bluuebunny/crossref_metadata_2025 huggingface dataset:
Wound‐induced p38MAPK‐dependent histone H3 phosphorylation correlates with increased COX‐2 expression in enterocytes
Authors: Karrasch Thomas , Steinbrecher Kris A. , Allard Brigitte , Baldwin Albert S. , Jobin Christian
Published: February 2006

Gastrointestinal epithelial cell damage triggers an important biological response called restitution, a process aimed at re‐epithelializing the wounded areas. Unfortunately, little is known about the intrinsic molecular signaling events implicated in this host response. We hypothesized that wounding intestinal epithelial cells activates signaling pathways leading to chromatin modification and COX‐2 upregulation during restitution. Confluent rat IEC18 cells were mechanically wounded by multiple parallel scratches using a pipet tip. NF‐κB(Ser536), p38, and histone H3(Ser10) (H3S10) phosphorylation were determined by Western blot using specific phospho‐antibodies. COX‐2 gene expression was evaluated by RT‐PCR, Western Blot, and ELISA. Association of phosphorylated H3, RelA (NF‐κB), and RNA polymerase II to the COX‐2 gene promoter was evaluated by chromatin immunoprecipitation (ChIP). The specific inhibitors Bay11‐7082 and SB239063 as well as Ad5IκB‐superrepressor (Ad5IκBAA) and Ad5dnp38 were used to block NF‐κB‐ and p38‐signaling pathways, respectively. Wounding induced a rapid and sustained (24 h) phosphorylation of RelAS536, H3S10, and p38MAPK in enterocytes. ChIP analysis of the COX‐2 gene promoter demonstrated the presence of phospho‐H3S10 and recruitment of RelA and RNA polymerase II, a process blocked by SB239063. Finally, molecular blockade of NF‐κB (Ad5IκBAA) or p38MAPK (Ad5dnp38) signaling strongly inhibited enterocyte restitution. p38MAPK‐dependent histone 3 phosphorylation is an important component of the intestinal wound‐healing response. Targeting‐signaling pathways selectively involved in healing/restitution may provide a novel means to maintain or re‐establish host intestinal barrier integrity. J. Cell. Physiol. © 2006 Wiley‐Liss, Inc.
RNA interference reveals a differential role of FAK and Pyk2 in cell migration, leading edge formation and increase in focal adhesions induced by LPA in intestinal epithelial cells
Authors: Jiang Xiaohua , Jacamo Rodrigo , Zhukova Elena , Sinnett‐Smith James , Rozengurt Enrique
Published: February 2006

In the gastrointestinal mucosa, cell migration plays a crucial role in the organization and maintenance of tissue integrity but the mechanisms involved remain incompletely understood. Here, we used small‐interfering RNA (siRNA)‐mediated depletion of focal adhesion kinase (FAK) protein to determine the role of FAK in wound‐induced migration and cytoskeletal organization in the non‐transformed intestinal epithelial cells IEC‐6 and IEC‐18 stimulated with the G protein‐coupled receptors (GPCR) agonist lysophosphatidic acid (LPA). Treatment of these cells with FAK siRNA substantially reduced FAK expression, but did not affect the expression of proline‐rich tyrosine kinase 2 (Pyk2). Knockdown of FAK protein significantly inhibited LPA‐induced migration of both IEC‐18 and IEC‐6 cells. LPA induced reorganization of actin and microtubule cytoskeleton in the leading edge was largely inhibited in FAK siRNA‐transfected IEC‐18 cells. Interestingly, in contrast to the FAK−/− cells, which exhibit an increased number of prominent focal adhesions when plated on fibronectin, FAK knockdown IEC‐18 cells exhibited dramatically decreased number of focal adhesions in response to both LPA and fibronectin as compared with the control cells. We also used siRNAs to knockdown Pyk2 expression without reducing FAK expression. Depletion of Pyk2 did not prevent LPA‐induced migration or cytoskeletal reorganization in IEC‐18 cells. In conclusion, our study shows that FAK plays a critical role in LPA‐induced migration, cytoskeletal reorganization, and assembly of focal adhesions in intestinal epithelial cells whereas depletion of Pyk2 did not interfere with any of these responses elicited by LPA. J. Cell. Physiol. © 2006 Wiley‐Liss, Inc.
Mechanisms of AAV transduction in glaucoma‐associated human trabecular meshwork cells
Authors: Borrás Teresa , Xue Wei , Choi Vivian W. , Bartlett Jeffrey S. , Li Guorong , Samulski Richard J. , Chisolm Sarah S.
Published: February 2006

Background

Glaucoma is a chronic eye disease which leads to irreversible blindness. The trabecular meshwork tissue controls intraocular pressure (IOP), which is the major risk factor for glaucoma. Gene therapy treatment of chronic diseases requires the use of long‐term expression, low toxicity and lack of immune response vectors. Adeno‐associated viruses (AAV) possess these characteristics but have been unable to transduce the trabecular meshwork. Because of the importance of regulating elevated IOP by long‐term gene therapy, we investigated mechanisms of AAV transduction to the human trabecular meshwork (TM).

