Huang, Norden E.; Hu, Kun; Yang, Albert C. C.; Chang, Hsing-Chih; Jia, Deng; Liang, Wei-Kuang; Yeh, Jia Rong; Kao, Chu-Lan; Juan, Chi-Hung; Peng, Chung Kang; Meijer, Johanna H.; Wang, Yung-Hung; Long, Steven R.; Wu, Zhauhua
2016-01-01
The Holo-Hilbert spectral analysis (HHSA) method is introduced to cure the deficiencies of traditional spectral analysis and to give a full informational representation of nonlinear and non-stationary data. It uses a nested empirical mode decomposition and Hilbert–Huang transform (HHT) approach to identify intrinsic amplitude and frequency modulations often present in nonlinear systems. Comparisons are first made with traditional spectrum analysis, which usually achieved its results through convolutional integral transforms based on additive expansions of an a priori determined basis, mostly under linear and stationary assumptions. Thus, for non-stationary processes, the best one could do historically was to use the time–frequency representations, in which the amplitude (or energy density) variation is still represented in terms of time. For nonlinear processes, the data can have both amplitude and frequency modulations (intra-mode and inter-mode) generated by two different mechanisms: linear additive or nonlinear multiplicative processes. As all existing spectral analysis methods are based on additive expansions, either a priori or adaptive, none of them could possibly represent the multiplicative processes. While the earlier adaptive HHT spectral analysis approach could accommodate the intra-wave nonlinearity quite remarkably, it remained that any inter-wave nonlinear multiplicative mechanisms that include cross-scale coupling and phase-lock modulations were left untreated. To resolve the multiplicative processes issue, additional dimensions in the spectrum result are needed to account for the variations in both the amplitude and frequency modulations simultaneously. HHSA accommodates all the processes: additive and multiplicative, intra-mode and inter-mode, stationary and non-stationary, linear and nonlinear interactions. The Holo prefix in HHSA denotes a multiple dimensional representation with both additive and multiplicative capabilities. PMID:26953180
Huang, Norden E; Hu, Kun; Yang, Albert C C; Chang, Hsing-Chih; Jia, Deng; Liang, Wei-Kuang; Yeh, Jia Rong; Kao, Chu-Lan; Juan, Chi-Hung; Peng, Chung Kang; Meijer, Johanna H; Wang, Yung-Hung; Long, Steven R; Wu, Zhauhua
2016-04-13
The Holo-Hilbert spectral analysis (HHSA) method is introduced to cure the deficiencies of traditional spectral analysis and to give a full informational representation of nonlinear and non-stationary data. It uses a nested empirical mode decomposition and Hilbert-Huang transform (HHT) approach to identify intrinsic amplitude and frequency modulations often present in nonlinear systems. Comparisons are first made with traditional spectrum analysis, which usually achieved its results through convolutional integral transforms based on additive expansions of an a priori determined basis, mostly under linear and stationary assumptions. Thus, for non-stationary processes, the best one could do historically was to use the time-frequency representations, in which the amplitude (or energy density) variation is still represented in terms of time. For nonlinear processes, the data can have both amplitude and frequency modulations (intra-mode and inter-mode) generated by two different mechanisms: linear additive or nonlinear multiplicative processes. As all existing spectral analysis methods are based on additive expansions, either a priori or adaptive, none of them could possibly represent the multiplicative processes. While the earlier adaptive HHT spectral analysis approach could accommodate the intra-wave nonlinearity quite remarkably, it remained that any inter-wave nonlinear multiplicative mechanisms that include cross-scale coupling and phase-lock modulations were left untreated. To resolve the multiplicative processes issue, additional dimensions in the spectrum result are needed to account for the variations in both the amplitude and frequency modulations simultaneously. HHSA accommodates all the processes: additive and multiplicative, intra-mode and inter-mode, stationary and non-stationary, linear and nonlinear interactions. The Holo prefix in HHSA denotes a multiple dimensional representation with both additive and multiplicative capabilities. PMID:26953180
Spectral resolvability of iterated rippled noise
NASA Astrophysics Data System (ADS)
Yost, William A.
2005-04-01
A forward-masking experiment was used to estimate the spectral ripple of iterated rippled noise (IRN) that is possibly resolved by the auditory system. Tonal signals were placed at spectral peaks and valleys of IRN maskers for a wide variety of IRN conditions that included different delays, number of iterations, and stimulus durations. The differences in the forward-masked thresholds of tones at spectral peaks and valleys were used to estimate spectral resolvability, and these results were compared to estimates obtained from a gamma-tone filter bank. The IRN spectrum has spectral peaks that are harmonics of the reciprocal of the delay used to generate IRN stimuli. As the number of iterations in the generation of IRN stimuli increases so does the difference in the spectral peak-to-valley ratio. For high number of iterations, long delays, and long durations evidence for spectral resolvability existed up to the 6th harmonic. For all other conditions spectral resolvability appeared to disappear at harmonics lower than the 6th, or was not measurable at all. These data will be discussed in terms of the role spectral resolvability might play in processing the pitch, pitch strength, and timbre of IRN stimuli. [Work supported by a grant from NIDCD.
A two dimensional power spectral estimate for some nonstationary processes. M.S. Thesis
NASA Technical Reports Server (NTRS)
Smith, Gregory L.
1989-01-01
A two dimensional estimate for the power spectral density of a nonstationary process is being developed. The estimate will be applied to helicopter noise data which is clearly nonstationary. The acoustic pressure from the isolated main rotor and isolated tail rotor is known to be periodically correlated (PC) and the combined noise from the main and tail rotors is assumed to be correlation autoregressive (CAR). The results of this nonstationary analysis will be compared with the current method of assuming that the data is stationary and analyzing it as such. Another method of analysis is to introduce a random phase shift into the data as shown by Papoulis to produce a time history which can then be accurately modeled as stationary. This method will also be investigated for the helicopter data. A method used to determine the period of a PC process when the period is not know is discussed. The period of a PC process must be known in order to produce an accurate spectral representation for the process. The spectral estimate is developed. The bias and variability of the estimate are also discussed. Finally, the current method for analyzing nonstationary data is compared to that of using a two dimensional spectral representation. In addition, the method of phase shifting the data is examined.
NASA Astrophysics Data System (ADS)
Boiti, M.; Pempinelli, F.; Pogrebkov, A. K.; Polivanov, M. C.
1992-11-01
The resolvent operator of the linear problem is determined as the full Green function continued in the complex domain in two variables. An analog of the known Hilbert identity is derived. We demonstrate the role of this identity in the study of two-dimensional scattering. Considering the nonstationary Schrödinger equation as an example, we show that all types of solutions of the linear problems, as well as spectral data known in the literature, are given as specific values of this unique function — the resolvent function. A new form of the inverse problem is formulated.
NASA Astrophysics Data System (ADS)
Chang, Ching-Min; Yeh, Hund-Der
2008-02-01
SummaryThis paper describes an investigation of the influence of uniformly distributed groundwater recharge on asymptotic macrodispersion in two-dimensional heterogeneous media. This is performed using a nonstationary spectral approach [Li, S.-G., McLaughlin, D., 1991. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour. Res. 27 (7), 1589-1605; Li, S.-G., McLaughlin, D., 1995. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour. Res. 31 (3), 541-551] based on Fourier-Stieltjes representations for the perturbed quantities. To solve the problem analytically, focus is placed on the case where the local longitudinal dispersivity αL is much smaller than the integral scale of log transmissivity λ (i.e., αL/ λ ≪ 1). The closed-form expressions are obtained for describing the spectrum of flow velocity, the variability of flow velocity and asymptotic macrodispersion, in terms of the statistical properties and the integral scale of log transmissivity, local transport parameters and a parameter β [Rubin, Y., Bellin, A., 1994. The effects of recharge on flow nonuniformity and macrodispersion. Water Resour. Res. 30 (4), 939-948] used to characterize the degree of flow nonuniformity due to the groundwater recharge. The impact of β on these results is examined.
NASA Astrophysics Data System (ADS)
Zhou, Huai-lai; Wang, Chang-cheng; Marfurt, Kurt J.; Jiang, Yi-wei; Bi, Jian-xia
2016-04-01
Maximizing vertical resolution is a key objective in seismic data processing. Early deconvolution and spectral balancing algorithms assumed that the seismic source wavelet was temporally invariant, or stationary. In practice, seismic scattering and attenuation give rise to non-stationary seismic source wavelets. To address this issue, most conventional time-varying deconvolution wavelet shaping and spectral modelling techniques using the stationary polynomial fitting assume the wavelet to be locally stationary within a small number of overlapping analysis windows while the fitting coefficients are invariant with all the frequencies. In this paper, we show an improvement obtained by modelling smoothly varying spectra of the seismic wavelet using non-stationary polynomial fitting in the time-frequency domain. We first decompose each seismic trace using a generalized S-transform that provides a good time-frequency distribution for the estimation of the time-varying wavelet spectra. We then model the slowly varying source wavelet spectrum at each time sample by a smooth low-order polynomial. Finally, we spectrally balance the modelled wavelet to flatten the seismic response, thereby increasing vertical resolution. We calibrate the algorithm on a simple synthetic and then apply it to a 3-D land survey acquired in western China, showing the value on both vertical slices through seismic amplitude and attribute time slices. Our new algorithm significantly improves the vertical resolution of the seismic signal, while not increasing the noise.
Spatially resolved spectral-imaging device
Bloom, Joshua Simon; Tyson, John Anthony
2016-02-09
A spatially resolved spectral device comprising a dispersive array to receive an incident light comprising a principal ray. The dispersive array comprising a plurality of dichroic layers, each of the plurality of dichroic layers disposed in a path of a direction of the principal ray. Each of the plurality of dichroic layers configured to at least one of reflect or transmit a different wavelength range of the incident light. The device further comprising a detection array operatively coupled with the dispersive array. The detection array comprising a photosensitive component including a plurality of detection pixels, each of the plurality of detection pixels having a light-receiving surface disposed parallel to the direction of the principal ray to detect a respective one of the different wavelength ranges of incident light reflected from a corresponding one of the plurality of dichroic layers.
Gruppetta, Steve; Chetty, Sabah
2011-01-01
Current implementations of structured illumination microscopy for depth-resolved (three-dimensional) imaging have limitations that restrict its use; specifically, they are not applicable to non-stationary objects imaged with relatively poor condenser optics and in non-fluorescent mode. This includes in-vivo retinal imaging. A novel implementation of structured illumination microscopy is presented that overcomes these issues. A three-wavelength illumination technique is used to obtain the three sub-images required for structured illumination simultaneously rather than sequentially, enabling use on non-stationary objects. An illumination method is presented that produces an incoherent pattern through interference, bypassing the limitations imposed by the aberrations of the condenser lens and thus enabling axial sectioning in non-fluorescent imaging. The application to retinal imaging can lead to a device with similar sectioning capabilities to confocal microscopy without the optical complexity (and cost) required for scanning systems. PMID:21339871
Spectrally resolved femtosecond photon echo spectroscopy of astaxanthin
NASA Astrophysics Data System (ADS)
Kumar, Ajitesh; Karthick Kumar, S. K.; Gupta, Aditya; Goswami, Debabrata
2010-12-01
We have studied the coherence and population dynamics of Astaxanthin solution in methanol and acetonitrile by spectrally resolving their photon echo signals. Our experiments indicate that methanol has a much stronger interaction with the ultrafast dynamics of Astaxanthin in comparison to that of acetonitrile.
Spectrally resolved femtosecond photon echo spectroscopy of astaxanthin
NASA Astrophysics Data System (ADS)
Kumar, Ajitesh; Karthick Kumar, S. K.; Gupta, Aditya; Goswami, Debabrata
2011-08-01
We have studied the coherence and population dynamics of Astaxanthin solution in methanol and acetonitrile by spectrally resolving their photon echo signals. Our experiments indicate that methanol has a much stronger interaction with the ultrafast dynamics of Astaxanthin in comparison to that of acetonitrile.
Modeling and image reconstruction in spectrally resolved bioluminescence tomography
NASA Astrophysics Data System (ADS)
Dehghani, Hamid; Pogue, Brian W.; Davis, Scott C.; Patterson, Michael S.
2007-02-01
Recent interest in modeling and reconstruction algorithms for Bioluminescence Tomography (BLT) has increased and led to the general consensus that non-spectrally resolved intensity-based BLT results in a non-unique problem. However, the light emitted from, for example firefly Luciferase, is widely distributed over the band of wavelengths from 500 nm to 650 nm and above, with the dominant fraction emitted from tissue being above 550 nm. This paper demonstrates the development of an algorithm used for multi-wavelength 3D spectrally resolved BLT image reconstruction in a mouse model. It is shown that using a single view data, bioluminescence sources of up to 15 mm deep can be successfully recovered given correct information about the underlying tissue absorption and scatter.
Spectral-resolved multifocal multiphoton microscopy with multianode photomultiplier tubes
Cha, Jae Won; Tzeranis, Dimitrios; Subramanian, Jaichandar; Yannas, Ioannis V.; Nedivi, Elly; So, Peter T. C.
2014-01-01
Multiphoton excitation fluorescence microscopy is the preferred method for in vivo deep tissue imaging. Many biological applications demand both high imaging speed and the ability to resolve multiple fluorophores. One of the successful methods to improve imaging speed in a highly turbid specimen is multifocal multiphoton microscopy (MMM) based on use of multi-anode photomultiplier tubes (MAPMT). This approach improves imaging speed by using multiple foci for parallelized excitation without sacrificing signal to noise ratio (SNR) due to the scattering of emission photons. In this work, we demonstrate that the MAPMT based MMM can be extended with spectral resolved imaging capability. Instead of generating multiple excitation foci in a 2D grid pattern, a linear array of foci is generated. This leaves one axis of the 2D MAPMT available for spectral dispersion and detection. The spectral-resolved MMM can detect several emission signals simultaneously with high imaging speed optimized for high-throughput, high-contents applications. The new procedure is illustrated using imaging data from the kidney, peripheral nerve regeneration and dendritic morphological data from the brain. PMID:25321515
Time-resolved spectral imaging: better photon economy, higher accuracy
NASA Astrophysics Data System (ADS)
Fereidouni, Farzad; Reitsma, Keimpe; Blab, Gerhard A.; Gerritsen, Hans C.
2015-03-01
Lifetime and spectral imaging are complementary techniques that offer a non-invasive solution for monitoring metabolic processes, identifying biochemical compounds, and characterizing their interactions in biological tissues, among other tasks. Newly developed instruments that perform time-resolved spectral imaging can provide even more information and reach higher sensitivity than either modality alone. Here we report a multispectral lifetime imaging system based on a field-programmable gate array (FPGA), capable of operating at high photon count rates (12 MHz) per spectral detection channel, and with time resolution of 200 ps. We performed error analyses to investigate the effect of gate width and spectral-channel width on the accuracy of estimated lifetimes and spectral widths. Temporal and spectral phasors were used for analysis of recorded data, and we demonstrated blind un-mixing of the fluorescent components using information from both modalities. Fractional intensities, spectra, and decay curves of components were extracted without need for prior information. We further tested this approach with fluorescently doubly-labeled DNA, and demonstrated its suitability for accurately estimating FRET efficiency in the presence of either non-interacting or interacting donor molecules.
The Sun's spectrally resolved center-to-limb variation
NASA Astrophysics Data System (ADS)
Stenflo, Jan Olof
2016-05-01
The center-to-limb variation (CLV) of the Sun's continuous spectrum is well known and has served as a major observational constraint on models of the solar atmosphere. The CLV however also varies dramatically with wavelength inside each spectral line. Here we report on two new atlases that show the properties of the CLV with high spectral resolution. One is a fully resolved spectral atlas from 4084 to 9950 Å of the ratio between the near limb spectrum, at 10 arcsec inside the limb, and the disk center spectrum, both recorded with the FTS at NSO/Kitt Peak. The other atlas gives the same kind of information but covers the whole range of limb distances by giving the ratio spectra for the nine μ positions 0.1, 0.2, …, 0.9. This set of nine atlases for different μ have been recorded over the last couple of years with the solar facility at IRSOL (Istituto Ricerche Solari Locarno) in Switzerland. We find that the CLV is spectrally as richly structured as the ordinary intensity spectrum, but the structuring is different and contains diagnostic information that is not contained in the intensity spectrum. Here we illustrate the properties of the new spectral structures and discuss what they mean.
Phase Resolved X-ray Spectral Analysis of Soft IPs
NASA Astrophysics Data System (ADS)
Pekon, Yakup
2016-07-01
As a subclass of Cataclysmic Variables, Intermediate Polars (IPs) are magnetic systems which mainly show hard X-ray emission. However, there have been an increasing number of systems that also show a soft emission component arising from reprocessed X-rays from the white dwarf limbs. Due to their relatively short periods, they pose as good canditates to perform phase resolved analysis. In this work, X-ray phase resolved spectral analysis of selected IPs with soft X-ray emission components (such as PQ Gem, V2069 Cyg etc.) over the orbital and/or spin periods will be presented. The analyses will help a better understanding of the complex absorption mechanisms and the nature of the soft X-ray emissions in soft IPs.
Spectrally resolved photon-echo spectroscopy of Rhodamine-6G
Kumar, Ajitesh; Karthick, S. K.; Goswami, D.
2013-01-01
Wavelength dependent study of a laser dye: Rhodamine-6G (Rh6G) by using spectrally resolved photon-echo spectroscopy is presented. The coherence and population dynamics of Rh6G solution in methanol changes as the excitation wavelength is tuned near its absorption maxima of 528 nm. Specifically, the central wavelength of the femtosecond laser pulse was set to 535 nm and to 560 nm while the respective spectra of the photon-echo signals were collected. This gives information on how the ultrafast dynamics of the Rh6G molecule changes with a change in the excitation wavelength. PMID:24098869
Spectrally resolved laser-induced fluorescence for bioaerosols standoff detection
NASA Astrophysics Data System (ADS)
Buteau, Sylvie; Stadnyk, Laurie; Rowsell, Susan; Simard, Jean-Robert; Ho, Jim; Déry, Bernard; McFee, John
2007-09-01
An efficient standoff biological warfare detection capability could become an important asset for both defence and security communities based on the increasing biological threat and the limits of the presently existing protection systems. Defence R&D Canada (DRDC) has developed, by the end of the 90s, a standoff bioaerosol sensor prototype based on intensified range-gated spectrometric detection of Laser Induced Fluorescence (LIF). This LIDAR system named SINBAHD monitors the spectrally resolved LIF originating from inelastic interactions with bioaerosols present in atmospheric cells customizable in size and in range. SINBAHD has demonstrated the capability of near real-time detection and classification of bioaerosolized threats at multi-kilometre ranges. In spring 2005, DRDC has initiated the BioSense demonstration project, which combines the SINBAHD technology with a geo-referenced Near InfraRed (NIR) LIDAR cloud mapper. SINBAHD is now being used to acquire more signatures to add in the spectral library and also to optimize and test the new BioSense algorithm strategy. In September 2006, SINBAHD has participated in a two-week trial held at DRDC-Suffield where different open-air wet releases of live and killed bioagent simulants, growth media and obscurants were performed. An autoclave killing procedure was performed on two biological materials (Bacillus subtilis var globigii or BG, and Bacillus thuringiensis or Bt) before being aerosolized, disseminated and spectrally characterized with SINBAHD. The obtained results showed no significant impact of this killing process on their normalised spectral signature in comparison with their live counterparts. Correlation between the detection signals from SINBAHD, an array of slit samplers and a FLuorescent Aerosol Particle Sensor (C-FLAPS) was obtained and SINBAHD's sensitivity could then be estimated. At the 2006 trial, a detection limit of a few tens of Agent Containing Particles per Liter of Air (ACPLA) was obtained
Spectrally resolved motional Stark effect measurements on ASDEX Upgrade
Reimer, R.; Dinklage, A.; Wolf, R.; Fischer, R.; Hobirk, J.; Löbhard, T.; Mlynek, A.; Reich, M.; Sawyer, L.; Collaboration: ASDEX Upgrade
2013-11-15
A spectrally resolved Motional Stark Effect (MSE) diagnostic has been installed at ASDEX Upgrade. The MSE data have been fitted by a forward model providing access to information about the magnetic field in the plasma interior [R. Reimer, A. Dinklage, J. Geiger et al., Contrib. Plasma Phys. 50, 731–735 (2010)]. The forward model for the beam emission spectra comprises also the fast ion D{sub α} signal [W. W. Heidbrink and G. J. Sadler, Nucl. Fusion 34, 535–615 (1994)] and the smearing on the CCD-chip. The calculated magnetic field data as well as the revealed (dia)magnetic effects are consistent with the results from equilibrium reconstruction solver. Measurements of the direction of the magnetic field are affected by unknown and varying polarization effects in the observation.
Arosa, Yago; Lago, Elena López; Varela, Luis Miguel; de la Fuente, Raúl
2016-07-25
In this paper we apply spectrally resolved white light interferometry to measure refractive and group index over a wide spectral band from 400 to 1000 nm. The output of a Michelson interferometer is spectrally decomposed by a homemade prism spectrometer with a high resolution camera. The group index is determined directly from the phase extracted from the spectral interferogram while the refractive index is estimated once its value at a given wavelength is known. PMID:27464179
Structural investigations of human hairs by spectrally resolved ellipsometry
NASA Astrophysics Data System (ADS)
Schulz, Benjamin; Chan, D.; Ruebhausen, M.; Wessel, S.; Wepf, R.
2006-03-01
Human hair is a biological layered system composed of two major layers, the cortex and the cuticle. We show spectrally resolved ellipsometry measurements of the ellipsometric parameters ψ and δ of single human hairs. The spectra reflect the layered nature of hair and the optical anisotropy of the hair’s structure. In addition, measurements on strands of human hair show a high reproducibility of the ellipsometric parameters for different hair fiber bundles from the same person. Based on the measurements, we develop a model of the dielectric function of hair that explains the spectra. This model includes the dielectric properties of the cuticle and cortex as well as their associated layer thicknesses. In addition, surface roughness effects modelled by a roughness layer with an complex refractive index given by an effective medium approach can have a significant effect on the measurements. We derive values for the parameters of the cuticle surface roughness layer of the thickness dACu= 273-360 nm and the air inclusion fA= 0.6 -5.7%. [1] accepted for publication in J. Biomed Opt., 2005
Spectrally Resolved Magnetic Resonance Imaging of the XenonBiosensor
Hilty, Christian; Lowery, Thomas; Wemmer, David; Pines, Alexander
2005-07-15
Due to its ability to non-invasively record images, as well as elucidate molecular structure, nuclear magnetic resonance is the method of choice for applications as widespread as chemical analysis and medical diagnostics. Its detection threshold is, however, limited by the small polarization of nuclear spins in even the highest available magnetic fields. This limitation can, under certain circumstances, be alleviated by using hyper-polarized substances. Xenon biosensors make use of the sensitivity gain of hyperpolarized xenon to provide magnetic resonance detection capability for a specific low-concentration target. They consist of a cryptophane cage, which binds one xenon atom, and which has been connected via a linker to a targeting moiety such as a ligand or antibody. Recent work has shown the possibility of using the xenon biosensor to detect small amounts of a substance in a heterogeneous environment by NMR. Here, we demonstrate that magnetic resonance (MR) provides the capability to obtain spectrally and spatially resolved images of the distribution of immobilized biosensor, opening the possibility for using the xenon biosensor for targeted imaging.
Data Inversion for Over-Resolved Spectral Imaging in Astronomy
NASA Astrophysics Data System (ADS)
Rodet, Thomas; Orieux, François; Giovannelli, Jean-François; Abergel, Alain
2008-11-01
We present an original method for reconstructing a 3-D object having two spatial dimensions and one spectral dimension from data provided by the infrared slit spectrograph on board the Spitzer Space Telescope. During acquisition, the light flux is deformed by a complex process comprising four main elements (the telescope aperture, the slit, the diffraction grating, and optical distortion) before it reaches the 2-D sensor. The originality of this work lies in the physical modeling, in integral form, of this process of data formation in continuous variables. The inversion is also approached with continuous variables in a semi-parametric format decomposing the object into a family of Gaussian functions. The estimate is built in a deterministic regularization framework as the minimizer of a quadratic criterion. These specificities give our method the power to over-resolve. Its performance is illustrated using real and simulated data. We also present a study of the resolution showing a 1.5-fold improvement relative to conventional methods.
Liu, Feilong; Kelley, Megan R.; Crooker, Scott A.; Nie, Wanyi; Mohite, Aditya D.; Ruden, P. Paul; Los Alamos National Lab.; Smith, Darryl L.; Los Alamos National Lab.
2014-12-22
The effect of a magnetic field on the electroluminescence of organic light emitting devices originates from the hyperfine interaction between the electron/hole polarons and the hydrogen nuclei of the host molecules. In this paper, we present an analytical theory of magnetoelectroluminescence for organic semiconductors. To be specific, we focus on bilayer heterostructure devices. In the case we are considering, light generation at the interface of the donor and acceptor layers results from the formation and recombination of exciplexes. The spin physics is described by a stochastic Liouville equation for the electron/hole spin density matrix. By finding the steady-state analytical solutionmore » using Bloch-Wangsness-Redfield theory, we explore how the singlet/triplet exciplex ratio is affected by the hyperfine interaction strength and by the external magnetic field. In order to validate the theory, spectrally resolved electroluminescence experiments on BPhen/m-MTDATA devices are analyzed. With increasing emission wavelength, the width of the magnetic field modulation curve of the electroluminescence increases while its depth decreases. Furthermore, these observations are consistent with the model.« less
Liu, Feilong; Kelley, Megan R.; Crooker, Scott A.; Nie, Wanyi; Mohite, Aditya D.; Ruden, P. Paul; Smith, Darryl L.
2014-12-22
The effect of a magnetic field on the electroluminescence of organic light emitting devices originates from the hyperfine interaction between the electron/hole polarons and the hydrogen nuclei of the host molecules. In this paper, we present an analytical theory of magnetoelectroluminescence for organic semiconductors. To be specific, we focus on bilayer heterostructure devices. In the case we are considering, light generation at the interface of the donor and acceptor layers results from the formation and recombination of exciplexes. The spin physics is described by a stochastic Liouville equation for the electron/hole spin density matrix. By finding the steady-state analytical solution using Bloch-Wangsness-Redfield theory, we explore how the singlet/triplet exciplex ratio is affected by the hyperfine interaction strength and by the external magnetic field. In order to validate the theory, spectrally resolved electroluminescence experiments on BPhen/m-MTDATA devices are analyzed. With increasing emission wavelength, the width of the magnetic field modulation curve of the electroluminescence increases while its depth decreases. Furthermore, these observations are consistent with the model.
Spectrally Resolved Maker Fringes in High-Order Harmonic Generation
NASA Astrophysics Data System (ADS)
Heyl, C. M.; Güdde, J.; Höfer, U.; L'Huillier, A.
2011-07-01
We investigate macroscopic interference effects in high-order harmonic generation using a Ti:sapphire laser operating at a 100 kHz repetition rate. The structure and behavior of spectral and spatial interference fringes are explained and analytically described by transient phase matching of the long electron trajectory contribution. Time-frequency mapping due to the temporal chirp of the harmonic emission allows us to observe Maker fringes directly in the spectral domain.
Debnath, Sanjit Kumar; Kothiyal, Mahendra Prasad
2006-09-20
In spectrally resolved white-light interferometry (SRWLI), the white-light interferogram is decomposed into its monochromatic constituent. The phase of the monochromatic constituents can be determined using a phase-shifting technique over a range of wavelengths. These phase value shave fringe order ambiguity. However, the variation of the phase with respect to the wavenumber is linear and its slope gives the absolute value of the optical-path difference. Since the path difference is related to the height of the test object at a point, a line profile can be determined without ambiguity. The slope value, though less precise helps us determine the fringe order. The fringe order combined with the monochromatic phase value gives the absolute profile, which has the precision of phase-shifting interferometry. The presence of noise in the phase may lead to the misidentification of fringe order, which in turn gives unnecessary jumps in the precise profile. The experimental details of measurement on standard samples with SRWLI are discussed in this paper.
Spectrally resolved fluorescence imaging of human colonic adenomas.
Chwirot, B W; Kowalska, M; Sypniewska, N; Michniewicz, Z; Gradziel, M
1999-06-01
Native fluorescence (autofluorescence) of human tissues can be a valuable source of diagnostic information for detecting premalignant and malignant lesions in the human body. Digital imaging of autofluorescence may be useful for localization of such lesions during endoscopic examinations. Tissue fluorescence of 31 adenomatous polyps obtained from 16 patients has been excited in vitro using the 325 nm line of a He-Cd laser. Digital images of the autofluorescence are recorded in six spectral bands. This study provides new data about the spatial distributions of autofluorescence intensities emitted in different spectral bands by colonic adenomatous lesions and normal colonic mucosa. Areas characterized by autofluorescence intensity lower than in normal mucosa are found for a majority of the polyps under study. The observed patterns of spatial distribution differ for the different spectral bands and for different polypoid lesions. No inverse correlation is found between the emission intensity and the thickness of colonic mucosa. The results indicate the spectral bands most useful for diagnostic applications and demonstrate the complexity of the optical processes involved in shaping both the spectra and intensities of the autofluorescence. PMID:10515079
Zhang, Zhengyang; Kenny, Samuel J; Hauser, Margaret; Li, Wan; Xu, Ke
2015-10-01
By developing a wide-field scheme for spectral measurement and implementing photoswitching, we synchronously obtained the fluorescence spectra and positions of ∼10(6) single molecules in labeled cells in minutes, which consequently enabled spectrally resolved, 'true-color' super-resolution microscopy. The method, called spectrally resolved stochastic optical reconstruction microscopy (SR-STORM), achieved cross-talk-free three-dimensional (3D) imaging for four dyes 10 nm apart in emission spectrum. Excellent resolution was obtained for every channel, and 3D localizations of all molecules were automatically aligned within one imaging path. PMID:26280329
Time-resolved spectral investigations of laser light induced microplasma
NASA Astrophysics Data System (ADS)
Nánai, L.; Hevesi, I.
1992-01-01
The dynamical and spectral properties of an optical breakdown microplasma created by pulses of different lasers on surfaces of insulators (KCI), metals (Cu) and semiconductors (V 2O 5), have been investigated. Experiments were carried out in air and vacuum using different wavelengths (λ = 0.694μm, type OGM-20,λ = 1.06μm with a home-made laser based on neodymium glass crystal, and λ = 10.6μm, similarly home-made) and pulse durations (Q-switched and free-running regimes). To follow the integral, dynamical and spectral characteristics of the luminous spot of microplasma we have used fast cameras (SFR-2M, IMACON-HADLAND), a high speed spectral camera (AGAT-2) and a spectrograph (STE-1). It has been shown that the microplasma consists of two parts: fast front (peak) with τ≈100 ns and slow front (tail) with τ≈1μs durations. The detonation front speed is of the order of ≈10 5 cm s -1 and follows the temporal dependence of to t0.4. It depends on the composition of the surrounding gas and its pressure and could be connected with quick evaporation of the material investigated (peak) and optical breakdown of the ambient gaseous atmosphere (tail). From the delay in appearance of different characteristic spectral lines of the target material and its gaseous surrounding we have shown that the evolution of the microplasma involves evaporation and ionization of the atoms of the parent material followed by optical breakdown due to the incident and absorbed laser light, together with microplasma expansion.
Spectrally resolved fast transient brain states in electrophysiological data.
Vidaurre, Diego; Quinn, Andrew J; Baker, Adam P; Dupret, David; Tejero-Cantero, Alvaro; Woolrich, Mark W
2016-02-01
The brain is capable of producing coordinated fast changing neural dynamics across multiple brain regions in order to adapt to rapidly changing environments. However, it is non-trivial to identify multiregion dynamics at fast sub-second time-scales in electrophysiological data. We propose a method that, with no knowledge of any task timings, can simultaneously identify and describe fast transient multiregion dynamics in terms of their temporal, spectral and spatial properties. The approach models brain activity using a discrete set of sequential states, with each state distinguished by its own multiregion spectral properties. This can identify potentially very short-lived visits to a brain state, at the same time as inferring the state's properties, by pooling over many repeated visits to that state. We show how this can be used to compute state-specific measures such as power spectra and coherence. We demonstrate that this can be used to identify short-lived transient brain states with distinct power and functional connectivity (e.g., coherence) properties in an MEG data set collected during a volitional motor task. PMID:26631815
Spectrally resolved fast transient brain states in electrophysiological data
Vidaurre, Diego; Quinn, Andrew J.; Baker, Adam P.; Dupret, David; Tejero-Cantero, Alvaro; Woolrich, Mark W.
2016-01-01
The brain is capable of producing coordinated fast changing neural dynamics across multiple brain regions in order to adapt to rapidly changing environments. However, it is non-trivial to identify multiregion dynamics at fast sub-second time-scales in electrophysiological data. We propose a method that, with no knowledge of any task timings, can simultaneously identify and describe fast transient multiregion dynamics in terms of their temporal, spectral and spatial properties. The approach models brain activity using a discrete set of sequential states, with each state distinguished by its own multiregion spectral properties. This can identify potentially very short-lived visits to a brain state, at the same time as inferring the state's properties, by pooling over many repeated visits to that state. We show how this can be used to compute state-specific measures such as power spectra and coherence. We demonstrate that this can be used to identify short-lived transient brain states with distinct power and functional connectivity (e.g., coherence) properties in an MEG data set collected during a volitional motor task. PMID:26631815
Spectral characteristics of time resolved magnonic spin Seebeck effect
NASA Astrophysics Data System (ADS)
Etesami, S. R.; Chotorlishvili, L.; Berakdar, J.
2015-09-01
Spin Seebeck effect (SSE) holds promise for new spintronic devices with low-energy consumption. The underlying physics, essential for a further progress, is yet to be fully clarified. This study of the time resolved longitudinal SSE in the magnetic insulator yttrium iron garnet concludes that a substantial contribution to the spin current stems from small wave-vector subthermal exchange magnons. Our finding is in line with the recent experiment by S. R. Boona and J. P. Heremans [Phys. Rev. B 90, 064421 (2014)]. Technically, the spin-current dynamics is treated based on the Landau-Lifshitz-Gilbert equation also including magnons back-action on thermal bath, while the formation of the time dependent thermal gradient is described self-consistently via the heat equation coupled to the magnetization dynamics.
Spectral characteristics of time resolved magnonic spin Seebeck effect
Etesami, S. R.; Chotorlishvili, L.; Berakdar, J.
2015-09-28
Spin Seebeck effect (SSE) holds promise for new spintronic devices with low-energy consumption. The underlying physics, essential for a further progress, is yet to be fully clarified. This study of the time resolved longitudinal SSE in the magnetic insulator yttrium iron garnet concludes that a substantial contribution to the spin current stems from small wave-vector subthermal exchange magnons. Our finding is in line with the recent experiment by S. R. Boona and J. P. Heremans [Phys. Rev. B 90, 064421 (2014)]. Technically, the spin-current dynamics is treated based on the Landau-Lifshitz-Gilbert equation also including magnons back-action on thermal bath, while the formation of the time dependent thermal gradient is described self-consistently via the heat equation coupled to the magnetization dynamics.
A fluorescence LIDAR sensor for hyper-spectral time-resolved remote sensing and mapping.
Palombi, Lorenzo; Alderighi, Daniele; Cecchi, Giovanna; Raimondi, Valentina; Toci, Guido; Lognoli, David
2013-06-17
In this work we present a LIDAR sensor devised for the acquisition of time resolved laser induced fluorescence spectra. The gating time for the acquisition of the fluorescence spectra can be sequentially delayed in order to achieve fluorescence data that are resolved both in the spectral and temporal domains. The sensor can provide sub-nanometric spectral resolution and nanosecond time resolution. The sensor has also imaging capabilities by means of a computer-controlled motorized steering mirror featuring a biaxial angular scanning with 200 μradiant angular resolution. The measurement can be repeated for each point of a geometric grid in order to collect a hyper-spectral time-resolved map of an extended target. PMID:23787661
Marine fluorescence from high spectrally resolved satellite measurements
NASA Astrophysics Data System (ADS)
Wolanin, Aleksandra; Dinter, Tilman; Rozanov, Vladimir; Noël, Stefan; Vountas, Marco; Burrows, John P.; Bracher, Astrid
2014-05-01
When chlorophyll molecules absorb light, most of this energy is transformed into chemical energy in a process of photosynthesis. However, a fraction of the energy absorbed is reemitted as fluorescence. As a result of its relationship to photosynthetic e?ciency, information about chlorophyll fluorescence can be used to assess the physiological state of phytoplankton (Falkowski and Kolber,1995). In-situ measurements of chlorophyll fluorescence are widespread in physiological and ecophysiological studies. When retrieved from space, chlorophyll fluorescence can improve our knowledge of global biogeochemical cycles and phytoplankton productivity (Behrenfeld et al., 2009; Huot et al., 2013) by providing high coverage and periodicity. So far, the only satellite retrieval of sun-induced marine fluorescence, Fluorescence Line Height (FLH), was designed for MODIS (Abbott and Letelier, 1999), and later also applied to the similar sensor MERIS (Gower et al., 2004). However, it could so far not be evaluated on global scale. Here, we present a different approach to observe marine chlorophyll fluorescence, based on the Differential Optical Absorption Spectroscopy (DOAS) technique (Perner and Platt, 1979) applied to the hyperspectral data from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Global Ozone Monitoring Experiment-2 (GOME-2). Since fluorescence, as a trans-spectral process, leads to the shift of the wavelength of the radiation, it can be observed in the filling-in of Fraunhofer lines. In our retrieval, we evaluate the filling-in of the Zeeman triplet Fraunhofer line FeI at 684.3 nm, which is located very close to the emission peak of marine fluorescence (~685 nm). In order to conduct the chlorophyll fluorescence retrieval with the DOAS method, we calculated the reference spectra for chlorophyll fluorescence, based on simulations performed with the coupled ocean-atmosphere radiative transfer model SCIATRAN (Rozanov et al., 2014
NASA Astrophysics Data System (ADS)
Stark, Julian; Müller, Dennis; Nothelfer, Steffen; Kienle, Alwin
2015-07-01
Spectrally and angular resolved light scattering from yeast cells was studied with a scattering microscope and a goniometer. Different cell models were investigated with help of analytical solutions of Maxwell's equations. It was found that extraction of precise morphological and optical cellular properties from the measured scattering patterns and phase functions requires more sophisticated cell models than standard Mie theory.
Comparing spectral resolvability in chinchillas and human listeners using phase discrimination
NASA Astrophysics Data System (ADS)
Shofner, William P.; Sparks, Kathryn; Wu, Yuanxing Esther; Pham, Ellen
2001-05-01
A tone complex made of harmonic components that are added in cosine-starting phase can be discriminated from complexes comprised of identical harmonics that are added with random-starting phases. Phase discrimination occurs when unresolved harmonics interact within a single auditory channel. When harmonics are resolved, there is less interaction among components resulting in poorer phase discrimination performance. Thus, phase discrimination indirectly reflects spectral resolvability. Performance in a phase discrimination task was measured in chinchillas and human listeners to compare spectral resolvability between the two groups. Subjects discriminated a cosine-phase tone complex from random-phase tone complexes in a go/no-go behavioral paradigm. Tone complexes were comprised of a 250-Hz fundamental frequency and N consecutive higher harmonics, where N was 5, 10, 20, and 40. Performance was evaluated in terms of d'. The results show that the measured d' increased as N increased, and values of d' for each N condition were similar between chinchillas and human listeners. Values of the criterion for each N condition were also similar between chinchillas and humans. The results do not support the hypothesis that spectral resolvability is poorer in chinchillas, but suggest that resolvability is similar between the two groups. [Work supported by NIH/NIDCD.
Time-resolved and spectral-resolved optical imaging to study brain hemodynamics in songbirds
NASA Astrophysics Data System (ADS)
Mottin, Stéphane; Montcel, Bruno; Guillet de Chatellus, Hugues; Ramstein, Stéphane; Vignal, Clémentine; Mathevon, Nicolas
2011-07-01
Contrary to the intense debate about brain oxygen dynamics and its uncoupling in mammals, very little is known in birds. In zebra finches, picosecond optical tomography (POT) with a white laser and a streak camera can measure in vivo oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb) concentration changes following physiological stimulation (familiar calls and songs). POT demonstrated sufficient sub-micromolar sensitivity to resolve the fast changes in hippocampus and auditory forebrain areas with 250 μm resolution. The time-course is composed of (i) an early 2s-long event with a significant decrease in Hb and HbO2, respectively -0.7 μMoles/L and -0.9 μMoles/L (ii) a subsequent increase in blood oxygen availability with a plateau of HbO2 (+0.3μMoles/L) and (iii) pronounced vasodilatation events immediately following the end of the stimulus. One of the findings of our work is the direct link between the blood oxygen level-dependent (BOLD) signals previously published in birds and our results. Furthermore, the early vasoconstriction event and post-stimulus ringing seem to be more pronounced in birds than in mammals. These results in bird, a tachymetabolic vertebrate with a long lifespan, can potentially yield new insights for example in brain aging.
An empirical method for correcting the detector spectral response in energy-resolved CT
NASA Astrophysics Data System (ADS)
Schmidt, Taly Gilat
2012-03-01
Energy-resolving photon-counting detectors have the potential for improved material decomposition compared to dual-kVp approaches. However, material decomposition accuracy is limited by the nonideal spectral response of the detectors. This work proposes an empirical method for correcting the nonideal spectral response, including spectrum-tailing effects. Unlike previous correction methods which relied on synchrotron measurements, the proposed method can be performed on the scanner. The proposed method estimates a spectral-response matrix by performing x-ray projection measurements through a range of known thicknesses of two or more calibration materials. Once estimated, the spectral-response matrix is incorporated into conventional material decomposition algorithms. A simulation study investigated preliminary feasibility of the proposed method. The spectral-response matrix was estimated using simulated projection measurements through PMMA, aluminum, and gadolinium. An energy-resolved acquisition of a thorax phantom with gadolinium in the blood pool was simulated assuming a five-bin detector with realistic spectral response. Energy-bin data was decomposed into Compton, photoelectric, and gadolinium basis projections with and without the proposed correction method. Basis images were reconstructed by filtered backprojection. Results demonstrated that the nonideal spectral response reduced the ability to distinguish gadolinium from materials such as bone, while images reconstructed with the proposed correction method successfully depicted the contrast agent. The proposed correction method reduced errors from 9% to 0.6% in the Compton image, 90% to 0.6% in the photoelectric image and from 40% to 6% in the gadolinium image when using a three-material calibration. Overall, results support feasibility of the proposed spectral-response correction method.
NASA Astrophysics Data System (ADS)
Che, Diping; Shapiro, Daniel B.; Esquerra, Raymond M.; Kliger, David S.
1994-07-01
A simple and sensitive technique is introduced to measure time-resolved linear dichroism of spectral transitions. This technique uses the fact that a linear dichroic sample rotates the polarization plane of linearly polarized light. The theoretical basis of the technique is presented using Mueller calculus and a detailed signal analysis is given to account for the effects of various optical imperfections. The results of this analysis are confirmed with the application of the technique to the time-resolved linear dichroism of bacteriorhodopsin in membrane patches (purple membrane) during its photocycle. These experimental results demonstrate the sentivity of the technique.
NASA Astrophysics Data System (ADS)
Nakamura, Kazutaka G.; Ohya, Kazuma; Takahashi, Hiroshi; Tsuruta, Tetsuya; Sasaki, Hiroya; Uozumi, Shin-ichi; Norimatsu, Katsura; Kitajima, Masahiro; Shikano, Yutaka; Kayanuma, Yosuke
2016-07-01
Coherent optical phonons in bulk solid systems play a crucial role in understanding and designing light-matter interactions and can be detected by the transient-reflectivity measurement. In this paper, we demonstrate spectrally resolved detection of coherent optical phonons in diamond from ultrashort infrared pump-probe measurements using optical bandpass filters. We show that this enhances the sensitivity approximately 35 times in measuring the coherent oscillations in the transient reflectivity compared with the commonly used spectrally integrated measurement. To explain this observation, we discuss its mechanism.
NASA Astrophysics Data System (ADS)
Gottlieb, J. J.; Groth, C. P. T.; Hawboldt, R. J.; Hawken, D. F.; Lock, G. D.; Wong, C. H.; Chan, Y. S.; Maillette, J.; Petrini, G. L.; Picket, J. S.
A review is provided of nonstationary gas dynamic investigations carried out at the University of Toronto Institute for Aerospace Studies. Numerical studies aimed at predicting the operation and performance of two stage light-gas guns and selecting optimum gas operating conditions are ongoing. Preliminary internal ballistics work on modelling the motions of propellant gases and projectiles in an experimental gun with a high pressure combustion section and a low pressure launch tube has been completed. The study of propellant combustion in a closed vessel to obtain propellant burning rates and combustion gas properties for use in modelling of gas guns is now underway. The nonequilibrium structure of a shock front in a dusty gas is being studied in a dusty shock tube facility to determine particle drag and heat transfer coefficients. Studies undertaken to provide data for the design of a large air-blast and thermal simulation facility include: investigation of the reflection eliminator, the venting from the test section of combustion products from thermal radiation sources, and the prediction of unsteady flow. A high pressure reservoir with an exit nozzle containing a slot has been constructed to obtain experimental data on discharge coefficients of orifices and slots in high-low pressure guns and on blast simulators.
DISPERSION ANALYSIS OF RADIATION/THERMAL FRONTS WITH FULL RESOLVED SPECTRAL OPACITY VARIATION.
L. AUER; R. LOWRIE
2000-12-01
The radiation transport and linearized thermal energy equations have been analyzed to find the temporal dependence of the component modes in a radiation/thermal front. The fully resolved spectral variation of the opacity as a function of energy, as well as the exact time and angular dependence, is treated in this work. As we are able to study arbitrarily complicated opacity spectra, we stress the importance of the new results as a check on the effect of using opacity averages.
Spectrally resolved optical probing of laser induced magnetization dynamics in bismuth iron garnet
NASA Astrophysics Data System (ADS)
Koene, Benny; Deb, Marwan; Popova, Elena; Keller, Niels; Rasing, Theo; Kirilyuk, Andrei
2016-07-01
The spectrally resolved magnetization dynamics in bismuth iron garnet shows a fluence dependent light induced modification of the magneto-optical Faraday spectrum. It is demonstrated that the relative contributions from the tetrahedral and octahedral iron sites to the Faraday spectrum change due to the impact of the pump pulse. This change explains the observed deviation from a linear dependence of the amplitude of the oscillations on the fluence, as expected for the inverse Faraday effect.
NASA Astrophysics Data System (ADS)
Lunt, Richard R.; Giebink, Noel C.; Belak, Anna A.; Benziger, Jay B.; Forrest, Stephen R.
2009-03-01
We demonstrate spectrally resolved photoluminescence quenching as a means to determine the exciton diffusion length of several archetype organic semiconductors used in thin film devices. We show that aggregation and crystal orientation influence the anisotropy of the diffusion length for vacuum-deposited polycrystalline films. The measurement of the singlet diffusion lengths is found to be in agreement with diffusion by Förster transfer, whereas triplet diffusion occurs primarily via Dexter transfer.
Spectrally resolved optical probing of laser induced magnetization dynamics in bismuth iron garnet.
Koene, Benny; Deb, Marwan; Popova, Elena; Keller, Niels; Rasing, Theo; Kirilyuk, Andrei
2016-07-13
The spectrally resolved magnetization dynamics in bismuth iron garnet shows a fluence dependent light induced modification of the magneto-optical Faraday spectrum. It is demonstrated that the relative contributions from the tetrahedral and octahedral iron sites to the Faraday spectrum change due to the impact of the pump pulse. This change explains the observed deviation from a linear dependence of the amplitude of the oscillations on the fluence, as expected for the inverse Faraday effect. PMID:27213266
NASA Astrophysics Data System (ADS)
Horilova, Julia; Cunderlikova, Beata; Marcek Chorvatova, Alzbeta
2015-05-01
Early detection of cancer is crucial for the successful diagnostics of its presence and its subsequent treatment. To improve cancer detection, we tested the progressive multimodal optical imaging of U87MG cells in culture. A combination of steady-state spectroscopic methods with the time-resolved approach provides a new insight into the native metabolism when focused on endogenous tissue fluorescence. In this contribution, we evaluated the metabolic state of living U87MG cancer cells in culture by means of endogenous flavin fluorescence. Confocal microscopy and time-resolved fluorescence imaging were employed to gather spectrally and time-resolved images of the flavin fluorescence. We observed that flavin fluorescence in U87MG cells was predominantly localized outside the cell nucleus in mitochondria, while exhibiting a spectral maximum under 500 nm and fluorescence lifetimes under 1.4 ns, suggesting the presence of bound flavins. In some cells, flavin fluorescence was also detected inside the cell nuclei in the nucleoli, exhibiting longer fluorescence lifetimes and a red-shifted spectral maximum, pointing to the presence of free flavin. Extra-nuclear flavin fluorescence was diminished by 2-deoxyglucose, but failed to increase with 2,4-dinitrophenol, the uncoupler of oxidative phosphorylation, indicating that the cells use glycolysis, rather than oxidative phosphorylation for functioning. These gathered data are the first step toward monitoring the metabolic state of U87MG cancer cells.
Spectrally-resolved measurement of concentrated light distributions for Fresnel lens concentrators.
Besson, P; White, P McVey; Dominguez, C; Voarino, P; Garcia-Linares, P; Lemiti, M; Schriemer, H; Hinzer, K; Baudrit, M
2016-01-25
A test method that measures spectrally resolved irradiance distribution for a concentrator photovoltaic (CPV) optical system is presented. In conjunction with electrical I-V curves, it is a means to visualize and characterize the effects of chromatic aberration and nonuniform flux profiles under controllable testing conditions. The indoor characterization test bench, METHOD (Measurement of Electrical, Thermal and Optical Devices), decouples the temperatures of the primary optical element (POE) and the cell allowing their respective effects on optical and electrical performance to be analysed. In varying the temperature of the POE, the effects on electrical efficiency, focal distance, spectral sensitivity, acceptance angle and multi-junction current matching profiles can be quantified. This work presents the calibration procedures to accurately image the spectral irradiance distribution of a CPV system and a study of system behavior over lens temperature. PMID:26832591
NASA Astrophysics Data System (ADS)
Encrenaz, T.; Tinetti, G.; Tessenyi, M.; Drossart, P.; Hartogh, P.; Coustenis, A.
2015-12-01
The study of exoplanets is an exploding field in astronomy. Recent discoveries have made possible the development of a new research field, the spectroscopic characterization of the exoplanetary atmospheres, using both primary and eclipse transits. A dedicated space mission will make possible the characterization of many classes of exoplanets, from the hot Jupiters to the temperate super-Earths. In this paper, we discuss how the spectral range and the spectral resolving power can be optimized for identifying a maximum number of candidate atmospheric species. Spectral modeling shows that the simultaneous observation of the whole spectral range, from 0.55 to 16 μm is ideal for (1) capturing all types of planets at different temperatures, (2) detecting the variety of chemical atmospheric compounds with some redundancy, and (3) enabling an optimal retrieval of the chemical abundances and thermal profile. Limiting the spectral interval to 11 μm would make the retrieval more difficult in the case of cold exoplanets. In the visible range, the extension down to 0.4 s at different temperatures, (2) detecting the variety of chemical atmospheric compounds with some redundancy, and (3) enabling an optimal retrieval of the chemical abundances andst candidate molecules.
NASA Astrophysics Data System (ADS)
Smolka, Jozef; Mateasik, Anton
2006-08-01
Aminolevulinic acid (ALA) is an efficient substance used in photodynamic therapy (PDT). It is a precursor of light-sensitive products that can selectively accumulate in malignant cells following the altered activity of the heme biosynthetic pathway enzymes in such cells. These products are synthesized in mitochondria and distributed to various cellular structures [1]. The localization of ALA products in subcellular structures depends on their chemical characteristics as well as on the properties of the intracellular environment [2]. Characterization of such properties is possible by means of fluorescent probes like JC-1 and carboxy SNARF-1. However, the emission spectra of these probes are overlapped with spectral pattern of typical ALA product -protoporphyrin IX (PpIX). Spectral overlap of fluorescence signals prevents to clearly separate a distribution of probes from PpIX distribution what can completely mess the applicability of these probes in characterization of cell properties. The spectrally resolved confocal laser microscopy can be used to overcome this problem. In this study, a distribution of ALA metabolic products in relation to the mitochondrial membrane potential and intracellular pH was examined. Human cell lines (KYSE-450, KYSE-70) from esophageal squamous cell carcinoma were used. Cells were incubated with 1mM solution of ALA for four hours. Two fluorescent probes, carboxy SNARF-1 and JC-1 , were used to monitor intracellular pH levels and to determine membrane potential changes, respectively. The samples were scanned by spectrally resolved laser scanning microscope. Spectral linear unmixing method was used to discriminate and separate regions of accumulation of ALA metabolic products of JC-1 and carboxy SNARF-1.
NASA Technical Reports Server (NTRS)
Panda, J.; Seasholtz, R. G.
2004-01-01
The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99, 1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the spectrally resolved application, laser light scattered by the air molecules is collected and analyzed using a Fabry-Perot interferometer (FPI). The difference between the incident laser frequency and the peak of the Rayleigh spectrum provides a measure of gas velocity. The temperature is measured from the spectral broadening caused by the random thermal motion and density is measured from the total light intensity. The present point measurement technique uses a CW laser, a scanning FPI and photon counting electronics. The 1 mm long probe volume is moved from point to point to survey the flow fields. Additional arrangements were made to remove particles from the main as well as the entrained flow and to isolate FPI from the high sound and vibration levels produced by the supersonic jets. In general, velocity is measured within +/- 10 m/s accuracy and temperature within +/- 10 K accuracy.
Yukawas, G-flux, and spectral covers from resolved Calabi-Yau's
NASA Astrophysics Data System (ADS)
Marsano, Joseph; Schäfer-Nameki, Sakura
2011-11-01
We use the resolution procedure of Esole and Yau [1] to study Yukawa couplings, G-flux, and the emergence of spectral covers from elliptically fibered Calabi-Yau's with a surface of A 4 singularities. We provide a global description of the Esole-Yau resolution and use it to explicitly compute Chern classes of the resolved 4-fold, proving the conjecture of [2] for the Euler character in the process. We comment on the physical implications of the surprising singular fibers in codimension 2 and 3 in [1] and emphasize a group theoretic interpretation based on the A 4 weight lattice. We then construct explicit G-fluxes by brute force in one of the 6 birationally equivalent Esole-Yau resolutions, quantize them explicitly using our result for the second Chern class, and compute the spectrum and flux-induced 3-brane charges, finding agreement with results and conjectures of local models in all cases. Finally, we provide a precise description of the spectral divisor formalism in this setting and sharpen the procedure described in [3] in order to explicitly demonstrate how the Higgs bundle spectral cover of the local model emerges from the resolved Calabi-Yau geometry. Along the way, we demonstrate explicitly how the quantization rules for fluxes in the local and global models are related.
Photophysical properties of DASPMI as revealed by spectrally resolved fluorescence decays.
Ramadass, Radhan; Bereiter-Hahn, Jürgen
2007-07-01
Photophysical properties of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) in various solvents were investigated using time- and space-correlated single photon counting. DASPMI is known to selectively stain mitochondria in living cells.1,2 The uptake and fluorescence intensity of DASPMI in mitochondria is a dynamic measure of membrane potential. Hence, an endeavor has been made to elucidate the mechanism of DASPMI fluorescence by obtaining spectrally resolved fluorescence decays in different solvents. A biexponential decay model was sufficient to globally describe the wavelength-dependent fluorescence in ethanol and chloroform. While in glycerol, a three-exponential decay model was necessary for global analysis. In the polar low-viscous solvent water, a monoexponential decay model fitted the decay data. The sensitivity of DASPMI to solvent viscosity was analyzed using various proportions of glycerol-ethanol mixtures. The lifetimes were found to increase with increasing solvent viscosity. The negative amplitudes of the short lifetime component found in chloroform and glycerol at the longer wavelengths validated the formation of new excited-state species from the initially excited state. Time-resolved emission spectra in chloroform and glycerol showed a biphasic increase of spectral width and emission maxima. The spectral width had an initial fast increase within 150 ps and a near constant thereafter. A three-state model of generalized scheme, on the basis of successive formation of locally excited state (LE), intramolecular charge transfer state (ICT), and twisted intramolecular charge transfer (TICT) state, has been proposed to explain the excited-state kinetics. The presumed role of solvation dynamics of ICT and TICT states leading to the asymmetrical broadening and structureless fluorescence has been substantiated by the decomposition of time-resolved emission spectra in chloroform, glycerol, and ethanol/glycerol mixtures. PMID:17559255
Spectrally resolved fluorescence cross sections of BG and BT with a 266-nm pump wavelength
NASA Astrophysics Data System (ADS)
Atkins, Joshua; Thomas, Michael E.; Joseph, Richard I.
2007-04-01
The spectrally resolved absolute fluorescence cross sections of Bacillus globigii (BG) and Bacillus thuringiensis (BT) were measured with a 266nm Nd:YAG laser source. The aerosol samples were prepared in dilute aqueous suspensions for measurement and the absolute cross section was found by use of the Raman scattering line from water. Integrated cross sections for BT and BG were found to be 1.1864 × 10 -12 cm2(spore sr) and 3.251 × 10 -13 cm2/ (spore sr) respectively.
Time-resolved spectral measurements for the boeing free-electron laser experiments
Lumpkin, A.H.; King, N.S.P.; Wilke, M.D.; Wei, S.P.; Davis, K.J.
1988-01-01
A time-resolved optical spectrometer based on the integration of a Jarrell-Ash 1/4-m spectrometer and a streak camera has been used to evaluate the Boeing Burst Mode Oscillator experiment. The system provides information on spectral evolution on both the micropulse (10 ps) and macropulse (50-100..mu..s) time scales. We have measured the micropulse duration, a wavelength shift within a micropulse and the development of a discrete second wavelength during a macropulse. 4 refs., 9 figs., 1 tab.
Spectrally resolved four-wave mixing experiments on bulk GaAs with 14-fs pulses
Wehner, M.U.; Steinbach, D.; Wegener, M.; Marschner, T.; Stolz, W.
1996-05-01
We investigate the coherent dynamics at the band edge of GaAs at low temperatures for carrier densities ranging from 4.3{times}10{sup 14} cm{sup {minus}3} to 4.4{times}10{sup 17} cm{sup {minus}3} by means of spectrally resolved transient four-wave mixing with 14-fs pulses. At large nonequilibrium carrier densities we observe oscillations with an energy-dependent oscillation period related to interference among continuum states. The experimental findings are compared with a simple model. This comparison delivers a weak energy dependence of dephasing in the initial buildup phase of screening. {copyright} {ital 1996 Optical Society of America.}
NASA Astrophysics Data System (ADS)
Orlov, S. V.; Naumov, A. V.; Vainer, Yu. G.; Kador, Lothar
2012-11-01
We present a method for the spectrally resolved analysis of fluorescence blinking of single quantum emitters. It is based on the well-known technique of repeated recording of single-molecule (SM) fluorescence excitation spectra. The potential of our approach is presented for the example of single tetra-tert-butylterrylene molecules in an amorphous polymer matrix (polyisobutylene), which exhibit fluorescence blinking at cryogenic temperatures. Measuring the spectral dependence of the blinking statistics improves the possibility to clarify the microscopic nature of the dark state(s) of the emitters. We demonstrate how the blinking statistics can be definitely attributed to conformational changes in the local environment of a SM and how the parameters of the corresponding elementary excitations can be measured. The analysis of the blinking statistics as a function of the optical excitation frequency allows us to discriminate between photo-induced and spontaneous transitions into a dark state.
Extended resolvent and inverse scattering with an application to KPI
NASA Astrophysics Data System (ADS)
Boiti, M.; Pempinelli, F.; Pogrebkov, A. K.; Prinari, B.
2003-08-01
We present in detail an extended resolvent approach for investigating linear problems associated to 2+1 dimensional integrable equations. Our presentation is based as an example on the nonstationary Schrödinger equation with potential being a perturbation of the one-soliton potential by means of a decaying two-dimensional function. Modification of the inverse scattering theory as well as properties of the Jost solutions and spectral data as follows from the resolvent approach are given.
NASA Astrophysics Data System (ADS)
Levitt, James A.; Chung, Pei-Hua; Suhling, Klaus
2015-09-01
Spectrally resolved confocal microscopy and fluorescence lifetime imaging have been used to measure the polarity of lipid-rich regions in living HeLa cells stained with Nile red. The emission peak from the solvatochromic dye in lipid droplets is at a shorter wavelength than other, more polar, stained internal membranes, and this is indicative of a low polarity environment. We estimate that the dielectric constant, ɛ, is around 5 in lipid droplets and 25<ɛ<40 in other lipid-rich regions. Our spectrally resolved fluorescence lifetime imaging microscopy (FLIM) data show that intracellular Nile red exhibits complex, multiexponential fluorescence decays due to emission from a short lifetime locally excited state and a longer lifetime intramolecular charge transfer state. We measure an increase in the average fluorescence lifetime of the dye with increasing emission wavelength, as shown using phasor plots of the FLIM data. We also show using these phasor plots that the shortest lifetime decay components arise from lipid droplets. Thus, fluorescence lifetime is a viable contrast parameter for distinguishing lipid droplets from other stained lipid-rich regions. Finally, we discuss the FLIM of Nile red as a method for simultaneously mapping both polarity and relative viscosity based on fluorescence lifetime measurements.
NASA Astrophysics Data System (ADS)
Rück, Angelika; Hauser, Carmen; Mosch, Simone; Kalinina, Sviatlana
2014-09-01
Fluorescence-guided diagnosis of tumor tissue is in many cases insufficient, because false positive results interfere with the outcome. Improvement through observation of cell metabolism might offer the solution, but needs a detailed understanding of the origin of autofluorescence. With respect to this, spectrally resolved multiphoton fluorescence lifetime imaging was investigated to analyze cell metabolism in metabolic phenotypes of malignant and nonmalignant oral mucosa cells. The time-resolved fluorescence characteristics of NADH were measured in cells of different origins. The fluorescence lifetime of bound and free NADH was calculated from biexponential fitting of the fluorescence intensity decay within different spectral regions. The mean lifetime was increased from nonmalignant oral mucosa cells to different squamous carcinoma cells, where the most aggressive cells showed the longest lifetime. In correlation with reports in the literature, the total amount of NADH seemed to be less for the carcinoma cells and the ratio of free/bound NADH was decreased from nonmalignant to squamous carcinoma cells. Moreover for squamous carcinoma cells a high concentration of bound NADH was found in cytoplasmic organelles (mainly mitochondria). This all together indicates that oxidative phosphorylation and a high redox potential play an important role in the energy metabolism of these cells.
