bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous flow‐driven inversion for arterial spin labeling using pulsed radio frequency and gradient fields
Authors: Dai Weiying , Garcia Dairon , de Bazelaire Cedric , Alsop David C. 
Published: November 2008

AbstractContinuous labeling by flow‐driven adiabatic inversion is advantageous for arterial spin labeling (ASL) perfusion studies, but details of the implementation, including inefficiency, magnetization transfer, and limited support for continuous‐mode operation on clinical scanners, have restricted the benefits of this approach. Here a new approach to continuous labeling that employs rapidly repeated gradient and radio frequency (RF) pulses to achieve continuous labeling with high efficiency is characterized. The theoretical underpinnings, numerical simulations, and in vivo implementation of this pulsed continuous ASL (PCASL) method are described. In vivo PCASL labeling efficiency of 96% relative to continuous labeling with comparable labeling parameters far exceeded the 33% duty cycle of the PCASL RF pulses. Imaging at 3T with body coil transmission was readily achieved. This technique should help to realize the benefits of continuous labeling in clinical imagers. Magn Reson Med 60:1488–1497, 2008. © 2008 Wiley‐Liss, Inc.
Characterization of tumor angiogenesis with dynamic contrast‐enhanced MRI and biodegradable macromolecular contrast agents in mice
Authors: Feng Yi , Jeong Eun‐Kee , Mohs Aaron M. , Emerson Lyska , Lu Zheng‐Rong 
Published: November 2008

AbstractThe efficacy of polydisulfide‐based biodegradable macromolecular contrast agents for characterizing tumor angiogenesis was investigated in a mouse model using dynamic contrast‐enhanced MRI (DCE‐MRI). Biodegradable macromolecular MRI contrast agents, gadopentetate dimeglumine (Gd‐DTPA) cystamine copolymers (GDCC), and Gd‐DTPA cystine copolymers (GDCP), with molecular weights of 20 and 70 kDa were used in the study. Gadodiamide (Gd [DTPA‐BMA]) and albumin labeled with Gd‐DTPA [albumin‐(Gd‐DTPA)] were used as the controls. The DCE‐MRI studies were performed in nude mice bearing prostate tumor xenografts from the MDA‐PCa‐2b cell line. Tumor angiogenic kinetic parameters, including endothelial transfer coefficient (KPS), fractional tumor plasma volume (fPV), and permeability surface area product (PS), were estimated from the DCE‐MRI data using a two‐compartment model. The KPS and fPV values estimated by the biodegradable macromolecular contrast agents were between those estimated by Gd(DTPA‐BMA) and albumin‐(Gd‐DTPA). The parameters estimated by the agent with a slow degradation rate and high molecular weight, GDCP‐70 (KPS = 2.09 ± 0.50 ml/min/100 cc and fPV = 0.075 ± 0.021), were closer to those by albumin‐(Gd‐DTPA) (KPS = 1.43 ± 0.64 ml/min/100 cc and fPV = 0.044 ± 0.007) than by other agents with relatively low molecular weight or rapid degradation rate. The polydisulfide‐based biodegradable macromolecular contrast agents are promising for characterizing tumor vascularity and angiogenesis with DCE‐MRI. Magn Reson Med 60:1347–1352, 2008. © 2008 Wiley‐Liss, Inc.
Nanoparticle pharmacokinetic profiling in vivo using magnetic resonance imaging
Authors: Neubauer Anne M. , Sim Hoon , Winter Patrick M. , Caruthers Shelton D. , Williams Todd A. , Robertson J. David , Sept David , Lanza Gregory M. , Wickline Samuel A. 
Published: November 2008

