bluuebunny/crossref_metadata_2025_split huggingface dataset:
Luminescence and defects creation in Ce3+‐doped Lu3Al5O12 crystals
Authors: Blazek K. , Krasnikov A. , Nejezchleb K. , Nikl M. , Savikhina T. , Zazubovich S. 
Published: March 2004

AbstractLuminescence, energy transfer and defects creation processes were studied at 4.2–300 K for Ce3+‐doped Lu3Al5O12 crystals under excitation in the 2.5–11.5 eV energy range. The results obtained were compared with the characteristics of Y3Al5O12:Ce crystals. It was concluded that in both systems the efficiency of energy transfer from the host lattice to the impurity ion can be noticeably increased by the decrease of concentration of the defects responsible for their intrinsic luminescence. The origin of the optically created defects and possible mechanisms of their formation are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conditions and possible mechanism of condensation of e–h pairs in bulk GaAs at room temperature
Authors: Vasil'ev Peter P. 
Published: March 2004

AbstractA mechanism of the condensation of e–h pairs in bulk GaAs at room temperature, which has been observed earlier, is proposed. The point is that the photon assisted pairing happens in a system of electrons and holes that occupy energy levels at the very bottoms of the bands. Due to a very high e–h density, the destruction of the pairs and loss of coherence does not occur because almost all energy levels inside a 30–60 meV band from the bottom of the conduction band prove to be occupied. As a result, a coherent ensemble of composite bosons (paired electrons and holes) with the minimum possible energy appears. The lifetime of this strongly non‐equilibrium coherent e–h BCS‐like state is as short as a few hundred of femtoseconds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model exchange‐spring nanocomposite magnetic grains
Authors: Szlaferek A. 
Published: March 2004

AbstractThe magnetization reversal in nanocomposite two‐phase grains embedded in a soft magnetic matrix is calculated using Brown's equation. The grains are spherical, consisting of a soft core surrounded by a hard shell. The calculation yields nonlinear algebraic expressions whose solutions describe the nucleation field as a function of the geometrical and magnetic parameters of the grains. The magnetization reversal depends not only on the total grain size but also on the shell thickness. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral representation theory for higher order nonlinear responses in random composites with arbitrary nonlinearity
Authors: Gu Liping , Gao Lei , Li Zhenya 
Published: March 2004

AbstractThe higher order nonlinear responses of random two‐phase composite media are investigated within spectral representation theory. The first component with the volume fraction p is assumed to have the nonlinear displacement (D)‐electric field (E) relation of the form D = ε1E+ χ1 |E|βE, where ε1 is the linear dielectric constant and χ1 is the (β + 1)th order nonlinear response; the second component is linear with the volume fraction 1–p and the dielectric constant ε2. The effective nonlinear responses of the composite media can be defined as 〈D〉 = εeE0 + χe|E0|βE0 + ηe|E0|2βE0, where εe, χe and ηe are the effective linear dielectric constant, the effective (β + 1)th order nonlinear response and (2β + 1)th order nonlinear response respectively. Based on spectral representation theory and the perturbative expansion method, general expressions for χe and ηe are derived as a function of the material parameters and the spectral density function m(x), which are indeed valid for arbitrary β and for any complicated microstructures. For the dilute limit and the Maxwell‐Garnett microstructures, our expressions yield the same formulae as those in previous works. Moreover, the theoretical results for Bruggeman effective medium microstructures are compared with numerical simulations, good agreement is found. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two deltons: An inseparable Schrödinger equation
Authors: Caylor McKinney Paul 
Published: March 2004

AbstractInseparable Schrödinger equations usually cannot be solved analytically. Most often their solutions are obtained numerically. It would be helpful to have an inseparable Schrödinger equation whose solution can be completely calculated. Perhaps more can be learned about appropriate wave function solutions of complex problems if the solutions of an inseparable Schrödinger equation, solved in terms of simple functions, are available. Such a study is possible using the Dirac delta function as the potential energy for two particles moving on a line. The Dirac delta function problem leads naturally to a consideration of the wave functions' symmetry properties. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Tandem mass spectrometry of half‐generation PAMAM dendrimer anions
Authors: He Min , McLuckey Scott A. 
Published: March 2004

