Search

We aim to hunt for massive binaries hosting a black hole companion (OB+BH) and establish the natal mass-ratio distribution of massive stars at the subsolar metallicity environment of the Large Magellanic Cloud (LMC). We use the shift-and-add grid disentangling technique to characterize the hidden companions in 51 SB1 O-type and evolved B-type binaries in the LMC monitored in the framework of the Tarantula Massive Binary Monitoring (TMBM). Out of the 51 SB1 systems, 43 (84%) are found to have non-degenerate stellar companions, of which 28 are confident detections, and 15 are less certain (SB1: or SB2:). Of these 43 targets, one is found to be a triple (VFTS 64), and two are found to be quadruples (VFTS 120, 702). The remaining eight targets (16%) retain an SB1 classification. Aside from the unambiguous case of VFTS 243, analysed in detailed in a separate paper, we identify two additional OB+BH candidates: VFTS 514 and VFTS 779. Additional black holes may be present in the sample but at a lower probability. Our study firmly establishes a virtually flat natal mass-ratio distribution for O-type stars at LMC metallicity, covering the entire mass-ratio range (0.05 < q < 1) and periods in the range 0 < log P < 3 [d]. The nature of the OB+BH candidates should be verified through future monitoring, but the frequency of OB+BH candidates is generally in line with recent predictions at LMC metallicity., 41 pages (14 main article + 27 appendix), accepted to A&A

A localized bond orbital analysis of the bonding in dioxygen and related species provides a unique fundamental insight into its bonding characteristics. It reveals the coalescence of the molecular orbital and valence bond/Lewis approaches and clearly demonstrates that the often stated inability of valence bond theory to describe the bonding of O2 is a myth. The analysis indicates that the σ-bond strength of 3O2 is not weak as previously believed and accounts for much of its enhanced stability compared with hydroperoxyl. We attribute the stability and persistence of 3O2 to a combination of this attribute and favorable maximization of exchange coupling between the valence electrons.

The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long-term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round-trip journey. The L4 mission concept is technically feasible, and is scientifically compelling. ISSN:1542-7390

ispartof: ASTRONOMY & ASTROPHYSICS vol:650 status: published

Dinitrogen activation in non-metallic systems has received considerable attention in recent years. Herein, we report the theoretical feasibility of N2 fixation using aminocarbenes (L) or their anionic derivatives. The molecular descriptors of L and anionic L‾, which affect the interaction of L and anionic L‾ with N2, were identified through multiple linear regression analysis. Additionally, the electron flow during C‒N bond formation was confirmed by performing intrinsic reaction coordination calculations with intrinsic bond orbital analysis for the reaction of anionic L‾ with N2.

Photoswitch triads comprising two dihydroazulene (DHA) units in conjugation with a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and para-disubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. In contrast, for the meta-connected triad, all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. Ultrafast spectroscopy of the photoisomerizations revealed a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversion with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computation (excitation spectra and orbital analysis of the transitions).

Magnetic response properties of 1,2,3,5-tetrazine derivatives including the newly synthesized 4,6-diphenyl-1,2,3,5-tetrazine have been studied computationally at the density functional theory (DFT) level. Calculations of magnetically induced current densities and induced magnetic fields show that the unsubstituted 1,2,3,5-tetrazine is almost as aromatic as benzene. Separating the magnetic shielding functions into molecular orbital components provided additional insights into the magnetic response. The aromatic character estimated from magnetically induced current densities and induced magnetic fields shows that NICS pi zz(0) values and ring-current strengths yield about the same degree of aromaticity, whereas NICSzz(0) and NICSzz(1) values are contaminated by sigma electron contributions. The studied 1,2,3,5-tetrazine derivatives are less aromatic than the unsubstituted one. Calculations of magnetic response properties of 4,6-diphenyl-1,2,3,5-tetrazine showed that it is the least aromatic among the studied molecules according to the ring-current criterion, while 4,6-[1,2,3,5]-ditetrazinyl-1,2,3,5-tetrazine is as aromatic as 4,6-dimethyl-1,2,3,5-tetrazine and slightly less aromatic than the unsubstituted 1,2,3,5-tetrazine.

