bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular events leading to chondrocyte death after cartilage impact injury
Authors: Green D. M. , Noble P. C. , Ahuero J. S. , Birdsall H. H.
Published: April 2006

Objective

We undertook this study to test our postulate that leukocytes extend the zone of injury in cartilage after acute mechanical trauma.

Methods

Fresh cadaveric canine femoral condyles were subjected to 20–25‐MPa impact injury. Condyle explants or dispersed chondrocytes were cultured with autologous blood mononuclear leukocytes (MNLs). Viability of chondrocytes at varying distances from the impact site was assessed by trypan blue exclusion.

Results

Mechanical injury caused a significant loss of viable chondrocytes over 7 days, even in cartilage >10 mm from the impact site. After biomechanical stress, death of cells within 10 mm of the impact could be largely prevented by addition of NG‐monomethyl‐L‐arginine to inhibit nitric oxide (NO) generation. Chondrocytes within 10 mm of the impact were also susceptible to killing by living MNLs, but not by incubation with the supernatants of endotoxin‐activated MNLs. Chondrocytes in this vulnerable zone expressed intercellular adhesion molecule 1 (ICAM‐1) (CD54), facilitating attachment of MNLs that localized adjacent to the chondrocytes. Leukocytes killed dispersed chondrocytes harvested from the impact zone by generation of reactive oxygen species. Leukocyte‐mediated killing could be blocked by desferoxamine or by antibodies to CD18, which prevent attachment of leukocytes to ICAM‐1–expressing chondrocytes.

Conclusion

Our data suggest that after mechanical injury, chondrocytes distant from the site may be killed through the generation of NO. Inflammatory leukocytes further extend the zone of chondrocyte death by adhering to chondrocytes expressing ICAM‐1 and by inducing the accumulation of free oxygen radicals in the chondrocyte cytoplasm. Patients may benefit from therapies that reduce infiltration of inflammatory leukocytes into acutely injured cartilage.
Fludarabine, cyclophosphamide, and rituximab for the treatment of patients with chronic lymphocytic leukemia or indolent non‐hodgkin lymphoma
Authors: Tam Constantine S. , Wolf Max , Prince H. Miles , Januszewicz E. Henry , Westerman David , Lin Katherine I. , Carney Dennis , Seymour John F.
Published: April 2006

BACKGROUND

The combination of fludarabine, cyclophosphamide, and rituximab (FC‐R) shows significant in vitro synergism and may improve patient outcome with little overlapping toxicity.

METHODS

Between December 2000 and June 2005, 77 patients completed therapy after a median of 4 cycles of FC‐R (fludarabine at a dose of 25 mg/m2 intravenously [i.v.] on Days 1–3, cyclophosphamide at a dose of 250 mg/m2 i.v. on Days 1–3, and rituximab at a dose of 375 mg/m2 on Day 1). The median age of the patients was 59 years, 65% were male; 31% had previously untreated disease; and 44% had chronic lymphocytic leukemia (CLL), 29% had follicular lymphoma, and 27% other indolent lymphoid malignancies. In addition to standard disease response criteria, patients underwent evaluation using flow cytometric and/or molecular studies.

RESULTS

Objective responses (OR) and complete responses (CR) were observed in 83% and 42%, respectively, of evaluable patients (n = 76), respectively. For patients with CLL, the respective OR and CR rates were 100% and 67% as firstline therapy, and 95% and 14% as salvage therapy. For patients with follicular lymphoma, the respective OR and CR rates were 100% and 86% as firstline therapy, and 87% and 67% as salvage therapy. Responders who had no detectable disease on flow cytometric and/or molecular studies experienced prolonged remissions with no recurrences reported at a median 25 months of follow‐up. Peripheral stem cell collection using stem cell factor plus granulocyte–colony‐stimulating factor was successful in 10 of 13 patients who underwent mobilization (77%).

CONCLUSIONS

FC‐R is highly active as initial or salvage therapy in patients with CLL or indolent non‐Hodgkin lymphoma. Collection of autologous stem cells during molecular remission is feasible and may facilitate future exploration of high‐dose therapy in these patients. Cancer 2006. © 2006 American Cancer Society.
Xeroderma pigmentosum group D haplotype predicts for response, survival, and toxicity after platinum‐based chemotherapy in advanced nonsmall cell lung cancer
Authors: Booton Richard , Ward Tim , Heighway Jim , Taylor Pat , Power Fiona , Ashcroft Linda , Morris Julie , Thatcher Nicholas
Published: April 2006

BACKGROUND

The treatment of lung cancer has reached a therapeutic plateau. Several mechanisms of platinum resistance have been described, including the removal of platinum‐DNA adduct by nucleotide excision repair (NER). Polymorphisms within the Xeroderma pigmentosum Group D protein (XPD), a member of the NER pathway, are associated with alterations in enzyme activity and may change sensitivity to platinum‐based chemotherapy. The authors investigated the relation between XPD polymorphisms and treatment response, toxicity, and overall survival in patients who received platinum‐based chemotherapy for advanced nonsmall cell lung cancer (NSCLC).

