bluuebunny/crossref_metadata_2025 huggingface dataset:
X‐band multi function GaAs MMIC for T/R modules in smart antenna applications
Authors: Giannini Franco , Limiti Ernesto , Longhi Patrick E. , Serino Antonio
Published: March 2008

This article presents the design, measurement, and test of a MMIC for the front‐end section of a composite multielement radiating system. The MMIC is composed of a 3‐BIT modified constant phase digital attenuator, a switch, and a pair of amplifiers for TX/RX operation. A uniform linear array can be realized attaching 15 MMICs to the T/R radiating elements. The so obtained array's co‐polarisation pattern is presented. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1667–1673, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23443
Microwave photonic filter inserting an electro‐absorption modulator in a variable polarization beam splitter‐based SAGNAC fiber loop
Authors: Ning G. , Shum P. , Zhou J. Q.
Published: March 2008

A coherence‐free microwave photonic filter configuration is presented. It is designed by using a Sagnac interferometer consisting of a variable polarization beam splitter and an electro‐absorption modulator. The variable polarization beam splitter generates π/2 phase difference between the clockwise and counterclockwise waves propagating inside the fiber loop interferometer. Measured results match closely with the theoretical analysis and demonstrate a robust notch filter response. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1665–1667, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23444
A novel dual‐frequency unequal Wilkinson power divider
Authors: Feng Cong , Zhao Gang , Liu Xu‐Feng , Zhang Fu‐Shun
Published: March 2008

This article presents the design of a novel dual‐frequency unequal Wilkinson power divider. This unequal power divider fulfills an arbitrary power split and all the other features of a conventional Wilkinson unequal power divider simultaneously at two arbitrary frequencies. The structure of this power divider and the formulas used to determine the design parameters have been given. Both simulated and measured results of the dual‐frequency unequal Wilkinson power divider are presented to validate our proposed idea. Good experimental performances of the proposed power divider, including an arbitrary power split and a good isolation between the output ports at both frequencies are obtained. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1695–1699, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23447
A 23‐GHz capacitive‐degeneration LC VCO with a FOM of −199 dBc/Hz
Authors: Lee J. Y. , Lee S. H. , Kim H. , Yu H. K.
Published: March 2008

In this article, we presents a fully differential 23‐GHz capacitively emitter‐degeneration double cross‐coupled LC‐tank VCO. The proposed capacitive‐degeneration negative‐resistance cell has higher ftrans and lower input capacitance than conventional cross‐coupled pairs at millimeter‐wave band. The proposed capacitive‐degeneration LC VCO shows low phase noise of −105 dBc/Hz at 100 kHz offset from 23 GHz carrier and wide tuning range of 20.8–24.2 GHz, and consumes 10 mA current. The proposed 23 GHz LC VCO shows a good FOM of −199 dBc/Hz. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1688–1690, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23453
Broadband Fabry‐Perot resonator printed antennas using FSS superstrate with dissimilar size
Authors: Liu ZhenGuo , Zhang WenXun , Fu DaoLin , Gu YingYing , Ge ZhiChen
Published: March 2008

In this paper, the broadband Fabry‐Perot resonator antenna composed of single‐layer FSS superstrate with dissimilar size square patch fed by U‐slotted patch is proposed, which is validated by two cases of samples. It is demonstrated that the common bandwidth for (3 dB directivity‐drop and −10 dB returned loss of the Fabry‐Perot resonator antenna with the tapered FSS superstrate increases by 7.99% to 12.2% for two different cases, as compared to that of previously single layer FSS with similar size. At the same time the side‐lobe level of antenna can also be improved.The simulated and measured results are good agreement each other. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1623–1627, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23456
Singularity treatment for integral equations in electromagnetic scattering using Monte Carlo integration technique
Authors: Mishra Mrinal , Gupta Nisha
Published: March 2008

A new numerical method is proposed for the analysis of metallic scatterers which can take care of the singular integrals arising in the Method of Moments (MoM) solution for determining the current distribution on the metallic scatterers. The method involves Monte Carlo Integration (MCI) technique in solving the Electric Field Integral Eq. (EFIE). The unknown current distribution is represented in terms of the entire domain polynomial basis functions. It is found that the proposed method is capable of removing the singularity problem arising in the MoM solution of the EFIE very easily and efficiently. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1619–1623, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23457
Divide‐by‐3 injection‐locked frequency divider implemented with active inductor
Authors: Jang Sheng‐Lyang , Tai Chia‐Wei , Lee Chien‐Feng
Published: March 2008

