Vertical distribution of NH3 in the upper Jovian atmosphere from IUE observations

The first unambiguous identification of ammonia in the upper atmosphere of Jupiter has been obtained from the observation of individual NH₃ bands in an IUE high resolution spectrum in the 2100–2400 Å spectral range. The variation with wavelength of the strengths of these NH₃ bands implies that the NH₃ abundance has to be strongly reduced by photolysis in the upper jovian atmosphere. Preliminary analysis by means of scattering models shows that the ammonia mixing ratio cannot be constant with altitude. The mixing ratio NH₃/H₂ ranges from 5 10^?8 to 5 10^?7 at the 250 mb pressure level, and decreases as P or P² toward higher altitudes.     

Mesospheric H2O and H2O2 densities inferred from in situ positive ion composition measurement

The measurements of positive ion composition in the high latitude D-region have revealed an excess of 34⁺ under distrubed conditions which has been interpreted as H₂O₂⁺. At the same altitude range near the transition height oxonium ions were measured as well. This paper presents a new model for the production and loss of oxonium ions with their production from H₂O₂⁺ + H₂O → H₃O⁺ + HO₂ and their loss by attachment of N₂ and/or CO₂. A reaction constant of 8.5×10^?28 (300/T)⁴ cm⁶s^?1 has been obtained for the three body attachment H₃O⁺ + CO₂ + M → H₃O⁺.CO₂ + M from the measured density profile of 63⁺ in flight 18.1020. Mesospheric H₂O and H₂O₂ densities are inferred from measurements of four high latitude ion compositions based on the oxonium model. The mixing ratios of hydrogen peroxide are up to two orders of magnitude higher compared to previous model calculations. In order to explain the missing production of odd hydrogen, we consider larger O(¹D) densities, surface reactions of O(³P) on particles, and cathalytic photodissociation of water vapor on aerosol particles.     

Occurrence features of simultaneous H+- and He+-band EMIC emissions in the outer radiation belt

As an important loss mechanism of radiation belt electrons, electromagnetic ion cyclotron (EMIC) waves show up as three distinct frequency bands below the hydrogen (H⁺), helium (He⁺), and oxygen (O⁺) ion gyrofrequencies. Compared to O⁺-band EMIC waves, H⁺- and He⁺-band emissions generally occur more frequently and result in more efficient scattering removal of <～5?MeV relativistic electrons. Therefore, knowledge about the occurrence of these two bands is important for understanding the evolution of the relativistic electron population. To evaluate the occurrence pattern and wave properties of H⁺- and He⁺-band EMIC waves when they occur concurrently, we investigate 64 events of multi-band EMIC emissions identified from high quality Van Allen Probes wave data. Our quantitative results demonstrate a strong occurrence dependence of the multi-band EMIC emissions on magnetic local time (MLT) and L-shell to mainly concentrate on the dayside region of L?=?～4–6. We also find that the average magnetic field amplitude of H⁺-band waves is larger than that of He⁺-band waves only when L?<?4.5 and AE¹?<?300?nT, and He⁺-band emissions are more intense under all other conditions. In contrast to 5 events that have average H⁺-band amplitude over 2 nT, 19 events exhibit >2 nT He⁺-band amplitude, indicating that the He⁺-band waves can be more easily amplified than the H⁺-band waves under the same circumstances. For simultaneous occurrences of the two EMIC wave bands, their frequencies vary with L-shell and geomagnetic activity: the peak wave frequency of H⁺-band emissions varies between 0.25 and 0.8 f_cp with the average between 0.25 and 0.6 f_cp, while that of He⁺-band emissions varies between 0.03 and 0.23 f_cp with the average between 0.05 and 0.15 f_cp. These newly observed occurrence features of simultaneous H⁺- and He⁺-band EMIC emissions provide improved information to quantify the overall contribution of multi-band EMIC waves to the loss processes of radiation belt electrons.     

