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941.
Nikita Agarwal Guilhem Pagès Loyola D' Silva Nicholas Said Philip W. Kuchel S. Sendhil Velan 《Magnetic resonance imaging》2014
Foot dorsi and plantar flexion affects the pennation angle of skeletal muscle fibers and changes the fiber direction with respect to the main magnetic field, thereby affecting MR spectrum of the muscle. In order to analyze the effect that foot flexion has on the MR spectrum, tibialis anterior (TA) and soleus muscles were studied in humans and rats. Localized MRS was performed at different foot angles in clinical and pre-clinical settings using a 3 T MRI/MRS GE Excite HD and 7 T Bruker Clinscan scanner, respectively. In this study we show the effect of foot angle variation on total Creatine (tCr) resonance of 1H spectrum at 3.03 and 3.93 ppm for TA and soleus muscles. In addition to this, we observe a 4-line splitting pattern for methylene resonance of tCr in the rat TA spectrum for a specific foot angle. This observation is attributed to the individual splitting of creatine and phosphocreatine of the tCr signal. Novel hydrogel application is demonstrated and used to support our in vivo observations and for the first time splitting of individual resonances of Cr and PCr has been shown in an in vitro set-up. 相似文献
942.
Quasi-two-dimensional superconductors with tunable spin-orbit coupling are very interesting systems with properties that are also potentially useful for applications. In this Letter we demonstrate that these systems exhibit undamped collective spin oscillations that can be excited by the application of a supercurrent. We propose to use these collective excitations to realize persistent spin oscillators operating in the frequency range of 10 GHz-1 THz. 相似文献
943.
Mihir Roychoudhury Shailendra Kumar ThakurPankaj Kumar Gaurav 《Journal of Molecular Liquids》2011,161(2):55-62
Two pyridine derivative “2-(4-butoxyphenyl)-5-hexyl pyridine” (Cpd 1) and “3-(4-butoxyphenyl)-6-hexyl pyridine” (Cpd 2) differing only in the relative position of nitrogen have been examined quantum mechanically to understand the possible reason of their different mesogenic character. The studies include geometry optimization, evaluation of interaction energy between a molecular pair at minimum energy configuration and tendency of ordering at various interacting conditions. It has been found that in Cpd 1, the phenyl and pyridine rings are almost coplanar with the butoxy tail while Cpd 2 differs significantly from planarity. Cpd 1 therefore stacks more closely than Cpd 2. An attempt has been made to correlate the results of intermolecular interaction energy calculation with the mesogenic behavior of the respective molecules. 相似文献
944.
Sahaj GuptaPiyush K. Agarwal Mohammad SaifuddinBijoy Kundu 《Tetrahedron letters》2011,52(44):5752-5757
An efficient strategy for the stereo- and regio-selective synthesis of N-alkenynes has been described. The salient feature of the reaction involves hydro-amination/amidation of 1,3-diynes with indoles/azoles/amides via transition-metal catalyzed activation of N-H bond. The resulting N-alkenynes derived from N-heterocycles and cyclic amides were obtained as a mixture of Z/E isomers with Z-stereoselectivity ranging from 60% to 95%. In contrast, acyclic amides afforded N-alkenynes with exclusive E-stereoselectivity, albeit in reduced yield ranging from ∼10% to 41%. 相似文献
945.
Srivastava S Awasthi R Gajbhiye NS Agarwal V Singh A Yadav A Gupta RK 《Journal of colloid and interface science》2011,359(1):104-111
In this study, we describe the development of a facile and effective route for the synthesis of Fe(3)O(4)-based T(1) contrast agent, which can be useful for in vivo magnetic resonance (MR) imaging. Citrate-coated Fe(3)O(4) nanoparticles (6 nm) with a narrow size distribution were synthesized by "one-pot green chemistry route" in diethylene glycol (DEG) solvent. The synthesized nanoparticles were characterized by different analytical techniques including XRD, TEM, HRTEM, and FTIR. At room temperature, nanoparticles exhibited superparamagnetic nature with high saturation magnetization. The longitudinal (r(1)) and transverse (r(2)) relaxivities were found to be 35.45 and 51.81 mM(-1)s(-1), respectively. Contrast agent developed by this method showed a relatively higher longitudinal relaxivity (r(1)) and the lowest relaxivity ratio (r(2)/r(1)=1.46) at 3T MR field. The anionic nature of citric acid facilitated non-specific internalization without impairment of cell viability and functionality. The in vitro studies showed both phagocitic and non-phagocytic uptake of these NPs. In vivo MR imaging of swine showed both T(1) and T(2) contrast effect. 相似文献
946.
