bluuebunny/crossref_metadata_2025 huggingface dataset:
Polytomous Disease Mapping to Detect Uncommon Risk Factors for Related Diseases
Authors: Dreassi Emanuela
Published: November 2006

A statistical model for jointly analysing the spatial variation of incidences of three (or more) diseases, with common and uncommon risk factors, is introduced. Deaths for different diseases are described by a logit model for multinomial responses (multinomial logit or polytomous logit model). For each area and confounding strata population (i.e. age‐class, sex, race) the probabilities of death for each cause (the response probabilities) are estimated. A specic disease, the one having a common risk factor only, acts as the baseline category. The log odds are decomposed additively into shared (common to diseases different by the reference disease) and specic structured spatial variability terms, unstructured unshared spatial terms and confounders terms (such as age, race and sex) to adjust the crude observed data for their effects. Disease specic spatially structured effects are estimated; these are considered as latent variables denoting disease‐specic risk factors.

The model is presented with reference to a specic application. We considered the mortality data (from 1990 to 1994) relative to oral cavity, larynx and lung cancers in 13 age groups of males, in the 287 municipalities of Region of Tuscany (Italy). All these pathologies share smoking as a common risk factor; furthermore, two of them (oral cavity and larynx cancer) share alcohol consumption as a risk factor. All studies suggest that smoking and alcohol consumption are the major known risk factors for oral cavity and larynx cancers; nevertheless, in this paper, we investigate the possibility of other different risk factors for these diseases, or even the presence of an interaction effect (between smoking and alcohol risk factors) but with different spatial patterns for oral and larynx cancer. For each municipality and age‐class the probabilities of death for each cause (the response probabilities) are estimated. Lung cancer acts as the baseline category. The log odds are decomposed additively into shared (common to oral cavity and larynx diseases) and specic structured spatial variability terms, unstructured unshared spatial terms and an age‐group term.

It turns out that oral cavity and larynx cancer have different spatial patterns for residual risk factors which are not the typical ones such as smoking habits and alcohol consumption. But, possibly, these patterns are due to different spatial interactions between smoking habits and alcohol consumption for the first and the second disease. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microsolvation of an Ionic Dopant in Small 4He Clusters: OH+(3Σ)(4He)N via Genetic Algorithm Optimizations
Authors: Marinetti Fabio , Bodo Enrico , Gianturco Franco A.
Published: November 2006

The optimized spatial structures of the small clusters (with N up to 33) formed by an increasing number of 4He atoms, which act as a microsolvent surrounding the OH+ ionic molecular dopant, are obtained using a sum‐of‐potentials scheme corrected by three‐body (3B) effects. The most stable structures are generated using the type of genetic algorithm described herein, and the sequential formation of regular shell structures is analyzed in detail. Possible quantum corrections for both the solvent distributions and the stable energetics are analyzed and discussed.
Local Structure and Thermodynamics of a Core‐Softened Potential Fluid: Theory and Simulation
Authors: Zhou Shiqi , Jamnik Andrej , Wolfe Elie , Buldyrev Sergey V.
Published: November 2006

Phase behavior and structural properties of homogeneous and inhomogeneous core‐softened (CS) fluid consisting of particles interacting via the potential, which combines the hard‐core repulsion and double attractive well interaction, are investigated. The vapour–liquid coexistence curves and critical points for various interaction ranges of the potential are determined by discrete molecular dynamics simulations to provide guidance for the choice of the bulk density and potential parameters for the study of homogeneous and inhomogeneous structures. Spatial correlations in the homogeneous CS system are studied by the Ornstein‐Zernike integral equation in combination with the modified hypernetted chain (MHNC) approximation. The local structure of CS fluid subjected to diverse external fields maintaining the equilibrium with the bulk CS fluid are studied on the basis of a recently proposed third order+second order perturbation density functional approximation (DFA). The accuracy of DFA predictions is tested against the results of a grand canonical ensemble Monte Carlo simulation. Reasonable agreement between the results of both methods proves that the DFA theory applied in this work is a convenient theoretical tool for the investigation of the CS fluid, which is practically applicable for modeling numerous real systems.
Treatment of new‐onset type 1 diabetes with peptide DiaPep277® is safe and associated with preserved beta‐cell function: extension of a randomized, double‐blind, phase II trial
Authors: Raz I. , Avron A. , Tamir M. , Metzger M. , Symer L. , Eldor R. , Cohen I. R. , Elias D.
Published: November 2006

Background

Treatment with DiaPep277®, a peptide derived from HSP60, has been shown to preserve beta‐cell function in non‐obese diabetic mouse (NOD) mice and in a trial with newly diagnosed human patients with type 1 diabetes treated over a 10‐month period. This article extends the clinical trial observations to a total of 20 months of treatment to determine the safety and the effects of repeated doses of DiaPep277 on endogenous insulin secretion, metabolic control, and exogenous insulin requirements.

Methods

Thirty‐five male patients (aged 16–58) with a basal C‐peptide greater than 0.1 nmol/L were assigned to periodic treatment with DiaPep277 (1 mg) or placebo for a 12‐month treatment and 18‐month observation protocol, later extended to an additional year of treatment. Stimulated C‐peptide, HbA1c, and an exogenous insulin dose were the clinical endpoints.