The gas phase proton transfer process in 1,2,4-triazolium dinitramide (TD) was studied using second-order perturbation theory to determine how the presence of one and two water molecules modifies the potential energy surface that connects the ion pair to the neutral pair. The presence of one water molecule can introduce small proton transfer energy barriers that separate the ion pair from the lower-energy neutral pair. These energy barriers are easily surmounted. Reaction paths were determined for single proton transfers and double proton transfers via one water molecule. In the presence of two water molecules, the global minimum is an ion pair, as are most of the lower-energy local minima. Energy barriers for single, double, and triple proton transfers were also found for TD in the presence of two water molecules. One TD ion pair structure with two water molecules has no corresponding neutral pair energy minimum. A quasi-atomic orbital analysis is used to understand the nature of the bonding in the various species studied in this work.

The effect of methanol group on absorption of SO2 by diamine compound was investigated via density functional theory. It was observed that the presence of methanol group increases the binding energy of absorption. According to the result of binding energy, the di-methanol-diamine (D-b) structure can be the best diamine for SO2 absorption and the results of Gibbs energy verified the most thermodynamically favorable structure. According to the weak energy analysis, the absorption interactions in D-b are both vdW and HB interactions. The result of second-order perturbation energy showed that the interaction of the donor atom of diamine with antibonding orbital of S-O (BD*S) in D-b is the highest which points to the most stable structure. According to molecular frontier orbital analysis, it can be concluded that the absorption of SO2 on the diamines is not very strong and desorption of SO2 would be easier than that the strong chemical absorption.

Often have you heard that complexes containing close Au(I) contacts are strongly influenced by what has come to be known as aurophilic interactions. In this work, local orbital analysis is carried out to separate competing metallophilic and other weak interactions at the correlated level in three selected molecular crystals. We carefully separate and discuss the different contributions to the total interaction energy of dimers and trimers according to their spatial location, and identify the relative weight in binding. Changes according to the orientation of the monomers have also been computed. Our results show that although metallophilic contacts contribute to the overall stability and the structure of the crystals, they are not at all dominant, and ligand–ligand interactions can easily outweigh the latter.

A device called Huge Space Shield (HSS) has been put forward for mitigating global warming. This is a space tethers system, which use cables to connect a shielding surface and a mechanism control. In this study, orbital analysis was carried out to choose the best orbit for getting the best effect. Simulation studies were employed to understand the HSS at the beginning of entering the orbit, which were based on completely and semi-simplified model. Therefore, the force analysis gives rise to the system would not fail in the period of running on the orbit. All the results show that the HSS is stable at launch and operation, which can help ease global warming.

A detailed orbital analysis of two seemingly ordinary classes of complexes of group 12 dications, [M(NH3)4]2+ and [M(PH3)4]2+, M = Zn, Cd, Hg, holds a surprise. The PH3 complexes are text-book examples of tetrahedral bonding, but in the ammine complexes calculations reveal a remarkable degree of mixing between occupied M (n-1)d and NH3 σπ orbitals. A perturbation-based Fock matrix examination traces the origin of this mixing to an energy resonance and improved overlap of interacting orbitals for NH3 ligands. The possibility of probing this anomalous mixing with valence-to-core X-ray emission spectroscopy (V2C XES) is discussed.

Context. A low-mass brown dwarf has been recently imaged around HR 2562 (HD 50571), a star hosting a debris disk resolved in the far infrared. Interestingly, the companion location is compatible with an orbit coplanar with the disk and interior to the debris belt. This feature makes the system a valuable laboratory to analyze the formation of substellar companions in a circumstellar disk and potential disk-companion dynamical interactions. Aims. We aim to further characterize the orbital motion of HR 2562 B and its interactions with the host star debris disk. Methods. We performed a monitoring of the system over ~10 months in 2016 and 2017 with the VLT/SPHERE exoplanet imager. Results. We confirm that the companion is comoving with the star and detect for the first time an orbital motion at high significance, with a current orbital motion projected in the plane of the sky of 25 mas (~0.85 au) per year. No orbital curvature is seen in the measurements. An orbital fit of the SPHERE and literature astrometry of the companion without priors on the orbital plane clearly indicates that its orbit is (quasi-)coplanar with the disk. To further constrain the other orbital parameters, we used empirical laws for a companion chaotic zone validated by N-body simulations to test the orbital solutions that are compatible with the estimated disk cavity size. Non-zero eccentricities (>0.15) are allowed for orbital periods shorter than 100 yr, while only moderate eccentricities up to ~0.3 for orbital periods longer than 200 yr are compatible with the disk observations. A comparison of synthetic Herschel images to the real data does not allow us to constrain the upper eccentricity of the companion., Accepted for publication in A&A. 14 pages, 14 figures, 3 tables. Updated to match published paper. Bug in the computation of the distributions of times at periastron passages corrected, minor effects on other orbital parameters

Bacterial resistance to standard (i.e., β-lactam-based) antibiotics has become a global pandemic. Simultaneously, research into the underlying causes of resistance has slowed substantially, although its importance is universally recognized. Key to unraveling critical details is characterization of the noncovalent interactions that govern binding and specificity (DD-peptidases, antibiotic targets, versus β-lactamases, the evolutionarily derived enzymes that play a major role in resistance) and ultimately resistance as a whole. Herein, we describe a detailed investigation that elicits new chemical insights into these underlying intermolecular interactions. Benzylpenicillin and a novel β-lactam peptidomimetic complexed to the Stremptomyces R61 peptidase are examined using an arsenal of computational techniques: MD simulations, QM/MM calculations, charge perturbation analysis, QM/MM orbital analysis, bioinformatics, flexible receptor/flexible ligand docking, and computational ADME predictions. Several key molecular level interactions are identified that not only shed light onto fundamental resistance mechanisms, but also offer explanations for observed specificity. Specifically, an extended π–π network is elucidated that suggests antibacterial resistance has evolved, in part, due to stabilizing aromatic interactions. Additionally, interactions between the protein and peptidomimetic substrate are identified and characterized. Of particular interest is a water-mediated salt bridge between Asp217 and the positively charged N-terminus of the peptidomimetic, revealing an interaction that may significantly contribute to β-lactam specificity. Finally, interaction information is used to suggest modifications to current β-lactam compounds that should both improve binding and specificity in DD-peptidases and their physiochemical properties.

A combination of computational techniques was used to study the phosphorescent emission of complexes with general formula [Cu 3 ( μ -dppm) 3 ( μ 3 - η 1 -C≡CAr) 2 ]BF 4 , with Ar = aryl. The calculated S 0 –T 1 transition energies are in good agreement with the experimental emission maxima. Natural Transition Orbital analysis of the lowest triplet states indicates that the emission largely originates from a π → π* excitation on one of the two acetylide ligands with only a marginal participation of the trinuclear copper(I) cluster, unlike previously proposed.

Using hybrid density functional theory and a relatively large basis set, the lowest energy equilibrium structure, vibrational spectrum, and natural orbital analysis were obtained for magnesium diboride clusters [(MgB2)x for x=1,2, and 3]. For comparison, boron clusters [Bx for x=2,4, and 6] were also considered. The MgB2 and (MgB2)2 showed equilibrium structures with the boron atoms in arrangements similar to what was obtained for pure boron atoms, whereas, for (MgB2)3 a different arrangement of boron was obtained. From the population analysis, large electron density in the boron atoms forming the clusters was observed.

