Attack Of Atom Research Articles

FuzzAGG: A Fuzzing-Driven Attack Graph Generation Framework for Industrial Robot Systems

As industrial robot systems (IRS) are increasingly utilized in smart factories, their information security issues have become particularly critical. Attack graphs, an essential system-level risk modeling technique, traditionally rely on predefined risk attributes and exploitation rules for their generation. However, this approach fails to meet the needs for attack graph generation and analysis in environments with missing risk data. To address this issue, this paper proposes a fuzzing-driven attack graph generation framework, FuzzAGG. This framework aims to provide an efficient and accurate method for generating attack graphs under conditions of incomplete risk data, thereby supporting information security analysis and risk assessment of IRS. In this paper, a risk data model (RDM) is constructed using the Meta Attack Language to achieve a structured description of the risk data of IRS. A fuzzing test case generation algorithm based on the MU-SeqGAN model is proposed, which can generate test cases suitable for the state machines of IRS and map them to specific Risk Data Model Objects (RDMOs). Additionally, a conversion unit is designed to integrate all RDMOs into a risk description file, which is then used by the generation unit to construct a graphical attack graph. In performance tests, FuzzAGG is able to achieve automated construction of IRS attack graphs containing 1000 state nodes in 42min and maintain 88% risk coverage. Taking the IRS of a PCB automated production line the effectiveness of the FuzzAGG framework is validated. The results demonstrate that FuzzAGG can automatically generate and validate an attack graph containing 184 attribute nodes and atomic attack nodes in 8min with high operational efficiency, proving the practicality and reliability of this method in automated attack graph generation.

Catalytic Effect of Potassium Xanthates and Related Compounds on Disulfide Bond Enrichment of Polyalkylene Sulfides Synthesized in the Course of Episulfide Polymerization.

The original method for the preparation of high-molecular-weight polyalkylene sulfides was reported. Assuming anomalous peculiarities of the reaction (high polymerization rates, high degrees of polymerization, and huge discrepancy between the expected Mn values and the experimentally obtained values), the priority task was set to study the mechanism underlying the observed new type of polymerization. Thus, it was demonstrated that xanthate and related molecules could act as pure catalysts, facilitating both the chain-growth polymerization (ring-opening of episulfides) realized via an anionic route and the direct attack of the sulfur atom of one episulfide molecule on the methylene carbon atom of the second (neighbor) episulfide molecule, accompanied by the subsequent formation of a stable thiiranium-based zwitterionic adduct. The role of xanthate and related compounds as catalysts and stabilizing particles was further supplemented by modeling the attack of thiolate on the sulfur atom of a thiiranium-based adduct. The xanthate molecule acting as a catalyst was found to be involved in all stages of the process discussed by sharing the potassium atom with the sulfur atoms of active components of the system (the initial episulfide molecule, thiolate, and the zwitterionic intermediate). The subsequent analysis revealed the exceptional transparency of the materials obtained, which was found to exceed 99%. The pronounced self-healing ability was also found to be a distinctive feature of the synthesized high-molecular-weight polyalkylene sulfides enriched with disulfide bonds.

Structural design of two types of composites with high resistance to atomic oxygen attack based on polyimide matrices: a molecular dynamics simulation study

Because of their exceptional properties, polyimide (PI) polymers are widely used in various types of spacecraft. However, in low Earth orbit, spacecraft using these polymers are susceptible to atomic oxygen (AO) erosion, which will cause them to lose their original performance. Covering the PI surface with a protective coating and adding fillers to the PI matrix are two traditional methods to improve the AO erosion resistance of PI. However, a single protective method does not provide a good protective effect and does not necessarily balance the relationship between the AO resistance of the composites and other properties, such as mechanical properties. The structural design of composites can perfectly solve such problems. Therefore, two kinds of AO-resistant materials based on the PI matrix are designed in this paper, one is a hybrid-filled composite with nano-silica filler and graphene filler, and the other is a double-layer coated composite based on the structural design of a traditional bulletproof vest. And the AO incidence simulation of these two types of materials was carried out using ReaxFF-based MD simulation. The results show that the mixed filling of graphene and nano-silica not only greatly improves the AO resistance of the PI matrix, but also greatly improves the tensile mechanical properties of the matrix by adjusting the appropriate mixing ratio. The structure of PI-Gr-SiO2 (The structures are PI, Gr and SiO2 from bottom up, respectively. SiO2 will be the first to take the impact of AO.) possesses excellent resistance to AO erosion, and at the end of 64 ps of AO erosion, the PI matrix did not suffer any damage. This paper provides a new idea of material structure design using the MD method, which provides a new approach to improve the AO erosion resistance of PI and is expected to design new composites adapted to a variety of extreme environments in the future.

