Brassinosteroids Inhibit Autotropic Root Straightening by Modifying Filamentous-Actin Organization and Dynamics

When positioned horizontally, roots grow down toward the direction of gravity. This phenomenon, called gravitropism, is influenced by most of the major plant hormones including brassinosteroids. Epi-brassinolide (eBL) was previously shown to enhance root gravitropism, a phenomenon similar to the response of roots exposed to the actin inhibitor, latrunculin B (LatB). This led us to hypothesize that eBL might enhance root gravitropism through its effects on filamentous-actin (F-actin). This hypothesis was tested by comparing gravitropic responses of maize (Zea mays) roots treated with eBL or LatB. LatB- and eBL-treated roots displayed similar enhanced downward growth compared with controls when vertical roots were oriented horizontally. Moreover, the effects of the two compounds on root growth directionality were more striking on a slowly-rotating twodimensional clinostat. Both compounds inhibited autotropism, a process in which the root straightened after the initial gravistimulus was withdrawn by clinorotation. Although eBL reduced F-actin density in chemically-fixed Z. mays roots, the impact was not as strong as that of LatB. Modification of F-actin organization after treatment with both compounds was also observed in living roots of barrel medic (Medicago truncatula) seedlings expressing genetically encoded F-actin reporters. Like in fixed Z. mays roots, eBL effects on F-actin in living M. truncatula roots were modest compared with those of LatB. Furthermore, live cell imaging revealed a decrease in global F-actin dynamics in hypocotyls of etiolated M. truncatula seedlings treated with eBL compared to controls. Collectively, our data indicate that eBL-and LatB-induced enhancement of root gravitropism can be explained by inhibited autotropic root straightening, and that eBL affects this process, in part, by modifying F-actin organization and dynamics

A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN feedback in a low-mass cluster of galaxies

We present detailed observations of MRC 0116+111, revealing a luminous, mini radio-halo of ~240 kpc diameter located at the centre of a cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio observations reveal a highly unusual radio source: showing a pair of giant (~100 kpc diameter) bubble-like diffuse structures, that are about three times larger than the analogous extended radio emission observed in M87 - the dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a compact core or active radio jets feeding the plasma bubbles. The radio emitting relativistic particles and magnetic fields were probably seeded in the past by a pair of radio-jets originating in the AGN of the central cD galaxy. The extremely steep high-frequency radio spectrum of the north-western bubble, located ~100 kpc from cluster centre, indicates radiation losses, possibly because having detached, it is rising buoyantly and moving away into the putative hot intra-cluster medium. The other bubble, closer to the cluster centre, shows signs of ongoing particle re-acceleration. We estimate that the radio jets which inflated these two bubbles might have also fed enough energy into the intra-cluster medium to create an enormous system of cavities and shock fronts, and to drive a massive outflow from the AGN, which could counter-balance and even quench a cooling flow. Therefore, this source presents an excellent opportunity to understand the energetics and the dynamical evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.Comment: 15 pages, 8 figures. Accepted for publication in MNRA

Real-time Monitoring for the Next Core-Collapse Supernova in JUNO

Core-collapse supernova (CCSN) is one of the most energetic astrophysical events in the Universe. The early and prompt detection of neutrinos before (pre-SN) and during the SN burst is a unique opportunity to realize the multi-messenger observation of the CCSN events. In this work, we describe the monitoring concept and present the sensitivity of the system to the pre-SN and SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is a 20 kton liquid scintillator detector under construction in South China. The real-time monitoring system is designed with both the prompt monitors on the electronic board and online monitors at the data acquisition stage, in order to ensure both the alert speed and alert coverage of progenitor stars. By assuming a false alert rate of 1 per year, this monitoring system can be sensitive to the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos up to about 370 (360) kpc for a progenitor mass of 30$M_{\odot}$ for the case of normal (inverted) mass ordering. The pointing ability of the CCSN is evaluated by using the accumulated event anisotropy of the inverse beta decay interactions from pre-SN or SN neutrinos, which, along with the early alert, can play important roles for the followup multi-messenger observations of the next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure

Graph-based tracing of filamentary structured objects with applications in neuronal and retinal images

Filamentary structured objects are everywhere in nature and man-made architectures. These are found in the network of neurons, blood vessels, roads and others, which can scale from a range of few microns (in case of neurons) to thousands of kilometers (in case of roads). Image-based analysis of these filamentary structured objects are of great interest as they offer important information about the structure and connectivity of such networks which can help us in applications such as drug screening for neurological disorders or computer-aided diagnosis of diabetic retinopathy. However, the task is challenging due to the bottleneck of filament crossover issue, which essentially hinders the use of existing systems in large-scale applications. The aim of the thesis is to build a generic graph-based framework for tracing the images of filamentary structured objects. The framework consists of two steps: preprocessing step consisting of segmentation, skeleton extraction, digraph representation and tracing step using graph-based methods. The main focus of this thesis is the second step. After the preprocessing step, the skeleton is represented as a directed graph structure where skeleton segments are represented as nodes in the graph and there is an edge between two nodes if the corresponding skeletons are touching each other. Now, the goal is to cluster the graph into disjoint trees where the number of clusters depends on the number of tree structures in the filament. This is achieved by assuming that at least one node is labeled in each cluster of the graph. Given the structure of the graph and one labeled node per cluster, the problem becomes that of assigning class labels to the rest of the unlabeled nodes. The problem is formulated as a label propagation problem on a weighted digraph using the Matrix Forest Theorem. The normalized conductance of a rooted spanning converging forest of a digraph is used as a similarity score between the labeled and unlabeled nodes. The label propagation problem can also be formulated as a random walk on an Absorbing Markov Chain (AMC). After converting the original graph into an AMC, the Fundamental Matrix is computed, which is the expected number of visits from one node to another before absorption. For tracing problem, this is another kind of similarity score between the labeled and unlabeled nodes. For both approaches, the class label for an unlabeled node is the same as that of a labeled node with largest similarity. If the weight matrix is formulated as parametric functions then the parameters can be determined by maximizing the sum of the logarithm of expected number of visits from unlabeled nodes to the labeled nodes. For the scenario where the class labels for only very few nodes are known, the parameter estimation problem is solved by Expectation Maximization (EM) algorithm. For comparison purpose, the tracing problem is also formulated as a Maximum A Posteriori (MAP) inference problem in Undirected Graphical Models. Empirical analysis is conducted for all the approaches using in-house dataset of 2D neuronal images (Downloadable at http://web.bii.a-star.edu.sg/~jaydeepd/tracing.htm ) and publicly available benchmark dataset of retinal images which proves the superiority of my approach compared to current state of art methods as well as widely used commercial software.DOCTOR OF PHILOSOPHY (SCE

Brassinosteroids Inhibit Autotropic Root Straightening by Modifying Filamentous-Actin Organization and Dynamics

When positioned horizontally, roots grow down toward the direction of gravity. This phenomenon, called gravitropism, is influenced by most of the major plant hormones including brassinosteroids. Epi-brassinolide (eBL) was previously shown to enhance root gravitropism, a phenomenon similar to the response of roots exposed to the actin inhibitor, latrunculin B (LatB). This led us to hypothesize that eBL might enhance root gravitropism through its effects on filamentous-actin (F-actin). This hypothesis was tested by comparing gravitropic responses of maize (Zea mays) roots treated with eBL or LatB. LatB- and eBL-treated roots displayed similar enhanced downward growth compared with controls when vertical roots were oriented horizontally. Moreover, the effects of the two compounds on root growth directionality were more striking on a slowly-rotating twodimensional clinostat. Both compounds inhibited autotropism, a process in which the root straightened after the initial gravistimulus was withdrawn by clinorotation. Although eBL reduced F-actin density in chemically-fixed Z. mays roots, the impact was not as strong as that of LatB. Modification of F-actin organization after treatment with both compounds was also observed in living roots of barrel medic (Medicago truncatula) seedlings expressing genetically encoded F-actin reporters. Like in fixed Z. mays roots, eBL effects on F-actin in living M. truncatula roots were modest compared with those of LatB. Furthermore, live cell imaging revealed a decrease in global F-actin dynamics in hypocotyls of etiolated M. truncatula seedlings treated with eBL compared to controls. Collectively, our data indicate that eBL-and LatB-induced enhancement of root gravitropism can be explained by inhibited autotropic root straightening, and that eBL affects this process, in part, by modifying F-actin organization and dynamics

