Hourly Production Rates Research Articles

Will Aggregator Reduce Renewable Power Surpluses? A System Dynamics Approach for the Latvia Case Study

Power demand-side management has been identified as one of the possible elements towards a more flexible power system in case of increased capacities of variable renewable energy sources—solar and wind energy. The market coordinators or aggregators are introduced to adjust the electricity consumption by following the market situation. However, the role of aggregators is mainly analysed from the economic perspective, and the demand side management is performed to maximise the utilisation of low price power during off-peak hours. However, this research focuses on analysing the introduction of aggregators as a future player to increase the total share of renewable power and decrease the surplus solar and wind electricity occurrence. An in-depth system dynamics model has been developed to analyse the hourly power production and power consumption rates at the national level for the Latvia case study. The results show that introducing aggregators and load shifting based on standard peak shaving can increase the share of surplus power and does not benefit from increased utilisation of solar and wind power. On the contrary, demand-side management based on available RES power can decrease the surplus power by 5%.

Oxygen and Triple Oxygen Isotope Measurements Provide Different Insights into Gross Oxygen Production in a Shallow Salt Marsh Pond

The metabolism of estuarine environments is often estimated by measuring changes in dissolved oxygen concentrations. A central assumption of common oxygen-based approaches is that oxygen consumption rates (primarily respiration) are similar under light and dark conditions. Evaluating this assumption is critical, especially in benthic-dominated systems, because differences between daytime and nighttime respiration could result in underestimation or overestimation of ecosystem productivity. We evaluated rates of gross oxygen production over hourly to seasonal time scales in a shallow, temperate salt marsh pond. To assess whether a dissolved oxygen diel mass balance underestimated gross oxygen productivity, we compared rates using this traditional approach and using the triple oxygen isotope tracer of photosynthesis. This is a powerful combination because the triple oxygen isotope approach is theoretically insensitive to respiration. The methods agreed well over daily to seasonal time scales. However, during midday periods of peak light and productivity, the triple oxygen isotope approach resulted in higher hourly scale gross oxygen production rates. The timing and magnitude of this short-term difference is consistent with light-dependent oxygen uptake fluxes including photoreduction and/or light-stimulated community respiration. Finally, aquatic vegetation was associated with variability in productivity across the pond. Such small-scale environmental heterogeneity is evidence that this shallow pond was not laterally well mixed, and likely contributes to the dynamism of these common estuarine environments.

Small-Scale Timber Harvesting: Mule Logging in Hyrcanian Forest

Animal-powered logging is a labour-intensive operation. Mule logging is still performed in the Hyrcanian forest ecoregion in Iran as a small-scale harvesting method. Mule logging in Namkhaneh district of Kheyrud Forest within this ecoregion was studied to develop hauling regression models and estimate haulage costs. A continuous time study was conducted of hauling of sawn-lumber, pulpwood and fuelwood, to assess mule logging productivity and cost for sawn-lumber and pulpwood as well as fuelwood hauling. Hauling distance was found to be the most important cost factor in wood extraction by mule. The hourly production rates of hauling with mule were 0.84, 0.52 and 0.42 m3 for sawn-lumber, pulpwood and fuelwood, respectively. The cost of the mule hauling system USD 13 per productive mule hours. Hourly costs of mule hauling of sawn-lumber, pulpwood and fuelwood logging were 15.5, 25, and 30.6 USD/m3. Increasing hauling distances caused a linear increase in haulage cost. There appears to be an opportunity to reduce cost of log production by increasing scheduled work hours, wider utilization of mules and reducing labour cost.

Technological Jump in Aluminium Ingot Production

Abstract Usual production of modern cast houses includes semi products and re-melt products. Billets, slabs and rod belong to the family of semi products, while T-bars, sows and ingots are incorporated in the category of re-melt products. Re-melt forms have been developed to be easily transported and easily processed in locations even far away from the cast house where these have been produced. Unlike sow and T-bars, ingots need to be stacked in bundles and securely strapped to allow safe and easier handling and transportation. Yet, the ingots can be processed one-by-one by small users or can be loaded into the melting furnace bundle-by-bundle. The shape and weight of pure aluminium ingots of the old prior art were determined with two aims: maximization of the production rate and minimization of the production costs: for many years heavy ingots have been produced by pouring molten aluminium into a chain of open top moulds. The traditional complex shape of the ingots was intended to facilitate de-moulding operations and bundle piling. For the above reasons, the most common ingot weight worldwide has ranged, until now, from 22.5 to 23.5kg. Now a new technology launched by Continuus-Properzi offers bigger hourly production rates and handy, safe and sound ingots of 30 pounds (13.6kg) as well as more compact and stable bundles. These advantages are paralleled by low maintenance costs and a very high yield near to 90%. With similar investment and production costs the new technology can give a 30% yearly production increase and winning ingot characteristics.

