bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of reservoir properties from seismic data by smooth neural networks
Authors: Saggaf M. M. , Toksöz M. Nafi , Mustafa H. M.
Published: November 2003

The performance of traditional back‐propagation networks for reservoir characterization in production settings has been inconsistent due to their nonmonotonous generalization, which necessitates extensive tweaking of their parameters in order to achieve satisfactory results and avoid overfitting the data. This makes the accuracy of these networks sensitive to the selection of the network parameters. We present an approach to estimate the reservoir rock properties from seismic data through the use of regularized back propagation networks that have inherent smoothness characteristics. This approach alleviates the nonmonotonous generalization problem associated with traditional networks and helps to avoid overfitting the data. We apply the approach to a 3D seismic survey in the Shedgum area of Ghawar field, Saudi Arabia, to estimate the reservoir porosity distribution of the Arab‐D zone, and we contrast the accuracy of our approach with that of traditional back‐propagation networks through cross‐validation tests. The results of these tests indicate that the accuracy of our approach remains consistent as the network parameters are varied, whereas that of the traditional network deteriorates as soon as deviations from the optimal parameters occur. The approach we present thus leads to more robust estimates of the reservoir properties and requires little or no tweaking of the network parameters to achieve optimal results.
Source‐independent full‐waveform inversion of seismic data
Authors: Lee Ki Ha , Kim Hee Joon
Published: November 2003

A rigorous full‐waveform inversion of seismic data has been a challenging subject, partly because of the lack of precise knowledge of the source. Since currently available approaches involve some form of approximations to the source, inversion results are subject to the quality and choice of the source information used. We propose a new full‐waveform inversion methodology that does not involve source spectrum information. Thus, potential inversion errors from source estimation can be eliminated. A gather of seismic traces is first Fourier transformed into the frequency domain, and a normalized wavefield is obtained for each trace in the frequency domain. Normalization is done with respect to the frequency response of a reference trace selected from the gather, so the complex‐valued normalized wavefield is dimensionless. The source spectrum is eliminated during the normalization procedure. With its source spectrum eliminated, the normalized wavefield lets us construct an inversion algorithm without the source information. The inversion algorithm minimizes misfits between a measured normalized wavefield and a numerically computed normalized wavefield. The proposed approach has been demonstrated successfully using a simple 2D scalar problem.
Analysis of image gathers in factorized VTI media
Authors: Sarkar Debashish , Tsvankin Ilya
Published: November 2003

Because events in image gathers generated after prestack depth migration are sensitive to the velocity field, they are often used in migration velocity analysis for isotropic media. Here, we present an analytic and numerical study of P‐wave image gathers in transversely isotropic media with a vertical symmetry axis (VTI) and establish the conditions for flattening such events and positioning them at the true reflector depth. Application of the weak‐anisotropy approximation leads to concise expressions for reflections in image gathers from homogeneous and factorized v(z) media in terms of the VTI parameters and the vertical velocity gradient kz. Flattening events in image gathers for any reflector dip requires accurate values of the zero‐dip NMO velocity at the surface [Vnmo (z = 0)], the gradient kz, and the anellipticity coefficient η. For a fixed error in Vnmo and kz, the magnitude of residual moveout of events in image gathers decreases with dip, while the moveout caused by an error in η initially increases for moderate dips but then decreases as dips approach 90°. Flat events in image gathers in VTI media, however, do not guarantee the correct depth scale of the model because reflector depth depends on the vertical migration velocity.

For factorized v(x, z) media with a linear velocity variation in both the x‐ and z‐directions, the moveout on image gathers is controlled by Vnmo (x = z = 0), kz, η, and a combination of the horizontal velocity gradient kx and the Thomsen parameter δ (specifically, kx[Formula: see text]). If too large a value of any of these four quantities is used in migration, reflections in the image gathers curve downward (i.e., they are undercorrected; the inferred depth increases with offset), while a negative error results in overcorrection. Lateral heterogeneity tends to increase the sensitivity of moveout of events in image gathers to the parameter η, and errors in η may lead to measurable residual moveout of horizontal events in v(x, z) media even for offset‐to‐depth ratios close to unity.

These results provide a basis for extending to VTI media conventional velocity analysis methods operating with image gathers. Although P‐wave traveltimes alone cannot be used to separate anisotropy from lateral heterogeneity (i.e., kx is coupled to δ), moveout of events in image gathers does constrain the vertical gradient kz. Hence, it may be possible to build VTI velocity models in depth by supplementing reflection data with minimal a priori information, such as the vertical velocity at the top of the factorized VTI layer.
Computation of differential seismograms and iteration adaptive regularization in prestack waveform inversion
Authors: Sen Mrinal K. , Roy Indrajit G.
Published: November 2003

