Double coherence resonance in neuron models driven by discrete correlated noise

We study the influence of correlations among discrete stochastic excitatory or inhibitory inputs on the response of the FitzHugh-Nagumo neuron model. For any level of correlation the emitted signal exhibits at some finite noise intensity a maximal degree of regularity, i.e., a coherence resonance. Furthermore, for either inhibitory or excitatory correlated stimuli a {\it Double Coherence Resonance} (DCR) is observable. DCR refers to a (absolute) maximum coherence in the output occurring for an optimal combination of noise variance and correlation. All these effects can be explained by taking advantage of the discrete nature of the correlated inputs.Comment: 4 pages, 3 figures in eps, to appear in Physical Review Letter

Exploring DCO+^+ as a tracer of thermal inversion in the disk around the Herbig Ae star HD163296

We aim to reproduce the DCO$^+$ emission in the disk around HD163296 using a simple 2D chemical model for the formation of DCO$^+$ through the cold deuteration channel and a parametric treatment of the warm deuteration channel. We use data from ALMA in band 6 to obtain a resolved spectral imaging data cube of the DCO$^+$ $J$=3--2 line in HD163296 with a synthesized beam of 0."53$\times$ 0."42. We adopt a physical structure of the disk from the literature that reproduces the spectral energy distribution. We then apply a simplified chemical network for the formation of DCO$^+$ that uses the physical structure of the disk as parameters along with a CO abundance profile, a constant HD abundance and a constant ionization rate. Finally, from the resulting DCO$^+$ abundances, we calculate the non-LTE emission using the 3D radiative transfer code LIME. The observed DCO$^+$ emission is reproduced by a model with cold deuteration producing abundances up to $1.6\times 10^{-11}$. Warm deuteration, at a constant abundance of $3.2\times 10^{-12}$, becomes fully effective below 32 K and tapers off at higher temperatures, reproducing the lack of DCO$^+$ inside 90 AU. Throughout the DCO$^+$ emitting zone a CO abundance of $2\times 10^{-7}$ is found, with $\sim$99\% of it frozen out below 19 K. At radii where both cold and warm deuteration are active, warm deuteration contributes up to 20\% of DCO$^+$, consistent with detailed chemical models. The decrease of DCO$^+$ at large radii is attributed to a temperature inversion at 250 AU, which raises temperatures above values where cold deuteration operates. Increased photodesorption may also limit the radial extent of DCO$^+$. The corresponding return of the DCO$^+$ layer to the midplane, together with a radially increasing ionization fraction, reproduces the local DCO$^+$ emission maximum at $\sim$260 AU.Comment: 9 pages, 5 figures, accepted 7th July 201

DCO+^+, DCN and N2_2D+^+ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296

The formation pathways of deuterated species trace different regions of protoplanetary disks and may shed light into their physical structure. We aim to constrain the radial extent of main deuterated species; we are particularly interested in spatially characterizing the high and low temperature pathways for enhancing deuteration of these species. We observed the disk surrounding the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved spectral imaging data of DCO$^+$ ($J$=3-2), DCN ($J$=3-2) and N$_2$D$^+$ ($J$=3-2). We model the radial emission profiles of DCO$^+$, DCN and N$_2$D$^+$, assuming their emission is optically thin, using a parametric model of their abundances and radial excitation temperature estimates. DCO$^+$ can be described by a three-region model, with constant-abundance rings centered at 70 AU, 150 AU and 260 AU. The DCN radial profile peaks at about ~60 AU and N$_2$D$^+$ is seen in a ring at ~160 AU. Simple models of both molecules using constant abundances reproduce the data. Assuming reasonable average excitation temperatures for the whole disk, their disk-averaged column densities (and deuterium fractionation ratios) are 1.6-2.6$\times 10^{12}$ cm$^{-2}$ (0.04-0.07), 2.9-5.2$\times 10^{12}$ cm$^{-2}$ ($\sim$0.02) and 1.6-2.5 $\times 10^{11}$ cm$^{-2}$ (0.34-0.45) for DCO$^+$, DCN and N$_2$D$^+$, respectively. Our simple best-fit models show a correlation between the radial location of the first two rings in DCO$^+$ and the DCN and N$_2$D$^+$ abundance distributions that can be interpreted as the high and low temperature deuteration pathways regimes. The origin of the third DCO$^+$ ring at 260 AU is unknown but may be due to a local decrease of ultraviolet opacity allowing the photodesorption of CO or due to thermal desorption of CO as a consequence of radial drift and settlement of dust grains

