We quantify the systematics in the size–luminosity relation of galaxies in the Sloan Digital Sky Survey main sample (i.e. at z ∼ 0.1) which arise from fitting different one- and two-component model ...profiles to the r-band images. For objects brighter than L
*, fitting a single Sérsic profile to what is really a two-component SerExp system leads to biases: the half-light radius is increasingly overestimated as n of the fitted single component increases; it is also overestimated at B/T ∼ 0.6. For such objects, the assumption of a single Sérsic component is particularly misleading. However, the net effect on the R-L relation is small, except for the most luminous tail. We then study how this relation depends on morphology. Our analysis is one of the first to use Bayesian-classifier-derived weights, rather than hard cuts, to define morphology. For the R-L relation Es, S0s and Sas are early types, whereas Sbs and Scds are late, although S0s tend to be 15 per cent smaller than Es of the same luminosity, and faint Sbs are more than 25 per cent smaller than faint Scds. Neither the early- nor the late-type relations are pure power laws: both show significant curvature, which we quantify. This curvature confirms that two mass scales are special for both early- and late-type galaxies: M
* ∼ 3 × 1010 and 2 × 1011 M⊙. Also, although the R
disc-L
disc and R
disc-M
*disc relations of discs of disc-dominated galaxies run parallel to the corresponding relations for the total light in late types (i.e. they are significantly curved), R
bulge-L
bulge and R
bulge-M
*bulge for bulge-dominated systems show almost no curvature (i.e. unlike for the total light of early-type galaxies). Finally, the intrinsic scatter in the R-L relation decreases at large L and/or M
* and should provide additional constraints on models of how the most massive galaxies formed.
Improvement in mixing quality under of low Reynolds number hydrodynamic flows in microchannel devices is mandatory and essential. This paper investigates the electrokinetic effects on mixing of two ...miscible fluid streams (ethanol and water) in two different micromixers (i.e., circular and square micromixers) with the help of analytical, semianalytical, and numerical methods. In the analytical method, we develop a closed form solution in order to evaluate normalized electric potential distribution as a function of normalized microchannel channel width, as well as a semianalytical solution for normalized concentration distribution across the normalized microchannel width. In addition, in the context of the numerical method (based on the Finite Element Method approach), we perform a parametric study by varying the input AC voltage and compare the extent of mixing in the two proposed micromixers. Moreover, we validate the analytical and semianalytical results with obtained numerical results, and also compare them with previously published literature. A good agreement between the analytical and semianalytical results with the obtained numerical solution is observed as ±15%.
The paired top and bottom Dirac surface states, each associated with a half-integer quantum Hall (QH) effect, and a resultant integer QH conductance (νe^{2}/h), are hallmarks of a three-dimensional ...topological insulator (TI). In a dual-gated system, chemical potentials of the paired surface states are controlled through separate gates. In this work, we establish tunable capacitive coupling between the surface states of a bulk-insulating TI BiSbTeSe_{2} and study the effect of this coupling on QH plateaus and Landau level (LL) fan diagram via dual-gate control. We observe nonlinear QH transitions at low charge density in strongly coupled surface states, which are related to the charge-density-dependent coupling strength. A splitting of the N=0 LL at the charge neutrality point for thin devices (but thicker than the 2D limit) indicates intersurface hybridization possibly beyond single-particle effects. By applying capacitor charging models to the surface states, we explore their chemical potential as a function of charge density and extract the fundamental electronic quantity of LL energy gaps from dual-gated transport measurements. These studies are essential for the realization of exotic quantum effects such as topological exciton condensation.
Display omitted
•Recent advances in the field of MOF-polymer composites are briefly reviewed.•Methods for making MOF-polymer composites are noted with their merits and demerits.•Utility of ...MOF-polymer composites in several relevant applications is reviewed.•Suggestions for future research that might help to further develop the field are discussed.
In this contribution, recent advances in the construction of MOF-polymer composites and their corresponding applications are briefly reviewed. The appearance of such architectures is becoming prominent in recent literature, due to the fact that the union of these two dissimilar components can give rise to a number of desirable properties that are not necessarily achieved by the individual components. For instance, while MOFs already boast unprecedented internal surface areas and highly tunable pore structures, they can often suffer from limited stability that results from the weak nature of the coordination bonding. However, recent work, outlined in this review, demonstrates that polymers can enhance MOF stability and even augment other important properties like electrical conductivity. Further, we discuss a number of other studies, where the addition of external polymer coatings or the insertion or grafting of polymer species inside the MOF pores can lead to noticeable performance enhancement in a variety of applications including water treatment, catalysis, small molecule adsorption/separation, small molecule/ion sensing, and bio-delivery. The hope is that this review will highlight the prominence of this newly emerging class of materials and demonstrate their potential in a variety of applications relevant to host–guest chemistry.
