bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flux compactification of M‐theory on compact manifolds with Spin(7) holonomy
Authors: Constantin D. 
Published: October 2005

AbstractAt the leading order, M‐theory admits minimal supersymmetric compactifications if the internal manifold has exceptional holonomy. The inclusion of non‐vanishing fluxes in M‐theory and string theory compactifications induce a superpotential in the lower dimensional theory, which depends on the fluxes. In this work, we check the conjectured form of this superpotential in the case of warped M‐theory compactifications on Spin(7) holonomy manifolds. We perform a Kaluza‐Klein reduction of the eleven‐dimensional supersymmetry transformation for the gravitino and we find by direct comparison the superpotential expression. We check the conjecture for the heterotic string compactified on a Calabi‐Yau three‐fold as well. The conjecture can be checked indirectly by inspecting the scalar potential obtained after the compactification of M‐theory on Spin(7) holonomy manifolds with non‐vanishing fluxes. The scalar potential can be written in terms of the superpotential and we show that this potential stabilizes all the moduli fields describing deformations of the metric except for the radial modulus.All the above analyses require the knowledge of the minimal supergravity action in three dimensions. Therefore we calculate the most general causal 𝒩 =1 three‐dimensional, gauge invariant action coupled to matter in superspace and derive its component form using Ectoplasmic integration theory. We also show that the three‐dimensional theory which results from the compactification is in agreement with the more general supergravity construction.The compactification procedure takes into account higher order quantum correction terms in the low energy effective action. We analyze the properties of these terms on a Spin(7) background. We derive a perturbative set of solutions which emerges from a warped compactification on a Spin(7) holonomy manifold with non‐vanishing flux for the M‐theory field strength and we show that in general the Ricci flatness of the internal manifold is lost, which means that the supergravity vacua are deformed away from the exceptional holonomy. Using the superpotential form we identify the supersymmetric vacua out of this general set of solutions.
Group functions approach based on the combination of strictly local geminals and molecular orbitals
Authors: Tokmachev A. M. , Tchougréeff A. L. 
Published: October 2005

AbstractThegroup functions technique is a natural way to introduce local description into quantum chemistry. It can also be a basis for construction of numerically effective computational schemes having almost linear growth of computational costs with that of the size of the system. Previously, we constructed a family of computationally efficient semiempirical methods based on the variationally determined strictly local geminals (SLGs). It was implemented with four popular parameterization schemes (MINDO/3, MNDO, AM1, and PM3). Because of construction details, its applicability was restricted only to compounds with well‐defined two‐electron two‐center chemical bonds and lone pairs. We generalize the previous treatment to make the electronic structure calculations possible for a wider class of compounds without loss of computational efficiency. The proposed scheme (SLG/SCF) is based on the general group function approach combining different descriptions for different electron groups: essentially local two‐electron ones are described by geminals, while those with other numbers of electrons are described in the one‐electron approximation. We implement the RHF, UHF, and ROHF approaches for the groups with delocalized electrons. This approach is tested for a series of radicals and molecules with extended π‐electron systems. It is shown that the SLG/SCF‐based methods describe the experimental data not worse than the corresponding SCF procedures and provide a good starting point for calculations of polyatomic molecular systems. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Dynamics of meso and thermo citrate synthases with implicit solvation
Authors: Cordeiro J. M. M. 
Published: October 2005

