bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon nanotube synthesis using ferrocene and ferrocenyl sulfide. The effect of sulfur
Authors: Mohlala M. Sarah , Liu Xin‐Ying , Witcomb Mike J. , Coville Neil J. 
Published: March 2007

AbstractMultiwalled carbon nanotubes (MWCNTs) have been synthesized by the floating catalyst method using toluene as the carbon source and mixtures of ferrocene and ferrocenyl sulfide as the catalyst. Products were characterized by both low‐resolution and high‐resolution (HR) TEM analysis. It was found that the presence of large amounts of sulfur in the reactant mixture generated only amorphous carbon while lower amounts of sulfur led to mixtures of MWCNTs and carbon fibres. The product distribution, yield and the tube diameters varied with the sulfur content. HRTEM analysis revealed that the MWCNTs were poorly graphitized. Comparison with data using other sulfur sources (S8, thiophene) suggested that the proximity of the sulfur to the Fe catalyst in the gas phase did play a role in the CNT formation and provides a method of ‘carrying’ elements to a catalytic site. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis of some aromatic aldehydes and acids by sodium ferrate in presence of copper nano‐particles adsorbed on K 10 montmorillonite using microwave irradiation
Authors: Tandon Praveen K. , Singh Santosh B. , Srivastava Manish 
Published: March 2007

AbstractExcellent yields were obtained in the oxidation of benzyl alcohol, benzaldehyde, 4‐methoxy benzyl alcohol and 4‐nitro benzaldehyde with sodium ferrate in the presence of copper nano particles adsorbed on montmorillonite K 10 under microwave irradiation. Aniline, p‐toluidine, phenol, catechol, resorcinol and p‐cresol polymerize under these conditions without exposing the mixture to microwaves. The one‐pot system does not require tedious separation of ferrate and is quick and environmentally benign. Copyright © 2007 John Wiley & Sons, Ltd.
Contamination of outdoor settled dust by butyltins in Malta
Authors: Decelis Rachel , Vella Alfred J. 
Published: March 2007

AbstractThe presence of compounds of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) was determined in outdoor settled dust collected from several sites on the island of Malta, mainly from flat rooftops of school buildings. The dust was separated into three size fractions with diameters (µm) > 250, 125–250 and < 125, and the two finer fractions were analysed for butyltins using extraction with glacial acetic acid followed by derivatization/solvent extraction with sodium tetraethylborate in the presence of iso‐octane and quantitation by gas chromatography with flame photometric detection. The presence of TBT, DBT and MBT was established in most of the samples and TBT concentrations varied from non‐detectable (<5 ng Sn g−1) to highs of 15.5 and 18.7 µg Sn g−1 in Senglea and Marsaxlokk. TBT was generally found at concentrations significantly higher than reported hitherto in house dust collected from European homes. The geographical distribution of total organotins in both dust fractions suggests that TBT originates mainly from antifouling marine paint residues which contaminate the urban environment when ships' hulls are sand‐ or hydro‐blasted during maintenance and repair at the drydocks facility in Grand Harbour. Other significant sources of TBT are located at Marsaxlokk fishing port and Wied iż‐Żurrieq creek, both hosting sizeable communities of fishermen and leisure boating. The data also suggest that the municipal solid waste landfill at Maghtab is an inland source of butyltins. We suggest that dust containing harmful butyltins could possibly be ingested to expose humans to a risk which is probably of concern especially for young children living close to the hotspots of contamination. Copyright © 2007 John Wiley & Sons, Ltd.
Spontaneous lesions in the reproductive tract and mammary gland of female non‐human primates
Authors: Cooper Timothy K. , Gabrielson Kathleen L. 
Published: March 2007

AbstractBecause of their close phylogenic relationship with humans, the use of non‐human primates (NHP) as experimental subjects has a long history in biomedical research. Although research topics have shifted focus and species used have changed, NHP remain vital as models in basic and applied research. While there is a wealth of information available on the spontaneous lesions of NHP, most of this information is fragmented, dated, or narrow in focus, often limited to single case reports. This review attempts to integrate this information to illustrate and enumerate the spectrum of spontaneous pathology of the reproductive tract and mammary gland of NHP. Although not the focus of this review, steroid‐related changes are inextricably linked to these tissues, and brief consideration is given to this subject as well. Birth Defects Res (Part B), 2007. © 2007 Wiley‐Liss, Inc.
The shielding tensor. Part I: Understanding its symmetry properties
Authors: Anet Frank A. L. , O'Leary Daniel J. 
Published: March 2007

