bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnosis of Abnormal Situations in a Continuous Solution Polymerization Reactor
Authors: Sotomayor Oscar A. Z. , Odloak Darci , Giudici Reinaldo
Published: March 2007

This work presents results on the problem of robust on‐line diagnosis of abnormal situations in the case of the free‐radical solution polymerization of styrene in a continuous well‐mixed reactor operating under feedback control. The control system is constituted of a model predictive control strategy in conjunction with a ratio control law. The proposed fault diagnosis system is based on an open‐loop approach, which uses a linearized model of the polymerization process for the implementation of a bank of reduced‐order unknown input observers. Each observer is designed to detect changes in a particular process parameter, external disturbance or malfunctioning of sensors and actuators. Fault isolation is obtained through a structured residual approach; meanwhile, fault estimation is performed using the degree of freedom remaining in the observer design. The effectiveness of the proposed technique is verified through numerical simulations carried out on a well‐defined industrial styrene polymerization benchmark.

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Compartmentalization in TEMPO‐Mediated Radical Polymerization in Dispersed Systems: Effects of Macroinitiator Concentration
Authors: Zetterlund Per B. , Okubo Masayoshi
Published: March 2007

The influence of the initial macroinitiator concentration ([PT]0) on compartmentalization effects (segregation effects and confined space effects) in 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO)‐mediated radical polymerization of styrene in a dispersed system at 125 °C has been investigated by simulations employing modified Smith‐Ewart equations. The modeling approach accounts for compartmentalization of both propagating radicals and nitroxide, as well as the generation of radicals by thermal initiation of styrene. The manifestation of compartmentalization effects occurs at significantly greater particle diameters (d) for low [PT]0; at [PT]0 = 0.002 M, the polymerization rate, control and livingness are affected by compartmentalization for d < 120 nm, whereas the system behaves as in the corresponding bulk system for d > 45 nm at [PT]0 = 0.2 M. The results are discussed with regards to the specific effects of compartmentalization on deactivation and bimolecular termination.

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An operator method for a numerical quadrature finite element method for a Maxwell‐eigenvalue problem
Authors: Hamelinck Wouter , Van Keer Roger
Published: March 2007

We consider a Maxwell‐eigenvalue problem on a brick. As is well known, we need to pay special attention to avoiding the so‐called spurious eigenmodes. We extend the results obtained in (SIAM J. Numer. Anal. 2000; 38:580–607) to include the use of numerical quadrature. For simplicity, we restrict ourselves to a Gauss–Lobatto integration scheme. The numerical quadrature variational problem can be recasted in an operator form. The main goal of the article consists of proving that a set of necessary and sufficient conditions for spurious freeness remain valid while using numerical quadrature with sufficient precision. Copyright © 2007 John Wiley & Sons, Ltd.
A GC‐FID method for analysis of Lysinoalanine
Authors: Montilla Antonia , Gómez‐Ruiz José Ángel , Olano Agustín , del Castillo María Dolores
Published: March 2007

Lysinoalanine (LAL) is an unwanted byproduct, which is formed during the processing of protein and protein‐containing foods and feeds. A GC method for the quantitative analysis of LAL under conventional chromatographic conditions has been developed. The method was applied to the analysis of pure standard substances, boiled eggs, commercial caseinates, fresh cheese, fresh cheese made from milk supplemented with caseinate, and fresh cheeses adulterated with caseinate after cheese making process. Results demonstrated the reliability of the GC capillary chromatography for the analysis of LAL in protein containing foods. LOD and LOQ of 50 and 152 ppm of LAL in protein, respectively, were achieved. Range of linearity, precision, and accuracy of the method, measured using diaminopimelic acid as internal standard, were satisfactory for quantification purpose. The method might also be suitable for the quantitative analysis of other amino acids such as lysine and arginine. Results also indicated the utility of this methodology for detecting protein quality of egg products and caseinates as well as fresh cheese adulterations.
Copper‐catalyzed ascorbate oxidation results in glyoxal/AGE formation and cytotoxicity
Authors: Shangari Nandita , Chan Tom S. , Chan Katie , Huai Wu Shuo , O'Brien Peter J.
Published: March 2007

Previously we showed that 10 μM glyoxal compromised hepatocyte resistance to hydrogen peroxide (H2O2) by increasing glutathione (GSH) and NADPH oxidation and decreasing mitochondrial membrane potential (MMP) before cytotoxicity ensued. Since transition metal‐catalyzed oxidation of ascorbate (Asc) has been shown to result in the generation of both glyoxal and H2O2, we hypothesized that glyoxal formation during this process compromises hepatocyte resistance to H2O2. We used isolated rat hepatocytes and incubated them with Asc/copper and measured cytotoxicity, glyoxal levels, H2O2, GSH levels, and MMP. To investigate the role of Asc/copper on glyoxal‐BSA adducts, we measured the appearance of advanced glycation end‐products (AGE) in the presence and absence of catalase or aminoguanidine (AG). Asc/copper increased glyoxal and H2O2 formation. Hepatocyte GSH levels were decreased and cytotoxicity ensued after a collapse of the hepatocyte MMP. Glyoxal traps protected hepatocytes against Asc/copper‐induced cytotoxicity. In cell‐free studies with BSA, incubation with Asc and copper resulted in glyoxal‐hydroimidazolone formation, which was decreased by both AG and catalase. To the best of our knowledge, this is the first study that illustrates the importance of glyoxal production by transition metal‐catalyzed Asc autoxidation. Understanding this mechanism of toxicity could lead to the development of novel copper chelating drug therapies to treat diabetic complications.
Reducing the formation of glucose degradation products in peritoneal dialysis solutions by ultrahigh temperature ohmic heating
Authors: Shapira Alina , Shazman Asher , Ungar Yael , Shimoni Eyal
Published: March 2007

