Angular Momentum Considerations Research Articles

On the Competition Between Electron Autodetachment and Dissociation of Molecular Anions

We treat the competition between autodetachment of electrons and unimolecular dissociation of excited molecular anions as a rigid-/loose-activated complex multichannel reaction system. To start, the temperature and pressure dependences under thermal excitation conditions are represented in terms of falloff curves of separated single-channel processes within the framework of unimolecular reaction kinetics. Channel couplings, caused by collisional energy transfer and “rotational channel switching” due to angular momentum effects, are introduced afterward. The importance of angular momentum considerations is stressed in addition to the usual energy treatment. Non-thermal excitation conditions, such as typical for chemical activation and complex-forming bimolecular reactions, are considered as well. The dynamics of excited SF6− anions serves as the principal example. Other anions such as CF3− and POCl3− are also discussed.

Disc formation in the collapse of supramassive neutron stars

Short gamma-ray bursts (sGRBs) show a large diversity in their properties. This suggests that the observed phenomenon can be caused by different "central engines" or that the engine produces a variety of outcomes depending on its parameters, or possibly both. The most popular engine scenario, the merger of two neutron stars, has received support from the recent Fermi and INTEGRAL detection of a burst of gamma rays (GRB170817A) following the neutron star merger GW170817, but at the moment it is not clear how peculiar this event potentially was. Several sGRBs engine models involve the collapse of a supramassive neutron star that produces a black hole plus an accretion disk. We study this scenario for a variety of equations of states both via angular momentum considerations based on equilibrium models and via fully dynamical Numerical Relativity simulations. We obtain a broader range of disk forming configurations than earlier studies but we agree with the latter that none of these configurations is likely to produce a phenomenon that would be classified as an sGRB.

Atomic spectroscopy with twisted photons: Separation of M1−E2 mixed multipoles

We analyze atomic photoexcitation into the discrete states by twisted photons, or photons carrying extra orbital angular momentum along their direction of propagation. From the angular momentum and parity considerations, we are able to relate twisted-photon photoexcitation amplitudes to their plane-wave analogues, independently of the details of the atomic wave functions. We analyzed the photo-absorption cross sections of mixed-multipolarity $E2-M1$ transitions in ionized atoms and found fundamental differences coming from the photon topology. Our theoretical analysis demonstrates that it is possible to extract the relative transition rates of different multipolar contributions by measuring the photo-excitation rate as a function of the atom's position (or the impact parameter) with respect to the optical vortex center. The proposed technique for separation of multipoles can be implemented if the target's atom position is resolved with sub-wavelength accuracy, for example, with Paul traps. Numerical examples are presented for Boron-like highly-charged ions (HCI).

Momentum considerations on the New MEXICO experiment

The present paper regards axial and angular momentum considerations combining detailed loads from pressure sensors and the flow field mapped with particle image velocimetry (PIV) techniques. For this end, the study implements important results leaning on experimental data from wind tunnel measurements of the New MEXICO project. The measurements, taken on a fully instrumented rotor, were carried out in the German Dutch Wind tunnel Organisation (DNW) testing the MEXICO rotor in the open section. The work revisits the so-called momentum theory, showing that the integral thrust and torque measured on the rotor correspond with an extent of 0.7 and 2.4% respectively to the momentum balance of the global flow field using the general momentum equations. Likewise, the sectional forces combined with the local induced velocities are found to plausibly obey the annular streamtube theory, albeit some limitations in the axial momentum become more apparent at high inductions after a=0.3. Finally, azimuth induced velocities are measured and compared to predictions from models of Glauert and Burton et al., showing close-matching forecasts for blade spans above 25%.

Inner-shell photoionization of atomic chlorine

Relative partial cross sections have been measured following photoexcitation of atomic chlorine near the Cl 2p and Cl 1s ionization thresholds. In addition, Breit-Pauli R-matrix calculations have been carried out in the region of the 2p thresholds, and the results are compared with experiment. Owing to angular-momentum considerations, it was found that the resonances associated with the higher 2p(-1) thresholds should be significantly wider than the lower ones, and this is borne out in both the experimental and the theoretical results. It is shown that a large number of resonance series contribute to the cross section, which make it difficult to untangle, and suggestions for further work to better understand the spectra are presented.

