bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct writing of photomask by ultrashort laser
Authors: Stanley P. , Venkatakrishnan K. , Lim L. E. N.
Published: February 2003

Photomasks are currently fabricated using the lithographic process, which is complex and time consuming because of several steps involved in the fabrication process. In order to address this a simple technique is proposed in this article which is a single-step process. The required pattern is transferred to mask blank by direct writing with ultrashort laser pulses without the aid of photoresist. A nonmechanical scanning system immune to effects of vibration has been developed in order to scan the laser beam with high positional accuracy and scan speed. It is a cost effective technique when compared with the lithographic process and is capable of fabricating photomasks with submicron features.
Selective deposition of molecules through poly(methylmethacrylate) patterns defined by electron-beam lithography
Authors: Hang Qingling , Wang Yuliang , Lieberman Marya , Bernstein Gary H.
Published: February 2003

Toward the development of a practical molecular computing scheme, certain molecules are thought to be able to perform quantum state switching at room temperature (for example, digital bit 1 to 0). For the implementation of logic functions, these molecules must be arranged on surfaces in a controlled manner. The Creutz–Taube molecule [(NH3)5Ru(pyrazine)Ru(NH3)5](o-toluenesulphonate)5 (CT5) can be viewed as a two-dot molecule for the purposes of molecular computing. We report here nanopatterning of CT5 molecules through the use of electron-beam lithography (EBL) and poly(methylmethacrylate) (PMMA) electron resist. After development of electron-beam modified PMMA films on SiO2, trenches with exposed surfaces were formed. These wafers were then soaked in CT5 aqueous solution. Atomic force microscopy and x-ray photoelectron spectroscopy were used to investigate the surface characteristics of wafers after dissolution of the PMMA and to confirm the binding of a monolayer of CT5 molecules on the wafer within the areas delimited by the PMMA trenches. CT5 molecules were deposited as a monolayer with two Ru atoms lying on the SiO2 surface. 35-nm-wide lines of a monolayer of CT5 molecules on a SiO2 surface were demonstrated.
Completion of the β tool and the recent progress of low energy e-beam proximity projection lithography
Authors: Endo Akihiro , Higuchi Akira , Nozue Hiroshi , Shimazu Nobuo , Fukui Toyoji , Yasumitsu Naoki , Miyatake Tsutomu , Anazawa Norimichi
Published: February 2003

We have proposed low energy electron-beam proximity projection lithography [T. Utsumi, Jpn. J. Appl. Phys., Part 1 38, 7046 (1999); J. Vac. Sci. Technol. B 17, 2897 (1999)] (LEEPL) for LSI production lithographic processes below 100-nm-feature size. One and one half years ago, the proof of concept (POC) of LEEPL was successfully completed using an α tool. Now, a β tool of LEEPL, which is similar to a mass production tool in the 100- and 70-nm-technology node, has been developed. We have already completed the performance evaluations of the β tool and confirmed proof of lithography. We obtained patterning resolution of 45-nm-L/S patterns and 48-nmφ-hole patterns in resist images and overlay accuracy of 23 nm (3σ) in the x direction and 31 nm (3σ) in the y direction over an effective area of 8 in. wafer. Furthermore, functionality of complementary mask alignment was demonstrated and logic type device-like patterns in 100-nm-technology node were fabricated.
Protective layer using plasma polymerized thin films in ac-plasma display panel
Authors: Kim Sung-O
Published: February 2003

Flat panel displays have recently received much attention in research and development as alternatives to the cathode ray tube (CRT). The plasma display panel (PDP) is considered a promising candidate for commercial development. The performance of an ac PDP is influenced strongly by the surface plasma characteristics on the protective layer. The objective of this study was to examine the potential use of a polymerized thin film to replace MgO conventionally use for this protective layer. This thin film was formed using an interelectrode capacitively coupled plasma polymerization apparatus using methyl methacrylate (MMA) to create a polymerized PPMMA plasma polymerized methyl methacrylate (PPMMA). Both the functional groups of PMMA and PPMMA were found in the analysis using Fourier transform infrared. The polymerization rate of plasma polymer increased as a function of the plasma power and decreased as a function of the system pressure using scanning electron microscopy (SEM). The plasma polymerized thin films showed high transparency of over 98% and had a secondary electron emission coefficient that was higher than the MgO thin films 0.02–0.14 over 50–150 V. The characteristics of the PPMMA made it a very attractive candidate protective layer. The next step in its qualification is to study sputtering and operational characteristics in demonstrative panel.
Low-field electron emission of Si microtip arrays produced by laser beam evaporation
Authors: Karabutov A. V. , Frolov V. D. , Simakin A. V. , Shafeev G. A.
Published: February 2003

Results are reported on low-field electron emission (FEE) from periodical arrays of microtips produced by a laser-assisted evaporation of single-crystal Si wafers in a vacuum. The best samples showed the emission at threshold fields of as low as 4–5 V/μm for an n-type Si substrate and of 1–2 V/μm for a p-doped Si substrate as measured with the flat screen technique. The emission was stable upon cyclic variations of the electric field. Microscopic studies using a special scanning tunneling microscopy device show that: (i) the typical radius of the tip apex is about 1 μm, (ii) there are well-conducting as well as poorly conducting regions on the tip surface, (iii) the emission originates from the well-conducting regions, and (iv) as a rule, the emitting sites are submicron in size and are associated with some features of the tip microrelief, such as folds or valleys, but the FEE maxima do not correlate with relief peaks (protrusions). The experimental data allow us to explain the FEE from the tip arrays by a geometric field enhancement on narrow conducting channels in the tip body.
Overview of field-emission information storage devices
Authors: Lam Si-Ty
Published: February 2003

