Clogging modeling in pleated filters for gas filtration

A model of clogging of a pleated filter in gas filtration is presented. The model is obtained by combining a semi-analytical model of the flow in a pleated filter and an empirical model of clogging of the planar filter medium applied locally along the pleated filter channels. The model takes into account the formation of a filtration cake of variable thickness at the porous wall of the pleated filter entrance channels and the resulting evolution of the entrance channels aperture distribution during the filtration/clogging process. Based on the numerical predictions, two main clogging scenarios are identified and analyzed. The optimum pleat density, defined as the pleat density maximizing the filter capacity, is determined and shown to be greater than the pleat density minimizing the pressure drop for a clean filter. Predictions of the evolution of overall pressure drop across the pleated filter due to clogging are compared with experimental data.     

消除运算放大器的意外正反馈

由运算放大器构成的反馈系统常用于使系统保持稳定。但是在一些情况下也有意外发生。比如太阳能船的玩具,当有时打开开关时,玩具甚至会发出“噗噗”的声响。这种情况有可能是由于运算放大器发生了意外正反馈（inadvertent positive feedback）导致的。     

Dietary assessment of pre-school children from Federal District Brazil

The objective was to assess food consumption among children attending non-profit nurseries in the Federal District, Brazil.A representative sample was obtained and stratified by income. Food intake among 678 children, between 4 and 82 months old, was analyzed in nine nurseries using the 24-h dietary recall and direct food weighing methods. In children under 13 months old mean intake was above AI between 93.6 to 100% for carbohydrates, proteins, vitamins B1, B2, B12, B6, and zinc. In children from 7-12 months 56.5% presented iron consumption below EAR. Calcium intake was above AI for 35.4% of children over 1 year old. For vitamins with EAR values, the prevalence of inadequate consumption was 53.2% for vitamin E, and 90% for folate for children over 12 months old. Iron and zinc intake was above UL for 6.4% and 32.5% of children under 1 year old, and 1.5% and 5.3% for the remaining children, respectively. Lipid percentage distribution range among children between 13 and 47 months old was within the acceptable range for only 16.2%. Nonetheless, children between 36 and 82 months of both genders presented mean intake below energy requirements. Inadequate consumption observed for some nutrients points to the need for improvements in the standard of meals and nutritional assistance offered to children enrolled in charitably run nurseries in the Federal District.     

Improvement of the stoichiometric network analysis for determination of instability conditions of complex nonlinear reaction systems

Stoichiometric network analysis (SNA), a known method for analyzing complex reaction systems including biochemical ones, is improved and applied to a nonlinear process studied far from equilibrium in a continuously fed, well stirred tank reactor (CSTR). A particular attention is focused on the determination of the narrow range of the control parameter values where the main steady state is unstable and where different dynamic states can be simulated numerically. The instability region, the most important feature of nonlinear reaction systems, is calculated as a function of the SNA parameters (current rates and reciprocal concentrations of intermediate species in the steady state) and simplified by retaining only the dominant terms. Since the number of the current rates is usually larger than the number of linearly independent equations to be used for their calculation, it is shown here that the current rates can be replaced with a smaller number of reaction rates at the steady state. These rates are related to the experimental data in a simple manner. The instability condition is also written as a function of dimensionless parameters derived from the SNA. This general approach is applied to a model of the Bray–Liebhafsky (BL) reaction having seven reactions without direct autocatalysis or autoinhibition, studied under CSTR conditions. Since the model has six intermediate species, it would be very difficult to analyze its instability condition by the conventional procedure, where a sixth order characteristic equation would have to be solved. On the other hand, the instability condition, obtained easily by the improved SNA, locates correctly the oscillatory region using numerical integration. Other dynamic states found earlier with a larger model of the BL reaction, such as mixed-mode oscillations, period doubling and chaos, are also obtained within the theoretically predicted oscillatory region. Thus, besides the general advantages of the improved stoichiometric network analysis as a method appropriate for the examination of complex nonlinear reactions, we show that the various mentioned dynamic states can be obtained by a very simple variant of the model of the BL reaction realized under CSTR conditions.     

Probing enzyme promiscuity of SGNH hydrolases

Several hydrolases of the SGNH superfamily, including the lipase SrLip from Streptomyces rimosus (Q93MW7), the acyl-CoA thioesterase I TesA from Pseudomonas aeruginosa (Q9HZY8) and the two lipolytic enzymes EstA (from P. aeruginosa, O33407) and EstP (from Pseudomonas putida, Q88QS0), were examined for promiscuity. These enzymes were tested against four chemically different classes of a total of 34 substrates known to be hydrolysed by esterases, thioesterases, lipases, phospholipases, Tweenases and proteases. Furthermore, they were also analysed with respect to their amino acid sequences and structural homology, and their phylogenetic relationship was determined. The Pseudomonas esterases EstA and EstP each have an N-terminal domain with catalytic activity together with a C-terminal autotransporter domain, and so the hybrid enzymes EstA(N)-EstP(C) and EstP(N)-EstA(C) were constructed by swapping the corresponding N- and C-terminal domains, and their hydrolytic activities were compared. Interestingly, substrate specificity and kinetic measurements indicated a significant influence of the autotransporter domains on the catalytic activities of these enzymes in solution. TesA, EstA and EstP were shown to function as esterases with different affinities and catalytic efficacies towards p-nitrophenyl butyrate. Of all the enzymes tested, only SrLip revealed lipase, phospholipase, esterase, thioesterase and Tweenase activities.     