The impact of dust grains on fast fly-by spacecraft: Momentum multiplication,measurements and theory

Energy partitioning during the very high impact speed encountered in a cometary fly-by mission causes a target mass expulsion which leads to a momentum impulse on the target exceeding that of the incident momentum. Theoretical and computational studies are required to provide a basis for predictions of the response at Halley encounter, since experimental data from acceleration of microspheres extends currently only to some 10 kms^?1. Such data obtained from the 2 MV Canterbury microparticle accelerator is presented: this demonstrates a target momentum enhancement E which can be approximated by a form E = 1+(V/V_o)^β. Over the range 1 to 8 kms^?1 the relationship is satisfied by V_o = 2 kms^?1 and β = 2. Theoretical considerations of energy partitioning lead to constraints on the extrapolation of this functional dependence to very high velocities and the transition to β ≤ 1 is shown to apply. Results are examined and their significance to impact sensing and spacecraft deceleration discussed. An enhancement of momentum nearer to 12±3 at 69 kms^?1 is anticipated for non-penetrating particles, from the ballistic pendulum data, but the ES data indicates a figure considerably higher.     

Antioxidant capacity reduced in scallions grown under elevated CO2 independent of assayed light intensity

Long-duration manned space missions mandate the development of a sustainable life support system and effective countermeasures against damaging space radiation. To mitigate the risk of inevitable exposure to space radiation, cultivation of fresh fruits and vegetables rich in antioxidants is an attractive alternative to pharmacological agents. However it has yet to be established whether antioxidant properties of crops can be preserved or enhanced in a space environment where environmental conditions differ from that which plants have acclimated to on earth. Scallion (Allium fistulosum) rich in antioxidant vitamins C and A, and flavonoids was used as a model plant to study the impact of a range of CO₂ concentrations and light intensities that are likely encountered in a space habitat on food quality traits. Scallions were hydroponically grown in controlled environmental chambers under a combination of 3 CO₂ concentrations of 400, 1200 and 4000 μmol mol⁻¹ and 3 light intensity levels of 150, 300, 450 μmol m⁻² s⁻¹. Total antioxidant activity (TAA) of scallion extracts was determined using a radical cation scavenging assay. Both elevated CO₂ and increasing light intensity enhanced biomass accumulation, but effects on TAA (based on dry weight) differed. TAA was reduced for plants grown under elevated CO₂, but remained unchanged with increases in light intensity. Elevated CO₂ stimulated greater biomass production than antioxidants, while an increase in photosynthetic photo flux promoted the synthesis of antioxidant compounds at a rate similar to that of biomass. Consequently light is a more effective stimulus than CO₂ for antioxidant production.     

Expanding shells of young pulsars as sources of high-energy neutrinos

The initial power outputs P_o of pulsars are not yet well known, but these seem to follow approximately a distribution law N(> P_o) ∝ P_o⁻ⁿ where 0.5 ≤ n ≤ 1.0. It seems likely that P_o ≥ 10³⁸ ergs/sec. With these assumptions, we estimate that the DUMAND detector can record ≥ 10³ high-energy (> 4 TeV) neutrino events in a four-month period per Galactic supernova; (in our Galaxy, these are estimated to occur at the rate of about 8 per century.) Neutrinos from supernova shells in the Virgo supercluster would be marginally detectable (one very bright supernova per decade at about 20 Mpc) if N(> P_o) ∝ P_o^−0.5, but undetectable if N(> P_o) ∝ P_o⁻¹. The diffuse flux summed over distant extragalactic supernovae is likely to be well below the detection threshold.     

Annealing of Hg2Cl2 crystals — Project of the experiment

The creep of polycrystalline Hg₂X₂ (where X = Cl, Br, J) under the terrestrial and space conditions is studied in the present experiment. The authors suppose that the creep of the Hg₂X₂ cylindrical sample can be studied by the help of the theory of micropolar (non-Newtonian) fluids. In accordance with this theory we obtain the flux of fluid through any cross-section as functions of the radius, viscosity coefficients, the gradient of pressure and the gravity acceleration. In this paper a comparison of the theoretical results for normal and zero- gravity conditions is given. It is shown that the annealing of materials having a broad region of plasticity under microgravity conditions can lead to great improvement in optical as well as mechanical qualities of the crystal. Technical aspects of the experiment are also described.     

