RESUMO
The sedimentation of solid objects into granular matter near boundaries is an almost virgin field of research. Here we describe in detail the penetration dynamics of a cylindrical object into a quasi-2D granular medium. By tracking the trajectory of the cylinder as it penetrates the granular bed, we characterize two distinct kinds of motion: its center of mass moves horizontally away from the lateral wall, and it rotates around its symmetry axis. While the repulsion is caused by the loading of force chains between the intruder and the wall, the rotation can be associated to the frictional forces between the grains and the intruder. Finally, we show the analogies between the sedimentation of twin intruders released far from any boundaries, and that of one intruder released near a vertical wall.
RESUMO
The precise and continuous tracking of millimetric-sized walkers-such as ants-is quite important in behavioral studies. However, due to technical limitations, most studies concentrate on trajectories within areas no more than 100 times bigger than the size of the walker or longer trajectories at the expense of either accuracy or continuity. Our work describes a scientific instrument designed to push the boundaries of precise and continuous motion analysis up to 1000 body lengths or more. It consists of a mobile robotic platform that uses digital image processing techniques to track the targets in real time by calculating their spatial position. During the experiments, all the images are stored and afterwards processed to estimate with higher precision the path traced by the walkers. Some preliminary results achieved using the proposed tracking system are presented.
RESUMO
We introduce an instrument for a wide spectrum of experiments on gravities other than our planet's. It is based on a large Atwood machine where one of the loads is a bucket equipped with a single board computer and different sensors. The computer is able to detect the falling (or rising) and then the stabilization of the effective gravity and to trigger actuators depending on the experiment. Gravities within the range 0.4 g-1.2 g are easily achieved with acceleration noise of the order of 0.01 g. Under Martian gravity, we are able to perform experiments of approximately 1.5 s duration. The system includes features such as WiFi and a web interface with tools for the setup, monitoring, and data analysis of the experiment. We briefly show a case study in testing the performance of a model Mars rover wheel in low gravities.
RESUMO
Chilaiditi syndrome is a strange disease which includes the existence of Chilaiditi sign and other abdominal symptoms. Chilaiditi sign refers the interposition of the colon between the liver and diaphragm that could be misinterpreted to be a pneumoperitoneum. We present a 46-year-old male patient who was admitted in the hospital with constipation and abdominal oppressive pain located in the epigastric area. He showed signs of peritoneal irritation, no bowel sounds, hernias, or organ enlargements. Laboratory analysis only revealed CPK elevation (462 U/L). Abdominal and chest radiographs showed an image which suggested a pneumoperitoneum. The patient underwent emergency surgical treatment, under diagnosis of viscera perforation. At laparotomy, an interposition of the transverse colon between the liver and diaphragm were visualized, although no perforations were present. Psychiatric treatment was held until this moment due to the high risk of schizophrenia outbreak. During the next 48 h, intestinal transit was restored and he was discharged on postoperative day 40, diagnosed with Ogilvie syndrome secondary to psychotropics. The relationship between Ogilvie syndrome and psychiatric treatments is known, but the association between Ogilvie and Chilaiditi syndrome is very strange. Nevertheless, it could be misinterpreted like a pneumoperitoneum and led to the performance of emergency surgery.