Associative ionization of N(2D) and O

Recent laboratory measurements have shown that N(²P) atoms, and thus probably hot N(²D) atoms, will recombine with atomic oxygen via an associative ionization process at the gas kinetic rate. While the reaction is endothermic, it has been suggested that this has interesting implications for the upper atmosphere in that N(²D) atoms in the tail of the velocity distribution could provide an additional source of NO⁺ through the reverse of the dissociative recombination reaction

$\text{NO}{}^{\mathrm{+}}\text{+ e ?}\text{N}\text{(}{}^2\text{D}\text{) +}\text{O}$

. It has also been suggested that this process might account for the difference between a laboratory determination of the rate coefficient and that determined from the Atmospheric Explorer Satellite data. In this paper we investigate further the likelihood of the associative ionization of N(²D) and O playing a significant role in the normal ionosphere, in the light of several recent relevant studies. We conclude that the associative ionization process is not an important factor and that a more probable cause for disagreements in the various determinations of the recombination coefficient, is the difference in excited states of the ions in the various experiments.     

Auroral implications of recent measurements on O(1S) and O(1S) formation in the reaction of N+ with O2

Recent flowing afterglow measurements have shown that the reaction of N⁺ with O₂ produces 70 ± 30% of the oxygen atom product as $\text{O}\text{(}{}^1\text{D}\text{)}$ and < 0.1% as $\text{O}\text{(}{}^1\text{S}\text{)}$. These results indicate that this reaction does not contribute to the auroral green line emission (5577 Å), but can account for ～10% of the observed red line (6300 Å) auroral emission.     

An efficient autofocus algorithm for a visible microscope on a Mars lander

The limited depth of focus of microscope optics precludes the observation of a three-dimensional surface in a single view. For an efficient operation of a planetary microscope observing a highly irregular surface, an autofocus algorithm must detect partially focused views and merge them into a completely focused image (extended depth of focus). In this paper we investigate the suitability of different algorithms for autonomous image focusing onboard a Mars lander. We show that all methods under study, except for the Variance method, produce reasonable results and that their performance depends (amongst other factors) on sample morphology. For reasons of simplicity and reduced computational requirements we favor Gradient and Roberts methods and present an efficient implementation thereof.     

Discovery of irradiation-induced variations in the light curve of the classical nova V2275 Cyg (N Cyg 2001 No. 2)

We present charge-coupled device (CCD) photometry, light curve and time-series analysis of the classical nova V2275 Cyg (N Cyg 2001 No. 2). The source was observed for 14 nights in total in 2002 and 2003 using an R filter with the 1.5-m Russian–Turkish joint telescope (RTT150) at the TUBITAK National Observatory in Antalya, Turkey, as part of a large programme on the CCD photometry of cataclysmic variables. We report the detection of two distinct periodicities in the light curve of the nova: (a)   P ₁= 0.314 49(15) d [7.6 h]  , and (b)   P ₂= 0.017 079(17) d [24.6 min]  . The first period is evident in both 2002 and 2003 whereas the second period is only detected in the 2003 data set. We interpret the first period as the orbital period of the system and attribute the orbital variations to aspect changes of the secondary irradiated by the hot white dwarf (WD). We suggest that the nova was a supersoft X-ray source in 2002 and, perhaps, in 2003. The second period could be a quasi-periodic oscillation originating from the oscillation of the ionization front (due to a hot WD) below the inner Lagrange point or a beat frequency in the system as a result of the magnetic nature of the WD if steady accretion has already been re-established.     

An efficient method for studying the stability and dynamics of the rotational motions of celestial bodies

We use the alternative MEGNO (Mean Exponential Growth of Nearby Orbits) technique developed by Cincotta and Simó to study the stability of orbital—rotational motions for plane oscillations and three-dimensional rotations. We present a detailed numerical—analytical study of a rigid body in the case where the proper rotation of the body is synchronized with its orbital motion as 3: 2(Mercurian—type synchronism). For plane rotations, the loss of stability of the periodic solution that corresponds to a 3: 2 resonance is shown to be soft, which should be taken into account to estimate the upper limit for the ellipticity of Mercury. In studying stable and chaotic translational—rotational motions, we point out that the MEGNO criterion can be effectively used. This criterion gives a clear picture of the resonant structures and allows the calculations to be conveniently presented in the form of the corresponding MEGNO stability maps for multidimensional systems. We developed an appropriate software package.     

