Bearing-Only Adaptive Formation Control Using Back-Stepping Method

In this paper, the bearing-only formation control problem of a class of second-order system with unknown disturbance is investigated, where the control law merely depends on the relative bearings between neighboring agents. In order to offset the effect of unknown disturbance on the system, adaptive estimation is introduced. In the design of the control law, the back-stepping design method and the negative gradient method are used. The Barbalat’s lemma is used to prove the global stability of the system. The simulation results prove the effectiveness of the proposed formation control algorithm.

Socio-Economic Differences in the Prevalence of Single Motherhood in North America and Europe

The study focuses on understanding the association between parental socio-economic status (SES) and the likelihood of women experiencing a first birth while single, and identifying societal factors that influence this association in 18 North American and European societies. Previous research has shown that single motherhood occurs disproportionately among those from with lower a lower parental SES. The study assesses whether this is caused by parental SES differences in the risk of single women experiencing a first conception leading to a live birth or by parental SES differences in how likely women are to enter a union during pregnancy. Additionally, an assessment is made of whether cross-national differences in these associations can be explained by a country’s access to family planning, norms regarding family formation, and economic inequality. Across countries, a negative gradient of parental SES was found on the likelihood of single women to experience a first pregnancy. The negative gradient was stronger in countries with better access to family planning. In some countries, the negative gradient of parental SES was aggravated during pregnancy because women from lower parental SES were less likely to enter a union. This was mostly found in societies with less conservative norms regarding marriage. The results suggest that certain developments in Western societies may increase socio-economic differentials in family demography.

Bumblebees (Bombus terrestris) Improve ‘Hass’ Avocado (Persea americana) Pollination

Pollination is limiting for avocado production. We examined whether adding bumblebees (BBs; ca. 10 hives/ha) to conventional honeybees (HB; 5 hives/ha) would improve ‘Hass’ avocado pollination and yields. A preliminary trial (2017/18) in an avocado orchard with four consecutive rows of ‘Hass’ followed by one row of ‘Ettinger’ serving as a pollenizer (20% ‘Ettinger’) showed a considerable increase in ‘Hass’ yield in rows adjacent to (up to 80 m from) the BB hives vs. distant rows (=controls). In 2018/19, the trials were extended to three additional orchards. A significant yield increase was obtained in the BB hive-adjacent trees compared to BB hive-distant ones. Similar results were obtained in 2019/20, in experiments conducted throughout the country. The SNP analysis, to determine the parents of ‘Hass’ fruit at varying distances from the BB hives, showed no differences in the cross-pollination rate (‘Hass’ × ‘Ettinger’). However, pollination rates and the number of germinating pollen grains per stigma decreased with distance from the hives, and correlated to the negative gradient in yield. Taken together, our data suggest that adding BB hives to ‘Hass’ avocado orchards, at ca. 10 hives/ha resulting in 0.5–1.0 BB visits/tree per min, increases pollination and, accordingly, total yield.

Are Older Adults’ Leisure Patterns Consistent with the Active Ageing Model? The Influence of the Ageist Stereotypes

More and more studies indicate that leisure plays a fundamental role in active ageing. Our study describes the current leisure patterns of older adults, comparing them with other age groups. Consequently, 445 adults, stratified by age (young, middle-aged and older adults), were selected and subsequently administered a set of tests. The results indicate that older people claim having more time for their leisure activities; however, the diversity of activities performed is lower, showing a negative gradient based on age. The leisure patterns of older people reflect a predominance of passive leisure, little cultural leisure time and moderate levels of social and physical leisure activities. Older people’s leisure seems to be influenced by ageist stereotypes and attribution biases. Our findings imply that these results could be used to design and implement programs aimed at promoting leisure styles that contribute to increase active ageing.

Vertical Characteristics of Raindrops Size Distribution over Sumatra Region from Global Precipitation Measurement Observation

The climatology of the vertical profile of raindrops size distribution (DSD) over Sumatra Region (10° S – 10° N, 90° E – 110° E) has been investigated using Global Precipitation Measurement (GPM) level 2 data from January 2015 to June 2018. DSD's vertical profile was observed through a vertical profile of corrected radar reflectivity (Ze) and two parameters of normalized gamma DSD, i.e., mass-weight mean diameter (Dm) and total drops concentration (Nw). Land-ocean contrast and rain type dependence of DSD over Sumatra were clearly observed. The values of Dm and Nw were larger in the land than in the ocean. Negative and positive gradients of Dm toward the surface were dominant during stratiform and convective rains, respectively, consistent with the Z gradient. Moreover, the negative gradient of stratiform rain in the ocean is larger than in land. Thus, the depletion of large drops is dominant over the ocean, which is due to the break-up process that can be observed from the increase of Nw. Raindrop growth of convective rains is more robust over the ocean than land that can be seen from a larger value of Dmgradient. The BB strength is slightly larger over land and coastal region than over the ocean, indicating that the riming process is more dominant over land and coastal regions than the ocean. Doi: 10.28991/esj-2021-01274 Full Text: PDF

Numerical Simulation of Physical Transportation Network

Prior experiments with physarum polycephalum, a plasmodial slime mold, have shown its inherent biological ability to adapt to the surroundings. When placed in an environment with food surrounding it, it builds a network of biological pipelines to the food that reinforces heavily used pipelines and withdraws those rarely used. Interestingly, the human body displays a similar ability. The development of our circulatory system is in the absence of our brain or nervous system, which suggests humans mimic low level organisms in the regard that our biological transportation systems are self-regulating and self-constructing. Like slime molds, this adaptive quality suggests that our biological networks follow a method of lowest energy consumption: energy is allocated to maintaining and constructing only the most efficient paths. Thus, the purpose of our model is to explain the biological mechanism of how organisms construct a pipeline network through a mathematical model. The model is developed using 2 main assumptions: (1) The network exists in a hexagonal grid system and (2) there only exists nodes that are sinks, sources, or neither. Borrowing Kirchhoff’s Law and other electric circuit principles, we determine an energy function for the construction and maintenance of a biological pipeline network in our model dependent on the current, conductivity, and pressure within the pipelines. The method we develop in this paper is called the negative gradient flow method. Given any initial values for the pipeline, the negative gradient flow method is an algorithm for unconstrained nonlinear optimization that finds at each instant the next set of values to most minimize the function until eventually reaching the minimizer values. Accomplishing the main goal of this paper, the negative gradient flow improves upon existing models at replicating natural phenomena since it is based on the evolutionary advantage of lowest energy consumption.

A Social Force Model for Pedestrians’ Movements Affected by Smoke Spreading

A social force (SF) model is proposed to simulate the egress of pedestrians while smoke is spreading. The advection-diffusion with source term is used to describe the propagation of smoke. It is incorporated into the SF model. The navigation field in our model is determined by the negative gradient of the solution of the Eikonal equation. It depends on the pedestrian and smoke density. Numerical experiments are performed in a room with multiple exits, and their results are shown.