Internal Cycling Research Articles

Internal phosphorus cycling in macrophyte-dominated eutrophic lakes and its implications

Macrophyte-dominated eutrophication (MDE) generally exhibits different characteristics from phytoplankton-dominated eutrophication (PDE). However, the significance of P cycling on eco-environmental management of MDE lakes is still not fully recognized. In this study, P-cycling mechanism was studied in a typical MDE lake (Wuliangsu Lake, China) based on a Before-After-Control-Impact design, taking advantage of the contrasting states between its 13 sub-lakes (with/without macrophytes and with/without external water flow). Our study demonstrated that P cycling predominantly occurs through “macrophyte ↔ sediment” in the MDE lakes, rather than “water ↔ sediment” as in PDE lakes; the biodynamics of the macrophytes acts as a primary driving force for this self-enforced P cycling. Our findings challenge the present lake eutrophication management strategies, which primarily limited to the water nutrient content, and demonstrate that successful MDE lake restoration should focus on stressors caused by the sustainable “macrophyte-sediment” P cycling. Macrophyte harvesting immediately before withering is recommended as the most sustainable technique in environment management for periodically frozen shallow MDE lakes. By this technique, sediment P can be gradually pumped up by the overgrown macrophytes each year until the advent of an alternative stable state (low sediment P, small biomass, and higher diversity), thereby forming a positive feedback loop “macrophyte harvesting → less sediment P → less macrophyte → higher diversity.” Also, the catastrophic shift from MDE to PDE is no longer a concern. Furthermore, the macrophyte debris will not pose a problem as long as the macrophytes are removed during the harvest.

Sources and internal cycling of dissolved barium in a tropical coastal lagoon (Chilika lagoon, India) system

The abundance and distribution of barium (Ba) serve as a reliable proxy for oceanic biogeochemical processes. Its cycling in the coastal regions, however, is complicatedly regulated by multiple sources/sinks. In this study, the spatial distribution of dissolved barium concentrations in a large coastal lagoon (Chilika lagoon, India) and its source waters have been investigated for three different seasons (pre-monsoon (May 2017), monsoon (August 2017), and post-monsoon (January 2018)). Additionally, contents of Ba and other elements in the bed and suspended sediments in their different fractions (bulk, clay, and exchangeable) have also been investigated. These data were used to constrain coastal processes in regulating coastal Ba inventory. The dissolved [Ba] of the Bay of Bengal (median ~ 37 nmol/kg (range: 30–53 nmol/kg)) are lower than that observed for the river (median ~ 319 nmol/kg (range: 256–583 nmol/kg)), and groundwater (median ~ 464 nmol/kg (range: 20–4428 nmol/kg)) samples. The salinity-weighted barium concentrations of the Chilika lagoon for the pre-monsoon (1052 nmol/kg) and monsoon (652 nmol/kg) seasons are higher compared to that during the post-monsoon period (332 nmol/kg). Covariations between salinity and [Ba] confirm the non-conservative behavior of barium during all three seasons. The salinity-[Ba] trends show barium removal in the low-salinity regions, attributable to its authigenic scavenging onto Fe-Mn oxyhydroxides. Mass balance calculations show that the relative contribution of barium via rivers (~18%), (freshwater) submarine groundwater discharge (SGD; ~25%), and desorption from particulate matters (~19%) to the lagoon during pre-monsoon seasons is nearly the same. During the monsoon season, the SGD supply of barium decreases to ~2%, whereas riverine (~20%) and desorption (~24%) contributions remain similar to that observed during the pre-monsoon. The sediment chemistry (Mg, Al, Fe) data and their correlations with Ba concentrations reveal that the desorptive release of barium to the lagoon is mainly via its cationic replacement from the suspended sediments by seawater Mg. In addition to these sources, our results show that about half of the dissolved barium during pre-monsoon and monsoon seasons remains unaccounted and may have been supplied by an additional source, which may be linked to subsurface supply of recirculated seawater and/or organic matter remineralization. Our quantitative approach emphasizes the importance of these additional sources in regulating the coastal barium inventory.