Methods

Primary human trabecular meshwork cells (HTM) and perfused organ cultures were infected with rAAV2‐GFP, RGD‐pseudotyped rAAV2‐GFP alone, or combined with recombinant ΔE1/E3 adenoviruses. Intracellular rAAV2 DNA and RNA were measured by relative quantitative and real‐time TaqMan polymerase chain reaction (PCR). Host transcriptome was analyzed using high‐density oligonucleotide microarrays. One transduction mechanism was tested using self‐complementary AAV (scAAV).

Results

The dramatic transduction enhancement obtained upon co‐infection of rAAV2 with ΔE1/E3 adenoviruses provides insights into transduction mechanisms in the HTM. Even if not transduced, rAAV2 enters TM cells. GeneChip analysis showed significant changes in host genes involved in cell cycle and DNA replication. Consequently, scAAV‐GFP transduction was highly efficient. Other transduction‐enhancement genes included coxsackie adenovirus receptor (CAR) and genes relevant to trabecular meshwork function.

Conclusions

The rate‐limiting step of AAV transduction was not viral entry failure but, at least in part, host downregulation of DNA replication. Additional specific host genes might be involved. Our study revealed genes and mechanisms which led for the first time to efficient AAV transduction of the HTM. Copyright © 2006 John Wiley & Sons, Ltd.
Radioprotective gene therapy through retroviral expression of manganese superoxide dismutase
Authors: Southgate Thomas D. , Sheard Victoria , Milsom Michael D. , Ward Timothy H. , Mairs Robert J. , Boyd Marie , Fairbairn Leslie J.
Published: February 2006

Background

Radiotherapy for the control of cancer, either alone or in conjunction with chemotherapy, is often limited by normal tissue toxicity including haematopoietic toxicity. Exposure of cells to ionizing radiation leads to the formation of reactive oxygen species that are associated with radiation‐induced cytotoxicity. The antioxidant enzyme manganese superoxide dismutase (SOD2) catalyzes the dismutation of the superoxide anions into hydrogen peroxide.

Methods

We have investigated the potential of SOD2 overexpression, through retroviral gene transfer using a retrovirus optimized for transcription in early haematopoietic cells, to enhance the radioresistance of a human erythroleukaemic cell line and primary murine bone marrow. Using these as in vitro models we have investigated whether SOD2 gene therapy may be suitable for the protection of the haematopoietic compartment from the effects of ionizing radiation.

Results

Here we demonstrate using both biological and physical assays that overexpression of SOD2 protects haematopoietic cells from ionizing radiation injury. Our results show that an increase in the levels of SOD2 enzymatic activity within K562 cells (from 160.7 ± 23.6 to 321.8 ± 45.2 U/mg protein) or primary murine haematopoietic progenitor cells leads to both a significant decrease in DNA fragmentation and a significant increase in clonogenic survival, as evident by a significant increase in Dbar (from 2.66 to 3.42Gy), SF2 (from 0.52 to 0.73) values, and a significant decrease in the alpha value (from 0.3040 ± 0.037 to 0.0630 ± 0.037 Gy−1) when compared either to cells transduced with a retroviral vector encoding eGFP alone or to the parental line.

Conclusions

The results presented suggest that retroviral radioprotective gene therapy may be applicable to the haematopoietic compartment, enabling radiation dose escalation in cancer therapy. Copyright © 2006 John Wiley & Sons, Ltd.
Phage ϕC31 integrase‐mediated genomic integration of the common cytokine receptor gamma chain in human T‐cell lines
Authors: Ishikawa Yoshinori , Tanaka Nobuyuki , Murakami Kazuhiro , Uchiyama Toru , Kumaki Satoru , Tsuchiya Shigeru , Kugoh Hiroyuki , Oshimura Mitsuo , Calos Michele P. , Sugamura Kazuo
Published: February 2006

Background

X‐linked severe combined immunodeficiency (SCID‐X1, X‐SCID) is a life‐threatening disease caused by a mutated common cytokine receptor γ chain (γc) gene. Although ex vivo gene therapy, i.e., transduction of the γc gene into autologous CD34+ cells, has been successful for treating SCID‐X1, the retrovirus vector‐mediated transfer allowed dysregulated integration, causing leukemias. Here, to explore an alternative gene transfer methodology that may offer less risk of insertional mutagenesis, we employed the ϕC31 integrase‐based integration system using human T‐cell lines, including the γc‐deficient ED40515(‐).

Methods

A ϕC31 integrase and a neor gene expression plasmid containing the ϕC31 attB sequence were co‐delivered by electroporation into Jurkat cells. After G418 selection, integration site analyses were performed using linear amplification mediated‐polymerase chain reaction (LAM‐PCR). ED40515(‐) cells were also transfected with a γc expression plasmid containing attB, and the integration sites were determined. IL‐2 stimulation was used to assess the functionality of the transduced γc in an ED40515(‐)‐derived clone.

Results

Following co‐introduction of the ϕC31 integrase expression plasmid and the plasmid carrying attB, the efficiency of integration into the unmodified human genome was assessed. Several integration sites were characterized, including new integration sites in intergenic regions on chromosomes 13 and 18 that may be preferred in hematopoietic cells. An ED40515(‐) line bearing the integrated γc gene exhibited stable expression of the γc protein, with normal IL‐2 signaling, as assessed by STAT5 activation.