Spectroscopic Characterization of the 1-Boratricyclo-[4.1.0.02,7]-heptane Radical with a Delocalized Four-Center-One-Electron Bond.

The boron atom is a highly electrophilic reagent due to the presence of its empty p orbital, making it prone to undergo electrophilic addition reactions with the carbon-carbon double bonds of olefins. In this study, the classical C=C reaction pathway occurs when a boron atom attacks the C=C bond of cyclohexene, resulting in the formation of the η2 (1,2)-BC6H10 complex (A) that contains a borirane radical subunit. This complex can further undergo photoisomerization, leading to the formation of a 3,4,5,6-tetrahydroborepine radical (C) through the cleavage of C-C bonds. In addition, two 1-boratricyclo[4.1.0.02,7]heptane radicals with chair (B) and boat (B') conformations were observed through α C-H cleavage reactions. Bonding analysis indicates that these radicals involve a four-center-one-electron (4c-1e) bond. Under UV light irradiation, these two radicals undergo ring-opening and rearrangement reactions, resulting in the formation of a 1-cyclohexen-1-yl-borane radical (D), which is a sp2 C-H activation product. These findings delineate a potential pathway for the synthesis of organoboron radicals through boron-mediated C-H and C-C bond cleavage reactions in cycloolefins.

Total synthesis of Comfreyn A and structural analogues via two photochemical key steps.

In this work the influence of o-fluorine substituents on the photo-dehydro-Diels-Alder (PDDA) reaction was investigated and the findings of this study were applied to the total synthesis of natural products. The reactant molecules consisted of two alkyl arylpropiolates, connected by a suberic acid tether and bearing fluorine substituents in each of the o-positions. While quantum chemical calculations suggested that a fluorine substituent prevents an attack of the adjacent carbon atom in the second C-C bond forming step of the PDDA reaction, this attack took place nevertheless. The subsequent fluoride elimination, assisted by protic solvents or trialkylsilanes, resulted in an "Umpolung" of the 4-position of the cycloallene intermediate enabling the introduction of nucleophiles at this position. The nucleophilic replacement of the second fluorine substituent could also be triggered photochemically. After removal of the tether, the two arene moieties stand nearly perpendicular to each other and a selective excitation of the naphthalene moiety was possible. This led to an intramolecular photoinduced electron transfer (PET) followed by a nucleophilic replacement of the fluoride according to a SR+N1Ar* mechanism. The formed phenolic hydroxyl group underwent spontaneous lactonization with the adjacent ester group. Based on these results, the first total synthesis of the lignan Comfreyn A and some structural analogues were developed.

A generic approach for network defense strategies generation based on evolutionary game theory

The generation of optimal defense strategies in dynamic adversarial environments is crucial for cybersecurity. Recently, defense approaches based on evolutionary game theory have gained significant achievements. However, they would fail when facing complex networks and sophisticated attack strategies, due to the fatal drawbacks of defense strategy generation considering atomic attacks only. To relieve this issue, a generic approach for generating defense strategies using evolutionary game theory is proposed in this paper. Initially, a novel payoff quantification method for network attack-defense games based on attack graphs is designed. Innovatively, two factors concerning the decision-maker's degree of irrationality (DI) and the level of environmental security (LES) are introduced into the replicator dynamics equation to model the impacts on equilibrium solutions. Noting that Active Directory (AD) domain service is one of the most used and representative information security management system in Windows domains, from which attack graphs and paths can be plainly extracted and analyzed. Therefore, it is necessary and imperative to anchor AD to unfold the theoretical analyses and experiments validation based on a real environment. Case studies on a real-world AD network demonstrate that the proposed approach is effective and can generate stable and efficient defense strategies.

