An Integrated Signal Allocation Model with Effective Collision Resolution Model for Performance Enhancement of Wireless Sensor Networks

A Wireless Sensor Network (WSN) differs from conventional wireless or wired networks in that it interacts with the environment. Orthogonal Frequency Division Multiplexing (OFDM) was investigated as a possible interface technology for making effective use of bandwidth. Such networks have been proposed for a variety of purposes such as search and rescue, disaster assistance, and smart positioning systems. These applications often require a large number of wireless sensors that are powered by batteries and are designed for long-term, human-free deployment. Collisions between network nodes can significantly degrade performance in WSNs. Although increased bandwidth facilitates wireless access to high data frequencies, it is prohibitively expensive to increase due to spectrum limits. This necessitates making good use of the available bandwidth. OFDM has been considered as a possible interface mechanism for efficiently utilising bandwidth. While many signals available in WSN technology can be employed to mitigate collisions, multi-signal allocations may have a significant impact on the efficiency of multistage communications. Real-time multimedia flow raises the chance of sensor network failures and congestion, which reduces the efficiency of Quality of Service (QoS). The main goal of the Signal Allocation Scheme is to allocate an appropriate number of signals to any node in order to use professional bandwidth and assure QoS. Load balancing is intended to measure and prevent collisions caused by the number of available slots in the frame. Preparation is another important component in preventing collisions because it decreases delay and optimises energy utilisation. In this paper, an Integrated Signal Allocation Model with Effective Collision Resolution Model (ICAM-ECR) is used to deploy non-overlapping signals dynamically for varying application loads based on expected bandwidth estimation. The suggested model is compared to standard methods, and the findings reveal that the proposed model outperforms existing models.

A Decision-Making Method for Autonomous Collision Avoidance for the Stand-On Vessel Based on Motion Process and COLREGs

A great number of collision accidents can be attributed to incongruous collision-avoidance actions between the give-way vessel and the stand-on vessel in a crossing or overtaking situation. If the give-way vessel does not take appropriate collision-avoidance action according to international regulations for preventing collisions at sea, the last barrier to pass safely is the appropriate and effective collision-avoidance action taken by the stand-on vessel. To find the proper autonomous collision-avoidance action of the stand-on vessel, a method is proposed that combines quantitative analysis rules of collision-avoidance with the deduction of nonlinear maneuvering motion process based on the mathematical model group, which conformity can reach 90%. This research presents a method to calculate the timing and most effective collision-avoidance actions for the stand-on vessel based on the four-stage theory of encountering vessels and the characteristics of vessel motion. The accuracy of the latest-action timing and the action amplitude for the stand-on vessel can be increased to the level of second and degree, respectively. A novel model of collision risk index is constructed by the latest time of the feasible collision-avoidance action on the precise of different course-altering amplitude. Methods to find the stand-on vessel’s proper collision-avoidance actions in the open sea are presented. The simulation indicates the proposed method for the stand-on vessel can make correct collision-avoidance decisions autonomously.

Reimagining full wave rf quasilinear theory in a tokamak

The velocity dependent resonant interaction of particles with applied radiofrequency (rf) waves during heating and current drive in the presence of pitch angle scattering collisions gives rise to narrow collisional velocity space boundary layers that dramatically enhance the role of collisions as recently shown by Catto (J. Plasma Phys., vol. 86, 2020, 815860302). The behaviour is a generalization of the narrow collisional boundary layer that forms during Landau damping as found by Johnston (Phys. Fluids, vol. 14, 1971, pp. 2719–2726) and Auerbach (Phys. Fluids, vol. 20, 1977, pp. 1836–1844). For a wave of parallel wave number ${k_{||}}$ interacting with weakly collisional plasma species of collision frequency $\nu$ and thermal speed ${v_{\textrm{th}}}$ , the effective collision frequency becomes of order $\nu {({k_{||}}{v_{th}}/\nu )^{2/3}} \gg \nu $ . The narrow boundary layers that arise because of the diffusive nature of the collisions allow a physically meaningful wave–particle interaction time to be defined that is the inverse of this effective collision frequency. The collisionality implied by the narrow boundary layer results in changes in the standard quasilinear treatment of applied rf fields in tokamaks while remaining consistent with causality. These changes occur because successive poloidal interactions with the rf are correlated in tokamak geometry and because the resonant velocity space dependent interactions are controlled by the spatial and temporal behaviour of the perturbed full wave fields rather than just the spatially local Landau and Doppler shifted cyclotron wave–particle resonance condition associated with unperturbed motion of the particles. The correlation of successive poloidal circuits of the tokamak leads to the appearance in the quasilinear operator of transit averaged resonance conditions localized in velocity space boundary layers that maintain negative definite entropy production.