Results

At 18 months, stimulated C‐peptide concentrations had fallen in the placebo group (p = 0.0005) but were maintained in the DiaPep277 group. The need for exogenous insulin was higher in the placebo group than in the DiaPep277 group. Mean HbA1c concentrations were similar in both groups. After extension of the study, patients continuing treatment with DiaPep277 and those switched from placebo to DiaPep277 manifested a trend towards a greater preservation of beta‐cell function compared to patients maintained on or switched to placebo. The safety profile of DiaPep277 was similar between the treatment and placebo groups, and no drug‐related adverse events occurred.

Conclusions

Periodic treatment of subjects with DiaPep277 over 2 years was safe and associated preservation of endogenous insulin secretion up to 18 months was observed. Copyright © 2007 John Wiley & Sons, Ltd.
A New Synthetic Approach to High‐Purity (15R)‐Latanoprost
Authors: Martynow Jacek G. , Jóźwik Julita , Szelejewski Wiesław , Achmatowicz Osman , Kutner Andrzej , Wiśniewski Krzysztof , Winiarski Jerzy , Zegrocka‐Stendel Oliwia , Gołębiewski Piotr
Published: November 2006

This paper describes a new synthesis of latanoprost (1) that afforded high purity latanoprost in 16.9 % overall yield in eight synthetic steps from sulfone 4. The “α chain” in a derivative of the (–)‐“Corey lactone” was elongated first, followed by the attachment of a novel, enantiomerically pure “ω chain” synthon. This ensured the absence of the undesired (15S)‐1 diastereomer in the synthesized prostaglandin. The crystalline nature of the novel sulfone 4 facilitated its purification. A variation of the new synthesis of latanoprost is described, where the laboratory‐scale synthesis was further adapted to a hundred‐gram scale. In the course of the present synthesis, a new prostaglandin sulfone intermediate, 21, which may find application in the synthesis of diverse prostaglandin analogs, was introduced. A practical synthesis of novel, enantiomerically pure “ω chain” synthons 15, 16, and 17 has also been carried out, employing diol 12, which was obtained from derivatives of the D‐mannitol chiral pool. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
C‐Disaccharides as Probes for Carbohydrate Recognition – Investigation of the Conformational Requirements for Binding of Disaccharide Mimetics of Sialyl Lewis X
Authors: Denton Richard W. , Cheng Xuhong , Tony Kurissery A. , Dilhas Anna , Hernández Juan José , Canales Angeles , Jiménez‐Barbero Jesús , Mootoo David R.
Published: November 2006

A set of C‐disaccharide analogs was designed to probe the recognition of a known O‐disaccharide mimetic of sialyl Lewis X, to P‐selectin. The synthesis of the C‐glycosides centered on the de novo construction of the galactose residue via an oxocarbenium ion/enol ether cyclization. Conformational analysis was performed by a combination of NMR spectroscopy and molecular mechanics (MM) and molecular dynamics (MD) calculations. The inhibition of P‐selectin binding was evaluated in a P‐selectin Biacore assay. At 12 mM, the O‐glycoside showed 48 % inhibition of binding, while the C‐glycoside analogs exhibited between 25–31 % inhibition. This data is discussed within the context of the active conformation of sLex and the conformational behavior of these ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Preconcentration Electroanalysis at Surfactant‐Templated Thiol‐Functionalized Silica Thin Films
Authors: Etienne Mathieu , Cortot Jérôme , Walcarius Alain
Published: November 2006

Surfactant‐templated thiol‐functionalized silica thin films have been deposited by spin‐coating on glassy carbon electrodes. Their permeability properties have been characterized using three solution phase redox probes (Ru(NH3), Fe(CN), FcMeOH) and their suitability to be applied for preconcentration electroanalysis has been studied using Ag+ as model analyte. Both the film permeability to redox probes and the performance of the modified electrodes towards Ag+ sensing were found to be dramatically influenced by the composition of the sol used for preparing the thin films, and especially its surfactant content. The best results were obtained with materials prepared from rather high surfactant concentration because they led (after template removal) to highly open mesoporous deposits with readily accessible thiol groups in the mesopore channels. The effect of various parameters on the electrode response have been investigated, including the composition of the detection medium, the accumulation time, the level of functionalization of the films and their preparation conditions, and the analyte concentration. A linear response for Ag+ was obtained in the 0.2–10 μM concentration range.
One‐step production of alkoxylated ethyl acetate with narrow adduct distribution
Authors: Xia Yong‐Mei , Shen Yong‐An , Ji Shi‐Run , Fang Yun , Wang Yi‐You , Tan Bing
Published: November 2006

Oligo‐ethylene/propylene glycol ethyl ether acetate (oligo‐EGEEA and oligo‐PGEEA) used to be synthesized in a two‐step process with acetic acid as starting material. This paper describes a one‐step production process catalyzed by the AlMg composite oxide, achieved by alkoxylation of ethyl acetate directly. Aiming at a narrow adduct distribution to get high product selectivity of mono‐derivatives, the alkoxylation parameters, such as the Al/Mg molar ratio of the catalyst, molar ratio of reactants, temperature, initial reaction pressure, and reactant feed rate were investigated. The highest content of mono‐ and di‐derivatives in the products was: w (oligo‐EGEEA) = 73.8%, w (oligo‐PGEEA) = 87.9%, respectively. The product selectivity of mono‐EGEEA was decreased by only 5% after reusing the catalyst for ten runs. A 1.26‐fold increase in the yield of mono‐PGEEA was achieved by treating the catalyst surface with alcoholic potash. Copyright © 2006 Society of Chemical Industry
Environmental links to reduced tropical cyclogenesis over the south‐east Caribbean
Authors: Georgiadis Alexandros P. , Bigg Grant
Published: November 2006