Peritoneal dialysis (PD) is commonly performed by using preprepared dialysis solutions containing glucose, which are thermally treated to achieve commercial sterilization. A series of glucose degradation products (GDPs) are being formed, which react with the tissue during the dialysis procedure, thus baring a negative effect on the patient and the dialysis process. The present study tested the efficacy of ohmic heating as an alternative thermal treatment for continuous sterilization of PD solutions. The process was compared to conventional retort treatment, and GDPs accumulation was measured. Thermal treatments using the ohmic heating system were performed at three temperatures (105, 125, and 150°C) with residence time at each temperature ranging from 0.84 to 12.0 s. The resulting concentrations of glyoxal (GO), methylglyoxal (MGO), and 3‐deoxyglucosone (3‐DG) in the PD solutions were measured. None of these GDPs were found in PD fluids treated by ohmic heating at 105°C. The concentration of 3‐DG, after a standard sterilization treatment (121°C, 20 or 40 min) was one order of magnitude higher (˜140 and 242 μM) than after ohmic heating treatment at 125°C. The results of the present study suggest that this technique can be used to produce solutions with much lower content of GDPs. It also demonstrates the advantage of using the ohmic heating technology as a tool for high temperature short time treatment of PD fluids.
The potential antimutagenic and antioxidant effects of Maillard reaction products used as “natural antibrowning” agents
Authors: Wagner Karl‐Heinz , Reichhold Stefanie , Koschutnig Karin , Chériot Sophie , Billaud Catherine
Published: March 2007

The aim of this study was to investigate the potential antioxidative and antimutagenic effects of Maillard reaction products (MRPs) formed from glucose or fructose and cysteine or glutathione in the Ames Salmonella test and the 2,2′‐azobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) assay. The mixtures were heated for 4 h 20 min or 14 h at 103 or 110°C and tested in five concentrations from 0.05 to 11 mg/plate in strains TA 98 and TA 102 in the plate incorporation assays. In order to promote the formation of mutant revertants the prooxidants hydrogenperoxide (H2O2) and tertiary‐butyl hydroperoxide (tBOOH) were used in the TA 102. Tests were conducted with preincubation with (+S9) and without (–S9) metabolic activation. 5‐Hydroxymethylfurfural (5‐HMF) was investigated as carbonyl compound. In TA 98, no effect of the MRPs was shown. The shorter heated samples (4 h 20 min) were in general more active than the longer heated ones (14 h). Up to 1 mg/plate (1%) all the reaction mixtures remained safe, but the 5% and in particular the 11% fractions increased the number of revertants significantly for the shorter heated mixtures. The 14 h mixtures did not show any response for almost all concentrations. No significant difference in the number of revertants could be observed between the cysteine and glutathione mixtures, the fructose mixtures increased revertants number to a higher extent than the glucose mixtures only in the 4 h 20 min heated mixtures for the highest concentration (11%). The highest activity was always observed in the +S9 tests. Antioxidative effects expressed as Trolox equivalents were higher in the 4 h 20 min heated samples. When detectable, HMF concentration was found to be higher in the 14 h MRP samples. In order to use the tested mixtures as antibrowning agents for technological purpose, the concentration should not be higher than 1% and the longer heated reaction mixtures were preferred since the brown pigments seemed to be less reactive than the intermediate products.
Forty years of furosine – Forty years of using Maillard reaction products as indicators of the nutritional quality of foods
Authors: Erbersdobler Helmut F. , Somoza Veronika
Published: March 2007

The Maillard reaction products (MRPs) most widely used as markers of the nutritional quality of foods are furosine, Nε‐carboxymethyllysine (CML), hydroxymethylfurfural, pyrraline, pentosidine and pronyl‐lysine. One of the MRPs identified first was furosine, which was quantified in foods 40 years ago as a chemical indicator of the Amadori compound Nε‐fructoselysine. Since then, furosine has gained broad attention by food chemists and biomedical researchers, as its formation upon heat treatment is well characterised. Moreover, it represents the Amadori products from early Maillard reactions in which amino acids react with reducing carbohydrates, resulting in a loss of their availability. This is of importance for the essential amino acid lysine, which is also the limiting amino acid in many proteins. In order to evaluate the nutritional quality of a protein, the concomitant analysis of free – and nutritionally available – lysine and the amount of lysine reacted to form the respective MRP is essential, even for mildly processed foods. The other chemical markers of heat treatment such as CML, pyrraline, pentosidine or pronyl‐lysine seem to be useful markers of the advanced stages of Maillard reactions. Compared to the conditions in which furosine is formed, these compounds are generated under more severe conditions of heat treatment. However, the concentrations analysed are significantly lower than those of furosine. Therefore, the nutritional evaluation of a food protein should include not only furosine, but also other chemical markers of heat treatment such as, for example, CML, pyrraline and pentosidine.
A novel 1 × 2 multimode interference optical wavelength filter based on photodefinable benzocyclobutene (BCB 4024–40) polymer
Authors: Ibrahim M. H. , Kassim N. M. , Mohammad A. B. , Lee Shuh‐Ying , Chin Mee‐Koy
Published: March 2007

