bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Chemistry and Molecular Darwinian Evolution in silico
Authors: Kvasnička Vladimír , Pospíchal Jiří
Published: February 2003

A simplified model of Darwinian evolution at the molecular level is studied by applying the methods of artificial chemistry. A chemical reactor (chemostat) contains molecules that are represented by binary strings, the strings being capable of replication with a probability proportional to their fitness. Moreover, the process of replication is not fully precise, sporadic mutations may produce new offspring strings, which are slightly different from their parent templates. The dynamics of such an autoreplicating system is described by Eigen's differential equations. These equations have a unique asymptotically stable state, which corresponds to those strings that have the highest rate constants (fitness). Fitness of binary string is calculated as a graph-theory similarity between a folding (phenotype) of respective string and the so-called required folding. The presented method offers a detailed view of mechanisms of the molecular Darwinian evolution, in particular of the meaning and importance of neutral mutations.
An Accurate Quartic Force Field and Fundamental Frequencies for the Ozonide Anion: A Rare Positive Anharmonicity for the Antisymmetric Stretch
Authors: Lee Timothy J. , Dateo Christopher E. , Rubio Mercedes , Roos Björn O.
Published: February 2003

The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all 16O and 18O isotopomers of the ozonide anion. The CCSD and CASPT2 methods have also been used to verify the reliability of the CCSD(T) fundamental frequencies. The computed fundamental frequencies are in agreement with gas-phase experiments, but disagree with matrix isolation experiments for the antisymmetric stretch, ν3. CASPT2 calculations show that the antisymmetric part of the O3- potential surface is sensitive to the external environment. It is concluded that the antisymmetric stretch exhibits a significant matrix shift in the matrix isolation experiments and that the matrix environment is not representative of the gas-phase environment for ozonide anion. It is hoped that the theoretical data provided here will aid in the interpretation of future high-resolution gas-phase experiments.
A new Late Cretaceous (Turonian) basal euteleostean fish from Lac des Bois of the Northwest Territories of Canada
Authors: Fielitz Christopher
Published: February 2003

A new genus and species of Late Cretaceous euteleost, Avitosmerus canadensis, is described from an assemblage of fossil fishes found in a Late Cretaceous (Turonian) unnamed member (unit E) of the Great Bear Basin from Lac des Bois, Northwest Territories, Canada. It is a small fusiform fish characterized by a long slender supraorbital, the presence of a small suprapreopercle, branches of the preopercular sensory canal that reach the edge of the preopercle, and an anterior supraneural that is twice as large as those posterior to it. Additionally, elements of its caudal fin show a high degree of fusion. Avitosmerus is one of ten described Cretaceous basal euteleosts that are found worldwide (Avitosmerus, Barcarenichthys, Erichalcis, Gaudryella, Gharbouria, Humbertia, Kermichthys, Manchurichthys, Paravinciguerria, and Stompooria). Avitosmerus and Erichalcis are the only two basal euteleosts that have been described from the Cretaceous of North America. Placement of Avitosmerus into the Euteleostei is based on the presence of a free stegural, and the large first supraneural. Both of these characters are somewhat controversial and are in need of reexamination. Avitosmerus shares a number of characters with the other Cretaceous basal euteleosts, as well as Recent basal euteleosts, including a separate rostrodermethmoid and mesethmoid (Gaudryella, Erichalcis, Gharbouria, the Osmeridae, and the Coregonidae), lobate condyles of the hyomandibula (Avitosmerus, Gaudryella, and Gharbouria), leaf-shaped neural spine on the first preural centrum (Kermichthys), and the fusion of the parhypural, first, and second hypurals (Gaudryella).
Late Quaternary glaciation in the Northern Ogilvie Mountains: revised correlations and implications for the stratigraphic record
Authors: Beierle Brandon D
Published: February 2003

New geomorphic, paleolimnological, and radiocarbon data suggest that a terminal moraine complex in the Northern Ogilvie Mountains, Yukon Territory, Canada, may represent the McConnell Glaciation (Late Wisconsinan), rather than the Reid Glaciation (marine isotope Stage 8; Illinoian) as previously thought. Relict fluvial channels on the surface of the moraine and analysis of a suite of lake sediment cores from Chapman Lake, a closed-basin kettle on the surface of the moraine, suggest that flow from the Blackstone River passed over the moraine and through the lake until ca. 12 500 BP, at which time the Blackstone River was captured by the East Blackstone River, diverting flow from the lake. Subsequent incision by the Blackstone River has left its base level more than 10 m below the level of Chapman Lake. Perched former outlets from Chapman Lake indicate that this incision must postdate stream capture. Because the Chapman Lake moraine is a topographic barrier across the Blackstone River valley, incision must have occurred shortly after deposition of the moraine, suggesting that the landscape surrounding Chapman Lake is substantially younger than previously thought. Additional radiocarbon dates also suggest that kettle subsidence at Chapman Lake was ongoing during the early Holocene and that North Fork Pass moraine, 15 km upvalley from the Chapman Lake moraine, may have been formed during the Late Glacial rather than the McConnell Glaciation.
The first 20 years (1978-1979 to 1998-1999) of active-layer development, Illisarvik experimental drained lake site, western Arctic coast, Canada1
Authors: Mackay J Ross , Burn C R
Published: February 2003

