Mesoscopic modelling of the interaction of infrared lasers with composite materials: an application to dental enamel

The mesostructure and composition of composite materials determine their mechanical, optical and thermal properties and, consequently, their response to incident radiation. We have developed general finite element models of porous composite materials under infrared radiation to examine the influence of pore size on one of the determining parameters of the stress distribution in the material: the temperature distribution. We apply them to the specific case of human dental enamel, a material which has nanometer scale pores containing water/organic, and predict the maximum temperature reached after a single 0.35 μs laser pulse of sub-ablative fluence by two lasers: Er:YAG (2.9 μm) and CO2 (10.6 μm). For the Er:YAG laser, the results imply a strong dependence of the maximum temperature reached at the pore on the area-to-volume ratio of the pore, whereas there is little such dependence for CO2 lasers. Thus, CO2 lasers may produce more reproducible results than Er:YAG lasers when it comes to enamel ablation, which may be of significant interest during clinical practice. More generally, when ablating composite materials by infrared lasers researchers should account for the material’s microstructure and composition when designing experiments or interpreting results, since a more simplistic continuum approach may not be sufficient to explain differences observed during ablation of materials with similar optical properties or of the same material but using different wavelengths

Mesoscopic modelling of enamel interaction with mid-infrared sub-ablative laser pulses

Using a finite element approach the authors model the influence of enamel's microstructure and water distribution on the temperature and stress at the centre of the laser spot, for a CO2 laser working at 10.6 μm, with 0.35 μs pulse duration and sub-ablative intensity. The authors found that the distribution of water in enamel significantly influences the stress generated at the end of one laser pulse: much lower (two orders of magnitude) stress values occur in models with homogeneously distributed water than in models with 0.27 vol.% water located in pores or 4 vol.% in layers. The amount of water in enamel has a strong influence on the stress distribution, but not on the maximum stress values reached. However, different water contents do not influence the temperature distribution in enamel. These results suggest that adequate modelling of the ablation mechanisms in enamel, as in other highly inhomogeneous materials, must include their structure at the mesoscopic scale

A log analysis study of 10 years of ebook consumption in academic library collections

Even though libraries have been offering eBooks for more than a decade, very little is known about eBook access and consumption in academic library collections. This paper addresses this gap with a log analysis study of eBook access at the library of the University of Waikato. This in-depth analysis covers a period spanning 10 years of eBook use at this university. We draw conclusions about the use of eBooks at this institution and compare the results with other published studies of eBook usage at tertiary institutes

Superconductivity and Stoichiometry in the BSCCO-family Materials

We report on magnetization, c-axis and ab-plane resistivity, critical current, electronic band structure and superconducting gap properties. Bulk measurements and photoemission data were taken on similar samples.Comment: 4 pages, latex, to be published in Journal of Superconductivity. two figures available from Jian Ma at [email protected]

Public health critical race praxis at the intersection of traffic stops and injury epidemiology

Background: Law enforcement traffic stops are one of the most common entryways to the US justice system. Conventional frameworks suggest traffic stops promote public safety by reducing dangerous driving practices and non-vehicular crime with little to no collateral damage to individuals and communities. Critical frameworks interrogate these assumptions, identifying significant individual and community harms that disparately impact Black, Indigenous, and People of Color (BIPOC) and low-income communities. Methods: The Public Health Critical Race Praxis (PHCRP) and multi-level frameworks from community anti-racist training were combined into a structured diagram to guide intervention and research teams in contrasting conventional and critical perspectives on traffic stops. The diagram divides law enforcement and drivers/residents as two separate agent types that interact during traffic stops. These two agent types have different conventional and critical histories, priorities, and perspectives at multiple levels, including individual, interpersonal, institutional, and cultural levels. Conventional solutions (identifying explicitly racist officers, “meet-a-cop” programs, police interaction training for drivers) are born from conventional frameworks (rewarding crime prevention regardless of cost, the war on drugs saves lives, driver behavior perfectionism). While conventional perspectives focus on individual and interpersonal levels, critical perspectives more deeply acknowledge dynamics at institutional and cultural levels. Critical solutions may be hard to discover without critical frameworks, including that law enforcement creates measurable collateral damage and disparate social control effects; neighborhood patrol priorities can be set without community self-determination or accountability and may trump individual and interpersonal dynamics; and the war on drugs is highly racialized and disproportionally enforced through traffic stop programs. Conclusions: Traffic stop enforcement and crash prevention programs that do not deeply and critically consider these dynamics at multiple levels, not just law enforcement-driver interactions at the individual and interpersonal levels, may be at increased risk of propagating histories of BIPOC discrimination. In contrast, public health and transportation researchers and practitioners engaged in crash and injury prevention strategies that employ law enforcement should critically consider disparate history and impacts of law enforcement in BIPOC communities. PHCRP, anti-racism frameworks, and the included diagram may assist them in organizing critical thinking about research studies, interventions, and impacts

Re-prioritizing traffic stops to reduce motor vehicle crash outcomes and racial disparities

