bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and properties of soluble aromatic polyamides derived from 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene
Authors: Wu Shen‐Chang , Shu Ching‐Fong
Published: March 2003

The synthesis of a new bis(ether carboxylic acid), 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene, in which two orthogonally arranged carboxyphenoxyfluorene entities are connected through an sp3 carbon atom (the spiro center), is reported. The direct phosphorylation polycondensation of this diacid monomer with various aromatic diamines yields aromatic polyamides containing 9,9′‐spirobifluorene moieties in the main chain. The presence of the spiro segment restricts the close packing of the polymer chains and decreases interchain interactions, resulting in amorphous polyamides with enhanced solubility, and high glass‐transition temperatures and good thermal stability are maintained through controlled segmental mobility. The glass‐transition temperatures of these polyamides are in the range of 234–306 °C, with 10% weight losses occurring at temperatures above 530 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1160–1166, 2003
Exfoliated poly(methyl methacrylate) and polystyrene nanocomposites occur when the clay cation contains a vinyl monomer
Authors: Su Shengpei , Wilkie Charles A.
Published: March 2003

The bulk polymerization of methyl methacrylate and styrene in the presence of an organically modified clay containing a vinyl group that can be involved in the polymerization produces exfoliated nanocomposites. These nanocomposites have been characterized by X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis, mechanical properties, and cone calorimetry. The onset temperature of thermal degradation increases with the mechanical properties. The peak heat release rate is significantly reduced for nanocomposites containing 3 or 5% clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1124–1135, 2003
Nanocomposites by melt intercalation based on polycaprolactone and organoclay
Authors: Di Yingwei , Iannace Salvatore , Di Maio Ernesto , Nicolais Luigi
Published: March 2003

Nanocomposites based on biodegradable polycaprolactone (PCL) and organically modified layered silicates (organoclay) were prepared by melt mixing. Their structures and properties were characterized by wide‐angle X‐ray diffraction, thermal analysis, and rheological measurements. The exfoliation of the organoclay was achieved via a melt mixing process in an internal mixer and showed a dependence on the type of organic modifier, the organoclay contents, and the processing temperature. The addition of the organoclay to PCL increased the crystallization temperature of PCL, but a high content of the organoclay could show an inverse effect. The PCL/organoclay nanocomposites showed a significant enhancement in their mechanical properties and thermal stability due to the exfoliation of the organoclay. The nanocomposites showed a much higher complex viscosity than the neat PCL and significant shear‐thinning behavior in the low frequency range. The shear storage modulus and loss modulus of the nanocomposites also exhibited less frequency dependence than the pure PCL in the low frequency range, and this was caused by the strong interactions between the organoclay layers and PCL molecules and by the good dispersion of exfoliated organoclay platelets in the PCL. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 670–678, 2003
Hydrogenated poly(styrene‐co‐α‐methylstyrene) polymers: A new class of high glass‐transition‐temperature polyolefins
Authors: Xu Jing J. , Nguyen Binh T. , Bates Frank S. , Hahn Stephen F. , Hudack Michelle L.
Published: March 2003

We demonstrate a method to prepare high glass‐transition‐temperature (Tg) materials with a two‐step process—anionic copolymerization of α‐methylstyrene with styrene (leading to copolymers referred to as SAMS), with subsequent catalytic hydrogenation. The product, poly(cyclohexyl ethylene‐co‐2‐cyclohexyl propylene), is referred to as PCEPx, where the subscript denotes the molar percentage of 2‐cyclohexyl propylene units in the copolymer. PCEPx exhibits Tg values between 140 and 178 °C depending on the composition and composition distribution in the polymerization product. To increase the toughness of PCEPx, we copolymerized SAMS with butadiene followed by hydrogenation to form PCEPx/PEEy block copolymers, where PEEy refers to poly(ethylene‐co‐ethyl ethylene), and y denotes the molar percentage of ethyl ethylene segments. Tg values as high as 162 °C were achieved for these block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 725–735, 2003
Mesenteric lymphadenopathy as a cause of abdominal pain in children with lobar or segmental pneumonia
Authors: Moustaki Maria , Zeis Petros M. , Katsikari Maria , Fretzayas Andrew , Grafakou Olga , Stabouli Stella , Tsolia Maria , Nicolaidou Polyxeni , Karpathios Themistocles
Published: March 2003

We investigated whether mesenteric lymphadenopathy could be a cause of abdominal pain in children with lobar or segmental pneumonia. The study population consisted of 1)119 consecutive children with lobar pneumonia, older than 4 years of age, and 2) 31 healthy controls. Demographic, clinical, inflammatory, and radiographic data were recorded in all patients. All study subjects underwent abdominal ultrasound, focusing on the identification of mesenteric lymphadenopathy. One month later, a follow‐up ultrasound was performed in patients with enlarged mesenteric lymph nodes at the initial examination. Forty patients complaining of abdominal pain were included in group 1, while the remaining 79 were in group 2. The two groups of patients did not significantly differ regarding their demographic, clinical (other than abdominal pain), and radiographic indices. In contrast, enlarged mesenteric lymph nodes with a sagittal diameter of at least 10 mm were identified significantly more commonly in the children of group 1 (P = 0.001). The association of enlarged lymph nodes with the presence of abdominal pain remained significant when the data were analyzed through multiple regression analysis (odds raio, 1.47; 95% confidence interval, 3–44). Enlarged mesenteric lymph nodes were found in a significantly lower ratio of healthy controls (3/31) compared to that observed in group 1 (P = 0.003). In all patients who were followed up, mesenteric lymph nodes had either decreased or were not detectable. Our findings indicate that mesenteric lymphadenopathy might be considered as a mechanism responsible for the development of abdominal pain in a relatively high percentage of children with pneumonia. Pediatr Pulmonol. 2003; 35:269–273. © 2003 Wiley‐Liss, Inc.
1,4‐Diformyl‐2,3,5,6‐Tetranitratopiperazine: A New Primary Explosive Based on Glyoxal
Authors: Karaghiosoff Konstantin , Klapötke Thomas M. , Michailovski Alexej , Nöth Heinrich , Suter Max , Holl Gerhard
Published: March 2003

