Variation Of Photosensitivity Research Articles

Diurnal Preference Contributes to Maximal UVB Sensitivity by the Hour of the Day in Human Skin In Vivo

Diurnal Preference Contributes to Maximal UVB Sensitivity by the Hour of the Day in Human Skin In Vivo

Ontogenetic variation in photosensitivity of developing echinoderm propagules

Swimming behaviours and sensory abilities of early pelagic stages play a prominent role in the life history and ecology of sessile/sedentary benthic species, with implications for settlement, recruitment and dispersal. Light is a particularly important driver of navigational behaviour in the ocean, as a signal of key habitat characteristics (e.g., depth, shelter). Work to date on phototaxis has largely focused on planktotrophic larvae that feed during development, and much less on the larger lecithotrophic larvae that rely on maternal provisions (yolk). It remains unclear how responses to light might differ among ciliated propagules of different sizes and nutritional modes. The present study explored if/how phototactic responses are modulated by ontogeny (from embryo to larva), nutritional mode and light colour (wavelength) in ciliated propagules using four co-occurring species of echinoderms: the sea stars Asterias rubens and Crossaster papposus, the sea urchin Strongylocentrotus droebachiensis and the sea cucumber Cucumaria frondosa. Two types of behavioural responses to stimuli (white, red, and blue light) were examined: 1) taxis when the light stimulus was placed at one end of the chamber (net movement towards or away from the light stimulus) and 2) activity level, using a suite of swimming metrics, under uniform illumination. All four species consistently displayed some level of photosensitivity to white light and responses varied intra- and interspecifically. When the stimulus was red or blue light, planktotrophs modified their phototactic responses in a species- and stage-specific manner, while lecithotrophs generally displayed responses without a clear net direction. Swimming speeds displayed stage and species-specific variation under constant red or blue light, but swimming trajectories were consistently straighter under red light, resulting in greater displacement. Taken together, the results suggest that propagules of species with different life-history strategies respond to light stimuli in distinctive stage-wise manners. Interestingly, ontogenetic patterns were not conserved within nutritional modes or taxa. Further investigations of species-specific responses to light might help clarify its roles, in combination with factors such as buoyancy and gravity, in the ecology of propagules of benthic invertebrates.

Photoconductive properties of hot wall deposited CdSe 0.6Te 0.4 thin films

CdSe 0.6Te 0.4 compound has been prepared using high purity elemental cadmium, tellurium and selenium. Thin films of CdSe 0.6Te 0.4 have been deposited on glass substrates by hot wall deposition technique. The main feature of the hot wall system is the heated linear quartz tube, which serves to enclose and direct the vapor from source to substrate. The hot wall setup used in the present study consists of a quartz tube of 6.5 cm length and 1 cm diameter with one end open and the other end closed. Kanthal wire wound closely along the length of the quartz tube heats the wall of the quartz tube. Independent heater coils are used to heat the source and wall of the tube. The composition of the films has been determined using energy dispersive X-ray analysis. The transmittance spectra of the deposited films show that the CdSe 0.6Te 0.4 films exhibit fairly good transparency above 800 nm. The photoconductive properties of the films have been studied as a function of light intensity and wavelength. From the spectral response characteristics of photocurrent the band gap of the CdSe 0.6Te 0.4 films has been determined and is found to be 1.46 eV. The variation of photosensitivity with light intensity has been studied.

A CdS photoconductivity gas sensor as an analytical tool for detection and analysis of hazardous gases in the environment

A highly sensitive gas sensor for detection and analytical identification of hazardous gases was developed, by depositing partially crystalline powder from an aqueous suspension of CdS powder on an alumina substrate. When the deposited layers were promoted with catalysts from Pt-group metals, they exhibited high sensitivity to different gas molecules upon modulation with light of certain frequency, depending on catalyst and impurity concentration. Dark resistance and photosensitivity of the sensors were monitored against gas concentration, sensor temperature, and frequency of the modulating light. Depending on the gas and its concentration, a change of up to 100% in sensor response was observed. Variation of photosensitivity with dark resistance showed different slopes for different molecules. Variation of the low frequency phase angle with photosensitivity at different concentrations also produced different slopes, depending on the type of molecule. This differentiation likely comes about by different interactions of gas molecules with surface recombination centers, depending on the nature of physisorption and/or chemisorption on the surface. Thus, in addition to detecting the gas, it can be identified from their slopes of variation with light frequency, and the sensor can be used as an analytical tool.

