Standard methods of scintillation spectroscopy were used to investigate the decay scheme of Kr⁸⁷. Natural krypton gas, containing 17 percent Kr⁸⁶, was irradiated in the 100 kilowatt V.P.I. research reactor to produce Kr⁸⁷ Which decays by beta emission to Rb⁸⁷. The halflife of Kr⁸⁷ was found to be 78 minutes in agreement with other investigators. Gamma spectra and gamma-gamma coincidence measurements employed two integral line NaI(Tl) detectors with 3 in. diameter by 3 in. long crystals. Beta measurements were made using a 2 in. diameter by 1/2 in. long CaF₂(Eu) integral line detector. Both the gamma spectrum and the beta spectrum were found to be complex. Energy values of 0.40, 0.85, 1.57, 1.75, 2.42, 2.97, and 3.30 MeV were assigned to excited states in Rb⁸⁷. Possible parities and spins were assigned to most of the excited states from beta-ray log ft values. End-point energies of the beta groups populating the ground state and the first and second excited states were measured and used in conjunction with the gamma-ray energy measurements to calculate a value of 3.85 ±.04 MeV for the Kr⁸⁷ disintegration energy. Gamma-ray relative intensity measurements provided a percent abundance estimate of the beta groups populating the various Rb⁸⁷ energy levels. Angular correlation measurements were performed for the 2.57 - 0.40 MeV gamma-gamma cascade proceeding from a level at 2.97 MeV. The results were consistent with log rt and shell model predictions and allowed a tentative assignment of 9/2⁺ to be made for this state. The ground state spin and parity or Kr⁸⁷ is inferred, on this basis, to be 7/2⁺. / Ph. D.

