Bright Days Research Articles

The visually controlled prey-capture behaviour of the European mantispid Mantispa styriaca.

Mantispids (Mantispa styriaca) are predatory insects; on bright sunny days, they wait in ambush for insect prey. The prey is captured as soon as it is within reach by means of lightning-speed strikes with the powerful forelegs. The strikes can take less than 60 ms. The mantispid accomplishes this almost as effectively as the larger praying mantis, which occupies a similar habitat, even though the praying mantis has apposition eyes with a high-resolution fovea, whereas the mantispid has unspecialized optical superposition eyes. Mantispa styriaca reacts to an item of prey when the latter covers a critical visual angle. The detection of prey immediately triggers adjustment reactions in the mantispid, which attempts to position the prey item in the visual field of both eyes and in the capture zone. Irrespective of the size of the prey, the capture reaction of the mantispid is always triggered if the distance to the prey falls below a certain critical value. As indicated by the analysis of individual video frames, immediately before an aimed strike, the item of prey is always positioned exactly in the centre of the binocular field of vision in the extended midsagittal plane of the mantispid's head. The strike may be triggered by the ommatidia of the left and right eyes, the lines of sight of which converge precisely on this region. The principal conclusion to be drawn is that the prey-capture behaviour of the mantispid appears to be based on a triangulation mechanism.

Transpiration and water relations of poplar trees growing close to the water table.

Sap flow was measured on five branches of two poplar (Populus trichocarpa Torr. & A. Gray x P. tacamahaca L.) trees from June to September 1994 in the south of England with stem-surface, heat balance gauges, and was scaled up to estimate transpiration from single trees on the basis of leaf area. On six days, stomatal conductance and plant water potential were measured simultaneously with a porometer and pressure chamber, respectively. The effects of solar radiation (S), vapor pressure deficit (D) and stomatal conductance on transpiration were evaluated. Sap flow per unit leaf area (F(a)) was closely related to the time course of demand attributable to S and D throughout the season, and only slightly affected by the water content of the top 120 cm of soil. Although F(a) increased linearly at low values of D, it showed a plateau with increases in D above 1.2 kPa. The canopy coupling coefficient (1 - Omega) ranged from 0.48 to 0.78 with a mean of 0.65 +/- 0.01, indicating that transpiration was controlled more by stomatal conductance than by incident radiation. The seasonal pattern of tree water loss followed potential evaporation with a peak in late June or early July. On bright days, daily transpiration over the projected crown area was 3.6 mm early in the season, 3.8 mm in mid-season, and 2.7 mm late in the season. The water balance of the system indicated that poplar trees took 15-60% of water transpired from groundwater, with the proportion increasing as the soil in the unsaturated zone dried out. Access to the water table resulted in high predawn water potentials throughout the season. Estimated hydraulic resistance to water flow in the soil-tree system was in the range of 1.5 to 1.93 x 10(6) MPa s m(-3).

Freire at the Beach: remembering Paulo in the bright days of summer

abstract Paulo Freire's work in literacy and conscientisation brought new depth and meaning to emancipatory and participatory pedagogy. In recent years Freire was concerned he would not be around for the beginning of the twenty‐first century. His death is a loss to adult education but all signs suggest there will be a continuing interest in his work. Many people had personal contact with Freire. Some acted like groupies trailing a rock star. Others had misgivings about his guru status. A few thought his work resembled that of Sylvia Ashton‐Wamer in New Zealand. Moreover, it was not easy to “know” Freire and, in one stream of thought, he was a chameleon that changed spots to suit the occasion and often took refuge in lofty generalisations. The notion that there was no “real” Freire, only a construct, is not welcomed by Marxist friends. Thus far there is little critique of his work. The author of this article more or less spent a summer with and interviewed Freire. In this article he asks—who was Freire? The answer consists of details concerning his biography, recollections of the summer of 1984, an interview in which he speaks in his own words and an analysis of what few people ever witnessed—a cultural circle in action.

Does Ozone Exposure Protect from Photoinhibition?