Conclusions

This study supports the possible future use of this ϕC31 integrase‐mediated genomic integration strategy as an alternative gene therapy approach for treating SCID‐X1. Copyright © 2006 John Wiley & Sons, Ltd.
EPI distortion correction from a simultaneously acquired distortion map using TRAIL
Authors: Priest Andrew N. , De Vita Enrico , Thomas David L. , Ordidge Roger J.
Published: March 2006

Purpose

To develop a method for shot‐by‐shot distortion correction of single‐shot echo‐planar imaging (EPI) that is capable of correcting each image individually using a distortion measurement performed during acquisition of the image itself.

Materials and Methods

The recently‐introduced method known as two reduced acquisitions interleaved (TRAIL) was extended to measure the distribution of the main magnetic field B0 with each shot. This corresponded to a map of distortion, and allowed distortion to be corrected in the acquired images.

Results

Distortion‐corrected images were demonstrated in the human brain. The distortion field could be directly visualized using the “stripe” distribution imposed by the TRAIL pulse sequence. This confirmed the success of the correction. Over a time‐course measurement of 10 images, variance was reduced by using shot‐by‐shot distortion correction compared to correction with a constant field map.

Conclusion

Shot‐by‐shot distortion correction may be performed for EPI images acquired using an extension of the TRAIL technique, ensuring that the correction reflects the actual distortion pattern and not merely a previously measured, but possibly no longer valid, distortion field. This avoids errors due to changes in the distortion field or misregistration of a previously measured distortion map resulting from subject motion. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Myocardial tagging and strain analysis at 3 Tesla: Comparison with 1.5 Tesla imaging
Authors: Valeti V. Uma , Chun Wookjin , Potter Donald D. , Araoz Philip A. , McGee Kiaran P. , Glockner James F. , Christian Timothy F.
Published: February 2006

Purpose

To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole.

Materials and Methods

Normal volunteers (N = 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG‐triggered, segmented k‐space, spoiled‐gradient‐echo grid‐tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNRtag). Matched short‐axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)).

Results

The average CNRtag over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 ± 12.1, 1.5 T: 9.8 ± 8.4; P < 0.0001). This difference remained significant at cycle initiation, end‐systole, and the end R‐R interval (at cycle termination: 3 T = 14.0 ± 11.0 vs. 1.5 T = 4.4 ± 3.5; P < 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R‐R interval for 3 T images.

Conclusion

Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
In vivo porcine liver radiofrequency ablation with simultaneous MR temperature imaging
Authors: Vigen Karl K. , Jarrard Jerry , Rieke Viola , Frisoli Joan , Daniel Bruce L. , Pauly Kim Butts
Published: February 2006

Purpose

To demonstrate in vivo MR‐guided temperature mapping during radiofrequency (RF) ablation of the liver with a commercially available RF generator modified to allow simultaneous RF treatment and MRI.

Materials And Methods

A commercial RF generator was modified using passive filtering to allow the continuous application of the treatment current during MRI studies. A total of six ablations were performed with the device in vivo in three porcine livers, and imaging was concurrently performed using one of two different temperature mapping strategies.

Results

MR images acquired during RF ablation demonstrated no noticeable interference from the RF ablation device, which was operated at clinically relevant power levels. Temperature maps showed areas of heating that were consistent with the dimensions of the RF ablation probe, with some asymmetry (likely depending on the orientation of the probe and heat propagation effects), and some differences in heating‐spot area stability depending on the specific temperature mapping strategy used. Lesions were visualized on post‐ablation imaging and sectioning.

Conclusion

The feasibility of performing RF ablation with a modified commercial RF generator simultaneously with MRI was demonstrated. Interference‐free MR temperature maps were produced with both variable respiratory motion and mechanical ventilation, and showed the extent of heating as the ablation progressed. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Alterations of the proton‐T2 time in relaxed skeletal muscle induced by passive extremity flexions
Authors: Rump Jens , Braun Jürgen , Papazoglou Sebastian , Taupitz Matthias , Sack Ingolf
Published: March 2006

Purpose

To demonstrate reciprocal changes of the apparent proton‐T2 time in the biceps and triceps due to passive contraction and extension of the muscle fibers.

Materials and Methods

The contraction state of the upper arm muscles of six healthy volunteers was passively changed by alternating the forearm position between the straight‐arm position and an elbow flexion of 90°. The relaxation of the muscle during passive contraction and extension was measured with the use of muscle electromyography (EMG) experiments. Spin‐echo (SE) MRI with increasing echo times (TEs) of 12–90 msec was used to acquire the averaged signal decay of the segmented biceps and triceps. The apparent T2 was deduced using monoexponential least‐square fitting.

Results

The median T2 alterations in biceps and triceps among all volunteers were found to be 1.2 and –1.3 msec in the straight and bent forearm positions, respectively. The confidence intervals (0.5 to 1.7 msec in biceps, and –2.6 to –1.1 msec in triceps) clearly indicate that proton‐T2 in MR images is significantly (P < 0.05) prolonged with muscle contraction.