Field-emission information storage devices present a number of promises in an era of mobile computing and applications. Commercialization of this type of device presents many technical challenges. In the device, an array of individually addressable electron field emitters is used for writing and reading information to and from a storage medium. Results and issues with respect to field emitters will be presented.
The Autocatalytic Reduction of Ferriin by Malonic Acid with Regard to the Ferroin-Catalyzed Belousov-Zhabotinsky Reaction
Authors: Mrákavová Marta , Melicherčík Milan , Olexová Anna , Treindl Ľudovít
Published: February 2003

The reduction of ferriin ([Fe(phen)3]3+, phen = 1,10-phenanthroline) by malonic acid (MA) differs from the reduction of Ce(IV) or Mn(III) ions by MA in its autocatalytic character and in a pregnant influence of oxygen, which behaves obviously as a catalyst. The time dependence of the ferroin-ferriin redox potential at the last stage of this reaction has a sigmoidal shape, which indicates autocatalysis. Under anaerobic conditions, the inflection time is of the order of several tens of minutes, since autocatalysis cannot proceed unless a sufficient amount of oxygen is produced via oxidation of water (OH- ions) with Fe(IV) formed by the ferriin dismutation. Under aerobic conditions, the inflection time decreases to a value of a few seconds. The probable reaction mechanism is discussed in detail.
Charge Transfer Between CO22+ and Ar or Ne at Collision Energies 3-10 eV
Authors: Mrázek Libor , Žabka Ján , Dolejšek Zdeněk , Herman Zdeněk
Published: February 2003

The beam scattering method was used to investigate non-dissociative single-electron charge transfer between the molecular dication CO22+ and Ar or Ne at several collision energies between 3-10 eV (centre-of-mass, c.m.). Relative translational energy distributions of the product ions showed that in the reaction with Ar the CO2+ product was mainly formed in reactions of the ground state of the dication, CO22+(X3Σg-), leading to the excited states of the product CO2+(A2Πu) and CO2+(B2Σu+). In the reaction with Ne, the largest probability had the process from the reactant dication excited state CO22+(1Σg+) leading to the product ion ground state CO2+(X2Πg). Less probable were processes between the other excited states of the dication CO22+, (1∆g), (1Σu-), (3∆u), also leading to the product ion ground state CO2+(X2Πg). Using the Landau-Zener model of the reaction window, relative populations of the ground and excited states of the dication CO22+ in the reactant beam were roughly estimated as (X3Σg):(1∆g):(1Σg+):(1Σu-):(3∆u) = 1.0:0.6:0.5:0.25:0.25.
Extending the ancient margin outboard in the Canadian Cordillera: record of Proterozoic crust and Paleocene regional metamorphism in the Nicola horst, southern British Columbia
Authors: Erdmer Philippe , Moore John M , Heaman Larry , Thompson Robert I , Daughtry Ken L , Creaser Robert A
Published: February 2003

The Nicola horst exposes plutonic and amphibolite-grade metamorphic rocks and is surrounded by low-grade arc rocks of the Late Triassic Nicola Group. We present new geological mapping and UPb, Nd, and metamorphic data for the Nicola horst near Bob Lake, ~40 km south of Kamloops, British Columbia. The Bob Lake assemblage includes felsic to intermediate metavolcaniclastic rocks, metaconglomerate, schist, phyllite, and other rock types. From UPb zircon analysis, a felsic metaporphyry clast in metaconglomerate is 1.04 Ga old. The oldest detrital zircons in metaconglomerate and schist are also near 1 Ga. The Bob Lake assemblage was intruded by 230 Ma tonalite, 219 Ma diorite, and 64 Ma leucogranite and includes 161 Ma felsic porphyry and 157 Ma rhyodacite. Amphibolite-grade metamorphism and ductile flattening and stretching affected all rocks except crosscutting Paleocene granite and granodiorite. The high-grade rocks may be exposed as a result of latest Cretaceous  Eocene extensional ductile flow beneath a thin brittle upper crust. A thickness of ~20 km of juvenile crust beneath the proposed Quesnel terrane is inconsistent with the evidence of Proterozoic source rocks at surface. We infer that most of the crustal lithosphere in this part of the Intermontane Belt is continental, which does not preclude possibly thick arc rocks in other parts. The local thinness of the Nicola Group, however, is inconsistent with emplacement as a regional allochthon and thus with their inclusion in a Quesnel "terrane." The Nicola arc succession appears to have been built on the ancient continental margin.
Late Archaean clastic sedimentary rocks (Shamvaian Group) of the Zimbabwe craton: first observations from the Bindura-Shamva greenstone belt
Authors: Hofmann A , Dirks PH GM , Jelsma H A
Published: February 2003