Observations of horizontal transport effects on high latitude metastable O(1D), N(2D) auroral emissions

An analysis is presented of photometric measurements of the NI (λ = 520nm),OI(λ = 630nm)and other emissions made at Nord, where the invariant latitude is Λ = 80°4. The time variations of the intensities are interpreted in the following way by comparison with simultaneous ground based or satellite measurements.The N(²D) atoms formed in the dayside cleft are carried by the neutral wind in a plume across the polar cap, so that the ratio of λ(630 nm) to λ(520 nm) intensities decreases along the plume with increasing distance from the source region.In the polar cap, but outside the plume region, 630 nm emission is produced by electron impact of polar rain and by substorms that reach high latitudes. Ionization produced at the same time, especially by the substorms, will produce further 630 nm emission through dissociative recombination. In any case, the region outside the plume may be regarded as a source region, with a high value of the ratio $\text{I(630)}\text{I(520)}$. This explains in part the diurnal variations, since this ratio is depressed as Nord crosses the dayside plume.The electron energy along the oval increases progressively from the dayside to the nightside. The intensity ratio increases with increasing electron energy because N(²D) is quenched more rapidly than O(¹D). Thus the ratio rises progressively from noon to midnight.An effect of the interplanetary magnetic field is superimposed on this pattern : as its North-South component B_z increases, the oval contracts so that Nord becomes nearer from the cleft source and the intensity ratio increases on the dayside. The inverse effect is also observed. On the nightside, negative B_z is associated with substorms that produce poleward expansions of the poleward oval boundary, that brings more energetic precipitation to Nord. This causes the intensity ratio to increase with decreasing B_z in a way that is opposite to that for the dayside.     

Nature and Properties of sub-DLAs (absorbers with 1019 ≤ N(HI) ≤ 2 * 1020 cm-2)

Quasar absorbers provide an alternative approach to the study of galaxies. In particular, the detection of high-column density systems allow to measure the cosmological evolution of the neutral gas mass and metals in the Universe. At z <3.5, 90% of the HI mass is in damped Lyα systems (DLAs). But it has been suggested that atz > 3.5, 45% of the HI lies in systems below the traditional DLA definition (2 x 10²⁰ cm^-2), in ‘sub-DLAs’ with 10¹⁹ < N(HI) < 2 x 10²⁰ cm^-2. Here we present a sample of sub-DLAs issued from UVES archive quasar spectra. We have measured the sub-DLA number density redshift evolution and directly establish their column density distribution function. We have also undertaken a detailed metal abundance analysis of this class of absorbers to compare with the characteristics of the well studied DLAs. This revised version was published online in September 2006 with corrections to the Cover Date.     

A general algorithm for the determination ofT j (n) andZ j *(n) in Hori's method for non-canonical systems

A general algorithm for the determination ofT _j ⁽ⁿ⁾ andZ _j ^*(n) is deduced. This algorithm is obtained from the general solution of non-homogeneous linear differential equations with variable coefficients in their matricial form. To do this a new functionX ^*(n) associated withZ ^*(n) is introduced. Then it is possible to calculateZ ^*(n) such that it contains secular or mixed secular terms and soT ⁽ⁿ⁾ is free from these terms.     

Measurements in N2-CH4(C2H2) discharges of reaction rates and thermochemical constants for Titan atmosphere study

The kinetic reactions in N2-xCH4(C2H2) gas discharges with x less than 1% have been studied by emission spectroscopy in the afterglow of D.C. discharges and by mass spectroscopy from radiolysis ionization using alpha particles. The pressure range is from several Torr to 100 Torr. At the end of N2 D.C. discharges at room temperature, for a residence time of about 10(-2) s, the dominant active species are the N atoms with density of 10(14)-10(15) cm-3 for N2 density of about 10(17) cm-3 (3 Torr), the N2(X,V) vibrational molecules with for example [N2(X,V = 10)] approximately 10(14) cm-3 and the electronic metastable molecules N2(A 3 sigma u +) with a density of 10(12) cm-3. In such conditions, the following kinetic reactions have been studied: N2(A) + N2(A) --> N2(C,B,V') + N2(X), N2(A) + N2(X,V>5) --> N2(X) + N2(B,V') in pure N2 post-discharges and N2(A) + CH4 --> products, C + N + M2 --> CN(B,V') + M2, N2(X,V>4) + CN --> N2(X) + CN(B,A,V'), in N2-1% CH4 post-discharges. The clustering reactions of N2-(1-5%)CH4(C2H2) gas mixtures after radiolysis ionization have been studied for the H2CN+ nN2 ions and the equilibrium constants have been determined in the temperature range T = 140-300 K.     

