Fluid Dynamics of Vortex Formation in Tundish Operations: Mathematical Modelling

A mathematical model was developed to study the significance of the fluid dynamics of vortex formation in tundish operations. The aim is to contribute to the fundamental understanding of vortex formation and related phenomena. For this purpose a typical slab tundish was employed; the mathematical model was solved using FLUENT® commercial software capable to simulate highly turbulent flows. The well known k‐? turbulence model was applied to compute this effect in the process. The mathematical simulations confirmed the results from a water analogue model. The vortex formation is directly related to the highly turbulent flows present in the reactor. Great changes in velocity fields during short times and large distances between the upper edge of the dam and the free surface of the bath enhance the formation of vortex flows.     

NUMERICAL SIMULATION OF THE EFFECTS OF BUOYANCY FORCES AND FLOW CONTROL DEVICES ON FLUID FLOW AND HEAT TRANSFER PHENOMENA OF LIQUID STEEL IN A TUNDISH

Fluid flow and heat transfer of liquid steel in a tundish of a continuous slab caster was numerically simulated. The importance of natural flow convection was established through a dimensionless number given by the ratio Gr/Re². Buoyancy forces proved to be as important as inertial ones, especially in the extremes of the tundish far from the entering liquid jet. The usual flow control devices like weirs and dams were not as effective as turbulence inhibitors, a kind of impact pad with lips, interior squared angles, and a square cross section. The simulations indicated that this device helps to decrease fluid turbulence in the zone of the entering liquid jet and has damping effects of step inputs of cold or hot steel, allowing for better control of the casting temperature.     

Experimental and Calculational Studies of the Interactions of BF3 with Fluoroethers

BF₃ was co-condensed with (C₂H₅)₂O, (CF₃CH₂)₂O, and (C₂F₅)₂O in excess argon at 15 K. Infrared spectra of the matrices showed a definite Lewis acid-base interaction between BF₃ and diethyl ether; a weak but definite interaction with bis(2,2,2,-trifluorodiethyl)ether, and no observable interaction with perfluorodiethyl ether. Molecular orbital (MO) calculations complemented the experimental observations by revealing that fluorine atoms on the ethers decreased electron localization about the oxygen atom. Thus, the experimental data and MO calculations indicated a clear trend between strength of interaction with BF₃ and the degree of ether F substitution. The implications of the results for commercial perfluoro ether lubricant/metal oxide surface interactions are discussed.     

Factors controlling flavors binding constants to cyclodextrins and their applications in foods

The binding constants of 14 different flavors (Maltol, Furaneol, Vanillin, Methyl Cinnamate, Cineole, Citral, Menthol, Geraniol, Camphor, Nootkatone, Eugenol, p-vinil Guayacol and Limonene) to cyclodextrins (α-cyclodextrin and β-cyclodextrin) have been determined by an UV–Vis spectrophotometric technique. In all cases the binding constant of flavors to β-cyclodextrin are bigger than the corresponding one to α-cyclodextrin. This fact is due to the different size of cyclodextrin cavity. As well as, a relationship between log P of each flavor and the binding constants was found, proving that the driving force for host–guest complex formation is hydrophobic/hydrophilic interactions.     

A proposal to evaluate the amount of corroded iron converted into adherent rust in steels exposed to corrosion

To calculate the amount of iron corroded from the steels that form part of the adherent rust, α, we propose a procedure that considers mass measurements and the use of spectroscopic techniques to estimate the relative iron phase abundances. We derived an equation to calculate α and evaluate it for carbon steels (CS) and weathering steels (WS) exposed to accelerated outdoor corrosion tests. The values of α are estimated at 0.93 and 0.76 for CS and WS after 2 years of exposure, respectively. The relative iron phase abundances pointed out to a non-protective and active type of rust.     

Performance tradeoffs among low‐complexity detection algorithms for MIMO‐LTE receivers

The upcoming Third‐Generation Partnership Project—Long‐Term Evolution (3GPP‐LTE) cellular standard will employ spatial multiplexing to significantly increase the data rates. Detection of the spatially multiplexed signals is an essential issue in the design of an LTE receiver. In this paper, we evaluate the performance–complexity tradeoffs for a set of low‐complexity multiple input multiple output (MIMO) detection algorithms in a realistic LTE downlink system. Specifically, antenna correlation and channel estimation errors have been considered for a practical MIMO‐LTE receiver. An LTE downlink model has been implemented in order to evaluate three types of detectors: linear, unsorted successive interference cancellation (SIC), and ordered SIC. Our simulation results show that the unsorted SIC detectors present a very poor performance–complexity tradeoff. Besides, linear detectors are shown to be the best candidates as the performance improvement for the ordered SIC detectors is not significant in a realistic scenario. Copyright © 2009 John Wiley & Sons, Ltd.     

Testing and evaluating virus detectors for handheld devices

The widespread use of personal digital assistants and smartphones gives securing these devices a high priority. Yet little attention has been placed on protecting handheld devices against viruses. Currently available antivirus software for handhelds is few in number. At this stage, the opportunity exists for the evaluation and improvement of current solutions. By pinpointing weaknesses in the current antivirus software, improvements can be made to properly protect these devices from a future tidal wave of viruses. This research evaluates four currently available antivirus solutions for handheld devices. A formal model of virus transformation that provides transformation traceability is presented. Two sets of ten tests each were administered; nine tests from each set involved the modification of source code of two known viruses for handheld devices. The testing techniques used are well established in PC testing; thus the focus of this research is solely on handheld devices. Statistical analysis of the test results show high false negative production rates for the antivirus software and an overall false negative production rate of 47.5% with a 95% confidence interval between 36.6% and 58.4%. This high rate shows that current solutions poorly identify modified versions of a virus. The virus is left undetected and capable of spreading, infecting and causing damage.     

Constant holdup times in gas chromatography by programming of column temperature and inlet pressure

The requirements for attaining constant holdup times in capillary gas chromatography (GC), while linearly programming both column temperature and inlet pressure, are illustrated. A scheme, which is based on a series of responses from isothermal and isobaric conditions, is proposed. The responses from two commonly used GC instruments, one with a mass-selective detector operating at near-vacuum pressure and another with a flame-ionization detector at ambient pressure, are analyzed. A significant deviation from Poiseuille flow is noted due to the use of helium as a carrier gas. Nonetheless, the experimental holdup times are approximately constant over a range of temperatures and pressures. Theoretical analysis reveals the spatial and temporal dependence of flow rates inside the column during the programmed runs.     

Approximation to conservative surgery of Leydig cell tumor

OBJECTIVES: To analyze the clinical and histological characteristics of 5 cases of Leydig cell tumor in order to establish the criteria for conservative surgical management. METHODS: Of 31 testicular tumors diagnosed from 1982-1993, 5(16.1%) were Leydig cell tumors. We analyzed patient general characteristics, the prevalent feminizing (60%) and hypogonadal features and the histopathological characteristics that might indicate a non aggressive course of the tumor. RESULTS: No metastasis was observed at 522.9 months mean follow up. Three patients underwent orchidectomy through the inguinal approach; one case had been incidentally discovered after subalbuginea resection due to a disseminated prostatic carcinoma and the fifth patient was treated conservatively by tumorectomy and is tumor-free at more than 120 months follow up. CONCLUSIONS: Parenchyma-sparing surgery may have a place in the treatment of interstitial cell tumor, with evident endocrinological and psychological benefits, especially in the young males that meet the clinical and histological criteria for conservative surgical management.