bluuebunny/crossref_metadata_2025 huggingface dataset:
Chains anisotropy in PDMS networks due to friction on gold surfaces
Authors: Elzein Tamara , Galliano Anthony , Bistac Sophie
Published: May 2004

In this article, we describe an experimental friction study of poly(dimethyl siloxane) (PDMS) networks on metallic substrates such as gold‐coated slides, and under different conditions. The friction generates a transfer of a thin layer of PDMS and a preferential orientation of the polymer chains at the interface. However, the characterization of this layer is complicated, given the small amount of matter and the contact with a metallic surface. The polarization‐modulation infrared reflexion‐absorption spectroscopy (PM‐IRRAS), which is an excellent tool for anisotropy and orientation studies, was used to characterize the PDMS transferred layer. Our results showed an induced anisotropy due to the friction, and in which PDMS chains are lying parallel to the gold substrate surface. Our spectroscopic analyzes allowed us to imagine a scheme of PDMS transfer on the gold surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2348–2353, 2004
1,2‐polybutadiene complexes with d8 pseudo‐square‐planar transition‐metal salts based on nickel(II), palladium(II), and platinum(II)
Authors: Belfiore Laurence A. , Das Pronab K.
Published: May 2004

The effects of four d8 transition‐metal complexes from Group 10 on the thermal, mechanical, optical, and spectroscopic properties of atactic 1,2‐polybutadiene are compared, in addition to their ability to induce gelation. Olefin coordination and subsequent metal‐catalyzed chemical crosslinking occur much more quickly, and to a greater extent, at ambient temperature with PdCl2(CH3CN)2 than with PtCl2(C6H5CN)2. Alkene side groups in the polymer attack the pseudo‐square‐planar metal center (i.e., Pd2+ or Pt2+) from above or below the plane of the coordinatively unsaturated low‐molecular‐weight organometallic complex and displace neutral acetonitrile or benzonitrile ligands via an associative mechanism. Gelation occurs much more quickly with Pd2+ than with Pt2+, and the ambient‐temperature elastic modulus of solid polybutadiene/palladium complexes increases significantly, without high‐temperature annealing, so that a weak rubbery polymer is transformed into a glass via 3 mol % Pd2+. Alkene functional groups in the side chain of the polymer do not coordinate to bis(dimethyl)glyoximatonickel(II) at ambient temperature because (1) it is difficult to displace anionic dimethylgloxime ligands that are bidentate; (2) these planar nickel complexes with C2h symmetry are stacked along the c axis via interlocking methyl groups on adjacent molecules; and (3) there is a lack of π back‐bonding between dxy on Ni(II) and empty π* antibonding orbitals of CC, which typically stabilizes olefin complexes with pseudo‐square‐planar d8 metal centers. Pseudo‐octahedral nickel(II) chloride hexahydrate does not form a complex with the polymer, in agreement with some macroscopic properties of these materials. The observed trend in the transition‐metal‐modified properties of atactic 1,2‐polybutadiene in the solid state and in the gel state is Pd(II) > Pt(II) ≫ Ni(II). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2270–2285, 2004
Surface modification of clay and its effect on the intercalation behavior of the polymer/clay nanocomposites
Authors: Lee Sang‐Soo , Kim Junkyung
Published: May 2004

Melt intercalation of the methylsilylated organoclays with polar polymers such as SAN was examined to verify the adhesive role of guest polymeric chains between hydrophilic clay layers, so‐called “glue effect” on intercalation behavior. Once methylsilylated organoclay was melt‐blended with SAN, it was found that the mixture presented significant retardation of increase of interlayer spacing, d001 with heating time, and a noticeable decrease of d001 after the methylsilylation of organoclay, implying that the diffusion of SAN was highly suppressed by the decrease of polar interaction force caused by conversion of OH to methylsiloxyl groups. However, when applying shear force for the methylsilylated organoclay/SAN nanocomposites during melt intercalation, a noticeable increase of d001 was observed, expressing that intercalation of clay by SAN occurred much more effectively because of the reduction of gluing force between host clay and guest polymers, which was well supported by dramatic improvements of mechanical properties after methylsilylation of organoclays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2367–2372, 2004
Magneto‐optical properties of Bi‐YIG nanoparticle with polymethacrylate matrix materials
Authors: Kim Tae‐Youb , Yamazaki Yohtaro , Hirano Teruyoshi
Published: May 2004

New magneto‐optical Bi1.8Y1.2Fe5O12 nanoparticle hybridized materials have been developed which are composed of the nanoparticles and methyl, ethyl and butyl methacrylate matrix with poly(methyl methacrylate). The Bi1.8Y1.2Fe5O12 nanoparticles were prepared with coprecipitation and heat‐treatment processes. The hybridized systems were prepared by a mechanical milling process. The magneto‐optical properties of the solidified clear materials were measured. The Faraday rotation angle θF was about 19°/cm and the figure of merit θF/α was about 1.3° at 520 nm for the Bi1.8Y1.2Fe5O12 nanoparticle and ethyl methaclyrate hybrid material. These hybrid material systems have the very attractive feature of an easy molding ability. This property is important for mass production processes of magneto‐optical devices. The Bi‐YIG nanoparticle dispersed fluid and its stiffened bulk material are new promising magneto‐optical materials. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Origin of the magnetic moment enhancement of the ordered Fe50Co50 alloys
Authors: Park C. H. , Kim I. G. , Lee B. C. , Lee J. I.
Published: May 2004