A Multi-Point Geostatistical Seismic Inversion Method Based on Local Probability Updating of Lithofacies

In order to solve the problem that elastic parameter constraints are not taken into account in local lithofacies updating in multi-point geostatistical inversion, a new multi-point geostatistical inversion method with local facies updating under seismic elastic constraints is proposed. The main improvement of the method is that the probability of multi-point facies modeling is combined with the facies probability reflected by the optimal elastic parameters retained from the previous inversion to predict and update the current lithofacies model. Constrained by the current lithofacies model, the elastic parameters were obtained via direct sampling based on the statistical relationship between the lithofacies and the elastic parameters. Forward simulation records were generated via convolution and were compared with the actual seismic records to obtain the optimal lithofacies and elastic parameters. The inversion method adopts the internal and external double cycle iteration mechanism, and the internal cycle updates and inverts the local lithofacies. The outer cycle determines whether the correlation between the entire seismic record and the actual seismic record meets the given conditions, and the cycle iterates until the given conditions are met in order to achieve seismic inversion prediction. The theoretical model of the Stanford Center for Reservoir Forecasting and the practical model of the Xinchang gas field in western China were used to test the new method. The results show that the correlation between the synthetic seismic records and the actual seismic records is the best, and the lithofacies matching degree of the inversion is the highest. The results of the conventional multi-point geostatistical inversion are the next best, and the results of the two-point geostatistical inversion are the worst. The results show that the reservoir parameters obtained using the local probability updating of lithofacies method are closer to the actual reservoir parameters. This method is worth popularizing in practical exploration and development.

The Role of Race, Sex, and Age in Circadian Disruption and Metabolic Disorders.

Circadian rhythms are 24-hour internal biological cycles that play an important role in metabolism, and their disruption has been implicated in the development of diseases such as diabetes mellitus type 2, obesity, coronary artery disease, hypertension, and metabolic syndrome. This phenomenon is illustrated by increased rates of risk factors for cardiovascular disease in night shift workers. Race, sex, and age are factors that play a role in circadian rhythms and metabolic disorders. The focus of this review article is to assess the link between circadian rhythm physiology and metabolic disorders from a race, sex, and age perspective. Black Americans were noted to have shorter free-running circadian periods, or tau, increased cortisol levels, and poorer sleep habits compared to white Americans, possibly contributing to increased rates of obesity, hypertension, and hyperlipidemia. Women were also noted to have shorter tau, increased levels of proinflammatory gut bacteria, and reduced sleep quality compared to men, possibly leading to higher rates of obesity, metabolic syndrome, hypertension (in postmenopausal women), and nonalcoholic fatty liver disease. Older people were noted to have decreased expression of anti-inflammatory clock genes compared to younger people, possibly leading to increased rates of obesity, diabetes, hyperlipidemia, and hypertension. Groups that are at a higher risk for metabolic disorders such as black Americans, women, and the elderly may have internal time keeping systems that place them at a higher risk for developing abnormal hormonal and/or inflammatory pathways.

Sustained high CO

Many of the world’s rivers have been found to be sources of CO2 to the atmosphere, however, there has been limited assessment in arid regions. This analysis of a long-term (1979–2013) dataset (n = 3496) along Australia’s largest river system (River Murray) showed that there were sustained high pCO2 (carbon dioxide partial pressure) levels, ranging from 1210 ± 107 to 3066 ± 579 µatm along the main river channel, and 5114 ± 1221 µatm on the major tributaries. As a consequence, the River Murray is a significant source of CO2 to the atmosphere, with an estimated average annual (±s.d.) flux of 218 ± 98 g C m−2 year−1 and total emissions of 355 000 ± 29 000 t CO2 year−1 over a total river area of 386 km2 from below Lake Hume to Tailem Bend, although there is some uncertainty with gas transfer coefficients. Supersaturation with CO2 relative to the atmosphere was maintained even under drought conditions with minimal external carbon inputs, suggesting internal carbon cycling and respiration is important in driving net CO2 production. Supersaturation of the river water relative to calcium carbonate minerals was also observed under low flow conditions. Hydro-climatic changes could be having significant impacts on the CO2 system in the River Murray and other arid river systems.

