Control of beam propagation in optically written waveguides beyond the paraxial approximation

Beam propagation beyond the paraxial approximation is studied in an optically written waveguide structure. The waveguide structure that leads to diffractionless light propagation, is imprinted on a medium consisting of a five-level atomic vapor driven by an incoherent pump and two coherent spatially dependent control and plane-wave fields. We first study propagation in a single optically written waveguide, and find that the paraxial approximation does not provide an accurate description of the probe propagation. We then employ coherent control fields such that two parallel and one tilted Gaussian beams produce a branched waveguide structure. The tilted beam allows selective steering of the probe beam into different branches of the waveguide structure. The transmission of the probe beam for a particular branch can be improved by changing the width of the titled Gaussian control beam as well as the intensity of the spatially dependent incoherent pump field.Comment: 10 pages, 9 figure

Investigation of older driver's takeover performance in highly automated vehicles in adverse weather conditions

Driving is important for older people to maintain mobility. To reduce age-related functional decline, older drivers may adjust their driving by avoiding difficult situations. One of these situations is driving in adverse weather conditions such as in the rain, snow and fog which reduce the visual clarity of the road ahead. The upcoming highly automated vehicle (HAV) has the potential of supporting older people. However, only limited work has been done to study older drivers' interaction with HAV, especially in adverse weather conditions. This study investigates the effect of age and weather on takeover control performance among drivers from HAV. A driving simulation study with 76 drivers has been implemented. The participants took over the vehicle control from HAV under four weather conditions clear weather, rain, snow and fog, where the time and quality of the takeover control are quantified and measured. Results show age did affect the takeover time (TOT) and quality. Moreover, adverse weather conditions, especially snow and fog, lead to a longer TOT and worst takeover quality. The results highlighted that a user-centred design of human-machine interaction would have the potential to facilitate a safe interaction with HAV under the adverse weather for older drivers

Automotive automation: Investigating the impact on drivers' mental workload

Recent advances in technology have meant that an increasing number of vehicle driving tasks are becoming automated. Such automation poses new problems for the ergonomist. Of particular concern in this paper are the twofold effects of automation on mental workload - novel technologies could increase attentional demand and workload, alternatively one could argue that fewer driving tasks will lead to the problem of reduced attentional demand and driver underload. A brief review of previous research is presented, followed by an overview of current research taking place in the Southampton Driving Simulator. Early results suggest that automation does reduce workload, and that underload is indeed a problem, with a significant proportion of drivers unable to effectively reclaim control of the vehicle in an automation failure scenario. Ultimately, this research and a subsequent program of studies will be interpreted within the framework of a recently proposed theory of action, with a view to maximizing both theoretical and applied benefits of this domain

The Effectiveness of Glare-Obscuring Glasses on Nighttime Driving Performance

Currently no driver-aid system effectively addresses glare-reduction for oncoming headlights. Glare at night has the ability to decrease our visual acuity and cause discomfort or pain. This decreased visual ability constitutes an increased risk for driver error and a potential roadway safety hazard. The severity of these detrimental effects has previously been shown to increase with driver age and is thought to be further exacerbated by the increased brightness of High Intensity Discharge (HID) headlights. In the current study, the effects of headlight glare from HID and halogen lights on driver performance was examined in a custom driving simulator. A novel polarized headlight glare-blocking system was also examined for its effectiveness in reducing headlight glare. Decreased visual field perception occurred across all age groups with the use of oncoming HID headlights compared to halogen headlights. In addition, older drivers\u27 performance on the visual awareness task was significantly decreased as compared to their younger counterparts. The performance-restoring effects of the headlight-blocking system were especially beneficial to older adults exposed to HID headlights, restoring visual field perceptual abilities to nearly that of the younger age group. As even brighter LED-based headlights reach the automotive market in the midst of an expanding older driver population, it is urged that automotive manufacturers consider glare-mitigation strategies when designing current headlight systems

Aerospace Medicine and Biology. A continuing bibliography with indexes

This bibliography lists 244 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1981. Aerospace medicine and aerobiology topics are included. Listings for physiological factors, astronaut performance, control theory, artificial intelligence, and cybernetics are included

An Operational evaluation of head up displays for civil transport operations. NASA/FAA phase 3 report

The advantages and disadvantages of head-up displays (HUDs) in commercial jet transport approach and landing operations was evaluated. Ten airline captains currently qualified in the B-727 aircraft flew a series of instrument landing system (ILS) and nonprecision approaches in a motion base simulator using both a flight director HUD concept and a flightpath HUD concept as well as conventional head-down instruments under a variety of environmental and operational conditions to assess: (1) the potential benefits of these HUDs in airline operations; (2) problems which might be associated with their use; and (3) flight crew training requirements and flight crew operating procedures suitable for use with the HUDs. Results are presented in terms of objective simulator based performance measures, subject pilot opinion and rating data, and observer data

