ABSTRACT
Since the discovery of z ∼ 6 quasars two decades ago, studies of their Ly α-transparent proximity zones have largely focused on their utility as a probe of cosmic reionization. But even when ...in a highly ionized intergalactic medium, these zones provide a rich laboratory for determining the time-scales that govern quasar activity and the concomitant growth of their supermassive black holes. In this work, we use a suite of 1D radiative transfer simulations of quasar proximity zones to explore their time-dependent behaviour for activity time-scales from ∼103 to 108 yr. The sizes of the simulated proximity zones, as quantified by the distance at which the smoothed Ly α transmission drops below 10 per cent (denoted Rp), are in excellent agreement with observations, with the exception of a handful of particularly small zones that have been attributed to extremely short ≲104 lifetimes. We develop a physically motivated semi-analytic model of proximity zones which captures the bulk of their equilibrium and non-equilibrium behaviour, and use this model to investigate how quasar variability on ≲105 yr time-scales is imprinted on the distribution of observed proximity zone sizes. We show that large variations in the ionizing luminosity of quasars on time-scales of ≲104 yr are disfavoured based on the good agreement between the observed distribution of Rp and our model prediction based on ‘lightbulb’ (i.e. steady constant emission) light curves.
In this study, the perovskite tandem solar cell (TPSC) has been accomplished using SCAPS-1D. The present study focuses on comprehensive exploration and detailed optimization using various strategies ...constructing a tandem device. To calculate high photovoltaic power conversion efficiency (PCE), the numerical analysis has been carried out for a wide-bandgap halide (WBH) FA0.75Cs0·25Pb(I0·8Br0.2)3 of bandgap 1.67eV and a Pb–Sn based narrow-bandgap halide (NBH) FA0.7MA0.3Pb0·5Sn0·5I3 of bandgap 1.22eV as absorber layer in top-cell (TCELL) and bottom-cell (BCELL) respectively. The WBH has huge potential as a front light absorber and the NBH based BCELL provides stability and high performance by accepting high and low energy photons respectively. This method mitigates thermalization and non-absorbed photon loss which results in the growth in PCE. The proposed work demonstrates the impact of active-layer thickness along with defect density on the solar-cell parameters. It has been observed that defect density is low for the optimal performance. An investigation for various electron transport medium (ETMs) and hole transport medium (HTMs) has been done to secure an optimum performing TCELL as well as BCELL. Using filtered-spectrum study along with current-matching method, every PV metric parameter has been analyzed after their deployment into tandem configuration. The numerical investigation has shown promising photovoltaic parameters with aa high open circuit voltage (VOC) of 2.33 V, a short circuit current density (JSC) of 17.07 mA/cm2, a fill factor (FF) of 79.34 % and PCE of 31.55 % in tandem configuration.
•Perovskite tandem solar cell (TPSC) has been accomplished using SCAPS-1D.•Wide-bandgap halide (WBH) FA0.75Cs0·25Pb(I0·8Br0.2)3 of bandgap 1.67eV and a Pb–Sn based narrow-bandgap halide (NBH) FA0.7MA0.3Pb0·5Sn0·5I3 of bandgap 1.22eV as absorber layer in TCELL and BCELL respectively have been studied.•Open circuit voltage (VOC) of 2.33 V, a short circuit current density (JSC) of 17.07 mA/cm2, a fill factor (FF) of 79.34 % and PCE of 31.55 % in tandem configuration.•Using filtered-spectrum study along with current-matching method, every PV metric parameter has been analyzed after their deployment into tandem configuration.•The proposed work demonstrates the impact of active-layer thickness along with defect density on the solar-cell parameters.
International entrepreneurship research maintains that firms with strong entrepreneurial orientations expand to international markets to enhance performance. Yet these firms can suffer from resource ...constraints as they move abroad. To alleviate this problem, previous research has suggested participation in strategic alliances. We developed and tested a theoretical perspective that merged these ideas, maintaining that firm–level entrepreneurial orientation is associated with higher international performance both directly and in combination with participation in foreign market research or marketing alliances. Based on surveys of U.S. and U.K. firms, our findings indicate that small and medium–sized enterprises (SMEs) have higher international performance when they possess greater entrepreneurial orientation (EO) and when the type of alliance (research or marketing) used is aligned with the capabilities of the firm. Further we find that participating in alliances strengthens the relation between EO and international performance. These results have important implications for managers and policy makers interested in improving SME international performance.
