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Theoretical Calculations (theoretical + calculation)
Selected AbstractsPreparation, Crystal Structure and Theoretical Calculation of N -(Pyrimidin-2-yl)- N, -methoxycarbonyl-thioureaCHINESE JOURNAL OF CHEMISTRY, Issue 4 2007Ying-Hui Ren Abstract The compound, N -(pyrimidin-2-yl)- N, -methoxycarbonyl-thiourea, has been synthesized. The single crystal structure has been determined by an X-ray diffractometer. The crystal belongs to triclinic with space group P -1 and a=0.72152(4) nm, b=0.8056(4) nm, c=0.90772(5) nm, ,=105.141(4)°, ,=94.588(4)°, ,=115.415(4)°, F(000)=220, the unit cell volume V=0.45704(4) nm3, the molecule number in one unit cell Z=2, the absorption coefficient ,=0.333 mm,1, the calculated density Dc=1.542 g/cm3. The theoretical investigation of the title compound was carried out with B3LYP/6-311G, HF/6-311G and MP2/6-311G methods, and the atomic charges and natural bond orbital analysis were also discussed. [source] NMR Conformational Analysis and Theoretical Calculations for 2-Aryl- 1,3-dihydroxy-4,4,5,5-tetramethylimidazolidinesHELVETICA CHIMICA ACTA, Issue 2 2004Antônio Conformational studies of 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-1-yl)imidazolidine (1a) and 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-3-yl)imidazolidine (1b), carried out by using 1D 1H- and 13C-NMR and 2D HMQC, HMBC, and NOESY experiments and with the aid of theoretical calculations, indicate that the OH groups are trans to the pyridinyl substituent. Because the two 1H-NMR signals of the Me groups are distinguishable and do not change between 290 and 380,K, it is proposed that 1a and 1b have each only one conformation in this temperature range. This behavior was not found with 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-2-yl)imidazolidine (1c) because its Me 1H-NMR signals cross over at 300,K. Hence, more than one conformation must be present, beyond those produced by simple inversions. Theoretical calculations including temperature and solvent effects were performed to provide further information on the conformational analysis and to help to assign the NMR data. The combination of NMR measurements and quantum-chemical calculations is shown to be a very promising strategy for conformational analysis studies in solution. [source] ChemInform Abstract: Infrared Spectra and Theoretical Calculations of KH and (KH)2 in Solid Hydrogen.CHEMINFORM, Issue 10 2008Xuefeng Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Towards a Molecular Understanding of Cation,Anion Interactions,Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy, X-ray Photoelectron Spectroscopy and Theoretical CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2010Till Cremer Abstract Ten [C8C1Im]+ (1-methyl-3-octylimidazolium)-based ionic liquids with anions Cl,, Br,, I,, [NO3],, [BF4],, [TfO],, [PF6],, [Tf2N],, [Pf2N],, and [FAP], (TfO=trifluoromethylsulfonate, Tf2N=bis(trifluoromethylsulfonyl)imide, Pf2N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C8C1C1Im]+ (1,2-dimethyl-3-octylimidazolium)-based ionic liquids with anions Br, and [Tf2N], were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While 1H,NMR spectroscopy is found to probe very specifically the strongest hydrogen-bond interaction between the hydrogen attached to the C2 position and the anion, a comparative XPS study provides first direct experimental evidence for cation,anion charge-transfer phenomena in ionic liquids as a function of the ionic liquid's anion. These charge-transfer effects are found to be surprisingly similar for [C8C1Im]+ and [C8C1C1Im]+ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions. [source] Theoretical Calculations on the Tetramethyldisilene Rearrangement: A New Approach to an Old Mechanistic ProblemCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Mrinmoy Nag Dr. Abstract Roark and Peddle first observed that, when not trapped, Me2SiSiMe2 underwent a series of rearrangements to give two major isomeric products: 1,1-dimethyl-1,3-disilacyclobutane and 1,3-dimethyl-1,3-disilacyclobutane. The widely accepted mechanism for this rearrangement was proposed by Barton and co-workers. However, little is known about the thermodynamic or kinetic properties of this reaction, because the relevant data are limited to the product ratios of the two isomers. Our calculations predict that the product ratio is driven by kinetic control rather than thermodynamic control. We also show that new DFT functionals, such as MPW1K and M052X, produce thermochemical results comparable with CCSD(T) calculations. [source] Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Frank Büttner Dr. Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source] Effect of High-Energy Vibromilling on Interfacial Interaction and Mechanical Properties of PVC/Nano-CaCO3 CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 9 2005Manhong Tian Abstract Summary: The effects of interfacial interaction between nano-CaCO3 and PVC on mechanical properties and morphology of PVC/nano-CaCO3 composites were studied. Nano-CaCO3 was treated with vibromilling in the presence of PVC and coupling agents. The mechanical properties of PVC/treated nano-CaCO3 are remarkably improved. Transmission electron microscopy results revealed that vibromilled nano-CaCO3 particles are well dispersed in PVC matrix with good homogeneity and well adhered to PVC matrix. Molau test indicated that chemical reaction between newly formed surface of nano-CaCO3 and PVC or coupling agent took place. Theoretical calculation results show that the interfacial interaction between PVC and nano-CaCO3 are substantially improved through vibromilling treatment of nano-CaCO3 in the presence of PVC and coupling agent. Molau test results of the samples in THF. [source] Asymmetric Epoxidation of Terminal Olefins with Binaphthyl Strapped Porphyrin Catalysts: (-( Stacking Interaction and Steric Effects on the EnantioselectivitiesCHINESE JOURNAL OF CHEMISTRY, Issue 5 2009Qizhi REN Abstract Two binaphthyl strapped porphyrins with similar chiral auxiliaries 1b and 2b were used as efficient catalysts for asymmetric epoxidation of both styrene derivatives and non-aromatic olefin substrates. Theoretical calculation of styrene approach to both catalysts has been performed. The subtle difference of the chiral cavities between two porphyrins has been analyzed by 1H NMR. The ,-, stacking interaction between aromatic substrates and catalysts might be one factor for the dramatic different enantioselectivities. Besides, the steric effect of the binaphthyl handle of 1b and 2b also causes the high ee values for non-aromatic olefin epoxidations. [source] Complexes of Yb3+ with EDTA and CDTA , Molecular and Electronic StructureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2008Janicki Abstract Two Yb3+ compounds, [C(NH2)3]2[Yb(EDTA)(H2O)2]ClO4·6H2O and [C(NH2)3][Yb(CDTA)(H2O)2]·4H2O, where EDTA is the ethylenediaminetetraacetate anion and CDTA is the trans -1,2-diaminecyclohexane- N,N,N,,N, -tetraacetate anion, were obtained and their crystal structures and spectroscopic properties were determined. In both compounds, the coordination geometries of the eight-coordinate Yb3+ ion are very similar. In each case, the inner sphere of the metal ion consists of four carboxyl oxygen atoms, two nitrogen atoms and two water molecules. The complexes were characterized by UV/Vis/NIR absorption at different temperatures and IR spectroscopy. The spectroscopic results revealed high sensitivity of the electronic 4f13 configuration upon minor changes in the coordination geometry around the Yb3+ ion. These data also demonstrate that species present in solutions of Yb3+,EDTA are similar to those found in the crystal, whereas in solutions of Yb3+,CDTA an equilibrium between at least two different forms exists. For the Yb3+,EDTA complex in solution and in the crystalline state, a charge-transfer transition was detected. Theoretical calculations revealed its complicated (Yb , ligand and ligand , Yb) character.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Bent and Linear Forms of the (,-Oxo)bis[trichloroferrate(III)] Dianion: An Intermolecular Effect , Structural, Electronic and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2003Agustí Lledós Abstract We have analyzed the great diversity of Fe,O,Fe angles, 140,180°, found in the X-ray structures of the (,-oxo)bis[trichloroferrate(III)] dianion [Cl3FeOFeCl3]2, from both experimental and theoretical points of view. Theoretical calculations show that only the linear isomer is found as a minimum on the potential energy surface. Detailed analysis of the crystal packing indicates that the angular form is due to attractive intermolecular interactions. Analysis of a selected reduced set of the 45 crystal structures retrieved from the Cambridge Structural Database allowed us to classify the bending of the [Cl3FeOFeCl3]2, dianion in three categories, depending on the balance and strength of the intermolecular O···H,X contacts. A crystal diffraction study on the bis(benzyltrimethylammonium) salt has shown both bent (144.6°) and linear (180°) forms of the (,-oxo)bis[trichloroferrate(III)] dianion. The magnetic susceptibility of this compound has been fitted by assuming two equally weighted contributions (Jang and Jlin) of the two forms, considering Jang , Jlin estimated by theoretical calculations. The obtained Jang and Jlin of ,117 and ,133 cm,1 respectively, agree well with B3LYP results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Spatiotemporal properties of cytoplasmic cyclic AMP gradients can alter the turning behaviour of neuronal growth conesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2004Sebastian Munck Abstract Growth cones, the terminal structures of elongating neurites, use extracellular guidance information in order to navigate to appropriate target cells. The directional information of guidance cues is transduced to a cytoplasmic gradient of messenger molecules across the growth cone leading to rearrangements of the cytoskeleton. One messenger