Biovolatilization of Metal(loid)s by Intestinal Microorganisms in the Simulator of the Human Intestinal Microbial Ecosystem

Methylation and hydrogenation of metal(loid)s by microorganisms are widespread and well-known processes in the environment by which mobility and in most cases toxicity are significantly enhanced in comparison to inorganic species. The human gut contains highly diverse and active microbiocenosis, yet little is known about the occurrence and importance of microbial metal(loid) methylation and hydrogenation. In this study, an in vitro gastrointestinal model, the Simulator of the Human Intestinal Microbial Ecosystem (SHIME),was used for investigating volatilization of metal(loid)s by intestinal microbiota. Suspensions from different compartments of the SHIME system analogous to different parts of the human intestinal tract were incubated with different concentrations of inorganic Ge, As, Se, Sn, Sb, Te, Hg, Pb, and Bi and analyzed by gas chromatography and inductively coupled plasma mass spectrometry (GC-ICP-MS). Significant volatilization was found for Se, As, and Te (maximal hourly production rates relative to the amount spiked; 0.6, 2, and 9 ng/mg/h, respectively). In addition, volatile species of Sb and Bi were detected. The occurrence of AsH3 and (CH3)2Te was toxicologically important. Furthermore, mixed Se/S and mixed As/S metabolites were detected in significant amounts in the gas phase of the incubation experiments of which two metabolites, (CH3)2AsSSCH3 and CH3As(SCH3)2, are described for the first time in environmental matrices. The toxicology of these species is unknown. These data show that the intestinal microbiota may increase the mobility of metal(loid)s, suggesting a significant modulation of their toxicity. Our research warrants further studies to investigate the extent of this process as well as the availability of metal(loid)s from different sources for microbial transformations.

Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification

Abstract. The nucleation of NAD and NAT from HNO3/H2O and HNO3/H2SO4/H2O solution droplets is investigated both theoretically and experimentally with respect to the formation of polar stratospheric clouds (PSCs). Our analysis shows that homogeneous NAD and NAT nucleation from liquid aerosols is insufficient to explain the number densities of large nitric acid containing particles recently observed in the Arctic stratosphere. This conclusion is based on new droplet freezing experiments employing optical microscopy combined with Raman spectroscopy. The homogeneous nucleation rate coefficients of NAD and NAT in liquid aerosols under polar stratospheric conditions derived from the experiments are < 2 x 10-5 cm-3 s-1 and < 8 x 10-2 cm-3 s-1, respectively. These nucleation rate coefficients are smaller by orders of magnitude than the value of ~103 cm-3 s-1 used in a recent denitrification modelling study that is based on a linear extrapolation of laboratory nucleation data to stratospheric conditions (Tabazadeh et al., Science, 291, 2591--2594, 2001). We show that this linear extrapolation is in disagreement with thermodynamics and with experimental data and, therefore, must not be used in microphysical models of PSCs. Our analysis of the experimental data yields maximum hourly production rates of nitric acid hydrate particles per cm3 of air of about 3 x 10-10 cm-3 (air) h-1 under polar stratospheric conditions. Assuming PSC particle production to proceed at this rate for two months we arrive at particle number densities of < 5 x 10-7 cm-3, much smaller than the value of ~10-4 cm-3 reported in recent field observations. In addition, the nitric acid hydrate production rate inferred from our data is much smaller than that required to reproduce the observed denitrification in the modelling study mentioned above. This clearly shows that homogeneous nucleation of NAD and NAT from liquid supercooled ternary solution aerosols cannot explain the observed polar denitrification.

