The formation of brown dwarfs in discs: Physics, numerics, and observations

A large fraction of brown dwarfs and low-mass stars may form by gravitational fragmentation of relatively massive (a few 0.1 Msun), extended (a few hundred AU) discs around Sun-like stars. We present an ensemble of radiative hydrodynamic simulations that examine the conditions for disc fragmentation. We demonstrate that this model can explain the low-mass IMF, the brown dwarf desert, and the binary properties of low-mass stars and brown dwarfs. Observing discs that are undergoing fragmentation is possible but very improbable, as the process of disc fragmentation is short lived (discs fragment within a few thousand years).Comment: 4 pages, for the proceedings of IAU Symposium 270: Computational Star Formation, Barcelona, 201

Climate Smart Farming for Women in East Africa

According to the United Nations Food and Agriculture Organization, 60% of East Africans live as subsistence farmers. This population is particularly vulnerable to the effects of climate change which has increased the duration and intensity of droughts and floods. Droughts and floods can destroy an entire season’s harvest, causing sustenance farmers and their families to struggle for food until the next season. In an attempt to mitigate the severe effects of climate change on these farmers and reduce food insecurity in East Africa, the team has designed a small-scale aquaponic farming system that simultaneously grows fish and vegetables. This system is founded on sustainability, as aquaponics uses significantly less water to grow crops than traditional farming, making it more resilient to both severe droughts and floods, the system also does not rely on external fertilizers, and it uses recycled materials as often as possible. This aquaponic system was designed for women’s collectives in East Africa who requested help in building a portfolio of projects that they can teach to women in rural East Africa. These women’s organizations work in rural villages throughout Uganda and Kenya to help local women and their families adapt to the changing climate. Currently, their efforts have been focused on improving the quality and supply of water in the villages by constructing latrines, water filters, and rainwater catchment systems. During the 2017-2018 academic year, team members designed and built the aquaponic system in Santa Clara, California, then deployed the first prototype in Kampala, Uganda, and trained several of the collective’s leaders how to build and operate the system

Breaking the Cycle: How Nevada Can Effectuate Meaningful Criminal Justice Reform

Why does society punish criminals? This paper examines what Nevada is attempting to accomplish through enacting and enforcing its criminal laws. We examine the current state of, as well as the challenges facing, Nevada’s criminal justice system. Additionally, we identify and propose certain solutions to reduce both recidivism and the financial burden that incarceration imposes on the state by looking to best practices in other states, as well as certain mechanisms and provisions that were, for one reason or another, removed from Nevada Assembly Bill 236

Brown dwarfs forming in discs: where to look for them?

A large fraction of the observed brown dwarfs may form by gravitational fragmentation of unstable discs. This model reproduces the brown dwarf desert, and provides an explanation the existence of planetary-mass objects and for the binary properties of low-mass objects. We have performed an ensemble of radiative hydrodynamic simulations and determined the statistical properties of the low-mass objects produced by gravitational fragmentation of discs. We suggest that there is a population of brown dwarfs loosely bound on wide orbits (100-5000 AU) around Sun-like stars that surveys of brown dwarf companions should target. Our simulations also indicate that planetary-mass companions to Sun-like stars are unlikely to form by disc fragmentation.Comment: To appear in the proceedings of the conference "New technologies for probing the diversity of brown dwarfs and exoplanets", Shanghai 200

The PINK1/Parkin pathway: a mitochondrial quality control system?

