495 research outputs found
Op soek na\u27n Mediabestel vir Suid·Afrika: \u27n Voorlopige antwoord aan Keyan Tomaselli
No full textCOMMUNICARE encourages the scientific debate. Our last contribu tion is published in response to the article of Tomaselli & Louw In 9(1), who questioned some of the predie tions regarding post-apartheid media In an earlier article by the author pub lished In 8(1). These are his repiles... Prof Keyan Tomaselli, Director of the Cultural Studies Unit at the University of Natal (Durban), is without doubt one of most prolific writers in the field of South African media and communication studies. This is not a matter of c tention; what is at stake in this review article Is the way in which Tomaselll deals with statements and facts in his pub lications. It is argued that Tomaselli Is prone to state a debatable point as a "scientific fact" and then proceeds to build a whole theoretical argument on this and similar "facts". It is fur ther argued that his article: \u27Vrye Weekblad\u27 and post-apartheld mania; what to do with the press? is a case In point
The neural mechanism underlying illusory complex motions
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PURPOSE: The Pinna illusion is a striking example of the perception of complex motion (rotation and radiation) in the absence of physical motion. For example, upon physically approaching or receding from the Pinna-Brelstaff figure, the observer experiences vivid illusory counter rotation of the figure. This visual phenomenon of illusory rotary motion is a well-known example of integration of local cues to form a global percept. Using psychophysical tests and functional magnetic resonance imaging (fMRI) of visual cortices, we recently found that the Pinna-Brelstaff figure (illusory rotation) and a real physical rotation control stimulus both predominantly activated subarea MST in hMT+, each with a similar response intensity. However, the detailed neural mechanisms underlying the Pinna illusory rotation as well as radiation remain unknown.
METHODS: By manipulation of the physical characteristics of the Pinna-Brelstaff figure, we could generate different types of illusory complex motion: rotation, expansion and contraction (radiation). We first test the illusory effect in human and nonhuman primate psychophysically, and then performed single-unit recordings of MST and MT in awake macaques.
RESULTS: We found that up to two-thirds of MST neurons encode Pinna illusory complex motions, with similar tuning preferences to their corresponding real physical motions. A subset of MT neurons was found to encode the local motion signals with earlier response latency than MST neurons.
CONCLUSIONS: These results demonstrate that neurons in area MST but not MT respond equivalently and respectively to Pinna illusory and real rotations, expansions and contractions. These findings suggest that the representation of illusory and real complex motion fields in primate MST relies on a similar cascade of neural integrative mechanisms from earlier visual areas to generate a global motion perception.</p
Formation of rings in a swirling gas flow
No full textThe main structure of this thesis is aimed to study the behaviour of a swirling air flow in a cylindrical chamber through experiments. Different tiny particles, water droplets and NaCl aerosol particles (μm and submicron scale), are adopted to trace the motion of air flow.In the preface, the background and motivation of this project are introduced. Inspired by the ring structures found in proto-planetary disks, we want to experimentally explore possible connections between angular momentum transport and flow structure.In the beginning part of this thesis, basic fluid dynamics and necessary models are introduced, for the convenience of the latter part of this thesis. A new parameter, coupling efficiency χ was introduced to characterize the coupling wellness between tracer particles and flow, specifically, in this experiment. We also list three examples of flow-particle coupling as supplementary materials, since they are related with this thesis’ topic.In the middle part, the detailed hardware setup and methods of this experiment are introduced. All of the important instrumentation information is