Overdamped dynamics of a Brownian particle levitated in a Paul trap

We study the dynamics of the center of mass of a Brownian particle levitated in a Paul trap. We focus on the overdamped regime in the context of levitodynamics, comparing theory with our numerical simulations and experimental data from a nanoparticle in a Paul trap. We provide an exact analytical solution to the stochastic equation of motion, expressions for the standard deviation of the motion, and thermalization times by using the WKB method under two different limits. Finally, we prove the power spectral density of the motion can be approximated by that of an Ornstein-Uhlenbeck process and use the found expression to calibrate the motion of a trapped particle

Unitarity of the infinite-volume three-particle scattering amplitude arising from a finite-volume formalism

In a previous publication, two of us derived a relation between the scattering amplitude of three identical bosons, $\mathcal M_3$, and a real function referred to as the {divergence-free} K matrix and denoted $\mathcal K_{\text{df},3}$. The result arose in the context of a relation between finite-volume energies and $\mathcal K_{\text{df},3}$, derived to all orders in the perturbative expansion of a generic low-energy effective field theory. In this work we set aside the role of the finite volume and focus on the infinite-volume relation between $\mathcal K_{\text{df},3}$ and $\mathcal M_3$. We show that, for any real choice of $\mathcal K_{\text{df},3}$, $\mathcal M_3$ satisfies the three-particle unitarity constraint to all orders. Given that $\mathcal K_{\text{df},3}$ is also free of a class of kinematic divergences, the function may provide a useful tool for parametrizing three-body scattering data. Applications include the phenomenological analysis of experimental data (where the connection to the finite volume is irrelevant) as well as calculations in lattice quantum chromodynamics (where the volume plays a key role).Comment: 19 pages, 4 figures, JLAB-THY-19-2945, CERN-TH-2019-07

Minimal model for active nematics: quasi-long-range order and giant fluctuations

We propose a minimal microscopic model for active nematic particles similar in spirit to the Vicsek model for self-propelled polar particles. In two dimensions, we show that this model exhibits a Kosterlitz-Thouless-like transition to quasi-long-range orientational order and that in this non-equilibrium context, the ordered phase is characterized by giant density fluctuations, in agreement with the predictions of Ramaswamy {\it et al.} [Europhys. Lett. {\bf 62}, 196 (2003)].Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figure

WKB Propagation of Gaussian Wavepackets

We analyze the semiclassical evolution of Gaussian wavepackets in chaotic systems. We prove that after some short time a Gaussian wavepacket becomes a primitive WKB state. From then on, the state can be propagated using the standard TDWKB scheme. Complex trajectories are not necessary to account for the long-time propagation. The Wigner function of the evolving state develops the structure of a classical filament plus quantum oscillations, with phase and amplitude being determined by geometric properties of a classical manifold.Comment: 4 pages, 4 figures; significant improvement

Diversity-induced resonance

We present conclusive evidence showing that different sources of diversity, such as those represented by quenched disorder or noise, can induce a resonant collective behavior in an ensemble of coupled bistable or excitable systems. Our analytical and numerical results show that when such systems are subjected to an external subthreshold signal, their response is optimized for an intermediate value of the diversity. These findings show that intrinsic diversity might have a constructive role and suggest that natural systems might profit from their diversity in order to optimize the response to an external stimulus.Comment: 4 pages, 3 figure

Valor predictivo de la procalcitonina en niños con sospecha de sepsis

ResumenIntroducciónEl uso de biomarcadores podría constituir una herramienta en el diagnóstico, pronóstico y estratificación en la sepsis. El objetivo fue analizar el valor de la procalcitonina (PCT), proteína C reactiva (PCR) y lactato en la predicción de shock séptico, mortalidad y en la estratificación en niños con sospecha de sepsis.Pacientes y métodoEstudio prospectivo en 81 pacientes en los cuales se midió niveles plasmáticos de PCT, PCR y lactato al ingreso en la unidad de cuidados intensivos. Los pacientes se categorizaron en síndrome de respuesta inflamatoria sistémica, sepsis, sepsis grave y shock séptico.ResultadosLas concentraciones de la PCT (ng/mL) aumentaron significativamente de acuerdo a la gravedad de la sepsis: 0,36 (0-1,2) para síndrome de respuesta inflamatoria sistémica; 1,96 (0,4-3,5) para sepsis; 7,5 (3,9-11,1) en sepsis grave; y 58,9 (35,1-82,7) para shock séptico (p<0,001). Comparada con la PCR y el lactato, el área bajo la curva ROC reveló un poder discriminativo favorable de la PCT para predecir shock séptico y mortalidad: 0,91 (IC95%: 0,83-0,97) y 0,80 (IC95%: 0,69-0,88), respectivamente.ConclusionesA diferencia de la PCR y el lactato, la determinación de la PCT al ingreso en la unidad de cuidados intensivos es un buen predictor de shock séptico y mortalidad, y permite estratificar a los pacientes de acuerdo a la gravedad de la sepsis.AbstractIntroductionThe use of biomarkers could be a tool for diagnosis, prognosis and stratifying children with sepsis. Our main goal was to analyze the value of procalcitonin (PCT), C reactive protein (CRP) and lactate in predicting mortality, septic shock and the stratification in children with suspected sepsisPatients and methodProspective study in 81 patients. Plasma levels of PCT, CRP and lactate were measured at admission in the pediatric intensive care unit. Patients were categorized into systemic inflammatory response syndrome, sepsis, severe sepsis and septic shock.ResultsConcentrations of PCT (ng/mL) increased significantly according to the severity of sepsis: 0.36 (0-1.2) for systemic inflammatory response syndrome; 1.96 (0.4-3.5) for sepsis; 7.5 (3.9-11.1) for severe sepsis; and 58.9 (35.1-82.7) for septic shock (P<.001). Compared to CRP and lactate, the area under the ROC curve revealed a good discriminative power of PCT to predict septic shock and mortality, 0.91 (95% CI: 0.83-0.97) and 0.80 (95% CI: 0.69-0.88), respectively.ConclusionsIn contrast to CRP and lactate, the determination of PCT in pediatric intensive care unit admission is a good predictor of mortality and septic shock and can stratify patients according to severity of sepsis

The sedimentary geology of the “Serras d’Aire e Candeeiros” natural park (Portugal) : importance of the geological heritage

The main goal of this work is to contribute to the conservation and interpretation of the geological heritage of the Serras de Aires e Candeeiros Natural Park. The selection of the most relevant geosites took into account criteria of representation, exception, scientific importance, didactic clarity, accessibility, and exposure conditions

Discrete Fracture Model with Anisotropic Load Sharing

A two-dimensional fracture model where the interaction among elements is modeled by an anisotropic stress-transfer function is presented. The influence of anisotropy on the macroscopic properties of the samples is clarified, by interpolating between several limiting cases of load sharing. Furthermore, the critical stress and the distribution of failure avalanches are obtained numerically for different values of the anisotropy parameter $\alpha$ and as a function of the interaction exponent $\gamma$. From numerical results, one can certainly conclude that the anisotropy does not change the crossover point $\gamma_c=2$ in 2D. Hence, in the limit of infinite system size, the crossover value $\gamma_c=2$ between local and global load sharing is the same as the one obtained in the isotropic case. In the case of finite systems, however, for $\gamma\le2$, the global load sharing behavior is approached very slowly