Seismic waveform inversion is a highly challenging task. Nonlinearity, nonuniqueness, and robustness issues tend to make the problem computationally intractable. We have developed a simple regularized Gauss‐Newton–type algorithm for the inversion of seismic data that addresses several of these issues. The salient features of our algorithm include an efficient approach to sensitivity computation, a strategy for band‐limiting the Jacobian matrix, and a novel approach to computing regularization weight that is iteration adaptive. In this paper, we first review various forward modeling and differential seismogram computation algorithms and then evaluate different strategies for choosing the regularization weight. Under the assumption of locally 1D earth models, we design an efficient algorithm by rearranging recursion formula in the reflection matrix approach to compute plane wave seismograms and the Fréchet derivative matrix as a by‐product of forward modeling. We then demonstrate that in a gradient‐descent–type optimization scheme, regularization is critical for obtaining stable and geologically realistic solutions. Although, in most applications, the regularization weight (relative importance between data and model misfit) is chosen in an ad‐hoc manner; the robustness in model estimation and computational stability improve significantly by allowing adaptivity in the choice of the regularization weight in each iterative step. We evaluate performances of several methods, namely, an L‐curve approach, generalized cross‐validation technique, and methods based on a discrepancy principle with application to field ocean‐bottom‐cable data, and we propose a new hybrid approach in computing iteration adaptive regularization weight for prestack inversion.
Weak‐contrast reflection–transmission coefficients in a generally anisotropic background
Authors: Klimeš Luděk
Published: November 2003

Explicit equations for approximate linearized reflection–transmission coefficients at a generally oriented weak‐contrast interface separating two generally and independently anisotropic media are presented. The equations are derived also for all singular directions and are thus valid in degenerate cases (e.g., in an isotropic background). The equations are expressed in general Cartesian coordinates, with arbitrary orientation of the interface. The explicit equations for linearized reflection–transmission coefficients have a very simple form—much simpler than the equations published previously. The equations for all reflection–transmission coefficients, with the exception of the unconverted transmitted wave, have a common form. The form of the equations is very suitable for inversion and for analyzing the sensitivity of seismic data to discontinuities in individual elastic moduli. The factors of proportionality of the contrasts of elastic moduli and density are expressed in terms of the slowness and polarization vectors of the corresponding generated wave and incidentwave.
Near‐surface seismic properties for elastic wavefield decomposition: Estimates based on multicomponent land and seabed recordings
Authors: Muijs Remco , Robertsson O. A. Johan , Curtis Andrew , Holliger Klaus
Published: November 2003

Accurate knowledge of the seismic material properties in the immediate vicinity of the receivers represents a prerequisite for elastic wavefield decomposition. We present strategies for estimating the elastic material properties for both land and seabed multicomponent seismic data. The proposed scheme for land data requires dense multicomponent geophone configurations, which allow spatial wavefield derivatives to be explicitly calculated. The required information can be obtained with four three‐component surface geophones positioned at the corners of a square, and a fifth geophone buried at a shallow depth below the center of the square. The technique yields local estimates of the near‐surface P‐ and S‐wave velocities, but the density cannot be constrained. Using a similar approach for four‐component (three orthogonal components of particle velocity plus pressure) seabed recordings allows the P‐ and S‐wave velocities as well as the density of the seafloor to be estimated. In this case, the proposed scheme does not require buried geophones, and it is applicable to multicomponent data recorded in routine seabed surveys. Compared to existing techniques, the new method allows the elastic sea‐floor properties to be more accurately determined, and it does not rely critically on the inclusion of large‐offset data. Numerical tests indicate that the proposed schemes are robust and yield accurate results, provided that the signal used for the inversion contains sufficient horizontal energy and can be clearly identified and separated from other signals. Although the schemes are designed for application on the first arrivals, they are, in principle, applicable to any data window containing isolated P‐ or S‐arrivals. The proposed scheme is successfully applied to a seabed data set acquired in the North Sea. In contrast, the application on a multicomponent land data set was unsuccessful, because of strong receiver‐to‐receiver variations in amplitude and phase, probably caused by differences in coupling and instrument response.
Geometrical spreading in a layered transversely isotropic medium with vertical symmetry axis
Authors: Ursin Bjørn , Hokstad Ketil
Published: November 2003

Compensation for geometrical spreading is important in prestack Kirchhoff migration and in amplitude versus offset/amplitude versus angle (AVO/AVA) analysis of seismic data. We present equations for the relative geometrical spreading of reflected and transmitted P‐ and S‐wave in horizontally layered transversely isotropic media with vertical symmetry axis (VTI). We show that relatively simple expressions are obtained when the geometrical spreading is expressed in terms of group velocities. In weakly anisotropic media, we obtain simple expressions also in terms of phase velocities. Also, we derive analytical equations for geometrical spreading based on the nonhyperbolic traveltime formula of Tsvankin and Thomsen, such that the geometrical spreading can be expressed in terms of the parameters used in time processing of seismic data.

Comparison with numerical ray tracing demonstrates that the weak anisotropy approximation to geometrical spreading is accurate for P‐waves. It is less accurate for SV‐waves, but has qualitatively the correct form. For P waves, the nonhyperbolic equation for geometrical spreading compares favorably with ray‐tracing results for offset‐depth ratios less than five. For SV‐waves, the analytical approximation is accurate only at small offsets, and breaks down at offset‐depth ratios less than unity. The numerical results are in agreement with the range of validity for the nonhyperbolic traveltime equations.
A general reconstruction scheme for dominant azimuth 3D seismic data
Authors: Schonewille M. A. , Romijn R. , Duijndam A. J. W. , Ongkiehong L.
Published: November 2003

Seismic data are usually irregularly and sparsely sampled along the spatial coordinates, which yields suboptimal imaging results. For time‐lapse data, differences in the spatial sampling of base and monitor surveys lead to undesired differences between the images of the surveys that are not due to differences in the subsurface.

