bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tunable spin‐injection and magnetoconductance in a novel 2DEG‐ferromagnet structure
Authors: Jiang Y. , Jalil M. B. A. 
Published: December 2002

AbstractIn this paper, we calculate the spin‐dependent ballistic transport through a two‐dimensional electron gas (2DEG) heterostructure sandwiched between two ferromagnetic metal (FM) layers. A strong spin‐injection effect is predicted when the magnetization directions of two FM layers are antiparallel. The spin‐injection rate can be tuned by both, applied voltage and magnetic field. The device also exhibits a significant magnetoconductance (MC) when the relative magnetization of FM layers is switched, which functions as a spin‐valve (SV). Using a GaAs system as a 2DEG material in our calculation, the MC can be tuned by both the applied voltage and the magnetic field, and reaches up to as high as 37.5%. The device's dual spin‐valve and spin‐injector characteristics open the possibility for spin electronic and sensor applications in semiconductor based systems.
Far‐infrared optical spectrum of donor impurities in quantum dots in a magnetic field
Authors: Pacheco M. , León A. , Barticevic Z. 
Published: December 2002

AbstractWe report calculations for far‐infrared absorption in GaAs/Ga1–xAlxAs quantum dots doped with shallow‐donor impurities in the presence of a magnetic field. The wave functions and the eigenvalues are obtained in the effective‐mass approximation by using a variational approach in which the ground and excited magneto‐impurity states are simultaneously obtained. The allowed intra‐donor transitions have been investigated by using far‐infrared radiation circularly polarized in the plane perpendicular to the magnetic field. We present results for the absorption coefficient as a function of the photon energy for several field strengths and arbitrary impurity positions. We have found that, as a consequence of the quantum dot confinement the infrared magneto‐absorption strongly depends on the position of the impurity in the dot.
Service innovations: second opinions in child and adolescent psychiatry
Authors: Richardson Greg , Cottrell David 
Published: December 2002

AIMS AND METHODSTo devise a protocol, reflecting best practice, for obtaining second opinions in child and adolescent psychiatry through discussion with consultants in child and adolescent psychiatry within the Yorkshire region at their quarterly meetings.ResultsThe major pressure for second opinions falls upon the Academic Unit of Child and Adolescent Mental Health and on the in-patient units. Other consultants who are considered to have specialist expertise in certain areas may also receive referrals for second opinions. Both consultants requesting and offering second opinions considered a protocol for obtaining them would be helpful to their practice.Clinical ImplicationsAn agreed protocol between consultants in child and adolescent psychiatry within a region ensures that young people with complex problems have access to second opinions on their diagnosis and management by consultants who can be recommended to referrers by other consultants. The network of consultants ensures such opinions are not requested excessively and that ‘rogue’ opinions without therapeutic follow-up are avoided.
Temperature‐Dependent Photonic Bandgap in a Self‐Assembled Hydrogen‐Bonded Liquid‐Crystalline Diblock Copolymer
Authors: Osuji C. , Chao C.‐Y. , Bita I. , Ober C.K. , Thomas E.L. 
Published: December 2002

AbstractWe take advantage of self‐assembly in a hierarchically structured, hybrid material to develop photonic bandgaps in the visible which may be systematically tuned by application of thermal or electric fields. Hydrogen bonding between a host polymer and a guest small molecule is used to augment the molecular weight of an appropriately selected coil–coil diblock copolymer to bring the microdomain structure onto the length scale needed for significant interaction with visible light. Further, the use of liquid‐crystal‐mesophase‐forming moieties as the guest hydrogen‐bonding units adds functionality to the system as the optical properties of the liquid‐crystalline domains can be modulated by external stimuli. We use hydrogen bonding to sequester varying amounts of imidazole terminated mesogens within the acid domains of a poly[styrene‐block‐poly‐(methacrylic acid)] (PS‐b‐MAA) diblock copolymer. The resulting PS‐b‐MAA/LC side‐group liquid‐crystalline diblock copolymer possesses a photonic bandgap in the green with the exact location and structure of the gap dependent on the composition of the system. Here, we discuss the structure and optical properties of these materials as a function of their composition and the response of the optical properties to temperature. Varying the order parameter of the LC domains by heating into the isotropic state changes the peak reflectivity by 40 nm, resulting in a color change from green to orange.
Super‐Hydrophobic Surfaces: From Natural to Artificial
Authors: Feng L. , Li S. , Li Y. , Li H. , Zhang L. , Zhai J. , Song Y. , Liu B. , Jiang L. , Zhu D. 
Published: December 2002

