Stationary Spectra Research Articles

Modelling the Spectrum of Potency a Stationary Random Process in the Form of Spline First Order at the Random Number of Data in Instant of Time

The spectrum of potency as same the function of correlation is one of the most important characteristic of the second process random order. The spectrum of potency allows to judge about, that structure of process gives opportunity to take estimation of spectrum composition of useful signals and hindrances, allows to produce synthesis (reconstruction) the signals and to build filters and to obtain the estimates filtration. The purpose of this presenting work is modeling of process random stationary potency spectrum by random dates number in measurement moments. Using by probability theory methods and mathematical statistics was derived unbiased estimator of the potency spectrum in the form of spline first order, and were researched statistic characteristics estimation.

Road-Aided Ground Slowly Moving Target 2D Motion Estimation for Single-Channel Synthetic Aperture Radar.

To detect and estimate ground slowly moving targets in airborne single-channel synthetic aperture radar (SAR), a road-aided ground moving target indication (GMTI) algorithm is proposed in this paper. First, the road area is extracted from a focused SAR image based on radar vision. Second, after stationary clutter suppression in the range-Doppler domain, a moving target is detected and located in the image domain via the watershed method. The target’s position on the road as well as its radial velocity can be determined according to the target’s offset distance and traffic rules. Furthermore, the target’s azimuth velocity is estimated based on the road slope obtained via polynomial fitting. Compared with the traditional algorithms, the proposed method can effectively cope with slowly moving targets partly submerged in a stationary clutter spectrum. In addition, the proposed method can be easily extended to a multi-channel system to further improve the performance of clutter suppression and motion estimation. Finally, the results of numerical experiments are provided to demonstrate the effectiveness of the proposed algorithm.

Phenomenological model for predicting stationary and non-stationary spectra of wave turbulence in vibrating plates

A phenomenological model describing the time-frequency dependence of the power spectrum of thin plates vibrating in a wave turbulence regime, is introduced. The model equation contains as basic solutions the Rayleigh–Jeans equipartition of energy, as well as the Kolmogorov–Zakharov spectrum of wave turbulence. In the Wave Turbulence Theory framework, the model is used to investigate the self-similar, non-stationary solutions of forced and free turbulent vibrations. Frequency-dependent damping laws can easily be accounted for. Their effects on the characteristics of the stationary spectra of turbulence are then investigated. Thanks to this analysis, self-similar universal solutions are given, relating the power spectrum to both the injected power and the damping law.

Compressive sensing based stochastic process power spectrum estimation subject to missing data

A compressive sensing (CS) based approach for stationary and non-stationary stochastic process power spectrum estimation subject to missing data is developed. Stochastic process records such as wind and sea wave excitations can often be represented with relative sparsity in the frequency domain. Relying on this attribute, a CS framework can be applied to reconstruct a signal that contains sampling gaps in the time domain, possibly occurring for reasons such as sensor failures, data corruption, limited bandwidth/storage capacity, and power outages. Specifically, first an appropriate basis is selected for expanding the signal recorded in the time domain. In this regard, Fourier and harmonic wavelet bases are utilized herein. Next, an L1 norm minimization procedure is performed for obtaining the sparsest representation of the signal in the selected basis. Finally, the signal can either be reconstructed in the time domain if required or, alternatively, the underlying stochastic process power spectrum can be estimated in a direct manner by utilizing the determined expansion coefficients; thus, circumventing the computational cost related to reconstructing the signal in the time domain. The technique is shown to estimate successfully the essential features of the stochastic process power spectrum, while it appears to be efficient even in cases with 65% missing data demonstrating superior performance in comparison with alternative existing techniques. A significant advantage of the approach is that it performs satisfactorily even in the presence of noise. Several numerical examples demonstrate the versatility and reliability of the approach both for stationary and non-stationary cases.

The New Molecular Dynamics Approach to Study Radiation Processes

A new modification of the classic method of molecular dynamics is proposed. Method allows clarifying the input of different intervals of the stationary energy spectrum of the incident particles to the final radiation effect. A shock function is introduced that describes the transfer of the corresponding pulse to the crystal atom. The action of shock function is determined by the random function that provides the necessary frequency and the magnitude of shocks. The approach is demonstrated on the example of the ion irradiation of trihydric crystal. It was found that in certain energy intervals “heavy clusters” are formed.

