bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating student retention and degree‐completion time: Decision trees and neural networks vis‐à‐vis regression
Authors: Herzog Serge
Published: November 2006

Focusing on student retention and time to degree completion, this study illustrates how institutional researchers may benefit from the power of predictive analyses associated with data‐mining tools.
Let the data talk: Developing models to explain IPEDS graduation rates
Authors: Bailey Brenda L.
Published: November 2006

Data mining of IPEDS data is used to develop models that calculate predicted graduation rates for two‐ and four‐year institutions.
The metabolic organization of a primitive air‐breathing fish, the Florida gar (lepisosteus platyrhincus)
Authors: Frick Natasha Therese , Scott Bystriansky Jason , Stuart Ballantyne James
Published: November 2006

The metabolic organization of the air‐breathing Florida gar, Lepisosteus platyrhincus, was assessed by measuring the maximal activities of key enzymes in several metabolic pathways in selected tissues, concentrations of plasma metabolites including nonesterified fatty acids (NEFA), free amino acids (FAA) and glucose as well as tissue FAA levels. In general, L. platyrhincus has an enhanced capacity for carbohydrate metabolism as indicated by elevated plasma glucose levels and high activities of gluconeogenic and glycolytic enzymes. Based upon these properties, glucose appears to function as the major fuel source in the Florida gar. The capacity for lipid metabolism in L. platyrhincus appears limited as plasma NEFA levels and the activities of enzymes involved in lipid oxidation are low relative to many other fish species. L. platyrhincus is capable of oxidizing both D‐ and L‐β‐hydroxybutyrate, with tissue‐specific preferences for each stereoisomer, yet the capacity for ketone body metabolism is low compared with other primitive fishes. Based on enzyme activities, the metabolism of the air‐breathing organ more closely resembles that of the mammalian lung than a fish swim bladder. The Florida gar sits phylogenetically and metabolically in an intermediate position between the “primitive” elasmobranchs and the “advanced” teleosts. The apparently unique metabolic organization of the gar may have evolved in the context of a bimodal air‐breathing environmental adaptation. J. Exp. Zool. 305A:7–17, 2007. © 2006 Wiley‐Liss, Inc.
Homology and the evolution of novelty duringDanioadult pigment pattern development
Authors: Parichy David M.
Published: November 2006

Recent studies using zebrafish and its relatives have provided insights into the development and evolution of adult pigment patterns. In this review, I describe how an iterative approach using a biomedical model organism and its close relatives can be used to elucidate both mechanistic and organismal aspects of pigment pattern formation. Such analyses have revealed critical roles for post‐embryonic latent precursors as well as interactions among different pigment cell classes during adult pigment pattern formation and diversification. These studies also have started to reveal homologous and novel features of the underlying developmental processes.J. Exp. Zool. (Mol. Dev. Evol.) 308B:578–590, 2007. © 2006 Wiley‐Liss, Inc.
A characterization of distinguished Fréchet spaces
Authors: Ferrando J. C. , Ka̧kol J. , López Pellicer M.
Published: November 2006

Bierstedt and Bonet proved in 1988 that if a metrizable locally convex space E satisfies the Heinrich's density condition, then every bounded set in the strong dual (E ′, β (E ′, E)) of E is metrizable; consequently E is distinguished, i.e. (E ′, β (E ′, E)) is quasibarrelled. However there are examples of distinguished Fréchet spaces whose strong dual contains nonmetrizable bounded sets. We prove that a metrizable locally convex space E is distinguished iff every bounded set in the strong dual (E ′, β (E ′, E)) has countable tightness, i.e. for every bounded set A in (E ′, β (E ′, E)) and every x in the closure of A there exists a countable subset B of A whose closure contains x. This extends also a classical result of Grothendieck. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Maximal Lp regularity for parabolic difference equations
Authors: Geissert Matthias
Published: November 2006

In this paper, we consider a family of finite difference operators {Ah }h >0 on discrete L q ‐spaces L q (ℝN h ). We show that the solution u h to u ′h (t) – A h u h(t) = f h (t), t > 0, u h (0) = 0 satisfies the estimate ‖A h u h ‖ ≤ C ‖f h ‖, where C is independent of h and f h . In this case, the family {A h }h >0 is said to have discrete maximal L p regularity on the discrete L q ‐space. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Placebo‐controlled, double‐blind dose‐finding study of entacapone in fluctuating parkinsonian patients
Authors: Mizuno Yoshikuni , Kanazawa Ichiro , Kuno Sadako , Yanagisawa Nobuo , Yamamoto Mitsutoshi , Kondo Tomoyoshi ,   Japanese Parkinson–Entacapone Study Group
Published: November 2006