Active-layer thickness, snow depth, minimum soil temperatures, near-surface ground ice, soil heave, and permafrost temperatures have been measured for over 20 years following the 1978 artificial drainage of Lake Illisarvik. Measurements of active-layer thickness and other variables have been made at 25-m intervals along the major and minor axes of the oval-shaped drained-lake bed. Permafrost aggradation commenced in the lake bottom during the first winter following drainage. Before the establishment of vegetation, there was little snow cover, minimum ground temperatures were low, and the active layer was relatively thin. However, both snow depth and minimum ground temperatures have risen where vegetation has grown, the active layer has thickened, and in response, the temperature in permafrost has gradually increased. In the lake bottom, the change in snow depth associated with vegetation growth has been the dominant control on variation in active-layer thickness and not summer weather conditions, which are well correlated with thaw depths along an active-layer course established in the adjacent tundra. Changes in elevation of the surface of the lake bed have been measured with respect to some 40 bench marks anchored in permafrost, and indicate vertical movements of the surface associated with frost heave, thaw subsidence, and the growth of aggradational ice. The ground ice content of near-surface permafrost determined by drilling is in close agreement with the measured uplift of the lake bed. The rate of growth of aggradational ice has been ~0.5 cm a1 over 20 years.
Geochemistry of the late Archean Banting Group, Yellowknife greenstone belt, Slave Province, Canada: simultaneous melting of the upper mantle and juvenile mafic crust
Authors: Cousens Brian , Facey Kathy , Falck Hendrik
Published: February 2003

This study investigates the geochemistry and tectonic setting of the 2.66 Ga Banting Group, the younger sequence of volcanic rocks in the Yellowknife greenstone belt, and its relationship to older tholeiitic volcanic rocks of the 2.722.70 Ga Kam Group. The Banting Group includes a much higher proportion of felsic volcanic and volcaniclastic rocks than the Kam Group, but mafic to intermediate volcanic rocks are common. Banting basalts are tholeiitic and are melts of Archean depleted upper mantle, as are basalts of the Kam Group. In contrast, Banting dacites and rhyolites have much lower heavy rare earth element abundances and generally have higher initial 143Nd/144Nd than Kam felsic rocks. The chemistry of the felsic rocks provides a geochemical signature to distinguish rocks of Kam versus Banting age where complex structures have obscured the stratigraphy. Whereas Kam felsic rocks evolved from mafic parents by assimilation  fractional crystallization processes, Banting felsic rocks have compositions similar to Archean tonalitetrondhjemitedacite suites, as well as modern adakites, and appear to be melts of juvenile, garnet-bearing, hydrated mafic crust, possibly underplated Kam basalts. The nearby 2.66 Ga felsic complex at Clan Lake mimics the geochemical systematics of the Banting Group, and thus Banting-like rocks may reflect a regional crustal melting event at this time.
1/fαFLUCTUATIONS OF SEISMIC SEQUENCES
Authors: TELESCA LUCIANO , CUOMO VINCENZO , LAPENNA VINCENZO , MACCHIATO MARIA
Published: February 2003

We investigate the time dynamics of sequences of earthquakes occurred in three different seismic zones in Italy. All the series analyzed present 1/fαtemporal fluctuations, shown by the power-law behaviour of several statistics (Fano Factor, Allan Factor and Count-based Periodogram), that allow to detect correlation properties in point processes.
The canopy effect in airborne EM
Authors: Beamish David
Published: February 2003

Airborne electromagnetic (AEM) surveys may be used to provide environmental subsurface assessments. Trial fixed‐wing AEM surveys were conducted in the central English Midlands for such purposes. This paper investigates a specific issue, that of the canopy effect, which needs to be addressed when high‐resolution AEM data are to be interpreted accurately. Any elevated feature (typically tree cover) that gives rise to underestimated altimeter readings causes the canopy effect. Half‐space models obtained from conventional, half‐space procedures together with formal numerical inversion techniques form the basis of the study. Both theory and survey data are used to assess the significance of the canopy thickness on the resistivity models. The pseudolayer half‐space method has a stated immunity to altitude errors. The method is found to be highly effective in returning resistivity estimates unbiased by altimeter errors. The associated positive apparent depths provide realistic estimates of canopy thickness while, elsewhere, negative values may be returned. Published numerical inversion schemes do not discuss any corresponding requirement to reduce canopy effect bias. Underestimated altitude measurements introduce false high‐resistivity zones with high wavenumber content unless an equivalent pseudolayer concept is used. The study indicates a requirement for a formal pseudolayer (an at‐surface perfect resistor of variable depth) to be included in the model when canopy zones are present.
2.5‐D inversion of frequency‐domain electromagnetic data generated by a grounded‐wire source
Authors: Mitsuhata Yuji , Uchida Toshihiro , Amano Hiroshi
Published: February 2003