We investigated the physical origin of the magnetic moment enhancements of the ordered Fe50Co50 alloys with B2 and L10 structures by using the all‐electron total‐energy full‐potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation. Pure Fe and Co with the Wigner‐Seitz radii taken from the alloys are also calculated for comparsion. It is confirmed that the magnetic moments of Fe in the alloys are enhanced significantly, while those of Co remain almost unchanged. The Fe magnetic moment enhancement in the alloy originates from “spin–flipping” of t2g electrons caused by the increase of the exchange splitting which makes the majority d electrons filled completely. In the case of the Co magnetic moment in the alloys, the spin‐up d band is already filled up in the pure phases, hence the magnetic moment stability against the alloy formation is preserved. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Novel phase modulation of magnetoresistance oscillations in Kondo/superconducting hybrid loops
Authors: Eom Jonghwa , Shin Yun‐Sok , Lee Hu‐Jong
Published: May 2004

Low temperature transport measurements have been performed for Kondo AuFe/superconducting hybrid loops. For both 26‐ppm‐AuFe/Al loop and 70‐ppm‐AuFe/Al loop, magnetoresistance shows Aharonov‐Bohm type oscillation with a period corresponding to the superconducting flux quantum. The phase of the oscillations can be modulated by applying dc bias current through the samples. However, phase shift by the dc current is so effective that only 26‐μA‐current can induce 2π change. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of a ferromagnetic Heusler alloy Co2MnSn
Authors: Lee Gahee , Kim I. G. , Lee J. I. , Jang Y.‐R.
Published: May 2004

The electronic and magnetic properties of the MnSn terminated (001) surfaces of the ferromagnetic full‐Heusler alloy Co2MnSn with half‐metallic character are investigated theoretically by using the all‐electron full‐potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) for exchange and correlation. The calculated magnetic moment for surface Mn (3.68 μB) exhibits much enhanced value compared with the bulk moment (3.17 μB). We can see that the MnSn terminated surface also affects the Co magnetic moment on the subsurface layer (1.10 μB) to be slightly larger than the bulk value (0.98 μB). The local magnetic moment on the Sn site couples antiferromagnetically to Mn moment with a very small value (less than 0.1 μB). The calculated density of states (DOS) shows that there is a very small finite spin‐down DOS at the Fermi level instead of a band gap for the Mn surface layer, which indicates that the half‐metallicity may be destroyed by surface states for the MnSn teminated surface. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transfer ratio of magnetic tunnel transistors with various Schottky materials
Authors: Hirose Takakazu , Fujiwara Yuji , Jimbo Mutsuko , Kobayashi Tadashi , Shiomi Shigeru
Published: May 2004

The transfer ratio and the magneto‐current were investigated for magnetic tunnel transistors with various Schottky materials. In the transistor with a Au/n‐Si Schottky junction, a transfer ratio of 0.81 × 10−4 and a magneto–current of 280% were obtained with an emitter voltage of 1.0 V. On the other hand, a transfer ratio of 0.76 × 10−3 and a magneto‐current of 110% with an emitter voltage of 1.0 V were obtained in the transistor with a NiFe/n‐Si Schottky junction. Thus the transfer ratio of the transistor with NiFe/n‐Si Schottky junction was about one order of magnitude larger than that with Au/n‐Si junction. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of Fe catalysts included in carbon nanotubes
Authors: Jang Jae Won , Lee Kyu Won , Lee Cheol Eui , Lee Tae Jae , Lee Cheol Jin , Lyu Seung Chul
Published: May 2004

We have synthesized multiwalled carbon nanotubes (MWNTs) including Fe catalysts by the vapor phase growth method at 950 °C. Different Fe concentrations were obtained by varying the Ar and CO flow rates during the vapor phase growing of the MWNTs. Magnetic properties of the MWNTs with different Fe concentrations were characterized by means of SQUID measurements in the temperature range of 5–300 K. As a result, superparamagnetic behaviors were observed at all the Fe concentrations. The form of the Fe catalysts included in MWNTs was discussed in view of the change of the average magnetic moment and the number of Fe particles with changing Fe concentration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Behavior of precipitates in GaMnN
Authors: Lee K. J. , Yu F. C. , Kim J. A. , Kim D. J. , Kim B. G. , Kang Y. H. , Kim H. J. , Ihm Y. E.
Published: May 2004

The behavior of precipitates in magnetic GaMnN films upon annealing was investigated. The major precipitate was Mn3GaN phase in GaMnN layers grown via molecular beam epitaxy using a single GaN precursor under high Mn flux. With heat treatment of the films, the Mn3GaN phase decomposed and a part of it was converted to magnetic Mn3Ga phase through detachment of nitrogen. The decomposition kinetics was further accelerated by neutron irradiation, which generated defects in the lattice and assisted the decomposition of the precipitates. The saturation magnetization of the homogeneous GaMnN layer was increased after the heat treatment while it was decreased in the precipitated GaMnN layer. The increase and decrease of the magnetization of the heat‐treated GaMnN films was explained consistently by the role of the precipitates in the films. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Highly ordered macroporous magnetic materials prepared by electrodeposition through colloidal template
Authors: Kim J. C. , Kim Y. N. , Hur N. H. , Kim W. S. , Kang Y. G.
Published: May 2004