Tropical cyclone formation over the Caribbean is not evenly distributed across the basin. Previous work identified the south‐western sector as the area that dominates the hurricane activity of the whole basin. The south‐eastern sector, in contrast, exhibits a distinct suppression in cyclogenesis. This study seeks to identify the restricting factors that differentiate the cyclogenesis climatology in the south‐east Caribbean. It is based on statistical analysis of eight environmental variables using principal component analysis. The first three components are examined in detail. The first component, accounting for 31.7% of the variance within the data, differentiates the Caribbean from the rest of the subtropical Atlantic, primarily in terms of an increased thermodynamic potential for cyclogenesis and enhanced atmospheric humidity in the boundary layer. The second component, accounting for 31% of the variance, marks the south‐west Caribbean as the only sub‐region within the area of analysis where the easterlies curve southwards and the relative vorticity is cyclonic. The third component, accounting for 20.3% of the variance, differentiates the South Caribbean from the rest of the Atlantic, indicating it to be a region of increased spatial variation in the intensity of the easterlies and in absolute vorticity. The variance of cyclogenesis within the Caribbean is greatest along the second and third components. Thus, the genesis pattern in the basin is likely associated with the low‐level wind‐field and absolute vorticity. The divergence of the flow, when combined with the vorticity of the wind‐field over the Caribbean, renders the background conditions of the eastern sector less prone to developing disturbances than is the case in the western Caribbean. Copyright © 2006 Royal Meteorological Society
Seismic response of slopes subjected to incident SV wave by an improved boundary element approach
Authors: Gatmiri Behrouz , Nguyen Khoa‐Van , Dehghan Kaveh
Published: November 2006

In this paper, an improved boundary element approach for 2D elastodynamics in time‐domain is presented. This approach consists in the truncation of time integrations, based on the rapid decrease of the fundamental solutions with time. It is shown that an important reduction of the computation time as well as the storage requirement can be achieved. Moreover, for half‐plane problems, the size of boundary element (BE) meshes and the computation time can be significantly reduced. The proposed approach is used to study the seismic response of slopes subjected to incident SV waves. It is found that large amplifications take place on the upper surface close to the slope, while attenuations are produced on the lower surface. The results also show that surface motions become very complex when the incident wavelength is comparable with the size of the slope or when the slope is steep. Copyright © 2006 John Wiley & Sons, Ltd.
Kinetic and mechanistic study of the reactions of aryl chloroformates with quinuclidines
Authors: Castro Enrique A. , Aliaga Margarita , Campodonico Paola R. , Leis J. Ramón , García‐Río Luis , Santos José G.
Published: November 2006

The reactions of quinuclidines with phenyl, 4‐methoxyphenyl, 4‐chlorophenyl, and 4‐nitrophenyl chloroformates (PClF, MOPClF, ClPClF, and NPClF, respectively) in aqueous solution (25 °C, ionic strength 0.2 M KCl) are followed spectrophotometrically and evaluated kinetically. Under amine excess, pseudo‐first‐order rate coefficients (kobsd) are found. Plots of kobsdversus [quinuclidine] are linear, with the pH‐independent slope (kN). The Brønsted‐type plots (log kNvs. pKa of quinuclidinium ions) are linear with slopes (β) of 0.32, 0.34, 0.31, and 0.23 for the reactions of PClF, MOPClF, ClPClF, and NPClF, respectively. The magnitude of the slopes suggests that these mechanisms are stepwise, with the formation of a zwitterionic tetrahedral intermediate (T±) being the rate‐determining step. The sensitivity of log kN to the basicity of the nonleaving group (βnlg) is −0.16. By comparing the reactions under investigation between each other and with similar aminolyses, the following conclusions can be drawn: (i) the mechanisms for the quinuclidinolysis of the four chloroformates studied are stepwise. (ii) The reactivity increases in the sequence MOPClF < PClF < ClPClF < NPClF. (iii) The change of the leaving group from 2,4‐dinitrophenoxide to chloro changes the mechanism from concerted to stepwise. (iv) Quinuclidines are more reactive toward aryl chloroformates than isobasic secondary alicyclic amines. Copyright © 2006 John Wiley & Sons, Ltd.
Lung function in infants and young children with chronic lung disease of infancy: The next steps?
Authors: Stocks Janet , Coates Allan , Bush Andrew
Published: November 2006