A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus

From CCD observations of a fixed and large star field that contained the binary TNO Orcus, we have been able to derive high-precision relative astrometry and photometry of the Orcus system with respect to background stars. The RA residuals of an orbital fit to the astrometric data revealed a periodicity of 9.7+-0.3 days, which is what one would expect to be induced by the known Orcus companion. The residuals are also correlated with the theoretical positions of the satellite with regard to the primary. We therefore have revealed the presence of Orcus' satellite in our astrometric measurements. The photocenter motion is much larger than the motion of Orcus around the barycenter, and we show here that detecting some binaries through a carefully devised astrometric technique might be feasible with telescopes of moderate size. We also analyzed the system's mid-term photometry to determine whether the rotation could be tidally locked to the satellite's orbital period. We found that a photometric variability of 9.7+-0.3 days is clear in our data, and is nearly coincident with the orbital period of the satellite. We believe this variability might be induced by the satellite's rotation. There is also a slight hint for an additional small variability in the 10 hr range that was already reported in the literature. This short-term variability would indicate that the primary is not tidally locked and therefore the system would not have reached a double synchronous state. Implications for the basic physical properties of the primary and its satellite are discussed. From angular momentum considerations we suspect that the Orcus satellite might have formed from a rotational fission. This requires that the mass of the satellite would be around 0.09 times that of the primary, close to the value that one derives by using an albedo of 0.12 for the satellite and assuming equal densities for both objects.

Grand Challenges in Planetary Nebulae Studies: Binary Evolution and MHD

We review work on the evolution of planetary nebulae and proto-planetaries via magneto-rotational mechanisms showing that a dynamo generated magnetic field can produce the energy and momentum needed to drive pPN and PNe outflows. Angular momentum considerations lead to the conclusion that single stars can not support strong fields for long times. Thus we take the working hypothesis that most PN may form via binary stars. We propose that the grand challenge for PN studies is fully understanding the diverse physical processes at work in binary late stage evolution including the development of disks, fields and outflows.

Dynamic analysis of stacked rigid blocks

The dynamic behavior of a structural model of two stacked rigid blocks subjected to ground excitation is examined. Assuming no sliding, the rocking response of the system standing free on a rigid foundation is investigated. The derivation of the equations of motion accounts for the consecutive transition from one pattern of motion to another, each being governed by a set of highly nonlinear differential equations. The system behavior is described in terms of four possible patterns of response and impact between either the two blocks or the base block and the ground. The equations governing the rocking response of the system to horizontal and vertical ground accelerations are derived for each pattern, and an impact model is developed by conservation of angular momentum considerations. Numerical results are obtained by developing an ad hoc computational scheme that is capable of determining the response of the system under an arbitrary base excitation. This feature is demonstrated by using accelerograms from the Northridge, CA, 1994, earthquake. It is hoped that the two-blocks model used herein can facilitate the development of more sophisticated multi-block structural models.

Rotation, planets, and the 'second parameter' of the horizontal branch

We analyze the angular momentum evolution from the red giant branch (RGB) to the horizontal branch (HB) and along the HB. Using rotation velocities for stars in the globular cluster M13, we find that the required angular momentum for the fast rotators is up to 1-3 orders of magnitude (depending on some assumptions) larger than that of the sun. Planets of masses up to five times Jupiter's mass and up to an initial orbital separation of about 2 AU are sufficient to spin-up the RGB progenitors of most of these fast rotators. Other stars have been spun-up by brown dwarfs or low-mass main sequence stars. Our results show that the fast rotating HB stars must have been spun-up by companions while they evolved on the RGB. The angular momentum considerations presented in this paper further supports the planet parameter model. In this model the second parameter process is interaction with low-mass companions, in most cases gas giant planets, and in a minority of cases with brown dwarfs or low-mass main sequence stars.

Element Ratios and the Formation of the Stellar Halo

It is well-established that the vast majority of metal-poor Galactic halo stars shows evidence for enrichment by solely massive stars. Recent observations have identified more varied behavior in the pattern of elemental abundances measured for metal-rich, [Fe/H]=-1, halo stars, with both high and low values of the ratio of [alpha/Fe]. The low values are most naturally due to the incorporation of iron from Type Ia supernovae. These `low-alpha' halo stars have been interpreted as being accreted from dwarf galaxies. However, these stars are on very high-energy radial orbits, that plunge into the Galactic center, from the outer regions of the stellar halo. We demonstrate here that known dwarf galaxies could not reproduce the observations. Rather, the observations are consistent with fragmentation of a gaseous proto-halo into transient star-forming regions, some of which are sufficiently dense to survive close to the Galactic center, and self-enrich to relatively high metallicities. Those that probe the outer halo sustain star formation long enough to incorporate the ejecta from Type Ia supernovae. The values of the `Type II plateau' in the element ratios for disk stars and for halo stars are equal. This implies that the (massive) stars that enriched the early disk and halo had the same IMF. However, there is a discontinuity in the chemical enrichment history between the halo and disk, as probed by these samples, consistent with previous inferences based on angular momentum considerations.

