bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydraulic model calibration for extreme floods in bedrock‐confined channels: case study from northern Thailand
Authors: Kidson R. L. , Richards K. S. , Carling P. A.
Published: December 2005

Palaeoflood reconstructions based on stage evidence are typically conducted in data‐poor field settings. Few opportunities exist to calibrate the hydraulic models used to estimate discharge from this evidence. Consequently, an important hydraulic model parameter, the roughness coefficient (e.g. Manning's n), is typically estimated by a range of approximate techniques, such as ‘visual estimation’ and semi‐empirical equations. These techniques contribute uncertainty to resulting discharge estimates, especially where the study reach exhibits sensitivity in the discharge–Manning's n relation. We study this uncertainty within a hydraulic model for a large flood of known discharge on the Mae Chaem River, northern Thailand. Comparison of the ‘calibrated’ Manning's n with that obtained from semi‐empirical equations indicates that these underestimate roughness. Substantial roughness elements in the extra‐channel zone, inundated during large events, contribute significant additional sources of flow resistance that are captured neither by the semi‐empirical equations, nor by existing models predicting stage–roughness variations. This bedrock channel exhibits a complex discharge–Manning's n relation, and reliable estimates of the former are dependent upon realistic assignment of the latter. Our study demonstrates that a large recent flood can provide a valuable opportunity to constrain this parameter, and this is illustrated when we model a palaeoflood event in the same reach, and subsequently examine the magnitude–return period consequences of discharge uncertainty within a flood frequency analysis, which contributes its own source of uncertainty. Copyright © 2005 John Wiley & Sons, Ltd.
Scoutless stepping‐table peripheral contrast‐enhanced MR angiography
Authors: Li Wei , Vu Anthony T. , Tutton Sean , Li Belinda S.Y. , Bejm Roland , Pierchala Linda , Edelman Robert R.
Published: December 2005

Purpose

To evaluate the feasibility of a scoutless method, termed EZ‐STEP, for stepping‐table peripheral contrast‐enhanced magnetic resonance angiography (CE‐MRA).

Materials and Methods

This scoutless method involves the use of a stepping‐table, fast 3D MRA acquisition that incorporates spatially nonselective radiofrequency (RF) pulses for excitation to reduce the repetition time (TR). The sequence was tested in a phantom. The EZ‐STEP protocol was optimized in four healthy volunteers and used in 15 subjects. The image quality was scored in a blinded fashion and compared with conventional MRA in eight patients.

Results

The acquisition speed of the EZ‐STEP sequence was approximately 30% faster in the phantom study compared to the conventional MRA sequence. The total examination time for EZ‐STEP was 6 minutes, compared to an average of 23 minutes for conventional MRA. The average image quality scores for EZ‐STEP and conventional MRA for stations 1–3 were 3.50 vs. 3.06 (P = 0.087), 3.53 vs. 3.00 (P = 0.033), and 2.97 vs. 2.50 (P = 0.090), respectively.

Conclusion

EZ‐STEP is a more efficient method than the conventional approach for stepping‐table peripheral CE‐MRA, and provides comparable or better image quality. This method shortens the examination time substantially and eliminates the risk of failing to image a vessel because of improper positioning of the scan volume. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Diffusion‐weighted imaging of normal and malignant prostate tissue at 3.0T
Authors: Pickles Martin D. , Gibbs Peter , Sreenivas Muthyala , Turnbull Lindsay W.
Published: December 2005

Purpose

To measure the apparent diffusion coefficient (ADC) of normal and malignant prostate tissue at 3.0T using a phased‐array coil and parallel imaging, and determine the utility of ADC values in differentiating tumor from normal peripheral zone (PZ).

Materials and Methods

ADC values were calculated for 49 patients (tumor and PZ) with evidence of prostate cancer. Additionally, for nine asymptomatic volunteers, ADC values were determined for apparently normal central gland and PZ. A single‐shot EPI diffusion‐weighted imaging (DWI) technique with b = 0 and 500 seconds/mm2 was employed.

Results

ADC values were significantly lower for tumor (1.38 ± 0.32 × 10−3 mm2/second) than for patient PZ (1.95 ± 0.50 × 10−3 mm2/second, P < 0.001) and volunteer PZ (1.60 ± 0.25 × 10−3 mm2/second, P = 0.031). A considerable overlap of ADC values was noted between patient tissue types.

Conclusion

DWI of the prostate at 3.0T in conjunction with a phased‐array coil and parallel imaging allows ADC calculation of the prostate. ADC values were lower for tumors compared to normal‐appearing PZ; however, there was considerable intersubject variability. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Fully MR‐guided hepatic artery catheterization for selective drug delivery: A feasibility study in pigs
Authors: Seppenwoolde Jan‐Henry , Bartels Lambertus W. , van der Weide Remko , Nijsen Johannes F.W. , van het Schip Alfred D. , Bakker Chris J.G.
Published: December 2005

Purpose

To demonstrate the feasibility of hepatic catheterization for selective delivery of therapeutic agents using a clinical MRI scanner for real‐time image guidance.

Materials and Methods

Experiments were performed in three domestic pigs (70–80 kg) using a clinical 1.5‐T MR scanner. After abdominal three‐dimensional contrast‐enhanced MR angiography (3D‐CE‐MRA) was performed, endovascular devices with susceptibility markers were tracked with passive tracking techniques. Catheters were maneuvered into the primary and secondary hepatic arteries. Selective catheterization was verified using selective time‐resolved CE angiography. Paramagnetic microspheres were administered to a different region for each liver. The resulting biodistributions were investigated using MR images.

