Instability of an inverse problem for the stationary radiative transport near the diffusion limit

In this work, we study the instability of an inverse problem of radiative transport equation with angularly averaged measurement near the diffusion limit, i.e. the normalized mean free path (the Knudsen number) 0 < \eps \ll 1. It is well-known that there is a transition of stability from H\"{o}lder type to logarithmic type with \eps\to 0, the theory of this transition of stability is still an open problem. In this study, we show the transition of stability by establishing the balance of two different regimes depending on the relative sizes of \eps and the perturbation in measurements. When \eps is sufficiently small, we obtain exponential instability, which stands for the diffusive regime, and otherwise we obtain H\"{o}lder instability instead, which stands for the transport regime.Comment: 20 page

Sanxian: re-/un-thinking Chinese urban hierarchy with a medium-sized city

A new trend is emerging in China that categorises cities according to economic conditions and political statuses and that formulates a new urban hierarchical system. This urban hierarchy has historical echoes from several decades ago, when the country was divided into three “fronts” for geopolitical concerns. Ironically, the Chinese character of “tiers” and “fronts” is identical: “.:% ” (xian). By referring to Luzhou, a medium-sized city in Western China that bears the same label as “=.:% ” (“third tier” / “third front”) in different periods, we explore the change of urban political economy and governing techniques that are underlying these two different (yet at the same time identical) labels of a city. It turns out that the two labels of Luzhou indicate dissimilar logics of the state. The “third front” in the Maoist era, with centrally-dominated redistribution of resources, rendered the local state a passive political subject. In contrast, the recent rise of “tiers” discourse has a lot of purchases from the local state. Situating in inter-city competitions, they are empowered yet also impelled to be more active in promoting the urbanisation process and boosting “urban-ness” in partnership with capital. Here, between the territorial logic of the planned economy half century ago and the ongoing entrepreneurial local governance at present, we are invited to further reflect on how the development trajectory of an ordinary (and even overlooked) city could contribute to more global urban studies

Secondhand space: unthinking the Quito papers

通过塑造一种全新的空间和尺度想象，资本及其权力便可经过“二手空间”的中介而实现全球范围的流动，最终改变（甚至摧毁）各个地方每条街道的日常生活。为了避免这样的状况及其恶化，我们应当首先反思类似《宣言》这样的二手空间观，然后从我们的身边和脚下出发去构想自己的空间观念。只有当我们认识到地方本质上就是种种全球/全局性过程的交错所在（a global sense of place），开始从本地出发去探索这些更广阔的、超越了本地尺度的空间属性，用比较的方法重新审视别人和自己，我们才可能真正把握空间和生活的密切关联，才可能发现和对抗萦绕四周的社会和空间不义，才可能重写多元且动态的城市宣言

Visual Servoing For Robotic Positioning And Tracking Systems

Visual servoing is a robot control method in which camera sensors are used inside the control loop and visual feedback is introduced into the robot control loop to enhance the robot control performance in accomplishing tasks in unstructured environments. In general, visual servoing can be categorized into image-based visual servoing (IBVS), position-based visual servoing (PBVS), and hybrid approach. To improve the performance and robustness of visual servoing systems, the research on IBVS for robotic positioning and tracking systems mainly focuses on aspects of camera configuration, image features, pose estimation, and depth determination. In the first part of this research, two novel multiple camera configurations of visual servoing systems are proposed for robotic manufacturing systems for positioning large-scale workpieces. The main advantage of these two multiple camera configurations is that the depths of target objects or target features are constant or can be determined precisely by using computer vision. Hence the accuracy of the interaction matrix is guaranteed, and thus the positioning performances of visual servoing systems can be improved remarkably. The simulation results show that the proposed multiple camera configurations of visual servoing for large-scale manufacturing systems can satisfy the demand of high-precision positioning and assembly in the aerospace industry. In the second part of this research, two improved image features for planar central symmetrical-shaped objects are proposed based on image moment invariants, which can represent the pose of target objects with respect to camera frame. A visual servoing controller based on the proposed image moment features is designed and thus the control performance of the robotic tracking system is improved compared with the method based on the commonly used image moment features. Experimental results on a 6-DOF robot visual servoing system demonstrate the efficiency of the proposed method. Lastly, to address the challenge of choosing proper image features for planar objects to get maximal decoupled structure of the interaction matrix, the neural network (NN) is applied as the estimator of target object poses with respect to camera frame based on the image moment invariants. Compared with previous methods, this scheme avoids image interaction matrix singularity and image local minima in IBVS. Furthermore, the analytical form of depth computation is given by using classical geometrical primitives and image moment invariants. A visual servoing controller is designed and the tracking performance is enhanced for robotic tracking systems. Experimental results on a 6-DOF robot system are provided to illustrate the effectiveness of the proposed scheme

Whither progressive urban futures? Critical reflections on the politics of temporality in Asia

Compressed development experiences, especially in Asia, have translated into expectations for ‘fast cities’ where time and space are compressed to materialise ‘real’ Asia experiences. However, what does ‘fast urbanism’ mean for those who see Asian cites as reference points? Moreover, what does ‘fast urbanism’ mean for those who have living memories of such fast-paced development, and how might this be different for their future generations? This intervention addresses these two questions by reflecting on the politics of temporality, calling for critical attention to the ideological imposition of ‘fast’ development in Asia and beyond. We argue that the ‘Asian speed’ of development was enabled in specific historical and geographical conjunctures, which entailed the appropriation of individual and collective aspirations through the invention of a certain kind of futurity and, in so doing, consolidated local politico-economic structures that displace both the present and the future

Green urbanism and speculative urbanisation at Forest City, Iskandar Malaysia

“While the discursive power of “green and smart” has been significant for the strategic marketing and branding of the project, it has also unevenly transformed the local way of life and endangered local and trans-local environmental dynamics”, write Dr Yimin Zhao (Renmin University of China), Dr Sin Yee Koh (Monash University Malaysia), and Prof. Hyun Bang Shin (LSE

The micropolitics of speculative green urbanism at Forest City, Iskandar Malaysia

There is an established urban studies literature on the discursive politics of green urbanism, especially with regards to eco-cities and (mega) greenfield developments. However, less attention has been paid to the micropolitics of cross-border transplantation of green urbanism ideas and practices, especially within Asia. This paper examines the case of Forest City, a mainland Chinese developer-led mega greenfield project in the Iskandar Malaysia special economic corridor, to be built on four reclaimed islands. Based on observations, in-depths interviews with local stakeholders and document analysis, we analyse the different ways in which green urbanism has been used by the local state and the developer as an apparatus for speculative city-making. On the one hand, the state seeks to position Iskandar Malaysia as greener than its global competitors through the development of a homegrown "low carbon society" green accreditation system. On the other hand, the (selectively) "green and smart" Forest city consolidates the developer's corporate brand image and marketing aesthetics at the cost of local residents' living environment. Attention to such entangled micropolitics of speculative green urbanism contextualises different stakeholders' rationales and practices and contributes to critical reflections on the entanglement of green urbanism and speculative urbanisation

Why Shallow Networks Struggle with Approximating and Learning High Frequency: A Numerical Study

In this work, a comprehensive numerical study involving analysis and experiments shows why a two-layer neural network has difficulties handling high frequencies in approximation and learning when machine precision and computation cost are important factors in real practice. In particular, the following basic computational issues are investigated: (1) the minimal numerical error one can achieve given a finite machine precision, (2) the computation cost to achieve a given accuracy, and (3) stability with respect to perturbations. The key to the study is the conditioning of the representation and its learning dynamics. Explicit answers to the above questions with numerical verifications are presented