Interstellar and cometary dust

Aspects of interstellar dust which are known from direct observation will be discussed. Some specific difficulties that various theories have in explaining the observations will be presented. Several theoretical interpretations which have been advanced will be discussed, highlighting first their similarities and then their differences. Also discussed will be the author's ideas about the conditions of interstellar dust throughout its life cycle, from origin to incorporation in pre-cometary ices. Dust is primarily observed by its effects on the spectra of background stars, so observations at optical and ultraviolet (UV) wavelengths are confined to the diffuse interstellar medium (ISM) or to the outer regions of dense clouds. Within this somewhat limited range of environments there are very few lines of sight which show any evidence for icy mantles, but there are major variations in the wavelength dependence of the extinction. In the infrared region of the spectrum, it is possible to observe a few stellar sources deeply embedded within molecular clouds

So you want to run an experiment, now what? Some Simple Rules of Thumb for Optimal Experimental Design

Experimental economics represents a strong growth industry. In the past several decades the method has expanded beyond intellectual curiosity, now meriting consideration alongside the other more traditional empirical approaches used in economics. Accompanying this growth is an influx of new experimenters who are in need of straightforward direction to make their designs more powerful. This study provides several simple rules of thumb that researchers can apply to improve the efficiency of their experimental designs. We buttress these points by including empirical examples from the literature.

The relationship between IR, optical, and UV extinction

An analysis is presented for the variability of absolute IR, optical, and UV extinction, A(sub lambda), derived through the ratio of total-to-selective extinction, R, for 31 lines of sight for which reliable UV extinction parameters were derived. These data sample a wide range of environments and are characterized by 2.5 is less than or equal to R is less than or equal to 6.0. It was found that there is a strong linear dependence between extinction expressed as A(sub lambda)/A(sub V) and 1/R for 1.25 micron is less than or equal to lambda is less than or equal to 0.12 micron. Differences in the general shape of extinction curves are largely due to variations in shape of optical/near-UV extinction corresponding to changes in R, with A(sub lambda)/A(sub V) decreasing for increasing R. From a least-squares fit of the observed R-dependence as a function of wavelength for 0.8/micron is less than or greater than 1/lambda is less than or equal to 8.3/micron, an analytic expression was generated from which IR, optical, and UV extinction curves of the form A(sub lambda)/A(sub V) can be reproduced with reasonable accuracy from a knowledge of R. It was also found that the absolute bump strength normalized to A(sub V) shows a general decrease with increasing R, suggesting that some fraction of bump grains may be selectively incorporated into coagulated grains. Finally, it was found that absolute extinction normalized by suitably chosen color indices results in a minimization of the R-dependence of portions of the UV curve, allowing A(sub lambda) to be estimated for these wavelengths independent of R

Analyse der Störfestigkeit nichtlinearer Schaltungen gegenüber leitungsgebundenen elektromagnetischen Störungen mit multi-input Wiener/Hammerstein-Modellen

In dieser Arbeit wird der Einfluss von leitungsgebundenen Störungen untersucht, welche in einen beliebigen Eingang (Signaleingang, Spannungsversorgung, Masse-Potenzial, etc.) einer Analogschaltung einkoppeln. Die zu untersuchende Schaltung wird dazu durch einen Wiener/Hammerstein-Ansatz als nichtlineares System mit zwei Eingängen modelliert. Mit Hilfe dieses Blockmodells werden analytische Ausdrücke derjenigen Frequenzanteile bestimmt, die durch Intermodulationen zwischen Stör- und Eingangssignal am Ausgang einer Schaltung entstehen.BMBF/03X4604

Masonite International Corporation: Case Study Of A Leveraged Buyout

This case study deals with the leveraged buyout of door manufacturer and merchandiser Masonite International Corporation, at a time of uncertainty, marked by the ever-increasing cost of raw materials, the tightening of monetary policy, and the concerning health of the housing market. It offers the opportunity to discuss leveraged buyouts, to value the company, and to analyze the financing of the transaction

Automated parametrical antenna modelling for ambient assisted living applications

