The NETmix reactor: Pressure drop measurements and 3D CFD modeling

NETmix is a new static mixing technology based on a network of mixing chambers interconnected by channels. Three NETmix reactors with different geometries were used to obtain experimental data for pressure drop and a generalized model for pressure drop in NETmix reactors has been developed. This model features a single adjustable parameter and it is only dependent on the geometric configuration of the NETmix design. The Z factor and the power number were also determined to compare the performance of different NETmix configurations with other existing mixers. The dynamic measurement of pressure drop was used to evaluate the mixing dynamics in the NETmix chambers and, above the critical Reynolds number, the natural oscillation frequency was quantified. Furthermore, a three-dimensional computational fluid dynamic transport model was also developed and validated. The energy performance of the three NETmix prototypes was quantified and shown to be very competitive with the compared existing static mixers. The developed 3D CFD transport model, validated by the reported experimental data, enables the computation of transport properties for any geometrical design and fluid properties, and avoids the need for experimental data each time a new NETmix configuration is designed.     

Marine main engine crankshaft failure analysis: A case study

A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under bending and torsion applied to crankshafts are presented. A microscopy (eye seen) observation showed that the crack initiation started on the fillet of the crankpin by rotary bending and the propagation was a combination of cyclic bending and steady torsion. The crack front profile approximately adopts a semi-elliptical shape with some distortion due to torsion and this study is supported by a previous research work already published by the authors. The number of cycles from crack initiation to final failure of this crankshaft was achieved by recording of the main engine operation on board, taking into account the beachmarks left on the fatigue crack surface. The cycles calculated by the linear elastic fracture mechanics approaches showed that the propagation was fast which means that the level of bending stress was relatively high when compared with total cycles of main engine in service. Microstructure defects or inclusion were not observed which can conclude that the failure was probably originated by an external cause and not due to an intrinsic latent defect. Possible effects of added torsional vibrations which induce stresses are also discussed. Some causes are analyzed and reported here but the origin of the fatigue fracture was not clearly determined.     

Fatigue crack growth with overloads/underloads: Interaction effects and surface roughness

The generalization of damage tolerance to variable amplitude fatigue is of prime importance in order to maintain the reliability of structures and mechanical components subjected to severe loading conditions. Engineering spectra usually contain overloads and underloads which distribution may not be random. However for predicting the life of a structure, a simplified spectrum is usually determined from the real one, in order to reduce testing periods on prototypes. Therefore it is thus important to know which cycles can contribute to crack growth and which can be neglected. This paper presents an analysis of fatigue crack growth on M (T) specimens made of a medium carbon steel DIN Ck45. The specimens are subjected to repeated blocks of cycles made up of one or several (1, 2, 6 or 10) overloads (or underloads) separated by a variable number (10, 1000 or 10 000) of baseline cycles. The main objective of this study is to better understand the mechanisms at the origin of interactions effects due to the presence of overloads (or underloads) at different locations of each block loading. Under constant amplitude loading, single variables ΔK and K_max are required in crack growth relationships. The transferability of fatigue laws, obtained under constant amplitude loading to variable amplitude fatigue, requires at least an additional variable, whose evolution with crack length accounts for the interactions effects between cycles of different types. Results have shown that the interaction effects in fatigue crack growth are closely related to the mechanisms of crack growth: cyclic plastic behaviour of the material and fracture surface roughness. Measurements of roughness of the surface fracture were carried out in both constant amplitude and variable amplitude tests. The roughness characterization helped to determine the importance of the mechanisms on variable amplitude fatigue crack growth and determine the influence of overloads/underloads on fatigue crack growth.     

Estimation of kLa Values in Bench‐Scale Stirred Tank Reactors with Self‐Inducing Impeller by Multiphase CFD Simulations

A multiphase computational fluid dynamics (CFD) simulation methodology is developed and proposed for the estimation of the spatial distribution of k_La values in a bench‐scale reactor equipped with a self‐inducing impeller. The importance of estimating an apparent drag coefficient, which considers the effect of turbulence on the gas bubble rising velocity, is also tackled by applying different correlations available in literature, namely, Brucato, modified Brucato, and Pinelli correlations. The spatial distribution of k_La values in the agitated vessel is found from the CFD results using Danckwert's surface renewal model. An analysis of the gas volume fraction distribution obtained from the simulations is performed in order to choose the most suitable drag model. The modified Brucato correction correlation for the drag force exhibits the best agreement with experimental data.     

Radioimmunoassay for the testosterone 5 alpha-reductase inhibitor turosteride in biological fluids

An antiserum against turosteride (code name FCE 26073), a potent testosterone 5 alpha-reductase inhibitor, has been raised in rabbits by immunization with an immunogen produced by conjugation of a derivative of FCE 26073 (FCE 27424) to bovine serum albumin. The antiserum was able to distinguish FCE 26073 from its derivatives modified at the 17 beta position and from all the endogenous steroids tested. A radioimmunoassay for the determination of FCE 26073 in human plasma and urine was developed using this antiserum and tritium labeled turosteride. FCE 26073 was extracted from 50 microliters of plasma or 25 microliters of urine using ethyl-ether with a recovery greater than 90%. Using this procedure it was possible to achieve a final limit of quantitation of 142 pg/ml in plasma and 284 pg/ml in urine. The assay was validated in terms of reproducibility, accuracy and precision in the range 3.9-250 pg/50 microliters of plasma and 25 microliters of urine. The plasma concentration of FCE 26073 in a healthy male volunteer who received 0.2 mg of the drug was measured using the radioimmunoassay.     

