Physical Modeling of Process Forces in Grinding

This paper deals with material removal mechanisms in grinding by considering single grit-workpiece interactions. Individual investigations were performed both experimentally and using finite element simulations. Firstly, a comparison between the Johnson-Cooke material model and a Crystal Plasticity finite element method was performed with the help of micro-indentation experiments. Here the research question was answered if an anisotropic material model better describe the grinding process and process forces compared to an isotropic material model. Secondly, four discretization approaches were employed: pure Lagrangian (LAG), Arbitrary Lagrange Eulerian (ALE), Particle Finite Element Method (PFEM), and Smooth Particle Hydrodynamics (SPH), to simulate a micro-cutting operation of A2024 T351 aluminium. This study aims to compare the conventional approaches (LAG and ALE) to newer approaches (PFEM and SPH). The orthogonal cutting models were benchmarked against a micro-cutting experiment presented in literature, by comparing the obtained cutting and passive forces. The study was then extended to negative rake angles to study the effect on the discretization approaches for grinding. Thirdly, scratch experiments were investigated for a brittle material sodalime glass and A2024 T351 aluminium. Effects of the linear speed of the device, depth of cut, and conical tool angle were analyzed and tendencies are built. Finally, a realistic simulation of the manufacturing process of a grinding wheel was developed, starting with the raw material, compression, sintering, and dressing until the final grinding surface. As a result of the simulations, virtual grinding wheel topographies can be visualized and analyzed with regard to the output variables from grinding wheels such as bonding strength and static grain count. The individual research studies help in understanding the material removal mechanisms in a single grit scratch process as well as in the understanding of the overall grinding wheel topography. This in turn helps in the developing an overall physical force model for scratching/grinding to predict mechanical output parameters and hence reduce the need for experimentation

Withdrawal of dietary phytoestrogens in adult male rats affects hypothalamic regulation of food intake, induces obesity and alters glucose metabolism

The absence of phytoestrogens in the diet during pregnancy has been reported to result in obesity later in adulthood. We investigated whether phytoestrogen withdrawal in adult life could alter the hypothalamic signals that regulate food intake and affect body weight and glucose homeostasis. Male Wistar rats fed from conception to adulthood with a high phytoestrogen diet were submitted to phytoestrogen withdrawal by feeding a low phytoestrogen diet, or a high phytoestrogen-high fat diet. Withdrawal of dietary phytoestrogens increased body weight, adiposity and energy intake through an orexigenic hypothalamic response characterized by upregulation of AGRP and downregulation of POMC. This was associated with elevated leptin and T4, reduced TSH, testosterone and estradiol, and diminished hypothalamic ERα expression, concomitant with alterations in glucose tolerance. Removing dietary phytoestrogens caused manifestations of obesity and diabetes that were more pronounced than those induced by the high phytoestrogen-high fat diet intake

Miniaturization of aqueous two-phase extraction for biological applications

Aqueous two-phase extraction (ATPE) is a biocompatible liquid-liquid (L-L) separation technique that has been under research for several decades towards the purification of biomolecules, ranging from small metabolites to large animal cells. More recently, with the emergence of rapid-prototyping techniques for fabrication of microfluidic structures with intricate designs, ATPE gained an expanded range of applications utilizing physical phenomena occurring exclusively at the microscale. Studies of ATPSs at nanoliter-scale are further extending the range of applications of these systems by taking advantage of rapid diffusion times, increased degree of control of individual liquid streams and droplets, continuous flow and the integration of multi-dimensional separation modes. Several examples of microfluidic ATPS platforms are described. The partition of molecules between two co-flowing liquid streams confined within a microchannel was successfully demonstrated by the on-line extraction of a fluorescein isothiocyanate (FITC) labeled immunoglobulin G (IgG) from a salt rich flow to a PEG rich flow. IgG diffusion to the PEG-rich phase was complete after 16 cm of channel using flow rates of 1 and 0.2 μL/min for the salt and PEGrich phases respectively. Besides proteins, ATPS have also been used to separate other more complex biomolecules in microfluidics such as virus-like particles. The potential of miniaturization as a high-throughput screening tool has also been explored. The developed setup allowed the screening of a wide range of concentrations inside the microchannel by varying the flow rates of the solutions while using sub-mL volumes for each ATPS-forming system. As a novel demonstration of the integrative potential of ATPE as a microfluidic sample preparation module, a microfluidic device comprising two modules was developed and used to perform a complex matrix clean-up in-line with an immunoassay. References: Silva, D. F., Azevedo, A. M., Fernandes, P., Chu, V. et al., Design of a microfluidic platform for monoclonal antibody extraction using an aqueous two-phase system. J. Chromatogr. A 2012, 1249, 1–7. Jacinto, M. J., Soares, R. R. G., Azevedo, A. M., Chu, V. et al., Optimization and miniaturization of aqueous two phase systems for the purification of recombinant human immunodeficiency virus-like particles from a CHO cell supernatant. Sep. Purif. Technol. 2015, 154, 27–35. Silva, D. F. C., Azevedo, A. M., Fernandes, P., Chu, V. et al., Determination of aqueous two phase system binodal curves using a microfluidic device. J. Chromatogr. A 2014, 1370, 115–120. Soares, R. R., Novo, P., Azevedo, A. M., Fernandes, P. et al., On-chip sample preparation and analyte quantification using a microfluidic aqueous two-phase extraction coupled with an immunoassay. Lab Chip 2014, 14, 4284–429

