Nastroje inwestorów wywołane przez COVID-19 i reakcje rynku w ekstremalnych warunkach meteorologicznych: dowody z sektora czystej energii w regionie Azji i Pacyfiku

The unprecedented global economic and social crisis caused by the coronavirus outbreak has not spared the energy sector. Using a dynamic model, we investigated the effect of COVID-19 cases on investor sentiments and stock returns of clean energy in the Asian-Pacific region. The results show that coronavirus cases negatively affect stock returns using investor sentiments as a transmission channel. We also find a negative effect of air pollution on stock returns. Since COVID-19 restricted trade and plummeted the oil prices, economies relied on non-renewable sources to meet energy demands. Nevertheless, the investor’s optimism and high sentiment level may deteriorate this link. On the other hand, we do not find any significant effect of low-high temperature on either investor sentiments or clean energy stock returns. Clean energy stocks were viewed as more sustainable and less vulnerable to external shocks, however, the fear and pessimism among investors induced by corona-virus are spilled over the renewable energy sector.Bezprecedensowy globalny kryzys gospodarczy i społeczny wywołany wybuchem koronawirusa uderzył także w sektor energetyczny. Korzystając z modelu dynamicznego, zbadaliśmy wpływ COVID-19 na nastroje inwestorów i stopy zwrotu w sektorze czystej energii w regionie Azji i Pacyfiku. Odkąd COVID-19 wpłynął negatyw-nie na handel i przyczynił się do gwałtownego spadku ceny ropy, wiele gospodarek wsparło odnawialne źródła energii, aby zaspokoić zapotrzebowanie na energię. Wyniki pokazują jednak, że koronawirus negatywnie wpływa na stopy zwrotu. Stwierdzamy również negatywny wpływ zanieczyszczenia powietrza na stopy zwrotu. Z drugiej strony nie widzimy istotnego wpływu zmian temperatury ani na nastroje inwestorów, ani na stopy zwrotu z czystej energii. Akcje czystej energii były postrzegane jako bardziej zrównoważone i mniej podatne na wstrząsy zewnętrzne, jednak strach i pesymizm inwestorów wywołany koronawirusem może wpłynąć nega-tywnie na sektor energii odnawialnej

Deterministic Spin-Orbit Torque Switching of Mn3Sn with the Interplay between Spin Polarization and Kagome Plane

Previous studies have demonstrated spin-orbit torque (SOT) switching of Mn3Sn where the spin polarization lies in the kagome plane (configuration I). However, the critical current density ($J_{crit}$) is unrealistically large ($J_{crit}$=$10^{14}$ A/$m^2$) and independent on the external field ($H_{ext}$). The stabilized magnetic state also depends on the initial state. These features conflict with the ferromagnet (FM) switching scheme as claimed in those studies, and thus call for other explanations. Alternatively, the system with the spin polarization perpendicular to the kagome plane (configuration II) is more like the FM based system since the spin polarization is orthogonal to all magnetic moments. In this work, we show SOT switching of Mn3Sn in configuration II. Similar to the FM, Jcrit and Hext are in the order of $10^{10}$ A/$m^2$ and hundreds of Oersted, respectively. The switching result is also independent of the initial state. Interestingly, the unique spin structure of Mn3Sn also leads to distinct features from FM systems. We demonstrate that Jcrit increases linearly with Hext, and extrapolation gives ultralow $J_{crit}$ for the field-free switching system. In addition, the switching polarity is opposite to the FM. We also provide the switching phase diagram as a guideline for experimental demonstration. Our work provides comprehensive understanding for the switching mechanism in both configurations. The switching protocol proposed in this work is more advantageous in realistic spintronic applications. We also clearly reveal the fundamental difference between FM and noncollinear antiferromagnetic switching