Tropospheric ozone and high light intensities are two stress factors that often occur simultaneously under natural conditions. Ozone is well known to form oxygen radicals in the apoplastic water and long lasting photoinhibition can cause photooxidative damage also by formation of several species of oxygen radicals. We were interested whether moderate levels of ozone would be able to modulate the response of leaves to photoinhibitory conditions naturally occurring around noon on a bright day. Cuttings of Populus sp. were cultivated in two separate greenhouse-compartments adapted as fumigation chambers. In the two compartments plants were grown in ambient air containing about 20 nmol mol(-1) ozone and in elevated ozone concentrations supplied for 8 h per day. During the midday of bright days Fv/Fm decreased by the same amount in all leaves, indicating photoinhibition. At the same time Fo increased in control leaves more than in ozone-exposed leaves indicating a higher amount of heat-deactivating PSII centres in the latter. This was confirmed by a higher epoxidation state in ozone-exposed leaves during midday of a bright day. The contents of chlorophyll a and chlorophyll b were significantly decreased in ozone-exposed leaves. In older leaves the ratios chlorophyll a : b, and xanthophylls: chlorophyll b were increased indicating an adaptation to higher light stress. From this we conclude that by increasing the amount of heat-deactivating centres ozone seems to protect PSII from photoinhibition.

Significance of pelagic and benthic primary production in two shallow coastal lagoons of different degrees of eutrophication in the southern Baltic Sea

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:273-284 (1999) - doi:10.3354/ame020273 Significance of pelagic and benthic primary production in two shallow coastal lagoons of different degrees of eutrophication in the southern Baltic Sea Jürgen Meyercordt*, Sabine Gerbersdorf, Lutz-Arend Meyer-Reil Institut für Ökologie, Ernst-Moritz-Arndt-Universität Greifswald, 18565 Kloster/Hiddensee, Germany *E-mail: meyercor@rz.uni-greifswald.de ABSTRACT: Primary production by pelagic and benthic microalgae was measured in 2 shallow coastal lagoons in the southern Baltic Sea by in situ and laboratory incubations to quantify the significance of these 2 major groups of primary producers in absolute and relative terms. Pelagic primary production rates per volume at saturating light conditions were 7 to 12 times higher at the polytrophic location Kirr-Bucht (Darss-Zingst Bodden) than at the meso-/eutrophic location Rassower Strom (Nordrügensche Bodden). Chlorophyll a specific primary production rates, however, were in the same range at both locations, except for 1 situation in spring which is explicitly discussed. The pelagic chlorophyll a specific maximum light utilization coefficient (a*) tended towards higher values in Kirr-Bucht samples, which can be interpreted as an adaptation to a lower supply of irradiance. Pelagic and benthic primary production varied seasonally, with highest rates occurring in June/July. A calculation of short-term variability due to cloud-modulated availability of irradiance revealed reductions of pelagic and benthic gross production (GP) rates on overcast days, compared to bright days, in the range of 26 to 69% and 62 to 82%, respectively. Net community production (NP) rates were more severely reduced than GP rates on overcast days. Benthic NP was generally reduced to below zero on overcast days, whereas it was mostly positive on bright days at both locations. To evaluate the significance of the different optical properties of both types of water (diffuse vertical attenuation coefficient, k = 3.3 to 3.7 and 0.5 to 0.7 m-1 at Kirr-Bucht and Rassower Strom, respectively) for primary production, the benthic and pelagic contributions at both sites were calculated regarding a water depth of 2 m, which is about the mean depth of the Bodden systems. This standardization revealed obvious differences in basic conditions for primary production which remained undetected when the comparison of the 2 sites was based on the water depths in which the in situ incubations had been carried out (0.6 and 3.4 m at Kirr-Bucht and Rassower Strom, respectively). In meso-/eutrophic Rassower Strom at a depth of 2 m, benthic GP would contribute about 30 to 45% to the total GP of microalgae, depending on weather conditions and seasons. At the same depth in polytrophic Kirr-Bucht, the microalgae on the sediment surface would account for only 0.3% or less of total GP. This demonstrates that optical properties of the water, which are closely related to the trophic state of the system, exert strong control on varying proportions of productivity, attributable to planktonic versus benthic microalgal communities. It can be concluded from the modeled data that the difference between both locations will be most prominent during periods of low supply of radiant energy, like on overcast days. KEY WORDS: Primary production · Phytoplankton · Microphytobenthos · Irradiance · Eutrophication · Estuary · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 3. Publication date: December 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

A note on effects of gender and time of day on the winter time-activity budget of adult ostriches ( Struthio camelus) in a farming environment