AbstractContrast agents targeted to molecular markers of disease are currently being developed with the goal of identifying disease early and evaluating treatment effectiveness using noninvasive imaging modalities such as MRI. Pharmacokinetic profiling of the binding of targeted contrast agents, while theoretically possible with MRI, has thus far only been demonstrated with more sensitive imaging techniques. Paramagnetic liquid perfluorocarbon nanoparticles were formulated to target αvβ3‐integrins associated with early atherosclerosis in cholesterol‐fed rabbits to produce a measurable signal increase on magnetic resonance images after binding. In this work, we combine quantitative information of the in vivo binding of this agent over time obtained by means of MRI with blood sampling to derive pharmacokinetic parameters using simultaneous and individual fitting of the data to a three compartment model. A doubling of tissue exposure (or area under the curve) is obtained with targeted as compared to control nanoparticles, and key parameter differences are discovered that may aid in development of models for targeted drug delivery. Magn Reson Med 60:1353–1361, 2008. © 2008 Wiley‐Liss, Inc.
Perfusion Tensor Imaging
Authors: Frank Lawrence R. , Lu Kun , Wong Eric C. 
Published: November 2008

AbstractArterial spin labeling (ASL) provides a method by which to noninvasively measure the spatial and temporal characteristics of local tissue perfusion. Standard methods employ spatial tagging schemes, but recently methods based on velocity dependent tags, called Velocity Selective ASL (VSASL), have been introduced wherein the tagging depends upon the vascular velocity profile. In this article, we point out an interesting feature of VSASL: the velocity can be encoded in any direction, thereby allowing for the measurement of perfusion with a specified angular resolution. This then facilitates the reconstruction of the local perfusion field, characterized by a perfusion tensor P, from which can be derived quantities related to the structure of the local perfusion field, such as the mean perfusion, the perfusion anisotropy, and the principal directions of flow feeding each voxel. We demonstrate this new method, Perfusion Tensor Imaging (PTI), in both the brain and skeletal muscle of normal human volunteers and discuss possible applications. Magn Reson Med 60:1284–1291, 2008. © 2008 Wiley‐Liss, Inc.
Estimation of base settlement from the surface subsidence profile: Plane‐field of displacements
Authors: Baxevanis Theocharis , Plexousakis Michael 
Published: November 2008

AbstractAccording to Litwiniszyn's theory, subsidence over a yielding underground geo‐structure is seen as a stochastic (Markov) process. This theory leads to a single, linear parabolic differential equation of diffusion–convection type (D–C equation) in the plane‐field of displacements. If the boundary conditions for the governing D–C equation are prescribed along the shear bands, i.e. at ‘moving’ boundaries—it has been observed from small‐scale model experiments that the subsiding process is always confined between a set of inclined shear bands—then the resulting equation is nonlinear. The inverse problem for this nonlinear equation, i.e. the problem of determining the base displacement using the surface subsidence as ‘initial’ condition, is ill‐posed and estimation of the base displacement from a given surface subsidence profile is not possible. In the present paper the domain of integration of the governing D–C equation is fixed (and bounded)—the boundaries are not evolving. Hence, the governing equation remains linear parabolic. The advantage is that this linear differential equation admits an analytical solution, under the trap‐door mechanism assumption, that enables a direct solution to the inverse problem. Copyright © 2008 John Wiley & Sons, Ltd.
Evaluation of pressor and visceromotor reflex responses to bladder distension in urethane anesthetized rats
Authors: Blatt Lauren K. , Lashinger Erin S.R. , Laping Nicholas J. , Su Xin 
Published: November 2008

