bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral activation by fasting induces lactate accumulation in the hypothalamus
Authors: Violante Inês R. , Anastasovska Jelena , Sanchez‐Canon Gina J. , Rodrigues Tiago B. , Righi Valeria , Nieto‐Charques Laura , Parkinson James R.C. , Bloom Stephen R. , Bell Jimmy D. , Cerdán Sebastián
Published: June 2009

Carbon‐13 (13C) high‐resolution magic angle spinning (HR‐MAS) spectroscopy was used to investigate the neuroglial coupling mechanisms underlying appetite regulation in the brain of C57BL/6J mice metabolizing [1‐13C]glucose. Control fed or overnight fasted mice received [1‐13C]glucose (20 μmol/g intraperitoneally [i.p.]), 15 min prior to brain fixation by focused microwaves. The hypothalamic region was dissected from the rest of the brain and 13C HR‐MAS spectra were obtained from both biopsies. Fasting resulted in a significant increase in hypothalamic [3‐13C]lactate and [2‐13C]γ‐aminobutyric acid (GABA) relative to the remaining brain. Administration of the orexigenic peptide ghrelin (0.3 nmol/g i.p.) did not increase hypothalamic [3‐13C]lactate or [2‐13C]GABA, suggesting that ghrelin signaling is not sufficient to elicit all the metabolic consequences of hypothalamic activation by fasting. Our results indicate that the hypothalamic regulation of appetite involves, in addition to the well‐known neuropeptide signaling, increased neuroglial lactate shuttling and augmented GABA concentrations. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Robust estimation of spatially variable noise fields
Authors: Landman Bennett A. , Bazin Pierre‐Louis , Smith Seth A. , Prince Jerry L.
Published: June 2009

Consideration of spatially variable noise fields is becoming increasingly necessary in MRI given recent innovations in artifact identification and statistically driven image processing. Fast imaging methods enable study of difficult anatomical targets and improve image quality but also increase the spatial variability in the noise field. Traditional analysis techniques have either assumed that the noise is constant across the field of view (or region of interest) or have relied on separate MRI acquisitions to measure the noise field. These methods are either inappropriate for many modern scanning protocols or are overly time‐consuming for already lengthy scanning sessions. We propose a new, general framework for estimating spatially variable noise fields from related, but independent MR scans that we call noise field equivalent scans. These heuristic analyses enable robust noise field estimation in the presence of artifacts. Generalization of noise estimators based on uniform regions, difference images, and maximum likelihood are presented and compared with the estimators derived from the proposed framework. Simulations of diffusion tensor imaging and T2‐relaxometry demonstrate a 10‐fold reduction in mean squared error in noise field estimation, and these improvements are shown to be robust to artifact contamination. In vivo studies show that spatially variable noise fields can be readily estimated with typical data acquired at 1.5T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Comparison of 1H blood oxygen level–dependent (BOLD) and 19F MRI to investigate tumor oxygenation
Authors: Zhao Dawen , Jiang Lan , Hahn Eric W. , Mason Ralph P.
Published: June 2009

Fluorine‐19 [19F] MRI oximetry and 1H blood oxygen level–dependent (BOLD) MRI were used to investigate tumor oxygenation in rat breast 13762NF carcinomas, and correlations between the techniques were examined. A range of tissue oxygen partial pressure (pO2) values was found in the nine tumors while the anesthetized rats breathed air, with individual tumor pO2 ranging from a mean of 1 to 36 torr and hypoxic fraction (HF10) (<10 torr) ranging from 0% to 75%, indicating a large intra‐ and intertumor heterogeneity. Breathing oxygen produced significant increase in tumor pO2 (mean ΔpO2 = 50 torr) and decrease in HF10 (P < 0.01). 1H BOLD MRI observed using a spin echo‐planar imaging (EPI) sequence revealed a heterogeneous response and significant increase in mean tumor signal intensity (SI) (ΔSI = 7%, P < 0.01). R measured by multigradient‐echo (MGRE) MRI decreased significantly in response to oxygen (mean ΔR = −4 s−1; P < 0.05). A significant correlation was found between changes in mean tumor pO2 and mean EPI BOLD ΔSI accompanying oxygen breathing (r2 > 0.7, P < 0.001). Our results suggest that BOLD MRI provides information about tumor oxygenation and may be useful to predict pO2 changes accompanying interventions. Significantly, the magnitude of the BOLD response appears to be predictive for residual tumor HFs. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Hybrid of opposite‐contrast MR angiography (HOP‐MRA) combining time‐of‐flight and flow‐sensitive black‐blood contrasts
Authors: Kimura Tokunori , Ikedo Masato , Takemoto Syuhei
Published: June 2009