METHODS

Between 2001 and 2002, 108 patients with chemotherapy‐naive, advanced NSCLC were recruited. Associations between XPD312/751 polymorphisms and XPD haplotype and treatment response, toxicity. and survival were evaluated.

RESULTS

Significant correlations were observed between XPD haplotype and Grade 4 neutropenia and overall survival together with a greater response to platinum‐based chemotherapy for the XPD *A haplotype.

CONCLUSIONS

The XPD haplotype may represent a useful pharmacogenomic marker of platinum‐based chemotherapy in patients with advanced NSCLC and requires prospective validation. Cancer 2006. © 2006 American Cancer Society.
Genetic analysis of early neurogenesis: Dedicated to the scientific contributions of Jose A. Campos‐Ortega (1940–2004)
Authors: Hartenstein Volker
Published: April 2006

Jose Campos‐Ortega stands out as one of the pioneers of developmental‐genetic studies of early neurogenesis. He also liked to reflect about the history of science: how one discovery leads to the next, and what role individuals play in the progress of science. He had indeed started to work on a book describing the history of developmental genetics during the last year of his life. His goal in this book was to “explain how developmental genetics originated, how it transformed developmental biology and, while doing so, how it contributed to achieve the biological synthesis.” In the following, I would like to reflect on the origin and growth of the field Campos‐Ortega contributed so much. In doing so, it is of particular interest to consider his scientific roots, and the manner in which he entered the stage of developmental genetics. I believe that Campos‐Ortega's unusual scientific background influenced in an important manner the way in which he shaped the study of early neurogenesis. Developmental Dynamics 235:2003–2008, 2006. © 2006 Wiley‐Liss, Inc.
The extracellular matrix in oral squamous cell carcinoma: Friend or foe?
Authors: Ziober Amy F. , Falls Erica M. , Ziober Barry L.
Published: April 2006

Oral squamous cell carcinoma is a disfiguring, highly invasive and metastatic cancer. Despite advances in detection and therapy, many patients will continue to face a poor prognosis. It is well established that the predominate factor determining overall survival in patients with oral squamous cell carcinoma is lymph node involvement. Tumor growth and progression to invasive cancer requires tumor cell interactions with the extracellular matrix. An understanding of how the extracellular matrix influences tumor development and invasion is fundamental in the development of new prognostic indicators and treatment strategies for oral squamous cell carcinoma. In this review, we summarize how changes in the extracellular matrix contribute to oral cancer development. © 2006 Wiley Periodicals, Inc. Head Neck, 2006
Digital photogrammetry for quantitative wear analysis of retrieved TKA components
Authors: Grochowsky J. C. , Alaways L. W. , Siskey R. , Most E. , Kurtz S. M.
Published: April 2006

The use of new materials in knee arthroplasty demands a way in which to accurately quantify wear in retrieved components. Methods such as damage scoring, coordinate measurement, and in vivo wear analysis have been used in the past. The limitations in these methods illustrate a need for a different methodology that can accurately quantify wear, which is relatively easy to perform and uses a minimal amount of expensive equipment. Off‐the‐shelf digital photogrammetry represents a potentially quick and easy alternative to what is readily available. Eighty tibial inserts were visually examined for front and backside wear and digitally photographed in the presence of two calibrated reference fields. All images were segmented (via manual and automated algorithms) using Adobe Photoshop and National Institute of Health ImageJ. Finally, wear was determined using ImageJ and Rhinoceros software. The absolute accuracy of the method and repeatability/reproducibility by different observers were measured in order to determine the uncertainty of wear measurements. To determine if variation in wear measurements was due to implant design, 35 implants of the three most prevalent designs were subjected to retrieval analysis. The overall accuracy of area measurements was 97.8%. The error in automated segmentation was found to be significantly lower than that of manual segmentation. The photogrammetry method was found to be reasonably accurate and repeatable in measuring 2‐D areas and applicable to determining wear. There was no significant variation in uncertainty detected among different implant designs. Photogrammetry has a broad range of applicability since it is size‐ and design‐independent. A minimal amount of off‐the‐shelf equipment is needed for the procedure and no proprietary knowledge of the implant is needed. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Effect of particle size of an amorphous calcium phosphate filler on the mechanical strength and ion release of polymeric composites
Authors: Lee Soo‐Young , Regnault W. F. , Antonucci J. M. , Skrtic D.
Published: April 2006

