Effect of severe geomagnetic storm conditions on atomic oxygen greenline dayglow emission in mesosphere

Severe geomagnetic storms and their effects on the 557.7 nm dayglow emission are studied in mesosphere. This study is primarily based on photochemical model with the necessary input obtained from a combination of experimental observations and empirical models. The model results are presented for a low latitude station Tirunelveli (8.7°N, 77.8°E). The volume emission rates are calculated using MSISE-90 and NRLMSISE-00 neutral atmospheric models. A comparison is made between the results obtained from these two models. A positive correlation amongst volume emission rate (VER), O, O₂ number densities and Dst index has been found. The present results indicate that the variation in emission rate is more for MSISE-90 than in NRLMSISE-00 model. The maximum depletion in the VER of greenline dayglow emission is found to be about 30% at 96 km during the main phase of the one of the geomagnetic storms investigated in the case of MSISE-90 (which is strongest with Dst index −216 nT). The O₂ density decreases about 22% at 96 km during the main phase of the same geomagnetic storm.The NRLSMSISE-00 model does not show any appreciable change in the number density of O during any of the two events. The present study also shows that the altitude of peak emission rate is unaffected by the geomagnetic storms. The effect of geomagnetic storm on the greenline nightglow emission has also been studied. It is found that almost no correlation can be established between the Dst index and variations in the volume emission rates using the NRLMSISE-00 neutral model atmosphere. However, a positive correlation is found in the case of MSISE-90 and the maximum depletion in the case of nightglow is about 40% for one of the storms. The present study shows that there are significant differences between the results obtained using MSISE-90 and NRLMSISE-00.     

Spatio-temporal structure of the wave packets generated by the solar terminator

Using long-term (1998--2009) total electron content (TEC) measurements from the GPS global network including dense network of GPS sites in USA and Japan, we have obtained the first data regarding the spatio-temporal structure and the statistics of medium-scale traveling wave packets (MS TWPs) excited by the solar terminator (ST). Total amount of the detected TWPs exceeds 565,000. There is no correlation between TWPs occurrence and geomagnetic and solar activity. We found that the diurnal, seasonal and spectral MS TWPs characteristics are specified by the solar terminator (ST) dynamics. MS TWPs are the chains of narrow-band TEC oscillations with single packet’s duration of about 1–2 h and oscillation periods of 10–20 min. The total duration of chain is about 4–6 h. The MS TWPs spatial structure is characterized by a high degree of anisotropy and coherence at the distance of more than 10 wavelengths. Occurrence rate of daytime MS TWPs is high in winter and during equinoxes. Occurrence rate of nighttime MS TWPs has its peak in summer. These features are consistent with previous MS travelling ionosphere disturbance (TID) statistics obtained from 630-nm airglow imaging observations in Japan. In winter, MS TWPs in the northern hemisphere are observed 3–4 h after the morning ST passage. In summer, MS TWPs are detected 1.5–2 h before the evening ST appearance at the point of observations, but at the moment of the evening ST passage in the magneto-conjugate point. The obtained results are the first experimental evidence for the hypothesis of the ST-generated ion sound waves.     

Progress in demonstrating homochiral selection in prebiotic RNA synthesis

The dual properties of RNA as an enzyme catalyst (ribozyme) and its ability to store genetic information suggest that early life could have been based on RNA. We have synthesized RNA oligomers up to 50-mer chain lengths by Na⁺-montmorillonite catalyzed reactions of 5′-activated mononucleotides. For studying chiral selectivity, the reactions of racemic mixtures of D, L-ImpA and D, L-ImpU were carried out on Na⁺-montmorillonite. The dimer, trimer, tetramer and pentamer fractions (yields 43.3%, 14.5%, 5.8% and 3.0%, respectively) were investigated for homochiral selection. These products were collected via ion exchange HPLC, their terminal 5′-phosphate was cleaved by alkaline phosphatase and further analyzed by reverse phase HPLC. Twelve linear and three cyclic dimers were isolated and characterized. The homochirality of dimers was 63.5 ± 0.8%. Out of the sixteen trimers isolated, ten were homochiral with an overall homochirality of 74.2 ± 1.6%. The tetramers and pentamers were separated into 24 and 20 isomers, respectively. Their co-elution with those formed in the binary reactions of D-ImpA with D-ImpU on Na⁺-montmorillonite revealed 92.7 ± 2.0% and 97.2 ± 0.5% homochirality, respectively. These results suggest that Na⁺-montmorillonite not only catalyzes the prebiotic synthesis of RNA but it also facilitates homochiral selection. Work is in progress to determine chiral selectivity in the reaction mixtures of activated nucleotides of racemic A, U, G and C on Na⁺-montmorillonite.     

