Variational principle for the Wheeler-Feynman electrodynamics

We adapt the formally-defined Fokker action into a variational principle for the electromagnetic two-body problem. We introduce properly defined boundary conditions to construct a Poincare-invariant-action-functional of a finite orbital segment into the reals. The boundary conditions for the variational principle are an endpoint along each trajectory plus the respective segment of trajectory for the other particle inside the lightcone of each endpoint. We show that the conditions for an extremum of our functional are the mixed-type-neutral-equations with implicit state-dependent-delay of the electromagnetic-two-body problem. We put the functional on a natural Banach space and show that the functional is Frechet-differentiable. We develop a method to calculate the second variation for C2 orbital perturbations in general and in particular about circular orbits of large enough radii. We prove that our functional has a local minimum at circular orbits of large enough radii, at variance with the limiting Kepler action that has a minimum at circular orbits of arbitrary radii. Our results suggest a bifurcation at some radius below which the circular orbits become saddle-point extrema. We give a precise definition for the distributional-like integrals of the Fokker action and discuss a generalization to a Sobolev space of trajectories where the equations of motion are satisfied almost everywhere. Last, we discuss the existence of solutions for the state-dependent delay equations with slightly perturbated arcs of circle as the boundary conditions and the possibility of nontrivial solenoidal orbits

Covariant EBK quantization of the electromagnetic two-body problem

We discuss a method to transform the covariant Fokker action into an implicit two-degree-of-freedom Hamiltonian for the electromagnetic two-body problem with arbitrary masses. This dynamical system appeared 100 years ago and it was popularized in the 1940's by the still incomplete Wheeler and Feynman program to quantize it as a means to overcome the divergencies of perturbative QED. Our finite-dimensional implicit Hamiltonian is closed and involves no series expansions. The Hamiltonian formalism is then used to motivate an EBK quantization based on the classical trajectories with a non-perturbative formula that predicts energies free of infinities.Comment: 21 page

Minimizers with discontinuous velocities for the electromagnetic variational method

The electromagnetic two-body problem has \emph{neutral differential delay} equations of motion that, for generic boundary data, can have solutions with \emph{discontinuous} derivatives. If one wants to use these neutral differential delay equations with \emph{arbitrary} boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined \emph{by} the Euler-Lagrange equations \emph{% on} trajectory points. Here we use the piecewise defined minimizers with the Li{\'{e}}nard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the \emph{generalized absorber hypothesis} that the far fields vanish asymptotically \emph{almost everywhere%} and show that localized orbits with far fields vanishing almost everywhere \emph{must} have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.Comment: corrected minor typo: piecewise differentiable on closed instead of open interval

CB1 Receptor Antagonism Blocks Stress-Potentiated Reinstatement of Cocaine Seeking in Rats

Rationale Under some conditions, stress, rather than directly triggering cocaine seeking, potentiates reinstatement to other stimuli, including a subthreshold cocaine dose. The mechanisms responsible for stress-potentiated reinstatement are not well defined. Endocannabinoid signaling is increased by stress and regulates synaptic transmission in brain regions implicated in motivated behavior. Objectives The objective of this study was to test the hypothesis that cannabinoid type 1 receptor (CB1R) signaling is required for stress-potentiated reinstatement of cocaine seeking in rats. Methods Following i.v. cocaine self-administration (2 h access/day) and extinction in male rats, footshock stress alone does not reinstate cocaine seeking but reinstatement is observed when footshock is followed by an injection of an otherwise subthreshold dose of cocaine (2.5 mg/kg, i.p.). CB1R involvement was tested by systemic administration of the CB1R antagonist AM251 (0, 1, or 3 mg/kg, i.p.) prior to testing for stress-potentiated reinstatement. Results Stress-potentiated reinstatement was blocked by both 1 and 3 mg/kg AM251. By contrast, AM251 only attenuated food-reinforced lever pressing at the higher dose (i.e., 3 mg/kg) and did not affect locomotor activity at either dose tested. Neither high-dose cocaine-primed reinstatement (10 mg/kg, i.p.) nor footshock stress-triggered reinstatement following long-access cocaine self-administration (6 h access/day) was affected by AM251 pretreatment. Footshock stress increased concentrations of both endocannabinoids, N-arachidonylethanolamine and 2-arachidonoylglycerol, in regions of the prefrontal cortex. Conclusions These findings demonstrate that footshock stress increases prefrontal cortical endocannabinoids and stress-potentiated reinstatement is CB1R-dependent, suggesting that CB1R is a potential therapeutic target for relapse prevention, particularly in individuals whose cocaine use is stress-related