For the purpose of visualizing low‐flow as well as high‐flow blood vessels without using contrast agents, we propose a new technique called a hybrid of opposite‐contrast MR angiography (HOP‐MRA). HOP‐MRA is a combination of standard time‐of‐flight (TOF) using a full first‐order velocity‐compensation for white‐blood (WB) and flow‐sensitive black‐blood (FSBB) techniques, which use motion‐probing gradients to introduce intravoxel flow dephasing. A dual‐echo three‐dimensional gradient echo sequence was used to reduce both imaging time and misregistration. HOP‐MRA images were obtained using a simple‐weighted subtraction (SWS) or a frequency‐weighted subtraction (FWS) applying different spatial filtering for WB and BB images. We then assessed the relationships among the contrast‐to‐noise ratios (CNR) of the blood‐to‐background signals for those three images. In both volunteer and clinical brain studies, low‐flow vessels were well visualized and the background signal was well suppressed by HOP‐MRA compared with standard TOF‐ or BB‐MRA. The FWS was better than the SWS when whole‐maximum intensity projection was performed on a larger volume including with different types of tissue. The proposed HOP‐MRA was proven to visualize low‐flow to high‐flow vessels and, therefore, demonstrates excellent potential to become a clinically useful technique, especially for visualizing collateral vessels which is difficult with standard TOF‐MRA. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
On the dual contrast enhancement mechanism in frequency‐selective inversion‐recovery magnetic resonance angiography (IRON‐MRA)
Authors: Vonken Evert‐jan , Korosoglou Grigorios , Yu Jing , Schär Michael , Weissleder Ralph , Stuber Matthias
Published: June 2009

The susceptibility of blood changes after administration of a paramagnetic contrast agent that shortens T1. Concomitantly, the resonance frequency of the blood vessels shifts in a geometry‐dependent way. This frequency change may be exploited for incremental contrast generation by applying a frequency‐selective saturation prepulse prior to the imaging sequence. The dual origin of vascular enhancement depending first on off‐resonance and second on T1 lowering was investigated in vitro, together with the geometry dependence of the signal at 3T. First results obtained in an in vivo rabbit model are presented. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Incidental magnetization transfer contrast by fat saturation preparation pulses in multislice look‐locker echo planar imaging
Authors: Shin Wanyong , Gu Hong , Yang Yihong
Published: June 2009

In this study, it is demonstrated that fat saturation (FS) preparation (prep) pulses generate incidental magnetization transfer contrast (MTC) in multislice Look‐Locker (LL) imaging. It is shown that frequency‐selective FS prep pulses can invoke MTC through the exchange between free and motion‐restricted protons. Simulation reveals that the fractional signal loss by these MTC effects is more severe for smaller flip angles (FAs), shorter repetition times (TRs), and greater number of slices (SN). These incidental MTC effects result in a signal attenuation at a steady state (up to 30%) and a T1 measurement bias (up to 20%) when using inversion recovery (IR) LL echo‐planar imaging (EPI) sequences. Furthermore, it is shown that water‐selective MRI using binomial pulses has the potential to minimize the signal attenuation and provide unbiased T1 measurement without fat artifacts in MR images. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Rapid estimation of cartilage T2 based on double echo at steady state (DESS) with 3 Tesla
Authors: Welsch Goetz H. , Scheffler Klaus , Mamisch Tallal C. , Hughes Timothy , Millington Steven , Deimling Michael , Trattnig Siegfried
Published: June 2009

The double‐echo‐steady‐state (DESS) sequence generates two signal echoes that are characterized by a different contrast behavior. Based on these two contrasts, the underlying T2 can be calculated. For a flip‐angle of 90°, the calculated T2 becomes independent of T1, but with very low signal‐to‐noise ratio. In the present study, the estimation of cartilage T2, based on DESS with a reduced flip‐angle, was investigated, with the goal of optimizing SNR, and simultaneously minimizing the error in T2. This approach was validated in phantoms and on volunteers. T2 estimations based on DESS at different flip‐angles were compared with standard multiecho, spin‐echo T2. Furthermore, DESS‐T2 estimations were used in a volunteer and in an initial study on patients after cartilage repair of the knee. A flip‐angle of 33° was the best compromise for the combination of DESS‐T2 mapping and morphological imaging. For this flip angle, the Pearson correlation was 0.993 in the phantom study (∼20% relative difference between SE‐T2 and DESS‐T2); and varied between 0.429 and 0.514 in the volunteer study. Measurements in patients showed comparable results for both techniques with regard to zonal assessment. This DESS‐T2 approach represents an opportunity to combine morphological and quantitative cartilage MRI in a rapid one‐step examination. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Absolute temperature MR imaging with thulium 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetramethyl‐1,4,7,10‐tetraacetic acid (TmDOTMA−)
Authors: James Judy R. , Gao Yong , Miller Michael A. , Babsky Andriy , Bansal Navin
Published: June 2009

MR thermometry based on the water 1H signal provides high temporal and spatial resolution, but it has low temperature sensitivity (∼0.01 ppm/°C) and requires monitoring of another weaker signal for absolute temperature measurements. The use of the paramagnetic lanthanide complex, thulium 1,4,7,10‐ tetraazacyclo‐dodecane‐1,4,7,10‐tetramethyl‐1,4,7,10‐tetraac‐ etate (TmDOTMA−), which is ∼60 times more sensitive to temperature than the water 1H signal, is advanced to image absolute temperatures in vivo using water signal as a reference. The temperature imaging technique was developed using gradient echo and asymmetric spin echo imaging sequences on 9.4 Tesla (T) horizontal and vertical MR scanners. A comparison of regional temperatures measured with TmDOTMA− and fiber‐optic probes showed that the accuracy of imaging temperature is <0.3°C. The temperature imaging technique was found to be insensitive to inhomogeneities in the main magnetic field. The feasibility of imaging temperature of intact rats at ∼1.4 mmol/kg dose with ∼1‐mm spatial resolution in only 3 min is demonstrated. TmDOTMA− should prove useful for imaging absolute temperatures in deep‐seated organs in numerous biomedical applications. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Correlative dynamic contrast MRI and microscopic assessments of tumor vascularity in RIP‐tag2 transgenic mice
Authors: Sennino Barbara , Raatschen Hans‐Juergen , Wendland Michael F. , Fu Yanjun , You Weon‐Kyoo , Shames David M. , McDonald Donald M. , Brasch Robert C.
Published: June 2009

