Bright Sunlight Research Articles

Temporal and Spatial Focusing in SPAD-Based Solid-State Pulsed Time-of-Flight Laser Range Imaging

The relation between signal and background noise strengths in single-photon avalanche diode (SPAD)-based pulsed time-of-flight 3-D range imaging is analyzed on the assumption that the SPAD detector is operating in the single photon detection mode. Several practical measurement cases using a 256-pixel solid-state pulsed time-of-flight (TOF) line profiler are presented and analyzed in the light of the resulting analysis. It is shown that in this case it is advantageous to concentrate the available optical average power in short, intensive pulses and to focus the optical energy in spatial terms. In 3-D range imaging, this could be achieved by using block-based illumination instead of the regularly used flood illumination. One modification of this approach could be a source that would illuminate the system FOV only in narrow laser stripes. It is shown that a 256-pixel SPAD-based pulsed TOF line profiler following these design principles can achieve a measurement range of 5–10 m to non-cooperative targets at a rate of ~10 lines/s under bright sunlight conditions using an average optical power of only 260 µW.

Thick-shell CdZnSe/ZnSe/ZnS quantum dots for bright white light-emitting diodes

Quantum dots (QDs) have become promising light sources for next-generation lightings and displays. Realizing their applications in optoelectronic devices requires that QDs should retain their superior optical performances in condense QD films. However, most QD systems suffer intense photoluminescence (PL) quenching after film formation. Here, we report device-grade thick-shell CdZnSe/ZnSe/ZnS QDs with near-unity PL quantum yield (QY) in QD solution and 82% PL QY in QD film. We demonstrate that the thick shell functions well in restraining undesired inter-dot energy transfer by separating the emitting cores in condense QD film, and therefore preserving their superior emission properties. White light-emitting diodes (WLEDs) integrated with 5 different CdZnSe/ZnSe/ZnS QDs cover the visible spectrum, delivering a color rendering index (CRI) Ra as high as 91.4, a luminous efficiency (LE) of 68.5 lm/W and a warm bright sun light with correlated color temperature (CCT) of 4138 K. In particular, the champion CdZnSe/ZnSe/ZnS based WLED exhibits a special color index R9 as high as 93.1.

Effects of brightness levels on stress recovery when viewing a virtual reality forest with simulated natural light

Although previous studies have shown that both forest and natural light exposure can significantly affect psycho-physiological responses, how different natural light levels influence stress recovery efficacy in forest environments has not been discussed yet. A pretest-posttest design was used to explore the influence of varying brightness levels on stress recovery effect in a virtual forest environment. Six immersive virtual environments (IVE) stimuli were generated from the lightest to the darkest through virtual reality simulation software. A total of 120 participants viewed the IVE using head-mounted display. Physiological and psychological responses and perceived environmental features were evaluated. The results of the present study confirmed previous findings that bright sunlight scenes (i.e., the lightest, lighter, light) allay stress more effectively than the darkest night scenes in the virtual forest. Another noteworthy finding is that dark scenes, such as daybreak without sunlight but with a little brightness, also has this property. An unexpected finding was that exposure to the natural light of medium-brightness (i.e., lighter, light, dark) in the virtual forest could significantly reduce the stress of the participants, compared to overly bright (i.e., the lightest level) or overly dark (i.e., the darkest level) levels. In addition, this study also found that perceived environmental features (i.e., maintenance, visibility, accessibility, variety, and perceived safety) and stress recovery were associated with different levels of brightness in the simulated forest environment. The results of this study contribute to existing forest therapy theory and offer insights for follow-up research to explore forest therapy and bright light therapy.

