An on-line method for the reduction of fouling of spin-filters for animal cell perfusion cultures

The main limitation in the use of spin-filters during perfusion cultures of animal cells was revealed to be filter fouling. This phenomenon involves cell-sieve interactions as well as cell attachment to, and growth on, the filter surface. The cell attachment effect has been analysed in the present study during long-term perfusion simulations with CHO animal cells. It was demonstrated that at low filter acceleration, below 6.2 m/s2, a high perfusion rate of 25 cm/h induced rapid filter pore clogging within 3 days, whereas increasing the filter acceleration to 25 m/s2 increased filter longevity from 3 to 25 days, for filters with a pore size of 8.5 microm. Increasing the filter pore size to 14.5 microm improved filter longevity by 84% with less viable and dead cell deposits on the filter surface. However, it was demonstrated that filter longevity was not necessarily dependent on the amount of cell deposit on the filter surface. In the second part of this study, ultrasonic technology was used to reduce filter fouling. Filter vibration, induced by a piezo actuator, improved filter longevity by 113% during CHO cells perfusion cultures.     

Adsorption of dissolved organic matter to the inorganic filter substrate and its implications for C uptake measurements

Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane-filtered samples because of adsorption of dissolved organic matter to the filter substrate. Experimentally derived values for adsorption onto filters were as follows (relative units): GF/F filter, 1, quartz filter, 1.1, GF/C filter, 0.6; GN-6 Gelman filter, 0.1; Nuclepore and Poretics filter, 0.0; Anodisc filter, 0.4 to 1.9.     

Adsorption of Dissolved Organic Matter to the Inorganic Filter Substrate and Its Implications for 14C Uptake Measurements

Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane-filtered samples because of adsorption of dissolved organic matter to the filter substrate. Experimentally derived values for adsorption onto filters were as follows (relative units): GF/F filter, 1, quartz filter, 1.1, GF/C filter, 0.6; GN-6 Gelman filter, 0.1; Nuclepore and Poretics filter, 0.0; Anodisc filter, 0.4 to 1.9.     

Filter elution assays for DNA damage: practical and mechanistic significance of the DNA in the filter support wash.

The alkaline and neutral (or nondenaturing) filter elution assays are popular methods for the measurement of DNA strand breakage and its repair in eukaryotic cells. In both alkaline and neutral elution, it is recommended practice to wash the filter support after removal of the filter and to analyze the DNA recovered by this procedure together with that remaining on the filter as uneluted DNA, although it is not obvious why the DNA in the filter support wash should be so interpreted. We have observed that the sum of the DNA on the filter and that recovered in the filter support wash is approximately constant when the pH of the alkaline filter elution assay for total strand breaks is increased from 12.1 to 12.6, whereas the fraction on the filter itself is markedly smaller at the higher pH. This behavior characterized DNA elution from undamaged cells, as well as from cells treated with various DNA-damaging agents. These findings are consistent with the "tug-of-war" mechanism that has been proposed for alkaline elution, but are inconsistent with the simplest mechanism of the "sieve" class. In the neutral filter elution assay for double-strand breaks, by contrast, the distribution of DNA between the filter and the filter support wash is pH-independent. This suggests that single- and double-stranded DNA segments traverse a filter by different physical mechanisms. Our observations underscore the importance of carrying out the filter support wash and the analysis of the DNA it contains as uneluted DNA in alkaline elution, while indicating that a different analysis of this DNA might be appropriate for neutral elution.     

彩超系统中壁滤波器设计和性能比较

本文首先介绍了多普勒原理和血流多普勒信号模型,推出了壁滤波器设计在彩色超声成像系统中具有极其重要的地位;其次分析了如何通过无限脉冲冲激响应（IIR）滤波器和回归型滤波器设计壁滤波器的原理,其中无限脉冲冲激响应（IIR）滤波器根据初始状态的不同又可以分为零初始化、阶跃初始化和投影初始化三种滤波器;然后根据上述原理分别对各种形式的壁滤波器进行设计,得到它们的频谱图;最后根据频谱图,对这几种壁滤波器进行性能比较,得到它们的优缺点,对从事壁滤波器设计相关的工作者有一定得借鉴意义。     

