Rise time of proton cut-off energy in 2D and 3D PIC simulations

The Target Normal Sheath Acceleration (TNSA) regime for proton acceleration by laser pulses is experimentally consolidated and fairly well understood. However, uncertainties remain in the analysis of particle-in-cell (PIC) simulation results. The energy spectrum is exponential with a cut-off, but the maximum energy depends on the simulation time, following different laws in two and three dimensional (2D, 3D) PIC simulations, so that the determination of an asymptotic value has some arbitrariness. We propose two empirical laws for rise time of the cut-off energy in 2D and 3D PIC simulations, suggested by a model in which the proton acceleration is due to a surface charge distribution on the target rear side. The kinetic energy of the protons that we obtain follows two distinct laws, which appear to be nicely satisfied by PIC simulations. The laws depend on two parameters: the scaling time, at which the energy starts to rise, and the asymptotic cut-off energy. The values of the cut-off energy, obtained by fitting the 2D and 3D simulations for the same target and laser pulse, are comparable. This suggests that parametric scans can be performed with 2D simulations, since 3D ones are computationally very expensive. In this paper, the simulations are carried out for $a_0=3$ with the PIC code ALaDyn by changing the target thickness $L$ and the incidence angle $\alpha$. A monotonic dependence, on $L$ for normal incidence and on $\alpha$ for fixed $L$, is found, as in the experimental results for high temporal contrast pulses

Bacteriostatic Effects of Apatite-Covered Ag/AgBr/TiO2 Nanocomposite in the Dark: Anomaly in Bacterial Motility

In this paper, we report a unique property of inactivating Gram-positive/negative bacteria in the dark via apatite-covered Ag/AgBr/TiO2 nanocomposites (AAAT). We demonstrate that the inactivation mechanism is bacteriostatic based on the cellular integrity and motility of bacteria, low toxicity and high durability of AAAT. From straight observations, the catalytic loading affects the bacterial replication and cell envelope as well as inducing an anomaly in bacterial motility (continuous rotation) for both types of bacteria. Both simulation and experimental analyses suggest that the anomaly could be due to posterior intracellular signals rather than purely mechanical effects (e.g., size enlargement and motility retardation). Provoked by chemomechanical stimuli, these signals increase the frequency of flagellar tumbling and eventually entangle the bacteria

Serotype-specific mortality from invasive Streptococcus pneumoniae disease revisited

BACKGROUND: Invasive infection with Streptococcus pneumoniae (pneumococci) causes significant morbidity and mortality. Case series and experimental data have shown that the capsular serotype is involved in the pathogenesis and a determinant of disease outcome. METHODS: Retrospective review of 464 cases of invasive disease among adults diagnosed between 1990 and 2001. Multivariate Cox proportional hazard analysis. RESULTS: After adjustment for other markers of disease severity, we found that infection with serotype 3 was associated with an increased relative risk (RR) of death of 2.54 (95% confidence interval (CI): 1.22–5.27), whereas infection with serotype 1 was associated with a decreased risk of death (RR 0.23 (95% CI, 0.06–0.97)). Additionally, older age, relative leucopenia and relative hypothermia were independent predictors of mortality. CONCLUSION: Our study shows that capsular serotypes independently influenced the outcome from invasive pneumococcal disease. The limitations of the current polysaccharide pneumococcal vaccine warrant the development of alternative vaccines. We suggest that the virulence of pneumococcal serotypes should be considered in the design of novel vaccines

Quantum Mechanical Study of Spin-Forbidden Reactions in Organometallic Catalysis and Astrochemistry

This dissertation presents a quantum mechanical investigation of spin-forbidden reactions in organometallic C-H bond activation and interstellar peptide-bond formation, as well as the derivation of the Morse empirical potential from an electrostatic model. In the first part, the role of triplet electronic state in spin-accelerated iron-catalyzed C(sp2)-H bond activation in a-benzoquinoline molecule is studied. The C-H activation facilitated by the electron donation from the sigma-bond to the iron dz2 orbital is promoted by the spin-orbit coupling of the triplet state to the quintet and singlet states. The calculated spin-orbit coupling values at the minimum energy crossing point geometries between the quintet-triplet and triplet-singlet potential energy surfaces indicate a strong coupling between these electronic states. This is in contrast to a very small spin-orbit coupling between the quintet and singlet states, responsible for the previously proposed two-state quintet-singlet reaction mechanism. Therefore, we propose a quintet-triplet-singlet multi-state mechanism that is thermodynamically more favorable than the two-state mechanism and the spin-allowed quintet pathway. The transition state (TS) in the quintet pathway is associated with a singly occupied dz2 orbital that accepts the C-H bond electron density, while a more stabilized TS in the multi-state mechanism is accessible via unoccupied dz2 orbital in the singlet state. In the second part, the spin-forbidden formation mechanisms of the acetamide and N-methyl-formamide (NMF) molecules in the interstellar medium are studied. Due to low temperature and particle densities in the interstellar medium, only barrierless bimolecular collisions lead to the formation of new molecular species. Two radiative association pathways are proposed for acetamide formation. The reaction mechanism proposed for the NMF formation is more complex and characterized by the formation of an intermediate species followed by an intramolecular hydrogen transfer. Moreover, we proposed a new formation mechanism for acetimidic acid, a molecule that is challenging to observe in the interstellar medium because of its small dipole moment. In the last part, we show that the Morse potential can be derived from a simple screened charge model in which an exponential function accounts for the electron screening of the positive nuclear charges. This derivation bridges the gap between the classical and quantum mechanical description of a chemical bond by connecting the electrostatic and covalent energies to the Morse potential