Results

Successful selective hepatic catheterization was repeatedly demonstrated using passive tracking techniques. 3D‐CE‐MRA significantly aided the interventional procedure by showing the vascular anatomy, and maximum‐intensity projections (MIPs) were used as roadmaps during the interventions. In all cases, microspheres were successfully delivered to the selected regions. The catheters were visualized at a maximum frame rate of five frames per second, allowing a good depiction of the devices and a reliable catheterization of the hepatic arteries.

Conclusion

Fully MR‐guided real‐time navigation of endovascular devices permits complex procedures such as selective intra‐arterial delivery of therapeutic agents to parts of the liver. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Proton magnetic resonance spectroscopic imaging to differentiate between nonneoplastic lesions and brain tumors in children
Authors: Hourani Roula , Horská Alena , Albayram Sait , Brant Larry J. , Melhem Elias , Cohen Kenneth J. , Burger Peter C. , Weingart John D. , Carson Benjamin , Wharam Moody D. , Barker Peter B.
Published: December 2005

Purpose

To investigate whether in vivo proton magnetic resonance spectroscopic imaging (MRSI) can differentiate between 1) tumors and nonneoplastic brain lesions, and 2) high‐ and low‐grade tumors in children.

Materials and Methods

Thirty‐two children (20 males and 12 females, mean age = 10 ± 5 years) with primary brain lesions were evaluated retrospectively. Nineteen patients had a neuropathologically confirmed brain tumor, and 13 patients had a benign lesion. Multislice proton MRSI was performed at TE = 280 msec. Ratios of N‐acetyl aspartate/choline (NAA/Cho), NAA/creatine (Cr), and Cho/Cr were evaluated in the lesion and the contralateral hemisphere. Normalized lesion peak areas (Chonorm, Crnorm, and NAAnorm) expressed relative to the contralateral hemisphere were also calculated. Discriminant function analysis was used for statistical evaluation.

Results

Considering all possible combinations of metabolite ratios, the best discriminant function to differentiate between nonneoplastic lesions and brain tumors was found to include only the ratio of Cho/Cr (Wilks' lambda, P = 0.012; 78.1% of original grouped cases correctly classified). The best discriminant function to differentiate between high‐ and low‐grade tumors included the ratios of NAA/Cr and Chonorm (Wilks' lambda, P = 0.001; 89.5% of original grouped cases correctly classified). Cr levels in low‐grade tumors were slightly lower than or comparable to control regions and ranged from 53% to 165% of the control values in high‐grade tumors.

Conclusion

Proton MRSI may have a promising role in differentiating pediatric brain lesions, and an important diagnostic value, particularly for inoperable or inaccessible lesions. J. Magn. Reson. Imaging 2006. Published 2005 Wiley‐Liss, Inc.
Shortened T2 after exercise in ischemic skeletal muscle
Authors: Nygren Anders T.
Published: December 2005

Purpose

To detect skeletal muscle ischemia with transverse relaxometry after ischemic exercise.

Materials and Methods

Ten subjects with intermittent claudication were studied. T2 was measured in the gastrocnemius and soleus muscles (m. gastrocnemius and m. soleus) at rest and repeatedly after exercise during 45 minutes of recovery. Prior to MRI a symptom‐limited treadmill exercise was performed, and the ankle‐arm blood pressure index (AAI) was measured at rest and after exercise.

Results

In the 14 legs with ischemic pain, a diverging response was found in the calf: T2 increased in m. gastrocnemius by 5.6% ± 4.9%, but decreased in m. soleus by –1.2% ± 4.4% (P < 0.001). Moreover, 13 regions in legs with ischemic pain and reduced AAI (from 0.7 ± 0.2 at rest to 0.31 ± 0.15 after exercise) had shortened T2 (–3.6% ± 1.8%) immediately after exercise. This finding was most frequent in m. soleus and two regions of m. gastrocnemius. Recovery was delayed in the latter two regions.

Conclusion

T2 may identify ischemic muscles after hypoxic exercise. Shortened T2 suggests a reduced water content (e.g., distribution volume of water) and may affect the upslope kinetics of an extravascular perfusion tracer. The different responses to ischemia by the soleus and gastrocnemius muscle may be due in part to their different fiber type compositions. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Delayed contrast agent kinetics in ischemic skeletal muscle
Authors: Nygren Anders T. , Greitz Dan
Published: December 2005

Purpose

To detect skeletal muscle ischemia with first‐pass gadolinium (Gd) kinetics after exercise.

Materials and Methods

Eleven subjects with intermittent claudication performed a symptom‐limited bilateral plantar flexion exercise in the magnet. Regional ROIs were placed bilaterally in the gastrocnemius and soleus muscles, and a signal intensity (SI) time‐curve analysis was performed. Induced ischemia was validated prior to the MRI with the systolic ankle‐arm blood pressure index (AAI) measured after a symptom‐limited treadmill exercise.

Results

Exercise induced ischemic pain in 16 of 22 legs with a significantly reduced AAI (0.31 ± 0.15). The time to contrast arrival (TCA) was delayed in symptomatic ischemic legs vs. asymptomatic legs (16.3 ± 6.9 seconds vs. 11.1 ± 2.7 seconds, P < 0.05). The maximum SI during recovery was higher in the soleus muscle than in the gastrocnemius muscle in ischemic legs (1.55 ± 0.1 vs. 1.44 ± 0.1, P < 0.05). Symptomatic regions had a less steep upslope than asymptomatic regions (43 ± 15 vs. 63 ± 14, P < 0.001), with a graded upslope response to ischemia. However, a normal upslope was found in 10 of 29 ischemic regions, and some of the regions showed delayed contrast arrival, suggesting a pseudonormal upslope in ischemic regions.

