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排序方式: 共有951条查询结果,搜索用时 62 毫秒
21.
Ordered Mesoporous In2O3: Synthesis by Structure Replication and Application as a Methane Gas Sensor
Thomas Waitz Thorsten Wagner Tilman Sauerwald Claus‐Dieter Kohl Michael Tiemann 《Advanced functional materials》2009,19(4):653-661
The synthesis and characterization of ordered mesoporous In2O3 materials by structure replication from hexagonal mesoporous SBA‐15 silica and cubic KIT‐6 silica is presented. Variation of the synthesis parameters allows for different pore sizes and pore wall thicknesses in the products. The In2O3 samples turn out to be stable up to temperatures between 450 °C and 650 °C; such high thermal stability is necessary for their application as gas sensors. Test measurements show a high sensitivity to methane gas in concentrations relevant for explosion prevention. The sensitivity is shown to be correlated not only with the surface‐to‐volume ratio, but also with the nanoscopic structural properties of the materials. 相似文献
22.
Anke Schbel-Ostertag Marina Braun-Unkhoff Claus Wahl Lambert Krebs 《Combustion and Flame》2005,140(4):359-370
The oxidation of benzene was studied as a function of residence time (τres=0–2.5 s), temperature (850–960 K), and oxygen concentration (O2=0.2–2.3%) in a heated laminar flow reactor at atmospheric pressure. Nitrogen, doped with 350 ppm benzene, was injected downstream of the burned gas from a near stoichiometric flame of methane + air. Gas samples were taken at different heights up the reactor and analyzed using GC-FID/TCD and HPLC techniques. Phenol and partially oxidized hydrocarbons such as acetaldehyde, formaldehyde, and acrolein were found with concentrations up to 50 ppm. At relatively low temperatures, the conversion of benzene was observed to proceed considerably more slowly at higher oxygen concentrations. Measured concentration profiles were modeled using detailed reaction schemes. A modified mechanism for the oxidation of benzene called BenWas was constructed from the mechanism of Zhang and McKinnon (Combust. Sci. Technol. 107 (1995) 261) by incorporating a submechanism for benzoquinone (OC6H4O) and by updating and enlarging the reaction scheme of cyclopentadiene (C5H6). The agreement between observed and predicted concentration profiles, e.g., of phenol (C6H5OH), acetylene (C2H2), and carbon monoxide (CO), was considerably improved by the use of the BenWas mechanism for rich and lean conditions, mainly due to the introduction of an additional pathway for phenyl oxidation (C6H5 + O2 = OC6H4O + H) and due to the changed kinetics of the oxidation of cyclopentadienyl (C5H5) in C5H5 + O2 = C5H4O + OH. The measured retardation of benzene oxidation with higher amounts of oxygen can be explained by the formation and reactions of peroxy radicals. 相似文献
23.
Claas Spille Anastasios Lyberis Maria Isabelle Maiwald Dirk Herzog Marko Hoffmann Claus Emmelmann Michael Schlüter 《化学工程与技术》2020,43(10):2053-2061
In chemical process engineering, fast gas-liquid reactions often suffer from an inefficient distribution of gas and therefore mixing and mass transfer performance. This study deals with the possibility of influencing the local gas holdup and bubble size distribution in a gas-liquid process using additively manufactured lattice structures (AMLS). The used measuring technique to study bubble size, velocity, and the local gas holdup is a photo-optical needle probe. By using AMLS, a significant radial homogenization of the local gas holdup and the mean bubble size is achieved. Furthermore, it can be demonstrated that the bubble size can be tailored by the geometry of the inserted structure. It is illustrated that the mean bubble velocities are lowered within the lattice resulting in a higher residence time of the dispersed phase with an impact on the mass transfer performance within the AMLS. 相似文献
24.
Anja Wessely Theresa Steeb Ulrike Leiter Claus Garbe Carola Berking Markus Vincent Heppt 《International journal of molecular sciences》2020,21(23)
Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer that predominantly arises in chronically sun-damaged skin. Immunosuppression, genetic disorders such as xeroderma pigmentosum (XP), exposure to certain drugs and environmental noxae have been identified as major risk factors. Surgical removal of cSCC is the therapy of choice and mostly curative in early stages. However, a minority of patients develop locally advanced tumors or distant metastases that are still challenging to treat. Immune checkpoint blockade (ICB) targeting CTLA-4, PD-L1 and PD-1 has tremendously changed the field of oncological therapy and especially the treatment of skin cancers as tumors with a high mutational burden. In this review, we focus on the differences between cSCC and cutaneous melanoma (CM) and their implications on therapy, summarize the current evidence on ICB for the treatment of advanced cSCC and discuss the chances and pitfalls of this therapy option for this cancer entity. Furthermore, we focus on special subgroups of interest such as organ transplant recipients, patients with hematologic malignancies, XP and field cancerization. 相似文献
25.
