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The constraining effect of gas and the dark matter halo on the vertical stellar distribution of the Milky Way
No full textWe study the vertical stellar distribution of the Milky Way thin disk in detail with particular focus on the outer disk. We treat the galactic disk as a gravitationally coupled, three-component system consisting of stars, atomic hydrogen gas, and molecular hydrogen gas in the gravitational field of the dark matter halo. The self-consistent vertical distribution for stars and gas in such a realistic system is obtained for radii between 4-22 kpc. The inclusion of an additional gravitating component constrains the vertical stellar distribution toward the mid-plane, so that the mid-plane density is higher, the disk thickness is reduced, and the vertical density profile is steeper than in the one-component, isothermal, stars-alone case. We show that the stellar distribution is constrained mainly by the gravitational field of gas and dark matter halo in the inner and the outer Galaxy, respectively. We find that the thickness of the stellar disk measured as the half-width at half-maximum of the vertical density distribution) increases with radius, flaring steeply beyond R = 17 kpc. The disk thickness is reduced by a factor of 3-4 in the outer Galaxy as a result of the gravitational field of the halo, which may help the disk resist distortion at large radii. The disk would flare even more if the effect of dark matter halo were not taken into account. Thus it is crucially important to include the effect of the dark matter halo when determining the vertical structure and dynamics of a galactic disk in the outer region
Multiresolution-based weighted regularization for denoised image interpolation from scattered samples with application to confocal microscopy
No full textThe problem of reconstructing an image from nonuniformly spaced, spatial point measurements is frequently encountered in bioimaging and other scientific disciplines. The most successful class of methods in handling this problem uses the regularization approach involving the minimization of a derivative-based roughness functional. It has been well demonstrated, in the presence of noise, that nonquadratic roughness functionals such as l(1), measure yield better performance compared to the quadratic ones in inverse problems in general and in deconvolution in particular. However, for the present problem, all well-evaluated methods use quadratic roughness measures; indeed, l(1) performs worse than the quadratic roughness when the sampling density is low. This is due to the fact that the mutual incoherence between the measurement operator (dirac-delta) and the regularization operator (derivative) is low in the present problem. Here we develop a new multiresolution-based roughness functional that performs better than l(1) and quadratic functionals under a wide range of sampling densities. We also propose an efficient iterative method for minimizing the resulting cost function. We demonstrate the superiority of the proposed regularization functional in the context of reconstructing full images from nonuniformly undersampled data obtained from a confocal microscope. (C) 2018 Optical Society of Americ
Genesis and evolution of premixed flames in turbulence
No full textFlames interacting with turbulence are continuously generated and annihilated by stretching and folding processes over a range of length-scales and time-scales. In this paper, we address: from where and how do the complex topology and physico-chemical state of a fully developed turbulent premixed flame generate and evolve in time by analyzing the motion of flame particles. Flame particles are points that co-move with reactive isoscalar surfaces which are representative of turbulent premixed flames. Direct Numerical Simulation (DNS) of H-2-air turbulent premixed flame with detailed chemistry is combined with a computational methodology called the Backward Flame Particle Tracking (BFPT) algorithm. Uniform distribution of flame particles that entirely span isotherms at time t(f) is tracked backwards to an earlier time t(i) (t(i) < t(f)). On backtracking, the once uniformly distributed flame particles form multiple clusters in the leading locations of the corresponding isotherms. Since Zeldovich, such leading locations or leading points have remained an enigmatic concept in combustion literature inducing strong hypotheses without concrete proofs on their role. The critical observation that entire flame surface evolves from multiple clusters of leading points at earlier time allows a Finite Strain Theoretic description of the turbulent flame in terms of these points. Stretching is initiated by flame propagation along the direction of maximum curvature. Using Finite Strain Theory, we observe that at the flame surface around the leading points, the direction of minimum curvature gets preferentially aligned with the most extensive direction of the left Cauchy-Green strain-rate tensor and vorticity. These two stretching mechanisms cause the leading regions to become finite sized surfaces, several of which subsequently join together generating the complete surface at tf. A relationship is developed between the turbulent flame speed at time tf and the flame displacement speed and flow-flame properties like stretch-rate of the leading points from an earlier time. Finally, we have used two distinct sets of flame particles: Set-G and Set-D, which generate and destroy the flame surface, respectively. Using the observations that the flame particles in these sets follow a modified Batchelor's pair dispersion law, we have identified an important length-scale known as the Gibson scale. Curved flame propagation dominates dispersion of flame particles upto Gibson scale, while turbulence dominates dispersion of flame particles beyond this scale. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Dual-Comparison One-Cycle Control for Single-Phase Bidirectional Power Converters
No full textDual-comparison one-cycle control for the bidirectional power flow in single-phase grid-connected converters is proposed in this paper. Advantages of dual-comparison one-cycle control when compared to conventional one-cycle control is that it does not give any steady-state dc offset, no light-load instability, and implements unipolar pulsewidth modulationwithout having to sense the grid voltage. Addition of a fictitious current term, which is generated from the gating signal of one of the active devices, using a bandpass filter, enables the bidirectional power flow. The quality factor of the bandpass filter is shown to impact the total harmonic distortion in current, fundamental displacement angle, and steady-state dc offset. The optimal value of a quality factor, obtained with aid of simulations, gives a superior performance. The current drawn or injected into the grid is seen to lag the grid voltage. The reason for a nonunity displacement power factor is analyzed and a compensation to achieve a unity displacement power factor is also proposed in this paper. Detailed simulation and experimental studies are carried out to validate the proposed control and the high performance that can be obtained