Determinants of the Presence and Size of Intracranial Aneurysms in the General Population The Rotterdam Study

BACKGROUND AND PURPOSE: The prevalence of unruptured intracranial aneurysms (UIAs) in the adult population is ≈3%. Rupture of an intracranial aneurysm can have devastating consequences, which emphasizes the importance of identification of potentially modifiable determinants for the presence and size of UIAs. Our aim was to study the association of a broad spectrum of potential determinants with the presence and size of UIAs in a general adult population. METHODS: Between 2005 and 2015, 5841 participants from the population-based Rotterdam Study (mean age, 64.4 years, 45.0% male) underwent brain magnetic resonance imaging (1.5T). These scans were evaluated for the presence of incidental UIAs. We determined number and volume of the UIAs. Using logistic and linear regression models, we assessed the association of cardiovascular, lifestyle and emerging inflammatory and hormonal determinants with the presence and volume of UIAs. RESULTS: In 134 (2.3%) participants, ≥1 UIAs were detected (149 UIAs in total), with a median volume of 61.1 mm3 (interquartile range, 33.2–134.0). In multivariable models, female sex (odds ratio, 1.92 [95% CI, 1.33–2.84]), hypertension (odds ratio, 1.73 [95% CI, 1.13–2.68]), and current smoking (odds ratio, 3.75 [95% CI, 2.27–6.33]) were associated with the presence of UIAs. We found no association of alcohol use, physical activity, or diet quality with UIA presence. Finally, we found white blood cell count to relate to larger aneurysm volume (difference in volume of 33.6 mm3 per 109/L increase in white blood cell [95% CI, 3.92–63.5]). CONCLUSIONS: In this population-based study, female sex, hypertension, and smoking, but no other lifestyle determinants, were associated with the presence of UIAs. White blood cell count is associated with size of UIAs. Preventive strategies should focus on treating hypertension and promoting cessation of smoking

Molecular spintronics: Coherent spin transfer in coupled quantum dots

Time-resolved Faraday rotation has recently demonstrated coherent transfer of electron spin between quantum dots coupled by conjugated molecules. Using a transfer Hamiltonian ansatz for the coupled quantum dots, we calculate the Faraday rotation signal as a function of the probe frequency in a pump-probe setup using neutral quantum dots. Additionally, we study the signal of one spin-polarized excess electron in the coupled dots. We show that, in both cases, the Faraday rotation angle is determined by the spin transfer probabilities and the Heisenberg spin exchange energy. By comparison of our results with experimental data, we find that the transfer matrix element for electrons in the conduction band is of order 0.08 eV and the spin transfer probabilities are of order 10%.Comment: 13 pages, 6 figures; minor change

Recent developments in the characterization of superconducting films by microwaves