To better understand the origin and difference associated with chemical stability, water resistance, and shearing viscosity of three types of different oxidized modified starch-based adhesives, a detailed theoretical investigation from a molecular viewpoint has been performed using the AM1 semiempirical level and the DFT-B3LYP level, respectively. As a result, our findings suggest that, by Mulliken population analysis (MPA), frontier orbital analysis, and electrostatic potential (EP) analysis based on B3LYP/6-31G calculations, the chemical stability, water resistance, and shearing viscosity of the oxidized modified starch-based adhesives are uniformly improved and corresponding difference for each property presents an identical order: the oxidized grafted cross-linked starch-based adhesive > the oxidized grafted starch-based adhesive > the oxidized starch-based adhesive, which is well consistent with experimental results.

Density functional theory as well as Møller-Plesset investigations has been carried out on tetrafluoro cyclobutadiene, C4F4, to explore the origin of its nonplanarity. Although Petersson et al. (Petersson, E. J.; Fanuele, J. C.; Nimlos, M. R.; Lemal, D. M.; Ellison, G. B.; Radziszewski, J. G. J. Am. Chem. Soc. 1997, 119, 11122-11123) had earlier predicted a nonplanar geometry of this compound on the basis of spectral and bond orbital analysis, the explanation of the same from a more fundamental point of view is still missing. In the present study, we provide a heuristic explanation for the origin of nonplanarity of C4F4. The two major driving forces behind this nonplanar geometry are the unusual aromaticity of this cyclic homoatomic 4pi electron system and the second-order Jahn-Teller effect (SOJTE). These driving forces can well be explained by various energy and density parameters and also by nucleus-independent chemical shift (NICS) values. Aromaticity of a cyclic homoatomic 4pi electron system is quite remarkable. The enhancement of pi- delocalization as evidenced from molecular orbital analysis may be attributed to s-ppi mixing in nonplanar C4F4.

Studying the interaction of some atmospheric gases (H2O, HCN, NH3, SO3 and H2S) with 3PT oligomers is important in the development of polymeric sensors for gas detection. In the present study, we studied the relaxed geometries, interaction energies, charge analysis, HOMO-LUMO orbital analysis, and UV-vis spectra of all interacted systems using first-principles density functional theory (DFT). All these analyses indicated the potential of polythiophene as an inexpensive polymeric sensor for the analytes mentioned. Interaction energy values of -19.90, -19.66, -14.01, -8.70, and -4.76 kJ mol(-1) were achieved for adsorption of SO3, H2O, NH3, HCN, and H2S on 3PT, respectively. Consequently, clarification of their physical parameters became the major focus of this study.

Very recently, a series of endohedral fullerenes Sc2O@C2n (n = 35-47) were facilely produced. However, only two of them have been further characterized so far. Theoretically, we studied another discandium oxide endohedral fullerene without any characterizations, Sc2O@C84, which is the second most-abundant species in terms of relative heights of all mass spectrum peaks. Two thermodynamically stable isomers with isolated pentagon rule-obeying cages were found, namely, Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84. This is the first case that an endohedral fullerene containing the C2v(51575)-C84 cage acts as the lowest-energy isomer, and it is the first report of a clusterfullerene containing the C1(51580)-C84 cage. The endohedral Sc2O cluster can keep its ideal structure after encapsulation, while both C84 cages have deformed dramatically. Orbital analysis suggests that nucleophilic and oxidization reactions of both isomers should take place on the cage, while regioselectivity of Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84 is different due to their different characteristics of the highest occupied orbital distribution. Two-dimensional electron localization function and Laplacian of electron density maps unambiguously indicate strong electrostatic interactions exist between one scandium atom and the oxygen one. Meanwhile, overlaps of occupied metal atom orbitals and the cage ones along with Mayer bond order analysis identify that covalent interactions between a scandium atom and each C84 cage cannot be neglected. At last, (13)C NMR, UV-vis-NIR, and IR spectra of both Sc2O@C84 isomers were simulated theoretically. Because of their structural difference, all spectra between two isomers are significantly divergent. Consequently, these spectra are helpful to distinguish Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84 in further experimental characterizations.

