A New Perspective for Dipolarization Front Dynamics: Electromagnetic Effects of Velocity Inhomogeneity

The stability of a quasi‐static near‐Earth dipolarization front (DF) is investigated with a two‐dimensional electromagnetic particle‐in‐cell model. Strongly localized ambipolar electric fields self‐consistently generate a highly sheared dawnward E→×B→ electron drift on the kinetic scale in the DF. Electromagnetic particle‐in‐cell simulations based on the observed DF thickness and gradients of plasma/magnetic field parameters reveal that the DF is susceptible to the kinetic electron‐ion hybrid (EIH) instability driven by the strong velocity inhomogeneity. The excited waves show a broadband spectrum in the lower hybrid (LH) frequency range, which has been often observed at DFs. The wavelength is comparable to the shear scale length, and the growth rate is also in the LH frequency range, which are consistent with the EIH theory. As a result of the LH wave emissions, the velocity shear is relaxed, and the DF is broadened. When the plasma beta increases, the wave mode shifts to longer wavelengths with reduced growth rates and enhanced magnetic fluctuations although the wave power is mostly in the electrostatic regime. This study highlights the role of velocity inhomogeneity in the dynamics of DF which has been long neglected. The EIH instability is suggested to be an important mechanism for the wave emissions and steady‐state structure at the DF.Key PointsMagnetotail DF contains a substantial velocity shear in the tangential electron driftThe sheared flow is susceptible to the EIH instability and can broaden the DF by emitting broadband LH wavesThe EIH emissions become more electromagnetic as plasma beta increasesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152027/1/jgra55215_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152027/2/jgra55215.pd

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Satellite Formation Flight Simulation Using Multi-Constellation GNSS and Applications to Ionospheric Remote Sensing

The Virginia Tech Formation Flying Testbed (VTFFTB) is a global navigation satellite system (GNSS)-based hardware-in-the-loop (HIL) simulation testbed for spacecraft formation flying with ionospheric remote sensing applications. Past applications considered only the Global Positioning System (GPS) constellation. The rapid GNSS modernization offers more signals from other constellations, including the growing European system&mdash;Galileo. This study presents an upgrade of VTFFTB with the incorporation of Galileo and the associated enhanced capabilities. By simulating an ionospheric plasma bubble scenario with a pair of LEO satellites flying in formation, the GPS-based simulations are compared to multi-constellation GNSS simulations including the Galileo constellation. A comparison between multi-constellation (GPS and Galileo) and single-constellation (GPS) shows the absolute mean and standard deviation of vertical electron density measurement errors for a specific Equatorial Spread F (ESF) scenario are decreased by 32.83% and 46.12% with the additional Galileo constellation using the 13 July 2018 almanac. Another comparison based on a simulation using the 8 March 2019 almanac shows the mean and standard deviation of vertical electron density measurement errors were decreased further to 43.34% and 49.92% by combining both GPS and Galileo data. A sensitivity study shows that the Galileo electron density measurements are correlated with the vertical separation of the formation configuration. Lower C/N 0 level increases the measurement errors and scattering level of vertical electron density retrieval. Relative state estimation errors are decreased, as well by utilizing GPS L1 plus Galileo E1 carrier phase instead of GPS L1 only. Overall, superior performance on both remote sensing and relative navigation applications is observed by adding Galileo to the VTFFTB

Ionospheric Remote Sensing with GNSS

The Global Navigation Satellite System (GNSS) plays a pivotal role in our modern positioning, navigation and timing (PNT) technologies. GNSS satellites fly at altitudes of approximately 20,000 km or higher. This altitude is above an ionized layer of the Earth’s upper atmosphere, the so called “ionosphere”. Before reaching a typical GNSS receiver on the ground, GNSS satellite signals penetrate through the Earth’s ionosphere. The ionosphere is a plasma medium consisting of free charged particles that can slow down, attenuate, refract, or scatter the GNSS signals. Ionospheric density structures (also known as irregularities) can cause GNSS signal scintillations (phase and intensity fluctuations). These ionospheric impacts on GNSS signals can be utilized to observe and study physical processes in the ionosphere and is referred to ionospheric remote sensing. This entry introduces some fundamentals of ionospheric remote sensing using GNSS

