; Schenk, Markus; Hommelhoff, Peter

2011-07-06

Attosecond science is based on steering electrons with the electric field of well controlled femtosecond laser pulses. It has led to the generation of extreme-ultraviolet pulses with a duration of less than 100 attoseconds (ref. 3; 1 as = 10(-18) s), to the measurement of intramolecular dynamics (by diffraction of an electron taken from the molecule under scrutiny) and to ultrafast electron holography. All these effects have been observed with atoms or molecules in the gas phase. Electrons liberated from solids by few-cycle laser pulses are also predicted to show a strong light-phase sensitivity, but only very small effects have been observed. Here we report that the spectra of electrons undergoing photoemission from a nanometre-scale tungsten tip show a dependence on the carrier-envelope phase of the laser, with a current modulation of up to 100 per cent. Depending on the carrier-envelope phase, electrons are emitted either from a single sub-500-attosecond interval of the 6-femtosecond laser pulse, or from two such intervals; the latter case leads to spectral interference. We also show that coherent elastic re-scattering of liberated electrons takes place at the metal surface. Owing to field enhancement at the tip, a simple laser oscillator reaches the peak electric field strengths required for attosecond experiments at 100-megahertz repetition rates, rendering complex amplified laser systems dispensable. Practically, this work represents a simple, extremely sensitive carrier-envelope phase sensor, which could be shrunk in volume to about one cubic centimetre. Our results indicate that the attosecond techniques developed with (and for) atoms and molecules can also be used with solids. In particular, we foresee subfemtosecond, subnanometre probing of collective electron dynamics (such as plasmon polaritons) in solid-state systems ranging in scale from mesoscopic solids to clusters and to single protruding atoms. ©2011 Macmillan Publishers Limited. All rights reserved

Optical pulse synthesis using brillouin selective sideband amplification

NASA Technical Reports Server (NTRS)

Yao, X. Steve (Inventor)

2002-01-01

Techniques for producing optical pulses based on Brillouin selective sideband amplification by using a common modulation control signal to modulate both a signal beam to produce multiple sideband signals and a single pump beam to produce multiple pump beams.

Synergetic effects of double laser pulses for the formation of mild plasma in water: Toward non-gated underwater laser-induced breakdown spectroscopy

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

Sakka, Tetsuo; Institute of Sustainability Science, Kyoto University, Uji, Kyoto 611-0011; Tamura, Ayaka

2012-05-07

We experimentally study the dynamics of the plasma induced by the double-laser-pulse irradiation of solid target in water, and find that an appropriate choice of the pulse energies and pulse interval results in the production of an unprecedentedly mild (low-density) plasma, the emission spectra of which are very narrow even without the time-gated detection. The optimum pulse interval and pulse energies are 15-30 {mu}s and about {approx}1 mJ, respectively, where the latter values are much smaller than those typically employed for this kind of study. In order to clarify the mechanism for the formation of mild plasma we examine themore » role of the first and second laser pulses, and find that the first pulse produces the cavitation bubble without emission (and hence plasma), and the second pulse induces the mild plasma in the cavitation bubble. These findings may present a new phase of underwater laser-induced breakdown spectroscopy.« less

Effects of temporal laser profile on the emission spectra for underwater laser-induced breakdown spectroscopy: Study by short-interval double pulses with different pulse durations

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

Tamura, Ayaka, E-mail: tamura.ayaka.88m@st.kyoto-u.ac.jp; Matsumoto, Ayumu; Nishi, Naoya

We investigate the effects of temporal laser profile on the emission spectra of laser ablation plasma in water. We use short-interval (76 ns) double pulses with different pulse durations of the composing two pulses for the irradiation of underwater target. Narrow atomic spectral lines in emission spectra are obtained by the irradiation, where the two pulses are wide enough to be merged into a single-pulse-like temporal profile, while deformed spectra are obtained when the two pulses are fully separated. The behavior of the atomic spectral lines for the different pulse durations is consistent with that of the temporal profiles of themore » optical emission intensities of the plasma. All these results suggest that continuous excitation of the plasma during the laser irradiation for ∼100 ns is a key to obtain narrow emission spectral lines.« less

High-speed pulse-shape generator, pulse multiplexer

DOEpatents

Burkhart, Scott C.

2002-01-01

The invention combines arbitrary amplitude high-speed pulses for precision pulse shaping for the National Ignition Facility (NIF). The circuitry combines arbitrary height pulses which are generated by replicating scaled versions of a trigger pulse and summing them delayed in time on a pulse line. The combined electrical pulses are connected to an electro-optic modulator which modulates a laser beam. The circuit can also be adapted to combine multiple channels of high speed data into a single train of electrical pulses which generates the optical pulses for very high speed optical communication. The invention has application in laser pulse shaping for inertial confinement fusion, in optical data links for computers, telecommunications, and in laser pulse shaping for atomic excitation studies. The invention can be used to effect at least a 10.times. increase in all fiber communication lines. It allows a greatly increased data transfer rate between high-performance computers. The invention is inexpensive enough to bring high-speed video and data services to homes through a super modem.

[Estimation of the atrioventricular time interval by pulse Doppler in the normal fetal heart].

PubMed

Hamela-Olkowska, Anita; Dangel, Joanna

2009-08-01

To assess normative values of the fetal atrioventricular (AV) time interval by pulse-wave Doppler methods on 5-chamber view. Fetal echocardiography exams were performed using Acuson Sequoia 512 in 140 singleton fetuses at 18 to 40 weeks of gestation with sinus rhythm and normal cardiac and extracardiac anatomy. Pulsed Doppler derived AV intervals were measured from left ventricular inflow/outflow view using transabdominal convex 3.5-6 MHz probe. The values of AV time interval ranged from 100 to 150 ms (mean 123 +/- 11.2). The AV interval was negatively correlated with the heart rhythm (p<0.001). Fetal heart rate decreased as gestation progressed (p<0.001). Thus, the AV intervals increased with the age of gestation (p=0.007). However, in the same subgroup of the fetal heart rate there was no relation between AV intervals and gestational age. Therefore, the AV intervals showed only the heart rate dependence. The 95th percentiles of AV intervals according to FHR ranged from 135 to 148 ms. 1. The AV interval duration was negatively correlated with the heart rhythm. 2. Measurement of AV time interval is easy to perform and has a good reproducibility. It may be used for the fetal heart block screening in anti-Ro and anti-La positive pregnancies. 3. Normative values established in the study may help obstetricians in assessing fetal abnormalities of the AV conduction.

High power solid state laser modulator

DOEpatents

Birx, Daniel L.; Ball, Don G.; Cook, Edward G.

2004-04-27

A multi-stage magnetic modulator provides a pulse train of .+-.40 kV electrical pulses at a 5-7 kHz repetition rate to a metal vapor laser. A fractional turn transformer steps up the voltage by a factor of 80 to 1 and magnetic pulse compression is used to reduce the pulse width of the pulse train. The transformer is fabricated utilizing a rod and plate stack type of construction to achieve a high packing factor. The pulses are controlled by an SCR stack where a plurality of SCRs are electrically connected in parallel, each SCR electrically connected to a saturable inductor, all saturable inductors being wound on the same core of magnetic material for enhanced power handling characteristics.

Origin of the double- and multi-pulse structure of echolocation signals in Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientialis)

NASA Astrophysics Data System (ADS)

Li, Songhai; Wang, Kexiong; Wang, Ding; Akamatsu, Tomonari

2005-12-01

The signals of dolphins and porpoises often exhibit a multi-pulse structure. Here, echolocation signal recordings were made from four geometrically distinct positions of seven Yangtze finless porpoises temporarily housed in a relatively small, enclosed area. Some clicks demonstrated double-pulse, and others multi-pulse, structure. The interpulse intervals between the first and second pulse of the double- and multi-pulse clicks were significantly different among data from the four different positions (p<0.01, one-way ANOVA). These results indicate that the interpulse interval and structure of the double- and multi-pulse echolocation signals depend on the hydrophone geometry of the animal, and that the double- and multi-pulse structure of echolocation signals in Yangtze finless porpoise is not caused by the phonating porpoise itself, but by the multipath propagation of the signal. Time delays in the 180° phase-shifted surface reflection pulse and the nonphase-shifted bottom reflection pulse of the multi-pulse structures, relative to the direct signal, can be used to calculate the distance to a phonating animal.

Programmable Pulse Generator

NASA Technical Reports Server (NTRS)

Rhim, W. K.; Dart, J. A.

1982-01-01

New pulse generator programmed to produce pulses from several ports at different pulse lengths and intervals and virtually any combination and sequence. Unit contains a 256-word-by-16-bit memory loaded with instructions either manually or by computer. Once loaded, unit operates independently of computer.

Transverse Mode Dynamics of VCSELs Undergoing Current Modulation

NASA Technical Reports Server (NTRS)

Goorjian, Peter M.; Ning, C. Z.; Agrawal, Govind

2000-01-01

Transverse mode dynamics of a 20-micron-diameter vertical-cavity surface-emitting laser (VCSEL) undergoing gain switching by deep current modulation is studied numerically. The direct current (dc) level is set slightly below threshold and is modulated by a large alternating current (ac). The resulting optical pulse train and transverse-mode patterns are obtained numerically. The ac frequency is varied from 2.5 GHz to 10 GHz, and the ac amplitude is varied from one-half to four times that of the dc level. At high modulation frequencies, a regular pulse train is not generated unless the ac amplitude is large enough. At all modulation frequencies, the transverse spatial profile switches from single-mode to multiple-mode pattern as the ac pumping level is increased. Optical pulse widths vary in the range 5-30 ps. with the pulse width decreasing when either the frequency is increased or the ac amplitude is decreased. The numerical modeling uses an approximation form of the semiconductor Maxwell-Bloch equations. Temporal evolution of the spatial profiles of the laser (and of carrier density) is determined without any assumptions about the type or number of modes. Keywords: VCSELs, current modulation, gain switching, transverse mode dynamics, computational modeling

Frequency modulation and compression of optical pulses in an optical fibre with a travelling refractive-index wave

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

Zolotovskii, I O; Lapin, V A; Sementsov, D I

2016-01-31

We have studied the conditions for spectral broadening, frequency modulation and compression (both temporal and spectral) of Gaussian pulses propagating in a fibre with a travelling refractive-index wave. Analytical expressions have been derived for the dependences of pulse duration, chirp and spectral width on the distance travelled through the fibre, parameters of the fibre and radiation launched into it. Based on the numerical analysis we have studied the behaviour of these characteristics by changing the coefficient of the refractive-index modulation and other parameters of the travelling refractive-index wave. (nonlinear optical phenomena)

Power supply circuit for an ion engine sequentially operated power inverters

NASA Technical Reports Server (NTRS)

Cardwell, Jr., Gilbert I. (Inventor)

2000-01-01

A power supply circuit for an ion engine suitable for a spacecraft has a voltage bus having input line and a return line. The power supply circuit includes a pulse width modulation circuit. A plurality of bridge inverter circuits is coupled to the bus and the pulse width modulation circuit. The pulse width modulation circuit generates operating signals having a variable duty cycle. Each bridge inverter has a primary winding and a secondary winding. Each secondary winding is coupled to a rectifier bridge. Each secondary winding is coupled in series with another of the plurality of rectifier bridges.

Modulation of soleus corticospinal excitability during Achilles tendon vibration.

PubMed

Lapole, Thomas; Temesi, John; Arnal, Pierrick J; Gimenez, Philippe; Petitjean, Michel; Millet, Guillaume Y

2015-09-01

Soleus (SOL) corticospinal excitability has been reported to increase during Achilles tendon vibration. The aim of the present study was to further investigate SOL corticospinal excitability and elucidate the changes to intracortical mechanisms during Achilles tendon vibration. Motor-evoked potentials (MEPs) were elicited in the SOL by transcranial magnetic stimulation (TMS) of the corresponding motor cortical area of the leg with and without 50-Hz Achilles tendon vibration. SOL input-output curves were determined. Paired-pulse protocols were also performed to investigate short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) by conditioning test TMS pulses with sub-threshold TMS pulses at inter-stimulus intervals of 3 and 13 ms, respectively. During Achilles tendon vibration, motor threshold was lower than in the control condition (43 ± 13 vs. 49 ± 11 % of maximal stimulator output; p = 0.008). Input-output curves were also influenced by vibration, i.e. there was increased maximal MEP amplitude (0.694 ± 0.347 vs. 0.268 ± 0.167 mV; p < 0.001), decreased TMS intensity to elicit a MEP of half the maximal MEP amplitude (100 ± 13 vs. 109 ± 9 % motor threshold; p = 0.009) and a strong tendency for decreased slope constant (0.076 ± 0.04 vs. 0.117 ± 0.04; p = 0.068). Vibration reduced ICF (98 ± 61 vs. 170 ± 105 % of test MEP amplitude; p = 0.05), but had no effect on SICI (53 ± 26 vs. 48 ± 22 % of test MEP amplitude; p = 0.68). The present results further document the increased vibration-induced corticospinal excitability in the soleus muscle and suggest that this increase is not mediated by changes in SICI or ICF.

Synchronous Seasonal Change in Fin Whale Song in the North Pacific

PubMed Central

Oleson, Erin M.; Širović, Ana; Bayless, Alexandra R.; Hildebrand, John A.

2014-01-01

Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here. PMID:25521493

Synchronous seasonal change in fin whale song in the North Pacific.

PubMed

Oleson, Erin M; Širović, Ana; Bayless, Alexandra R; Hildebrand, John A

2014-01-01

Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here.

Influence of waveform and current direction on short-interval intracortical facilitation: a paired-pulse TMS study.

PubMed

Delvendahl, Igor; Lindemann, Hannes; Jung, Nikolai H; Pechmann, Astrid; Siebner, Hartwig R; Mall, Volker

2014-01-01

Transcranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF). We examined whether SICF depends on waveform and current direction of the TMS pulses. In young healthy volunteers, we applied single- and paired-pulse TMS to M1-HAND. We probed SICF by pairs of monophasic or half-sine pulses at suprathreshold stimulation intensity and inter-stimulus intervals (ISIs) between 1.0 and 5.0 ms. For monophasic paired-pulse stimulation, both pulses had either a posterior-anterior (PA) or anterior-posterior (AP) current direction (AP-AP or PA-PA), whereas current direction was reversed between first and second pulse for half-sine paired-pulse stimulation (PA-AP and AP-PA). Monophasic AP-AP stimulation resulted in stronger early SICF at 1.4 ms relative to late SICF at 2.8 and 4.4 ms, whereas monophasic PA-PA stimulation produced SICF of comparable size at all three peaks. With half-sine stimulation the third SICF peak was reduced for PA-AP current orientation compared with AP-PA. SICF elicited using monophasic as well as half-sine pulses is affected by current direction at clearly suprathreshold intensities. The impact of current orientation is stronger for monophasic compared with half-sine pulses. The direction-specific effect of paired-pulse TMS on the strength of early versus late SICF shows that different cortical circuits mediate early and late SICF. Copyright © 2014 Elsevier Inc. All rights reserved.

Nanosecond pulse shaping at 780 nm with fiber-based electro-optical modulators and a double-pass tapered amplifier

DOE PAGES

Rogers, III, C. E.; Gould, P. L.

2016-02-01

Here, we describe a system for generating frequency-chirped and amplitude-shaped pulses on time scales from sub-nanosecond to ten nanoseconds. The system starts with cw diode-laser light at 780 nm and utilizes fiber-based electro-optical phase and intensity modulators, driven by an arbitrary waveform generator, to generate the shaped pulses. These pulses are subsequently amplified to several hundred mW with a tapered amplifier in a delayed double-pass configuration. Frequency chirps up to 5 GHz in 2 ns and pulse widths as short as 0.15 ns have been realized.

Optimisation of thulium fibre laser parameters with generation of pulses by pump modulation

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

Obronov, I V; Larin, S V; Sypin, V E

2015-07-31

The formation of relaxation pulses of a thulium fibre laser (λ = 1.9 μm) by modulating the power of a pump erbium fibre laser (λ = 1.55 μm) is studied. A theoretical model is developed to find the dependences of pulse duration and peak power on different cavity parameters. The optimal cavity parameters for achieving the minimal pulse duration are determined. The results are confirmed by experimental development of a laser emitting pulses with a duration shorter than 10 ns, a peak power of 1.8 kW and a repetition rate of 50 kHz. (control of radiation parameters)

Nanosecond pulse shaping at 780 nm with fiber-based electro-optical modulators and a double-pass tapered amplifier.

PubMed

Rogers, C E; Gould, P L

2016-02-08

We describe a system for generating frequency-chirped and amplitude-shaped pulses on time scales from sub-nanosecond to ten nanoseconds. The system starts with cw diode-laser light at 780 nm and utilizes fiber-based electro-optical phase and intensity modulators, driven by an arbitrary waveform generator, to generate the shaped pulses. These pulses are subsequently amplified to several hundred mW with a tapered amplifier in a delayed double-pass configuration. Frequency chirps up to 5 GHz in 2 ns and pulse widths as short as 0.15 ns have been realized.

Modified Dual Three-Pulse Modulation technique for single-phase inverter topology

NASA Astrophysics Data System (ADS)

Sree Harsha, N. R.; Anitha, G. S.; Sreedevi, A.

2016-01-01

In a recent paper, a new modulation technique called Dual Three Pulse Modulation (DTPM) was proposed to improve the efficiency of the power converters of the Electric/Hybrid/Fuel-cell vehicles. It was simulated in PSIM 9.0.4 and uses analog multiplexers to generate the modulating signals for the DC/DC converter and inverter. The circuit used is complex and many other simulation softwares do not support the analog multiplexers as well. Also, the DTPM technique produces modulating signals for the converter, which are essentially needed to produce the modulating signals for the inverter. Hence, it cannot be used efficiently to switch the valves of a stand-alone inverter. We propose a new method to generate the modulating signals to switch MOSFETs of a single phase Dual-Three pulse Modulation based stand-alone inverter. The circuits proposed are simulated in Multisim 12.0. We also show an alternate way to switch a DC/DC converter in a way depicted by DTPM technique both in simulation (MATLAB/Simulink) and hardware. The circuitry is relatively simple and can be used for the further investigations of DTPM technique.

Coherent pulse position modulation quantum cipher

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

Sohma, Masaki; Hirota, Osamu

2014-12-04

On the basis of fundamental idea of Yuen, we present a new type of quantum random cipher, where pulse position modulated signals are encrypted in the picture of quantum Gaussian wave form. We discuss the security of our proposed system with a phase mask encryption.

Development and performance of pulse-width-modulated static inverter and converter modules

NASA Technical Reports Server (NTRS)

Pittman, P. F.; Gourash, F.; Birchenough, A. G.; Pittman, P. F.; Ravas, R. J.; Hall, W. G.

1971-01-01

Pulse-width-modulated inverter and converter modules are being developed for modular aerospace electrical power systems. The modules, rate 2.5 kilowatts per module and 10-minute - 150-percent overload, operate from 56 volts dc. The converter module provides two output voltages: a nominal link voltage of 200 volts dc when used with the inverter, and 150 volts dc to a load bus when used separately. The inverter module output is 400-hertz, sinusoidal, three-phase, 120/208 volts. Tests of breadboard models with standard parts and integrated circuits show rated power efficiencies of 71.4 and 85.1 percent and voltage regulation of 5 and 3.1 percent for inverter and converter modules, respectively. Sine-wave output distortion is 0.74 percent.

High average power magnetic modulator for metal vapor lasers

DOEpatents

Ball, Don G.; Birx, Daniel L.; Cook, Edward G.; Miller, John L.

1994-01-01

A three-stage magnetic modulator utilizing magnetic pulse compression designed to provide a 60 kV pulse to a copper vapor laser at a 4.5 kHz repetition rate is disclosed. This modulator operates at 34 kW input power. The circuit includes a step up auto transformer and utilizes a rod and plate stack construction technique to achieve a high packing factor.

Electromagnetically-induced-transparency-based cross-phase-modulation at attojoule levels

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

Lo, Hsiang-Yu; Chen, Yen-Chun; Su, Po-Ching

2011-04-15

We report the experimental demonstration of electromagnetically-induced-transparency-based cross-phase-modulation at attojoule or, equivalently, few-hundred-photon levels. A phase shift of 0.005 rad of a probe pulse modulated by a signal pulse with an energy of {approx}100 aJ, equivalent to {approx}400 photons, was observed in a four-level system of cold {sup 87}Rb atoms.

Solid state pulsed power generator

DOEpatents

Tao, Fengfeng; Saddoughi, Seyed Gholamali; Herbon, John Thomas

2014-02-11

A power generator includes one or more full bridge inverter modules coupled to a semiconductor opening switch (SOS) through an inductive resonant branch. Each module includes a plurality of switches that are switched in a fashion causing the one or more full bridge inverter modules to drive the semiconductor opening switch SOS through the resonant circuit to generate pulses to a load connected in parallel with the SOS.

Encoding of the amplitude modulation of pulsatile electrical stimulation in the feline cochlear nucleus by neurons in the inferior colliculus; effects of stimulus pulse rate

NASA Astrophysics Data System (ADS)

McCreery, Douglas; Han, Martin; Pikov, Victor; Yadav, Kamal; Pannu, Satinderpall

2013-10-01

Objectives. Persons without a functional auditory nerve cannot benefit from cochlear implants, but some hearing can be restored by an auditory brainstem implant (ABI) with stimulating electrodes implanted on the surface of the cochlear nucleus (CN). Most users benefit from their ABI, but speech recognition tends to be poorer than for users of cochlear implants. Psychophysical studies suggest that poor modulation detection may contribute to the limited performance of ABI users. In a cat model, we determined how the pulse rate of the electrical stimulus applied within or on the CN affects temporal and rate encoding of amplitude modulation (AM) by neurons in the central nucleus of the inferior colliculus (ICC). Approach. Stimulating microelectrodes were implanted chronically in and on the cats' CN, and multi-site recording microelectrodes were implanted chronically into the ICC. Encoding of AM pulse trains by neurons in the ICC was characterized as vector strength (VS), the synchrony of neural activity with the AM, and as the mean rate of neuronal action potentials (neuronal spike rate (NSR)). Main results. For intranuclear microstimulation, encoding of AM as VS was up to 3 dB greater when stimulus pulse rate was increased from 250 to 500 pps, but only for neuronal units with low best acoustic frequencies, and when the electrical stimulation was modulated at low frequencies (10-20 Hz). For stimulation on the surface of the CN, VS was similar at 250 and 500 pps, and the dynamic range of the VS was reduced for pulse rates greater than 250 pps. Modulation depth was encoded strongly as VS when the maximum stimulus amplitude was held constant across a range of modulation depth. This ‘constant maximum’ protocol allows enhancement of modulation depth while preserving overall dynamic range. However, modulation depth was not encoded as strongly as NSR. Significance. The findings have implications for improved sound processors for present and future ABIs. The performance of ABIs may benefit from using pulse rates greater than those presently used in most ABIs, and by sound processing strategies that enhance the modulation depth of the electrical stimulus while preserving dynamic range.

Development of 873 nm Raman Seed Pulse for Raman-seeded Laser Wakefield Acceleration

NASA Astrophysics Data System (ADS)

Grigsby, F.; Peng, D.; Downer, M. C.

2004-12-01

By using a Raman-shifted seed pulse coincident with a main driving pulse, laser wakefields can be generated with sub-relativistic intensity, coherent control and high repetition rate in the self-modulated regime. Experimentally, the generation of a chirped Stokes laser pulse by inserting a solid state Raman shifter, Ba(NO3)2, into a CPA system before the compressor (to suppress self-phase modulation) will be described. We will also report on design, modeling and experimental demonstration of a novel compressor for the Stokes pulse that uses a mismatched grating pair to achieve a near transform-limited seed pulse. Finally, we will describe the design, simulation and current status of Raman-seeded LWFA experiments that use this novel source.

Modulation and coding for throughput-efficient optical free-space links

NASA Technical Reports Server (NTRS)

Georghiades, Costas N.

1993-01-01

Optical direct-detection systems are currently being considered for some high-speed inter-satellite links, where data-rates of a few hundred megabits per second are evisioned under power and pulsewidth constraints. In this paper we investigate the capacity, cutoff-rate and error-probability performance of uncoded and trellis-coded systems for various modulation schemes and under various throughput and power constraints. Modulation schemes considered are on-off keying (OOK), pulse-position modulation (PPM), overlapping PPM (OPPM) and multi-pulse (combinatorial) PPM (MPPM).

Demonstration of pulse controlled all-optical switch/modulator.

PubMed

Akin, Osman; Dinleyici, M S

2014-03-15

An all-optical pulse controlled switch/modulator based on evanescent coupling between a polymer slab waveguide and a single mode fiber is demonstrated. Very fast all-optical modulation/switching is achieved via Kerr effect of the nonlinear polymer placed in the evanescent region of the optical fiber. Local refractive index perturbation (Δn=-1.45612×10(-5)) on the thin film leads to 0.374 nW power modulation at the fiber output, which results in a switching efficiency of ≈1.5%.

Primary investigation the impacts of the external memory (DDR3) failures on the performance of Xilinx Zynq-7010 SoC based system (MicroZed) using laser irradiation

NASA Astrophysics Data System (ADS)

Liu, Shuhuan; Du, Xuecheng; Du, Xiaozhi; Zhang, Yao; Mubashiru, Lawal Olarewaju; Luo, Dongyang; yuan, Yuan; Deng, Tianxiang; Li, Zhuoqi; Zang, Hang; Li, Yonghong; He, Chaohui; Ma, Yingqi; Shangguan, Shipeng

2017-09-01

The impacts of the external dynamic memory (DDR3) failures on the performance of 28 nm Xilinx Zynq-7010 SoC based system (MicroZed) were investigated with two sets of 1064 nm laser platforms. The failure sensitive area distributionsons on the back surface of the test DDR3 were primarily localized with a CW laser irradiation platform. During the CW laser scanning on the back surface of the DDR3 of the test board system, various failure modes except SEU and SEL (MBU, SEFI, data storage address error, rebooting, etc) were found in the testing embedded modules (ALU, PL, Register, Cache and DMA, etc) of SoC. Moreover, the experimental results demonstrated that there were 16 failure sensitive blocks symmetrically distributed on the back surface of the DDR3 with every sensitive block area measured was about 1 mm × 0.5 mm. The influence factors on the failure modes of the embedded modules were primarily analyzed and the SEE characteristics of DDR3 induced by the picoseconds pulsed laser were tested. The failure modes of DDR3 found were SEU, SEFI, SEL, test board rebooting by itself, unknown data, etc. Furthermore, the time interval distributions of failure occurrence in DDR3 changes with the pulsed laser irradiation energy and the CPU operating frequency were measured and compared. Meanwhile, the failure characteristics of DDR3 induced by pulsed laser irradiation were primarily explored. The measured results and the testing techniques designed in this paper provide some reference information for evaluating the reliability of the test system or other similar electronic system in harsh environment.

Total Ionizing Dose Test Report for the UC1823A Pulse Width Modulator

NASA Technical Reports Server (NTRS)

Chen, Dakai; Forney, James

2017-01-01

The purpose of this study is to examine the total ionizing dose susceptibility for the UC1823A pulse width modulator manufactured by Texas Instruments, Inc. The part is suspected to be vulnerable to enhanced low dose rate sensitivity (ELDRS).

Nonlinear processes associated with the amplification of MHz-linewidth laser pulses in single-mode Tm:fiber

NASA Astrophysics Data System (ADS)

Sincore, Alex; Bodnar, Nathan; Bradford, Joshua; Abdulfattah, Ali; Shah, Lawrence; Richardson, Martin C.

2017-03-01

This work studies the accumulated nonlinearities when amplifying a narrow linewidth 2053 nm seed in a single mode Tm:fiber amplifier. A <2 MHz linewidth CW diode seed is externally modulated using a fiberized acousto-optic modulator. This enables independent control of repetition rate and pulse duration (>30 ns). The pulses are subsequently amplified and the repetition rate is further reduced using a second acousto-optic modulator. It is well known that spectral degradation occurs in such fibers for peak powers over 100's of watts due to self-phase modulation, four-wave mixing, and stimulated Raman scattering. In addition to enabling a thorough test bed to study such spectral broadening, this system will also enable the investigation of stimulated Brillouin scattering thresholds in the same system. This detailed study of the nonlinearities encountered in 2 μm fiber amplifiers is important in a range of applications from telecommunications to the amplification of ultrashort laser pulses.

Self-phase modulation of submicrojoule femtosecond pulses in a hollow-core photonic-crystal fiber

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

Konorov, S.O.; Sidorov-Biryukov, D.A.; Zheltikov, A.M.

Hollow-core photonic-crystal fibers (PCFs) capable of transporting sub-100-fs pulses of Ti:sapphire laser radiation in one of their transmission peaks centered around 800 nm have been designed and demonstrated. These fibers are shown to enhance self-phase modulation of submicrojoule 100-fs Ti:sapphire laser pulses, allowing a spectral bandwidth of 35 nm to be achieved with an 8-cm PCF sample.

Digital micromirror device-based ultrafast pulse shaping for femtosecond laser.

PubMed

Gu, Chenglin; Zhang, Dapeng; Chang, Yina; Chen, Shih-Chi

2015-06-15

In this Letter, we present a new digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., DUPS. To the best of our knowledge, the DUPS is the first binary pulse shaper that can modulate high repetition rate laser sources at up to a 32 kHz rate (limited by the DMD pattern rate). Since pulse modulation occurs in the frequency domain through reflective two-dimensional micromirror arrays, i.e., DMD, the DUPS is not only compact and low in cost, but also possesses a high damage threshold that is critical for high pulse energy laser applications. In this work, a grating pair was introduced in the DUPS to compensate the DMD induced dispersion. Double pulses were generated to validate the effectiveness of the DUPS and calibrate the system. Subsequently, we demonstrated arbitrary phase shaping capability by continuous tuning of group velocity dispersion (GVD) and modulation of half-spectrum shifted by π. The overall efficiency was measured to be 1.7%, while an efficiency of up to 5% can be expected when high efficiency gratings and properly coated DMDs are used.

Auditory Temporal Acuity Probed With Cochlear Implant Stimulation and Cortical Recording

PubMed Central

Kirby, Alana E.

2010-01-01

Cochlear implants stimulate the auditory nerve with amplitude-modulated (AM) electric pulse trains. Pulse rates >2,000 pulses per second (pps) have been hypothesized to enhance transmission of temporal information. Recent studies, however, have shown that higher pulse rates impair phase locking to sinusoidal AM in the auditory cortex and impair perceptual modulation detection. Here, we investigated the effects of high pulse rates on the temporal acuity of transmission of pulse trains to the auditory cortex. In anesthetized guinea pigs, signal-detection analysis was used to measure the thresholds for detection of gaps in pulse trains at rates of 254, 1,017, and 4,069 pps and in acoustic noise. Gap-detection thresholds decreased by an order of magnitude with increases in pulse rate from 254 to 4,069 pps. Such a pulse-rate dependence would likely influence speech reception through clinical speech processors. To elucidate the neural mechanisms of gap detection, we measured recovery from forward masking after a 196.6-ms pulse train. Recovery from masking was faster at higher carrier pulse rates and masking increased linearly with current level. We fit the data with a dual-exponential recovery function, consistent with a peripheral and a more central process. High-rate pulse trains evoked less central masking, possibly due to adaptation of the response in the auditory nerve. Neither gap detection nor forward masking varied with cortical depth, indicating that these processes are likely subcortical. These results indicate that gap detection and modulation detection are mediated by two separate neural mechanisms. PMID:19923242

Integration of cortical and pallidal inputs in the basal ganglia-recipient thalamus of singing birds

PubMed Central

Goldberg, Jesse H.; Farries, Michael A.

2012-01-01

The basal ganglia-recipient thalamus receives inhibitory inputs from the pallidum and excitatory inputs from cortex, but it is unclear how these inputs interact during behavior. We recorded simultaneously from thalamic neurons and their putative synaptically connected pallidal inputs in singing zebra finches. We find, first, that each pallidal spike produces an extremely brief (∼5 ms) pulse of inhibition that completely suppresses thalamic spiking. As a result, thalamic spikes are entrained to pallidal spikes with submillisecond precision. Second, we find that the number of thalamic spikes that discharge within a single pallidal interspike interval (ISI) depends linearly on the duration of that interval but does not depend on pallidal activity prior to the interval. In a detailed biophysical model, our results were not easily explained by the postinhibitory “rebound” mechanism previously observed in anesthetized birds and in brain slices, nor could most of our data be characterized as “gating” of excitatory transmission by inhibitory pallidal input. Instead, we propose a novel “entrainment” mechanism of pallidothalamic transmission that highlights the importance of an excitatory conductance that drives spiking, interacting with brief pulses of pallidal inhibition. Building on our recent finding that cortical inputs can drive syllable-locked rate modulations in thalamic neurons during singing, we report here that excitatory inputs affect thalamic spiking in two ways: by shortening the latency of a thalamic spike after a pallidal spike and by increasing thalamic firing rates within individual pallidal ISIs. We present a unifying biophysical model that can reproduce all known modes of pallidothalamic transmission—rebound, gating, and entrainment—depending on the amount of excitation the thalamic neuron receives. PMID:22673333

Pulse-width-modulated servo valve for autopilot system

NASA Technical Reports Server (NTRS)

Garner, H. D.

1974-01-01

Valve was developed for autopilot wing-lever system and is to be used in light, single-engine aircraft. Valve is controlled by electronic circuit which feeds pulse-width-modulated correction signals to two solenoids. Valve housing is cast from plastic, making it very economical to fabricate.

Femtosecond fiber CPA system based on picosecond master oscillator and power amplifier with CCC fiber.