Replanting of broadleaved trees alters internal nutrient cycles of native and exotic pines in subtropical plantations of China

Replanting of broadleaved trees alters internal nutrient cycles of native and exotic pines in subtropical plantations of China

Глобальні фінансові цикли і проблема регулювання міжнародних потоків капіталу: роль банків і макропруденційної політики у протидії кризам

The aggravation of crisis processes in the global financial system produces a request to find tools to eliminate the systemic risk of global instability, which arises primarily through the interaction between the global financial cycle, key global factors (global risk and monetary policy in major economies) and cross-border banking activities. The situation in the monetary and financial spheres of countries with large open economies has a powerful impact on the economic situation, exacerbating the asymmetries of interaction on a global scale, which actualizes the need for macroprudential authorities in countries with small open economies to take preventive measures to maintain internal balance from destructive crisis processes in key economies of the world. The article provides a comprehensive analysis of approaches to substantiating the channels of mutual influence of the internal financial cycle, the global financial cycle and macroprudential policy, and also assesses the potential of macroprudential policy in smoothing out procyclical processes in order to stimulate economic growth. The interdependence of global banks on the dynamics of the global financial cycle and vice versa is determined, because global banks determine the specifics of the manifestations of the latter, given the way they manage their liquidity on a global scale, thereby contributing to the international transmission of shocks. It is found that the existence of a domestic capital market for global banks exacerbates the international spread of domestic liquidity shocks due to the strategic complementarity effect arising from strategic interactions between banks, other financial institutions and agents, which can increase systemic vulnerabilities during booms and busts due to increased competition between banks. It was revealed that the impact of the global financial cycle on the internal financial environment of banks and financial institutions through the mechanisms of external obligations of national banks and the determination of the cost of financing affects the availability of loans for companies and households. This means that the economies of small open economies are more vulnerable to external shocks and are affected by financing conditions determined in the world's financial centers. Under these conditions, the dynamics of global liquidity limits the effectiveness of national monetary policy, and therefore the demand for effective international coordination of macroprudential policy becomes even more urgent. The need to revise monetary policy in order to increase its ability to mitigate the risks of financial instability depends on: (1) the effectiveness of macroprudential policy (for example, the ability to manage the financial cycle); (2) the contribution of monetary policy (including its traditional and non-traditional instruments) to the exacerbation of financial instability; (3) the degree of independence of monetary policy, especially during a crisis.

Uloga cirkadijalnog sistema u nastanku kardiovaskularnih bolesti i kliničke implikacije

Circadian rhythm, an internal 24-hour cycle biological clock, regulates important biologic functions such as metabolism, body temperature, heart and respiratory rate, circulating levels of hormones, sleep-wake pattern, behaviour. It is also a very important in regulation of the cardiovascular (CV) system components such as arterial blood pressure, pulse, endothelial function. In this comprehensive review of the literature, we will discuss how interaction between environment/behavior stressors and circadian phases modulate individual cardiovascular risk. Potential therapeutical targets will be also discussed.

Changing Biogeochemistry of the Arctic Ocean: Surface Nutrient and CO2 Cycling in a Warming, Melting North

The physical system of the Arctic is changing in profound ways, with implications for the transport of nutrients to and from the Arctic Ocean as well as the internal cycling of material on shelves and in deep basins. Significant increases in Arctic Ocean primary production have been observed in the last two decades, potentially driven by enhancements to a suite of mechanisms that increase nutrient availability to upper ocean waters, including transport from adjacent subpolar regions, storm-induced mixing, and mobilization of nutrients from terrestrial pools. The relative strength of these mechanisms varies substantially within Arctic Ocean subregions, leading to a mosaic of biogeochemical responses. Changes in primary production are also driving regional changes in the biologically mediated air-sea exchange of CO2, while warming, enhanced stratification, and increased mobilization of carbon from terrestrial pools are also driving regionally variable trends.