Interpretation of controlled‐source electromagnetic (CSEM) data is usually based on 1‐D inversions, whereas data of direct current (dc) resistivity and magnetotelluric (MT) measurements are commonly interpreted by 2‐D inversions. We have developed an algorithm to invert frequency‐Domain vertical magnetic data generated by a grounded‐wire source for a 2‐D model of the earth—a so‐called 2.5‐D inversion. To stabilize the inversion, we adopt a smoothness constraint for the model parameters and adjust the regularization parameter objectively using a statistical criterion. A test using synthetic data from a realistic model reveals the insufficiency of only one source to recover an acceptable result. In contrast, the joint use of data generated by a left‐side source and a right‐side source dramatically improves the inversion result. We applied our inversion algorithm to a field data set, which was transformed from long‐offset transient electromagnetic (LOTEM) data acquired in a Japanese oil and gas field. As demonstrated by the synthetic data set, the inversion of the joint data set automatically converged and provided a better resultant model than that of the data generated by each source. In addition, our 2.5‐D inversion accounted for the reversals in the LOTEM measurements, which is impossible using 1‐D inversions. The shallow parts (above about 1 km depth) of the final model obtained by our 2.5‐D inversion agree well with those of a 2‐D inversion of MT data.
Geoelectric mapping of near‐surface karstic fractures by using null arrays
Authors: Szalai Sándor , Szarka László , Prácser Erno˝ , Bosch Frank , Müller Imre , Turberg Pascal
Published: February 2003

The term “null array” is introduced for those electrode configurations where the measured potential difference is zero above a homogeneous half‐space when using a measuring dipole M0N0. Different types of null arrays (three‐electrode, Schlumberger, and dipole axial/equatorial null arrays) and their corresponding traditional arrays are studied. It was shown in a field study carried out in a karstified limestone area covered by thin sediments that it is possible to obtain geologically meaningful results with null‐array techniques. The main features of the null‐array data are as follows. (1) Null‐array data appear to be more spatially variable than the classical data. The spatial variability provides information about the presence of karstic fractures in the subsurface; (2) The null‐array anomalies caused by nearly vertical karstic fractures in the limestone basement do not decay with depth as quickly as the classical array anomalies. (3) The strike direction of the fractures is much less ambiguous than that found by using classical arrays. Nevertheless, the depth variation of the basement is more reliably observed in geoelectric anomalies obtained using traditional arrays. Therefore a joint use of classical arrays and their corresponding null methods is recommended, because the combined methods provide more information about the subsurface structure.
Analyzing the effectiveness of receiver arrays for multicomponent seismic exploration
Authors: Hoffe Brian H. , Margrave Gary F. , Stewart Robert R. , Foltinek Darren S. , Bland Henry C. , Manning Peter M.
Published: February 2003

This paper uses an experimental seismic line recorded with three‐component (3C) receivers to develop a case history demonstrating very little benefit from receiver arrays as compared to point receivers. Two common array designs are tested; they are detrimental to the P‐S wavefield and provide little additional benefit for P‐P data. The seismic data are a 3C 2‐D line recorded at closely spaced (2 m) point receivers over the Blackfoot oil field, Alberta. The 3C receiver arrays are constructed by summing five (one group interval) and ten (two group intervals) point receivers. The shorter array emphasizes signal preservation while the longer array places priority on noise rejection. The effectiveness of the arrays versus the single geophones is compared in both the t−x and f−k domains of common source gathers. The quality of poststack data is also compared by analyzing the f−x spectra for signal bandwidth on both the vertical receiver component (P‐P) and radial receiver component (P‐S) structure stacks produced using these two array design philosophies.

The prestack analysis shows that the two arrays effectively suppress coherent noise on both the vertical and radial geophone data and perform reasonably as spatial antialias filters. The poststack analysis reveals that, for both the P‐P and P‐S data, neither of the two arrays significantly improves the quality of the final seismic image over that obtained from point receiver data. For the P‐P data there are subtle differences between the final stacked sections, while for the P‐S data there is a significant deterioration in image quality from the application of the arrays. This P‐S image deterioration is attributed to significant variation of shear‐wave statics across the array. For this specific survey area and acquisition parameters, 3C receiver arrays are unnecessary for P‐P data and are detrimental to P‐S data.
Offset‐domain pseudoscreen prestack depth migration
Authors: Jin Shengwen , Mosher Charles C. , Wu Ru‐Shan
Published: February 2003

The double square root equation for laterally varying media in midpoint‐offset coordinates provides a convenient framework for developing efficient 3‐D prestack wave‐equation depth migrations with screen propagators. Offset‐domain pseudoscreen prestack depth migration downward continues the source and receiver wavefields simultaneously in midpoint‐offset coordinates. Wavefield extrapolation is performed with a wavenumber‐domain phase shift in a constant background medium followed by a phase correction in the space domain that accommodates smooth lateral velocity variations. An extra wide‐angle compensation term is also applied to enhance steep dips in the presence of strong velocity contrasts. The algorithm is implemented using fast Fourier transforms and tri‐diagonal matrix solvers, resulting in a computationally efficient implementation. Combined with the common‐azimuth approximation, 3‐D pseudoscreen migration provides a fast wavefield extrapolation for 3‐D marine streamer data. Migration of the 2‐D Marmousi model shows that offset domain pseudoscreen migration provides a significant improvement over first‐arrival Kirchhoff migration for steeply dipping events in strong contrast heterogeneous media. For the 3‐D SEG‐EAGE C3 Narrow Angle synthetic dataset, image quality from offset‐domain pseudoscreen migration is comparable to shot‐record finite‐difference migration results, but with computation times more than 100 times faster for full aperture imaging of the same data volume.
Depth image focusing in traveltime map‐based wide‐angle migration
Authors: Morozov Igor B. , Levander Alan
Published: February 2003