The purpose of this study was to define the feasibility of dynamic contrast‐enhanced magnetic resonance imaging (MRI) to estimate the vascular density and leakiness of spontaneous islet cell tumors in RIP‐Tag2 transgenic mice. Dynamic T1‐weighted spoiled gradient echo (SPGR) imaging at 2.0 T was performed in 17 RIP‐Tag2 mice using a prototype blood pool macromolecular contrast medium (MMCM), albumin‐(Gd‐DTPA)35. Kinetic analysis of the dynamic enhancement responses based on a two‐compartment model was used to estimate fractional plasma volume (fPV) and the coefficient of endothelial permeability (KPS) for each tumor. The MRI estimate of fPV was correlated on a tumor‐by‐tumor basis with corresponding microscopic measurements of vascular density. The fPV assays by MMCM‐enhanced imaging ranged from 2.4%–14.1% of tissue volume. Individual tumor fPV values correlated significantly (r = 0.79, P < 0.001) with the corresponding microscopic estimates of vascularity consisting of the combined area densities of lectin‐perfused microvessels plus erythrocyte‐stained blood lakes. A biotinylated derivative of the albumin‐based MMCM confirmed extravasation of the contrast agent from some tumor blood vessels and accumulation in 25% of blood lakes. The KPS values ranged from 0 (no detectable leak) to 0.356 mL/min/100 cm3. Dynamic MMCM‐enhanced MRI is feasible in RIP‐Tag2 pancreatic tumors, yielding estimates of vascular permeability and microscopically validated measurements of vascular richness. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
In vivo13C magnetic resonance spectroscopy of human brain on a clinical 3 T scanner using [2‐13C]glucose infusion and low‐power stochastic decoupling
Authors: Li Shizhe , Zhang Yan , Wang Shumin , Yang Jehoon , Ferraris Araneta Maria , Farris Amanda , Johnson Christopher , Fox Stephen , Innis Robert , Shen Jun
Published: June 2009

This study presents the detection of [2‐13C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2‐13C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low‐power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of13C label incorporation from [2‐13C]glucose into glutamate, glutamine, aspartate, γ‐aminobutyric acid, and N‐acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of ≈700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Breathhold multiecho fast spin‐echo pulse sequence for accurate R2 measurement in the heart and liver
Authors: Kim Daniel , Jensen Jens H. , Wu Ed X. , Sheth Sujit S. , Brittenham Gary M.
Published: June 2009

Measurement of proton transverse relaxation rates (R2) is a generally useful means for quantitative characterization of pathological changes in tissue with a variety of clinical applications. The most widely used R2 measurement method is the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence but its relatively long scan time requires respiratory gating for chest or body MRI, rendering this approach impractical for comprehensive assessment within a clinically‐acceptable examination time. The purpose of our study was to develop a breathhold multiecho fast spin‐echo (FSE) sequence for accurate measurement of R2 in the liver and heart. Phantom experiments and studies of subjects in vivo were performed to compare the FSE data with the corresponding even‐echo CPMG data. For pooled data, the R2 measurements were strongly correlated (Pearson correlation coefficient = 0.99) and in excellent agreement (mean difference [CPMG – FSE] = 0.10 s–1; 95% limits of agreement were 1.98 and –1.78 s–1) between the two pulse sequences. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Experimental determination of human peripheral nerve stimulation thresholds in a 3‐axis planar gradient system
Authors: Feldman Rebecca E. , Hardy Christopher J. , Aksel Bulent , Schenck John , Chronik Blaine A.
Published: June 2009

In MRI, strong, rapidly switched gradient fields are desirable because they can be used to reduce imaging time, obtain images with better resolution, or improve image signal‐to‐noise ratios. Improvements in gradient strength can be made by either increasing the gradient amplifier strength or by enhancing gradient efficiency. Unfortunately, many MRI pulse sequences, in combination with high‐performance amplifiers and existing gradient hardware, can cause peripheral nerve stimulation (PNS). This makes improvements in gradient amplifiers ineffective at increasing safely usable gradient strength. Customized gradient coils are one way to achieve significant improvements in gradient performance. One specific gradient configuration, a planar gradient system, promises improved gradient strength and switching time for cardiac imaging. The PNS thresholds for planar gradients were characterized through human stimulation experiments on all three gradient axes. The specialized gradient was shown to have significantly higher stimulation thresholds than traditional cylindrical designs (y‐axis SRmin = 210 ± 18 mT/m/ms and ΔGmin = 133 ± 13 mT/m; x‐axis SRmin = 222 ± 24 mT/m/ms and ΔGmin = 147 ± 17 mT/m; z‐axis SRmin = 252 ± 26 mT/m/ms and ΔGmin = 218 ± 26 mT/m). This system could be operated at gradient strengths 2 to 3 times higher than cylindrical configurations without causing stimulation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Assessment of 31P relaxation times in the human calf muscle: A comparison between 3 T and 7 T in vivo
Authors: Bogner W. , Chmelik M. , Schmid A.I. , Moser E. , Trattnig S. , Gruber S.
Published: June 2009

