Multiple Feedback Effects Research Articles

The Tension within Norms: Agency and Risks in Pursuit of Global Climate Justice

Abstract How can IR theory capture both the possibilities of agency for historically underrepresented groups and the limitations that different social struggles present for them? This paper proposes a framework based on relational approaches, decolonial perspectives, and the concept of “tension” between possibilities and risks of agency to analyze the dynamics of norm emergence and circulation. It builds on, but moves beyond, constructivist analyses of the norm life cycle and adopts a relational and decolonial lens in order to probe normative agency and its consequences within the context of international negotiations. Focusing on constructivist theories of socialization with multiple feedback effects, the paper calls for a fourth agentic turn in the study of norms and their genealogy and offers an analytical and empirical roadmap to chart a more complex scenario of co-constitution for norms. The paper refers to the case of climate justice to illustrate, empirically, the importance of employing the concept of tension to unveil agentic moments in norm circulation, while also highlighting, theoretically, the risks and limitations that are present in meanings that continue to reinforce colonial legacies.

Improved two-mode dynamic model for external-cavity quantum cascade lasers under strong optical feedback

In this paper, we propose an improved model for describing the dynamical behavior and mode selection mechanism of an external-cavity quantum-cascade laser (EC-QCL) when subject to strong optical feedback. Theoretical analysis including the dynamical effective reflectivity model, two-mode rate-equation model and Lang-Kobayashi equations are employed to carry out the laser output characteristics under the multiple feedback effects. A main aspect of the model is that the excess mirror loss caused by the EC effective reflectivity is incorporated into the laser dynamical equations as a nonlinear dynamical variable. Because of accounting the multiple round-trip feedback terms in the EC effective reflectivity, the analysis is valid for the arbitrary feedback regimes from weak to strong levels. Besides the stationary characteristics, the model accurately predicts the dynamical competition between the fundamental laser-cavity mode and the desired EC mode that reflected strongly by external diffraction grating. The results are in well agreement with theoretical and experimental data reported earlier for the EC-QCLs.

Increased response of vegetation to soil moisture in the northern hemisphere drylands

Vegetation plays a significant role in terrestrial ecosystems due to its strong carbon absorption capability and multiple feedback effects on the climate system. The soil moisture availability determines vegetation growth, especially in the drylands. Although there has been increasing interest in issues such as the vegetation’s response to a specific climate variable, it remains unclear how soil moisture can quantitatively influence the vegetation in the drylands. In this study, we investigated the increased response of the vegetation to soil moisture and identified its key mechanism in the northern hemisphere drylands (NHD) from 1982 to 2010. The Methods included the use of the Lindeman-Merenda-Gold method. The results showed that the sensitivity of the vegetation dynamics to soil moisture significantly increased over the past 29 years (slope = 0.008, p < 0.0001), and the trend during 1996–2007 (slope = 0.025 m3/m3/yr, p < 0.0001) increased more rapidly than the trend during 1984–1995 (slope = −0.005 m3/m3/yr, p = 0.0143), which indicates increased water restrictions in recent years. Further analysis showed that atmospheric CO2 was the major contributor (27.2%) to the sensitivity changes, followed by climate change (27%), and nitrogen deposition (19%). The changes in the ecosystem structure (represented by the non-tree cover areas) and climate vacillation contributed similarly to the sensitivity change (14% and 12%). These findings can help with understanding the spatiotemporal impact of water restrictions on vegetation in the NHD and the related influencing mechanisms of vegetation growth and soil moisture in the greening and warming of the NHD.

Will colleges survive the storm of declining enrollments?A computational model.

The approaching decline in the U.S. college-age population, sometimes referred to as a “demographic storm,” has been identified as an existential threat to the future of American colleges and universities. This article conducts a model-driven analysis of three plausible college-level responses to declining applications. It draws on systems theory to conceptualize a tuition-dependent college as a complex service system and to develop a system dynamics model that captures key causal interrelationships and multiple feedback effects between faculty, facilities, tuition revenue, financials, reputation, and outcomes. Simulations with the college model suggest that common solutions such as reducing faculty or adding campus facilities may improve the college’s short-term financial position, but they are insufficient to ensure its long-term viability. This model contributes to the research literature on the economics of higher education, and model-driven academic management and strategy. It also provides useful implications and insights that can inform policy-makers and college leaders.

Will Colleges Survive the Storm of Declining Enrollments? A Computational Model

The approaching decline in the U.S. college-age population, sometimes referred to as a “demographic storm,” has been identified as an existential threat to the future of American colleges and universities. This article conducts a model-driven analysis of three plausible college-level responses to declining applications. It draws on systems theory to conceptualize a tuition-dependent college as a complex service system and to develop a system dynamics model that captures key causal interrelationships and multiple feedback effects between faculty, facilities, tuition revenue, financials, reputation, and outcomes. Simulations with the college model suggest that common solutions such as reducing faculty or adding campus facilities may improve the college’s short-term financial position, but they are insufficient to ensure the long-term viability without the continuous tuition hikes. This model contributes to the research literature on the economics of higher education, and model-driven academic management and strategy. It also provides useful implications and insights that can inform policy-makers and college leaders.