We report magnetic properties of macroporous magnetic materials with highly ordered spherical voids prepared by an electrochemical technique. The interstitial sites in close‐packed arrays of colloidal silicas were filled by the electrodeposition of Fe, Co, and Fe3O4. The silica templates were removed by soaking the deposited templates into a 2% HF solution. SEM images of the template‐free macroporous magnetic materials clearly exhibit spherical voids arranged in a three dimensionally ordered structure. The magnetization curves of the Fe and Co films show a decreasing tendency with decreasing temperature, which might be associated with magnetic polarization and domain wall propagation. On the other hand, the Fe3O4 film exhibits a typical ferromagnetic behavior but has the reduced Curie temperature, which is due to the 2D Heisenberg type of the Fe spins. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mössbauer studies of the Cr doped ordered perovskite
Authors: Ahn Geun Young , Kim Je Hoon , Park Seung‐Iel , Kim Chul Sung
Published: May 2004

The Cr doped ordered perovskite powder of Sr2Fe0.93Cr0.07MoO6 has been prepared by a solid‐state reaction method. The chemical composition and the crystalline structure of the sample were confirmed with the Rutherford backscattering spectrometer spectrum and X‐ray diffraction pattern analysis. The crystalline structure was determined to be tetragonal with lattice parameters a0 = 5.572 Å and c0 = 7.900 Å, respectively. The magnetic properties of the Sr2Fe0.93Cr0.07MoO6 have been studied by the vibrating sample magnetometer and the Mössbauer spectroscopy. The saturation magnetization and the coercive force were 26.5 emu/g and 101.2 Oe at room temperature. Mössbauer spectra measurements of the Sr2Fe0.93Cr0.07MoO6 have been taken at various temperatures ranging from 15 to 450 K. Analysis of Mössbauer spectra has considered with next nearest‐neighbour interactions and the anisotropic hyperfine field fluctuation. The anisotropic field fluctuation of +H (P+ = 0.85) is greater than that of −H (P− = 0.15). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of inverse magnetoresistance in perovskite oxide tunnel junctions
Authors: Noh J. S. , Eom C. B. , Lagally M. G. , Sun J. Z. , Kim H. C.
Published: May 2004

We have observed a distinct inverse magnetoresistance in a hybrid tunnel junction. Two types of perovskite oxides, La0.67Sr0.33MnO3 and SrRuO3, were used as ferromagnetic electrodes with an SrTiO3 barrier in between them. Micron‐scale junctions were fabricated from 90° off‐axis sputtered trilayers, using standard optical lithography. Homo‐junctions that incorporate either La0.67Sr0.33MnO3 or SrRuO3 as both electrodes showed only normal positive magnetoresistances. In contrast, a clear inverse magnetic switching was found at 10 K for the hybrid junction. The spin polarization of SrRuO3 is about –9% as calculated based upon Julliere model, which is in quantitative agreement with the value (–10%) determined by the earlier tunneling experiment on SrRuO3/SrTiO3/Al structures. This is not only the manifestation of the existence of a negatively polarized material at the Fermi level, but also demonstrates that the widely‐cited Julliere model is applicable even to a negative polarization case. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Valence changes in La1−xCaxMnO3 thin films by NEXAFS
Authors: Lee Y. S. , Shin H. J. , Lee Y. P.
Published: May 2004

La1−xCaxMnO3 (LCMO) thin films were prepared on LaAlO3 (100) substrate by rf magnetron sputtering with various deposition conditions, i.e., temperature, thickness, composition, etc. The Mn valence states associated with the ferromagnetic transition of LCMO films have been investigated by using the O K‐edge X‐ray absorption spectra. The Mn4+/Mn3+ ratio in LCMO films changed by deposition conditions. It was found that the deposition condition in film fabrication leads to a change not only in Mn valence states, but in ferromagnetic transition. Finally, the valence states in LCMO films can be controlled by depositon conditions such as temperature, thickness, and composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A first‐principles study on the magnetism of an Fe chain along the [110] direction on Cu(001)
Authors: Jin Ying Jiu , Kim In Gee , Lee Jae Il
Published: May 2004

The electronic structures and magnetism of an Fe chain along the [110] direction on Cu(001) (Fe[110] chain) were investigated by using the all‐electron full‐potential linearized augmented plane‐wave method within the generalized gradient approximation. The calculated results showed that the Fe magnetic moment of the Fe[110] chain is 2.99 μB/atom. This value is much larger than that (2.22 μB/atom) of the bcc bulk iron, but the value is smaller than that (3.20 μB/atom) of the free standing Fe chain and that (3.11 μB/atom) of the Fe chain along the [010] direction on Cu(001). Large enhancement of the Fe magnetic moment of the Fe[110] chain is explained by the localization of the Fe d‐band due to the reduced coordination number which is confirmed from the calculated spin‐polarized layer‐projected density of states. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
EPR study of Pr0.7Sr0.3−xBaxMnO3 lanthanum manganites
Authors: Quang P. H. , Chung Y. S. , Ulyanov A. N. , Pismenova N. E. , Yu S. C.
Published: May 2004

Among the wide variety of colossal magnetoresistance materials the Pr‐compositions occupy some special places. Namely, in zero magnetic field the Pr1−yCayMnO3 samples are insulators for any level of Ca doping and show low field hysteresis. Pr0.7Ba0.3MnO3 composition is also insulating at low as well as at high temperatures. The combined Pr‐ and (Sr, Ba)‐doped perovskite‐like manganites should show interesting properties due to the large difference between the Pr and Sr, Ba ionic size. In this work we present an electron paramagnetic resonance (EPR) study of Pr0.7Sr0.3−xBaxMnO3 perovskite (x = 0.00, 0.15 and 0.30). We observed that the intensity of the EPR line decreases exponentially with temperature. The activation energy values derived from the temperature dependencies of EPR line intensity equals 0.16 eV, 0.09 eV and 0.08 eV for the x = 0.00, 0.15 and 0.30 compositions, respectively. The temperature dependence of the EPR linewidth showed a minimum near the TC. The temperature and concentration dependencies of EPR linewidth and line intensity will be discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First principles calculations on electronic structure and magnetism of (CrAs)1(GaAs)x (x = 1, 3, and 5) superlattices
Authors: Cha Gi‐Beom , Cho Sunglae , Hong Soon C.
Published: May 2004

