Anomalous Amplitudes Research Articles

Effect of low-energy dynamics on anomalous vibrational amplitudes in vitreous silica

The role of low-energy dynamics in vitreous silica is discussed from the viewpoint of atomic motion. Coherent inelastic neutron scattering measurements have given the averaged mean-square displacements through an evaluation of Debye-Waller factor. The temperature dependences of the averaged mean-square displacements have been obtained in various types of ${\mathrm{SiO}}_{2}.$ The averaged mean-square displacements of vitreous silica are significantly greater than those of other ${\mathrm{SiO}}_{2}$ samples at any temperatures. This finding is explained based on the distribution of double-well potentials, whose barriers are significantly small. The anisotropic and flexible atomic motions in vitreous silica should be realized for small barrier potentials, giving rise to an excess density of states around 5 meV, the so-called boson peak.

THE SEISMIC REFLECTION RESPONSE TO CHANGES IN PRESSURE

Hydrocarbons are often interpreted using seismic attributes, the most common being high anomalous amplitudes or bright spots. Seismic data processing and interpretation is involved in enhancing such anomalies, thereby improving the interpretation for both optimised drilling and volumetric assessment. However, not all bright spots are hydrocarbons since there have been occasions when an economically drillable bright spot unexpectedly produces a dry hole. This paper discusses the first laboratory-based experiments aimed at understanding seismic reflection effects caused by changes in pressure. Water-saturated unconsolidated sand in an unconfining container was pressured from room pressure to over 2 MPa in step manner and then reduced back to room pressure. After each step in application of overburden pressure change, a zero offset 3D seismic survey was performed using ultrasonic transducers. This approach was repeated after the injection of air, to observe the seismic response to gas under changing pressure.The velocity of sand increased as a function of pressure until a value of approximately 1 MPa was attained, when fracturing became apparent. Upon pressure reduction below 2MPa, fracture healing became apparent; there were also rapid changes in reflection amplitudes due to changes in pressure. It is under high pressure that preferential alignment of parallel grains at specific distances relative to the seismic wavelength may result in ‘seismic tuning’, and apparent bright spots. It was noted that a pressure increase caused anti-clockwise rotation of the AVO fluid line; this may provide an indication of whether a change in seismic character is a result of a pressure or gas reduction. Some apparent bright spots within sand/shale sequences may also result from seismic tuning effects developed at specific seismic wavelengths, rather than from the presence of hydrocarbons; the sense of rotation of the fluid line may also help to differentiate between a pressure change or gas reduction.

Anomalous processes at high temperature and density in a two-dimensional linear σ model

We use the 2-dimensional $\sigma$ model as a toy model to study the behavior of anomalous amplitudes in the limit where the constituent quark mass is small. Symmetry arguments tell that the $\pi^o\to\gamma$ amplitude should vanish if $m\to 0$, but we show that this conclusion is spoiled by infrared singularities. When a proper regularization (resummation of a thermal mass, for instance) is taken into account, this amplitude vanishes as expected. We also study the amplitude $\pi^o\sigma\to\gamma$ and show that it does not vanish in the same limit.

Sigma-model symmetry in orientifold models

We investigate in the simplest compact D=4 N=1 Type IIB orientifold models the sigma-model symmetry suggested by the proposed duality of these models to heterotic orbifold vacua. This symmetry is known to be present at the classical level, and is associated to a composite connection involving untwisted moduli in the low-energy supergravity theory. In order to study possible anomalies arising at the quantum level, we compute potentially anomalous one-loop amplitudes involving gluons, gravitons and composite connections. We argue that the effective vertex operator associated to the composite connection has the same form as that for a geometric deformation of the orbifold. Assuming this, we are able to compute the complete anomaly polynomial, and find that all the anomalies are canceled through a Green-Schwarz mechanism mediated by twisted RR axions, as previously conjectured. Some questions about the field theory interpretation of our results remain open.

Anomalies and tadpoles

We show that massless RR tadpoles in vacuum configurations with open and unoriented strings are always related to anomalies. RR tadpoles arising from sectors of the internal SCFT with non-vanishing Witten index are in one-to-one correspondence with conventional irreducible anomalies. The anomalous content of the remaining RR tadpoles can be disclosed by considering anomalous amplitudes with higher numbers of external legs. We then provide an explicit parametrization of the anomaly polynomial in terms of the boundary reflection coefficients, i.e. one-point functions of massless RR fields on the disk. After factorization of the reducible anomaly, we extract the relevant WZ couplings in the effective lagrangians.