Over the past year, a series of papers have reviewed the literature concerning assessment and interpretation of lung function in infants and young children with chronic lung disease of infancy. This manuscript, which represents the final paper in that series, summarizes the findings to date and highlights key areas for future research. Despite the huge literature in this field, interpretation of results and their use in guiding clinical management are still limited by difficulties in ‘normalizing data’ according to body size and maturation and selection of appropriate control groups. Furthermore, sensitive tests that more closely reflect the underlying pathophysiology of ‘new’ bronchopulmonary dysplasia, together with simple and reliable methods of assessing lung maturity at birth and true oxygen requirements at specified time points are urgently required. Research in this field is also challenged by the need to separate the independent effects of genetic predisposition, gene–environment interactions, preterm delivery, neonatal respiratory disorders and various treatment strategies on the growing lung. The extent to which disruption of lung growth following premature exposure to the extra‐uterine environment leads to an earlier or more aggravated decline in respiratory function in later adult life remains to be elucidated. Whatever its origin, given the increasing survival of smaller and more immature infants, the long term sequelae of neonatal lung disease, are likely to continue to change, requiring ongoing, carefully designed longitudinal studies. Future research strategies need to encompass a multicenter, multi‐disciplinary, collaborative approach with closer links between clinicians and basic scientists, to ensure that the most relevant research questions are addressed using appropriate methodology and that findings are implemented into clinical practice in a more timely fashion. Pediatr Pulmonol. 2007; 42:3–9. © 2006 Wiley‐Liss, Inc.
Managing isolated subglottic juvenile xanthogranuloma without tracheostomy: Case report and review of literature
Authors: Somorai Marta , Goldstein Nira A. , Alexis Richard , Giusti Robert J.
Published: November 2006

Juvenile Xanthogranuloma (JXG) is a dendritic cell related histiocytic disorder which usually presents in the first year of life as a solitary cutaneous granuloma. Isolated presentation in the upper airway is very rare but can result in severe respiratory distress, especially in young children. We present the case of a 5‐month‐old male with an isolated subglottic JXG lesion. Endoscopic excision provided symptomatic relief and avoided the need for tracheostomy. The lesion has completely resolved 17 months later. Surgical excision without tracheostomy was the treatment of choice in two of the four additional cases of upper airway JXG presented in the literature. JXG has an excellent prognosis with spontaneous regression over time. Histology alone is frequently inadequate to differentiate JXG from the more common Langerhans Cell Histiocytosis (LCH), which carries a much less favorable prognosis. The evolving field of immunohistochemistry provides an essential tool to establish the correct diagnosis. The typical phenotype of JXG is Factor XIIIa+/Fascin+/CD68+/CD163+/CD14+/CD1a−/S100−. Pediatr Pulmonol. 2007; 42:181–185. © 2006 Wiley‐Liss, Inc.
The repeatability of submaximal endurance exercise testing in cystic fibrosis
Authors: Barry Sinead C. , Gallagher Charles G.
Published: November 2006

Submaximal endurance cycle ergometer exercise tests are used to measure the efficacy of an exercise intervention, but the repeatability of these tests in patients with cystic fibrosis (CF) has not been established. The purpose of this study was to examine the repeatability of submaximal endurance testing in stable CF. Fifteen adults with CF underwent two submaximal endurance tests carried out over a 7‐day period. A subset of six subjects returned 28 days later for a third submaximal endurance test. Workload was set at 80% of maximum workload and exercise was performed to exhaustion. Oxygen consumption, minute ventilation, tidal volume, carbon dioxide output, respiratory rate, heart rate, and oxygen saturation were measured at rest, at end exercise and at four matched times during the submaximal endurance tests (20, 40, 60, and 80% of exercise duration calculated from the first endurance test). Submaximal endurance test time was highly repeatable with no significant learning effect identified on multiple testing. Submaximal endurance exercise time demonstrated a variability of 5.7% which is consistent with high levels of repeatability. Metabolic, ventilatory and cardiac variables were all also highly reproducible between test days. Submaximal endurance testing is repeatable in stable CF, confirming that submaximal endurance tests are a reliable tool for assessment of therapeutic benefit in patients with CF. Pediatr Pulmonol. 2007; 42:75–82. © 2006 Wiley‐Liss, Inc.
Functional ability in female leg ulcer patients — a challenge for physiotherapy
Authors: Roaldsen Kirsti Skavberg , Rollman Ola , Torebjörk Erik , Olsson Elisabeth , Stanghelle Johan Kvalvik
Published: November 2006

Background and Purpose. Venous leg ulceration represents a global health problem affecting predominantly elderly women. Traditionally, functional problems in this group of patients have attracted modest attention from wound care providers and physiotherapists. The aim of the present study was to describe and quantify disease consequences in female leg ulcer patients as a background for future physiotherapy interventions, using the nomenclature of the WHO International Classification of Functioning, Disability and Health (ICF). Method. A prospective study was conducted in 34 women aged 60–85 years with current or previous venous leg ulcer as compared to 27 age‐matched non‐ulcer subjects. The outcome variables were pain, ankle range of motion, walking speed, walking endurance, self‐perceived exertion, mobility, activities of daily living (ADL), physical activity, general health, life satisfaction and use of walking aids and community services. Established instruments were utilized and categorized within ICF domains to provide a conceptual framework and basis for physiotherapeutic research. Results. Leg ulcer patients showed significantly reduced values of ankle range of motion, walking speed and endurance, self‐perceived exertion, mobility, ADL and physical activity level as compared to control subjects. Patients suffering from active ulceration were more negatively affected, and more of them had pain than post‐ulcer fellows. By contrast, general health and life satisfaction were similarly rated by the two study groups. Conclusions. Elderly females in our study with chronic leg ulcer of venous aetiology had significant mobility impairments, but the reasons and consequences of these impairments remain to be elucidated. The potential of preventive measures and physical rehabilitation to aid functioning and prospects of leg ulcer repair need to be investigated in future studies. Copyright © 2006 John Wiley & Sons, Ltd.
Solid‐phase synthesis and purification of a set of uniformly 13C, 15N labelled de novo designed membrane fusogenic peptides
Authors: Agrawal Prashant R. , Hofmann Mathias W. , Meeuwenoord Nico J. , Filippov Dmitri V. , Stalz Holger , Hulsbergen Frans , Langosch Dieter , Overkleeft Hermen S. , De Groot Huub
Published: November 2006