When the Sun Meets Okeanos

In the Aegean, a landscape of small islands and peninsulas means that views of theSun rising or setting over the sea are commonplace. Yet this everyday occurrence can produce adazzling spectacle known as the “glitter path” – a line of bright sunlight reflected on the water,linking the seashore and the horizon. This paper explores how this phenomenon was elaboratedas a form of seascape by the Aegean Greeks from Late Bronze Age (LBA) III through to the Archaicperiod, examining how it was incorporated into their worldview as something natural assimilatedinto the cultural. The diachronic perspective focuses on elements of continuity and discontinuityregarding beliefs about the world beyond. First, funerary pottery iconography from LB III (ca.1400–1100 BC) is examined: in particular, a close relationship between the Sun and the sea can beinferred from imagery on Octopus Style funerary jars, where abstract representations of glitterpaths seem to appear in the shape of hybrid octopuses. The evidence suggests that the octopuswas depicted as the light-bearer within the darkness of the sea, with marked eyes to emphasisevision. The second part of the study gathers proof of allusions to the phenomenon of the glitterpath in early Greek poetry as suggested by the descriptions of the door of Hades and gates of theSun in the first literary documents produced in Greece from the eighth century BC, most notablyin the works of Homer and Hesiod, but also in the poetry of Pindar, Mimnermus and Stesichorus.

AquaE-lite Hybrid-Solar-Cell Receiver-Modality for Energy-Autonomous Terrestrial and Underwater Internet-of-Things

Our goal is to develop an energy-autonomous solar cell receiver that can be integrated with a variety of smart devices to implement the Internet of Things in next-generation applications. This paper details efforts to develop such a prototype, called AquaE-lite. Owing to the capability of detecting low-intensity optical signals, 20-m and 30-m long-distance lighting and optical wireless communication with data rates of 1.6 Mbit/s and 1.2 Mbit/s have been achieved on a laboratory testbed, respectively. Moreover, field trials on an outdoor solar cell testbed and in the turbid water of a harbor by the Red Sea have been conducted. Under bright sunlight, energy autonomy and 1.2-Mbit/s optical wireless communication over a transmission distance of 15 m have been implemented, which demonstrated that AquaE-lite with an elaborate receiver circuit has excellent performance in energy harvesting and resistance to background noise. In a more challenging underwater environment, 1.2-Mbit/s signals were successfully received over a transmission distance of 2 m. It indicates that energy-autonomous AquaE-lite with large detection area has promising prospects in future underwater mobile sensor networks to significantly relieve the requirement of pointing, acquisition and tracking while resolving the energy issues.

Associations between outdoor temperature and bright sunlight with metabolites in two population-based European cohorts

Background and aimsOutdoor temperature and bright sunlight may directly and/or indirectly modulate systemic metabolism. We assessed the associations between outdoor temperature and bright sunlight duration with metabolomics. Methods and resultsCross-sectional analyses were undertaken in non-diabetic individuals from the Oxford BioBank (OBB; N = 6368; mean age 47.0 years, males 44%) and the Netherlands Epidemiology of Obesity (NEO; N = 5916; mean age 55.6 years, males 43%) study. Data on mean outdoor bright sunlight and temperature were collected from local weather stations in the week prior to blood sampling. Fasting serum levels of 148 metabolites, including 14 lipoprotein subclasses, were measured using NMR spectroscopy. Linear regression analyses were performed to assess the associations between mean outdoor temperature and bright sunlight duration with metabolomics adjusted for age, sex, body mass index, season and either outdoor temperature or bright sunlight. A higher mean outdoor temperature was associated with increased serum concentrations of lipoprotein (sub)particles (β (SE) = 0.064 (0.018) SD per 5 °C, p = 5.03e−4) and certain amino acids such as phenylalanine (0.066 (0.016) SD, p = 6.44e−05) and leucine (0.111 (0.018) SD, p = 1.25e−09). In contrast, longer duration of bright sunlight was specifically associated with lower concentrations of very low-density lipoprotein (sub)particles (e.g., VLDL cholesterol (−0.024 (0.005) SD per 1-h bright sunlight, p = 8.06e−6)). The direction of effects was generally consistent between the OBB and NEO, although effect sizes were generally larger in the OBB. ConclusionsIncreased bright sunlight duration is associated with an improved metabolic profile whilst higher outdoor temperature may adversely impact cardiometabolic health.

Light adaptation mechanisms in the eye of the fiddler crab Afruca tangeri.

