The reaction between silylene and ammonia: some gas-phase kinetic and quantum chemical studies

Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by 193 nm laser flash photolysis of silacyclopent-3-ene, have been carried out in the presence of ammonia, NH3. Second order kinetics were observed. The reaction was studied in the gas phase at 10 Torr total pressure in SF6 bath gas at each of the three temperatures, 299, 340 and 400 K. The second order rate constants (laser pulse energy of 60 mJ/pulse) fitted the Arrhenius equation: log(k/cm3 molecule-1 s-1) = (-10.37 ± 0.17) + (0.36 ± 1.12 kJ mol-1)/RTln10 Experiments at other pressures showed that these rate constants were unaffected by pressure in the range 10-100 Torr, but showed small decreases in value at 3 and 1 Torr. There was also a weak intensity dependence, with rate constants decreasing at laser pulse energies of 30 mJ/pulse. Ab initio calculations at the G3 level of theory, show that SiH2 + NH3 should form an initial adduct (donor-acceptor complex), but that energy barriers are too great for further reaction of the adduct. This implies that SiH2 + NH3 should be a pressure dependent association reaction. The experimental data are inconsistent with this and we conclude that SiH2 decays are better explained by reaction of SiH2 with the amino radical, NH2, formed by photodissociation of NH3 at 193 nm. The mechanism of this previously unstudied reaction is discussed

Correlated photon pairs generated from a warm atomic ensemble

We present measurements of the cross-correlation function of photon pairs at 780 nm and 1367 nm, generated in a hot rubidium vapor cell. The temporal character of the biphoton is determined by the dispersive properties of the medium where the pair generation takes place. We show that short correlation times occur for optically thick samples, which can be understood in terms of off-resonant pair generation. By modifying the linear response of the sample, we produce near-resonant photon pairs, which could in principle be used for entanglement distribution

Displaced geostationary orbit design using hybrid sail propulsion

Because of an increase in the number of geostationary spacecraft and the limits imposed by east–west spacing requirements, the geostationary orbit is becoming congested. To increase its capacity, this paper proposes to create new geostationary slots by displacing the geostationary orbit either out of or in the equatorial plane by means of hybrid solar sail and solar electric propulsion. To minimize propellant consumption, optimal steering laws for the solar sail and solar-electric-propulsion thrust vectors are derived and the performance in terms of mission lifetime is assessed. For comparison, similar analyses are performed for conventional propulsion, including impulsive and pure solar electric propulsion. It is shown that hybrid sails outperform these propulsion techniques and that out-of-plane displacements outperform in-plane displacements. The out-of-plane case is therefore further investigated in a spacecraft mass budget to determine the payload mass capacity. Finally, two transfers that enable a further improvement of the performance of hybrid sails for the out-of-plane case are optimized using a direct pseudospectral method: a seasonal transit between orbits displaced above and below the equatorial plane and a transit to a parking orbit when geostationary coverage is not needed. Both transfers are shown to require only a modest propellant budget, outweighing the improvements they can establish

A dramatic isotope effect in the reaction of ClSiH with trimethylsilane-1-d: experimental evidence for intermediate complexes in silylene Si-H(D) insertion reactions

A kinetic isotope effect (kD/kH) of 7.4 has been found for the reaction of chlorosilylene with trimethysilane (Me3SiD vs Me3SiH). Such a value can be accounted for by theoretical modelling, but only if an internal rearrangement of the initially form complex is included in the mechanism. This provides the first concrete evidence for such complexes

Fear vs. Facts: Examining the Economic Impact of Undocumented Immigrants in the U.S.

Undocumented immigration has become a contentious issue in the U.S. over the past decade. Opponents of undocumented immigration have argued that undocumented immigrants are a social and financial burden to the U.S. which has led to the passage of drastic and costly policies. This paper examined existing state and national data and found that undocumented immigrants do contribute to the economies of federal, state, and local governments through taxes and can stimulate job growth, but the cost of providing law enforcement, health care, and education impacts federal, state, and local governments differently. At the federal level, undocumented immigrants tend to contribute more money in taxes than they consume in services, however, the net economic costs or benefits to state and local governments varies throughout the U.S

Measuring emotion regulation ability across negative and positive emotions: The Perth Emotion Regulation Competency Inventory (PERCI)

Emotion regulation problems underlie the abnormal levels of negative or positive emotion that characterise many forms of psychopathology. Several self-report measures of emotion regulation ability exist, but many are inconsistent with contemporary emotion regulation theory, and none comprehensively assess this construct across both negative and positive emotions. In this paper, we report our attempt to remedy these measurement limitations by developing and validating the Perth Emotion Regulation Competency Inventory (PERCI), a 32 item self-report questionnaire that measures emotion regulation ability as it is defined by the extended process model of emotion regulation. In Study 1, our confirmatory factor analyses in a sample of adults (N = 231) suggested that the PERCI had a factor structure consistent with its theoretical basis and could separately measure people\u27s ability to regulate their negative and positive emotions. All subscale and composite scores had high internal consistency reliability. Study 2 (N = 1175) replicated these findings with respect to factor structure and internal consistency reliability, and correlational or regression analyses with measures of psychopathology, emotion regulation processes, alexithymia, and interpersonal attachment style also supported the validity of the PERCI. We conclude that the PERCI appears to have strong psychometric properties. Clinical and research implications are discussed

Analytical sun synchronous low-thrust manoeuvres

Article describes analytical sun synchronous low-thrust manoeuvres

The pp-Daugavet property for function spaces

A natural extension of the Daugavet property for $p$-convex Banach function spaces and related classes is analysed. As an application, we extend the arguments given in the setting of the Daugavet property to show that no reflexive space falls into this class