In this paper, an efficient two‐step reconstruction method is proposed for irregularly and sparsely sampled 3D seismic data recorded with a dominant azimuth for large offsets. The first step is reconstruction along the receiver lines such that the midpoints are exactly on crosslines. The second step is a 2D reconstruction in the crossline midpoint‐offset domain using a least‐squares estimation of Fourier components.

Sparse sampling can be handled by optimizing the parameterization of the least‐squares estimation of the Fourier coefficients, and consequently it is possible to reconstruct data that would be aliased when considering single common‐midpoint gathers.

The method can be used to do a geometry transformation of the data to any desired spatial grid. Since the method yields consistent results independent of the actual sampling, it is very well suited for 4D processing.
Photoperiodic effects on body mass, energy balance and hypothalamic gene expression in the bank vole
Authors: Peacock W. L. , Król E. , Moar K. M. , McLaren J. S. , Mercer J. G. , Speakman J. R.
Published: November 2003

We examined the effect of increasing photoperiod, at a constant low temperature, on the body mass and energy budget of the bank vole Clethrionomys glareolus. Simultaneously, we determined the hypothalamic gene expression of neuropeptides and receptors known to be involved in short-term energy balance. Despite an increase in body mass(approximately 10% of initial mass), we found no significant changes in any energetic parameters (food intake, energy assimilation rate, resting metabolic rate and total daily energy expenditure by doubly-labelled water). Apparent energy assimilation efficiency was higher in voles exposed to long-days (LD)compared to short-days (SD). Surprisingly, gene expression of corticotrophin releasing factor (CRF; in the paraventricular nucleus), and the melanocortin-3 receptor (in the arcuate nucleus), both known to be involved in appetite suppression and elevation of energy expenditure in short-term energy balance,were higher in voles kept in LD compared to SD. CRF expression was also elevated in females compared to males. These paradoxical data suggest an alternative mechanism for the control of seasonal body mass changes compared to short-term body mass changes, and between male and female voles. Furthermore, they highlight the need for studies to perform simultaneous measurements at both the molecular and whole animal levels.
The low-affinity glucocorticoid receptor regulates feeding and lipid breakdown in the migratory Gambel's white-crowned sparrowZonotrichia leucophrys gambelii
Authors: Landys Mėta M. , Ramenofsky Marilyn , Guglielmo Christopher G. , Wingfield John C.
Published: November 2003

Plasma corticosterone increases during spring migration in a variety of bird species, including the Gambel's white-crowned sparrow Zonotrichia leucophrys gambelii. Corticosterone is elevated specifically in association with migratory flight, suggesting that corticosterone may promote processes such as energy mobilization and/or migratory activity. General effects of glucocorticoids support such a prediction. Because glucocorticoids exert permissive effects on food intake, corticosterone may also participate in the regulation of migratory hyperphagia. To examine the role of corticosterone during migration, we induced Gambel's white-crowned sparrows to enter the migratory condition and compared food intake and locomotor activity between controls and birds injected with RU486 - an antagonist to the low-affinity glucocorticoid receptor (GR). In addition, we investigated effects of RU486 in birds that were subjected to a short-term fast. Results indicate that RU486 did not affect locomotor activity. However, consistent with its effects in mammals, RU486 suppressed food intake. Thus, hyperphagia and migratory restlessness, the two behaviors that characterize migration, may be regulated by different mechanisms. Lastly, RU486 antagonized fasting-induced lipid mobilization, as evidenced by decreased plasma free fatty acids. Thus, data on spring migrants suggest that endogenous corticosterone levels act through the GR to support hyperphagia and that the GR promotes availability of lipid fuel substrates in association with periods of energetic demand, e.g. during migratory flight.
Do we care what others Get? A Behaviorist Approach to Targeted Promotions
Authors: Feinberg Fred M. , Krishna Aradhna , Zhang Z. John
Published: November 2003

Increased access to individual customers and their purchase histories has led to a growth in targeted promotions, including the practice of offering different pricing policies to prospective, as opposed to current, customers. Prior research on targeted promotions has adopted a tenet of the standard economic theory of choice, whereby what a consumer chooses depends exclusively on the prices available to that consumer. In this article, the authors propose that consumer preference for firms is affected not just by prices the consumers themselves are offered but also by prices available to others. This departure from the conventional strong-rationality approach to targeted promotion results in a decidedly different optimal policy. Through a laboratory experiment, calibration of a stochastic model, and game-theoretic analysis, the authors demonstrate that ignoring behaviorist effects exaggerates the importance of targeting switchers as opposed to loyals. This occurs, though with intriguing differences, even when only part of the market is aware of firms’ differing promotional policies. The authors show that both the deal percentage and the proportion of aware consumers affect the optimal strategy of the firm. Furthermore, the authors find that offering lower prices to switchers may not be a sustainable practice in the long run, as information spreads and the proportion of aware consumers grows. The model cautions practitioners against overpromoting and/or promoting to the wrong segment and suggests avenues for improving the effectiveness of targeted promotional policies.
Price Competition under Stockpiling and Flexible Consumption
Authors: Bell David R. , Iyer Ganesh , Padmanabhan V.
Published: November 2003