Biosynthesis of the Myxobacterial Antibiotic Corallopyronin A

Corallopyronin A is a myxobacterial compound with potent antibacterial activity. Feeding experiments with labelled precursors resulted in the deduction of all biosynthetic building blocks for corallopyronin A and revealed an unusual feature of this metabolite: its biosynthesis from two chains, one solely PKS‐derived and the other NRPS/PKS‐derived. The starter molecule is believed to be carbonic acid or its monomethyl ester. The putative corallopyronin A biosynthetic gene cluster is a trans‐AT‐type mixed PKS/NRPS gene cluster, containing a β‐branching cassette. Striking features of this gene cluster are a NRPS‐like adenylation domain that is part of a PKS‐type module and is believed to be responsible for glycine incorporation, as well as split modules with individual domains occurring on different genes. It is suggested that CorB is a trans‐acting ketosynthase and it is proposed that it catalyses the Claisen condensation responsible for the interconnection of the two chains. Additionally, the stereochemistry of corallopyronin A was deduced by a combination of a modified Mosher's method and ozonolysis with subsequent chiral GC analyses.     

Leakage of Metallic Ball Seat Valves with Anisotropic Surfaces

Metallic ball seat valves are an essential component of many hydraulic systems. They are used for many different purposes such as pressure relief valves or check valves. Despite their universal usage, their sealing mechanism is not yet fully understood. In previous works, a successful method for the simulation of the fluid leakage of metallic ball seat valves has been developed and confirmed experimentally. The method is based on Persson's contact mechanics theory, which is based on surface roughness power spectrum C(q). This theory takes a wide range of roughness values at different length scales into account. The previous method has been restricted to isotropic surfaces, but most surfaces of practical interest are highly anisotropic. A method for the calculation of pressure flow factors using Persson's method is presented. Based on these, a model for the leakage calculation can be developed. The simulation results are validated using an experiment.     

Phase correction for frequency response function measurements

In modal testing, an impulse is often used to excite the structure and a linear transducer is used to measure the response. For these impact tests, two signals are measured: the impulsive force and the vibration response. Any lack of synchronization in the time domain acquisition of the two signals results in a frequency-dependent phase error in the frequency response function, or FRF. However, knowledge of the time delay may be used to correct the corresponding phase error. In this research, tests were conducted to measure the frequency-dependent phase error for a capacitive sensor and a frequency domain technique is proposed to correct the FRF. The method was validated using an FRF measurement of a cylindrical artifact mounted in a milling machine spindle.     

Structure of evaporating single- and multicomponent fuel sprays for 2nd generation gasoline direct injection

In the present paper the effect of fuel properties on spray formation and evaporation was investigated for a hollow-cone spray of a piezoelectric injector for Direct Injection Spark Ignition (DISI) engines. Late injection timing in a high-pressure atmosphere (1.5 MPa, 200 °C) was simulated in an injection chamber. Liquid and vapor phase structure of the hollow-cone spray were studied with 2D-Mie scattering, laser-induced fluorescence (LIF) as well as phase-Doppler anemometry (PDA). The spray structure was investigated for several alkanes with high and low volatility (n-hexane, n-heptane, iso-octane, n-decane) and a three-component mixture of the n-alkanes with similar fuel properties like a multicomponent gasoline fuel. It is found that the rapid evaporation of high volatility fuels can lead to spray destabilization, whereas low volatility single-component fuels overestimate radial spray propagation and vortex formation. For iso-octane the droplet size distribution is shifted to smaller droplets and the spray appeared to be less dense compared to n-heptane despite almost identical boiling behavior. However, the much higher viscosity of iso-octane determines the internal nozzle flow which results in a reduced injected fuel mass and changed atomization. A well defined three-component fuel models the global spray characteristics as well as the droplet size, droplet momentum distribution and evaporation behavior of the used multicomponent gasoline fuel very precisely. Small amounts of low volatility fractions delay the droplet evaporation and support the overall spray stability also for multicomponent mixtures. This leads to an increased spray width as well as larger droplet sizes and momenta. The evaporation characteristic of multicomponent fuels at increased ambient pressure is complex. At the studied injection conditions it is situated between the two limiting cases of distillation-like behavior and coevaporation of the components. Moreover, the results in comparison with theoretical estimations indicate a demixing of light and heavy boiling fractions in the three-component and multicomponent fuel under conditions which are typical for DISI strategies with late injection.