Longitudinal Distribution of Benthic Macroinvertebrate Assemblages in a Central Highlands River, The Tons (Central India)

The median density of benthic macroinvertebrate assemblage declined longitudinally from headwater to mouth (except increase at T3) in the river Tons. Arthropoda was largest component followed by Mollusca and Annelida. The abundance of assemblages forming taxa Brachycentridae, Helidae and Leptophlebiidae declined at T2 and was replaced by Neoephemeridae and Glossocolecidae. Similarly, abundance of Baetidae and Caenidae decreased at T4 and was replaced by Chironomidae and Nephthydae at T4. The assemblages varied from the T1 to T4 but were dominated by Thiaridae at all stations except Neoephemeridae at T3. Principal component analysis revealed that Glossosomatidae, Glossocolecidae, Thiaridae and Neoephemeridae were the characteristic taxa at T1, T2–T4 and T3, respectively. Canonical correspondence analysis indicated that the substratum was an important factor for T1, T2 and T3, while water temperature for Chironomidae at T4. Rhyacophilidae, Neoephemeridae, Caenidae were associated with landuse and substratum, while current velocity was responsible for the abundance of Thiaridae. Thus, landuse, slope and substratum were the effective variables responsible for assemblage in the river Tons.     

Comparative evaluation of bond strength of all-metal crowns with different luting agents after undergoing various modes of surface treatments: An in-vitro study

Aim:

This study includes a comparative evaluation of the various surface treatments of the intaglio surface of crowns in combination with various luting agents for maximal retention.

Materials and Methods:

Totally, 150 dies of a standard complete crown preparation were fabricated. Wax pattern with a loop on the occlusal surface was prepared on each die using standard procedures, and then crowns were cast with nickel-chromium alloy. These crowns were randomly divided into five groups as per the surface of the intaglio surface of the metal copings. The crowns in each group were again subdivided randomly into three groups as per the luting agents used resin-modified glass ionomer cement, glass ionomer cement, and zinc phosphate cement. Retention was measured (MPa) by separating the metal crowns from the metallic die under tension on a Universal testing machine.

Statistical Analysis Used:

The data were recorded and statistically analyzed using one-way analysis of variance followed by Tukey''s test.

Results:

The retention differed both with surface treatment and type of luting agents. Untreated group showed the least bond strengths < sandblasting with 50 µm alumina < sandblasting with 50 µm alumina with ultrasonic cleaning < sandblasting with 110 µm alumina < sandblasting with 110 µm alumina along with ultrasonic cleaning. For luting agents, glass ionomer cement showed least bond strength because there was no chemical bonding present between metal crown and metallic die, followed by zinc phosphate cement and maximum bond strength were found for resin-modified glass ionomer cement.

Conclusion:

Among all types of surface treatments used in this study, maximum bond strength was yielded by sandblasting with 110 µm alumina + ultrasonic cleaning and the best luting agent was resin-modified glass ionomer cement.Key Words: Luting agents, retention, sandblasting, surface treatment, ultrasonic cleaning     

The pediatric disease spectrum in emergency departments across Pakistan: data from a pilot surveillance system

Background

There is an increasing number of urgently ill and injured children being seen in emergency departments (ED) of developing countries. The pediatric disease burden in EDs across Pakistan is generally unknown. Our main objective was to determine the spectrum of disease and injury among children seen in EDs in Pakistan through a nationwide ED-based surveillance system.

Methods

Through the Pakistan National Emergency Department Surveillance (Pak-NEDS), data were collected from November 2010 to March 2011 in seven major tertiary care centers representing all provinces of Pakistan. These included five public and two private hospitals, with a collective annual census of over one million ED encounters.

Results

Of 25,052 children registered in Pak-NEDS (10% of all patients seen): 61% were male, 13% under 5 years, while almost 65% were between 10 to < 16 years. The majority (90%) were seen in public hospital EDs. About half the patients were discharged from the EDs, 9% admitted to hospitals and only 1.3% died in the EDs. Injury (39%) was the most common presenting complaint, followed by fever/malaise (19%) and gastrointestinal symptoms (18%). Injury was more likely in males vs. females (43% vs. 33%; p < 0.001), with a peak presentation in the 5-12 year age group (45%).

Conclusions

Pediatric patients constitute a smaller proportion among general ED users in Pakistan. Injury is the most common presenting complaint for children seen in the ED. These data will help in resource allocation for cost effective pediatric ED service delivery systems. Prospective longer duration surveillance is needed in more representative pediatric EDs across Pakistan.