Phosphorus (31P) T1 and T2 relaxation times in the resting human calf muscle were assessed by interleaved, surface coil localized inversion recovery and frequency‐selective spin‐echo at 3 and 7 T. The obtained T1 (mean ± SD) decreased significantly (P < 0.05) from 3 to 7 T for phosphomonoesters (PME) (8.1 ± 1.7 s to 3.1 ± 0.9 s), phosphodiesters (PDE) (8.6 ± 1.2 s to 6.0 ± 1.1 s), phosphocreatine (PCr) (6.7 ± 0.4 s to 4.0 ± 0.2 s), γ‐NTP (nucleotide triphosphate) (5.5 ± 0.4 s to 3.3 ± 0.2 s), α‐NTP (3.4 ± 0.3 s to 1.8 ± 0.1 s), and β‐NTP (3.9 ± 0.4 s to 1.8 ± 0.1 s), but not for inorganic phosphate (Pi) (6.9 ± 0.6 s to 6.3 ± 1.0 s). The decrease in T2 was significant for Pi (153 ± 9 ms to 109 ± 17 ms), PDE (414 ± 128 ms to 314 ± 35 ms), PCr (354 ± 16 ms to 217 ± 14 ms), and γ‐NTP (61.9 ± 8.6 ms to 29.0 ± 3.3 ms). This decrease in T1 with increasing field strength of up to 62% can be explained by the increasing influence of chemical shift anisotropy on relaxation mechanisms and may allow shorter measurements at higher field strengths or up to 62% additional signal‐to‐noise ratio (SNR) per unit time. The fully relaxed SNR increased by +96%, while the linewidth increased from 6.5 ± 1.2 Hz to 11.2 ± 1.9 Hz or +72%. At 7 T 31P‐MRS in the human calf muscle offers more than twice as much SNR per unit time in reduced measurement time compared to 3 T. This will facilitate in vivo 31P‐MRS of the human muscle at 7 T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Visualization of seminiferous tubules in rat testes in normal and diseased conditions by high‐resolution MRI
Authors: Yamaguchi Masayuki , Mitsumori Fumiyuki , Watanabe Hidehiro , Takaya Nobuhiro , Minami Manabu
Published: June 2009

Rat seminiferous tubules were visualized for the first time using high‐spatial‐resolution MRI and their MRI features were investigated under normal and various kinds of pathological conditions. All testes images were obtained at 4.7 T with a dedicated quadrature surface coil. T2‐ and T‐weighted images with in‐plane resolution of 66 × 66 μm2 demonstrated numerous tubular structures with low‐signal‐intensity walls and high‐signal‐intensity lumens tightly packed throughout the entire testicle. The tubular structures were attributed to the seminiferous tubules in the histological specimens. In testicular ischemia, T‐weighted images demonstrated prominent low‐signal‐intensity bands along the radiate veins and normal‐appearing seminiferous tubules. As the ischemic condition persisted, the contour of the seminiferous tubules became less visible on both T2‐ and T‐weighted images, reflecting the disorganization of the seminiferous epithelia and severe interstitial edema. Changes in the images of testes treated with glycerol or diethylstilbestrol, a synthetic estrogen hormone, were also investigated. In the chronic spermatogenic impairment caused by these substances, extensive shrinkage of the seminiferous tubules was demonstrated. High‐resolution MRI aids in noninvasive evaluation of seminiferous tubules, and therefore has potential as a diagnostic test for human testes. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
In vivo detection of serine in the human brain by proton magnetic resonance spectroscopy (1H‐MRS) at 7 Tesla
Authors: Choi Changho , Dimitrov Ivan , Douglas Deborah , Zhao Chenguang , Hawesa Halima , Ghose Subroto , Tamminga Carol A.
Published: June 2009

A single‐voxel proton magnetic resonance spectroscopy (1H‐MRS) filtering strategy for in vivo detection of serine (Ser) in human brain at 7T is proposed. Spectral difference of coupled resonances arising from different subecho times of triple refocusing at a constant total echo time (TE) was utilized to detect the Ser multiplet and cancel the overlapping creatine (Cr) 3.92‐ppm singlet via difference editing. Dependence of the Ser signal on subecho times was investigated using density‐matrix simulation incorporating the slice‐selective radio frequency (RF) pulses. The simulation indicated that the difference‐edited Ser CH2 multiplet at ∼3.96 ppm is maximized with (TE1, TE2, TE3) = (54, 78, 78) and (36, 152, 22) ms. The edited Ser peak amplitude was estimated, with both numerical and phantom analyses of the performance, as 83% with respect to 90° acquisition for a localized volume, ignoring relaxation effects. From the area ratio of the edited Ser and unedited Cr 3.03‐ppm peaks, assuming identical T1 and T2 between Ser and Cr, the Ser‐to‐Cr concentration ratio for the frontal cortex of healthy adults was estimated to be 0.8 ± 0.2 (mean ± SD; N = 6). Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
T‐spline finite element method for the analysis of shell structures
Authors: Uhm Tae‐Kyoung , Youn Sung‐Kie
Published: June 2009

