550 research outputs found
Low Densities Instability of Relativistic Mean Field Models
The effects of the symmetry energy softening of the relativistic mean field
(RMF) models on the properties of matter with neutrino trapping are
investigated. It is found that the effects are less significant than those in
the case without neutrino trapping. The weak dependence of the equation of
state on the symmetry energy is shown as the main reason of this finding. Using
different RMF models the dynamical instabilities of uniform matters, with and
without neutrino trapping, have been also studied. The interplay between the
dominant contribution of the variation of matter composition and the role of
effective masses of mesons and nucleons leads to higher critical densities for
matter with neutrino trapping. Furthermore, the predicted critical density is
insensitive to the number of trapped neutrinos as well as to the RMF model used
in the investigation. It is also found that additional nonlinear terms in the
Horowitz-Piekarewicz and Furnstahl-Serot-Tang models prevent another kind of
instability, which occurs at relatively high densities. The reason is that the
effective sigma meson mass in their models increases as a function of the
matter density.Comment: 25 pages, 10 figures, submitted to Phys. Rev.
Isovector Channel Role of Relativistic Mean Field Models in the Neutrino Mean Free Path
An improvement in the treatment of the isovector channel of relativistic mean
field (RMF) models based on effective field theory (E-RMF) is suggested, by
adding an isovector scalar (delta) meson and using a similar procedure to the
one used by Horowitz and Piekarewicz to adjust the isovector-vector channel in
order to achieve a softer density dependent symmetry energy of the nuclear
matter at high density. Their effects on the equation of state (EOS) at high
density and on the neutrino mean free path (NMFP) in neutron stars are
discussed.Comment: 20 pages, 8 figure
Neutrino Electromagnetic Form Factors Effect on the Neutrino Cross Section in Dense Matter
The sensitivity of the differential cross section of the interaction between
neutrino-electron with dense matter to the possibly nonzero neutrino
electromagnetic properties has been investigated. Here, the relativistic mean
field model inspired by effective field theory has been used to describe non
strange dense matter, both with and without the neutrino trapping. We have
found that the cross section becomes more sensitive to the constituent
distribution of the matter, once electromagnetic properties of the neutrino are
taken into account. The effects of electromagnetic properties of neutrino on
the cross section become more significant for the neutrino magnetic moment
mu_nu > 10^{-10} mu_B and for the neutrino charge radius R > 10^{-5} MeV^{-1}.Comment: 24 pages, 10 figures, submitted to Physical Review
Frequency domain stability and relaxed convergence conditions for filtered error adaptive feedforward
The convergence of filtered error and filtered reference adaptive feedforward is limited by three effects: model mismatch, unintended input-disturbance interaction and too fast parameter adaptation. In this article, the first two effects are considered for MIMO systems under the slow parameter adaptation assumption. The convergence with model mismatch is conventionally guaranteed using a strictly positive-real condition. This condition can be easily verified in the frequency domain, but due the high-frequency parasitic dynamics of real systems, it is hardly ever satisfied. Nevertheless, filtered error and filtered reference adaptive feedforward have successfully been implemented in numerous applications without satisfying the strictly positive-real condition. It is shown in this article that the strictly positive-real condition can be relaxed to a power-weighted integral condition, that is less conservative and provides a practical check for the convergence of filtered error adaptive feedforward for real systems in the frequency domain. The effects of input-disturbance interaction are analysed and conditions for the stability are given in the frequency domain. Both conditions give clear indicators for frequency domain filter tuning, and are verified on an experimental active vibration isolation system.</p
The spin-Peierls instability in spin 1/2 XY chain in the non adiabatic limit
The spin-Peierls instability in spin 1/2 XY chain coupled to dispersionless
phonons of frequency has been studied in the nonadiabatic limit. We
have chosen the Lang-Firsov variational wave function for the phonon subsystem
to obtain an effective spin Hamiltonian. The effective spin Hamiltonian is then
solved in the framework of mean-field approximation. We observed a dimerized
phase when g is less than a critical value and an anti-ferromagnetic phase when
it is greater than a critical value . The variation of lattice distortion,
dimerized order parameter and energy gap with spin phonon coupling parameter