The random clustering of amorphous calcium phosphate (ACP) particles within resin matrices is thought to diminish the strength of their polymerized composites. The objective of this study was to elucidate the effect of ball‐milling on the particle size distribution (PSD) of ACP fillers and assess if improved dispersion of milled ACP in methacrylate resin sufficiently enhanced filler/matrix interactions to result in improved biaxial flexure strength (BFS), without compromising the remineralizing potential of the composites. Unmilled and wet‐milled zirconia‐hybridized ACP (Zr‐ACP) fillers were characterized by PSD analysis, X‐ray diffraction, thermogravimetric and chemical analysis, infrared spectroscopy, and scanning electron microscopy. Composite specimens made from a photoactivated, ternary methacrylate resin admixed with a mass fraction of 40% of un‐milled or milled Zr‐ACP were evaluated for the BFS (dry and wet) and for the release of calcium and phosphate ions into saline solutions. While having no apparent effect on the structure, composition, and morphology/topology of the fillers, milling significantly reduced the average size of Zr‐ACP particulates (median diameter, dm = 0.9 ± 0.2 μm) and the spread of their PSD. Better dispersion of milled Zr‐ACP in the resins resulted in the improved BFS of the composites, even after aqueous soaking, and also gave a satisfactory ion release profile. The demonstrated improvement in the mechanical stability of anti‐demineralizing/remineralizing ACP composites based on milled Zr‐ACP filler may be beneficial in potentially extending their dental utility. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007
Combining EEG and fMRI: A multimodal tool for epilepsy research
Authors: Gotman Jean , Kobayashi Eliane , Bagshaw Andrew P. , Bénar Christian‐G. , Dubeau François
Published: April 2006

Patients with epilepsy often present in their electroencephalogram (EEG) short electrical potentials (spikes or spike‐wave bursts) that are not accompanied by clinical manifestations but are of important diagnostic significance. They result from a population of abnormally hyperactive and hypersynchronous neurons. It is not easy to determine the location of the cerebral generators and the other brain regions that may be involved as a result of this abnormal activity. The possibility to combine EEG recording with functional MRI (fMRI) scanning opens the opportunity to uncover the regions of the brain showing changes in the fMRI signal in response to epileptic spikes seen in the EEG. These regions are presumably involved in the abnormal neuronal activity at the origin of epileptic discharges. This paper reviews the methodology involved in performing such studies, particularly the challenge of recording a good quality EEG inside the MR scanner while scanning is taking place, and the methods required for the statistical analysis of the combined EEG and fMRI time series. We review the results obtained in patients with different types of epileptic disorders and discuss the difficult theoretical problems raised by the interpretation of an increase (activation) and decrease (deactivation) in blood oxygen level dependent (BOLD) signal, both frequently seen in response to spikes. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Special considerations for functional magnetic resonance imaging of pediatric populations
Authors: Kotsoni Eleni , Byrd Dana , Casey B.J.
Published: April 2006

Functional MRI (fMRI) provides a noninvasive means of studying both typical and atypical brain development in vivo. However, the developmental and clinical status of the populations of interest impact how neuroimaging data should be collected, analyzed, and interpreted. In the present work, we review methodological and theoretical issues relevant to developmental and clinical neuroimaging research and provide possible approaches for addressing each. These issues include accounting for differences in biological noise, neuroanatomy, motion, and task performance. Finally, we emphasize the importance of a converging methods approach in constraining and supporting interpretations of pediatric imaging results. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Presurgical planning for tumor resectioning
Authors: Sunaert Stefan
Published: April 2006

Since the birth of functional magnetic resonance imaging (fMRI)—a noninvasive tool able to visualize brain function—now 15 years ago, several clinical applications have emerged. fMRI follows from the neurovascular coupling between neuronal electrical activity and cerebrovascular physiology that leads to three effects that can contribute to the fMRI signal: an increase in the blood flow velocity, in the blood volume and in the blood oxygenation level. The latter effect, gave the technique the name blood oxygenation level dependent (BOLD) fMRI. One of the major clinical uses is presurgical fMRI in patients with brain abnormalities. The goals of presurgical fMRI are threefold: 1) assessing the risk of neurological deficit that follows a surgical procedure, 2) selecting patients for invasive intraoperative mapping, and 3) guiding of the surgical procedure itself. These are reviewed here. Unfortunately, randomized trials or outcome studies that definitively show benefits to the final outcome of the patient when applying fMRI presurgically have not been performed. Therefore, fMRI has not yet reached the status of clinical acceptance. The final purpose of this article is to define a roadmap of future research and developments in order to tilt pre‐surgical fMRI to the status of clinical validity and acceptance. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Role of fMRI in the decision‐making process: Epilepsy surgery for children
Authors: Liégeois Frédérique , Cross J. Helen , Gadian David G. , Connelly Alan
Published: April 2006

Functional MRI (fMRI) is increasingly being used to evaluate children and adolescents who are candidates for surgical treatment of intractable epilepsy. It has the advantage of being noninvasive and well tolerated by young people. By identifying important functional regions within the brain, including unpredictable patterns of functional reorganization, it can aid in surgical decision‐making. Here we illustrate this using a number of case studies from the pediatric epilepsy surgery program at our institution. We describe how fMRI, used in conjunction with conventional investigative methods such as neuropsychological assessment, MRI, and electrophysiology, can 1) help to improve functional outcome by enabling resective surgery that spares functional cortex, 2) guide surgical intervention by revealing when reorganization of function has occurred, and 3) show when abnormal cortex is also functionally active, and hence that surgery may not be the best option. Altogether, these roles have reduced the need for invasive procedures that can be both risky and distressing for young people with epilepsy. In our experience, fMRI has significantly contributed to the decision‐making process, and improved the counseling and management of young people with intractable epilepsy. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Role of functional imaging in neurological disorders
Authors: Weiller Cornelius , May Arne , Sach Miriam , Buhmann Carsten , Rijntjes Michel
Published: April 2006

