bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed‐field gradient NMR study of sodium dodecyl sulfate micelle–peptide association
Authors: Deaton Kimberly R. , Feyen Elizabeth A. , Nkulabi Hassan J. , Morris Kevin F.
Published: September 2002

Pulsed‐field gradient (PFG) NMR spectroscopy was used to characterize the interactions between a series of small peptides and sodium dodecyl sulfate (SDS) micelles. The study was undertaken because peptide–micelle interactions are often exploited in the chromatographic analysis of complex mixtures, and therefore an accurate knowledge of peptide–micelle association constants is essential for a thorough understanding of the separation mechanism in these techniques. In the PFG‐NMR experiment, diffusion coefficients for each peptide were measured in free solution and in the presence of SDS micelles. These diffusion coefficients allowed the mole fraction of peptide molecules associated with SDS micelles and the peptide–micelle association constants, Keq, to be calculated. In a study of dipeptides derived from the leucine enkephalin (YGGFL) and D‐(Ala)2‐leucine enkephalin (YAGFL) amino acid sequences, only Phe–Leu was found to associate strongly with the micellar aggregates. The equilibrium constant for this dipeptide was found to be 69 ± 6 M−1. The dipeptides Tyr–Gly, Tyr–Ala, Gly–Gly and Gly–Phe exhibited little to no micelle binding, whereas Tyr–Leu had an association constant that was a factor of four less than the Phe–Leu value. Furthermore, the association constants for the pentapeptides leucine enkephalin and D‐(Ala)2‐leucine enkephalin (130 ± 8 and 584 ± 38, respectively) were both higher than the Keq values for all dipeptides investigated. These results suggest that micelle–induced changes in peptide conformation and peptide hydrophobicity both play important roles in governing peptide–micelle binding. Copyright © 2001 John Wiley & Sons, Ltd.
Real‐time measurements of cellular oxygen consumption, pH, and energy metabolism using nuclear magnetic resonance spectroscopy
Authors: Pilatus Ulrich , Aboagye Eric , Artemov Dmitri , Mori Noriko , Ackerstaff Ellen , Bhujwalla Zaver M.
Published: September 2002

Changes in molecular expression or apoptotic behavior, induced by malignant transformation or anticancer treatment, are frequently reflected in cellular metabolism and oxygen consumption. A technique to monitor oxygen consumption, cell physiology, and metabolism noninvasively would provide a better understanding of interactions between molecular changes and metabolism in malignant transformation and following cancer treatment. Such a system was developed in this study by adapting multinuclear MRI and spectroscopic techniques to an isolated cell perfusion system. The system was evaluated by studying the effects of two agents, carbonyl cyanide m‐chlorophenylhydrazone (CCCP) which is an uncoupler of oxidative phosphorylation, and antimycin, an inhibitor of oxidative phosphorylation, on the oxygen consumption and metabolism of MCF‐7 and MatLyLu cancer cell lines. Magn Reson Med 45:749–755, 2001. © 2001 Wiley‐Liss, Inc.
Detection of myocardial viability based on measurement of sodium content: A 23Na‐NMR study
Authors: Horn Michael , Weidensteiner Claudia , Scheffer Heike , Meininger Martin , de Groot Mark , Remkes Helga , Dienesch Charlotte , Przyklenk Karin , von Kienlin Markus , Neubauer Stefan
Published: September 2002

MRI of total sodium (Na) content may allow assessment of myocardial viability, but information on Na content in normal myocardium, necrotic/scar tissue, and stunned or hibernating myocardium is lacking. Thus, the aims of the study were to: 1) quantify the temporal changes in myocardial Na content post‐myocardial infarction (MI) in a rat model (Protocol 1); 2) compare Na in normally perfused, hibernating, and stunned canine myocardium (Protocol 2); and 3) determine whether, in buffer‐perfused rat hearts, infarct scar can be differentiated from intact myocardium by 23Na‐MRI (Protocol 3). In Protocol 1, rats were subjected to LAD ligation. Infarct/scar tissue was excised at control and 1, 3, 7, 28, 56, and 128 days post‐MI (N = 6–8 each), Na content was determined by 23Na‐NMR spectroscopy (MRS) and ion chromatography. Na content was persistently increased at all time points post‐MI averaging 306*–160*% of control values (*P < 0.0083 vs. control). In Protocol 2, 23Na‐MRS of control (baseline), stunned and hibernating samples revealed no difference in Na. In Protocol 3, 23Na‐MRI revealed a mean increase in signal intensity, to 142 ± 6% of control values, in scar tissue. A threshold of 2 standard deviations of the image intensity allowed determination of infarct size, correlating with histologically determined infarct size (r = 0.91, P < 0.0001). Magn Reson Med 45:756–764, 2001. © 2001 Wiley‐Liss, Inc.
Single‐voxel proton MRS of the human brain at 1.5T and 3.0T
Authors: Barker Peter B. , Hearshen David O. , Boska Michael D.
Published: September 2002