Significant insight into the mechanisms that contribute to dopaminergic neurodegeneration in Parkinson disease has been gained from the analysis of genes linked to rare heritable forms of parkinsonism such as PINK1 and parkin, loss-of-function mutations of which cause autosomal recessive parkinsonism. PINK1 encodes a mitochondrially targeted Ser/Thr kinase and parkin encodes a ubiquitin-protein ligase. Functional studies of PINK1 and Parkin in animal and cellular model systems have shown that both proteins play important roles in maintaining mitochondrial integrity. Genetic studies of PINK1 and Parkin orthologs in flies have shown that PINK1 acts upstream from Parkin in a common pathway that appears to regulate mitochondrial morphology. Mitochondrial morphology is regulated by mitochondrial fission and fusion-promoting proteins, and is important in a variety of contexts, including mitochondrial trafficking and mitochondrial quality control. In particular, mitochondrial fission appears to promote the segregation of terminally dysfunctional mitochondria for degradation in the lysosome through a process termed mitophagy. Recent work has shown that Parkin promotes the degradation of dysfunctional mitochondria in vertebrate cell culture. Here we postulate a model whereby the PINK1/Parkin pathway regulates mitochondrial dynamics in an effort to promote the turnover of damaged mitochondria

Are the majority of Sun-like stars single?

It has recently been suggested that, in the field, $\sim\!\!56\%$ of Sun-like stars ($0.8\,{\rm M}_{_\odot}\lesssim M_\star\lesssim 1.2\,{\rm M}_{_\odot}$) are single. We argue here that this suggestion may be incorrect, since it appears to be based on the multiplicity frequency of systems with Sun-like primaries, and therefore takes no account of Sun-like stars that are secondary (or higher-order) components in multiple systems. When these components are included in the reckoning, it seems likely that only $\sim\!46\%$ of Sun-like stars are single. This estimate is based on a model in which the system mass function has the form proposed by Chabrier, with a power-law Salpeter extension to high masses; there is a flat distribution of mass ratios; and the probability that a system of mass $M$ is a binary is $\,0.50 + 0.46\log_{_{10}}\!\left(M/{\rm M}_{_\odot}\right)\,$ for $\,0.08\,{\rm M}_{_\odot}\leq M\leq 12.5\,{\rm M}_{_\odot}$, $\,0\,$ for $\,M<0.08\,{\rm M}_{_\odot}$, and $\,1\,$ for $\,M>12.5\,{\rm M}_{_\odot}$. The constants in this last relation are chosen so that the model also reproduces the observed variation of multiplicity frequency with primary mass. However, the more qualitative conclusion, that a minority of Sun-like stars are single, holds up for virtually all reasonable values of the model parameters. Parenthetically, it is still likely that the majority of {\it all} stars in the field are single, but that is because most M Dwarfs probably are single.Comment: 6 pages. Accepted by MNRA

Monte Carlo Radiative Transfer in Embedded Prestellar Cores

We implement a Monte Carlo radiative transfer method, that uses a large number of monochromatic luminosity packets to represent the radiation transported through a system. These packets are injected into the system and interact stochastically with it. We test our code against various benchmark calculations and determine the number of packets required to obtain accurate results under different circumstances. We then use this method to study cores that are directly exposed to the interstellar radiation field (non-embedded cores) and find similar results with previous studies. We also explore a large number of models of cores that are embedded in the centre of a molecular cloud. Our study indicates that the temperature profiles in embedded cores are less steep than those in non-embedded cores. Deeply embedded cores (ambient cloud with visual extinction larger than 15-25) are almost isothermal at around 7-8 K. The temperature inside cores surrounded by an ambient cloud of even moderate thickness (Av~5) is less than 12 K, which is lower than previous studies have assumed. Thus, previous mass calculations of embedded cores (for example in the rho Ophiuchi protocluster), based on mm continuum observations, may underestimate core masses by up to a factor of 2. Our study shows that the best wavelength region to observe embedded cores is between 400 and 500 microns, where the core is quite distinct from the background. We also predict that very sensitive observations (~1-3 MJy/sr) at 170-200 microns can be used to estimate how deeply a core is embedded in its parent molecular cloud. The upcoming HERSCHEL mission (ESA, 2007) will, in principle, be able to detect these features and test our models.Comment: 15 pages, 18 figures, accepted by A&