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In this paper, we discuss the use of a 3rd harmonic component to the drive voltage on the grid of an inductive output tube (IOT). High-efficiency inductive output tubes (IOTs) are typically characterized by efficiencies up to 70 - 75%. However, the achievement of efficiencies greater than 80% would substantially reduce the operating costs of next-generation accelerators. In order to achieve this goal, we consider the addition of a 3rd harmonic component to the drive signal on the grid of an inductive output tube. The use of a 3rd harmonic drive component in IOT guns has been considered in order to apply such a gun as the injector [1] of radio frequency linear accelerators (RF linacs). Here we consider that the IOT will be used to provide the rf power to drive RF linacs and apply the 3rd harmonic with the intention of increasing the efficiency of the RF output of the IOT. We consider a model IOT with a 700 MHz resonant cavity and using an annular beam with a voltage of 30 kV, an average current of 6.67 A yielding a perveance of about 1.3e-6 P. We simulate this IOT using the NEMESIS simulation code [2] which has been successfully validated by comparison with the K5H90W-2 IOT developed by Communications and Power Industries. It is found that the effect of the 3rd harmonic on the efficiency is greatest when the phase of the 3rd harmonic is shifted by pi radians with respect to the fundamental drive signal and with 3rd harmonic powers greater than about 50% that of the fundamental drive power. For the present example, we show that efficiencies approaching 86% are possible by this means., Comment: 4 pages, 7 figures

From October through mid-December 2015, influenza activity remained low in most regions of the United States. Activity began to increase in late December 2015 and continued to increase slowly through early February 2016. Influenza A viruses have been most frequently identified, with influenza A (H3N2) viruses predominating during October until early December, and influenza A (H1N1)pdm09 viruses predominating from mid-December until early February. Most of the influenza viruses characterized during that time are antigenically similar to vaccine virus strains recommended for inclusion in the 2015-16 Northern Hemisphere vaccines. This report summarizes U.S. influenza activity* during October 4, 2015-February 6, 2016, and updates the previous summary (1).

Early influenza activity during the 2012-13 season enabled estimation of the unadjusted effectiveness of the seasonal influenza vaccine. This report presents updated adjusted estimates based on 2,697 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness (Flu VE) Network during December 3, 2012-January 19, 2013. During this period, overall vaccine effectiveness (VE) (adjusted for age, site, race/ethnicity, self-rated health, and days from illness onset to enrollment) against influenza A and B virus infections associated with medically attended acute respiratory illness was 56%, similar to the earlier interim estimate (62%). VE was estimated as 47% against influenza A (H3N2) virus infections and 67% against B virus infections. When stratified by age group, the point estimates for VE against influenza A (H3N2) and B infections were largely consistent across age groups, with the exception that lower VE against influenza A (H3N2) was observed among adults aged ≥65 years. These adjusted VE estimates indicate that vaccination with the 2012-13 influenza season vaccine reduced the risk for outpatient medical visits resulting from influenza by approximately one half to two thirds for most persons, although VE was lower and not statistically significant among older adults. Antiviral medications should be used as recommended for treatment of suspected influenza in certain patients, including those aged ≥65 years, regardless of their influenza vaccination status.