A Kinetic model for submerged citric acid production by Aspergillus versicolor using oil palm empty fruit bunch

The fermentation kinetics of citric acid by Aspergillus versicolor was studied in a submerged batch system. The logistic equation for growth, the Luedeking–Piret equation for citric acid production and modified Luedeking–Piret-like equation for glucose consumption was proposed for this study. The model appeared to provide a reasonable description for each parameter during the growth phase. The production of citric acid was growth-associated.

Effects of Bio-Syngas Blends on Combustion Characteristics of Coal: Kinetic Analysis

The coupled combustion of biomass and coal can utilize large amounts of renewable biomass and reduce the emission of pollutants during power generation. In this study, the coal combustion characteristics were analyzed at different heating value-based biomass blending ratios and temperatures in the coupled combustion of bio-syngas and coal. The kinetic reaction mechanism of coal combustion was investigated by Micro-fluidized Bed Reaction Analyzer (MFBRA). The results indicated that the reaction time decreased with increasing the heating value-based biomass blending ratio and temperature in the coupled combustion process of bio-syngas and coal. The major conversion process of coal combustion usually took 15 s at 1273 K and the maximum reaction rate was usually below 0.14 at 873 K to 1273 K and decreased with increasing reaction temperature. The nucleation and growth model offered a most reasonable description of the coal combustion process. The activation energy was about 121.04 kJ/mol and the pre-exponential factor was of the order of 5.01 × 104 s−1 in the combustion of coal. These data are important to the understanding of the coupled combustion mechanism of bio-syngas and coal, which is beneficial for improving combustion efficiency as well as operating a combustion furnace.

Shock Characteristics of the Opposed Disc Springs (ODS) Shock Isolator with Pretightening under Boundary Friction Condition

In this study, to solve the problems of shock environment and shock isolation, about which there is still a lack of reasonable description, an isokinetic shock distinguishing method (ISDM), which can quantitatively distinguish between shock and forced vibration state, is presented. And the shock isolation performance of an opposed disc springs (ODS) shock isolator with pretightening under boundary friction condition is investigated. The static and dynamic stiffness properties of the ODS shock isolator are discussed. Relying on ISDM, a shock dynamic model of the ODS shock isolator with pretightening under boundary friction condition is established. The average method is adopted to solve the model theoretically. The shock acceleration ratio (SAR), shock displacement ratio (SDR), and relative displacement ratio (RDR) of the model are calculated using the numerical method and verified by experiments. Both numerical and experimental results show that ISDM is effective. And the effects on isolation efficiency of the number of disc springs, additional supporting force, pretightening force, load, and the shock velocity constant of the ODS shock isolator are discussed, which provide guidelines for its further practical application.

COVID-19 crisis and the continuous use of virtual classes

COVID-19 is a serious epidemic that has an unmistakable impact on all aspects of our lives, including the educational process. Most of the world has adopted Virtual Classes (VCs) to sustain teaching and learning. While prior research about such e-learning technologies has been focusing on the initial adoption, this research investigates the factors influencing the students’ desire and intention to continue using VCs, especially after the crisis subsides. This study extends the literature by developing a model that integrates pre-and post-adoption constructs and incorporates technological characteristics, namely, task technology fit, convenience, and compatibility into the Expectation Confirmation Model (ECM) to study the post-adoption Continuance Intention (CI) of VCs. The model is empirically validated using the partial least squares–structural equation modelling method and proved to have a reasonable description power (R2=62%) in terms of students’ CI. The survey empirical data is also supported by interviews with some students. The results support all the hypothesized relationships and confirm that the integration of technical characteristics in the ECM provides an appropriate framework to explain students’ intention to continue using VCs, which forms a good base for practitioners to consider a wide range of technological features for preparing applications. Yet, the model still requires to be extended with other stakeholders, including teachers, and other constructs like personal, psychological, social, and environmental factors.

What determines the structure of short gamma-ray burst jets?

The discovery of GRB 170817A, the first unambiguous off-axis short gamma-ray burst arising from a neutron star merger, has challenged our understanding of the angular structure of relativistic jets. Studies of the jet propagation usually assume that the jet is ejected from the central engine with a top-hat structure and its final structure, which determines the observed light curve and spectra, is primarily regulated by the interaction with the nearby environment. However, jets are expected to be produced with a structure that is more complex than a simple top-hat, as shown by global accretion simulations. We present numerical simulations of short GRBs launched with a wide range of initial structures, durations and luminosities. We follow the jet interaction with the merger remnant wind and compute its final structure at distances ≳ 1011 cm from the central engine. We show that the final jet structure, as well as the resulting afterglow emission, depend strongly on the initial structure of the jet, its luminosity and duration. While the initial structure at the jet is preserved for long-lasting SGRBs, it is strongly modified for jets barely making their way through the wind. This illustrates the importance of combining the results of global simulations with propagation studies in order to better predict the expected afterglow signatures from neutron star mergers. Structured jets provide a reasonable description of the GRB 170817A afterglow emission with an off-axis angle θobs ≈ 22.5○.