Partial Syntheses of Cardenolides and Cardenolide Analogues. XIII. Synthesis of Substituted 14,21-Epoxy-5β,14β-card-20(22)-enolide The 12-substituted 14,21-epoxy-5β,14β-card-20(22)-enolides 3 and 5 were synthesized by oxidation of the appropriate 17β-(3-furyl) derivatives 2b and 2c , respectively, with chromic acid. 5 was converted to the conjugated Δ9(11)-12-ketone 6 by dehydrogenation with selenium dioxide. The biological activities of the new compounds were investigated and are discussed. 相似文献
26.
The ability of nonproteolytic Clostridium botulinum type B spores to grow and produce toxin in cooked, uncured turkey packaged under modified atmospheres was investigated at refrigeration and mild to moderate abuse temperatures. Cook-in-bag turkey breast was carved into small chunks, surface-inoculated with a mixture of nonproteolytic C. botulinum type B spores, packaged in O2-impermeable bags under two modified atmospheres (100% N2 and 30% CO2:70% N2), and stored at 4, 10, and 15 degrees C. Samples were analyzed for botulinal toxin and indigenous microorganisms, as well as subjected to sensory evaluation, on days 0, 7, 14, 28, 42, and 60. Given sufficient incubation time, nonproteolytic C. botulinum type B grew and produced toxin in all temperature and modified atmosphere treatment combinations. At moderate temperature abuse (15 degrees C), toxin was detected by day 7, independent of packaging atmosphere. At mild temperature abuse (10 degrees C), toxin was detected by day 14, also independent of packaging atmosphere. At refrigeration temperature (4 degrees C), toxin was detected by day 14 in product packaged under 100% N2 and by day 28 in product packaged under 30% CO2:70% N2. Reduced storage temperature significantly delayed toxin production and extended the period of sensory acceptability of cooked turkey, but even strict refrigeration did not prevent growth and toxigenesis by nonproteolytic C. botulinum. At all three storage temperatures, toxin detection preceded or coincided with development of sensory characteristics of spoilage, demonstrating the potential for consumption of toxic product when spoilage-signaling sensory cues are absent. 相似文献
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29.
Claus RA Wüstholz A Müller S Bockmeyer CL Riedel NH Kinscherf R Deigner HP 《Chembiochem : a European journal of chemical biology》2005,6(4):726-737
The enantioselective synthesis of an analogue of scyphostatin, a potent inhibitor of the neutral sphingomyelinase, is described. The synthesis starts with cyclohexanone and a protected D-serine derivative. The key step is an asymmetric hydroxylation to access a hydroxycyclohexanone, which is transformed into a substituted hydroxycyclohexenone. This is converted into the scyphostatin analogue 14, a chemically and metabolically stabilised compound lacking the epoxy function of the natural congener and carrying a palmitic acid group instead of the native trienoyl residue. An evaluation of the biological activity of 14 revealed neutral sphingomyelinase inhibition in several in vivo test systems (monocytes, macrophages, hepatocytes) monitoring antiapoptotic effects and the inversion of phorbolester-induced translocation of green fluorescent protein labelled kinase (protein kinase C-alpha). 相似文献
30.
Amanda Baker Michael Lanagan Clive Randall Elena Semouchkina George Semouchkin Khalid Z. Rajab Richard Eitel Khalid Z. Rajab Raj Mittra Sorah Rhee Peter Geggier Claus Duschl Günter Fuhr 《International Journal of Applied Ceramic Technology》2005,2(6):514-520
At the Keck Smart Materials Integration Laboratory at Penn State University, low-temperature co-fired ceramic (LTCC) material systems have been used to fabricate a number of devices for a variety of applications. This article presents an overview of the integration of the concepts and materials that we have used to achieve miniaturization and unique device function. Examples of microwave filters, metamaterial antennas, and a dielectrophoretic cell sorter will be presented, with emphasis on device modeling and design, prototype construction methods, and test results. 相似文献