PubMed

Želudevičius, J; Danilevičius, R; Viskontas, K; Rusteika, N; Regelskis, K

2013-03-11

Results of numerical and experimental investigations of the simple fiber CPA system seeded by nearly bandwidth-limited pulses from the picosecond oscillator are presented. We utilized self-phase modulation in a stretcher fiber to broaden the pulse spectrum and dispersion of the fiber to stretch pulses in time. During amplification in the ytterbium-doped CCC fiber, gain-shaping and self-phase modulation effects were observed, which improved pulse compression with a bulk diffraction grating compressor. After compression with spectral filtering, pulses with the duration of 400 fs and energy as high as 50 µJ were achieved, and the output beam quality was nearly diffraction-limited.

Laser Energy Monitor for Double-Pulsed 2-Micrometer IPDA Lidar Application

NASA Technical Reports Server (NTRS)

Refaat, Tamer F.; Petros, Mulugeta; Remus, Ruben; Yu, Jirong; Singh, Upendra N.

2014-01-01

Integrated path differential absorption (IPDA) lidar is a remote sensing technique for monitoring different atmospheric species. The technique relies on wavelength differentiation between strong and weak absorbing features normalized to the transmitted energy. 2-micron double-pulsed IPDA lidar is best suited for atmospheric carbon dioxide measurements. In such case, the transmitter produces two successive laser pulses separated by short interval (200 microseconds), with low repetition rate (10Hz). Conventional laser energy monitors, based on thermal detectors, are suitable for low repetition rate single pulse lasers. Due to the short pulse interval in double-pulsed lasers, thermal energy monitors underestimate the total transmitted energy. This leads to measurement biases and errors in double-pulsed IPDA technique. The design and calibration of a 2-micron double-pulse laser energy monitor is presented. The design is based on a high-speed, extended range InGaAs pin quantum detectors suitable for separating the two pulse events. Pulse integration is applied for converting the detected pulse power into energy. Results are compared to a photo-electro-magnetic (PEM) detector for impulse response verification. Calibration included comparing the three detection technologies in single-pulsed mode, then comparing the pin and PEM detectors in double-pulsed mode. Energy monitor linearity will be addressed.

Design of a Radiographic Integrated Test Stand (RITS) Based on a Voltage Adder, To Drive a Diode Immersed in a High Magnetic Field

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

Bailey, V.L.; Corcoran, P.; Droemer, D.

Recent experiments (1) have adapted existing magne-tically insulated induction voltage adders (Sabre, Hermes III) to drive a 10 MV diode immersed in magnetic fields as high as 50 T. In such a diode, an electron beam of tens of kA can be confined by the magnetic field to a diameter of about 1 mm, and when it strikes a high-Z anode it can create a bremsstrahlung x-ray source intense enough to radiograph massive objects with high resolution. RITS is an adder system designed specially to drive such diodes, and it will be used to develop and exploit them. As inmore » other adder-based pulsers such as Sabre, Hermes III, and Kalif-Heliq the induction cells have amorphous- iron cores, and the pulse-forming system consists of water dielectric pulse lines and self-closing water switches that are pulse-charged from Marx-charged intermediate water capacitors through laser-triggered Rimfire switches. An oil prepulse switch in series with each pulse line is designed to reduce cathode prepulse to less than ± 5 kV, and a means is provided to bias the cathode and avoid negative prepulse entirely. The RITS pulse-forming system consists of two modules. Each module has one Marx that charges two 3 MV intermediate stores, each of which charges three 7.8 ohm pulselines, making six pulselines per module. The two modules in concert can supply 1.35 MV, 50 ns pulses to a twelve-cell adder and thus drive a 16 MV diode with a single pulse. The 1.35 MV induction cells each have a single-point feed, from which a single, slotted azimuthal oil transmission line distributes energy uniformly around the cell. The modules can also be pulsed separately at different times, either to power two 8 MV adders that each drive one of two closely-spaced cathodes immersed in a common magnetic field, or to provide two separate pulses to a common six- cell adder and a single 8 NIV diode; in these two-pulse modes, the spacing of the two 50 ns pulses may be chosen to be anything from a few hundred ns upward. The use of only one pulse line per cell has been shown to increase the extent to which the cell voltages can vary with the timing of closure of the water switches. This and all other functions of RITS have been simulated in detail, and a conservative electrical design has been developed. This will be illustrated, along with the conceptual design of a pulse-sorting network that can couple two pulselines efilciently to one cell when the two RITS modules drive a common adder in two-pulse mode.« less

On the power spectral density of quadrature modulated signals. [satellite communication

NASA Technical Reports Server (NTRS)

Yan, T. Y.

1981-01-01

The conventional (no-offset) quadriphase modulation technique suffers from the fact that hardlimiting will restore the frequency sidelobes removed by proper filtering. Thus, offset keyed quadriphase modulation techniques are often proposed for satellite communication with bandpass hardlimiting. A unified theory is developed which is capable of describing the power spectral density before and after the hardlimiting process. Using the in-phase and the quadrature phase channel with arbitrary pulse shaping, analytical results are established for generalized quadriphase modulation. In particular MSK, OPSK or the recently introduced overlapped raised cosine keying all fall into this general category. It is shown that for a linear communication channel, the power spectral density of the modulated signal remains unchanged regardless of the offset delay. Furthermore, if the in phase and the quadrature phase channel have identical pulse shapes without offset, the spectrum after bandpass hardlimiting will be identical to that of the conventional QPSK modulation. Numerical examples are given for various modulation techniques. A case of different pulse shapes in the in phase and the quadrature phase channel is also considered.

Accumulation effects in modulation spectroscopy with high-repetition-rate pulses: Recursive solution of optical Bloch equations

NASA Astrophysics Data System (ADS)

Osipov, Vladimir Al.; Pullerits, Tõnu

2017-10-01

Application of the phase-modulated pulsed light for advance spectroscopic measurements is the area of growing interest. The phase modulation of the light causes modulation of the signal. Separation of the spectral components of the modulations allows to distinguish the contributions of various interaction pathways. The lasers with high repetition rate used in such experiments can lead to appearance of the accumulation effects, which become especially pronounced in systems with long-living excited states. Recently it was shown that such accumulation effects can be used to evaluate parameters of the dynamical processes in the material. In this work we demonstrate that the accumulation effects are also important in the quantum characteristics measurements provided by modulation spectroscopy. In particular, we consider a model of quantum two-level system driven by a train of phase-modulated light pulses, organized in analogy with the two-dimensional spectroscopy experiments. We evaluate the harmonics' amplitudes in the fluorescent signal and calculate corrections appearing from the accumulation effects. We show that the corrections can be significant and have to be taken into account at analysis of experimental data.

Neural pulse frequency modulation of an exponentially correlated Gaussian process

NASA Technical Reports Server (NTRS)

Hutchinson, C. E.; Chon, Y.-T.

1976-01-01

The effect of NPFM (Neural Pulse Frequency Modulation) on a stationary Gaussian input, namely an exponentially correlated Gaussian input, is investigated with special emphasis on the determination of the average number of pulses in unit time, known also as the average frequency of pulse occurrence. For some classes of stationary input processes where the formulation of the appropriate multidimensional Markov diffusion model of the input-plus-NPFM system is possible, the average impulse frequency may be obtained by a generalization of the approach adopted. The results are approximate and numerical, but are in close agreement with Monte Carlo computer simulation results.

Synchronization using pulsed edge tracking in optical PPM communication system

NASA Technical Reports Server (NTRS)

Gagliardi, R.

1972-01-01

A pulse position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge tracking method of maintaining the necessary timing. The edge tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to pure synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal to noise ratio.

Improved safety of retinal photocoagulation with a shaped beam and modulated pulse

NASA Astrophysics Data System (ADS)

Sramek, Christopher; Brown, Jefferson; Paulus, Yannis M.; Nomoto, Hiroyuki; Palanker, Daniel

2010-02-01

Shorter pulse durations help confine thermal damage during retinal photocoagulation, decrease treatment time and minimize pain. However, safe therapeutic window (the ratio of threshold powers for rupture and mild coagulation) decreases with shorter exposures. A ring-shaped beam enables safer photocoagulation than conventional beams by reducing the maximum temperature in the center of the spot. Similarly, a temporal pulse modulation decreasing its power over time improves safety by maintaining constant temperature for a significant portion of the pulse. Optimization of the beam and pulse shapes was performed using a computational model. In vivo experiments were performed to verify the predicted improvement. With each of these approaches, the pulse duration can be decreased by a factor of two, from 20 ms down to 10 ms while maintaining the same therapeutic window.

Evaluation of cardiac modulation in children in response to apnea/hypopnea using the Phone Oximeter(™).

PubMed

Dehkordi, Parastoo; Garde, Ainara; Karlen, Walter; Petersen, Christian L; Wensley, David; Dumont, Guy A; Mark Ansermino, J

2016-02-01

Individuals with sleep disordered breathing (SDB) can experience changes in automatic cardiac regulation as a result of frequent sleep fragmentation and disturbance in normal respiration and oxygenation that accompany most apnea/hypopnea events. In adults, these changes are reflected in enhanced sympathetic and reduced parasympathetic activity. In this study, we examined the autonomic cardiac regulation in children with and without SDB, through spectral and detrended fluctuation analysis (DFA) of pulse rate variability (PRV). PRV was measured from pulse-to-pulse intervals (PPIs) of the photoplethysmogram (PPG) recorded from 160 children using the Phone Oximeter(™) in the standard setting of overnight polysomnography. Spectral analysis of PRV showed the cardiac parasympathetic index (high frequency, HF) was lower (p < 0.01) and cardiac sympathetic indices (low frequency, LF and LF/HF ratio) were higher (p < 0.01) during apnea/hypopnea events for more than 95% of children with SDB. DFA showed the short- and long-range fluctuations of heart rate were more strongly correlated in children with SDB compared to children without SDB. These findings confirm that the analysis of the PPG recorded using the Phone Oximeter(™) could be the basis for a new screening tool for assessing PRV in non-clinical environment.

Thermal Simulation of Switching Pulses in an Insulated Gate Bipolar Transistor (IGBT) Power Module

DTIC Science & Technology

2015-02-01

executed with SolidWorks Flow Simulation , a computational fluid-dynamics code. The graph in Fig. 2 shows the timing and amplitudes of power pulses...defined a convective flow of air perpendicular to the bottom surface of the mounting plate, with a velocity of 10 ft/s. The thermal simulations were...Thermal Simulation of Switching Pulses in an Insulated Gate Bipolar Transistor (IGBT) Power Module by Gregory K Ovrebo ARL-TR-7210

a New Approach for Accuracy Improvement of Pulsed LIDAR Remote Sensing Data

NASA Astrophysics Data System (ADS)

Zhou, G.; Huang, W.; Zhou, X.; He, C.; Li, X.; Huang, Y.; Zhang, L.

2018-05-01

In remote sensing applications, the accuracy of time interval measurement is one of the most important parameters that affect the quality of pulsed lidar data. The traditional time interval measurement technique has the disadvantages of low measurement accuracy, complicated circuit structure and large error. A high-precision time interval data cannot be obtained in these traditional methods. In order to obtain higher quality of remote sensing cloud images based on the time interval measurement, a higher accuracy time interval measurement method is proposed. The method is based on charging the capacitance and sampling the change of capacitor voltage at the same time. Firstly, the approximate model of the capacitance voltage curve in the time of flight of pulse is fitted based on the sampled data. Then, the whole charging time is obtained with the fitting function. In this method, only a high-speed A/D sampler and capacitor are required in a single receiving channel, and the collected data is processed directly in the main control unit. The experimental results show that the proposed method can get error less than 3 ps. Compared with other methods, the proposed method improves the time interval accuracy by at least 20 %.

Effect of inter-train interval on the induction of repetition suppression of motor-evoked potentials using transcranial magnetic stimulation.

PubMed

Pitkänen, Minna; Kallioniemi, Elisa; Julkunen, Petro

2017-01-01

Repetition suppression (RS) is evident as a weakened response to repeated stimuli after the initial response. RS has been demonstrated in motor-evoked potentials (MEPs) induced with transcranial magnetic stimulation (TMS). Here, we investigated the effect of inter-train interval (ITI) on the induction of RS of MEPs with the attempt to optimize the investigative protocols. Trains of TMS pulses, targeted to the primary motor cortex by neuronavigation, were applied at a stimulation intensity of 120% of the resting motor threshold. The stimulus trains included either four or twenty pulses with an inter-stimulus interval (ISI) of 1 s. The ITI was here defined as the interval between the last pulse in a train and the first pulse in the next train; the ITIs used here were 1, 3, 4, 6, 7, 12, and 17 s. RS was observed with all ITIs except with the ITI of 1 s, in which the ITI was equal to ISI. RS was more pronounced with longer ITIs. Shorter ITIs may not allow sufficient time for a return to baseline. RS may reflect a startle-like response to the first pulse of a train followed by habituation. Longer ITIs may allow more recovery time and in turn demonstrate greater RS. Our results indicate that RS can be studied with confidence at relatively short ITIs of 6 s and above.

Selective ablation of rabbit atherosclerotic plaque with less thermal effect by the control of pulse structure of a quantum cascade laser in the 5.7 μm wavelength range

NASA Astrophysics Data System (ADS)

Hashimura, Keisuke; Ishii, Katsunori; Awazu, Kunio

2016-03-01

Cholesteryl esters are main components of atherosclerotic plaques and have an absorption peak at the wavelength of 5.75 μm originated from C=O stretching vibration mode of ester bond. Our group achieved the selective ablation of atherosclerotic lesions using a quantum cascade laser (QCL) in the 5.7 μm wavelength range. QCLs are relatively new types of semiconductor lasers that can emit mid-infrared range. They are sufficiently compact and considered to be useful for clinical application. However, large thermal effects were observed because the QCL worked as quasicontinuous wave (CW) lasers due to its short pulse interval. Then we tried macro pulse irradiation (irradiation of pulses at intervals) of the QCL and achieved effective ablation with less-thermal effects than conventional quasi-CW irradiation. However, lesion selectivity might be changed by changing pulse structure. Therefore, in this study, irradiation effects of the macro pulse irradiation to rabbit atherosclerotic plaque and normal vessel were compared. The macro pulse width and the macro pulse interval were set to 0.5 and 12 ms, respectively, because the thermal relaxation time of rabbit normal and atherosclerotic aortas in the oscillation wavelength of the QCL was 0.5-12 ms. As a result, cutting difference was achieved between rabbit atherosclerotic and normal aortas by the macro pulse irradiation. Therefore, macro pulse irradiation of a QCL in the 5.7 μm wavelength range is effective for reducing thermal effects and selective ablation of the atherosclerotic plaque. QCLs have the potential of realizing less-invasive laser angioplasty.

Detecting Pulsing Denial-of-Service Attacks with Nondeterministic Attack Intervals

NASA Astrophysics Data System (ADS)

Luo, Xiapu; Chan, Edmond W. W.; Chang, Rocky K. C.

2009-12-01

This paper addresses the important problem of detecting pulsing denial of service (PDoS) attacks which send a sequence of attack pulses to reduce TCP throughput. Unlike previous works which focused on a restricted form of attacks, we consider a very broad class of attacks. In particular, our attack model admits any attack interval between two adjacent pulses, whether deterministic or not. It also includes the traditional flooding-based attacks as a limiting case (i.e., zero attack interval). Our main contribution is Vanguard, a new anomaly-based detection scheme for this class of PDoS attacks. The Vanguard detection is based on three traffic anomalies induced by the attacks, and it detects them using a CUSUM algorithm. We have prototyped Vanguard and evaluated it on a testbed. The experiment results show that Vanguard is more effective than the previous methods that are based on other traffic anomalies (after a transformation using wavelet transform, Fourier transform, and autocorrelation) and detection algorithms (e.g., dynamic time warping).

The determination of the pulse pile-up reject (PUR) counting for X and gamma ray spectrometry

NASA Astrophysics Data System (ADS)

Karabıdak, S. M.; Kaya, S.

2017-02-01

The collection the charged particles produced by the incident radiation on a detector requires a time interval. If this time interval is not sufficiently short compared with the peaking time of the amplifier, a loss in the recovered signal amplitude occurs. Another major constraint on the throughput of modern x or gamma-ray spectrometers is the time required for the subsequent the pulse processing by the electronics. Two above-mentioned limitations are cause of counting losses resulting from the dead time and the pile-up. The pulse pile-up is a common problem in x and gamma ray radiation detection systems. The pulses pile-up in spectroscopic analysis can cause significant errors. Therefore, inhibition of these pulses is a vital step. A way to reduce errors due to the pulse pile-up is a pile-up inspection circuitry (PUR). Such a circuit rejects some of the pulse pile-up. Therefore, this circuit leads to counting losses. Determination of these counting losses is an important problem. In this work, a new method is suggested for the determination of the pulse pile-up reject.

Doubly-excited pulse-waves on flowing liquid films: experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Adebayo, Idris; Xie, Zhihua; Che, Zhizhao; Wray, Alex; Matar, Omar

2016-11-01

The interaction patterns between doubly-excited pulse waves on a flowing liquid film are studied both experimentally and numerically. The flowing film is constituted on an inclined glass substrate while pulse-waves are excited on the film surface by means of a solenoid valve connected to a relay which receives signals from customised Matlab routines. The effect of varying the system parameters i.e. film flow rate, inter-pulse interval and substrate inclination angle on the pulse interaction patterns are then studied. Results show that different interaction patterns exist for these binary pulses; which include a singular behaviour, complete merger, partial merger and total non-coalescence. A regime map of these patterns is then plotted for each inclination angles examined, based on the film Re and the inter-pulse interval. Finally, the individual effect of the system parameters on the merging distance of these binary pulses in the merger mode is then studied and the results validated using both numerical simulations and mathematical modelling. Funding from the Nigerian Government (for Idris Adebayo), and the EPSRC through a programme Grant MEMPHIS (EP/K003976/1) gratefully acknowledged.

Mechanisms of femtosecond LIPSS formation induced by periodic surface temperature modulation

NASA Astrophysics Data System (ADS)

Gurevich, Evgeny L.

2016-06-01

Here we analyze the formation of laser-induced periodic surface structures (LIPSS) on metal surfaces upon single femtosecond laser pulses. Most of the existing models of the femtosecond LIPSS formation discuss only the appearance of a periodic modulation of the electron and ion temperatures. However the mechanism how the inhomogeneous surface temperature distribution induces the periodically-modulated surface profile under the conditions corresponding to ultrashort-pulse laser ablation is still not clear. Estimations made on the basis of different hydrodynamic instabilities allow to sort out mechanisms, which can bridge the gap between the temperature modulation and the LIPSS. The proposed theory shows that the periodic structures can be generated by single ultrashort laser pulses due to ablative instabilities. The Marangoni and Rayleigh-Bénard convection on the contrary cannot cause the LIPSS formation.

Influence of gravitational sympathetic stimulation on the Surgical Plethysmographic Index.

PubMed

Colombo, R; Marchi, A; Borghi, B; Fossali, T; Tobaldini, E; Guzzetti, S; Raimondi, F

2015-01-01

Surgical Plethysmographic Index (SPI), calculated from pulse photo-plethysmographic amplitude oscillations, has been proposed as a tool to measure nociception anti-nociception balance during general anesthesia, but it is affected by several confounding factor that alter the autonomic nervous system (ANS) modulation. We hypothesized that SPI may be mainly affected by sympathetic stimulation independently from nociception. We studied the effects of two sympathetic stimuli on SPI, delivered through passive head-up tilt at 45 and 90 degrees angles, in nine awake healthy adults. The sympathetic modulation was assessed by means of heart rate variability (HRV) analysis. Mean (SD) SPI significantly increased from baseline to 45 degrees [from 38.6 (13.7) to 60.8 (7.6), p<0.001)] and to 90 degrees angle tilt [82.3 (5.4), p<0.001]. The electrocardiographic mean R-to-R interval significantly shortened during both passive tilts, whereas systolic arterial pressure did not change during the study protocol. HRV changed significantly during the study protocol towards a predominance of sympathetic modulation during passive tilt. Gravitational sympathetic stimulation at two increasing angles, in absence of any painful stimuli, affects SPI in awake healthy volunteers. SPI seems to reflect the sympathetic outflow directed to peripheral vessels.

Solid state modulator for klystron power supply XFEL TDS INJ

NASA Astrophysics Data System (ADS)

Zavadtsev, A. A.; Zavadtsev, D. A.; Zybin, D. A.; Churanov, D. V.; Shemarykin, P. V.

2016-09-01

The transverse deflecting system XFEL TDS INJ for European X-ray Free Electron Laser includes power supply for the CPI VKS-8262HS klystron. It has been designed for pulse high-voltage, cathode heating, solenoid and klystron ion pump. The klystron power supply includes solid state modulator, pulse transformer, controlled power supply for cathode heating and commercial power supplies for solenoid and ion pump. Main parameters of the modulator are 110 kV of peak voltage, 72 A peak current, and pulse length up to 6 μs. The klystron power supply has been developed, designed, manufactured, tuned, tested and installed in the XFEL building. All designed parameters are satisfied.

Time-resolved speckle effects on the estimation of laser-pulse arrival times

NASA Technical Reports Server (NTRS)

Tsai, B.-M.; Gardner, C. S.

1985-01-01

A maximum-likelihood (ML) estimator of the pulse arrival in laser ranging and altimetry is derived for the case of a pulse distorted by shot noise and time-resolved speckle. The performance of the estimator is evaluated for pulse reflections from flat diffuse targets and compared with the performance of a suboptimal centroid estimator and a suboptimal Bar-David ML estimator derived under the assumption of no speckle. In the large-signal limit the accuracy of the estimator was found to improve as the width of the receiver observational interval increases. The timing performance of the estimator is expected to be highly sensitive to background noise when the received pulse energy is high and the receiver observational interval is large. Finally, in the speckle-limited regime the ML estimator performs considerably better than the suboptimal estimators.

Lock-in detection for pulsed electrically detected magnetic resonance

NASA Astrophysics Data System (ADS)

Hoehne, Felix; Dreher, Lukas; Behrends, Jan; Fehr, Matthias; Huebl, Hans; Lips, Klaus; Schnegg, Alexander; Suckert, Max; Stutzmann, Martin; Brandt, Martin S.

2012-04-01

We show that in pulsed electrically detected magnetic resonance (pEDMR) signal modulation in combination with a lock-in detection scheme can reduce the low-frequency noise level by one order of magnitude and in addition removes the microwave-induced non-resonant background. This is exemplarily demonstrated for spin-echo measurements in phosphorus-doped silicon. The modulation of the signal is achieved by cycling the phase of the projection pulse used in pEDMR for the readout of the spin state.

Compact 1 mJ fiber MOPA for space-based laser-ablation resonant ionization mass spectrometry (LARIMS)

NASA Astrophysics Data System (ADS)

Mu, Xiaodong; Crain, William; Nguyen, Can; Ionov, Pavel; Steinvurzel, Paul; Dotan, Yaniv; Karuza, Petras; Lotshaw, William; Rose, Todd; Beck, Steven; Anderson, F. Scott

2018-02-01

A 1064 nm, 1 mJ pulsed fiber MOPA module, housed in 16"x14"x2.5" package for application in a lunar and planetary in-situ surface dating instrument is demonstrated. The module is based on a three-stage MOPA with a 60 μm core tapered fiber terminal amplifier. The master oscillator and first two preamplifier stages, which generate 20 μJ pulses, are all contained on a 13"x11"x1" board. Several improvements to the electronic signal control were instrumental to the laser development, including bipolar drive of the phase modulator for SBS suppression, shaping of the seed pulse to compensate pulse steepening, and pulsed operation of the power amplifier pump to reduce spontaneous emission at low pulse repetition frequency. The packaged laser runs at a repetition rate of 10 kHz and generates 10 ns pulses at 1 mJ with a 40 GHz linewidth, an M2 1.2 beam quality, and an 18 dB polarization extinction ratio. The modular design enables seven independent lasers to be stacked in a 20"x18"x16.25" enclosure, supporting a path towards a fiber laser based LARIMS for advanced materials characterization and chronological dating in harsh and remote environments.

Acousto-optic modulation and opto-acoustic gating in piezo-optomechanical circuits

PubMed Central

Balram, Krishna C.; Davanço, Marcelo I.; Ilic, B. Robert; Kyhm, Ji-Hoon; Song, Jin Dong; Srinivasan, Kartik

2017-01-01

Acoustic wave devices provide a promising chip-scale platform for efficiently coupling radio frequency (RF) and optical fields. Here, we use an integrated piezo-optomechanical circuit platform that exploits both the piezoelectric and photoelastic coupling mechanisms to link 2.4 GHz RF waves to 194 THz (1550 nm) optical waves, through coupling to propagating and localized 2.4 GHz acoustic waves. We demonstrate acousto-optic modulation, resonant in both the optical and mechanical domains, in which waveforms encoded on the RF carrier are mapped to the optical field. We also show opto-acoustic gating, in which the application of modulated optical pulses interferometrically gates the transmission of propagating acoustic pulses. The time-domain characteristics of this system under both pulsed RF and pulsed optical excitation are considered in the context of the different physical pathways involved in driving the acoustic waves, and modelled through the coupled mode equations of cavity optomechanics. PMID:28580373

Ultrafast saturable absorption in TiS2 induced by non-equilibrium electrons and the generation of a femtosecond mode-locked laser.

PubMed

Tian, Xiangling; Wei, Rongfei; Liu, Meng; Zhu, Chunhui; Luo, Zhichao; Wang, Fengqiu; Qiu, Jianrong

2018-05-24

Non-equilibrium electrons induced by ultrafast laser excitation in a correlated electron material can disturb the Fermi energy as well as optical nonlinearity. Here, non-equilibrium electrons translate a semiconductor TiS2 material into a plasma to generate broad band nonlinear optical saturable absorption with a sub-picosecond recovery time of ∼768 fs (corresponding to modulation frequencies over 1.3 THz) and a modulation response up to ∼145%. Based on this optical nonlinear modulator, a stable femtosecond mode-locked pulse with a pulse duration of ∼402 fs and a pulse train with a period of ∼175.5 ns is observed in the all-optical system. The findings indicate that non-equilibrium electrons can promote a TiS2-based saturable absorber to be an ultrafast switch for a femtosecond pulse output.

System and method for generating micro-seismic events and characterizing properties of a medium with non-linear acoustic interactions

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

Vu, Cung Khac; Nihei, Kurt; Johnson, Paul A.

2015-12-29

A method and system includes generating a first coded acoustic signal including pulses each having a modulated signal at a central frequency; and a second coded acoustic signal each pulse of which includes a modulated signal a central frequency of which is a fraction d of the central frequency of the modulated signal for the corresponding pulse in the first plurality of pulses. A receiver detects a third signal generated by a non-linear mixing process in the mixing zone and the signal is processed to extract the third signal to obtain an emulated micro-seismic event signal occurring at the mixingmore » zone; and to characterize properties of the medium or creating a 3D image of the properties of the medium, or both, based on the emulated micro-seismic event signal.« less

Attosecond time-energy structure of X-ray free-electron laser pulses

NASA Astrophysics Data System (ADS)

Hartmann, N.; Hartmann, G.; Heider, R.; Wagner, M. S.; Ilchen, M.; Buck, J.; Lindahl, A. O.; Benko, C.; Grünert, J.; Krzywinski, J.; Liu, J.; Lutman, A. A.; Marinelli, A.; Maxwell, T.; Miahnahri, A. A.; Moeller, S. P.; Planas, M.; Robinson, J.; Kazansky, A. K.; Kabachnik, N. M.; Viefhaus, J.; Feurer, T.; Kienberger, R.; Coffee, R. N.; Helml, W.

2018-04-01

The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

Effect of pulsed discharge on the ignition of pulse modulated radio frequency glow discharge at atmospheric pressure

NASA Astrophysics Data System (ADS)

Qiu, Shenjie; Guo, Ying; Han, Qianhan; Bao, Yun; Zhang, Jing; Shi, J. J.

2018-01-01

A pulsed discharge is introduced between two sequential pulse-modulated radio frequency glow discharges in atmospheric helium. The dependence of radio frequency discharge ignition on pulsed discharge intensity is investigated experimentally with the pulse voltage amplitudes of 650, 850, and 1250 V. The discharge characteristics and dynamics are studied in terms of voltage and current waveforms, and spatial-temporal evolution of optical emission. With the elevated pulsed discharge intensity of two orders of magnitude, the ignition of radio frequency discharge is enhanced by reducing the ignition time and achieving the stable operation with a double-hump spatial profile. The ignition time of radio frequency discharge is estimated to be 2.0 μs, 1.5 μs, and 1.0 μs with the pulse voltage amplitudes of 650, 850, and 1250 V, respectively, which is also demonstrated by the spatial-temporal evolution of optical emission at 706 and 777 nm.

Modulators for the S-band test linac at DESY

NASA Astrophysics Data System (ADS)

Bieler, M.; Choroba, S.; Hameister, J.; Lewin, H.-Ch.

1995-07-01

The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD S-band linear collider study 150 MW rf-pulse power at 50 Hz repetition rate and 3 μs pulse duration is required [1]. Two different modulator schemes are under investigation. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a hard tube pulser, using a dc power source at the full klystron voltage and a switch tube. This paper is focused on the modulator development for the S-band Test Linac at DESY. After a short overview over the test linac and a brief description of the 150 MW S-band klystron the circuitry of the line type pulse (LTP) is given. A hard tube pulser (HTP), which switches the high voltage directly from a storage capacitor to the klystron, has been built up at DESY. Circuitry and the results of the commissioning of the switch tube are reported.

Sideband pump-probe technique resolves nonlinear modulation response of PbS/CdS quantum dots on a silicon nitride waveguide

NASA Astrophysics Data System (ADS)

Kolarczik, Mirco; Ulbrich, Christian; Geiregat, Pieter; Zhu, Yunpeng; Sagar, Laxmi Kishore; Singh, Akshay; Herzog, Bastian; Achtstein, Alexander W.; Li, Xiaoqin; van Thourhout, Dries; Hens, Zeger; Owschimikow, Nina; Woggon, Ulrike

2018-01-01

For possible applications of colloidal nanocrystals in optoelectronics and nanophotonics, it is of high interest to study their response at low excitation intensity with high repetition rates, as switching energies in the pJ/bit to sub-pJ/bit range are targeted. We develop a sensitive pump-probe method to study the carrier dynamics in colloidal PbS/CdS quantum dots deposited on a silicon nitride waveguide after excitation by laser pulses with an average energy of few pJ/pulse. We combine an amplitude modulation of the pump pulse with phase-sensitive heterodyne detection. This approach permits to use co-linearly propagating co-polarized pulses. The method allows resolving transmission changes of the order of 10-5 and phase changes of arcseconds. We find a modulation on a sub-nanosecond time scale caused by Auger processes and biexciton decay in the quantum dots. With ground state lifetimes exceeding 1 μs, these processes become important for possible realizations of opto-electronic switching and modulation based on colloidal quantum dots emitting in the telecommunication wavelength regime.

Analysis of a modular generator for high-voltage, high-frequency pulsed applications, using low voltage semiconductors (< 1 kV) and series connected step-up (1:10) transformers.

PubMed

Redondo, L M; Fernando Silva, J; Margato, E

2007-03-01

This article discusses the operation of a modular generator topology, which has been developed for high-frequency (kHz), high-voltage (kV) pulsed applications. The proposed generator uses individual modules, each one consisting of a pulse circuit based on a modified forward converter, which takes advantage of the required low duty cycle to operate with a low voltage clamp reset circuit for the step-up transformer. This reduces the maximum voltage on the semiconductor devices of both primary and secondary transformer sides. The secondary winding of each step-up transformer is series connected, delivering a fraction of the total voltage. Each individual pulsed module is supplied via an isolation transformer. The assembled modular laboratorial prototype, with three 5 kV modules, 800 V semiconductor switches, and 1:10 step-up transformers, has 80% efficiency, and is capable of delivering, into resistive loads, -15 kV1 A pulses with 5 micros width, 10 kHz repetition rate, with less than 1 micros pulse rise time. Experimental results for resistive loads are presented and discussed.

A novel compact low impedance Marx generator with quasi-rectangular pulse output

NASA Astrophysics Data System (ADS)

Liu, Hongwei; Jiang, Ping; Yuan, Jianqiang; Wang, Lingyun; Ma, Xun; Xie, Weiping

2018-04-01

In this paper, a novel low impedance compact Marx generator with near-square pulse output based on the Fourier theory is developed. Compared with the traditional Marx generator, capacitors with different capacity have been used. It can generate a high-voltage quasi-rectangular pulse with a width of 100 ns at low impedance load, and it also has high energy density and power density. The generator consists of 16 modules. Each module comprises an integrative single-ended plastic case capacitor with a nominal value of 54 nF, four ceramic capacitors with a nominal value of 1.5 nF, a gas switch, a charging inductor, a grounding inductor, and insulators which provide mechanical support for all elements. In the module, different discharge periods from different capacitors add to the main circuit to form a quasi-rectangular pulse. The design process of the generator is analyzed, and the test results are provided here. The generator achieved pulse output with a rise time of 32 ns, pulse width of 120 ns, flat-topped width (95%-95%) of 50 ns, voltage of 550 kV, and power of 20 GW.

Survey Probe Infrared Celestial Experiment (SPICE).

DTIC Science & Technology

1985-01-01

amplitude modulation (PAM) Word clock Bit clock 3.1.2.3.2 Each signal shall be buffered and short- circuit proofed and capable of delivering a signal...TABLE OF CONTENTS I Appendix A I SPICE II Electronic Test Report Appendix B VC409-OOOl Pulse Code Modulator Specification - SPICE I VC409-OOOl-21 Pulse...Code Modulator Specification - SPICE II Appendix C - Specifications AA0209-103 Evacuation AA0209-104 Cryogen Filling AA0209-105 Leak Rate AA0209-106

Extraction of pulse repetition intervals from sperm whale click trains for ocean acoustic data mining.

