Musical imagery: sound of silence activates auditory cortex

Auditory imagery occurs when one mentally rehearses telephone numbers or has a song 'on the brain'--it is the subjective experience of hearing in the absence of auditory stimulation, and is useful for investigating aspects of human cognition. Here we use functional magnetic resonance imaging to identify and characterize the neural substrates that support unprompted auditory imagery and find that auditory and visual imagery seem to obey similar basic neural principles.     

A single type of progenitor cell maintains normal epidermis

According to the current model of adult epidermal homeostasis, skin tissue is maintained by two discrete populations of progenitor cells: self-renewing stem cells; and their progeny, known as transit amplifying cells, which differentiate after several rounds of cell division. By making use of inducible genetic labelling, we have tracked the fate of a representative sample of progenitor cells in mouse tail epidermis at single-cell resolution in vivo at time intervals up to one year. Here we show that clone-size distributions are consistent with a new model of homeostasis involving only one type of progenitor cell. These cells are found to undergo both symmetric and asymmetric division at rates that ensure epidermal homeostasis. The results raise important questions about the potential role of stem cells on tissue maintenance in vivo.     

A Hedgehog- and Antennapedia-dependent niche maintains Drosophila haematopoietic precursors

The Drosophila melanogaster lymph gland is a haematopoietic organ in which pluripotent blood cell progenitors proliferate and mature into differentiated haemocytes. Previous work has defined three domains, the medullary zone, the cortical zone and the posterior signalling centre (PSC), within the developing third-instar lymph gland. The medullary zone is populated by a core of undifferentiated, slowly cycling progenitor cells, whereas mature haemocytes comprising plasmatocytes, crystal cells and lamellocytes are peripherally located in the cortical zone. The PSC comprises a third region that was first defined as a small group of cells expressing the Notch ligand Serrate. Here we show that the PSC is specified early in the embryo by the homeotic gene Antennapedia (Antp) and expresses the signalling molecule Hedgehog. In the absence of the PSC or the Hedgehog signal, the precursor population of the medullary zone is lost because cells differentiate prematurely. We conclude that the PSC functions as a haematopoietic niche that is essential for the maintenance of blood cell precursors in Drosophila. Identification of this system allows the opportunity for genetic manipulation and direct in vivo imaging of a haematopoietic niche interacting with blood precursors.     

扫描声强法测量四极子声源声功率时参数确定

以四极子声源为例,建立了以矩形测量面锯齿形为扫描路径扫描声强法测量机器声功率的误差函数的数学模型,分析了声功率测量时矩形测量面大小、扫描测量面到声源的距离、扫描线密度误差的影响.根据声功率测量误差仿真曲线,给出了测量机器声功率时矩形测量面尺寸、测量面距声源距离、扫描线密度的确定方法.依此方法确定矩形测量面几何参数,提高了测量效率,为快速准确地测量声源的声功率奠定了基础.     

A diffusion barrier maintains distribution of membrane proteins in polarized neurons

The asymmetric distribution of proteins to distinct domains in the plasma membrane is crucial to the function of many polarized cells. In epithelia, distinct apical and basolateral surfaces are maintained by tight junctions that prevent diffusion of proteins and lipids between the two domains. Polarized neurons maintain axonal and somatodendritic plasma membrane domains without an obvious physical barrier. Indeed, the artificial lipid Dil encounters no diffusion barrier at the presumptive domain boundary, the axon hillock. By measuring the lateral mobility of membrane proteins using optical tweezers, we show here that some membrane proteins exhibit markedly reduced mobility in the initial segment of the axon. Disruption of F-actin and low levels of dimethyl sulphoxide (DMSO) abolish this diffusion barrier and lead to redistribution of membrane markers that had previously been polarized. Immobilization in the initial segment may reflect, at least in part, differential tethering to cytoskeletal components. Therefore, the ability to maintain a polarized distribution of membrane proteins depends on a specialized domain at the initial segment of the axon, which restricts lateral mobility and serves as a new type of diffusion barrier that acts in the absence of cell-cell contact.     

