On Pressure Gradients and Rapid Migration of Solids in an Inhomogeneous Solar Nebula

We study the motions of small solids, ranging from micron-sized dust grains to 100-m objects, in the vicinity of a local density enhancement of an isothermal gaseous solar nebula. Being interested in possible application of the results to the formation of clumps and spiral arms in a circumstellar disk, we numerically integrate the equations of motion of such solids and study their migration for different values of their sizes and masses and also for different physical properties of the gas, such as its density and temperature. We show that, considering the drag force of the gas and also the gravitational attraction of the nebula, it is possible for solids, within a certain range of size and mass, to migrate rapidly (i.e. within ~1000 years) toward the location of a local maximum density where collisions and coagulation may result in an accelerated rate of planetesimal formation.Comment: 20 pages, 7 figures, submitted for publicatio

Eminence Grise Coalitions: On the Shaping of Public Opinion

We consider a network of evolving opinions. It includes multiple individuals with first-order opinion dynamics defined in continuous time and evolving based on a general exogenously defined time-varying underlying graph. In such a network, for an arbitrary fixed initial time, a subset of individuals forms an eminence grise coalition, abbreviated as EGC, if the individuals in that subset are capable of leading the entire network to agreeing on any desired opinion, through a cooperative choice of their own initial opinions. In this endeavor, the coalition members are assumed to have access to full profile of the underlying graph of the network as well as the initial opinions of all other individuals. While the complete coalition of individuals always qualifies as an EGC, we establish the existence of a minimum size EGC for an arbitrary time-varying network; also, we develop a non-trivial set of upper and lower bounds on that size. As a result, we show that, even when the underlying graph does not guarantee convergence to a global or multiple consensus, a generally restricted coalition of agents can steer public opinion towards a desired global consensus without affecting any of the predefined graph interactions, provided they can cooperatively adjust their own initial opinions. Geometric insights into the structure of EGC's are given. The results are also extended to the discrete time case where the relation with Decomposition-Separation Theorem is also made explicit.Comment: 35 page

Limits to ion energy control in high density glow discharges: Measurement of absolute metastable ion concentrations

Unprecedented demands for uniformity, throughput, anisotropy, and damage control in submicron pattern transfer are spurring development of new, low pressure, high charge density plasma reactors. Wafer biasing, independent of plasma production in these new systems is intended to provide improved ion flux and energy control so that selectivity can be optimized and damage can be minimized. However, as we show here, an inherent property of such discharges is the generation of significant densities of excited, metastable ionic states that can bombard workpiece surfaces with higher translational and internal energy. Absolute metastable ion densities are measured using the technique of self-absorption, while the corresponding velocity distributions and density scaling with pressure and electron density are measured using laser-induced fluorescence. For a low pressure, helicon-wave excited plasma, the metastable ion flux is at least 24% of the total ion flux to device surfaces. Because the metastable ion density scales roughly as the reciprocal of the pressure and as the square of the electron density, the metastable flux is largest in low pressure, high charge density plasmas. This metastable ion energy flux effectively limits ion energy and flux control in these plasma reactors, but the consequences for etching and deposition of thin films depend on the material system and remain an open question

A New Perspective on Path Integral Quantum Mechanics in Curved Space-Time

A fundamentally different approach to path integral quantum mechanics in curved space-time is presented, as compared to the standard approaches currently available in the literature. Within the context of scalar particle propagation in a locally curved background, such as described by Fermi or Riemann normal co-ordinates, this approach requires use of a constructed operator to rotate the initial, intermediate, and final position ket vectors onto their respective local tangent spaces, defined at each local time step along some arbitrary classical reference worldline. Local time translation is described using a quantum mechanical representation of Lie transport, that while strictly non-unitary in operator form, nevertheless correctly recovers the free-particle Lagrangian in curved space-time, along with new contributions. This propagator yields the prediction that all probability violating terms due to curvature contribute to a quantum violation of the weak equivalence principle, while the remaining terms that conserve probability also correspondingly satisfy the weak equivalence principle, at least to leading-order in the particle's Compton wavelength. Furthermore, this propagator possesses an overall curvature-dependent and gauge-invariant phase factor that can be interpreted as the gravitational Aharonov-Bohm effect and Berry's phase.Comment: 14 pages, 1 figure; major additions and revisions introduced; main conclusions are unchanged; new affiliation adde

The Influence of Career Management to Perceived Job Performance of Bahrainis in Ebrahim Khalil Kanoo in the Kingdom of Bahrain

Like most organizations, EKK recognizes that career management is essential in achieving organizational objectives. In fact, it prides itself as one of the country’s best in terms of managing employee career growth. As well as it has an existing career management which been established from 1999 till now which is 20 years ago. However, it has been noted that there is yet a formal study conducted in EKK to assess the Influence of Career Management to Job Performance of Bahrainis. Thus, this study aims to assess the influence of Career Management Implementation to Perceived Job Performance of Bahrainis in Ebrahim Khalil Kanoo in the kingdom of Bahrain. The study utilized a descriptive research design involving 162 sampled respondents. The research made use of an adopted questionnaire as data gathering tool. The results of the study showed that over-all implementation of Career Management influences perceived employee performance. In addition, the study also found that among all dimensions of Career Management assessed in the study, Basic, Formal, Active Planning and Active Management Activities significantly influence Perceived Employee Performance. Finally, Multi-Directional Activity does not significantly influence perceived employee performance

Power, Control and Optimization

The guest editors are very grateful to all the collaborators of the journal, for their welcoming and approval of this special issue and for their guidance, help, and close advice at every stage. We guest editors wish all the readers an enjoyable, instructive, and inspiring study of the contributions of this journal special issue. Indeed, we cordially hope that our special issue will represent this journal as a rising and premium journal of science, which strongly supports research, education, and development everywhere on the globe