THE EFFECTS OF COMBINING REDUCED LUMINANCE AND INCREASED BLUR ON OLDER DRIVER SPEED AND VISUAL ACUITY

Drivers may be at more risk to themselves and other roadway users when vision is blurred or when luminance levels are reduced. Past research has investigated these visual conditions separately, finding that each degrades acuity without severely impairing steering ability. However, it is unknown how reduced luminance in combination with increased blur will affect driving performance. This study sought to quantify this combined effect on older adults\u27 comfortable driving speed and visual acuity by testing 10 participants in a driving simulator. The majority of the luminance and blur conditions are comparable to those the driving population may realistically encounter. Participants were asked to drive the speed at which they feel comfortable and could stay within their lane without using the speedometer. To ensure participants followed the instructions to stay in their lane, a percentage-of-time-in-lane measure was used to confirm no differences in steering performance existed across conditions. The older adult drivers only slowed down during the extreme blur condition; however, visual acuity was impaired by each manipulation. Interestingly, after the training conditions requiring a speed above 50 mph, drivers were given the opportunity to choose their speed and dramatically slowed down. This unexpected finding illustrates an important difference in what aging drivers choose to do in comparison with what they can do. This finding has important applied implications

Bowtie models as preventive models in maritime safety

Aquest treball ha sorgit d’una proposta del Dr. Rodrigo de Larrucea que ha acabat de publicar un llibre ambiciós sobre Seguretat Marítima. Com ell mateix diu, el tema “excedeix amb molt les potencialitats de l’autor”, així que en el meu cas això és més cert. Es pot aspirar, però, a fer una modesta contribució a l’estudi i difusió de la seguretat de la cultura marítima, que només apareix a les notícies quan tenen lloc desastres molt puntuals. En qualsevol cas, el professor em va proposar que em centrés en els Bowtie Models, models en corbatí, que integren l’arbre de causes y el de conseqüències (en anglès el Fault Tree Analysis, FTA, i l’Event Tree Analysis, ETA). Certament, existeixen altres metodologies i aproximacions (i en el seu llibre en presenta vàries, resumides), però per la seva senzillesa conceptual i possibilitat de generalització i integració dels resultats era una bona aposta. Així, després d’una fase de meditació i recopilació de informació, em vaig decidir a presentar un model en corbatí molt general on caben les principals causes d’accidents (factores ambientals, error humà i fallada mecànica), comptant també que pot existir una combinació de causes. De tota manera, a l’hora d’explotar aquest model existeix la gran dificultat de donar una probabilitat de ocurrència, un nombre entre 0 i 1, a cada branca. Normalment les probabilitats d’ocurrència són petites i degut a això difícils d’estimar. Cada accident és diferent, de grans catàstrofes n’hi ha poques, i cada accident ja és estudiat de manera exhaustiva (més exhaustiva quan més greu és). Un altre factor que dificulta l’estima de la probabilitat de fallada és l’evolució constant del món marítim, tant des del punt de vista tècnic, de formació, legal i fins i tot generacional doncs cada generació de marins és diferent. Els esforços estan doncs enfocats a augmentar la seguretat, encara que sempre amb un ull posat sobre els costs. Així, he presentat un model en corbatí pel seu valor didàctic i gràfic però sense entrar en detalls numèrics, que si s’escau ja aniré afinant i interioritzant en l’exercici de la professió. En aquest treball també he intentat no mantenir-me totalment al costat de la teoria (ja se sap que si tot es fa bé, tot surt perfecte, etc…) sinó presentar amb cert detall 2 casos ben coneguts d’accidents marítims: el petroler Exxon Valdez, el 1989 i el ferry Estonia en 1994, entre altres esmentats. Són casos ja una mica vells però que van contribuir a augmentar la cultura de la seguretat, fins a arribar al nivell del que gaudim actualment, al menys als països occidentals. Doncs la seguretat, com esmenta Rodrigo de Larrucea “és una actitud i mai és fortuïta; sempre és el resultat d’una voluntat decidida, un esforç sincer, una direcció intel·ligent i una execució acurada. Sens lloc a dubtes, sempre suposa la millor alternativa”. The work has been inspired in its initial aspects by the book of my tutor Jaime Rodrigo de Larrucea, that presents a state of the art of all the maritime aspects related to safety. Evidently, since it covers all the topics, it cannot deepen on every topic. It was my opportunity to deepen in the Bowtie Model but finally I have also covered a wide variety of topics. Later, when I began to study the topics, I realized that the people in the maritime world usually do not understand to a great extent statistics. Everybody is concerned about safety but few nautical students take a probabilistic approach to the accidents. For this it is extremely important to study the population that is going to be studied: in our case the SOLAS ships Also, during my time at Riga, I have been very concerned with the most diverse accidents, some of them studied during the courses at Barcelona. I have seen that it is difficult to model mathematically the accidents, since each one has different characteristics, angles, and surely there are not 2 equal. Finally, it was accorded that I should concentrate on the Bowtie Model, which is not very complex from a statistical point of view. It is simply a fault tree of events model and a tree of effects. I present some examples in this Chapter 2. The difficulty I point out is to try to estimate the probabilities of occurrence of events that are unusual. We concentrated at major accidents, those that may cause victims or heavy losses. Then, for the sake of generality, at Chapter 4, I have divided the causes in 4 great classes: Natural hazards, human factor, mechanical failure and attacks (piracy and terrorism). The last concern maybe should not be included beside the others since terrorism and piracy acts are not accidents, but since there is an important code dedicated to prevent security threats, ISPS, it is example of design of barriers to prevent an undesired event (although it gives mainly guidelines to follow by the States, Port Terminals and Shipping Companies). I have presented a detailed study of the tragedy of the Estonia, showing how a mechanical failure triggered the failure of the ferry, by its nature a delicate ship, but there were other factors such as poor maintenance and heavy seas. At the next Chapter, certain characteristics of error chains are analyzed. Finally, the conclusions are drawn, offering a pretty optimistic view of the safety (and security) culture at the Western World but that may not easily permeate the entire World, due to the associated costs