Nonlinear limits to the information capacity of optical fibre communications.

The exponential growth in the rate at which information can be communicated through an optical fibre is a key element in the 'information revolution'. However, as for all exponential growth laws, physical limits must be considered. The nonlinear nature of the propagation of light in optical fibre has made these limits difficult to elucidate. Here we use a key simplification to investigate the theoretical limits to the information capacity of an optical fibre arising from these nonlinearities. The success of our approach lies in relating the nonlinear channel to a linear channel with multiplicative noise, for which we are able to obtain analytical results. In fundamental distinction to linear channels with additive noise, the capacity of a nonlinear channel does not grow indefinitely with increasing signal power, but has a maximal value. The ideas presented here may have broader implications for other nonlinear information channels, such as those involved in sensory transduction in neurobiology. These have been often examined using additive noise linear channel models but, as we show here, nonlinearities can change the picture qualitatively.     

The optic tectum controls visually guided adaptive plasticity in the owl's auditory space map.

The midbrain contains an auditory map of space that is shaped by visual experience. When barn owls are raised wearing spectacles that horizontally displace the visual field, the auditory space map in the external nucleus of the inferior colliculus (ICX) shifts according to the optical displacement of the prisms. Topographic visual activity in the optic tectum could serve as the template that instructs the auditory space map. We studied the effects of a restricted, unilateral lesion in the portion of the optic tectum that represents frontal space. Here we show that such a lesion eliminates adaptive adjustments specifically in the portion of the auditory map that represents frontal space on the same side of the brain, while the rest of the map continues to adjust adaptively. Thus, activity in the tectum calibrates the auditory space map in a location-specific manner. Because the site of adaptive changes is the ICX, the results also indicate that the tectum provides a topographic instructive signal that controls adaptive auditory plasticity in the ICX.     

斜二测图中XOY坐标面上圆的投影的探讨

运用透仿对应的基本作图法,在已知椭圆一对共轭直径的条件下,作出椭圆长短轴的方向和大小.利用数学公式,计算出椭圆长轴与轴测轴O1X1之夹角α的大小,以及椭圆长短轴的大小.     

利用隐空间投影算法的模型自适应方法

为了降低语音识别系统中噪声的影响,提出了一种利用隐空间投影算法的模型自适应方法。该方法利用状态间的相关性提取出反映码本和待识别语音共同特性的基矢量。由于语音与噪声是相互独立的,因此,当语音识别系统中有噪声存在时,认为不能用基矢量表示的那部分余量就是噪声。与本征音方法相比,该方法可以有效地降低噪声对语音识别系统的影响。该方法在提取基矢量时利用了自适应数据,并且节省了存储空间。实验结果表明:该方法在噪声环境下相对于最大似然线性回归自适应方法有4-9个百分点的提高,相对于最大后验概率和本征音方法有更大的提高。     

利用隐空间投影算法的模型自适应方法

为了降低语音识别系统中噪声的影响,提出一种利用隐空间投影算法的模型自适应方法。该方法利用状态间的相关性提取出反映码本和待识别语音共同特性的基矢量。由于语音与噪声是相互独立的,因此,当语音识别系统中有噪声存在时,认为不能用基矢量表示的那部分余量就是噪声。与本征音方法相比,该方法可以有效地降低噪声对语音识别系统的影响。该方法在提取基矢量时利用了自适应数据,并且节省了存储空间。实验结果表明:该方法在噪声环境下相对于最大似然线性回归自适应方法有4~9百分点的提高,相对于最大后验概率和本征音方法有更大的提高。     

投影变换在斜孔加工确定工艺角度方面的应用

论证了直线投影变换的倾角与投影角之间的关系,并给出了几个重要公式。结合实际,指出了它们在生产加工确定工艺角度方面的具体应用。     

Towards the clarity limit in optical fibre

An important scientific and technological goal in the field of optical communications is the achievement of the clarity limit in optical fibres--that is, ensuring that the SiO2 glass from which fibres are made is as transparent as possible. The clarity of the wavelength transmission window (and the width of that window) in existing fibres is already sufficient to form the basis of a world-wide optical communication system, yet it is still limited by contamination of the fibre by water. Here we measure the spatial distribution of water in the glass rods from which optical fibres are drawn and explain the distribution quantitatively with a mathematical model of diffusion in a medium with essentially perfect cylindrical symmetry. Our analysis shows that the water enters from the outside of the rod and diffuses into the molten, flowing glass much faster than is expected from extrapolation of low-temperature measurements. Our elucidation of the physics underlying the contamination process has already led to the fabrication of dry fibres, which have a clarified and broadened communications window. The improved operational range of wavelengths should yield applications for new lasers, optical amplifiers and detectors, and should substantially increase the information-carrying capacity of optical communications systems.     