This study examined the time–activity budget of adult ostriches under winter conditions during morning and afternoon time periods. Male and female adult ostriches, maintained in pairs and trios on a commercial ostrich farm in Britain, were observed during February 1997. Weather conditions experienced by the ostriches included periods of rain, high winds, overcast days and bright sunny days. Temperatures ranged from 0 to 13°C. Feeding on concentrate food was the most frequent behaviour during the morning, whereas foraging from the pasture was the largest part of the time–activity budget in the afternoon. This difference was due to the concentrate ration being delivered during the morning. During either time period, feeding and foraging combined took up over 50% of the time–activity budget with standing taking up another 20%. The frequency of sitting was higher during the afternoon. Locomotory behaviours formed a small part of the time–activity budget with movement around the enclosure usually being achieved whilst foraging. With the exception of searching, no significant gender differences were observed for any behaviour. Males had a more varied behavioural repertoire in the afternoon. Welfare concerns have been raised over the suitability of the European climate for keeping ostriches on farms. Given the importance of feeding and foraging during winter, freedom from hunger has to a high priority in developing the appropriate husbandry systems for ostriches.

Efficiency of sunlight utilization: tubular versus flat photobioreactors

The light saturation effect imposes a serious limitation on the efficiency with which solar energy can be utilized in outdoor algal cultures. One solution proposed to reduce the intensity of incident solar radiation and overcome the light saturation effect is "spatial dilution of light" (i.e., distribution of the impinging photon flux on a greater photosynthetic surface area), but consistent experimental data supporting a significant positive influence of spatial light dilution on the productivity and the photosynthetic efficiency of outdoor algal cultures have never been reported. We used a coiled tubular reactor and compared a near-horizontal straight tubular reactor and a near-horizontal flat panel in outdoor cultivation of the cyanobacterium Arthrospira (Spirulina) platensis under defined operating conditions for optimum productivity. The photosynthetic efficiency achieved in the tubular systems was significantly higher because their curved surface "diluted" the impinging solar radiation and thus reduced the light saturation effect. This interpretation was supported by the results of experiments carried out in the laboratory under continuous artificial illumination using both a flat and a curved chamber reactor. The study also showed that, when the effect of light saturation is eliminated or reduced, productivity and solar irradiance are linearly correlated even at very high diurnal irradiance values, and supported findings that outdoor algal cultures are light-limited even during bright summer days. It was also observed that, besides improving the photosynthetic efficiency of the culture, spatial dilution of light also leads to higher growth rates and lowers the cellular content of accessory pigments; that is, it reduces mutual shading in the culture. The inadequacy of using volumetric productivity as the sole criterion for comparing reactors of different surface-to-volume ratio and of the areal productivity for evaluating the performance of elevated photobioreactors operated outdoors is stressed; it is furthermore suggested that the photosynthetic efficiency achieved by the culture also be calculated to provide a suitable parameter for comparison of different algal cultivation systems operated under similar climatic conditions. Copyright 1998 John Wiley & Sons, Inc.

The Archaeology of Australia's History

Foreword Preface 1. 'There are no traces now': the material heritage of Australian history 2. 'They came by sea': the historical archaeology of precolonial contact 3. The birth of a nation: seeking the remains of early Sydney 4. 'It didn't always work': investigating the sites of failed settlements 5. The convict contribution: vestiges of the penal system 6. 'I built a little homestead': extracting history from houses 7. 'I cleared the land and fenced it': reading the rural landscape 8. 'Out of the ground came wealth': the archaeological evidence for mining 9. Made in Australia: information from industrial relics 10. 'The glad bright days have vanished': the potential of Australian historical archaeology Suggested activities Suggested reading Index.