     

Layered composites composed of multi-walled carbon nanotubes/manganese dioxide/carbon fiber cloth for microwave absorption in the X-band

In this paper, multi-layered composites are fabricated for their application in electromagnetic interference (EMI) shielding. Composites of multi-walled carbon nanotubes/manganese dioxide (MnO₂)/epoxy are used as a microwave absorption layer, and a commercial carbon fiber cloth is used as a reflection layer. When the electromagnetic (EM) waves impinge on such layered composites, the absorption layer can absorb most of the EM waves, and the transmitted EM waves from the absorption layer will be reflected back by the reflection layer and absorbed by the absorption layer. Based on the rational design, the composites with four absorption layers and one reflection layer (with a total thickness of 2.85 mm) show a high EMI shielding effectiveness of 41.24 dB, while the average reflection loss of 13.62 dB can be attained in the X-band (8.2–12.4 GHz). Moreover, the layered composites can absorb nearly 95% of the EM waves at the operating frequency, and provide an absorption dominant EMI shielding which are favorable for commercial and military applications.

Multi-layered composites of MWCNTs/MnO₂/epoxy show high microwave absorption ability due to interface reflection and synergetic effects of MWCNTs and MnO₂.     

2D BeP2 monolayer: investigation of electronic and optical properties by driven modulated strain

Recently, the two-dimensional (2D) material beryllium diphosphide (BeP₂) has attracted significant attention for potential device applications due to its Dirac semimetal state, dynamic and thermal stability, and high carrier mobility. In this work, we investigated its electronic and optical properties under biaxial Lagrangian strain using density functional theory (DFT). Electronic band gaps and effective charge carrier mass were highly sensitive to the Lagrangian strain of BeP₂ monolayer. The bandgaps of BeP₂ varied from 0 eV to 0.30 eV for 2% to 8% strain, where the strain range is based on the final stable condition of the system. The absorption spectra for the dielectric properties show the highest absorption peaks in the infrared (IR) region. These abundant strain-dependent studies of the BeP₂ monolayer provide guidelines for its application in infrared sensors and devices.

BeP₂ monolayer is a promising material for the novel IR optical device.     

Review of ethnic disparities in access to renal transplantation

Renal transplantation is the gold standard treatment for patients with end-stage renal disease and is associated with several advantages over dialysis, including increased quality of life, reduced morbidity and mortality, and lower healthcare costs. Barring the constraints of a limited organ supply, the goals of the patient care should focus on attaining renal transplantation while minimizing, or even eliminating, time spent on dialysis. Disparities in access to renal transplantation between African Americans and Caucasians have been extensively documented, with African Americans having significantly poorer access. There is a growing corpus of literature examining the determinants of reduced access among other racial ethnic minority groups, including Hispanics. These determinants include patient and physician preference, socioeconomic status, insurance type, patient education, and immunologic factors. We review these determinants in access to renal transplantation in the United States among all races and ethnicities.     

Subretinal hyperreflective material morphology in neovascular age-related macular degeneration: A case control study

Purpose:The aim of this study was to evaluate the association of morphological features of subretinal hyperreflective material (SHRM) with visual acuity (VA), geographic atrophy (GA) and scar formation in eyes with neovascular age-related macular degeneration (neovascular AMD) and to compare with controls of neovascular AMD without SHRM.Methods:Retrospective analysis of 157 wet AMD eyes with SHRM and 50 eyes without SHRM treated with Anti-VEGF. Baseline spectral domain-OCT characteristics (SHRM location, height, width, area, reflectivity, border definition) were collected and were correlated with VA at baseline, 3, 6, 12 months and looked for development of scar and geographical atrophy (GA) and were compared to the control group.Results:When compared to the control, baseline parameters with a significant predictive value of 12-VA were presence of SHRM, foveal involvement of SHRM, high reflective SHRM, well-defined SHRM borders and thick SHRM. VA was decreased with greater SHRM height, width and area (P < 0.001). Decreasing reflectivity of SHRM lesions and disappearance of SHRM correlated with better VA at 12 months (P < 0.05). At 12 months, scar and GA was present more often in eyes with persistent SHRM than in eyes with SHRM that resolved and those without SHRM in the control group.Conclusion:SHRM can be considered as a surrogate OCT biomarker in predicting final visual outcome in neovascular age-related macular degeneration. Baseline parameters predicting poorer vision at 12-follow-up were presence of SHRM involving the fovea, well-defined SHRM borders, greater SHRM height, width and area and persistence of SHRM with Anti-VEGF therapy.     