molecule regulating growth cone turning is cAMP, which is also known to be sufficient to direct growth cone attraction. Cytoplasmic cAMP gradients have been generated in the present study by photolysing caged cAMP with UV light focused on one side of growth cones of chick sensory neurons. Using this method we show that only specific time patterns of pulsed cAMP release are capable of inducing growth cone turning whereas others, which release the same amount of cAMP, are ineffective. Theoretical calculations show that diverse time patterns produce different intracellular gradients, which were visualized directly in HeLa cells expressing cAMP-sensitive ion channels as a reporter system. Together these data indicate that the spatiotemporal properties of the intracellular gradient are crucial for growth cone turning. [source] Synthesis of Pyrazolyl-2-pyrazolines by Treatment of 3-(3-Aryl-3-oxopropenyl)chromen-4-ones with Hydrazine and Their Oxidation to Bis(pyrazoles)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004Albert Lévai Abstract The synthesis of several 1-acetyl-3-aryl-5-[3-(2-hydroxyphenyl)pyrazol-4-yl]-2-pyrazolines 3a,3h has been accomplished by treatment of the 3-(3-aryl-3-oxopropenyl)chromen-4-ones 1a,h with hydrazine hydrate in hot acetic acid. The 1-acetyl-3-aryl-5-(3-chromonyl)-2-pyrazolines 2a,2f were also obtained as by-products. Oxidation of the 1-acetyl-4-pyrazolyl-2-pyrazolines 3a,3f with DDQ gave the 3(5)-aryl-5(3)-[3-(2-hydroxyphenyl)pyrazol-4-yl]pyrazoles 5a,5f. The oxidation of the 2-pyrazoline rings was accompanied by N -deacylation. The reaction mechanisms of both transformations are discussed, the first one being supported by experimental results. The structures of all new derivatives were established by NMR and the evidence of prototropic tautomerism is carefully discussed. Theoretical calculations of energies and of the 1H and 13C NMR chemical shifts of the possible tautomeric forms of 5(3)-[3-(2-hydroxyphenyl)pyrazol-4-yl]-3(5)-(4-methoxyphenyl)pyrazole (5c), by B3LYP and GIAO, showed that compounds of this type probably exist as mixtures of two tautomers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] NMR Conformational Analysis and Theoretical Calculations for 2-Aryl- 1,3-dihydroxy-4,4,5,5-tetramethylimidazolidinesHELVETICA CHIMICA ACTA, Issue 2 2004Antônio Conformational studies of 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-1-yl)imidazolidine (1a) and 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-3-yl)imidazolidine (1b), carried out by using 1D 1H- and 13C-NMR and 2D HMQC, HMBC, and NOESY experiments and with the aid of theoretical calculations, indicate that the OH groups are trans to the pyridinyl substituent. Because the two 1H-NMR signals of the Me groups are distinguishable and do not change between 290 and 380,K, it is proposed that 1a and 1b have each only one conformation in this temperature range. This behavior was not found with 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-2-yl)imidazolidine (1c) because its Me 1H-NMR signals cross over at 300,K. Hence, more than one conformation must be present, beyond those produced by simple inversions. Theoretical calculations including temperature and solvent effects were performed to provide further information on the conformational analysis and to help to assign the NMR data. The combination of NMR measurements and quantum-chemical calculations is shown to be a very promising strategy for conformational analysis studies in solution. [source] Theoretical calculations of transition probabilities and oscillator strengths for Ti III and Ti IVINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2009Tian-Yi Zhang Abstract Due to the complicated electronic configuration of atoms and ions of the transition metal elements, the studies for properties such as transition probabilities and oscillator strengths for these atoms and ions are not systematic. Because of the existence in a variety of stellar objects and wide use in the field of astrophysics, titanium has long been of interest for many researchers. In this article within the Weakest Bound Electron Potential Model (WBEPM) theory, comprehensive set of calculations for transition probabilities and oscillator strengths for Ti III and Ti IV are performed. Many of our results had no previous experimental or theoretical values, so these predictive results could be of some value to the workers in this field. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Effect of b value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic strokeJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2002Raoul S. Pereira PhD Abstract Purpose To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, ,S) between damaged and normal tissue during diffusion-weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke. Materials and Methods Phantoms with diffusion values approximating those expected in acutely infarcted and normal tissue were constructed from a mixture of agar and formaldehyde and imaged at varying b values (0,3000 mm,2 second). Ten patients were imaged with multiple b values (500,2500 mm,2 second) within 12 hours of stroke onset. Results Theoretical calculations showed that for any combination of diffusion coefficients there existed an optimal b value that was higher than the standard setting of 1000 mm,2 second, and this was confirmed by the phantom studies. In the patients, increasing b from 1000 to 1500 mm,2 second increased ,S (average, 22.4%; P = 0.001), but no consistent benefit was seen at b = 2000 mm,2 second (P = 0.408). This compared favorably with the average optimal b value of 1662 mm, 2 second calculated from the patients. Conclusion These results suggest that increasing the b value from 1000 to 1500 mm,2 second would increase contrast between infarcted and normal tissue in the setting of acute ischemic stroke. J. Magn. Reson. Imaging 2002;15:591,596. © 2002 Wiley-Liss, Inc. [source] HYDROTHERMALLY FLUORITIZED ORDOVICIAN CARBONATES AS RESERVOIR ROCKS IN THE TAZHONG AREA, CENTRALTARIM BASIN, NW CHINAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2006Zhijun Jin Reservoir rocks at the Tazhong 45 oil pool, central Tarim Basin, consist of fluoritized carbonate strata of Middle - Late Ordovician age. Petrological observations indicate that the fluorite replaces calcite. Several other hydrothermal minerals including pyrite, quartz, sphalerite and chlorite accompany the fluorite. Two generations of fluid inclusions are present in the fluorite. Homogenization temperatures (Th) for primary inclusions are mostly between 260°C and 310°C and represent the temperature of the hydrothermal fluid responsible for fluorite precipitation. Th for secondary inclusions range from 100°C to 130°C, and represent the hydrocarbon charging temperature as shown by the presence of hydrocarbons trapped in some secondary inclusions. The mineral assemblage and the homogenization temperatures of the primary fluid inclusions indicate that the precipitation of fluorite is related to hydrothermal activity in the Tazhong area. Strontium isotope analyses imply that the hydrothermal fluids responsible for fluorite precipitation are related to late-stage magmatic activity, and felsic magmas were generated by mixing of mafic magma and crustal materials during the Permian. Theoretical calculations show that the molecular volume of a carbonate rock decreases by 33.5% when calcite is replaced by fluorite, and the volume shrinkage can greatly enhance reservoir porosity by the formation of abundant intercrystalline pores. Fluoritization has thus greatly enhanced the reservoir quality of Ordovician carbonates in the Tazhong 45 area, so that the fluorite and limestone host rocks have become an efficient hydrocarbon reservoir. According to the modelled burial and thermal history of the Tazhong 45 well, and the homogenization temperatures of secondary fluid inclusions in the fluorite, hydrocarbon charging at the Tazhong 45 reservoir took place in the Tertiary. [source] A study of sulfamerazine single crystals using atomic force microscopy, transmission light microscopy, and Raman spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Xiaoping Cao Abstract Sulfamerazine (SMZ) Form I and II single crystals were prepared from aqueous dispersions of SMZ bulk samples and studied using several microscopic and spectroscopic techniques. Transmission light microscopy and Raman spectroscopy were used to observe and identify single crystals. The results indicated that Form I single crystals tended to be rectangular laths while Form II ones tended to be hexagonal laths. Surface morphology of individual single crystals was further investigated by atomic force microscopy (AFM). AFM images revealed a smooth top surface, a uniform height, and sharp edges for both forms of single crystals. Both height and phase images showed crystalline terraces with different step heights for the top surface of Form I. Surface properties of single crystals were evaluated using AFM force measurements. Experimental results indicated that the top surface of Form I single crystals was more hydrophilic than that of Form II. Theoretical calculations predicted a dominant crystal face of (020) for the Form I single crystals and (002) for the Form II ones. The correlations between calculation predictions and experimental results were discussed. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1881,1892, 2005 [source] A DFT/TD-DFT study for the ground and excited states of peramine and some pyrrolopyrazinone compoundsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2009Andrzej Abstract Peramine, a heterocyclic natural molecule, reveals two main, different in nature, electronic absorption bands. Theoretical calculations at the TD-B3LYP/6,311++G(d,p) level of theory show that the electronic excitations are connected predominantly with ,,,,,* and charge-transfer (CT) transitions. Excitation of electrons from the pyrrolopyrazinone ring to the side chain plays a role in creating the CT transition. The character and energy of the first 30 singlet,singlet electronic transitions have also been investigated for the most stable conformation of peramine. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis and vibrational analysis of N-(2,-Furyl)-ImidazoleJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2009A. E. Ledesma Abstract The N-(2,-furyl)-imidazole (1) has been prepared and characterized using infrared, Raman and multidimensional nuclear magnetic resonance spectroscopies. Theoretical calculations have been carried out by employing the Density Functional Theory (DFT) method, in order to optimize the geometry of their two conformers in the gas phase and to support the assignments of the vibrational bands of 1 to their normal modes. For a complete assignment of the compound, DFT calculations were combined with Scaled Quamtum Mecanic Force Field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental one. Furthermore, Natural Bond Orbital (NBO) and topological properties by Atoms In Molecules (AIM) calculations were performed to analyze the nature and magnitude of the intramolecular interactions. The result reveals that two conformers are expected in liquid phase. Copyright © 2009 John Wiley & Sons, Ltd. [source] Turboprop IDEAL: A motion-resistant fat,water separation techniqueMAGNETIC RESONANCE IN MEDICINE, Issue 1 2009Donglai Huo Abstract Suppression of the fat signal in MRI is very important for many clinical applications. Multi-point water,fat separation methods, such as IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation), can robustly separate water and fat signal, but inevitably increase scan time, making separated images more easily affected by patient motions. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) and Turboprop techniques offer an effective approach to correct for motion artifacts. By combining these techniques together, we demonstrate that the new TP-IDEAL method can provide reliable water,fat separation with robust motion correction. The Turboprop sequence was modified to acquire source images, and motion correction algorithms were adjusted to assure the registration between different echo images. Theoretical calculations were performed to predict the optimal shift and spacing of the gradient echoes. Phantom images were acquired, and results were compared with regular FSE-IDEAL. Both T1- and T2-weighted images of the human brain were used to demonstrate the effectiveness of motion correction. TP-IDEAL images were also acquired for pelvis, knee, and foot, showing great potential of this technique for general clinical applications. Magn Reson Med 61:188,195, 2009. © 2008 Wiley-Liss, Inc. [source] Compact dual-band multilayer antenna element for nonlinear junction detector applicationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2009Krzysztof Wincza Abstract A compact dual-band antenna element for application in a nonlinear junction detector is proposed. To achieve broadband characteristics in two separate frequency ranges a stratified structure is proposed in which two driven and two parasitic patches are properly placed. For transmitting, a circularly polarized antenna is used in which stacked square ring resonators are applied to achieve simultaneously broadband operation and compact size. For receiving, a dual-polarized antenna is proposed in which a square patch is loaded by a square ring resonator to provide wide band and to allow for integration with the transmitting antenna. Theoretical calculations confirmed by measurement results are presented. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 696,699, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24136 [source] Transmission properties of two shifted magnetoinductive waveguidesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2007A. Radkovskaya Abstract Transmission properties of magnetoinductive waves propagating in two coupled one-dimensional metamaterial arrays are studied both experimentally and theoretically for the case when one of the arrays is shifted relative to the other one. Two different kinds of resonant metamaterial elements, split-pipe and spiral resonators, are investigated in the frequency bands centred at 46.2 and 586 MHz, respectively. It is shown that within a certain frequency range close to the resonant frequencies the transmission is strongly dependent on the shift. Theoretical calculations based on the impedance matrix show good agreement with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1054,1058, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22344 [source] Critical buckling load of paper honeycomb under out-of-plane pressure,PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2005Li-Xin Lu Abstract Two out-of-plane buckling criteria for paper honeycomb are proposed by analysing the structure properties and the collapse mechanism of paper honeycomb: these are based on the peeling strength and ring crush strength of the chipboard wall. Taking into account the orthotropic, initial deflection and large deflection properties of the chipboard wall, the two new mechanical