Single‐voxel proton spectra of the human brain were recorded in five subjects at both 1.5T and 3.0T using the STEAM pulse sequence. Data acquisition parameters were closely matched between the two field strengths. Spectra were recorded in the white matter of the centrum semiovale and in phantoms. Spectra were compared in terms of resolution and signal‐to‐noise ratio (SNR), and transverse relaxation times (T2) were estimated at both field strengths. Spectra at 3T demonstrated a 20% improvement in sensitivity compared to 1.5T at short echo times (TE = 20 msec), which was lower than the theoretical 100% improvement. Spectra at long echo times (TE = 272 msec) exhibited similar SNR at both field strengths. T2 relaxation times were almost twofold shorter at the higher field strength. Spectra in phantoms demonstrated significantly improved resolution at 3T compared to 1.5T, but resolution improvements in in vivo spectra were almost completely offset by increased linewidths at higher field. Magn Reson Med 45:765–769, 2001. © 2001 Wiley‐Liss, Inc.
Examining a canine model of stunned myocardium with Gd‐DTPA‐enhanced MRI
Authors: Thornhill Rebecca E. , Prato Frank S. , Pereira Raoul S. , Wisenberg Gerald , Sykes Jane
Published: September 2002

It has previously been shown that the distribution volume of Gd‐DTPA (λ) in infarcted, canine myocardium is higher than that of normal tissue. The purpose of this study was to determine whether stunned myocardium exhibits increased λ. Stunning was produced in beagles by means of 30 min LAD occlusion followed by 3 weeks (n = 4) reperfusion. Gd‐DTPA was infused at each imaging session and λ determined in vivo using a saturation recovery turboFLASH sequence; cine imaging was used to assess ventricular wall thickening (%WT). 201Tl uptake was used as an independent assessment of viability. %WT data confirmed that the brief insult caused prolonged, yet reversible, regional contractile dysfunction in each animal. %WT was not significantly different from baseline values by 3 weeks post‐reflow. Normal 201Tl uptake confirmed the absence of infarction. The λ of stunned tissue (λ = 0.381 ± 0.030 ml/g) was not elevated above that of normal tissue (λ = 0.398 ± 0.027 ml/g, P = NS), at any time point studied, in vivo. These data suggest that an increase in λ is a specific indicator of irreversible damage. Magn Reson Med 45:864–871, 2001. © 2001 Wiley‐Liss, Inc.
Incidence of F waves in single human thenar motor units
Authors: Thomas Christine K. , Johansson Roland S. , Bigland‐Ritchie Brenda
Published: September 2002

F‐wave generation, axon conduction velocities, and contractile properties were compared in 44 healthy individual human thenar motor units. Force and muscle action potentials were recorded when single motor axons were stimulated intraneurally about 10 cm proximal to the elbow. Each stimulus usually evoked only one electromyographic (EMG) potential. However, in seven units (16%), a single stimulus elicited an F wave in response to 1.7 ± 1.6% (mean ± SD) of the stimuli applied. Axon conduction velocity proximal to the site of stimulation was faster than distal conduction velocity (72.7 ± 8.0 m/s versus 64.2 ± 10.5 m/s). Distal conduction velocities, twitch forces, and contraction times were similar for units that did and did not generate F waves. Thus, no obvious subset of thenar motor units generated F waves. These results provide valuable baseline information on F waves that can be used to assess changes in axon conduction, motor unit contractile properties, and motoneuron excitability in disease. © 2002 John Wiley & Sons, Inc. Muscle Nerve 25: 77–82, 2002
Diabetes, peripheral neuropathy, and old age disability
Authors: Resnick Helaine E. , Stansberry Kevin B. , Harris Tamar B. , Tirivedi Mahdvi , Smith Kimberly , Morgan Polly , Vinik Aaaron I.
Published: September 2002

The purpose of this study was to determine whether peripheral neuropathy explains the apparent association between diabetes and disability in old age, and to evaluate the utility of lower extremity function tests in older diabetic adults with and without neuropathy. We evaluated 39 adults, aged 70–79 years, for pressure sensation (log10g), vibration perception threshold (VPT; microns), and electrophysiologic function of the peroneal nerve. The subjects included patients with established diabetic neuropathy (DN; n = 14), diabetic controls without neuropathy (DC; n = 13), and nondiabetic controls (NDC; n = 12). Nonparametric statistical methods were used to relate neuropathy measures to performance in tests of walking speed, static and dynamic balance, coordination, and ankle strength (kilograms). Significant age‐adjusted correlations were observed between measures of sensory neuropathy and a variety of performance measures, and electrophysiologic measures were related to static balance. DN subjects had significantly higher pressure sensation than NDC (5.17 vs 3.38g, P < 0.05), higher VPT (62.5 vs 21.7 μm, P < 0.05), and lower peroneal motor response amplitudes at multiple sites. Pressure sensation and nerve conduction measures did not differ between DC and NDC. Compared with NDC, DN subjects performed significantly worse on tests of walking speed (0.99 vs 1.34 m/s; P < 0.05), static balance (4.9 vs 20.4 s; P < 0.05), dynamic balance (9.23 vs 25.52 s; P < 0.05), and coordination (6.73 vs 4.76 s; P < 0.05). No differences were observed in these measures between DC and NDC. Observed differences in physical abilities between older diabetic and nondiabetic adults may have been due to the subset of diabetic individuals with peripheral neuropathy. Quantitative measures of sensory and motor nerve function have distinct effects on physical performance. Interventions aimed at reducing the impact of diabetes‐associated disability in old age may have the greatest impact among people with peripheral neuropathy. © 2002 John Wiley & Sons, Inc. Muscle Nerve 25: 43–50, 2002
Differential regulation of survival and growth in adult sympathetic neurons: An invitro study of neurotrophin responsiveness
Authors: Orike N. , Thrasivoulou C. , Wrigley A. , Cowen T.
Published: September 2002

