Effect of Molecular Structure on the Optoelectronic Properties of Isoindigo-based Semiconductors

Organic electronics have developed rapidly over the past few decades. Despite this progress, device performance must be further improved before organic photovoltaic devices and organic field effect transistors can be widely commercialized. Therefore, both the design of new organic semiconductors and understanding how molecular structure affects the optoelectronic properties of these semiconductors are critically important. In this context, this thesis discusses the effect of molecular structure on the optoelectronic properties (e.g., oscillator strength, frontier orbital energies, optical band gap, and charge carrier mobilities) of organic semiconductors. The thesis deals with two different types of structural modifications to isoindigo-based semiconductors. The first section focuses on the effect of linear-conjugation and cross-conjugation on the oscillator strength of molecular organic semiconductors based on a ring-expanded isoindigo derivative. Compared to isoindigo analogues, extending the conjugation of the -system through ring fusion substantially red-shifted the absorption maximum of the HOMO to LUMO transition; however, the cross-conjugation significantly reduced the oscillator strength. As a result, the photocurrent was significantly lower for organic photovoltaic devices made with cross-conjugated materials compared to linearly conjugated materials. The second section discusses the effect of torsional strain in two new polymeric semiconductors, namely poly(ethynyl-alt-isoindigo) and polybisisoindigo, on their electron mobilities. The electron mobilities are compared to the control polymer polyisoindigo, which exhibited a relatively poor electron mobility because of a large torsion angle. In the ethynyl-alt-isoindigo copolymer, the sterically unencumbered ethynyl spacer helps reduce the torsion angle between adjacent isoindigo units and conserve planarity in the polymer backbone. In polybisisoindigo, every second isoindigo unit was fused together, replacing a single bond between repeating units. This lowers the overall degree of torsional strain in the polymer chain. The increased planarity improved the electron mobility of these new polymers relative to polyisoindigo. Out of the two new polymers, thin-film transistors fabricated using polybisisoindigo displayed the highest electron mobility of 1.26 10-3 cm2/V·s. This was attributed to the extended conjugation of the ring-fused bisisoindigo-based system which increased intra-chain electron transport along the polymer backbone. In addition, the larger size of this ring-fused -system might have made polybisisoindigo less sensitive towards positional disorder. In conclusion, a substitution pattern leading to linear conjugation is essential for high oscillator strengths. This increases the absorption coefficient of the material, resulting in a higher photocurrent when incorporated in photovoltaic devices. A minimized torsional strain in the semiconductor backbone is also crucial to improve the charge carrier mobilities

Mechanisms for regulation of plant kinesins

Throughout the eukaryotic world, kinesins serve as molecular motors for the directional transport of cellular cargo along microtubule tracks. Plants contain a large number of kinesins that have conserved as well as specialized functions. These functions depend on mechanisms that regulate when, where and what kinesins transport. In this review, we highlight recent studies that have revealed conserved modes of regulation between plant kinesins and their non-photosynthetic counterparts. These findings lay the groundwork for understanding how plant kinesins are differentially engaged in various cellular processes that underlie plant growth and development

Exploring non minimal Universal Extra Dimensional Model at the LHC

We study the collider phenomenology of non minimal universal extra dimensional (nmUED) model in the context of the Large Hadron Collider at CERN. nmUED is an incarnation of the Standard Model in $(4+1)$ space-time dimensions compactified on an $\bf{S_1}/\bf{Z_2}$ orbifold supplemented with boundary localized operators with unknown coefficients. These coefficients parametrize the radiative corrections which are somehow arbitrary due to the lack of knowledge of the cut-off scale of such effective theory. It is possible to tune the masses and couplings of the Kaluza Klein (KK) excitations by tuning these parameters. Two scenarios with different mass hierarchies among the KK-excitations have been considered. A detailed study of production cross-sections and different decay modes of KK-particles are also presented. We calculate the correlated bounds on masses of KK-particles using the LHC $nl + mj + E\!\!\!\!/_T$ data (in case of production of strongly interacting particles) and $3l + E\!\!\!\!/_T$ data (in case of electroweak productions). We work in a KK-parity conserving scenario where the lightest KK-particle is a potential dark (DM) matter candidate. We use the additional constraints coming from the observed DM relic density of the universe to identify the allowed parameter space. The current status of a nmUED model in the light of DM direct detection data is also examined. The present investigation reveals that production and subsequent leptonic decays of KK-electroweak gauge bosons as massive as 1 TeV, lead to observable trilepton signature with a luminosity of 1 ab$^{-1}$ which will be realized in near future.Comment: 23 pages, 12 figure

The Arabidopsis kinesin-4, FRA1, requires a high level of processive motility to function correctly