This article presents a wide locking‐range divide‐by‐3 injection‐locked frequency divider (ILFD) employing tunable active inductors (TAIs), which are used to extend the locking range and to reduce die area. The CMOS ILFD is based on a voltage‐controlled oscillator (VCO) with cross‐coupled switching pairs and TAI‐C tanks, and was fabricated in the 0.18‐μm 1P6M CMOS technology. The divide‐by‐3 function is performed by injecting differential signal to the gates of two injection MOSFETs with the drains connected to the VCO outputs and with grounded sources. Measurement results show that at the supply voltage of 1.8 V, the divider free‐running frequency is tunable from 1.20 to 1.284 GHz, and at the incident power of 4 dBm the locking range is about 1.9 GHz (45.2%), from the incident frequency 3.3 to 5.2 GHz. The core power consumption is 12.96 mW. The die area is 0.45 × 0.513 mm2. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1682–1685, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23458
An experimental realization of a fully adaptive smart antenna
Authors: Azaro R. , Ioriatti L. , Martinelli M. , Benedetti M. , Massa A.
Published: March 2008

In this letter, the structure of the prototype of a smart antenna working in the 2.4‐GHz band is described. The radiating structure is composed by an eight‐element linear array with a finite reflecting plane and its adaptive behavior is obtained by means of a set of electronically driven vector modulators that control the array weights. The antenna system is equipped with a control software based on a particle swarm optimizer algorithm that enables the system to adapt to the complex interference scenario. A selected set of numerical and experimental results are reported and discussed to assess the effectiveness of the proposed architecture. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1715–1716, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23459
A novel compact branch‐line coupler using four coupled transmission lines
Authors: Nosrati Mehdi , Karbasi Valashani Salman
Published: March 2008

A compact branch line coupler (BLC) using four coupled transmission lines is introduced. The loaded part of the proposed model has a same performance with a cascade two unit elements and it is equaled by a quarter wavelength line. The quarter wavelength lines of each branch in the conventional coupler are replaced by an equivalent circuit composed of a four coupled transmission line and two transmission lines. A compact branch‐line coupler (BLC) is designed, analyzed, and tested using this technique. The size reduction is about 65% with comparable performance. The measurement results are in good agreement with the theoretical ones. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1712–1714, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23460
Electronically tunable pulse generator with programmable pulse repetition rate for 6.0 8.5 GHz ultra‐wideband communications
Authors: Seifarth Christoph , Heynicke Ralf G. , Scholl Gerd
Published: March 2008

An ultra‐wideband (UWB) carrier based pulse generator with tunable carrier frequency for 6.0–8.5 GHz UWB communications compliant to European and United States indoor regulations is presented. Pulses with a pulsewidth of 2.5 ns are generated using D‐type flip‐flops and are upconverted by a frequency mixer and a tunable voltage controlled oscillator providing a carrier frequency of 6.6–7.9 GHz. For the generation of pulse trains, a pulse repetition rate of up to 333 MHz is realized using a programmable clock multiplier offering optional spread spectrum clocking to smooth the output spectrum. Suitable modulation formats are pulse position modulation and on‐off‐keying which can be easily implemented by changing baseband data. Measurement results in time domain and frequency domain are presented showing the functionality of the fabricated device and its conformity to European and US UWB regulations. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1649–1651, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23462
Linear optical amplifier‐based semiconductor fiber ring laser with 93‐nm tuning range
Authors: Qureshi K. K. , Tam H. Y.
Published: March 2008

We propose a simple configuration of a traveling wave tunable semiconductor fiber ring laser. The proposed laser can be tuned over 93 nm with an output power of 1.3 dBm using a thin film fiber Fabry Pérot filter. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1702–1704, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23469
Interdevice isolation characteristics for design and fabrication of 60‐GHz WPAN SoCs
Authors: Kim Sungil , Lee Chul‐Wook , Yun Suck‐Won , Kang Kwang‐Yong , Lee Hai‐Young
Published: March 2008

The high interdevice isolation levels is one of the key technologies in the design and fabrication of 60‐GHz WPAN SoC. To obtain proper interdevice isolation levels, we have analyzed and measured substrate coupling effects with various isolation techniques like a trench and implant structure. From the analyzed and measured results, the feasibility of the implant has confirmed to be applicable to the mm‐wave SoC, and also derived an equivalent circuit form these results, which can be helpful to the design and fabrication of the 60‐GHz WPAN SoC. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1699–1702, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23470
Reconfigurable un‐equal division power divider with the compact size for high efficiency power amplifiers
Authors: Jeong Jinho , Hyeong Park Chan
Published: March 2008

In this letter, a reconfigurable un‐equal division two‐way power divider with the compact size is presented for high efficiency power amplifiers. It is based on the Wilkinson power divider of which the quarter‐wave long lines are replaced by coupled lines. Two ends of each coupled line are terminated with switches which provide the two modes of operation, or two‐way power divider and one‐way transmission line. These switches are used to adjust the characteristics of the coupled line in order to allow the good insertion and return loss performance in both modes. At the design frequency of 2.14 GHz, the fabricated 1:2 power divider showed the input return loss (S11) of −23.0 dB, isolation (S32) of −27.2 dB, and insertion loss of −5.05 dB (S21) and −2.25 dB (S31) in the power divider mode. The insertion loss (S21) was measured to be −0.90 dB with the return loss (S11) of −21.1 dB in the power transmission mode. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1662–1665, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23471
Iterative GRAPPA (iGRAPPA) for improved parallel imaging reconstruction
Authors: Zhao Tiejun , Hu Xiaoping
Published: March 2008

