OAK (Online Access to Knowledge) Commons (Young Harris College)
Not a member yet
33676 research outputs found
Sort by
Realization of 3D Epoxy resin/Ti3C2Tx MXene Aerogel Composites for Low-Voltage Electrothermal Heating
No full textEthical responsibilities of tenured academics supervising non-tenured researchers in times of neoliberalism and precarity
No full textNeoliberal reform of the university sector has resulted in increasing numbers of academics employed on casual or fixed-term contracts. While there is an emergent body of literature on issues of precarity in the academy, relatively little attention has been paid to the roles and responsibilities of those tenured academics who employ and manage non-tenured researchers. The work involved in hiring and managing a contract researcher is rarely acknowledged or supported, and managers receive little to no training. In this paper, we draw on Dorothy Smith’s feminist sociological approach to analyse interviews with 22 non-tenured researchers to examine how managerial relationships shape the employment experiences of those working precariously. We argue that tenured academics have ethical responsibilities to provide a working environment that is fair, supports the ongoing development and wellbeing of non-tenured staff and challenges dominant discourses of precarious academics as ‘other’
Energy-Efficient Resource Allocation for NOMA-MEC Networks with Imperfect CSI
No full textThe combination of non-orthogonal multiple access (NOMA) and multi-access edge computing (MEC) can significantly improve the system performance including communication coverage, spectrum efficiency, etc. In this paper, we focus on energy-efficient resource allocation for a multi-user multi-BS NOMA-MEC network with imperfect channel state information (CSI), where each user can upload its tasks to multiple base stations (BSs) for remote executions. We propose an optimization scheme, including task assignment, power allocation and user association, to minimize energy consumption. Specifically, we transform the probabilistic problem into a non-probabilistic one. To efficiently solve this nonconvex energy minimization problem, we first investigate the one-user two-BS case and derive the optimal closed-form expressions of task assignment and power allocation via the bilevel programming method. Subsequently, based on the derived optimal solution, we propose a low complexity algorithm for the user association in the multi-user multi-BS scenario. Simulations demonstrate that the proposed algorithm can yield much better performance than the conventional OMA scheme and the identical results with lower complexity from the exhaustive search with the small number of BSs
How do electrostatic perturbations of the protein affect the bifurcation pathways of substrate hydroxylation versus desaturation in the nonheme iron-dependent viomycin biosynthesis enzyme?
No full textThe viomycin biosynthesis enzyme VioC is a non-heme iron and α-ketoglutarate-dependent dioxygenase involved in the selective hydroxylation of L-arginine at the C3-position for antibiotics biosynthesis. Interestingly, experimental studies showed that using the substrate analogue, namely L-homo-arginine, a mixture of products was obtained originating from C3-hydroxylation, C4-hydroxylation and C3‒C4 desaturation. To understand how the addition of one CH2 group to a substrate can lead to such a dramatic change in selectivity and activity, we decided to do a computational study using QM cluster models. We set up a large active-site cluster model of 245 atoms that includes the oxidant with its first- and second-coordination sphere influence as well as the substrate-binding pocket. The model was validated against experimental work on related enzymes and previous computational studies. Thereafter, possible pathways leading to products and byproducts were investigated for a model containing L-Arg and one for L-homo-Arg as substrate. The calcu-lated free energies of activation predict product distributions that match experimental observation and give a low-energy C3-hydroxylation pathway for L-Arg, while for L-homo-Arg several barriers are found to be close in energy leading to a mixture of products. We then analyzed the origins of the differences in product distributions using thermochemical, va-lence bond and electrostatic models. Our studies show that the C3-H and C4-H bond strengths of L-Arg and L-homo-Arg are similar; however, external perturbations from an induced electric field of the protein affect the relative C-H bond strengths of L-Arg dramatically and make the C3-H bond the weakest and guide the reaction to a selective C3-hydroxylation channel. Therefore, the charge distribution in the protein and the induced electric dipole field of the active site of VioC guides the L-Arg substrate activation to C3-hydroxylation and disfavors the C4-hydroxylation pathway, while this does not happen for L-homo-Arg. Tight substrate positioning and electrostatic perturbations from the second-coordination sphere residues in VioC also result in a slower overall reaction for L-Arg; however, they enable a high sub-strate selectivity. Our studies highlight the importance of the second-coordination sphere in proteins that position the substrate and oxidant, perturb charge distributions and enable substrate selectivity
Density functional theory study into the reaction mechanism of isonitrile biosynthesis by the nonheme iron enzyme ScoE
No full textThe nonheme iron enzyme ScoE catalyzes the biosynthesis of an isonitrile substituent in a peptide chain. To understand details of the reaction mechanism we created a large active site cluster model of 212 atoms that contains substrate, the active oxidant and the first- and second-coordination sphere protein and solvent. Several possible reaction mechanisms were tested and it is shown that isonitrile can only be formed through two consecutive catalytic cycles that both use one molecule of dioxygen and -ketoglutarate. In both cycles the active species is an iron(IV)-oxo species that in the first reaction cycle reacts through two consecutive hydrogen atom abstraction steps: first from the N-H group and thereafter from the C-H group to desaturate the N=C bond. The alternative ordering of hydrogen atom abstraction steps was also tested but found to be higher in energy. Moreover, the electronic configurations along that pathway implicate an initial hydride transfer followed by proton transfer. We highlight an active site Lys residue that is shown to donate charge interactions in the transition states and influence the relative barrier heights and bifurcation pathways. A second catalytic cycle of the reaction of iron(IV)-oxo with desaturated substrate starts with hydrogen atom abstraction followed by decarboxylation to give isonitrile directly. The latter will require a proton transfer to iron(II)-hydroxo to generate iron(II)-water and close the catalytic cycle. The work is compared with experimental observation and previous computational studies on this system and put in a larger perspective of nonheme iron chemistry