AbstractIons derived from negative electrospray ionization of polyamidoamine (PAMAM) dendrimer generation 0.5 were subjected to ion trap tandem mass spectrometry. Ion/ion proton transfer reactions were used to manipulate the charge states of PAMAM precursor ions to form lower charge states from those initially formed by electrospray, as well as to facilitate the interpretation of the product ion mass spectra. Most of the products derived from dendrimer precursor ions could be rationalized by retro‐Michael decomposition reactions. The dominant fragmentation channels are highly dependent on the composition of the counter‐ions, which in this case are restricted to different numbers of sodium ions and protons, and whether the precursor ion is multiply charged or singly charged. An interpretation is given that is consistent with all of the observations made with the various anions associated with this study. The nature of the structural information that can be obtained via ion trap tandem mass spectrometry of the dendrimers is dependent on the types of precursor ions subjected to study. The tandem mass spectrometry data also provided information about the structure of faulty synthesis products present in the PAMAM dendrimer sample. Copyright © 2004 John Wiley & Sons, Ltd.
H∞tracking of linear continuous‐time systems with stochastic uncertainties and preview
Authors: Gershon E. , Shaked U. , Yaesh I. 
Published: March 2004

AbstractThe problem of finite‐horizonH∞tracking for linear continuous time‐invariant systems with stochastic parameter uncertainties is investigated for both, the state‐feedback and the output‐feedback control problems. We consider three tracking patterns depending on the nature of the reference signal i.e. whether it is perfectly known in advance, measured on line or previewed in a fixed time‐interval ahead. The stochastic uncertainties appear in both the dynamic and measurement matrices of the system. In the state‐feedback case, for each of the above three cases a game theory approach is applied where, given a specific reference signal, the controller plays against nature which chooses the initial condition and the energy‐bounded disturbance. The problems are solved using the expected value of the standard performance index over the stochastic parameters, where, in the state‐feedback case, necessary and sufficient conditions are found for the existence of a saddle‐point equilibrium. The corresponding infinite‐horizon time‐invariant tracking problem is also solved for the latter case, where a dissipativity approach is considered. The output‐feedback control problem is solved as a max–min problem for the three tracking patterns, where necessary and sufficient condition are obtained for the solution. The theory developed is demonstrated by a simple example where we compare our solution with an alternative solution which models the tracking signal as a disturbance. Copyright © 2004 John Wiley & Sons, Ltd.
H∞ preview tracking in output feedback setting
Authors: Kojima Akira , Ishijima Shintaro 
Published: March 2004

AbstractThe performance of preview control is investigated in terms of H∞‐criterion. In the output feedback setting, an H∞ preview control problem is discussed and the analytic solution is characterized by introducing matrix Riccati equations. The strength and the limitation of the H∞ preview performance are illustrated with numerical examples. Copyright © 2004 John Wiley & Sons, Ltd.
Angle‐resolved XPS of fluorinated and semi‐fluorinated side‐chain polymers
Authors: Beamson G. , Alexander M. R. 
Published: March 2004