Characterization of in situ elastic properties of gas hydrate‐bearing sediments on the Blake Ridge

During Ocean Drilling Program Leg 164, shear sonic velocity and other geophysical logs were acquired in gas hydrate‐bearing sediments on the Blake Ridge to characterize the very distinct seismic signature of such formations: anomalous low amplitudes overlying a strong bottom‐simulating reflector (BSR). A comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the BSR at 440 meters below seafloor (mbsf) because of the presence of hydrates. Below the bottom of the thermodynamic hydrate stability zone at ∼520 mbsf, the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas. Between these two depths, gas hydrate and free gas seem to coexist. Within the Gas hydrate stability zone, we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation. In close agreement with measurements made on discrete in situ samples, the latter describes most accurately the interactions between the matrix, the pore fluids, and the hydrates. This model indicates that 5 to 10% of the pore space is occupied by hydrates deposited uniformly on the surface of the grains. The comparison with Gassmann's model also show that the amount of free gas below the BSR never exceeds 5% of the pore space but is high enough to generate the BSR. The coexistence of free gas and gas hydrates below the BSR may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition.

The Greenshank anomaly – An AVO case history

The Greenshank anomaly straddles the border between WA–246–P and WA–l–P, in the Dampier Sub–basin on the North West Shelf of Western Australia. It is located approximately 70 km northwest of Dampier and 25 km northwest of the Stag Oilfield.Seismic data over the Greenshank anomaly displays a series of high amplitude events, dipping basinward near the centre of a northeasterly trending fault block. These anomalous amplitudes were correlated from regional seismic control to the lower M. australis Sandstone within the lower Cretaceous. Pre–drill seismic interpretation, AVO and acoustic impedance studies over the anomaly suggested the presence of a stratigraphic trap that comprised either a high porosity brine filled sand, or a hydrocarbon saturated low acoustic impedance sand. However, the drilling of Greenshank–1 in June 1996 encountered a low acoustic impedance shale with minor gas shows beneath a higher velocity cemented claystone at the level of the seismic anomaly. The higher acoustic impedance lower M. australis Sandstone intersected below the shale was very poor quality and water wet.A post–drill AVO study was conducted to explain the difference between the observed AVO behaviour and the well results. Synthetic forward AVO modelling was performed using the Greenshank–1 measured sonic, density and synthetic shear sonic data. This study showed that the fluid factor anomaly is caused by the low acoustic impedance shale above the reservoir and not the sand as interpreted pre–drill. The acoustic impedance and Poisson’s ratio in the shale decreases relative to the overlying high acoustic impedance claystone unit, resulting in a positive AVO anomaly.

Radiative tau lepton pair production as a probe of anomalous electromagnetic couplings of the tau

We calculate the squared matrix element for the process e + e − → τ + τ − γ allowing for anomalous magnetic and electric dipole moments at the ττγ vertex. No interferences are neglected and no approximations of light fermion masses are made. We show that anomalous moments affect not only the cross section, but also the shape of the photon energy and angular distributions. We also demonstrate that in the case of the anomalous magnetic dipole moment, the contribution from interference involving Standard Model and anomalous amplitudes is significant compared to the contribution from anomalous amplitudes alone. A program to perform the calculation is available and it may be employed as a Monte Carlo generator.

The generation of intensive short-period internal waves in the frontal zone of a coastal upwelling

The measurements data provided by an antenna of distributed temperature sensors, mounted on an oceanographic tower in the South Crimea continental shelf area, were applied to study the mechanism for the generation of short-period internal waves with anomalous amplitudes in the Black Sea. For analysis, information was incorporated concerning the background hydrological and meteorological conditions that were observed during the experiment. A mathematical model for the phenomenon under study has been constructed, and calculations of the anomalous internal wave generation have been presented. The paper contains a comparative analysis of thein situ data and simulation results, and demonstrates a good qualitative/quantitative agreement between the parameters of internal waves.