Conclusion

Exercise‐induced ischemia was detected with the use of an SI time‐curve analysis. However, disregarding the arterial input function and distribution volume of the tracer may lead to misinterpretation of some ischemic regions. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Cardiac CINE MR imaging with a 32‐channel cardiac coil and parallel imaging: Impact of acceleration factors on image quality and volumetric accuracy
Authors: Wintersperger Bernd J. , Reeder Scott B. , Nikolaou Konstantin , Dietrich Olaf , Huber Armin , Greiser Andreas , Lanz Titus , Reiser Maximilian F. , Schoenberg Stefan O.
Published: December 2005

Purpose

To assess the impact of parallel imaging algorithms on image quality and volumetric accuracy of CINE magnetic resonance imaging (MRI) with high temporal and spatial resolution using a new 32‐channel dedicated cardiac phased array coil.

Materials and Methods

Fourteen individuals underwent steady‐state free precession (SSFP) CINE MRI using a 32‐element phased‐array coil and parallel imaging acceleration using spatiotemporal sensitivity encoding (TSENSE). Acquisition acceleration ranged from R = 2 to 7. In conjunction with data extracted from phantom measurements, contrast‐to‐noise ratio (CNR) performance was evaluated for each acceleration factor and subjective image quality was evaluated by two independent readers. In addition, volumetric assessment was performed for each acceleration factor based on a single breath‐hold multi‐slice data acquisition. Results were compared to nonTSENSE measurements.

Results

CNR for non‐accelerated CINE (R = 1) was 45.7 ± 12.8 and showed a constant decrease with increase in acceleration of 51% at R = 4 and 86% at R = 7. CNR losses accompanied reductions in subjective image quality. Volumetric evaluation was accurate for R ≤ 4, with significant underestimation of ejection fraction (EF) at higher accelerations.

Conclusion

This study shows that one‐dimensional acceleration factors up to R = 4 allow accurate SSFP CINE MRI even though CNR is significantly reduced. This allows for a marked reduction in scan time and allows for multi‐slice CINE imaging with high spatial and temporal resolution. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Exposure, health complaints and cognitive performance among employees of an MRI scanners manufacturing department
Authors: de Vocht Frank , van Drooge Hinkelien , Engels Hans , Kromhout Hans
Published: December 2005

Purpose

To assess sensory effects and other health complaints that are reported by system testers working near magnetic resonance imaging (MRI) magnets, realizing that it is believed that exposure up to 8 T is safe for humans.

Materials and Methods

Levels of exposure to static magnetic fields (SMFs), movement speed during exposure, health complaints, and cognitive performance among employees in an MRI‐manufacturing department and at a reference department have been analyzed. Mercury concentrations in urine samples were determined to analyze whether they depend on exposure to SMFs.

Results

Average exposure of system testers was 25.9 mT/8 hours at a 1.0‐T system and 40.4 mT/8 hours at a 1.5‐T system. Vertigo, metallic taste, and concentration problems were more reported among workers of MRI‐fabrication than in the reference department. Cognitive performance was tested outside the SMF, and no significant changes were detected.

Conclusion

This study suggests that any effects on cognitive functions are acute and transient and disappear rapidly after exposure has ended. All complaints, except for headaches, were more frequently reported by “fast movers” than by “slow movers,” and depended on field strength and duration of exposure. Mercury‐levels in urine were not affected. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
A polymer‐based MR‐compatible guidewire: A study to explore new prospects for interventional peripheral magnetic resonance angiography (ipMRA)
Authors: Mekle Ralf , Hofmann Eugen , Scheffler Klaus , Bilecen Deniz
Published: December 2005

Purpose

To introduce a newly developed polymer‐based and magnetic resonance (MR)‐compatible guidewire and to explore its capabilities with respect to interventional peripheral magnetic resonance angiography (ipMRA) in a flow phantom.

Materials and Methods

The guidewire is based on a polyetheretherketone (PEEK) polymer core, and small iron particles are embedded in its coating. A passive device tracking technique was designed utilizing a susceptibility artifact induced by the wire in images acquired with a balanced steady‐state free precession (b‐SSFP) sequence using small flip angles. The position of the guidewire tip was determined from image intensity maxima and overlayed onto a roadmap in near real‐time. Guidewire tracking and balloon angioplasty of an artificial stenosis were attempted in two configurations of a flow phantom.

Results

Successful passive guidewire tracking was performed for all phantom configurations. Robustness and accuracy of the tracking technique were sufficient for phantom studies. A balloon catheter was placed into the stenosis using the guidewire under complete MR guidance, and subsequent balloon angioplasty yielded improved flow conditions.

Conclusion

The new guidewire is well‐suited for clinical application due to an absence of the risk of core fracture and its atraumatic flexible tip. It opens novel prospects for the realization of ipMRA in humans that need to be explored in further studies. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Determination of thigh muscle stiffness using magnetic resonance elastography
Authors: Bensamoun Sabine F. , Ringleb Stacie I. , Littrell Laurel , Chen Qingshan , Brennan Michael , Ehman Richard L. , An Kai‐Nan
Published: December 2005

Purpose

To measure the elastic properties of the vastus lateralis (VL), vastus medialis (VM), and sartorius (Sr) muscles using magnetic resonance elastography (MRE).

