bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of inflammatory and parenchymal cells in acute pancreatitis
Authors: Vonlaufen A , Apte MV , Imhof BA , Frossard JL
Published: September 2007

The infiltration of inflammatory cells into the pancreas is an early and central event in acute pancreatitis that promotes local injury and systemic complications of the disease. Recent research has yielded the important finding that resident cells of the pancreas (particularly acinar and pancreatic stellate cells) play a dynamic role in leukocyte attraction via secretion of chemokines and cytokines and expression of adhesion molecules. Significant progress has been made in recent years in our understanding of the role of leukocyte movement (adhesion to the blood vessel wall, transmigration through the blood vessel wall and infiltration into the parenchyma) in the pathophysiology of acute pancreatitis. This review discusses recent studies and describes the current state of knowledge in the field. It is clear that detailed elucidation of the numerous processes in the inflammatory cascade is an essential step towards the development of improved therapeutic strategies in acute pancreatitis. Studies to date suggest that combination therapy targeting different steps of the inflammatory cascade may be the treatment of choice for this disease. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
A hierarchical analysis of transcriptome alterations in intrauterine growth restriction (IUGR) reveals common pathophysiological pathways in mammals
Authors: Buffat C , Mondon F , Rigourd V , Boubred F , Bessières B , Fayol L , Feuerstein J‐M , Gamerre M , Jammes H , Rebourcet R , Miralles F , Courbières B , Basire A , Dignat‐Georges F , Carbonne B , Simeoni U , Vaiman D
Published: September 2007

Intra‐uterine growth restriction (IUGR) is a frequent disease, affecting up to 10% of human pregnancies and responsible for increased perinatal morbidity and mortality. Moreover, low birth weight is an important cause of the metabolic syndrome in the adult. Protein depletion during the gestation of rat females has been widely used as a model for human IUGR. By transcriptome analysis of control and protein‐deprived rat placentas, we were able to identify 2543 transcripts modified more than 2.5 fold (1347 induced and 1196 repressed). Automatic functional classification enabled us to identify clusters of induced genes affecting chromosome structure, transcription, intracellular transport, protein modifications and apoptosis. In particular, we suggest the existence of a complex balance regulating apoptosis. Among repressed genes, we noted several groups of genes involved in immunity, signalling and degradation of noxious chemicals. These observations suggest that IUGR placentas have a decreased resistance to external aggression. The promoters of the most induced and most repressed genes were contrasted for their composition in putative transcription factor binding sites. There was an over‐representation of Zn finger (ZNF) proteins and Pdx1 (pancreatic and duodenal homeobox protein 1) putative binding sites. Consistently, Pdx1 and a high proportion of ZNF genes were induced at the transcriptional level. A similar analysis of ZNF promoters showed an increased presence of putative binding sites for the Tata box binding protein (Tbp). Consistently again, we showed that the Tbp and TBP‐associated factors (Tafs) were up‐regulated in IUGR placentas. Also, samples of human IUGR and control placentas showed that human orthologous ZNFs and PDX1 were transcriptionnally induced, especially in non‐vascular IUGR. Immunohistochemistry revealed increased expression of PDX1 in IUGR human placentas. In conclusion, our approach permitted the proposition of hypotheses on a hierarchy of gene inductions/repressions leading to massive transcriptional alterations in the IUGR placenta, in humans and in rodents. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Analysis of copy number changes suggests chromosomal instability in a minority of large colorectal adenomas
Authors: Jones AM , Thirlwell C , Howarth KM , Graham T , Chambers W , Segditsas S , Page KM , Phillips RKS , Thomas HJW , Sieber OM , Sawyer EJ , Tomlinson IPM
Published: September 2007

We have examined chromosomal‐scale mutations in 34 large colorectal adenomas (CRAs). A small number of changes (median = 2, IQR = 0–4) were found by array‐comparative genomic hybridization (aCGH) in most tumours. The most common changes were deletions of chromosomes 1p, 9q, 17, 19, and 22, and gains of chromosomes 13 and 21. SNP‐LOH analysis and pseudo‐digital SNP‐PCR analysis detected occasional copy‐neutral LOH. Some aCGH changes found frequently in colorectal carcinomas, such as deletions of chromosomes 4q and 18q, were very infrequent in the adenomas. Almost all copy number changes were of small magnitude, far below the predicted levels even for single copy gain/loss; investigation suggested that these changes were either artefactual or occurred in sub‐clones within the tumours. In some cases, these sub‐clones may have represented progression towards carcinoma, but comparison with aCGH data from carcinomas showed this to be unlikely in most cases. In two adenomas, there was evidence of a large, outlying number of copy number changes, mostly resulting from part‐chromosome deletions. Overall, moreover, there was evidence of a tendency towards part‐chromosome deletions—consistent with chromosomal instability (CIN)—in about one‐sixth of all tumours. However, there was no evidence of CIN in the form of whole‐chromosome copy number changes. Our data did not support previous contentions that CRAs tend to show chromosome breakage at fragile sites owing to CIN associated with an elevated DNA damage response. Chromosomal‐scale mutations occur in some CRAs; although CIN is not the norm in these lesions, it probably affects a minority of cases. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
A urokinase‐type plasminogen activator deficiency diminishes the frequency of intestinal adenomas in ApcMin/+ mice
Authors: Ploplis VA , Tipton H , Menchen H , Castellino FJ
Published: September 2007