listed, as well as the preparations and general experiment methods.In the following part, the experiment results are presented. We also conduct a COMSOL flow simulation, to give a rough idea on the flow velocity profile inside the chamber, though we don’t expect the accuracy of the simulation. The recorded images are processed with MATLAB for measurements. We have found that water droplets and NaCl aerosol particles are behaving differently as tracers, mainly, in the central flow. Besides, we also find continuous and random expanding rings emerging from the centre in water droplet experiments. These expanding rings are much more common in water droplet experiments than that of NaCl experiments. The flow structure and radial expansion speed of those expanding rings are measured with MATLAB.Finally, we have two conclusions based on what we’ve found. The first one is that, the larger water droplets are decoupled from the gas flow in the central flow region. The second one is that, with some assumptions, we have a hypothesis that the expanding rings we find are representing the separation of water droplets from the flow. This possibility is verified by comparing the radial drifting speed of particles from a theoretical model solved by COMSOL ODE module with our measurements. The results prove our hypothesis, given the assumptions. But the proof for the second conclusion isn’t comprehensive, which is a possible direction for future work. Additionally, we further propose that, if both of our conclusions hold, it means that the water droplets, which receive the angular momentum and decoupled from the gas, are drifting outward in the form of pulsed expanding rings. This conclusion could be described as "he who gains angular momentum shall expand like rings", and it’s useful in explaining the ring formation found in proto-planetary disks,In the last chapter, the main drawbacks and future improvements are discussed. Mainly, we lack a precise understanding on the flow’s velocity profiles, which could be improved by introducing more advanced measuring technologies into the experiment.本文主要通過實驗來研究在一個圓柱容器的旋轉氣流的動力學特徵。我們用兩種不同尺寸的示蹤顆粒：水霧（約微米尺寸）和氯化鈉（小於微米尺寸）顆粒作示蹤粒子來表徵氣流的運動。本文的前言部分是一個簡要的研究背景介紹。從原初行星盤中發現的環帶狀結構得到靈感，我們嘗試從實驗的角度去驗證角動量輸運和旋轉氣流所表徵出的結構是否有關聯。本文的第一部分將簡要介紹一些本文所將涉及到的流體力學理論和模型。本文提出一個參數χ用於表徵本文所述實驗中的示蹤粒子和氣流的耦合程度。需要注明的是，這個參數是專門為本實驗而優化的。本文也另外列舉了三個粒子-氣流耦合問題的例子，作與本實驗的參考。本文第二部分詳細介紹本文所述實驗的硬件搭建細節與實驗方法，包括所使用的儀器和測量設備的詳細參數。另外，一些準備工作和前序實驗也會順帶被提到。本文第三部分將會展示實驗結果。首先通過COMSOL的流體力學仿真，我們可以粗略瞭解容器旋轉氣流的速度場。雖然仿真結果未必準確，但仍不妨當作一個參考。隨後，本研究利用MATLAB來分析相機所記錄下來的氣流圖像。我們發現實驗中所采用的兩種不同的示蹤粒子表現出不同的與氣流的耦合程度，特別是在漩渦中心更加明顯。除此之外，我們還在所記錄的圖像中發現了連續但不規律性的環狀結構；并且這些環狀結構都會持續向外擴張。相較於以氯化鈉顆粒作示蹤粒子，此類結構在以水霧顆粒作示蹤粒子的實驗中更明顯。以MATLAB為工具，通過測量此類環狀結構的半徑變化，我們推測出這些環狀結構的徑向擴散速度。本文的結尾部分，我們得出兩個初步結論。第一個結論是，由於尺寸較大，水霧顆粒在漩渦中已經失去了與氣流的耦合性。第二個結論是，在一些假設作前提下，我們猜測（在水霧作示蹤粒子的實驗中）所觀察到的環狀結構正是失去與氣流耦合而被分離出的水霧顆粒。進一步研究，我們設計了一個簡化的顆粒-氣流耦合的動力學模型並通過COMSOL ODE模塊來求解顆粒在氣流中的理論漂移速度。通過計算，我們發現所觀察到的環狀結構的徑向速度與模型所推導出的示蹤粒子徑向漂移速度高度一致。但是，因這個理論模型中做出了許多假設以簡化複雜程度，故這個結論的證明與確認過程仍然存在不充分性。這也是未來後續工作一個需要補充的實驗方向。撇開上述不足之處，本文進一步指出，若兩個結論都成立，則表明在本實驗中，失去與氣流耦合性的水霧顆粒從旋轉氣體中得到了角動量，並以間隔性的環狀結構向外漂移。這個結論可以總結為，“但凡得到角動量的，必將以環狀結構向外擴散”。這個結論在解釋原初行星盤中的環狀結構可能會有一定意義。在本文的最後一部分，我們分析了本次實驗中的不足之處與缺陷。簡而言之，由於缺乏更精確的測量手段，我們對於氣流速度場的分析存在局限。在未來的後續工作中，引入更精確有效的速度場測量手段可以彌補這個不足。Li, Keyan.M.Phil. Chinese University of Hong Kong 2021.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …)
Ethical Procedures? A Critical Intervention: The sacred, the profane, and the planet
No full textIssues relating to ethical clearance, how these procedures relate to very different ontologies, ways of making sense,conditions of existence, and the ideological implications thereof are critically discussed. Written as an invited intervention, the author takes readers through a variety of paradigms: indigenous approaches involving the sacred and the profane, instrumentalization of research; multispeciesism and research as a lived practice. Comments are offered on the nature of science and some questions are posed on the contradictions of ethical practices that readers encounter. The method is eclectic, read through a Peirceian pragmatism, and the outcome proposes relationality rather than the inevitability of discrete findings. Some conclusions are offered on the geographical distribution of populations sampled.</jats:p
