147 research outputs found
Decomposing virulence to understand bacterial clearance in persistent infections
Following an infection, hosts cannot always clear the pathogen, instead either dying or surviving with a persistent infection. Such variation is ecologically and evolutionarily important because it can affect infection prevalence and transmission, and virulence evolution. However, the factors causing variation in infection outcomes, and the relationship between clearance and virulence are not well understood. Here we show that sustained persistent infection and clearance are both possible outcomes across bacterial species showing a range of virulence in Drosophila melanogaster. Variation in virulence arises because of differences in the two components of virulence: bacterial infection intensity inside the host (exploitation), and the amount of damage caused per bacterium (per parasite pathogenicity). As early-phase exploitation increased, clearance rates later in the infection decreased, whereas there was no apparent effect of per parasite pathogenicity on clearance rates. Variation in infection outcomes is thereby determined by how virulence â and its components â relate to the rate of pathogen clearance. Taken together we demonstrate that the virulence decomposition framework is broadly applicable and can provide valuable insights into host-pathogen interactions
Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon
Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon are investigated by means of a phase-resolving non-hydrostatic wave model (SWASH). This model solves the nonlinear shallow water equations including non-hydrostatic pressure. The one-dimensional version of the model is implemented in order to investigate wave transformation in fringing reefs. Firstly, the numerical model is validated with (i) laboratory experiments conducted on a physical model (Demirbilek et al., 2007)and (ii) field observations (Coronado et al., 2007). Numerical results show good agreement with both experimental and field data. The comparison against the physical model results, for energetic wave conditions, indicates that high- and low-frequency wave transformation is well reproduced. Moreover, extreme water-level conditions measured during the passage of Hurricane Ivan in Puerto Morelos are also estimated by the numerical tool. Subsequently, the model is implemented at different along-reef locations in Puerto Morelos. Extreme water levels, wave-induced setup, and infragravity wave energy are estimated inside the reef lagoon for different storm wave conditions (<i>H</i><sub>s</sub> >2 m). The numerical results revealed a strong correlation between the offshore sea-swell wave energy and the setup. In contrast, infragravity waves are shown to be the result of a more complex pattern which heavily relies on the reef geometry. Indeed, the southern end of the reef lagoon provides evidence of resonance excitation, suggesting that the reef barrier may act as either a natural flood protection morphological feature, or as an inundation hazard enhancer depending on the incident wave conditions
Many-Exciton Quantum Dynamics in a Ruddlesden-Popper Tin Iodide
We present a study on the many-body exciton interactions in a prototype
Ruddlesden-Popper metal halide (RPMH), namely \ce{(PEA)2SnI4} (PEA =
phenylethylammine), using coherent two-dimensional electronic spectroscopy. The
optical dephasing times of the third-order polarization observed in these
systems are determined by exciton many-body interactions and lattice
fluctuations. We investigate the excitation-induced dephasing (EID) and observe
a significant reduction of the contribution to the dephasing time with
increasing excitation density as compared to its lead counterpart
\ce{(PEA)2PbI4}, which we have previously reported
[A.~R.~Srimath~Kandada~\textit{et~al.}, J.\ Chem.\ Phys.\ \textbf{153}, 164706
(2020)]. Surprisingly, we find that the EID interaction parameter is four
orders of magnitude higher in \ce{(PEA)2SnI4} than that in \ce{(PEA)2PbI4}.
This increase in the EID rate may be due to exciton localization arising from a
more strongly statically disordered lattice in the tin derivative. This is
supported by the observation of multiple closely spaced exciton states and the
broadening of the linewidth with increasing population time (spectral
diffusion), which suggests a static disordered structure relative to the highly
dynamic lead-halide. Additionally, we find that the exciton nonlinear coherent
lineshape shows evidence of a biexcitonic state with low binding energy
(\,meV) not observed in the lead system. We model the lineshapes based on
a stochastic scattering theory that accounts for the interaction with a
non-stationary population of dark background excitations. Our study provides
evidence of differences in the exciton quantum dynamics between tin- and
lead-based RPMHs and links them to the exciton-exciton interaction strength and
the static disorder aspect of the crystalline structure.Comment: Submitted for publicatio
Resolving Nonlinear Recombination Dynamics in Semiconductors via Ultrafast Excitation Correlation Spectroscopy: Photoluminescence versus Photocurrent Detection.
