Search results for "7a"
showing 10 items of 161 documents
Use of HFC fluids as suitable replacements in low-temperature refrigeration plants
2014
An experimental investigation of the performance of a low-temperature refrigerating unit working with R22 and a comparison of its performance when operating with replacement HFC fluids in accordance with the European Regulation CE-1005/2009 are presented in this paper. Plant working efficiency was tested with R22, as baseline, and then compared with four different HFC fluids: R413A, R417A, R422A and R422D. The refrigerating unit was a vapour-compression plant equipped with a reciprocating double-cylinder compressor able to keep the cold room at -20ºC. Lower values of the temperature at the end of compression and polytrophic exponent can be achieved with the HFC tested. Substituting the R22 …
Lattice operations on Rickart *-rings
2014
Various authors have investigated properties of the star order (introduced by M.P. Drazin in 1978) on algebras of matrices and of bounded linear operators on a Hilbert space. Rickart involution rings (*-rings) are a certain algebraic analogue of von Neumann algebras, which cover these particular algebras. In 1983, M.F. Janowitz proved, in particular, that, in a star-ordered Rickart *-ring, every pair of elements bounded from above has a meet and also a join. However, the latter conclusion seems to be based on some wrong assumption. We show that the conclusion is nevertheless correct, and provide equational descriptions of joins and meets for this case. We also present various general proper…
Sesquilinear forms associated to sequences on Hilbert spaces
2019
The possibility of defining sesquilinear forms starting from one or two sequences of elements of a Hilbert space is investigated. One can associate operators to these forms and in particular look for conditions to apply representation theorems of sesquilinear forms, such as Kato's theorems. The associated operators correspond to classical frame operators or weakly-defined multipliers in the bounded context. In general some properties of them, such as the invertibility and the resolvent set, are related to properties of the sesquilinear forms. As an upshot of this approach new features of sequences (or pairs of sequences) which are semi-frames (or reproducing pairs) are obtained.
Collisionless shock heating of heavy ions in SN 1987A
2019
Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock waves, are typically "collisionless", because the thickness of their jump region is much shorter than the collisional mean free path. Across these jumps, electrons, protons, and ions are expected to be heated at different temperatures. Supernova remnants (SNRs) are ideal targets to study collisionless processes because of their bright post-shock emission and fast shocks. Although optical observations of Balmer-dominated shocks in young SNRs showed that the post-shock proton temperature is higher than the electron temperature, the actual dependence of the post-shock temperature on the particle mass…
3D MHD modeling of the expanding remnant of SN 1987A : role of magnetic field and non-thermal radio emission
2018
Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field on the dynamics of the expanding remnant of SN 1987A and the origin and evolution of the radio emission from the remnant, in particular, during the interaction of the blast wave with the nebula surrounding the SN. Methods. We model the evolution of SN 1987A from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula by 3D MHD simulations. The model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-SN ambie…
Supernova 1987A: a Template to Link Supernovae to their Remnants
2015
The emission of supernova remnants reflects the properties of both the progenitor supernovae and the surrounding environment. The complex morphology of the remnants, however, hampers the disentanglement of the two contributions. Here we aim at identifying the imprint of SN 1987A on the X-ray emission of its remnant and at constraining the structure of the environment surrounding the supernova. We performed high-resolution hydrodynamic simulations describing SN 1987A soon after the core-collapse and the following three-dimensional expansion of its remnant between days 1 and 15000 after the supernova. We demonstrated that the physical model reproducing the main observables of SN 1987A during …
CCDC 1831369: Experimental Crystal Structure Determination
2018
Related Article: Katja Kärki, Juha H. Siitonen, Mona Cederström, Sami Kortet, Petri M. Pihko|2018|Synlett|29|1723|doi:10.1055/s-0037-1610109
CCDC 639296: Experimental Crystal Structure Determination
2007
Related Article: J.Becker, R.Frohlich, K.Salorinne, D.Hoppe|2007|Eur.J.Org.Chem.|2007|3337|doi:10.1002/ejoc.200700219
CCDC 1017369: Experimental Crystal Structure Determination
2014
Related Article: K. Chandralekha, D. Gavaskar, A.R. Sureshbabu, S. Lakshmi|2014|Acta Crystallogr.,Sect.E:Struct.Rep.Online|70|124|doi:10.1107/S1600536814017644
CCDC 795371: Experimental Crystal Structure Determination
2011
Related Article: J.Barjau, G.Schnakenburg, S.R.Waldvogel|2011|Angew.Chem.,Int.Ed.|50|1415|doi:10.1002/anie.201006637