Sound propagation in isotropically and uni-axially compressed cohesive, frictional granular solids

Using an advanced contact model in DEM simulations, involving elasto-plasticity, adhesion, and friction, pressure-sintered tablets are formed from primary particles and prepared for unconfined tests. Sound propagation in such packings is studied under various friction and adhesion conditions. Small differences can be explained by differences in the structure that are due to the sensitivity of the packing on the contact properties during preparation history. In some cases the signals show unexpected propagation behaviour, but the power-spectra are similar for all values of adhesion and friction tested. Furthermore, one of these tablets is compressed uni-axially and under unconfined conditions and the sound propagation characteristics are examined at different strains: (i) in the elastic regime, (ii) during failure, and (iii) during critical flow: the results vary astonishingly little for packings at different externally applied strains

The wild boar Sus scrofa L. as neighbor in an agricultural landscape – a new project

Herbst, C., Keuling, O

The spectral type of CHS7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster

We present the spectroscopic characterization of the unusual high-amplitude very low mass pre-main-sequence periodic variable CHS7797. This study is based on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range, carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been carried out at two distinct phases of the 17.8d period, namely at maximum and four days before maximum. Four different spectral indices were used for the spectral classification at these two phases, all of them well-suited for spectral classification of young and obscured late M dwarfs. In addition, the gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were used to confirm the young age of CHS7797. From the spectrum obtained at maximum light we derived a spectral type (SpT) of M6.05, while for the spectrum taken four days before maximum the derived SpT is M5.75. The derived SpTs confirm that CHS7797 has a mass in the stellar-substellar boundary mass range. In addition, the small differences in the derived SpTs at the two observed phases may provide indirect hints that CHS7797 is a binary system of similar mass components surrounded by a tilted circumbinary disk, a system similar to KH15D.Comment: 6 pages, accepted for publication A&

Monte Carlo simulations of H2 formation on stochastically heated grains

Continuous-time, random-walk Monte Carlo simulations of H2 formation on grains have been performed for surfaces that are stochastically heated by photons. We have assumed diffuse cloud conditions and used a variety of grains of varying roughness and size based on olivine. The simulations were performed at different optical depths. We confirmed that small grains (r <= 0.02 micron) have low modal temperatures with strong fluctuations, which have a large effect on the efficiency of the formation of molecular hydrogen. The grain size distribution highly favours small grains and therefore H2 formation on these particles makes a large contribution to the overall formation rate for all but the roughest surfaces. We find that at A_V=0 only the roughest surfaces can produce the required amount of molecular hydrogen, but by A_V=1, smoother surfaces are possible alternatives. Use of a larger value for the evaporation energy of atomic hydrogen, but one still consistent with experiment, allows smoother surfaces to produce more H2.Comment: MNRAS LaTeX, 10 pages, 11 eps-figures to be published in MNRA

Kitchen-Sink Enlightenment: A Review of “Grace for Amateurs”

Excerpt: Here’s an honest admission: Several times while reading Lily Burana’s new book Grace for Amateurs: Field Notes on a Journey Back to Faith, I consulted the copyright page, confirming again that Grace for Amateurs was really published by Thomas Nelson, the notoriously evangelical (and, in my mind, notoriously traditional) press. After all, it wasn’t that long ago that Thomas Nelson asked another writer to remove the word “vagina” from her book, well aware that Christian readers would balk at language so closely associated with women and S-E-X. Would this same publisher be willing to support a memoir as edgy and progressive as Burana’s

Comparative analysis of model behaviour for flood prediction purposes using Self-Organizing Maps

Distributed watershed models constitute a key component in flood forecasting systems. It is widely recognized that models because of their structural differences have varying capabilities of capturing different aspects of the system behaviour equally well. Of course, this also applies to the reproduction of peak discharges by a simulation model which is of particular interest regarding the flood forecasting problem. &lt;br&gt;&lt;br&gt; In our study we use a Self-Organizing Map (SOM) in combination with index measures which are derived from the flow duration curve in order to examine the conditions under which three different distributed watershed models are capable of reproducing flood events present in the calibration data. These indices are specifically conceptualized to extract data on the peak discharge characteristics of model output time series which are obtained from Monte-Carlo simulations with the distributed watershed models NASIM, LARSIM and WaSIM-ETH. The SOM helps to analyze this data by producing a discretized mapping of their distribution in the index space onto a two dimensional plane such that their pattern and consequently the patterns of model behaviour can be conveyed in a comprehensive manner. It is demonstrated how the SOM provides useful information about details of model behaviour and also helps identifying the model parameters that are relevant for the reproduction of peak discharges and thus for flood prediction problems. It is further shown how the SOM can be used to identify those parameter sets from among the Monte-Carlo data that most closely approximate the peak discharges of a measured time series. The results represent the characteristics of the observed time series with partially superior accuracy than the reference simulation obtained by implementing a simple calibration strategy using the global optimization algorithm SCE-UA. The most prominent advantage of using SOM in the context of model analysis is that it allows to comparatively evaluating the data from two or more models. Our results highlight the individuality of the model realizations in terms of the index measures and shed a critical light on the use and implementation of simple and yet too rigorous calibration strategies

D-brane Categories for Orientifolds -- The Landau-Ginzburg Case

We construct and classify categories of D-branes in orientifolds based on Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet parity action on the matrix factorizations plays the key role. This provides all the requisite data for an orientifold construction after embedding in string theory. One of our main results is a computation of topological field theory correlators on unoriented worldsheets, generalizing the formulas of Vafa and Kapustin-Li for oriented worldsheets, as well as the extension of these results to orbifolds. We also find a doubling of Knoerrer periodicity in the orientifold context.Comment: 45 pages, 6 figure

Equivalences between GIT quotients of Landau-Ginzburg B-models

We define the category of B-branes in a (not necessarily affine) Landau-Ginzburg B-model, incorporating the notion of R-charge. Our definition is a direct generalization of the category of perfect complexes. We then consider pairs of Landau-Ginzburg B-models that arise as different GIT quotients of a vector space by a one-dimensional torus, and show that for each such pair the two categories of B-branes are quasi-equivalent. In fact we produce a whole set of quasi-equivalences indexed by the integers, and show that the resulting auto-equivalences are all spherical twists.Comment: v3: Added two references. Final version, to appear in Comm. Math. Phy