Design and responses of Butterworth and critically damped digital filters

For many years the Butterworth lowpass filter has been used to smooth many kinds of biomechanical data, despite the fact that it is underdamped and therefore overshoots and/or undershoots data during rapid transitions. A comparison of the conventional Butterworth filter with a critically damped filter shows that the critically damped filter not only removes the undershooting and overshooting, but has a superior rise time during rapid transitions. While analog filters always create phase distortion, both the critically damped and Butterworth filters can be modified to become zero-lag filters when the data are processed in both the forward and reverse directions. In such cases little improvement is realized by applying multiple passes. The Butterworth filter has superior ‘roll-off’ (attenuation of noise above the cutoff frequency) than the critically damped filter, but by increasing the number of passes of the critically damped filter the same ‘roll-off’ can be achieved. In summary, the critically damped filter was shown to have superior performance in the time domain than the Butterworth filter, but for data that need to be double differentiated (e.g. displacement data) the Butterworth filter may still be the better choice.     

基于DSP与FPAA的电化学信号滤波器

目的：研究对自主研发的DNA电化学分析仪所采集电化学信号的噪声的滤除方法。方法：根据电化学噪声信号的特征及其频率分布范围,采用由现场可编程模拟阵列（FPAA）实现的有高阶低通滤波器和基于DSP实现的FIR数字滤波器相结合的方式,对混合在电化学信号中的高频噪声信号进行滤除。结果：对滤波结果进行分析,频率在100HZ以上的噪声信号基本滤除。结论：FPAA与DSP芯片的结合构成了一个稳定性高,线性相位特性好,实时性强的高效滤波器。     

Application of the membrane filter technique to bromodeoxyuridine immunochemistry for exfoliative cytology

The membrane filter technique for smear specimens of tumors in bromodeoxyuridine (BrdU) immunochemistry is described. The staining results of Raji cells processed using the filter technique was compared with that obtained by the conventional cytospin method. Although the BrdU mean labeling index (LI) for in cytospin specimens was almost the same as the LI in membrane filter specimens, filter specimens showed excellent staining and less cell destruction compared with those processed by cytospin. Small amounts of tumor specimens such as squamous cell carcinoma and polymorphous low-grade adenocarcinoma also were processed using the membrane filter appliance. For squamous cell carcinoma, the LI for the filter specimens was 5.36 ± 0.38 and that of the paraffin sections was 5.56 ± 0.38. The membrane filter technique provided relatively undamaged specimens for exfoliative cytology and will be useful for immunohistochemical evaluation of tumor cells and for routine, noninvasive cytological screening.     

A simple technique for supporting single cells in electron microscopic immunocytochemistry and embedding.

Cell suspensions of rat anterior pituitaries were filtered with a polycarbonate filter (pore size 3 micron) and fixed on the filter. After fixation the cells were adherent to the filter and immunocytochemical staining could be accomplished by simply dipping the filter into the different incubation media. The cells could be dehydrated and embedded in Epon 812 on the filter. After polymerization the embedded filter was sawn into small blocks and the cell layer was sectioned tangentially on an ultramicrotome. This method also seems to be applicable to other histochemical studies on single cells.     

Statistical development and evaluation of microarray gene expression data filters.

Filtering is a common practice used to simplify the analysis of microarray data by removing from subsequent consideration probe sets believed to be unexpressed. The m/n filter, which is widely used in the analysis of Affymetrix data, removes all probe sets having fewer than m present calls among a set of n chips. The m/n filter has been widely used without considering its statistical properties. The level and power of the m/n filter are derived. Two alternative filters, the pooled p-value filter and the error-minimizing pooled p-value filter are proposed. The pooled p-value filter combines information from the present-absent p-values into a single summary p-value which is subsequently compared to a selected significance threshold. We show that pooled p-value filter is the uniformly most powerful statistical test under a reasonable beta model and that it exhibits greater power than the m/n filter in all scenarios considered in a simulation study. The error-minimizing pooled p-value filter compares the summary p-value with a threshold determined to minimize a total-error criterion based on a partition of the distribution of all probes' summary p-values. The pooled p-value and error-minimizing pooled p-value filters clearly perform better than the m/n filter in a case-study analysis. The case-study analysis also demonstrates a proposed method for estimating the number of differentially expressed probe sets excluded by filtering and subsequent impact on the final analysis. The filter impact analysis shows that the use of even the best filter may hinder, rather than enhance, the ability to discover interesting probe sets or genes. S-plus and R routines to implement the pooled p-value and error-minimizing pooled p-value filters have been developed and are available from www.stjuderesearch.org/depts/biostats/index.html.     