We conducted a multicenter randomized, placebo‐controlled double‐blind parallel‐group study in Japanese Parkinson's disease (PD) patients with wearing‐off motor fluctuations to determine the clinical efficacy and safety of entacapone as an adjunct to concomitant treatment with levodopa and a dopa decarboxylase inhibitor (DCI). We randomized 341 patients to receive entacapone 100 or 200 mg or placebo per dose of levodopa/DCI for 8 weeks. The primary efficacy variable was on time change while awake, determined by patients' diaries. Mean baseline on time in each group was approximately 8 hours. Mean on time change at final assessment was 1.4 hours each for entacapone 100‐mg and 200‐mg groups and by 0.5 hours for the placebo group (P < 0.05). The two entacapone doses were equally efficacious. Adverse events occurred in 79 patients (69.9%) in placebo, 82 (72.6%) in 100 mg, and 98 (86.0%) in 200 mg. The most common adverse event with entacapone was an increase in dyskinesias. The overall safety profile was satisfactory in both entacapone groups. In conclusion, both entacapone 100 and 200 mg were equally effective in increasing on time of PD patients with wearing‐off fluctuations, although the safety and tolerability profile appeared more favorable for the 100‐mg dose. © 2006 Movement Disorder Society
Sarizotan as a treatment for dyskinesias in Parkinson's disease: A double‐blind placebo‐controlled trial
Authors: Goetz Christopher G. , Damier Philippe , Hicking Christine , Laska Eugene , Müller Thomas , Olanow C. Warren , Rascol Olivier , Russ Hermann
Published: November 2006

The objective of this study is to conduct a dose‐finding study of sarizotan in Parkinson's disease (PD) patients with dyskinesia to identify a safe dose and to identify a sensitive dyskinesia rating measure. Sarizotan is a novel compound with full 5‐HT1A agonist properties and additional high affinity for D3 and D4 receptors. An open label study documented improvements in PD patients with levodopa‐induced dyskinesia. There is no precedent for study designs or outcome measures in pivotal trials of antidyskinesia therapies. The approach used here was a multicenter, randomized, placebo‐controlled, double‐blind, parallel study. Included were PD patients optimized to levodopa and dopaminergic drugs with moderately disabling dyskinesias present greater than or equal to 25% of the waking day. Interventions included sarizotan 2, 4, or 10 mg/day or matching placebo, given in two doses. There were two outcome measures: the primary measure was change from baseline in diary‐based on time without dyskinesia; the secondary measures were change from baseline in scores on the Abnormal Involuntary Movement Scale (AIMS), the composite score of Unified Parkinson's Disease Rating Scale (UPDRS) Items 32+33 (dyskinesia duration and disability) and total UPDRS. A total of 398 subjects were randomized, with 381 included in the intention‐to‐treat population. No significant changes occurred on sarizotan compared to placebo on any diary‐based measure of dyskinesia or the AIMS score. The composite score of UPDRS Items 32+33 was significantly improved with 2 mg/day sarizotan, with a trend at 10 mg/day. Adverse events were not significantly different in sarizotan‐ and placebo‐treated patients, but off time significantly increased with sarizotan 10 mg/day. Sarizotan 2 mg/day is a safe agent in PD patients with dyskinesia. To test its role in abating dyskinesia, future studies should focus on this dose and will use the composite score of UPDRS Items 32+33 as the primary outcome. © 2006 Movement Disorder Society
Unambiguous assignment of trifluoromethylpyrazole regioisomers by 19F–15N correlation spectroscopy
Authors: Kline Mike , Cheatham Steve
Published: November 2006

Analysis of the 19F chemical shifts of trifluoromethylpyrazole regioisomers has shown that while chemical shift is in general a reliable predictor of regiochemistry in this series, there is a narrow chemical shift range in which the two isomers overlap and the regiochemistry cannot be assigned with certainty. We have examined the usage of 19F15N correlation spectroscopy as a method to provide a second unambiguous confirmation of regiochemistry of 3‐ and 5‐trifluoromethylpyrazole regioisomers. In the case of 3‐trifluoromethyl analogs, one expects a three‐bond coupling to the pyridine type nitrogen (N–2). In the case of the 5‐trifluoromethyl pyrazole the situation is exactly reversed, with the fluorines of the trifluoromethyl moiety being 3‐bonds from the pyrrole type nitrogen (N‐1). We have observed that 3‐trifluromethyl analogs follow the expected pattern of readily observable 3‐bond coupling. However, 19F15N couplings in 5‐trifluromethyl analogs do not follow the normal pattern of 3‐bond coupling. Using this information we have been able to develop unambiguous methods to distinguish the isomers. Copyright © 2007 John Wiley & Sons, Ltd.
Nanoreinforcement of flexible epoxy using layered silicate
Authors: Ratna D. , Chakraborty B. C. , Dutta H. , Banthia A. K.
Published: November 2006

Flexible epoxy matrices, having a good vibration damping capability, were nanoreinforced using an organoclay. The nanocomposites were characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The effect of matrix flexibility on the reinforcing effect was investigated. It was found that the reinforcing effect increased with an increase in flexibility of the matrix. The reinforcement is achieved without any sacrifice in flexibility and Tg. In addition, a reduction in solvent diffusion and flammability has been demonstrated. DMA study indicates that the height of the loss peak, decreases with incorporation of the clay because of the intercalation. Nevertheless, the nanocomposite samples having up to 10 wt% of the clay show a high damping capability as evident from the tan δmax values. POLYM. ENG. SCI., 46:1667–1673, 2006. © 2006 Society of Plastics Engineers
Natural rubber–polyurethane block copolymers: Nonlinear structural variations with NCO/OH ratio
Authors: Gopakumar S. , Nair M.R. Gopinathan
Published: November 2006

