A new approach for efficient simulation of Coulomb interactions in ionic fluids

We propose a simplified version of local molecular field (LMF) theory to treat Coulomb interactions in simulations of ionic fluids. LMF theory relies on splitting the Coulomb potential into a short-ranged part that combines with other short-ranged core interactions and is simulated explicitly. The averaged effects of the remaining long-ranged part are taken into account through a self-consistently determined effective external field. The theory contains an adjustable length parameter sigma that specifies the cut-off distance for the short-ranged interaction. This can be chosen to minimize the errors resulting from the mean-field treatment of the complementary long-ranged part. Here we suggest that in many cases an accurate approximation to the effective field can be obtained directly from the equilibrium charge density given by the Debye theory of screening, thus eliminating the need for a self-consistent treatment. In the limit sigma -> 0, this assumption reduces to the classical Debye approximation. We examine the numerical performance of this approximation for a simple model of a symmetric ionic mixture. Our results for thermodynamic and structural properties of uniform ionic mixtures agree well with similar results of Ewald simulations of the full ionic system. In addition we have used the simplified theory in a grand-canonical simulation of a nonuniform ionic mixture where an ion has been fixed at the origin. Simulations using short-ranged truncations of the Coulomb interactions alone do not satisfy the exact condition of complete screening of the fixed ion, but this condition is recovered when the effective field is taken into account. We argue that this simplified approach can also be used in the simulations of more complex nonuniform systems.Comment: To be published in Journal of Chemical Physic

Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently unknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC photometry accurate to $\sim$3% for four DAZs and one DA with circumstellar absorption lines in the UV. We search for excesses due to unseen companions or circumstellar dust disks. We use {\em Hubble Space Telescope} NICMOS imaging of these white dwarfs to gauge the level of background contamination to our targets as well as rule out common proper motion companions to WD 1620-391. All of our targets show no excesses due to companions $>$20 M$_{J}$, ruling out all but very low mass companions to these white dwarfs at all separations. No excesses due to circumstellar disks are observed, and we place limits on what types of disks may still be present.Comment: 18 pages, 8 figures, Accepted to A

The Digital Engine Model: Lead Generation Through Applied DCM Strategies

Digital Content Marketing (DCM) has become a primary tool for marketers in driving lead generation in today’s digital marketing world. Leading brands are creating and curating content in order to develop brand equity, connecting content to brand story and narrative. And while strong theoretical models of content marketing have been discussed in the marketing literature, like Hollebeek and Macky (2019), there is a dearth of understanding about the application and direct impact of organic digital content strategies on marketing directives. This paper investigates an applied model, called The Digital Engine, which provides instruction on proper digital content marketing instruction and then measures the impact of this instruction through a live 8-week campaign across 221 active websites. Results indicate that the Digital Engine instruction not only provides applicable understanding but that the applied methodology provides significant impact in driving users through various methods of brand acquisition and retention through to the website where created and curated content lead website users to complete call-to-action forms. Most importantly, completion of these online forms produces serviceable leads to the sales team, whereby supporting the overarching aim of all DCM strategies, lead generation

Gender and Racial Gaps in Support for Policing and Correctional Reforms: Are the Gaps a Consequence of Political Partisanship?

Divisive criminal justice issues are typically framed through gender and racial lenses, with little empirical work considering the increasing role of political partisanship. Using the 2016 Cooperative Congressional Election Study (N = 55,000), we estimate multivariate models of support for four policing and correctional reforms. The models initially point to gender gaps and racial gaps. However, as with many public policy issues, support for criminal justice reforms are largely a product of political partisanship—the gender and racial gaps are largely a consequence of gender and racial gaps in partisanship and appear to be driven by white Republican men. As legislative bodies continue to be overrepresented with individuals with the same demographic profile, criminal justice reform prospects are limited.</p

Consanguinity and rare mutations outside of MCCC genes underlie nonspecific phenotypes of MCCD.

Purpose3-Methylcrotonyl-CoA carboxylase deficiency (MCCD) is an autosomal recessive disorder of leucine catabolism that has a highly variable clinical phenotype, ranging from acute metabolic acidosis to nonspecific symptoms such as developmental delay, failure to thrive, hemiparesis, muscular hypotonia, and multiple sclerosis. Implementation of newborn screening for MCCD has resulted in broadening the range of phenotypic expression to include asymptomatic adults. The purpose of this study was to identify factors underlying the varying phenotypes of MCCD.MethodsWe performed exome sequencing on DNA from 33 cases and 108 healthy controls. We examined these data for associations between either MCC mutational status, genetic ancestry, or consanguinity and the absence or presence/specificity of clinical symptoms in MCCD cases.ResultsWe determined that individuals with nonspecific clinical phenotypes are highly inbred compared with cases that are asymptomatic and healthy controls. For 5 of these 10 individuals, we discovered a homozygous damaging mutation in a disease gene that is likely to underlie their nonspecific clinical phenotypes previously attributed to MCCD.ConclusionOur study shows that nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes.Genet Med 17 8, 660-667

Assessing law enforcement websites: a comparative analysis exploring types, quantity and quality of information available

PurposeThe purpose of this study is to explore the availability of information on law enforcement websites in the state of Wisconsin.Design/methodology/approachThe study conducted a content analysis of all 179 county and municipal local law enforcement agency websites within Wisconsin. The authors then implemented a comparative analysis that explored whether the quantity and quality of information available on law enforcement websites are similar to those of local governments and school districts. The authors then estimated models to test whether there is a relationship between the population size served and gender distribution of law enforcement departments to the availability of information on law enforcement websites.FindingsLaw enforcement websites contain a noticeable lack of information. The finding is even more apparent when comparing law enforcement websites to the websites of local governments and school districts. Finally, the authors show a positive link between information sharing on law enforcement websites and the proportion of the civilian staff at an agency that are women.Originality/valuePast studies that reviewed the make-up of law enforcement websites analyzed large law enforcement departments rather than local law enforcement departments, which notably represent the majority of most law enforcement departments. The authors also explicitly demonstrate that the commitment to information sharing is lagging within law enforcement websites compared to local-level governments. Future scholarship and law enforcement departments may benefit from exploring the employment of female civilians.</p

Escape of Trajectories From a Vase-Shaped Cavity

We consider the escape of ballistic trajectories from an open, vase-shaped cavity. Such a system serves as a model for microwaves escaping from a cavity or electrons escaping from a microjunction. Fixing the initial position of a particle and recording its escape time as a function of the initial launch direction, the resulting escape-time plot shows “epistrophic fractal” structure—repeated structure within structure at all levels of resolution with new features appearing in the fractal at longer time scales. By launching trajectories simultaneously in all directions (modeling an outgoing wave), a detector placed outside the cavity would measure a train of escaping pulses. We connect the structure of this chaotic pulse train with the fractal structure of the escape-time plot