Conventional wisdom suggests that the main effect of price promotion is on brand switching (i.e., secondary demand); however, some recent studies demonstrate that the primary demand expansion effect can be considerably larger than previously believed. A significant driver of this primary demand effect is consumer stockpiling in response to price promotions. Indeed, experimental studies have shown that additional inventory on hand can lead to an endogenous increase in consumption. The authors develop a model of price competition between firms in response to the stockpiling and subsequent consumption dynamics of consumers. In this setting, the flexible consumption effect causes more intense price competition, deeper promotions, and an increase in the frequency of promotions. The authors use two years of scanner panel data from eight product categories and 4313 stockkeeping units to test three implications of the theoretical model; they find strong support for each.
The Effects of Temporal Consistency of Sales Promotions and Availability on Consumer Choice Behavior
Authors: Swait Joffre , Erdem Tülin
Published: November 2003

The importance of consistency of the marketing mix is widely regarded as a key marketing principle. Consistency is commonly understood to apply among marketing mix elements, but it also involves a temporal dimension: Marketing messages and, more generally, marketing mix strategies should achieve some degree of consistency over time. In this article, the authors focus on a particular aspect of marketing mix consistency over time in the context of frequently purchased packaged consumer goods: They investigate the impact of temporal consistency on store promotions, as well as the availability of the product on the shelf, on consumer product evaluations (utilities) and choices. In this specific context, temporal (in)consistency captures the degree of variability of prices, displays, and features, as well as availability over time, for a stockkeeping unit. The authors find that sales promotion mix consistency over time affects both consumer utility mean and scale and thus consumers’ choices and brand shares. Lack of sales promotion mix consistency is generally deleterious to consumer brand evaluations through (1) decreases to average valuations and (2) decreases in scale, both of which can lead to decreases in market share.
Whose Culture Matters? Near-Market Knowledge and Its Impact on Foreign Market Entry Timing
Authors: Mitra Debanjan , Golder Peter N.
Published: November 2003

Market entry decisions are some of a firm's most important strategic choices. Although some recent studies have begun to consider the impact of learning and experience on foreign market entry, no study has examined the impact of a firm's own operations in similar markets on subsequent entry decisions. In this study, the authors introduce the concept of near-market knowledge to reflect the knowledge firms generate by operating in markets that are culturally and economically similar. The authors compile extensive data on the complete foreign market entries of 19 multinational firms. They use a hazard model on 722 entry observations to evaluate the impact of the dynamic near-market knowledge measures and other economic and cultural variables on foreign market entry timing. In contrast with much previous research, the authors find that cultural distance from the domestic market is not a significant factor. However, the authors find significant effects for the new measures of near-market cultural and economic knowledge and for several other economic variables as well. The authors discuss the implications of these findings for further research and management practice.
Assessing When Increased Media Weight of Real-World Advertisements Helps Sales
Authors: Macinnis Deborah J. , Rao Ambar G. , Weiss Allen M.
Published: November 2003

A prevailing view is that increased media weight for frequently purchased brands in mature product categories usually does not lead to increases in sales. However, the role of advertising executional cues and viewer responses on media weight-induced sales has not yet been examined. The authors find that whether weight helps or has no sales impact depends on the creative characteristics of the advertisements and the responses they evoke in viewers. Study 1 showed that real-world advertisements for frequently purchased brands in mature categories were likely to create greater media weight-induced sales when they used affectively based executional cues. Study 2 found that greater media weight was related to the sales impact of advertisements that evoked positive feelings and failed to evoke negative feelings in viewers. The authors develop hypotheses related to these results within the context of prior work on consumer persuasion (including the elaboration likelihood model), memory processes, and advertising wearout.
An Empirical Investigation of the Spillover Effects of Advertising and Sales Promotions in Umbrella Branding
Authors: Erdem Tülin , Sun Baohong
Published: November 2003

The authors investigate and find evidence for advertising and sales promotion spillover effects for umbrella brands in frequently purchased packaged product categories. The authors also capture the impact of advertising (as well as use experience) on both utility mean and variance across two categories. They show that variance of the random component of utility declines over time on the basis of advertising (and use experience) in either category. This constitutes the first empirical evidence for the uncertainty-reducing role of advertising across categories for umbrella brands.
Effects of Implicit Memory on Memory-Based versus Stimulus-Based Brand Choice
Authors: Lee Angela Y.
Published: November 2003

The author introduces implicit (versus explicit) memory to examine advertising effects on brand choice. Whereas explicit memory is demonstrated by the conscious recollection of an event, implicit memory is inferred by an improvement in some task performance as the result of having experienced the event. This research shows that memory-based choice benefits from advertising that enhances conceptually driven implicit memory whereas stimulus-based choice benefits from advertising that enhances perceptually driven implicit memory. The findings provide evidence that the two types of implicit memory and explicit memory are distinct constructs of memory; the findings also suggest that implicit memory measures may be more useful indicators of advertising effectiveness than explicit memory measures.
Determining the Appropriate Depth and Breadth of a Firm's Product Portfolio
Authors: Bordley Robert
Published: November 2003

