Synthesis Of Envelopes Research Articles

Envelope broadening and scattering attenuation of a scalar wavelet in random media having power-law spectra

Peak delay and envelope broadening of an S-wavelet with travel distance increasing are seen in short-period seismograms of small earthquakes. Those phenomena are results of scattering by random velocity inhomogeneities in the earth medium. As shown in sonic well-log data we may suppose that random velocity fluctuation has power-law spectra even in the seismic spectral range. As a simple mathematical model, we study how the envelope of a scalar wavelet varies in von Kármán-type random media, which have power-law spectra at large wavenumbers. Since the centre wavenumber of a wavelet is a unique scale in the power-law spectral range, using it as a reference, we divide the random media into the low-wavenumber spectral (long-scale) component and the high-wavenumber spectral (short-scale) component. For the wave propagation through the long-scale component of random media, we may apply the parabolic approximation to the wave equation. Using the Markov approximation, which is a stochastic extension of the phase screen method, we directly synthesize the energy density, which is the mean-square (MS) envelope of a wavelet in a given frequency band. The envelope duration increases according to the second power of travel distance. There is an additional factor, the wandering effect which increases the envelope duration according to the traveltime fluctuation. Wide angle scattering caused by the short-scale component of random media attenuates wave amplitude with travel distance increasing. We use the total scattering coefficient of the short-scale component as a measure of scattering attenuation per distance, which is well described by the Born approximation. Multiplying the exponential scattering attenuation factor by the MS envelope derived by the Markov approximation, we can synthesize the MS envelope reflecting all the spectral components of random media. When the random medium power spectra have a steep role-off at large wavenumbers, the envelope broadening is small and frequency independent, and scattering attenuation is weak. When the random medium power spectra have a small role-off, however, the envelope broadening is large and increases with frequency, and the scattering attenuation is strong and increases with frequency. The proposed synthesis of MS envelopes is fully analytic; therefore, it can be a theoretical basis for the evaluation of random heterogeneity of the earth medium from the analysis of seismogram envelopes.

Synthesis and applicable condition of vector wave envelopes in layered random elastic media with anisotropic autocorrelation function based on the Markov approximation

SUMMARY The Markov approximation is a powerful stochastic method for the direct synthesis of wave envelopes in random velocity fluctuated media when the wavelength is shorter than their correlation distance. To apply the Markov approximation to realistic cases, we consider horizontal layered random media characterized by an anisotropic autocorrelation function (ACF), where different layers have different randomnesses and different background velocities having step-like changes. Solving the parabolic master equation for the two frequency mutual coherence function (TFMCF) in random elastic media for the vertical incidence of a plane wavelet from the bottom, we calculate the angular spectrum just before the first velocity boundary. Multiplying transmission or PS conversion coefficients of the boundary by the angular spectrum, we calculate the angular spectrum and TFMCF on the other side of the boundary. Then we solve the master equation for the forward propagating wavelet in the second layer. Taking the same procedure for each layer boundary, we finally obtain the mean square (MS) vector envelopes on the free surface on the top layer. For the practical simulation, we use 2-D random media characterized by a Gaussian ACF. We numerically confirm the validity of the envelope synthesis for a specific case of layered random media with anisotropic ACF by comparing with finite difference (FD) simulations of elastic waves. Considering the Earth structure, the horizontal correlation distance is larger than the vertical one and the velocity fractional fluctuation becomes weak as depth increases, the Markov approximation is good for modelling the primary wavelet and also the converted wavelet for the vertical incident wavelet. We derive an applicable range of the Markov approximation for random media with anisotropic ACF by comparing with FD simulations. The results show that the Markov approximation is accurate when the wavelength is comparable or shorter than the both of vertical and horizontal correlation distances and the MS fractional fluctuation is much smaller than the ratio of squared horizontal correlation distance to the product of the vertical correlation distance and propagation distance.

Gamete interactions in teleost fish: the egg envelope. Basic studies and perspectives as environmental biomonitor.

The current knowledge about teleost fish egg envelope is summarized. The paper analyzes the organization and deposition process of the protein composition and genes involved in the synthesis of teleost fish egg envelopes and their role in gamete interaction during fertilization. Pelagic and demersal species that our research group is working with are especially considered. The vertebrate ZP family of proteins, the evolution and relationship among the different genes and their expression are taken into account. We consider fish envelope as a possible biomonitor for ecological contaminants. The biotechnological applications for aquaculture and genomic and post-genomic approaches are auspicious.