AbstractThe dynamics of hydration of meso and thermo citrate synthases has been investigated using the EEF1 methodology implemented with the CHARMM program. The native enzymes are composed of two identical subunits, each divided into a small and large domain. The dynamics behavior of both enzymes at 30°C and 60°C has been compared. The results of simulations show that during the hydration process, each subunit follows a different pathway of hydration, in spite of the identical sequence. The hydrated structures were compared with the crystalline structure, and the root mean square deviation (RMSD) of each residue along the trajectory was calculated. The regions with larger and smaller mobility were identified. In particular, helices belonging to the small domain are more mobile than those of the large domain. In contrast, the residues that constitute the active site show a much lower displacement compared with the crystalline structure. Hydration free energy calculations point out that Thermoplasma acidophilum citrate synthase (TCS) is more stable than chicken citrate synthase (CCS), at high temperatures. Such result has been ascribed to the higher number of superficial charges in the thermophilic homologue, which stabilizes the enzyme, while the mesophilic homologue denatures. These results are in accord with the experimental found that TCS keeps activity at temperatures farther apart from the catalysis regular temperature than the CCS. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Analysis of the bonding in XH3Cu+(XB, Al, Ga) complexes
Authors: Corral Inés , Mó Otilia , Yáñez Manuel 
Published: October 2005

AbstractHigh‐level density functional theory (DFT) calculations on XH3Cu+(XB, Al, Ga) complexes show that the attachment of the metal cation to the base takes place through agostic‐type interactions. These interactions that can be viewed as dative bonds from the σXHbonding orbitals of the base toward low‐lying empty 4sorbitals of the metal cation, and back‐donations from the lone pairs of the metal into the σantibonding orbitals of the neutral, are particularly favored when the XH bonds have a high X+δH−δpolarity. Accordingly, the AlH3and GaH3Cu+binding energies are very similar, but much larger than that of BH3. Depopulation of the σXHbonding orbital and the concomitant population of the σantibonding orbital involved in the agostic interaction result in a significant weakening of the corresponding XH linkages, whose bond length increases and whose stretching frequency appears red‐shifted. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Stable isotope analysis of safety matches using isotope ratio mass spectrometry–a forensic case study
Authors: Farmer N. L. , Meier‐Augenstein W. , Kalin R. M. 
Published: October 2005

AbstractIsotope ratio mass spectrometry (IRMS) was used to assess what contribution the technique could make towards the comparative analysis of matchstick samples within the ‘normal’ framework of a forensic investigation. A method was developed to allow the comparison of samples submitted as a result of an investigation, with the added advantage of rapid sample turn‐around expected within this field. To the best of our knowledge this is the first time that wooden safety matches have been analysed using IRMS. In this particular case, bulk stable isotope analysis carrried out on a ‘like‐for‐like’ basis could demonstrate conclusively that matches seized from a suspect were different from those collected at the scene of crime. The maximum δ13C variability observed within one box was 2.5‰, which, in conjunction with the error of measurement, was regarded to yield too wide an error margin as to permit differentiation of matchsticks based on 13C isotopic composition alone given that the ‘natural’ 13C abundance in wood ranges from −20 to −30‰. However, from the δ2H values obtained for crime scene matches and seized matches of −114.5‰ and −65‰, respectively, it was concluded that the matches seized were distinctly different from those collected at the crime scene. Copyright © 2005 John Wiley & Sons, Ltd.
Carbon isotope analysis of bulk keratin and single amino acids from British and North American hair
Authors: McCullagh James S. O. , Tripp Jennifer A. , Hedges Robert E. M. 
Published: October 2005

AbstractThe reconstruction of ancient diets using isotopic measurements of bone collagen, and other tissues, which survive in archaeological contexts, relies on known isotopic relationships between diet and body tissues. Examination of these relationships often requires the study of modern human and animal subjects. While hair keratin can act as a useful proxy for bone collagen in isotopic studies on living humans, where it is inappropriate to sample tissues such as collagen, it can, in addition, act as a chronological indicator of dietary change. This study investigates hair keratin δ13C values from current residents of the UK and the USA. Residents in the USA showed a clear bulk hair δ13C enrichment of approximately 3‰ over UK individuals, attributed to an elevated C4 dietary input from maize fed to livestock in North America. The keratin δ13C of subjects who moved between the UK and USA showed a pronounced change after relocation, taking approximately 4 months to reach isotopic equilibrium. To investigate these differences further, we measured δ13C values of dispensable and indispensable amino acids as a group, and selected individual amino acids. As a group, enrichment of dispensable amino acids compared with indispensable amino acids occurred in samples from both continents, averaging 7.2‰ in the UK and 7.9‰ in the USA. Dispensable and indispensable amino acids, as well as all individual amino acids measured, were enriched in samples from the USA compared with those from the UK. Copyright © 2005 John Wiley & Sons, Ltd.
Advances in coupling a commercial total organic carbon analyser with an isotope ratio mass spectrometer to determine the isotopic signal of the total dissolved nitrogen pool
Authors: Huygens D. , Boeckx P. , Vermeulen J. , Paepe X. De , Park A. , Barker S. , Pullan C. , Cleemput O. Van 
Published: October 2005