Materials and Methods

To obtain a normative database of the aforementioned muscles, oblique scan directions were prescribed passing through each muscle. Shear waves were induced into the muscles using pneumatic and mechanical drivers at 90 and 120 Hz, respectively. These drivers were attached to the distal end of the right thigh with the knee flexed at 30°. The foot was placed in a footplate containing MR‐compatible load cells to record the force during a contraction (10% and 20% of the maximum voluntary contraction).

Results

The shear moduli measured at rest in the VL (N = 12), VM (N = 14), and Sr (N = 13) were 3.73 ± 0.85 kPa, 3.91 ± 1.15 kPa, and 7.53 ± 1.63 kPa, respectively. The stiffness of both vasti increased with the level of contraction, while the stiffness of the Sr remained the same.

Conclusion

The MRE technique was able to approximate the stiffness of different thigh muscles. Furthermore, the wave length was sensitive to the morphology (unipennate or longitudinal) and fiber composition (type I or II) in each muscle. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Line scan diffusion tensor MRI at low magnetic field strength: Feasibility study of cervical spondylotic myelopathy in an early clinical stage
Authors: Hori Masaaki , Okubo Toshiyuki , Aoki Shigeki , Kumagai Hiroshi , Araki Tsutomu
Published: December 2005

Purpose

To implement line scan diffusion tensor MR imaging (LSDTI) on a 0.2 Tesla MR imager, and investigate the findings in the spinal cord of patients with cervical spondylotic myelopathy in an early clinical stage.

Materials and Methods

Fourteen patients with clinical symptoms of cervical myelopathy underwent LSDTI. The signal‐to‐noise ratio (SNR) in the spinal cord and cerebrospinal fluid (CSF) was evaluated. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured. We classified the ROIs into two groups: 1) unaffected (no clinical symptoms and no abnormality on conventional images) and 2) affected (some clinical symptoms but no abnormal signal on conventional images). Three‐dimensional (3D) fiber‐tracking was also studied.

Results

The isotropic ADC values (10–3mm2/sec) were 1.28 ± 0.11 in group 1 and 1.59 ± 0.23 in group 2. The FAs were 0.55 ± 0.07 in group 1, and 0.47 ± 0.11 in group 2. The ADC value in group 2 increased (P < .001, Mann‐Whitney U‐test) and the FA in group 2 decreased (P = 0.24) on average, compared to those in group 1. 3D fiber‐tracking was successful in 64% (9/14) of the cases.

Conclusion

LSDT images at low field strength may be a sensitive method for elucidating the structural characteristics of spinal cord pathology in vivo. However, clinical correlation and a long‐term follow‐up study will be needed. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
R2 relaxometry with MRI for the quantification of tissue iron overload in β‐thalassemic patients
Authors: Alexopoulou Efthymia , Stripeli Fotini , Baras Panagiotis , Seimenis Ioannis , Kattamis Antonis , Ladis Vasilis , Efstathopoulos Efstathios , Brountzos Elias N. , Kelekis Alexis D. , Kelekis Nikolaos L.
Published: December 2005

Purpose

To evaluate the usefulness of a time‐efficient MRI method for the quantitative determination of tissue iron in the liver and heart of β‐thalassemic patients using spin‐spin relaxation rate, R2, measurements.

Materials and Methods

Images were obtained at 1.5 T from aqueous Gd‐DTPA solutions (0.106–8 mM) and from the liver and heart of 46 β‐thalassemic patients and 10 controls. The imaging sequence used was a respiratory‐triggered 16‐echo Carr‐Purcell‐Meiboom‐Gill (CPMG) spin‐echo (SE) pulse sequence (TR = 2000 msec, TEmin = 5 msec, echo spacing (ES) = 5 msec, matrix = 192 × 256, slice thickness = 10 mm). Liver iron concentration (LIC) measurements were obtained for 22 patients through biopsy specimens excised from the relevant liver segment. Biopsy specimens were also evaluated regarding iron grade and fibrosis. Serum ferritin (SF) measurements were obtained in all patients.

Results

A statistically significant difference was found between patients and healthy controls in mean liver (P < 0.004) and myocardium (P < 0.004) R2 values. The R2 values correlated well with Gd DTPA concentration (r = 0.996, P < 0.0001) and LIC (r = 0.874, P < 0.0001). A less significant relationship (r = 0.791, P < 0.0001) was found between LIC measurements and SF levels. R2 measurements appear to be significantly affected (P = 0.04) by different degrees of hepatic fibrosis. The patients' liver R2 values did not correlate with myocardial R2 values (r = 0.038, P < 0.21).