The survival and growth of embryonic and postnatal sympathetic neurons is dependent on both NGF and NT3. While it has been established that adult sensory neurons survive independently of neurotrophins, the case is less clear for adult sympathetic neurons, where the studies of survival responses to neurotrophins have relied upon using long‐term cultures of embryonic neurons. We have previously established a method to culture purified young (7 day) and adult (12 week) sympathetic neurons isolated from adult rat superior cervical ganglia (SCG) in order to examine their survival and growth responses to neurotrophins. We now show that by 12 weeks after birth virtually all neurons (90%) survive for 24 h in the absence of neurotrophins. Neuron survival is unaffected by treatment with anti‐NGF antibodies (anti‐NGF) or with the tyrosine kinase inhibitor, K252a, confirming the lack of dependence on extrinsic neurotrophins. Duration of neuron survival in culture increases significantly between E19 and day 7 and week 12 posnatally, and is similarly unaffected by the presence of anti‐NGF or K252a. Saturating concentrations of NGF and NT3 are equipotent in promoting neurite extension and branching. However, we find that NGF is more potent than NT3 in promoting neurite growth, irrespective of postnatal age. The growth‐promoting effects of NGF and NT3 are almost entirely blocked by K252a, demonstrating that these effects are mediated via activation of Trk receptors, which therefore appear to remain crucial to plasticity of adult neurons. Our results indicate that maturing neurons acquire protection against cell death, induced in the absence of neurotrophin, while retaining their growth responsiveness to these factors. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 295–305, 2001
Local stability in endogenous growth models
Authors: Martínez‐García María Pilar
Published: September 2002

The local stability of balanced paths in endogenous growth models is investigated. Under the fulfillment of transversality conditions, a general instability result is established. It has been proved that models with one state variable are completely unstable, whereas two alternatives are possible in models with two states: complete instability or saddle point property. Balanced paths of models with three state variables can either be completely unstable, satisfy the saddle point property with a one‐dimensional stable manifold, or have a two‐dimensional manifold approaching them. Necessary and sufficient conditions for the saddle point property to occur are given. Transversality conditions guarantee that closed contours and periodic sinuoidal motions around the balanced path are ruled out. Copyright © 2001 John Wiley & Sons, Ltd.
A small civil service in transition: the case of Estonia
Authors: Randma Tiina
Published: September 2002

Although scholars have shown consistent interest in small states in past decades, the Republic of Estonia has not been included in any study of small states owing to its brief history of independent statehood. This article provides an overview of the development of the Estonian civil service, to enable readers to understand the background and scope of reforms in the 1990s. The objective of the study is to test previous findings on small states using empirical research into the Estonian civil service. Interviews with civil servants reveal a few new characteristics attributable to the size of a state such as personalization of units and organizational objectives, and additional sources of organizational instability. However, it is argued that several problems of public administration in developing countries and small states overlap, which creates difficulties in distinguishing between developmental factors and the size of the state as determinants. Copyright © 2001 John Wiley & Sons, Ltd.
Decentralization of road administration: case studies in Africa and Asia
Authors: Robinson Richard , Stiedl David
Published: September 2002

A study of decentralization of road administration in developing countries has been undertaken, including a literature review, and field studies in Nepal, Uganda and Zambia. The findings are reported under the headings of: constitutions and governance; policy and planning; financial and fiscal aspects; institutions, management and human resources; operations; and contribution to poverty alleviation. Decentralization of road administration has potential for improving the delivery of rural transport infrastructure services. But the evidence from this study suggests that it is proving difficult to realize fully the expected benefits. Problems include: lack of local government powers to exercise political influence; insufficient financial resources; lack of management capability; and a lack of accountability mechanisms. Limited data also suggest that there is little evidence of existing decentralized systems being particularly responsive to addressing the needs of the rural poor. There is a need for the poor to be involved more actively in the planning, financing and implementation process. Different models for administrative decentralization are described and recommendations are made for approaches likely to be the most appropriate for rural transport infrastructure administration and management. Copyright © 2001 John Wiley & Sons, Ltd.
Prenatal diagnosis of two rare de novo structural aberrations of the Y chromosome: cytogenetic and molecular analysis
Authors: Velissariou Voula , Antoniadi Thalia , Patsalis Philippos , Christopoulou Stavroula , Hatzipouliou Athina , Donoghue Jackie , Bakou Katerina , Kaminopetros Petros , Athanassiou Vassilis , Petersen Michael B.
Published: September 2002

Two rare de novo structural aberrations of the Y chromosome were detected during routine prenatal diagnosis: a satellited non‐fluorescent Y chromosome (Yqs), the first de novo Yqs to be reported in a fetus, and a terminal deletion of the Y chromosome long arm del(Y)(q11). In both cases detailed cytogenetic and molecular analyses were undertaken. In the case of the Yqs it was demonstrated by fluorescence in situ hybridization (FISH) that the satellites were derived from chromosome 15. In the case of the del(Yq), it was shown with molecular analysis by polymerase chain reaction (PCR) amplification of sequence‐tagged sites (STS‐PCR) that the deleted portion of the long arm of chromosome Y included the azoospermia factor loci, AZFb and AZFc. The clinical significance of these findings is discussed. Copyright © 2001 John Wiley & Sons, Ltd.
Synthesis and properties of polydimethylsiloxane‐containing block copolymers via living radical polymerization
Authors: Huan Kim , Bes Laurence , Haddleton David M. , Khoshdel Ezat
Published: September 2002

