Novel Engineered Ion Channel Provides Controllable Ion Permeability for Polyelectrolyte Microcapsules Coated with a Lipid Membrane

The development of nanostructured microcapsules based on a biomimetic lipid bilayer membrane (BLM) coating of poly(sodium styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) polyelectrolyte hollow microcapsules is reported. A novel engineered ion channel, gramicidin (bis‐gA), incorporated into the lipid membrane coating provides a functional capability to control transport across the microcapsule wall. The microcapsules provide transport and permeation for drug‐analog neutral species, as well as positively and negatively charged ionic species. This controlled transport can be tuned for selective release biomimetically by controlling the gating of incorporated bis‐gA ion channels. This system provides a platform for the creation of “smart” biomimetic delivery vessels for the effective and selective therapeutic delivery and targeting of drugs.     

Effects of mite resistance mechanism of geraniums on mortality and behavior of foxglove aphid (Acyrthosiphon solani Kaltenbach)

Geraniums (Pelargonium xhortorum Bailey) possess a pest-resistance mechanism, based on glandular trichomes and the exudate they produce, that has been shown to be effective against the two-spotted spider mite (Tetranychus urticae Koch). Using an intact plant bioassay, the effectiveness of the resistance mechanism was determined for another potential pest, the foxglove aphid (Acyrthosiphon solani Kaltenbach). Comparisons were made between plant lines previously analyzed for their degree of resistance to mites, as well as their glandular trichome density and trichome exudate production. Over 100 aphid adults were bioassayed on each of the five plant lines used in the experiment. In addition to adult aphid survival, the production and survival of nymphs was determined in this bioassay. The results indicate that plant lines that are resistant to the two-spotted spider mite are also resistant to the foxglove aphid, while lines susceptible to mites are susceptible to the aphids. To evaluate the physical impediment features of the trichome exudate, the behavior of foxglove aphid nymphs was compared on two geranium lines, one a resistant line with high trichome densities and large quantities of exudate and the second a susceptible line with few trichomes and reduced exudate. A third leaf surface type was produced by washing the exudate from resistant leaves using a mildly basic buffer solution prior to the bioassay. Aphid behavior was divided into five categories: feeding or probing, resting, wandering, struggling, and immobilized. On both susceptible leaves and resistant leaves from which the exudate had been removed by washing, the aphids settled quickly and were observed with inserted stylets during most of the observation intervals. In contrast, aphids on the unwashed resistant leaf surfaces often became ensnared in the sticky trichome exudate and had difficulty in settling to probe the leaf. Physical entrapment by glandular trichome exudate appears to be an important aspect of aphid resistance in geraniums.     

CROSS-FLOW FILTRATION OF FUNGAL SUSPENSION WITH REVERSED-FLOW CLEANING

The separation of fungal suspension Trichoderma reesei was studied by using cross-flow filtration(CFF)with re-versed-flow cleaning(RFC)technique.The advantage of this technique is demonstrated in comparison with other filtra-tion techniques.The filtration rate is influenced by different frequencies of RFC.For optimum combination of CFF andRFC,both experimental and theoretical considerations are necessary and are discussed.An expression has been derivedfor the optimum filtration time needed to maximize the flux for a given RFC period assuming that the filtration stage canbe approximated by Ruth’s equation.The practical usefulness of this calculation is demonstrated on a batch thickening op-eration.     

Thermally Stimulated Polarization and Depolarization in Halogen-Containing Lead Silicate Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements were made on lead halide silicate glasses having compositions (65 − x )PbO· x PbX₂·35SiO₂ where x = 0, 0.1, 2, 10 and X = F, CI, Br, and I. The addition of halogen ions to lead silicate glasses gives rise to a new high-temperature TSDC peak in the vicinity of the peak previously observed in binary lead silicate glasses. The integrated area of the new peak is dependent on the amount and type of halogen ion present in the glass and does not saturate in the temperature range of our measurements. This new peak is attributed to space charge polarization of halogen ions.     

Ractions of SiC with H2/H2O/Ar Mixtures at 1300°C

The reactions of a sintered α-SiC with 5% H₂/H₂O/Ar at 1300°C were studied. Thermomchemical modeling indicates that three reaction regions are expected, depending on the initial water vapor or equivalently oxygen content of the gas stream. A high oxygen content ( P (O₂) > 10⁻²² atm) leads to a SiO₂ formation. This generally forms as a protective film and limits consumption of the SiC (passive oxidation). An intermediate oxygen content (10⁻²² atm > P (O₂) > 10⁻²⁶ atm) leads to SiO and CO formation. These gaseous products can lead to rapid consumption of the SiC (active oxidation). Thermogravimetric studies in this intermediate region gave reaction rates which appear to be controlled by H₂O gas-phase transport to the sample and reacted microstructures showed extensive grain-boundary attack in this region. Finally, a very low oxygen content ( P (O₂) < 10⁻²⁶ atm) is thermochemically predicted to lead to selective removal of carbon and formation of free silicon. Experimentally low weight losses and iron silicides are observed in this region. The iron silicides are attributed to reaction of free silicon and iron impurities in the system.     