Spatially Nonuniform Oscillations in Ferrimagnets Based on an Atomistic Model

The ferrimagnets, such as GdxFeCo(1-x), can produce ultrafast magnetic switching and oscillation due to the strong exchange field. The two-sublattices macrospin model has been widely used to explain the experimental results. However, it fails in describing the spatial nonuniform magnetic dynamics which gives rises to many important phenomenons such as the domain walls and skyrmions. Here we develop the two-dimensional atomistic model and provide a torque analysis method to study the ferrimagnetic oscillation. Under the spin-transfer torque, the magnetization oscillates in the exchange mode or the flipped exchange mode. When the Gd composition is increased, the exchange mode firstly disappears, and then appears again as the magnetization compensation point is reached. We show that these results can only be explained by analyzing the spatial distribution of magnetization and effective fields. In particular, when the sample is small, a spatial nonuniform oscillation is also observed in the square film. Our work reveals the importance of spatial magnetic distributions in understanding the ferrimagnetic dynamics. The method developed in this paper provides an important tool to gain a deeper understanding of ferrimagnets and antiferromagnets. The observed ultrafast dynamics can also stimulate the development of THz oscillators.Comment: 17 pages, 4 figure

Anomalous impact of thermal fluctuations on spintransfer torque induced ferrimagnetic switching

The dynamics of a spin torque driven ferrimagnetic (FiM) system is investigated using the two-sublattice macrospin model. We demonstrate an ultrafast switching in the picosecond range. However, we find that the excessive current leads to the magnetic oscillation. Therefore, faster switching cannot be achieved by unlimitedly increasing the current. By systematically studying the impact of thermal fluctuations, we find the dynamics of FiMs can also be distinguished into the precessional region, the thermally activated region, and the cross-over region. However, in the precessional region, there is a significant deviation between FiM and ferromagnet (FM), i.e., the FM is insensitive to thermal fluctuations since its switching is only determined by the amount of net charge. In contrast, we find that the thermal effect is pronounced even a very short current pulse is applied to the FiM. We attribute this anomalous effect to the complex relation between the anisotropy and overdrive current. By controlling the magnetic anisotropy, we demonstrate that the FiM can also be configured to be insensitive to thermal fluctuations. This controllable thermal property makes the FiM promising in many emerging applications such as the implementation of tunable activation functions in the neuromorphic computing.Comment: 27 pages, 8 figure

How far is brain-inspired artificial intelligence away from brain?

Fueled by the development of neuroscience and artificial intelligence (AI), recent advances in the brain-inspired AI have manifested a tipping-point in the collaboration of the two fields. AI began with the inspiration of neuroscience, but has evolved to achieve a remarkable performance with little dependence upon neuroscience. However, in a recent collaboration, research into neurobiological explainability of AI models found that these highly accurate models may resemble the neurobiological representation of the same computational processes in the brain, although these models have been developed in the absence of such neuroscientific references. In this perspective, we review the cooperation and separation between neuroscience and AI, and emphasize on the current advance, that is, a new cooperation, the neurobiological explainability of AI. Under the intertwined development of the two fields, we propose a practical framework to evaluate the brain-likeness of AI models, paving the way for their further improvements

Mitochondrial Dysfunction and Sirtuins: Important Targets in Hearing Loss

Mitochondrial dysfunction has been suggested to be a risk factor for sensorineural hearing loss (SNHL) induced by aging, noise, ototoxic drugs, and gene. Reactive oxygen species (ROS) are mainly derived from mitochondria, and oxidative stress induced by ROS contributes to cochlear damage as well as mitochondrial DNA mutations, which may enhance the sensitivity and severity of hearing loss and disrupt ion homeostasis (e.g., Ca2+ homeostasis). The formation and accumulation of ROS further undermine mitochondrial components and ultimately lead to apoptosis and necrosis. SIRT3–5, located in mitochondria, belong to the family of sirtuins, which are highly conserved deacetylases dependent on nicotinamide adenine dinucleotide (NAD+). These deacetylases regulate diverse cellular biochemical activities. Recent studies have revealed that mitochondrial sirtuins, especially SIRT3, modulate ROS levels in hearing loss pathologies. Although the precise functions of SIRT4 and SIRT5 in the cochlea remain unclear, the molecular mechanisms in other tissues indicate a potential protective effect against hearing loss. In this review, we summarize the current knowledge regarding the role of mitochondrial dysfunction in hearing loss, discuss possible functional links between mitochondrial sirtuins and SNHL, and propose a perspective that SIRT3–5 have a positive effect on SNHL

