宋庄美术馆

村民们对此的评价是颇像村里老娘们搭的篱笆墙。我们认为这是一个积极的评价。     

Study of iodide sorption to the argillite of Tournemire in alkaline media

Argillaceous rocks are considered potential host rocks for radioactive waste repositories. The concrete matrix that could be used as a barrier could react with the groundwater of the geological site, inducing a drastic change in its chemical composition and its pH (10–13). Consequently, the physicochemical properties of the rock in contact with this alkaline solution may be modified and, in turn, may induce modification on the behaviour of radioelements. This study, applied to the argillite of Tournemire, involves characterizing I⁻ sorption to an argillaceous rock in alkaline media in batch experiments under N₂-controlled conditions. I⁻ was added as a ¹²⁵I radiotracer and measured by γ spectrometry.Preliminary experiments were conducted with different solution/solid ratios (v/m=2.5, 5 and 20 ml g⁻¹) and contact times (1–14 days) in order to determine the optimal experimental conditions. The chosen v/m ratio was 5 ml g⁻¹ as the best compromise between a high K_d value and a low error of the measure. The chosen experiment duration was 1 day because I⁻ sorption was highest and to limit the effects of pyrite oxidation. One of the experiments, performed with a radio-sterilized sample to test possible effects from microorganisms, showed that they could enhance iodide retention, particularly during the first 2 contact days.The influence of pH on I⁻ sorption was tested using solutions between values of 8.3 and 12.8. The K_d values were independent of pH and very low (0.3 ml g⁻¹).Finally, the influence of the chemical composition of concrete fluids was also tested. Three solution compositions corresponding to different steps in the evolution of fluids in contact with altering concrete were used: fluid in contact with fresh concrete (pH 13.2), with moderately degraded concrete (pH 12.1) and with strongly degraded concrete (pH 11.5). Each solution contained variable amounts of sodium, potassium, calcium, silica and sulphate. I⁻ sorption was also very low (K_d0.2 ml g⁻¹). Additional experiments were conducted with alkaline solutions containing different amounts of SO₄²⁻ ions (10⁻³–10⁻² M) to test sulphate–iodide sorption competition. I⁻ retention was independent of the sulphate concentration.     

Wastewater disinfection by ozone: main parameters for process design

Wastewater disinfection by ozone was investigated at pilot scale on different wastewater effluents. Variations in operating conditions showed that a very low hydraulic retention time (2 min) was sufficient for efficient fecal coliform inactivation, provided a sufficient ozone dose was transferred to the effluent. Therefore, the transferred ozone dose appeared to be the critical parameter for the design of wastewater disinfection. As a consequence, the "Ct" approach commonly applied in drinking water treatment should not be used for wastewater ozonation. Design parameters of ozonation were proposed for two types of regulations, and for effluents of different qualities. It was demonstrated that only with an efficient filtration step one can meet stringent standards such as the California Title 22 criteria. In all cases, viruses were totally inactivated; consequently, viruses do not constitute a limiting factor in wastewater disinfection by ozone. The standard drinking water model failed to match the experimental data obtained on real wastewater effluents. A modified approach was successfully developed, based on the simultaneous consumption of ozone by the microorganisms and the organic matrix.     

Effect of UV System Modifications on Disinfection Performance

Numerical simulations have been performed to gain a better understanding of ultraviolet (UV) disinfection process performance. Similar simulations in previous studies revealed critical paths through which particles moved and experienced low UV doses. In vertical UV systems, these paths generally are found near the channel walls with characteristics of high velocity and low turbulence intensity. Moreover, these paths generally coincide with low UV intensity zones and appear to represent the primary limitation of process performance. Reactor modifications have been designed to eliminate or modify these trajectories, thereby improving process performance. In a pilot-scale open-channel system with a vertical lamp orientation, two geometric modifications with “wave” and “baffle” shapes have been developed and examined. The results of these pilot tests confirmed the improvement of process performance when compared with an unmodified UV system. As in the case of the unmodified UV systems, a numerical model that combines kinetic information from a well-mixed batch reactor with a dose-distribution function was used to predict process performance of the UV system with the wave-shaped modification. A dose-distribution function that incorporates the effects of spatial nonuniformities in both hydrodynamics (through a random-walk model) and UV intensity (through a point-source-summation model) was developed. The dose-response function for microorganisms was obtained from completely mixed batch reactor experiments with a collimated beam. Predictions of disinfection efficacy confirmed the ability of the modified systems to improve microbial inactivation.     

