排序方式: 共有62条查询结果,搜索用时 31 毫秒
1.
The complexes [1,3-diphenyl-1,3-propanedionato]tricyclohexyltin(IV), (tropolonato)triphenyltin(IV), and (tropolonato)tricyclohexyltin(IV) have been prepared for the first time and have been found to be five-coordinate in the solid state. These and related five-coordinate complexes prepared previously have been studied by a variety of physical methods; 13C NMR, UV, IR, Raman, dipole moments and the Kerr effect. While all structures are demonstrably five-coordinate, and all chelates bidentate in the solid state, the geometries of two of the complexes in solution appear to vary somewhat from the expected fac or mer. There is evidence from the solution Kerr effect and 13C NMR that cyclohexyl derivatives may disproportionate. 相似文献
2.
Treatment of α,β-unsaturated esters with triethylsilane in benzene in the presence of a catalytic amount of tris(triphenylphosphine)rhodium chloride at room temperature followed by chromatography on silica gel gave rise to the corresponding saturated esters. Under similar conditions, fully conjugated diene esters were reduced to the dihydrolevel to give β,γ- or γ,δ-unsaturated esters depending upon the substitution pattern of the starting substrate. 相似文献
3.
Ni Made Dwi Mara Widyani Nayaka Maria Malida Vernandes Sasadara Dwi Arymbhi Sanjaya Putu Era Sandhi Kusuma Yuda Ni Luh Kade Arman Anita Dewi Erna Cahyaningsih Rika Hartati 《Molecules (Basel, Switzerland)》2021,26(8)
Piper betle (L) is a popular medicinal plant in Asia. Plant leaves have been used as a traditional medicine to treat various health conditions. It is highly abundant and inexpensive, therefore promoting further research and industrialization development, including in the food and pharmaceutical industries. Articles published from 2010 to 2020 were reviewed in detail to show recent updates on the antibacterial and antifungal properties of betel leaves. This current review showed that betel leaves extract, essential oil, preparations, and isolates could inhibit microbial growth and kill various Gram-negative and Gram-positive bacteria as well as fungal species, including those that are multidrug-resistant and cause serious infectious diseases. P. betle leaves displayed high efficiency on Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa, Gram-positive bacteria such as Staphylococcus aureus, and Candida albicans. The ratio of MBC/MIC indicated bactericidal and bacteriostatic effects of P. betle leaves, while MFC/MIC values showed fungicidal and fungistatic effects. This review also provides a list of phytochemical compounds in betel leaves extracts and essential oils, safety profiles, and value-added products of betel leaves. Some studies also showed that the combination of betel leaves extract and essential oil with antibiotics (streptomycin, chloramphenicol and gentamicin) could provide potentiating antibacterial properties. Moreover, this review delivers a scientific resume for researchers in respected areas and manufacturers who want to develop betel leaves-based products. 相似文献
4.
Stabilization of Catalytically Active Cu+ Surface Sites on Titanium–Copper Mixed‐Oxide Films
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Ashleigh E. Baber Dr. Xiaofang Yang Dr. Hyun You Kim Dr. Kumudu Mudiyanselage Markus Soldemo Dr. Jonas Weissenrieder Dr. Sanjaya D. Senanayake Dr. Abdullah Al‐Mahboob Dr. Jerzy T. Sadowski Dr. Jaime Evans Dr. José A. Rodriguez Dr. Ping Liu Dr. Friedrich M. Hoffmann Dr. Jingguang G. Chen Dr. Darío J. Stacchiola 《Angewandte Chemie (International ed. in English)》2014,53(21):5336-5340
The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper‐based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed‐metal oxide with a Cu+ terminated surface that is highly active for CO oxidation. 相似文献
5.
Prediction of stagnation point heat transfer for a single round jet impinging on a concave hemispherical surface 总被引:1,自引:0,他引:1
This paper deals with a systematic procedure for assessment of fluid flow and heat transfer parameters for a single round jet impinging on a concave hemispherical surface. Based on Scholkemeier's modifications of the Karman-Pohlhausen integral method, expressions are derived for evaluation of the momentum thickness, boundary layer thickness and the displacement thickness at the stagnation point. This is followed by the estimation of thermal boundary layer thickness and local heat transfer coefficients. A correlation is presented for the Nusselt number at the stagnation point as a function of the Reynolds number for different non-dimensional distances from the exit plane of the jet to the impingement surface.