Induction of functional retinal projections to the somatosensory system

Optic axons can be induced to form permanent, retinotopic connections in the auditory (medial geniculate, MG) and somatosensory (ventrobasal, VB) nuclei of the Syrian hamster thalamus; this occurs when the principal targets of retinofugal axons are ablated in newborn hamsters and alternative terminal space is created by partial deafferentation of MG or VB. The experimentally induced retinal projection to the somatosensory nucleus occurs by the stabilization of an early, normally transient projection. The present study was undertaken to determine whether the anomalous, stabilized retino-VB projection is functional. Newborn hamsters were operated on to produce permanent retino-VB projections and when the animals were mature, neurophysiological recordings were made in the cortical targets of VB, the first and second somatosensory cortices (SI and SII, respectively). Visual stimulation within well-defined receptive fields reliably evoked multi-unit responses in SI and SII of operated, but not normal hamsters. The representations of the visual field in SI and SII showed a partially retinotopic organization. These results demonstrate that optic tract axons can form functional synapses in the thalamic somatosensory nucleus, and suggest that neural structures which normally process information specific to one sensory modality have the potential to mediate function for other modalities.     

后入路副神经移位修复肩胛上神经术式的临床应用研究

介绍后入路副神经移位修复肩胛上神经、治疗臂丛神经损伤、恢复肩关节外展功能的新术式,并探讨其临床疗效。将后入路副神经移位修复肩胛上神经术式成功地应用于11例病人,并随访术后疗效;结果表明:后入路副神经移位修复肩胛上神经术式操作简单、安全可行,术后疗效确切,恢复早于传统术式,并且术后斜方肌上部肌力及其耸肩功能无影响,使恢复的肩关节外展接近于正常动作。     

基于模拟退火算法的投影寻踪方向优化

投影寻踪是一种降维处理技术,通过它可以将多维分析问题通过投影方向转化为一维问题分析.应用该法的关键在于寻求最佳投影方向,这可以转化为一个优化问题来进行解决.针对投影寻踪评价模型中的最佳投影方向优化问题,采用模拟退火算法来优化此问题.仿真结果表明了模拟退火算法在解决此类复杂函数优化问题上的适用性和有效性.     

覆铜箔层压板增强用玻纤纱的优化设计

电子级 7628织物是覆铜箔层压板生产厂家的主要生产原料,在国内纺织加工领域属前沿性科研课题目前国内还需进口用量的一半以满足高速增长的电子工业需要同时我国研制生产的巨型电子计算机和大型程控交换机等高技术产品也急需性能优良的 PCB产品因此,开展 7628织物工艺优化设计的研究 ,通过对 7628织物质量和性能的技术攻坚,满足计算机、通讯、仪表及家用电器等电子产品的特殊需求,显得尤为重要     

投影寻踪模型在水污染控制规划中的应用

在水污染控制规划中,方案优选对于正确评价备选方案,使规划方案兼顾经济效益和环境效益的最佳平衡点具有重要意义。但方案优选涉及众多评价指标,且各指标量纲不尽相同及其权重较难确定等问题,目前常用的方法难以客观反映各指标数据所携带的数字信息;该文应用投影寻踪(PP)模型,建立水污染控制方案优选模型,并采用实码加速遗传算法来简化PP模型建模过程。为客观反映各指标的权重,构造新的投影指标函数,达到局部凝聚、整体分散的效果;实例计算表明,PP模型既可客观反映各指标的权重,又能正确评价各方案,具有有效性和通用性,可以适用于水污染控制规划管理中。     

人工神经网络在压裂选井及选层中的应用

根据中原油田砂岩油藏200多口压裂井及压裂层的静、动态地质资料和压裂施工参数、对影响压裂效果的单因素、多因素和主参数进行了分析,采用人工神经网络技术,建立了砂岩油藏压裂选井及选层人工智能系统,并将其用于中原油田复杂断块压裂选井及选层识别,利用该系统可以估算压裂后单位厚度油层的日增产油量,并能预测压裂效果,可为压裂选井及选层提供科学依据。     

Mutations in the human retinal degeneration slow gene in autosomal dominant retinitis pigmentosa.