Recently CrAs, which has a NiAs structure in nature, was grown epitaxially in a zinc‐blende structure on a GaAs substrate and was proved to be a ferromagnetic half‐metal with Curie temperature over 400 K. In this study, we investigated zinc‐blende bulk CrAs and (CrAs)1(GaAs)x (x = 1, 3, and 5) superlattices, using the full‐potential linearized augmented plane‐wave method based on local spin density approximation. Their ferromagnetic states were found to be energetically more stable, compared to their antiferromagnetic states. The magnetism and electronic structure of CrAs in the superlattices were not modified significantly from those of the bulk zinc‐blende CrAs. The calculated total magnetic moments per Cr are 3.0 μB for all the systems, and As atoms are coupled antiferromagnetically to the Cr atoms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large magnetocaloric effect in La0.845Sr0.155Mn1−xMxO3 (M = Mn, Cu, Co) perovskites
Authors: Phan Manh‐Huong , Phan The‐Long , Yu Seong‐Cho , Tho Nguyen Duc , Chau Nguyen
Published: May 2004

We present the results of an investigation on the magnetocaloric effect in the perovskites of La0.845Sr0.155Mn1−xMxO3 (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto‐caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu‐doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic‐paramagnetic transition temperature (TC) – which is experimentally verified by electron paramagnetic resonance study. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and transport properties of La0.5Sr0.5(FexCo1−x)O3 (0 ≤ x ≤ 0.2) perovskites
Authors: Phan T. L. , Huynh T. N. , Phan M. H. , Khiem N. V. , Phuc N. X. , Chung Y. S. , Rhee J. R. , Yu S. C.
Published: May 2004

The magnetic and transport properties of La0.5Sr0.5(FexCo1−x)O3 (0 ≤ x ≤ 0.2) compounds were investigated. TC decreased slightly and the resistivity increased, even with a very small extent of Fe substitution. The Fe substitution induced additional antiferromagnetic Fe–O–Fe interactions that suppress strongly the ferromagnetism and conductivity, thus causing a separation between two phases at around 124 K for both x = 0.1 and 0.2 compositions. Spin‐glass behavior was observed for the Fe‐doped samples. The resistivity, can be described by the Mott's variable range hopping model in the low temperature region.
New materials search for spintronics applications: Synthesis of BiMn1−xFexO3 films via combinatorial chemistry
Authors: Yang C.‐H. , Song J. H. , Lee H. J. , Yoon S. , Koo T. Y. , Jeong Y. H.
Published: May 2004

The combinatorial chemistry method that employs multiple metal‐masks and shutters in the pulsed laser deposition of thin films was used to synthesize a series of BiMn1−xFexO3 (x = 0–0.4) films on single SrTiO3(001) substrates. The films showed a systematic variation of c‐axis x‐ray diffraction peaks with a discontinuity at x ∼ 0.15. They also possessed narrow full‐width‐at‐half‐maximum in the rocking curves. From the temperature dependence of magnetization, we were able to conclude that as substitution of Fe for Mn is increased, antiferromagnetic interaction becomes enhanced with consequent suppression of the ferromagnetic ordering and eventually antiferromagnetic states prevail below 45 K for x > 0.15. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoemission study of Zn1−xCoxO as a possible DMS
Authors: Wi S. C. , Kang J.‐S. , Kim J. H. , Lee S. S. , Cho S.‐B. , Kim B. J. , Yoon S. , Suh B. J. , Han S. W. , Kim K. H. , Kim K. J. , Kim B. S. , Song H. J. , Song H. J. , Shin H. J. , Shim J. H. , Min B. I.
Published: May 2004

We report a photoemission spectroscopy (PES) and X‐ray absorption spectroscopy (XAS) study for bulk Zn1−xCoxO samples (x = 0 and 0.1). Both the Co 2p XAS and the Co 2p core‐level PES spectra show that the doped Co ions in Zn1−xCoxO are in the divalent Co2+ (d7) states under the tetrahedral symmetry. A Co 2p → 3d resonant photoemission spectroscopy measurement shows that the Co 3d states lie near the top of the O 2p valence band. This work suggests that the doped Co ions in Zn1−xCoxO substitute properly for the Zn sites with Co2+ valence states. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structures and magnetic properties of Fen (n = 1–4) nanowires
Authors: Jo Chulsu , Lee J. I.
Published: May 2004

Spin polarized total energy and electronic structure calculations are performed for thin Fe nanowires using the ab initio pseudopotential plane wave method within generalized gradient approximation. Binding energy, density of states, and magnetic moment are calculated for planar and staggered thin Fe wires, which are composed of four atoms or less. The most stable configuration is attained in zigzag geometry of which the bond length is stretched relatively to the planar nanowire. The Fe‐zigzag wire has the largest magnetic moment among isomers. Upon stretching the Fe2‐zigzag wire to a linear one, the magnetic moment increased to be proportional to the nearest‐neighbor distance. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of spinel‐type magnetic semiconductor ZnCo2O4 by reactive magnetron sputtering
Authors: Kim Hyun Jung , Song In Chang , Sim Jae Ho , Kim Hyojin , Kim Dojin , Ihm Young Eon , Choo Woong Kil
Published: May 2004