Neuroimaging in recent years has greatly contributed to our understanding of a wide range of aspects related to central neurological diseases. These include the classification and localization of disease, such as in headache; the understanding of pathology, such as in Parkinson's disease (PD); the mechanisms of reorganization, such as in stroke and multiple sclerosis (MS); and the subclinical progress of disease, such as in amyotrophic lateral sclerosis (ALS). Apart from presurgical mapping, however, the clinical applications so far are limited. Nevertheless, functional imaging does enable the formulation of neurobiological hypotheses that can be tested clinically, and thus is well suited for testing classic clinical hypotheses about how the brain works. Understanding the mechanisms and sites of pathology, such as has been achieved in cluster headaches, facilitates the development of new therapeutic strategies. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Self‐Expansion Behavior of Silk Fibroin Film
Authors: Kawahara Yutaka , Furukawa Keiko , Yamamoto Takeshi
Published: April 2006

Summary: Silk fibroin cast film was prepared using a ternary solvent system of CaCl2/CH3CH2OH/H2O (1/2/8 in mole ratio). A drying temperature at casting influenced crystal structure of fibroin. When a drying temperature was set lower than 9 °C, the cast film became amorphous. When a drying temperature was set higher than 40 °C, a fibroin film of silk‐II structure was obtained. In order to produce a fibroin film of silk‐I structure, a preferable temperature range was from 20 to 26 °C. The crystal transformation from random coil structure into silk‐I could be made through exposure of an amorphous film to water vapor. As for the crystal transformation from silk‐I into silk‐II, the treatment with a glycerin solution was effective. In the course of the treatment a film showed self‐thinning and self‐expanding. The expansion ratio exceeded 40% at maximum. The film produced accompanying self‐expansion was ductile in nature.

The apparent self‐expansion percentage as a function of initial thickness of the film. The ductility of the film was classified into four stages from the observation of recovery behavior after folding: •, very soft; ♦, soft; ▪, middle; ▴, hard (see Figure 5).

image

The apparent self‐expansion percentage as a function of initial thickness of the film. The ductility of the film was classified into four stages from the observation of recovery behavior after folding: •, very soft; ♦, soft; ▪, middle; ▴, hard (see Figure 5).
Gelation Inside Block Copolymer Aggregates and Organic/Inorganic Nanohybrids
Authors: Chen Yongming , Du Jianzhong , Xiong Ming , Zhang Ke , Zhu Hui
Published: April 2006

Summary:Like in many other cases, block copolymers bearing alkoxysilyl groups in one segment self‐assemble into aggregates. However, they may allow one to study the sol‐gel reaction by making use of the gelable groups located in the domains of the aggregates, therefore, the gelation process can be made in a selected domain of the nanoscale. As a result, the organic nanostructure is transformed into an organic/inorganic hybrid. The process of using covalently grafted alkoxysilane groups along the block copolymer precursors is applicable not only to the aggregates formed in solution, but also to the other forms of aggregates in melts, thin films, and interfaces. In this feature article, this emerging field is introduced, mainly focusing on the gelation that occurs inside the preformed block copolymer aggregates in solution. The morphologically fixed hybrid nanoparticles, such as spheres, hollow particles, and complex hollow particles, are presented and discussed. This technology has great potentials in the fields of nanomaterials and nanotechnologies, since various organic/inorganic hybrid nanoparticles and nanostructures can be effectively generated using this process.

Gelation in preformed block‐copolymer aggregates generates controlled structures.

magnified image

Gelation in preformed block‐copolymer aggregates generates controlled structures.
Fiber‐reinforced polymer bars embedded in a resin concrete: Study of both materials and their bond behavior
Authors: San‐José J. Tomás , Manso Juan M.
Published: April 2006

The study aims to analyze resin concrete (RC) bond behavior based on an isophthalic polyester resin, reinforced with nonmetallic rebars and is formed by pultruded glass fiber‐reinforced polymer (GFRP). The material is described at micro‐ and macrolevel by presenting the key physical and mechanical properties using different experimental techniques such as Hg porosimetry, scanning electron microscopy, and mechanical testing. Furthermore, a full description of GFRP bars is presented with regard to evaluation of its structural expectancies, embedded in the RC matrix. Given the closed porosity obtained in RC, its microstructure continuity, and organic nature of the binder, this material is highly protected against atmospheric conditions, corrosion and chemical attacks, requiring less cover for tensile reinforcing steel than Portland cement concrete. This research work concludes how the structural compatibility between RC and GFRP is obtained in monotonic bonding tests, providing greater adherence values than those of traditional reinforced concrete. Polym. Compos. 27:315–322, 2006. © 2006 Society of Plastics Engineers
A heuristic approach of calculating spray water flux needed to avert fire‐induced runaway reactions
Authors: Das Dilip K.
Published: April 2006

In general all reactions have some heat effects. When the ability of the equipment to remove the heat is exceeded by the heat generated by a reaction, a hazardous situation called a runaway reaction may take place.