Spectrally resolving and scattering-compensated x-ray luminescence/fluorescence computed tomography
Cong, Wenxiang; Shen, Haiou; Wang, Ge
2011-01-01
The nanophosphors, or other similar materials, emit near-infrared (NIR) light upon x-ray excitation. They were designed as optical probes for in vivo visualization and analysis of molecular and cellular targets, pathways, and responses. Based on the previous work on x-ray fluorescence computed tomography (XFCT) and x-ray luminescence computed tomography (XLCT), here we propose a spectrally-resolving and scattering-compensated x-ray luminescence/fluorescence computed tomography (SXLCT or SXFCT) approach to quantify a spatial distribution of nanophosphors (other similar materials or chemical elements) within a biological object. In this paper, the x-ray scattering is taken into account in the reconstruction algorithm. The NIR scattering is described in the diffusion approximation model. Then, x-ray excitations are applied with different spectra, and NIR signals are measured in a spectrally resolving fashion. Finally, a linear relationship is established between the nanophosphor distribution and measured NIR data using the finite element method and inverted using the compressive sensing technique. The numerical simulation results demonstrate the feasibility and merits of the proposed approach. PMID:21721815
The complex ion structure of warm dense carbon measured by spectrally resolved x-ray scattering
Kraus, D.; Barbrel, B.; Falcone, R. W.; Vorberger, J.; Helfrich, J.; Frydrych, S.; Ortner, A.; Otten, A.; Roth, F.; Schaumann, G.; Schumacher, D.; Siegenthaler, K.; Wagner, F.; Roth, M.; Gericke, D. O.; Wünsch, K.; Bachmann, B.; Döppner, T.; Bagnoud, V.; Blažević, A.; and others
2015-05-15
We present measurements of the complex ion structure of warm dense carbon close to the melting line at pressures around 100 GPa. High-pressure samples were created by laser-driven shock compression of graphite and probed by intense laser-generated x-ray sources with photon energies of 4.75 keV and 4.95 keV. High-efficiency crystal spectrometers allow for spectrally resolving the scattered radiation. Comparing the ratio of elastically and inelastically scattered radiation, we find evidence for a complex bonded liquid that is predicted by ab-initio quantum simulations showing the influence of chemical bonds under these conditions. Using graphite samples of different initial densities we demonstrate the capability of spectrally resolved x-ray scattering to monitor the carbon solid-liquid transition at relatively constant pressure of 150 GPa. Showing first single-pulse scattering spectra from cold graphite of unprecedented quality recorded at the Linac Coherent Light Source, we demonstrate the outstanding possibilities for future high-precision measurements at 4th Generation Light Sources.
NASA Astrophysics Data System (ADS)
Kraus, D.; Döppner, T.; Kritcher, A. L.; Yi, A.; Boehm, K.; Bachmann, B.; Divol, L.; Fletcher, L. B.; Glenzer, S. H.; Landen, O. L.; Masters, N.; Saunders, A. M.; Weber, C.; Falcone, R. W.; Neumayer, P.
2016-05-01
We present a new experimental platform to perform spectrally resolved x-ray scattering measurements of ionization, density and temperature in imploding CH or beryllium capsules at the National Ignition Facility. Scattered x-rays at 9 keV from a zinc He-alpha plasma source at a scattering angle of 120 degrees are highly sensitive to K-shell ionization, while at the same time constraining density and temperature. This platform will allow for x-ray scattering studies of dense plasmas with free electron densities up to 1025 cm-3 giving the possibility to investigate effects of pressure ionization and Pauli blocking on the ablator ionization state right before or shortly after stagnation of the implosion.
Spectrally resolved microprobe cathodoluminescence of intergrowth Bi5-xLaxTiNbWO15 ferroelectrics
NASA Astrophysics Data System (ADS)
Ge, Wanyin; Zhu, Wenliang; Higashino, Masayuki; Li, Yongxiang; Yi, Zhiguo; Pezzotti, Giuseppe
2007-10-01
Spectrally resolved cathodoluminescence measurements of Bi5-xLaxTiNbWO15 (x=0-1.50) ceramics at room temperature showed three distinct luminescence bands located at about 380, 502, and 660nm, respectively, which were tentatively assigned to F+ center, oxygen vacancy-related defect and octahedron structure-related luminescence center, respectively. These assignments could be made in light of electron irradiation experiments with different exposure times. Bands related to oxygen vacancies were clearly enhanced by lanthanum doping, indicating that charge compensation occurred by the substitution of Bi for La3+ in perovskitelike structured intergrowth ferroelectrics. We observed that, for contents of La3+ x >0.75, La3+ ions entered the [Bi2O2]2+ layer according to a doping mechanism which is briefly discussed in this letter.
NASA Astrophysics Data System (ADS)
Meier, Amanda; Adams, Daniel; Squier, Jeff; Durfee, Charles
2010-10-01
Characterization of the nonlinear refractive index of a material is important in order to fully understand the nonlinear propagation of femtosecond laser pulses. The most common method to obtaining the nonlinear refractive index is Z-scan. However, since it averages over pulse duration and beam profile, Z-scan is not reliable when there is time- and intensity-dependence of the nonlinear response. The new method we are exploring to make these nonlinear refractive index measurements is spatially and spectrally resolved interferometry (SSRI). SSRI is a method that can give a simultaneous measurement of the spatial wave-front across the frequency or temporal profile of the pulse. The SSRI method proves better in measuring response at specific y and t, allowing it to measure both delayed response and saturation effects. The ability to make a measurement in both dimensions enables understanding of spatiotemporal dynamics in other experiments as cross-wave polarization and filamentation.
NASA Astrophysics Data System (ADS)
Moran, Andrew M.; Nome, Rene A.; Scherer, Norbert F.
2007-11-01
The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute's electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of
Spectrally-resolved Soft X-ray Observations and the Temperature Structure of the Solar Corona
NASA Astrophysics Data System (ADS)
Caspi, Amir; Warren, Harry; McTiernan, James; Woods, Thomas N.
2015-04-01
Solar X-ray observations provide important diagnostics of plasma heating and particle acceleration, during solar flares and quiescent periods. How the corona is heated to its ~1-3 MK nominal temperature remains one of the fundamental unanswered questions of solar physics; heating of plasma to tens of MK during solar flares -- particularly to the hottest observed temperatures of up to ~50 MK -- is also still poorly understood. Soft X-ray emission (~0.1-10 keV; or ~0.1-10 nm) is particularly sensitive to hot coronal plasma and serves as a probe of the thermal processes driving coronal plasma heating. Spectrally- and temporally-resolved measurements are crucial for understanding these energetic processes, but there have historically been very few such observations. We present new solar soft X-ray spectra from the Amptek X123-SDD, measuring quiescent solar X-ray emission from ~0.5 to ~30 keV with ~0.15 keV FWHM resolution from two SDO/EVE calibration sounding rocket underflights in 2012 and 2013. Combined with observations from RHESSI, GOES/XRS, SDO/EVE, and SDO/AIA, the temperature distribution derived from these data suggest significant hot (5-10 MK) emission from active regions, and the 2013 spectra suggest a low-FIP enhancement of only ~1.6 relative to the photosphere, 40% of the usually-observed value from quiescent coronal plasma. We explore the implications of these findings on coronal heating. We discuss future missions for spectrally-resolved soft X-ray observations using the X123-SDD, including the upcoming MinXSS 3U CubeSat using the X123-SDD and scheduled for deployment in mid-2015, and the CubIXSS 6U CubeSat mission concept.
Moran, Andrew M.; Nome, Rene A.; Scherer, Norbert F.
2007-11-14
The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute's electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of
NASA Technical Reports Server (NTRS)
Smith, Stephen
2011-01-01
We are developing arrays of transition-edge sensor (TES) X-ray detectors optimized for high count-rate solar astronomy applications where characterizing the high velocity motions of X-ray jets in solar flares is of particular interest. These devices are fabricated on thick Si substrates and consist of 35x35micron^2 TESs with 4.5micron thick, 60micron pitch, electroplated absorbers. We have tested devices fabricated with different geometric stem contact areas with the TES and surrounding substrate area, which allows us to investigate the loss of athermal phonons to the substrate. Results show a correlation between the stem contact area and a non-Gaussian broadening in the spectral line shape consistent with athermal phonon loss. When the contact area is minimized we have obtained remarkable board-band spectral resolving capabilities of 1.3 plus or minus 0.leV at an energy of 1.5 keV, 1.6 plus or minus 0.1 eV at 5.9 keV and 2.0 plus or minus 0.1 eV at 8 keV. This, coupled with a capability of accommodating 100's of counts per second per pixel makes these devices an exciting prospect of future x-ray astronomy applications.
NASA Astrophysics Data System (ADS)
Yu, Hoi-Fung; Preece, Robert D.; Greiner, Jochen; Narayana Bhat, P.; Bissaldi, Elisabetta; Briggs, Michael S.; Cleveland, William H.; Connaughton, Valerie; Goldstein, Adam; von Kienlin, Andreas; Kouveliotou, Chryssa; Mailyan, Bagrat; Meegan, Charles A.; Paciesas, William S.; Rau, Arne; Roberts, Oliver J.; Veres, Péter; Wilson-Hodge, Colleen; Zhang, Bin-Bin; van Eerten, Hendrik J.
2016-04-01
Aims: We aim to obtain high-quality time-resolved spectral fits of gamma-ray bursts observed by the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope. Methods: We performed time-resolved spectral analysis with high temporal and spectral resolution of the brightest bursts observed by Fermi GBM in its first four years of mission. Results: We present the complete catalog containing 1491 spectra from 81 bursts with high spectral and temporal resolution. Distributions of parameters, statistics of the parameter populations, parameter-parameter and parameter-uncertainty correlations, and their exact values are obtained and presented as main results in this catalog. We report a criterion that is robust enough to automatically distinguish between different spectral evolutionary trends between bursts. We also search for plausible blackbody emission components and find that only three bursts (36 spectra in total) show evidence of a pure Planck function. It is observed that peak energy and the averaged, time-resolved power-law index at low energy are slightly harder than the time-integrated values. Time-resolved spectroscopic results should be used instead of time-integrated results when interpreting physics from the observed spectra. Tables A.1 and B.1 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A135
NASA Astrophysics Data System (ADS)
Stoneman, M. R.; Singh, D. R.; Raicu, V.
2010-02-01
Resonance Energy Transfer (RET) between a donor molecule in an electronically excited state and an acceptor molecule in close proximity has been frequently utilized for studies of protein-protein interactions in living cells. Typically, the cell under study is scanned a number of times in order to accumulate enough spectral information to accurately determine the RET efficiency for each region of interest within the cell. However, the composition of these regions may change during the course of the acquisition period, limiting the spatial determination of the RET efficiency to an average over entire cells. By means of a novel spectrally resolved two-photon microscope, we were able to obtain a full set of spectrally resolved images after only one complete excitation scan of the sample of interest. From this pixel-level spectral data, a map of RET efficiencies throughout the cell is calculated. By applying a simple theory of RET in oligomeric complexes to the experimentally obtained distribution of RET efficiencies throughout the cell, a single spectrally resolved scan reveals stoichiometric and structural information about the oligomer complex under study. This presentation will describe our experimental setup and data analysis procedure, as well as an application of the method to the determination of RET efficiencies throughout yeast cells (S. cerevisiae) expressing a G-protein-coupled receptor, Sterile 2 α factor protein (Ste2p), in the presence and absence of α-factor - a yeast mating pheromone.
NASA Astrophysics Data System (ADS)
Lee, Seungwan; Choi, Yu-Na; Kim, Hee-Joung
2014-09-01
Dual-energy computed tomography (CT) techniques have been used to decompose materials and characterize tissues according to their physical and chemical compositions. However, these techniques are hampered by the limitations of conventional x-ray detectors operated in charge integrating mode. Energy-resolved photon-counting detectors provide spectral information from polychromatic x-rays using multiple energy thresholds. These detectors allow simultaneous acquisition of data in different energy ranges without spectral overlap, resulting in more efficient material decomposition and quantification for dual-energy CT. In this study, a pre-reconstruction dual-energy CT technique based on volume conservation was proposed for three-material decomposition. The technique was combined with iterative reconstruction algorithms by using a ray-driven projector in order to improve the quality of decomposition images and reduce radiation dose. A spectral CT system equipped with a CZT-based photon-counting detector was used to implement the proposed dual-energy CT technique. We obtained dual-energy images of calibration and three-material phantoms consisting of low atomic number materials from the optimal energy bins determined by Monte Carlo simulations. The material decomposition process was accomplished by both the proposed and post-reconstruction dual-energy CT techniques. Linear regression and normalized root-mean-square error (NRMSE) analyses were performed to evaluate the quantitative accuracy of decomposition images. The calibration accuracy of the proposed dual-energy CT technique was higher than that of the post-reconstruction dual-energy CT technique, with fitted slopes of 0.97-1.01 and NRMSEs of 0.20-4.50% for all basis materials. In the three-material phantom study, the proposed dual-energy CT technique decreased the NRMSEs of measured volume fractions by factors of 0.17-0.28 compared to the post-reconstruction dual-energy CT technique. It was concluded that the
Lee, Seungwan; Choi, Yu-Na; Kim, Hee-Joung
2014-09-21
Dual-energy computed tomography (CT) techniques have been used to decompose materials and characterize tissues according to their physical and chemical compositions. However, these techniques are hampered by the limitations of conventional x-ray detectors operated in charge integrating mode. Energy-resolved photon-counting detectors provide spectral information from polychromatic x-rays using multiple energy thresholds. These detectors allow simultaneous acquisition of data in different energy ranges without spectral overlap, resulting in more efficient material decomposition and quantification for dual-energy CT. In this study, a pre-reconstruction dual-energy CT technique based on volume conservation was proposed for three-material decomposition. The technique was combined with iterative reconstruction algorithms by using a ray-driven projector in order to improve the quality of decomposition images and reduce radiation dose. A spectral CT system equipped with a CZT-based photon-counting detector was used to implement the proposed dual-energy CT technique. We obtained dual-energy images of calibration and three-material phantoms consisting of low atomic number materials from the optimal energy bins determined by Monte Carlo simulations. The material decomposition process was accomplished by both the proposed and post-reconstruction dual-energy CT techniques. Linear regression and normalized root-mean-square error (NRMSE) analyses were performed to evaluate the quantitative accuracy of decomposition images. The calibration accuracy of the proposed dual-energy CT technique was higher than that of the post-reconstruction dual-energy CT technique, with fitted slopes of 0.97-1.01 and NRMSEs of 0.20-4.50% for all basis materials. In the three-material phantom study, the proposed dual-energy CT technique decreased the NRMSEs of measured volume fractions by factors of 0.17-0.28 compared to the post-reconstruction dual-energy CT technique. It was concluded that the
Application of a Phase-resolving, Directional Nonlinear Spectral Wave Model
NASA Astrophysics Data System (ADS)
Davis, J. R.; Sheremet, A.; Tian, M.; Hanson, J. L.
2014-12-01
We describe several applications of a phase-resolving, directional nonlinear spectral wave model. The model describes a 2D surface gravity wave field approaching a mildly sloping beach with parallel depth contours at an arbitrary angle accounting for nonlinear, quadratic triad interactions. The model is hyperbolic, with the initial wave spectrum specified in deep water. Complex amplitudes are generated based on the random phase approximation. The numerical implementation includes unidirectional propagation as a special case. In directional mode, it solves the system of equations in the frequency-alongshore wave number space. Recent enhancements of the model include the incorporation of dissipation caused by breaking and propagation over a viscous mud layer and the calculation of wave induced setup. Applications presented include: a JONSWAP spectrum with a cos2s directional distribution, for shore-perpendicular and oblique propagation, a study of the evolution of a single directional triad, and several preliminary comparisons to wave spectra collected at the USACE-FRF in Duck, NC which show encouraging results although further validation with a wider range of beach slopes and wave conditions is needed.
Tizei, L H G; Kociak, M
2012-05-01
Here we report the spectrally and spatially resolved cathodoluminescence of diamond nanoparticles using focused fast electron beams in a transmission electron microscope. We demonstrate the possibility of quickly detecting various individual colour centres of different kinds on wide areas (several micrometres square) contained in nanoparticles separated by subwavelength distances. Among them, nanoparticles containing one or more neutral nitrogen-vacancy (NV(0)) intensity maxima have been seen, attributable to individual emitters. Thanks to a spatial resolution which is solely limited by charge carrier diffusion in the case of a fast electron (80 keV) setup, the spectra of two individual NV(0) emitters separated by 80 nm inside a nanoparticle have been spatially discerned. A shift of the zero phonon line (ZPL) between the two emitters, which we attribute to internal stress, is shown to arise even within the same nanoparticle. Detailed emission spectra (ZPL, phonon lines and Huang-Rhys factor, directly linked to the relaxation energy of the colour centre) in 51 individual NV(0) centres have been measured in 39 particles. The ZPL and Huang-Rhys factor are found to be measurably dispersed, while the phonon energies keep constant. PMID:22481219
Lu, Yujie; Zhang, Xiaoqun; Douraghy, Ali; Stout, David; Tian, Jie; Chan, Tony F.; Chatziioannou, Arion F.
2009-01-01
Through restoration of the light source information in small animals in vivo, optical molecular imaging, such as fluorescence molecular tomography (FMT) and bioluminescence tomography (BLT), can depict biological and physiological changes observed using molecular probes. A priori information plays an indispensable role in tomographic reconstruction. As a type of a priori information, the sparsity characteristic of the light source has not been sufficiently considered to date. In this paper, we introduce a compressed sensing method to develop a new tomographic algorithm for spectrally-resolved bioluminescence tomography. This method uses the nature of the source sparsity to improve the reconstruction quality with a regularization implementation. Based on verification of the inverse crime, the proposed algorithm is validated with Monte Carlo-based synthetic data and the popular Tikhonov regularization method. Testing with different noise levels and single/multiple source settings at different depths demonstrates the improved performance of this algorithm. Experimental reconstruction with a mouse-shaped phantom further shows the potential of the proposed algorithm. PMID:19434138
NASA Astrophysics Data System (ADS)
Haralampus-Grynaviski, Nicole Marie
A unique spectrally-resolved confocal microscope is developed for use in biophysical applications. This microscope enables the rapid collection of the complete emission spectra for every pixel in a fluorescence image. The basic optical design and function of the device are assessed through examination of fluorescently labeled beads, using both one- and two-photon excitation. The spatial resolution of the device is found to approach the diffraction limit in the lateral plane and ˜2 mum in the axial plane. This device can readily distinguish between overlapping emissions which are not easily differentiated using standard filter techniques. The potential of this device to be used as a detection method in DNA sequence experiments is demonstrated. Images of a human skin tissue section and a mouse kidney section are presented which demonstrate the structure and spectra of biologic samples can be resolved. The emission properties of human ocular lipofuscin, LF, a heterogeneous auto-fluorescent material associated with age-related macular degeneration is investigated in detail. Isolated LF granules show substantial variation in emission spectra. Near-field scanning microscopy experiments find the emissive regions on a single LF granule are homogeneous on the ˜150 nm scale and confirm results obtained on the microscope developed here. For ˜100 studied LF deposits, the histogram of the measured peak emission is centered around 18,000 cm-1 (555 nm). The average emission spectra for large LF aggregates (peak 17,150 cm-1) is red-shifted compared to the average emission from small individual granules (peak 17,600 cm-1). The average LF granule emission observed here is similar to previously reported bulk LF emission and the emission of a previously identified LF chromophore, A2E. Individual LF granules show a broad range in emission maximum whether the LF is isolated from multiple donors or examined within the cells of a single donor. Multiple as yet unidentified chromophores
Good, Philipp; Cooper, Thomas; Querci, Marco; Wiik, Nicolay; Ambrosetti, Gianluca; Steinfeld, Aldo
2015-01-01
The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300−2500 nm at incidence angles 15–60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0–60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350–1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article “Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators” in Solar Energy Materials and Solar Cells. PMID:26862556
Njegovec, Matej; Donlagic, Denis
2010-11-01
This paper presents a spectrally-resolved integration system suitable for the reading of Bragg grating, all-fiber Fabry-Perot, and similar spectrally-resolved fiber-optic sensors. This system is based on a standard telecommunication dense wavelength division multiplexing transmission module that contains a distributed feedback laser diode and a wavelength locker. Besides the transmission module, only a few additional opto-electronic components were needed to build an experimental interrogation system that demonstrated over a 2 nm wide wavelength interrogation range, and a 1 pm wavelength resolution. When the system was combined with a typical Bragg grating sensor, a strain resolution of 1 με and temperature resolution of 0.1 °C were demonstrated experimentally. The proposed interrogation system relies entirely on Telecordia standard compliant photonic components and can thus be straightforwardly qualified for use within the range of demanding applications. PMID:21164765
NASA Astrophysics Data System (ADS)
Caspi, A.; Shih, A.; Warren, H. P.; DeForest, C. E.; Woods, T. N.
2015-12-01
Solar soft X-ray (SXR) observations provide important diagnostics of plasma heating, during solar flares and quiescent times. Spectrally- and temporally-resolved measurements are crucial for understanding the dynamics and evolution of these energetic processes; spatially-resolved measurements are critical for understanding energy transport. A better understanding of the thermal plasma informs our interpretation of hard X-ray (HXR) observations of nonthermal particles, improving our understanding of the relationships between particle acceleration, plasma heating, and the underlying release of magnetic energy during reconnection. We introduce a new proposed mission, the CubeSat Imaging X-ray Solar Spectrometer (CubIXSS), to measure spectrally- and spatially-resolved SXRs from the quiescent and flaring Sun from a 6U CubeSat platform in low-Earth orbit during a nominal 1-year mission. CubIXSS includes the Amptek X123-SDD silicon drift detector, a low-noise, commercial off-the-shelf (COTS) instrument enabling solar SXR spectroscopy from ~0.5 to ~30 keV with ~0.15 keV FWHM spectral resolution with low power, mass, and volume requirements. An X123-CdTe cadmium-telluride detector is also included for ~5-100 keV HXR spectroscopy with ~0.5-1 keV FWHM resolution. CubIXSS also includes a novel spectro-spatial imager -- the first ever solar imager on a CubeSat -- utilizing a pinhole aperture and X-ray transmission diffraction grating to provide full-Sun imaging from ~0.1 to ~10 keV, with ~25 arcsec and ~0.1 Å FWHM spatial and spectral resolutions, respectively. We discuss scaled versions of these instruments, with greater sensitivity and dynamic range, and significantly improved spectral and spatial resolutions for the imager, for deployment on larger platforms such as Small Explorer missions.
NASA Astrophysics Data System (ADS)
Snyder, Gregory Frantz
2013-03-01
In extragalactic astronomy, a central challenge is that we cannot directly watch what happens to galaxies before and after they are observed. This dissertation focuses on linking predictions of galaxy time-evolution directly with observations, evaluating how interactions, mergers, and other processes affect the appearance of elliptical galaxies. The primary approach is to combine hydrodynamical simulations of galaxy formation, including all major components, with dust radiative transfer to predict their observational signatures The current paradigm implies that a quiescent elliptical emerges following a formative starburst event. These trigger accretion onto the central supermassive black hole (SMBH), which then radiates as an active galactic nucleus (AGN). However, it is not clear the extent to which SMBH growth is fueled by these events nor how important is their energy input at setting the appearance of the remnant. This thesis presents results drawing from three phases in the formation of a typical elliptical: 1) I evaluate how to disentangle AGN from star formation signatures in mid-infrared spectra during a dust-enshrouded starburst, making testable predictions for robustly tracing SMBH growth with the James Webb Space Telescope; 2) I develop a model for the rate of merger-induced post-starburst galaxies selected from optical spectra, resolving tension between their observed rarity and merger rates from other estimates; and 3) I present results from Hubble Space Telescope imaging of elliptical galaxies in galaxy clusters at 1 < z < 2, the precursors of present-day massive clusters with M ~ 1015 solar masses, demonstrating that their stars formed over an extended period and ruling out the simplest model for their formation history. These results lend support to a stochastic formation history for ellipticals driven by mergers or interactions. However, significant uncertainties remain in how to evaluate the implications of galaxy appearance, in particular their
A Comparison of PSD Enveloping Methods for Nonstationary Vibration
NASA Technical Reports Server (NTRS)
Irvine, Tom
2015-01-01
There is a need to derive a power spectral density (PSD) envelope for nonstationary acceleration time histories, including launch vehicle data, so that components can be designed and tested accordingly. This paper presents the results of the three methods for an actual flight accelerometer record. Guidelines are given for the application of each method to nonstationary data. The method can be extended to other scenarios, including transportation vibration.
NASA Astrophysics Data System (ADS)
Mermut, O.; Gallant, P.; Le Bouch, N.; Leclair, S.; Noiseux, I.; Vernon, M.; Morin, J.-F.; Diamond, K.; Patterson, M. S.; Samkoe, K.; Pogue, B.
2009-02-01
Multimodal agents that serve as both probes for contrast and light-activated effectors of cellular processes in diseased tissue were developed. These agents were introduced into multicellular tumor spheroids (3D tissue models) and in the chorioallantoic membrane (CAM) of a chicken embryo. The luminescence decay was examined using a novel technique involving a spectrally-resolved fluorescence lifetime apparatus integrated with a weak electromagnet. A spectrallyresolved lifetime setup was used to identify magneto-optic species sensitive to magnetic field effects and distinguish from background emissions. We demonstrate that the applied magnetic fields can alter reaction rates and product distribution of some dyes detected by time- and spectrally-resolved luminescence changes. We will discuss the use of exogenous magneto-optical probes taken up in tumors to both induce phototoxicity, a process that is governed by complex and dynamically evolving mechanisms involving reactive oxygen species, and monitor treatment progress. The magnetic field enhancement, measured over a range of weak fields (0-300 mT) is correlated to oxygenation and may be used to monitor dynamic changes occurring due to oxygen consumption over the course of photodynamic therapy. Such online measurements provide the possibility to derive real-time information about response to treatment via monitoring magnetic field enhancement/suppression of the time-resolved, spectrally-resolved luminescence of the probe at the site of the treatment directly. Magnetic perturbation of lifetime can serve as a status reporter, providing optical feedback of oxygen-mediated treatments in situ and allowing for real-time adjustment of a phototherapy treatment plan.
Spectrally interleaved, comb-mode-resolved spectroscopy using swept dual terahertz combs
Hsieh, Yi-Da; Iyonaga, Yuki; Sakaguchi, Yoshiyuki; Yokoyama, Shuko; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Araki, Tsutomu; Yasui, Takeshi
2014-01-01
Optical frequency combs are innovative tools for broadband spectroscopy because a series of comb modes can serve as frequency markers that are traceable to a microwave frequency standard. However, a mode distribution that is too discrete limits the spectral sampling interval to the mode frequency spacing even though individual mode linewidth is sufficiently narrow. Here, using a combination of a spectral interleaving and dual-comb spectroscopy in the terahertz (THz) region, we achieved a spectral sampling interval equal to the mode linewidth rather than the mode spacing. The spectrally interleaved THz comb was realized by sweeping the laser repetition frequency and interleaving additional frequency marks. In low-pressure gas spectroscopy, we achieved an improved spectral sampling density of 2.5 MHz and enhanced spectral accuracy of 8.39 × 10−7 in the THz region. The proposed method is a powerful tool for simultaneously achieving high resolution, high accuracy, and broad spectral coverage in THz spectroscopy. PMID:24448604
NASA Astrophysics Data System (ADS)
Yuan, Zhen; Zhang, Qizhi; Grobmyer, Stephen; Jiang, Huabei
2009-02-01
We describe a new spectral approach for inversion of photoacoustic data with multi-wavelength pulsed laser illumination. Multi-spectral PAT provides a means of recovery of different chromophore concentrations and ultrasound velocity simultaneously and directly by incorporating prior spectral information into the image reconstruction process. It is demonstrated from simulation tests and small animal experiments that the multi-parameter recovery based on multispectral PAT is reliable and accurate. The reconstructed multiple parameter images may provide us a key tool to quantify physiological function, disease progression, or response to intervention.
Spectrally resolved eclipse maps of the accretion disk in UX Ursae Majoris
NASA Technical Reports Server (NTRS)
Rutten, Rene G. M.; Dhillon, V. S.; Horne, Keith; Kuulkers, E.; Van Paradijs, J.
1993-01-01
An effort is made to observationally constrain accretion disks on the basis of light curves from the eclipsing cataclysmic variable UX Ursae Majoris, reconstructing the spectral energy distribution across the face of an accretion disk. The spectral resolution obtained suffices to reveal not only the radial dependence of absorption and emission line features within the disk, but also the spectral details of the bright spot that is formed where the accretion stream from the secondary star collides with the disk. The importance of such constraints for theoretical models is noted.
Chorvat, D; Chorvatova, A
2006-12-01
A new setup for time-resolved fluorescence micro-spectroscopy of cells, based on multi-dimensional time-correlated single photon counting, was designed and tested. Here we demonstrate that the spectrometer allows fast and reproducible measurements of endogenous flavin fluorescence measured directly in living cardiac cells after excitation with visible picosecond laser diodes. Two complementary approaches for the analysis of spectrally- and time-resolved autofluorescence data are presented, comprising the fluorescence decay fitting by exponential series and the time-resolved emission spectroscopy analysis. In isolated cardiac myocytes, we observed three distinct lifetime pools with characteristic lifetime values spanning from picosecond to nanosecond range and the time-dependent red shift of the autofluorescence emission spectra. We compared obtained results to in vitro recordings of free flavin adenine dinucleotide (FAD) and FAD in lipoamide dehydrogenase (LipDH). The developed setup combines the strength of both spectral and fluorescence lifetime analysis and provides a solid base for the study of complex systems with intrinsic fluorescence, such as identification of the individual flavinoprotein components in living cardiac cells. This approach therefore constitutes an important instrumental advancement towards redox fluorimetry of living cardiomyocytes, with the perspective of its applications in the investigation of oxidative metabolic state under pathophysiological conditions, such as ischemia and/or metabolic disorders. PMID:17033778
Kassianov, Evgueni I.; Barnard, James C.; Flynn, Connor J.; Riihimaki, Laura D.; Michalsky, Joseph; Hodges, G. B.
2014-08-22
We present here a simple retrieval of the areal-averaged and spectrally resolved surface albedo using only ground-based measurements of atmospheric transmission under fully overcast conditions. Our retrieval is based on a one-line equation and widely accepted assumptions regarding the weak spectral dependence of cloud optical properties in the visible and near-infrared spectral range. The feasibility of our approach for the routine determinations of albedo is demonstrated for different landscapes with various degrees of heterogeneity using three sets of measurements:(1) spectrally resolved atmospheric transmission from Multi-Filter Rotating Shadowband Radiometer (MFRSR) at wavelength 415, 500, 615, 673, and 870 nm, (2) tower-based measurements of local surface albedo at the same wavelengths, and (3) areal-averaged surface albedo at four wavelengths (470, 560, 670 and 860 nm) from collocated and coincident Moderate Resolution Imaging Spectroradiometer (MODIS) observations. These integrated datasets cover both long (2008-2013) and short (April-May, 2010) periods at the ARM Southern Great Plains (SGP) site and the NOAA Table Mountain site, respectively. The calculated root mean square error (RMSE), which is defined here as the root mean squared difference between the MODIS-derived surface albedo and the retrieved area-averaged albedo, is quite small (RMSE≤0.01) and comparable with that obtained previously by other investigators for the shortwave broadband albedo. Good agreement between the tower-based daily averages of surface albedo for the completely overcast and non-overcast conditions is also demonstrated. This agreement suggests that our retrieval originally developed for the overcast conditions likely will work for non-overcast conditions as well.
Chromatic-aberration diagnostic based on a spectrally resolved lateral-shearing interferometer
Bahk, Seung -Whan; Dorrer, Christopher; Roides, Rick G.; Bromage, Jake
2016-03-18
Here, a simple diagnostic characterizing one-dimensional chromatic aberrations in a broadband beam is introduced. A Ronchi grating placed in front of a spectrometer entrance slit provides spectrally coupled spatial phase information. The radial-group delay of a refractive system and the pulse-front delay of a wedged glass plate have been characterized accurately in a demonstration experiment.
Spectral Characterization of A Resolved M dwarf-M dwarf Binary
NASA Astrophysics Data System (ADS)
Tamiya, Tomoki; Burgasser, Adam J.; Aganze, Christian; Mercado, Gretel; Suarez, Adrian
2016-06-01
We report characterization of the resolved binary M dwarf SDSS J155526.53+095409.5AB through spectroscopic and imaging analysis. Classification of resolved near-infrared spectra with IRTF/SpeX and tools in the SpeX Prism Library Analysis Toolkit (SPLAT) indicate component types of M3.5 and M8, separated by about 4''. We match the data to atmosphere models using an Monte Carlo Markov Chain routine to determine preliminary physical properties for each component (temperature, surface gravity and metallicity), and obtain estimates for the distance (106±11 pc) and projected separation (419±45 AU).Funding acknowledgement: This project is supported by the National Aeronautics and Space Administration under Grant No. NNX15AI75G.
SPATIALLY AND SPECTRALLY RESOLVED HYDROGEN GAS WITHIN 0.1 AU OF T TAURI AND HERBIG Ae/Be STARS
Eisner, J. A.; Monnier, J. D.; Woillez, J.; Ragland, S.; Wizinowich, P.; Akeson, R. L.; Millan-Gabet, R.; Graham, J. R.; Hillenbrand, L. A.; Pott, J.-U.
2010-08-01
We present near-infrared observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milliarcseconds and a spectral resolution of {approx}2000. Our observations spatially resolve gas and dust in the inner regions of protoplanetary disks, and spectrally resolve broad-linewidth emission from the Br{gamma} transition of hydrogen gas. We use the technique of spectro-astrometry to determine centroids of different velocity components of this gaseous emission at a precision orders of magnitude better than the angular resolution. In all sources, we find the gaseous emission to be more compact than or distributed on similar spatial scales to the dust emission. We attempt to fit the data with models including both dust and Br{gamma}-emitting gas, and we consider both disk and infall/outflow morphologies for the gaseous matter. In most cases where we can distinguish between these two models, the data show a preference for infall/outflow models. In all cases, our data appear consistent with the presence of some gas at stellocentric radii of {approx}0.01 AU. Our findings support the hypothesis that Br{gamma} emission generally traces magnetospherically driven accretion and/or outflows in young star/disk systems.
Time-resolved optically stimulated luminescence and spectral emission features of α-Al2O3:C
NASA Astrophysics Data System (ADS)
Chithambo, M. L.; Nyirenda, A. N.; Finch, A. A.; Rawat, N. S.
2015-09-01
This report is concerned with the influence of measurement temperature on luminescence lifetime and on the spectral emission features of luminescence from α-Al2O3:C. The lifetimes were determined from time-resolved luminescence spectra. Spectral measurements were done using thermoluminescence and X-ray excited optical luminescence. The emission spectra of α-Al2O3:C studied in this work shows prominent bands at 330, 380 and 420 nm associated with vacancies in the oxygen sub-lattice in α-Al2O3:C and an additional band at 695 nm due to Cr substitution for Al. Emission bands below 500 nm are independent of temperature below 125 °C but widen with temperature. Direct evidence of thermal quenching of the 420 nm emission band is provided. Beyond 200 °C, the 380 and 420 nm bands merge and widen, with the 420 nm emission dominant. Before the onset of thermal quenching, luminescence lifetimes are affected by retrapping both in the shallow- and in the main electron trap. This was deduced from features of time-resolved luminescence spectra measured from samples with and without the shallow trap. Additional measurements with temperature decreasing from 160 to 20 °C, after phototransfer as well as after a considerable delay between irradiation and measurement, suggest that the change in lifetimes could also be related to other factors including slight shifts in emission wavelength for the 380 and 420 nm emissions.
Near-infrared optical mammography with broadband spectral imaging for spatially resolved oximetry
NASA Astrophysics Data System (ADS)
Yu, Yang; Sassaroli, Angelo; Homer, Marc J.; Graham, Roger A.; Fantini, Sergio
2011-02-01
We report the development of an instrument for diffuse spectral imaging of the human breast operating over the wavelength range 650-900 nm. This instrument images the slightly compressed human breast in a planar geometry by performing a tandem scan, over the x-y plane, of a 3 mm illumination optical fiber and a 5 mm collection optical fiber that are collinear and located on opposite sides of the breast. An edge-correction algorithm accounts for breast thickness variability over the x-y plane, a second-derivative imaging algorithm enhances the display of optical inhomogeneities, and a paired-wavelength spectral method yields oxygenation maps. We report our results of oxygenation mapping in eighteen human subjects, two of which are breast cancer patients, one with a ductal carcinoma in situ, the other with an invasive ductal carcinoma.
Time-resolved spatial phase measurements with 2-dimensional spectral interferometry
NASA Astrophysics Data System (ADS)
Childress, Colby; Planchon, Thomas; Amir, Wafa; Squier, Jeff A.; Durfee, Charles G.
2007-03-01
We are using 2-dimensional spectral interferometry for sensitive measurements of spatial phase distortions. The reference pulse and the time-delayed probe pulse are coincident on an imaging spectrometer, yielding spectral and spatial phase information. This technique offers the potential of higher sensitivity than traditional spatial interferometry since there are many fringes of data for each spatial point. We illustrate this technique with measurements of the thermal lensing profile in a cryogenically cooled Ti:sapphire amplifier crystal that is pumped by tens of watts of power from four frequency-doubled Nd:YLF lasers running at 1 kHz. By adjusting the relative delay of the probe and reference pulses, we characterize the thermal transients during and after the pump pulses. We compare the measured transient thermal profiles with those calculated with a finite-element model.
Spectrally-resolved measurements of aerosol extinction at ultraviolet and visible wavelengths
NASA Astrophysics Data System (ADS)
Flores, M.; Washenfelder, R. A.; Brock, C. A.; Brown, S. S.; Rudich, Y.
2012-12-01
Aerosols play an important role in the Earth's radiative budget. Aerosol extinction includes both the scattering and absorption of light, and these vary with wavelength, aerosol diameter, and aerosol composition. Historically, aerosol absorption has been measured using filter-based or extraction methods that are prone to artifacts. There have been few investigations of ambient aerosol optical properties at the blue end of the visible spectrum and into the ultraviolet. Brown carbon is particularly important in this spectral region, because it both absorbs and scatters light, and encompasses a large and variable group of organic compounds from biomass burning and secondary organic aerosol. We have developed a laboratory instrument that combines new, high-power LED light sources with high-finesse optical cavities to achieve sensitive measurements of aerosol optical extinction. This instrument contains two broadband channels, with spectral coverage from 360 - 390 nm and 385 - 420 nm. Using this instrument, we report aerosol extinction in the ultraviolet and near-visible spectral region as a function of chemical composition and structure. We have measured the extinction cross-sections between 360 - 420 nm with 0.5 nm resolution using different sizes and concentrations of polystyrene latex spheres, ammonium sulfate, and Suwannee River fulvic acid. Fitting the real and imaginary part of the refractive index allows the absorption and scattering to be determined.
Westphal, Peter; Kaltenbach, Johannes-Maria; Wicker, Kai
2016-04-01
A good understanding of the corneal birefringence properties is essential for polarimetric glucose monitoring in the aqueous humor of the eye. Therefore, we have measured complete 16-element Mueller matrices of single-pass transitions through nine porcine corneas in-vitro, spectrally resolved in the range 300…1000 nm. These ellipsometric measurements have been performed at several angles of incidence at the apex and partially at the periphery of the corneas. The Mueller matrices have been decomposed into linear birefringence, circular birefringence (i.e. optical rotation), depolarization, and diattenuation. We found considerable circular birefringence, strongly increasing with decreasing wavelength, for most corneas. Furthermore, the decomposition revealed significant dependence of the linear retardance (in nm) on the wavelength below 500 nm. These findings suggest that uniaxial and biaxial crystals are insufficient models for a general description of the corneal birefringence, especially in the blue and in the UV spectral range. The implications on spectral-polarimetric approaches for glucose monitoring in the eye (for diabetics) are discussed. PMID:27446644
Westphal, Peter; Kaltenbach, Johannes-Maria; Wicker, Kai
2016-01-01
A good understanding of the corneal birefringence properties is essential for polarimetric glucose monitoring in the aqueous humor of the eye. Therefore, we have measured complete 16-element Mueller matrices of single-pass transitions through nine porcine corneas in-vitro, spectrally resolved in the range 300…1000 nm. These ellipsometric measurements have been performed at several angles of incidence at the apex and partially at the periphery of the corneas. The Mueller matrices have been decomposed into linear birefringence, circular birefringence (i.e. optical rotation), depolarization, and diattenuation. We found considerable circular birefringence, strongly increasing with decreasing wavelength, for most corneas. Furthermore, the decomposition revealed significant dependence of the linear retardance (in nm) on the wavelength below 500 nm. These findings suggest that uniaxial and biaxial crystals are insufficient models for a general description of the corneal birefringence, especially in the blue and in the UV spectral range. The implications on spectral-polarimetric approaches for glucose monitoring in the eye (for diabetics) are discussed. PMID:27446644
Probing Gamma-ray Emission of Geminga and Vela with Non-stationary Models
NASA Astrophysics Data System (ADS)
Chai, Yating; Cheng, Kwong-Sang; Takata, Jumpei
2016-06-01
It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.
Two-photon spectral amplitude of entangled states resolved in separable Schmidt modes
NASA Astrophysics Data System (ADS)
Avella, A.; Brida, G.; Chekhova, M.; Gramegna, M.; Shurupov, A.; Genovese, M.
2015-10-01
The ability to access high dimensionality in Hilbert spaces represents a demanding key-stone for state-of-the-art quantum information. The manipulation of entangled states in continuous variables, wavevector as well frequency, represents a powerful resource in this sense. The number of dimensions of the Hilbert space that can be used in practical information protocols can be determined by the number of Schmidt modes that it is possible to address one by one. In the case of wavevector variables, the Schmidt modes can be losslessly selected using single-mode fibre and a spatial light modulator, but no similar procedure exists for the frequency space. The aim of this work is to present a technique to engineer the spectral properties of biphoton light, emitted via ultrafast spontaneous parametric down conversion, in such a way that the two-photon spectral amplitude (TPSA) contains several non-overlapping Schmidt modes, each of which can be filtered losslessly in frequency variables. Such TPSA manipulation is operated by a fine balancing of parameters like the pump frequency, the shaping of pump pulse spectrum, the dispersion dependence of spontaneous parametric down-conversion crystals as well as their length. Measurements have been performed exploiting the group velocity dispersion induced by the passage of optical fields through dispersive media, operating a frequency-to-time two-dimensional Fourier transform of the TPSA. Exploiting this kind of measurement we experimentally demonstrate the ability to control the Schmidt modes structure in TPSA through the pump spectrum manipulation.
NASA Technical Reports Server (NTRS)
Wood, Brian E.; Linsky, Jeffrey L.
2010-01-01
On 2008 May 2, Chandra observed the X-ray spectrum of xi Boo (G8 V+K4 V), resolving the binary for the first time in X-rays and allowing the coronae of the two stars to be studied separately. With the contributions of ξ Boo A and B to the system's total X-ray emission now observationally established (88.5% and 11.5% respectively), consideration of mass loss measurements for GK dwarfs of various activity levels (including one for xi Boo) leads to the surprising conclusion that xi Boo B may dominate the wind from the binary, with xi Boo A's wind being very weak despite its active corona. Emission measure (EM) distributions and coronal abundances are computed for both stars and compared with Chandra measurements of other moderately active stars with G8-K5 spectral types, all of which exhibit a narrow peak in EM near log T = 6.6, indicating that the coronal heating process in these stars has a strong preference for this temperature. As is the case for the Sun and many other stars, our sample of stars shows coronal abundance anomalies dependent on the first ionization potential (FIP) of the element. We see no dependence of the degree of FIP effect on activity, but there is a dependence on spectral type, a correlation that becomes more convincing when moderately active main-sequence stars with a broader range of spectral types are considered. This clear dependence of coronal abundances on spectral type weakens if the stellar sample is allowed to be contaminated by evolved stars, interacting binaries or extremely active stars with logLX 29, explaining why this correlation has not been recognized in the past.
NASA Astrophysics Data System (ADS)
Wood, Brian E.; Linsky, Jeffrey L.
2010-07-01
On 2008 May 2, Chandra observed the X-ray spectrum of ξ Boo (G8 V+K4 V), resolving the binary for the first time in X-rays and allowing the coronae of the two stars to be studied separately. With the contributions of ξ Boo A and B to the system's total X-ray emission now observationally established (88.5% and 11.5%, respectively), consideration of mass loss measurements for GK dwarfs of various activity levels (including one for ξ Boo) leads to the surprising conclusion that ξ Boo B may dominate the wind from the binary, with ξ Boo A's wind being very weak despite its active corona. Emission measure (EM) distributions and coronal abundances are computed for both stars and compared with Chandra measurements of other moderately active stars with G8-K5 spectral types, all of which exhibit a narrow peak in EM near log T = 6.6, indicating that the coronal heating process in these stars has a strong preference for this temperature. As is the case for the Sun and many other stars, our sample of stars shows coronal abundance anomalies dependent on the first ionization potential (FIP) of the element. We see no dependence of the degree of "FIP effect" on activity, but there is a dependence on spectral type, a correlation that becomes more convincing when moderately active main-sequence stars with a broader range of spectral types are considered. This clear dependence of coronal abundances on spectral type weakens if the stellar sample is allowed to be contaminated by evolved stars, interacting binaries, or extremely active stars with log LX >29, explaining why this correlation has not been recognized in the past.
Wood, Brian E.; Linsky, Jeffrey L. E-mail: jlinsky@jila.colorado.ed
2010-07-10
On 2008 May 2, Chandra observed the X-ray spectrum of {xi} Boo (G8 V+K4 V), resolving the binary for the first time in X-rays and allowing the coronae of the two stars to be studied separately. With the contributions of {xi} Boo A and B to the system's total X-ray emission now observationally established (88.5% and 11.5%, respectively), consideration of mass loss measurements for GK dwarfs of various activity levels (including one for {xi} Boo) leads to the surprising conclusion that {xi} Boo B may dominate the wind from the binary, with {xi} Boo A's wind being very weak despite its active corona. Emission measure (EM) distributions and coronal abundances are computed for both stars and compared with Chandra measurements of other moderately active stars with G8-K5 spectral types, all of which exhibit a narrow peak in EM near log T = 6.6, indicating that the coronal heating process in these stars has a strong preference for this temperature. As is the case for the Sun and many other stars, our sample of stars shows coronal abundance anomalies dependent on the first ionization potential (FIP) of the element. We see no dependence of the degree of 'FIP effect' on activity, but there is a dependence on spectral type, a correlation that becomes more convincing when moderately active main-sequence stars with a broader range of spectral types are considered. This clear dependence of coronal abundances on spectral type weakens if the stellar sample is allowed to be contaminated by evolved stars, interacting binaries, or extremely active stars with log L{sub X} >29, explaining why this correlation has not been recognized in the past.
Time- and spectrally resolved measurements of laser-driven hohlraum radiation
Hessling, T.; Blazevic, A.; Stoehlker, T.; Frank, A.; Kraus, D.; Roth, M.; Schaumann, G.; Schumacher, D.; Hoffmann, D. H. H.
2011-07-15
At the GSI Helmholtz center for heavy-ion research combined experiments with heavy ions and laser-produced plasmas are investigated. As a preparation to utilize indirectly heated targets, where a converter hohlraum provides thermal radiation to create a more homogeneous plasma, this converter target has to be characterized. In this paper the latest results of these measurements are presented. Small spherical cavities with diameters between 600 and 750 {mu}m were heated with laser energies up to 30 J at 532-nm wavelength. Radiation temperatures could be determined by time-resolved as well as time-integrated diagnostics, and maximum values of up to 35 eV were achieved.
Time- and spectrally resolved measurements of laser-driven hohlraum radiation.
Hessling, T; Blažević, A; Frank, A; Kraus, D; Roth, M; Schaumann, G; Schumacher, D; Stöhlker, T; Hoffmann, D H H
2011-07-01
At the GSI Helmholtz center for heavy-ion research combined experiments with heavy ions and laser-produced plasmas are investigated. As a preparation to utilize indirectly heated targets, where a converter hohlraum provides thermal radiation to create a more homogeneous plasma, this converter target has to be characterized. In this paper the latest results of these measurements are presented. Small spherical cavities with diameters between 600 and 750 μm were heated with laser energies up to 30 J at 532-nm wavelength. Radiation temperatures could be determined by time-resolved as well as time-integrated diagnostics, and maximum values of up to 35 eV were achieved. PMID:21867327
Gas temperature and density measurements based on spectrally resolved Rayleigh-Brillouin scattering
NASA Technical Reports Server (NTRS)
Seasholtz, Richard G.; Lock, James A.
1992-01-01
The use of molecular Rayleigh scattering for measurements of gas density and temperature is evaluated. The technique used is based on the measurement of the spectrum of the scattered light, where both temperature and density are determined from the spectral shape. Planar imaging of Rayleigh scattering from air using a laser light sheet is evaluated for ambient conditions. The Cramer-Rao lower bounds for the shot-noise limited density and temperature measurement uncertainties are calculated for an ideal optical spectrum analyzer and for a planar mirror Fabry-Perot interferometer used in a static, imaging mode. With this technique, a single image of the Rayleigh scattered light can be analyzed to obtain density (or pressure) and temperature. Experimental results are presented for planar measurements taken in a heated air stream.
Advanced microscopy :time-resolved multi-spectral imaging of single biomolecules.
Hayden, Carl C.; Chandler, David W.; Gradinaru, Claudiu C.; Luong, A. Khai
2005-12-01
Over the past few years we have developed the ability to acquire images through a confocal microscope that contain, for each pixel, the simultaneous fluorescence lifetime and spectra of multiple fluorophores within that pixel. We have demonstrated that our system has the sensitivity to make these measurements on single molecules. The spectra and lifetimes of fluorophores bound to complex molecules contain a wealth of information on the conformational dynamics and local chemical environments of the molecules. However, the detailed record of spectral and temporal information our system provides from fluorophores in single molecules has not been previously available. Therefore, we have studied several fluorophores and simple fluorophore-molecule systems that are representative of the use of fluorophores in biological systems. Experiments include studies of a simple fluorescence resonance energy transfer (FRET) system, green fluorescent probe variants and quantum dots. This work is intended to provide a basis for understanding how fluorophores report on the chemistry of more complex biological molecules.
Spectrally resolved multi-channel contributions to the harmonic emission in N2
NASA Astrophysics Data System (ADS)
Diveki, Z.; Camper, A.; Haessler, S.; Auguste, T.; Ruchon, T.; Carré, B.; Salières, P.; Guichard, R.; Caillat, J.; Maquet, A.; Taïeb, R.
2012-02-01
When generated in molecules, high-order harmonics can be emitted through different ionization channels. The coherent and ultrafast electron dynamics occurring in the ion during the generation process is directly imprinted in the harmonic signal, i.e. in its amplitude and spectral phase. In aligned N2 molecules, we find evidence for a fast variation of this phase as a function of the harmonic order when varying the driving laser intensity. Basing our analysis on a three-step model, we find that this phase variation is a signature of transitions from a single- to a multi-channel regime. In particular, we show that significant nuclear dynamics may occur in the ionization channels on the attosecond timescale, affecting both the amplitude and the phase of the harmonic signal.
Zhang, Yun; Dong, Bo; Bai, Yulei; Ye, Shuangli; Lei, Zhenkun; Zhou, Yanzhou
2015-10-19
An updated B-scan method is proposed for measuring the evolution of thermal deformation fields in polymers. In order to measure the distributions of out-of-plane deformation and normal strain field, phase-contrast spectral optical coherence tomography (PC-SOCT) was performed with the depth range and resolution of 4.3 mm and 10.7 μm, respectively, as thermal loads were applied to three different multilayer samples. The relation between temperature and material refractive index was predetermined before the measurement. After accounting for the refractive index, the thermal deformation fields in the polymer were obtained. The measured thermal expansion coefficient of silicone sealant was approximately equal to its reference value. This method allows correctly assessing the mechanical properties in semitransparent polymers. PMID:26480464
Peak Flux Distributions of Solar Radio Type-i Bursts from Highly Resolved Spectral Observations
NASA Astrophysics Data System (ADS)
Iwai, K.; Masuda, S.; Miyoshi, Y.; Tsuchiya, F.; Morioka, A.; Misawa, H.
2013-05-01
Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.
PEAK FLUX DISTRIBUTIONS OF SOLAR RADIO TYPE-I BURSTS FROM HIGHLY RESOLVED SPECTRAL OBSERVATIONS
Iwai, K.; Masuda, S.; Miyoshi, Y.; Tsuchiya, F.; Morioka, A.; Misawa, H.
2013-05-01
Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.
NASA Astrophysics Data System (ADS)
Costabile, F.; Barnaba, F.; Angelini, F.; Gobbi, G. P.
2013-03-01
Characterizing chemical and physical aerosol properties is important to understand their sources, effects, and feedback mechanisms in the atmosphere. This study proposes a scheme to classify aerosol populations based on their spectral optical properties (absorption and scattering). The scheme is obtained thanks to the outstanding set of information on particle size and composition these properties contain. The spectral variability of the aerosol single scattering albedo (dSSA), and the extinction, scattering and absorption Angstrom exponents (EAE, SAE and AAE, respectively) were observed on the basis of two-year measurements of aerosol optical properties (scattering and absorption coefficients at blue, green and red wavelengths) performed in the suburbs of Rome (Italy). Optical measurements of various aerosol types were coupled to measurements of particle number size distributions and relevant optical properties simulations (Mie theory). These latter allowed the investigation of the role of the particle size and composition in the bulk aerosol properties observed. The combination of simulations and measurements suggested a general "paradigm" built on dSSA, SAE and AAE to optically classify aerosols. The paradigm proved suitable to identify the presence of key aerosol populations, including soot, biomass burning, organics, dust and marine particles. The work highlights that (i) aerosol populations show distinctive combinations of SAE and dSSA times AAE, these variables being linked by a linear inverse relation varying with varying SSA; (ii) fine particles show EAE > 1.5, whilst EAE < 2 is found for both coarse particles and ultrafine soot-rich aerosols; (iii) fine and coarse particles both show SSA > 0.8, whilst ultrafine urban Aitken mode and soot particles show SSA < 0.8. The proposed paradigm agrees with aerosol observations performed during past major field campaigns, this indicating that relations concerning the paradigm have a general validity.
NASA Astrophysics Data System (ADS)
Crooker, S. A.; Liu, F.; Kelley, M. R.; Martinez, N. J. D.; Nie, W.; Mohite, A.; Nayyar, I. H.; Tretiak, S.; Smith, D. L.; Ruden, P. P.
2014-10-01
We use spectrally resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic light-emitting diodes. Using layered devices that generate bright exciplex emission, we show that the increase in EL emission intensity I due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (ΔI/I ˜ 11%) than at the low-energy red end (˜4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons.
Crooker, S. A.; Kelley, M. R.; Martinez, N. J. D.; Nie, W.; Mohite, A.; Nayyar, I. H.; Tretiak, S.; Smith, D. L.; Liu, F.; Ruden, P. P.
2014-10-13
We use spectrally resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic light-emitting diodes. Using layered devices that generate bright exciplex emission, we show that the increase in EL emission intensity I due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (ΔI/I ∼ 11%) than at the low-energy red end (∼4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons.
Nagloo, Nicolas; Collin, Shaun P; Hemmi, Jan M; Hart, Nathan S
2016-05-01
Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semi-aquatic lifestyle and ambush hunting mode are reflected in specific adaptations in the peripheral visual system. Design-based stereology and microspectrophotometry were used to assess spatial resolving power and spectral sensitivity of saltwater (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni). Both species possess a foveal streak that spans the naso-temporal axis and mediates high spatial acuity across the central visual field. The saltwater crocodile and freshwater crocodile have a peak spatial resolving power of 8.8 and 8.0 cycles deg(-1), respectively. Measurement of the outer segment dimensions and spectral absorbance revealed five distinct photoreceptor types consisting of three single cones, one twin cone and a rod. The three single cones (saltwater/freshwater crocodile) are violet (424/426 nm λmax), green (502/510 nm λmax) and red (546/554 nm λmax) sensitive, indicating the potential for trichromatic colour vision. The visual pigments of both members of the twin cones have the same λmax as the red-sensitive single cone and the rod has a λmax at 503/510 nm (saltwater/freshwater). The λmax values of all types of visual pigment occur at longer wavelengths in the freshwater crocodile compared with the saltwater crocodile. Given that there is a greater abundance of long wavelength light in freshwater compared with a saltwater environment, the photoreceptors would be more effective at detecting light in their respective habitats. This suggests that the visual systems of both species are adapted to the photic conditions of their respective ecological niche. PMID:27208035
Spectral mapping of 3D multi-cellular tumor spheroids: time-resolved confocal microscopy.
Mohapatra, Saswat; Nandi, Somen; Chowdhury, Rajdeep; Das, Gaurav; Ghosh, Surajit; Bhattacharyya, Kankan
2016-07-21
A tumor-like multi-cellular spheroid (3D) differs from a 2D cell in a number of ways. This is demonstrated using time resolved confocal microscopy. Two different tumor spheroids - HeLa (cervical cancer) and A549 (lung cancer) - are studied using 3 different fluorescent dyes - C153 (non-covalent), CPM (covalent) and doxorubicin (non-covalent, anti-cancer drug). The pattern of localization of these three fluorescent probes in the 3D tumor cell exhibits significant differences from that in the conventional 2D cells. For both the cells (HeLa and A549), the total uptake of doxorubicin in the 3D cell is much lower than that in the 2D cell. The uptake of doxorubicin molecules in the A549 spheroid is significantly different compared to the HeLa spheroid. The local polarity (i.e. emission maxima) and solvation dynamics in the 3D tumor cell differ from those in 2D cells. The covalent probe CPM exhibits intermittent fluorescence oscillations in the 1-2 s time scale. This is attributed to redox processes. These results may provide new insights into 3D tumors. PMID:27336201
NASA Astrophysics Data System (ADS)
Shmaenok, L. A.; Golovkin, S. V.; Govorun, V. N.; Ekimov, A. V.; Salashchenko, N. N.; Pickalov, V. V.; Belik, V. P.; Schüller, F. C.; Donné, A. J. H.; Oomens, A. A. M.; Prokhorov, K. A.; Andreev, S. S.; Sorokin, A. A.; Podlaskin, B. G.; Khasanov, L. V.
2001-02-01
A novel instrumentation for wavelength- and time-resolved plasma emission tomography in the range 0.1-4 keV has been demonstrated on the Torus Experiment for Technology Oriented Research (TEXTOR). The technique is intended for reconstruction of distributions of local emission coefficients (LEC) for selected spectral lines of impurity ions. Further determination (with additional data on electron density and temperature) of spatial distributions of impurity ions at particular ionization stages will become feasible. Spectrally selective plasma images at several viewpoints around plasma are obtained with miniature pinhole cameras supplemented with multilayer mirrors as dispersion elements. The x-ray image is converted to a visible image and transported by a fiber bundle to a gain enhanced recording camera with an electron bombarded charge coupled device tube. A part of the system has been installed on temporary TEXTOR ports. First demonstration results have been obtained on plasma imaging and on subsequent LEC reconstruction using a modified iterative sinogram restoration tomography algorithm. The complete diagnostics will be operational after the TEXTOR shutdown in 2001.
SPATIALLY AND SPECTRALLY RESOLVED OBSERVATIONS OF A ZEBRA PATTERN IN A SOLAR DECIMETRIC RADIO BURST
Chen Bin; Bastian, T. S.; Gary, D. E.; Jing Ju
2011-07-20
We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral ({approx}1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 2006 December 14. By using OVSA to calibrate the FST, the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance model in which the radio emission occurs in resonance layers where the upper-hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop.
Phenomenology of spectrally and temporally resolved infrared emissions from bomb detonations
NASA Astrophysics Data System (ADS)
Gross, Kevin; Dills, Anthony; Tuttle, Ron; Perram, Glen
2002-10-01
The remote sensing of infrared signatures from exothermic reactions during military operations, including missile launches, muzzle flashes, and bomb detonations has been studied using fast FTIR techniques. Battle space characterization includes the ability to classify the munitions type, size, and other characteristics. One possible approach to munitions classification is to understand the spectral and temporal signatures from explosive ordinance. To investigate this possibility, experimental data has been collected remotely from ground-based sensors, processed, and analyzed for several conventional munitions. Field observations of 56 detonation events included a set of aircraft delivered ordnance and a series of static ground detonations for a variety of bomb sizes, types and environmental conditions. The emission is well represented by a gray body with continuously decreasing temperature and characteristic decay times of 1-4 s, providing only limited variability with detonation conditions. However, the fireball size times the emissivity as a function of time can be determined from the spectra without imaging and provides a more sensitive signature. The degree of temporal overlap as a function of frequency for a pair of detonation events provides a very sensitive discriminator for explosion conditions. The temporal overlap decreases with increasing emission frequency for all the observed events, indicating more information content at higher frequencies. Finally, the temporal nature of the emissions has been analyzed, providing a significant reduction in the dimensionality of the data.
"Cat"-ology: Spectrally resolved neurophotonics in the mammalian brain and phantom studies
NASA Astrophysics Data System (ADS)
Tanner, Kandice
Physicists provide significant contributions to the field of Biology and Medical Sciences by applying basic physics principles to the field. Specifically, in this work, we probed the light-matter interactions in the NIR region to understand physiological processes in the mammalian brain. We sought to improve on existing principles and propose a new technique by which we can decipher these processes spectrally. This technique touted to be independent of the light transport regime allowed us to examine the hemodynamics and neuronal activity. The aim was then to test this technique and see if it produces results that were comparable to the well established Fd-NIRS in distinguishing physiological processes. Secondly, we wanted to prove that this technique was light transport regime independent which is not the case for the Fd-NIRS. The cat was chosen as an ideal test subject as its anatomy is such that photons are not fully diffusive before being detected as the total size of the grey matter in the cat is roughly 3mm thick. Additionally, we had a priori information about the activation of the visual cortex as a response to specific stimuli.
NASA Astrophysics Data System (ADS)
Dang, Wei; Mao, Pengcheng; Weng, Yuxiang
2013-07-01
We report an improved setup of femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS) with a 210 fs temporal response. The system employs a Cassegrain objective to collect and focus fluorescence photons, which eliminates the interference from the coherent photons in the fluorescence amplification by temporal separation of the coherent photons and the fluorescence photons. The gain factor of the Cassegrain objective-assisted FNOPAS is characterized as 1.24 × 105 for Rhodamine 6G. Spectral corrections have been performed on the transient fluorescence spectra of Rhodamine 6G and Rhodamine 640 in ethanol by using an intrinsic calibration curve derived from the spectrum of superfluorescence, which is generated from the amplification of the vacuum quantum noise. The validity of spectral correction is illustrated by comparisons of spectral shape and peak wavelength between the corrected transient fluorescence spectra of these two dyes acquired by FNOPAS and their corresponding standard reference spectra collected by the commercial streak camera. The transient fluorescence spectra of the Rhodamine 6G were acquired in an optimized phase match condition, which gives a deviation in the peak wavelength between the retrieved spectrum and the reference spectrum of 1.0 nm, while those of Rhodamine 640 were collected in a non-optimized phase match condition, leading to a deviation in a range of 1.0-3.0 nm. Our results indicate that the improved FNOPAS can be a reliable tool in the measurement of transient fluorescence spectrum for its high temporal resolution and faithfully corrected spectrum.
NASA Astrophysics Data System (ADS)
Cooray, Asantha
2013-10-01
We propose WFC3 G102 and G141 grism spectral imaging of two gravitationally lensed dusty, starburst galaxies found with the 600 square degree Herschel-ATLAS survey. One galaxy is the brightest {both in far-IR at 250 micron and in near-IR in J/K-band}, while the second is the largest {11 arcsec on the sky} of the lensed sub-mm galaxies in a sample of 200 imaged with WFC3/F110W. The two galaxies are at redshifts that are optimal for grism observations with HST/WFC3. The lensing flux magnification and spatial enhancement makes them very unique for the study proposed hereand will increase the number of lensed galaxies imaged in spectral lines with WFC3 grisms to three from existing single serendipitous lens studied in HST-3D survey. With WFC3 grism spectra taken in a specific orientation to minimize foreground and lensing galaxy confusion we can map each of these galaxies in a variety of spatially-resolved spectral lines in the rest-frame optical, including impostant Balmer lines for studies on the interstellar medium. The grism spectra will allow us to determine the gas-phase metallicities of these two galaxies and to study the extinction of optically-thin regions compared to direct sub-mm emission seen in interferometric continuum images of optically thick dust in starbursting knots and clumps. With spatial resolution provided by gravitational lensing combined with HST/WFC3 resolution, we will be able to study the dependence of line ratios in high density/SFR regions to low dense diffuse environments.
