Browsing by Subject "SYSTEM"

Now showing 1 - 9 of 9
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    A Modular Multilevel Series/Parallel Converter for a Wide Frequency Range Operation
    (IEEE Transactions on Power Electronics, 2019-10-01) Li, Z; Ricardo Lizana, F; Yu, Z; Sha, S; Peterchev, AV; Goetz, SM
    When providing ac output, modular multilevel converters (MMCs) experience power fluctuation in the phase arms. The power fluctuation causes voltage ripple on the module capacitors, which grows with the output power and inversely to the output frequency. Thus, low-frequency operations of MMCs, e.g., for motor drives, require injecting common-mode voltages and circulating currents, and strict dc voltage output relative to ground is impossible. To address this problem, this paper introduces a novel module topology that allows parallel module connectivity in addition to the series and bypass states. The parallel state directly transfers power across the modules and arms to cancel the power fluctuations and hence suppresses the capacitor voltage ripple. The proposed series/parallel converter can operate at a wide frequency range down to dc without common-mode voltages or circulating currents; it also allows sensorless operation and full utilization of the components at higher output frequencies. We present detailed simulation and experiment results to characterize the advantages and limitations of the proposed solution.
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    Agents with Principles: The Control of Labor in the Dutch East India Company, 1700-1796
    (American Sociological Review, 2017) Wezel, F; Ruef, M
    Principal-agent problems plagued early modern corporations. The existing literature emphasizes the potential benefits provided by private trade in aligning the interests of company agents to those of their principals. We contribute to this line of work by analyzing the organizational and social mechanisms that may help address principal-agent problems in the presence of private trading opportunities. Drawing on personnel records of more than half a million seafarers employed by the Dutch East India Company (VOC) over nearly a century, we show that monitoring was effective in reducing desertion when private trade was conceived as a market activity subordinated to hierarchy. Social bonds were more effective in preventing desertion when the company elevated private trade above hierarchy. Our analysis clarifies how early corporations could maintain control over a geographically dispersed and diverse labor force in the absence of modern tools of organizational governance.
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    Assessing Africa-Wide Pangolin Exploitation by Scaling Local Data
    (Conservation Letters, 2018-03) Ingram, DJ; Coad, L; Abernethy, KA; Maisels, F; Stokes, EJ; Bobo, KS; Breuer, T; Gandiwa, E; Ghiurghi, A; Greengrass, E; Holmern, T; Kamgaing, TOW; Ndong Obiang, AM; Poulsen, JR; Schleicher, J; Nielsen, MR; Solly, H; Vath, CL; Waltert, M; Whitham, CEL; Wilkie, DS; Scharlemann, JPW
    Copyright and Photocopying: © 2017 The Authors. Conservation Letters published by Wiley Periodicals, Inc. Overexploitation is one of the main pressures driving wildlife closer to extinction, yet broad-scale data to evaluate species’ declines are limited. Using African pangolins (Family: Pholidota) as a case study, we demonstrate that collating local-scale data can provide crucial information on regional trends in exploitation of threatened species to inform conservation actions and policy. We estimate that 0.4-2.7 million pangolins are hunted annually in Central African forests. The number of pangolins hunted has increased by ∼150% and the proportion of pangolins of all vertebrates hunted increased from 0.04% to 1.83% over the past four decades. However, there were no trends in pangolins observed at markets, suggesting use of alternative supply chains. The price of giant (Smutsia gigantea) and arboreal (Phataginus sp.) pangolins in urban markets has increased 5.8 and 2.3 times respectively, mirroring trends in Asian pangolins. Efforts and resources are needed to increase law enforcement and population monitoring, and investigate linkages between subsistence hunting and illegal wildlife trade.
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    Automatic word count estimation from daylong child-centered recordings in various language environments using language-independent syllabification of speech
    (Speech Communication, 2019-10-01) Räsänen, O; Seshadri, S; Karadayi, J; Riebling, E; Bunce, J; Cristia, A; Metze, F; Casillas, M; Rosemberg, C; Bergelson, E; Soderstrom, M
    © 2019 The Authors Automatic word count estimation (WCE) from audio recordings can be used to quantify the amount of verbal communication in a recording environment. One key application of WCE is to measure language input heard by infants and toddlers in their natural environments, as captured by daylong recordings from microphones worn by the infants. Although WCE is nearly trivial for high-quality signals in high-resource languages, daylong recordings are substantially more challenging due to the unconstrained acoustic environments and the presence of near- and far-field speech. Moreover, many use cases of interest involve languages for which reliable ASR systems or even well-defined lexicons are not available. A good WCE system should also perform similarly for low- and high-resource languages in order to enable unbiased comparisons across different cultures and environments. Unfortunately, the current state-of-the-art solution, the LENA system, is based on proprietary software and has only been optimized for American English, limiting its applicability. In this paper, we build on existing work on WCE and present the steps we have taken towards a freely available system for WCE that can be adapted to different languages or dialects with a limited amount of orthographically transcribed speech data. Our system is based on language-independent syllabification of speech, followed by a language-dependent mapping from syllable counts (and a number of other acoustic features) to the corresponding word count estimates. We evaluate our system on samples from daylong infant recordings from six different corpora consisting of several languages and socioeconomic environments, all manually annotated with the same protocol to allow direct comparison. We compare a number of alternative techniques for the two key components in our system: speech activity detection and automatic syllabification of speech. As a result, we show that our system can reach relatively consistent WCE accuracy across multiple corpora and languages (with some limitations). In addition, the system outperforms LENA on three of the four corpora consisting of different varieties of English. We also demonstrate how an automatic neural network-based syllabifier, when trained on multiple languages, generalizes well to novel languages beyond the training data, outperforming two previously proposed unsupervised syllabifiers as a feature extractor for WCE.