声光控元件性能模拟演示器的设计与制作

通过用声、光敏传感器等常用电子元器件设计制作声、光控电路模拟演示器,利用LED发光管的有序流动效果模拟演示声光控元件的导通性能,这对声光控原理的讲述起到画龙点睛的效果,由于该演示电路的创新之处是将声光控及闪光电路集为一体,简单明了,说服力强,便于学生实际动手操作,加深学生对传感器知识的理解,激发学生学习的探索欲望,使老师的教学可取得很好的教学效果.     

正交磁场对电火花单脉冲放电中电蚀凹坑的影响规律

电火花放电通道在正交磁场的作用下向洛伦兹力方向偏转、延伸,进而导致电蚀凹坑形貌发生变化,研究磁场辅助电火花加工(MF-EDM)过程中电蚀凹坑的形貌变化规律及特点,对进一步明晰电火花加工机理具有重要意义.基于MF-EDM气中单脉冲放电试验,使用表面轮廓仪观测电蚀凹坑延伸长度、深度、宽度及放电起始点偏移量,并得出磁场及放电参数对电蚀凹坑的影响规律.结果表明:电蚀凹坑长度随着磁感应强度、开路电压的增大而增大;电极外伸长度的影响结果相反;电蚀凹坑深度随着磁感应强度、开路电压、电极外伸长度的增加没有明显的变化规律;电容与磁感应强度存在最优参数组合以使凹坑长度最大;随着磁感应强度及放电能量的增加放电起始点的偏移量增加.     

脉冲放电等离子体技术处理偶氮染料废水

为有效处理染料废水,以甲基橙和刚果红溶液为例研究高压脉冲放电等离子体技术的脱色效果.通过测定脉冲放电处理前后甲基橙和刚果红溶液的紫外-可见吸收光谱来计算脱色率,考察放电参数、添加剂对染料脱色率的影响.实验结果表明,脉冲放电对甲基橙和刚果红溶液脱色效果显著,且相同条件下甲基橙(单偶氮)比刚果红(双偶氮)脱色率高.两者脱色率均随峰值电压、脉冲频率的增大而提高,随溶液电导率的增大而降低,随H2O2的加入而提高.当电极间距由15 mm增大到25 mm时,放电形式也由火花放电逐渐向电晕放电转变,溶液的脱色率由90%降到44%.     

高产琥珀酸菌株的等离子体诱变选育

以谷氨酸棒杆菌作为原始出发菌株,通过常压室温等离子体诱变技术,确定高产琥珀酸等离子体诱变的物理参数和最佳诱变条件,采用在培养基中添加溴甲酚紫作为酸碱指示剂的方法,测定发酵液前后在波长590 nm处的吸光值,高通量筛选出在该波长处吸光值变化较大的突变株.结果表明:在诱变菌株的存活率为8％的条件下获得的突变株的正突变率达到22％.用40 g/L的葡萄糖对突变株进行摇瓶分批发酵,筛选得到诱变菌E7产琥珀酸15.6 g/L,乳酸22.8 g/L,该菌具备良好的产琥珀酸与有机酸的能力.     

水中高压脉冲放电诱导产生过氧化氢的初步研究

为了考察水中高压脉冲放电降解有机物的基本机理,采用针-板电极研究了水中高压脉中放电产生过氧化氢的过程,探讨了不同放电条件下过氧化氢的产量,分析了过氧化氢的产生机理以及能量的利用效率.随着放电电压的升高、电极间距的减小和溶液电导率的降低,水中的过氧化氢产量增加.在放电电压为40kV,电极间距为2.0 cm,电导率为2.0μs/cm的情况下,放电80 min后水中的过氧化氢浓度可以达到0.895mmol/L.低电压、低电导率以及小的电机间距有利于提高单位电量过氧化氢的产率.电压为20 kV,电极间距为2.0 cm,电导率为2.0 μs/cm时,过氧化氢的产率为21.24mmol/(kW·h).放电过程引起了溶液本身的一些变化,包括pH值的降低和温度的升高.温度的升高以及能量效率的研究表明,放电中的一部分能量变成热量散失.pH值的降低表明过氧化氢的生成来自于放电而不是电解.     