Spectral Stochastic Isogeometric Analysis
No full textThe traditional stochastic analysis methods are becoming increasingly unappreciated for modern engineering practices. The inconsistency between intentionally designed CAD model and the traditional stochastic analysis model inevitably obstructs the accuracy, efficiency, and applicability of the traditional stochastic analysis methods. However, these requirements are becoming increasingly significant in contemporary engineering practices. Therefore, it is requisite to develop a new stochastic analysis framework complied with the requirements of modern engineering practices.
This dissertation presents a CAD-CAE integrated spectral stochastic isogeometric analysis (SSIGA) framework. And a series of structural analysis problems with uncertainties are investigated within the proposed framework. Firstly, the SSIGA is developed and investigated for the stochastic linear elasticity problem. Then, the SSIGA is further developed for the stochastic linear elasticity problem of composite plates. Moreover, the SSIGA is extended for the structural free vibration problem, namely, the stochastic eigenvalue problem. After that, the extended support vector regression (X-SVR) method is adopted within SSIGA framework for the stochastic linear stability analysis of plates. The accuracy, efficiency, and applicability of the proposed SSIGA framework for different structural problems are comprehensively investigated and verified through several elaborately selected numerical examples.
The proposed SSIGA framework provides a CAD-CAE integrated stochastic analysis framework for the modern engineering practices. By meticulously adopting the basis functions within CAD system, the SSIGA framework can maintain the exact geometries of the structures and the random fields between the CAD model and the SSIGA stochastic analysis model, even for those complex geometries inspired from real-life engineering practices. Such rigor can thoroughly eliminate the geometric errors that permanently embedded in traditional approaches. The stochastic analysis by SSIGA framework will be assuredly implemented on the intentionally designed model in CAD system. Moreover, basis functions within CAD system are always higher-order continuous over the whole physical domain. Therefore, the novel SSIGA approach can guarantee a globally smooth random field modelling and finally a globally smooth stochastic analysis result. Additionally, by implementing stochastic analysis directly on the CAD model and avoiding the mesh process in traditional stochastic analysis routines, SSIGA framework will promise an efficient stochastic analysis method for real-life engineering practices
Targeting Seasonal Marketing Campaigns: Rebalancing Exploration and Exploitation
No full textOnce a firm has a targeting policy, the firm incurs an opportunity cost when varying its action to learn how to improve that policy. This results in what is classically considered an exploration vs. exploitation tradeoff. This tradeoff is widely studied in online learning domains. However, firms are forced to learn in batches that occur infrequently in many marketing channels, such as seasonal marketing campaigns and salesperson marketing. For example, when demand is seasonal, marketing campaigns often occur annually, with retailers using data from last year to train this year’s policy. This essay identifies an information externality when assigning actions to customers in the same batch: the incremental information contributed by the focal customer depends upon the assignment decisions foe other customers. This essay investigates how to optimally rebalance exploration (more variation) and exploitation (direct implementation) in these settings leveraging this externality. The algorithm this essay proposes balances the expected value and opportunity cost of new information from each new batch. This essay validates the findings using data from a field experiment.¹
¹This essay is based on joint work with Duncan Simester.S.M
Essays in Marketing Innovations
No full textThe dissertation consists of three chapters on understanding marketing innovations, including targeted marketing and new product development.