The ~2.65 Ga old Shamvaian Group sedimentary rocks occur as a folded succession in the central part of the BinduraShamva greenstone belt of Zimbabwe. The strata comprise distinct, shear zone-bounded tectonostratigraphic units which may be stratigraphically arranged as follows. The lower part of the succession is represented by a transgressive, fining-upward sequence of alluvial fan conglomerate, overlain by fluvial braid-plain pebbly sandstone and marine shoreface sandstone. Detritus was derived from a mid-Archaean granitoid-gneiss terrain situated to the east. Sediment supply and subsidence rate must have been high. Shallow shelf sedimentation was followed by deep-water (sub-wave base) deposition by turbidity currents, giving rise to a thick succession of fine to coarse clastic material. The turbidite deposits were locally overlain by shallow-marine sandstone and fluvial to alluvial fan conglomerate. An upward increase in the abundance of intermediate and felsic volcanic clasts suggests an increase in the proximity of a volcanic terrain, such as a volcanic arc. Deposition was followed by layer-parallel shearing during thrust belt-style tectonism. Major shear zones developed preferentially along the contact between shallow- and deep-marine facies associations. Basin initiation may have been related to extensional tectonics, possibly on rifted continental crust, whereas later stages of basin history were characterized by compression, suggesting a foreland or fore-arc basin setting. Sedimentary facies, stratigraphy, and facies distribution are remarkably similar to some late Archaean sedimentary sequences of the Superior Province in Canada.
SUPERCONDUCTING COSMIC STRING IN LYRA GEOMETRY
Authors: RAHAMAN FAROOK
Published: February 2003

The gravitational field of a superconducting cosmic string in the context of Lyra geometry is investigated. It has been shown that such a string has only a repulsive gravitational effects on a free moving particle. It is dissimilar to the case of a superconducting cosmic string in general relativity and Brans–Dicke theory, which gives rise to an attractive effect.
RARE $B_S\to \gamma\nu \bar \nu$ DECAY WITH POLARIZED PHOTON AND NEW PHYSICS EFFECTS
Authors: ŞIRVANLI BERIN , TURAN GÜRSEVIL
Published: February 2003

Using the most general, model-independent effective Hamiltonian, the rare [Formula: see text] decay with polarized photon is studied. The sensitivity of the branching ratio and photon polarization to the new Wilson coefficients are investigated. It is shown that these physical observables are sensitive to the vector and tensor type interactions, which would be useful in search of new physics.
ORIENTATION AND DEFORMATION DEPENDENCE OF THE REACTION CROSS-SECTION FOR A DEFORMED TARGET NUCLEUS
Authors: ISMAIL M. , OSMAN M. M. , EL GEBALY H. , ABOU-SHADY H.
Published: February 2003

The optical limit approximation to Glauber theory was used to calculate the reaction cross-section, σR, for a deformed target nucleus. A method is presented to include both density dependence of NN reaction cross-section and higher order deformations of the target nucleus. We studied orientation, energy and deformation dependence of σR for C 12– N 17 and C 12– U 238 interacting pairs. We found that the orientation dependence of σR for the heavy target U 238 depends on the value and sign of hexadecapole deformation and it is more than 2.2 times compared to the light deformed target nucleus N 17. The presence of hexadecapole deformation does not affect the value of σR averaged over all orientation of the target nucleus. A geometrical model was proposed to account for the orientation dependence of σR. We found that the error in this model is less than 10%.
ELECTRIC CHARGE QUANTIZATION AND EXTRA DIMENSIONS
Authors: PÉREZ-LORENZANA A. , DE S. PIRES C. A.
Published: February 2003

In models with flat extra dimensions tiny Dirac neutrino masses can be generated via the coupling of four-dimensional Standard Model fields to a higher dimensional fermion. Here we argue that, in spite of the Dirac nature of the neutrino, quantization of the electric charge can still be understood as a result of anomaly cancellation, charge conservation and naturalness requirements.
Shallow seismic surveying of an Alpine rock glacier
Authors: Musil Martin , Maurer Hansruedi , Green Alan G. , Horstmeyer Heinrich , Nitsche Frank O. , Mühll Daniel Vonder , Springman Sarah
Published: February 2003

To map the internal structure and lower boundary of an alpine rock glacier, we recorded three shallow seismic profiles and drilled four ∼70‐m‐deep holes through to the underlying bedrock. Although analysis of the seismic data using standard reflection processing schemes did not yield conclusive results because of the dominantly low‐frequency returned signals and the presence of strong source‐generated noise, tomographic inversions of first‐arrival times were successful in mapping several critical subsurface features. A thin, low‐velocity layer of loose boulders, air voids, and snow was found to extend across the entire surveyed area. Below this layer, two distinct velocity regimes superimposed on a general increase in velocity with depth were identified. A broad regime of high velocities was interpreted to contain boulders with numerous ice‐filled voids, whereas an adjacent regime of relatively low velocities was explained in terms of boulders with air‐ and water‐filled voids. This latter region of degraded permafrost, which was unexpected, may be an early result of global warming. The transition from rock glacier to gneissic bedrock was delineated approximately by the 4300‐m/s isovelocity line. Although poorly resolved, its depth varied from ∼35 to ∼70 m beneath the surface of the rock glacier. The tomographic inversion results also provided an explanation for the occurrence of strong source‐generated noise in our data.