In the present work we describe synthesis and properties of 1,4‐diformyl‐2,3,5,6‐tetranitratopiperazine. The 1,4‐diformyl‐2,3,5,6‐tetranitratopiperazine turned out to be a powerful highly energetic compound. Its physical and chemical properties were investigated by theoretical as well as experimental methods. The detonation energy of 1,4‐diformyl‐2,3,5,6‐tetranitratopiperazine was determined to 5376 kJ/kg or 93% compared to HMX. Molecular and crystal structure of 1,4‐diformyl‐2,3,5,6‐tetranitratopiperazine was elucidated by single crystal X‐ray diffraction analysis. An interesting feature of the title substance, its rotamer equilibrium, was investigated by 2D NMR methods.
From unambiguous quantum state discrimination to quantum state filtering
Authors: Bergou J.A. , Herzog U. , Hillery M.
Published: March 2003

Unambiguous discrimination among nonorthogonal but linearly independent quantum states is possible with a certain probability of success. Here, we consider a new variant of that problem. Instead of discriminating among all of the N different states, we now ask for less. We want to unambiguously assign the state to one of two complementary subsets of the set of N given non‐orthogonal quantum states, each occurring with given a priori probabilities. We refer to the special case when one subset contains only one state and the other contains the remaining N‐1 states as unambiguous quantum state filtering. We present an optimal analytical solution for the special case of N=3, and discuss the optimal strategy to unambiguously distinguish |ψ1〉 from the set {|ψ2〉,|ψ3〉}. For unambiguous filtering the subsets need not be linearly independent. We briefly discuss how to construct generalized interferometers (multiports) which provide a fully linear optical implementation of the optimal strategy.
Entangling two spatially separate cavities
Authors: Napoli A. , Messina A. , Compagno G.
Published: March 2003

A scheme for the transfer of entanglement among systems via successive coupling with an intermediate system is described. This method is applied to a simple experimental realizable situation for entangling two spatially separated cavities. In this scheme entanglement, initially stored in two modes of the first cavity, is transferred by an atom interacting successively with the cavities, into entanglement between two non resonant modes of the different cavities.
An operator for simultaneous unsharp measurement of coordinate and momentum
Authors: Davidović D.M. , Arsenović D.
Published: March 2003

Starting from a complete but not overcomplete set of coherent states defined on a lattice in the phase space, we construct the orthonormal basis using the procedure due to Lödwin, in which all states to be normalized enter the procedure on equal footing. We show that our normalized states may be interpreted as eigenstates of the operator of simultaneous unsharp measurement of coordinate and momentum. In a sense we followed the classical idea of von Neumann but without drawbacks which in his construction of such an operator were due to the use of the Gram‐Schmidt orthonormalization procedure which is somewhat inappropriate for this purpose. We discuss the obtained results.
Electron‐electron Coulomb interaction for coherent entangled states
Authors: Gnatovskyy V.O. , Usenko C.V.
Published: March 2003

We have analyzed the influence of Coulomb repulsion on the behavior of two coherent electrons. It turns out that interaction can be ignored irrespective of the distance between the electrons, if either the momentum uncertainty of the electrons or the relative momentum of the electrons is large.
Femtosecond light pulses in GaAs, third harmonic generation by carrier wave Rabi flopping
Authors: Serényi T. , Benedek C. , Benedict M.G.
Published: March 2003

We consider the nonlinear optical response of a GaAs layer excited by an ultrafast laser pulse consisting of only a few cycles. The third harmonic component of the transmitted pulse is calculated and compared with experimental results. We use a reduced set of the semiconductor Bloch equations as a model of the electron‐hole system. To describe the propagation of the ultrashort pulse we apply the integral equation method, which explicitly follows time and space evolution without the slowly varying envelope approximation. We use a procedure that efficiently includes the background refractive index, which is very important in the interpretation of the experimental results.
Entanglement of two atoms
Authors: Tanaś R. , Ficek Z.
Published: March 2003

We discuss the problem of creation of entangled states in a system of two two‐level atoms which are separated by an arbitrary distance r12 and interact with each other via the dipole‐dipole interaction and both are driven by a laser field. The entangled antisymmetric state of the system is included throughout, even for small inter‐atomic separations. Different mechanisms leading to effective transfer of population to the antisymmetric state are identified. The steady‐state values of concurrence which is a measure of entanglement are calculated showing that perfect entanglement can be reached in case of two non‐identical atoms.
A single qubit Landau‐Zener gate
Authors: Benza V.G. , Strini G.
Published: March 2003