PubMed

Zaugg, Serge; van der Schaar, Mike; Houégnigan, Ludwig; André, Michel

2013-02-01

The analysis of acoustic data from the ocean is a valuable tool to study free ranging cetaceans and anthropogenic noise. Due to the typically large volume of acquired data, there is a demand for automated analysis techniques. Many cetaceans produce acoustic pulses (echolocation clicks) with a pulse repetition interval (PRI) remaining nearly constant over several pulses. Analyzing these pulse trains is challenging because they are often interleaved. This article presents an algorithm that estimates a pulse's PRI with respect to neighboring pulses. It includes a deinterleaving step that operates via a spectral dissimilarity metric. The sperm whale (SW) produces trains with PRIs between 0.5 and 2 s. As a validation, the algorithm was used for the PRI-based identification of SW click trains with data from the NEMO-ONDE observatory that contained other pulsed sounds, mainly from ship propellers. Separation of files containing SW clicks with a medium and high signal to noise ratio from files containing other pulsed sounds gave an area under the receiver operating characteristic curve value of 0.96. This study demonstrates that PRI can be used for the automated identification of SW clicks and that deinterleaving via spectral dissimilarity contributes to algorithm performance.

ADJUSTABLE DOUBLE PULSE GENERATOR

DOEpatents

Gratian, J.W.; Gratian, A.C.

1961-08-01

>A modulator pulse source having adjustable pulse width and adjustable pulse spacing is described. The generator consists of a cross coupled multivibrator having adjustable time constant circuitry in each leg, an adjustable differentiating circuit in the output of each leg, a mixing and rectifying circuit for combining the differentiated pulses and generating in its output a resultant sequence of negative pulses, and a final amplifying circuit for inverting and square-topping the pulses. (AEC)

In-line monitoring technique with visible light from 1.3 microm-band SHG module for optical access systems.

PubMed

Kubo, Takahiro; Taniguchi, Tomohiro; Tadanaga, Osamu; Sakurai, Naoya; Kimura, Hideaki; Hadama, Hisaya; Asobe, Masaki

2010-02-01

We propose an in-line monitoring technique that uses 650 nm visible light for performing maintenance work on Fiber-to-the-home (FTTH) network quickly without the need for measuring skills or external devices. This technique is characterized by visible light (650 nm) generated by an SHG module from the 1.3 microm-band line signal. We fabricate a 1.3 microm-band quasi phase matched LiNbO(3) (QPM-LN) module, and the measure the 650 nm second harmonic (SH) power to test the proposed short-pulse modulation method. The results confirm the feasibility of the short-pulse modulation method with different peak factors (PFs) (1.0-7.3). We also examine the effect of short-pulse modulation on system performance at the optical receiver by measuring the bit error rate (BER) of received data (1.25 Gb/s). The BER is basically unaffected by the PF (1.0-5.5). This means that the proposed technique has little influence on data reception as regards PF (1.0-5.5).

Frequency-Dependent Modulation of Dopamine Release by Nicotine and Dopamine D1 Receptor Ligands: An In Vitro Fast Cyclic Voltammetry Study in Rat Striatum.

PubMed

Goutier, W; Lowry, J P; McCreary, A C; O'Connor, J J

2016-05-01

Nicotine is a highly addictive drug and exerts this effect partially through the modulation of dopamine release and increasing extracellular dopamine in regions such as the brain reward systems. Nicotine acts in these regions on nicotinic acetylcholine receptors. The effect of nicotine on the frequency dependent modulation of dopamine release is well established and the purpose of this study was to investigate whether dopamine D1 receptor (D1R) ligands have an influence on this. Using fast cyclic voltammetry and rat corticostriatal slices, we show that D1R ligands are able to modulate the effect of nicotine on dopamine release. Nicotine (500 nM) induced a decrease in dopamine efflux at low frequency (single pulse or five pulses at 10 Hz) and an increase at high frequency (100 Hz) electrical field stimulation. The D1R agonist SKF-38393, whilst having no effect on dopamine release on its own or on the effect of nicotine upon multiple pulse evoked dopamine release, did significantly prevent and reverse the effect of nicotine on single pulse dopamine release. Interestingly similar results were obtained with the D1R antagonist SCH-23390. In this study we have demonstrated that the modulation of dopamine release by nicotine can be altered by D1R ligands, but only when evoked by single pulse stimulation, and are likely working via cholinergic interneuron driven dopamine release.

1995 second modulator-klystron workshop: A modulator-klystron workshop for future linear colliders

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

NONE

1996-03-01

This second workshop examined the present state of modulator design and attempted an extrapolation for future electron-positron linear colliders. These colliders are currently viewed as multikilometer-long accelerators consisting of a thousand or more RF sources with 500 to 1,000, or more, pulsed power systems. The workshop opened with two introductory talks that presented the current approaches to designing these linear colliders, the anticipated RF sources, and the design constraints for pulse power. The cost of main AC power is a major economic consideration for a future collider, consequently the workshop investigated efficient modulator designs. Techniques that effectively apply the artmore » of power conversion, from the AC mains to the RF output, and specifically, designs that generate output pulses with very fast rise times as compared to the flattop. There were six sessions that involved one or more presentations based on problems specific to the design and production of thousands of modulator-klystron stations, followed by discussion and debate on the material.« less

Pulsed welding plasma source

NASA Astrophysics Data System (ADS)

Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Tyasto, A.

2016-04-01

It is shown that in order to form the current pulse of a near rectangular shape, which provides conversion of the welding arc into a dynamic mode, it is rational to connect a forming element made on the basis of an artificial forming line in series to the welding DC circuit. The paper presents a diagram of a pulsed device for welding with a non-consumable electrode in argon which was developed using the forming element. The conversion of the arc into the dynamic mode is illustrated by the current and voltage oscillograms of the arc gap and the dynamic characteristic of the arc within the interval of one pulse generation time in the arc gap. The background current travels in the interpulse interval.

Laser detection of material thickness

DOEpatents

Early, James W.

2002-01-01

There is provided a method for measuring material thickness comprising: (a) contacting a surface of a material to be measured with a high intensity short duration laser pulse at a light wavelength which heats the area of contact with the material, thereby creating an acoustical pulse within the material: (b) timing the intervals between deflections in the contacted surface caused by the reverberation of acoustical pulses between the contacted surface and the opposite surface of the material: and (c) determining the thickness of the material by calculating the proportion of the thickness of the material to the measured time intervals between deflections of the contacted surface.

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.

Orthogonal on-off control of radar pulses for the suppression of mutual interference

NASA Astrophysics Data System (ADS)

Kim, Yong Cheol

1998-10-01

Intelligent vehicles of the future will be guided by radars and other sensors to avoid obstacles. When multiple vehicles move simultaneously in autonomous navigational mode, mutual interference among car radars becomes a serious problem. An obstacle is illuminated with electromagnetic pulses from several radars. The signal at a radar receiver is actually a mixture of the self-reflection and the reflection of interfering pulses emitted by others. When standardized pulse- type radars are employed on vehicles for obstacle avoidance and so self-pulse and interfering pulses have identical pulse repetition interval, this SI (synchronous Interference) is very difficult to separate from the true reflection. We present a method of suppressing such a synchronous interference. By controlling the pulse emission of a radar in a binary orthogonal ON, OFF pattern, the true self-reflection can be separated from the false one. Two range maps are generated, TRM (true-reflection map) and SIM (synchronous- interference map). TRM is updated for every ON interval and SIM is updated for every OFF interval of the self-radar. SIM represents the SI of interfering radars while TRM keeps a record of a mixture of the true self-reflection and SI. Hence the true obstacles can be identified by the set subtraction operation. The performance of the proposed method is compared with that of the conventional M of N method. Bayesian analysis shows that the probability of false alarm is improved by order of 103 to approximately 106 while the deterioration in the probability of detection is negligible.

Method and apparatus for pulse stacking

DOEpatents

Harney, Robert C.

1977-01-01

An active pulse stacking system including an etalon and an electro-optical modulator apparatus combined with a pulse-forming network capable of forming and summing a sequence of time-delayed optical waveforms arising from, for example, a single laser pulse. The Pockels cell pulse stacker may attain an efficiency of about 2.6% while providing a controllable faster-than-exponential time rise in transmitted pulse intensity.

Perturbing laser field dependent high harmonic phase modulations

NASA Astrophysics Data System (ADS)

Li, Zhengyan; Kong, Fanqi; Brown, Graham; Hammond, TJ; Ko, Dong-Hyuk; Zhang, Chunmei; Corkum, P. B.

2018-06-01

A perturbing laser pulse modulates and controls the phase of the high harmonic radiation driven by an intense fundamental pulse. Thus, a structured wave front can impress a specific spatial phase onto the generated high harmonic wave front. This modulation procedure leads to all-optical spatial light modulators for VUV or XUV radiation created by high harmonic generation. Here, through theoretical analysis and experiment, we study the correlation between the high harmonic phase modulations and the perturbing laser field amplitude and phase, providing guidelines for practical high harmonic spatial light modulators. In addition, we show that the petahertz optical oscilloscope for measuring electric fields of a perturbing beam is most robust using low order harmonics, far from the cut-off.

Actively mode-locked erbium fiber ring laser using a Fabry-Perot semiconductor modulator as mode locker and tunable filter

NASA Astrophysics Data System (ADS)

Li, Shenping; Chan, K. T.

1999-05-01

A wavelength-tunable actively mode-locked erbium fiber ring laser was demonstrated using a Fabry-Perot semiconductor modulator. The modulator played the simultaneous roles of an intensity mode locker and a tunable optical filter. Stable single- or dual-wavelength nearly transform-limited picosecond pulses at gigabit repetition rates were generated. Continuous wavelength tuning was achieved by simply controlling the temperature of the modulator. Pulse train with a repetition rate up to 19.93 GHz (eight times the driving frequency) was obtained by using rational harmonic mode-locking technique.

An experimental investigation of using carbon foam-PCM-MWCNTs composite materials for thermal management of electronic devices under pulsed power modes

NASA Astrophysics Data System (ADS)

Alshaer, W. G.; Rady, M. A.; Nada, S. A.; Palomo Del Barrio, Elena; Sommier, Alain

2017-02-01

The present article reports on a detailed experimental investigation of using carbon foam-PCM-MWCNTs composite materials for thermal management (TM) of electronic devices subjected to pulsed power. The TM module was fabricated by infiltrating paraffin wax (RT65) as a phase change material (PCM) and multi walled carbon nanotubes (MWCNTs) as a thermal conductivity enhancer in a carbon foam as a base structure. Two carbon foam materials of low and high values of thermal conductivities, CF20 and KL1-250 (3.1 and 40 W/m K), were tested as a base structure for the TM modules. Tests were conducted at different power intensities and power cycling/loading modes. Results showed that for all power varying modes and all carbon foams, the infiltration of RT65 into carbon foam reduces the temperature of TM module and results in damping the temperature spikes height. Infiltration of MWCNTS into RT65 further improves the effectiveness of TM module. Temperature damping was more pronounced in stand-alone pulsed power cycles as compared to pulsed power spikes modes. The effectiveness of inclusion of RT65 and RT65/MWCNTs in damping the temperature spikes height is remarkable in TM modules based on KL1-250 as compared to CF-20.

A simple approach to detect and correct signal faults of Hall position sensors for brushless DC motors at steady speed

NASA Astrophysics Data System (ADS)

Shi, Yongli; Wu, Zhong; Zhi, Kangyi; Xiong, Jun

2018-03-01

In order to realize reliable commutation of brushless DC motors (BLDCMs), a simple approach is proposed to detect and correct signal faults of Hall position sensors in this paper. First, the time instant of the next jumping edge for Hall signals is predicted by using prior information of pulse intervals in the last electrical period. Considering the possible errors between the predicted instant and the real one, a confidence interval is set by using the predicted value and a suitable tolerance for the next pulse edge. According to the relationship between the real pulse edge and the confidence interval, Hall signals can be judged and the signal faults can be corrected. Experimental results of a BLDCM at steady speed demonstrate the effectiveness of the approach.

Study of the electromagnetic characteristics of multiple HTSPPT modules based on the configuration of toroidal structure for inductive pulsed power supply

NASA Astrophysics Data System (ADS)

Zhang, Cunshan; Zheng, Xinxin; Li, Haitao; Li, Zhenmei; Zhang, Tao; Jiao, Can

2018-04-01

High temperature superconducting pulsed power transformer (HTSPPT) is an important device for pulsed power supplies. It consists of a superconducting primary and a normal conducting secondary, which is used for energy storage and current amplification. The critical current density, the energy storage, and the coupling coefficient are three main performance indexes. They are affected by the geometry parameters of HTSPPT modules, such as the height and the width of the superconducting coils. In addition, the hoop stress of the HTSPPT coils is limited by the maximum tensile strength of high temperature superconducting (HTS) tapes. In this paper, Bi-2223/Ag HTS tapes are selected as the wire of primary inductor and the toroidal structure model is selected for multiple HTSPPT modules. The relationships between the geometry parameters of HTSPPT modules and the electrical performance are studied.

A laser based frequency modulated NL-OSL phenomenon

NASA Astrophysics Data System (ADS)

Mishra, D. R.; Bishnoi, A. S.; Soni, Anuj; Rawat, N. S.; Bhatt, B. C.; Kulkarni, M. S.; Babu, D. A. R.

2015-01-01

The detailed theoretical and experimental approach to novel technique of pulse frequency modulated stimulation (PFMS) method has been described for NL-OSL phenomenon. This method involved pulsed frequency modulation with respect to time for fixed pulse width of 532 nm continuous wave (CW)-laser light. The linearly modulated (LM)-, non-linearly (NL)-stimulation profiles have been generated using fast electromagnetic optical shutter. The PFMS parameters have been determined for present experimental setup. The PFMS based LM-, NL-OSL studies have been carried out on dosimetry grade single crystal α-Al2O3:C. The photo ionization cross section of α-Al2O3:C has been found to be ∼9.97 × 10-19 cm2 for 532 nm laser light using PFMS LM-OSL studies under assumption of first order of kinetic. This method of PFMS is found to be a potential alternative to generate different stimulation profiles using CW-light sources.

Frequency modulation of high-order harmonic generation in an orthogonally polarized two-color laser field.

PubMed

Li, Guicun; Zheng, Yinghui; Ge, Xiaochun; Zeng, Zhinan; Li, Ruxin

2016-08-08

We have experimentally investigated the frequency modulation of high-order harmonics in an orthogonally polarized two-color laser field consisting of a mid-infrared 1800nm fundamental pulse and its second harmonic pulse. It is demonstrated that the high harmonic spectra can be fine-tuned as we slightly change the relative delay of the two-color laser pulses. By analyzing the relative frequency shift of each harmonic at different two-color delays, the nonadiabatic spectral shift induced by the rapid variation of the intensity-dependent intrinsic dipole phase can be distinguished from the blueshift induced by the change of the refractive index during self-phase modulation (SPM). Our comprehensive analysis shows that the frequency modulation pattern is a reflection of the average emission time of high-order harmonic generation (HHG), thus offering a simple method to fine-tune the spectra of the harmonics on a sub-cycle time scale.

A Study on the Transient Behavior of Pulse Modulated Dual-Frequency Capacitive Discharges based on Circuit Analysis

NASA Astrophysics Data System (ADS)

Na, Byungkeun; Bae, Inshik; Park, Gi Jung; Chang, Hong-Young

2016-09-01

Multi-frequency capacitively coupled plasma (CCP) has been studied to independently control the ion energy and the ion flux; pulsing technique is used to reduce the electron temperature and finally the charging effects. The use of these techniques is a key to high aspect ratio contact (HARC) etching in the recent semiconductor processing. In this study, the characteristics of pulsed dual frequency (DF) CCP is investigated. Two separate powers of 3 MHz and 40 MHz are delivered to the powered electrode of an asymmetric CCP, and each frequency is modulated by an external 1 kHz pulse. Due to the complexity of the RF compensation in DF CCP, the characteristics of the plasma and the sheath are analyzed by high speed impedance measurement. The transient behavior of pulse modulated DF CCP is analyzed based on the result of continuous wave (CW) DF CCP. The optimized experimental condition for high ion energy will be presented. The difference between electronegative oxygen plasma and electropositive argon plasma is discussed as well.

Hypoxia, Monitoring, and Mitigation System

DTIC Science & Technology

2015-08-01

Oxygen Saturation Measured via Pulse - Oximeter SRS Software Requirements Specification SW Software TI Texas Instruments uPROC Micro-Processor USAARL...Financial) Table of Figures Figure 1: Pulse OX custom module...Tasks 3, 4 and 5 have not been exercised. Sensor definition testing continued on the custom pulse -ox design. Additional refinement on the pulse

Generation of arbitrarily shaped picosecond optical pulses using an integrated electrooptic waveguide modulator.

PubMed

Haner, M; Warren, W S

1987-09-01

We have produced complex software adjustable laser pulse shapes with ~10-ps resolution, and pulse energies up to 100 microJ for spectroscopic applications. The key devices are a high damage threshold electrooptic directional coupler and a GaAs circuit for synthesizing arbitrarily shaped microwave pulses.

Frequency-Accommodating Manchester Decoder

NASA Technical Reports Server (NTRS)

Vasquez, Mario J.

1988-01-01

No adjustment necessary to cover a 10:1 frequency range. Decoding circuit converts biphase-level pulse-code modulation to nonreturn-to-zero (NRZ)-level pulse-code modulation plus clock signal. Circuit accommodates input data rate of 50 to 500 kb/s. Tracks gradual changes in rate automatically, eliminating need for extra circuits and manual switching to adjust to different rates.

Optically Driven Q-Switches For Lasers

NASA Technical Reports Server (NTRS)

Hemmati, Hamid

1994-01-01

Optically driven Q-switches for pulsed lasers proposed, taking place of acousto-optical, magneto-optical, and electro-optical switches. Optical switching beams of proposed Q-switching most likely generated in pulsed diode lasers or light-emitting diodes, outputs of which are amplitude-modulated easily by direct modulation of relatively small input currents. Energy efficiencies exceed those of electrically driven Q-switches.

Acousto-optic laser projection systems for displaying TV information

NASA Astrophysics Data System (ADS)

Gulyaev, Yu V.; Kazaryan, M. A.; Mokrushin, Yu M.; Shakin, O. V.

2015-04-01

This review addresses various approaches to television projection imaging on large screens using lasers. Results are presented of theoretical and experimental studies of an acousto-optic projection system operating on the principle of projecting an image of an entire amplitude-modulated television line in a single laser pulse. We consider characteristic features of image formation in such a system and the requirements for its individual components. Particular attention is paid to nonlinear distortions of the image signal, which show up most severely at low modulation signal frequencies. We discuss the feasibility of improving the process efficiency and image quality using acousto-optic modulators and pulsed lasers. Real-time projectors with pulsed line imaging can be used for controlling high-intensity laser radiation.

Web-based multi-channel analyzer

DOEpatents

Gritzo, Russ E.

2003-12-23

The present invention provides an improved multi-channel analyzer designed to conveniently gather, process, and distribute spectrographic pulse data. The multi-channel analyzer may operate on a computer system having memory, a processor, and the capability to connect to a network and to receive digitized spectrographic pulses. The multi-channel analyzer may have a software module integrated with a general-purpose operating system that may receive digitized spectrographic pulses for at least 10,000 pulses per second. The multi-channel analyzer may further have a user-level software module that may receive user-specified controls dictating the operation of the multi-channel analyzer, making the multi-channel analyzer customizable by the end-user. The user-level software may further categorize and conveniently distribute spectrographic pulse data employing non-proprietary, standard communication protocols and formats.

30W, 10μJ, 10-ps SPM-induced spectrally compressed pulse generation in a low non-linearity ytterbium-doped rod-type fibre amplifier

NASA Astrophysics Data System (ADS)

Zaouter, Y.; Cormier, E.; Rigail, P.; Hönninger, C.; Mottay, E.

2007-02-01

The concept of spectral compression induced by self phase modulation is used to generate transform-limited 10ps pulses in a rare-earth-doped low nonlinearity fibre amplifier. The seed source of the amplifier stage is a high power, Yb 3+:KGW bulk oscillator which delivers 500 fs transform-limited pulses at 10MHz repetition rate. After a reduction of the repetition rate down to 3MHz, the femtosecond pulses are negatively chirped by transmission gratings in a compressor arrangement. The resulting 10ps pulses are further seeded into the power amplifier and up to 32W output power is obtained while the spectral bandwidth is reduced to less than 0.5 nm by means of self phase modulation.

Study on 3-inch Hamamatsu photomultipliers

NASA Astrophysics Data System (ADS)

Giordano, Valentina; Aiello, Sebastiano; Leonora, Emanuele

2016-07-01

Several kinds of photomultipliers are widely used in astroparticle physics detectors to measure Cherenkov light in media like water or ice. In neutrino telescopes the key element of the detector is the optical module, which consists of one or more photodetectors inside a transparent pressure-resistant glass sphere. It serves as mechanical protection while ensuring good light transmission. The KM3NeT collaboration has developed an innovative design of an optical module composed by 31 photomultipliers (PMTs) of 3-inch diameter housed in a 17-inch glass shpere. The performance of the telescope is largely dependent on the presence on noise pulses present on the anode of the photomultipliers. A study was conducted of noise pulses of Hamamatsu 3-inch diameter photomultipliers measuring time and charge distributions of dark pulses, pre-pulses, delayed pulses and after-pulses, focusing in particular on analysis on multiple afterpulses. Effects of the Earth's magnetic field on 3-inch PMTs were also studied.

On-target diagnosing of few-cycle pulses by high-order-harmonic generation

NASA Astrophysics Data System (ADS)

Brambila, Danilo S.; Husakou, Anton; Ivanov, Misha; Zhavoronkov, Nickolai

2017-12-01

We propose an approach to determine the residual phase distortion directly in the interaction region of few-cycle laser radiation with a gaseous target. We describe how the spectra of the generated high harmonics measured as a function of externally introduced dispersion into the driving few-cycle laser pulse can be used to decode small amounts of second- and third-order spectral phase, including the sign. The diagnosis is based on the analysis of several key features in the high-harmonic spectrum: the depth of spectral modulation, the position of the cutoff, and the symmetry of the spectrum with respect to the introduced dispersion. The approach is applicable to pulses without carrier-envelope phase (CEP) stabilization. Surprisingly, we find that for nearly-single-cycle pulses with nonstabilized CEP, deep spectral modulations in the harmonic spectra emerge for positively rather than negatively chirped pulses, in contrast to the case of CEP-stabilized pulses.

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

Micro-scale patterning of indium tin oxide film by spatially modulated pulsed Nd:YAG laser beam

NASA Astrophysics Data System (ADS)

Lee, Jinsoo; Kim, Seongsu; Lee, Myeongkyu

2012-09-01

Here we demonstrate that indium tin oxide (ITO) films deposited on glass can be directly patterned by a spatially -modulated pulsed Nd-YAG laser beam (wavelength = 1064 nm, pulse width = 6 ns) incident onto the film. This method utilizes a pulsed laser-induced thermo-elastic force exerting on the film which plays a role to detach it from the substrate. Sharp-edged clean patterns with feature size as small as 4 μm could be obtained. The threshold pulse energy density for patterning was estimated to be ˜0.8 J/cm2 for 150 nm-thick ITO film, making it possible to pattern over one square centimeter by a single pulse with energy of 850 mJ. Not only being free from photoresist and chemical etching steps, the presented method can also provide much higher throughput than the tradition photoablation process utilizing a tightly focused beam.

The interaction of reflexes elicited by stimulation of carotid body chemoreceptors and receptors in the nasal mucosa affecting respiration and pulse interval in the dog

PubMed Central

Angell-James, Jennifer E.; Daly, M. de Burgh

1973-01-01

1. The effects on respiration and pulse interval of stimulation of the carotid body chemoreceptors before, during and after stimulation of receptors in the nose have been studied in the anaesthetized dog. 2. Stimulation of a carotid body by infusion of cyanide into the ipsi-lateral common carotid artery causes hyperpnoea and either an increase, decrease or no change in pulse interval. 3. Excitation of receptors in the nasal mucosa leads to reflex apnoea or a reduction in breathing, and an increase in pulse interval. 4. When the carotid bodies are excited by the same dose of cyanide during stimulation of the nasal mucosa, the chemoreceptor-respiratory response is abolished or reduced in size compared with the control effect. On the other hand, the chemoreceptor-cardio-inhibitory response is considerably enhanced. 5. The potentiated cardio-inhibitory response of combined chemoreceptor and nasal stimulation could not be accounted for by the change in pulmonary ventilation, arterial PO2 or PCO2, or mean arterial blood pressure. 6. These results indicate that excitation of the nasal reflex inhibits the chemoreceptor-respiratory reflex response but facilitates the chemoreceptor-cardio-inhibitory reflex response. The possible sites of these interactions between the nasal and chemoreceptor reflexes are discussed. PMID:4689961

Pulsatile operation of a continuous-flow right ventricular assist device (RVAD) to improve vascular pulsatility

PubMed Central

Ng, Boon C.; Timms, Daniel; Cohn, William E.

2018-01-01

Despite the widespread acceptance of rotary blood pump (RBP) in clinical use over the past decades, the diminished flow pulsatility generated by a fixed speed RBP has been regarded as a potential factor that may lead to adverse events such as vasculature stiffening and hemorrhagic strokes. In this study, we investigate the feasibility of generating physiological pulse pressure in the pulmonary circulation by modulating the speed of a right ventricular assist device (RVAD) in a mock circulation loop. A rectangular pulse profile with predetermined pulse width has been implemented as the pump speed pattern with two different phase shifts (0% and 50%) with respect to the ventricular contraction. In addition, the performance of the speed modulation strategy has been assessed under different cardiovascular states, including variation in ventricular contractility and pulmonary arterial compliance. Our results indicated that the proposed pulse profile with optimised parameters (Apulse = 10000 rpm and ωmin = 3000 rpm) was able to generate pulmonary arterial pulse pressure within the physiological range (9–15 mmHg) while avoiding undesirable pump backflow under both co- and counter-pulsation modes. As compared to co-pulsation, stroke work was reduced by over 44% under counter-pulsation, suggesting that mechanical workload of the right ventricle can be efficiently mitigated through counter-pulsing the pump speed. Furthermore, our results showed that improved ventricular contractility could potentially lead to higher risk of ventricular suction and pump backflow, while stiffening of the pulmonary artery resulted in increased pulse pressure. In conclusion, the proposed speed modulation strategy produces pulsatile hemodynamics, which is more physiologic than continuous blood flow. The findings also provide valuable insight into the interaction between RVAD speed modulation and the pulmonary circulation under various cardiovascular states. PMID:29677212

Characterizing isolated attosecond pulses with angular streaking

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

Li, Siqi; Guo, Zhaoheng; Coffee, Ryan N.

Here, we present a reconstruction algorithm for isolated attosecond pulses, which exploits the phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field. The energy modulation due to a circularly polarized laser field is manifest strongly in the angle-resolved photoelectron momentum distribution, allowing for complete reconstruction of the temporal and spectral profile of an attosecond burst. We show that this type of reconstruction algorithm is robust against counting noise and suitable for single-shot experiments. This algorithm holds potential for a variety of applications for attosecond pulse sources.

Characterizing isolated attosecond pulses with angular streaking

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

Li, Sigi; Guo, Zhaoheng; Coffee, Ryan N.

We present a reconstruction algorithm for isolated attosecond pulses, which exploits the phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field. The energy modulation due to a circularly polarized laser field is manifest strongly in the angle-resolved photoelectron momentum distribution, allowing for complete reconstruction of the temporal and spectral profile of an attosecond burst. We show that this type of reconstruction algorithm is robust against counting noise and suitable for single-shot experiments. This algorithm holds potential for a variety of applications for attosecond pulse sources.

Characterizing isolated attosecond pulses with angular streaking

DOE PAGES

Li, Siqi; Guo, Zhaoheng; Coffee, Ryan N.; ...

2018-02-12

Here, we present a reconstruction algorithm for isolated attosecond pulses, which exploits the phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field. The energy modulation due to a circularly polarized laser field is manifest strongly in the angle-resolved photoelectron momentum distribution, allowing for complete reconstruction of the temporal and spectral profile of an attosecond burst. We show that this type of reconstruction algorithm is robust against counting noise and suitable for single-shot experiments. This algorithm holds potential for a variety of applications for attosecond pulse sources.

Characterizing isolated attosecond pulses with angular streaking

DOE PAGES

Li, Sigi; Guo, Zhaoheng; Coffee, Ryan N.; ...

2018-02-13

We present a reconstruction algorithm for isolated attosecond pulses, which exploits the phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field. The energy modulation due to a circularly polarized laser field is manifest strongly in the angle-resolved photoelectron momentum distribution, allowing for complete reconstruction of the temporal and spectral profile of an attosecond burst. We show that this type of reconstruction algorithm is robust against counting noise and suitable for single-shot experiments. This algorithm holds potential for a variety of applications for attosecond pulse sources.

Methods And System Suppressing Clutter In A Gain-Block, Radar-Responsive Tag System

DOEpatents

Ormesher, Richard C.; Axline, Robert M.

2006-04-18

Methods and systems reduce clutter interference in a radar-responsive tag system. A radar transmits a series of linear-frequency-modulated pulses and receives echo pulses from nearby terrain and from radar-responsive tags that may be in the imaged scene. Tags in the vicinity of the radar are activated by the radar's pulses. The tags receive and remodulate the radar pulses. Tag processing reverses the direction, in time, of the received waveform's linear frequency modulation. The tag retransmits the remodulated pulses. The radar uses a reversed-chirp de-ramp pulse to process the tag's echo. The invention applies to radar systems compatible with coherent gain-block tags. The invention provides a marked reduction in the strength of residual clutter echoes on each and every echo pulse received by the radar. SAR receiver processing effectively whitens passive-clutter signatures across the range dimension. Clutter suppression of approximately 14 dB is achievable for a typical radar system.

Generation of dark hollow femtosecond pulsed beam by phase-only liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Nie, Yongming; Ma, Haotong; Li, Xiujian; Hu, Wenhua; Yang, Jiankun

2011-07-01

Based on the refractive laser beam shaping system, the dark hollow femtosecond pulse beam shaping technique with a phase-only liquid crystal spatial light modulator (LC-SLM) is demonstrated. The phase distribution of the LC-SLM is derived by the energy conservation and constant optical path principle. The effects of the shaping system on the temporal properties, including spectral phase distribution and bandwidth of the femtosecond pulse, are analyzed in detail. Experimental results show that the hollow intensity distribution of the output pulsed beam can be maintained much at more than 1200mm. The spectral phase of the pulse is changed, and the pulse width is expanded from 199 to 230fs, which is caused by the spatial--temporal coupling effect. The coupling effect mainly depends on the phase-only LC-SLM itself, not on its loaded phase distribution. The experimental results indicate that the proposed shaping setup can generate a dark hollow femtosecond pulsed beam effectively, because the temporal Gaussian waveform is unchanged.

All-optical short pulse translation through cross-phase modulation in a VO₂ thin film.

PubMed

Fardad, Shima; Das, Susobhan; Salandrino, Alessandro; Breckenfeld, Eric; Kim, Heungsoo; Wu, Judy; Hui, Rongqing

2016-01-15

VO2 is a promising material for reconfigurable photonic devices due to the ultrafast changes in electronic and optical properties associated with its dielectric-to-metal phase transition. Based on a fiber-optic, pump-probe setup at 1550 nm wavelength window, and by varying the pump-pulse duration, we show that the material phase transition is primarily caused by the pump-pulse energy. For the first time, we demonstrate that the instantaneous optical phase modulation of probe during pump leading edge can be utilized to create short optical pulses at probe wavelength, through optical frequency discrimination. This circumvents the impact of long recovery time well known for the phase transition of VO2.

Synchronization of pulses from mode-locked lasers

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

Harvey, G.T.

A study of the synchronization of mode-locked lasers is presented. In particular, we investigate the timing of the laser output pulses with respect to the radio frequency (RF) signal driving the mode-locking elements in the laser cavity. Two types of mode-locked lasers are considered: a cw loss-modulated mode-locked argon ion laser; and a q-switched active-passive mode-locked Nd:YAG laser. We develop theoretical models for the treatment of laser pulse synchronization in both types of lasers. Experimental results are presented on a combined laser system that synchronizes pulses from both an argon ion and a Nd:YAG laser by using a common RFmore » signal to drive independent mode-lockers in both laser cavities. Shot to shot jitter as low as 18 ps (RMS) was measured between the output pulses from the two lasers. The theory of pulse synchronization for the cw loss-modulated mode-locked argon ion laser is based on the relationship between the timing of the mode-locked laser pulse (with respect to the peak of the RF signal) and the length of the laser cavity. Experiments on the argon laser include the measurement of the phase shift of the mode-locked pulse as a function of cavity length and intracavity intensity. The theory of synchronization of the active-passive mode-locked Nd:YAG laser is an extension of the pulse selection model of the active-passive laser. Experiments on the active-passive Nd:YAG laser include: measurement of the early noise fluctuations; measurement of the duration of the linear build-up stage (time between laser threshold and saturation of the absorber); measurement of jitter as a function of the mode-locker modulation depth; and measurement of the output pulse phase shift as a function of cavity length.« less

Distinguishing synchronous and time-varying synergies using point process interval statistics: motor primitives in frog and rat

PubMed Central

Hart, Corey B.; Giszter, Simon F.

2013-01-01

We present and apply a method that uses point process statistics to discriminate the forms of synergies in motor pattern data, prior to explicit synergy extraction. The method uses electromyogram (EMG) pulse peak timing or onset timing. Peak timing is preferable in complex patterns where pulse onsets may be overlapping. An interval statistic derived from the point processes of EMG peak timings distinguishes time-varying synergies from synchronous synergies (SS). Model data shows that the statistic is robust for most conditions. Its application to both frog hindlimb EMG and rat locomotion hindlimb EMG show data from these preparations is clearly most consistent with synchronous synergy models (p < 0.001). Additional direct tests of pulse and interval relations in frog data further bolster the support for synchronous synergy mechanisms in these data. Our method and analyses support separated control of rhythm and pattern of motor primitives, with the low level execution primitives comprising pulsed SS in both frog and rat, and both episodic and rhythmic behaviors. PMID:23675341

Kilohertz binary phase modulator for pulsed laser sources using a digital micromirror device.