Stress and Burnout in Nurse Leaders

Problem: Nurse leaders commonly experience stress and self-reported burnout. The associated negative consequences are compelling, yet few studies to date consider the nurse leader population. Stress is “a multidimensional phenomenon determined by a person’s perceptions and may be assessed as harm, loss, threat, or challenge” (Udod, Cummings, Care, & Jenkins, 2017a, p. 160). Burnout is a lack of professional fulfillment caused by emotional, physical, and psychological stress (Nurse Burnout, 2019). Drivers are associated and contributing factors which lead to stress and self-reported burnout. Purpose: The purposes of this correlational study are to (a) identify drivers from the literature and adapt an existing model to nurse leader populations, (b) investigate associations between drivers of stress among two nurse leader groups: Nurse Mangers/Nurse Supervisors and Chief Nursing Officers/Nurse Directors, (c) investigate association between drivers and self-reported burnout among all nurse leaders, and (d) compare drivers identified in the literature to drivers from the Minnesota Organization of Leaders in Nursing (MOLN) study. Conceptual Framework: The Job Demands-Resources (JD-R) Model of Burnout guided the literature review. We adapted our own model on stress leading to burnout in nurse leaders entitled Johnson, Nichols, and Sakhitab (JNS) Model of Stress Leading to Burnout in Nurse Leaders. The focus of the JNS model was to identify the drivers of stress leading to burnout in nurse leaders. Literature Search: Eight drivers of stress leading to burnout from the literature were: administrative duties, organizational constraints, role overload, lack of control, preparation, personal characteristics, quality patient care, and social support. Methods Data Analysis: The research method used for this thesis was a secondary analysis of the 2018 MOLN and the Minnesota Hospital Association Nurse Leader Burnout Survey. The Pearson product-moment correlation was used to assess relationships between drivers, stress, and burnout. The total sample included 210 nurse leaders. Results Data Analysis: Results from this secondary analysis found statistically significant drivers of stress in Nurse Managers and Nurse Supervisors (n = 90) were time (r = -.500, p = .000), control (r = -.321, p = .002), and resources (r = -.254, p = .016). The statistically significant drivers of stress in Chief Nursing Officers and Nurse Directors (n = 74) were time (r = -.492, p \u3c .000), resources (r = -.441, p = .000) control (r = -.387, p = .001), team efficiency (r = -.338, p = .003), and autonomy (r = -.250, p =.031). Drivers of self-reported burnout in nurse leaders (n = 210) in order of correlational strength were control, time, autonomy, resources, appreciation, team efficiency, value and quality (-.419 \u3c r \u3c -.181, p ≤ .009). Implications for Practice: Nurse leaders carry a high degree of responsibility and are unable to achieve optimal work/life balance. One solution is to restructure leadership hierarchy to include a co-manager role. A second implication for practice relates to the lack of control driver of stress; nurse leaders desire the freedom, empowerment, and autonomy to make decisions without fear for retribution. Lastly, an implication for practice relates to the drivers of social support and appreciation. It will be prudent for health care administrators to re-focus energies on provision of appreciation and recognition to nurse leaders. Implications for Research: The gap in longitudinal designed studies creates an opportunity for future research. We recommend replicating the MOLN study longitudinally and nationally to support findings from this secondary analysis. Future studies focusing on self-reported burnout need a standardized measurement tool. This will allow for direct comparison of data and stronger analysis of findings. Lastly, drivers of stress leading to burnout in nurse leaders must be universally defined

Aedes aegypti vector competence studies: A review.

Abstract Aedes aegypti is the primary transmitter of the four viruses that have had the greatest impact on human health, the viruses causing yellow fever, dengue fever, chikungunya, and Zika fever. Because this mosquito is easy to rear in the laboratory and these viruses grow in laboratory tissue culture cells, many studies have been performed testing the relative competence of different populations of the mosquito to transmit many different strains of viruses. We review here this large literature including studies on the effect of the mosquito microbiota on competence. Because of the heterogeneity of both mosquito populations and virus strains used, as well as methods measuring potential to transmit, it is very difficult to perform detailed meta-analysis of the studies. However, a few conclusions can be drawn: (1) almost no population of Ae. aegypti is 100% naturally refractory to virus infection. Complete susceptibility to infection has been observed for Zika (ZIKV), dengue (DENV) and chikungunya (CHIKV), but not yellow fever viruses (YFV); (2) the dose of virus used is directly correlated to the rate of infection; (3) Brazilian populations of mosquito are particularly susceptible to DENV-2 infections; (4) the Asian lineage of ZIKV is less infective to Ae. aegypti populations from the American continent than is the African ZIKV lineage; (5) virus adaptation to different species of mosquitoes has been demonstrated with CHIKV; (6) co-infection with more than one virus sometimes causes displacement while in other cases has little effect; (7) the microbiota in the mosquito also has important effects on level of susceptibility to arboviral infection; (8) resistance to virus infection due to the microbiota may be direct (e.g., bacteria producing antiviral proteins) or indirect in activating the mosquito host innate immune system; (9) non-pathogenic insect specific viruses (ISVs) are also common in mosquitoes including genome insertions. These too have been shown to have an impact on the susceptibility of mosquitoes to pathogenic viruses. One clear conclusion is that it would be a great advance in this type of research to implement standardized procedures in order to obtain comparable and reproducible results