A great diversity of adaptations is found among animals with compound eyes and even closely related taxa can show variation in their light-adaptation strategies. A prime example of a visual system evolved to function in specific light environments is the fiddler crab, used widely as a model to research aspects of crustacean vision and neural pathways. However, questions remain regarding how their eyes respond to the changes in brightness spanning many orders of magnitude, associated with their habitat and ecology. The fiddler crab Afruca tangeri forages at low tide on tropical and semi-tropical mudflats, under bright sunlight and on moonless nights, suggesting that their eyes undergo effective light adaptation. Using synchrotron X-ray tomography, light and transmission electron microscopy and in vivo ophthalmoscopy, we describe the ultrastructural changes in the eye between day and night. Dark adaptation at dusk triggered extensive widening of the rhabdoms and crystalline cone tips. This doubled the ommatidial acceptance angles and increased microvillar surface area for light capture in the rhabdom, theoretically boosting optical sensitivity 7.4 times. During daytime, only partial dark-adaptation was achieved and rhabdoms remained narrow, indicating strong circadian control on the process. Bright light did not evoke changes in screening pigment distributions, suggesting a structural inability to adapt rapidly to the light level fluctuations frequently experienced when entering their burrow to escape predators. This should enable fiddler crabs to shelter for several minutes without undergoing significant dark-adaptation, their vision remaining effectively adapted for predator detection when surfacing again in bright light.

Genetic Diversity of a Post-Cryogenic Fragaria vesca L. Clone after Long-Term Cultivation in vitro and Influenced by Abiotic Factors

The effects of bright light and high temperature stresses on the genetic diversity of a Fragaria vesca L. clone recovered from meristems frozen in liquid nitrogen after two years of cultivation in vitro were analyzed. After two-year cultivation in vitro of post-cryogenic plant material, the percentage of polymorphic DNA-markers, which was half (4.5%) of its initial value after cryopreservation, immediately returned to its initial value (9%). The Shannon index increased insignificantly. The stress effects of high temperature or bright sunlight stress effects on plantlets of the post-cryogenic clone recovered after two years liquid nitrogen did not cause the appearance of additional polymorphic fragments or significant changes in the Shannon Index.

Advanced Ocular Lesions in Growing Calves with Avitaminosis A

A beef cattle farm was visited due to blindness in a group of 28 calves aged 10-12 months. According to farmer, the first blind calves were observed about 20 days before and no sign of lacrimation or corneal opacity was observed. He first noticed that 3 calves were disoriented, hitting on the pen walls and preferred to stand near the feed and water troughs. Gradually, more than half of calves of this group developed similar signs. The calves were fed ad libitum with wheat straw and a homemade concentrate mixture consisting of corn, wheat bran, soybean meal and a mixture of vitamins and trace minerals. The mixture was added at the concentrate feed at the 1/10 of the recommended dosage. At animals’ inspection it was revealed that 18 out of 28 had the ocular lesions presented in (Figures 1 and 2). They were characterized by bilateral exophthalmos with dilated pupils. The degree of exophthalmos varied among animals. The pupils were unresponsive even in bright sunlight and the menace response was absent. The observed ocular lesions are typical of a vitaminosis A in young calves [1-3]. Blindness and absence of the pupillary light reflex are the result of optic nerve necrosis caused by stenosis of the optic foramen due to failure of bone resorption and increase inosteoblastic activity [1-4]. Exophthalmos is always bilateral, with the most advanced cases showing a prominent eye with large area of sclera visible all around cornea. It is regarded that protruding eyes are the result of blindness alone since no macroscopic lesions are observed at retro bulbar tissues [3]. Such advanced lesions are not reversible [1-3]; so, it was recommended all the affected animals to be slaughtered. It was suggested the rest of the animals to be treated with injectable administration of vitamin A along with the inclusion of the mixture of vitamins and trace minerals at the appropriate dosage in the concentrates.

Barriers and Enabling Factors Associated with the Implementation of Household Solar Water Disinfection: A Qualitative Study in Northwest Ethiopia.