Neural and computational processes of accelerated perceptual awareness and decisions: A 7T fMRI study

Rapidly detecting salient information in our environments is critical for survival. Visual processing in subcortical areas like the pulvinar and amygdala has been shown to facilitate unconscious processing of salient stimuli. It is unknown, however, if and how these areas might interact with cortical regions to facilitate faster conscious perception of salient stimuli. Here we investigated these neural processes using 7T functional magnetic resonance imaging (fMRI) in concert with computational modelling while participants (n = 33) engaged in a breaking continuous flash suppression paradigm (bCFS) in which fearful and neutral faces are initially suppressed from conscious perception but then eventually ‘breakthrough’ into awareness. Participants reported faster breakthrough times for fearful faces compared with neutral faces. Drift‐diffusion modelling suggested that perceptual evidence was accumulated at a faster rate for fearful faces compared with neutral faces. For both neutral and fearful faces, faster response times were associated with greater activity in the amygdala (specifically within its subregions, including superficial, basolateral and amygdalo‐striatal transition area) and the insula. Faster rates of evidence accumulation coincided with greater activity in frontoparietal regions and occipital lobe, as well as the amygdala. A lower decision‐boundary correlated with activity in the insula and the posterior cingulate cortex (PCC), but not with the amygdala. Overall, our findings suggest that hastened perceptual awareness of salient stimuli recruits the amygdala and, more specifically, is driven by accelerated evidence accumulation in fronto‐parietal and visual areas. In sum, we have mapped distinct neural computations that accelerate perceptual awareness of visually suppressed faces.     

Distributed algorithms from arboreal ants for the shortest path problem

Colonies of the arboreal turtle ant create networks of trails that link nests and food sources on the graph formed by branches and vines in the canopy of the tropical forest. Ants put down a volatile pheromone on the edges as they traverse them. At each vertex, the next edge to traverse is chosen using a decision rule based on the current pheromone level. There is a bidirectional flow of ants around the network. In a previous field study, it was observed that the trail networks approximately minimize the number of vertices, thus solving a variant of the popular shortest path problem without any central control and with minimal computational resources. We propose a biologically plausible model, based on a variant of the reinforced random walk on a graph, which explains this observation and suggests surprising algorithms for the shortest path problem and its variants. Through simulations and analysis, we show that when the rate of flow of ants does not change, the dynamics converges to the path with the minimum number of vertices, as observed in the field. The dynamics converges to the shortest path when the rate of flow increases with time, so the colony can solve the shortest path problem merely by increasing the flow rate. We also show that to guarantee convergence to the shortest path, bidirectional flow and a decision rule dividing the flow in proportion to the pheromone level are necessary, but convergence to approximately short paths is possible with other decision rules.

Biological systems, such as ant trail networks, are fascinating examples of distributed algorithms in nature (1–4), often finding globally optimum solutions using simple local interactions among individuals, devoid of central control. The study of natural algorithms has led to synergistic exchange between biology and computer science (5, 6). The algorithmic lens has enhanced our understanding of biological phenomena such as how birds flock (7), how slime molds solve the shortest path problem (8–10), and how computation takes place in the brain (11, 12). Moreover, the process of evolution itself has been studied using an algorithmic lens (13–16). Also, inspiration from nature has led to algorithmic ideas such as ant-inspired algorithms for distributed density estimation (17), artificial neural networks in machine learning (18), and algorithms for similarity search inspired by the fruit fly brain (19), among others (20–23).Here, we investigate how the trail networks of the arboreal turtle ant (Cephalotes goniodontus) can solve variants of the shortest path problem, a basic optimization problem on graphs (24–26). Textbook algorithms for this problem find optimum solutions using knowledge of the entire network (27–29). Turtle ants nest and forage in the tree canopy of the tropical forest; their trail network is constrained to lie on a natural graph formed by tangled branches and vines (Fig. 1), and no ant has any global information about the network. Observations of turtle ants in the field show that a colony’s trail network approximately minimizes the number of vertices (30). We develop a model that gives a biologically plausible explanation for this observation and outlines other intriguing phenomena as described in the next section.Open in a separate windowFig. 1.Tangled branches in which turtle ants forage.A. Summary of Model and Results.Turtle ant colonies form trails on a graph whose vertices correspond to junctions in the vegetation and edges correspond to branches connecting these junctions. A colony’s network of trails connects many nests and food sources. The trail network minimizes the number of vertices (30) (compared to simulated random networks), approximately solving a variant of the Steiner tree problem (31–33), which is a generalization of the shortest path problem for multiple terminal vertices. Here, we focus on a section of this network, considering two terminal vertices, such as a nest and a food source, and we seek to explain how a colony can find the path with the minimum number of vertices between the two terminals. We model trails as a bidirectional flow of ants between the two terminal vertices; bidirectional flow is characteristic of the trails of this species (34). The flow in our model is similar to models of flow in traffic networks (35–37). Ants lay trail pheromone on edges as they traverse them, and the next edge to traverse is chosen based on the level of the pheromone. The pheromone decays with time. Some fraction of flow leaks as it passes through each vertex, modeling the loss of ants due to exploration. Chandrasekhar et al. (30) hypothesized loss of ants at the vertices to be the reason why ants prefer paths with fewer vertices.Our model leads to four main results:

