Inverse four-wave mixing and self-parametric amplification in optical fibre

An important group of nonlinear processes in optical fibre involve the mixing of four waves due to the intensity dependence of the refractive index. It is customary to distinguish between nonlinear effects that require external/pumping waves (cross-phase modulation and parametric processes such as four-wave mixing) and those arising from self-action of the propagating optical field (self-phase modulation and modulation instability). Here, we present a new nonlinear self-action effect—self-parametric amplification—which manifests itself as optical spectrum narrowing in normal dispersion fibre, leading to very stable propagation with a distinctive spectral distribution. The narrowing results from inverse four-wave mixing, resembling an effective parametric amplification of the central part of the spectrum by energy transfer from the spectral tails. Self-parametric amplification and the observed stable nonlinear spectral propagation with a random temporal waveform can find applications in optical communications and high-power fibre lasers with nonlinear intracavity dynamics.

How doctors' communication style and race concordance influence African-Caribbean patients when disclosing depression

Objective: To determine the impact of doctors' communication style and doctor-patient race concordance on UK African-Caribbeans' comfort in disclosing depression. Methods: 160 African-Caribbean and 160 white British subjects, stratified by gender and history of depression, participated in simulated depression consultations with video-recorded doctors. Doctors were stratified by black or white race, gender and a high (HPC) or low patient-centred (LPC) communication style, giving a full 2. ×. 2. ×. 2 factorial design. Afterwards, participants rated aspects of doctors' communication style, their comfort in disclosing depression and treatment preferences. Results: Race concordance had no impact on African-Caribbeans' comfort in disclosing depression. However a HPC versus LPC communication style made them significantly more positive about their interactions with doctors (p = 0.000), their overall comfort (p = 0.003), their comfort in disclosing their emotional state (p = 0.001), and about considering talking therapy (p = 0.01); but less positive about considering antidepressant medication (p =0.01). Conclusion: Doctors' communication style was shown to be more important than patient race or race concordance in influencing African Caribbeans' depression consultation experiences. Changing doctors' communication style may help reduce disparities in depression care. Practice Implications: Practitioners should cultivate a HPC style to make African-Caribbeans more comfortable when disclosing depression, so that it is less likely to be missed.

Impact of inter-modal four-wave mixing on the performance of mode- and wavelength-division-multiplexing systems

In this paper, we investigate the impact of inter-modal four-wave mixing on mode- and wavelength-division-multiplexing systems. A set of coupled nonlinear Schrödinger equations, including linear mode coupling, is derived allowing to isolate the inter-modal four-wave mixing terms. The efficiency of inter-modal four-wave mixing between degenerate LP modes is found to be significantly higher than the intra-modal four-wave mixing efficiency. However, it is shown that the inter-modal four-wave mixing efficiency between degenerate modes is significantly reduced by the linear mode coupling.

Effect of mixing sequence on the workability and performance of asphalt mixtures

In Sweden, during recent years, a new type of mixing protocol has been applied, in which the order of mixing is changed from the conventional method. Improved workability and diminished mixing and compaction energy needs have been important drivers for this. Considering that it is the mastic phase, which is modified by changing the mixing order, it provides an interesting case study for explaining the mechanisms of workability in connection with the mastic phase. To do so, an analytical viscosity framework was combined with a mixture morphology framework to upscale to the mixing level and tribology principles to explain the interaction between the mastic and the aggregates. From the mastic viscosity protocol, it was found that the mixing order significantly affects the resulting mastic viscosity. To analyse the effect of this on the workability and resulting mixture performance, X-ray computed tomography was used to analyse mixtures produced by the two different mixing sequences. Mechanical testing was utilised to determine the long-term mechanical performance. In this part of the study, mastic viscosity as a function of particle concentration and distribution was directly coupled to improved mixture workability and enhanced long-term performance.