In this work an iterative reconstruction method based on generalized autocalibrating partially parallel acquisitions (GRAPPA) reconstruction is introduced. In the new method the reconstructed lines are used to reestimate and refine the weights from all the acquired data by applying the GRAPPA procedure iteratively with regularization. Both phantom and in vivo MRI experiments demonstrated that, compared to GRAPPA, the iterative approach reduces parallel imaging artifacts and permits high‐quality image reconstruction with a relatively small number of calibration lines and slight changes of GRAPPA weights. Magn Reson Med 59:903–907, 2008. © 2008 Wiley‐Liss, Inc.
Pittfalls of MRI measurement of white matter perfusion based on arterial spin labeling
Authors: van Gelderen P. , de Zwart J.A. , Duyn J.H.
Published: March 2008

Although arterial spin labeling (ASL) MRI has been successfully applied to measure gray matter (GM) perfusion in vivo, accurate detection of white matter (WM) perfusion has proven difficult. Reported literature values are not consistent with each other or with perfusion measured with other modalities. In this work, the cause of these inconsistencies is investigated. The results suggest that WM perfusion values are substantially affected by the limited image resolution and by signal losses caused by the long transit times in WM, which significantly affect the label. From gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) bolus‐tracking experiments (N = 6), it is estimated that the transit time can be several seconds long in deep WM. Furthermore, simulations show that even at a spatial resolution of 7 μl voxel size, contamination by the GM signals can exceed 40% of the actual WM signal. From 10‐min long flow‐sensitive alternating inversion recovery ASL (FAIR‐ASL) measurements at 3T in normal subjects (N = 7), using highly sensitive detectors, it is shown that single‐voxel (7 μl) deep WM perfusion values have an signal‐to‐noise ratio (SNR) less than 1. The poor sensitivity and heterogeneous transit time limit the applicability of ASL for measurement of perfusion in WM. Magn Reson Med 59:788–795, 2008. © 2008 Wiley‐Liss, Inc.
Robust MRI brain tissue parameter estimation by multistage outlier rejection
Authors: Manjón José V. , Tohka Jussi , García‐Martí Gracian , Carbonell‐Caballero José , Lull Juan J. , Martí‐Bonmatí Luís , Robles Montserrat
Published: March 2008

This article addresses the problem of the tissue type parameter estimation in brain MRI in the presence of partial volume effects. Automatic MRI brain tissue classification is hampered by partial volume effects that are caused by the finite resolution of the acquisition process. Due to this effect intensity distributions in brain MRI cannot be well modeled by a simple mixture of Gaussians and therefore more complex models have been developed. Unfortunately, these models do not seem to be robust enough for clinical conditions, as the quality of the tissue classification decreases rapidly with the image quality. Also, the application of these methods for pathological images with unmodeled intensities (e.g. MS plaques, tumors, etc.) remains uncertain. In the present work a new robust method for brain tissue characterization is presented, treating the partial volume affected voxels as outliers of the pure tissue distributions. The proposed method estimates the tissue characteristics from a reduced set of intensities belonging to a particular pure tissue class. This reduced set is selected by using a trimming procedure based on local gradient information and distributional data. This feature makes the method highly tolerant of a large amount of unexpected intensities without degrading its performance. The proposed method has been evaluated using both synthetic and real MR data and compared with state‐of‐the‐art methods showing the best results in the comparative. Magn Reson Med 59:866–873, 2008. © 2008 Wiley‐Liss, Inc.
Magnetic resonance imaging of neuronal and glial swelling as an indicator of function in cerebral tissue slices
Authors: Stroman P.W. , Lee A.S. , Pitchers K.K. , Andrew R.D.
Published: March 2008

Here we demonstrate a new basis of signal change in magnetic resonance imaging (MRI) related to neuronal function, independent of blood oxygenation or flow. Time series MRI data acquired from living, superfused brain slices of adult rats revealed that the signal intensity reversibly increased with depolarization evoked by briefly elevating extracellular K+. This was presumably a consequence of increased tissue water in the intracellular compartment. Reversible increases in light transmittance (LT) demonstrating a similar time course in response to K+elevation supported cellular swelling as generating the MRI signal intensity changes. This was confirmed by reversibly swelling cells in the slice under hypoosmotic challenge, which increased both MRI and LT signals with an identical time course. Conversely, shrinking cells under hyperosmotic challenge reversibly decreased the MRI and LT signals. We propose that specific MRI of neuronal function (fMRI) signals detected under identical parameters during predominantly proton‐density‐weighted fMRI of the spinal cord can now be explained by neuronal and glial swelling in activated central nervous system (CNS) regions. These observations demonstrate the biophysical basis of the fMRI contrast mechanism that has been termed “signal enhancement by extravascular water protons,” or SEEP. Magn Reson Med 59:700–706, 2008. © 2008 Wiley‐Liss, Inc.
Cross‐validation‐based kernel support selection for improved GRAPPA reconstruction
Authors: Nana Roger , Zhao Tiejun , Heberlein Keith , LaConte Stephen M. , Hu Xiaoping
Published: March 2008