The interaction of urokinase‐type plasminogen activator (uPA) and its receptor, uPAR, on cell surfaces facilitates the generation of cell‐bound plasmin, thus allowing cells to establish a proteolytic front that enables their migration through protein barriers. This complex also activates cell signalling pathways that influence cell functions. Clinical studies have identified uPA as an indicator of poor overall survival in patients with colorectal cancer. In the current study, a mouse model of colon cancer, ApcMin/+, with an additional deficiency of uPA (ApcMin/+/Plau−/−) was used to determine the effects of uPA on tumour initiation and growth. Utilizing this model, it was found that the number of tumours was diminished in these mice relative to ApcMin/+ mice, which correlated with the decreased leukocyte infiltration in the tumours. However, tumour growth was not impeded in ApcMin/+/Plau−/− mice, and proliferation and tumour vascularization were, in fact, enhanced in ApcMin/+/Plau−/− mice. These latter effects are consistent with a mechanism involving up‐regulation of COX‐2 expression and Akt pathway activation in ApcMin/+/Plau−/− mice. The results from this study suggest that uPA plays dual and opposing roles in regulating lesion development: one early, during the transition from normal epithelia to dysplastic lesions, and another later during tumour growth. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
The p53–Mdm2 network in progenitor cell expansion during mouse postnatal development
Authors: Liu G , Terzian T , Xiong S , Van Pelt CS , Audiffred A , Box NF , Lozano G
Published: September 2007

Mdm2, an E3 ubiquitin ligase, negatively regulates the tumour suppressor p53. Loss of Mdm2 in mice results in p53‐dependent apoptosis and embryonic lethality. This phenotype was rescued by the p53515C allele, which encodes an apoptosis‐deficient p53R172P protein. However, these mice died within 2 weeks of birth, due to a severe impairment of progenitor cell expansion during postnatal haematopoiesis and cerebellar development, leading to p53‐dependent cell cycle arrest. Loss of Mdm2 led to phosphorylation of the p53R172P protein, p53R172P stability and activation of the cell cycle inhibitor p21 in proliferating cells, but not in differentiated cells, in multiple tissue compartments. Proliferating cells of epithelial origin were not affected. The haematopoietic and neural defects were alleviated in mice lacking Mdm2 and containing one p53515C and one p53‐null allele, but spermatogenesis was arrested. These findings establish a crucial role for the p53–Mdm2 network in regulating proliferation and progenitor expansion in many cell lineages and have important implications for the use of drugs that aim to disrupt the p53–Mdm2 interaction. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Suction blister fluid as potential body fluid for biomarker proteins
Authors: Kool Jeroen , Reubsaet Léon , Wesseldijk Feikje , Maravilha Raquel T. , Pinkse Martijn W. , D'Santos Clive S. , van Hilten Jacobus J. , Zijlstra Freek J. , Heck Albert J. R.
Published: September 2007

Early diagnosis is important for effective disease management. Measurement of biomarkers present at the local level of the skin could be advantageous in facilitating the diagnostic process. The analysis of the proteome of suction blister fluid, representative for the interstitial fluid of the skin, is therefore a desirable first step in the search for potential biomarkers involved in biological pathways of particular diseases. Here, we describe a global analysis of the suction blister fluid proteome as potential body fluid for biomarker proteins. The suction blister fluid proteome was compared with a serum proteome analyzed using identical protocols. By using stringent criteria allowing less than 1% false positive identifications, we were able to detect, using identical experimental conditions and amount of starting material, 401 proteins in suction blister fluid and 240 proteins in serum. As a major result of our analysis we construct a prejudiced list of 34 proteins, relatively highly and uniquely detected in suction blister fluid as compared to serum, with established and putative characteristics as biomarkers. We conclude that suction blister fluid might potentially serve as a good alternative biomarker body fluid for diseases that involve the skin.
Dihydroxyacetone‐induced death is accompanied by advanced glycation endproduct formation in selected proteins of Saccharomyces cerevisiae and Caenorhabditis elegans
Authors: Molin Mikael , Pilon Marc , Blomberg Anders
Published: September 2007

Advanced glycation endproduct (AGE) formation is an important mechanism for protein deterioration during diabetic complications and ageing. The effects on AGE formation following dihydroxyacetone (DHA) stress were studied in two model organisms, the yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans. Total protein AGEs, detected using an anti‐Nϵ‐carboxyalkyllysine‐specific monoclonal antibody, displayed a strong correlation to DHA‐induced yeast cell mortality in the wild‐type and hypersensitive as well as resistant mutant strains. During DHA‐induced cell death we also detected AGEs as the formation of acidic protein modifications by 2‐D PAGE. Furthermore, we confirmed AGE targets immunologically on 2‐D gel‐separated protein extracted from DHA‐treated cells. AGE modification of several metabolic enzymes (Eno2p, Adh1p, Met6 and Pgk1p) and actin (Act1p) displayed a strong correlation to DHA‐induced cell death. DHA was toxic to C. elegans even at low concentration and also in this organism AGE formation accompanied death. We propose the use of DHA as a model AGE‐generating substance for its apparent lack of a clear oxidative stress connection, and yeast and worm as model organisms to identify genetic determinants of protein AGE formation.
Static and shear induced crystallization of glass fiber reinforced poly(m‐xylylene adipamide) with nucleating additives
Authors: Naudy Sophie , Fulchiron René
Published: September 2007