Some firms have broad product lines; others have lean product lines. To determine the appropriate number of entries in a specific firm's product line, the author develops a model that balances the benefits of increased revenue from a broad product line against production and engineering costs. Two innovations were central in the development of the model: (1) redefining how products are scored on various product attributes so that attribute scores vary normally across the population of products and (2) redefining how the number of entries in a product portfolio is calculated in order to discount the significance of entries that are highly similar to existing products. The author also introduces the notion of a centroid time to more easily adjust sales and total development costs for product life cycle and investment life cycle effects. These redefinitions enable a firm's profit to be modeled as a simple function of its effective number of product entries, the effective number of competitors entries, the total sales in the segment, variable profits adjusted for capacity constraints, and product development costs. This leads to a simple expression for the profit-maximizing number of effective entries, both when competitor portfolios are fixed and when competitors dynamically adjust their portfolios. The author illustrates how to estimate and apply the model on a realistic example.
Affect, Framing, and Persuasion
Authors: Keller Punam Anand , Lipkus Isaac M. , Rimer Barbara K.
Published: November 2003

The authors conduct two experiments that indicate that the effectiveness of loss- versus gain-framed messages depends on the affective state of the message recipient. In Experiment 1, the authors find that participants induced with a positive mood are more persuaded by the loss-framed message, whereas participants induced with a negative mood are more persuaded by the gain-framed message. In addition, the authors observe that participants in a positive mood have higher risk estimates and lower costs in response to the loss frame than the gain frame, whereas the reverse is true for participants in a negative mood. The authors replicate these effects in Experiment 2 in which they measure rather than induce the participants' affective state.
Stickier Priors: The Effects of Nonanalytic versus Analytic Thinking in New Product Forecasting
Authors: Bolton Lisa E.
Published: November 2003

The author investigates scenario generation and analogical reasoning as potential sources of bias in new product forecasting. In a series of studies, scenarios and analogies are shown to have persistent effects on judgment, despite subsequent use of corrective analytic techniques (e.g., counterfactual reasoning, counterscenarios, counteranalogies, decomposition, accountability). These findings demonstrate the robustness of nonanalytic processes on judgment and the need to be aware of their seductive effects.
Parameteridentifikation für ereignisdiskrete Systeme (Parameter Identification for Discrete Event Systems)
Authors: Schullerus G. , Krebs V.
Published: November 2003

Der vorliegende Beitrag befasst sich mit der experimentellen Modellbildung für zeitbewertete ereignisdiskrete Systeme und stellt ein Verfahren zur Identifikation solcher Systeme vor. Ausgangspunkt ist die Darstellung der Dynamik der Ereigniszeitpunkte eines Synchronisationsgraphen mit Hilfe der Max-Plus-Algebra in einer der Zustandsraumdarstellung zeitdiskreter Systeme strukturell ähnlichen Form. Auf der Grundlage dieser Struktur erfolgt eine Schätzung der Zeitbewertungen, so dass ein Gleichungsfehler minimiert wird. Der Beitrag befasst sich zudem mit dem Entwurf geeigneter Anregungssignale, die eine exakte Bestimmung der Systemparameter ermöglichen.
DFG-Schwerpunktprogramm "Sicherheit in der Informations- und Kommunikationstechnik" (Priority Program "Security in the Information and Communication Technology")
Authors: Wohlgemuth S. , Gerd tom Markotten Daniela , Jendricke Uwe , Müller Gordon
Published: November 2003

Das Schwerpunktprogramm "Sicherheit in der Informations- und Kommunikationstechnik" wird seit Ende 1999 für die Dauer von sechs Jahren von der Deutschen Forschungsgemeinschaft gefördert. In diesem Schwerpunktprogramm forschen zwölf Universitäten und Forschungseinrichtungen an der Konzeption und der praktischen Entwicklung von Sicherheitsmechanismen und deren Integration zu einem sicheren Gesamtsystem für heutige und zukünftige Szenarien. Dieser Artikel stellt das Referenzszenario, die Projekte sowie ihren Beitrag zum sicheren Gesamtsystem des Schwerpunktprogramms vor.
Extended bond-valence model as a tool for designing topology of inorganic crystal structures
Authors: Urusov Vadim S.
Published: November 2003

The simple rules, based on the bond-valence matching and coordination numbers balance, are extended to minimum-size polyhedral cluster in order to describe all probable bonding topologies for a given inorganic substance. This approach, referred to as the Extended Bond-Valence Model (EBVM), allows one to construct the corresponding connectivity matrices and then to calculate predicted bond valences and bond lengths. The subsequent estimates of individual and average bond distortion indices make it possible to select most probable bonding geometry and compare it with experimental data, whenever feasible. The EBVM approach is applied to predict the bonding topologies of Al2SiO5 polymorphs and hypothetical structures for all allowable coordination environments of cations and anions.
Domain structure and refinement of the triclinic superstructure of 1T-TaSe2 by single crystal X-ray diffraction
Authors: Wiegers G. A. , de Boer J. L. , Meetsma A. , van Smaalen S.
Published: November 2003

