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G-quadruplex Structures Contribute to Differential Radiosensitivity of the Human Genome
No full textDNA, the fundamental unit of human cell, generally exists in Watson-Crick base-paired B-DNA form. Often, DNA folds into non-B forms, such as four-stranded G-quadruplexes. It is generally believed that ionizing radiation (IR) induces DNA strand-breaks in a random manner. Here, we show that regions of DNA enriched in G-quadruplex structures are less sensitive to IR compared with B-DNA in vitro and inside cells. Planar G-quartet of G4-DNA is shielded from IR-induced free radicals, unlike single- and double-stranded DNA. Whole-genome sequence analysis and real-time PCR reveal that genomic regions abundant in G4-DNA are protected from radiation-induced breaks and can be modulated by G4 stabilizers. Thus, our results reveal that formation of G4 structures contribute toward differential radiosensitivity of the human genome
N-Heterocyclic Carbene-Catalyzed Formal 6+2] Annulation Reaction via Cross-Conjugated Aza-Trienolate Intermediates
No full textThe diverse reactivity of N-heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modes of action. Although NHC-bound enolates and dienolates are known, the related NHC-bound cross-conjugated aza-trienolates remain elusive. Herein, we demonstrate the NHC-catalyzed formal 6+2] annulation of nitrogen-containing heterocyclic aldehydes with alpha,alpha,alpha-trifluoroacetophenones leading to the formation of versatile pyrrolooxazolones (29 examples). The catalytically generated cross-conjugated aza-trienolates (aza-fulvene type) underwent smooth 6+2] annulation with electrophilic ketones to afford the product in moderate to good yields under mild conditions. Preliminary DFT studies on the mechanism are also provided
Effect of nanostructured Al on microstructure, microhardness and sliding wear behavior of Al-xGnP composites by powder metallurgy (PM) route
No full textIn the present work, Al-based metal matrix composites (MMCs) have been developed by the powder metallurgy (PM) route using exfoliated graphite nanoplatelets (xGnP) as nanofillers and their microstructure, microhardness and sliding wear behaviour were investigated. The Al-based MMCs were developed by using nanostructured Al powder developed by mechanical milling for 25 h in a high energy planetary ball mill. The crystallite size and lattice strain of Al after 25 h of milling were found to be 32 nm and 0.383%, respectively. Al-1, 2, 3 wt.% xGnP composites were developed by the PM route. A significant improvement in both the microhardness and wear resistance of the Al-xGnP up to addition of 3 wt.% of the nanofiller was observed. For Al-3 wt.% xGnP composite developed using as-milled nanostructured Al, a microhardness of similar to 1 GPa could be achieved, which is similar to 6 times higher than that of the pure sintered Al sample (similar to 169.7 MPa). Nanostructured Al also leads to enhancement of the wear behaviour as compared to as-received Al. The wear mechanism in the various composites was found to involve a combination of abrasion, ploughing, delamination, microcracks, deep grooves and pullout of nanofillers
Increasing intervention of nonferroelectric distortion and weakening of ferroelectricity at the morphotropic phase boundary in Na0.5Bi0.5TiO3-BaTiO3
No full textMorphotropic phase boundary (MPB) and polymorphic phase boundary ferroelectric solid solutions show enhanced electromechanical response and are sought after as actuator and transducer materials. Compared to others, the lead-free piezoelectric solid solution Na0.5Bi0.5TiO3-BaTiO3 stands out in two important respects: (i) low piezoelectric coefficients (similar to 200 pC/N) and (ii) anomalous decrease in the depolarization temperature at the MPB, the reason for which is still unclear. Here we show that both features are related; this is caused by an increasing intervention of a nonferroelectric structural distortion which compromises the gains the system acquires at the MPB via the interferroelectric instability. The propensity of the intervening nonferroelectric distortion, identified as in-phase octahedral tilt, grows considerably as the MPB is approached causing considerable structural-polar disorder, weakening the overall strength of ferroelectric interaction
Structural, linear and non-linear optical properties of annealed and irradiated Ag/Se heterostructure films for optoelectronic applications
No full textThe present work demonstrates the effect of annealing and laser irradiation on the linear, nonlinear optical properties as well as the structural properties of thermally deposited Ag/Se bilayer thin films. The Ag diffusion into the Se layer by thermal annealing (annealed at 90 degrees C) and laser irradiation (532 nm) brings the changes which have been investigated. The structure of the studied films has been studied by X-ray diffraction and the surface morphology by field emission scanning electron microscopy. The optical transmission data of the films was collected from UV-vis-NIR spectrophotometer in the wavelength range 500-1200 nm. The refractive index (n) and extinction coefficient (k) were observed to be increased with photo thermal treatment. The indirect allowed optical band gap decreases with Ag diffusion as the width of the localised states increased. The dispersion of refractive index was analysed in terms of single oscillator Wemple-Di Domenico model. The third order nonlinear susceptibility (chi((3))) and nonlinear refractive index (n(2)) were calculated from the linear parameters using semi-empirical relations. The changes in the optical parameters with annealing and laser irradiation were explained on the basis of defect states and density of localised states due to Ag diffusion into Se matrix. The Raman study reveals the vibrational bonding information in the films. The tuneable optical properties can be used in various optoelectronic applications
Event-Based Concurrency: Applications, Abstractions, and Analyses