Time-space evolution characteristics of abrupt variation of wave velocity ratio in the seismogenic process of recent strong earthquakes in Yunnan area

Within a short period of 7 months from July 12, 1995 to February 3, 1996, three earthquakes occurred continually to west Menglian in the border area of China-Myanmar (M=7.3), in Wuding county M=6.5 and in Lijiang (M=7.0) in Yunnan area. In this paper, the authors have studied the time-space evolution characteristics of wave velocity ratio (γ) in observed at 5 single stations and the average value of several stations before the recent strong earthquakes. It is discovered that 5–8 years before the earthquake with M=7, source precursors of long-medium term, with high (low) drastic variations of wave velocity ratio, appeared within 120 km from the epicenters, and the source precursors of long-medium term entered into medium-short term stage when the amplitude of wave velocity ratio suddenly increased (decreased) or times of earthquake increase drastically. Three to five years before M=6 earthquakes, source precursors of long-medium term and near field precursors of long-medium term, with abrupt velocity change of high values, appeared within 40 and 150 km; however, the indicator is not clear in the period of transition to medium-short stage. The anomaly of γ within 150 km from the epicenter reaches as much as 3.0, while the maximum value is 2.36 in the area 250 km away, showing the characteristics that the shorter the distance the bigger the abrupt change. Namely, the anomalous amplitudes of source precursors and near field precursors are 20%–60% bigger than that of far precursors. The reliability of abrupt variation data of γ and its physical mechanism have also been explored in this paper.

Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.

Anomalous mesonic interactions near a chiral phase transition.

Using constituent quarks coupled to a linear sigma model at nonzero temperature, I show that many anomalous mesonic amplitudes, such as ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$, vanish in a chirally symmetric phase. Processes which are allowed, such as ${\ensuremath{\pi}}^{0}\ensuremath{\sigma}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$, are computed to leading order in a loop expansion.

Seismic anisotropy caused by rock fabric

SUMMARY As part of an experiment to investigate the influence of cracks produced by tectonic stress on the observed in situ anisotropic properties of crustal rocks at Kent Cliffs, New York, the contribution of rock fabric anisotropy was studied using laboratory core-sample ultrasonic measurements. Measured velocities of intact unfractured specimens, corrected to lithostatic pressure, allow the effect of rock fabric anisotropy to be evaluated. Computed phase-velocity surfaces and wave surfaces show varying degrees of anisotropy at different depths. These surfaces predict various anisotropic phenomena, such as S-wave splitting and anomalous amplitudes and polarizations. Some predictions can be applied to the case of a general transversely isotropic medium, including negligible P-wave, in contrast to large S-wave, polarization anomalies, generation of cusps in the wave surface by strong anisotropy, and the importance of the elastic stiffness coefficient, C1133, to the strength of anisotropy. Computed ray velocities in the borehole axis direction are compared with acoustic logging results. The comparison shows reasonable consistency. S-wave splitting caused by rock fabric for zero-offset vertical seismic profiling (VSP) is also predicted. These results can be used to separate the anisotropy caused by cracks and fractures from the overall observed in situ seismic anisotropy.

Critical non-linearO(N) ?-Models at 2<d<4: The degeneracy of quasi-primary fields and its resolution

Quasi-primary fields with dimensions that differ at most byO(1/N) and whose other quantum numbers are all equal, are called degenerate. Multiplets of such fields are produced by a chain of fusion processes. Forcing the fusion to run through different intermediate states leads to matrices of fusion and anomalous dimension amplitudes whose simultaneous diagonalization allows to resolve the degeneracy.

Non-leptonic kaon decays and the chiral anomaly

An investigation is performed of all non-leptonic kaon decays sensitive to the chiral anomaly. Within the framework of chiral perturbation theory, there are two classes of anomalous amplitudes at O( p 4): reducible and direct contributions. Only radiative transitions are affected by the anomaly. The phenomenology of the decays K L → π + π − γ and K + → π + π 0 γ is studied in detail. Including the dominant contributions of O( p 6), the experimentally observed dependence of he direct emission amplitude for K L → π + π − γ on the photon energy can be understood. A survey is made of the rare “anomalous” decays K → ππγγ and K → 3 πγ ( γ), including some numerical estimates.