Using the derived velocity distributions as input, synthetic shot gathers were calculated using a finite‐difference viscoelastic scheme that accounted for surface topography. The resultant synthetic data were dominated by the overwhelming effects of back‐ and side‐scattered waves from shallow heterogeneities and high‐amplitude guided phases that originated from the thin, surficial low‐velocity zone. Had the guided phases not been correctly identified and eliminated during processing, they would have appeared as reflections in the stacked sections. Since low‐velocity layers overlying heterogeneous media are common features of the shallow subsurface, our findings may have implications for a broad range of engineering‐scale seismic investigations (e.g., studies of landfills, rockslides, moraines, talus slopes, alluvial fans).
Biot–Gassmann theory for velocities of gas hydrate‐bearing sediments
Authors: Lee Myung W.
Published: February 2003

Elevated elastic velocities are a distinct physical property of gas hydrate‐bearing sediments. A number of velocity models and equations (e.g., pore‐filling model, cementation model, effective medium theories, weighted equations, and time‐average equations) have been used to describe this effect. In particular, the weighted equation and effective medium theory predict reasonably well the elastic properties of unconsolidated gas hydrate‐bearing sediments. A weakness of the weighted equation is its use of the empirical relationship of the time‐average equation as one element of the equation. One drawback of the effective medium theory is its prediction of unreasonably higher shear‐wave velocity at high porosities, so that the predicted velocity ratio does not agree well with the observed velocity ratio. To overcome these weaknesses, a method is proposed, based on Biot–Gassmann theories and assuming the formation velocity ratio (shear to compressional velocity) of an unconsolidated sediment is related to the velocity ratio of the matrix material of the formation and its porosity. Using the Biot coefficient calculated from either the weighted equation or from the effective medium theory, the proposed method accurately predicts the elastic properties of unconsolidated sediments with or without gas hydrate concentration. This method was applied to the observed velocities at the Mallik 2L‐39 well, Mackenzie Delta, Canada.
Joint inversion of EM and magnetic data for near‐surface studies
Authors: Benech Christophe , Tabbagh Alain , Desvignes Guy
Published: February 2003

Magnetic and electromagnetic measurements are influenced by magnetic susceptibility and, thus, are widely used in geophysical surveys for archeology or pedology. To date, the data inversion is performed separately. A filtering process incorporating both types of data is presented here. After testing the algorithm with synthetic data, the algorithm is used in several case studies in archeological prospecting. This approach presents two advantages: establishing the presence of remanent magnetizations (viscous or thermoremanent), and achieving more refined depth analysis of the anomaly.
Time‐lapse inversion of crosswell radar data
Authors: Day‐Lewis Frederick D. , Harris Jerry M. , Gorelick Steven M.
Published: February 2003

The combination of differential radar tomography with conventional tracer and/or hydraulic tests facilitates high‐resolution characterization of subsurface heterogeneity and enables the identification of preferential flow paths. In dynamic imaging, each tomogram is typically inverted independently, under the assumption that data sets are collected quickly relative to changes in the imaged property (e.g., attenuation or velocity); however, such “snapshot” tomograms may contain large errors if the imaged property changes significantly during data collection. Acquisition of less data over a shorter time interval could ameliorate the problem, but the resulting decrease in ray density and angular coverage could degrade model resolution. To address these problems, we propose a new sequential approach for time‐lapse tomographic inversion. The method uses space‐time parameterization and regularization to combine data collected at multiple times and to account for temporal variation. The inverse algorithm minimizes the sum of weighted squared residuals and a measure of solution complexity based on an a priori space‐time covariance function and a spatiotemporally variable mean. We demonstrate our approach using a synthetic 2‐D time‐lapse (x,z,t) data set based loosely on a field experiment in which difference‐attenuation radar tomography was used to monitor the migration of a saline tracer in fractured rock. We quantitatively show the benefits of space‐time inversion by comparing results for snapshot and time‐lapse inversion schemes. Inversion over both space and time results in superior estimation error, model resolution, and data reproduction compared to conventional snapshot inversion. Finally, we suggest strategies to improve time‐lapse cross‐hole inversions using ray‐based inversion constraints and a modified survey design in which different sets of rays are collected in alternating time steps.
The electromagnetic smoke ring in a transversely isotropic medium
Authors: Wang Tsili
Published: February 2003

The electromagnetic smoke ring describes the spatial distribution characteristics of a diffusive electromagnetic field induced in a conductive medium. It provides an intuitive basis for qualitative interpretation of electromagnetic data in both the time and frequency domains. In this paper, I examine the smoke ring behavior in a transversely isotropic (TI) medium. Both a uniform and a two‐layer TI media are studied. It is observed that for a vertical‐coil (horizontal dipole) source in a uniform TI medium the smoke ring becomes elliptic‐like, with the long axis parallel to the bedding plane, as opposed to the circular shape for a uniform isotropic medium. The short axis length depends on both the horizontal and vertical resistivities of the medium. The long axis length, however, is merely a function of the vertical resistivity of the medium. When the anisotropy ratio is relatively high (e.g., 5) the smoke ring may become poorly defined, making the smoke‐ring concept more useful for relatively low anisotropy ratios. In a layered TI medium, the smoke ring characteristics for a horizontal‐loop source is the same as that for a layered isotropic medium if the horizontal resistivities of the TI layers are the same as the resistivities of the isotropic layers. For a vertical‐loop source in the two‐layer TI medium, however, the smoke ring may be poorly defined when the layers have different vertical resistivities. It is shown that the smoke ring has a clear connection to the magnetic field response of the medium. The zero crossover of the coplanar magnetic field follows the smoke ring locus to expand as frequency decreases, thus providing the basis for the use of smoke ring theory to aid in interpretation of induction measurements in TI media.
Borehole electrical resistivity modeling using neural networks
Authors: Zhang Lin , Poulton Mary M. , Wang Tsili
Published: February 2003

