Net Hours Research Articles

Experimental evaluation of a non-isothermal high temperature solar particle receiver

The experimental evaluation of a solar particle receiver is reported. Concentrated irradiation was converted into thermal energy in a gas flow by a cloud of radiation absorbing sub-micrometre carbon particles. Average solar concentration was 2500 on an 80 mm diameter aperture. Cloud particle mass fractions were in the range of 0.2–0.5%. Exit gas temperatures exceeding 2100 K were measured with nitrogen, 1900 K with CO 2, and 2000 K with air, which is 1000 K higher than previously reported using a particle receiver. The air heating tests reveal that the particle/gas heat transfer exceeded the oxygen/carbon oxidation rate up to 2000 K. A carbon particle mass fraction of less than 0.5% in the gas stream ensures that the heated air contains only a negligible amount of CO 2 and NO x . The axial receiver cavity wall temperature increased with distance from the aperture, peaking at 60% of the total cavity length, and then slightly decreasing towards the exit plane. At steady conditions, the wall temperatures in the gas exit plane were at least 100 K cooler than the gas’s, alleviating structural constraints associated with conventional volumetric receivers. Estimated radiation to thermal energy conversion efficiencies surpassed 80% at the highest mass flow rates. The receiver accumulated over 12 net hours at temperatures above 1700 K without any major failures.

Bat Species Richness in Atlantic Forest: What Is the Minimum Sampling Effort?

ABSTRACTSpecies lists are sources of information for studies of both conservation and macroecology. It is, however, important to differentiate between relatively complete lists and extremely incomplete ones. The aim of this study was to evaluate how sampling effort typically used in inventories affects the number of bat species captured in areas of Atlantic Forest in southeastern Brazil. We also evaluated if the number of sampled sites, size of the sampled area, and sampling effort (net hours) affect species richness. We used previously reported data from studies in Rio de Janeiro, São Paulo, and Minas Gerais States, and our own data collected during 1989 and 2001. Nonlinear models fit well the data for Rio de Janeiro and Minas Gerais States and all states together, but not for São Paulo State. Genera richness showed a similar pattern to that of species richness. The model used to explain the relationship between species richness and size of the study area, number of sites, and sampling effort sampled was significant. The number of sites sampled explained a significant part of the variation observed; however, other variables contributed nothing to the model, suggesting that capturing beta diversity is the most important aspect of biodiversity surveys for bats, and that increasing net hours at a given location is much more inefficient than distributing net hours across locations. We suggest 1000 captures as the minimum necessary when sampling with mist nets to capture the majority of phyllostomid species for a given site (alpha diversity). In addition, we suggest that shifting the position of the mist nets between nights will increase the probability of capturing more species.RESUMOAs listas de espécies são fontes de informações para estudos, tanto de conservação quanto de macroecologia. Entretanto, é importante diferenciar entre listas relativamente completas daquelas seriamente incompletas. O objetivo deste estudo foi avaliar como o esforco amostral mínimo tipicamente usado em inventários afeta o número de especies de morcegos capturados em áreas de Mata Atlãntica do sudeste do Brasil. Nós também avaliamos se o número de pontos amostrados, o tamanho da área amostrada e o esforço de captura (hora‐rede) afetam a riqueza de espécies. Nós usamos dados disponíveis de estudos desenvolvidos nos estados do Rio de Janeiro, São Paulo e Minas Gerais, e os nossos próprios dados coletados de 1989 a 2001. Modelos não‐lineares se ajustaram para os estados do Rio de Janeiro e Minas Gerais e todos os estados juntos, mas não para o Estado de São Paulo. A riqueza de gȩneros mostrou o mesmo padrão da riqueza de espécies. O modelo usado para expliçãr a relacao entre riqueza de espécies e tamanho da área de estudo, número de pontos amostrados e esforço amostral foi significative. O número de pontos amostrados explicou uma parte significante da variação observada. Contudo, as outras variáveis não contribuiram para o modelo, sugerindo que capturar a diversidade Beta é o aspecto mais importante de inventários de biodiversidade para morcegos, e que o aumento de horas‐rede numa dada localidade é muito mais ineficiente do que distribuir horas‐rede entre localidades. Nós sugerimos 1000 capturas como o mínimo necessário para amostrar, com redes de neblina, a maioria das espécies de filostomídeos de uma dada área (diversidade Alfa). Adicionalmente, sugerimos que mudando a posição das redes entre noites aumentará a probabilidade de capturar um maior número de espéciesS.

