合成纤维和玻璃纤维制成的Ashrae过滤介质的性能比较

对常用的超细玻璃纤维制成的Ashrae袋式过滤介质、标准驻极熔喷聚丙烯Ashrae袋式过滤介质和一种新型的熔喷聚丙烯细纤维Ashrae袋式过滤介质进行了比较。标准玻璃纤维毡所用的纤维非常微细,密实性(固体体积分数)很低,导致α值(品质因子)较高,但该材料不能吸附静电荷。标准熔喷聚丙烯过滤介质所用的纤维比玻璃纤维粗得多,密实性也更高,因能吸附很多静电荷,其初始α值比玻璃纤维毡要大得多,但放电后的α值却比玻璃纤维毡低得多。新型的熔喷聚丙烯细纤维过滤介质可完全驻极,其初始α值和标准熔喷聚丙烯过滤介质一样高,但由于更加细微的纤维结构,在放电后所保持的α值更高。     

Dichotomous feedback: a signal sequestration-based feedback mechanism for biocontroller design

We introduce a new design framework for implementing negative feedback regulation in synthetic biology, which we term ‘dichotomous feedback’. Our approach is different from current methods, in that it sequesters existing fluxes in the process to be controlled, and in this way takes advantage of the process’s architecture to design the control law. This signal sequestration mechanism appears in many natural biological systems and can potentially be easier to realize than ‘molecular sequestration’ and other comparison motifs that are nowadays common in biomolecular feedback control design. The loop is closed by linking the strength of signal sequestration to the process output. Our feedback regulation mechanism is motivated by two-component signalling systems, where a second response regulator could be competing with the natural response regulator thus sequestering kinase activity. Here, dichotomous feedback is established by increasing the concentration of the second response regulator as the level of the output of the natural process increases. Extensive analysis demonstrates how this type of feedback shapes the signal response, attenuates intrinsic noise while increasing robustness and reducing crosstalk.     

Visual Notes and the Acquisition of Architectural Knowledge

This article discusses the value and purpose of drawing in its relationship to the design process and understanding architecture. The authors base much of their discussion on their own experiences in teaching both drawing and architectural design to undergraduates. These experiences however are informed and supported both by architectural history and theory and theories of perception and art. The authors discuss the importance of visual notes to architects of the past, note both the decline of the usage of visual notes in the twentieth century as well as their continued use by important architects of our time. This article stresses the analytical and critical value of such drawing as opposed to its pictorial purposes.     

Effect of various phenol additives on viscosity of SRC blends

Coal-derived liquids are susceptible to oxidative degradation. Two different weight ratios of SRC-I/SRC-II blends, with or without phenol derivatives, have been subjected to accelerated ageing studies. Viscosity, infrared, elemental analysis, molecular weight determination, and solvent analysis are used to examine the properties of the degradation products. On ageing, there is a large increase in the amount of toluene-insoluble material, decrease in oil components, and a relatively constant amount of asphaltenes. The oxygen content increases in the aged toluene-insoluble and asphaltene fractions, and a new absorption at ≈1700 cm^?1 (the C = 0 group) appears in these two fractions only. On the addition of phenol itself and the less hindered phenol derivatives, the original hydrogen-bonding between the acidic and basic fuctional groups in the coal liquids is apparently disrupted because the added phenol can now interact with the proton-accepting species in the liquids, thus leading to a lower viscosity. This does not mean that the unhindered phenols retard the rate of ageing. The original hydrogen-bonding in the coal-derived liquid now gives way to a new hydrogen-bonding, and ageing occurs with the latter. The more hindered phenol derivatives are not as effective as phenol in disrupting the original hydrogen-bonding in the coal-derived liquids.     

Molecular mass calibration in size-exclusion chromatography of coal derivatives

A number of procedures have been investigated for the calibration of a size-exclusion chromatography (s.e.c.) column in the determination of molecular mass (MM) distributions of coal derivatives. The behaviour of narrow fractions of coal extracts in the MM range 200–3000 was compared with a variety of the more generally available calibration standards. Calibration with preparative s.e.c. subfractions of materials similar to those under study has been recommended. Polystyrene standards are satisfactory, however, for MM < 1000, but above this range other polymer standards should be sought. Universal and molar volume calibration do not apply to coal-derived materials.     

Aging and carbon dioxide plasticization of thin polyetherimide films

Industrial gas separation membranes have selective dense layers with thicknesses around 100 nm. It has long been assumed that these thin layers have the same properties as thick (bulk) films. However, recent research has shown that thin films with such thickness experience accelerated physical aging relative to bulk films and, thus, their permeation properties can differ significantly from the bulk. Thin films made from Extem^® XH 1015, a new commercial polyetherimide, have been investigated by monitoring their gas permeability. The permeability of the thin films is originally greater than the thick films but eventually decreases well below the permeability of the thick film. The CO₂ plasticization of Extem thin films is explored using a series of exposure protocols that indicate CO₂ plasticization is a function of film thickness, aging time, exposure time, pressure and prior history.     

Composition of a protein-like fluorophore of dissolved organic matter in coastal wetland and estuarine ecosystems

This study demonstrates the compositional heterogeneity of a protein-like fluorescence emission signal (T-peak; excitation/emission maximum at 280/325 nm) of dissolved organic matter (DOM) samples collected from subtropical river and estuarine environments. Natural water samples were collected from the Florida Coastal Everglades ecosystem. The samples were ultrafiltered and excitation-emission fluorescence matrices were obtained. The T-peak intensity correlated positively with N concentration of the ultrafiltered DOM solution (UDON), although, the low correlation coefficient (r(2)=0.140, p<0.05) suggested the coexistence of proteins with other classes of compounds in the T-peak. As such, the T-peak was unbundled on size exclusion chromatography. The elution curves showed that the T-peak was composed of two compounds with distinct molecular weights (MW) with nominal MWs of about >5 x 10(4) (T(1)) and approximately 7.6 x 10(3) (T(2)) and with varying relative abundance among samples. The T(1)-peak intensity correlated strongly with [UDON] (r(2)=0.516, p<0.001), while T(2)-peak did not, which suggested that the T-peak is composed of a mixture of compounds with different chemical structures and ecological roles, namely proteinaceous materials and presumably phenolic moieties in humic-like substances. Natural source of the latter may include polyphenols leached from senescent plant materials, which are important precursors of humic substances. This idea is supported by the fact that polyphenols, such as gallic acid, an important constituent of hydrolysable tannins, and condensed tannins extracted from red mangrove (Rhizophora mangle) leaves exhibited the fluorescence peak in the close vicinity of the T-peak (260/346 and 275/313 nm, respectively). Based on this study the application of the T-peak as a proxy for [DON] in natural waters may have limitations in coastal zones with significant terrestrial DOM input.