Static and shear induced crystallization studies were carried out on a glass fiber reinforced poly(m‐xylylene adipamide) with various fiber contents. The crystallization experiments were performed using calorimetry and a shearing hot stage coupled with an optical microscope. The crystallization times were measured as a function of the temperature, the shear rate, and the fiber content. In static conditions, no nucleating ability of the fibers was highlighted. However, the shear treatment led to a substantial decrease of the crystallization times for all materials. Moreover, the shear effect is largely influenced by the fiber content, because the shear really undergone by the matrix between the fibers is locally higher than the nominal shear. A previously proposed crystallization kinetics model based on both Avrami and Hoffman–Lauritzen equations and taking into account the nucleating effect of the shear is improved. Hence, the fibers effect is included taking into account the higher local shear between the fibers. The nucleation rate due to the shear is described by a power law of the shear rate, where the prefactor is linked to the fibers amount. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2982–2992, 2007
Preparation and properties of the biodegradable graded blend of poly(L‐lactic acid) and poly(ethylene oxide)
Authors: Agari Yasuyuki , Sakai Kiyofumi , Kano Yosikazu , Nomura Ryoki
Published: September 2007

We prepared biodegradable poly(ethylene oxide) (PEO)/poly(L‐lactic acid) (PLLA) graded blends by the dissolution–diffusion process, and discussed the biodegradability and tensile strength of the graded blends by comparing isotropic blend and PLLA only. All the graded blends were degraded more largely than the PLLA only and isotropic blend (PEO: 37.5 wt %), which had the same content as the total content of those graded blends. The graded blend having most excellent wide compositional gradient was degraded most largely with the enzyme. Thus, graded structure of the blends promoted their biodegradabilities large. It was considered that the dissolution of PEO with water increased the surface area attacked by the enzyme, while PEO caught PLLA oligomers to promote the biodegradation of PLLA. Then, the biodegradabilities of the graded blends were suppressed by the increasing crystallinity of PLLA. Furthermore, the strengths of all the graded blends were larger than those of the isotropic blend. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2972–2981, 2007
Phase equilibrium and charge fractionation in polyelectrolyte solutions
Authors: Erukhimovich Igor , Olvera de la Cruz Monica
Published: September 2007

A new type of phase separation in the polyelectrolyte solutions consisting of several types of charged macromolecules differing in their degree of ionization is presented. Via a general thermodynamic consideration we show that even a small difference in the degree of ionization of otherwise equivalent high‐molecular components results in their spatial separation occurring upon decreasing the temperature much earlier than precipitation of any of the pure components from the solution. Some implications of charge fractionation are discussed, including the separation of DNA (or RNA) strands interacting with different proteins and the appearance of heterogeneities in polyelectrolyte solutions of partially charged hydrophobic chains with polydispersed charge distributions such as sodium polystyrene sulfonate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3003–3009, 2007
Electrical and Optical Properties of AC Microdischarges in Porous Ceramics
Authors: Hensel Karol , Martišovitš Viktor , Machala Zdenko , Janda Mário , Leštinský Michal , Tardiveau Pierre , Mizuno Akira
Published: September 2007

Generation of microdischarges inside porous ceramics by AC high voltage was explored. The physical properties of the microdischarges were investigated by electrical measurements, photographic visualization, and optical emission spectroscopy. The effects of pore size, discharge power, and gas mixture composition on the discharge properties and its development are described. The optimum generation and distribution of the microdischarges was observed with pore sizes of 50 and 80 µm. The emission spectra of the microdischarges indicated their strongly non‐equilibrium character. A theoretical analysis of the microdischarge mechanism is provided, accounting for the pore size and the elementary processes such as ionization, recombination, and ambipolar diffusion.

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Oropharyngeal aspiration and pneumonia in children
Authors: Weir Kelly , McMahon Sandra , Barry Linda , Ware Robert , Masters I Brent , Chang Anne B.
Published: September 2007