Instruments and the Imagination ed. by Thomas L. Hankins and Robert J. Silverman

TECHNOLOGY AND CULTURE Book Reviews 233 tween structure and agency, have led to the development oftheories like ANT. She offers a variation on poststructuralist analysis as a solu­ tion to some of these dilemmas. The theoretical circle is closed by Grint and Steve Woolgar, who critique “failures of nerve” in con­ structivist and feminist analyses of technology (p. 48). The volume also includes six case studies. Telephones, household appliances, reproductive technologies, software, and computers are the technologies analyzed. The methods and sources used vary widely. For instance: Valerie Frissen’s essay on the gendering of tele­ phone use borrows from a wide variety of contemporary and histori­ cal secondary sources. Danielle Chabaud-Rychter followed a group of appliance designers through the design process of coffeemakers and food processors. The result is a suggestive analysis of the gen­ dered nature of the producer-consumer dichotomy. Vicky Singleton offers a highly theorized use ofANT in analyzing cervical screening programs. These case studies are most convincing when they employ field research rather than examples gleaned from secondary sources. Most ofthe technologies in question have already been wellstudied and are gendered in conspicuous ways. Hopefully, as this debate continues, researchers will take on other, less obvious, cases. In the introduction to The Social Construction of Technological Sys­ tems, Bijker, Pinch, and Hughes wrote that it began as a conversation between historians and sociologists over glasses of pink champagne. Both the virtues and the shortcomings of Grint and Gill’s volume suggest that perhaps another conversation is in order, between histo­ rians and sociologists interested in gender. This time, the cham­ pagne need not be pink. Arwen Palmer Mohun Dr. Mohun is an assistant professor of history at the University of Delaware. She is currently completing a comparative history ofgender and technology in the steam laundry industry. Instruments and the Imagination. Edited by Thomas L. Hankins and Robert J. Silverman. Princeton, N.J.: Princeton University Press, 1995. Pp. xiv+337; illustrations, notes, bibliography, index. $39.50 (cloth). An interestin scientific instruments has become an importantpart of new directions in the history of science. This interest is not nar­ rowly focused upon the artifacts themselves. Instead, key instru­ ments, placed in a societal and intellectual framework, are used to clarify the social, and especially the philosophical, foundations of modern science. Hankins and Silverman’s book extends this new approach to include the marginal instruments that hover some­ where between science and the magical and the occult. A new kind of instrument emerged in the Scientific Revolution 234 Book Reviews TECHNOLOGY AND CULTURE of the 17th century. Telescopes, microscopes, and air pumps were unlike traditional instruments because they distorted nature. The distortion was accomplished through magnification, in the case of optical instruments, or by creating an unnatural void in the evacu­ ated chambers of an air pump. These new instruments, termed phil­ osophical, quickly earned a place in early modern science. The origins of philosophical instruments are more complex and problematic than we have been led to suppose. Our familiarity with telescopes and microscopes masks the fact that many philosophical instruments began as devices of natural magic used to produce won­ drous, awe-inspiring effects. Hankins and Silverman investigate the place ofinstruments in natural magic and early modern science and reveal the philosophical presuppositions that governed their diverse uses. Convincing proof of the authors’ ability to make the most bizarre instrument yield a valuable philosophical and historical lesson is found in their chapter recounting the famous sunflower clock de­ vised by the 17th-century polymath, Athanasius Kircher. According to Kircher, a sunflower blossom placed on a freely moving platform will rotate following the motion of the sun. This botanical timepiece was said to operate indoors from sunrise to sunset on bright or cloudy days. The driving force, Kircher claimed, was the magnetic influence the sun exerted on the sunflower. Notable scientific fig­ ures, including Galileo and Descartes, joined the discussion about the clock’s operation. It would be wrong to declare Kircher a fraud when we learn that his sunflower acted like a clock because hidden magnets, driven by a clockwork mechanism, caused the blossom to rotate in a regular fashion, argue Hankins and Silverman. Kircher did...

Daytime Photometric Requirements for Pedestrian Signals

Forty-eight senior citizens participated in a field study of the visibility of letters and symbols in pedestrian traffic signals. Subjects were asked to identify signal messages from distances of 18.3 m and 29.3 m, with signal voltage set at 100 percent, 75 percent, and 50 percent of full power. Incandescent, fiber-optic, and light-emitting diode commercially available pedestrian signals were tested, including 22.9-cm and 30.5-cm rectangular signal housings and two round red-amber-green signals with symbol masks. Each subject was asked to identify the signal’s location in the test stimuli array, to name the signal’s display configuration (Walk, Don’t Walk, walking person, or hand), and to assess the signal’s brightness on a five-point scale. Analyses also were conducted on the percentage of responses about “too bright” signals and subject uncertainty about the signal message. Testing was conducted only on bright sunny days but did not include the worst-case condition of direct sunlight on the signal face. The analysis of recognition, uncertainty, and “too bright” responses suggested that a signal intensity of 25 cd minimizes the frequency of both “too bright” and uncertain responses regardless of size, distance, or technology, or whether the message is symbol or text. The data further suggest that 22.9-cm incandescent signals provide sufficient visibility with less phantom effect than 30.5-cm signals.