A T‐spline surface is a nonuniform rational B‐spline (NURBS) surface with T‐junctions, and is defined by a control grid called T‐mesh. The T‐mesh is similar to a NURBS control mesh except that in a T‐mesh, a row or column of control points is allowed to terminate in the inner parametric space. This property of T‐splines makes local refinement possible. In the present study, shell formulation based on the T‐spline finite element method (FEM) is presented. Shell formulation based on NURBS or T‐splines has fundamental limitations because rotational DOFs, which are necessary in the shell formulation, cannot be defined on control points. In this study, the simple mapping scheme, in which every control point is mapped into one geometric point on the surface, is employed to eliminate the limitations. Using this mapping scheme, T‐spline FEM can be easily extended to the analysis of shells. The proposed shell formulation is verified through various benchmarking problems. This study is a part of the efforts by the authors for the integration of CAD–CAE processes. Copyright © 2009 John Wiley & Sons, Ltd.
Multi‐level incomplete factorizations for the iterative solution of non‐linear finite element problems
Authors: Janna Carlo , Ferronato Massimiliano , Gambolati Giuseppe
Published: June 2009

Several engineering applications give rise quite naturally to linearized FE systems of equations possessing a multi‐level structure. An example is provided by geomechanical models of layered and faulted geological formations. For such problems the use of a multi‐level incomplete factorization (MIF) as a preconditioner for Krylov subspace methods can prove a robust and efficient solution accelerator, allowing for a fine tuning of the fill‐in degree with a significant improvement in both the solver performance and the memory consumption. The present paper develops two novel MIF variants for the solution of multi‐level symmetric positive definite systems. Two correction algorithms are proposed with the aim of preserving the positive definiteness of the preconditioner, thus avoiding possible breakdowns of the preconditioned conjugate gradient solver. The MIF variants are experimented with in the solution of both a single system and a long‐term quasi‐static simulation dealing with a multi‐level geomechanical application. The numerical results show that MIF typically outperforms by up to a factor 3 a more traditional algebraic preconditioner such as an incomplete Cholesky factorization with partial fill‐in. The advantage is emphasized in a long‐term simulation where the fine fill‐in tuning allowed for by MIF yields a significant improvement for the computer memory requirement as well. Copyright © 2009 John Wiley & Sons, Ltd.
Discrimination of three medicinal materials from the Citrus genus by HPLC fingerprint coupled with two complementary software
Authors: Qin Xue‐Mei , Dai Yun‐Tao , Zhang Li‐Zeng , Guo Xiao‐Qing , Shao Hong‐Xia
Published: June 2009

Introduction

Pericarpium Citri Reticulatae, Pericarpium Citri Reticulatae Viride and Fructus Aurantii come from the fruit of Citrus genus and possess analogous pharmacological activities. Either two or three of them are often present in one preparation. However, there is no standard method to differentiate the three herbal medicines for quality control.

Objective

To develop a fingerprint method for authentication of these three herbal medicines by HPLC.

Methodology

Methanol extracts were analysed by HPLC, with a mobile phase of 0.1% phosphoric acid in water (A) and acetonitrile (B) in a gradient programme. The flow rate was set at 0.8 mL/min and UV detection at 320 nm. Principal component analysis and similarity evaluation were employed to analyse the chromatographic dataset.

Results

The chromatograms of 20 Pericarpium Citri Reticulatae, 13 Pericarpium Citri Reticulatae Viride and 15 Fructus Aurantii samples from diverse habitats had 13 peaks in common, and showed one peak characteristic for Pericarpium Citri Reticulatae Viride and two peaks characteristic for Fructus Aurantii. Furthermore, it was possible to differentiate the three medicines by a ‘fingerprint region’. The difference between Pericarpium Citri Reticulatae and Fructus Aurantii was much bigger than that between Pericarpium Citri Reticulatae and Pericarpium Citri Reticulatae Viride, as could be shown by calculation of common peak ratio and variation peak ratio.

Conclusion

A reliable HPLC fingerprint method coupled with principal component analysis and similarity evaluation was developed and showed substantial differentiation power for the three medicines. Copyright © 2009 John Wiley & Sons, Ltd.
Curing of diglycidyl ether of bisphenol‐A epoxy resin using a poly(aryl ether ketone) bearing pendant carboxyl groups as macromolecular curing agent
Authors: Liu Fuhua , Wang Zhonggang , Liu Dan , Li Jianfeng
Published: June 2009

BACKGROUND: Reactive thermoplastics have received increasing attention in the field of epoxy resin toughening. This paper presents the first report of using a novel polyaryletherketone bearing one pendant carboxyl group per repeat unit to cure the diglycidyl ether of bisphenol‐A epoxy resin (DGEBA). The curing reactions of DGEBA/PEK‐L mixtures of various molar ratios and with different catalysts were investigated by means of dynamic differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy methods.

RESULTS: FTIR results for the DGEBA/PEK‐L system before curing and after curing at 135 °C for different times demonstrated that the carboxyl groups of PEK‐L were indeed involved in the curing reaction to form a crosslinked network, as evidenced by the marked decreased peak intensities of the carboxyl group at 1705 cm−1 and the epoxy group at 915 cm−1 as well as the newly emerged strong absorptions of ester bonds at 1721 cm−1 and hydroxyl groups at 3447 cm−1. Curing kinetic analysis showed that the value of the activation energy (Ea) was the highest at the beginning of curing, followed by a decrease with increasing conversion (α), which was attributed to the autocatalytic effect of hydroxyls generated in the curing reaction.

