Visual Collaboration Leader-Follower UAV-Formation for Indoor Exploration

UAVs operating in a leader-follower formation demand the knowledge of the relative pose between the collaborating members. This necessitates the RF-communication of this information which increases the communication latency and can easily result in lost data packets. In this work, rather than relying on this autopilot data exchange, a visual scheme using passive markers is presented. Each formation-member carries passive markers in a RhOct configuration. These markers are visually detected and the relative pose of the members is on-board determined, thus eliminating the need for RF-communication. A reference path is then evaluated for each follower that tracks the leader and maintains a constant distance between the formation-members. Experimental studies show a mean position detection error (5 × 5 × 10cm) or less than 0.0031% of the available workspace [0.5 up to 5m, 50.43° × 38.75° Field of View (FoV)]. The efficiency of the suggested scheme against varying delays are examined in these studies, where it is shown that a delay up to 1.25s can be tolerated for the follower to track the leader as long as the latter one remains within its FoV.

Laser-stimulated fluorescence reveals unseen details in fossils from the Upper Jurassic Solnhofen Limestones

Laser-stimulated fluorescence (LSF) has seen increased use in palaeontological investigations in recent years. The method uses the high flux of laser light of visible wavelengths to reveal details sometimes missed by traditional long-wave ultraviolet (UV) methods using a lamp. In this study, we compare the results of LSF with UV-A-generated fluorescence on a range of fossils from the Upper Jurassic Solnhofen Limestone Konservat-Lagerstätte of Bavaria, Germany. The methodology follows previous protocols of LSF with modifications made to enhance laser beam intensity, namely keeping the laser at a constant distance from the specimen, using a camera track. Our experiments show that along with making surface details more vivid than UV-A or revealing them for the first time, LSF has the additional value of revealing shallow subsurface specimen detail. Fossil decapods from the Solnhofen Limestone reveal full body outlines, even under the matrix, along with details of segmentation within the appendages such as limbs and antennae. The results indicate that LSF can be used on invertebrate fossils along with vertebrates and may often surpass the information provided by traditional UV methods.

A Computational Study of Hydrodynamic Interactions Between Pairs of Sperm With Planar and Quasi-Planar Beat Forms

Although hydrodynamic interactions and cooperative swimming of mammalian sperm are observed, the key factors that lead to attraction or repulsion in different confined geometries are not well understood. In this study, we simulate the 3-dimensional fluid-structure interaction of pairs of swimmers utilizing the Method of Regularized Stokeslets, accounting for a nearby wall via a regularized image system. To investigate emergent trajectories of swimmers, we look at different preferred beat forms, planar or quasi-planar (helical with unequal radii). We also explored different initializations of swimmers in either the same plane (co-planar) or with centerlines in parallel planes. In free space, swimmers with quasi-planar beat forms and those with planar beat forms that are co-planar exhibit stable attraction. The swimmers reach a maintained minimum distance apart that is smaller than their initial distance apart. In contrast, for swimmers initialized in parallel beat planes with a planar beat form, we observe alternating periods of attraction and repulsion. When the pairs of swimmers are perpendicular to a nearby wall, for all cases considered, they approach the wall and reach a constant distance between swimmers. Interestingly, we observe sperm rolling in the case of swimmers with preferred planar beat forms that are initialized in parallel beat planes and near a wall.

Processing of Ordinal Information in Math-Anxious Individuals

This study aimed to investigate whether the ordinal judgments of high math-anxious (HMA) and low math-anxious (LMA) individuals differ. Two groups of 20 participants with extreme scores on the Shortened Mathematics Anxiety Rating Scale (sMARS) had to decide whether a triplet of numbers was presented in ascending order. Triplets could contain one-digit or two-digit numbers and be formed by consecutive numbers (counting condition), numbers with a constant distance of two or three (balanced) or numbers with variable distances between them (neutral). All these triplets were also presented unordered: sequence order in these trials could be broken at the second (D2) or third (D3) number. A reverse distance effect (worse performance for ordered balanced than for counting trials) of equal size was found in both anxiety groups. However, HMA participants made more judgment errors than their LMA peers when they judged one-digit counting ordered triplets. This effect was related to worse performance of HMA individuals on a symmetry span test and might be related to group differences on working memory. Importantly, HMAs were less accurate than LMA participants at rejecting unordered D2 sequences. This result is interpreted in terms of worse cognitive flexibility in HMA individuals.