Transpiration of natural rain forest and its dependence on climatic factors

Sap flow was measured on several species from the tropical rain forest in French Guiana during two successive years over the dry season. On bright days, sap flow densities (i.e. sap flow per unit of sapwood area) exhibited high variations from one species to another. Higher rates (3 to 4 kg dim −2 h −1) were observed on late stage forest species like Dicorynia guianensis, Eperua falcata or E. grandifolia, and lower rates on Vouacapoua americana and Carapa procera (1.0 to 1.5 kg dm −2 h −1). Calculated stand sap flow ( F) was closely dependant on air vapour pressure deficit and less correlated to global radiation. A simple model of canopy conductance variations and hence of stand transpiration was derived from these measurements. Sap flow was linearly related to Penman Evapotranspiration (PET), the ratio F/PET being close to 0.75 under dry canopy conditions, as previously reported by Shuttleworth et al. (1984) in Central Amazon.

Changes in the photosynthetic light response curve during leaf development of field grown maize with implications for modelling canopy photosynthesis

Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (Asat) and convexity (Θ) of the light-response curve occurred during leaf development, but the maximum quantum yield of CO2 assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of Asat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (AL) to reductions in the Asat, Θ and the initial slope (Φ) of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, AL was ca. twice as sensitive to reductions in Asat than to reductions in Φ and Θ. In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of Φ was greatest during early leaf growth, while older leaves were most sensitive to depressions in Asat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.

Expression of Early Light-Inducible Proteins in Flag Leaves of Field-Grown Barley.

Early light-inducible protein (ELIP) mRNA and protein levels were analyzed during maturation and senescence of barley (Hordeum vulgare L.) flag leaves under field conditions. The data clearly demonstrate that ELIP mRNA levels are related to the sunlight intensity before sample collection. Levels of mRNAs encoding both low and high molecular mass ELIPs fluctuate in parallel. Changes in mRNA levels are accompanied by corresponding changes in protein levels except for days when average temperatures are high. Comparison of flag leaves at different stages of development in spring and winter barley varieties suggests that light-stress-regulated ELIP gene expression is independent of the developmental stage of the leaves. Although chlorophyll content, photosystem II (PSII) efficiency, and 32-kD herbicide-binding protein of PSII levels decrease drastically after the onset of senescence, ELIP mRNA and protein still accumulate to high levels on bright days.

Seasonal Affective Disorder

un-starved northerners have long flown south in the winter, as much for the psychological "lift" of bright light and long days as to escape the snow. Apparently, they intuitively knew what scientists are only now establishing: For some people, sunlight is curative. Light has been shown effective in treating a pattern of symptoms known as seasonal affective disorder (SAD)(1). SAD is a psycho-physiological syndrome characterized by symptoms of depression: most commonly, hypersomnia, social withdrawal, irritability, reduced libido, lethargy, weight gain, and an insatiable appetite, often with insatiable cravings for carbohydrates and/or sweets(2-4). Some victims whose SAD depression is severe may become suicidal(5). Symptoms usually appear in the fall and subside in the spring, but they may also react to changes in latitude, thus distinguishing this disorder from other forms of depression(6). Seasonal affective disorder has yet to be recognized as a distinct syndrome in the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association and widely accepted in the United States as the "bible" of mental-health clinicians and researchers. However, the DSMIII-R (third edition, revised) does suggest that certain depressive disorders be examined for a "seasonal pattern," which is defined as "a regular cyclic relationship between onset of the mood episodes and a particular 60-day period ofthe year"(7).

Of the hut I builded: the archaeology of Australia's history

Foreword Preface 1. 'There are no traces now': the material heritage of Australian history 2. 'They came by sea': the historical archaeology of precolonial contact 3. The birth of a nation: seeking the remains of early Sydney 4. 'It didn't always work': investigating the sites of failed settlements 5. The convict contribution: vestiges of the penal system 6. 'I built a little homestead': extracting history from houses 7. 'I cleared the land and fenced it': reading the rural landscape 8. 'Out of the ground came wealth': the archaeological evidence for mining 9. Made in Australia: information from industrial relics 10. 'The glad bright days have vanished': the potential of Australian historical archaeology Suggested activities Suggested reading Index.

Whole Leaf Carbon Exchange Characteristics of Phosphate Deficient Soybeans (Glycine max L.)