CONCLUSION: The pendant carboxyl groups in PEK‐L can react with epoxy groups of DGEBA during thermal curing, and covalently participate in the crosslinking network. PEK‐L is thus expected to significantly improve the fracture toughness of DGEBA epoxy resin. Copyright © 2009 Society of Chemical Industry
Toughening effects of poly(butylene terephthalate) with blocked isocyanate‐functionalized poly(ethylene octene)
Authors: Yin Ligang , Shi Dean , Liu Yanlong , Yin Jinghua
Published: June 2009

BACKGROUND: Blocked isocyanate‐functionalized polyolefins have great potential for use in semicrystalline polymer blends to obtain toughened polymers. In this study, poly(butylene terephthalate) (PBT) was blended with allyl N‐[2‐methyl‐4‐(2‐oxohexahydroazepine‐1‐carboxamido)phenyl] carbamate‐functionalized poly(ethylene octene) (POE‐g‐AMPC).

RESULTS: New peaks at 2272 and 1720 cm−1, corresponding to the stretching vibrations of NCO and the carbonyl of NHCON, respectively, in AMPC, appeared in the infrared spectrum of POE‐g‐AMPC. Both rheological and X‐ray photoelectron spectroscopy results indicated a new copolymer was formed in the reactive blends. Compared to uncompatibilized PBT/POE blends, smaller dispersed particle sizes with narrower distribution were found in the compatibilized PBT/POE‐g‐AMPC blends. There was a marked increase in impact strength by about 10‐fold over that of PBT/POE blends with the same rubber content and almost 30‐fold higher than that of pure PBT when the POE‐g‐AMPC content was 25 wt%.

CONCLUSION: The blocked isocyanate‐functionalized POE is an effective toughener for semicrystalline polymers. Super‐toughened PBT blends can be obtained when the POE‐g‐AMPC content is equal to or more than 15 wt%. Copyright © 2009 Society of Chemical Industry
Influence of chain microstructure on the hydrolytic degradation of copolymers from 1,3‐trimethylene carbonate and L‐lactide
Authors: Hua Jiajie , Gebarowska Katarzyna , Dobrzynski Piotr , Kasperczyk Janusz , Wei Jia , Li Suming
Published: June 2009

Ring‐opening copolymerization of L‐lactide (LLA) and 1,3‐trimethylene carbonate (TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110 or at 180 °C for various time periods, using low toxic zirconium (IV) acetylacetonate (Zr(Acac)4) as initiator. The resulting copolymers exhibit different chain microstructures. Copolymers obtained at 110 °C exhibit a gradient chain structure with the presence of lactidyl sequences next to very short ones, and are semicrystalline. In contrast, copolymers obtained at 180 °C are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences. Degradation of the copolymers was carried out in pH 7.4 phosphate buffer at 37 °C. Analytical techniques such as 1H NMR, DSC, GPC, and XRD were used to monitor the degradation. Initially amorphous copolymers can remain amorphous during degradation because of the highly random unit's distribution, and equivalent LLA and TMC contents. However, initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar, as initially semicrystalline copolymers are concerned, degradation occurs preferentially in the amorphous zones. Therefore, various degradation behaviors and degradation rates can be obtained by varying the chemical composition, chain microstructure, and morphology of PLLA‐PTMC copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3869–3879, 2009
Effects of polydepsipeptide side‐chain groups on the temperature sensitivity of triblock copolymers composed of polydepsipeptides and poly(ethylene glycol)
Authors: Ohya Yuichi , Yamamoto Hidetoshi , Nagahama Koji , Ouchi Tatsuro
Published: June 2009

To develop new types of biodegradable polymers possessing predictable responses to changes in temperature, ABA‐type and BAB‐type triblock copolymers composed of various polydepsipeptides (PDP) and poly(ethylene glycol) (PEG) (PDP‐PEG‐PDP and PEG‐PDP‐PEG) were synthesized. The specific focus of this study was on the effect of the different side‐chain groups of various amino acids on the temperature‐responsive behavior of the triblock copolymers. An ABA‐type triblock copolymer containing the less hydrophobic glycine (PGG‐PEG‐PGG) did not exhibit any temperature‐responsive behavior; however, ABA‐type triblock copolymers containing the hydrophobic α‐amino acids, L‐leucine and L‐phenylalanine (PGL‐PEG‐PGL or PGF‐PEG‐PGF), did exhibit temperature‐responsive behavior. The cloud point of PGF‐PEG‐PGF was 10 °C lower than that of PGL‐PEG‐PGL. It can be possible to control temperature‐sensitivity by changing not only PDP segment length but also kind of α‐amino acid in PDP segment. Moreover, BAB‐type triblock copolymer containing L‐leucine (PEG‐PGL‐PEG) showed temperature‐responsive sol‐gel transition. Because polydepsipeptides are biodegradable polymers, the information obtained in this study is useful to design biodegradable injectable polymers having controllable temperature‐sensitivity for biomedical use.© 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3892–3903, 2009
Synthesis and properties of poly(sulfone‐arylate) copolymers
Authors: Stephen Ranimol , Gibon Cécile M. , Weber Martin , Gaymans Reinoud J.
Published: June 2009