A series of segmented block copolymers was prepared by the chain extension of hydroxyl terminated liquid natural rubber (HTNR) with polyurethane oligomers derived from toluene diisocyanate (TDI) and 1,3‐butane diol at varying NCO/OH ratio. The previously reported two‐step method of synthesis was modified to get improved products. This was done by optimizing the formation of polyurethane oligomers in the first step of the synthesis. All the samples were characterized by solubility testing, DSC, tensile testing, etching studies, and SEM. The data obtained were correlated to the structural features of the block copolymers. It was found that NCO/OH ratio played an important role in determining the structural variations in the block copolymers. POLYM. ENG. SCI. 46:1812–1821, 2006. © 2006 Society of Plastics Engineers
Preparation and properties of the self‐crosslinked acrylic rubber via gamma ray initiated emulsion polymerization
Authors: Geng Hongwei , Wang Mozhen , Ge Xuewu , Wang Weiwei
Published: November 2006

In this study, a series of self‐crosslinked acrylic rubbers were prepared by gamma ray initiated emulsion copolymerization. Acrylic acid and N‐hydroxymethl acrylamide were used as the cure‐site monomers. The vulcanizing properties, tensile properties, and dynamic mechanical analysis of the self‐crosslinked acrylic rubbers were investigated. It was found that the curing characteristics could be influenced significantly by the content and species of the cure‐site monomers. Improvement in mechanical properties like tensile strength, modulus and elongation at break was observed in the prepared self‐crosslinked rubber. The structure‐property correlation of the self‐crosslinked acrylic rubber was discussed. POLYM. ENG. SCI. 46:1748–1753, 2006. © 2006 Society of Plastics Engineers.
Multiplex shear stress‐induced nucleation in dynamic microcellular foaming process
Authors: Zhu Wenli , Zhou Nanqiao , Wu Hongwei
Published: November 2006

The effect of multiplex shear stress on the cell nucleation during microcellular foaming process was investigated using a dynamic foaming experimental apparatus. The multiplex oscillatory shear, which is different from previous one‐dimensional screw shear in a “stable” extrusion foaming process, is applied to the polymer melt through an axially vibrated rotor. The experimental results show that, by superimposing an axial vibration on the rotating rotor, the cell density increases and cell size decreases significantly when the shear rate is low. Both the uniformity of cell size and cell distribution are improved under vibration when compared with that without vibration regardless of how the shear rate changes. In addition, a simplified nucleation model based on shear energy has been carried out to qualitatively investigate the effect of both the simple steady shear and the multiplex oscillatory shear on the cell nucleation. Experiments and theoretical predictions all show that cell nucleation could be greatly improved by superimposing the oscillatory shear when the nucleation driving force induced by the steady shear is insufficient. Finally, the shear heat generated by excessive shear and strong vibration should be considered carefully although the isothermal condition was supposed in the present model. POLYM. ENG. SCI. 46:1728–1738, 2006. © 2006 Society of Plastics Engineers.
Rheokinetics of ring‐opening metathesis polymerization of norbornene‐based monomers intended for self‐healing applications
Authors: Larin G. E. , Bernklau N. , Kessler M. R. , DiCesare J. C.
Published: November 2006

Constant shear rate rheokinetics was used to evaluate the polymerization of four norbornene‐based monomer systems as candidate healing agents in self‐healing composites: endo‐dicyclopentadiene (endo‐DCPD), exo‐DCPD, 5‐ethylidene‐2‐norbornene (ENB), and a 1:1 volume mixture of endo‐DCPD:ENB. The ruthenium catalyst induced ring‐opening metathesis polymerization of the healing agent candidates were measured experimentally under isothermal conditions while the influences of several different variables were considered (e.g., test temperature, catalyst concentration, catalyst form). Analyzing the increase in viscosity during the polymerization, comparisons of the reaction kinetics of the different monomers were quantified by defining two parameters, tt and Δt, which correspond to the polymerization initiation and propagation rates respectively. Generally, ENB shows the fastest polymerization kinetics, and endo‐DCPD the slowest. POLYM. ENG. SCI. 46:1804–1811, 2006. © 2006 Society of Plastics Engineers
The effect of screw geometry on melt temperature profile in single screw extrusion
Authors: Kelly A.L. , Brown E.C. , Coates P.D.
Published: November 2006