Prediction of monomer reactivity in radical copolymerizations from transition state quantum chemical descriptors

In comparison with the Q-e scheme, the Revised Patterns Scheme: the U, V Version (the U-V scheme) has greatly improved both its accessibility and its accuracy in interpreting and predicting the reactivity of a monomer in free-radical copolymerizations. Quantitative structure-activity relationship (QSAR) models were developed to predict the reactivity parameters u and v of the U-V scheme, by applying genetic algorithm (GA) and support vector machine (SVM) techniques. Quantum chemical descriptors used for QSAR models were calculated from transition state species with structures C¹H3 - C²HR³• or •C¹H2 - C²H2R³ (formed from vinyl monomers C¹H²=C²HR³ + H•), using density functional theory (DFT), at the UB3LYP level of theory with 6-31G(d) basis set. The optimum support vector regression (SVR) model of the reactivity parameter u based on Gaussian radial basis function (RBF) kernel (C = 10, ε = 10- 5 and γ = 1.0) produced root-mean-square (rms) errors for the training, validation and prediction sets being 0.220, 0.326 and 0.345, respectively. The optimal SVR model for v with the RBF kernel (C = 20, ε = 10- 4 and γ = 1.2) produced rms errors for the training set of 0.123, the validation set of 0.206 and the prediction set of 0.238. The feasibility of applying the transition state quantum chemical descriptors to develop SVM models for reactivity parameters u and v in the U-V scheme has been demonstrated

Nastroje inwestorów wywołane przez COVID-19 i reakcje rynku w ekstremalnych warunkach meteorologicznych:dowody z sektora czystej energii w regionie Azji i Pacyfiku

The unprecedented global economic and social crisis caused by the coronavirus outbreak has not spared the energy sector. Using a dynamic model, we investigated the effect of COVID-19 cases on investor sentiments and stock returns of clean energy in the Asian-Pacific region. The results show that coronavirus cases negatively affect stock returns using investor sentiments as a transmission channel. We also find a negative effect of air pollution on stock returns. Since COVID-19 restricted trade and plummeted the oil prices, economies relied on non-renewable sources to meet energy demands. Nevertheless, the investor’s optimism and high sentiment level may deteriorate this link. On the other hand, we do not find any significant effect of low-high temperature on either investor sentiments or clean energy stock returns. Clean energy stocks were viewed as more sustainable and less vulnerable to external shocks, however, the fear and pessimism among investors induced by corona-virus are spilled over the renewable energy sector.Bezprecedensowy globalny kryzys gospodarczy i społeczny wywołany wybuchem koronawirusa uderzył także w sektor energetyczny. Korzystając z modelu dynamicznego, zbadaliśmy wpływ COVID-19 na nastroje inwestorów i stopy zwrotu w sektorze czystej energii w regionie Azji i Pacyfiku. Odkąd COVID-19 wpłynął negatyw-nie na handel i przyczynił się do gwałtownego spadku ceny ropy, wiele gospodarek wsparło odnawialne źródła energii, aby zaspokoić zapotrzebowanie na energię. Wyniki pokazują jednak, że koronawirus negatywnie wpływa na stopy zwrotu. Stwierdzamy również negatywny wpływ zanieczyszczenia powietrza na stopy zwrotu. Z drugiej strony nie widzimy istotnego wpływu zmian temperatury ani na nastroje inwestorów, ani na stopy zwrotu z czystej energii. Akcje czystej energii były postrzegane jako bardziej zrównoważone i mniej podatne na wstrząsy zewnętrzne, jednak strach i pesymizm inwestorów wywołany koronawirusem może wpłynąć nega-tywnie na sektor energii odnawialnej