The 131/2
a
0 x 131/2
a
0 superstructure of 1T-TaSe2 at room temperature has been studied by singel-crystal X-ray diffraction. The basic structure has symmetry P3̅m1 with a
0 = 3.4733 Å and c
0 = 6.2715 Å. The superstructure has a pseudo hexagonal lattice, but it is triclinic with a 169-fold, 131/2
a
0 x 131/2
a
0 x 13c
0 hexagonal supercell with 13 centering vectors. Structure refinements have been performed using space group P1̅ and the primitive unit cell with a basal plane 131/2
a
0 x 131/2
a
0 supercell, and with C = 2a
0 + c
0. Refinements converged to R
F = 0.086 for 2327 observed reflections. Hexagram shaped clusters of 13 Ta atoms are the principle feature of this 13-fold superstructure, in accordance with the study of Brouwer and Jellinek (Physica B 99 (1980) 51). In the present refinement, significant deviations are found from local 6/m symmetry as it was assumed by Brouwer and Jellinek. The relative phase of the superstructure on neighbouring layers represents the most favourable packing of the buckled planes of Se atoms, and elastic coupling between Se atoms of consecutive layers is identified as the driving force for the observed inter-layer shift vector 2a
0. The small deviations from trigonal symmetry of the clusters are responsible for the observation of an ordered superstructure, as it is opposed to a stacking of layers according a random selection of shift vectors (2a
0, 2a
0 + b
0, and -a
0 - 3b
0) that are equivalent by the trigonal symmetry of the basic structure.
Adsorption of 1,10-Phenanthroline and Sodium Naphthalene 2-Sulfonate onto Activated Charcoal from Mixed Solutions
Authors: de Bussetti Silvia G. , Ferreiro Eladio A.
Published: November 2003

The adsorption (pH = 10) of single solution and binary mixtures of 1,10-phenanthroline (OP) and sodium naphthalene 2-sulfonate (SNS) on activated charcoal was studied. The maximum values for single solution adsorption were 1.811 mmol/g and 0.611 mmol/g for OP and SNS, respectively. Taking into account the total surface area of each molecule and the total maximum area of coverage on the charcoal, a specific area of 899.7 m2/g was determined for OP and 231.8 m2/g for SNS, indicating that orthophenanthroline molecules have a higher affinity for charcoal and that SNS adsorption occurs at specific sites. The results with binary mixtures show that OP hinders SNS adsorption, probably due to a steric impediment, and that adsorption of OP itself is independent of SNS, reaching comparable levels to the single solution. Using a competitive adsorption model it was shown that the two molecules do not compete for charcoal surface area. Application of the Langmuir two-surface adsorption model to the single solutions and binary mixtures indicates the existence of specific sites on charcoal with affinity for OP and SNS, respectively. In the case of the binary mixtures it was shown that the sum of the individual maximum quantities of adsorbed molecules lies within the same order of magnitude as the value determined by applying the Langmuir equation to each one individually.
Growth Hormone Stimulates Proliferation of Old–Aged Regenerating Liver Through Forkhead Box M1b
Authors: Krupczak-Hollis Katherine , Wang Xinhe , Dennewitz Margaret B. , Costa Robert H.
Published: November 2003

The Forkhead Box (Fox) proteins are an extensive family of transcription factors that shares homology in the winged helix DNA–binding domain and the members of which play essential roles in cellular proliferation, differentiation, and longevity. Reduced cellular proliferation during aging is associated with a progressive decline in both growth hormone (GH) secretion and Foxm1b expression. Liver regeneration studies with 12–month–old (old–aged) transgenic mice indicated that increased hepatocyte expression of Foxm1b alone is sufficient to restore hepatocyte proliferation to levels found in 2–month–old (young) regenerating liver. GH therapy in older people has been shown to cause an increase in cellular proliferation, but the transcription factors that mediated this stimulation in proliferation remain uncharacterized. In this study, we showed that human GH administration to old–aged Balb/c mice dramatically increased both expression of Foxm1b and regenerating hepatocyte proliferation. This increase in old–aged regenerating hepatocyte proliferation was associated with elevated protein expression of Cdc25A, Cdc25B, and cyclin B1, with reduced protein levels of cyclin–dependent kinase inhibitor p27Kip1 (p27). GH treatment also was found to stimulate hepatocyte proliferation and expression of Foxm1b protein without partial hepatectomy (PHx). Furthermore, GH treatment of young Foxm1b -/- mice failed to restore regenerating hepatocyte DNA replication and mitosis caused by Foxm1b deficiency. These genetic studies provided strong evidence that the presence of Foxm1b is essential for GH to stimulate regenerating hepatocyte proliferation. In conclusion, our old–aged liver regeneration studies show that increased Foxm1b levels are essential for GH to stimulate hepatocyte proliferation, thus providing a mechanism for GH action in the elderly.
Hepatic Overexpression of Caveolins Increases Bile Salt Secretion in Mice
Authors: Moreno Mauricio , Molina Hector , Amigo Ludwig , Zanlungo Silvana , Arrese Marco , Rigotti Attilio , Miquel Juan Francisco
Published: November 2003

