79,091 research outputs found
Giant Microwave Absorption in Metallic Grains: Relaxation Mechanism
We show that the low frequency microwave absorption of an ensemble of small
metallic grains at low temperatures is dominated by a mesoscopic relaxation
mechanism. Giant positive magnetoresistance and very strong temperature
dependence of the microwave conductivity is predicted.Comment: 4 pages, REVTeX3+mutlticol+epsf, one EPS figur
Ultrafast and octave-spanning optical nonlinearities from strongly phase-mismatched cascaded interactions
Cascaded nonlinearities have attracted much interest, but ultrafast
applications have been seriously hampered by the simultaneous requirements of
being near phase-matching and having ultrafast femtosecond response times. Here
we show that in strongly phase-mismatched nonlinear frequency conversion
crystals the pump pulse can experience a large and extremely broadband
self-defocusing cascaded Kerr-like nonlinearity. The large cascaded
nonlinearity is ensured through interaction with the largest quadratic tensor
element in the crystal, and the strong phase-mismatch ensures an ultrafast
nonlinear response with an octave-spanning bandwidth. We verify this
experimentally by showing few-cycle soliton compression with noncritical
cascaded second-harmonic generation: Energetic 47 fs infrared pulses are
compressed in a just 1-mm long bulk lithium niobate crystal to 17 fs (under 4
optical cycles) with 80% efficiency, and upon further propagation an
octave-spanning supercontinuum is observed. Such ultrafast cascading is
expected to occur for a broad range of pump wavelengths spanning the near- and
mid-IR using standard nonlinear crystals.Comment: resubmitted, revised version, accepted for Phys. Rev. Let
Determination of organic acids evolution during apple cider fermentation using an improved HPLC analysis method
An efficient method for analyzing ten organic acids in food, namely citric, pyruvic, malic, lactic, succinic, formic, acetic, adipic, propionic and butyric acids, using HPLC was developed. Boric acid was added into the mobile phase to separate lactic and succinic acids, and a post-column buffer solution [5 mmol/L p-toluensulfonic acid (p-TSA) + 20 mmol/L bis (2-hydroxyethyl) iminotris (hydroxymethyl) methane (bisÂżtris) + 100 Âżmol/L sodium ethylenediaminetetraacetic (EDTA-2Na)] was used to improve the sensitivity of detection. The average spiked recoveries for the ten organic acids ranged from 82.9 to 127.9% with relative standard deviations of 1.44Âż4.71%. The linear ranges of determination were from 15 to 1,000 mg/L with correlation coefficients of 0.9995Âż0.9999. The metabolism of organic acids in cider, and the effect of nutrients including diammonium phosphate (DAP), thiamine, biotin, niacinamide and pantothenic acid on their metabolism, were studied using this method of analysis. We found that before cider brewing, additions of 200 mg/L DAP and 0.3 mg/L thiamine to apple juice concentrate results in a high quality cider
Elastic Wave Scattering and Dynamic Stress Concentrations in Stretching Thick Plates with Two Cutouts by Using the Refined Dynamic Theory
Based on the refined dynamic equation of stretching plates, the elastic tension–compression wave scattering and dynamic stress concentrations in the thick plate with two cutouts are studied. In view of the problem that the shear stress is automatically satisfied under the free boundary condition, the generalized stress of the first-order vanishing moment of shear stress is considered. The numerical results indicate that, as the cutout is thick, the maximum value of the dynamic stress factor obtained using the refined dynamic theory is 19% higher than that from the solution of plane stress problems of elastic dynamics
Numerical study on concrete-filled aluminium circular hollow section columns
A numerical study on concrete-filled aluminium circular hollow section columns is presented. A nonlinear finite element model was developed in this study. The model was verified against test results. The finite element model was used for a parametric study and investigated the diameter-to-thickness ratio of the aluminium hollow sections and the concrete strength. The aluminium tubes of high strength material using the nominal concrete cylinder strengths of 70 and 100 MPa were investigated. The results obtained from the numerical study were compared with the design strengths calculated from the American and Australian/New Zealand specifications for aluminium and concrete structures. Design equations for concrete-filled aluminium circular hollow section columns are proposed. It is shown that the proposed design equations accurately predicted the column strengths.postprin
Web Crippling Behaviour of Cold-formed Duplex Stainless Steel Tubular Sections at Elevated Temperatures
postprin
- …