PubMed

Hoffmann, Maximilian; Papadopoulos, Ioannis N; Judkewitz, Benjamin

2018-01-01

The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation, or patterned photostimulation. For most of these applications, it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy. Here we introduce a DMD-based optical design that overcomes these limitations and achieves dispersion-free high-speed binary phase modulation. We show that this phase modulation can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.

Kilohertz binary phase modulator for pulsed laser sources using a digital micromirror device

NASA Astrophysics Data System (ADS)

Hoffmann, Maximilian; Papadopoulos, Ioannis N.; Judkewitz, Benjamin

2018-01-01

The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation or patterned photostimulation. For most of these applications it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator, but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy. Here we introduce a DMD-based optical design that overcomes these limitations and achieves dispersion-free high-speed binary phase modulation. We show that this phase modulation can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.

Time-of-flight direct recoil ion scattering spectrometer

DOEpatents

Krauss, A.R.; Gruen, D.M.; Lamich, G.J.

1994-09-13

A time-of-flight direct recoil and ion scattering spectrometer beam line is disclosed. The beam line includes an ion source which injects ions into pulse deflection regions and separated by a drift space. A final optics stage includes an ion lens and deflection plate assembly. The ion pulse length and pulse interval are determined by computerized adjustment of the timing between the voltage pulses applied to the pulsed deflection regions. 23 figs.

Prefire identification for pulse-power systems

DOEpatents

Longmire, J.L.; Thuot, M.E.; Warren, D.S.

1982-08-23

Prefires in a high-power, high-frequency, multi-stage pulse generator are detected by a system having an EMI shielded pulse timing transmitter associated with and tailored to each stage of the pulse generator. Each pulse timing transmitter upon detection of a pulse triggers a laser diode to send an optical signal through a high frequency fiber optic cable to a pulse timing receiver which converts the optical signal to an electrical pulse. The electrical pulses from all pulse timing receivers are fed through an OR circuit to start a time interval measuring device and each electrical pulse is used to stop an individual channel in the measuring device thereby recording the firing sequence of the multi-stage pulse generator.

Prefire identification for pulse power systems

DOEpatents

Longmire, Jerry L.; Thuot, Michael E.; Warren, David S.

1985-01-01

Prefires in a high-power, high-frequency, multi-stage pulse generator are detected by a system having an EMI shielded pulse timing transmitter associated with and tailored to each stage of the pulse generator. Each pulse timing transmitter upon detection of a pulse triggers a laser diode to send an optical signal through a high frequency fiber optic cable to a pulse timing receiver which converts the optical signal to an electrical pulse. The electrical pulses from all pulse timing receivers are fed through an OR circuit to start a time interval measuring device and each electrical pulse is used to stop an individual channel in the measuring device thereby recording the firing sequence of the multi-stage pulse generator.

Dynamic adjustment of echolocation pulse structure of big-footed myotis (Myotis macrodactylus) in response to different habitats.

PubMed

Wang, Lei; Luo, Jinhong; Wang, Hongna; Ou, Wei; Jiang, Tinglei; Liu, Ying; Lyle, Dennis; Feng, Jiang

2014-02-01

Studying relationships between characteristics of sonar pulses and habitat clutter level is important for the understanding of signal design in bat echolocation. However, most studies have focused on overall spectral and temporal parameters of such vocalizations, with focus less on potential variation in frequency modulation rates (MRs) occurring within each pulse. In the current study, frequency modulation (FM) characteristics were examined in echolocation pulses recorded from big-footed myotis (Myotis macrodactylus) bats as these animals searched for prey in five habitats differing in relative clutter level. Pulses were analyzed using ten parameters, including four structure-related characters which were derived by dividing each pulse into three elements based on two knees in the FM sweep. Results showed that overall frequency, pulse duration, and MR all varied across habitat. The strongest effects were found for MR in the body of the pulse, implying that this particular component plays a major role as M. macrodactylus, and potentially other bat species, adjust to varying clutter levels in their foraging habitats.

Large-area tungsten disulfide for ultrafast photonics.

PubMed

Yan, Peiguang; Chen, Hao; Yin, Jinde; Xu, Zihan; Li, Jiarong; Jiang, Zike; Zhang, Wenfei; Wang, Jinzhang; Li, Irene Ling; Sun, Zhipei; Ruan, Shuangchen

2017-02-02

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have attracted significant interest in various optoelectronic applications due to their excellent nonlinear optical properties. One of the most important applications of TMDs is to be employed as an extraordinary optical modulation material (e.g., the saturable absorber (SA)) in ultrafast photonics. The main challenge arises while embedding TMDs into fiber laser systems to generate ultrafast pulse trains and thus constraints their practical applications. Herein, few-layered WS 2 with a large-area was directly transferred on the facet of the pigtail and acted as a SA for erbium-doped fiber laser (EDFL) systems. In our study, WS 2 SA exhibited remarkable nonlinear optical properties (e.g., modulation depth of 15.1% and saturable intensity of 157.6 MW cm -2 ) and was used for ultrafast pulse generation. The soliton pulses with remarkable performances (e.g., ultrashort pulse duration of 1.49 ps, high stability of 71.8 dB, and large pulse average output power of 62.5 mW) could be obtained in a telecommunication band. To the best of our knowledge, the average output power of the mode-locked pulse trains is the highest by employing TMD materials in fiber laser systems. These results indicate that atomically large-area WS 2 could be used as excellent optical modulation materials in ultrafast photonics.

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.

Effect of posture on arterial baroreflex control of heart rate in humans

NASA Technical Reports Server (NTRS)

Harrison, M. H.; Rittenhouse, D.; Greenleaf, J. E.

1986-01-01

The effects of blood-volume redistribution induced by postural changes on baroreflex activity are investigated. The central blood volume and baroreceptor functions of ten males between 23-51 years old were examined while they were in the head-up tilt (HUT), head-down tilt (HDT), and supine positions. It is observed that during HDT at 15 deg the pulse interval over the first five cardiac cycles following neck suction onset is 51 + or - 18 ms longer, at 30 deg it is 61 + or - 20 ms longer, and at 45 deg it is 74 + or - 35 ms longer than at supine; during HUT at 15 deg the pulse interval is 25 + or - 9 ms shorter than when supine, but for the 30 and 45 deg there is no significant difference in pulse interval detected. The data reveal that posture does modify arterial baroreflex control of heart rate.

Absorption of subcutaneously infused insulin: influence of the basal rate pulse interval.

PubMed

Hildebrandt, P; Birch, K; Jensen, B M; Kühl, C; Brange, J

1985-01-01

Eight insulin-dependent diabetic patients were given two constant infusions (each 1 IU/h) of 125I-labeled insulin into the abdominal subcutaneous tissue for about 12 h. Insulin was infused in pulses into one side of the abdomen in 6-min intervals (by means of an Auto-Syringe pump) and in the other side of the abdomen, insulin was infused in 1-h intervals (by means of a Medix pump). The size of the subcutaneous depots was continuously measured by counting the radioactivity at the infusion sites. After starting the infusions, the two depots were built up to steady-state levels at the same time and of the same size (approximately 3 IU) and with similar absorption rates. Thus, during basal rate insulin infusion, identical insulin absorption kinetics was achieved, irrespective of a 10-fold difference in the pulse rate.

The 1.06 micrometer wideband laser modulator: Fabrication and life testing

NASA Technical Reports Server (NTRS)

Teague, J. R.

1975-01-01

The design, fabrication, testing and delivery of an optical modulator which will operate with a mode-locked Nd:YAG laser at 1.06 micrometers were performed. The system transfers data at a nominal rate of 400 Mbps. This wideband laser modulator can transmit either Pulse Gated Binary Modulation (PGBM) or Pulse Polarization Binary Modulation (PPBM) formats. The laser beam enters the modulator and passes through both crystals; approximately 1% of the transmitted beam is split from the main beam and analyzed for the AEC signal; the remaining part of the beam exits the modulator. The delivered modulator when initially aligned and integrated with laser and electronics performed very well. The optical transmission was 69.5%. The static extinction ratio was 69:1. A 1000 hour life test was conducted with the delivered modulator. A 63 bit pseudorandom code signal was used as a driver input. At the conclusion of the life test the modulator optical transmission was 71.5% and the static extinction ratio 65:1.

Parallel-Processing CMOS Circuitry for M-QAM and 8PSK TCM

NASA Technical Reports Server (NTRS)

Gray, Andrew; Lee, Dennis; Hoy, Scott; Fisher, Dave; Fong, Wai; Ghuman, Parminder

2009-01-01

There has been some additional development of parts reported in "Multi-Modulator for Bandwidth-Efficient Communication" (NPO-40807), NASA Tech Briefs, Vol. 32, No. 6 (June 2009), page 34. The focus was on 1) The generation of M-order quadrature amplitude modulation (M-QAM) and octonary-phase-shift-keying, trellis-coded modulation (8PSK TCM), 2) The use of square-root raised-cosine pulse-shaping filters, 3) A parallel-processing architecture that enables low-speed [complementary metal oxide/semiconductor (CMOS)] circuitry to perform the coding, modulation, and pulse-shaping computations at a high rate; and 4) Implementation of the architecture in a CMOS field-programmable gate array.

Optimizing the electrical excitation of an atmospheric pressure plasma advanced oxidation process.

PubMed

Olszewski, P; Li, J F; Liu, D X; Walsh, J L

2014-08-30

The impact of pulse-modulated generation of atmospheric pressure plasma on the efficiency of organic dye degradation has been investigated. Aqueous samples of methyl orange were exposed to low temperature air plasma and the degradation efficiency was determined by absorbance spectroscopy. The plasma was driven at a constant frequency of 35kHz with a duty cycle of 25%, 50%, 75% and 100%. Relative concentrations of dissolved nitrogen oxides, pH, conductivity and the time evolution of gas phase ozone were measured to identify key parameters responsible for the changes observed in degradation efficiency. The results indicate that pulse modulation significantly improved dye degradation efficiency, with a plasma pulsed at 25% duty showing a two-fold enhancement. Additionally, pulse modulation led to a reduction in the amount of nitrate contamination added to the solution by the plasma. The results clearly demonstrate that optimization of the electrical excitation of the plasma can enhance both degradation efficiency and the final water quality. Copyright © 2014 Elsevier B.V. All rights reserved.

Reducing Energy Degradation Due to Back-bombardment Effect with Modulated RF Input in S-band Thermionic RF Gun

NASA Astrophysics Data System (ADS)

Kii, Toshiteru; Nakai, Yoko; Fukui, Toshio; Zen, Heishun; Kusukame, Kohichi; Okawachi, Norihito; Nakano, Masatsugu; Masuda, Kai; Ohgaki, Hideaki; Yoshikawa, Kiyoshi; Yamazaki, Tetsuo

2007-01-01

Energy degradation due to back-bombardment effect is quite serious to produce high-brightness electron beam with long macro-pulse with thermionic rf gun. To avoid the back-bombardment problem, a laser photo cathode is used at many FEL facilities, but usually it costs high and not easy to operate. Thus we have studied long pulse operation of the rf gun with thermionic cathode, which is inexpensive and easy to operate compared to the photocathode rf gun. In this work, to reduce the energy degradation, we controlled input rf power amplitude by controlling pulse forming network of the power modulator for klystron. We have successfully increased the pulse duration up to 4 μs by increasing the rf power from 7.8 MW to 8.5 MW during the macro pulse.

Enhanced Pulse Compression in Nonlinear Fiber by a WDM Optical Pulse

NASA Technical Reports Server (NTRS)

Yeh, C.; Bergman, L.

1997-01-01

A new way to compress an optical pulse in a single-mode fiber is presented in this paper. By the use of the cross phase modulation (CPM) effect caused by the nonlinearity of the optical fiber, a shepherd pulse propagating on a different wavelength beam in a wavelength division multiplexed (WDM) single-mode fiber system can be used to enhance the pulse compression of a co-propagating primary pulse.

Transit time of optical pulses propagating through a finite length medium.

PubMed

Bloemer, Mark; Myneni, Krishna; Centini, Marco; Scalora, Michael; D'Aguanno, Giuseppe

2002-05-01

We present experimental and theoretical results on the transit time of optical pulses propagating through bulk media of finite length, specifically GaAs and silica. The transit time of the peak of the pulse varies with the central wavelength due to the étalon effects caused by the reflectivity at the air/medium boundaries. For transform limited optical pulses, the transit time as a function of wavelength follows the transmittance spectrum, that is, the longest transit time occurs at the transmittance maxima where the cavity dwell time is the longest and the shortest transit time occurs at the transmittance minima. The results are dramatically different for chirped pulses obtained by modulating the injection current of a diode laser. The range in the transit times for chirped pulses is a factor of four times larger compared with transform limited pulses. In addition, the transit time for chirped pulses propagating through the GaAs sample is negative at certain wavelengths. Also, the transmitted pulse is not distorted. Although modulating the injection current of a diode laser is the most common method for generating optical pulses, to our knowledge this is the first reported observation of the transit time of these chirped optical pulses propagating through a simple étalon structure.

A hybrid pulse combining topology utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer.

PubMed

Li, Jiangtao; Zhao, Zheng; Sun, Yi; Liu, Yuhao; Ren, Ziyuan; He, Jiaxin; Cao, Hui; Zheng, Minjun

2017-03-01

Numerous applications driven by pulsed voltage require pulses to be with high amplitude, high repetitive frequency, and narrow width, which could be satisfied by utilizing avalanche transistors. The output improvement is severely limited by power capacities of transistors. Pulse combining is an effective approach to increase the output amplitude while still adopting conventional pulse generating modules. However, there are drawbacks in traditional topologies including the saturation tendency of combining efficiency and waveform oscillation. In this paper, a hybrid pulse combining topology was adopted utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer. The factors affecting the combining efficiency were determined including the output time synchronization of Marx circuits, and the quantity and position of magnetic cores. The numbers of the parallel modules and the stages were determined by the output characteristics of each combining method. Experimental results illustrated the ability of generating pulses with 2-14 kV amplitude, 7-11 ns width, and a maximum 10 kHz repetitive rate on a matched 50-300 Ω resistive load. The hybrid topology would be a convinced pulse combining method for similar nanosecond pulse generators based on the solid-state switches.

A hybrid pulse combining topology utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer

NASA Astrophysics Data System (ADS)

Li, Jiangtao; Zhao, Zheng; Sun, Yi; Liu, Yuhao; Ren, Ziyuan; He, Jiaxin; Cao, Hui; Zheng, Minjun

2017-03-01

Numerous applications driven by pulsed voltage require pulses to be with high amplitude, high repetitive frequency, and narrow width, which could be satisfied by utilizing avalanche transistors. The output improvement is severely limited by power capacities of transistors. Pulse combining is an effective approach to increase the output amplitude while still adopting conventional pulse generating modules. However, there are drawbacks in traditional topologies including the saturation tendency of combining efficiency and waveform oscillation. In this paper, a hybrid pulse combining topology was adopted utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer. The factors affecting the combining efficiency were determined including the output time synchronization of Marx circuits, and the quantity and position of magnetic cores. The numbers of the parallel modules and the stages were determined by the output characteristics of each combining method. Experimental results illustrated the ability of generating pulses with 2-14 kV amplitude, 7-11 ns width, and a maximum 10 kHz repetitive rate on a matched 50-300 Ω resistive load. The hybrid topology would be a convinced pulse combining method for similar nanosecond pulse generators based on the solid-state switches.

Urinary 1H Nuclear Magnetic Resonance Metabolomic Fingerprinting Reveals Biomarkers of Pulse Consumption Related to Energy-Metabolism Modulation in a Subcohort from the PREDIMED study.

PubMed

Madrid-Gambin, Francisco; Llorach, Rafael; Vázquez-Fresno, Rosa; Urpi-Sarda, Mireia; Almanza-Aguilera, Enrique; Garcia-Aloy, Mar; Estruch, Ramon; Corella, Dolores; Andres-Lacueva, Cristina

2017-04-07

Little is known about the metabolome fingerprint of pulse consumption. The study of robust and accurate biomarkers for pulse dietary assessment has great value for nutritional epidemiology regarding health benefits and their mechanisms. To characterize the fingerprinting of dietary pulses (chickpeas, lentils, and beans), spot urine samples from a subcohort from the PREDIMED study were stratified using a validated food frequency questionnaire. Urine samples of nonpulse consumers (≤4 g/day of pulse intake) and habitual pulse consumers (≥25 g/day of pulse intake) were analyzed using a 1 H nuclear magnetic resonance (NMR) metabolomics approach combined with multi- and univariate data analysis. Pulse consumption showed differences through 16 metabolites coming from (i) choline metabolism, (ii) protein-related compounds, and (iii) energy metabolism (including lower urinary glucose). Stepwise logistic regression analysis was applied to design a combined model of pulse exposure, which resulted in glutamine, dimethylamine, and 3-methylhistidine. This model was evaluated by a receiver operating characteristic curve (AUC > 90% in both training and validation sets). The application of NMR-based metabolomics to reported pulse exposure highlighted new candidates for biomarkers of pulse consumption and the impact on energy metabolism, generating new hypotheses on energy modulation. Further intervention studies will confirm these findings.

Relaxation dynamics of femtosecond-laser-induced temperature modulation on the surfaces of metals and semiconductors

NASA Astrophysics Data System (ADS)

Levy, Yoann; Derrien, Thibault J.-Y.; Bulgakova, Nadezhda M.; Gurevich, Evgeny L.; Mocek, Tomáš

2016-06-01

Formation of laser-induced periodic surface structures (LIPSS) is a complicated phenomenon which involves periodic spatial modulation of laser energy absorption on the irradiated surface, transient changes in optical response, surface layer melting and/or ablation. The listed processes strongly depend on laser fluence and pulse duration as well as on material properties. This paper is aimed at studying the spatiotemporal evolution of a periodic modulation of the deposited laser energy, once formed upon irradiation of metal (Ti) and semiconductor (Si) surfaces. Assuming that the incoming laser pulse interferes with a surface electromagnetic wave, the resulting sinusoidal modulation of the absorbed laser energy is introduced into a two-dimensional two-temperature model developed for titanium and silicon. Simulations reveal that the lattice temperature modulation on the surfaces of both materials following from the modulated absorption remains significant for longer than 50 ps after the laser pulse. In the cases considered here, the partially molten phase exists 10 ps in Ti and more than 50 ps in Si, suggesting that molten matter can be subjected to temperature-driven relocation toward LIPSS formation, due to the modulated temperature profile on the material surfaces. Molten phase at nanometric distances (nano-melting) is also revealed.

Implementation and initial test result of a prototype solid state modulator for pulsed magnetron

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

Dake, Vishal; Mangalvedekar, H.A., E-mail: vishaldake90@gmail.com; Tillu, Abhijit

2014-07-01

A solid-state modulator rated for 50 kV, 120A, 4μs and 250 Hz has been designed. The discharging circuit of the modulator is being tested at ∼ 33 kV, 40-80A, at a maximum pulse repetition rate of 30 pps. The paper discusses development and testing of prototype discharging circuit on resistive load and magnetron. The technique used for measurement of pulse transformer leakage inductance, distributed capacitance and stray primary circuit series inductance will also be discussed in detail. It is necessary to have Energy Storage Capacitors with low ESL for these applications (ESL < 40 nH). The method used for evaluatingmore » the ESL of locally available metalized polypropylene capacitors will also be presented. (author)« less

Thomson Scattering Diagnostic Data Acquisition Systems for Modern Fusion Systems

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

Ivanenko, S.V.; Khilchenko, A.D.; Ovchar, V.K.

2015-07-01

Uniquely designed complex data acquisition system for Thomson scattering diagnostic was developed. It allows recording short duration (3-5 ns) scattered pulses with 2 GHz sampling rate and 10-bit total resolution in oscilloscope mode. The system consists up to 48 photo detector modules with 0- 200 MHz bandwidth, 1-48 simultaneously sampling ADC modules and synchronization subsystem. The photo detector modules are based on avalanche photodiodes (APD) and ultra-low noise trans-impedance amplifiers. ADC modules include fast analog to digital converters and digital units based on the FPGA (Field- Programmable Gate Array) for data processing and storage. The synchronization subsystem is used tomore » form triggering pulses and to organize the simultaneously mode of ADC modules operation. (authors)« less

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

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

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2018-01-31

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Homogeneous spectral broadening of pulsed terahertz quantum cascade lasers by radio frequency modulation.

PubMed

Wan, W J; Li, H; Cao, J C

2018-01-22

The authors present an experimental investigation of radio frequency modulation on pulsed terahertz quantum cascade lasers (QCLs) emitting around 4.3 THz. The QCL chip used in this work is based on a resonant phonon design which is able to generate a 1.2 W peak power at 10 K from a 400-µm-wide and 4-mm-long laser with a single plasmon waveguide. To enhance the radio frequency modulation efficiency and significantly broaden the terahertz spectra, the QCLs are also processed into a double-metal waveguide geometry with a Silicon lens out-coupler to improve the far-field beam quality. The measured beam patterns of the double-metal QCL show a record low divergence of 2.6° in vertical direction and 2.4° in horizontal direction. Finally we perform the inter-mode beat note and terahertz spectra measurements for both single plasmon and double-metal QCLs working in pulsed mode. Since the double-metal waveguide is more suitable for microwave signal transmission, the radio frequency modulation shows stronger effects on the spectral broadening for the double-metal QCL. Although we are not able to achieve comb operation in this work for the pulsed lasers due to the large phase noise, the homogeneous spectral broadening resulted from the radio frequency modulation can be potentially used for spectroscopic applications.

Time-of-flight direct recoil ion scattering spectrometer

DOEpatents

Krauss, Alan R.; Gruen, Dieter M.; Lamich, George J.

1994-01-01

A time of flight direct recoil and ion scattering spectrometer beam line (10). The beam line (10) includes an ion source (12) which injects ions into pulse deflection regions (14) and (16) separated by a drift space (18). A final optics stage includes an ion lens and deflection plate assembly (22). The ion pulse length and pulse interval are determined by computerized adjustment of the timing between the voltage pulses applied to the pulsed deflection regions (14) and (16).

Sensitivity enhancements in MQ-MAS NMR of spin-5/2 nuclei using modulated rf mixing pulses

NASA Astrophysics Data System (ADS)

Vosegaard, Thomas; Massiot, Dominique; Grandinetti, Philip J.

2000-08-01

An X- overlineX pulse train with stepped modulation frequency was employed to enhance the multiple-quantum to single-quantum coherence transfer in the mixing period of the multiple-quantum magic-angle spinning (MQ-MAS) experiment for spin I=5/2 nuclei. Two MQ-MAS pulse sequences employing this mixing scheme for the triple-to-single and quintuple-to-single quantum coherence transfers have been designed and their performance is demonstrated for 27Al on samples of NaSi 3AlO 8 and 9Al 2O 3·2B 2O 3 . Compared to the standard single-pulse mixing sequences, the sensitivity is approximately doubled in the present experiments.

Mach-zehnder based optical marker/comb generator for streak camera calibration

DOEpatents

Miller, Edward Kirk

2015-03-03

This disclosure is directed to a method and apparatus for generating marker and comb indicia in an optical environment using a Mach-Zehnder (M-Z) modulator. High speed recording devices are configured to record image or other data defining a high speed event. To calibrate and establish time reference, the markers or combs are indicia which serve as timing pulses (markers) or a constant-frequency train of optical pulses (comb) to be imaged on a streak camera for accurate time based calibration and time reference. The system includes a camera, an optic signal generator which provides an optic signal to an M-Z modulator and biasing and modulation signal generators configured to provide input to the M-Z modulator. An optical reference signal is provided to the M-Z modulator. The M-Z modulator modulates the reference signal to a higher frequency optical signal which is output through a fiber coupled link to the streak camera.

Relationship Between Peripheral and Psychophysical Measures of Amplitude Modulation Detection in Cochlear Implant Users.

PubMed

Tejani, Viral D; Abbas, Paul J; Brown, Carolyn J

This study investigates the relationship between electrophysiological and psychophysical measures of amplitude modulation (AM) detection. Prior studies have reported both measures of AM detection recorded separately from cochlear implant (CI) users and acutely deafened animals, but no study has made both measures in the same CI users. Animal studies suggest a progressive loss of high-frequency encoding as one ascends the auditory pathway from the auditory nerve to the cortex. Because the CI speech processor uses the envelope of an ongoing acoustic signal to modulate pulse trains that are subsequently delivered to the intracochlear electrodes, it is of interest to explore auditory nerve responses to modulated stimuli. In addition, psychophysical AM detection abilities have been correlated with speech perception outcomes. Thus, the goal was to explore how the auditory nerve responds to AM stimuli and to relate those physiologic measures to perception. Eight patients using Cochlear Ltd. Implants participated in this study. Electrically evoked compound action potentials (ECAPs) were recorded using a 4000 pps pulse train that was sinusoidally amplitude modulated at 125, 250, 500, and 1000 Hz rates. Responses were measured for each pulse over at least one modulation cycle for an apical, medial, and basal electrode. Psychophysical modulation detection thresholds (MDTs) were also measured via a three-alternative forced choice, two-down, one-up adaptive procedure using the same modulation frequencies and electrodes. ECAPs were recorded from individual pulses in the AM pulse train. ECAP amplitudes varied sinusoidally, reflecting the sinusoidal variation in the stimulus. A modulated response amplitude (MRA) metric was calculated as the difference in the maximal and minimum ECAP amplitudes over the modulation cycles. MRA increased as modulation frequency increased, with no apparent cutoff (up to 1000 Hz). In contrast, MDTs increased as the modulation frequency increased. This trend is inconsistent with the physiologic measures. For a fixed modulation frequency, correlations were observed between MDTs and MRAs; this trend was evident at all frequencies except 1000 Hz (although only statistically significant for 250 and 500 Hz AM rates), possibly an indication of central limitations in processing of high modulation frequencies. Finally, peripheral responses were larger and psychophysical thresholds were lower in the apical electrodes relative to basal and medial electrodes, which may reflect better cochlear health and neural survival evidenced by lower preoperative low-frequency audiometric thresholds and steeper growth of neural responses in ECAP amplitude growth functions for apical electrodes. Robust ECAPs were recorded for all modulation frequencies tested. ECAP amplitudes varied sinusoidally, reflecting the periodicity of the modulated stimuli. MRAs increased as the modulation frequency increased, a trend we attribute to neural adaptation. For low modulation frequencies, there are multiple current steps between the peak and valley of the modulation cycle, which means successive stimuli are more similar to one another and neural responses are more likely to adapt. Higher MRAs were correlated with lower psychophysical thresholds at low modulation frequencies but not at 1000 Hz, implying a central limitation to processing of modulated stimuli.

HAMS (Hypoxia, Monitoring, and Mitigation System) II Quarterly Progress Report (Technical and Financial)

DTIC Science & Technology

2015-04-10

Peripheral Interface SpO2 Arterial Oxygen Saturation Measured via Pulse - Oximeter SRS Software Requirements Specification SV Stroke Volume SVR Systemic...viewer ....................................................................................................... 9 Figure 3: Pulse OX custom module...analysis approaches will be gathered. Sensors which detect SpO2, pulse / pulse rate, ECG, and skin temperature will be researched and evaluated for

Research Laboratory of Electronic Progress Report Number 135.

DTIC Science & Technology

1993-06-01

78 @ 1.12 Ultrashort Pulse Generation in Solid State Lasers ...generation the use of intracavity self-phase-modulation and of ultrashort laser pulses is essential for studies of negative group velocity dispersion... pulses . Our studies focus on exploiting mode locked solid state lasers . While the dominant the short pulse durations and high peak intensity of effect of

Periodic equivalence ratio modulation method and apparatus for controlling combustion instability

DOEpatents

Richards, George A.; Janus, Michael C.; Griffith, Richard A.

2000-01-01

The periodic equivalence ratio modulation (PERM) method and apparatus significantly reduces and/or eliminates unstable conditions within a combustion chamber. The method involves modulating the equivalence ratio for the combustion device, such that the combustion device periodically operates outside of an identified unstable oscillation region. The equivalence ratio is modulated between preselected reference points, according to the shape of the oscillation region and operating parameters of the system. Preferably, the equivalence ratio is modulated from a first stable condition to a second stable condition, and, alternatively, the equivalence ratio is modulated from a stable condition to an unstable condition. The method is further applicable to multi-nozzle combustor designs, whereby individual nozzles are alternately modulated from stable to unstable conditions. Periodic equivalence ratio modulation (PERM) is accomplished by active control involving periodic, low frequency fuel modulation, whereby low frequency fuel pulses are injected into the main fuel delivery. Importantly, the fuel pulses are injected at a rate so as not to affect the desired time-average equivalence ratio for the combustion device.

Pulse amplitude modulated chlorophyll fluorometer

DOEpatents

Greenbaum, Elias; Wu, Jie

2015-12-29

Chlorophyll fluorometry may be used for detecting toxins in a sample because of changes in micro algae. A portable lab on a chip ("LOAC") based chlorophyll fluorometer may be used for toxin detection and environmental monitoring. In particular, the system may include a microfluidic pulse amplitude modulated ("PAM") chlorophyll fluorometer. The LOAC PAM chlorophyll fluorometer may analyze microalgae and cyanobacteria that grow naturally in source drinking water.

Analyzing Pulse-Code Modulation On A Small Computer

NASA Technical Reports Server (NTRS)

Massey, David E.

1988-01-01

System for analysis pulse-code modulation (PCM) comprises personal computer, computer program, and peripheral interface adapter on circuit board that plugs into expansion bus of computer. Functions essentially as "snapshot" PCM decommutator, which accepts and stores thousands of frames of PCM data, sifts through them repeatedly to process according to routines specified by operator. Enables faster testing and involves less equipment than older testing systems.

Single event effects in pulse width modulation controllers

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

Penzin, S.H.; Crain, W.R.; Crawford, K.B.

1996-12-01

SEE testing was performed on pulse width modulation (PWM) controllers which are commonly used in switching mode power supply systems. The devices are designed using both Set-Reset (SR) flip-flops and Toggle (T) flip-flops which are vulnerable to single event upset (SEU) in a radiation environment. Depending on the implementation of the different devices the effect can be significant in spaceflight hardware.

Multi-Pulse Extraction from Los Alamos Proton Storage Ring for Radiographic Applications

NASA Astrophysics Data System (ADS)

Thiessen, Henry A.; Neri, Filippo; Rust, Kenneth R.; Redd, Dale B.

1997-05-01

For radiography of moving objects, two or more pulses with adjustable time spacing are required. The existing Proton Stotage Ring (PSR) extraction system is configured to extract the entire beam in a single turn. Two kickers and two kicker modulators fired at the same time perform the normal extraction function. By reconfiguring the two kickers and two modulators, it is possible to obtain two half-sized extraction kicks with adjustable time spacing. In this way, we have extracted two pulses with adjustable relative timing. The setup will be described and experimental results will be presented.

Programmable Pulse-Position-Modulation Encoder

NASA Technical Reports Server (NTRS)

Zhu, David; Farr, William

2006-01-01

A programmable pulse-position-modulation (PPM) encoder has been designed for use in testing an optical communication link. The encoder includes a programmable state machine and an electronic code book that can be updated to accommodate different PPM coding schemes. The encoder includes a field-programmable gate array (FPGA) that is programmed to step through the stored state machine and code book and that drives a custom high-speed serializer circuit board that is capable of generating subnanosecond pulses. The stored state machine and code book can be updated by means of a simple text interface through the serial port of a personal computer.

Dual-pulses and harmonic patterns of a square-wave soliton in passively mode-locked fiber laser

NASA Astrophysics Data System (ADS)

Ma, Wanzhuo; Wang, Tianshu; Su, Qingchao; Zhang, Jing; Jia, Qingsong; Jiang, Huilin

2018-06-01

We demonstrate a square-wave soliton pulse passively mode-locked fiber laser. The mode-locked pulses are achieved by using a nonlinear amplifying loop mirror. Single-pulse operation at a fundamental repetition rate of 3.2 MHz is obtained. The optical spectrum presents the soliton feature of several sidebands. The pulse duration expands with increasing pump power, but the amplitude hardly varies. Pulse breaking occurs and a stable dual-pulse is obtained with a fixed interval of 48 ns. Harmonic mode-locked states can be achieved when the total pump power is higher than 740 mW. The harmonic pulses can also operate in both single-pulse and dual-pulse states.

Structure and Utility of Blind Speed Intervals Associated with Doppler Measurements of Range Rate

DTIC Science & Technology

1993-02-01

computer programming concepts of speed, memory , and data structures that can be exploited to fabricate efficient software realizations of two phase range...to the effect that it is possible to derive a reasonable unambiguous estimate of range rate from the measurement of the pulse-to-pulse phase shift in...the properties of the blind speed intervals generated by the base speeds involved in two measurement equations. Sections 12 through 18 make up the

Measuring Differential Delays With Sine-Squared Pulses

NASA Technical Reports Server (NTRS)

Hurst, Robert N.

1994-01-01

Technique for measuring differential delays among red, green, and blue components of video signal transmitted on different parallel channels exploits sine-squared pulses that are parts of standard test signals transmitted during vertical blanking interval of frame period. Technique does not entail expense of test-signal generator. Also applicable to nonvideo signals including sine-squared pulses.

Effect of level, duration, and inter-pulse interval of 1-2 kHz sonar signal exposures on harbor porpoise hearing.