has also been investigated here.Comment: 15 pages (Revtex, including 5 .ps figures); Submitted to PR
A preliminary investigation of additive manufacture to fabricate human nail plate surrogates for pharmaceutical testing
In vitro permeation studies using nail clippings or nail plates are commonly used in the development of transungual formulations. However, there are ethical, safety and cost issues associated with sourcing such tissues. Herein, we describe a preliminary approach is described for the design and manufacture of a human nail model surrogate based on 3D printing. To evaluate these 3D printed constructs, nails were mounted in conventional glass Franz cells and a commercial antifungal lacquer formulation containing ciclopirox olamine was applied daily to the surrogate printed surfaces for a period of 14 days. On days 8 and 14, the surfaces of the 3D printed nails were washed with ethanol to remove excess formulation. Confocal Raman spectroscopy (CRS) was used to profile the drug in the 3D printed nail. At the end of the Franz cell studies, no drug was observed in the receptor phase. CRS studies confirmed penetration of the active into the model nails with reproducible depth profiles. Our ongoing work is focused on synthesising commercial and non-commercial printable resins that can replicate the physical and chemical characteristics of the human nail. This will allow further evaluation of actives for ungual therapy and advance the development of the surrogate nail tissue model
Nuclei in Strongly Magnetised Neutron Star Crusts
We discuss the ground state properties of matter in outer and inner crusts of
neutron stars under the influence of strong magnetic fields. In particular, we
demonstrate the effects of Landau quantization of electrons on compositions of
neutron star crusts. First we revisit the sequence of nuclei and the equation
of state of the outer crust adopting the Baym, Pethick and Sutherland (BPS)
model in the presence of strong magnetic fields and most recent versions of the
theoretical and experimental nuclear mass tables. Next we deal with nuclei in
the inner crust. Nuclei which are arranged in a lattice, are immersed in a
nucleonic gas as well as a uniform background of electrons in the inner crust.
The Wigner-Seitz approximation is adopted in this calculation and each lattice
volume is replaced by a spherical cell. The coexistence of two phases of
nuclear matter - liquid and gas, is considered in this case. We obtain the
equilibrium nucleus corresponding to each baryon density by minimizing the free
energy of the cell. We perform this calculation using Skyrme nucleon-nucleon
interaction with different parameter sets. We find nuclei with larger mass and
charge numbers in the inner crust in the presence of strong magnetic fields
than those of the zero field case for all nucleon-nucleon interactions
considered here. However, SLy4 interaction has dramatic effects on the proton
fraction as well as masses and charges of nuclei. This may be attributed to the
behaviour of symmetry energy with density in the sub-saturation density regime.
Further we discuss the implications of our results to shear mode oscillations
of magnetars.Comment: presented in "Exciting Physics Symposium" held in Makutsi, South
Africa in November, 2011 and to be published in a book by Springer Verla
Rigidly linked dinuclear platinum( ii ) complexes showing intense, excimer-like, near-infrared luminescence
Many luminescent platinum(ii) complexes undergo face-to-face interactions between neighbouring molecules, leading to bimolecular excited states that may emit at lower energy (dimers and/or excimers). Detailed photophysical studies are reported on dinuclear complexes, in which two NCN-coordinated Pt(ii) units are covalently linked by a xanthene such that intramolecular formation of such dimeric or excimeric states is possible. These complexes display strong excimer-like photoluminescence at low concentrations where their monometallic analogues do not. However, a striking difference emerges between complexes where the Pt(NCN) units are directly connected to the xanthene through the tridentate ligand (denoted Class a) and a new class of compounds reported here (Class b) in which the attachment is through a monodentate acetylide ligand. The former require a substantial geometrical rearrangement to move the metal centres of the Pt(NCN) units to a distance short enough to form excimer-like states. The latter require only a small deformation. Consequently, Class a compounds display negligible excimer-like emission in solid films, as the rigid environment hinders the requisite geometric rearrangement. Class b complexes, in contrast, display strong excimer-like emission in film, even at very low loadings. The new dinuclear molecular architecture may thus offer new opportunities in the quest for efficient NIR-emitting devices
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