Computing the orientational-average of diffusion-weighted MRI signals: a comparison of different techniques

Numerous applications in diffusion MRI involve computing the orientationally-averaged diffusion-weighted signal. Most approaches implicitly assume, for a given b-value, that the gradient sampling vectors are uniformly distributed on a sphere (or ‘shell’), computing the orientationally-averaged signal through simple arithmetic averaging. One challenge with this approach is that not all acquisition schemes have gradient sampling vectors distributed over perfect spheres. To ameliorate this challenge, alternative averaging methods include: weighted signal averaging; spherical harmonic representation of the signal in each shell; and using Mean Apparent Propagator MRI (MAP-MRI) to derive a three-dimensional signal representation and estimate its ‘isotropic part’. Here, these different methods are simulated and compared under different signal-to-noise (SNR) realizations. With sufficiently dense sampling points (61 orientations per shell), and isotropically-distributed sampling vectors, all averaging methods give comparable results, (MAP-MRI-based estimates give slightly higher accuracy, albeit with slightly elevated bias as b-value increases). As the SNR and number of data points per shell are reduced, MAP-MRI-based approaches give significantly higher accuracy compared with the other methods. We also apply these approaches to in vivo data where the results are broadly consistent with our simulations. A statistical analysis of the simulated data shows that the orientationally-averaged signals at each b-value are largely Gaussian distributed.

Prolonged recovery time after eruptive disturbance of a deep-sea hydrothermal vent community

Deep-sea hydrothermal vents are associated with seafloor tectonic and magmatic activity, and the communities living there are subject to disturbance. Eruptions can be frequent and catastrophic, raising questions about how these communities persist and maintain regional biodiversity. Prior studies of frequently disturbed vents have led to suggestions that faunal recovery can occur within 2–4 years. We use an unprecedented long-term (11-year) series of colonization data following a catastrophic 2006 seafloor eruption on the East Pacific Rise to show that faunal successional changes continue beyond a decade following the disturbance. Species composition at nine months post-eruption was conspicuously different than the pre-eruption ‘baseline' state, which had been characterized in 1998 (85 months after disturbance by the previous 1991 eruption). By 96 months post-eruption, species composition was approaching the pre-eruption state, but continued to change up through to the end of our measurements at 135 months, indicating that the ‘baseline' state was not a climax community. The strong variation observed in species composition across environmental gradients and successional stages highlights the importance of long-term, distributed sampling in order to understand the consequences of disturbance for maintenance of a diverse regional species pool. This perspective is critical for characterizing the resilience of vent species to both natural disturbance and human impacts such as deep-sea mining.

Computing the Orientational-Average of Diffusion-Weighted MRI Signals: A Comparison of Different Techniques

ABSTRACTNumerous applications in diffusion MRI, from multi-compartment modeling to power-law analyses, involves computing the orientationally-averaged diffusion-weighted signal. Most approaches implicitly assume, for a given b-value, that the gradient sampling vectors are uniformly distributed on a sphere (or ‘shell’), computing the orientationally-averaged signal through simple arithmetic averaging. One challenge with this approach is that not all acquisition schemes have gradient sampling vectors distributed over perfect spheres (either by design, or due to gradient non-linearities). To ameliorate this challenge, alternative averaging methods include: weighted signal averaging; spherical harmonic representation of the signal in each shell; and using Mean Apparent Propagator MRI (MAP-MRI) to derive a three-dimensional signal representation and estimate its ‘isotropic part’. This latter approach can be applied to all q-space sampling schemes, making it suitable for multi-shell acquisitions when unwanted gradient non-linearities are present.Here, these different methods are compared under different signal-to-noise (SNR) realizations. With sufficiently dense sampling points (61points per shell), and isotropically-distributed sampling vectors, all methods give comparable results, (accuracy of MAP-MRI-based estimates being slightly higher albeit with slightly elevated bias as b-value increases). As the SNR and number of data points per shell are reduced, MAP-MRI-based approaches give pronounced improvements in accuracy over the other methods.

