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排序方式: 共有143条查询结果,搜索用时 15 毫秒
1.
Extension of a combined analytical/numerical initial value problem solver for unsteady periodic flow
Here we describe analytical and numerical modifications that extend the Differential Reduced Ejector/ mixer Analysis (DREA), a combined analytical/numerical, multiple species ejector/mixing code developed for preliminary design applications, to apply to periodic unsteady flow. An unsteady periodic flow modelling capability opens a range of pertinent simulation problems including pulse detonation engines (PDE), internal combustion engine ICE applications, mixing enhancement and more fundamental fluid dynamic unsteadiness, e.g. fan instability/vortex shedding problems. Although mapping between steady and periodic forms for a scalar equation is a classical problem in applied mathematics, we will show that extension to systems of equations and, moreover, problems with complex initial conditions are more challenging. Additionally, the inherent large gradient initial condition singularities that are characteristic of mixing flows and that have greatly influenced the DREA code formulation, place considerable limitations on the use of numerical solution methods. Fortunately, using the combined analytical–numerical form of the DREA formulation, a successful formulation is developed and described. Comparison of this method with experimental measurements for jet flows with excitation shows reasonable agreement with the simulation. Other flow fields are presented to demonstrate the capabilities of the model. As such, we demonstrate that unsteady periodic effects can be included within the simple, efficient, coarse grid DREA implementation that has been the original intent of the DREA development effort, namely, to provide a viable tool where more complex and expensive models are inappropriate. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Phanstiel O IV Price HL Wang L Juusola J Kline M Shah SM 《The Journal of organic chemistry》2000,65(18):5590-5599
An efficient five-step synthetic method was developed to access a homologous series of spermidine-acridine and spermidine-anthracene conjugates. The derivatives were comprised of a spermidine fragment covalently tethered at its N4 position to either an acridine or anthracene nucleus via an aliphatic chain (e.g., spermidine-[aliphatic tether]-acridine). The distance separating the spermidine and aromatic nucleus was altered by using different tethers comprised of four or five methylene units, respectively. These ligands (2-5) were shown to inhibit human DNA topoisomerase-II (TOPO-II) activity at 10 microM. Enzymatic activity was assessed as the ability to unknot (decatenate) and cleave kinetoplast DNA (kDNA). Polyamine conjugation did not disrupt the ability of the acridine-spermidine conjugates 2 and 3 to inhibit TOPO-II activity as compared with the 9-aminoacridine and 9-(N-butyl)aminoacridine controls (at 10 microM). In general, the acridine derivatives (2 and 3) showed higher TOPO-II inhibitory activity than their anthracene counterparts (4 and 5). However, this trend was reversed in a whole cell assay with L1210 (murine leukemia) cells, wherein the anthracene analogues were more potent than their acridine counterparts. In this regard the qualitative enzyme-based assay did not predict the trends in the corresponding IC(50) values. Within either series insertion of an additional methylene unit did not significantly alter activity. While the appended spermidine unit did not disrupt TOPO II inhibition by the tethered DNA intercalator, it did provide an alternative mode of entry into the cell as demonstrated by spermidine protection assays. These results were compared with a spermine-intercalator analogue. Of all the conjugates tested the N(4)-(4-(9-aminoacridinyl)butyl)spermine hexahydrochloride (conjugate 16)resulted in the highest degree of L1210 cell rescue upon cotreatment of the cells with exogenous spermidine. It was concluded that the monoalkylated spermine motif present in 16 holds promise as a better vector than its N4 monoalkylated spermidine counterpart. 相似文献
3.
Summary Effects of gamma radiation on the dynamic mechanical properties of polyvinyl chloride (PVC) have been studied at audio frequencies from 80 K to 450 K for doses up to 1400 megarads. Two damping peaks were observed between 80 K and 400 K. The onset of main relaxation near 350 K shifted to lower temperatures at low doses, and then shifted to higher temperatures at a dose of 1400 megarads. Only slight changes are discernible in the damping peak near 250 K upon irradiation, but definite variations are noted in the modulus curves. Upon irradiation to 270 megarads an additional damping peak appeared near 150 K accompanied by an increase in modulus at lower temperatures. The height of this peak increased with increasing radiation dose.Crosslinking was confirmed from rubber elastic behavior, swelling, and solvent extraction studies. Some tentative explanations for the changes occurring in the dynamic mechanical properties of irradiated PVC are given in terms of crosslinking, loss of crystallinity, and dehydrochlorination followed by the formation of conjugated series of double bonds.
