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Young Peoples’ Online Science Practices as a Gateway to Higher Education STEM
Get PDFThe purpose of this manuscript is to explore how students perceive that online practices have enabled their participation in university physics programmes. In order to conceptualise how students bridge their science participation across physical and online spaces, we make use of the learning ecology perspective. This perspective is complemented with the notion of science capital, analysing how students have been able to strengthen different aspects of science capital through online participation. Data has been generated through semi-structured interviews guided by a timeline, constructed in collaboration between the interviewer and the interviewee. Twenty-one students enrolled in higher education physics have been interviewed, with a focus on their trajectories into higher education physics. The findings focus on four students who in various ways all have struggled to access science learning resources and found ways to utilise online spaces as a complement to their physical learning ecologies. In the manuscript, we show how online practices have contributed to the students’ learning ecologies, e.g. in terms of building networks and functioning as learning support, and how resources acquired through online science practices have both use and exchange value in the wider science community. Online science participation is thus both curiosity driven and founded in instrumental reasons (using online tutoring to pass school science). Furthermore, we argue that online spaces have the potential to offer opportunities for participation and network building for students who do not have access to science activities and science people in their everyday surroundings.The purpose of this manuscript is to explore how students perceive that online practices have enabled their participation in university physics programmes. In order to conceptualise how students bridge their science participation across physical and online spaces, we make use of the learning ecology perspective. This perspective is complemented with the notion of science capital, analysing how students have been able to strengthen different aspects of science capital through online participation. Data has been generated through semi-structured interviews guided by a timeline, constructed in collaboration between the interviewer and the interviewee. Twenty-one students enrolled in higher education physics have been interviewed, with a focus on their trajectories into higher education physics. The findings focus on four students who in various ways all have struggled to access science learning resources and found ways to utilise online spaces as a complement to their physical learning ecologies. In the manuscript, we show how online practices have contributed to the students’ learning ecologies, e.g. in terms of building networks and functioning as learning support, and how resources acquired through online science practices have both use and exchange value in the wider science community. Online science participation is thus both curiosity driven and founded in instrumental reasons (using online tutoring to pass school science). Furthermore, we argue that online spaces have the potential to offer opportunities for participation and network building for students who do not have access to science activities and science people in their everyday surroundings
Can fluorophlogopite mica be used as an alkali metal ion source to boost the growth of two-dimensional molybdenum dioxide?
No full textEveryone familiar with two-dimensional (2D) materials is aware of fluorophlogopite mica (FM), which has an atomic-level flat surface that provides an ideal platform for the growth of 2D materials. Since it has been demonstrated that the alkali metal ions (AMI) can aid in the growth of large-sized 2D materials by chemical vapor deposition (CVD) in recent years, it became a major mystery whether FM which contains AMI benefits from them in the preparation of 2D materials by CVD, too. In this article, we dispelled this ambiguity and discovered that temperature is the key for FM as an AMI source to boost the growth of large-sized 2D materials. We carried out variable temperature experiments and found that FM can indeed be incorporated into the growth of large-sized 2D materials as an AMI source at high temperatures and successfully obtained the highly crystalline MoO2 with a larger size compared to those without FM. This finding is of great importance to the understanding of the growth mechanism of FM for 2D materials by CVD and to better exploit its role in the growth of 2D materials
Successive Cancellation Decoding of Single Parity-Check Product Codes: Analysis and Improved Decoding
No full textA product code with single parity-check component codes can be described via the tools of a multi-kernel polar code, where the rows of the generator matrix are chosen according to the constraints imposed by the product code construction. Following this observation, successive cancellation decoding of such codes is introduced. In particular, the error probability of single parity-check product codes over binary memoryless symmetric channels under successive cancellation decoding is characterized. A bridge with the analysis of product codes introduced by Elias is also established for the binary erasure channel. Successive cancellation list decoding of single parity-check product codes is then described. For the provided example, simulations over the binary input additive white Gaussian channel show that successive cancellation list decoding outperforms belief propagation decoding applied to the code graph. Finally, the performance of the concatenation of a product code with a high-rate outer code is investigated via distance spectrum analysis. Examples of concatenations performing within 0.7 dB from the random coding union bound are provided