AbstractThe shielding tensor and the chemical shift tensor are not necessarily symmetric, and in general they have both symmetric and antisymmetric parts. The antisymmetric part (not to be confused with the anisotropy of the symmetric part) does not give rise to an observable shift, even in the solid phase, but it does cause relaxation. The antisymmetric part of the shielding tensor can be considered in its corresponding axial vector form, and this allows the effect of symmetry at a nuclear site to be deduced easily. Instead of considering the complete symmetry point group at the nucleus, it is easier to consider only certain key elements of symmetry; this leads to four simple rules that determine the zero and nonzero components of the complete shielding tensor.
Product operators and coherence transfer in multiple‐pulse NMR experiments
Authors: Shriver John 
Published: March 2007

AbstractA practical introduction to coherence and coherence transfer pathways in NMR is provided using the density matrix and product‐operator formalisms. The concept of coherence in NMR is first introduced using the density matrix formalism. Pictorial and quantitative representations of coherence are provided using product operators in the Cartesian basis. A simple transformation from the Cartesian basis to a spherical basis is used to follow coherence order during multiple‐pulse experiments with coherence transfer pathways. The rules are introduced for designing phase cycles to eliminate unwanted coherences and pathways. An appendix contains a computer program written in Mathematica for performing product‐operator calculations interactively.
Fat and water differentiation by nuclear magnetic resonance imaging
Authors: Kaldoudi Eleni , Williams Steve C. R. 
Published: March 2007

AbstractDifferentiation between fat and water is important in proton magnetic resonance imaging. The need for creating separate fat and water images is discussed, and a review is presented of current practices, including chemical‐shift and coupled‐spin imaging, as well as techniques based on relaxation time differences. The virtues and limitations of each regime are discussed, and future directions are suggested.
Optimum tip angle and relaxation delay for quantitative analysis
Authors: Traficante Daniel D. 
Published: March 2007

AbstractFor the quantitative analysis of NMR spectra, the relationship between the tip angle and the relaxation delay is examined. It is shown that the common procedure of using a small tip angle combined with a short delay is not the optimum. Instead, an angle of approximately 83° with a pulse‐repetition period of 4.5 multiplied by the longest T1 is the optimum procedure. However, the results obtained from this procedure are only slightly better than those obtained from the standard „90 ‐ wait 5T1,”︁ method. It is further shown that the 83° angle is independent of T1, but that the integral accuracy is relatively dependent on the estimate of T1.
Nonlinear least‐squares fitting procedure for solid‐state NMR powder patterns
Authors: Kim Ae Ja , Butler Leslie G. 
Published: March 2007

AbstractA fitting procedure for the extraction of the characteristic NMR parameters from solid‐state NMR powder patterns is described at an introductory level. The Levenberg‐Marquardt nonlinear least‐squares algorithm is recoded in Matlab, a vector‐oriented programming language, so that the NMR simulation programs are more condensed than are those in traditional programming languages. Three examples of line‐shape fitting are shown: the deuterium powder pattern for the bridging deuterium site in [Et4N] [2HCr2(CO)10], the proton‐coupled 13C powder pattern for the bridging methylene site in cis‐(μ‐CH2)(μ‐CO)[FeCp(CO)]2, and the (14N, 195Pt)‐coupled 13C powder pattern for the Pt‐CN system in K2Pt(CN)4 · 3H2O. The results provide information about quadrupolar, dipolar, and chemical‐shielding tensors. In each case, the line‐shape is calculated from the spin Hamiltonian expressed in a simple, uncoupled basis set. The variables in each case are a small set of NMR parameters: the quadruple‐coupling constant and the asymmetry parameter. The effects of finite pulse‐lengths or anisotropic cross‐polarization are not included in the line‐shape simulations. The line‐shapes are powder patterns; averaging over the Euler angles, θ and x, is done either with constant angle step size or by the Conroy‐Wolfsberg tiling scheme.
Parameterized description of NMR signal reception systems part I: Impedance of transmission line and probe
Authors: Cho Shin‐Il , Sullivan Neil S. 
Published: March 2007

