984 research outputs found
Prediction of Particle Size of Ammonium Perchlorate during Pulverisation
Ammonium perchlorate has been pulverised by an impact mill (air classifier mill) to studythe influence of different operating parameters, viz., effect of mill speed, classifier speed, feedrate, and damper opening (suction rate) on the particle size. Further based on the differentgrinding parameters, an empirical equation has been developed and used for the prediction ofparticle size. The experimental results indicate that the values are very close to the predictedones. In addition, particle size distribution has also been studied by applying different modelequations and it has been found that Rosin-Rammler model is the most suitable model for thisoperation
Effect of a mixture of caffeine and nicotinamide on the solubility of vitamin (B2) in aqueous solution
The effect of caffeine (CAF) and nicotinamide (NMD) on the solubility of a vitamin B2 derivative (FMN) has been evaluated for mixtures containing either a single hydrotrope (CAF or NMD) or the two hydrotropes simultaneously. A model for analysis of ternary systems, which takes into account all possible complexes between the molecules, has been developed and tested with experimental NMR data on the three-component mixture FMN–CAF–NMD. The results indicate that special attention should be given to the concentration of a hydrotropic agent used to enhance the solubility of a particular drug. A decrease in the efficacy of solubility of the vitamin on addition of large amounts of hydrotropic agent is expected in the two-component systems due to the increased proportion of self-association of the hydrotrope. It is found that a mixture of two hydrotropic agents leads to an increase in the solubility of the vitamin in three-component compared to the two-component system. Rather than using just one hydrotropic agent, it is proposed that a strategy for optimising the solubility of aromatic drugs is to use a mixture of hydrotropic agents
Magnetoroton instabilities and static susceptibilities in higher Landau levels
We present analytical results concerning the magneto-roton instability in
higher Landau levels evaluated in the single mode approximation. The roton gap
appears at a finite wave vector, which is approximately independent of the LL
index n, in agreement with numerical calculations in the composite-fermion
picture. However, a large maximum in the static susceptibility indicates a
charge density modulation with wave vectors , as
expected from Hartree-Fock predictions. We thus obtain a unified description of
the leading charge instabilities in all LLs.Comment: 4 pages, 5 figure
Structures for Interacting Composite Fermions: Stripes, Bubbles, and Fractional Quantum Hall Effect
Much of the present day qualitative phenomenology of the fractional quantum
Hall effect can be understood by neglecting the interactions between composite
fermions altogether. For example the fractional quantum Hall effect at
corresponds to filled composite-fermion Landau levels,and
the compressible state at to the Fermi sea of composite fermions.
Away from these filling factors, the residual interactions between composite
fermions will determine the nature of the ground state. In this article, a
model is constructed for the residual interaction between composite fermions,
and various possible states are considered in a variational approach. Our study
suggests formation of composite-fermion stripes, bubble crystals, as well as
fractional quantum Hall states for appropriate situations.Comment: 16 pages, 7 figure
Competition between quantum-liquid and electron-solid phases in intermediate Landau levels
On the basis of energy calculations we investigate the competition between
quantum-liquid and electron-solid phases in the Landau levels n=1,2, and 3 as a
function of their partial filling factor. Whereas the quantum-liquid phases are
stable only in the vicinity of quantized values 1/(2s+1) of the partial filling
factor, an electron solid in the form of a triangular lattice of clusters with
a few number of electrons (bubble phase) is energetically favorable between
these fillings. This alternation of electron-solid phases, which are insulating
because they are pinned by the residual impurities in the sample, and quantum
liquids displaying the fractional quantum Hall effect explains a recently
observed reentrance of the integral quantum Hall effect in the Landau levels
n=1 and 2. Around half-filling of the last Landau level, a uni-directional
charge density wave (stripe phase) has a lower energy than the bubble phase.Comment: 12 pages, 9 figures; calculation of exact exchange potential for
n=1,2,3 included, energies of electron-solid phases now calculated with the
help of the exact potential, and discussion of approximation include
Exotic baryon multiplets at large number of colours
We generalize the usual octet, decuplet and exotic antidecuplet and higher
baryon multiplets to any number of colours Nc. We show that the multiplets fall
into a sequence of bands with O(1/Nc) splittings inside the band and
O(1)splittings between the bands characterized by "exoticness", that is the
number of extra quark-antiquark pairs needed to compose the multiplet. Each
time one adds a pair the baryon mass is increased by the same constant which
can be interpreted as a mass of a quark-antiquark pair. At the same time, we
prove that masses of exotic rotational multiplets are reliably determined at
large Nc from collective quantization of chiral solitons.Comment: 13 p., 5 figs. New section and references adde
Magnetic Nanoparticles for Power Absorption: optimizing size, shape and magnetic properties
We present a study on the magnetic properties of naked and silica-coated
Fe3O4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as
heating agents was assessed through specific power absorption (SPA)
measurements as a function of particle size and shape. The results show a
strong dependence of the SPA with the particle size, with a maximum around 30
nm, as expected for a Neel relaxation mechanism in single-domain particles. The
SiO2 shell thickness was found to play an important role in the SPA mechanism
by hindering the heat outflow, thus decreasing the heating efficiency. It is
concluded that a compromise between good heating efficiency and surface
functionality for biomedical purposes can be attained by making the SiO2
functional coating as thin as possible.Comment: 15 pages, 7 figures, 2 table
Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh
Based on ab initio total energy calculations we show that two magnetic states
of rhodium atoms together with competing ferromagnetic and antiferromagnetic
exchange interactions are responsible for a temperature induced metamagnetic
phase transition, which experimentally is observed for stoichiometric
alpha-FeRh. A first-principle spin-based model allows to reproduce this
first-order metamagnetic transition by means of Monte Carlo simulations.
Further inclusion of spacial variation of exchange parameters leads to a
realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.
Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation
The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a
zero- configuration and for parallel propagation of waves does not allow
the existence of surface waves. When oblique propagation of perturbations is
considered both surface and body waves are able to propagate. When the
perpendicular wave number is larger than a certain value, the body kink mode
becomes a surface wave. In addition, a sausage surface mode is found below the
internal cut-off frequency. When non-uniformity in the equilibrium is included,
surface and body modes are damped due to resonant absorption. In this paper,
first, a normal-mode analysis is performed and the period, the damping rate,
and the spatial structure of eigenfunctions are obtained. Then, the
time-dependent problem is solved, and the conditions under which one or the
other type of mode is excited are investigated.Comment: 19 pages, 9 figures, accepted for publication in Solar Physic
Beyond paired quantum Hall states: parafermions and incompressible states in the first excited Landau level
The Pfaffian quantum Hall states, which can be viewed as involving pairing
either of spin-polarized electrons or of composite fermions, are generalized by
finding the exact ground states of certain Hamiltonians with k+1-body
interactions, for all integers k > 0. The remarkably simple wavefunctions of
these states involve clusters of k particles, and are related to correlators of
parafermion currents in two-dimensional conformal field theory. The k=2 case is
the Pfaffian. For k > 1, the quasiparticle excitations of these systems are
expected to possess nonabelian statistics, like those of the Pfaffian. For k=3,
these ground states have large overlaps with the ground states of the (2-body)
Coulomb-interaction Hamiltonian for electrons in the first excited Landau level
at total filling factors \nu=2+3/5, 2+2/5.Comment: 11 pages Revtex in two column format with 4 eps figures included in
the M
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