We report the synthesis of spinel oxide ZnCo2O4 thin films and the effects of the oxygen partial pressure in the sputtering gas mixture on their electrical and magnetic properties. The conduction type and carrier concentration were found to be dependent on the oxygen partial pressure ratio: n‐type and p‐type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. A ferromagnetic coupling was observable in p‐type ZnCo2O4, whereas an antiferromagnetic interaction was found for insulating and n‐type ZnCo2O4 film, revealing hole‐mediated ferromagnetic transition in ZnCo2O4. Arrott plot analysis of magnetization data at 5 K also indicated non‐zero spontaneous magnetization for p‐type ZnCo2O4. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and characteristics of magnetic tunnel transistors using amorphous n‐type Si films
Authors: Lee S. S. , Lee J. Y. , Kim M. S. , Choi J. G. , Hwang D. G. , Rhie K. , Rhee J. R.
Published: May 2004

A magnetic tunnel transistor (MTT) device using an amorphous n‐type Si semiconductor film for the base and collector consisting of [CoFe/NiFe] (free layer) and Si (top layer) multilayers is used to study the spin‐dependent hot electron magnetocurrent (MC) and the tunneling magnetoresistance at room temperature. A large MC of more than 40.2% is observed at the emitter–base bias voltage VBE of 0.62 V. The increasing emitter hot current and transfer ratio with the increase of the emitter–base voltage are due mainly to a rapid creation of a number of conduction‐band states in the Si collector. However, above a VBE of 0.62 V, a rapid decrease of the MC is observed in an amorphous Si‐based MTT. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular quantum theory: Separable electronuclear wave functions and vibronic states—A generalized diabatic approach
Authors: Tapia O.
Published: May 2004

The linear superposition principle is used to represent chemical and physical processes. A quantum state representation is obtained for model molecular systems. An exact Hamiltonian is first introduced and thereafter approximated by a sum of Coulomb Hamiltonian, electron–phonon (e–ph), relativistic effects, and coupling to external fields. A sharp separability ansatz is used to study the Coulomb Hamiltonian first; the electronic part is fully represented in Hilbert space (q space); a background of positive charge replaces nuclei in real space (ξ space). This QC model leads to diabatic electronic functions and diabatic potential energy (DPE) surfaces in real space. Next, the nuclear masses are introduced via a kinetic energy operator and added to the DPEs. The attractor property of the diabatic electronic functions is used to study mass fluctuation regimes. Fluctuations, if quantized, lead to the Q2C model; mass dynamics takes place in real space. The set of product functions {ϕj(q)ζjl(ξ)} provides a base to represent arbitrary electronic states. In this context, the linear superposition principle is naturally introduced. The formulation of chemical reactions, pump–probe experiments and a detailed study of H are topics examined from the present perspective. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
DFT study of HCN and NCCN reactions with hydrogen species
Authors: Basiuk Vladimir A. , Kobayashi Kensei
Published: May 2004

Energetic feasibility of the formation of aminoacetonitrile (or glycine nitrile) through a sequence of reactions of cyanogen (NCCN) with hydrogen species was evaluated, using density functional theory (DFT) calculations at the B3LYP/ 6‐31++G(d,p) theoretical level. A critical step in the cyanogen hydrogenation is the addition of first H atom. As a result of a positive activation barrier of ∼3–6 kcal mol−1 (depending on the attachment site), this process is hardly feasible under cold gas‐phase interstellar conditions, but might possibly be facilitated in the solid phase by proton tunneling effects. The addition of a third hydrogen atom requires much lower activation energy, especially if H adds on the NH group (0.2–0.8 kcal mol−1). The second and fourth steps (combination of C2HN2 and C2H3N2 radical species with hydrogen atoms) are highly exothermic; the need to get rid of excess energy makes them possible through grain‐surface processes only. As a whole, most of the hydrogenation reactions under study can be expected to take place in the solid phase (icy and silicate grains), and not in the gas phase under cold interstellar conditions. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
A (1 + ϵ)‐approximation algorithm for partitioning hypergraphs using a new algorithmic version of the Lovász Local Lemma*
Authors: Salavatipour Mohammad R.
Published: May 2004

In his seminal result, Beck gave the first algorithmic version of the Lovász Local Lemma by giving polynomial time algorithms for 2‐coloring and partitioning uniform hypergraphs. His work was later generalized by Alon, and Molloy and Reed. Recently, Czumaj and Scheideler gave an efficient algorithm for 2‐coloring nonuniform hypergraphs. But the partitioning algorithm obtained based on their second paper only applies to a more limited range of hypergraphs, so much so that their work doesn't imply the result of Beck for the uniform case. Here we give an algorithmic version of the general form of the Local Lemma which captures (almost) all applications of the results of Beck and Czumaj and Scheideler, with an overall simpler proof. In particular, if H is a nonuniform hypergraph in which every edge ei intersects at most |ei|2αk other edges of size at most k, for some small constant α, then we can find a partitioning of H in expected linear time. This result implies the result of Beck for uniform hypergraphs along with a speedup in his running time. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004
Some bounds on the coupon collector problem
Authors: Martinez Servet
Published: May 2004

This work addresses on the coupon collector problem and its generalization introduced by Flajolet, Gardy, and Thimonier. In our main results, we show a ratio limit theorem for the random time of the generalized coupon collector problem, and, further, we give the leading term and the geometric rate for the distribution of this random time, when the number of throws is large. For the classical coupon collector problem, we give a bound on the conditional second moment for the number of visits to the coupons, relying strongly on a result of Holst on extremal distributions. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004
Teaching students “ideas‐about‐science”: Five dimensions of effective practice
Authors: Bartholomew Hannah , Osborne Jonathan , Ratcliffe Mary
Published: May 2004