Lateral Shock of the R Aquarii Jet

The R Aqr jet was observed with the VLA B-configuration at two epochs separated by approximately 13.2 yr. Comparison of the resulting 6 cm continuum images show that the radio jet has undergone a lateral counterclockwise rotation of approximately 6 deg-12 deg on the plane of the sky. The model of jet parcels on independent trajectories is difficult to reconcile with these observations and leads us to consider a path-oriented jet (i.e., younger parcels follow the same path as older parcels). Comparison of the most recent radio image with a nearly contemporaneous HST/FOC ultraviolet image at approximately 2330 Angstroms suggests that the ultraviolet emission lies along the leading side of the rotating radio jet. In conjunction with a proper motion analysis of the jet material that yields empirical space-velocity and resulting acceleration-magnitude relationships as a function of distance from the central source, we evaluate the observational results in terms of a schematic model in which the jet emission consists of plane-parallel isothermal shocks along the leading edge of rotation. In such a radiating shock, the ultraviolet-emitting region is consistent with the adiabatic region in the form of a high-temperature, low-density sheath that surrounds the cooled postshock radio-emitting region. Within the context of the schematic model, we obtain the temperatures, densities, and pressures within the preshock, adiabatic, and postshock regions as a function of distance from the central source; the physical parameters so derived compare favorably to previously published estimates. We obtain a total jet mass of 3.1 x 10(exp -5) solar mass and an age of approximately 115 yr. We evaluate the model in the context of its density-boundary condition, its applicability to an episodic or quasi-continuous jet, and angular momentum considerations.

The cores of dwarf galaxy haloes

We use N-body simulations to examine the effects of mass outflows on the density profiles of cold dark matter (CDM) halos surrounding dwarf galaxies. In particular, we investigate the consequences of supernova-driven winds that expel a large fraction of the baryonic component from a dwarf galaxy disk after a vigorous episode of star formation. We show that this sudden loss of mass leads to the formation of a core in the dark matter density profile, although the original halo is modeled by a coreless (Hernquist) profile. The core radius thus created is a sensitive function of the mass and radius of the baryonic disk being blown up. The loss of a disk with mass and size consistent with primordial nucleosynthesis constraints and angular momentum considerations imprints a core radius which is only a small fraction of the original scale-length of the halo. These small perturbations are, however, enough to reconcile the rotation curves of dwarf irregulars with the density profiles of haloes formed in the standard CDM scenario.

Upper Extremity Function in Running. II: Angular Momentum Considerations

Ten male recreational runners were filmed using three-dimensional cinematography while running on a treadmill at 3.8 m/s, 4.5 m/s, and 5.4 m/s. A 14-segment mathematical model was used to examine the contributions of the arms to the total-body angular momentum about three orthogonal axes passing through the body center of mass. The results showed that while the body possessed varying amounts of angular momentum about all three coordinate axes, the arms made a meaningful contribution to only the vertical component (Hz). The arms were found to generate an alternating positive and negative Hz pattern during the running cycle. This tended to cancel out an opposite Hz pattern of the legs. The trunk was found to be an active participant in this balance of angular momentum, the upper trunk rotating back and forth with the arms and, to a lesser extent, the lower trunk with the legs. The result was a relatively small total-body Hz throughout the running cycle. The inverse relationship between upper- and lower-body angular momentum suggests that the arms and upper trunk provide the majority of the angular impulse about the z axis needed to put the legs through their alternating strides in running.

Statistical multistep compound reactions ? with renormalized exciton state densities

The master equation which takes into account angular momentum considerations is used to obtain the emission spectra for statistical multistep compound reactions. Realistic wave functions are used to evaluate the radial integrals appearing in the escape and spreading widths. The renormalized particle hole state density of Akkermans et al. is used in the calculations. The improvements over the one component formulation are discussed.