AbstractA new method has been developed to analyse15N of the total dissolved nitrogen (TDN) pool. The method operates on a commercial total organic carbon (TOC) analyser coupled to an elemental analyser/isotope ratio mass spectrometer (EA‐IRMS). Nitrogen compounds are combusted to nitric oxide (NO) and nitrogen dioxide (NO2) by high‐temperature catalytic oxidation (HTCO), after which the NOxgas is transferred to an EA‐IRMS for isotopic nitrogen analysis. The system is described, including five modifications of the system in order to overcome analytical problems. First, flow paths were modified to run both systems on helium as carrier gas, while complete sample oxidation was maintained. Secondly, the catalyst structure was adapted to allow high injection volumes at the given backpressures delivered by the EA system. Thirdly, we installed a Permapure® dehumidification system as the standard Peltier element did not satisfy dehumidification requirements. Finally, we prevented the inflow of atmospheric nitrogen into the system. In a final stage, we are planning to automate the coupled system in order to run a continuous batch of up to 60 samples. We have obtained satisfactory results on the accuracy and precision of 180 ± 1‰ potassium nitrate samples (IAEA, USGS‐32). Running a batch of five samples resulted in a mean isotopic value of 178.8‰ with a standard deviation of 2.8‰. Some important issues could not yet be addressed here, and will have to be evaluated once the system is running on a continuous base. However, the results appear promising and this system has the potential to become a method for TD15N analysis. An appropriate TD15N analysis method might open new challenges in aquatic and terrestrial ecosystem nitrogen studies, including a more comprehensive study of the dissolved organic nitrogen pool. Copyright © 2005 John Wiley & Sons, Ltd.
Porous polymer monolith assisted electrospray from a glass microdevice
Authors: Koerner Terry , Oleschuk Richard D. 
Published: October 2005

AbstractThe coupling of a lab‐on‐a‐chip microfluidic device to a nanoelectrospray ionization mass spectrometer has the potential to automate many routine analytical procedures and produce a powerful analytical tool. However, past coupling strategies have relied on complex manufacturing steps including drilling and etching the device to attach a capillary or building a nanospray emitter directly into the device. This study shows that a nanospray emitter can be easily fabricated using a porous polymer monolith (PPM) at the end of a glass microdevice. These devices are able to obtain a stable electrospray at a variety of flow rates (50–500 nL/min) but optimal results are obtained at lower flow rates (50–100 nL/min) compatible with electroosmotic flow processes. The PPM is photo‐patterned so that it can be placed in any position within the channel of the device with no dead volume. The porous character and the hydrophobic nature of the PPM both aid in development of a stable electrospray process. Total ion current traces for the constant infusion of leucine‐enkephalin and PPG show relative standard errors as low as 4%, and produce mass spectra with good signal‐to‐noise (S/N 43) from only 2 fmol of material. In addition, multiple experiments in a given day show good repeatability with variability as low as 13%, and the multiple flow paths inherent in the PPM limit sprayer clogging. Copyright © 2005 John Wiley & Sons, Ltd.
Photodissociation of singly protonated peptides at 193 nm investigated with tandem time‐of‐flight mass spectrometry
Authors: Moon Jeong Hee , Yoon So Hee , Kim Myung Soo 
Published: October 2005