AbstractAngle‐resolved XPS data (elemental quantification and high‐energy‐resolution C 1s) are presented for ten polymers with side‐chains of the form OCO(CF2)yF, COO(CH2)2OCO(CF2)yF (y = 1, 2, 3) and COO(CH2)x(CF2)yF (x = 1, y = 1, 2, 3; x = 2, y = 8). Particular attention was paid to charge compensation and speed of data acquisition, with co‐addition from multiple fresh samples to give spectra with good energy resolution and good signal‐to‐noise ratio free from the effects of x‐ray‐induced degradation. Water contact angles for the polymers are also reported. The XPS data demonstrate preferential surface segregation of fluorine‐containing groups for all but the shortest side‐chain polymer, where the OCOCF3 side‐chain either does not surface segregate or is too short for surface segregation to be detectable by angle‐resolved XPS. In the other polymers studied the relative positions of functional groups in the side‐chains correlate with the angle‐resolved behaviour of the corresponding C 1s components. This shows that the surface side‐chains are oriented towards the polymer surface. For the COO(CH2)2OCO(CF2)yF (y = 1) side‐chain, the angle‐resolved C 1s data suggest reduced ordering and linearity compared with y = 2 and 3. For any particular series of polymers, e.g. COO(CH2)x(CF2)yF, the water contact angles increase with y, consistent with burying of the hydrophilic ester groups as y increases. For any particular value of y the sequence of water contact angles is COO(CH2)x(CF2)yF > OCO(CF2)yF ∼ COO(CH2)2OCO(CF2)yF, suggesting greater ordering and density of fluorocarbon species at the surface of the COO(CH2)x(CF2)yF side‐chain polymers compared with the other polymers studied. For the COO(CH2)2(CF2)8F polymer a water contact angle of 124° is measured, which is greater than that of poly(tetrafluoroethene). The COO(CH2)2OCO(CF2)F polymer is unusual in that it shows a particularly low water contact angle (83° ), suggesting that the probe fluid is able to sense both ester groups, consistent with the reduced ordering of the side‐chain detected by angle‐resolved XPS. Copyright © 2004 John Wiley & Sons, Ltd.
Comparative study of self‐assembly of a range of monofunctional aliphatic molecules on magnetron‐sputtered aluminium
Authors: Liakos Ioannis L. , Newman Roger C. , McAlpine Eoghan , Alexander Morgan R. 
Published: March 2004

AbstractThe adsorption of a range of organic molecules from toluene onto the oxidized surface of magnetron‐sputtered aluminium metal is studied using sessile drop water contact angle measurements. Molecules with different head group functionalities and various chain lengths are considered, including alkyl carboxylic acids, alkyl phosphonic acids, alkyl amines, alkyl trimethoxysilanes, alkyl trichlorosilanes and epoxy alkanes. Alkyl phosphonic and carboxylic acids are identified as readily forming the most well‐packed monolayers on the aluminium surface, whereas the others adsorb less well and the chlorosilanes polymerize as a result of combination with moisture to form a thick deposit. The high‐adsorption‐density monolayers of alkyl phosphonic and carboxylic acids were studied using polarization modulation infrared reflection–absorption spectroscopy (PM‐IRRAS) and x‐ray photoelectron spectroscopy (XPS): PM‐IRRAS reveals relatively poorer ordering of the C10 alkyl carboxylic acid monolayer compared with that formed from the phosphonic acid, and XPS data suggest that this is likely to relate to a lower ability to displace preadsorbed volatile organic compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Cloning and functional characterization of the SUR2/SYR2 gene encoding sphinganine hydroxylase in Pichia ciferrii
Authors: Bae Jung‐Hoon , Sohn Jung‐Hoon , Park Chang‐Seo , Rhee Joon‐Shick , Choi Eui‐Sung 
Published: March 2004

AbstractSaccharomyces cerevisiae sphinganine C4‐hydroxylase encoded by the SUR2 gene catalyses the conversion of sphinganine to phytosphingosine. We isolated the SUR2 gene from Pichia ciferrii using nucleotide sequence homology to S. cerevisiae SUR2 to study hydroxylation of sphinganine in the sphingoid base overproducing yeast P. ciferrii. A positive clone was confirmed by nucleotide sequencing. A syringomycin‐E resistance phenotype of a S. cerevisiae sur2‐null mutant was complemented by expression of the cloned P. ciferrii SUR2 gene. Restoration of phytosphingosine production in the complemented strain was also confirmed, indicating that the cloned gene is a functional homologue of S. cerevisiae SUR2. The nucleotide sequence of the P. ciferrii SUR2 gene was submitted to GenBank under Accession No. AY151276. Copyright © 2004 John Wiley & Sons, Ltd.
On localized Kelvin‐Voigt damping
Authors: Renardy M. 
Published: March 2004