Synchrotron self-Compton emission by relativistic electrons under stochastic acceleration: application to Mrk 421 and Mrk 501

We examine the applicability of the stochastic electron acceleration to two high synchrotron peaked blazars, Mrk 421 and Mrk 501, assuming synchrotron self-Compton emission of gamma-rays. Our model considers an emitting region moving at relativistic speed, where non-thermal electrons are accelerated and attain a steady-state energy spectrum together with the photons they emit. The kinetic equations of the electrons and photons are solved numerically, given a stationary wave number spectrum of the magnetohydrodynamic (MHD) disturbances, which are responsible for the electron acceleration and escape. Our simple formulation appears to reproduce the two well-sampled, long-term averaged photon spectra. In order to fit the model to the emission component from the radio to the X-ray bands, we need both a steeper wave spectral index than the Kolmogorov spectrum and efficient particle escape. Although the model provides a natural explanation for the high-energy cutoff of the electron energy distribution, the derived physical parameters raise a problem with an energy budget if the MHD waves with the Alfv{\'e}n velocity are assumed to be the acceleration agent.

Ultrafast relaxation dynamics of 5,10,15,20-meso-tetrakis pentafluorophenyl porphyrin studied by fluorescence up-conversion and transient absorption spectroscopy.

The ultrafast photophysical characterization of 5,10,15,20-meso-tetrakis pentafluorophenyl porphyrin (H2F20TPP) in 4:1 dichloromethane (DCM) and tetrahydrofuran (THF) solution has been done in the femtosecond-picosecond time domain, by combining fluorescence up-conversion and femtosecond transient absorption spectroscopy. Fluorescence up-conversion studies on H2F20TPP were done demonstrating fluorescence dynamics over the whole spectral range from 440 to 650 nm when excited at 405 nm, 360.5 cm(-1) excess vibrational energy of Soret band (411 nm). Single-exponential decay with ∼160 ± 50 fs lifetime of Soret fluorescence (also called S2 fluorescence or B band fluorescence) at around 440 nm was observed. On going from 440 nm, S2 fluorescence to S1 fluorescence, (Q-band) around 640 nm (wavelength of 0-0 transition in the stationary spectrum), single-exponential fluorescence time profile turns into a multiexponential time profile and it could be resolved critically into five-exponential components. An ultrafast rise component with ∼160 ± 50 fs followed by two decay components: a very fast decay component with 200 ± 50 fs time constant and another relatively slower 1.8 ± 0.5 ps decay component. Next, a very prominent rise component with 105 ± 30 ps lifetime followed by long-lived 10 ns decay component. The initial rise of S1 (Q-band) fluorescence around 640 nm agreed with the decay time of S2 (Soret or B band) fluorescence indicates that internal conversion (IC) from relaxed S2 to vibrationally excited S1 occurs in the ∼160 fs time scale and subsequent very fast decay with 200 fs time constant, which is assigned to be intramolecular vibrational dephasing or redistribution. The 1.8 ps decay component of S1 fluorescence is attributed to be "hot" fluorescence from vibrationally excited S1 state, and it reveals the vibrational relaxation time induced by elastic or quasi-elastic collision with solvent molecules. The 105 ps rise component is the creation time of the thermally equilibrated S1 state population, and it could be attributed either to an excited state conformational relaxation/intramolecular charge transfer or a molecular cooling process by dissipation of excess energy within the solvent by inelastic collision. Finally, the decay of equilibrated S1(Qx state) occurs on 10 ns to S0 by fluorescence. Femtosecond resolved transient absorption studies on H2F20TPP in the spectral range 390-620 nm following both S2 (Soret band) and S1 (Qx) band excitation have been done and they complement the observations found in fluorescence up-conversion studies. The stimulated emission (SE) kinetics observed at 640 nm, S1 emission peak, in 2-10 ps time domain rebuilds a dynamic similar to that observed by fluorescence up-conversion study. The transient absorption kinetics upon S1 excitation were observed mainly to be biexponential with decay constants 105 ps and 10 ns, respectively. At a long time window (6 ns), a long-lived rise component could be predicted followed by two long-lived decay components for both the excitations in between 450 and 500 nm probe wavelengths. The lifetimes of these components were longer-lived than were possible to exactly measure using our existing femtosecond transient absorption system. However, this apparent rise component is assigned to be a Tn ← T1 transition, and the longest decay component is attributed to the lifetime of the T1 state.

Solvent-Controlled Excited State Relaxation Path of 4-Acetyl-4'-(dimethylamino)biphenyl.