The transmembrane segments of soluble N‐ethylmaleimide‐sensitive factor (SNARE) proteins or viral envelope proteins drive membrane fusion, which suggests that simple synthetic biology constructs for fusion exist and can be evaluated. We describe the high‐yield synthesis of a set of de novo designed fusogenic peptides for use in functional investigations, which are highly enriched in 13C and 15N using three equivalents of labelled amino acids and optimized reaction conditions minimizing aggregation. The biomimetic peptides have a high purity >90% and show reproducible and fusogenic activity that correlates well with the intended functional design characteristics, from strongly fusogenic to almost non‐fusogenic. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd.
Limiting racemization and aspartimide formation in microwave‐enhanced Fmoc solid phase peptide synthesis
Authors: Palasek Stacey A. , Cox Zachary J. , Collins Jonathan M.
Published: November 2006

Microwave energy represents an efficient manner to accelerate both the deprotection and coupling reactions in 9‐fluorenylmethyloxycarbonyl (Fmoc) solid phase peptide synthesis (SPPS). Typical SPPS side reactions including racemization and aspartimide formation can occur with microwave energy but can easily be controlled by routine use of optimized methods. Cysteine, histidine, and aspartic acid were susceptible to racemization during microwave SPPS of a model 20mer peptide containing all 20 natural amino acids. Lowering the microwave coupling temperature from 80 °C to 50 °C limited racemization of histidine and cysteine. Additionally, coupling of both histidine and cysteine can be performed conventionally while the rest of the peptide is synthesized using microwave without any deleterious effect, as racemization during the coupling reaction was limited to the activated ester state of the amino acids up to 80 °C. Use of the hindered amine, collidine, in the coupling reaction also minimized formation of D‐cysteine. Aspartimide formation and subsequent racemization of aspartic acid was reduced by the addition of HOBt to the deprotection solution and/or use of piperazine in place of piperidine. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd.
The way composition affects martensitic transformation temperatures of Ni–Mn–Ga Heusler alloys
Authors: Chen X. Q. , Yang F. J. , Lu X. , Qin Z. X.
Published: November 2006

A systematic substitution of Ge, Si, C and Co for Ga in the non‐stoichiometric Ni–Mn–Ga alloys was performed. The relationship between the compositions of different elements including Ni, Mn, Ga, Ge, Si, C, Co, In and martensitic transformation temperature (Ms) was studied in detail for the present alloys together with data collected from a variety of sources. It is found that Ms is a sensitive parameter to the composition. The size factor and electron concentration are usually thought to be the way the composition influences Ms in the Ni–Mn–Ga alloys. Here, analyzing by linear regression, the electron density maybe a most appropriate parameter to describe the way the composition influences Ms when compared with size factor and electron concentration. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of AlN and GaN under pressure: An ab‐initio study
Authors: Laskowski Robert , Christensen Niels Egede
Published: November 2006

Theoretically calculated dielectric functions are presented for wurtzite and high pressure rocksalt phases of AlN and GaN. The spectra are calculated in a wide range of photon energies as well as in a a very narrow window near the band gap. The binding energies of excitons have been estimated. For the wurtzite phases they are: 0.105 and 0.033 eV for AlN and GaN, and for the high pressure rocksalt phases they are: 0.11 and 0.061 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrostatic pressure experiments on dilute nitride alloys
Authors: Klar P. J. , Teubert J. , Güngerich M. , Niebling T. , Grüning H. , Heimbrodt W. , Volz K. , Stolz W. , Polimeni A. , Capizzi M. , O'Reilly E. P. , Lindsay A. , Galluppi M. , Geelhaar L. , Riechert H. , Tomić S.
Published: November 2006

GaNx As1–x and Ga1–y Iny Nx As1–x are the most prominent members of a novel class of non‐amalgamation type semiconductor alloys where a fraction x of the anions of the host (e.g., GaAs or Ga1–y Iny As) is replaced by N isovalent impurity atoms. The localized N‐states in GaNx As1–x and Ga1–y Iny Nx As1–x form a series of discrete energy levels (e.g., isolated N‐state, N‐pairs and higher order N‐cluster states) resonant with the conduction band of the host. The effect of the alloying with nitrogen on the bandstructure of GaNx As1–x and Ga1–y Iny Nx As1–x can be well parameterized using a band‐anticrossing (BAC) model, namely, assuming a level repulsion between an effective N‐state and the conduction band‐edge state. The dependence of several physical properties on nitrogen incorporation can be predicted qualitatively in the framework of this model, e.g., a tremendous increase of the electron effective mass in GaNx Asx with increasing x, a huge cross section for scattering of electrons by N impurities in electronic transport, etc. Most of these predictions can be tested and verified by performing hydrostatic pressure experiments which, within the picture of the BAC model, allow one to tune continuously the energy difference between the host‐like conduction band edge and the effective N‐level within one and the same specimen. Several examples of this kind will be discussed. Furthermore, we will demonstrate the limitations of the BAC model in the case of GaNx P1–x and also of GaNx As1–x . In particular, we will show several examples where the description by a single effective N‐state fails and that the multiplicity of the N‐states needs to be taken into account. Again hydrostatic pressure experiments prove to be a useful and suitable tool for revealing the effects due to N‐cluster states. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of polarization‐induced electric field screening in InGaN light emitting diodes by means of hydrostatic pressure
Authors: Franssen G. , Suski T. , Perlin P. , Bohdan R. , Trzeciakowski W. , Teisseyre H. , Khachapuridze A. , Targowski G. , Krowicki K. , Czernecki R. , Leszczyński M. , Kurouchi M. , Nanishi Y. , Lu H. , Schaff W.
Published: November 2006