Experimental observations of melt temperature profiles and melting performance of extruder screws are reported. A novel temperature sensor consisting of a grid of thermocouple junctions was used to take multiple temperature readings in real time across melt flow in a single screw extruder. Melt pressure in the die and power consumption were also monitored. Three extruder screws at a range of screw speeds were examined for a commercial grade of low density polyethylene. Results showed melt temperature fields at low throughputs to be relatively independent of screw geometry with a flat‐shaped temperature profile dominated by conduction. At high throughputs, melting performance and measured temperature fields were highly dependent upon screw geometry. A barrier‐flighted screw with Maddock mixer achieved significantly better melting than single flighted screws. Low temperature “shoulder” regions were observed in the temperature profiles of single‐flighted screws at high throughput, due to late melting of the solid bed. Stability of the melt flow was also dependent upon screw geometry and the barrier‐flighted screw achieving flow with lower variation in melt pressure and temperature. Dimensionless numbers were used to analyze the relative importance of conduction, convection, and viscous shear to the state of the melt at a range of extrusion conditions. Polym. Eng. Sci. 46:1706–1714, 2006. © 2006 Society of Plastics Engineers
Evaluation of agreement between physicians' notation of ‘no evidence of disease’ (NED) and patients' report of cancer status
Authors: Oates Carolyn T. , Sloane Richard , Ingram Sally S. , Seo Pearl H. , Cohen Harvey J. , Clipp Elizabeth C.
Published: November 2006

This study examines extent of agreement between oncologists' and cancer patients' reports of current cancer status. Participants with history of cancer were given a comprehensive geriatric assessment in which they were asked whether they had cancer at the present time. This was compared to cancer status concurrently recorded by their physicians in the chart. 75.5% of patients whose physicians reported ‘no evidence of disease’ (NED) reported that they currently had cancer. 30% of them were anxious and 27% were depressed. Among patients for whom both the patient and physician reported no cancer, only 12.5% were anxious and 7% depressed. Compared to patients with concordant responses, those who discrepantly reported they had cancer had significantly more comorbid illnesses, medications, and pain, and lower levels of social, emotional, and physical functioning. Moreover, equal levels of distress and dysfunction were found between those who reported cancer but had NED and those who reported cancer and did have active disease by physician notation. Although conclusions about cause and effect are limited due to study design, findings suggest that some patients might suffer unnecessarily from lack of understanding about current disease status. These findings also suggest the need for improved physician–patient communication and symptom recognition/management. Copyright © 2006 John Wiley & Sons, Ltd.
Cryogenic landforms in the Sierras de Alvear, Fuegian Andes, subantarctic Argentina
Authors: Valcárcel‐Díaz Marcos , Carrera‐Gómez Pedro , Coronato Andrea , Castillo‐Rodríguez Francisco , Rabassa Jorge , Pérez‐Alberti Augusto
Published: November 2006

A preliminary survey of periglacial landforms found in the Monte Alvear region of the Fuegian Andes, subantarctic Argentina has revealed the presence of nivation hollows, subnival ‘boulder’ (clast) pavements, protalus ramparts, debris lobes, patterned ground and cryo‐ejected clasts. With the exception of debris lobes and cryo‐ejected clasts, all the landforms show some degree of activity and are, therefore, considered as indicators of present‐day cryonival morphodynamics at higher elevations in these mountains. A number of small tors, while not necessarily periglacial in origin, are also apparently experiencing cryogenic weathering. Copyright © 2006 John Wiley & Sons, Ltd.
Mechanisms of guanosine triphosphate hydrolysis by Ras and Ras‐GAP proteins as rationalized by ab initio QM/MM simulations
Authors: Grigorenko Bella L. , Nemukhin Alexander V. , Shadrina Maria S. , Topol Igor A. , Burt Stanley K.
Published: November 2006

The hydrolysis reaction of guanosine triphosphate (GTP) by p21ras (Ras) has been modeled by using the ab initio type quantum mechanical–molecular mechanical simulations. Initial geometry configurations have been prompted by atomic coordinates of the crystal structure (PDBID: 1QRA) corresponding to the prehydrolysis state of Ras in complex with GTP. Multiple searches of minimum energy geometry configurations consistent with the hydrogen bond networks have been performed, resulting in a series of stationary points on the potential energy surface for reaction intermediates and transition states. It is shown that the minimum energy reaction path is consistent with an assumption of a two‐step mechanism of GTP hydrolysis. At the first stage, a unified action of the nearest residues of Ras and the nearest water molecules results in a substantial spatial separation of the γ‐phosphate group of GTP from the rest of the molecule (GDP). This phase of hydrolysis process proceeds through the low barrier (16.7 kcal/mol) transition state TS1. At the second stage, the inorganic phosphate is formed in consequence of proton transfers mediated by two water molecules and assisted by the Gln61 residue from Ras. The highest transition state at this segment, TS3, is estimated to have an energy 7.5 kcal/mol above the enzyme–substrate complex. The results of simulations are compared to the previous findings for the GTP hydrolysis in the Ras‐GAP (p21ras–p120GAP) protein complex. Conclusions of the modeling lead to a better understanding of the anticatalytic effect of cancer causing mutation of Gln61 from Ras, which has been debated in recent years. Proteins 2007. © 2006 Wiley‐Liss, Inc.
Dust collector explosion prevention and control
Authors: Going John E. , Lombardo Tony
Published: November 2006

