Partial Sun Research Articles

Solar energy on the Moon for fixed or tracked photovoltaic systems

Moon exploration will require local renewable energy production system, which design needs estimations of the received solar energy as a function of the location and the installation mode. We developed a novel method to compute the solar energy received by a 1 m2 flat surface anywhere on the Moon, for any period and using four different installation modes used for photovoltaic systems (fixed, 1-axis tracked vertical or horizontal and 2-axis tracked). By computing hourly elevations and azimuths of the Sun from the lunar year 2012 to 2031, we determined the incident angle between the solar rays and the surface, enabling the calculation of the solar energy received over a 20-year cycle, encompassing nearly all Sun-Moon relative positions on a human scale. We applied this method to compare the solar energy received on a one-axis tracked surface (vertical or horizontal axis), a two-axis tracked surface and a fixed surface at optimal azimuth and tilt, at ten locations from equator to poles. While the two-axis tracker exhibits the highest solar energy levels, comparable solar energies are observed near the poles with a vertical axis tracker and near the equator with a horizontal axis tracker. A fixed system, on the other hand, experiences a significant loss of solar energy in comparison to a two-axis tracker, ranging from 37% to 64%. Additionally, we showed that the partial Sun visibility results in reduced solar energy levels, particularly prevalent near the poles where the Sun remains close to the horizon. Near the poles, a vertical axis tracker seems the best solution, and could be theoretically applied with a perfect concentrator photovoltaic system with an acceptance angle above +/−3.5°.

62 The Impact of Hair Coat Color on Body Temperature in Beef Cattle

Abstract Ambient temperature has a fundamental role in animal health and performance. Selecting for coat color may improve animal productivity and welfare through management and breeding decisions. The thermoneutral zone of cattle, 0°C - 25°C, is characterized as the range in ambient temperature that does not require cattle to expend energy to maintain core body temperature. When the ambient temperature is above or below these values, cattle must expend energy to keep their body temperature in homeostasis resulting in a reduction in efficiency. A proper herd management plan to mitigate heat stress can increase efficiency and decrease mortality in serious cases. Registered Hereford and commercial black cows (n = 39; average 4 yr of age) were placed in a 23-ha pasture, to determine if coat color affects internal body temperature. Cattle were on a typical fescue dominated pasture located in Mountain Grove, MO, with areas of shade and one pond centralized in the pasture. Cattle were divided into treatments based on hair coat color: black (n =13) or red (n = 26). Using temperature data loggers, vaginal temperatures were recorded in 5-min intervals during a 14-d period in Mid-July 2022, and combined into 6-hour timing intervals, A = 0400-1000 h, B = 1001-1600 h, C = 1601-2200 h, and D = 2201-0359 h. Environmental temperature data loggers were suspended in two locations of partial sun to record ambient temperature. In addition, the Mountain Grove weather station operated by the University of Missouri Extension provided a daily data archive that recorded wind speed, total precipitation, maximum and minimum air temperature. Throughout the study, the mean environmental temperature was 34.4°C and ranged from 19.5°C to 40.2°C. Temperature data were evaluated using the Glimmix procedure of SAS and pairwise comparisons between timepoints were determined utilizing the GLM procedure of SAS. Differences were considered significant at P = 0.05. Black-haired cattle were warmer at all intervals (P ≤ 0.04) with temperature differences between the treatments of 0.07, 0.10, 0.03, and 0.09°C for timepoints A, B, C and D, respectively (Table 1). Based on our results black-hided cattle get warmer earlier in the day and take longer to dissipate heat than those with red hair coats.

Disinfection of Phi6, MS2, and Escherichia coli by Natural Sunlight on Healthcare Critical Surfaces.