Theoretical kinetic investigation of the multichannel mechanism of O(3P) atmospheric oxidation reaction of but-3-enal

Several levels of theory such as Møller-Plesset MP2, G3, and CBS-QB3, have been used in order to investigate the complex and multichannel potential energy surface of the reaction of but-3-enal with the triplet oxygen atom. The results show that the O-addition channel is dominant. The different possible pathways of oxygen atom attack are thoroughly studied to better understand and explain the reaction mechanism. Regarding the oxidation of but-3-enal by triplet oxygen O(3P), it is shown that the major thermodynamic product is H3CC(O)CH2C(O)H (P3) being the most stable for the whole reaction. However, the most favored product kinetically is H2CC(OH)CH2C(O)H (P2). For the H-abstraction second possible pathway, the most favored product both kinetically and thermodynamically is found to be P8. The activation energy and calculated rate constants are consistent with the proposed addition mechanism.

Nitrous oxide and dinitrogen complexes as intermediates in the decomposition of metal carbonyl nitrosyls: The triruthenium system

The stability of some metal carbonyl nitrosyls is limited by the oxidation of CO groups by adjacent NO groups to eliminate CO2. Theoretical studies show how intermediates in such processes can be trapped as molecular species using the central Ru3 unit found in the stable and experimentally known Ru3(CO)10(µ-NO)2. Two stages of such NO reduction by adjacent CO ligands have been identified in the Ru3 system. The first stage, as demonstrated by conversion of Ru3(CO)10(µ-NO)2 to the N2O complex Ru3(CO)9(µ3-N2O), involves attack of the oxygen atom of an NO group on the carbon atom of an adjacent CO group to eliminate CO2. This leaves a reactive nitride ligand that can couple with a second NO group to form an N2O complex. The oxygen atom on such an N2O ligand can convert an adjacent CO group to CO2 thereby leaving behind a metal dinitrogen complex.

Catalytic dechlorination of carbon tetrachloride to combustible hydrocarbons by Pd-Fe hydroxides through atomic hydrogen attack and direct electron transfer

Carbon tetrachloride (CT), a common persistent pollutant in groundwater, has attracted widespread attention from environmental researchers. The dechlorination from CT to combustible hydrocarbons not only represents the removal of contaminants, but also offers the possibility of recovering carbon resources from water. In this work, we used the coprecipitation of Fe(II) and Pd(II) to synthesize Pd-Fe hydroxides for the dechlorination of CT. When Pd and Fe dosages were 0.4 and 5 mM respectively, CT with 26 µM concentration can be fast removed within 5 min, and 43.3 % of CH4 and 11.6 % of C2H6 (mol%) were generated after 110 min. The alkaline condition was more conducive to the complete dechlorination of CT comparing with acidic and neutral conditions. During the olation process, Fe(II) as electron donor transferred electrons to Pd(II) to form Pd(0) clusters. Pd(0) active sites act on the binding of CT and transfer electron to H+/H2O to form adsorbed atomic hydrogen (Hads•). The adsorbed CT molecules on the surface of Pd-Fe hydroxides undergo continuous dechlorination to form CH4 and C2H6 through the attack of Hads• and direct electron transfer. In real groundwater applications, CT was rapidly removed, with CH4 and C2H6 yields reaching 24.5 % and 4.6 % (mol%), respectively. Encouragingly, incomplete dechlorinated products, including chloroform and dichloromethane, did not show signs of subsequent rebound even after 60 min. Furthermore, Pd-Fe hydroxides also exhibit resistance to the oxidation effects of dissolved oxygen, which demonstrates the promising application prospects.

QM/MM Study Into the Mechanism of Oxidative C=C Double Bond Cleavage by Lignostilbene-α,β-Dioxygenase.

The enzymatic biosynthesis of fragrance molecules from lignin fragments is an important reaction in biotechnology for the sustainable production of fine chemicals. In this work we investigated the biosynthesis of vanillin from lignostilbene by a nonheme iron dioxygenase using QM/MM and tested several suggested proposals via either an epoxide or dioxetane intermediate. Binding of dioxygen to the active site of the protein results in the formation of an iron(II)-superoxo species with lignostilbene cation radical. The dioxygenase mechanism starts with electrophilic attack of the terminal oxygen atom of the superoxo group on the central C=C bond of lignostilbene, and the second-coordination sphere effects in the substrate binding pocket guide the reaction towards dioxetane formation. The computed mechanism is rationalized with thermochemical cycles and valence bond schemes that explain the electron transfer processes during the reaction mechanism. Particularly, the polarity of the protein and the local electric field and dipole moments enable a facile electron transfer and an exergonic dioxetane formation pathway.