The handling of fine particles of a combustible material is a major and inevitable part of many industrial processes. The objective may be fugitive and emission controls or the collection of a product. The challenge will increase as the use of finer particles increases. The risks will increase simultaneously as the hazard properties such as ignitability increase with the reduction of particle size. Dust collectors are a component, if not the most common component, of particle handling and are also often the origin or termination of an explosion. The design of dust collector protection is a systematic process that includes and requires process information as well as protection objectives. The theory of protection and the selection of protection techniques will be reviewed. The practice of dust collector protection is often less routine because of many physical and process complications. Examples of both simple and complicated applications are presented with brief illustrations of the consequence of no or inadequate protection. © 2006 American Institute of Chemical Engineers Process Saf Prog 2007
Structure, ferromagnetism and magnetotransport of epitaxial (Ga,Mn)As/GaAs structures
Authors: Brunner K. , Gould C. , Schmidt G. , Molenkamp L. W.
Published: November 2006

In this review, we describe the structural, magnetic and magnetotransport properties of one of the most advanced ferromagnetic semiconductor material systems, (Ga,Mn)As/GaAs heterostructures and nanostructures. Molecular beam epitaxy at low substrate temperature is applied to deposit epitaxial layers without MnAs cluster formation but with homogeneous incorporation of substitutional Mn up to about 8% content and with concomitant hole carrier densities in the 1021 cm–3 range. Epitaxial strain, Mn content, p‐doping and defects that are related to low‐temperature growth may strongly influence the ferromagnetic properties, like Curie temperature, remanent magnetization and magnetic anisotropy. This is well understood within the Zener model for ferromagnetic ordering of Mn ions that is mediated by p–d exchange interaction with free holes in the complex, anisotropic valence band states. The interplay of ferromagnetism and electronic band structure manifests in the various magnetotransport phenomena, like anomalous Hall effect and spin valve tunneling transport. In particular, tunneling structures reveal many novel features, such as the tunneling anisotropic magnetoresistance (TAMR), that highlight the interplay of magnetic and electronic properties and may be pathways to future spintronics devices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanically controlled preparation of protein intermediates in single molecule experiments
Authors: Berkemeier Felix , Schlierf Michael , Rief Matthias
Published: November 2006

Single molecule mechanical experiments allow the controlled manipulation of proteins and the population of intermediate states within their high dimensional energy landscape. Here we report single molecule refolding measurements of domain 4 from the protein ddFilamin using a novel digital control scheme. First, the protein is unfolded mechanically to an intermediate state. An on‐line detection scheme then detects population of the intermediate and rapidly switches to refolding conditions. This control scheme allows direct measurement of the refolding kinetics. A comparison to the results from conventional single molecule refolding schemes allows important conclusion on the structural relation between unfolding and refolding intermediates in this protein domain. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Infrared imaging with InAs/GaSb type‐II superlattices
Authors: Walther M. , Weimann G.
Published: November 2006

InAs/GaSb short period superlattices (SLs) with broken gap typ‐II band alignment are very well suited for the fabrication of high performance infrared camera systems for the second atmospheric window (3–5 µm). High resolution focal plane arrays for single‐ and dual‐colour applications based on InAs/GaSb SLs have been fabricated. Those camera systems reveal excellent performance data which are comparable and even superior to state of the art thermal imaging systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromagnetic properties of MnAs‐on‐GaAs(001) films
Authors: Ploog K. H. , Däweritz L. , Engel‐Herbert R. , Hesjedal T.
Published: November 2006

Strained MnAs films on GaAs(001) grown by molecular beam epitaxy exhibit unique micro‐magnetic properties due to the strain‐mediated coexistence of hexagonal ferromagnetic α‐MnAs and orthorhombic paramagnetic β‐MnAs arranged in selforganized periodic stripe patterns. To explore the internal structure of the magnetization, which is not accessible by the magnetic imaging techniques AFM and XMCDPEEM, detailed micromagnetic simulations are needed. Otherwise, physically unreasonable models would be developed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical excitations of quasi‐one‐dimensional systems: carbon nanotubes versus polymers and semiconductor wires
Authors: Prezzi D. , Molinari E.
Published: November 2006

We review the main characteristics of optical excitations of semiconductor nanotubes, as obtained from accurate ab‐initio theories and model calculations as well as experimental evidence, and discuss them in light of the previous understanding of other quasi‐one‐dimensional semiconducting systems. We point out striking similarities of nanotubes with III–V quantum wires and conjugated polymers, especially (i) the clear excitonic nature of absorption, very far from the single‐particle behaviour; (ii) its manifestations in optical spectra, where excitonic peaks are accompanied by a strong intensity reduction at the onset of the free‐particle continuum; (iii) the strategies that allow experimental access to exciton binding energies. The recent theoretical and experimental evidence obtained on semiconducting single‐walled nanotubes converges quantitatively to a picture of strongly bound excitons (about 0.3–1.0 eV for nanotubes with 0.4–1.0 nm diameter). We discuss its implications and list a few open issues of relevance to fundamental understanding and optoelectronic applications. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Supported membranes on polyelectrolyte layers studied by X‐ray reflectometry
Authors: Reich Christian , Neff Petra A. , Bausch Andreas R. , Rädler Joachim O. , Nickel Bert
Published: November 2006

Supported lipid membranes on polymer layers were investigated by X‐ray reflectivity in aqueous environment using a microfluidic setup. Polyallylamine hydrochloride and poly(sodium 4‐styrenesulfonate) were used for building up multilayer architectures with alternating charge distribution.