AbstractSuper‐hydrophobic surfaces, with a water contact angle (CA) greater than 150°, have attracted much interest for both fundamental research and practical applications. Recent studies on lotus and rice leaves reveal that a super‐hydrophobic surface with both a large CA and small sliding angle (α) needs the cooperation of micro‐ and nanostructures, and the arrangement of the microstructures on this surface can influence the way a water droplet tends to move. These results from the natural world provide a guide for constructing artificial super‐hydrophobic surfaces and designing surfaces with controllable wettability. Accordingly, super‐hydrophobic surfaces of polymer nanofibers and differently patterned aligned carbon nanotube (ACNT) films have been fabricated.
Light‐Emitting Silicon Nanocrystals from Laser Pyrolysis
Authors: Huisken F. , Ledoux G. , Guillois O. , Reynaud C. 
Published: December 2002

AbstractCrystalline Si nanoparticles with diameters between 2.5 and 20 nm are prepared by CO2‐laser‐induced decomposition of silane in a gas flow reactor. A small portion of the products created in the reaction zone is extracted through a nozzle into a high‐acuum apparatus to form a freely propagating molecular beam of clusters and nanoparticles that can be deposited on suitable substrates. The strong visible photoluminescence (PL) of the Si nanocrystals is studied as a function of their size, and as a function of the time for which they are exposed to air. All observations can be explained on the basis of quantum confinement as the only origin of the PL. Chemical methods are exploited to modify the surface of the Si nanoparticles and to reduce their size, thus shifting their PL to shorter wavelengths. With this technique, the Si nanoparticles, collected in much larger quantities in the filter of the flow reactor, can be made strongly luminescent so that they may be used for various applications.
Acute myelogenous leukemia associated with extreme symptomatic thrombocytosis and chromosome 3q translocation: Case report and review of literature
Authors: Chang Victor T. , Aviv Hana , Howard Leslie M. , Padberg Frank 
Published: December 2002

AbstractAcute leukemias with thrombocytosis have been recently linked with structural abnormalities of the short arm of chromosome 3. A 46‐year‐old man with a 2‐month history of recurrent transient ischemic attacks and abdominal pain developed an ischemic left foot and a gangrenous toe as his initial symptoms. Platelet count was 3.5 × 106/μL, and despite plateletpheresis, the patient required left‐leg amputation. Pathologic examination was remarkable for arterial thrombosis in the absence of atherosclerotic lesions. A diagnosis of acute myeloid leukemia with a novel translocation between chromosomes 3q21, 16, and 7 was made. Induction therapy was unsuccessful, and the patient died of overwhelming sepsis within 5 weeks of diagnosis. The striking features of this case were extreme symptomatic thrombocytosis, peripheral gangrene without atherosclerosis, and a novel three‐way chromosomal translocation involving chromosome 3q21. Am. J. Hematol. 72:20–26, 2003. © 2002 Wiley‐Liss, Inc.
Synthesis and in vitro Antimicrobial Evaluation of 5‐(1‐Methyl‐5‐nitro‐2‐imidazolyl)‐4H‐1, 2, 4‐triazoles
Authors: Shafiee Abbas , Sayadi Abolfazl , Roozbahani Marjan Hosseini , Foroumadi Alireza , Kamal Fatemeh 
Published: December 2002

AbstractThe increasing clinical importance of drug‐resistant pathogens has lent additional urgency to antimicrobial research. Various 5‐(1‐methyl‐5‐nitro‐2‐imidazolyl)‐4H‐1, 2, 4‐triazoles (4a—6f) were synthesized and tested in vitro for their antibacterial and antifungal activities. Compounds 4a and 4b exhibited significant effects against Bacillus subtilis at MIC ranges of 0.5—1 μg/mL and moderate effects against Staphylococcus aureus.
Fine Tuning of Photophysical Properties of meso–meso‐Linked ZnII–Diporphyrins by Dihedral Angle Control
Authors: Yoshida Naoya , Ishizuka Tomoya , Osuka Atsuhiro , Jeong Dae Hong , Cho Hyun Sun , Kim Dongho , Matsuzaki Yoichi , Nogami Atsushi , Tanaka Kazuyoshi 
Published: December 2002