In situ results on the variation of neutral atmospheric hydrogen at venus

The concentrations of neutral hydrogen within the atmosphere of Venus are investigated for the period 1979–1980. During this period, the planet made nearly three orbits about the Sun, so that nearly three complete diurnal cycles were observed from the Pioneer Venus Orbiter (PVO). Values of n(H) are derived from in-situ ion and neutral composition measurements from the Orbiter Ion Mass Spectrometer (OIMS) and the Orbiter Neutral Mass Spectrometer (ONMS) using a charge exchange relationship involving O⁺, H⁺, O and CO₂. The dawn bulge in the diurnal distribution of n(H), reported from the first diurnal cycle by Brinton et al., is found to persist with n(H) peaking at levels near 2 - 5 × 10⁷/cm³ at altitudes below 165 km. At peak levels, the bulge exhibits a concentration ratio up to 400/1 relative to dayside values. Large day to day variations of up to a factor of five in n(H) are frequently encountered, and are attributed to perturbations induced by the solar wind interaction. These short term variations, plus a suggestion of some local time variation in the bulk location, make precise assessment of interannual variations in the n(H) difficult. Between the first diurnal cycle in early 1979 and the third in mid 1980, the decline in solar euv flux was of the order of 10% or less. Allowing for uncertainties due to short term variations, no clear evidence is found for an interannual variation in the hydrogen concentrations.     

Measurement of minor species (H2, Cl,O3, NO) in the earth's atmosphere by the occultation technique

The stellar occultation technique is a clean and powerful means of detecting and quantifying minor gases in the earth's atmosphere. The results obtained are totally insensitive to knowledge of the absolute flux of the star, and are not influenced by instrument calibration problems. Pioneering observations of nocturnal mesospheric ozone and thermospheric molecular oxygen by the stellar occultation technique were made in 1970 and 1971 with the Wisconsin stellar photometers on board the Orbiting Astronomical Observatory-2. A limb crossing geometry was used. The high resolution Princeton ultraviolet spectrometer aboard Copernicus was used in the summers of 1975, 1976 and 1977 to measure altitude profiles of molecular hydrogen, atomic chlorine and nitric oxide in addition to ozone and molecular oxygen. A limb grazing geometry was employed. The ozone densities show wide variation from orbit to orbit and particularly betewen the OAO-2 and Copernicus observations. A H₂ density of 1×10⁸ cm^?3 at 95 km, and a NO density less than 10⁶ cm^?3 for altitudes greater than 85 km were measured.     

The O2+ vibrational distribution in the Venusian ionosphere

Calculations are presented of the vibrational distribution of O₂⁺ in the Venusian ionosphere for a model atmosphere based on Pioneer Venus data. At 100 km, quenching precludes the survival of vibrationally excited O₂⁺. At the exobase, near 200 km, more than half are vibrationally excited. The effects of vibrationally excited O₂⁺ on the hot oxygen corona and the airglow are discussed.     

F-Region ion composition modeling

Measurements of the principal ion species of the F₁- and F₂- regions have been used to develop an empirical model of the ion composition for altitudes between 150 and 500 km. The species measured by the S3-1 satellite include N⁺, O⁺, N₂⁺, NO⁺ and O₂⁺. The data were obtained near the minimum of the solar cycle, thus limited information on the ionospheric variation with solar flux is available. However, the range of latitude, altitude, local time and geomagnetic activity does provide a useful basis for modeling the F-region. The ion composition measurements have been used to provide a model for relative ion composition which is compatible with the total ion density from the International Reference Ionosphere model.     

