We have used STM to observe directly a process which can be described as two-dimensional, surface-mediated Ostwald ripening, occurring during the decomposition of methoxy intermediates on a Cu(l10) surface. Some islands get bigger during the course of the reaction, at the expense of smaller ones, and it is shown that this diffusion is important for dictating the rate of methanol decomposition. This is proposed to occur from the dilute phase of methoxy existing in the inter-island region and the methoxy maintains a pseudo steady state there, supplied by diffusion from, and between, islands of adsorbate on the surface. 相似文献
A research study has been performed to determine the ultraviolet (UV) fluence-response of several target non-pathogenic microorganisms to UV light emitting diodes (UV-LEDs) by performing collimated beam tests. UV-LEDs do not contain toxic mercury, offer design flexibility due to their small size, and have a longer operational life than mercury lamps. Comsol Multiphysics was utilized to create an optimal UV-LED collimated beam design based on number and spacing of UV-LEDs and distance of the sample from the light source while minimizing the overall cost. The optimized UV-LED collimated beam apparatus and a low-pressure mercury lamp collimated beam apparatus were used to determine the UV fluence-response of three surrogate microorganisms (Escherichia coli, MS-2, T7) to 255 nm UV-LEDs, 275 nm UV-LEDs, and 254 nm low-pressure mercury lamps. Irradiation by low-pressure mercury lamps produced greater E. coli and MS-2 inactivation than 255 nm and 275 nm UV-LEDs and similar T7 inactivation to irradiation by 275 nm UV-LEDs. The 275 nm UV-LEDs produced more efficient T7 and E. coli inactivation than 255 nm UV-LEDs while both 255 nm and 275 nm UV-LEDs produced comparable microbial inactivation for MS-2. Differences may have been caused by a departure from the time-dose reciprocity law due to microbial repair mechanisms. 相似文献
The objective was to determine the meat quality effects of rapidly thawing beef steaks in a water bath. Frozen beef strip loins (n = 24) were cut into steaks sequentially from the rib end and identified by anatomical location (anterior, middle, posterior) within the loin. Within location, steaks were randomly assigned to conventional (C; 18 to 20 h, 4 °C) or rapid thawing methods. Rapid thawing methods, fast (20 min, 20 °C) or very fast (11 min, 39 °C), were conducted in a circulating water bath. The physical, thawing, cooking, color, and texture characteristics of each steak were recorded. Data were analyzed as a randomized complete block design with a 3 thawing treatments × 3 locations factorial analysis with loin as a block. No location by thawing method interaction was detected (P > 0.05) for the measured variables. Compared to C steaks, rapidly thawed steaks exhibited lower thaw drip loss (P < 0.001) and higher a* values (P < 0.001). Thawing treatment did not influence L*, b*, cook yield, or shear force. Steaks from the posterior end had higher (P < 0.001) surface to volume ratios that may have contributed to the higher thaw loss (P < 0.01), longer cooking time (P < 0.001), lower cooking yield (P < 0.001), and higher shear force (P < 0.02) compared to steaks from the anterior and middle portions of the loins. These data indicate that beef steaks taken from the entire length of the loin can be rapidly thawed in a water bath following food safety guidelines with minimal impact on meat quality. Practical Application: Freezing rate and frozen storage effects on meat quality have been well documented; however, there is comparatively little information on the meat quality effects of rapid thawing within food safety guidelines. This study demonstrates that beef strip loin steaks can be rapidly thawed in as few as 11 min without affecting texture or cooking yield, while reducing thaw drip loss. Thus, rapid thawing may enhance the apparent juiciness of steaks for consumers and provide an effective method for maintaining consistent control of experimental conditions for researchers. 相似文献
The current controversy regarding the interaction between the output of the excimer laser and human tissue concerns the relative importance of photothermal and photoablative effects. Two experiments using an excimer laser on vascular tissue, aimed at defining the precise laser-tissue interaction, were performed. The experiments argue strongly in favor of photoablative effects that result from multiple photon interactions with ablated tissue. 相似文献
The diffusion current of hydrogen through palladium in an electrochemical cell initially rises linearly with the charging
current, reaches a steady “plateau” value, and then rises again. The diffusivity of hydrogen in palladium was measured using
standard transient techniques in the initial region of low current density. Combining this value with the measured value of
diffusion current at the plateau level gave a concentration of hydrogen at the entrance surface of the palladium that was
the same for three different palladium thicknesses, and was equal to the saturation value in α palladium. It is proposed that
this can be used as a known and reproducible effective hydrogen pressure (0.019 atm) if palladium is plated onto other metals
before measuring their permeability in an electrochemical cell. Experimental evidence for this was obtained from permeability
measurements made on several thicknesses of iron. Permeation studies were also made on AISI 410 stainless steel and tin plated
mild steel. The measured value for electrolytic tinplate was 107 times that expected from extrapolation of high temperature data. This could be attributed to grain boundaries or porosity
covering 0.003 pct of the area. The permeability values of iron and stainless steel are 8.4 x 1012 and 2.8 x 1013 H atom/cm • s • √atm, respectively.
Former Postdoctorate Fellow at McMaster University 相似文献
The oxidation of methanol has been measured on MoO3 and MoO2. The properties of these two materials are interchangeable, depending upon the conditions in which the reaction is run. MoO3 produces high yields of formaldehyde, but MoO2 does not, due to the importance of the Mo6+ state for the selective reaction. However, if the MoO3 material is run in anaerobic conditions it behaves in a very similar way to MoO2, due to the presence of Mo4+ in the surface layers. In complement to this MoO2 converts to high yield behaviour when run in aerobic conditions, due to the conversion of the material to Mo6+ at the surface, and, ultimately to MoO3 in the bulk. In TPD experiments MoO3 yields formaldehyde, whereas MoO2 yields CO. In both materials oxygen transport within the lattice becomes appreciable above 300 °C, and the reaction proceeds
via the Mars-van Krevelen mechanism. 相似文献
It is generally thought that catalysts produced by incipient wetness impregnation (IW) are very poor for low temperature CO oxidation, and that it is necessary to use methods such as deposition–precipitation (DP) to make high activity materials. The former is true, indeed such IW catalysts are poor, and we present reactor data, XPS and TEM analysis which show that this is due to the very negative effect of the chloride anion involved in the preparation, which results in poisoning and excessive sintering of the Au particles. With the DP method, the chloride is largely removed during the preparation and so poisoning and sintering are avoided.
However, we show here that, contrary to previous considerations, high activity catalysts can indeed be prepared by the incipient wetness method, if care is taken to remove the chloride ion during the process. This is achieved by using the double impregnation method (DIM). In this a double impregnation of chloroauric acid and a base are made to precipitate out gold hydroxide within the pores of the catalyst, followed by limited washing. This results in a much more active catalyst, which is active for CO oxidation at ambient temperature. The results for DIM and DP are compared, and it is proposed that the DIM method may represent an environmentally and economically more favorable route to high activity gold catalyst production. 相似文献