Plastic constraint of large aspect ratio solder joints

The aspect ratio (joint area/joint thickness) of thin (0.001-0.006 in.) surface mount solder (60S-40Pb) joints plays an important role in determining the mechanical properties and fracture behavior of the joints. This study demon-strates that plastic constraint of a large aspect ratio 60Sn-40Pb solder joint can develop triaxial (hydrostatic) stresses several times greater than the average tensile strength of the bulk solder material. A four to sixfold increase in average joint stress and up to a tenfold increase in peak stress was measured on joints with aspect ratios ranging from 400 to 1000. Although a direct relationship of the aspect ratio to the average tensile stress is shown, as the Friction Hill model predicts, the observed stress increase is not nearly as high but proportional to the classical prediction. This is attributed to the existence of internal defects (oxide particles and micro-voids) and transverse grain boundaries which fail producing internal free surfaces. Thus, the actual aspect ratio is thickness/d², where d equals the distance between internal surfaces. The fracture of these constrained joints was brittle, with the separation occurring between a tin-rich copper tin intermetallic at the interface and the solder matrix. Voids within the solder joint are shown to relieve the plastic constraint and lower the average tensile stress of the joint. The Friction Hill model may play an important role in explaining the small percentage of atypical solder joint failures which sometimes occur on electronic assemblies. In particular, the sudden failure of a thin joint in a strain controlled environment may be attributed to the development of a large hydrostatic stress component. Therefore, a flaw free, plastically constrained joint which develops a high stress state will be a high risk candidate for failure.     

Determination of vitamin a in foods ‐ a review

Formerly, few foods were routinely analyzed for vitamin A, but recent emphasis on nutrient requirements, nutrient labeling, and use of dietary convenience foods has created need for determining vitamin A in a variety of foods. There are many vitamin A methods — some suitable for certain products only. For regulatory purposes, the FDA specifies the AOAC method where it is applicable. However, some food analysts and organizations continue with their own vitamin A methods. If possible, a single, widely applicable general method should be used for vitamin A in foods. Vitamin A may be determined by spectrophotometric, colorimetric, and fluorometric procedures. Sometimes chromatography is required as an important part of the method. Colorimetric procedures with SbCl₃ are now most widely used to measure vitamin A (retinol) in foods. If vitamin A content is high enough and extracts sufficiently free of interfering substances, spectrophotometric or flurometric methods are satisfactory. Methods in various stages of development for determining vitamin A in foods are based on flurospectrophotometry, gas‐liquid chromatography, high‐performance liquid chromatography, and automation. To estimate total vitamin A nutritional value of certain foods may also require determination of vitamin A isomerization and contents of carotenes, cryptoxanthin, reinaldehyde, and apo‐carotenal.     

The effects of sulphur fertilisers on the content of sulpho-amino acids in seeds of cowpea (Vigna unguiculata)

Seed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur-deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/10⁶ sulphate-S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho-amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate-S fertilisation up to ca 5 parts/10⁶. Compared with the control the sulpho-amino acid content in seeds of cowpea TVu 76 increased with S-supplementation up to 5 parts/10⁶ and that of cowpea Sitao Pole increased with S up to 1.8 parts/10⁶. Similar levels (7 and 2 parts/10⁶ respectively) of sulphate-S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho-amino acids in the seeds from 5 parts/10⁶ treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield.     

从USB端口“偷电”的动态虹吸技术

USB端口为辅助设备提供方便的5V电源.USB端口不仅向微控制器和其它基本电路供电,而且还提供足够的额外电流净空来给小电池或超级电容器储能元件充电.     

现代通信系统电源设计

通信设备使用的电源器件有很多种,从前端的功率因数校正(PFC)AC／DC电源到后端的高效DC／DC模块和负载点(POL)转换器,不一而足。从需要很高效率的中间总线转换器(IBC),到那些日趋细小轻巧的VoIP数字电话,以及要求多路紧密调节电压(7～13路输出)的数字用户线(xDSL)电源等,DC／DC电源在现代通信中获得了广泛应用。