Spatially resolved Spitzer-IRS spectral maps of the superwind in M82
NASA Astrophysics Data System (ADS)
Beirão, P.; Armus, L.; Lehnert, M. D.; Guillard, P.; Heckman, T.; Draine, B.; Hollenbach, D.; Walter, F.; Sheth, K.; Smith, J. D.; Shopbell, P.; Boulanger, F.; Surace, J.; Hoopes, C.; Engelbracht, C.
2015-08-01
We have mapped the superwind/halo region of the nearby starburst galaxy M82 in the mid-infrared with Spitzer - IRS. The spectral regions covered include the H2 S(1)-S(3), [Ne II], [Ne III] emission lines and polycyclic aromatic hydrocarbon (PAH) features. We estimate the total warm H2 mass and the kinetic energy of the outflowing warm molecular gas to be between Mwarm ˜ 5 and 17 × 106 M⊙ and EK ˜ 6 and 20 × 1053 erg. Using the ratios of the 6.2, 7.7 and 11.3 μm PAH features in the IRS spectra, we are able to estimate the average size and ionization state of the small grains in the superwind. There are large variations in the PAH flux ratios throughout the outflow. The 11.3/7.7 and the 6.2/7.7 PAH ratios both vary by more than a factor of 5 across the wind region. The northern part of the wind has a significant population of PAH's with smaller 6.2/7.7 ratios than either the starburst disc or the southern wind, indicating that on average, PAH emitters are larger and more ionized. The warm molecular gas to PAH flux ratios (H2/PAH) are enhanced in the outflow by factors of 10-100 as compared to the starburst disc. This enhancement in the H2/PAH ratio does not seem to follow the ionization of the atomic gas (as measured with the [Ne III]/[Ne II] line flux ratio) in the outflow. This suggests that much of the warm H2 in the outflow is excited by shocks. The observed H2 line intensities can be reproduced with low-velocity shocks (v < 40 km s-1) driven into moderately dense molecular gas (102 < nH < 104 cm-3) entrained in the outflow.
Protein interaction quantified in vivo by spectrally resolved fluorescence resonance energy transfer
2004-01-01
We describe a fluorescence resonance energy transfer (FRET)-based method for finding in living cells the fraction of a protein population (αT) forming complexes, and the average number (n) of those protein molecules in each complex. The method relies both on sensitized acceptor emission and on donor de-quenching (by photobleaching of the acceptor molecules), coupled with full spectral analysis of the differential fluorescence signature, in order to quantify the donor/acceptor energy transfer. The approach and sensitivity limits are well suited for in vivo microscopic investigations. This is demonstrated using a scanning laser confocal microscope to study complex formation of the sterile 2 α-factor receptor protein (Ste2p), labelled with green, cyan, and yellow fluorescent proteins (GFP, CFP, and YFP respectively), in budding yeast Saccharomyces cerevisiae. A theoretical model is presented that relates the efficiency of energy transfer in protein populations (the apparent FRET efficiency, Eapp) to the energy transferred in a single donor/acceptor pair (E, the true FRET efficiency). We determined E by using a new method that relies on Eapp measurements for two donor/acceptor pairs, Ste2p–CFP/Ste2p–YFP and Ste2p–GFP/Ste2p–YFP. From Eapp and E we determined αT≈1 and n≈2 for Ste2 proteins. Since the Ste2p complexes are formed in the absence of the ligand in our experiments, we conclude that the α-factor pheromone is not necessary for dimerization. PMID:15352875
NASA Astrophysics Data System (ADS)
Cid Fernandes, R.; González Delgado, R. M.; Storchi-Bergmann, T.; Martins, L. Pires; Schmitt, H.
2005-01-01
In a recently completed survey of the stellar population properties of low-ionization nuclear emission-line regions (LINERs) and LINER/HII transition objects (TOs), we have identified a numerous class of galactic nuclei which stand out because of their conspicuous 108-9 yr populations, traced by high-order Balmer absorption lines and other stellar indices. These objects are called `young-TOs', because they all have TO-like emission-line ratios. In this paper we extend this previous work, which concentrated on the nuclear properties, by investigating the radial variations of spectral properties in low-luminosity active galactic nuclei (LLAGNs). Our analysis is based on high signal-to-noise ratio (S/N) long-slit spectra in the 3500-5500 Å interval for a sample of 47 galaxies. The data probe distances of typically up to 850 pc from the nucleus with a resolution of ~100 pc (~1 arcsec) and S/N ~ 30. Stellar population gradients are mapped by the radial profiles of absorption-line equivalent widths and continuum colours along the slit. These variations are further analysed by means of a decomposition of each spectrum in terms of template galaxies representative of very young (<=107 yr), intermediate age (108-9 yr) and old (1010 yr) stellar populations. This study reveals that young-TOs also differ from old-TOs and old-LINERs in terms of the spatial distributions of their stellar populations and dust. Specifically, our main findings are as follows. (i) Significant stellar population gradients are found almost exclusively in young-TOs. (ii) The intermediate age population of young-TOs, although heavily concentrated in the nucleus, reaches distances of up to a few hundred pc from the nucleus. Nevertheless, the half width at half-maximum of its brightness profile is more typically 100 pc or less. (iii) Objects with predominantly old stellar populations present spatially homogeneous spectra, be they LINERs or TOs. (iv) Young-TOs have much more dust in their central regions
First spectrally-resolved H2 observations towards HH 54 . Low H2O abundance in shocks
NASA Astrophysics Data System (ADS)
Santangelo, G.; Antoniucci, S.; Nisini, B.; Codella, C.; Bjerkeli, P.; Giannini, T.; Lorenzani, A.; Lundin, L. K.; Cabrit, S.; Calzoletti, L.; Liseau, R.; Neufeld, D.; Tafalla, M.; van Dishoeck, E. F.
2014-09-01
Context. Herschel observations suggest that the H2O distribution in outflows from low-mass stars resembles the H2 emission. It is still unclear which of the different excitation components that characterise the mid- and near-IR H2 distribution is associated with H2O. Aims: The aim is to spectrally resolve the different excitation components observed in the H2 emission. This will allow us to identify the H2 counterpart associated with H2O and finally derive directly an H2O abundance estimate with respect to H2. Methods: We present new high spectral resolution observations of H2 0-0 S(4), 0-0 S(9), and 1-0 S(1) towards HH 54, a bright nearby shock region in the southern sky. In addition, new Herschel/HIFI H2O (212 - 101) observations at 1670 GHz are presented. Results: Our observations show for the first time a clear separation in velocity of the different H2 lines: the 0-0 S(4) line at the lowest excitation peaks at -7 km s-1, while the more excited 0-0 S(9) and 1-0 S(1) lines peak at -15 km s-1. H2O and high-J CO appear to be associated with the H2 0-0 S(4) emission, which traces a gas component with a temperature of 700-1000 K. The H2O abundance with respect to H2 0-0 S(4) is estimated to be X(H2O) < 1.4 × 10-5 in the shocked gas over an area of 13''. Conclusions: We resolve two distinct gas components associated with the HH 54 shock region at different velocities and excitations. This allows us to constrain the temperature of the H2O emitting gas (≤1000 K) and to derive correct estimates of H2O abundance in the shocked gas, which is lower than what is expected from shock model predictions. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme IDs: 089.C-0772, 292.C-5025.
NASA Astrophysics Data System (ADS)
Munro, Eugene
2013-12-01
In this paper, we will solve the Hamiltonian constraint describing a curved general relativistic spacetime to find initial data describing how a black hole exists in vacuum. This has been done before by other researchers [Ansorg, 2004], and we will be adapting our own methods to an existing pseudo spectral Poisson solver [Gourgoulhon, 2001]. The need for this adaptation arises from improper numerical handling, done by pseudo spectral-methods, of a large part the Hamiltonian constraint equation due to the presence of the black hole singularity. To resolve a portion of this issue up to a given order, we will determine irregularities by executing a polynomial expansion on the Hamiltonian constraint, analytically solving the troublesome components of the equation and subtracting those out of the numerical process. This technique will increase the equation's differentiability and allow the numerical solver to run more efficiently. We will cover all the calculations needed to describe one black hole with arbitrary spin and linear momentum. Our process is easily expanded into cases with n black holes [Brandt, 1997], which we will show in chapter 2. We will implement a spherical harmonic decomposition of the black hole conformal factor, using them as basis functions by which to further expand and dissect the Hamiltonian Constraint equation. In the end, the expansion and subtraction method will be done out to the order of r4, where r is the spherical radius assuming the black hole is at the coordinate origin, making the Hamiltonian equation, which, unaltered, is a C 2 equation, become a C7 equation. Smoothing the Hamiltonian improves numerical precision, especially near the BH where the most interesting physics occurs. The method used in this paper can be further implemented to higher orders of r to yield even smoother conditions. We will test the numerical results of using this method against the existing solver that uses the publicly available Lorene numerical libraries
NASA Technical Reports Server (NTRS)
Huang, Xianglei; Yang, Wenze; Loeb, Norman G.; Ramaswamy, V.
2008-01-01
Spectrally resolved outgoing IR flux, the integrand of the outgoing longwave radiation (OLR), has its unique value in evaluating model simulations. Here we describe an algorithm of deriving such clear-sky outgoing spectral flux through the whole IR region from the collocated Atmospheric Infrared Sounder (AIRS) and the Clouds & the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. Based on the scene types and corresponding angular distribution models (ADMs) used in the CERES Single Satellite Footprint (SSF) dataset, spectrally-dependent ADMs are developed and used to estimate the spectral flux at each AIRS channel. A multivariate linear prediction scheme is then used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The whole algorithm is validated using synthetic spectra as well as the CERES OLR measurements. Using the GFDL AM2 model simulation as a case study, the application of the derived clear-sky outgoing spectral flux in model evaluation is illustrated. By comparing the observed and simulated spectral flux in 2004, compensating errors in the simulated OLR from different absorption bands can be revealed, so does the errors from frequencies within a given absorption band. Discrepancies between the simulated and observed spatial distributions and seasonal evolutions of the spectral fluxes at different spectral ranges are further discussed. The methodology described in this study can be applied to other surface types as well as cloudy-sky observations and corresponding model evaluations.
Mancini, R. C.; Johns, H. M.; Joshi, T.; Mayes, D.; Nagayama, T.; Hsu, S. C.; Baumgaertel, J. A.; Cobble, J.; Krasheninnikova, N. S.; Bradley, P. A.; Hakel, P.; Murphy, T. J.; Schmitt, M. J.; Shah, R. C.; Tregillis, I. L.; Wysocki, F. J.
2014-12-15
We present spatially, temporally, and spectrally resolved narrow- and broad-band x-ray images of polar-direct-drive (PDD) implosions on OMEGA. These self-emission images were obtained during the deceleration phase and bang time using several multiple monochromatic x-ray imaging instruments fielded along two or three quasi-orthogonal lines-of-sight, including equatorial and polar views. The instruments recorded images based on K-shell lines from a titanium tracer located in the shell as well as continuum emission. These observations constitute the first such data obtained for PDD implosions. The image data show features attributed to laser imprinting and zero-order hydrodynamics. Equatorial-view images show a “double bun” structure that is consistent with synthetic images obtained from post-processing 2D and 3D radiation-hydrodynamic simulations of the experiment. Polar-view images show a pentagonal, petal pattern that correlates with the PDD laser illumination used on OMEGA, thus revealing a 3D aspect of PDD OMEGA implosions not previously observed. Differences are noted with respect to a PDD experiment performed at National Ignition Facility.
Guse, Joanna A; Soufiani, Arman M; Jiang, Liangcong; Kim, Jincheol; Cheng, Yi-Bing; Schmidt, Timothy W; Ho-Baillie, Anita; McCamey, Dane R
2016-04-28
Elucidating the decay mechanisms of photoexcited charge carriers is key to improving the efficiency of solar cells based on organo-lead halide perovskites. Here we investigate the spectral dependence (via above-, inter- and sub-bandgap optical excitations) of direct and trap-mediated decay processes in CH3NH3PbI3 using time resolved microwave conductivity (TRMC). We find that the total end-of-pulse mobility is excitation wavelength dependent - the mobility is maximized (172 cm(2) V(-1) s(-1)) when charge carriers are excited by near bandgap light (780 nm) in the low charge carrier density regime (10(9) photons per cm(2)), and is lower for above- and sub-bandgap excitations. Direct recombination is found to occur on the 100-400 ns timescale across excitation wavelengths near and above the bandgap, whereas indirect recombination processes displayed distinct behaviour following above- and sub-bandgap excitations, suggesting the influence of different trap distributions on recombination dynamics. PMID:27067120
Chen, Shih-Hung; Chen, Liu
2013-12-15
The nonstationary oscillation of the gyrotron backward wave oscillator (gyro-BWO) with cylindrical interaction structure was studied utilizing both steady-state analyses and time-dependent simulations. Comparisons of the numerical results reveal that the gyro-BWO becomes nonstationary when the trailing field structure completely forms due to the dephasing energetic electrons. The backward propagation of radiated waves with a lower resonant frequency from the trailing field structure interferes with the main internal feedback loop, thereby inducing the nonstationary oscillation of the gyro-BWO. The nonstationary gyro-BWO exhibits the same spectral pattern of modulated oscillations with a constant frequency separation between the central frequency and sidebands throughout the whole system. The frequency separation is found to be scaled with the square root of the maximum field amplitude, thus further demonstrating that the nonstationary oscillation of the gyro-BWO is associated with the beam-wave resonance detuning.
NASA Astrophysics Data System (ADS)
Bardalez Gagliuffi, Daniella C.; Gelino, Christopher R.; Burgasser, Adam J.
2015-11-01
We present high resolution Laser Guide Star Adaptive Optics imaging of 43 late-M, L and T dwarf systems with Keck/NIRC2. These include 17 spectral binary candidates, systems whose spectra suggest the presence of a T dwarf secondary. We resolve three systems: 2MASS J1341-3052, SDSS J1511+0607 and SDSS J2052-1609 the first two are resolved for the first time. All three have projected separations <8 AU and estimated periods of 14-80 years. We also report a preliminary orbit determination for SDSS J2052-1609 based on six epochs of resolved astrometry between 2005 and 2010. Among the 14 unresolved spectral binaries, 5 systems were confirmed binaries but remained unresolved, implying a minimum binary fraction of {47}-11+12% for this sample. Our inability to resolve most of the spectral binaries, including the confirmed binaries, supports the hypothesis that a large fraction of very low mass systems have relatively small separations and are missed with direct imaging. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.
NASA Astrophysics Data System (ADS)
Liu, Y. C.; Fan, J.; Zhang, G. J.; Xu, K. M.; Ghan, S. J.
2014-12-01
Convective momentum transport (CMT) has been demonstrated to have a large impact on global atmospheric circulation in both observational and numerical studies. In General Circulation Models (GCMs) CMT is often parameterized in a simple way by assuming that in-cloud horizontal momentum depends only on lateral entrainment and detrainment rates [Schneider and Lindzen, 1976]. In addition to lateral entrainment and detrainment rates the effect of perturbation pressure gradient force induced by convection (Pc) on momentum transport is significant. Because it is the most complicated term to be parameterized, a very simple form of products among a constant coefficient, mass flux, and environment vertical wind shear was employed to parameterize it [Gregory et al., 1997]. In addition, none of these CMT parameterizations deal with the scale problems. Thus, the goal of this study is to evaluate the past CMT parameterizations and explore the scale dependencies of Pc and CMT using Cloud Resolving Model (CRM) simulations from the Weather Research and Forecasting (WRF) coupled with the most sophisticated spectral-bin microphysics. Our preliminary results show that the parameterized CMT from the top-hat approach is underestimated especially at the gray zone scale (~4-50 km); using the simplified 3-updraft and 1-downdraft formulation proposed in our previous study for eddy transport of moisture, the CMT can be represented well. The formulation also produced a more accurate mass flux compared to the top-hat approach, which can potentially improve the parameterization of Pc. We investigate the relative contributions from linear and nonlinear forcing to Pc at different model grid spacing (dx). Our results show that the assumption that non-linear forcing is much smaller than linear force is valid only at dx > 128 km and dx < 8 km. At the dx = 32~16 km, linear and nonlinear forcings become compatible, suggesting a more sophisticated formula for Pc might be needed.
Information retrieval for nonstationary data records
NASA Technical Reports Server (NTRS)
Su, M. Y.
1971-01-01
A review and a critical discussion are made on the existing methods for analysis of nonstationary time series, and a new algorithm for splitting nonstationary time series, is applied to the analysis of sunspot data.
NASA Astrophysics Data System (ADS)
Vinsen, Kevin; Thilker, David
2013-11-01
In this work we present our experience from the first year of theSkyNet Pan-STARRS1 Optical Galaxy Survey (POGS) project. This citizen-scientist driven research project uses the Berkeley Open Infrastructure for Network Computing (BOINC) middleware and thousands of Internet-connected computers to measure the resolved galactic structural properties of ˜100,000 low redshift galaxies. We are combining the spectral coverage of GALEX, Pan-STARRS1, SDSS, and WISE to generate a value-added, multi-wavelength UV-optical-NIR galaxy atlas for the nearby Universe. Specifically, we are measuring physical parameters (such as local stellar mass, star formation rate, and first-order star formation history) on a resolved pixel-by-pixel basis using spectral energy distribution (SED) fitting techniques in a distributed computing mode. Berkeley Open Infrastructure for Network Computing.
Nonstationary statistical theory for multipactor
Anza, S.; Vicente, C.; Gil, J.
2010-06-15
This work presents a new and general approach to the real dynamics of the multipactor process: the nonstationary statistical multipactor theory. The nonstationary theory removes the stationarity assumption of the classical theory and, as a consequence, it is able to adequately model electron exponential growth as well as absorption processes, above and below the multipactor breakdown level. In addition, it considers both double-surface and single-surface interactions constituting a full framework for nonresonant polyphase multipactor analysis. This work formulates the new theory and validates it with numerical and experimental results with excellent agreement.
NASA Astrophysics Data System (ADS)
Moura, R. C.; Sherwin, S. J.; Peiró, J.
2015-10-01
We investigate the potential of linear dispersion-diffusion analysis in providing direct guidelines for turbulence simulations through the under-resolved DNS (sometimes called implicit LES) approach via spectral/hp methods. The discontinuous Galerkin (DG) formulation is assessed in particular as a representative of these methods. We revisit the eigensolutions technique as applied to linear advection and suggest a new perspective to the role of multiple numerical modes, peculiar to spectral/hp methods. From this new perspective, "secondary" eigenmodes are seen to replicate the propagation behaviour of a "primary" mode, so that DG's propagation characteristics can be obtained directly from the dispersion-diffusion curves of the primary mode. Numerical dissipation is then appraised from these primary eigencurves and its effect over poorly-resolved scales is quantified. Within this scenario, a simple criterion is proposed to estimate DG's effective resolution in terms of the largest wavenumber it can accurately resolve in a given hp approximation space, also allowing us to present points per wavelength estimates typically used in spectral and finite difference methods. Although strictly valid for linear advection, the devised criterion is tested against (1D) Burgers turbulence and found to predict with good accuracy the beginning of the dissipation range on the energy spectra of under-resolved simulations. The analysis of these test cases through the proposed methodology clarifies why and how the DG formulation can be used for under-resolved turbulence simulations without explicit subgrid-scale modelling. In particular, when dealing with communication limited hardware which forces one to consider the performance for a fixed number of degrees of freedom, the use of higher polynomial orders along with moderately coarser meshes is shown to be the best way to translate available degrees of freedom into resolution power.
NASA Astrophysics Data System (ADS)
Bjerkeli, P.; Liseau, R.; Brinch, C.; Olofsson, G.; Santangelo, G.; Cabrit, S.; Benedettini, M.; Black, J. H.; Herczeg, G.; Justtanont, , K.; Kristensen, L. E.; Larsson, B.; Nisini, B.; Tafalla, M.
2014-11-01
Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims: Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods: We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results: The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO (10-9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 - 7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by -7 km s-1. The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O i]63, 145 μm) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Ash, C; Town, G; Clement, M
2010-02-01
High quality intense pulsed light (IPL) systems can offer simple, safe and effective treatments for long-term hair reduction, skin rejuvenation and removal of benign vascular and pigmented lesions. Considerable differences in clinical efficacy and adverse effects have been recorded amongst different IPL systems despite comparable display settings. This study examines the variation in pulse structures exhibited by several popular professional IPL systems that can cause a spectral change within the broadband output depending on the pulse structure chosen by the system designers. A fast spectrometer was used to capture IPL spectral outputs. A spectral distribution shift that occurs both within a pulse and between pulses is clearly demonstrated and is more prominent with uncontrolled free discharge systems than with square pulsed technology, which provides a constant spectral distribution throughout the pulse duration. PMID:20017711
NASA Astrophysics Data System (ADS)
Johns, H. M.; Mancini, R. C.; Nagayama, T.; Mayes, D. C.; Tommasini, R.; Smalyuk, V. A.; Regan, S. P.; Delettrez, J. A.
2016-01-01
In warm target direct-drive inertial confinement fusion implosion experiments performed at the OMEGA laser facility, plastic micro-balloons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolved titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (Te) = 400 ± 28 eV, electron number density (Ne) = 8.5 × 1024 ± 2.5 × 1024 cm-3, and average areal density <ρR> = 86 ± 7 mg/cm2. Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2-9, dominated by l = 2. We extract a target breakup fraction of 7.1 ± 1.5% from our Fourier analysis. A new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5 ± 1 μm.
NASA Astrophysics Data System (ADS)
Pawlak, M.; Chirtoc, M.; Horny, N.; Pelzl, J.
2016-03-01
Spectrally resolved modulated infrared radiometry (SR-MIRR) with super-band gap photoexcitation is introduced as a self-consistent method for semiconductor characterization (CdSe crystals grown under different conditions). Starting from a theoretical model combining the contributions of the photothermal (PT) and photocarrier (PC) signal components, an expression is derived for the thermal-to-plasma wave transition frequency ftc which is found to be wavelength-independent. The deviation of the PC component from the model at high frequency is quantitatively explained by a quasi-continuous distribution of carrier recombination lifetimes. The integral, broad frequency band (0.1 Hz-1 MHz) MIRR measurements simultaneously yielded the thermal diffusivity a, the effective IR optical absorption coefficient βeff, and the bulk carrier lifetime τc. Spectrally resolved frequency scans were conducted with interchangeable IR bandpass filters (2.2-11.3 μm) in front of the detector. The perfect spectral match of the PT and PC components is the direct experimental evidence of the key assumption in MIRR that de-exciting carriers are equivalent to blackbody (Planck) radiators. The exploitation of the β spectrum measured by MIRR allowed determining the background (equilibrium) free carrier concentration n0. At the shortest wavelength (3.3 μm), the photoluminescence (PL) component supersedes the PC one and has distinct features. The average sample temperature influences the PC component but not the PT one.
Johns, H. M.; Mancini, R. C.; Nagayama, T.; Mayes, D. C.; Tommasini, R.; Smalyuk, V. A.; Regan, S. P.; Delettrez, J. A.
2016-01-25
In warm target direct-drive ICF implosion experiments performed at the OMEGA laser facility, plastic microballoons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolvedmore » titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (Te) = 400±28eV, electron number density (Ne) = 8.5x1024±2.5x1024 cm-3, and average areal density <ρR> = 86±7mg/cm2. Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2-9, dominated by l = 2. We extract a target breakup fraction of 7.1±1.5% from our Fourier analysis. A new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5±1μm.« less
NASA Astrophysics Data System (ADS)
Zachor, A. S.; Sharma, R. D.; Yap, B. K.; Riehl, J. P.
1989-04-01
The importance of atomic oxygen and translational temperature in mesospheric/thermospheric processes is the motivation to study the feasibility of recovering vertical profiles of the temperature and O-atom density from limb scan data obtained near 147 micrometer and/or 63 micrometer wavelength, corresponding to the oxygen atom ground electronic state (OI) transitions. The limb radiance data must be spectrally resolved to recover both temperature and atomic oxygen density if only one of the OI lines is used, which is the approach investigated in this report. We show how the two vertical profiles can be recovered by applying an onion-peeling method to synthetic data. The temperature and O-atom density in each peeled layer are obtained simultaneously by nonlinear least-squares spectrum fitting. Spectral data in the 147 micrometer line was found to yield reasonably accurate and stable profiles from 300 km down to an altitude between 130 and 90 km, depending on the noise level and spectral resolution, and gave better results than the stronger 63 micrometer data below 140 km. We estimate that the S/N and spectral resolution required for successful retrievals could be provided by a confocal Fabry-Perot system operating near 147 micrometer although retrievals down to 90 km from data obtained at orbital altitude would require cooled foreoptics roughly a meter in diameter.
Pan, Yong-Le; Hill, Steven C; Santarpia, Joshua L; Brinkley, Kelly; Sickler, Todd; Coleman, Mark; Williamson, Chatt; Gurton, Kris; Felton, Melvin; Pinnick, Ronald G; Baker, Neal; Eshbaugh, Jonathan; Hahn, Jerry; Smith, Emily; Alvarez, Ben; Prugh, Amber; Gardner, Warren
2014-04-01
A system for measuring spectrally-resolved fluorescence cross sections of single bioaerosol particles has been developed and employed in a biological safety level 3 (BSL-3) facility at Edgewood Chemical and Biological Center (ECBC). It is used to aerosolize the slurry or solution of live agents and surrogates into dried micron-size particles, and to measure the fluorescence spectra and sizes of the particles one at a time. Spectrally-resolved fluorescence cross sections were measured for (1) bacterial spores: Bacillus anthracis Ames (BaA), B. atrophaeus var. globigii (BG) (formerly known as Bacillus globigii), B. thuringiensis israelensis (Bti), B. thuringiensis kurstaki (Btk), B. anthracis Sterne (BaS); (2) vegetative bacteria: Escherichia coli (E. coli), Pantoea agglomerans (Eh) (formerly known as Erwinia herbicola), Yersinia rohdei (Yr), Yersinia pestis CO92 (Yp); and (3) virus preparations: Venezuelan equine encephalitis TC83 (VEE) and the bacteriophage MS2. The excitation wavelengths were 266 nm, 273 nm, 280 nm, 365 nm and 405 nm. PMID:24718194
NASA Astrophysics Data System (ADS)
Marcott, Curtis; Lo, Michael; Hu, Qichi; Kjoller, Kevin; Boskey, Adele; Noda, Isao
2014-07-01
The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm-1 that sequentially disappear before a band at 1740 cm-1 due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 μm of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.
A spectral-timing analysis of the kHz QPOs in 4U 1636-53: the frequency-energy resolved RMS spectrum
NASA Astrophysics Data System (ADS)
Ribeiro, Evandro M.; Mendez, Mariano; Zhang, Guo-Bao; De Avellar, Márcio G. B.
2016-07-01
Our understanding of quasi-periodic oscillations (QPO) has been further advanced in the last few years by the use of combined spectral and timing techniques, and it is now clear that QPO properties are closely related to the spectral state of the source in which they appear. In this work we used all the available RXTE observations of the neutron-star low-mass X-ray binary 4U~1636-53 to study the properties of the kilohertz QPO as a function of energy and frequency. By following the frequency evolution of the kHz QPOs we created frequency-resolved fractional RMS spectra. We also studied the connection between the frequency of the kHz QPOs and the parameters of the model that fits the X-ray energy spectrum. We show the dependence of the QPO properties in a multi-parameter space, and we discuss the implication of our results to the mechanism that produces the QPOs. Our results provide input to the next generation of spectral-timing models, which will help us understand the variability and the environment around the neutron star in these systems.
NASA Astrophysics Data System (ADS)
van Roekeghem, Ambroise; Richard, Pierre; Ding, Hong; Biermann, Silke
2016-01-01
Electronic Coulomb correlations lead to characteristic signatures in the spectroscopy of transition metal pnictides and chalcogenides: quasi-particle renormalizations, lifetime effects or incoherent badly metallic behavior above relatively low coherence temperatures are measures of many-body effects due to local Hubbard and Hund's couplings. We review and compare the results of angle-resolved photoemission spectroscopy experiments (ARPES) and of combined density functional/dynamical mean-field theory (DFT+DMFT) calculations. We emphasize the doping-dependence of the quasi-particle mass renormalization and coherence properties.
NASA Astrophysics Data System (ADS)
France, Kevin; Parke Loyd, R. O.; Youngblood, Allison; Linsky, Jeffrey; MUSCLES Treasury Survey Team
2016-01-01
The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. High-energy photons (X-ray to near-UV; 5 - 3200 Ang) from these stars regulate the atmospheric temperature profiles and photochemistry on orbiting planets, influencing the production of potential "biomarker" gases. It has been shown that the atmospheric signatures of potentially habitable planets around low-mass stars may be significantly different from planets orbiting Sun-like stars owing to the different UV spectral energy distribution. I will present results from a panchromatic survey (Hubble/Chandra/XMM/optical) of M and K dwarf exoplanet hosts, the MUSCLES Treasury Survey (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems). We reconstruct the Lyman-alpha and extreme-UV (100-900 Ang) radiation lost to interstellar attenuation and create 5 Angstrom to 5 micron stellar irradiance spectra; these data will be publically available as a High-Level Science Product on MAST. We find that all low-mass exoplanet host stars exhibit significant chromospheric/transition region/coronal emission -- no "UV inactive" M dwarfs are observed. The F(far-UV)/F(near-UV) flux ratio, a driver for possible abiotic production of the suggested biomarkers O2 and O3, increases by ~3 orders of magnitude as the habitable zone moves inward from 1 to 0.1 AU, while the incident far-UV (912 - 1700 Ang) and XUV (5 - 900 Ang) radiation field strengths decrease by factors of a few across this range. Far-UV flare activity is common in 'optically inactive' M dwarfs; statistics from the entire sample indicate that large UV flares (E(300 - 1700 Ang) >= 10^31 erg) occur several times per day on typical M dwarf exoplanet hosts.
NASA Astrophysics Data System (ADS)
Schmalz, M.; Key, G.
2012-09-01
Accurate spectral signature classification is key to reliable nonresolved detection and recognition of spaceborne objects. In classical signature-based recognition applications, classification accuracy has been shown to depend on accurate spectral endmember discrimination. Unfortunately, signatures are corrupted by noise and clutter that can be nonergodic in astronomical imaging practice. In previous work, we have shown that object class separation and classifier refinement results can be severely corrupted by input noise, leading to suboptimal classification. We have also shown that computed pattern recognition, like its human counterpart, can benefit from processes such as learning or forgetting, which in spectral signature classification can support adaptive tracking of input nonergodicities. In this paper, we model learning as the acquisition or insertion of a new pattern into a classifier's knowledge base. For example, in neural nets (NNs), this insertion process could correspond to the superposition of a new pattern onto the NN weight matrix. Similarly, we model forgetting as the deletion of a pattern currently stored in the classifier knowledge base, for example, as a pattern deletion operation on the NN weight matrix, which is a difficult goal with classical neural nets (CNNs). In particular, this paper discusses the implementation of feedback control for pattern insertion and deletion in lattice associative memories (LAMs) and dynamically adaptive statistical data fusion (DASDAF) paradigms, in support of signature classification. It is shown that adaptive classifiers based on LNN or DASDAF technology can achieve accurate signature classification in the presence of nonergodic Gaussian and non-Gaussian noise, at low signal-to-noise ratio (SNR). Demonstration involves classification of multiple closely spaced, noise corrupted signatures from a NASA database of space material signatures at SNR > 0.1:1.
Non-Markovian dynamics of an open quantum system with nonstationary coupling
Kalandarov, S. A.; Adamian, G. G.; Kanokov, Z.; Antonenko, N. V.; Scheid, W.
2011-04-15
The spectral, dissipative, and statistical properties of the damped quantum oscillator are studied in the case of non-Markovian and nonstationary system-heat bath coupling. The dissipation of collective energy is shown to be slowed down, and the decoherence rate and entropy grow with modulation frequency.
Non-Markovian dynamics of an open quantum system with nonstationary coupling.
Kalandarov, S A; Kanokov, Z; Adamian, G G; Antonenko, N V; Scheid, W
2011-04-01
The spectral, dissipative, and statistical properties of the damped quantum oscillator are studied in the case of non-Markovian and nonstationary system-heat bath coupling. The dissipation of collective energy is shown to be slowed down, and the decoherence rate and entropy grow with modulation frequency. PMID:21599112
Model of non-stationary, inhomogeneous turbulence
NASA Astrophysics Data System (ADS)
Bragg, Andrew D.; Kurien, Susan; Clark, Timothy T.
2016-07-01
We compare results from a spectral model for non-stationary, inhomogeneous turbulence (Besnard et al. in Theor Comp Fluid Dyn 8:1-35, 1996) with direct numerical simulation (DNS) data of a shear-free mixing layer (SFML) (Tordella et al. in Phys Rev E 77:016309, 2008). The SFML is used as a test case in which the efficacy of the model closure for the physical-space transport of the fluid velocity field can be tested in a flow with inhomogeneity, without the additional complexity of mean-flow coupling. The model is able to capture certain features of the SFML quite well for intermediate to long times, including the evolution of the mixing-layer width and turbulent kinetic energy. At short-times, and for more sensitive statistics such as the generation of the velocity field anisotropy, the model is less accurate. We propose two possible causes for the discrepancies. The first is the local approximation to the pressure-transport and the second is the a priori spherical averaging used to reduce the dimensionality of the solution space of the model, from wavevector to wavenumber space. DNS data are then used to gauge the relative importance of both possible deficiencies in the model.
NASA Technical Reports Server (NTRS)
Zhou, D. K.; Mlynczak, M. G.; Lopez-Puertas, M.; Zaragoza, G.
1999-01-01
Evidence of non-LTE effects in mesospheric water vapor as determined by infrared spectral emission measurements taken from the space shuttle is reported. A cryogenic Michelson interferometer in the CIRRIS-1A shuttle payload yielded high quality, atmospheric infrared spectra. These measurements demonstrate the enhanced daytime emissions of H2O (020-010) which are the result of non-LTE processes and in agreement with non-LTE models. The radiance ratios of H2O (010 to 000) and (020 to 010) Q(1) transitions during daytime are compared with non-LTE model calculations to assess the vibration-to-vibration exchange rate between H2O and O2 in the mesosphere. An exchange rate of 1.2 x 10(exp -12)cc/s is derived.
Pan, C B; Zha, F X; Song, Y X; Shao, J; Dai, Y; Chen, X R; Ye, J Y; Wang, S M
2015-07-15
Femtosecond laser drilled holes of GaSbBi were characterized by the joint measurements of photoconductivity (PC) spectroscopy and laser-beam-induced current (LBIC) mapping. The excitation light in PC was focused down to 60 μm presenting the spectral information of local electronic property of individual holes. A redshift of energy band edge of about 6-8 meV was observed by the PC measurement when the excitation light irradiated on the laser drilled holes. The spatial resolving of photoelectric property was achieved by the LBIC mapping which shows "pseudo-holes" with much larger dimensions than the geometric sizes of the holes. The reduced LBIC current with the pseudo-holes is associated with the redshift effect indicating that the electronic property of the rim areas of the holes is modified by the femtosecond laser drilling. PMID:26176477
Zhao, Weixiong; Dong, Meili; Chen, Weidong; Gu, Xuejun; Hu, Changjin; Gao, Xiaoming; Huang, Wei; Zhang, Weijun
2013-02-19
Despite the significant progress in the measurements of aerosol extinction and absorption using spectroscopy approaches such as cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS), the widely used single-wavelength instruments may suffer from the interferences of gases absorption present in the real environment. A second instrument for simultaneous measurement of absorbing gases is required to characterize the effect of light extinction resulted from gases absorption. We present in this paper the development of a blue light-emitting diode (LED)-based incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach for broad-band measurements of wavelength-resolved aerosol extinction over the spectral range of 445-480 nm. This method also allows for simultaneous measurement of trace gases absorption present in the air sample using the same instrument. On the basis of the measured wavelength-dependent aerosol extinction cross section, the real part of the refractive index (RI) can be directly retrieved in a case where the RI does not vary strongly with the wavelength over the relevant spectral region. Laboratory-generated monodispersed aerosols, polystyrene latex spheres (PSL) and ammonium sulfate (AS), were employed for validation of the RI determination by IBBCEAS measurements. On the basis of a Mie scattering model, the real parts of the aerosol RI were retrieved from the measured wavelength-resolved extinction cross sections for both aerosol samples, which are in good agreement with the reported values. The developed IBBCEAS instrument was deployed for simultaneous measurements of aerosol extinction coefficient and NO(2) concentration in ambient air in a suburban site during two representative days. PMID:23320530
Inoue, Ken-Ichi; Ishiyama, Tatsuya; Nihonyanagi, Satoshi; Yamaguchi, Shoichi; Morita, Akihiro; Tahara, Tahei
2016-05-19
Femtosecond vibrational dynamics at the air/water interface is investigated by time-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy and molecular dynamics (MD) simulation. The low- and high-frequency sides of the hydrogen-bonded (HB) OH stretch band at the interface are selectively excited with special attention to the bandwidth and energy of the pump pulses. Narrow bleach is observed immediately after excitation of the high-frequency side of the HB OH band at ∼3500 cm(-1), compared to the broad bleach observed with excitation of the low-frequency side at ∼3300 cm(-1). However, the time-resolved spectra observed with the two different excitations become very similar at 0.5 ps and almost indistinguishable by 1.0 ps. This reveals that efficient spectral diffusion occurs regardless of the difference of the pump frequency. The experimental observations are well-reproduced by complementary MD simulation. There is no experimental and theoretical evidence that supports extraordinary slow dynamics in the high-frequency side of the HB OH band, which was reported before. PMID:27120559
Spatial methods for nonstationary fields
NASA Astrophysics Data System (ADS)
Nychka, D. W.
2012-12-01
Kriging is a non-parametric regression method used in geostatistics for estimating curves and surfaces and forms the core of most statistical methods for spatial data. In climate science these methods are very useful for estimating how climate varies over a geographic region when the observational data is sparse or the computer model runs are limited. A statistical challenge is to implement spatial methods for large sample sizes and also the heterogenity in the physical fields. Both common features of many geophysical problems. Equally important is to provide companion measures of uncertainty so that the estimated surfaces can be compared and interpreted in an objective way. Here we present a new statistical method that can represent nonstationary structure in a field and also scale to large numbers of spatial locations. A practical example is also presented for a subset of the North American Regional Climate Change and Assessment Program model data.
Nonstationary oscillations in gyrotrons revisited
Dumbrajs, O.; Kalis, H.
2015-05-15
Development of gyrotrons requires careful understanding of different regimes of gyrotron oscillations. It is known that in the planes of the generalized gyrotron variables: cyclotron resonance mismatch and dimensionless current or cyclotron resonance mismatch and dimensionless interaction length complicated alternating sequences of regions of stationary, periodic, automodulation, and chaotic oscillations exist. In the past, these regions were investigated on the supposition that the transit time of electrons through the interaction space is much shorter than the cavity decay time. This assumption is valid for short and/or high diffraction quality resonators. However, in the case of long and/or low diffraction quality resonators, which are often utilized, this assumption is no longer valid. In such a case, a different mathematical formalism has to be used for studying nonstationary oscillations. One example of such a formalism is described in the present paper.
Resolving the Large Scale Spectral Variability of the Luminous Seyfert 1 Galaxy 1H 0419-577
NASA Technical Reports Server (NTRS)
Pounds, K. A.; Reeves, J. N.; Page, K. L.; OBrien, P. T.
2004-01-01
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in September 2002, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below approximately 1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was X-ray bright indicated the dominant spectral variability was due to a steep power law or cool Comptonized thermal emission. Four further XMM-Newton observations, with 1H 0419-577 in intermediate flux states, now support that conclusion, while we also find the variable emission component in intermediate state difference spectra to be strongly modified by absorption in low ionisation matter. The variable soft excess is seen to be an artefact of absorption of the underlying continuum while the core soft emission is attributed to recombination in an extended region of more highly ionised gas. This new analysis underlines the importance of fully accounting for absorption in characterizing AGN X-ray spectra.
Sato, Shigeo; Arai, Yuuki; Wagatsuma, Kazuaki
2014-01-01
When a nitrogen microwave-induced plasma produced with an Okamoto-cavity was employed as a source for the nitridation of steel samples, the characteristics of the plasma were investigated by analyzing a spatially-resolved emission image of nitrogen excited species obtained with a two-dimensionally imaging spectrograph. Our previous study had reported on an excellent performance of the Okamoto-cavity microwave-induced plasma (MIP), enabling a nitrided layer having a several-micrometer-thickness to form on an iron substrate, even if the treatment is completed within 1 min, which is superior to a conventional plasma nitriding using low-pressure glow discharges requiring a prolonged treatment time. In this paper, the reason for this is discussed based on a spectrometric investigation. The emission images of band heads of nitrogen molecule and nitrogen molecule ion extended toward the axial/radial directions of the plasma at larger microwave powers supplied to the MIP, thus elevating the number density of the excited species of nitrogen, which would activate any chemical reaction on the iron substrate. However, a drastic increase in the growth rate of the nitrided layer when increasing the microwave power from 600 to 700 W, which had been observed in our previous study, could not be explained only from such a variation in the excited species of nitrogen. This result is probably because the growth process is dominantly controlled by thermal diffusion of nitrogen atom after it enters into the iron substrate, where the substrate temperature is the most important parameter concerning the mobility in the iron lattice. Therefore, the Okamoto-cavity MIP could contribute to a thermal source through radiative heating as well as a source of nitrogen excited species, especially in the growth process of the nitrided layer. PMID:24521910
Non-Stationary Signals: Phase-Energy APPROACH—THEORY and Simulations
NASA Astrophysics Data System (ADS)
Klein, R.; Ingman, D.; Braun, S.
2001-11-01
Modern time-frequency methods are intended to deal with a variety of non-stationary signals. One specific class, prevalent in the area of rotating machines, is that of harmonic signals of varying frequencies and amplitude. This paper presents a new adaptive phase-energy (APE) approach for time-frequency representation of varying harmonic signals. It is based on the concept of phase (frequency) paths and the instantaneous power spectral density (PSD). It is this path which represents the dynamic behaviour of the system generating the observed signal. The proposed method utilises dynamic filters based on an extended Nyquist theorem, enabling to extract signal components with optimal signal-to-noise ratio. The APE detects the most energetic harmonic components (frequency paths) in the analysed signal. Tests on simulated signals show the superiority of the APE in resolution and resolving power as compared to STFT and wavelets wave-packet decomposition. The dynamic filters also enable the reconstruction of the signal components (paths) from the noisy signal. A quantitative comparison was performed both for the detected path in the time-frequency plane as well as for the reconstructed signal, demonstrating the performance of the APE.
NASA Astrophysics Data System (ADS)
Isabelle, Martin; Davis, Scott; Li, Zan; Gunn, Jason; Hoopes, P. J.; Pereira, S.; Mosse, C. A.; Hasan, T.; Pogue, B. W.
2012-02-01
Photodynamic therapy (PDT) mediated with verteporfin is currently being investigated to treat pancreatic cancer in patients who are not surgical candidates. Clinically, interstitial light delivery is administered through a fiber, via percutaneous needle implantation guided by ultrasound and/or verified by CT. Tumor response to PDT is based on photosensitizer (PS) dose, light dose, light dose rate and the timing of light application following PS injection. However, studies have shown that even when matching administered PDT treatment parameters such as drug dose and light level, there can be significant inter-patient variation in tissue damage post-PDT, and this has been primarily attributed to imprecise PS concentration at the target tissue site. In order to achieve optimal tumor response from PDT without causing major damage to surrounding tissue, it would be advantageous to measure the PS concentration in the target tissue just prior to light application. From these measurements, the clinician can adapt the light application dose to the measured target tissue PS concentration (i.e. insufficient target tissue PS concentrations compensated by higher light doses and vice versa.) in order to provide an optimal light dose for each patient. In animal studies, a spectrometer-based in-vivo fluorescence dosimetry system has been used to assess accumulated PS levels (verteporfin) in situ. Measurements are taken from skin, leg muscle, buccal mucosa and tumor tissue locations one hour after injection of the photosensitizer. Real-time spectral fitting, subtraction of background autofluorescence and ratiometric analysis is performed on the raw data to extract out only the photosensitizer fluorescence and therefore concentration. Using a pre-measured calibration data set of varying concentrations for verteporfin in tissue phantoms composed of intralipid and whole blood, it was possible detect concentrations of the photosensitizer below 0.5nM. In the clinical studies being
NASA Astrophysics Data System (ADS)
Elgass, Kirstin; Zell, Martina; Maurino, Veronica G.; Schleifenbaum, Frank
2011-02-01
Leaf cells of living plants exhibit strong fluorescence from chloroplasts, the reaction centers of photosynthesis. Mutations in the photosystems change their structure and can, thus, be monitored by recording the fluorescence spectra of the emitted chlorophyll light. These measurements have, up to now, mostly been carried out at low temperatures (77 K), as these conditions enable the differentiation between the fluorescence of Photosystem I (PSI) and Photosystem II (PSII). In contrast, at room temperature, energy transfer processes between the various photosynthetic complexes result in very similar fluorescence emissions, which mainly consist of fluorescence photons emitted by PSII hindering a discrimination based on spectral ROIs (regions of interest). However, by statistical analysis of high resolution fluorescence spectra recorded at room temperature, it is possible to draw conclusions about the relative PSI/PSII ratio. Here, the possibility of determining the relative PSI/PSII ratio by fluorescence spectroscopy is demonstrated in living maize plants. Bundle-sheath chloroplasts of mature maize plants have a special morphologic characteristic; they are agranal, or exhibit only rudimentary grana, respectively. These chloroplasts are depleted in PSII activity and it could be shown that PSII is progressively reduced during leaf differentiation. A direct comparison of PSII activity in isolated chloroplasts is nearly impossible, since the activity of PSII in both mesophyll- and bundle-sheath chloroplasts decays with time after isolation and it takes significantly longer to isolate bundle-sheath chloroplasts. Considering this fact the measurement of PSI/PSII ratios with the 77K method, which includes taking fluorescence spectra from a diluted suspension of isolated chloroplasts at 77K, is questionable. These spectra are then used to analyze the distribution of energy between PSI and PSII. After rapid cooling to 77K secondary biochemical influences, which attenuate the
Quantum radiation of general nonstationary black holes
NASA Astrophysics Data System (ADS)
Hua, Jia-Chen; Huang, Yong-Chang
2009-02-01
Quantum radiation of general nonstationary black holes is investigated by using the method of generalized tortoise-coordinate transformation (GTT). It is shown in general that the temperature and the shape of the event horizon of this kind of black holes depend on time and angle. Further, we find that the chemical potential in the thermal-radiation spectrum is equal to the highest energy of the negative-energy state of particles in nonthermal radiation for general nonstationary black holes.
NASA Astrophysics Data System (ADS)
Sambri, A.; Aruta, C.; Di Gennaro, E.; Wang, X.; Scotti di Uccio, U.; Miletto Granozio, F.; Amoruso, S.
2016-03-01
The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to ≈10-1 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters.
Tamaki, Ryo Shoji, Yasushi; Okada, Yoshitaka; Miyano, Kenjiro
2014-08-18
Two-step photon absorption processes in a self-organized In{sub 0.4}Ga{sub 0.6}As/GaAs quantum dot (QD) solar cell have been investigated by monitoring the mid-infrared (IR) photoinduced modulation of the external quantum efficiency (ΔEQE) at low temperature. The first step interband and the second step intraband transitions were both spectrally resolved by scanning photon energies of visible to near-IR CW light and mid-IR pulse lasers, respectively. A peak centered at 0.20 eV corresponding to the transition to virtual bound states and a band above 0.42 eV probably due to photoexcitation to GaAs continuum states were observed in ΔEQE spectra, when the interband transition was above 1.4 eV, directly exciting wetting layers or GaAs spacer layers. On the other hand, resonant excitation of the ground state of QDs at 1.35 eV resulted in a reduction of EQE. The sign of ΔEQE below 1.40 eV changed from negative to positive by increasing the excitation intensity of the interband transition. We ascribe this to the filling of higher energy trap states.
Spectrally resolved multidepth fluorescence imaging
Luo, Yuan; Zervantonakis, Ioannis K.; Oh, Se Baek; Kamm, Roger D.; Barbastathis, George
2011-01-01
We present a multicolor fluorescence imaging modality to visualize in real-time tissue structures emitting multispectral fluorescent light from different focal depths. Each designated spectrum of fluorescent emission from a specific depth within a volumetric tissue is probed by a depth-spectrum selective holographic grating. The grating for each fluorescent color are multiplexed within a volume hologram, which enables simultaneously obtaining multicolored fluorescent information at different depths within a biological tissue sample. We demonstrate the imaging modality's ability to obtain laser-induced multicolored fluorescence images of a biological sample from different depths without scanning. We also experimentally demonstrate that the imaging modality can be simultaneously operated at both fluorescent and bright field modes to provide complementary information of volumetric tissue structures at different depths in real-time. PMID:21950929
Spectrally resolved multidepth fluorescence imaging
NASA Astrophysics Data System (ADS)
Luo, Yuan; Zervantonakis, Ioannis K.; Oh, Se Baek; Kamm, Roger D.; Barbastathis, George
2011-09-01
We present a multicolor fluorescence imaging modality to visualize in real-time tissue structures emitting multispectral fluorescent light from different focal depths. Each designated spectrum of fluorescent emission from a specific depth within a volumetric tissue is probed by a depth-spectrum selective holographic grating. The grating for each fluorescent color are multiplexed within a volume hologram, which enables simultaneously obtaining multicolored fluorescent information at different depths within a biological tissue sample. We demonstrate the imaging modality's ability to obtain laser-induced multicolored fluorescence images of a biological sample from different depths without scanning. We also experimentally demonstrate that the imaging modality can be simultaneously operated at both fluorescent and bright field modes to provide complementary information of volumetric tissue structures at different depths in real-time.
Wavelet analysis as a nonstationary plasma fluctuation diagnostic tool
Santoso, S.; Powers, E.J.; Ouroua, A.; Heard, J.W.; Bengtson, R.D.
1996-12-31
Analysis of nonstationary plasma fluctuation data has been a long-time challenge for the plasma diagnostic community. For this reason, in this paper the authors present and apply wavelet transforms as a new diagnostic tool to analyze nonstationary plasma fluctuation data. Unlike the Fourier transform, which represents a given signal globally without temporal resolution, the wavelet transform provides a local representation of the given signal in the time-scale domain. The fundamental concepts and multiresolution properties of wavelet transforms, along with a brief comparison with the short-time Fourier transform, are presented in this paper. The selection of a prototype wavelet or a mother wavelet is also discussed. Digital implementation of wavelet spectral analysis, which include time-scale power spectra and scale power spectra are described. The efficacy of the wavelet approach is demonstrated by analyzing transient broadband electrostatic potential fluctuations inside the inversion radius of sawtoothing TEXT-U plasmas during electron cyclotron resonance heating. The potential signals are collected using a 2 MeV heavy ion beam probe.
Axisymmetric, Nonstationary Black Hole Magnetospheres: Revisited
NASA Astrophysics Data System (ADS)
Song, Yoo Geun; Park, Seok Jae
2015-10-01
An axisymmetric, stationary, general-relativistic, electrodynamic engine model of an active galactic nucleus was formulated by Macdonald and Thorne that consisted of a supermassive black hole surrounded by a plasma magnetosphere and a magnetized accretion disk. Based on this initial formulation, a nonstationary, force-free version of their model was constructed by Park & Vishniac (PV), with the simplifying assumption that the poloidal component of the magnetic field line velocity be confined along the radial direction in cylindrical polar coordinates. In this paper, we derive the new, nonstationary “Transfield Equation,” which was not specified in PV. If we can solve this “Transfield Equation” numerically, then we will understand the axisymmetric, nonstationary black hole magnetosphere in more rigorous ways.
Heuristic segmentation of a nonstationary time series
NASA Astrophysics Data System (ADS)
Fukuda, Kensuke; Eugene Stanley, H.; Nunes Amaral, Luís A.
2004-02-01
Many phenomena, both natural and human influenced, give rise to signals whose statistical properties change under time translation, i.e., are nonstationary. For some practical purposes, a nonstationary time series can be seen as a concatenation of stationary segments. However, the exact segmentation of a nonstationary time series is a hard computational problem which cannot be solved exactly by existing methods. For this reason, heuristic methods have been proposed. Using one such method, it has been reported that for several cases of interest—e.g., heart beat data and Internet traffic fluctuations—the distribution of durations of these stationary segments decays with a power-law tail. A potential technical difficulty that has not been thoroughly investigated is that a nonstationary time series with a (scalefree) power-law distribution of stationary segments is harder to segment than other nonstationary time series because of the wider range of possible segment lengths. Here, we investigate the validity of a heuristic segmentation algorithm recently proposed by Bernaola-Galván et al. [Phys. Rev. Lett. 87, 168105 (2001)] by systematically analyzing surrogate time series with different statistical properties. We find that if a given nonstationary time series has stationary periods whose length is distributed as a power law, the algorithm can split the time series into a set of stationary segments with the correct statistical properties. We also find that the estimated power-law exponent of the distribution of stationary-segment lengths is affected by (i) the minimum segment length and (ii) the ratio R≡σɛ/σx¯, where σx¯ is the standard deviation of the mean values of the segments and σɛ is the standard deviation of the fluctuations within a segment. Furthermore, we determine that the performance of the algorithm is generally not affected by uncorrelated noise spikes or by weak long-range temporal correlations of the fluctuations within segments.
NASA Astrophysics Data System (ADS)
Fiorenza, C.; Coppola, E.; Cimini, D.; Marzano, F. S.; Visconti, G.
2003-04-01
Testing Numerical Prediction Models (NPM) is a major issue for climate studies. Different approaches are possible, based on comparison between numerical output and atmospheric and oceanic measurements, such as air temperature, humidity, sea surface temperature. More recently, another approach has been proposed [Haskins et al, 1995; 1997; 1998; Goody et al., 1998], which make use of direct observations, such as outgoing long-wave radiance, instead of retrieved products. In order to accomplish this goal, it?'s necessary to obtain an equivalent set of data from numerical models and observations. Spectrally resolved outgoing long-wave radiance from the Earth-Atmosphere system has been measured by the IRIS and IMG [Hanel et al., 1972; Kobayashi et al., 1999; Cimini et al., 2002] interferometers. On the other hand, NPM do not provide this information directly. However, by processing the thermodynamical and chemical information from the NPM about the Earth-Atmosphere system with a Radiative Tranfer Model (RTM) code, we are able to produce this quantity. Although, since NPM do not provide detailed information about the microphysics of hydrometeors, which is necessary to compute exactly the radiation extinction by clouds, we are forced to reduced our analysis to clear-sky cases [Huang et al., 2002]. Thus, from the simulation point of view, we simply don?t input clouds in the RTM, while for the observations we need to detect and remove cloud-contaminated cases from the entire dataset. Several screening techniques are available in the open literature, each one using a different approach to detect cloud contamination, which forces us to make a choice. Thus, we take in account four different techniques, and apply each one independently to the observations data set. Finally, we discuss the results, motivating our choice of the optimum? " screening technique.
NASA Astrophysics Data System (ADS)
Kobayashi, Hisataka; Hama, Yukihiro; Koyama, Yoshinori; Barrett, Tristan; Urano, Yasuteru; Choyke, Peter L.
2007-02-01
Target-specific contrast agents are being developed for the molecular imaging of cancer. Optically detectable target-specific agents are promising for clinical applications because of their high sensitivity and specificity. Pre clinical testing is needed, however, to validate the actual sensitivity and specificity of these agents in animal models, and involves both conventional histology and immunohistochemistry, which requires large numbers of animals and samples with costly handling. However, a superior validation tool takes advantage of genetic engineering technology whereby cell lines are transfected with genes that induce the target cell to produce fluorescent proteins with characteristic emission spectra thus, identifying them as cancer cells. Multicolor fluorescence imaging of these genetically engineered probes can provide rapid validation of newly developed exogenous probes that fluoresce at different wavelengths. For example, the plasmid containing the gene encoding red fluorescent protein (RFP) was transfected into cell lines previously developed to either express or not-express specific cell surface receptors. Various antibody-based or receptor ligand-based optical contrast agents with either green or near infrared fluorophores were developed to concurrently target and validate cancer cells and their positive and negative controls, such as β-D-galactose receptor, HER1 and HER2 in a single animal/organ. Spectrally resolved fluorescence multicolor imaging was used to detect separate fluorescent emission spectra from the exogenous agents and RFP. Therefore, using this in vivo imaging technique, we were able to demonstrate the sensitivity and specificity of the target-specific optical contrast agents, thus reducing the number of animals needed to conduct these experiments.
Nonstationary Transient Vibroacoustic Response of a Beam Structure
NASA Technical Reports Server (NTRS)
Caimi, R. E.; Margasahayam, R. N.; Nayfeh, Jamal F.
1997-01-01
This study consists of an investigation into the nonstationary transient response of the Verification Test Article (VETA) when subjected to random acoustic excitation. The goal is to assess excitation models that can be used in the design of structures and equipment when knowledge of the structure and the excitation is limited. The VETA is an instrumented cantilever beam that was exposed to acoustic loading during five Space Shuttle launches. The VETA analytical structural model response is estimated using the direct averaged power spectral density and the normalized pressure spectra methods. The estimated responses are compared to the measured response of the VETA. These comparisons are discussed with a focus on prediction conservatism and current design practice.
EDITORIAL: CAMOP: Quantum Non-Stationary Systems CAMOP: Quantum Non-Stationary Systems
NASA Astrophysics Data System (ADS)
Dodonov, Victor V.; Man'ko, Margarita A.
2010-09-01
Although time-dependent quantum systems have been studied since the very beginning of quantum mechanics, they continue to attract the attention of many researchers, and almost every decade new important discoveries or new fields of application are made. Among the impressive results or by-products of these studies, one should note the discovery of the path integral method in the 1940s, coherent and squeezed states in the 1960-70s, quantum tunneling in Josephson contacts and SQUIDs in the 1960s, the theory of time-dependent quantum invariants in the 1960-70s, different forms of quantum master equations in the 1960-70s, the Zeno effect in the 1970s, the concept of geometric phase in the 1980s, decoherence of macroscopic superpositions in the 1980s, quantum non-demolition measurements in the 1980s, dynamics of particles in quantum traps and cavity QED in the 1980-90s, and time-dependent processes in mesoscopic quantum devices in the 1990s. All these topics continue to be the subject of many publications. Now we are witnessing a new wave of interest in quantum non-stationary systems in different areas, from cosmology (the very first moments of the Universe) and quantum field theory (particle pair creation in ultra-strong fields) to elementary particle physics (neutrino oscillations). A rapid increase in the number of theoretical and experimental works on time-dependent phenomena is also observed in quantum optics, quantum information theory and condensed matter physics. Time-dependent tunneling and time-dependent transport in nano-structures are examples of such phenomena. Another emerging direction of study, stimulated by impressive progress in experimental techniques, is related to attempts to observe the quantum behavior of macroscopic objects, such as mirrors interacting with quantum fields in nano-resonators. Quantum effects manifest themselves in the dynamics of nano-electromechanical systems; they are dominant in the quite new and very promising field of circuit
2012-01-01
Background and aims: Acne remains a severe problem for both patients and clinicians. Various approaches using photosurgery and phototherapy have been reported with varying degrees of success and robustness of results. An improved intense pulsed light (IPL) system has become available with interesting beam characteristic which might improve IPL treatment of inflammatory acne in the Asian skin, Fitzpatrick type III/IV. Subjects and Methods: The 18 study subjects comprised 15 females and 3 males with active mild to moderately severe inflammatory acne (mean age 25.3 ± 7.70 yr, range 17–47 yr, Burton scale 1-4, all Fitzpatrick type III Asian skin). They were treated once (8 subjects) or twice (10 subjects) with an IPL system offering both square pulse and time resolved spectral distribution technologies (420 nm cut-off filter, 30 ms pulse, 8 – 12 J/cm2, 2–3 passes). Clinical photography was taken at baseline and at 4 weeks after the final treatment. Percentage of acne clearance was assessed by an independent dermatological panel and graded from zero to 5, 5 being total clearance. Results: All subjects completed the study. Post-treatment side effects were mild and transient, with virtually no downtime or postinflammatory hyperpigmentation (PIH) experienced by any subject. All subjects had some improvement and no exacerbation was seen in any subject. Clearance was evaluated by the panel as grade 4 in 5 subjects, grade 3 in 8, grade 2 in 4 and grade 1 in 1, so that 14 of 18 subjects (78%) had clearance of at least 60%. Patient evaluation was in general slightly better than that of the panel. Conclusions: The special beam characteristics of the IPL system used in the present preliminary study achieved good to very good results in the treatment of acne in the Fitzpatrick type III Asian skin without PIH induction. The results suggested that acne treatment in the Asian skin using this system is both safe and effective, and merits larger population studies to further
NASA Astrophysics Data System (ADS)
Konrad, Alexander; Metzger, Michael; Kern, Andreas M.; Brecht, Marc; Meixner, Alfred J.
2016-07-01
Using a Fabry-Pérot-microresonator with controllable cavity lengths in the λ/2-regime, we show the controlled modification of the vibronic relaxation dynamics of a fluorescent dye molecule in the spectral and time domain. By altering the photonic mode density around the fluorophores we are able to shape the fluorescence spectrum and enhance specifically the probability of the radiative transitions from the electronic excited state to distinct vibronic excited states of the electronic ground state. Analysis and correlation of the spectral and time resolved measurements by a theoretical model and a global fitting procedure allows us to reveal quantitatively the spectrally distributed radiative and non-radiative relaxation dynamics of the respective dye molecule under ambient conditions at the ensemble level.Using a Fabry-Pérot-microresonator with controllable cavity lengths in the λ/2-regime, we show the controlled modification of the vibronic relaxation dynamics of a fluorescent dye molecule in the spectral and time domain. By altering the photonic mode density around the fluorophores we are able to shape the fluorescence spectrum and enhance specifically the probability of the radiative transitions from the electronic excited state to distinct vibronic excited states of the electronic ground state. Analysis and correlation of the spectral and time resolved measurements by a theoretical model and a global fitting procedure allows us to reveal quantitatively the spectrally distributed radiative and non-radiative relaxation dynamics of the respective dye molecule under ambient conditions at the ensemble level. Electronic supplementary information (ESI) available. See DOI: 10.1039/C6NR02380K
Resolution enhancement of non-stationary seismic data using amplitude-frequency partition
NASA Astrophysics Data System (ADS)
Xie, Yujiang; Liu, Gao
2015-02-01
As the Earth's inhomogeneous and viscoelastic properties, seismic signal attenuation we are trying to mitigate is a long-standing problem facing with high-resolution techniques. For addressing such a problem in the fields of time-frequency transform, Gabor transform methods such as atom-window method (AWM) and molecular window method (MWM) have been reported recently. However, we observed that these methods might be much better if we partition the non-stationary seismic data into adaptive stationary segments based on the amplitude and frequency information of the seismic signal. In this study, we present a new method called amplitude-frequency partition (AFP) to implement this process in the time-frequency domain. Cases of a synthetic and field seismic data indicated that the AFP method could partition the non-stationary seismic data into stationary segments approximately, and significantly, a high-resolution result would be achieved by combining the AFP method with conventional spectral-whitening method, which could be considered superior to previous resolution-enhancement methods like time-variant spectral whitening method, the AWM and the MWM as well. This AFP method presented in this study would be an effective resolution-enhancement tool for the non-stationary seismic data in the fields of an adaptive time-frequency transform.
New wave effects in nonstationary plasma
Schmit, P. F.; Fisch, N. J.