A neural network approach has been applied to model downhole resistivity tools, i.e., to generate a synthetic tool response for a given earth resistivity model. The microlaterolog (MLL), shallow dual laterolog (DLLs), and deep dual laterolog (DLLd) tools are modeled using neural networks to demonstrate this approach. Efforts have been made to select various neural network parameters, including the type of neural network, the length of input data for training, the number of hidden nodes, and the number of training samples.

A modular neural network (MNN) has been selected because it can facilitate the training and prediction of tool responses in formations with large resistivity variations. The input data for training are taken to be the model formation resistivity values sampled over a depth window. The window length is chosen based on the tool lengths. Three different window lengths are used for experiments: 6.1, 9.1, and 30.5 m. We found the longer window lengths generally have higher modeling accuracy for the three different types of logging tools. The number of hidden nodes needed to yield satisfactory training and prediction data varies from 8 to 25, depending on the type of tool and the window length.

Up to 30 000 training samples have been collected to train the MNN. Our modeling examples show that the trained MNN can achieve about 90% accuracy for the MLL log response and about 83% accuracy for the DLLs and DLLd responses. The modeling errors can be described roughly with a Gaussian distribution.
Seismic‐while‐drilling by using tunnel boring machine noise
Authors: Petronio Lorenzo , Poletto Flavio
Published: February 2003

The tunnel boring machine (TBM) is used extensively to mechanically excavate tunnels. To optimize the mechanical drilling and work safely, an estimate of the geology to be drilled is necessary. We consider using the elastic waves produced by the TBM cutting wheel to obtain seismic‐while‐drilling (SWD) information for predicting the geology ahead of the drilling front. This method uses accelerometers mounted on the TBM together with geophones located along and outside the tunnel, similar to the technique successfully used to drill oil and geothermal wells. Study of noise and the resolution of the signal produced by the large‐diameter cutting head shows that nonstationary noise separation can be achieved by locating sensors at the front and rear ends of the tunnel. The (higher) resolution in front of the TBM is limited by pilot delays, while the (lower) lateral resolution is limited by the radial dimension of the TBM. Analysis of seismic data acquired in a field test shows that P‐ and S‐wave arrivals have a wide frequency band and high amplitude in seismic traces measured 700 m away from the drilling front. In comparison with SWD applications in wells, tunnel SWD technology has the advantage of allowing direct access to the tunnel front, which makes it easy to connect the TBM reference sensors for while‐drilling monitoring. This method can be successfully applied without interfering with drilling activity to monitor tunnel excavation continuously, reduce risks, and optimize drilling.
Smooth fitting of geophysical data using continuous global surfaces
Authors: Billings Stephen D. , Newsam Garry N. , Beatson Rick K.
Published: February 2003

Continuous global surfaces (CGS) are a general framework for interpolation and smoothing of geophysical data. The first of two smoothing techniques we consider in this paper is generalized cross validation (GCV), which is a bootstrap measure of the predictive error of a surface that requires no prior knowledge of noise levels. The second smoothing technique is to define the CGS surface with fewer centers than data points, and compute the fit by least squares (LSQR); the noise levels are implicitly estimated by the number and placement of the centers relative to the data points. We show that both smoothing methods can be implemented using extensions to the existing fast framework for interpolation, so that it is now possible to construct realistic smooth fits to the very large data sets typically collected in geophysics.

Thin‐plate spline and kriging surfaces with GCV smoothing appear to produce realistic fits to noisy radiometric data. The resulting surfaces are similar, yet the thin‐plate spline required less parameterization. Given the simplicity and parsimony of GCV, this makes a combination of the two methods a reasonable default choice for the smoothing problem. LSQR smooth fitting with sinc functions defined on a regular grid of centers, effectively low‐pass filters the data and produces a reasonable surface, although one not as visually appealing as for splines and kriging.
Stochastic fluid modulus inversion
Authors: White Luther , Castagna John
Published: February 2003

A probabilistic inversion approach is used with Gassmann's equation to determine pore fluid modulus using elastic wave velocity without reference information from a rock saturated with a second fluid of known modulus. Numerical examples show that even when uncertainties in input parameters are relatively large, useful estimates of fluid modulus can be obtained. For a well‐log data example, water saturation derived from the inverted fluid modulus compares favorably to saturations derived from well log analysis.
Using high‐order cumulants to extrapolate spatially variant seismic wavelets
Authors: Liang Guanghe , Cai Xinping , Li Qianyu
Published: February 2003