Single frequency laser multiple feedback effects based on ray tracing method

提出一种基于非准直平凹回馈腔的单频激光多重回馈光线追迹模型，采用该模型阐明了单频激光多重回馈效应的产生机理，分析了多重回馈高分辨率条纹的特性，明确了影响多重回馈条纹形状的主要因素，包括回馈镜的倾角、曲率半径、反射率以及回馈外腔长等，获得了回馈镜在不同倾角时的有效回馈阶次及其耦合系数。光线追迹分析与实验结果表明：当回馈镜倾斜角为1.7时，多重回馈效应会产生调制幅度均匀、没有大包络的高分辨率回馈条纹，每个条纹的分辨率可达/50。

Intensity modulation in single-mode microchip Nd:YAG lasers with asymmetric external cavity

Intensity modulation induced by the asymmetric external cavity in single-mode microchip Nd:YAG lasers is presented. Two kinds of experimental results are discussed based on multiple feedback effects. In one case, the intensity modulation curve is a normal sine wave, whose fringe frequency is four times higher than that of a conventional optical feedback system, caused by multiple feedback effects. In the other case, the intensity modulation curve is the overlapping of the above quadruple-frequency signal and conventional optical feedback signal, which is determined by the additional phase difference induced by the asymmetric external cavity. The theoretical analyses are in good agreement with the experimental results. The quadruple-frequency modulation of the laser output intensity can greatly increase the resolution of displacement measurement of an optical feedback system.

High-frequency intensity modulation in orthogonal polarized dual frequency lasers with optical feedback

High-frequency modulation of laser output intensity is studied with asymmetric feedback induced by the misalignment of an external feedback reflector in an orthogonal polarized dual frequency laser. The fringe frequency of the optical feedback system is seven times higher than that of a conventional optical feedback system, due to multiple feedback effects. The output characteristics of two orthogonal polarized modes are also investigated. Mode competition is observed between the two modes. When initial intensities of the two modes are unequal, the mode competition will be strong. The difference in initial intensity between the two orthogonally polarized modes plays an important role in the mode competition with optical feedback. Experimental results are presented, as well as a theoretical explanation. The high-frequency modulation of laser intensity can greatly increase the resolution of an optical feedback sensing system.

Optical Feedback Characteristics in He–Ne Dual Frequency Lasers

Optical feedback characteristics in He–Ne dual frequency lasers arestudied systematically in different feedback power ratios with avariable attenuator. Feedback power ratios vary from 0.010 up to 0.998.Five distinct regimes of self-interference effects are found and definedas regimes I, II, III, IV and V. Accordingly, five opticalfeedback levels have been put forward in He–Ne dual frequency lasers.Strong mode competitions are observed in regimes III and IV.In regime V, multiple feedback effects are investigated. The basictheoretical analysis is also presented. Our results can advance theresearch of self-mixing interferometer and displacement sensor of He–Neorthogonally polarized dual frequency lasers.

Low-frequency self-pulsations in asymmetric external-cavity semiconductor lasers due to multiple-feedback effects

We investigate the dynamical stability of external-cavity semiconductor lasers with deliberate tilt asymmetries. Experimentally observed low-frequency self-pulsations are explained by small-signal analysis based on a new rateequation model that uses a time-dependent effective reflectivity to include multiple-feedback effects. We observe and explain the dependence of the self-pulsation frequency on the strength and degree of asymmetry of the feedback, on the injection current, and on the external-cavity length. These results are important in interpreting instabilities, chaos, and other complex dynamical phenomena in external-cavity semiconductor lasers.

Multiple feedback effects in asymmetric external cavity semiconductor lasers

Multiple feedback effects on the output power and spectral characteristics of an external cavity semiconductor laser with asymmetric feedback induced by misalignment of an external mirror are discussed. The external mirror tilt modifies the round-trip phase condition as well as the coupling efficiency. Undulation in power as a function of external mirror tilt have been observed. At particular tilt angles where strong interaction between odd-order round-trip beams and even-order round-trip beams occurs, unique optical spectra featuring double peaks within a compound-cavity mode spectrum or uneven compound-cavity mode spacings have been observed. A quasi-static model for asymmetric external cavity systems explains qualitatively the power undulations and complex spectral characteristics. The model also predicts the existence of two nearby phase-matched mode groups, which may result in complex and chaotic instabilities. >

Learning from outcome studies: Toward a comprehensive biological-psychosocial understanding of schizophrenia

According to results from three major European long-term outcome studies on schizophrenia, from other comparable studies, and from additional investigations on rehabilitation and on the influence of psychosocial factors, long-term evolution of schizophrenia is much more variable and considerably better than hitherto admitted. On this basis, the author presents a comprehensive biological-psychosocial evolutionary model of schizophrenia in three phases, centered around the vulnerability- and information-processing hypotheses. Long-term evolution of schizophrenia cannot be sufficiently represented by a linear organic process mainly determined by genetic factors. Environmental and, in particular, psychosocial factors, also seem to play an important role. Vicious biological-psychosocial circles with multiple feedback effects can lead to non-linear escalating processes. Chronic states appear to be the result of complex interactions between preexisting vulnerability and autoprotective counterregulations on a biological, psychological and social level. Some therapeutic consequences and possible future developments of these concepts are presented.