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81.
Ashok G. Bajaj Sukh Dev Bruce Tagle Joshua Telser Jon Clardy 《Tetrahedron letters》1980,21(4):325-326
Allohimachalol, an unusual rearranged sesquiterpene from the essential oil of Loud., is shown to have structure 3. 相似文献
82.
In order to examine the validity of the impulse approximation for pion-nucleus scattering in the 33-resonance energy region, we consider pion-scattering from a “nucleus” which consists of a single nucleon bound in a harmonic oscillator potential. A separable πN interaction is assumed. The oscillator parameter is chosen such that the nuclear sizes are fitted for 4He ~ 16O. The binding effect is found to result in a downward shift of the resonance energy (by about 20 MeV), and an increase (by 50 ~ 70%) of the total cross section near the resonance. The angular distribution is also strongly modified. In connection with the binding effect, the importance of a careful treatment of nucleon recoil is emphasized. It is pointed out that the closure approximation which is often used to sum over intermediate nuclear states leads to very misleading results. The effect of the Pauli principle is also examined by excluding some intermediate states. 相似文献
83.
Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB6 at temperatures below 4·2 K are presented using the external magnetic field,H
ext, in the range of 0 ⩽H
ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB6,T
1 is approximately 5 × 103 times larger thanT
2 at 1·7 K with the 10 kG magnetic field. Thus the effect ofT
1 onT
2 can be neglected. From the experimental value ofT
2, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method
is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR. 相似文献
84.
Monica Rao Amrita Bajaj Ishwar Khole Ghanshyam Munjapara Francesco Trotta 《Journal of inclusion phenomena and macrocyclic chemistry》2013,77(1-4):135-145
Telmisartan (TEL) is a BCS Class II drug having dissolution rate limited bioavailability. The aim of work was to enhance the solubility of TEL so that bioavailability problems are solved. β-Cyclodextrin (β-CD) based nanosponges (NSs) were formed by cross-linking β-CD with carbonate bonds, which were porous as well as nanosized. Drug was incorporated by solvent evaporation method. The effect of ternary component alkalizer (NaHCO3) on solubility of TEL was studied. In order to find out the solubilization efficiency of NS, phase solubility study was carried out. Saturation solubility and in vitro dissolution study of β-CD complex of TEL was compared with plain TEL and NS complexes of TEL. The NS and NS complexes of TEL were characterized by differential scanning calorimetry, powder X-ray diffraction, Fourier transform infrared spectroscopy, nuclear magnetic resonance and scanning electron microscope. It was found that solubility of TEL was increased by 8.53-fold in distilled water; 3.35-fold in 0.1 N HCl and 4.66-fold in phosphate buffer pH 6.8 by incorporating NaHCO3 in drug–NS complex than TEL. It was found that the NaHCO3 in NS based complex synergistically enhanced dissolution of TEL by modulating microenvironmental pH and by changing amorphization of the drug. The highest solubility and in vitro drug release was observed in inclusion complex prepared from NS and NaHCO3. An increase of 54.4 % in AUC was seen in case the ternary NS complex whereas β-CD ternary complex exhibited an increase of 79.65 %. 相似文献
85.
86.
An understanding of the fatigue and fracture behavior of hard tissues (e.g., bone and tissues of the human tooth) is critical
to the maintenance of physical and oral health. Recent studies suggest that there are a number of mechanisms contributing
to crack extension and crack arrest in these materials, and that they appear to be a function of moisture and age of the tissue.
An understanding of these processes can provide new ideas that are relevant to the design of multi-functional engineering
materials. As a result, we have adopted the use of microscopic Digital Image Correlation (DIC) to examine the mechanisms of
crack growth resistance and near-tip displacement distribution for cracks in human dentin that are subjected to opening mode
loads. We have also developed a special compact tension (CT) specimen that permits evaluation of crack extension within small
portions of tissue under both quasi-static and fatigue loads. The specimen embodies a selected portion of hard tissue within
a resin composite restorative and enables an examination of diseased tissue, or portion with specific physiology, that would
otherwise be impossible to evaluate. In this paper we describe application of these experimental methods and present some
recent results concerning fatigue crack growth and stable crack extension in dentin and across the dentin-enamel-junction
(DEJ) of human teeth.
相似文献
D. Arola (SEM member)Email: |
87.
In this paper, a study of the global dynamics of an autoparametric four degree-of-freedom (DOF) spring–mass–pendulum system
with a rigid body mode is presented. Following a modal decoupling procedure, typical approximate periodic solutions are obtained
for the autoparametrically coupled modes in 1:2 internal resonance. A novel technique based on forward-time solutions for
finite-time Lyapunov exponent is used to establish global convergence and domains of attraction of different solutions. The
results are compared to numerically constructed domains of attraction in the plane of initial position and initial velocity
for the pendulum. Simulations are also provided for a few interesting cases of interest near critical values of parameters.
Results also shed some light on the role played by other modes present in a multi-DOF system in shaping the overall system
response. 相似文献
88.
Saponification kinetics of acrylic terpolymer and polyacrylonitrile were studied. The influence of alkali concentration and the time of hydrolysis on the degree of saponification were determined by the residual nitrogen content. The order of reaction was graphically determined and the rate of saponification was found to be faster in the terpolymer than in the homopolymer. Chemical and infrared spectroscopy methods reveal that the reaction is initiated through cyclization of nitrile groups, followed by hydrolysis to amide and carboxylic groups of the [sbnd](C[dbnd]N)n[sbnd] segments produced. The saponification of nitrile groups in the terpolymer initially yields amide groups, then slows down to yield carboxylic groups. 相似文献
89.
Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1?xAlxAs are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed. 相似文献
90.
Styrene has been copolymerized to high conversions with vinylmethyl diacetoxysilane (VMDAS) and vinylmethyldiethoxysilane (VMDES) in bulk and in toluene at 60 using azobisisobutyronitrile (AIBN) as initiator. Acrylonitrile has also been copolymerized with VMDAS at 50 in bulk using AIBN. The compositions of the copolymers were determined from the silicon contents; reactivity ratios were calculated by the Kelen-Tüdös method. The reactivity ratio r1 (styrene) is higher for styrene-VMDES than for styrene-VMDAS, indicating higher reactivity of VMDAS towards polystyryl radical. VMDAS was found to be more reactive towards the polyacrylonitrile than towards the polystyrene radical. The influences of the silicon comonomer on properties such as intrinsic viscosity, solubility, molecular weight distribution and thermal behaviour were also studied. 相似文献