Reflections on race in contemporary Ireland

Any reflection on the category "race" in the contemporary world is inevitably framed by the cumulative layers of meanings and practices attached to bodies and cultures over the previous centuries. If the idea of race resembles anything, it is a palimpsest,1with past interpretations leaking through to make the ink of the present run. Accordingly, I present some historical notes not as a distinct prelude to the "real" story, positing a rupture of past and present, but as the beginning of the story proper.

Thermalized polarization dynamics of a discrete optical-waveguide system with four-wave mixing

Statistical mechanics of two coupled vector fields is studied in the tight-binding model that describes propagation of polarized light in discrete waveguides in the presence of the four-wave mixing. The energy and power conservation laws enable the formulation of the equilibrium properties of the polarization state in terms of the Gibbs measure with positive temperature. The transition line T=∞ is established beyond which the discrete vector solitons are created. Also in the limit of the large nonlinearity an analytical expression for the distribution of Stokes parameters is obtained, which is found to be dependent only on the statistical properties of the initial polarization state and not on the strength of nonlinearity. The evolution of the system to the final equilibrium state is shown to pass through the intermediate stage when the energy exchange between the waveguides is still negligible. The distribution of the Stokes parameters in this regime has a complex multimodal structure strongly dependent on the nonlinear coupling coefficients and the initial conditions.

Suppression of WDM four-wave mixing crosstalk in fibre optic parametric amplifier using Raman-assisted pumping

We perform an extensive numerical analysis of Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPA) in the context of WDM QPSK signal amplification. A detailed comparison of the conventional FOPA and RA-FOPA is reported and the important advantages offered by the Raman pumping are clarified. We assess the impact of pump power ratios, channel count, and highly nonlinear fibre (HNLF) length on crosstalk levels at different amplifier gains. We show that for a fixed 200 m HNLF length, maximum crosstalk can be reduced by up to 7 dB when amplifying 10x58Gb/s QPSK signals at 20 dB net-gain using a Raman pump of 37 dBm and parametric pump of 28.5 dBm in comparison to a standard single-pump FOPA using 33.4 dBm pump power. It is shown that a significant reduction in four-wave mixing crosstalk is also obtained by reducing the highly nonlinear fibre interaction length. The trend is shown to be generally valid for different net-gain conditions and channel grid size. Crosstalk levels are additionally shown to strongly depend on the Raman/parametric pump power ratio, with a reduction in crosstalk seen for increased Raman pump power contribution.

Big city days: Race and labor in early Miami, 1914--1925

The purpose of this study was to recast Miami's social history during the first three decades of the twentieth century through an examination of working class life. The thesis attempts to fill a gap in the literature while also expanding on the advances made in race and class studies of the United States. Through an analysis of local newspapers, minutes of a carpenter's union, and other archival sources, the thesis demonstrates how white workers obtained a virtual monopoly in skilled jobs over black workers, particularly in the construction industry, and exacted economic pressure on business through the threat of work stoppages. Driven by the concern to maintain smooth and steady growth amidst a vibrant tourist economy, business reluctantly worked with labor to maintain harmonious market conditions. Blacks, however, were able to gain certain privileges in the labor market through challenging the rigid system of segregation and notions of what constituted skilled labor. The findings demonstrate that Miami's labor unions shaped the city's social, cultural, and political landscape but the extent of their power was limited by booster discourse and the city's dependence on tourism. ^

The absence of race in democratic politics: The case of the Dominican Republic

This dissertation explores the relationship between race and democratization. Through the examination of the case of the Dominican Republic, this study challenges mainstream explanations of democratic transitions. At its core, this dissertation aims at calling attention to the absence of race and ethnic allegiances as explanatory variables of the democratic processes and debates in the region. By focusing on structural variables, the analysis shies away from elite and actor-centered explanations that fall short in predicting the developments and outcomes of transitions. The central research questions of this study are: Why is there an absence of the treatment of race and ethnic allegiances during the democratic transitions in Latin America and the Caribbean? How has the absence of ethnic identities affected the nature and depth of democratic transitions? Unlike previous explanations of democratic transitions, this dissertation argues that the absence of race in democratic transitions has been a deliberate attempt to perpetuate limited citizenship by political and economic elites. Findings reveal a difficulty to overcome nationalist discourses where limited citizenship has affected the quality of democracy. Original field research data for the study has been gathered through semi-structured interviews and focus groups conducted from October 2008 to December 2009 in the Dominican Republic.

