Mass transfer measurements and modeling in a microchannel photocatalytic reactor

The main objective of this paper was to evaluate the influence of mass transfer on the photocatalytic efficiency at a low flow rate in the order of several mL per hour. Several continuous flow microchannel reactors have been used to study the degradation of salicylic acid (SA) taken as a model pollutant. The photocatalytic degradation of salicylic acid, under UV illumination of 1.5 mW cm⁻², was assessed from the outlet concentration measured by liquid chromatography HPLC. It was shown that the degradation of SA by UV was limited by mass transfer. Numerical simulations have allowed establishing a relationship of the Sherwood number valuable for all the microchannel geometries. Computational fluid dynamics with Comsol Multiphysics is useful for predicting the degradation yield for a given geometry of the microreactor. The best representation of the experimental data is obtained by introducing a kinetic law taking into account mass transfer limitation.     

Lipid and fatty acid composition of diatoms revisited: rapid wound-activated change of food quality parameters influences herbivorous copepod reproductive success

Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton. We show that cell disruption, as it occurs during a predator's grazing on diatoms can drastically change the lipid and fatty acid content of the food. In some algae, a rapid depletion of polyunsaturated fatty acids (PUFAs) is observed within the first minutes after cell disruption. This fatty acid depletion is directly linked to the production of PUFA-derived polyunsaturated aldehydes (PUA); these are molecules that are thought to be involved in the chemical defence of the algae. PUA-releasing diatoms are even capable of transforming lipids from other sources if these are available in the vicinity of the wounded cells. Fluorescent staining reveals that the enzymes involved in lipid transformation are active in the foregut of copepods, and therefore link the depletion processes directly to food uptake. Incubation experiments with the calanoid copepod Temora longicornis showed that PUFA depletion in PUA-producing diatoms is correlated to reduced hatching success, and can be compensated for by externally added single fatty acids.     

A kinetic spectrophotometric method for simultaneous determination of phenol and its three derivatives with the aid of artificial neural network

A novel kinetic spectrophotometric method was developed for determination of pyrocatechol, resorcin, hydroquinone and phenol based on their inhibitory effect on the oxidation of Rhodamine B (RhB) in acid medium at pH = 3.0. A linear relationship was observed between the inhibitory effect and the concentrations of the compounds. The absorbance associated with the kinetic reactions was monitored at the maximum wavelength of 557 nm. The effects of different parameters such as pH, concentration of RhB and KBrO₃, and temperature of the reaction were investigated and optimum conditions were established. The linear ranges were 0.22-3.30, 0.108-0.828, 0.36-3.96 and 1.52-19.76 μg mL⁻¹ for pyrocatechol, resorcin, hydroquinone and phenol, respectively, and their corresponding detection limits were 0.15, 0.044, 0.16 and 0.60 μg mL⁻¹. The measured data were processed by several chemometrics methods, such as principal component regression (PCR), partial least squares (PLS) and artificial neural network (ANN), and a set of synthetic mixtures of these compounds was used to verify the established models. It was found that the prediction ability of PLS, PCR and RBF-ANN was similar, however, the RBF-ANN model did perform somewhat better than the other methods. The proposed method was also applied satisfactorily for the simultaneous determination of pyrocatechol, resorcin, hydroquinone and phenol in real water samples.     

Oscillator frequency stability improvement by means of negative feedback

A novel, simple method is proposed to increase the frequency stability of an oscillator. An additional negative feedback is used in combination with the positive loop of the harmonic oscillator to decrease the phase sensitivity to fluctuations of parameters other than the resonator. The main advantage of the proposed correction approach is that it does not require expensive external elements such as mixers or resonators. The validity of the method is theoretically demonstrated on a Colpitts oscillator using the control system theory approach and numerical simulations, and is experimentally verified with phase noise measurements of an actual oscillator-mockup. It is shown that the medium-term frequency stability can be easily improved by a factor of ten.     

LORD: Tracking mobile clients in a real mesh

Localizing a mobile client in a Wireless mesh network (WMN) consists in finding the router this client is attached to. Intuitively, the simplest manner to perform this task is to flood the whole network asking for the location of this client. Flooding the network is good for reliability but leads to increased latency and broadcast storm problems, affecting the efficiency of the localization service. In this paper, we design, implement, and evaluate LORD, a new client localization scheme based on a Distributed Hash Table (DHT). The originality of LORD is that it avoids exponential search on the DHT by relying on a proactive routing protocol running among the routers in the wireless backbone. Furthermore, it avoids flooding and provides fully transparency to end-users. Through experimental evaluation on a real WMN testbed, we show that LORD improves performance versus current flooding-based approaches by up to 3.5 times in terms of number of packets generated and 2.5 times in terms of link activations. Furthermore, although we mainly expected gains with reference to overhead, we also observed reductions of up to 50% in the handover time.     