2013-05-15
Through particle-in-cell simulations and analytics, a host of interesting and novel wave effects in nonstationary plasma are examined. In particular, Langmuir waves serve as a model system to explore wave dynamics in plasmas undergoing compression, expansion, and charge recombination. The entire wave life-cycle is explored, including wave excitation, adiabatic evolution and action conservation, nonadiabatic evolution and resonant wave-particle effects, collisional dissipation, and potential laboratory applications of the aforementioned phenomenology.
Sequential decision analysis for nonstationary stochastic processes
NASA Technical Reports Server (NTRS)
Schaefer, B.
1974-01-01
A formulation of the problem of making decisions concerning the state of nonstationary stochastic processes is given. An optimal decision rule, for the case in which the stochastic process is independent of the decisions made, is derived. It is shown that this rule is a generalization of the Bayesian likelihood ratio test; and an analog to Wald's sequential likelihood ratio test is given, in which the optimal thresholds may vary with time.
Hazard function theory for nonstationary natural hazards
NASA Astrophysics Data System (ADS)
Read, L.; Vogel, R. M.
2015-12-01
Studies from the natural hazards literature indicate that many natural processes, including wind speeds, landslides, wildfires, precipitation, streamflow and earthquakes, show evidence of nonstationary behavior such as trends in magnitudes through time. Traditional probabilistic analysis of natural hazards based on partial duration series (PDS) generally assumes stationarity in the magnitudes and arrivals of events, i.e. that the probability of exceedance is constant through time. Given evidence of trends and the consequent expected growth in devastating impacts from natural hazards across the world, new methods are needed to characterize their probabilistic behavior. The field of hazard function analysis (HFA) is ideally suited to this problem because its primary goal is to describe changes in the exceedance probability of an event over time. HFA is widely used in medicine, manufacturing, actuarial statistics, reliability engineering, economics, and elsewhere. HFA provides a rich theory to relate the natural hazard event series (x) with its failure time series (t), enabling computation of corresponding average return periods and reliabilities associated with nonstationary event series. This work investigates the suitability of HFA to characterize nonstationary natural hazards whose PDS magnitudes are assumed to follow the widely applied Poisson-GP model. We derive a 2-parameter Generalized Pareto hazard model and demonstrate how metrics such as reliability and average return period are impacted by nonstationarity and discuss the implications for planning and design. Our theoretical analysis linking hazard event series x, with corresponding failure time series t, should have application to a wide class of natural hazards.
Time-frequency filtering for classifying targets in nonstationary clutter
NASA Astrophysics Data System (ADS)
Gomatam, Vikram Thiruneermalai; Loughlin, Patrick
2014-06-01
Classifying underwater targets from their sonar backscatter is often complicated by induced or self-noise (i.e. clutter, reverberation) arising from the scattering of the sonar pulse from non-target objects. Because clutter is inherently nonstationary, and because the propagation environment can induce nonstationarities as well, in addition to any nonstationarities / time-varying spectral components of the target echo itself, a joint phase space approach to target classification has been explored. In this paper, we apply a previously developed minimum mean square time-frequency spectral estimation method to design a bank of time-frequency filters from training data to distinguish targets from clutter. The method is implemented in the ambiguity domain in order to reduce computational requirements. In this domain, the optimal filter (more commonly called a "kernel" in the time-frequency literature) multiples the ambiguity function of the received signal, and then the mean squared distance to each target class is computed. Simulations demonstrate that the class-specific optimal kernel better separates each target from the clutter and other targets, compared to a simple mean-squared distance measure with no kernel processing.
First-excursion probability in non-stationary random vibration.
NASA Technical Reports Server (NTRS)
Yang, J.-N.
1973-01-01
The first-excursion probability of a non-stationary Gaussian process with zero mean has been studied. Within the framework of the point process approach, a variety of analytical approximations applicable to stationary random processes is extended herein to non-stationary random processes. The extension is possible owing to a recent definition of non-stationary envelope processes proposed by the author. With the aid of numerical examples, merits of each approximation are examined by comparing with the results of simulation. It is found that under non-stationary excitations with short duration, the Markov approximation is the best among all the approximations discussed in this paper.
Velarde Ruiz Esparza, Luis A.; Wang, Hongfei
2013-12-14
The emergence of sub-wavenumber high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BBSFG-VS) [Velarde et al., J. Chem. Phys., 2011, 135, 241102] has offered new opportunities in obtaining and understanding the spectral lineshape and temporal effects on the surface vibrational spectroscopy. Particularly, the high accuracy in the HR-BBSFG-VS spectral lineshape measurement provides detailed information on the complex coherent vibrational dynamics through spectral measurement. Here we present a unified formalism of the theoretical and experimental approaches for obtaining the accurate lineshape of the SFG response, and then present a analysis on the higher and lower spectral resolution SFG spectra as well as their temporal effects of the cholesterol molecules at the air/water interface. With the high spectral resolution and accurate lineshape, it is shown that the parameters from the sub-wavenumber resolution SFG spectra can be used not only to understand but also to quantitatively reproduce the temporal effects in the lower resolution SFG measurement. These not only provide a unified picture in understanding both the frequency-domain and the time-domain SFG response of the complex molecular interface, but also provide novel experimental approaches that can directly measure them.
NASA Astrophysics Data System (ADS)
Batehup, R.; McGregor, S.; Gallant, A. J. E.
2015-08-01
Reconstructions of the El Niño-Southern Oscillation (ENSO) ideally require high-quality, annually-resolved and long-running paleoclimate proxy records in the eastern tropical Pacific Ocean, located in ENSO's centre-of-action. However, to date, the paleoclimate records that have been extracted in the region are short or temporally and spatially sporadic, limiting the information that can be provided by these reconstructions. Consequently, most ENSO reconstructions exploit the downstream influences of ENSO on remote locations, known as teleconnections, where longer records from paleoclimate proxies exist. However, using teleconnections to reconstruct ENSO relies on the assumption that the relationship between ENSO and the remote location is stationary in time. Increasing evidence from observations and climate models suggests that some teleconnections are, in fact, non-stationary, potentially threatening the validity of those paleoclimate reconstructions that exploit teleconnections. This study examines the implications of non-stationary teleconnections on modern multi-proxy reconstructions of ENSO. The sensitivity of the reconstructions to non-stationary teleconnections were tested using a suite of idealized pseudoproxy experiments that employed output from a fully coupled global climate model. Reconstructions of the variance in the Niño 3.4 index, representing ENSO variability, were generated using four different methods to which surface temperature data from the GFDL CM2.1 was applied as a pseudoproxy. As well as sensitivity of the reconstruction to the method, the experiments tested the sensitivity of the reconstruction to the number of non-stationary pseudoproxies and the location of these proxies. ENSO reconstructions in the pseudoproxy experiments were not sensitive to non-stationary teleconnections when global, uniformly-spaced networks of a minimum of approximately 20 proxies were employed. Neglecting proxies from ENSO's center-of-action still produced
Stationary versus non-stationary (13)C-MFA: a comparison using a consistent dataset.
Noack, Stephan; Nöh, Katharina; Moch, Matthias; Oldiges, Marco; Wiechert, Wolfgang
2011-07-10
Besides the well-established (13)C-metabolic flux analysis ((13)C-MFA) which characterizes a cell's fluxome in a metabolic and isotopic stationary state a current area of research is isotopically non-stationary MFA. Non-stationary (13)C-MFA uses short-time isotopic transient data instead of long-time isotopic equilibrium data and thus is capable to resolve fluxes within much shorter labeling experiments. However, a comparison of both methods with data from one single experiment has not been made so far. In order to create a consistent database for directly comparing both methods a (13)C-labeling experiment in a fed-batch cultivation with a Corynebacterium glutamicum lysine producer was carried out. During the experiment the substrate glucose was switched from unlabeled to a specifically labeled glucose mixture which was immediately traced by fast sampling and metabolite quenching. The time course of labeling enrichments in intracellular metabolites until isotopic stationarity was monitored by LC-MS/MS. The resulting dataset was evaluated using the classical as well as the isotopic non-stationary MFA approach. The results show that not only the obtained relative data, i.e. intracellular flux distributions, but also the more informative quantitative fluxome data significantly depend on the combination of the measurements and the underlying modeling approach used for data integration. Taking further criteria on the experimental and computational part into consideration, the current limitations of both methods are demonstrated and possible pitfalls are concluded. PMID:20638432
Hazard function theory for nonstationary natural hazards
NASA Astrophysics Data System (ADS)
Read, Laura K.; Vogel, Richard M.
2016-04-01
Impact from natural hazards is a shared global problem that causes tremendous loss of life and property, economic cost, and damage to the environment. Increasingly, many natural processes show evidence of nonstationary behavior including wind speeds, landslides, wildfires, precipitation, streamflow, sea levels, and earthquakes. Traditional probabilistic analysis of natural hazards based on peaks over threshold (POT) generally assumes stationarity in the magnitudes and arrivals of events, i.e., that the probability of exceedance of some critical event is constant through time. Given increasing evidence of trends in natural hazards, new methods are needed to characterize their probabilistic behavior. The well-developed field of hazard function analysis (HFA) is ideally suited to this problem because its primary goal is to describe changes in the exceedance probability of an event over time. HFA is widely used in medicine, manufacturing, actuarial statistics, reliability engineering, economics, and elsewhere. HFA provides a rich theory to relate the natural hazard event series (X) with its failure time series (T), enabling computation of corresponding average return periods, risk, and reliabilities associated with nonstationary event series. This work investigates the suitability of HFA to characterize nonstationary natural hazards whose POT magnitudes are assumed to follow the widely applied generalized Pareto model. We derive the hazard function for this case and demonstrate how metrics such as reliability and average return period are impacted by nonstationarity and discuss the implications for planning and design. Our theoretical analysis linking hazard random variable X with corresponding failure time series T should have application to a wide class of natural hazards with opportunities for future extensions.
Hazard function theory for nonstationary natural hazards
NASA Astrophysics Data System (ADS)
Read, L. K.; Vogel, R. M.
2015-11-01
Impact from natural hazards is a shared global problem that causes tremendous loss of life and property, economic cost, and damage to the environment. Increasingly, many natural processes show evidence of nonstationary behavior including wind speeds, landslides, wildfires, precipitation, streamflow, sea levels, and earthquakes. Traditional probabilistic analysis of natural hazards based on peaks over threshold (POT) generally assumes stationarity in the magnitudes and arrivals of events, i.e. that the probability of exceedance of some critical event is constant through time. Given increasing evidence of trends in natural hazards, new methods are needed to characterize their probabilistic behavior. The well-developed field of hazard function analysis (HFA) is ideally suited to this problem because its primary goal is to describe changes in the exceedance probability of an event over time. HFA is widely used in medicine, manufacturing, actuarial statistics, reliability engineering, economics, and elsewhere. HFA provides a rich theory to relate the natural hazard event series (X) with its failure time series (T), enabling computation of corresponding average return periods, risk and reliabilities associated with nonstationary event series. This work investigates the suitability of HFA to characterize nonstationary natural hazards whose POT magnitudes are assumed to follow the widely applied Generalized Pareto (GP) model. We derive the hazard function for this case and demonstrate how metrics such as reliability and average return period are impacted by nonstationarity and discuss the implications for planning and design. Our theoretical analysis linking hazard event series X, with corresponding failure time series T, should have application to a wide class of natural hazards with rich opportunities for future extensions.
Hazard function theory for nonstationary natural hazards
Read, Laura K.; Vogel, Richard M.
2016-04-11
Impact from natural hazards is a shared global problem that causes tremendous loss of life and property, economic cost, and damage to the environment. Increasingly, many natural processes show evidence of nonstationary behavior including wind speeds, landslides, wildfires, precipitation, streamflow, sea levels, and earthquakes. Traditional probabilistic analysis of natural hazards based on peaks over threshold (POT) generally assumes stationarity in the magnitudes and arrivals of events, i.e., that the probability of exceedance of some critical event is constant through time. Given increasing evidence of trends in natural hazards, new methods are needed to characterize their probabilistic behavior. The well-developed field ofmore » hazard function analysis (HFA) is ideally suited to this problem because its primary goal is to describe changes in the exceedance probability of an event over time. HFA is widely used in medicine, manufacturing, actuarial statistics, reliability engineering, economics, and elsewhere. HFA provides a rich theory to relate the natural hazard event series (X) with its failure time series (T), enabling computation of corresponding average return periods, risk, and reliabilities associated with nonstationary event series. This work investigates the suitability of HFA to characterize nonstationary natural hazards whose POT magnitudes are assumed to follow the widely applied generalized Pareto model. We derive the hazard function for this case and demonstrate how metrics such as reliability and average return period are impacted by nonstationarity and discuss the implications for planning and design. As a result, our theoretical analysis linking hazard random variable X with corresponding failure time series T should have application to a wide class of natural hazards with opportunities for future extensions.« less
Multiaxis Rainflow Fatigue Methods for Nonstationary Vibration
NASA Technical Reports Server (NTRS)
Irvine, T.
2016-01-01
Mechanical structures and components may be subjected to cyclical loading conditions, including sine and random vibration. Such systems must be designed and tested accordingly. Rainflow cycle counting is the standard method for reducing a stress time history to a table of amplitude-cycle pairings prior to the Palmgren-Miner cumulative damage calculation. The damage calculation is straightforward for sinusoidal stress but very complicated for random stress, particularly for nonstationary vibration. This paper evaluates candidate methods and makes a recommendation for further study of a hybrid technique.
Harmonic demodulation of nonstationary shot noise.
Gray, M B; Stevenson, A J; Bachor, H A; McClelland, D E
1993-05-15
We report on experimental demodulation of nonstationary shot noise, which is associated with strongly modulated light. For sinusoidal modulation and demodulation, measurements confirm theoretical predictions of 1.8-dB excess noise in the modulation quadrature and 3-dB noise reduction in the opposite quadrature, relative to the standard quantum limit. Demodulation with a third harmonic produces noise correlated with that which is due to the fundamental. Reducing excess noise by 0.8 dB in the modulation quadrature, by combining the fundamental and third harmonics in a 2:1 ratio, is shown to be feasible. PMID:19802263
The Stokes phenomenon and quantum tunneling for de Sitter radiation in nonstationary coordinates
NASA Astrophysics Data System (ADS)
Kim, Sang Pyo
2010-09-01
We study quantum tunneling for the de Sitter radiation in the planar coordinates and global coordinates, which are nonstationary coordinates and describe the expanding geometry. Using the phase-integral approximation for the Hamilton-Jacobi action in the complex plane of time, we obtain the particle-production rate in both coordinates and derive the additional sinusoidal factor depending on the dimensionality of spacetime and the quantum number for spherical harmonics in the global coordinates. This approach resolves the factor of two problem in the tunneling method.
Decoupled tracking and thermal monitoring of non-stationary targets.
Tan, Kok Kiong; Zhang, Yi; Huang, Sunan; Wong, Yoke San; Lee, Tong Heng
2009-10-01
Fault diagnosis and predictive maintenance address pertinent economic issues relating to production systems as an efficient technique can continuously monitor key health parameters and trigger alerts when critical changes in these variables are detected, before they lead to system failures and production shutdowns. In this paper, we present a decoupled tracking and thermal monitoring system which can be used on non-stationary targets of closed systems such as machine tools. There are three main contributions from the paper. First, a vision component is developed to track moving targets under a monitor. Image processing techniques are used to resolve the target location to be tracked. Thus, the system is decoupled and applicable to closed systems without the need for a physical integration. Second, an infrared temperature sensor with a built-in laser for locating the measurement spot is deployed for non-contact temperature measurement of the moving target. Third, a predictive motion control system holds the thermal sensor and follows the moving target efficiently to enable continuous temperature measurement and monitoring. PMID:19539922
NASA Astrophysics Data System (ADS)
Subhash, Hrebesh M.; Nguyen-Huynh, Anh; Wang, Ruikang K.; Jacques, Steven L.; Nuttall, Alfred L.
2012-02-01
We describe a novel method for the detection of the tiny motions of the middle ear (ME) ossicles and their morphological features with a spectral-domain phase sensitive optical coherence tomography (PS-OCT). Laser Doppler Vibrometry (LDV) and its variations are the most extensively used methods for studding the vibrational modes of the ME. However, most techniques are limited to single point analysis methods, and do not have the ability to provide depth resolved simultaneous imaging of multiple points on the ossicles especially with the intact eardrum. Consequently, the methods have the limited ability to provide relative vibration information at these points. In this study, we demonstrated the feasibility of using PS-OCT for simultaneous depth resolved imaging of both vibration information and morphological features in a cadaver human middle ear with high sensitivity and resolution. This technique has the potential to provide meaningful vibration of ossicles with a vibration sensitivity of ~0.5nm at 1kHz acoustic stimulation. To the best of our knowledge, this is the first demonstration of depth-resolved vibration imaging of ossicles with a PS-OCT system at sub-nanometer scale.
Waves, shocks and non-stationary phenomena in the outer solar atmosphere
NASA Technical Reports Server (NTRS)
Hansteen, V. H.
1997-01-01
The dynamics of the solar chromosphere, transition region and corona were investigated. The consequences of the solar dynamics on the formation of spectral features in solar atmosphere regions are discussed. Data mainly from the solar ultraviolet measurement of emitted radiation (SUMER) instrument, showing signatures of non-stationary processes, are presented. These data are compared to the predictions of numerical models of the chromosphere and transition region. The observations seem to support the importance of upwardly propagating acoustic shocks in the heating of the chromosphere.
NASA Astrophysics Data System (ADS)
Konugolu Venkata Sekar, Sanathana; Farina, Andrea; Martinenghi, Edoardo; Dalla Mora, Alberto; Taroni, Paola; Pifferi, Antonio; Durduran, Turgut; Pagliazzi, Marco; Lindner, Claus; Farzam, Parisa; Mora, Mireia; Squarcia, Mattia; Urbano-Ispizua, A.
2015-07-01
We report on the design, performance assessment, and first in vivo measurement of a Time-Resolved Diffuse Optical system for broadband (600-1350 nm) nm measurement of absorption and scattering spectra of biological tissues for non-invasive clinical diagnostics. Two strategies to reduce drift and enhance responsivity are adopted. The system was enrolled in a first in vivo test phase on healthy volunteers, carrying out non-invasive, in vivo quantification of key tissue constituents (oxy- and deoxy-hemoglobin, water, lipids, collagen) and tissue micro-structure (scatterer size and density).
Schmitt, F.
2010-05-03
Samples of Nd{sub 2-x}Ce{sub x}CuO{sub 4}, an electron-doped high temperature superconducting cuprate (HTSC), near optimal doping at x = 0.155 were measured via angle resolved photoemission (ARPES). We report a renormalization feature in the self energy ('kink') in the band dispersion at {approx} 50-60 meV present in nodal and antinodal cuts across the Fermi surface. Specifically, while the kink had been seen in the antinodal region, it is now observed also in the nodal region, reminiscent of what has been observed in hole-doped cuprates.
NASA Astrophysics Data System (ADS)
Hosseini, S.; Harris, W.
2014-12-01
We present initial results, calibration and data reduction process from observations of wide-field targets using Khayyam at Mt. Hamilton, a new instrument based on a reflective spatial heterodyne spectrometer (SHS) at the focus of the Coudé Auxiliary Telescope (CAT). SHS instruments are common path two-beam Fourier transform spectrometers that produce 2-D spatial interference patterns without the requirement for moving parts. The utility of SHS comes from its combination of a wide input acceptance angle (0.5-1°), high resolving power (of order ~105), compact format, high dynamic range, and relaxed optical tolerances compared with other interferometer designs. This combination makes them extremely useful for velocity resolved for observations of wide field targets from both small and large telescopes. This report focuses on the tunable instrument at Mt Hamilton, The CAT provides a test case for on-axis use of SHS, and the impact of the resulting field non-uniformity caused by the spider pattern will be discussed. Observations of several targets will be presented that demonstrate the capabilities of SHS, including comet C/2014 E2 (Jacques), Jupiter, and both the day sky and night glow. Raw interferometric data and transformed power spectra will be shown and evaluated in terms of instrumental stability.
NASA Astrophysics Data System (ADS)
Mizell, Steve A.; Gutjahr, Allan L.; Gelhar, Lynn W.
1982-08-01
Two-dimensional steady groundwater flow in a confined aquifer with spatially variable transmissivity T is analyzed stochastically using spectral analysis and the theory of intrinsic random functions. Conditions that ensure a stationary (statistically homogeneous) head process are derived, and using two convenient forms for the covariance function of the ln T process, the head covariance function is studied. In addition, the head variogram is obtained for a particular nonstationary case, and the asymptotic head variogram is derived under very general conditions. Results are compared to those obtained by Gelhar (1976) for one- and two-dimensional phreatic flow and Bakr et al. (1978) for one- and three-dimensional confined flow. Multidimensional flow analysis results in a significantly reduced head variance. The head correlation remains high over much greater distances than the ln T correlation. The variogram obtained when stationary heads are assumed is identical to that obtained for nonstationary heads for dimensionless lag distances up to 2½ times the correlation scale of the log transmissivity. The variogram for nonstationary heads continues to grow logarithmically as lag distance increases, independent of the form of the input covariance in the nonstationary case. The conditions for stationarity are contrasted with the corresponding results obtained for the one- and three-dimensional cases of Gutjahr and Gelhar (1981). The head variance calculated from the stationary theory is found to agree with that of previous Monte Carlo simulations.
NASA Astrophysics Data System (ADS)
Medvedev, Ivan R.; Fortman, Sarah M.; Neese, Christopher F.; De Lucia, Frank C.
2009-06-01
Experimental determination of the lower state energy for every transition in molecular spectra, made possible by temperature resolved 3-D spectroscopy, opens new frontiers in our ability to predict molecular spectra over a wide range of temperatures and to assign rotational spectra in many vibrational states. Our improved collisional cooling cell design extends temperature coverage of this technique to 77 K. This enhances our ability to simulate molecular spectra at temperatures of astronomical relevance. We are reporting on experimental and numerical aspects of dealing with exceptionally high information content of these spectra. New data reduction algorithms allow us to process this data in timely fashion in an attempt to make them available to astronomical community.
Linear response to nonstationary random excitation.
NASA Technical Reports Server (NTRS)
Hasselman, T.
1972-01-01
Development of a method for computing the mean-square response of linear systems to nonstationary random excitation of the form given by y(t) = f(t) x(t), in which x(t) = a stationary process and f(t) is deterministic. The method is suitable for application to multidegree-of-freedom systems when the mean-square response at a point due to excitation applied at another point is desired. Both the stationary process, x(t), and the modulating function, f(t), may be arbitrary. The method utilizes a fundamental component of transient response dependent only on x(t) and the system, and independent of f(t) to synthesize the total response. The role played by this component is analogous to that played by the Green's function or impulse response function in the convolution integral.
Credibility of statistical downscaling under nonstationary climate
NASA Astrophysics Data System (ADS)
Salvi, Kaustubh; Ghosh, Subimal; Ganguly, Auroop R.
2016-03-01
Statistical downscaling (SD) establishes empirical relationships between coarse-resolution climate model simulations with higher-resolution climate variables of interest to stakeholders. These statistical relations are estimated based on historical observations at the finer resolutions and used for future projections. The implicit assumption is that the SD relations, extracted from data are stationary or remain unaltered, despite non-stationary change in climate. The validity of this assumption relates directly to the credibility of SD. Falsifiability of climate projections is a challenging proposition. Calibration and verification, while necessary for SD, are unlikely to be able to reproduce the full range of behavior that could manifest at decadal to century scale lead times. We propose a design-of-experiments (DOE) strategy to assess SD performance under nonstationary climate and evaluate the strategy via a transfer-function based SD approach. The strategy relies on selection of calibration and validation periods such that they represent contrasting climatic conditions like hot-versus-cold and ENSO-versus-non-ENSO years. The underlying assumption is that conditions such as warming or predominance of El Niño may be more prevalent under climate change. In addition, two different historical time periods are identified, which resemble pre-industrial and the most severe future emissions scenarios. The ability of the empirical relations to generalize under these proxy conditions is considered an indicator of their performance under future nonstationarity. Case studies over two climatologically disjoint study regions, specifically India and Northeast United States, reveal robustness of DOE in identifying the locations where nonstationarity prevails as well as the role of effective predictor selection under nonstationarity.
Online updating and uncertainty quantification using nonstationary output-only measurement
NASA Astrophysics Data System (ADS)
Yuen, Ka-Veng; Kuok, Sin-Chi
2016-01-01
Extended Kalman filter (EKF) is widely adopted for state estimation and parametric identification of dynamical systems. In this algorithm, it is required to specify the covariance matrices of the process noise and measurement noise based on prior knowledge. However, improper assignment of these noise covariance matrices leads to unreliable estimation and misleading uncertainty estimation on the system state and model parameters. Furthermore, it may induce diverging estimation. To resolve these problems, we propose a Bayesian probabilistic algorithm for online estimation of the noise parameters which are used to characterize the noise covariance matrices. There are three major appealing features of the proposed approach. First, it resolves the divergence problem in the conventional usage of EKF due to improper choice of the noise covariance matrices. Second, the proposed approach ensures the reliability of the uncertainty quantification. Finally, since the noise parameters are allowed to be time-varying, nonstationary process noise and/or measurement noise are explicitly taken into account. Examples using stationary/nonstationary response of linear/nonlinear time-varying dynamical systems are presented to demonstrate the efficacy of the proposed approach. Furthermore, comparison with the conventional usage of EKF will be provided to reveal the necessity of the proposed approach for reliable model updating and uncertainty quantification.
Andree, Stefan; Reble, Carina; Helfmann, Jurgen; Gersonde, Ingo; Illing, Gerd
2010-01-01
We present a new variant of a noncontact, oblique incidence spatially resolved reflectance setup. The continuously variable source detector separation enables adaptation to high and low albedo samples. Absorption (μ(a)) and reduced scattering coefficients (μ(') (s)) are determined in the wavelength range of 400-1000 nm using a lookup table, calculated by a Monte Carlo simulation of the light transport. The method is characterized by an silicone phantom study covering a wide parameter range 0.01 mm(-1) ≤ μ(a) ≤ 2.5 mm(-1) and 0.2 mm(-1) ≤ μ(') (s) ≤ 10 mm(-1), which includes the optical parameters of tissue in the visible and near infrared. The influence of the incident angle and the detection aperture on the simulated remission was examined. Using perpendicular incidence and 90-deg detection aperture in the Monte Carlo simulation in contrast to the experimental situation with 30-deg incidence and 4.6-deg detection aperture is shown to be valid for the parameter range μ(') (s) > 1 mm(-1) and μ(a) < 1.2 mm(-1). A Mie calculation is presented, showing that a decreasing reduced scattering coefficient for increasing absorption can be the consequence of real physics instead of cross talk. PMID:21198213
On the nonstationary Stokes system in a cone
NASA Astrophysics Data System (ADS)
Kozlov, Vladimir; Rossmann, Jürgen
2016-06-01
The authors consider the Dirichlet problem for the nonstationary Stokes system in a threedimensional cone. They obtain existence and uniqueness results for solutions in weighted Sobolev spaces and prove a regularity assertion for the solutions.
Hess, S; Chachisvilis, M; Timpmann, K; Jones, M R; Fowler, G J; Hunter, C N; Sundström, V
1995-01-01
We report studies of energy transfer from the 800-nm absorbing pigment (B800) to the 850-nm absorbing pigment (B850) of the LH2 peripheral antenna complex and from LH2 to the core antenna complex (LH1) in Rhodobacter (Rb.) sphaeroides. The B800 to B850 process was studied in membranes from a LH2-reaction center (no LH1) mutant of Rb. sphaeroides and the LH2 to LH1 transfer was studied in both the wild-type species and in LH2 mutants with blue-shifted B850. The measurements were performed by using approximately 100-fs pulses to probe the formation of acceptor excitations in a two-color pump-probe measurement. Our experiments reveal a B800 to B850 transfer time of approximately 0.7 ps at 296 K and energy transfer from LH2 to LH1 is characterized by a time constant of approximately 3 ps at 296 K and approximately 5 ps at 77 K. In the blue-shifted B850 mutants, the transfer time from B850 to LH1 becomes gradually longer with increasing blue-shift of the B850 band as a result of the decreasing spectral overlap between the antennae. The results have been used to produce a model for the association between the ring-like structures that are characteristic of both the LH2 and LH1 antennae. PMID:11607622
Epple, Franz M; Ehn, Sebastian; Thibault, Pierre; Koehler, Thomas; Potdevin, Guillaume; Herzen, Julia; Pennicard, David; Graafsma, Heinz; Noël, Peter B; Pfeiffer, Franz
2015-03-01
Grating-based differential phase-contrast imaging has proven to be feasible with conventional X-ray sources. The polychromatic spectrum generally limits the performance of the interferometer but benefit can be gained with an energy-sensitive detector. In the presented work, we employ the energy-discrimination capability to correct for phase-wrapping artefacts. We propose to use the phase shifts, which are measured in distinct energy bins, to estimate the optimal phase shift in the sense of maximum likelihood. We demonstrate that our method is able to correct for phase-wrapping artefacts, to improve the contrast-to-noise ratio and to reduce beam hardening due to the modelled energy dependency. The method is evaluated on experimental data which are measured with a laboratory Talbot-Lau interferometer equipped with a conventional polychromatic X-ray source and an energy-sensitive photon-counting pixel detector. Our work shows, that spectral imaging is an important step to move differential phase-contrast imaging closer to pre-clinical and clinical applications, where phase wrapping is particularly problematic. PMID:25163054
Tunnelling effect of the non-stationary Kerr black hole
NASA Astrophysics Data System (ADS)
Yang, Shu-Zheng; Chen, De-You
2008-03-01
Extending Parikh and Wilczek's work to the non-stationary black hole, we study the Hawking radiation of the non-stationary Kerr black hole by the Hamilton-Jacobi method. The result shows that the radiation spectrum is not purely thermal and the tunnelling probability is related to the change of Bekenstein-Hawking entropy, which gives a correction to the Hawking thermal radiation of the black hole.
Measuring correlations between non-stationary series with DCCA coefficient
NASA Astrophysics Data System (ADS)
Kristoufek, Ladislav
2014-05-01
In this short report, we investigate the ability of the DCCA coefficient to measure correlation level between non-stationary series. Based on a wide Monte Carlo simulation study, we show that the DCCA coefficient can estimate the correlation coefficient accurately regardless the strength of non-stationarity (measured by the fractional differencing parameter d). For a comparison, we also report the results for the standard Pearson correlation coefficient. The DCCA coefficient dominates the Pearson coefficient for non-stationary series.
Yveborg, Moa; Danielsson, Mats; Bornefalk, Hans
2012-04-21
We are developing a photon-counting silicon strip detector with 0.4 × 0.5 mm² detector elements for clinical CT applications. Except for the limited detection efficiency of approximately 0.8 for a spectrum of 80 kVp, the largest discrepancies from ideal spectral behaviour have been shown to be Compton interactions in the detector and electronic noise. Using the framework of cascaded system analysis, we reconstruct the 3D MTF and NPS of a silicon strip detector including the influence of scatter and charge sharing inside the detector. We compare the reconstructed noise and signal characteristics with a reconstructed 3D MTF and NPS of an ideal energy-integrating detector system with unity detection efficiency, no scatter or charge sharing inside the detector, unity presampling MTF and 1 × 1 mm² detector elements. The comparison is done by calculating the dose-normalized detectability index for some clinically relevant imaging tasks and spectra. This work demonstrates that although the detection efficiency of the silicon detector rapidly drops for the acceleration voltages encountered in clinical computed tomography practice, and despite the high fraction of Compton interactions due to the low atomic number, silicon detectors can perform on a par with ideal energy-integrating detectors for routine imaging tasks containing low-frequency components. For imaging tasks containing high-frequency components, the proposed silicon detector system can perform approximately 1.1-1.3 times better than a fully ideal energy-integrating system. PMID:22469924
Liu, Yangqing Tan, Yi; Xie, Huiqiao; Wang, Wenhao; Gao, Zhe
2014-07-15
An improved Hilbert-Huang transform method is developed to the time-frequency analysis of non-stationary signals in tokamak plasmas. Maximal overlap discrete wavelet packet transform rather than wavelet packet transform is proposed as a preprocessor to decompose a signal into various narrow-band components. Then, a correlation coefficient based selection method is utilized to eliminate the irrelevant intrinsic mode functions obtained from empirical mode decomposition of those narrow-band components. Subsequently, a time varying vector autoregressive moving average model instead of Hilbert spectral analysis is performed to compute the Hilbert spectrum, i.e., a three-dimensional time-frequency distribution of the signal. The feasibility and effectiveness of the improved Hilbert-Huang transform method is demonstrated by analyzing a non-stationary simulated signal and actual experimental signals in fusion plasmas.
NASA Astrophysics Data System (ADS)
van der Wiel, M. H. D.; van der Tak, F. F. S.; Lis, D. C.; Bell, T.; Bergin, E. A.; Comito, C.; Emprechtinger, M.; Schilke, P.; Caux, E.; Ceccarelli, C.; Baudry, A.; Goldsmith, P. F.; Herbst, E.; Langer, W.; Lord, S.; Neufeld, D.; Pearson, J.; Phillips, T.; Rolffs, R.; Yorke, H.; Bacmann, A.; Benedettini, M.; Blake, G. A.; Boogert, A.; Bottinelli, S.; Cabrit, S.; Caselli, P.; Castets, A.; Cernicharo, J.; Codella, C.; Coutens, A.; Crimier, N.; Demyk, K.; Dominik, C.; Encrenaz, P.; Falgarone, E.; Fuente, A.; Gerin, M.; Helmich, F.; Hennebelle, P.; Henning, T.; Hily-Blant, P.; Jacq, T.; Kahane, C.; Kama, M.; Klotz, A.; Lefloch, B.; Lorenzani, A.; Maret, S.; Melnick, G.; Nisini, B.; Pacheco, S.; Pagani, L.; Parise, B.; Salez, M.; Saraceno, P.; Schuster, K.; Tielens, A. G. G. M.; Vastel, C.; Viti, S.; Wakelam, V.; Walters, A.; Wyrowski, F.; Edwards, K.; Zmuidzinas, J.; Morris, P.; Samoska, L. A.; Teyssier, D.
2010-10-01
Context. In contrast to the more extensively studied dense star-forming cores, little is known about diffuse gas surrounding star-forming regions. Aims: We study the molecular gas in the Galactic high-mass star-forming region NGC 6334I, which contains diffuse, quiescent components that are inconspicuous in widely used molecular tracers such as CO. Methods: We present Herschel/HIFI observations of methylidyne (CH) toward NGC 6334I observed as part of the “Chemical HErschel Survey of Star forming regions” (CHESS) key program. HIFI resolves each of the six hyperfine components of the lowest rotational transition (J = 3/2 - 1/2) of CH, observed in both emission and absorption. Results: The CH emission features appear close to the systemic velocity of NGC 6334I, while its measured FWHM linewidth of 3 km s-1 is smaller than previously observed in dense gas tracers such as NH3 and SiO. The CH abundance in the hot core is ~7 × 10-11, two to three orders of magnitude lower than in diffuse clouds. While other studies find distinct outflows in, e.g., CO and H2O toward NGC 6334I, we do not detect any outflow signatures in CH. At least two redshifted components of cold absorbing material must be present at -3.0 and +6.5 km s-1 to explain the absorption signatures. We derive a CH column density (NCH) of 7 × 1013 and 3 × 1013 cm-2 for these two absorbing clouds. We find evidence of two additional absorbing clouds at +8.0 and 0.0 km s-1, both with NCH ≈ 2 × 1013 cm-2. Turbulent linewidths for the four absorption components vary between 1.5 and 5.0 km s-1 in FWHM. We constrain the physical properties and locations of the clouds by matching our CH absorbers with the absorption signatures seen in other molecular tracers. Conclusions: In the hot core, molecules such as H2O and CO trace gas that is heated and dynamically influenced by outflow activity, whereas the CH molecule traces more quiescent material. The four CH absorbing clouds have column densities and turbulent
Nonstationary Analysis of Annual Maximum Streamflow of Canada
NASA Astrophysics Data System (ADS)
Yew Gan, Thian; Tan, Xuezhi
2016-04-01
Both natural climate change and anthropogenic impacts may cause nonstationarities in hydrological ex-tremes. In this study, long-term annual maximum streamflow (AMS) records from 145 stations over Canada were used to investigate the nonstationary characteristics of AMS, which include abrupt changes and monotonic temporal trends. The nonparameteric Pettitt test was applied to detect abrupt changes, while temporal monotonic trend analysis in AMS series was conducted using the nonparameteric Mann-Kendall and Spearman tests, as well as a parametric Pearson test. Nonstationary frequency analysis of the AMS series was done using a group of nonstationary probability distributions. The nonstationary characteristics of Ca-nadian AMS were further investigated in terms of the Hurst exponent (H), which represents the long-term persistence (LTP) of streamflow data. The results presented here indicate that for Canadian AMS data, abrupt changes are detected more frequently than monotonic trends, partly because many rivers began to be regulated in the twentieth century. Drainage basins that have experienced significant land-use changes are more likely to show temporal trends in AMS, compared to pristine basins with stable land-use conditions. The nonstationary characteristics of AMS were accounted for by fitting the data with probability distributions with time-varying parameters. Large H found in almost 2/ 3 of the Canadian AMS dataset indicates strong LTP, which may partly represent the presence of long-term memories in many Canadian river basins. Furthermore, H values of AMS data are positively correlated with the basin area of Canadian rivers. It seems that non-stationary frequency analysis, instead of the traditional stationary hydrologic frequency analysis, should be employed in the future. Reference: Tan, X., and Gan, T. Y., 2015, Nonstationary analysis of annual maximum streamflow of Canada, Journal of Climate, DOI: 10.1175/JCLI-D-14-00538.1
Bayesian soft X-ray tomography using non-stationary Gaussian Processes
Li, Dong; Svensson, J.; Thomsen, H.; Werner, A.; Wolf, R.; Medina, F.
2013-08-15
In this study, a Bayesian based non-stationary Gaussian Process (GP) method for the inference of soft X-ray emissivity distribution along with its associated uncertainties has been developed. For the investigation of equilibrium condition and fast magnetohydrodynamic behaviors in nuclear fusion plasmas, it is of importance to infer, especially in the plasma center, spatially resolved soft X-ray profiles from a limited number of noisy line integral measurements. For this ill-posed inversion problem, Bayesian probability theory can provide a posterior probability distribution over all possible solutions under given model assumptions. Specifically, the use of a non-stationary GP to model the emission allows the model to adapt to the varying length scales of the underlying diffusion process. In contrast to other conventional methods, the prior regularization is realized in a probability form which enhances the capability of uncertainty analysis, in consequence, scientists who concern the reliability of their results will benefit from it. Under the assumption of normally distributed noise, the posterior distribution evaluated at a discrete number of points becomes a multivariate normal distribution whose mean and covariance are analytically available, making inversions and calculation of uncertainty fast. Additionally, the hyper-parameters embedded in the model assumption can be optimized through a Bayesian Occam's Razor formalism and thereby automatically adjust the model complexity. This method is shown to produce convincing reconstructions and good agreements with independently calculated results from the Maximum Entropy and Equilibrium-Based Iterative Tomography Algorithm methods.
Bayesian soft X-ray tomography using non-stationary Gaussian Processes
NASA Astrophysics Data System (ADS)
Li, Dong; Svensson, J.; Thomsen, H.; Medina, F.; Werner, A.; Wolf, R.
2013-08-01
In this study, a Bayesian based non-stationary Gaussian Process (GP) method for the inference of soft X-ray emissivity distribution along with its associated uncertainties has been developed. For the investigation of equilibrium condition and fast magnetohydrodynamic behaviors in nuclear fusion plasmas, it is of importance to infer, especially in the plasma center, spatially resolved soft X-ray profiles from a limited number of noisy line integral measurements. For this ill-posed inversion problem, Bayesian probability theory can provide a posterior probability distribution over all possible solutions under given model assumptions. Specifically, the use of a non-stationary GP to model the emission allows the model to adapt to the varying length scales of the underlying diffusion process. In contrast to other conventional methods, the prior regularization is realized in a probability form which enhances the capability of uncertainty analysis, in consequence, scientists who concern the reliability of their results will benefit from it. Under the assumption of normally distributed noise, the posterior distribution evaluated at a discrete number of points becomes a multivariate normal distribution whose mean and covariance are analytically available, making inversions and calculation of uncertainty fast. Additionally, the hyper-parameters embedded in the model assumption can be optimized through a Bayesian Occam's Razor formalism and thereby automatically adjust the model complexity. This method is shown to produce convincing reconstructions and good agreements with independently calculated results from the Maximum Entropy and Equilibrium-Based Iterative Tomography Algorithm methods.
NASA Astrophysics Data System (ADS)
Batehup, R.; McGregor, S.; Gallant, A. J. E.
2015-12-01
Reconstructions of the El Niño-Southern Oscillation (ENSO) ideally require high-quality, annually resolved and long-running palaeoclimate proxy records in the eastern tropical Pacific Ocean, located in ENSO's centre of action. However, to date, the palaeoclimate records that have been extracted in the region are short or temporally and spatially sporadic, limiting the information that can be provided by these reconstructions. Consequently, most ENSO reconstructions exploit the downstream influences of ENSO on remote locations, known as teleconnections, where longer records from palaeoclimate proxies exist. However, using teleconnections to reconstruct ENSO relies on the assumption that the relationship between ENSO and the remote location is stationary in time. Increasing evidence from observations and climate models suggests that some teleconnections are, in fact, non-stationary, potentially threatening the validity of those palaeoclimate reconstructions that exploit teleconnections. This study examines the implications of non-stationary teleconnections on modern multi-proxy reconstructions of ENSO variance. The sensitivity of the reconstructions to non-stationary teleconnections were tested using a suite of idealised pseudoproxy experiments that employed output from a fully coupled global climate model. Reconstructions of the variance in the Niño 3.4 index representing ENSO variability were generated using four different methods. Surface temperature data from the GFDL CM2.1 were used as pseudoproxies for these reconstruction methods. As well as sensitivity of the reconstruction to the method, the experiments tested the sensitivity of the reconstruction to the number of non-stationary pseudoproxies and the location of these proxies. We find that non-stationarities can act to degrade the skill of ENSO variance reconstructions. However, when global, randomly spaced networks (assuming a minimum of approximately 20 proxies) were employed, the resulting pseudoproxy
Non-stationary random ground vibration due to loads moving along a railway track
NASA Astrophysics Data System (ADS)
Lu, Feng; Gao, Qiang; Lin, J. H.; Williams, F. W.
2006-11-01
The pseudo-excitation method (PEM) and the precise integration algorithm are combined to compute the non-stationary random ground vibration caused by loads moving along a railway track at constant speed. The rails are modeled as a single infinite Euler beam connected to sleepers and hence to ballast. This ballast rests on the ground, which is assumed to consist of layered transversely isotropic soil. The equations of motion of the system are established in a Cartesian coordinate system which moves with the loads. The non-stationary power spectral density and the time-dependent standard deviation can be derived conveniently by means of PEM, while the precise integration algorithm for two-point boundary value problems is applied to the solution of the equations of motion in the frequency/wavenumber domain. By virtue of the transverse isotropic property of the layered soils, the threefold iteration process in the frequency/wavenumber domain is reduced into a twofold iteration process. Hence the computational efficiency is improved considerably.
Non-stationary resonance dynamics of weakly coupled pendula
NASA Astrophysics Data System (ADS)
Manevitch, L. I.; Romeo, F.
2015-11-01
In this letter we fill the gap in understanding the non-stationary Hamiltonian dynamics of the weakly coupled pendula model having significant applications in numerous fields of physics. While common knowledge of this model is predominantly based on the stationary theory and quasi-linear approach to non-stationary dynamics, we consider a strongly nonlinear system without any polynomial approximation of the anharmonic potential. In the adopted asymptotics only closeness to any inter-pendulum resonance frequency is assumed. Being able to explore the whole diapason of initial conditions, two key nonlinear features are revealed by means of the Limiting Phase Trajectories concept: the conditions of intense energy exchange between the pendula and transition to energy localization. The roots and the domain of chaotic behavior are clarified as they are associated with the latter, purely non-stationary, topological transition.
Non-Stationary Internal Tides Observed with Satellite Altimetry
NASA Technical Reports Server (NTRS)
Ray, Richard D.; Zaron, E. D.
2011-01-01
Temporal variability of the internal tide is inferred from a 17-year combined record of Topex/Poseidon and Jason satellite altimeters. A global sampling of along-track sea-surface height wavenumber spectra finds that non-stationary variance is generally 25% or less of the average variance at wavenumbers characteristic of mode-l tidal internal waves. With some exceptions the non-stationary variance does not exceed 0.25 sq cm. The mode-2 signal, where detectable, contains a larger fraction of non-stationary variance, typically 50% or more. Temporal subsetting of the data reveals interannual variability barely significant compared with tidal estimation error from 3-year records. Comparison of summer vs. winter conditions shows only one region of noteworthy seasonal changes, the northern South China Sea. Implications for the anticipated SWOT altimeter mission are briefly discussed.
Distribution of a nonstationary electron beam in a dense gas
Sklyarov, Y.M.; Shelepin, L.A.; Syts'ko, Y.L.
1986-11-01
The problem of the temporal and spatial dependences of the parameters of the action of a modulated fast-electron beam on a dense gas is posed on the basis of the transport equation. The problem is simplified by making it nondimensional and by transforming to the Fokker-Planck approximation. A Green's function formalism is developed for this problem and is used to express the solution of the general nonstationary problem in the form of a convolution of a nonstationary boundary flow with a stationary Green's function. The use of the derived equation is illustrated using as an example the solution of a problem with the simplest stationary Green's function corresponding to the ''straight-ahead'' approximation. This approximation is used to consider a general relativistic case with model scattering cross sections. The methods and results of a numerical computer solution of the nonstationary problem of electron retardation in the upper layer of the atmosphere are surveyed.
Theory, implementation and applications of nonstationary Gabor frames
Balazs, P.; Dörfler, M.; Jaillet, F.; Holighaus, N.; Velasco, G.
2011-01-01
Signal analysis with classical Gabor frames leads to a fixed time–frequency resolution over the whole time–frequency plane. To overcome the limitations imposed by this rigidity, we propose an extension of Gabor theory that leads to the construction of frames with time–frequency resolution changing over time or frequency. We describe the construction of the resulting nonstationary Gabor frames and give the explicit formula for the canonical dual frame for a particular case, the painless case. We show that wavelet transforms, constant-Q transforms and more general filter banks may be modeled in the framework of nonstationary Gabor frames. Further, we present the results in the finite-dimensional case, which provides a method for implementing the above-mentioned transforms with perfect reconstruction. Finally, we elaborate on two applications of nonstationary Gabor frames in audio signal processing, namely a method for automatic adaptation to transients and an algorithm for an invertible constant-Q transform. PMID:22267893
DIFFEOMORPHIC POINT SET REGISTRATION USING NON-STATIONARY MIXTURE MODELS
Wassermann, D.; Ross, J.; Washko, G.; Westin, C-F; Estépar, R. San José
2013-01-01
This paper investigates a diffeomorphic point-set registration based on non-stationary mixture models. The goal is to improve the non-linear registration of anatomical structures by representing each point as a general non-stationary kernel that provides information about the shape of that point. Our framework generalizes work done by others that use stationary models. We achieve this by integrating the shape at each point when calculating the point-set similarity and transforming it according to the calculated deformation. We also restrict the non-rigid transform to the space of symmetric diffeomorphisms. Our algorithm is validated in synthetic and human datasets in two different applications: fiber bundle and lung airways registration. Our results shows that non-stationary mixture models are superior to Gaussian mixture models and methods that do not take into account the shape of each point. PMID:24419463
The Effect of White Nonstationary and Colored Nonstationary Noise on Signal Detection
NASA Astrophysics Data System (ADS)
Flores, Mauricio; Benacquista, Matthew; Stroeer, Alexander
2012-02-01
We analyze the effect of non-stationary noise on the detection of signals on unevenly sampled data. Initial frequency estimation is obtained from a Lomb-Scargle periodogram; which is followed by a global multi-start optimization, as working on a dense local Nelder-Mead iterator for parameter estimates. It has been found that a varying white noise level has no effect on the required relative signal-to-noise ratio for detection in the proposed algorithm, though affecting the absolute amplitude strength of the signal recording. Further analysis has been done on realistic colored noise. Different whitening routines have been incorporated to the proposed algorithm. Detection efficiency is compared for these different routines.
Nonstationary Analysis of Annual Maximum Streamflow of Canada
NASA Astrophysics Data System (ADS)
Gan, T. Y.; Tan, X.
2015-12-01
Both natural climate change and anthropogenic impacts may cause nonstationarities in hydrological ex-tremes. In this study, long-term annual maximum streamflow (AMS) records from 145 stations over Canada were used to investigate the nonstationary characteristics of AMS, which include abrupt changes and monotonic temporal trends. The nonparameteric Pettitt test was applied to detect abrupt changes, while temporal monotonic trend analysis in AMS series was conducted using the nonparameteric Mann-Kendall and Spearman tests, as well as a parametric Pearson test. Nonstationary frequency analysis of the AMS series was done using a group of nonstationary probability distributions. The nonstationary characteristics of Ca-nadian AMS were further investigated in terms of the Hurst exponent (H), which represents the long-term persistence (LTP) of streamflow data. The results presented here indicate that for Canadian AMS data, abrupt changes are detected more frequently than monotonic trends, partly because many rivers began to be regulated in the twentieth century. Drainage basins that have experienced significant land-use changes are more likely to show temporal trends in AMS, compared to pristine basins with stable land-use conditions. The nonstationary characteristics of AMS were accounted for by fitting the data with probability distributions with time-varying parameters. Large H found in almost 2/ 3 of the Canadian AMS dataset indicates strong LTP, which may partly represent the presence of long-term memories in many Canadian river basins. Furthermore, H values of AMS data are positively correlated with the basin area of Canadian rivers. It seems that non-stationary frequency analysis, instead of the traditional stationary hydrologic frequency analysis, should be employed in the future.
Learning geotemporal nonstationary failure and recovery of power distribution.
Wei, Yun; Ji, Chuanyi; Galvan, Floyd; Couvillon, Stephen; Orellana, George; Momoh, James
2014-01-01
Smart energy grid is an emerging area for new applications of machine learning in a nonstationary environment. Such a nonstationary environment emerges when large-scale failures occur at power networks because of external disruptions such as hurricanes and severe storms. Power distribution networks lie at the edge of the grid, and are especially vulnerable to external disruptions. Quantifiable approaches are lacking and needed to learn nonstationary behaviors of large-scale failure and recovery of power distribution. This paper studies such nonstationary behaviors in three aspects. First, a novel formulation is derived for an entire life cycle of large-scale failure and recovery of power distribution. Second, spatial-temporal models of failure and recovery of power distribution are developed as geolocation-based multivariate nonstationary GI(t)/G(t)/∞ queues. Third, the nonstationary spatial-temporal models identify a small number of parameters to be learned. Learning is applied to two real-life examples of large-scale disruptions. One is from Hurricane Ike, where data from an operational network is exact on failures and recoveries. The other is from Hurricane Sandy, where aggregated data is used for inferring failure and recovery processes at one of the impacted areas. Model parameters are learned using real data. Two findings emerge as results of learning: 1) failure rates behave similarly at the two different provider networks for two different hurricanes but differently at the geographical regions and 2) both the rapid and slow-recovery are present for Hurricane Ike but only slow recovery is shown for a regional distribution network from Hurricane Sandy. PMID:24806656
Characterization of stationary and nonstationary behavior in gyrotron oscillators.
Chang, T H; Chen, S H; Barnett, L R; Chu, K R
2001-08-01
The transition from the stationary state to a sequence of nonstationary states in the gyromonotron oscillator is experimentally characterized for the first time. We have also demonstrated the stationary operation of a gyrotron backward-wave oscillator at a beam current far in excess of the generally predicted nonstationary threshold. This difference in nonlinear behavior has been investigated and shown to be fundamental with a comparative analysis of the feedback mechanisms, energy deposition profiles, and field shaping processes involved in these two types of oscillations. PMID:11497832
On the temporal variability of the surface solar radiation by means of spectral representations
NASA Astrophysics Data System (ADS)
Bengulescu, Marc; Blanc, Philippe; Wald, Lucien
2016-07-01
This work deals with the temporal variability of daily means of the global broadband surface solar irradiance (SSI) impinging on a horizontal plane by studying a decennial time-series of high-quality measurements recorded at a BSRN ground station. Since the data have a non-linear and non-stationary character, two time-frequency-energy representations of signal processing are compared in their ability to resolve the temporal variability of the pyranometric signal. First, the continuous wavelet transform is used to construct the wavelet power spectrum of the data. Second, the adaptive, noise-assisted empirical mode decomposition is employed to extract the intrinsic mode functions of the signal, followed by Hilbert spectral analysis. In both spectral representations, the temporal variability of the SSI is portrayed having clearly distinguishable features: a plateau between scales of two days and two-three months that has decreasing power with increasing scale, a large spectral peak corresponding to the annual variability cycle, and a low power regime in between the previous two. It is shown that the data-driven, noise-assisted method yields a somewhat more sparse representation and that it is a suitable tool for inspecting the temporal variability of SSI measurements.
The Spectral Shift Function and Spectral Flow
NASA Astrophysics Data System (ADS)
Azamov, N. A.; Carey, A. L.; Sukochev, F. A.
2007-11-01
At the 1974 International Congress, I. M. Singer proposed that eta invariants and hence spectral flow should be thought of as the integral of a one form. In the intervening years this idea has lead to many interesting developments in the study of both eta invariants and spectral flow. Using ideas of [24] Singer’s proposal was brought to an advanced level in [16] where a very general formula for spectral flow as the integral of a one form was produced in the framework of noncommutative geometry. This formula can be used for computing spectral flow in a general semifinite von Neumann algebra as described and reviewed in [5]. In the present paper we take the analytic approach to spectral flow much further by giving a large family of formulae for spectral flow between a pair of unbounded self-adjoint operators D and D + V with D having compact resolvent belonging to a general semifinite von Neumann algebra {mathcal{N}} and the perturbation V in {mathcal{N}} . In noncommutative geometry terms we remove summability hypotheses. This level of generality is made possible by introducing a new idea from [3]. There it was observed that M. G. Krein’s spectral shift function (in certain restricted cases with V trace class) computes spectral flow. The present paper extends Krein’s theory to the setting of semifinite spectral triples where D has compact resolvent belonging to {mathcal{N}} and V is any bounded self-adjoint operator in {mathcal{N}} . We give a definition of the spectral shift function under these hypotheses and show that it computes spectral flow. This is made possible by the understanding discovered in the present paper of the interplay between spectral shift function theory and the analytic theory of spectral flow. It is this interplay that enables us to take Singer’s idea much further to create a large class of one forms whose integrals calculate spectral flow. These advances depend critically on a new approach to the calculus of functions of non
Diagnosing non-stationary behaviour in a hydrological model
NASA Astrophysics Data System (ADS)
Thyer, Mark; Westra, Seth; Leonard, Michael; Kavetski, Dmitri; Lambert, Martin
2013-04-01
The stationarity of hydrological models is increasingly being called into question, due partly to changes in land cover as well as natural and anthropogenic climate change. This issue is manifest in model parameters which change over time, creating challenges in calibration and validation (as the joint distribution of model parameters is conditional to the period used for model calibration), and in prediction when one wishes to investigate runoff properties in the future. This paper describes the incorporation of non-stationary parameters into a well established rainfall-runoff model - GR4J - using a Bayesian framework for calibration and prediction, and the use of an information theoretic approach to evaluate whether the inclusion of non-stationary parameters was justified. A subcatchment of the Onkaparinga river in South Australia was used as a case study, and it was found that GR4J parameter 'x1' varied significantly seasonally and also exhibited a longer-term increasing trend over the calibration period from 1974 to 1999. The inclusion of this non-stationary parameter in the model reduced the over-prediction in the drier validation period from 2000 to 2010 from 25% to 1.5%. Whilst including non-stationarity parameters provided substantial improvements in prediction, it is advocated that this non-stationary parameters be used as a diagnostic tool to identify model deficiencies, rather than for prediction. Techniques to reduce the non-stationarity by enhancing the model structure will to include one or more missing processes will be discussed.
Time reversibility from visibility graphs of nonstationary processes
NASA Astrophysics Data System (ADS)
Lacasa, Lucas; Flanagan, Ryan
2015-08-01
Visibility algorithms are a family of methods to map time series into networks, with the aim of describing the structure of time series and their underlying dynamical properties in graph-theoretical terms. Here we explore some properties of both natural and horizontal visibility graphs associated to several nonstationary processes, and we pay particular attention to their capacity to assess time irreversibility. Nonstationary signals are (infinitely) irreversible by definition (independently of whether the process is Markovian or producing entropy at a positive rate), and thus the link between entropy production and time series irreversibility has only been explored in nonequilibrium stationary states. Here we show that the visibility formalism naturally induces a new working definition of time irreversibility, which allows us to quantify several degrees of irreversibility for stationary and nonstationary series, yielding finite values that can be used to efficiently assess the presence of memory and off-equilibrium dynamics in nonstationary processes without the need to differentiate or detrend them. We provide rigorous results complemented by extensive numerical simulations on several classes of stochastic processes.
Redefine Water Infrastructure Adaptation to a Nonstationary Climate (Editorial)
The statement “Climate Stationarity is Dead” by Milly et al. (2008) stresses the need to evaluate and when necessary, incorporate non-stationary hydroclimatic changes into water resources and infrastructure planning and engineering. Variations of this theme echo in several other ...
Nonstationary Gas Flow in Thin Pipes of Variable Cross Section
NASA Technical Reports Server (NTRS)
Guderley, G.
1948-01-01
Characteristic methods for nonstationary flows have been published only for the special case of the isentropic flow up until the present, althought they are applicable in various places to more difficult questions too. This report derives the characteristic method for the flows which depend only on the position coordinates and time. At the same time the treatment of compression shocks is shown.
Ultrafast CARS with Improved Spectral Resolution
NASA Astrophysics Data System (ADS)
Lütgens, M.; Chatzipapadopoulos, S.; Lochbrunner, S.
2013-03-01
Molecular vibrations are investigated by time and frequency resolved CARS applying ultrafast excitation and picosecond probing for high spectral resolution. Enhanced spectral structure and beating phenomena are demonstrated for coalescing Raman bands.
Spectral correlations of fractional Brownian motion
Oigaard, Tor Arne; Hanssen, Alfred; Scharf, Louis L.
2006-09-15
Fractional Brownian motion (fBm) is a ubiquitous nonstationary model for many physical processes with power-law time-averaged spectra. In this paper, we exploit the nonstationarity to derive the full spectral correlation structure of fBm. Starting from the time-varying correlation function, we derive two different time-frequency spectral correlation functions (the ambiguity function and the Kirkwood-Rihaczek spectrum), and one dual-frequency spectral correlation function. The dual-frequency spectral correlation has a surprisingly simple structure, with spectral support on three discrete lines. The theoretical predictions are verified by spectrum estimates of Monte Carlo simulations and of a time series of earthquakes with a magnitude of 7 and higher.
Compounding approach for univariate time series with nonstationary variances.
Schäfer, Rudi; Barkhofen, Sonja; Guhr, Thomas; Stöckmann, Hans-Jürgen; Kuhl, Ulrich
2015-12-01
A defining feature of nonstationary systems is the time dependence of their statistical parameters. Measured time series may exhibit Gaussian statistics on short time horizons, due to the central limit theorem. The sample statistics for long time horizons, however, averages over the time-dependent variances. To model the long-term statistical behavior, we compound the local distribution with the distribution of its parameters. Here, we consider two concrete, but diverse, examples of such nonstationary systems: the turbulent air flow of a fan and a time series of foreign exchange rates. Our main focus is to empirically determine the appropriate parameter distribution for the compounding approach. To this end, we extract the relevant time scales by decomposing the time signals into windows and determine the distribution function of the thus obtained local variances. PMID:26764768
Hawking's radiation in non-stationary rotating de Sitter background
NASA Astrophysics Data System (ADS)
Ibohal, N.; Ibungochouba, T.
2011-05-01
Hawking's radiation effect of Klein-Gordon scalar field, Dirac particles and Maxwell's electromagnetic field in the non-stationary rotating de Sitter cosmological space-time is investigated by using a method of generalized tortoise co-ordinates transformation. The locations and the temperatures of the cosmological horizons of the non-stationary rotating de Sitter model are derived. It is found that the locations and the temperatures of the rotating cosmological model depend not only on the time but also on the angle. The stress-energy regularization techniques are applied to the two dimensional analog of the de Sitter metrics and the calculated stress-energy tensor contains the thermal radiation effect.
Quantum tunneling of the non-stationary BTZ black hole
NASA Astrophysics Data System (ADS)
Yang, Juan; Yang, Shu Zheng
2009-07-01
The semi-classical tunneling method is extended to study the Hawking tunneling radiation from the non-stationary BTZ black hole via general tortoise coordination transformation and WKB approximation. In this paper, we simplify the spin-0 scalar field equation and the spin-1/2 Dirac equation at the event horizon of this black hole, and then the quantum tunneling probability and Hawking temperature are obtained. Finally, the correctional tunneling rate is researched, and the results show that after considering the changed background space-time of the non-stationary BTZ black hole, the tunneling rate depends not only on the entropy change but also on the integral about {\\dot r}_H .
Energy expectation values of a particle in nonstationary fields
NASA Astrophysics Data System (ADS)
Silenko, Alexander J.
2015-01-01
We show that the origin of the nonequivalence of Hamiltonians in different representations is a change of the form of the time-derivative operator at a time-dependent unitary transformation. This nonequivalence does not lead to an ambiguity of the energy expectation values of a particle in nonstationary fields but assigns the basic representation. It has been explicitly or implicitly supposed in previous investigations that this representation is the Dirac one. We prove the alternative assertion about the basic role of the Foldy-Wouthuysen representation. We also derive the general equation for the energy expectation values in the Dirac representation. As an example, we consider a spin-1/2 particle with anomalous magnetic and electric dipole moments in strong time-dependent electromagnetic fields. We apply the obtained results to a spin-1/2 particle in a plane monochromatic electromagnetic wave and give an example of the exact Foldy-Wouthuysen transformation in the nonstationary case.
Compounding approach for univariate time series with nonstationary variances
NASA Astrophysics Data System (ADS)
Schäfer, Rudi; Barkhofen, Sonja; Guhr, Thomas; Stöckmann, Hans-Jürgen; Kuhl, Ulrich
2015-12-01
A defining feature of nonstationary systems is the time dependence of their statistical parameters. Measured time series may exhibit Gaussian statistics on short time horizons, due to the central limit theorem. The sample statistics for long time horizons, however, averages over the time-dependent variances. To model the long-term statistical behavior, we compound the local distribution with the distribution of its parameters. Here, we consider two concrete, but diverse, examples of such nonstationary systems: the turbulent air flow of a fan and a time series of foreign exchange rates. Our main focus is to empirically determine the appropriate parameter distribution for the compounding approach. To this end, we extract the relevant time scales by decomposing the time signals into windows and determine the distribution function of the thus obtained local variances.
The evaluation of regional frequency analyses methods for nonstationary data
NASA Astrophysics Data System (ADS)
Nam, W.; Kim, S.; Kim, H.; Joo, K.; Heo, J.-H.
2015-06-01
Regional frequency analysis is widely used to estimate more reliable quantiles of extreme hydro-meteorological events. The stationarity of data is required for its application. This assumption tends to be violated due to climate change. In this paper, four nonstationary index flood models were used to analyze the nonstationary regional data. Monte Carlo simulation was used to evaluate the performances of these models for the generalized extreme value distribution with linearly time varying location parameter and constant scale and shape parameters. As a results, it was found that the index flood model with time-invariant index flood and time-variant growth curve could yield more statistically efficient quantile when record is long enough to show significant nonstationarity.