Polydimethylsiloxane (PDMS) block copolymers were synthesized by using PDMS macroinitiators with copper‐mediated living radical polymerization. Diamino PDMS led to initiators that gave ABA block copolymers, but there was low initiator efficiency and molecular weights are somewhat uncontrolled. The use of mono‐ and difunctional carbinol–hydroxyl functional initiators led to AB and ABA block copolymers with narrow polydispersity indices (PDIs) and controlled number‐average molecular weights (Mn's). Polymerization with methyl methacrylate (MMA) and 2‐dimethylaminoethyl methacrylate (DMAEMA) was discovered with a range of molecular weights produced. Polymerizations proceeded with excellent first‐order kinetics indicative of living polymerization. ABA block copolymers with MMA were prepared with between 28 and 84 wt % poly(methyl methacrylate) with Mn's between 7.6 and 35 K (PDI <1.30), which show thermal transitions characteristic of block copolymers. ABA block copolymers with DMAEMA led to amphiphilic block copolymers with Mn's between 9.5 and 45.7 K (PDIs of 1.25–1.70), which formed aggregates in solution with a critical micelle concentration of 0.1 g dm−3 as determined by pyrene fluorimetry experiments. Monocarbinol functional PDMS gave AB block copolymers with both MMA and DMAEMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1833–1842, 2001
Syntheses of amphiphilic block copolymers by living cationic polymerization of vinyl ethers and their selective solvent‐induced physical gelation
Authors: Sugihara Shinji , Matsuzono Shin‐Ichiro , Sakai Hideki , Abe Masahiko , Aoshima Sadahito
Published: September 2002

Amphiphilic diblock copolymers were prepared by the living cationic polymerization of vinyl ethers in the presence of added bases, and their selective solvent‐induced physical gelation behavior was investigated. The block copolymerization of 2‐phenoxyethyl vinyl ether (PhOVE) and 2‐methoxyethyl vinyl ether (MOVE) was carried out in the presence of ethyl acetate with Et1.5AlCl1.5 in toluene at 0 °C. Despite the rate difference, diblock copolymers with a very narrow molecular weight distribution were obtained, quantitatively. By adding the selective solvent, water, to the acetone solution of the diblock copolymer, PhOVE200‐b‐MOVE400, physical gelation occurred suddenly and the system ceased to flow, maintaining transparency. Viscoelastic measurements and transmission electron microscopic observations were performed to examine the characteristic gelation behavior and structure of the obtained gels. Various gelation conditions and physical gelation by other amphiphilic block copolymers were also designed on the basis of the solubility of each block segment. Further, new forms of physical gelation, accompanied by the solubilization of immiscible organic compounds, were achieved using similar diblock copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3190–3197, 2001
Online monitoring of birefringence development in heat‐setting polymer films with a fast dual‐wavelength optical technique. I. Uniaxially oriented poly(ethylene naphthalate)
Authors: Galay J. , Cakmak M.
Published: September 2002

The purpose of this article is to study the fast structural changes that take place during the deformation and heat setting of uniaxially preoriented poly(ethylene 2,6‐naphthalate) films. For this purpose, an online birefringence measurement system coupled with a heat‐setting oven was used. In the online birefringence system, whose details were reported previously (H. Venkatesvaran and M. Cakmak, SPE ANTEC Tech Pap 1993, 39, 257; H. Venkatesvaran and M. Cakmak, Polym Eng Sci 2001, 41, 341), a green and red laser is passed through the films being annealed in a heat‐setting chamber; the resulting data are analyzed for the details of structural mechanisms that take place during this process. This technique is shown to be capable of detecting reversals in birefringence development; as a result, complex sequences of structural evolution can be tracked. The design of this system allows one to observe not only the increase or decrease in birefringence during the course of the heat‐setting process but also the rate dependencies on processing variables. In this study, we establish that the rate of structural rearrangement, as detected by birefringence, depends strongly on the state of the pre‐existing chain orientation and the level of crystallinity. Increased levels of preorientation in the films results in decreases in the rate of birefringence change during heat setting. This is primarily attributed to the increased levels of steric hindrance developed with the increase in orientation and crystallinity in the preoriented samples. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1107–1121, 2001
Steel plated structures
Authors: Johansson Bernt , Veljkovic Milan
Published: September 2002

Steel plated structures are important because they are used in large structures of vital importance for society. For the steel construction industry they are however of less importance as they are a small part of the turnover. Since the big disasters with box girder bridges more than thirty years ago very little money, public or private, has been spent on development of plated structures and hence progress has been fairly slow. Fortunately, the scientific interest in buckling problems is still high and this has led to some important steps forward. The European project of harmonizing design standards has brought plated structures onto the agenda again in connection with the conversion of Eurocode 3 to EN. There are several open questions, some of which are discussed in the context of new experimental and theoretical results.
Seismic monitoring and early damage assessment systems in Japan
Authors: Yamazaki Fumio
Published: September 2002