Poly(sulfone‐arylate) was synthesized in a reaction between dihydroxy polysulfone prepolymers and either diphenyl terephthalate or terephthaloyl chloride. The dihydroxy polysulfone prepolymers had molecular weights of 2000 and 4000 g/mol. The polymerization with diphenyl terephthalate was carried out at high temperature (280 °C) in the presence of a catalyst, whereas the polymerization with terephthalic chloride was conducted in solution at low temperature in the presence of an acid acceptor. High‐molecular weight copolymers (ηinh ∼ 0.60 dL/g) could be obtained through both methods. The copolymers were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, DMA, and differential scanning calorimetry measurements and were found to exhibit high Tg values. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3904–3913, 2009
Synthesis of dendritic macromolecules through divergent iterative thio‐bromo “Click” chemistry and SET‐LRP
Authors: Rosen Brad M. , Lligadas Gerard , Hahn Christian , Percec Virgil
Published: June 2009

The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters was reported in an earlier article. The combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐ propionate) (PTP) dendrimers. In this article, the addition of a third step, the single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate (MA), was shown to provides access to a three‐step “branch” and “grow” divergent approach to dendritic macromolecules wherein poly(methyl acrylate) (PMA) connects the branching subunits. This facile methodology can provide a diversity of dendritic macromolecular topologies and will ultimately provide the means to the development of self‐organizable dendritic macromolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3940–3948, 2009
Synthesis of dendrimers through divergent iterative thio‐bromo “Click” chemistry
Authors: Rosen Brad M. , Lligadas Gerard , Hahn Christian , Percec Virgil
Published: June 2009

The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters, is reported. Combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high‐structural fidelity. The isolated G1–G4 bromide‐terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star‐polymers via SET‐LRP. Additionally, the intermediate hydroxy‐terminated dendrimers are analogs of other water‐soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009
Effect of molecular weight of macro‐iniferter on electro‐optical properties of polymer dispersed liquid crystal films prepared by iniferter polymerization
Authors: Yan Bin , He Jie , Du Xin , Qin Ailin , Zhang Qin , Wang Yinghan
Published: June 2009

Polymer dispersed liquid crystal (PDLC) films were prepared by a devised method, in which photo‐polymerization induced phase separation in a mixtures of a macro‐iniferter, methyl acrylater, and liquid crystal. The morphology of the obtained PDLC films was examined on a polarized optical microscopy, and the effect of molecular weight of MIs on the electro‐optical properties was deliberately investigated. Decreasing the molecular weight of MIs in the films led to formation of larger liquid crystal droplets and a lower Vth values. Vsat increased and the memory effect decreased because of the increased interface anchoring strength induced by the higher molecular weight of polymer matrices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1530–1534, 2009
The effects of melt annealing and counterpart's molecular weight on the thermal properties and phase morphology of poly(L‐lactide)‐based blends
Authors: Chiu Fang‐Chyou , Kan Chin‐Yu , Yang Jen‐Chang
Published: June 2009

The thermal properties and phase morphology of poly(L‐lactide) (PLLA)‐based blends have been studied. Two poly(ethylene glycol)s (PEGs) with molecular weight (MW) of about 1,500 (1.5k) g/mol and 2,000,000 (2M) g/mol, respectively, were used as counterparts. The blends were annealed at a preselected temperature of 200 °C for either 2 min or 30 min before the characterizations. Both PEGs were determined to enhance the crystallizability of PLLA. After a 2‐min process of annealing, the PEG(1.5k)'s crystallization efficiency on PLLA has been noted to increase with the increase of its content. Conversely, PEG(2M)'s crystallization efficiency declined with the increase of its content. Extending the annealing time has evidently changed the PEGs' crystallization effect on PLLA. Moreover, the PEG(1.5k) has, to a greater extent, brought about the depression of PLLA's melting temperature by increasing its content, and this depression increased with the annealing time. The blends exhibited lower thermal stability than those of the parent components, particularly for the PEG(1.5k)‐included system with a higher PEG content. Regardless of the annealing time, the PEG(1.5k)‐included blends have shown homogeneous melt morphology under light microscope, whereas the PEG(2M)‐included blends have displayed phase‐separated melt morphology. In addition to the composition, PEG's MW and annealing time influence the crystalline morphology of the blends. The ringed PLLA spherulites have appeared mostly in the 2‐min annealed PEG(1.5k)‐included blends. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1497–1510, 2009
Effective in situ synthesis and characteristics of polystyrene nanoparticle‐covered multiwall carbon nanotube composite
Authors: Patole Archana S. , Patole S. P. , Yoo Ji‐Beom , Ahn Jeong‐Ho , Kim Tae‐Ho
Published: June 2009

The higher surface area of selectively grown multiwall carbon nanotubes (MWCNTs) and the better proximity of the reactant species in in situ microemulsion polymerization were used to attach the polystyrene (PS) nanoparticles to the outer wall of MWCNTs. Attachment were achieved by replacing surfactant with PS nanoparticles. SEM showed that the MWCNTs and PS nanoparticles were distributed in the composite. High resolution transmission electron microscopy showed successful anchoring of PS nanoparticles to the outer wall of the MWCNTs. In addition, anchoring enhanced the Raman's G/D ratio of the MWCNT and degradation temperature in PS nanoparticles. A mechanism of attachment of PS nanoparticles on the outer wall of MWCNT was proposed. The modified MWCNTs exhibited good durability and dispersability in different organic solvents. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1523–1529, 2009
A potential low‐rate DoS attack against network firewalls
Authors: Salah K. , Sattar K. , Sqalli M. , Al‐Shaer Ehab
Published: June 2009