We study the hamiltonian and dissipative dynamics of a system undergoing a sequence of level crossings. The resulting Landau‐Zener effect makes a new implementation of a general single qubit gate possible. In the dissipative case, with a periodic bias, the level crossing counteracts the interlevel relaxation and drives the system toward a two dimensional attractor. This feature can in principle be used to implement quantum memory devices of new type.
Magnetic ground state of Kagomé systems: the example of the jarosites compounds
Authors: Ballou R. , Canals B. , Elhajal M. , Lacroix C. , Wills A. S.
Published: March 2003

Localized spins on the Kagomé lattice remain disordered if only nearest neighbor exchange is considered. We study two different mechanisms which induce unconventional behavior on the Kagomé lattice: the Dzyaloshinsky–Moriya interaction and the effect of strong uniaxial anisotropy associated with ferromagnetic interactions (Kagomé spin ice). Both models are applied to members of the jarosite family.
Semiconductor EuS–PbS ferromagnetic multilayers
Authors: Story T.
Published: March 2003

EuS–PbS ferromagnetic multilayers constitute all‐semiconductor ferromagnetic‐nonmagnetic structures with magnetic layers of EuS (a model nonmetallic ferromagnet) and diamagnetic layers of PbS (IV–VI narrow gap semiconductor compound). The ferromagnetic transition temperature in EuS–PbS multilayers depends on the thickness of the magnetic layer as well as on thermal strain. For ultrathin PbS spacer layers one observes in EuS–PbS–EuS trilayers and superlattices pronounced magnetic effects related to the antiferromagnetic interlayer coupling between ferromagnetic layers of EuS via nonmagnetic semiconductor PbS spacer. These effects are discussed for EuS–PbS structures grown epitaxially on various substrates: insulating KCl(100) and BaF2(111) as well as conducting n‐PbS(100) monocrystals.
Excitons in the upper Hubbard band
Authors: Wróbel P. , Eder R.
Published: March 2003

Motivated by recent Raman and resonant inelastic X‐ray scattering experiments performed for Mott insulators, which suggest existence of excitons in these systems, we present a theory of exciton formation in the upper Hubbard band. These objects consist of a hole and a double occupancy. We demonstrate that the effective Hamiltonian representing propagation and interaction of these particles has a dual form which reflects the particle–hole symmetry. The analytical analysis of this Hamiltonian is based on the spin polaron approach. The results confirm existence of excitons and show resemblance with experimental data despite the crudeness of the approach. The driving mechanism of exciton formation is the kinetic energy saving achieved by formation of a spin bipolaron consisting of a hole and a double occupancy connected by a line formed by spin defects in the antiferromagnetic background which moves freely by expanding at one end of the line and shrinking at the other. Our results also demonstrate that even if the Coulomb attraction between the hole and the double occupancy is screened, bound states will form and that the underlying mechanism of the exciton formation is similar to that of pairing in weakly doped antiferromagnets.
Interaction between TLS and the conduction electronsin actinide arsenoselenides: a high‐pressure study
Authors: Cichorek T. , Bauer E. D. , Wojakowski A. , Henkie Z. , Maple M. B. , Steglich F.
Published: March 2003

Electrical resistance R(T) measurements on UAsSe and ThAsSe single crystals were performed under hydrostatic conditions at pressures up to 1.88 GPa (2 K ≤ T ≤ 300 K). For ferromagnetic UAsSe, a reduction of a low‐T upturn in R(T) accompanied by an increase of TC was observed. However, this effect is smaller than that introduced by chemical substitution. For diamagnetic ThAsSe, a hump‐like anomaly (T = 65 K, p = 0) vanishes at p = 1.88 GPa. However, the ratio R(4.2 K)/R(300 K) was only slightly reduced by pressure. Below 20 K, a pressure‐independent logarithmic increase of R(T) over one decade in temperature has been found. The results reported here fit well with the theoretical predictions of the non‐magnetic TLS Kondo model.
Flux pinning model and pinning pressure in superconductors with randomly distributed columnar defects
Authors: Zablotskii V. , Polyakova T.
Published: March 2003

We propose a new phenomenological model of flux pinning in type‐II superconductors with randomly distributed columnar defects. In a two‐dimensional vortex lattice three energies associated with (i) vortex‐vortex interaction, (ii) pin‐vortex interaction, and (iii) thermal fluctuations are taken into account. By free energy minimization we determine the equilibrium number of vortices pinned by a random pinning disorder, the associated pinning pressure, and the critical current density as a function of magnetic field, temperature and concentration of pins. A corporate action of pinning and shearing pressures can lead to appearance of the peak effect if the former is lower than the latter.
Vortex pinning in electron‐doped cuprate superconductor La2–xCexCuO4
Authors: Zuev Yuri , Lemberger Thomas R. , Skinta John A. , Greibe Tine , Naito Michio
Published: March 2003