AbstractA series of meso–meso‐linked diporphyrins Sn strapped with a dioxymethylene group of various length were synthesized by intramolecular AgI‐promoted coupling of dioxymethylene‐bridged diporphyrins Bn, for n=10, 8, 6, 5, 4, 3, 2, and 1. Shortening of the strap length causes a gradual decrease in the dihedral angle between the porphyrins and increasing distortion of porphyrin ring, as suggested by MM2 calculations and 1H NMR studies. This trend has been also suggested by X‐ray crystallographic studies on the corresponding CuII complexes of nonstrapped diporphyrin 2 Cu, and strapped diporphyrins S8Cu, S4Cu, and S2Cu. The absorption spectrum of relatively unconstrained diporphyrins S10 strapped with a long chain exhibits split Soret bands at 414 and 447 nm and weak Q(0,0)‐ and prominent Q(1,0)‐bands, both of which are similar to those of nonstrapped diporphyrin 2. Shortening of the strap length causes systematic changes in the absorption spectra, in which the intensities of the split Soret bands decrease, the absorption bands at about 400 nm and > 460 nm increase in intensity, and a prominent one‐band feature of a Q‐band is changed to a distinct two‐band feature with concurrent progressive red‐shifts of the lowest Q(0,0)‐band. The fluorescence spectra also exhibit systematic changes, roughly reflecting the changes of the absorption spectra. The strapped diporphyrins Sn are all chiral and have been separated into enantiomers over a chiral column. The CD spectra of the optically active Sn display two Cotton effects at 430–450 and at about 400 nm with the opposite signs. The latter effect can be explained in terms of oblique arrangement of m⊥1 and m⊥2 dipole moments, while the former effect cannot be accunted for within a framework of the exction coupling theory. The resonance Raman (RR) spectra taken for excitation at 457.9 nm are variable among Sn, while the RR spectra taken for excitation at 488.0 nm are constant throughout the Sn series. These photophysical properties can be explained in terms of INDO/S‐SCI calculations, which have revealed charge transfer (CT) transitions accidentally located close in energy to the excitonic Soret transitions. This feature arises from a close proximity of the two porphyrins in meso–meso‐linked diporphyrins. In addition to the gradual red‐shift of the exciton split Soret band, the calculations predict that the high‐energy absorption band at about 400 nm, the lower energy Cotton effect, and the RR spectra taken for excitation at 457.9 nm are due to the CT states which are intensified upon a decrease in the dihedral angle.
Synthesis and Formation Mechanism of Manganese Dioxide Nanowires/Nanorods
Authors: Wang Xun , Li Yadong 
Published: December 2002

Abstractα‐, β‐, γ‐, and δ‐MnO2 single‐crystal nanowires/nanorods with different aspect ratios have been successfully prepared by a common hydrothermal method based on the redox reactions of MnO4− and/or Mn2+. The influences of oxidant, temperature, and inorganic cation (NH4+ and K+) template concentrations on the morphology and crystallographic forms of the final products are discussed in this paper. It is interesting to find that all the MnO2 one‐dimensional nanostructures have a similar formation process: δ‐MnO2, which has a layer structure, serves as an important intermediate to other forms of MnO2, and is believed to be responsible for the initial formation of MnO2 one‐dimensional nanostructures. A rolling mechanism has been proposed based on the results of the series of TEM images and XRD patterns of the intermediate.
The Molecular Structure of Different Species of Cuprous Chloride from Gas‐Phase Electron Diffraction and Quantum Chemical Calculations
Authors: Hargittai Magdolna , Schwerdtfeger Peter , Réffy Balázs , Brown Reuben 
Published: December 2002

AbstractThe molecular geometry of gaseous cuprous chloride oligomers was determined by gas‐phase electron diffraction at two different temperatures. Quantum chemical calculations were also performed for CunCln(n=1–4) molecules. A complex vapor composition was found in both experiments. Molecules of Cu3Cl3and Cu4Cl4were present at the lower temperature (689 K), while dimeric molecules (Cu2Cl2) were found in addition to the trimers and tetramers at the higher temperature (1333 K). All CunClnspecies were found to have planar rings by both experiment and computation. The bond lengths from electron diffraction (rg) at 689 K are 2.166±0.008 Å and 2.141±0.008 Å and the Cu‐Cl‐Cu bond angles are 73.9±0.6° and 88.0±0.6° for the trimer and the tetramer, respectively. At 1333 K the bond lengths are 2.254±0.011 Å, 2.180±0.011 Å, and 2.155±0.011 Å, and the CuClCu bond angles 67.3±1.1°, 74.4±1.1°, and 83.6±1.1° for the dimer, trimer, and tetramer, respectively.
Recycling of Homogeneous Hydrogenation Catalysts by Dialysis Coupled Catalysis
Authors: De Smet Koen , Pleysier Annick , Vankelecom Ivo F. J. , Jacobs Pierre A. 
Published: December 2002