Caveolins are cholesterol–binding proteins involved in the regulation of several intracellular processes, including cholesterol transport. Because hepatocytes express caveolin–1 and caveolin–2, these proteins might modulate hepatic lipid metabolism and biliary lipid secretion. Our aim was to investigate the potential physiologic role of caveolins in hepatic cholesterol and bile salt (BS) metabolism and transport using adenoviral gene transfer. C57BL/6 mice were infected with recombinant human caveolin–1 and caveolin–2 adenoviruses. Mice infected with adenovirus lacking the transgene were used as controls. Hepatic caveolin expression was evaluated by immunochemical methods. Reverse–transcription polymerase chain reaction (RT–PCR) and immunoblotting were used to assess messenger RNA (mRNA) levels and protein mass of BS transporters (sodium taurocholate cotransporting polypeptide [Ntcp] and bile salt export pump [Bsep]). Serum, liver, biliary, and fecal biochemical determinations and BS maximal secretory rate (SRm) were performed by standard methods. Ad.Cav–1– and Ad.Cav–2–infected mice exhibited a 10– and 7–fold increase in hepatic caveolin–1 and caveolin–2 protein expression, respectively. Caveolin–1–overexpressing mice had a significant increase in plasma high–density lipoprotein (HDL) cholesterol and hepatic free cholesterol content, whereas total plasma cholesterol and triglyceride levels remained unchanged. Hepatic caveolin–1 and/or caveolin–2 overexpression significantly increased bile flow and secretion of all biliary lipids. Caveolin–1–overexpressing mice showed a 2.5–fold increase in taurocholate (TC) SRm, indicating increased canalicular BS transport capacity. BS pool size and fecal BS excretion remained within the normal range in mice with Cav–1 overexpression. No changes were seen in the protein mass of BS transporters Ntcp and Bsep. In conclusion, our findings indicate that caveolins may play an important role in regulating hepatic BS and cholesterol metabolism.
Suppression of Hcv–Specific T Cells Without Differential Hierarchy Demonstrated Ex Vivo In Persistent Hcv Infection
Authors: Sugimoto Kazushi , Ikeda Fusao , Stadanlick Jason , Nunes Frederick A. , Alter Harvey J. , Chang Kyong-Mi
Published: November 2003

Hepatitis C virus (HCV) has a high propensity for persistence. To better define the immunologic determinants of HCV clearance and persistence, we examined the circulating HCV–specific T–cell frequency, repertoire, and cytokine phenotype ex vivo in 24 HCV seropositive subjects (12 chronic, 12 recovered), using 361 overlapping peptides in 36 antigenic pools that span the entire HCV core, NS3–NS5. Consistent with T–cell–mediated control of HCV, the overall HCV–specific type–1 T–cell response was significantly greater in average frequency (0.24% vs. 0.04% circulating lymphocytes, P = .001) and scope (14/36 vs. 4/36 pools, P = .002) among the recovered than the chronic subjects, and the T–cell response correlated inversely with HCV titer among the chronic subjects (R = -0.51, P = .049). Although highly antigenic regions were identified throughout the HCV genome, there was no apparent difference in the overall HCV–specific T–cell repertoire or type–1/type–2 cytokine profile relative to outcome. Notably, HCV persistence was associated with a reversible CD4–mediated suppression of HCV–specific CD8 T cells and with higher frequency of CD4+CD25+ regulatory T cells (7.3% chronic vs. 2.5% recovered, P = .002) that could directly suppress HCV–specific type–1 CD8 T cells ex vivo. In conclusion, we found that HCV persistence is associated with a global quantitative and functional suppression of HCV–specific T cells but not differential antigenic hierarchy or cytokine phenotype relative to HCV clearance. The high frequency of CD4+CD25+ regulatory T cells and their suppression of HCV–specific CD8 T cells ex vivo suggests a novel role for regulatory T cells in HCV persistence.
Polyunsaturated Fatty Acids Ameliorate Hepatic Steatosis in Obese Mice by Srebp–1 Suppression
Authors: Sekiya Motohiro , Yahagi Naoya , Matsuzaka Takashi , Najima Yuho , Nakakuki Masanori , Nagai Ryozo , Ishibashi Shun , Osuga Jun-ichi , Yamada Nobuhiro , Shimano Hitoshi
Published: November 2003

Leptin–deficient ob/ob mice show many characteristics of obesity, including excess peripheral adiposity as well as severe hepatic steatosis, at least in part, due to increased hepatic lipogenesis. Polyunsaturated fatty acids (PUFAs) are not only ligands for peroxisome proliferator–activated receptor (PPAR) α but are also negative regulators of hepatic lipogenesis, which is thought to be mediated by the repression of sterol regulatory element–binding protein (SREBP)–1. We have previously shown that the disruption of SREBP–1 in ob/ob mice decreased their liver triglyceride storage. To examine whether PUFAs could reduce hepatic triglyceride deposition, we challenged ob/ob mice with dietary PUFA. It is demonstrated that PUFA markedly decreased the mature form of SREBP–1 protein and thereby reduced the expression of lipogenic genes such as fatty acid synthase (FAS) and stearoyl–CoA desaturase 1 (SCD1) in the livers of ob/ob mice. Consequently, the liver triglyceride content and plasma alanine aminotransferase (ALT) levels were decreased. Furthermore, both hyperglycemia and hyperinsulinemia in ob/ob mice were improved by PUFA administration, similar to the effect of PPARα activators. In conclusion, PUFAs ameliorate obesity–associated symptoms, such as hepatic steatosis and insulin resistance, presumably through both down–regulation of SREBP–1 and activation of PPARα.
Dexamethasone Inhibits Early Regenerative Response of Rat Liver After Cold Preservation and Transplantation
Authors: Debonera Fotini , Krasinkas Alyssa M. , Gelman Andrew E. , Aldeguer Xavier , Que Xingye , Shaked Abraham , Olthoff Kim M.
Published: November 2003