Spectrometric Prediction of Nitrogen Content in Different Tissues of Slash Pine Trees.

The internal cycling of nitrogen (N) storage and consumption in trees is an important physiological mechanism associated with tree growth. Here, we examined the capability of near-infrared spectroscopy (NIR) to quantify the N concentration across tissue types (needle, trunk, branch, and root) without time and cost-consuming. The NIR spectral data of different tissues from slash pine trees were collected, and the N concentration in each tissue was determined using standard analytical method in laboratory. Partial least squares regression (PLSR) models were performed on a set of training data randomly selected. The full-length spectra and the significant multivariate correlation (sMC) variable selected spectra were used for model calibration. Branch, needle, and trunk PLSR models performed well for the N concentration using both full length and sMC selected NIR spectra. The generic model preformatted a reliable accuracy with R2C and R2CV of 0.62 and 0.66 using the full-length spectra, and 0.61 and 0.65 using sMC-selected spectra, respectively. Individual tissue models did not perform well when being used in other tissues. Five significantly important regions, i.e., 1480, 1650, 1744, 2170, and 2390 nm, were found highly related to the N content in plant tissues. This study evaluates a rapid and efficient method for the estimation of N content in different tissues that can help to serve as a tool for tree N storage and recompilation study.

A Comparative Study of Dual Circulation Development Pattern in China and the United States

The proposal of constructing the new pattern of dual circulation development is the product of the comprehensive effect of internal and external factors in the new stage of China’s development, which meets the needs of China’s economic and social development. Based on the comparative study of the internal and external circulation development of China and the United States, this paper concludes the similarities and differences of these two countries in the dual circulation development. The similarities mainly include: First, the early export-oriented economy gathered strength; Second, the industrial foundation is relatively solid; Third, China and the US have a strong domestic demand. The differences mainly include: First, the technological strength of the US is superior to that of China; Second, the US has the hegemony of the world currency; Third, the external environment for the development of the US is superior; Fourth, China’s real economy is more stable. Through comparison, this paper finds that: First, the early export-oriented economic development provides the economic foundation for the dual circulation transition; Second, the industrial base is the prerequisite for the positive interaction between internal and external circulation; Third, the huge domestic consumption demand is the driving force for the development of internal cycle. Based on the above research, this paper puts forward the corresponding policy enlightenment.

Removing harvest residues from hardwood stands affects tree growth, wood density and stem wood nutrient concentration in European beech (Fagus sylvatica) and oak (Quercus spp.)

Higher exportation of harvest residues from forests due to increased demand for woody biomass, has reportedly diminished soil mineral resources and may lead to degraded tree nutrition as well as growth. However, as nutrients become less available in the soil, the remobilization of nutrients in biomass tissues (plant internal cycling) helps sustain tree nutrition. Our study aims to quantify the impact of Removing Harvest Residues and Litter (RHRL) during five years on tree growth, wood density, and stem wood nutrient concentrations in young beech and oak forest stands. Our study found that, RHRL significantly decreased tree growth ring width by 14%, and wood density by 3%, in beech trees, in near bark rings. RHRL also significantly reduced nutrient concentration in near bark and near pith areas of both studied species. Mg, Na and S were found lower by 44%, 76%, and 56%, respectively, in near bark area of beech trees. In near bark area of oak trees, K, Ca, Mg, Na, S, and Fe were lower by 20%, 25%, 41%, 48%, 41%, and 16%, respectively. K and Mg concentrations decreased more strongly in near pith area compared to near bark area suggesting internal translocation of these two elements. In beech trees, wood density proved to be an important factor while quantifying the effect of removing harvest residuals on tree growth and biomass. Soil nutrient loss intensified the remobilization of nutrients contained in older tree rings (close to the pith) towards newly formed rings (close to bark). In our study, in beech trees, K was found to be the most recycled major nutrient. These results demonstrate the potential of such analysis for providing valuable insight into the effect of RHRL in premature stands on the physiological adaptive strategies of trees and an indication of soil fertility status.

