Granular viscosity from plastic yield surfaces: The role of the deformation type in granular flows

Numerical simulations of granular flows with Navier–Stokes type models emerged in the last decade, challenging the well established depth-averaged models. The structure of these equations allows for extension to general rheologies based on complex and realistic constitutive models. Substantial effort has been put into describing the effect of the shear rate, i.e. the magnitude of the velocity gradient, on the shear stress. Here we analyse the effect of the deformation type. We apply the theories of Mohr–Coulomb and Matsuoka–Nakai to calculate the stresses under different deformation types and compare results to the theory of Drucker–Prager, which is formulated independently of the deformation type. This model is particularly relevant because it is the basis for many granular rheologies, such as the –rheology. All models have been implemented into the open-source toolkit OpenFOAM® for a practical application. We found that, within the context of these models, the deformation type has a large influence on the stress. However, for the geometries considered here, these differences are limited to specific zones which have little influence on the landslide kinematics. Finally we are able to give indicators on when the deformation type should be considered in modelling of landslides and when it can be neglected

Ion and aerosol precursor densities in Titan's ionosphere: A multi-instrument case study

The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan-specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion-ion (dusty) plasma below ~1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor ≥2 in the terminator and nightside ionosphere (ne/ni ≤ 0.1). We suggest that ion-ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (ne/ni < 0.5 at 1000 km altitude). The average charge of the dust grains (≥1000 amu) is estimated to be between −2.5 and −1.5 elementary charges, increasing toward lower altitudes

Decay of Nb94 and Nb94m

Gamma rays in Mo94 following the decay of Nb94 have been studied using coincidence and directional correlation measurements. The 700 keV transition was found to be in coincidence with the 873 keV gamma ray. The intensity of the crossover transition of 1573 keV was found to be less than 0.1 % of the 873 keV gamma ray intensity. The directional correlation of the 700 keV - 873 keV cascade was measured and the corrected expansion coefficients were found to be A2 = 0.0965 +/- 0.0076 and A4 = 0.019 +/- 0.011. These data indicate spins of 4 and 2 for the 1573 keV and 873 keV levels, respectively. Gamma rays following the decay of Nb94m were studied with proportional and scintillation counters. The conversion coefficient [alpha]K of the 42 keV gamma ray in the decay of 6.6 min Nb94m was measured to be 1600 +/- 350 and the branching ratio of the transition from Nb94m to the 873 keV level of Mo94 was found to be 0.19 +/- 0.03 %. The intensity ratio of the 600 keV beta ray to the 1.3 MeV beta ray in the decay of Nb94m was determined to be 3.0 +/- 0.6 %. These measurements support a spin and parity of 3- for the isomeric state.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32305/1/0000373.pd

Effects of Saturn's magnetospheric dynamics on Titan's ionosphere

We use the Cassini Radio and Plasma Wave Science/Langmuir probe measurements of the electron density from the first 110 flybys of Titan to study how Saturn´s magnetosphere influences Titan´s ionosphere. The data is first corrected for biased sampling due to varying solar zenith angle and solar energy flux (solar cycle effects). We then present results showing that the electron density in Titan´s ionosphere, in the altitude range 1600-2400 km, is increased by about a factor of 2.5 when Titan is located on the nightside of Saturn (Saturn local time (SLT) 21-03 h) compared to when on the dayside (SLT 09-15 h). For lower altitudes (1100-1600 km) the main dividing factor for the ionospheric density is the ambient magnetospheric conditions. When Titan is located in the magnetospheric current sheet, the electron density in Titan´s ionosphere is about a factor of 1.4 higher compared to when Titan is located in the magnetospheric lobes. The factor of 1.4 increase in between sheet and lobe flybys is interpreted as an effect of increased particle impact ionization from 200 eV sheet electrons. The factor of 2.5 increase in electron density between flybys on Saturn´s nightside and dayside is suggested to be an effect of the pressure balance between thermal plus magnetic pressure in Titan´s ionosphere against the dynamic pressure and energetic particle pressure in Saturn´s magnetosphere.Fil: Edberg, N. J. T.. University of Iowa; Estados Unidos. Swedish Institute of Space Physics; SueciaFil: Andrews, D. J.. Swedish Institute of Space Physics; SueciaFil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Gurnett, D. A.. University of Iowa; Estados UnidosFil: Holmberg, M. K. G.. Swedish Institute of Space Physics; SueciaFil: Jackman, C. M.. University Of Southampton; Reino UnidoFil: Kurth, W. S.. University of Iowa; Estados UnidosFil: Menietti, J. D.. University Of Iowa; Estados UnidosFil: Opgenoorth, H. J.. Swedish Institute of Space Physics; SueciaFil: Shebanits, O.. Swedish Institute of Space Physics; SueciaFil: Vigren, E.. Swedish Institute of Space Physics; SueciaFil: Wahlund, J. E.. Swedish Institute of Space Physics; Sueci