断裂韧性K1C和断裂门槛值 Δ Kth可靠性测定方法

采用定量方程随机化方法,建立了断裂p-J_R-Δa曲线方程,断裂p-J_R-Δa曲线与钝化线的交点即为试验测定具有可靠度p的J积分临界值(J_1C)_p值,根据断裂力学测试原理,由试验测定(J_1C)_p值可转化出断裂韧性(K_1C)_p值;还建立了断裂门槛ΔK_th值的可靠性测定方法,并对试验数据进行了统计分析处理,得到了一些具有重要应用价值的结果和数据.研究发现:断裂门槛值ΔK_th服从正态分布.     

Collisional excitation of vinylidene (H2CC)

Though H₂CO, H₂CS, H₂CCC, H₂CCCC, H₂CCO have been identified in cool interstellar molecular clouds, identification of H₂CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H₂CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H₂CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ as a function of energy E   of the colliding partner. After averaging the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ over a Maxwellian distribution, the parameters Q(L,M,M^′|T)$Q(L\text{,}M\text{,}{M}^{\prime }|T)$ as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated.     

Solar cycle effect on temporal and spatial variation of topside ion density measured by SROSS C2 and ROCSAT 1 over the Indian longitude sector

We investigated the diurnal, seasonal and latitudinal variations of ion density Ni over the Indian low and equatorial topside ionosphere within 17.5°S to 17.5°N magnetic latitudes by combining the data from SROSS C2 and ROCSAT 1 for the 9 year period from 1995 to 2003 during solar cycle 23. The diurnal maximum density is found in the local noon or in the afternoon hours and the minimum occurs in the pre sunrise hours. The density is higher during the equinoxes as compared to that in the June and December solstice. The local time spread of the daytime maximum ion density increases with increase in solar activity. A north south asymmetry with higher ion density over northern hemisphere in the June solstice and over southern hemisphere in December solstice has been observed in moderate and high solar activity years. The crest to crest distance increases with increase in solar flux. Ion density bears a nonlinear relationship with F_10.7 cm solar flux and EUV flux in general. The density increases linearly with solar flux up to ∼150 sfu (1 sfu = 10⁻²²Wm⁻²Hz⁻¹) and EUV flux up to ∼50 units (10⁹ photons cm⁻² s⁻¹). But beyond this the density saturates. Inverse saturation and linear relationship have been observed in some season or latitude also. Inter-comparison of the three solar activity indices F_10.7 cm flux, EUV flux and F_10.7P (= (F_10.7 + F_10.7A)/2, where F_10.7A is the 81 day running average value of F_10.7) shows that the ion density correlates better with F_10.7P and F_10.7 cm fluxes. The annual average daytime total ion density from 1995 to 2003 follows a hysteresis loop as the solar cycle reverses. The ion density at 500 km over the Indian longitude sector as obtained by the international reference ionosphere is in general lower than the measured densities during moderate and high solar activity years. In low solar activity years the model densities are equal or higher than measured densities. The IRI EIA peaks are symmetric (±10°) in equinox while densities are higher at 10°N in June solstice and at 10°S in the December solstice. The model density follows F_10.7 linearly up to about F_10.7 > ∼150 sfu and then saturates.     

Direct and indirect estimates of turbulence around the turbopause

Direct and indirect estimates of turbulence parameters at altitudes 80–120 km are reviewed. It is shown that there are contradictions in data on absolute value, shape, seasonal variations etc. of eddy diffusion coefficient K_t revealed or accepted by different authors. The strongest contradiction is in the views on the seasonal variations of turbulence. Possible explanation may be connected with the correct account for mean motions. Data on turbopause height obtained from neutral composition data (Ar, N₂) are discussed. The revealed reverse connection of this height with the temperature at 120 km is discussed in terms of K_t dependence on temperature gradient.     

