Abstract Plasmonic photothermal therapy (PPTT) is a promising cancer treatment where plasmonic nanoparticles are used to convert near infrared light to localized heat to cause cell death, mainly via ...apoptosis and necrosis. Modulating PPTT to induce cell apoptosis is more favorable than necrosis. Herein, we used a mild treatment condition using gold nanorods (AuNRs) to trigger apoptosis and tested how different cell lines responded to it. Three different cancer cell lines of epithelial origin: HSC (oral), MCF-7 (breast) and Huh7.5 (liver) had comparable AuNRs uptake and were heated to same environmental temperature (under 50 °C). However, Huh7.5 cells displayed a significant increase in cell apoptosis after PPTT as compared to the other two cell lines. As HSP70 is known to increase cellular resistance to heat, we determined relative HSP70 levels in these cells and results indicated that Huh7.5 cells had ten-fold decreased levels of HSP70 as compared with HSC and MCF-7 cells. We then down-regulated HSP70 with a siRNA and observed that all three cell lines displayed significant reduction in viability and an increase in apoptosis after PPTT. As an enhancement to PPTT, we conjugated AuNRs with Quercetin, an inhibitor of HSP70 which displayed anti-cancer effects via apoptosis.
In this paper we study the interaction of kinetic Alfven waves generated near the equatorial plane of the magnetosphere with electrons having initial energies up to ∼100 eV. Wave‐particle ...interactions are investigated using a theoretical model of trapping into an effective potential generated by the wave parallel electric field and the mirror force acting along geomagnetic field lines. It is demonstrated that waves with an effective potential amplitude on the order of ∼100–400 V and with perpendicular wavelengths on the order of the ion gyroradius can trap and efficiently accelerate electrons up to energies of several keV. Trapping acceleration corresponds to conservation of the electron magnetic moment and, thus, results in a significant decrease of the electron equatorial pitch angle with time. Analytical and numerical estimates of the maximum energy and probability of trapping are presented, and the application of the proposed model is discussed.
Key Points
Kinetic Alfven waves in the equatorial inner magnetosphere can trap 100 eV electrons
Tapped electrons are accelerated up to energies of several keV
Trapping acceleration results in a significant decrease of the electron equatorial pitch angle
The feedback instability in the ionospheric Alfvén resonator in Earth's magnetosphere is examined using a two‐dimensional multifluid numerical model of coupled ionosphere and magnetosphere. Two ...simulation configurations are used to demonstrate that the instability occurs under an assumption that is unrealistic for Earth's ionosphere. In the first configuration, a flat sheet height‐integrated conducting boundary replaces the ionospheric E layer. In the second configuration, plasma dynamics in a simplified E layer is resolved ignoring ion production, loss, and diffusion. For the same parameters (plasma and neutral density profiles and convection electric field), the instability develops only with the flat sheet boundary. When the E layer is resolved, the variation of ion‐neutral collision frequencies with altitude produces vertical shear in the horizontal ion flow velocity. The shear prevents density perturbations from remaining field aligned, causing them to decay rather than grow. It is suggested that the instability cannot occur in Earth's ionosphere because ion‐neutral collision frequencies always have a significant variation with altitude through the E layer.
Key Points
The ionospheric feedback instability is stabilized due to the strong vertical shear of horizontal ion flow in the E layer
The shear distorts initially field‐aligned shape of an ionospheric density perturbation causing the perturbation to decay rather than grow
Rapid decay of ion‐neutral collision frequency with altitude in the Earth's is not captured by available theories of feedback instability
This article describes the relationship between shear Alfvén waves and auroral electron acceleration, with an emphasis on long-period standing waves that correlate with redline auroral arcs in the ...Earth’s magnetosphere. Discrete auroral arcs were correlated with high-latitude field line resonances in the early 1990’s. The past decade has seen advances in all-sky camera technology improve the detection and categorization of “FLR arcs” and establish them as a distinct population. We review observations of redline arcs and discuss estimates of wave amplitudes, wavelengths perpendicular to the geomagnetic field, and saturation times obtained within the framework of two-fluid theories. The two-fluid theory explains the spatial and temporal evolution of FLR optical signatures, but the estimated parallel electric field strengths are insufficient to accelerate electrons and produce 6300 Å auroral emissions. A kinetic theory of FLRs is necessary since electron bounce motion in long-wavelength standing waves affects the ac conductivity and hence the strength of parallel electric fields. In the kinetic theory, the current-voltage relation comprises a conductivity kernel that is a function of the wave frequency, field line length, electron thermal speed, and the number of electron trajectories nearly parallel to geomagnetic field lines close to the ionosphere. The ensuing nonlocal relationship between wave parallel currents and parallel electric fields provides a feasible explanation of the correlation between long-period field line resonances and redline arcs in the terrestrial magnetosphere. The mirror force and particle trapping in the wave fields of shear Alfvén waves are demonstrated to be important aspects of the kinetics of FLRs.