Deviations from uniform power law scaling in nonstationary time series
NASA Technical Reports Server (NTRS)
Viswanathan, G. M.; Peng, C. K.; Stanley, H. E.; Goldberger, A. L.
1997-01-01
A classic problem in physics is the analysis of highly nonstationary time series that typically exhibit long-range correlations. Here we test the hypothesis that the scaling properties of the dynamics of healthy physiological systems are more stable than those of pathological systems by studying beat-to-beat fluctuations in the human heart rate. We develop techniques based on the Fano factor and Allan factor functions, as well as on detrended fluctuation analysis, for quantifying deviations from uniform power-law scaling in nonstationary time series. By analyzing extremely long data sets of up to N = 10(5) beats for 11 healthy subjects, we find that the fluctuations in the heart rate scale approximately uniformly over several temporal orders of magnitude. By contrast, we find that in data sets of comparable length for 14 subjects with heart disease, the fluctuations grow erratically, indicating a loss of scaling stability.
Non-stationary frequency domain system identification using time-frequency representations
NASA Astrophysics Data System (ADS)
Guo, Yanlin; Kareem, Ahsan
2016-05-01
System properties of buildings and bridges may vary with time due to temperature changes, aging or extreme loadings. To identify these time-varying system properties, this study proposes a new output-only non-stationary system identification (SI) framework based on instantaneous or marginal spectra derived from the time-frequency representation, e.g., short time Fourier or wavelet transform. Spectra derived from these time-frequency representations are very popular in tracking time-varying frequencies; however, they have seldom been used to identify the time-varying damping ratio because a short window needed to capture the time-varying information amplifies the bandwidth significantly, which may lead to considerably overestimating the damping ratio. To overcome this shortcoming, this study modifies the theoretical frequency response function (FRF) to explicitly account for the windowing effect, and therefore enables SI directly using instantaneous or marginal spectra derived from the wavelet or short time Fourier transform. The response spectrum estimated using the short time window and the modified FRF are both influenced by the same time window, thus the instantaneous or time-localized marginal spectrum of response can be fitted to the modified FRF to identify frequency and damping ratio at each time instant. This spectral-based SI framework can reliably identify damping in time-varying systems under non-stationary excitations. The efficacy of the proposed framework is demonstrated by both numerical and full-scale examples, and also compared to the time-domain SI method, stochastic subspace identification (SSI), since the time-domain SI approaches and their extensions are popular in identifying time-varying systems utilizing recursive algorithms or moving windows.
Wave Propagation in Non-Stationary Statistical Mantle Models at the Global Scale
NASA Astrophysics Data System (ADS)
Meschede, M.; Romanowicz, B. A.
2014-12-01
We study the effect of statistically distributed heterogeneities that are smaller than the resolution of current tomographic models on seismic waves that propagate through the Earth's mantle at teleseismic distances. Current global tomographic models are missing small-scale structure as evidenced by the failure of even accurate numerical synthetics to explain enhanced coda in observed body and surface waveforms. One way to characterize small scale heterogeneity is to construct random models and confront observed coda waveforms with predictions from these models. Statistical studies of the coda typically rely on models with simplified isotropic and stationary correlation functions in Cartesian geometries. We show how to construct more complex random models for the mantle that can account for arbitrary non-stationary and anisotropic correlation functions as well as for complex geometries. Although this method is computationally heavy, model characteristics such as translational, cylindrical or spherical symmetries can be used to greatly reduce the complexity such that this method becomes practical. With this approach, we can create 3D models of the full spherical Earth that can be radially anisotropic, i.e. with different horizontal and radial correlation functions, and radially non-stationary, i.e. with radially varying model power and correlation functions. Both of these features are crucial for a statistical description of the mantle in which structure depends to first order on the spherical geometry of the Earth. We combine different random model realizations of S velocity with current global tomographic models that are robust at long wavelengths (e.g. Meschede and Romanowicz, 2014, GJI submitted), and compute the effects of these hybrid models on the wavefield with a spectral element code (SPECFEM3D_GLOBE). We finally analyze the resulting coda waves for our model selection and compare our computations with observations. Based on these observations, we make
Estimation of Parameters from Discrete Random Nonstationary Time Series
NASA Astrophysics Data System (ADS)
Takayasu, H.; Nakamura, T.
For the analysis of nonstationary stochastic time series we introduce a formulation to estimate the underlying time-dependent parameters. This method is designed for random events with small numbers that are out of the applicability range of the normal distribution. The method is demonstrated for numerical data generated by a known system, and applied to time series of traffic accidents, batting average of a baseball player and sales volume of home electronics.
Effect of water compressibility on nonstationary characteristics of hydraulic turbines
NASA Astrophysics Data System (ADS)
Kurzin, V. B.
2013-09-01
We have investigated the effect of water compressibility on the nonstationary characteristics of turbines connected with the ability of the liquid to execute natural hydroacoustic vibrations in the setting of hydroelectric units. We have constructed a model of the setting up of forced hydroacoustic vibrations in the water conduit due to the precession of the vortex core running off the turbine. The conditions for the possibility that low-frequency hydroacoustic natural vibrations will arise have been considered.
Nonstationary Mass Transfer Near the Surface of a Cylindrical Body
NASA Astrophysics Data System (ADS)
Rudobashta, S. P.; Kosheleva, M. K.; Kartashov, É. M.
2015-11-01
The problem of nonstationary diffusion of the target component to a phase that is external relative to the surface of a cylindrical body has been formulated and solved analytically. From the found solution the dependences have been obtained for calculating the instantaneous mass transfer coefficient and the phase-contact-time mean mass transfer coefficient, on the basis of which the process of extraction of technological pollutants from fibrous materials has been analyzed.
Response of laminated plates to non-stationary random excitation
NASA Technical Reports Server (NTRS)
Cederbaum, Gabriel; Librescu, Liviu; Elishakoff, Isaac
1989-01-01
The response of composite laminated plates subjected to nonstationary random excitation is determined. First-order shear deformation theory is used for the analysis of symmetric cross-ply and antisymmetric angle-ply plates. The time-dependent component of the forcing function is taken as a product of a well-defined, slowly varying envelope function, and a noise function, assumed to be white or narrow-band random excitation.
Macroscopic vacuum effects in an inhomogeneous and nonstationary electromagnetic field
Gal'tsov, D.V.; Nikitina, N.S.
1983-04-01
Macroscopic effects of vacuum polarization by a strong nonuniform and nonstationary fields, which are kinematically forbidden in the case of a uniform magnetic field, are considered. Calculations are perfomed for the deflection of a light beam in the field of a magnetic dipole, for the production of photon pairs by an inclined rotator, and for doubling and modulation of the frequency in scattering of low-frequency electromagnetic waves by the magnetic field of an inclined rotator.
NASA Astrophysics Data System (ADS)
Kim, S.; Joo, K.; Kim, H.; Heo, J. H.
2014-12-01
Recently, the various approaches for the nonstationary frequency analysis have been studied since the effect of climate change was widely recognized for hydrologic data. Most nonstationary studies proposed the nonstationary general extreme value (GEV) and generalized Pareto models for the annual maximum and POT (peak-over-threshold) data, respectively. However, various alternatives is needed to analyze the nonstationary hydrologic data because of the complicated influence of climate change. This study proposed the nonstationary generalized logistic models containing time-dependent location and scale parameters. These models contain only or both nonstationary location and scale parameters that change linearly over time. The parameters are estimated using the method of maximum likelihood based on the Newton-Raphson method. In addition, the proposed models apply to the annual maximum rainfall data of Korea in order to evaluate the applicability of the proposed models.
NASA Technical Reports Server (NTRS)
Parker, Ray; Coan, Mary; Cryderman, Kate; Captain, Janine
2013-01-01
The RESOLVE project is a lunar prospecting mission whose primary goal is to characterize water and other volatiles in lunar regolith. The Lunar Advanced Volatiles Analysis (LAVA) subsystem is comprised of a fluid subsystem that transports flow to the gas chromatograph - mass spectrometer (GC-MS) instruments that characterize volatiles and the Water Droplet Demonstration (WDD) that will capture and display water condensation in the gas stream. The LAVA Engineering Test Unit (ETU) is undergoing risk reduction testing this summer and fall within a vacuum chamber to understand and characterize component and integrated system performance. Testing of line heaters, printed circuit heaters, pressure transducers, temperature sensors, regulators, and valves in atmospheric and vacuum environments was done. Test procedures were developed to guide experimental tests and test reports to analyze and draw conclusions from the data. In addition, knowledge and experience was gained with preparing a vacuum chamber with fluid and electrical connections. Further testing will include integrated testing of the fluid subsystem with the gas supply system, near-infrared spectrometer, WDD, Sample Delivery System, and GC-MS in the vacuum chamber. This testing will provide hands-on exposure to a flight forward spaceflight subsystem, the processes associated with testing equipment in a vacuum chamber, and experience working in a laboratory setting. Examples of specific analysis conducted include: pneumatic analysis to calculate the WDD's efficiency at extracting water vapor from the gas stream to form condensation; thermal analysis of the conduction and radiation along a line connecting two thermal masses; and proportional-integral-derivative (PID) heater control analysis. Since LAVA is a scientific subsystem, the near-infrared spectrometer and GC-MS instruments will be tested during the ETU testing phase.
NASA Astrophysics Data System (ADS)
Baudin, Sophie; Rémond, Didier; Antoni, Jérôme; Sauvage, Olivier
2016-03-01
This work proposes an original non-intrusive approach to detect and quantify rattle noise in automotive gearboxes operating under non-stationary conditions by means of vibration or instantaneous angular speed measurements. Rattle noise is produced by vibro impacts between teeth of unloaded gears excited by the engine acyclism. It appears during acceleration or deceleration phases and its detection requires the analysis of non-stationary signals. In order to take advantage of the repetitive nature of the impacts, an angle/time cyclostationary approach is introduced. Rattle noise is thus characterized through the angle/time duality: the cyclic frequency expressed in events per revolution is directly linked to the periodicity of the impacts while their frequency content is expressed in Hertz. The proposed detection method uses an order/frequency spectral coherence and may be applied either on vibration signals or instantaneous angular speed signals. For validation purposes, a specific instrumentation of a gearbox is set up. The relative speed of the unloaded meshing gears is observed by means of optical encoders to directly detect the instants of impact which then serve as a basis for validation of the non-intrusive detection method proposed in this paper.
Simulation of phase conjugation for laser radiation upon nonstationary SBS
Bogachev, V A; Maslov, N V; Starikov, F A
2010-06-23
We report the three-dimensional simulation results of phase conjugation upon nonstationary stimulated Brillouin scattering of a focused laser beam. It is shown that in the case of deep focusing of laser radiation in the SBS cell, the phase conjugation quality decreases with increasing laser power and reflection coefficient, in agreement with experimental results. In calculations, the process of Stokes radiation generation is studied in detail, the reasons for a decrease in the phase conjugation quality are explained, and a means of its improvement is proposed. (nonlinear optical phenomena)
Nonstationary Dynamics Data Analysis with Wavelet-SVD Filtering
NASA Technical Reports Server (NTRS)
Brenner, Marty; Groutage, Dale; Bessette, Denis (Technical Monitor)
2001-01-01
Nonstationary time-frequency analysis is used for identification and classification of aeroelastic and aeroservoelastic dynamics. Time-frequency multiscale wavelet processing generates discrete energy density distributions. The distributions are processed using the singular value decomposition (SVD). Discrete density functions derived from the SVD generate moments that detect the principal features in the data. The SVD standard basis vectors are applied and then compared with a transformed-SVD, or TSVD, which reduces the number of features into more compact energy density concentrations. Finally, from the feature extraction, wavelet-based modal parameter estimation is applied.
Nonstationary combustion of condensed substances subjected to radiation
Zarko, V.E.; Simonenko, V.N.; Kiskin, A.B.
1988-03-01
Results of an experimental and theoretical investigation of the nonstationary combustion of condensed substances are represented, where the double-based propellants H, H + 1% C, H + 1% PbO and miscible compositions on an ammonium perchlorate base were the substances. Attention was paid to the specifics of physical and mathematical modeling of the processes under irradiation and interrelation of the responses of the burning system to pressure and radiation flux perturbations, and the possibilities of quantitative predictions of the combustion rate under irradiation were analyzed. A xenon lamp, a carbon dioxide laser, and a neodymium laser were used as the radiation sources.
NASA Technical Reports Server (NTRS)
Parker, Ray O.
2012-01-01
The RESOLVE project is a lunar prospecting mission whose primary goal is to characterize water and other volatiles in lunar regolith. The Lunar Advanced Volatiles Analysis (LAVA) subsystem is comprised of a fluid subsystem that transports flow to the gas chromatograph- mass spectrometer (GC-MS) instruments that characterize volatiles and the Water Droplet Demonstration (WDD) that will capture and display water condensation in the gas stream. The LAVA Engineering Test Unit (ETU) is undergoing risk reduction testing this summer and fall within a vacuum chamber to understand and characterize C!Jmponent and integrated system performance. Ray will be assisting with component testing of line heaters, printed circuit heaters, pressure transducers, temperature sensors, regulators, and valves in atmospheric and vacuum environments. He will be developing procedures to guide these tests and test reports to analyze and draw conclusions from the data. In addition, he will gain experience with preparing a vacuum chamber with fluid and electrical connections. Further testing will include integrated testing of the fluid subsystem with the gas supply system, near-infrared spectrometer, WDD, Sample Delivery System, and GC-MS in the vacuum chamber. This testing will provide hands-on exposure to a flight forward spaceflight subsystem, the processes associated with testing equipment in a vacuum chamber, and experience working in a laboratory setting. Examples of specific analysis Ray will conduct include: pneumatic analysis to calculate the WOO's efficiency at extracting water vapor from the gas stream to form condensation; thermal analysis of the conduction and radiation along a line connecting two thermal masses; and proportional-integral-derivative (PID) heater control analysis. In this Research and Technology environment, Ray will be asked to problem solve real-time as issues arise. Since LAVA is a scientific subsystem, Ray will be utilizing his chemical engineering background to
On clustering of non-stationary meteorological time series
NASA Astrophysics Data System (ADS)
Horenko, Illia
2010-04-01
A method for clustering of multidimensional non-stationary meteorological time series is presented. The approach is based on optimization of the regularized averaged clustering functional describing the quality of data representation in terms of several regression models and a metastable hidden process switching between them. Proposed numerical clustering algorithm is based on application of the finite element method ( FEM) to the problem of non-stationary time series analysis. The main advantage of the presented algorithm compared to Hidden Markov Models (HMMs) and to finite mixture models is that no a priori assumptions about the probability model for the hidden and observed processes (e.g., Markovianity or stationarity) are necessary for the proposed method. Another attractive numerical feature of the discussed algorithm is the possibility to choose the optimal number of metastable clusters and a natural opportunity to control the fuzziness of the resulting decomposition a posteriory, based on the statistical distinguishability of the resulting persistent cluster states. The resulting FEM-K-trends algorithm is compared with some standard fuzzy clustering methods on toy model examples and on analysis of multidimensional historical temperature data locally in Europe and on the global temperature data set.
Non-stationary measurements of Chiral Magnetic Effect
Shevchenko, V.I.
2013-12-15
We discuss the Chiral Magnetic Effect from the quantum theory of measurements point of view for non-stationary measurements. The effect of anisotropy for fluctuations of electric currents in a magnetic field is addressed. It is shown that anisotropy caused by nonzero axial chemical potential is indistinguishable in this framework from anisotropy caused by finite measurement time or finite lifetime of the magnetic field, and in all cases it is related to abelian triangle anomaly. Possible P-odd effects in central heavy-ion collisions (where the Chiral Magnetic Effect is absent) are discussed in this context. This paper is dedicated to the memory of Professor Mikhail Polikarpov (1952–2013). -- Highlights: •Asymmetry in the response function for vector currents of massless fermions in the magnetic field is computed. •Asymmetry caused by axial chemical potential is practically indistinguishable from the one caused by non-stationarity. •The CME current is non-dissipative in the stationary case and dissipative in the non-stationary case. •Importance of studies of P-odd signatures in central collisions is emphasized.
Nonstationary stochastic charge fluctuations of a dust particle in plasmas
Shotorban, B.
2011-06-15
Stochastic charge fluctuations of a dust particle that are due to discreteness of electrons and ions in plasmas can be described by a one-step process master equation [T. Matsoukas and M. Russell, J. Appl. Phys. 77, 4285 (1995)] with no exact solution. In the present work, using the system size expansion method of Van Kampen along with the linear noise approximation, a Fokker-Planck equation with an exact Gaussian solution is developed by expanding the master equation. The Gaussian solution has time-dependent mean and variance governed by two ordinary differential equations modeling the nonstationary process of dust particle charging. The model is tested via the comparison of its results to the results obtained by solving the master equation numerically. The electron and ion currents are calculated through the orbital motion limited theory. At various times of the nonstationary process of charging, the model results are in a very good agreement with the master equation results. The deviation is more significant when the standard deviation of the charge is comparable to the mean charge in magnitude.
Nonstationary multistate Coulomb and multistate exponential models for nonadiabatic transitions
Ostrovsky, V. N.
2003-07-01
The nonstationary Schroedinger equation is considered in a finite basis of states. The model Hamiltonian matrix corresponds to a single diabatic potential curve with a Coulombic {approx}1/t time dependence. An arbitrary number of other diabatic potential curves are flat, i.e., time independent and have arbitrary energies. Related states are coupled by constant interactions with the Coulomb state. The resulting nonstationary Schroedinger equation is solved by the method of contour integral. Probabilities of transitions to any other state are obtained as t{yields}{infinity} in a simple analytical form for the case when the Coulomb state is populated initially (at instant of time t{yields}+0). The formulas apply both to the cases when a horizontal diabatic potential curve is crossed by the Coulomb one and to a noncrossing situation. In the limit of weak coupling, the transition probabilities are interpreted in terms of a sequence of pairwise Landau-Zener-type transitions. Mapping of the Coulomb model onto an exactly solvable exponential multistate model is established. For the special two-state case, the well-known Nikitin model is recovered.
NASA Astrophysics Data System (ADS)
Villarroel, Javier; Ablowitz, Mark J.
The discrete spectrum of the nonstationary Schrödinger equation and localized solutions of the Kadomtsev-Petviashvili-I (KPI) equation are studied via the inverse scattering transform. It is shown that there exist infinitely many real and rationally decaying potentials which correspond to a discrete spectrum whose related eigenfunctions have multiple poles in the spectral parameter. An index or winding number is asssociated with each of these solutions. The resulting localized solutions of KPI behave as collection of individual humps with nonuniform dynamics.
NASA Astrophysics Data System (ADS)
Cardona-Morales, O.; Avendaño, L. D.; Castellanos-Domínguez, G.
2014-02-01
Condition monitoring of mechanical systems is an important topic for industry since it improves machine maintenance and reduce the total associated operational cost. In this sense, vibration analysis is a useful tool for failure prevention in rotating machines, and its main challenge is to perform on-line estimation of dynamic behavior, due to non-stationary operating conditions. To this, estimation of both, amplitude and instantaneous frequency, holding most of process information should be carried out. Nevertheless, approaches for estimating those parameters require to have the shaft speed reference signal, which is not always provided in several industrial applications. In this paper, a novel Order Tracking (OT) scheme of estimation is proposed that is based on the state space model that avoids the shaft speed reference signal. The nonlinear oscillatory model designed as frequency tracker is adapted for estimating the phase and the amplitude of each particular harmonic component. Specifically, nonlinear filtering (namely, the Square-Root Cubature Kalman Filter) is used to estimate the spectral components from the vibration signal. The proposed approach is tested and compared with baseline Vold-Kalman Filtering over four different datasets. The obtained results show that proposed approach is robust and it performs with high accuracy estimation of the order component and the instantaneous frequency under different operating conditions; both allow capturing machine dynamic behavior.
Channel characterization and object classification in non-stationary and uncertain environments
NASA Astrophysics Data System (ADS)
Gomatam, Vikram Thiruneermalai
Classification of SONAR targets in underwater environments has long been a challenging problem. These are mainly due to the presence of undesirable effects like dispersion, attenuation and self-noise. Furthermore, we also have to contend with range dependent environ- ments, like the continental shelf/littoral regions, where most of the human and aquatic life's activities occur. Our work consists of analyzing the propagation in these environments from a pulse-evolution perspective. We look at cases where characterizing wave propagation using conventional Fourier-spectral analysis is infeasible for practical applications and instead resort to a phase-space approximation for it. We derive the phase-space approximations for a variety of propagating waves and limiting boundary conditions. We continue our past work on invariant features to enhance classification performance; we simulate the derived features for waves with cylindrical spreading. Another area of our work includes looking at the equation governing the wave propagation from a phase space perspective. It has been shown before that reformulating the classical wave equation in the phase-space provides interesting insights to the solution of the equation. It has been posited that this would be especially useful for non-stationary functions, like the ones governing SONAR propagation underwater. We perform classification of real world SONAR data measured by the JRP ( DRDC- Atlantic, NURC, ARL-PSU, NRL) program. We use a 'classic' MPE classifier on the given non-stationary and contrast its performance with an MPE classifier augmented by a Linear Time Varying (LTV) filter, to assess the impact of adding a time-varying pre-filter to a classidfier (MPE) deemed optimal for stationary additive white Gaussian noise. We show that the addition of the time-varying pre-filter to augment the standard MPE classifier does increase the performance of the classifier. Finally, we look at the self-noise problem that is commonly
Energy resolved X-ray grating interferometry
Thuering, T.; Stampanoni, M.; Barber, W. C.; Iwanczyk, J. S.; Seo, Y.; Alhassen, F.
2013-05-13
Although compatible with polychromatic radiation, the sensitivity in X-ray phase contrast imaging with a grating interferometer is strongly dependent on the X-ray spectrum. We used an energy resolving detector to quantitatively investigate the dependency of the noise from the spectral bandwidth and to consequently optimize the system-by selecting the best energy band matching the experimental conditions-with respect to sensitivity maximization and, eventually, dose. Further, since theoretical calculations of the spectrum are usually limited due to non-ideal conditions, an energy resolving detector accurately quantifies the spectral changes induced by the interferometer including flux reduction and beam hardening.
Spectral and correlation analysis with applications to middle-atmosphere radars
NASA Technical Reports Server (NTRS)
Rastogi, Prabhat K.
1989-01-01
The correlation and spectral analysis methods for uniformly sampled stationary random signals, estimation of their spectral moments, and problems arising due to nonstationary are reviewed. Some of these methods are already in routine use in atmospheric radar experiments. Other methods based on the maximum entropy principle and time series models have been used in analyzing data, but are just beginning to receive attention in the analysis of radar signals. These methods are also briefly discussed.
Spectral and Spread Spectral Teleportation
Humble, Travis S
2010-01-01
We report how quantum information encoded into the spectral degree of freedom of a single-photon state is teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of a teleported waveform can be controllably and coherently dilated using a spread spectral variant of teleportation. We present analytical fidelities for spectral and spread spectral teleportation when complex-valued Gaussian states are prepared using a proposed experimental approach, and we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.
Pixelwise-adaptive blind optical flow assuming nonstationary statistics.
Foroosh, Hassan
2005-02-01
In this paper, we address some of the major issues in optical flow within a new framework assuming nonstationary statistics for the motion field and for the errors. Problems addressed include the preservation of discontinuities, model/data errors, outliers, confidence measures, and performance evaluation. In solving these problems, we assume that the statistics of the motion field and the errors are not only spatially varying, but also unknown. We, thus, derive a blind adaptive technique based on generalized cross validation for estimating an independent regularization parameter for each pixel. Our formulation is pixelwise and combines existing first- and second-order constraints with a new second-order temporal constraint. We derive a new confidence measure for an adaptive rejection of erroneous and outlying motion vectors, and compare our results to other techniques in the literature. A new performance measure is also derived for estimating the signal-to-noise ratio for real sequences when the ground truth is unknown. PMID:15700527
Nonstationary time series prediction combined with slow feature analysis
NASA Astrophysics Data System (ADS)
Wang, G.; Chen, X.
2015-07-01
Almost all climate time series have some degree of nonstationarity due to external driving forces perturbing the observed system. Therefore, these external driving forces should be taken into account when constructing the climate dynamics. This paper presents a new technique of obtaining the driving forces of a time series from the slow feature analysis (SFA) approach, and then introduces them into a predictive model to predict nonstationary time series. The basic theory of the technique is to consider the driving forces as state variables and to incorporate them into the predictive model. Experiments using a modified logistic time series and winter ozone data in Arosa, Switzerland, were conducted to test the model. The results showed improved prediction skills.
Response of a rigid aircraft to nonstationary atmospheric turbulence.
NASA Technical Reports Server (NTRS)
Verdon, J. M.; Steiner, R.
1973-01-01
The plunging response of an aircraft to a type of nonstationary turbulent excitation is considered. The latter consists of stationary Gaussian noise modulated by a well-defined envelope function. The intent of the investigation is to model the excitation experienced by an airplane flying through turbulence of varying intensity and to examine the influence of intensity variations on exceedance frequencies of the gust velocity and the airplane's plunging velocity and acceleration. One analytical advantage of the proposed model is that the Gaussian assumption for the gust excitation is retained. The analysis described herein is developed in terms of an envelope function of arbitrary form; however, numerical calculations are limited to the case of harmonic modulation.
General solutions of optimum problems in nonstationary flight
NASA Technical Reports Server (NTRS)
Miele, Angelo
1955-01-01
A general method concerning optimum problems in nonstationary flight is developed and discussed. Best flight techniques are determined for the following conditions: climb with minimum time, climb with minimum fuel consumption, steepest climb, descending and gliding flight with maximum time or with maximum distance. Optimum distributions of speed with altitude are derived assuming constant airplane weight and neglecting curvatures and squares of path inclination in the projection of the equation of motion on the normal to the flight path. The results of this paper differ from the well-known results obtained by neglecting accelerations with one exception, namely the case of gliding with maximum range. The paper is concluded with criticisms and remarks concerning the physical nature of the solutions and their usefulness for practical applications.
Nondestructive evaluation of concrete structures by nonstationary thermal wave imaging
NASA Astrophysics Data System (ADS)
Mulaveesala, Ravibabu; Panda, Soma Sekhara Balaji; Mude, Rupla Naik; Amarnath, Muniyappa
2012-06-01
Reinforced concrete structures (RCS) have potential application in civil engineering and with the advent of nuclear engineering RCS to be capable enough to withstanding a variety of adverse environmental conditions. However, failures/loss of durability of designed structures due to premature reinforcement corrosion of rebar is a major constrain. Growing concern of safety of structure due to pre-mature deterioration has led to a great demand for development of non-destructive and non-contact testing techniques for monitoring and assessing health of RCS. This paper presents an experimental investigation of rebar corrosion by non-stationary thermal wave imaging. Experimental results have been proven, proposed approach is an effective technique for identification of corrosion in rebar in the concrete samples.
Simulation of nonstationary phenomena in atmospheric-pressure glow discharge
NASA Astrophysics Data System (ADS)
Korolev, Yu. D.; Frants, O. B.; Nekhoroshev, V. O.; Suslov, A. I.; Kas'yanov, V. S.; Shemyakin, I. A.; Bolotov, A. V.
2016-06-01
Nonstationary processes in atmospheric-pressure glow discharge manifest themselves in spontaneous transitions from the normal glow discharge into a spark. In the experiments, both so-called completed transitions in which a highly conductive constricted channel arises and incomplete transitions accompanied by the formation of a diffuse channel are observed. A model of the positive column of a discharge in air is elaborated that allows one to interpret specific features of the discharge both in the stationary stage and during its transition into a spark and makes it possible to calculate the characteristic oscillatory current waveforms for completed transitions into a spark and aperiodic ones for incomplete transitions. The calculated parameters of the positive column in the glow discharge mode agree well with experiment. Data on the densities of the most abundant species generated in the discharge (such as atomic oxygen, metastable nitrogen molecules, ozone, nitrogen oxides, and negative oxygen ions) are presented.
Quantum nonthermal radiation of nonstationary rotating de Sitter cosmological model
NASA Astrophysics Data System (ADS)
Meitei, Irom Ablu; Singh, T. Ibungochouba; Singh, K. Yugindro
2014-08-01
Using the Hamilton-Jacobi method a study of quantum nonthermal radiation of nonstationary rotating de Sitter cosmological model is carried out. It is shown that there exist seas of positive and negative energy states in the vicinity of the cosmological event horizon and there also exists a forbidden energy gap between the two seas. The forbidden energy gap vanishes on the surface of the cosmological event horizon so that the positive and negative energy levels overlap. The width of the forbidden energy gap and the energy of the particle at the cosmological event horizon are found to depend on the cosmological constant, the rotation parameter, positions of the particle and the cosmological event horizon, angular momentum of the particle, evaporation rate and shape of the cosmological event horizon. The tunneling probability of the emitted particles constituting Hawking radiation is also deduced for stationary nonrotating de Sitter cosmological model and the standard Hawking temperature is recovered.
System for monitoring non-coincident, nonstationary process signals
Gross, Kenneth C.; Wegerich, Stephan W.
2005-01-04
An improved system for monitoring non-coincident, non-stationary, process signals. The mean, variance, and length of a reference signal is defined by an automated system, followed by the identification of the leading and falling edges of a monitored signal and the length of the monitored signal. The monitored signal is compared to the reference signal, and the monitored signal is resampled in accordance with the reference signal. The reference signal is then correlated with the resampled monitored signal such that the reference signal and the resampled monitored signal are coincident in time with each other. The resampled monitored signal is then compared to the reference signal to determine whether the resampled monitored signal is within a set of predesignated operating conditions.
Nonstationary LPV control for trajectory tracking: a double pendulum example
NASA Astrophysics Data System (ADS)
Farhood, Mazen
2012-05-01
This article focusses on the implementation of recently developed nonstationary linear-parameter varying (NSLPV) control algorithms for the regulation of nonlinear systems about pre-specified trajectories. The trajectories of interest eventually settle into periodic orbits, and hence are duly called eventually periodic trajectories. Parameterising the nonlinear system equations about such trajectories results in eventually periodic NSLPV models, and then NSLPV controllers are designed for these models to ensure accurate trajectory tracking despite various disturbances and uncertainties. These control algorithms will be applied to control a double pendulum where a vessel containing fluid is rigidly attached to the end of the second link of the pendulum. The mass of the fluid varies in time and, together with its rate of variation, is available for measurement during plant operation.
Martingales, nonstationary increments, and the efficient market hypothesis
NASA Astrophysics Data System (ADS)
McCauley, Joseph L.; Bassler, Kevin E.; Gunaratne, Gemunu H.
2008-06-01
We discuss the deep connection between nonstationary increments, martingales, and the efficient market hypothesis for stochastic processes x(t) with arbitrary diffusion coefficients D(x,t). We explain why a test for a martingale is generally a test for uncorrelated increments. We explain why martingales look Markovian at the level of both simple averages and 2-point correlations. But while a Markovian market has no memory to exploit and cannot be beaten systematically, a martingale admits memory that might be exploitable in higher order correlations. We also use the analysis of this paper to correct a misstatement of the ‘fair game’ condition in terms of serial correlations in Fama’s paper on the EMH. We emphasize that the use of the log increment as a variable in data analysis generates spurious fat tails and spurious Hurst exponents.
Local adaptive filtering of images corrupted by nonstationary noise
NASA Astrophysics Data System (ADS)
Lukin, Vladimir V.; Fevralev, Dmitriy V.; Ponomarenko, Nikolay N.; Pogrebnyak, Oleksiy B.; Egiazarian, Karen O.; Astola, Jaakko T.
2009-02-01
In various practical situations of remote sensing image processing it is assumed that noise is nonstationary and no a priory information on noise dependence on local mean or about local properties of noise statistics is available. It is shown that in such situations it is difficult to find a proper filter for effective image processing, i.e., for noise removal with simultaneous edge/detail preservation. To deal with such images, a local adaptive filter based on discrete cosine transform in overlapping blocks is proposed. A threshold is set locally based on a noise standard deviation estimate obtained for each block. Several other operations to improve performance of the locally adaptive filter are proposed and studied. The designed filter effectiveness is demonstrated for simulated data as well as for real life radar remote sensing and marine polarimetric radar images.
Nonstationary elementary-field light randomly triggered by Poisson impulses.
Fernández-Pousa, Carlos R
2013-05-01
A stochastic theory of nonstationary light describing the random emission of elementary pulses is presented. The emission is governed by a nonhomogeneous Poisson point process determined by a time-varying emission rate. The model describes, in the appropriate limits, stationary, cyclostationary, locally stationary, and pulsed radiation, and reduces to a Gaussian theory in the limit of dense emission rate. The first- and second-order coherence theories are solved after the computation of second- and fourth-order correlation functions by use of the characteristic function. The ergodicity of second-order correlations under various types of detectors is explored and a number of observables, including optical spectrum, amplitude, and intensity correlations, are analyzed. PMID:23695325
Non-stationary (13)C-metabolic flux ratio analysis.
Hörl, Manuel; Schnidder, Julian; Sauer, Uwe; Zamboni, Nicola
2013-12-01
(13)C-metabolic flux analysis ((13)C-MFA) has become a key method for metabolic engineering and systems biology. In the most common methodology, fluxes are calculated by global isotopomer balancing and iterative fitting to stationary (13)C-labeling data. This approach requires a closed carbon balance, long-lasting metabolic steady state, and the detection of (13)C-patterns in a large number of metabolites. These restrictions mostly reduced the application of (13)C-MFA to the central carbon metabolism of well-studied model organisms grown in minimal media with a single carbon source. Here we introduce non-stationary (13)C-metabolic flux ratio analysis as a novel method for (13)C-MFA to allow estimating local, relative fluxes from ultra-short (13)C-labeling experiments and without the need for global isotopomer balancing. The approach relies on the acquisition of non-stationary (13)C-labeling data exclusively for metabolites in the proximity of a node of converging fluxes and a local parameter estimation with a system of ordinary differential equations. We developed a generalized workflow that takes into account reaction types and the availability of mass spectrometric data on molecular ions or fragments for data processing, modeling, parameter and error estimation. We demonstrated the approach by analyzing three key nodes of converging fluxes in central metabolism of Bacillus subtilis. We obtained flux estimates that are in agreement with published results obtained from steady state experiments, but reduced the duration of the necessary (13)C-labeling experiment to less than a minute. These results show that our strategy enables to formally estimate relative pathway fluxes on extremely short time scale, neglecting cellular carbon balancing. Hence this approach paves the road to targeted (13)C-MFA in dynamic systems with multiple carbon sources and towards rich media. PMID:23860906
A Nonstationary Markov Model Detects Directional Evolution in Hymenopteran Morphology
Klopfstein, Seraina; Vilhelmsen, Lars; Ronquist, Fredrik
2015-01-01
Directional evolution has played an important role in shaping the morphological, ecological, and molecular diversity of life. However, standard substitution models assume stationarity of the evolutionary process over the time scale examined, thus impeding the study of directionality. Here we explore a simple, nonstationary model of evolution for discrete data, which assumes that the state frequencies at the root differ from the equilibrium frequencies of the homogeneous evolutionary process along the rest of the tree (i.e., the process is nonstationary, nonreversible, but homogeneous). Within this framework, we develop a Bayesian approach for testing directional versus stationary evolution using a reversible-jump algorithm. Simulations show that when only data from extant taxa are available, the success in inferring directionality is strongly dependent on the evolutionary rate, the shape of the tree, the relative branch lengths, and the number of taxa. Given suitable evolutionary rates (0.1–0.5 expected substitutions between root and tips), accounting for directionality improves tree inference and often allows correct rooting of the tree without the use of an outgroup. As an empirical test, we apply our method to study directional evolution in hymenopteran morphology. We focus on three character systems: wing veins, muscles, and sclerites. We find strong support for a trend toward loss of wing veins and muscles, while stationarity cannot be ruled out for sclerites. Adding fossil and time information in a total-evidence dating approach, we show that accounting for directionality results in more precise estimates not only of the ancestral state at the root of the tree, but also of the divergence times. Our model relaxes the assumption of stationarity and reversibility by adding a minimum of additional parameters, and is thus well suited to studying the nature of the evolutionary process in data sets of limited size, such as morphology and ecology. PMID:26272507
A Nonstationary Markov Model Detects Directional Evolution in Hymenopteran Morphology.
Klopfstein, Seraina; Vilhelmsen, Lars; Ronquist, Fredrik
2015-11-01
Directional evolution has played an important role in shaping the morphological, ecological, and molecular diversity of life. However, standard substitution models assume stationarity of the evolutionary process over the time scale examined, thus impeding the study of directionality. Here we explore a simple, nonstationary model of evolution for discrete data, which assumes that the state frequencies at the root differ from the equilibrium frequencies of the homogeneous evolutionary process along the rest of the tree (i.e., the process is nonstationary, nonreversible, but homogeneous). Within this framework, we develop a Bayesian approach for testing directional versus stationary evolution using a reversible-jump algorithm. Simulations show that when only data from extant taxa are available, the success in inferring directionality is strongly dependent on the evolutionary rate, the shape of the tree, the relative branch lengths, and the number of taxa. Given suitable evolutionary rates (0.1-0.5 expected substitutions between root and tips), accounting for directionality improves tree inference and often allows correct rooting of the tree without the use of an outgroup. As an empirical test, we apply our method to study directional evolution in hymenopteran morphology. We focus on three character systems: wing veins, muscles, and sclerites. We find strong support for a trend toward loss of wing veins and muscles, while stationarity cannot be ruled out for sclerites. Adding fossil and time information in a total-evidence dating approach, we show that accounting for directionality results in more precise estimates not only of the ancestral state at the root of the tree, but also of the divergence times. Our model relaxes the assumption of stationarity and reversibility by adding a minimum of additional parameters, and is thus well suited to studying the nature of the evolutionary process in data sets of limited size, such as morphology and ecology. PMID:26272507
Spectral ladar as a UGV navigation sensor
NASA Astrophysics Data System (ADS)
Powers, Michael A.; Davis, Christopher C.
2011-06-01
We demonstrate new results using our Spectral LADAR prototype, which highlight the benefits of this sensor for Unmanned Ground Vehicle (UGV) navigation applications. This sensor is an augmentation of conventional LADAR and uses a polychromatic source to obtain range-resolved 3D spectral point clouds. These point cloud images can be used to identify objects based on combined spatial and spectral features in three dimensions and at long standoff range. The Spectral LADAR transmits nanosecond supercontinuum pulses generated in a photonic crystal fiber. Backscatter from distant targets is dispersed into 25 spectral bands, where each spectral band is independently range resolved with multiple return pulse recognition. Our new results show that Spectral LADAR can spectrally differentiate hazardous terrain (mud) from favorable driving surfaces (dry ground). This is a critical capability, since in UGV contexts mud is potentially hazardous, requires modified vehicle dynamics, and is difficult to identify based on 3D spatial signatures. Additionally, we demonstrate the benefits of range resolved spectral imaging, where highly cluttered 3D images of scenes (e.g. containing camouflage, foliage) are spectrally unmixed by range separation and segmented accordingly. Spectral LADAR can achieve this unambiguously and without the need for stereo correspondence, sub-pixel detection algorithms, or multi-sensor registration and data fusion.
Spectral multigrid methods for the solution of homogeneous turbulence problems
NASA Technical Reports Server (NTRS)
Erlebacher, G.; Zang, T. A.; Hussaini, M. Y.
1987-01-01
New three-dimensional spectral multigrid algorithms are analyzed and implemented to solve the variable coefficient Helmholtz equation. Periodicity is assumed in all three directions which leads to a Fourier collocation representation. Convergence rates are theoretically predicted and confirmed through numerical tests. Residual averaging results in a spectral radius of 0.2 for the variable coefficient Poisson equation. In general, non-stationary Richardson must be used for the Helmholtz equation. The algorithms developed are applied to the large-eddy simulation of incompressible isotropic turbulence.
Sigernes, F; Lorentzen, D A; Heia, K; Svenøe, T
2000-06-20
A small spectral imaging system is presented that images static or moving objects simultaneously as a function of wavelength. The main physical principle is outlined and demonstrated. The instrument is capable of resolving both spectral and spatial information from targets throughout the entire visible region. The spectral domain has a bandpass of 12 A. One can achieve the spatial domain by rotating the system's front mirror with a high-resolution stepper motor. The spatial resolution range from millimeters to several meters depends mainly on the front optics used and whether the target is fixed (static) or movable relative to the instrument. Different applications and examples are explored, including outdoor landscapes, industrial fish-related targets, and ground-level objects observed in the more traditional way from an airborne carrier (remote sensing). Through the examples, we found that the instrument correctly classifies whether a shrimp is peeled and whether it can disclose the spectral and spatial microcharacteristics of targets such as a fish nematode (parasite). In the macroregime, we were able to distinguish a marine vessel from the surrounding sea and sky. A study of the directional spectral albedo from clouds, mountains, snow cover, and vegetation has also been included. With the airborne experiment, the imager successfully classified snow cover, leads, and new and rafted ice, as seen from 10.000 ft (3.048 m). PMID:18345245
Multitaper spectral analysis of high-frequency seismograms
NASA Astrophysics Data System (ADS)
Park, Jeffrey; Lindberg, Craig R.; Vernon, Frank L., III
1987-11-01
Spectral estimation procedures which employ several prolate spheroidal sequences as tapers have been shown to yield better results than standard single-taper spectral analysis when used on a variety of engineering data. We apply the adaptive multitaper spectral estimation method of Thomson (1982) to a number of high-resolution digital seismic records and compare the results to those obtained using standard single-taper spectral estimates. Single-taper smoothed-spectrum estimates are plagued by a trade-off between the variance of the estimate and the bias caused by spectral leakage. Applying a taper to reduce bias discards data, increasing the variance of the estimate. Using a taper also unevenly samples the record. Throwing out data from the ends of the record can result in a spectral estimate which does not adequately represent the character of the spectrum of nonstationary processes like seismic waveforms. For example, a discrete Fourier transform of an untapered record (i.e., using a boxcar taper) produces a reasonable spectral estimate of the large-amplitude portion of the seismic source spectrum but cannot be trusted to provide a good estimate of the high-frequency roll-off. A discrete Fourier transform of the record multiplied by a more severe taper (like the Hann taper) which is resistant to spectral leakage leads to a reliable estimate of high-frequency spectral roll-off, but this estimate weights the analyzed data unequally. Therefore single-taper estimators which are less affected by leakage not only have increased variance but also can misrepresent the spectra of nonstationary data. The adaptive multitaper algorithm automatically adjusts between these extremes. We demonstrate its advantages using 16-bit seismic data recorded by instruments in the Anza Telemetered Seismic Network. We also present an analysis demonstrating the superiority of the multitaper algorithm in providing low-variance spectral estimates with good leakage resistance which do not
NASA Astrophysics Data System (ADS)
Manevitch, Leonid I.; Kovaleva, Agnessa; Sigalov, Grigori
2016-03-01
In this paper we study the effect of nonstationary energy localization in a nonlinear conservative resonant system of two weakly coupled oscillators. This effect is alternative to the well-known stationary energy localization associated with the existence of localized normal modes and resulting from a local topological transformation of the phase portraits of the system. In this work we show that nonstationary energy localization results from a global transformation of the phase portrait. A key to solving the problem is the introduction of the concept of limiting phase trajectories (LPTs) corresponding to maximum possible energy exchange between the oscillators. We present two scenarios of nonstationary energy localization under the condition of 1:1 resonance. It is demonstrated that the conditions of nonstationary localization determine the conditions of efficient targeted energy transfer in a generating dynamical system. A possible extension to multi-particle systems is briefly discussed.
NASA Astrophysics Data System (ADS)
Jin, X. L.; Huang, Z. L.
The nonstationary probability densities of system responses are obtained for nonlinear multi-degree-of-freedom systems subject to stochastic parametric and external excitations. First, the stochastic averaging method is used to obtain the averaged Itô equation for amplitude envelopes of the system response. Then, the corresponding Fokker-Planck-Kolmogorov equation governing the nonstationary probability density of the amplitude envelopes is deduced. By applying the Galerkin method, the nonstationary probability density can be expressed as a series expansion in terms of a set of orthogonal base functions with time-dependent coefficients. Finally, the nonstationary probability densities for the amplitude response, as well as those for the state-space response, are solved approximately. To illustrate the applicability, the proposed method is applied to a two-degree-of-freedom van der Pol oscillator subject to external excitations of Gaussian white noises.
Moryakov, A. V. Pylyov, S. S.
2012-12-15
This paper presents the formulation of the problem and the methodical approach for solving large systems of linear differential equations describing nonstationary processes with the use of CUDA technology; this approach is implemented in the ANGEL program. Results for a test problem on transport of radioactive products over loops of a nuclear power plant are given. The possibilities for the use of the ANGEL program for solving various problems that simulate arbitrary nonstationary processes are discussed.
Analyzing nonstationary financial time series via hilbert-huang transform (HHT)
NASA Technical Reports Server (NTRS)
Huang, Norden E. (Inventor)
2008-01-01
An apparatus, computer program product and method of analyzing non-stationary time varying phenomena. A representation of a non-stationary time varying phenomenon is recursively sifted using Empirical Mode Decomposition (EMD) to extract intrinsic mode functions (IMFs). The representation is filtered to extract intrinsic trends by combining a number of IMFs. The intrinsic trend is inherent in the data and identifies an IMF indicating the variability of the phenomena. The trend also may be used to detrend the data.
Physical significance of least mean squares criterion in nonstationary lattice predictors
NASA Astrophysics Data System (ADS)
Martinelli, G.; Orlandi, G.; Prinaricotti, L.; Ragazzini, S.
1985-06-01
An acoustical nonstationary model of the vocal tract is discussed. The effectiveness of the nonstationary lattice predictor in recovering the model is illustrated. The reflection coefficients are linearly decomposed on a function basis and the weights of the linear combinations are the new parameters of the model. Parameters are determined by an algorithm similar to Burg's by minimizing the sum of the variances of the forward and backward residuals. Synthetic signals of good approximation are obtained in two examples.
Quantum theory of optical coherence of nonstationary light in the space-frequency domain
Lahiri, Mayukh; Wolf, Emil
2010-10-15
Classical theories of coherence for statistically stationary, as well as, nonstationary optical fields are frequently discussed both in the space-time and in the space-frequency domains. However, the quantum treatment of coherence theory is generally carried out in the space-time domain. In this paper, we present a quantum-mechanical theory of first-order coherence for statistically nonstationary light in the space-frequency domain.
NASA Astrophysics Data System (ADS)
Chang, Y.; Hung, S.; Chiao, L.; Yang, H.
2010-12-01
Whether different forward theories or parameterization methods employed in seismic tomographic imaging lead to the improvement of the resulting Earth structures has been a focus of attention in the seismological community. Recent advance in tomographic theory has gone beyond classical ray theory and incorporated the 3-D sensitivity kernels of frequency-dependent travel-time data into probing the mantle velocity heterogeneity with unprecedented resolution. On the other hand, the conception of multi-scale parameterization has been introduced to deal with naturally uneven data distribution and spatially-varying model resolution for the tomographic inverse problems. The multi-resolution model automatically built through the wavelet decomposition and synthesis results in the non-stationary spatial resolution and data-adaptive resolvable scales. Because the Gram matrix of Frechét derivatives that relates observed data to seismic velocity variations is usually too large to be practically inverted by singular value decomposition (SVD), the iterative LSQR algorithm is instead employed in the inversion which inhibits the direct calculation of resolution matrix to assess the model performance. Recently, with the increasing computing power, we are now able to calculate the SVD of the Gram matrix more efficiently using the parallel PROPACK solver. In this study, we compute the ground-truth pseudo-spectral seismograms in random media with certain heterogeneity strengths and scale lengths. The finite-frequency travel-time residuals measured from waveform cross correlation are then used to invert for the implanted random structure based on different forward theory and model parameterization. For each inversion approach, the trade-off between model covariance and model spread is utilized to determine the optimal solution, showing that the multi-scale model yields a much lower model covariance and remains better spectral resolution for longer-wavelength velocity structures than the
Teaching geographical hydrology in a non-stationary world
NASA Astrophysics Data System (ADS)
Hendriks, Martin R.; Karssenberg, Derek
2010-05-01
Understanding hydrological processes in a non-stationary world requires knowledge of hydrological processes and their interactions. Also, one needs to understand the (non-linear) relations between the hydrological system and other parts of our Earth system, such as the climate system, the socio-economic system, and the ecosystem. To provide this knowledge and understanding we think that three components are essential when teaching geographical hydrology. First of all, a student needs to acquire a thorough understanding of classical hydrology. For this, knowledge of the basic hydrological equations, such as the energy equation (Bernoulli), flow equation (Darcy), continuity (or water balance) equation is needed. This, however, is not sufficient to make a student fully understand the interactions between hydrological compartments, or between hydrological subsystems and other parts of the Earth system. Therefore, secondly, a student also needs to be knowledgeable of methods by which the different subsystems can be coupled; in general, numerical models are used for this. A major disadvantage of numerical models is their complexity. A solution may be to use simpler models, provided that a student really understands how hydrological processes function in our real, non-stationary world. The challenge for a student then lies in understanding the interactions between the subsystems, and to be able to answer questions such as: what is the effect of a change in vegetation or land use on runoff? Thirdly, knowledge of field hydrology is of utmost importance. For this a student needs to be trained in the field. Fieldwork is very important as a student is confronted in the field with spatial and temporal variability, as well as with real life uncertainties, rather than being lured into believing the world as presented in hydrological textbooks and models, e.g. the world under study is homogeneous, isotropic, or lumped (averaged). Also, students in the field learn to plan and
Discriminant non-stationary signal features' clustering using hard and fuzzy cluster labeling
NASA Astrophysics Data System (ADS)
Ghoraani, Behnaz; Krishnan, Sridhar
2012-12-01
Current approaches to improve the pattern recognition performance mainly focus on either extracting non-stationary and discriminant features of each class, or employing complex and nonlinear feature classifiers. However, little attention has been paid to the integration of these two approaches. Combining non-stationary feature analysis with complex feature classifiers, this article presents a novel direction to enhance the discriminatory power of pattern recognition methods. This approach, which is based on a fusion of non-stationary feature analysis with clustering techniques, proposes an algorithm to adaptively identify the feature vectors according to their importance in representing the patterns of discrimination. Non-stationary feature vectors are extracted using a non-stationary method based on time-frequency distribution and non-negative matrix factorization. The clustering algorithms including the K-means and self-organizing tree maps are utilized as unsupervised clustering methods followed by a supervised labeling. Two labeling methods are introduced: hard and fuzzy labeling. The article covers in detail the formulation of the proposed discriminant feature clustering method. Experiments performed with pathological speech classification, T-wave alternans evaluation from the surface electrocardiogram, audio scene analysis, and telemonitoring of Parkinson's disease problems produced desirable results. The outcome demonstrates the benefits of non-stationary feature fusion with clustering methods for complex data analysis where existing approaches do not exhibit a high performance.
Extracting stationary segments from non-stationary synthetic and cardiac signals
NASA Astrophysics Data System (ADS)
Rodríguez, María. G.; Ledezma, Carlos A.; Perpiñán, Gilberto; Wong, Sara; Altuve, Miguel
2015-01-01
Physiological signals are commonly the result of complex interactions between systems and organs, these interactions lead to signals that exhibit a non-stationary behaviour. For cardiac signals, non-stationary heart rate variability (HRV) may produce misinterpretations. A previous work proposed to divide a non-stationary signal into stationary segments by looking for changes in the signal's properties related to changes in the mean of the signal. In this paper, we extract stationary segments from non-stationary synthetic and cardiac signals. For synthetic signals with different signal-to-noise ratio levels, we detect the beginning and end of the stationary segments and the result is compared to the known values of the occurrence of these events. For cardiac signals, RR interval (cardiac cycle length) time series, obtained from electrocardiographic records during stress tests for two populations (diabetic patients with cardiovascular autonomic neuropathy and control subjects), were divided into stationary segments. Results on synthetic signals reveal that the non-stationary sequence is divided into more stationary segments than needed. Additionally, due to HRV reduction and exercise intolerance reported on diabetic cardiovascular autonomic neuropathy patients, non-stationary RR interval sequences from these subjects can be divided into longer stationary segments compared to the control group.
Modelling exploration of non-stationary hydrological system
NASA Astrophysics Data System (ADS)
Kim, Kue Bum; Kwon, Hyun-Han; Han, Dawei
2015-04-01
Traditional hydrological modelling assumes that the catchment does not change with time (i.e., stationary conditions) which means the model calibrated for the historical period is valid for the future period. However, in reality, due to change of climate and catchment conditions this stationarity assumption may not be valid in the future. It is a challenge to make the hydrological model adaptive to the future climate and catchment conditions that are not observable at the present time. In this study a lumped conceptual rainfall-runoff model called IHACRES was applied to a catchment in southwest England. Long observation data from 1961 to 2008 were used and seasonal calibration (in this study only summer period is further explored because it is more sensitive to climate and land cover change than the other three seasons) has been done since there are significant seasonal rainfall patterns. We expect that the model performance can be improved by calibrating the model based on individual seasons. The data is split into calibration and validation periods with the intention of using the validation period to represent the future unobserved situations. The success of the non-stationary model will depend not only on good performance during the calibration period but also the validation period. Initially, the calibration is based on changing the model parameters with time. Methodology is proposed to adapt the parameters using the step forward and backward selection schemes. However, in the validation both the forward and backward multiple parameter changing models failed. One problem is that the regression with time is not reliable since the trend may not be in a monotonic linear relationship with time. The second issue is that changing multiple parameters makes the selection process very complex which is time consuming and not effective in the validation period. As a result, two new concepts are explored. First, only one parameter is selected for adjustment while the other
Non-Stationary Effects and Cross Correlations in Solar Activity
NASA Astrophysics Data System (ADS)
Nefedyev, Yuri; Panischev, Oleg; Demin, Sergey
2016-07-01
In this paper within the framework of the Flicker-Noise Spectroscopy (FNS) we consider the dynamic properties of the solar activity by analyzing the Zurich sunspot numbers. As is well-known astrophysics objects are the non-stationary open systems, whose evolution are the quite individual and have the alternation effects. The main difference of FNS compared to other related methods is the separation of the original signal reflecting the dynamics of solar activity into three frequency bands: system-specific "resonances" and their interferential contributions at lower frequencies, chaotic "random walk" ("irregularity-jump") components at larger frequencies, and chaotic "irregularity-spike" (inertial) components in the highest frequency range. Specific parameters corresponding to each of the bands are introduced and calculated. These irregularities as well as specific resonance frequencies are considered as the information carriers on every hierarchical level of the evolution of a complex natural system with intermittent behavior, consecutive alternation of rapid chaotic changes in the values of dynamic variables on small time intervals with small variations of the values on longer time intervals ("laminar" phases). The jump and spike irregularities are described by power spectra and difference moments (transient structural functions) of the second order. FNS allows revealing the most crucial points of the solar activity dynamics by means of "spikiness" factor. It is shown that this variable behaves as the predictor of crucial changes of the sunspot number dynamics, particularly when the number comes up to maximum value. The change of averaging interval allows revealing the non-stationary effects depending by 11-year cycle and by inside processes in a cycle. To consider the cross correlations between the different variables of solar activity we use the Zurich sunspot numbers and the sequence of corona's radiation energy. The FNS-approach allows extracting the
Broadband ringdown spectral photography.
Scherer, J J; Paul, J B; Jiao, H; O'Keefe, A
2001-12-20
A new technique that enables frequency-resolved cavity ringdown absorption spectra to be obtained over a large optical bandwidth by a single laser shot is described. The technique, ringdown spectral photography (RSP), simultaneously employs two key principles to record the time and frequency response of an optical cavity along orthogonal axes of a CCD array detector. Previously, the principles employed in RSP were demonstrated with narrow-band laser light that was scanned in frequency [Chem. Phys. Lett. 292, 143 (1998)]. Here, the RSP method is demonstrated using single pulses of broadband visible laser light. The ability to obtain broad as well as rotationally resolved spectra over a large bandwidth with high sensitivity is demonstrated. PMID:18364983
Pollard, W.T.; Peteanu, L.A.; Mathies, R.A.
1992-07-23
A time-dependent theory for femtosecond dynamic absorption spectroscopy is used to describe the creation and observation of molecular ground-state vibrational coherence through the resonance impulsive stimulated Raman mechanism. Model calculations show that the oscillatory absorption signal that arises from this ground-state coherence is maximized for a limited range of pulse lengths and that there is a complex relationship between the probe wavelength and the strength of the spectral oscillations. The generalized time-dependent linear susceptibility of the nonstationary system created by the impulsive pump pulse is defined and used to discuss the strong dependence of the measured signals on the properties of the probe pulse. Finally, calculations are presented to analyze the high-frequency oscillations ({approximately}20-fs period) recently observed in the transient absorption spectra of light-adapted bacteriorhodopsin (BR{sub 568}) following excitation with a 12-fs optical pulse. At the probe wavelengths used in this experiment, the contribution of stimulated emission is negligible at long times because of the extremely rapid excited-state isomerization; as a result, the spectral oscillations observed after this time are due to the impulsive excitation of coherent vibrations in the ground state. The transient response observed for BR{sub 568} is calculated using a 29-mode harmonic potential surface derived from a prior resonance Raman intensity analysis. Both the oscillatory signals and their dependence on the probe wavelength are satisfactorily reproduced. 68 refs., 11 figs.
Solar cycle signal in Earth rotation: nonstationary behavior.
Currie, R G
1981-01-23
Following the discovery of the 11-year solar cycle signal in earth rotation, linear techniques were employed to investigate the amplitude and phase of the difference between ephemeris time and universal time (DeltaT) as a function of time. The amplitude is nonstationary. This difference was related to Delta(LOD), the difference between the length of day and its nominal value. The 11-year term in Delta(LOD) was 0.8 millisecond at the close of the 18th century and decreased below noise level from 1840 to 1860. From 1875 to 1925, Delta(LOD) was about 0.16 millisecond, and it decreased to about 0.08 millisecond by the 1950's. Except for anomalous behavior from 1797 to 1838, DeltaT lags sunspot numbers by 3.0 +/- 0.4 years. Since DeltaT lags Delta(LOD) by 2.7 years, the result is that Delta(LOD) is approximately in phase with sunspot numbers. PMID:17748272
Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind
NASA Technical Reports Server (NTRS)
Alexander, M. J.; Rosenlof, K. H.
1996-01-01
The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.
Modelling nonstationary Doppler noise in exoplanetary radial velocity data
NASA Astrophysics Data System (ADS)
Baluev, Roman V.
2015-08-01
We construct a new class of analytic nonstationary noise models for exoplanetary Doppler data. The observable correlated noise is represented as a convolution of a parent activity process with a given memory function. The model honours the casuality principle, meaning that only past values of the activity may affect the observable value. This model does not approximate detailedly any real stellar activity phenomena, but it becomes mathematically simple, simultaneously satisfying the basic natural principles of physical sensibility and self-consistency.Additionally, we develop a new type of periodograms that can be used to detect periodic modulations in the Doppler noise characteristics, rather than in the observed radial velocity curve itself. We present first results of applying this technique to public Doppler time series available for a set of planet-hosting stars.This work was supported by the Russian Foundation for Basic Research (project No. 14-02-92615 KO_a), the UK Royal Society International Exchange grant IE140055, by the President of Russia grant for young scientists (No. MK-733.2014.2), by the programme of the Presidium of Russian Academy of Sciences P21, and by the Saint Petersburg State University research grant 6.37.341.2015.
Tropical SST and Sahel rainfall: A non-stationary relationship
NASA Astrophysics Data System (ADS)
Losada, T.; Rodriguez-Fonseca, B.; Mohino, E.; Bader, J.; Janicot, S.; Mechoso, C. R.
2012-06-01
Sea surface temperature (SST) anomalies in the tropical Atlantic have been associated with precipitation anomalies in West Africa that form a dipole pattern with centers over the Sahel and the Gulf of Guinea. Whilst this was clear before the 1970's, the dipole pattern almost disappeared after that date, as the anti-correlation between rainfall anomalies in the Sahel and Guinea dropped abruptly. Simultaneously, the anti-correlations between Sahel rainfall and tropical Pacific SSTs strengthened. It has been posited that these changes after the 1970's developed as rainfall over West Africa started to co-vary with SSTs in the global tropics. In this co-variability, enhanced summer rainfall over West Africa with a monopole pattern corresponds to warmer SSTs in the tropical Atlantic and Maritime Continent, and colder SSTs in the tropical Pacific and western Indian Oceans. The present paper describes the hitherto unexplored seasonal evolution of this co-variability and the physical mechanisms at work. Sensitivity experiments with two atmospheric general circulation models demonstrate that, after the 1970's, the impacts of SST anomalies in the Indo-Pacific counteract those in the Atlantic in terms of generating rainfall anomalies over the Sahel, and that this superposition of effects is primarily linear. Therefore, at interannual timescales, the change in the patterns of co-variability between West African rainfall and tropical SSTs can explain the non-stationary relationship between the anomalies in these two fields.
On the entrainment dynamics of inergodic, non-stationary flows
NASA Astrophysics Data System (ADS)
Rosi, Giuseppe; Rival, David
2014-11-01
Entrainment is typically studied through the conditional averaging along the turbulent non-turbulent interface (TNTI) of ergodic flows. However, this method is unsuitable for inergodic, non-stationary flows, as the TNTI is non-similar at different points in space and time. To understand how a TNTI's mean time dependence effects entrainment, the current study investigates the transport of irrotational fluid into a vortex forming behind an accelerating plate. The plate accelerates to a final velocity within a full-, half- and quarter-chord tow. Phase-averaged, planar, particle tracking velocimetry data is acquired and the forward finite-time Lyapunov exponent and vorticity fields are used to identify the TNTI. The TNTI is then represented by a contour, which is used to approximate the entrainment rate and investigate the transport mechanisms across the TNTI. Early results show that increasing acceleration suppresses vortex growth and entrainment. We hypothesize that shear-layer structure is integral to entrainment by altering the feeding rate of rotational fluid and the TNTI's convexity. The hypothesis is tested by altering plate-edge geometry and by varying the final chord-based Reynolds number from 5000 to 20 000. Natural Sciences and Engineering Council of Canada.
Laplace Approximation for Divisive Gaussian Processes for Nonstationary Regression.
Muñoz-González, Luis; Lázaro-Gredilla, Miguel; Figueiras-Vidal, Aníbal R
2016-03-01
The standard Gaussian Process regression (GP) is usually formulated under stationary hypotheses: The noise power is considered constant throughout the input space and the covariance of the prior distribution is typically modeled as depending only on the difference between input samples. These assumptions can be too restrictive and unrealistic for many real-world problems. Although nonstationarity can be achieved using specific covariance functions, they require a prior knowledge of the kind of nonstationarity, not available for most applications. In this paper we propose to use the Laplace approximation to make inference in a divisive GP model to perform nonstationary regression, including heteroscedastic noise cases. The log-concavity of the likelihood ensures a unimodal posterior and makes that the Laplace approximation converges to a unique maximum. The characteristics of the likelihood also allow to obtain accurate posterior approximations when compared to the Expectation Propagation (EP) approximations and the asymptotically exact posterior provided by a Markov Chain Monte Carlo implementation with Elliptical Slice Sampling (ESS), but at a reduced computational load with respect to both, EP and ESS. PMID:26890623
Estimating nonstationary input signals from a single neuronal spike train
NASA Astrophysics Data System (ADS)
Kim, Hideaki; Shinomoto, Shigeru
2012-11-01
Neurons temporally integrate input signals, translating them into timed output spikes. Because neurons nonperiodically emit spikes, examining spike timing can reveal information about input signals, which are determined by activities in the populations of excitatory and inhibitory presynaptic neurons. Although a number of mathematical methods have been developed to estimate such input parameters as the mean and fluctuation of the input current, these techniques are based on the unrealistic assumption that presynaptic activity is constant over time. Here, we propose tracking temporal variations in input parameters with a two-step analysis method. First, nonstationary firing characteristics comprising the firing rate and non-Poisson irregularity are estimated from a spike train using a computationally feasible state-space algorithm. Then, information about the firing characteristics is converted into likely input parameters over time using a transformation formula, which was constructed by inverting the neuronal forward transformation of the input current to output spikes. By analyzing spike trains recorded in vivo, we found that neuronal input parameters are similar in the primary visual cortex V1 and middle temporal area, whereas parameters in the lateral geniculate nucleus of the thalamus were markedly different.