A multiple filtration device for glass fibre filters

A practical multiple filter holder is described for collection of particles on glass fibre filters. The device utilizes large diameter discs and the ends of individual filter tubes compress against the filter so that, after filtration, the separate filtering areas can easily be taken from the large disc with forceps. If analyses of collected particulate matter are to be made at a later time, the filtering areas are left attached to the original filter. Precise volumes of water can be filtered by attaching volumetric pipettes to individual filter tubes.     

Cell retention culture with an internal filter module: continuous ethanol fermentation

A new internal filter feedback system with a stainless steel filter was introduced and its application for continuous ethanol fermentation was investigated. The filter performance was highly influenced by agitation speed and yeast concentration. Retention coefficient with a filter of 2 mum pore size was found more than 97.5%, and the filter was suitable for yeast separation. Maximum yeast concentration was 157 g/L and the best operable cell concentration was between 90 and 150 g/L. Which was similar to that obtained in the external membrane cell recycle culture. The cell concentration in the fermentor was maintained by manipulation of dilution rate and bleed ratio with the growth rate. The internal filter feedback system was successfully operated for more than 10 days. This study shows that the internal filter feedback system with a stainless steel filter can be used high-density cell culture and ethanol fermentation. Furthermore, it can be scaled up more easily than the external cell recycle system. (c) 1993 John Wiley & Sons, Inc.     

Phlegm and Filters

Male mass radiography volunteers aged 40 or more were questioned about their sputum production and cigarette consumption in relation to type (filter or plain) smoked. Of 10,414 volunteers, 3,045 smoked filter cigarettes and 2,393 smoked plain cigarettes. The rate of persistent daily sputum of filter smokers (31·9%) was significantly lower than that of plain cigarette smokers (37·2%). A similar pattern was maintained when age and cigarette consumption were standardized. These figures are thought to understate the less injurious nature of filter cigarettes, since more than half of the filter smokers with persistent sputum developed this while previously smoking plain cigarettes.Whatever the reasons for the less injurious nature of filter cigarettes, it seems that cigarette smokers unable to stop smoking might suffer less from chronic bronchitis if they changed to filter cigarettes.     

Cover filter unit for on-line sampling of fungal broths

New cover filter sampling unit was tested in fungal fermentations in the presence of antifoam agents producing sticky fungal polysaccharides. Cover filter unit long-term filter capacity depends on the intensity of the pumping capacity of impeller as well as on the position of the filter unit.     

Studies on water and ion transport in homopteran insects: ultrastructure and cytochemistry of the cicadoid and cercopoid Malpighian tubules and filter chamber

The filter chamber is a complex junction of anterior and posterior extremities of the midgut and Malpighian tubules. The sac-like anterior extremity, or filter chamber proper, comprises two cell types. These are large cuboidal cells which secrete a mucoprotein, and extremely thin cells which have regular tubular invaginations of the basal plasma membrane. The posterior extremity of the midgut and the internal Malpighian tubules coil round the filter chamber proper. They consist of thin epithelial cells identical in ultrastructure. The basal plasma membrane in these cells is formed into leaflets. A thin cellular sheath and thick muscle layers surround the filter chamber. The filter chamber proper is lined by the mucoprotein secretion of the cuboidal cells. This secretion appears to bind potassium ions. ATPase and alkaline phosphatase cannot be detected in the filter chamber epithelia. The structure and cytochemistry of the filter chamber suggests that water flows from filter chamber proper to midgut and Malpighian tubules by passive osmosis. This may be facilitated by ion binding in the filter chamber proper and by hydrostatic pressure engendered by contraction of the muscular coat. The Malpighian tubules appear to be structurally and chemically adapted for ion secretion by active transport and possibly for reabsorption in the Malpighian duct segment.     