Navigating racial boundaries: The one-drop rule and mixed-race Jamaicans in South Florida

Like many West Indians, mixed-race Jamaican immigrants enter the United States with fluid notions about race and racial identifications that reflect socio-political events in their home country and that conflict with the more rigid constructions of race they encounter in the U.S. This dissertation explores the experiences of racially mixed Jamaicans in South Florida and the impact of those experiences on their racial self-characterizations through the boundary-work theoretical framework. Specifically, the study examines the impact of participants’ exposure to the one-drop rule in the U.S., by which racial identification has been historically determined by the existence or non-existence of black forebears. Employing qualitative data collected through both focus group and face-to-face semi-structured interviews, the study analyzes mixed-race Jamaicans’ encounters in the U.S. with racial boundaries, and the boundary-work that reinforces them, as well their response to these encounters. Through their stories, the dissertation examines participants’ efforts to navigate racial boundaries through choices of various racial identifications. Further, it discusses the ways in which structural forces and individual agency have interacted in the formation of these identifications. The study finds that in spite of participants’ expressed preference for non-racialism, and despite their objections to rigid racial categories, in seeking to carve out alternative identities, they are participating in the boundary-making of which they are so critical.^

Design Optimization of Submerged Jet Nozzles for Enhanced Mixing

The purpose of this thesis was to identify the optimal design parameters for a jet nozzle which obtains a local maximum shear stress while maximizing the average shear stress on the floor of a fluid filled system. This research examined how geometric parameters of a jet nozzle, such as the nozzle's angle, height, and orifice, influence the shear stress created on the bottom surface of a tank. Simulations were run using a Computational Fluid Dynamics (CFD) software package to determine shear stress values for a parameterized geometric domain including the jet nozzle. A response surface was created based on the shear stress values obtained from 112 simulated designs. A multi-objective optimization software utilized the response surface to generate designs with the best combination of parameters to achieve maximum shear stress and maximum average shear stress. The optimal configuration of parameters achieved larger shear stress values over a commercially available design.

The influence of spirituality, race/ethnicity and religion on parent grief and mental health at one and three months after their infant's/child's death in the neonatal or pediatric intensive care unit

The death of an infant/child is one of the most devastating experiences for parents and immediately throws them into crisis. Spiritual and religious coping strategies may help parents with their loss. The purposes of this longitudinal study were to: (1) describe differences in bereaved parents' use of spiritual coping strategies across racial/ethnic and religious groups, mother/father dyads, and time—one (T1) and three (T2) months after the infant's/child's death in the neonatal (NICU) or pediatric intensive care unit (PICU), and (2) test the relationship between spiritual coping strategies and grief, mental health, and personal growth for mothers and fathers at T1 and T2. A sample of 126 Hispanic, Black/African American, and White parents of 119 deceased children completed the Spiritual Coping Strategies scale, Beck Depression Inventory-II, Impact of Events-Revised, Hogan Grief Reaction Checklist, and a demographic form at T1 and T2. Controlling for race and religion, spiritual coping was a strong predictor of lower grief, better mental health, and greater personal growth for mothers at T1 and T2 and lower grief for fathers at T1. The findings of this study will guide bereaved parents to effective strategies to help them cope with their early grief.

Critical Race Theory: Focusing the Lens on Human Resource Development

The challenge that continues to face HRD is how to integrate real concerns for diversity into programs, practices, and research. Critical race theory was used as a lens to examine work on diversity published in Human Resource Development Quarterly (HRDQ). Eight publications were selected and analyzed.