555 research outputs found
Progress in Artificial Economics
Artificial economics aims to provide a generative approach to understanding problems in economics and social sciences. It is based on the consistent use of agent-based models and computational techniques. It encompasses a rich variety of techniques that generalize numerical analysis, mathematical programming, and micro-simulations. The peer-reviewed contributions in this volume address applications of artificial economics to markets and trading, auctions, networks, management, industry sectors, macroeconomics, and demographics and culture
The Equity Premium Puzzle: An Application of an Agent-Based Evolutionary Model
We describe an agent-based model of a financial market with a stock and a bond. Agents compete in repeated rounds, decide whether to acquire costly information and can pick one of 16 strategies to allocate their investments, under evolutionary pressure driven by the comparison of the realized short-term revenues from trading. We show that, while in- formed traders survive in some cases, the equilibrium shares are strongly biased in favor of strategies that make little use of information and sys- tematically overestimate the riskiness of the stock. As a consequence, the majority of the population ends up in buying fewer stocks than would be otherwise expected or deemed rational.
This evolutionary dynamics offers a novel way to explain the equity pre- mium puzzle first described by Mehra and Prescott (The equity pre- mium: A puzzle. Journal of Monetary Economics 1985), according to which it’s hard to find reasons for the widespread lack of investment in risky assets. Evolution based on a straightforward comparison of rev- enues is a simple and cognitively appealing avenue to reach a population of traders using (over-)cautious strategies to curb the risk of long-term “financial extinction”. Simulations run in NetLogo also demonstrate that very little information may be used in noisy markets or when the cost of information is substantial
Thyroid-specific transcription factors control Hex promoter activity
The homeobox-containing gene Hex is expressed in several cell types, including thyroid follicular cells, in which it regulates the transcription of tissue-specific genes. In this study the regulation of Hex promoter activity was investigated. Using co-transfection experiments, we demonstrated that the transcriptional activity of the Hex gene promoter in rat thyroid FRTL-5 cells is ∼10-fold greater than that observed in HeLa and NIH 3T3 cell lines (which do not normally express the Hex gene). To identify the molecular mechanisms underlying these differences, we evaluated the effect of the thyroid-specific transcription factor TTF-1 on the Hex promoter activity. TTF-1 produced 3-4-fold increases in the Hex promoter activity. Gel-retardation assays and mutagenesis experiments revealed the presence of functionally relevant TTF-1 binding sites in the Hex promoter region. These in vitro data may also have functional relevance in vivo, since a positive correlation between TTF-1 and Hex mRNAs was demonstrated in human thyroid tissues by means of RT-PCR analysis. The TTF-1 effect, however, is not sufficient to explain the difference in Hex promoter activity between FRTL-5 and cells that do not express the Hex gene. For this reason, we tested whether Hex protein is able to activate the Hex promoter. Indeed, co-transfection experiments indicate that Hex protein is able to increase the activity of its own promoter in HeLa cells ∼4-fold. TTF-1 and Hex effects are additive: when transfected together in HeLa cells, the Hex promoter activity is increased 6-7-fold. Thus, the contemporary presence of both TTF-1 and Hex could be sufficient to explain the higher transcriptional activity of the Hex promoter in thyroid cells with respect to cell lines that do not express the Hex gene. These findings demonstrate the existence of direct cross-regulation between thyroid-specific transcription factors
Effect of the Austempering Process on the Microstructure and Mechanical Properties of 27MnCrB5-2 Steel
AbstractThe effect of austempering parameters on the microstructure and mechanical properties of 27MnCrB5-2 steel has been investigated by means of: dilatometric, microstructural and fractographic analyses; tensile and Charpy V-notch (CVN) impact tests at room temperature and a low temperature.Microstructural analyses showed that upper bainite developed at a higher austempering temperature, while a mixed bainitic-martensitic microstructure formed at lower temperatures, with a different amount of bainite and martensite and a different size of bainite sheaf depending on the temperature. Tensile tests highlighted superior yield and tensile strengths (≈30%) for the mixed microstructure, with respect to both fully bainitic and Q&T microstructures, with only a low reduction in elongation to failure (≈10%). Impact tests confirmed that mixed microstructures have higher impact properties, at both room temperature and a low temperature
Codes for the Quantum Erasure Channel
The quantum erasure channel (QEC) is considered. Codes for the QEC have to
correct for erasures, i. e., arbitrary errors at known positions. We show that
four qubits are necessary and sufficient to encode one qubit and correct one
erasure, in contrast to five qubits for unknown positions. Moreover, a family
of quantum codes for the QEC, the quantum BCH codes, that can be efficiently
decoded is introduced.Comment: 6 pages, RevTeX, no figures, submitted to Physical Review A, code
extended to encode 2 qubits, references adde
Error Prevention Scheme with Four Particles
It is shown that a simplified version of the error correction code recently
suggested by Shor exhibits manifestation of the quantum Zeno effect. Thus,
under certain conditions, protection of an unknown quantum state is achieved.
Error prevention procedures based on four-particle and two-particle encoding
are proposed and it is argued that they have feasible practical
implementations.Comment: 4 pages, RevTeX, references updated and improved protocol adde
Holonomic quantum computation with neutral atoms
We propose an all-geometric implementation of quantum computation using
neutral atoms in cavity QED. We show how to perform generic single- and
two-qubit gates, the latter by encoding a two-atom state onto a single,
many-level atom. We compare different strategies to overcome limitations due to
cavity imperfections.Comment: 14 pages, 9 figure
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