PubMed

Kastelein, Ronald A; Hoek, Lean; Gransier, Robin; Rambags, Martijn; Claeys, Naomi

2014-07-01

Safety criteria for underwater low-frequency active sonar sounds produced during naval exercises are needed to protect harbor porpoise hearing. As a first step toward defining criteria, a porpoise was exposed to sequences consisting of series of 1-s, 1-2 kHz sonar down-sweeps without harmonics (as fatiguing noise) at various combinations of average received sound pressure levels (SPLs; 144-179 dB re 1 μPa), exposure durations (1.9-240 min), and duty cycles (5%-100%). Hearing thresholds were determined for a narrow-band frequency-swept sine wave centered at 1.5 kHz before exposure to the fatiguing noise, and at 1-4, 4-8, 8-12, 48, 96, 144, and 1400 min after exposure, to quantify temporary threshold shifts (TTSs) and recovery of hearing. Results show that the inter-pulse interval of the fatiguing noise is an important parameter in determining the magnitude of noise-induced TTS. For the reported range of exposure combinations (duration and SPL), the energy of the exposure (i.e., cumulative sound exposure level; SELcum) can be used to predict the induced TTS, if the inter-pulse interval is known. Exposures with equal SELcum but with different inter-pulse intervals do not result in the same induced TTS.

Observation of Pulsed Gamma Rays with Energies Greater than 250 keV from the Crab Nebula Pulsar NP 0532. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Orwig, L. E.

1971-01-01

Data from a balloon flight experiment using an Na I scintillation spectrometer were analyzed for gamma ray pulsation. The payload was carried to a nominal atmospheric depth of 3.5 g/cm2. A superposed epoch analysis was performed on a 12,000 second portion of the data spanning a total time interval of 16,700 seconds at float altitude. A positive pulsed contribution was observed at the expected apparent frequency of NP 0532 having the typical double pulse structure. The results indicate a time-averaged pulse photon flux of 0.00144 + or - 0.00057 photons/sq cm/sec in the energy interval from 250 keV to 2.3 MeV. This represents a time-averaged pulsed power of 0.000649 + or - 0.000257 keV/sq cm/sec/keV. The ratio of interpulse to main pulse was found to be 2.4 + or - 1.9. The analysis indicates a positive photon flux from 250 keV to 725 keV of 0.00120 + or - 0.00052 photons/sq cm/sec.

Miniature multichannel biotelemeter system

NASA Technical Reports Server (NTRS)

Carraway, J. B.; Sumida, J. T. (Inventor)

1974-01-01

A miniature multichannel biotelemeter system is described. The system includes a transmitter where signals from different sources are sampled to produce a wavetrain of pulses. The transmitter also separates signals by sync pulses. The pulses amplitude modulate a radio frequency carrier which is received at a receiver unit. There the sync pulses are detected by a demultiplexer which routes the pulses from each different source to a separate output channel where the pulses are used to reconstruct the signals from the particular source.

A frequency and pulse-width co-modulation strategy for transcutaneous neuromuscular electrical stimulation based on sEMG time-domain features

NASA Astrophysics Data System (ADS)

Zhou, Yu-Xuan; Wang, Hai-Peng; Bao, Xue-Liang; Lü, Xiao-Ying; Wang, Zhi-Gong

2016-02-01

Objective. Surface electromyography (sEMG) is often used as a control signal in neuromuscular electrical stimulation (NMES) systems to enhance the voluntary control and proprioceptive sensory feedback of paralyzed patients. Most sEMG-controlled NMES systems use the envelope of the sEMG signal to modulate the stimulation intensity (current amplitude or pulse width) with a constant frequency. The aims of this study were to develop a strategy that co-modulates frequency and pulse width based on features of the sEMG signal and to investigate the torque-reproduction performance and the level of fatigue resistance achieved with our strategy. Approach. We examined the relationships between wrist torque and two stimulation parameters (frequency and pulse width) and between wrist torque and two sEMG time-domain features (mean absolute value (MAV) and number of slope sign changes (NSS)) in eight healthy volunteers. By using wrist torque as an intermediate variable, customized and generalized transfer functions were constructed to convert the two features of the sEMG signal into the two stimulation parameters, thereby establishing a MAV/NSS dual-coding (MNDC) algorithm. Wrist torque reproduction performance was assessed by comparing the torque generated by the algorithms with that originally recorded during voluntary contractions. Muscle fatigue was assessed by measuring the decline percentage of the peak torque and by comparing the torque time integral of the response to test stimulation trains before and after fatigue sessions. Main Results. The MNDC approach could produce a wrist torque that closely matched the voluntary wrist torque. In addition, a smaller decay in the wrist torque was observed after the MNDC-coded fatigue stimulation was applied than after stimulation using pulse-width modulation alone. Significance. Compared with pulse-width modulation stimulation strategies that are based on sEMG detection, the MNDC strategy is more effective for both voluntary muscle force reproduction and muscle fatigue reduction.

Passive measurement-device-independent quantum key distribution with orbital angular momentum and pulse position modulation

NASA Astrophysics Data System (ADS)

Wang, Lian; Zhou, Yuan-yuan; Zhou, Xue-jun; Chen, Xiao

2018-03-01

Based on the orbital angular momentum and pulse position modulation, we present a novel passive measurement-device-independent quantum key distribution (MDI-QKD) scheme with the two-mode source. Combining with the tight bounds of the yield and error rate of single-photon pairs given in our paper, we conduct performance analysis on the scheme with heralded single-photon source. The numerical simulations show that the performance of our scheme is significantly superior to the traditional MDI-QKD in the error rate, key generation rate and secure transmission distance, since the application of orbital angular momentum and pulse position modulation can exclude the basis-dependent flaw and increase the information content for each single photon. Moreover, the performance is improved with the rise of the frame length. Therefore, our scheme, without intensity modulation, avoids the source side channels and enhances the key generation rate. It has greatly utility value in the MDI-QKD setups.

Influence of current pulse shape on directly modulated system performance in metro area optical networks

NASA Astrophysics Data System (ADS)

Campos, Carmina del Rio; Horche, Paloma R.; Martin-Minguez, Alfredo

2011-03-01

Due to the fact that a metro network market is very cost sensitive, direct modulated schemes appear attractive. In this paper a CWDM (Coarse Wavelength Division Multiplexing) system is studied in detail by means of an Optical Communication System Design Software; a detailed study of the modulated current shape (exponential, sine and gaussian) for 2.5 Gb/s CWDM Metropolitan Area Networks is performed to evaluate its tolerance to linear impairments such as signal-to-noise-ratio degradation and dispersion. Point-to-point links are investigated and optimum design parameters are obtained. Through extensive sets of simulation results, it is shown that some of these shape pulses are more tolerant to dispersion when compared with conventional gaussian shape pulses. In order to achieve a low Bit Error Rate (BER), different types of optical transmitters are considered including strongly adiabatic and transient chirp dominated Directly Modulated Lasers (DMLs). We have used fibers with different dispersion characteristics, showing that the system performance depends, strongly, on the chosen DML-fiber couple.

Solid-state Marx based two-switch voltage modulator for the On-Line Isotope Mass Separator accelerator at the European Organization for Nuclear Research

NASA Astrophysics Data System (ADS)

Redondo, L. M.; Silva, J. Fernando; Canacsinh, H.; Ferrão, N.; Mendes, C.; Soares, R.; Schipper, J.; Fowler, A.

2010-07-01

A new circuit topology is proposed to replace the actual pulse transformer and thyratron based resonant modulator that supplies the 60 kV target potential for the ion acceleration of the On-Line Isotope Mass Separator accelerator, the stability of which is critical for the mass resolution downstream separator, at the European Organization for Nuclear Research. The improved modulator uses two solid-state switches working together, each one based on the Marx generator concept, operating as series and parallel switches, reducing the stress on the series stacked semiconductors, and also as auxiliary pulse generator in order to fulfill the target requirements. Preliminary results of a 10 kV prototype, using 1200 V insulated gate bipolar transistors and capacitors in the solid-state Marx circuits, ten stages each, with an electrical equivalent circuit of the target, are presented, demonstrating both the improved voltage stability and pulse flexibility potential wanted for this new modulator.

Pulse width and height modulation for multi-level resistance in bi-layer TaOx based RRAM

NASA Astrophysics Data System (ADS)

Alamgir, Zahiruddin; Beckmann, Karsten; Holt, Joshua; Cady, Nathaniel C.

2017-08-01

Mutli-level switching in resistive memory devices enables a wide range of computational paradigms, including neuromorphic and cognitive computing. To this end, we have developed a bi-layer tantalum oxide based resistive random access memory device using Hf as the oxygen exchange layer. Multiple, discrete resistance levels were achieved by modulating the RESET pulse width and height, ranging from 2 kΩ to several MΩ. For a fixed pulse height, OFF state resistance was found to increase gradually with the increase in the pulse width, whereas for a fixed pulse width, the increase in the pulse height resulted in drastic changes in resistance. Resistive switching in these devices transitioned from Schottky emission in the OFF state to tunneling based conduction in the ON state, based on I-V curve fitting and temperature dependent current measurements. These devices also demonstrated endurance of more than 108 cycles with a satisfactory Roff/Ron ratio and retention greater than 104 s.

Model for a pulsed terahertz quantum cascade laser under optical feedback.

PubMed

Agnew, Gary; Grier, Andrew; Taimre, Thomas; Lim, Yah Leng; Bertling, Karl; Ikonić, Zoran; Valavanis, Alexander; Dean, Paul; Cooper, Jonathan; Khanna, Suraj P; Lachab, Mohammad; Linfield, Edmund H; Davies, A Giles; Harrison, Paul; Indjin, Dragan; Rakić, Aleksandar D

2016-09-05

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

[Design of MC-III low frequency pulsed strong magnetic fields generator].

PubMed

Wen, Jun; Zhong, Lisheng; Xie, Hengkun; Qu, Xuemin; Ju, Hongbo; Yang, Jiqing; Wang, Sigang

2002-12-01

In this paper, We designed and accomplished a low frequency pulsed strong magnetic fields generator, which provides a pulsed magnetic field with the intensity range from 0.1-2.5 T and the adjusted time interval of pulse. This device is easy to operate and performs reliably. It can work steady for a long time and has been successful used in the experiments of biological effects of electromagnetics.

Airgun inter-pulse noise field during a seismic survey in an Arctic ultra shallow marine environment.

PubMed

Guan, Shane; Vignola, Joseph; Judge, John; Turo, Diego

2015-12-01

Offshore oil and gas exploration using seismic airguns generates intense underwater pulses that could cause marine mammal hearing impairment and/or behavioral disturbances. However, few studies have investigated the resulting multipath propagation and reverberation from airgun pulses. This research uses continuous acoustic recordings collected in the Arctic during a low-level open-water shallow marine seismic survey, to measure noise levels between airgun pulses. Two methods were used to quantify noise levels during these inter-pulse intervals. The first, based on calculating the root-mean-square sound pressure level in various sub-intervals, is referred to as the increment computation method, and the second, which employs the Hilbert transform to calculate instantaneous acoustic amplitudes, is referred to as the Hilbert transform method. Analyses using both methods yield similar results, showing that the inter-pulse sound field exceeds ambient noise levels by as much as 9 dB during relatively quiet conditions. Inter-pulse noise levels are also related to the source distance, probably due to the higher reverberant conditions of the very shallow water environment. These methods can be used to quantify acoustic environment impacts from anthropogenic transient noises (e.g., seismic pulses, impact pile driving, and sonar pings) and to address potential acoustic masking affecting marine mammals.

Migration of cell surface concanavalin A receptors in pulsed electric fields.

PubMed Central

Lin-Liu, S; Adey, W R; Poo, M M

1984-01-01

Concanavalin A (con A) receptors on the surface of cultured Xenopus myoblasts redistributed in response to monopolar, pulsed electric fields. The prefield uniform distribution of the receptors became asymmetrical, and was polarized toward the cathodal pole, in the same way as in DC fields. The extent of asymmetry depended on the duration of field exposure, pulse width (or alternatively, interpulse interval), frequency, and intensity. This relationship was most conveniently expressed by using duty cycle, a quantity determined by both pulse width and frequency. Pulses of average intensity 1.5 V/cm induced detectable asymmetry within 5 min. At the lowest average field intensity used, 0.8 V/cm, significant asymmetry was detected at 150 min. For pulses of high duty cycle (greater than 25%), steady state was reached after 30 min exposure and the steady state asymmetry was dependent on average field intensity. For low duty cycle fields, the time required to reach steady state was prolonged (greater than 50 min). Before reaching a steady state, effectiveness of the pulses, as compared with DC fields of equivalent intensity, was a function of duty cycle. A low duty cycle field (fixed number of pulses at low frequency or long interpulse interval) was less effective than high duty cycle fields or DC. PMID:6743751

Pulsed helium ionization detection system

DOEpatents

Ramsey, R.S.; Todd, R.A.

1985-04-09

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Pulsed helium ionization detection system

DOEpatents

Ramsey, Roswitha S.; Todd, Richard A.

1987-01-01

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

A novel pulse compression algorithm for frequency modulated active thermography using band-pass filter

NASA Astrophysics Data System (ADS)

Chatterjee, Krishnendu; Roy, Deboshree; Tuli, Suneet

2017-05-01

This paper proposes a novel pulse compression algorithm, in the context of frequency modulated thermal wave imaging. The compression filter is derived from a predefined reference pixel in a recorded video, which contains direct measurement of the excitation signal alongside the thermal image of a test piece. The filter causes all the phases of the constituent frequencies to be adjusted to nearly zero value, so that on reconstruction a pulse is obtained. Further, due to band-limited nature of the excitation, signal-to-noise ratio is improved by suppressing out-of-band noise. The result is similar to that of a pulsed thermography experiment, although the peak power is drastically reduced. The algorithm is successfully demonstrated on mild steel and carbon fibre reference samples. Objective comparisons of the proposed pulse compression algorithm with the existing techniques are presented.

Effect of second harmonic in pulse-width-modulation-based DAC for feedback of digital fluxgate magnetometer

NASA Astrophysics Data System (ADS)

Belyayev, Serhiy; Ivchenko, Nickolay

2018-04-01

Digital fluxgate magnetometers employ processing of the measured pickup signal to produce the value of the compensation current. Using pulse-width modulation with filtering for digital to analog conversion is a convenient approach, but it can introduce an intrinsic source of nonlinearity, which we discuss in this design note. A code shift of one least significant bit changes the second harmonic content of the pulse train, which feeds into the pick-up signal chain despite the heavy filtering. This effect produces a code-dependent nonlinearity. This nonlinearity can be overcome by the specific design of the timing of the pulse train signal. The second harmonic is suppressed if the first and third quarters of the excitation period pulse train are repeated in the second and fourth quarters. We demonstrate this principle on a digital magnetometer, achieving a magnetometer noise level corresponding to that of the sensor itself.

Generation of dark hollow femtosecond pulsed beam by phase-only liquid crystal spatial light modulator.

PubMed

Nie, Yongming; Ma, Haotong; Li, Xiujian; Hu, Wenhua; Yang, Jiankun

2011-07-20

Based on the refractive laser beam shaping system, the dark hollow femtosecond pulse beam shaping technique with a phase-only liquid crystal spatial light modulator (LC-SLM) is demonstrated. The phase distribution of the LC-SLM is derived by the energy conservation and constant optical path principle. The effects of the shaping system on the temporal properties, including spectral phase distribution and bandwidth of the femtosecond pulse, are analyzed in detail. Experimental results show that the hollow intensity distribution of the output pulsed beam can be maintained much at more than 1200 mm. The spectral phase of the pulse is changed, and the pulse width is expanded from 199 to 230 fs, which is caused by the spatial-temporal coupling effect. The coupling effect mainly depends on the phase-only LC-SLM itself, not on its loaded phase distribution. The experimental results indicate that the proposed shaping setup can generate a dark hollow femtosecond pulsed beam effectively, because the temporal Gaussian waveform is unchanged. © 2011 Optical Society of America

Investigation of pulsed IMRT and VMAT for re-irradiation treatments: dosimetric and delivery feasibilities

NASA Astrophysics Data System (ADS)

Lin, Mu-Han; Price, Robert A., Jr.; Li, Jinsheng; Kang, Shengwei; Li, Jie; Ma, C.-M.

2013-11-01

Many tumor cells demonstrate hyperradiosensitivity at doses below ˜50 cGy. Together with the increased normal tissue repair under low dose rate, the pulsed low dose rate radiotherapy (PLDR), which separates a daily fractional dose of 200 cGy into 10 pulses with 3 min interval between pulses (˜20 cGy/pulse and effective dose rate 6.7 cGy min-1), potentially reduces late normal tissue toxicity while still providing significant tumor control for re-irradiation treatments. This work investigates the dosimetric and technical feasibilities of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)-based PLDR treatments using Varian Linacs. Twenty one cases (12 real re-irradiation cases) including treatment sites of pancreas, prostate, pelvis, lung, head-and-neck, and breast were recruited for this study. The lowest machine operation dose rate (100 MU min-1) was employed in the plan delivery. Ten-field step-and-shoot IMRT and dual-arc VMAT plans were generated using the Eclipse TPS with routine planning strategies. The dual-arc plans were delivered five times to achieve a 200 cGy daily dose (˜20 cGy arc-1). The resulting plan quality was evaluated according to the heterogeneity and conformity indexes (HI and CI) of the planning target volume (PTV). The dosimetric feasibility of retaining the hyperradiosensitivity for PLDR was assessed based on the minimum and maximum dose in the target volume from each pulse. The delivery accuracy of VMAT and IMRT at the 100 MU min-1 machine operation dose rate was verified using a 2D diode array and ion chamber measurements. The delivery reproducibility was further investigated by analyzing the Dynalog files of repeated deliveries. A comparable plan quality was achieved by the IMRT (CI 1.10-1.38 HI 1.04-1.10) and the VMAT (CI 1.08-1.26 HI 1.05-1.10) techniques. The minimum/maximum PTV dose per pulse is 7.9 ± 5.1 cGy/33.7 ± 6.9 cGy for the IMRT and 12.3 ± 4.1 cGy/29.2 ± 4.7 cGy for the VMAT. Six out of the 186 IMRT pulses (fields) were found to exceed 50 cGy maximum PTV dose per pulse while the maximum PTV dose per pulse was within 40 cGy for all the VMAT pulses (arcs). However, for VMAT plans, the dosimetric quality of the entire treatment plan was less superior for the breast cases and large irregular targets. The gamma passing rates for both techniques at the 100 MU min-1 dose rate were at least 94.1% (3%/3 mm) and the point dose measurements agreed with the planned values to within 2.2%. The average root mean square error of the leaf position was 0.93 ± 0.83 mm for IMRT and 0.53 ± 0.48 mm for VMAT based on the Dynalog file analysis. The RMS error of the leaf position was nearly identical for the repeated deliveries of the same plans. In general, both techniques are feasible for PLDR treatments. VMAT was more advantageous for PLDR with more uniform target dose per pulse, especially for centrally located tumors. However, for large, irregular and/or peripheral tumors, IMRT could produce more favorable PLDR plans. By taking the biological benefit of PLDR delivery and the dosimetric benefit of IMRT and VMAT, the proposed methods have a great potential for those previously-irradiated recurrent patients.

Design of power electronics for TVC EMA systems

NASA Technical Reports Server (NTRS)

Nelms, R. Mark

1993-01-01

The Composite Development Division of the Propulsion Laboratory at Marshall Space Flight Center (MSFC) is currently developing a class of electromechanical actuators (EMA's) for use in space transportation applications such as thrust vector control (TVC) and propellant control valves (PCV). These high power servomechanisms will require rugged, reliable, and compact power electronic modules capable of modulating several hundred amperes of current at up to 270 volts. MSFC has selected the brushless dc motor for implementation in EMA's. This report presents the results of an investigation into the applicability of two new technologies, MOS-controlled thyristors (MCT's) and pulse density modulation (PDM), to the control of brushless dc motors in EMA systems. MCT's are new power semiconductor devices, which combine the high voltage and current capabilities of conventional thyristors and the low gate drive requirements of metal oxide semiconductor field effect transistors (MOSFET's). The commanded signals in a PDM system are synthesized using a series of sinusoidal pulses instead of a series of square pulses as in a pulse width modulation (PWM) system. A resonant dc link inverter is employed to generate the sinusoidal pulses in the PDM system. This inverter permits zero-voltage switching of all semiconductors which reduces switching losses and switching stresses. The objectives of this project are to develop and validate an analytical model of the MCT device when used in high power motor control applications and to design, fabricate, and test a prototype electronic circuit employing both MCT and PDM technology for controlling a brushless dc motor.

Refractive index modulation of Sb70Te30 phase-change thin films by multiple femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Lei, Kai; Wang, Yang; Jiang, Minghui; Wu, Yiqun

2016-05-01

In this study, the controllable effective refractive index modulation of Sb70Te30 phase-change thin films between amorphous and crystalline states was achieved experimentally by multiple femtosecond laser pulses. The modulation mechanism was analyzed comprehensively by a spectral ellipsometer measurement, surface morphology observation, and two-temperature model calculations. We numerically demonstrate the application of the optically modulated refractive index of the phase-change thin films in a precisely adjustable color display. These results may provide further insights into ultrafast phase-transition mechanics and are useful in the design of programmable photonic and opto-electrical devices based on phase-change memory materials.

Constructive polarization modulation for coherent population trapping clock

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

Yun, Peter, E-mail: enxue.yun@obspm.fr; Danet, Jean-Marie; Holleville, David

2014-12-08

We propose a constructive polarization modulation scheme for atomic clocks based on coherent population trapping (CPT). In this scheme, the polarization of a bichromatic laser beam is modulated between two opposite circular polarizations to avoid trapping the atomic populations in the extreme Zeeman sublevels. We show that if an appropriate phase modulation between the two optical components of the bichromatic laser is applied synchronously, the two CPT dark states which are produced successively by the alternate polarizations add constructively. Measured CPT resonance contrasts up to 20% in one-pulse CPT and 12% in two-pulse Ramsey-CPT experiments are reported, demonstrating the potentialmore » of this scheme for applications to high performance atomic clocks.« less

Refractive index modulation of Sb{sub 70}Te{sub 30} phase-change thin films by multiple femtosecond laser pulses

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

Lei, Kai; Wang, Yang, E-mail: ywang@siom.ac.cn; Jiang, Minghui

2016-05-07

In this study, the controllable effective refractive index modulation of Sb{sub 70}Te{sub 30} phase-change thin films between amorphous and crystalline states was achieved experimentally by multiple femtosecond laser pulses. The modulation mechanism was analyzed comprehensively by a spectral ellipsometer measurement, surface morphology observation, and two-temperature model calculations. We numerically demonstrate the application of the optically modulated refractive index of the phase-change thin films in a precisely adjustable color display. These results may provide further insights into ultrafast phase-transition mechanics and are useful in the design of programmable photonic and opto-electrical devices based on phase-change memory materials.

Pulse compression favourable aperiodic infrared imaging approach for non-destructive testing and evaluation of bio-materials

NASA Astrophysics Data System (ADS)

Mulaveesala, Ravibabu; Dua, Geetika; Arora, Vanita; Siddiqui, Juned A.; Muniyappa, Amarnath

2017-05-01

In recent years, aperiodic, transient pulse compression favourable infrared imaging methodologies demonstrated as reliable, quantitative, remote characterization and evaluation techniques for testing and evaluation of various biomaterials. This present work demonstrates a pulse compression favourable aperiodic thermal wave imaging technique, frequency modulated thermal wave imaging technique for bone diagnostics, especially by considering the bone with tissue, skin and muscle over layers. In order to find the capabilities of the proposed frequency modulated thermal wave imaging technique to detect the density variations in a multi layered skin-fat-muscle-bone structure, finite element modeling and simulation studies have been carried out. Further, frequency and time domain post processing approaches have been adopted on the temporal temperature data in order to improve the detection capabilities of frequency modulated thermal wave imaging.

Modulated heat pulse propagation and partial transport barriers in chaotic magnetic fields

DOE PAGES

del-Castillo-Negrete, Diego; Blazevski, Daniel

2016-04-01

Direct numerical simulations of the time dependent parallel heat transport equation modeling heat pulses driven by power modulation in 3-dimensional chaotic magnetic fields are presented. The numerical method is based on the Fourier formulation of a Lagrangian-Green's function method that provides an accurate and efficient technique for the solution of the parallel heat transport equation in the presence of harmonic power modulation. The numerical results presented provide conclusive evidence that even in the absence of magnetic flux surfaces, chaotic magnetic field configurations with intermediate levels of stochasticity exhibit transport barriers to modulated heat pulse propagation. In particular, high-order islands and remnants of destroyed flux surfaces (Cantori) act as partial barriers that slow down or even stop the propagation of heat waves at places where the magnetic field connection length exhibits a strong gradient. The key parameter ismore » $$\\gamma=\\sqrt{\\omega/2 \\chi_\\parallel}$$ that determines the length scale, $$1/\\gamma$$, of the heat wave penetration along the magnetic field line. For large perturbation frequencies, $$\\omega \\gg 1$$, or small parallel thermal conductivities, $$\\chi_\\parallel \\ll 1$$, parallel heat transport is strongly damped and the magnetic field partial barriers act as robust barriers where the heat wave amplitude vanishes and its phase speed slows down to a halt. On the other hand, in the limit of small $$\\gamma$$, parallel heat transport is largely unimpeded, global transport is observed and the radial amplitude and phase speed of the heat wave remain finite. Results on modulated heat pulse propagation in fully stochastic fields and across magnetic islands are also presented. In qualitative agreement with recent experiments in LHD and DIII-D, it is shown that the elliptic (O) and hyperbolic (X) points of magnetic islands have a direct impact on the spatio-temporal dependence of the amplitude and the time delay of modulated heat pulses.« less

Full quaternion based finite-time cascade attitude control approach via pulse modulation synthesis for a spacecraft.

PubMed

Mazinan, A H; Pasand, M; Soltani, B

2015-09-01

In the aspect of further development of investigations in the area of spacecraft modeling and analysis of the control scheme, a new hybrid finite-time robust three-axis cascade attitude control approach is proposed via pulse modulation synthesis. The full quaternion based control approach proposed here is organized in association with both the inner and the outer closed loops. It is shown that the inner closed loop, which consists of the sliding mode finite-time control approach, the pulse width pulse frequency modulator, the control allocation and finally the dynamics of the spacecraft is realized to track the three-axis referenced commands of the angular velocities. The pulse width pulse frequency modulators are in fact employed in the inner closed loop to accommodate the control signals to a number of on-off thrusters, while the control allocation algorithm provides the commanded firing times for the reaction control thrusters in the overactuated spacecraft. Hereinafter, the outer closed loop, which consists of the proportional linear control approach and the kinematics of the spacecraft is correspondingly designed to deal with the attitude angles that are presented by quaternion vector. It should be noted that the main motivation of the present research is to realize a hybrid control method by using linear and nonlinear terms and to provide a reliable and robust control structure, which is able to track time varying three-axis referenced commands. Subsequently, a stability analysis is presented to verify the performance of the overall proposed cascade attitude control approach. To prove the effectiveness of the presented approach, a thorough investigation is presented compared to a number of recent corresponding benchmarks. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Neuroendocrine abnormalities in hypothalamic amenorrhea: spectrum, stability, and response to neurotransmitter modulation.

PubMed

Perkins, R B; Hall, J E; Martin, K A

1999-06-01

To characterize the neuroendocrine patterns of abnormal GnRH secretion in hypothalamic amenorrhea (HA), 49 women with primary and secondary HA underwent frequent sampling of LH in a total of 72 baseline studies over 12-24 h. A subset of women participated in more than one study to address 1) the variability of LH pulse patterns over time; and 2) the impact of modulating opioid, dopaminergic, and adrenergic tone on LH secretory patterns. The frequency and amplitude of LH secretion was compared with that seen in the early follicular phase (EFP) of normally cycling women. The spectrum of abnormalities of LH pulses was 8% apulsatile, 27% low frequency/low amplitude, 8% low amplitude/normal frequency, 43% low frequency/normal amplitude, 14% normal frequency/normal amplitude. Of patients studied overnight, 45% demonstrated a pubertal pattern of augmented LH secretion during sleep. Of patients studied repeatedly, 75% demonstrated at least 2 different patterns of LH secretion, and 33% reverted at least once to a normal pattern of secretion. An increase in LH pulse frequency was seen in 12 of 15 subjects in response to naloxone (opioid receptor antagonist). Clonidine (alpha-2 adrenergic agonist) was associated with a decrease in mean LH in 3 of 3 subjects. An increase in LH pulse frequency was seen in 4 of 8 subjects in response to metoclopramide (dopamine receptor antagonist), but the response was not statistically significant. Baseline abnormalities in LH secretion did not appear to influence response to neurotransmitter modulation. 1) HA represents a spectrum of disordered GnRH secretion that can vary over time; 2) LH pulse patterns at baseline do not appear to influence the ability to respond to neurotransmitter modulation; 3) Opioid and adrenergic tone appear to influence the hypothalamic GnRH pulse generator in some individuals with HA.

Linear induction accelerators made from pulse-line cavities with external pulse injection.

PubMed

Smith, I

1979-06-01

Two types of linear induction accelerator have been reported previously. In one, unidirectional voltage pulses are generated outside the accelerator and injected into the accelerator cavity modules, which contain ferromagnetic material to reduce energy losses in the form of currents induced, in parallel with the beam, in the cavity structure. In the other type, the accelerator cavity modules are themselves pulse-forming lines with energy storage and switches; parallel current losses are made zero by the use of circuits that generate bidirectional acceleration waveforms with a zero voltage-time integral. In a third type of design described here, the cavities are externally driven, and 100% efficient coupling of energy to the beam is obtained by designing the external pulse generators to produce bidirectional voltage waveforms with zero voltage-time integral. A design for such a pulse generator is described that is itself one hundred percent efficient and which is well suited to existing pulse power techniques. Two accelerator cavity designs are described that can couple the pulse from such a generator to the beam; one of these designs provides voltage doubling. Comparison is made between the accelerating gradients that can be obtained with this and the preceding types of induction accelerator.

Components for monolithic fiber chirped pulse amplification laser systems

NASA Astrophysics Data System (ADS)

Swan, Michael Craig

The first portion of this work develops techniques for generating femtosecond-pulses from conventional fabry-perot laser diodes using nonlinear-spectral-broadening techniques in Yb-doped positive dispersion fiber ampliers. The approach employed an injection-locked fabry-perot laser diode followed by two stages of nonlinear-spectral-broadening to generate sub-200fs pulses. This thesis demonstrated that a 60ps gain-switched fabry-perot laser-diode can be injection-locked to generate a single-longitudinal-mode pulse and compressed by nonlinear spectral broadening to 4ps. Two problems have been identified that must be resolved before moving forward with this approach. First, gain-switched pulses from a standard diode-laser have a number of characteristics not well suited for producing clean self-phase-modulation-broadened pulses, such as an asymmetric temporal shape, which has a long pulse tail. Second, though parabolic pulse formation occurs for any arbitrary temporal input pulse profile, deviation from the optimum parabolic input results in extensively spectrally modulated self-phase-modulation-broadened pulses. In conclusion, the approach of generating self-phase-modulation-broadened pulses from pulsed laser diodes has to be modified from the initial approach explored in this thesis. The first Yb-doped chirally-coupled-core ber based systems are demonstrated and characterized in the second portion of this work. Robust single-mode performance independent of excitation or any other external mode management techniques have been demonstrated in Yb-doped chirally-coupled-core fibers. Gain and power efficiency characteristics are not compromised in any way in this novel fiber structure up to the 87W maximum power achieved. Both the small signal gain at 1064nm of 30.3dB, and the wavelength dependence of the small signal gain were comparable to currently deployed large-mode-area-fiber technology. The efficiencies of the laser and amplifier were measured to be 75% and 54% respectively. With the inherent design tradeoff between the fundamental mode loss and higher order mode suppression, loss effects on system efficiency in different configurations were investigated. From these investigations it was seen that the slope-efficiency depends only on the total loss of the active fiber, and that when loss is present, the counter-propagating configuration has substantial advantages over the co-propagating case. In this thesis chirally-coupled-core fiber as the technological basis for the next generation of monolithic high power fiber laser systems has been established.

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

DOEpatents

Nekoogar, Faranak [San Ramon, CA; Dowla, Farid U [Castro Valley, CA

2012-01-24

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

Power requirements reducing of FBG based all-optical switching

NASA Astrophysics Data System (ADS)

Scholtz, Ľubomír.; Solanská, Michaela; Ladányi, Libor; Müllerová, Jarmila

2017-12-01

Although Fiber Bragg gratings (FBGs) are well known devices, their using as all-optical switching elements has been still examined. Current research is focused on optimization of their properties for their using in future all-optical networks. The main problem are high switching intensities needed for achieving the changes of the transmission state. Over several years switching intensities have been reduced from hundreds of GW/cm2 to tens of MW/cm2 by selecting appropriate gratings and signal parameters or using suitable materials. Two principal nonlinear effects with similar power requirements can result in the bistable transmission/reflection of an input optical pulse. In the self-phase modulation (SPM) regime switching is achieved by the intense probe pulse itself. Using cross-phase modulation (XPM) a strong pump alters the FBG refractive index experienced by a weak probe pulse. As a result of this the detuning of the probe pulse from the center of the photonic band gap occurs. Using of XPM the effect of modulation instability is reduced. Modulation instability which is the main SPM degradation mechanism. We focused on nonlinear FBGs based on chalcogenide glasses which are very often used in various applications. Thanks to high nonlinear parameters chalcogenide glasses are suitable candidates for reducing switching intensities of nonlinear FBGs.

Characterization of pulse amplitude and pulse rate modulation for a human vestibular implant during acute electrical stimulation

NASA Astrophysics Data System (ADS)

Nguyen, T. A. K.; DiGiovanna, J.; Cavuscens, S.; Ranieri, M.; Guinand, N.; van de Berg, R.; Carpaneto, J.; Kingma, H.; Guyot, J.-P.; Micera, S.; Perez Fornos, A.