Conclusion

Tissue iron deposition in β‐thalassemic patients may be adequately quantified using R2 measurements obtained with a 16‐echo MRI sequence with short ES (5 msec), even in patients with a relatively increased iron burden. J. Magn. Reson. Imaging 2006. © 2005 Wiley‐Liss, Inc.
Paraglacial response of steep, sediment‐mantled slopes to post‐‘Little Ice Age’ glacier recession in the central Swiss Alps
Authors: Curry A. M. , Cleasby V. , Zukowskyj P.
Published: December 2005

This research assesses the morphological consequences of recent (post‐‘Little Ice Age’) paraglacial reworking of valley‐side sediment mantles in the European Alps. It aims to identify the extent and conditioning factors of slope adjustment at sites in the Swiss Alps, model the temporal pattern, and assess the rates of sediment reworking involved. Gully systems have cut into steep, high‐level lateral moraines, and debris cones have accumulated downslope. Debris flow is the dominant agent of sediment transfer. Factors controlling the extent of this activity include moraine slope gradient, relief and moisture availability. Gullies appear to have reached their maximum dimensions within ca. 50 yr of deglaciation, after which gully relief is reduced by removal of inter‐gully slopes and gully infilling (within 80–140 yr). On the most recently deglaciated terrain, minimum erosion rates average ca. 95 mm yr−1 since gully initiation, greatly exceeding ‘normal’ erosion rates in other environments. Mean annual accumulation of a single debris cone since ice retreat was calculated to be ca. 30 mm yr−1. Implications of these findings are applied to patterns of paraglacial sediment‐mantled slope adjustment, conceptualising paraglacial landscape response in terms of a sediment release exhaustion model, and paraglacial landform succession. Copyright © 2005 John Wiley & Sons, Ltd.
Sea‐level changes, river activity, soil development and glaciation around the western margins of the southern North Sea Basin during the Early and early Middle Pleistocene: evidence from Pakefield, Suffolk, UK
Authors: Lee Jonathan R. , Rose James , Candy Ian , Barendregt Rene W.
Published: December 2005

This paper outlines evidence from Pakefield (northern Suffolk), eastern England, for sea‐level changes, river activity, soil development and glaciation during the late Early and early Middle Pleistocene (MIS 20–12) within the western margins of the southern North Sea Basin. During this time period, the area consisted of a low‐lying coastal plain and a shallow offshore shelf. The area was drained by major river systems including the Thames and Bytham. Changes in sea‐level caused several major transgressive–regressive cycles across this low‐relief region, and these changes are identified by the stratigraphic relationship between shallow marine (Wroxham Crag Formation), fluvial (Cromer Forest‐bed and Bytham formations) and glacial (Happisburgh and Lowestoft formations) sediments. Two separate glaciations are recognised—the Happisburgh (MIS 16) and Anglian (MIS 12) glaciations, and these are separated by a high sea level represented by a new member of the Wroxham Crag Formation, and several phases of river aggradation and incision. The principal driving mechanism behind sea‐level changes and river terrace development within the region during this time period is solar insolation operating over 100‐kyr eccentricity cycles. This effect is achieved by the impact of cold climate processes upon coastal, river and glacial systems and these climatically forced processes obscure the neotectonic drivers that operated over this period of time. © British Geological Survey/Natural Environment Research Council copyright 2005. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.
Climatic cycles inferred from the aminostratigraphy and aminochronology of Quaternary dunes and palaeosols from the eastern islands of the Canary Archipelago
Authors: Ortiz J. E. , Torres T. , Yanes Y. , Castillo C. , Nuez J. De La , Ibáñez M. , Alonso M. R.
Published: December 2005

Aminochronological and aminostratigraphical methods have been used to study the Quaternary aeolian deposits from the islands located east of the Canary Archipelago (Fuerteventura and Lanzarote islands and La Graciosa, Montaña Clara and Alegranza islets). The extent of racemisation/epimerisation of four amino acids (isoleucine, aspartic acid, phenylalanine and glutamic acid) was measured in land snail shells of the genus Theba. The age calculation algorithms of these amino acids have been determined to permit the numerical dating of these deposits. Eight Aminozones, each defining dune/palaeosol‐formation episodes, have been distinguished and dated at 48.6 ± 6.4, 42.5 ± 6.0, 37.8 ± 4.6, 29.4 ± 4.8, 22.4 ± 4.5, 14.9 ± 3.6, 11.0 ± 4.0 and 5.4 ± 1.1 ka BP, the first five of them defining cycles of 5–7 ka.

The alternation of palaeosols and aeolian deposits, which are related to abrupt transitions from humid to arid conditions, are the reflection of globally induced changes in North Africa palaeoenvironmental conditions linked to the effect of African palaeomonsoons on the trade winds and the Saharan Air Layer. Probably these aeolian cycles, with a recurrence period of 5–7 ka, are the expression of multiples of the ∼2.4 ka solar‐cycle. Copyright © 2005 John Wiley & Sons, Ltd.
Cover Picture: Macromol. Mater. Eng. 1/2006
Authors: Lu Yong‐Lai , Liang Yu‐Rong , Wu You‐Ping , Zhang Li‐Qun
Published: December 2005

Cover: The picture on the cover shows TEM images and WAXD patterns (insert graphs) of untreated and treated S‐IIRCNs. The microstructural changing behaviors of S‐IIRCNs induced by thermal treatments are strongly dependent on the treating temperature. Some experiments suggested that residual solvent in the system should play an important role. Further details can be found in the article by Y.‐L. Lu, Y.‐R. Liang,* Y.‐P. Wu, and L.‐Q. Zhang* on page 27.
On the asymptotic behavior of the eigenvectors of large banded Toeplitz matrices
Authors: Böttcher A. , Grudsky S. , Ramírez de Arellano E.
Published: December 2005

Let λ be an eigenvalue of an infinite Toeplitz band matrix A and let λn be an eigenvalue of the n ×n truncation An of A . Suppose λn converges to λ as n → ∞. We show that generically the eigenspaces for λn are onedimensional and contain a vector xn whose first component is 1 if only n is large enough, and we prove that xn converges to an eigenvector x 0 of A that is independent of the particular choice of the λn . The eigenspace of A corresponding to λ is spanned by x 0 and a finite number of shifts of x 0. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Density of C∞(Ω) inW1,p (x )(Ω) with discontinuous exponent p (x )
Authors: Fan Xianling , Wang Suyun , Zhao Dun
Published: December 2005