Wavelet analysis for non-stationary, nonlinear time series
NASA Astrophysics Data System (ADS)
Schulte, Justin A.
2016-08-01
Methods for detecting and quantifying nonlinearities in nonstationary time series are introduced and developed. In particular, higher-order wavelet analysis was applied to an ideal time series and the quasi-biennial oscillation (QBO) time series. Multiple-testing problems inherent in wavelet analysis were addressed by controlling the false discovery rate. A new local autobicoherence spectrum facilitated the detection of local nonlinearities and the quantification of cycle geometry. The local autobicoherence spectrum of the QBO time series showed that the QBO time series contained a mode with a period of 28 months that was phase coupled to a harmonic with a period of 14 months. An additional nonlinearly interacting triad was found among modes with periods of 10, 16 and 26 months. Local biphase spectra determined that the nonlinear interactions were not quadratic and that the effect of the nonlinearities was to produce non-smoothly varying oscillations. The oscillations were found to be skewed so that negative QBO regimes were preferred, and also asymmetric in the sense that phase transitions between the easterly and westerly phases occurred more rapidly than those from westerly to easterly regimes.
Reciprocal relations based on the non-stationary Boltzmann equation
NASA Astrophysics Data System (ADS)
Sharipov, Felix
2012-03-01
The reciprocal relations for open gaseous systems are obtained on the basis of main properties of the non-stationary Boltzmann equation and gas-surface interaction law. It is shown that the main principles to derive the kinetic coefficients satisfying the reciprocal relations remain the same as those used for time-independent gaseous systems [F. Sharipov, Onsager-Casimir reciprocal relations based on the Boltzmann equation and gas-surface interaction law single gas, Phys. Rev. 73 (2006) 026110]. First, the kinetic coefficients are obtained from the entropy production expression; then it is proved that the coefficient matrix calculated for time reversed source functions is symmetric. The proof is based on the reversibility of the gas-gas and gas-surface interactions. Three examples of applications of the present theory are given. None of these examples can be treated in the frame of the classical Onsager-Casimir reciprocal relations, which are valid only in a particular case, when the kinetic coefficients are odd or even with respect to the time reversion. The approach is generalized for gaseous mixtures.
Progress in Operational Analysis of Launch Vehicles in Nonstationary Flight
NASA Technical Reports Server (NTRS)
James, George; Kaouk, Mo; Cao, Timothy
2013-01-01
This paper presents recent results in an ongoing effort to understand and develop techniques to process launch vehicle data, which is extremely challenging for modal parameter identification. The primary source of difficulty is due to the nonstationary nature of the situation. The system is changing, the environment is not steady, and there is an active control system operating. Hence, the primary tool for producing clean operational results (significant data lengths and data averaging) is not available to the user. This work reported herein uses a correlation-based two step operational modal analysis approach to process the relevant data sets for understanding and development of processes. A significant drawback for such processing of short time histories is a series of beating phenomena due to the inability to average out random modal excitations. A recursive correlation process coupled to a new convergence metric (designed to mitigate the beating phenomena) is the object of this study. It has been found in limited studies that this process creates clean modal frequency estimates but numerically alters the damping.
Non-stationary wave height climate modeling and simulation
NASA Astrophysics Data System (ADS)
Solari, S.; Losada, M. A.
2011-09-01
The most popular methods of simulating time series for wave heights and other meteorological and oceanic variables are based on the use of autoregressive models and the transformation of variables to make them normal and stationary. Generally, when these models are used, attention is centered on their capacity to represent the autocorrelation of the series. In this article, a simulation model is proposed that is based on the following: (i) a non-stationary parametric mixture model for the marginal distribution of the variable, that combines a log-normal distribution for main-mass regime and generalized Pareto distributions for upper and lower tail regimes, and (ii) the use of copulas to model the time dependency of the variable. The model has been evaluated by comparing the original series and the simulated series in terms of the autocorrelation function, the mean, the annual maxima and peaks-over-threshold regimes, and the persistences regime. It has also been compared to an ARMA model and found to yield more satisfactory results.
NASA Technical Reports Server (NTRS)
Lang, Harold R.
1991-01-01
A new approach to stratigraphic analysis is described which uses photogeologic and spectral interpretation of multispectral remote sensing data combined with topographic information to determine the attitude, thickness, and lithology of strata exposed at the surface. The new stratigraphic procedure is illustrated by examples in the literature. The published results demonstrate the potential of spectral stratigraphy for mapping strata, determining dip and strike, measuring and correlating stratigraphic sequences, defining lithofacies, mapping biofacies, and interpreting geological structures.
NASA Technical Reports Server (NTRS)
Pounds, K. A.; Reeves, J. N.; Page, K. L.; OBrien, P. T.
2004-01-01
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in September 2002, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below -1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was X-ray bright indicated the dominant spectral variability was due to a steep power law or cool Comptonised thermal emission. Four further XMM-Newton observations, with 1H 0419-577 in intermediate flux states, now support that conclusion, while we also find the variable emission component in intermediate state difference spectra to be strongly modified by absorption in low ionisation matter. The variable soft excess then appears to be an artefact of absorption of the underlying continuum while the core soft emission can be attributed to re- combination in an extended region of more highly ionised gas. We note the wider implications of finding substantial cold dense matter overlying (or embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.
Pulsed thermography in multiple infrared spectral bands
NASA Astrophysics Data System (ADS)
Netzelmann, U.; Abuhamad, M.
2010-03-01
Spectrally resolved active thermography by flash pulse excitation was performed in four sub-bands of a mid-wave infrared camera using spectral filtering and in the full long-wave band of a second infrared camera. On zirconia thermal barrier coatings on steel and PVC blocks, spectrally dependent decay rates of the thermal contrast were found. The observed behaviour can be explained by the infrared spectra of the specimens.
NASA Astrophysics Data System (ADS)
Liu, Tao; Yan, Shaoze; Zhang, Wei
2016-06-01
Deployable structures have been widely used in on-orbit servicing spacecrafts, and the vibration properties of such structures have become increasingly important in the aerospace industry. The constant-Q nonstationary Gabor transform (CQ-NSGT) is introduced in this paper to accurately evaluate the variation in the frequency and amplitude of vibration signals along with time. First, an example signal is constructed on the basis of the vibration properties of deployable structures and is processed by the short-time Fourier transform, Wigner-Ville distribution, Hilbert-Huang transform, and CQ-NSGT. Results show that time and frequency resolutions are simultaneously fine only by employing CQ-NSGT. Subsequently, a zero padding operation is conducted to correct the calculation error at the end of the transform results. Finally, a set of experimental devices is constructed. The vibration signal of the experimental mode is processed by CQ-NSGT. On this basis, the experimental signal properties are discussed. This time-frequency method may be useful for formulating the dynamics for complex deployable structures.
On the Application of Hilbert Spectral Analysis for Climate Studies
NASA Technical Reports Server (NTRS)
Huang, Norden E.; Koblinsky, Chester J. (Technical Monitor)
2001-01-01
The Hilbert spectral analysis (Huang et al, 1998, Proceedings of the Royal Society of London, A 454, pp 903-995) consisted of two steps: First, the data has to be reduced into a finite number of Intrinsic Mode Function by the Empirical Mode Decomposition method, then the resulting Intrinsic Mode Functions are converted to time-frequency-energy distribution through Hilbert transform. In this approach, the Empirical Mode Functions served as the basis functions with which the data is expanded. This basis function is adaptive, and the decomposition is nonlinear. Furthermore, as the Hilbert transform is a singular transform, it retains a high degree of local information. The instantaneous frequency is determined by differentiation of the phase function; therefore, there is no restriction of the 'uncertainty principle' for all the time-frequency analysis resulting from a priori basis approach. With the adaptive basis and the instantaneous frequency, the Hilbert Spectral analysis can represent data from nonlinear and nonstationary processes without resorting to the harmonics. Another advantage of using instantaneous frequency is the ability to find out frequency from limited length of data, which is a critical problem in climate studies. As the processes driving the climate changes could be both nonlinear and nonstationary, the Hilbert Spectral Analysis could be of great use in examining the underlying mechanisms. A preliminary study based on the length of day data will be presented as example for the application of the Hilbert Spectral Analysis for climate study.
NASA Astrophysics Data System (ADS)
Zimroz, Radoslaw; Bartkowiak, Anna
2013-07-01
This paper deals with the diagnostics of planetary gearboxes under nonstationary operating conditions. In most diagnostics applications, energy of vibration signals (calculated directly from time series or extracted from spectral representation of signal) is used. Unfortunately energy based features are sensitive to load conditions and it makes diagnostics difficult. In this paper we used energy based 15D data vectors (namely spectral amplitudes of planetary mesh frequency and its harmonics) in order to investigate if it is possible to improve diagnostics efficiency in comparison to previous, one dimensional, approaches proposed for the same problem. Two multivariate methods, Principal Component Analysis (PCA) and Canonical Discriminant Analysis (CDA), were used as techniques for data analysis. We used these techniques in order to investigate dimensionality of the data and to visualize data in 3D and 2D spaces in order to understand data behavior and assess classification ability. As a case study the data from two planetary gearboxes used in complex mining machines (one in bad condition and the other in good condition) were analyzed. For these two machines more than 2000 15D vectors were acquired. It should be noted that due to non-stationarity of loading conditions, previous diagnostics results obtained using other techniques were moderately good (ca. 80% recognition efficiency); however there is still some need to improve diagnostics classification ability. After application of the proposed approaches it was found that the entire data could be reduced to 2 dimensions whereby data instances became visible and a good discriminant function (characterized by a misclassification rate of .0023, i.e. only 5 erroneous classifications for a total of 2183 instances) could be derived. This paper suggests a novel way for condition monitoring of planetary gearboxes based on multivariate statistics. The emphasis is put on the algebraic and geometric interpretations of the PCA
NASA Astrophysics Data System (ADS)
Lang, Harold R.
1991-09-01
Stratigraphic and structural studies of the Wind River and Bighorn basins, Wyoming, and the Guerrero-Morelos basin, Mexico, have resulted in development of ''spectral stratigraphy.'' This approach to stratigraphic analysis uses photogeologic and spectral interpretation of multispectral remote sensing data combined with topographic information to determine the attitude, thickness, and lithology of strata exposed at the surface. This paper reviews selected published examples that illustrate this new stratigraphic procedure. Visible to thermal infrared laboratory, spectral measurements of sedimentary rocks are the physical basis for spectral stratigraphy. Results show that laboratory, field, and remote spectroscopy can augment conventional laboratory and field methods for petrologic analysis, stratigraphic correlation, interpretation of depositional environments, and construction of facies models. Landsat thematic mapper data are used to map strata and construct stratigraphic columns and structural cross sections at 1:24,000 scale or less. Experimental multispectral thermal infrared aircraft data facilitate lithofacies/biofacies analyses. Visible short-wavelength infrared imaging spectrometer data allow remote determination of the stratigraphic distribution of iron oxides, quartz, calcite, dolomite, gypsum, specific clay species, and other minerals diagnostic of environments of deposition. Development of a desk-top, computer-based, geologic analysis system that provides for automated application of these approaches to coregistered digital image and topographic data portends major expansion in the use of spectral stratigraphy for purely scientific (lithospheric research) or practical (resource exploration) objectives.
Climate Informed Low Flow Frequency Analysis Using Nonstationary Modeling
NASA Astrophysics Data System (ADS)
Liu, D.; Guo, S.; Lian, Y.
2014-12-01
Stationarity is often assumed for frequency analysis of low flows in water resources management and planning. However, many studies have shown that flow characteristics, particularly the frequency spectrum of extreme hydrologic events,were modified by climate change and human activities and the conventional frequency analysis without considering the non-stationary characteristics may lead to costly design. The analysis presented in this paper was based on the more than 100 years of daily flow data from the Yichang gaging station 44 kilometers downstream of the Three Gorges Dam. The Mann-Kendall trend test under the scaling hypothesis showed that the annual low flows had significant monotonic trend, whereas an abrupt change point was identified in 1936 by the Pettitt test. The climate informed low flow frequency analysis and the divided and combined method are employed to account for the impacts from related climate variables and the nonstationarities in annual low flows. Without prior knowledge of the probability density function for the gaging station, six distribution functions including the Generalized Extreme Values (GEV), Pearson Type III, Gumbel, Gamma, Lognormal, and Weibull distributions have been tested to find the best fit, in which the local likelihood method is used to estimate the parameters. Analyses show that GEV had the best fit for the observed low flows. This study has also shown that the climate informed low flow frequency analysis is able to exploit the link between climate indices and low flows, which would account for the dynamic feature for reservoir management and provide more accurate and reliable designs for infrastructure and water supply.
Separation of stationary and non-stationary sources with a generalized eigenvalue problem.
Hara, Satoshi; Kawahara, Yoshinobu; Washio, Takashi; von Bünau, Paul; Tokunaga, Terumasa; Yumoto, Kiyohumi
2012-09-01
Non-stationary effects are ubiquitous in real world data. In many settings, the observed signals are a mixture of underlying stationary and non-stationary sources that cannot be measured directly. For example, in EEG analysis, electrodes on the scalp record the activity from several sources located inside the brain, which one could only measure invasively. Discerning stationary and non-stationary contributions is an important step towards uncovering the mechanisms of the data generating system. To that end, in Stationary Subspace Analysis (SSA), the observed signal is modeled as a linear superposition of stationary and non-stationary sources, where the aim is to separate the two groups in the mixture. In this paper, we propose the first SSA algorithm that has a closed form solution. The novel method, Analytic SSA (ASSA), is more than 100 times faster than the state-of-the-art, numerically stable, and guaranteed to be optimal when the covariance between stationary and non-stationary sources is time-constant. In numerical simulations on wide range of settings, we show that our method yields superior results, even for signals with time-varying group-wise covariance. In an application to geophysical data analysis, ASSA extracts meaningful components that shed new light on the Pi 2 pulsations of the geomagnetic field. PMID:22551683
Solar Spectral Irradiance and Climate
NASA Technical Reports Server (NTRS)
Pilewskie, P.; Woods, T.; Cahalan, R.
2012-01-01
Spectrally resolved solar irradiance is recognized as being increasingly important to improving our understanding of the manner in which the Sun influences climate. There is strong empirical evidence linking total solar irradiance to surface temperature trends - even though the Sun has likely made only a small contribution to the last half-century's global temperature anomaly - but the amplitudes cannot be explained by direct solar heating alone. The wavelength and height dependence of solar radiation deposition, for example, ozone absorption in the stratosphere, absorption in the ocean mixed layer, and water vapor absorption in the lower troposphere, contribute to the "top-down" and "bottom-up" mechanisms that have been proposed as possible amplifiers of the solar signal. New observations and models of solar spectral irradiance are needed to study these processes and to quantify their impacts on climate. Some of the most recent observations of solar spectral variability from the mid-ultraviolet to the near-infrared have revealed some unexpected behavior that was not anticipated prior to their measurement, based on an understanding from model reconstructions. The atmospheric response to the observed spectral variability, as quantified in climate model simulations, have revealed similarly surprising and in some cases, conflicting results. This talk will provide an overview on the state of our understanding of the spectrally resolved solar irradiance, its variability over many time scales, potential climate impacts, and finally, a discussion on what is required for improving our understanding of Sun-climate connections, including a look forward to future observations.
Fuzzy stochastic elements method. Spectral approach
NASA Astrophysics Data System (ADS)
Sniady, Pawel; Mazur-Sniady, Krystyna; Sieniawska, Roza; Zukowski, Stanislaw
2013-05-01
We study a complex dynamic problem, which concerns a structure with uncertain parameters subjected to a stochastic excitation. Formulation of such a problem introduces fuzzy random variables for parameters of the structure and fuzzy stochastic processes for the load process. The uncertainty has two sources, namely the randomness of structural parameters such as geometry characteristics, material and damping properties, load process and imprecision of the theoretical model and incomplete information or uncertain data. All of these have a great influence on the response of the structure. By analyzing such problems we describe the random variability using the probability theory and the imprecision by use of fuzzy sets. Due to the fact that it is difficult to find an analytic expression for the inversion of the stochastic operator in the stochastic differential equation, a number of approximate methods have been proposed in the literature which can be connected to the finite element method. To evaluate the effects of excitation in the frequency domain we use the spectral density function. The spectral analysis is widely used in stochastic dynamics field of linear systems for stationary random excitation. The concept of the evolutionary spectral density is used in the case of non-stationary random excitation. We solve the considered problem using fuzzy stochastic finite element method. The solution is based on the idea of a fuzzy random frequency response vector for stationary input excitation and a transient fuzzy random frequency response vector for the fuzzy non-stationary one. We use the fuzzy random frequency response vector and the transient fuzzy random frequency response vector in the context of spectral analysis in order to determine the influence of structural uncertainty on the fuzzy random response of the structure. We study a linear system with random parameters subjected to two particular cases of stochastic excitation in a frequency domain. The first one
A Comparative Study of Stationary and Non-stationary Wind Models Using Field Measurements
NASA Astrophysics Data System (ADS)
Chen, Jun; Hui, Michael C. H.; Xu, Y. L.
2007-01-01
We present a comparative study of the conventional stationary wind speed model and a newly proposed non-stationary wind speed model using field measurements. The concept of, and the differences between, the two wind models are briefly reviewed. Wind data recorded by a field measurement system for wind turbulence parameters (FMS-WTP) of 1-year duration are analyzed using the two wind models. Comparisons were made between the wind characteristics obtained from the two models, including hourly mean wind speed, turbulence intensity, the wind spectrum, integral length scale, root coherence function and probability density function. The effects of wind types (monsoon or typhoon), statistical properties (stationary or non-stationary), and surface roughness (open-sea fetch or overland fetch) on wind characteristics are discussed. The comparative study demonstrates that the non-stationary wind model appears to be more appropriate than the conventional stationary wind speed model for characterizing turbulent winds of one-hour duration over complex terrain.
Causal Inference Based on the Analysis of Events of Relations for Non-stationary Variables.
Yin, Yu; Yao, Dezhong
2016-01-01
The main concept behind causality involves both statistical conditions and temporal relations. However, current approaches to causal inference, focusing on the probability vs. conditional probability contrast, are based on model functions or parametric estimation. These approaches are not appropriate when addressing non-stationary variables. In this work, we propose a causal inference approach based on the analysis of Events of Relations (CER). CER focuses on the temporal delay relation between cause and effect, and a binomial test is established to determine whether an "event of relation" with a non-zero delay is significantly different from one with zero delay. Because CER avoids parameter estimation of non-stationary variables per se, the method can be applied to both stationary and non-stationary signals. PMID:27389921
Nonstationary desertification dynamics of desert oasis under climate change and human interference
NASA Astrophysics Data System (ADS)
Huang, Guohe; Qin, Xiaosheng; He, Li; Zhang, Hua; Li, Yongping; Li, Zhong
2015-12-01
Desertification is becoming a major ecological concern in arid and semiarid regions, especially under climate change. Globally, it is burning up lands for human habitats with a rapidly spreading tendency. Many scientists have been struggling to explore the related mechanisms. Challenges remain in revealing the fundamental principle in terms of desert-oasis interactions that are associated with nonstationary variations. Here we present a theory of desertification dynamics through examining nonstationary effects of climate change and human interference. We hypothesize that such dynamics can be described as the fate and transport of dry air mass continuously generated from desert. We simulate a region in northwestern China and reveal that dynamics of the nonstationary desertification process is subject to interactive impacts from a variety of factors. Our study moves forward the field of desertification studies through initiation of the dynamics and nonstationarity concepts which allow the fundamental mechanism to be disclosed.
Causal Inference Based on the Analysis of Events of Relations for Non-stationary Variables
Yin, Yu; Yao, Dezhong
2016-01-01
The main concept behind causality involves both statistical conditions and temporal relations. However, current approaches to causal inference, focusing on the probability vs. conditional probability contrast, are based on model functions or parametric estimation. These approaches are not appropriate when addressing non-stationary variables. In this work, we propose a causal inference approach based on the analysis of Events of Relations (CER). CER focuses on the temporal delay relation between cause and effect, and a binomial test is established to determine whether an “event of relation” with a non-zero delay is significantly different from one with zero delay. Because CER avoids parameter estimation of non-stationary variables per se, the method can be applied to both stationary and non-stationary signals. PMID:27389921
Surface Stress with Non-stationary Weak Winds and Stable Stratification
NASA Astrophysics Data System (ADS)
Mahrt, L.; Thomas, Christoph K.
2016-04-01
The behaviour of turbulent transport in the weak-wind, stably-stratified, boundary layer over land is examined in terms of the non-stationarity of the wind field using measurements from three field programs. These field programs include towers ranging from 12 to 20 m in height and an extensive horizontal network of sonic anemometers. The relationship of the friction velocity to the stratification and non-stationary submeso motions is investigated from several points of view and nominally quantified. The relationship of the turbulence to the stratification is less systematic than expected partly due to enhancement of the turbulence by submeso motions. Cause and effect relationships are difficult to isolate because the non-stationary momentum flux significantly modifies the profile of the non-stationary mean flow. The link between the turbulence and accelerations at the surface is examined in terms of the changing vertical structure of the wind profile and sudden increases in the downward transport of momentum.
Recognizing Non-Stationary Walking based on Gait Analysis using Laser Scanners
NASA Astrophysics Data System (ADS)
Nakamura, Katsuyuki; Shao, Xiaowei; Zhao, Huijing; Shibasaki, Ryosuke
In this paper the authors propose a method for recognizing non-stationary walking based on a gait analysis using multiple laser range scanners. The proposed method consists of the following procedures: (1) people tracking; (2) detection of gait features; (3) recognition of non-stationary walking. First, people tracking is performed by recognizing patterns in which the range data obtained near ankle rhythmically. Next, gait analysis is performed by the spatio-temporal clustering using Mean Shift algorithm. Finally, One Class Support Vector Machine (One Class SVM) is applied for learning and classifying a non-stationary walking. The experiment in a station concourse in Tokyo shows the overall accuracy of 98.4% by the proposed method.
A new adaptive exponential smoothing method for non-stationary time series with level shifts
NASA Astrophysics Data System (ADS)
Monfared, Mohammad Ali Saniee; Ghandali, Razieh; Esmaeili, Maryam
2014-07-01
Simple exponential smoothing (SES) methods are the most commonly used methods in forecasting and time series analysis. However, they are generally insensitive to non-stationary structural events such as level shifts, ramp shifts, and spikes or impulses. Similar to that of outliers in stationary time series, these non-stationary events will lead to increased level of errors in the forecasting process. This paper generalizes the SES method into a new adaptive method called revised simple exponential smoothing (RSES), as an alternative method to recognize non-stationary level shifts in the time series. We show that the new method improves the accuracy of the forecasting process. This is done by controlling the number of observations and the smoothing parameter in an adaptive approach, and in accordance with the laws of statistical control limits and the Bayes rule of conditioning. We use a numerical example to show how the new RSES method outperforms its traditional counterpart, SES.
The evolution of the electric field at a nonstationary perpendicular shock
Yang, Z. W.; Lu, Q. M.; Wang, S.
2009-12-15
Particle-in-cell simulations evidenced that supercritical, quasiperpendicular shocks are nonstationary and may suffer a self-reformation on the ion gyroscale. In this brief communication, we investigate the evolution of the electric field at a nonstationary, supercritial perpendicular shock. The contributions of the ion Lorentz, Hall, and electron pressure terms to the electric field are analyzed. During the evolution of the perpendicular shock, a new ramp may be formed in front of the old ramp, and its amplitude becomes larger and larger. At last, the new ramp exceeds the old one, and such a nonstationary process can be formed periodically. When the new ramp begins to be formed in front of the old ramp, the Hall term becomes more and more important. The electric field E{sub x} is dominated by the Hall term when the new ramp exceeds the old one. The significance of the evolution of the electric field on shock acceleration is also discussed.
Seismic trace interpolation with nonstationary prediction-error filters
NASA Astrophysics Data System (ADS)
Crawley, Sean Edan
Theory predicts that time and space domain prediction-error filters (PEFs) may be used to interpolate aliased signals. I explore the utility of the theory, applying PEF-based interpolation to aliased seismic field data, to dealias it without lowpass filtering by inserting new traces between those originally recorded. But before theoretical potential is realized on 3-D field data, some practical aspects must be addressed. Most importantly, while PEF theory assumes stationarity, seismic data are not stationary. We can divide the data into assumed-stationary patches, as is often done in other interpolation algorithms. We interpolate with PEFs in patches, and get near-perfect results in those parts of the data where events are mostly local plane waves, lying along straight lines. However, we find that the results are unimpressive where the data are noticeably curved. As an alternative to assumed-stationary patches, I calculate PEFs everywhere in the data, and force filters which are calculated at adjacent coordinates in data space to be similar to each other. The result is a set of smoothly-varying PEFs, which we call adaptive or nonstationary. The coefficients of the adaptive PEFs constitute a large model space. Using SEP's helical coordinate, we precondition the filter calculation problem so that it converges in manageable time. To address the difficult problem of curved events not fitting the plane wave model, we can control the degree of smoothness in the filters as a function of direction in data coordinates. To get statistically robust filter estimates, we want to maximize the area in data space over which we estimate a filter, while still approximately honoring stationarity. The local dip spectrum on a CMP gather is nearly constant in a region which is elongated in the radial direction, so I estimate PEFs that are smooth along radial lines but which may vary quickly with radial angle. In principle that addresses the curvature issue, and I find it performs well
NASA Astrophysics Data System (ADS)
Worthington, R. M.
2015-06-01
Mountain waves can cause surface wind variations shown by synthetic aperture radar measurements of sea surface roughness. Since mountain waves are quasi-stationary, it can be difficult to identify the mountain-wave component of a surface anemometer time series. However, orographic gravity waves are non-stationary on rare occasions. This study examines two anomalous case studies found in four years of data, when surface wind downwind of mountains oscillates with a period of 20-60 min. Meso-strato-troposphere radar shows vertical wind oscillations of the same period, the amplitude a maximum in the lower troposphere, apparently trapped waves. Satellite images show ordinary mountain-wave clouds with horizontal wavelengths 9.0 and 5.7 km in the two case studies. Phase speeds are 5.3 and 4.8 m s-1, assuming a fixed wavelength. Surface wind direction reverses a few times through 180° in one instance, consistent with propagating rotors. A multi-beam method is used to find if phase propagation is upwind or downwind for one case study, based on cross-correlation of the high-frequency component of wind time series in off-vertical radar beams. Surprisingly, phase propagation is found to be mostly upwind. Both changing background wind and/or stability, and non-linear wave interactions, can cause mountain waves to drift upwind or downwind, and the exact cause could be resolved by numerical modelling.
Parity retransmission hybrid ARQ using rate 1/2 convolutional codes on a nonstationary channel
NASA Technical Reports Server (NTRS)
Lugand, Laurent R.; Costello, Daniel J., Jr.; Deng, Robert H.
1989-01-01
A parity retransmission hybrid automatic repeat request (ARQ) scheme is proposed which uses rate 1/2 convolutional codes and Viterbi decoding. A protocol is described which is capable of achieving higher throughputs than previously proposed parity retransmission schemes. The performance analysis is based on a two-state Markov model of a nonstationary channel. This model constitutes a first approximation to a nonstationary channel. The two-state channel model is used to analyze the throughput and undetected error probability of the protocol presented when the receiver has both an infinite and a finite buffer size. It is shown that the throughput improves as the channel becomes more bursty.
Experimental study of nonstationary regimes of ascent of a single bubble
NASA Astrophysics Data System (ADS)
Arkhipov, V. A.; Vasenin, I. M.; Usanina, A. S.
2013-09-01
Results of experimental study of the dynamics of ascent of a single spherical bubble in a viscous fluid at small Reynolds numbers (Re < 1) have been presented. A refined empirical dependence has been obtained for the resistance coefficient in a stationary regime of motion of the bubble. The influence of nonstationary and "hereditary" effects on the dynamics of ascent of the bubble has been evaluated. A substantial influence of the Basset force on the characteristic of a nonstationary regime of motion of the bubble, in particular, on the characteristic time of dynamic relaxation, in the region of small Reynolds numbers has been shown.
Charged particle tunnels from the stationary and non-stationary Kerr-Newman black holes
NASA Astrophysics Data System (ADS)
Chen, Deyou; Yang, Shuzheng
2007-09-01
Considering the unfixed background space-time and self-gravitational interaction, we view the Hawking radiation of a stationary Kerr-Newman black hole by Hamilton-Jacobi method. Meanwhile, extending this work to non-stationary black holes, we attempt to investigate the Hawking radiation of the non-stationary Kerr-Newman black hole. Both of the results show the tunneling probabilities are related to the change of Bekenstein- Hawking entropy and the radiation spectrums deviate from the purely thermal one, which is in accordance with the known result.
NASA Astrophysics Data System (ADS)
Solodov, V. G.; Gnesin, V. I.
1997-12-01
Three-dimensional nonstationary model of aerodynamical interaction of turbine stage and exhaust hood is realized, based on nonstationary 3D codes for calculation of inviscid transonic flow through stage[3] and exhaust hood[4] which consist of diffuser and space under casing. The codes are built with the use of the explicit Godunov’s 2nd order difference scheme. Some results of flow simulation through the compartments “stage-exhaust hood,” “stage-exhaust axial-radial diffuser” for wide range of volumetric flow rates are represented.
Calculation of non-stationary aerodynamic forces in the near sonic range
NASA Technical Reports Server (NTRS)
Teipel, I.
1988-01-01
The development of a mathematical method for calculating nonstationary supersonic flow in the near-sonic range is described. A perturbation formula is derived based on the exact stationary values; it is applicable to the equation for potential. The problem can thus be divided into stationary and nonstationary fields. The pressure distribution in an oscillating profile is determined, based on hyperbolic differential equations. It is shown that there are important corollaries concerning the application of linear theory. With suitable extrapolations, linear theory can be used up to about Mach 0.8. Linear theory is not applicable, however, when determining the moment coefficients; for this case, a special technique is described.
Hartwig, J. T.; Stokman, J. V.
2013-02-15
We realize an extended version of the trigonometric Cherednik algebra as affine Dunkl operators involving Heaviside functions. We use the quadratic Casimir element of the extended trigonometric Cherednik algebra to define an explicit nonstationary Schroedinger equation with delta-potential. We use coordinate Bethe ansatz methods to construct solutions of the nonstationary Schroedinger equation in terms of generalized Bethe wave functions. It is shown that the generalized Bethe wave functions satisfy affine difference Knizhnik-Zamolodchikov equations as functions of the momenta. The relation to the vector valued root system analogs of the quantum Bose gas on the circle with delta-function interactions is indicated.
Ibarria, L; Lindstrom, P; Rossignac, J
2006-11-17
Many scientific, imaging, and geospatial applications produce large high-precision scalar fields sampled on a regular grid. Lossless compression of such data is commonly done using predictive coding, in which weighted combinations of previously coded samples known to both encoder and decoder are used to predict subsequent nearby samples. In hierarchical, incremental, or selective transmission, the spatial pattern of the known neighbors is often irregular and varies from one sample to the next, which precludes prediction based on a single stencil and fixed set of weights. To handle such situations and make the best use of available neighboring samples, we propose a local spectral predictor that offers optimal prediction by tailoring the weights to each configuration of known nearby samples. These weights may be precomputed and stored in a small lookup table. We show that predictive coding using our spectral predictor improves compression for various sources of high-precision data.
Kim, Sangtae; Gupta, Nitin; Bandeira, Nuno; Pevzner, Pavel A.
2009-01-01
Database search tools identify peptides by matching tandem mass spectra against a protein database. We study an alternative approach when all plausible de novo interpretations of a spectrum (spectral dictionary) are generated and then quickly matched against the database. We present a new MS-Dictionary algorithm for efficiently generating spectral dictionaries and demonstrate that MS-Dictionary can identify spectra that are missed in the database search. We argue that MS-Dictionary enables proteogenomics searches in six-frame translation of genomic sequences that may be prohibitively time-consuming for existing database search approaches. We show that such searches allow one to correct sequencing errors and find programmed frameshifts. PMID:18703573
Spectral density of velocity fluctuations under switching field conditions in graphene
NASA Astrophysics Data System (ADS)
Iglesias, J. M.; Martín, M. J.; Pascual, E.; Rengel, R.
2016-05-01
In this paper we present an analysis of the velocity fluctuations during transient regimes arising from an abrupt shift of the electric field in bulk monolayer graphene. For this purpose a material Ensemble Monte Carlo simulator is used to examine these fluctuations by means of the transient autocorrelation function and power spectral density. The evolution of these quantities as well as the non-stationary phenomena taking place during the transients is explained with a microscopic approach.
NASA Astrophysics Data System (ADS)
Wisdom, Jack
2015-10-01
The Wisdom-Holman mapping method and its variations have become a mainstay of research in solar system dynamics. But the method is not without its limitations. Rauch & Holman noted that at large eccentricities sufficiently small steps must be taken to resolve the pericenter. In this paper, I explore in more detail what it means to resolve the pericenter.
NASA Astrophysics Data System (ADS)
Bracken, C. W.; Rajagopalan, B.; Zagona, E. A.
2011-12-01
Upper Colorado River Basin annual flow exhibits very low autocorrelation but regime shifting behavior causing long departures from the historical average flow producing sustained wet and dry periods. Traditional stochastic time series models do not capture this feature thereby misleading the water resources system risk and consequently impacting the management and planning efforts. To address this, we developed a nonstationary Hidden Markov (HM) model with Gamma component distributions, as opposed to Normal distributions which is widely used in literature, for stochastic simulation and short term forecasting. Global decoding from this model reveals and captures strong underlying persistent structure in the Lees Ferry flow time series. In addition to capturing the shifting mean, simulations from this model have a 20% greater chance than a first order Auto Regressive model (AR1), the best time series model for this data, of simulating wet and dry runs of 6 or more years. Relative to AR1 the HM model also captures the spectral features quite well. When applied to short term forecasting (i.e. of 1-2 years) they show higher skill relative to climatology but also to an AR1 model.
Depth-resolved fluorescence of biological tissue
NASA Astrophysics Data System (ADS)
Wu, Yicong; Xi, Peng; Cheung, Tak-Hong; Yim, So Fan; Yu, Mei-Yung; Qu, Jianan Y.
2005-06-01
The depth-resolved autofluorescence ofrabbit oral tissue, normal and dysplastic human ectocervical tissue within l20μm depth were investigated utilizing a confocal fluorescence spectroscopy with the excitations at 355nm and 457nm. From the topmost keratinizing layer of oral and ectocervical tissue, strong keratin fluorescence with the spectral characteristics similar to collagen was observed. The fluorescence signal from epithelial tissue between the keratinizing layer and stroma can be well resolved. Furthermore, NADH and FADfluorescence measured from the underlying non-keratinizing epithelial layer were strongly correlated to the tissue pathology. This study demonstrates that the depth-resolved fluorescence spectroscopy can reveal fine structural information on epithelial tissue and potentially provide more accurate diagnostic information for determining tissue pathology.
Self-Consistent Non-Stationary Theory of Multipactor in DLA Structures
Sinitsyn, O. V.; Nusinovich, G. S.; Antonsen, T. M.; Kishek, R.
2009-01-22
In this paper a non-stationary self-consistent theoretical model of multipactor in dielectric loaded accelerator structures is proposed. In comparison with our previous work, the effects of the cylindricity are included. The corresponding numerical implementation of the model is described and some simulation results are shown.
NASA Astrophysics Data System (ADS)
Guo, Leicheng; van der Wegen, Mick; Jay, David A.; Matte, Pascal; Wang, Zheng Bing; Roelvink, Dano; He, Qing
2015-05-01
River-tide dynamics remain poorly understood, in part because conventional harmonic analysis (HA) does not cope effectively with nonstationary signals. To explore nonstationary behavior of river tides and the modulation effects of river discharge, this work analyzes tidal signals in the Yangtze River estuary using both HA in a nonstationary mode and continuous wavelet transforms (CWT). The Yangtze is an excellent natural laboratory to analyze river tides because of its high and variable flow, its length, and the fact that there are do dams or reflecting barriers within the tidal part of the system. Analysis of tidal frequencies by CWT and analysis of subtidal water level and tidal ranges reveal a broad range of subtidal variations over fortnightly, monthly, semiannual, and annual frequencies driven by subtidal variations in friction and by variable river discharges. We employ HA in a nonstationary mode (NSHA) by segregating data within defined flow ranges into separate analyses. NSHA quantifies the decay of the principal tides and the modulation of M4 tide with increasing river discharges. M4 amplitudes decrease far upriver (landward portion of the estuary) and conversely increase close to the ocean as river discharge increases. The fortnightly frequencies reach an amplitude maximum upriver of that for over tide frequencies, due to the longer wavelength of the fortnightly constituents. These methods and findings should be applicable to large tidal rivers globally and have broad implications regarding management of navigation channels and ecosystems in tidal rivers.
Figueiredo, Antonio C. A.; Bizarro, Joao P. S.
2006-10-15
The spectrogram capability to track the amplitude of signal components is discussed. A study using theoretical signal models shows that significant discrepancies may exist between the evolutions of the amplitude of a nonstationary signal component and of the magnitude of the corresponding spectrogram. To illustrate the practical consequences of this spectrogram shortcoming, the growth of magnetohydrodynamic modes observed in the JET tokamak is addressed.
Robust H∞ control of active vehicle suspension under non-stationary running
NASA Astrophysics Data System (ADS)
Guo, Li-Xin; Zhang, Li-Ping
2012-12-01
Due to complexity of the controlled objects, the selection of control strategies and algorithms in vehicle control system designs is an important task. Moreover, the control problem of automobile active suspensions has been become one of the important relevant investigations due to the constrained peculiarity and parameter uncertainty of mathematical models. In this study, after establishing the non-stationary road surface excitation model, a study on the active suspension control for non-stationary running condition was conducted using robust H∞ control and linear matrix inequality optimization. The dynamic equation of a two-degree-of-freedom quarter car model with parameter uncertainty was derived. The H∞ state feedback control strategy with time-domain hard constraints was proposed, and then was used to design the active suspension control system of the quarter car model. Time-domain analysis and parameter robustness analysis were carried out to evaluate the proposed controller stability. Simulation results show that the proposed control strategy has high systemic stability on the condition of non-stationary running and parameter uncertainty (including suspension mass, suspension stiffness and tire stiffness). The proposed control strategy can achieve a promising improvement on ride comfort and satisfy the requirements of dynamic suspension deflection, dynamic tire loads and required control forces within given constraints, as well as non-stationary running condition.
Stationary and non-stationary nonlinear optical spectroscopy on surface polaritons
NASA Technical Reports Server (NTRS)
Ponath, H. E.
1984-01-01
A phenomenological theory is given for non-stationary electromagnetic surface waves propagating along the boundary plane between two homogeneous isotropic media. The description of nonlinear optical effects using shortened wave equations is demonstrated for spontaneous and simulated Raman scattering processes on surface polaritons.
Non-stationary dynamics of climate variability in synchronous influenza epidemics in Japan
NASA Astrophysics Data System (ADS)
Onozuka, Daisuke; Hagihara, Akihito
2015-09-01
Seasonal variation in the incidence of influenza is widely assumed. However, few studies have examined non-stationary relationships between global climate factors and influenza epidemics. We examined the monthly incidence of influenza in Fukuoka, Japan, from 2000 to 2012 using cross-wavelet coherency analysis to assess the patterns of associations between indices for the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). The monthly incidence of influenza showed cycles of 1 year with the IOD and 2 years with ENSO indices (Multivariate, Niño 4, and Niño 3.4). These associations were non-stationary and appeared to have major influences on the synchrony of influenza epidemics. Our study provides quantitative evidence that non-stationary associations have major influences on synchrony between the monthly incidence of influenza and the dynamics of the IOD and ENSO. Our results call for the consideration of non-stationary patterns of association between influenza cases and climatic factors in early warning systems.
Nonstationary Extreme Value Analysis in a Changing Climate: A Software Package
NASA Astrophysics Data System (ADS)
Cheng, L.; AghaKouchak, A.; Gilleland, E.
2013-12-01
Numerous studies show that climatic extremes have increased substantially in the second half of the 20th century. For this reason, analysis of extremes under a nonstationary assumption has received a great deal of attention. This paper presents a software package developed for estimation of return levels, return periods, and risks of climatic extremes in a changing climate. This MATLAB software package offers tools for analysis of climate extremes under both stationary and non-stationary assumptions. The Nonstationary Extreme Value Analysis (hereafter, NEVA) provides an efficient and generalized framework for analyzing extremes using Bayesian inference. NEVA estimates the extreme value parameters using a Differential Evolution Markov Chain (DE-MC) which utilizes the genetic algorithm Differential Evolution (DE) for global optimization over the real parameter space with the Markov Chain Monte Carlo (MCMC) approach and has the advantage of simplicity, speed of calculation and convergence over conventional MCMC. NEVA also offers the confidence interval and uncertainty bounds of estimated return levels based on the sampled parameters. NEVA integrates extreme value design concepts, data analysis tools, optimization and visualization, explicitly designed to facilitate analysis extremes in geosciences. The generalized input and output files of this software package make it attractive for users from across different fields. Both stationary and nonstationary components of the package are validated for a number of case studies using empirical return levels. The results show that NEVA reliably describes extremes and their return levels.
Bivariate Frequency Analysis with Nonstationary Gumbel/GEV Marginal Distributions for Rainfall Event
NASA Astrophysics Data System (ADS)
Joo, Kyungwon; Kim, Sunghun; Kim, Hanbeen; Ahn, Hyunjun; Heo, Jun-Haeng
2016-04-01
Multivariate frequency analysis has been developing for hydrological data recently. Particularly, the copula model has been used as an effective method which has no limitation on deciding marginal distributions. The time-series rainfall data can be characterized to rainfall event by inter-event time definition and each rainfall event has rainfall depth and duration. In addition, changes in rainfall depth have been studied recently due to climate change. The nonstationary (time-varying) Gumbel and Generalized Extreme Value (GEV) have been developed and their performances have been investigated from many studies. In the current study, bivariate frequency analysis has performed for rainfall depth and duration using Archimedean copula on stationary and nonstationary hourly rainfall data to consider the effect of climate change. The parameter of copula model is estimated by inference function for margin (IFM) method and stationary/nonstationary Gumbel and GEV distributions are used for marginal distributions. As a result, level curve of copula model is obtained and goodness-of-fit test is performed to choose appropriate marginal distribution among the applied stationary and nonstationary Gumbel and GEV distributions.
Effect of non-stationary climate on infectious gastroenteritis transmission in Japan.
Onozuka, Daisuke
2014-01-01
Local weather factors are widely considered to influence the transmission of infectious gastroenteritis. Few studies, however, have examined the non-stationary relationships between global climatic factors and transmission of infectious gastroenteritis. We analyzed monthly data for cases of infectious gastroenteritis in Fukuoka, Japan from 2000 to 2012 using cross-wavelet coherency analysis to assess the pattern of associations between indices for the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Infectious gastroenteritis cases were non-stationary and significantly associated with the IOD and ENSO (Multivariate ENSO Index [MEI], Niño 1 + 2, Niño 3, Niño 4, and Niño 3.4) for a period of approximately 1 to 2 years. This association was non-stationary and appeared to have a major influence on the synchrony of infectious gastroenteritis transmission. Our results suggest that non-stationary patterns of association between global climate factors and incidence of infectious gastroenteritis should be considered when developing early warning systems for epidemics of infectious gastroenteritis. PMID:24889802
NASA Astrophysics Data System (ADS)
Lin, Kai; Yang, Shu-Zheng
2009-10-01
Fermions tunneling of the non-stationary Dilaton-Maxwell black hole is investigated with general tortoise coordinate transformation. The Dirac equation is simplified by semiclassical approximation so that the Hamilton-Jacobi equation is generated. Finally the tunneling rate and the Hawking temperature is calculated.
A maximal regularity estimate for the non-stationary Stokes equation in the strip
NASA Astrophysics Data System (ADS)
Choffrut, Antoine; Nobili, Camilla; Otto, Felix
2016-04-01
In a d-dimensional strip with d ≥ 2, we study the non-stationary Stokes equation with no-slip boundary condition in the lower and upper plates and periodic boundary condition in the horizontal directions. In this paper we establish a new maximal regularity estimate in the real interpolation norm
Non-stationary dynamics of climate variability in synchronous influenza epidemics in Japan.
Onozuka, Daisuke; Hagihara, Akihito
2015-09-01
Seasonal variation in the incidence of influenza is widely assumed. However, few studies have examined non-stationary relationships between global climate factors and influenza epidemics. We examined the monthly incidence of influenza in Fukuoka, Japan, from 2000 to 2012 using cross-wavelet coherency analysis to assess the patterns of associations between indices for the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). The monthly incidence of influenza showed cycles of 1 year with the IOD and 2 years with ENSO indices (Multivariate, Niño 4, and Niño 3.4). These associations were non-stationary and appeared to have major influences on the synchrony of influenza epidemics. Our study provides quantitative evidence that non-stationary associations have major influences on synchrony between the monthly incidence of influenza and the dynamics of the IOD and ENSO. Our results call for the consideration of non-stationary patterns of association between influenza cases and climatic factors in early warning systems. PMID:25409872
NASA Technical Reports Server (NTRS)
Racette, Paul; Lang, Roger; Zhang, Zhao-Nan; Zacharias, David; Krebs, Carolyn A. (Technical Monitor)
2002-01-01
Radiometers must be periodically calibrated because the receiver response fluctuates. Many techniques exist to correct for the time varying response of a radiometer receiver. An analytical technique has been developed that uses generalized least squares regression (LSR) to predict the performance of a wide variety of calibration algorithms. The total measurement uncertainty including the uncertainty of the calibration can be computed using LSR. The uncertainties of the calibration samples used in the regression are based upon treating the receiver fluctuations as non-stationary processes. Signals originating from the different sources of emission are treated as simultaneously existing random processes. Thus, the radiometer output is a series of samples obtained from these random processes. The samples are treated as random variables but because the underlying processes are non-stationary the statistics of the samples are treated as non-stationary. The statistics of the calibration samples depend upon the time for which the samples are to be applied. The statistics of the random variables are equated to the mean statistics of the non-stationary processes over the interval defined by the time of calibration sample and when it is applied. This analysis opens the opportunity for experimental investigation into the underlying properties of receiver non stationarity through the use of multiple calibration references. In this presentation we will discuss the application of LSR to the analysis of various calibration algorithms, requirements for experimental verification of the theory, and preliminary results from analyzing experiment measurements.
Time-Resolved Spectral Analysis of Blazar 0716+714
NASA Astrophysics Data System (ADS)
Diaz, Rosamaria; Harp, Gerald
2016-01-01
As electromagnetic (EM) waves from sources such as blazars travel through the intergalactic medium (IGM), they are slowed by electrons; a phenomenon called dispersion delay [2]. We study the propagation effects in emissions of EM waves from blazar source BL 0716+714 by estimating the average electron density, or dispersion measure (DM), of the IGM on a line of sight to the blazar. Measuring the variations in these effects with time allow us to understand the properties of the intervening material. Toward this goal we analyzed months of archived observations of BL 0716+714 taken by the Allen Telescope Array (ATA). The ATA's correlator produces cross-power vs. frequency spectra for every baseline (distance between a pair of antennas) in ten-second intervals. To reduce this immense load of data we used a technique based on interferometry called bispectrum, which does not depend on complicated array calibration and simplifies our work. The bispectrum multiplies baselines, three at a time, so that they form a closed loop, then the cube root of spectra are averaged [1]. This technique is independent of phase errors associated with any individual antenna and has a better SNR ratio than simply taking the average of all the baselines. We developed a numerical analysis program that takes in archived blazar files containing correlation data, computes the bispectrum, and outputs FITS images for each day of observations. The results show that our observations do not have sufficient sensitivity to reveal blazar variations in the frequency ranges that were studied. It is suggested that future observations at higher frequencies and/or with another telescope having greater sensitivity would reveal the time/frequency dependence of emission structure that would allow measurements of electron content. This work shows that but bispectrum is a useful tool for rapid characterization of interferometer data that does not require interferometer caclibration which could introduce artifacts into radio light curves.References:[1] Law C.J. and Bower G.C. (2012) Astrophysical Journal, 749:143[2] Rani B. et al. (2013) A&A, ms, 1-25.
Spectrally Resolved Intensities of Ultra-Dense Hot Aluminum Plasmas
Gil, J. M.; Rodriguez, R.; Florido, R.; Rubiano, J. G.; Martel, P.; Minguez, E.; Sauvan, P.; Angelo, P.; Dalimier, E.; Schott, R.; Mancini, R.
2008-10-22
We present a first study of spectroscopic determination of electron temperature and density spatial profiles of aluminum K-shell line emission spectra from laser-shocked aluminum experiments performed at LULI. The radiation emitted by the aluminum plasma was dispersed with an ultra-high resolution spectrograph ({lambda}/{delta}{lambda}{approx_equal}6000). From the recorded films one can extract a set of time-integrated emission lineouts associated with the corresponding spatial region of the plasma. The observed spectra include the Ly{alpha}, He{beta}, He{gamma}, Ly{beta} and Ly{gamma} line emissions and their associated He- and Li-like satellites thus covering a photon energy range from 1700 eV to 2400 eV approximately. The data analysis rely on the ABAKO/RAPCAL computational package, which has been recently developed at the University of Las Palmas de Gran Canaria and takes into account non-equilibrium collisional-radiative atomic kinetics, Stark broadened line shapes and radiation transport calculations.
Spectrally Resolved Intensities of Ultra-Dense Hot Aluminum Plasmas
NASA Astrophysics Data System (ADS)
Gil, J. M.; Rodríguez, R.; Florido, R.; Rubiano, J. G.; Martel, P.; Mínguez, E.; Sauvan, P.; Angelo, P.; Schott, R.; Dalimier, E.; Mancini, R.
2008-10-01
We present a first study of spectroscopic determination of electron temperature and density spatial profiles of aluminum K-shell line emission spectra from laser-shocked aluminum experiments performed at LULI. The radiation emitted by the aluminum plasma was dispersed with an ultra-high resolution spectrograph (λ/Δλ≈6000). From the recorded films one can extract a set of time-integrated emission lineouts associated with the corresponding spatial region of the plasma. The observed spectra include the Lyα, Heβ, Heγ, Lyβ and Lyγ line emissions and their associated He- and Li-like satellites thus covering a photon energy range from 1700 eV to 2400 eV approximately. The data analysis rely on the ABAKO/RAPCAL computational package, which has been recently developed at the University of Las Palmas de Gran Canaria and takes into account non-equilibrium collisional-radiative atomic kinetics, Stark broadened line shapes and radiation transport calculations.
Resolving Spectral Lines with a Periscope-Type DVD Spectroscope
ERIC Educational Resources Information Center
Wakabayashi, Fumitaka
2008-01-01
A new type of DVD spectroscope, the periscope type, is described and the numerical analysis of the observed emission and absorption spectra is demonstrated. A small and thin mirror is put inside and an eighth part of a DVD is used as a grating. Using this improved DVD spectroscope, one can observe and photograph visible spectra more easily and…
Circumstellar Matter Studied by Spectrally-Resolved Interferometry
NASA Astrophysics Data System (ADS)
Millour, F.
2012-12-01
This paper describes some generalities about spectro-interferometry and the role it has played in the last decade for the better understanding of circumstellar matter. I provide a small history of the technique and its origins, and recall the basics of differential phase and its central role for the recent discoveries. I finally provide a small set of simple interpretations of differential phases for specific astrophysical cases, and intend to provide a "cookbook" for the other cases.
System identification through nonstationary data using Time-Frequency Blind Source Separation
NASA Astrophysics Data System (ADS)
Guo, Yanlin; Kareem, Ahsan
2016-06-01
Classical output-only system identification (SI) methods are based on the assumption of stationarity of the system response. However, measured response of buildings and bridges is usually non-stationary due to strong winds (e.g. typhoon, and thunder storm etc.), earthquakes and time-varying vehicle motions. Accordingly, the response data may have time-varying frequency contents and/or overlapping of modal frequencies due to non-stationary colored excitation. This renders traditional methods problematic for modal separation and identification. To address these challenges, a new SI technique based on Time-Frequency Blind Source Separation (TFBSS) is proposed. By selectively utilizing "effective" information in local regions of the time-frequency plane, where only one mode contributes to energy, the proposed technique can successfully identify mode shapes and recover modal responses from the non-stationary response where the traditional SI methods often encounter difficulties. This technique can also handle response with closely spaced modes which is a well-known challenge for the identification of large-scale structures. Based on the separated modal responses, frequency and damping can be easily identified using SI methods based on a single degree of freedom (SDOF) system. In addition to the exclusive advantage of handling non-stationary data and closely spaced modes, the proposed technique also benefits from the absence of the end effects and low sensitivity to noise in modal separation. The efficacy of the proposed technique is demonstrated using several simulation based studies, and compared to the popular Second-Order Blind Identification (SOBI) scheme. It is also noted that even some non-stationary response data can be analyzed by the stationary method SOBI. This paper also delineates non-stationary cases where SOBI and the proposed scheme perform comparably and highlights cases where the proposed approach is more advantageous. Finally, the performance of the
Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets
Dixit, Gopal; Santra, Robin
2013-04-07
Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)]. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.
Climate change and non-stationary flood risk for the Upper Truckee River Basin
NASA Astrophysics Data System (ADS)
Condon, L. E.; Gangopadhyay, S.; Pruitt, T.
2014-05-01
Future flood frequency for the Upper Truckee River Basin (UTRB) is assessed using non-stationary extreme value models and design life risk methodology. Historical floods are simulated at two UTRB gauge locations, Farad and Reno using the Variable Infiltration Capacity (VIC) model and non-stationary Generalized Extreme Value (GEV) models. The non-stationary GEV models are fit to the cool season (November-April) monthly maximum flows using historical monthly precipitation totals and average temperature. Future cool season flood distributions are subsequently calculated using downscaled projections of precipitation and temperature from the Coupled Model Intercomparison Project Phase-5 (CMIP-5) archive. The resulting exceedance probabilities are combined into a single risk metric using recent developments in design life risk methodologies. This paper provides the first end-to-end analysis using non-stationary GEV methods coupled with contemporary downscaled climate projections to demonstrate how the risk profile of existing infrastructure evolves with time over its design life. Results show that flood risk increases significantly over the analysis period (from 1950 through 2099). This highlights the potential to underestimate flood risk using traditional methodologies that do not account for time varying risk. Although model parameters, for the non-stationary method are sensitive to small changes in input parameters, analysis shows that the changes in risk over time are robust. Overall, flood risk at both locations (Farad and Reno) is projected to increase 10-20% between the historical period 1950-1999 and the future period 2000-2050 and 30-50% between the same historical period and 2050-2099.
Climate change and non-stationary flood risk for the upper Truckee River basin
NASA Astrophysics Data System (ADS)
Condon, L. E.; Gangopadhyay, S.; Pruitt, T.
2015-01-01
Future flood frequency for the upper Truckee River basin (UTRB) is assessed using non-stationary extreme value models and design-life risk methodology. Historical floods are simulated at two UTRB gauge locations, Farad and Reno, using the Variable Infiltration Capacity (VIC) model and non-stationary Generalized Extreme Value (GEV) models. The non-stationary GEV models are fit to the cool season (November-April) monthly maximum flows using historical monthly precipitation totals and average temperature. Future cool season flood distributions are subsequently calculated using downscaled projections of precipitation and temperature from the Coupled Model Intercomparison Project Phase 5 (CMIP-5) archive. The resulting exceedance probabilities are combined to calculate the probability of a flood of a given magnitude occurring over a specific time period (referred to as flood risk) using recent developments in design-life risk methodologies. This paper provides the first end-to-end analysis using non-stationary GEV methods coupled with contemporary downscaled climate projections to demonstrate the evolution of a flood risk profile over typical design life periods of existing infrastructure that are vulnerable to flooding (e.g., dams, levees, bridges and sewers). Results show that flood risk increases significantly over the analysis period (from 1950 through 2099). This highlights the potential to underestimate flood risk using traditional methodologies that do not account for time-varying risk. Although model parameters for the non-stationary method are sensitive to small changes in input parameters, analysis shows that the changes in risk over time are robust. Overall, flood risk at both locations (Farad and Reno) is projected to increase 10-20% between the historical period 1950 to 1999 and the future period 2000 to 2050 and 30-50% between the same historical period and a future period of 2050 to 2099.
Power-density spectrum of non-stationary short-lived light curves
NASA Astrophysics Data System (ADS)
Guidorzi, Cristiano
2011-08-01
The power-density spectrum of a light curve is often calculated as the average of a number of spectra derived on individual time intervals the light curve is divided into. This procedure implicitly assumes that each time interval is a different sample function of the same stochastic ergodic process. While this assumption can be applied to many astrophysical sources, there remains a class of transient, highly non-stationary and short-lived events, such as gamma-ray bursts, for which this approach is often inadequate. The power spectrum statistics of a constant signal affected by statistical (Poisson) noise are known to be a χ22 in the Leahy normalization. However, this is no more the case when a non-stationary signal is also present. As a consequence, the uncertainties on the power spectrum cannot be calculated on the basis of the χ22 properties, as assumed by tools such as XRONOS POWSPEC. We generalize the result in the case of a non-stationary signal affected by uncorrelated white noise and show that the new distribution is a non-central χ22(λ), whose non-central value λ is the power spectrum of the deterministic function describing the non-stationary signal. Finally, we test these results in the case of synthetic curves of gamma-ray bursts. We end up with a new formula for calculating the power spectrum uncertainties. This is crucial in the case of non-stationary short-lived processes affected by uncorrelated statistical noise, for which ensemble averaging does not make any physical sense.
Multicolor spectral karyotyping of human chromosomes.
Schröck, E; du Manoir, S; Veldman, T; Schoell, B; Wienberg, J; Ferguson-Smith, M A; Ning, Y; Ledbetter, D H; Bar-Am, I; Soenksen, D; Garini, Y; Ried, T
1996-07-26
The simultaneous and unequivocal discernment of all human chromosomes in different colors would be of significant clinical and biologic importance. Whole-genome scanning by spectral karyotyping allowed instantaneous visualization of defined emission spectra for each human chromosome after fluorescence in situ hybridization. By means of computer separation (classification) of spectra, spectrally overlapping chromosome-specific DNA probes could be resolved, and all human chromosomes were simultaneously identified. PMID:8662537
Time-resolved photoelectron spectroscopy of liquids
NASA Astrophysics Data System (ADS)
Buchner, Franziska; Lübcke, Andrea; Heine, Nadja; Schultz, Thomas
2010-11-01
We present a novel setup for the investigation of ultrafast dynamic processes in a liquid jet using time-resolved photoelectron spectroscopy. A magnetic-bottle type spectrometer with a high collection efficiency allows the very sensitive detection of photoelectrons emitted from a 10 μm thick liquid jet. This translates into good signal/noise ratio and rapid data acquisition making femtosecond time-resolved experiments feasible. We describe the experimental setup, a detailed spectrometer characterization based on the spectroscopy of nitric oxide in the gas phase, and results from femtosecond time-resolved experiments on sodium iodide solutions. The latter experiments reveal the formation and evolution of the solvated electron and we characterize two distinct spectral components corresponding to initially thermalized and unthermalized solvated electrons. The absence of dark states in photoionization, the direct measurement of electron binding energies, and the ability to resolve dynamic processes on the femtosecond time scale make time-resolved photoelectron spectroscopy from the liquid jet a very promising method for the characterization of photochemical processes in liquids.
Time-resolved photoelectron spectroscopy of liquids.
Buchner, Franziska; Lübcke, Andrea; Heine, Nadja; Schultz, Thomas
2010-11-01
We present a novel setup for the investigation of ultrafast dynamic processes in a liquid jet using time-resolved photoelectron spectroscopy. A magnetic-bottle type spectrometer with a high collection efficiency allows the very sensitive detection of photoelectrons emitted from a 10 μm thick liquid jet. This translates into good signal/noise ratio and rapid data acquisition making femtosecond time-resolved experiments feasible. We describe the experimental setup, a detailed spectrometer characterization based on the spectroscopy of nitric oxide in the gas phase, and results from femtosecond time-resolved experiments on sodium iodide solutions. The latter experiments reveal the formation and evolution of the solvated electron and we characterize two distinct spectral components corresponding to initially thermalized and unthermalized solvated electrons. The absence of dark states in photoionization, the direct measurement of electron binding energies, and the ability to resolve dynamic processes on the femtosecond time scale make time-resolved photoelectron spectroscopy from the liquid jet a very promising method for the characterization of photochemical processes in liquids. PMID:21133461
On the joint spectral density of bivariate random sequences. Thesis Technical Report No. 21
NASA Technical Reports Server (NTRS)
Aalfs, David D.
1995-01-01
For univariate random sequences, the power spectral density acts like a probability density function of the frequencies present in the sequence. This dissertation extends that concept to bivariate random sequences. For this purpose, a function called the joint spectral density is defined that represents a joint probability weighing of the frequency content of pairs of random sequences. Given a pair of random sequences, the joint spectral density is not uniquely determined in the absence of any constraints. Two approaches to constraining the sequences are suggested: (1) assume the sequences are the margins of some stationary random field, (2) assume the sequences conform to a particular model that is linked to the joint spectral density. For both approaches, the properties of the resulting sequences are investigated in some detail, and simulation is used to corroborate theoretical results. It is concluded that under either of these two constraints, the joint spectral density can be computed from the non-stationary cross-correlation.
The spectral analysis of cyclo-non-stationary signals
NASA Astrophysics Data System (ADS)
Abboud, D.; Baudin, S.; Antoni, J.; Rémond, D.; Eltabach, M.; Sauvage, O.
2016-06-01
Condition monitoring of rotating machines in speed-varying conditions remains a challenging task and an active field of research. Specifically, the produced vibrations belong to a particular class of non-stationary signals called cyclo-non-stationary: although highly non-stationary, they contain hidden periodicities related to the shaft angle; the phenomenon of long term modulations is what makes them different from cyclostationary signals which are encountered under constant speed regimes. In this paper, it is shown that the optimal way of describing cyclo-non-stationary signals is jointly in the time and the angular domains. While the first domain describes the waveform characteristics related to the system dynamics, the second one reveals existing periodicities linked to the system kinematics. Therefore, a specific class of signals - coined angle-time cyclostationary is considered, expressing the angle-time interaction. Accordingly, the related spectral representations, the order-frequency spectral correlation and coherence functions are proposed and their efficiency is demonstrated on two industrial cases.
Frequency- and time-resolved coherence transfer spectroscopy.
Rickard, Mark A; Pakoulev, Andrei V; Mathew, Nathan A; Kornau, Kathryn M; Wright, John C
2007-02-22
Frequency-domain two-color triply vibrational enhanced four-wave mixing using a new phase-matching geometry discriminates against coherent multidimensional spectral features created solely by radiative transitions, spectrally resolves pathways with different numbers of coherence transfer steps, and temporally resolves modulations created by interference between coherence transfer pathways. Coherence transfer is a nonradiative transition where a superposition of quantum states evolves to a different superposition. The asymmetric and symmetric C[triple bond]O stretching modes of rhodium(I) dicarbonyl acetylacetonate are used as a model system for coherence transfer. A simplified theoretical model based on Redfield theory is used to describe the experimental results. PMID:17300169
TIMESCALE-RESOLVED SPECTROSCOPY OF Cyg X-1
Wu, Y. X.; Li, T. P.; Belloni, T. M.; Wang, T. S.; Liu, H.
