Atmospheres and Spectra of Strongly Magnetized Neutron Stars -- III. Partially Ionized Hydrogen Models

We construct partially ionized hydrogen atmosphere models for magnetized neutron stars in radiative equilibrium with surface fields B=10^12-5 \times 10^14 G and effective temperatures T_eff \sim a few \times 10^5-10^6 K. These models are based on the latest equation of state and opacity results for magnetized, partially ionized hydrogen plasmas that take into account various magnetic and dense medium effects. The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars. For the models with B=10^12-10^13 G, the spectral features due to neutral atoms lie at extreme UV and very soft X-ray energy bands and therefore are difficult to observe. However, the continuum flux is also different from the fully ionized case, especially at lower energies. For the superstrong field models (B\ga 10^14 G), we show that the vacuum polarization effect not only suppresses the proton cyclotron line as shown previously, but also suppresses spectral features due to bound species; therefore spectral lines or features in thermal radiation are more difficult to observe when the neutron star magnetic field is \ga 10^14 G.Comment: 12 pages, 10 figures; ApJ, accepted (v599: Dec 20, 2003

Identification of the Factors of Sustainable Development of Regional Agricultural Systems Using Regression Model

The study is aimed at providing a theoretical basis for the relevance of sustainable development of regional agricultural systems and the development of practical recommendations for the implementation of the algorithm evaluation of the factors affecting the condition of agricultural production at the regional level. The study uses a systematic approach, supplemented with multifunctionality paradigm of agricultural production, which has enabled to develop an algorithm that includes a series of steps aimed at creating a regression model that reflects the significance of selected factors and their impact on the development of regional agricultural system. The developed method is tested in a study of rural areas of the Penza region, situated in the Central European part of Russia. The proposed indicators of sustainable development of regional agricultural systems are able to objectify the process of further evaluation of the spatial inhomogeneity of the factors determining sustainability of the agricultural production. The research findings provide additional opportunities in the agricultural development of the region. Keywords: sustainable development factors, agricultural system, rural areas, regional development, regression model JEL Classifications: 013, R1

Equation of state and opacities for hydrogen atmospheres of magnetars

The equation of state and radiative opacities of partially ionized, strongly magnetized hydrogen plasmas, presented in a previous paper [ApJ 585, 955 (2003), astro-ph/0212062] for the magnetic field strengths 8.e11 G < B < 3.e13 G, are extended to the field strengths 3.e13 G < B < 1.e15 G, relevant for magnetars. The first- and second-order thermodynamic functions and radiative opacities are calculated and tabulated for 5.e5 < T < 4.e7 K in a wide range of densities. We show that bound-free transitions give an important contribution to the opacities in the considered range of B in the outer neutron-star atmosphere layers. Unlike the case of weaker fields, bound-bound transitions are unimportant.Comment: 7 pages, 6 figures, LaTeX using emulateapj.cls (included). Accepted by Ap

Model reduction by moment matching with preservation of global stability for a class of nonlinear models

Model reduction by time-domain moment matching naturally extends to nonlinear models, where the notion of moments has a local nature stemming from the center manifold theorem. In this paper, the notion of moments of nonlinear models is extended to the global case and is, subsequently, utilized for model order reduction of convergent Lur'e-type nonlinear models. This model order reduction approach preserves the Lur'e-type model structure, inherits the frequency-response function interpretation of moment matching, preserves the convergence property, and allows formulating a posteriori error bound. By the grace of the preservation of the convergence property, the reduced-order Lur'e-type model can be reliably used for generalized excitation signals without exhibiting instability issues. In a case study, the reduced-order model accurately matches the moment of the full-order Lur'e-type model and accurately describes the steady-state model response under input variations.</p

Model reduction by moment matching with preservation of global stability for a class of nonlinear models

Model reduction by time-domain moment matching naturally extends to nonlinear models, where the notion of moments has a local nature stemming from the center manifold theorem. In this paper, the notion of moments of nonlinear models is extended to the global case and is, subsequently, utilized for model order reduction of convergent Lur'e-type nonlinear models. This model order reduction approach preserves the Lur'e-type model structure, inherits the frequency-response function interpretation of moment matching, preserves the convergence property, and allows formulating a posteriori error bound. By the grace of the preservation of the convergence property, the reduced-order Lur'e-type model can be reliably used for generalized excitation signals without exhibiting instability issues. In a case study, the reduced-order model accurately matches the moment of the full-order Lur'e-type model and accurately describes the steady-state model response under input variations.</p

Hamiltonian structure for dispersive and dissipative dynamical systems

We develop a Hamiltonian theory of a time dispersive and dissipative inhomogeneous medium, as described by a linear response equation respecting causality and power dissipation. The proposed Hamiltonian couples the given system to auxiliary fields, in the universal form of a so-called canonical heat bath. After integrating out the heat bath the original dissipative evolution is exactly reproduced. Furthermore, we show that the dynamics associated to a minimal Hamiltonian are essentially unique, up to a natural class of isomorphisms. Using this formalism, we obtain closed form expressions for the energy density, energy flux, momentum density, and stress tensor involving the auxiliary fields, from which we derive an approximate, ``Brillouin-type,'' formula for the time averaged energy density and stress tensor associated to an almost mono-chromatic wave.Comment: 68 pages, 1 figure; introduction revised, typos correcte

Twisted Nanotubes of Transition Metal Dichalcogenides with Split Optical Modes for Tunable Radiated Light Resonators

Synthesized micro- and nanotubes composed of transition metal dichalcogenides (TMDCs) such as MoS$_2$ are promising for many applications in nanophotonics, because they combine the abilities to emit strong exciton luminescence and to act as whispering gallery microcavities even at room temperature. In addition to tubes in the form of hollow cylinders, there is an insufficiently-studied class of twisted tubes, the flattened cross section of which rotates along the tube axis. As shown by theoretical analysis, in such nanotubes the interaction of electromagnetic waves excited at opposite sides of the cross section can cause splitting of the whispering gallery modes. By studying micro-photoluminescence spectra measured along individual MoS$_2$ tubes, it has been established that the splitting value, which controls the energies of the split modes, depends exponentially on the aspect ratio of the cross section, which varies in "breathing" tubes, while the relative intensity of the modes in a pair is determined by the angle of rotation of the cross section. These results open up the possibility of creating multifunctional tubular TMDC nanodevices that provide resonant amplification of self-emitting light at adjustable frequencies