The first chapter studies a novel targeting problem that many firms face and develops a new method for targeting experimentation. Adaptive learning policies that guide how firms trade off acquiring new information to improve a current targeting policy, versus exploiting the current policy to harvest, typically focus on settings in which customers arrive individually, in a frequent sequence. However, in practice, firms often conduct marketing campaigns in batches, in which they target a large group of customers with personalized marketing actions together. This has an important implication for how firms resolve the tradeoff between acquiring new information and exploiting the current policy. The large number of customers in each batch (campaign) introduces an information externality: the incremental information contributed by a single customer depends upon the assignment decisions for other customers in the batch. We investigate how to optimally acquire and coordinate information in these settings. The algorithm we propose uses Gaussian processes to estimate the value of incremental information, while accounting for the information externality between customers in the same batch. Findings are validated using data from a field experiment.
The second chapter studies customer demand in a non-market-oriented economy. The economics and marketing literature has primarily focused on market economies and studied factors such as price and advertising when analyzing customer demand. However, in non-market-oriented economies, social factors like corruption can have a significant influence on customer decisions. In particular, this paper focuses on the demand for luxury products, which are widely used for gift-giving and even bribery in emerging markets. One possible mechanism is that when the relative size of non-market-oriented sectors in the local economy increases, luxury products can be used to identify those who have a higher willingness to pay for scarce resources. As a result, the demand for luxury products moves together with the degree of corruption. By leveraging natural experiments of top-down anti-corruption campaigns that temporarily halt this channel, an empirical study is performed using a comprehensive dataset that covers the sales of all cigarette brands and the local social environment in China. The results suggest that these social factors can have an unanticipated impact on the demand for luxury products.
The third chapter studies how customer search can stifle product innovations. Conventional wisdom suggests that when an incumbent fails to innovate, there is a greater risk to the incumbent of competition from other innovators. I show conditions in which the opposite is true: by delaying innovation, an incumbent can create entry barriers that deter innovation by competitors. Consequently, both competition and innovation are suppressed. The key insight driving these outcomes is that customer search is endogenous, and absence of innovation today can disincentivize customers from searching in the future. Since customers need to search to discover innovations, when they search less, it both creates entry barriers for competitors, and reduces the competitors' incentives to innovate. Postponing innovation can benefit incumbents if it motivates customers to search less, and thus competitors to innovate less. Notably, I show that searching less is a rational customer response.Ph.D
Precipitation over the past four centuries in the Dieshan Mountains as inferred from tree rings: An introduction to an HHT-based method
No full textTo improve our understanding of the Asian monsoon system, we developed a hydroclimate reconstruction in a marginal monsoon shoulder region for the period prior to the industrial era. Here, we present the first moisture sensitive tree-ring chronology, spanning 501 years for the Dieshan Mountain area, a boundary region of the Asian summer monsoon in the northeastern Tibetan Plateau. This reconstruction was derived from 101 cores of 68 old-growth Chinese pine (Pinus tabulaeformis) trees. We introduce a Hilbert–Huang Transform (HHT) based standardization method to develop the tree-ring chronology, which has the advantages of excluding non-climatic disturbances in individual tree-ring series. Based on the reliable portion of the chronology, we reconstructed the annual (prior July to current June) precipitation history since 1637 for the Dieshan Mountain area and were able to explain 41.3% of the variance. The extremely dry years in this reconstruction were also found in historical documents and are also associated with El Niño episodes. Dry periods were reconstructed for 1718–1725, 1766–1770 and 1920–1933, whereas 1782–1788 and 1979–1985 were wet periods. The spatial signatures of these events were supported by data from other marginal regions of the Asian summer monsoon. Over the past four centuries, out-of-phase relationships between hydroclimate variations in the Dieshan Mountain area and far western Mongolia were observed during the 1718–1725 and 1766–1770 dry periods and the 1979–1985 wet period
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