We have measured the vortex pinning strength in thin films of the electron‐doped cuprate La2–xCexCuO4 for various doping x from x = 0.075 (Tc = 25 K) to x = 0.15 (Tc = 12.5 K). The optimal doping for this compound is ≈0.11, at which Tc = 29 K. Films were prepared by a molecular‐beam epitaxy method. A structural XRD investigation revealed no doping‐induced lattice strain. We use a two‐coil technique at frequencies from 10 to 100 kHz. The superfluid density ns(0) grows rapidly with x on the underdoped side and decreases slowly on the overdoped side. The Labusch parameter κ, i.e. the spring constant for a pinned vortex, shows large variations as the doping changes. It increases with x rapidly to a maximum at slight underdoping and then it decreases on the overdoped side more rapidly than ns(0). Even at optimal doping κ (0) is an order of magnitude lower than the highest values observed in YBCO.
Properties of the η‐pairing phase of the Penson–Kolb model
Authors: Robaszkiewicz S. , Czart W. R.
Published: March 2003

Penson–Kolb model, i.e. the tight‐binding model with the pair‐hopping (intersite charge exchange) interaction J is considered. In the analysis we focus on the properties of the superconducting state with Cooper‐pair center‐of‐mass momentum q = Q (η‐phase), which can develop in this model for the case of repulsive J(J < 0). The evolutions of the phase diagrams, the critical temperatures and superfluid characteristics with particle concentration and pairing strength are discussed.
Pressure and magnetic field effect on magnetic properties of RMn6Ge6–x Gax (R = Y, Sc, Lu) solid solutions
Authors: Duraj R. , Szytuła A. , G. Venturini
Published: March 2003

Temperature and pressure dependence of magnetic properties in YMn6Ge6–xGax for x = 0.56, ScMn6Ge6–xGax for x = 0.65 and x = 0.75 and LuMn6Ge6–xGax for x = 0.6 and x = 0.7 are reported. For the first three compounds the external pressure causes an increase in the Néel temperature while for Lu compounds dTN/dP = 0. Only for LuMn6Ge5.35Ga0.65 the external pressure changes the magnetic properties at low temperatures.
Noncollinear magnetism of the UFexAl12–x series: ab initio calculations
Authors: Cardoso C. , Gasche T. , Sandratskii L. M. , Godinho M.
Published: March 2003

The UFexAl12–x series was the object of a systematic experimental study in single crystals with different compositions [Phys. Rev. B 60, 9494 (1999)]. Several experimental technics were used to suggest a magnetic phase diagram of the system. Three different ranges of composition were found to have different magnetic behaviour: x < 4 + δ1, 4 + δ1 < x < 5 – δ2, and x > 5 – δ2. Here δ1 and δ2 are small positive numbers. The UFe4Al8 and UFe5Al7 compounds belong to two different regions of the phase diagram. DFT calculations and symmetry analysis for these two compounds [Phys. Rev. B 60, R 6961 (1999); 65, 94413 (2002)] contributed to the understanding of the origin of the complex magnetic behaviour of the series. In order to complete the systematic study of the series we report calculations of magnetic properties for UFe4.5Al7.5. The latter compound belongs to the third and the most interesting region of the phase diagram with two magnetic phase transitions. Based on this ab initio study, we discuss the proposed phase diagram.
Stripe fractionalization: the quantum spin nematic and the Abrikosov lattice
Authors: Zaanen J. , Nussinov Z.
Published: March 2003

The cover picture of physica status solidi (b), taken from the Editor's Choice of this issue, shows a scheme of construction of the spin nematic ordered state and the topological interaction between spatially disconnected gauge defects. The gauge symmetry is broken by applying an external field B. The theory described in the paper [1] offers a potential explanation for recent observations of magnetic field induced antiferromagnetism in La1.9Sr0.1CuO4.

The first author, Jan Zaanen, is Professor of Physics at the Instituut‐Lorentz in Leiden where he works on quantum field theory in condensed matter physics, concentrating on problems in high‐TC superconductivity, quantum magnetism, quantum liquid crystals, doped Mott insulators, and strongly correlated electron systems.

This paper is an invited presentation from the European Conference Physics of Magnetism (PM'02), held in Poznań, Poland, 1–5 July 2002. The proceedings of this conference are published in two parts: in the present issue of phys. stat. sol. (b) and in phys. stat. sol. (a) 196, No. 1 (2003).
Radial and angular correlation in heliumlike ions
Authors: Saha B. , Bhattacharyya S. , Mukherjee T. K. , Mukherjee P. K.
Published: March 2003

In the framework of nonrelativistic variational formalism a new type of basis set is proposed, to estimate separately the effect of radial and angular correlations on the ground‐state energy for helium isoelectronic sequence H− to Ar16+. Effect of radial correlation is incorporated by using multiexponential functions arising from product basis sets suitably formed out of Slater‐type one‐particle orbitals. The angular correlation can be switched on by incorporating an expansion in terms of basis involving interparticle coordinates. With a set of six‐term Slater‐type one‐particle basis and five‐term interparticle expansion, the ground‐state energy of helium is estimated as −2.9037236 (a.u.) compared with the multiterm variational estimates −2.9037244 (a.u.) due to Pekeris and Thakkar and Smith and Drake. Matrix elements of different operators in the ground state have been calculated and found to be in good agreement with available accurate results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Useful parameter describing magnetic interactions in extended bis‐bidentate bridged dimers
Authors: Hu Haiquan , Chen Zhida , Liu Chengbu
Published: March 2003