Ionospheric Remote Sensing with GNSS

The Global Navigation Satellite System (GNSS) plays a pivotal role in our modern positioning, navigation and timing (PNT) technologies. GNSS satellites fly at altitudes of approximately 20,000 km or higher. This altitude is above an ionized layer of the Earth&rsquo;s upper atmosphere, the so called &ldquo;ionosphere&rdquo;. Before reaching a typical GNSS receiver on the ground, GNSS satellite signals penetrate through the Earth&rsquo;s ionosphere. The ionosphere is a plasma medium consisting of free charged particles that can slow down, attenuate, refract, or scatter the GNSS signals. Ionospheric density structures (also known as irregularities) can cause GNSS signal scintillations (phase and intensity fluctuations). These ionospheric impacts on GNSS signals can be utilized to observe and study physical processes in the ionosphere and is referred to ionospheric remote sensing. This entry introduces some fundamentals of ionospheric remote sensing using GNSS

Hearn 16 th Annual/USU Conference on Small Satellites

Abstract. Utah State University, the University of Washington, and Virginia Tech are teamed to form the Ionospheric Observation Nanosatellite Formation (ION-F) to investigate ionospheric turbulence and formation-flying requirements for multiple small satellite missions. A communication subsystem for the mission will be composed of an uplink, a downlink, and satellite-tosatellite crosslink. The uplink will operate at UHF. The downlink and crosslink both will operate in the S-band. The design and successful implementation of a low profile, compact element with desirable properties at UHF within the physical constraints of a nanosatellite is a challenge. A resonant loop antenna mounted above the bottom surface of the spacecraft was selected for a possible satellite antenna. The linearly polarized resonant loop was chosen to satisfy the physical requirements of the spacecraft while still achieving efficient operation for a UHF signal. A full-scale prototype was fabricated to measure the frequency dependent characteristics of the antenna. A gamma match and a quarter-wave sleeve balun transformer were integrated to the system to optimize the impedance match between the antenna and the transmission line. Measured results presented in this paper indicate sufficient performance for the initial design. The antenna operating bandwidth of approximately one percent covers the estimated bandwidth of the uplink channel. However, integration with other components during fabrication could easily detune the resonant frequency of the loop antenna out of the required band. Further development of the uplink antenna design should include adjustable mounts and a capacitive tuning element

Nanosatellite Applications By Christian W. Hearn

Virginia Tech, Utah State University, and the University of Washington were teamed to form the Ionospheric Observation Nanosat Formation to investigate formationflying requirements for multiple spacecraft missions. A communication subsystem for the mission will comprise an uplink, downlink and a satellite-to-satellite crosslink. A linearly polarized resonant loop antenna mounted above the bottom surface of the spacecraft was selected for a possible satellite uplink receive antenna. The resonant loop was chosen to satisfy the physical requirements of the spacecraft while still achieving efficient operation for a UHF signal. A full-scale prototype was fabricated to measure frequency dependent characteristics of the antenna. A gamma match and a quarter-wave sleeve balun transformer were integrated to the system to minimize the power reflected at the antenna input and to isolate the antenna from the feed line. The uplink antenna demonstrated sufficient performance; however, the final bandwidth of less than one percent will require additional tuning as other subsystems are integrated into the final flight-ready prototype. iii ACKNOWLEDGEMENTS The author would like to express his appreciation to R. Michael Barts for his invaluable technical assistance and direction in completing this project. Additional thanks are owed to Josh Arritt, Derek Wells, Koichiro Takamizawa, and other students in the Virginia Tech Antenna Group (VTAG) who offered their assistance in the final preparation of this document. iv Table of Contents Abstract...............................................................................................................................ii Acknowledgements ..........................................................................................................