A Study on the Guidance Needs of Pupils Institutions from both Literate and Illiterate parents’ background & Management

The present study aims to explore the nature of Guidance Needs of Pupils for 11th Grade Institutions from both Literate and Illiterate parents’ background & Management for Pupils of 8th Grade Institutions: An Analytical Study of Murshidabad District, West Bengal, India. The populations consist of Pupils for 11th Grade Institutions from both Literate and Illiterate parents’ background & Management for Pupils of 8th Grade Institutions Murshidabad district. Questionnaire on guidance need was distributed. Sampling Random technique was applied to collect the data among the 400 for Pupils for 11th Grade Institutions from both Literate and Illiterate parents’ background & 186 for Management for Pupils of 8th Grade Institutions Govt.Aided School and Private Schools. The study identifies the phenomena related to various guidance needs the pupils coming from both literate and illiterate Parents’ background & Govt.Aided School pupils and Private Schools pupils. The complex and varied nature of the world of service pose a huge challenge to the youngest pupils today. Many pupils with higher secondary/secondary schools/Madrasahs knowledge face difficulties in making decisions due to lack of sufficient guidance, which hampers their progression. The Results and finding shows there is a significant difference in mean score on the (physical, social, psychological, educational and vocational) guidance needs among 11th grade pupils with respect to their parents as literate and illiterate. There is a significant difference in Guidance needs (physical, social, psychological, educational and vocational) among 8th Grade institutions pupils with respect to their management.

A morphological and phylogenetic evaluation of Marasmius sect. Globulares (Globulares-Sicci complex) with nine new taxa from the Neotropical Atlantic Forest

The largest and most recently emended Marasmius sect. Globulares (Globulares-Sicci complex) has increased in number of species annually while its infrasectional organization remains inconclusive. During forays in remnants of the Atlantic Rainforest in Brazil, 24 taxa of Marasmius belonging to sect. Globulares were collected from which nine are herein proposed as new: Marasmius altoribeirensis, M. ambicellularis, M. hobbitii, M. luteoolivaceus, M. neotropicalis, M. pallidibrunneus, M. pseudoniveoaffinis, M. rhabarbarinoides and M. venatifolius. We took this opportunity to evaluate sect. Globulares sensu Antonín & Noordel. in particular, combining morphological examination and both single and multilocus phylogenetic analyses using LSU and ITS data, including Neotropical samples to a broader and more globally distributed sampling of over 200 strains. Three different approaches were developed in order to better use the genetic information via Bayesian and Maximum Likelihood analyses. The implementation of these approaches resulted in: i) the phylogenetic placement of the new and known taxa herein studied among the other taxa of a wide sampling of the section; ii) the reconstruction of improved phylogenetic trees presenting more strongly supported resolution especially from intermediate to deep nodes; iii) clearer evidence indicating that the series within sect. Sicci and sect. Globulares in the traditional concept are non-monophyletic by this more stringent evaluation; and iv) the existence of several monophyletic suprespecific groups equivalent to the stirpes of Singer – clusters of morphologically similar species. These two latter points corroborate with findings of previous studies implementing analyses with the entire genus. Based on these results, we proposed a new infrasectional classification elevating Singer's concept of stirpes to series. Thirteen new series, the emendation of three extant series and three subsections gathering these series based on the major clades are proposed.

The Bayesian superorganism: externalized memories facilitate distributed sampling

A key challenge for any animal (or sampling technique) is to avoid wasting time by searching for resources (information) in places already found to be unprofitable. In biology, this challenge is particularly strong when the organism is a central place forager—returning to a nest between foraging bouts—because it is destined repeatedly to cover much the same ground. This problem will be particularly acute if many individuals forage from the same central place, as in social insects such as the ants. Foraging (sampling) performance may be greatly enhanced by coordinating movement trajectories such that each ant (walker) visits separate parts of the surrounding (unknown) space. We find experimental evidence for an externalized spatial memory in Temnothorax albipennis ants: chemical markers (either pheromones or cues such as cuticular hydrocarbon footprints) that are used by nest-mates to mark explored space. We show these markers could be used by the ants to scout the space surrounding their nest more efficiently through indirect coordination. We also develop a simple model of this marking behaviour that can be applied in the context of Markov chain Monte Carlo methods (Baddeley et al . 2019 J. R. Soc. Interface 16 , 20190162 ( doi:10.1098/rsif.2019.0162 )). This substantially enhances the performance of standard methods like the Metropolis–Hastings algorithm in sampling from sparse probability distributions (such as those confronted by the ants) with only a little additional computational cost. Our Bayesian framework for superorganismal behaviour motivates the evolution of exploratory mechanisms such as trail marking in terms of enhanced collective information processing.