A novel 1 × 2 multimode interference (MMI) optical wavelength filter for 1310 and 1550 nm operation based on photodefinable BenzoCyclobutene (BCB 4024–40) polymer is demonstrated. The device is fabricated on BK7 glass substrate with thin layer of SiO2 as cover. A cost effective chemical etching technique is used in the fabrication process to take advantage of the photosensitive nature of the polymer. The filter length is significantly reduced by adopting the restricted MMI scheme, lower beat length ratio, and cascaded MMI couplers. At 1550 nm filtering operation, the measured crosstalk is −20.6 dB and at 1310 nm filtering is −14.4 dB. The measured insertion loss is around 3.2–3.5 dB for both ports. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1024–1028, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22327
Effect of SNR of input signal on the accuracy of a ratiometric wavelength measurement system
Authors: Rajan Ginu , Wang Qian , Farrell Gerald , Semenova Yuliya , Wang Pengfei
Published: March 2007

The impact of a change in signal‐to‐noise ratio (SNR) of the input signal on the accuracy of a ratiometric wavelength measurement system is studied. The variation of the output ratio of the system due to the change in SNR of the input signal is modeled and the experimental investigation has been carried out, and both indicate that the accuracy is influenced significantly by variations in the SNR of the input signal. The demonstration example shows a wavelength shift of 0.055 nm when the SNR of the input signal varies from 47 dB to 42 dB (the measurable range is from 1500 nm to 1600 nm and the edge filter used has a slope of 0.15 dB/nm). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1022–1024, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22328
Frequency selective surfaces on ISO/anisotropic substrates with dielectric losses
Authors: Campos A. L. P. S. , d'Assunção A. G.
Published: March 2007

The analysis of periodic structures on isotropic and anisotropic substrates with dielectric losses is presented. Frequency selective surface structures composed by an array of conducting patch elements are considered. This analysis uses the Galerkin method in combination with the equivalent transmission line method, in the Fourier domain, to determine the reflection and transmission characteristics of the considered structures. The analysis provides very accurate results compared with those presented by other authors, for several particular cases. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1041–1044, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22334
Small size quad band microstrip antenna
Authors: Thakur Jay Prakash , Park Jun‐Seok , Jang Byoung‐Jun , Cho Hong‐Gu
Published: March 2007

A novel compact microstrip patch antenna is proposed for quad band, GSM850, GSM900, GPS (L1–1575 and L2–1227), and UMTS‐2110 application for cellular telephone system. Design is particularly unique since it supports the new generation mobile phone where multiband operation with minimum size is greatly desired. Two microstrip line feeds placed in orthogonal directions are used for the excitation of the proposed antenna. Microstrip patch has been meandered to lengthen the electrical paths and to achieve quad frequency bands. Detail of design criteria with respect to physical parameters is described. Radiation Patterns and impedance bandwidths are measured and shown. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 997–1001, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22341
Transmission properties of two shifted magnetoinductive waveguides
Authors: Radkovskaya A. , Sydoruk O. , Shamonin M. , Stevens C. J. , Faulkner G. , Edwards D. J. , Shamonina E. , Solymar L.
Published: March 2007

Transmission properties of magnetoinductive waves propagating in two coupled one‐dimensional metamaterial arrays are studied both experimentally and theoretically for the case when one of the arrays is shifted relative to the other one. Two different kinds of resonant metamaterial elements, split‐pipe and spiral resonators, are investigated in the frequency bands centred at 46.2 and 586 MHz, respectively. It is shown that within a certain frequency range close to the resonant frequencies the transmission is strongly dependent on the shift. Theoretical calculations based on the impedance matrix show good agreement with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1054–1058, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22344
Planar multilateral disc monopole antenna for UWB application
Authors: Hsu Cheng‐Hsing
Published: March 2007

A planar multilateral disc monopole antenna for ultrawideband (UWB) application is proposed and experimentally studied. The proposed antenna has wide impedance bandwidth from 2.85 GHz to more than 15 GHz with better than −10 dB return loss. Moreover, the proposed antenna is simple in structure and easy to fabricate. The design is demonstrated assuming FR4 substrate with a relative dielectric constant of 4.4 and thickness of 1.6 mm. The size of the antenna is 40 mm × 50 mm. Experimental patterns are showing the behavior of omnidirectional beam pattern in H‐plane. Details of the proposed antenna design and simulation results for UWB operations are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1101–1103, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22353
Fully embedded high Q circular stacked spiral inductors into organic substrate
Authors: Lee Hwan H. , Park Jae Y.
Published: March 2007