Sometimes the exothermicity of runaway reactions is so high that the size of an emergency vent becomes impractical to install. A water spray system can sometimes be used to avert a fire‐induced runaway reaction.

Because the water spray system has a finite activation time, insulation helps to prolong the time required to reach the decomposition temperature.

This article concludes that the required water flux to avert the fire‐induced runaway reaction may be conservatively estimated by adding the water flux necessary to maintain an unbroken water film on the external surface of the equipment and the water flux necessary to absorb the fire heat after allowing for the splash loss and the in‐flight loss.

When adequate spray water is used, the metal temperature of the insulation jacket cannot theoretically exceed the boiling point of water thereby ensuring the avoidance of fire‐induced runaway reactions whose adjusted onset decomposition temperature exceeds 100 ° C. Fire‐induced runaway reactions with lower onset temperature can also be avoided depending on the initial temperature of the contents, mass of the contents and equipment, insulation thickness, and fire duration, for example, but a detailed calculation including dynamic simulation is necessary and the burden of proof lies with the designer.

The reliability of the spray water system must be maintained high to include its credit as an environmental factor defined according to NFPA 30 to avoid the fire‐induced runaway reaction as a scenario. Although API RP 521 does not allow any credit for sprinkler water, it allows credit, unlike NFPA 30, for insulation thickness and thus a runaway reaction can be avoided by using insulation alone according to API RP 521. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006
Electrical properties of individual and small ensembles of InAs/InP nanostructures
Authors: Vicaro K. O. , Gutiérrez H. R. , Bortoleto J. R. R. , Nieto L. , Zuben A. A. G. von , Seabra A. C. , Schulz P. A. , Cotta M. A.
Published: April 2006

We investigate electrical properties of InAs/InP semiconductor nanostructures by conductive atomic force microscopy (C‐AFM) and current measurements at low temperatures in processed devices. Different conductances and threshold voltages for current onset were observed for each type of nanostructure. In particular, the extremity of the wire could be compared to a dot with similar dimensions. The processed devices were used in order to access the in‐plane conductance of an assembly of a reduced number of nanostructures. Here, fluctuations on I –V curves at low temperatures (<40 K) were observed. At these low temperatures and for a suitable range of applied voltages, random telegraph noise (RTN) in the current was observed for devices with dots. These fluctuations can be associated to electrons trapped in dots, as suggested by numerical simulations. A crossover from a semiconductor‐like to a metallic transport behavior is also observed for similar parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error analysis of boundary condition approximations in the modeling of coaxially‐gated carbon nanotube field‐effect transistors
Authors: McGuire Dylan L. , Pulfrey David L.
Published: April 2006

In the modeling of carbon nanotube field‐effect transistors, non‐physical boundary conditions are often employed at the borders of the simulation space. This paper investigates the consequences of imposing these boundary conditions on common geometries, and proposes solutions which reduce the error without compromising simulation efficiency. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of MBE growth conditions on the surface morphology of Al(Ga)As nanowhiskers
Authors: Tonkikh A. A. , Cirlin G. E. , Dubrovskii V. G. , Sibirev N. V. , Soshnikov I. P. , Samsonenko Yu. B. , Polyakov N. K. , Ustinov V. M.
Published: April 2006

The structural properties of GaAs and AlGaAs nanowhiskers (NWs) grown by molecular beam epitaxy (MBE) on a GaAs substrate surfaces of different crystallographic orientations are investigated. Under optimal growth conditions, the aspect ratio of MBE grown GaAs NWs is higher than 100. The maximum length of NWs is several times (up to 10) larger than the effective thickness of deposited GaAs. A kinetic model of the diffusion‐induced NW growth is used to predict the dependence of NW length on the technologically controlled MBE growth conditions. The obtained results demonstrate that the NW growth in our experiments is mainly controlled by the adatom diffusion towards their tip rather than by the conventional adsorption controlled vapor–liquid–solid mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparative study of GaAs‐based 1.5 micron‐range InAs/InGaAs and InAs/InAlAs self‐assembled quantum dots
Authors: Gladyshev A. G. , Kryzhanovskaya N. V. , Nadtochy A. M. , Semenova E. S. , Zhukov A. E. , Vasil'ev A. P. , Mikhrin V. S. , Musikhin Yu. G. , Maximov M. V. , Ledentsov N. N. , Ustinov V. M.
Published: April 2006

Optical properties of self‐organized QDs grown on thick metamorphic InGaAs layers with different In composition are studied. The dots are formed by an overgrowth of original InAs islands with thin InGaAs or InAlAs layers. Room temperature photoluminescence at 1.55 µm is demonstrated for the sample with 27% In composition in the matrix. The overgrowth with InAlAs layers permits to eliminate the wetting layer states and increase energy separation between QD ground and excited states. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic field influence on nanocrystallization process of FeCoSiBCuNb alloys
Authors: Marín Pilar , López Miguel , Ruiz‐González Luisa , Cortés Gil Raquel , González‐Calbet Jose María , Hernando Antonio
Published: April 2006