AbstractWe consider one‐dimensional wave propagation through two layers consisting, respectively, of an elastic and a viscoelastic medium. The viscoelastic medium is of Kelvin‐Voigt type. We assume that the material coefficients change smoothly without a discontinuity near the interface. It is proved that the decay rate of high frequency modes tends to infinity with frequency.
Spurious weather radar echo identification and removal using multisource temperature information
Authors: Michelson Daniel B. , Sunhede Daniel 
Published: March 2004

AbstractA simple and pragmatic method utilising the difference between analysed near‐surface and Meteosat IR temperatures (ΔT) is presented and applied with the aim of identifying and removing non‐precipitation echoes in weather radar composite imagery. Despite inherent deficiencies in these multisource data, such as lower spatial and temporal resolutions relative to the radar data, T is demonstrated to efficiently identify efficiently those areas void of potentially precipitating clouds, and to remove radar echoes in them. A set of 243 manually analysed composites from the summer of 2000 was used to evaluate the method. False alarm rates (FAR), percent correct (PC) and Hanssen‐Kuipers skill (HKS) scores were calculated from standard contingency tables for five echo classes: weak, strong, land, sea, and all. FAR was lowered in all classes, PC was generally raised by a few percent to be over 95%, while HKS either remained unchanged or was slightly lowered through the application of T. These results indicate that T successfully removes a significant amount of non‐precipitation, sometimes at the expense of a small amount of true precipitation. This penalty is larger over sea, which indicates that the method may need to be tuned differently for land and sea environments. This method may act as a foundation on which improvements to radar data quality control can be made with the introduction of new and improved satellite instrumentation such as that found on board the Meteosat Second Generation platform. However, this type of method should remain complementary to improved signal processing and radar data analysis techniques. Copyright © 2004 Royal Meteorological Society.
The accuracy of downward short‐ and long‐wave radiation at the earth's surface calculated using simple models
Authors: Finch J. W. , Best M. J. 
Published: March 2004

AbstractEstimates of the downward global solar and long‐wave radiations are commonly made using simple models. We have tested the estimates produced by a number of these simple models against the values predicted by the radiative transfer model used in a climate model in order to determine their suitability for global applications. For clear sky, two simple models were comparable, but under cloudy conditions a combination of a clear‐sky model based on the Angstrom‐Prescott equation (which deals with the downwelling solar radiation) with a cloud transmissivity utilising total cloud fraction proved best. The lowest root mean square errors were 27 W m−2 for clear‐sky global solar radiation and 90 W m−2 for cloudy conditions. For downward long‐wave radiation in clear‐sky conditions, the model of Garratt (1992) performed best with a root mean square error of 24 W m−2. However, in cloudy conditions the model of Idso & Jackson (1969) performed best with a root mean square error of 22 W m−2, and, as it performs nearly as well as that of Garratt (1992) in clear‐sky conditions, it is probably the best choice. Copyright © 2004 Royal Meteorological Society.
Defining transcription modules using large-scale gene expression data
Authors: Ihmels Jan , Bergmann Sven , Barkai Naama 
Published: March 2004