Limitations of Interview-Based Risk Assessment of RF Exposure from Appliances

This study was conducted to assess the quality of interview-based exposure estimates obtained in a large epidemiologic case-control study: The Northern Germany Leukemia and Lymphoma Study (1997-2002) (NLL). The NLL used standardized, face-to-face, computer-assisted interviews to record subjects' lifetime use of radiofrequency (RF)-emitting appliances such as cellular telephones, cordless telephones, baby monitors, and television headphones. Exposure assessment comprised 3 levels of precision: ever use, gross vs. net appliance-years, and lifetime cumulative exposure hours. In the current study, the authors analyzed data from 3041 interviews of NLL controls, representing an age-stratified random sample of the general populations of 6 counties in Northern Germany. Weighted kappa coefficients for gross vs. net appliance-years for men were 0.59 (95% confidence interval [CI] = 0.46, 0.71) for baby monitors and 0.98 (95% CI = 0.97, 0.99) for cordless phones; for women, the coefficients were 0.68 (95% CI = 0.56, 0.79) and 0.97 (95% CI = 0.94, 0.98), respectively. Weighted kappa values were considerably lower when net appliance-years and lifetime cumulative exposure hours were compared. Study results demonstrated that interview information on use of RF-emitting appliances, when measured at different levels of precision, can result in misclassification and biased risk estimates.

Abundance and Richness of Neotropical Migrants During Stopover at Farmstead Woodlots and Associated Habitats in Southeastern South Dakota

Woodland habitats are scarce in the northern Great Plains and were historically concentrated along river corridors. Over the past century, riparian habitats in this area have been much reduced, but new woodland habitats in the form of farmstead woodlots and shelterbelts have appeared. We used mist net sampling and point counts to document richness and abundance of Neotropical migrant birds in farmstead woodlot habitats during spring and fall migrations (1996–1997) in southeastern South Dakota. A total of 668 individuals of 30 Neotropical migrant species (excluding the taxa Coccyzus, Troglodytes, Mimidae, Icterus and Pheucticus, in which migratory and non-migratory individuals were difficult to distinguish) was captured in 4342 net hours (using 9-m, rather than the standard 12-m mist nets) in spring. The corresponding fall totals (again using 9-m nets) were 3250 net h, 231 individuals and 29 species. If fall captures in a ragweed (Ambrosia trifida) patch occurring within the woodlot are included, however, the fall totals were 5107 net h, 1211 individuals and 29 species. Overall densities of Neotropical migrants from point counts were 1302 birds · km−2 in spring and 898 birds · km−2 in fall. Capture and point count data followed similar phenologies, with peak abundance during mid-May in spring and late August-early September in fall. Both methods indicated seasonal abundance differences for some species, with Swainson's thrush (Catharus ustulatus) and blackpoll warbler (Dendroica striata) more abundant in spring. Orange-crowned (Vermivora celata), Nashville (V. ruficapilla) and Wilson's (Wilsonia pusilla) warblers were more abundant in fall. Captures within the woodlot were evenly distributed among different microhabitats during spring migration, but fall captures occurred disproportionately in scrubby edge-related microhabitats, especially in ragweed, suggesting that seasonal shifts in microhabitat selection may occur within woodlots. Density and capture rate data were similar to previously reported values for riparian habitats in this area. Thus, a diverse assemblage of Neotropical migrants occurs in woodlots during migration, suggesting that woodlots are regularly used as stopover sites and supplement available natural woodland habitats along river corridors.

Factors Influencing Growth and Body Condition of Alewives in Connecticut Lakes

ABSTRACT Alewives were collected by nighttime gill netting during summer 1999 from 12 Connecticut lakes that support landlocked populations to determine relationships between population characteristics and physicochemical lake variables. Mean catch-per-unit-effort (CPUE) ranged from 0.2 to 16.4 age-1 and older alewives per net hour. Maximum ages of alewives among lakes ranged from two to five years, and mean back-calculated length-at-age-1, used to index growth rate, ranged from 78 to 146 mm. Mean back-calculated length-at-age-1 was positively correlated with mean relative condition factor (Kn), watershed area:lake surface area ratio, watershed area:lake volume ratio, lake surface area:lake volume ratio, conductivity, total nitrogen, alkalinity, calcium, magnesium, and chlorophyll a, and negatively correlated with retention time, maximum lake depth, mean lake depth, and transparency. Mean Kn ranged from 0.93 to 1.23 and was positively correlated with mean back-calculated length-at-age-1, watershed area:lake volume ratio, lake surface area:lake volume ratio, total nitrogen, chlorophyll a, and potassium, and negatively correlated with maximum lake depth and transparency. Growth and Kn of alewives were highest in shallow, productive lakes with low transparencies. CPUE was not related to growth rate or to any physicochemical lake variable.