Modelling the primary productivity of intertidal microphytobenthos:time scales of variability and effects of migratory rhythms

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 192:13-30 (2000) - doi:10.3354/meps192013 Modelling the primary productivity of intertidal microphytobenthos: time scales of variability and effects of migratory rhythms João Serôdio*, Fernando Catarino Instituto de Oceanografia and Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal *E-mail: joao.serodio@fc.ul.pt ABSTRACT: A simulation model based on the short-term variability of in situ irradiance and productive biomass, defined as the fraction of total biomass contributing to measurable production, was developed to describe the primary productivity of intertidal microphytobenthos in the Tagus estuary, Portugal. Hourly primary production was modelled based on the assumption that short-term variations in the community-level photosynthetic light response were caused by changes in productive biomass associated with the vertical migratory rhythms of motile microalgae. The hourly variability in productive biomass was quantified by non-destructively measuring the dark-level chlorophyll a fluorescence, Fo, emitted from undisturbed microphytobenthos samples. Fo was found to be a good predictor of community-level photosynthesis versus irradiance curve parameters α (initial slope) and Pm (maximum photosynthesis) under the range of conditions found in situ, which allowed for the estimation of hourly production rates from hourly time series of in situ observations of Fo and irradiance. By modelling the hourly and fortnightly variability in Fo, the model was used to calculate hourly production throughout the annual cycle, which resulted in an annual pattern characterised by fortnightly oscillations in daily production comparable in amplitude with those occurring at the seasonal time scale. A comparison of the variability in production on hourly (intraday), fortnightly (within spring-neap tidal cycles) and seasonal (month-to-month) time scales confirmed that microphytobenthic production is dominated by variability on sub-seasonal (hourly and fortnightly) time scales. Significant variability in hourly primary production rates was detected on hourly and fortnightly time scales but not among seasons. A sensitivity analysis made on the model showed that the occurrence of migratory rhythms may be expected to increase the variability in primary production both on hourly and on fortnightly time scales, and also to contribute to the high levels of primary productivity of intertidal microphytobenthos. The mean annual areal primary production was found to reach 156 g C m-2 yr-1. By considering the variation of production with tidal height, the model was used to calculate the annual production of the entire intertidal area of the Tagus estuary, which resulted in a total of 4265 t C yr-1. KEY WORDS: Microphytobenthos · Primary production · Modelling · Migratory rhythms · Chlorophyll a fluorescence Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 192. Publication date: January 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Inhibition of 5 alpha-reductase activity impairs the testosterone-dependent restoration of spermiogenesis in adult rats.

Testosterone (T) is required for spermatogenesis, particularly in the conversion of round spermatids between stages VII and VIII of spermatogenesis. T is generally thought to be the major androgen involved in adult spermatogenesis due to the high local concentration within the testis, whereas its more potent 5alpha-reduced metabolite dihydrotestosterone (DHT) is thought to be the active androgen in peripheral tissues. The current study investigated whether 5alpha-reduction of T to DHT is involved in the restoration of spermiogenesis in vivo in a setting in which testicular T levels were markedly reduced. Adult male rats were given 3-cm T plus 0.4-cm estradiol implants for 9 weeks to suppress serum LH and testicular T levels and thereby inhibit spermatogenesis. Increasing doses of T (3-, 6-, 10-, and 24-cm implants) were then given for 4 days to restore spermatogenesis in the presence or absence of a 5alpha-reductase inhibitor (L685,273). The hourly production rates of round spermatids in stages I-III, IV-VI, VII, and VIII were assessed using stereological techniques, and the conversion of round spermatids between stages VII and VIII was then assessed as an index of androgen action on spermiogenesis. Testicular androgen levels were measured by HPLC and RIA. The 5alpha-reductase inhibitor significantly suppressed (P < 0.05) the hourly production rate of round spermatids at the 3- and 6-cm T doses, but not at the 10- and 24-cm doses. The conversion of round spermatids between stages VII and VIII was suppressed (P < 0.05) by the inhibitor only at the 3- and 6-cm doses. The 5alpha-reductase inhibitor had no effect on testicular T levels, but suppressed (P < 0.05) DHT levels at the 6-, 10-, and 24-cm doses. We conclude that the 5alpha-reduction of T is involved in the restoration of spermiogenesis at the lower administered doses of T and that these data are the first description of a role for 5alpha-reduced androgens in adult spermatogenesis.