Conclusion

The observed increase of the proton‐T2 time was correlated with a passive contraction of skeletal muscle fibers. This passive effect can be attributed to changes in the intracellular water mobility corresponding to the well‐known “active” T2 increase that occurs after stimulation of muscle. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Holocene vegetation and land‐use changes in response to climatic changes in the forelands of the southwestern Alps, Italy
Authors: Finsinger Walter , Tinner Willy
Published: February 2006

The Holocene sediment of Lago Piccolo di Avigliana (Piedmont, Italy, 356 m a.s.l.) was dated by 14C and analysed for pollen to reconstruct the vegetation history of the area. The early‐ and mid‐Holocene pollen record shows environmental responses to centennial‐scale climatic changes as evidenced by independent palaeoclimatic proxies. When human impact was low or negligible, continental mixed‐oak forests decreased at ca. 9300 BC in response to the early‐Holocene Preboreal climatic oscillation. Abies alba expanded in two phases, probably in response to higher moisture availability at ca. 6000 and ca. 4000 BC, while Fagus expanded later, possibly in response to a climatic change at 3300 BC.

During and after the Bronze Age five distinct phases of intensified land use were detected. The near synchroneity with the land‐use phases detected in wetter regions in northern and southern Switzerland points to a common forcing factor in spite of cultural differences. Increasing minerogenic input to the lake since 1000 BC coincided with Late Bronze—Iron Age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment. The highest values for cultural indicators occurred at 700–450 and at 300–50 BC, coinciding with periods of high solar activity (inferred from Δ14C). This suggests that Iron Age land use was enhanced by high solar activity, while re‐occupation of partly abandoned areas after crises in earlier periods match better with the GRIP stable isotope record. On the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than temperature oscillations in driving vegetation and societal changes throughout the Holocene. Copyright © 2006 John Wiley & Sons, Ltd.
Late Quaternary glacial and deglacial history of eastern Vestfirdir, Iceland using cosmogenic isotope (36Cl) exposure ages and marine cores
Authors: Principato Sarah M. , Geirsdóttir Áslaug , Jóhannsdóttir Gudrún Eva , Andrews John T.
Published: February 2006

The late glacial and deglacial history of Vestfirdir, NW Iceland is interpreted from terrestrial field‐based evidence and compared with marine cores and seismic studies. Understanding the timing of deglaciation is complicated by a lack of dateable organic material on land, uncertainties associated with interpretation of diamictons, and ambiguities in radiocarbon dating. New36Cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice‐free by approximately 20 ka. Deglaciation of the valleys followed. Boulders from the crest of an end‐moraine in the Selá river valley have a mean36Cl age of 14.6 ka ± 0.8 ka (n = 4), and the outermost moraine in the valley adjacent to Kaldalónjökull has a mean36Cl age of 11.7 ka ± 0.9 ka (n = 2). Tephrochronology provides a link between the terrestrial and marine sequences around Vestfirdir. The Vedde Ash (ca. 12 k cal. yr BP) is present in some offshore cores, but it is absent from terrestrial sites, suggesting that its distribution provides a constraint on ice extent during the Younger Dryas. The Saksunarvatn Ash (10.2 ± 0.6 k cal. yr BP), confirmed by geochemical analyses and radiocarbon dating, is present in at least three terrestrial locations on eastern Vestfirdir and in many cores from the fjords and shelf, which constrains early Holocene ice extent. Copyright © 2006 John Wiley & Sons, Ltd.
Hybrid Hydrogels Self‐Assembled from HPMA Copolymers Containing Peptide Grafts
Authors: Yang Jiyuan , Xu Chunyu , Kopečková Pavla , Kopeček Jindřich
Published: March 2006

Summary: Graft copolymers were designed that self‐assemble into hydrogels mediated by the interaction of coiled‐coil peptide domains. A linear hydrophilic polymer of HPMA was chosen as the backbone, and coiled‐coil forming peptides, covalently attached to the backbone, formed the grafts. Microrheology was used to evaluate the self‐assembly of graft copolymers into hydrogels. The results revealed that the length and the number of coiled‐coil grafts per chain had a significant influence on the gelation process. At least 4 heptads were needed to achieve the association of graft copolymers into hydrogels. CD spectra of the copolymer containing 5 heptad grafts further suggested that coiled‐coil formation may contribute to the self‐assembly. Gelation of graft copolymers containing CC4 peptides indicated that a threshold amount of grafts per macromolecule is needed to form a three‐dimensional structure. These studies demonstrated a potential of the graft copolymers to create self‐assembling hydrogels with desirable and controllable structures.

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A Reversible and Highly Selective Fluorescent Sensor for Mercury(II) Using Poly(thiophene)s that Contain Thymine Moieties
Authors: Tang Yanli , He Fang , Yu Minghui , Feng Fude , An Lingling , Sun Huan , Wang Shu , Li Yuliang , Zhu Daoben
Published: March 2006

Summary: A reversible and highly selective assay method has been developed to detect mercury(II) (Hg2+) ions using a conjugated polymer (CP). The transduction mechanism is based on Hg2+‐mediated interpolymer π‐stacking aggregation, which results in the fluorescence self‐quenching of the CP. CPs that contain thymine moieties, poly[3‐(N‐thymin‐1‐ylacetyl)ethylamine‐thiophene] (PTT), have been synthesized and characterized. In the absence of Hg2+ ions, the PTT chains remain separated from each other and the CP exhibits strong fluorescence emission. Upon adding Hg2+ ions, the formation of interpolymer π‐stacking aggregation induced by specific thymine–Hg–thymine interactions results in the fluorescence quenching of PTT. Distinguishing aspects of this assay include the signal amplification of CPs and the specific binding of Hg2+ ions to thymine‐thymine (T–T) base pairs.

