RAVAN: CubeSat Demonstration for Multi-Point Earth Radiation Budget Measurements.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) 3U CubeSat mission is a pathfinder to demonstrate technologies for the measurement of Earth's radiation budget, the quantification of which is critical for predicting the future course of climate change. A specific motivation is the need for lower-cost technology alternatives that could be used for multi-point constellation measurements of Earth outgoing radiation. RAVAN launched 11 November 2016, into a nearly 600-km, Sun-synchronous orbit, and collected data for over 20 months. RAVAN successfully demonstrates two key technologies. The first is the use of vertically aligned carbon nanotubes (VACNTs) as absorbers in broadband radiometers for measuring Earth's outgoing radiation and the total solar irradiance. VACNT forests are arguably the blackest material known and have an extremely flat spectral response over a wide wavelength range, from the ultraviolet to the far infrared. As radiometer absorbers, they have greater sensitivity for a given time constant and are more compact than traditional cavity absorbers. The second technology demonstrated is a pair of gallium phase-change black body cells that are used as a stable reference to monitor the degradation of RAVAN's radiometer sensors on orbit. Four radiometers (two VACNT, two cavity), the pair of gallium black bodies, and associated electronics are accommodated in the payload of an agile 3U CubeSat bus that allows for routine solar and deep-space attitude maneuvers, which are essential for calibrating the Earth irradiance measurements. The radiometers show excellent long-term stability over the course of the mission and a high correlation between the VACNT and cavity radiometer technologies. Short-term variability-at greater than the tenths-of-a-Watt/m2 needed for climate accuracy-is a challenge that remains, consistent with insufficient thermal knowledge and control on a 3U CubeSat. There are also VACNT-cavity biases of 3% and 6% in the Total and SW channels, respectively, which would have to be overcome in a future mission. Although one of the black bodies failed after four months, the other provided a repeatable standard for the duration of the project. We present representative measurements from the mission and demonstrate how the radiometer time series can be used to reconstruct outgoing radiation spatial information. Improvements to the technology and approach that would lead to better performance and greater accuracy in future missions are discussed.

Tick-borne relapsing fever.

Each year, many residents of and visitors to endemic regions of the western United States are exposed to the tick vectors of tick-borne relapsing fever (TBRF), Ornithodoros hermsi, Ornithodoros turicata, or Ornithodoros parkeri. This disease is remarkable because the human host is unaware of the tick bite, usually becomes very ill, may experience an exacerbation of symptoms rather than improvement shortly after beginning appropriate treatment, and, despite often high numbers of the etiologic organism in the blood, rarely dies as a result of the illness. Although relapsing fever is acquired in many parts of the world, this article focuses primarily on knowledge about TBRF in North America.

Variable tick protein in two genomic groups of the relapsing fever spirochete Borrelia hermsii in western North America.

Borrelia hermsii is the primary cause of tick-borne relapsing fever in North America. When its tick vector, Ornithodoros hermsi, acquires these spirochetes from the blood of an infected mammal, the bacteria switch their outer surface from one of many bloodstream variable major proteins (Vmps) to a unique protein, Vtp (Vsp33). Vtp may be critical for successful tick transmission of B. hermsii; however, the gene encoding this protein has been described previously in only one isolate. Here we identified and sequenced the vtp gene in 31 isolates of B. hermsii collected over 40 years from localities throughout much of its known geographic distribution. Seven major Vtp types were found. Little or no sequence variation existed within types, but between them significant variation was observed, similar to the pattern of diversity described for the outer surface protein C (OspC) gene in Lyme disease spirochetes. The pattern of sequence relatedness among the Vtp types was incongruent in two branches compared to two genomic groups identified among the isolates by multilocus sequence typing of the 16S rRNA, flaB, gyrB, and glpQ genes. Therefore, both horizontal transfer and recombination within and between the two genomic groups were responsible for some of the variation observed in the vtp gene. O. hermsi ticks were capable of transmitting spirochetes in the newly identified genomic group. Therefore, given the longevity of the tick vector and persistent infection of spirochetes in ticks, these arthropods rather than mammals may be the likely host where the exchange of spirochetal DNA occurs.

The epidemiology of tick-borne relapsing fever in the United States.

Each year, many residents of and visitors to endemic regions of the western United States are exposed to the vector of tick-borne relapsing fever (TBRF), an underrecognized and underreported disease. Through review of report forms and literature review, we identified 450 cases of TBRF acquired in the United States in 11 western states (and in British Columbia by a U.S. resident) from January 1977 to January 2000. Exposure sites were in forested areas, at varying elevations, in mountainous regions (Cascade, Rocky Mountain, San Bernardino, and Sierra Nevada ranges) of the United States and Canada and in limestone caves in central Texas. Only 13 counties accounted for approximately 50% of all cases. Forty percent of the cases were not residents of the state where TBRF exposure occurred, including 7% from 11 states where TBRF is not endemic. TBRF is endemic in the United States and is a disease affecting travelers, who may return home with the disease to areas where physicians are not familiar with it.

Tick-borne relapsing fever in North America.

Relapsing fever is characterized by recurring episodes of fever and nonspecific symptoms (e.g., headache, myalgia, arthralgia, shaking chills, and abdominal complaints). The illness is caused by an infection from the Borrelia species (spirochetes) that may be acquired through the bite of an infected tick (Ornithodoros species) or contact with the hemolymph of an infected human body louse (Pediculus humanus). In North America, most cases have been acquired in the western United States, southern British Columbia, and few cases have been reported from Mexico. Most cases have been acquired from exposure to rustic tick-infested cabins and caves. This article reviews relapsing fever, especially tick-borne relapsing fever in North America.