Abstract
Motivation: Large-scale gene expression data comprising a variety of cellular conditions hold the promise of a global view on the transcription program. While conventional clustering algorithms have been successfully applied to smaller datasets, the utility of many algorithms for the analysis of large-scale data is limited by their inability to capture combinatorial and condition-specific co-regulation. In addition, there is an increasing need to integrate the rapidly accumulating body of other high-throughput biological data with the expression analysis. In a previous work, we introduced the signature algorithm, which overcomes the problems of conventional clustering and allows for intuitive integration of additional biological data. However, this approach is constrained by the comprehensiveness of relevant external data and its lacking ability to capture hierarchical modularity.
Methods: We present a novel method for the analysis of large-scale expression data, which assigns genes into context-dependent and potentially overlapping regulatory units. We introduce the notion of a transcription module as a self-consistent regulatory unit consisting of a set of co-regulated genes as well as the experimental conditions that induce their co-regulation. Self-consistency is defined by a rigorous mathematical criterion. We propose an efficient algorithm to identify such modules, which is based on the iterative application of the signature algorithm. A threshold parameter that determines the resolution of the modular decomposition is introduced.
Results: The method is applied systematically to over 1000 expression profiles of the yeast Saccharomyces cerevisiae, and the results are presented using two complementary visualization schemes we developed. The average biological coherence, as measured by the conservation of putative cis-regulatory motifs between four related yeast species, is higher for transcription modules than for clusters identified by other methods applied to the same dataset. Our method is related to singular value decomposition (SVD) and to the pairwise average linkage clustering algorithm. It extends SVD by filtering out noise in the expression data and offering variable resolution to reveal hierarchical organization. It furthermore has the advantage over both methods of capturing overlapping modules in the presence of combinatorial regulation.
Supplementary information: http://www.weizmann.ac.il/~barkai/modules
A comparison of cluster analysis methods using DNA methylation data
Authors: Siegmund Kimberly D. , Laird Peter W. , Laird-Offringa Ite A. 
Published: March 2004

Abstract
Motivation: Aberrant DNA methylation is common in cancer. DNA methylation profiles differ between tumor types and subtypes and provide a powerful diagnostic tool for identifying clusters of samples and/or genes. DNA methylation data obtained with the quantitative, highly sensitive MethyLight technology is not normally distributed; it frequently contains an excess of zeros. Established tools to analyze this type of data do not exist. Here, we evaluate a variety of methods for cluster analysis to determine which is most reliable.
Results: We introduce a Bernoulli–lognormal mixture model for clustering DNA methylation data obtained using MethyLight. We model the outcomes using a two-part distribution having discrete and continuous components. It is compared with standard cluster analysis approaches for continuous data and for discrete data. In a simulation study, we find that the two-part model has the lowest classification error rate for mixture outcome data compared with other approaches. The methods are illustrated using DNA methylation data from a study of lung cancer cell lines. Compared with competing hierarchical clustering methods, the mixture model approaches have the lowest cross-validation error for detecting lung cancer subtype (non-small versus small cell). The Bernoulli–lognormal mixture assigns observations to subgroups with the lowest uncertainty.
Availability: Software is available upon request from the authors.
Supplementary information: http://www-rcf.usc.edu/~kims/SupplementaryInfo.html
Supervised cluster analysis for microarray data based on multivariate Gaussian mixture
Authors: Qu Yi , Xu Shizhong 
Published: March 2004

Abstract
Motivation: Grouping genes having similar expression patterns is called gene clustering, which has been proved to be a useful tool for extracting underlying biological information of gene expression data. Many clustering procedures have shown success in microarray gene clustering; most of them belong to the family of heuristic clustering algorithms. Model-based algorithms are alternative clustering algorithms, which are based on the assumption that the whole set of microarray data is a finite mixture of a certain type of distributions with different parameters. Application of the model-based algorithms to unsupervised clustering has been reported. Here, for the first time, we demonstrated the use of the model-based algorithm in supervised clustering of microarray data.
Results: We applied the proposed methods to real gene expression data and simulated data. We showed that the supervised model-based algorithm is superior over the unsupervised method and the support vector machines (SVM) method.
Availability: The program written in the SAS language implementing methods I–III in this report is available upon request. The software of SVMs is available in the website http://svm.sdsc.edu/cgi-bin/nph-SVMsubmit.cgi