2009-04-20
We propose the timescale-resolved spectroscopy (TRS) as a new method to combine the timing and spectral study. The TRS is based on the time domain power spectrum and reflects the variable amplitudes of spectral components on different timescales. We produce the TRS with the RXTE PCA data for Cyg X-1 and study the spectral parameters (the power-law photon index and the equivalent width of the iron fluorescent line) as a function of timescale. The results of TRS and frequency-resolved spectra have been compared, and similarities have been found for the two methods with the identical motivations. We also discover the correspondences between the evolution of photon index with timescale and the evolution of the equivalent width with timescale. The observations can be divided into three types according to the correspondences and different type is connected with different spectral state.
NASA Technical Reports Server (NTRS)
Morozov, S. K.; Krasitskiy, O. P.
1978-01-01
A computational scheme and a standard program is proposed for solving systems of nonstationary spatially one-dimensional nonlinear differential equations using Newton's method. The proposed scheme is universal in its applicability and its reduces to a minimum the work of programming. The program is written in the FORTRAN language and can be used without change on electronic computers of type YeS and BESM-6. The standard program described permits the identification of nonstationary (or stationary) solutions to systems of spatially one-dimensional nonlinear (or linear) partial differential equations. The proposed method may be used to solve a series of geophysical problems which take chemical reactions, diffusion, and heat conductivity into account, to evaluate nonstationary thermal fields in two-dimensional structures when in one of the geometrical directions it can take a small number of discrete levels, and to solve problems in nonstationary gas dynamics.
NASA Astrophysics Data System (ADS)
Tomas, A.; Menendez, M.; Mendez, F. J.; Coco, G.; Losada, I. J.
2012-04-01
In the last decades, freak or rogue waves have become an important topic in engineering and science. Forecasting the occurrence probability of freak waves is a challenge for oceanographers, engineers, physicists and statisticians. There are several mechanisms responsible for the formation of freak waves, and different theoretical formulations (primarily based on numerical models with simplifying assumption) have been proposed to predict the occurrence probability of freak wave in a sea state as a function of N (number of individual waves) and kurtosis (k). On the other hand, different attempts to parameterize k as a function of spectral parameters such as the Benjamin-Feir Index (BFI) and the directional spreading (Mori et al., 2011) have been proposed. The objective of this work is twofold: (1) develop a statistical model to describe the uncertainty of maxima individual wave height, Hmax, considering N and k as covariates; (2) obtain a predictive formulation to estimate k as a function of aggregated sea state spectral parameters. For both purposes, we use free surface measurements (more than 300,000 20-minutes sea states) from the Spanish deep water buoy network (Puertos del Estado, Spanish Ministry of Public Works). Non-stationary extreme value models are nowadays widely used to analyze the time-dependent or directional-dependent behavior of extreme values of geophysical variables such as significant wave height (Izaguirre et al., 2010). In this work, a Generalized Extreme Value (GEV) statistical model for the dimensionless maximum wave height (x=Hmax/Hs) in every sea state is used to assess the probability of freak waves. We allow the location, scale and shape parameters of the GEV distribution to vary as a function of k and N. The kurtosis-dependency is parameterized using third-order polynomials and the model is fitted using standard log-likelihood theory, obtaining a very good behavior to predict the occurrence probability of freak waves (x>2). Regarding the
Versatile approach for frequency resolved wavefront characterization
NASA Astrophysics Data System (ADS)
Frumker, Eugene; Paulus, Gerhard G.; Niikura, Hiromichi; Villeneuve, David M.; Corkum, Paul B.
2011-03-01
Spatial characterization of high harmonics (HH) and XUV coherent radiation is of paramount importance, along with its temporal characterization. For many applications it will be necessary to accurately measure the beam properties, just as it is important to know the beam characteristics for many laser experiments. For example, high harmonics and attosecond pulses are being proposed as a front-end for the next generation X-ray free electron lasers. This oscillator-amplifier-like arrangement will require well characterized high harmonic sources. On the other hand, the electromagnetic radiation carries the combined signature of underlying quantum physical processes at the molecular level and of the cooperative phase matching. For example, accurate reconstruction of the high harmonic spatial wavefront, along with its temporal profile, gives us a complete range of tools to apply to the fundamental quantum properties and dynamics associated with high harmonic generation. We present a new concept of frequency resolved wavefront characterization that is particularly suitable for characterizing XUV radiation. In keeping with tradition in the area we give it an acronym - SWORD (Spectral Wavefront Optical Reconstruction by Diffraction). Our approach is based on an analysis of the diffraction pattern of a slit situated in front of a flat-field spectrometer. As the slit is scanned, the spectrally resolved diffraction pattern is recorded. Analyzing the measured diffractogram, we can reconstruct the wavefront. The technique can be easily extended beyond the XUV spectral region. When combined with temporal characterization techniques all information about the beam can be measured.
Detection of Unusual Events and Trends in Complex Non-Stationary Data Streams
Perez, Rafael B; Protopopescu, Vladimir A; Worley, Brian Addison; Perez, Cristina
2006-01-01
The search for unusual events and trends hidden in multi-component, nonlinear, non-stationary, noisy signals is extremely important for a host of different applications, ranging from nuclear power plant and electric grid operation to internet traffic and implementation of non-proliferation protocols. In the context of this work, we define an unusual event as a local signal disturbance and a trend as a continuous carrier of information added to and different from the underlying baseline dynamics. The goal of this paper is to investigate the feasibility of detecting hidden intermittent events inside non-stationary signal data sets corrupted by high levels of noise, by using the Hilbert-Huang empirical mode decomposition method.
Non-stationary dynamics in the bouncing ball: A wavelet perspective
Behera, Abhinna K. Panigrahi, Prasanta K.; Sekar Iyengar, A. N.
2014-12-01
The non-stationary dynamics of a bouncing ball, comprising both periodic as well as chaotic behavior, is studied through wavelet transform. The multi-scale characterization of the time series displays clear signatures of self-similarity, complex scaling behavior, and periodicity. Self-similar behavior is quantified by the generalized Hurst exponent, obtained through both wavelet based multi-fractal detrended fluctuation analysis and Fourier methods. The scale dependent variable window size of the wavelets aptly captures both the transients and non-stationary periodic behavior, including the phase synchronization of different modes. The optimal time-frequency localization of the continuous Morlet wavelet is found to delineate the scales corresponding to neutral turbulence, viscous dissipation regions, and different time varying periodic modulations.
Entropy of Non-stationary and Slowly Changing Reissner-Nordström Black Hole
NASA Astrophysics Data System (ADS)
Yan, Han
2014-01-01
Simplifying Dirac equation near the horizon, Hawking temperature is obtained by applying a new tortoise coordinate transformation. Using the improved thin film brick-wall model and WKB approximation, the entropy of Dirac field in the non-stationary and slowly changing Reissner-Nordström black hole is calculated. The result shows that the entropy of the black hole is still proportional to the horizon area, and black hole entropy is just identical to the entropy of the quantum state at the horizon. In addition, the new tortoise coordinate transformation can make the cut-off parameter introduced in solving the entropy of non-stationary black hole simplified to the same as that in the static and stationary cases.
Characteristics of Quantum Radiation of Slowly Varying Nonstationary Kerr-Newman Black Holes
NASA Astrophysics Data System (ADS)
Hua, Jia-Chen; Huang, Yong-Chang
Quantum radiative characteristics of slowly varying nonstationary Kerr-Newman black holes are investigated by using the method of generalized tortoise coordinate transformation. It is shown that the temperature and the shape of the event horizon of this kind of black holes depend on the time and the angle. Further, we reveal a previously ignored relationship between thermal radiation and nonthermal radiation, which is that the chemical potential in the thermal radiation spectrum is equal to the highest energy of the negative energy state of particles in nonthermal radiation for slowly varying nonstationary Kerr-Newman black holes. Also, we show that the deduced general results can be degenerated to the known conclusion of stationary Kerr-Newman black holes.
Onset of convective flows in a near-wall granular layer during nonstationary liquid boiling
NASA Astrophysics Data System (ADS)
Pokusaev, B. G.; Karlov, S. P.; Nekrasov, D. A.; Zakharov, N. S.
2014-08-01
The onset and development of convective flows during nonstationary conductive heating of a cell with a layer of cylindrical pebbles placed in a liquid medium have been studied using a proposed and implemented optical method. The temperature fields have been measured using a holographic interferometry technique with immersion optical tomography elements, which is based upon the dependence of the index of refraction on the temperature and properties of a continuous medium. The mechanism of the pebble-bed influence on the time and character of microconvection formed near the cell wall heated from below has been studied for variable thermal properties of the liquid medium and pebbles in the granular layer and supplied heat flux. Data on the visualization of temperature fields and the development of convective flows in a pebble-bed reactor cell of complicated shape during nonstationary heating have been obtained for the first time.
NASA Astrophysics Data System (ADS)
Pedrosa, Inácio A.; Melo, Jilvan L.; Salatiel, Sadoque
2014-11-01
We present an alternative quantum treatment for a generalized mesoscopic RLC circuit with time-dependent resistance, inductance and capacitance. Taking advantage of the Lewis and Riesenfeld quantum invariant method and using quadratic invariants we obtain exact nonstationary Schrödinger states for this electromagnetic oscillation system. Afterwards, we construct coherent and squeezed states for the quantized RLC circuit and employ them to investigate some of the system's quantum properties, such as quantum fluctuations of the charge and the magnetic flux and the corresponding uncertainty product. In addition, we derive the geometric, dynamical and Berry phases for this nonstationary mesoscopic circuit. Finally we evaluate the dynamical and Berry phases for three special circuits. Surprisingly, we find identical expressions for the dynamical phase and the same formulae for the Berry's phase.
Time-series analysis of nonstationary plasma fluctuations using wavelet transforms
Santoso, S.; Powers, E.J.; Bengtson, R.D.; Ouroua, A.
1997-01-01
A wavelet or time-scale approach to analyzing a single time series and two time series, in which the fluctuating quantities are statistically nonstationary, is presented. The time scale and scale {open_quotes}power spectra{close_quotes} are introduced and utilized to analyze transient potential fluctuations measured at the core of sawtoothing TEXT-U plasmas. The results show features that have not been previously observed using any Fourier techniques. In addition, the linear time-scale {open_quotes}coherence spectrum{close_quotes} is developed to quantify the degree of linear relationship between two nonstationary fluctuating quantities in the time-scale domain. Such a spectrum is also useful in tracking the time-varying phase difference. A numerical example is provided to demonstrate the efficacy of the time-scale spectra. {copyright} {ital 1997 American Institute of Physics.}
Non-stationary dynamics in the bouncing ball: a wavelet perspective.
Behera, Abhinna K; Iyengar, A N Sekar; Panigrahi, Prasanta K
2014-12-01
The non-stationary dynamics of a bouncing ball, comprising both periodic as well as chaotic behavior, is studied through wavelet transform. The multi-scale characterization of the time series displays clear signatures of self-similarity, complex scaling behavior, and periodicity. Self-similar behavior is quantified by the generalized Hurst exponent, obtained through both wavelet based multi-fractal detrended fluctuation analysis and Fourier methods. The scale dependent variable window size of the wavelets aptly captures both the transients and non-stationary periodic behavior, including the phase synchronization of different modes. The optimal time-frequency localization of the continuous Morlet wavelet is found to delineate the scales corresponding to neutral turbulence, viscous dissipation regions, and different time varying periodic modulations. PMID:25554027
A self-normalized confidence interval for the mean of a class of nonstationary processes.
Zhao, Zhibiao
2011-01-01
We construct an asymptotic confidence interval for the mean of a class of nonstationary processes with constant mean and time-varying variances. Due to the large number of unknown parameters, traditional approaches based on consistent estimation of the limiting variance of sample mean through moving block or non-overlapping block methods are not applicable. Under a block-wise asymptotically equal cumulative variance assumption, we propose a self-normalized confidence interval that is robust against the nonstationarity and dependence structure of the data. We also apply the same idea to construct an asymptotic confidence interval for the mean difference of nonstationary processes with piecewise constant means. The proposed methods are illustrated through simulations and an application to global temperature series. PMID:24319293
A self-normalized confidence interval for the mean of a class of nonstationary processes
ZHAO, ZHIBIAO
2013-01-01
Summary We construct an asymptotic confidence interval for the mean of a class of nonstationary processes with constant mean and time-varying variances. Due to the large number of unknown parameters, traditional approaches based on consistent estimation of the limiting variance of sample mean through moving block or non-overlapping block methods are not applicable. Under a block-wise asymptotically equal cumulative variance assumption, we propose a self-normalized confidence interval that is robust against the nonstationarity and dependence structure of the data. We also apply the same idea to construct an asymptotic confidence interval for the mean difference of nonstationary processes with piecewise constant means. The proposed methods are illustrated through simulations and an application to global temperature series. PMID:24319293
Ijaz, Umer Zeeshan; Khambampati, Anil Kumar; Lee, Jeong Seong; Kim, Sin; Kim, Kyung Youn
2008-07-20
In this paper, an effective nonstationary phase boundary estimation scheme in electrical impedance tomography is presented based on the unscented Kalman filter. The inverse problem is treated as a stochastic nonlinear state estimation problem with the nonstationary phase boundary (state) being estimated online with the aid of unscented Kalman filter. This research targets the industrial applications, such as imaging of stirrer vessel for detection of air distribution or detecting large air bubbles in pipelines. Within the domains, there exist 'voids' having zero conductivity. The design variables for phase boundary estimation are truncated Fourier coefficients. Computer simulations and experimental results are provided to evaluate the performance of unscented Kalman filter in comparison with extended Kalman filter to show a better performance of the unscented Kalman filter approach.
Spectral ladar: towards active 3D multispectral imaging
NASA Astrophysics Data System (ADS)
Powers, Michael A.; Davis, Christopher C.
2010-04-01
In this paper we present our Spectral LADAR concept, an augmented implementation of traditional LADAR. This sensor uses a polychromatic source to obtain range-resolved 3D spectral images which are used to identify objects based on combined spatial and spectral features, resolving positions in three dimensions and up to hundreds of meters in distance. We report on a proof-of-concept Spectral LADAR demonstrator that generates spectral point clouds from static scenes. The demonstrator transmits nanosecond supercontinuum pulses generated in a photonic crystal fiber. Currently we use a rapidly tuned receiver with a high-speed InGaAs APD for 25 spectral bands with the future expectation of implementing a linear APD array spectrograph. Each spectral band is independently range resolved with multiple return pulse recognition. This is a critical feature, enabling simultaneous spectral and spatial unmixing of partially obscured objects when not achievable using image fusion of monochromatic LADAR and passive spectral imagers. This enables higher identification confidence in highly cluttered environments such as forested or urban areas (e.g. vehicles behind camouflage or foliage). These environments present challenges for situational awareness and robotic perception which can benefit from the unique attributes of Spectral LADAR. Results from this demonstrator unit are presented for scenes typical of military operations and characterize the operation of the device. The results are discussed here in the context of autonomous vehicle navigation and target recognition.
Antoniewicz, Maciek R; Kraynie, David F; Laffend, Lisa A; González-Lergier, Joanna; Kelleher, Joanne K; Stephanopoulos, Gregory
2007-05-01
Metabolic fluxes estimated from stable-isotope studies provide a key to understanding cell physiology and regulation of metabolism. A limitation of the classical method for metabolic flux analysis (MFA) is the requirement for isotopic steady state. To extend the scope of flux determination from stationary to nonstationary systems, we present a novel modeling strategy that combines key ideas from isotopomer spectral analysis (ISA) and stationary MFA. Isotopic transients of the precursor pool and the sampled products are described by two parameters, D and G parameters, respectively, which are incorporated into the flux model. The G value is the fraction of labeled product in the sample, and the D value is the fractional contribution of the feed for the production of labeled products. We illustrate the novel modeling strategy with a nonstationary system that closely resembles industrial production conditions, i.e. fed-batch fermentation of Escherichia coli that produces 1,3-propanediol (PDO). Metabolic fluxes and the D and G parameters were estimated by fitting labeling distributions of biomass amino acids measured by GC/MS to a model of E. coli metabolism. We obtained highly consistent fits from the data with 82 redundant measurements. Metabolic fluxes were estimated for 20 time points during course of the fermentation. As such we established, for the first time, detailed time profiles of in vivo fluxes. We found that intracellular fluxes changed significantly during the fed-batch. The intracellular flux associated with PDO pathway increased by 10%. Concurrently, we observed a decrease in the split ratio between glycolysis and pentose phosphate pathway from 70/30 to 50/50 as a function of time. The TCA cycle flux, on the other hand, remained constant throughout the fermentation. Furthermore, our flux results provided additional insight in support of the assumed genotype of the organism. PMID:17400499
Resolving Problems through Mediation.
ERIC Educational Resources Information Center
Notar, Susan
1997-01-01
Examines state variations in use of mediation to resolve domestic relations disputes. Mediation may be optional or mandatory, requested by the parties or the judge. Mediator qualifications vary considerably. Child support is less likely than custody and visitation to be the sole topic for mediation. More states are likely to use mediation in…
Has Abstractness Been Resolved?
ERIC Educational Resources Information Center
Al-Omoush, Ahmad
1989-01-01
A discussion focusing on the abstractness of analysis in phonology, debated since the 1960s, describes the issue, reviews the literature on the subject, cites specific natural language examples, and examines the extent to which the issue has been resolved. An underlying representation is said to be abstract if it is different from the derived one,…
An Improved Approach for Nonstationary Strong Ground Motion Simulation
NASA Astrophysics Data System (ADS)
Li, Yanan; Wang, Guoxin
2016-05-01
A new stochastic ground motion model for generating a suite of ground motion time history with both temporal and frequency nonstationarities for specified earthquake and site characteristics is proposed based on the wavelet method. This new model is defined in terms of 6 key parameters that characterize the duration, evolving intensity, predominant frequency, bandwidth and frequency variation of the ground acceleration process. All parameters, except for peak ground acceleration (PGA), are identified manually from a database of 2444 recorded horizontal accelerations. The two-stage regression analysis method is used to investigate the inter- and intra-event residuals. For any given earthquake and site characteristics in terms of the fault mechanism, moment magnitude, Joyner and Boore distance and site shear-wave velocity, sets of the model parameters are generated and used, in turn, by the stochastic model to generate strong ground motion accelerograms, which can capture and properly embody the primary features of real strong ground motions, including the duration, evolving intensity, spectral content, frequency variation and peak values. In addition, it is shown that the characteristics of the simulated and observed response spectra are similar, and the amplitude of the simulated response spectra are in line with the predicted values from the published seismic ground motion prediction equations (SGMPE) after a systematic comparison. The proposed method can be used to estimate the strong ground motions as inputs for structural seismic dynamic analysis in engineering practice in conjunction with or instead of recorded ground motions.
Quantum Radiation of a Non-stationary Kerr Newman Black Hole in de Sitter Space Time
NASA Astrophysics Data System (ADS)
Jiang, Qing-Quan; Yang, Shu-Zheng
2006-12-01
Hawking radiation of Klein-Gordon and Dirac particles in a non-stationary Kerr-Newman-de-Sitter black hole is studied by introducing a new tortoise coordinate transformation. The result shows that the Fermi-Dirac radiant spectrum displays a new term that represents the interaction between the spin of spinor particles and the rotation of black holes, which is absent in the Bose-Einstein distribution of Klein-Gordon particles.
Variance fluctuations in nonstationary time series: a comparative study of music genres
NASA Astrophysics Data System (ADS)
Jennings, Heather D.; Ivanov, Plamen Ch.; De Martins, Allan M.; da Silva, P. C.; Viswanathan, G. M.
2004-05-01
An important problem in physics concerns the analysis of audio time series generated by transduced acoustic phenomena. Here, we develop a new method to quantify the scaling properties of the local variance of nonstationary time series. We apply this technique to analyze audio signals obtained from selected genres of music. We find quantitative differences in the correlation properties of high art music, popular music, and dance music. We discuss the relevance of these objective findings in relation to the subjective experience of music.
Blind estimation of statistical properties of non-stationary random variables
NASA Astrophysics Data System (ADS)
Mansour, Ali; Mesleh, Raed; Aggoune, el-Hadi M.
2014-12-01
To identify or equalize wireless transmission channels, or alternatively to evaluate the performance of many wireless communication algorithms, coefficients or statistical properties of the used transmission channels are often assumed to be known or can be estimated at the receiver end. For most of the proposed algorithms, the knowledge of transmission channel statistical properties is essential to detect signals and retrieve data. To the best of our knowledge, most proposed approaches assume that transmission channels are static and can be modeled by stationary random variables (uniform, Gaussian, exponential, Weilbul, Rayleigh, etc.). In the majority of sensor networks or cellular systems applications, transmitters and/or receivers are in motion. Therefore, the validity of static transmission channels and the underlying assumptions may not be valid. In this case, coefficients and statistical properties change and therefore the stationary model falls short of making an accurate representation. In order to estimate the statistical properties (represented by the high-order statistics and probability density function, PDF) of dynamic channels, we firstly assume that the dynamic channels can be modeled by short-term stationary but long-term non-stationary random variable (RV), i.e., the RVs are stationary within unknown successive periods but they may suddenly change their statistical properties between two successive periods. Therefore, this manuscript proposes an algorithm to detect the transition phases of non-stationary random variables and introduces an indicator based on high-order statistics for non-stationary transmission which can be used to alter channel properties and initiate the estimation process. Additionally, PDF estimators based on kernel functions are also developed. The first part of the manuscript provides a brief introduction for unbiased estimators of the second and fourth-order cumulants. Then, the non-stationary indicators are formulated
NASA Astrophysics Data System (ADS)
Wolkovich, E. M.; Donahue, M. J.
2014-12-01
Recent work has found links between how a species' phenology shifts with climate change and its changes in performance with climate change. Species that appear to 'track' climate change, for example North American temperate plant species that shift leafing or flowering earlier with warmer springs, also tend to increase in abundance or other metrics of plant performance, while the reverse is generally seen for species that delay phenology with warming. This correlation between phenological tracking and performance has been implicated in plant invasions and appears to be an important factor in predicting future plant populations and communities under climate change scenarios. We have, however, little theory on why--or why not--species may phenologically track the start of spring. Early-season phenology gives priority access to light and soil resources and thus, in a simplistic model where the start of season varies between years, all species should strongly track the start of season, yet communities are always a mix of phenological tracking strategies (from species that do not track the start of season to strong trackers). Using a stochastic community assembly model we examined how phenological tracking influences species abundances across time under two different environmental scenarios: one with a stationary environment and one with a nonstationary environment where the start of season shifts earlier over time. Our model shows that trade-offs are required between phenological tracking and parameters related to species-specific resource use to maintain a community with a diversity of phenological tracking strategies and that nonstationary environments strongly favor species that track the start of season. Our results suggest that trade-offs established under a stationary climate that allow a diversity of phenological tracking strategies across species in a community may not hold under non-stationary environments to maintain the same diversity of species. Instead
Kraus, B.; Tittel, W.; Gisin, N.; Nilsson, M.; Kroell, S.; Cirac, J. I.
2006-02-15
We propose a method for efficient storage and recall of arbitrary nonstationary light fields, such as, for instance, single photon time-bin qubits or intense fields, in optically dense atomic ensembles. Our approach to quantum memory is based on controlled, reversible, inhomogeneous broadening and relies on a hidden time-reversal symmetry of the optical Bloch equations describing the propagation of the light field. We briefly discuss experimental realizations of our proposal.
Modeling of nonstationary phenomena in the MHD-channel-inverter-substation system
Gusev, Y.P.; Zatelepin, V.N.; Kuznetsova, T.N.; Medin, S.A.; Pishchikov, V.I.
1986-07-01
A method for constructing a mathematical model of nonstationary phenomena in a system consisting of an MHD channel and an inverter substation, operating on a powerful ac grid, is examined. The variants of the realization of the model on a computer are discussed. Results of the solution of model problems with a diagonal MHD channel are presented. It is found that there is a significant coupling between the MHD channel and the inverter substation in transient processes.
COMPOSE: A semisupervised learning framework for initially labeled nonstationary streaming data.
Dyer, Karl B; Capo, Robert; Polikar, Robi
2014-01-01
An increasing number of real-world applications are associated with streaming data drawn from drifting and nonstationary distributions that change over time. These applications demand new algorithms that can learn and adapt to such changes, also known as concept drift. Proper characterization of such data with existing approaches typically requires substantial amount of labeled instances, which may be difficult, expensive, or even impractical to obtain. In this paper, we introduce compacted object sample extraction (COMPOSE), a computational geometry-based framework to learn from nonstationary streaming data, where labels are unavailable (or presented very sporadically) after initialization. We introduce the algorithm in detail, and discuss its results and performances on several synthetic and real-world data sets, which demonstrate the ability of the algorithm to learn under several different scenarios of initially labeled streaming environments. On carefully designed synthetic data sets, we compare the performance of COMPOSE against the optimal Bayes classifier, as well as the arbitrary subpopulation tracker algorithm, which addresses a similar environment referred to as extreme verification latency. Furthermore, using the real-world National Oceanic and Atmospheric Administration weather data set, we demonstrate that COMPOSE is competitive even with a well-established and fully supervised nonstationary learning algorithm that receives labeled data in every batch. PMID:24806641
Predictability of nonstationary time series using wavelet and EMD based ARMA models
NASA Astrophysics Data System (ADS)
Karthikeyan, L.; Nagesh Kumar, D.
2013-10-01
Research has been undertaken to ascertain the predictability of non-stationary time series using wavelet and Empirical Mode Decomposition (EMD) based time series models. Methods have been developed in the past to decompose a time series into components. Forecasting of these components combined with random component could yield predictions. Using this ideology, wavelet and EMD analyses have been incorporated separately which decomposes a time series into independent orthogonal components with both time and frequency localizations. The component series are fit with specific auto-regressive models to obtain forecasts which are later combined to obtain the actual predictions. Four non-stationary streamflow sites (USGS data resources) of monthly total volumes and two non-stationary gridded rainfall sites (IMD) of monthly total rainfall are considered for the study. The predictability is checked for six and twelve months ahead forecasts across both the methodologies. Based on performance measures, it is observed that wavelet based method has better prediction capabilities over EMD based method despite some of the limitations of time series methods and the manner in which decomposition takes place. Finally, the study concludes that the wavelet based time series algorithm can be used to model events such as droughts with reasonable accuracy. Also, some modifications that can be made in the model have been discussed that could extend the scope of applicability to other areas in the field of hydrology.
Non-stationary noise estimation using dictionary learning and Gaussian mixture models
NASA Astrophysics Data System (ADS)
Hughes, James M.; Rockmore, Daniel N.; Wang, Yang
2014-02-01
Stationarity of the noise distribution is a common assumption in image processing. This assumption greatly simplifies denoising estimators and other model parameters and consequently assuming stationarity is often a matter of convenience rather than an accurate model of noise characteristics. The problematic nature of this assumption is exacerbated in real-world contexts, where noise is often highly non-stationary and can possess time- and space-varying characteristics. Regardless of model complexity, estimating the parameters of noise dis- tributions in digital images is a difficult task, and estimates are often based on heuristic assumptions. Recently, sparse Bayesian dictionary learning methods were shown to produce accurate estimates of the level of additive white Gaussian noise in images with minimal assumptions. We show that a similar model is capable of accu- rately modeling certain kinds of non-stationary noise processes, allowing for space-varying noise in images to be estimated, detected, and removed. We apply this modeling concept to several types of non-stationary noise and demonstrate the model's effectiveness on real-world problems, including denoising and segmentation of images according to noise characteristics, which has applications in image forensics.
NASA Astrophysics Data System (ADS)
O'Malley, Daniel; Cushman, John H.
2012-03-01
Anomalous diffusion processes are often classified by their mean square displacement. If the mean square displacement grows linearly in time, the process is considered classical. If it grows like t β with β<1 or β>1, the process is considered subdiffusive or superdiffusive, respectively. Processes with infinite mean square displacement are considered superdiffusive. We begin by examining the ways in which power-law mean square displacements can arise; namely via non-zero drift, nonstationary increments, and correlated increments. Subsequently, we describe examples which illustrate that the above classification scheme does not work well when nonstationary increments are present. Finally, we introduce an alternative classification scheme based on renormalization groups. This scheme classifies processes with stationary increments such as Brownian motion and fractional Brownian motion in the same groups as the mean square displacement scheme, but does a better job of classifying processes with nonstationary increments and/or processes with infinite second moments such as α-stable Lévy motion. A numerical approach to analyzing data based on the renormalization group classification is also presented.
Time-varying nonstationary multivariate risk analysis using a dynamic Bayesian copula
NASA Astrophysics Data System (ADS)
Sarhadi, Ali; Burn, Donald H.; Concepción Ausín, María.; Wiper, Michael P.
2016-03-01
A time-varying risk analysis is proposed for an adaptive design framework in nonstationary conditions arising from climate change. A Bayesian, dynamic conditional copula is developed for modeling the time-varying dependence structure between mixed continuous and discrete multiattributes of multidimensional hydrometeorological phenomena. Joint Bayesian inference is carried out to fit the marginals and copula in an illustrative example using an adaptive, Gibbs Markov Chain Monte Carlo (MCMC) sampler. Posterior mean estimates and credible intervals are provided for the model parameters and the Deviance Information Criterion (DIC) is used to select the model that best captures different forms of nonstationarity over time. This study also introduces a fully Bayesian, time-varying joint return period for multivariate time-dependent risk analysis in nonstationary environments. The results demonstrate that the nature and the risk of extreme-climate multidimensional processes are changed over time under the impact of climate change, and accordingly the long-term decision making strategies should be updated based on the anomalies of the nonstationary environment.
Nonstationary Influence of El Niño on the Synchronous Dengue Epidemics in Thailand
2005-01-01
Background Several factors, including environmental and climatic factors, influence the transmission of vector-borne diseases. Nevertheless, the identification and relative importance of climatic factors for vector-borne diseases remain controversial. Dengue is the world's most important viral vector-borne disease, and the controversy about climatic effects also applies in this case. Here we address the role of climate variability in shaping the interannual pattern of dengue epidemics. Methods and Findings We have analysed monthly data for Thailand from 1983 to 1997 using wavelet approaches that can describe nonstationary phenomena and that also allow the quantification of nonstationary associations between time series. We report a strong association between monthly dengue incidence in Thailand and the dynamics of El Niño for the 2–3-y periodic mode. This association is nonstationary, seen only from 1986 to 1992, and appears to have a major influence on the synchrony of dengue epidemics in Thailand. Conclusion The underlying mechanism for the synchronisation of dengue epidemics may resemble that of a pacemaker, in which intrinsic disease dynamics interact with climate variations driven by El Niño to propagate travelling waves of infection. When association with El Niño is strong in the 2–3-y periodic mode, one observes high synchrony of dengue epidemics over Thailand. When this association is absent, the seasonal dynamics become dominant and the synchrony initiated in Bangkok collapses. PMID:15839751
A non-stationary earthquake probability assessment with the Mohr-Coulomb failure criterion
NASA Astrophysics Data System (ADS)
Wang, J. P.; Xu, Y.
2015-10-01
From theory to experience, earthquake probability associated with an active fault should be gradually increasing with time since the last event. In this paper, a new non-stationary earthquake assessment motivated/derived from the Mohr-Coulomb failure criterion is introduced. Different from other non-stationary earthquake analyses, the new model can more clearly define and calculate the stress states between two characteristic earthquakes. In addition to the model development and the algorithms, this paper also presents an example calculation to help explain and validate the new model. On the condition of best-estimate model parameters, the example calculation shows a 7.6 % probability for the Meishan fault in central Taiwan to induce a major earthquake in years 2015-2025, and if the earthquake does not occur by 2025, the earthquake probability will increase to 8 % in 2025-2035, which validates the new model that can calculate non-stationary earthquake probability as it should vary with time.
Studying the Dynamics of Non-stationary Jet Streams Formation in the Northern Hemisphere Troposphere
NASA Astrophysics Data System (ADS)
Emtsev, Sergey; Krasouski, Aliaksandr; Svetashev, Alexander; Turishev, Leonid; Barodka, Siarhei
2015-04-01
In the present study, we investigate dynamics of non-stationary jets formation in troposphere by means of mesoscale simulations in the Weather Research & Forecasting (WRF) modeling system, analyzing jet streams that affected the territory of Belarus over the time period of 2010-2012. For that purpose, we perform modeling on domains with 5 km, 3 km and 1 km grid steps and 35 vertical coordinate levels with an upper boundary of 10 hPa. We focus our attention to identification of basic regularities in formation, movements and transformations of jet streams, as well as to analysis of their characteristic features, geographical position and underlying atmospheric processes and their classification. On the basis of these regularities, we define basic meteorological parameters that can be used to directly or indirectly (as well as qualitatively and quantitatively) identify the presence of jet streams in the specific region of troposphere, and also to determine their localization, stage of development and other characteristics. Furthermore, we estimate energetic parameters of the identified jet streams and their impact on synoptic situation in the surrounding region. Analyzing meteorological fields obtained from satellite observations, we elaborate a methodology of operational detection and localization of non-stationary jet streams from satellite data. Validation of WRF modeling results with these data proves that mesoscale simulations with WRF are able to provide quite successful forecasts of non-stationary tropospheric jet streams occurrence and also determination of their localization and main characteristics up to 3 days in advance.
NASA Technical Reports Server (NTRS)
Huang, Norden E.; Zukor, Dorothy J. (Technical Monitor)
2001-01-01
A new method for analyzing nonlinear and nonstationary data has been developed. The key part of the method is the Empirical Mode Decomposition method with which any complicated data set can be decomposed into a finite and often small number of Intrinsic Mode Functions (IMF). An IMF is defined as any function having the same numbers of zero-crossing and extrema, and also having symmetric envelopes defined by the local maxima and minima respectively. The IMF also admits well-behaved Hilbert transform. This decomposition method is adaptive, and, therefore, highly efficient. Since the decomposition is based on the local characteristic time scale of the data, it is applicable to nonlinear and nonstationary processes. With the Hilbert transform, the Intrinsic Mode Functions yield instantaneous frequencies as functions of time that give sharp identifications of imbedded structures. The final presentation of the results is an energy-frequency-time distribution, designated as the Hilbert Spectrum. Classical nonlinear system models are used to illustrate the roles played by the nonlinear and nonstationary effects in the energy-frequency-time distribution.
Self-organising mixture autoregressive model for non-stationary time series modelling.
Ni, He; Yin, Hujun
2008-12-01
Modelling non-stationary time series has been a difficult task for both parametric and nonparametric methods. One promising solution is to combine the flexibility of nonparametric models with the simplicity of parametric models. In this paper, the self-organising mixture autoregressive (SOMAR) network is adopted as a such mixture model. It breaks time series into underlying segments and at the same time fits local linear regressive models to the clusters of segments. In such a way, a global non-stationary time series is represented by a dynamic set of local linear regressive models. Neural gas is used for a more flexible structure of the mixture model. Furthermore, a new similarity measure has been introduced in the self-organising network to better quantify the similarity of time series segments. The network can be used naturally in modelling and forecasting non-stationary time series. Experiments on artificial, benchmark time series (e.g. Mackey-Glass) and real-world data (e.g. numbers of sunspots and Forex rates) are presented and the results show that the proposed SOMAR network is effective and superior to other similar approaches. PMID:19145663
Time-resolved multispectral imaging of combustion reaction
NASA Astrophysics Data System (ADS)
Huot, Alexandrine; Gagnon, Marc-André; Jahjah, Karl-Alexandre; Tremblay, Pierre; Savary, Simon; Farley, Vincent; Lagueux, Philippe; Guyot, Éric; Chamberland, Martin; Marcotte, Fréderick
2015-05-01
Thermal infrared imaging is a field of science that evolves rapidly. Scientists have used for years the simplest tool: thermal broadband cameras. This allows to perform target characterization in both the longwave (LWIR) and midwave (MWIR) infrared spectral range. Infrared thermal imaging is used for a wide range of applications, especially in the combustion domain. For example, it can be used to follow combustion reactions, in order to characterize the injection and the ignition in a combustion chamber or even to observe gases produced by a flare or smokestack. Most combustion gases such as carbon dioxide (CO2) selectively absorb/emit infrared radiation at discrete energies, i.e. over a very narrow spectral range. Therefore, temperatures derived from broadband imaging are not reliable without prior knowledge about spectral emissivity. This information is not directly available from broadband images. However, spectral information is available using spectral filters. In this work, combustion analysis was carried out using Telops MS-IR MW camera which allows multispectral imaging at a high frame rate. A motorized filter wheel allowing synchronized acquisitions on eight (8) different channels was used to provide time-resolved multispectral imaging of combustion products of a candle in which black powder has been burnt to create a burst. It was then possible to estimate the temperature by modeling spectral profile derived from information obtained with the different spectral filters. Comparison with temperatures obtained using conventional broadband imaging illustrates the benefits of time-resolved multispectral imaging for the characterization of combustion processes.
Time-resolved multispectral imaging of combustion reactions
NASA Astrophysics Data System (ADS)
Huot, Alexandrine; Gagnon, Marc-André; Jahjah, Karl-Alexandre; Tremblay, Pierre; Savary, Simon; Farley, Vincent; Lagueux, Philippe; Guyot, Éric; Chamberland, Martin; Marcotte, Frédérick
2015-10-01
Thermal infrared imaging is a field of science that evolves rapidly. Scientists have used for years the simplest tool: thermal broadband cameras. These allow to perform target characterization in both the longwave (LWIR) and midwave (MWIR) infrared spectral range. Infrared thermal imaging is used for a wide range of applications, especially in the combustion domain. For example, it can be used to follow combustion reactions, in order to characterize the injection and the ignition in a combustion chamber or even to observe gases produced by a flare or smokestack. Most combustion gases, such as carbon dioxide (CO2), selectively absorb/emit infrared radiation at discrete energies, i.e. over a very narrow spectral range. Therefore, temperatures derived from broadband imaging are not reliable without prior knowledge of spectral emissivity. This information is not directly available from broadband images. However, spectral information is available using spectral filters. In this work, combustion analysis was carried out using a Telops MS-IR MW camera, which allows multispectral imaging at a high frame rate. A motorized filter wheel allowing synchronized acquisitions on eight (8) different channels was used to provide time-resolved multispectral imaging of combustion products of a candle in which black powder has been burnt to create a burst. It was then possible to estimate the temperature by modeling spectral profiles derived from information obtained with the different spectral filters. Comparison with temperatures obtained using conventional broadband imaging illustrates the benefits of time-resolved multispectral imaging for the characterization of combustion processes.
Spectral and spread-spectral teleportation
Humble, Travis S.
2010-06-15
We report how quantum information encoded into the spectral degree of freedom of a single-photon state may be teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of the teleported wave form can be controllably and coherently dilated using a spread-spectral variant of teleportation. We calculate analytical expressions for the fidelities of spectral and spread-spectral teleportation when complex-valued Gaussian states are transferred using a proposed experimental approach. Finally, we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.
Choi, Heejin; Wadduwage, Dushan; Matsudaira, Paul T; So, Peter T C
2014-10-01
A depth resolved hyperspectral imaging spectrometer can provide depth resolved imaging both in the spatial and the spectral domain. Images acquired through a standard imaging Fourier transform spectrometer do not have the depth-resolution. By post processing the spectral cubes (x, y, λ) obtained through a Sagnac interferometer under uniform illumination and structured illumination, spectrally resolved images with depth resolution can be recovered using structured light illumination algorithms such as the HiLo method. The proposed scheme is validated with in vitro specimens including fluorescent solution and fluorescent beads with known spectra. The system is further demonstrated in quantifying spectra from 3D resolved features in biological specimens. The system has demonstrated depth resolution of 1.8 μm and spectral resolution of 7 nm respectively. PMID:25360367
Choi, Heejin; Wadduwage, Dushan; Matsudaira, Paul T.; So, Peter T.C.
2014-01-01
A depth resolved hyperspectral imaging spectrometer can provide depth resolved imaging both in the spatial and the spectral domain. Images acquired through a standard imaging Fourier transform spectrometer do not have the depth-resolution. By post processing the spectral cubes (x, y, λ) obtained through a Sagnac interferometer under uniform illumination and structured illumination, spectrally resolved images with depth resolution can be recovered using structured light illumination algorithms such as the HiLo method. The proposed scheme is validated with in vitro specimens including fluorescent solution and fluorescent beads with known spectra. The system is further demonstrated in quantifying spectra from 3D resolved features in biological specimens. The system has demonstrated depth resolution of 1.8 μm and spectral resolution of 7 nm respectively. PMID:25360367
NASA Astrophysics Data System (ADS)
Chang, Ching-Min; Yeh, Hund-Der
2009-01-01
This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier-Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589-605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541-51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775-84].
Resource Prospector: The RESOLVE Payload
NASA Astrophysics Data System (ADS)
Quinn, J.; Smith, J.; J., Captain; Paz, A.; Colaprete, A.; Elphic, R.; Zacny, K.
2015-10-01
NASA has been developing a lunar volatiles exploration payload named RESOLVE. Now the primary science payload on-board the Resource Prospector (RP) mission, RESOLVE, consists of several instruments that evaluate lunar volatiles.
Dual Brushless Resolver Rate Sensor
NASA Technical Reports Server (NTRS)
Howard, David E. (Inventor)
1997-01-01
A resolver rate sensor is disclosed in which dual brushless resolvers are mechanically coupled to the same output shaft. Diverse inputs are provided to each resolver by providing the first resolver with a DC input and the second resolver with an AC sinusoidal input. A trigonometric identity in which the sum of the squares of the sin and cosine components equal one is used to advantage in providing a sensor of increased accuracy. The first resolver may have a fixed or variable DC input to permit dynamic adjustment of resolver sensitivity thus permitting a wide range of coverage. In one embodiment of the invention the outputs of the first resolver are directly inputted into two separate multipliers and the outputs of the second resolver are inputted into the two separate multipliers, after being demodulated in a pair of demodulator circuits. The multiplied signals are then added in an adder circuit to provide a directional sensitive output. In another embodiment the outputs from the first resolver is modulated in separate modulator circuits and the output from the modulator circuits are used to excite the second resolver. The outputs from the second resolver are demodulated in separate demodulator circuit and added in an adder circuit to provide a direction sensitive rate output.
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo
2007-01-01
One of the most promising methods to test the representation of cloud processes used in climate models is to use observations together with cloud-resolving models (CRMs). CRMs use more sophisticated and realistic representations of cloud microphysical processes, and they can reasonably well resolve the time evolution, structure, and life cycles of clouds and cloud systems (with sizes ranging from about 2-200 km). CRMs also allow for explicit interaction between clouds, outgoing longwave (cooling) and incoming solar (heating) radiation, and ocean and land surface processes. Observations are required to initialize CRMs and to validate their results. This paper provides a brief discussion and review of the main characteristics of CRMs as well as some of their major applications. These include the use of CRMs to improve our understanding of: (1) convective organization, (2) cloud temperature and water vapor budgets, and convective momentum transport, (3) diurnal variation of precipitation processes, (4) radiative-convective quasi-equilibrium states, (5) cloud-chemistry interaction, (6) aerosol-precipitation interaction, and (7) improving moist processes in large-scale models. In addition, current and future developments and applications of CRMs will be presented.
NASA Technical Reports Server (NTRS)
Captain, J.; Quinn, J.; Moss, T.; Weis, K.
2010-01-01
This slide presentation reviews the field tests conducted in 2010 of the Regolith Environment Science & Oxygen & Lunar Volatile Extraction (RESOLVE). The Resolve program consist of several mechanism: (1) Excavation and Bulk Regolith Characterization (EBRC) which is designed to act as a drill and crusher, (2) Regolith Volatiles Characterization (RVC) which is a reactor and does gas analysis,(3) Lunar Water Resources Demonstration (LWRD) which is a fluid system, water and hydrogen capture device and (4) the Rover. The scientific goal of this test is to demonstrate evolution of low levels of hydrogen and water as a function of temperature. The Engineering goals of this test are to demonstrate:(1) Integration onto new rover (2) Miniaturization of electronics rack (3) Operation from battery packs (elimination of generator) (4) Remote command/control and (5) Operation while roving. Views of the 2008 and the 2010 mechanisms, a overhead view of the mission path, a view of the terrain, the two drill sites, and a graphic of the Master Events Controller Graphical User Interface (MEC GUI) are shown. There are descriptions of the Gas chromatography (GC), the operational procedure, water and hydrogen doping of tephra. There is also a review of some of the results, and future direction for research and tests.
Modeling channel-floodplain hydrologic connectivity under non-stationary conditions
NASA Astrophysics Data System (ADS)
Call, B.; Belmont, P.
2015-12-01
Traditional floodplain inundation models typically rely on the assumption of stationary flood frequency distributions and static channel geometries. However, changes in climate, land cover, or water management have been shown to systematically shift the mean and variance of flood flows. Further, changes in flood magnitudes have been shown to cause systematic changes in channel widths and depths. Therefore, some amount of change in the flood regime will be absorbed by changes in channel conveyance, but the subsequent changes to the frequency and magnitude of floodplain inundation are not obvious. This work presents a numerical model of channel-floodplain hydrologic connectivity under non-stationary conditions. Specifically, the model predicts the width of floodplain inundation in response to a time series of synthetically generated floods. Flood time series are generated via generalized extreme value probability density functions (PDFs) with specified mean, variance, and skew parameters. To simulate non-stationary conditions, we modify the mean, variance, and/or skew systematically during each run. Throughout each model run, the geometry of the alluvial channel changes in response to flood flows according to simple hydraulic geometry relations. Results suggest that a river's inundation regime is more sensitive to changes in the variance parameter of a governing PDF than to changes in the mean parameter. Simple changes in the mean of the governing PDF result in changes to channel geometry (e.g. channel widening or narrowing), but the frequency and magnitude of inundation may adjust with time after the onset of non-stationary hydrology towards a state of dynamic equilibrium similar to the previous inundation regime. However, changes in the PDF's variance parameter can induce greater variation in channel geometry, often resulting in less frequent, but greater magnitudes of floodplain inundation.
Tracer breakthrough curves in a complex lysimeter system: evidence of non-stationary transport
NASA Astrophysics Data System (ADS)
Queloz, P.; Bertuzzo, E.; Botter, G.; Rao, P.; Rinaldo, A.
2013-12-01
We report on the outcomes of a lysimeter experiment aimed at the measurement of travel time distributions of water and certain nonreactive solutes under non-stationary conditions to examine the kinematics of age mixing. In order to simulate the release of a compound in a receiving water body, it is common in hydrology to attribute a travel time probability distribution to each particle, which reflects the response of a catchment unit to a solute input. Hence, the concentration measured at a control section becomes the convolution between the travel time distribution and the concentration of the inputs throughout the past. This study aims at experimentally demonstrating that the tracer travel time probability distribution is, in fact, strongly dependent on the antecedent conditions at the time of tracer injection and the subsequent states experienced in the system. It is therefore a function of numerous transient processes such as hydrologic filtering in soils, climatic forcing or evapotranspiration patterns. A 2-meter deep weighing lysimeter was equipped with a discharge measurement system coupled with a sample collector, an array of water content sensors and an array of porous cups for soil water sampling at three different depths. Controlled random rainfall following a Poisson process was generated, and evapotranspiration losses from two willow trees planted in the lysimeter created an important soil-water storage deficit. Five species of fluorobenzoic acids were used as tracers, and sequentially injected through rainfall at different times. The measurement system installed allowed a precise and accurate monitoring of every input and output flux and water storage, which is crucial to determine the conditions influencing the travel time distribution and to calculate the mass loads and recovery rates. Breakthrough curves for multiple tracers measured at several depths within the lysimeter and at the lysimeter outlet provide support for non-stationary tracer travel
Wong, Alexander; Wang, Xiao Yu; Gorbet, Maud
2015-01-01
Fluorescence microscopy is widely used for the study of biological specimens. Deconvolution can significantly improve the resolution and contrast of images produced using fluorescence microscopy; in particular, Bayesian-based methods have become very popular in deconvolution fluorescence microscopy. An ongoing challenge with Bayesian-based methods is in dealing with the presence of noise in low SNR imaging conditions. In this study, we present a Bayesian-based method for performing deconvolution using dynamically updated nonstationary expectation estimates that can improve the fluorescence microscopy image quality in the presence of noise, without explicit use of spatial regularization. PMID:26054051
Wong, Alexander; Wang, Xiao Yu; Gorbet, Maud
2015-01-01
Fluorescence microscopy is widely used for the study of biological specimens. Deconvolution can significantly improve the resolution and contrast of images produced using fluorescence microscopy; in particular, Bayesian-based methods have become very popular in deconvolution fluorescence microscopy. An ongoing challenge with Bayesian-based methods is in dealing with the presence of noise in low SNR imaging conditions. In this study, we present a Bayesian-based method for performing deconvolution using dynamically updated nonstationary expectation estimates that can improve the fluorescence microscopy image quality in the presence of noise, without explicit use of spatial regularization. PMID:26054051
The effect of white non-stationary data on drifting signal detection
NASA Astrophysics Data System (ADS)
Flores, Mauricio; Stroeer, Alexander; Benacquista, Matthew
2011-10-01
We analyze the effect of non-stationary noise in the detection of drifting signals on unevenly sampled data. Initial frequency estimation is obtained from a Lomb-Scargle periodogram; which is followed by a global multi-start optimization, as working on a dense local Nelder-Mead iterator for parameter estimates. It has been found that a varying white noise level has no effect on the required relative signal-to-noise ratio for detection in the proposed algorithm, though affecting the absolute amplitude strength of the signal recording. Future work includes the addition of colored noise to this analysis.
NASA Astrophysics Data System (ADS)
Lan, X. G.; Jiang, Q. Q.; Wei, L. F.
2012-04-01
We apply the Damour-Ruffini-Sannan method to study the Hawking radiations of scalar and Dirac particles in non-stationary Kerr black holes under different tortoise coordinate transformations. We found that all the relevant Hawking radiation spectra show still the blackbody ones, while the Hawking temperatures are strongly related to the used tortoise coordinate transformations. The properties of these dependences are discussed analytically and numerically. Our results imply that proper selections of tortoise coordinate transformations should be important in the studies of Hawking radiations and the correct selection would be given by the experimental observations in the future.
NASA Astrophysics Data System (ADS)
Wang, Ben; Zhang, Yimin D.; Qin, Si; Amin, Moeness G.
2016-05-01
In this paper, we propose a nonstationary jammer suppression method for GPS receivers when the signals are sparsely sampled. Missing data samples induce noise-like artifacts in the time-frequency (TF) distribution and ambiguity function of the received signals, which lead to reduced capability and degraded performance in jammer signature estimation and excision. In the proposed method, a data-dependent TF kernel is utilized to mitigate the artifacts and sparse reconstruction methods are then applied to obtain instantaneous frequency (IF) estimation of the jammers. In addition, an error tolerance of the IF estimate is applied is applied to achieve robust jammer suppression performance in the presence of IF estimation inaccuracy.
Acceleration of reinforcement learning by policy evaluation using nonstationary iterative method.
Senda, Kei; Hattori, Suguru; Hishinuma, Toru; Kohda, Takehisa
2014-12-01
Typical methods for solving reinforcement learning problems iterate two steps, policy evaluation and policy improvement. This paper proposes algorithms for the policy evaluation to improve learning efficiency. The proposed algorithms are based on the Krylov Subspace Method (KSM), which is a nonstationary iterative method. The algorithms based on KSM are tens to hundreds times more efficient than existing algorithms based on the stationary iterative methods. Algorithms based on KSM are far more efficient than they have been generally expected. This paper clarifies what makes algorithms based on KSM makes more efficient with numerical examples and theoretical discussions. PMID:24733037
A 1981-2012 Non-stationary AVHRR NDVI Global 8-km Data Set (Invited)
NASA Astrophysics Data System (ADS)
Tucker, C. J.; Pinzon, J. E.
2013-12-01
The longest global daily satellite data record is from the polar-orbiting advanced very high resolution radiometer or AVHRR instruments that started in July 1981 and continues uninterrupted to this day. In spite of non-optimum visible and near-infrared bandwidths, lack of orbital station-keeping early in the record, and '4-km' spatial resolution, we have produced a non-stationary and consistent NDVI record from that matches up well with coincident MODIS NDVI data. We review our processing methods and describe detailed coincident comparisons with MODIS NDVI data in many climate regions.
Optimal Fitting of Non-linear Detector Pulses with Nonstationary Noise
NASA Technical Reports Server (NTRS)
Fixsen, D. J.; Moseley, S. H.; Cabera, B.; Figueroa-Felicianco, E.; Oegerle, William (Technical Monitor)
2002-01-01
Optimal extraction of pulses of constant known shape from a time series with stationary noise is well understood and widely used in detection applications. Applications where high resolution is required over a wide range of input signal amplitudes use much of the dynamic range of the sensor. The noise will in general vary over this signal range, and the response may be a nonlinear function of the energy input. We present an optimal least squares procedure for inferring input energy in such a detector with nonstationary noise and nonlinear energy response.
On the functional optimization of a certain class of nonstationary spatial functions
Christakos, G.; Paraskevopoulos, P.N.
1987-01-01
Procedures are developed in order to obtain optimal estimates of linear functionals for a wide class of nonstationary spatial functions. These procedures rely on well-established constrained minimum-norm criteria, and are applicable to multidimensional phenomena which are characterized by the so-called hypothesis of inherentity. The latter requires elimination of the polynomial, trend-related components of the spatial function leading to stationary quantities, and also it generates some interesting mathematics within the context of modelling and optimization in several dimensions. The arguments are illustrated using various examples, and a case study computed in detail. ?? 1987 Plenum Publishing Corporation.
Application of a hybrid approach in nonstationary flood frequency analysis - a Polish perspective
NASA Astrophysics Data System (ADS)
Kochanek, K.; Strupczewski, W. G.; Bogdanowicz, E.; Feluch, W.; Markiewicz, I.
2013-10-01
The alleged changes in rivers' flow regime resulted in the surge in the methods of non-stationary flood frequency analysis (NFFA). The maximum likelihood method is said to produce big systematic errors in moments and quantiles resulting mainly from bad assumption of the model (model error) unless this model is the normal distribution. Since the estimators by the method of linear moments (L-moments) yield much lower model errors than those by the maximum likelihood, to improve the accuracy of the parameters and quantiles in non-stationary case, a new two-stage methodology of NFFA based on the concept of L-moments was developed. Despite taking advantage of the positive characteristics of L-moments, a new technique also allows to keep the calculations "distribution independent" as long as possible. These two stages consists in (1) least square estimation of trends in mean value and/or in standard deviation and "de-trendisation" of the time series and (2) estimation of parameters and quantiles by means of stationary sample with L-moments method and "re-trendisation" of quantiles. As a result time-dependent quantiles for a given time and return period can be calculated. The comparative results of Monte Carlo simulations confirmed the superiority of two-stage NFFA methodology over the classical maximum likelihood one. Further analysis of trends in GEV-parent-distributed generic time series by means of both NFFA methods revealed big differences between classical and two-stage estimators of trends got for the same data by the same model (GEV or Gumbel). Additionally, it turned out that the quantiles estimated by the methods of traditional stationary flood frequency analysis equal only to those non-stationary calculated for a strict middle of the time series. It proves that use of traditional stationary methods in conditions of variable regime is too much a simplification and leads to erroneous results. Therefore, when the phenomenon is non-stationary, so should be the
NASA Astrophysics Data System (ADS)
Plachenov, A. B.
An algorithm is proposed for the transition from the short-wave asymptotics of stationary problems to the space-time asymptotics of nonstationary problems of linear wave propagation. The relationship between this algorithm and constructs of the spatial-temporal ray tracing method is examined. As an example, the algorithm is applied to the problem of the detection of a diffraction wave in the deep shade behind a smooth convex obstacle in the case where the incident wave is specified by its spatial-temporal ray expansion.
Nonstationary heat transfer in a channel containing saturated He II: stepped heat loading
Shaposhnikov, V.A.; Mikhailov, I.I.; Efimova, L.N.; Romchenko, D.G.
1988-09-01
Measurements have been made on the nonstationary temperature distribution in a channel containing saturated superfluid He II under countercurrent conditions with local heat input to the middle of the channel as a stepped function. A numerical method has been developed which incorporates the variable thermophysical parameters for the helium. Those parameters include local heat flux and thermal conductivity related to internal component convection, heat flux density, specific enthalpy and entropy, the Goerter-Mellink friction constant, and the Kapitza conductivity coefficient. Agreement of the variable-property calculations with experiment is evaluated. It is concluded that saturated He II responds to pulse loading as does underheated He II.
Solution to the backward-Kolmogorov equation for a nonstationary oscillation problem
NASA Technical Reports Server (NTRS)
Solomos, G. P.; Spanos, P.-T. D.
1982-01-01
The transition probability density function of a Markovian approximation of the response amplitude of an oscillator under nonstationary excitation is determined in an analytical form. A solution is presented for the associated backward-Kolmogorov equation by transforming the equation into a form amenable to solution by the method of the separation of variables. This procedure results in a boundary value problem which is then solved by using an infinite series of Laguerre polynomials. It is found that the infinite series solution is equivalent to a closed-form solution involving a Bessel function.
Two-Microphone Noise Reduction Using Spatial Information-Based Spectral Amplitude Estimation
NASA Astrophysics Data System (ADS)
Li, Kai; Guo, Yanmeng; Fu, Qiang; Li, Junfeng; Yan, Yonghong
Traditional two-microphone noise reduction algorithms to deal with highly nonstationary directional noises generally use the direction of arrival or phase difference information. The performance of these algorithms deteriorate when diffuse noises coexist with nonstationary directional noises in realistic adverse environments. In this paper, we present a two-channel noise reduction algorithm using a spatial information-based speech estimator and a spatial-information-controlled soft-decision noise estimator to improve the noise reduction performance in realistic non-stationary noisy environments. A target presence probability estimator based on Bayes rules using both phase difference and magnitude squared coherence is proposed for soft-decision of noise estimation, so that they can share complementary advantages when both directional noises and diffuse noises are present. Performances of the proposed two-microphone noise reduction algorithm are evaluated by noise reduction, log-spectral distance (LSD) and word recognition rate (WRR) of a distant-talking ASR system in a real room's noisy environment. Experimental results show that the proposed algorithm achieves better noises suppression without further distorting the desired signal components over the comparative dual-channel noise reduction algorithms.
Time-Spectral Rotorcraft Simulations on Overset Grids
NASA Technical Reports Server (NTRS)
Leffell, Joshua I.; Murman, Scott M.; Pulliam, Thomas H.
2014-01-01
The Time-Spectral method is derived as a Fourier collocation scheme and applied to NASA's overset Reynolds-averaged Navier-Stokes (RANS) solver OVERFLOW. The paper outlines the Time-Spectral OVERFLOWimplementation. Successful low-speed laminar plunging NACA 0012 airfoil simulations demonstrate the capability of the Time-Spectral method to resolve the highly-vortical wakes typical of more expensive three-dimensional rotorcraft configurations. Dealiasing, in the form of spectral vanishing viscosity (SVV), facilitates the convergence of Time-Spectral calculations of high-frequency flows. Finally, simulations of the isolated V-22 Osprey tiltrotor for both hover and forward (edgewise) flight validate the three-dimensional Time-Spectral OVERFLOW implementation. The Time-Spectral hover simulation matches the time-accurate calculation using a single harmonic. Significantly more temporal modes and SVV are required to accurately compute the forward flight case because of its more active, high-frequency wake.
Spectral topography of histopathological samples
NASA Astrophysics Data System (ADS)
Lerner, Jeremy M.; Lu, Thomas T.; Vari, Sandor G.
1998-06-01
The goal of imaging spectroscopy is to obtain independent spectra from individual objects in a field-of-view. In the case of biological materials, such as histopathology samples, it has been well established that spectral characteristic can be indicative of specific diseases including cancer. Diagnosis can be enhanced by the use of probes and stains to indicate the presence of individual genome or other biologically active cell components or substances. To assess a specimen through a microscope is directly analogous to serving the Earth from space to assess natural features. This paper describes a simple and inexpensive imaging spectrometer, with an origin in remote sensing, that demonstrates that it is possible to rapidly identify evidence of disease in histopathology samples using spatially resolved spectral data. The PARISS imaging spectrometer enables a researcher to acquire multi-spectral images that yield functional maps, showing what and where biological molecules are located within a structure. It is the powerful combination of imaging and spectroscopy that provides the tools not readily available to the Life Sciences. The PARISS system incorporates a powerful hybrid neural network analysis to break the data logjam that is often associated with the acquisition and processing of multiple spectra.
Spectral methods to detect surface mines
NASA Astrophysics Data System (ADS)
Winter, Edwin M.; Schatten Silvious, Miranda
2008-04-01
Over the past five years, advances have been made in the spectral detection of surface mines under minefield detection programs at the U. S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate (NVESD). The problem of detecting surface land mines ranges from the relatively simple, the detection of large anti-vehicle mines on bare soil, to the very difficult, the detection of anti-personnel mines in thick vegetation. While spatial and spectral approaches can be applied to the detection of surface mines, spatial-only detection requires many pixels-on-target such that the mine is actually imaged and shape-based features can be exploited. This method is unreliable in vegetated areas because only part of the mine may be exposed, while spectral detection is possible without the mine being resolved. At NVESD, hyperspectral and multi-spectral sensors throughout the reflection and thermal spectral regimes have been applied to the mine detection problem. Data has been collected on mines in forest and desert regions and algorithms have been developed both to detect the mines as anomalies and to detect the mines based on their spectral signature. In addition to the detection of individual mines, algorithms have been developed to exploit the similarities of mines in a minefield to improve their detection probability. In this paper, the types of spectral data collected over the past five years will be summarized along with the advances in algorithm development.
Spectral response of multilayer optical structures to dynamic mechanical loading
NASA Astrophysics Data System (ADS)
Scripka, David; LeCroy, Garrett; Summers, Christopher J.; Thadhani, Naresh N.
2015-05-01
A computational study of Distributed Bragg Reflectors (DBR) and Optical Microcavities (OMC) was conducted to ascertain their potential as time-resolved mesoscale sensors due to their unique structure-driven spectral characteristics. Shock wave propagation simulations of polymer-based DBRs and glass/ceramic-based OMCs were coupled with spectral response calculations to demonstrate the combined dynamic mechanical and spectral response of the structures. Clear spectral shifts in both structures are predicted as a function of dynamic loading magnitude. Potential applications of the structures include high spatial and temporal resolution surface maps of material states, and in-situ probing of material interfaces during dynamic loading.
Georges Bank conflict resolved
NASA Astrophysics Data System (ADS)
Robb, David W.
1984-04-01
The International Court of Justice has resolved the long-term conflict between the United States and Canada over claims to mineral and living resources lying along the countries' common Atlantic maritime border. On October 12, in a 4-1 decision, the World Court rejected the United States' claim to the entire Georges Bank area, a region of the Continental Shelf off Massachusetts and Nova Scotia that is a prime fishing ground and is believed to have good potential for oil and gas deposits as well. The disputed area is roughly the top third of the Georges Bank area. The court awarded each country approximately half of this disputed area. No appeals are allowed under this decision.
The effect of scattering on nonstationary radiation-conduction heat transfer in a two-layer system
NASA Astrophysics Data System (ADS)
Rubtsov, N. A.; Golova, E. P.
