Preliminary criteria for internal acoustic environments of orbiting space stations

Maximum noise levels for manned orbiting space station

Third World Revolutionaries: The Activism of the Third World Women’s Alliance and Alliance Against Women’s Oppression, 1970s-1980s

The Third World Women’s Alliance (TWWA) emerged from the Black Power politics of the Student Nonviolent Coordinating Committee and two black women’s caucuses, the Black Women’s Liberation Committee and the Black Women’s Alliance. Formed in 1970, as a multiracial, socialist feminist organization, the TWWA engaged in transnational and intersectional activism. This thesis examines how the Alliance articulated a Third World feminist identity from their founding to their reconfiguration in 1980 to the Alliance Against Women’s Oppression. I argue that through their publication Triple Jeopardy and their coalition building efforts, the Alliance developed a Third World feminist collective identity with the purpose of challenging racism, sexism, and imperialism. The thesis focuses on two of the TWWA’s projects: their role in organizing International Women’s Day Celebrations in the Bay area during the 1970s and their engagement with the Coalition to Fight Infant Mortality in East Oakland. The thesis is informed by the Third World Women’s Alliance and Alliance Against Women’s Oppression Records, both of which are housed at Smith College. Chapter one provides the intellectual foundation for the thesis by examining the TWWA’s ideological organ, Triple Jeopardy. Through the publication, the Alliance examined capitalist, racist, and sexist oppression and used the publication as a tool to radicalize and educate their readership. Chapter two examines the organization’s coalition work with the Third World Women’s Committee to Celebrate International Women’s Day. I contend that through the performance of music, skits, and poetry, the organization articulated a multifaceted Third World identity. Moreover, the Alliance’s attempt to expand their work beyond their organization and build coalitions with revolutionary organizations in the Bay Area reflected their goal of forming a mass people’s movement with Third World women at its center. Chapter three’s focus shifts to the Alliance’s fight for complete reproductive autonomy, arguing that the organization moved beyond the reproductive rights framework established by second wave feminists to one of reproductive justice. Their reproductive justice framework focused on more than just abortion, considering involuntary sterilization throughout the Third World and in the United States. The chapter will forefront the TWWA’s work with the Coalition to Fight Infant Mortality, when they spearheaded a community-driven investigation into high infant mortality rates at Highland Hospital in East Oakland during the 1970s

The X-ray Ridge Surrounding Sgr A* at the Galactic Center

We present the first detailed simulation of the interaction between the supernova explosion that produced Sgr A East and the wind-swept inner ~ 2-pc region at the Galactic center. The passage of the supernova ejecta through this medium produces an X-ray ridge ~ 9'' to 15'' to the NE of the supermassive black hole Sagittarius A* (Sgr A*). We show that the morphology and X-ray intensity of this feature match very well with recently obtained Chandra images, and we infer a supernova remnant age of less than 2,000 years. This young age--a factor 3--4 lower than previous estimates--arises from our inclusion of stellar wind effects in the initial (pre-explosion) conditions in the medium. The supernova does not clear out the central ~ 0.2-pc region around Sgr~A* and does not significantly alter the accretion rate onto the central black hole upon passage through the Galactic center.Comment: 10 pages, 3 figures, submitted to ApJ

Self-gravitating fragmentation of eccentric accretion disks

We consider the effects of eccentricity on the fragmentation of gravitationally unstable accretion disks, using numerical hydrodynamics. We find that eccentricity does not affect the overall stability of the disk against fragmentation, but significantly alters the manner in which such fragments accrete gas. Variable tidal forces around an eccentric orbit slow the accretion process, and suppress the formation of weakly-bound clumps. The "stellar" mass function resulting from the fragmentation of an eccentric disk is found to have a significantly higher characteristic mass than that from a corresponding circular disk. We discuss our results in terms of the disk(s) of massive stars at ~0.1pc from the Galactic Center, and find that the fragmentation of an eccentric accretion disk, due to gravitational instability, is a viable mechanism for the formation of these systems.Comment: 9 pages, 7 figures. Accepted for publication in Ap

Topological Quantum Critical Points in the Extended Bose-Hubbard Model

The combination of topology and quantum criticality can give rise to an exotic mix of counterintuitive effects. Here, we show that unexpected topological properties take place in a paradigmatic strongly correlated Hamiltonian: the 1D extended Bose-Hubbard model. In particular, we reveal the presence of two distinct topological quantum critical points with localized edge states and gapless bulk excitations. Our results show that the topological critical points separate two phases, one topologically protected and the other topologically trivial, both characterized by a long-range ordered string correlation function. The long-range order persists also at the topological critical points and explains the presence of localized edge states protected by a finite charge gap. Finally, we introduce a superresolution quantum gas microscopy scheme for dipolar dysprosium atoms, which provides a reliable route towards the experimental study of topological quantum critical points

Is there really a debris disc around ζ2 Reticuli\zeta^2\,\mathrm{Reticuli} ?

The presence of a debris disc around the Gyr-old solar-type star $\zeta^2\,\mathrm{Reticuli}$ was suggested by the $\mathit{Spitzer}$ infrared excess detection. Follow-up observations with $\mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $\zeta^2\,\mathrm{Reticuli}$. In these observations, no flux has been detected around $\zeta^2\,\mathrm{Reticuli}$ that exceeds the $3\sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $\zeta^2\,\mathrm{Reticuli}$ are $5.7\,\mathrm{\mu Jy/arcsec^2}$ at 1.3 mm, and $26\,\mathrm{\mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $\mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion.Comment: 6 pages, 2 figures, 2 table

On the development of QPOs in Bondi-Hoyle accretion flows

The numerical investigation of Bondi-Hoyle accretion onto a moving black hole has a long history, both in Newtonian and in general-relativistic physics. By performing new two-dimensional and general-relativistic simulations onto a rotating black hole, we point out a novel feature, namely, that quasi-periodic oscillations (QPOs) are naturally produced in the shock cone that develops in the downstream part of the flow. Because the shock cone in the downstream part of the flow acts as a cavity trapping pressure perturbations, modes with frequencies in the integer ratios 2:1 and 3:1 are easily produced. The frequencies of these modes depend on the black-hole spin and on the properties of the flow, and scale linearly with the inverse of the black-hole mass. Our results may be relevant for explaining the detection of QPOs in Sagittarius A*, once such detection is confirmed by further observations. Finally, we report on the development of the flip-flop instability, which can affect the shock cone under suitable conditions; such an instability has been discussed before in Newtonian simulations but was never found in a relativistic regime.Comment: 11 pages, 7 figure