In this paper, fully embedded circular‐stacked spiral inductors are investigated into a multilayered PCB substrate for low cost and miniaturized RF system on package (SOP) applications. The embedded circular‐stacked inductors are optimally designed to obtain high quality factor and self‐resonant frequency by using 3D EM simulator. The fabricated two‐turn circular‐stacked inductor has an inductance of 8.4 nH and a maximum quality factor of 67 at 1.2 GHz. The device size of the staked inductor is ∼65% of the planar inductor. The measured performance characteristics are well matched with the 3D EM‐simulated ones. The embedded circular stacked spiral inductors are promising for organic‐based SOP, which needs various functionality, low cost, small size and volume, and high packaging density. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1074–1077, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22354
Flexible‐substrate low‐cost construction of a coplanar‐waveguide aperture‐coupled microstrip patch antenna
Authors: Depret Dominic , Rogier Hendrik , Dhaenens Kristof , Vanfleteren Jan
Published: March 2007

An innovative and cost‐effective procedure for building multi‐layered planar antennas is presented. The antenna is constructed by defining copper patterns forming the feed plane and the antenna plane on a single flexible polyimide substrate and by folding the flex around a low εr and low‐loss spacer. By a suitable choice of transfer tape to assemble the different layers, a high alignment accuracy and low substrate losses are ensured. To illustrate our new approach, the design and manufacturing of a coplanar‐waveguide aperture‐coupled patch antenna covering the complete 2.45 GHz ISM band is described. By means of reflection and transmission measurements, the high gain and high efficiency of the antenna prototypes are demonstrated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1071–1074, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22355
All‐optical diode in photorefractive crystal
Authors: Yuan W. , Wang B.
Published: March 2007

In this letter, we present a technique that employs photorefractive crystals for all‐optical diode. We theoretically designed a structure using two‐pieces of photorefractive crystals, this special crystals set show significantly potentials for applications in unidirectional diffraction beams. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1092–1095, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22360
Analysis of the band‐stop techniques for ultrawideband antenna
Authors: Hong Seokjin , Shin Jaewoong , Park Hoon , Choi Jaehoon
Published: March 2007

Two band‐stop techniques for UWB antenna design are suggested in this article. The proposed antennas have wide bandwidth enough to cover UWB services along with the band‐stop characteristic for 5 GHz WLAN band. By inserting an U‐shaped slot or attaching an inverted Y‐shaped short‐circuited stub, the band‐stop characteristic is obtained. Prototypes of the proposed antennas are implemented and the parametric studies of the two band‐stop techniques are performed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1058–1062, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22363
Integrated electro‐optic Mach–Zehnder modulator fabricated by vapour Zn‐diffusion in LiNbO3
Authors: Suárez I. , Pernas P. L. , Lifante G.
Published: March 2007

A novel integrated Mach–Zehnder modulator fabricated on Z‐cut lithium niobate wafers is presented. The optical waveguides were fabricated by the Zn‐diffusion method, which allows monomode TM propagation at the wavelength of interests by choosing the channel waveguide width. The TM‐mode is shown to be buried beneath the surface, which avoids the need of using a dielectric buffer to reduce propagation losses induced by the metallic electrodes to perform electro‐optic modulation. A figure of merit of 9.2 V cm has been obtained for the switching voltage‐interaction length product, which is slightly higher than the calculated theoretical value using the overlap between the externally applied electrical field and the propagating optical field. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1194–1196, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22376
Design and modeling of RF MEMS switch by reducing the number of interfaces
Authors: Sboui N. , Gharsallah A. , Baudrand H. , Gharbi A.
Published: March 2007

The transverse wave concept iterative procedure is presented for full wave investigation of MEMS capacitive switch. Using the transverse wave approach we can reduce the number of interfaces in planar circuit by the introduction of adequate boundary conditions. The circuit plane includes four subdomains: Metal (M), Dielectric (I), Sources (S1 and S2), and switch (SW). The switch subdomain is characterized as a lumped element model in the two states that are on and off. Taking use of the major advantages of the wave concept iterative procedure method offered by the developed fast modal transform (FMT), which is based on the 2D‐FFT algorithm, minimum computation time, and less memory, is needed to calculate the scattering parameters of the switch. Two different MEMS switches are studied that are the cantilever and the air bridge. The simulated results for these examples show very good agreement compared with those obtained by other methods. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1166–1170, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22378
Design approach for realizing two‐dimensional electromagnetic band gap structures
Authors: Shaker George S. A. , Safavi‐Naeini Safieddin
Published: March 2007

This paper presents a simple approach for designing two‐dimensional electromagnetic band gap structures (EBGs). The approach is based on designing a planar band pass filter at a desired center frequency. A simple modification is introduced to the well known design steps of the filter. This modification allows for specifying the high impedance property of the structure, as well as its stop band, using a circuit simulator. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1189–1192, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22382
Closely coupled triple layer hybrid FSS/EBG for increased directivity
Authors: Davies Ryan W. , Morrow Ivor L.
Published: March 2007

A novel frequency selective surface (FSS)/electromagnetic bandgap material (EBG) is presented, which operates as a spectral (frequency domain) and spatial/directional filter. The filter antenna filter (FAF) is shown to increase directivity of a compact EBG monopole antenna in simulation and measurement, resulting in a gain of 15 dB. The FAF can achieve a filtering response equivalent to multiple stacked λ/4 separated FSSs with a triple layer tightly coupled (0.16λ electrical length) surface. Its reflection phase properties exhibit those of an EBG material in its operating frequency making it possible to integrate closely to a radiating source and its reflector. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1125–1128, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22387
Picosecond ultra‐wideband short pulse radiated by antenna arrays
Authors: Ruan Chi , Zhao Wei , Chen Guo‐Fu , Zhu Shao‐Lan , Liu Bai‐Yu , Yang Hong‐Chun , Ruan Cheng‐Li
Published: March 2007

This report presents the experiments to study the characteristics of the picosecond ultra‐wideband pulses coherent radiation. The testing involves bow‐tie horn antennas for both the transmitting and receiving antenna. Sixteen channels of electrical pulses with 290 ps duration and jitter <30 ps have been used. The antenna arrays with various frames of 4 × 1, 4 × 2, 4 × 3, 4 × 4 are employed to radiate the pulses. The receiving antenna measures the electrical field in different distance from the transmitting antennas array. The results show that if the pulses are in coherent condition, the peak power pulse of output by antennas array with N elements are N2of that of the single element antenna. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1148–1151, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22391
Design of compact microstrip diplexer with simple coupled resonators
Authors: Weng Min‐Hang , Wu Hung‐Wei , Shu Kevin
Published: March 2007

This article presents a microstrip diplexer with 2.4/5.2 GHz response by using the simple coupled resonators for reducing the circuit size. Stepped impedance resonator (SIR) can be shared by the two filter channels for the designed diplexer if their fundamental and the higher order frequencies are properly assigned. The diplexer has only three simple resonators which can achieve both two good passbands and effectively reduce the circuit size. Measured results of the proposed diplexer have a good agreement with the electromagnetic (EM) simulated results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1222–1225, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22397
Numerical computation of the Green′s function of a layered media with rough interfaces
Authors: Altuncu Yasemin , Yapar Ali , Akduman Ibrahim
Published: March 2007

A numerical method for the calculation of the Green's function related to a layered media containing rough interfaces is presented. The method is based on the assumption that the perturbations of the rough surfaces from planar ones are objects located at both sides of the planar boundaries. Such an approach allows one to formulate the problem as a scattering of cylindrical or spherical waves from buried bodies, which can be solved by means of MoM. The method is effective for surfaces having a localized and arbitrary roughness. This asymptotic behavior of the Green's function is also derived for large distances. The Green's function obtained here is applied to some direct and inverse scattering problems related to objects buried in a layered background to see its effectiveness and applicability. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1204–1209, 2007; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.22401
Proton transfer ratio, lactate, and intracellular pH in acute cerebral ischemia
Authors: Jokivarsi Kimmo T. , Gröhn Heidi I. , Gröhn Olli H. , Kauppinen Risto A.
Published: March 2007

The amide proton transfer ratio (APTR) from the asymmetry of the Z‐spectrum was determined in rat brain tissue during and after unilateral middle cerebral artery occlusion (MCAo). Cerebral lactate (Lac) as determined by 1H NMR spectroscopy, water diffusion, and T1ρ were quantified as well. Lac concentrations were used to estimate intracellular pH (pHi) in the brain during the MCA occlusion. A decrease in APTR during occlusion indicated acidification from 7.1 to 6.79 ± 0.19 (a drop by 0.3 ± 0.2 pH units), whereas pHi computed from Lac concentration was 6.3 ± 0.2 (a drop by 0.8 ± 0.2 pH units). Despite the disagreement between the two methods in terms of the size of the change in the absolute pHi during ischemia, ΔAPTR and pHi (and Lac concentration) displayed a strong correlation during the MCAo. Diffusion and T1ρ indicated cytotoxic edema following MCA occlusion; however, APTR returned slowly toward the values determined in the contralateral hemisphere post‐ischemia. These data argue that the APTR during ischemia is affected not only by pHi but by other physicochemical factors as well, and indicates different aspects of pathology in the post‐ischemic brain compared to those that influence water diffusion and T1ρ. Magn Reson Med 57:647–653, 2007. © 2007 Wiley‐Liss, Inc.
Concomitant gradient field effects in balanced steady‐state free precession
Authors: Sica Christopher T. , Meyer Craig H.
Published: March 2007