We report the influence of magnetic field in the first stages of nanocrystallization process of FeCoSiBCuNb alloys. Amorphous ribbons have been annealed under longitudinal magnetic field. Depending on annealing temperature and magnetic field intensity, we observe the formation of different microstructures. In particular, when annealing at a temperature corresponding to the first stages of nanocrystallization process in the presence of magnetic field, an alignment of grains associated to grain growth related with a decrease of amorphous percentage has been obtained for certain intensities of applied magnetic field. Sample microstructure has been observed by means of TEM and the influence of microstructure in magnetic behaviour has been analysed by means of magnetization and coercivity field evolution with measuring temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carbon nanotubes and nucleic acids: tools and targets
Authors: Onoa Bibiana , Zheng Ming , Dresselhaus Mildred S. , Diner Bruce A.
Published: April 2006

Nucleic acids are playing an important role in the rapid development of nanotechnologies. Our Editor's Choice [1] discusses the use of nucleic acids to disperse and sort single walled carbon nanotubes (SWNTs). The cover picture shows a two‐dimensional photoluminescence (PL) spectrum of highly purified (6,5) SWNT:DNA hybrids. The fine resolution of the PL peaks displays photo‐excited intermediates in a range of energies between ES22 and ES11 transitions revealing for the first time specific phonon‐assisted optical absorption and energy relaxation mechanisms.

The first author, Bibiana Onoa, has been working on carbon nanotubes and nucleic acids in the molecular electronics group of Dupont Central Research and Development. Her current research focuses on the development of nanotechnologies that allow fast and economical detection of pathogens.

This special issue of physica status solidi (a) presents representative contributions and main topics on “Trends in Nanotechnology” from the TNT2005 International Conference in Oviedo (Spain).
Singular effects of surface tension in evolving Hele-Shaw flows
Authors: Siegel Michael , Tanveer Saleh , Dai Wei-Shen
Published: April 2006

In this paper, we present evidence to show that a smoothly evolving zero-surface tension solution of the Hele-Shaw equations can be singularly perturbed by the presence of arbitrarily small non-zero surface tension in order-one time. These effects are explained by the impact of ‘daughter singularities’ on the physical interface, whose formation was suggested in a prior paper (Tanveer 1993). For the case of finger motion in a channel, it is seen that the daughter singularity effect is strong enough to produce the transition from a finger of arbitrary width to one with the selected steady-state width in O(1) time.
Viscous and inviscid instabilities of non-parallel self-similar axisymmetric vortex cores
Authors: Fernandez-Feria R.
Published: April 2006

A spectral collocation method is used to analyse the linear stability, both viscous and inviscid, of a family of self-similar vortex viscous cores matching external inviscid vortices with velocity u varying as a negative power of the distance r to their axis of symmetry, u ∼ rm−2 (0 < m < 2). Non-parallel effects are shown to contribute at the same order as the viscous terms in the linear governing equations for the perturbations, and are consequently retained. The viscous stability analysis for the particular case m = 1, corresponding to Long's vortex, has recently been performed by Khorrami & Trivedi (1994). In addition to the inviscid non-axisymmetric modes of instability found by these authors, some inviscid axisymmetric unstable modes, and purely viscous unstable modes, both axisymmetric and non-axisymmetric, are also found. It is shown that, while both solution branches (I and II) of Long's vortex are destabilized by perturbations having negative azimuthal wavenumber (n < 0), only the Type II Long's vortex is also unstable for axisymmetric disturbances n = 0, as well as for disturbances with n > 0. Global pictures of instabilities of Long's vortex are given. For m > 1, the vortex cores have the interesting property of losing existence when the swirl number is larger than an m-dependent critical value, in close connection with experimental results on vortex breakdown. The instability pattern for m > 1 is similar to that found for Long's vortex, but with the important difference that the parameter characterizing the different vortices, and therefore their stability, is a swirl parameter, which is precisely the one known to govern the real problem, while this is not the case in the highly degenerate case m = 1.
Mixing driven by vertically variable forcing: an application to the case of Langmuir circulation
Authors: Gnanadesikan Anand
Published: April 2006

Two-dimensional mixing driven by an instability mechanism which is concentrated near one of the boundaries is considered, with particular application to Langmuir circulations driven by a wave spectrum. The question of how to define the equivalent of the Rayleigh number is attacked using the energy balance equations and simple truncated models of the instability. Given a particular horizontal wavelength for the disturbance, the strength of the forcing on the cells, and thus the growth rate, is determined by a tradeoff between maximizing the depth-averaged forcing and maximizing the depth of penetration. As a result of this tradeoff, long-wavelength cells grow more slowly, but penetrate more deeply and have a larger equivalent Rayleigh number. At finite amplitude, these long-wavelength cells come to dominate the flow field. The depth of penetration of, and density transport accomplished by, Langmuir cells is considered as a function of the mean stratification and diffusion. An application to oceanic mixed layers is considered assuming the Mellor-Yamada 2½-level turbulence closure model to define the background level of turbulent mixing. For many realistic cases, Langmuir cells are predicted to dominate the vertical transport of momentum and density.
Ignition in the supersonic hydrogen/air mixing layer with reduced reaction mechanisms
Authors: Im H. G. , Helenbrook B. T. , Lee S. R. , Law C. K.
Published: April 2006