Household water treatment including solar disinfection (SODIS) is recognized worldwide as an important intervention for prevention and control of diarrheal and other waterborne diseases. However, in Ethiopia's countryside, SODIS is not being practiced. Therefore, the objective of this qualitative study conducted in villages of Dabat district in northwest Ethiopia was to explore barriers to and enabling factors for consistent and wider implementation of SODIS. This phenomenological study design included four focus group discussions with 25 parents of children younger than 5 years and interviews with four key informants to elicit their experiences and opinions. ATLAS.ti 8.0 software (GmbH, Berlin, Germany) was used for data organization, and the content was analyzed thematically. Enabling factors were categorized into four themes, such as supportive values for SODIS (positive attitude, advantage of SODIS, and cultural acceptance of SODIS), consistent use of SODIS (community's interest, health education, availability of bright sunlight, and simplicity of the method), participation of family and community in daily implementation of the SODIS process (controlling theft of bottles and recognizing the importance of SODIS technology), and willingness to pay for new polyethylene terephthalate (PET) bottles. On the other hand, barriers were grouped into three themes such as sociocultural (poor knowledge, hesitation to leave SODIS bottles unguarded outdoor, less attention, and unplanned social events), environmental (cloud, shadow over SODIS bottles, turbidity and leeches in source water, and geographical settings), and behavioral (mishandling of SODIS bottles and drinking water). The analysis of the data revealed that all the participants had positive attitude toward the implementation of SODIS, and it was culturally accepted. They identified the barriers to and enabling factors for the implementation of SODIS. Promoting enabling factors and mitigating barriers are substantially important for consistent implementation of SODIS as a long-term interventional measure widely in rural Ethiopia for the achievement of the goal of safe drinking water for all.

Luminance Information Is Required for the Accurate Estimation of Contrast in Rapidly Changing Visual Contexts.

Visual perception scales with changes in the visual stimulus, or contrast, irrespective of background illumination. However, visual perception is challenged when adaptation is not fast enough to deal with sudden declines in overall illumination, for example, when gaze follows a moving object from bright sunlight into a shaded area. Here, we show that the visual system of the fly employs a solution by propagating a correctiveluminance-sensitive signal. We use invivo 2-photon imaging and behavioral analyses to demonstrate that distinct OFF-pathway inputs encode contrast and luminance. Predictions of contrast-sensitive neuronal responses show that contrast information alone cannot explain behavioral responses in sudden dim light. The luminance-sensitive pathway via the L3 neuron is required for visual processing in such rapidly changing light conditions, ensuring contrast constancy when pure contrast sensitivity underestimates a stimulus. Thus, retaining a peripheral feature, luminance, in visual processing is required for robust behavioral responses.

Impact of cataract surgery on vision-related quality of life

Background: Blindness and visual impairment have been shown to reduce vision-related quality of life (VRQoL), general health and social status and increase mortality. Understanding the influence of different cataract surgery techniques on VRQoL can enhance the understanding of which technique may be most suitable to achieve the best outcomes from a patient’s perspective. Previous studies have focused exclusively on the phacoemulsification technique, with limited attention on other techniques that are common in developing countries, such as the extracapsular cataract extraction (ECCE) and manual small-incision cataract surgery (MSICS) techniques. Aim: To evaluate the impact of cataract surgery on VRQoL for the ECCE and MSICS techniques. Setting: The study was conducted at the Themba Hospital in the Mpumalanga province. Methods: A case study research design was used at the Themba Hospital. Participants underwent either the ECCE or the MSICS technique and were followed for a period of 6-weeks post-surgery. The VRQoL was assessed using the 33-item Indian Vision Functioning Questionnaire (IND-VFQ-33). Data were presented using frequencies, percentages and means ± standard deviations. Results: The sample included 101 participants, with a mean age of ~66 years. Following cataract surgery, there was an increase in the frequency of the ‘not at all’ response for the majority of the questions in the IND-VQ-33 questionnaire in all three domains. There were statistically significant differences ( p < 0.05) between the pre-surgery and post-surgery mean scores for all the questions, with the exceptions being those related to problems experienced when seeing outside in bright sunlight, bright light hurting the eyes and closing the eyes because of light from vehicles. Conclusion: Individuals who underwent both the ECCE and MSICS techniques showed improvement in VRQoL in terms of general functioning, psychosocial impact and vision symptoms domains.