Oropharyngeal aspiration (OPA) of food and fluids is known to be associated with pneumonia in dysphagic children with neurological disease and direct causality is often assumed. However, little is known about the relationship between OPA and pneumonia in medically complex children when other possible risk factors for pneumonia are considered. We examined the association of World Health Organization (WHO)‐defined pneumonia in a heterogeneous group of children with swallowing dysfunction identified by a videofluoroscopic swallow study (VFSS). A retrospective chart review of 150 children (aged 2 weeks to 20 years) was undertaken to determine the relationship between pneumonia and (i) type of swallowing dysfunction (including OPA), (ii) consistency of aspirated food/fluid, and (iii) other factors including multisystem involvement and age (≤1 year or >1 year). In univariate analysis, the odds ratio (OR) for pneumonia was significantly increased in children with post‐swallow residue (PSR) (OR 2.5) or aspiration on thin fluids (OR 2.4), but not with aspiration of thick fluids or purees. In multi‐logistic regression, type of swallowing dysfunction or aspirated food/fluid were no longer significant. Instead, pneumonia was significantly associated with diagnosis of asthma (OR 13.25), Down syndrome (OR 22.10), gastroesophageal reflux disease (GERD) (OR 4.28), or history of LRTI (OR 8.28), moist cough (OR 9.17) or oxygen supplementation (OR 6.19). Children with multisystem involvement demonstrated a higher association with pneumonia, but no difference was found for age. We conclude that the impact of OPA on development of pneumonia is considerably reduced once other factors in children with multisystem involvement are taken into account. 2007;42:1024–1031. © 2007 Wiley‐Liss, Inc.
Topical, residual and ovicidal contact toxicity of three reduced‐risk insecticides against the European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae), on potato
Authors: Boiteau Gilles , Noronha Christine
Published: September 2007

BACKGROUND: The goal of the research was to gather efficacy data required to introduce reduced‐risk insecticides in sustainable control programs for European corn borer, Ostrinia nubilalis Hubner, on potato.

RESULTS: Laboratory tests confirmed that sprays of indoxacarb and novaluron at recommended field rates are as effective as spinosad against neonate larvae of O. nubilalis. However, there is evidence that higher rates would enhance the inhibition of chitin synthesis by novaluron. The three insecticides showed ovilarvicidal activity when applied to O. nubilalis egg masses 2 days prior to black head stage. The ovicidal activity of spinosad and novaluron was almost twice that of indoxacarb. At the recommended field rates, the residues of the three insecticides displayed contact toxicity to O. nubilalis larvae. Spinosad residues 16 h old or less provided the highest immediate (24 h after exposure) contact mortality, followed by indoxacarb and then by novaluron. Also, residues of spinosad had faster contact efficacy than indoxacarb, which had faster efficacy than novaluron.

CONCLUSION: Spinosad, indoxacarb and novaluron have ovicidal properties, which could enhance O. nubilalis management programs. However, the contact residual toxicity is limited in duration and would likely only play a minor role in O. nubilalis control. © Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.
Reduced viability of Colorado potato beetle, Leptinotarsa decemlineata, eggs exposed to novaluron
Authors: Alyokhin Andrei , Sewell Gary , Choban Raymond
Published: September 2007

BACKGROUND: Novaluron is a benzoylphenyl urea chitin synthesis inhibitor that combines good activity against larval stages of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with low mammalian toxicity. Previous studies suggest that it has deleterious sublethal effects on adults.

RESULTS: Continuous exposure of adult Colorado potato beetles to novaluron‐treated foliage as both ovipositional and feeding substrate did not affect their survivorship or the number of eggs produced, but viable larvae hatched only from the eggs that were laid on the first day of the experiment. Viability was restored after adult beetles spent 48–96 hours on untreated leaves. In a separate experiment, direct exposure to novaluron of eggs laid by unexposed beetles also reduced the number of larvae hatching.

CONCLUSIONS: Results confirm a negative effect of novaluron on the number of progeny produced by the Colorado potato beetle. Direct toxicity did not explain all of the reduction in egg hatch observed, suggesting that novaluron probably acted on reproductive adults as well as on eggs after they were deposited. Copyright © 2007 Society of Chemical Industry
Backbone‐modified amylin derivatives: implications for amyloid inhibitor design and as template for self‐assembling bionanomaterials
Authors: Elgersma Ronald C. , Posthuma George , Rijkers Dirk T. S. , Liskamp Rob M. J.
Published: September 2007

This report reviews our approach to the design, synthesis and structural/morphological analysis of backbone‐modified amylin(20–29) derivatives. Depending on the position in the peptide backbone and the type of amide bond isostere/modification, the amylin(20–29) peptides behave either as inhibitors of amyloid fibril formation, which are able to retard amyloid formation of native amylin(20–29), or as templates for the formation of self‐assembled supramolecular structures. Molecular fine‐tuning of the hydrogen‐bond accepting/donating properties allows the control over the morphology of the supramolecular aggregation motifs such as helical ribbons and tapes, ribbons progressing to closed peptide nanotubes, (twisted) lamellar sheets or amyloid fibrils. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Structure‐guided design of peptidic ligand for human prostate specific antigen
Authors: Hassan MD Imtaiyaz , Kumar Vijay , Somvanshi Rishi K. , Dey Sharmistha , Singh Tej P. , Yadav Savita
Published: September 2007

