Fast Changing Phenomena Research Articles

Numerical Simulations of Bird Strikes with the Use of Various Equations of State

Abstract The paper presents results of numerical analyses of the collision of various bird models (dummies) with a helicopter windshield. Three different numerical bird models were elaborated. According to the subject literature, applying an appropriate equation of state has an influence on impact parameters. The author used the LS_DYNA software package. This is a computational code designed to analyse fast-changing phenomena by means of the finite-element method. SPH method has been used for bird strike simulations. In the research, three different equations of state have been used: Grüneisen's, polynomial and tabulated.

A Programmable Optical Filter With Arbitrary Transmittance for Fast Spectroscopic Imaging and Spectral Data Post-Processing

Spectral reconstruction method based on narrow-band measurements has been demonstrated to achieve ultrafast spectroscopic imaging with high spatial and spectral resolution, in which multiple narrow-band images are collected by using several specific filters. Although commercially available filters can be employed in such method, filters with complex transmittance that are difficult to be fabricated typically show significant improvement in spectral reconstruction accuracy. In this study, a two dimensional programmable optical filter based on digital micromirror device (DMD) is proposed, in which its transmittance spectrum can be arbitrarily and quickly switched to realize complex transmittance. Furthermore, its flexible transmittance enables directly hardware-based spectral data post-processing, which can perform data acquisition and analysis simultaneously. Those have been evaluated by the diffuse reflectance spectra from normal and occluded skin flaps, as well as Raman spectra from live, apoptosis and necrosis leukemia cells. Our simulation results show that much higher spectral reconstruction accuracies can be achieved by the optimized filters with complex transmittance. Furthermore, the classification accuracy by using the proposed method is comparable to those achieved by conventional numerical methods. Therefore, based on the proposed programmable optical filter, fast spectroscopic imaging with high spatial and spectral resolution can be achieved for observing fast changing phenomena and even real-time target identification.

An analysis of fast-changing phenomena in the cutting zone during the turning of a TI-6AL-4V titanium alloy shaft

An analysis of fast-changing phenomena in the cutting zone during the turning of a TI-6AL-4V titanium alloy shaft

Hard x-ray bursts observed in association with Rayleigh-Taylor instigated current disruption in a solar-relevant lab experiment

Measurements by multiple X-ray detectors show transient emission of a 1 μs pulse of non-mono-energetic ∼6 keV X-rays by a cold, dense MHD-driven plasma jet. Because the collision mean free path is much smaller than the jet dimensions, the acceleration of particles to high energy was not expected. The X-ray pulse occurs when the jet undergoes a kink instability which accelerates the jet laterally so that a fast-growing secondary Rayleigh-Taylor instability is triggered which then breaks the jet. The jet breaking is correlated in time with several other fast changing phenomena. It is proposed that despite the short collision mean free path, an inductive electric field associated with this breaking accelerates a certain subgroup of electrons to keV energies without any of these electrons undergoing collisions. It is further proposed that after being accelerated to high energy, these fast electrons are suddenly decelerated via collisions and radiate X-rays.

Stepwise method based on Wiener estimation for spectral reconstruction in spectroscopic Raman imaging.

Raman spectroscopy has demonstrated great potential in biomedical applications. However, spectroscopic Raman imaging is limited in the investigation of fast changing phenomena because of slow data acquisition. Our previous studies have indicated that spectroscopic Raman imaging can be significantly sped up using the approach of narrow-band imaging followed by spectral reconstruction. A multi-channel system was built to demonstrate the feasibility of fast wide-field spectroscopic Raman imaging using the approach of simultaneous narrow-band image acquisition followed by spectral reconstruction based on Wiener estimation in phantoms. To further improve the accuracy of reconstructed Raman spectra, we propose a stepwise spectral reconstruction method in this study, which can be combined with the earlier developed sequential weighted Wiener estimation to improve spectral reconstruction accuracy. The stepwise spectral reconstruction method first reconstructs the fluorescence background spectrum from narrow-band measurements and then the pure Raman narrow-band measurements can be estimated by subtracting the estimated fluorescence background from the overall narrow-band measurements. Thereafter, the pure Raman spectrum can be reconstructed from the estimated pure Raman narrow-band measurements. The result indicates that the stepwise spectral reconstruction method can improve spectral reconstruction accuracy significantly when combined with sequential weighted Wiener estimation, compared with the traditional Wiener estimation. In addition, qualitatively accurate cell Raman spectra were successfully reconstructed using the stepwise spectral reconstruction method from the narrow-band measurements acquired by a four-channel wide-field Raman spectroscopic imaging system. This method can potentially facilitate the adoption of spectroscopic Raman imaging to the investigation of fast changing phenomena.

Fast reconstruction of Raman spectra from narrow‐band measurements based on Wiener estimation

Raman spectroscopy has demonstrated great potential in clinical and biomedical applications. However, slow data acquisition due to weak Raman signals has prevented its wide use, especially in an imaging setup. In this paper, we propose a novel solution in which the full Raman spectrum can be rapidly reconstructed from a few narrow‐band measurements based on Wiener estimation. This method, using both traditional Wiener estimation and modified Wiener estimation, has been evaluated on Raman spectra collected from live, apoptotic and necrotic leukemia cells with several different types of band‐pass filter choices. Two rules of thumb were identified to guide the choice of filters. Our results indicate that the agreement between reconstructed and measured Raman spectra was excellent according to either the mean root mean square error or the classification accuracy. Therefore, Raman reconstruction from narrow‐band measurements represents a new direction in fast Raman imaging for the investigation of fast changing phenomena. Copyright © 2013 John Wiley & Sons, Ltd.

Fourier analysis of a four-dimensional imaging spectrometer with a fiber optic dimension transform element

A four-dimensional imaging spectrometer with a fiber optic dimension transform element has the ability to capture all four dimensions of data (2D spatial, spectral and temporal) with a single, radiometrically calibrated sensor at a single exposure, which satisfies the need to record transient events and fast changing phenomena of interest. In order to analyze the corresponding relation between the input light intensity and the output light intensity of a four-dimensional imaging spectrometer with a fiber optic dimension transform element, this paper utilizes the Fourier optics theory and complex Gaussian functions expansion method to derive and analyze the transmission characteristics of the imaging spectrometer optical system. This paper introduces the light intensity distribution formula when the detector is fixed on the negative first order spectral image plane and establishes and simulates the corresponding relation between the light intensity distribution of the detector and the spatial/spectral information on the target space. The research results show that the target information can be extracted and analyzed directly according to the corresponding relation.

A brief history of principles used in high speed cameras

High-speed imaging records valuable information of events that occur in microscopic timescales and provides an insight into fast changing phenomena that eludes visual understanding. Over the past hundred and fifty years cameras have evolved from very basic devices to present day complex electro optical imaging systems that require computers programmed with innovative software to manage the multitude of operational parameters. This evolutionary process has passed through numerous stages advancing alongside other technologies as they have become available. However, two overriding factors have been influential in camera development; the first being the need to generate sufficiently bright images that can be recorded in microscopic timescales, and the need to synchronize the framing window to allow the critical dissection of the area of interest. Unless these fundamental requirements are satisfied other parameters such as resolution and image numbers become less relevant. The extraction of temporally related data was difficult and time consuming particularly if multiple cameras were used which introduced parallax errors. However, the continued development of solid state imaging sensors has provided flexibility for integration into imaging systems that record image sequences which can be critically interrogated providing a detailed account of events that occur in microscopic timescales.