Increased H2_2CO production in the outer disk around HD 163296

Three formaldehyde lines were observed (H$_2$CO 3$_{03}$--2$_{02}$, H$_2$CO 3$_{22}$--2$_{21}$, and H$_2$CO 3$_{21}$--2$_{20}$) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at 0.5 arcsecond (60 AU) spatial resolution. H$_2$CO 3$_{03}$--2$_{02}$ was readily detected via imaging, while the weaker H$_2$CO 3$_{22}$--2$_{21}$ and H$_2$CO 3$_{21}$--2$_{20}$ lines required matched filter analysis to detect. H$_2$CO is present throughout most of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of the H$_2$CO emission is likely caused by an optically thick dust continuum. The H$_2$CO radial intensity profile shows a peak at 100 AU and a secondary bump at around 300 AU, suggesting increased production in the outer disk. Different parameterizations of the H$_2$CO abundance were compared to the observed visibilities with $\chi^2$ minimization, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H$_2$CO chemistry. Similar models were applied to ALMA Science Verification data of C$^{18}$O. In all modeling scenarios, fits to the H$_2$CO data show an increased abundance in the outer disk. The overall best-fit H$_2$CO model shows a factor of two enhancement beyond a radius of 270$\pm$20 AU, with an inner abundance of $2\!-\!5 \times 10^{-12}$. The H$_2$CO emitting region has a lower limit on the kinetic temperature of $T > 20$ K. The C$^{18}$O modeling suggests an order of magnitude depletion in the outer disk and an abundance of $4\!-\!12 \times 10^{-8}$ in the inner disk. The increase in H$_2$CO outer disk emission could be a result of hydrogenation of CO ices on dust grains that are then sublimated via thermal desorption or UV photodesorption, or more efficient gas-phase production beyond about 300 AU if CO is photodisocciated in this region

Auto and crosscorrelograms for the spike response of LIF neurons with slow synapses

An analytical description of the response properties of simple but realistic neuron models in the presence of noise is still lacking. We determine completely up to the second order the firing statistics of a single and a pair of leaky integrate-and-fire neurons (LIFs) receiving some common slowly filtered white noise. In particular, the auto- and cross-correlation functions of the output spike trains of pairs of cells are obtained from an improvement of the adiabatic approximation introduced in \cite{Mor+04}. These two functions define the firing variability and firing synchronization between neurons, and are of much importance for understanding neuron communication.Comment: 5 pages, 3 figure

Parental Awareness of Early Intervention for Hispanic Children with Communication Disorders

Purpose: Children at risk of delayed speech and language development and speech-language disorders come from a broad range of demographic backgrounds, including ethnicities, sexes, and socioeconomic statuses. A vast body of research in speech-language pathology has demonstrated that early intervention is crucial for helping children acquire the necessary communication skills they need to become effective communicators, successful students, and ultimately accomplished adults. Currently, commercials, billboards, online sources, and personal referrals are the methods most often used to promote awareness of early childhood intervention services. Method: This study aimed to identify whether the current promotional methods used to increase parental awareness of early childhood speech therapy intervention are effective in the Hispanic population in South Texas. A total of 299 parents and guardians recruited from 18 Head Start programs took part in the survey study. The 18-item Early Intervention Parental Awareness Questionnaire was utilized to assess the participants’ level of awareness. Results: The results of this study suggest face-to-face interaction is needed to increase awareness of services for early childhood intervention amongst the Hispanic population. Conclusion: These findings support the need for increasing recognition of the value of early intervention for children with communication disorders amongst the Hispanic population