AbstractAimsWe tested cardiovascular and visceromotor reflex (VMR) responses to urinary bladder distension (UBD) in urethane anesthetized rats to see if it can replicate the response pattern and the inhibition of bladder nociceptive transmission by analgesics seen in isoflurane anesthetized animals.MethodsFemale Sprague‐Dawley rats under 3% isoflurane anesthesia were acutely instrumented with jugular venous, carotid arterial, and bladder cannulas for drug administration, blood pressure (BP) measurement, and bladder distension, respectively. Needle electrodes were placed directly into the abdominal musculature to measure myoelectrical activity subsequent to phasic UBD (30 sec in 3 min intervals). A cardiovascular response (pressor) and a VMR response (a contraction of abdominal and hind limb musculature) to UBD were evaluated in urethane (1.2 g/kg, i.v.) or isoflurane (1%) anesthetized rats.ResultsPressor and VMR responses to noxious UBD (60 mmHg) were generated under both anesthesics. The thresholds of stimulus response functions for both pressor and VMR responses were not affected by either anesthesics. However, the magnitude of the maximal pressor response was significantly reduced in urethane anesthesia. The analgesics, morphine, and mexiletine, significantly inhibited the VMR response to noxious UBD under both anesthetics, but the intensities of the inhibition from both analgesics under urethane anesthesia were much lower than under isoflurane anesthesia (ID50: 2.07 mg/kg vs. 0.88 mg/kg for morphine, >10 mg/kg vs. 0.47 mg/kg for mexiletine).ConclusionsThe rat urinary bladder distension model in urethane anesthetized rats demonstrates a blunted maximal pressor response and a reduced inhibition of visceral nociceptive transmission by analgesics. Neurourol. Urodynam. 28:442–446, 2009. © 2008 Wiley‐Liss, Inc.
Effects of 17ββ‐estradiol on rat urinary bladder: Gender differences in anoxia–glucopenia and reperfusion damage
Authors: Valeri Aurora , Ceccarelli Ilaria , Fiorenzani Paolo , Aloisi Anna Maria , Sgaragli Giampietro , Pessina Federica 
Published: November 2008

AbstractAimTo study the effect of 17β‐estradiol (E2) as a neuroprotective agent in male and female rat urinary bladders subjected to Anoxia‐Glucopenia and Reperfusion (A/G‐R) damage.MethodsRat urinary bladders were exposed to 1 hour of A—G and 2 hours of reperfusion (R). Intrinsic nerves underwent electrical field stimulation. The effect of E2 on the contractile response and its recovery in R phase, was monitored by adding it to the bath medium, at different concentrations, 60 min before A—G, during the A—G and the first 30 min of R. Furthermore, on both genders, in vivo treatments with E2, testosterone, IC1 182,780 and anastrozole were performed.ResultsAfter A—G the recovery of the nerve function in female bladders were significantly higher than in male. E2 given both in vivo (increased of E2 plasma levels were monitored) and in vitro, resulted to be neuroprotective in male bladder subjected to A—G/R damage. When rats were treated with anastrozole, a lower recovery of nerve responses both in male and female bladders was observed. Finally, treatments with E2 receptor antagonist ICI 182,780 increased E2 plasma levels and showed to abolished E2 neuroprotection, thus suggesting that E2 promotes nelronal survival likely through a rapid estrogen receptor mediated response.ConclusionsMale rat urinary bladder serves are more susceptible to A—G/R damage than female. E2 exhibits neuroprotective properties and could be a lead for novel agents capable to protect the urinary bladder from ischaemia/reperfusion damage associated with urinary bladder disorders. Neurourol. Urodyn. 28:535–541, 2009. © 2008 Wiley‐Liss, Inc.
Study of crystal structure of (polyvinylidene fluoride/clay) nanocomposite films: Effect of process conditions and clay type
Authors: Sadeghi Farhad , Ajji Abdellah 
Published: November 2008

AbstractThree Polyvinylidene fluoride (PVDF) different in molecular structure were used to produce nanocomposities films by cast extrusion with a particular emphasis on maximizing the β crystal phase content. The PVDF/clay compounding followed by cast film production was carried out through melt extrusion using a twin screw extruder equipped with a slit die. X‐ray diffraction (XRD) results showed that clay melt intercalation is almost similar for all three PVDFs. The XRD results also revealed that nanocomposite films from PVDF with branched chain structure (PVDFB) generated the greatest amount of β phase. FTIR spectroscopy measurements confirmed the XRD results but also revealed that significant stretching of the melt films at the die or rapid cooling would adversely affect the formation of β phase. The amount of β phase obtained based on nanoclay compounding was compared with that obtained from conventional method: stretching of molded PVDF film with initial α phase. Stretching of PVDF film at 60°C yielded pure β phase that means complete transformation of α to β. From mechanical properties, tensile tests were carried out on PVDF nanocomposite films to evaluate mechanical strength. PVDF with low molecular weight exhibited a very low strain at break while branched PVDF and high molecular weight PVDF could sustain more strain. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers
Synthesis and characterization of novel polyurethanes based on aminolysis of poly(ethylene terephthalate) wastes, and evaluation of their thermal and mechanical properties
Authors: Shamsi Ramin , Abdouss Majid , Sadeghi Gity Mir Mohamad , Taromi Faramarz Afshar 
Published: November 2008