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    Dynamics of a qubit in a high-impedance transmission line from a bath perspective
    (Physical Review A, 2016-03-28) Bera, S; Baranger, HU; Florens, S
    We investigate the quantum dynamics of a generic model of light-matter interaction in the context of high-impedance waveguides, focusing on the behavior of the photonic states generated in the waveguide. The model treated consists simply of a two-level system coupled to a bosonic bath (the Ohmic spin-boson model). Quantum quenches as well as scattering of an incident coherent pulse are studied using two complementary methods. First, we develop an approximate ansatz for the electromagnetic waves based on a single multimode coherent state wave function; formally, this approach combines in a single framework ideas from adiabatic renormalization, the Born-Markov approximation, and input-output theory. Second, we present numerically exact results for scattering of a weak intensity pulse by using numerical renormalization group (NRG) calculations. NRG provides a benchmark for any linear response property throughout the ultrastrong-coupling regime. We find that in a sudden quantum quench, the coherent state approach produces physical artifacts, such as improper relaxation to the steady state. These previously unnoticed problems are related to the simplified form of the ansatz that generates spurious correlations within the bath. In the scattering problem, NRG is used to find the transmission and reflection of a single photon, as well as the inelastic scattering of that single photon. Simple analytical formulas are established and tested against the NRG data that predict quantitatively the transport coefficients for up to moderate environmental impedance. These formulas resolve pending issues regarding the presence of inelastic losses in the spin-boson model near absorption resonances, and could be used for comparison to experiments in Josephson waveguide quantum electrodynamics. Finally, the scattering results using the coherent state wave-function approach are compared favorably to the NRG results for very weak incident intensity. We end our study by presenting results at higher power where the response of the system is nonlinear.
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    Mapping the Dynamic Complexity of Chronic Disease Care in Singapore: Using Group Model Building in Knowledge Elicitation
    (Systems Research and Behavioral Science, 2018-11-01) Ansah, JP; Matchar, DB; Koh, V; Schoenenberger, L
    This study describes a group model building exercise that aims to develop a deeper understanding of the dynamic complexity of chronic disease care delivery within a primary care setting in Singapore, leveraging on the insights of stakeholders with personal and institutional knowledge of the health care system. A group model building exercise, which included 50 stakeholders, was used to develop the qualitative model. The qualitative model helped to bring a feedback perspective to understanding the dynamic complexity of chronic disease care delivery. The feedback perspective helped in identifying the systemic issues within chronic disease care delivery, which has the potential to inform system-wide interventions and policies to improve health. Enhancing chronic care in Singapore will require an enhancement of both the capacity and capability of the primary care sector. © 2018 John Wiley & Sons, Ltd.
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    Rescuing a Quantum Phase Transition with Quantum Noise.
    (Physical review letters, 2017-02) Zhang, Gu; Novais, E; Baranger, Harold U
    We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroy quantum effects, as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment, the source of quantum noise. While the charge transport inhibits a quantum phase transition, the quantum noise reduces charge transport and restores the transition. We find a non-Fermi-liquid intermediate fixed point for all strengths of the noise. For strong noise, it is similar to the intermediate fixed point of the two-impurity Kondo model.
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    SEGREGATION OF SIMULATED RFID MARKERS DURING HANDLING AND TRANSPORT OF WHEAT
    (TRANSACTIONS OF THE ASABE, 2014-01-01) Steinmeier, U; Neudecker, M; Witt, A; von Hoersten, D; Schroeter, M
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    Transport signatures of Majorana quantum criticality realized by dissipative resonant tunneling
    (Physical Review B - Condensed Matter and Materials Physics, 2014-06-27) Zheng, H; Florens, S; Baranger, HU
    We consider theoretically the transport properties of a spinless resonant electronic level coupled to strongly dissipative leads, in the regime of circuit impedance near the resistance quantum. Using the Luttinger liquid analogy, one obtains an effective Hamiltonian expressed in terms of interacting Majorana fermions, in which all environmental degrees of freedom (leads and electromagnetic modes) are encapsulated in a single fermionic bath. General transport equations for this system are then derived in terms of the Majorana T-matrix. A perturbative treatment of the Majorana interaction term yields the appearance of a marginal, linear dependence of the conductance on temperature when the system is tuned to its quantum critical point, in agreement with recent experimental observations. We investigate in detail the different crossovers involved in the problem, and analyze the role of the interaction terms in the transport scaling functions. In particular, we show that single barrier scaling applies when the system is slightly tuned away from its Majorana critical point, strengthening the general picture of dynamical Coulomb blockade. © 2014 American Physical Society.