Tuning of MST neurons to spiral motions

Cells in the dorsal division of the medial superior temporal area (MSTd) have large receptive fields and respond to expansion/contraction, rotation, and translation motions. These same motions are generated as we move through the environment, leading investigators to suggest that area MSTd analyzes the optical flow. One influential idea suggests that navigation is achieved by decomposing the optical flow into the separate and discrete channels mentioned above, that is, expansion/contraction, rotation, and translation. We directly tested whether MSTd neurons perform such a decomposition by examining whether there are cells that are preferentially tuned to intermediate spiral motions, which combine both expansion/contraction and rotation components. The finding that many cells in MSTd are preferentially selective for spiral motions indicates that this simple three-channel decomposition hypothesis for MSTd does not appear to be correct. Instead, there is a continuum of patterns to which MSTd cells are selective. In addition, we find that MSTd cells maintain their selectivity when stimuli are moved to different locations in their large receptive fields. This position invariance indicates that MSTd cells selective for expansion cannot give precise information about the retinal location of the focus of expansion. Thus, individual MSTd neurons cannot code, in a precise fashion, the direction of heading by using the location of the focus of expansion. The only way this navigational information could be accurately derived from MSTd is through the use of a coarse, population encoding. Positional invariance and selectivity for a wide array of stimuli suggest that MSTd neurons encode patterns of motion per se, regardless of whether these motions are generated by moving objects or by motion induced by observer locomotion.     

Multicast routing and bandwidth dimensioning in overlay networks

Multicast services can be provided either as a basic network service or as an application-layer service. Higher level multicast implementations often provide more sophisticated features and can provide multicast services at places where no network layer support is available. Overlay multicast networks offer an intermediate option, potentially combining the flexibility and advanced features of application layer multicast with the greater efficiency of network layer multicast. In this paper, we introduce the multicast routing problem specific to the overlay network environment and the related capacity assignment problem for overlay network planning. Our main contributions are the design of several routing algorithms that optimize the end-to-end delay and the interface bandwidth usage at the multicast service nodes within the overlay network. The interface bandwidth is typically a key resource for an overlay network provider, and needs to be carefully managed in order to maximize the number of users that can be served. Through simulations, we evaluate the performance of these algorithms under various traffic conditions and on various network topologies. The results show that our approach is cost-effective and robust under traffic variations.     

Logical foundations of nonmonotonic reasoning

In this paper we shall review the main appraches to nonmonotonic reasoning which we classify from the perspective of their underlying logical settings as classical, intuitionistic, three-valued/partial models, and conditional. We shall be placing special emphasis on some of the prominent approaches. We shall also give hints on potential future directions and emphasize that more theoretical work is still needed before a move to application is made.     

4-bit adder-accumulator at 41-GHz clock frequency in InP DHBT technology

A 41-GHz 4-b adder-accumulator test circuit implemented in InP double heterojunction bipolar transistor (DHBT) technology using 624 transistors is reported. High clock rates are obtained by combining the logic functions into pipelined latches. The adder-accumulator contains a single-level parallel-gated carry circuit that is used as a step toward reduced power consumption. The carry circuit has a maximum clock frequency of 55 GHz. The accumulator architecture employs modular, pipelined 2-b adders and is cascadable to 2 N-bits. The test circuit includes a 4-b digital to analog converter (DAC) that facilitates demonstration of high-speed operation.     

项目管理学派：过程（和成功）学派

在目前的系列文章中，我正在阐述项目管理的八个学派。前两期我讨论了（硬）系统学派和合同学派（治理学派的一部分）。从历史沿革来看下一个出现的学派是成功和失败学派，不过去年我已经以此为主题撰写过一系列文章，因此这里就不再赘述。本期我将转而讨论过程学派，如图1所示，过程学派坐落在迄今为止讨论过的其他三个学派之间。     

移动视频点播比移动广播方式更有市场

在车站等车的时候你或许有几分钟的时间需要打发。这时，你拿起手机输入一串紧缩码，只几秒钟，便看到一段你想看的电影片花或是最近朋友们谈论的YouTube上的某个3min的视频剪辑。     

管理技术--创新、学习及成熟度(中)

在基于项目的组织中实现创新 在本节我们将探讨如何在项目环境中进行创新.首先我们来了解一下人们进行改变,进而实现创新的规律;然后我们介绍两种截然不同的管理创新的方法,即常用的线性推理方法和有机推进法;最后,我们对它们的优缺点做一个比较,看看它们各自适用于什么情况.