Explicit formulation for natural frequencies of double-beam system with arbitrary boundary conditions

In this paper, free transverse vibration of two parallel beams connected through Winkler type elastic layer is investigated. Euler-Bernoulli beam hypothesis has been applied and it is assumed that boundary conditions of upper and lower beams are similar while arbitrary without any limitation even for non-ideal boundary conditions. Material properties and cross-section geometry of beams could be different from each other. The motion of the system is described by a homogeneous set of two partial differential equations, which is solved by using the classical Bernoulli-Fourier method. Explicit expressions are derived for the natural frequencies. In order to verify accuracy of results, the problem once again solved using modified Adomian decomposition method. Comparison between results indicates excellent accuracy of proposed formulation for any arbitrary boundary conditions. Derived explicit formulation is simplest method to determine natural frequencies of double-beam systems with high level of accuracy in comparison with other methods in literature.     

QUANTITATIVE SEPARATION AND EVALUATION OF FISCHER-TROPSCH REACTION PRODUCTS HAVING LOW 14C-ISOTOPIC ACTIVITY

ABSTRACT

A method has been developed to effect the separation of Fischer-Tropsch products, predominately hydrocarbons, into, first, alkane and alkene fractions, and, secondly, each of these fractions into their normal and branched components. Conditions for methods using a “dry” silica column for the first separation and molecular sieves for the second separation have identified that permit collection of sufficiently large samples for subsequent separations. The first separation has been effected so the normal to branched chain ratio has not been altered. Liquid chromatographic conditions have been found whereby the n-alkane fraction can then be separated to provide a pure sample of each alkane in the C₈ - C₂₄ carbon number range. The alkane fractions have been collected so that the ¹⁴C activity can be determined for each alkane.     

Intraventricular interferon-alpha stops seizures in Rasmussen's encephalitis: a case report

A 3.5-year-old girl had epilepsia partialis continua of the right side. Clinical and laboratory findings were consistent with Rasmussen's encephalitis. Treatment with high-dose methylprednisolone led to temporary control of seizures, but for 2 years, the seizures remained refractory to phenobarbital, phenytoin, lorazepam, carbamazepine, valproic acid, vigabatrin, gabapentin, and lamotrigine. A 6-week course, and later a 6-month course, of intraventricular interferon-alpha almost totally suppressed the seizures. Although moderately hemiparetic, the child has reasonable neurologic function with mild speech delay. She is receiving her third course of treatment, and seizures remain completely controlled.     

Static stability analysis of agglomerated multi-scale hybrid nanocomposites via a refined theory

Present paper is proposed to capture the influences of carbon nanotubes’ agglomeration on the stability behaviors of multi-scale hybrid nanocomposite beams within the frameworks of refined higher order beam theories for the first time. In this research, a mixture of macroscale and nanoscale fillers will be utilized to be dispersed in an initial matrix to possess a multi-scale hybrid nanocomposite. The equivalent material properties are seemed to be calculated coupling the Eshelby–Mori–Tanaka model with the rule of the mixture to consider the effects of carbon nanotubes inside the probably generated clusters while finding the mechanical properties of such novel hybrid nanocomposites. Furthermore, an energy-based approach is implemented to obtain the governing equations of the problem utilizing a refined higher order beam theorem. Next, the derived equations will be solved in the framework of Galerkin’s well-known analytical method to reach the critical buckling load. It is worth mentioning that influence of various boundary conditions is included, too. Once the validity of presented results is proven, a set of numerical examples are presented to explain how each variant can affect the structure’s stability endurance.

     

A fast modeling of chemical reactions in industrial-scale olefin polymerization fluidized beds using recurrence CFD

We present a novel approach for the fast modeling of exothermic chemical reactions in industrial-scale fluidized bed reactors. It implicates a fast olefin polymerization process, accounting for the catalyst activity, the solubility of the reaction gases in polymer, the particles crystallinity, and the reaction masses and heat transfer. We principally apply the transport-based recurrence computational fluid dynamics (rCFD) model upon the base of a short-term non-reactive simulation performed by a coarse-grained two-fluid model (cgTFM). Following the captured recurrent flows, the methodology propagates rapidly passive scalars far beyond the recorded simulation. The reaction kinetics of production/consumption rates due to polymerization are locally embedded into the individual solid/gas species concentrations. These in turn are considered in transporting the enthalpy and the generated heat by reaction. By doing so, the significant computational effort required to couple the thermodynamic effects of polymerization with the cgTFM (hybrid model), is drastically reduced using rCFD with very reliable agreement.     

Effect of sintering temperature on the microstructures and mechanical properties of sodalite infiltrate all-ceramic material for dental restorations

ABSTRACT

Potassium bromide sodalite (KBr-SOD) zeolite has been developed to enhance the mechanical properties of these restorations using a direct in situ hydrothermal condition followed by the sintering process. The purpose of this study was to determine the effects of sintering temperature on the microstructures and mechanical properties of porous alumina (A) and zirconia-toughened alumina (ZTA) discs infiltrated by KBr-SOD. Hundred and twenty disc-shaped samples were sintered at various temperatures and prepared for biaxial flexural strength and Vickers microhardness tests. The results showed that sintering temperatures from 1100 to 1600°C for both A-SOD and ZTA-SOD samples has resulted in a significant improvement in the density (2.8 and 1.1%, respectively), flexural strength (257 and 254%, respectively), Vickers hardness (109 and 112%, respectively), and Weibull modulus (7.5 and 3%, respectively). The present study concludes that infiltrated SOD material sintered at 1600°C is suitable for the fabrication of all-ceramic dental prostheses with adequate mechanical properties.     

A 0.5 V offset cancelled latch comparator in standard 0.18 μm CMOS process

This paper presents a new 0.5 V high-speed dynamic latch comparator with built-in foreground offset cancellation capability and rail-to-rail input range. Traditional latch comparators lose their speed performance in low voltage condition, especially in sub-1V applications. The proposed latch comparator utilizes a speed-up technique based on a novel boosting method to mitigate the low voltage imperfections on circuit operation. Employing a new offset cancellation technique based on the same boosting capacitors is another key idea. This enhances the accuracy of the ultra low-voltage latch comparators and relaxes the need for preamplifier stage, which is conventionally used in the low offset latch comparator. The performed Monte Carlo simulations over corners in 0.18 μm standard CMOS process show the improvement of input referred offset voltage with a standard deviation of 29.9 mV/299 μV before and after offset cancellation, respectively. The designed comparator dissipates 34 μW power from 0.5 V voltage supply while operating in 200 MHz clock frequency and detects 1 mV input difference.