Extraction of seismic wavelets is important for impedance inversion and forward modeling. We propose a method for estimating spatial variant seismic wavelets. The method uses third‐ and fourth‐order cumulants of seismic data. It combines third‐ and fourth‐order moments of seismic wavelets with those obtained by a deterministic method at well locations. We design a multidimensional filter at a well by matching the high‐order cumulants of seismic data to the high‐order moments of seismic wavelets. Applying the filter to the high‐order culumants of other seismic traces away from the well yields the corresponding wavelets. The new method for seismic wavelet extraction is thus constrained by well‐log data. Synthetic tests show that this method can produce accurate spatially varying wavelets. A real data test of the method is also successful.
Simultaneous inversion of prestack seismic data for rock properties using simulated annealing
Authors: Ma Xin‐Quan
Published: February 2003

A new prestack inversion algorithm has been developed to simultaneously estimate acoustic and shear impedances from P‐wave reflection seismic data. The algorithm uses a global optimization procedure in the form of simulated annealing. The goal of optimization is to find a global minimum of the objective function, which includes the misfit between synthetic and observed prestack seismic data. During the iterative inversion process, the acoustic and shear impedance models are randomly perturbed, and the synthetic seismic data are calculated and compared with the observed seismic data. To increase stability, constraints have been built into the inversion algorithm, using the low‐frequency impedance and background Vs/Vpmodels. The inversion method has been successfully applied to synthetic and field data examples to produce acoustic and shear impedances comparable to log data of similar bandwidth. The estimated acoustic and shear impedances can be combined to derive other elastic parameters, which may be used for identifying of lithology and fluid content of reservoirs.
Multicomponent prestack depth migration by scalar wavefield extrapolation
Authors: Hou Anning , Marfurt Kurt J.
Published: February 2003

We present a new multicomponent prestack depth migration methodology based on successive application of conventional scalar wave equation migration. We do not separate the data into PP‐ and PS‐waves; rather, we migrate each x‐, y‐, and z‐component of the data using both P and S propagation velocities, followed by polarization filtering in the depth domain. By generating intermediate images in the depth domain, we can account for polarity reversals of the PS reflection for all dips. Since the polarization angles are calculated from the data, it is straightforward to accommodate anisotropic effects (quasi‐P and quasi‐S) into multicomponent migration.

The multicomponent migration results in our synthetic examples demonstrate that even for a single shot gather, we can obtain clean PP‐ and PS‐wave images over complex structures and resolve the problem of PS‐wave polarity reversals.
Processing‐induced anisotropy
Authors: Grechka Vladimir , Tsvankin Ilya
Published: February 2003

Processing of seismic data is often performed under the assumption that the velocity distribution in the subsurface can be approximated by a macromodel composed of isotropic homogeneous layers or blocks. Despite being physically unrealistic, such models are believed to be sufficient for describing the kinematics of reflection arrivals.

In this paper, we examine the distortions in normal‐moveout (NMO) velocities caused by the intralayer vertical heterogeneity unaccounted for in velocity analysis. To match P‐wave moveout measurements from a horizontal or a dipping reflector overlaid by a vertically heterogeneous isotropic medium, the effective homogeneous overburden has to be anisotropic. This apparent anisotropy is caused not only by velocity monotonically increasing with depth, but also by random velocity variations similar to those routinely observed in well logs.

Assuming that the effective homogeneous medium is transversely isotropic with a vertical symmetry axis (VTI), we express the VTI parameters through the actual depth‐dependent isotropic velocity function. If the reflector is horizontal, combining the NMO and vertical velocities always results in nonnegative values of Thomsen's coefficient δ. For a dipping reflector, the inversion of the P‐wave NMO ellipse yields a nonnegative Alkhalifah‐Tsvankin coefficient η that increases with dip. The values of η obtained by two other methods (2‐D dip‐moveout inversion and nonhyperbolic moveout analysis) are also nonnegative but generally differ from that needed to fit the NMO ellipse. For truly anisotropic (VTI) media, the influence of vertical heterogeneity above the reflector can lead to a bias toward positive δ and η estimates in velocity analysis.
PP + PS = SS
Authors: Grechka Vladimir , Tsvankin Ilya
Published: February 2003

Converted (PS) waves can provide important information about shear‐wave velocity and, in the presence of anisotropy, about the medium parameters responsible for both P‐ and S‐wave propagation. Kinematics and amplitudes of reflected PS‐waves, however, possess such undesirable features as moveout asymmetry, reflection point dispersal, and polarity reversal, which preclude application of conventional velocity‐analysis methods to mode conversions.

Rather than using PS‐wave kinematics directly, here we propose a method for reconstructing SS‐wave reflection traveltimes from PP and PS data. The required preprocessing steps include picking of PP and PS traveltimes on prestack data and identification (correlation) of the PP and PS events from the same interfaces. The key idea of the method is to match the reflection slopes (horizontal slownesses) on common‐receiver PP and PS gathers. This procedure allows us to find the coordinates of receivers that record PP‐ and PS‐waves reflected at exactly the same (albeit unknown) subsurface points and to determine the shear‐wave reflection traveltime tSSas a simple combination of the PP and PS traveltimes. The reconstructed SS‐wave moveout can then be processed by velocity‐analysis methods designed for pure reflection modes. The developed technique, however, cannot be used to compute the true amplitudes of the reflected SS‐waves.