Low-dose nicotine nasal spray use and effects during initial smoking cessation.

The purposes of this study were to determine if smokers wanting to quit smoking would use a low-dose nicotine nasal spray (i.e., acceptability) and what effect this spray use would have on withdrawal during the 1st week of cessation. Smokers (n?=? 52) were assigned double-blind to either placebo or nicotine spray (1.5 μg/kg. or approx. 0.1 mg, per spray) for ad lib use during the first week of cessation. All received group behavioral counseling. There was no difference in continuous 1-week abstinence (daily COa?     

The discriminative stimulus, subjective, cardiovascular, and reinforcing effects of nicotine as a function of light physical activity.

Smokers often experience the acute effects of cigarette smoking while they are engaged in the light physical activity of routine tasks. However, virtually all laboratory-based research on these effects is conducted under conditions of quiet rest and, thus, may not generalize to effects in the natural environment. We examined changes in the discriminative stimulus, subjective, cardiovascular, and reinforcing effects of nicotine in humans as a function of the level of concurrent physical activity. Men and women smokers (N = 17) were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo (0 microg/kg) at rest. Three sessions then followed, in which the generalization of discrimination was tested across a range of doses (0-20 microg/kg) while at rest or engaged in very light or light physical activity (15% and 30% of heart rate reserve, respectively) via bicycle ergometer. Generalization testing involved both two- and three-choice ("novel" option) quantitative procedures. Self-reported mood via the Profile of Mood States and visual analog scales, and cardiovascular measures of heart rate and blood pressure were obtained concurrent with discrimination responding. Nicotine reinforcement was assessed after the end of generalization testing using a choice procedure under the same rest or activity conditions. Results showed that physical activity did not significantly alter nicotine discrimination or reinforcement, as no interactions between activity and nicotine were observed. When activity and nicotine influenced the same subjective and cardiovascular responses, they acted in a generally additive fashion. These findings suggest that research on the acute effects of nicotine conducted under typical resting laboratory conditions generally are not altered by light physical activity and so may generalize to the effects of nicotine under conditions common in the natural environment.     

Dynamically Controlled Formation of TiN by Combustion of Ti in Air

This paper studies the formation of titanium nitride (TiN) by combustion of Ti particles in air. It is proposed that the combustion reaction is a dynamically controlled process, in which the formation of TiN is fulfilled by delayed gas infiltration behind the propagation of combustion wave. With the addition of NH₄Cl or carbon black, the yield of TiN can be enhanced. The as-synthesized TiN grains show a terraced morphology with parallel layers stacked in the normal direction. It is thought that this terraced morphology has been derived from a surface-coarsening process. The parallel layers show regular hexagonal outlines and thus are considered to be (111) planes according to the symmetric characters of the FCC structure. The (111) texture is also revealed by X-ray diffraction results, where the relative intensity of (111) peak is clearly higher than the reference in the JCPDS card. In addition, nanoscale twinning areas are observed in TiN grains. From transmission electron microscopy (TEM) results, it is determined that the twinning plane is (111) and the twinning direction is [ 2 11]. The movement of atoms during twinning is discussed according to the FCC structure of TiN and high-resolution TEM images.     

Soil aggregates control N cycling efficiency in long-term conventional and alternative cropping systems

This paper presents novel data illustrating how soil aggregates control nitrogen (N) dynamics within conventional and alternative Mediterranean cropping systems. An experiment with ¹⁵N-labeled cover crop residue and synthetic fertilizer was conducted in long-term (11 years) maize–tomato rotations: conventional (synthetic N only), low-input (reduced synthetic and cover crop-N), and organic (composted manure- and cover crop-N). Soil and nitrous oxide (N₂O) samples were collected throughout the maize growing season. Soil samples were separated into three aggregate size classes. We observed a trend of shorter mean residence times in the silt-and-clay fraction than macro- (>250 μm) and microaggregate fractions (53–250 μm). The majority of synthetic fertilizer-derived ¹⁵N in the conventional system was associated with the silt-and-clay fraction (<53 μm), which showed shorter mean residence times (2.6 months) than cover crop-derived ¹⁵N in the silt-and-clay fractions in the low-input (14.5 months) and organic systems (18.3 months). This, combined with greater N₂O fluxes and low fertilizer-N recoveries in both the soil and the crop, suggest that rapid aggregate-N turnover induced greater N losses and reduced the retention of synthetic fertilizer-N in the conventional system. The organic system, which received 11 years of organic amendments, sequestered soil organic carbon (SOC) and soil N, whereas the conventional and low-input systems merely maintained SOC and soil N levels. Nevertheless, the low-input system showed the highest yield per unit of N applied. Our data suggests that the alternating application of cover crop-N and synthetic fertilizer-N in the low-input system accelerates aggregate-N turnover in comparison to the organic system, thereby, leading to tradeoffs among N loss, benefits of organic amendments to SOC and soil N sequestration, and N availability for plant uptake.     

4,9-Diaminoacridines and 4-Aminoacridines as Dual-Stage Antiplasmodial Hits

Multi-stage drugs have been prioritized in antimalarial drug discovery, as targeting more than one process in the Plasmodium life cycle is likely to increase efficiency, while decreasing the chances of emergence of resistance by the parasite. Herein, we disclose two novel acridine-based families of compounds that combine the structural features of primaquine and chloroquine. Compounds prepared and studied thus far retained the in vitro activity displayed by the parent drugs against the erythrocytic stages of chloroquine-sensitive and -resistant Plasmodium falciparum strains, and against the hepatic stages of Plasmodium berghei, hence acting as dual-stage antiplasmodial hits.