Gamete interactions in teleost fish: the egg envelope. Basic studies and perspectives as environmental biomonitor

The current knowledge about teleost fish egg envelope is summarized. The paper analyzes the organization and deposition process of the protein composition and genes involved in the synthesis of teleost fish egg envelopes and their role in gamete interaction during fertilization. Pelagic and demersal species that our research group is working with are especially considered. The vertebrate ZP family of proteins, the evolution and relationship among the different genes and their expression are taken into account. We consider fish envelope as a possible biomonitor for ecological contaminants. The biotechnological applications for aquaculture and genomic and post-genomic approaches are auspicious.

Cytochrome P450 metabolizing fatty acids in living organisms

Cytochrome P450s (P450s) are ubiquitous enzymes found in most classes of organisms including animals, plants, bacteria and fungi. P450s are heme–thiolate metalloenzymes that are usually membrane-bound on the cytosolic face of the endoplasmic reticulum (except the bacterial ones which are often soluble). The vast majority of P450s catalyse, in the presence of NADPH or NADH, the insertion of an atom of oxygen from O2 into a molecule of substrate according to the overall reaction RH + NAD(P)H + O2 + H + fi ROH + NAD(P) + H2O. They are thus monooxygenases catalysing mostly hydroxylation reactions. The number of genes encoding P450s ranges from a few dozen in animal genomes to several hundreds in bacterial genomes or in plant genomes, in which they represent up to 1% of total genes. Cytochrome P450s are classified in the same family when they share > 40% identity in amino acid sequence and in the same subfamily when they share > 55% identity. They are major actors in the metabolism of xenobiotics, as well as endogenous compounds like plant hormones, many secondary metabolites and oxygenated derivatives of fatty acids. Since the pioneering work of Preiss and Block (1964), Lebeault et al. (1971) and Soliday and Kolattukudy (1977), shed light on the presence of cytochrome P450s metabolizing fatty acids (FA) in animals, micro-organisms and plants, respectively, interest in the study of these enzymes in all organisms has greatly increased because the products of the reactions possess fundamental biological activities. Bioactivation of arachidonic acid (C20:4) in the so-called ‘arachidonic cascade’ in mammals illustrates the diversity and biological activities of oxygenated FAs, as well as the role of cytochrome P450s in their production. A large amount of data was recently acquired on P450 functions in animals and also in microbes and plants. The goal of this minireview series is to draw attention to this new knowledge. Mammalian P450s cover many aspects of biology. In this series of minireviews, we have chosen to focus on involvement of FA x-hydroxylases in human genetic diseases. In plants, studies of Arabidopsis mutants have confirmed key roles for cytochrome P450s in the synthesis of FA-based hydrophobic barriers. Recent biochemical studies have also revealed the existence of FA-metabolizing P450s with different specificities. The possible biological roles of these newly characterized P450s is discussed. In bacteria and fungi, P450s metabolizing FA are mainly studied as actors in FA and alkane degradation, but as shown here, they are also involved in the production of molecules like sphingolipids, polyketides and oxylipins. Recent progress in the functional characterization of P450 families, combined with the wealth of phylogenetic information coming from sequencing projects for a wide array of organisms, has started to give insights into the evolution of P450-dependent functions. Concerning FA metabolism, it is clear that many P450 families have evolved in connection with a specific common biological function. A typical example concerns plant FA x-hydroxylases from the CYP86 family, which is dedicated to the synthesis of protective envelopes (i.e. cutin and suberin). Another important observation is that identical P450-dependent catalytic activities have evolved separately several times during evolution. This point is again illustrated by FA x-hydroxylation, which is carried out by different families in animals, plants and fungi (CYP4A, CYP86A and CYP52 respectively). Despite the great progress made in recent years in the characterization of the biological roles of P450s in all kingdoms, the functions of many P450 families and family members revealed by genome sequencing projects remain unknown. Elucidation of their function, which is some cases might be species specific, will undoubtedly be a major challenge in P450 research in the years to come.

