Fundamentals of polymer precursor method for synthesizing silicon carbide based ceramic fibers

Inorganic fibers become major materials in modern industry. In particular, the carbon fiber technology shows remarkable development. Nowadays, carbon fibers with extreme strength and flexibility play an important role in airplane industry as carbon fiber reinforced plastic matrix composites (CFRP). Success of carbon fiber gives a clue that even the materials with no fusibility or with high melting points can be shaped to thin fiber form by using polymers as starting precursors. In a decade of 1970s, Yajima evidenced that thin continuous SiC based fibers can be obtained from a kind of organosilicon polymers. This polymer, PCS, was synthesized by thermal condensation reaction of polydimethylsilane (PDMS). PDMS is intrinsically infusible and not soluble to any kinds of organic solvents because of the symmetric backbone structure. During the thermal condensation, chain scissions and recombination process introduce Si-CH2-Si bridges and Si-H side groups in the polymer structure, which is called Kumada rearrangement process. PCS, thus obtained, is stable at a room temperature in an oxidation or humid atmosphere. The introduced Si-H side groups play an important role in curing process, which is necessary to make spun fiber infusible during the successive pyrolysis process. It should be paid attention that chemical composition of the PCS is not equal to the original PDMS. C/Si and H/Si molar ratios of PCS (1.87 and 4.55, respectively) is apparently lower than those of PDMS. It means that backbone of PCS possesses ladder-like or locally cross-linked structure. Relatively high softening point of PCS also suggests the existence of such rigid structure. Most of “polycarbosilane”, synthesized by synthetic chemistry is viscous liquid at room temperature. It is unfortunate that thermal condensation reaction of PDMS is mainly accompanied by evolution of gaseous silanes with monomethyl or dimethyl chemical groups, while evolution of methane and hydrogen is minor. Because of a large amount of such “silanes” removal, PCS yield from PDMS is known to be limited in the range of 60-65 mass%. Melt spinnability is an essential issue in applying the polymer precursors for ceramic fiber technology. “Spinability” is however, rather a pragmatic term and the assessment is not easy. Evaluation of PCS melt viscosity suggested that the viscosity range of 5-10 Pa·s was appropriate for the fiber spinning. From the temperature dependence, the apparent activation energy of 180 kJ mol-1 was estimated for PCS, and addition of the plasticizer seemed to decrease the activation energy. By adjusting the plasticizer combination, thinner precursor fiber or the fiber with unique - controlled morphology was synthesized The C/Si ratio of PCS exceeds 1.0, and thermal oxidation curing, adopted in early days, introduces a considerable amount of oxygen in the system. Thus, the classic SiC based fibers were generally amorphous with chemical compositions of Si-C-O or Si-C-O-M (M: metal). Development of ceramic-matrix composites (CMC), however, began to require maintenance of the fiber performance even at high temperatures beyond 1600 C. Near stoichiometric and more crystalline SiC fibers were developed in recent years in order to respond such market demands. One is Hi-Nicalon-Type S (NGS Advanced Fibers Co., Ltd), which uses electron beam curing and hydrogen decarboinization for adjusting the fiber chemical composition. Another is Tyranno SA (UBE industries, Ltd.), which becomes stoichiometric SiC via carbothermal reduction process. Existence of Al is believed to be essential for homogeneous crystallization. The technology of these advanced fiber production, however, contains more complex factors than the cases of classic ceramic fibers because the process contains the step of the large volume-weight shrinkage influenced by surrounding an atmosphere. Deeper information about local composition change, bond rearrangements and nano-micro crystallization process will become necessary for precise control of the whole process

Utility of Plain Chest Computed Tomography in Diagnosing Cardioembolic Stroke due to Paroxysmal Atrial Fibrillation