Linear magnetic field gradients spatially encode the image information in MRI. Concomitant gradients are undesired magnetic fields that accompany the desired gradients and occur as an unavoidable consequence of Maxwell's equations. These concomitant gradients result in undesired phase accumulation during MRI scans. Balanced steady‐state free precession (bSSFP) is a rapid imaging method that is known to suffer from signal dropout from off‐resonance phase accrual. In this work it is shown that concomitant gradient phase accrual can induce signal dropout in bSSFP. The spatial variation of the concomitant phase is explored and shown to be a function of gradient strength, slice orientation, phase‐encoding (PE) direction, distance from isocenter, and main field strength. The effect on the imaging signal level was simulated and then verified in phantom and in vivo experiments. The nearest signal‐loss artifacts occurred in scans that were offset from isocenter along the z direction with a transverse readout. Methods for eliminating these artifacts, such as applying compensatory frequency or shim offsets, are demonstrated. Concomitant gradient artifacts can occur at 1.5T, particularly in high‐resolution scans or with additional main field inhomogeneity. These artifacts will occur closer to isocenter at field strengths below 1.5T because concomitant gradients are inversely proportional to the main field strength. Magn Reson Med 57:721–730, 2007. © 2007 Wiley‐Liss, Inc.
Correction for geometric distortion and N/2 ghosting in EPI by phase labeling for additional coordinate encoding (PLACE)
Authors: Xiang Qing‐San , Ye Frank Q.
Published: March 2007

Echo‐planar imaging (EPI) is vulnerable to geometric distortion and N/2 ghosting. These artifacts can be analyzed with an intuitive k‐t space tool, and here we propose a simple method for their correction. In a slightly modified additional EPI acquisition, we sample the k‐t space with a shift in ky by adding a small area to the phase‐encoding (PE) gradient. Physically, the added gradient area creates a relative phase ramp across the object and directly encodes the undistorted original y‐coordinate of each voxel into a phase difference between two distorted complex images, in a method called “phase labeling for additional coordinate encoding” (PLACE). The phase information is then used to map the mismapped signals back to their original locations for geometric and intensity correction. Smoothing of expanded complex data matrix effectively reduces noise in the differential phase map and allows subpixel warping. The two acquired images can also be averaged to effectively suppress the N/2 ghost. Efficient correction for both artifacts can be achieved with three acquisitions. These acquisitions can also serve as reference scans to correct for geometric distortion and/or N/2 ghost artifacts on all images in a time series. The technique was successfully demonstrated in phantom and animal studies. Magn Reson Med 57:731–741, 2007. © 2007 Wiley‐Liss, Inc.
Assessment of the morphological and functional effects of the anti‐angiogenic agent SU11657 on 9L gliosarcoma vasculature using dynamic susceptibility contrast MRI
Authors: Quarles C.C. , Schmainda K.M.
Published: March 2007

To investigate the influence of anti‐angiogenic agents on tumor perfusion, we employed a dynamic susceptibility contrast (DSC)‐MRI method that utilizes a simultaneous gradient‐echo (GE) and spin‐echo (SE) imaging sequence to derive perfusion parameters (blood flow, blood volume, and mean transit time (MTT)). These parameters are sensitive to both the total vasculature (from the GE data) and the microvasculature (from the SE data), and can also provide a measure of the mean vessel diameter (mVD). This approach was used to evaluate the response of a 9L rat brain tumor model to 20 mg/kg and 40 mg/kg of the anti‐angiogenic agent SU11657. The 20‐mg/kg dose significantly decreased mVD by 29.9% (P = 0.02). The 40‐mg/kg dose significantly decreased mVD by 30.4% (P = 0.0007), SE blood volume by 31.8% (P = 0.03), GE and SE MTT by 46.9% (P = 0.03) and 62.0% (P = 0.0005), and increased GE and SE blood flow by 36.6% (P = 0.04) and 52.6% (P = 0.02). These findings demonstrate that DSC‐MRI perfusion methods can play a key role in the noninvasive evaluation of morphological and functional changes in tumor vasculature in response to therapy. Magn Reson Med 57:680–687, 2007. © 2007 Wiley‐Liss, Inc.
Strategies for improved temporal and spectral resolution in in vivo oximetric imaging using time‐domain EPR
Authors: Devasahayam Nallathamby , Subramanian Sankaran , Murugesan Ramachandran , Hyodo Fuminori , Matsumoto Ken‐Ichiro , Mitchell James B. , Krishna Murali C.
Published: March 2007

A radiofrequency (RF) time‐domain electron paramagnetic resonance (EPR) instrument operating at 300, 600, and 750 MHz was used to image tumor hypoxia with high spatial and temporal resolution. A high‐speed signal‐averaging Peripheral Component Interconnect (PCI) board with flexibility in the input signal level and the number of digitized samples per free induction decay (FID) was incorporated into the receive arm of the spectrometer. This enabled effective and fast averaging of FIDs. Modification of the phase‐encoding protocol, and replacement of the General Purpose Interface Bus (GPIB)‐based handshake with a PCI‐based D/A board for direct control of the gradient amplifier decreased the gradient settling and communication overhead times by nearly two orders of magnitude. Cyclically‐ordered phase sequence (CYCLOPS) phase cycling was implemented to correct for pulse imperfections and cancel out unwanted constant signals. These upgrades considerably enhanced the performance of the imager in terms of image collection time, sensitivity, and temporal resolution. We demonstrated this by collecting a large number of 2D images successively and rapidly. The results show that it is feasible to achieve accurate, 2D pO2 maps of tumor hypoxia with 1‐mm2 resolution and minimal artifacts using a set of multigradient images within an acceptable measuring time of about 3 s, and 3D maps can be obtained in less than 1 min. Magn Reson Med 57:776–783, 2007. © 2007 Wiley‐Liss, Inc.
Gradient‐echo and CRAZED imaging for minute detection of Alzheimer plaques in an APPV717I × ADAM10‐dn mouse model
Authors: Faber Cornelius , Zahneisen Benjamin , Tippmann Frank , Schroeder Anja , Fahrenholz Falk
Published: March 2007

