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 $\alpha = -0.41\pm0.12$. 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 $\alpha>-0.5$. 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 $\sim40$pc which implies a distance of $\sim1.3$kpc and a position of $\sim140$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

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

Perception of academic stress among Health Science Preparatory Program students in two Saudi universities

Saleh Alsulami, Zaid Al Omar, Mohammed S Binnwejim, Fahad Alhamdan, Amr Aldrees, Abdulkarim Al-bawardi, Meshary Alsohim, Mohammed Alhabeeb Departments of Family Medicine and Medical Education, College of Medicine, Imam Mohammad ibn Saud Islamic University, Riyadh, Saudi Arabia Abstract: The Health Science Preparatory Program (HSPP) is a special program that aims to enhance the educational preparedness of students for participation in a health sciences career. Students spend their first university year in a combined extensive teaching program before they can be assigned to a particular health science specialty. It is thought that students enrolled in a highly competitive environment such as HSPP with a long list of potential stressors, including developmental, academic overload, language barriers and competition, are more disposed to stress and stress-related complications. This study aims to measure the level of academic stress and to determine its risk factors in students enrolled in HSPP-adapted local universities in Saudi Arabia. The study was conducted at two Saudi universities, King Saud University (KSU) and Imam Mohammad ibn Saud Islamic University (IMSU) with competition-based and non-competition-based HSPP learning models, respectively. Both universities adopt the HSPP system. The scale for assessing academic stress (SAAS) was used to assess students’ perceived stress. A total of 290 students successfully completed the questionnaire (N=290), with a mean age of 18.66 years. Mean SAAS scores for KSU and IMSU students were 8.37 (SD = 4.641) and 7.97 (SD = 5.104), P=0.480, respectively. Only “satisfaction” and “associated social and health problems” have shown statistically significant correlation with university (P=0.000 and P=0.049, respectively). This study has found mean SAAS score for two local universities with competition-based versus non-competition-based HSPP learning models. Academic stress correlation with age, gender and universities was discussed, and valuable future work guidance was recommended. Keywords: academic stress, HSPP, competition, stress mediators, SAAS scor