In this paper, we report work undertaken with a group of 11 UK teachers over a period of a year to teach aspects of the nature of science, its process, and its practices. The teachers, who taught science in a mix of elementary, junior high, and high schools, were asked to teach a set of “ideas‐about‐scienc” for which consensual support had been established using a Delphi study in the first phase of the project. Data were collected through field notes, videos of the teachers' lessons, teachers' reflective diaries, and instruments that measured their understanding of the nature of science and their views on the role and value of discussion in the classroom. In this paper, drawing on a sample of the data we explore the factors that afforded or inhibited the teachers' pedagogic performance in this domain. Using these data, we argue that there are five critical dimensions that distinguish and determine a teacher's ability to teach effectively about science. Whilst these dimensions are neither mutually independent nor equally important, they serve as a valuable analytical tool for evaluating and explaining the success, or otherwise, that individual teachers of science have when confronted with teaching aspects about science. In addition, we argue that they are an important means of identifying salient aspects of pedagogy for initial and in‐service training of science teachers for curricula that incorporate elements of “ideas‐about‐science” © 2004 Wiley Periodicals, Inc. Sci Ed, 88:655–682, 2004
Neurochemical interaction between dopaminergic and noradrenergic neurons in the medial prefrontal cortex
Authors: Pan Wynn H.T. , Yang Sze‐Yuan , Lin Shi‐Kwang
Published: May 2004

Growing evidence indicates that there is an interaction between the transmission of dopamine (DA) and norepinephrine (NE) in the noradrenergic and dopaminergic projections that converge in the medial prefrontal cortex (mPFC). The effects of the noradrenergic α1 and α2 receptors and the NE transporters on the DA outflow and those of the dopaminergic D1 and D2 receptors on NE release in the mPFC were investigated. Local infusions of NE (90, 150, and 300 nM) into the mPFC increased the extracellular release of DA in anesthetized rats. The α1 receptor antagonist (10 μM prazosin), but not the α2 receptor antagonist (100 μM piperoxan), blocked the NE‐induced increase of DA in the mPFC. In addition, local infusion of α1 receptor agonist (10 μM phenylephrine) enhanced DA release in the mPFC. Local application of DA in different concentrations into the mPFC increased extracellular NE levels. Intra‐mPFC infusion of a D1 receptor antagonist (10 nM SCH23390), inhibited the DA‐induced increase of NE; this did not happen with a D2 receptor antagonist (1 nM eticlopride). Local administration of a selective NE uptake inhibitor (1 μM desmethylimipramine) into the mPFC increased the outflows of both DA and NE in the mPFC. However, co‐infusion of DMI and prazosin blunted, but did not totally abolish, the DMI‐increase in the extracellular levels of DA and NE. These results suggest that in the mPFC, 1) extracellular NE could enhance DA release by activating the α1 receptors; and 2) extracellular DA increased the extracellular levels of NE by activating the D1 receptors. Synapse 53:44–52, 2004. © 2004 Wiley‐Liss, Inc.
Development of vigabatrin‐induced lesions in the rat brain studied by magnetic resonance imaging, histology, and immunocytochemistry
Authors: Preece N.E. , Houseman J. , King M.D. , Weller R.O. , Williams S.R.
Published: May 2004

Vigabatrin, the γ‐aminobutyric acid transaminase (GABA‐T)‐inhibiting anticonvulsant drug, was given orally at a dose of 275 mg/kg/day to rats (n = 6) in their feed for a period of 12 weeks, during which T2‐weighted magnetic resonance images (MRIs) and diffusion‐weighted MRIs (DWIs) were collected at weeks 1, 3, 6, 9, and 12. Half the rats (n = 3; and half their age‐matched littermate controls; n = 3) were then killed for histopathological confirmation of the observed VGB‐induced cerebellar and cortical white‐matter lesions. VGB was removed from the diet and additional MRIs of the remaining rats taken at weeks 14, 17, 20, and 24, at which time they (n = 3), along with remaining controls (n = 3), were also killed for histopathology. The T2‐weighted MRIs acquired were used to compute T2 relaxation time maps. Statistically significant VGB‐induced T2 increases were observed in the frontal and occipital cortices and in the cerebellar white matter (CWM). The cerebellar lesions were more clearly discerned by eye in the DWIs than by T2‐contrast alone. During the recovery period the VGB‐treatment group CWM‐T2 and CWM‐DWI hyperintensity greatly decreased as the reversible lesion disappeared. As expected, histological and immunocytochemical examinations demonstrated the presence of intra‐myelinic edema, microvacuolation, and reactive astrocytosis in the CWM and cortex after 12 weeks VGB‐treatment. In the remaining animals microvacuolation of the white matter had not completely resolved during the 12‐week recovery phase. The data show that quantitative MRI T2‐relaxometry can be used to detect VGB‐induced CNS pathology, and also suggest that DWI is particularly sensitive to the cerebellar lesion. The reversible neurotoxicity of global GABA‐elevation in experimental animals is discussed. Synapse 53:36–43, 2004. © 2004 Wiley‐Liss, Inc.
Unintended consequences of the Global Positioning System
Authors: Lever John A.
Published: May 2004

