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Hadwiger's conjecture for squares of 2-trees
No full textHadwiger's conjecture asserts that any graph contains a clique minor with order no less than the chromatic number of the graph. We prove that this well-known conjecture is true for all graphs if and only if it is true for squares of split graphs. This observation implies that Hadwiger's conjecture for squares of chordal graphs is as difficult as the general case, since chordal graphs are a superclass of split graphs. Then we consider 2-trees which are a subclass of each of planar graphs, 2-degenerate graphs and chordal graphs. We prove that Hadwiger's conjecture is true for squares of 2-trees. We achieve this by proving the following stronger result: for any 2-tree T, its square T-2 has a clique minor of order chi(T-2) for which each branch set induces a path, where chi(T-2) is the chromatic number of T-2. (C) 2018 Elsevier Ltd. All rights reserved
Mycobacterium tuberculosis WhiB3 maintains redox homeostasis and survival in response to reactive oxygen and nitrogen species
No full textMycobacterium tuberculosis (Mtb) survives under oxidatively and nitosatively hostile niches inside host phagocytes. In other bacteria, adaptation to these stresses is dependent upon the redox sensitive two component systems (e.g., ArcAB) and transcription factors (e.g., FNR/SoxR). However, these factors are absent in Mtb. Therefore, it is not completely understood how Mtb maintains survival and redox balance in response to reactive oxygen species (ROS) and reactive nitrogen species (RNS). Here, we present evidences that a 4Fe-4S-cofactor containing redox-sensitive transcription factor (WhiB3) is exploited by Mtb to adapt under ROS and RNS stress. We show that Mtb Delta whiB3 is acutely sensitive to oxidants and to nitrosative agents. Using a genetic biosensor of cytoplasmic redox state (Mrx1-roGFP2) of Mtb, we show that WhiB3 facilitates recovery from ROS (cumene hydroperoxide and hydrogen peroxide) and RNS (acidified nitrite and peroxynitrite). Also, Mtb.whiB3 displayed reduced survival inside RAW 264.7 macrophages. Consistent with the role of WhiB3 in modulating host-pathogen interaction, we discovered that WhiB3 coordinates the formation of early human granulomas during interaction of Mtb with human peripheral blood mononuclear cells (PBMCs). Altogether, our study provides empirical proof that WhiB3 is required to mitigate redox stress induced by ROS and RNS, which may be important to activate host/bacterial pathways required for the granuloma development and maintenance
An optimal bidimensional multi-armed bandit auction for multi-unit procurement
No full textWe study the problem of a buyer who gains stochastic rewards by procuring through an auction, multiple units of a service or item from a pool of heterogeneous agents who are strategic on two dimensions, namely cost and capacity. The reward obtained for a single unit from an allocated agent depends on the inherent quality of the agent; the agent's quality is fixed but unknown. Each agent can only supply a limited number of units (capacity of the agent). The cost incurred per unit and capacity (maximum number of units that can be supplied) are private information of each agent. The auctioneer is required to elicit from the agents their costs as well as capacities (making the mechanism design bidimensional) and further, learn the qualities of the agents as well, with a view to maximize her utility. Motivated by this, we design a bidimensional multi-armed bandit procurement auction that seeks to maximize the expected utility of the auctioneer subject to incentive compatibility and individual rationality, while simultaneously learning the unknown qualities of the agents. We first work with the assumption that the qualities are known, and propose an optimal, truthful mechanism 2D-OPT for the auctioneer to elicit costs and capacities. Next, in order to learn the qualities of the agents as well, we provide sufficient conditions for a learning algorithm to be Bayesian incentive compatible and individually rational. We finally design a novel learning mechanism, 2D-UCB that is stochastic Bayesian incentive compatible and individually rational
Probing the gluon Sivers function through direct photon production at RHIC
No full textWe study the production of prompt photons at the RHIC in the context of a generalized parton model framework, with a view to obtain information on the gluon Sivers function (GSF). At RHIC energy (root s = 200 GeV), the Compton process gq -> gamma q contributes significantly to the production of direct photons at midrapidity and dominates it in the negative (backward) rapidity region. We find that for direct photons, asymmetries of up to 10% are allowed by a maximal gluon Sivers function. However, the asymmetry obtained using existing fits of the GSF available in the literature is negligible. We also estimate the impact that photons produced via fragmentation can have on the signal and find that their inclusion can dilute the asymmetry by between 10% and 50% of the direct photon value. Finally, using the color-gauge invariant generalized parton model (CGI-GPM) approach, we consider the effects of initial-state and final-state interactions which can affect the universality of the Sivers functions in different processes. We find that the inclusion of these effects leads to the size of the gluon contributions being roughly halved. However, in the backward region which we are interested in, the sizes of the quark contributions are suppressed even further, leading to increased dominance of the gluon contributions
Fundamental exciton linewidth broadening in monolayer transition metal dichalcogenides