The bat fauna of Lamanai, Belize: roosts and trophic roles

Thirty-six of the 70 species of bats known from Belize were recorded from the area around Lamanai, Orange Walk County: two in roosts and 34 in about 680 mist net hours that produced 560 captures. Day roosts used by 35 of the species were located using radio-tracking (Sturnira lilium, Platyrrhinus helleri, Centurio senex and Bauerus dubiaquercus) or general searching for roosts (Rhynchonycteris naso, Saccopteryx bilineata, Saccopteryx leptura, Dicli durus albus, Mimon bennettii, Micronycteris schmidtorum, Carollia brevicauda, Carollia perspicillata and Eptesicus furinalis). Data on the day roosts of 23 other species were determined from the literature. Most species reported from Lamanai (19) roosted in hollows, while others used foliage (6), tents (3), sheltered sites (2), crevices (2), open sites (1), and a few species used more than one type of day roost (hollows and crevices (1); hollows and foliage (1); hollows, foliage and tents (1)). The fauna consisted of 13 aerial foragers, 9 gleaners, 11 fruit/leaf eaters, one trawler, one flower-visitor and one blood-feeder. In day roost use and foraging behaviour, the Lamanai fauna did not differ significantly from that of Paracou, French Guiana, but both these locations differed from the bat fauna of Kruger National Park, South Africa, in foraging behaviour.

A bat (Chiroptera) survey of Mora rainforest in Trinidad's Victoria-Mayaro Forest Reserve

The bat fauna of the Mora excelsa-dominated rainforest in the Victoria-Mayaro Forest Reserve (VMFR) in south-east Trinidad was assessed over a six-week period. Trapping effort totaled 271 mist net hours and caught 143 bats of 22 species at a rate of one bat every two net-hours. Simpsons diversity index (1/D) was 1.28 for primary Mora forest and extrapolation using Chaos' estimator, a non-parametric method, estimated the total number of species as 39. Phyllostomid bats of the subfamilies Phyllostominae and Stenodermatinae were well represented, and frugivores predominated in number, accounting for 77% of all captures in primary forest. The most abundant bat, the ground-storey frugivore, Carollia perspicillata, accounted for 43% of all captures in primary forest and, in contrast to most bats, was also abundant on man-made paths through the forest. Four species not previously recorded from the reserve, Tonatia bidens, Trachops cirrhosus, a Myotis sp., and the rare Phylloderma stenops, were captured, bringing the total number of bats species known from the reserve to 35. Thus, over half (52%) of Trinidad's 67 bat species occur in this one forest reserve, making it a high priority area for effective protection and management.

Species Richness and Pollen Loads of Hummingbirds Using Forest Fragments in Southern Costa Rica1

In many areas of the humid tropics, relatively small patches of forest is the habitat most commonly available for forestdwelling organisms. To assess resident hummingbird use of forest fragments near the Las Cruces Biological Station in southwestern Costa Rica, we mist-netted birds in five fragments (0.3‐20 ha; ca 1300 m elev.) and the station’s 226ha forest preserve (ca 900‐1280 m elev.). From January 1994 through mid-March 1999, we recorded 1069 captures of 21 hummingbird species during 49,900 net hours. Species richness, diversity indices, and capture rates increased asymptotically with patch size, as expected. We captured 16 hummingbird species in both the largest fragment (20 ha) and in the nearby forest preserve. Non-forest hummingbirds did not occur more frequently in the fragments than in the preserve, and all fragments supported a mixture of forest-interior and canopy-dwelling hummingbird species, along with a diverse group of hummingbird-pollinated plants. Phaethornis guy was common at all sites and visited .13 plant species in the fragments during the 1998 dry season (based on analyses of pollen collected from the birds’ heads). In contrast, Eutoxeres aquila was found at only the largest three sites (10, 20, and 226 ha) and carried pollen from only one plant species during the 1998 dry season. Lampornis castaneoventris, a high-elevation hummingbird species, was far more common in the fragments than in the preserve, while three species typically found at lower elevations were rare in the fragments and common in the preserve. These distribution patterns could be influenced by local climatic differences because the fragments are higher and receive more cloud mist and annual precipitation than the preserve. Our data show that pollen loads on hummingbird species vary, and this has implications for gene flow among hummingbird-pollinated plants. Although our results are consistent with previous reports that hummingbird species may be less affected by deforestation than insectivorous avian species such as army ant followers, it is important to note that from the perspective of the genetics and demographics of hummingbird-pollinated plants, the important issue is whether appropriate pollinator species are able to move plant propagules among subpopulations of plants in fragmented landscapes. We conclude that the biodiversity of tropical forest fragments as small as 10 to 20 ha is high enough to warrant long-term preservation of these areas, especially if they are located near larger tracts of forest.

