2,598 research outputs found
Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets
We investigate the effect of magnetic fields on the propagation dynamics and
morphology of overdense, radiatively cooling, supermagnetosonic jets, with the
help of fully three-dimensional SPMHD simulations. Evaluated for a set of
parameters which are mainly suitable for protostellar jets (with density ratios
between the jet and the ambient medium 3-10, and ambient Mach number ~ 24),
these simulations are also compared with baseline non-magnetic and adiabatic
calculations. We find that, after amplification by compression and
re-orientation in nonparallel shocks at the working surface, the magnetic field
that is carried backward with the shocked gas into the cocoon improves the jet
collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude,
approximately equally spaced internal shocks (which are absent in the HD
systems) are produced by MHD K-H reflection pinch modes. The longitudinal field
geometry also excites non-axisymmetric helical modes which cause some beam
wiggling. The strength and amount of these modes are, however, reduced (by ~
twice) in the presence of radiative cooling relative to the adiabatic cases.
Besides, a large density ratio between the jet and the ambient medium also
reduces, in general, the number of the internal shocks. As a consequence, the
weakness of the induced internal shocks makes it doubtful that the magnetic
pinches could produce by themselves the bright knots observed in the overdense,
radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of
figures are available at http://www.iagusp.usp.br/preprints/preprint.htm
Limitations of model fitting methods for lensing shear estimation
Gravitational lensing shear has the potential to be the most powerful tool
for constraining the nature of dark energy. However, accurate measurement of
galaxy shear is crucial and has been shown to be non-trivial by the Shear
TEsting Programme. Here we demonstrate a fundamental limit to the accuracy
achievable by model-fitting techniques, if oversimplistic models are used. We
show that even if galaxies have elliptical isophotes, model-fitting methods
which assume elliptical isophotes can have significant biases if they use the
wrong profile. We use noise-free simulations to show that on allowing
sufficient flexibility in the profile the biases can be made negligible. This
is no longer the case if elliptical isophote models are used to fit galaxies
made up of a bulge plus a disk, if these two components have different
ellipticities. The limiting accuracy is dependent on the galaxy shape but we
find the most significant biases for simple spiral-like galaxies. The
implications for a given cosmic shear survey will depend on the actual
distribution of galaxy morphologies in the universe, taking into account the
survey selection function and the point spread function. However our results
suggest that the impact on cosmic shear results from current and near future
surveys may be negligible. Meanwhile, these results should encourage the
development of existing approaches which are less sensitive to morphology, as
well as methods which use priors on galaxy shapes learnt from deep surveys.Comment: 10 pages, 8 figure
Yang-Lee zeros for a nonequilibrium phase transition
Equilibrium systems which exhibit a phase transition can be studied by
investigating the complex zeros of the partition function. This method,
pioneered by Yang and Lee, has been widely used in equilibrium statistical
physics. We show that an analogous treatment is possible for a nonequilibrium
phase transition into an absorbing state. By investigating the complex zeros of
the survival probability of directed percolation processes we demonstrate that
the zeros provide information about universal properties. Moreover we identify
certain non-trivial points where the survival probability for bond percolation
can be computed exactly.Comment: LaTeX, IOP-style, 13 pages, 10 eps figure
Optical echo in photonic crystals
The dynamics of photonic wavepacket in the effective oscillator potential is
studied. The oscillator potential is constructed on a base of one dimensional
photonic crystal with a period of unit cell adiabatically varied in space. The
structure has a locally equidistant discrete spectrum. This leads to an echo
effect, i.e. the periodical reconstruction of the packet shape. The effect can
be observed in a nonlinear response of the system. Numerical estimations for
porous-silicon based structures are presented for femtosecond Ti:Sapphire laser
pump.Comment: 4 page
Discovery of Novel Backusella (Backusellaceae, Mucorales) Isolated from Invertebrates and Toads in Cheongyang, Korea
