31 research outputs found
Variational description of multi-fluid hydrodynamics: Uncharged fluids
We present a formalism for Newtonian multi-fluid hydrodynamics derived from
an unconstrained variational principle. This approach provides a natural way of
obtaining the general equations of motion for a wide range of hydrodynamic
systems containing an arbitrary number of interacting fluids and superfluids.
In addition to spatial variations we use ``time shifts'' in the variational
principle, which allows us to describe dissipative processes with entropy
creation, such as chemical reactions, friction or the effects of external
non-conservative forces. The resulting framework incorporates the
generalization of the entrainment effect originally discussed in the case of
the mixture of two superfluids by Andreev and Bashkin. In addition to the
conservation of energy and momentum, we derive the generalized conservation
laws of vorticity and helicity, and the special case of Ertel's theorem for the
single perfect fluid.
We explicitly discuss the application of this framework to thermally
conducting fluids, superfluids, and superfluid neutron star matter. The
equations governing thermally conducting fluids are found to be more general
than the standard description, as the effect of entrainment usually seems to be
overlooked in this context. In the case of superfluid He4 we recover the
Landau--Khalatnikov equations of the two-fluid model via a translation to the
``orthodox'' framework of superfluidity, which is based on a rather awkward
choice of variables. Our two-fluid model for superfluid neutron star matter
allows for dissipation via mutual friction and also ``transfusion'' via
beta-reactions between the neutron fluid and the proton-electron fluid.Comment: uses RevTeX 4; 20 pages. To appear in PRD. v2: removed discussion of
charged fluids and coupling to electromagnetic fields, which are submitted as
a separate paper for a clearer presentation v3: fixed typo in Eq.(9), updated
some reference
3-D Perturbations in Conformal Turbulence
The effects of three-dimensional perturbations in two-dimensional turbulence
are investigated, through a conformal field theory approach. We compute scaling
exponents for the energy spectra of enstrophy and energy cascades, in a strong
coupling limit, and compare them to the values found in recent experiments. The
extension of unperturbed conformal turbulence to the present situation is
performed by means of a simple physical picture in which the existence of small
scale random forces is closely related to deviations of the exact
two-dimensional fluid motion.Comment: Discussion of intermittency improved. Figure include
Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices
NGC 1316 is a giant, elliptical galaxy containing a complex network of dark,
dust features. The morphology of these features has been examined in some
detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is
found that most of the features are constituted of long filaments. There also
exist a great number of dark structures protruding inwards from the filaments.
Many of these structures are strikingly similar to elephant trunks in H II
regions in the Milky Way Galaxy, although much larger. The structures, termed
mammoth trunks, generally are filamentary and often have shapes resembling the
letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved
into two or more filaments, many of which showing signs of being intertwined. A
model of the mammoth trunks, related to a recent theory of elephant trunks, is
proposed. Based on magnetized filaments, the model is capable of giving an
account of the various shapes of the mammoth trunks observed, including the
twined structures.Comment: Accepted for publication in Astrophysics & Space Scienc
Preparation and evaluation of azithromycin binary solid dispersions using various polyethylene glycols for the improvement of the drug solubility and dissolution rate
Experimental and Computational Simulation of Free Jet Characteristics Under Transverse Field Gradients
Inducible Ternary Control Of Transgene Expression and Cell Ablation In Drosophila
In Drosophila, P-GAL4 enhancer trap lines can target expression of a cloned gene, under control of a UAS(GAL) element, to any cells of interest, However, additional expression of GAL4 in other cells can produce unwanted lethality or side-effects, particularly when It drives expression of a toxic gene product. To target the toxic gene product ricin A chain specifically to adult neurons, we have superimposed a second layer of regulation on the GAL4 control. We have constructed flies in which an effector gene is separated from UAS(GAL), by a polyadenylation site flanked by two FRT sites in the same orientation; A recombination event between the two FRT sites, catalysed by yeast FLP recombinase, brings the effector gene under control of UAS(GAL). Consequently, expression of tile effector gene is turned on in that cell and its descendants, if they also express GAL4. Recombinase is supplied by heat shock induction of a FLP transgene, allowing both tinting and frequency of recombination events to be regulated, Using a lacZ effector (reporter) to test the system, we have generated labelled clones in the embryonic mesoderm and shown that most recombination events occur soon after FLP recombinase is supplied. By substituting the ricin A chain gene for lacZ, we have performed mosaic cell ablations in one GAL4 line that marks the adult giant descending neurons, and in a second which marks mushroom body neurons. In a number of cases we observed loss of one or both the adult giant descending neurons, or of subsets of mushroom body neurons. In association with the mushroom body ablations, we also observed misrouting of surviving axons
Generation of the magnetic helicity in a neutron star driven by the electroweak electron-nucleon interaction
We study the instability of magnetic fields in a neutron star core driven by
the parity violating part of the electron-nucleon interaction in the Standard
Model. Assuming a seed field of the order , that is
a common value for pulsars, one obtains its amplification due to such a novel
mechanism by about five orders of magnitude, up to ,
at time scales . This effect is
suggested to be a possible explanation of the origin of the strongest magnetic
fields observed in magnetars. The growth of a seed magnetic field energy
density is stipulated by the corresponding growth of the magnetic helicity
density due to the presence of the anomalous electric current in the Maxwell
equation. Such an anomaly is the sum of the two competitive effects: (i) the
chiral magnetic effect driven by the difference of chemical potentials for the
right and left handed massless electrons and (ii) constant chiral electroweak
electron-nucleon interaction term, which has the polarization origin and
depends on the constant neutron density in a neutron star core. The remarkable
issue for the decisive role of the magnetic helicity evolution in the suggested
mechanism is the arbitrariness of an initial magnetic helicity including the
case of non-helical fields from the beginning. The tendency of the magnetic
helicity density to the maximal helicity case at large evolution times provides
the growth of a seed magnetic field to the strongest magnetic fields in
astrophysics.Comment: 17 pages in JCAP LaTeX style, 10 esp figures, paper is significantly
revised, several new references are added, multiple misprints are corrected,
version to be published in JCA