In this paper, we present a sufficient condition for the density of C ∞(Ω) inW 1,p (x )(Ω) with p (x ) being discontinuous. Roughly speaking, we can get the density under the following assumptions: 1) Ω can be divided into some open pieces Ωi such that p (x ) is “fine”on each Ωi , for example, p (x ) satisfies the Dini–Lipschitz condition on each Ωi . 2) The corresponding pieces “get along with each other regularly ”. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The international drivers of domestic airline mergers in twenty nations: integrating industrial organization and international business
Authors: Clougherty Joseph A.
Published: December 2005

The domestic airline merger phenomenon of the late 1980s and early 1990s sparked a great deal of Industrial Organization (IO) literature; yet, that literature neglected non‐US domestic mergers and potential for international competitive gains. Using an International Business perspective to complement an IO analysis, I argue that factoring international competitive incentives helps explain domestic airline merger activity. A Cournot model of airline competition illustrates that domestic mergers, via enhanced domestic networks and reduced domestic competition, generate international competitive gains. Further, empirical tests—using a structural equations approach on panel data covering interhyphen‐national city‐pair market segments—support domestic mergers improving international competitiveness. Copyright © 2006 John Wiley & Sons, Ltd.
Lower bounds for the relative greedy algorithm for approximating Steiner trees
Authors: Hougardy Stefan , Kirchner Stefan
Published: December 2005

The Steiner tree problem is to find a shortest subgraph that spans a given set of vertices in a graph. This problem is known to be NP‐hard, and it is well known that a polynomial time 2‐approximation algorithm exists. In 1996, Zelikovsky suggested an approximation algorithm for the Steiner tree problem that is called the relative greedy algorithm. Until now the performance ratio of this algorithm has not been known. Zelikovsky provided 1.694 as an upper bound, and Gröpl, Hougardy, Nierhoff, and Prömel proved that 1.333 is a lower bound. In this article we improve the lower bound for the performance ratio of the relative greedy algorithm to 1.385. © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 47(2), 111–115 2006
Physical and mechanical properties of pultruded composites containing fillers and low profile additives
Authors: Boukhili R. , Boukehili H. , Daly H. Ben , Gasmi A.
Published: December 2005

This article deals with the effect of fillers and additives content on the physical and mechanical properties of unidirectional pultruded glass/polyester composites. The physical characterization consisted of determining the void volume fraction (Vv), density, shrinkage ratio, coefficient of thermal expansion (CTE), and dynamic mechanical properties. The mechanical tests consisted of three‐point‐bending tests under static, impact, and fatigue loading. The low profile additive (LPA) has been found to compensate the cure shrinkage by microvoid formation. Dynamic mechanical analysis measurements show that the LPA slightly lowers the glass transition temperature Tg and increases the internal damping Tan δ. The transverse coefficient of thermal expansion was found to be sensitive to the LPA content. Three‐point bending tests show that the interlaminar shear strength (ILSS) is slightly sensitive to the fillers and LPA content, but the flexural strength is not affected. Impact test results on short beam shear and flexural specimens show the same behavior as in the static tests except that the LPA content has a detrimental effect on the flexural impact properties. The fatigue tests performed show that the effect of fillers is not significant, while the LPA effect is mixed. It seems that there is an LPA content for which the fatigue resistance is maximized. Finally, the wide range of behaviors and span‐to‐depth ratios investigated suggest that the ILSS as measured according to the ASTM 2344 recommendations can be largely misleading because of the unavoidable compressive yielding under the loading nose. For the materials investigated, higher span‐to‐depth ratio are more representative of the ILSS. POLYM. COMPOS., 27:71–81, 2006. © 2005 Society of Plastics Engineers
Synthesis and properties of poly(methyl methacrylate)/clay nanocomposites using natural montmorillonite and synthetic Fe‐montmorillonite by emulsion polymerization
Authors: Kong Qinghong , Hu Yuan , Yang Ling , Fan Weicheng , Chen Zuyao
Published: December 2005

In this article, Fe‐montmorillonite (Fe‐MMT) was synthesized by hydrothermal method. For the first time, Fe‐MMT was modified by cetyltrimethyl ammonium bromide (CTAB), and poly(methyl methacrylate)(PMMA)/Fe‐MMT nanocomposites were synthesized by emulsion polymerization. Then poly(methyl methacrylate)(PMMA)/natural montmorillonite (Na‐MMT) and PMMA/Fe‐MMT nanocomposites were compared by Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD) patterns, transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). By XRD and TEM, it was found out that the morphology of PMMA/Fe‐MMT nanocomposites was different from that of the PMMA/Fe‐MMT nanocomposites when the content of two types of clay was same in the PMMA matrix. It was possible that the presence of iron may lead to some radical trapping, which enhances intragallery polymerization to be developed to improve layer dispersion in PMMA/Fe‐MMT systems. In TGA curves, the thermal stability and residue at 600°C of PMMA/Fe‐MMT nanocomposites were higher than those of PMMA/Na‐MMT nanocomposites. Those dissimilarities were probably caused by structural Fe ion in the lattice of Fe‐MMT. POLYM. COMPOS., 27:49–54, 2006. © 2005 Society of Plastics Engineers
Finite element approach to composite mold design based on Darcy flow with velocity clipping
Authors: Turner D.Z. , Nakshatrala K.B. , Hjelmstad K.D.
Published: December 2005

