Fluorescence lifetime spectroscopy for pH sensing in scattering media

Fluorescence lifetime spectroscopy in the presence of tissuelike scattering is demonstrated from measurements of phase and modulation ratio as a function of modulation frequency using a pH-sensitive dye, Carboxy Seminaphthofluorescein-1 (C-SNAFL-1). From the optical diffusion equation describing the propagation and generation of fluorescence within solutions of 0.5 microM C-SNAFL-1 containing 2.0% (by volume) of Intralipid as a scatterer, the values of the average lifetime of C-SNAFL-1 were determined as the solution pH varied between 5 and 9. Average lifetime values were found to match those measured using traditional phase-modulation measurement in nonscattering media. Furthermore, the robustness of the spectroscopic technique was demonstrated by conducting lifetime measurements at varying scatterer concentrations (1.5-3.0 vol % Intralipid). These results confirm the approach for analytical sensing in scattering media via fluorescence lifetime kinetics in order to track changes in analyte concentrations.     

General-Purpose Situational Simulation Environment for Construction Education

The traditional construction education model based on precise well-defined problems and formal definitions is not satisfactorily fulfilling its mission of educating the decision makers of tomorrow. This realization has moved several researchers to explore alternatives where problem solving is carried out in conjunction with the environment, and concepts are embedded in the context promoting learning within the nexus of the activity. Several efforts have been undertaken to develop these environments resulting in a variety of special-purpose situational simulations. However, special-purpose situational simulations exhibit inherent limitations related to their application breadth, flexibility, and promotion of collaborations. These limitations cannot be resolved within the framework of special-purpose learning environments. A general-purpose environment is required to overcome these shortcomings and take full advantage of the situational learning paradigm. This paper describes the conceptual framework and pilot implementation of such an environment called the Virtual Coach.     

Solvent extraction successfully applied

Summary Extraction efficiency clearly points to counter-current extraction and with the other requirements indicates continuous operation. So our investigations and plant experience together with consideration of modern production methods have led us to the firm conclusion that the future of large scale solvent extraction of vegetable oils lies in continuous counter-current extraction. Presented at Fourth Annual Fall Meeting of the American Oil Chemsits' Society, Chicago, Nov. 13, 1930. Prosco Oils Corporation.     

Direct observations of colloid retention in granular media in the presence of energy barriers, and implications for inferred mechanisms from indirect observations

In this paper we present direct observations of retention of colloids in granular porous media over a large size range (0.21-9.0 μm) and generalize the significance of attachment in grain to grain contacts and attachment on the open surface as a function of colloid:collector ratio. We examine reversibility of attachment via these mechanisms with respect to ionic strength reduction and fluid velocity increase. We relate these direct observations to existing literature, and in some cases offer alternative interpretations of mechanisms of retention drawn from indirect observations (e.g. via column effluent and retained concentrations).     

Characterization of Recessed-Gate AlGaN/GaN HEMTs as a Function of Etch Depth

Recessed-gate high-electron-mobility transistors (HEMTs) were fabricated using a Cl₂-based plasma etch to study device performance as a function of recess depth. Devices were fabricated with recess depths varying from 0 nm to 25 nm on a standard HEMT structure using a controllable, low-power etch recipe. It is shown that the threshold voltage approached zero as the recess approached the AlGaN/GaN heterojunction. At the same time, mobility decreased an order of magnitude over the etch range studied, and sheet carrier density also decreased. In addition to direct-current (DC) I–V and Hall measurements, electroluminescence was also used to characterize plasma damage in these devices.     

Use of fecal steroids to infer the sources of fecal indicator bacteria in the Lower Santa Ana River Watershed, California: sewage is unlikely a significant source

The Santa Ana River (SAR), CA and adjacent wetlands have been identified as potential sources of fecal indicator bacteria (FIB) to the surf zone at Huntington Beach, CA. A suite of fecal steroids, including coprostanol (COP), epicoprostanol (eCOP), cholesterol (CHOE), cholestanol (CHOA), alpha-cholestanone (aONE), beta-cholestanone (bONE), beta-sitosterol (bSIT), stigmasterol (STIG), stigmastanol (STAN), and campesterol (CAM), were used as chemical markers to examine whether sewage was a significant source of FIB within the lower Santa Ana River watershed. A total of 54 water samples were collected from three locations in the intertidal zone near the mouth of the Santa Ana River at different tidal stages. Steroid ratios in SAR samples were different from those found in raw and treated sewage from a local wastewater treatment plant or in nearby effluent plume and did not appear to be influenced by the sampling location, daily tides, and spring/neap tidal cycle. The characteristics of steroid ratios suggested a diagenetic ratherthan a biogenic source forthe COP content of the samples. The log-based concentrations of COP and FIB in the SAR samples were not significantly correlated, inconsistent with sewage being the source of FIB in the study area. In addition, multivariate statistical analysis showed that the concentrations of FIB were better correlated with bird fecal steroids than with the typical sewage sterols. The results implied that sewage was not a significant source of fecal steroids, and therefore perhaps FIB to the study area. Instead, birds may be one possible source of the intermittently high levels of FIB observed in the lower Santa Ana River watershed and the nearby surf zone.     

