How strong are the Rossby vortices?

The Rossby wave instability, associated with density bumps in differentially rotating discs, may arise in several different astrophysical contexts, such as galactic or protoplanetary discs. While the linear phase of the instability has been well studied, the nonlinear evolution and especially the saturation phase remain poorly understood. In this paper, we test the non-linear saturation mechanism analogous to that derived for wave-particle interaction in plasma physics. To this end we perform global numerical simulations of the evolution of the instability in a two-dimensional disc. We confirm the physical mechanism for the instability saturation and show that the maximum amplitude of vorticity can be estimated as twice the linear growth rate of the instability. We provide an empirical fitting formula for this growth rate for various parameters of the density bump. We also investigate the effects of the azimuthal mode number of the instability and the energy leakage in the spiral density waves. Finally, we show that our results can be extrapolated to 3D discs.Comment: Accepted for publication in MNRA

Relativistic Jets from Accretion Disks

The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf., 200

Identifying Industrial Education and Training Needs: Developing a Community College Custom Program

This study examined manufacturing firms\u27 characteristics and environmental factors and their relationships to the perceived importance of basic workplace skills and the preferences of employers toward customized training partnerships with community colleges. Key individuals in the human resource departments responsible for planning and decision making of employing companies were surveyed. The Workplace Education Survey was used to collect data on the employers\u27 perceptions about the importance of basic skills groups, about workplace-based customized training as the preferred means of delivering training in each of seven basic skills groups to their employees, and to determine their preferences for providers of the training. The survey also included customized training partnerships with community colleges. The study analyzed the relationships that exist in comparing the size of the firm and other characteristics identified in the literature with the respondents perceptions regarding the importance of the seven basic skills groups, workplace-based customized training, and partnerships with community colleges. Adaptability Skills, Communication Skills, and Group Effectiveness skills emerge as the most important workplace skills groups, and community colleges as the preferred providers according to the respondents to this study. Findings also revealed that changes in the nature of work and workplace skills are being dictated by the application of computers

Miles H. Lovelace to Dr. Silver, 30 August 1963

Personal correspondenc

Martin, Ghana, and Global Legal Studies

This brief essay uses global legal studies to reconsider Dr. Martin Luther King, Jr.\u27s activism after Gayle v. Browder. During this undertheorized portion of King\u27s career, the civil rights leader traveled the world and gained a greater appreciation for comparative legal and political analysis. This essay explores King\u27s first trip abroad and demonstrates how King\u27s close study of Kwame Nkrumah\u27s approaches to law reform helped to lay the foundation for watershed moments in King\u27s own life. In To Redeem the Soul of America: The Southern Christian Leadership Conference and Martin Luther King, Jr., renowned civil rights scholar and author, Adam Fairclough, offered penetrating and important assessments of Dr. King\u27s civil rights activism from 1957 to 1959. Fairclough asserted that the Montgomery Bus Boycott captured the world\u27s imagination, with King becoming a figure of national and international significance, easily overshadowing the South\u27s other black leadership. Yet after the U.S. Supreme Court\u27s decision in Gayle v. Browder, Fairclough rightfully notes, King attempted, but was unable, to spark Montgomery-style, mass protests elsewhere. The minister\u27s newly established Southern Christian Leadership Conference (SCLC) also had serious difficulty in sustaining a formidable political agenda. King\u27s inexperience with organizational management, and more importantly, the organization\u27s loose, top-down structure undermined the SCLC\u27s effectiveness and eventually led to the group\u27s decline. The late 1950s, in Fairclough\u27s view, were the civil rights leader\u27s fallow years. In the wake of Gayle, the racial icon traveled the globe. In 1957, King flew to Accra to celebrate Ghana\u27s independence as a guest of Prime Minister Kwame Nkrumah. But King\u27s first trip abroad took him far beyond the festivities in Accra. The minister\u27s itinerary was stacked with other foreign capitals. King trekked across West Africa, stopping over in Monrovia, Dakar, and Kano, and he crisscrossed Western Europe, exploring Lisbon, London, Paris, Rome, and Geneva. In 1959, King made a pilgrimage to the land of Gandhi at the request of India\u27s Prime Minister Jawaharlal Nehru. And again, King used the foreign leader\u27s invitation as a chance to tour the world. Before King returned to the United States, he ventured to Karachi, Athens, Beirut, Jerusalem, and Cairo. King\u27s overseas travels allowed him to participate in major global events, provided him respite from the day-today toils of the Southern struggle, and gave him the ability to forge stronger transnational ties with other liberation movements. And while King\u27s foreign stays are underappreciated, his close study of these nations\u27 legal and political systems are even more so. These travels created new opportunities for the recently minted Ph.D. to examine foreign law and affairs and apply the lessons he learned abroad to the burgeoning civil rights at home. Martin, Ghana, and Global Legal Studies is part of a larger project which details King\u27s interest in comparative law and politics. This brief essay examines how King used Nkrumah\u27s early approach to constitutional politics in the former Gold Coast to frame his own commitment to the First Amendment of the U.S. Constitution. Such a reappraisal of King\u27s experiences in Ghana, in turn, offers a fresh understanding of King\u27s fallow years

Of Protest and Property: An Essay in Pursuit of Justice for Breonna Taylor

In March 2020, Louisville police officers fatally shot Breanna Taylor in her apartment while executing a no-knock warrant. There was great outrage over the killing of the innocent woman, and Kentucky Attorney General Daniel Cameron led an investigation of the officer-involved shooting. Activists protested in Louisville after Taylor\u27s killing, and when Cameron\u27s investigation appeared stalled, these activists even conducted a sit-in on Cameron\u27s front lawn. They demanded immediate justice for Taylor. Cameron sharply responded, lecturing the activists on how to achieve justice. He contended that neither trespassing on private property nor escalation in tactics could advance the cause of justice. Cameron\u27s bold assertion invites a discussion of how civil rights activists have and continue to use trespassing and escalation to pursue justice. This Essay explores the relationship between civil rights and property rights and finds parallels between the sit-in movement of the 1960s and the Black Lives Matter Movement. This Essay also finds parallels between Cameron\u27s criticisms of the Black Lives Matter Movement and criticisms of the sit-in movement of the 1960s. The Essay concludes by suggesting paths forward in the struggle to find justice for Taylor