Regeneration is crucial for the recovery of hepatic mass following liver transplantation. Glucocorticoids, immunosuppressive and antiinflammatory agents commonly used in transplantation, are known to inhibit the expression of specific cytokines and growth factors. Some of these proteins, namely tumor necrosis factor α (TNF–α) and interleukin 6 (IL–6), play a critical role in the initiation of liver regeneration. Following cold preservation and reperfusion of the transplanted liver, the normal recovery process is marked by increased expression of TNF–α and IL–6, followed by activation of cytokine–responsive transcription factors and progression of the cell cycle resulting in hepatocyte proliferation. We hypothesized that glucocorticoids may influence the repair mechanisms initiated after extended cold preservation and transplantation. Using a rat orthotopic liver transplant model, recipient animals were treated with dexamethasone at the time of transplantation of liver grafts with prolonged cold storage (16 hours). Treatment with dexamethasone suppressed and delayed the expression of TNF–α and IL–6 compared with animals receiving no treatment and attenuated downstream nuclear factor κB (NF–κB), signal transduction and activator of transcription 3 (STAT3), and activation protein 1 (AP–1) activation. This suppression was accompanied by poor cell–cycle progression, delayed cyclin D1 nuclear transposition, and impaired hepatocyte proliferation by BrdU uptake. Histologically, the liver grafts in treated animals demonstrated more injury than controls, which appeared to be necrosis, rather than apoptosis. In conclusion, these data provide evidence that the administration of glucocorticoids at the time of transplantation inhibits the initiation of the regenerative process and may have a deleterious effect on the recovery of liver grafts requiring significant regeneration. This may be particularly relevant for transplantation of partial liver grafts in the living donor setting.
Severe Cholestasis Induced by Cholic Acid Feeding in Knockout Mice of Sister of P–Glycoprotein
Authors: Wang Renxue , Lam Ping , Liu Lin , Forrest Dana , Yousef Ibrahim M. , Mignault Diane , Phillips James M. , Ling Victor
Published: November 2003

Intrahepatic cholestasis is often associated with impairment of biliary bile acid secretion, a process mediated by the sister of P–glycoprotein (Spgp or Abcb11) also known as the bile salt export pump (Bsep). In humans, mutations in the Spgp gene are associated with a fatal childhood disease, type 2 progressive familial intrahepatic cholestasis (PFIC2). However in mice, the “knockout” of Spgp only results in mild cholestasis. In this study, we fed spgp
-/- knockout mice with a cholic acid (CA)–supplemented diet to determine whether a more pronounced PFIC2–like phenotype could be induced. Such mice developed severe cholestasis characterized by jaundice, weight loss, elevated plasma bile acid, elevated transaminase, cholangiopathy (proliferation of bile ductules and cholangitis), liver necrosis, high mortality, and wide–ranging changes in the mRNA expression of major liver genes (16/36 examined). A surprising observation was that the bile acid output and bile flow in CA–fed mutant mice was significantly higher than anticipated. This suggests that the spgp
-/- mice are able to utilize an alternative bile salt transport system. However, unlike Spgp, this system is insufficient to protect the knockout mice from cholestasis despite its high capacity. In conclusion, the spgp
-/- mice provide a unique model to investigate molecular pathways associated with cholestasis and related diseases.
The Brickworkers of Khatunabad: A Striking Record (1953–1979)
Authors: Floor Willem
Published: November 2003

This article discusses the working and living conditions of unskilled labourers in South Tehran, and pays particular attention to the workers of the brick-kiln factories of Khatunabad. The brick-kiln workers, mostly transient rural workers, were among the poorest of the Iranian labour class. At the same time, in terms of sheer numbers they represented 5 per cent of the population of Tehran in 1960. They lived and worked under appalling conditions but, nevertheless, they only seldom went on strike. The brickworkers' main concern was not so much their working conditions, but rather to get and hold a job. This was difficult, because (1) they were seasonal labour; (2) they had no representative workers' organization to speak for them; (3) the way their industry was organized left them with little power; and (4) there was strong competition from other unskilled and unemployed labourers. Finally, the six known strikes by the brick-kiln workers will be highlighted, and used to discuss the context in which all Iranian workers had to operate.
Luther and the Via Moderna: The Philosophical Backdrop of the Reformation Breakthrough
Authors: OBERMAN HEIKO A.
Published: November 2003

The momentous paradigm shift from God as Being to God as Person provides us with the context for gaining a firm grasp of Luther's own redefinition of the range and role of philosophy. By no means the life-long combatant, distorter or victim of scholasticism as later scholarship often claims, Luther at once unfolded and redirected a tradition that stretched back through St Bonaventura to St Francis of Assisi, a tradition that rejected the Thomistic ‘Unmoved Mover’ and envisaged a covenantal ‘God who acts’. For Luther, the ‘God who acts’ became the ‘God who acts in Christ’, who is unpredictable and foils any systematic search, who contrary to ‘reason’ carries the cross from Christmas to Easter.