Nomenclature c p specific heat at constant pressure - d diameter of single round nozzle - h 0 heat transfer coefficient at the stagnation point - H distance from the exit plane of the jet to the impingement surface - k thermal conductivity - Nu 0.5 Nusselt number based on impinging jet quantities=h 0.50/k - Nu 0.5, 0 stagnation point Nusselt number=h 0 0,50/k - p pressure - p a ambient pressure - p 0 maximum pressure or stagnation pressure - p(x) static pressure at a distancex from the stagnation point - R radius of curvature of the hemisphere - Re J jet Reynolds number=U Jd/ - Re 0.5 Reynolds number based on impinging jet quantities=u m0 0.50/ - T temperature - T a room temperature - T J jet temperature - T W wall temperature - u velocity component inx andx directions (Fig. 1) - u m jet centerline (or maximum) free jet velocity: external (or maximum) boundary layer velocity aty= m - u m0 arrival velocity defined as the maximum velocity the free jet would have at the plane of impingement if the plane were not there - U J jet exit velocity - x* non-dimensional coordinate starting at the stagnation point=x/2 0.50 - x, y rectangular Cartesian coordinates - y coordinate normal to the wall starting at the wall - ratio of thermal to velocity boundary layer thickness= T/m - 0 ratio of thermal to velocity boundary layer thickness at the stagnation point - * inner layer displacement thickness - 0.50 jet half width at the plane of impingement if the plate were not there - m inner boundary layer thickness atu=u m - Pohlhausen's form parameter - dynamic viscosity - kinematic viscosity=/ - fluid density - momentum thickness - 0 momentum thickness at the stagnation point 相似文献
Bestimmung des Staupunktes bei der Wärmeübertragung für einen einzelnen Strahl, der auf eine konkave halbkugelige Oberfläche trifft
Zusammenfassung Diese Arbeit beschäftigt sich mit dem systematischen Verfahren der Bewertung von Fluidströmungen und Wärmeübertragungsparametern für einen einzelnen runden Strahl, der auf eine konkave halbkugelförmige Oberfläche trifft. Das Verfahren beruht auf Scholkemeiers Modifikation des Karman-Pohlhausen Integrationsverfahrens. Ausdrücke sind für die Berechnung der Impuls-Dicke, der Grenzschichtdicke und der Verschiebungsdicke am Staupunkt hergeleitet worden. Dies ist aus der Berechnung der thermischen Grenzschichtdicke und des lokalen Wärmeübertragungskoeffizienten abgeleitet worden. Es wird eine Gleichung für die Nusselt-Zahl am Staupunkt als Funktion der Reynolds-Zahl für verschiedene dimensionslose Abstände vom Strahlaustrittspunkt bis zum Auftreffpunkt auf die Oberfläche vorgestellt.
Nomenclature c p specific heat at constant pressure - d diameter of single round nozzle - h 0 heat transfer coefficient at the stagnation point - H distance from the exit plane of the jet to the impingement surface - k thermal conductivity - Nu 0.5 Nusselt number based on impinging jet quantities=h 0.50/k - Nu 0.5, 0 stagnation point Nusselt number=h 0 0,50/k - p pressure - p a ambient pressure - p 0 maximum pressure or stagnation pressure - p(x) static pressure at a distancex from the stagnation point - R radius of curvature of the hemisphere - Re J jet Reynolds number=U Jd/ - Re 0.5 Reynolds number based on impinging jet quantities=u m0 0.50/ - T temperature - T a room temperature - T J jet temperature - T W wall temperature - u velocity component inx andx directions (Fig. 1) - u m jet centerline (or maximum) free jet velocity: external (or maximum) boundary layer velocity aty= m - u m0 arrival velocity defined as the maximum velocity the free jet would have at the plane of impingement if the plane were not there - U J jet exit velocity - x* non-dimensional coordinate starting at the stagnation point=x/2 0.50 - x, y rectangular Cartesian coordinates - y coordinate normal to the wall starting at the wall - ratio of thermal to velocity boundary layer thickness= T/m - 0 ratio of thermal to velocity boundary layer thickness at the stagnation point - * inner layer displacement thickness - 0.50 jet half width at the plane of impingement if the plate were not there - m inner boundary layer thickness atu=u m - Pohlhausen's form parameter - dynamic viscosity - kinematic viscosity=/ - fluid density - momentum thickness - 0 momentum thickness at the stagnation point 相似文献
6.
An experimental investigation is made to study the flow characteristics of slot jet impingement on a cylinder. The velocity profiles and pressure distribution around the cylinder are reported for various parameters namely, the flow rate, width of the nozzle, distance of the cylinder from the jet exit and eccentricity of the cylinder to the jet axis.