A study on the orbital interactions of [3+2] cycloaddition by means of molecular orbital tracing method

Both synthesis and DFT calculation of [3 + 2] cycloaddition reaction (32CA) of quinolone-5,8‑dione with 1,3-dipole CF3CHN2 are studied. The focus of this work is to study the orbital interactions of this reaction by using molecular orbital tracing (MOT) method. MOT result shows that both quinolone-5,8‑dione and CF3CHN2 use three electrons occupied molecular orbitals (MOs) to interact with each other, and the evolutive courses of the six molecular orbitals of reactants (initial MOs) to six electrons occupied molecular orbitals of product (final MOs) are given in this work. Three of the six initial MOs can evolve as final MOs directly, but rest of them need to go through media orbitals to complete the evolution. Perhaps the role of the media orbitals is to enable the reaction to proceed concertedly. APT charges analysis and changes of bond lengths during the reaction are also afforded in this work, and the result shows that the reaction begins with a nucleophilic attack of CF3CHN2 on quinolone-5,8‑dione. Accompanying with the attack, negative charge transfers from CF3CHN2 to a carbon atom of quinolone-5,8‑dione, then the carbon atom attacks nitrogen atom of CF3CHN2 to complete the cycloaddition. At last, a mechanism and a diagram of the molecular orbital interactions of the reaction are given.

The role of halogens in Au–S bond cleavage for energy-differentiated catalysis at the single-bond limit

The transformation from one compound to another involves the breaking and formation of chemical bonds at the single-bond level, especially during catalytic reactions that are of great significance in broad fields such as energy conversion, environmental science, life science and chemical synthesis. The study of the reaction process at the single-bond limit is the key to understanding the catalytic reaction mechanism and further rationally designing catalysts. Here, we develop a method to monitor the catalytic process from the perspective of the single-bond energy using high-resolution scanning tunneling microscopy single-molecule junctions. Experimental and theoretical studies consistently reveal that the attack of a halogen atom on an Au atom can reduce the breaking energy of Au−S bonds, thereby accelerating the bond cleavage reaction and shortening the plateau length during the single-molecule junction breaking. Furthermore, the distinction in catalytic activity between different halogen atoms can be compared as well. This study establishes the intrinsic relationship among the reaction activation energy, the chemical bond breaking energy and the single-molecule junction breaking process, strengthening our mastery of catalytic reactions towards precise chemistry.

Examining the Morality of the U.S. Atomic Bombings: Strategic Necessity or Controversial Decision?

The morality of the two atomic bombings conducted by the United States on the Japanese cities of Hiroshima and Nagasaki has long raised contention among both strategists and the general public. This paper discusses the strategic context of World War IIs Pacific theater and proposes that despite the unprecedented cruelty casted on Hiroshima and Nagasaki by atomic weapons, the bombs were dropped out of the strategic necessity to bring a swift end to the war. By reviewing the diaries of key commanders, the U.S. Armys reports and forecasts of a land invasion of Japan, and account of Japanese resilience and unfathomable refusal to surrender under conventional circumstances, this study demonstrates that by forcing an early Japanese surrender, the atomic attacks obviated a land invasion of Japan, which would have inflicted much heavier casualties and thus provide the moral underpinnings of the atomic weapon attacks.

A dynamic state sharding blockchain architecture for scalable and secure crowdsourcing systems

Currently, the crowdsourcing system has serious problems such as single point of failure of the server, leakage of user privacy, unfair arbitration, etc. By storing the interactions between workers, requesters, and crowdsourcing platforms in the form of transactions on the blockchain, these problems can be effectively addressed. However, the improvement in total computing power on the blockchain is difficult to provide positive feedback to the efficiency of transaction confirmation, thereby limiting the performance of crowdsourcing systems. On the other hand, the increasing amount of data in blockchain further increases the difficulty of nodes participating in consensus, affecting the security of crowdsourcing systems. To address the above problems, in this paper we design a blockchain architecture based on dynamic state sharding, called DSSBD. Firstly, we solve the problems caused by cross sharding transactions and reconfiguration in blockchain state sharding through graph segmentation and relay transactions. Then, we model the optimal block generation problem as a Markov decision process. By utilizing deep reinforcement learning, we can dynamically adjust the number of shards, block spacing, and block size. This approach helps improve both the throughput of the blockchain and the proportion of non-malicious nodes. Security analysis has proven that the proposed DSSBD can effectively resist attacks such as transaction atomic attacks, double spending attacks, sybil attacks, replay attacks, etc. The experimental results show that the crowdsourcing system with the proposed DSSBD has better performance in throughput, latency, balancing, cross-shard transaction proportion, and node reconfiguration proportion, etc., while ensuring security.

