Minimum Disturbance Attitude Control Algorithm for DFFSR

Aiming at the attitude disturbance problem of Dual-arm Free Flying Space Robot(DFFSR), firstly, the kinematics equation of DFFSR has been established by using the geometric relationship of each link of DFFSR, the characteristic equation of manipulator, and the linear momentum and angular momentum conservation law of the system in microgravity environment; Secondly, based on the established Generalized Jacobian Matrix(GJM) describing the relationship between the end-effector motion velocity of DFFSR manipulator and the motion velocity of each joint, the relationship between the motion velocity of each joint of DFFSR manipulator and the angular velocity of satellite base has been derived, and the attitude interference model of DFFSR has been established; Finally, the Minimum Attitude Disturbance Map(MADM) algorithm for calculating the DFFSR manipulator has been established, and the attitude control algorithm based on MADM has been proposed. The attitude control method can ensure that the attitude of the satellite base of DFFSR remains unchanged during the movement of the manipulator.

Design of the upstream decay pipe window of the long baseline neutrino facility

The beam windows of high-energy beam lines are important, and it is sometimes difficult to design because it is necessary to ensure particle propagation with minimum disturbance and fulfill mechanical requirements at the same time. The upstream decay pipe window of the long baseline neutrino facility at Fermilab has an extremely large diameter (1.8 m), with a thickness of only 1.5 mm to separate the helium atmosphere in the decay pipe and the nitrogen atmosphere on the other side. Furthermore, the center of this dish-shaped window is expected to be a 200-mm-diameter beryllium dish welded to the outside aluminum alloy A6061, and this welded combination must withstand extreme conditions of a 2.4-MW, high-energy proton beam without leakage. These severe conditions make the design of this window an unprecedented challenge. This paper describes the static thermal-structural analyses based on which the structure has been optimized, as well as dynamic analyses for understanding the shockwave effects originating in the beam. After optimization, the maximum von Mises stresses in the window decreased significantly in both normal operation and accident cases, making our design very reasonable.

GENETIC DIVERSITY OF Digitaria horizontalis Willd. IN BUILT ENVIRONMENTS IN BENIN CITY, NIGERIA

The influence of humans on biodiversity at the genetic, species, community, and ecosystem levels is enormous. This is even more impactful on plant populations, which, being immobile, are at the mercy of their immediate environment. Digitaria horizontalis is a very common grass species in Benin City. Its ruderal nature accounts mostly for its widespread. The current study investigated the existence of possible genetic diversity of the grass in built environment in Benin City. Plant samples were randomly collected from 21 built environment locations within 6 Local Government Council Areas that make up Benin City. Test plants were allowed to acclimatize in experimental bowls and then allowed to grow for 4 weeks after which morphological characteristics were determined. Genetic diversity was determined by Random Amplification of Polymorphic DNA. Significant differences in plant height (33.0 – 59.0 cm) occurred when plants were compared based on location of collection. Changes in patterns of the association with weeds within the vicinity of the test plant was observed. The most prevalent plant species associated with the test plant was Pennisetum purpureum with a 12.18% prevalence. RAPD analysis using primer OPA 04 revealed a locus (about 600bp) that was absent in one or more of the locations with minimum disturbance. This 600pb fragment was however observed in most samples from highly built up and trampled environments. Primer OPA 03 showed monomorphic bands in 2 test samples with a band size of 400bp. It is therefore reported that there is an existence of the genetic diversity in a landscape of grass species (Digitaria horizontalis) found in different built environment in Benin City, Edo State, Nigeria.

Method for Predicting the Liquid-Sloshing Characteristics of a Microsatellite Propulsion System

In this study, a method for establishing a prediction model for the liquid-sloshing characteristics of microsatellite propulsion systems is proposed. The ideal states of the liquid-sloshing characteristics are considered for the following three models: (1) storage tank, (2) coupled storage tank and microsatellite, and (3) coupled storage tank and microsatellite with a deployment mechanism. The smoothed-particle hydrodynamics method is implemented in ABAQUS to study the effect of sloshing on a storage tank and microsatellite disturbance for the above three cases. Relationship models between the sloshing time, sloshing angular velocity, amount of fluid filled, and satellite attitude angular velocity are established. The analysis results show that the disturbance angular velocity of the empty storage tank and sloshing angular velocity have a linear relationship. Furthermore, the disturbance angular velocity of the liquid-filled storage tank exhibits a surface relationship with the sloshing angular velocity and amount of fluid filled in a three-dimensional coordinate system. Additionally, the disturbance angular velocity in the liquid-filled state of the storage tank is higher than that of the empty storage tank, and the degree of disturbance decreases with the increase in the mass of the coupling. The disturbance of the storage tank and microsatellite with the deployment mechanism is 10−2°/s when the angular velocities of the satellite are ωx′=3, ωy′=3, and ωz′=2. The maximum and minimum deviations between the calculation and simulation results of the three models are 7.6% and 1.1%, respectively. The model is used to predict the disturbance angular velocity of the microsatellite. When the calculation results of the model are compared with the orbit satellite data, the maximum and minimum disturbance angular velocity deviations occur in the y and z directions with a deviation of 43.36% and 14.86%, respectively. This demonstrates the accuracy of the analysis and model. The results of this study can provide theoretical guidance for the engineering design and attitude and orbital control of a microsatellite propulsion system.

