High-pressure total internal reflection fluorescence apparatus

Important interfacial processes in disciplines ranging from medicine to the separations sciences occur over a wide range of pressures, temperatures, and time scales. In this paper we report a new high-pressure total internal reflection fluorescence (HP-TIRF) apparatus that allows rapid fluorescence measurements of sub-monolayers in contact with liquids and supercritical fluids between 293 K and 353 K and up to 250 bar with picosecond time resolution. We use the HP-TIRF system to study the in-plane rotational reorientation dynamics of the fluorescent probe BODIPY 494/503 (C(2v) symmetry) covalently attached to silica surfaces that have been silanized with n-propyltrimethoxysilane (C(3)-TMOS) or 3,3,3-trifluoropropyltrimethoxysilane (CF(3)-TMOS) when the interface is subjected to pure supercritical carbon dioxide (scCO(2)). The in-plane BODIPY 494/503 rotational reorientation dynamics are assessed by using the Debye-Stokes-Einstein expression. As the scCO(2) density increases the local microviscosity surrounding the tethered BODIPY 494/503 molecule decreases. The terminal group (CH(3) versus CF(3)) within the silane monolayer governs the onset and absolute magnitude of the observed viscosity changes. The results are explained in terms of the wellknown solubility of fluorine-containing species in scCO(2).     

Heat Sealing measurement by an innovative technique

To obtain a proper heat seal is an important requirement in packaging, since seal failure is a more frequent cause of product deterioration than the package itself. Different kinds of seal, such as peelable or non‐peelable, can be obtained by changing the conditions under which a material is sealed. Therefore, identifying these conditions is very important. A new technique, the m ethod for m easuring t emperature of m elting s urface (MTMS), was used to predict the strongest peelable seal on various packaging commercial films. The temperature of the seal interface was measured using a thermocouple. The time–temperature profile, which was obtained by means of a thermocouple, was electronically processed so as to obtain the derivatives of the profile. The inflection point, also called the fusion point, was located on these profiles. This inflection point is associated with the physical change of the state of the material being sealed. The inflection point analysis was done using two different methods: (a) the MTMS method, based on the second derivative of temperature data with time; (b) ‘Table Curve’ software, based on non‐linear regression. This technique was successfully used to evaluate widely used packaging films such as LDPE, HDPE, LLDPE and CPP. The inflection point for these films was identified and the seal strength was verified using a universal testing machine. This method appears to be applicable to design the strongest peelable heat seals for many packaging materials. It also seems to have promise as a method of process measurement and validation for heat seal processes. Copyright © 2006 John Wiley & Sons, Ltd.     

污氦气配气系统研制和实验研究

为了研究氦基混合气体在氦液化器中内纯化器里的分凝分离纯化机理,同时积累更多的内纯化器设计、研制和性能提高的相关实验数据,需要开展氦基混合气体在低温下纯化实验研究。因此,搭建了内纯化器实验平台,配气系统装置是内纯化器实验平台的重要组成部分。配气系统可以实现不同组分的氦基两元混合气体的配比,通过对配气系统配置的气体进行分析检测,测量结果与理论计算的误差在5%范围内。最终配气实验的结果表明配气系统能满足内纯化实验对氦基混合气体的要求。     

Ultrasonic Sealing of Flexible Packaging Films – Principle and Characteristics of an Alternative Sealing Method

The closure process for packaging is a key process. It ensures the protective function of packaging and assures the packaged goods a long life. In this context, efficient and reliable sealing processes are essential for the production of sustainable packages. In this paper, several characteristics of the ultrasonic sealing process will be discussed and accompanied by experimental results. The introduction provides an insight into the ultrasonic sealing process, its heating mechanisms and the process steps. A comparison is made with conduction sealing. Furthermore, basic principles of heating and energy dissipation are related to the influences of the sealing parameters on the seam strength. The experimental studies were carried out on typical packaging films, such as polyamide‐polyethylene laminates. The seam strength in ultrasonic sealing is compared with that in conductive sealing. A lower seam strength was found for ultrasonic sealing in all the tested films. Furthermore, the sealing behaviour of the packaging films contaminated with different kinds of foods was analysed for both sealing methods. Although the ultrasonic sealing method has marginal advantages for bulk materials such as wheat flour, conduction sealing was shown to be better for other products. A comparison of the energy consumption during the ultrasonic and conduction sealing verified the advantages of ultrasonic sealing. In particular for thick packaging films, the amount of energy required for bonding is significantly lower than for conduction sealing. In summary, this paper provides a survey of the characteristics of the ultrasonic sealing method in packaging applications – its advantages and limitations. Copyright © 2011 John Wiley & Sons, Ltd.     

Results with an apparatus for pressurized planar electrochromatography

Pressurized planar electrochromatography (PPEC) is a fast and efficient planar chromatographic technique. The mobile phase is driven by electroosmotic flow, while the system is pressurized in a manner that allows heat to flow between the sorbent layer and the pressurizing medium. The reproducibility of solute retention was not satisfactory in the initial report describing PPEC. In the current report, this reproducibility is improved by better control of several experimental variables. The pressure at which PPEC is performed is now free of drift, and the temperature at which the layer is preconditioned is maintained to within +/-1 degrees C. The best reproducibility of retention is obtained when the plate is soaked in the mobile phase for a defined time before each run. In the original prototype, the temperature of the sorbent layer was not controlled. In the present apparatus, water, at a constant temperature between 3 and 60 degrees C, is circulated through channels in the two die blocks that pressurize the layer. The highest efficiency is obtained at an intermediate temperature. This behavior is ascribed to high resistance to mass transfer at the lower temperatures and increased diffusion at higher temperatures. Efficiency, as measured by the number of theoretical plates, increases with increasing migration distance. The height equivalent of a theoretical plate diminishes with increasing migration distance, and values as low as 0.0106 mm are obtained under appropriate conditions. This extrapolates to 94 000 plates/m. Manual spotting was used in this report. Evidence is presented that substantially better efficiency would be obtained if the initial spot size were smaller. The efficiency of PPEC in its current form is illustrated by a chromatogram showing the separation of nine solutes in 2 min. PPEC was also performed with TLC plates in a back-to-back configuration, and this doubles the number of samples that can be simultaneously separated.     

Sensitivity of an imaging space infrared interferometer

We study the sensitivities of space infrared interferometers. We formulate the signal-to-noise ratios of infrared images obtained by aperture synthesis in the presence of source shot noise, background shot noise, and detector read noise. We consider the case in which n beams are combined pairwise at n(n - 1)/2 detectors and the case in which all the n beams are combined at a single detector. We apply the results to future missions, Terrestrial Planet Finder and Darwin. We also discuss the potential of a far-infrared interferometer for a deep galaxy survey.