We explore the application of excitation correlation spectroscopy to detect nonlinear photophysical dynamics in two distinct semiconductor classes through time-integrated photoluminescence and photocurrent measurements. In this experiment, two variably delayed femtosecond pulses excite the semiconductor, and the time-integrated photoluminescence or photocurrent component arising from the nonlinear dynamics of the populations induced by each pulse is measured as a function of inter-pulse delay by phase-sensitive detection with a lock-in amplifier. We focus on two limiting materials systems with contrasting optical properties: a prototypical lead-halide perovskite (LHP) solar cell, in which primary photoexcitations are charge photocarriers, and a single-component organic-semiconductor diode, which features Frenkel excitons as primary photoexcitations. The photoexcitation dynamics perceived by the two detection schemes in these contrasting systems are distinct. Nonlinear-dynamic contributions in the photoluminescence detection scheme arise from contributions to radiative recombination in both materials systems, while photocurrent arises directly in the LHP but indirectly following exciton dissociation in the organic system. Consequently, the basic photophysics of the two systems are reflected differently when comparing measurements with the two detection schemes. Our results indicate that photoluminescence detection in the LHP system provides valuable information about trap-assisted and Auger recombination processes, but that these processes are convoluted in a nontrivial way in the photocurrent response and are therefore difficult to differentiate. In contrast, the organic-semiconductor system exhibits more directly correlated responses in the nonlinear photoluminescence and photocurrent measurements, as charge carriers are secondary excitations only generated through exciton dissociation processes. We propose that bimolecular annihilation pathways mainly contribute to the generation of charge carriers in single-component organic semiconductor devices. Overall, our work highlights the utility of excitation correlation spectroscopy in modern semiconductor materials research, particularly in the analysis of nonlinear photophysical processes, which are deterministic for their electronic and optical properties
A Simple Artificial Life Model Explains Irrational Behavior in Human Decision-Making
Although praised for their rationality, humans often make poor decisions, even in simple situations. In the repeated binary choice experiment, an individual has to choose repeatedly between the same two alternatives, where a reward is assigned to one of them with fixed probability. The optimal strategy is to perseverate with choosing the alternative with the best expected return. Whereas many species perseverate, humans tend to match the frequencies of their choices to the frequencies of the alternatives, a sub-optimal strategy known as probability matching. Our goal was to find the primary cognitive constraints under which a set of simple evolutionary rules can lead to such contrasting behaviors. We simulated the evolution of artificial populations, wherein the fitness of each animat (artificial animal) depended on its ability to predict the next element of a sequence made up of a repeating binary string of varying size. When the string was short relative to the animatsâ neural capacity, they could learn it and correctly predict the next element of the sequence. When it was long, they could not learn it, turning to the next best option: to perseverate. Animats from the last generation then performed the task of predicting the next element of a non-periodical binary sequence. We found that, whereas animats with smaller neural capacity kept perseverating with the best alternative as before, animats with larger neural capacity, which had previously been able to learn the pattern of repeating strings, adopted probability matching, being outperformed by the perseverating animats. Our results demonstrate how the ability to make predictions in an environment endowed with regular patterns may lead to probability matching under less structured conditions. They point to probability matching as a likely by-product of adaptive cognitive strategies that were crucial in human evolution, but may lead to sub-optimal performances in other environments
Segundo Congreso Salesiano de Ciencia, TecnologĂa e InnovaciĂłn para la Sociedad
La segunda ediciĂłn del Congreso Salesiano de Ciencia, TecnologĂa e InnovaciĂłn para la Sociedad, CITIS, realizado el 2 y 3 de diciembre de 2015 y organizado por la Universidad PolitĂ©cnica Salesiana (sede Guayaquil), ofreciĂł un espacio idĂłneo para la presentaciĂłn, difusiĂłn e intercambio de importantes investigaciones (nacionales e internacionales) a los docentes investigadores y a la comunidad universitaria en general.
Los trabajos recogidos en estas Memorias AcadĂ©micas pertenecen a diferentes lĂneas de investigaciĂłn del ĂĄrea de la IngenierĂa: Telecomunicaciones, AutomatizaciĂłn y Control, Procesos Industriales, Sistemas ElĂ©ctricos de Potencia, TelemĂĄtica e InformĂĄtica Aplicada, ĂĄreas de interĂ©s en esta segunda ediciĂłn del CITIS. Cabe destacar que se evidencia la preocupaciĂłn por la dimensiĂłn humana y social mediante el desarrollo responsable de la ciencia y la tecnologĂa.
La realización de este Congreso ha puesto en evidencia la importancia y pertinencia de la actividad investigativa que se genera en las universidades (en proyectos desarrollados por los docentes investigadores e, incluso, por los estudiantes de grado y posgrado), asà como los altos niveles de compromiso académico y social
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