Different strategies to visualize amyloid plaques with MRI at 17.6 Tesla were investigated in a novel mouse model of Alzheimer's disease (AD). Large iron‐containing plaques were observed in the thalamus, but cortical plaques did not show iron deposits. Plaques in the thalamus were visualized in vivo with the use of low‐resolution, 3D gradient‐echo (GRE) imaging in 82 s, and with 94‐μm resolution in 34 min. The feasibility of obtaining bright contrast from plaques using the COSY revamped with asymmetric z‐GRE detection (CRAZED) technique was investigated in experiments on fixed brains. The original CRAZED approach provided reduced signal near the plaques (similarly to GRE imaging) and additionally emphasized small structures in the brain. In CRAZED images acquired with mismatched gradients, elevated signal near the plaques was obtained, while background signal was suppressed almost to the noise level. Bright‐contrast images were acquired in 2.6 min with the use of a 2D GRE sequence with slightly mismatched slice refocusing gradients. For future detection of plaques in patients, such bright‐contrast visualization protocols may be of particular value when contrast agents that allow labeling of early plaques with iron oxide nanoparticles become available. Magn Reson Med 57:696–703, 2007. © 2007 Wiley‐Liss, Inc.
Projection reconstruction MR imaging using FOCUSS
Authors: Ye Jong Chul , Tak Sungho , Han Yeji , Park Hyun Wook
Published: March 2007

The focal underdetermined system solver (FOCUSS) was originally designed to obtain sparse solutions by successively solving quadratic optimization problems. This article adapts FOCUSS for a projection reconstruction MR imaging problem to obtain high resolution reconstructions from angular under‐sampled radial k‐space data. We show that FOCUSS is effective for projection reconstruction MRI, since medical images are usually sparse in some sense and the center region of the undersampled radial k‐space samples still provides a low resolution, yet meaningful, image essential for the convergence of FOCUSS. The new algorithm is successfully applied for synthetic data as well as in vivo brain imaging obtained by under‐sampled radial spin echo sequence. Magn Reson Med 57:764–775, 2007. © 2007 Wiley‐Liss, Inc.
Myocardial and liver iron status using a fast T quantitative MRI (TqMRI) technique
Authors: Maris Thomas G. , Papakonstantinou Olympia , Chatzimanoli Vasiliki , Papadakis Alekos , Pagonidis Konstantinos , Papanikolaou Nickolas , Karantanas Apostolos , Gourtsoyiannis Nicholas
Published: March 2007

This work demonstrates the use of a fast and precise methodology for evaluating myocardial and liver iron status in multitransfused thalassemic patients by means of a fast T quantitative MRI (TqMRI) technique. Myocardial and liver T values were calculated in 48 thalassemic patients and 21 normal subjects on a 1.5T MRI system using a breath‐hold 2D single‐slice multiecho gradient‐echo (MEGRE) sequence (16 echoes, TR/TE1/TE16/FA = 160/2.7/37.65 ms/25°). No ECG gating was used. Myocardial T, liver T, and myocardial to muscle (CR/MS) and liver to muscle (LV/MS) T ratios were correlated with serum ferritin concentration (SFC) levels for all patients. Significant differences in myocardial and liver mean T, CR/MS, and LV/MS T values between patients and normal subjects were found (P < 0.0005). Differences in paraspinous muscle mean T values between patients and normal subjects were not significant. Myocardial T and CR/MS T values were not correlated with SFC levels. Liver T and LV/MS T values were significantly correlated with SFC (r = 0.540, P < 0.0005). Myocardial T and CR/MS T values were not correlated with either liver T or LV/MS T values, respectively. We conclude that myocardial and liver iron deposition can be evaluated using the fast non‐ECG‐gated TqMRI technique. Magn Reson Med 57:742–753, 2007. © 2007 Wiley‐Liss, Inc.
Phantom‐based evaluation of geometric distortions in functional magnetic resonance and diffusion tensor imaging
Authors: Mattila Seppo , Renvall Ville , Hiltunen Jaana , Kirven Douglas , Sepponen Raimo , Hari Riitta , Tarkiainen Antti
Published: March 2007

Phantom‐based evaluation of geometric distortions in functional MRI and diffusion tensor imaging (DTI) was investigated. An acrylic water‐filled phantom with a grid structure was designed and manufactured to provide accurate geometric information over the volume measured in human brain imaging. The grid structures were well detected in data acquired using a 3‐T MRI scanner with echo‐planar imaging (EPI) sequences commonly applied in functional MRI and DTI. A method for quantifying distortions in the phantom data was presented and applied for the images. The validity of the phantom for EPI was evaluated by quantitatively comparing the distortions present in and induced by the phantom and a human brain when imaged under identical conditions. The results suggest that the new phantom can reveal geometric distortions easily undermined by standard MRI phantoms. For example, prominent variability in the distortions was found as a function of the orientation of the diffusion‐sensitizing gradient. Possible future applications for this type of phantom include quality assurance and calibration of the hardware and software used in EPI‐based functional MRI and DTI. Magn Reson Med 57:754–763, 2007. © 2007 Wiley‐Liss, Inc.
A branch‐and‐regret heuristic for stochastic and dynamic vehicle routing problems
Authors: Hvattum Lars Magnus , Løkketangen Arne , Laporte Gilbert
Published: March 2007