Ultraviolet (UV) radiation systems, commonly used to disinfect surfaces, drinking water, and air, stem from historical practice to use sunlight to disinfect household items after contagious illness. Currently, it is still recommended in viral outbreak contexts such as COVID-19, Ebola, and Marburg to expose soft surfaces to sunlight after washing with detergent or disinfecting with chlorine. However, sunlight that reaches the Earth's surface is in the UVA/UVB wavelengths, whereas UV disinfection systems typically rely on biocidal UVC. Our goal was to fill the evidence gap on the efficacy of sunlight disinfection on surface materials common in low-resource healthcare settings by seeding four surfaces (stainless steel, nitrile, tarp, cloth) with three microorganisms (viral surrogate bacteriophages Phi6 and MS2 and Escherichia coli bacteria), with and without soil load, and exposing to three sunlight conditions (full sun, partial sun, cloudy). We conducted 144 tests in triplicate and found: solar radiation averaged 737 W/m2 (SD = 333), 519 W/m2 (SD = 65), and 149 W/m2 (SD = 24) for full sun, partial sun, and cloudy conditions; significantly more surfaces averaged ≥4 log10 reduction value (LRV) for Phi6 than MS2 and E. coli (P < 0.001) after full sun exposure, and no samples achieved ≥4 LRV for partial sun or cloudy conditions. On the basis of our results, we recommend no change to current protocols of disinfecting materials first with a 0.5% chlorine solution then moving to sunlight to dry. Additional field-based research is recommended to understand sunlight disinfection efficacy against pathogenic organisms on healthcare relevant surfaces during actual outbreak contexts.

Distance Laplacian spectral ordering of sun type graphs

Let G be a simple, connected graph of order n. Its distance Laplacian energy DLE(G) is given by DLE(G)=∑i=1n|ρiL−2W(G)n|, where ρ1L≥ρ2L≥⋯≥ρnL are the distance Laplacian eigenvalues and W(G) is the Wiener index of G. Distance Laplacian eigenvalues of sun and partial sun graphs have been characterized. We order the partial sun graphs by using their second largest distance Laplacian eigenvalue. Moreover, the distance Laplacian energy of sun and partial sun graphs have been derived in this paper. These graphs are also ordered by using their distance Laplacian energies.

Effects of nest management methods on hatching success and predation rates of hawksbill turtles on Cousine Island, Seychelles

Sea turtle populations have declined globally and are of conservation concern. We investigated the effects of nest management methods on hatching success and egg/hatchling predation rates of hawksbill turtles Eretmochelys imbricata on Cousine Island, Seychelles. We determined the effectiveness of two different crab-barrier methods (netted and fenced) on hatching success and predation rates. We examined the relative influence of nest-site cover (full sun, partial sun or full shade) and location (zones of high risk or low risk of predation) on hatching success and predation rates. We also examined temperature disparity between netted and control nests to estimate potential effects on sex ratios and measured typical beach-substrate temperatures in the different nesting habitats. We compared data from 40 netted, 40 fenced and 40 control nests during the 2014/2015 breeding season. Overall, hawksbill turtle hatching success was not significantly affected by treatment or cover; however, netted nests and nests incubating in full sun had the highest mean hatching success. Predation rate was generally low but variable, and the rates differed significantly between the three treatments. Nest temperatures differed significantly between the netted and control nests, with netting used to protect nests having a substantial cooling effect. Hatchling sex ratios for natural nests were skewed towards females and those for netted nests skewed towards males. With climate change and increasing ambient temperatures imminent, a better understanding of how the spatial distribution of nests and variations in environmental factors influence hawksbill turtle hatching success and the levels of predation on eggs and hatchlings will assist future conservation measures.

Hybrid PCM and Transparent Solar Cells in Zero Energy Buildings

Zero energy building design could be realized by passive design. Having energy conservation concepts and active mechanical renewable energy generation systems could be considered as passive technique. This concept becomes a very interesting technique in countries that consume a lot of energy for their domestic sector. The purpose of the recent paper is to investigate the effect of hybrid construction material that merges phase change material, PCM walls for heat load minimization and transparent solar cells, and TSC in the windows for electricity generation for the purpose of illumination in such typical design. PCMs could be used for storing thermal energy and utilizing this energy during different annual seasons by absorption or release mechanisms to keep the building’s inside temperature at thermal comfort state. While TSC,s are substances that allow partial Sun light penetration for illumination during day and use the other part for electricity generation at night. The paper introduce a typical architectural design for residential building that utilizes such type of constructional material for energy saving and analyzes thermal effectiveness of using PCM and power production effectiveness of using TSC as passive technique integrated with the zero-energy building envelope. Proper modeling tool has been used to investigate the impact of these materials on the thermal comfort perceived by the occupants. Results show that using such type of hybrid materials reduces annual energy consumption. It has been concluded that the passive structural heat isolation and power production material is a very effective manner in countries like Iraq which has severe temperature differences between summer and winter seasons.