Multi-Modal Regulation of Circadian Physiology by Interactive Features of Biological Clocks.

Simple SummaryCircadian rhythms, driven by molecular clockwork, exist in nearly all cells and tissues throughout the body, and these rhythmic oscillators constitute tightly coupled network systems that generate rhythmic physiology and behavior. Common circadian disrupting factors, such as night shift work and mistimed eating, can increase the risk of disease onset and symptoms. Disease can then, in turn, promote circadian disruption, leading to a vicious cycle of adverse circadian and overall health effects. This relationship suggests the importance of well-coordinated internal clock systems that maintain optimal synchrony with environmental and metabolic cues. In this review, we will recount the recent advances in circadian clock research and discuss how circadian clocks reciprocally interact with other signaling and metabolic factors to coordinate the daily rhythms of physiology.The circadian clock is a fundamental biological timing mechanism that generates nearly 24 h rhythms of physiology and behaviors, including sleep/wake cycles, hormone secretion, and metabolism. Evolutionarily, the endogenous clock is thought to confer living organisms, including humans, with survival benefits by adapting internal rhythms to the day and night cycles of the local environment. Mirroring the evolutionary fitness bestowed by the circadian clock, daily mismatches between the internal body clock and environmental cycles, such as irregular work (e.g., night shift work) and life schedules (e.g., jet lag, mistimed eating), have been recognized to increase the risk of cardiac, metabolic, and neurological diseases. Moreover, increasing numbers of studies with cellular and animal models have detected the presence of functional circadian oscillators at multiple levels, ranging from individual neurons and fibroblasts to brain and peripheral organs. These oscillators are tightly coupled to timely modulate cellular and bodily responses to physiological and metabolic cues. In this review, we will discuss the roles of central and peripheral clocks in physiology and diseases, highlighting the dynamic regulatory interactions between circadian timing systems and multiple metabolic factors.

Research on the method of travel area clustering of urban public transport based on Sage-Husa adaptive filter and improved DBSCAN algorithm.

The travel trajectory data of mobile intelligent terminal users are characterized by clutter, incompleteness, noise, fuzzy randomness. The accuracy of original data is an essential prerequisite for better results of trajectory data mining. The Density-Based Spatial Clustering of Applications with Noise (DBSCAN) is one of the most effective trajectory data mining methods, but the selection of input parameters often limits it. The Sage-Husa adaptive filtering algorithm effectively controls the error range of mobile phone GPS data, which can meet the positioning accuracy requirements for DBSCAN spatial clustering having the advantages of low cost and convenient use. Then, a novel cluster validity index was proposed based on the internal and external duty cycle to balance the influence of the distance within-cluster, the distance between clusters, and the number of coordinate points in the process of clustering. The index can automatically choose input parameters of density clustering, and the effective clustering can be formed on different data sets. The optimized clustering method can be applied to the in-depth analysis and mining of traveler behavior trajectories. Experiments show that the Sage -Husa adaptive filtering algorithm proposed further improves the positioning accuracy of GPS, which is 17.34% and 15.24% higher eastward and northward, 14.25%, and 18.17% higher in 2D and 3D dimensions, respectively. The number of noise points is significantly reduced. At the same time, compared with the traditional validity index, the evaluation index based on the duty cycle proposed can optimize the input parameters and obtain better clustering results of traveler location information.

