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排序方式: 共有222条查询结果,搜索用时 31 毫秒
21.
Oluseye K. Onajole Maya M. Makatini Patrick Govender Thavendran Govender Glenn E. M. Maguire Hendrik G. Kruger 《Magnetic resonance in chemistry : MRC》2010,48(3):249-255
The synthesis and complete NMR elucidation of eight novel pentacycloundecane (PCU) derivatives are reported. These compounds are precursors in the synthesis of PCU‐based anti‐tuberculosis (TB) agents and potential human immunodeficiency virus (HIV) protease inhibitors. Two‐dimensional (2D) NMR techniques were used to assign the NMR spectra for these compounds. Substitution of the cage molecule at (C‐8/11) further complicates the assignment, since some of the substituted alkyl chain groups overlap with the cage proton signals. The side chain heteroatoms also introduce a rare through‐space deshielding effect to some of the carbon atoms of the cage skeleton. Ring strain in the rigid cage skeleton appears to induce drastic electronic changes in some parts of the cage framework. This observation is more dramatic for the C‐4 methylene group of the cage diols and the cage ethers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
22.
T G Levitskaia B A Moyer P V Bonnesen A P Marchand K Krishnudu Z Chen Z Huang H G Kruger A S McKim 《Journal of the American Chemical Society》2001,123(48):12099-12100
23.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
24.
Nonintrusive measurements in a sediment-laden flow using two laser-based techniques, Discriminator Laser-Doppler Velocimetry
(DLDV) and Particle Tracking Velocimetry (PTV), are compared. DLDV was previously developed at the Iowa Institute of Hydraulic
Research, while PTV was specially configured for this application. Mean and fluctuating velocity components for both flow
fractions were simultaneously measured in a laboratory-scale, submerged water jet loaded with alluvial sand. This information
cannot be obtained using existing measurement techniques. The jet Reynolds number was 6120, and the sediment sieve diameter
ranged from 0.5 to 0.6 mm. Small mass loadings of sand with inertial time constant τ
p
of 0.6 ms were examined.
The configuration, operation, and results obtained using the DLDV and PTV are presented. For each technique, means to precisely
distinguish between the light scattered by suspended sand and that originating from seed-particles following the water were
implemented. The agreement in measurement for the two methods validates one another since they are based on completely different
principles of operation. The capabilities of DLDV and PTV to reliably measure sand and water velocities in sediment-laden
flows are further indicated by the agreement of the present findings with those obtained previously in similar studies. The
comparison suggests that PTV, due to its whole field nature, could become a powerful tool for flow and particle-related diagnostics,
yielding fundamental information in an area with a long history of conflicting experimental evidence.
Received: 27 August 1996 / Accepted: 25 June 1997 相似文献
25.
Results of one-dimensional calculations for unsteady state diffusion of a vapour in a closed tube are compared to calculations (a) for unsteady state diffusion of a vapour in an open tube, and (b) for heat conduction in a finite slab and an infinite slab. In the cases of (b) the effect of the convective term in the transport equation is absent.The total pressure is calculated and differences in the two cases are explained.An experiment is described in which the pressure increase in a closed tube due to the diffusion of water vapour in dry air is measured as a function of time. The experimental results agree quite well with the theoretical predictions. The results of this investigation may be used for the experimental determination of the diffusion coefficient of a vapour in a gas and in pressure measurements in systems with an evaporating liquid.Nomenclature
a
thermal diffusivity
-
D
diffusion coefficient
-
w
mean particle velocity
-
g
particle flux in the laboratory system
-
g*
particle flux in a system moving with the mean particle velocity w
-
L
length of the tube
-
n
number density of molecules
-
n
vs
saturation number density of vapour molecules
-
p
pressure
-
p
vs
saturation pressure of the vapour
-
t
time
-
z
distance from the liquid surface
-
N
total quantity of evaporated liquid 相似文献
26.
J Zwislocki B Kruger J D Miller A F Niemoeller E A Shaw G Studebaker 《The Journal of the Acoustical Society of America》1988,83(4):1688-1689
The advantages and disadvantages of three types of earphones for audiometric testing are discussed. Supraaural earphones continue to be recommended for this purpose, in preference to circumaural and insert types. 相似文献
27.
Localized corrosion processes such as pitting, intergranular corrosion, crevice corrosion, and stress corrosion involve many aspects that are not amenable to a quantitative study by ellipsometry. This paper describes uses of ellipsometry that can, however, provide valuable insights into localized corrosion processes without having to determine the optical constants of absorbing films. The uses described are as follows: (1) the determination of induction times for pit initiation and the demonstration that changes occur in the passive film prior to pitting; (2) the measurement of the rate of repassivation, a process of importance to stress corrosion, for a metal surface whose protective film has been removed by abrasion (triboellipsometry); and (3) the identification of three stages leading to crevice corrosion by ellipsometric measurements made within a crevice. 相似文献
28.
W.D. Apel K.H. Augenstein E. Bertolucci S.V. Donskov A.V. Inyakin V.A. Kachanov R.N. Krasnokutsky M. Kruger G. Leder A.A. Lednev I. Mannelli Yu.V. Mikhailov H. Müller G.M. Pierazzini Yu.D. Prokoshkin M. Quaglia H. Schneider A. Scribano M.L. Vincelli 《Physics letters. [Part B]》1978,72(4):500-502
The invariant mass spectrum of neutral final states produced in π?p charge-exchange scattering at 40 GeV/c has been studied, searching for heavy particles decaying in 2γ. A peak is observed around 2.85 GeV/c2. The cross section of the reaction π?p→X(2.85)+n, times the branching ratio of the X→2γ decay, is measured to be . 相似文献
29.
Homocystinuria is a metabolic disorder caused by a deficiency of cystathionine beta-synthase (CBS). The major clinical symptoms of this disease are mental retardation, lens dislocation, vascular disease with life-threatening thromboembolisms, and skeletal deformities. The major treatments for CBS deficiency include pharmacologic doses of pyridoxine or dietary restriction of methionine. There is currently no effective long-term treatment to lower the elevated plasma levels of homocysteine. However, gene therapy could be an effective novel approach for the treatment of homocystinuria. A recombinant adeno- associated virus vector carrying human CBS cDNA (rAAV-hCBS) was constructed and administered to CBS-/- mice by intramuscular (IM) and intraperitoneal (IP) injections. Serum homocysteine concentrations significantly decreased in treated mice compared with age-matched controls two weeks after treatment. The treated CBS-/- mice had life spans 3-7 days longer compared with untreated CBS-/- mice. In CBS-/- mice treated with rAAV-hCBS via IP injection, the vector was detected in all organs examined including liver, spleen, and kidney, and CBS gene expression was observed by immunohistochemical staining in the liver. These results indicate the efficacy of gene delivery and demonstrate the possibility of gene therapy mediated by AAV gene transfer in this mouse model of homocystinuria. 相似文献
30.
Positivity - This paper continues the study of ‘good arrangements’ of collections of sets near a point in their intersection. Our aim is to develop a general scheme for quantitative... 相似文献