Kinetic studies and production rate of melatonin in pony mares

The aims of the present study were to determine basic kinetic parameters and the nycthemeral production rate of melatonin in the horse. Seven pony mares were used for the kinetic studies. Five other pony mares were used under long and short days for the production rate studies. Melatonin was administered by intravenous, oral, and intragastric routes at different dose levels. The plasma melatonin clearance was 1.02 +/- 0.31 l.kg-1.h-1, and the volume of distribution was 0.89 +/- 0.53 l/kg for the 0.4 microgram/kg melatonin dose. The systemic availability after oral and intragastric administration was consistently low (< or = 10%). The hourly melatonin production rates during short (36 +/- 33.6 ng.kg-1.h-1) and long nights (42 +/- 24.0 ng.kg-1.h-1) were not significantly different. It is concluded that the oral dose of exogenous melatonin required to control reproductive pattern in horses would need to be 10 times higher than the nocturnal melatonin production (0.5 microgram/kg) to obtain a physiological plasma melatonin concentration.

Testosterone promotes the conversion of round spermatids between stages VII and VIII of the rat spermatogenic cycle.

Several spermatogenic cell types have been reported to be responsive to testosterone (T) in vivo. We have proposed that the principal action of T is to facilitate the maturation of round to elongated spermatids during spermiogenesis. To identify T-dependent cell types during spermiogenesis, round spermatid populations were counted using stereological techniques in adult rats after T withdrawal and replacement. The number of round spermatids per testis in stages I-III, IV-VI, VII, and VIII of the spermatogenic cycle were determined and, based on the known duration of each stage, the hourly production rates of round spermatid populations calculated. Sprague-Dawley rats received 3 cm T and 0.4 cm estradiol implants (TE treatment) for 11 weeks to suppress LH, testicular T levels, and spermatogenesis. To restore sperm production, high-dose T (24 cm) implants were then given, and animals were perfused 0, 2, 4, and 7 days later. Total testicular T levels were suppressed to 2.9% of control levels by TE treatment and significantly increased (P < 0.05) after 2 days of high-dose T, to remain between 7-12% of control. The hourly production rates of round spermatids between stages I and VII were suppressed to 29-35% of control by TE treatment and remained unchanged by high-dose T administration. Stage VIII round spermatid hourly production rates however, were markedly reduced to 5% of control by TE treatment and increased significantly (P < 0.05) to 27% of control after 4 days of high-dose T. The efficiency of conversion of spermatids through spermiogenesis was estimated from the ratios of the hourly production rates of successive spermatid groups. The conversion of spermatids between stages I-VII of the cycle did not differ from control regardless of the treatment. However, the conversion of round spermatids between stages VII and VIII was markedly suppressed to 16% of control by TE treatment and was then normalized after 4 days of high-dose T administration. We conclude that the conversion of round spermatids between stages VII and VIII is a highly T-dependent step during spermiogenesis.

Testosterone promotes the conversion of round spermatids between stages VII and VIII of the rat spermatogenic cycle

Several spermatogenic cell types have been reported to be responsive to testosterone (T) in vivo. We have proposed that the principal action of T is to facilitate the maturation of round to elongated spermatids during spermiogenesis. To identify T-dependent cell types during spermiogenesis, round spermatid populations were counted using stereological techniques in adult rats after T withdrawal and replacement. The number of round spermatids per testis in stages I-III, IV-VI, VII, and VIII of the spermatogenic cycle were determined and, based on the known duration of each stage, the hourly production rates of round spermatid populations calculated. Sprague-Dawley rats received 3 cm T and 0.4 cm estradiol implants (TE treatment) for 11 weeks to suppress LH, testicular T levels, and spermatogenesis. To restore sperm production, high-dose T (24 cm) implants were then given, and animals were perfused 0, 2, 4, and 7 days later. Total testicular T levels were suppressed to 2.9% of control levels by TE treatment and significantly increased (P < 0.05) after 2 days of high-dose T, to remain between 7-12% of control. The hourly production rates of round spermatids between stages I and VII were suppressed to 29-35% of control by TE treatment and remained unchanged by high-dose T administration. Stage VIII round spermatid hourly production rates however, were markedly reduced to 5% of control by TE treatment and increased significantly (P < 0.05) to 27% of control after 4 days of high-dose T. The efficiency of conversion of spermatids through spermiogenesis was estimated from the ratios of the hourly production rates of successive spermatid groups. The conversion of spermatids between stages I-VII of the cycle did not differ from control regardless of the treatment. However, the conversion of round spermatids between stages VII and VIII was markedly suppressed to 16% of control by TE treatment and was then normalized after 4 days of high-dose T administration. We conclude that the conversion of round spermatids between stages VII and VIII is a highly T-dependent step during spermiogenesis.