Low phosphate nutrition results in increased chlorophyll fluorescence, reduced photosynthetic rate, accumulation of starch and sucrose in leaves, and low crop yields. This study investigated physiological responses of soybean (Glycine max [L.] Merr.) leaves to low inorganic phosphate (Pi) conditions. Responses of photosynthesis to light and CO(2) were examined for leaves of soybean grown at high (0.50 millimolar) or low (0.05 millimolar) Pi. Leaves of low Pi plants exhibited paraheliotropic orientation on bright sunny days rather than the normal diaheliotropic orientation exhibited by leaves of high Pi soybeans. Leaves of plants grown at high Pi had significantly higher light saturation points (1000 versus 630 micromole photons [400-700 nanometers] per square meter per second) and higher apparent quantum efficiency (0.062 versus 0.044 mole CO(2) per mole photons) at ambient (34 pascals) CO(2) than did low Pi leaves, yet stomatal conductances were similar. High Pi leaves also had significantly higher carboxylation efficiency (2.90 versus 0.49 micromole CO(2) per square meter per second per pascal), a lower CO(2) compensation point (6.9 versus 11.9 pascals), and a higher photosynthetic rate at 34 pascals CO(2) (19.5 versus 6.7 micromoles CO(2) per square meter per second) than did low Pi leaves. Soluble protein (0.94 versus 0.73 milligram per square centimeter), ribulose-1,5-bisphosphate carboxylase/oxygenase content (0.33 versus 0.25 milligram per square centimeter), and ribulose-1,5-bisphosphate carboxylase/oxygenase specific activity (25.0 versus 16.7 micromoles per square meter per second) were significantly greater in leaves of plants in the high Pi treatment. The data indicate that Pi stress alters the plant's CO(2) reduction characteristics, which may in turn affect the plant's capacity to accommodate normal radiation loads.

EVALUATION OF PERFORMANCE OF THE 1 MW CERAMIC TUBE RECEIVER AT THE WEIZMANN INSTITUTE OF SCIENCE

Simulations were performed to evaluate the performance of a subsystem of the Thermochemical Pipeline Project (WITP) of the Weizmann Institute of Science. This subsystem includes a compressor, a 41 m long pipe, a cavity-type central receiver, and a mass-flow control element. The results show that the solar energy available for absorption into the tubes amounts to 1884 MWh/year, under the assumption that the working fluid (air) enters the cavity at 300 K and leaves at 1200 K. For bright days conditions, the average efficiency of the system increases from 56% (at 7 A.M. ) to 69% (at midday), with a yearly average efficiency of 63%. The mass flow is represented by the correlation: where FM is the total mass flow rate of the working fluid (kg/s(, and Ein is the total solar energy entering into the cavity (MW). It is suggested to increase the performance of the receiver by: 1) exploiting a part of the solar power flux existing as spillage, and 2) capturing the energy of the hot air otherwise dissipated by conve...

Stepping Westward

“When early summer with its bright clear days has brought the academic year to a close, emptying chalky classrooms and leaving books at rest on library shelves, then academic folk long to go on pilgrimages.”

Diel activity of the adult Argentine stem weevil

Abstract Feeding intensity of adult Listronotus bonariensis (Kuschel) in the laboratory increased linearly with temperature, between approximate lower and upper thresholds of 5°C and 42°C. Diel fluctuations in abundance, as indicated by sweep netting, was used as a measure of field activity. During summer, activity was mainly nocturnal, with a peak after sunset, but some activity occurred during overcast and bright sunny days. Summer weevil activity during darkness was related to temperature. In winter, activity occurred predominantly during daylight. Day and night activity was related to temperature; on many winter nights the temperature was below the lower threshold for activity.

Seasonal Response of ‘Anjou’ Pear Trees to Different Irrigation Regimes. I. Soil Moisture, Water Relations, Tree and Fruit Growth

Abstract Mature bearing pear [Pyrus communis L. ‘Beurre d’Anjou’ (‘Anjou’)] trees in an arid climate were irrigated weekly at 125% of pan evaporation (wet), biweekly at 100% of pan evaporation (normal), or irrigated only twice (dry) during the summer (1980, 1981), and were fertilized with and without 0.9 kg of supplemental N. Prior to final fruit harvest in 1981, depletion of available soil moisture (ASM) averaged 10%, 16.7%, and 89% for the wet, normal, and dry treatments, respectively. Mid-day leaf water potential (ψL) was correlated with the level of ASM only on bright days of high vapor pressure deficit. Stomatal conductance (κs) and transpirational flux density (F) of dry treatment leaves was lower than that of either wet or normal treatment leaves ψL exceeded −1.4 to −1.7 MPa. Resistance to vapor (water) transport (Rν) of fruit was independent of irrigation regime. Terminal buds had set on shoots from all 3 irrigation regimes at 58 days after full bloom (AFB) in 1981, but resumed growth on normal and wet treatment shoots at 87 days AFB. On 7 of 10 sampling dates during 1981, dry treatment fruit weighed less than normal or wet treatment fruit.