Perspectives in science最新文献

The beginning of the universe, the Big Bang, being an important subdomain in cosmology, marks the very beginning of space and time. Therefore, it has formed the modern scientific worldview. Transferring this to students through science teaching is a frequent request in science literacy discussion (e.g., American Association for the Advancement of Science, 1993, Schecker et al., 2004).

However, it is not yet clear in science education if students’ conceptions about the Big Bang vary by nationality, and therefore, if it is possible to apply the same teaching modules to students from different countries, who may have diverse social and cultural backgrounds and different curricula. These conceptions with which students enter the classroom were investigated in our study. We implemented an open-ended questionnaire survey in Germany, with questions based on recent U.S. studies. The results clearly showed, with high interrater reliabilities, widespread misconceptions like the Big Bang being an explosion of preexisting matter into empty space or the universe having a centre. Furthermore, a comparison of results from researchers in the USA, Sweden and Germany allowed us to identify differences in students’ conceptions between the countries. Our findings appear to indicate that German students have slightly better pre-instructional conceptions about the Big Bang theory.

Upon completing 100 years since it was published, the work Die Kinetik der Invertinwirkung by Michaelis and Menten (MM) was celebrated during the 6th Beilstein ESCEC Symposium 2013. As the 7th Beilstein ESCEC Symposium 2015 debates enzymology in the context of complex biological systems, a post-MM approach is required to address cell-like conditions that are well beyond the steady-state limitations. The present contribution specifically addresses two hitherto ambiguous constants whose interest was, however, intuited in the original MM paper: (i) the characteristic time constant τ_∞, which can be determined using the late stages of any progress curve independently of the substrate concentration adopted; and (ii) the dissociation constant K_S, which is indicative of the enzyme–substrate affinity and completes the kinetic portrayal of the Briggs–Haldane reaction scheme. The rationale behind τ_∞ and K_S prompted us to revise widespread concepts of enzyme's efficiency, defined by the specificity constant k_cat/K_M, and of the Michaelis constant K_M seen as the substrate concentration yielding half-maximal rates. The alternative definitions here presented should help recovering the wealth of published k_cat/K_M and K_M data from the criticism that they are subjected. Finally, a practical method is envisaged for objectively determining enzyme's activity, efficiency and affinity – (EA)² – from single progress curves. The (EA)² assay can be conveniently applied even when the concentrations of substrate and enzyme are not accurately known.

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, pervasive environmental pollutants with mutagenic, teratogenic, and carcinogenic properties. There is interest in exploiting the nutritional capabilities of microbes to remove PAHs from various environments including those impacted by improper disposal or spills. Although there is a considerable body of literature on PAH degradation, the substrates and products for many of the enzymes have never been identified and many proposed activities have never been confirmed. This is particularly true for high molecular weight PAHs (e.g., phenanthrene, fluoranthene, and pyrene). As a result, pathways for the degradation of these compounds are proposed to follow one elucidated for naphthalene with limited experimental verification. In this pathway, ring fission produces a species that can undergo a non-enzymatic cyclization reaction. An isomerase opens the ring and catalyzes a cis to trans double bond isomerization. The resulting product is the substrate for a hydratase-aldolase, which catalyzes the addition of water to the double bond of an α,β-unsaturated ketone, followed by a retro-aldol cleavage. Initial kinetic and mechanistic studies of the hydratase-aldolase in the naphthalene pathway (designated NahE) and two hydratase-aldolases in the phenanthrene pathway (PhdG and PhdJ) have been completed. Crystallographic work on two of the enzymes (NahE and PhdJ) provides a rudimentary picture of the mechanism and a platform for future work to identify the structural basis for catalysis and the individual specificities of these hydratase-aldolases.

Experiential science learning based on the in-built sensors of handheld devices such as smartphones, tablet computer and game consoles has seen quite a strong development in recent years. In particular, such devices with internal acceleration sensors offer an innovative approach to kinematics learning in classroom physics, a notoriously difficult topic for pupils. In view of research and teaching in this domain, the practical advantages and disadvantages of two such devices, the Nintendo WiiMote and the Apple iPod touch, are discussed.