This article describes a framework for characterizing unintended consequences, especially in terms of the vernacular “Law of Unintended Consequences” as applied to the known and potential consequences of the Global Positioning System (GPS). It is shown that a subset of the unintended consequences related to the GPS belongs to the larger class of general locator devices. The risk of vulnerability of GPS is characterized in terms of impact of unavailability. The general usage or misuse effects are considered in the category of human factors. Privacy is treated in a legal context, and the potential losses of privacy from general locator devices are discussed. Also, legal devices to limit loss of privacy are described, as well as the use of locator devices by law enforcement agencies. The general framework of the article is to describe GPS as a particular case of the larger need to consider secondary consequences in the development and socialization of technology. © 2004 Wiley Periodicals, Inc. Syst Eng 7: 217–228, 2004
Expectant management of tubal ectopic pregnancy: prediction of successful outcome using decision tree analysis
Authors: Elson J. , Tailor A. , Banerjee S. , Salim R. , Hillaby K. , Jurkovic D.
Published: May 2004

Objective

To establish whether a decision tree based on a combination of clinical, morphological and biochemical parameters could be constructed to help in the selection of women with tubal ectopic pregnancies for expectant management.

Methods

This was a prospective observational study in a tertiary referral early pregnancy unit in an inner city teaching hospital. The study group consisted of 179 women with ultrasound diagnosis of ectopic pregnancy. Demographic, clinical and ultrasound data were recorded in each case at the initial visit. In addition all women had a blood sample taken for the measurements of serum β‐human chorionic gonadotropin (β‐hCG) and progesterone. Clinically stable women with non‐viable pregnancies and no signs of hematoperitoneum were managed expectantly on an outpatient basis until their serum β‐hCG declined to <20 IU/L. Women who developed pelvic pain during follow‐up and those with non‐declining serum β‐hCG were offered surgery.

Results

A total of 107/179 (59.8%) tubal ectopics were considered suitable for expectant management. Ectopic pregnancy resolved spontaneously in 75/107 (70%) women, which was 41.9% of the total number of tubal ectopics. Maternal age, initial serum β‐hCG and progesterone were all significantly different in pregnancies that resolved spontaneously compared to those requiring surgery (P < 0.05). Initial serum β‐hCG level was the best predictor of the outcome of expectant management. These differences enabled a construction of a four‐level decision tree to estimate the likelihood of successful expectant management.

Conclusions

There are significant differences in demographic, ultrasound and biochemical findings between spontaneously resolving ectopics and those requiring treatment. Decision tree analysis may be used as a guide to estimate the probability of successful expectant management in individual cases. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Intra‐ and interobserver repeatability of femur length measurement in early pregnancy
Authors: Rosati P. , Bartolozzi F. , Guariglia L.
Published: May 2004

Objective

To assess the intra‐ and interobserver reproducibility of songographic measurement of fetal femur length between 10 and 16 weeks of gestation.

Methods

Femur length was measured three times by the same trained observer in each fetus of 136 pregnant women. A second trained observer then repeated the measurements. The coefficient of variation, intraclass correlation coefficient and repeatability coefficient with 95% CIs were calculated for each observer and between the two observers.

Results

The inter‐ and intraobserver repeatabilities of femur length were good. For interobserver correlation, the coefficient of variation was 4.6% (95% CI, 3.0–6.2), the intraclass correlation coefficient was 0.82 (95% CI, 0.69–0.95) and the repeatability coefficient was 2.1 (95% CI, 1.8–2.7). For intraobserver correlation, the coefficient of variation was 4.2% (95% CI, 3.2–5.6), the intraclass correlation coefficient was 0.91 (95% CI, 0.75–0.97) and the repeatability coefficient was 3.23 (95% CI, 2.33–3.86) for Observer 2. Similar results were obtained for the other observer.

Conclusion

Transvaginal femur length measurement is technically feasible and easy to perform between 10 and 16 weeks of gestation. The high degree of intra‐ and interobserver repeatability indicates it to be a reproducible method. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Sequence variation of the Cytochrome b gene of various human infecting members of the genus Leishmania and their phylogeny
Authors: LUYO-ACERO G. E. , UEZATO H. , OSHIRO M. , TAKEI K. , KARIYA K. , KATAKURA K. , GOMEZ-LANDIRES E. , HASHIGUCHI Y. , NONAKA S.
Published: May 2004

The Cytochrome b (Cyt b) gene has proved to be useful for identification and classification of many mammals and plants. In order to evaluate the utility of this gene for discrimination of Leishmania parasites as well as for exploring their phylogenetic relationships, we determined the nucleotide sequences of the Cyt b gene from 13 human-infecting Leishmania species (14 strains) from the New and Old Worlds. The Cyt b genes, approximately 1080 base pairs, were found to be A/T rich, and their 5′ terminal-editing regions were highly conserved. The nucleotide sequence variation among them was enough to discriminate parasite species; 245 nucleotide positions were polymorphic and 190 positions were parsimony informative. The phylogenetic relationships based on this gene, showed good agreement with the classification of Lainson & Shaw (1987) except for the inclusion of L. (L.) major in the L. (L.) tropica complex and the placement of L. tarentolae in another genus. These data show that the Cyt b gene is useful for phylogenetic study of Leishmania parasites.
The potential signalling pathways which regulate surface changes induced by phytohormones in the potato cyst nematode (Globodera rostochiensis)
Authors: AKHKHA A. , CURTIS R. , KENNEDY M. , KUSEL J.
Published: May 2004

