The Effect of Magnetic Field Tilt and Divergence on the Mass Flux and Flow Speed in a Line-Driven Stellar Wind

We carry out an extended analytic study of how the tilt and faster-than-radial expansion from a magnetic field affect the mass flux and flow speed of a line-driven stellar wind. A key motivation is to reconcile results of numerical MHD simulations with previous analyses that had predicted non-spherical expansion would lead to a strong speed enhancement. By including finite-disk correction effects, a dynamically more consistent form for the non-spherical expansion, and a moderate value of the line-driving power index $\alpha$, we infer more modest speed enhancements that are in good quantitative agreement with MHD simulations, and also are more consistent with observational results. Our analysis also explains simulation results that show the latitudinal variation of the surface mass flux scales with the square of the cosine of the local tilt angle between the magnetic field and the radial direction. Finally, we present a perturbation analysis of the effects of a finite gas pressure on the wind mass loss rate and flow speed in both spherical and magnetic wind models, showing that these scale with the ratio of the sound speed to surface escape speed, $a/v_{esc}$, and are typically 10-20% compared to an idealized, zero-gas-pressure model.Comment: Accepted for publication in ApJ, for the full version of the paper go to: http://www.bartol.udel.edu/~owocki/preprints/btiltdiv-mdotvinf.pd

Non-agricultural Market Access: A South Asian Perspective

A key element of the Doha Round of trade negotiations is liberalisation of trade in industrial products, commonly known as non-agricultural market access (NAMA). These negotiations are important for developing countries as these will determine the market access opportunities through which they can improve their growth prospects. This paper examines the key issues of NAMA from the South Asian perspective, outlines a negotiating strategy for increased market access, and spells out some policy implications.

A Rigid-Field Hydrodynamics approach to modeling the magnetospheres of massive stars

We introduce a new Rigid-Field Hydrodynamics approach to modeling the magnetospheres of massive stars in the limit of very-strong magnetic fields. Treating the field lines as effectively rigid, we develop hydrodynamical equations describing the 1-dimensional flow along each, subject to pressure, radiative, gravitational, and centrifugal forces. We solve these equations numerically for a large ensemble of field lines, to build up a 3-dimensional time-dependent simulation of a model star with parameters similar to the archetypal Bp star sigma Ori E. Since the flow along each field line can be solved for independently of other field lines, the computational cost of this approach is a fraction of an equivalent magnetohydrodynamical treatment. The simulations confirm many of the predictions of previous analytical and numerical studies. Collisions between wind streams from opposing magnetic hemispheres lead to strong shock heating. The post-shock plasma cools initially via X-ray emission, and eventually accumulates into a warped, rigidly rotating disk defined by the locus of minima of the effective (gravitational plus centrifugal) potential. But a number of novel results also emerge. For field lines extending far from the star, the rapid area divergence enhances the radiative acceleration of the wind, resulting in high shock velocities (up to ~3,000 km/s) and hard X-rays. Moreover, the release of centrifugal potential energy continues to heat the wind plasma after the shocks, up to temperatures around twice those achieved at the shocks themselves. Finally, in some circumstances the cool plasma in the accumulating disk can oscillate about its equilibrium position, possibly due to radiative cooling instabilities in the adjacent post-shock regions.Comment: 21 pages, 12 figures w/ color, accepted by MNRA

Magnetic fields, winds and X-rays of the massive stars in the Orion Nebula Cluster

In some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.Comment: Proceedings of IAUS272: Active OB star

A dynamical magnetosphere model for periodic Halpha emission from the slowly rotating magnetic O star HD191612

The magnetic O-star HD191612 exhibits strongly variable, cyclic Balmer line emission on a 538-day period. We show here that its variable Halpha emission can be well reproduced by the rotational phase variation of synthetic spectra computed directly from full radiation magneto-hydrodynamical simulations of a magnetically confined wind. In slow rotators such as HD191612, wind material on closed magnetic field loops falls back to the star, but the transient suspension of material within the loops leads to a statistically overdense, low velocity region around the magnetic equator, causing the spectral variations. We contrast such "dynamical magnetospheres" (DMs) with the more steady-state "centrifugal magnetospheres" of stars with rapid rotation, and discuss the prospects of using this DM paradigm to explain periodic line emission from also other non-rapidly rotating magnetic massive stars.Comment: 5 pages, 5 figures, accepted for publication in MNRAS letter