The extended version of the generalized autocalibrating partially parallel acquisition (GRAPPA) technique incorporates multiple lines and multiple columns of measuredk‐space data to estimate missing data. For a given accelerated dataset, the selection of the measured data points for fitting a missing datum (i.e., the kernel support) that provides optimal reconstruction depends on coil array configuration, noise level in the acquired data, imaging configuration, and number and position of autocalibrating signal lines. In this work, cross‐validation is used to select the kernel support that best balances the conflicting demands of fit accuracy and stability in GRAPPA reconstruction. The result is an optimized tradeoff between artifacts and noise. As demonstrated with experimental data, the method improves image reconstruction with GRAPPA. Because the method is simple and applied in postprocessing, it can be used with GRAPPA routinely. Magn Reson Med 59:819–825, 2008. © 2008 Wiley‐Liss, Inc.
Water chemical shift in 1H NMR of red cells: Effects of pH when transmembrane magnetic susceptibility differences are low
Authors: Larkin Timothy J. , Bubb William A. , Kuchel Philip W.
Published: March 2008

The 1H magic angle spinning (MAS) NMR spectrum of water in erythrocyte suspensions shows peaks from each of the intracellular and extracellular water pools. The splitting is a true chemical shift and is brought about by the elimination of water exchange under MAS conditions due to physical separation of the two water populations. The size of the chemical shift difference is determined by the concentration of intracellular protein affecting the average extent of hydrogen bonding of water. We present here a model of the chemical shift behavior for water in erythrocytes under normal high‐resolution NMR conditions based on results from MAS experiments on these cells exposed to different pH and osmotic conditions. The model accurately predicts the chemical shift of water for a static sample, and the results demonstrate that in high‐resolution NMR experiments the chemical shift of water will appear to be invariant if differences in magnetic susceptibility across the cell membrane are minimal (<10% of the magnetic susceptibility of water). Thus, changes in the shape and chemical shift of the water resonance are not due to pH changes in the physiological range. The findings are fundamental to an interpretation of the mechanism of chemical shift effects on the water resonance that may occur in functional MRI. Magn Reson Med 59:707–711, 2008. © 2008 Wiley‐Liss, Inc.
Self‐calibrating GRAPPA operator gridding for radial and spiral trajectories
Authors: Seiberlich Nicole , Breuer Felix , Blaimer Martin , Jakob Peter , Griswold Mark
Published: March 2008

Self‐calibrating GRAPPA operator gridding (GROG) is a method by which non‐Cartesian MRI data can be gridded using spatial information from a multichannel coil array without the need for an additional calibration dataset. Using self‐calibrating GROG, the non‐Cartesian datapoints are shifted to nearby k‐space locations using parallel imaging weight sets determined from the datapoints themselves. GROG employs the GRAPPA Operator, a special formulation of the general reconstruction method GRAPPA, to perform these shifts. Although GROG can be used to grid undersampled datasets, it is important to note that this method uses parallel imaging only for gridding, and not to reconstruct artifact‐free images from undersampled data. The innovation introduced here, namely, self‐calibrating GROG, allows the shift operators to be calculated directly out of the non‐Cartesian data themselves. This eliminates the need for an additional calibration dataset, which reduces the imaging time and also makes the GROG reconstruction more robust by removing possible inconsistencies between the calibration and non‐Cartesian datasets. Simulated and in vivo examples of radial and spiral datasets gridded using self‐calibrating GROG are compared to images gridded using the standard method of convolution gridding. Magn Reson Med 59:930–935, 2008. © 2008 Wiley‐Liss, Inc.
Quantitative mapping of ventilation‐perfusion ratios in lungs by 19F MR imaging of T1 of inert fluorinated gases
Authors: Adolphi Natalie L. , Kuethe Dean O.
Published: March 2008

A new method is presented for quantitative mapping of ventilation‐to‐perfusion ratios (VA/Q) in the lung: MRI of the 19F longitudinal relaxation time (T1) of an inert fluorinated gas at thermal polarization. The method takes advantage of the dependence of the 19F T1 on the local SF6 partial pressure, which depends on the local value of VA/Q. In contrast to hyperpolarized noble gases, with very long T1s, the T1 of SF6 in mammal lungs is 0.8–1.3 ms. Thus, rapid signal averaging overcomes the low thermal equilibrium polarization. T1 imaging of a phantom consisting of four different SF6/air mixtures with known T1 values validates the modified Look‐Locker T1 imaging sequence. To demonstrate the method in vivo, partial obstruction of the left bronchus was attempted in three rats; 3D free induction decay (FID)‐projection T1 images (2 mm isotropic resolution) revealed obstructed ventilation in two of the animals. In those images, ≈1700 lung voxels contained sufficient SF6 for analysis and T1 was determined in each voxel with a standard error of 8–10%. For comparison, independent VA/Q images of the same animals were obtained using a previously described SF6 MRI technique, and good agreement between the two techniques was obtained. Relative to the previous technique the resolution achieved using the T1 method is lower (for similar VA/Q precision and imaging time); however, the T1 method offers the potential advantages of eliminating the need for image coregistration and allowing patients with impaired lung function to breathe a 70% O2 gas mixture during the entire imaging procedure. Magn Reson Med 59:739–746, 2008. © 2008 Wiley‐Liss, Inc.
A new model of resorbable device degradation and drug release ‐ part I: zero order model
Authors: Arosio Paolo , Busini Valentina , Perale Giuseppe , Moscatelli Davide , Masi Maurizio
Published: March 2008

BACKGROUND: Within the field of resorbable devices, recent years have seen an increased demand for better reliability from drug delivery systems and resorbable polymer degradation control, causing researchers to abandon trial‐and‐error approaches towards model‐based methods. In this context, we developed a lumped‐parameters zero‐order model for the degradation of resorbable polymeric drug release systems. Such a model is thought to be applicable in the design of specific devices based on the expected degradation time and drug delivery rates, as it is based on a ‘shrinking core’ approach and takes into account the main physicochemical parameters involved in polymer degradation, in drug release and in mechanical strength prediction, all independently estimated.

RESULTS: The model, based on conservation equations, leads to numerically solved ordinary differential equations, the predictions of which were verified through literature data. Data of different authors and various systems were satisfactorily matched by model predictions, thus confirming the reliability of parameter estimation procedures.

CONCLUSION: The present model is among the very few that completely address all aspects involved in device degradation and drug delivery altogether, and thus represents a step ahead with respect to current available solutions, firmly enforcing itself into the ongoing debate on the modelling of degradation and release behaviour. Copyright © 2008 Society of Chemical Industry
Facile syntheses of 4‐vinyl‐1,2,3‐triazole monomers by click azide/acetylene coupling
Authors: Takizawa Kenichi , Nulwala Hunaid , Thibault Raymond J. , Lowenhielm Peter , Yoshinaga Kohji , Wooley Karen L. , Hawker Craig J.
Published: March 2008

Synthetic strategies for the preparation of a new family of vinyl monomers, 4‐vinyl‐1,2,3‐triazoles, have been developed. These monomers are noteworthy as they combine the stability and aromaticity of styrenics with the polarity of vinylpyridines and the structural versatility of acrylate/methacrylate derivatives. To enable the wide adoption of these unique monomers, new methodologies for their synthesis have been elaborated which rely on Cu‐catalyzed azide/acetylene cycloaddition reactions—“click chemistry”—as the key step, with the vinyl substituent being formed by either elimination or Wittig‐type reactions. In addition, one‐pot “click” reactions have been developed from alkyl halides, which allow for monomer synthesis without isolation of the intermediate organic azides. The high yield and facile nature of these procedures has allowed a library of new monomers including the parent compound, 1‐H‐4‐vinyl‐1,2,3‐triazole, to be prepared on large scales. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2897–2912, 2008
Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/ZnCoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure
Authors: Sun Xue‐Ke , Zhang Xing‐Hong , Liu Fei , Chen Shang , Du Bin‐Yang , Wang Qi , Fan Zhi‐Qiang , Qi Guo‐Rong
Published: March 2008

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn3[Co(CN)6]2 (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ∼40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO2 content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h−1, and apparent efficiency of 7.5 kg polymer/g ZHCC (∼24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (Mn) of ∼10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO2 units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with ZnCoIII DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008
Effect of interaction between poly(ethylene terephthalate) and carbon nanotubes on the morphology and properties of their nanocomposites
Authors: Yoo Hye Jin , Jung Yong Chae , Cho Jae Whan
Published: March 2008

Poly(ethylene terephthalate) (PET) nanocomposites were prepared by melt‐extruding mixtures of PET and functionalized multiwalled carbon nanotubes (MWNTs) with some interaction with PET molecules. For the functionalization of MWNTs, benzyl isocyanate and phenyl isocyanate with different molecular flexibility were employed on the surface of the MWNTs via chemical modification, respectively. The reaction for functionalization of MWNTs was confirmed by FTIR and transmission electron microscopy (TEM) measurements. TEM observations indicated that both benzyl and phenyl isocyanate groups covered the surface of the MWNTs after functionalization. The PET nanocomposites containing isocyanate groups showed improved mechanical properties, including the tensile strength and tensile modulus, compared with those with pristine and acid‐treated nanotubes. These improvements were ascribed to π–π interactions between the aromatic rings of PET molecules and the isocyanate group in MWNTs. The functionalized MWNTs showed a better dispersion of carbon nanotubes in the matrix polymer and a different fractured cross‐section morphology in scanning electron microscope measurements relative to the pristine MWNTs. The crystallinity of the functionalized MWNT‐PET nanocomposites was significantly higher than that of the pristine and acid‐treated MWNTs. FTIR results indicated that the presence of carbon nanotubes induced trans‐conformation of PET chains, and trans conformation was particularly dominant in PET composites incorporating MWNT‐phenyl. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 900–910, 2008
Crystallization and melting behaviors of isotactic polypropylene nucleated with compound nucleating agents
Authors: Zhang Yue‐Fei
Published: March 2008