Recent developments of seismic monitoring systems and early damage assessment systems in Japan are reviewed. National and local governments in Japan have deployed numerous seismic instruments for the purpose of disaster management, mostly after the 1995 Kobe earthquake. Utility companies and highway authorities have also established seismic networks in order to use earthquake information for supply or traffic control just after the occurrence of an earthquake. Based on the collected seismic information and the GIS‐based inventory data, held on computer, early damage assessments are conducted and the results are used for emergency management at the stage when actual damage information is scarce. In this paper, typical seismic networks and early damage assessment systems recently developed in Japan are presented and their roles in disaster management and future directions are discussed.
Migration of protons in a chain of tyrosine residues
Authors: Stefanov V. E. , Tulub A. A.
Published: September 2002

This article deals with the proton migration in a tyrosine stack, which models the proton channels existing in a number of proteins, including tubulin. The magnesium ion Mg2+ within the complex with guanosine triphosphate facilitates dissociation of a water molecule through initiating a shift of protons along the chain composed of relatively distant tyrosine residues. The process is thermodynamically stable (ΔG298<0). The energy barrier for the protein shift does not exceed 3.15 kJ/mole. A relatively weak electrostatic field mimicking electret properties of proteins facilitates long‐distance proton migration. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 409–415, 2001
Multiresolution analysis of density operators, electron density, and energy functionals
Authors: Nagy Szilvia , Pipek János
Published: September 2002

Numerical calculations show that, in extended electronic systems, complex one‐particle states appear with different shape characteristics at different length scales. New results in the theory of wavelets are applied in this contribution for a consistent description of densities and density operators with a continuous kernel at various length scales. It is proved here that, for real physical systems, according to physical intuition, neither arbitrarily fine nor arbitrarily rough details of the wave function and density operators can exist. It is also shown that the calculation of both kinetic energy and interaction energy expectation values can be reduced to the determination of some universal functions defined on integer‐valued arguments. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Conformational study of a new SGTx1 neurotoxin from the spider Scodra griseipes using mass spectrometry
Authors: Marvin Laure , Lange Catherine
Published: September 2002

SGTx1 is a new neurotoxin from the venom of Scodra griseipes. Because of the small quantity of this natural peptide available, mass spectrometry was used to obtain information on its higher‐order structure. The kinetics of reduction by 1,4‐dithiothreitol (DTT) was monitored by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS), and showed that one of the three disulfide bridges was appreciably more accessible to the DTT. Studies based on the charge state distribution (CSD) and H/D exchange of the non‐reduced peptide, under neutral and acidic conditions, were performed using electrospray mass spectrometry (ES‐MS). In neutral solution, SGTx1 showed a maximum charge state of four compared with seven potentially protonated basic residues, and all labile hydrogens were exchanged. However, under acidic conditions, a maximum charge state of only five was observed, and four of the labile hydrogens could not be deuterated. These observations are interpreted in terms of a rigid structure maintained by the disulfide bridges, which can be temporarily relaxed by disulfide bridge scrambling only at higher pH values. Copyright © 2001 John Wiley & Sons, Ltd.
On‐line measurement of the absolute humidity of air, breath and liquid headspace samples by selected ion flow tube mass spectrometry
Authors: S̆panĕl Patrik , Smith David
Published: September 2002

We describe how selected ion flow tube mass spectrometry (SIFT‐MS) can be used to determine the absolute humidity of air, breath and liquid headspace samples. This involves the determination of the relative count rates of the H3O+ ions and those H3O+.(H2O)1,2,3 hydrate ions that inevitably form in the helium carrier gas when humid samples are being analysed by SIFT‐MS using H3O+ precursor ions. This requires an understanding of the kinetics of hydrated hydronium ion formation, the involvement of mass discrimination in the analytical quadrupole mass spectrometer and the decreased diffusive loss of the heavier hydrates along the flow tube. Thus, we show that the humidity of breath and liquid headspace samples, typically at the few percent level, can be directly obtained on‐line to the SIFT‐MS instrument along with the concentrations of trace gases, which are present at much lower levels. We emphasise the value of parallel humidity measurements in ensuring good real‐time sampling of breath and liquid headspace and the value of such measurements to trace gas analysis using SIFT‐MS. Copyright © 2001 John Wiley & Sons, Ltd.
Reactivity of anomeric 1α‐ and 1β‐pentofuranosyl azide derivatives in ammonia chemical ionization
Authors: Kralj Bogdan , Kocjan Darko , Kobe Jože
Published: September 2002

Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric 1α‐ and 1β‐azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that β‐anomers have higher affinities for H+ and NH4+ ions than α‐azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN3 giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3]+ ion, a competitive product to the ammonium‐attached [SN3NH4]+ ion. The fragmentation pathways of the stable and metastable [MNH4]+, MH+ ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4]+ and/or [SNHN2NH3]+ ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3]+, [SNH3]+ and SNH+ in some examples correlates with the exothermicity of the corresponding [MNH4]+ and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high‐pressure region of the CI ion source. Copyright © 2001 John Wiley & Sons, Ltd.
Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry δ13C analysis of small polyfunctional compounds
Authors: Docherty Gordon , Jones Vicky , Evershed Richard P.
Published: September 2002