This work was supported in part by the National Science Foundation and the National Aeronautics and Space Administration. 相似文献
Zusammenfassung Es wurde die Wirkung von-Strahlung auf die dynamisch-mechanischen Eigenschaften von Polyvinylchlorid (PVC) bei Hörfrequenzen von 80 K bis 450 K für Dosen bis zu 1400 Megarad untersucht. Zwei Dämpfungspiks zeigen sich zwischen 80 und 400 K. Das Einsetzen der Hauptrelaxation nahe 350 K verlagert sich zu tieferen Temperaturen bei kleineren Dosen, um dann zu höheren Temperaturen bei einer Dosis von 1400 Megarad hinaufzugehen. Nur leichte änderungen sind im Dämpfungspik nahe 250 K durch die Strahlung zu beobachten; aber in der Modulkurve werden definierte Variationen erkennbar. Nach Bestrahlung mit 270 Megarad erscheint ein zusätzlicher Dämpfungspik nahe 150 K, begleitet durch ein Anwachsen des Moduls zu tieferen Temperaturen. Die Höhe dieses Piks wächst mit wachsender Strahlungsdosis.Die Vernetzung wurde aus dem gummielastischen Verhalten, der Quellung und aus Lösungsmittel-Extraktionen bestimmt. Die im dynamisch-mechanischen Verhalten durch die Strahlung des PVC auftretenden änderungen werden auf Grund der Vernetzung, der Abnahme an Kristallinität, der Dehydrochlorierung — gefolgt durch die Bildung von Serien konjugierter Doppelbildungen — erklärt.
This work was supported in part by the National Science Foundation and the National Aeronautics and Space Administration. 相似文献
4.
Zartler ER Hanson J Jones BE Kline AD Martin G Mo H Shapiro MJ Wang R Wu H Yan J 《Journal of the American Chemical Society》2003,125(36):10941-10946
The crucial step in drug discovery is the identification of a lead compound from a vast chemical library by any number of screening techniques. NMR-based screening has the advantage of directly detecting binding of a compound to the target. The spectra resulting from these screens can also be very complex and difficult to analyze, making this an inefficient process. We present here a method, RAMPED-UP NMR, (Rapid Analysis and Multiplexing of Experimentally Discriminated Uniquely Labeled Proteins using NMR) which generates simple spectra which are easy to interpret and allows several proteins to be screened simultaneously. In this method, the proteins to be screened are uniquely labeled with one amino acid type. There are several benefits derived from this unique labeling strategy: the spectra are greatly simplified, resonances that are most likely to be affected by binding are the only ones observed, and peaks that yield little or no information upon binding are eliminated, allowing the analysis of multiple proteins easily and simultaneously. We demonstrate the ability of three different proteins to be analyzed simultaneously for binding to two different ligands. This method will have significant impact in the use of NMR spectroscopy for both the lead generation and lead optimization phases of drug discovery by its ability to increase screening throughput and the ability to examine selectivity. To the best of our knowledge, this is the first time in any format that multiple proteins can be screened in one tube. 相似文献
5.
Yan J Kline AD Mo H Shapiro MJ Zartler ER 《Magnetic resonance in chemistry : MRC》2004,42(11):962-967
A novel methodology using the order matrix calculation to determine the absolute sign of spin-spin couplings based on the structure of organic compounds is presented. The sign of the residual dipolar coupling (RDC) depends on the sign of corresponding scalar spin-spin coupling constant and the sign of the RDC has a dramatic influence on the order matrix calculation. Therefore, the sign of the spin-spin coupling constant can be obtained by an order matrix calculation through the corresponding RDC. Six types of spin-spin coupling constants, including 2J(H,H), 1J(C,F), 2J(C,F), 3J(C,F), 2J(F,H) and 3J(F,H), were obtained simultaneously. Except for 3J(C,F) where the measured RDCs have very small magnitudes, the signs were determined unambiguously. 相似文献
6.
