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This article presents quantile autoregressive modeling (QAR), a new tool in relation to structural health monitoring addressing the problems associated with sudden changes in linear stiffness, transitions from linear to non-linear structural states and contiguous non-linear changes of states. Acceleration data is modeled using QAR process which involves fitting autoregressive (AR) coefficients at various pre-selected quantiles. The necessity of such a modeling stems from the inability of traditional AR models to account for non-stationary variance and the presence of non-linearity. Percentage changes in the QAR coefficients at different quantiles is proposed as a conditional indicator to detect changes in state of the structural systems. Numerical simulations on a hysteretic system subjected to El-Centro ground motion and a laboratory-scale experiment on a two-storied shear building model undergoing real time mass-loss demonstrate the robustness of the proposed methodology. [ABSTRACT FROM AUTHOR]

Abstract: Temperature-dependent magnetic properties of a core/shell nanostructure are reported employing magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the sample synthesized by NaBH4 reduction of FeCl3 was done by x-ray diffraction, TEM and Mössbauer spectroscopy and showed a core/shell nanostructure with a core of diameter D≃20nm consisting of α-Fe and amorphous Fe–B alloy and a shell of 7nm thickness made up of principally γ-Fe2O3. Temperature-dependent EMR studies at 9.28GHz show a narrow line with g≃2.01 superimposed on a broad line with g≃2.20. The narrow line assigned to the oxide shell disappears below about 60K, in agreement with a blocking temperature T B≃30K measured in SQUID magnetometry. The EMR parameters of the broad EMR line are similar to those reported for α-Fe nanoparticles imbedded in amorphous SiO2 matrix. The magnitude of the saturation magnetization M S=70emu/g of the nanostructure is smaller than that of bulk α-Fe (M S=220emu/g) and bulk γ-Fe2O3 (M S=88emu/g). Size dependence is used to interpret the absence of exchange-bias in the field-cooled sample of the nanostructure. [Copyright &y& Elsevier]

Abstract: Synthesis and characterization of the structural and magnetic properties of a 2-line (2L) ferrihydrite (FHYD) sample based on the composition Fe:Al:Cu=100:25:5 are reported. Typical of 2L-FHYDs, this sample also yields the two broad lines in X-ray diffraction and triplet in the 1400–1700cm−1 range in IR spectroscopy. However, in transmission electron microscopy, nanoflakes of about 5–20nm size but without any hint of diffraction fringes characteristic of crystalline order were observed. Temperature dependence (2–380K) of the magnetization M vs. applied field H (up to ±65kOe) of this non-crystalline ferrihydrite is used to establish a blocking temperature T B ≃20K, Néel temperature T N ≃365K and a spin-glass ordering of the surface Fe3+ spins at T S ≃6K. These magnitudes of T B and T S are considerably smaller than those of a 5nm undoped 2L crystalline ferrihydrite with T B =70K and T S =30K. The fit of the M vs. H data for several T>T B to a modified Langevin function is shown to collapse onto a universal curve yielding a temperature-independent average magnetic moment μ P =70(5)μ B per nanoflake. Analysis of these parameters obtained from the fits of M vs. H data above T B is used to show that the effective average volume of the nanoflakes is about 1/3 that of spherical 5nm crystalline 2L-FHYD. It is argued that these lower magnitudes of μ P , T B , and T S for the nanoflakes result from their smaller effective volume determined here. [ABSTRACT FROM AUTHOR]

We demonstrate a first simultaneous measurement of both the refractive index and the attenuation coefficient (defined as the sum of the scattering and absorption coefficients) of highly turbid milk and milk-cream mixtures. We achieve this by observing the real-time reflectance profile of a divergent laser beam made incident on the surface of the milk sample. The experiments were carried out on commercial milk samples with fat volume concentrations of 0.5 or less, 1.6, and 3.3%, and on milk-cream mixtures with fat volume concentrations of 10 and 33.3%, without any dilutions of these samples. We find that the reflectance data are well described, for the first time without any empirical fit-parameters, by Fresnel theory that correctly includes the effect of angle-dependent penetration into the turbid medium on the total internally reflected signal. Therefore, our method provides the most accurate determination to date of the refractive index and attenuation coefficient of milk and milk-cream mixtures. Our sensor is compact, portable, and inexpensive. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that one may safely float a composite system of mechanically coupled heavy-duty optics tables with a stability of for several months without requiring the presence of an air compressor in the building. Furthermore, we demonstrate a simple and non-disruptive method to mechanically couple two floating tables such that the two-table system has sufficient stability for most optics experiments, and describe precautions that need to be taken in order to avoid mechanical damage to the tables. We checked the stability of the coupled system by use of a Michelson interferometer that spanned across the two tables. [Copyright &y& Elsevier]