Stationary vortical flows in two-dimensional plasma and in planetary atmospheres

We derive the equation governing the asymptotic stationary states generated by decaying turbulence in two-dimensional plasma and planetary atmosphere. These fluids may be described by the Charney-Hasegawa-Mima equation and their relaxation states show a high degree of organization in vortical flows, similar to the Euler fluid. We develop a field-theoretical framework and show that these systems attain at stationarity the extremum of an energy functional corresponding to self-dual fields.     

Forming metastable carbon-rich anions in planetary atmospheres: the case of diacetylene

Alignment of the L ₃ ? (J = 3 / 2) subshell vacancy states in the Au, Bi, Th and U elements following photoinisation have been investigated through angular distribution measurements of subsequently emitted L ₃ subshell X-rays. The 59.54 keV unpolarised γ-rays from the ²⁴¹Am radioactive point-source were used to ionize the target and the subsequently emitted L X-rays were measured using an HPGe detector. The improved experimental procedure along with correct evaluation scheme permits straight-forward method for investigating anisotropy in photo-excited L X-ray emission. The efficiency of the detector and the absorption correction for the emitted L X-rays in the target remain fairly constant as the target-detector assemblage remains undisturbed in the present measurements at various angles. Isotropically emitted L ₁ subshell (J = 1 / 2) X-rays measured simultaneously were used to normalize the L X-ray spectra taken at different emission angles. The present measurements clearly support small theoretical predicted values of the alignment parameter; however, it is difficult to infer regarding the predicted anisotropic trends. The angular distribution measurements for the L ₃ subshell X-ray emission were also performed by placing the target in magnetic field  ～ 0.6 T. The earlier reported large anisotropy in angular distribution of the emitted L ₃ subshell X-rays and significant effect of external magnetic field on the angular distribution are ruled out.     

Intersubband absorption in modulation doped p-type Si1-xGex quantum wells: theory and experiment

A study of intersubband infrared absorption in modulation doped p-type Si/SiGe quantum wells is presented for SiGe wells with thicknesses between 22 Å and 64 Å and Ge contents in the range from 23% to 58%. The peak positions of the absorption lines are observed between 500 cm^-1 and 2200 cm^-1. Depending on the barrier height (i.e., on the Ge content of the wells), the heavy-hole states excited by the infrared radiation are either localized in the wells or strongly mixed with barrier-bound states and therefore delocalized. The shape of the absorption line correspondingly changes from a narrow Lorentz line to a rather broad absorption band. Using the structural parameters determined by high-resolution triple-axis x-ray diffraction, the results of a self-consistent Luttinger-Kohn type envelope function approach with the explicit inclusion of the strain in the quantum wells are in excellent agreement with the measured spectra.     

Nonlinearity management in optics: experiment, theory, and simulation

We conduct an experimental investigation of nonlinearity management in optics using femtosecond pulses and layered Kerr media consisting of glass and air. By examining the propagation properties over several diffraction lengths, we show that wave collapse can be prevented. We corroborate these experimental results with numerical simulations of the (2+1)-dimensional focusing cubic nonlinear Schr?dinger equation with piecewise constant coefficients and a theoretical analysis of this setting using a moment method.     

Water in planetary and cometary atmospheres: H2O/HDO transmittance and fluorescence models

We developed a modern methodology to retrieve water (H₂O) and deuterated water (HDO) in planetary and cometary atmospheres, and constructed an accurate spectral database that combines theoretical and empirical results. On the basis of a greatly expanded set of spectroscopic parameters, we built a full non-resonance cascade fluorescence model and computed fluorescence efficiencies for H₂O (500 million lines) and HDO (700 million lines). The new line list was also integrated into an advanced terrestrial radiative transfer code (LBLRTM) and adapted to the CO₂ rich atmosphere of Mars, for which we adopted the complex Robert–Bonamy formalism for line shapes. We retrieved water and D/H in the atmospheres of Mars, comet C/2007 W1 (Boattini), and Earth by applying the new formalism to spectra obtained with the high-resolution spectrograph NIRSPEC/Keck II atop Mauna Kea (Hawaii). The new model accurately describes the complex morphology of the water bands and greatly increases the accuracy of the retrieved abundances (and the D/H ratio in water) with respect to previously available models. The new model provides improved agreement of predicted and measured intensities for many H₂O lines already identified in comets, and it identifies several unassigned cometary emission lines as new emission lines of H₂O. The improved spectral accuracy permits retrieval of more accurate rotational temperatures and production rates for cometary water.     

Exact results in modeling planetary atmospheres—I. Gray atmospheres

An exact model is proposed for a gray, isotropically scattering planetary atmosphere in radiative equilibrium. The slab is illuminated on one side by a collimated beam and is bounded on the other side by an emitting and partially reflecting ground. We provide expressions for the incident and reflected fluxes on both boundary surfaces, as well as the temperature of the ground and the temperature distribution in the atmosphere, assuming the latter to be in local thermodynamic equilibrium. Tables and curves of the temperature distribution are included for various values of the optical thickness. Finally, semi-infinite atmospheres illuminated from the outside or by sources at infinity is dealt with.     