First results from synchrotron reflectivity experiments demonstrate that such polyelectrolyte layers can act as aqueous spacers with almost negligible electron density contrast as compared to water. Lipid membranes on top of such polymer spacers are expected to show only minor structural denaturation. Thus this model system is proposed as a step towards decoupling lipid membranes from solid substrates. The accessibility to such biological systems using high‐resolution X‐ray reflectivity and the possibility to insert well‐defined spacers with minimum contrast are highly competitive to established methods of neutron reflectivity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of end grafted DNA molecules and possible biosensor applications
Authors: Sendner C. , Kim Yong W. , Rant U. , Arinaga K. , Tornow M. , Netz R. R.
Published: November 2006

Polymers that are terminally attached to solid supports, so called brushes, form the basis for a wide variety of different applications in colloidal and biophysical sciences. For grafted charged chains a conducting surface allows to manipulate the brush structure by applying electric fields across the brush. The dynamics of oligomeric DNA molecules under the action of repulsive and attractive surface electric fields is studied by Brownian dynamics simulations including hydrodynamic effects and compared to experimental results. The difference in flexibility between double and single stranded DNA molecules leads to a change in the switching dynamics when repeatedly reversing the surface charge. This effect allows to detect hybridization of surface anchored DNA. Similar kinetic changes occur when other molecules bind terminally to DNA, opening the possibility to use end grafted polymers for general biosensing applications. We in particular discuss the influence of the adsorbate size and change on the switching dynamics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transistor based study of the electrolyte/SiO2 interface
Authors: Gentil Cédric , Côte Denis , Bockelmann Ulrich
Published: November 2006

An experimental and theoretical study of the silica surface in aqueous environment is presented. The current/voltage characteristics of silicon field effect transistors are measured as a function of the salt concentration of a KCl solution in contact with the SiO2 gate oxide. We find that a model assuming constant interface charge can describe the global trend of the measured salt dependence. A refined model, allowing for a varying interface charge, provides a quantitative description of the measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Label‐free detection of DNA using field‐effect transistors
Authors: Ingebrandt Sven , Offenhäusser Andreas
Published: November 2006

Electronic DNA sensors based on field‐effect transistor arrays operating in liquid environment, offer an alternative method for the detection of biomolecular binding events, without the requirement to label the target molecules. These semiconductor devices are sensitive to electrical charge variations that occur at the surface/electrolyte interface. Using such devices, the hybridization reaction of oligonucleotides with complementary single‐stranded oligonucleotides, which are immobilized on the oxide surface of the transistor gate, can be detected. The detection principle is based on the intrinsic charge of the nucleic acid molecules in liquid environment. In this article we present a summary of the ‘DNA BioFET’ project, which has been conducted in our group in recent years. We compare an electrostatic and a covalent immobilization protocol for the probe DNA. Most important for reliable signal readout is the use of a differential approach, for which a DNA microarray represents an ideal bioassay. With our FET setup we can either use a chip‐to‐chip reference with two electrically identical chips, which are coated with different probe sequences. A more sophisticated method, which makes use of the DNA microarray technology, was established with an aligned microspotting system enabling the coating of different channels out of the microarray with different probe sequences. So far our current chip design uses 16 channels enabling first proof‐of‐principle experiments. The detection method itself, however, offers the possibility to be up scaled to many thousands of sensor spots like currently used in fluorescence based DNA microarray chips. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High speed nanophotonic devices based on quantum dots
Authors: Bimberg D. , Fiol G. , Kuntz M. , Meuer C. , Lämmlin M. , Ledentsov N. N. , Kovsh A. R.
Published: November 2006

For InAs‐GaAs based quantum dot lasers emitting at 1300 nm digital modulation with bit error rates below 10–11 at –2 dBm receiver power is demonstrated. Error rates of 10–9 or better are realized between 23 °C and 70 °C without current adjustment. Passive and hybrid mode‐locked QD lasers are shown to generate optical pulses with repetition frequencies up to 80 GHz and 40 GHz, respectively, with an ultra‐short minimum pulse length of 710 fs at 20 GHz. The minimum root mean square jitter of 40 GHz hybrid mode‐locked pulses is found to be 400 fs with a corresponding pulse width of 4 ps.

Quantum dot based 1.3 µm fiber‐coupled amplifier modules show 40 Gb/s operation with bit error rates below 10–11. Amplifier chip gain up to 26 dB is demonstrated. 710 fs pulses are amplified without pulse broadening. For all devices we use deeply etched narrow ridge waveguide structures which show excellent current and optical confinement.

Along with suppressed beam filamentation of the fundamental mode, a low α ‐factor and strongly reduced sensitivity to optical feedback our results demonstrate that QD laser performance is now comparable or even superior to quantum well lasers. These achievements became possible due to systematic devel‐opment of self‐organized growth technologies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Special Issue: Frontiers in Semiconductor Nanoscience (Part A)
Authors: Bougeard Dominique , Finley Jonathan , Grayson Matthew , Tornow Marc
Published: November 2006

The present special issue of physica status solidi is dedicated to Professor Gerhard Abstreiter on the occasion of his 60th birthday. Guest edited by Dominique Bougeard, Jonathan Finley, Matthew Grayson, and Marc Tornow, it contains 24 papers covering different aspects of semiconductor physics and nanoscience. Additional contributions can be found in Part B published in phys. stat. sol. (b) 243, No. 14 (2006). Together the twin volumes of pss(a) and pss(b) cover many advanced topics, including quantum transport, optical properties and coherent phenomena, nano‐biological systems and novel materials and nanostructures.