The LARES satellite was successfully launched in 2012 for tests of General Relativity and gravitational physics including the accurate measurement of frame-dragging. It is currently very well observed all over the world by the stations of the International Laser Ranging Service. Its preliminary orbital analyses show that LARES behaves as the best artificial massive test particle today available in the solar system, providing an optimal approximation to the time-like geodesic motion of General Relativity. Furthermore, on the basis of a test using almost three years of observations of LARES, we concluded that LARES, together with the LAGEOS and LAGEOS 2 satellites, provides excellent preliminary results for testing General Relativity.

Two-dimensional 6,6,18-graphdiyne and the corresponding one-dimensional nanoribbons are investigated using crystal orbital method. Based on HSE06 functional, the one-dimensional confinement increases the band gaps. With band gaps larger than 0.4 eV, thirty-three 6,6,18-graphdiyne nanoribbons have larger majority carrier mobilities at room temperature than the highest value of armchair graphene nanoribbons. Unlike γ-graphdiyne, 6,6,18-graphdiyne nanoribbons have both huge hole and electron mobilities, depending on whether they are armchair or zigzag type. The huge mobilities are explained by crystal orbital analysis. The superior capabilities of 6,6,18-graphdiyne nanoribbons make them possible candidates for high speed electronic devices in complementary circuits.

The doubly Si-bridged ansa -tungstenocene, [W(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 ], ( a -Si 2 Cp 2 W) is calculated to have singlet and triplet states of comparable energy, in contrast to other tungstenocenes which have triplet ground states. Therefore, on an SCF energy surface there is no barrier to formation of a sigma complex with methane, and formation of a methyl hydride is exo-energetic by −125 kJ mol −1 . Orbital analysis of the tungstenocenes shows that the singlet ground state is favoured by a ring conformation that stabilizes the 2b 1 orbital by back donation, and that a double ansa bridge promotes this ring conformation.

A first-principles study of the dissociative adsorption of water on Ge(100)-(2 x 1) is described, on the basis of density functional theory with a cluster model of the surface. Experiments have shown that water incident on the Ge(100)-(2 x 1) surface has a very small probability of dissociative adsorption, indicating the presence of an activation barrier. This is in contrast to the analogous reaction on Si(100)-(2 x 1), which is unactivated. This difference is reproduced in the calculations, demonstrating the predictive capability of the methods used, though some caveats about basis sets are necessary. A frontier orbital analysis is used to identify the interactions that determine the transition state energy and underlie the difference between reactivity on Si and Ge.

After the successful launch and operation of UWE-3 in 2013, UWE-4 is the next picosatellite in the University of Würzburg Experimental satellite program. UWE-4 is first from its series to have integrated propulsion system and with a mission objective to demonstrate attitude and orbit control using the miniature propulsion system. In future, this will pave the way to perform complicated missions such as formation flying using picosatellites. Major challenge in UWE-4 is the integration of the propulsion system (which includes both thrusters and power processing unit) into the 1U CubeSat. Integrating the thruster into the Picosatellite has several constraints, few include accommodation of the system within the structure at minimum mass and volume impact, structural design to withstand the critical launch conditions.In the scope of this master thesis project, the design of UWE-3 system arrangement is studied and the regions of possible integration of thruster units are identified. The two propulsion systems considered for the UWE-4 mission are the Micro Vacuum Arc Thrusters (µVAT) developed at UniBW in Munich, Germany and the NanoFEEP (highly miniaturized Field Emission Electric Propulsion) thrusters developed at TUDresden, Germany. During design phase, different concepts are created for the CubeSat rails to integrate the thrusters and the concepts are validated against the functional requirements as well as the CubeSat design specifications. Detailed CAD designs are completed for UWE-4 satellite using SolidWorks 2014. To validate the structural design, the CAD models are then subjected to Finite Element Modeling and Analysis (structural and thermal) using Siemens NX CAE. During static Structural analysis, various loading conditions and constraints are identified and applied to the system. Later NX NASTRAN solver is used to study and simulate the impact on the UWE-4 model. Also modal analysis was performed to study the natural frequencies of the system. With the motivation to study the thermal behavior of the system in orbit, transient analysis for orbital heating was performed using NX SPACE SYSTEMS THERMAL. The solution results from both structural analysis and thermal analysis are validated for different scenarios. Based on the results the generic design is qualified and expected to serve as a platform for future missions. Validerat; 20150709 (global_studentproject_submitter)