Asymptotic analysis of ignition within the supersonic hydrogen/air mixing layer is performed using reduced mechanisms. Two distinct reduced mechanisms for the high-temperature and the low-temperature regimes are used depending on the characteristic temperature of the reaction zone relative to the crossover temperature at which the reaction rates of the H + 02 branching and termination steps are equal. Each regime further requires two distinct analyses for the hot-stream and the viscous-heating cases, depending on the relative dominance of external and internal ignition energy sources. These four cases are analysed separately, and it is shown that the present analysis successfully describes the ignition process by exhibiting turning point or thermal runaway behaviour in the low-temperature regime, and radical branching followed by thermal runaway in the high-temperature regime. Results for the predicted ignition distances are then mapped out over the entire range of the parameters, showing consistent behaviour with the previous one-step model analysis. Furthermore, it is demonstrated that ignition in the low-temperature regime is controlled by a larger activation energy process, so that the ignition distance is more sensitive to its characteristic temperature than that in the high-temperature regime. The ignition distance is also found to vary non-monotonically with the system pressure in the manner of the well-known hydrogen/oxygen explosion limits, thereby further substantiating the importance of chemical chain mechanisms in this class of chemically reacting boundary layer flows.
Bioconvection in suspensions of oxytactic bacteria: linear theory
Authors: Hillesdon A. J. , Pedley T. J.
Published: April 2006

When a suspension of the bacteriumBacillus subtilisis placed in a chamber with its upper surface open to the atmosphere, complex bioconvection patterns form. These arise because the cells (a) are denser than water, and (b) swim upwards on average so that the density of an initially uniform suspension becomes greater at the top than at the bottom. When the vertical density gradient becomes large enough an overturning instability occurs which evolves ultimately into the observed patterns. The cells swim upwards because they are oxytactic, i.e. they swim up gradients of oxygen, and they consume oxygen. These properties are incorporated in conservation equations for the cell and oxygen concentrations, which, for the pre-instability stage of the pattern formation process, have been solved in a previous paper (Hillesdon, Pedley & Kessler 1995). In this paper we carry out a linear instability analysis of the steady-state cell and oxygen concentration distributions. There are intrinsic differences between the shallow-and deep-chamber cell concentration distributions, with the consequence that the instability is non-oscillatory in shallow chambers, but must be oscillatory in deep chambers whenever the critical wavenumber is non-zero. We investigate how the critical Rayleigh number for the suspension varies with the three independent parameters of the problem and discuss the most appropriate definition of the Rayleigh number. Several qualitative aspects of the solution of the linear instability problem agree with experimental observation.
Displacement of inviscid fluid by a sphere moving away from a wall
Authors: Eames I. , Hunt J. C. R. , Belcher S. E.
Published: April 2006

We develop a theoretical analysis of the displacement of inviscid fluid particles and material surfaces caused by the unsteady flow around a solid body that is moving away from a wall. The body starts at position hs from the wall, and the material surface is initially parallel to the wall and at distance hL from it. A volume of fluid Df+ is displaced away from the wall and a volume Df- towards the wall. Df+ and Df- are found to be sensitive to the ratio hL/hs. The results of our specific calculations for a sphere can be extended in general to other shapes of bodies.

When the sphere moves perpendicular to the wall the fluid displacement and drift volume Df+ are calculated numerically by computing the flow around the sphere. These numerical results are compared with analytical expressions calculated by approximating the flow around the sphere as a dipole moving away from the wall. The two methods agree well because displacement is an integrated effect of the fluid flow and the largest contribution to displacement is produced when the sphere is more than two radii away from the wall, i.e. when the dipole approximation adequately describes the flow. Analytic expressions for fluid displacement are used to calculate Df+ when the sphere moves at an acute angle α away from the wall.

In general the presence of the wall reduces the volume displaced forward and this effect is still significant when the sphere starts 100 radii from the wall. A sphere travelling perpendicular to the wall, α = 0, displaces forward a volume Df+(0) = 4πa3hL/33/2hS when the marked surface starts downstream, or behind the sphere, and displaces a volume Df+(0) ∼ 2πa3/3 forward when it is marked upstream or in front of the body. A sphere travelling at an acute angle away from the wall displaces a volume Df+(α) ∼ Df+(0) cos α forward when the surface starts downstream of the sphere. When the marked surface is initially upstream of the sphere, there are two separate regions displaced forward and a simple cosine dependence on α is not found.