models and the calculation methods are developed to represent the out-of-plane critical load of paper honeycomb. Theoretical calculations and test results show that the models are suitable for describing the collapse mechanism of paper honeycomb. The peeling strength and ring crush strength determine the critical buckling load of paper honeycomb in different stretch phases. The out-of-plane critical buckling load can be predicted when the two models are integrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Aspirin increases mortality in diabetic patients without cardiovascular disease: a Swedish record linkage study,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 12 2009Lennart Welin MD Abstract Purpose Aspirin is effective in secondary prevention of cardiovascular disease. The results are less convincing when aspirin is used for primary prevention even in high-risk patients (i.e., patients with diabetes). We therefore analyzed the effect of aspirin on mortality and serious bleeding in diabetic patients with and without cardiovascular disease. Methods We performed a record linkage study of the patient registry of the Västra Götaland region in south-western Sweden, the Swedish mortality register and the Swedish register of dispensed drugs. All diabetic patients (n,=,58,465) from 1 July 2005 to 30 June 2006 were followed up with respect to bleeding until 31 October 2006, and mortality until 31 December 2006. Results When 19 confounding factors (diseases and interventions) were assessed, aspirin significantly increased mortality in diabetic patients without cardiovascular disease from 17% (95% confidence interval; 95%CI, 1,36) at age 50 years to 29% (16,43) at age 85 years. In contrast aspirin tended to decrease mortality among elderly diabetic patients with cardiovascular disease. Theoretical calculations indicated that aspirin caused 107 excess deaths among diabetic patients without cardiovascular disease and prevented 164 deaths among diabetic patients with cardiovascular disease. Aspirin also increased the risk of serious bleeding by 46% (95%CI, 22,75) in diabetic patients without cardiovascular disease but decreased the risk among those with cardiovascular disease. Conclusion Aspirin use in diabetes patients without cardiovascular disease remains controversial and current guidelines should be revised until results from ongoing large randomized controlled trials become available. Copyright © 2009 John Wiley & Sons, Ltd. [source] Spectroscopic Properties of Various Quinolone Antibiotics in Aqueous,organic Solvent Mixtures¶PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2004Hyoung-Ryun Park The spectroscopic properties of enoxacin (ENO), oxolinic acid (OXO) and nalidixic acid (NAL) were studied in various H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. ENO has piperazinyl group, but OXO and NAL do not have this substituent. The fluorescence emission spectra of ENO were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data, clear reverse solvatochromism was exhibited for ENO in both mixed solvents. This observation can be explained using the excited state twisted intramolecular charge transfer (TICT) from the nitrogen of the piperazinyl group to the keto oxygen. Theoretical calculations further support this observation. The nonradiative and radiative rate constants of these molecules were analyzed as a function of dipolarity,polarizability (,*) and hydrogen bond donor acidity (,) of the mixed solvents. These results for ENO were consistent with the suggested mechanism of the TICT very well. The influence of bulk dielectric effect was more significant relative to the specific hydrogen bonding interactions. The emission spectra of OXO and NAL do not exhibit any characteristic responses to the properties of the solvent. [source] Anisotropic polarization of non-polar GaN quantum dot emissionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009R. Mata Abstract We report on experimental and theoretical studies of the polarization selection rules of the emission of non-polar GaN/AlN self-assembled quantum dots. Time-integrated and time-resolved photoluminescence measurements have been performed to determine the degree of polarization. It is found that the emission of some samples can be predominantly polarized parallel to the wurtzite c axis, in striking difference with the previously reported results for bulk GaN and its heterostructures, in which the emission was preferentially polarized perpendicular to the c axis. Theoretical calculations based on an 8-band k·p model are used to analyze the relative importance of strain, confinement and quantum dot shape on the polarization selection rules. