Spectral Windowing Research Articles

First experimental demonstration of real-time neutron capture discrimination in helium and carbon ion therapy

This work provides the first experimental proof of an increased neutron capture photon signal following the introduction of boron to a PMMA phantom during helium and carbon ion therapies in Neutron Capture Enhanced Particle Therapy (NCEPT). NCEPT leverages 10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{10}$$\\end{document}B neutron capture, leading to the emission of detectable 478 keV photons. Experiments were performed at the Heavy Ion Medical Accelerator in Chiba, Japan, with two Poly(methyl methacrylate) (PMMA) targets, one bearing a boron insert. The BeNEdiCTE gamma-ray detector measured an increase in the 478 keV signal of 45 ± 7% and 26 ± 2% for carbon and helium ion irradiation, respectively. Our Geant4 Monte Carlo simulation model, developed to investigate photon origins, found less than 30% of detected photons originated from the insert, while boron in the detector’s circuit boards contributed over 65%. Further, the model investigated detector sensitivity, establishing its capability to record a 10% increase in 478 keV photon detection at a target 10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{10}$$\\end{document}B concentration of 500 ppm using spectral windowing alone, and 25% when combined with temporal windowing. The linear response extended to concentrations up to 20,000 ppm. The increase in the signal in all evaluated cases confirm the potential of the proposed detector design for neutron capture quantification in NCEPT.

Effect of Perftoran on Membrane Nanostructure of Discocyte and Stomatocyte after Acute Blood Loss

The purpose of the study: to evaluate the effect of Perftoran (PF) on the membrane nanostructure of discocytes and stomatocytes after acute blood loss. Materials and methods. The study was performed in white male rats. Nembutal was administered intraperitoneally at a dose of 25 mg/kg. The study model was as follows: acute blood loss followed by hypotension for 60 min with the BP maintained at the level of 40 mm Hg with subsequent reinfusion of lost blood. Blood samples were collected from the tail artery before the blood loss and 2 hours after reinfusion. PF was administered intraarterially at a dose 3 ml/kg of body mass immediately after the blood loss replacement. Animals who did not receive Perftoran served as a reference group. The RBC membrane structure was studied using the Femtoscan atomic force microscope at ranges with different spatial periods. The ranges were selected using the Fourier transform and spectral windowing. Periods (T) and heights (h) of RBC surface corrugation were calculated for each spectral window according to the isolated profiles of the membrane surface. Results. At a baseline; discocytes and stomatocytes exhibited different structural characteristics of RBC membrane at a spatial range of 600—1200 nm in the form of a higher period of vibration of stomatocytes vs. discocytes. Hypovolemia and subsequent reinfusion of autologous blood affected studied parameters by increasing the period of spatial oscillation both in discocytes and stomatocytes as compared to the initial state. Administration of PF significantly decreased the period of spatial oscillation of the cell membrane both in discocytes and stomatocytes as compared to animal RBCs who underwent hypovolemia and reinfusion without PF administration and baseline parameters. Conclusion. The period of vibration within the range of 6001200 nm reflecting the state of the bilayer of RBC membrane is not related to the discocyte transformation into the stomatocyte. Data suggest that the PF-induced shortage in vibration within this range was associated with the increased ability of a RBC to deform.

On Analytic Methods for 2.5-D Local Sound Field Synthesis Using Circular Distributions of Secondary Sources

Local sound field synthesis allows for synthesizing a given desired sound field inside a limited target region such that the field is free of considerable spatial aliasing artifacts. Spatial aliasing artifacts are a consequence of overlaps due to unavoidable repetitions of the space-spectral coefficients of the secondary source driving function. We analyze various conceivable analytic ways of restricting the bandwidth of the spatial spectrum of the driving function such that considerable overlapping is prevented: local spatial bandlimitation (A), spectral windowing (B), and local spatial bandlimitation plus spectral windowing (C). While solution B is computationally significantly more efficient than A and C, it provides only limited control over the spatial location around which the aliasing-free region evolves. Solutions A and C provide more flexibility and higher accuracy whereby both achieve largely identical results so that the spectral windowing after the local spatial bandlimitation may be skipped. We present a detailed analysis of the properties of the spatial aliasing artifacts arising in the synthesis of a virtual plane wave. We establish a procedure for predicting the maximum possible size of the aliasing-free target region depending on its location and on the propagation direction of the desired sound field. The results can help reducing regularization in numerical solutions as they represent physical limitations that can be considered in the choice of parameters.