MIGRANT STOPOVER AND POSTFLEDGING DISPERSAL AT A MONTANE FOREST SITE IN VERMONT

To investigate the use of high elevation fir forests by fall passage migrants, we conducted standardized mist-netting and banding at a 1150-1175 m elevation site on Mt. Mansfield in north-central Vermont during the autumns of 1995-1997. Overall, we captured 3024 individuals of 62 species in 10,048 cumulative net hours (30.1 birds/100 net hr). We divided species into 3 classes: (1) those breeding regularly on Mt. Mansfield above 916 m elevation (16 species), (2) those breeding only sporadically or at very low densities above 916 m (6 species), and (3) those occurring only as transients (40 species). Breeding species accounted for 68% of new captures, followed by transients (22%), and sporadic/low density breeders (10%). Of the ten most abundant species captured, only two, Black-throated Blue Warbler (Dendroica caerulescens)and Ovenbird (Seiurus au- rocapillus), were transients, accounting for 50% and 9%, respectively, of all transient captures. Hatching-year birds accounted for 94% of known-age transients and 81% of known-age individuals among locally breeding species. Recapture rates of transients were extremely low (0.3%), while recapture rates among species known to breed locally (including presumed transient individuals) were higher (2.2%). Nearly 75% of all birds captured were very lean at first capture, and only 26% of recaptured individuals increased their fat scores between first and final captures. Weight changes of recaptured birds varied: 48% lost weight, 44% gained weight, and 8% maintained the same weight between first and final captures. Our data suggest that conditions on the Mt. Mans- field ridgeline are not conducive to prolonged migratory stopovers and that most migrants may be unable to meet their energetic requirements for continued migration. However, we believe that montane forest habitats may be preferentially selected by those migrants that use them for breeding. We further believe that montane fir forests may be an important postfledging dispersal habitat for Black-throated Blue Warblers and other low or mid-elevation breeding species, and that conservation planning for montane forest sites should carefully consider the needs of migrants outside the breeding season. Received 18 March 1999, accepted 25 Oct. 1999. Of the numerous demands that migrant birds face during their annual migrations, se- lection of enroute stopover habitat is para- mount. Choice of stopover habitat may play a pivotal role in determining a migrant's surviv- al and is dependent both on intrinsic suitabil- ity of the habitat and on extrinsic factors such as weather, time constraints, energetic condi- tion, and availability of the habitat (Hutto 1985, Moore and Simons 1992). Stopover mi- grants must resolve potentially conflicting needs to meet their energy demands, avoid predation, adjust to unfamiliar habitats, com- pete with other migrants and residents, and deal with unfavorable weather conditions (Moore et al. 1995). Loss or degradation of

A Survey of the Small Mammals of the Gonja Forest Reserve, Tanzania

ABSTRACT Small mammals were surveyed in the lowland forest of the Gonja Forest Reserve of north-eastern Tanzania. In 565 trap-nights 10 rodents (three species) were captured. In 12.5 net hours 27 bats (11 species) were netted. Comparisons of similar surveys in nearby montane forests indicate a lower density and diversity of rodents and shrews in Gonja than in higher elevation habitats. Information is presented on external measurements, weight and reproductive condition of the specimens collected.

Diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants: test of a feedback-based model

assimilation. While the purely photosynthetic assumption is convenient, a more realistic metabolism subA simple model is proposed to describe diurnal net model is needed. nitrate uptake rate patterns observed experimentally on young plants grown under constant non-limiting Key words: Light/dark cycles, day, night, water content, nutrition. It rests on two hypotheses: net uptake rate nitrogen, hydroponic. is under negative feedback control by internal plant nitrate content, and nitrogen metabolism occurs only during the light period. The model parameters were Introduction determined from the results of three independent experiments performed under non-disturbing condi- During plant growth, nitrate uptake is mainly determined tions in a growth room at constant air and solution by dry mass production in relation to ontogeny and temperatures. Net hourly nitrate uptake rate was environmental parameters (Imsande and Touraine, 1994). measured through a diurnal cycle and after an However, at an hourly time scale, under constant nutriextended 28 h period of darkness. It increased con- tion, uptake rate undergoes continuous variations tinuously during the light period and decreased during (Clement et al., 1978; Triboi-Blondel, 1979; Pearson et al., the dark period. Under prolonged darkness, net uptake 1981; Le Bot and Kirkby, 1992; Delhon et al., 1995a; declined to an asymptotic positive uptake rate of about Andriolo et al., 1996), with peak values during day time, 10’5 mol h’1 g’1 total plant dry weight. The measured and lowest values during the night. This eVect, clearly hourly nitrate uptake rate values were consistent with related to light interception, is based on still unclear independent determinations of long-term nitrate and mechanisms. On a large time scale, nitrate uptake correltotal N accumulations in the plant. Realistic simula- ates with transpiration, but it has been shown that in the tions of experimental data are achieved with the pro- diurnal cycle they are independent ( Triboi-Blondel, 1979; posed model. Furthermore, the maintenance of a Le Bot and Kirkby, 1992; Delhon et al., 1995b; Andriolo positive net uptake rate, measured in non-growing et al., 1996). As nitrate uptake also correlates with CO 2 plants subjected to prolonged darkness, is explained assimilation (Clement et al., 1978), an indirect control by in the model by the continuous increase of plant water photosynthesis has been suggested ( Wild et al., 1987). content. The importance of the diurnal variations of The flow of carbon compounds from the shoots might plant water content for nitrate uptake rate is emphas- regulate nitrate uptake, an ATP-dependent process, ized and gives consistency to the homeostasis hypo- through root respiration (Glass, 1989). Indeed, diurnal thesis of the model. The diurnal changes in nitrate root respiration seems closely related to nitrate uptake uptake predicted by the model are strongly dependent rate (Hansen, 1980). However, this hypothesis is still under discussion, as uptake regulation is expected to

Responses of Avian Assemblages to a Natural Edge in a Chaco Semiarid Forest in Argentina

We assessed differences in breeding bird assemblages and vegetation struc- ture between a natural forest edge and the adjacent forest interior in an old-growth Chaco forest of Argentina. The edge had a dense cover of thin stems at low heights and high species richness of woody plants, whereas the interior had high canopy cover, high tree density, high density of thick stems, and a more heterogeneous vertical profile. We used mist-net and point-count surveys to sample bird assemblages, capturing 374 birds during 3,553 net hours and detecting 826 individuals during point counts. Overall, we recorded a total of 74 bird species. Bird species richness and bird abundance appeared to be higher in the edge, al- though differences between habitats were not entirely consistent for mist-net and point- count data. Several early successional bird species were closely associated with edge, and other species occurred exclusively in the interior of the forest. At the guild level, frugivores, terrestrial granivores, arboreal granivores, terrestrial insectivores, and long-flight insect- hunters were more abundant at the edge than in the interior, whereas the reverse was true for bark insectivores and short-flight insectivores. Our results indicate that edge and interior bird assemblages are different. The distribution of birds between these habitats appeared to reflect constraints on habitat use imposed by vegetation structure, and also could be related to differential distribution of food resources, especially fruit. Received 27 February 1997, ac- cepted 11 November 1997.

The Effect of Environmental Variables on Capture Success of The Platypus Using Gill and Fyke Nets.

Capture success of platypuses using gill and fyke nets over the period 1986-1993 has been assessed against a range of environmental variables using the Spearman's Rank Correlation Coefficient and in some cases simple linear regression models. Approximately 90% of all animals captured during this study have been netted between 1730 hours and 0I00 hours regardless of age or sex. The peak capture period during which approximately 60% of animals were captured is between 1730 and 2230 hours. Variables examined included; number of platypuses captured, giII and fyke net hours, number of nets used, time nets set up and taken down, maximum and minimum day temperatures, time of sunrise and sunset, moon phase, time of moon rise and set, cloud cover, wind and rain conditions during trapping, 24 hour rainfall history prior to netting and some flow data. The number of nets, netting time, rainfall within 24 hours and temperature conditions all effect the chance of platypus capture in fyke nets (p<0.05). The number of gill nets and the time they are utilised are both positively correlated with platypus captures (p<0.05). However, there are differences between sexes and age groups. Using gill nets, platypuses are more likely to be captured during clear nights and less likely to be captured during summer months. The probability of trapping males, females, adults and juveniles varies with the seasons.