Silicon Vibrating Wires at Low Temperatures

Nowadays microfabrication techniques originating from micro-electro nics enable to create mechanical objects of micron-size. The field of Micro-Electro-Mechanical devices (MEMs) is continuously expanding, with an amazingly broad range of applications at room temperature. Vibrating objects (torsional oscillators, vibrating wires) widely used at low temperatures to study quantum fluids, can be replaced advantageously by Silicon MEMs. In this letter we report on the study of Silicon vibrating wire devices. A goal-post structure covered with a metal layer is driven at resonance by the Laplace force acting on a current in a magnetic field, while the induced voltage arising from the cut magnetic flux allows to detect the motion. The characteristics of the resonance have been studied from 10 mK to 30 K, in vacuum and in ⁴He gas. In this article, we focus on the results obtained above 1.5 K, in vacuum and gas, and introduce some features observed at lower temperatures. The resonant properties can be quantitatively understood by means of simple models, from the linear regime to a highly non-linear response at strong drives. We demonstrate that the non-linearity is mostly due to the geometry of the vibrators. We also show that in our device the friction mechanisms originate in the metallic layers, and can be fully characterized. The interaction with ⁴He gas is fit to theory without adjustable parameters.      

Carbon-Dioxide-Based Microsortation of Postconsumer Polyolefins and its Effect on Polyolefin Properties

Postconsumer polyolefin flake has been sorted using liquid carbon dioxide as a float-sink medium. This separation of PP and LDPE from HDPE was conducted at ambient temperature and a pressure that yielded a CO₂ specific gravity of 0.955, causing the HDPE to sink and the LDPE and PP to float. Although this process provided a high-purity (99+%) HDPE product stream, the effect of immersing the plastics in liquid carbon dioxide at these conditions was not previously measured. Therefore, six HDPE samples, two LDPE samples, and five PP samples were exposed to high-pressure carbon dioxide for 20 min. After this exposure, the polyolefins did not foam when the carbon dioxide was rapidly vented from the vessel. The weight reduction averaged 0.17%, which was attributed to the dissolution of low-molecular-weight additives or contaminants present on the surface of the plastics. No significant change in the melting point or latent heat of melting was observed, indicating that the degree of crystallinity was not affected by the exposure to carbon dioxide. No reduction was observed in the temperature at which the onset of thermal degradation occurred, because of the low solubility and degree of extraction of thermal stabilizers during the immersion in carbon dioxide. These results indicated that no deleterious effects on the polyolefin properties were associated with this separation technique.     

Methods to evaluate egg freshness in research and industry: A review

The modern poultry industry is not satisfied with the traditional system of the handling and processing of eggs which is based on candling and visual inspection of the eggs. Currently, the operator of the conveyer does not have the opportunity to inspect 120 000 eggs per hour and to estimate the freshness, weight, bacterial infection, presence of technical spoilage, eggshell defects without elimination of subjectivity, fatigability and destruction. That is why the problem of automatization of egg quality control is rather difficult. In order to assure a high and consistent egg quality, an attractive and alternative strategy for determining the state of egg freshness can be achieved by sensors technologies. These techniques (e.g., near-infrared, mid-infrared, fluorescence spectroscopies, etc.) appear to be very promising for non-destructively determining egg freshness because they are relatively not expensive. Such methods cannot eliminate the need for more detailed physico-chemical analyses, but they may help to screen samples that require further examination.     

IMEC在面向SOC和嵌入式系统的系统级设计领域的研究工作

1.引言 位于比利时鲁汶Leuven)的IMEC,作为欧洲最大的独立的微电子研发中心,在微电子工艺研究方面已确立了其国际领先的地位,在国内也已为产业界所熟悉.