In this paper we identify a potential Denial of Service (DoS) attack that targets the last‐matching rules of the security policy of a firewall. The last‐matching rules are those rules that are located at the bottom of the ruleset of a firewall's security policy, and would require the most processing time by the firewall. If these rules are discovered, an attacker can potentially launch an effective low‐rate DoS attack to trigger worst‐case or near worst‐case processing, thereby overwhelming the firewall and bringing it to its knees. In this paper, we present a probing technique to remotely discover the last‐matching rules of a firewall. We study experimentally the effectiveness of this probing technique taking into account important factors such as the firewall's motherboard architecture and load conditions at network links and hosts. In addition we examine the impact of launching a low‐rate DoS attack on a firewall's performance. The performance is studied in terms of the firewall's CPU utilization and throughput, packet loss, and latency. Copyright © 2009 John Wiley & Sons, Ltd.
Investigation of transfer film of PTFE/bronze composites on 2024Al surface
Authors: Wang Yunxia , Wang Hongling , Yan Fengyuan
Published: June 2009

Polytetrafluoroethylene (PTFE) composites filled with 10–30% volume content of bronze powder were prepared through molding and sintering process. Transfer films of these composites were prepared on surface of 2024 Al bar through friction method under certain condition. Roughness, morphology, andelement of these transfer films were investigated using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) methods. Tribological propertiesof these transfer films sliding against GCr15 steel ball were tested using a DFPM reciprocating tribometer. Worn surfaces were observed and analyzed using SEM and EDS methods. It was found that uniformity and continuity of the transfer films were obviously improved by the increase of bronze content of the composites. Transfer films with better uniformity and continuity holds longer wear life. Considerably lower friction coefficient and longer wear life of these transfer films indicate that the transfer films prepared in the experiment could effectively prevent direct contact of metal friction pair and thus protect them from heavy wear. SEM and EDS analyses of the worn surfaces indicate that adhesion wear and fatigue wear were main wear modes of the transfer film. Copyright © 2009 John Wiley & Sons, Ltd.
c‐Fos expression associated with reinstatement of cocaine‐seeking behavior by response‐contingent conditioned cues
Authors: Kufahl Peter R. , Zavala Arturo R. , Singh Akanksha , Thiel Kenneth J. , Dickey Erin D. , Joyce Jeffrey N. , Neisewander Janet L.
Published: June 2009

The capability of cocaine cues to generate craving in cocaine‐dependent humans, even after extended abstinence, is modeled in rats using cue reinstatement of extinguished cocaine‐seeking behavior. We investigated neural activity associated with incentive motivational effects of cocaine cues usingc‐fosmRNA and Fos protein expression as markers. Unlike preceding studies, we used response‐contingent presentation of discrete cues to elicit cocaine seeking. Rats were first trained to press a lever, resulting in cocaine reinforcement and light and tone cues. Rats then underwent extinction training, during which lever presses decreased. On the test day, rats either received response‐contingent cocaine cues or received no cues. The cues reinstated extinguished cocaine‐seeking behavior on the test day. In general, cue‐elicitedc‐fosmRNA and protein expression were similar and both were enhanced in the prefrontal cortex, ventral tegmental area (VTA), dorsal striatum, and nucleus accumbens. Cues elicited more widespread Fos protein expression relative to our previous research in which cues were presented noncontingently without prior extinction training, including increases in the VTA, substantia nigra, ventral subiculum, and lateral entorhinal cortex. We also observed a correlation between cocaine‐seeking behavior and Fos in the agranular insula (AgI) and basolateral amygdala (BLA). The findings suggest that connections between BLA and AgI play a role in cue‐elicited incentive motivation for cocaine and that reinstatement of cocaine seeking by response‐contingent cues activates a similar corticolimbic circuit as that observed with other modes of cue presentation; however, activation of midbrain and ventral hippocampal regions may be unique to reinstatement by response‐contingent cues. Synapse 63:823–835, 2009. © 2009 Wiley‐Liss, Inc.
Building International Collaborative Capacity: Contributions of Community Psychologists to a European Network
Authors: García-Ramírez Manuel , Paloma Virginia , Suarez-Balcazar Yolanda , Balcazar Fabricio
Published: June 2009

Europe is in the process of building a more participative, just, and inclusive European Union.The European Social Fund, which is an initiative developed to actively promote multinational partnerships that address pressing social issues, is a good example of the European transformation. This article describes the steps taken to develop and evaluate the activities of an international network promoting collaborative capacity among regional partners involved in the prevention of labor discrimination toward immigrants in three European countries—Spain, Belgium, and Italy. An international team of community psychologists proposed an empowering approach to assess the collaborative capacity of the network. This approach consisted of three steps: (1) establishing a collaborative relationship among partners, (2) building collaborative capacity, and (3) evaluating the collaborative capacity of the network. We conclude with lessons learned from the process and provide recommendations for addressing the challenges inherent in international collaboration processes.