“Hey Pepé!”: The Two Words That Changed My Life

"Hey Pepé!":The Two Words That Changed My Life Tony Kiene (bio) In the summer of 1978 I had only one record to my name; a 45 of the Jackson 5's "Dancing Machine." As my parents had recently purchased our first stereo system, a turntable with an 8-track tape deck, I made good use of the needle and played that 7-inch single constantly. Sometime later that summer, just a few months shy of my eighth birthday, I was visiting a friend's house where I noticed an 8-track tape on his shelf. The translucent image on the tape was of a man with a giant, perfectly shaped afro who seemingly channeled the backdrop of bright sunlight through his doe eyes and into my soul. I can't explain why, but it was one of the coolest things I'd ever seen and to this day it remains my favorite album cover of all time. On a gut feeling, I traded my Jackson 5 single straight up for this 8-track of Prince's debut album, For You, unaware of the enduring impact it would have on the rest of my life. I took the tape home, popped it in the stereo, and in those next 33 minutes and 11 seconds I became a lifer. From the harmonic genius of its a cappella title track to the prodigious drums and torrential guitar of its finale, For You left me mesmerized. It would be more than a year before Prince released his eponymous second album and nearly another year after that until Dirty Mind. By then I was earning a little bit of an allowance and had developed a distinct preference for the sound of vinyl, so, I began to steadily build a record collection. For whatever reason I never worried much about my parent's curiosity as to what I was listening to, but I wasn't confident that I could successfully hide the back of an album cover featuring nude Prince on a white, winged horse, much less the libidinous imagery of the Dirty Mind artwork or the famous shower poster that accompanied Prince's fourth LP, Controversy. Therefore, I would borrow those records from friends minus the packaging and hide them in the album sleeves of other titles I had purchased, such as Michael Jackson's Off the Wall, Kool and the [End Page 153] Gang's Something Special, the Commodore's In the Pocket, Earth Wind and Fire's Raise, and even The Time's first album. In 1981, I did not know that Jamie Starr was a Prince pseudonym and thus was initially unaware of the connection between him and The Time. However, by the summer of 1982 I knew a lot more about what was going on 500 miles or so northwest of my hometown of South Bend, Indiana, when Vanity 6 debuted their own self-titled album, immediately shadowed by the release of What Time Is It?, and soon after by Prince's masterstroke 1999. Since I was only around 12 at the time, my parents would never consider allowing to me witness the 1999 Tour (aka the Triple Threat Tour) when it arrived in nearby cities like Gary, Kalamazoo, and Chicago, let alone those locations a little further away such as Indianapolis, Detroit, or Cleveland. Notwithstanding my disappointment, I remained obsessed with the Minneapolis sound and I didn't believe anything could transcend the brilliance of 1999. Not to mention, now that André Cymone had embarked on a solo career, I couldn't think of a cooler sideman than Dez Dickerson. There was just something about his trademark Kamikaze headband and his black and white Gibson Explorer. And, of course, there was no way to convince me that there were three more beautiful women in the world than Vanity, Jill Jones, and Lisa Coleman. But then came Purple Rain. And with the mania that accompanied the soundtrack and the film arose the first wave of books about Prince's journey from North Minneapolis to international superstar, including unauthorized biographies by Jon Bream and Steven Ivory. It was in Bream's Prince: Inside the Purple Reign that I first learned of...

On the impact of seasonal solar activity on the progression of retinopathy of prematurity: preliminary research results

Purpose. To study the effect of bright sunlight on immature retina of a premature baby at different periods of solar activity.Material and methods. The study involved two groups of premature babies: 32 babies (64 eyes) in 2016 and 50 babies (100 eyes) in 2017. Both groups were tested using a retinal camera (RetCam Shuttle, USA) on the 3rd or 4th week after birth. In cases of threshold stages of retinopathy of prematurity (ROP) binocular ophthalmoscopy were performed. In such cases, laser coagulation of the retina was performed using "ALOD 01" (ALCOM Medica, Russia).Results. The greatest number of ROP with the greatest number of surgical interventions and adverse outcomes that required vitreoretinal surgery were revealed in the second seasonal period (May — August), which experienced the highest solar activity. In 2016, the amount of ROP cases diagnosed in this period amounted to 59 %, which is comparable with the corresponding amount revealed in 2017 (61.1 %).Conclusions. Stronger solar activity and its longer periods increase the risk of ROP; consequently, to prevent this pathology, the eyes of the newborn should be protected from the negative effects of daylight and artificial light, including that emitted by diagnostic equipment.