These results can all be generalized to calculate material surfaces when the sphere moves at variable speed, displacements no longer being expressed in terms of time, but in relation to the distance travelled by the sphere.
The linear stability of mixed convection in a vertical channel flow
Authors: Chen Yen-Cho , Chung J. N.
Published: April 2006

In this study, the linear stability of mixed-convection flow in a vertical channel is investigated for both buoyancy-assisted and -opposed conditions. The disturbance momentum and energy equations were solved by the Galerkin method. In addition to the case with a zero heat flux perturbation boundary condition, we also examined the zero temperature perturbation boundary condition. In general, the mixed-convection flow is strongly destabilized by the heat transfer and therefore the fully developed heated flow is very unstable and very difficult to maintain in nature. For buoyancy-assisted flow, the two-dimensional disturbances dominate, while for buoyancy-opposed flow, the Rayleigh–Taylor instability prevails for zero heat flux perturbation boundary condition, and for the zero temperature perturbation on the boundaries the two-dimensional disturbances dominate except at lower Reynolds numbers where the Rayleigh–Taylor instability dominates again. The instability characteristics of buoyancy-assisted flow are found to be strongly dependent on the Prandtl number whereas the Prandtl number is a weak parameter for buoyancy-opposed flow. Also the least-stable disturbances are nearly one-dimensional for liquids and heavy oils at high Reynolds numbers in buoyancy-assisted flows.

From an energy budget analysis, we found that the thermal–buoyant instability is the dominant type for buoyancy-assisted flow. In buoyancy-opposed flow, under the zero temperature perturbation boundary condition the Rayleigh–Taylor instability dominates for low-Reynolds-number flow and then the thermal–shear instability takes over for the higher Reynolds numbers whereas the Rayleigh–Taylor instability dominates solely for the zero heat flux perturbation boundary condition. It is found that the instability characteristics for some cases of channel flow in this study are significantly different from previous results for heated annulus and pipe flows. Based on the distinctly different wave speed characteristics and disturbance amplification rates, we offer some suggestions regarding the totally different laminar–turbulent transition patterns for buoyancy-assisted and -opposed flows.
Dynamic simulation of suspensions of non-Brownian hard spheres
Authors: Dratler D. I. , Schowalter W. R.
Published: April 2006

In this work, we investigate the suitability of models based solely on continuum hydrodynamics for Stokesian Dynamics simulations of sheared suspensions of non-Brownian hard spheres. The suspensions of interest consist of monolayers of uniform rigid spheres subjected to a linear shear field. Areal fractions ranged from ϕa = 0.2 to 0.6. For these suspensions, two sets of Stokesian Dynamics simulations were performed. For the first set, particle interactions were assumed to be strictly hydrodynamic in nature. These simulations are analogous to those of Brady & Bossis (1985) and Chang & Powell (1993). For the second set of simulations, particles were subjected to both hydrodynamic and short-range repulsive forces. The repulsion serves as a qualitative model of non-hydrodynamic effects important when particle separation distances are small. Results from both sets of simulations were found to be within the range of established experimental data for viscosities of suspensions. However, simulations employing the pure hydrodynamic model lead to very small separation distances between particles. These small separations give rise to particle overlaps that could not be eliminated by time-step refinement. The instantaneous number of overlaps increased with density and typically exceeded the number of particles at the highest densities considered. More critically, for very dense suspensions the simulations failed to approach a long-time asymptotic state. For simulations employing a short-range repulsive force, these problems were eliminated. The repulsion had the effect of preventing extremely small separations, thereby eliminating particle overlaps. At high concentrations, viscosities computed using the two methods are significantly different. This suggests that the dynamics of particles near contact have a significant impact on bulk properties. Furthermore, the results suggest that a critical aspect of the physics important at small particle separation distances is missing from the pure hydrodynamic model, making it unusable for computing microstructures of dense suspensions. In contrast, simulations employing a short-range repulsive force appear to produce more realistic microstructures, and can be performed even at very high densities.
On vortex/wave interactions. Part 2. Originating from axisymmetric flow with swirl
Authors: Allen T. , Brown S. N. , Smith F. T.
Published: April 2006

Following the study in Part 1 of cross-flow and other non-symmetric effects on vortex/wave interactions in boundary layers, the present Part 2 applies the ideas of Part 1 and related works to an incident axisymmetric flow supplemented by a small swirl or azimuthal velocity. This is with a view to possibly increasing understanding of vortex breakdown. The wave components involved are predominantly inviscid Rayleigh-like ones. The presence of the swirl leads to extra features and complications associated mainly with extra logarithmic contributions but for the dominant interactions essentially the same equations as in Part 1 are found. These dominant nonlinear interactions must be based on azimuthal wavenumbers of ± 1 in the case of the Squire jet with swirl. In contrast to Part 1, which consisted mainly of an analysis of the quasi-bounded solutions, a representative set of numerical solutions of the full integro-differential amplitude equations is presented, for realistic axial and swirl velocity profiles. The work points also to the influence of further increases in the incident swirl.
Three-dimensional long-wave instability of unidirectional spatially periodic viscous flows
Authors: Khazan Y. S. , Nepomnyashchy A. A.
Published: April 2006

The long-wave instability of unidirectional spatially periodic flows is investigated by means of asymptotic expansions. It is shown that the wavevector of the most dangerous disturbances is generally inclined to the direction of the basic stream. A new type of long-wave oscillatory instability is discovered, and a comparison with results of previous investigations is performed.