We describe and analyze selected surface impedance data recently obtained by different groups on cuprate, ruthenate and diboride superconducting films on metallic and dielectric substrates for fundamental studies and microwave applications. The discussion includes a first review of microwave data on MgB2, the weak-link behaviour of RABiTS-type YBa2Cu3O7-d tapes, and the observation of a strong anomalous power-dependence of the microwave losses in MgO at low temperatures. We demonstrate how microwave measurements can be used to investigate electronic, magnetic, and dielectric dissipation and relaxation in the films and substrates. The impact of such studies reaches from the extraction of microscopic information to the engineering of materials and further on to applications in power systems and communication technology.Comment: Invited contribution to EUCAS2001, accepted for publication in Physica C in its present for

Elastic Scattering by Deterministic and Random Fractals: Self-Affinity of the Diffraction Spectrum

The diffraction spectrum of coherent waves scattered from fractal supports is calculated exactly. The fractals considered are of the class generated iteratively by successive dilations and translations, and include generalizations of the Cantor set and Sierpinski carpet as special cases. Also randomized versions of these fractals are treated. The general result is that the diffraction intensities obey a strict recursion relation, and become self-affine in the limit of large iteration number, with a self-affinity exponent related directly to the fractal dimension of the scattering object. Applications include neutron scattering, x-rays, optical diffraction, magnetic resonance imaging, electron diffraction, and He scattering, which all display the same universal scaling.Comment: 20 pages, 11 figures. Phys. Rev. E, in press. More info available at http://www.fh.huji.ac.il/~dani

The staggered domain wall fermion method

A different lattice fermion method is introduced. Staggered domain wall fermions are defined in 2n+1 dimensions and describe 2^n flavors of light lattice fermions with exact U(1) x U(1) chiral symmetry in 2n dimensions. As the size of the extra dimension becomes large, 2^n chiral flavors with the same chiral charge are expected to be localized on each boundary and the full SU(2^n) x SU(2^n) flavor chiral symmetry is expected to be recovered. SDWF give a different perspective into the inherent flavor mixing of lattice fermions and by design present an advantage for numerical simulations of lattice QCD thermodynamics. The chiral and topological index properties of the SDWF Dirac operator are investigated. And, there is a surprise ending...Comment: revtex4, 7 figures, minor revisions, 2 references adde

Cosmic Chronometers: Constraining the Equation of State of Dark Energy. I: H(z) Measurements

We present new determinations of the cosmic expansion history from red-envelope galaxies. We have obtained for this purpose high-quality spectra with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with high-quality, publicly available archival spectra from the SPICES and VVDS surveys. We improve over our previous expansion history measurements in Simon et al. (2005) by providing two new determinations of the expansion history: H(z) = 97 +- 62 km/sec/Mpc at z = 0.5 and H(z) = 90 +- 40 km/sec/Mpc at z = 0.8. We discuss the uncertainty in the expansion history determination that arises from uncertainties in the synthetic stellar-population models. We then use these new measurements in concert with cosmic-microwave-background (CMB) measurements to constrain cosmological parameters, with a special emphasis on dark-energy parameters and constraints to the curvature. In particular, we demonstrate the usefulness of direct H(z) measurements by constraining the dark- energy equation of state parameterized by w0 and wa and allowing for arbitrary curvature. Further, we also constrain, using only CMB and H(z) data, the number of relativistic degrees of freedom to be 4 +- 0.5 and their total mass to be < 0.2 eV, both at 1-sigma.Comment: Submitted to JCA

Phantom Divide Crossing with General Non-minimal Kinetic Coupling

We propose a model of dark energy consists of a single scalar field with a general non-minimal kinetic couplings to itself and to the curvature. We study the cosmological dynamics of the equation of state in this setup. The coupling terms have the form $\xi_{1} R f(\phi)\partial_{\mu}\phi\partial^{\mu}\phi$ and $\xi_{2} R_{\mu\nu}f(\phi)\partial^{\mu}\phi\partial^{\nu}\phi$ where $\xi_{1}$ and $\xi_{2}$ are coupling parameters and their dimensions depend on the type of function $f(\phi)$. We obtain the conditions required for phantom divide crossing and show numerically that a cosmological model with general non-minimal derivative coupling to the scalar and Ricci curvatures can realize such a crossing.Comment: 12 pages, 4 figures. Accepted for publication in Gen. Rel. Grav. arXiv admin note: substantial text overlap with arXiv:1105.4967, arXiv:1201.1627, and with arXiv:astro-ph/0610092 by other author