Prostate specific antigen (PSA) is a member of kallikrein family having serine protease‐like activity and acts as a prognostic marker of prostate carcinoma. Various studies have been performed on inhibition of PSA and such targeting requires the identification of highly selective peptide inhibitors. PSA was purified from human seminal plasma by rapid and efficient methods, and binding studies for various peptides were carried out by fluorescence spectroscopy and SPR. The ‘S’ of PSA is predominated by hydrophobic residues, and hence many hydrophobic peptides were used to determine their binding affinity to PSA by fluorescence spectroscopy. We observed that LLFW, FFKW, and KFW binds strongly to PSA, among them LLFW showed strong binding. SPR also showed strong binding affinity of PSA toward peptides with hydrophobic and basic residues. Among the peptides used, FWYS showed dramatic increase in binding affinity (10−10 M). The peptides analyzed for binding studies, suggests that peptide with Trp residue along with basic or hydrophobic amino acids may be useful for designing specific inhibitors for PSA. The strong affinities of designed peptides for PSA can be a valuable tool for designing therapeutic agents for prostate carcinomas. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Fast conventional Fmoc solid‐phase peptide synthesis with HCTU
Authors: Hood Christina A. , Fuentes German , Patel Hirendra , Page Karen , Menakuru Mahendra , Park Jae H.
Published: September 2007

1H‐Benzotriazolium 1‐[bis(dimethyl‐amino)methylene]‐5‐chloro‐hexafluorophosphate (1‐),3‐oxide (HCTU) is a nontoxic, nonirritating and noncorrosive coupling reagent. Seven biologically active peptides (GHRP‐6, 65–74ACP, oxytocin, G‐LHRH, C‐peptide, hAmylin1–37, and β‐amyloid1–42) were synthesized with reaction times reduced to deprotection times of 3 min or less and coupling times of 5 min or less using HCTU as the coupling reagent. Expensive coupling reagents or special techniques were not used. Total peptide synthesis times were dramatically reduced by as much as 42.5 h (1.8 days) without reducing the crude peptide purities. It was shown that HCTU can be used as an affordable, efficient coupling reagent for fast Fmoc solid‐phase peptide synthesis. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Appearance of ferroelectricity in thin films of incipient ferroelectric
Authors: Eliseev E. A. , Glinchuk M. D. , Morozovska A. N.
Published: September 2007

The consideration of a size‐induced ferroelectric–paraelectric phase transition for conventional and incipient ferroelectric thin films with perovskite structure was carried out in the phenomenological theory framework of Ginsburg–Landau–Devonshire. The more general form of surface free energy expansion that includes intrinsic surface stress tensor, the surface piezoelectric effect and electrostriction as well as quadratic and quartic powers of surface polarization has been considered. The analytical expressions for the thickness dependence of the transition temperature was derived both for the conventional and incipient ferroelectrics. It was shown that although there is no ferroelectricity in the bulk incipient ferroelectrics it appears in thin film for the negative extrapolation length that is realized, e.g., at positive surface stress coefficients and negative or zero misfit strain. In our consideration we came to the conclusion about thickness‐induced ferroelectricity in incipient ferroelectrics KTaO3 at room temperature for films that were sufficiently thin. The similar surface effects can strongly influence the phase transitions in the thin films of another incipient ferroelectric, SrTiO3. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive finite element method for simulation of optical nano structures
Authors: Pomplun Jan , Burger Sven , Zschiedrich Lin , Schmidt Frank
Published: September 2007

We discuss realization, properties and performance of the adaptive finite element approach to the design of nano‐photonic components. Central issues are the construction of vectorial finite elements and the embedding of bounded components into the unbounded and possibly heterogeneous exterior. We apply the finite element method to the optimization of the design of a hollow core photonic crystal fiber. Thereby we look at the convergence of the method and discuss automatic and adaptive grid refinement and the performance of higher order elements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Perfectly matched layer method in the finite‐difference time‐domain and frequency‐domain calculations
Authors: Shyroki D. M. , Lavrinenko A. V.
Published: September 2007

A complex‐coordinate method known under the guise of the perfectly matched layer (PML) method for treating unbounded domains in computational electrodynamics is related to similar techniques in fluid dynamics and classical quantum theory. It may also find use in electronic‐structure finite‐difference simulations. Straightforward transfer of the PML formulation to other fields does not seem feasible, however, since it is a unique feature of electrodynamics – the natural invariance – that allows analytic trick of complex coordinate scaling to be represented as pure modification of local material parameters within thin layers of space adjacent to the computational domain boundaries, i.e., the PMLs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Krylov‐subspace based solver for the linear and nonlinear Maxwell equations
Authors: Busch Kurt , Niegemann Jens , Pototschnig Martin , Tkeshelashvili Lasha
Published: September 2007

We describe an efficient Krylov‐subspace based operator‐exponential approach for solving the Maxwell equations. This solver exhibits excellent stability properties and high‐order time‐stepping capabilities that allow to address nonlinear wave propagation phenomena and/or coupled system dynamics. Furthermore, the usage of a non‐uniform spatial grid facilitates the realization of a high‐order spatial discretization in the presence of discontinuous material properties. This ideally complements the time‐stepping capabilities of our solver so that complex nano‐photonic problems may be treated with high accuracy and efficiency. We illustrate these features through an analysis of the prototypical problem of spontaneous emission from a collection of two‐level atoms that are embedded in finite Photonic Crystals and are exposed to dephasing as well as non‐radiative decay processes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Breakdown of the adiabatic approximation in a doped graphene monolayer and in metallic carbon nanotubes
Authors: Lazzeri Michele , Saitta A. Marco , Mauri Francesco
Published: September 2007