Sim-to-real transfer and reality gap modeling in model predictive control for autonomous driving
Get PDFThe main challenge for the adoption of autonomous driving is to ensure an adequate level of safety. Considering the almost infinite variability of possible scenarios that autonomous vehicles would have to face, the use of autonomous driving simulators is becoming of utmost importance. Simulation suites allow the used of automated validation techniques in a wide variety of scenarios, and enable the development of closed-loop validation methods, such as machine learning and reinforcement learning approaches. However, simulation tools suffer from a standing flaw in that there is a noticeable gap between the simulation conditions and real-world scenarios. Although the use of simulators powers most of the research around autonomous driving, and is generally used within all domains it is divided into, there is an inherent source of error given the stochastic nature of activities performed in real world, which are unreplicable in computer environments. This paper proposes a new approach to assess the real-to-sim gap for path tracking systems. The aim is to narrow down the sources of error between simulation results and real-world conditions, and to evaluate the performance of the simulation suite in the design process by employing the information extracted from gap analysis, which adds a new dimension of development against other approaches for autonomous driving. A real-time model predictive controller (MPC) based on adaptive potential fields was developed and validated using the CARLA simulator. Both the path planning and vehicle control systems where tested in real traffic conditions. The error between the simulator and the real data acquisition was evaluated using the Pearson correlation coefficient (PCC) and the max normalized cross-correlation (MNCC). The controller was further evaluated on a process of sim-to-real transfer, and was finally tested both in simulation and real traffic conditions. A comparison was performed against an optimal-control ILQR-based model predictive controller was carried out to further showcase the validity of this approach
Associations of PFAS-related plasma metabolites with cholesterol and triglyceride concentrations
Get PDFThe wide-spread environmental pollutants per- and polyfluoroalkyl substances (PFAS) have repeatedly been associated with elevated serum cholesterol in humans. However, underlying mechanisms are still unclear. Furthermore, we have previously observed inverse associations with plasma triglycerides. To better understand PFAS-induced effects on lipid pathways we investigated associations of PFAS-related metabolite features with plasma cholesterol and triglyceride concentrations. We used 290 PFAS-related metabolite features that we previously discovered from untargeted liquid chromatography-mass spectometry metabolomics in a case-control study within the Swedish V\ue4sterbotten Intervention Programme cohort. Herein, we studied associations of these PFAS-related metabolite features with plasma cholesterol and triglyceride concentrations in plasma samples from 187 healthy control subjects collected on two occasions between 1991 and 2013. The PFAS-related features did not associate with cholesterol, but 50 features were associated with triglycerides. Principal component analysis on these features indicated that one metabolite pattern, dominated by glycerophospholipids, correlated with longer chain PFAS and associated inversely with triglycerides (both cross-sectionally and prospectively), after adjustment for confounders. The observed time-trend of the metabolite pattern resembled that of the longer chain PFAS, with higher levels during the years 2004–2010. Mechanisms linking PFAS exposures to triglycerides may thus occur via longer chain PFAS affecting glycerophospholipid metabolism. If the results reflect a cause-effect association, as implied by the time-trend and prospective analyses, this may affect the general adult population
Simplified Kinetic Model for NH3‑SCR Over Cu‑CHA Based on First‑Principles Calculations
Get PDFSelective catalytic reduction with ammonia as reducing agent (NH3-SCR) is an efficient technology to control NOx emission during oxygen excess. Catalysts based on Cu-chabazite (Cu-CHA) have shown good performance for NH3-SCR with high activity and selectivity at low temperature and good hydrothermal stability. Here, we explore a first-principles based kinetic model to analyze in detail which reaction steps that control the selectivity for N2 and the light-off temperature. Moreover, a simplified kinetic model is developed by fitting lumped kinetic parameters to the full model. The simplified model describes the reaction with high accuracy using only five reaction steps. The present work provides insight into the governing reaction mechanism and stimulates design of knowledge-based Cu-CHA catalysts for NH3-SCR
Revisiting the bioavailability of flavan-3-ols in humans: A systematic review and comprehensive data analysis
