Modulational Instability in Equations of KdV Type

It is a matter of experience that nonlinear waves in dispersive media, propagating primarily in one direction, may appear periodic in small space and time scales, but their characteristics --- amplitude, phase, wave number, etc. --- slowly vary in large space and time scales. In the 1970's, Whitham developed an asymptotic (WKB) method to study the effects of small "modulations" on nonlinear periodic wave trains. Since then, there has been a great deal of work aiming at rigorously justifying the predictions from Whitham's formal theory. We discuss recent advances in the mathematical understanding of the dynamics, in particular, the instability of slowly modulated wave trains for nonlinear dispersive equations of KdV type.Comment: 40 pages. To appear in upcoming title in Lecture Notes in Physic

Natural infection by the protozoan Leptomonas wallacei impacts the morphology, physiology, reproduction, and lifespan of the insect Oncopeltus fasciatus

Trypanosomatids are protozoan parasites that infect thousands of globally dispersed hosts, potentially affecting their physiology. Several species of trypanosomatids are commonly found in phytophagous insects. Leptomonas wallacei is a gut-restricted insect trypanosomatid only retrieved from Oncopeltus fasciatus. The insects get infected by coprophagy and transovum transmission of L. wallacei cysts. The main goal of the present study was to investigate the effects of a natural infection by L. wallacei on the hemipteran insect O. fasciatus, by comparing infected and uninfected individuals in a controlled environment. The L. wallacei-infected individuals showed reduced lifespan and morphological alterations. Also, we demonstrated a higher infection burden in females than in males. The infection caused by L. wallacei reduced host reproductive fitness by negatively impacting egg load, oviposition, and eclosion, and promoting an increase in egg reabsorption. Moreover, we associated the egg reabsorption observed in infected females, with a decrease in the intersex gene expression. Finally, we suggest alterations in population dynamics induced by L. wallacei infection using a mathematical model. Collectively, our findings demonstrated that L. wallacei infection negatively affected the physiology of O. fasciatus, which suggests that L. wallacei potentially has a vast ecological impact on host population growth

Native American Age at Death in the USA

There are persistent disparities in mortality rates between Native Americans and other groups in the USA. Public-use mortality data severely limits the ability of researchers to examine contextual factors that might explain these disparities. Using restricted-use mortality microdata, we examine the relationship between geographic location, specific causes of death, and age at death. We show that Native American women, on average, die 13 years earlier than White women; Native American men, on average, die 12 years earlier than White men. These disparities are largest in the northern Great Plains and Rocky Mountain states. The disparity in age at death is in part due to Native Americans dying from diseases at younger ages than White Americans. Native American women and men die younger and more often from homicide in counties with persistently higher White male to female ratios. Native American men also die younger and more often from homicide when White male to female ratios increase within their county over time

The S2 VLBI System

The S2 VLBI system is described in some detail, including the S2 data acquisition system, data recorder & playback terminals, and the correlator. 1 Introduction The S2 VLBI system is a low cost, high performance, end-to-end VLBI system recently developed in Canada for general research applications including radio astrophysics and astrometry, geodesy and geodynamics, and space VLBI. It consists of the S2 VLBI Data Acquisition System (S2-DAS), the S2 VLBI Data Record Terminal (S2-RT), the S2 VLBI Data Playback Terminal (S2PT) , and the S2 VLBI correlator. The S2 VLBI system includes enhancements such as the S2 Tape-to-Computer Interface (S2-TCI) which enables a direct interface between the S2 recorded baseband samples and a computer memory and associated disk storage. S2-TCI is intended for applications to pulsar research and remote sensing. Preprint submitted to Elsevier Science 27 February Through the use of the S2 VLBI System Interface Adapter (S2-VIA) the S2RT can be interfaced at ..

Native American Age at Death in the USA

There are persistent disparities in mortality rates between Native Americans and other groups in the USA. Public-use mortality data severely limits the ability of researchers to examine contextual factors that might explain these disparities. Using restricted-use mortality microdata, we examine the relationship between geographic location, specific causes of death, and age at death. We show that Native American women, on average, die 13 years earlier than White women; Native American men, on average, die 12 years earlier than White men. These disparities are largest in the northern Great Plains and Rocky Mountain states. The disparity in age at death is in part due to Native Americans dying from diseases at younger ages than White Americans. Native American women and men die younger and more often from homicide in counties with persistently higher White male to female ratios. Native American men also die younger and more often from homicide when White male to female ratios increase within their county over time