We compute, from first‐principles, the frequency of the phonons associated to the Raman G‐bands in a graphene monolayer and in metallic nanotubes as a function of the charge doping. In both cases, the frequency displays an important measurable shift in the range of doping reached experimentally. As a consequence, Raman spectroscopy can be used as a direct probe of the doping of these systems. Calculations are done using (i) the adiabatic Born–Oppenheimer approximation and (ii) time‐dependent perturbation theory to explore dynamic effects beyond this approximation. The two approaches provide very different results. The frequency shift of the G‐band in graphene and of the G– in metallic tubes represent remarkable failures of the adiabatic Born–Oppenheimer approximation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of multiwall boron nitride nanotubes
Authors: Jaffrennou P. , Barjon J. , Lauret J.‐S. , Maguer A. , Golberg D. , Attal‐Trétout B. , Ducastelle F. , Loiseau A.
Published: September 2007

Optical properties of multiwall boron nitride nanotubes are investigated by means of luminescence and absorption spectroscopies. Cathodoluminescence imaging shows that boron nitride nanotubes are highly UV luminescent materials and that the luminescence is located all along the nanotube. In comparison with the related bulk material, hexagonal boron nitride, luminescence and absorption experiments point out the role of excitonic effects in this nanoobject. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Equilibrium and non‐equilibrium optical properties of MoSI nanowires
Authors: Gadermaier C. , Kusar P. , Vengust D. , Vilfan I. , Mihailovic D.
Published: September 2007

The optical absorbance of oriented Mo6S3I6 nanowire thin films is measured and compared to spectra calculated using density functional theory. The expected sharp Van Hove singularities in the optical absorption spectra are not observed, partly because of the large density of interpenetrating electron sub‐bands and partly due to damping and disorder. Using femtosecond pump–probe spectroscopy we have measured the reflection of an optical pulse from a propagating acoustical disturbance in a randomly formed Mo6S3I6 nanowire network. This allows us to determine the sound velocity in a highly damped medium, which is not measurable by other techniques. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Single‐walled carbon nanotube silica composites obtained by an inorganic sol–gel route
Authors: Jung de Andrade M. , Lima M. Dias , Stein L. , Pérez C. , Roth S.
Published: September 2007

In the present work we first report on a successful incorporation of single‐walled carbon nanotubes (SWCNTs) into silica matrix prepared using an inorganic sol–gel method. Through this route non‐aqueous solvents are avoided and the stability of the carbon nanotubes suspensions is not affected. SWCNTs produced by Catalytic Chemical Vapor Deposition (CCVD) were dispersed in deionized water using an amphilic surfactant. As a precursor for the silica matrix an inexpensive silicic acid was used. By this route SWCNTs/silica composites were produced in the form of films and pellets. Microhardness measurements and electron microscopy suggest an important interaction between SWCNTs and the silica matrix what is important from the application point of view. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman spectroscopy on chemically functionalized carbon nanotubes
Authors: Müller M. , Maultzsch J. , Wunderlich D. , Hirsch A. , Thomsen C.
Published: September 2007

We present Raman spectroscopy on carbon nanotubes, functionalized with alkyl groups to different degrees and with different addition reactions. We observe effects in particular on the intensities of the radial breathing mode (RBM). From the RBM we can assign the diameter and chiral indices of the tubes and study the influence of functionalization on different tubes, their transition energies, Raman shifts and RBM intensities. We observe a diameter dependence of the chemical reaction under certain reaction conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Six‐fold rotationally symmetric vanadium oxide nanostructures by a morphotropic phase transition
Authors: O'Dwyer C. , Lavayen V. , Fuenzalida D. , Newcomb S. B. , Santa Ana M. A. , Benavente E. , González G. , Sotomayor Torres C. M.
Published: September 2007

In this work, we report the first observation of unique hierarchical six‐fold rotational symmetrical vanadium oxide based nanocomposite synthesized by a simple chemical route and highlight the first observation of a morphotropic reconstructive phase transistion from a lamellar V2O5 to that of a single crystalline V6O11 nanostructure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tunneling through molecular wires: a comparison of the Franz two‐band model with exact results
Authors: Malysheva L. , Onipko A.
Published: September 2007

This report concerns finding the tunneling exponential factor exp [–2κ (E) d ], on the basis of electronic band structure of organic oligomers, which are d ‐long molecular wires. It is shown that energy dependence κ (E) given by the Franz two‐band model agrees remarkably well with exact model calculations, provided that the quadratic dispersion parameter is calculated from the real (non‐parabolic) band structure of organic oligomers. For narrow and moderate band gaps (with respect to the band width), the approximate dependence is practically indistinguishable from that which is obtained from these exact calculations. The divergence (particularly, in the mid of the band gap) becomes appreciable and increases with an increase of the band‐gap/band‐width ratio. The apparent effective mass (as it is estimated from κ (E) measured at the Fermi energy E = EF) is defined in terms of the inherent parameters of the wire. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The fulleride polymer Mg5C60
Authors: Quintavalle D. , Simon F. , Jánossy A. , Borondics F. , Baserga A. , Kamarás K. , Pekker S.
Published: September 2007