Synthesis of vector wave envelopes on the free surface of a random medium for the vertical incidence of a plane wavelet based on the Markov approximation

In short‐period seismograms of earthquakes, we often observe the broadening of apparent duration of P and/or S waves and the excitation of the transverse component especially for P waves as travel distance increases. Such phenomena are well explained by scattering caused by random velocity fluctuation in the lithosphere. The Markov approximation is known as one of the powerful stochastic methods for the direct synthesis of wave envelopes. We extend the method to synthesize vector wave envelopes on the free surface of a random medium since seismic observation is usually done on the ground surface. We evaluate the mean square (MS) envelope on the free surface by multiplying the amplification factor on the free surface to the angular spectrum in an infinite random medium. We synthesize MS envelopes for the vertical incidence of an impulsive plane P or S wavelet into a 3‐D random medium characterized by a Gaussian autocorrelation function with typical parameters of the lithosphere. As a result, the vertical and horizontal component MS envelopes show different amplification rates on the free surface; however, we may say that “a factor of 4” is a good approximation for the amplification rate for both components. Finally, we numerically confirm the validity of our direct envelope syntheses by the comparison with finite difference simulations of waves in 2‐D random media. The Markov approximation is accurate when the wavelength is shorter than the correlation distance and the fractional fluctuation is much smaller than the ratio of the correlation distance to the propagation distance.

Synthesis of coda wave envelopes in randomly inhomogeneous elastic media in a half-space: single scattering model including Rayleigh waves

SUMMARY Seismograms of local earthquakes consist of not only direct waves but also coda waves originating from scattering due to lithospheric inhomogeneities. As a mathematical basis for interpreting these seismograms, we present a synthesis of coda wave envelope propagating through randomly inhomogeneous medium in a half-space by considering elastic conversion scattering modes of body-to-body waves, Rayleigh-to-body waves, body-to-Rayleigh waves and Rayleigh-to-Rayleigh waves. We first evaluate scattering amplitudes of above scattering modes by elastic inhomogeneity localized in a block by applying the Born approximation to the elastic wave equation in the frequency domain. Scattering amplitudes of all conversion scattering modes are represented by the Fourier spectrum of the elastic inhomogeneity multiplied by the basic scattering pattern which determines the non-isotropic scattering pattern in the long-wavelength limit. Then, considering an ensemble of random media, we derive scattering coefficients which represent the scattering power per unit volume as ensemble averages. By summing up the scattered energy from distributed scattering blocks in a half-space for a point shear dislocation source with the omega-square model, we synthesize the coda-wave envelope for each scattering mode. Numerical evaluation of three-component MS envelopes for a shallow source shows strong frequency dependence. Though scattered body waves are dominant in high frequencies, Rayleigh-to-Rayleigh scattered waves with smaller decay with increasing lapse time become dominant for low frequencies.

Envelope syntheses of cylindrical vector-waves in 2-D random elastic media based on the Markov approximation

Abstract Seismograms of microearthquakes are complex; however, their envelopes broaden as the travel distance increases. P-waves are recorded in transverse components, S-waves are recorded in the longitudinal component, and waves are observed at sites even in the nodal direction of the source radiation. These phenomena, which are typically found in short-period seismograms, can be interpreted to be the result of scattering due to lithospheric inhomogeneity. We report here our study of a simple statistical model in which the propagation of waves radiated from a point source in two-dimensional (2-D) random elastic media is characterized by a Gaussian autocorrelation function. For the case that the wavelength is shorter than the correlation distance, two methods based on the Markov approximation are introduced for the direct synthesis of vector wave envelopes. One is to analytically solve the stochastic equation for the two-frequency mutual coherence function; the validity of the solution is confirmed by using finite difference simulations. The second is to numerically solve the stochastic equation for the mutual coherence function. The two methods are equivalent, but the latter is applicable to nonisotropic source radiation. For the case of a point shear dislocation source, a peak delay from the onset and a smoothly decaying tail are found to be common to synthesized envelopes in all azimuths. Scattered waves are excited even at receivers in the nodal direction, and amplitudes become independent of the radiation pattern as lapse time increases.