Statistical Tests for Detecting Granger Causality
No full textDetection of a causal relationship between two or more sets of data is an important problem across various scientific disciplines. The Granger causality index and its derivatives are important metrics developed and used for this purpose. However, the test statistics based on these metrics ignore the effect of practical measurement impairments such as subsampling, additive noise, and finite sample effects. In this paper, we model the problem of detecting a causal relationship between two time series as a binary hypothesis test with the null and alternate hypotheses corresponding to the absence and presence of a causal relationship, respectively. We derive the distribution of the test statistic under the two hypotheses and show that measurement impairments can lead to suppression of a causal relationship between the signals, as well as false detection of a causal relationship, where there is none. We also use the derived results to propose two alternative test statistics for causality detection. These detectors are analytically tractable, which allows us to design the detection threshold and determine the number of samples required to achieve a given missed detection and false alarm rate. Finally, we validate the derived results using extensive Monte Carlo simulations as well as experiments based on real-world data, and illustrate the dependence of detection performance of the conventional and proposed causality detectors on parameters such as the additive noise variance and the strength of the causal relationship
New minimal supersymmetric GUT emergence and sub-Planckian renormalization group flow
No full textConsistency of trans-unification renormalization group (RG) evolution is used to discuss the domain of definition of the New Minimal Supersymmetric SO(10)GUT (NMSGUT). We define the 1-loop RGE beta functions, simplifying generic formulae using constraints of gauge invariance and superpotential structure. We also calculate the 2 loop contributions to the gauge coupling and gaugino mass and indicate how to get full 2 loop results for all couplings. Our method overcomes combinatorial barriers that frustrate computer algebra based attempts to calculate SO(10) beta functions involving large irreps. Use of the RGEs identifies a perturbative domain Q < M-E, where M-E < M-planck is the scale of emergence where the NMSGUT, with GUT compatible soft supersymmetry breaking terms emerges from the strong UV dynamics associated with the Landau poles in gauge and Yukawa couplings. Due to the strength of the RG flows the Landau poles for gauge and Yukawa couplings lie near a cutoff scale A(E) for the perturbative dynamics of the NMSGUT which just above M- (E). SO(10) RG flows into the IR are shown to facilitate small gaugino masses and generation of negative Non Universal Higgs masses squared needed by realistic NMSGUT fits of low energy data. Running the simple canonical theory emergent at M-E through M-x down to the electroweak scale enables tests of candidate scenarios such as supergravity based NMSGUT with canonical kinetic terms and NMSGUT based dynamical Yukawa unification
Microenvironment Sensitive Charge-Transfer Dye for Tandem Sensing of Multiple Analytes at Mesoscopic Interfaces
No full textAn easy to synthesize amphiphilic dye is developed whose sensing behavior in surfactant assemblies can be modulated through surface-charge, micropolarity, and local pH, etc. Thus, the micelle-bound probe shows remarkable ion dependent bathochromic shifts in the charge-transfer band, enabling simultaneous ratiometric detection of four different metal ions, such as Cu2+, Ni2+, Hg2+, and Zn2+, at parts per billion (ppb) level in water. This is indeed a striking observation since naked-eye sensing of multiple metal ions at the mesoscopic interface is not known to date. Moreover, the probe even shows distinct color response against copper ion in different oxidation states, which is also unheard of. Further, the in situ formed metal complexes can be employed for naked-eye screening of three different amino acids, such as histidine, cysteine, and aspartic acid, in aqueous medium. Probes of this class, which are capable of multiplexing, offer new ways of efficiently screening multiple analytes in complex, real-life samples (e.g., wastewater management, analysis of pharmaceutical drugs, etc.). Further, low-cost reusable dye-coated paper discs were also developed as an ecofriendly method for on-site sensing of metal ions
Covariation and phenotypic integration in chemical communication displays: biosynthetic constraints and eco-evolutionary implications
No full textChemical communication is ubiquitous. The identification of conserved structural elements in visual and acoustic communication is well established, but comparable information on chemical communication displays (CCDs) is lacking. We assessed the phenotypic integration of CCDs in a meta-analysis to characterize patterns of covariation in CCDs and identified functional or biosynthetically constrained modules. Poorly integrated plant CCDs (i.e. low covariation between scent compounds) support the notion that plants often utilize one or few key compounds to repel antagonists or to attract pollinators and enemies of herbivores. Animal CCDs (mostly insect pheromones) were usually more integrated than those of plants (i.e. stronger covariation), suggesting that animals communicate via fixed proportions among compounds. Both plant and animal CCDs were composed of modules, which are groups of strongly covarying compounds. Biosynthetic similarity of compounds revealed biosynthetic constraints in the covariation patterns of plant CCDs. We provide a novel perspective on chemical communication and a basis for future investigations on structural properties of CCDs. This will facilitate identifying modules and biosynthetic constraints that may affect the outcome of selection and thus provide a predictive framework for evolutionary trajectories of CCDs in plants and animals
Confirmation Of Two Galactic Supernova Remnant Candidates Discovered by THOR
No full textAnderson et al. identified 76 candidate supernova remnants (SNRs) using data from the HI/OH/Recombination line survey of the Milky Way. The spectral index and polarization properties can help distinguish between SNRs and H II regions, which are often confused. We confirm two SNR candidates using spectral index data and morphology. However, we observe that the fractional linear polarization cannot distinguish between SNRs and H II regions, likely due to contamination by diffuse Galactic synchrotron emission. We also comment on the association of SNR candidates with pulsars through geometric and age considerations