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排序方式: 共有512条查询结果,搜索用时 12 毫秒
1.
The reaction between (Z)-1-alkenyllithium and (E)-β-(N, N-dialkylamino)-α, β-alkenals, (E)-β-(N, N-dialkylamino)-α, β-alkenones or (E)-β-(N, N-dialkylamino)-α, β-alkenoic esters yields mainly (E, Z)-α, β-γ, δ-diunsaturated aldehydes, ketones, or esters and is therefore highly stereospecific. 相似文献
2.
Jan E. Almlöf P. Ulf Isacsson P. Johan Mjöberg Wiktor M. Ralowski 《Chemical physics letters》1974,26(2):215-217
Minimal basis set ab initio SCF LCAO MO calculations with gaussian-type have been performed for different conformations of the styrene molecule. The computations show the molecule to be planar and the rotational barrier of the vinyl group is estimated to 3.9 kcal/mole. 相似文献
3.
J. Kristóf J. Inczédy J. Paulik F. Paulik 《Journal of Thermal Analysis and Calorimetry》1979,15(1):151-157
A technique developed for the continuous and selective detection of water vapour formed during thermal decomposition reactions is described. The device can be connected to different types of thermoanalytical instruments without any difficulties. The detector can closely follow changes in the amount of water released during decomposition reactions, with negligible time delay. The signal curves obtained by the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which the water was released. The device as a free standing unit can be used to detect water plugs in different gas flows as well. 相似文献
4.
Lars-Olöf Sundelof 《Journal of Dispersion Science and Technology》2013,34(5):1289-1294
5.
Alkali-ion conducting glasses/glass ceramics of the system Me2O-A12O3-SiO2 (Me=Li, Na) were applied as solid electrolytes in potentiometric gas sensors to detect CO2 in the presence of O2 at increased temperatures. The corresponding Me-Carbonates were utilized as auxiliary electrodes. Sensors using the direct
Au-glass contact as a kind of reference electrode (type I), as well as symmetrical sensors with carbonate phase at the reference
and measuring electrode (type II - for comparative measurements) were manufactured.
By applying Au as electrode metal, the theoretically expected EMF difference and the observed EMF difference of both sensor
types agree quite well with the expected values according to the Nernst equation between 500 and 600 °C (over four orders
of magnitude of CO2 partial pressure (10−5 – 10−1 bar) at constant O2 partial pressure (2.1×10−1 bar)). A long time stability of 120 days for sensors of type I with Li glasses has been observed, although evaporation of
carbonate phase (Li2CO3) was detected under the conditions of sensor application. Sensors of type I (with Li2CO3) show thermodynamically unexpected cross-sensitivities to H2O.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
6.
Potentiometric CO2 gas sensors with Li conducting glasses/glass ceramics of the system Li2O-Al2O3-SiO2 (different nominal composition) as solid electrolytes have been investigated. Li2CO3 was used as CO2 and O2 sensitive auxiliary electrode. During the sensor test measurements, the CO2 partial pressure was varied between 1×10−3 and 1×10−1 bar at a constant O2 partial pressure of 2.1×10−1 bar whereas N2 was used as carrier gas. Comparative measurements were accomplished with sensors comprising Na and K ion conducting glasses.
A metastable reference electrode was formed at the contact zone between the Au metal electrode and the former Li glasses of
definite nominal composition by crystallization processes taking place, which lead to stable, reproducible CO2 dependent EMF signals for more than 90d. The thermodynamically expected EMF difference and the observed EMF difference agree
quite well between 500 and 600 °C.
At 600 °C, the drift of sensors with glasses as solid electrolytes and direct Au glass/glass ceramics contact as reference
electrode amounts typically 0.32 mV/d (p(CO2)=1×10−3 bar, p(O2)=2.1×10−1 bar at the measuring electrode), if a metastable multiphase equilibrium is formed. At identical partial pressures of CO2 and O2, the signal reproducibility of these sensors with different solid electrolyte glasses of the same nominal composition lies
within 30 mV at 600 °C.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
7.
8.
The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain. 相似文献
9.
Farshad?Merrikh-BayatEmail author Meysam?Parvizi 《Applied Physics A: Materials Science & Processing》2016,122(6):602
A new method to realize a discrete memristor is proposed. The device under study consists of a tube filled of aqueous saturated solution of copper sulfate which can be electrolyzed by using two asymmetric copper electrodes, one of which has a considerably smaller cross-sectional area than to the other one. It is shown both theoretically and experimentally that this device has exactly the properties of a memristor if it is designed such that the electrical field and the current density on the thinner electrode when it acts as anode are sufficiently large. Different aspects of the proposed discrete memristor, including pinched hysteresis loop, on-off resistance ratio and memory volatilization, are studied and experimental results are presented. 相似文献
10.
A new approach is suggested to realize negative magnetic permeability that follows directly from quantum mechanics. It is
shown that a Λ-type three-level atomic system with proper atomic parameters can give rise to striking magnetic responses,
which could exhibit negative permeability in an optical frequency band. Both steady and transient behaviors of the magnetic
permeability in the atomic vapor are studied. The present negative-permeability vapor could be mixed with a quantum coherent
vapor whose electric permittivity is negative. Such a mixed vapor may give an isotropic left-handed vapor medium at the atomic-scale
level.
PACS 32.10.Dk; 42.50.Gy; 78.20.Ci 相似文献