Carbohydrates and proteins are among the most abundant naturally occurring biomolecules and so suitable methods for their reliable stable isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) are required. Due to the non‐volatile nature of these compounds they require hydrolytic cleavage to their lower molecular weight subunits and derivatisation prior to GC/C/IRMS analysis. The addition of carbon to the molecules and any kinetic isotopic fractionation associated with derivatisation must be accounted for in order to provide meaningful stable isotope values and estimates of propagated errors. To illustrate these points amino acid trifluoroacetate/isopropyl esters and alditol acetates were prepared from authentic amino acids and monosaccharides, respectively. As predicted from the derivatisation reaction mechanisms, a kinetic isotope effect was observed which precludes direct calculation of δ13C values of the amino acids and monosaccharides by simple mass balance equations. This study shows that the kinetic isotope effect associated with derivatisation is both reproducible and robust, thereby allowing the use of correction factors. We show how correction factors can be determined and accurately account for the addition of derivative carbon. As a consequence of the addition of a molar excess of carbon and the existence of a kinetic isotope effect during derivatisation, errors associated with determined δ13C values must be assessed. We illustrate how such errors can be quantified (for monosaccharides ±1.3‰ and for amino acids between ±0.8‰ and ±1.4‰). With the magnitude of the errors for a given δ13C value of a monosaccharide or amino acid quantified, it is possible to make reliable interpretations of δ13C values, thereby validating the determination of δ13C values of amino acids as TFA/IP esters and monosaccharides as alditol acetates. Copyright © 2001 John Wiley & Sons, Ltd.
Quantitative determination of noncovalently bound acridinium in protein conjugates by liquid chromatography/electrospray ion trap mass spectrometry
Authors: Adamczyk Maciej , Gebler John C. , Shreder Kevin , Wu Jiang
Published: September 2002

A sensitive and robust liquid chromatography/electrospray ion trap mass spectrometry (LC/MS/MS) method has been developed for the quantitative determination of noncovalently bound acridinium free acid in protein‐acridinium conjugates. The lower level of quantitation (LOQ) for acridinium free acid was determined to be 0.6 ng. The assay was validated with a linear concentration range of 0.6–60 ng. The method requires minimum sample handling and is specific, reproducible, and provides a new aspect for protein‐acridinium conjugate characterization. Copyright © 2001 John Wiley & Sons, Ltd.
Hydrogen isotope analysis of natural abundance and deuterium‐enriched waters by reduction over chromium on‐line to a dynamic dual inlet isotope‐ratio mass spectrometer
Authors: Donnelly Terry , Waldron Susan , Tait Andrew , Dougans Julie , Bearhop Stuart
Published: September 2002

This paper describes the application of a simple chromium reduction furnace which can be interfaced with a dual inlet isotope‐ratio mass spectrometer thus providing the capacity for cheap, fast, accurate and precise measurement of δDV−SMOW by dynamic mass spectrometry. Measurements are precise to the order of ≤0.5‰. Mean 95% confidence intervals for the Vienna Standard Mean Ocean Water (V‐SMOW) to Standard Light Antarctic Precipitation (SLAP) range are in the order of 2.5‰ and the system is linear over the range −428 to 23,000‰. Memory effects do exist, but are small for natural abundance samples and can be minimised by careful planning of the analytical load. Copyright © 2001 John Wiley & Sons, Ltd.
Study on application of CMA to land mobile LEO satellite communication systems based on a deterministic channel model
Authors: Xu Chang Qing , Law Choi Look , Yoshida Susumu
Published: September 2002

This paper studies the application of the constant modulus algorithm (CMA) in land mobile low earth orbit (LEO) satellite communication systems. Two propagation phenomena prevail in narrow band land mobile LEO satellite channel, namely, adjacent channel interference (ACI) and frequency‐non‐selective fading. The performance of CMA for ACI cancellation and the behaviours of CMA in frequency‐non‐selective fading channels are evaluated using a digital beamforming (DBF) array antenna simulation scheme. All these evaluations are based on a simple but efficient channel model which provides a good and fast simulation method for land mobile LEO satellite channels. The restricted Jakes Doppler power spectral density (psd) function is incorporated into the model to ensure that it will be appropriate for the evaluation of a DBF antenna. Our results reveal that CMA can reject ACI and work well in frequency‐non‐selective fading channels. Copyright © 2002 John Wiley & Sons, Ltd.
Oscillatory adsorption: a first‐principles linear kinetic model
Authors: Quinton J. S. , Dastoor P. C.
Published: September 2002

The kinetics of propyltrimethoxysilane (PTMS) films exhibit oscillatory adsorption when grown upon aluminium and iron oxide surfaces. This phenomenon is identified by the presence of non‐linear oscillations in adsorbate surface coverage, measured by X‐ray photoelectron spectroscopy (XPS), as a function of exposure time and solution concentration. In this paper, a mathematical model based upon the chemistry of the adsorption system is presented to describe the time‐dependent behaviour. The oscillatory nature of organosilane adsorption can be modelled by the evolution of three unique adsorbate species whose presence at the surface is dominated by displacement processes. The model presented here quantitatively describes the rate, non‐linearity and influence of experimental deposition parameters on PTMS adsorption. From the mathematical construct, a model of the physical origins of the oscillatory adsorption phenomenon is presented. Copyright © 2001 John Wiley & Sons, Ltd.
Surface and structure analysis of ultrathin multilayer structures for copper diffusion studies
Authors: Sun Y.‐M. , Lee S. Y. , Lemonds A. , Lozano J. , Zhou J.‐P. , Ekerdt J. G. , White J. M. , Imesh I.
Published: September 2002