We present a statistical analysis of the laser ranging data of LAGEOS and LAGEOS 2 satellites which have provided a test of dragging of inertial frames, or frame-dragging, by rotating mass as predicted by General Relativity. As a result, the analysis of the residuals, after filtering out the periodic effects, is consistent with a Gaussian model, with a nonzero mean in agreement with the one predicted by Lense–Thirring effect.

A novel Au19 nanocluster with a composition of [Au19(PhC≡C)9(Hdppa)3](SbF6)2 was synthesized (Hdppa = N,N-bis(diphenylphosphino)amine). Single crystal X-ray structural analysis reveals that the cluster comprises a centered icosahedral Au13 core hugged by three V-shaped PhC≡C–Au–C≡C(Ph)–Au–C≡CPh motifs. Such motif is observed for the first time in an alkynyl-protected gold nanocluster. The Au19 cluster shows two main optical-absorption bands at 1.25 and 2.25 eV, confirmed by time-dependent density functional theory. Orbital analysis indicates that PhC≡C– groups can actively participate in the frontier orbitals of the whole cluster. The new Au19 cluster and the novel alkynyl–gold motif open the door to understanding the alkynyl–gold interface and discovering many potential members of this new class of gold clusters.

We present the analysis of the atmospheric trajectory and orbital data of four bright bolides observed over Spain, one of which is a potential meteorite dropping event. Their absolute magnitude ranges from -10 to -11. Two of these are of sporadic origin, although a Geminid and a kappa-Cygnid fireball are also considered. These events were recorded in the framework of the continuous fireball monitoring and spectroscopy campaigns developed by the SPanish Meteor Network (SPMN) between 2010 and 2012. The tensile strength of the parent meteoroids is estimated and the abundances of the main rock-forming elements in these particles are calculated from the emission spectrum obtained for three of these events. This analysis revealed a chondritic nature for these meteoroids., Comment: Manuscript in press in Monthly Notices of the Royal Astronomical Society

The first example of a dyotropic rearrangement of an enantiomerically pure, conformationally unconstrained, vicinal dibromide confirms theoretical predictions: D and L-1,2-dibromo-1,2-diphenylethane racemise stereospecifically in refluxing benzene without crossover to the meso-isomer. An orbital analysis of this six-electron pericyclic process is presented.

We present and analyze a new M' detection of the young exoplanet beta Pictoris b from 2008 VLT/NaCo data at a separation of ~ 4 AU and a high signal-to-noise rereduction of L' data taken in December 2009. Based on our orbital analysis, the planet's orbit is viewed almost perfectly edge-on (i ~ 89 degrees) and has a Saturn-like semimajor axis of 9.50 (+3.93, -1.7) AU. Intriguingly, the planet's orbit is aligned with the major axis of the outer disk (Omega ~ 31 degrees) but probably misaligned with the warp/inclined disk at 80 AU often cited as a signpost for the planet's existence. Our results motivate new studies to clarify how $\beta$ Pic b sculpts debris disk structures and whether a second planet is required to explain the warp/inclined disk., Comment: 6 pages, 4 figures, 1 table; accepted for publication in The Astrophysical Journal Letters

