Delay-dependent stability of linear multistep methods for differential systems with distributed delays

This paper deals with the stability of linear multistep methods for multidimensional differential systems with distributed delays. The delay-dependent stability of linear multistep methods with compound quadrature rules is studied. Several new sufficient criteria of delay-dependent stability are obtained by means of the argument principle. An algorithm is provided to check delay-dependent stability. An example that illustrates the effectiveness of the derived theoretical results is given.

儿童青少年时期脑功能连接梯度的发育规律

成年人脑功能网络呈现从初级皮层到联合皮层渐变的核心连接梯度模式,支持了从初级感知觉到复杂抽象认知的信息加工过程.然而,目前对于人脑网络的初级皮层-联合皮层连接梯度如何发育,及其与认知发展、基因表达的关系依然知之甚少.本研究基于两个独立的6~14岁大样本儿童青少年静息态脑功能影像数据库,定量描绘了人脑功能网络的初级皮层-联合皮层连接梯度的发育轨迹.发现该连接梯度在儿童早期已经出现,并在8~11岁从次级梯度上升为首要核心梯度;其全局指标和局部分数都具有显著的年龄效应,梯度分数变化主要位于默认网络和感知觉皮层;梯度指标与个体工作记忆能力显著正相关,且连接梯度的发育受到脑功能网络分化与整合的中介调控.通过连接组-转录组联合分析,发现核心连接梯度的发育与突触传递等基因的表达水平显著相关.研究结果对理解人脑功能连接组的发育规则,建立脑发育性障碍的临床评估具有重要价值.

Mapping Domain- and Age-Specific Functional Brain Activity for Children’s Cognitive and Affective Development

The human brain undergoes rapid development during childhood,with significant improvement in a wide spectrum of cognitive and affective functions.Mapping domain-and age-specific brain activity patterns has important implications for characterizing the development of children’s cognitive and affective functions.The current mainstay of brain templates is primarily derived from structural magnetic resonance imaging(MRI),and thus is not ideal for mapping children’s cognitive and affective brain development.By integrating task-dependent functional MRI data from a large sample of 250 children(aged 7 to 12)across multiple domains and the latest easy-to-use and transparent preprocessing workflow,we here created a set of age-specific brain functional activity maps across four domains:attention,executive function,emotion,and risky decision-making.Moreover,we developed a toolbox named Developmental Brain Functional Activity maps across multiple domains that enables researchers to visualize and download domain-and age-specific brain activity maps for various needs.This toolbox and maps have been released on the Neuroimaging Informatics Tools and Resources Clearinghouse website(http://www.nitrc.org/projects/dbfa).Our study provides domain-and age-specific brain activity maps for future developmental neuroimaging studies in both healthy and clinical populations.

Spiro-conjugated indenodiarylethenes: enabling steric-induced electronic tuning of photochromic and photoluminescent properties by spiro-conjugation

Light-operated excited-state photochemical reactions and the resulting photochromic materials have gained significant attention for their promising technological applications in molecular electronic and photonic devices.To obtain photochromic materials(e.g.,diarylethenes)with desired properties,the way to tune energy processes of the excited state is essentially important,from both fundamental and practical viewpoints.The modified diarylethenes mostly focused on structural improvements to achieve efficient photochromism.We report here two new spiro-conjugated indenodiarylethenes(named,SFI-Th and SFI-Sul)with an orthogonally arranged spiroπ-scaffold.The spiro fluorene sterically constrains the free volume of photoactive side aromatic rings,while the spiro-conjugation points toward modulation of the decaying channels of excited-state energy,thus allowing for tuning photochromic performances.These spirodiarylethenes SFI-Th and SFI-Sul are readily accessible with low cost and show distinct photochromic and photoluminescent properties.On one hand,the SFI-Th bearing bisthienyl side rings,is an excellent photochromic switch showing high thermal stability and high fatigue resistance in both solution and amorphous state,likely benefited from steric-induced excited-state energy transfer into reversible photochemical reactions,owing to higherπ-orbital spiro-conjugation between the two molecular halves.On the other hand,the SFI-Sul with bissulfonyl side rings,most notably,displays quantitative photocyclization to yield SFI-Sulc upon excitation.However,the ring-closed SFI-Sulc has an extremely slow photocycloreversion,and meanwhile immediately switches on emissive state with a strong fluorescence(Φf=0.57 in amorphous powder state).We study the modulated roles of spiroπ-scaffold in both cases computationally and experimentally,and attribute the facilitated photochemical reaction to the positively electronic effects of spiro-conjugation,and the photo-responsive radiative transition to the negatively electronic effects of spiro-conjugation,respectively.In all,this work demonstrates that the spiro-conjugation is a new and efficient strategy to deliver excitation energy transfer(EET)for featured photochromic properties,due to its advantage in steric-induced electronic modulation.