Despite the proliferation of HRM research, only a small fraction explores the context of small and medium‐sized enterprises (SMEs). Where HRM in SMEs has received attention, the literature base ...remains fragmented and variable, comprising a plurality of definitions, explanations, and methods. To advance understanding, this paper uses a quarter‐century systematic review drawing on an evidence base of 137 peer‐reviewed articles. A cumulative framework is presented capturing key developments and synthesizing existing areas of research focus. Analysis of limitations and knowledge‐gaps finds a failure to differentiate across various types of SMEs, limited appreciation of SME characteristics and contextual conditions, and a dominance of managerial perspectives. An agenda for future research on HRM in SMEs is outlined with respect to definitional parameters, HR practices, HRM–performance, key determinants, and presenting issues. The paper concludes that SMEs offer a unique, fruitful, and timely context for investigations of HRM.
Purpose: This study aims to explore the potential of in vitro culture as a method for scaling up the production of saffron based medicinal compounds, the most expensive spice renowned. Emphasis is ...placed on the critical role of friable callus (FC) formation as a prerequisite for successful suspension culture. Research method: The research primarily investigates FC formation, focusing on the impact of varying strengths of Murashige and Skoog (MS) medium as well as combinations of NAA or 2,4-D and BA or Kin on compact callus. Subsequently, the study involves supplementing the MS medium with different concentrations of 2,4-D, kin, zeatin, glutamine, sucrose, and nitrogen to establish a cell suspension culture. Findings: The highest FC yield was achieved on a solid medium containing 2,4-D (1 mg l-1)+Kin (0.2 mg l-1), resulting in a fresh weight (FW) of 0.413 g. Furthermore, MS combined with 2,4-D (1 mg l-1)+Kin (0.2 mg l-1)+glutamine (10 mg l-1), as well as MS+2,4-D (0.5 mg l-1)+zeatin (0.3 mg l-1)+glutamine (10 mg l-1), demonstrated the highest FW under suspension conditions. The study also identified that 30 g l-1 sucrose and 30 µM were optimal for inducing maximum FW. Research limitations: Cell biomass is influenced by several factors that should to be optimized. Originality/Value: This research concludes that a cell suspension system holds promise for rapidly generating sufficient cell biomass to produce valuable secondary metabolites within a limited timeframe and space. Notably, the system successfully increased biomass from 0.2 to 1.2 g, underscoring its potential for efficient saffron-based product development.
Background: Spirulina is a multicellular, filamentous cyanobacterium, belonging to the Phormidiaceae family which appears as blue-green filaments composed of cylindrical cells arranged in unbranched ...helicoidal trichomes. It contains a wide spectrum of nutrients that include proteins with all essential amino acids, carbohydrates, vitamins, minerals, pigments, carotenoids and super antioxidants apart from trace elements. Methods: The aim of the present study is to optimize the growth of cyanobacterium i.e., Spirulina platensis in selected media such as Zarrouk’s modified medium, Zarrouk’s medium, BG11 medium and F-2 medium. The growth analyses were recognized after 30 days. The temperature was maintained at 30±2°C under 12:12 hour light-dark cycles, light illuminated (4500 lux). Result: The maximum biomass of 0.641 gm/ml was achieved in Zarrouk’s modified medium. The inoculation of S. platensis in the F-2 medium showed the least growth of alga. The maximum concentration of phycocyanin content (0.19 mg/ml) and total carotenoid contents (5.99 µg/ml) were observed in Zarrouk’s modified medium followed by Zarrouk’s medium (0.12 mg/ml and 5.51 µg/ml) and minimum amounts were observed in F-2 medium (0.08 mg/ml and 3.08 µg/ml). According to the results, this study concluded that the growth and biomass of Spirulina with significant cell count and higher pigment proteins can be enhanced by using the naturally modified medium.
ABSTRACT
We perform a suite of simulations with realistic gravity and thermal balance in shells to quantify the role of the ratio of cooling time to the free-fall time (tcool/tff) and the amplitude ...of density perturbations (δρ/ρ) in the production of multiphase gas in the circumgalactic medium (CGM). Previous idealized simulations, focusing on small amplitude perturbations in the intracluster medium (ICM), found that cold gas can condense out of the hot ICM in global thermal balance when the background tcool/tff ≲ 10. Recent observations suggest the presence of cold gas even when the background profiles have somewhat large values of tcool/tff. This partly motivates a better understanding of additional factors such as large density perturbations that can enhance the propensity for cooling and condensation even when the background tcool/tff is high. Such large density contrasts can be seeded by galaxy wakes or dense cosmological filaments. From our simulations, we introduce a condensation curve in the (δρ/ρ) – min(tcool/tff) space, which defines the threshold for condensation of multiphase gas in the CGM. We show that this condensation curve corresponds to (tcool/tff)blob ≲ 10 applied to the overdense blob instead of the background for which tcool/tff can be higher. We also study the modification in the condensation curve by varying entropy stratification. Steeper (positive) entropy gradients shift the condensation curve to higher amplitudes of perturbations (i.e. make condensation difficult). A constant entropy core, applicable to the CGM in smaller haloes, shows condensation over a larger range of radii as compared to the steeper entropy profiles in the ICM.
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