Improved SOT (Hinode mission) high resolution solar imaging observations: 2—Photometric properties of sunspot umbral dots

The origin and evolution of solar sunspots in deep photospheric layers are not yet well understood. The case of a quasi-symmetric single mature sunspot near the solar centre is selected for analysis. We use the best available observations of the partial Sun free of turbulent Earth atmospheric effects from the Solar Optical Telescope (SOT) onboard the Hinode spacecraft, after greatly improving the resolution with an optimum Max-likelihood deconvolution with the Point Spread Function (PSF) deduced in a preceding paper. For several different images both the smearing due to the instrumental diffraction effects (PSF core) and the large angle stray light are removed. The selected iterative processing depends on both the signal/noise ratio and on the desired contrast of the ultimate details under examination. The photometric properties of bright umbral dots (BUDs) are deduced from corrected frames. Calibrated isophote maps are provided to show the intensity variations around each UD across the background umbra and the surrounding photospheric field, including the penumbra. We deduce the typical photometrical properties of bright UDs that populate the whole umbral surface down to sub-pixel scales of $0.05448''$ . The analysis demonstrates the basic heterogeneous nature of the umbra, similar to a network of minute bright and dark round or elongated cells with a spacing of order of $0.35''$ . For the first time a complete and detailed map of the color index and temperature deduced from the analysis of deeply corrected continuum images is provided, showing that tiny bright UDs can reach photospheric temperatures and even higher for the peripheral BUDs. In the umbra, there are some very dark small regions with temperatures as low as 3100 K. Close links seemingly exist with bright UDs. Central BUDs and peripheral BUDs are found to have similar properties but significantly different contrast values. Photometric analysis shows a large dispersion that reflects the broad range of dynamical phenomena involved in the umbra and its periphery, suggesting that the small scale activity observed in the deepest measured photospheric layers of the umbra determines the more impressive rapid phenomena observed in higher layers.

Light coupling into the Whispering Gallery Modes of a fiber array thin film solar cell for fixed partial Sun tracking

We propose the use of whispering gallery mode coupling in a novel configuration based on implementing a thin film cell on the backside of an array of parallel fibers. We performed numerical calculations using the parameters of a thin film organic cell which demonstrate that light coupling becomes more effective as the angle for the incident light relative to the fiber array normal increases up to an optimal angle close to 55 deg. At this angle the power conversion efficiency of the fiber array solar cell we propose becomes 30% times larger than the one from an equivalent planar cell configuration. We demonstrate that the micro fiber array solar cell we propose may perform an effective partial tracking of the sun movement for over 100 degrees without any mechanical help. In addition, in the event that such fiber array cell would be installed with the adequate orientation on a vertical façade, an optimal photon-to-charge conversion would be reached for sunlight incident at 55 deg with respect to the horizon line, very close to the yearly average position for the sun at Latitude of 40 deg.

GROWTH AND SURVIVAL OF PIONEER AND LATE SUCCESSIONAL SPECIES IN SIMULATED LIGHT ENVIRONMENTS IN A SRI LANKAN LOWLAND RAIN FOREST

Growth and survival of two pioneer and four late successional species in different light levels inshade houses were investigated over a period of one year from January 2000 to January 200 1 atthe Sinharaja field research station.Schumacheria castaneifo/ia (Dilleniaceae) and Vltex altissima (Verbenaceae) represented thepioneer species. Psychotria nigra, Gaertnera vaginans (Rubiaceae), Syzygium operculatum andS. rubicundum and (Myrtaceae) were selected as late successional species. The four latesuccessional species were further subdivided into two canopy species (S. operculatum and S.rubicundum) and two understorey species (Psychotria nigra and Gaertnera vaginans) based onheight at maturity oftheir parent trees. Seedlings were grown under four light environments (fullsun, 1200; partial sun, 800; partial shade, 350; shade, 50j.Lmolm-2s-1) that represented a range ofPPFD (photosynthetic photon flux density) found within the forest. Five seedlings of eachspecies were grown in each light environment, which was replicated three times. At the end ofone year the height increments and percentage survival of seedlings were measured.The study revealed that two Syzygium species, Gaertnera vaginans and S. castaneifolia showingthe lowest height increments 'when grown in shade. But no significant difference was observedbetween shade and full sun for these species. Although the lowest height increments for Valtissima and P. nigra were observed in full sun and in partial shade respectively, there is nosignificant difference among shade, partial sun and full sun for V altissima. Psychotria nigra didnot show any significant difference among four light treatments. The greatest relative heightgrowth was observed in partial shade for G. vag/nans and S. castaneifoliz; V altissima, and inpartial sun for two Syzygium species. Plasticity (ratio between highest and lowest values amonglight treatments) measurement of height increment was highest in G. vaginans (3.47), the lowestin P. nigra (l.52) compared to s. operculatum (1.79), S rubicundum (2.18), V altissima (2.19),S. castaneifolia (3.08). Percentage seedling survival of S. castaneifolia, and V a/tissima was100% under all light levels .All species survived equally well in partial sun light level. In shade,seedling survival of G. vaginans, and S operculatum was 93% and in Psychotria nigra, it was80%. G. vaginans and P. nigra showed 93% seedling survival in partial shade .In full sun G.vaginans and S. rubicundum exhibited 93.3% survival while P nigra showed 67 % survival.These results suggest that pioneer species grow and survive well in all light levels than latesuccessional species in early stage of their life cycle.

