The role of nonlinear optical absorption in narrow-band difference frequency terahertz-wave generation

We present a general analysis of the influence of nonlinear optical absorption on terahertz generation via optical difference frequency generation, when reaching for the quantum conversion efficiency limit. By casting the equations governing the process in a suitably normalized form, including either two-photon- or three-photon-absorption terms, we have been able to plot universal charts for phase matched optical-to-terahertz conversion for different values of the nonlinear absorption coefficients. We apply our analysis to some experiments reported to date, in order to understand to what extent multiphoton absorption could have played a role and also to predict the maximum achievable conversion efficiency at higher peak pump intensities.Comment: 16 pages, 2 figures. Some correction and some explanation adde

Universal charts for optical difference frequency generation in the terahertz domain

We present a universal and rigorous approach to study difference frequency generation in the terahertz domain, keeping the number of degrees of freedom to a minimum, through the definition of a suitable figure of merit. The proposed method relies on suitably normalized charts, that enable to predict the optical-to-terahertz conversion efficiency of any system based on wave propagation in quadratic nonlinear materials. The predictions of our approach are found to be in good agreement with the best experimental results reported to date, enabling also to estimate the d22 nonlinear coefficient of high quality GaSe.Comment: 3 pages in 2 columns format, 3 figures. GaSe analysis has been corrected. Fig. 3 has been replace

Estimating the Effects of Length of Exposure to a Training Program: The Case of Job Corps

Most of the literature on the evaluation of training programs focuses on the effect of participation on a particular outcome (e.g. earnings). The “treatment” is generally represented by a binary variable equal to one if participation in the program occurs, and equal to zero if no participation occurs. While the use of a binary treatment indicator is attractive for ease of interpretation and estimation, it treats all exposure the same. The extent of exposure to the treatment, however, is potentially important in determining the outcome; particularly in training programs where a main feature is the varying length of the training spells of participating individuals. In this paper, we illustrate how recently developed methods for the estimation of causal effects from continuous treatments can be used to learn about the consequences of heterogeneous lengths of enrollment in the evaluation of training programs. We apply these methods to data on Job Corps (JC), America’s largest and most comprehensive job training program for disadvantaged youth. The length of exposure is a significant source of heterogeneity in these data: while the average participation spell in JC is 28 weeks, its standard deviation and interdecile range are 27 and 62 weeks, respectively. We estimate average causal effects of different lengths of exposure to JC using the “generalized propensity score” under the assumption that the length of the individual’s JC spell is randomly assigned, conditional on a rich set of covariates. Finally, using this approach, we document important differences across different spell lengths and across three racial and ethnic groups of participants (blacks, whites and Hispanics) that help understand why the benefits these groups receive from JC are so disparate from estimates derived using traditional methods.Training Programs, Continuous Treatments, Generalized Propensity Score, Dose- Response Function

Cancer therapeutic potential of combinatorial immuno- and vaso-modulatory interventions

Currently, most of the basic mechanisms governing tumor-immune system interactions, in combination with modulations of tumor-associated vasculature, are far from being completely understood. Here, we propose a mathematical model of vascularized tumor growth, where the main novelty is the modeling of the interplay between functional tumor vasculature and effector cell recruitment dynamics. Parameters are calibrated on the basis of different in vivo immunocompromised Rag1-/- and wild-type (WT) BALB/c murine tumor growth experiments. The model analysis supports that tumor vasculature normalization can be a plausible and effective strategy to treat cancer when combined with appropriate immuno-stimulations. We find that improved levels of functional tumor vasculature, potentially mediated by normalization or stress alleviation strategies, can provide beneficial outcomes in terms of tumor burden reduction and growth control. Normalization of tumor blood vessels opens a therapeutic window of opportunity to augment the antitumor immune responses, as well as to reduce the intratumoral immunosuppression and induced-hypoxia due to vascular abnormalities. The potential success of normalizing tumor-associated vasculature closely depends on the effector cell recruitment dynamics and tumor sizes. Furthermore, an arbitrary increase of initial effector cell concentration does not necessarily imply a better tumor control. We evidence the existence of an optimal concentration range of effector cells for tumor shrinkage. Based on these findings, we suggest a theory-driven therapeutic proposal that optimally combines immuno- and vaso-modulatory interventions

HSP: A Tool for Heat Stress Prevention for Farm Workers

We present the initial development of an integrated application for heat stress and heat related illness prevention in farm workers. In developing the application we have follow the OSHA guidelines and an extended project includes the social, cultural and economic factors of farm workers. Even though, our development focus is on workers in the California fields, we believe our project will be useful in multiple situations where individuals are exposed to extreme heat working conditions. This paper describes the motivation for our development, the overall approach we are following, and the first version of our application

Some Unique Constants Associated with Extremal Black Holes

In recent papers we had developed a unified picture of black hole entropy and curvature which was shown to lead to Hawking radiation. It was shown that for any black hole mass, holography implies a phase space of just one quantum associated with the interior of the black hole. Here we study extremal rotating and charged black holes and obtain unique values for ratios of angular momentum to entropy, charge to entropy, etc. It turns out that these ratios can be expressed in terms of fundamental constants in nature, having analogies with other physical systems, like in condensed matter physics.Comment: "Accepted for publication in Astrophysics & Space Science" 4 pages, 10 equation