2016-08-01

Objective. The vestibular system provides essential information about balance and spatial orientation via the brain to other sensory and motor systems. Bilateral vestibular loss significantly reduces quality of life, but vestibular implants (VIs) have demonstrated potential to restore lost function. However, optimal electrical stimulation strategies have not yet been identified in patients. In this study, we compared the two most common strategies, pulse amplitude modulation (PAM) and pulse rate modulation (PRM), in patients. Approach. Four subjects with a modified cochlear implant including electrodes targeting the peripheral vestibular nerve branches were tested. Charge-equivalent PAM and PRM were applied after adaptation to baseline stimulation. Vestibulo-ocular reflex eye movement responses were recorded to evaluate stimulation efficacy during acute clinical testing sessions. Main results. PAM evoked larger amplitude eye movement responses than PRM. Eye movement response axes for lateral canal stimulation were marginally better aligned with PRM than with PAM. A neural network model was developed for the tested stimulation strategies to provide insights on possible neural mechanisms. This model suggested that PAM would consistently cause a larger ensemble firing rate of neurons and thus larger responses than PRM. Significance. Due to the larger magnitude of eye movement responses, our findings strongly suggest PAM as the preferred strategy for initial VI modulation.

Pulse Oximeter Plethysmographic Waveform Changes in Awake, Spontaneously Breathing, Hypovolemic Volunteers

DTIC Science & Technology

2011-02-01

Methods of Measurement All subjects were instrumented with 3 Nonin pulse oximeter sensors ( Nonin Medical, Plymouth, MN; OEM III module, 16-bit data...ring finger of the left hand. Unlike standard pulse oximeters that have autocalibration capability, the Nonin pulse oximeter did not alter the raw...stroke volume and are therefore presented as percentage change from baseline levels. The PPG and Spo2 values from the Nonin pulse oxime- ter sensors were

Super-contrast photoacoustic resonance imaging

NASA Astrophysics Data System (ADS)

Gao, Fei; Zhang, Ruochong; Feng, Xiaohua; Liu, Siyu; Zheng, Yuanjin

2018-02-01

In this paper, a new imaging modality, named photoacoustic resonance imaging (PARI), is proposed and experimentally demonstrated. Being distinct from conventional single nanosecond laser pulse induced wideband PA signal, the proposed PARI method utilizes multi-burst modulated laser source to induce PA resonant signal with enhanced signal strength and narrower bandwidth. Moreover, imaging contrast could be clearly improved than conventional single-pulse laser based PA imaging by selecting optimum modulation frequency of the laser source, which originates from physical properties of different materials beyond the optical absorption coefficient. Specifically, the imaging steps is as follows: 1: Perform conventional PA imaging by modulating the laser source as a short pulse to identify the location of the target and the background. 2: Shine modulated laser beam on the background and target respectively to characterize their individual resonance frequency by sweeping the modulation frequency of the CW laser source. 3: Select the resonance frequency of the target as the modulation frequency of the laser source, perform imaging and get the first PARI image. Then choose the resonance frequency of the background as the modulation frequency of the laser source, perform imaging and get the second PARI image. 4: subtract the first PARI image from the second PARI image, then we get the contrast-enhanced PARI results over the conventional PA imaging in step 1. Experimental validation on phantoms have been performed to show the merits of the proposed PARI method with much improved image contrast.

Generation and transmission of multilevel quadrature amplitude modulation formats using only one optical modulator: MATLAB Simulink simulation models

NASA Astrophysics Data System (ADS)

Binh, Le Nguyen

2009-04-01

A geometrical and phasor representation technique is presented to illustrate the modulation of the lightwave carrier to generate quadrature amplitude modulated (QAM) signals. The modulation of the amplitude and phase of the lightwave carrier is implemented using only one dual-drive Mach-Zehnder interferometric modulator (MZIM) with the assistance of phasor techniques. Any multilevel modulation scheme can be generated, but we illustrate specifically, the multilevel amplitude and differential phase shift keying (MADPSK) signals. The driving voltage levels are estimated for driving the traveling wave electrodes of the modulator. Phasor diagrams are extensively used to demonstrate the effectiveness of modulation schemes. MATLAB Simulink models are formed to generate the multilevel modulation formats, transmission, and detection in optically amplified fiber communication systems. Transmission performance is obtained for the multilevel optical signals and proven to be equivalent or better than those of binary level with equivalent bit rate. Further, the resilience to nonlinear effects is much higher for MADPSK of 50% and 33% pulse width as compared to non-return-to-zero (NRZ) pulse shaping.

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.

Error Rates and Channel Capacities in Multipulse PPM

NASA Technical Reports Server (NTRS)

Hamkins, Jon; Moision, Bruce

2007-01-01

A method of computing channel capacities and error rates in multipulse pulse-position modulation (multipulse PPM) has been developed. The method makes it possible, when designing an optical PPM communication system, to determine whether and under what conditions a given multipulse PPM scheme would be more or less advantageous, relative to other candidate modulation schemes. In conventional M-ary PPM, each symbol is transmitted in a time frame that is divided into M time slots (where M is an integer >1), defining an M-symbol alphabet. A symbol is represented by transmitting a pulse (representing 1) during one of the time slots and no pulse (representing 0 ) during the other M 1 time slots. Multipulse PPM is a generalization of PPM in which pulses are transmitted during two or more of the M time slots.

Modulational-instability-induced supercontinuum generation with saturable nonlinear response

NASA Astrophysics Data System (ADS)

Raja, R. Vasantha Jayakantha; Porsezian, K.; Nithyanandan, K.

2010-07-01

We theoretically investigate the supercontinuum generation (SCG) on the basis of modulational instability (MI) in liquid-core photonic crystal fibers (LCPCF) with CS2-filled central core. The effect of saturable nonlinearity of LCPCF on SCG in the femtosecond regime is studied using an appropriately modified nonlinear Schrödinger equation. We also compare the MI induced spectral broadening with SCG obtained by soliton fission. To analyze the quality of the pulse broadening, we study the coherence of the SC pulse numerically. It is evident from the numerical simulation that the response of the saturable nonlinearity suppresses the broadening of the pulse. We also observe that the MI induced SCG in the presence of saturable nonlinearity degrades the coherence of the SCG pulse when compared to unsaturated medium.

Modulational-instability-induced supercontinuum generation with saturable nonlinear response

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

Raja, R. Vasantha Jayakantha; Porsezian, K.; Nithyanandan, K.

2010-07-15

We theoretically investigate the supercontinuum generation (SCG) on the basis of modulational instability (MI) in liquid-core photonic crystal fibers (LCPCF) with CS{sub 2}-filled central core. The effect of saturable nonlinearity of LCPCF on SCG in the femtosecond regime is studied using an appropriately modified nonlinear Schroedinger equation. We also compare the MI induced spectral broadening with SCG obtained by soliton fission. To analyze the quality of the pulse broadening, we study the coherence of the SC pulse numerically. It is evident from the numerical simulation that the response of the saturable nonlinearity suppresses the broadening of the pulse. We alsomore » observe that the MI induced SCG in the presence of saturable nonlinearity degrades the coherence of the SCG pulse when compared to unsaturated medium.« less

Variable-pulse switching circuit accurately controls solenoid-valve actuations

NASA Technical Reports Server (NTRS)

Gillett, J. D.

1967-01-01

Solid state circuit generating adjustable square wave pulses of sufficient power operates a 28 volt dc solenoid valve at precise time intervals. This circuit is used for precise time control of fluid flow in combustion experiments.

Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser.

PubMed

Lv, Hui; Yu, Yonglin; Shu, Tan; Huang, Dexiu; Jiang, Shan; Barry, Liam P

2010-03-29

Photonic ultra-wideband (UWB) pulses are generated by direct current modulation of a semiconductor optical amplifier (SOA) section of an SOA-integrated sampled grating distributed Bragg reflector (SGDBR) laser. Modulation responses of the SOA section of the laser are first simulated with a microwave equivalent circuit model. Simulated results show a resonance behavior indicating the possibility to generate UWB signals with complex shapes in the time domain. The UWB pulse generation is then experimentally demonstrated for different selected wavelength channels with an SOA-integrated SGDBR laser.

VERNIER CHRONOTRON UTILIZING AT LEAST TWO SHORTED DELAY LINES

DOEpatents

Rufer, R.P.

1964-02-25

An improved vernier chronotron featuring pulse-forming circuits of a ringing'' or back and forth'' oscillatory type is described. A delay line shorted at both ends together with transistor circuitry to introduce a pulse into that line and also to provide reinforcement of the pulse as it oscillates between the pulse-reflective extremities is provided. A transistorized coincidence circuit is also provided. Enhanced measurement of time intervals in the nanosecond range is afforded. (AEC)

Biologically Inspired Waveform Diversity for Synthetic Autonomous Navigation Sensing

DTIC Science & Technology

2009-11-01

Pulse interval and repetition rate When searching for prey, bats often emit one pulse per wing beat . This is because the mechanics of flapping the...wings, breathing, and producing sound pulses are all coupled. Because of this coupling, the pulse repetition rate is often the same as wing beat ...give accurate measures of delay and hence range [26]. For determination of direction, the horizontal angle of a target is determined from binaural

Beam modulation: A novel ToF-technique for high resolution diffraction at the Beamline for European Materials Engineering Research (BEER)

NASA Astrophysics Data System (ADS)

Rouijaa, M.; Kampmann, R.; Šaroun, J.; Fenske, J.; Beran, P.; Müller, M.; Lukáš, P.; Schreyer, A.

2018-05-01

The Beamline for European Materials Engineering Research (BEER) is under construction at the European Spallation Source (ESS) in Lund, Sweden. A basic requirement on BEER is to make best use of the long ESS pulse (2.86 ms) for engineering investigations. High-resolution diffraction, however, demands timing resolution up to 0.1% corresponding to a pulse length down to about 70 μs for the case of thermal neutrons (λ ∼ 1.8 Å). Such timing resolution can be achieved by pulse shaping techniques cutting a short section out of the long pulse, and thus paying for resolution by strong loss of intensity. In contrast to this, BEER proposes a novel operation mode called pulse modulation technique based on a new chopper design, which extracts several short pulses out of the long ESS pulse, and hence leads to a remarkable gain of intensity compared to nowadays existing conventional pulse shaping techniques. The potential of the new technique can be used with full advantage for investigating strains and textures of highly symmetric materials. Due to its instrument design and the high brilliance of the ESS pulse, BEER is expected to become the European flagship for engineering research for strain mapping and texture analysis.

Multifunction audio digitizer for communications systems

NASA Technical Reports Server (NTRS)

Monford, L. G., Jr.

1971-01-01

Digitizer accomplishes both N bit pulse code modulation /PCM/ and delta modulation, and provides modulation indicating variable signal gain and variable sidetone. Other features include - low package count, variable clock rate to optimize bandwidth, and easily expanded PCM output.

Encoding and decoding amplitude-modulated cochlear implant stimuli—a point process analysis

PubMed Central

Shea-Brown, Eric; Rubinstein, Jay T.

2010-01-01

Cochlear implant speech processors stimulate the auditory nerve by delivering amplitude-modulated electrical pulse trains to intracochlear electrodes. Studying how auditory nerve cells encode modulation information is of fundamental importance, therefore, to understanding cochlear implant function and improving speech perception in cochlear implant users. In this paper, we analyze simulated responses of the auditory nerve to amplitude-modulated cochlear implant stimuli using a point process model. First, we quantify the information encoded in the spike trains by testing an ideal observer’s ability to detect amplitude modulation in a two-alternative forced-choice task. We vary the amount of information available to the observer to probe how spike timing and averaged firing rate encode modulation. Second, we construct a neural decoding method that predicts several qualitative trends observed in psychophysical tests of amplitude modulation detection in cochlear implant listeners. We find that modulation information is primarily available in the sequence of spike times. The performance of an ideal observer, however, is inconsistent with observed trends in psychophysical data. Using a neural decoding method that jitters spike times to degrade its temporal resolution and then computes a common measure of phase locking from spike trains of a heterogeneous population of model nerve cells, we predict the correct qualitative dependence of modulation detection thresholds on modulation frequency and stimulus level. The decoder does not predict the observed loss of modulation sensitivity at high carrier pulse rates, but this framework can be applied to future models that better represent auditory nerve responses to high carrier pulse rate stimuli. The supplemental material of this article contains the article’s data in an active, re-usable format. PMID:20177761

A Hierarchical Modulation Coherent Communication Scheme for Simultaneous Four-State Continuous-Variable Quantum Key Distribution and Classical Communication

NASA Astrophysics Data System (ADS)

Yang, Can; Ma, Cheng; Hu, Linxi; He, Guangqiang

2018-06-01

We present a hierarchical modulation coherent communication protocol, which simultaneously achieves classical optical communication and continuous-variable quantum key distribution. Our hierarchical modulation scheme consists of a quadrature phase-shifting keying modulation for classical communication and a four-state discrete modulation for continuous-variable quantum key distribution. The simulation results based on practical parameters show that it is feasible to transmit both quantum information and classical information on a single carrier. We obtained a secure key rate of 10^{-3} bits/pulse to 10^{-1} bits/pulse within 40 kilometers, and in the meantime the maximum bit error rate for classical information is about 10^{-7}. Because continuous-variable quantum key distribution protocol is compatible with standard telecommunication technology, we think our hierarchical modulation scheme can be used to upgrade the digital communication systems to extend system function in the future.

Performance improvement by orthogonal pulse amplitude modulation and discrete multitone modulation signals in hybrid fiber-visible laser light communication system

NASA Astrophysics Data System (ADS)

Zhang, Fangliu; He, Jing; Deng, Rui; Chen, Qinghui; Chen, Lin

2016-10-01

A modulation format, orthogonal pulse amplitude modulation and discrete multitone modulation (O-PAM-DMT), is experimentally demonstrated in a hybrid fiber-visible laser light communication (fiber-VLLC) system using a cost-effective directly modulated laser and blue laser diode. In addition, low overhead is achieved by utilizing only one training sequence to implement synchronization and channel estimation. Through adjusting the ratio of PAM and DMT signal, three types of O-PAM-DMT signals are investigated. After transmission over a 20-km standard single-mode fiber and 5-m free-space VLLC, the receiver sensitivity for 4.36-Gbit/s O-PAM-DMT signals can be improved by 0.4, 1.4, and 2.7 dB, respectively, at a bit error rate of 1×10-3, compared with a conventional DMT signal.

FPGA Techniques Based New Hybrid Modulation Strategies for Voltage Source Inverters

PubMed Central

Sudha, L. U.; Baskaran, J.; Elankurisil, S. A.

2015-01-01

This paper corroborates three different hybrid modulation strategies suitable for single-phase voltage source inverter. The proposed method is formulated using fundamental switching and carrier based pulse width modulation methods. The main tale of this proposed method is to optimize a specific performance criterion, such as minimization of the total harmonic distortion (THD), lower order harmonics, switching losses, and heat losses. The proposed method is articulated using fundamental switching and carrier based pulse width modulation methods. Thus, the harmonic pollution in the power system will be reduced and the power quality will be augmented with better harmonic profile for a target fundamental output voltage. The proposed modulation strategies are simulated in MATLAB r2010a and implemented in a Xilinx spartan 3E-500 FG 320 FPGA processor. The feasibility of these modulation strategies is authenticated through simulation and experimental results. PMID:25821852

Microwave influence on the isolated heart function. 1: Effect of modulation

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

Pakhomov, A.G.; Dubovick, B.V.; Degtyariov, I.G.

1995-09-01

Dependence of the microwave effect on modulation parameters (pulse width, duty ratio, and peak intensity) was studied in an isolated frog auricle preparation. The rate and amplitude of spontaneous auricle twitches were measured during and after a 2 min exposure to 915 or 885 MHz microwaves and were compared to preexposure values. The studied ranges of modulation parameters were: pulse width, 10{sup {minus}6}--10{sup {minus}2} s; duty ratio, 7:100000, and peak specific absorption rate, 100--3,000 W/kg. Combinations of the parameters were chosen by chance, and about 400 various exposure regimes were tested. The experiments established that no regime was effective unlessmore » the average microwave power was high enough to induce preparation heating (0.1--0.4 C). The twitch rate instantly increased, and the amplitude decreased, as the temperature rose; similar changes could be induced by equivalent conventional heating. the data provide evidence that the effect of short-term microwave exposure on the isolated heart pacemaker and contractile functions depends on pulse modulation just as much as modulation determines the average absorbed power. These functions demonstrated no specific dependence on exposure parameters such as frequency or power windows.« less

Wave packet interferometry and quantum state reconstruction by acousto-optic phase modulation

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

Tekavec, Patrick F.; Dyke, Thomas R.; Marcus, Andrew H.

2006-11-21

Studies of wave packet dynamics often involve phase-selective measurements of coherent optical signals generated from sequences of ultrashort laser pulses. In wave packet interferometry (WPI), the separation between the temporal envelopes of the pulses must be precisely monitored or maintained. Here we introduce a new (and easy to implement) experimental scheme for phase-selective measurements that combines acousto-optic phase modulation with ultrashort laser excitation to produce an intensity-modulated fluorescence signal. Synchronous detection, with respect to an appropriately constructed reference, allows the signal to be simultaneously measured at two phases differing by 90 deg. Our method effectively decouples the relative temporal phasemore » from the pulse envelopes of a collinear train of optical pulse pairs. We thus achieve a robust and high signal-to-noise scheme for WPI applications, such as quantum state reconstruction and electronic spectroscopy. The validity of the method is demonstrated, and state reconstruction is performed, on a model quantum system - atomic Rb vapor. Moreover, we show that our measurements recover the correct separation between the absorptive and dispersive contributions to the system susceptibility.« less

Antibody responses of mice exposed to low-power microwaves under combined, pulse-and-amplitude modulation

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

Veyret, B.; Bouthet, C.; Deschaux, P.

Irradiation by pulsed microwaves (9.4 GHz, 1 microsecond pulses at 1,000/s), both with and without concurrent amplitude modulation (AM) by a sinusoid at discrete frequencies between 14 and 41 MHz, was assessed for effects on the immune system of Balb/C mice. The mice were immunized either by sheep red blood cells (SRBC) or by glutaric-anhydride conjugated bovine serum albumin (GA-BSA), then exposed to the microwaves at a low rms power density (30 microW/cm2; whole-body-averaged SAR approximately 0.015 W/kg). Sham exposure or microwave irradiation took place during each of five contiguous days, 10 h/day. The antibody response was evaluated by themore » plaque-forming cell assay (SRBC experiment) or by the titration of IgM and IgG antibodies (GA-BSA experiment). In the absence of AM, the pulsed field did not greatly alter immune responsiveness. In contrast, exposure to the field under the combined-modulation condition resulted in significant, AM-frequency-dependent augmentation or weakening of immune responses.« less

Background-free millimeter-wave ultra-wideband signal generation based on a dual-parallel Mach-Zehnder modulator.

PubMed

Zhang, Fangzheng; Pan, Shilong

2013-11-04

A novel scheme for photonic generation of a millimeter-wave ultra-wideband (MMW-UWB) signal is proposed and experimentally demonstrated based on a dual-parallel Mach-Zehnder modulator (DPMZM). In the proposed scheme, a single-frequency radio frequency (RF) signal is applied to one sub-MZM of the DPMZM to achieve optical suppressed-carrier modulation, and an electrical control pulse train is applied to the other sub-MZM biased at the minimum transmission point, to get an on/off switchable optical carrier. By filtering out the optical carrier with one of the first-order sidebands, and properly setting the amplitude of the control pulse, an MMW-UWB pulse train without the residual local oscillation is generated after photo-detection. The generated MMW-UWB signal is background-free, because the low-frequency components in the electrical spectrum are effectively suppressed. In the experiment, an MMW-UWB pulse train centered at 25 GHz with a 10-dB bandwidth of 5.5 GHz is successfully generated. The low frequency components are suppressed by 22 dB.

Pulse-voltammetric glucose detection at gold junction electrodes.

PubMed

Rassaei, Liza; Marken, Frank

2010-09-01

A novel glucose sensing concept based on the localized change or "modulation" in pH within a symmetric gold-gold junction electrode is proposed. A paired gold-gold junction electrode (average gap size ca. 500 nm) is prepared by simultaneous bipotentiostatic electrodeposition of gold onto two closely spaced platinum disk electrodes. For glucose detection in neutral aqueous solution, the potential of the "pH-modulator" electrode is set to -1.5 V vs saturated calomel reference electrode (SCE) to locally increase the pH, and simultaneously, either cyclic voltammetry or square wave voltammetry experiments are conducted at the sensor electrode. A considerable improvement in the sensor electrode response is observed when a normal pulse voltammetry sequence is applied to the modulator electrode (to generate "hydroxide pulses") and the glucose sensor electrode is operated with fixed bias at +0.5 V vs SCE (to eliminate capacitive charging currents). Preliminary data suggest good linearity for the glucose response in the medically relevant 1-10 mM concentration range (corresponding to 0.18-1.8 g L(-1)). Future electroanalytical applications of multidimensional pulse voltammetry in junction electrodes are discussed.

Accurate and agile digital control of optical phase, amplitude and frequency for coherent atomic manipulation of atomic systems.

PubMed

Thom, Joseph; Wilpers, Guido; Riis, Erling; Sinclair, Alastair G

2013-08-12

We demonstrate a system for fast and agile digital control of laser phase, amplitude and frequency for applications in coherent atomic systems. The full versatility of a direct digital synthesis radiofrequency source is faithfully transferred to laser radiation via acousto-optic modulation. Optical beatnotes are used to measure phase steps up to 2π, which are accurately implemented with a resolution of ≤ 10 mrad. By linearizing the optical modulation process, amplitude-shaped pulses of durations ranging from 500 ns to 500 ms, in excellent agreement with the programmed functional form, are demonstrated. Pulse durations are limited only by the 30 ns rise time of the modulation process, and a measured extinction ratio of > 5 × 10(11) is achieved. The system presented here was developed specifically for controlling the quantum state of trapped ions with sequences of multiple laser pulses, including composite and bichromatic pulses. The demonstrated techniques are widely applicable to other atomic systems ranging across quantum information processing, frequency metrology, atom interferometry, and single-photon generation.

Cavity length dependence of mode beating in passively Q-switched Nd-solid state lasers

NASA Astrophysics Data System (ADS)

Zameroski, Nathan D.; Wanke, Michael; Bossert, David

2013-03-01

The temporal intensity profile of pulse(s) from passively Q-switched and passively Q-switched mode locked (QSML) solid-state lasers is known to be dependent on cavity length. In this work, the pulse width, modulation depth, and beat frequencies of a Nd:Cr:GSGG laser using a Cr+4:YAG passive Q-switch are investigated as function cavity length. Measured temporal widths are linearly correlated with cavity length but generally 3-5 ns larger than theoretical predictions. Some cavity lengths exhibit pulse profiles with no modulation while other lengths exhibit complete amplitude modulation. The observed beat frequencies at certain cavity lengths cannot be accounted for with passively QSML models in which the pulse train repetition rate is τRT-1, τRT= round-trip time. They can be explained, however, by including coupled cavity mode-locking effects. A theoretical model developed for a two section coupled cavity semiconductor laser is adapted to a solid-state laser to interpret measured beat frequencies. We also numerically evaluate the temporal criterion required to achieve temporally smooth Q-switched pulses, versus cavity length and pump rate. We show that in flash lamp pumped systems, the difference in buildup time between longitudinal modes is largely dependent on the pump rate. In applications where short pulse delay is important, the pumping rate may limit the ability to achieve temporally smooth pulses in passively Q-switched lasers. Simulations support trends in experimental data. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

High power high repetition rate VCSEL array side-pumped pulsed blue laser

NASA Astrophysics Data System (ADS)

van Leeuwen, Robert; Zhao, Pu; Chen, Tong; Xu, Bing; Watkins, Laurence; Seurin, Jean-Francois; Xu, Guoyang; Miglo, Alexander; Wang, Qing; Ghosh, Chuni

2013-03-01

High power, kW-class, 808 nm pump modules based on the vertical-cavity surface-emitting laser (VCSEL) technology were developed for side-pumping of solid-state lasers. Two 1.2 kW VCSEL pump modules were implemented in a dual side-pumped Q-switched Nd:YAG laser operating at 946 nm. The laser output was frequency doubled in a BBO crystal to produce pulsed blue light. With 125 μs pump pulses at a 300 Hz repetition rate 6.1 W QCW 946 nm laser power was produced. The laser power was limited by thermal lensing in the Nd:YAG rod.

Giant asymmetric self-phase modulation in superconductor thin films

NASA Astrophysics Data System (ADS)

Robson, Charles W.; Biancalana, Fabio

2018-04-01

Self-phase modulation (SPM) of light pulses is found to occur strongly, at low incident intensities, in the coupling of light with superconductors. We develop a theory from a synthesis of the time-dependent Ginzburg-Landau (TDGL) equation and basic electrodynamics which shows the strongly non-linear phase accumulated in the interaction. Unusually, the SPM of the pulse in this system is found to be highly asymmetric, producing a strongly redshifted spectrum when interacting with a superconducting thin film, and it develops in just a few nanometers of propagation. In this paper we present theoretical results and simulations in the THz regime, for both hyperbolic secant and supergaussian-shaped pulses.

PULSE SORTER

DOEpatents

Wade, E.J.

1958-07-29

An apparatus is described for counting and recording the number of electrical pulses occurring in each of a timed sequence of groups of pulses. The particular feature of the invention resides in a novel timing circuit of the univibrator type which provides very accurately timed pulses for opening each of a series of coincidence channels in sequence. The univibrator is shown incorporated in a pulse analyzing system wherein a series of pulse counting channels are periodically opened in order, one at a time, for a predetermtned open time interval, so that only one channel will be open at the time of occurrence of any of the electrical pulses to be sorted.

A Quantitative Analysis of Pulsed Signals Emitted by Wild Bottlenose Dolphins.

PubMed

Luís, Ana Rita; Couchinho, Miguel N; Dos Santos, Manuel E

2016-01-01

Common bottlenose dolphins (Tursiops truncatus), produce a wide variety of vocal emissions for communication and echolocation, of which the pulsed repertoire has been the most difficult to categorize. Packets of high repetition, broadband pulses are still largely reported under a general designation of burst-pulses, and traditional attempts to classify these emissions rely mainly in their aural characteristics and in graphical aspects of spectrograms. Here, we present a quantitative analysis of pulsed signals emitted by wild bottlenose dolphins, in the Sado estuary, Portugal (2011-2014), and test the reliability of a traditional classification approach. Acoustic parameters (minimum frequency, maximum frequency, peak frequency, duration, repetition rate and inter-click-interval) were extracted from 930 pulsed signals, previously categorized using a traditional approach. Discriminant function analysis revealed a high reliability of the traditional classification approach (93.5% of pulsed signals were consistently assigned to their aurally based categories). According to the discriminant function analysis (Wilk's Λ = 0.11, F3, 2.41 = 282.75, P < 0.001), repetition rate is the feature that best enables the discrimination of different pulsed signals (structure coefficient = 0.98). Classification using hierarchical cluster analysis led to a similar categorization pattern: two main signal types with distinct magnitudes of repetition rate were clustered into five groups. The pulsed signals, here described, present significant differences in their time-frequency features, especially repetition rate (P < 0.001), inter-click-interval (P < 0.001) and duration (P < 0.001). We document the occurrence of a distinct signal type-short burst-pulses, and highlight the existence of a diverse repertoire of pulsed vocalizations emitted in graded sequences. The use of quantitative analysis of pulsed signals is essential to improve classifications and to better assess the contexts of emission, geographic variation and the functional significance of pulsed signals.

Analysis of originating ultra-short optical dissipative solitary pulses in the actively mode-locked semiconductor heterolasers with an external fiber cavity

NASA Astrophysics Data System (ADS)

Shcherbakov, Alexandre S.; Campos Acosta, Joaquin; Pons Aglio, Alicia; Moreno Zarate, Pedro; Mansurova, Svetlana

2010-06-01

We present an advanced approach to describing low-power trains of bright picosecond optical dissipative solitary pulses with an internal frequency modulation in practically important case of exploiting semiconductor heterolaser operating in near-infrared range in the active mode-locking regime. In the chosen schematic arrangement, process of the active mode-locking is caused by a hybrid nonlinear cavity consisting of this heterolaser and an external rather long single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and small linear optical losses. Our analysis of shaping dissipative solitary pulses includes three principal contributions associated with the modulated gain, total optical losses, as well as with linear and nonlinear phase shifts. In fact, various trains of the non-interacting to one another optical dissipative solitons appear within simultaneous balance between the second-order dispersion and cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in a hybrid cavity. Our specific approach makes possible taking the modulating signals providing non-conventional composite regimes of a multi-pulse active mode-locking. Within our model, a contribution of the appearing nonlinear Ginzburg-Landau operator to the parameters of dissipative solitary pulses is described via exploiting an approximate variational procedure involving the technique of trial functions.

Hybrid Modeling of SiH4/Ar Discharge in a Pulse Modulated RF Capacitively Coupled Plasma

NASA Astrophysics Data System (ADS)

Xi-Feng, Wang; Yuan-Hong, Song; You-Nian, Wang; PSEG Team

2015-09-01

Pulsed plasmas have offered important advantages in future micro-devices, especially for electronegative gas plasmas. In this work, a one-dimensional fluid and Monte-Carlo (MC) hybrid model is developed to simulate SiH4/Ar discharge in a pulse modulated radio-frequency (RF) capacitively coupled plasma (CCP). Time evolution densities of different species, such as electrons, ions, radicals, are calculated, as well as the electron energy probability function (EEPF) which is obtained by a MC simulation. By pulsing the RF source, the electron energy distributions and plasma properties can be modulated by pulse frequency and duty cycle. High electron energy tails are obtained during power-on period, with the SiHx densities increasing rapidly mainly by SiH4 dissociation. As the RF power is off, the densities in the bulk region decrease rapidly owing to high energy electrons disappear, but increase near electrodes since diffusion without the confinement of high electric field, which can prolong the time of radials deposition on the plate. Especially, in the afterglow, the increase of negative ions near the electrodes results from cool electron attachment, which are good for film deposition. This work was supported by the National Natural Science Foundation of China (Grant No. 11275038).

Tailpulse signal generator

DOEpatents

Baker, John [Walnut Creek, CA; Archer, Daniel E [Knoxville, TN; Luke, Stanley John [Pleasanton, CA; Decman, Daniel J [Livermore, CA; White, Gregory K [Livermore, CA

2009-06-23

A tailpulse signal generating/simulating apparatus, system, and method designed to produce electronic pulses which simulate tailpulses produced by a gamma radiation detector, including the pileup effect caused by the characteristic exponential decay of the detector pulses, and the random Poisson distribution pulse timing for radioactive materials. A digital signal process (DSP) is programmed and configured to produce digital values corresponding to pseudo-randomly selected pulse amplitudes and pseudo-randomly selected Poisson timing intervals of the tailpulses. Pulse amplitude values are exponentially decayed while outputting the digital value to a digital to analog converter (DAC). And pulse amplitudes of new pulses are added to decaying pulses to simulate the pileup effect for enhanced realism in the simulation.

Applications of Space-Time Duality

NASA Astrophysics Data System (ADS)

Plansinis, Brent W.

The concept of space-time duality is based on a mathematical analogy between paraxial diffraction and narrowband dispersion, and has led to the development of temporal imaging systems. The first part of this thesis focuses on the development of a temporal imaging system for the Laboratory for Laser Energetics. Using an electro-optic phase modulator as a time lens, a time-to-frequency converter is constructed capable of imaging pulses between 3 and 12 ps. Numerical simulations show how this system can be improved to image the 1-30 ps range used in OMEGA-EP. By adjusting the timing between the pulse and the sinusoidal clock of the phase modulator, the pulse spectrum can be selectively narrowed, broadened, or shifted. An experimental demonstration of this effect achieved spectral narrowing and broadening by a factor of 2. Numerical simulations show narrowing by a factor of 8 is possible with modern phase modulators. The second part of this thesis explores the space-time analog of reflection and refraction from a moving refractive index boundary. From a physics perspective, a temporal boundary breaks translational symmetry in time, requiring the momentum of the photon to remain unchanged while its energy may change. This leads to a shifting and splitting of the pulse spectrum as the boundary is crossed. Equations for the reflected and transmitted frequencies and a condition for total internal reflection are found. Two of these boundaries form a temporal waveguide, which confines the pulse to a narrow temporal window. These waveguides have a finite number of modes, which do not change during propagation. A single-mode waveguide can be created, allowing only a single pulse shape to form within the waveguide. Temporal reflection and refraction produce a frequency dependent phase shift on the incident pulse, leading to interference fringes between the incident light and the reflected light. In a waveguide, this leads to self-imaging, where the pulse shape reforms periodically at finite propagation lengths. Numerical simulations are performed for the specific case where the moving boundary is produced through cross-phase modulation. In this case, the Kerr nonlinearity causes the boundary to change during propagation, leading to unique temporal and spectral behavior.

Ultra-narrow band diode lasers with arbitrary pulse shape modulation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ryasnyanskiy, Aleksandr I.; Smirnov, Vadim; Mokhun, Oleksiy; Glebov, Alexei L.; Glebov, Leon B.

2017-03-01

Wideband emission spectra of laser diode bars (several nanometers) can be largely narrowed by the usage of thick volume Bragg gratings (VBGs) recorded in photo-thermo-refractive glass. Such narrowband systems, with GHz-wide emission spectra, found broad applications for Diode Pumped Alkali vapor Lasers, optically pumped rare gas metastable lasers, Spin Exchange Optical Pumping, atom cooling, etc. Although the majority of current applications of narrow line diode lasers require CW operation, there are a variety of fields where operation in a different pulse mode regime is necessary. Commercial electric pulse generators can provide arbitrary current pulse profiles (sinusoidal, rectangular, triangular and their combinations). The pulse duration and repetition rate however, have an influence on the laser diode temperature, and therefore, the emitting wavelength. Thus, a detailed analysis is needed to understand the correspondence between the optical pulse profiles from a diode laser and the current pulse profiles; how the pulse profile and duty cycle affects the laser performance (e.g. the wavelength stability, signal to noise ratio, power stability etc.). We present the results of detailed studies of the narrowband laser diode performance operating in different temporal regimes with arbitrary pulse profiles. The developed narrowband (16 pm) tunable laser systems at 795 nm are capable of operating in different pulse regimes while keeping the linewidth, wavelength, and signal-to-noise ratio (>20 dB) similar to the corresponding CW modules.