Three novel fungal species, Backusella chlamydospora sp. nov., B. koreana sp. nov., and B. thermophila sp. nov., as well as two new records, B. oblongielliptica and B. oblongispora, were found in Cheongyang, Korea, during an investigation of fungal species from invertebrates and toads. All species are described here using morphological characters and sequence data from internal transcribed spacer sequences of ribosomal DNA and large subunit of the ribosomal DNA. Backusella chlamydospora is different from other Backusella species by producing chlamydospores. Backusella koreana can be distinguished from other Backusella species by producing abundant yeast-like cells. Backusella thermophila is characterized by a variable (subglobose to oblong, applanate to oval, conical and ellipsoidal to pyriform) columellae and grows well at 37 ◦C. Multigene phylogenetic analyses of the combined ITS and LSU rDNA sequences data generated from maximum likelihood and MrBayes analyses indicate that B. chlamydospora, B. koreana, and B. thermophila form distinct lineages in the family Backusellaceae. Detailed descriptions, illustrations, phylogenetic tree, and taxonomic key to the Backusella species present in Korea are provided
H3K36 methylation and DNA-binding both promote Ioc4 recruitment and Isw1b remodeler function
The Isw1b chromatin-remodeling complex is specifically recruited to gene bodies to help retain pre-existing histones during transcription by RNA polymerase II. Recruitment is dependent on H3K36 methylation and the Isw1b subunit Ioc4, which contains an N-terminal PWWP domain. Here, we present the crystal structure of the Ioc4-PWWP domain, including a detailed functional characterization of the domain on its own as well as in the context of full-length Ioc4 and the Isw1b remodeler. The Ioc4-PWWP domain preferentially binds H3K36me3-containing nucleosomes. Its ability to bind DNA is required for nucleosome binding. It is also furthered by the unique insertion motif present in Ioc4-PWWP. The ability to bind H3K36me3 and DNA promotes the interaction of full-length Ioc4 with nucleosomes in vitro and they are necessary for its recruitment to gene bodies in vivo. Furthermore, a fully functional Ioc4-PWWP domain promotes efficient remodeling by Isw1b and the maintenance of ordered chromatin in vivo, thereby preventing the production of non-coding RNAs
Influence of a partially oxidized calcium cathode on the performance of polymeric light emitting diodes
We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the
performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent
polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere of less than or equal to 10 -9 mbar. For further investigations the calcium deposition was carried out in an oxygen atmosphere from 10 -8 to 10 -5 mbar. We determined the amount of oxygen in the different layers of the current–voltage-light characterized pLEDs with elastic recoil detection analysis and
correlated it with the characteristics of the devices. The external efficiency of the pLEDs decreases continuously with increasing oxygen pressure, the current shows a pronounced minimum. The brightness mostly decreases with increasing oxygen with an indication of a slight minimum. PLEDs
with completely oxidized calcium are not operational. The first contact of the pLEDs with the dry glove box environment leads to an immediate reduction of current and brightness which is caused by the cooling of the devices by several degrees. Determining reproducible characteristics of pLEDs
in the vacuum requires the measurement of their temperature
Nuclear structure of 178Hf related to the spin-16, 31-year isomer
The projected shell model is used to study the multi-quasiparticle and
collective excitations of 178Hf. With an axially symmetric basis, the spin-16
isomer at 2.4 MeV appears to be well separated in energy/spin space from other
configurations. However, projected energy surface calculations suggest that
178Hf has significant softness to axially asymmetric shapes, which can strongly
modify the level distribution. The implications for photodeexitation of the
isomer are discussed.Comment: 8 pages, 4 figure
Evaluation and refinement of thermodynamic databases for mineral carbonation
Thermodynamic models are often used to quantify fluid-rock interactions. The validity of such models critically depends on the accuracy of the thermodynamic database used. This study evaluated the quality of existing PHREEQC databases (phreeqc.dat, llnl.dat, and core10.dat) through the analysis of mineral saturation states for various carbonates, sulfur-containing minerals, silicates, and hydroxides. The comparison between data from available equilibrated dissolution-precipitation experiments and predicted saturation states reveals: i) systematic deviations when using phreeqc.dat at temperatures higher than ~ 90 °C; ii) a lack of direct solubility measurements of numerous sulfide and silicate minerals; iii) systematic solubility underestimates for kaolinite and brucite. To address these issues the carbfix.dat database was created based on the core10.dat database, revising several mineral solubilities and aqueous species stabilities to improve our ability to model fluid-rock interactions during basalt-hosted mineral carbonation efforts
Triangle-Free Penny Graphs: Degeneracy, Choosability, and Edge Count
We show that triangle-free penny graphs have degeneracy at most two, list
coloring number (choosability) at most three, diameter , and
at most edges.Comment: 10 pages, 2 figures. To appear at the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
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