Anand G Zhang F Linhardt RJ Belfort G 《Langmuir : the ACS journal of surfaces and colloids》2011,27(5):1830-1836
Removing adsorbed protein from metals has significant health and industrial consequences. There are numerous protein-adsorption studies using model self-assembled monolayers or polymeric substrates but hardly any high-resolution measurements of adsorption and removal of proteins on industrially relevant transition metals. Surgeons and ship owners desire clean metal surfaces to reduce transmission of disease via surgical instruments and minimize surface fouling (to reduce friction and corrosion), respectively. A major finding of this work is that, besides hydrophobic interaction adhesion energy, water content in an adsorbed protein layer and secondary structure of proteins determined the access and hence ability to remove adsorbed proteins from metal surfaces with a strong alkaline-surfactant solution (NaOH and 5 mg/mL SDS in PBS at pH 11). This is demonstrated with three blood proteins (bovine serum albumin, immunoglobulin, and fibrinogen) and four transition metal substrates and stainless steel (platinum (Pt), gold (Au), tungsten (W), titanium (Ti), and 316 grade stainless steel (SS)). All the metallic substrates were checked for chemical contaminations like carbon and sulfur and were characterized using X-ray photoelectron spectroscopy (XPS). While Pt and Au surfaces were oxide-free (fairly inert elements), W, Ti, and SS substrates were associated with native oxide. Difference measurements between a quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance spectroscopy (SPR) provided a measure of the water content in the protein-adsorbed layers. Hydrophobic adhesion forces, obtained with atomic force microscopy, between the proteins and the metals correlated with the amount of the adsorbed protein-water complex. Thus, the amount of protein adsorbed decreased with Pt, Au, W, Ti and SS, in this order. Neither sessile contact angle nor surface roughness of the metal substrates was useful as predictors here. All three globular proteins behaved similarly on addition of the alkaline-surfactant cleaning solution, in that platinum and gold exhibited an increase, while tungsten, titanium, and stainless steel showed a decrease in weight. According to dissipation measurements with the QCM-D, the adsorbed layer for platinum and gold was rigid, while that for the tungsten, titanium, and stainless steel was much more flexible. The removal efficiency of adsorbed-protein by alkaline solution of SDS depended on the water content of the adsorbed layers for W, Ti, and SS, while for Pt and Au, it depended on secondary structural content. When protein adsorption was high (Pt, Au), protein-protein interactions and protein-surface interactions were dominant and the removal of protein layers was limited. Water content of the adsorbed protein layer was the determining factor for how efficiently the layer was removed by alkaline SDS when protein adsorption was low. Hence, protein-protein and protein-surface interactions were minimal and protein structure was less perturbed in comparison with those for high protein adsorption. Secondary structural content determined the efficient removal of adsorbed protein for high adsorbed amount. 相似文献
947.
Bartlett AP Agarwal AK Yethiraj A 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4313-4318
Order-disorder transitions in colloidal systems are an attractive option for making switchable materials. Electric-field-driven order-disorder transitions are especially attractive for this purpose because the tuning parameter is easily and externally controllable. However, precise positional control of 3D structure is immensely challenging. Using patterned electrodes, we demonstrate that ac electric fields-dominantly dielectrophoresis (DEP) coupled with an electrohydrodynamic mechanism consisting of induced-charge electro-osmosis (ICEO)-can be used to template colloidal order dynamically in three dimensions. We find that the electric field geometry dictates the location, size, and shape of colloidal patterns and can produce patterns with surprising complexity. 相似文献
948.
Sinkel C Schwarzer MC Frenking G Greiner A Agarwal S 《Magnetic resonance in chemistry : MRC》2011,49(2):70-75
Heterodimers based on the polymer-bound chromophore 4-methylcoumarin and the prodrug 1-heptanoyl-5-fluorouracil, synthesized by photochemical [2 + 2]-cycloaddition are promising photoresponsive drug depots. Drug release experiments are one possibility to deliver proof of a successful reversible drug immobilization, whereas NMR spectroscopy is a potent tool for further structural characterization of these polymer-bound heterodimers. In case of the random copolymer poly(methyl methacrylate-co-7-(2'-methacryloyloxyethoxy)-4-methylcoumarin) three dimers have been identified of which the syn head-to-tail was the predominant one. In contrast, only the syn head-to-head dimer was formed in reasonable yield when the 4-methylcoumarin monofunctionalized pMMA was used as the base polymer. 1D and 2D NMR spectroscopic techniques combined with some theoretical calculations helped in successfully closing one major gap concerning polymer bound 4-methylcoumarin/1-heptanoyl-5-fluorouracil heterodimers that are of potential use in photoresponsive drug delivery devices. 相似文献
949.
Patra A Bandyopadhyay D Tomar G Sharma A Biswas G 《The Journal of chemical physics》2011,134(6):064705
Instability and dewetting engendered by the van der Waals force in soft thin (<100 nm) linear viscoelastic solid (e.g., elastomeric gel) films on uniform and patterned surfaces are explored. Linear stability analysis shows that, although the elasticity of the film controls the onset of instability and the corresponding critical wavelength, the dominant length-scale remains invariant with the elastic modulus of the film. The unstable modes are found to be long-wave, for which a nonlinear long-wave analysis and simulations are performed to uncover the dynamics and morphology of dewetting. The stored elastic energy slows down the temporal growth of instability significantly. The simulations also show that a thermodynamically stable film with zero-frequency elasticity can be made unstable in the presence of physico-chemical defects on the substrate and can follow an entirely different pathway with far fewer holes as compared to the viscous films. Further, the elastic restoring force can retard the growth of a depression adjacent to the hole-rim and thus suppress the formation of satellite holes bordering the primary holes. These findings are in contrast to the dewetting of viscoelastic liquid films where nonzero frequency elasticity accelerates the film rupture and promotes the secondary instabilities. Thus, the zero-frequency elasticity can play a major role in imposing a better-defined long-range order to the dewetted structures by arresting the secondary instabilities. 相似文献
950.