Tracing retinal vessel trees by transductive inference

Background Structural study of retinal blood vessels provides an early indication of diseases such as diabetic retinopathy, glaucoma, and hypertensive retinopathy. These studies require accurate tracing of retinal vessel tree structure from fundus images in an automated manner. However, the existing work encounters great difficulties when dealing with the crossover issue commonly-seen in vessel networks. Results In this paper, we consider a novel graph-based approach to address this tracing with crossover problem: After initial steps of segmentation and skeleton extraction, its graph representation can be established, where each segment in the skeleton map becomes a node, and a direct contact between two adjacent segments is translated to an undirected edge of the two corresponding nodes. The segments in the skeleton map touching the optical disk area are considered as root nodes. This determines the number of trees to-be-found in the vessel network, which is always equal to the number of root nodes. Based on this undirected graph representation, the tracing problem is further connected to the well-studied transductive inference in machine learning, where the goal becomes that of properly propagating the tree labels from those known root nodes to the rest of the graph, such that the graph is partitioned into disjoint sub-graphs, or equivalently, each of the trees is traced and separated from the rest of the vessel network. This connection enables us to address the tracing problem by exploiting established development in transductive inference. Empirical experiments on public available fundus image datasets demonstrate the applicability of our approach. Conclusions We provide a novel and systematic approach to trace retinal vessel trees with the present of crossovers by solving a transductive learning problem on induced undirected graphs.Published versio

Transduction on directed graphs via absorbing random walks

In this paper we consider the problem of graph-based transductive classification, and we are particularly interested in the directed graph scenario which is a natural form for many real world applications. Different from existing research efforts that either only deal with undirected graphs or circumvent directionality by means of symmetrization, we propose a novel random walk approach on directed graphs using absorbing Markov chains, which can be regarded as maximizing the accumulated expected number of visits from the unlabeled transient states. Our algorithm is simple, easy to implement, and works with large-scale graphs on binary, multiclass, and multi-label prediction problems. Moreover, it is capable of preserving the graph structure even when the input graph is sparse and changes over time, as well as retaining weak signals presented in the directed edges. We present its intimate connections to a number of existing methods, including graph kernels, graph Laplacian based methods, and spanning forest of graphs. Its computational complexity and the generalization error are also studied. Empirically, our algorithm is evaluated on a wide range of applications, where it has shown to perform competitively comparing to a suite of state-of-the-art methods. In particular, our algorithm is shown to work exceptionally well with large sparse directed graphs with e.g., millions of nodes and tens of millions of edges, where it significantly outperforms other state-of-the-art methods. In the dynamic graph setting involving insertion or deletion of nodes and edge-weight changes over time, it also allows efficient online updates that produce the same results as of the batch update counterparts.ASTAR (Agency for Sci., Tech. and Research, S’pore

Syntheses, spectroscopic studies, crystal structure and complexation reactions of N- (2 or 4-hydroxylphenyl) benzaldimine

207-213Two monobasic bidentate Schiff base ligands (SBH) derived from the condensation reaction between benzaldehyde and 2-aminophenol (BENOPH) or 4-aminophenol (BENPAPH) have been subjected to complexation reactions stabilising the bis-ligated complexes MII(SB)₂ (MII=Cu, Ni, Co and Zn) where aminophenolic (-OH) groups participate in the complexation reaction. The newly synthesized Schiff bases and their complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical studies. Crystal structure studies performed on BENPAPH show it to crystallize in the monoclinic form, space group P2₁/c; Z=4 with a, 6.500(7); b, 14.885(3); c, 10.852(2) Å and β, 91.489(12)º