The development of ultrathin multilayer structures suitable for copper diffusion studies was investigated. The structures were examined by x‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS). Copper/barrier/SiO2/Si(100) and barrier/Cu/SiO2/Si(100) structures were fabricated on thermally grown SiO2 by physical vapor deposition. Both tantalum and tungsten were chosen as the copper diffusion barrier and their thickness was held at <10 nm. For 2 nm of Cu on 10 nm of Ta, XPS showed steadily increasing Ta 4f and decreasing Cu 2p signals with annealing time at 400 °C, with changes occurring rapidly over the first 60 min and then much slower for the remaining time (up to 8 h). Cross‐sectional TEM indicated copper island formation on the tantalum surface. Copper islands were also found on tungsten films. For the reverse structure, W(5 nm)/Cu(700 nm)/SiO2/Si(100), no island formation was found after the thermal treatment. X‐ray photoelectron spectroscopy did detect a very weak Cu 2p signal after annealing for 8 h at 400 °C, which is equivalent to ∼0.2% copper bulk concentration in the tungsten barrier. Copyright © 2001 John Wiley & Sons, Ltd.
Distribution of the composition and micromechanical properties of Be/316L stainless steel following diffusion bonding
Authors: Zhang Peng‐cheng , Bai Bin , Shen Liang , Zhou Jue‐sheng
Published: September 2002

Joining of beryllium and 316L stainless steel by hot isostatic pressing (HIP) with and without an interlayer was investigated. Metallurgical observation, scanning Auger microscopy (SAM) and nanoindentation were performed for basic characterization of bonded joints. It is shown that the diffusion depth of Be into 316L stainless steel is much greater than that of Cr, Ni or Fe into beryllium, and it is ∼400 µm. The nanohardness of the diffusion zone on the beryllium side increases sharply due to intermetallic compounds, and the tensile strength of the Be/316L joint is <10 MPa. For a Be/Cu/316L joint, a Cu interlayer blocks the diffusion of Fe into Be, but Ni is gathered at the Cu/316L interface and a crack is formed at this stress field. For a Be/Cu/Ni/316L joint, the diffusion depth increases further. Change of composition, mechanical property with distance in diffusion zone is smooth, and the tensile strength increases to ∼50 MPa. Copyright © 2001 John Wiley & Sons, Ltd.
Analysis of inhomogeneous thin films of ZrO2 by the combined optical method and atomic force microscopy
Authors: Franta D. , Ohlídal I. , Klapetek P. , Pokorný P. , Ohlídal M.
Published: September 2002

In this paper results concerning the complete optical analysis of inhomogeneous ZrO2 films are introduced. The optical analysis of these films is carried out using the combined optical method based on interpreting experimental data corresponding to variable angle of incidence spectroscopic ellipsometry (VASE) and near‐normal incidence spectroscopic reflectometry (NNSR). The model of the ZrO2 films used for interpretation of the experimental data achieved using the combined method exhibits a continuous refractive index profile. It is shown that this model is satisfactory for treating the experimental data. Further, it is shown that all the parameters characterizing the model mentioned can be determined with high accuracy. By means of atomic force microscopy (AFM) it is found that the upper boundaries of the inhomogeneous ZrO2 films are slightly rough. The values of the basic statistical quantities characterizing this boundary roughness are evaluated using the AFM data. The optical inhomogeneity of the ZrO2 films studied is explained by the columnar structure of these films. Copyright © 2001 John Wiley & Sons, Ltd.
Selective catalytic reduction of NOx by methane over Co/ZrO2 catalysts
Authors: Hadjiivanov K. , Avreyska V. , Tzvetkov G. , Stefanov P. , Chupin C. , Mirodatos C. , Marinova Ts.
Published: September 2002

The effect of the preparation on the catalytic performances of Co/ZrO2 catalysts in the selective catalytic reduction of nitrogen oxides with methane was studied. The samples were prepared by grafting and impregnation with different solutions of cobalt salts. X‐ray photoelectron spectroscopy analysis showed that the cobalt oxidation state is 2+ in all samples. It was found that a high cobalt dispersion favours nitrogen selectivity, especially at temperatures below 350 °C. All samples show a maximum NO conversion in the temperature interval 300–350 °C, but the nitrogen selectivity decrease at this temperature range. The Fourier transform infrared spectroscopic studies showed that although the surface nitrates formed on bare zirconia are highly inert, the nitrates on cobalt particles fully interact with methane at 300 °C to produce an organic nitrogen‐containing deposit that is known to react with NOx to form nitrogen. Compared with the reference Co‐ZSM‐5 catalyst, the nitrates on Co/ZrO2 samples react with methane at a higher temperature, which accounts for their catalytic performances. Copyright © 2001 John Wiley & Sons, Ltd.
Morphogenesis of surface patterns and incorporation of redox‐active metals in mesoporous silicate molecular sieves
Authors: Yuan Z. Y. , Zhou W. , Zhang Z. L. , Liu J. Q. , Wang J. Z. , Li H. X. , Peng L. M.
Published: September 2002

Hierarchically ordered mesoporous metallosilicate MCM‐41 molecular sieves have been synthesized. The redox‐active metals Ti, V, Cr and Mn were incorporated in the framework, as characterized by various spectroscopic techniques. These materials have extraordinary morphologies in terms of their diverse and remarkable shapes and impressive surface patterns, such as centipede‐like, rope, vesicle and gyroidal spheroid, as revealed by transmission electron microscopy (TEM) images. The spatial relationship between the channel axis and the morphologies of the mesoporous silicates was investigated. The morphology formation of metallosilicates could be affected by the properties of the incorporated transition metal species. Copyright © 2001 John Wiley & Sons, Ltd.
Identification of hydrogen bond characterizations of isomeric 4Bpy and 2Bpy by STM
Authors: Xu Bo , Yin Shuxia , Wang Chen , Zeng Qingdao , Qiu Xiaohui , Bai Chunli
Published: September 2002