Substantial evidence shows that skeletal fragility should be considered among the complications associated with type 2 diabetes. Individuals with type 2 diabetes have increased fracture risk, despite ...normal bone mineral density (BMD) and high BMI-factors that are generally protective against fractures. The mechanisms underlying skeletal fragility in diabetes are not completely understood, but are multifactorial and likely include effects of obesity, hyperglycaemia, oxidative stress, and accumulation of advanced glycation end products, leading to altered bone metabolism, structure, and strength. Clinicians should be aware that BMD measurements underestimate fracture risk in people with type 2 diabetes, and that new treatments for diabetes, with neutral or positive effects on skeletal health, might play a part in the management of diabetes in those at high risk of fracture. Data for the optimum management of osteoporosis in patients with type 2 diabetes are scarce, but in the absence of evidence to the contrary, physicians should follow guidelines established for postmenopausal osteoporosis.
W49B is a supernova remnant (SNR) discovered over 60 yr ago in early radio surveys. It has since been observed over the entire wavelength range, with the X-ray morphology resembling a centrally ...filled SNR. The nature of its progenitor star is still debated. Applying Smoothed Particle Inference techniques to analyze the X-Ray emission from W49B, we characterize the morphology and abundance distribution over the entire remnant. We also infer the density structure and derive the mass of individual elements present in the plasma. The morphology is consistent with an interaction between the remnant and a dense medium along the eastern edge, and some obstruction toward the west. We find a total mass of 130 M and an estimated ejecta mass of 1.2 M . Comparison of the inferred abundance values and individual element masses with a wide selection of SN models suggests that deflagration-to-detonation (DDT) Type Ia models are the most compatible, with Fe abundance being the major discriminating factor. The general agreement between our abundance measurements and those from previous studies suggests that disagreement between various authors is more likely due to the choice of models used for comparison, rather than the abundance values themselves. While our abundance results lean toward a Type Ia origin, ambiguities in the interpretation of various morphological and spectral characteristics of W49B do not allow us to provide a definitive classification.
The dimeric diketopiperazine (DKPs) alkaloids are a diverse family of natural products (NPs) whose unique structural architectures and biological activities have inspired the development of new ...synthetic methodologies to access these molecules. However, catalyst-controlled methods that enable the selective formation of constitutional and stereoisomeric dimers from a single monomer are lacking. To resolve this long-standing synthetic challenge, we sought to characterize the biosynthetic enzymes that assemble these NPs for application in biocatalytic syntheses. Genome mining enabled identification of the cytochrome P450, NzeB (Streptomyces sp. NRRL F-5053), which catalyzes both intermolecular carbon–carbon (C–C) and carbon–nitrogen (C–N) bond formation. To identify the molecular basis for the flexible site-selectivity, stereoselectivity, and chemoselectivity of NzeB, we obtained high-resolution crystal structures (1.5 Å) of the protein in complex with native and non-native substrates. This, to our knowledge, represents the first crystal structure of an oxidase catalyzing direct, intermolecular C–H amination. Site-directed mutagenesis was utilized to assess the role individual active-site residues play in guiding selective DKP dimerization. Finally, computational approaches were employed to evaluate plausible mechanisms regarding NzeB function and its ability to catalyze both C–C and C–N bond formation. These results provide a structural and computational rationale for the catalytic versatility of NzeB, as well as new insights into variables that control selectivity of CYP450 diketopiperazine dimerases.
Mass loss from massive stars leads to the formation of circumstellar wind-blown bubbles surrounding the star, bordered by a dense shell. When the star ends its life in a supernova (SN) explosion, the ...resulting shock wave expands within this modified medium. Following up on an introductory paper (Dwarkadas), herein we study the evolution of a SN in the bubble formed by a 35 M unk star that evolves through the phases O star, red supergiant, and Wolf-Rayet star. We model the evolution of the circumstellar medium, and the expansion of the SN shock wave within this medium. Our multidimensional simulations clearly reveal density and pressure fluctuations within the surrounding medium, the presence of hydrodynamic instabilities, the growth of vorticity, and the onset of turbulence. The SN shock interaction with this medium, and then with the dense shell, gives rise to transmitted and reflected shocks. Their effect on the X-ray emission is examined. In this particular case the shock wave is trapped in the dense shell for several doubling times. The turbulent interior, coupled with the density and pressure fluctuations, lead to a corrugated SN shock that impacts the dense shell. The impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before others. As each interaction is accompanied by an increase in the X-ray and optical emission, different parts of the shell will "light up" at different times. The situation is resemblant of the scenario in SN 1987A. The reflected shock formed upon shell impact comprises several smaller shocks with different velocities, which are not necessarily moving radially inward. The spherical symmetry of the initial shock wave is completely destroyed.
PDF