Integrated electronic shutter for back-illuminated charge-coupleddevices

A novel electronic shutter has been integrated into the structure of a back-illuminated frame-transfer charge-coupled device (CCD) to permit short optical exposure times and to reduce the smear that occurs during the transfer of an image from the CCD detection area. The shutter consists of an n⁺ shutter drain placed in the vertical channel stop regions and stepped p-type buried layers formed by a high-energy implantation (1.0-1.5 MeV) located between the CCD n-type buried channel the and p substrate. These structures create electric fields that direct the photoelectrons to either the CCD detection region or the n⁺ shutter drain. The ratio of photons detected with the shutter open to photons detected with the shutter closed has been measured to be greater than 75000 for wavelengths below 540 nm. The corresponding shutter rise and fall times are less than 55 ns     

Wastewater Disinfection by Ozone: Influence of Water Quality and Kinetics Modeling

Wastewater disinfection by ozone was investigated at pilot scale on different effluents. The organic matter (COD and TOC) was shown to have the biggest influence on the ozone demand of the effluents. Disinfection of fecal indicators could be modeled as the reaction on a double population. The presence of more resistant microorganisms results in the need for higher treatment doses and a tertiary filtration when the effluent has to meet the stringent Title 22 standard. Eventually, the high virucidal power of ozone makes it very attractive when viruses are targeted.     

Application of negative electron affinity materials to imaging devices

Recent advances in materials technology, activation technology, and device technology have brought to fruition practical imaging devices utilizing NEA photoemitters. This paper describes the characteristics of proximity-focused image tubes utilizing large-area semitransparent, single-crystal III-V photocathode structures. Since the spectral response of the photocathode is determined by choice of the material used as the photoemitting layer, specific choices allow optimization for specific applications; e.g., laser illuminators. The material selection criteria and methods of fabricating the photocathode material structure will be discussed. The use of NEA materials allows the separation of the bulk photocathode material from other tube processing variables and has allowed a high degree of reproducibility from device to device. Specific device characteristics to be included in this discussion are resolution, stability of the photocathode during operation, and photocathode spectral data.     

Mobility of cesium through the Callovo-Oxfordian claystones under partially saturated conditions

The diffusion of cesium was studied in an unsaturated core of Callovo-Oxfordian claystone, which is a potential host rock for retrievable disposal of high-level radioactive wastes. In-diffusion laboratory experiments were performed on rock samples with water saturation degrees ranging from 81% to 100%. The analysis of both cesium concentration monitoring in the source reservoir and post-mortem cesium rock concentration profile of the samples was carried out using a chemical-transport code where the sorption of cesium was described by a multisite ion-exchange model. The results showed that cesium exhibited a clear trend related to the saturation degree of the sample. The more dehydrated the rock sample, the slower the decrease of cesium concentration, and the thinner the penetration depth of cesium was. The effective diffusion coefficient (De) for cesium decreased from 18.5 × 10(-11) m(2) s(-1) at full-saturation to 0.3 × 10(-11) m(2) s(-1) for the more dehydrated sample. This decrease is almost 1 order of magnitude higher than that for tritiated water (HTO), although a similar behavior could have been expected, since cesium is known to diffuse in the same parts of the pore space as HTO in fully saturated claystones.     

An epitaxially-grown charge modulation device

A charge modulation device (CMD) has been fabricated in a p-type epitaxial layer grown from the buried-channel silicon region of a charge-coupled device (CCD). Construction of the CMD directly above the CCD buried-channel and over the oxidized CCD transfer gates lowers the effective sense capacitance while providing isolation of the CMD source/drain regions. Responsivity values of 28 and 66 μV/e for feedback and no feedback conditions, respectively, were measured dynamically on test devices. Input-referred noise values of approximately four electrons r.m.s. were calculated from noise spectral density measurements assuming a low-pass filter 3 dB cutoff frequency of 5 MHz and correlated double sampling