Beyond the specific examples, this comparison of the advantages and disadvantages of two different “philosophies” of instructional technology with regard to their use in science learning experiments provides arguments for discussions and decisions related to such technology in other and future settings, which can be of interest to both researchers and practitioners in the field.

This paper presents a technique that aimed to accomplish an efficient balance between video compression using H.265 protocol and retention of 8K resolution. The study implements multi-level of optimization in the encoding process using H.265 where JPEG2000 standards play a crucial role. The study also applies a novel concept of orthogonal projection that manages pixels metadata required in every frame transition followed by motion compensation. By using multiple file formats of 30 video datasets, the outcome of the study is found to be accomplishing approximately 49% of enhancement in data quality and around 59% of improvement in video compression in comparison to the existing techniques of HEVC-based video compression.

The thermal performance of open earth pan furnace used conventionally for preparing jaggery (gur) is very low. Dry bagasse is used as a fuel to produce heat in a combustion process in the open earth furnace. The energy loss due to inefficient combustion process, the energy loss through exhaust gases and other losses due to furnace wall, convection and radiation bring the thermal efficiency of open earth pan furnace to a low value. Certain quantity of energy produced in combustion process is used to sensibly heat the sugarcane juice to its evaporation temperature. Solar collectors can supply the sensible heat required to raise the sugarcane juice temperature up to its boiling point, thereby reducing the total quantity of heat required in preparing the jaggery. Solar drier can be used to supply hot air required for the combustion process to burn the bagasse in more efficient manner. This paper presents analytical calculations done to study the performance improvement of the jaggery making unit using solar collector and solar drier.

The stable operation of a bottom ash cooler is vital for the operation of the circulating fluidized bed boiler. To assess, the stability of the ash cooler, it is important to have a thorough understanding of the flow behaviour. Although, many experimental results been reported in literature, CFD modelling of the ash cooler has not been carried out. In this paper, the transient computational analysis of a novel stripper ash cooler has been carried out using the Eulerian–Eulerian multiphase approach. The phase coupled SIMPLE algorithm has been used to solve the multiphase equations and the Gidaspow drag model has been employed to model the interaction between the fluidized air and ash. Two cases have been analysed in this paper. In the first case, the filling of the ash in the cooler has been analysed and in the second case, the phenomenon of fluidized bed bubbling in the ash cooler has been simulated. The study the of flow characteristics of hot ash has been studied. The contours of temperature, phase volume and bubbling have been analyzed in this paper.

This paper evaluates the change in metabolic energy required to maintain the signalling activity of neurons in the presence of an external electric field. We have analysed the Hodgkin–Huxley type conductance based fast spiking neuron model as electrical circuit by changing the frequency and amplitude of the applied electric field. The study has shown that, the presence of electric field increases the membrane potential, electrical energy supply and metabolic energy consumption. As the amplitude of applied electric field increases by keeping a constant frequency, the membrane potential increases and consequently the electrical energy supply and metabolic energy consumption increases. On increasing the frequency of the applied field, the peak value of membrane potential after depolarization gradually decreases as a result electrical energy supply decreases which results in a lower rate of hydrolysis of ATP molecules.

Conventional method of defining half velocity widths is applicable only for axisymmetric jets. Hence, geometry based definition of half velocity width is used for non-circular jets. Usefulness of this method becomes less when there is no symmetry based on geometry. Hence, a new half velocity width is proposed based on equivalent area method. Newly proposed half velocity width is computed for a conventional circular jet and a non-circular jet. The comparison of half velocity widths obtained using conventional method and newly proposed method shows good agreement with each other for circular jet. Geometry based half width and equivalent area based half velocity width agree in the near field for the non-circular jet. Equivalent area based method is found as better representation of half velocity width for non-circular turbulent jets.