We show that the hydrostatic pressure coefficient dE E/dp of luminescence in Inx Ga1–x N epilayers is in the range 20–38 meV/GPa for the entire alloy (0 ≥ x ≥ 1) and corresponds roughly to the bandgap increase with applied pressure. It is argued that lowering of dE E/dp in quantum structures of InGaN with respect to this range can be attributed to polarization‐induced electric fields (PIEFs). Possible contribution to dE E/dp originating from In‐segregation effects is of secondary importance. This information is used to investigate PIEF screening by free carriers in InGaN‐based light emitting diodes (LEDs). We observe that Si doping at a level of 1019 cm–2 of the barriers in the active region of such LEDs leads to a significant increase of dE E/dp as compared to LEDs with undoped barriers. This is evidence for efficient screening of PIEFs in the Si‐doped devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transport measurements under pressure in III–IV layered semiconductors
Authors: Segura A. , Errandonea D. , Martínez‐García D. , Manjón F. J. , Chevy A. , Tobias G. , Ordejón P. , Canadell E.
Published: November 2006

This paper reports on Hall effect, resistivity and thermopower effect measurements under high pressure up to 12 GPa in p‐type γ‐indium selenide (InSe) and ε‐gallium selenide (GaSe). The paper focuses on two applications of transport measurements under pressure: electronic structure and phase transition studies. As concerns the electronic structure, we investigate the origin of the striking differences between the pressure behaviour of transport parameters in both layered compounds. While the hole concentration and mobility increase moderately and monotonously in ε‐GaSe up to 10 GPa, a large increase of the hole concentration at near 0.8 GPa and a large continuous increase of the hole mobility, which doubled its ambient pressure value by 3.2 GPa, is observed in γ‐InSe. Based on electronic structure calculations the difference is found to arise from the pressure evolution of the valence band maximum. While the shape of the valence band maximum is virtually pressure‐insensitive in ε‐GaSe, it changes dramatically in γ‐InSe, with the emergence of a ring‐shaped subsidiary maximum that becomes the absolute valence‐band maximum as pressure increases. Transport measurements as a function of pressure and temperature are also used to investigate the phase diagram of InSe and, in particular, the transition to the rock‐salt polymorph. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dependence of the band‐gap pressure coefficients of self‐assembled InAs/GaAs quantum dots on the quantum dot size
Authors: Kristukat C. , Goñi A. R. , Pötschke K. , Bimberg D. , Thomsen C.
Published: November 2006

We report on low‐temperature photoluminescence experiments on self‐assembled InAs/GaAs quantum dots under high hydrostatic pressure up to 8 GPa using a diamond anvil cell. The sample exhibits a multimodal size distribution of the quantum dots, which gives rise to a characteristic emission profile displaying up to nine clearly separable peaks attributed to the ground‐state recombination from each quantum dot subensemble with different size. Structural analysis revealed that their size differs in entire monolayer steps. The measured pressure coefficients for each subensemble show a linear dependence on their zero‐pressure emission energy ranging from 65 meV/GPa for the largest dots to 112 meV/GPa for the smallest ones. Pressure dependent strain simulations based on an atomistic valence‐force field yield that the pressure coefficient of the InAs band‐gap is strongly reduced when InAs is embedded in a GaAs matrix. Taking into account confinement effects within the envelope function approximation, the calculated pressure coefficients are in good agreement with the experimental findings. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of pressure on the Raman scattering of wurtzite AlN
Authors: Manjón F. J. , Errandonea D. , Garro N. , Romero A. H. , Serrano J. , Kuball M.
Published: November 2006

High‐pressure Raman spectra of wurtzite aluminum nitride were measured up to 25 GPa. The Raman‐active modes in wurtzite‐AlN were obtained up to the wurtzite‐to‐rocksalt transition at 20 GPa and their pressure coefficients compared with those obtained from ab initio lattice dynamics calculations. A slight decrease of the LO–TO splitting under pressure has been measured. We also report Raman scattering of the rocksalt phase of AlN during downstroke. The comparison of previously reported Raman scattering in rocksalt‐GaN and ab initio calculations suggests that the Raman scattering we have measured in rocksalt‐AlN likely corresponds to the one‐phonon density of states of the rocksalt phase. A partial return to the wurtzite phase is found at ambient pressure after fully releasing pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐pressure Raman study on two modifications of BaAl2Si2
Authors: Shimizu H. , Kume T. , Narita Y. , Sasaki S. , Kikudome T. , Yamanaka S.
Published: November 2006