电性拓扑态指数预测硝基类含能材料撞击感度

应用电性拓扑态(E-state)指数模拟分析了硝基类含能化合物的撞击感度,采用逐步回归构建了5个变量的定量结构-性质相关模型,模型的相关系数和标准偏差分别为0.907和0.1713,交叉验证相关系数及均方根误差分别为0.941和0.1869,模型具有较高的可靠性、相关度和预测能力。模型分析表明,电性拓扑态指数与硝基类化合物的撞击感度有较好的相关性,原子的电性状态是影响撞击感度的重要因素。     

Morphology of OI 8446 Å dayglow emission

A comprehensive model is developed to study the atomic oxygen OI 8446 Å dayglow emission. The emission rate profiles and intensities are obtained using the recently developed Solar2000 EUV (Extreme Ultra Violet) flux model. These emission profiles are used to construct the morphology of the 8446 Å emission between equator and 45°N in the northern hemisphere. The longitudinal variation of 8446 Å dayglow emission is found about 5% and is not included in the presentation of morphology. A span of five years is chosen to study the effect of varying solar activity on the morphology of the OI 8446 Å dayglow emission. The morphology is studied on April 3 which lies under the equinox conditions. In year 2001 the solar F10.7 index on the chosen date was as high as 223.1 which is the case of solar maximum. From the present calculations it is found that the intensity does not vary linearly with the F10.7 solar index. The morphology shows that the region of maximum emission rate expands towards the higher latitudes as F10.7 solar index increases. The similar effects have also been found in the morphology of 7320 Å dayglow emission (Sunil Krishna and Singh, 2009). The similarities in the morphology of 7320 Å and 8446 Å dayglow emissions further suggest that the photoelectron flux has strong bearing on the production of these emissions.     

A model study of the negative chlorine ion chemistry in the Earth’s mesosphere

An ion chemistry model is used to investigate the negative chlorine ion chemistry of the mesosphere for quiet ionospheric conditions. Model results are presented for high latitudes in February as well as for the equator in Summer. For nighttime, Cl^-${\text{Cl}}^{-}$, Cl^-${\text{Cl}}^{-}$(HCl), and NO₃⁻(HCl) are the most abundant chlorine anions in the mesosphere. The concentration of ClO₃⁻ depends significantly on its stability against collision-induced dissociation. In contrast to previous model predictions, the abundance of Cl^-(_H2O)${\text{Cl}}^{-}({\mathrm{H}}_2\mathrm{O})$ is small. For daytime, photoelectron detachment and photodissociation have pronounced impact on the negative chlorine ion chemistry in the mesosphere. The abundance of all anion cluster is considerably smaller than at night. While Cl^-${\text{Cl}}^{-}$ decreases in the upper mesosphere, its abundance increases at lower altitudes.     

离子束增强沉积TiB2薄膜的耐蚀性能研究

研究了在紫铜基材上用离子束增强沉积法（ＩＢＥＤ）沉积ＴｉＢ２薄膜后，在６００，７００和８００℃的空气中氧化的动力学曲线；在ＩＮＨ２ＳＯ４溶液中，用动电位扫描法测定了其极化曲线和极化阻力，用ＳＥＭ观察了其形貌，用俄歇电子谱仪（ＡＥＳ）分析了膜的成份，用Ｘ－射线衍射仪（ＸＲＤ）研究了膜的微观结构；讨论了ＴｉＢ２薄膜具有优良耐蚀性的机理。     

Nonlinear quantum ion acoustic shock wave dynamics with exchange-correlation effects

The dynamics of linear and nonlinear electrostatic shock excitations is studied in homogeneous, unmagnetized, unbounded and dissipative quantum plasma consisting of electrons and ions. The dissipation in the system is taken into account by incorporating the ion kinematic viscosity. The system is modelled using the quantum hydrodynamic equations in which the electrons are significantly affected by the quantum forces, viz., the quantum statistical pressure, the quantum Bohm potential and electron exchange-correlations due to electron spin. In the weakly nonlinear limit, using reductive perturbation method deformed Korteweg-de Vries Burgers’s (KdVB) equation, which elegantly combines the effects of nonlinearity, dispersion and dissipation is derived. It is found that the present model predicts the existence of both nonlinear oscillatory and monotonic shock structures. The temporal evolution, stability and phase-space dynamics of nonlinear ion acoustic shocks are investigated numerically to elucidate the effects of quantum diffraction, electron exchange correlation and ion kinematic viscosity.     

基于薄膜热电堆的新型高温瞬态热流密度传感器的研制

目前针对国内薄膜瞬态热流传感器一致性较差、制备工艺不成熟等问题，提出了一种基于光刻工艺和离子束溅射镀膜工艺的制备方法，200对T型金属薄膜热电偶沉积在10mm×10mm的水冷块上，测量1μm的氧化铝热阻层温差，从而得到瞬态热流密度值。对新型高温瞬态热流密度传感器进行比对法标定，一致性误差为0.211%，即工艺的一致性约为99.79%。实验表明，研制的新型高温瞬态热流密度传感器的一致性好,制备工艺具备良好重复性和可移植性，能够满足高温瞬态热流检测需要，为热流传感器的推广应用及标准化、批量化生产提供了良好的技术支撑。