Exploring aerial perching and grasping with dual symmetric manipulators and compliant end-effectors

Inspired by talon of a predator bird, this paper presents a quadrotor with two 2- Degree of Freedoms (DOFs) compliant manipulators which could mimic bird perching and grasping. The symmetric configuration of the manipulators causes minimum shift in center of gravity and a minimum disturbance to the angular momentum of the platform during grasping and perching maneuvers. Thus, the dynamics of the manipulator is independent to that of the platform. Moreover, a compliant end-effector is introduced to decouple the dynamics of the unmanned aerial vehicles from the force interaction with the environment or target objects. Therefore, aerial manipulation problem is significantly simplified due to the minimum amount of disturbance among components. In addition, the manipulators could function as the landing gear, which allows larger work envelope, weight saving and less landing impact. It also has the potential to achieve a bird-like “perch and watch” to increase the endurance of unmanned aerial vehicles in missions that involve extended endurance.

Geomagnetic field H, Z, and electromagnetic induction features of coronal mass ejections in association with geomagnetic storm at African longitudes

The largest geomagnetic disturbance caused by a coronal mass ejection (CME) of solar cycle 24 recorded on both 17 March and 22 June 2015 with minimum disturbance storm time values of −223 and −195 nT, respectively, was investigated. This study examines the effect of CME on Earth’s geomagnetic field, which includes the time derivatives of horizontal (H) and vertical (Z) components of the geomagnetic field and the rate of induction ΔZ/ΔH at African longitudes (AAE, MBO, HBK, HER, and TAM). The results demonstrated enhancement of dH/dt and dZ/dt in the daytime over the equatorial zone (AAE and MBO) and mid-latitudes (TAM, HER, and HBK) on 17 March 2015. Nighttime enhancement was observed on 22 June 2015 over the equatorial zones and mid-latitudes. Wavelet spectrum approach is used to investigate ΔZ/ΔH variation observed at AAE, MBO, HBK, HER, and TAM. The CME may have influence on time derivatives of geomagnetic field H, Z, and electromagnetic induction at the African longitudes, which may be associated with perturbations in electric fields and currents in the equatorial and low-latitude magnetic field linked with the changes in magnetospheric convection.

Environmental dose rate determination using a passive dosimeter: Techniques and workflow for α-Al2O3:C chips

In situ dosimetry (active, passive dosimeters) provides high accuracy by determining environmental dose rates directly in the field. Passive dosimeters, such as α-Al2O3:C, are of particular interest for sites with desired minimum disturbance (e.g., archaeological sites). Here, we present a comprehensive approach obtaining the environmental cosmic and γ-dose rate using α-Al2O3:C chips. Our procedure consists of (1) homemade field containers, (2) a homemade bleaching box, (3) a rapid measurement sequence and (4) software based on R to process the measurement results. Our validation steps include reproducibility, irradiation time correction, cross-talk evaluation and source calibration. We further simulate the effect of the container against the infinite matrix dose rate, resulting in attenuation of ca. 6%. Our measurement design uses a lexsyg SMART luminescence reader equipped with green LEDs. The irradiation is carried out under the closed β-source. The minimum dose that can be determined was estimated with ca. 10 μGy. However, we also show that for the equipment used, an irradiation time correction of ca. 2.6 s is needed and irradiation cross-talk should be taken into account. The suggested procedure is cross-checked with four reference sites at Clermont-Ferrand showing a good γ-dose rate for three out of the four sites. Finally, an application example, including needed analytical steps, is presented for dosimeters buried at the archaeological site of the Sierra de Atapuerca (Spain).

Defense against Malicious Users in Cooperative Spectrum Sensing Using Genetic Algorithm

In cognitive radio network (CRN), secondary users (SUs) try to sense and utilize the vacant spectrum of the legitimate primary user (PU) in an efficient manner. The process of cooperation among SUs makes the sensing more authentic with minimum disturbance to the PU in achieving maximum utilization of the vacant spectrum. One problem in cooperative spectrum sensing (CSS) is the occurrence of malicious users (MUs) sending false data to the fusion center (FC). In this paper, the FC takes a global decision based on the hard binary decisions received from all SUs. Genetic algorithm (GA) using one-to-many neighbor distance along with z-score as a fitness function is used for the identification of accurate sensing information in the presence of MUs. The proposed scheme is able to avoid the effect of MUs in CSS without identification of MUs. Four types of abnormal SUs, opposite malicious user (OMU), random opposite malicious user (ROMU), always yes malicious user (AYMU), and always no malicious user (ANMU), are discussed in this paper. Simulation results show that the proposed hard fusion scheme has surpassed the existing hard fusion scheme, equal gain combination (EGC), and maximum gain combination (MGC) schemes by employing GA.