Multi-cloud model (MCM) method and its applications to the study on asymmetric spectral profiles

A method of multi-cloud model (MCM) is proposed in this paper in order to research asymmetric profiles of spectral line formed by solar discrete active objects aligned along the line-of-sight difection. Based on the MCM method, under the conditions of certain assumptions and approximations, the line-of-sight velocityV and three other physical parameter approximation values, (i.e. Doppler width _D , source functionS and optical depth at line center ₀) within different clouds may be derived simultaneously by fitting both profiles theoretical and observational. An application example of the method withm=3 shows that MCM method is suitable to measure the velocity fields of multi-object at the same time from their non-Gaussian profiles of complex. TheV and _D derived from the method are reliable,S and ₀ are approximation. An influence of the variations of initial values in the parameter on the solution is given as well.     

The spatial extent of aurorae in O(5577) and Na2(4278) emissions

An investigation of the spatial extent of aurorae was undertaken from College, Alaska, by the ground based Lockheed two channel (5577 and 4278 Å) image intensifier TV system and with a multichannel boresighted tilting filter photometer. The measurements indicate that even on clear nights the extinction due to scattering in the 4278 Å is significant unless the measurements are taken at small zenith angles. To confirm the results and to avoid the low altitude scattering problem, measurements were made on a quite arc with the Lockheed 6 channel tilting filter zenith photometer during the NASA CV 990 expedition. These results show that in the cases observed there was no significant difference between the latitude profiles of O(5577) and N₂⁺(4278) emissions.     

An indirect mechanism for the production of O(1S) in the aurora

Recent laboratory measurements of the deactivation rate constants for O(¹S) have suggested that the dominant production mechanism for the green line in the nightglow is a two-step process. A similar mechanism involving energy transfer from an excited state of molecular oxygen is considered as a potential source of the OI (5577 Å) emission in the aurora. It is shown that the mechanism, $\text{O}{}_2\text{+ e → O}{}_2{}^1\text{+ e O}{}_2{}^1\text{+ O → O}{}_2\text{+ O(}{}^1\text{S}\text{)}$, is consistent with auroral observations; the intermediate excited state has been tentatively identified as the O₂(c¹∑^?_u) state. For the proposed energy transfer mechanism to be the primary source of the auroral green line, the peak electron impact cross-section for O₂¹ production must be approximately 2 × 10^?17 cm².     

一种基于MUSIC算法的天地波识别方法

基于我国BPL长波脉冲信号的特征,利用MUSIC(多信号分类)算法对BPL天、地波延迟进行估计,实现天、地波识别。对传统谱估计IFFT(快速傅里叶逆变换)算法和现代谱估计MUSIC算法进行了仿真和比较,结果表明,这两种方法在较低信噪比条件下可有效分离天、地波,且识别误差都能控制在±5μs内,但MUSIC算法比IFFT算法具有更高的精度和分辨率。     

An Accessible Model of Dynamics and Cycle for Interstellar OH and H2O Maser Associations

An accessible model for interstellar OH/H₂O maser associations is presented. It can be classified into radiative pumping model. It can close the dynamical cycle of H₂O and OH species, and can give an interpretation on interstellar OH/H₂O associations. A reasonable scheme for both regeneration and destruction of interstellar H₂O and OH molecules is argued. Our model has overcome the defects of former radiative models, and is compatible with astronomical conditions. It is shown that the rotational population of H₂O and OH in these regions is much less affected by collisions than by radiation. Some experiments have confirmed our proposal.     

Suggestion for searh of ethylene oxide ($$-C2H4O) in a osmi objet

Ethylene oxide (\(c\)-C₂H₄O) and its isomer acetaldehyde (CH₃CHO) are important organic molecules because of their potential role in the formation of amino acids. The \(c\)-C₂H₄O molecule is a \(b\)-type asymmetric top molecule and owing to half-spin of each of the four hydrogen atoms, it has two distinct ortho (nuclear spin one) and para (nuclear spin zero and two) species. It has been detected in the Sgr B2N. Using the rotational and centrifugal distortion constants along with the electric dipole moment, we have calculated energies of 100 rotational levels of each of the ortho and para species of \(c\)-C₂H₄O molecule and the Einstein \(A\)-coefficients for radiative transitions between the levels. The values of Einstein \(A\)-coefficients along with the scaled values for the collisional rate coefficients are used for solving a set of statistical equilibrium equations coupled with the equations of radiative transfer.Brightness-temperatures of five rotational transitions of each of the ortho and para species of \(c\)-C₂H₄O molecule are investigated. Out of these ten transitions, three transitions are found to show the anomalous absorption and rest seven are found to show the emission feature. We have also investigated seven transitions observed unblended in the Sgr B2(N). We have found that the transitions \(3_{3 0} - 3_{2 1}\) (23.134 GHz), \(2_{2 0} - 2_{1 1}\) (15.603 GHz), \(3_{3 1} - 3_{2 2}\) (39.680 GHz) and \(1_{1 1} - 0_{0 0}\) (39.582 GHz) may play important role for the identification of ethylene oxide in a cosmic object.     