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Copolymers of N -methylpyrrole and 3,4-ethylenedioxythiophene: structural, physical and electronic propertiesPOLYMER INTERNATIONAL, Issue 6 2007Cintia Ocampo Abstract The structural, electric and electronic properties of copolymers derived from mixtures of N -methylpyrrole and 3,4-ethylenedioxythiophene (EDOT) with various concentration ratios have been investigated and, additionally, compared with those of the corresponding homopolymers. The electropolymerization kinetics of all the generated copolymers and the homopolymers was examined in terms of current productivity using chronoamperometry. The chemical structure of the linkages between adjacent monomers and the microstructure of the chains were investigated using Fourier transform infrared spectroscopy and quantum mechanical calculations, respectively. The results indicate that the linkages between monomeric units formed during the anodic copolymerization are of the ,,, type, while the microstructure of the copolymers depends on the EDOT content. Theoretical calculations were also used to examine the electronic properties of the systems under study, while the conductivity and the electrical stability were studied using the sheet-resistance method. Interestingly, the electric properties are consistent with the random and block microstructures predicted for the copolymers with low and high EDOT content, respectively. Copyright © 2006 Society of Chemical Industry [source] Alternating poly(ester amide)s from succinic anhydride and ,,,-amino alcohols: synthesis and thermal characterization,,POLYMER INTERNATIONAL, Issue 10 2003Thomas Fey Abstract Alternating poly(ester amide)s 6a,e from succinic anhydride and ,,,-amino alcohols H2N,(CH2)x,OH (x = 2,6) 2a,e were obtained in two steps: ,-carboxyl-,-hydroxy amides 3a,e were prepared from the starting materials in a highly selective reaction, followed by a polycondensation reaction. 1H and 13C NMR analyses of the poly(ester amide)s clearly reveal the alternating microstructure. The poly(ester amide)s with homologous ,,,-amino alcohols H2N,(CH2)x,OH (x = 2,6) are semi-crystalline materials, their melting points show the odd/even effect observed for [n]-polyamides and [n]-polyurethanes. Heating the poly(ester amide)s 6a,e yields the corresponding N -(hydroxyalkyl) imides 4a,e with no trace of cyclic ester amides. Theoretical calculations revealed that the cyclic ester amides 5a,e are clearly richer in energy than the isomeric N -(hydroxyalkyl) imides. These results show that cyclic ester amides can not be prepared from N -(hydroxyalkyl) imides by ring-enlargement reactions. Copyright © 2003 Society of Chemical Industry [source] Stress,optical behaviour of polyester networksPOLYMER INTERNATIONAL, Issue 3 2002Evaristo Riande Abstract Thermoelastic networks were prepared by end-linking hydroxyl terminated chains of poly(neopentylglycol hexafluoroglutarate) (PNGHFG) and poly(diethylene glycol terephthalate) (PDET) using, respectively, tri(p -isocyanate-phenyl)-thiophosphate and 2,4-bis(p -isocyanate benzyl)- p -phenylisocyanate as crosslinking agents. The plots of birefringence versus stress for PNGHFG and PDET networks exhibit negative deviations from linearity at elongation ratios greater than 1.9 and 5, respectively. The values of the optical configuration parameter ,a for the former and latter networks are 2.98,Ĺ3 at 5,°C and 20.80,Ĺ3 at 30,°C, respectively. Theoretical calculations carried out using the conformational energies obtained from the critical analysis of the mean-square dipole moments of diethyl hexafluoroglutarate and poly(neopentylglycol hexafluoroglutarate) give the value of 2.24,Ĺ3 at 5,°C for this parameter, in fair agreement with the experimental result. Similar calculations carried out on PDET networks give ,a,,=,3.74,Ĺ3 at 30,°C, a value significantly lower than the experimental result. The cause of the strong discrepancy between the theoretical and experimental results observed for the optical configuration parameter of PDET is discussed. © 2002 Society of Chemical Industry [source] Towards a generalized vision of oxides: disclosing the role of cations and anions in determining unit-cell dimensionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Ángel Vegas Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic and sc: simple cubic, respectively) exhibit charge concentration zones which coincide with the positions occupied by the O atoms in their oxides. Similar features, also observed for the pairs Ca/CaF2 and BaSn/BaSnO3, are supported by recent high-pressure experiments as well as electron-localization function (ELF) calculations, carried out on elemental K. At very high pressures, the elemental K adopts the hP4 structure, topologically identical to that of the K atoms in high-pressure K2S and high-temperature ,-K2SO4. Moreover, the ELF for the hP4 structure shows charge concentration (,,2 electrons) at the sites occupied by the S atoms in the high-pressure K2S phase. All these features confirm the oxidation/high-pressure equivalence as well as the prediction of how cation arrays should be metastable phases of the parent metals. For the first time to our knowledge, the structure type, dimension and topology of several oxides and fluorides (CaO, CaF2 and BaSnO3) are explained in univocal physical terms. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||