Crystallization and melting behaviors of isotactic polypropylene (iPP) nucleated with compound nucleating agents of sodium 2,2′‐methylene‐bis (4,6‐di‐tert‐butylphenyl) phosphate (hereinafter called as NA40)/dicyclohexylterephthalamide (hereinafter called as NABW) (weight ratio of NA40 to NABW is 1:1) were studied by differential scanning calorimetry and wide‐angle X‐ray diffraction (WAXD), the relative β‐amount of iPP nucleated with these compound nucleating agents was also calculated in Turner‐Jones equation by using wide‐angle X‐ray diffraction data. Under isothermal crystallization, there exists a temperature range favorable for formation of β‐iPP. When the concentration of compound nucleating agents is 0.2 wt %, the temperature range is from 100 to 140 °C. While in nonisothermal crystallization, lower cooling rate is favorable for form of β‐iPP and the relative β‐amount of iPP increases with the decreasing of cooling rate in crystallization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 911–916, 2008
Efficacy of five selected acaricides against Tetranychus urticae (Acari: Tetranychidae) and their side effects on relevant natural enemies occurring in citrus orchards
Authors: Urbaneja Alberto , Pascual‐Ruiz Sara , Pina Tatiana , Abad‐Moyano Raquel , Vanaclocha Pilar , Montón Helga , Dembilio Oscar , Castañera Pedro , Jacas Josep A.
Published: March 2008

BACKGROUND: Three groups of natural enemies are fundamental in citrus IPM in Spain: coccinellid and phytoseiid predators and hymenopteran parasitoids. Tetranychus urticae Koch is an important pest affecting citrus, for which biological control has not yet been achieved; therefore, acaricides are commonly used to control it. The goal of this study was to measure the efficacy of different acaricides on this mite and their side effects on three natural enemies relevant for citrus (Cryptolaemus montrouzieri Mulsant, Neoseiulus californicus McGregor and Aphidius colemani Viereck).

RESULTS: Some products proved highly effective against T. urticae and harmless to A. colemani (mineral oil, tebufenpyrad, clofentezine and fenazaquin). However, almost all products tested were slightly harmful for both the predators considered. Fenazaquin was even moderately harmful for N. californicus.

CONCLUSION: Further studies, like that presented here, are necessary to gain a better understanding of integrating biological and chemical controls. When considering both efficacy and side effects on beneficial arthropods, the best options would seem to be mineral oil, tebufenpyrad and clofentezine. However, it is urgent to complete testing of the side effects of the acaricides used in citrus. This question is crucial if the fact that two recently introduced Tetranychidae are being controlled in citrus by chemical means exclusively is considered. Copyright © 2008 Society of Chemical Industry
Simulating trends in reaction path geometry as a function of external fields. A generalized electronic diabatic model for two‐dimensional energy surfaces
Authors: Arteca Gustavo A. , Rank Jean Pierre , Tapia Orlando
Published: March 2008

We introduce a protocol to represent quantum states as a linear superposition of model electronic diabatic basis states coupled in an external (static) electric field. By considering an entire family of these models, we uncover trends in reaction‐path geometry and the topology of potential‐energy surfaces, including all those that can be realized in a two‐dimensional configurational space. Our approach can be used as a tool to model the key parameters (e.g., diabatic basis states, external field intensity) that yield desired geometrical characteristics in an actual potential energy surface. In this work, external agents such as laser fields, or a group of neighboring charges, are regarded as essential requirements to prompt, or trigger, the occurrence of a chemical process. In these cases, reaction path geometry can be modulated externally so as to yield processes that would appear to occur far from gas‐phase geometries. This phenomenology is intrinsically nonadiabatic. Our present approach accounts for the possibility of such features, i.e., the occurrence of quantum states whose electronic structures resemble products, while at geometries that are more similar to those of reactants. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
A generic method to detect electrophilic intermediates using isotopic pattern triggered data‐dependent high‐resolution accurate mass spectrometry
Authors: Lim Heng‐Keang , Chen Jie , Cook Kevin , Sensenhauser Carlo , Silva Jose , Evans David C.
Published: March 2008