Get PDFThis systematic review summarizes findings from human studies investigating the different routes of absorption, metabolism, distribution and excretion (ADME) of dietary flavan-3-ols and their circulating metabolites in healthy subjects. Literature searches were performed in PubMed, Scopus and the Web of Science. Human intervention studies using single and/or multiple intake of flavan-3-ols from food, extracts, and pure compounds were included. Forty-nine human intervention studies met inclusion criteria. Up to 180 metabolites were quantified from blood and urine samples following intake of flavan-3-ols, mainly as phase 2 conjugates of microbial catabolites (n = 97), with phenyl-γ-valerolactones being the most representative ones (n = 34). Phase 2 conjugates of monomers and phenyl-γ-valerolactones, the main compounds in both plasma and urine, reached two peak plasma concentrations (Cmax) of 260 and 88 nmol/L at 1.8 and 5.3 h (Tmax) after flavan-3-ol intake. They contributed to the bioavailability of flavan-3-ols for over 20%. Mean bioavailability for flavan-3-ols was moderate (31 \ub1 23%, n bioavailability values = 20), and it seems to be scarcely affected by the amount of ingested compounds. While intra- and inter-source differences in flavan-3-ol bioavailability emerged, mean flavan-3-ol bioavailability was 82% (n = 1) and 63% (n = 2) after (−)-epicatechin and nut (hazelnuts, almonds) intake, respectively, followed by 25% after consumption of tea (n = 7), cocoa (n = 5), apples (n = 3) and grape (n = 2). This highlights the need to better clarify the metabolic yield with which monomer flavan-3-ols and proanthocyanidins are metabolized in humans. This work clarified in a comprehensive way for the first time the ADME of a (poly)phenol family, highlighting the pool of circulating compounds that might be determinants of the putative beneficial effects linked to flavan-3-ol intake. Lastly, methodological inputs for implementing well-designed human and experimental model studies were provided
Electronegativity at the Shock Front
Get PDFIn this work, a scale for pressure-adapted atomic electronegativity is used to make general predictions of bond polarity in H-, C-, N- and O-based compounds experiencing shock conditions. The qualitative picture that emerges is one of increasing polarity of several bonds common in energetic materials. The general predictions made are compared to, and found to support, claims of ionic decomposition routes in compressed nitromethane and nitrate esters at high pressure. Changing electronegativity is also suggested as a factor driving the ionic disproportionation of various molecular phases with compression. Calculations using the eXtreme-Polarizable Continuum Model (XP-PCM) predict increasing energy differences between ground and excited states in non-bonded H, C, N, and O atoms as a function of pressure. This data enables for a discussion on the reliability of electronegativity-based rationales at more extreme thermodynamic conditions
On the Maxwell-wave equation coupling problem and its explicit finite-element solution
No full textIt is well known that in the case of constant dielectric permittivity and magnetic permeability, the electric field solving the Maxwell’s equations is also a solution to the wave equation. The converse is also true under certain conditions. Here we study an intermediate situation in which the magnetic permeability is constant and a region with variable dielectric permittivity is surrounded by a region with a constant one, in which the unknown field satisfies the wave equation. In this case, such a field will be the solution of Maxwell’s equation in the whole domain, as long as proper conditions are prescribed on its boundary. We show that an explicit finite-element scheme can be used to solve the resulting Maxwell-wave equation coupling problem in an inexpensive and reliable way. Optimal convergence in natural norms under reasonable assumptions holds for such a scheme, which is certified by numerical exemplification
Self-Stabilizing and Private Distributed Shared Atomic Memory in Seldomly Fair Message Passing Networks
Get PDFWe study the problem of privately emulating shared memory in message-passing networks. The system includes clients that store and retrieve replicated information on N servers, out of which e are data-corrupting malicious. When a client accesses a data-corrupting malicious server, the data field of that server response might be different from the value it originally stored. However, all other control variables in the server reply and protocol actions are according to the server algorithm. For the coded atomic storage algorithms by Cadambe et al., we present an enhancement that ensures no information leakage and data-corrupting malicious fault-tolerance. We also consider recovery after the occurrence of transient faults that violate the assumptions according to which the system was designed to operate. After their last occurrence, transient faults leave the system in an arbitrary state (while the program code stays intact). We present a self-stabilizing algorithm, which recovers after the occurrence of transient faults. This addition to Cadambe et al. considers asynchronous settings as long as no transient faults occur. The recovery from transient faults that bring the system counters (close) to their maximal values may include the use of a global reset procedure, which requires the system run to be controlled by a fair scheduler. After the recovery period, the safety properties are provided for asynchronous system runs that are not necessarily controlled by fair schedulers. Since the recovery period is bounded and the occurrence of transient faults is extremely rare, we call this design criteria self-stabilization in the presence of seldom fairness. Our self-stabilizing algorithm uses a bounded amount of storage during asynchronous executions (that are not necessarily controlled by fair schedulers). To the best of our knowledge, we are the first to address privacy, data-corrupting malicious behavior, and self-stabilization in the context of emulating atomic shared memory in message-passing systems