Synthesis of vector wave envelopes in three‐dimensional random elastic media characterized by a Gaussian autocorrelation function based on the Markov approximation: Spherical wave case

High‐frequency seismograms of microearthquakes show broadened envelopes with travel distance increasing. Scattered P waves appear in the transverse components and scattered S waves also appear in the longitudinal component. These phenomena are clear evidence of scattering due to random inhomogeneities spreading over the lithosphere. There is a statistical method to directly simulate wave envelopes when the medium inhomogeneity is weak and the wavelength is shorter than the medium‐scale length. Applying the Markov approximation to spherically outgoing vector waves radiated from a point source in three‐dimensional random elastic media statistically characterized by a Gaussian autocorrelation function, we synthesize their envelopes. Solving the stochastic master equation for the development of the two‐frequency mutual coherence function of potential with travel distance, and taking the Fourier transform of it, we newly derive analytic representation of mean square (MS) envelopes of three component vector waves by using the elliptic theta function. For P waves, the radial component shows a broadened envelope with a delayed peak and a smoothly decaying tail, where the peak MS amplitude is approximately proportional to the minus fourth power of travel distance. The transverse component shows a broadened envelope with a smaller peak value and a longer peak delay and a longer tail compared with those in the radial component, where the peak MS amplitude is proportional to the minus third power of travel distance. S wave envelopes are also solved. S wave envelope broadening is larger than that of P wave broadening. These features well explain qualitatively the characteristics of seismogram envelopes of microearthquakes.

Synthesis of vector wave envelopes in three‐dimensional random elastic media characterized by a Gaussian autocorrelation function based on the Markov approximation: Plane wave case

High‐frequency seismograms of microearthquakes observed at long travel distances have longer apparent durations than the source durations caused by scattering due to lithospheric inhomogeneity. Frequency dependence of the peak delay from the onset and the broadening of seismogram envelope well reflect the spectra of random velocity inhomogeneity. Here we propose a formulation for the envelope synthesis of vector waves in three‐dimensional random elastic media in the case that wavelengths are smaller than the characteristic scale of random inhomogeneity. A stochastic master equation for the two‐frequency mutual coherence function (TFMCF) of potential field is derived on the basis of the Markov approximation, which is a stochastic extension of the phase screen method for solving the parabolic wave equation. From the Fourier transform of TFMCF at a given travel distance, we are able to synthesize the mean square traces of three vector wave components. For the incidence of an impulsive plane P wavelet to random elastic media characterized by a Gaussian autocorrelation function, the mean square envelope of each component at a long travel distance is analytically written by using an elliptic theta function. Each synthesized envelope shows peak delay from the onset and broadening with travel distance increasing; however, the peak delay of the transverse component is larger than that of the longitudinal component. For the same fractional velocity fluctuation, the envelope broadening for S waves is larger than that for P waves.

Synthesis of scalar-wave envelopes in two-dimensional weakly anisotropic random media by using the Markov approximation

SUMMARY Due to the Earth's inhomogeneity, seismogram envelopes increase in duration and decrease in amplitude with increasing travel distance. Those features have been explained on the basis of the forward scattering in random media using the Markov approximation. Since the conventional studies assumed isotropic random media, they were not realistic enough to represent the anisotropic lithosphere characterized by long horizontal and short vertical correlation distances. Using the Markov approximation, the present study formulates the envelope synthesis in 2-D weakly anisotropic random media characterized by Gaussian and von Karman-type autocorrelation functions (ACF). Also, wave propagation is numerically simulated with the finite-difference (FD) method; 2 Hz Ricker wavelets propagate through the random media characterized by 4 km s−1 average velocity and the Gaussian ACF with 5 km horizontal correlation distance, 2.5 km vertical correlation distance, and 5 per cent rms fractional velocity fluctuation. We find a good coincidence between the envelopes of the Markov approximation and those of the FD simulations, which supports the reliability of the synthesis method using the Markov approximation. The envelopes of the Markov approximation are scaled by using a characteristic time, which is a function of propagation direction and other model parameters. It predicts that envelopes increase in duration and decrease in maximum amplitude more rapidly in the horizontal propagation than in the vertical when the media are characterized by long horizontal and short vertical correlation distances. In the case of the vertical wave propagation, the envelope of the anisotropic random media has shorter duration and larger maximum amplitude than those of the isotropic random media. It means that the intensity of the inhomogeneity is underestimated when one analyses seismogram envelopes of deep events considering anisotropic lithosphere as isotropic random media.