For decades, the increasing applications in engineering field, such as space exploration, ocean sampling, aerial vehicle formation flight and so on, have made the cooperative control problem of multi-agent systems a research focus. In this thesis, we will further study the consensus problem, one of the basic cooperative control problems, for two classes of nonlinear multi-agent systems: the Euler-Lagrange systems and the rigid spacecraft attitude control systems. / An Euler-Lagrange system refers to a system whose motion equation is derived by the Euler-Lagrange equation. Euler-Lagrange systems can describe many practical systems, such as robot manipulators and AC motors. The rigid spacecraft attitude control system is usually embedded in the overall control system for a rigid spacecraft to perform attitude maneuver, such as spin stabilization or target acquisition. The consensus problems for these two classes of systems have many applications, like robot manipulators coordination and spacecraft formation flying. Being one of the basic cooperative control problems, consensus problem lays the foundation for some typical cooperative control problems, such as rendezvous, flocking and formation control. So far, two kinds of consensus problems have been investigated, i.e., the leader-following consensus problem and the leaderless consensus problem. For a multi-agent system, each agent will be viewed as a subsystem of the overall multi-agent system. The leader-following consensus problem aims to design a control law such that the state and/or output of each subsystem will asymptotically track a prescribed trajectory, which is usually generated by another subsystem called the leader system, while the leaderless consensus problem requires that the control law drive the state and/or output of each subsystem to a common trajectory. / The leader-following consensus problems for both the Euler-Lagrange systems and the rigid spacecraft attitude control systems present certain technical difficulties. On one hand, the controller is constrained by the communication network, which describes the information flow among all subsystems. On the other hand, both the Euler-Lagrange system and the rigid spacecraft attitude control system are nonlinear systems with complex kinematic or dynamic equations. To overcome these difficulties, we have employed the distributed observer approach, which consists of two steps: first, given a leader system, a distributed observer is designed for each follower subsystem to estimate the state of the leader system and recover the reference signal; second, by making use of the estimated reference signal, a certainty equivalence controller will be synthesized to control the overall multi-agent system. Whether or not the distributed observer approach will work depends on two crucial issues: the existence of the distributed observer for a given leader system and the stability of the closed-loop system subject to the certainty equivalence controller. / In the first part of this thesis, we have considered both the leader-following and leader-less consensus problems for multiple uncertain Euler-Lagrange systems under a switching communication network. The main results are summarized as follows: / 1. The leader-following consensus problem for multiple uncertain Euler-Lagrange systems under switching communication network was studied. Since the kinematic equation of the Euler-Lagrange system is linear, the leader system is linear. Given this leader system, we have established the distributed observers for all follower subsystems under a jointly connected communication network. To show the stability of the closed-loop system, we resorted to a generalized Barbalat’s lemma to deal with the discontinuity resulted from the switching of the communication network. / 2. Inspired by the idea of the distributed observer approach, we have employed an auxiliary system for each subsystem to further solve the leaderless consensus problem for multiple uncertain Euler-Lagrange systems under jointly connected communication network. When the communication network is undirected, we pointed out that the final common trajectory will be uniquely decided by the initial values and will not be affected by the communication network. / The second part of this thesis addresses the leader-following attitude consensus problem for multiple rigid spacecraft systems. Owing to the nonlinear kinematic equation of the rigid spacecraft attitude control system, the leader system is also nonlinear and we have established a nonlinear distributed observer for each follower subsystem to estimate the state of the leader system. Three scenarios were considered and are summarized as follows: / 1. In the first scenario, the controller uses the control feedback of both the attitude and angular velocity. We posed a technical lemma to show that the couplings between subsystems do not change the asymptotic behavior of each follower subsystem and hence the stability of the closed-loop system can be guaranteed. / 2. In the second scenario, only the attitude is available for control feedback. In the absence of the angular velocity, it is more difficult to prove the stability of the closed loop system. In order to do so, we have enhanced the performance of the distributed observers by making the convergent speed exponential. / 3. In the third scenario, we further solved the attitude consensus problem for multiple rigid spacecraft systems subject to unknown system parameters and external disturbances. For each follower subsystem, an adaptive law is used to estimate the unknown parameters and a dynamic compensator is attached to eliminate the influence of the external disturbances. / 近十年来，随着在空间探索，海洋监测，以及飞行器编队飞行等工程领域内的逐步应用，多智能体系统的协作式控制问题受到了广泛的关注。