This report presents an analysis of the orbital and ground coverage aspects of the third Chinese manned mission, Shenzhou-7, carried out in September 2008. The flight was supported by the Malindi tracking station, in Kenya, managed by the Italian Space Agency (ASI). Before and during the mission, the Space Flight Dynamics Laboratory of ISTI/CNR provided the ASI personnel in Malindi with trajectory and maneuver analysis, together with flight monitoring. Tracking passes and re-entry events predictions were independently derived and reconstructed with in-house research and simulations. In addition, also the most appropriate time windows for the first Chinese spacewalk, planned during this mission, were autonomously predicted and made available in advance to the ASI personnel in Malindi. The Malindi ground station played an important role in the Shenzhou-7 flight, as it was in the case of the previous two manned missions. Due to its critical geographical position, in fact, Malindi neatly integrated the existing network of ground stations and tracking ships, covering also the beginning of the first Chinese extravehicular activity and a critical portion of the spacecraft re-entry, between the retro-rocket firing and the impact with the atmospheric interface.

Analysis of Seasat laser range data over long arcs has identified geomagnetic modelling within atmospheric density models as a significant source of error. In particular, a major deficiency is the absence or mis-modelling of persistence of a geomagnetic event at heights near 800km. A logical step is to refine persistence and the geomagnetic model parameters within the least-squares differential correction procedure of the orbital refinement. To investigate the feasibility of this approach, persistence has been studied and parameters adjusted within the J71 atmospheric model and its variant due to Slowey, JS84. In J71 two parameters were derived by combination of 7 or 8 Seasat arcs. No advantage was found by refining the 3 extra parameters within JS84. The validity of the solution has been tested on 17 Starlette arcs for which the level of improvement is significant, particularly during levels of high geomagnetic activity. This is the first occasion that atmospheric density parameters have been derived within the orbital analysis data-reduction procedure and paves the way for more extensive analyses in the future.

During the summer of 2006, the accreting X-ray pulsar EXO 2030+375 underwent its first giant outburst since its discovery in 1985. Our observations include the first ever of the rise of a giant outburst of EXO 2030+375. EXO 2030+375 was monitored daily with the Rossi X-ray Timing Explorer (RXTE) from 2006 June through 2007 May. During the giant outburst, we discovered evidence for a cyclotron feature at ~11 keV. This feature was confidently detected for about 90 days, during the brighter portion of the outburst. Daily observations of the next five EXO 2030+375 orbits detected pulsations at all orbital phases and normal outbursts shifted to a later orbital phase than before the giant outburst. An accretion disk appears to be present in both the normal and giant outbursts, suggesting that the long-term behavior is a product of the state of the Be star disk and the accretion disk. Here we will present flux and frequency histories from our detailed RXTE observations of the giant outburst and the normal outbursts that surrounded it. A new orbital analysis is presented that includes observations from 1991 through 2007 August., Comment: 28 pages, 11 figures. Accepted for publication in the Astrophysical Journal

The 1,4-cyclization was studied in three model systems; formylketene, imidoylketene, and vinylketene, using ab initio MO methods. Structures of stationary points on the reaction potential energy surfaces were located at the HF/6-31G** level. Relative energies, estimated at the MP4SDQ/6-31G** level together with zero-point contributions, are as follows (in kcal/mol): formylketene (−17)→TS(4)→oxetone (0); imidoylketene (−10)→TS(15)→azetinone (0); and vinylketene (0)→TS(31)→cyclobutenone (0). The ring-opening of cyclobutenone is energetically more favorable than that of cyclobutene. The electonic reorganization accompanying the ring-closure of substituted ketenes was also examined using a localized orbital analysis. The process is found to be similar to the 1,5-cyclization of vinylazide and imidoylazide. Finally, the ketoketene-ketoketene rearrangement, including migration of a hydrogen in the formylketene, was considered