The binding of Hg2+ ions causes the separate conducting polymer chains to aggregate with subsequent fluorescence self‐quenching.

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The binding of Hg2+ ions causes the separate conducting polymer chains to aggregate with subsequent fluorescence self‐quenching.
Hydrophilicity Impact upon Physical Properties of the Environmentally Friendly Poly(3‐hydroxybutyrate) Blends: Modification Via Blending
Authors: Iordanskii Alexey L. , Ol'khov Anatoliy A. , Pankova Yulia N. , Bonartsev Anton P. , Bonartseva Garina A. , Popov Vladimir O.
Published: March 2006

We have integrated scientific research of polymer blends on the base of poly‐3‐hydroxybutyrate (PHB and its copolymers) with bench testing in blend preparation by both solvent casting and melt extrusion. As a second component, we have used traditional synthetic macromolecules with various hydrophilicity degree and hence with different morphologies and physical behavior. Besides, variation of polymer hydrophilicity permits to control both the service characteristic and the rate of (bio)degradation operating in the presence of water. Therefore, a substantial part of our work is devoted to water transport in the parent PHB and its blends. Combining the morphology knowledge (SEM, WAXS, FTIR tecynique), transport characteristics (permeability cells and McBain spring microbalance), and mechanical testing, we propose that blending of the parent biodegradable polymer with synthetic macromolecules is a perspective tool to design novel materials with improved characteristics. Both the water transport coefficients and the mechanical characteristics are essentially sensitive to structure and morphology of the blends. Hydrophilicity variation in the order LDPE < SPEU < PVA at blending with PHB shows that the morphology transformation in immicsible or partly miscible blends shifted along the PHB concentration scale as LDPE (at ∼16 wt% PHB) < PVA (∼30 wt% PHB) < SPEU (∼50 wt% PHB) Our instrumental monitoring the structural hierarchy of parent polymers and their blends as well as , simultaneously, the study of transport processes, their modeling, and computer simulating open up the way to understanding the precepts of polymer operation in corrosive and bioactive media.
Thermo‐mechanical Properties of In‐situ Silica Filled Silicone Resins
Authors: Chevalier Pierre , Ou Duan‐Li , Lee Yeong , Robson Steven , Dupont Anne
Published: March 2006

Silicone resins were investigated as a replacement of silica filled organic polymers for microelectronic packaging. Self‐curable silicone resins containing up to 40 mol% of in‐situ generated silica‐like species were prepared by a novel process involving controlled hydrolysis‐condensation of SiH moieties without gelation. These in‐situ Q filled resins are stable and easy to process compared to post‐filled organic polymers. The thermo‐mechanical properties upon self‐addition and condensation cure of the in‐situ filled silicone resins are superior to conventional addition and condensation cured silicone resins and are in the range of organic polymers with the added advantage of high thermal and moisture resistance critical in microelectronic. Storage modulus and plateau modulus as high as 3.5 GPa with a very low fall in modulus below 5% were demonstrated. Coefficients of thermal expansion were as low as 55 to 65 ppm/K in the application temperature up to 170 °C.
Polypropylene/Nylon‐66/Carbon Black Blends Processed at Temperatures Just Below the Nylon Melting: Anisotropy in Structure and Properties
Authors: Zoldan Janet , Siegmann Arnon , Narkis Moshe
Published: March 2006

In‐situ fibrillation of nylon (Ny) is obtained by compounding and processing its binary blends with polypropylene (PP) and ternary carbon black (CB) containing blends just below the melting temperature (Tm) of the dispersed, Ny phase, yet, above that of the PP. At such low temperatures the Ny behaves as an elastic solid deforming under the elongational flow of the molten PP matrix. Without the mediation of PP, Ny could not be processed or compounded at such low temperatures. This structured anisotropy in both binary and ternary blends resulted in anisotropy in the electrical and dielectric properties of the blends. Moreover, the dynamic electrical behavior was used as a powerful tool to study the CB dispersion mode in the polymer blends.
Development of PVC/Silica Hybrids Using PVC Plastisols
Authors: Gilbert Marianne , Haghighat Siavash , Chua Soo Keow , Ng Soo Yeng
Published: March 2006

A novel method for producing a plasticised PVC with increased porosity has been developed, by the use of an organic‐inorganic hybrid. Silica was produced in situ from tetraethoxysilane via a hydrolytic sol‐gel processing route. Tetrahydrofuran was used as co‐solvent, and γ‐glycidyloxypropyl‐trimethoxysilane as coupling agent. The films produced were transparent, with moderate mechanical properties. A film containing 20% silica showed a 45% increase in water vapour permeability.
High Barrier Polyamide/Polyolefin/Organoclay Nanocomposites
Authors: Brulé Benoît , Flat Jean‐Jacques
Published: March 2006