在本论文中，我们将进一步采用基于分布式观测器的方法来研究两类非线性多智能体系统，即Euler-Lagrange系统与刚性航天器姿态控制系统的一类基本协作式控制问题-趋同问题。 / Euler-Lagrange系统指代一类系统，其动态方程可由Euler-Lagrange方程导出。Euler-Lagrange系统可以描述许多实际系统，例如机器人手臂与交流电机。航天器姿态控制系统通常被嵌入航天器的全局控制系统中以调整航天器姿态，例如自旋镇定与目标跟踪。这两类系统的趋同问题有诸多应用，例如机器人手臂协作与航天器编队飞行。作为一类基本的协作式控制问题，趋同问题是一些典型的协作式控制问题的基础，例如蜂拥，聚类与编队。目前，趋同问题主要分为两类：有领导者的趋同问题与无领导者的趋同问题。在一个多智能体系统中，每一个智能体都作为全局系统的一个子系统。有领导者的趋同问题的控制目标是设计控制器使得所有子系统的状态和/或输出渐近地跟踪一个指定的轨迹，该轨迹通常由另一个被称作领导者的子系统产生，而无领导者的趋同问题则要求设计控制器使所有子系统的状态和/或输出渐近地趋于一个共同的轨迹。 / 目前，Euler-Lagrange系统与刚性航天器姿态控制系统的趋同问题都面临着技术上的挑战。一方面，控制器的设计受限于用于描述信息流动的通信网络。另一方面，Euler-Lagrange系统与刚性性航天器姿态控制系统都是非线性系统，且具有复杂的运动学方程或动力学方程。为了克服这些困难，我们采用了基于分布式观测器的方法。该方法包含两步：首先，为每一个跟随者设计一个分布式观测器以估测领导者的状态；其次，根据观测器的估测信号设计全局控制器。该方法能否成功取决于两个关键因素：一，对某个给定的领导者系统，分布式观测器是否存在；二，根据估测信号设计的确定性等价控制器是否能保证闭环系统的稳定性。 / 在本论文的第一部分中， 我们将分别考虑在通信网络联合连通条件下Euler-Lagrange 系统有领导者的和无领导者的趋同问题。主要结论总结如下 / 1. 我们将研究Euler-Lagrange系统的有领导者的趋同问题。因Euler-Lagrange系统的运动学方程是线性方程，其领导者系统也为线性系统。在联合联通的通信网络下，我们为每一个跟随者系统设计了线性的分布式观测器，并引用了一个广义Barbalat引理来证明闭环系统的稳定性。 / 2. 受分布式观测器方法的启发，我们将借由一个辅助系统来研究通信网络联合连通条件下Euler-Lagrange系统无领导者的趋同问题，并进一步指出，如果通信网络是无向的，那么系统的稳态将完全取决于系统的初态而与通信网络无关。 / 在本论文的第二部分中，我们将探讨刚性航天器系统的姿态趋同问题。由于刚性航天器系统的姿态运动学方程是非线性方程，其领导者系统也是一个非线性系统。我们为每一个跟随者系统设计了非线性的分布式观测器，并考虑了如下三类情况。 / 1. 在第一类情况下，控制器可同时采用角位置与角速度反馈。为确保子系统间的耦合不影响闭环系统稳定性，我们确立了一个引理用以说明此类耦合并不改变系统的稳态特性。 / 2. 在第二类情况下，控制器只能采用角位置反馈。这使得证明闭环系统的稳定性变得困难。为此，分布式观测器的收敛速度被提高至指数收敛。 / 3. 在第三类情况下，刚性航天器系统包含未知系统参数且受到外部干扰。我们采用了自适应控制技术以及动态补偿技术用以估计未知参数及抵消外部干扰。 / Cai, He. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 116-127). / Abstracts also in Chinese. / Title from PDF title page (viewed on 05, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Cette thèse s’inscrit au croisement de plusieurs domaines de la recherche économique de l’innovation. Notre démarche fait appel à des résultats empiriques issus de l’économétrie de l’innovation. Pour étudier la relation entre innovation et demande, l’outil le plus adapté nous semble être le modèle de la croissance endogène fondé sur l’innovation par opposition au modèle de la croissance exogène. La nature et la direction de cette relation ont été explorées par différents courants économiques qui peuvent être classés selon deux grandes écoles. Les premiers sont les tenants de la thèse dite de la poussée technologique de l’innovation (« Technology-Push Innovation ») que l’on peut considérer très globalement comme « tirés » par les travaux de Joseph Schumpeter. Les seconds sont les tenants de l’approche dite de l’impulsion par la demande de l’innovation (« Demand-Pull Innovation ») dont les travaux pionniers ont été baptisés par Jacob Schmookler. Les travaux de Kleinknecht et Verspagen (1990) nous ont fortement inspiré pour démarrer cette thèse. Notre démarche constitue un prolongement et une complexification de leur analyse. En effet, l’objectif de cette thèse est double : monter que la relation entre innovation et demande n’est pas unidirectionnelle et, ce constat vérifié, examiner la possibilité d’étudier l’hétérogénéité des industries au sens de ces deux approches en fonction de leurs niveaux technologiques.Il nous semble que notre travail contribue à la compréhension des déterminants de l’innovation tels qu’ils ressortent de la controverse « Demand-Pull » versus « Technology-push », de trois façons :1) En proposant un survey problématisé de la littérature sur l’innovation,2) En présentant de façon originale des données sur la R&D et la productivité des industries des pays de l’OCDE,3) En suggérant que les modèles à correction d’erreur, maintenant très bien maîtrisés, peuvent apporter d’utiles éclairages à la question des modèles d’innovation (« Demand-Pull » versus « Technology-push »). / This thesis is at the intersection of several fields of economic research of innovation. Our approach uses empirical results from the econometrics of innovation. To study the relationship between innovation and demand, the most suitable seems to be the endogenous growth model based on innovation as opposed to the exogenous growth model. The nature and the direction of this relationship have been explored by various economic flows that can be classified into two major schools. The first are the proponents of so-called “Technology-Push Innovation” which may be regarded very broadly as “learned” by the work of Joseph Schumpeter. The latter are the proponents of the approach “Demand-Pull Innovation”, whose pioneering works have been baptized by Jacob Schmookler.The works of Kleinknecht and Verspagen (1990) have greatly inspired us to start this thesis. Our approach is an extension of this analysis. The purpose of this thesis is twofold: 1) showing that the relationship between innovation and demand is not unidirectional, 2) and this finding verified, examining the heterogeneity of industries within the meaning of these two approaches based on their technology levels.It seems to us that our work contributes to understanding the determinants of innovation as they emerge from the controversy “Demand-Pull” versus “Technology-push”, in three ways: 1) By offering a problematized survey of the literature on innovation, 2) By presenting, in an original way, data on R&D and productivity of industries in OECD countries, 3) By suggesting that the error correction models, now very well controlled, can provide useful insights to the issue of innovation models (“Demand-Pull” versus “Technology-push”).