Wide‐aperture, prestack depth migration requires application of challenging and time‐consuming velocity analysis and depth focusing, collectively referred to here as depth focusing. We present an approach to depth focusing using (1) a detailed starting velocity model obtained by a 1‐D transformation of the first‐arrival times, followed iteratively by (2) interactive analysis of the common‐image gathers, (3) computation of coherency attributes of the wavefield in the depth domain, and (4) 2‐D traveltime tomography to update the background velocity model. We employ two interactive method of migration velocities refinement. In the first method (similar to the common‐midpoint velocity spectrum approach), residual velocity updates are picked directly from the common‐image gathers. In another method (analogous to the common velocity stacks), we pick the velocity updates from the areas of maximum coherency in depth sections that are migrated using rescaled traveltime maps. Both types of migration velocity picks, optionally combined with the first arrivals, are inputs for a 2‐D traveltime inversion scheme that uses either the infinite‐frequency or a finite‐bandwidth approximation. This flexible and versatile depth focusing approach is implemented for several prestack depth migration algorithms and illustrated on an application to a real, ultrashallow seismic data set. The technique resolves overburden velocity variations and facilitates reliable high‐resolution reflection imaging of a paleochannel that was the target of the study.
The joint nonhyperbolic moveout inversion of PP and PS data in VTI media
Authors: Grechka Vladimir , Tsvankin Ilya
Published: February 2003

Nonhyperbolic moveout of P‐waves in horizontally layered transversely isotropic media with a vertical symmetry axis (VTI) can be used to estimate the anellipticity coefficient η in addition to the NMO velocity Vnmo,P. Those two parameters are sufficient for time processing of P‐wave data (despite a certain instability in the inversion for η), but they do not constrain the vertical velocity VP0and the depth scale of the model. It has been suggested in the literature that this ambiguity in the depth‐domain velocity analysis for layer‐cake VTI media can be resolved by combining long‐spread reflection traveltimes of P‐waves and mode‐converted PSV‐waves.

Here, we show that reflection traveltimes of horizontal PSV events help to determine the ratio of the P‐ and S‐wave vertical velocities and the NMO velocity of SV‐waves, and they give a more accurate estimate of η. However, nonhyperbolic moveout of PSV‐waves turns out to be mostly controlled by wide‐angle P‐wave traveltimes and does not provide independent information for the inversion. As a result, even for a single‐layer model and uncommonly large offsets, traveltimes of P‐ and PSV‐waves cannot be inverted for the vertical velocity and anisotropic parameters ε and δ. To reconstruct the horizontally layered VTI model from surface data, it is necessary to combine long‐spread traveltimes of pure P and SV reflections.
Local discontinuity measures for 3‐D seismic data
Authors: Cohen Israel , Coifman Ronald R.
Published: February 2003

In this work, an analysis method is developed for the robust and efficient estimation of 3‐D seismic local structural entropy, which is a measure of local discontinuity. This method avoids the computation of large covariance matrices and eigenvalues, associated with the eigenstructure‐based and semblance‐based coherency estimates. We introduce a number of local discontinuity measures, based on the relations between subvolumes (quadrants) of the analysis cube. The scale of the analysis is determined by the type of geological feature that is of interest to the interpreter. By combining local structural entropy volumes using various scales, we obtain a higher lateral resolution and better discrimination between incoherent and coherent seismic events. Furthermore, the method developed is computationally much more efficient than the eigenstructure‐based coherency method. Its robustness is demonstrated by synthetic and real data examples.
Geopressure prediction using seismic data: Current status and the road ahead
Authors: Dutta N. C.
Published: February 2003

The subject of seismic detection of abnormally high‐pressured formations has received a great deal of attention in exploration and production geophysics because of increasing exploration and production activities in frontier areas (such as the deepwater) and a need to lower cost without compromising safety and environment, and manage risk and uncertainty associated with very expensive drilling. The purpose of this review is to capture the “best practice” in this highly specialized discipline and document it. Pressure prediction from seismic data is based on fundamentals of science, especially those of rock physics and seismic attribute analysis. Nonetheless, since the first seismic application in the 1960s, practitioners of the technology have relied increasingly on empiricism, and the fundamental limitations of the tools applied to detect such hazardous formations were lost. The most successful approach to seismic pressure prediction is one that combines a good understanding of rock properties of subsurface formations with the best practice for seismic velocity analysis appropriate for rock physics applications, not for stacking purposes. With the step change that the industry has seen in the application of the modern digital computing technology to solving large‐scale exploration and production problems using seismic data, the detection of pressured formations can now be made with more confidence and better resolution. The challenge of the future is to break the communication and the “language barrier” that still exists between the seismologists, the rock physicists, and the drilling community.
Influence of Several Process Parameters on Sourdough Fermentation
Authors: Wick M. , Stolz P. , Böcker G. , Lebeault J.‐M.
Published: February 2003