AbstractBACKGROUND: Much research is currently directed towards recycling post‐consumer poly(ethylene terephthalate) (PET) products for both environmental and economic reasons. Aminolysis of PET wastes using different amines, such as allylamine, morpholine, hydrazine and polyamines, leads to different reaction products as diamides of terephthalic acid, which do not possess any potential for further chemical reactions. In the past, the use of ethanolamine has been investigated for the aminolytic degradation of PET waste in the presence of different simple chemicals such as sodium acetate as catalysts. The product obtained, bis(2‐hydroxyethylene) terephthalamide (BHETA), has potential for further reactions to obtain useful products. Nevertheless, there has been no report on using recycled BHETA from PET to synthesize polyurethanes.RESULTS: In this research the product of aminolysis of PET waste, BHETA, was prepared. Then novel polyurethanes were synthesized based on the BHETA prepared, 1,4‐butanediol, ether‐type polyol and various molar ratios of hexamethylene diisocyanate. To evaluate the effect of BHETA, the properties of the polyurethanes without and with BHETA were compared. Fourier transform infrared spectra, thermal transitions, degradation, swelling ratio and chemical resistance of the synthesized polyurethanes were investigated. Also, the polyurethanes were applied as adhesives on various substrates. Comparison of the maximum bond strength of the synthesized polyurethane to that of commercial adhesives shows an about 2.2‐fold increase.CONCLUSION: It is possible to synthesize new polyurethanes with interesting properties using BHETA as an aminolysis product of PET waste. These kinds of materials have potential for many applications, such as adhesives and coatings. Copyright © 2008 Society of Chemical Industry
Copolymers of N‐alkyl‐ and N‐arylalkylacrylamides with acrylamide: influence of hydrophobic structure on associative properties. Part II: rheological behaviour in semi‐dilute solution
Authors: Camail Michel , Margaillan André , Martin Isabelle 
Published: November 2008

AbstractBACKGROUND: Hydrophobically associating water‐soluble polymers are of great interest because they possess unique rheological behaviour that results from the reversible association/dissociation process of their hydrophobic moieties. In this study, we focused on the structure of hydrophobic monomers related to the rheological and viscoelastic behaviours in semi‐dilute solutions of acrylamide polymers modified with small amounts of N‐alkyl‐ and N‐arylalkylacrylamides (0.5 and 1 mol%).RESULTS: Associative efficiency increases with the length of the graft alkyl chain, with its proportion in the copolymer and with the presence of an aromatic group at the end of the alkyl graft chain. Introduction of hydrophobic groups induces a slowing down of the dynamics of the system, particularly marked for copolymers containing phenyldecyl chains.CONCLUSION: At low frequencies, solutions behave as Newtonian liquids; at higher frequencies, solutions of strongly associative systems behave as a solid with a storage modulus higher than the loss modulus and little dependency on the frequency. The system is a transient network whose dynamics depend on entanglements and hydrophobic associations. The presence of the hydrophobic groups induces an increase of the final relaxation time, even more pronounced since these associations are strong. Copyright © 2008 Society of Chemical Industry
Poly(acrylonitrile‐co‐methyl methacrylate‐co‐methyl acrylate): Synthesis and stereosequence distribution analysis by 2D NMR
Authors: Brar Ajaib S. , Goyal Ashok K. , Hooda Sunita , Shankar Ravi 
Published: November 2008