Stationary and picosecond time-resolved fluorescence (TRF) and absorption spectra were compared in different aprotic solvents at various temperatures for 4-acetyl-4'-(dimethylamino)biphenyl (ADAB). A large value of the excited state dipole moment, 18-25 D, was estimated from the plot of solvatochromic shift. TRF spectra of ADAB recorded as a function of solvent polarity and temperature show unusual temporal evolution (shift and decay) of the fluorescence bands. In some cases, the dynamic Stokes shifts occur on a time scale much shorter than expected on the basis of literature data on solvent relaxation. In order to investigate variations in the energy of electronic transitions, oscillator strengths, and dipole moments upon changing the molecular geometry, quantum chemical modeling (DFT, TD-DFT, CIS) was performed for ADAB and its ground-state pretwisted derivative, 4-acetyl-4'-dimethylamino-2,2'-dimethylbiphenyl (ADAB-Me). Combination of spectroscopic data and computational results leads to the model of excited state relaxation which involves dynamic solvent-dependent interaction between two close-lying (1)nπ* and (1)ππ* excited electronic states.

Deblurring Images using a Wiener Filter

This paper basically represents how to deblurring images using a wiener filter [1]. Basically wiener filter is used to produce an estimate of a desired or target random process by linear time-invariant filtering [2] of an observed noisy process, assuming known stationary signal and noise spectra, and additive noise. The Wiener filter minimizes the mean square error between the estimated random process and the desired process. In here it has been introduced about the image processing capabilities in MATHLAB. Dividing some steps it has been shown how an image can be processed with the help of MATHLAB [3][4] command. Moreover how image can be effected by noise & how noise can be removed from image this also described in this paper properly

A Survey on Spectrum Sharing in Cognitive Radio Networks

With the rapid development of wireless communication, the confliction between the scarce frequency resources and the low spectral efficiency caused by the stationary spectrum sharing strategies seriously restricts the evolution of the future mobile communication. For this purpose, cognitive radio (CR) emerges as one of the most promising inventions which can overcome the spectrum shortage. As the key technology and main objective of CR, spectrum sharing can make full use of the limited spectrum, alleviate the scarcity of frequency resources and improve the system utilities, playing thereby an important role in improving the system performance of cognitive radio networks (CRNs). In this survey, the spectrum sharing in CRNs is discussed in terms of the sharing process, mainstream sharing technologies and spectrum sharing models. In particular, comparisons of different spectrum sharing strategies are concluded, as well as that of different spectrum sensing schemes in sharing procedure. Moreover, some application examples of the spectrum sharing in CRNs, such as smart grid, public safety, cellular network and medical body area networks are also introduced. In addition, our previous related works are presented and the open research issues in the field of spectrum sharing are stated as well.

Energy structure and absorption spectra of colloidal CdS nanocrystals in gelatin matrix

We investigate the energy structure of colloidal CdS nanocrystals by measuring the UV–vis absorption spectra. Nanocrystals were synthesized by sol–gel method in a gelatin matrix in the size range from 2.5 to 3.9 (±0.2)nm. In order to interpret the UV–vis absorption spectra we calculate the energy spectrum of electron quasi-stationary states using the model of open nanocrystal as well as the hole stationary spectrum in a two-band approach. It is shown that the main contribution to the absorption spectrum is made by interband transitions 1S3/2→1Se and 1P3/2→1Pe, and its shape is determined by the size distribution of nanoparticles. For this system the estimated values of the effective masses of the heavy hole and light hole are 1.44m0 and 0.28m0, respectively.

Radiative and nonradioactive electron transfer in donor-acceptor phenanthrimidazoles.

Photoinduced electron transfer in a series of naphthyl substituted phenanthrimidazoles has been studied in solutions. The intramolecular charge transfer (CT) leads to a large Stokes shift and large dipole moment in the fluorescent state. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all the compounds studied. An analysis of the CT fluorescence lead to the quantities relevant for the electron transfer in the Marcus inverted region.

Modulational stability of electron plasma wave spectra

Analytical models for weakly nonlinear electron plasma waves are considered in order to obtain dynamic equations for the space-time evolution of their local power spectra. The model contains the wave kinetic equation as a limiting case for slow, long wavelength modulations. It is demonstrated that a finite spectral width in wavenumbers has a stabilizing effect on the modulational instability. The results invite a simple heuristic relation between the spectral width and the root-mean-square amplitude of stable stationary turbulent Langmuir wave spectra. A non-local average dispersion relation is derived as a limiting form by using the formalism developed for the spectral dynamics.

Application of Luminescent Methods to the Diagnosis of the Functional State of Single-Celled Algae in Liquid Media**

The possibility of diagnosing the state of single-celled algae in liquid media using their luminescent parameters was analyzed. It was concluded that the conventional method of induction curves was hardly applicable for the diagnosis of single-celled algae in suspensions. Instead, the functional state of the cells could be evaluated using their stationary photoluminescence spectra. Recommendations for optimizing the corresponding experiment were given.

