Directional light emitters and image sensors based on plasmonic metasurfaces

Advances in optical device fabrication techniques and continued research have enabled many exciting new scientific possibilities in the manipulation of light radiation. With the great strides made in nanofabrication technologies and the huge body of work done on nano-related research, we now have a better understanding of light-matter interactions at the nanoscale and have the ability to make structures functioning at this scale with unprecedented design flexibility. This has led to an explosion of knowledge in nanooptics and opened great possibilities in light manipulation. In this work we explore the use of nanophotonic structures for the directional control of light emission and photodetection. Typical optoelectoronic devices such as LEDs and light detectors are intrinsically isotropic, and directionality is usually enforced by external optical elements like lenses, pinholes and reflectors. Similarly, standard off-the-shelf light sensors are typically non-directional with a Lambertian angular response profile. Here, we investigate the unique properties of plasmonic metasurfaces that can be harnessed to enforce directionality at the device level, without the need for bulky and often complex external light control techniques, greatly favoring miniaturization which often allows for faster, more efficient, and cheaper devices. Optimized designs are presented with proof-of-concept simulation results and experimental testing. With these designs, we also explore an exciting new application in imaging, the development of a lens-less ultra-thin flat camera based on the compound-eye vision modality, where each individual imaging unit is a single directional detector.2021-06-04T00:00:00

Types of Cyberbullying Experienced on Facebook by Undergraduate Students in Kenyan Universities

Cyberbullying is a form of bullying meted out online using digital devices and platforms. This study investigated the types of cyberbullying undergraduate students in Kenyan universities experience. Specifically, it sought to determine the students' presence on Facebook, establish how the students used Facebook, identify the types of cyberbullying they experienced, and recommend strategies of mitigating cyberbullying as a means of making Facebook safer for undergraduate students in Kenya. The study was conducted using mixed research methods. Data was collected from 4770 undergraduate students and 24 deans of students in 16 public and 8 private chartered universities in Kenya. Quantitative data was collected from the students' using questionnaires while qualitative data was collected from students using focus group discussions and deans of students using key informant interviews. Quantitative data was analysed statistically using STATA while qualitative data was analysed thematically using ATLAS.ti. The findings of the study confirm the popularity of Facebook among undergraduate students in Kenya. Students use the platform mainly for dating, business, academics and politics. The main types of cyberbullying experienced by the students on Facebook include shaming, impersonation, blackmail, exposure and cyberstalking. In dealing with cyberbullying, university authorities should create awareness about the vice among their students; the affected students should be counselled to overcome the effects of cyberbullying; and students should be advised to be vigilant in cyberspace. The findings of this study may be applied by universities to develop a students' support service model that makes it easy to detect and mitigate cyberbullying

A method of IPD normalization to eliminate IP timing covert channels

Covert channels are used for information transmission in a manner that is not intended for communication and is difficult to detect. We propose a technique to eliminate the information leakage via IP timing covert channels by inter-packet delays normalization in the process of packets’ sending. The advantage of our approach is that the influence of counteraction tool on the communication channel's capacity is negligible. The novelty of the investigation undertaken is that the covert channel is eliminated preliminary, whereas state of the art methods focus on detecting active IP covert channels that may be insecure.This work was supported by the Competitiveness Program of MEPhI

A concept of continuous user authentication based on behavioral biometrics

This paper focuses on continuous user authentication based on its interaction with the device. Behavioral authentication provides the ability to partially abandon passwords. Furthermore, the use of human behavior, for example, how he holds the device in hand, interacts with a screen, as a means of authentication is sufficiently protected from compromise, since an attacker cannot make an exact copy your gait or motion. Use of auxiliary factors such as the proximity of the trusted peripheral device, Wi-Fi network, location, helps simplify authentication

Factors Influencing the Occurrence of Cyberbullying on Facebook among Undergraduate Students in Kenyan Universities

This study investigated on factors influencing the occurrence of cyberbullying on Facebook among undergraduate students in Kenyan Universities. The study employed the mixed methods. Data was collected from 3,020 undergraduate students and 24 deans of students from 16 public and 8 private chartered universities in Kenya. A questionnaire was used to collect quantitative data from students while qualitative data was collected through focus group discussions with the students and key informant interviews with the deans of students. Qualitative data was analysed thematically using ATLAS.ti while quantitative data was analysed statistically using STATA. The findings revealed that most undergraduate students in Kenyan universities experienced cyberbullying on Facebook. Factors which influenced the prevalence include number of friends and interactions on Facebook as well as selected demographic attributes. The study recommends that students should be made aware of the prevalence of cyberbullying through a comprehensive sensitisation programme in universities. Users of Facebook should be cautious about their interactions online by limiting friendships with strangers. Finally, students should use security settings to block or report bullying offences

Impact of Irritability and Impulsive Aggressive Behavior on Impairment and Social Functioning in Youth with Cyclothymic Disorder

Objective: Research on adults with cyclothymic disorder (CycD) suggests that irritability and impulsive aggression (IA) are highly prevalent among this population. Less is known about whether these behaviors might also distinguish youth with CycD from youth without CycD. Additionally, little is known about how irritability and IA relate to one another, and whether they are associated with different outcomes. This study aimed to compare irritability and IA across diagnostic subtypes to determine whether CycD is uniquely associated with these behaviors, and to assess how irritability and IA relate to youth social and general functioning

Comparing the Diagnostic Accuracy of Five Instruments for Detecting Posttraumatic Stress Disorder in Youth

To compare diagnostic accuracy of five posttraumatic stress disorder (PTSD) measures in a large outpatient sample of youths aged 11 to 18 years

Plasmonic ommatidia for lensless compound-eye vision

The vision system of arthropods such as insects and crustaceans is based on the compound-eye architecture, consisting of a dense array of individual imaging elements (ommatidia) pointing along different directions. This arrangement is particularly attractive for imaging applications requiring extreme size miniaturization, wide-angle fields of view, and high sensitivity to motion. However, the implementation of cameras directly mimicking the eyes of common arthropods is complicated by their curved geometry. Here, we describe a lensless planar architecture, where each pixel of a standard image-sensor array is coated with an ensemble of metallic plasmonic nanostructures that only transmits light incident along a small geometrically-tunable distribution of angles. A set of near-infrared devices providing directional photodetection peaked at different angles is designed, fabricated, and tested. Computational imaging techniques are then employed to demonstrate the ability of these devices to reconstruct high-quality images of relatively complex objects.Published versio