No full textMonolayer transition metal dichalcogenides (TMDS) are highly luminescent materials despite being sub-nanometer thick. This is due to the ultrashort (<1 ps) radiative lifetime of the strongly bound bright excitons hosted by these materials. The intrinsically short radiative lifetime results in a large broadening in the exciton band with a magnitude that is about two orders greater than the spread of the light cone itself. The situation calls for a need to revisit the conventional light cone picture. We present a modified light cone concept which places the light line (<(h)over bar>cQ) as the generalized lower bound for allowed radiative recombination. A self-consistent methodology, which becomes crucial upon inclusion of large radiative broadening in the exciton band, is proposed to segregate the radiative and the nonradiative components of the homogeneous exciton linewidth. We estimate a fundamental radiative linewidth of 1.54 +/- 0.17 meV, owing purely to finite radiative lifetime in the absence of nonradiative dephasing processes. As a direct consequence of the large radiative limit, we find a surprisingly large (similar to 0.27 meV) linewidth broadening due to zero-point energy of acoustic phonons. This obscures the precise experimental determination of the intrinsic radiative linewidth and sets a fundamental limit on the nonradiative linewidth broadening at T = 0 K
Transition-Metal-Free Thioamination of Arynes Using Sulfenamides
No full textThe insertion of arynes into the S-N sigma-bond of sulfenamides allowing the synthesis of o-sulfanylaniline derivatives with reasonable functional group compatibility is presented. The aryne generated from 2-(trimethylsilyl)aryl triflates using CsF in DME was the key for the success of this transition-metal-free thioamination reaction, which involves new C-N and C-S bond formations in a single step under mild conditions. Moreover, the synthetic potential of this method was demonstrated by the synthesis of the antidepressant drug vortioxetine
Nano-Graphene Oxide Based Multichannel Sensor Arrays towards Sensing of Protein Mixtures
No full textOptical array-based sensors are attractive candidates for the detection of various bio-analytes due to their convenient fabrication and measurements. For array-based sensors, multichannel arrays are more advantageous and used frequently in many electronic sensors. But most reported optically array based sensors are constructed on a single channel array. This difficulty is mainly instigated from the overlap in optical responses. In this report we have used nano-graphene oxide (nGO) and suitable fluorophores as sensor elements to construct a multichannel sensor array for the detection of protein analytes. By using the optimized multichannel array we are able to detect different proteins and mixtures of proteins with 100 % classification accuracy at sub-nanomolar concentration. This modified method expedites the sensing analysis as well as minimizes the use of both analyte and sensor elements in array-based protein sensing. We have also used this system for the single channel array-based sensing to compare the sensitivity and the efficacy of these two systems for other applications. This work demonstrated an intrinsic trade-off associated with these two methods which may be necessary to balance for array-based analyte detections
Electronic structure and optical properties of F centers in alpha-alumina
No full textWe use a state-of-the-art GW Bethe-Salpeter equation (BSE) formalism to study electronic structure and optical properties of oxygen vacancies (F centers) in alpha-alumina. The density functional theory (DFT) + GW formalism has been employed to compute the charge transition levels (CTLs) for oxygen vacancies. We propose a reformulation of the DFT+GW approach to calculate these CTLs. Our new approach allows for transparent application of electrostatic corrections required in finite supercell calculations using periodic boundary conditions. We find that F centers in this material introduce deep donor levels, (+2/+1) at 2.4 eV, and a (+1/0) level at 3.9 eV above the valence band maximum. We also study F-center absorption and emission processes using constrained DFT and BSE. Our calculated absorption and emission energies are in excellent agreement with experiments and provide an unambiguous interpretation of the same
On-Field Detection of Helicoverpa armigera Nuclear Polyhedrosis Virus Using Luminescent Amphiphilic Probe: Screening of Agricultural Crops and Commercial Formulations
No full textAn easy to synthesize luminescent, amphiphilic probe has been designed for the first time in optical sensing of a biopesticide, Helicoverpa armigera nuclear polyhedrosis virus (HaNPV). The compound showed formation of a pH-sensitive, thermoreversible nanoaggregate in the aqueous medium. The addition of HaNPV resulted in the rapid change in emission color from blue to cyan at pH 7.4. Till date, no optical assay is known in the literature, which can achieve fast, on-field detection of HaNPV as low as similar to 10(3) POBs/mL. Most importantly, because of naked-eye response, this method does not need the involvement of trained personnel or any sophisticated visualizing instrument. In addition, the distinct optical response also allows us to distinguish the freshly prepared pesticide solution from its storage-old analogue. The quantification of HaNPV is achieved in a wide range of agricultural crop extracts, known to be infected by H. armigera. Inexpensive reusable paper strips are developed for on-location detection purposes. Moreover, the presence of residual HaNPV can also be traced on leaf surfaces. Thus, studies of such kind will be beneficial for quality verification of HaNPV and will surely add a new dimension to the better management of H. armigera and minimize the extent of crop loss