An analytic algorithm for global coverage of the revisiting orbit and its application to the CFOSAT satellite

This paper addresses a new analytic algorithm for global coverage of the revisiting orbit and its application to the mission revisiting the Earth within long periods of time, such as Chinese-French Oceanic Satellite (abbr., CFOSAT). In the first, it is presented that the traditional design methodology of the revisiting orbit for some imaging satellites only on the single (ascending or descending) pass, and the repeating orbit is employed to perform the global coverage within short periods of time. However, the selection of the repeating orbit is essentially to yield the suboptimum from the rare measure of rational numbers of passes per day, which will lose lots of available revisiting orbits. Thus, an innovative design scheme is proposed to check both rational and irrational passes per day to acquire the relationship between the coverage percentage and the altitude. To improve the traditional imaging only on the single pass, the proposed algorithm is mapping every pass into its ascending and descending nodes on the specified latitude circle, and then is accumulating the projected width on the circle by the field of view of the satellite. The ergodic geometry of coverage percentage produced from the algorithm is affecting the final scheme, such as the optimal one owning the largest percentage, and the balance one possessing the less gradient in its vicinity, and is guiding to heuristic design for the station-keeping control strategies. The application of CFOSAT validates the feasibility of the algorithm.     

Dynamics of the O H2O charge-transfer reaction and its implications for space-borne measurements

O⁺(⁴S) + H₂O charge-transfer cross-section and product-ion time-of-flight measurements are presented over a center-of-mass collision energy range of 0.2–15 eV. The results are obtained with a newly constructed guided-ion beam experiment. The measured energy dependence of the charge-transfer crosssection agrees well with previous measurements and ADO model predictions of Bates [Chem. Phys. Lett. 82, 396 (1981) Proc. R. Soc. Lond. A384, 289 (1982) Chem. Phys. Lett. 111, 428 (1984)] at low collision energies, but exhibits significant differences at collision energies above 2 eV. The product kinetic energy analysis shows that most of the product ions are produced with near-thermal kinetic energies. At low collision energies, a significant backscattered channel is observed that is associated with complex formation. This channel exhibits a cross-section of approximately 1.4 Ųat a collision energy of 2.65 eV, corresponding to a laboratory ion energy of 5 eV.     

Jupiter: An inhomogeneous atmospheric model analysis of spatial variations of the H2 4-0 S(1) line

An analysis of the structure of the Jovian atmosphere, primarily based on center-to-limb variations (CTLV) of the equivalent width of the hydrogen quadrupole 4-0 S(1) line, is presented. These data require that the atmosphere have regions of both long- and short- scattering mean free paths. Two alternative cloud structures which fit the data are developed. The first is a two-cloud model (TCM) consisting of a thin upper cloud and a lower semi-infinite cloud, with absorbing gas between the clouds and above the upper cloud. The second model is a reflecting-scattering model (RSM), in which a gas layer lies above a haze consisting of scattering particles and absorbing gas. The cloud-scattering phase function in both models must have a strong forward peak. The CTLV data require, however, the presence of a backscattering lobe on the phase function, with the backscattering intensity about 4% of the forward scattering. The decrease in reflectivity of all regions from the visible to the ultraviolet is explained by the presence of dust particles mixed with the gas. Most of the ultraviolet absorption in the atmosphere must occur above the upper cloud layer. Particles with a uniform distribution of radii from 0.0 to 0.1 μm with a complex index of refraction varying as λ^?2.5 are used. The contrast in reflectivity between belts and zones may be explained by the larger concentration of dust in the belts than in the zones. Spatially resolved ultraviolet limb-darkening curves will help to determine the dust distribution of the Jovian atmosphere. The visible methane bands at λλ 6190, 5430, and 4860 Å are analyzed in terms of these models. We derive a methane-to-hydrogen mixing ratio of 2.8 × 10^?3, which is about 4.5 times the value for solar composition.