Insights into intermetallic phases on pulse welded dissimilar metal joints

The Magnetic Pulse Welding (MPW) process has been developed to an industrially used joining method which is considered to be a fast, noncontact, clean and "cold" solid state welding process. Unlike fusion welding, the absence of direct heat during the welding cycle makes it possible to join dissimilar metals, for instance aluminium to copper or copper to steel, without noticeable detrimental metallurgical defects. This is very desirable, as today s industry lacks technologies to join often not fusion-weldable dissimilar materials effectively. However, current metallographic studies show that for many material combinations the formation of intermetallic seams in the joint region of magnetic pulse welds can not be completely avoided. Modern technical equipment for MPW is used to join aluminium with copper in order to study the microstructure and the intermetallic phases formed in the weld region in dependence of the processing parameters. The welds are analysed by means of metallographic and electron microscopic (SEM) methods. Relations between the parameters and the microstructures formed within the weld joints are shown. Based on the obtained results conclusions will be drawn with respect to the intermetallic phase formation process and the optimization of the weld microstructure and properties

Photometry Results for the Globular Clusters M10 and M12: Extinction Maps, Color-Magnitude Diagrams, and Variable Star Candidates

We report on photometry results of the equatorial globular clusters (GCs) M10 and M12. These two clusters are part of our sample of GCs which we are probing for the existence of photometrically varying eclipsing binary stars. During the search for binaries in M10 and M12, we discovered the signature of differential reddening across the fields of the clusters. The effect is stronger for M10 than for M12. Using our previously described dereddening technique, we create differential extinction maps for the clusters which dramatically improve the appearance of the color-magnitude diagrams (CMDs). Comparison of our maps with the dust emissivity maps of Schlegel, Finkbeiner, & Davis (SFD) shows good agreement in terms of spatial extinction features. Several methods of adding an E_{V-I} zero point to our differential maps are presented of which isochrone fitting proved to be the most successful. Our E_{V-I} values fall within the range of widely varying literature values. More specifically, our reddening zero point estimate for M12 agrees well with the SFD estimate, whereas the one for M10 falls below the SFD value. Our search for variable stars in the clusters produced a total of five variables: three in M10 and two in M12. The M10 variables include a binary system of the W Ursa Majoris (W UMa) type, a background RR Lyrae star, and an SX Phoenicis pulsator, none of which is physically associated with M10. M12's variables are two W UMa binaries, one of which is most likely a member of the cluster. We present the phased photometry lightcurves for the variable stars, estimate their distances, and show their locations in the fields and the CMDs of the GCs.Comment: 22 pages, 21 figures, to be published in AJ October 2002. For a higher-resolution version of this paper, please visit http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.ps.gz (gzipped postscript) or http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.pdf (pdf file

Sound absorption performance of sustainable foam materials: Application of analytical and numerical tools for the optimization of forecasting models

Traditional models used to predict acoustic properties of poroelastic materials are usually applied to fibrous layers or polyurethane foams. However, for new materials like complex cellular foams these procedures may not be applied due to the different cell microstructure. To this aim, the sound absorbing properties of novel sustainable foam materials are investigated as a function of the nature and loading of waste powders and their effects on the microstructure and the acoustic properties. The foams are prepared from naturally occurring alginates that are in situ polymerized. The morphology and the acoustic properties of the foam-cells appear linked to the particle size distribution of the starting powder. Determination of the parameters of Johnson\u2013Champoux\u2013Allard acoustic model (tortuosity, viscous characteristic length, thermal characteristic length, porosity and flow resistivity) was performed using five different forecasting methods, including traditional analytical model for fibrous materials as well as inverse procedure. A new procedure for tortuosity computation of foam is proposed and validated. Transfer Matrix Method calculation of the absorption coefficient was performed and compared with the experimental data, in order to assess the validity of the model. Indirect method technique is demonstrated to be dependent on experimental measurement of thermal characteristic length

Are Coronae of Magnetically Active Stars Heated by Flares? III. Analytical Distribution of Superimposed Flares

(abridged) We study the hypothesis that observed X-ray/extreme ultraviolet emission from coronae of magnetically active stars is entirely (or to a large part) due to the superposition of flares, using an analytic approach to determine the amplitude distribution of flares in light curves. The flare-heating hypothesis is motivated by time series that show continuous variability suggesting the presence of a large number of superimposed flares with similar rise and decay time scales. We rigorously relate the amplitude distribution of stellar flares to the observed histograms of binned counts and photon waiting times, under the assumption that the flares occur at random and have similar shapes. Applying these results to EUVE/DS observations of the flaring star AD Leo, we find that the flare amplitude distribution can be represented by a truncated power law with a power law index of 2.3 +/- 0.1. Our analytical results agree with existing Monte Carlo results of Kashyap et al. (2002) and Guedel et al. (2003). The method is applicable to a wide range of further stochastically bursting astrophysical sources such as cataclysmic variables, Gamma Ray Burst substructures, X-ray binaries, and spatially resolved observations of solar flares.Comment: accepted for publication in Ap

Variable Stars in the Field of the Globular Cluster NGC 3201

We report on the discovery and analysis of 14 short-period variable stars in the field of the southern globular cluster NGC 3201, located within roughly two magnitudes on either side of the main-sequence turnoff. 11 of these variable stars are eclipsing binaries, one is an RR Lyrae, and two are thus far unclassified systems. Among the eclipsing binary stars, nine are of the W Ursa Majoris (W UMa) type, one an Algol (EA) system, and one a detached system. Using spectroscopic follow-up observations as well as analysis of the variables' locations in the color-magnitude diagram of the cluster, we find that only one variable star (a W UMa type blue straggler) is actually a member of NGC 3201. We present the phased photometry lightcurves for all the variable star systems as well as their locations in the field-of-view and in the color-magnitude diagram.Comment: 18 pages, 8 figures, 3 tables; accepted for the January 2002 issue of AJ. For full resolution versions of this paper, go to: http://www.astro.lsa.umich.edu/users/kaspar/html/vars3201.ps.gz or http://www.astro.lsa.umich.edu/users/kaspar/html/vars3201.pd

Test of candidate light distributors for the muon (g−-2) laser calibration system

The new muon (g-2) experiment E989 at Fermilab will be equipped with a laser calibration system for all the 1296 channels of the calorimeters. An integrating sphere and an alternative system based on an engineered diffuser have been considered as possible light distributors for the experiment. We present here a detailed comparison of the two based on temporal response, spatial uniformity, transmittance and time stability.Comment: accepted to Nucl.Instrum.Meth.