This article discusses various numerical techniques that are widely used in industry to solve the Darcy flow equations. We outline their merits and limitations. We also present a new stabilized finite element formulation that has been proposed recently (Nakshatrala et al., Comput. Meth. Appl. Mech. Eng., doi: 10.1016/j.cma.2005.07.009). This method is the best available numerical method in the present literature for solving Darcy flow equations and it is the ideal formulation for three‐dimensional Darcy flow simulations because of its accuracy and stability characteristics. This formulation can be easily implemented in an existing finite element code and it is the only formulation based on continuous finite elements to pass three‐dimensional constant flow patch tests. Next, we present a computational methodology that is based on a velocity clipping finite element approach and a steady‐state solution of the Darcy flow equations to model and visualize resin flow during the resin transfer molding process. We show that steady‐state Darcy flow can be a valuable tool for a composite manufacturer to decide on the location of the inlets and outlets, and also to visualize resin flow. The methodology is promising for the design of the manufacturing process for complex composite members because it is computationally efficient. We also present a novel approach to model open space within the mold that results from cutting and bending of fibers. In the end, we provide some experimental results and compare them with the numerical results. POLYM. COMPOS., 27:65–70, 2006. © 2005 Society of Plastics Engineers
Preparation, characterization, and properties of poly(vinyl chloride)/organophilic‐montmorillonite nanocomposites
Authors: Ren Tianbin , Yang Jun , Huang Yanxia , Ren Jie , Liu Yan
Published: December 2005

Poly(vinyl chloride) (PVC)/organophilic‐montmorillonite (OMMT) nanocomposites were prepared by direct melt intercalation. PVC/compatibilizer ((vinyl acetate) copolymer (VAc))/OMMT nanocomposites were also prepared by melt intercalation by a masterbatch process. The effect of OMMT content on the nanostructures and properties of nanocomposites was studied. The nanostructures were studied by wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM). The linear viscoelastic properties and dynamic mechanical properties of PVC/OMMT nanocomposites were also investigated by an advanced rheometric expansion system (ARES) rheometer. The results showed that partially exfoliated and partially intercalated structures coexisted in the PVC/OMMT and PVC/VAc/OMMT nanocomposites. The mechanical properties test results indicated that the notched Charpy impact strengths of nanocomposites were improved compared to that of pristine PVC and had a maximum value at 1 phr OMMT loadings. The compatibilizer could further improve the impact strengths. But the existence of OMMT decreased the thermal stability of PVC/OMMT and PVC/VAc/OMMT nanocomposites. The linear viscoelastic properties test results indicated the dependence of G′ and G″ on ω shows nonterminal behaviors, and they had better processibility compared with pristine PVC. However, the glass transition temperatures of PVC/OMMT nanocomposites almost had little change compared to that of pristine PVC. POLYM. COMPOS., 27:55–64, 2006. © 2005 Society of Plastics Engineers
Investigation of basalt fiber composite mechanical properties for applications in transportation
Authors: Liu Qiang , Shaw Montgomery T. , Parnas Richard S. , McDonnell Anne‐Marie
Published: December 2005

New materials offer the promise of innovative applications in transportation. One such new material is basalt fiber, which is used in other industries because of documented strengths [Ramakrishnan et al., “Performance Evaluation of 3‐D Basalt Fiber Reinforced Concrete and Basalt Rod Reinforced Concrete,” NCHRP‐IDEA Program Project Final Report, Transportation Research Board, Washington, DC, 1998]. Use in transportation, however, requires a better knowledge of many properties. This article discusses initial work with basalt‐reinforced polymer composites. Polymer composites reinforced by basalt fabric and glass fabrics were produced for these tests. Void content below 3% were measured for all the composites produced for the testing program. No significant differences in Young's modulus, tensile strength, flexure strength, shear strength, and compression strength were found between basalt composites and glass composites. Environmental durability testing of basalt composites is ongoing. POLYM. COMPOS. 27:41–48, 2006. © 2005 Society of Plastics Engineers
Modeling of fiber–polymer coupling for suspensions of mono‐modal fibers
Authors: Huq A.M.A. , Azaiez J.
Published: December 2005

The rheology of suspensions of fibers in polymer solutions is strongly dependent on fiber–fiber and fiber–polymer interactions. To model these interactions and their dependence on the flow and suspension properties, the steady shear viscosity of glass fibers in a polyethylene oxide polymer solution are measured for different fiber volume fractions and aspect‐ratios. The measurements are conducted for well characterized fiber samples that have a uniform and well defined aspect‐ratio and for moderate volume fractions. The results of the experimental study are used to correlate the polymer–fiber coupling factor and the fiber–fiber interaction coefficient using a mathematical model based on a modified FENE‐P (finitely extensible nonlinear elastic) constitutive equation. It was found that both parameters are strongly dependent on the characteristics of the suspension, but also depend on the flow shear rate that determines the degree of fiber orientation. In general, fiber–fiber and polymer–fiber interactions increase with both the aspect‐ratio and the volume fraction and are more important when the fibers are not fully oriented. POLYM. COMPOS., 27:82–91, 2006. © 2005 Society of Plastics Engineers
Wear behavior of carbon fiber‐reinforced poly(phenylene sulfide)
Authors: Quintelier J. , Samyn P. , De Baets P. , Tuzolana T. , Van Paepegem W. , Van den Abeele F. , Vermeulen J.
Published: December 2005