AbstractThe impedance‐matched condition and its relation to the reflection coefficient are discussed. Some important properties of transmission lines for impedance‐matching are considered. Resonance tank circuits in NMR probes are discussed with analogies to microwave cavity resonances. By analyzing reflection coefficients in terms of Q factors, the impedance‐matched condition is re‐derived in a manner that highlights practical considerations for high‐frequency applications.
Nuclear overhauser effect in coupled‐spin systems using selective perturbation
Authors: Krishnan V. V. , Kumar Anil 
Published: March 2007

AbstractInterest in the nuclear Overhauser effect (NOE) has increased enormously in recent years because of its wide application to the structure determination of molecules in the liquid state, particularly large molecules, such as biomolecules. Most NOE studies are carried out in spin systems that exhibit splittings because of indirect spin‐spin (J) couplings, but the most common NMR analyses ignore I splitting. We focus attention on the presence of J coupling and particularly on selective perturbation of a transition of coupled spins. Both steady‐state and transient NOE have been calculated in closed form. There is a large multiplet effect that results from the direct pumping effect that is observed in the intensities, careful measurement of which requires the use of small‐angle pulses. The use of a 90° pulse obliterates the multiplet effect. As an extension, cross‐correlation effects in the three‐spin system and the three‐spin effect in NOE spectra also are discussed. A brief analysis of spin diffusion in a multiple‐spin system is also included.
NMR rotating‐frame relaxation measurements of conformational exchanges on the microsecond time scale. Part I: Theory
Authors: Wang Yu‐Sen 
Published: March 2007

AbstractNMR rotating‐frame spin‐lattice relaxation (Tip) is a potentially powerful tool for the investigation of chemical exchange processes in the microsecond time range, a time range that is not readily examined by the usual solution NMR methods. This article deals with on‐resonance rotating‐frame‐relaxation measurements. The relaxation mechanism is analyzed to provide a theoretical basis for accurate evaluation of the contribution of chemical exchange to T1p rates. The procedure described permits T1p measurements for medium‐sued and large molecules in solution. Interpretation of the exchange contribution provides the dynamic parameters of exchange lifetime and chemical shift difference between exchange sites.
Methods of single‐ and double‐selective excitation: Theory and applications. Part I
Authors: Gaggelli Elena , Valensin Gianni 
Published: March 2007

AbstractThe use of selective excitation of individual multiplets or transitions in an NMR spectrum has long been suggested for spectral interpretation, observation of nuclear Overhauser effects, investigation of exchange kinetics, polarization transfer, suppression of unwanted signals, spectral editing, measurement of dipolar cross‐relaxation rates, slice and/or volume in in vivo spectroscopy, microscopy, and NMR imaging. A general view of theory and applications of selective excitation techniques are provided. The different ways of achieving the desired frequency selectivity or biselectivity (tailoring of hard pulses, shaping of soft pulses, trains of hard pulses) in the excitation profile are summarized.
Chemical shift imaging in nuclear magnetic resonance: A comparison of methods
Authors: Rumpel Helmut , Pope James M. 
Published: March 2007

AbstractChemical shift imaging techniques are magnetic resonance imaging methods that separately map the spatial distribution of individual peaks or components in a complex NMR spectrum. A range of chemical shift imaging techniques based around the commonly employed spin‐echo Fourier imaging sequences is classified and described. The performance of the methods with regard to field dependence, chemical shift selectivity, signal‐to‐noise ratio, and imaging times is compared as a guide to selecting the most appropriate technique for a particular application.
Review of MRI gradient waveform design methods with application in the study of motion
Authors: Duerk Jeffrey L. , Simonetti Orlando P. 
Published: March 2007

AbstractMany design techniques for magnetic resonance gradient waveforms have aimed at controlling the phase that results from spin motion during the application of gradients. This paper discusses the evolution of gradient waveform design into the gradient‐moment‐nulling and motion‐encoding efforts common today. It also describes current design methods and technology.
The Hamiltonians of NMR. Part III
Authors: Smith Scott A. , Palke William E. , Gerig J. T. 
Published: March 2007

