Rapid dissipation in a current sheet driven by footpoints motions

Context.Wave energy dissipation by viscous and resistive damping in magnetic coronal plasmas is addressed. A two and one half dimensional, line-tied magnetic channel is considered whose footpoints are disturbed by buffeting motions of the photosphere. Aims.The aim of the analysis is to determine how effectively shear Alfvén waves, driven by footpoint motions and resonating in the channel, can be damped by visco-resistive friction. Methods.The problem is analyzed using a mixture of numerical and analytic techniques. Dynamic simulations, based on a cyclic footpoint driver, show that phase mixing resulting from variations in the magnetic field of the channel is instrumental in setting up a permanent "resonance regime" for the system. Analytic methods are used to analyze the resonance regime and to develop scaling laws for the rate of energy dissipation. Results.We show that in the general case where the Alfvén velocity profile may be linearized around the resonance, the dissipation rate is "fast" in that it is not limited by small damping coefficients. Although large energies can accumulate within the channel in the limit of very small damping, we show that by tuning the driver to low frequencies, both the energy level and the dissipation rate can be made insensitive to the level of the damping

Visco-resistive shear wave dissipation in magnetic X-points

We consider the viscous and resistive dissipation of perpendicularly polarized shear waves propagating within a planar magnetic X-point. To highlight the role played by the two-dimensional geometry, the damping of travelling Alfvèn waves that propagate within an unbounded, but non-orthogonal X-point topology is analyzed. It is shown that the separatrix geometry affects both the dissipation time and the visco-resistive scaling of the energy decay. Our main focus, however, is on developing a theoretical description of standing wave dissipation for orthogonal, line-tied X-points. A combination of numerical and analytic treatments confirms that phase mixing provides a very effective mechanism for dissipating the wave energy. We show that wave decay comprises two main phases, an initial rapid decay followed by slower eigenmode evolution, both of which are only weakly dependent on the visco-resistive damping coefficients

Near Optimal Exploration-Exploitation in Non-Communicating Markov Decision Processes

While designing the state space of an MDP, it is common to include states that are transient or not reachable by any policy (e.g., in mountain car, the product space of speed and position contains configurations that are not physically reachable). This leads to defining weakly-communicating or multi-chain MDPs. In this paper, we introduce \tucrl, the first algorithm able to perform efficient exploration-exploitation in any finite Markov Decision Process (MDP) without requiring any form of prior knowledge. In particular, for any MDP with $S^{\texttt{C}}$ communicating states, $A$ actions and $\Gamma^{\texttt{C}} \leq S^{\texttt{C}}$ possible communicating next states, we derive a $\widetilde{O}(D^{\texttt{C}} \sqrt{\Gamma^{\texttt{C}} S^{\texttt{C}} AT})$ regret bound, where $D^{\texttt{C}}$ is the diameter (i.e., the longest shortest path) of the communicating part of the MDP. This is in contrast with optimistic algorithms (e.g., UCRL, Optimistic PSRL) that suffer linear regret in weakly-communicating MDPs, as well as posterior sampling or regularised algorithms (e.g., REGAL), which require prior knowledge on the bias span of the optimal policy to bias the exploration to achieve sub-linear regret. We also prove that in weakly-communicating MDPs, no algorithm can ever achieve a logarithmic growth of the regret without first suffering a linear regret for a number of steps that is exponential in the parameters of the MDP. Finally, we report numerical simulations supporting our theoretical findings and showing how TUCRL overcomes the limitations of the state-of-the-art

Sorteerwater gereinigd met ozon

Energie uit de lucht wordt het tegenwoordig ook wel genoemd. Futuroloog Wim de Ridder weet het zeker : uit zonne-energie gehaalde elektriciteit wordt steeds goedkoper. Over zo'n tien jaar komt er een omslag en wordt het mogelijk stroom voor een habbekrats te producere

Evolution of Occupational Therapy Practice: Life History of Charlie Baumer, COTA

Charlie Baumer is a Certified Occupational Therapy Assistant (COTA) who was interviewed by two year II occupational therapy students at the University of North Dakota at Casper College as part of a life history qualitative study. The interview was a semi-structured interview that lasted two hours with questions that were geared toward the history and evolution of occupational therapy in Wyoming. This single interview is a part of a larger life history qualitative study to gather information in regards to the history and evolution of occupational therapy practice in North Dakota and Wyoming through the life histories of occupational therapy in both states. The students designed a series of questions regarding Charlie\u27s perspective on the profession, his experiences, and how the profession has changed in Wyoming overtime. This study is intended to contribute to current and future generations of occupational therapy practice has evolved over time in North Dakota and Wyoming. Upon data analysis, the students identified three categories, Legality, OT Practice, and Characteristics. Charlie demonstrated his passion for occupational therapy by sharing his experiences within the profession. His contribution to the profession indicated how occupational therapy has evolved in the state of Wyoming and how it will continue to evolve.https://commons.und.edu/ot-oral-histories-posters/1006/thumbnail.jp

