RESUMO

In this paper, we conduct experimental investigations on the behavior of confined self-propelled particles within a circular arena, employing small commercial robots capable of locomotion, communication, and information processing. These robots execute circular trajectories, which can be clockwise or counterclockwise, based on two internal states. Using a majority-based stochastic decision algorithm, each robot can reverse its direction based on the states of two neighboring robots. By manipulating a control parameter governing the interaction, the system exhibits a transition from a state where all robots rotate randomly to one where they rotate uniformly in the same direction. Moreover, this transition significantly impacts the trajectories of the robots. To extend our findings to larger systems, we introduce a mathematical model enabling characterization of the order transition type and the resulting trajectories. Our results reveal a second-order transition from active Brownian to chiral motion.

RESUMO

In this paper, the dynamics of a self-propelled stochastic particle under the influence of an axisymmetric light field is experimentally studied. The particle under consideration has the main characteristic of carrying a light sensor in an eccentric location. For the chosen experimental conditions, the emerging trajectories are orbital, and, more interestingly, they suggest the existence of bistability. A mathematical model incorporating the key experimental components is introduced. By means of numerical simulations and theoretical analysis, it is found that, in addition to the orbiting behavior, the sensor location could produce trapped or diffusive behaviors. Furthermore, the study reveals that stochastic perturbation and the eccentric location of the sensor are responsible for inducing bistability in the orbital trajectories, supporting experimental observations.

RESUMO

We study experimentally the properties of the flow of mechanical vibration-driven vehicles confined in two chambers connected through a narrow opening. We report that the density of particles around the opening presents critical behavior and scaling properties. By mapping this density to the financial market price, we document that the main stylized facts observed in financial systems have their counterparts in the mechanical system. The experimental model accurately reproduces financial properties such as scaling of the price fluctuation, volatility clustering, and multiscaling.

RESUMO

We report experimental results on the competitive passage of elongated self-propelled vehicles rushing through a constriction. For the chosen experimental conditions, we observe the emergence of intermittencies similar to those reported previously for active matter passing through narrow doors. Noteworthy, we find that, when the number of individuals crowding in front of the bottleneck increases, there is a transition from an unclogged to a clogged state characterized by a lack of convergence of the mean clog duration as the measuring time increases. It is demonstrated that this transition-which was reported previously only for externally vibrated systems such as colloids or granulars-appears also for self-propelled agents. This suggests that the transition should also occur for the flow through constrictions of living agents (e.g., humans and sheep), an issue that has been elusive so far in experiments due to safety risks.

Assuntos

RESUMO

In this paper we study the role of noise in the context of resistive switching phenomena by means of experiments and numerical simulations. Experiments are conducted on a manganite sample. We show that the addition of external Gaussian noise to a small amplitude driving signal yields a contrast ratio between low- and high-resistance states, comparable to that obtained by the application of a large amplitude noiseless signal. Furthermore, excellent agreement between numerical simulation and measurement allows us to study resistive switching under varying input conditions and, thus, properly characterize the beneficial role of noise. We believe these results might be of relevance in the area of memory devices where the large scale of electronic integration renders the presence of noise unavoidable.

Assuntos

RESUMO

OBJECTIVE: Abnormal uroflowmetries are common after tubularized incised plate urethroplasties (TIP), perhaps due to low compliance. We hypothesized that (1) abnormal uroflowmetries after TIP might be caused by segmental lower compliance; (2) by adding a graft to the raw area in the incised plate (TIPG), compliance might be improved by preventing secondary intention healing of the dorsal incision. METHODS: A standardized penectomy was performed in 27 adult male rabbits: 9 normal non-operated controls (G1), 6 weeks after TIP (G2: n = 9) or TIPG (G3: n = 9). A standardized isolated segment (including the whole urethroplasty in G1 and G2) was progressively distended with air (1, 2 and 3 ml) in the 3 groups. The respective intraluminal pressures were measured with a tensiometer. RESULTS: Pressure measurements were feasible and reproducible for this model. Mean pressures tended to be higher in the experimental groups (G1: 59.7 mmHg vs. G2: 79.6 mmHg vs. G3: 100.1 mmHg for 1 ml injections; G1: 233.1 mmHg vs. G2: 241 mmHg vs. G3: 308.4 mmHg for 2 ml injections and G1: 457.3 mmHg vs. G2: 429 mmHg vs. G3: 520 mmHg for 3 ml injections) without reaching the statistical significance. CONCLUSION: In this model, the elasticity of the TIP or TIPG neourethras tended to be reduced when compared to controls. The placement of an inlay graft on the dorsal incised area did not increase the compliance. This model allows the measurement of segmental intraluminal urethral pressures generated by controlled air distension and may be a useful tool to evaluate the experimental urethroplasty models.

Assuntos

RESUMO

A compreensäo do significado fisiológico dos eventos bioquímicos após a preservaçäo pulmonar em ratos, tem sido dificultada pela falta de um modelo adequado para assessar a fisiologia envolvida. Nós desenvolvemos um modelo de perfusäo "ex vivo" paracorpóreo de pulmäo de rato, o qual permite a avaliaçäo de trocas gasosas e da hemodinâmica da funçäo pulmonar. Após anestesia e heparinizaçäo o bloco coraçäo/pulmäo era removido e o pulmäo esquerdo reperfundido durante uma hora num fluxo constante de 4 ml/min com sangue venoso homólogo drenado da veia cava inferior do rato paracorpóreo (hospedador). O pulmäo efluente era retornado no mesmo fluxo para a aorta distal do hospedeiro. O modelo foi validado pela verificaçäo da funçäo pulmonar após isquemia a temperatura ambiente. Os animais foram divididos em 3 grupos (N=6), de acordo com o intervalo de isquemia (grupo 1:20min; grupo 2:3 horas; grupo 3:4horas). Nos grupos 1 e 2 PO2' PCO2' pressäo média da via aérea (Paw) e pressäo da artéria pulmonar (Ppa) estavam dentro dos limites da normalidade e estável durante o experimento. Em contraste, os pulmöes no grupo 3 demonstraram alta Ppa e baixa PO2 no sangue efluente (PeffO2), quando comparado aqueles encontrados em grupo 1 ou 2. Ocorreu um ganho significante de peso durante a reperfusäo no grupo 3 (4.23 + ou - 0.9g; p menor do que 0.002). Para cada pulmäo, o PeffO2 final correlacionava com o ganho de peso (R2=0.81; p menor do que 0.0001). Nossos resultados indicam que este modelo pode ser de forma confiável usado para detectar a disfunçäo pulmonar após lesäo isquemica

Assuntos

Assuntos

Assuntos

RESUMO

The treatment of facial pain disorders has become a multifaceted discipline that involves numerous scientific fields. Diagnostic and treatment modalities may be beneficial to the patient but at times may also complicate the problem and compromise the outcome. We present an interesting case of left trigeminal neuralgia complicated by unassociated lingual nerve dysesthesia.

Assuntos