Processivity is important for kinesins that mediate intracellular transport. Structure–function analyses of N-terminal kinesins (i.e. kinesins comprising their motor domains at the N-terminus) have identified several non-motor regions that affect processivity in vitro. However, whether these structural elements affect kinesin processivity and function in vivo is not known. Here, we used an Arabidopsis thaliana kinesin-4, called Fragile Fiber 1 (FRA1, also known as KIN4A), which is thought to mediate vesicle transport, to test whether mutations that alter processivity in vitro lead to similar changes in behavior in vivo and whether processivity is important for the function of FRA1. We generated several FRA1 mutants that differed in their ‘run lengths’ in vitro and then transformed them into the fra1-5 mutant for complementation and in vivo motility analyses. Our data show that the behavior of processivity mutants in vivo can differ dramatically from in vitro properties, underscoring the need to extend structure–function analyses of kinesins in vivo. In addition, we found that a high density of processive motility is necessary for the physiological function of FRA1

Unveiling the Dark Side

Discovery and characterisation of black holes (BHs), neutron stars (NSs), and white dwarfs (WDs) with detached luminous companions (LCs) in wide orbits are exciting because they are important test beds for dark remnant (DR) formation physics as well as binary stellar evolution models. Recently, 187 candidates have been identified from Gaia's non-single star catalog as wide orbit (P_orb > 45 days), detached binaries hosting DRs. We identify UV counterparts for 49 of these sources in the archival GALEX data. Modeling the observed spectral energy distribution (SED) spanning FUV-NUV to IR for these sources and stellar evolution models, we constrain the LC properties including mass, bolometric luminosity, and effective temperature for these 49 sources. Using the LC masses, and the astrometric mass function constrained by Gaia, we constrain the DR masses for these sources. We find that 9 have masses clearly in the NS or BH mass range. Fifteen sources exhibit significant NUV excess and 4 show excess both in FUV and NUV. The simplest explanation for these excess UV flux is that the DRs in these sources are white dwarfs (WDs). Using SED modeling we constrain the effective temperature and bolometric luminosity for these 15 sources. Our estimated DR masses for all of these 15 sources are lower than the Chandrasekhar mass limit for WDs. Interestingly, five of these sources had been wrongly identified as neutron stars in literature.Comment: 11 pages, 8 figures, 2 tables, comments welcom

Hunting Down White Dwarf--Main Sequence Binaries Using Multi-Wavelength Observations

Identification of white dwarfs (WD) with main-sequence (MS) companions and characterization of their properties can put important constraints on our understanding of binary stellar evolution and guide the theoretical predictions for a wide range of interesting transient events relevant for, e.g., LSST, ZTF, and LISA. In this study, we combine ultraviolet (UV) and optical color-magnitude diagrams (CMDs) to identify unresolved WD--MS binaries. In particular, we combine high-precision astrometric and photometric data in the optical from \gaia\ -DR3 and UV data from GALEX GR6/7 to identify 111 WD--MS candidates within 100 pc. Of these, 92 are newly identified. Using the Virtual Observatory SED Analyzer (VOSA) we fit the spectral energy distributions (SEDs) of all our candidates and derive stellar parameters, such as effective temperature, bolometric luminosity, and radius for both companions. We find that our identification method helps identify hotter and smaller WD companions (majority with $\geq$10,000 K and $\leq$0.02 $R_\odot$) relative to the WDs identified by past surveys. We infer that these WDs are relatively more massive ($>0.3 M_\odot$). We find that most of the MS companions in our binaries are of the $K$ and $M$ spectral types.Comment: 11 pages, 7 figures, one table, Submitted to MNRAS journa

VDOO: A Short, Fast, Post-Quantum Multivariate Digital Signature Scheme

Hard lattice problems are predominant in constructing post-quantum cryptosystems. However, we need to continue developing post-quantum cryptosystems based on other quantum hard problems to prevent a complete collapse of post-quantum cryptography due to a sudden breakthrough in solving hard lattice problems. Solving large multivariate quadratic systems is one such quantum hard problem. Unbalanced Oil-Vinegar is a signature scheme based on the hardness of solving multivariate equations. In this work, we present a post-quantum digital signature algorithm VDOO (Vinegar-Diagonal-Oil-Oil) based on solving multivariate equations. We introduce a new layer called the diagonal layer over the oil-vinegar-based signature scheme Rainbow. This layer helps to improve the security of our scheme without increasing the parameters considerably. Due to this modification, the complexity of the main computational bottleneck of multivariate quadratic systems i.e. the Gaussian elimination reduces significantly. Thus making our scheme one of the fastest multivariate quadratic signature schemes. Further, we show that our carefully chosen parameters can resist all existing state-of-the-art attacks. The signature sizes of our scheme for the National Institute of Standards and Technology\u27s security level of I, III, and V are 96, 226, and 316 bytes, respectively. This is the smallest signature size among all known post-quantum signature schemes of similar security

Neuropeptide F regulates courtship in Drosophila through a male-specific neuronal circuit.