Ethanol-mediated metal transfer printing on organic films

Ethanol-mediated metal transfer printing (mTP) is a soft method, which allows to efficiently deposit metals onto various organic surfaces for applications in organic electronics. This simple approach in based on the stronger adhesion of the metals to the organic materials in the presence of thin ethanol layer between the metallized PDMS and the substrate due to the capillary action. Patterns with a resolution of at least 20 μm have been obtained on organic polymeric materials and photoresists without heating or applied pressure. Compared to other methods ethanol mediated mTP is considerably faster and has smaller limitations on the stamp depth. Residual silicone layer detected on the metal surface after the transfer by XPS studies has been mostly removed by UV/ozone treatment. Organic field-effect transistors (OTFTs) based on the metal electrodes deposited by mTP have been successfully fabricated and tested.     

Integrated multiscale modeling of the nervous system: predicting changes in hippocampal network activity by a positive AMPA receptor modulator

One of the fundamental characteristics of the brain is its hierarchical organization. Scales in both space and time that must be considered when integrating across hierarchies of the nervous system are sufficiently great as to have impeded the development of routine multilevel modeling methodologies. Complex molecular interactions at the level of receptors and channels regulate activity at the level of neurons; interactions between multiple populations of neurons ultimately give rise to complex neural systems function and behavior. This spatial complexity takes place in the context of a composite temporal integration of multiple, different events unfolding at the millisecond, second, minute, hour, and longer time scales. In this study, we present a multiscale modeling methodology that integrates synaptic models into single neuron, and multineuron, network models. We have applied this approach to the specific problem of how changes at the level of kinetic parameters of a receptor-channel model are translated into changes in the temporal firing pattern of a single neuron, and ultimately, changes in the spatiotemporal activity of a network of neurons. These results demonstrate how this powerful methodology can be applied to understand the effects of a given local process within multiple hierarchical levels of the nervous system.     

Effect of the Temperature on the Nonlinear Acoustic Behavior of Reinforced Concrete Using Dynamic Acoustoelastic Method of Time Shift

During field tests, there is almost no effective way to control thermal changes in concrete structures. It is obvious that temperature fluctuations influence nonlinear acoustic behavior of concrete, which may lead to incoherent results during field investigations. The research presented herein was conducted to assess the effects of temperature changes on the nonlinear acoustic behavior of the reinforced concrete using Time Shift method. The Time Shift method, based on dynamic acoustoelastic principle, takes its roots from the coda wave interferometry method and combines it with the study of the nonlinear behavior in cementitious materials in a methodological manner that allows field investigations. Near-to-field environmental conditions were simulated in the laboratory using an automatic climatic room. The specimens were subjected to temperature changes ranging from \(-\) 10 to 40  \(^{\circ }\) C. Such a thermal regime is close to the thermal conditions prevailing for most concrete structures. The effect of the temperature variations was assessed in both sound and damaged concrete elements affected by alkali–silica reaction (ASR). The test-results demonstrate that the nonlinear acoustic responses of concrete depend on the temperature. However, the nonlinear parameter seems to get minimized in low temperatures ranging from \(-\) 10 to 10  \(^{\circ }\) C. Moreover, the state of medium (i.e. intact or damaged) can alter the sensitivity level of the nonlinear behavior to temperature variations.     

Alternative Reagents for Methotrexate as Immobilizing Anchor Moieties in the Optimization of MASPIT: Synthesis and Biological Evaluation

We report the evaluation of two alternative chemical dimerizer approaches aimed at increasing the sensitivity of MASPIT, a three‐hybrid system that enables small‐molecule target protein profiling in intact human cells. To circumvent the potential limitations related to the binding of methotrexate (MTX) to endogenous human dihydrofolate reductase (DHFR), we explored trimethoprim (TMP) as an alternative prokaryote‐specific DHFR ligand. MASPIT evaluation of TMP fusion compounds with tamoxifen, reversine, and simvastatin as model baits, resulted in dose–response curves shifted towards lower EC₅₀ values than those of their MTX congeners. Furthermore, a scalable azido‐TMP reagent was synthesized that displayed a similar improvement in sensitivity, possibly owing to increased membrane permeability relative to the MTX anchor. Applying the SNAP‐tag approach to introduce a covalent bond into the system, on the other hand, produced an inferior readout than in the MTX‐ or TMP‐tag based assay.