Ca2+ Signaling in Drosophila Photoreceptor Cells.

In Drosophila photoreceptor cells, Ca2+ exerts regulatory functions that control the shape, duration, and amplitude of the light response. Ca2+ also orchestrates light adaptation allowing Drosophila to see in light intensity regimes that span several orders of magnitude ranging from single photons to bright sunlight. The prime source for Ca2+ elevation in the cytosol is Ca2+ influx from the extracellular space through light-activated TRP channels. This Ca2+ influx is counterbalanced by constitutive Ca2+ extrusion via the Na+/Ca2+ exchanger, CalX. The light-triggered rise in intracellular Ca2+ exerts its regulatory functions through interaction with about a dozen well-characterized Ca2+ and Ca2+/CaM binding proteins. In this review we will discuss the dynamic changes in Ca2+ concentration upon illumination of photoreceptor cells. We will present the proteins that are known to interact with Ca2+ (/CaM) and elucidate the physiological functions of these interactions.

Photosynthetic adaptability in mature and young leaves of Medicago sativa L. seedlings under transplanted condition from greenhouse to sunlight

The effect of transplanting alfalfa (Medicago sativa) seedlings from artificial, low-intensity light into bright sunlight was investigated. The variance of photosynthetic function in young and mature leaves was investigated in plants grown in a low-light greenhouse environment (controls) and then the plants were subjected to high-intensity light for 12 hrs (treatment). The results showed that the photosynthetic capacity of young leaf blades was significantly lower than that of mature blades, and, the ability to capture and use light was low for young leaves. In control plants, the parameters of chlorophyll-dependent photochemical efficiency (ФPSII), electron transfer rate (ETR), photochemical quenching coefficiency (qP) and non-photochemical quenching coefficiency (qN) were all significantly lower in younger than mature leaves. There was no significant difference in the photochemical efficiency (Fv/Fm) or light energy distribution parameters between young and mature leaves of control plants. After light treatment, the photosynthetic carbon assimilation capacity and photochemical activity of the PS II reaction center decreased significantly, and both net photosynthetic ratio and chlorophyll b fluorescence parameters changed significantly more than in young leaves than in mature leaves under different PFD. This was particularly evident for Fv/Fm of the young leaves, whose decrease proved that the adaptability of young leaves to convert light was significantly lower than that of mature leaves. Obvious differences in the degree and mechanism of protection against light damage exist between young and mature leaves. Mature leaves dissipated excess excitation energy. In contrast, young leaves dissipated excess excitation by inactivation of the photosynthetic reaction center.

Prevalence of trigger factors in migraine

Background: Migraine is one of the most common types of headache. Many patients with migraine have precipitating factors known as trigger factors, recognition of which may lead to a better diagnostic, preventive and therapeutic approach. Objective: To study the prevalence of various trigger factors in patients with migraine, and to analyse various socio-demographic factors with respect to trigger factors. Materials and Methods: A total number of 500 patients of either sex fulfilling the ICHD3 diagnostic criteria for migraine aged more than 15 years attending Neurology Department of SMS Medical College, Jaipur, between January 2018 and February 2019 were studied. Patient enrolled in the study underwent a detailed structured interview and the information regarding the characteristics of headache including the time of onset, duration, frequency, character, site and associated features with due stress on the trigger or precipitating factors. Chi-square and t-test were performed to determine the statistical significance of the results. Results: As per the analysis, 91% of the patients reported more than one trigger factor for headache. Bright sunlight (43%), physical activity (43%), noise (42%), stressful events (41%), tea/coffee deprivation (38%), travelling (34%), hunger (33%), sleep (31%), and fatigue (29%) were some of the major trigger factors reported by the sample. People living in urban areas reported a higher number of trigger factor as compared to rural areas, which includes factors such as stress and fatigue. Sleep deprivation and physical stress were higher among rural areas. Conclusion: The present study presents a general idea about trigger factors related to headache in the North-western part of India. Bright sunlight, physical activity, noise, stressful events, tea/coffee deprivation, travelling, hunger, sleep, and fatigue parameters were some of the major trigger factors reported by the sample. Moreover, people living in urban areas reported a higher

Light adaptation controls visual sensitivity by adjusting the speed and gain of the response to light.