AbstractPhotodissociation at 193 nm of some singly protonated peptides generated by matrix‐assisted laser desorption/ionization was investigated using tandem time‐of‐flight mass spectrometry. For peptides with arginine at the C‐terminus, x, υ, and w fragment ions were generated preferentially while a and d fragment ions dominated for peptides with arginine at the N‐terminus. These are the same characteristics as photodissociation at 157 nm reported previously. Overall, the photodissociation spectra obtained at 157 and 193 nm were strikingly similar. Copyright © 2005 John Wiley & Sons, Ltd.
Multiple losses of neutral C14H14 in the tandem mass spectrometry of several perbenzyl ether intermediates in the synthesis of green tea constituents
Authors: Lesimple Alain , Di Falco Marcos , Richard Yannick , Lesimple Souad , Wang Zhigang , Chan Tak Hang , Mamer Orval A. 
Published: October 2005

AbstractElectrospray and matrix‐assisted laser desorption/ionization (MALDI) tandem mass spectrometry (MS/MS) experiments were used to investigate an unusual fragmentation in collision‐induced dissociation (CID) of sodiated and potassiated perbenzyl ether intermediates obtained in the total synthesis of gallate ester constituents of green tea. Prominent fragments correspond to multiple sequential losses of neutral C14H14 that were not observed in the protonated and ammoniated species, that instead present fragment ion series in which members are separated by C7H6. High‐resolution MALDI quadrupole time‐of‐flight (Q‐TOF) and electrospray‐Fourier transform mass spectrometry (FTMS) were used to confirm elemental compositions of these and related ions. Copyright © 2005 John Wiley & Sons, Ltd.
A novel on‐line solid‐phase extraction approach integrated with a monolithic column and tandem mass spectrometry for direct plasma analysis of multiple drugs and metabolites
Authors: Zang Xu , Luo Rosa , Song Ning , Chen Ta Kung , Bozigian Haig 
Published: October 2005

AbstractAn on‐line solid‐phase extraction liquid chromatography/tandem mass spectrometry (SPE LC/MS/MS) assay using a newly developed SPE column and a monolithic column was developed and validated for direct analysis of plasma samples containing multiple analytes. This assay was developed in an effort to increase bioanalysis throughput and reduce the complexity of on‐line SPE LC/MS/MS systems. A simple column‐switching configuration that requires only one six‐port valve and one HPLC pumping system was employed for on‐line plasma sample preparation and subsequent gradient chromatographic separation. The resulting analytical method couples the desired sensitivity with ease of use. The method was found to perform satisfactorily for direct plasma analysis with respect to assay linearity, specificity, sensitivity, precision, accuracy, carryover, and short‐term stability of an eight‐analyte mixture in plasma. A gradient LC condition was applied to separate the eight analytes that cannot be distinctly differentiated by MS/MS. With a run time for every injection of 2.8 min, a minimum of 300 direct plasma injections were made on one on‐line SPE column without noticeable changes in system performance. Due to the ruggedness and simplicity of this system, generic methods can be easily developed and applied to analyze a wide variety of compounds in a high‐throughput manner without laborious off‐line sample preparation. Copyright © 2005 John Wiley & Sons, Ltd.
Combination of solid‐phase affinity capture on magnetic beads and mass spectrometry to study non‐covalent interactions: example of minor groove binding drugs
Authors: Schlosser Gitta , Vékey Károly , Malorni Antonio , Pocsfalvi Gabriella 
Published: October 2005