Algorithm for calculating the optimal value of the field substation voltage

The article is devoted to improving the energy efficiency of mechanized mining by selecting the optimal voltage level at the field substation, which provides the required optimization criterion. An unbranched line extending from the field substation, which supplies an arbitrary number of electrical complexes of producing wells, is considered. It is shown that these complexes can contain both submersible centrifugal pumps and rod borehole pumping units driven by asynchronous motors. Mathematical models of electrical complexes of producing wells are nonlinear and are described by high-order differential equations. Therefore, the problem of finding the optimal voltage level of a field substation can only be solved using numerical methods. An algorithm for calculating the optimal voltage value is developed, taking into account the technological features of mechanized oil production. It is a search algorithm that contains three internal cycles: voltage variations at the asynchronous motor farthest from the field substation, sorting out the nodes of the outgoing line, and equalizing the voltage at the nodes when the load of the electrical complexes of the producing wells changes. Well-known analytical expressions are given for calculating the active, reactive and full load of step-up and step-down transformers used in the considered electrical complexes, as well as power losses on these elements and on air and cable lines. A distinctive feature of the presented algorithm is the calculation of the speed of submersible and ground asynchronous motors when the supply voltage changes, taking into account the mechanical characteristics of centrifugal and plunger pumps. An example of calculating the optimal voltage value of a field substation feeding a hypothetical outgoing line with three nodes is given. It is noted that the developed algorithm is a reflection of the method of choosing the optimal voltage of the field substation. Moreover, this algorithm can be adapted to any outgoing line, no matter how complex and branched it is.

Dynamics of natural discharge of the hydrothermal system and geyser eruption regime in the Valley of Geysers, Kamchatka

The total deep component natural mass discharge Qd (defined in terms of chloride mass discharge Qcl) of the Valley of Geysers, on an average ranges from 280 kg/s from 1961 to 1984, to 230 kg/s after 2015. Post 2012, discharge measurements reveal a seasonal variation: the discharge increases (340–370 kg/s) during the winter-frozen period, and decreases during the summer flooding period (≈100 kg/s). Long term annually averaged Qd is 274 kg/s, Qcl is 0.247 kg/s and heat flow is 265 MW. In the course of using high-frequency (min−1) observations specific conductance measurements from 2017 to 2020, the total natural discharge was found to be cycling due to the internal cycling of geysers. It was mostly sensitive to the Bolshoy and Velikan geysers with averaged intervals between eruptions of 60 min and 70 min, respectively. The tracer chloride method estimates the volume of hot water erupted from geysers. This method yielded the following estimates: 5–34 m3 of hot water cyclically erupted from the Bolshoy geyser; 0.5–4.5 m3 erupted from the Velikan geyser between 2018 and 2020, and 24–144 m3 erupted before the 2014 mud-flow disaster; and 289–330 m3 erupted from the Grot geyser between May–June 2012. The seasonal features of natural discharge mentioned above may be explained in terms of cold-water infiltration into a two-phase geyser geothermal reservoir, especially if gas-phase condensation induces vacuum conditions, which may further reduce some thermal discharge features.

Increased soil organic matter after 28 years of nitrogen fertilization only with plastic film mulching is controlled by maize root biomass

Nitrogen (N) fertilization and plastic film mulching (PFM) are two widely applied management practices for crop production. Both of them impact soil organic matter individually, but their interactive effects as well as the underlying mechanisms are unknown. Soils from a 28-year field experiment with maize monoculture under three levels of N fertilization (0, 135, and 270 kg N ha−1 yr−1) and with or without PFM were analyzed for soil organic C (SOC) content, total soil nitrogen (N), root biomass, enzyme activities, and SOC mineralization rates. After 28 years, N fertilization increased root biomass and consequently, SOC by 26% (averaged across the two fertilizer application rates) and total soil N by 25%. These increases, however, were only in soil with PFM, as PFM reduced N leaching and loss, as a result of a diurnal internal water cycle under the mulch. The SOC mineralization was slower with N fertilization, regardless of the PFM treatment. This trend was attributed to the 43% decrease of β-glucosidase activity (C cycle enzyme) and 51% drop of leucine aminopeptidase (N cycle) with N fertilization, as a result of a strong decrease in soil pH. In conclusion, root biomass acting as the main source of soil C, resulted in an increase of soil organic matter after 28 year of N fertilization only with PFM.

Stimulation of dissimilatory sulfate reduction in response to sulfate in microcosm incubations from two contrasting temperate peatlands near Ithaca, NY, USA.