The influence of several process parameters (starter, sourdough refreshment, dough yield, ingredients) on sourdough fermentation was investigated. This was realised by online measurement of both pH and gas pressure in sourdough in a closed air‐tight reactor. Firstly, the effect of sourdough refreshment on both gas pressure and acidification was evaluated and shown to be accompanied by an increase in both acidification and gas pressure evolution rates. Secondly, two commercial starters (BRS and BIO) differing in their microflora were compared as regards to their gassing power and acidifying properties. BRS exhibited faster acidification but less gassing power. Moreover, the variation of sourdough yield for BRS starter induced a different evolution of the acidification profile. Sourdough fermentation varied also depending on the presence of NaCl. 2% of NaCl induced a lower gassing power in sourdough by inhibiting the yeasts.
Production of Industrial Enzymes (Amylase, Carboxymethylcellulase and Protease) by Bacteria Isolated from Marine Sedentary Organisms
Authors: Mohapatra B. R. , Bapuji M. , Sree A.
Published: February 2003

The abilities of bacteria isolated from eight marine sedentary organisms, six marine sponges (Spirastrella sp., Phyllospongia sp., Ircinia sp., Aaptos sp., Azorica sp. and Axinella sp.), one soft coral (Lobophytum sp.) and one alga (Sargassum sp.) to produce industrial enzymes (amylase, carboxymethylcellulase and protease) were examined. The mean total viable counts of the bacterial isolates ranged from 8.7 × 104 to 8.4 × 105 cfu/g wet weight of the organism. All eight organisms harboured amylase (0.05–0.5 IU/ml), carboxymethylcellulase (0.05–0.5 IU/ml) and protease (0.1–0.5 IU/ml) producing bacteria. Of 56 bacterial strains tested, as many as 60 to 83% of the strains produced at least one of the three enzymes, and 47% of strains were able to produce all three enzymes. High activities (> 0.5 IU/ml) of the three enzymes were recorded in bacterial strains belonging to the genera Alcaligenes and Bacillus. From the results of this study, it appears that bacteria associated with marine sedentary organisms are the novel source of industrial enzymes for possible commercial applications and may play an important role in enzyme‐catalysed organic matter cycling in marine environments.
Citric Acid Fermentation and the Effects of Temperature
Authors: Selahzadeh R. M. , Roehr M.
Published: February 2003

The temperature of the fermentation media heavily affects yields as well as rates of citric acid fermentations. At 26–28 °C, more than 40% of the available carbohydrate raw material is wasted, apparently through the respiratory activity of the fungus. At 30–32 °C, these losses are decreased to about 10%. The results thus emphasise the economic importance of adequate temperature control in industrial citric acid fermentation.
Electron Transport in a Methanofullerene
Authors: Mihailetchi V.D. , van Duren J.K.J. , Blom P.W.M. , Hummelen J.C. , Janssen R.A.J. , Kroon J.M. , Rispens M.T. , Verhees W.J.H. , Wienk M.M.
Published: February 2003

The current–voltage characteristics of methanofullerene [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM)‐based devices are investigated as a function of temperature. The occurrence of space–charge limited current enables a direct determination of the electron mobility. At room temperature, an electron mobility of μe = 2 × 10–7 m2 V–1 s–1 has been obtained. This electron mobility is more than three orders of magnitude larger than the hole mobility of donor‐type conjugated polymer poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐p‐phenylene vinylene) (OC1C10‐PPV). As a result, the dark current in PCBM/OC1C10‐PPV based devices is completely dominated by electrons. The observed field and temperature‐dependence of the electron mobility of PCBM can be described with a Gaussian disorder model. This provides information about the energetic disorder and average transport‐site separation in PCBM.
Self‐Assembly and Characterization of Mesostructured Silica Films with a 3D Arrangement of Isolated Spherical Mesopores
Authors: Yu K. , Smarsly B. , Brinker C.J.
Published: February 2003

We report the self‐assembly and characterization of mesoporous silica thin films with a 3D ordered arrangement of isolated spherical pores. The preparation method was based on solvent‐evaporation induced self‐assembly (EISA), with MTES (CH3–Si(OCH2CH3)3) as the silica precursor and a polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) diblock copolymer as the structure‐directing agent. The synthetic approach was designed to suppress the siloxane condensation rate of the siloxane network, allowing co‐self‐assembly of the silica and the amphiphile, followed by retraction of the PEO chains from the silica matrix and matrix consolidation, to occur unimpeded. The calcined films retained the methyl ligands and exhibited no measurable microporosity, thereby indicating that the 3D‐ordered spherical mesopores are not interconnected. A solvent‐mediated formation mechanism is proposed for the absence of microporosity. Due to their closed porosity and hydrophobicity, the MTES‐based films and MTES‐TEOS (Si(OCH2CH3)4)‐based hybrid films we describe should be promising for applications such as low‐k dielectrics.
Raman Anisotropy Measurements: An Effective Probe of Molecular Orientation in Conjugated Polymer Thin Films
Authors: Liem H.‐M. , Etchegoin P. , Whitehead K.S. , Bradley D.D.C.
Published: February 2003