Relation of chromospheric activity to convection, rotation, and pre-main-sequence evolution

Simon et al. (1985) have considered the hypothesis that the nonradiative flux levels of PMS stars can be explained as a direct extension of the work of Noyes et al. (1984), who showed that the Ca II H and K emission flux levels in main-sequence stars are well correlated with the Rossby number (Ro). Ro is identical with the ratio P-rot/tau-conv, where P-rot is the stellar rotation period and tau-conv is a characteristic turnover time scale for convection. Detailed evaluations of tau-conv on the PMS are reported and employed to test the hypothesis considered by Simon et al. that T Tauri nonradiative fluxes follow from having large tau-conv on the PMS. It is found that the evolution of tau-conv on the PMS is a strong function of stellar mass and age. Attention is given to stellar evolution results, chromospheric flux generation, and angular momentum considerations.

Periodic Laughlin-Jastrow wave functions for the fractional quantized Hall effect.

We present Laughlin-Jastrow wave functions for incompressible fluid states of two-dimensional electrons at Landau-level filling factor 1/m that satisfy periodic boundary conditions. This rederivation of Laughlin-type states emphasizes that it is correct short-distance behavior of the wave functions rather than angular momentum considerations that lie behind the explanation of the fractional quantized effect.

Rotational dynamics of celestial bodies: Generalized rotation and considerations of angular momentum

The transformation equations under generalized rotation are obtained for an initially defined reduced velocity tensor governing the motion of a deformable finite material continuum. Then angular momentum considerations lead to relations between flow properties of the continuum and properties of a coordinate system introduced to describe generalized rotation of the continuum. Such relations could define preferable coordinate systems perceiving zero angular momentum for the continuum or referring that it moves according to linear laws.

Resonances in 12C + 13C at Ec.m. = 9.4 and 10.3 MeV observed in the total fusion cross section

The 12C + 13C total fusion cross section has been measured from E c.m. = 8.8 to 10.9 MeV to search for evidence of two resonances previously reported at 9.4 and 10.3 MeV on the basis of elastic scattering data. Enhancements of about 6 % are observed in the total fusion cross section at E c.m. = 9.35 + 0.05 and 10.21±0.05 MeV. If the previously assigned resonance parameters are correct, the observed resonant contribution to the fusion cross section at 10.3 MeV is too large to be consistent with the non-resonant absorption of ∼ 80 % predicted from available optical-model parameters. It is concluded that these two resonances in 12C+ 13C are comparable to the strongest resonances observed in 12C + 12C and 12C + 16O. The apparent weakness of 12C+ 13C resonances in measured reaction cross sections is expected on the basis of simple angular momentum considerations.

Second-order cascading in third-order nonlinear optical processes

Because cascaded second-order processes make substantial qualitative and quanitative differences to the results of third-order nonlinear optical experiments, a formalism for their treatment is presented. The symmetry dictates concerning the occurrence and relationships of magnitudes of cascading are tabulated for the higher symmetry crystal classes. Angular momentum considerations are applied to the situations allowing circularly polarized light waves.

Nuclear recoil chemical activation studies. Vibrational energy transfer from cyclobutane-t

A method is demonstrated for the determination of intermolecular energy transfer efficiencies in systems chemically activated by nuclear recoil reaction. Relative vibrational energy transfer efficiencies are determined for highly excited cyclobutane-t formed with ∼5 eV of internal energy in the hot tritium for hydrogen replacement reaction on cyclobutane in the presence of several inert bath gases. The pressure dependence of the hot yields is used to probe the overall reaction mechanism and results indicate that a sizable fraction of the hot reaction product does not undergo competitive unimolecular decomposition. The general systematics of these side reactions are discussed. From the composition dependence of the unimolecular reaction at a constant pressure of 800 torr, the relative energy transfer efficiencies for the respective bath gases are found to be c-C4H8, 1.0; CF4, 1.05; N2, 0.32; He, 0.12; Ne, 0.24; Ar, 0.25; Kr, 0.31; Xe, 0.39. Simple collision models for the cyclobutane–noble gas cases suggest V–T transfer occurs most efficiently through delocalized interactions. Furthermore, angular momentum considerations indicate low impact parameter collisions are most effective in forming transition modes through which statistical redistribution of energy can occur.