In this paper a parametric modeling technique for a fast polynomial extraction of the physically relevant parameters of inductively coupled RFID/NFC (radio frequency identification/near field communication) antennas is presented. The polynomial model equations are obtained by means of a three-step procedure: first, full Partial Element Equivalent Circuit (PEEC) antenna models are determined by means of a number of parametric simulations within the input parameter range of a certain antenna class. Based on these models, the RLC antenna parameters are extracted in a subsequent model reduction step. Employing these parameters, polynomial equations describing the antenna parameter with respect to (w.r.t.) the overall antenna input parameter range are extracted by means of polynomial interpolation and approximation of the change of the polynomials' coefficients. The described approach is compared to the results of a reference PEEC solver with regard to accuracy and computation effort

Calculating Cross Sections of Composite Interstellar Grains

Interstellar grains may be composite collections of particles of distinct materials, including voids, agglomerated together. We determine the various optical cross sections of such composite grains, given the optical properties of each constituent, using an approximate model of the composite grain. We assume it consists of many concentric spherical layers of the various materials, each with a specified volume fraction. In such a case the usual Mie theory can be generalized and the extinction, scattering, and other cross sections determined exactly. We find that the ordering of the materials in the layering makes some difference to the derived cross sections, but averaging over the various permutations of the order of the materials provides rapid convergence as the number of shells (each of which is filled by all of the materials proportionately to their volume fractions) is increased. Three shells, each with one layer of a particular constituent material, give a very satisfactory estimate of the average cross section produced by larger numbers of shells. We give the formulae for the Rayleigh limit (small size parameter) for multi-layered spheres and use it to propose an ``Effective Medium Theory'' (EMT), in which an average optical constant is taken to represent the ensemble of materials. Multi-layered models are used to compare the accuracies of several EMTs already in the literature.Comment: 29 pages, 6 figures, accepted for publication in the Astrophysical Journal (part 1, scheduled in Vol. 526, #1, Nov. 20

The Warm Ionized Medium in the Milky Way and Other Galaxies

Observations of the "Warm Ionized Medium" (or, equivalently, the "Diffuse Ionized Gas") of the local ISM, the Perseus arm in the Milky Way, and also in several other galaxies show strong [NII]6563 (~H-alpha in some cases) and [SII]6717/[NII]6583 = 0.6 - 0.7 in all locations and objects. Other line ratios (e.g., [O III]5007/H-beta) vary considerably. Simple photoionization models reproduce the observed spectra, providing extra heating beyond that supplied by photoionization is assumed (Reynolds, Haffner, & Tufte 1999). With observed gas-phase abundances (not solar), the line ratios in the local arm at b = 0 deg are fitted with no extra heating and (S/H) = 13 ppm (solar is 20 ppm). Local gas observed at b = -35 deg requires extra heating of about gamma = 0.75, where gamma is the extra heating in units of 10^{-25} erg H^{-1} s^{-1}. In the Perseus arm, there are similar results, with a domposition consistent with the Galactic abundance gradient. The requirements for NGC 891 are similar to the Perseus arm: little or no extra heating at |z| = 1 kpc and gamma 3 at 2 kpc. In NGC 891 there is also an increase of 5007/H-alpha with |z| that can only come about if most of the ionizing radiation is supplied by stars with T~50000 K. Either their radiation must propagate from the plane to high |z| through very little intervening matter, or else the stars are located at high |z|. The total power requirement of the extra heating is <15% of the photoionization power. [O~II]3727/H-beta can serve as a useful diagnostic of extra heating, but [S~III] 9065,9531/H-alpha is not useful in this regard.Comment: 32 pages, including 2 figures. To appear in November 20 Ap

An identification procedure of multi-input Wiener models for the distortion analysis of nonlinear circuits

In this contribution, a system identification procedure of a two-input Wiener model suitable for the analysis of the disturbance behavior of integrated nonlinear circuits is presented. The identified block model is comprised of two linear dynamic and one static nonlinear block, which are determined using an parameterized approach. In order to characterize the linear blocks, an correlation analysis using a white noise input in combination with a model reduction scheme is adopted. After having characterized the linear blocks, from the output spectrum under single tone excitation at each input a linear set of equations will be set up, whose solution gives the coefficients of the nonlinear block. By this data based black box approach, the distortion behavior of a nonlinear circuit under the influence of an interfering signal at an arbitrary input port can be determined. Such an interfering signal can be, for example, an electromagnetic interference signal which conductively couples into the port of consideration