A useful parameter describing magnetic coupling interactions has been inspected in transition metal dimers, in which two transition metal ions are bridged by extended bis‐bidentate ligands. This parameter is the square of overlap integral between the spatial parts of magnetic orbitals in the broken symmetry state. The oxalato‐bridged Cu (II) dimers, in which the Cu (II) atom is either in tetrahedral or square pyramid coordination environment, have been calculated with the density functional theory coupling the broken symmetry approach. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Planar Translational Cable‐Direct‐Driven Robots
Authors: Williams Robert L. , Gallina Paolo , Vadia Jigar
Published: March 2003

We present the simulated dynamics and control of a planar, translational cable‐directdriven robot (CDDR). The motivation behind this work is to improve the serious cable interference problem with existing CDDRs and to avoid configurations where negative cable tensions are required to exert general forces and moments on the environment and during dynamic motions. Generally for CDDRs the commanded rotations are more demanding than commanded translations in terms of slack cable conditions. Therefore we propose a translational CDDR whose end‐effector may be fitted with a traditional serial wrist mechanism to provide rotational freedom (assuming proper design to resist the moments). Only the translational CDDR is considered in this article, including kinematics and statics modeling, statics workspace (wherein all possible Cartesian forces and moments may be exerted with only positive cable tensions), plus a dynamics model and simulated control for planar CDDRs. Here we focus only on planar CDDRs, to clearly demonstrate our dynamics and control work; we will extend this work to spatial CDDRs in the future. Examples are presented to demonstrate simulated control including feedback linearization of the four‐cable CDDR (with one degree of actuation redundancy) performing a Cartesian task. An on‐line dynamic minimum torque estimation algorithm is introduced to ensure all cable tensions remain positive for all motion; otherwise slack cables can result from CDDR dynamics and control is lost. © 2003 Wiley Periodicals, Inc.
Toledo Bend reservoir and geomorphic response in the lower Sabine River
Authors: Phillips Jonathan D.
Published: March 2003

Downstream geomorphic responses of stream channels to dams are complex, variable, and difficult to predict, apparently because the effects of local geological, hydrological, and operational details confound and complicate efforts to apply models and generalizations to individual streams. This sort of complex geomorphic response characterizes the Sabine River, along the Texas and Louisiana border, downstream of the Toledo Bend dam and reservoir. Toledo Bend controls the flow of water and essentially prevents the flux of sediment from three‐quarters of the drainage basin to the lower Sabine River. Although the channel is scoured immediately downstream of the dam, further downstream there is little evidence of major changes in sediment transport or deposition, sand supply, or channel morphology attributable to the impoundment. Channels are actively shifting, banks are eroding, and sandbars are migrating, but not in any discernibly different way than before the dam was constructed. The Sabine River continues to transport sand downstream, and alluvial floodplains continue to accrete. The relatively small geomorphic response can be attributed to several factors. While dam releases are unnaturally flashy and abrupt on a day‐to‐day basis, the long‐term pattern of releases combined with some downstream smoothing creates a flow regime in the lower basin which mimics the pre‐dam regime, at least at monthly and annual time scales. Sediment production within the lower Sabine basin is sufficient to satisfy the river's sediment transport capacity and maintain pre‐dam alluvial sedimentation regimes. Toledo Bend reservoir has a capacity: annual inflow ratio of 1.2 and impounds 74% of the Sabine drainage basin, yet there has been minimal geomorphic response in the lower river, which may seem counterintuitive. However, the complex linked geomorphic processes of discharge, sediment transport and loads, tributary inputs, and channel erosion include interactions which might increase as well as decrease sediment loads. Furthermore, if a stream is transport‐limited before impoundment, the reduced sediment supply after damming may have limited impact. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis and management of unseasonal flooding in the Barmah–Millewa Forest, Australia
Authors: Chong Joanne , Ladson Anthony R.
Published: March 2003

The Barmah‐Millewa Forest is the largest red gum forest in the world and lies adjacent to the middle reaches of Australia's River Murray. Regulation of the River Murray, to supply water for irrigation, has changed the watering regime of the forest and thus is degrading its environmental values. The watering regime has been changed in two ways: (1) there are now fewer large winter/spring events that inundate extensive areas because these floods are mitigated by irrigation storages; and (2) there are more small summer/autumn events that flood low‐lying areas and are caused by the way the river is operated to supply irrigation demand. The increased frequency of these small unseasonal floods is the subject of this paper.

During the irrigation season, water to meet irrigation requirements must be released four days in advance to allow for travel time from storages to irrigation areas upstream of the Barmah‐Millewa Forest. If there is heavy summer rainfall, irrigators cancel their orders so the flow that would have been diverted, remains in the river and causes a small ‘rain rejection’ flood. At the same time, river freshets from unregulated tributaries can also increase river flows. The River Murray channel in this area has low capacity and these high flows result in water spilling into the forest. Based on analysis of pre‐regulation conditions (1908–1929) and current conditions (1980–2000), forest flooding has increased from 15.5% of days to 36.5% of days between December and April. In particular, small, localized floods, which cover less than 10% of the forest, occur at least eight times more frequently now, than before regulation. Work by others has related these hydrologic changes to tree death and changes in floristic structure in wetland systems. There are also economic costs because much of the water that spills into the forest is not available for irrigation.