The murine retinal degeneration slow (rds) gene is a semidominant mutation with a phenotype having rod and cone photoreceptors that develop abnormally and then slowly degenerate. The phenotype is a possible model for retinitis pigmentosa, one of the scores of hereditary human retinal degenerations, which is also characterized by photoreceptor degeneration. We report here three mutations of the human homologue of the rds gene (RDS) that cosegregate with autosomal dominant retinitis pigmentosa in separate families. Our results indicate that some cases of autosomal dominant retinitis pigmentosa are due to mutations at the RDS locus.     

Evidence for enhanced mixing over rough topography in the abyssal ocean

The overturning circulation of the ocean plays an important role in modulating the Earth's climate. But whereas the mechanisms for the vertical transport of water into the deep ocean--deep water formation at high latitudes--and horizontal transport in ocean currents have been largely identified, it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished. Turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise. However, measurements of the internal wave field, the main source of energy for mixing, and of turbulent dissipation rates, have typically implied diffusivities across surfaces of equal density of only approximately 0.1 cm2 s(-1), too small to account for the return flow. Here we report measurements of tracer dispersion and turbulent energy dissipation in the Brazil basin that reveal diffusivities of 2-4 cm2 s(-1) at a depth of 500 m above abyssal hills on the flank of the Mid-Atlantic Ridge, and approximately 10 cm2 s(-1) nearer the bottom. This amount of mixing, probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry, may be large enough to close the buoyancy budget for the Brazil basin and suggests a mechanism for closing the global overturning circulation.     

高斯投影反算中求底点纬度值的牛顿迭代法

高斯投影反算问题是利用高斯平面直角坐标系坐标(x，y)来求其对应的大地地理坐标系坐标(B，L)的理论和方法。在高斯投影反算问题中，底点纬度Bf是一个重要的中间变量。对底点纬度Bf的计算通常采用两种方法，而这两种方法在具体应用中不够方便。本文对该问题进行了探讨，在研究牛顿迭代法应用的前提下，以高斯投影正算中求X0的数学模型为基础，构造了求底点纬度Bf的牛顿迭代模型。给出了相应的牛顿迭代法程序设计的框图，编写了C语言子程序。通过实例计算，表明相对于求底点纬度Bf值的常用算法，该方法具有方法简便、程序设计简单、计算速度快、精度高等特点，在大量数据计算中可以满足高斯投影计算对计算速度和计算精度的双重要求。该方法对实际工作中相关问题有一定的实用和参考价值。     

透射层析成像中完全投影数据的获取

在证明典型跨孔方式所获投影数据提不完全的基础上，首次提出了四种在采用离散图像重建技术进行地震透射波走时反演层析成像时的完全投影数据的采集系统，并比较了四种采集系统所获数据在迭代反演时的收敛速度，最后给出了模型试验结果。     

Visual behaviour mediated by retinal projections directed to the auditory pathway

An unresolved issue in cortical development concerns the relative contributions of intrinsic and extrinsic factors to the functional specification of different cortical areas. Ferrets in which retinal projections are redirected neonatally to the auditory thalamus have visually responsive cells in auditory thalamus and cortex, form a retinotopic map in auditory cortex and have visual receptive field properties in auditory cortex that are typical of cells in visual cortex. Here we report that this cross-modal projection and its representation in auditory cortex can mediate visual behaviour. When light stimuli are presented in the portion of the visual field that is 'seen' only by this projection, 'rewired' ferrets respond as though they perceive the stimuli to be visual rather than auditory. Thus the perceptual modality of a neocortical region is instructed to a significant extent by its extrinsic inputs. In addition, gratings of different spatial frequencies can be discriminated by the rewired pathway, although the grating acuity is lower than that of the normal visual pathway.