Accounting for small bipolar magnetic regions in solar irradiance reconstructions

<p>Historical solar irradiance is a critical input to climate models. As no direct measurements are available before 1978, reconstructions of past irradiance changes are employed instead. Such reconstructions are based on the knowledge that solar irradiance on time scales of interest to climate studies is modulated by the evolution of the solar surface magnetic structures, such as sunspots and faculae. This calls for historical records or proxies of such features. The longest direct, and thus mostly used, record is the sunspot number. It allows a reasonable description of the emergence and evolution of active regions, which are larger magnetic regions containing sunspots. At the same time, a significant amount of the magnetic flux on the Sun emerges in the form of the so-called ephemeral magnetic regions, which are weaker short-lived bipolar regions that do not contain sunspots. Due to their high frequency, ephemeral regions are an important source of the irradiance variability, especially on time scales longer than the solar cycle. Difficulties in their proper accounting are a main reason for the high uncertainty in the secular irradiance variability. Existing models either do not account for their evolution at all or link them linearly to active regions. We use a new, more realistic model of the ephemeral region emergence, relying on recent independent solar observations, as input to a surface flux transport model (SFTM) to simulate the evolution of the magnetic field in such regions. The latter can then be used to reconstruct the solar irradiance since the Maunder minimum.</p>

Bethe-Salpeter Study of the Optical Absorption of trans and cis Azobenzene-Functionalized Metal-Organic Frameworks using Molecular and Periodic Models

The optical absorption spectra of the azobenzene-functionalized metal-organic framework, PCN-123, are calculated in cis and trans configurations using the Bethe-Salpeter equation (BSE) formalism and the GW approximation using periodic and non-periodic models. In the visible, near-UV and mid-UV region the optical excitations in the MOF are associated with the azobenzene functionalities and this results in spectral features similar to the case of the gas phase azobenzene and the azo-functionalized ligand. The most noticeable difference is the significantly more intense S₁ band for cis in the MOF as compared to the free molecules which points to a faster and more complete cis→trans isomerization in the framework, with strong implications for the design of MOFs with high photoconversion efficiencies. Consistent with these findings, all the molecular models employed to represent the MOF, including the smallest, are found to yield a reasonable description of the low energy optical spectra (between 2 and 5 eV) of the periodic framework, with the exception of the stronger S₁ band of cis in the MOF, a feature that we attribute to a limitation of the fragment model to correctly represent the wavefunction of the extended framework.

Bethe-Salpeter Study of the Optical Absorption of trans and cis Azobenzene-Functionalized Metal-Organic Frameworks using Molecular and Periodic Models

The optical absorption spectra of the azobenzene-functionalized metal-organic framework, PCN-123, are calculated in cis and trans configurations using the Bethe-Salpeter equation (BSE) formalism and the GW approximation using periodic and non-periodic models. In the visible, near-UV and mid-UV region the optical excitations in the MOF are associated with the azobenzene functionalities and this results in spectral features similar to the case of the gas phase azobenzene and the azo-functionalized ligand. The most noticeable difference is the significantly more intense S₁ band for cis in the MOF as compared to the free molecules which points to a faster and more complete cis→trans isomerization in the framework, with strong implications for the design of MOFs with high photoconversion efficiencies. Consistent with these findings, all the molecular models employed to represent the MOF, including the smallest, are found to yield a reasonable description of the low energy optical spectra (between 2 and 5 eV) of the periodic framework, with the exception of the stronger S₁ band of cis in the MOF, a feature that we attribute to a limitation of the fragment model to correctly represent the wavefunction of the extended framework.

Free Surface Flows in Electrohydrodynamics with a Constant Vorticity Distribution

In 1895, Korteweg and de Vries (KdV), derived their celebrated equation describing the motion of waves of long wavelength in shallow water. In doing so they made a number of quite reasonable assumptions, incompressibility of the water and irrotational fluid. The resulting equation, the celebrated KdV equation, has been shown to be a very reasonable description of real water waves. However there are other phenomena which have an impact on the shape of the wave, that of vorticity and viscosity. This paper examines how a constant vorticity affects the shape of waves in electrohydrodynamics. For constant vorticity, the vertical component of the velocity obeys a Laplace equation and also has the usual lower boundary condition. In making the vertical component of the velocity take central stage, the Burns condition can be thus bypassed.

Modeling and Simulation of Opinion Natural Reversal Dynamics with Opinion Leader Based on HK Bounded Confidence Model

Opinion natural reversals are important and common phenomena in network management. It is a naturally emerging process of opinions characterized by interactions between individuals and the evolution of attitudes themselves. To explore the underlying mechanism of this social phenomenon and to reveal its dynamic traits, we propose here a novel model which takes the effects of natural reversal parameter and opinion interaction on the individual’s view choice behavior into account based on the Hegselmann and Krause (HK) bounded confidence model. Experimental results show that the evolution of individual opinions is not only influenced by the interactions between neighboring individuals but also updated naturally due to individual factors themselves in the absence of interaction, which in turn proves that the proposed model can provide a reasonable description of the entire process of public opinion natural reversal under the Internet environment. Besides, the proportion of group opinion tendency, network topology, identification method, and the influence weight of opinion leader will play significant roles in this process, which further indicates our improved model is very robust and thus can provide some insightful evidence to understand the phenomena of opinion natural reversal.