Diffusion of Globular Macromolecules in Liquid Crystals of Colloidal Cuboids
No full textMacromolecular diffusion in dense colloidal suspensions is an intriguing topic of interdisciplinary relevance in Science and Engineering. While significant efforts have been undertaken to establish the impact of crowding on the dynamics of macromolecules, less clear is the role played by long-range ordering. In this work, we perform Dynamic Monte Carlo simulations to assess the importance of ordered crowding on the diffusion of globular macromolecules, here modelled as spherical tracers, in suspensions of colloidal cuboids. We first investigate the diffusion of such guest tracers in very weakly ordered host phases of cuboids and, by increasing density above the isotropic-to-nematic phase boundary, study the influence of long-range orientational ordering imposed by the occurrence of liquid-crystalline phases. To this end, we analyse a spectrum of dynamical properties that clarify the existence of slow and fast tracers and the extent of deviations from Gaussian behaviour. Our results unveil the existence of randomly oriented clusters of cuboids that display a relatively large size in dense isotropic phases, but are basically absent in the nematic phase. We believe that these clusters are responsible for a pronounced non-Gaussian dynamics that is much weaker in the nematic phase, where orientational ordering smooths out such structural heterogeneities
Towards A Peace with Global Justice? The Struggle within the International Peace Architecture
No full textThe growing connection between peace and justice depends upon a long history of expanded rights claims emanating from critical agency and global subalterns. Their political scripts have partly driven the development of the international peace architecture (IPA), a series of layers, sediments, and theories built up through international and local scale peace praxis over the last century. It has often required an alliance with powerful actors and an international consensus. Its evolution challenges the Western framed approach to peacemaking from various directions- regional, methodological, theoretical, and ethical. The logical scientific conclusion of this process appears to equate peace with post-colonial versions of global justice and sustainability, drawing on subaltern perspectives and epistemological advances. However, blockages, counter-peace dynamics, including spoiling and authoritarian outcomes in many peace processes across the world, tend to underline the limited pragmatic traction of the peace-justice nexu
Investigation of the Performance of Donor-Acceptor Conjugated Polymers in Electrolyte-Gated Organic Field-Effect Transistors
No full textElectrolyte-gated organic field-effect transistors (EGOFETs) are low-power thin-film electronic device that is gaining interest for application in healthcare and environmental science. However, robust performance in terms of charge-carrier mobility, on-to-off drain current ratio, and turn-on speed are required for real application. Here, donor-acceptor (D-A) conjugated polymers, namely poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (PDPPDTT) and indacenodithiophene-co-benzothiadiazole (PIDTBT), are evaluated in EGOFETs. The operational performance of these materials is compared to that of the well-established liquid crystalline poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). The effective mobility extracted for the PDPPDTT (0.18 cm2.V-1.s-1), and PIDTBT (0.16 cm2.V-1.s-1) devices was almost double that of the PBTTT (0.10 cm2.V-1.s-1) based device and the on-to-off current ratio was one ((PDPPDTT): 3 × 103) or two ((PIDTBT): 2 × 104) order of magnitude higher than that of PBTTT (2 × 102) devices. The extracted values compare favourably to those of the highest performing EGOFETs presented in the literature and EGOFETs based on the D-A polymers turn from off to on state two to ten times faster the analogous PBTTT device with an improved subthreshold swing. These results show that D-A polymers with a planar conjugated backbone enable the development of robust EGOFETs that are well appropriate for applications in bioelectronic and environmental science
Magnetization Signature of Topological Surface States in a Non-symmorphic Superconductor
No full textSuperconductors with non-trivial band structure topology represent a class of materials with unconventional and potentially useful properties. Recent years have seen much success in creating artificial hybrid structures exhibiting main characteristics of two-dimensional (2D) topological superconductors. Yet, bulk materials known to combine inherent superconductivity with nontrivial topology remain scarce, largely because distinguishing their central characteristic – topological surface states – proved challenging due to a dominant contribution from the superconducting bulk. Reported here is a highly anomalous behaviour of surface superconductivity in topologically nontrivial 3D superconductor In2Bi where the surface states result from its nontrivial band structure, which itself is a consequence of the non-symmorphic crystal symmetry and strong spin-orbit coupling. In contrast to smoothly decreasing diamagnetic susceptibility above the bulk critical field Hc2, associated with surface superconductivity in conventional superconductors, we observe near-perfect, Meissner-like screening of low-frequency magnetic fields well above Hc2. The enhanced diamagnetism disappears at a new phase transition close to the critical field of surface superconductivity Hc3. Using theoretical modelling, we show that the anomalous screening is consistent with modification of surface superconductivity due to the presence of topological surface states. The demonstrated possibility to detect signatures of the surface states using macroscopic magnetization measurements provides an important new tool for discovery and identification of topological superconductors