Seeds of EndangeredHarrisia fragransform Persistent Soil Seed Banks and Withstand Orthodox Storage Conditions

Understanding soil seed-bank dynamics of endangered species is crucial for their effective management and conservation. Whether or not seeds of Harrisia fragrans Small, a U.S. endangered cactus endemic to Florida (USA) form persistent soil seed-banks or withstand drying and/or freezing under storage conditions was unknown. We conducted a seed burial experiment with seeds collected from three sites (North, Middle, and South) within the Savannas Preserve State Park, FL, USA. We buried the seeds in plots with three light conditions (sun, partial sun, and shade) at each of the three sites and tested their viability in germination trials after 3.5, 8, 11, 16, 19 and 23 months of burial in soil. Buried seeds remained alive throughout the 23 months of the study period with germination ranging from 64 to 100%, which suggests that this species forms a persistent soil seed-bank. Microhabitat conditions markedly affected seed-bank size and subsequent seed viability. Seeds from the South site exhibited higher and faster germination than seeds from the Middle or North sites. We also evaluated if H. fragrans seeds could withstand dry storage under low relative humidity (RH) and low temperature. In the laboratory 76% of seeds stored under 12% RH and -20°C for 1 and 24 weeks germinated faster than seeds stored under 21–23°C and 50% RH. Thus, the capacity of Harrisia fragrans to form a persistent soil seed bank influences population persistence. Its ability to be stored in orthodox ex-situ conditions offers viable options for its future conservation and regeneration.

Sicyos angulatus

<i>Sicyos angulatus</i>

Thermal pollution of streams by runoff from paved surfaces

AbstractUrban development dramatically alters a drainage system by landscaping, changes in surface cover, and addition of stormwater handling systems. Increased and warmer runoff from impervious surfaces into streams can lead to a degradation of habitat for coldwater fish. For the projection of thermal impacts of new land development projects, hydro‐thermal simulation models have been developed. With measured climate as input, these deterministic models can be used to predict the thermal impact of individual storm events. Surface runoff and runoff temperature were simulated for an asphalt parking lot using 6 years of climate data from Minnesota, USA, with 282 individual rainfall events. The thermal loading from each rainfall event was quantified by three parameters: runoff temperature ( °C), rate of heat export (W/m2) and total (integral) heat export (J/m2). Many storm events were found to have little thermal impact, but a few events per year have high thermal impact, either due to large rainfall amounts at a high dew point temperature or due to high land surface temperature combined with moderate rainfall amounts. The amount of heat added to the runoff is highly dependent on both the characteristics of the rainfall event and the weather conditions prior to the storm event. Runoff temperatures from asphalt were found to be well correlated to a linear combination of three parameters: average dew point temperature during the storm, air temperature prior to the storm, and solar radiation prior to the storm. The study results imply that stormwater thermal pollution is more severe when (1) atmospheric air and dew point temperatures are higher than stream temperature, e.g. for streams that are fed by groundwater that is colder than the ambient air, (2) rainfall events are short, intense and preceded by full or partial sun, and (3) watersheds have a high percentage of impervious, particular paved, surfaces. Copyright © 2008 John Wiley &amp; Sons, Ltd.

