Numerical study of heat transfer by natural convection and surface thermal radiation in an open cavity receiver

In this work the numerical results of natural convection and surface thermal radiation in an open cavity receiver considering large temperature differences and variable fluid properties are presented. Numerical calculations were conducted for Rayleigh number (Ra) values in the range of 10⁴–10⁶. The temperature difference between the hot wall and the bulk fluid (ΔT) was varied between 100 and 400 K, and was represented as a dimensionless temperature difference (φ) for the purpose of generalization of the trends observed. Noticeable differences are observed between the streamlines and temperature fields obtained for φ = 1.333 (ΔT = 400 K) and φ = 0.333 (ΔT = 100 K). The total average Nusselt number in the cavity increased by 79.8% (Ra = 10⁶) and 88.0% (Ra = 10⁴) as φ was varied from 0.333 to 1.333. Furthermore the results indicate that for large temperature differences (0.667 ? φ ? 1.333) the radiative heat transfer is more important that convective heat transfer.     

Pulsed optically pumped rubidium clock with high frequency-stability performance

In this paper, we present the performance of a vapor-cell rubidium frequency standard working in the pulsed regime, in which the clock signal is represented by a Ramsey pattern observed on an optically detected laser absorption signal. The main experimental results agree with previously reported theoretical predictions. In particular, we measured a relative frequency stability of σy(τ) - 1.6 × 10(-13)τ-1/2 for integration times, τ, up to 200 s, which represents a record in short-term stability for a vapor-cell clock. We also discuss the most important physical phenomena that contribute to this result.     

Equivalent circuit modeling of electrokinetically driven analytical microsystems

Equivalent circuit modeling of microfluidic chips accounts for the transport of fluid and electricity in the entire network of microchannels as a function of the applied pressure and electric potentials. For these calculations, each microchannel is represented by a set of conductance coefficients that relates to driving forces and conjugate flows. Theoretical expressions of the coefficients for rectangular microchannels with arbitrary values of the cross-sectional aspect ratio are derived from the fundamentals of electrokinetic phenomena. Particular emphasis is placed on the analysis of the conditions under which the equivalent circuit model can be accurately employed. Model predictions successfully match data on electrokinetically driven chips for immunoassays reported in the literature. A simulation example is also given to illustrate the capability of the technique for the design and manipulation of analytical microsystems.     

Design space exploration of an open-source, IP-reusable, scalable floating-point engine for embedded applications

This paper describes an open-source and highly scalable floating-point unit (FPU) for embedded systems. Our FPU is fast and efficient, due to the high parallelism of its architecture: the functional units inside the datapath can operate in parallel and independently from each other. A comparison between different versions of the FPU has been made to highlight how performance scales accordingly. Logic synthesis results show that our FPU requires 105 Kgates and runs at 400 MHz on a low-power 90 nm std-cells low-power technology, and requires 20 K Logic Elements running at 67 MHz of an Altera Stratix FPGA. The proposed FPU is supported by a software tool suite which compiles programs written using the C/C++ language. A set of DSP and 3D graphics algorithms have been benchmarked, showing that using our FPU the amount of clock cycles required to perform each algorithm is one order of magnitude smaller than what is required by its corresponding software implementation.     

One-qubit quantum gates associated with topological defects in solids

We show a new proposal for implementing one-qubit quantum gates in a solid associated with the presence of topological defects. We discuss a new way of obtaining quantum holonomies for a spin-half particle, and the implementation of a set of one-qubit quantum gates based on the topological phases provided by the presence of a defect in a crystalline solid.     

Effect of Zeolite Chemical Surface Properties on Catalytic Ozonation of Methylene Blue Contaminated Waters

Heterogeneous catalytic ozonation using natural zeolite has been recently reported. However, there is a lack in the information related to the influence of zeolite active surface sites in this combined system. This work presents experimental results on the effect of zeolite chemical surface properties on catalytic ozonation. Zeolite samples with different chemical surface compositions were prepared from natural zeolite. The effect of pH, and the presence of radical scavengers were assessed at laboratory scale. Results obtained here indicate that hydrous oxide sites present on zeolite surface (S–OH₂ ⁺, S–OH, S–O^?) play a key role on the catalytic ozonation mechanism.     