Background：Diagnosing cardioembolic stroke due to paroxysmal atrial fibrillation（PAF）is difficult, mainly due to low detection rate. We evaluated whether left atrial volume, which can be simply measured using non-contrast chest computed tomography（CT-LAV）, can contribute to the diagnosis of cardioembolic stroke due to PAF（PAF-CE）.Methods：Fifty-one consecutive patients with acute ischemic stroke within 24 h of onset were included in this study. Upon admission, we measured the left atrial diameter using transthoracic echocardiography（TTE-LAD）and CT-LAV. Patient background factors such as sex, age, and stroke risk factors were noted as well as brain natriuretic peptide（BNP）value and QTc interval were evaluated on admission. Utilities of BNP value, CT-ALV, and TTE-LAD in PAF-CE diagnosis were compared.Results：Patients were classified into three groups：cerebral thrombosis（CTB）group including large-artery atherosclerosis and small-vessel occlusion（n＝16）, cardioembolic stroke due to non-valvular atrial fibrillation（AF-CE）group（n＝20）, and cardioembolic stroke due to paroxysmal atrial fibrillation（PAF-CE）group（n＝15）. BNP value was highest in the AF-CE group（240.5 pg/mL）, followed by the PAF-CE（187.9 pg/mL）and CTB groups（35.0 pg/mL）（p＜0.001）. There was a significant difference in TTE-LAD among the groups（AF-CE group, 43.8 mm；PAF-CE group, 38.3 mm；CTB group, 34.1 mm）（p＜0.001）. CT-LAV was higher in the AF-CE group（142 mm3）than in the PAF-CE（95.8 mm3）and CTB groups（95.8 mm3）（p＜0.001）. In differentiating PAF-CE, the area under the receiver operating characteristic curve was 0.867, 0.742, and 0.845 for BNP value, TTE-LAD, and CT-LAV, respectively. A cut-off CT-LAV value of ≥ 69.6 mm3 had a high diagnostic rate（＞80％ of sensitivity, specificity, positive predictive value, negative predictive value, and accuracy）.Conclusion：CT-LAV can be useful in diagnosing PAF-CE. Further studies with larger sample size are required to confirm our findings and determine better cut-off value for CT-LAV

Reduced Nogo-P3 in adults with developmental coordination disorder (DCD)

Nogo-N2 is associated with the premotor cognitive process that precedes motor response (e.g., conflict monitoring), whereas Nogo-P3 is related to the inhibition of the actual motor response. We examined the influence of motor clumsiness of developmental coordination disorder (DCD) on components of the event-related potential in a Go/Nogo task. Participants were healthy adults (N = 81) that were classified into control and DCD groups based on the Movement Assessment Battery for Children Second Edition. We manipulated the difficulty in stopping a response by varying the frequency of Nogo stimuli in a response task into rare (20%) and frequent (80%) conditions, and Nogo-N2 and Nogo-P3 were calculated from electroencephalograms (EEGs) during the Go/Nogo tasks. The commission error rate in the rare condition was significantly higher in the DCD group than in the control group, indicating that motor clumsiness decreases task performance. There were no differences in Nogo-N2 between DCD and control groups. However, Nogo-P3 in the rare condition was reduced in the DCD group compared to the control group. These results suggest that the influence of motor clumsiness is limited to the cognitive process after the initiation of the actual motor response.Peer reviewe

From species sorting to mass effects: spatial network structure mediates the shift between metacommunity archetypes

Local assemblages are embedded in networks of communities connected by dispersal, and understanding the processes that mediate this local-regional interaction is central to understanding biodiversity patterns. In this network (i.e. metacommunity), the strength of dispersal relative to the intensity of environmental selection typically determines whether local communities are comprised of species well-adapted to the local environment (i.e. species sorting) or are dominated by regionally successful species that may not be locally adapted (i.e. mass effects), which by extension determines the capacity of the landscape to sustain diversity. Despite the fundamentally spatial nature of these dispersal-mediated processes, much of our theoretical understanding comes from spatially implicit systems, a special case of spatial structure in which patches are all connected to each other equally. In many real systems, both the connections among patches (i.e. network topology) and the distributions of environments across patches (i.e. spatial autocorrelation) are not arranged uniformly. Here, we use a metacommunity model to investigate how spatial heterogeneities may change the balance between species sorting versus mass effects and diversity outcomes. Our simulations show that, in general, the spatially implicit model generates an outlier in biodiversity patterns compared to other networks, and most likely amplifies mass effects relative to species sorting. Network topology has a strong effect on metacommunity outcome, with topologies of sparse connections and few loops promoting sorting of species into suitable patches. Spatial autocorrelation is another key factor; by interacting with spatial topology, intermediate-scale clusters of similar patches can emerge, leading to a reduction of regional competition, and hence maintenance of gamma diversity. These results provide a better understanding of the role that complex spatial landscape structure plays in metacommunity processes, a necessary step to understanding how metacommunity processes relate to biodiversity conservation

Does Pramipexole Treatment Improve Headache in Patients with Concomitant Migraine and Restless Legs Syndrome?