Tunneling in Fractional Quantum Mechanics

We study the tunneling through delta and double delta potentials in fractional quantum mechanics. After solving the fractional Schr\"odinger equation for these potentials, we calculate the corresponding reflection and transmission coefficients. These coefficients have a very interesting behaviour. In particular, we can have zero energy tunneling when the order of the Riesz fractional derivative is different from 2. For both potentials, the zero energy limit of the transmission coefficient is given by $\mathcal{T}_0 = \cos^2{\pi/\alpha}$, where $\alpha$ is the order of the derivative ($1 < \alpha \leq 2$).Comment: 21 pages, 3 figures. Revised version; accepted for publication in Journal of Physics A: Mathematical and Theoretica

Enhancing the Educational Experience for Deaf and Hard of Hearing Students in Software Engineering

Software engineering is largely a communication-driven, team-oriented discipline. There are numerous hurdles for ensuring proper communication and interaction between all project stakeholders, including physical, technological, and cultural barriers. These obstructions not only affect software engineering in industry, but in academia as well. One possible issue that is often overlooked in software engineering education is how to best educate Deaf and hard-of-hearing (Deaf/HoH) students, and how to fully engage them in the classroom. In this paper, we present our experiences in teaching software engineering to Deaf/HoH students. In the classroom, these students work very closely in activities and on project teams with their hearing peers. We also present recommendations for creating a more robust software engineering educational experience for not only Deaf/HoH students, but for hearing students as well. We encourage instructors not only in software engineering programs, but in other computing disciplines to consider our recommendations and observations in order to enhance the educational experience for all students in the classroom, whether Deaf/HoH or hearing

Composição química de vinte e cinco híbridos de sorgo com capim-sudão (Sorghum bicolor x Sorghum sudanense) utilizados para produção de forragem.

Utilizando-se um delineamento experimental de blocos ao acaso e a comparacao das medias pelo teste de agrupamentos de Scott-Knott, vinte e tres hibridos experimentais e dos hibridos comerciais (AG 2501C e BRS 800) de Sorghum bicolor x Sorghum sudanense, foram avaliados quanto ao teor de materia seca (MS), fibra em detergente neutro (FDN), fibra em detergente acido (FDA), lignina e proteina bruta (PB). Com a colheita realizada aos 57 dias apos o plantio, os teores de MS variaram de 13,78 a 17,67% com media de 15,30%. Nao foram observadas diferenaas significativas (P<0,05) para os teores FDN e FDA, que variaram de 65,07 a 70,47% e 37,38 a 41,90%, respectivamente. Os valores obtidos para a lignina, tambem sem diferencas significativas (P<0,05) entre os 25 hibridos, ficaram entre 3,84 a 6,45%. Ja os conteudos de PB foram de 10,81 a 14,52%. alguns dos 23 hibridos experimentais demonstraram ter potencial para serem lancados comercialmente e apresentaram teores de MS e PB mais elevados (P<0,05) que os hibridos comerciais. Contudo, novos estudos que incluam avaliacoes com animais ainda sao necessarias

Qualidade e valor nutritivo das silagens de três híbridos de sorgo (Sorghum bicolor L.) colhidos em diferentes estádios de maturação.

Dois híbridos de sorgo de porte médio e colmo seco e um híbrido de porte alto e colmo suculento foram ensilados em oito estádios de maturação, a partir do florescimento. Foram 24 tratamentos com três repetições cada, sendo os três híbridos (AG 2006 e BR 700 - colmo seco, e BR 601 - colmo suculento) colhidos em oito estádios de maturação. Foram determinados os teores de MS, PB, perdas de MS, densidade, pH, nitrogênio amoniacal (N-NH3), fibra em detergente neutro (FDN), hemicelulose, celulose e lignina, DIVMS e porcentagem de fenóis totais. Utilizou-se o teste SNK para comparação das médias, com um delineamento inteiramente casualizado, em esquema fatorial 3x8. Com o avanço do estádio de maturação, ocorreu aumento na produção de MS até o quinto estádio. Houve, ainda, aumento nos teores de MS, que atingiram o nível ideal entre 21 e 28 dias após o florescimento. Os teores de PB e das frações fibrosas reduziram-se com a maturidade. Obtiveram-se baixos níveis de pH e N-NH3 em todas as silagens, além de baixas perdas de MS. Os híbridos tiveram comportamentos diferentes nos parâmetros lignina e DIVMS. Avaliaram-se os fenóis totais pelo método de azul da Prússia e todas as silagens apresentaram-se com tanino. Não foi encontrada correlação negativa entre os fenóis e a DIVMS. O híbrido AG2006 foi superior aos outros dois híbridos em algumas características e o híbrido BR 601 apesar de ser de porte alto, foi superior ao híbrido BR 700, de duplo propósito, nas variáveis DIVMS e frações fibrosas. Palavras-chave: ensilagem, forragem, nutrição animal, ruminante