Local employment concentration and hourly earnings

Using data from the 1980 PUMS D and OLS regression, I indirectly test a model of how local labor market structure affects individual hourly earnings through the intra-area rollout effect. I find (1) beyond influencing wages through the jobs individuals receive, the local labor market's employment structure has a very small impact on individual hourly earnings and (2) local employment concentration in high paying industries tends to have a positive impact on individual net hourly earnings; employment concentration in low paying industries tends to negatively influence individual net hourly earnings.

The economic design of [formula omitted] control charts with repair cost depending on detection delay

This study extends Duncan's [1] model to two different manufacturing process models in which the processes continue and discontinue in operations during the search for the assignable cause. A more realistic assumption considered in this paper is that the cost of repair and the net hourly out-of-control income are functions of detection delay. In the continuous model, detection delay is defined as the elapsed time from the time when the shift of the process occurs until it is identified by x control charts and the assignable cause is eliminated. The discontinuous model defines detection delay as the time interval from the occurrence of the process shift to the completion of testing a set of samples and interpreting the results. An efficient procedure is developed to determine the optimal designs without using any approximation approach. Thus, the proposed procedure can obtain the truly optimal designs rather than those approximate designs determined by Duncan [1] and other subsequent researchers. This paper illustrates several numerical examples and makes some relevant comparisons. The results indicate that this optimal solution procedure is more accurate than that of Panagos et al. [2]. Also, detection delay is sensitive to the economic design of x control charts.

The Effects of Hurricane Hugo on Bats of the Luquillo Experimental Forest of Puerto Rico

Natural disturbances can have large effects on ecosystem structure and function depending on their scale, intensity, and frequency. On 18 September 1989 Hurricane Hugo struck Puerto Rico, with the eye of the hurricane passing within 10 km of the Luquillo Experimental Forest. This provided a rare opportunity to evaluate the effects of an infrequent but large scale and high intensity disturbance on tropical bat species. Data on demographic parameters of three common phyllostomid bats (Artibeusjamaicensis, Stenoderma rufum, and Monophyllus redmani) were examined for three years prior and three years after the hurricane. Population levels as estimated by captures per net hour of all three species were affected by Hurricane Hugo. Populations of A. jamaicensis and M. redmani returned to predisturbance levels within two years. In contrast, population levels of S. rufum declined to about 30 percent of prehurricane levels and have not recovered after three years. Moreover, telemetry data indicate that foraging and home range size expanded to encompass an area approximately five times larger than its prehurricane size. The cost of foraging, in terms of time and energy, may be considerably elevated over prehurricane scenarios. In fact, a significant change in the age structure of the population (juvenile individuals have been absent from the population since Hurricane Hugo) as well as significant decline in the percent of reproductively active females indicate a failure to reproduce in the posthurricane environment.

Sustainable Use of the Tropical Rain Forest: Evidence from the Avifauna in a Shifting‐Cultivation Habitat Mosaic in the Colombian Amazon

We carried out a one‐year study of the avifauna along a regeneration gradient created by indigenous shifting cultivation in the Colombian Amazon rain forest. Regenerating one‐hectare crop fields, from 1 to 17 years after abandonment, and undisturbed understory sites were compared in a sample effort of 4323 net hours. We made 878 captures of 103 species belonging to 11 trophic groups. Differences in species richness and number of individuals captured between regenerating areas and primary forest were low. A comparison of similarity indices among the sites for each habitat type showed no consistent differences, suggesting similar levels of local heterogeneity. Similarity indices calculated between sites of different‐aged habitats, however, showed that young secondary growth at less than 10 years of abandonment was least similar to other sites, whereas old secondary growth between 13 to 17 years of abandonment, and forest understories, had the most similar avifauna. Two trophic groups were absent from the samples of the forest interior, and the abundance of the other nine varied among sites of regeneration. We conclude that slash and burn agriculture represents a high‐intensity, small‐magnitude disturbance to the forest avifauna. Large changes occur when the crop field is established and last until about 10 years after abandonment. Our data suggest that abandoned crop fields older than this age mimic the natural patch dynamics of the forest, making this type of agriculture an example of a potentially sustainable use of tropical forests, at least from the standpoint of its impact on bird communities.

