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Search Results: 1 - 10 of 10584 matches for " Andreas Hugi "
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Coherent Frequency Combs produced by Self Frequency Modulation in Quantum Cascade Lasers
Jacob Khurgin,Yamac Dikmelik,Andreas Hugi,Jerome Faist
Physics , 2013, DOI: 10.1063/1.4866868
Abstract: One salient characteristic of Quantum Cascade Laser (QCL) is its very shor gain recovery time that so far thwarted the attempts to achieve self-mode locking of the device into a train of single pulses. We show theoretically that four wave mixing, combined with the short gain recovery time causes QCL to operate in the self-frequency-modulated regime characterized by a constant power in time domain and stable coherent comb in the frequency domain.Coherent frequency comb may enable many potential applications of QCL in sensing and measurement.
On-chip Dual-comb based on Quantum Cascade Laser Frequency Combs
Gustavo Villares,Johanna Wolf,Dmitry Kazakov,Martin J Süess,Andreas Hugi,Mattias Beck,Jér?me Faist
Physics , 2015,
Abstract: Dual-comb spectroscopy is emerging as one of the most appealing applications of mid-infrared frequency combs for high-resolution molecular spectroscopy, as it leverages on the unique coherence properties of frequency combs combined with the high sensitivities achievable by mid-infrared molecular spectroscopy. Here we present an on-chip dual-comb source based on mid-infrared quantum cascade laser frequency combs, where two frequency combs are integrated on a single chip. Control of the combs repetition and offset frequencies is obtained by integrating micro-heaters next to each laser. We show that a full control of the dual-comb system is possible, by measuring a multi-heterodyne beating corresponding to an optical bandwidth of 32 cm$^{-1}$ at a center frequency of 1330 cm$^{-1}$ (7.52 $\mu$m), demonstrating that this device is ideal for compact dual-comb spectroscopy systems.
Quantum Cascade Laser Frequency Combs
Jér?me Faist,Gustavo Villares,Giacomo Scalari,Markus R?sch,Christopher Bonzon,Andreas Hugi,Mattias Beck
Physics , 2015,
Abstract: It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100 mW and frequency coverage of 100 cm$^{-1}$ in the mid-infrared. In the THz range, 10 mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the first dual-comb spectroscopy measurements. The capability of the structure to integrate monolithically non-linear optical element as well as to operate as a detector show great promise for future chip integration of dual-comb systems.
Los a os sesenta y sus huellas en el presente.
Hugi Fazio Vengoa.
Revista de Estudios Sociales , 2009,
Abstract: The present is a condition of time that varies in its length. The contemporary present is an interval of time whose origins date back to the year and events of 1968, a conjuncture that catalyzed a powerful and silent socio-cultural revolution. Some of the main features of this revolution include the beginning of a new modality of capitalism, the emergence of new actors and social movements, the subsumption of clasic modernity within world global modernity, the development of a regime of global and present-focused historiocity, the intensification of globalization, the transformation of the world into a historical category, and the transition towards global history.
New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides
V. Garnier,E. Giannini,S. Hugi,B. Seeber,R. Flukiger
Physics , 2004, DOI: 10.1088/0953-2048/17/3/017
Abstract: A new DTA (Differential Thermal Analysis) device was designed and installed in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The calibration of the DTA apparatus under pressure was successfully performed using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard calibration references. The thermal properties of these metals have been studied under pressure. The values of DV (volume variation between liquid and solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal expansion coefficient at Tm) have been extracted. A very good agreement was found with the existing literature and new data were added. This HP-DTA apparatus is very useful for studying the thermodynamics of those systems where one or more volatile elements are present, such as high TC superconducting oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading to the formation of the 2223 phase was found to occur at higher temperatures when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared to the reaction at 1 bar. This temperature shift is due to the higher stability of the Pb-rich precursor phases under pressure, as the high isostatic pressure prevents Pb from evaporating.
Economic Growth and a Low Carbon Economy―Does the Earth Suffer from an “Easter Island Syndrome”?  [PDF]
Andreas Oberheitmann
Low Carbon Economy (LCE) , 2011, DOI: 10.4236/lce.2011.24024
Abstract: The history of the Eastern Islands in the Pacific with an increasing over-utilization of natural resources reminds us of the mistakes modern societies are making and the question is obvious whether the Earth is suffering from an Eastern Islands Syndrome, in other words whether the egoism inherent in humans long-term might have fatal consequences for our species homo sapiens. Climate research identified two important phenomena, which should remind us of the Easter Islands: feedbacks and tipping points, i.e. self-accelerating phenomena of global warming and reaching irreversible points of climate change. Only a quick worldwide return to a low carbon economy is able to stabilize global warming on a bearable level. Both, Annex-I countries and Non-Annex-I countries have to contribute to reaching this goal taking their historical, current and future responsibilities into account. A post Kyoto regime based on cumulative per-capita CO2-emission rights and a international emission trading could provide for incentives to achieve a low carbon economy, especially for newly industrialized countries.