The cover picture shows a schematic image of a coupled quantum dot nanostructure formed by two‐fold cleaved edge overgrowth of a GaAs–AlGaAs heterostructure [1]. Such advanced nanostructure fabrication technologies were pioneered in Gerhard Abstreiter's group at the Walter Schottky Institut almost ten years ago. The molecular like electronic structure in such an artificial molecule remains subject to intense study even today in the context of solid‐state implementations of quantum information technologies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SC2: A Novel Process for Manufacturing Multipurpose High‐Density Chemical Microarrays
Authors: Dikmans Antonius , Beutling Ulrike , Schmeisser Edelgard , Thiele Sabine , Frank Ronald
Published: November 2006

Various formats of miniaturized arrays of cellulose‐bound synthetic probe molecules to suit a broad range of technical and assay configurations have been produced by a novel process which we call spotting compound‐support conjugates, SC2. This process involves parallel chemical assembly of the probe molecules by SPOT‐synthesis on a special cellulose membrane, post‐synthesis separation of the tethered compound spots, solubilization of the cellulose matrix and spotting of the soluble cellulose‐probe conjugates onto various types of planar surfaces. The performance of such arrays are demonstrated using a set of synthetic peptide analogues, assayed with a monoclonal antibody, as well as utilizing a small molecule library of diketopiperazines assayed with fluorescently labelled calmodulin.
Geometrical parameters, vibrational wavenumbers, and relationships established with six difluorobenzonitriles
Authors: Rastogi V. K. , Palafox M. A. , Singhal Surabhi , Ojha S. P. , Kiefer W.
Published: November 2006

The geometry, vibrational wavenumbers, and thermodynamical parameters have been calculated using density functional methods (DFT) for benzonitrile (BN) and the six difluorobenzonitriles (DFBNs) of the series. The results were compared with the available experimental data, and correlations were established for the CN and CF moieties between the natural atomic charges and the geometrical parameters of the compounds. These relations were found as linear or slightly parabolic in most cases. Investigations were carried out to examine the effect of substituents on structural deformations and other properties. Correlations were also determined with the stretching vibrations. Other general conclusions have also been drawn. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Placental shelf—a common, typically transient and benign finding on early second‐trimester sonography
Authors: Shen O. , Golomb E. , Lavie O. , Goldberg Y. , Eitan R. , Rabinowitz R. R.
Published: November 2006

Objective

Placental shelves are believed to represent circumvallate placentae. It is thought that circumvallate placenta may be associated with adverse perinatal outcome when present at delivery. The objective of this study was to determine the prevalence, persistence and significance of placental shelves detected in the early second trimester.

Methods

In 152 consecutive anomaly scans performed between 13 and 16 weeks of gestation, special attention was directed to placental structure and the presence of a placental shelf. When present, a mid‐gestation scan was performed to verify if the finding persisted. If so, a third‐trimester scan was performed. Delivery charts were reviewed for all cases initially diagnosed with a placental shelf, recording any placenta‐related complications.

Results

In 17 of 152 (11.2%) early second‐trimester scans a placental shelf was detected. In three of these 17 cases the shelf persisted to the 20–22‐week scan. In the two cases that presented for the third‐trimester scan the shelf was no longer present. In all 17 cases the perinatal outcome was good.

Conclusions

In our study group early second‐trimester placental shelves rarely persisted to mid‐gestation and never to the third trimester. There were no placenta‐related perinatal problems. Early second‐trimester placental shelf appears to be a common, benign and transient sonographic finding. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.
Dynamics of age‐ and size‐structured populations in fluctuating environments: Applications of stochastic matrix models to natural populations
Authors: Nakaoka Masahiro
Published: November 2006

Recent developments of the theory of stochastic matrix modeling have made it possible to estimate general properties of age‐ and size‐structured populations in fluctuating environments. However, applications of the theory to natural populations are still few. The empirical studies which have used stochastic matrix models are reviewed here to examine whether predictions made by the theory can be generally found in wild populations. The organisms studied include terrestrial grasses and herbs, a seaweed, a fish, a reptile, a deer and some marine invertebrates. In all the studies, the stochastic population growth rate (ln λs) was no greater than the deterministic population growth rate determined using average vital rates, suggesting that the model based only on average vital rates may overestimate growth rates of populations in fluctuating environments. Factors affecting ln λs include the magnitude of variation in vital rates, probability distribution of random environments, fluctuation in different types of vital rates, covariances between vital rates, and autocorrelation between successive environments. However, comprehensive rules were hardly found through the comparisons of the empirical studies. Based on shortcomings of previous studies, I address some important subjects which should be examined in future studies.
Interactions among fungal endophytes, grasses and herbivores
Authors: Clay Keith
Published: November 2006