On a pin‐on‐disc test rig, online measurements of the wear and friction of steel sliding against carbon fiber‐reinforced polyphenylene sulfide were done. Instead of the standard set‐up, a rotating composite disc and steel pin are used. The frictional behavior of this material pair results in a friction coefficient of 0.33, while a carbide film is formed in the wear track. This results in the lowering of the frictional behavior. The wear rate is rather low, but when the wear track is covered with a carbide film, suddenly the wear rate raises. This is not due to the wear of the composite material but only as a result of the start of terrible wear of the steel counter face. Moreover, the wear of the pin is strongly related to the wear track. The pin is flattened at the sides of the formed wear track, but in contact with the carbide film there is less wear, resulting in a pin with two flat sides, making contact with the original surface, and a rig in the middle of the pin following the roundness of the wear track. The frictional behavior is strongly dependent on the weft‐warp direction. POLYM. COMPOS., 27:92–98, 2006. © 2005 Society of Plastics Engineers
Joining of fiber‐reinforced polymer tubes for high‐pressure applications
Authors: Mertiny P. , Ellyin F.
Published: December 2005

Fiber‐reinforced polymer composites offer superior performance particularly in harsh environments; hence, they are recognized as an attractive material, especially for the transportation of pressurized fluids. However, an extensive use of these composites has been hampered, in part due to unsatisfactory solutions for the joining of subcomponents, and insufficient knowledge on the associated damage behavior. A favorable connection design for a piping system can be an adhesively bonded joint. In this study, a unique adhesive injection technique is presented that joins composite pipe sections using filament‐wound overlap sleeve couplers. The purpose of the present study was to characterize the performance and associated damage behavior of a prototype‐size pipe structure joined by the above procedure. Internal pressure and axial traction were applied to specimens at various biaxial ratios. In addition to the experimental investigation, the joint geometry was also modeled numerically employing the finite element technique. This yielded a better understanding of the damage behavior and enabled a parametric study that provided recommendations for an improved joint design. POLYM. COMPOS., 27:99–109, 2006. © 2005 Society of Plastics Engineers
Validity of asthma diagnoses recorded in the Medical Services database of Quebec
Authors: Blais Lucie , Lemière Catherine , Menzies Dick , Berbiche Djamal
Published: December 2005

The goal of this study was to evaluate the validity of asthma diagnoses recorded in the Medical Services (physician billing) database of the Canadian province of Quebec. The predictive positive value (PPV) and predictive negative value (PNV) of two operational definitions of asthma based on diagnoses recorded in the database were evaluated. Patients 16–80 years old treated by a respiratory or a family physician in 2002 were selected from the database. The diagnosis derived from the Medical Services database was compared to the diagnosis written in the patient's medical chart. The PPV and PNV of the first operational definition based on one asthma diagnosis or more recorded in the database over a 1‐year period were found to be 0.75 and 0.96 for respiratory physicians and 0.67 and 0.99 for family physicians, for patients 16–44 years old. The PPV increased to 0.78 for family physicians and to 0.77 for respiratory physicians when the second operational definition based on two diagnoses of asthma or more was used. Results tended to be lower for 45–80 years old patients. We conclude that diagnoses recorded in the Medical Services database of Quebec are valid to identify patients with asthma. Copyright © 2005 John Wiley & Sons, Ltd.
Flexible supercritical CO2‐assisted process for poly(methyl methacrylate) structure formation
Authors: Reverchon E. , Rappo E. Schiavo , Cardea S.
Published: December 2005

Poly(methyl methacrylate) membranes have been prepared using a supercritical fluid‐phase inversion process in which CO2 acts as the nonsolvent. Series of experiments were performed at various polymer concentrations, temperatures, and pressures using three different solvents, dimethylsulfoxide, acetone, and tetrahydrofuran. We operated at polymer concentrations ranging between 25 and 1% (w/w) in DMSO, acetone, and THF, obtaining membranes that change with continuity from cellular structure to a structure formed by networked microparticles. The membrane formation parameters in the case of DMSO and acetone have also been varied between 15 and 25 MPa and between 35 and 65°C. We observed that on increasing the pressure and decreasing the temperature, the cell size decreased. The influence of the solvent used on membrane formation has also been analyzed. On increasing the mutual affinity between solvent and nonsolvent, cell and pore sizes decrease and the structure changes from nearly closed to open interconnected cells. POLYM. ENG. SCI. 46:188–197, 2006. © 2005 Society of Plastics Engineers
Kinetic analysis of thermo‐oxidative degradation of PEEK/thermotropic liquid crystalline polymer blends
Authors: Naffakh M. , Gómez M.A. , Marco C. , Ellis G.
Published: December 2005

The thermal degradation behavior of blends of poly(aryl ether ether ketone), PEEK, with a thermotropic liquid crystalline polymer (TLCP), Vectra®, were investigated in an oxidative atmosphere, using thermogravimetric analysis under dynamic conditions. The theoretical weight loss curves of the blends were compared with the experimental curves in order to explain the effect of blending on the thermal stability of the pure polymers. The thermo‐oxidative degradation of PEEK/Vectra® blends of different compositions takes place in various steps and the characteristic degradation temperatures and the kinetic parameters such as activation energy are strongly influenced by blending. Polymer blends based on this TLCP polymer had not been previously studied from kinetic viewpoint. POLYM. ENG. SCI. 46:129–138, 2006. © 2005 Society of Plastics Engineers