Development of a Low Carbon Economy in Wuxi City  [PDF]
Andreas Oberheitmann
American Journal of Climate Change (AJCC) , 2012, DOI: 10.4236/ajcc.2012.12007
Abstract: The development of a Low Carbon Economy is a vital instrument to encounter climate change and take into account the growing challenges of an increasing urbanization in China. Wuxi City in East China’s Jiangsu Province is starting to implement a Low Carbon City Plan for safeguarding a sustainable development of the city until 2020 and beyond. This paper aims at estimating the impact of the Low Carbon City plan for Wuxi’s energy demand and CO2-emissions until 2050. Using an econometric energy supply and demand model to estimate and forecast the Wuxi energy and CO2-balance aggregates until 2050, it compares a scenario without specific Low Carbon City measures to reduce sectoral CO2-intensities to a Low Carbon scenario implementing these measures according to the Low Carbon City Plan until 2020 and beyond. The decomposition of the Kaya-identity reveals that the increase of per capita income has the largest impact on the growth of CO2-emissions and the decrease of energy intensity of Gross Value Added the largest impact on the reduction of CO2-emissions in Wuxi. A decrease of population and CO2-intensity of Primary energy supply only have average contributions. The decrease of energy intensity of Gross Value Added is due to energy efficiency gains in the single economic sectors, but to a large extent due to structural changes of the economy away from energy intensive sectors such as iron and steel, chemical industry or cement industry towards the energy extensive service sectors. A growing residential sector also reduces the industrial share of energy demand. Only following the assumed national trend with a shift from CO2-intensive industries to a CO2-extensive service economy, the Low Carbon goal of a 50% reduction of CO2-intensity of Gross Value Added compared to 2005 cannot be reached in Wuxi. Specific sectoral CO2 -intensity goals have to be successfully observed by the economic sectors in Wuxi, especially by the industry. The promotion of combined heat and power generation also has to contribute to the specific activities in Wuxi.
A Global Solution of the Einstein-Maxwell Field Equations for Rotating Charged Matter  [PDF]
Andreas Georgiou
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.329168
Abstract: A stationary axially symmetric exterior electrovacuum solution of the Einstein-Maxwell field equations was obtained. An interior solution for rotating charged dust with vanishing Lorentz force was also obtained. The two spacetimes are separated by a boundary which is a surface layer with surface stress-energy tensor and surface electric 4-current. The layer is the spherical surface bounding the charged matter. It was further shown, that all the exterior physical quantities vanished at the asymptotic spatial infinity where spacetime was shown to be flat. There are two different sets of junction conditions: the electromagnetic junction conditions, which were expressed in the traditional 3-dimensional form of classical electromagnetic theory; and the considerably more complicated gravitational junction conditions. It was shown that both—the electromagnetic and gravitational junction conditions—were satisfied. The mass, charge and angular momentum were determined from the metric. Exact analytical formulae for the dipole moment and gyromagnetic ratio were also derived. The conditions, under which the latter formulae gave Blackett’s empirical result for rotating stars, were investigated.
The Breakdown of the Traditional Mechanistic Worldview, the Development of Complexity Sciences and the Pretence of Knowledge in Economics  [PDF]
Andreas Liening
Modern Economy (ME) , 2013, DOI: 10.4236/me.2013.44034
Abstract:

This article is an introduction to complexity theory, which will be discussed using the example of economic science. In this context, a short historical overview is intended to demonstrate why the traditional mechanistic worldview persistently remains a part of economic science and how it led to the development of the theory of complex systems, which, for example, can be subsumed under chaos theory. Furthermore, a simple supply and demand model is employed as an example to discuss this new theory and to describe the characteristics of complexity in comparison with the general mechanistic principle. For this purpose, specially designed software is used for the simulation and analysis of selected complex systems.

Growth Theory and Endogenous Human Capital Development: A Contribution to the Theory of Complex Systems  [PDF]
Andreas Liening
Theoretical Economics Letters (TEL) , 2013, DOI: 10.4236/tel.2013.32016
Abstract:

As economic phenomena become increasingly complex, the demands on models to reflect this complexity also increase. Economic growth, for example, which depends on a variety of factors, is such a complex phenomenon. Especially the relevance of human capital development for modern service societies is a significant growth factor. This is, however, considered only in few discussions. In order to represent such complex phenomena, adequate models are needed that go beyond linear approaches. This paper points out that models from the dynamic system theories are well suited to illustrate human capital as a factor of economic growth.

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