ABSTRACT We present time-resolved spectral analysis of the steep decay segments of 29 bright X-ray flares of gamma-ray bursts (GRBs) observed with the Swift/X-ray telescope, and model their light ...curves and spectral index evolution behaviors with the curvature effect model. Our results show that the observed rapid flux decay and strong spectral index evolution with time can be well fitted with this model, and the derived characteristic timescales (tc) are in the range of 23 ∼ 264 s. Using an empirical relation between the peak luminosity and the Lorentz factor derived from the prompt gamma-rays, we estimate the Lorentz factors of the flares (ΓX). We obtain ΓX = 17 ∼ 87 with a median value of 52, which is smaller than the initial Lorentz factors of prompt gamma-ray fireballs. With the derived tc and ΓX, we constrain the radiating regions of 13 X-ray flares, yielding RX = (0.2 ∼ 1.1) × 1016 cm, which are smaller than the radii of the afterglow fireballs at the peak times of the flares. A long evolution feature from prompt gamma-ray phase to the X-ray epoch is found by incorporating our results with a sample of GRBs whose initial Lorentz factors are available in the literature, i.e., . These results may shed light on the long-term evolution of GRB central engines.
Background
Learning and memory deficits and pathologic changes in the hippocampus caused by toothlessness and soft diet feeding are related to reduced masseter muscle (MM) function.
Objective
Myosin ...heavy chain (MyHC) isoform expression in the MM also changes under different chewing conditions. The neurotransmitter calcitonin gene‐related peptide (CGRP) and vascular endothelial growth factor A (VEGF‐A) are involved in MM formation. However, the relationship between CGRP, VEGF‐A and MyHC isoforms in the MM in the senescence‐accelerated mouse prone 8 (SAMP8) strain, a model of learning and memory deficits, remains unclear.
Methods
Changes in CGRP, VEGF‐A, vasculogenesis marker and MyHC isoform mRNA expression in the MMs of ageing SAMP8 and senescence‐accelerated mouse resistant 1 (SAMR1) mice was investigated through quantitative real‐time polymerase chain reaction (qRT–PCR) and in situ hybridization.
Results
qRT–PCR revealed obviously high CGRP levels in the SAMP8 mouse MM (p < .001). MyHC‐IId/x mRNA expression in the MM was higher in 24‐week‐old SAMP8 mice than 24‐week‐old SAMR1 mice (p < .001) but lower in slow‐MyHC SAMP8 mice than SAMR1 mice (p < .001). CGRP mRNA was observed on the muscle fibres of the SAMP8 mouse MM but not the SAMR1 mouse MM through in situ hybridization. Principal component analysis (PCA) revealed strong positive contributions of SAMP8‐MyHC‐IId/x, SAMP8‐CGRP, SAMR1‐MyHC‐emb, SAMR1‐CGRP, SAMR1‐VEGF‐A, SAMR1‐CD31, SAMP8‐VEGF‐A, and SAMP8‐CD31 in the MM at 12 and 24 weeks.
Conclusion
Calcitonin gene‐related peptide is also key for the MyHC‐IId/x and slow‐MyHC patterns in the MMs of SAMP8 mice.
With aging, the sympathetic nerve becomes dominant, and more CGRP is released from the hippocampus or trigeminal ganglion, which is transported to the masseter muscle. CGRP may be effected to the composition and vascularity of muscle fiber types in the model of learning and memory deficits masseter muscle.
A dual nickel‐/palladium‐catalyzed direct gem‐difluorovinylation of readily available aryl/vinyl triflates with substituted gem‐difluorovinyl tosylates is presented. This protocol affords various ...diaryldifluoroalkene, arylalkyldifluoroalkene and 1,1‐difluoro‐2‐substituted‐1,3‐dienes under mild reaction conditions with excellent functional group compatibility, and provides a potential pathway to the late‐stage functionalization of complex bioactive molecules.
Although freeze-drying is an excellent method for preserving microorganisms, it inevitably reduces cell activity and function. Moreover, probiotic strains differ in terms of their sensitivity to the ...freeze-drying process. Therefore, it is necessary to optimize the variables relevant to this process. The pre-freezing temperature is a critical parameter of the freeze-drying process, but it remains unclear whether the optimal pre-freezing temperature differs among strains and protectants. This study explored the effects of 4 different pre-freezing temperatures on the survival rates of different Lactobacillus plantarum strains after freeze-drying in the presence of different protectants. Using phosphate-buffered saline solution and sorbitol as protectants, pre-freezing at −196°C, −40°C, and −20°C ensured the highest survival rates after freeze-drying for AR113, AR307, and WCFS1, respectively. Using trehalose, pre-freezing at −20°C ensured the best survival rate for AR113, and −60°C was the best pre-freezing temperature for AR307 and WCFS1. These results indicate that the pre-freezing temperature can be changed to improve the survival rate of L. plantarum, and that this effect is strain-specific. Further studies have demonstrated that pre-freezing temperature affected viability via changes in cell membrane integrity, membrane permeability, and lactate dehydrogenase activity. In summary, pre-freezing temperature is a crucial factor in L. plantarum survival after freeze-drying, and the choice of pre-freezing temperature depends on the strain and the protectant.