Synthesis of plane vector wave envelopes in two-dimensional random elastic media based on the Markov approximation and comparison with finite-difference simulations

SUMMARY High-frequency seismograms mainly consist of incoherently scattered waves. Their envelopes are a stable measure exhibiting characteristic features like peak amplitude decay and envelope broadening with increasing travel distance which can be used to infer stochastic parameters of the inhomogeneous Earth medium. As a simple model we study the propagation of plane P and S waves through a 2-D random elastic medium. If the wavelength is less than the correlation distance and the medium inhomogeneity is weak conversion scattering can be neglected, and a stochastic parabolic wave equation is derived. Solving the master equation for the two-frequency mutual coherence function and taking the Fourier transform, we obtain the temporal change of the mean squared amplitude at a fixed distance. The distribution of energy between longitudinal and transverse components can then be calculated by using the angular spectrum representation. For the case of a Gaussian autocorrelation function the solution is completely analytical. The theoretical envelopes are compared with the results of 2-D elastic finite-difference (FD) simulations. For a stable estimate of mean-squared envelopes the squared FD traces from different receiver positions and several realizations of the random medium have been averaged. The theoretical curves well explain the delay of the peak arrival from the onset and the broadening of the envelope with increasing propagation distance. Also the transverse component amplitude for P-wave incidence and the longitudinal component amplitude for S-wave incidence are precisely explained by the theory. The time integral of the mean-squared transverse component for P-wave incidence and of the mean-squared longitudinal component for S-wave incidence linearly increases with travel distance. The linear coefficient is a measure of the ratio of mean-squared fractional fluctuation to correlation distance.

Hybrid synthesis of scalar wave envelopes in two‐dimensional random media having rich short‐wavelength spectra

Wave trains in high‐frequency seismograms of local earthquakes are mostly composed of incoherent waves that are scattered by distributed heterogeneities within the lithosphere. Their phase variations are very complex; however, their wave envelopes are systematic, frequency‐dependent, and vary regionally. Stochastic approaches are superior to deterministic wave‐theoretical approaches for modeling wave envelopes in random media. The time width of a wavelet is broadened with increasing travel distance mostly because of diffraction caused by the long‐wavelength components of random velocity inhomogeneity. The Markov approximation for the parabolic wave equation is effective for the synthesis of envelopes for random media whose spectra are poor in short‐wavelength components; however, we have to consider the contribution of large‐angle nonisotropic scattering if the random media are rich in short‐wavelength inhomogeneities. Multiple nonisotropic scattering can be reliably modeled as isotropic scattering by using an effective isotropic scattering coefficient given by the momentum transfer scattering coefficient, which is a reciprocal of the transport mean free path. It is mostly controlled by the short‐wavelength spectra of random media. We propose a hybrid method for the synthesis of whole wave envelopes that uses the envelope derived from the Markov approximation as a propagator in the radiative transfer integral equation for isotropic scattering. The envelopes resulting from the hybrid method agree well with ensemble average envelopes calculated by averaging envelopes from individual finite difference simulations of the wave equation for a suite of random media.

Seismic wave propagation and scattering in the heterogeneous earth

Introduction.- Heterogeneity in the Lithosphere.- Phenomenological Approaches to Seismogram Envelopes in short-periods.- Born approximation for Wave Scattering in Random Media.- Attenuation of High-Frequency Seismic Waves.- Synthesis of Three-Component Seismogram Envelopes for Earthquakes Using Scattering Amplitudes from the Born Approximation.- Envelope Synthesis Based on the Radiative Transfer Theory: Multiple Scattering Models.- Parabolic approximation and Envelope Synthesis based on the Markov Approximation. Summary and Epilogue.

Short-wavelength crustal heterogeneities in the Nikko area, Central Japan, revealed from the three-component seismogram envelope analysis

The short-wavelength crustal heterogeneity is investigated in the Nikko area (Central Japan), using a three-component seismogram envelope analysis applied to small local earthquakes. We stochastically model fluctuations in crustal density and seismic wave velocities by using an exponential auto-correlation function. The model parameters are correlation length a and root mean square (rms) fractional fluctuation strength ε. Free surface and non-spherical source radiation effects are incorporated in the synthesis of three-component seismogram envelopes. We use 149 short-period seismograms recorded by array stations from 10 local earthquakes with magnitudes 1 ∼ 2 and epicentral distances less than 15 km. A best fit minimum residual between observed and synthetic envelopes in the frequency band of 8 ∼ 16 Hz gives ε 2 a ⋍ 8 × 10 −6 m −1 . With the additional information on the strength of direct wave attenuation and the excitation of coda waves at low frequencies, we estimate that a = 300 ∼ 800 m and ε = 5 ∼ 8%. This strong heterogeneity and short correlation length probably reflect the geological condition of the Nikko area which is located in the vicinity of the volcanic front.