New techniques of applying multi-wavelength anomalous scattering data

Several different methods of using multi-wavelength anomalous scattering data are described and illustrated by application to the solution of the known protein structure, core streptavidin, for which data at three wavelengths were available. Three of the methods depend on the calculation of Patterson-like functions for which the Fourier coefficients involve combinations of the anomalous structure amplitudes from either two or three wavelengths. Each of these maps should show either vectors between anomalous scatterers or between anomalous scatterers and non-anomalous scatterers. While they do so when ideal data are used, with real data they give little information; it is concluded that these methods are far too sensitive to errors in the data and to the scaling of the data-sets to each other. Another Patterson-type function, the P s function, which uses only single-wavelength data can be made more effective by combining the information from several wavelengths. Two analytical methods are described, called AGREE and ROTATE, both of which were very successfully applied to the core streptavidin data. They are both made more effective by preprocessing the data with a procedure called REVISE which brings a measure of mutual consistency to the data from different wavelengths. The best phases obtained from AGREE lead to a map with a conventional correlation coefficient of 0.549 and this should readily be interpreted in terms of a structural model.

Radial mode observations from the 5/23/89 MacQuarie Ridge Earthquake

The radial modes 1S0–5S0 axe clearly observable on several long‐period seismic records from the 5/23/89 Macquarie Ridge earthquake. Observations of 0S0 are weaker, but stacking demonstrates significant excitation. Calculations suggest that, for spherical‐earth models, no simple double couple in the uppermost mantle can explain the excitation amplitudes of 1S0–5S0 relative to 0S0. Calculations suggest that the anomalous amplitudes of 1S0–5S0 can be explained by coupling to other modes induced by plausible levels of deep‐earth lateral structure. The coupling of 0S0 is much weaker, and its observed amplitude suggests that roughly 4% of the total moment release inferred from surface wave studies deviated from pure strike‐slip geometry. This can be modeled by ⪎8° deviations from λ = 0°, δ = 90° in a simple double‐couple point source, or by thrust subevents within the main shock.

Acoustic reflections from complex strata

Rock strata may contain fine‐scale structures which are too small to be identified directly, but which can give rise to anomalous seismic reflection amplitudes. The variance caused by such anomalies severely hampers the use of reflection amplitudes for layer identification, and techniques are required which can identify or correct for the effects of such fine structure. We have done calculations which explore the consequences of two general structure types: wavy interfaces and very thin layers. In each case, a formalism is set up which enables us to identify systematically all of their effects. Computer modeling of realistic formations verified our calculations. We suggest that the strongly wavelength‐dependent response of such layers and their characteristic response waveforms may provide convenient tools for identifying fine‐scale features in strata.

Testing chiral anomalies with hadronic currents

Chiral anomalies are calculated using an effective-Lagrangian technique introduced for anomalies by Wess and Zumino and recently reformulated by Witten. Anomalous amplitudes for vector currents decaying into three pseudoscalars are tested by comparison with ${K}_{l4}$ decay, $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$, and strong decays of vector mesons. The agreement with experiment for ${K}_{l4}$ is an impressive verification of the anomaly in the vector current. For $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ decay, the results are excellent, and for the strong decays, good. Since the electromagnetic and strong amplitudes have been extrapolated to higher momenta with a final-state-interaction approximation, it is not surprising that the agreement is less good here, where, indeed, further dynamical assumptions are needed. A number of new predictions are made for hadronic decays of ${\ensuremath{\rho}}^{\ensuremath{'}}$, ${\ensuremath{\omega}}^{\ensuremath{'}}$, and ${\ensuremath{\varphi}}^{\ensuremath{'}}$.

On the octupole excitation in236U

Measurements of theK,LI,LII andMI conversion lines of the 687.7 keV transition in236U are evaluated within the electron penetration formalism. The spin-parity assignment of the octupole bandhead is found to be 1− in accordance with reaction data, and an assignment of 2− to the 687.7 keV state is ruled out. The penetration matrix element ∥η∥ has the value of 13.5 for theK-shell and increases slightly for higher main shells. An estimate of the anomalous amplitudes is compared with values reported for transitions in the odd even actinide nuclei. Furthermore electron conversion data for the 1−→2+ and 1−→4+ transitions are given.