Static Osteogenesis Versus Dynamic Osteogenesis: A Comparison between Two Different Types of Bone Formation

In contrary to what has traditionally been believed, bone formation can occur through two different types of osteogenesis: static (SO) and dynamic (DO) osteogenesis, which are thus named because the former is characterized by pluristratified cords of unexpectedly stationary osteoblasts which differentiate at a fairly constant distance from the blood capillaries and transform into osteocytes without moving from the onset site, while the latter is distinguished by the well-known typical monostratified laminae of movable osteoblasts. The two types of osteogenesis differ in multiple aspects from both structural and functional viewpoints. Besides osteoblast arrangement, polarization, and motion, SO and DO differ in terms of time of occurrence (first SO and later DO), conditioning factors to which they are sensitive (endothelial-derived cytokines or mechanical loading, respectively), distribution of osteocytes to which they give rise (haphazard or ordered in planes, respectively), the collagen texture resulting from the different deposition types (woven or lamellar, respectively), the mechanical properties of the bone they form (poor for SO due to the high cellularity and woven texture and good for DO since osteocytes are located in more suitable conditions to perceive loading), and finally the functions of each, i.e., SO provides a preliminary rigid scaffold on which DO can take place, while DO produces bone tissue according to mechanical/metabolic needs..

Development of Testbed AUV for Formation Control and its Fundamental Experiment in Actual Sea Model Basin

The formation control of multiple autonomous underwater vehicles (AUVs) is increasingly becoming a vital factor in enhancing the efficiency of ocean resources exploration. However, it is currently difficult to deploy such a package of AUVs for operation at sea because of their large size. The aim of our study is to create a demonstration system for formation control algorithms using actual hardware. To implement a prototype system, we developed a testbed AUV usable in a test basin and performed a simple formation control test in the Actual Sea Model Basin of the National Maritime Research Institute, Japan. Two AUVs, the simulated “virtual” leader and the developed “real” follower, communicate through an acoustic link and hence cruise to maintain a constant distance between them. Tests for more sophisticated formation control algorithms will be enabled using the system; consequently rapid implementation at sea will be realized.

Variation of radiofrequency intensities from the DTTV-transmitter in Kampala Metropolitan; Uganda

This paper presents the variation of radiofrequencies intensities from the DTTV-transmitter in Kampala Metropolitan for the sub 700 MHz (470-694 MHz) and the 700 MHz (694-790 MHz) frequency bands. The results of this study showed that though all the measurement locations from the transmitter have a good reception of DTTV signals, their radiofrequency intensities varied at the different points on the same measurement location at a constant distance from the DTTV transmitter. The study further showed that there is a general decrease in the radiofrequency intensities for the sub 700 MHz frequency band and a slight general increase in the radiofrequency intensities for the 700 MHz frequency band. This research revealed that the measured Reference Signal Received Power (RSRP) values for all the measurement locations where within the IEEE and FCC recommended values for any DTTV signal reception.

Modeling multi-sensory feedback control of zebrafish in a flow

Understanding how animals navigate complex environments is a fundamental challenge in biology and a source of inspiration for the design of autonomous systems in engineering. Animal orientation and navigation is a complex process that integrates multiple senses, whose function and contribution are yet to be fully clarified. Here, we propose a data-driven mathematical model of adult zebrafish engaging in counter-flow swimming, an innate behavior known as rheotaxis. Zebrafish locomotion in a two-dimensional fluid flow is described within the finite-dipole model, which consists of a pair of vortices separated by a constant distance. The strength of these vortices is adjusted in real time by the fish to afford orientation and navigation control, in response to of the multi-sensory input from vision, lateral line, and touch. Model parameters for the resulting stochastic differential equations are calibrated through a series of experiments, in which zebrafish swam in a water channel under different illumination conditions. The accuracy of the model is validated through the study of a series of measures of rheotactic behavior, contrasting results of real and in-silico experiments. Our results point at a critical role of hydromechanical feedback during rheotaxis, in the form of a gradient-following strategy.