AbstractBuilding on our previous discussions of the Hamiltonian operators that are important in the description of high‐resolution NMR experiments, we use here the same symbolism and approach to develop formulations for time‐dependent operators. These considerations lead to discussions of free precession and the influence of applied radio‐frequency fields. As with the previous articles, the presentations are explicit, the mathematical operations are explained in detail, and all assumptions made are indicated.
Orientational dependence of vicinal proton‐proton NMR coupling constants: The Karplus relationship
Authors: Minch Michael J. 
Published: March 2007

AbstractVicinal proton‐proton coupling constants depend on a variety of stereochemical parameters such as bond angle, bond length, substituent electronegativity and orientation, and — most importantly — on the torsion angle between the coupling protons. The sensitivity of vicinal proton‐proton coupling constants 3JHH′, to variations of dihedral angle ϕwas first rationalized in valence bond terms by Karplus, who showed that the coupling constants could be approximately fitted to a cos2ϕ function. The Karplus equation 3JHH′ = Acos2ϕ + Bcosϕ + C (or variants thereof) has been a major tool of the structural chemist for 35 years. Karplus started with the Ramsey formula for Fermi contact contribution, expressed by ground‐state wave functions and a mean excitation energy. More sophisticated molecular orbital (MO) treatments have afforded analogous expressions that may be used to predict trends correctly but are rarely useful for accurate estimations of dihedral angles. Numerous attempts have been made to account for the effect of substituents, bond angles, and lengths — either empirically by the choice of A, B, and C (with different values for each type of compound) or semiempirically, starting with theoretically more sophisticated expressions with statistically adjustable parameters. Theoretical and empirical approaches are reviewed and compared.
Signal‐to‐noise ratio: A calculation from first principle applied to NMR in the earth's field
Authors: Laukien Dirk D. , Weaver David , Tschopp Werner H. 
Published: March 2007

AbstractNMR in the Earth's field is used as an example for calculating the signal‐to‐noise ratio from first principle. A simple loop is used as a transmitter and a receiver coil. Parameters significant in a signal‐to‐noise calculation are derived for this application. The influence of the receiving electronics is included in the calculations. Example spectra of NMR signals obtained in the Earth's field are given.
ENC, a motor of progress in NMR
Authors: Ernst Richard R. 
Published: March 2007

AbstractDuring the course of my scientific career I have accumulated an uncountable number of debts to people, organizations, and fortunate events. I am particularly obliged to a long series of Experimental Nuclear Magnetic Resonance Conferences, the ENC's. Not only have they been an invaluable source of inspiration and an occasion for establishing new friendships, but the yearly ENC had, and still has, the same function as the first warm Sunday afternoon in spring time when people are eagerly promenading and showing their most pretty dress, prepared with much love during the preceding dark winter months. Each ENC is a landmark, an hour of truth where success or failure of the previous twelve months of intense research becomes evident.Indeed from 1964 to very recently, I was working and living truly from ENC to ENC, having only one thought in mind: to be properly prepared with a new experiment or a new revealing insight to be presented at the next conference. I think it is important in the unstructured life of a scientist to have these regular caesuras to account for ones achievements.In this article I would like to present, based on a special request by the editors, the abstracts of all my personal and co‐authored abstracts of ENC presentations from 1964 to 1992 as a token of appreciation for the importance the ENC's have played in my scientific life. They will be adorned with remarks on the context of their emergence.
Two‐dimensional 13C, heteroelement correlation spectroscopy
Authors: Fäcke Thomas , Wagner Ronald , Berger Stefan 
Published: March 2007

AbstractTwo‐dimensional heteronuclear correlation spectroscopy between the spin pairs 13C, nX (with n X = 2H, 6Li, 11B, 15N, 19F, 29Si, 31P, 77Se, 119Sn, 125Te, 195Pt, 199Hg, and 207Pb) is discussed. The necessary hardware requirements are explained, and the three most important correlation techniques are compared using product operator formalism. Selected simple examples demonstrate the usefulness of this new method.
Planar surface gradient coil
Authors: Cho Z. H. , Yi J. H. 
Published: March 2007