A need still exists for a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method that can detect broad classes of glutathione (GSH) conjugates and provide characterization of their structures. We now describe the development of a method that multiplexes high‐resolution accurate mass analysis with isotope pattern triggered data‐dependent product ion scans, for simultaneous detection and structural elucidation of GSH conjugates within a single analysis using a LTQ/Orbitrap. This method was initially developed to detect GSH conjugates generated from incubating 10 µM test compound with pooled human liver microsomes fortified with NADPH‐regenerating system and a 2:1 ratio of 5 mM glutathione and [13CN‐Gly]glutathione. The GSH conjugates were detected by isotope search of mass defect filtered and control subtracted full scan accurate MS data using MetWorks software. This was followed by elucidation of reactive intermediate structures using chemical formulae for both protonated molecules and their product ions from accurate masses in a single analysis. The mass accuracies measured for the precursor and product ions by the Orbitrap were <2 ppm in external mass calibration mode. Successful detection and characterization of GSH conjugates of acetaminophen, tienilic acid, clozapine, ticlopidine and mifepristone validated this method. In each case, the detected GSH conjugates were within the top five hits by isotope search. This method also has a broader detection capability since it is independent of the collision‐induced dissociation behavior of the GSH conjugates. Furthermore, this method is amenable to a broad class of reactive intermediate trapping agents as exemplified by the simultaneous detection and structural elucidation of the cyano‐N‐methylene iminium ion conjugates of verapamil and its O‐desmethyl metabolites, which we report for the first time. In addition to the chemically tagged reactive intermediates, this method also provides information on stable metabolites from the full scan accurate MS data. Copyright © 2008 John Wiley & Sons, Ltd.
Probing genetic algorithms for feature selection in comprehensive metabolic profiling approach
Authors: Zou Wei , Tolstikov Vladimir V.
Published: March 2008

Six different clones of 1‐year‐old loblolly pine (Pinus taeda L.) seedlings grown under standardized conditions in a green house were used for sample preparation and further analysis. Three independent and complementary analytical techniques for metabolic profiling were applied in the present study: hydrophilic interaction chromatography (HILIC‐LC/ESI‐MS), reversed‐phase liquid chromatography (RP‐LC/ESI‐MS), and gas chromatography all coupled to mass spectrometry (GC/TOF‐MS). Unsupervised methods, such as principle component analysis (PCA) and clustering, and supervised methods, such as classification, were used for data mining. Genetic algorithms (GA), a multivariate approach, was probed for selection of the smallest subsets of potentially discriminative classifiers. From more than 2000 peaks found in total, small subsets were selected by GA as highly potential classifiers allowing discrimination among six investigated genotypes. Annotated GC/TOF‐MS data allowed the generation of a small subset of identified metabolites. LC/ESI‐MS data and small subsets require further annotation. The present study demonstrated that combination of comprehensive metabolic profiling and advanced data mining techniques provides a powerful metabolomic approach for biomarker discovery among small molecules. Utilizing GA for feature selection allowed the generation of small subsets of potent classifiers. Copyright © 2008 John Wiley & Sons, Ltd.
Robust fault estimation of uncertain systems using an LMI‐based approach
Authors: Nobrega Euripedes G. , Abdalla Musa O. , Grigoriadis Karolos M.
Published: March 2008

General recent techniques in fault detection and isolation (FDI) are based onH∞optimization methods to address the issue of robustness in the presence of disturbances, uncertainties and modeling errors. Recently developed linear matrix inequality (LMI) optimization methods are currently used to design controllers and filters, which present several advantages over the Riccati equation‐based design methods. This article presents an LMI formulation to design full‐order and reduced‐order robustH∞FDI filters to estimate the faulty input signals in the presence of uncertainty and model errors. Several cases are examined for nominal and uncertain plants, which consider a weight function for the disturbance and a reference model for the faults. The FDI LMI synthesis conditions are obtained based on the bounded real lemma for the nominal case and on a sufficient extension for the uncertain case. The conditions for the existence of a feasible solution form a convex problem for the full‐order filter, which may be solved via recently developed LMI optimization techniques. For the reduced‐order FDI filter, the inequalities include a non‐convex constraint, and an alternating projections method is presented to address this case. The examples presented in this paper compare the simulated results of a structural model for the nominal and uncertain cases and show that a degree of conservatism exists in the robust fault estimation; however, more reliable solutions are achieved than the nominal design. Copyright © 2008 John Wiley & Sons, Ltd.
Sense of place in the practice and assessment of place‐based science teaching
Authors: Semken Steven , Freeman Carol Butler
Published: March 2008

