Estimation of drift and diffusion functions from time series data: A maximum likelihood framework

Complex systems are characterized by a huge number of degrees of freedom often interacting in a non-linear manner. In many cases macroscopic states, however, can be characterized by a small number of order parameters that obey stochastic dynamics in time. Recently techniques for the estimation of the corresponding stochastic differential equations from measured data have been introduced. This contribution develops a framework for the estimation of the functions and their respective (Bayesian posterior) confidence regions based on likelihood estimators. In succession approximations are introduced that significantly improve the efficiency of the estimation procedure. While being consistent with standard approaches to the problem this contribution solves important problems concerning the applicability and the accuracy of estimated parameters.Comment: 18 pages, 2 figure

On the proper reconstruction of complex dynamical systems spoilt by strong measurement noise

This article reports on a new approach to properly analyze time series of dynamical systems which are spoilt by the simultaneous presence of dynamical noise and measurement noise. It is shown that even strong external measurement noise as well as dynamical noise which is an intrinsic part of the dynamical process can be quantified correctly, solely on the basis of measured times series and proper data analysis. Finally real world data sets are presented pointing out the relevance of the new approach

Improved estimation of Fokker-Planck equations through optimisation

An improved method for the description of hierarchical complex systems by means of a Fokker-Planck equation is presented. In particular the limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm for constraint problems (L-BFGS-B) is used to minimize the distance between the numerical solutions of the Fokker-Planck equation and the empirical probability density functions and thus to estimate properly the drift and diffusion term of the Fokker-Planck equation. The optimisation routine is applied to a time series of velocity measurements obtained from a turbulent helium gas jet in order to demonstrate the benefits and to quantify the improvements of this new optimisation routine

Magnetocaloric properties of (RE)3_3Ga5_5O12_{12} (RE=Tb,Gd,Nd,Dy)

We report the characteristic magnetic properties of several members of the rare earth garnet family, Gd$_3$Ga$_5$O$_{12}$ (GGG), Dy$_3$Ga$_5$O$_{12}$ (DGG), Tb$_3$Ga$_5$O$_{12}$ (TGG), and Nd$_3$Ga$_5$O$_{12}$ (NGG), and compare their relative potential utility for magnetocaloric cooling, including their minimal adiabatic demagnetisation refrigeration (ADR) temperatures and relative cooling parameters. A main objective of this work was to find potential improvements over the magnetocaloric properties of GGG for use in low temperature ADR cryostats. Using Tb$^{+3}$ and Dy$^{+3}$ in the RE-site offers in principle higher saturation magnetisation and Nd$^{+3}$ gives a lower de Gennes factor and therefore potentially low transition temperature. Our results show that Dy$_3$Ga$_5$O$_{12}$ yields an optimal relative cooling parameter ($RCP$) at low applied fields and a low transition temperature, which would allow for the design of more efficient ADR cryostats.Comment: 10 pages, 10 figures, submitted to Physical Review Applie

Trehalose Is A Chemical Attractant In The Establishment Of Coral Symbiosis

Coral reefs have evolved with a crucial symbiosis between photosynthetic dinoflagellates (genus Symbiodinium) and their cnidarian hosts (Scleractinians). Most coral larvae take up Symbiodinium from their environment; however, the earliest steps in this process have been elusive. Here we demonstrate that the disaccharide trehalose may be an important signal from the symbiont to potential larval hosts. Symbiodinium freshly isolated from Fungia scutaria corals constantly released trehalose (but not sucrose, maltose or glucose) into seawater, and released glycerol only in the presence of coral tissue. Spawning Fungia adults increased symbiont number in their immediate area by excreting pellets of Symbiodinium, and when these naturally discharged Symbiodinium were cultured, they also released trehalose. In Y-maze experiments, coral larvae demonstrated chemoattractant and feeding behaviors only towards a chamber with trehalose or glycerol. Concomitantly, coral larvae and adult tissue, but not symbionts, had significant trehalase enzymatic activities, suggesting the capacity to utilize trehalose. Trehalase activity was developmentally regulated in F. scutaria larvae, rising as the time for symbiont uptake occurs. Consistent with the enzymatic assays, gene finding demonstrated the presence of a trehalase enzyme in the genome of a related coral, Acropora digitifera, and a likely trehalase in the transcriptome of F. scutaria. Taken together, these data suggest that adult F. scutaria seed the reef with Symbiodinium during spawning and the exuded Symbiodinium release trehalose into the environment, which acts as a chemoattractant for F. scutaria larvae and as an initiator of feeding behavior- the first stages toward establishing the coral-Symbiodinium relationship. Because trehalose is a fixed carbon compound, this cue would accurately demonstrate to the cnidarian larvae the photosynthetic ability of the potential symbiont in the ambient environment. To our knowledge, this is the first report of a chemical cue attracting the motile coral larvae to the symbiont