The new compound BaAl2Si2 exists in two structural modifications at ambient condition; a clathrate‐like low‐pressure phase α‐BaAl2Si2 and a layered high‐pressure phase β‐BaAl2Si2. Raman scattering of α‐BaAl2Si2 and β‐BaAl2Si2 has been measured at 1 bar and room temperature, and that of α‐BaAl2Si2 under high pressures up to 20 GPa. For α‐BaAl2Si2, 17 Raman vibrational modes were observed at frequency of 40–450 cm–1, which is almost consistent with the group theoretical analysis. Low‐frequency vibrational modes associated with Ba atoms in the polyhedrons were found around 65–80 cm–1 compa‐ rable to the typical clathrate Ba8Si46. The 4 Raman bands predicted by the group theory were found for β‐BaAl2Si2. Pressure dependence of Raman modes for α‐BaAl2Si2 indicates the existence of phase transformation at about 20 GPa, which was irreversible with decreasing pressure. The decompressed α‐BaAl2Si2 from 20 GPa to 1 bar shows Raman spectrum close to that of β‐BaAl2Si2 at ambient pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical high‐pressure study of spinel‐type MnIn2S4
Authors: Manjón F. J. , Segura A. , Amboage M. , Pellicer‐Porres J. , Sánchez‐Royo J. F. , Itié J. P. , Flank A. M. , Lagarde P. , Polian A. , Ursaki V.V. , Tiginyanu I. M.
Published: November 2006

We report a combined study of the structural and electronic properties of the spinel‐type semiconductor MnIn2S4 under high pressures by means of X‐ray diffraction (ADXRD), X‐ray absorption (XAS), and optical absorption measurements. The three techniques evidence a reversible structural phase transition near 7 GPa, that according to ADXRD measurements is to a double‐NaCl structure. XAS measurements evidence predominant tetrahedral coordination for Mn in the spinel phase that does not noticeably change with increasing pressure up to the phase transition. XAS measurements indicate that the static disorder increases considerably when the sample reverts from the double‐NaCl phase to the spinel phase. Optical absorption measurements show that the direct gap of MnIn2S4 exhibits a nonlinear behaviour with a positive pressure coefficient at pressures below 2.5 GPa and a negative pressure coefficient between 2.5 and 7 GPa. The pressure behavior of the bandgap seems to be affected by the defect concentration. The double‐NaCl phase also exhibits a bandgap with a negative pressure coefficient. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of CdSe quantum dots with Zn0.38Cd0.23Mg0.39Se barriers under hydrostatic pressure
Authors: Reparaz J. S. , Goñi A. R. , Alonso M. I. , Perez‐Paz M. N. , Tamargo M. C.
Published: November 2006

We have investigated the pressure dependence of the room‐temperature photoluminescence (PL) of self‐assembled CdSe quantum dots (QDs) with quaternary ZnCdMgSe barriers. Four samples with different CdSe deposition times, i.e. different average dot size, were studied. Samples exhibit a very distinct emission energy covering the visible spectrum from the red to the blue. We found, however, a similar pressure coefficient of around 47 meV/GPa for the PL emission of all samples. This value is close to that of bulk CdSe, which gives evidence that dot and quaternary barrier material have a similar compressibility. In contrast, the PL linewidth displays a clear trend with respect to the emission energy, the PL line being broader for the smaller dots emitting in the blue. This is explained by taking into account the huge band‐gap offset of ≈1 eV between dot and barrier and considering quantum confinement effects within a very simplistic infinitely deep square‐well model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure dependence of photoluminescence of InAs/InP self‐assembled quantum wires
Authors: Ruiz‐Castillo M. , Segura A. , Sans J. A. , Martínez‐Pastor J. , Fuster D. , González Y. , González L.
Published: November 2006

This paper investigates the electronic structure of self‐assembled InAs quantum wires (QWrs), grown under different conditions by molecular beam epitaxy on InP, by means of photoluminescence measurements under pressure. In samples with regularly distributed QWrs, room pressure photoluminescence spectra consist of a broad band centred at about 0.85 eV, which can be easily de‐convoluted in a few Gaussian peaks. In samples with isolated QWrs, photoluminescence spectra exhibit up to four clearly resolved bands. Applying hydrostatic pressure, the whole emission band monotonously shifts towards higher photon energies with pressure coefficients ranging from 72 to 98 meV/GPa. In contrast to InAs quantum dots on GaAs, quantum wires photoluminescence is observed up to 10 GPa, indicating that InAs QWrs are metastable well above pressure at which bulk InAs undergoes a phase transition to the rock‐salt phase (7 GPa). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band gap dependence of the recombination processes in InAs/GaAs quantum dots studied using hydrostatic pressure
Authors: Marko I. P. , Adams A. R. , Sweeney S. J. , Massé N. F. , Krebs R. , Reithmaier J. P. , Forchel A. , Mowbray D. J. , Skolnick M. S. , Liu H. Y. , Groom K. M. , Hatori N. , Sugawara M.
Published: November 2006

We present the results based upon a systematic study of the properties of quantum dot (QD) lasers with emission wavelengths around 0.98 and 1.3 µm at room temperature and atmospheric pressure. To investigate the radiative and non‐radiative components of the threshold current, we studied the temperature and high hydrostatic pressure dependencies of spontaneous and stimulated emission. Although important parameters such as lasing wavelength, QD density, ridge width, cavity length, threshold current density (J th) varied greatly, we found that all the lasers have nearly the same dependence of the radiative component, J rad, on band gap when it was tuned by the application of high pressure. It was observed that J rad increases strongly with band gap. Therefore the different dependencies of J th are explained in terms of the relative importance of different non‐radiative recombination mechanisms, such as Auger recombination and thermal carrier escape. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cross‐layer design for call admission control of a high‐capacity GEO satellite network with on‐board cross‐connect
Authors: Qingyang Hu Rose , Qian Yi , Cheng Yu , Kota Sastri
Published: November 2006