Spectral characterization of the stochastically simulated vehicle queue on bridges

Monte Carlo simulation in conjunction with Fourier transform based spectral windowing is used to model the live load on bridges. Vehicles are classified into a few groups and the probability distributions of axle weight and length associated with each group are estimated. The vehicle arriving at an instant is determined through Monte Carlo simulation, which uses a vehicle group density function derived from measurement data on the relative contribution of each group in total vehicles. The weight and length of the arriving vehicle is also simulated by Monte Carlo using the distribution function for the corresponding group. Vehicle arrivals are modeled by the Poisson distribution. The vehicle velocities are realized through spectral simulation based on decaying power spectra of the velocity time series. The simulations are performed for a sufficient time interval in several lanes, thus the ensemble sampling of load is obtained. Fourier transform based windowing is used to characterize the power spectra of mechanical load on the bridge. The study shows the white noise nature of the load spectral density, which is in agreement with the assumptions of previous investigators. Parametric sensitivity of the spectra is also performed and recommendations are made to include site-specific parameters in the model. Finally, applications are illustrated for frequency domain random vibration analysis of a simple model of bridge structures.

Synthetic wavelength based phase unwrapping in spectral domain optical coherence tomography

Phase sensing implementations of spectral domain optical coherence tomography (SDOCT) have demonstrated the ability to measure nanometer-scale temporal and spatial profiles of samples. However, the phase information suffers from a 2pi ambiguity that limits observations of larger sample displacements to lengths less than half the source center wavelength. We introduce a synthetic wavelength phase unwrapping technique in SDOCT that uses spectral windowing and corrects the 2pi ambiguity, providing accurate measurements of sample motion with information gained from standard SDOCT processing. We demonstrate this technique by using a common path implementation of SDOCT and correctly measure phase profiles from a phantom phase object and human epithelial cheek cells which produce multiple wrapping artifacts. Using a synthetic wavelength for phase unwrapping could prove useful in Doppler or other phase based implementations of OCT.

Quasi-transform-limited pulse transmission in dispersion managed soliton system

A Gaussian pulse with frequency chirping is transmitted in a dispersion management (DM) soliton system. The existence of an initial chirping makes the pulsewidth and amplitude fluctuate over distance around their initial values, and increases the energy enhancement factor. The quasi-transform-limited pulse generated with spectral windowing is also propagated in the DM soliton system. With proper energy enhancement, the quasi-transform-limited pulse can propagate very stably, and the performance is better than that in a uniform low dispersion soliton system, which suggests that a DM system has more chirping and waveform tolerance in soliton sources than a uniform fiber system.

Complex pulse evolution in a femtosecond laser with spectral windowing

We report complex evolution in a colliding pulse passively mode-locked dye laser when a spectral windowing is introduced in the cavity. These observations are in good accordance with theoretical models.

Local geoid computation from gravity using the fast fourier transform technique

Model computations were performed for the study of numerical errors which are interjected into local geoid computations byFFT. The gravity field model was generated through the attractions of granitic prisms derived from actual geology. Changes in sampling interval introduced only0.3 cm variation in geoid heights. Although zero padding alone provided an improvement of more than5 cm in theFFT generated geoid, the combination of spectral windowing (tapering) and padding further reduced numerical errors. For theGPS survey of Franklin County, Ohio, the parameters selected as a result of model computations, allow large reduction in local data requirements while still retaining the centimeter accuracy when tapering and padding is applied.

Transform-limited pulse generation in the gigahertz region from a gain-switched distributed-feedback laser diode using spectral windowing

For the first time, to our knowledge, transform-limited and high-power picosecond pulses in the gigahertz region are successfully generated from a distributed-feedback laser diode using spectral manipulation with a narrow-band Fabry-Perot resonator and erbium fiber amplifiers. The pulses, which before the optical filtering have a width of 27 psec and a spectral width of 1.24 nm, are transformed to transform-limited pulses with a width of 17 psec and a spectral width of 0.21 nm. The peak power of the pulse at a 6-GHz repetition rate is amplified to greater than 90 mW with an erbium fiber amplifier.