Tax reform, population ageing and the changing labour supply behaviour of married women.

"The burden of financing retirement incomes in an ageing population is predicted to rise sharply in future decades. This paper investigates the effects of reforms to the Australian tax-benefit system involving a greater reliance on proportional taxation for raising revenue and a more targeted welfare system for cutting government expenditure, in order to reduce expected budget deficits. Estimates of changes in net incomes and hours of work suggest that reforms of this kind shift the tax burden to lower and middle income households with a second earner and that they can have counter-productive labour supply effects. The study explores the impact of projected increases in female work force participation and illustrates the importance of shifts in the labour supply of married women in predicting the fiscal effects of demographic change."

Endogenous extrapolation of labor force participation rates of married women

This study establishes a relationship between the age-specific participation rates of married women and a limited number of exogenous variables, such as the number of young children present in the household, the male and female unemployment rate, the net hourly wage, the attained level of education and the availability of part-time work. The relationship that results is used, in combination with the extrapolated exogenous variables, to predict the participation rate for the period 1986–1990. Multiplication of the predicted participation rates and the population forecast results in a prognosis of the number of married women in the labor force. The empirical approach consists of a pooling of cross-section and time-series data. A logistic transformation of the endogenous activity rate is regressed on a linear combination of exogenous variables including an age-specific constant term. This method appears more reliable than a pure exogenous extrapolation of the participation rates because it offers the possibility to predict the exogenous variables with a reasonable degree of accuracy. Moreover this method makes it possible (through simulation) to estimate the scope of such things as discouraged worker effects on the participation process.

Pancreatic carboxypeptidase hydrolysis of bile acid-amino acid conjugates: Selective resistance of glycine and taurine amidates

To find a possible explanation for the selective hepatic conjugation of bile acids with glycine or taurine, the N-acyl amidates of cholic acid and a number of amino acids and amino acid analogues were synthesized, and their susceptibility to hydrolysis by pancreatic juice, gastric juice, serum, or small intestinal mucosal enzymes was measured. Deconjugation by pure carboxypeptidase A and B was also examined, and hydrolysis by these tissue fluids and enzymes was compared with that mediated by a bacterial cholylglycine hydrolase. Human pancreatic juice efficiently hydrolyzed cholyl conjugates of all neutral-l-amino acids (cholyl-l-alanine, cholyl-l-valine, cholyl-l-leucine, and cholyl-l-tyrosine), except cholylglycine. The net hourly rate of hydrolysis (in micromales per milligram protein per hour) increased when the terminal residue was aromatic or branched aliphatic, and appeared to be specific for l-α-amino acids as cholyl-β-alanine and cholyl-d-valine were not cleaved. From cholyl glycylglycine, only the terminal glycine was efficiently removed. Cholyltaurine and cholyl conjugates with the methyl and propyl analogues of taurine were resistant to hydrolysis. Two basic amino acid conjugates (cholyl-l-lysine and cholyl-l-arginine) were cleaved, whereas conjugates of acidic amino acids (cholyl-aspartate and cholyl-cysteate) were not cleaved. Studies using pure enzymes showed that bovine carboxypeptidase A hydrolyzed the cholyl conjugates of the neutral l-α-amino acids with similar specificity as observed for the human pancreatic juice, whereas bovine carboxypeptidase B cleaved the basic amino acid conjugates. Cholyl-l-lysine and cholyl-l-arginine were also cleaved by serum and plasma, which are known to possess carboxypeptidase activity. Cholyl conjugates were not cleaved by gastric juice, by trypsin, or by homogenates of rat small intestinal mucosa. In contrast, all cholyl conjugates were cleaved by a bacterial cholylglycine hydrolase. These experiments indicate that glycine and taurine amidates of cholic acid differ from a number of other conjugates with neutral and basic amino acid in being resistant to hydrolysis by pancreatic and plasma carboxypeptidases. These data, together with other data indicating that bile acid conjugation greatly decreases passive intestinal absorption, indicate that a physiologic function of bile acid conjugation with glycine or taurine is to form surfactants that remain indigestible and rather nonabsorbable during digestion in the proximal small intestine.