This paper addresses cross‐layer design of end‐to‐end call admission control and beam‐to‐beam connectivity provisioning for a high‐capacity multi‐beam GEO satellite network with on‐board cross‐connectivity. On‐board satellite switching is a technology designed to offer heterogeneous services, especially in demographically dispersed areas. Nevertheless, full on‐board switching techniques are far from maturity. Their implementations have been proven expensive and difficult. There are also high risks involved in launching satellites for the stationary orbit surrounding the Earth. As a substitute, a satellite network with on‐board cross‐connect is devised in this paper. Connectivity provisioning and call admission control mechanisms associated with such a network are also presented. Simulation studies are conducted to show the effectiveness of the proposed mechanisms. Copyright © 2006 John Wiley & Sons, Ltd.
Semantic Web approach to smart link generation for Web navigations
Authors: Kao Shang‐Juh , Hsu I‐Ching
Published: November 2006

The rapid development of the Internet has led to diverse applications of accessing various Web resources, such as Web pages, XML documents, pictures and video and audio files. Intelligently discovering how these Web resources are related in order to enable effective Web surfing is a current challenge in Internet development. The XML Link Language (XLink), which is a W3C recommendation for describing the relationships among Web resources, is a potential solution to this problem. However, XLink is still short of knowledge representation in handling computer‐interpretable effects, such as dynamic link generations. This study attempts to integrate knowledge into XLink by defining a multi‐layered semantic framework. The proposed framework is across four layers of the semantic Web stack, including the URI layer, XML (XLink) layer, ontology layer and rule layer, to facilitate machine understanding. The ontology, which is based on description logics, provides sound reasoning, while the rule is a logic program built on top of an ontology to support complementary inference capabilities. Based on the multi‐layered semantic framework, an intelligent XLink shell, called XLinker, is also developed to facilitate three semantic approaches of linking associations, i.e. XLink‐based metadata, ontology‐based reasoning and rule‐based inference. To demonstrate the feasibility of XLinker, an XLink Transcoding Web Server is also implemented to reveal smart hyperlink generation for Web navigations. Copyright © 2006 John Wiley & Sons, Ltd.
OmniCon: a Mobile IP‐based vertical handoff system for wireless LAN and GPRS links
Authors: Sharma Srikant , Baek Inho , Chiueh Tzi‐cker
Published: November 2006

Wi‐Fi based hotspots offer mobile users broadband wireless Internet connectivity in public work spaces and corporate/university campuses. Despite the aggressive deployment of these hotspots in recent years, high‐speed wireless Internet access remains restricted to small geographical areas due to the limited physical coverage of wireless LANs. On the other hand, despite their lower throughput, cellular networks have a significantly wider coverage and are thus much more available. Recognizing that 2.5G or 3G cellular networks can effectively complement wireless LANs, we set out to develop a vertical handoff system that allows mobile users to seamlessly fall back to such cellular networks as the general packet radio service (GPRS) or 3G whenever wireless LAN connectivity is not available. The resulting handoff mechanism allows a network connection of a mobile node to operate over multiple wireless access networks in a way that is transparent to end user applications. In this paper, we present the design, implementation, and evaluation of a fully operational vertical handoff system, called OmniCon, which enables mobile nodes to automatically switch between wireless LAN and GPRS, based on wireless LAN availability, by introducing a simple extension to the existing Mobile IP implementation. We discuss the design issues in the proposed vertical handoff system for heterogeneous networks, including connection setup problems due to network address translation, and the disparity in link characteristics between wireless LANs and GPRS. A detailed performance evaluation study of the OmniCon prototype demonstrates its ability to migrate active network connections between these two wireless technologies with low handoff latency and close to zero packet loss. Copyright © 2006 John Wiley & Sons, Ltd.
The Esperanto Broker: a communication platform for nomadic computing systems
Authors: Cotroneo Domenico , Migliaccio Armando , Russo Stefano
Published: November 2006

There is an increasing demand for middleware for nomadic computing applications. Owing to the inherent characteristics of such environments, these platforms have to address two fundamental issues: (i) device disconnections and the limitations of wireless networks may force users to experience short periods of service unavailability; and (ii) the complexity to design and develop next‐generation mobile computing applications. This paper proposes the Esperanto Broker (EB), a communication platform that addresses mobility issues via an integrated approach, i.e. at data‐link, network, and middleware levels. Decoupling interactions are achieved via a tuple‐space underlying infrastructure. To support developers with advanced services, the EB enhances the distributed objects computing model providing the abstraction for the communication paradigms standardized by the W3C. Esperanto applications can be modeled as sets of objects that are distributed over mobile devices, which communicate via remote method invocations (RMIs). RMIs natively implement pull and push models, in both one‐to‐one and one‐to‐many multiplicity. The paper focuses on the EB design issues, essential aspects of the implementation, and performance evaluations of the implemented prototype. Copyright © 2006 John Wiley & Sons, Ltd.