Understanding the molecular alignment of conjugated polymers within thin‐film samples is essential for a complete picture of their optical and transport properties, and hence for the continued development of optoelectronic device applications. We report here on the efficacy of Raman anisotropy measurements as a probe of molecular orientation, presenting results for aligned polyfluorene nematic glass films. Comparison is made with the results of optical dichroism measurements performed on the same samples. We show that in many cases molecular orientation can be more directly characterized by Raman anisotropy, and that it can have a greater sensitivity to the degree of molecular orientation than conventional optical dichroism. The fact that the Raman measurements can be readily performed on the same thin films (∼ 100 nm thickness) that are required for optical dichroism means that there is no ambiguity in a direct comparison of results. This situation differs from that for standard X‐ray diffraction measurements (these require film thicknesses of several μm) and electron diffraction or electron energy loss spectroscopy measurements (these require film thicknesses of 10 nm or less). The Raman data allow the angle (relative to the chain axis) for the optical dipole transition moment to be deduced from the dichroic ratio, and confirm the role that its off‐axis component plays in limiting this ratio. The added fact that Raman anisotropy data can be collected in situ, in reflection geometry for standard device structures, and with microscopic resolution and chemical specificity makes the technique even more attractive as a non‐invasive device probe.
Effects of Postproduction Treatment on Plastic Solar Cells
Authors: Padinger F. , Rittberger R.S. , Sariciftci N.S.
Published: February 2003

Efficiencies of organic solar cells based on an interpenetrating network of a conjugated polymer and a fullerene as donor and acceptor materials still need to be improved for commercial use. We have developed a postproduction treatment that improves the performance of solar cells based on poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) by means of a tempering cycle at elevated temperatures in which an external voltage is simultaneously applied, resulting in a significant increase of the short‐circuit current. Using this postproduction treatment, an enhancement of the short‐circuit current density, Isc, to 8.5 mA cm–2 under illumination with white light at an illumination intensity of 800 W m–2 and an increase in external quantum efficiency (IPCE, incident photon to collected electron efficiency) to 70 % are demonstrated.
Preparation and Properties of Resorcinol–Formaldehyde Organic and Carbon Gels
Authors: Al‐Muhtaseb S.A. , Ritter J.A.
Published: February 2003

A brief overview on the preparation and properties of resorcinol–formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics. The resulting nanostructure was very sensitive to the various synthesis and processing conditions. This leads to a remarkable potential for designing and tailoring these materials to fit specific applications. Based on step‐by‐step comparisons of the published studies, approximate generalizations on the specific roles the synthesis and processing conditions play on the final properties are provided. Overall, resorcinol–formaldehyde organic gels undergo two main stages during synthesis. The first stage is associated with the preparation of the sol mixture, and the subsequent gelation and curing of the gel. The second stage is associated with the drying of the wet gel. The most important factors that affect the properties of the organic gel during the first stage are the catalyst concentration, the initial gel pH, and the concentration of the solids in the sol. The most important factors that affect the properties of the organic gel during the second stage are the drying procedure (e.g., super‐ or subcritical drying), and the difference between the surface tensions of the solvent before and after drying. The corresponding resorcinol–formaldehyde carbon gels are produced from the organic gels during a third stage, which is associated with carbonization or activation. Depending on the conditions, carbonization and activation both impact the structural and performance characteristics significantly.
Electron‐Beam‐Induced Crosslinking of Electroluminescent Polymers for the Production of Multi‐Color Patterned Devices
Authors: Hikmet R.A.M. , Thomassen R.
Published: February 2003

Electron‐beam irradiation is used to crosslink an electroluminescent poly(phenylene vinylene). Increased irradiation leads to increased crosslinking and decreased hole mobility within the polymer, while the electroluminescence quantum efficiency remains constant. An electroluminescent device emitting various colours (see Figure) has been prepared by patterning the polymer through a shadow mask.
Photoinduced Electron Transfer and Photovoltaic Response of a MDMO‐PPV:TiO2 Bulk‐Heterojunction
Authors: van Hal P.A. , Wienk M.M. , Kroon J.M. , Verhees W.J.H. , Slooff L.H. , van Gennip W.J.H. , Jonkheijm P. , Janssen R.A.J.
Published: February 2003

Combining conjugated poylmers and TiO2 in hybrid bulk‐heterojunctions is a promising method for producing novel solar cells. Here TiO2 is introduced into a poly(p‐phenylene vinylene) layer. Nanometer‐scale phase separation allows efficient photoinduced charge transfer between the two components. The films can be used as the active layer in a photovoltaic cell and provide external quantum efficiencies of up to 11 % (see Figure).
Relationship Between the Electro‐Optic Performance of Polymer‐Stabilized Liquid‐Crystal Devices and the Fractal Dimension of Their Network Morphology
Authors: Dierking I.
Published: February 2003

A quantitative relationship is established between the electro‐optic performance (reflectivity, transmittance, threshold field, response time) of a polymer‐stabilized liquid‐crystal and the network morphology of the cholesteric textures (see Figure). By analysis of independent preparation series, varying curing temperature, UV intensity, and irradiation time, respective scaling relations are proposed.
Orthogonal Carbon Nanofibers by Template‐Mediated Assembly of Discotic Mesophase Pitch
Authors: Jian K.Q. , Shim H.‐S. , Schwartzman A. , Crawford G.P. , Hurt R.H.
Published: February 2003

Novel carbon nanofibers (see Figure) are synthesized by capillary impregnation of discotic mesophase pitch into nanochannel alumina. Heating and chemical etching produces nanofibers with a unique “orthogonal” arrangement of graphene layers. Unlike conventional nanofibers and ‐tubes, the graphene planes lie transverse to the fiber axis, which reflects the equilibrium state for the discotic precursor confined to nanocylindrical geometry.
Titelbild: 100 Jahre Didehydroaromaten (Angew. Chem. 5/2003)
Authors: Wenk Hans Henning , Winkler Michael , Sander Wolfram
Published: February 2003