This paper describes a new Branch‐and‐Regret Heuristic for a class of dynamic and stochastic vehicle routing problems. This work is motivated by a real‐life problem faced by a major transporter in Norway. The heuristic uses stochastic information during the solution process. The new method is shown to be superior to previous heuristics that are uniquely based on a pure dynamic approach. The proposed heuristic is well suited to problems containing stochastic customers, stochastic demands, or both. © 2007 Wiley Periodicals, Inc. NETWORKS, Vol. 49(4), 330–340 2007
A linearly conforming point interpolation method (LC‐PIM) for three‐dimensional elasticity problems
Authors: Zhang G. Y. , Liu G. R. , Wang Y. Y. , Huang H. T. , Zhong Z. H. , Li G. Y. , Han X.
Published: March 2007

Linearly conforming point interpolation method (LC‐PIM) is formulated for three‐dimensional elasticity problems. In this method, shape functions are generated using point interpolation method by adopting polynomial basis functions and local supporting nodes are selected based on the background cells. The shape functions so constructed have the Kronecker delta functions property and it allows straightforward imposition of point essential boundary conditions. Galerkin weak form is used for creating discretized system equations, and a nodal integration scheme with strain‐smoothing operation is used to perform the numerical integration. The present LC‐PIM can guarantee linear exactness and monotonic convergence for the numerical results. Numerical examples are used to examine the present method in terms of accuracy, convergence, and efficiency. Compared with the finite element method using linear elements, the LC‐PIM can achieve better efficiency, and higher accuracy especially for stresses. Copyright © 2007 John Wiley & Sons, Ltd.
Evaluating adverse events after vaccination in the Medicare population
Authors: Burwen Dale R. , La Voie Lawrence , Braun M. Miles , Houck Peter , Ball Robert
Published: March 2007

Purpose

Post‐licensure observational studies using large linked databases can provide important data about whether adverse events are associated with vaccines, but databases that have been used may not have sufficient statistical power to examine rare events, and may underrepresent the elderly. We assessed the utility of Medicare data for evaluating adverse events after influenza and pneumococcal vaccines, by using an example involving selected clinical conditions, and evaluating aspects of data quality relevant to vaccine safety analyses.

Methods

We used 2001 data from the National Claims History File and Enrollment Database to determine if hospitalization for urinary tract infection (not likely associated with vaccination) or for cellulitis and abscess of the upper arm and forearm is associated with vaccination.

Results

For influenza vaccine, the 7‐day period after vaccination did not demonstrate an elevation in hospitalization with cellulitis and abscess of the upper arm and forearm; for pneumococcal vaccine, a clear peak was evident. No increase in urinary tract infection was found after either influenza or pneumococcal vaccine. Having a prior Medicare claim for pneumococcal vaccine within 5 years was a risk factor for hospitalization with cellulitis and abscess of the upper arm and forearm (relative risk, 2.6; 95% confidence limits (CL), 1.3, 5.0).

Conclusions

Medicare data are a useful source for evaluating adverse events after vaccination. Screening analyses can be performed using administrative data, but medical record review to validate diagnoses will often be needed for rigorous study of vaccine‐adverse event associations. Published in 2007 by John Wiley & Sons, Ltd.
The effect of a secondary process on the course of polymer crystallisation
Authors: Hay J. N. , Booth A.
Published: March 2007

The possibility that the presence of several processes occurring during the crystallisation of polymers may account for anomalous constant fractional values of the Avrami exponent is reconsidered, and for various reasons rejected. Experimental isotherms exhibit systematic variations when analysed as two stage processes, which can only be accounted for by fractional n values of no theoretical significance. An explanation for these deviations must be sought in the mechanism of spherulitic crystallisation, and in particular the mechanism of branching and impurity rejection of the basic fibrillar units.
Reaction between chlorophosphazenes and some alkyl phosphates: Formation of temperature‐stable thermosetting materials
Authors: Emblem H. G. , Fothergill E. W.
Published: March 2007

The reaction between chlorophosphazenes and triethyl, tri‐n‐butyl and acid ethyl phosphates has been studied as a means of preparing temperature‐stable thermosetting resinous materials. Ethyl or n‐butyl chlorides were eliminated (together with hydrogen chloride in the case of acid ethyl phosphate) and thermosetting resinous products were obtained. The products are film forming when stoved in air. Asbestos laminates, which retain up to 64% of their strength when heated to 500 °C for 50 h in air, have been made with the thermosetting resinous products obtained from the reaction between a chlorophosphazene and triethyl or tri‐n‐butyl phosphates.