It has been demonstrated that the surface lipophilicity of the plant-parasitic nematodeGlobodera rostochiensisdecreases when infective larvae are exposed to the phytohormones indole-3-acetic acid (auxin) or kinetin (cytokinin). In the present study, it was shown that inhibition of phospholipase C (PLC) or phosphatidylinositol 3 kinase (PI3-kinase) reversed the effect of phytohormones on surface lipophilicity. The signalling pathway(s) involved in surface modification were investigated using ‘caged’ signalling molecules and stimulators or inhibitors of different signalling enzymes. Photolysis of the ‘caged’ signalling molecules, NPE-caged Ins 1,4,5-P3, NITR-5/AM or caged-cAMP to liberate IP3, Ca2+or cAMP respectively, decreased the surface lipophilicity. Activation of adenylate cyclase also decreased the surface lipophilicity. In contrast, inhibition of PI3-kinase using Wortmannin, LY-294002 or Quercetin, and inhibition of PLC using U-73122 all increased the surface lipophilicity. Two possible signalling pathways involved in phytohormone-induced surface modification are proposed.
Echinococcus granulosusstrain differentiation based on sequence heterogeneity in mitochondrial genes of cytochromecoxidase-1 and NADH dehydrogenase-1
Authors: OBWALLER A. , SCHNEIDER R. , WALOCHNIK J. , GOLLACKNER B. , DEUTZ A. , JANITSCHKE K. , ASPÖCK H. , AUER H.
Published: May 2004

Genetic analyses ofEchinococcus granulosusisolates from different intermediate host species have demonstrated substantial levels of variation for some genotype (strain) clusters. To determine the range of genetic variability within and between genotypes we amplified and cloned partialcox1andnadh1genes from 16 isolates ofE. granulosusfrom 4 continents. Furthermore, we sequenced different clones from a PCR product to analyse the intra-individual genetic variance. The findings showed a moderate degree of variance within single isolates and a significant degree of variance between the cluster of genotypes G1–G3 (sheep, Tasmanian sheep and buffalo strain), genotypes G4 (horse strain) and G5 (cattle strain) and the cluster of the genotypes G6 (camel strain) and G7 (pig strain). The variance of up to 2·2% within genotypes was relatively low compared with that of 4·3–15·7% among genotypes. The present results indicate that a re-examination of the classification of 5 genotypes ofEchinococcusis warranted. Hence, our data highly support a re-evaluation of the taxonomy of the clades G1–G3, G4, G5, G6/7 and G8 (cervid strain) within the genusEchinococcus.
Antioxidant enzymes in intramolluscanSchistosoma mansoniand ROS-induced changes in expression
Authors: ZELCK U. E. , VON JANOWSKY B.
Published: May 2004

Killing of intramolluscan schistosomes by host haemocytes is mediated by reactive oxygen metabolites. Hence, defence against oxidative damage is essential for the parasite to survive. In this study, expression of three key antioxidant enzymes, superoxide dismutase (EC 1.15.1.1), glutathione peroxidase (EC 1.11.1.9) and glutathione-S-transferase (EC 2.5.1.18) was determined inSchistosoma mansonimiracidia, sporocysts and cercariae. Stage-dependent expression of these enzymes was shown to be regulated at the transcriptional level. Second, the influence on enzyme expression of reactive oxygen species (ROS) and of haemocytes from schistosome-resistant and -susceptible host snails was determined. Generation of ROS by xanthine/xanthine oxidase resulted in increased transcript levels for all three enzymes. Addition of hydrogen peroxide induced a significantly increased expression of GPx and SOD but not GST. Snail haemocytes induced an up-regulation of SOD and GPx at 12 and 18 h post-exposure, respectively. Susceptible haemocytes elicited a stronger induction of transcript expression than resistant haemocytes. After 36–48 h, SOD remained up-regulated in sporocysts encapsulated by haemocytes from susceptible hosts, whereas a down-regulation of SOD and GPx occurred in schistosomes encapsulated by haemocytes from resistant snails. These observations indicate that schistosomes express elevated levels of antioxidant enzymes in interaction with haemocytes from susceptible snail hosts in which they survive. On the other hand, haemocytes of resistant snails may interfere with reactive oxygen detoxification via down-regulation of schistosome antioxidant enzymes, thus shifting the balance towards parasite killing.
Sexual transmission of a nematode parasite of Wood Mice (Apodemus sylvaticus)?
Authors: CLARKE J. R. , ANDERSON T. J. C. , BANDI C.
Published: May 2004

Sexual transmission occurs commonly in microparasites such as viruses and bacteria, but this is an unusual transmission route for macroparasites. Here we present evidence which suggests that a nematode parasite of Wood Mice (Apodemus sylvaticus) may be sexually transmitted and we have classified the nematode using molecular data. Wood Mice were collected annually in the course of work on their reproductive physiology. Larval nematodes were found in the epididymides of 19·6% of males. It seems likely that they would be transmitted to females at ejaculation. To identify these larval nematodes, which we were unable to do using morphological features, we sequenced the 18S rDNA. Sequence comparisons with the molecular phylogeny of Blaxteret al. (1998) demonstrated that they were bursate nematodes (Order Strongylida). The relationships between strongylid taxa were poorly resolved by 18S rDNA. However, both distance and parsimony analyses grouped the nematode with the superfamily Metastrongylidea in a clade containingFilaroidesandAngiostrongylussp. Importantly, the sequences were distinct from those ofHeligmosomoides polygyrusandAngiostrongylus dujardini, two common strongylid nematodes ofApodemus. We were therefore unable positively to identify these worms by matching their sequences with those from morphologically identifiable adult strongylid nematodes infectingApodemus. These results demonstrate that an as yet unidentified strongylid is quite commonly found in large numbers in the male reproductive tract of Wood Mice. Further work is required to understand the biology and transmission dynamics of this interesting system.