1986-06-01
The boundary value problem of nonstationary radiation-conduction heat transfer in a system of two plane layers with different thermophysical properties has been formulated with allowance for scattering in one of the layers. An algorithm for solving the problem has been developed and implemented in software written in FORTRAN. An analysis is made of the effect of the radiation-conduction parameter, single scattering albedo, and scattering anisotropy on the nonstationary temperature field of the system. It is shown that the temperature field depends to a large degree on the optical inhomogeneity of the system.
Non-Stationary Hydrologic Frequency Analysis using B-Splines Quantile Regression
NASA Astrophysics Data System (ADS)
Nasri, B.; St-Hilaire, A.; Bouezmarni, T.; Ouarda, T.
2015-12-01
Hydrologic frequency analysis is commonly used by engineers and hydrologists to provide the basic information on planning, design and management of hydraulic structures and water resources system under the assumption of stationarity. However, with increasing evidence of changing climate, it is possible that the assumption of stationarity would no longer be valid and the results of conventional analysis would become questionable. In this study, we consider a framework for frequency analysis of extreme flows based on B-Splines quantile regression, which allows to model non-stationary data that have a dependence on covariates. Such covariates may have linear or nonlinear dependence. A Markov Chain Monte Carlo (MCMC) algorithm is used to estimate quantiles and their posterior distributions. A coefficient of determination for quantiles regression is proposed to evaluate the estimation of the proposed model for each quantile level. The method is applied on annual maximum and minimum streamflow records in Ontario, Canada. Climate indices are considered to describe the non-stationarity in these variables and to estimate the quantiles in this case. The results show large differences between the non-stationary quantiles and their stationary equivalents for annual maximum and minimum discharge with high annual non-exceedance probabilities. Keywords: Quantile regression, B-Splines functions, MCMC, Streamflow, Climate indices, non-stationarity.
Nonstationary filtered shot-noise processes and applications to neuronal membranes
NASA Astrophysics Data System (ADS)
Brigham, Marco; Destexhe, Alain
2015-06-01
Filtered shot noise processes have proven to be very effective in modeling the evolution of systems exposed to shot noise sources and have been applied to a wide variety of fields ranging from electronics through biology. In particular, they can model the membrane potential Vm of neurons driven by stochastic input, where these filtered processes are able to capture the nonstationary characteristics of Vm fluctuations in response to presynaptic input with variable rate. In this paper we apply the general framework of Poisson point processes transformations to analyze these systems in the general case of nonstationary input rates. We obtain exact analytic expressions, as well as different approximations, for the joint cumulants of filtered shot noise processes with multiplicative noise. These general results are then applied to a model of neuronal membranes subject to conductance shot noise with a continuously variable rate of presynaptic spikes. We propose very effective approximations for the time evolution of the Vm distribution and a simple method to estimate the presynaptic rate from a small number of Vm traces. This work opens the perspective of obtaining analytic access to important statistical properties of conductance-based neuronal models such as the first passage time.
Control-nonlinear-nonstationary structural response and radiation near a supersonic jet
NASA Technical Reports Server (NTRS)
Maestrello, Lucio
1994-01-01
This paper is on the control of nonlinear-nonstationary vibration of a frame-stringer structure resulting from high levels of excitaation from a nearby supersonic jet exhaust. The structure exhibits periodic, chaotic, or random behaviors when forced by high-intensity sound from a supersonic jet exhaust with shock loading superimposed on the broadband response. The time history of the pressure, showing the rotation and flapping of the shock structure in the jet column due to large-scale instabilities, indicates that the response is not only nonlinear but also nonstationary. The acoustic pressure radiated by the structure also contains shocks and the formation of harmonics with distance. Control of the structural response is achieved by actively forcing the structure with an actuator at the shock oscillation frequency whose amplitude is locked into a self-control cycle. Results show that the peak power level is reduced by a factor of 63, or 18 dB. As a result, new broadband components emerge with at least four harmonics. At accelerating and decelerating supersonic speeds, the exhaust from the jet induces higher transient loading on the nearby flexible structure due to the occurence of multiple shocks from the jet.
Control-nonlinear-nonstationary structural response and radiation near a supersonic jet
NASA Technical Reports Server (NTRS)
Maestrello, Lucio
1994-01-01
This paper is on the control of nonlinear-nonstationary vibration of a frame-stringer structure resulting from high levels of excitation from a nearby supersonic jet exhaust. The structure exhibits periodic, chaotic, or random behaviors when forced by high-intensity sound from a supersonic jet exhaust with 'shock' loading superimposed on a broadband response. The time history of the pressure, showing the rotation and flapping of the shock structure in the jet column due to large-scale instabilities, indicates that the response is not only nonlinear but also nonstationary. The acoustic pressure radiated by the structure also contains shocks and the formation of harmonics with distance. Control of the structural response is achieved by actively forcing the structure with an actuator at the shock oscillation frequency whose amplitude is locked into a self-control cycle. Results show that the peak power level is reduced by a factor of 63, or 18 dB. As a result, new broadband components emerge with at least four harmonics. At accelerating and decelerating supersonic speeds, the exhaust from the jet induces higher transient loading on the nearby flexible structure due to the occurrence of multiple shock from the jet.
Anomalous diffusion as modeled by a nonstationary extension of Brownian motion
NASA Astrophysics Data System (ADS)
Cushman, John H.; O'Malley, Daniel; Park, Moongyu
2009-03-01
If the mean-square displacement of a stochastic process is proportional to tβ , β≠1 , then it is said to be anomalous. We construct a family of Markovian stochastic processes with independent nonstationary increments and arbitrary but a priori specified mean-square displacement. We label the family as an extended Brownian motion and show that they satisfy a Langevin equation with time-dependent diffusion coefficient. If the time derivative of the variance of the process is homogeneous, then by computing the fractal dimension it can be shown that the complexity of the family is the same as that of the Brownian motion. For two particles initially separated by a distance x , the finite-size Lyapunov exponent (FSLE) measures the average rate of exponential separation to a distance ax . An analytical expression is developed for the FSLEs of the extended Brownian processes and numerical examples presented. The explicit construction of these processes illustrates that contrary to what has been stated in the literature, a power-law mean-square displacement is not necessarily related to a breakdown in the classical central limit theorem (CLT) caused by, for example, correlation (fractional Brownian motion or correlated continuous-time random-walk schemes) or infinite variance (Levy motion). The classical CLT, coupled with nonstationary increments, can and often does give rise to power-law moments such as the mean-square displacement.
A novel data-driven learning method for radar target detection in nonstationary environments
Akcakaya, Murat; Nehorai, Arye; Sen, Satyabrata
2016-04-12
Most existing radar algorithms are developed under the assumption that the environment (clutter) is stationary. However, in practice, the characteristics of the clutter can vary enormously depending on the radar-operational scenarios. If unaccounted for, these nonstationary variabilities may drastically hinder the radar performance. Therefore, to overcome such shortcomings, we develop a data-driven method for target detection in nonstationary environments. In this method, the radar dynamically detects changes in the environment and adapts to these changes by learning the new statistical characteristics of the environment and by intelligibly updating its statistical detection algorithm. Specifically, we employ drift detection algorithms to detectmore » changes in the environment; incremental learning, particularly learning under concept drift algorithms, to learn the new statistical characteristics of the environment from the new radar data that become available in batches over a period of time. The newly learned environment characteristics are then integrated in the detection algorithm. Furthermore, we use Monte Carlo simulations to demonstrate that the developed method provides a significant improvement in the detection performance compared with detection techniques that are not aware of the environmental changes.« less
Separation of non-stationary sound fields with single layer pressure-velocity measurements.
Bi, Chuan-Xing; Geng, Lin; Zhang, Xiao-Zheng
2016-02-01
This paper examines the feasibility of extracting the non-stationary sound field generated by a target source in the presence of disturbing source from single layer pressure-velocity measurements. Unlike the method described in a previous paper [Bi, Geng, and Zhang, J. Acoust. Soc. Am. 135(6), 3474-3482 (2014)], the proposed method allows measurements of pressure and particle velocity signals on a single plane instead of pressure signals on two planes, and the time-dependent pressure generated by the target source is extracted by a simple superposition of the measured pressure and the convolution between the measured particle velocity and the corresponding impulse response function. Because the particle velocity here is measured directly, the error caused by the finite difference approximation can be avoided, which makes it possible to perform the separation better than the previous method. In this paper, a Microflown pressure-velocity probe is used to perform the experimental measurements, and the calibration procedure of the probe in the time domain is given. The experimental results demonstrate that the proposed method is effective in extracting the desired non-stationary sound field generated by the target source from the mixed one in both time and space domains, and it obtains more accurate results than the previous method. PMID:26936560
Dempster-Shafer fusion of multisensor signals in nonstationary Markovian context
NASA Astrophysics Data System (ADS)
Boudaren, Mohamed El Yazid; Monfrini, Emmanuel; Pieczynski, Wojciech; Aïssani, Amar
2012-12-01
The latest developments in Markov models' theory and their corresponding computational techniques have opened new rooms for image and signal modeling. In particular, the use of Dempster-Shafer theory of evidence within Markov models has brought some keys to several challenging difficulties that the conventional hidden Markov models cannot handle. These difficulties are concerned mainly with two situations: multisensor data, where the use of the Dempster-Shafer fusion is unworkable; and nonstationary data, due to the mismatch between the estimated stationary model and the actual data. For each of the two situations, the Dempster-Shafer combination rule has been applied, thanks to the triplet Markov models' formalism, to overcome the drawbacks of the standard Bayesian models. However, so far, both situations have not been considered in the same time. In this article, we propose an evidential Markov chain that uses the Dempster-Shafer combination rule to bring the effect of contextual information into segmentation of multisensor nonstationary data. We also provide the Expectation-Maximization parameters' estimation and the maximum posterior marginal's restoration procedures. To validate the proposed model, experiments are conducted on some synthetic multisensor data and noised images. The obtained segmentation results are then compared to those obtained with conventional approaches to bring out the efficiency of the present model.
Signal Restoration of Non-stationary Acoustic Signals in the Time Domain
NASA Technical Reports Server (NTRS)
Babkin, Alexander S.
1988-01-01
Signal restoration is a method of transforming a nonstationary signal acquired by a ground based microphone to an equivalent stationary signal. The benefit of the signal restoration is a simplification of the flight test requirements because it could dispense with the need to acquire acoustic data with another aircraft flying in concert with the rotorcraft. The data quality is also generally improved because the contamination of the signal by the propeller and wind noise is not present. The restoration methodology can also be combined with other data acquisition methods, such as a multiple linear microphone array for further improvement of the test results. The methodology and software are presented for performing the signal restoration in the time domain. The method has no restrictions on flight path geometry or flight regimes. Only requirement is that the aircraft spatial position be known relative to the microphone location and synchronized with the acoustic data. The restoration process assumes that the moving source radiates a stationary signal, which is then transformed into a nonstationary signal by various modulation processes. The restoration contains only the modulation due to the source motion.
NASA Astrophysics Data System (ADS)
Rocha, Paulo; Raischel, Frank; Boto, João P.; Lind, Pedro G.
2016-05-01
We present a framework for describing the evolution of stochastic observables having a nonstationary distribution of values. The framework is applied to empirical volume-prices from assets traded at the New York Stock Exchange, about which several remarks are pointed out from our analysis. Using Kullback-Leibler divergence we evaluate the best model out of four biparametric models commonly used in the context of financial data analysis. In our present data sets we conclude that the inverse Γ distribution is a good model, particularly for the distribution tail of the largest volume-price fluctuations. Extracting the time series of the corresponding parameter values we show that they evolve in time as stochastic variables themselves. For the particular case of the parameter controlling the volume-price distribution tail we are able to extract an Ornstein-Uhlenbeck equation which describes the fluctuations of the highest volume-prices observed in the data. Finally, we discuss how to bridge the gap from the stochastic evolution of the distribution parameters to the stochastic evolution of the (nonstationary) observable and put our conclusions into perspective for other applications in geophysics and biology.
Local multifractal detrended fluctuation analysis for non-stationary image's texture segmentation
NASA Astrophysics Data System (ADS)
Wang, Fang; Li, Zong-shou; Li, Jin-wei
2014-12-01
Feature extraction plays a great important role in image processing and pattern recognition. As a power tool, multifractal theory is recently employed for this job. However, traditional multifractal methods are proposed to analyze the objects with stationary measure and cannot for non-stationary measure. The works of this paper is twofold. First, the definition of stationary image and 2D image feature detection methods are proposed. Second, a novel feature extraction scheme for non-stationary image is proposed by local multifractal detrended fluctuation analysis (Local MF-DFA), which is based on 2D MF-DFA. A set of new multifractal descriptors, called local generalized Hurst exponent (Lhq) is defined to characterize the local scaling properties of textures. To test the proposed method, both the novel texture descriptor and other two multifractal indicators, namely, local Hölder coefficients based on capacity measure and multifractal dimension Dq based on multifractal differential box-counting (MDBC) method, are compared in segmentation experiments. The first experiment indicates that the segmentation results obtained by the proposed Lhq are better than the MDBC-based Dq slightly and superior to the local Hölder coefficients significantly. The results in the second experiment demonstrate that the Lhq can distinguish the texture images more effectively and provide more robust segmentations than the MDBC-based Dq significantly.
Rocha, Paulo; Raischel, Frank; Boto, João P; Lind, Pedro G
2016-05-01
We present a framework for describing the evolution of stochastic observables having a nonstationary distribution of values. The framework is applied to empirical volume-prices from assets traded at the New York Stock Exchange, about which several remarks are pointed out from our analysis. Using Kullback-Leibler divergence we evaluate the best model out of four biparametric models commonly used in the context of financial data analysis. In our present data sets we conclude that the inverse Γ distribution is a good model, particularly for the distribution tail of the largest volume-price fluctuations. Extracting the time series of the corresponding parameter values we show that they evolve in time as stochastic variables themselves. For the particular case of the parameter controlling the volume-price distribution tail we are able to extract an Ornstein-Uhlenbeck equation which describes the fluctuations of the highest volume-prices observed in the data. Finally, we discuss how to bridge the gap from the stochastic evolution of the distribution parameters to the stochastic evolution of the (nonstationary) observable and put our conclusions into perspective for other applications in geophysics and biology. PMID:27300845
NASA Astrophysics Data System (ADS)
Feng, Zhipeng; Chen, Xiaowang; Liang, Ming
2015-02-01
The synchrosqueezing transform can effectively improve the readability of time-frequency representation of mono-component and constant frequency signals. However, for multi-component and time-variant frequency signals, it still suffers from time-frequency blurs. In order to address this issue, the synchrosqueezing transform is improved using iterative generalized demodulation. Firstly, the complex nonstationary signal is decomposed into mono-components of constant frequency by iterative generalized demodulation. Then, the instantaneous frequency of each mono-component is accurately estimated via the synchrosqueezing transform, by exploiting its merit of enhanced time-frequency resolution. Finally, the time-frequency representation of the original signal is obtained by superposing the time-frequency representations of all the mono-components with restored instantaneous frequency. This proposed method generalizes the synchrosqueezing transform to multi-component and time-variant frequency signals, and it has fine time-frequency resolution and is free of cross-term interferences. The proposed method was validated using both numerically simulated and lab experimental vibration signals of planetary gearboxes under nonstationary conditions. The time-variant planetary gearbox characteristic frequencies were effectively identified, and the gear faults were correctly diagnosed.
Kjeldsen, T. R.; Miller, J. D.
2015-01-01
Abstract This study investigates whether long‐term changes in observed series of high flows can be attributed to changes in land use via nonstationary flood‐frequency analyses. A point process characterization of threshold exceedances is used, which allows for direct inclusion of covariates in the model; as well as a nonstationary model for block maxima series. In particular, changes in annual, winter, and summer block maxima and peaks over threshold extracted from gauged instantaneous flows records in two hydrologically similar catchments located in proximity to one another in northern England are investigated. The study catchment is characterized by large increases in urbanization levels in recent decades, while the paired control catchment has remained undeveloped during the study period (1970–2010). To avoid the potential confounding effect of natural variability, a covariate which summarizes key climatological properties is included in the flood‐frequency model. A significant effect of the increasing urbanization levels on high flows is detected, in particular in the summer season. Point process models appear to be superior to block maxima models in their ability to detect the effect of the increase in urbanization levels on high flows. PMID:26877559
Climate Cycles and Forecasts of Cutaneous Leishmaniasis, a Nonstationary Vector-Borne Disease
Chaves, Luis Fernando; Pascual, Mercedes
2006-01-01
Background Cutaneous leishmaniasis (CL) is one of the main emergent diseases in the Americas. As in other vector-transmitted diseases, its transmission is sensitive to the physical environment, but no study has addressed the nonstationary nature of such relationships or the interannual patterns of cycling of the disease. Methods and Findings We studied monthly data, spanning from 1991 to 2001, of CL incidence in Costa Rica using several approaches for nonstationary time series analysis in order to ensure robustness in the description of CL's cycles. Interannual cycles of the disease and the association of these cycles to climate variables were described using frequency and time-frequency techniques for time series analysis. We fitted linear models to the data using climatic predictors, and tested forecasting accuracy for several intervals of time. Forecasts were evaluated using “out of fit” data (i.e., data not used to fit the models). We showed that CL has cycles of approximately 3 y that are coherent with those of temperature and El Niño Southern Oscillation indices (Sea Surface Temperature 4 and Multivariate ENSO Index). Conclusions Linear models using temperature and MEI can predict satisfactorily CL incidence dynamics up to 12 mo ahead, with an accuracy that varies from 72% to 77% depending on prediction time. They clearly outperform simpler models with no climate predictors, a finding that further supports a dynamical link between the disease and climate. PMID:16903778
A review on prognostic techniques for non-stationary and non-linear rotating systems
NASA Astrophysics Data System (ADS)
Kan, Man Shan; Tan, Andy C. C.; Mathew, Joseph
2015-10-01
The field of prognostics has attracted significant interest from the research community in recent times. Prognostics enables the prediction of failures in machines resulting in benefits to plant operators such as shorter downtimes, higher operation reliability, reduced operations and maintenance cost, and more effective maintenance and logistics planning. Prognostic systems have been successfully deployed for the monitoring of relatively simple rotating machines. However, machines and associated systems today are increasingly complex. As such, there is an urgent need to develop prognostic techniques for such complex systems operating in the real world. This review paper focuses on prognostic techniques that can be applied to rotating machinery operating under non-linear and non-stationary conditions. The general concept of these techniques, the pros and cons of applying these methods, as well as their applications in the research field are discussed. Finally, the opportunities and challenges in implementing prognostic systems and developing effective techniques for monitoring machines operating under non-stationary and non-linear conditions are also discussed.
An intelligent approach for variable size segmentation of non-stationary signals.
Azami, Hamed; Hassanpour, Hamid; Escudero, Javier; Sanei, Saeid
2015-09-01
In numerous signal processing applications, non-stationary signals should be segmented to piece-wise stationary epochs before being further analyzed. In this article, an enhanced segmentation method based on fractal dimension (FD) and evolutionary algorithms (EAs) for non-stationary signals, such as electroencephalogram (EEG), magnetoencephalogram (MEG) and electromyogram (EMG), is proposed. In the proposed approach, discrete wavelet transform (DWT) decomposes the signal into orthonormal time series with different frequency bands. Then, the FD of the decomposed signal is calculated within two sliding windows. The accuracy of the segmentation method depends on these parameters of FD. In this study, four EAs are used to increase the accuracy of segmentation method and choose acceptable parameters of the FD. These include particle swarm optimization (PSO), new PSO (NPSO), PSO with mutation, and bee colony optimization (BCO). The suggested methods are compared with other most popular approaches (improved nonlinear energy operator (INLEO), wavelet generalized likelihood ratio (WGLR), and Varri's method) using synthetic signals, real EEG data, and the difference in the received photons of galactic objects. The results demonstrate the absolute superiority of the suggested approach. PMID:26425359
Statistical approaches to nonstationary EEGs for the detection of slow vertex responses.
Fujikake, M; Ninomija, S P; Fujita, H
1989-06-01
A slow vertex response (SVR) is an electric auditory evoked response used for an objective hearing power test. One of the aims of an objective hearing power test is to find infants whose hearing is less than that of normal infants. Early medical treatment is important for infants with a loss of hearing so that they do not have retarded growth. To measure SVRs, we generally use the averaged summation method of an electroencephalogram (EEG), because the signal-to-noise ratio (SVR to EEG and etc.) is very poor. To increase the reliability and stability of measured SVRs, and at the same time, to make the burden of testing light, it is necessary to device an effective measurement method of SVR. Two factors must be considered: (1) SVR waveforms change following the changes of EEGs caused by sleeping and (2) EEGs are considered as nonstationary data in prolonged measurement. In this paper, five statistical methods are used on two different models; a stationary model and a nonstationary model. Through the comparison of waves obtained by each method, we will clarify the statistical characteristics of the original data (EEGs including SVRs), and consider the conditions that effect the measurement method of an SVR. PMID:2794816
Sporadic randomness: the transition from the stationary to the nonstationary condition.
Ignaccolo, M; Grigolini, P; Rosa, A
2001-08-01
We address the study of sporadic randomness by means of the Manneville map. We point out that the Manneville map is the generator of fluctuations yielding the Lévy processes, and that these processes are currently regarded by some authors as statistical manifestations of a nonextensive form of thermodynamics. For this reason we study the sensitivity to initial conditions with the help of a nonextensive form of the Lyapunov coefficient. The purpose of this research is twofold. The former is to assess whether a finite diffusion coefficient might emerge from the nonextensive approach. This property, at first sight, seems to be plausible in the nonstationary case, where conventional Kolmogorov-Sinai analysis predicts a vanishing Lyapunov coefficient. The latter purpose is to confirm or reject conjectures about the nonextensive nature of Lévy processes. We find that the adoption of a nonextensive approach does not serve any predictive purpose: It does not even signal a transition from a stationary to a nonstationary regime. These conclusions are reached by means of both numerical and analytical calculations that shed light on why the Lévy processes do not imply any need to depart from the adoption of traditional complexity measures. PMID:11497680
Spatially Resolved Infrared Spectroscopy of Seyfert Galaxies
NASA Astrophysics Data System (ADS)
Knop, Robert Andrew, Jr.
This thesis presents infrared spectroscopy of the circumnuclear regions of 23 Seyfert galaxies. Observations are spectrally resolved with a resolution of λΔλ~1000 and spatially resolved to ~1'', corresponding to ~102 pc for the objects in the sample. The instrument used for the observations, the Palomar Near-Infrared Spectrometer, is described, and problems peculiar to reduction of data from it are discussed. The lines observed include Paβ, Brγ, (FeII) (λ=1.2567μm), and H2 (λ=2.1213μm). In nine objects, the coronal line (SIX) (λ=1.2524μm) is also detected. Spatially resolved line emission is clearly visible in approximately half of the objects observed. The data for five of the objects showing the best spatially resolved infrared line emission are analyzed in detail. These objects include Seyfert 1.5 galaxy NGC 4151 and Seyfert 2 galaxies Mk 1066, NGC 2110, NGC 4388, and Mk 3. The data for the remaining objects is presented in tabular form, and each object is discussed briefly. The data argue that processes associated with the Seyfert nucleus are responsible for the bulk of the observed (FeII) emission. Kinematic and spatial associations can be drawn between features in the (FeII) line profiles and other processes associated with the active nucleus, such as outflows seen in ionized optical emission and radio lobes. Most of the (FeII) appears to emerge from partially ionized regions excited by nuclear x-rays, with an additional contribution from fast shocks. Some of the H2 emission also appears to be associated with the nuclear activity. However, in some cases the H2 emission is observed to have a different spatial distribution from (FeII) and the H+ emission. The H2 emission is probably thermally excited. No significant differences are found between the infrared line emission of Seyfert and Seyfert 1.x galaxies.
A New View of Earthquake Ground Motion Data: The Hilbert Spectral Analysis
NASA Technical Reports Server (NTRS)
Huang, Norden; Busalacchi, Antonio J. (Technical Monitor)
2000-01-01
A brief description of the newly developed Empirical Mode Decomposition (ENID) and Hilbert Spectral Analysis (HSA) method will be given. The decomposition is adaptive and can be applied to both nonlinear and nonstationary data. Example of the method applied to a sample earthquake record will be given. The results indicate those low frequency components, totally missed by the Fourier analysis, are clearly identified by the new method. Comparisons with Wavelet and window Fourier analysis show the new method offers much better temporal and frequency resolutions.
Some problems in the measurement of the frequency-resolving ability of hearing.
Supin, A Ya
2005-10-01
Despite the detailed development of masking methods for measurement of the frequency selectivity of hearing, these measurements are hardly used for diagnostic purposes because they are time-consuming and because of the uncertain extrapolation of the results to the perception of complex spectral patterns. A method for the direct measurement of the spectral resolving ability of hearing using test signals with rippled spectra is proposed. These measurements showed 1) that the resolving ability of the auditory system in terms of discriminating complex spectra is greater than that suggested by the acuity of auditory frequency filters; 2) that changes in the acuity of frequency auditory filters associated with sound intensity hardly affect the ability to resolve complex spectra; 3) that the effects of interference on frequency-resolving ability do not lead to decreases in the spectral contrast of signals due to superimposition of noise. PMID:16132266
Early stages of wind wave and drift current generation under non-stationary wind conditions.
NASA Astrophysics Data System (ADS)
Robles-Diaz, Lucia; Ocampo-Torres, Francisco J.; Branger, Hubert
2016-04-01
Generation and amplification mechanisms of ocean waves are well understood under constant wind speed or limited fetch conditions. Under these situations, the momentum and energy transfers from air to water are also quite well known. However during the wind field evolution over the ocean, we may observe sometime high wind acceleration/deceleration situations (e.g. Mexican Tehuano or Mediterranean Mistral wind systems). The evolution of wave systems under these conditions is not well understood. The purpose of these laboratory experiments is to better understand the early stages of water-waves and surface-drift currents under non-stationary wind conditions and to determine the balance between transfers creating waves and surface currents during non-equilibrium situations. The experiments were conducted in the Institut Pythéas wind-wave facility in Marseille-France. The wave tank is 40 m long, 2.7 m wide and 1 m deep. The air section is 50 m long, 3 m wide and 1.8 m height. We used 11 different resistive wave-gauges located along the tank. The momentum fluxes in the air column were estimated from single and X hot-film anemometer measurements. The sampling frequency for wind velocity and surface displacement measurements was 256 Hz. Water-current measurements were performed with a profiling velocimeter. This device measures the first 3.5 cm of the water column with a frequency rate of 100Hz. During the experiments, the wind intensity was abruptly modified with a constant acceleration and deceleration over time. We observed that wind drag coefficient values for accelerated wind periods are lower than the ones reported in previous studies for constant wind speed (Large and Pond 1981; Ocampo-Torres et al. 2010; Smith 1980; Yelland and Taylor 1996). This is probably because the turbulent boundary layer is not completely developed during the increasing-wind sequence. As it was reported in some theoretical studies (Miles 1957; Phillips 1957; Kahma and Donelan 1988), we
Early stages of wind wave and drift current generation under non-stationary wind conditions.
NASA Astrophysics Data System (ADS)
Robles-Diaz, Lucia; Ocampo-Torres, Francisco J.; Branger, Hubert
2016-04-01
Generation and amplification mechanisms of ocean waves are well understood under constant wind speed or limited fetch conditions. Under these situations, the momentum and energy transfers from air to water are also quite well known. However during the wind field evolution over the ocean, we may observe sometime high wind acceleration/deceleration situations (e.g. Mexican Tehuano or Mediterranean Mistral wind systems). The evolution of wave systems under these conditions is not well understood. The purpose of these laboratory experiments is to better understand the early stages of water-waves and surface-drift currents under non-stationary wind conditions and to determine the balance between transfers creating waves and surface currents during non-equilibrium situations. The experiments were conducted in the Institut Pythéas wind-wave facility in Marseille-France. The wave tank is 40 m long, 2.7 m wide and 1 m deep. The air section is 50 m long, 3 m wide and 1.8 m height. We used 11 different resistive wave-gauges located along the tank. The momentum fluxes in the air column were estimated from single and X hot-film anemometer measurements. The sampling frequency for wind velocity and surface displacement measurements was 256 Hz. Water-current measurements were performed with a profiling velocimeter. This device measures the first 3.5 cm of the water column with a frequency rate of 100Hz. During the experiments, the wind intensity was abruptly modified with a constant acceleration and deceleration over time. We observed that wind drag coefficient values for accelerated wind periods are lower than the ones reported in previous studies for constant wind speed (Large and Pond 1981; Ocampo-Torres et al. 2010; Smith 1980; Yelland and Taylor 1996). This is probably because the turbulent boundary layer is not completely developed during the increasing-wind sequence. As it was reported in some theoretical studies (Miles 1957; Phillips 1957; Kahma and Donelan 1988), we
Time-resolved hard x-ray spectrometer
NASA Astrophysics Data System (ADS)
Moy, Kenneth; Cuneo, Michael; McKenna, Ian; Keenan, Thomas; Sanford, Thomas; Mock, Ray
2006-08-01
Wired array studies are being conducted at the SNL Z accelerator to maximize the x-ray generation for inertial confinement fusion targets and high energy density physics experiments. An integral component of these studies is the characterization of the time-resolved spectral content of the x-rays. Due to potential spatial anisotropy in the emitted radiation, it is also critical to diagnose the time-evolved spectral content in a space-resolved manner. To accomplish these two measurement goals, we developed an x-ray spectrometer using a set of high-speed detectors (silicon PIN diodes) with a collimated field-of-view that converged on a 1-cm-diameter spot at the pinch axis. Spectral discrimination is achieved by placing high Z absorbers in front of these detectors. We built two spectrometers to permit simultaneous different angular views of the emitted radiation. Spectral data have been acquired from recent Z shots for the radial and axial (polar) views. UNSPEC 1 has been adapted to analyze and unfold the measured data to reconstruct the x-ray spectrum. The unfold operator code, UFO2, is being adapted for a more comprehensive spectral unfolding treatment.
Time-Resolved Hard X-Ray Spectrometer
Kenneth Moya; Ian McKennaa; Thomas Keenana; Michael Cuneob
2007-03-01
Wired array studies are being conducted at the SNL Z accelerator to maximize the x-ray generation for inertial confinement fusion targets and high energy density physics experiments. An integral component of these studies is the characterization of the time-resolved spectral content of the x-rays. Due to potential spatial anisotropy in the emitted radiation, it is also critical to diagnose the time-evolved spectral content in a space-resolved manner. To accomplish these two measurement goals, we developed an x-ray spectrometer using a set of high-speed detectors (silicon PIN diodes) with a collimated field-of-view that converged on a 1-cm-diameter spot at the pinch axis. Spectral discrimination is achieved by placing high Z absorbers in front of these detectors. We built two spectrometers to permit simultaneous different angular views of the emitted radiation. Spectral data have been acquired from recent Z shots for the radial and polar views. UNSPEC1 has been adapted to analyze and unfold the measured data to reconstruct the x-ray spectrum. The unfold operator code, UFO2, is being adapted for a more comprehensive spectral unfolding treatment.
A Critical Examination of Wind-Wave Spectral Functional Form
NASA Technical Reports Server (NTRS)
Huang, Norden E.; Long, Steven R.
1999-01-01
Traditionally, data from random ocean waves are presented in spectral functions. The spectra are the result of Fourier analysis. Fourier spectral analysis has dominated data analysis for, at least, the last hundred years. It has been the standard method for is examining the global amplitude-frequency distributions. Although Fourier transform valid under extremely general conditions, there are some crucial restrictions for the Fourier spectral analysis. The system must be linear, and the data must be stationary- otherwise, the resulting spectrum will make little physical sense. The stationarity requirement is also a common required criterion for most of other available data analysis methods. Nevertheless, few, if any, natural phenomena are linear and stationary. To compound these complications is the imperfection of our probes or numerical schemes the interactions of the imperfect probes even with a perfect linear system can make the final data nonlinear. Furthermore, all the available data are usually of finite duration. Under these conditions, Fourier analysis is of limited use, For lack of alternatives, however, Fourier analysis is still used to process such data. The loose application of Fourier analysis and the insouciant adoption of the stationary and linear assumptions may lead to misleading conclusions. Ocean waves are know to be nonlinear, and the wind system generating the wave field are seldom stationary- As a result, the traditional examination of the spectral form hardly made physical sense. A new method for analyzing nonlinear and nonstationary data has been developed. The key part is the Empirical Mode Decomposition (EMD) method with which any complicated data set can be decomposed into a finite and often small number of Intrinsic Mode Functions (IMF) that serve as the basis of the representation of the data, This decomposition method is adaptive, and, therefore, highly efficient. The IMFs admit well-behaved Hilbert transforms, and yield instantaneous
Dual Brushless Resolver Rate Sensor
NASA Technical Reports Server (NTRS)
Howard, David E. (Inventor)
1996-01-01
This invention relates to dual analog angular rate sensors which are implemented without the use of mechanical brushes. A resolver rate sensor which includes two brushless resolvers which are mechanically coupled to the same output shaft is provided with inputs which are provided to each resolver by providing the first resolver with a DC input and the second resolver with an AC sinusoidal input. A trigonometric identity in which the sum of the squares of the sin and cosine components equal one is used to advantage in providing a sensor of increased accuracy. The first resolver may have a fixed or variable DC input to permit dynamic adjustment of resolver sensitivity thus permitting a wide range of coverage. Novelty and advantages of the invention reside in the excitation of a resolver with a DC signal and in the utilization of two resolvers and the trigonometric identity of cos(exp 2)(theta) + sin(exp 2)(theta) = 1 to provide an accurate rate sensor which is sensitive to direction and accurate through zero rate.
Depth resolved detection of lipid using spectroscopic optical coherence tomography
Fleming, Christine P.; Eckert, Jocelyn; Halpern, Elkan F.; Gardecki, Joseph A.; Tearney, Guillermo J.
2013-01-01
Optical frequency domain imaging (OFDI) can identify key components related to plaque vulnerability but can suffer from artifacts that could prevent accurate identification of lipid rich regions. In this paper, we present a model of depth resolved spectral analysis of OFDI data for improved detection of lipid. A quadratic Discriminant analysis model was developed based on phantom compositions known chemical mixtures and applied to a tissue phantom of a lipid-rich plaque. We demonstrate that a combined spectral and attenuation model can be used to predict the presence of lipid in OFDI images. PMID:24009991
Multidimensional spectral load balancing
Hendrickson, B.; Leland, R.
1993-01-01
We describe an algorithm for the static load balancing of scientific computations that generalizes and improves upon spectral bisection. Through a novel use of multiple eigenvectors, our new spectral algorithm can divide a computation into 4 or 8 pieces at once. These multidimensional spectral partitioning algorithms generate balanced partitions that have lower communication overhead and are less expensive to compute than those produced by spectral bisection. In addition, they automatically work to minimize message contention on a hypercube or mesh architecture. These spectral partitions are further improved by a multidimensional generalization of the Kernighan-Lin graph partitioning algorithm. Results on several computational grids are given and compared with other popular methods.
NASA Astrophysics Data System (ADS)
Dzyubenko, B. V.; Ashmantas, L. A.; Baggdonavichyus, A. B.; Segal', M. D.
1988-04-01
The results of an investigation of the nonstationary mixing of the heat-transfer agent accompanying the reduction of the heat load in a bundle of twisted tubes are presented, and a generalizing dependence for calculating the effective coefficient of diffusion is derived.
Flood frequency analysis of historical flood data under stationary and non-stationary modelling
NASA Astrophysics Data System (ADS)
Machado, M. J.; Botero, B. A.; López, J.; Francés, F.; Díez-Herrero, A.; Benito, G.
2015-06-01
Historical records are an important source of information on extreme and rare floods and fundamental to establish a reliable flood return frequency. The use of long historical records for flood frequency analysis brings in the question of flood stationarity, since climatic and land-use conditions can affect the relevance of past flooding as a predictor of future flooding. In this paper, a detailed 400 yr flood record from the Tagus River in Aranjuez (central Spain) was analysed under stationary and non-stationary flood frequency approaches, to assess their contribution within hazard studies. Historical flood records in Aranjuez were obtained from documents (Proceedings of the City Council, diaries, chronicles, memoirs, etc.), epigraphic marks, and indirect historical sources and reports. The water levels associated with different floods (derived from descriptions or epigraphic marks) were computed into discharge values using a one-dimensional hydraulic model. Secular variations in flood magnitude and frequency, found to respond to climate and environmental drivers, showed a good correlation between high values of historical flood discharges and a negative mode of the North Atlantic Oscillation (NAO) index. Over the systematic gauge record (1913-2008), an abrupt change on flood magnitude was produced in 1957 due to constructions of three major reservoirs in the Tagus headwaters (Bolarque, Entrepeñas and Buendia) controlling 80% of the watershed surface draining to Aranjuez. Two different models were used for the flood frequency analysis: (a) a stationary model estimating statistical distributions incorporating imprecise and categorical data based on maximum likelihood estimators, and (b) a time-varying model based on "generalized additive models for location, scale and shape" (GAMLSS) modelling, which incorporates external covariates related to climate variability (NAO index) and catchment hydrology factors (in this paper a reservoir index; RI). Flood frequency
Flood frequency analysis of historical flood data under stationary and non-stationary modelling
NASA Astrophysics Data System (ADS)
Machado, M. J.; Botero, B. A.; López, J.; Francés, F.; Díez-Herrero, A.; Benito, G.
2015-01-01
Historical records are an important source of information about extreme and rare floods with a great value to establish a reliable flood return frequency. The use of long historic records for flood frequency analysis brings in the question of flood stationarity, since climatic and land-use conditions can affect the relevance of past flooding as a predictor of future flooding. In this paper, a detailed 400 year flood record from the Tagus River in Aranjuez (Central Spain) was analysed under stationary and non-stationary flood frequency approaches, to assess their implications on hazard studies. Historical flood records in Aranjuez were obtained from documents (Proceedings of the City Council, diaries, chronicles, memoirs, etc.), epigraphic marks, and indirect historical sources and reports. The water levels associated with different floods (derived from descriptions or epigraphic marks) were computed into discharge values using a one-dimensional hydraulic model. Secular variations on flood magnitude and frequency, found to respond to climate and environmental drivers, showed a good correlation between high values of historical flood discharges and a negative mode of the North Atlantic Oscillation index (NAO index). Over the systematic gauge record (1913-2008), an abrupt change on flood magnitude was produced in 1957 due to constructions of three major reservoirs in the Tagus headwaters (Bolarque, Entrepeñas and Buendia) controlling 80% of the watershed surface draining to Aranjuez. Two different models were used for the flood frequency analysis: (a) a stationary model estimating statistical distributions incorporating imprecise and categorical data based on maximum likelihood estimators; (b) a time-varying model based on "generalized additive models for location, scale and shape" (GAMLSS) modelling, that incorporates external covariates related to climate variability (NAO index) and catchment hydrology factors (in this paper a reservoir index; RI). Flood frequency
Modelling hydrological extremes under non-stationary conditions using climate covariates
NASA Astrophysics Data System (ADS)
Vasiliades, Lampros; Galiatsatou, Panagiota; Loukas, Athanasios
2013-04-01
Extreme value theory is a probabilistic theory that can interpret the future probabilities of occurrence of extreme events (e.g. extreme precipitation and streamflow) using past observed records. Traditionally, extreme value theory requires the assumption of temporal stationarity. This assumption implies that the historical patterns of recurrence of extreme events are static over time. However, the hydroclimatic system is nonstationary on time scales that are relevant to extreme value analysis, due to human-mediated and natural environmental change. In this study the generalized extreme value (GEV) distribution is used to assess nonstationarity in annual maximum daily rainfall and streamflow timeseries at selected meteorological and hydrometric stations in Greece and Cyprus. The GEV distribution parameters (location, scale, and shape) are specified as functions of time-varying covariates and estimated using the conditional density network (CDN) as proposed by Cannon (2010). The CDN is a probabilistic extension of the multilayer perceptron neural network. Model parameters are estimated via the generalized maximum likelihood (GML) approach using the quasi-Newton BFGS optimization algorithm, and the appropriate GEV-CDN model architecture for the selected meteorological and hydrometric stations is selected by fitting increasingly complicated models and choosing the one that minimizes the Akaike information criterion with small sample size correction. For all case studies in Greece and Cyprus different formulations are tested with combinational cases of stationary and nonstationary parameters of the GEV distribution, linear and non-linear architecture of the CDN and combinations of the input climatic covariates. Climatic indices such as the Southern Oscillation Index (SOI), which describes atmospheric circulation in the eastern tropical pacific related to El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) index that varies on an interdecadal
A Decision-Oriented Approach for Detecting and Modeling Non-Stationary Flood Frequency
NASA Astrophysics Data System (ADS)
Hecht, J. S.; Vogel, R. M.
2014-12-01
Changes in the frequency of extreme floods have been observed and anticipated in many hydrologic settings in response to numerous drivers of environmental change, including climate, land cover, and infrastructure. To help decision-makers design flood control infrastructure in settings with non-stationary hydrologic regimes, a parsimonious approach for detecting and modeling trends in extreme floods is needed. An approach using ordinary least squares (OLS) regression can accommodate nonstationarity in both the mean and variance of flood series while simultaneously offering a means of (i) analytically evaluating type I and type II trend detection errors, (ii) analytically generating expressions of uncertainty, such as confidence and prediction intervals, (iii) providing updated estimates of the frequency of floods exceeding the flood of record, (iv) accommodating a wide range of non-linear functions through ladder of powers transformations, and (v) communicating hydrologic changes in a single graphical image. Previous research has shown that the two-parameter lognormal distribution can adequately model the annual maximum flood distribution of both stationary and non-stationary hydrologic regimes in many regions of the United States. A simple logarithmic transformation of annual maximum flood series makes an OLS regression modeling approach especially suitable for creating a non-stationary flood frequency distribution with parameters that are conditional upon time or a physically meaningful covariate. While the heteroscedasticity of some OLS models may be viewed as an impediment, it also presents an opportunity for characterizing both the conditional mean and variance of annual maximum floods. Through a case study of an urbanizing watershed, we demonstrate that accounting for trends in both the mean and variance can yield substantially different estimates of time-dependent extreme flood quantiles than only considering trends in the mean. When applied to risk
Non-stationary resonance dynamics of a nonlinear sonic vacuum with grounding supports
NASA Astrophysics Data System (ADS)
Koroleva (Kikot), I. P.; Manevitch, L. I.; Vakakis, Alexander F.
2015-11-01
In a recent work [L.I. Manevitch, A.F.Vakakis, Nonlinear oscillatory acoustic vacuum, SIAM Journal of Applied Mathematics 74(6) (2014), 1742-1762] it was shown that a periodic chain of linearly coupled particles performing low-energy in-plane transverse oscillations behaves as a strongly nonlinear sonic vacuum (with corresponding speed of sound equal to zero). In this work we consider the grounded version of this system by coupling each particle to the ground through lateral springs in order to study the effect of the grounding stiffness on the strongly nonlinear dynamics. In that context we consider the simplest possible such system consisting of two coupled particles and present analytical and numerical studies of the non-stationary planar dynamics. The most significant limiting case corresponding to predominant low energy transversal excitations is considered by taking into account leading order geometric nonlinearities. Then we show that the grounded system behaves as a nonlinear sonic vacuum due to the purely cubic stiffness nonlinearities in the governing equations of motion and the complete absence of any linear stiffness terms. Under certain assumptions the nonlinear normal modes (i.e., the time-periodic nonlinear oscillations) in the configuration space of this system coincide with those of the corresponding linear one, so they obey the same orthogonality relations. Moreover, we analytically find that there are two transitions in the dynamics of this system, with the parameter governing these transitions being the relation between the lateral (grounding) and the interchain stiffnesses. The first transition concerns a bifurcation of one of the nonlinear normal modes (NNMs), whereas the second provides conditions for intense energy transfers and mixing between the NNMs. The drastic effects of these bifurcations on the non-stationary resonant dynamics are discussed. Specifically, the second transition relates to strongly non-stationary dynamics, and signifies
Shortwave spectral radiative forcing of cumulus clouds from surface observations
NASA Astrophysics Data System (ADS)
Kassianov, E.; Barnard, J.; Berg, L. K.; Long, C. N.; Flynn, C.
2011-04-01
The spectral changes of the shortwave total, direct and diffuse cloud radiative forcing (CRF) at surface are examined for the first time using spectrally resolved all-sky flux observations and clear-sky fluxes. The latter are computed applying a physically based approach, which accounts for the spectral changes of aerosol optical properties and surface albedo. Application of this approach to 13 summertime days with single-layer continental cumuli demonstrates: (i) the substantial contribution of the diffuse component to the total CRF, (ii) the well-defined spectral variations of total CRF in the visible spectral region, and (iii) the strong statistical relationship between spectral (500 nm) and shortwave broadband values of total CRF. Our results suggest that the framework based on the visible narrowband fluxes can provide important radiative quantities for rigorous evaluation of radiative transfer parameterizations and also can be applied for estimation of the shortwave broadband CRF.
Digital phantoms generated by spectral and spatial light modulators
NASA Astrophysics Data System (ADS)
Chon, Bonghwan; Tokumasu, Fuyuki; Lee, Ji Youn; Allen, David W.; Rice, Joseph P.; Hwang, Jeeseong
2015-12-01
A hyperspectral image projector (HIP) based on liquid crystal on silicon spatial light modulators is explained and demonstrated to generate data cubes. The HIP-constructed data cubes are three-dimensional images of the spatial distribution of spectrally resolved abundances of intracellular light-absorbing oxyhemoglobin molecules in single erythrocytes. Spectrally and spatially resolved image data indistinguishable from the real scene may be used as standard data cubes, so-called digital phantoms, to calibrate image sensors and validate image analysis algorithms for their measurement quality, performance consistency, and interlaboratory comparisons for quantitative biomedical imaging applications.
Digital phantoms generated by spectral and spatial light modulators.
Chon, Bonghwan; Tokumasu, Fuyuki; Lee, Ji Youn; Allen, David W; Rice, Joseph P; Hwang, Jeeseong
2015-01-01
A hyperspectral image projector (HIP) based on liquid crystal on silicon spatial light modulators is explained and demonstrated to generate data cubes. The HIP-constructed data cubes are three-dimensional images of the spatial distribution of spectrally resolved abundances of intracellular light-absorbing oxyhemoglobin molecules in single erythrocytes. Spectrally and spatially resolved image data indistinguishable from the real scene may be used as standard data cubes, so-called digital phantoms, to calibrate image sensors and validate image analysis algorithms for their measurement quality, performance consistency, and interlaboratory comparisons for quantitative biomedical imaging applications. PMID:26361340
Digital phantoms generated by spectral and spatial light modulators.
Chon, Bonghwan; Tokumasu, Fuyuki; Lee, Ji Youn; Allen, David W; Rice, Joseph P; Hwang, Jeeseong
2015-12-01
A hyperspectral image projector (HIP) based on liquid crystal on silicon spatial light modulators is explained and demonstrated to generate data cubes. The HIP-constructed data cubes are three-dimensional images of the spatial distribution of spectrally resolved abundances of intracellular light-absorbing oxyhemoglobin molecules in single erythrocytes. Spectrally and spatially resolved image data indistinguishable from the real scene may be used as standard data cubes, so-called digital phantoms, to calibrate image sensors and validate image analysis algorithms for their measurement quality, performance consistency, and interlaboratory comparisons for quantitative biomedical imaging applications. PMID:26502383
Momentum Resolved Radio Frequency Spectroscopy in Trapped Fermi Gases
Chen Qijin; Levin, K.
2009-05-15
We address recent momentum-resolved radio frequency (rf) spectroscopy experiments, showing how they yield more stringent tests than other comparisons with theory, associated with the ultracold Fermi gases. We demonstrate that, by providing a clear dispersion signature of pairing, they remove the ambiguity plaguing the interpretation of previous rf experiments. Our calculated spectral intensities are in semiquantitative agreement with the data. Even in the presence of a trap, the spectra are predicted to exhibit two BCS-like branches.
The RATIO method for time-resolved Laue crystallography
Coppens, Philip; Pitak, Mateusz; Gembicky, Milan; Messerschmidt, Marc; Scheins, Stephan; Benedict, Jason; Adachi, Shin-ichi; Sato, Tokushi; Nozawa, Shunsuke; Ichiyanagi, Kohei; Chollet, Matthieu; Koshihara, Shin-ya
2009-01-01
A RATIO method for analysis of intensity changes in time-resolved pump–probe Laue diffraction experiments is described. The method eliminates the need for scaling the data with a wavelength curve representing the spectral distribution of the source and removes the effect of possible anisotropic absorption. It does not require relative scaling of series of frames and removes errors due to all but very short term fluctuations in the synchrotron beam. PMID:19240334
Stability of nonstationary states of spin-1 Bose-Einstein condensates
Maekelae, H.; Lundh, E.; Johansson, M.; Zelan, M.
2011-10-15
The stability of nonstationary states of homogeneous spin-1 Bose-Einstein condensates is studied by performing Bogoliubov analysis in a frame of reference where the state is stationary. In particular, the effect of an external magnetic field is examined. It is found that a nonzero magnetic field introduces instability in a {sup 23}Na condensate. The wavelengths of this instability can be controlled by tuning the strength of the magnetic field. In a {sup 87}Rb condensate this instability is present already at zero magnetic field. Furthermore, an analytical bound for the size of a stable condensate is found, and a condition for the validity of the single-mode approximation is presented. Realization of the system in a toroidal trap is discussed, and the full time development is simulated.
NASA Astrophysics Data System (ADS)
Cushman, J. H.; O'Malley, D.; Park, M.
2009-04-01
We construct a family of stochastic processes with independent, nonstationary increments and arbitrary, but apriori specified mean square displacement. The family of processes is shown to be an extension of Brownian motion. If the time derivative of the variance of the process is homogeneous, then by computing the fractal dimension it can be shown that the complexity of the family is the same as that of Brownian motion. For two particles initially separated by a distance x, the finite-size Lyapunov exponent (FSLE), measures the average rate of exponential separation to a distance ax. An analytical expression is developed for the FSLE of the extended Brownian processes and numerical examples presented. The construction of the extended Brownian processes illustrates that contrary to what has been stated in the literature, a power-law mean-square displacement is not related to a breakdown in the classical CLT.
Spurious cross-frequency amplitude-amplitude coupling in nonstationary, nonlinear signals
NASA Astrophysics Data System (ADS)
Yeh, Chien-Hung; Lo, Men-Tzung; Hu, Kun
2016-07-01
Recent studies of brain activities show that cross-frequency coupling (CFC) plays an important role in memory and learning. Many measures have been proposed to investigate the CFC phenomenon, including the correlation between the amplitude envelopes of two brain waves at different frequencies - cross-frequency amplitude-amplitude coupling (AAC). In this short communication, we describe how nonstationary, nonlinear oscillatory signals may produce spurious cross-frequency AAC. Utilizing the empirical mode decomposition, we also propose a new method for assessment of AAC that can potentially reduce the effects of nonlinearity and nonstationarity and, thus, help to avoid the detection of artificial AACs. We compare the performances of this new method and the traditional Fourier-based AAC method. We also discuss the strategies to identify potential spurious AACs.
The Effect of Non-stationary Noise on Drifting Signal Detection
NASA Astrophysics Data System (ADS)
Flores, Mauricio; Benacquista, M.; Stroeer, A.
2012-01-01
We analyze the effect of non-stationary noise in the detection of drifting signals on unevenly sampled data. Initial frequency estimation is obtained from a Lomb-Scargle periodogram; which is followed by a global multi-start optimization, as working on a dense local Nelder-Mead iterator for parameter estimates. It has been found that a varying white noise level has no effect on the required relative signal-to-noise ratio for detection in the proposed algorithm, though affecting the absolute amplitude strength of the signal recording. Future work includes the addition of colored noise to this analysis. We plan to investigate how this work can be applied to gravitational wave data analysis, for example LISA or LIGO. This work is funded by NASA URC Grant NASA NNX09AV06A, ARCC grant NSF AST0750913 and CREST grant NSF HRD0734800.
NASA Astrophysics Data System (ADS)
Khambampati, A. K.; Rashid, A.; Kim, B. S.; Liu, Dong; Kim, S.; Kim, K. Y.
2010-04-01
EIT has been used for the dynamic estimation of organ boundaries. One specific application in this context is the estimation of lung boundaries during pulmonary circulation. This would help track the size and shape of lungs of the patients suffering from diseases like pulmonary edema and acute respiratory failure (ARF). The dynamic boundary estimation of the lungs can also be utilized to set and control the air volume and pressure delivered to the patients during artificial ventilation. In this paper, the expectation-maximization (EM) algorithm is used as an inverse algorithm to estimate the non-stationary lung boundary. The uncertainties caused in Kalman-type filters due to inaccurate selection of model parameters are overcome using EM algorithm. Numerical experiments using chest shaped geometry are carried out with proposed method and the performance is compared with extended Kalman filter (EKF). Results show superior performance of EM in estimation of the lung boundary.
Cheng, Linyin; AghaKouchak, Amir
2014-01-01
Extreme climatic events are growing more severe and frequent, calling into question how prepared our infrastructure is to deal with these changes. Current infrastructure design is primarily based on precipitation Intensity-Duration-Frequency (IDF) curves with the so-called stationary assumption, meaning extremes will not vary significantly over time. However, climate change is expected to alter climatic extremes, a concept termed nonstationarity. Here we show that given nonstationarity, current IDF curves can substantially underestimate precipitation extremes and thus, they may not be suitable for infrastructure design in a changing climate. We show that a stationary climate assumption may lead to underestimation of extreme precipitation by as much as 60%, which increases the flood risk and failure risk in infrastructure systems. We then present a generalized framework for estimating nonstationary IDF curves and their uncertainties using Bayesian inference. The methodology can potentially be integrated in future design concepts. PMID:25403227
Non-stationary time series modeling on caterpillars pest of palm oil for early warning system
NASA Astrophysics Data System (ADS)
Setiyowati, Susi; Nugraha, Rida F.; Mukhaiyar, Utriweni
2015-12-01
The oil palm production has an important role for the plantation and economic sector in Indonesia. One of the important problems in the cultivation of oil palm plantation is pests which causes damage to the quality of fruits. The caterpillar pest which feed palm tree's leaves will cause decline in quality of palm oil production. Early warning system is needed to minimize losses due to this pest. Here, we applied non-stationary time series modeling, especially the family of autoregressive models to predict the number of pests based on its historical data. We realized that there is some uniqueness of these pests data, i.e. the spike value that occur almost periodically. Through some simulations and case study, we obtain that the selection of constant factor has a significance influence to the model so that it can shoot the spikes value precisely.
Quantum radiation of Maxwell’s electromagnetic field in nonstationary Kerr-de Sitter black hole
NASA Astrophysics Data System (ADS)
Ibungochouba Singh, T.; Ablu Meitei, I.; Yugindro Singh, K.
2016-03-01
Quantum radiation properties of nonstationary Kerr-de Sitter (KdS) black hole is investigated using the method of generalized tortoise coordinate transformation. The locations of horizons and the temperature of the thermal radiation as well as the maximum energy of the nonthermal radiation are derived. It is found that the surface gravity and the Hawking temperature depend on both time and different angles. An extra coupling effect is obtained in the thermal radiation spectrum of Maxwell’s electromagnetic field equations which is absent in the thermal radiation spectrum of scalar particles. Further, the chemical potential derived from the thermal radiation spectrum of scalar particle has been found to be equal to the highest energy of the negative energy state of the scalar particle in the nonthermal radiation for KdS black hole. It is also shown that the generalized tortoise coordinate transformation produces a constant term in the expression of the surface gravity and Hawking temperature.
Scaling in non-stationary time series. (II). Teen birth phenomenon
NASA Astrophysics Data System (ADS)
Ignaccolo, M.; Allegrini, P.; Grigolini, P.; Hamilton, P.; West, B. J.
2004-05-01
This paper is devoted to the problem of statistical mechanics raised by the analysis of an issue of sociological interest: the teen birth phenomenon. It is expected that these data are characterized by correlated fluctuations, reflecting the cooperative properties of the process. However, the assessment of the anomalous scaling generated by these correlations is made difficult, and ambiguous as well, by the non-stationary nature of the data that shows a clear dependence on seasonal periodicity (periodic component) and an average changing slowly in time (slow component) as well. We use the detrending techniques described in the companion paper [The earlier companion paper], to safely remove all the biases and to derive the genuine scaling of the teen birth phenomenon.
A non-stationary panel data investigation of the unemployment-crime relationship.
Blomquist, Johan; Westerlund, Joakim
2014-03-01
Many empirical studies of the economics of crime focus solely on the determinants thereof, and do not consider the dynamic and cross-sectional properties of their data. As a response to this, the current paper offers an in-depth analysis of this issue using data covering 21 Swedish counties from 1975 to 2010. The results suggest that the crimes considered are non-stationary, and that this cannot be attributed to county-specific disparities alone, but that there are also a small number of common stochastic trends to which groups of counties tend to revert. In an attempt to explain these common stochastic trends, we look for a long-run cointegrated relationship between unemployment and crime. Overall, the results do not support cointegration, and suggest that previous findings of a significant unemployment-crime relationship might be spurious. PMID:24468438
Nonstationary probability densities of a class of nonlinear system excited by external colored noise
NASA Astrophysics Data System (ADS)
Qi, LuYuan; Xu, Wei; Gu, XuDong
2012-03-01
This paper deals with the approximate nonstationary probability density of a class of nonlinear vibrating system excited by colored noise. First, the stochastic averaging method is adopted to obtain the averaged Itô equation for the amplitude of the system. The corresponding Fokker-Planck-Kolmogorov equation governing the evolutionary probability density function is deduced. Then, the approximate solution of the Fokker-Planck-Kolmogorov equation is derived by applying the Galerkin method. The solution is expressed as a sum of a series of expansion in terms of a set of proper basis functions with time-depended coefficients. Finally, an example is given to illustrate the proposed procedure. The validity of the proposed method is confirmed by Monte Carlo Simulation.
Pinault, Jean Louis; Dubus, Igor G
2008-08-20
An autoregressive approach for the prediction of water quality trends in systems subject to varying meteorological conditions and short observation periods is discussed. Under these conditions, the dynamics of the system can be reliably forecast, provided their internal processes are understood and characterized independently of the external inputs. A methodology based on stationary and non-stationary autoregressive processes with external inputs (ARX) is proposed to assess and predict trends in hydrosystems which are at risk of contamination by organic and inorganic pollutants, such as pesticides or nutrients. The procedures are exemplified for the transport of atrazine and its main metabolite deethylatrazine in a small agricultural catchment in France. The approach is expected to be of particular value to assess current and future trends in water quality as part of the European Water Framework Directive and Groundwater Directives. PMID:18554747
Reproducing pairs and the continuous nonstationary Gabor transform on LCA groups
NASA Astrophysics Data System (ADS)
Speckbacher, Michael; Balazs, Peter
2015-10-01
In this paper we introduce and investigate the concept of reproducing pairs as a generalization of continuous frames. Reproducing pairs yield a bounded analysis and synthesis process while the frame condition can be omitted at both stages. Moreover, we will investigate certain continuous frames (resp. reproducing pairs) on LCA groups, which can be described as a continuous version of nonstationary Gabor systems and state sufficient conditions for these systems to form a continuous frame (resp. reproducing pair). As a byproduct we identify the structure of the frame operator (resp. resolution operator). We will apply our results to systems generated by a unitary action of a subset of the affine Weyl-Heisenberg group in {L}2({{R}}). This setup will also serve as a nontrivial example of a system for which, whereas continuous frames exist, no dual system with the same structure exists even if we drop the frame property.
NASA Astrophysics Data System (ADS)
Fan, Qingju; Wu, Yonghong
2015-08-01
In this paper, we develop a new method for the multifractal characterization of two-dimensional nonstationary signal, which is based on the detrended fluctuation analysis (DFA). By applying to two artificially generated signals of two-component ARFIMA process and binomial multifractal model, we show that the new method can reliably determine the multifractal scaling behavior of two-dimensional signal. We also illustrate the applications of this method in finance and physiology. The analyzing results exhibit that the two-dimensional signals under investigation are power-law correlations, and the electricity market consists of electricity price and trading volume is multifractal, while the two-dimensional EEG signal in sleep recorded for a single patient is weak multifractal. The new method based on the detrended fluctuation analysis may add diagnostic power to existing statistical methods.
Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers
NASA Astrophysics Data System (ADS)
Gajjar, J. S. B.
1995-05-01
The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.
Discrete cosine transform-based local adaptive filtering of images corrupted by nonstationary noise
NASA Astrophysics Data System (ADS)
Lukin, Vladimir V.; Fevralev, Dmitriy V.; Ponomarenko, Nikolay N.; Abramov, Sergey K.; Pogrebnyak, Oleksiy; Egiazarian, Karen O.; Astola, Jaakko T.
2010-04-01
In many image-processing applications, observed images are contaminated by a nonstationary noise and no a priori information on noise dependence on local mean or about local properties of noise statistics is available. In order to remove such a noise, a locally adaptive filter has to be applied. We study a locally adaptive filter based on evaluation of image local activity in a ``blind'' manner and on discrete cosine transform computed in overlapping blocks. Two mechanisms of local adaptation are proposed and applied. The first mechanism takes into account local estimates of noise standard deviation while the second one exploits discrimination of homogeneous and heterogeneous image regions by adaptive threshold setting. The designed filter performance is tested for simulated data as well as for real-life remote-sensing and maritime radar images. Recommendations concerning filter parameter setting are provided. An area of applicability of the proposed filter is defined.
The synchro-Compton limit of the brightness temperature of nonstationary radio sources
NASA Astrophysics Data System (ADS)
Slysh, V. I.
1992-06-01
The brightness temperature of synchrotron emission from nonstationary radio sources during the cooling down by the inverse Compton effect is calculated. It is shown that brightness temperatures as high as 5 x 10 exp 15 K at 1 GHz are allowed during the first day after injection of relativistic electrons of sufficiently high energy. This is about four orders of magnitude higher than the canonical synchro-Compton limit introduced by Kellermann and Pauliny-Toth (1969) for stationary radio sources. A stationary situation with the in situ first-order Fermi acceleration will give a brightness temperature of about 10 exp 15 K at 1 GHz due to the compensation of the inverse Compton losses by particle acceleration. The high brightness temperature effect is most pronounced at low frequencies and is proposed as the explanation of the LF variability phenomenon. Strong high-energy emission is predicted during phases of high brightness temperature.
Stability of nonstationary solutions of the generalized KdV-Burgers equation
NASA Astrophysics Data System (ADS)
Chugainova, A. P.; Shargatov, V. A.
2015-02-01
The stability of nonstationary solutions to the Cauchy problem for a model equation with a complex nonlinearity, dispersion, and dissipation is analyzed. The equation describes the propagation of nonlinear longitudinal waves in rods. Previously, complex behavior of traveling waves was found, which can be treated as discontinuity structures in solutions of the same equation without dissipation and dispersion. As a result, the solutions of standard self-similar problems constructed as a sequence of Riemann waves and shocks with a stationary structure become multivalued. The multivaluedness of the solutions is attributed to special discontinuities caused by the large effect of dispersion in conjunction with viscosity. The stability of special discontinuities in the case of varying dispersion and dissipation parameters is analyzed numerically. The computations performed concern the stability analysis of a special discontinuity propagating through a layer with varying dispersion and dissipation parameters.
Li, Dan; Jung, Ranu
2002-07-01
A time-varying covariance method for detecting and quantifying the evolution of rhythmicity (frequency) in persistently varying quasi-periodic nonstationary signals is presented. The basic method, evaluated using chirp signals, utilizes a shifting window of fixed length. A substantial reduction in estimation bias and variability are obtained by utilizing an adaptive window whose length is dependent on past frequency estimates. The adaptive window yields estimates that are comparable in accuracy to those obtained using high-resolution time-frequency representation but with lower computation requirements and the potential for on-line application. Finally, an example of the application of the method for analyzing a neural recording is also illustrated. PMID:11931864