Solid-state 47/49Ti Nuclear Magnetic Resonance of TiO2

Abstract We present 47/49Ti stationary NMR spectra of TiO2 produced in Canada, Australia, and India, acquired at 21.8 T, demonstrating that solid-state 47/49Ti NMR potentially enables one to distinguish the production areas of TiO2.

Line-Shape Analyses of Solid-state 17O NMR Spectra for Hexagonal Ice

We present the results of experimental and theoretical investigations of line shapes in solid-state 17O NMR spectra of hexagonal ice, Ih. Stationary 17O NMR spectra of Ih at temperatures from 143 to 280 K were obtained at 11.7 and 16.4 T. Line shapes changed drastically as the temperature was increased from 143 to 243 K; at 253 K and above, pseudo-isotropic line shapes appear, indicating the presence of reorientational motions. We find that Ratcliffe’s model, which involves twelve orientations and four-step jumps for water reorientational motions, is effective for analyzing the NMR spectra at temperatures below 243 K. The present analysis demonstrates that the isotropic line shapes arise from proton disorder with respect to the solid-state 17O NMR time scale, producing pseudoicosahedral motional averaging that can completely average out second-order quadrupole interactions.

ChemInform Abstract: Role of Heteroaromatic Cycles in the Inter‐ and Intra‐Molecular Dynamics of Excited Aryl Ketones

AbstractReview: 217 refs.

Energy-Efficient Nonstationary Spectrum Sharing

We develop a novel design framework for energy-efficient spectrum sharing among autonomous users who aim to minimize their energy consumptions subject to minimum throughput requirements. Most existing works proposed stationary spectrum sharing policies, in which users transmit at fixed power levels. Since users transmit simultaneously under stationary policies, to fulfill minimum throughput requirements, they need to transmit at high power levels to overcome interference. To improve energy efficiency, we construct nonstationary spectrum sharing policies, in which the users transmit at time-varying power levels. Specifically, we focus on TDMA (time-division multiple access) policies in which one user transmits at each time (but not in a round-robin fashion). The proposed policy can be implemented by each user running a low-complexity algorithm in a decentralized manner. It achieves high energy efficiency even when the users have erroneous and binary feedback about their interference levels. Moreover, it can adapt to dynamic entry and exit of users. The proposed policy is also deviation-proof, namely autonomous users will find it in their self-interests to follow it. Compared to existing policies, the proposed policy can achieve an energy saving of up to 90% under a large number of users.

Triplet harvesting in poly(9‐vinylcarbazole) and poly(9‐(2,3‐epoxypropyl)carbazole) doped with CdSe/ZnS quantum dots encapsulated with 16‐(N‐carbazolyl) hexadecanoic acid ligands

ABSTRACTSemiconductor quantum dots (QDs) can be used as alternative for transition metal complexes to harvest the nonemissive triplet excitons in organic light‐emitting diodes (OLEDs). In search for a QD‐based OLED material generating blue emission, poly(9‐vinylcarbazole) (PVK) and poly(9‐(2,3‐epoxypropyl) carbazole) (PEPK) are chosen as host for blue‐emitting CdSe/ZnS core/shell QDs. The QDs are encapsulated with 16‐(N‐carbazolyl) hexadecanoic acid (C16), a ligand terminated by a carbazole moiety. As alternative for PVK, PEPK, where the lower molecular weight and less extensive excimer formation could promise a better film formation and more extensive exciton hopping, is explored. The efficiencies of singlet ( ) and triplet ( ) energy transfer to the C16 capped QDs are estimated by combining stationary photoluminescence spectra and fluorescence decays of pristine polymer films with those of polymer films doped with the QDs. At a loading of 30 wt % of the QDs, increases from 12 ± 1% in PVK to 41 ± 2% in PEPK while increases from 37 ± 22% in PVK to 72 ± 48% in PEPK. The investigation of the film morphology by atomic force microscopy confirms that the main factor limiting the triplet transfer efficiency in the PVK matrix is the clustering of the C16 capped QDs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 539–551

Output three-mode entanglement via coherently prepared inverted Y-type atoms

In this paper, the output quantum correlations of three fields interacting with inverted Y-type atoms inside a three-mode cavity are investigated. By numerically calculating the stationary noise spectra of the fields, we show that it is possible to generate the genuine tripartite continuous variable entanglement outside the cavity by coherently preparing the atoms in a superposition of the upper excited state and two ground states initially. Our numerical results demonstrate that both zero frequency entanglement and sideband frequency entanglement can be obtained under different initial coherent conditions. In addition, we investigate the thermal fluctuation effects on the quantum entanglement. It is found out that the entanglement occurring in a high frequency regime is more robust against thermal noise than the zero frequency entanglement, which may be useful for quantum communication.