Paul C. Kline Bruce C. Noll Hongqiu Zhao Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(2):o137-o140
1‐(β‐d ‐Erythrofuranosyl)cytidine, C8H11N3O4, (I), a derivative of β‐cytidine, (II), lacks an exocyclic hydroxymethyl (–CH2OH) substituent at C4′ and crystallizes in a global conformation different from that observed for (II). In (I), the β‐d ‐erythrofuranosyl ring assumes an E3 conformation (C3′‐exo; S, i.e. south), and the N‐glycoside bond conformation is syn. In contrast, (II) contains a β‐d ‐ribofuranosyl ring in a 3T2 conformation (N, i.e. north) and an anti‐N‐glycoside linkage. These crystallographic properties mimic those found in aqueous solution by NMR with respect to furanose conformation. Removal of the –CH2OH group thus affects the global conformation of the aldofuranosyl ring. These results provide further support for S/syn–anti and N/anti correlations in pyrimidine nucleosides. The crystal structure of (I) was determined at 200 K. 相似文献
7.
Nieh MP Raghunathan VA Kline SR Harroun TA Huang CY Pencer J Katsaras J 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6656-6661
We observe the spontaneous formation of path-dependent monodisperse and polydisperse phospholipid unilamellar vesicles (ULV) from two different equilibrium morphologies specifically, disklike micelles and extended lamellae, respectively. On heating beyond a temperature Tc, low temperature disklike micelles, or so-called bicelles, transform into lamellae. Dilution of the lamellar phase, at a fixed temperature, results in a complete unbinding transition and the formation of polydisperse ULV, demonstrating the instability of the lamellar phase. On the other hand, heating of a dilute bicellar phase above Tc results in monodisperse ULV, which on cooling revert back to bicelles for lipid concentrations phi > or = 0.5 wt % and transform into oblate ellipsoids for phi = 0.1 wt %, a morphology not previously seen in "bicellar" lipid mixtures. Monodisperse ULV reform on heating of the oblate ellipsoids. 相似文献
8.
9.
Dependence of electrical performance on structural organization in polymer field effect transistors
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Emily G. Bittle Hyun Wook Ro Chad R. Snyder Sebastian Engmann R. Joseph Kline Xinran Zhang Oana D. Jurchescu Dean M. DeLongchamp David J. Gundlach 《Journal of Polymer Science.Polymer Physics》2017,55(14):1063-1074
Organic semiconductors (OSCs) are strong contenders for use in printed, flexible electronics. Although organic electronic materials have been studied for many years, the physics of charge transport is still under investigation. This is in part due to variability resulting from the large variety of molecules that can be synthesized and inconsistency in electrical characterization due to device and processing conditions. Molecular ordering in OSCs is known to alter the charge transport characteristics and attention to long range and short range ordering provides clues as to the nature of transport pathways. Here, we study ordered regioregular poly(3‐hexylthiophene‐2,5‐diyl) films carefully prepared to obtain a set of three samples with incrementally increasing order on identical transistor architectures. Ordering was characterized using a variety of short and long range techniques to probe the coherence and number of crystallites formed during processing, and the correlation between these different measures of order are quantified. We observe three changes in transistor behavior that show a shift from non‐ideal to more textbook‐like characteristics with increasing order: reduction of the contact resistance, shift to field‐independent mobility, and a shift from a diode‐like (S‐shaped) to linear response at low lateral fields. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1063–1074 相似文献
10.
Kline JL Scime EE Boivin RF Keesee AM Sun X Mikhailenko VS 《Physical review letters》2002,88(19):195002
Experimental data are presented that are consistent with the hypothesis that anomalous rf absorption in helicon sources is due to electron scattering arising from parametrically driven ion-acoustic waves downstream from the antenna. Also presented are ion temperature measurements demonstrating anisotropic heating (T( perpendicular)>T(parallel)) at the edge of the discharge. The most likely explanation is ion-Landau damping of electrostatic slow waves at a local lower-hybrid-frequency resonance. 相似文献