100 Jahre Didehydroaromatenchemie haben das Interesse an dieser Klasse reaktiver Zwischenstufen nicht erlahmen lassen. Das Titelbild zeigt die Struktur eines Calicheamicin‐DNA‐Komplexes mit einer cyclischen Endiineinheit als „Sprengkopf“ (gelb). Die biologische Wirkung der Endiin‐Cytostatika beruht auf der im Zentrum dargestellten Bergman‐Cyclisierung des Endiins unter Bildung eines Didehydrobenzol‐Diradikals. Mehr über die Chemie dieser kurzlebigen Spezies berichten W. Sander et al. auf S. 518 ff.
Protein‐Mikroarray‐Technologie – Prinzipien und neuere Entwicklungen
Authors: Wilson David S. , Nock Steffen
Published: February 2003

Die Sequenzierung des menschlichen Genoms, die Entwicklung von DNA‐Chips und die Bioinformatikprogramme ermöglichen, ganzheitliche Blicke auf biologische Systeme zu werfen und die natürlich vorkommenden genetischen Variationen zu untersuchen. Antikörper‐Mikroarrays können die Konzentration vieler Proteine gleichzeitig und schnell messen. Mikroarrays genetisch kodierter Proteine ermöglichen Wissenschaftlern, das gesamte Genom nach Proteinen zu durchsuchen, die mit bestimmten Faktoren interagieren, bestimmte Reaktionen katalysieren oder als Substrate für Protein‐modifizierende Enzyme sowie als Zielproteine bei einer Autoimmunreaktion dienen. Die neuartigen Protein‐Mikroarray‐Verfahren werden die Entdeckung und Entwicklung von Wirkstoffen sowie diagnostischen Biomarkern stark beschleunigen.
Removal of heavy metal ions using the chelating polymers derived by the condensation of poly(3‐hydroxy‐4‐acetylphenyl methacrylate) with different diamines
Authors: Reddy K. Hussain , Reddy A. Ravikumar
Published: February 2003

A series of methacrylate‐based chelating polymers was synthesized by the reaction of 3‐hydroxy‐4‐acetylphenyl methacrylate with amines (e.g., ethylenediamine, propylenediamine, and phenylenediamine) in tetrahydrofuran. The chelating polymers were characterized by infrared (IR) and carbon‐13 nuclear magnetic resonance (13C–NMR) spectroscopic techniques. The thermal stabilities of these polymers were investigated by thermogravimetric (TG) and differential thermal analyses (DTA). Heavy metal ions [viz., Pb(II), Hg(II), Cd(II), and Cr(VI)] were removed with these chelating polymers, and metal ion uptake efficiency, reusability of the resins, and effects of pH and time on the metal removal were also studied. The chelating polymers possess appreciable selectivity for Pb(II) and Hg(II) compared with Cd(II) and Cr(VI). The chelating ability of the polymers towards the heavy metal ions is a sensitive function of the nature of the substituent on the nitrogen atom. The amount of metal uptake by the chelating polymer was determined by atomic absorption spectrophotometry (AAS). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 414–421, 2003
Preparation of composite particles made from solid powders and wasted plastics by semichemical recycle method
Authors: Taguchi Yoshinari , Tanaka Masto
Published: February 2003

Composite particles composed of solid powders and polymer were prepared by semichemical recycle of wasted plastics. Waste expanded polystyrene was used as raw materials of polymer matrix of composite particles. Both magnetite and silicon carbide powders were used as solid powders to give thermal and electric conductivity and magnetization, respectively. In the experiment, the oil‐phase dissolving expanded polystyrene was dispersed in fine droplets into the continuous water phase. Two kinds of powders were added at the same time or separately in the O/W dispersion. Composite particles were found to have the structure that polymer particle was covered with two kinds of solid powders. The mean diameter of composite particles and the content of each solid powder were strongly affected by the addition time when silicon carbide powder was added into the dispersion. Furthermore, it was found that the gradient adhesion layer due to two solid powders was able to be formed on the surface of polymer particle. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 483–488, 2003
Quality of well‐being in older people with osteoarthritis
Authors: Groessl Erik J. , Kaplan Robert M. , Cronan Terry A.
Published: February 2003

Objective

To examine the sensitivity of the Quality of Well‐Being Scale (QWB) as a measure of health‐related quality of life (HRQOL) in people with osteoarthritis (OA).

Methods

The QWB was administered, along with the Arthritis Impact Measurement Scale (AIMS) and other health measures. Health care utilization data were also obtained.

Results

People with OA had a mean QWB score of 0.643. The QWB scores were significantly correlated with total AIMS scores, self‐rated health status, health care costs, depression scores, and most AIMS subscales. In addition, changes in QWB scores after 1 year were significantly correlated with changes in total AIMS scores and some AIMS subscales.