Effects of testosterone on spermatogenic cell populations in the adult rat.

The aim of this study was to investigate the progression of germ cell populations through the rat spermatogenic cycle when spermatogenesis was suppressed by LH withdrawal through the use of a combination of testosterone (T) and estradiol (E) and then reinitiated by the administration of high doses of T. Adult Sprague-Dawley rats received 3-cm T and 0.4-cm E silastic implants for 6, 8, or 12 wk to suppress spermatogenesis followed by high-dose T (24-cm implants) for up to 12 wk to reinitiate spermatogenesis. The number of spermatogonia, primary spermatocytes, and round spermatids per testis was established by stereological techniques, and the elongated spermatid number was determined by the testicular content of nuclei resistant to homogenization in Triton X-100. Suppression for 6-12 wk resulted in moderate and significant (p < 0.05) reductions in the numbers of type A and type B spermatogonia (to 44-59% of control levels), preleptotene (68-72% of control), and leptotene/zygotene spermatocytes (62-79% of control) as well as in the numbers of stage I-VII (56-69% of control) and stage VIII-XIV (35-43% of control) pachytene spermatocytes. Round spermatids were suppressed to 29-45% of control levels (p < 0.05) while elongated spermatids were undetectable. The hourly production rates of germ cells (calculated using published time divisors) were used to study the cellular conversions through spermatogenesis (based on the ratios of the hourly production rates) and revealed that T withdrawal consistently abolished the conversion of round to elongated spermatids. The duration of suppression (6, 8, or 12 wk) had no effect on the degree to which germ cell populations or conversions were reduced. In response to high-dose T administration, spermatogonial and spermatocyte numbers and production rates (up to stage I-VII pachytene) remained suppressed, while stage VIII-XIV pachytene spermatocytes showed an increase of borderline significance. On the other hand, round and elongated spermatid numbers and production rates increased significantly (to 81% and 78% of control, respectively) and their conversion was normalized, i.e., the spermiogenic process was restored to a level consistent with the numbers of earlier germ cells proceeding through the cycle. These data suggest that, in the presence of low T levels, spermatogenesis proceeds at approximately 65% of normal levels between the spermatogonial and round spermatid stages, irrespective of the duration of T-induced suppression. This is followed by a precipitous decline in elongated spermatid number that is attributed to the disappearance of round spermatids.(ABSTRACT TRUNCATED AT 400 WORDS)

Primary production dynamics in seagrass beds of Mississippi Sound: the contributions of seagrass epiphytic algae, sand microflora, and phytoplankton

Primary production rates of 4 autotrophic components in Halodule wrightii Aschers. beds off Horn Island in Mississippi Sound (USA) were measured over an annual cycle. Hourly production rates varied from as little as 0.9 mg C m-' for H, wrightii leaves in winter to as high as 1143 mg C m-' for eplphytic algae during summer. Stepwise multiple regression showed that only 15 % of the variation in hourly epiphytic algal production could be related to a single environmental variable (i.e. light energy). Variations in hourly production rates for the other productivity components were best explained by light energy, water temperature, tidal range and blade density; R2 for these regressions was 0.66 and 0.80 for phytoplankton and seagrass blades respectively. The epiphytic algal assemblage on H. wrightii leaves was dominated by the red alga Acrochaetium flexuosum Vickers and 12 taxa of araphid, monoraphid and biraphid diatoms. Phytoplankton over the beds were virtually all centric diatoms, whereas the microflora associated with the sandy sediments in which H. wrightii was rooted was dominated by small pennate diatoms. Annual production rates (g C were estimated as follows: epiphytic algae (905), phytoplankton (468), sand microflora (339) and Halodule wriyhtij (256). System production was dominated by the microalgae, with the contribution of H. rvrightji blades being only 13 % of the total. Epiphytic algae were the single most important productivity con~ponent, being responsible for 46 and 60 % of total system and benthic production respectively. The high standing crops and production rates of the epiphytic and benthic microalgae are of interest in that recent studies have indicated these algae can be the principal source of organic matter in seagrass food webs.

Hexitol repression effects in the high corn ethanol fermentation system

Manitol and sorbitol were used in theSaccharomyces cerevisiae glucose ethanol fermentation to study osmotic and membrane transport effects in the presence of non-saccharified high corn solids. Both hexitols caused temporary depression of alcohol yield during the early growth period but did not appear to affect maximum hourly production rates.