An efficient 1-D periodic boundary integral equation technique to analyze radiation onto straight and meandering microstrip lines

A modeling technique to analyze the radiation onto arbitrary 1-D periodic metallizations residing on a microstrip substrate is presented. In particular, straight and meandering lines are being studied. The method is based on a boundary integral equation, more specifically on a mixed potential integral equation (MPIE), that is solved by means of the method of moments. A plane wave excites the microstrip structure, and according to the Floquet-Bloch theorem, the analysis can be restricted to one single unit cell. Thereto, the MPIE must be constructed using the pertinent 1-D periodic layered medium Green's functions. Here, these Green's functions are obtained in closed form by invoking the perfectly matched layer paradigm. The proposed method is applied to assess the radiation onto 1) a semi-infinite plate, 2) a straight microstrip line, and 3) a serpentine delay line. These three types of examples clearly illustrate and validate the method. Also, its efficiency, compared to a previously developed fast microstrip analysis technique, is demonstrated

Radiative Transfer in a Translucent Cloud Illuminated by an Extended Background Source

We discuss the radiative transfer theory for translucent clouds illuminated by an extended background source. First we derive a rigorous solution based on the assumption that multiple scattering produce an isotropic flux. Then we derive a more manageable analytic approximation showing that it nicely matches the results of the rigorous approach. To validate our model, we compare our predictions with accurate laboratory measurements for various types of well characterized grains, including purely dielectric and strongly absorbing materials representative of astronomical icy and metallic grains, respectively, finding excellent agreement without the need of adding free parameters. We use our model to explore the behavior of an astrophysical cloud illuminated by a diffuse source with dust grains having parameters typical of the classic ISM grains of Draine & Lee (1984) and protoplanetary disks, with an application to the dark silhouette disk 114-426 in Orion Nebula. We find that the scattering term modifies the transmitted radiation, both in terms of intensity (extinction) and shape (reddening) of the spectral distribution. In particular, for small optical thickness our results show that scattering makes reddening almost negligible at visible wavelengths. Once the optical thickness increases enough and the probability of scattering events become close to or larger than 1, reddening becomes present but appreciably modified with respect to the standard expression for line-of-sight absorption. Moreover, variations of the grain refractive index, in particular the amount of absorption, also play an important role changing the shape of the spectral transmission curve, with dielectric grain showing the minimum amount of reddening.Comment: 19 pages, 11 figures, accepted for publication on The Astrophysical Journa

Dust yields in clumpy SN shells: SN 1987A revisited

We present a study of the effects of clumping on the emergent spectral energy distribution (SED) from dusty supernova (SN) shells illuminated by a diffuse radiation source distributed throughout the medium. (...) The fully 3D radiation transport problem is solved using a Monte Carlo code, MOCASSIN, and we present a set of models aimed at investigating the sensitivity of the SEDs to various clumping parameters. We find that, contrary to the predictions of analytical prescriptions, the combination of an optical and IR observational data set is sufficient to constrain dust masses even in the case where optically thick clumps are present. Using both smoothly varying and clumped grain density distributions, we obtain new estimates for the mass of dust condensed by the Type II SN 1987A by fitting the optical and infrared spectrophotometric data of Wooden et al. (1993) at two epochs (day 615 and day 775). (...) From our numerical models we derive dust masses for SN 1987A that are comparable to previous analytic clumped graphite grain mass estimates, and at least two orders of magnitude below the 0.1-0.3 Msol that have been predicted to condense as dust grains in primordial core collapse supernova ejecta. This low condensation efficiency for SN 1987A is in contrast to the case of SN 2003gd, for which a dust condensation efficiency as large as 0.12 has recently been estimated. (Abridged)Comment: accepted for publication in MNRAS. The paper contains 15 figures and 1 tabl

Rotationally Warm Molecular Hydrogen in the Orion Bar

The Orion Bar is one of the nearest and best-studied photodissociation or photon-dominated regions (PDRs). Observations reveal the presence of H2 lines from vibrationally or rotationally excited upper levels that suggest warm gas temperatures (400 to 700 K). However, standard models of PDRs are unable to reproduce such warm rotational temperatures. In this paper we attempt to explain these observations with new comprehensive models which extend from the H+ region through the Bar and include the magnetic field in the equation of state. We adopt the model parameters from our previous paper which successfully reproduced a wide variety of spectral observations across the Bar. In this model the local cosmic-ray density is enhanced above the galactic background, as is the magnetic field, and which increases the cosmic-ray heating elevating the temperature in the molecular region. The pressure is further enhanced above the gas pressure in the H+ region by the momentum transferred from the absorbed starlight. Here we investigate whether the observed H2 lines can be reproduced with standard assumptions concerning the grain photoelectric emission. We also explore the effects due to the inclusion of recently computed H2 + H2, H2 + H and H2 + He collisional rate coefficients.Comment: Accepted for publication in ApJ (34 pages, including 16 figures

Probing microwave fields and enabling in-situ experiments in a transmission electron microscope.

A technique is presented whereby the performance of a microwave device is evaluated by mapping local field distributions using Lorentz transmission electron microscopy (L-TEM). We demonstrate the method by measuring the polarisation state of the electromagnetic fields produced by a microstrip waveguide as a function of its gigahertz operating frequency. The forward and backward propagating electromagnetic fields produced by the waveguide, in a specimen-free experiment, exert Lorentz forces on the propagating electron beam. Importantly, in addition to the mapping of dynamic fields, this novel method allows detection of effects of microwave fields on specimens, such as observing ferromagnetic materials at resonance

The polar clasps of a bank vole PrP(168--176) prion protofibril revisiting

On 2018-01-17 two electron crystallography structures (with PDB entries 6AXZ, 6BTK) on a prion protofibril of bank vole PrP(168-176) (a segment in the PrP $\beta$2-$\alpha$2 loop) were released into the PDB Bank. The paper published by [Nat Struct Mol Biol 25(2):131-134 (2018)] reports some polar clasps for these two crystal structures, and "an intersheet hydrogen bond between Tyr169 and the backbone carbonyl of Asn171 on an opposing strand." - this hydrogen bond is not between the neighbouring Chain B and Chain A directly. In addition, by revisiting the polar clasps, we found another two hydrogen bonds ([email protected]@OE1, [email protected]@N) between the strand A of one sheet and the opposing strand B of the mating sheet. For the neighbouring two single $\beta$-sheets AB, the two new hydrogen bonds are completely different from the experimental one (an intersheet hydrogen bond between Tyr169 and the backbone carbonyl of Asn171 on an opposing strand) in [Nat Struct Mol Biol 25(2):131-134 (2018)]