强电离放电制取高浓度臭氧的实验研究

采用不同型号多个臭氧发生器进行了强电离放电制取高浓度臭氧的实验。结果表明：能流密度为某一特定值时,臭氧产生浓度最高;在一定的输入电压和频率下,臭氧产生浓度随电源脉冲导通时间的增加而增大;当输入功率大于一定数值时,臭氧产生效率随输入功率的增加而降低;臭氧产生浓度随气体流通量的增加或冷却水温度的升高而降低。     

从基本观点对气体放电理论的探讨

从基本观点，对汤森气体放电理论和流柱击穿理论进行了分析和探讨，指出了其中的弱点和不足。以近期完成的气体放电理论为基础，对上述理论提出了新的解释并进行了补充和修正。新提出的各表达式是从基本原理严密推导而成的，它具有自恰性，连续性。这些表达式所得的结果与其他作者的实验结果相比，基本一致。     

废水零排放的一种复合型方法

提出了一种复合型零排放方法．即通过回用、再生回用、再生循环实施的废水最小化来确定系统中最小新鲜水耗量,然后采用分布式废水治理系统,利用常规治理方法使废水达到深度治理要求的进口浓度．深度治理产生足够品质的水通过再生循环可满足新鲜水使用过程的用水要求．实例证明了废水零排放的可能性和所提方法的可行性．     

非导电工程陶瓷电火花磨削热量分配模型

对非导电工程陶瓷加工新技术--双电极同步伺服跟踪电火花磨削加工(EDGSSDE)中产生的热量进行了分析,建立了EDGSSDE的热源模型和热量在非导电工程陶瓷、金属结合剂砂轮、磨屑和工作液间的分配模型,并进行了数值计算.计算结果表明,热量在金属结合剂砂轮和工作液间的分配随着加工深度的增加而逐渐减小,热量在非导电工程陶瓷间的分配随着加工深度的增加而逐渐增大,热量在磨屑间的分配比很小,且随着加工深度的增加变化不大.加工中工作液和砂轮带走大部分的热量.     

非导电工程陶瓷电火花磨削热量分配模型

对非导电工程陶瓷加工新技术——双电极同步伺服跟踪电火花磨削加工（EDGSSDE）中产生的热量进行了分析，建立了EDGSSDE的热源模型和热量在非导电工程陶瓷、金属结合剂砂轮、磨屑和工作液间的分配模型，并进行了数值计算。计算结果表明，热量在金属结合剂砂轮和工作液间的分配随着加工深度的增加而逐渐减小，热量在非导电工程陶瓷间的分配随着加工深度的增加而逐渐增大，热量在磨屑间的分配比很小，且随着加工深度的增加变化不大。加工中工作液和砂轮带走大部分的热量。     

Vocal tract resonances in oscine bird sound production: evidence from birdsongs in a helium atmosphere

The complexity and dependence on learning of many bird sounds have suggested parallels between birdsong and human speech, but the mechanisms by which each is produced have been supposed to differ markedly. In human speech, resonances of the vocal tract are thought to modulate in complex ways the sound produced by vibration of the vocal folds. The current theory of birdsong production holds that all variation in sound quality arises from the primary sound-producing organ, the syrinx, and that resonances of the vocal tract play no part. Here I present evidence, obtained from acoustic analyses of birdsongs recorded in a helium atmosphere, which contradicts this hypothesis. Not only does the songbird's vocal tract act as an acoustic filter, but its filter characteristics are actively coordinated with the output of the syrinx. Songbird and human phonation are thus more analogous than previously thought, in that both require coordination of an array of diverse motor systems.     

压缩过程中天然沉积土应力灵敏度的变化规律

为了描述压缩过程中天然沉积土应力灵敏度随固结压力的变化规律,基于耦合应力灵敏度的概念和Liu-Cater模型的建模思路,将Liu-Cater模型引入应力灵敏度评价体系中,建立了应力灵敏度变化模型.将已有文献中天然沉积土原状样与重塑样的一维压缩试验实测结果与应力灵敏度变化模型预测结果相比较,以验证所提模型的适用性.结果表明:应力灵敏度变化模型预测结果与试验实测结果均具有良好的一致性;应力灵敏度在固结屈服压力时处于最大值,之后随固结压力的增大而逐渐减小至1;应力灵敏度衰减指数的大小主要决定于土的种类及土结构性的特征,软黏土的应力灵敏度衰减指数通常大于硬黏土;土结构性破坏越剧烈,应力灵敏度衰减指数越高.