Computing Shear Flow and Sludge Blanket in Secondary Clarifiers

Recent developments in computing turbulent and buoyant flow in sedimentation tanks are introduced. The test case is a circular, center-feed secondary clarifier with inclined bottom and central sludge withdrawal. Axisymmetry is assumed, and the flow and settling processes are modeled in a radial section by using the k-ε turbulence model on a two-dimensional, nonorthogonal grid. The computation domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. The aim of the present study is to evaluate the sensitivity of the flow and concentration fields to parameters that characterize (1) the rheological properties of highly concentrated regions; (2) the settling of sludge; and (3) the effect of stratification on the turbulent diffusion. The overall appearance of the fields proves to be similar, whereas the regions of high velocities and high gradients are strongly affected by using different parameters or approaches on rheology, settling, and diffusive transport, resulting in different sludge blanket heights.     

Antioxidant and antibacterial effects of Lavandula and Mentha essential oils in minced beef inoculated with E. coli O157:H7 and S. aureus during storage at abuse refrigeration temperature

The essential oils (EOs) of Lavandula angustifolia L. and Mentha piperita L. were analyzed by gas chromatography mass spectrometry (GC/MS). The major constituents were linalool (22.35%), linalyl acetate (21.80%), trans-ocimene (6.16%) and 4-terpineol (5.19%) for L. angustifolia and menthol (33.28%), menthone (22.03%), and menthyl acetate (6.40%) for M. piperita. In vitro antibacterial activity of both EOs against Escherichia coli O157:H7 and Staphylococcus aureus CECT 4459 showed high inhibition against S. aureus. The lowest minimal inhibitory concentrations (MIC) were obtained with L. angustifolia (0.25μL/mL) against S. aureus; M. piperita exhibited a MIC of 0.50μL/mL against both microorganisms. Both EOs caused a significant decrease of bacterial growth in minced beef (p<0.05) stored at 9±1°C. Minced beef treated with EOs showed the lowest TBARS values (lipid oxidation). Moreover, the results showed that the addition of EOs significantly extended fresh meat odor even at abuse temperature.     

Numerical analysis of earth air heat exchangers at operating conditions in arid climates

This paper presents the modeling and simulation of an earth air heat exchanger (EAHE), employed as an air-conditioning device for buildings in the climate conditions of the south of Algeria. The earth tubes buried in the ground can offer considerable advantages in terms of energy savings. The appropriate depth of the buried tubes was calculated taking into account the physical properties of the soil in the region under study and using a specific program developed by the authors. A parametric analysis was carried out taking into account the length and the radius of the pipe and the velocity of the air in the pipe. The results of performance and overall energy savings are presented. The maximum daily cooling capacity of the EAHE studied was 1.755 kWh. Results showed that a simple EAHE system can provide 246.815 kWh in a period of one year.     

Oxygen and Carbon Distribution in 80Kg Multicrystalline Silicon Ingot

Silicon - Multicrystalline silicon (mc-Si) wafers produced by directional solidification still dominate the world market, due to the factor quality/price. The performance of solar cell depends...     

BOD‐LEACH: broadcasting over duty‐cycled radio using LEACH clustering for delay/power efficient dissimilation in wireless sensor networks

Broadcasting delay‐sensitive information over a duty‐cycled wireless sensor network is considered, and a cluster‐based protocol is proposed. The proposed protocol, namely Broadcast over Duty‐Cycle and LEACH (BOD‐LEACH), takes advantage of the LEACH's energy‐efficient clustering. This approach shifts the total burden of energy consumption of a single cluster head by rotating the cluster‐head role among all nodes in the network. It also permits the ordinary (member) nodes in a cluster to turn off their radios whenever they enter inactive TDMA slots. However, LEACH does not consider broadcast messages, and the member nodes scheduling is established as a sequence of Time Division Multiple Access (TDMA) without any common active period. A broadcast message should then be postponed to the next TDMA schedule and transmitted in a sequence of unicast messages, which is inefficient in terms of latency, bandwidth occupation, and power consumption. The proposed protocol adds new common static and dynamic broadcast periods to support and accelerate broadcasting. The dynamic periods are scheduled following the past arrivals of messages and using a Markov chain model. To our knowledge, this work is the first that proposes the use of clustering to perform simultaneous local broadcasts at several clusters. This reduces broadcast latency and ensures scalability. The protocol has been simulated, numerically analyzed, and compared with LEACH. The results show clear improvement over LEACH with regard to broadcast latency, at a low energy cost. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental and theoretical study of Parabolic trough collector (PTC) with a flat glass cover in the region of algerian sahara (Ouargla)

Journal of Mechanical Science and Technology - In the present work, an experimental study has been performed at Ouargla in the south of Algeria to determinate the outlet water temperature and...     

A new enhanced assumed strain quadrilateral membrane element with drilling degree of freedom and modified shape functions

A new four‐node quadrilateral membrane finite element with drilling rotational degree of freedom based on the enhanced assumed strain formulation is presented. A simple formulation is achieved by five incompatible modes that are added to the Allman‐type interpolation. Furthermore, modified shape functions are used to improve the behaviour of distorted elements. Numerical results show that the proposed new element exhibits good numerical accuracy and improved performance, and in many cases, superior to existing elements. In particular, Poisson's locking in nearly incompressible elasticity fades and the element performs well when it becomes considerably distorted even when it takes almost triangular shape. Copyright © 2016 John Wiley & Sons, Ltd.     

Comments on “A General Model of Multipath Error for Coherently Tracked BOC Modulated Signals”

The mathematical formulation of the discriminator and the multipath error models presented by Harris and Lightsey contains some typing errors. In this comment, we review the formalism of aforementioned models and we fix and correct these typing errors. The simulation results show that the original analytical models, with these corrections, coincide with the numerical models.     

Antimicrobial activity of Pistacia lentiscus and Satureja montana essential oils against Listeria monocytogenes CECT 935 using laboratory media: Efficacy and synergistic potential in minced beef

The aim of this study was to optimize the antimicrobial efficacy of plant essential oils (EOs) for control of Listeria monocytogenes (L. monocytogenes) serovar 4b CECT 935 using laboratory media and minced beef stored at 5 ± 1 °C. Commercial EOs obtained from leave parts of Mediterranean Pistacia lentiscus (P. lentiscus) and Satureja montana (S. montana) were analyzed by gas chromatography–mass spectrometry (GC–MS). The main components of EOs obtained were β-myrcene (15.18%) and carvacrol (29.19%), respectively for P. lentiscus and S. montana. The in vitro antimicrobial activity of both EOs was evaluated against L. monocytogenes using the agar diffusion technique, the minimum inhibitory concentrations (MIC) were also determined against the same microorganism using the broth microdilution method. According to the diameters of inhibition, S. montana EO had more antibacterial effects than that from P. lentiscus. MICs showed a range of 0.03 and 0.10% (vol/vol) respectively for S. montana and P. lentiscus. S. montana and P. lentiscus EOs were added respectively in minced beef (twofold MIC values) at 0.06 and 0.20%, experimentally inoculated with L. monocytogenes at a level of 3 × 10⁵ CFU/g and stored at 5 ± 1 °C during one week. S. montana EO was the more effective (P < 0.05) against target bacteria. P. lentiscus EO also demonstrated antibacterial effect against the same bacterium. EO combinations were also investigated in minced beef and P. lentiscus combined with S. montana had synergistic effects. This work shows that the combined EOs might be more effective against L. monocytogenes when applied to minced beef at the ratio of 1/1 to 2/2 according to the MIC values. Sensory evaluation revealed that minced beef treated with EOs was acceptable by panelists at the levels used.