Electron-impact excitation of Ni II

Aims. Energy levels, transition probabilities, and oscillator strengths are calculated for the second most abundant iron peak element Ni II. The difficulty in obtaining an accurate target representation is related to the open d-shell nature of the target, which has a minimum requirement of single and double promotions from the ground state configuration to the n = 4 shells. Therefore, in order to achieve an accurate representation of the target ion, we have also included configurations containing the 4d, 5s, and 5p subshells. We have undertaken a study of the electron impact excitation of Ni II and present here the collision strengths for forbidden and allowed transitions among the lowest 800 fine-structure levels as well as the corresponding Maxwellian-averaged effective collision strengths for a range of astrophysically relevant electron temperatures. Methods. An accurate Ni II target structure was generated using the modified General-purpose Relativistic Atomic Structure Package (GRASP0) for the lowest lying 1220 jj fine-structure levels, comprising the 11 configurations: 3p63d9, 3p63d84s, 3p63d84p, 3p63d84d, 3p63d85s, 3p63d85p, 3p63d74s2, 3p63d75s2, 3p63d74s4p, 3p63d74s4d, and 3p43d94s4d. The relativistic parallel Dirac atomic R-matrix codes (DARC) were utilised in the scattering calculations to generate the collision strengths for incident electron energies between 0 and 2 Ryd and, by employing infinite dipole and non-dipole limit points, we also generated the effective collision strengths for temperatures in the range from 1000 to 400 000 K. Two separate calculations were performed, both comprised of truncated close-coupling expansions of 800 jj-levels with the first calculation retaining the theoretical ab initio energy levels generated in the GRASP0 evaluations, whereas in the second calculation these energies were shifted to their predicted National Institute of Standards and Technology (NIST) values where possible. This should provide a lower estimate on the uncertainty. Results. Comparisons are made between the radiative data and the collisional cross sections with past theoretical and experimental studies. The effective collision strengths when compared with the most recent published calculations, are found to agree to within 10% for the majority of the transitions considered. In addition, the data are used to model the spectrum of Ni II and good agreement is found with previous investigations and observations.

R-matrix electron-impact excitation data for the N-like iso-electronic sequence

Context. Spectral lines from N-like ions can be used to measure the temperature and density of various types of astrophysical plasmas. The atomic databases of astrophysical plasma modelling codes still have room for improvement in their electron-impact excitation data sets for N-like ions, especially for R-matrix data. This is particularly relevant for future observatories (e.g. Arcus), which will host high-resolution spectrometers. Aims. We aim to obtain level-resolved effective collision strengths for all transitions up to nl = 5d over a wide range of temperatures for N-like ions from O II to Zn XXIV (i.e. O+ to Zn23+) and to assess the accuracy of the present work. We also examine the impact of our new data on plasma diagnostics by modelling solar observations with CHIANTI. Methods. We carried out systematic R-matrix calculations for N-like ions, which included 725 fine-structure target levels in both the configuration interaction target and close-coupling collision expansions. The R-matrix intermediate coupling frame transformation method was used to calculate the collision strengths, while the AUTOSTRUCTURE code was used for the atomic structures. Results. We compare the present results for selected ions with those in archival databases and the literature. The comparison covers energy levels, oscillator strengths, and effective collision strengths. We show examples of improved plasma diagnostics when compared to CHIANTI models, which use only distorted wave data as well as some using previous R-matrix data. The electron-impact excitation data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS. The data can be used to improve the atomic databases for astrophysical plasma diagnostics.

Atomic Data Assessment with PyNeb

PyNeb is a Python package widely used to model emission lines in gaseous nebulae. We take advantage of its object-oriented architecture, class methods, and historical atomic database to structure a practical environment for atomic data assessment. Our aim is to reduce the uncertainties in the parameter space (line ratio diagnostics, electron density and temperature, and ionic abundances) arising from the underlying atomic data by critically selecting the PyNeb default datasets. We evaluate the questioned radiative-rate accuracy of the collisionally excited forbidden lines of the N- and P-like ions (O ii, Ne iv, S ii, Cl iii, and Ar iv), which are used as density diagnostics. With the aid of observed line ratios in the dense NGC 7027 planetary nebula and careful data analysis, we arrive at emissivity ratio uncertainties from the radiative rates within 10%, a considerable improvement over a previously predicted 50%. We also examine the accuracy of an extensive dataset of electron-impact effective collision strengths for the carbon isoelectronic sequence recently published. By estimating the impact of the new data on the pivotal [N ii] and [O iii] temperature diagnostics and by benchmarking the collision strength with a measured resonance position, we question their usefulness in nebular modeling. We confirm that the effective-collision-strength scatter of selected datasets for these two ions does not lead to uncertainties in the temperature diagnostics larger than 10%.

Drone-Drone Collisions Over New York City

Delivery of packages by drones to homes and workplaces is faster and cheaper than delivery by van and hence has significant potential. That potential can only be realized if delivery by drones is safe. In particular, such drones must not pose a threat from in-air drone-drone collisions. To determine how serious the drone collision problem might be, we: 1) focus on a situation where they would be maximized, New York City, and 2) investigate the “do nothing” alternative, in which the drones do nothing to avoid collisions. Such drones, lacking a collision-avoidance capability, are “dumb” drones, and will have a much higher collision rate than “smart” drones, which do have that capability and will ultimately be deployed. The do nothing alternative is useful for determining the extent to which a collision-avoidance capability is needed. The dumb drone collision rate is found to be unacceptably high. Actual smart drones to be ultimately deployed must therefore have a highly effective collision-avoidance capability to bring collision rates close to zero. The needed effectiveness is quantified.

Reply to the comment by K.M. Aggarwal on “Collision strength and effective collision strength for Ba XLVIII”

We show that the comment of K.M. Aggarwal (2018, Can. J. Phys. 96(10), doi: https://www.nrcresearchpress.com/doi/pdf/10.1139/cjp-2017-0842 ), although being only marginally relevant to the content of the original paper (2017, Can. J. Phys. 95(2), doi: https://www.nrcresearchpress.com/doi/pdf/10.1139/cjp-2016-0513 ), misinterprets our results and leads to an incorrect conclusion.

R-matrix electron-impact excitation data for the C-like iso-electronic sequence

Context. Emission and absorption features from C-like ions serve as temperature and density diagnostics of astrophysical plasmas. R-matrix electron-impact excitation data sets for C-like ions in the literature merely cover a few ions, and often only for the ground configuration. Aims. Our goal is to obtain level-resolved effective collision strength over a wide temperature range for C-like ions from N II to Kr XXXI (i.e., N+ to Kr30+) with a systematic set of R-matrix calculations. We also aim to assess their accuracy. Methods. For each ion, we included a total of 590 fine-structure levels in both the configuration interaction target and close-coupling collision expansion. These levels arise from 24 configurations 2l3nl′ with n = 2−4, l = 0−1, and l′ = 0−3 plus the three configurations 2s22p5l with l = 0−2. The AUTOSTRUCTURE code was used to calculate the target structure. Additionally, the R-matrix intermediate coupling frame transformation method was used to calculate the collision strengths. Results. We compare the present results of selected ions with archival databases and results in the literature. The comparison covers energy levels, transition rates, and effective collision strengths. We illustrate the impact of using the present results on an Ar XIII density diagnostic for the solar corona. The electron-impact excitation data is archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS. The data will be incorporated into spectral codes, such as CHIANTI and SPEX, for plasma diagnostics.