Catalytic Control of the Nanomorphology and Mechanical Properties of Aliphatic Shape-Memory Aerogels

Shape-memory poly(isocyanurate-urethane) (PIR-PUR) aerogels are nanoporous solids that can return to their original shape after being compressed, through a heating actuation step. This thesis compares the effectiveness of various metal ions as catalysts in the formation of PIR-PUR aerogels, and explores the correlation between catalytic activity, nanomorphology, and mechanical properties of the resulting aerogels. The gelation rate was found to increase from Fe to Cu and then decline from Cu to Ga in the periodic table. CuCl2 was found to be the fastest catalyst, and FeCl3 the slowest. The morphology of the aerogels changed from bicontinuous to spheroidal as the catalyst concentration decreased. The elastic modulus (E) was found to be correlated with gelation time, by tuning the nano porosity of PIR-PUR aerogels. The shape-memory of PIR-PUR aerogels was also used for synthesizing meta-materials by tuning the micro porous design of flexible aerogels. The shape-memory response of these aerogels has been improved by incorporating an auxetic effect, resulting in a negative Poisson\u27s ratio. This means that the aerogels experience volume contraction upon compression and can be stored indefinitely in a temporary shape by cooling below the glass transition temperature. Upon heating above the glass transition temperature, the compressed form expands to its original shape/size. This technology has various applications in commercial, aeronautical, and aerospace industries, including minimally invasive medical devices, soft robotics, and storage of deployable space structures and planetary habitats during transport -- Abstract, p. i

Human factor security: evaluating the cybersecurity capacity of the industrial workforce

Purpose: As cyber-attacks continue to grow, organisations adopting the internet-of-things (IoT) have continued to react to security concerns that threaten their businesses within the current highly competitive environment. Many recorded industrial cyber-attacks have successfully beaten technical security solutions by exploiting human-factor vulnerabilities related to security knowledge and skills and manipulating human elements into inadvertently conveying access to critical industrial assets. Knowledge and skill capabilities contribute to human analytical proficiencies for enhanced cybersecurity readiness. Thus, a human-factored security endeavour is required to investigate the capabilities of the human constituents (workforce) to appropriately recognise and respond to cyber intrusion events within the industrial control system (ICS) environment. / Design/methodology/approach: A quantitative approach (statistical analysis) is adopted to provide an approach to quantify the potential cybersecurity capability aptitudes of industrial human actors, identify the least security-capable workforce in the operational domain with the greatest susceptibility likelihood to cyber-attacks (i.e. weakest link) and guide the enhancement of security assurance. To support these objectives, a Human-factored Cyber Security Capability Evaluation approach is presented using conceptual analysis techniques. / Findings: Using a test scenario, the approach demonstrates the capacity to proffer an efficient evaluation of workforce security knowledge and skills capabilities and the identification of weakest link in the workforce. / Practical implications: The approach can enable organisations to gain better workforce security perspectives like security-consciousness, alertness and response aptitudes, thus guiding organisations into adopting strategic means of appropriating security remediation outlines, scopes and resources without undue wastes or redundancies. / Originality/value: This paper demonstrates originality by providing a framework and computational approach for characterising and quantify human-factor security capabilities based on security knowledge and security skills. It also supports the identification of potential security weakest links amongst an evaluated industrial workforce (human agents), some key security susceptibility areas and relevant control interventions. The model and validation results demonstrate the application of action research. This paper demonstrates originality by illustrating how action research can be applied within socio-technical dimensions to solve recurrent and dynamic problems related to industrial environment cyber security improvement. It provides value by demonstrating how theoretical security knowledge (awareness) and practical security skills can help resolve cyber security response and control uncertainties within industrial organisations