Risk factors for melanoma

Skin types 1 and 2, increased numbers of moles, and excessive intermittent sun exposure are known risk factors for cutaneous melanoma, but the inter-relationship between UV radiation exposure, moles and melanoma remains unclear. There is a noteworthy site variation in melanoma, it being more common on the lower leg in women and on the back in men. In order to determine whether this site variation could provide further clues to the pathogenesis of melanoma, we examined site variation in photosensitivity and its relationship to other known melanoma risk factors (number of moles, skin type and skin colour) in 25 healthy volunteers. A marked site variation in photosensitivity was found. The pale skin of the volar aspect of the forearm was markedly less photosensitive than the darker skin of the back. Females were more photoresistant than males on the lower legs even though this is the more common site for melanoma in women. There was some correlation between the number of moles and photosensitivity at the two sites.

Process and properties of the modern multialkali photocathode used in a cascade image intensifier

A new processing technology and the properties of multialkali antimonide photocathodes are described. The technique requires an initial antimony layer to be deposited on a fiber-optic window at a suitable temperature. After that, the layer is activated by multialkali and antimonide. Thus, the multialkali photocathodes named “The Modern Multialkali Photocathode” are obtained. It has been found that a photocathode thus processed gives a sensitivity of 200 to 300μA/lm for white light at a color temperature of 2854K. This paper shows the variation of photosensitivity during processing of a Modern Multialkali Photocathode and the variation of spectral sensitivity at different wavelengths. The author discusses the results, gives a supposition of “photoemission center”, and discusses the role of Cs in multialkali photocathodes.

Termination of seasonal breeding in the photoperiodic weaver bird

AbstractTermination of seasonal breeding in the photoperiodic weaver bird does not occur as a result of photorefractoriness, and yet, in nature birds become refractory. Earlier studies indicated a seasonal variation in photosensitivity of this bird during the reproductive cycle and it was suggested that setting of the photoperiodic response threshold at a higher level might explain gonadal regression. Such a possibility was now examined by keeping birds in constant 13L/11D (the near maximal day length at Varanasi, India) and 15L/9D simultaneously for over 8 mo. While breeding in birds in 15L/9D continued, gonads regressed in 13L/11D indicating that the day length which was stimulatory in spring is no more sufficient to permit gonadal activity. Cyclicity in 13L (and in artificial 12L as well as natural daylength) may be explained on the basis that these schedules exceed the basic photoperiodic response threshold—hence the initiation of gonadal development. Once the gonads are developed due to decline in photosensitivity (caused perhaps by sex hormones) gonadal regression occurs, thus resulting in reproductive periodicity.

Photopolymer design: Photocrosslinkable styrylpyridinium substituted vinyl polymers with absorption maxima from 270 nm to 540 nm

AbstractStyrylpyridinium substituted vinyl polymers (6), which are in effect polymeric dyes, may easily be prepared by condensing poly[1‐(1,6‐dimethylpyridinium‐3‐yl)ethylene methyl sulfate] (3) with various aromatic aldehydes (5) using piperidine as catalyst. The preparation of 40 of these polymers prepared from 39 different aldehydes or combinations of them is reported. The spectral data show that they may be designed for maximum absorption almost anywhere from 270–540 nm and with a great variation in photosensitivity and solubility. It is possible to prepare the vinyl substituted styrylpyridinium salts and then polymerize them, or to prepare the styrylpyridine substituted vinyl polymer and then quaternize it, but the preferred method is to prepare the quaternized polymer 3 and then condense it with an aromatic aldehyde 5 to form the styrylpyridinium substituted vinyl polymer 6. These polymers do not require spectral sensitization and, in fact, we found no compounds that act as sensitizers.

Interspecific differences in photosensitivity between three closely related species of pigeons

It is known from field observations that vernal gonad recrudescence begins in January for the Stock dove, a month later at the end of February for the Wood pigeon, while many town pigeons (Columba livia) have active gonads throughout the year.Photostimulation experiments demonstrate that spermatogenesis can be stimulated in the Stock dove by exposure to an artificial daylength regimeincreasing from 9.1 to 10.8 hours over 28 days. This photoperiod is the approximate equivalent of natural daylength changes occurring from late January onwards at 52° N. The same phototreatment, however, was not stimulatory for the testes of Wood pigeons, which required the equivalent of a March photoperiod. Natural daylength changes occurring in late November and December failed to evoke gametogenetic recovery in Stock dove controls.The gonads of feral pigeons in full breeding condition were unaffected when the subjects were transferred from full summer photoperiods to those found in midwinter and spermatogenesis was maintained in birds kept under winter daylengths for four months.The discussion mentions the problem of intraspecific geographical variation in photosensitivity. Scottish Wood pigeons begin their gonad recovery earlier and by March have considerably larger testes than birds in the south of England. Furthermore, they achieve this more advanced condition before the vernal equinox when daylengths are shorter in Scotland than in the south of England.