AbstractTerpolymers of acrylonitrile (A), methyl methacrylate (B), and methyl acrylate (M) were synthesized under optimized atom transfer radical polymerization conditions using 2‐bromopropionitrile as an initiator and CuBr/dinonyl bipyridine as a catalyst. Variation of the feed composition led to terpolymers with different compositions. Composition of synthesized terpolymers were calculated from quantitative 13C{1H} NMR spectra. Number average molecular weight and polydispersity index were determined by gel permeation chromatography. The overlapping and broad signals of the terpolymers were assigned completely to various compositional and configurational sequences by correlation of one‐dimensional 1H, 13C{1H}, and distortionless enhancement by polarization transfer and two‐dimensional heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). 2D HSQC NMR study shows one to one correlation between carbon and proton signals, while 2D TOCSY spectra were used to confirm 1, 2 bond geminal couplings between nonequivalent protons of same methylene group. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 25–37, 2009
Polyisobutylene‐based segmented polyureas. I. Synthesis of hydrolytically and oxidatively stable polyureas
Authors: Jewrajka Suresh K. , Yilgor Emel , Yilgor Iskender , Kennedy Joseph P. 
Published: November 2008

AbstractNovel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine‐telechelic PIB oligomers (NH2‐PIB‐NH2) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB‐based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain‐extended and chain‐extended polyureas showed a linear dependence on the urea hard segment content. PIB‐based polyureas prepared with NH2‐PIB‐NH2 of Mn = 2500 g/mol, 4,4′‐methylendbis(cyclohexylisocyantate), and 1,6‐diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 °C for 12 h. With increasing hard segment content, elongation at break decreased from ∼ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB‐based polyureas were unprecedented. Although commercial “oxidatively resistant” thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38–48, 2009
Preparation of H‐shaped ABCAB terpolymers by atom transfer radical coupling
Authors: Luo Xiaolan , Wang Guowei , Huang Junlian 
Published: November 2008

AbstractH‐shaped ABCAB terpolymers composed of polystyrene (PS) (A), poly(ethylene oxide) (PEO) (B), and poly(tert‐butyl acrylate) (PtBA) (C) were prepared by atom transfer radical coupling reaction using ABC star terpolymers as precursors, CuBr and N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalysts, and nanosize copper as the reducing agent. The synthesis of 3‐miktoarm star terpolymer PS‐PEO‐(PtBA‐Br) involved following steps: (1) the preparation of PS with an active and an ethoxyethyl‐ptotected hydroxyl group at the same end; (2) the preparation of diblock copolymer PS‐b‐PEO with ethoxyethyl‐protected group at the junction point through the ring‐opening polymerization (ROP) of EO; (3) after de‐protection of ethoxyethyl group and further modification of hydroxyl group, tBA was polymerized by atom transfer radical polymerization using PS‐b‐PEO with 2‐bromoisobutyryl functional group as macroinitiator. The H‐shaped terpolymer could be successfully formed by atom transfer radical coupling reaction in the presence of small quantity of styrene, CuBr/PMDETA, and Cu at 90 °C. The copolymers were characterized by SEC, 1H NMR, and FTIR in detail. The optimized coupling temperature is 90 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 59–68, 2009
Unimolecular micelles and reverse micelles based on hyperbranched polyethers—Comparative study of AB2 + A‐R and A2 + B3 + A‐R type strategies
Authors: Saha Animesh , Ramakrishnan S. 
Published: November 2008

AbstractCore‐shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB2 + A‐R and A2 + B3 + A‐R type copolymerizations. In case of micelle‐forming polymers, an AB2 monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A‐R type comonomer. One the other hand, for the preparation of reverse micelle‐forming polymers, an AB2 monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A‐R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65–70% of the terminal B groups were capped by the A‐R comonomer. Dye‐uptake measurements revealed that the polymers prepared via the AB2 + A‐R approach exhibited a significantly larger uptake compared with those prepared via the A2 + B3 + A‐R approach. This suggests that the AB2 + A‐R approach generates hyperbranched polymers with better defined core‐shell topology when compared with polymers prepared via the A2 + B3 + A‐R approach, which is in accordance with previous studies that suggest that A2 + B3 approach yields polymers with significantly lower branching levels and consequently less compact structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 80–91, 2009