Dynamic optical soliton communication

Digitally coded optical solitons at 5 and 10 Gb/s have been successfully transmitted over 400 and 300 km, respectively, using erbium-doped fiber amplifiers and repeaters. The soliton pulse source is a gain-switched distributed-feedback laser diode with spectral windowing. The repeater spacing for the 10-Gb/s transmission with an input soliton of A=1.4 is 25 km, which is extended to 50 km for 5-Gb/s transmission with an input soliton of N=1.8-2.0. >

Optical fibre-grating pulse compression

Numerical simulation is used to consider non-linear pulse propagation in fibres and subsequent pulse compression in a dispersive delay line. It is shown that for small initial pulse powers the conventional non-linear Schrodinger equation (NSE) is quite accurate to describe the process of pulse propagation in fibres. In this case initially symmetrical pulses undergo squaring and spectral broadening in fibres, and frequency chirp is linearized over most of the pulse, while shapes of the pulse, spectrum and frequency chirp remain symmetrical at the output of the fibre. There is a certain optimum fibre lengthZopt which is determined by the initial pulse parameters and fibre characteristics for pulse compression in the dispersive delay line. When the fibre lengthZ>Zopt the optical wave breaking effect distorts the linearity of the frequency chirp and thus deteriorates the quality of the compressed pulse. The region of NSE approximation accuracy is determined. It is demonstrated that at increase of the initial pulse power (initial pulse width makes no difference) the NSE approximation becomes inaccurate. So the pulse dynamics in the fibre were described by the modified NSE derived in the higher-order approximation of the method of slowly varying amplitudes from Maxwell's equations. In this case the shock wave appears at the trailing edge of the pulse, which accelerates the wave breaking process. This results in a decrease of the optimum fibre length and deterioration of compressed pulse parameters, compared with the NSE case. Spectral windowing of the extreme Stokes components of the pulse spectrum permits significant improvement in the quality of the compressed pulse. The main features of the compression of pulses with asymmetrical initial shape are also considered.

Optical pulse narrowing by the spectral windowing of self-phase modulated picosecond pulses

An extra-cavity pulse narrowing technique is demonstrated in which a frequency-swept optical pulse is compressed by the application of a spectral window. The pulses from a cw mode-locked Nd:YAG laser were passed through an optical fibre in a regime where self-phase modulation was the dominant nonlinear mechanism, and group velocity dispersion and stimulated Raman scattering were negligible. A 3-fold compression ratio was obtained, in good agreement with theoritical predictions.

Optically biased tunable femtosecond dye laser and spectral windowing of the compressed second harmonic of Nd:YAG

We describe a technique for enhancing tunable ultrashort pulse pumped dye laser performance based on the use of "long" pump pulses to optically bias the cavity toward minimal losses. Increases in dye laser output power of 155 percent and powers as high as 125 mW have been measured with pulse durations under 300 fs. Optical pulses as short as 180 fs are reported for this ultrashort pulse pumped dye laser oscillator. We also report the first measurements of the spectral windowing of compressed 532 nm pulses for temporal pulse shaping, in the optimal group velocity dispersion limit. Temporal pulse shaping is demonstrated with small losses in power and minimal pulse broadening.

Spectral windowing of frequency-modulated optical pulses in a grating compressor

Spectral windowing or apodization of the spatially dispersed frequency components within a grating compressor has been used to control the temporal shape of compressed optical pulses. Windowing of undesirable high and low-frequency components, which are not linearly chirped, results in nearly complete elimination of the energy in the wings of the compressed pulse. We have applied this technique to improve the quality of pulses from a mode-locked neodymium: yttrium aluminum garnet laser compressed to less than 2 ps using a fiber and double-pass grating pair with an internal aperture.

High-speed coherence processing using the sectionalized Fourier transform

The sectionalized Fourier transform of a band-limited signal (defined as a Fourier transform which is computed over incremented temporal sections of the function) is equivalent to basebanding, filtering, and sampling the signal in time domain. Spectral windowing is employed, through appropriately summing a sequence of the Fourier transform bins, to control the passband and leakage characteristics of the resulting filter. This in turn controls the distortion of the signal induced as a result of the transform process. The use of the sectionalized Fourier transform is exploited to conveniently and rapidly map the cross-correlation envelope of narrow-band signals over the time-register Doppler-ratio (ambiguity) plane. By using the ambiguity kernel <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\exp(i2\pi\alphaft)</tex> as an approximation of signal time compression (or expansion), the coherence between transformed signals (along the Doppler-ratio axis) may further be expedited through use of the discrete Fourier transform. The resulting error is negligible when the time-bandwidth product of the process is less than the inverse of the maximum Doppler ratio employed. The resulting algorithms have proved advantageous in underwater acoustic applications. It is concluded that the sectionalized Fourier Transform has many applications in time-domain signal processing using modern array digital computers.