New composites coupling the alloy and nanocomposite technologies have been successfully produced with regular co rotating twin screw extruder. These new composites, Polyamide(PA6)/Polyolefin(PO)/compatibilizer/nanoclay, have been blown to end up with monolayer films. The thermo mechanical performances of these new composites do not reveal any improvement at high temperature resulting from the presence of nanoclays, as required by emergent needs in automotive field. More interesting are the high barrier properties obtained with these new composites. For specific permeating species, the association of alloy and nanocomposite technologies lead to new materials with superior barrier performances comparing to the materials making up the alloys. Physical explanation of such behavior is detailled in this paper.
Nanostructured Composites with Layered Morphology: Structure and Properties
Authors: Adhikari Rameshwar , Henning Sven , Michler Goerg H.
Published: March 2006

Using different microscopic techniques, we investigate the morphology and the micro‐deformation processes in two entirely different classes of polymer based composites: natural biocomposites and synthetic polymer composites. The emphasis has been put on the comparison of the micromechanical properties of those composite materials. In the natural layered composites exemplified by human cortical bone, analogous to the synthetic glassy polymers, craze‐like deformation zones were formed. A strong dependence of deformation mechanisms (such as transition from formation of single crazes to multiple crazing behaviour) on the layer dimension was observed in the layered composites made up of different amorphous polymers.
Mechanical Properties and Hysteresis Behaviour of Multigraft Copolymers
Authors: Staudinger U. , Weidisch R. , Zhu Y. , Gido S. P. , Uhrig D. , Mays J. W. , Iatrou H. , Hadjichristidis N.
Published: March 2006

PS‐PI multigraft copolymers with tri‐ tetra‐ and hexafunctional polystyrene branch points have been studied to investigate the influence of molecular architecture on morphological and tensile properties and to find novel material concepts. It was found that the morphological behaviour of these grafted copolymers can be predicted using theoretical approaches. The number of branch points, however, greatly influences the long‐range order of microphase separation. Additionally, two new parameters for adjusting mechanical properties of multigraft copolymers are found in our investigations: 1) functionality of the graft copolymer: tri‐, tetra‐ or hexafunctional and 2) number of branch points per molecule. Tetrafunctional multigraft copolymers show surprising high strain at break values up to 1550 %. With increasing number of branch points strain at break and tensile strength increase, where a linear dependence of mechanical properties on the number of branch points is obvious. Excellent elasticity of tetra and hexafunctional multigraft copolymers at high deformation was proved in hysteresis experiments.
The Effect of the Compatibilization Route of PA/PO Blends on the Physico‐chemical Phenomena Developing Along a Twin‐screw Extruder
Authors: Vera Machado Ana , Yquel Virginie , Covas José Antonio , Flat Jean‐Jacques , Ghamri Nessim , Wollny Andreas
Published: March 2006

The effect of the compatibilization method (ex‐situ, in‐situ, cross linking) on the chemical conversion, morphological and rheological evolution of polyamide/polyolefin blends along a twin screw extruder is investigated. For this purpose, samples were quickly collected from the extruder at specific barrel locations, quenched and subsequently characterized off‐line. While significant changes occur very quickly in the melting zone for the ex‐situ and in‐situ routes, changes of the cross linking system could be detected along all the extruder. Correlations between chemical conversion, particle size and linear viscoelastic response could be established.
Conducting Elastomer Blends Based on Nitrile Rubber and Pani.DBSA
Authors: Soares Bluma G. , Amorim Gabriel S. , Oliveira Marcia G. , Pereira da Silva J.E.
Published: March 2006

Electrically conductive elastomer blends based on polyaniline‐dodecylbenzene sulfonic acid (Pani.DBSA) and nitrile rubber (NBR) were prepared by polymerization of aniline in the presence of NBR, using a direct, one‐step in situ emulsion polymerization method. At the same PAni content, the conductivity of the in situ emulsion‐polymerized blends is higher than that of blends produced by mechanical mixing of both components. In addition, a morphology with the presence of PAni in the form of microtubules was achieved by the in situ process. Stronger interaction between the components were also confirmed by Rheological processing analysis (RPA). The vulcanization process decreases the conductivity of the blends prepared by both methods. The in situ polymerized blends also display higher tensile strength and also higher crosslink density
A switchable triple‐wavelength erbium‐doped fiber laser with a linear laser cavity
Authors: Liu D. , Ngo N. Q. , Chan H. N. , Teu C. K. , Tjin S. C.
Published: February 2006

A simple and switchable triple‐wavelength erbium‐doped fiber laser (EDFL) with a linear laser cavity is proposed and experimentally demonstrated. In the experiment, by changing the state of polarization (SOP) inside the laser cavity through a polarization controller (PC), stable single, dual, and triple wavelengths under room temperature were obtained. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 632–635, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21429
3D analysis of a quasi circular microstrip antenna by finite element method
Authors: Bourry M. , Drissi M.
Published: February 2006

In this work a complementary study of an elliptical antenna circularly polarized designed on a glass substrate is proposed using a 3D finite‐element method that takes into account the finite size of the substrate. This simulation type gave more reliable results in near‐ and far‐field analyses that were performed using a compact‐range measurement system. The parasitic effect of the feeding line is confirmed in simulations and in measurements. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 635–639, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21430
New design concept of dual‐mode bandpass filter by using nonorthogonal input and output ports for wireless application
Authors: Chen Han‐Jan , Huang Tsung‐Hui , Chen Lih‐Shan , Horng Jui‐Hong , Houng Mau‐Phou
Published: February 2006