Exact results in modeling planetary atmospheres—II. Semi-gray atmospheres

We solve the radiative transfer equation for a semi-gray planetary atmosphere in radiative equilibrium, in an attempt to define an entirely analytical non-gray model atmosphere of finite optical thickness. The salient feature of the model is that the incident solar radiation is partitioned between two adjacent spectral domains—the “visible” and the “infrared”—in each of which the atmosphere's (effective) opacity is assumed to be independent of frequency (the semi-gray assumption). We envisage a plane-parallel atmosphere illuminated by a beam of parallel radiation and bounded below by a partially reflecting and emitting ground. The former emits infrared radiation, induced by the absorption of radiation both visible and infrared, deriving from the external irradiation as well as from the emission of the planet's surface layer. For an atmosphere with given single-scattering albedos and optical thicknesses in both the visible and infrared domains, we compute the temperature at every depth of the atmosphere, as well as the ground's temperature.     

On the computation of angular distributions of radiation in planetary atmospheres

The discrete ordinate approximation to the radiative transfer equation is used to derive simple analytic expressions for the intensity in a vertically inhomogeneous plane parallel atmosphere. This approach allows one to compute the intensity at arbitrary depths and angles. The merit and soundness of these expressions, which are interpolatory in nature, are discussed and it is conjectured that they are superior to any other standard interpolation scheme as far as accuracy is concerned. The computational time also compares favorably with that of standard interpolation schemes such as cubic splines.     

Stabilizing dicyanoacetylene anions in planetary atmospheres: quantum dynamics of its transient negative ions

Quantum computations that follow the electron-attachment process at low energies (<10 eV) to the NCCCCN gaseous molecule are carried out in order to understand the role of transient negative ions (TNIs) which act as “doorway states" to molecular stabilization and/or fragmentation after resonant attachment of an environmental electron. The computed behaviour of the found TNIs suggests that an NCCCCN^*- intermediate could be formed under conditions which justify and explain the existence of stable carbonaceous anions in the interstellar medium, while further anionic fragments of the title molecule, already seen in laboratory experiments, are also identified by the present calculations.     

Some remarks on coherent structures out of chaos in planetary atmospheres and oceans

In the context of planetary atmospheres and oceans, it is natural to define "coherent structures" as "long-lived," or "solitary," Rossby vortices. These can be described by the generalized Charney-Obukhov equation (in fluid dynamics) or the analogous generalized Hasegawa-Mima equation (in plasma physics). These two equations contain KdV-type nonlinearities which (together with the compensating dispersive spreading) determine the formation of the coherent structures and explain the clear-cut cyclonic/anticyclonic asymmetry observed experimentally in long-lived planetary Rossby vortices. Examples are given of natural vortices which are (and which are not) coherent structures.     

Formation of spectral lines in planetary atmospheres—V. Collision narrowed profiles of quadrupole lines in hydrogen atmospheres

The interpretation of a hydrogen quadrupole spectrum is complicated by the collision narrowing phenomenon exhibited by these lines. The profile must be accurately computed for use within any interpretative technique since the spectroscopic features of line profile and center to limb variation of the equivalent width are sensitive to the quadrupole line shape.The Dicke profile, which assumes that the quadrupole line shape is Lorentzian with a half-width that varies inversely as the pressure has been suggested as a simple alternative to the Galatry profile. In this paper, we present comparisons of the line profile, equivalent width and center-to-limb variation of the equivalent width of quadrupole lines for a characteristic scattering and nonscattering hydrogen atmosphere, where the line profile has been computed by the Dicke and Galatry shapes. Our computations show that the results produced by the Dicke profile may be very different from the features predicted by the Galatry profile, which has been shown to give results in good agreement with experiment.We therefore conclude that it is invalid to use the Dicke approximation for computing collision-narrowed profiles of hydrogen quadrupole lines at visible and near infrared spectroscopic wavelengths in any hydrogen atmosphere.     

Chirped-pulse oscillators: theory and experiment

Theory of chirped-pulse oscillators operating in the positive dispersion regime is presented. It is found that the chirped pulses can be described analytically as solitary pulse solutions of the nonlinear cubic-quintic complex Ginzburg–Landau equation. Due to the closed form of the solution, basic characteristics of the regime under consideration are easily traceable. Numerical simulations validate the analytical technique and the chirped-pulse stability. Experiments with 10 MHz Ti:Sa oscillator providing up to 150 nJ chirped pulses, which are compressible down to 30 fs, are in agreement with the theory. PACS 42.65.Re; 42.65.Tg; 42.55.Rz     

Metastable anions of polyynes: Dynamics of fragmentation/stabilization in planetary atmospheres after electron attachment

The quantum dynamics of low-energy free electrons colliding with linear carbonaceous species like HC₃N and HC₅N is examined to identify the locations and structural features of their metastable negative ions (resonant compound states of the colliding partners) with the aim of suggesting, at the molecular level, the possible mechanisms of anionic stabilization which lead to the several stable species observed in the interstellar and circumstellar media in connection with polyyne structures.     

Band spectrum and optical absorption in n-CdSnAs2

Using the crystal splitting (CS) method in perturbation theory, the energy spectrum of the valence zone and the conductivity zone is calculated in the neighborhood of the point of the Brillouin zone for the semiconductor CdSnAs₂. The parameters necessary for calculating the spectrum were found from analysis of the edge of optical absorption in n-CdSnAs₂. Using the found values of the parameters, the effective masses at the point and the density of states are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–34, June, 1978.In conclusion, we thank N. A. Zakharov for the calculation of the energy spectrum and wave functions of InAs.     

Four-wave mixing assisted stability enhancement: theory, experiment, and application

Stability enhancement on the basis of four-wave mixing (FWM) is proposed and proved for the first time to our knowledge. This technique is applied to dual-wavelength erbium-doped fiber lasers. Significant uniformity and stability of the novel fiber lasers are demonstrated experimentally.