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The thermal transformations which take place in solid methyl-substituted ammonium perchlorates have been studied using high-temperature X-ray diffraction and differential thermal analysis techniques. In the temperature range from 20°C to their decomposition temperature (above 300°C), ammonium perchlorate and tetramethyl ammonium perchlorate undergo only one enantiomorphic phase transition, namely at 240 and 340°C (with decomposition), respectively. This I—II transition is ascribed to the beginning of the free rotation of the ClO4− ions. The rotation of the cations, however, begins below room temperature. If the symmetry of the cation is lowered by having both methyl groups and hydrogens arranged around the nitrogen (as in monomethyl, dimethyl, and trimethyl ammonium perchlorates), there is an additional enantiomorphic phase transition. This I—II transformation is ascribed to the rotation of the cations which have, in the partially substituted ions, two sets of non-equivalent symmetry axes (different moments of inertia). The temperatures of transformation are discussed in terms of the space requirements for rotation. Symmetries and cell dimensions of some modifications were determined.
This essay offers a critical examination of use of the term “long civil rights movement” as a framework for understanding the legal history of the battle against racial inequality in twentieth-century America. Proponents of the long movement argue that expanding the chronological boundaries of the movement beyond the 1950s and 1960s allows scholars to better capture the diverse social mobilization efforts and ideas that fueled the black freedom struggle. While not questioning the long framework's usefulness for studying the social movement dynamics of racial justice activism, I suggest that the long framework is of more limited value for those who seek to understand the development of civil rights, as a legal claim, particularly in the first half of the twentieth century. The tendency of long movement scholars to treat civil rights as a pliable category into which they can put any and all racial justice claims is in tension with historical understandings of the term. Susan Carle's Defining the Struggle: National Organizing for Racial Justice, 1880–1915 suggests an alternative approach. Her detailed and nuanced account of a period in American history when racial justice activists understood civil rights as a relatively narrow subset of legal remedies within a much broader struggle for racial equality indicates the need for an alternate history of civil rights—one that places the evolving, contested, and historically particularized concept of civil rights at the center of inquiry.
“Civil Rights” is a term that did not evolve out of black culture, but, rather, out of American law. As such, it is a term of limitation.
This essay provides a summary and critical appraisal of Risa Goluboff's Vagrant Nation: Police Power, Constitutional Change, and the Making of the 1960s, a book that interweaves the stories of an eclectic cast of characters who were the targets of vagrancy law prosecutions with stories of the lawyers who challenged these prosecutions. In charting the demise of what she terms a “vagrancy law regime,” Goluboff provides insights on the major social and political developments of the 1940s through the 1970s, including the labor movement, the black freedom struggle, the antiwar movement, and the sexual revolution. Goluboff's most significant achievement is her ability to identify in seemingly scattered challenges to vagrancy law a coherent and historically significant episode of constitutional change. Although I question whether the book delivers on its promise to reframe the way we understand the “long 1960s,” Vagrant Nation nonetheless offers a model of how to integrate social history and doctrinal history into a compelling narrative of constitutional change.
Laser-based compact MeV X-ray sources are useful for a variety of applications such as radiography and active interrogation of nuclear materials. MeV X rays are typically generated by impinging the intense laser onto ~mm-thick high-Z foil. Here, we have characterized such a MeV X-ray source from 120 TW (80 J, 650 fs) laser interaction with a 1 mm-thick tantalum foil. Our measurements show X-ray temperature of 2.5 MeV, flux of 3 × 1012 photons/sr/shot, beam divergence of ~0.1 sr, conversion efficiency of ~1%, that is, ~1 J of MeV X rays out of 80 J incident laser, and source size of 80 m. Our measurement also shows that MeV X-ray yield and temperature is largely insensitive to nanosecond laser contrasts up to 10−5. Also, preliminary measurements of similar MeV X-ray source using a double-foil scheme, where the laser-driven hot electrons from a thin foil undergoing relativistic transparency impinging onto a second high-Z converter foil separated by 50–400 m, show MeV X-ray yield more than an order of magnitude lower compared with the single-foil results.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
Coho salmon (Oncorhynchus kisutch), Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) in Puget Sound and the Strait of Georgia have exhibited declines in marine survival over the last 40 years. While the cause of these declines is unknown, multiple factors, acting cumulatively or synergistically, have likely contributed. To evaluate the potential contribution of a broad suite of drivers on salmon survival, we used qualitative network modelling (QNM). QNM is a conceptually based tool that uses networks with specified relationships between the variables. In a simulation framework, linkages are weighted and then the models are subjected to user-specified perturbations. Our network had 33 variables, including: environmental and oceanographic drivers (e.g., temperature and precipitation), primary production variables, food web components from zooplankton to predators and anthropogenic impacts (e.g., habitat loss and hatcheries). We included salmon traits (survival, abundance, residence time, fitness and size) as response variables. We invoked perturbations to each node and to suites of drivers and evaluated the responses of these variables. The model showed that anthropogenic impacts resulted in the strongest negative responses in salmon survival and abundance. Additionally, feedbacks through the food web were strong, beginning with primary production, suggesting that several food web variables may be important in mediating effects on salmon survival within the system. With this model, we were able to compare the relative influence of multiple drivers on salmon survival.