We synthesized a series of Mgx C60 samples with nominal composition of x between 1 and 6 via solid state reaction between C60 and Mg powder. For x = 5 a two dimensional structure was found. The polymer phase is unusually stable up to high temperatures, it remains unchanged at 823 K for 20 minutes as confirmed by ESR. The mid‐infrared absorption spectrum suggests that the polymer sheets contain single bonded fulleride ions. Both the spin susceptibility and microwave conductivity measurements show that Mg5C60 is metallic for T > 200 K. The transition from metallic to insulating states around 200 K may be attributed to Anderson localization. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐yield synthesis of single‐walled carbon nanotubes with a pulsed arc‐discharge technique
Authors: Roch Aljoscha , Jost Oliver , Schultrich Bernd , Beyer Eckhard
Published: September 2007

This contribution deals with the synthesis of Single‐Walled Carbon Canotubes (SWCNT) with a novel pulsed arc‐discharge technique. Pulsed arc‐discharge is a very interesting technique because it is similar to the well‐known laser evaporation technique for the synthesis of SWCNT and should allow a scale‐up to reach a SWCNT volume production. We performed a number of experiments to find optimal conditions for the arc‐based SWCNT synthesis. The obtained data have been compared with known results from laser evaporation synthesis of SWCNT. The results indicate that it is possible to get specifically optimized synthesis conditions for the arc‐discharge method that are very similar to that of the laser evaporation synthesis. Both methods allow to get similar nanotube qualities (high yield, narrow diameter distribution). We discuss similarities in the formation mechanisms between both methods. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical conductivity recovery in carbon nanotube–polymer composites after transient shear
Authors: Alig I. , Skipa T. , Engel M. , Lellinger D. , Pegel S. , Pötschke P.
Published: September 2007

Investigations on electric conductivity have been performed on polycarbonate (PC) containing 0.6 vol% of multi‐walled carbon nanotubes (MWNT) in a rheometer, where the plates act as capacitor plates for dielectric spectroscopy. The time dependent recovery of the DC‐conductivity was recorded in the rest time after a transient shear deformation. The DC‐conductivity shows a tremendous increase with the time after shearing. This conductivity recovery is explained by the reorganization of the conducting MWNT‐network, which was destroyed by the shear. The reformation kinetics of MWNT‐clusters is considered as a cooperative cluster‐cluster aggregation coupled to electrical percolation of conductive MWNT. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nanocarbons: efficient synthesis using natural lava as supported catalyst
Authors: Su D. S. , Rinaldi A. , Frandsen W. , Weinberg G.
Published: September 2007

Low‐cost mass production of CNTs becomes prerequisite for their applications in chemistry and catalysis in which the availability of large amounts of material with well‐defined surface, chemical and mechanical properties is required. Natural occurring iron oxides in volcanic lavas are used as catalysts for CNT synthesis in the well‐established CVD (chemical vapor deposition) process while the lava itself acts as support. As in a common CVD process, the quality of the CNTs can be controlled by the synthesis parameters such as flow rate, hydrocarbon to hydrogen ratio and growth temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Novel organometallic fullerene complexes for vehicular hydrogen storage
Authors: Dillon A. C. , Whitney E. , Engtrakul C. , Curtis C. J. , O'Neill K. J. , Parilla P. A. , Simpson L. J. , Heben M. J. , Zhao Y. , Kim Y.‐H. , Zhang S. B.
Published: September 2007

Theoretical studies have predicted that scandium can bind to the twelve five‐membered rings in C60. It is then possible to stabilize four dihydrogen ligands (H2) on each Sc atom with a binding energy of ∼30 kJ/mol, ideal for vehicular hydrogen storage. The resulting C60[ScH2(H2)4]12 complex is predicted to be a minimum energy structure with ∼7.0 wt% reversible hydrogen capacity. However, wet chemical synthesis of the calculated η5‐coordinated fullerene complex is unprecedented. The chemistry of C60 is generally olefinic (i.e., η2‐coordination, in which the metal is coordinated to two carbon atoms contributing two electrons to the bonding). Furthermore, stabilization of multiple dihydrogen ligands on a single transition metal has not been demonstrated. Recently we have probed new synthesis techniques in order to coordinate C60 with either Fe, Sc, Cr, Co or Li. The new compounds were characterized with solid‐state nuclear magnetic resonance, and structures have been proposed. All of the structures were found to have unique binding sites for hydrogen employing the technique of temperature programmed desorption. Furthermore, some of the structures were shown to have significant hydrogen capacities with volumetric measurements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropy in the X‐ray absorption of vertically aligned single wall carbon nanotubes
Authors: Kramberger C. , Shiozawa H. , Rauf H. , Grüneis A. , Rümmeli M. H. , Pichler T. , Büchner B. , Batchelor D. , Einarsson E. , Maruyama S.
Published: September 2007