In this paper, new design concept of nonorthogonal input and output (I/O) ports applied to optimize dual‐mode bandpass ring filter is proposed. Compared to conventional dual‐mode filters, the proposed filter with nonorthogonal I/O could not only support two degenerate modes operation, but also increase design flexibility. Moreover, the design of dual‐mode filters would not have an I/O geometry limitation, corresponding to high integration. Finally, a simple structure and high selectivity for the dual‐mode bandpass filters were obtained. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 639–641, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21431
Broadband coaxial antenna for WiMAX access‐point application
Authors: Wong Kin‐Lu , Wu Chih‐Hsien , Chang Fa‐Shian
Published: February 2006

A broadband coaxial antenna mainly comprising an upper square cylindrical plate and a lower square cylindrical ground is presented. The antenna functions like a two‐wire dipole antenna, and furthermore provides a wide operating bandwidth of about 4 GHz (about 1.9 to 5.9 GHz in the study), making it very promising for application in Worldwide Interoperability for Microwave Access Forum (WiMAX) access points. The antenna has been successfully implemented, and experimental results are presented. The effects of the lower square cylindrical ground on the antenna performances are also analyzed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 641–644, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21432
Miniaturized low‐loss Wilkinson power divider for RF front‐end module applications
Authors: Kangasvieri T. , Hautajärvi I. , Jantunen H. , Vähäkangas J.
Published: February 2006

A miniaturized low‐loss Wilkinson power divider was designed and fabricated using standard LTCC technology. Size reduction was implemented by folding the quarter‐wave transmission lines into tightly coupled meander lines. Parameters determining the electrical performance of the divider structure were analyzed using both circuit and full‐wave electromagnetic simulations. Scattering‐parameter measurements correlated very well with the simulations and demonstrated excellent RF performance and manufacturability. Insertion loss of 0.1 dB, return loss of 30 dB, and isolation of 27 dB were measured at the operation frequency. Furthermore, compared to a traditional ring‐type Wilkinson divider, an approximately 67% size reduction was achieved. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 660–663, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21436
A novel microstrip bandpass filter using a dual‐mode square‐ring resonator
Authors: Huang X. D. , Cheng C. H.
Published: February 2006

A novel microstrip bandpass filter using a dual‐mode square‐ring resonator is presented in this paper, in which the input/output microstrip lines are arranged under the square‐ring to improve the coupling between the microstrip lines and the square‐ring. The filter has been investigated numerically and experimentally. The measured result shows that the filter has a minimum insertion loss of 1.5 dB inside its passband and the out‐of‐band rejection level of below −26 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technical Lett 48:667–669, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21438
A conically coupled waveguide‐to‐coaxial line transition in a reduced‐height waveguide for compact transceivers
Authors: Kim Kang Wook , Woo Dong Sik , Cho Young Ki
Published: February 2006

A conically coupled waveguide‐to‐coaxial line transition in a rectangular waveguide whose height is very small compared with that of the standard Ku‐band waveguide is designed and characterized. The input power to the reduced‐height waveguide is coupled to the coaxial line through a metallic cone attached on the waveguide wall. The guiding property of EM waves in the reduced‐height waveguide is found to be drastically different from that in the regular waveguide. The transition structures have been comprehensively analyzed using 3D EM simulators. The measured performance of the fabricated transition shows good agreement with the simulated results over the Ku‐band frequencies, providing broad bandwidth of 5 GHz. The insertion loss of the transition is measured to be about 0.4 dB and the return loss is about 15 dB at 16 GHz. These transitions can be utilized for the construction of broadband compact‐sized transceivers for the input coupling of closely spaced array antennas. © 2006 Wiley Periodicals, Inc. Microwave Opt Technical Lett 48: 669–673, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21439
A spectral‐element time‐domain solution of Maxwell's equations
Authors: Liu Yaxing , Lee Joon‐Ho , Xiao Tian , Liu Qing H.
Published: February 2006

A spectral‐element time‐domain (SETD) method based on Gauss–Lobatto–Legendre (GLL) polynomials is presented to solve Maxwell's equations. The proposed SETD method combines the advantages of spectral accuracy with the geometric flexibility of unstructured grids. In addition, a 4th‐order Runge–Kutta method for time integration provides high‐order accuracy and thus reduces the temporal discretization errors. The numerical results demonstrate its spectral accuracy with the order of basis function and show the high efficiency of the proposed method due to its exponential convergence. © 2006 Wiley Periodicals, Inc. Microwave Opt Technical Lett 48: 673–680, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21440
Characteristics of a two‐layer microstrip patch antenna for Bluetooth applications
Authors: Lu Lu , Coetzee Jacob Carl
Published: February 2006

A double‐layer rectangular patch microstrip antenna suitable for Bluetooth applications is investigated. The patch is etched on a separate substrate which is suspended above the ground plane and supported by an MCX connector. The air gap between the patch and the ground plane increases the impedance bandwidth and can be used to tune the resonant frequency. This paper presents experimental results on the effects of various parameters on the antenna characteristics and provides guidelines for the design of such an antenna. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 683–686, 2006; Pubished online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21442
Effective and tolerant wide‐range solutions for ultra‐wideband indented‐disk monopole antenna
Authors: Pan Chin‐Ju , Chou Ta‐Yuan , Lee Chungnan , Huang Chih‐Yu
Published: February 2006