Two solutions to unseasonal flooding are described in this paper. One is to limit the maximum flow in the river during the irrigation season so there is capacity to convey at least some of the rain rejection flows without spilling water into the forest. The other is to maintain airspace in a diversion weir (Lake Mulwala) upstream of the forest to store the surplus water when orders are cancelled. Preliminary economic analysis shows the preferred option is to increase airspace in Lake Mulwala which provides net benefits of at least Aus$1.4 million per year along with unquantified environmental benefits from decreased unseasonal forest flooding. Copyright © 2003 John Wiley & Sons, Ltd.
Newton‐SOR method for fast statistical tomographic image reconstruction
Authors: Kudo Hiroyuki , Sawada Shinji
Published: March 2003

There are recent studies on image reconstruction for emission CT and transmission CT, using the maximum likelihood (ML) estimation or the maximum a posteriori (MAP) estimation, aiming at quality improvement of the reconstructed image. Those methods in general have the problem that minimization of the convex cost function by iterations is required, which increases the computational complexity. This paper proposes a new image reconstruction method, which requires less computation per iteration and realizes a fast convergence. The proposed method is based on the principle that the convex cost function is approximated in the iteration by a quadratic function, and the value of the quadratic function is reduced by SOR method, which is the solution procedure for the linear equation. The method can be called the Newton‐SOR method in the sense that both methods are combined. In order to guarantee global convergence of the Newton‐SOR method, mathematical techniques, called trust region and line search methods, are used, and the projection SOR method with the nonnegative condition is used, where a negative value appearing in the iteration is replaced by zero. The proposed method satisfies all of the desired properties of the iteration method as follows. (1) The convergence to the true solution minimizing the cost function is guaranteed. (2) The computational complexity per iteration is less, and a fast convergence is realized. (3) The method can be applied in a unified way to a wide range of convex cost functions. (4) The nonnegative condition can be handled easily. The effectiveness of the proposed method is demonstrated by a simulation experiment. The result of application to the clinical PET data is also shown. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(4): 1–11, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10178
CMOS Single‐chip Gas Detection Systems: Part II
Authors: Hagleitner C. , Hierlemann A. , Baltes H.
Published: March 2003

Sensor arrays based on industrial CMOS‐technology combined with post‐CMOS micromachining (CMOS MEMS) are a promising approach to low‐cost sensors. In the first part of this article [1], the state of research on CMOS‐based gas sensor systems was reviewed, and a platform technology for monolithic integration of three different transducers on a single chip was described. In this second part, the transduction principles of three polymer‐based gas sensors are detailed and the read‐out circuitry is portrayed. The first transducer is a micromachined resonant cantilever. The absorption of analyte in the chemically sensitive polymer causes shifts in resonance frequency as a consequence of changes in the oscillating mass. The cantilever acts as the frequency‐determining element in an oscillator circuit, and the resulting frequency change is read out by an on‐chip counter. The second transducer is a planar capacitor with polymer‐coated interdigitated electrodes. This transducer monitors changes in the dielectric constant upon absorption of the analyte into the polymer matrix. The sensor response is read out as a differential signal between the coated sensing capacitor and a passivated reference capacitor, both of which are incorporated into the input stage of a switched capacitor second‐order ΣΔ‐modulator. The third transducer is a thermoelectric calorimeter, which detects enthalpy changes upon ab‐/desorption of analyte molecules into a polymer film located on a thermally insulated membrane. The enthalpy changes in the polymer film cause transient temperature variations, which are detected via polysilicon/aluminum thermocouples (Seebeck effect). The small signals in the μV‐range are first amplified with a low‐noise chopper amplifier, then converted to a digital signal using a ΣΔ‐A/D‐converter and finally decimated and filtered with a digital decimation filter.
Market Data — Sensors in Household Appliances
Authors: Tschulena Guido R.
Published: March 2003

In Europe, the household industry produces millions of washing machines, dishwashers, cookers, refrigerators, home comfort appliances, small appliances, heating and climate control and security and safety‐related devices. Here, the use of sensors and microsystem products has a long tradition regarding relatively simple devices, such as temperature sensors or level sensors. However, the rate of introduction of new and improved sensors in household appliances has now increased, and the use of modern sensors with intelligent control systems is a key for differentiation between different appliance products and companies. Therefore, some more general sensor application areas are described, and also specific sensors which have been developed in recent years. Additionally, an outlook is given for possible new products and features which may be introduced in the future.
XPS in‐depth composition study on commercial monocrystalline silicon solar cells
Authors: Ariza M. J. , Martín F. , Leinen D.
Published: March 2003

From large‐scale production, two monocrystalline silicon solar cells of different quality, i.e. ISC = 3.0 A (good cell) and ISC = 1.6 A (bad cell), have been studied by XPS combined with 4 keV Ar+ depth profiling. Depth profiling was carried out through the anti‐reflection coating (TiO2), the passivation layer (SiO2) and up into the phosphorus‐doped silicon bulk. At the solar cell surface the elemental composition is similar for both cells, although the bad one presents slightly more carbon, phosphorus and lead but less silver than the good one. During profiling, carbon and silver could be followed by XPS. It was found that the carbon content is distinguishably higher in the bad cell than in the good one. Furthermore, it was found that silver atoms have not diffused in the same way in both cells. Only the good cell presents silver atoms up into the silicon bulk. Copyright © 2003 John Wiley & Sons, Ltd.
Characterization of Sb2O3 subjected to different ion and plasma surface treatments
Authors: Reiche R. , Holgado J. P. , Yubero F. , Espinos J. P. , Gonzalez‐Elipe A. R.
Published: March 2003