Air Filters for Germ-free Isolators

A germ-free isolator must have a perfect bacterial filter. This paper describes a new, relatively inexpensive, stainless-steel filter frame, which is easily and quickly assembled and protects the enclosed filter material at all times. Resistance to the flow of air was less than 4 inches of water at an airflow of 30 ft³/min through the filter frame with 204 inches² of surface area and four, one-half inch thick pieces of fiberglass filter material. This filter performed satisfactorily in our gnotobiotic laboratory and was found to be consistently 100% efficient in removing an aerosol containing Serratia marcescens from an air stream under a variety of operating conditions.     

Drum filter performance in a recirculating eel culture unit

The performance of a drum filter of a recirculating eel culture unit was studied. Electron microscopy scanning micrographs of drum filter panels showed a high degree of clogging of the filter mesh (after 4 months of operation). Mean removal efficiency for Total Suspended Solids (TSS) fluctuated considerably between subsequent sampling periods (9.6–18.4%). Drum filtration changed the particle size distribution of fish tank drainage water, resulting in increasing amounts (from 56 to 67% of dry weight, before and after filter passage) of the smaller particle fractions (< 20 μm), thereby indicating a partial breakdown of larger particles during the filtration process. Possible reasons for rapid filter clogging and suggestions for improvements in filter performance are discussed.     

Potassium channel, ions, and water: simulation studies based on the high resolution X-ray structure of KcsA

Interactions of Na(+), K(+), Rb(+), and Cs(+) ions within the selectivity filter of a potassium channel have been investigated via multiple molecular dynamics simulations (total simulation time, 48 ns) based on the high resolution structure of KcsA, embedded in a phospholipid bilayer. As in simulations based on a lower resolution structure of KcsA, concerted motions of ions and water within the filter are seen. Despite the use of a higher resolution structure and the inclusion of four buried water molecules thought to stabilize the filter, this region exhibits a significant degree of flexibility. In particular, pronounced distortion of filter occurs if no ions are present within it. The two most readily permeant ions, K(+) and Rb(+), are similar in their interactions with the selectivity filter. In contrast, Na(+) ions tend to distort the filter by binding to a ring of four carbonyl oxygens. The larger Cs(+) ions result in a small degree of expansion of the filter relative to the x-ray structure. Cs(+) ions also appear to interact differently with the gate region of the channel, showing some tendency to bind within a predominantly hydrophobic pocket. The four water molecules buried between the back of the selectivity filter and the remainder of the protein show comparable mobility to the surrounding protein and do not exchange with water molecules within the filter or the central cavity. A preliminary comparison of the use of particle mesh Ewald versus cutoff protocols for the treatment of long-range electrostatics suggests some difference in the kinetics of ion translocation within the filter.     

基于频域反卷积滤波器的光声成像

采用探测器的脉冲响应在频域反卷积滤波光声信号以进一步提高光声成像的分辨率.由仿真和实验结果表明,频域反卷积滤波重建相对于时域反投影重建和滤波反投影重建具有更好的成像效果,明显地提高重建图像的分辨率,经仿真结果的计算,其重建图像的分辨率由2.58 mm提高到了0.16 mm.实验所用的光源为YAG激光器,波长为1064 ...     

Effect of light quality on leaf photosynthetic characteristics and fruit quality of peach (<Emphasis Type="Italic">Prunus persica</Emphasis> L. Batch)

Different light filters affect leaf photosynthetic features and fruit quality. Consequently, selecting the appropriate covering filter for rain-shelter cultivation of peaches is a key part of successful production. We used a late-maturing peach variety ‘Xiahui 8’ to study differences in leaf photosynthetic features, chlorophyll fluorescence characteristics, and fruit quality under neutral, red, yellow, green, and blue filter, with natural light as control. The results showed that the leaf photosynthetic ability and internal quality under the neutral filter treatment were elevated compared with the control, and the appearance color was the same as the control. Leaves under neutral filter could maintain higher photosynthetic ability than other filter treatments. In addition, the fruits could also keep higher quality when treated with neutral filter. Therefore, the application of neutral filter in rain-shelter cultivation of ‘Xinhui 8’ peaches is recommended for maintaining high photosynthetic capacity and for improving fruit quality.