Carbon nanotubes are archetypical one dimensional systems, with peculiar anisotropic electronic properties. Only recently μm thick films of vertically aligned SWNT became available. The vertical alignment of the nanotube mats allows the realization of scattering geometries promoting specific dipole transitions parallel and normal to the axis of the SWNT. We find well expressed mosaic spreads for the π* and σ * resonances. Full three dimensional modelling of the dipole transitions as well as of the alignment demonstrate polarization dependent X‐ray absorption to be an accurate, versatile non destructive and reliable tool to quantify the alignment of SWNT on a bulk scale. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metallic bundles of single‐wall carbon nanotubes probed by electron spin resonance
Authors: Simon F. , Quintavalle D. , Jánossy A. , Náfrádi B. , Forró L. , Kuzmany H. , Hauke F. , Hirsch A. , Mende J. , Mehring M.
Published: September 2007

C59N magnetic fullerenes inside single‐wall carbon nanotubes (SWCNTs) are used to probe the density of states (DOS) on the host tubes using electron spin resonance (ESR). The C59N radicals are separated by C60 fullerenes to prevent dimerization and C59N–C60 heterodimers are formed at low temperatures. The electron spin–lattice relaxation time, T1, of the heterodimers is deduced from the homogeneous ESR line‐width. The analysis is supported by saturation ESR studies. The inverse of the heterodimer T1 follows a linear behavior in the 20–300 K temperature range, the so‐called Korringa law, evidencing a metallic DOS on all tubes in a bundle. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Special section: Computational Nano‐Photonics
Authors: Busch Kurt , Chigrin Dmitry N.
Published: September 2007

This issue of physica status solidi (b) contains a special section which was guest‐edited by Kurt Busch and Dmitry N. Chigrin. It contains selected contributions presented at the 386th Wilhelm and Else Heraeus Seminar on “Computational Nano‐Photonics” held in Bad Honnef, Germany, 25–28 February 2007.

The cover picture demonstrates some of the many computational aspects of the analysis of a dielectric micro‐disc resonator. In the center of the picture, the three‐dimensional intensity distribution of a resonator mode is displayed together with the outline of the micro‐disc's shape. In addition, a strongly coarsened cross‐section of an unstructured computational grid that has been employed for this computation is visualized in the upper right corner. The emission spectrum of a broad‐band source that is located inside the micro‐disc and covers several resonances is shown in the lower left corner. The picture is courtesy of Jens Niegemann, Universität Karlsruhe, Germany.
On the boundedness of the set of stabilizing controllers
Authors: Malik Waqar A. , Darbha Swaroop , Bhattacharyya S. P.
Published: September 2007

This paper shows that the set of rational, strictly proper, robustly stabilizing controllers for single‐input single‐output linear‐time invariant plants will form a bounded (can even be empty) set in the controller parameter space if and only if the order of the stabilizing controller cannot be reduced any further; if the set of proper stabilizing controllers of order r is not empty and the set of strictly proper controllers of order r is bounded, then r is the minimal order of stabilization.

The paper also extends this result to characterize the set of controllers that guarantee some pre‐specified performance specifications. In particular, it is shown here that the minimal order of a controller that guarantees specified performance is l iff (1) there is a controller of order l guaranteeing the specified performance and (2) the set of strictly proper, robustly stabilizing controllers of order l and guaranteeing the performance is bounded. Moreover, if the order of the controller is increased, the set of higher‐order controllers which satisfies the specified performance will necessarily be unbounded. This characterization is provided for performance specifications, such as gain margin and robust stability, which require a one‐parameter family of real polynomials to be Hurwitz, where the parameter is in a closed interval. Other performance specifications, such as phase margin and ℋ︁∞ norm, can be reduced to the problem of determining a set of stabilizing controllers that renders a family of complex polynomials Hurwitz. The characterization of the set of controllers for the stabilization of complex polynomials is provided and is used to show the boundedness properties for the set of controllers that guarantee a given phase margin or an upper bound on the ℋ︁∞ norm. Copyright © 2007 John Wiley & Sons, Ltd.
Regulation in bimodal systems
Authors: Wu Zhizheng , Ben Amara Foued
Published: September 2007

This paper considers the regulation problem for bimodal systems against known disturbance and reference signals. Switching between the two plant models as well as between the disturbance and reference signals is defined according to a switching surface. The design of the proposed regulators involves three main steps. First, a set of observer‐based Q‐parameterized stabilizing controllers for the switched system is constructed. The stability and the input/output properties for the resulting closed‐loop switched system with the Q‐parameterized controllers are analysed. Second, regulation conditions for each of the two subsystems in the resulting bimodal switched closed‐loop system are presented. In the third step, regulation conditions for the switched closed‐loop system are developed using two approaches. In the first approach, sufficient regulation conditions are derived based on the closed‐loop system's input–output properties. In the second approach, the forced switched closed‐loop system is transformed into an unforced impulsive switched system using an appropriate coordinate transformation. Hence, the regulation problem for the switched closed‐loop system is transformed into a stability analysis problem for the origin of an impulsive switched system. A regulator synthesis method based on solving some linear matrix inequalities is proposed. Finally, a numerical example is presented to illustrate the effectiveness of the proposed method. Copyright © 2007 John Wiley & Sons, Ltd.