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91.
92.
ABSTRACT

Using a hyperbolic function type-potential and Schrödinger’s equation transformed into a hypergeometric differential equation along with the results presented from an ab-initio CASSCF(10,11)/cc-pVTZ calculation we show that the potential well of the classical vinyl cation minimum is incapable of supporting a zero point vibrational motion for the protons. Furthermore, as opposed to the previously found transition state linking the classical and bridged vinyl cations, we suggest that it becomes a transition state for the interconversion or tautomerization of the bridged vinyl cation.  相似文献   
93.
ABSTRACT

In this work we study the possibility of the photochemical formation of the symmetrical Dewar pyridine (1-azabicyclo-[2,2,0]-hexa-2,5-diene), by applying the complete active space self-consistent field method and the multiconfigurational second-order perturbation theory to explore the corresponding ground and excited state potential energy surfaces. According to our theoretical calculations there are three possible paths that can be followed, one is a biphotonic process which involves irradiating pyridine in its ground state with a 358?nm laser guiding the system to an intersystem crossing S1/T1/S0 of triple character whereby deactivation to the ground state, S0, Dewar minimum occurs, the second one, which is a ground state thermal reaction involves the use of a far-Infra-Red laser where planar pyridine is vibrationally excited to a very high vibrational level whose energy is comparable to that of the ground state transition structure, S0(TS), connecting the symmetrical S0 Dewar pyridine and the ground state of planar pyridine. The third process is also a biphotonic one involving excitation of planar pyridine with an energy which is in the limits of its ionisation potential. In this case there is a theoretically accessible S1/S0 Conical Intersection which leads directly to the ground state of the symmetrical Dewar pyridine.  相似文献   
94.
A series of novel multi‐responsive disulfide cross‐linked polypeptide nanogels has been synthesized by a one‐step ring‐opening polymerization process. The pH‐responsive core of the prepared nanogels was based on poly(L‐histidine), the difunctional N‐carboxy anhydride of l ‐cystine (l ‐Cys‐NCA) was used as a reduction‐cleavable cross‐linking agent, while the outer hydrophilic corona was comprised of a poly(ethylene oxide) block. Extensive molecular characterization studies were conducted in order to confirm the formation of the desired polymeric nanostructures and also to prove their responsiveness to external stimuli within the physiological values of healthy and cancer tissues. Furthermore, the disruption of the disulfide‐bond linkages between the polymeric chains was achieved by the presence of the reductive tripeptide glutathione (GSH), leading to size variations that were monitored by dynamic light scattering (DLS) and size‐exclusion chromatography (SEC). “Stealth” properties of the formed nanostructures were examined by zeta potential measurements. The described nanogels are clearly promising candidates for drug delivery applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1278–1288  相似文献   
95.
Volume holographic gratings (VHGs) can be exploited to narrow the spectral output of high-power laser-diode arrays (LDAs) by nearly an order of magnitude, permitting more efficient generation of laser-polarized noble gases for various applications. A 3-fold improvement in 129Xe nuclear spin polarization, PXe, (compared to a conventional LDA) was achieved with the VHG-LDA’s center wavelength tuned to a wing of the Rb D1 line. Additionally, an anomalous dependence of PXe on the xenon density within the OP cell is reported—including high PXe values (>10%) at high xenon partial pressures (1000 torr).  相似文献   
96.
The aim of this study was to evaluate a flat rectangular (3 × 10 mm2) MRI compatible transducer operating at 5 MHz. The main task was to explore the feasibility of creating deep lesions in heart at a depth of at least 15 mm. The size of thermal necrosis in heart tissue was estimated as a function of power and time using a simulation model. The system was then tested in an excised lamb heart. In this study, we were able to create lesions of 15 mm deep with acoustic power of 6 W for an exposure of approximately 1 min. The contrast to noise ratio (CNR) between lesion and heart tissue was evaluated using fast spin echo (FSE). The CNR value was approximately 22 using T1 W FSE. Maximum CNR was achieved with repetition time (TR) between 300 and 800 ms. Using T2W FSE, the corresponding CNR was approximately 13 for the 14 in vivo experiments. The average lesion depth was 11.93 mm with a standard deviation of 0.62 mm. In vivo irradiation conditions were 6 W for 60 s. The size of the lesion in the other two dimensions was close to 3 × 10 mm2 (size of the transducer element).  相似文献   
97.
Spherical water microtraps were prepared via a two steps process, which comprises the preparation of cross-linked poly(methacrylic acid) spheres by distillation–precipitation polymerization and the subsequent conversion of carboxylic groups to the corresponding sodium salts by treatment with aqueous sodium hydroxide solution. The influence of the cross-linker amount was investigated in order to achieve greater water absorption and a reversibility of the initial spheres after drying the formed hydrogel or washing with an excess of organic solvent. We achieved the highest water absorbency of about 70 times their weight occurring rapidly and unlimited times reversible after going through repeatable cycles of absorption and drying. This new material, called microtraps, was developed for its incorporation into multilayer anticorrosive coatings to prevent contact of water with metallic substrates.  相似文献   
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We introduce and study an envelope-type region ɛ(A) in the complex plane that contains the eigenvalues of a given n×n complex matrix A. ɛ(A) is the intersection of an infinite number of regions defined by cubic curves. The notion and method of construction of ɛ(A) extend the notion of the numerical range of A, F(A), which is known to be an intersection of an infinite number of half-planes; as a consequence, ɛ(A) is contained in F(A) and represents an improvement in localizing the spectrum of A.  相似文献   
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