Sensitivity of the r-process to nuclear masses

The rapid neutron capture process (r-process) is thought to be responsible for the creation of more than half of all elements beyond iron. The scientific challenges to understanding the origin of the heavy elements beyond iron lie in both the uncertainties associated with astrophysical conditions that are needed to allow an r-process to occur and a vast lack of knowledge about the properties of nuclei far from stability. There is great global competition to access and measure the most exotic nuclei that existing facilities can reach, while simultaneously building new, more powerful accelerators to make even more exotic nuclei. This work is an attempt to determine the most crucial nuclear masses to measure using an r-process simulation code and several mass models (FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure are determined by the changes in the resulting r-process abundances. Nuclei around the closed shells near N=50, 82, and 126 have the largest impact on r-process abundances irrespective of the mass models used.Comment: 5 pages, 4 figures, accepted in European Physical Journal

Double step structure and meandering due to the many body interaction at GaN(0001) surface in N-rich conditions

Growth of gallium nitride on GaN(0001) surface is modeled by Monte Carlo method. Simulated growth is conducted in N-rich conditions, hence it is controlled by Ga atoms surface diffusion. It is shown that dominating four-body interactions of Ga atoms can cause step flow anisotropy. Kinetic Monte Carlo simulations show that parallel steps with periodic boundary conditions form double terrace structures, whereas initially V -shaped parallel step train initially bends and then every second step moves forward, building regular, stationary ordering as observed during MOVPE or HVPE growth of GaN layers. These two phenomena recover surface meandered pair step pattern observed, since 1953, on many semiconductor surfaces, such as SiC, Si or GaN. Change of terrace width or step orientation particle diffusion jump barriers leads either to step meandering or surface roughening. Additionally it is shown that step behavior changes with the Schwoebel barrier height. Furthermore, simulations under conditions corresponding to very high external particle flux result in triangular islands grown at the terraces. All structures, emerging in the simulations, have their corresponding cases in the experimental results.Comment: 25 pages, 8 figure

Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios

In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and beta decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r-process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r-process, a cold r-process in which the temperature and density drop rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International Nuclear Physics Conference (INPC) 201

Smart cities wouldn’t let housing costs drive the worse-off into deeper disadvantage

Scholarly article published online. Article describing new peer reviewed research on housing affordability and home owner and rental mobility. Contributes a policy reflection on the process by which Australian cities are being shaped by the housing affordably crisis.Emma Baker, Andrew Beer, Rebecca Bentle

Distributed digital contexts and learning : personal empowerment and social transformation in marginalized populations

The role of digital media and learning has often been synonymous with the use of open education resources in formal institutional settings. Further, open and distance learning has been criticized for focusing narrowly on educational objectives, ignoring socio-political issues of access and participation by marginalized populations. This study examines the lived experiences of female migrant domestic workers (N=20) in Singapore attending Open University. Mobile and social media supplement open and distance learning resources to allow for open practices of consumption, production and sharing in distributed contexts of digital learning. Marginalized students engaged in participation and collaboration activities, with specific privacy practices due to their social positions. Digital learning led to substantive learning for personal empowerment and social transformation, with aspirational strategies often involving digital skills. The discussion reflects on identity management across formal and informal digital settings as a means of transforming societal discourses of discrimination

Cultural Evolutionary Tipping Points in the Storage and Transmission of Information

Human culture has evolved through a series of major tipping points in information storage and communication. The first was the appearance of language, which enabled communication between brains and allowed humans to specialize in what they do and to participate in complex mating games. The second was information storage outside the brain, most obviously expressed in the Upper Paleolithic Revolution - the sudden proliferation of cave art, personal adornment, and ritual in Europe some 35,000-45,000 years ago. More recently, this storage has taken the form of writing, mass media, and now the Internet, which is arguably overwhelming humans\u27 ability to discern relevant information. The third tipping point was the appearance of technology capable of accumulating and manipulating vast amounts of information outside humans, thus removing them as bottlenecks to a seemingly self-perpetuating process of knowledge explosion. Important components of any discussion of cultural evolutionary tipping points are tempo and mode, given that the rate of change, as well as the kind of change, in information storage and transmission has not been constant over the previous million years

‘The sword that was broken …’: the detection of recycled iron in the archaeological record

Although the recycling of materials such as copper and glass is widely known and generally well understood within archaeological contexts, far less is known about the recycling of iron. Iron recycling is more complex than that of other metals for two reasons. First, normal manufacturing processes, which include forging several components to make a composite object, offer the opportunity to include recycled iron. Second, the material itself is more complex than Cu alloys. The alloys of Fe, depending primarily on C content, are very different in terms of properties and can be interconverted by (normally) removing C such as decarburizing cast iron to make wrought iron. Thus, recycling practices are potentially intimately combined with such processes. These factors, combined with the poor preservation of archaeological iron and the consequent reluctance to carry out extensive studies (which often require destructive analysis via metallography), mean that there are no clear criteria for identifying recycled iron. However, limited historical documentation suggests, at least indirectly, that such recycling was common. This paper is neither comprehensive nor definitive, but merely intends to promote discussion and awareness of iron recycling by hypothesizing several possible mechanisms and providing a few illustrative archaeological examples