Nomenclature B breadth of the nozzle at the exit - D diameter of the cylinder - C p pressure coefficient - g acceleration due to gravity - L distance of the cylinder from jet exit - P a atmospheric pressure - P c static pressure along the jet center-line - P 0 stagnation pressure - P W wall static pressure - Re D Reynolds numberu j D/ a - Re W Reynolds numberu j W/ a - r distance measured from cylinder surface in radial direction - r m position of maximum velocity from cylinder surface - r 0.5 half width of the jet - u mean velocity - u j mean velocity at the jet exit - u m maximum velocity - W width of the nozzle - a density of air - m density of mercury - w density of water - absolute viscosity - kinematic viscosity 相似文献
Experimentelle Untersuchung über die Strömungseigenschaften eines Düsenstrahls, der auf einen Zylinder aufprallt
Zusammenfassung Es wurde eine experimentelle Untersuchung gemacht, um die Strömungseigenschaften eines Düsenstrahls zu unterschen, der auf einen Zylinder prallt. Die Geschwindigkeitsprofile und die Druckverteilungen an dem Zylinder wurden für unterschiedliche Parameter dokumentiert. Die Parameter sind die Strömungsgeschwindigkeit, Düsengröße, Abstand zwischen Zylinder und Strahlaustritt und die Exzentrizität von Zylinder und Strahlachse.
Nomenclature B breadth of the nozzle at the exit - D diameter of the cylinder - C p pressure coefficient - g acceleration due to gravity - L distance of the cylinder from jet exit - P a atmospheric pressure - P c static pressure along the jet center-line - P 0 stagnation pressure - P W wall static pressure - Re D Reynolds numberu j D/ a - Re W Reynolds numberu j W/ a - r distance measured from cylinder surface in radial direction - r m position of maximum velocity from cylinder surface - r 0.5 half width of the jet - u mean velocity - u j mean velocity at the jet exit - u m maximum velocity - W width of the nozzle - a density of air - m density of mercury - w density of water - absolute viscosity - kinematic viscosity 相似文献
7.
8.
Jan Ingo Flege Jan Höcker Jerzy T. Sadowski Sanjaya D. Senanayake Jens Falta 《Surface and interface analysis : SIA》2019,51(1):110-114
The early stages of ceria growth on Rh(111) at high temperature have been investigated by low-energy electron microscopy and photoemission electron microscopy. Ceria was deposited by reactive Ce deposition at substrate temperatures between 700°C and 900°C in an oxygen ambient of 5 × 10−7 Torr. At 700°C, we observe a high nucleation density of 100-nm-sized islands. With elevated temperature, the average island size increases, and the nucleation density decreases. Triangularly shaped islands nucleate preferentially at step edges, with seemingly abrupt interfaces between Ce and Rh. At 900°C, the island edges are still straight, but during growth the islands lose their triangular form. Instead, growth along the substrate step edges becomes favorable, leading to a maze-like morphology. Atomic force microscopy reveals islands of 0.3 to 0.6-nm height, consistent with ceria islands formed by one or two trilayers (O―Ce―O) of ceria. Moreover, the second layer of the islands is also triangularly shaped, with lateral dimensions of 50 nm and similar step heights. IV-LEEM analysis leads to the conclusion that the rhodium surface is covered by a layer of reduced cerium oxide, which is partially overgrown by smaller islands of CeO2. 相似文献
9.
Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B. Sc. Zongyuan Liu Dr. David C. Grinter Dr. Pablo G. Lustemberg Dr. Thuy‐Duong Nguyen‐Phan Dr. Yinghui Zhou B. Sc. Si Luo Dr. Iradwikanari Waluyo Dr. Ethan J. Crumlin Dr. Dario J. Stacchiola Prof. Jing Zhou Dr. Javier Carrasco Prof. H. Fabio Busnengo Dr. M. Verónica Ganduglia‐Pirovano Dr. Sanjaya D. Senanayake Prof. José A. Rodriguez 《Angewandte Chemie (International ed. in English)》2016,55(26):7455-7459
Ni‐CeO2 is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHx or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way. 相似文献
10.
Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due
to flow separation around a square prism at Reynolds number 2.6 × 104, blockage ratio 0.1, different height-ratios and various angles of attack. The static pressure distribution has been measured
on all faces of the square prism. The results have been presented in the form of pressure coefficient, drag coefficient for
various height-ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative
values of the pressure coefficient have been observed. The positive pressure coefficient for different height-ratios does
not vary too much but the negative values of pressure coefficient are higher for all points on the surface as the bluff body
approaches towards the upper wall of the wind tunnel. The drag coefficient decreases with the increase in angle of attack
as the height-ratio decreases. The maximum value of drag coefficient has been observed at an angle of attack nearly 50° for
the square prism at all height-ratios. The heat transfer experiments have been carried out under constant heat flux condition.
Heat transfer coefficient are determined from the measured wall temperature and ambient temperature and presented in the form
of Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of
local Nusselt number has been shown with non-dimensional distance for different angles of attack. The variation of average
Nusselt number has also been shown with different angles of attack. The local as well as average Nusselt number decreases
as the height-ratio decreases for all non-dimensional distance and angle of attack, respectively, for the square prism. The
average Nusselt number for the square prism varies with the angle of attack. But there is no definite angle of attack at which
the value of average Nusselt number is either maximum or minimum. 相似文献