The SACT Template:A Human Brain Diffusion Tensor Template for School-age Children

School-age children are in a specific development stage corresponding to juvenility,when the white matter of the brain experiences ongoing maturation.Dffusion-weighted magnetic resonance imaging(DWI),especially diffusion tensor imaging(DTI),is extensively used to characterize the maturation by assessing white matter properties in vivo.In the analysis of DWI data,spatial normalization is crucial for conducting inter-subject analyses or linking the individual space with the reference space.Using tensor-based registration with an appropriate diffusion tensor template presents high accuracy regarding spatial normalization.However,there is a lack of a standardized diffusion tensor template dedicated to school-age children with ongoing brain development.Here,we established the school-age children diffusion tensor(SACT)template by optimizing tensor reorientation on high-quality DTI data from a large sample of cognitively normal participants aged 6-12 years.With an age-balanced design,the SACT template represented the entire age range well by showing high similarity to the age-specific templates.Compared with the tensor template of adults,the SACT template revealed significantly higher spatial normalization accuracy and inter-subject coherence upon evaluation of subjects in two different datasets of schoolage children.A practical application regarding the age associations with the normalized DTI-derived data was conducted to further compare the SACT template and the adult template.Although similar spatial patterns were found,the SACT template showed significant effects on the distributions of the statistical results,which may be related to the performance of spatial normalization.Looking forward,the SACT template could contribute to future studies of white matter development in both healthy and clinical populations.The SACT template is publicly available now(tp://igshare com/aricles/dataseu'SACT_.template/14071283).

Spiro-fused bicyclo[3,2,2]octatriene-cored triptycene:synthesis,molecular packing,and functional aggregates

Aggregate science has led to the existence of functional properties at the aggregate level that significantly differs from those of corresponding single-molecule species,leading to a number of novel conceptual materials with state-dependent functionality.For developing such materials,new molecular scaffolds that allow modulating the structural and functional properties of aggregates in a controlled manner could be extremely helpful.In this study,we report a class of spiro-fused bicyclo[3,2,2]octatriene triptycene derivatives with a unique 3 D molecular scaffolding structure that displays aggregation-induced emission(AIE)activity with bright solid-state blue luminescence.The core scaffold features a Y-shaped bicyclo[3,2,2]octatriene backbone and a vertical crossover arrangement of adjacent spiro-conjugated rings.Unlike classic bicyclo[2,2,2]octatrienes with high rigidity,this stereoscopic bicyclo[3,2,2]octatriene containing a seven-membered ring allows retaining certain flexibility in the molecular scaffold,which results in a weak fluorescence in dilute solutions(Φ_(F)<10%).However,the corresponding molecular aggregates emit intense fluorescence(Φ_(F)=50%-75%)and show prominent AIE activity because of the restriction of intramolecular scaffold motions.Moreover,in principle,these stereoscopic scaffold constructions with partially restricted flexibility facilitate the assembly of multiple different crystalline packing structures in both porous and nonporous forms depending on the growth conditions of crystalline aggregates.The obtained crystals with regular voids(12.85×6.89Aeach)show reversible luminescence in response to the adsorption/desorption of iodine vapor.These materials based on an unusual 3 D scaffold exhibit a high degree of structural modulation at the aggregate level and demonstrate potential applications in chemical sensing and flexible optoelectronics,which may open up the exploration of highly stereoscopic molecular building blocks for developing functional aggregates.

A Simple Approach to Achieve Organic Radicals with Unusual Solid-State Emission and Persistent Stability

Sable organic radicals are promising materials for information storage,molecular magnetism,electronic devices,and biological probes.Many organic radicals have been prepared,but most are non-or weakly emissive and degrade easily upon photoexcitation.It remains challenging to produce stable and efficient luminescent radicals because of the absence of general guidelines for their synthesis.Herein,we present a photoactivation approach to generate a stable luminescent radical from tris(4-chlorophenyl)phosph ine(TCPP)with red emission in the crystal state.The mechanistic study suggests that the molecular symmetry breaking in the crystal causes changes of molecular conformation,redox properties,andmolecular packing that facilitates radical generation and stabilization.This design strategy demonstrates a straightforward approach to develop stable organic luminescent radicals that will open new doors to photoinduced luminescent radical materials.

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

We report an air-stable tetraradicaloid based on a rarely explored perylenequinonoid(PQ)core,namely,tetrabenzo-annulated tetracyclopenta[b,e,k,n]perylene(TBCP),which has a quadruple helical structure.As validated by X-ray crystallographic analysis and theoretical calculations,the nonplanar TBCP possesses unique hybrid resonance structures of two open-shell singlet diradicaloids.Remarkably,magnetic measurements reveal that TBCP in powder form shows unusual magnetic hysteresis upon heating followed by cooling,corresponding to interconversion of structure isomers with different magnetic properties.Such electronic properties can be rationalized as the response of structural changes to external thermal stimuli,accompanied by a subtle balance of two types of intramolecular magnetic interactions between four-site spin centers.The results provide a novel organic polyradicaloid as an unprecedented example of a functional material with the potential for intramolecular magnetic switching.