Morphogenesis of African swine fever virus in monkey kidney cells after reversible inhibition of replication by cycloheximide.

The late cytoplasmic phases of African swine fever virus (ASFV) morphogenesis in monkey kidney cells have been studied by transmission electron microscopy, focusing attention on the synthesis of viral envelopes. Morphogenesis was studied after reversible cycloheximide blockage of monkey kidney cells infected with ASFV. ASFV appears to synthesize its external and internal envelopes within the cellular cytoplasm, at the same time as the capsid is formed, with intracellular and extracellular virions showing similar structure and polypeptide composition.

Synthesis and deposition of oocyte envelopes in the Colorado beetle, Leptinotarsa decemlineata Say.

Electron microscopical and autoradiographic methods demonstrate that the secretion vesicles (SV), which are condensed by the Golgi-complexes of the follicle cells of the Colorado beetle, contain proteins which can be labelled with 3H-leucine. The labelled proteins are transported to the oocyte during vitellogenesis. At the end of yolk deposition, a few SV, situated just above the microvilli, disintegrate and give rise to the two layers of the vitelline membrane (VM). During the laying down of the VM or perhaps at a slightly earlier stage a layer is deposited beneath the basement membrane of the follicle cells. This layer may be important in inducing the formation of the egg membranes. Once the VM has formed, the follicle cells degenerate completely. The chorionic inner layer arises from the breakdown of SV, while the chorionic outer layer is formed from the degenerated follicle cells.

Synthesis and deposition of oocyte envelopes (vitelline membrane, chorion) and the uptake of yolk in the dragonfly (Odonata:Aeschnidae).

ABSTRACT Light and electron-microscope studies on dragonfly ovarioles reveal evidence that the precursor vitelline membrane and chorion secretions are synthesized within the follicle cells. It is suggested that the sequence of synthesis and deposition of the vitelline membrane occurs as follows. The vitelline membrane presecretion appears to be synthesized by the rough-surfaced endoplasmic reticulum, giving rise to intracisternal granules. These appear to migrate in the cisternae to the region of the Golgi complex where the endoplasmic reticulum loses most of its ribosomes and the intracisternal granules move into the Golgi region where they appear within small vesicles. These seem to find their way into the Golgi cisternae where they may be incorporated with the secretions from the Golgi cisternae to produce the definitive previtelline secretion. The previtelline secretion bodies are eventually discharged into the space between the oocyte and follicle cells, forming rows of secretion bodies between the microvilli. These fuse into progressively larger bodies until a complete membrane is established. Follicle cells actively secreting precursor vitelline membrane substance show many disk-shaped, relatively clear vesicles in the cytoplasm. After the vitelline membrane is laid down, the follicle cells take on an entirely different function; namely, the synthesis and deposition of the chorion. The first visible chorion secretion appears in profile as elongate dense bodies within the Golgi cisternae which tend to coil, and in so doing, expand the cisternae. As this occurs, the enlarged cisterna, loaded with concentric coiled secretion material, separates from the remainder of the Golgi cisternae and becomes free in the cytoplasm as a prechorion secretion body. These migrate to, and collect below, the surface of the cell where they are eventually ejected between the surface folds and become incorporated into the developing chorion. Uptake of yolk in the dragonfly seems to be predominantly by micropinocytosis. The oocyte surface during active vitellogenesis bears many pits which contain an extracellular material closely applied to the outer surface of the plasma membrane. Thin, radially oriented bristles are continuous with the inner surface of the plasma membrane in this region. The pits continue to invaginate until they are cut off from the plasma membrane and come to lie in the oocyte cortex as coated vesicles. These appear to lose their coats gradually and fuse with one another to produce definitive yolk spheres.