AbstractIn NMR imaging, spatial information of an object is made possible by the gradient fields. Desirable qualities in a gradient field for conventional imaging include linearity, speed, and strength. Recent developments in high resolution or fast imaging or both require strong gradient fields and fast switching capability. Until recently, most conventional gradient coils available were the Golay‐type, together with Helmholtz‐type coil, mounted on a cylindrical support. Some of the drawbacks of the cylindrically shaped coils include the fixed geometry and relatively weak gradient fields due to the limitation imposed on the object size, which necessitate the large coil diameter. In this article, a novel gradient coil, namely the surface gradient coil (SGC), is described and reviewed. The SGC, an unconventional gradient coil that is constructed on a flat surface, is presented as an alternative to the conventional Golay‐type coil. This flat and arbitrarily sized surface gradient coil could satisfy two important requirements. First, it could provide much larger gradient fields while providing substantially improved switching speed due to its small size. Secondly, the planar structure of the surface gradient coil, in conjunction with a surface radio frequency (RF) coil, provides a movable probe for localized imaging of large objects. The latter, i.e., the possibility of integrating the SGC with the surface RF coil suggests a new direction in NMR imaging similar to the movable probe, widely used in ultrasound imaging. The movable probe would then allow us to carry out fast in vivo high‐resolution imaging of the human body hitherto difficult to carry out with conventional gradient coils. The basic design concepts, together with the improved design, achieved through numerical optimization, and some experimental results obtained with the prototype SGC probes, are given.
Calculation of CIDNP signal intensities
Authors: Goez Martin 
Published: March 2007

AbstractA quantitative treatment of the radical pair mechanism, which is the predominant mechanism giving rise to chemically induced dynamic nuclear polarization (CIDNP), is presented. Calculation of the spin evolution of radical pairs is performed with the density matrix formalism. Combination of the results with the equations describing the radical pair dynamics leads to general relationships that allow the populations of the nuclear spin states in the reaction products to be obtained. Finally, it is shown how the line intensities observed in pulsed NMR experiments can be extracted from the computed nuclear spin polarizations.
Selection of coherence transfer pathways by pulsed‐field gradients in nmr spectroscopy
Authors: Zhu Jian‐Ming , Smith Ian C. P. 
Published: March 2007

AbstractThe use of pulsed‐field gradients has emerged as a promising approach for the selection of coherence transfer pathways in NMR spectroscopy. Applying field gradient pulses instead of phase cycling can reduce data acquisition time, minimize artifacts, and provide new ways to suppress solvent signals. This paper provides a practical introduction to the technique. The selection of coherence transfer pathways by field gradient pulses is based on the characteristic sensitivities of coherence to field gradients and on the formation of coherence transfer echoes. A general formulation for selection of coherence transfer pathways by field gradient pulses is provided. Examples are used to illustrate the design of field gradient pulse sequences for the selection of specific coherence transfer pathways in multiple‐pulse experiments.
Outcome of patients with Philadelphia chromosome‐positive chronic myelogenous leukemia post‐imatinib mesylate failure
Authors: Kantarjian Hagop , O'Brien Susan , Talpaz Moshe , Borthakur Gautam , Ravandi Farhad , Faderl Stefan , Verstovsek Srdan , Rios Mary Beth , Shan Jianqin , Giles Francis , Cortes Jorge 
Published: March 2007

AbstractBACKGROUND.The prognosis of patients with chronic myelogenous leukemia (CML) after failure of imatinib mesylate therapy is not well documented.METHODS.The outcome of 420 patients with CML post‐imatinib failure (resistance‐recurrence in 374; toxicities in 46) were reviewed in relation to survival, overall, and by different therapies.RESULTS.The estimated 3‐year survival rates were 72% in 88 patients who progressed in chronic phase, 30% in 130 patients who progressed in accelerated phase, 7% in 156 patients who progressed in blastic phase, and 75% in 37 patients in chronic phase with imatinib intolerance. Survival in chronic phase was better when subsequent therapy was nilotinib or dasatinib vs allogeneic stem cell transplant vs others (estimated 2‐year survival rates 100% vs 72% vs 67%; P = .01), but not in accelerated‐blastic phase.CONCLUSIONS.Prognosis post‐imatinib failure in chronic phase is reasonable; it is poor if the CML phase post‐imatinib failure is accelerated or blastic. Cancer 2007. © 2007 American Cancer Society.