We teach earth, ecological, and environmental sciences in and aboutplacesimbued with meaning by human experience. Scientific understanding is but one of the many types of meanings that can accrue to a given place. People develop emotional attachments to meaningful places. Thesense of place, encompassing the meanings and attachments that places hold for people, has been well characterized in environmental psychology. Its components, place attachment and place meaning, can be measured psychometrically.Place‐basedscience teaching focuses on local and regional environments and synthesizes different ways of knowing them, leveraging the senses of place of students and teachers. Place‐based teaching has been advocated for its relevance and potential to attract underrepresented groups to science. We posit that sense of place is a measurable learning outcome of place‐based science teaching. We developed an Arizona‐based, culturally inclusive, meaning‐rich introductory geology course, and used published surveys to assess place attachment and meaning in students who took the course. We observed significant gains in student place attachment and place meaning, indicating that these instruments are generalizable and sensitive enough for use in this context. Sense of place should be engaged by teachers of place‐based science, and further explored as an assessment measure. © 2008 Wiley Periodicals, Inc.Sci Ed92:1042–1057, 2008
Nanowires Enabling Signal‐Enhanced Nanoscale Raman Spectroscopy
Authors: Becker Michael , Sivakov Vladimir , Gösele Ulrich , Stelzner Thomas , Andrä Gudrun , Reich Hans J. , Hoffmann Samuel , Michler Johannes , Christiansen Silke H.
Published: March 2008

Silicon nanowires grown by the vapor–liquid–solid (VLS) mechanism catalyzed by gold show gold caps (droplets) ≈20–500 nm in diameter with a half spherical towards almost spherical shape. These gold droplets are well suited to exploit the surface‐enhanced Raman scattering (SERS) effect and could be used for tip‐enhanced Raman spectroscopy (TERS). The gold droplet of a nanowire attached to an atomic force microscopy (AFM) tip could locally enhance the Raman signal and increase the spatial resolution. Used as a SERS template, an ensemble of self‐organizing nanowires grown bottom up on a silicon substrate could allow highly sensitive signal‐enhanced Raman spectroscopy of materials that show a characteristic Raman signature. A combination of a nanowire‐based TERS probe and a nanowire‐based SERS substrate promises optimized signal enhancement so that the detection of highly dilute species, even single molecules or single bacteria or DNA strands, and other soft matter is within reach. Potential applications of this novel nanowire‐based SERS and TERS solution lie in the fields of biomedical and life sciences, as well as security and solid‐state research such as silicon technology.
Adaptive wireless thin‐client model for mobile computing
Authors: Al‐Turkistany Mohammad , (Sumi) Helal Abdelsalam , Schmalz Mark
Published: March 2008

The thin‐client computing model has the potential to significantly increase the performance of mobile computing environments. By delivering any application through a single, small‐footprint client (called a thin client) implemented on a mobile device, it is possible to optimize application performance without the need for building wireless application gateways. We thus present two significant contributions in the area of wireless thin‐client computing. Firstly, a mathematical performance model is derived for wireless thin‐client system. This model identifies factors that affect the performance of the system and supports derivation and analysis of adaptation strategies to maintain a user‐specified quality of service (QoS). Secondly, a proxy‐based adaptation framework is developed for wireless thin‐client systems, which dynamically optimizes performance of a wireless thin client via dynamically discovered context. This is implemented with rule‐based fuzzy logic that responds to variations in wireless link bandwidth and client processing power. Our fuzzy inference engine uses contextual data to dynamically optimize tradeoffs among different quality of service parameters offered to the end users. Additionally, our adaptation framework uses highly scalable wavelet‐based image coding to provide scalable QoS that can degrade gracefully. Our thin‐client adaptation framework shields the user from ill effects of highly variable wireless network quality and mobile device resources. This improves performance of active applications, in which the display changes frequently. Further, active application behaviour may produce high transmission latency for screen updates, which can adversely affect user perception of QoS, resulting in poor interactivity. We report measured adaptive performance under realistic mobile device and network conditions for several different clients and servers. Copyright © 2008 John Wiley & Sons, Ltd.
Effects of High Frequency Exercise in Patients before and after Elective Percutaneous Coronary Intervention
Authors: Bäck Maria , Wennerblom Bertil , Wittboldt Susanna , Cider Åsa
Published: March 2008

Background: The aim of this study was to evaluate the effects of high frequency exercise for patients before and after an elective percutaneous coronary intervention (PCI), with special reference to maximal aerobic capacity, muscle function, health related quality of life (HRQoL), waist–hip ratio (WHR) and restenosis.

Methods: A randomised, controlled study was performed in Sweden between 2004 and 2006 in thirty-seven patients (five women) with stable coronary artery disease (CAD), age 63.6 ± 6.9 years, randomised to either high frequency exercise or control group. The patients in the training group performed three endurance resistance exercises and trained on a cycle ergometer 30 min, 5 times a week for 8 months at 70% of VO2max.

Results: Patients in the training group significantly improved their maximal aerobic capacity (15 (9–46) vs. 8 (0–18)% p ≤ 0.05), shoulder flexion ( p ≤ 0.01), shoulder abduction ( p ≤ 0.01) and heel-lift ( p ≤ 0.05) compared to the control group. There were no significant differences between the groups in HRQoL, WHR and restenosis.

Conclusion: High frequency exercise in patients treated with PCI seems to improve maximal aerobic capacity and muscle function, which may reduce the risks of further progression of atherosclerosis. However, further larger studies are needed to fully investigate the effects of exercise in patients with PCI.