During the past decade, renewable energy sources have become an indispensable pillar in European electricity generation. This paper aims at examining if the increasing importance of renewables stimulates investment in European power transmission networks. The question of interest is addressed by an error correction investment model that builds on Neoclassical theory and is further augmented by recent literary findings. Under the proposed threefold estimation strategy, the share of renewables is not found to significantly influence investment spending when the full set of transmission system operators are considered. However, a slight and justified sample restriction leads to the conclusion that a rising share of renewable energy sources substantially increases investment in power transmission networks. / Series: Department of Economics Working Paper Series

Has economic integration improved the postwar growth performance of the actual fifteen member states of the European Union (EU)? To answer this question, we first construct an index of integration for each member state that explicitly accounts for global integration (GATT) as well as regional (European) integration. Using this variable, we test for permanent and temporary growth effects in a dynamic growth accounting framework, both in a time series setting for the (aggregate) EU and a panel approach for the EU member states. Although the hypothesis of permanent growth effects as postulated by endogenous growth models with scale effects is clearly rejected, we find significant levels effects: GDP per capita of the EU would be approximately one fifth lower today, if no integration had taken place since 1950. Interestingly, two third of this effect are due to GATT-liberalization. (author's abstract) / Series: EI Working Papers / Europainstitut

In this paper we analyse the implications of the euro for the international reserves in the Eurosystem. Two conceptually different effects of the changeover have to be distinguished: a technical effect that largely arises as a matter of accounting, and a behavioural effect that stems from the fact that the optimal demand of the aggregate Eurosystem is not equal to the sum of the optimal country levels. The technical effect arises from two main sources: the abolishment of the ECU-creating mechanism, and the redefinition of international reserves which precludes (former) reserves that were denominated in euro-currencies. As a result the average reserves of the Eurosystem in 1999 amounted to $287 billion, considerably less than in 1998 ($345 billion). We then derive a reserve demand function for the aggregate Eurosystem using panel data estimation techniques and simulate reserve demand for the situation after the regime shift. The optimal aggregate level of reserves turns out to be some $188 billion, which implies excess reserves in the Eurosystem amounting to approximately $100 billion in the year 1999. We go on by proposing a key by which this excess could be allocated to the individual countries taking the asymmetric distribution of reserves in the Eurosystem into account. Finally we classify and enumerate the proposals for making use of the estimated reserve overhang. (author's abstract) / Series: EI Working Papers / Europainstitut

We analyze empirically the role played by energy inflation as a determinant of downward corrections in house prices. Using a dataset for 18 OECD economies spanning the last four decades, we identify periods of downward house price adjustment and estimate conditional logit models to measure the effect of energy inflation on the probability of these house price corrections after controlling for other relevant macroeconomic variables. Our results give strong evidence that increases in energy price inflation raise the probability of such corrective periods taking place. This phenomenon could be explained by various channels: through the adverse effects of energy prices on economic activity and income reducing the demand for housing; through the particular impact on construction and operation costs and their effects on the supply and demand of housing; through the reaction of monetary policy on inflation withdrawing liquidity and further reducing demand; through improving attractiveness of commodity versus housing investment on asset markets; or through a lagging impact of common factors on both variables, such as economic growth. Our results contribute to the understanding of the pass-through of oil price shocks to financial markets and imply that energy price inflation should serve as a leading indicator for the analysis of macro-financial risks. (authors' abstract)

Spillover phenomena are usually statistically estimated on the basis of regional and temporal panel data. In this paper we review and investigate exploratory and confirmatory statistical panel data techniques. We illustrate the methods by calculations in the stetting of the well known Research and Development Spillover study by Coe and Helpman (1995). It will be demonstrated that alternative estimation techniques that are well compatible with the data can lead to opposite conclusions. (author's abstract) / Series: Working Papers Series "Growth and Employment in Europe: Sustainability and Competitiveness"

This paper investigates a new category of influential factors on business cycle synchronization (BCS), so far hardly regarded in the BCS literature: It provides an empirical assessment of the impact of macroeconomic imbalances, as monitored by the European Commission by the scoreboard indicators since 2011, on BCS in the Euozone. We use a quarterly data set covering the period 2002-2012 and estimate the direct and indirect effects of macroeconomic imbalances in the pre- and post-crisis period in a simultaneous equations model. Business cycle correlation between EA members is measured by the recently proposed dynamic conditional correlation of Engle 2002 which can better identify synchronous and asynchronous behaviour of BC than the commonly used measures. We find that appearing differences between EA members in the current account, in government deficit and public debt, in private debt and unit labor cost developments have reduced BCS in the EA, even more in the post-crisis period than before. Moreover, these explanatory factors of BCS, generally reinforce each other and are also influenced by other critical macro imbalances. Since BCS is essential in a monetary union, this paper provides clear support that a stronger, common economic governance would be important for the functioning and survival of the Eurozone. (authors' abstract) / Series: Department of Economics Working Paper Series

This paper uses data for 255 NUTS-2 European regions over the period 1995-2003 to test the relative explanatory performance of two important rival theories seeking to explain variations in the level of economic development across regions, namely the neoclassical model originating from the work of Solow (1956) and the so-called Wage Equation, which is one of a set of simultaneous equations consistent with the short-run equilibrium of new economic geography (NEG) theory, as described by Fujita, Krugman and Venables (1999). The rivals are non-nested, so that testing is accomplished both by fitting the reduced form models individually and by simply combining the two rivals to create a composite model in an attempt to identify the dominant theory. We use different estimators for the resulting panel data model to account variously for interregional heterogeneity, endogeneity, and temporal and spatial dependence, including maximum likelihood with and without fixed effects, two stage least squares and feasible generalised spatial two stage least squares plus GMM; also most of these models embody a spatial autoregressive error process. These show that the estimated NEG model parameters correspond to theoretical expectation, whereas the parameter estimates derived from the neoclassical model reduced form are sometimes insignificant or take on counterintuitive signs. This casts doubt on the appropriateness of neoclassical theory as a basis for explaining cross-regional variation in economic development in Europe, whereas NEG theory seems to hold in the face of competition from its rival. (authors' abstract)