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111.
Morphology development during isothermal annealing of poly(ether-ester) multiblock copolymers with hard segments containing poly(tetramethylene isophthalate) is examined by differential scanning calorimetry (DSC) and small-angle x-ray scattering (SAXS). Reorganization in the solid-state occurs by melting and recrystallization. At temperatures close to the melting point, glass transition measurements after quenching from the annealing temperature suggest microphase mixing follows melting. The temperature of maximum recrystallization rate is elevated relative to that of isothermal crystallization. SAXS experiments suggest that a memory of the initial morphology is retained during annealing. Aspects of the DSC scans related to crystallization on cooling and rescanning also suggest that the morphology at the annealing temperature plays a governing role in the determination of the degree of order possible on cooling. The crystalline regions stable at the annealing temperature are envisioned to function in a dual role, acting as nucleation centers for recrystallization and as a form of “constraint” to ordering on cooling. © 1996 John Wiley & Sons, Inc. 相似文献
112.
Kunlun Wang Prabin Rai Ashani Fernando Tibor Szilvási Huaizhe Yu Nicholas L. Abbott 《Liquid crystals》2020,47(1):3-16
ABSTRACTA series of fluorine tail-terminated alkoxy and alkyl cyanobiphenyl compounds and some cyano-p-terphenyl derivatives were synthesised and mesogenic properties described. Comparison with the non-fluorinated K series and M series indicates that the terminal fluorine atom generally decreases the transition temperatures and, more interestingly, depresses the formation of a smectic phase. Several binary LC mixtures formed by the fluorine tail-terminated compounds were found exhibiting promising room temperature nematic phases with wide ranges. The mixture F7OCB and F8OCB shows homeotropic ordering at the metal salts-decorated surfaces and planar ordering at the free surface, which may have potential application in designing a more sensitive and faster LC system to targeted analytes. 相似文献
113.
A novel, stable and highly sensitive non-enzymatic glucose (Glc) sensor was developed using vertically well-aligned multi-walled carbon nanotubes array (MWCNTs) incorporated with cupric oxide (CuO) nanoparticles. The MWCNTs array was prepared by catalytic chemical vapor deposition on a tantalum (Ta) substrate, while a simple and rapid two-step electrodeposition technique was used to prepare the CuO-MWCNTs nanocomposite. First, Cu nanoparticles were deposited onto MWCNTs at constant potential and then they were oxidized into CuO by potential cycling. The electrocatalytic activity of CuO-MWCNTs array was investigated for Glc under alkaline conditions using cyclic voltammetry and chronoamperometry. The sensor exhibited a linear response up to 3 mM of Glc and sensitivity of 2190 μA mM−1 cm−2, which is two to three orders of magnitude higher than that of most non-enzymatic Glc sensors reported in the literature. The sensor response time is less than 2 s and detection limit is 800 nM (at signal/noise = 3). When tested with human blood serum samples, the sensor exhibited high electrocatalytic activity, stability, fast response and good selectivity against common interfering species, suggesting its potential to be developed as a non-enzymatic Glc sensor. 相似文献
114.
Cornelis E. C. A. Hop Dovas A. Saulys Donald F. Gaines 《Journal of the American Society for Mass Spectrometry》1995,6(9):860-865
Two borane salts ([(Me)4N][B3H8] and Cs[B3H8]) were examined by electrospray mass spectrometry in the positive ion mode. Acetonitrile solutions provided the most informative spectra; the salts exhibited a remarkable degree of clustering under electrospray conditions, and virtually all signals corresponded to cationic cluster ions of the general formula {[cation m+] x [anion n?] y }(mx ? ny)+. In contrast, methanol solutions of these salts produced only B(OCH3) 4 ? cluster ions under otherwise identical conditions. 11B NMR analyses corroborate the identities of the methanol solution species that enter the electrospray source and the reaction product generated during the electrospray process. 相似文献
115.
《Physics letters. [Part B]》1987,198(3):336-342
The gravitational supermultiplet for target space-time supersymmetry of four-dimensional heterotic strings is obtained. By an explicit construction of supervertex operators it is shown that the underlying superspace geometry corresponds to the “new-minimal” formulation of N = 1, 4D supergravity. The relation between R-symmetry in target space and the U(1) symmetry of the world-sheet N = 2 superconformal algebra is outlined. 相似文献
116.