Assessing math anxiety in elementary schoolchildren through a Spanish version of the Scale for Early Mathematics Anxiety (SEMA)

Math anxiety (MA) affects students of all age groups. Because of its effects on children’s academic development, the need to recognize its early manifestations has been highlighted. We designed a European-Spanish version of the Scale for Early Mathematics Anxiety (SEMA; Wu et al. (2012)), and assessed its psychometric properties in a sample of children aged 7 to 12 years. The participants (967 typically developing children) were elementary school students recruited from ten schools. Children reported their general and math anxiety levels in an individual session and performed nonverbal IQ and math abilities subtests in a group session. Teachers reported the final math grades. The psychometric indices obtained, and the resulting factor structure revealed that the European-Spanish version of the SEMA developed in this study is a reliable and valid measure to evaluate MA in children from 3rd to 6th grade. Moreover, we explored gender differences, that resulted in small effect sizes, which disappeared when controlling for trait anxiety. Differences across grades were found for both global MA and the numerical processing anxiety factor but not for the situational and performance anxiety factor. Finally, MA was negatively associated with students’ math achievement, although the strength of the associations varied with the MA measure selected, the kind of math achievement analyzed, and the school stage considered. Our findings highlight the relevance of MA in elementary school and highlight the need for an early identification of students at risk of suffering MA to palliate the negative consequences of MA in children’s cognitive and academic development

Field behavior of an Ising model with aperiodic interactions

We derive exact renormalization-group recursion relations for an Ising model, in the presence of external fields, with ferromagnetic nearest-neighbor interactions on Migdal-Kadanoff hierarchical lattices. We consider layered distributions of aperiodic exchange interactions, according to a class of two-letter substitutional sequences. For irrelevant geometric fluctuations, the recursion relations in parameter space display a nontrivial uniform fixed point of hyperbolic character that governs the universal critical behavior. For relevant fluctuations, in agreement with previous work, this fixed point becomes fully unstable, and there appears a two-cycle attractor associated with a new critical universality class.Comment: 9 pages, 1 figure (included). Accepted for publication in Int. J. Mod. Phys.

Dynamic evolution of selenocysteine utilization in bacteria: a balance between selenoprotein loss and evolution of selenocysteine from redox active cysteine residues

BACKGROUND: Selenocysteine (Sec) is co-translationally inserted into protein in response to UGA codons. It occurs in oxidoreductase active sites and often is catalytically superior to cysteine (Cys). However, Sec is used very selectively in proteins and organisms. The wide distribution of Sec and its restricted use have not been explained. RESULTS: We conducted comparative genomics and phylogenetic analyses to examine dynamics of Sec decoding in bacteria at both selenium utilization trait and selenoproteome levels. These searches revealed that 21.5% of sequenced bacteria utilize Sec, their selenoproteomes have 1 to 31 selenoproteins, and selenoprotein-rich organisms are mostly Deltaproteobacteria or Firmicutes/Clostridia. Evolutionary histories of selenoproteins suggest that Cys-to-Sec replacement is a general trend for most selenoproteins. In contrast, only a small number of Sec-to-Cys replacements were detected, and these were mostly restricted to formate dehydrogenase and selenophosphate synthetase families. In addition, specific selenoprotein gene losses were observed in many sister genomes. Thus, the Sec/Cys replacements were mostly unidirectional, and increased utilization of Sec by existing protein families was counterbalanced by loss of selenoprotein genes or entire selenoproteomes. Lateral transfers of the Sec trait were an additional factor, and we describe the first example of selenoprotein gene transfer between archaea and bacteria. Finally, oxygen requirement and optimal growth temperature were identified as environmental factors that correlate with changes in Sec utilization. CONCLUSION: Our data reveal a dynamic balance between selenoprotein origin and loss, and may account for the discrepancy between catalytic advantages provided by Sec and the observed low number of selenoprotein families and Sec-utilizing organisms