999 resultados para Natural Sciences


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Ultrashort light-matter interactions between a linear chirped pulse and a biased semiconductor thin film GaAs are investigated. Using different chirped pulses, the dependence of infrared spectra on chirp rate is demonstrated for a 5 fs pulse. It is found that the infrared spectra can be controlled by the linear chirp of the pulse. Furthermore, the infrared spectral intensity could be enhanced by two orders of magnitude via appropriately choosing values of the linear chirp rates. Our results suggest a possible scheme to control the infrared signal.

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The ionization rate of molecules in intense laser fields may be much lower than that of atoms with similar binding energy. This phenomenon is termed the ionization suppression of molecules and is caused by the molecular inner structure. In this paper, we perform a comprehensive study of the ionization suppression of homonuclear diatomic molecules in intense laser fields of linear and circular polarizations. We find that for linear polarization the total ionization rate and the ionization suppression depend greatly on the molecular alignment, and that for circular polarization the ionization suppression of molecules in the antibonding (bonding) shells disappears (appears) for laser intensities around 10(15) W/cm(2). We also find that the molecular photoelectron energy spectra are greatly changed by the interference effect, even though the total ionization rate of molecules remains almost the same as that of their companion atoms.

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We investigate the nonlinear propagation of ultrashort pulses on resonant intersubband transitions in multiple semiconductor quantum wells. It is shown that the nonlinearity rooted from electron-electron interactions destroys the condition giving rise to self-induced transparency. However, by adjusting the area of input pulse, we find the signatures of self-induced transmission due to a full Rabi flopping of the electron density, and this phenomenon can be approximately interpreted by the traditional standard area theorem via defining the effective area of input pulse.

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We investigate the effect of the electric field maximum on the Rabi flopping and the generated higher frequency spectra properties by solving Maxwell-Bloch equations without invoking any standard approximations. It is found that the maximum of the electric field will lead to carrier-wave Rabi flopping (CWRF) through reversion dynamics which will be more evident when the applied field enters the sub-one-cycle regime. Therefore, under the interaction of sub-one-cycle pulses, the Rabi flopping follows the transient electric field tightly through the oscillation and reversion dynamics, which is in contrast to the conventional envelope Rabi flopping. Complete or incomplete population inversion can be realized through the control of the carrier-envelope phase (CEP). Furthermore, the generated higher frequency spectra will be changed from distinct to continuous or irregular with the variation of the CEP. Our results demonstrate that due to the evident maximum behavior of the electric field, pulses with different CEP give rise to different CWRFs, and then different degree of interferences lead to different higher frequency spectral features.

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We investigate the emission spectra of the semiconductor quantum well for few-cycle and sub-cycle pulse exciting. We find that Fano interference may induce third harmonic enhancement. Third harmonic enhancement varies with the magnitude and duration of the incident pulse, and may be enhanced by approximately one order of magnitude for the low intensity region of the sub-cycle incident pulse exciting.

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Trichromatic manipulation of Kerr nonlinearity in a three-level A atomic configuration is investigated theoretically. It is shown that for a weak monochromatic probe field, the enhanced Kerr nonlinearity can be achieved in multiple separate transparent windows due to interference effect of multiple two-photon Raman channels. Furthermore, the property of Kerr nonlinearity can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field compared to the central component.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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通过求解麦克斯韦-布洛赫方程组,分别在存在传播效应和无传播效应两种情况下,研究了调制掺杂的半导体量子阱中子带间的拉比振荡。研究发现,与电子-电子之间的相互作用的非线性相比较,传播效应对拉比振荡的影响更大;在不考虑传播效应时,脉冲可以使量子阱中的电子实现一次完整的布居反转,但是当传播效应存在情况下,完全的粒子数反转已不能实现。另外,研究还发现通过改变载流子的密度可以改变传播效应所产生的影响。

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina.

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A tese propõe novos fundamentos para a abordagem da conjugalidade contemporânea, tendo como eixo de referência a superação da monogamia como princípio estruturante do estatuto jurídico da família. Alguns fios condutores perpassam a tese e norteiam o tratamento do tema: (i) o princípio jurídico da monogamia como mecanismo legitimador da dominação masculina; (ii) a preocupação com a construção de lugares de não-direito e de invisibilidade jurídica de determinadas pessoas, mormente, as concubinas, excluídas da condição de sujeito de direito; (iii) o concubinato, campo privilegiado de estudo, é referido e analisado como estatuto de exclusão; (iv) os fatores decisivos para a reconfiguração da conjugalidade contemporânea: a democracia, o pluralismo cultural e a laicização do Direito; (v) a perspectiva do Direito Civil constitucionalizado é tomada como referência para a problematização da questão central da tese, e os princípios constitucionais da dignidade humana, solidariedade, igualdade, liberdade e democracia prestam-se ao estabelecimento de um banco de provas a que é submetida a assertiva que constitui o enunciado da própria tese: a superação da monogamia como princípio estruturante do estatuto jurídico das famílias contemporâneas. O tratamento dado à matéria é necessariamente interdisciplinar, tendo-se mostrado indispensável a interlocução, ainda que pontual, com historiadores, antropólogos, e sociólogos e mesmo com autores das ciências naturais. O princípio da monogamia consolidado no Ocidente, por força do monopólio da regulação das relações familiares pelo Direito Canônico, especialmente, pelos decretos e cânones tridentinos, e transposto ao domínio jurídico do Estado, a partir das revoluções burguesas experimenta, na reconfiguração da conjugalidade contemporânea, efetivo arrefecimento. Fatores, como a superação da dominação masculina, a laicização do Estado e do Direito, a primazia alcançada pela autonomia privada no campo das situações subjetivas existenciais e coexistenciais, a consagração do princípio do pluralismo das entidades familiares, nítida expressão da democratização da intimidade, são indicados como razões decisivas para a superação da monogamia como princípio jurídico.