Determination of Contamination Ratio and Risk Factors Associated with Alveolar and Cystic Echinococcosis by ELISA and Portable Ultrasonography in Moghan Plain, Ardabil Province, Northwest of Iran

Background & objectives: Alveolar and cystic echinococcosis (CE and AE) are caused by the larval stages of Echinococcus multilocularis and Echinococcus granolosus, respectively. This study was conducted to determine the spread of human AE and CE diseases among the tribes and livestock breeders and farmers in the Moghan plain. The prevalence of infection (CE and AE) significantly increases with a rise in age. Methods: In this study, using ELISA and HCF-Ag (raw liquid antigen of hydatid cyst) was used for the first time to perform screening, and then the prevalence of cystic echinococcosis and alveolar echinococcosis was evaluated by specific anti-genes Ag-5 and EM2+, respectively. A total of 2003 serum samples were collected randomly from normal populations of five different areas of Moghan plain. In the first stage, serum screening was tested using an enzyme-linked immunosorbent assay and HCF-Ag. After that, the serology of all sera was evaluated by ELISA and specific antigens for alveolar and cystic Echinococcus. Results: From 2003 samples, 24 serum samples were (1.19%) AE-positive. Infection was higher in men than women (2.1% vs. 0.6%). The age group of 5-19years had the lowest infection rate and the age group 40- 59 years had the highest infection rate (2%). In the case of cystic ecinococcosis, 164 serum samples were positive for Ag-5 specific antigen, i.e. 7.6% infection, and 156 serum samples were positive for Ag-B-specific antigen. Conclusion: The findings showed that the highest infection rate was found in the Boran and Eivazlou (Palanglou) regions of Moghan plain and the lowest level of human infection was reported in Parsabad region (Nadar-kandi and Agh-ghabagh). In areas with higher contamination, the risk factor associated with CE and AE were the type of water used, the method of washing edible and wild vegetables, occupation and having or not having knowledge of hydatid disease. The infection of Moghan region dogs is one of the main indicators and potential risk factors for human infection

Second Order Saddle Points Dictate the Products of Electrocyclic Reactions

The conventional understanding of chemical reactions, primarily focused on one-dimensional minimum energy pathways, has been expanded in recent years to include phenomena like second order saddle points or bifurcations. In this study, we explore these intricacies within the context of electrocyclizations and present a novel approach that moves beyond the traditional view of activation barriers, revealing that second order saddle points are crucial in dictating the competition between disrotatory and conrotatory pathways. Our findings suggest opportunities to manipulate the competition between conrotatory and disrotatory pathways through geometric constraints, fundamentally altering the connectivity of the potential energy surface. Through the development of a minimal model Hamiltonian, we illustrate the generality of our findings and highlight the importance of the multi-reference nature of states near the second order saddle point. This study emphasizes the necessity of multi-reference methods and the need to conduct higher-dimensional explorations for competing pathways. It opens new avenues for systematic control of selectivity in electrocyclic reactions and offers a rich perspective on the complex interplay of steric considerations and electronic correlations

Derivation of Morse Potential Function

The Morse potential is widely used in chemistry to describe interatomic interactions. However, there is no explicit derivation for this empirical potential from physically meaningful atomic quan- tities. We show that the Morse potential can be derived from a simple atomic screened charge model, which accounts for the shielded nuclear charge by the electron density and exponentially de- cays with distance. The bond dissociation energy of a diatomic molecule is obtained by combining the quantum mechanical covalent and classical electrostatic interactions. The revealed connec- tions between the parameters of the Morse potential, the Pauling bond order and electronegativity bridge the gap between the classical and quantum mechanical descriptions of chemical bonds. The proposed derivation and interpretation of the Morse potential in terms of atomic quantities such as electron-nuclear attraction energy and orbital exponents will be valuable in helping students to form a simple picture of chemical bond

An online scalarization multi-objective reinforcement learning algorithm : TOPSIS Q-learning

Conventional reinforcement learning focuses on problems with single objective. However, many problems have multiple objectives or criteria that may be independent, related, or contradictory. In such cases, multi-objective reinforcement learning is used to propose a compromise among the solutions to balance the objectives. TOPSIS is a multi-criteria decision method that selects the alternative with minimum distance from the positive ideal solution and the maximum distance from the negative ideal solution, so it can be used effectively in the decision-making process to select the next action. In this research a single-policy algorithm called TOPSIS Q-Learning is provided with focus on its performance in online mode. Unlike all single-policy methods, in the first version of the algorithm, there is no need for the user to specify the weights of the objectives. The user's preferences may not be completely definite, so all weight preferences are combined together as decision criteria and a solution is generated by considering all these preferences at once and user can model the uncertainty and weight changes of objectives around their specified preferences of objectives. If the user only wants to apply the algorithm for a specific set of weights the second version of the algorithm efficiently accomplishes that.