Montmorillonite Catalyzed Synthesis of Novel Steroid Dimers.

The reactions of sterols (androst-5-en-3β-ol-17-one, diosgenin, and cholesterol) and their tosylates with hydroquinone aimed at the synthesis of O,O-1,4-phenylene-linked steroid dimers were studied. The reaction course strongly depended on the conditions used. The study has shown that the major reaction products are the elimination products and unusual steroid dimers resulting from the nucleophilic attack of the hydroquinone C2 carbon atom on the steroid C3 position, followed by an intramolecular addition to the C5-C6 double bond. A different reaction course was observed when montmorillonite K10 was used as a catalyst. The reaction of androst-5-en-3β-ol-17-one under the promotion of this catalyst afforded the O,O-1,4-phenylene-linked steroid dimer in addition to the disteroidal ether. The formation of the latter compound was suppressed by using 3-tosylate as a substrate instead of the free sterol. The reactions of androst-5-en-3β-ol-17-one tosylate and cholesteryl tosylate with hydroquinone catalyzed by montmorillonite K10 carried out under optimized conditions afforded the desired dimers in 31% and 67% yield, respectively.

Quantum Chemical Study of the Cycloaddition Reaction of Tropone with 1,1-Diethoxyethene Catalyzed by B(C6F5)3 or BPh3.

Cycloaddition reaction of tropone with 1,1-diethoxyethene catalyzed by Lewis acid (LA), B(C6F5)3 or BPh3, was examined by using ωB97X-D-level density functional theory (DFT) calculations. In the absence of LA, the reaction proceeds in a stepwise fashion to form two chemical bonds, first between the C2 atom in tropone and the C2 atom in ethene and then between the C5 atom in the former and the C1 atom in the latter. When B(C6F5)3 is attached to the O atom in tropone, the C5 atom in tropone is attacked preferentially by the C1 atom in ethene in the second stage. The attack of the O atom in tropone is shown to be less likely; thus, the [4 + 2] addition is favored in the B(C6F5)3-catalyzed reaction. In contrast, the attack of the O atom in the BPh3-attached tropone to the C1 atom in ethene is preferred over the attack of the C5 atom, indicating that the [8 + 2] cycloaddition instead of the [4 + 2] cycloaddition proceeds in the BPh3-catalyzed reaction. Whether the C1 atom in ethene is attacked by C5 or by O in the second bond formation step is shown in this study to be governed mainly by the nucleophilicity of σ-lone pair electrons of the carbonyl O atom of tropone in the presence of LA. These results are consistent with the experiments reported by Li and Yamamoto.

Ionizing radiation-induced cancer: perplexities of the bystander effect.

Ionizing radiation (IR) is a carcinogen. This has been established beyond doubt from many years of studies such as those conducted among the survivors of the atomic bomb attacks on Hiroshima and Nagasaki and later from the Chernobyl accident. Despite immense progress in the field of carcinogenesis, complete understanding of the underlying mechanisms behind IR-induced cancer remains elusive. In particular, the long gestation period between exposure to IR and the onset of cancer, frequently unpredictable, and sometimes lasting for many years, remains poorly understood. The centrality of DNA damage and misrepair in carcinogenesis research has not entirely benefited IR-induced cancer research and the past decade has seen a shift in understanding radiation-driven cellular mechanisms beyond simplistic models of targeted DNA damage. This paper presents a viewpoint on the gaps in our knowledge of IR-induced cancer with a focus on the non-targeted bystander effect, the mechanisms underlying which may be key to radiotherapeutic advances.