No full textDue to the increased emphasis on responsiveness, event-based design has become mainstream in software development. Software applications are required to maintain responsiveness even while performing multiple tasks simultaneously. This has resulted in the adoption of a combination of thread and event-based concurrency in modern software such as smartphone applications. In this chapter, we present the fundamental programming and semantic concepts in the combined concurrency model of threads and events. The paradigm of event-based concurrency cuts across programming languages and application frameworks. We give a flavor of event-driven programming in a few languages and application frameworks. The mix of threads and events complicates reasoning about correctness of applications under all possible interleavings. We discuss advances in the core concurrency analysis techniques for event-driven applications with focus on happens-before analysis, race detection, and model checking. We also survey other analysis techniques and related programming abstractions
Large Collective Lamb Shift of Two Distant Superconducting Artificial Atoms
No full textVirtual photons can mediate interaction between atoms, resulting in an energy shift known as a collective Lamb shift. Observing the collective Lamb shift is challenging, since it can be obscured by radiative decay and direct atom-atom interactions. Here, we place two superconducting qubits in a transmission line terminated by a mirror, which suppresses decay. We measure a collective Lamb shift reaching 0.8% of the qubit transition frequency and twice the transition linewidth. We also show that the qubits can interact via the transmission line even if one of them does not decay into it
High efficiency DBR assisted grating chirp generators for silicon nitride fiber-chip coupling
No full textSilicon Nitride (SiN) is emerging as a promising material for a variety of integrated photonic applications. Given its low index contrast however, a key challenge remains to design efficient couplers for the numerous platforms in SiN photonics portfolio. Using a combination of bottom reflector and a chirp generating algorithm, we propose and demonstrate high efficiency, grating couplers on two distinct SiN platforms. For a partially etched grating on 500 nm thick SiN, a calculated peak efficiency of -0.5 dB/coupler is predicted, while for a fully etched grating on 400 nm thick SiN, an efficiency of -0.4 dB/coupler is predicted. Experimentally measured coupling efficiencies are observed to be -1.17 and -1.24 dB/coupler for the partial and fully etched grating couplers respectively in the C-L band region. Furthermore, through numerical simulations, it is shown that the chirping algorithm can be implemented in eight additional combinations comprising SiN film thickness between 300-700 nm as well as alternate claddings, to achieve a per coupler loss between -0.33 to -0.65 dB
On the position of La, Lu, Ac and Lr in the periodic table: a perspective
No full textThe periodic table of elements, organised as blocks of elements that contain similar properties, occupies a central role in chemistry. However, the position of some of the elements in the periodic table is a debate that has been ensuing over the past one and a half long centuries. Particularly, the positions of lanthanum (La), lutetium (Lu), actinium (Ac) and lawrencium (Lr) in the periodic table have been quite controversial. Different kinds of studies carried out by various research groups have yet left the fate of these elements undecided as the results of these investigations suggested that these elements could potentially be placed in the d-block, p-block or all four in the f-block. Our recent work looked into this question from a new perspective, involving encapsulation of La, Lu, Ac and Lr into Zintl ion clusters, Pb-12(2-) and Sn-12(2-). These clusters were chosen as they provide a fitting environment for the determination of structural, thermodynamic and electronic properties of the encapsulated species. Various results that have been evaluated and subsequently analysed (Joshi et al. in Phys. Chem. Chem. Phys. 20:15253-15272, 2018) in order to seek out similarities and differences for making justified conclusions about the placement of all these four elements in the periodic table are the subject matter of this review article
Halogen Bonding in the Molecular Recognition of Thyroid Hormones and Their Metabolites by Transport Proteins and Thyroid Hormone Receptors
No full textHalogen bonding (XB) is an attractive interaction between a halogen atom and an electron donor. Although halogens are electron-rich atoms, they act as electrophiles in these types of interactions. This is due to the presence of a significant positive charge (sigma-hole) on the halogen atoms in organic halides along the R-X (R = carbon, nitrogen, halogen) bond. With an increase in the polarizability down the group from fluorine to iodine, the positive charge on the sigma-hole increases, which leads to an increase in the strength of XB. Numerous studies revealed that XB is a useful tool to develop supramolecular architectures by self-assembly. Interestingly, XBs are also observed in many biomolecules, such as protein-ligand complexes and nucleic acids containing halogenated nucleotides. In fact, XBs are extensively used to increase the potency and selectivity of small molecule ligands to a target protein. In this minireview, we discuss the role of XBs in the molecular recognition of thyroid hormones (THs) and their metabolites by various transport proteins and thyroid hormone receptors (TRs). THs are naturally occurring iodinated small molecules that are synthesized by the thyroid gland and carried to various target organs by several serum transport proteins, such as transthyretin, human serum albumin, and thyroxine-binding globulin. Interestingly, all these proteins form XBs with THs and these interactions play important roles in the high affinity binding. Furthermore, TRs, such as TR alpha and TR beta also form XBs with the 3-iodine of THs and triiodothyroacetic acid, an endogenous TH metabolite that shows thyromimetic activity