AbstractA simple and novel approach was developed to detect non‐covalent interactions. It is based on combination of solid‐phase affinity capture with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). One of the interacting molecules is bound to magnetic beads and is incubated with the target molecules in solution. The complex bound on the solid support is removed from the solution and transferred for MALDI analysis. Mass spectrometry is used only to detect the target compound, which is far more straightforward than detecting the intact non‐covalent complex. To demonstrate the applicability of the method, an AT‐rich oligonucleotide (5′‐CCCCCAATTCCCCC‐3′) and its complementary biotinylated sequence (5′‐biotin‐GGGGGAATTGGGGG‐3′) were hybridized and immobilized to paramagnetic particles by streptavidin‐biotin interaction. The immobilized duplex oligonucleotide was reacted with minor groove binding drugs, Netropsin, Distamycin A, Hoechst 33258 and 4′,6‐diamidino‐2‐phenylindole. The resulting DNA‐drug complex bound to the particles was separated and analyzed by linear MALDI‐TOFMS after washing. Drugs were selectively detected in the spectra. Relative binding strengths were also estimated using competitive complexation. Copyright © 2005 John Wiley & Sons, Ltd.
Hydropyrolysis of steroids: a preparative step for compound‐specific carbon isotope ratio analysis
Authors: Sephton Mark A. , Meredith Will , Sun Cheng‐Gong , Snape Colin E. 
Published: October 2005

AbstractCompound‐specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry is an important method for the detection of steroid abuse in athletes. However, steroids in their natural form exhibit poor chromatographic resolution, while derivatization adds carbon thereby corrupting the starting stable isotopic composition. Hydropyrolysis is a new approach, which defunctionalizes steroids but leaves their carbon skeleton intact. The process improves chromatography, allowing the faithful measurement of carbon isotope ratios and enabling a more effective apportionment for the source of steroids and their metabolites. Copyright © 2005 John Wiley & Sons, Ltd.
The reassessment of trial perspectives from interim data—a critical view
Authors: Bauer Peter , Koenig Franz 
Published: October 2005

AbstractIf an interim analysis is performed during a trial it is tempting to determine the conditional power to reach a rejection in the trial given the observed results in the interim analysis. Since the true effect size is unknown the conditional power may be calculated by using the effect size, which the study has been powered for in the planning phase or by using an interim estimate of the true size (or a combination of both). In either case the conditional power is a random variable and its density is investigated depending on the analysis time and the true effect size. Under the null hypothesis, in early interim analyses after a small proportion of sample units, the conditional power typically will be close to the overall power when the effect size from the planning stage is used for calculation. In this case the majority of observations must still be made and the small first‐stage sample in general will be dominated by the hypothetical second‐stage chance based on the wrong parameter value. It is shown that the conditional power in moderately underpowered studies can have a distribution symmetric around 0.5. When using the interim estimate for calculating the conditional power the density in general will be u‐shaped. The impact of using conditional power to reassess the sample size using flexible two‐stage combination tests is shown for a specific example in terms of overall power and average sample size as compared to the corresponding group sequential design. For small true effect sizes mid‐trial sample size recalculation based on an interim estimate may lead to an overly large price to be paid in average sample size in relation to the gain in overall power. Finally, the problem is discussed in terms of estimating the true conditional power. Copyright © 2005 John Wiley & Sons, Ltd.
Efficient group sequential designs when there are several effect sizes under consideration
Authors: Jennison Christopher , Turnbull Bruce W. 
Published: October 2005

AbstractWe consider the construction of efficient group sequential designs where the goal is a low expected sample size not only at the null hypothesis and the alternative (taken to be the minimal clinically meaningful effect size), but also at more optimistic anticipated effect sizes. Pre‐specified Type I error rate and power requirements can be achieved both by standard group sequential tests and by more recently proposed adaptive procedures. We investigate four nested classes of designs: (A) group sequential tests with equal group sizes and stopping boundaries determined by a monomial error spending function (the ‘ρ‐family’); (B) as A but the initial group size is allowed to be different from the others; (C) group sequential tests with arbitrary group sizes and arbitrary boundaries, fixed in advance; (D) adaptive tests—as C but at each analysis, future group sizes and critical values are updated depending on the current value of the test statistic. By examining the performance of optimal procedures within each class, we conclude that class B provides simple and efficient designs with efficiency close to that of the more complex designs of classes C and D. We provide tables and figures illustrating the performances of optimal designs within each class and defining the optimal procedures of classes A and B. Copyright © 2005 John Wiley & Sons, Ltd.