Effects of pressure toasting on in situ degradability and intestinal protein and protein‐free organic matter digestibility of rapeseed

BACKGROUND: Rapeseed is a protein supplement that contains up to 40% crude protein (CP) on a dry matter (DM) basis, but a large part of its protein can be easily degraded in the rumen. Therefore, before inclusion in ruminant's diet, the extent of its protein degradation in the rumen must be reduced without altering its intestinal digestibility. A study was conducted to investigate the effects of pressure toasting (T, 130 °C) at two residence times (1.5 and 10 min) alone or in combination with soaking in water (ST, 4 h) on ruminal degradability and intestinal digestibility of CP and protein‐free organic matter (PFOM) in whole full‐fat rapeseed. RESULTS: Regardless of the processing time (1.5 or 10 min), T significantly (P < 0.05) increased the fraction of undegraded intake protein (UIP) compared to the untreated rapeseed samples. Soaking prior to further toasting did not improve the rumen degradation characteristics of rapeseed CP. Compared to the untreated rapeseed samples, both T and ST significantly (P < 0.0001) improved the true protein digested in the small intestine (DVE) and degraded protein balance (OEB), effects that were more evident in samples heated for 10 min. Soaking prior to pressure toasting, however, did not further improve the DVE or OEB in the rapeseed samples in comparison with T treatment. CONCLUSIONS: It was concluded that ruminal protein degradability of rapeseed decreased after pressure toasting, without seriously affecting its intestinal digestibility. Copyright © 2008 Society of Chemical Industry     

Modification of model ethylene-butene copolymers using an organic peroxide

Well-characterized linear ethylene-butene-1 copolymers with polydispersities lower than 1.1 were modified using an organic peroxide with the purpose of assessing the relative importance of chain-linking processes. The copolymers used in this work were obtained by hydrogenation of polybutadienes, which were synthesized by anionic polymerization of butadiene. All the copolymers were modified in the molten state using 2,5-dimethyl-2,5 di(terbutyl peroxy)-hexane with concentrations varying on a ample range. The changes in the molecular structure of the polymers due to the chemical attack of the peroxide were evaluated combining selective solvent extraction and GPC-MALLS techniques. As expected, the critical concentration required for the onset of gelation, C_c, decreases with average molecular mass of the original copolymer. When concentrations of peroxide below C_c are employed, the weight-average molecular mass of the modified copolymers augments and the molecular mass distribution gets wider as the concentration of peroxide added to the copolymer increases. Although, the chain-linking reactions govern the modification process, there is a fraction of molecular chains that suffers scission. The measurable fraction of molecules having molecular mass lower than the original quasi-monodisperse copolymers ranges between 15% and 24% of the total mass when the copolymers were modified with concentrations of peroxide below C_c. Beyond the onset of gelation, the gel amount increases continuously with the peroxide concentration added to the copolymers. At a given peroxide concentration, the amount of gel produced for a given polymer is higher the greater is the initial molecular mass of the modified polymer. The limiting amount of gel was between 90% and 98% of the total mass, which was reached using concentrations 20 times larger than the critical one. The efficiency of the peroxide as cross-linking agent seems to be dependent on the concentration of peroxide.     

Numerical Simulation of Model Tests of Pier-Shallow Foundation Systems Subjected to Earthquake Loads Using an Elasto-Uplift-Plastic Macro Element

A dynamic analysis model for the nonlinear behavior of a shallow foundation subjected to seismic loads is developed. A macro-element approach is revised assuming elasto-uplift-plastic behavior, in which uplifting and coupling effects of vertical, horizontal, and moment loads are taken into account. Large-scale shake table experiments of model pier footings are also conducted and simulated using the revised macro-element model. The numerical result reveals that the shape of the hysteresis loops for coupled load-displacement relationships is predicted very well, including the effects of uplift. In addition, the revised model can account for settlement with some inclination that has accumulated during the excitation.