Quaternary pulse position modulation electronics for free-space laser communications

NASA Technical Reports Server (NTRS)

Budinger, J. M.; Kerslake, S. D.; Nagy, L. A.; Shalkhauser, M. J.; Soni, N. J.; Cauley, M. A.; Mohamed, J. H.; Stover, J. B.; Romanofsky, R. R.; Lizanich, P. J.

1991-01-01

The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (GPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented.

Response of surge protection devices to fast rising pulses

NASA Technical Reports Server (NTRS)

Mindel, I. N.

1980-01-01

Two types of lightning protection modules incorporating leadless (pill type) Zener like devices were evaluated with regard to their ability to suppress EMP induced transients. Two series of tests were performed to evaluate the ability of these modules to react to fast rate of rise ( 1Kv/ns) transients, and the attenuation introduced and the ability to limit damped sinusoid pulses which may be induced due to an EMP resulting from a nuclear detonation.

Quaternary pulse position modulation electronics for free-space laser communications

NASA Technical Reports Server (NTRS)

Budinger, J. M.; Kerslake, S. D.; Nagy, L. A.; Shalkhauser, M. J.; Soni, N. J.; Cauley, M. A.; Mohamed, J. H.; Stover, J. B.; Romanofsky, R. R.; Lizanich, P. J.

1991-01-01

The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (QPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented.

Photonic generation of background-free millimeter-wave ultra-wideband pulses based on a single dual-drive Mach-Zehnder modulator.

PubMed

Li, Wei; Wang, Wen Ting; Sun, Wen Hui; Wang, Li Xian; Zhu, Ning Hua

2014-03-01

We propose a novel photonic approach for generating a background-free millimeter-wave (MMW) ultra-wideband (UWB) signal based on a conventional dual-drive Mach-Zehnder modulator (DMZM). One arm of the DMZM is driven by a local oscillator (LO) signal. The LO power is optimized to realize optical carrier suppressed modulation. The other arm is fed by a rectangular signal. The MMW UWB pulses are generated by truncating the continuous wave LO signal into a pulsed one in a photodetector (PD). The generated MMW UWB signal is background-free by eliminating the baseband frequency components because the optical power launched to the PD keeps constant all the time. The proposed method is theoretically analyzed and experimentally verified. The generated MMW UWB signal centered at a frequency of 26 GHz meets the Federal Communications Commission spectral mask very well.

Analysis of High Power IGBT Short Circuit Failures

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

Pappas, G.

2005-02-11

The Next Linear Collider (NLC) accelerator proposal at SLAC requires a highly efficient and reliable, low cost, pulsed-power modulator to drive the klystrons. A solid-state induction modulator has been developed at SLAC to power the klystrons; this modulator uses commercial high voltage and high current Insulated Gate Bipolar Transistor (IGBT) modules. Testing of these IGBT modules under pulsed conditions was very successful; however, the IGBTs failed when tests were performed into a low inductance short circuit. The internal electrical connections of a commercial IGBT module have been analyzed to extract self and mutual partial inductances for the main current pathsmore » as well as for the gate structure. The IGBT module, together with the partial inductances, has been modeled using PSpice. Predictions for electrical paths that carry the highest current correlate with the sites of failed die under short circuit tests. A similar analysis has been carried out for a SLAC proposal for an IGBT module layout. This paper discusses the mathematical model of the IGBT module geometry and presents simulation results.« less

Higher-order modulation instability in nonlinear fiber optics.

PubMed

Erkintalo, Miro; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe; Akhmediev, Nail; Dudley, John M; Genty, Goëry

2011-12-16

We report theoretical, numerical, and experimental studies of higher-order modulation instability in the focusing nonlinear Schrödinger equation. This higher-order instability arises from the nonlinear superposition of elementary instabilities, associated with initial single breather evolution followed by a regime of complex, yet deterministic, pulse splitting. We analytically describe the process using the Darboux transformation and compare with experiments in optical fiber. We show how a suitably low frequency modulation on a continuous wave field induces higher-order modulation instability splitting with the pulse characteristics at different phases of evolution related by a simple scaling relationship. We anticipate that similar processes are likely to be observed in many other systems including plasmas, Bose-Einstein condensates, and deep water waves. © 2011 American Physical Society

Jitter model and signal processing techniques for pulse width modulation optical recording

NASA Technical Reports Server (NTRS)

Liu, Max M.-K.

1991-01-01

A jitter model and signal processing techniques are discussed for data recovery in Pulse Width Modulation (PWM) optical recording. In PWM, information is stored through modulating sizes of sequential marks alternating in magnetic polarization or in material structure. Jitter, defined as the deviation from the original mark size in the time domain, will result in error detection if it is excessively large. A new approach is taken in data recovery by first using a high speed counter clock to convert time marks to amplitude marks, and signal processing techniques are used to minimize jitter according to the jitter model. The signal processing techniques include motor speed and intersymbol interference equalization, differential and additive detection, and differential and additive modulation.

Proceeding of the 1999 Particle Accelerator Conference. Volume 1

DTIC Science & Technology

1999-04-02

protons -e.6 within a 35-ns wide pulse . Dynamic shots of high - explosive (HE) during detonation usually had pulses spaced at 1-microsecond intervals... protons per pulse could be obtained by 800 Radiography on a Dynamic Object," 1 1th Biennial Nuclear Explosives MeV H’ injection from the existing 800 MeV...3713 Pondermotive Acceleration of Ions By Relativistically Self-Focused High- Intensity Short Pulse Laser -- A.Maksimchuky, S.Gu, K.Flippo,

Properties of the unusually short pulse sequences occurring prior to the first strokes of negative cloud-to-ground lightning flashes

NASA Astrophysics Data System (ADS)

Kolmasova, Ivana; Santolik, Ondrej; Farges, Thomas; Rison, William; Lan, Radek; Uhlir, Ludek

2014-05-01

We analyze pulse sequences occurring prior to first return strokes of negative cloud-to-ground lightning flashes. The magnetic-field waveforms are measured close to the thunderstorm using a broad-band analyzer with a sampling interval of 12.5 ns. The electric-field waveforms are measured at the distance of ~ 400 km using an analyzer with a sampling interval of 80 ns. The sequence is usually composed of three parts. It begins with a larger pulse train which is believed to be connected with initial breakdown processes. The train of preliminary breakdown pulses ("B" part) is followed by a relatively low and irregular pulse activity ("I" part), which is sometimes missing. The sequence ends with a pulse train attributed to the stepped leader ("L" part). We recognize two different patterns ("B-I-L" and "B-L" types) in recorded waveforms. For the first time, we analyze the time evolution of the pulse amplitudes in the "B" part of "B-I-L" type sequences. The pulse amplitude is decreasing on average by 34% of the maximum value within a given train. We observe an unusually short duration of sequences. This is probably linked to a low height of the thundercloud. Another possible explanation may be based on an untypical precipitation mix resulting in faster steeped leaders.

Independent and combined effects of resting heart rate and pulse pressure with metabolic syndrome in Chinese rural population: The Henan Rural Cohort study.

PubMed

Zhang, Xia; Li, Yuqian; Wang, Fang; Zang, Jianguo; Liu, Xiaotian; Zhang, Honglei; Yang, Kaili; Zhang, Gongyuan; Wang, Chongjian

2018-06-07

We examined the independent and cumulative associations of resting heart rate and pulse pressure with metabolic syndrome in Chinese rural population based on epidemiological research. A total of 38,708 participants were derived from the Henan Rural Cohort study. Restricted cubic splines and logistic regression model were used to estimate the odds ratios and 95% confidence intervals of metabolic syndrome risk in relation to resting heart rate and pulse pressure. After adjusting for potential confounders, the odds ratio (95% confidence intervals) of resting heart rate and pulse pressure in the highest quartile with the risk of metabolic syndrome were 1.59 (1.48-1.70) and1.81 (1.67-1.95), respectively. Simultaneously, the cumulative effect analysis indicated that the adjusted the odd ratio of resting heart rate and pulse pressure in the highest quartile was 2.89 (2.40-3.47). Furthermore, there was a significantly additive interaction between resting heart rate and pulse pressure on the risk of metabolic syndrome. Increased resting heart rate and pulse pressure are associated with the higher risk of metabolic syndrome as well as the influences of resting heart rate with pulse pressure might cumulatively increase the risk of metabolic syndrome. However, the potential clinical application remains to be determined. Copyright © 2018. Published by Elsevier B.V.

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

Implementation of STUD Pulses at the Trident Laser and Initial Results

NASA Astrophysics Data System (ADS)

Johnson, R. P.; Shimada, T.; Montgomery, D. S.; Afeyan, B.; Hüller, S.

2012-10-01

Controlling and mitigating laser-plasma instabilities such as stimulated Brillouin scattering, stimulated Raman scattering, and crossed-beam energy transfer is important to achieve high-gain inertial fusion using laser drivers. Recent theory and simulations show that these instabilities can be largely controlled using laser pulses consisting of spike trains of uneven duration and delay (STUD) by modulating the laser on a picosecond time scale [1,2]. We have designed and implemented a STUD pulse generator at the LANL Trident Laser Facility using Fourier synthesis to produce a 0.5-ns envelope of psec-duration STUD pulses using a spatial light modulator. Initial results from laser propagation tests and measurements as well as initial laser-plasma characterization experiments will be presented.[4pt] [1] B. Afeyan and S. H"uller, ``Optimal Control of Laser Plasma Instabilities using STUD pulses,'' IFSA 2011, P.Mo.1, to appear in Euro. Phys. J. Web of Conf. (2012).[2] S. H"uller and B. Afeyan, ``Simulations of drastically reduced SBS with STUD pulses,'' IFSA 2011, O.Tu8-1, to appear in Euro. Phys. J. Web of Conf. (2012).

Miniature Optical Communications Transceiver (MOCT)

NASA Technical Reports Server (NTRS)

Conklin, John W.; Hunter, Roger C.; Baker, Christopher

2017-01-01

This project will advance the technology readiness of the Miniature Optical Communications Transceiver (MOCT) from TRL 3 to TRL 4. MOCT consists of a novel software-defined pulse modulator (SDPM),integrated laser system, and avalanche photodetection system, and is designed for optical communications between small spacecraft, including CubeSats, using a pulse position modulation (PPM) scheme. PPM encodes data in the timing of optical pulses with respect to a set of timing windows known as slots. The MOCT design focuses on power-efficiency making it particularly interesting for small satellites. We have demonstrated in the laboratory that this technology can generate shorter than 1 nanosecond-wide 1550 nanometer (nm) optical pulses with better than 50 picosecond (ps) timing accuracy. The timing resolution of this system is roughly a factor of four better than previously flown systems, meaning that it can transmit more bits of data with each optical pulse. Because this technology can both generate and time stamp the arrival of short optical pulses with 50 ps precision, it simultaneously provides power efficient communications and relative ranging between small spacecraft at the centimeter (cm) level.

Mapping Rotational Wavepacket Dynamics with Chirped Probe Pulses

NASA Astrophysics Data System (ADS)

Romanov, Dmitri; Odhner, Johanan; Levis, Robert

2014-05-01

We develop an analytical model description of the strong-field pump-probe polarization spectroscopy of rotational transients in molecular gases in a situation when the probe pulse is considerably chirped: the frequency modulation over the pulse duration is comparable with the carrier frequency. In this scenario, a femtosecond pump laser pulse prepares a rotational wavepacket in a gas-phase sample at room temperature. The rotational revivals of the wavepacket are then mapped onto a chirped broadband probe pulse derived from a laser filament. The slow-varying envelope approximation being inapplicable, an alternative approach is proposed which is capable of incorporating the substantial chirp and the related temporal dispersion of refractive indices. Analytical expressions are obtained for the probe signal modulation over the interaction region and for the resulting heterodyned transient birefringence spectra. Dependencies of the outputs on the probe pulse parameters reveal the trade-offs and the ways to optimize the temporal-spectral imaging. The results are in good agreement with the experiments on snapshot imaging of rotational revival patterns in nitrogen gas. We gratefully acknowledge financial support through AFOSR MURI Grant No. FA9550-10-1-0561.

Quadrature demodulation based circuit implementation of pulse stream for ultrasonic signal FRI sparse sampling

NASA Astrophysics Data System (ADS)

Shoupeng, Song; Zhou, Jiang

2017-03-01

Converting ultrasonic signal to ultrasonic pulse stream is the key step of finite rate of innovation (FRI) sparse sampling. At present, ultrasonic pulse-stream-forming techniques are mainly based on digital algorithms. No hardware circuit that can achieve it has been reported. This paper proposes a new quadrature demodulation (QD) based circuit implementation method for forming an ultrasonic pulse stream. Elaborating on FRI sparse sampling theory, the process of ultrasonic signal is explained, followed by a discussion and analysis of ultrasonic pulse-stream-forming methods. In contrast to ultrasonic signal envelope extracting techniques, a quadrature demodulation method (QDM) is proposed. Simulation experiments were performed to determine its performance at various signal-to-noise ratios (SNRs). The circuit was then designed, with mixing module, oscillator, low pass filter (LPF), and root of square sum module. Finally, application experiments were carried out on pipeline sample ultrasonic flaw testing. The experimental results indicate that the QDM can accurately convert ultrasonic signal to ultrasonic pulse stream, and reverse the original signal information, such as pulse width, amplitude, and time of arrival. This technique lays the foundation for ultrasonic signal FRI sparse sampling directly with hardware circuitry.

Two-pulse control of Raman scattering in liquid methanol: The dominance of classical nonlinear optical effects

NASA Astrophysics Data System (ADS)

Spanner, Michael; Brumer, Paul

2006-02-01

Experimental results on adaptive feedback control of transient (i.e., nonimpulsive) Stokes emission in liquid methanol [Pearson and Bucksbaum, Phys. Rev. Lett. 92, 243003 (2004)] are analyzed. In the experiment, a pump pulse comprising two frequency-shifted Gaussian pulses was used to control the ratio of two Stokes emission lines by varying the relative phase ϕL between the pulses. Extending the theory of stimulated Raman scattering to accommodate two coupled levels, we show that control of this type is possible, in the strongly driven regime, using Raman coupling alone. Control via variation of ϕL is shown to also result from self- and cross-phase-modulation of the pump and Stokes pulses as well as via the focused-beam geometry of the pump pulse. In all cases, the general control mechanism is nonlinear optical modulation between the pump and the Stokes pulse; no coherent quantum interference effects are involved. Finally, although the vibrational populations are affected by the same control mechanisms that affect the Stokes spectra, the ratio of the Stokes spectra peak heights does not directly reflect the ratio of the level populations, as was assumed in the experiment.

Simultaneous Wireless Power Transfer and Data Communication Using Synchronous Pulse-Controlled Load Modulation.

PubMed

Mao, Shitong; Wang, Hao; Zhu, Chunbo; Mao, Zhi-Hong; Sun, Mingui

2017-10-01

Wireless Power Transfer (WPT) and wireless data communication are both important problems of research with various applications, especially in medicine. However, these two problems are usually studied separately. In this work, we present a joint study of both problems. Most medical electronic devices, such as smart implants, must have both a power supply to allow continuous operation and a communication link to pass information. Traditionally, separate wireless channels for power transfer and communication are utilized, which complicate the system structure, increase power consumption and make device miniaturization difficult. A more effective approach is to use a single wireless link with both functions of delivering power and passing information. We present a design of such a wireless link in which power and data travel in opposite directions. In order to aggressively miniaturize the implant and reduce power consumption, we eliminate the traditional multi-bit Analog-to-Digital Converter (ADC), digital memory and data transmission circuits all together. Instead, we use a pulse stream, which is obtained from the original biological signal, by a sigma-delta converter and an edge detector, to alter the load properties of the WPT channel. The resulting WPT signal is synchronized with the load changes therefore requiring no memory elements to record inter-pulse intervals. We take advantage of the high sensitivity of the resonant WPT to the load change, and the system dynamic response is used to transfer each pulse. The transient time of the WPT system is analyzed using the coupling mode theory (CMT). Our experimental results show that the memoryless approach works well for both power delivery and data transmission, providing a new wireless platform for the design of future miniaturized medical implants.

Counteracting radio frequency inhomogeneity in the human brain at 7 Tesla using strongly modulating pulses.

PubMed

Boulant, N; Mangin, J-F; Amadon, A

2009-05-01

We report flip angle and spoiled gradient echo measurements at 7 Tesla on human brains in three-dimensional imaging, using strongly modulating pulses to counteract the transmitted radiofrequency inhomogeneity problem. Compared with the standard square pulse results, three points of improvement are demonstrated, namely: (i) the removal of the bright center (typical at high fields when using a quadrature head coil), (ii) the substantial gain of signal in the regions of low B(1) intensity, and (iii) an increased 35% signal uniformity over the whole brain at the flip angle where maximum contrast between white and gray matter occurs. We also find by means of simulations that standard BIR-4 adiabatic pulses need several times more energy to reach a similar performance at the same field strength. (c) 2009 Wiley-Liss, Inc.

Pulse transducer with artifact signal attenuator. [heart rate sensors

NASA Technical Reports Server (NTRS)

Cash, W. H., Jr.; Polhemus, J. T. (Inventor)

1980-01-01

An artifact signal attenuator for a pulse rate sensor is described. The circuit for attenuating background noise signals is connected with a pulse rate transducer which has a light source and a detector for light reflected from blood vessels of a living body. The heart signal provided consists of a modulated dc signal voltage indicative of pulse rate. The artifact signal resulting from light reflected from the skin of the body comprises both a constant dc signal voltage and a modulated dc signal voltage. The amplitude of the artifact signal is greater and the frequency less than that of the heart signal. The signal attenuator circuit includes an operational amplifier for canceling the artifact signal from the output signal of the transducer and has the capability of meeting packaging requirements for wrist-watch-size packages.

Strong polarization-dependent terahertz modulation of aligned Ag nanowires on Si substrate.

PubMed

Lee, Gyuseok; Maeng, Inhee; Kang, Chul; Oh, Myoung-Kyu; Kee, Chul-Sik

2018-05-14

Optically tunable, strong polarization-dependent transmission of terahertz pulses through aligned Ag nanowires on a Si substrate is demonstrated. Terahertz pulses primarily pass through the Ag nanowires and the transmittance is weakly dependent on the angle between the direction of polarization of the terahertz pulse and the direction of nanowire alignment. However, the transmission of a terahertz pulse through optically excited materials strongly depends on the polarization direction. The extinction ratio increases as the power of the pumping laser increases. The enhanced polarization dependency is explained by the redistribution of photocarriers, which accelerates the sintering effect along the direction of alignment of the Ag nanowires. The photocarrier redistribution effect is examined by the enhancement of terahertz emission from the sample. Oblique metal nanowires on Si could be utilized for designing optically tunable terahertz polarization modulators.

A powerful graphical pulse sequence programming tool for magnetic resonance imaging.

PubMed

Jie, Shen; Ying, Liu; Jianqi, Li; Gengying, Li

2005-12-01

A powerful graphical pulse sequence programming tool has been designed for creating magnetic resonance imaging (MRI) applications. It allows rapid development of pulse sequences in graphical mode (allowing for the visualization of sequences), and consists of three modules which include a graphical sequence editor, a parameter management module and a sequence compiler. Its key features are ease to use, flexibility and hardware independence. When graphic elements are combined with a certain text expressions, the graphical pulse sequence programming is as flexible as text-based programming tool. In addition, a hardware-independent design is implemented by using the strategy of two step compilations. To demonstrate the flexibility and the capability of this graphical sequence programming tool, a multi-slice fast spin echo experiment is performed on our home-made 0.3 T permanent magnet MRI system.

Design and Testing of a Fast, 50 kV Solid-State Kicker Pulser

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

Cook, E G; Hickman, B C; Lee, B S

2002-06-24

The ability to extract particle beam bunches from a ring accelerator in arbitrary order can greatly extend an accelerator's capabilities and applications. A prototype solid-state kicker pulser capable of generating asynchronous bursts of 50 kV pulses has been designed and tested into a 50{Omega} load. The pulser features fast rise and fall times and is capable of generating an arbitrary pattern of pulses with a maximum burst frequency exceeding 5 MHz If required, the pulse-width of each pulse in the burst is independently adjustable. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy ismore » switched into each section of the adder by a parallel array of MOSFETs. Test data, capabilities, and limitations of the prototype pulser are described.« less

Comprehensive two-dimensional gas chromatography using partial modulation via a pulsed flow valve with a short modulation period.

PubMed

Freye, Chris E; Bahaghighat, H Daniel; Synovec, Robert E

2018-01-15

Partial modulation via a pulsed flow valve for comprehensive two-dimensional (2D) gas chromatography (GC × GC) is demonstrated, producing narrow peak widths, 2 W b , on the secondary separation dimension, 2 D, coupled with short modulation periods, P M , thus producing a high peak capacity on the 2 D dimension, 2 n c . The GC × GC modulator is a pulse flow valve that injects a pulse of carrier gas at the specified P M , at the connection between the primary, 1 D, column and the 2 D column. Using a commercially available pulse flow valve, this injection technique performs a combination of vacancy chromatography and frontal analysis, whereby each pulse disturbance in the analyte concentration profile as it exits the 1 D column results in data that is readily converted into a 2 D separation. A three-step process converts the raw data into a format analogous to a GC × GC separation, incorporating signal differentiation, baseline correction and conversion to a GC × GC chromatogram representation. A 115-component test mixture with a wide range of boiling points (36-372°C) of nine compound classes is demonstrated using modulation periods of P M = 50, 100, 250, and 500ms, respectively. For the test mixture with a P M of 250ms, peak shapes on 2 D are symmetric with apparent 2 W b ranging from 12 to 45ms producing a 2 n c of ~ 10. Based on the average peak width of 0.93s on the 1 D separation for a time window of 400s, the 1 D peak capacity is 1 n c ∼ 430. Thus, the ideal 2D peak capacity n c,2D is 4300 or a peak capacity production of 650 peaks/min using the P M of 250ms. Additionally, for a P M of 50, 100 and 500ms, the 2 n c are 4, 7, and 12, respectively. Retention times on 2 D, 2 t R , are reproducible having standard deviations less than 1ms. Finally, the processed data is shown to be quantitative, with an average RSD of 4.7% for test analytes. Copyright © 2017 Elsevier B.V. All rights reserved.

Effects of electrical stimulus composition on cardiac electrophysiology in a rodent model of electroconvulsive therapy.

PubMed

Singh, Nagendra Madan; Sathyaprabha, T N; Thirthalli, Jagadisha; Andrade, Chittaranjan

2018-01-01

No electroconvulsive therapy (ECT) study on humans or in animal models has so far examined whether differently composed electrical stimuli exert different cardiac electrophysiological effects at constant electrical dose. The subject is important because cardiac electrophysiological changes may provide indirect information about ECT seizure quality as modulated by stimulus composition. Adult female Wistar rats ( n = 20/group) received fixed, moderately suprathreshold (18 mC) electrical stimuli. This stimulus in each of eight groups was formed by varying pulse amplitude, pulse width, pulse frequency, and stimulus duration. The electrocardiogram was recorded, and time and frequency domain variables were examined in 30 s epochs in preictal (30 s before electroconvulsive shock [ECS]), early postictal (starting 15 s after stimulation), and late postictal (5 h after ECS) periods. Alpha for statistical significance was set at P < 0.01 to adjust for multiple hypothesis testing. Cardiac electrophysiological indices in the eight groups did not differ significantly at baseline. At both early and late postictal time points, almost no analysis yielded statistically significant differences between groups for four time domain variables, including heart rate and standard deviation of R-R intervals, and for six frequency domain variables, including low-frequency power, high-frequency power, and total power. Cardiac electrophysiological measures may not be helpful to identify differences in seizure quality that are driven by differences in the composition of electrical stimuli at constant, moderately suprathreshold electrical dose. The generalization of this conclusion to threshold electrical doses and to human contexts requires a study.

Excitation of collective modes in a quantum flute

NASA Astrophysics Data System (ADS)

Torfason, Kristinn; Manolescu, Andrei; Molodoveanu, Valeriu; Gudmundsson, Vidar

2012-06-01

We use a generalized master equation (GME) formalism to describe the nonequilibrium time-dependent transport of Coulomb interacting electrons through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire is modulated by out-of-phase time-dependent potentials that simulate a turnstile device. We explore this setup by keeping the contact with one lead at a fixed location at one end of the wire, whereas the contact with the other lead is placed on various sites along the length of the wire. We study the propagation of sinusoidal and rectangular pulses. We find that the current profiles in both leads depend not only on the shape of the pulses, but also on the position of the second contact. The current reflects standing waves created by the contact potentials, like in a wind musical instrument (for example, a flute), but occurring on the background of the equilibrium charge distribution. The number of electrons in our quantum “flute” device varies between two and three. We find that for rectangular pulses the currents in the leads may flow against the bias for short time intervals, due to the higher harmonics of the charge response. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method. The system (leads plus sample wire) is described by a lattice model.

Optimization of ultrasound parameters of myocardial cavitation microlesions for therapeutic application.

PubMed

Miller, Douglas L; Dou, Chunyan; Owens, Gabe E; Kripfgans, Oliver D

2014-06-01

Intermittent high intensity ultrasound scanning with contrast microbubbles can induce scattered cavitation microlesions in the myocardium, which may be of value for tissue reduction therapy. Anesthetized rats were treated in a heated water bath with 1.5 MHz focused ultrasound pulses, guided by an 8 MHz imaging transducer. The relative efficacy with 2 or 4 MPa pulses, 1:4 or 1:8 trigger intervals and 5 or 10 cycle pulses was explored in six groups. Electrocardiogram premature complexes (PCs) induced by the triggered pulse bursts were counted, and Evans blue stained cardiomyocyte scores (SCSs) were obtained. The increase from 2 to 4 MPa produced significant increases in PCs and SCSs and eliminated an anticipated decline in the rate of PC induction with time, which might hinder therapeutic efficacy. Increased intervals and pulse durations did not yield significant increases in the effects. The results suggest that cavitation microlesion production can be refined and potentially lead to a clinically robust therapeutic method. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Ventilation-Induced Modulation of Pulse Oximeter Waveforms: A Method for the Assessment of Early Changes in Intravascular Volume During Spinal Fusion Surgery in Pediatric Patients.

PubMed

Alian, Aymen A; Atteya, Gourg; Gaal, Dorothy; Golembeski, Thomas; Smith, Brian G; Dai, Feng; Silverman, David G; Shelley, Kirk

2016-08-01

Scoliosis surgery is often associated with substantial blood loss, requiring fluid resuscitation and blood transfusions. In adults, dynamic preload indices have been shown to be more reliable for guiding fluid resuscitation, but these indices have not been useful in children undergoing surgery. The aim of this study was to introduce frequency-analyzed photoplethysmogram (PPG) and arterial pressure waveform variables and to study the ability of these parameters to detect early bleeding in children during surgery. We studied 20 children undergoing spinal fusion. Electrocardiogram, arterial pressure, finger pulse oximetry (finger PPG), and airway pressure waveforms were analyzed using time domain and frequency domain methods of analysis. Frequency domain analysis consisted of calculating the amplitude density of PPG and arterial pressure waveforms at the respiratory and cardiac frequencies using Fourier analysis. This generated 2 measurements: The first is related to slow mean arterial pressure modulation induced by ventilation (also known as DC modulation when referring to the PPG), and the second corresponds to pulse pressure modulation (AC modulation or changes in the amplitude of pulse oximeter plethysmograph when referring to the PPG). Both PPG and arterial pressure measurements were divided by their respective cardiac pulse amplitude to generate DC% and AC% (normalized values). Standard hemodynamic data were also recorded. Data at baseline and after bleeding (estimated blood loss about 9% of blood volume) were presented as median and interquartile range and compared using Wilcoxon signed-rank tests; a Bonferroni-corrected P value <0.05 was considered statistically significant. There were significant increases in PPG DC% (median [interquartile range] = 359% [210 to 541], P = 0.002), PPG AC% (160% [87 to 251], P = 0.003), and arterial DC% (44% [19 to 84], P = 0.012) modulations, respectively, whereas arterial AC% modulations showed nonsignificant increase (41% [1 to 85], P = 0.12). The change in PPG DC% was significantly higher than that in PPG AC%, arterial DC%, arterial AC%, and systolic blood pressure with P values of 0.008, 0.002, 0.003, and 0.002, respectively. Only systolic blood pressure showed significant changes (11% [4 to 21], P = 0.003) between bleeding phase and baseline. Finger PPG and arterial waveform parameters (using frequency analysis) can track changes in blood volume during the bleeding phase, suggesting the potential for a noninvasive monitor for tracking changes in blood volume in pediatric patients. PPG waveform baseline modulation (PPG DC%) was more sensitive to changes in venous blood volume when compared with respiration-induced modulation seen in the arterial pressure waveform.

Rabi oscillation and electron-spin-echo envelope modulation of the photoexcited triplet spin system in silicon

NASA Astrophysics Data System (ADS)

Akhtar, Waseem; Sekiguchi, Takeharu; Itahashi, Tatsumasa; Filidou, Vasileia; Morton, John J. L.; Vlasenko, Leonid; Itoh, Kohei M.

2012-09-01

We report on a pulsed electron paramagnetic resonance (EPR) study of the photoexcited triplet state (S=1) of oxygen-vacancy centers in silicon. Rabi oscillations between the triplet sublevels are observed using coherent manipulation with a resonant microwave pulse. The Hahn echo and stimulated echo decay profiles are superimposed with strong modulations known as electron-spin-echo envelope modulation (ESEEM). The ESEEM spectra reveal a weak but anisotropic hyperfine coupling between the triplet electron spin and a 29Si nuclear spin (I=1/2) residing at a nearby lattice site, that cannot be resolved in conventional field-swept EPR spectra.

Development of a wideband pulse quaternary modulation system. [for an operational 400 Mbps baseband laser communication system

NASA Technical Reports Server (NTRS)

Federhofer, J. A.

1974-01-01

Laboratory data verifying the pulse quaternary modulation (PQM) theoretical predictions is presented. The first laboratory PQM laser communication system was successfully fabricated, integrated, tested and demonstrated. System bit error rate tests were performed and, in general, indicated approximately a 2 db degradation from the theoretically predicted results. These tests indicated that no gross errors were made in the initial theoretical analysis of PQM. The relative ease with which the entire PQM laboratory system was integrated and tested indicates that PQM is a viable candidate modulation scheme for an operational 400 Mbps baseband laser communication system.

Simplified flexible-PON upstream transmission using pulse position modulation at ONU and DSP-enabled soft-combining at OLT for adaptive link budgets.

PubMed

Liu, Xiang; Effenberger, Frank; Chand, Naresh

2015-03-09

We demonstrate a flexible modulation and detection scheme for upstream transmission in passive optical networks using pulse position modulation at optical network unit, facilitating burst-mode detection with automatic decision threshold tracking, and DSP-enabled soft-combining at optical line terminal. Adaptive receiver sensitivities of -33.1 dBm, -36.6 dBm and -38.3 dBm at a bit error ratio of 10(-4) are respectively achieved for 2.5 Gb/s, 1.25 Gb/s and 625 Mb/s after transmission over a 20-km standard single-mode fiber without any optical amplification.

The theory and implementation of a high quality pulse width modulated waveform synthesiser applicable to voltage FED inverters

NASA Astrophysics Data System (ADS)

Lower, Kim Nigel

1985-03-01

Modulation processes associated with the digital implementation of pulse width modulation (PWM) switching strategies were examined. A software package based on a portable turnkey structure is presented. Waveform synthesizer implementation techniques are reviewed. A three phase PWM waveform synthesizer for voltage fed inverters was realized. It is based on a constant carrier frequency of 18 kHz and a regular sample, single edge, asynchronous PWM switching scheme. With high carrier frequencies, it is possible to utilize simple switching strategies and as a consequence, many advantages are highlighted, emphasizing the importance to industrial and office markets.

A Pulse Code Modulated Fiber Optic Link Design for Quinault Under-Water Tracking Range.

DTIC Science & Technology

1980-09-01

invented and patented a light-wave communications device, the Photophone . The light beam was acoustically modulated, transmitted through the atmosphere and...a load resistor or feedback resistor. This voltage can be cal- culated by multiplying the received power, the respcnsiv ity and the effective load...frequency is not real critical since the clock, in effect , is synchronized after every eight bits by the timing pulse. The more interesting part of the

Theory of active mode locking of a semiconductor laser in an external cavity

NASA Technical Reports Server (NTRS)

Yeung, J. A.

1981-01-01

An analytical treatment is given for the active mode locking of a semiconductor laser in an external resonator. The width of the mode-locked pulses is obtained as a function of the laser and cavity parameters and the amount of frequency detuning. The effects of self-modulation and saturation are included in the treatment. The pulse output is compared with that obtained by a strong modulation of the laser diode with no external cavity.

Homodyne impulse radar hidden object locator

DOEpatents

McEwan, T.E.

1996-04-30

An electromagnetic detector is designed to locate an object hidden behind a separator or a cavity within a solid object. The detector includes a PRF generator for generating 2 MHz pulses, a homodyne oscillator for generating a 2 kHz square wave, and for modulating the pulses from the PRF generator. A transmit antenna transmits the modulated pulses through the separator, and a receive antenna receives the signals reflected off the object. The receiver path of the detector includes a sample and hold circuit, an AC coupled amplifier which filters out DC bias level shifts in the sample and hold circuit, and a rectifier circuit connected to the homodyne oscillator and to the AC coupled amplifier, for synchronously rectifying the modulated pulses transmitted over the transmit antenna. The homodyne oscillator modulates the signal from the PRF generator with a continuous wave (CW) signal, and the AC coupled amplifier operates with a passband centered on that CW signal. The present detector can be used in several applications, including the detection of metallic and non-metallic objects, such as pipes, studs, joists, nails, rebars, conduits and electrical wiring, behind wood wall, ceiling, plywood, particle board, dense hardwood, masonry and cement structure. The detector is portable, light weight, simple to use, inexpensive, and has a low power emission which facilitates the compliance with Part 15 of the FCC rules. 15 figs.