'Florida Blizzard'—A White Fancy-leaved Caladium for Large Pots or Shady Landscapes

Received for publication 14 May 2001. Accepted for publication 21 Sept. 2001. This research was supported by the Florida Agricultural Experiment Station and grants from the Gloeckner Foundation and the Florida Caladium Growers’ Association, and approved for publication as Journal Series R08380. Caladiums [Caladium bicolor (Ait.) Vent., syn. Caladium ×hortulanum Birdsey, Araceae Juss.] are tropical foliage plants possessing a diversity of leaf colors and shapes found in few cultivated plants. Their popularity is increasing because of their ability to tolerate summer heat and to grow in shaded locations (Harbaugh and Tjia, 1985). The general color groupings in caladium are white, red, and pink, with accents such as spots and blotches possible within each group. Leaf shapes are grouped as strap, lance, and fancy (heartshaped). A recent survey (Bell and Wilfret, 1998) revealed that white fancy-leaved cultivars are the most commonly grown group, accounting for 28% of the commercial tuber production acreage. ‘Candidum’ and ‘White Christmas’ are the most important caladium cultivars, based on acreage. Although these cultivars have been reliable producers for many years and perform well as landscape plants, especially in partial sun or shaded conditions, their performance in containers could be improved. ‘Florida Blizzard’ (Fig. 1), when compared with major white-fancy cultivars, has demonstrated the potential to produce a superior number of leaves and to produce an attractive 10-cm container plant when buds are excised (Evans et al., 1992). The unique leaf color of ‘Florida Blizzard’ is complementary to ‘Candidum’ and ‘White Christmas’, offering an attractive addition to the white-fancy segment of caladiums.

Ecology and Behavior of Lizards of the Parthenogenetic Cnemidophorus laredoensis Complex and Their Gonochoristic Relative Cnemidophorus gularis: Implications for Coexistence

The Cnemidophorus laredoensis complex consists of two, all-female parthenogenetic lizard species, designated LAR-A and LAR-B, that commonly coexist with their gonochoristic (= bisexual) relative Cnemidophorus gularis in southern Texas. The ecology and behavior of these Cnemidophorus lizards was studied in a Texas state park where LAR-A, LAR-B, and C. gularis coexist. I used time of capture records to estimate daily activity periods and used focal animal observations of free-ranging individuals to determine what proportion of time lizards spent using different microhabitats, occupying different exposures (full sun, partial sun, shade), and performing different behaviors during the May-June breeding seasons of 1994- 1996. There was little difference among the three species in daily activity period, microhabitat use, or exposure occupancy; added to previously published data on diet similarity, these results suggest that com- petition between the two parthenogens and C. gularis potentially is severe. The greatest behavioral differ- ences were between male C. gularis and female C. gularis, LAR-A, and LAR-B: male C. gularis spent a much greater percentage of their time interacting with other lizards and moved significantly farther per unit time than did females. These results reflect the large proportion of time male C. gularis devoted to trailing and courting female C. gularis as well as parthenogenetic females, especially LAR-A. The only major difference between C. gularis and the two parthenogens was that the latter spent a greater proportion of their time searching for prey. Despite this, LAR-A and LAR-B did not achieve a greater prey capture rate, nor a greater success at locating the preferred prey of termites than did C. gularis, suggesting the two parthenogens are less efficient foragers than their gonochoristic relative. This may account for the reason why the two par- thenogens are not competitively excluding C. gularis from the park despite advantage of a much greater population size. Overall, data from this and other studies lend support to the idea that parthenogenetic Cnemidophorus are ecologically and behaviorally inferior to their gonochoristic congeners and should, therefore, be able to coexist with them only in habitats where selective forces are relaxed.

Epiphyllous Hepatics from Southern Alabama

Epiphyllous Hepatics from Southern Alabama

The Effect of Moisture and Sunlight on the Severity of Dogwood Anthracnose in Street Trees

The effect of supplemental irrigation and sunlight on the severity of dogwood anthracnose was evaluated on Cornus florida street trees in New Jersey during 1989 and 1990. Fewer leaf spot and twig blight symptoms were observed on trees that received supplemental irrigation in the summer during periods of drought. In addition, those trees placed in full or partial sun were less diseased than trees grown in the shade.

