81690 research outputs found
Sort by
Direct evidence for a carbon-carbon one-electron σ-bond
No full textCovalent bonds share electron pairs between two atoms and make up the skeletons of most organic compounds in single, double and triple bonds. In contrast, examples of one-electron bonds remain scarce, most probably due to their intrinsic weakness1-4. Although several pioneering studies have reported one-electron bonds between heteroatoms, direct evidence for one-electron bonds between carbon atoms remains elusive. Here we report the isolation of a compound with a one-electron sigma-bond between carbon atoms by means of the one-electron oxidation of a hydrocarbon with an elongated C-C single bond5,6. The presence of the C center dot C one-electron sigma-bond (2.921(3) & Aring; at 100 K) was confirmed experimentally by single-crystal X-ray diffraction analysis and Raman spectroscopy, and theoretically by density functional theory calculations. The results of this paper unequivocally demonstrate the existence of a C center dot C one-electron sigma-bond, which was postulated nearly a century ago7, and can thus be expected to pave the way for further development in different areas of chemistry by probing the boundary between bonded and non-bonded states. The one-electron oxidation of a hydrocarbon with an elongated C-C single bond provides direct evidence for a one-electron sigma-bond between carbon atoms
Numerical Simulation on the Electrical Conductivity of Ternary Mixtures Containing NaCl Solution, Quartz, and Smectite
No full textWhile the electrical conductivity of smectite-rich rocks is high, previous studies have only partially revealed its dependence on temperature, salinity, and porosity. This knowledge gap mainly arises from challenges in controlling various experimental conditions when measuring the conductivity of real smectite-bearing rock samples and quantifying the smectite content. To mimic conductivity measurements under ideal conditions, this study aimed to develop a simulator capable of accurately configuring the conditions to predict the direct-current conductivity of saturated rocks composed of an aqueous NaCl solution, quartz, and smectite under various temperatures (20°C–200°C), salinities (10−4–5 mol kg−1), porosities (0–1), and smectite fractions (0–1). The simulator reproduced the experimental conductivity measurements from drilled core samples by giving the anisotropy of those components' distribution. In addition, simulations with randomly assigned components revealed that when rocks contain abundant smectite, the bulk conductivity partially decreases with increasing NaCl solution's salinity or volume fraction. These negative slopes were approximated using empirical equations derived from previous studies. Percolation analysis further revealed that when the components are randomly assigned, conductive paths begin to form between the ends of the modeled sample once the sum of the volume fraction of bulk pore and smectite reaches 0.1
Presentations of Schur covers of braid groups
No full textIn this paper, we consider several basic facts of Schur covers of the symmetric groups and braid groups. In particular, we give explicit presentations of Schur covers of braid groups
Brain activity supporting alternating speech for semantic words : simultaneous magnetoencephalographic recording
No full textCommunication, especially conversation, is essential for human social life. Many previous studies have examined the neuroscientific underpinnings of conversation, i.e. language comprehension and speech production. However, conversation inherently involves two or more people, and unless two people actually interact with one another, the nature of the conversation cannot be truly revealed. Therefore, in this study, we used two magnetoencephalographs that were connected together, and simultaneously recorded brain activity while two people took turns speaking in a word association/alphabet completion task. We compared the amplitude modulation of the alpha- and beta-band rhythms within each of the 62 brain regions under semantic (word association; less predictable) and non-semantic (alphabet completion; more predictable) conditions. We found that the amplitudes of the rhythms were significantly different between conditions in a wide range of brain regions. Additionally, significant differences were observed in nearly the same group of brain regions after versus before each utterance, indicating that a wide range of brain areas is involved in predicting a conversation partner’s next utterance. This result supports the idea that mentalizing, e.g. predicting another person's speech, plays an important role in conversation, and suggests that the neural network implicated in mentalizing extends over a wide range of brain regions
Current understanding of comparative pathology and prospective research approaches for canine hemangiosarcoma
No full textHemangiosarcoma (HSA) is a malignant tumor originating from endothelial cells. HSA typically develops in dogs, but is rare in other animals, including humans. Although surgery and chemotherapy are conventional treatments for HSA, neither treatment can significantly improve patient prognosis. To develop novel and effective therapeutics, a deeper understanding of HSA pathogenesis must be acquired. However, the limited research tools for HSA have been unable to make a breakthrough; therefore, it is crucial to widely utilize or establish novel research tools such as patient-derived xenograft models, organoids, and chicken embryo xenograft models. The pathogenesis of the human counterpart of HSA, angiosarcoma (AS), also remains incompletely understood, preventing the extrapolation of findings from humans to dogs, unlike other diseases. In this review, we summarize the clinicopathological and morphological features of HSA, and then we discuss the current understanding of the molecular pathology of HSA. Finally, we highlight promising research tools that may accelerate HSA basic research toward developing novel therapeutics. We also briefly summarize AS to help researchers comprehend HSA from the perspective of comparative pathology
Lyapunov-based approach to event-triggered control with self-triggered sampling
No full textIn this paper, a Lyapunov-based design method for event-triggered control with self-triggered sampling is proposed. In the proposed method, update of the control input and sampling of the state are individually determined based on two kinds of upper bounds of the Lyapunov function. By the proposed method, a non-monotonic Lyapunov function can be constructed. By non-monotonic decrease of a Lyapunov function, the number of communications can be reduced. In the neighborhood of the origin, we consider a control method such that the state stays in a certain set. As a result, it is guaranteed that the closed-loop system is uniformly ultimately bounded. Through a numerical example, we demonstrate the effectiveness of the proposed method
Invasion status of hatchery-origin pink salmon in an unstocked river at the Shiretoko World Natural Heritage Site in northern Japan
No full textHatchery fish and their offspring (including hatchery-wild hybrids) have lower reproductive success than wild fish. Thus, the straying of hatchery fish may negatively impact wild populations, depending on the number of wild salmon returning and hatchery strays. We investigated the straying status of hatchery-origin pink salmon (Oncorhynchus gorbuscha), which have a higher straying rate than other salmonids, in an unstocked river at the Shiretoko World Natural Heritage Site, Japan. The hatchery strays accounted for 40.0% and 19.0% of the total samples in 2021 and 2022, respectively. These results indicate that hatchery pink salmon have invaded unstocked rivers and potentially genetically affect wild populations
Exploring topological spin order by inverse Hamiltonian design : A stabilization mechanism for square skyrmion crystals
No full textWe propose a framework to construct a real-space spin model based on the inverse Hamiltonian design. The method provides an efficient way of realizing unconventional topological spin textures by optimizing the interaction parameters. In order to demonstrate its usefulness, we show that the tuning of the long-range exchange interactions can give rise to a square skyrmion crystal even without factors that have been previously identified as prerequisites for its stabilization, such as a Dzyaloshinskii-Moriya interaction, a multispin interaction, and bond-dependent magnetic anisotropy. Moreover, we elucidate the essence for the emergence of the square skyrmion crystal by classifying the parameter sets we obtain by the method. Since the present framework by adopting machine learning techniques can be universally applied to any magnetic system irrespective of lattice structures, it serves as the efficient construction of an effective spin model and the understanding of the stabilization mechanisms for unconventional topological spin orders