Peatlands are responsible for over half of wetland methane emissions, yet major uncertainties remain regarding carbon flow, especially when increased availability of electron acceptors stimulates competing physiologies. We used microcosm incubations to study the effects of sulfate on microorganisms in two temperate peatlands, one bog and one fen. Three different electron donor treatments were used (13C-acetate, 13C-formate and a mixture of 12C short-chain fatty acids) to elucidate the responses of sulfate-reducing bacteria (SRB) and methanogens to sulfate stimulation. Methane production was measured and metagenomic sequencing was performed, with only the heavy DNA fraction sequenced from treatments receiving 13C electron donors. Our data demonstrate stimulation of dissimilatory sulfate reduction in both sites, with contrasting community responses. In McLean Bog (MB), hydrogenotrophic Deltaproteobacteria and acetotrophic Peptococcaceae lineages of SRB were stimulated, as were lineages with unclassified dissimilatory sulfite reductases. In Michigan Hollow Fen (MHF), there was little stimulation of Peptococcaceae populations, and a small stimulation of Deltaproteobacteria SRB populations only in the presence of formate as electron donor. Sulfate stimulated an increase in relative abundance of reads for both oxidative and reductive sulfite reductases, suggesting stimulation of an internal sulfur cycle. Together, these data indicate a stimulation of SRB activity in response to sulfate in both sites, with a stronger growth response in MB than MHF. This study provides valuable insights into microbial community responses to sulfate in temperate peatlands and is an important first step to understanding how SRB and methanogens compete to regulate carbon flow in these systems.

A Physical Model for the Quasar Luminosity Function Evolution between Cosmic Dawn and High Noon

Abstract Modeling the evolution of the number density distribution of quasars through the quasar luminosity function (QLF) is critical to improving our understanding of the connection between black holes, galaxies, and their halos. Here we present a novel semiempirical model for the evolution of the QLF that is fully defined after the specification of a free parameter, the internal duty cycle, ε DC, along with minimal other assumptions. All remaining model parameters are fixed upon calibration against the QLF at two redshifts, z = 4 and z = 5. Our modeling shows that the evolution at the bright end results from the stochasticity in the median quasar luminosity versus halo mass relation, while the faint end shape is determined by the evolution of the halo mass function (HMF) with redshift. Additionally, our model suggests the overall quasar density is determined by the evolution of the HMF, irrespective of the value of ε DC. The z ≥ 4 QLFs from our model are in excellent agreement with current observations for all ε DC, with model predictions suggesting that observations at z ≳ 7.5 are needed to discriminate between different ε DC. We further extend the model at z ≤ 4, successfully describing the QLF between 1 ≤ z ≤ 4, albeit with additional assumptions on Σ and ε DC. We use the existing measurements of quasar duty cycle from clustering to constrain ε DC, finding ε DC ∼ 0.01 or ε DC ≳ 0.1 dependent on observational data sets used for reference. Finally, we present forecasts for future wide-area surveys with promising expectations for the Nancy Grace Roman Telescope to discover N ≳ 10, bright, m UV < 26.5 quasars at z ∼ 8.

Language learners as invisible planners: a case study of an Arabic language program in a Chinese university

ABSTRACT Despite the predominant position of global English, teaching and learning of languages other than English (LOTEs) are gaining increasing attention in foreign language planning in China. This study aims to showcase the development of an elective Arabic language program in a Chinese university through the lens of agency as a spatial, temporal, and dialogical construct. We investigated how 24 participants representing three groups of actors—people with power, people with expertise, and people with interest—exercised their agency during the five stages of language planning stipulated by the process model of Language Management Theory (i.e. noting, evaluation, adjustment design, implementation, feedback). Drawing on narrative accounts and semi-structured interviews, the findings revealed constant interactions between different actors distributed through the five stages. In particular, we found that the five stages did not proceed in a linear way, and the findings demonstrated the presence of an internal cycle in addition to the external cycle in the micro language planning process. Language learners are invisible planners in the LOTE program. The study concludes that different actors in the local context need to make coordinated efforts to negotiate spaces to sustain the teaching and learning of less commonly taught languages, despite various structural constraints.