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Joao Rodrigues

Publications and source records attributed to Joao Rodrigues.

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Photon Dynamics and Collision Risks in Relativistic Spaceflight: A Comparative Study of Methods and Implications

This dissertation explores the dynamics of relativistic spaceflight, focusing on the risks associated with collisions and photon interactions as a spacecraft approaches velocities near the speed of light. The study emphasizes two primary collision types: (1) collisions with interstellar dust and particles, and (2) interactions with cosmic molecules, specifically hydrogen. Using principles of energy conservation and relativistic mechanics, the energy transfer from these collisions is calculated, showing that even small particles can impart massive energy at relativistic speeds. The dissertation also examines the impact of the cosmic microwave background (CMB) radiation, particularly its blue-shifting effect at high velocities, which influences photon interactions with the spacecraft. Additionally, the Schwinger limit, which sets an upper bound on the electromagnetic field strength for sustained relativistic travel, is discussed in the context of photon-induced pair production. Lastly, advanced photon interactions, such as Compton scattering, are analyzed for their role in thermal management and spacecraft design. The findings highlight the importance of shielding, thermal regulation, and collision avoidance strategies in the design of spacecraft for interstellar travel, offering insights into the potential challenges and solutions for achieving relativistic spaceflight.

astro-ph.HE

Development of antibacterial compounds that block evolutionary pathways to resistance

Antibiotic resistance is a worldwide challenge. A potential approach to block resistance is to simultaneously inhibit WT and known escape variants of the target bacterial protein. Here we applied an integrated computational and experimental approach to discover compounds that inhibit both WT and trimethoprim (TMP) resistant mutants of E. coli dihydrofolate reductase (DHFR). We identified a novel compound (CD15-3) that inhibits WT DHFR and its TMP resistant variants L28R, P21L and A26T with IC50 50-75 micromoles against WT and TMP-resistant strains. Resistance to CD15-3 was dramatically delayed compared to TMP in in vitro evolution. Whole genome sequencing of CD15-3 resistant strains showed no mutations in the target folA locus. Rather, gene duplication of several efflux pumps gave rise to weak (about twofold increase in IC50) resistance against CD15-3. Altogether, our results demonstrate the promise of strategy to develop evolution drugs - compounds which block evolutionary escape routes in pathogens.

q-bio.BM

Investments in Random Environments

We present analytical investigations of a multiplicative stochastic process that models a simple investor dynamics in a random environment. The dynamics of the investor's budget, $x(t)$, depends on the stochasticity of the return on investment, $r(t)$, for which different model assumptions are discussed. The fat-tail distribution of the budget is investigated and compared with theoretical predictions. Weare mainly interested in the most probable value $x_mp$ of the budget that reaches a constant value over time. Based on an analytical investigation of the dynamics, we are able to predict $x_mp^stat$. We find a scaling law that relates the most probable value to the characteristic parameters describing the stochastic process. Our analytical results are confirmed by stochastic computer simulations that show a very good agreement with the predictions.

q-fin.PM