Effects of the Charge-Dipole Interaction on the Coagulation of Fractal Aggregates

A numerical model with broad applications to complex (dusty) plasmas is presented. The self-consistent N-body code allows simulation of the coagulation of fractal aggregates, including the charge-dipole interaction of the clusters due to the spatial arrangement of charge on the aggregate. It is shown that not only does a population of oppositely charged particles increase the coagulation rate, the inclusion of the charge-dipole interaction of the aggregates as well as the electric dipole potential of the dust ensemble decreases the gelation time by a factor of up to twenty. It is further shown that these interactions can also stimulate the onset of gelation, or "runaway growth," even in a population of particles charged to a monopotential where previously it was believed that like-charged grains would inhibit coagulation. Gelation is observed to occur due to the formation of high-mass aggregates with fractal dimensions greater than two which act as seeds for runaway growth.Comment: 9 page

Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216

We have used the Robert C. Byrd Green Bank Telescope to perform the most sensitive search to date for neutral atomic hydrogen (HI) in the circumstellar envelope (CSE) of the carbon star IRC+10216. Our observations have uncovered a low surface brightness HI shell of diameter ~1300" (~0.8 pc), centered on IRC+10216. The HI shell has an angular extent comparable to the far ultraviolet-emitting astrosphere of IRC+10216 previously detected with the GALEX satellite, and its kinematics are consistent with circumstellar matter that has been decelerated by the local interstellar medium. The shell appears to completely surround the star, but the highest HI column densities are measured along the leading edge of the shell, near the location of a previously identified bow shock. We estimate a total mass of atomic hydrogen associated with IRC+10216 CSE of M_HI~3x10e-3 M_sun. This is only a small fraction of the expected total mass of the CSE (<1%) and is consistent with the bulk of the stellar wind originating in molecular rather than atomic form, as expected for a cool star with an effective temperature T_eff<~2200 K. HI mapping of a 2 deg x 2 deg region surrounding IRC+10216 has also allowed us to characterize the line-of-sight interstellar emission in the region and has uncovered a link between diffuse FUV emission southwest of IRC+10216 and the Local Leo Cold Cloud.Comment: Accepted to MNRAS. 16 pages. A version with full resolution figures may be found at http://www.haystack.mit.edu/hay/staff/lmatthew/Matthews_etal_IRC+10216.pd

HI emission from the red giant Y CVn with the VLA and FAST

Imaging studies with the VLA have revealed HI emission associated with the extended circumstellar shells of red giants. We analyse the spectral map obtained on Y CVn, a J-type carbon star on the AGB. The HI line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar medium. We reproduce the spectral map by introducing a distortion along a direction corresponding to the star's motion in space. We then use this fitting to simulate observations expected from the FAST radiotelescope, and discuss its potential for improving ourdescription of the outer regions of circumstellar shells.Comment: accepted for publication in RA

Dusty plasma cavities: probe-induced and natural

A comprehensive exploration of regional dust evacuation in complex plasma crystals is presented. Voids created in 3D crystals on the International Space Station have provided a rich foundation for experiments, but cavities in dust crystals formed in ground-based experiments have not received as much attention. Inside a modified GEC RF cell, a powered vertical probe was used to clear the central area of a dust crystal, producing a cavity with high cylindrical symmetry. Cavities generated by three mechanisms are examined. First, repulsion of micrometer-sized particles by a negatively charged probe is investigated. A model of this effect developed for a DC plasma is modified and applied to explain new experimental data in RF plasma. Second, the formation of natural cavities is surveyed; a radial ion drag proposed to occur due to a curved sheath is considered in conjunction with thermophoresis and a flattened confinement potential above the center of the electrode. Finally, cavity formation unexpectedly occurs upon increasing the probe potential above the plasma floating potential. The cavities produced by these methods appear similar, but each are shown to be facilitated by fundamentally different processes.Comment: 10 pages, 12 figure

Charging and coagulation of dust in protoplanetary plasma environments

Combining a particle-particle, particle-cluster and cluster-cluster agglomeration model with an aggregate charging model, the coagulation and charging of dust particles in various plasma environments relevant for proto-planetary disks have been investigated. The results show that charged aggregates tend to grow by adding small particles and clusters to larger particles and clusters, leading to greater sizes and masses as compared to neutral aggregates, for the same number of monomers in the aggregate. In addition, aggregates coagulating in a Lorentzian plasma (containing a larger fraction of high-energy plasma particles) are more massive and larger than aggregates coagulating in a Maxwellian plasma, for the same plasma densities and characteristic temperature. Comparisons of the grain structure, utilizing the compactness factor, {\phi}{\sigma}, demonstrate that a Lorentzian plasma environment results in fluffier aggregates, with small {\phi}{\sigma}, which exhibit a narrow compactness factor distribution. Neutral aggregates are more compact, with larger {\phi}{\sigma}, and exhibit a larger variation in fluffiness. Measurement of the compactness factor of large populations of aggregates is shown to provide information on the disk parameters that were present during aggregation

Interstate Differences in Insured Unemployment: Some Recent Evidence

Recent panel data is used to reconsider the determinants of interstate differences in the ratio of insured to total unemployment. We conclude that previous research on the influence of replacement rates, duration of jobless spells and female labor force participation is robust, but find that political affiliations and attitudes could be more important, and unionization rates less important, than once believed.insured unemployment, work norms, replacement rates, unionization

Research in planetary Astronomy

The focus was on the study, via near infrared observations, of the outer planets and their satellites. In the last year, these observations have emphasized imaging observations using the Cassegrain infrared camera at the f/70 focus of the 200 inch Hale telescope

An HI Imaging Survey of Asymptotic Giant Branch Stars

We present an imaging study of a sample of eight asymptotic giant branch (AGB) stars in the HI 21-cm line. Using observations from the Very Large Array, we have unambiguously detected HI emission associated with the extended circumstellar envelopes of six of the targets. The detected HI masses range from M_HI ~ 0.015-0.055 M_sun. The HI morphologies and kinematics are diverse, but in all cases appear to be significantly influenced by the interaction between the circumstellar envelope and the surrounding medium. Four stars (RX Lep, Y UMa, Y CVn, and V1942 Sgr) are surrounded by detached HI shells ranging from 0.36 to 0.76 pc across. We interpret these shells as resulting from material entrained in a stellar outflow being abruptly slowed at a termination shock where it meets the local medium. RX Lep and TX Psc, two stars with moderately high space velocities (V_space>56 km/s), exhibit extended gaseous wakes (~0.3 and 0.6 pc in the plane of the sky), trailing their motion through space. The other detected star, R Peg, displays a peculiar "horseshoe-shaped" HI morphology with emission extended on scales up to ~1.7 pc; in this case, the circumstellar debris may have been distorted by transverse flows in the local interstellar medium. We briefly discuss our new results in the context of the entire sample of evolved stars that has been imaged in HI to date.Comment: Accepted to AJ. A version with full resolution figures is available at http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_HI_survey.pd

The Effects of Job Stress on Law Enforcement Marriages and Methods of Combating the Job Stress

The reality of how law enforcement stress affects individuals and marriages will be presented in light of its causes and dangers to officers, as well as how the stress affects officers’ marriages. The marital problems stemming from law enforcement stress can progress from producing less spousal interaction and communication issues, to presenting opportunities for infidelity, and eventually result in divorce. Before countering the impact of job stress upon marriage, officers must first deal with the stress individually. Marriages do not have to end as a result of job stress. By seeking family therapy and by relying on God, law enforcement marriages can be saved