Background: Recent studies have suggested a strong link between migraines and restless legs syndrome (RLS). It is possible that these disorders share a dopaminergic dysfunction in the hypothalamic A11 nucleus that contributes to this association. However, there have been no clinical studies to evaluate the effect of dopaminergic treatment on migraine symptoms in patients with concomitant migraines and RLS. Methods: We present an illustrative patient with concomitant RLS and migraine who showed improvement in her headache frequency and RLS symptoms following immediate‐release pramipexole (P‐IR) treatment and provide review results from the medical records of patients who experienced both migraines and RLS in our previous cross‐sectional study. Results: Ten patients (nine patients from the previously completed single‐center study) received P‐IR treatment were included in the study. RLS symptoms improved markedly in all of the subjects. Five out of the 10 patients (50%) reported improvement in migraine headaches. Of these five patients, four (80%) had reported morning headaches before P‐IR treatment. Discussion: Our results indicate that the identification of RLS in migraine patients is clinically significant and that dopaminergic treatment may improve both migraines, particularly morning headache (80% improvement in this study), and RLS symptoms. However, further clinical studies are warranted to verify our results

Comparison of Impressions of COVID-19 Vaccination and Influenza Vaccination in Japan by Analyzing Social Media Using Text Mining

The aim of this study was to compare impressions of COVID-19 vaccination and influenza vaccination in Japan by analyzing social media (Twitter®) using a text-mining method. We obtained 10,000 tweets using the keywords “corona vaccine” and “influenza vaccine” on 15 December 2022 and 19 February 2023. We then counted the number of times the words were used and listed frequency of these words by a text-mining method called KH Coder. We also investigated concepts in the data using groups of words that often appeared together or groups of documents that contained the same words using multi-dimensional scaling (MDS). “Death” in relation to corona vaccine and “severe disease” for influenza vaccine were frequently used on 15 December 2022. The number of times the word “death” was used decreased, “after effect” was newly recognized for corona vaccine, and “severe disease” was not used in relation to influenza vaccine. Through this comprehensive analysis of social media data, we observed distinct variations in public perceptions of corona vaccination and influenza vaccination in Japan. These findings provide valuable insights for public health authorities and policymakers to better understand public sentiment and tailor their communication strategies accordingly

Paradoxical nature of narrative in analytical psychotherapy

This study explored the changes, obstacles for changes and the sharing of narratives in psychotherapeutic case studies. Study 1 developed an index for analyzing the process of narratives in psychotherapy, based on 101 cases. In Study 2, 203 cases were evaluated using the index generated from Study 1. As a result, three paradoxical natures of narrative became evident. Narrative in psychotherapy is thought to include (1) recognizing the beginning of a narrative, which can also signify the completion of the narrative, (2) negative movements that hinder the development of the narrative while at the same time move it forward and (3) an individual’s narrative that is uniquely one’s own, but easily influences and is influenced by the narratives of others

BIOMECHANICAL STUDY ON DIFFERENT DIRECTIONS FOR RUNNING JUMPS FOCUSED ON THE TAKEOFF PREPARATION

This study aimed to elucidate the difference in CG parameters from three steps, prejump to takeoff step of the jump motion (running jump), and obtain primary data on takeoff preparation action. Five male jumpers associated with the university track and field department were trained to perform their best at (1) approach run with no takeoff (RUN), (2) jumping as far as possible (long jump [LJ]), and (3) jumping as high as possible (high jump [HJ]), which were recorded using a three-dimensional capture system. As a result, significant differences were observed in not only the takeoff but also the takeoff preparation phase regarding CG parameters, suggesting the need to focus on the takeoff preparation phase as a factor that determines jump direction. Moreover, HJ and LJ suppressed an increase in vertical velocity one step prior, and by takeoff at a lower CG, the athletes allowed for an easier increase in takeoff angle and jump height. However, to resist a decrease in horizontal velocity, LJ transitioned to takeoff in a manner closer to RUN and without changing takeoff preparation as much as that in HJ. Thus, adjusting vertical velocity and height one step before takeoff can influence takeoff angle