This paper presents a study of Sb2O3 subjected to oxygen plasma and to ion beam bombardment (Ar+ and O2+ ions of 4 keV) by x‐ray photoelectron and reflected electron energy‐loss spectroscopies. Changes in stoichiometry (i.e O/Sb ratio) and oxidation state of Sb have been detected and correlated with the chemical and ballistic effects of the beams used for alteration of the Sb2O3 surface. Thus, oxygen plasma treatments lead to a significant oxidation of the surface layers of this material with the formation of up to 51% Sb5+ species as found by Sb 4d curve‐fitting analysis. By contrast, O2+ ion bombardment only produces a mild oxidation of the target with the formation of ∼13% Sb5+ species. Argon ion bombardment induces a complex process where Sb5+ and Sb0 species are formed simultaneously. This result has been discussed in terms of a disproportionation reaction of the type Sb3+ → Sb5+ + Sb0. The changes in the electronic properties of the treated material are consistent with the loss upon oxidation to Sb5+ of the valence states associated to the 5s2 electron pair of antimony. Approximate shapes of valence bands for Sb2O3 and Sb2O5 pure compounds have been extracted by applying factor analysis to valence band spectra of Sb2O3 subjected to different ion and plasma treatments. Copyright © 2003 John Wiley & Sons, Ltd.
Calculation of electron inelastic mean free paths (IMFPs) VII. Reliability of the TPP‐2M IMFP predictive equation
Authors: Tanuma S. , Powell C. J. , Penn D. R.
Published: March 2003

We report comparisons of electron inelastic mean free paths (IMFPs) determined from our predictive IMFP equation TPP‐2M and reference IMFPs calculated from optical data. These comparisons were made for values of the parameter Nv (the number of valence electrons per atom or molecule) that we have recommended and those that were recommended in a recent paper by Seah et al. (Surf. Interface Anal. 2001; 31: 778). The comparisons were made for eight elemental solids (K, Y, Gd, Tb, Dy, Hf, Ta and Bi) and two compounds (KBr and Y2O3) for which there were appreciable differences in the recommended Nv values from the two sources and for which optical data were available for the IMFP calculations. The average of the root‐mean‐square (RMS) deviations for the ten materials between IMFPs from the TPP‐2M equation with our Nv values and the reference IMFPs was 11.0%, whereas the corresponding average with the Seah et al. Nv values was 20.2%. The larger average in the latter comparison was mainly due to large (>20%) RMS deviations for four materials (K, Hf, Ta and KBr). For the other six materials, the RMS deviations with the Seah et al. values of Nv were similar to those with our values of Nv. Based on the comparisons for these ten materials, we believe that it is preferable to use our values of Nv in the TPP‐2M equation. Copyright © 2003 John Wiley & Sons, Ltd.
SIMS/XPS characterization of surface layers formed in 3 mass% Si‐steel by annealing in oxygen at low partial pressure
Authors: Suzuki S. , Yanagihara K. , Yamazaki S. , Tanaka K. , Waseda Y.
Published: March 2003

Selective oxidation in silicon steel shows several interesting phenomena, such as the formation of an internal oxidation zone that depends on the oxidation conditions and the steel composition. In this work, SIMS and XPS were used for characterizing the formation processes of surface layers formed during selective oxidation of a typical silicon steel. The starting material is a secondary‐recrystallized 3 mass% Si‐steel sheet with a surface orientation of (011). Sample sheets were annealed at a temperature of 948–1023 K under an atmosphere with a low partial pressure of oxygen. The SIMS depth profiles show that the internal oxidation zone thickens and an iron‐rich layer that formed on the internal oxidation zone expands as the annealing temperature increases. Manganese and chromium levels increase outside the internal oxidation zone, whereas tin exists in the internal oxidation zone. The XPS results of the sample surface show that silicon and manganese levels increase on the sample surface to form oxides, and the chemical composition and state of these elements depend on the annealing temperature. In addition, tin increases on the surface of a relatively thick iron‐rich layer that formed on the internal oxidation layer. These experimental results are discussed on the basis of the thermodynamic characteristics of the elements. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of photoelectron attenuation lengths in calcium phosphate ceramic films using XPS and RBS
Authors: Feddes B. , Vredenberg A. M. , Wolke J. G. C. , Jansen J. A.
Published: March 2003