Developmental and Radiobiologic Characteristics of Canine Multinucleated, Osteoclast-Like Cells Generated in Vitro from Canine Bone Marrow

We report here our initial observations on the growth and morphology, and developmental radiosensitivity of giant, multinucleated, osteoclast-like cells (MN-OS} generated through in vitro cultivation of hematopoietic progenitor-enriched canine bone marrow samples. Maximum cell densities of 5.5 x 103 to 6.5 x 103 MN-OS per cm2 of growth area were achieved following 10 to 14 days of culture at 37°C. Acute gamma irradiation of the initial marrow inocula resulted in significant, dose-dependent perturbations of MN-OS formation, growth, and development. Attempts to estimate radiosensitivity of MN-OS progenitors from canine marrow yielded a range of DO values from a low of 212 cGy measured at six days of culture to higher values of 405 to 542 cGy following 10 to 22 days of culture. At the intermediate times of culture (10 to 14 days}, the radiation-induced responses were clearly biphasic, reflecting either (a) the presence of multiple subpopulations of MN-OS progenitors with varying degrees of radiosensitivity or (b) the inherent biphasic nature of MN-OS development involving early progenitor cell proliferation followed by maturation and subsequent fusion. Morphologically, MN-OS generated from irradiated marrow inocula appeared only marginally altered, with alterations expressed largely in a biphasic, dose-dependent fashion in terms of smaller cell size, reduced number of nuclei, increased expression of both surface microprojections, and a unique set of crystalloid cytoplasmic inclusions. Functionally, MN-OS appeared to be impaired by irradiation of marrow progenitors, as evidenced by failure to initiate resorptive attachments to devitalized bone spicules in vitro

The Effect of Coherent Structures on Stochastic Acceleration in MHD Turbulence

We investigate the influence of coherent structures on particle acceleration in the strongly turbulent solar corona. By randomizing the Fourier phases of a pseudo-spectral simulation of isotropic MHD turbulence (Re $\sim 300$), and tracing collisionless test protons in both the exact-MHD and phase-randomized fields, it is found that the phase correlations enhance the acceleration efficiency during the first adiabatic stage of the acceleration process. The underlying physical mechanism is identified as the dynamical MHD alignment of the magnetic field with the electric current, which favours parallel (resistive) electric fields responsible for initial injection. Conversely, the alignment of the magnetic field with the bulk velocity weakens the acceleration by convective electric fields - \bfu \times \bfb at a non-adiabatic stage of the acceleration process. We point out that non-physical parallel electric fields in random-phase turbulence proxies lead to artificial acceleration, and that the dynamical MHD alignment can be taken into account on the level of the joint two-point function of the magnetic and electric fields, and is therefore amenable to Fokker-Planck descriptions of stochastic acceleration.Comment: accepted for publication in Ap

Time Interval Between Cover Crop Termination and Planting Influences Corn Seedling Disease, Plant Growth, and Yield

Experiments were established in a controlled-growth chamber and in the field to evaluate the effect of the length of time intervals between winter rye cover crop termination and corn planting on corn seedling disease, corn growth, and grain yield in 2014 and 2015. Rye termination dates ranged from 25 days before planting (DBP) to 2 days after planting (DAP) corn in the field and from 21 DBP to 1 DAP in controlled studies. Results were similar in both environments. In general, shorter intervals increased seedling disease and reduced corn emergence, shoot growth, and grain yield of corn following winter rye compared with corn planted 10 or more days after rye termination or without rye. Incidence of Pythium spp. increased with shorter intervals (less than 8 DBP); incidence of Fusarium spp. was not consistent between runs and experiments. In 2014, in the 1-DAP treatment, number of ears and grain yield were reduced (P = 0.05 and 0.02, respectively). In 2015, all termination intervals reduced plant population, number of ears, and yield (P = 0.01), with the 2-DBP treatment causing the biggest decrease. A 10- to 14-day interval between rye termination and corn planting should be followed to improve corn yield following a rye cover crop

Particle Acceleration in Multiple Dissipation Regions

The sharp magnetic discontinuities which naturally appear in solar magnetic flux tubes driven by turbulent photospheric motions are associated with intense currents. \citet{Par83} proposed that these currents can become unstable to a variety of microscopic processes, with the net result of dramatically enhanced resistivity and heating (nanoflares). The electric fields associated with such ``hot spots'' are also expected to enhance particle acceleration. We test this hypothesis by exact relativistic orbit simulations in strong random phase magnetohydrodynamic (MHD) turbulence which is forming localized super-Dreicer Ohm electric fields ($E_\Omega/E_D$ = $10^2 ... 10^5$) occurring in 2..15 % of the volume. It is found that these fields indeed yield a large amplification of acceleration of electrons and ions, and can effectively overcome the injection problem. We suggest in this article that nanoflare heating will be associated with sporadic particle acceleration.Comment: 12 pages, 5 figures, to appear in ApJ