Declaració de Barcelona per l'alliberament de les patents

Declaració institucional elaborada en el context de desconfinament davant l’emergència provocada per la COVID-19.Professionals de l’àmbit científic i sanitari, agències públiques, organitzacions internacionals de la salut global i ONG’s han ratificat el seu suport per l’alliberament temporal de les patents que pesen sobre les vacunes contra la Covid-19 mentre duri l’actual situació d’emergència humanitària.Institutional statement prepared in the context of deconfinement to the emergency caused by COVID-19.Declaración institucional elaborada en el contexto de desconfinamiento ante la emergencia provocada por la COVID-19

Complement system activation contributes to the ependymal damage induced by microbial neuraminidase

Background In the rat brain, a single intracerebroventricular injection of neuraminidase from Clostridium perfringens induces ependymal detachment and death. This injury occurs before the infiltration of inflammatory blood cells; some reports implicate the complement system as a cause of these injuries. Here, we set out to test the role of complement. Methods The assembly of the complement membrane attack complex on the ependymal epithelium of rats injected with neuraminidase was analyzed by immunohistochemistry. Complement activation, triggered by neuraminidase, and the participation of different activation pathways were analyzed by Western blot. In vitro studies used primary cultures of ependymal cells and explants of the septal ventricular wall. In these models, ependymal cells were exposed to neuraminidase in the presence or absence of complement, and their viability was assessed by observing beating of cilia or by trypan blue staining. The role of complement in ependymal damage induced by neuraminidase was analyzed in vivo in two rat models of complement blockade: systemic inhibition of C5 by using a function blocking antibody and testing in C6-deficient rats. Results The complement membrane attack complex immunolocalized on the ependymal surface in rats injected intracerebroventricularly with neuraminidase. C3 activation fragments were found in serum and cerebrospinal fluid of rats treated with neuraminidase, suggesting that neuraminidase itself activates complement. In ventricular wall explants and isolated ependymal cells, treatment with neuraminidase alone induced ependymal cell death; however, the addition of complement caused increased cell death and disorganization of the ependymal epithelium. In rats treated with anti-C5 and in C6-deficient rats, intracerebroventricular injection of neuraminidase provoked reduced ependymal alterations compared to non-treated or control rats. Immunohistochemistry confirmed the absence of membrane attack complex on the ependymal surfaces of neuraminidase-exposed rats treated with anti-C5 or deficient in C6. Conclusions These results demonstrate that the complement system contributes to ependymal damage and death caused by neuraminidase. However, neuraminidase alone can induce moderate ependymal damage without the aid of complement

Police Chemistry

Johann von Justi, the foremost literary cameralist of his generation, served as chief police commissioner in Göttingen between 1755 and 1757. While in Göttingen, Justi offered lectures at the university on the “economic, police and cameral sciences.” He also arrested vagrants, wrote on chemistry, disciplined unruly students, conducted chemical experiments, supervised the pricing of Göttingen\u27s staple goods, engaged in a public controversy with a prominent Berlin chemist, edited and published a bi-weekly periodical (Göttingische Policey-Amts Nachrichien), and worked with the university\u27s curator to refashion the academic structure of the sciences. Taken together, these various activities reflected his broad vision for social and academic change, a vision with important implications for the form and content of the sciences. Drawing on archival material in Göttingen, on articles from the Policey-Amts Nachrichten, and on Justi\u27s other cameralist and chemical writings, I use his everyday experiences as a local police official to explore the meaning of his chemical work. I argue that Justi\u27s chemistry was suffused with the cameralist dreams and ambitions of a small-town police commissioner. It is what I call police chemistry