An investigation into the enhancement of fingermarks in blood on fruit and vegetables

A number of studies have reported the successful enhancement of latent fingermarks on fruit and vegetables. A study was set up to identify the most effective technique for the enhancement of fingermarks in blood on various fruit and vegetables. The enhancement techniques targeted different components in blood and consisted of protein stains (e.g. acid black 1), peroxidase reagents (e.g. leuco crystal violet) and amino acid stains (e.g. ninhydrin). Different variables such as the ageing periods of the marks and a diminishing series were employed to assess the suitability and sensitivity of the enhancement techniques.Overall, the use of different protein stains appeared to be the most effective techniques for the enhancement of fingermarks in blood on fruit and vegetables. In addition, the aubergine and cucumber skins appeared to be the most responsive surface to the different chemical techniques during enhancement. On the contrary, little or no enhancement was achieved for fingermarks in blood on the nectarine fruit

RECENT ADVANCES IN METAL-CATALYZED C-H FUNCTIONALIZATION OF PYRIMIDINONES, QUINAZOLINONES AND FUSED QUINAZOLINONES

International audienceThis review emphasises the recent developments in metal-catalyzed functionalization using direct C-H bond activation of pyrimidinones (uracils), quinazolinones and quinazolinone-based fused poly-N-heterocycles as well as metal-catalyzed C-H functionalization of high valuable 2-arylquinazolinones

From Here to There: An Occupational Screening Tool for Transitioning Soldiers

Time has shown that it can be difficult for military personnel to resume their typical life roles within civilian life. The wars in Iraq and Afghanistan were the longest wars in United States history and involved some of the most intense ground engagements since Vietnam (Cogan, 2014). This left many soldiers to deal with the traumatic experiences they went through. This study aimed at developing a screening tool to address the difficulties experienced by veterans during their transition into civilian life. The researchers began with a thorough review of literature to identify the occupational challenges the project would address. Following completion of the literature review, the researchers identified an occupational therapy model to guide the development of the screening tool and accompanying manual. Once the tool and the manual was created the researchers presented the documents to a local veterans club and finally presented the project at oral comprehensive exams at the university. The researchers created the Military Community Reintegration Screen (MCRS), which addresses three domains related to the person, occupation, and environment. Each domain is further broken down into subdomains and tasks that are specific to a veteran’s transition to civilian life. The manual addresses how to use and score the screening tool, as well as when to make a referral to occupational therapy services. This tool has not been clinically tested or used. Further research on the development, usefulness, and effectiveness of the screening tool is still desired by the researchers. Screening tools and assessments are available to military personnel for reintegration into the community; however, they are generally used from research purposes or are not part of the separation requirements, therefore, are not being completed by the soldiers. There are still individuals who are not receiving the treatment they need and due to the stigma around mental illness, many soldiers who are vulnerable to mental illness are denying their need for mental health treatment

Stochastic dynamic simulation of fruit abortion: a case study of sweet pepper

Abortion of reproductive organs diminishes yields in many crops. In indeterminate greenhouse crops, alternating periods of fruit abortion and fruit set exist, resulting in fluctuations in fruit yield. Factors affecting the level of abortion are e.g., the supply and demand for assimilates (source and sink strength, respectively), temperature and cultivar. However, simulation of fruit abortion is still a weak part of crop simulation models. Variation in fruit abortion exists between plants, which results in differences in the timing and the number of set fruits. Therefore, simulating fruit abortion with variation could give more realistic simulation results. The probability of a fruit to abort should be related to factors like source strength and sink strength. The more favourable the circumstances are for fruit abortion, e.g., low source strength or high sink strength, the more likely it is that the fruit aborts. Survival analysis estimates parameters quantifying the influence of explanatory variables on the abortion rate. Time-varying explanatory variables can be used in the analysis. In a case study, we used survival analysis to analyse a data set with observations on flowering, fruit abortion and fruit harvest for sweet pepper. Source and sink strength were used as explanatory variables. The resulting equation determining the probability of abortion per day was implemented in a simple simulation model to simulate fruit set. The model output, as an average of 100 plants, showed similar timing in the fluctuations in fruit set as the observations, although the amplitude of the fluctuations was in some cases underestimated. The percentage fruit set was simulated correctl