Background: Law enforcement traffic stops are one of the most common entryways to the US justice system. Conventional frameworks suggest traffic stops promote public safety by reducing dangerous driving practices and non-vehicular crime. Law enforcement agencies have wide latitude in enforcement, including prioritization of stop types: (1) safety (e.g. moving violation) stops, (2) investigatory stops, or (3) economic (regulatory and equipment) stops. In order to prevent traffic crash fatalities and reduce racial disparities, the police department of Fayetteville, North Carolina significantly re-prioritized safety stops. Methods: Annual traffic stop, motor vehicle crash, and crime data from 2002 to 2016 were combined to examine intervention (2013-2016) effects. Fayetteville was compared against synthetic control agencies built from 8 similar North Carolina agencies by weighted matching on pre-intervention period trends and comparison against post-intervention trends. Results: On average over the intervention period as compared to synthetic controls, Fayetteville increased both the number of safety stops + 121% (95% confidence interval + 17%, + 318%) and the relative proportion of safety stops (+ 47%). Traffic crash and injury outcomes were reduced, including traffic fatalities - 28% (- 64%, + 43%), injurious crashes - 23% (- 49%, + 16%), and total crashes - 13% (- 48%, + 21%). Disparity measures were reduced, including Black percent of traffic stops - 7% (- 9%, - 5%) and Black vs. White traffic stop rate ratio - 21% (- 29%, - 13%). In contrast to the Ferguson Effect hypothesis, the relative de-prioritization of investigatory stops was not associated with an increase in non-traffic crime outcomes, which were reduced or unchanged, including index crimes - 10% (- 25%, + 8%) and violent crimes - 2% (- 33%, + 43%). Confidence intervals were estimated using a different technique and, given small samples, may be asymmetrical. Conclusions: The re-prioritization of traffic stop types by law enforcement agencies may have positive public health consequences both for motor vehicle injury and racial disparity outcomes while having little impact on non-traffic crime

The impact of the COVID-19 pandemic on the utilization of emergency department services for the treatment of injuries

Context: The global COVID-19 pandemic has had a major impact on the utilization of healthcare services; however, the impact on population-level emergency department (ED) utilization patterns for the treatment of acute injuries has not been fully characterized. Objective: This study examined the frequency of North Carolina (NC) EDs visits for selected injury mechanisms during the first eleven months of the COVID-19 pandemic. Methods: Data were obtained from the NC Disease Event Tracking and Epidemiologic Collection Tool (NC DETECT), NC's legislatively mandated statewide syndromic surveillance system for the years 2019 and 2020. Frequencies of January – November 2020 NC ED visits were compared to frequencies of 2019 visits for selected injury mechanisms, classified according to International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) injury diagnosis and mechanism codes. Results: In 2020, the total number of injury-related visits declined by 19.5% (N = 651,158) as compared to 2019 (N = 809,095). Visits related to motor vehicle traffic crashes declined by a greater percentage (29%) and falls (19%) declined by a comparable percentage to total injury-related visits. Visits related to assault (15%) and self-harm (10%) declined by smaller percentages. Medication/drug overdose visits increased (10%), the only injury mechanism studied to increase during this period. Conclusion: Both ED avoidance and decreased exposures may have contributed to these declines, creating implications for injury morbidity and mortality. Injury outcomes exacerbated by the pandemic should be addressed by timely public health responses

Extensions of the matrix Gelfand-Dickey hierarchy from generalized Drinfeld-Sokolov reduction

The $p\times p$ matrix version of the $r$-KdV hierarchy has been recently treated as the reduced system arising in a Drinfeld-Sokolov type Hamiltonian symmetry reduction applied to a Poisson submanifold in the dual of the Lie algebra $\widehat{gl}_{pr}\otimes {\Complex}[\lambda, \lambda^{-1}]$. Here a series of extensions of this matrix Gelfand-Dickey system is derived by means of a generalized Drinfeld-Sokolov reduction defined for the Lie algebra $\widehat{gl}_{pr+s}\otimes {\Complex}[\lambda,\lambda^{-1}]$ using the natural embedding $gl_{pr}\subset gl_{pr+s}$ for $s$ any positive integer. The hierarchies obtained admit a description in terms of a $p\times p$ matrix pseudo-differential operator comprising an $r$-KdV type positive part and a non-trivial negative part. This system has been investigated previously in the $p=1$ case as a constrained KP system. In this paper the previous results are considerably extended and a systematic study is presented on the basis of the Drinfeld-Sokolov approach that has the advantage that it leads to local Poisson brackets and makes clear the conformal ($\cal W$-algebra) structures related to the KdV type hierarchies. Discrete reductions and modified versions of the extended $r$-KdV hierarchies are also discussed.Comment: 60 pages, plain TE

Continuous variable entanglement and quantum state teleportation between optical and macroscopic vibrational modes through radiation pressure

We study an isolated, perfectly reflecting, mirror illuminated by an intense laser pulse. We show that the resulting radiation pressure efficiently entangles a mirror vibrational mode with the two reflected optical sideband modes of the incident carrier beam. The entanglement of the resulting three-mode state is studied in detail and it is shown to be robust against the mirror mode temperature. We then show how this continuous variable entanglement can be profitably used to teleport an unknown quantum state of an optical mode onto the vibrational mode of the mirror.Comment: 18 pages, 10 figure