The range of c. 1012 ambient light levels to which we can be exposed massively exceeds the <103 response range of neurons in the visual system, but we can see well in dim starlight and bright sunlight. This remarkable ability is achieved largely by a speeding up of the visual response as light levels increase, causing characteristic changes in our sensitivity to different rates of flicker. Here, we account for over 65 years of flicker-sensitivity measurements with an elegantly-simple, physiologically-relevant model built from first-order low-pass filters and subtractive inhibition. There are only two intensity-dependent model parameters: one adjusts the speed of the visual response by shortening the time constants of some of the filters in the direct cascade as well as those in the inhibitory stages; the other parameter adjusts the overall gain at higher light levels. After reviewing the physiological literature, we associate the variable gain and three of the variable-speed filters with biochemical processes in cone photoreceptors, and a further variable-speed filter with processes in ganglion cells. The variable-speed but fixed-strength subtractive inhibition is most likely associated with lateral connections in the retina. Additional fixed-speed filters may be more central. The model can explain the important characteristics of human flicker-sensitivity including the approximate dependences of low-frequency sensitivity on contrast (Weber’s law) and of high-frequency sensitivity on amplitude (“high-frequency linearity”), the exponential loss of high-frequency sensitivity with increasing frequency, and the logarithmic increase in temporal acuity with light level (Ferry-Porter law). In the time-domain, the model can account for several characteristics of flash sensitivity including changes in contrast sensitivity with light level (de Vries-Rose and Weber’s laws) and changes in temporal summation (Bloch’s law). The new model provides fundamental insights into the workings of the visual system and gives a simple account of many visual phenomena.

Photoacoustic remote sensing of suspicious objects for defence and forensic applications.

Quantum cascade laser (QCL) based photoacoustic spectroscopic technique has been developed for detection of hazardous molecules contaminants/adsorbed on surfaces such as plastic and cloth from short standoff distances. The laser source and detection system is integrated together in a single unit. Spectra were recorded for traces of various molecules in mid-infrared spectral band (1130-1430 cm-1) from distance of 0.5 m. Pulsed quantum cascade laser source, modulated at 25 kHz and 42 kHz frequency was used to detect molecular species adsorbed on surfaces of cloth and plastic. Ultrasonic microphones operating at 25 and 42 kHz resonant frequencies were used as detectors. The photoacoustic spectra of hazardous chemicals, explosive materials and bio-chemicals such as acetic acid, PETN (pentaerythritol tetranitrate), DPA (dipicolinic acid) in very low quantities were recorded. Sensitivities of 5 and 10 μg/cm2 of these analytes were achieved with frequencies of 25 and 42 kHz respectively at distance of 0.5 m. In the present technique there was no interference of audio frequency (20 Hz to 20 kHz) and bright sunlight. The technique can be applied for screening of suspicious objects for homeland security and forensic applications. The present spectroscopic technique can be developed in man portable standalone product.

Ionic liquids stabilize perovskite cells

Solar cells made with sunlight-absorbing metallo-organic perovskite materials have basked in the photovoltaic (PV) spotlight in recent years. The reason is that perovskite materials such as methyl ammonium lead trihalides can be much less expensive to make and process than crystalline silicon, a conventional PV material, yet they offer comparable performance. But perovskite cells are not stable: the photoactive layer decomposes when exposed to heat and bright sunlight, which erodes device performance and impedes commercialization. A team led by Sai Bai, Feng Gao, and Henry J. Snaith of the University of Oxford now report that incorporating an ionic liquid in the perovskite layer stabilizes the device’s performance (Nature 2019, DOI: 10.1038/s41586-019-1357-2). Specifically, the team added an imidazolium tetrafluoroborate to the perovskite layer and sandwiched it between layers of nickel oxide and a polymer known as PCBM, materials that extract positive and negative charges, respectively. The researchers f...