Models for weather and climate prediction are complex, and each
model typi-cally has at least a small number of phenomena that are
poorly represented, such as perhaps the Madden-Julian Oscillation
(MJO for short) or El Ni\~{n}o-Southern Oscillation (ENSO for short)
or sea ice. Furthermore, it is often a very challenging task to
modify and improve a complex model without creating new
deficiencies. On the other hand, it is sometimes possible to design
a low-dimensional model for a particular phenomenon, such as the MJO
or ENSO, with significant skill, although the model may not
represent the dynamics of the full weather-climate system. Here a
strategy is proposed to mitigate these model errors by taking
advantage of each model''s strengths. The strategy involves
inter-model data assimilation, during a forecast simulation, whereby
models can exchange information in order to obtain more faithful
representations of the full weather-climate system. As an initial
investigation, the method is examined here using a simplified
scenario of linear models, involving a system of stochastic partial
differential equations (SPDEs for short) as an imperfect tropical
climate model and stochastic differential equations (SDEs for short)
as a low-dimensional model for the MJO. It is shown that the MJO
prediction skill of the imperfect climate model can be enhanced to
equal the predictive skill of the low-dimensional model. Such an
approach could provide a route to improving global model forecasts
in a minimally invasive way, with modifications to the prediction
system but without modifying the complex global physical model
itself. 相似文献
117.
《Tetrahedron》1988,44(13):4135-4145
The title carbanion species are generated from the corresponding α-haloorganosilicon compounds by the action of a catalytic amount of tris(diethylamino)sulfonium difluorotrimethylsilicate and are found to undergo addition to aldehyde carbonyl efficiently at ambient temperature. The synthetic potential of the reaction is demonstrated by application to the synthesis of some insecticides. 相似文献
118.
《Tetrahedron letters》1988,29(47):6087-6090
Crystalline, optically pure N-fluoro sultams (−)-3 and (+)-5 are the first examples of enantioselective fluorinating reagents. Thus unprecedented enantiomeric excesses up to 70% are observed when various prochiral metal enolates are fluorinated by using these new reagents. 相似文献
119.
《Physics letters. [Part B]》1987,199(1):101-107
We describe and compare various methods to numerically simulate measures that are non-positive definite. We argue that variations of importance sampling will fail for large enough volume but some type of Riemann integration scheme might work. Using exact results for the three-dimensional Ising model, we show that to get anything distinguishable from noise, the phase of the measure must be known extremely precisely. We suggest that a recent method to compute the density of states may be the best method to use. 相似文献
120.
P. A. Frey E. Cardemil R. Iyengar J. Van Pelt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):563-566
Abstract Mevalonate 5-pyrophosphate (MVAPP) decarboxylase catalyzes the decarboxylation of MVAPP to isopentenyl pyro-phosphate, an ATP-dependent process in which 3-phospho-MVAPP is a transient intermediate that undergoes concomitant decarboxylation and elimination of phosphate. Reaction of (Sp)-adenosine 5′-0-3-thio [3-17O 2,180] triphosphate in place of ATP produces (R)-[17O,18O] thiophosphate in place of phosphate. Therefore, the phosphotransfer step producing 3-phospho-MVAPP proceeds with inversion of configuration at P. Gentamicin nucleotidyl-transferase catalyzes the reaction of ATP with the C-2″ hydroxyl group of aminoglycoside antibiotics to produce AMP-2″-aminoglycosides, thereby inactivating the drugs. Enzymatic reaction of (Sp)-2′-deoxyadenosine 5′-O[α-17O] triphosphate with tobramycin produces (Rp)-[α-17O]dAMP-2″-tobramycin. Therefore, transfer of the 2′-deoxyadenosine 5′-phosphoryl group proceeds with inversion of configuration. Since both reactions are uncomplicated bisubstrate processes and both proceed with inversion at P, it is likely that both proceed by mechanisms involving direct, single-step phosphotransfer from the phospho-donor substrate to the acceptor, rather than by double-displacement mechanisms involving covalent, phosphoenzyme-intermediates. 相似文献