AbstractAlthough transition‐metal complexes are very attractive as homogeneous catalysts in fine chemistry, their high prices often limit their applications. A means to recycle those catalysts would solve this problem and would simultaneously facilitate the downstream purification of the product. This is now realized in a new concept in which homogeneous catalysis is coupled to dialysis. The advantages of homogeneous catalysis (off‐the‐shelf catalysts, high activities and selectivities) are thus combined with those of heterogeneous catalysis (easy catalyst separation from product solution, reuse of catalyst, and possibility for continuous operation). Since the heart of the process is the membrane, self‐prepared membranes were preferred as they allow a better control and understanding of the separation characteristics. Rhodamine B was used as a probe molecule to define the working conditions of the membrane. The concept is proven to work for two relevant chiral reactions: a hydrogenation with Ru–BINAP and a hydrogen transfer reaction with Ru–TsDPEN [BINAP=(1,1′‐binaphthalene)‐2,2′‐diylbis(diphenylphosphine); TsDPEN= tosyl‐N,N′‐diphenyl‐1,2‐ethanediamine].
New Mechanistic Insights into the Iridium–Phosphanooxazoline‐Catalyzed Hydrogenation of Unfunctionalized Olefins: A DFT and Kinetic Study
Authors: Brandt Peter , Hedberg Christian , Andersson Pher G. 
Published: December 2002

AbstractThe reaction mechanism of the iridium–phosphanooxazoline‐catalyzed hydrogenation of unfunctionalized olefins has been studied by means of density functional theory calculations (B3LYP) and kinetic experiments. The calculations suggest that the reaction involves an unexpected IrIII–IrV catalytic cycle facilitated by coordination of a second equivalent of dihydrogen. Thus, in the rate‐determining migratory insertion of the substrate alkene into an iridium–hydride bond, simultaneous oxidative addition of the bound dihydrogen occurs. The kinetic data shows that the reaction is first order with respect to hydrogen pressure. This is interpreted in terms of an endergonic coordination of this second equivalent of dihydrogen, although a rate‐determining step, in which coordinated solvent is replaced by dihydrogen, could not be ruled out. Furthermore, the reaction was found to be zeroth order with respect to the alkene concentration. This correlates well with the calculated exothermicity of substrate coordination, and the catalyst is thus believed to coordinate an alkene in the resting state. On the basis of the proposed catalytic cycle, calculations were performed on a full‐sized system with 88 atoms to assess the appropriateness of the model calculations. These calculations were also used to explain the enantioselectivity exerted by the catalyst.
Raman Spectroscopy—A Prospective Tool in the Life Sciences
Authors: Petry Renate , Schmitt Michael , Popp Jürgen 
Published: December 2002

AbstractAlthough the physics of Raman spectroscopy and its application to purely chemical problems is long established, it offers a noninvasive, nondestructive, and water‐insensitive probe to problems in the life sciences. Starting from the principles of Raman spectroscopy, its advantages, and methods for signal enhancement, the bulk of the review highlights recent applications. Structural investigations of a hormone receptor, testing the biocompatibility of dental implants, probing soil components and plant tissue alkaloids, and localization of single bacteria are just four problems in which Raman spectroscopy offers a solution or complements existing methods.
Molecular Logic Circuits
Authors: Balzani Vincenzo , Credi Alberto , Venturi Margherita 
Published: December 2002

AbstractMiniaturization has been an essential ingredient in the outstanding progress of information technology over the past fifty years. The next, perhaps ultimate, limit of miniaturization is that of molecules, which are the smallest entities with definite size, shape, and properties. Recently, great effort has been devoted to design and investigate molecular‐level systems that are capable of transferring, processing, and storing information in binary form. Some of these nanoscale devices can, in fact, perform logic operations of remarkable complexity. This research—although far from being transferred into technology—is attracting interest, as the nanometer realm seems to be out of reach for the “top‐down” techniques currently available to microelectronics industry. Moreover, such studies introduce new concepts in the “old” field of chemistry and stimulate the ingenuity of researchers engaged in the “bottom‐up” approach to nanotechnology.
On the Dissociation of Aromatic Radical Anions in Solution
Authors: Laage Damien , Burghardt Irène , Sommerfeld Thomas , Hynes James T. 
Published: December 2002

AbstractA new theoretical formulation is given for the reaction rate and path for the important reaction class of aromatic radical anion dissociation in solution [ArX]−.→Ar.+X−, and is illustrated for the case of the cyanochlorobenzene radical anion [CNΦCl]−. in dimethylformamide. Among the theory's novel features is the inclusion of the conical intersection aspect of this ground electronic state problem, which is key in allowing the reaction to occur and which has a significant impact on the reaction barrier height. Reasonable agreement with the experimental rate is found.
Correlation of Molecular Assembly and Interactions in Crystals and Langmuir–Blodgett Films of N‐(2,4‐dinitrophenyl)‐n‐octadecylamine
Authors: Sharma Sonika , Radhakrishnan T. P. 
Published: December 2002