Solutions obtained from a wide range of parameters for the optimized design of the antenna are presented. Wide‐bandwidth impedance matching can be achieved using a simply designed indented‐disk monopole antenna for ultra‐wideband (UWB) applications. The design is based on a genetic algorithm (GA)‐based refined method to improve the solution to the UWB antenna design problem. A new optimization process is used to determine a wide range of feasible solutions rather than just the few solutions that can be obtained by trial and error. The wide range of solutions support the manufacturing tolerance effectively. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 693–695, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21445
Stepped impedance hairpin design of a tunable bandpass filter with harmonic suppression
Authors: Chen Yu‐Wei , Ho Min‐Hua
Published: February 2006

Stepped impedance hairpin resonators (SIHRs) with harmonic suppression and capability of frequency tuning are incorporated into a bandpass filter design. A tapped‐in U‐shaped feed structure is introduced to suppress harmonics and to reduce the passband insertion losses. The passband flexibility is accomplished by using a pair of tuning varactors. A simple method to implant a zero in the frequency response is also studied herein to further deepen the passband skirt. A 176% (4.32 GHz) stopband bandwidth is observed under more than 20‐dB band rejection. A measured minimum insertion loss of 1.19 dB is observed for the circuit with absence of the tuning varactors. Using the varactors, this filter has achieved a 22% frequency tuning range with all the insertion losses less than 5 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 697–701, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21447
Parallel‐coupled bandpass filters with broad rejection band using interdigital fingers and DGS
Authors: Her Man‐Long , Ko Wen , Hsu Ming‐Wei , Wang Yu‐Lin , Hsu Chou‐Jung
Published: February 2006

A novel parallel‐coupled bandpass filter (PC‐BPF) with a fundamental frequency of 2.4 GHz is presented in this paper. This proposed filter achieves a broad rejection bandwidth and a sufficient attenuation level by using the distributed interdigital fingers to attenuate the spurious even harmonics of 2f0 and 4f0, and employing a defected ground structure (DGS) resonator to suppress the 3f0 spurious response. The measured results show a satisfactory rejection bandwidth of 8.6 GHz with a rejection level of −30 dB at 2f0. The improved performance will be very attractive for application in many communication systems. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 705–707, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21449
A new contention‐resolution scheme for time‐critical applications in multifiber optical packet‐switched networks
Authors: Li Yi , Xiao Gaoxi , Ghafouri‐Shiraz H.
Published: February 2006

In this paper, we propose a new contention‐resolution scheme for supporting time‐critical applications in multifiber optical packet‐switched networks. The main idea is to utilize redundant idle fibers in optical cables rather than the conventional optical‐fiber delay lines to transfer the contending packets, such that the packets do not need to be buffered on any node. The buffering delay therefore can be eliminated and the quality of the optical signal can be improved as well. The switching‐node architecture is demonstrated and its packet‐loss performance is evaluated. Extensive simulations results show that the new scheme is efficient in resolving packet contentions. It is also shown that better performance is achieved by sparing several fibers in each link solely for the purpose of contention‐resolution rather than simply increasing the number of fibers per link and then averaging data traffic on these fibers. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 717–719, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21453.
Internal UMTS patch antenna for a sliding mobile phone
Authors: Wong Kin‐Lu , Lin Chun‐Yi , Chang Fa‐Shian
Published: February 2006

A shorted patch antenna suitable for application in the sliding mobile phone as an internal antenna is presented. The shorted patch antenna is mounted at the bottom end of the lower ground plane of the mobile phone, and can generate a wide operating band for UMTS (1920–2170 MHz) operation in the talk condition (the mobile phone is slid open for use). In addition, when the mobile phone is in the standby condition (not slid open), the antenna can still provide acceptable impedance matching for operating frequencies over the UMTS band. Details of the antenna design are described, and experimental results of a constructed prototype are presented. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 726–729, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21457
A wideband low‐profile microstrip antenna and array
Authors: Mak Ka‐Ming , Wong Hang , Luk Kwai‐Man
Published: February 2006

A high‐gain wideband low‐profile microstrip patch antenna array is designed and tested. A method for enhancing the impedance bandwidth through the combination of a driven rectangular patch with parasitic elements is proposed. The array, which has 16 elements in a 4 × 4 arrangement, is pasted on a 2‐mm dielectric substrate. The impedance bandwidth and the gain of the array is 12% (for SWR ≤ 2) centered at 4.5 GHz and 20 dBi, respectively. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 729–730, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21458
Analytical modelling of the current distribution in resistive loaded thin‐wire antennas excited by a transient electric field
Authors: Sagnard F.
Published: February 2006

The analytical modelling of the excitation of a Wu and King loaded dipole by an oblique transient electric‐plane wavefront has been revisited and extended in order to analyze in detail the physical phenomena involved in the time and space domains. The role of several components of the current induced along a dipole as a function of different parameters is discussed. The modelling developed herein allows us to consider a V‐dipole. This study will allow us to consider, in a future work, the case of an assembly of dipoles in the space domain for representing more complex antenna geometries. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 730–736, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21459