Homodyne impulse radar hidden object locator

DOEpatents

McEwan, Thomas E.

1996-01-01

An electromagnetic detector is designed to locate an object hidden behind a separator or a cavity within a solid object. The detector includes a PRF generator for generating 2 MHz pulses, a homodyne oscillator for generating a 2 kHz square wave, and for modulating the pulses from the PRF generator. A transmit antenna transmits the modulated pulses through the separator, and a receive antenna receives the signals reflected off the object. The receiver path of the detector includes a sample and hold circuit, an AC coupled amplifier which filters out DC bias level shifts in the sample and hold circuit, and a rectifier circuit connected to the homodyne oscillator and to the AC coupled amplifier, for synchronously rectifying the modulated pulses transmitted over the transmit antenna. The homodyne oscillator modulates the signal from the PRF generator with a continuous wave (CW) signal, and the AC coupled amplifier operates with a passband centered on that CW signal. The present detector can be used in several applications, including the detection of metallic and non-metallic objects, such as pipes, studs, joists, nails, rebars, conduits and electrical wiring, behind wood wall, ceiling, plywood, particle board, dense hardwood, masonry and cement structure. The detector is portable, light weight, simple to use, inexpensive, and has a low power emission which facilitates the compliance with Part 15 of the FCC rules.

Fear conditioning is associated with dynamic directed functional interactions between and within the human amygdala, hippocampus, and frontal lobe.

PubMed

Liu, C C; Crone, N E; Franaszczuk, P J; Cheng, D T; Schretlen, D S; Lenz, F A

2011-08-25

The current model of fear conditioning suggests that it is mediated through modules involving the amygdala (AMY), hippocampus (HIP), and frontal lobe (FL). We now test the hypothesis that habituation and acquisition stages of a fear conditioning protocol are characterized by different event-related causal interactions (ERCs) within and between these modules. The protocol used the painful cutaneous laser as the unconditioned stimulus and ERC was estimated by analysis of local field potentials recorded through electrodes implanted for investigation of epilepsy. During the prestimulus interval of the habituation stage FL>AMY ERC interactions were common. For comparison, in the poststimulus interval of the habituation stage, only a subdivision of the FL (dorsolateral prefrontal cortex, dlPFC) still exerted the FL>AMY ERC interaction (dlFC>AMY). For a further comparison, during the poststimulus interval of the acquisition stage, the dlPFC>AMY interaction persisted and an AMY>FL interaction appeared. In addition to these ERC interactions between modules, the results also show ERC interactions within modules. During the poststimulus interval, HIP>HIP ERC interactions were more common during acquisition, and deep hippocampal contacts exerted causal interactions on superficial contacts, possibly explained by connectivity between the perihippocampal gyrus and the HIP. During the prestimulus interval of the habituation stage, AMY>AMY ERC interactions were commonly found, while interactions between the deep and superficial AMY (indirect pathway) were independent of intervals and stages. These results suggest that the network subserving fear includes distributed or widespread modules, some of which are themselves "local networks." ERC interactions between and within modules can be either static or change dynamically across intervals or stages of fear conditioning. Copyright © 2011 IBRO. Published by Elsevier Ltd. All rights reserved.

Ultrafast two-photon absorption generated free-carrier modulation in a silicon nanoplasmonic resonator

NASA Astrophysics Data System (ADS)

Nielsen, M. P.; Elezzabi, A. Y.

2014-03-01

Ultrafast all-optical modulation in Ag/HfO2/Si/HfO2/Ag metal-insulator-semiconductor-insulator-metal (MISIM) nanoring resonators through two-photon absorption photogenerated free-carriers is studied using self-consistent 3-D finite difference time domain (FDTD) simulations. The self-consistent FDTD simulations incorporate the two-photon absorption, free carrier absorption, and plasma dispersion effects in silicon. The nanorings are aperture coupled to Ag/HfO2/Si(100nm)/HfO2/Ag MISIM waveguides by 300nm wide and 50nm deep apertures. The effects of pump pulse energy, HfO2 spacer thickness, and device footprint on the modulation characteristics are studied. Nanoring radius is varied between 540nm and 1μm, the HfO2 spacer thickness is varied between 10nm and 20nm, and the pump pulse energy is explored up to 60pJ. Modulation amplitude, switching time, average generated carrier density, and wavelength resonant shift is studied for each of the device configurations. In a compact device footprint of only 1.4μm2, a 13.1dB modulation amplitude was obtained with a switching time of only 2ps using a modest pump pulse energy of 16.0pJ. The larger bandwidth associated with more compact nanorings and thinner spacer layers is shown to result in increased modulation amplitude.

Characteristics of biosonar signals from the northern bottlenose whale, Hyperoodon ampullatus.

PubMed

Wahlberg, Magnus; Beedholm, Kristian; Heerfordt, Anders; Møhl, Bertel

2011-11-01

The biosonar pulses from free-ranging northern bottlenose whales (Hyperoodon ampullatus) were recorded with a linear hydrophone array. Signals fulfilling criteria for being recorded close to the acoustic axis of the animal (a total of 10 clicks) had a frequency upsweep from 20 to 55 kHz and durations of 207 to 377 μs (measured as the time interval containing 95% of the signal energy). The source level of these signals, denoted pulses, was 175-202 dB re 1 μPa rms at 1 m. The pulses had a directionality index of at least 18 dB. Interpulse intervals ranged from 73 to 949 ms (N = 856). Signals of higher repetition rates had interclick intervals of 5.8-13.1 ms (two sequences, made up of 59 and 410 clicks, respectively). These signals, denoted clicks, had a shorter duration (43-200 μs) and did not have the frequency upsweep characterizing the pulses of low repetition rates. The data show that the northern bottlenose whale emits signals similar to three other species of beaked whale. These signals are distinct from the three other types of biosonar signals of toothed whales. It remains unclear why the signals show this grouping, and what consequences it has on echolocation performance.

Application of millisecond pulsed laser for thermal fatigue property evaluation

NASA Astrophysics Data System (ADS)

Pan, Sining; Yu, Gang; Li, Shaoxia; He, Xiuli; Xia, Chunyang; Ning, Weijian; Zheng, Caiyun

2018-02-01

An approach based on millisecond pulsed laser is proposed for thermal fatigue property evaluation in this paper. Cyclic thermal stresses and strains within millisecond interval are induced by complex and transient temperature gradients with pulsed laser heating. The influence of laser parameters on surface temperature is studied. The combination of low pulse repetition rate and high pulse energy produces small temperature oscillation, while high pulse repetition rate and low pulse energy introduces large temperature shock. The possibility of application is confirmed by two thermal fatigue tests of compacted graphite iron with different laser controlled modes. The developed approach is able to fulfill the preset temperature cycles and simulate thermal fatigue failure of engine components.

Respiratory modulation of oscillometric cuff pressure pulses and Korotkoff sounds during clinical blood pressure measurement in healthy adults.

PubMed

Chen, Diliang; Chen, Fei; Murray, Alan; Zheng, Dingchang

2016-05-10

Accurate blood pressure (BP) measurement depends on the reliability of oscillometric cuff pressure pulses (OscP) and Korotkoff sounds (KorS) for automated oscillometric and manual techniques. It has been widely accepted that respiration is one of the main factors affecting BP measurement. However, little is known about how respiration affects the signals from which BP measurement is obtained. The aim was to quantify the modulation effect of respiration on oscillometric pulses and KorS during clinical BP measurement. Systolic and diastolic BPs were measured manually from 40 healthy subjects (from 23 to 65 years old) under normal and regular deep breathing. The following signals were digitally recorded during linear cuff deflation: chest motion from a magnetometer to obtain reference respiration, cuff pressure from an electronic pressure sensor to derive OscP, and KorS from a digital stethoscope. The effects of respiration on both OscP and KorS were determined from changes in their amplitude associated with respiration between systole and diastole. These changes were normalized to the mean signal amplitude of OscP and KorS to derive the respiratory modulation depth. Reference respiration frequency, and the frequencies derived from the amplitude modulation of OscP and KorS were also calculated and compared. Respiratory modulation depth was 14 and 40 % for OscP and KorS respectively under normal breathing condition, with significant increases (both p < 0.05) to 16 and 49 % with deeper breathing. There was no statistically significant difference between the reference respiration frequency and those derived from the oscillometric and Korotkoff signals (both p > 0.05) during deep breathing, and for the oscillometric signal during normal breathing (p > 0.05). Our study confirmed and quantified the respiratory modulation effect on the oscillometric pulses and KorS during clinical BP measurement, with increased modulation depth under regular deeper breathing.

Optical timing receiver for the NASA laser ranging system. Part 2: High precision time interval digitizer

NASA Technical Reports Server (NTRS)

Leskovar, B.; Turko, B.

1977-01-01

The development of a high precision time interval digitizer is described. The time digitizer is a 10 psec resolution stop watch covering a range of up to 340 msec. The measured time interval is determined as a separation between leading edges of a pair of pulses applied externally to the start input and the stop input of the digitizer. Employing an interpolation techniques and a 50 MHz high precision master oscillator, the equivalent of a 100 GHz clock frequency standard is achieved. Absolute accuracy and stability of the digitizer are determined by the external 50 MHz master oscillator, which serves as a standard time marker. The start and stop pulses are fast 1 nsec rise time signals, according to the Nuclear Instrument means of tunnel diode discriminators. Firing level of the discriminator define start and stop points between which the time interval is digitized.

Increasing Flexibility in Two-Dimensional Liquid Chromatography by Pulsed Elution of the First Dimension: A Proof of Concept.

PubMed

Jakobsen, Simon S; Christensen, Jan H; Verdier, Sylvain; Mallet, Claude R; Nielsen, Nikoline J

2017-09-05

This work demonstrates the development of an online two-dimensional liquid chromatography (2D-LC) method where the first dimension column is eluted by a sequence of pulses of increasing eluotropic strength generated by the LC pumps (pulsed-elution 2D-LC). Between the pulses, the first dimension is kept in a no-elution state using low eluent strength. The eluate from the first dimension is actively modulated using trap columns and subsequently analyzed in the second dimension. We demonstrate that by tuning the length and eluotropic strength of the pulses, peaks with retention factors in water, k w , above 150 can be manipulated to elute in 3-4 pulses. The no-elution state can be kept for 1-10 min with only minor changes as to which and how many pulses the peaks elute in. Pulsed-elution 2D-LC combined with active modulation tackles three of the main challenges encountered in 2D-LC and specifically online comprehensive 2D-LC: undersampling, difficulties in refocusing, and lack of flexibility in the selection of column dimensions and flow rates because the two dimensions constrain each other. The pulsed-elution 2D-LC was applied for the analysis of a basic fraction of vacuum gas oil. Peak capacity was 4018 for a 540 min analysis and 4610 for a 1040 min analysis.

Body monitoring and imaging apparatus and method

DOEpatents

McEwan, T.E.

1996-11-12

A non-acoustic pulse-echo radar monitor is employed in the repetitive mode, whereby a large number of reflected pulses are averaged to produce a voltage that modulates an audio oscillator to produce a tone that corresponds to the heart motion. The antenna used in this monitor generally comprises two flat copper foils, thus permitting the antenna to be housed in a substantially flat housing. The monitor converts the detected voltage to an audible signal with both amplitude modulation and Doppler effect. It further uses a dual time constant to reduce the effect of gross sensor-to-surface movement. The monitor detects the movement of one or more internal body parts, such as the heart, lungs, arteries, and vocal chords, and includes a pulse generator for simultaneously inputting a sequence of pulses to a transmit path and a gating path. The pulses transmitted along the transmit path drive an impulse generator and provide corresponding transmit pulses that are applied to a transmit antenna. The gating path includes a range delay generator which generates timed gating pulses. The timed gating pulses cause the receive path to selectively conduct pulses reflected from the body parts and received by a receive antenna. The monitor output potential can be separated into a cardiac output indicative of the physical movement of the heart, and a pulmonary output indicative of the physical movement of the lung. 12 figs.

Body monitoring and imaging apparatus and method

DOEpatents

McEwan, Thomas E.

1996-01-01

A non-acoustic pulse-echo radar monitor is employed in the repetitive mode, whereby a large number of reflected pulses are averaged to produce a voltage that modulates an audio oscillator to produce a tone that corresponds to the heart motion. The antenna used in this monitor generally comprises two flat copper foils, thus permitting the antenna to be housed in a substantially flat housing. The monitor converts the detected voltage to an audible signal with both amplitude modulation and Doppler effect. It further uses a dual time constant to reduce the effect of gross sensor-to-surface movement. The monitor detects the movement of one or more internal body parts, such as the heart, lungs, arteries, and vocal chords, and includes a pulse generator for simultaneously inputting a sequence of pulses to a transmit path and a gating path. The pulses transmitted along the transmit path drive an impulse generator and provide corresponding transmit pulses that are applied to a transmit antenna. The gating path includes a range delay generator which generates timed gating pulses. The timed gating pulses cause the receive path to selectively conduct pulses reflected from the body parts and received by a receive antenna. The monitor output potential can be separated into a cardiac output indicative of the physical movement of the heart, and a pulmonary output indicative of the physical movement of the lung.

A new scalable modular data acquisition system for SPECT (PET)

NASA Astrophysics Data System (ADS)

Stenstrom, P.; Rillbert, A.; Bergquist, M.; Habte, F.; Bohm, C.; Larsson, S. A.

1998-06-01

Describes a modular decentralized data acquisition system that continuously samples shaped PMT pulses from a SPECT detector. The pulse waveform data are used by signal processors to accurately reconstruct amplitude and time for each scintillation event. Data acquisition for a PMT channel is triggered in two alternative ways, either when its own signal exceeds a selected digital threshold, or when it receives a trigger pulse from one of its neighboring PMTs. The triggered region is restricted to seven, thirteen or nineteen neighboring PMT channels. Each acquisition module supports three PMT channels and connects to all other modules and a reconstruction computer via Firewire to cover the 72 channels in the Stockholm University/Karolinska Hospital cylindrical SPECT camera.

Research on multi-switch synchronization based on single trigger generator

NASA Astrophysics Data System (ADS)

Geng, Jiuyuan; Cheng, Xinbing; Yang, Jianhua; Yang, Xiao; Chen, Rong

2018-05-01

Multi-switch synchronous operation is an effective approach to provide high-voltage high-current for a high-power device. In this paper, we present a synchronization system with a corona stabilized triggered switch (CSTS) as main switch and an all-solid modularized quasi-square pulse forming system. In addition, this paper provides explanations of low jitter and accurate triggering of CSTS based on streamer theory. Different switches of the module are triggered by an electrical pulse created by a trigger generator, a quasi-square pulse can be created on the load. The experimental results show that it is able to switch voltages in excess of 40kV with nanosecond system jitter for three-module synchronous operation.

Pulse oximeter for cyclists in smartphone

NASA Astrophysics Data System (ADS)

Martins, L.; Gaidos, O.; dos Santos, I.

2015-01-01

The monitoring of cyclists during physical activity is an important factor to improve their performance. We discuss a new approaches based on smartphone for monitoring physiological signal wirelessly for cyclists, using a pulse oximeter sensor attached to the rider's forehead. This paper presents a wireless pulse Oximeter that was developed with a Nellcor's module, which uses the Standard Host Interface Protocol (SHIP) for communication with the Bluetooth module and sends data for a Smartphone with Android O.S. Then these data are shown in the screen: the heartbeat and saturation percentage. The application was created with App Inventor and the data are sent to Google Maps via Twitter. The results demonstrate the possibility of developing a successful prototype.

Large energy pulse generation modulated by graphene epitaxially grown on silicon carbide.

PubMed

Yu, Haohai; Chen, Xiufang; Zhang, Huaijin; Xu, Xiangang; Hu, Xiaobo; Wang, Zhengping; Wang, Jiyang; Zhuang, Shidong; Jiang, Minhua

2010-12-28

Graphene grown by thermal decomposition of a two-inch 6H silicon carbide (SiC) wafers surface was used to modulate a large energy pulse laser. Because of its saturable absorbing properties, graphene was used as a passive Q-switcher, and because of its high refractive index the SiC substrate was used as an output coupler. Together they formed a setup where the passively Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal laser was realized with the pulse energy of 159.2 nJ. Our results illustrate the feasibility of using graphene as an inexpensive Q-switcher for solid-state lasers and its promising applications in integrated optics.

Temporally resolved diagnosis of an atmospheric-pressure pulse-modulated argon surface wave plasma by optical emission spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Chuan-Jie; Li, Shou-Zhe; Zhang, Jialiang; Liu, Dongping

2018-01-01

A pulse-modulated argon surface wave plasma generated at atmospheric pressure is characterized by means of temporally resolved optical emission spectroscopy (OES). The temporal evolution of the gas temperature, the electron temperature and density, the radiative species of atomic Ar, and the molecular band of OH(A) and N2(C) are investigated experimentally by altering the instantaneous power, pulse repetitive frequency, and duty ratio. We focused on the physical phenomena occurring at the onset of the time-on period and after the power interruption at the start of the time-off period. Meanwhile, the results are discussed qualitatively for an in-depth insight of its dynamic evolution.

Self-starting picosecond optical pulse source using stimulated Brillouin scattering in an optical fiber.

PubMed

Tang, W W; Shu, C

2005-02-21

We demonstrate a regeneratively mode-locked optical pulse source at about 10 GHz using an optoelectronic oscillator constructed with an electro-absorption modulator integrated distributed feedback laser diode. The 10 GHz RF component is derived from the interaction between the pump wave and the backscattered, frequency-downshifted Stokes wave resulted from stimulated Brillouin scattering in an optical fiber. The component serves as a modulation source for the 1556 nm laser diode without the need for any electrical or optical RF filter to perform the frequency extraction. Dispersion-compensated fiber, dispersion-shifted fiber, and standard single-mode fiber have been used respectively to generate optical pulses at variable repetition rates.

Beam-induced electron modulations observed during TSS 1R

NASA Astrophysics Data System (ADS)

Rubin, A. G.; Burke, W. J.; Gough, M. P.; Machuzak, J. S.; Gentile, L. C.; Huang, C. Y.; Hardy, D. A.; Thompson, D. C.; Raitt, W. J.

1999-08-01

We report on modulations of electron fluxes at megahertz frequencies measured by the Shuttle Potential and Return Electron Experiment (SPREE) during fast pulsed electron gun (FPEG) beam experiments conducted after the tether break event of the Tethered Satellite System Reflight. Six intervals of sustained modulations were identified while FPEG emitted a 100 mA beam of 1 kev electrons. During five events the beam pitch angle αB was near 90° and the modulations were near even or odd half harmonics of the electron gyrofrequency fce. In the sixth event with 60°>=αB>=45°, electron modulations were near estimated values of the electron plasma frequency fpe and 2fpe. Whenever SPREE detected beam electrons modulated at a given frequency, secondary electrons were also modulated at the same frequency over a broad range of energies. Occasionally, some secondary electrons were modulated simultaneously at a second frequency. Multiple frequencies were related as ratios of low integers. In one case the beam electrons were simultaneously modulated at 0.8 MHz and 1.25 kHz. SPREE measurements suggest that the beam electrons propagate in cylindrical shells whose inner edge is marked by steep spatial gradients in fluxes at 1 keV [Hardy et al., 1995]. Inside the shell, electron distribution functions have positive slopes ∂f/∂v⊥>0 at velocities near that of the beam. Velocity space gradients act as free-energy sources to drive cavity modes that alter the instantaneous guiding centers of electrons causing SPREE to sample alternating parts of the beam cylinder's inner edge. Associated time-varying electric fields also modulated the fluxes of secondary electrons reaching SPREE. Other cavity modes may be excited through nonlinear processes [Calvert, 1982]. With αB far from 90°, electrons in the beam cylinder evolved toward bump-on-tail distributions to excite large-amplitude Langmuir modulations at fpe and its harmonics [Klimas, 1983]. Low-frequency modulations are attributed to electron interactions with ion acoustic-like waves generated as the beam moved across magnetic field lines in the ionosphere at supersonic speeds.

Slow wave contraction frequency plateaus in the small intestine are composed of discrete waves of interval increase associated with dislocations.

PubMed

Parsons, Sean P; Huizinga, Jan D

2018-06-03

What is the central question of this study? What is the nature of slow wave driven contraction frequency gradients in the small intestine? What is the main finding and its importance? Frequency plateaus are composed of discrete waves of increased interval, each wave associated with a contraction dislocation. Smooth frequency gradients are generated by localised neural modulation of wave frequency, leading to functionally important wave turbulence. Both patterns are emergent properties of a network of coupled oscillators, the interstitial cells of Cajal. A gut-wide network of interstitial cells of Cajal (ICC) generate electrical oscillations (slow waves) that orchestrate waves of muscle contraction. In the small intestine there is a gradient in slow wave frequency from high at the duodenum to low at the terminal ileum. Time-averaged measurements of frequency have suggested either a smooth or stepped (plateaued) gradient. We measured individual contraction intervals from diameter maps of the mouse small intestine to create interval maps (IMaps). IMaps showed that each frequency plateau was composed of discrete waves of increased interval. Each interval wave originated at a terminating contraction wave, a "dislocation", at the plateau's proximal boundary. In a model chain of coupled phase oscillators, interval wave frequency increased as coupling decreased or as the natural frequency gradient or noise increased. Injuring the intestine at a proximal point to destroy coupling, suppressed distal steps which then reappeared with gap junction block by carbenoxolone. This lent further support to our previous hypothesis that lines of dislocations were fixed by points of low coupling strength. Dislocations induced by electrical field pulses in the intestine and by equivalent phase shift in the model, were associated with interval waves. When the enteric nervous system was active, IMaps showed a chaotic, turbulent pattern of interval change with no frequency steps or plateaus. This probably resulted from local, stochastic release of neurotransmitters. Plateaus, dislocations, interval waves and wave turbulence arise from a dynamic interplay between natural frequency and coupling in the ICC network. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Numerical investigation of output beam quality in efficient broadband optical parametric chirped pulse amplification

NASA Astrophysics Data System (ADS)

Liu, Xiao-Di; Xu, Lu; Liang, Xiao-Yan

2017-01-01

We theoretically analyzed output beam quality of broad bandwidth non-collinear optical parametric chirped pulse amplification (NOPCPA) in LiB3O5 (LBO) centered at 800 nm. With a three-dimensional numerical model, the influence of the pump intensity, pump and signal spatial modulations, and the walk-off effect on the OPCPA output beam quality are presented, together with conversion efficiency and the gain spectrum. The pump modulation is a dominant factor that affects the output beam quality. Comparatively, the influence of signal modulation is insignificant. For a low-energy system with small beam sizes, walk-off effect has to be considered. Pump modulation and walk-off effect lead to asymmetric output beam profile with increased modulation. A special pump modulation type is found to optimize output beam quality and efficiency. For a high-energy system with large beam sizes, the walk-off effect can be neglected, certain back conversion is beneficial to reduce the output modulation. A trade-off must be made between the output beam quality and the conversion efficiency, especially when the pump modulation is large since. A relatively high conversion efficiency and a low output modulation are both achievable by controlling the pump modulation and intensity.

Tandem-pulsed acousto-optics: an analytical framework of modulated high-contrast speckle patterns.

PubMed

Resink, S G; Steenbergen, W

2015-06-07

Recently we presented acousto-optic (AO) probing of scattering media using addition or subtraction of speckle patterns due to tandem nanosecond pulses. Here we present a theoretical framework for ideal (polarized, noise-free) speckle patterns with unity contrast that links ultrasound-induced optical phase modulation, the fraction of light that is tagged by ultrasound, speckle contrast, mean square difference of speckle patterns and the contrast of the summation of speckle patterns acquired at different ultrasound phases. We derive the important relations from basic assumptions and definitions, and then validate them with simulations. For ultrasound-generated phase modulation angles below 0.7 rad (assuming uniform modulation), we are now able to relate speckle pattern statistics to the acousto-optic phase modulation. Hence our theory allows quantifying speckle observations in terms of ultrasonically tagged fractions of light for near-unity-contrast speckle patterns.

Intra-pulse modulation recognition using short-time ramanujan Fourier transform spectrogram

NASA Astrophysics Data System (ADS)

Ma, Xiurong; Liu, Dan; Shan, Yunlong

2017-12-01

Intra-pulse modulation recognition under negative signal-to-noise ratio (SNR) environment is a research challenge. This article presents a robust algorithm for the recognition of 5 types of radar signals with large variation range in the signal parameters in low SNR using the combination of the Short-time Ramanujan Fourier transform (ST-RFT) and pseudo-Zernike moments invariant features. The ST-RFT provides the time-frequency distribution features for 5 modulations. The pseudo-Zernike moments provide invariance properties that are able to recognize different modulation schemes on different parameter variation conditions from the ST-RFT spectrograms. Simulation results demonstrate that the proposed algorithm achieves the probability of successful recognition (PSR) of over 90% when SNR is above -5 dB with large variation range in the signal parameters: carrier frequency (CF) for all considered signals, hop size (HS) for frequency shift keying (FSK) signals, and the time-bandwidth product for Linear Frequency Modulation (LFM) signals.

The application of pulse modulated plasma to the plasma enhanced chemical vapor deposition of dielectric materials

NASA Astrophysics Data System (ADS)

Qi, Yu

This dissertation work applied the pulse modulated plasma to the plasma enhanced chemical vapor deposition (PECVD) of two types of dielectric materials: SiO2-like coatings and Teflon-like coatings. SiO2-like coatings were firstly implemented with continuous plasma. It was proven that three different precursors: hexamethyldisiloxane (HMDSO), 1, 3, 5, 7-tetramethylcyclotetrasiloxane (TMCTS) and octamethylcyclotetrasiloxane (OMCTS) can be used to generate hard, clear and high density SiO2 deposition with coupled high growth rate and low processing temperature via PECVD. Under similar conditions, HMDSO has the lowest growth rate, lowest hardness and highest carbon content; TMCTS has the highest growth rate and hardness, and lowest carbon content; and OMCTS has moderate rates of these deposition qualities, but the best corrosion resistance. Substrate bias seems to have no effect on any deposition quality. High chamber pressure can significantly lower the carbon content in the thin films but does not affect any other qualities; the O2/precursor ratio is the most influential factor among all variables considered in this experiment. The deposition hardness and O:Si ratio always increase with this ratio while the carbon content always decreases. However, different precursors require different optimal ratios to achieve the highest growth rate. Pulse modulation was introduced into PECVD of SiO2-like coatings and OMCTS was selected as the precursor. It was demonstrated that pulse frequency, duty ratio and peak power have significant effects on deposition qualities. The proper combination of the pulse parameters and other traditional plasma parameters can significantly lower the processing temperature while retaining or even improving other deposition qualities, such as growth rate, corrosion resistance and elemental composition. Hardness is the only sacrifice of the lower time-average power caused by pulsing. Therefore, pulse modulation can effectively expand the possible range of combinations of desired deposition qualities. Finally, the pulsed plasma was used to implement PECVD of teflon-like coatings. An important discovery in this application is that in addition to pulse period, on-time and on-time peak power, the power level during the off-time is an important factor. The density of CF2 is a function of all these pulse parameters. The best result obtained is up to 67.2% CF2 and a 1.87:1 of F:C ratio when the off-time power level is ˜100--130 W the frequency is several Hz, the on-time peak power is ˜1000 W and the duty ratio is ˜7--10%.

Modulation of frequency doubled DFB-tapered diode lasers for medical treatment

NASA Astrophysics Data System (ADS)

Christensen, Mathias; Hansen, Anders K.; Noordegraaf, Danny; Jensen, Ole B.; Skovgaard, Peter M. W.

2017-02-01

The use of visible lasers for medical treatments is on the rise, and together with this comes higher expectations for the laser systems. For many medical treatments, such as ophthalmology, doctors require pulse on demand operation together with a complete extinction of the light between pulses. We have demonstrated power modulation from 0.1 Hz to 10 kHz at 532 nm with a modulation depth above 97% by wavelength detuning of the laser diode. The laser diode is a 1064 nm monolithic device with a distributed feedback (DFB) laser as the master oscillator (MO), and a tapered power amplifier (PA). The MO and PA have separate electrical contacts and the modulation is achieved with wavelength tuning by adjusting the current through the MO 40 mA.

Behavioral neurocardiac training in hypertension: a randomized, controlled trial.

PubMed

Nolan, Robert P; Floras, John S; Harvey, Paula J; Kamath, Markad V; Picton, Peter E; Chessex, Caroline; Hiscock, Natalie; Powell, Jonathan; Catt, Michael; Hendrickx, Hilde; Talbot, Duncan; Chen, Maggie H

2010-04-01

It is not established whether behavioral interventions add benefit to pharmacological therapy for hypertension. We hypothesized that behavioral neurocardiac training (BNT) with heart rate variability biofeedback would reduce blood pressure further by modifying vagal heart rate modulation during reactivity and recovery from standardized cognitive tasks ("mental stress"). This randomized, controlled trial enrolled 65 patients with uncomplicated hypertension to BNT or active control (autogenic relaxation), with six 1-hour sessions over 2 months with home practice. Outcomes were analyzed with linear mixed models that adjusted for antihypertensive drugs. BNT reduced daytime and 24-hour systolic blood pressures (-2.4+/-0.9 mm Hg, P=0.009, and -2.1+/-0.9 mm Hg, P=0.03, respectively) and pulse pressures (-1.7+/-0.6 mm Hg, P=0.004, and -1.4+/-0.6 mm Hg, P=0.02, respectively). No effect was observed for controls (P>0.10 for all indices). BNT also increased RR-high-frequency power (0.15 to 0.40 Hz; P=0.01) and RR interval (P<0.001) during cognitive tasks. Among controls, high-frequency power was unchanged (P=0.29), and RR interval decreased (P=0.03). Neither intervention altered spontaneous baroreflex sensitivity (P>0.10). In contrast to relaxation therapy, BNT with heart rate variability biofeedback modestly lowers ambulatory blood pressure during wakefulness, and it augments tonic vagal heart rate modulation. It is unknown whether efficacy of this treatment can be improved with biofeedback of baroreflex gain. BNT, alone or as an adjunct to drug therapy, may represent a promising new intervention for hypertension.

Across-site patterns of modulation detection: Relation to speech recognitiona)

PubMed Central

Garadat, Soha N.; Zwolan, Teresa A.; Pfingst, Bryan E.

2012-01-01

The aim of this study was to identify across-site patterns of modulation detection thresholds (MDTs) in subjects with cochlear implants and to determine if removal of sites with the poorest MDTs from speech processor programs would result in improved speech recognition. Five hundred millisecond trains of symmetric-biphasic pulses were modulated sinusoidally at 10 Hz and presented at a rate of 900 pps using monopolar stimulation. Subjects were asked to discriminate a modulated pulse train from an unmodulated pulse train for all electrodes in quiet and in the presence of an interleaved unmodulated masker presented on the adjacent site. Across-site patterns of masked MDTs were then used to construct two 10-channel MAPs such that one MAP consisted of sites with the best masked MDTs and the other MAP consisted of sites with the worst masked MDTs. Subjects’ speech recognition skills were compared when they used these two different MAPs. Results showed that MDTs were variable across sites and were elevated in the presence of a masker by various amounts across sites. Better speech recognition was observed when the processor MAP consisted of sites with best masked MDTs, suggesting that temporal modulation sensitivity has important contributions to speech recognition with a cochlear implant. PMID:22559376

A practical implementation of multi-frequency widefield frequency-domain FLIM

PubMed Central

Chen, Hongtao

2013-01-01

Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime, especially in kinetic studies in biomedical researches. However, the small range of modulation frequencies available in commercial instruments makes this technique limited in its applications. Here we describe a practical implementation of multi-frequency widefield FD-FLIM using a pulsed supercontinuum laser and a direct digital synthesizer. In this instrument we use a pulse to modulate the image intensifier rather than the more conventional sine wave modulation. This allows parallel multi-frequency FLIM measurement using the Fast Fourier Transform and the cross-correlation technique, which permits precise and simultaneous isolation of individual frequencies. In addition, the pulse modulation at the cathode of image intensifier restored the loss of optical resolution caused by the defocusing effect when the voltage at the cathode is sinusoidally modulated. Furthermore, in our implementation of this technique, data can be graphically analyzed by the phasor method while data are acquired, which allows easy fit-free lifetime analysis of FLIM images. Here our measurements of standard fluorescent samples and a Föster resonance energy transfer pair demonstrate that the widefield multi-frequency FLIM system is a valuable and simple tool in fluorescence imaging studies. PMID:23296945

Linear optical pulse compression based on temporal zone plates.

PubMed

Li, Bo; Li, Ming; Lou, Shuqin; Azaña, José

2013-07-15

We propose and demonstrate time-domain equivalents of spatial zone plates, namely temporal zone plates, as alternatives to conventional time lenses. Both temporal intensity zone plates, based on intensity-only temporal modulation, and temporal phase zone plates, based on phase-only temporal modulation, are introduced and studied. Temporal zone plates do not exhibit the limiting tradeoff between temporal aperture and frequency bandwidth (temporal resolution) of conventional linear time lenses. As a result, these zone plates can be ideally designed to offer a time-bandwidth product (TBP) as large as desired, practically limited by the achievable temporal modulation bandwidth (limiting the temporal resolution) and the amount of dispersion needed in the target processing systems (limiting the temporal aperture). We numerically and experimentally demonstrate linear optical pulse compression by using temporal zone plates based on linear electro-optic temporal modulation followed by fiber-optics dispersion. In the pulse-compression experiment based on temporal phase zone plates, we achieve a resolution of ~25.5 ps over a temporal aperture of ~5.77 ns, representing an experimental TBP larger than 226 using a phase-modulation amplitude of only ~0.8π rad. We also numerically study the potential of these devices to achieve temporal imaging of optical waveforms and present a comparative analysis on the performance of different temporal intensity and phase zone plates.