A large fraction of barred galaxies host secondary bars that are embedded in their large-scale primary counterparts. These are common also in gas poor early-type barred galaxies. The evolution of such double-barred galaxies is still not well understood, partly because of a lack of realistic $N$-body models with which to study them. Here we report a new mechanism for generating such systems, namely the presence of rotating pseudo-bulges. We demonstate with high mass and force resolution collisionless $N$-body simulations that long-lived secondary bars can form spontaneously without requiring gas, contrary to previous claims. We find that secondary bars rotate faster than primary ones. The rotation is not, however, rigid: the secondary bars pulsate, with their amplitude and pattern speed oscillating as they rotate through the primary bars. This self-consistent study supports previous work based on orbital analysis in the potential of two rigidly rotating bars. The pulsating nature of secondary bars may have important implications for understanding the central region of double-barred galaxies., Paper submitted to ApJL

A theoretical quantum chemical study of the intramolecular hydrogen bonding interactions in 8-mercaptoquinoline has been carried out. Special attention has been paid to the rotation of S-H bond and intramolecular proton-transfer reactions. Therewith, the B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p), MPW1K/6-311++G(d,p), MPW1K/6-31+G(2d,2p), BHHLYP/6-311++G(d,p), and G96LYP/6-311++G(d,p) methods have been used. By means of the Onsager and PCM reaction field methods, the effects of solvent on hydrogen-bond energies, conformational equilibria, rotational barriers, and tautomerism in aqueous solution have been studied. These simulations were done at the MPW1K/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels. Natural-bond orbital analysis has been performed to study the intramolecular hydrogen bond (IHB) in the gaseous phase and in aqueous medium. The stability of forms under consideration in solution does not coincide with that in the gaseous phase, underlining a great importance of the electrostatic influence of solvent. Double-proton transfer in the prototropic tautomerization of 8-mercaptoquinoline, one water molecule complex in the gaseous phase and in solution, has been systematically studied. The double-proton transfer occurs concertedly and synchronously. The water-assisted tautomerization is kinetically less, but thermodynamically more favorable, compared to that of the single-proton transfer. As in the case with single-proton transfer, for water-assisted reaction, the tautomerization energies and barrier heights decrease with the increase in dielectric constant, which implies faster and more complete tautomerization of 8-mercaptoquinoline in a polar solvent.

oz RS CVn türü örten çift yıldız RT And' ın yayınlanmış minimum zamanlan literatürden toplanarak sistemin yörünge dönemindeki değişim için O-C analizi yapılmıştır. Sistemin yörünge döneminin parabol üzerine binmiş sinüs salınımları şeklinde olduğu saptanmıştır. Yörünge dönemindeki bu tür değişim, (i) sistemde kütle kaybı ya da kütle aktarımı, (ii) görülemeyen üçüncü bir cismin varlığı ve (iii) konvektif katmanda manyetik etkinlikle ilgili bozulmalar açısından tartışılmıştır. Ayrıca, RT And çift yıldızının yayınlanmış ışık eğrileri literatürden toplanarak sistemin ışık eğrilerinde görülen asimetriler incelenmiş ve sistemin ışık değişiminde rol oynadığı varsayılan manyetik etkinlikle yörünge dönemi değişimi arasında bir ilişki aranmıştır. Anahtar Kelimeler: Örten değişen çift yıldızlar - RT And: yörünge dönemi değişimi, ışık değişimi. ABSTRACT The (0-C) diagram formed by all available published times of minima of RT Andromedae were intensively analyzed to deduce the general form of period variation for RT And. It is established that the orbital period change of the system has a quasi-sinusoidal form superposed on a downward parabola. Such variations of the orbital period have been examined in terms of three plausible mechanisms, namely (i) mass loss or mass transfer, (ii) a light-time effect due to an unseen third star in the system, and (iii) a orbital period modulation due to magnetic activity cycle of a component star. Only the future data will add information on the nature of the secular (O-C) variation. Secular light variation of the system was also studied and was found no correlation with the orbital period variation. Key words: stars: binaries: close - stars: individual: RT Andromedae - orbital period variation - light changes. 82