bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blue light‐emitting poly(p‐phenylenevinylene) derivatives containing alternating conjugated segments and aliphatic spacers
Authors: Mpallas John G. , Spiliopoulos Ioakim K. , Mikroyannidis John A. 
Published: March 2003

AbstractTwo new poly(p‐phenylenevinylene) derivatives were prepared by Heck coupling. They contained alternating conjugated segments on the basis of p‐distyrylbenzene and flexible nonconjugated spacers. The synthesized polymers P1 and P2 carried two m‐terphenyl of four tertbutyl pendants, respectively, per repeat unit. Both polymers were amorphous and exhibited satisfactory thermal stability. Polymer P1 displayed a limited solubility in common organic solvents, whereas P2 dissolved readily in these solvents. The glass‐transition temperature values were 128 °C for P1 and 37 °C for P2. The polymers emitted blue or violet‐blue light with photoluminescent maxima at about 445 and 460 nm for solutions and thin films, respectively. The bulky pendants reduced their tendency to form aggregates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1091–1098, 2003
Polyester polyols: Synthesis and characterization of diethylene glycol terephthalate oligomers
Authors: Kadkin Oleg , Osajda Karol , Kaszynski Piotr , Barber Thomas A. 
Published: March 2003

AbstractThe composition of polyester polyols derived from terephthalic acid (TPA) and diethylene glycol (DEG) was examined. The synthesis of individual oligomers 1,n is described. The compounds were characterized with 1H and 13C NMR, mass spectrometry, and elemental analyses. The resonance signals arising from aromatic protons in 1,n = 1–3 were identified in 1H NMR spectra of TPA‐DEG condensates. From 1H NMR studies and chromatographic separation, it was concluded that the condensation of TPA and DEG in a 1:2 molar ratio results in a mixture of linear oligomers 1 with the average ñ varying from 1.1 to 2.2, and containing about 2% of cyclic oligomer 2. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1114–1123, 2003
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

AbstractThe 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

AbstractThe 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

AbstractNanocomposites 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

AbstractWe 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

AbstractWe 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

AbstractIn 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

AbstractUnambiguous 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

AbstractA 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

AbstractStarting 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

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractLocalized 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

AbstractEuS–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

AbstractMotivated 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

AbstractElectrical 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

AbstractWe 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

AbstractWe 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

AbstractPenson–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

AbstractTemperature 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

AbstractThe 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

AbstractThe 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).