Background
Aneurysm wall enhancement on high‐resolution vessel wall imaging (HR‐VWI) may represent vessel wall inflammation for unruptured intracranial aneurysms (UIAs). Further evidence for the role ...of circumferential aneurysm wall enhancement (CAWE) in evaluating the instability of UIAs is required, especially in small aneurysms (<7 mm).
Methods
We analyzed patients with saccular UIAs who prospectively underwent HR‐VWI on a 3.0 T MRI scanner in our center from September 2017 to August 2021. The presence of AWE was identified and quantitatively measured using the aneurysm‐to‐pituitary stalk contrast ratio (CRstalk) with maximal signal intensity value. The PHASES and ELAPSS scores were used to assess the risk of aneurysm rupture and growth. We evaluated the association of CAWE and CRstalk value with intracranial aneurysm instability.
Results
One hundred patients with 109 saccular UIAs were included in this study. Eighty‐three UIAs (76.1%) had a size smaller than 7 mm. PHASES and ELAPSS scores were significantly higher in UIAs with CAWE than in UIAs without CAWE (p < .01). The association of CAWE with PHASES and ELAPSS scores remained in small UIAs (<7 mm). The optimal cutoff value of CRstalk for CAWE was 0.5. PHASES and ELAPSS scores were significantly higher in UIAs with CRstalk ≥0.5 than in UIAs with CRstalk <0.5 (p < .01).
Conclusions
CAWE on HR‐VWI is a valuable imaging marker for aneurysm instability in UIAs. CRstalk value ≥0.5 may be associated with a higher risk of intracranial aneurysm rupture and growth.
Circumferential aneurysm wall enhancement (CAWE) on high‐resolution vessel wall imaging (HR‐VWI) is a valuable imaging marker for aneurysm instability in small unruptured intracranial aneurysms. The value of aneurysm‐to‐pituitary stalk contrast ratio (CRstalk) ≥0.5 may be associated with a higher risk of intracranial aneurysm rupture and growth.
We jointly analyze the gamma-ray burst (GRB) data observed with Burst Alert Telescope (BAT) and X-ray Telescope on board the Swift mission to present a global view on the internal energy dissipation ...processes in GRBs, including precursors, prompt gamma-ray emission, extended soft gamma-ray emission, and late X-ray flares. The Bayesian block method is utilized to analyze the BAT light curves to identify various emission episodes. Our results suggest that these emission components likely share the same physical origin, which is the repeated activation of the GRB central engine. What we observe in the gamma-ray band may be a small part of more extended underlying activities. The precursor emission, which is detected in about 10% of Swift GRBs, is preferably detected in those GRBs that have a massive star core-collapse origin. The soft extended emission tail, on the other hand, is preferably detected in those GRBs that have a compact star merger origin. Bright X-ray emission is detected during the BAT quiescent phases prior to subsequent gamma-ray peaks, implying that X-ray emission may be detectable prior the BAT trigger time. Future GRB alert instruments with soft X-ray capability are essential for revealing the early stages of GRB central engine activities, and shedding light on jet composition and the jet launching mechanism in GRBs.
Aryl fluorides are important structural motifs in many pharmaceuticals. Although the Balz–Schiemann reaction provides an entry to aryl fluorides from aryldiazonium tetrafluoroborates, it suffers from ...drawbacks such as long reaction time, high temperature, toxic solvent, toxic gas release, and low functional group tolerance. Here, we describe a general method for the synthesis of aryl fluorides from aryldiazonium tetrafluoroborates using a piezoelectric material as redox catalyst under ball milling conditions in the presence of Selectfluor. This approach effectively addresses the aforementioned limitations. Furthermore, the piezoelectric material can be recycled multiple times. Mechanistic investigations indicate that this fluorination reaction may proceed via a radical pathway, and Selectfluor plays a dual role as both a source of fluorine and a terminal reductant.
Aryl fluorides are important structural motifs in many pharmaceuticals. A new protocol, starting from aryldiazonium salts, that uses ball milling and piezoelectric materials as redox catalysts is described. This process addresses the limitations of the Balz–Schiemann procedure, which is currently used in industry. In addition, the mechanism of this fluorination reaction is also investigated.
PDF