Male courtship is provoked by perception of a potential mate. In addition, the likelihood and intensity of courtship are influenced by recent mating experience, which affects sexual drive. Using Drosophila melanogaster, we found that the homolog of mammalian neuropeptide Y, neuropeptide F (NPF), and a cluster of male-specific NPF (NPFM) neurons, regulate courtship through affecting courtship drive. Disrupting NPF signaling produces sexually hyperactive males, which are resistant to sexual satiation, and whose courtship is triggered by sub-optimal stimuli. We found that NPFM neurons make synaptic connections with P1 neurons, which comprise the courtship decision center. Activation of P1 neurons elevates NPFM neuronal activity, which then act through NPF receptor neurons to suppress male courtship, and maintain the proper level of male courtship drive

The M3 phosphorylation motif has been functionally conserved for intracellular trafficking of long-looped PIN-FORMEDs in the Arabidopsis root hair cell

Background : PIN-FORMED (PIN) efflux carriers contribute to polar auxin transport and plant development by exhibiting dynamic and diverse asymmetrical localization patterns in the plasma membrane (PM). Phosphorylation of the central hydrophilic loop (HL) of PINs has been implicated in the regulation of PIN trafficking. Recently, we reported that a phosphorylatable motif (M3) in the PIN3-HL is necessary for the polarity, intracellular trafficking, and biological functions of PIN3. In this study, using the root hair system for PIN activity assay, we investigated whether this motif has been functionally conserved among long-HL PINs. Results : Root hair-specific overexpression of wild-type PIN1, 2, or 7 greatly inhibited root hair growth by depleting auxin levels in the root hair cell, whereas overexpression of M3 phosphorylation-defective PIN mutants failed to inhibit root hair growth. Consistent with this root hair phenotype, the PM localization of M3 phosphorylation-defective PIN1 and PIN7 was partially disrupted, resulting in less auxin efflux and restoration of root hair growth. Partial formation of brefeldin A-compartments in these phosphorylation-mutant PIN lines also suggested that their PM targeting was partially disrupted. On the other hand, compared with the PIN1 and PIN7 mutant proteins, M3-phosphorylation-defective PIN2 proteins were almost undetectable. However, the mutant PIN2 protein levels were restored by wortmannin treatment almost to the wild-type PIN2 level, indicating that the M3 motif of PIN2, unlike that of other PINs, is implicated in PIN2 trafficking to the vacuolar lytic pathway. Conclusions : These results suggest that the M3 phosphorylation motif has been functionally conserved to modulate the intracellular trafficking of long-HL PINs, but its specific function in trafficking has diverged among PIN members.This work was supported by grants from the Mid-career Researcher Program (2011–0017242, NRF, MEST) and the Next-Generation BioGreen 21 programs (TAGC PJ00820701 and SSAC PJ00951404) of the Rural Development Administration.Peer Reviewe

The M3 phosphorylation motif has been functionally conserved for intracellular trafficking of long-looped PIN-FORMEDs in the Arabidopsis root hair cell

Background : PIN-FORMED (PIN) efflux carriers contribute to polar auxin transport and plant development by exhibiting dynamic and diverse asymmetrical localization patterns in the plasma membrane (PM). Phosphorylation of the central hydrophilic loop (HL) of PINs has been implicated in the regulation of PIN trafficking. Recently, we reported that a phosphorylatable motif (M3) in the PIN3-HL is necessary for the polarity, intracellular trafficking, and biological functions of PIN3. In this study, using the root hair system for PIN activity assay, we investigated whether this motif has been functionally conserved among long-HL PINs. Results : Root hair-specific overexpression of wild-type PIN1, 2, or 7 greatly inhibited root hair growth by depleting auxin levels in the root hair cell, whereas overexpression of M3 phosphorylation-defective PIN mutants failed to inhibit root hair growth. Consistent with this root hair phenotype, the PM localization of M3 phosphorylation-defective PIN1 and PIN7 was partially disrupted, resulting in less auxin efflux and restoration of root hair growth. Partial formation of brefeldin A-compartments in these phosphorylation-mutant PIN lines also suggested that their PM targeting was partially disrupted. On the other hand, compared with the PIN1 and PIN7 mutant proteins, M3-phosphorylation-defective PIN2 proteins were almost undetectable. However, the mutant PIN2 protein levels were restored by wortmannin treatment almost to the wild-type PIN2 level, indicating that the M3 motif of PIN2, unlike that of other PINs, is implicated in PIN2 trafficking to the vacuolar lytic pathway. Conclusions : These results suggest that the M3 phosphorylation motif has been functionally conserved to modulate the intracellular trafficking of long-HL PINs, but its specific function in trafficking has diverged among PIN members.This work was supported by grants from the Mid-career Researcher Program (2011–0017242, NRF, MEST) and the Next-Generation BioGreen 21 programs (TAGC PJ00820701 and SSAC PJ00951404) of the Rural Development Administration.Peer Reviewe