High-density and high-temperature molecular gas around the AGN in M51

We investigated the physical properties of molecular gas in the nuclear region of M51 (Seyfert 2). We obtained an aperture synthesis ¹³CO(J = 1 − 0) image using the Nobeyama Millimeter Array (NMA), and compared it with NMA ¹²CO(J = 1 − 0) and HCN(J = 1 − 0) maps at similar spatial resolutions. Within a radius of 180 pc from the center, the ¹³CO(1 − 0) integrated intensity was found to be 3 times weaker than that of HCN(1 − 0). Large-Velocity-Gradient (LVG) calculations suggest that the observed high HCN(1 − 0)/¹³CO(1 − 0) intensity ratio would arise from dense (n_H2 ∼ 10⁵ cm⁻³) and hot (T_kin ≳ 300 K) molecular clouds in the nuclear molecular disk. We also observed in the ¹²CO(1 − 0), (3 − 2), ¹³CO(1 − 0), and (3 − 2) lines using the Nobeyama 45m and JCMT 15m telescopes. We detected weak ¹³CO lines as well as strong ¹²CO lines. The LVG calculations assuming a two-component model suggest that there is a large amount of low-density (n_H2 ∼ 3 − 6 × 10² cm⁻³), low-temperature (T_kin ∼ 20 – 50 K) gas, and a small amount of high-density (n_H2 ≳ 10⁴ cm⁻³), high-temperature (T_kin ≳ 500 K) gas. The existence of the high-density and high-temperature component, although having a quite small beam filling factor, supports the aperture synthesis observation results mentioned above. Since this dense, hot gas is located in the nuclear molecular disk around the Active Galactic Nucleus (AGN), it may be heated by the strong X-ray radiation and/or by the shock induced by the radio jet.     

Possibility to detect the cluster emission up to R200 with XMM-Newton data

We present the results of analysis XMM-Newton data of galaxy cluster CL0016+16, which enables us to trace X-ray emission and temperature profile up to the virial radius. We obtained similar results using three different backgrounds. We checked the possibility of detection of cluster emission up to the virial radius with XMM-Newton data with hydrodynamical cosmology simulation from the Adaptive Mesh Refinement technique, code RAMSES by Teyssier [Teyssier, R. Cosmological hydrodynamics with adaptive mesh refinement. A new high resolution code called RAMSES. A&A 385, 337, 2002], convolution with XMM-Newton and the data base of the spectra by Sauvageot et al. [Sauvageot, J.-L., Belsole, E., Pratt, G.W. The late merging phase of a galaxy cluster: XMM EPIC observations of A 3266. A&A, 444, 673, 2005]. For the first time we were able to compute the mass of CL0016 up to R₂₀₀, we found, assuming hydrostatic equilibrium framework, M₂₀₀ = (1.15 ± 0.11) × 10¹⁵M_⊙.     

Vertical distribution of SO2 in upper cloud layer of Venus and Origin of U.V.-absorption

It is shown that decline of spherical albedo of Venus toward the ultraviolet can be explained by the presence of two absorbing agents: a) SO₂, for which abundance is 10¹¹ cm^?3 at height 68 km and scale height is about 1 km; b) some unknown aerosol absorbent, possibly a 1% FeCl₃ admixture in a sulfuric acid concentrated solution. A mechanism of aerosol formation is proposed.     

Scaling and universality of the thermal conductivity of liquid 4He near the superfluid transition and in restricted geometries

We present measurements of the thermal conductivity λ(t, P, L) = l/ρ(t, P, L) near the superfluid transition of ⁴He at saturated vapor pressure and confined in cylindrical geometries with radii L = 0.5 and 1.0 μm (t ≡ T/T_λ(P) − 1). For L = 1.0 μm measurements at six pressures P are presented. At and above T_λ the data are consistent with a universal scaling function F(X) = (L/ξ_o)^x/ν(ρ/ρ₀), X = (L/ξ_o)^1/νt valid for all P (ρ₀ and x are the pressure-dependent amplitude and effective exponent of the bulk resistivity ρ(t, P, ∞) = ρ₀t^x and ξ = ξ₀t^−ν is the correlation length). Indications of breakdown of scaling and universality are observed below T_λ.