Mechanistic Insight and Intersystem Crossing Dynamics of the C(3P) + H2CO/D2CO Reaction

The reaction of atomic carbon, C(3P), with H2CO has been investigated using the direct dynamics trajectory surface hopping (DDTSH) method with Tully's fewest switches algorithm. The lowest lying ground triplet and single states are considered for the dynamics study at a reagent collision energy of 8.0 kcal/mol. From the trajectory calculations, we observed that CH2 + CO and H + HCCO are the two major product channels for the title reaction. The insertion mechanism of the C(3P) + H2CO reaction is rather complex and is followed by three distinct intermediates with no entrance channel barrier to the reaction on the B3LYP/6-31G(d,p) potential energy surfaces. The triplet insertion complexes are formed by three different approaches; "Sideways", "End-on" and "Head-on" attack of the triplet carbon atom toward H2CO molecule. Our dynamics calculations predict a new product channel (H + HCCO(X 2A'')) with a contribution of ∼46% of the overall products formation via ketocarbene intermediate through "Head-on" approach. Despite the weak spin-orbit coupling (SOC) interactions, intersystem crossing (ISC) via a ketocarbene intermediate has a small but significant contribution, about 2.3%, for the CH2 + CO channel. To understand the kinetic isotope effects on the reaction dynamics, we have extended our study for the C(3P) + D2CO reaction. It is seen that isotopic substitution of both the H atoms has a small reduction in the extent of ISC dynamics for the carbene formation. Our results, certainly, reveal the importance of the ketocarbene intermediate and the H + HCCO products channel as one of the major product formation channels in the title reaction, which was not reported earlier.

Comprehensive Study of the Mechanism of the “Aromatic Nitroso Oxide–Olefin” Interaction as a Function of the Reagents’ Structure

Using reaction model systems (nitroso oxide ArNOO, Ar = Me2NC6H4 or O2NC6H4; exhaustive set of methyl- and cyano-substituted ethylenes), a detailed study of the reaction mechanism of ArNOO with unsaturated compounds was carried out using the density functional theory (M06L/6311 + G(d,p)). The reaction is preceded by the formation of a reagent complex of stacking type, which is favorable for further transformation. Depending on the structure of alkene, the reaction may proceed via two extreme mechanisms: synchronous (3 + 2)-cycloaddition (the most typical case) or one-center nucleophilic attack of the terminal oxygen atom of ArNOO on the less substituted carbon atom of the double bond. The last direction becomes dominant only under special reaction conditions: ArNOO with a strong electron-donating substituent in the aromatic ring, an unsaturated compound with a significantly depleted electron density on C═C bonds, and a polar solvent. In other cases, a different degree of asynchrony in the (3 + 2)-cycloaddition is possible; however, the main intermediate preceding stable reaction products is 4,5-substituted 3-aryl-1,2,3 dioxazolidine in any event. Both thermodynamic and kinetic arguments suggest the most probable decomposition of dioxazolidine into a nitrone and a carbonyl compound. It has been shown for the first time that the polarization of the C═C bond is a powerful factor regulating the reactivity in the reaction under study. The results of the theoretical study show excellent agreement with known experimental data for a wide variety of reacting systems.

Cleavage of an Aromatic C–C Bond in Ferrocene by Insertion of an Iridium Nitrido Nitrogen Atom

The intermolecular cleavage of C-C bonds is a rare event. Herein, we report on a late transition-metal terminal nitrido complex, which upon oxidation undergoes insertion of the nitrido nitrogen atom into the aromatic C-C bond of ferrocene. This reaction path was confirmed through 15N and deuterium isotope labeling experiments of the nitrido complex and ferrocenium, respectively. Cyclic voltammetry and UV/vis spectroscopy monitoring of the reaction revealed that oxidation is the initial step, yielding the tentative radical cationic nitrido complex, which is experimentally supported by extended X and Q-band electron paramagnetic resonance (EPR) and ENDOR, UV/vis, vT 1H NMR, and vibrational spectroscopic data. Density functional theory (DFT) and multireference calculations of this highly reactive intermediate revealed an S = 1/2 ground state. The high reactivity can be traced to the increased electrophilicity in the oxidized complex. Based on high-level PNO-UCCSD(T) calculations and UV/vis kinetic measurements, it is proposed that the reaction proceeds by initial electrophilic exo attack of the nitrido nitrogen atom at the cyclopentadienyl ring and consecutive ring expansion to a pyridine ring.