AbstractCorrelation of molecular organization in crystals and in ultrathin films is of fundamental interest in the design of molecular materials based on thin films. We have chosen as a test case, N‐(2,4‐dinitrophenyl)‐n‐octadecylamine (DNPOA), a potential candidate for the fabrication of Langmuir–Blodgett (LB) films for quadratic nonlinear optical applications. Like several other 4‐nitroaniline derivatives, DNPOA does not form stable monolayers at the air–water interface. This has precluded investigations of their organization in LB films. We have stabilized composite Langmuir films of DNPOA with the phospholipid molecule DSPC and fabricated their LB films. Successful growth of single crystals of DNPOA allowed structure determination and detailed analysis of molecular associations in the solid state. Electronic absorption spectra of DNPOA in solution, in the solid state and in the LB film are investigated. Modeling of the various spectral signatures by semiempirical computations on molecular clusters extracted from the crystal lattice provides insight into the correlation between the molecular organization in crystals and in LB films.
15‐Membered Triolefinic Macrocycles − Catalytic Role of (E,E,E)‐1,6,11‐Tris(arenesulfonyl)‐1,6,11‐triazacyclopentadeca‐3,8,13‐triene Complexes of Palladium(0) in the Presence of Phosphanes
Authors: Moreno‐Mañas Marcial , Pleixats Roser , Spengler Jan , Chevrin Carole , Estrine Boris , Bouquillon Sandrine , Hénin Françoise , Muzart Jacques , Pla‐Quintana Anna , Roglans Anna 
Published: December 2002

AbstractThe palladium(0) complexes of (E,E,E)‐1,6,11‐tris(arenesulfonyl)‐1,6,11‐triazacyclopentadeca‐3,8,13‐trienes deliver palladium to phosphanes with the generation of high concentrations of catalytically active species such as Pd(PPh3)2. After oxidation of the phosphanes, the palladium is reincorporated into the macrocycle, thus avoiding agglomeration and precipitation. These conclusions were reached by 31P NMR, 19F NMR, and electrospray ionization mass spectrometry studies of telomerization and Tsuji−Trost reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Plakohypaphorines A−C, Iodine‐Containing Alkaloids from the Caribbean Sponge Plakortis simplex
Authors: Campagnuolo Claudio , Fattorusso Ernesto , Taglialatela‐Scafati Orazio 
Published: December 2002

AbstractInvestigation of the most polar fractions obtained from the organic extract of the Caribbean marine sponge Plakortis simplex has led to the isolation of three novel iodine‐containing tryptophan betaines structurally related to the known hypaphorine (5), which have been named plakohypaphorine A (2), B (3) and C (4). Their structures have been determined by spectroscopic methods. Isolation of compounds 2−4 is particularly remarkable since it represents the first finding of iodoindole derivatives in a natural source, either marine or terrestrial. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
An Efficient Synthesis of 1‐Naphthylbis(oxazoline) and Exploration of the Scope in Asymmetric Catalysis
Authors: van Lingen Hester L. , van de Mortel Jeroen K. W. , Hekking Koen F. W. , van Delft Floris L. , Sonke Theo , Rutjes Floris P. J. T. 
Published: December 2002

AbstractBoth enantiomers of 1‐naphthylglycine were obtained in 99%eeby enzymatic resolution of the corresponding racemic amino acid amide, giving access to the novel ligands (R)‐ and (S)‐naphthylbis(oxazoline). Initial studies provided insight into the scope and limitations of the (S)‐naphthyl‐substituted bis(oxazoline) and its steric influence compared to other bis(oxazolines) in catalytic asymmetric synthesis. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)
Cycloisomerisations in Pd‐Catalysed Spiroannulations onto Chiral Pyrazine Derivatives
Authors: Møller Bjørg , Undheim Kjell 
Published: December 2002

AbstractA method for 5‐exo‐trig‐spiroannulations is described which uses the Pd complex trans‐bis(μ‐acetato)bis[o‐(di‐o‐tolylphosphanyl)benzyl]dipalladium(II) as catalyst in cyclisation reactions of dienes with the chiral auxiliary (2R)‐2,5‐dihydro‐2‐isopropyl‐3,6‐dimethoxypyrazine. Extensive NMR assignments are described and used in structure determinations. Isomer identification has been verified by a separate unequivocal synthesis. Nickel catalysis with MeMgBr was compatible with cross‐coupling in the spiroannulated chiral auxiliary. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)