Isolation of a potassium bis(1,2,3-triazol-5-ylidene) carbazolide: a stabilizing pincer ligand for reactive late transition metal complexes

The synthesis and X-ray crystal structure of a potassium adduct of a monoanionic CNC-pincer ligand featuring two mesoionic carbenes is reported. Owing to the peculiar electronic and steric properties of this ligand, the first neutral stable Ni(II)-hydride, and an unusual Cu(II) complex displaying a seesaw geometry, have been isolated

Successful cryopreservation of coral larvae using vitrification and laser warming.

Climate change has increased the incidence of coral bleaching events, resulting in the loss of ecosystem function and biodiversity on reefs around the world. As reef degradation accelerates, the need for innovative restoration tools has become acute. Despite past successes with ultra-low temperature storage of coral sperm to conserve genetic diversity, cryopreservation of larvae has remained elusive due to their large volume, membrane complexity, and sensitivity to chilling injury. Here we show for the first time that coral larvae can survive cryopreservation and resume swimming after warming. Vitrification in a 3.5 M cryoprotectant solution (10% v/v propylene glycol, 5% v/v dimethyl sulfoxide, and 1 M trehalose in phosphate buffered saline) followed by warming at a rate of approximately 4,500,000 °C/min with an infrared laser resulted in up to 43% survival of Fungia scutaria larvae on day 2 post-fertilization. Surviving larvae swam and continued to develop for at least 12 hours after laser-warming. This technology will enable biobanking of coral larvae to secure biodiversity, and, if managed in a high-throughput manner where millions of larvae in a species are frozen at one time, could become an invaluable research and conservation tool to help restore and diversify wild reef habitats

Knowledge and attitudes of HIV pre-exposure prophylaxis among nurses in South Africa

Background: Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) has shown efficacy and effectiveness in populations who practise high-risk sexual activity. Nurses’ knowledge and positive attitudes enhance PrEP implementation. Aim: This study aimed to investigate the knowledge of and attitudes towards PrEP among nurses in primary health care facilities. Setting: The study was conducted in 10 health facilities that offer comprehensive services in Tshwane, South Africa. Methods: A cross-sectional survey assessed the knowledge of and attitudes towards PrEP among 114 nurses. Univariate, bivariate and logistic regressions were performed to estimate odds ratios and to determine whether age, sex and education had an association with the knowledge and attitudes. Results: Majority of the study sample consisted of female nurses (92.1%), and most respondents (68%) had moderate PrEP knowledge. Logistic regression showed that age and education were not associated with high level of knowledge. Pre-exposure prophylaxis was viewed negatively by 84.5% of the respondents. The odds of positive attitudes towards PrEP were 1.92 times higher among males than females (95% CI 0.54–6.83) and 1.24 times higher among nurses who had bachelor’s degree than diploma holders (95% CI 0.51–3.01). Conclusion: This study found that there is a need to strengthen the dissemination of information about PrEP, and nurses in South Africa require training to improve their knowledge of and attitudes towards PrEP. Contribution: The findings of the study add to the current knowledge base regarding PrEP access in the public healthcare system and it highlights gaps in the training of healthcare providers