Conclusion

The QWB appears to be a useful and sensitive generic, utility‐based measure of HRQOL in people with OA.
Assessment of the molecular dynamics structure of DNA in solution based on calculated and observed NMR NOESY volumes and dihedral angles from scalar coupling constants
Authors: Arthanari Haribabu , McConnell Kevin J. , Beger Richard , Young Matthew A. , Beveridge D. L. , Bolton Philip H.
Published: February 2003

To assess the accuracy of the molecular dynamics (MD) models of nucleic acids, a detailed comparison between MD‐calculated and NMR‐observed indices of the dynamical structure of DNA in solution has been carried out. The specific focus of our comparison is the oligonucleotide duplex, d(CGCGAATTCGCG)2, for which considerable structural data have been obtained from crystallography and NMR spectroscopy. An MD model for the structure of d(CGCGAATTCGCG)2 in solution, based on the AMBER force field, has been extended with a 14 ns trajectory. New NMR data for this sequence have been obtained in order to allow a detailed and critical comparison between the calculated and observed parameters. Observable two‐dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY) volumes and scalar coupling constants were back‐calculated from the MD trajectory and compared with the corresponding NMR data. The comparison of these results indicate that the MD model is in generally good agreement with the NMR data, and shows closer accord with experiment than back‐calculations based on the crystal structure of d(CGCGAATTCGCG)2 or the canonical A or B forms of the sequence. The NMR parameters are not particularly sensitive to the known deficiency in the AMBER MD model, which is a tendency toward undertwisting of the double helix when the parm.94 force field is used. The MD results are also compared with a new determination of the solution structure of d(CGCGAATTCGCG)2 using NMR dipolar coupling data. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 3–15, 2003
Extractive fermentation for butyric acid production from glucose by Clostridium tyrobutyricum
Authors: Wu Zetang , Yang Shang‐Tian
Published: February 2003

A novel extractive fermentation for butyric acid production from glucose, using immobilized cells of Clostridium tyrobutyricum in a fibrous bed bioreactor, was developed by using 10% (v/v) Alamine 336 in oleyl alcohol as the extractant contained in a hollow‐fiber membrane extractor for selective removal of butyric acid from the fermentation broth. The extractant was simultaneously regenerated by stripping with NaOH in a second membrane extractor. The fermentation pH was self‐regulated by a balance between acid production and removal by extraction, and was kept at ∼pH 5.5 throughout the study. Compared with conventional fermentation, extractive fermentation resulted in a much higher product concentration (>300 g/L) and product purity (91%). It also resulted in higher reactor productivity (7.37 g/L · h) and butyric acid yield (0.45 g/g). Without on‐line extraction to remove the acid products, at the optimal pH of 6.0, the final butyric acid concentration was only ∼43.4 g/L, butyric acid yield was 0.423 g/g, and reactor productivity was 6.77 g/L · h. These values were much lower at pH 5.5: 20.4 g/L, 0.38 g/g, and 5.11 g/L · h, respectively. The improved performance for extractive fermentation can be attributed to the reduced product inhibition by selective removal of butyric acid from the fermentation broth. The solvent was found to be toxic to free cells in suspension, but not harmful to cells immobilized in the fibrous bed. The process was stable and provided consistent long‐term performance for the entire 2‐week period of study. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 93–102, 2003.
Surface functionalization of porous polypropylene membranes with polyaniline for protein immobilization
Authors: Piletsky Sergey , Piletska Elena , Bossi Alessandra , Turner Nicholas , Turner Anthony
Published: February 2003

Commercial porous polypropylene membranes were chemically modified with polyaniline (PANI) using ammonium persulfate as the oxidizer. The influence of polymerization conditions on the membrane properties was studied by adsorption analysis and membrane permeability. The PANI‐coated polypropylene (PANI/PP) membranes possessed high affinity toward the proteins, which can be immobilized onto the membrane surface through physical adsorption or covalent immobilization. The quantity of immobilized horseradish peroxidase (HRP) and its activity depended on the quantity and quality (oxidation level) of PANI. The storage conditions for PANI/PP membranes containing immobilized HRP were studied. HRP immobilized on the PANI/PP membrane was shown to retain 70% of its activity after 3‐month storage at +5°C, suggesting that this material can be used for practical application, such as in bioreactors as enzyme membranes. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 86–92, 2003.
Pulsed addition of limiting‐carbon during Aspergillus oryzae fermentation leads to improved productivity of a recombinant enzyme
Authors: Bhargava Swapnil , Wenger Kevin S. , Marten Mark R.
Published: February 2003

Fungal morphology in many filamentous fungal fermentations leads to high broth viscosity which limits oxygen mass transfer, and often results in reduced productivity. The objective in this study was to determine if a simple, fed‐batch, process strategy—pulsed addition of limiting‐carbon source—could be used to reduce fungal broth viscosity, and increase productivity of an industrially relevant recombinant enzyme (glucoamylase). As a control, three Aspergillus oryzae fed‐batch fermentations were carried out with continuous addition of limiting‐carbon. To determine the effect of pulse‐feeding, three additional fermentations were carried out with limiting‐carbon added in 90‐second pulses, during repeated five‐minute cycles. In both cases, overall carbon feed‐rate was used to control dissolved oxygen concentration, such that increased oxygen availability led to increased addition of limiting‐carbon. Pulse‐fed fermentations were found to have smaller fungal mycelia, lower broth viscosity, and improved oxygen mass transfer. As a result, more carbon was added to pulse‐fed fermentations that led to increased enzyme productivity by as much as 75%. This finding has significant implications for the bioprocessing industry, as a simple process modification which is likely to cost very little to implement in most production facilities, has the potential to substantially increase productivity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 111–117, 2003.