With submolecular resolution, scanning tunneling microscopy (STM) has been used extensively to study adsorption phenomena of organic molecules on surfaces. In this paper, we report a STM study of the isomeric compound of 4,4′‐bipyridyl (4Bpy) and 2,2′‐bipyridyl (2Bpy) co‐adsorbed with stearic acid on a highly oriented pyrolytic graphite (HOPG) surface. The 4Bpy and 2Bpy are isomeric compounds, and their only difference is the positions of the nitrogen atoms in each molecule. When Bpy molecules are mixed with stearic acid, the nitrogen atoms of Bpy can hydrogen bond with the COOH group of stearic acid, and hence the positions of the nitrogen atoms determine the hydrogen bond structure. It is observed that in the 4Bpy – stearic acid system the angle of the 4Bpy to the stearic acid molecular axis is ∼165°, whereas in the 2Bpy – stearic acid system the angle of the 2Bpy to the stearic acid molecular axis is ∼125°. The distances between two neighbouring ‘bright’ rows in an STM image are different in these two systems. Thus, by using this hydrogen bond method we can distinguish the 4Bpy molecule from its isomeric 2Bpy molecule. Furthermore, as reported previously, we observe the enantiomeric molecular patterns in both 4Bpy and 2Bpy systems. Copyright © 2001 John Wiley & Sons, Ltd.
Frictional properties of molecular thin films
Authors: Shi Bing , Lu Xinchun , Luo Jianbin , Chen Darong , Liang Hong
Published: September 2002

In this paper, we discuss the frictional behaviour of molecular thin films on a mica surface at a nanometre scale. Carbon 60 (C60)‐based macromolecules were synthesized experimentally. Analytical techniques such as Fourier transform infrared spectroscopy, UV–VIS spectroscopy and gel permeation chromatography were used to analyze the synthesized product. The Langmuir–Blodgett technique was used in making the macromolecules in the thin film on the mica surface. Atomic force microscopy and friction force microscopy were used for surface characterization. The properties, novel structures and their effects on frictional properties are discussed based on experiment results. It is found that the molecular thin films can be transferred onto the mica surface. These thin films possess significant tribological properties. Copyright © 2001 John Wiley & Sons, Ltd.
Detection of shear force with a piezoelectric bimorph cantilever for scanning near‐field optical microscopy
Authors: Shang Guangyi , Wang Chen , Lei Hening , Bai Chunli
Published: September 2002

We present a non‐optical shear force method to control the probe–sample distance for scanning near‐field optical microscopy (SNOM). In this system, the detection of shear force is accomplished by attaching a tapered fibre‐optic probe to a piezoelectric bimorph cantilever, which realizes the excitation and the detection simultaneously. The decrease in amplitude of the cantilever is observed when the probe approaches the sample and the shifts in resonance frequency are measured as a function of set‐point. The shear force images can be obtained reliably because the set‐point is >0.8. These results suggest that the system is reasonably sensitive to shear force and can be used easily for SNOM. Copyright © 2001 John Wiley & Sons, Ltd.
Quantitative X‐ray photoelectron spectroscopy study of enargite (Cu3AsS4) surface
Authors: Rossi A. , Atzei D. , Da Pelo S. , Frau F. , Lattanzi P. , England K. E. R. , Vaughan D. J.
Published: September 2002

The surface chemical state and composition of natural and synthetic enargite samples were characterized with X‐ray photoelectron spectroscopy (XPS). Freshly cleaved, powdered and ‘as received’ samples were analysed at liquid nitrogen temperature. For the natural ‘as received’ samples as well as for the natural and synthetic powdered samples the binding energies of Cu 2p3/2, As 3d5/2 and S 2p are consistently found at 932.5 ± 0.2, 43.9 ± 0.2 and 162.2 ± 0.2 eV, respectively. A second component of S 2p at 163.9 ± 0.2 eV is present and may be assigned to elemental sulphur. Freshly cleaved enargite samples showed binding energies of 43.2 and 161.3 eV, respectively, for As 3d5/2 and S 2p3/2. At the surface of crystals ‘as received’, an additional signal at ∽169 eV, referable to sulphate sulphur, is also present, as well as additional signals for Cu 2p3/2 (∽934 eV), and As 3d5/2 (∽45.5 eV). The thickness and the composition of this outer oxidized layer together with the composition of the interface beneath the film are calculated on the basis of a model developed for this purpose, taking into account the attenuation of the photoelectrons due to the contamination and the oxidized layer. An oxidized film of ∽0.5 nm is present at the surface of the ‘as received’ crystals whose composition was found to be ∽45% copper, 24% arsenic and 31% sulphur; hence, the oxidized layer appears to be enriched in arsenic compared with the bulk composition. The composition of the material beneath the oxidized layer was found to be enriched in copper and depleted in sulphur with respect to the bulk analysis. Any further study of the interaction of natural enargite samples with the environment has to take into account the existence of this thin outer layer. Copyright © 2001 John Wiley & Sons, Ltd.