Our method has the following attractive features:

1) No information about the velocity field or anisotropic parameters is required to obtain SS‐wave traveltimes from PP and PS data. If the input PP and PS arrivals are picked correctly and correspond to the same reflector, the method produces exact traveltimes tSS.

2) The estimates of traveltimes and reflection slopes are local, which makes reflection‐point dispersal irrelevant.

3) Another consequence of the local nature of this procedure is that the portion of PS data in the vicinity of the polarity reversal (where the PS amplitudes are small) can be muted out without compromising the quality of tSSestimates for source–receiver pairs with high PS amplitudes.
Perturbation analysis of an explicit wavefield separation scheme for P‐ and S‐waves
Authors: Muijs Remco , Holliger Klaus , Robertsson Johan O. A.
Published: February 2003

Dense spatial recording patterns of three‐component (3C) receivers allow for direct wavefield decomposition through explicit calculation of divergence and curl of the recorded elastic wavefield. Since this approach is based upon the observation of small phase shifts, it requires highly accurate deployment of the receiver configurations. To study the feasibility of a recently proposed P/S‐wave separation scheme, we systematically assess the effects of position and orientation errors of one or several geophones within the recording pattern on technique performance.

We find that realistic deployment errors can significantly affect estimates of the divergence and curl of particle velocity. The errors induced by mispositioned or misoriented geophones differ for each of the geophones that make up a pattern. Moreover, the inaccuracies vary with the angle of incidence, potentially affecting analysis procedures applied to the data at a later stage, such as amplitude variation with offset (AVO). Based on a relative L1‐criterion, the position of each receiver needs to be accurate within 10% of the length of the sides of the configuration to obtain meaningful divergence and curl estimates. Furthermore, the output is particularly sensitive to misorientations of geophones, requiring that the orientations of all geophones be accurate within 2°. These observations point to significant difficulties when applying this technique.

To alleviate this problem, we present an approach to detect and compensate for such deployment‐related inaccuracies prior to explicit P/S‐wave separation. This strategy is based on a pyramid‐shaped receiver configuration and relies on minimizing the differences between the divergence and curl estimates calculated over the pyramid and each of the four subtetrahedra that comprise the pyramid.
Toward optimal spatial filters for demultiple and wavefield splitting of ocean‐bottom seismic data
Authors: Osen Are , Amundsen Lasse , Reitan Arne
Published: February 2003

Suppressing the receiver‐side sea‐surface ghost with its accompanying water‐layer reverberations in multicomponent sea‐floor data can be performed in both the frequency–wavenumber and the frequency–space domains. Similarly, separation of ocean‐bottom seismic (OBS) data into upgoing P‐ and S‐mode responses can be formulated in both domains. The frequency–space domain algorithms can be attractive when the sea‐floor medium has lateral velocity variations or the data are irregularly sampled along the sea floor, which requires that the data be processed with local, compact decomposition filters having optimal angular (wavenumber) response.

By deriving the frequency–space domain formulas, we find an exact representation for the demultipled pressure response. This formula involves filter convolutions over the data, with filters having a long spatial impulse response. The filtering can be approximated in the wavenumber domain by, for example, power series, Chebyshev polynonomial fitting, Pade approximants, or continued fraction expansions. The filters must then be Fourier transformed back to the frequency–space domain, where the resulting filter is convolved with the data. The implies that the demultipled OBS data must be computed by numerical solution of a differential equation.

Alternatively, the spatial filtering can be formulated as a filter design problem, where the filtering is performed by an optimal filter. This latter formulation can to some extent handle local variations in the medium properties along the sea floor, and it does not require solving a differential equation for the multiple suppressed pressure.
Estimating shallow shear velocities with marine multicomponent seismic data
Authors: Ritzwoller Michael H. , Levshin Anatoli L.
Published: February 2003

Accurate models of shear velocities in the shallow subsurface (<300 m depth beneath the sea floor) would help to focus images of structural discontinuities constructed, for example, with P to S converted phases in marine environments. Although multicomponent marine seismic data hold a wealth of information about shear velocities from the sea floor to depths of hundreds of meters, this information remains largely unexploited in oil and gas exploration. We present a method, called the multiwave inversion (MWI) method, designed to use a wide variety of information in marine seismic data. As presented here, MWI jointly uses the observed traveltimes of P and S refracted waves, the group and phase velocities of fundamental mode and first overtone interface waves, and the group velocities of guided waves to infer shear velocities and Vp/Vsratios. We show how to obtain measurements of the traveltimes of these diverse and, in some cases, dispersive waves and how they are used in the MWI method to estimate shallow shear velocities. We illuminate the method with synthetic and real multicomponent marine data and apply MWI to some real data to obtain a model of Vswith uncertainty estimates to a depth of 225 m and Vp/Vsto about 100‐m depth. We conclude by discussing the design of offshore surveys necessary to provide information about shallow shear‐velocity structures, with particular emphasis on the height of the acoustic source above the sea floor.
Rough‐sea deghosting using a single streamer and a pressure gradient approximation
Authors: Robertsson Johan O. A. , Kragh Ed
Published: February 2003

We present a method for receiver ghost correction of towed streamer data that accounts for the rough sea surface. The method explicitly uses the fact that the pressure is zero at the free (sea) surface to estimate the vertical pressure gradient. Continuous elevation measurements of the wave height directly above the hydrophones are required—a measurement which is currently unavailable. The new deghosting method is fundamentally limited to frequencies below the first ghost notch. The lowest‐order implementation requires that the streamer is towed no deeper than approximately 6 m and a receiver spatial sampling interval of about 3 m or less.

