Nano-polishing substrates for optics and microelectronics

В результаті дослідження полірування монокристалічних матеріалів показано, що полірування плоских поверхонь оптоелектронних елементів з монокристалів карбіду кремнію доцільно здійснювати з використанням полірувальної суспензії порошків на основі МАХ-фази Ti3AlC2 та колоїдних систем наночастинок, а монокристалів сапфіру – за допомогою суспензії з алмазних мікропорошків, порошків кубічного нітриду бору та MAX-фази Ti3AlC2. Нанополірування поверхонь елементів монокристалів сапфіру слід здійснювати при використанні колоїдної системи наночастинок або традиційних складів на основі колоїдного двооксиду кремнію. Показано також, що продуктивність полірування монокристалів карбіду кремнію та сапфіру обернено пропорційна енергії переносу, максимальне значення якої відповідає мінімальній шорсткості.As a result of research of polishing single crystal materials it was shown that the polishing flat surfaces of optoelectronic elements of single crystal silicon carbide is advantageously carried out by using a polishing slurry of the powders based on MAXphase Ti3AlC2 and colloidal nanoparticulate systems, and single crystal sapphire - using suspensions of diamond micron powders of the cubic boron nitride powders and MAX-phase Ti3AlC2. Nano-polishing surfaces of elements of single crystal sapphire should be performed using colloidal nanoparticulate systems or traditional formulations based on colloidal silica. It is also shown that the polishing efficiency of single crystal silicon carbide and sapphire is inversely proportional to the transfer energy, the maximum value of which correspond to a minimum roughness.В результате исследования полирования монокристаллических материалов показано, что полирование плоских поверхностей оптоэлектронных элементов из монокристаллов карбида кремния целесообразно осуществлять с использованием полировочной суспензии порошков на основе МАХ-фазы Ti3AlC2 и коллоидных систем наночастиц, а монокристаллов сапфира - с помощью суспензии из алмазных микропорошков, порошков кубического нитрида бора и MAXфазы Ti3AlC2. Нанополирование поверхностей элементов монокристаллов сапфира следует осуществлять при использовании коллоидной системы наночастиц или традиционных составов на основе коллоидного диоксида кремния. Показано также, что производительность полировки монокристаллов карбида кремния и сапфира обратно пропорциональна энергии переноса, максимальное значение которой соответствует минимальной шероховатости

A Parametric Study of Erupting Flux Rope Rotation. Modeling the "Cartwheel CME" on 9 April 2008

The rotation of erupting filaments in the solar corona is addressed through a parametric simulation study of unstable, rotating flux ropes in bipolar force-free initial equilibrium. The Lorentz force due to the external shear field component and the relaxation of tension in the twisted field are the major contributors to the rotation in this model, while reconnection with the ambient field is of minor importance. Both major mechanisms writhe the flux rope axis, converting part of the initial twist helicity, and produce rotation profiles which, to a large part, are very similar in a range of shear-twist combinations. A difference lies in the tendency of twist-driven rotation to saturate at lower heights than shear-driven rotation. For parameters characteristic of the source regions of erupting filaments and coronal mass ejections, the shear field is found to be the dominant origin of rotations in the corona and to be required if the rotation reaches angles of order 90 degrees and higher; it dominates even if the twist exceeds the threshold of the helical kink instability. The contributions by shear and twist to the total rotation can be disentangled in the analysis of observations if the rotation and rise profiles are simultaneously compared with model calculations. The resulting twist estimate allows one to judge whether the helical kink instability occurred. This is demonstrated for the erupting prominence in the "Cartwheel CME" on 9 April 2008, which has shown a rotation of \approx 115 degrees up to a height of 1.5 R_sun above the photosphere. Out of a range of initial equilibria which include strongly kink-unstable (twist Phi=5pi), weakly kink-unstable (Phi=3.5pi), and kink-stable (Phi=2.5pi) configurations, only the evolution of the weakly kink-unstable flux rope matches the observations in their entirety.Comment: Solar Physics, submitte

Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this paper, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out an helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by \citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic

Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results

The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant amounts of energy to the interface region and corona. In recent years an abundance of high-resolution observations from state-of-the-art facilities have provided new and exciting ways of disentangling the characteristics of oscillatory phenomena propagating through the dynamic chromosphere. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate the role waves play in supplying energy to sustain chromospheric and coronal heating. Here, we review the recent progress made in characterising, categorising and interpreting oscillations manifesting in the solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review

The Physical Processes of CME/ICME Evolution

As observed in Thomson-scattered white light, coronal mass ejections (CMEs) are manifest as large-scale expulsions of plasma magnetically driven from the corona in the most energetic eruptions from the Sun. It remains a tantalizing mystery as to how these erupting magnetic fields evolve to form the complex structures we observe in the solar wind at Earth. Here, we strive to provide a fresh perspective on the post-eruption and interplanetary evolution of CMEs, focusing on the physical processes that define the many complex interactions of the ejected plasma with its surroundings as it departs the corona and propagates through the heliosphere. We summarize the ways CMEs and their interplanetary CMEs (ICMEs) are rotated, reconfigured, deformed, deflected, decelerated and disguised during their journey through the solar wind. This study then leads to consideration of how structures originating in coronal eruptions can be connected to their far removed interplanetary counterparts. Given that ICMEs are the drivers of most geomagnetic storms (and the sole driver of extreme storms), this work provides a guide to the processes that must be considered in making space weather forecasts from remote observations of the corona.Peer reviewe

The Origin, Early Evolution and Predictability of Solar Eruptions

Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt