40 research outputs found
Reinforcement Learning for Resource Allocation in Steerable Laser-based Optical Wireless Systems
Vertical Cavity Surface Emitting Lasers (VCSELs) have demonstrated
suitability for data transmission in indoor optical wireless communication
(OWC) systems due to the high modulation bandwidth and low manufacturing cost
of these sources. Specifically, resource allocation is one of the major
challenges that can affect the performance of multi-user optical wireless
systems. In this paper, an optimisation problem is formulated to optimally
assign each user to an optical access point (AP) composed of multiple VCSELs
within a VCSEL array at a certain time to maximise the signal to interference
plus noise ratio (SINR). In this context, a mixed-integer linear programming
(MILP) model is introduced to solve this optimisation problem. Despite the
optimality of the MILP model, it is considered impractical due to its high
complexity, high memory and full system information requirements. Therefore,
reinforcement Learning (RL) is considered, which recently has been widely
investigated as a practical solution for various optimization problems in
cellular networks due to its ability to interact with environments with no
previous experience. In particular, a Q-learning (QL) algorithm is investigated
to perform resource management in a steerable VCSEL-based OWC systems. The
results demonstrate the ability of the QL algorithm to achieve optimal
solutions close to the MILP model. Moreover, the adoption of beam steering,
using holograms implemented by exploiting liquid crystal devices, results in
further enhancement in the performance of the network considered
EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8-6.3
We present the serendipitous detection of a new Galactic Supernova Remnant
(SNR), G288.8-6.3 using data from the Australian Square Kilometre Array
Pathfinder (ASKAP)-Evolutionary Map of the Universe (EMU) survey. Using
multi-frequency analysis, we confirm this object as an evolved Galactic SNR at
high Galactic latitude with low radio surface brightness and typical SNR
spectral index of . To determine the magnetic field
strength in SNR G288.8-6.3, we present the first derivation of the
equipartition formulae for SNRs with spectral indices . The
angular size is 1.\!^\circ 8\times 1.\!^\circ 6 (107.\!^\prime 6 \times
98.\!^\prime 4) and we estimate that its intrinsic size is pc which
implies a distance of kpc and a position of pc above the
Galactic plane. This is one of the largest angular size and closest Galactic
SNRs. Given its low radio surface brightness, we suggest that it is about 13000
years old.Comment: Accepted for publication in The Astrophysical Journa
Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm−2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells
Causes of Medication Administration Errors in Hospitals: a Systematic Review of Quantitative and Qualitative Evidence
A preliminary analysis of the perception gap between employers and vocational students for career sustainability
(1) Background: Nowadays, technological advancement plays a key role in the economic uplift of developing countries, and it is paramount that the youth of these countries are well-equipped with both vocational and technical skills to bring about sustainability in their ca-reers. (2) Methods: The present study aims to investigate the perception gap between vocational students and industrial employers with regard to employability skills. In this regard, data were collected from 683 vocational students from urban/rural areas studying in the public/private vocational institutions of a developing country. Similarly, 82 vocational employers were contacted about their perception of employability skills. A questionnaire comprising 20 questions was ad-ministered online to both students and employers for registering their responses. Data were ana-lyzed with the help of descriptive statistics, interval plots, and an Ishikawa diagram. (3) Results: The findings reveal that vocational employers give maximum importance to interpersonal, tech-nical, and entrepreneurial skills, while students perceive that their technical and computing skills are vital for sustainable careers. Similarly, the rural/public students showed minimum levels of competency in these skills as compared with their counterparts living in rural areas and studying in the private institutions. Furthermore, structured interviews were conducted with the concerned stakeholders to develop a remedial framework for the sustainable careers of these vocational stu-dents. (4) Conclusions: The results of the study not only bring sustainability to the vocational sector of developing countries, but to all those countries enjoying similar socioeconomic backgrounds. © 2021 by the authors. Licensee MDPI, Basel, Switzerland