The SkyMapper Transient survey (SMT) is exploring variability in the southern sky by performing (a) a rolling search to discover and study supernovæ, and (b) a Target of Opportunity programme that uses the robotic SkyMapper Telescope at Siding Spring Observatory. The supernova survey is obtaining a non-targeted sample of Type Ia supernovæ (SNe Ia) at low redshifts, z < 0.1, and studying other interesting transients found with the search strategy. We have a Target of Opportunity programme with an automatic response mechanism to search for optical counterparts to gravitational-wave and fast radio-burst events; it benefits from SkyMapper’s large field of view of 5.7 sq. deg. and a rapid data reduction pipeline.
We present first results of the SMT survey. The SMT pipeline can process and obtain potential candidates within 12 hours of observation. It disentangles real transients from processing artefacts using a machine-learning algorithm. To date, SMT has discovered over 60 spectroscopically confirmed supernovæ, several peculiar objects, and over 40 SNe Ia including one (SNIa 2016hhd) which was found within the first few days of explosion. We have also participated in searches for optical counterparts of gravitational waves, fast radio bursts and other transients, and have published observations of the optical counterpart of the gravitational-wave event GW170817. We also participate in coordinated observations with the Deeper Wider Faster programme, and the Kepler K2 cosmology project.
Polycyclic Aromatic Hydrocarbon (PAH) molecules have been proposed as candidates to explain the Diffuse Interstellar Bands (DIBs). We have performed laboratory measurements of coronene, using rare gas matrix isolation techniques and UV photolysis. Our aim was to search for a possible identification of the 4430 Å DIB, but also to provide data almost free from environmental band shifts and broadening, which can be used for astronomical identification of the species.
Sublimation (vaporization) of the icy component of a cometary nucleus determines the initial composition of the coma gas as it streams outward and escapes. Photolytic reactions in the inner coma, escape of fast, light species such as atomic and molecular hydrogen, and solar wind interaction in the outer coma alter the chemical composition and the physical nature of the coma gas. Models that describe these interactions must include (1) chemical kinetics, (2) coma energy balance, (3) multifluid flow for the rapidly escaping light components, the heavier bulk fluid, and the plasma with separate temperatures for electrons and the remainder of the gas, (4) transition from a collision dominated inner region to free molecular flow of neutrals in the outer region, (5) pickup of cometary ions by the solar wind, (6) counter and cross streaming of neutrals with respect to the plasma which outside of the contact surface also contains solar wind ions, and (7) magnetic fields carried by the solar wind. Progress on such models is described and results including velocity, temperature, and number density profiles for important chemical species are presented and compared with observations.
The magnetic structure of a simple, relatively symmetric sunspot is determined using the extremely Zeeman sensitive Landé g = 3 line of Fe I at 1.5648 μm. From the measured strength and inclination of the magnetic field we estimate the fraction of the total magnetic flux of the sunspot passing through the solar surface in the penumbra. It is found that on average approximately 1/2–2/3 of the total magnetic flux of the spot emerges in the penumbra. Sunspot penumbrae are therefore deep, i.e., the τ = 1 level does not correspond to the lower magnetic boundary of the spot in its penumbra.
In continuation of a series of studies devoted to the dynamics of the solar photosphere and chromosphere we have attempted to further extend the range of heights in the atmosphere towards the transition region by including observations of the He I 10830 line. We have recorded simultaneous time series of He I 10830 and Mg I 8807 spectra in the quiet solar atmosphere using the echelle spectrograph at the German Vacuum Tower Telescope in Izaña, Tenerife. The velocity signal derived from the Doppler shifts of He 10830 clearly reveals oscillatory motions. The intensity of He 10830, on the other hand, is hardly affected by the oscillations. In the cell interior the 3-min oscillations prevail. Longer periods are found ain the cell boundaries of the chromospheric network where He absorption is enhanced. The V–V phase difference spectrum between the oscillations of He 10830 and those of Mg 8807 confirms previous observations of a non-propagating component that dominates the acoustic wave spectrum in the chromosphere.
Compound-specific radiocarbon analysis (CSRA) of benzene polycarboxylic acids (BPCAs) yields molecular-level, source-specific information necessary to constrain isotopic signatures of pyrogenic carbon. However, the purification of individual BPCAs requires a multistep procedure that typically results in only microgram quantities of the target analyte(s). Such small samples are highly susceptible to contamination by extraneous carbon, which needs to be minimized and carefully accounted for in order to yield accurate results. Here, we undertook comprehensive characterization and quantification of contamination associated with molecular radiocarbon (14C) BPCA analyses through systematic processing of multiple authentic standards with both fossil and modern 14C signatures at various concentrations. Using this approach, we precisely apportion the contribution of extraneous carbon with respect to the four implemented subprocedures. Assuming a constant source and quantity of extraneous carbon we correct and statistically evaluate uncertainties in resulting 14C data. Subsequently, we examine the results of triplicate analyses of reference materials representing four different environmental matrices (sediment, soil, aerosol, riverine natural organic matter) and apportion their BPCA sources in terms of carbon residues derived from biomass or fossil fuel combustion. This comprehensive approach to CSRA facilitates retrieval of robust 14C data, with application in environmental studies of the continuum of pyrogenic carbon.
Oxtotitlán Cave paintings have been considered among the earliest in Mesoamerica on stylistic grounds, but confirmation of this hypothesis through absolute dating has not been attempted until now. We describe the application of advanced radiocarbon strategies developed for situations such as caves with high carbon backgrounds. Using a low-temperature plasma oxidation system, we dated both the ancient paint and the biogenic rock coatings that cover the paint layers at Oxtotitlán. Our research has significantly expanded the time frame for the production of polychrome rock paintings encompassing the Early Formative and Late Formative/Early Classic periods, statistically spanning a long era from before ca. 1500 cal B.C. to cal A.D. 600.