Emission Characteristics of a Polyethylene Pheromone Dispenser for Mating Disruption of Codling Moth (Lepidoptera: Tortricidae)

Evaporative release characteristics of a polyethylene dispenser containing a mixture of (E, E)-8,10-dodecadien-l-ol (E8, E10-12:OH), dodecan-l-ol (12:OH), and tetradecan- l-ol for disruption of mating of the codling moth, Cydia pomonella (L.), were evaluated. The factors examined for each pheromone component were temperature, dispenser age, and exposure to sunlight. Increases in temperature caused an exponential increase in the release rate of each component. Evaporation rates declined over time for each component and were expressed as a function of accumulated degree-hours (DH). The combined effect of accumulated DH and instantaneous temperature (T) on release rates of dispensers placed in the orchard canopy was described by the equation In(release rate) = a + b(l/T) + c(DH), where a, b, and c are regression coefficients specific for each component, T is temperature (OK), and DH is degree-hours accumulated above OOK in the orchard. Differences in evaporation rates for each component changed both the ratio of the pheromone blend inside the dispenser and that released from dispensers over time. The model did not predict evaporation rates as well for dispensers placed in full sun or total shade. In full sun, evaporation rates of E8, E10-12:0H declined significantly faster than from dispensers placed in partial sun. No significant differences were found for the evaporation rate of 12:0H or 14:0H among full or partial sun or complete shade over time. A tacky film formed on the exterior surface of dispensers exposed to sunlight. A portion of this film consisted of pheromone components in a ratio different from that found within the dispenser. Removal of this surface film from the dispenser significantly increased rates of evaporation of 12:0H and E8, E10-12:0H.

PHOTOSYNTHETIC RESPONSES TO LIGHT IN AN UNDERSTORY HERB, ASTER ACUMINATUS

Previous studies of the understory herb, Aster acuminatus, have shown that variation among natural patches in ramet growth, reproduction and population dynamics reflects environmentally induced responses to differences in patch light regimes. This set of experiments was undertaken to determine if photosynthetic responses to variation in light could provide a physiological explanation for the observed differences among patches. Ramets were raised in pots under different light regimes in either the field or growth chambers and then were taken to the lab for analyses of photosynthetic light responses. Ramets acclimated to the light conditions they experienced. Low‐light plants had lower maximum photosynthetic rates, light saturation points and light compensation points compared to high‐light plants. These differences were more pronounced for growth chamber‐grown plants than for those from the field. Differences between ramets grown in deep shade and partial sun in the field were greatest early in the season and then became less as photosynthetic rates for all plants declined. Photosynthetic rates were strongly correlated with leaf nitrogen level, and there was no evidence that nitrogen was any more limiting for one treatment compared to others. These results demonstrate a physiological basis for patch differences in growth, reproduction and dynamics.

Photosynthetic Responses to Light in an Understory Herb, Aster acuminatus

Previous studies of the understory herb, Aster acuminatus, have shown that variation among natural patches in ramet growth, reproduction and population dynamics reflects environmentally induced responses to differences in patch light regimes. This set of experiments was undertaken to determine if photosynthetic responses to variation in light could provide a physiological explanation for the observed differences among patches. Ramets were raised in pots under different light regimes in either the field or growth chambers and then were taken to the lab for analyses of photosynthetic light responses. Ramets acclimated to the light conditions they experienced. Low-light plants had lower maximum photosynthetic rates, light saturation points and light compensation points compared to high-light plants. These differences were more pronounced for growth chamber-grown plants than for those from the field. Differences between ramets grown in deep shade and partial sun in the field were greatest early in the season and then became less as photosynthetic rates for all plants declined. Photosynthetic rates were strongly correlated with leaf nitrogen level, and there was no evidence that nitrogen was any more limiting for one treatment compared to others. These results demonstrate a physiological basis for patch differences in growth, reproduction and dynamics.

The continuum of the extreme limb and the chromosphere at the 1970 eclipse

The flash spectra of the partial Sun and the chromosphere were obtained at the total solar eclipse on 7 March, 1970. We studied the distributions of the surface brightness of the continuum at six wavelengths in the visual region to compare them with the previous observations and the existing model atmospheres. All of the distributions show a shallow dip and a small hump similar to those of Heintze's observation at the 1954 eclipse. But the hump in our results is of quite a different type from that given by Heintze's revised model. It was found that none of the existing model atmospheres can reproduce this hump. The intensity distribution in the low chromosphere was also examined.