Using the lowest‐order and simplest implementation of the new method, the rough‐sea error is reduced from 1.5–2.5 dB to about 1–1.5 dB in amplitude and from 20° to 10° in phase, at 50 Hz in a 4‐m significant wave height sea. Higher‐order terms in the approximation promise to further reduce the error.
Structural characterization of oligomers from the polycondensation of citric acid with ethylene glycol and long‐chain aliphatic alcohols
Authors: Barroso‐Bujans Fabienne , Martínez Ricardo , Ortiz Pedro
Published: February 2003

The structural characterization of polyesters of citric acid (CA) with ethylene glycol and long‐chain aliphatic alcohols (ROH), prepared by the composition of the reaction mixture being adjusted slightly away from stoichiometric equivalence, was performed with 1H‐ and 13C‐NMR spectroscopy. The aliphatic alcohols employed were 1‐decanol, 1‐dodecanol, and 1‐octadecanol. The 13C‐NMR carbonyl region presented four groups of signals, two corresponding to the ester groups and two corresponding to the acid groups. However, symmetric and asymmetric groups of CA moieties were identified in the 13C‐NMR spectra. The ester yield from ROH decreased as the number of carbon atoms in the alcohols increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 302–306, 2003
Low addition of melamine salts for improved melamine‐urea‐formaldehyde adhesive water resistance
Authors: Zanetti M. , Pizzi A.
Published: February 2003

The addition of melamine acetate salts to an adhesive glue mix can allow the use of melamine–urea–formaldehyde (MUF) resins of lower melamine contents (rather than just urea–formaldehyde resins) and lower total amounts of melamine. Performances can be obtained that are characteristic of the top‐of‐the‐line, generally higher melamine content MUF adhesive resins for the preparation of wood particleboard panels. Improvements in the panel internal‐bond strength of greater than 30% can be obtained by the addition of melamine acetate salts to top‐of‐the‐line MUF resins. The approach to the concept of increased melamine solubility with a melamine salt is compatible with the approach of increasing melamine solubility with solvents such as acetals (e.g., methylal). However, the synergy advantage of using the two approaches jointly is not very marked. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 287–292, 2003
Kinetic study on the reaction of 2,4‐ and 2,6‐tolylene diisocyanate with 1‐butanol in the presence of styrene, as a model reaction for the process that yields interpenetrating polyurethane–polyester networks
Authors: Król Piotr , Wojturska Joanna
Published: February 2003

A classical method was utilized for determination of free isocyanates to study the kinetics of a model reaction of 2,4‐ and 2,6‐tolylene diisocyanate (TDI) with 1‐butanol, which was run in the reaction medium of liquid aliphatic hydrocarbons. Such conditions made it possible to find rate constants and activation energy values for the second‐order reactions under isothermal conditions. Those reactions can be employed to produce isocyanate prepolymers, which make intermediates for downstream polyurethanes. The findings are commented upon against the background of earlier kinetic data that can widely be found in the research reports published. Further, part of our work utilized the findings to provide interpretation of kinetic parameters for analogous reactions, the kinetic data being found in the presence of styrene—the monomer employed when producing polyurethane–polyester interpenetrating polymer network (IPN) systems. The hypothesis was put forward that styrene and isocyanate component(s) could react at the final stages of the process when the system becomes short in the hydroxyl substrate. That hypothesis was based on disturbances observed in the reactivity of NCO groups (in 2,4‐TDI) in the reaction system studied. The rate constants and activation energy values were determined and presented for the urethanization reaction of 1‐butanol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 327–336, 2003
Studies on polyamide‐6/polyolefin blend system compatibilized with epoxidized natural rubber
Authors: Xie Bang‐hu , Yang Ming‐bo , Li Si‐dong , Li Zhong‐ming , Feng Jian‐min
Published: February 2003

Infrared spectra of polyamide‐6 (PA6) with and without epoxidized natural rubber (ENR) are presented. The influence of ENR used as a compatibilizer on the morphologies, crystallizability, mechanical properties, and thermal behavior of the polyamide‐6/polyolefins (PO) blends are studied. The infrared spectra suggest that under normal processing conditions, the carboxyl end groups of PA6 could chemically react in situ with the epoxy groups of ENR, and ester groups are created. This means that the PA6‐ENR grafting copolymer could be obtained during processing. All the morphological characterizations and thermal analyses show that the compatibility of PA6/PO blends is obviously improved by ENR because the copolymer increases the interaction between PA6 and PO. It is also found that the toughness of PA6/PO blends increase significantly after using ENR, while the tensile strength and the softening temperature of PA6/PO blends have almost no change. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 398–403, 2003