The interaction between two species often depends on the presence or absence of a third species. One widespread three‐species interaction involves fungal endophytes infecting grasses and the herbivores that feed upon them. The endophytes are allied with the fungal family Clavicipitaceae and grow systemically in intercellular spaces in above‐ground plant tissues including seeds. Like related Claviceps species, the endophytes produce a variety of alkaloids that make the host plants toxic or distasteful to herbivores. A large number of grass species are infected, especially cool‐season grasses in temperate areas. Field and laboratory studies have shown that herbivores avoid infected plants in choice trials and suffer increased mortality and decreased growth on infected grasses in feeding experiments. Resistance to herbivores may provide a selective advantage to infected plants in competitive interactions with noninfected plants. Recent studies have shown that differential herbivory can reverse competitive hierarchies among plant species. Both endophyte‐infected and noninfected tall fescue grass (Festuca arundinacea) are outcompeted by orchardgrass (Dactylis glomerata) in the absence of insect herbivory. However, when herbivores are present infected tall fescue outcompetes orchardgrass. These results suggest that the frequency of infection in grass species and grassland communities will increase over time. Several studies are reviewed illustrating increases in infection frequency within grass populations subject to herbivore pressure. Endophytic fungi may be important regulators of plant‐herbivore interactions and so indirectly affect the structure and dynamics of plant communities.
Species richness and altitudinal variation in the aquatic metazoan community in bamboo phytotelmata from north Sulawesi
Authors: Sota T. , Mogi M.
Published: November 2006

We compared the aquatic metazoan community structure in bamboo stumps between a lowland (Kosinggolan; 200 m a.s.l.) and a highland site (Moat; 1030–1050 m a.s.l.) in North Sulawesi. The lowland bamboo stumps harbored 38 taxa including 2 predators, and the highland stumps harbored 35 taxa including 2 predators. In total 45 taxa were recorded, including 3 predators. Dominant detritivores were Tipulidae, Scirtidae, Chironomidae, Culicidae and Ceratopogonidae. The sole dominant predators wereToxorhynchitesmosquito larvae, which occurred in 67% and 28% of stumps at the lowland and the highland sites, respectively. Although the mean biomass per stump did not differ significantly between the sites, the mean number of species per stump was significantly smaller at the lowland site. In addition, the variation in species composition among stumps was greater at the lowland site than at the highland site. Among dominant taxonomic groups, the number of non‐predatory culicid species per stump was smaller at the lowland site where their predator,Toxorhynchites, was more abundant, although both sites had the same number of culicid species. In the presence ofToxorhynchites, the density and biomass of other culicids per stump were reduced significantly. The difference in predator density might affect differences in the local‐scale community structure of individual bamboo stumps.
Analysis of changes of insect‐plant ratio‐improvement of key‐factor analysis for evaluating bottom‐up effects in insect population dynamics
Authors: Yamada Yoshihiro
Published: November 2006

A revised key‐factor analysis was presented for analyzing the temporal changes in the ratio of insect absolute number to plant resource. Ten data sets for 5 insect species were then analyzed. In this key‐factor analysis, the key factor is defined as the factor contributing highly to between‐year variation in Rr, the log rate of the inter‐year change of the insect‐plant ratio. The yearly change of plant resource was handled as a separate factor, expressed by rpl, log ratio of plant resource in year n to plant resource in year n+1. The following was revealed: 1) In 7 of the 10 data sets examined, rpl influenced variations of Rr; in particular in 3 cases rpl was the main key factor. 2) Generation‐to‐generation fluctuations of absolute insect densities showed density dependence in 4 cases, while those of insect‐plant ratios, in 8 cases. 3) The Royama model or a linear model, explained well the relationship between log insect‐plant ratio (Xr) and Rr and the relationship between Xr and log yearly change rate of absolute insect density (Rabs). However, in the 7 cases in which rpl was a critical factor for variations of Rr, with, increase of Xr,Rr showed a steeper, decrease around the equilibrium point (the point for which Rr is 0) than Rabs. This occurred because rpl tended to be negatively correlated with Xr. Consequently, in two cases Xr fluctuated cyclicly or chaotically although without the changes in plant resource, fluctuations of Xr would be damped oscillations approaching equilibrium.
Strain differences in the indian meal moth, Plodia interpunctella, in response to a granulosis virus
Authors: Boots Michael , Begon Michael
Published: November 2006

Three strains of the Indian Meal Moth, Plodia interpunctella, were compared in terms of their response to a granulosis virus under different environmental conditions. A significant difference in the relative susceptibilities to the virus of the three laboratory strains was established. Evidence of potential trade‐offs with resistance was found in overall fecundity, pupal size and mortality at adult emergence. There was however little evidence that a reduction in resource level led to more trade‐offs being apparent. No clear relationship was found between resistance to the lethal effects of the virus and susceptibility to the sublethal effects of the virus.
The demise of the population regulation controversy?
Authors: Wolda Henk
Published: November 2006

For many decades a controversy in population dynamics theory has been raging concerning whether or not populations are regulated by density dependent factors, without reaching a satisfactory conclusion. It is suggested that this failure to solve the problem is due to asking the wrong question and it is suggested that this controversy should be buried and forgotten.