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    Tendas, Giacomo

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    Computational study into the oxidative ring‐closure mechanism during the biosynthesis of deoxypodophyllotoxin

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    The nonheme iron dioxygenase deoxypodophyllotoxin synthase performs an oxidative ring-closure reaction as part of natural product synthesis in plants. How the enzyme enables the oxidative ring-closure reaction of (-)-yatein and avoids substrate hydroxylation remains unknown. To gain insight into the reaction mechanism and understand the details of the pathways leading to products and byproducts we performed a comprehensive computational study. The work shows that substrate is bound tightly into the substrate binding pocket with the C7’−H bond closest to the iron(IV)-oxo species. The reaction proceeds with hydrogen atom abstraction from the C7’−H position followed by ring-closure and a final hydrogen transfer to form iron(II)-water and deoxypodophyllotoxin. Alternative mechanisms including substrate hydroxylation and an electron transfer pathway were explored but found to be higher in energy. The mechanism is guided by electrostatic perturbations of charged residues in the second-coordination sphere that prevent alternative pathways.<br/

    Revolutionizing Cyber Threat Detection with Large Language Models:A privacy-preserving BERT-based Lightweight Model for IoT/IIoT Devices

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    The field of Natural Language Processing (NLP) is currently undergoing a revolutionary transformation driven by the power of pre-trained Large Language Models (LLMs) based on groundbreaking Transformer architectures. As the frequency and diversity of cybersecurity attacks continue to rise, the importance of incident detection has significantly increased. IoT devices are expanding rapidly, resulting in a growing need for efficient techniques to autonomously identify network-based attacks in IoT networks with both high precision and minimal computational requirements. This paper presents SecurityBERT, a novel architecture that leverages the Bidirectional Encoder Representations from Transformers (BERT) model for cyber threat detection in IoT networks. During the training of SecurityBERT, we incorporated a novel privacy-preserving encoding technique called Privacy-Preserving Fixed-Length Encoding (PPFLE). We effectively represented network traffic data in a structured format by combining PPFLE with the Byte-level Byte-Pair Encoder (BBPE) Tokenizer. Our research demonstrates that SecurityBERT outperforms traditional Machine Learning (ML) and Deep Learning (DL) methods, such as Convolutional Neural Networks (CNNs) or Recurrent Neural Networks (RNNs), in cyber threat detection. Employing the Edge-IIoTset cybersecurity dataset, our experimental analysis shows that SecurityBERT achieved an impressive 98.2% overall accuracy in identifying fourteen distinct attack types, surpassing previous records set by hybrid solutions such as GAN-Transformer-based architectures and CNN-LSTM models. With an inference time of less than 0.15 seconds on an average CPU and a compact model size of just 16.7MB, SecurityBERT is ideally suited for real-life traffic analysis and a suitable choice for deployment on resource-constrained IoT devices

    The impact of CEO education on convertible bond issuance

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    We examine the impact of managerial education on a firm’s decision to issue convertible bonds instead of standard, non-hybrid securities. Upper echelons theory argues that better managerial education attainment fosters a higher ability to process complex information and tolerate ambiguity. Exploiting convertible bonds’ higher degree of complexity, relative to seasoned equity and straight bonds, we hypothesise that Chief Executive Officers (CEOs) with higher education levels are more likely to issue convertible bonds instead of non-hybrid security types. A multinomial probit model analysing firms’ choice between convertibles, seasoned equity, and straight bonds provides evidence consistent with this hypothesis. A one-level increase in a CEO’s highest academic degree raises the likelihood of substituting convertibles for non-hybrid securities by 2.86%, after controlling for standard corporate security choice determinants. Chief Financial Officer (CFO) education levels, by contrast, have no significant impact on convertible bond issuance. Consistent with higher managerial education attainment being associated with a higher cognitive ability, we also find a positive association between CEO education levels and the level of complexity in convertible bond design. Our findings, which hold under a range of alternative specifications, illustrate the influence of CEOs’ personal characteristics on securities issuance and design

    Overclaimed refunds, undeclared sales, and invoice mills: Nature and extent of noncompliance in a value-added tax

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    Value-added tax has seen phenomenal expansion in recent decades. Its appeal in part lies in its robustness to tax evasion relative to other tax instruments. Exploiting a tax reform from Pakistan that cuts the tax rate on five major industries of the country substantially, I estimate the size and nature of VAT evasion in the treated industries, finding that it ranges from 31–46% of the potential revenue. One important channel through which the evasion occurs is the overclaim of refunds, which constitute 11–23% of the potential revenue. Roughly two-fifths of the overclaimed refund is based on spurious invoices issued by invoice mills. Qualitatively, noncompliance is stronger in the latter stages of the supply chain, but it runs deep inside the chain, suggesting that on their own the self-enforcement mechanisms built into a VAT do not deter tax evasion fully

    In situ TEM study of heavy-ion irradiation-induced amorphisation and electron beam-induced recrystallisation in powellite (CaMoO4)

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    Molybdenum-rich radioactive waste streams in the UK will be vitrified into glass composite high-level waste (HLW) products containing powellite (CaMoO4) crystals. These materials will be exposed to self-irradiation in a geological disposal facility for thousands of years. Our heavy-ion and electron irradiation results, together with a comprehensive review of previous studies, reveal new details on the radiation tolerance of powellite. In this study, powellite crystals were exposed to 500 keV Ar2+ and 600 keV Xe2+ ion irradiations between -160 and -80 °C and were analysed in situ via transmission electron microscopy (TEM). At low temperatures (between - 160 and -105 °C), the critical amorphisation dose (Dc) is higher for the Xe irradiation, most likely due to the significant defect recovery in the cascade core. Above -105 °C, the Dc is higher for the Ar irradiation. The dynamic annealing of radiation-induced defects becomes more efficient as the temperature increases; our results suggest that point defects formed during Ar irradiation are more susceptible to dynamic annealing compared with defects in the cascades generated during Xe irradiation. We also present the first evidence of 300 keV electron beam-induced recrystallisation in amorphous powellite by studying its response from room temperature to cryogenic temperatures inside the TEM using a wide range of electron fluxes (0.6-5.2×1016 e/cm2/s). In contrast to previous research, our new data suggest that powellite is susceptible to amorphisation by alpha recoil nuclei, and that beta irradiation may cause defect recombination.<br/

    Effects of metal acetate addition on the gas separation properties of polymers of intrinsic microporosity PIM-1 and PIM-Py

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    Gas separation properties are reported for self-standing polymer of intrinsic microporosity (PIM) films after addition of palladium (II) acetate or iron (II) acetate by solid state or liquid state mixing. Membranes, with thicknesses in the range 35–55 μm, were prepared from three high molar mass PIMs, two different branched versions of the much-reported PIM-1 (PIM-1a and PIM-1b) and of PIM-Py. Addition of either Fe(OAc)2 or Pd(OAc)2 to all three PIMs led to a reduction in permeability and increase in selectivity, but the permeability reduction was much greater for Pd(OAc)2, which is able to interact with branch points in the PIM and crosslink the polymer. CO2/CH4 selectivity of membranes containing Pd(OAc)2 was poor upon aging, especially after solid state addition to the PIM-1 polymers, for which CO2 permeabilities dropped to below 200 Barrer after 85 days. Hydrogen permeability and H2/N2 selectivity of membranes containing Pd(OAc)2 did more closely follow conventional permeability/selectivity trade off upon aging. This illustrates the profound differences that can arise in gas permeation properties and aging behaviour from variations in chemical structure and macromolecular characteristics, and from the addition of metal acetates that interact with the polymer in different ways

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