Calcium phosphate (CaP) coatings are used to improve the biological performance of an implant. A technique that is often used to measure the composition of this material is XPS. When extremely thin coatings are measured, for example to study the interface between CaP and a substrate, the quantification of the XPS results is complicated by the varying attenuation lengths (ALs) of the photoelectrons at different energies. To correct for this, AL data are needed. In this work we measured these ALs by comparing XPS yields with the coating coverage (as measured by Rutherford backscattering spectrometry). We were able to determine the AL for several calcium and phosphorus peaks. Determination of the oxygen ALs was not possible owing to diffusion of oxygen into the polymeric substrates. For the peaks that are most often used for quantification of XPS yields (the Ca 2p and the P 2p peak), we found ALs of 21.8 × 1015 atoms cm−2 and 26.8 × 1015 atoms cm−2, respectively. Concentration profiles near the interface, growth mode and interfacial roughness appeared to have no measurable effect on the measured ALs. For the ALs, an energy dependence with an exponent of 0.55 was found. The measured ALs are best predicted by the empirical CS1 equation of Cumpson and Seah. Copyright © 2003 John Wiley & Sons, Ltd.
Power and sample size calculations for generalized regression models with covariate measurement error
Authors: Tosteson Tor D. , Buzas Jeffrey S. , Demidenko Eugene , Karagas Margaret
Published: March 2003

Covariate measurement error is often a feature of scientific data used for regression modelling. The consequences of such errors include a loss of power of tests of significance for the regression parameters corresponding to the true covariates. Power and sample size calculations that ignore covariate measurement error tend to overestimate power and underestimate the actual sample size required to achieve a desired power. In this paper we derive a novel measurement error corrected power function for generalized linear models using a generalized score test based on quasi‐likelihood methods. Our power function is flexible in that it is adaptable to designs with a discrete or continuous scalar covariate (exposure) that can be measured with or without error, allows for additional confounding variables and applies to a broad class of generalized regression and measurement error models. A program is described that provides sample size or power for a continuous exposure with a normal measurement error model and a single normal confounder variable in logistic regression. We demonstrate the improved properties of our power calculations with simulations and numerical studies. An example is given from an ongoing study of cancer and exposure to arsenic as measured by toenail concentrations and tap water samples. Copyright © 2003 John Wiley & Sons, Ltd.
Dynamic Cox modelling based on fractional polynomials: time‐variations in gastric cancer prognosis
Authors: Berger Ursula , Schäfer Juliane , Ulm Kurt
Published: March 2003

The most popular model used for survival analysis is the proportional hazards regression model proposed by Cox. This is mainly due to its exceptional simplicity. Nevertheless the fundamental assumption of the Cox model is the proportionality of the hazards. For many applications, however, this assumption is doubtful. Proposals to extend the Cox model for non‐proportional hazards to allow for dynamic effect structures usually either depend on prespecifications or require non‐standard estimation techniques and are thus not favoured in application. Moreover, tests to verify the dynamic effect structures are not straightforward or lack omnibus power. In this paper we propose a flexible method for modelling dynamic effects in survival data within the Cox framework. The method is based on fractional polynomials as introduced by Royston and Altman. This allows for a transformation of the dynamic predictor which leads back to the conventional Cox model and hence fitting is straightforward using standard estimation techniques. In addition, it offers the possibility of easily verifying the existence of time‐variation. We describe a model selection algorithm which selects time‐varying effects only when evidence is given in the data. We illustrate the properties of the approach in a simulation study and compare it with other methods. In a survival study of gastric cancer patients, we apply the approach to analyse dynamic structures in the effects of prognostic factors. Copyright © 2003 John Wiley & Sons, Ltd.
Two‐treatment comparison based on joint toxicity and efficacy ordered alternatives in cancer trials
Authors: Letierce Alexia , Tubert‐Bitter Pascale , Kramar Andrew , Maccario Jean
Published: March 2003

The primary goal of anticancer treatments is to attain efficacy, however toxicity could affect the course of the therapy. Methods have been proposed for comparing two treatments on the basis of the joint distribution for safety and efficacy outcomes, but they do not take into account the cumulative doses of drugs (chemotherapy) or radiation (radiotherapy) received by each patient. Moreover, these methods assume a parametric form for the joint distribution. In this paper we define a multi‐dimensional parameter including toxicity and efficacy outcomes and the dose at which one, none or both occur. Each patient is classified into an ordered category depending on the order of occurrence of these two criteria: the sooner the patient benefits from efficacy and/or the later he/she experiences toxicity, the better is the treatment. We then apply likelihood ratio tests with ordered alternatives. This procedure requires constrained maximum likelihood estimation via isotonic regression. A large set of simulations compares the proposed tests to other more usual tests and the results show a good power and a satisfactory type I error control. Our approach is illustrated with a multi‐centre randomized clinical trial involving patients with metastatic non‐seminomatous germ cell tumours. Copyright © 2003 John Wiley & Sons, Ltd.
Assessing non‐inferiority of a new treatment in a three‐arm clinical trial including a placebo
Authors: Pigeot Iris , Schäfer Juliane , Röhmel Joachim , Hauschke Dieter
Published: March 2003

In non‐inferiority trials, where non‐inferiority of a new experimental drug compared to an active control has to be shown, it may be advisable to use an additional placebo group for internal validation if ethically justifiable. The focus of this paper is on such designs. Assuming normality and homogeneity of variances we will derive a statistical test procedure which turns out to be equivalent to the assessment based on Fieller's confidence interval. Based on the power function of this test, sample size calculations are carried out to achieve a given power. Additionally, the optimal allocation of the total sample size is derived. As an alternative to this parametric procedure, the bootstrap percentile interval is discussed and finally compared with Fieller's confidence interval in a study on mildly asthmatic patients. Copyright © 2003 John Wiley & Sons, Ltd.