1. We first consider the linear decision rule, which, at each vertex, divides the flow among the next set of edges in proportion to their pheromone level. We show through simulations and analysis that when the incoming rate of flow remains unchanged, the dynamics converges to the path with the minimum leakage. This is also the path with the minimum number of vertices when all vertices have equal leakage. This result describes a biologically plausible process that explains how colonies can find paths with the minimum number of vertices.
2. We show that when the rate of flow increases with time, in the absence of leakage, the dynamics converges to the shortest path. The flow rate on ant trails can change over time (38–42), for example, in turtle ants, the flow rate can increase in response to new food sources (39). In other ant species, it has been shown that ant trails converge to the shortest path in certain simple graphs (43). Our result shows a surprising link between these two phenomena: Ant colonies can use their ability to increase the flow rate to find the shortest path.
3. We establish the utility of bidirectional flow by showing that it is necessary for convergence to the shortest or the minimum leakage path. In contrast, most flow-based problems considered in computer science and operations research have unidirectional flow (37, 44–46).
4. We investigate the effect of increasing flow and leakage with decision rules other than the linear rule. For a general family of decision rules, we show that the linear rule is its unique member with guaranteed convergence to the shortest and the minimum leakage path. However, for various nonlinear rules, we show that the dynamics still often converges to a path with a smaller length and less leakage, compared to the path found in the absence of increasing flow and leakage respectively. Thus, the utility of increasing flow and leakage is not limited to the linear decision rule.

Our model builds on a previous model by Chandrasekhar et al. (47), adding components such as leakage and variation in the flow rate. These components were not present in the model of Chandrasekhar et al. (47) and are crucial for the phenomena we discuss above. Chandrasekhar et al. (47) investigated how ants find alternative paths, not necessarily the ones with the minimum number of vertices, to route around ruptured links in a network. Here, we ask how ants can find the path with the minimum number of vertices and how the flow rate impacts the path found. We demonstrate that leakage at vertices can lead to convergence to the path with the minimum number of vertices, and increase in the flow rate over time can lead to convergence to the shortest path.Our work is different from traditional ant-colony optimization (48–50), in which the algorithms considered are not required to be biologically plausible. Models of ant colony optimization (ACO), inspired by ant behavior, solve combinatorial optimization problems, such as the traveling salesman problem (51) and the shortest path problem (52, 53). In ACO, individual agents, simulating ants, construct candidate solutions using heuristics and then use limited communication, simulating trail pheromone, to lead other agents toward better solutions. The simulated ants have significantly more computational power than is biologically plausible for real ants. Unlike real ants, the simulated ants have the ability to remember, retrace, and reinforce entire paths and can use the quality of the global solution to determine the amount of “pheromone” to be laid.Our model resembles the reinforced random walks introduced by Diaconis et al. (54–56), which have found applications in biology (57–59). Here, a single agent traverses a graph by choosing edges with probability proportional to their edge weight, with edge weight here analogous to the level of trail pheromone. This edge weight increases additively each time the edge is traversed. However, there are a few key differences between the model we study and the setup for reinforced random walks: 1) Our model involves many agents, modeled by a flow, and their behavior is affected by their collective action in putting down pheromone, while the model for reinforced random walks considers a single agent whose behavior is influenced by its past random choices. 2) Pheromone decays geometrically over time in our model, but edge weights do not decrease in reinforced random walks. 3) Our model has leakage at each vertex, which is not present in the setup for reinforced random walks. Nevertheless, in a similar spirit to random walk-like processes studied before, the model we investigate is a Markov process of particular relevance to biology.