In situ conjugate electromagnetic ion cyclotron (EMIC) waves observed by the Swarm mission in both hemispheres are presented. A complex and unusual pattern of Alfvénic EMIC wave energy is observed, ...with a mid‐latitude peak close to the source at L =3.3, as well as a secondary lower L‐peak. A wave propagation model reveals that the secondary peak at L =1.7 may be explained by wave power being redirected equatorward due to the Buchsbaum resonance, crossing and interfering with the same EMIC wave power propagating equatorwards from the opposite hemisphere. This interference creates a coherent equatorial driver for a low‐L field line resonance at the secondary peak, and which is associated with strong shear‐to‐fast mode coupling in the ionosphere. This behavior complicates the interpretation of low‐Earth orbit EMIC data for applications assessing radiation belt loss. Combined low Earth orbit observations and modeling enable these novel and localized magnetosphere‐ionosphere EMIC wave propagation pathways to be identified.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) waves are important in near‐Earth space due to their role in reducing the amount of radiation in the Earth's radiation belts following geomagnetic storms. They are also often observed during non‐storm times. They are studied using satellites and ground observatories. Our paper reveals how these waves can follow complicated and previously unknown pathways to reach the upper atmosphere where they can be detected on the ground. This study shows a new and unusual effect where some EMIC wave energy is reflected and diverted toward the equator, where it meets its opposite‐hemisphere counterpart, interferes with it and sets up a resonance. This resonance then creates a new signal peak in the upper atmosphere at lower latitudes, far away from the location of the initial source. This presents a new and hitherto unseen pathway for wave energy to travel from their generation region in near‐Earth space down to the ionosphere. Understanding such pathways is very important for correctly diagnosing the location of these wave populations in space, and assessing their role in causing reductions in the levels of space radiation.
Key Points
Electromagnetic ion cyclotron wave propagation from the magnetosphere to the ionosphere is complicated by reflection from the Buchsbaum resonance and interference
Waves reflected from the Buchsbaum resonance interfere to generate a coherent driver for a secondary lower latitude field line resonance
This generates a field‐guided secondary lower‐latitude peak associated with strong shear‐to‐fast mode energy conversion in the ionosphere
During periods of storm activity and enhanced convection, the plasma density in the afternoon sector of the magnetosphere is highly dynamic due to the development of plasmaspheric drainage plume ...(PDP) structure. This significantly affects the local Alfvén speed and alters the propagation of ULF waves launched from the magnetopause. Therefore, it can be expected that the accessibility of ULF wave power for radiation belt energization is sensitively dependent on the recent history of magnetospheric convection and the stage of development of the PDP. This is investigated using a 3‐D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (VollandStern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic field day/night asymmetry and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. We find that the plume structure significantly alters the field line resonance location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than outside, providing an avenue for electron energization.
Key Points
ULF wave accessibility to the inner magnetosphere depends on plasmaspheric density structure generated during periods of strong convection
A 3‐D MHD model for ULF waves shows that eigenmodes are excited within plasmaspheric drainage plume density structures
This provides a pathway for radiation belt energization by ULF waves at lower L shell than would otherwise be possible
Six years of Van Allen Probes data are used to investigate cold plasmaspheric electrons affected by ultralow‐frequency (ULF) waves in the inner magnetosphere (L<7) including spatial distributions, ...occurrence conditions, and resonant energy range. Events exhibit a global distribution within L= 4–7 but preferentially occur at L∼5.5–7 in the dayside, while there is higher occurrence rate in the duskside than dawnside. They can occur under different geomagnetic activities and solar wind velocities (VS), but the occurrence rates are increasing with larger AE, |SYMH|, and VS. These features are closely associated with the generation and propagation of ULF waves in Pc4 (45–150 s) and Pc5 (150–600 s) bands. Combined with electron observations from HOPE instrument, the resonant energies inferred from wave power indicate that cold electrons at ones to hundreds of electron volts can be affected by ULF waves. This study may shed new light on further investigations on the acceleration and transportation of cold plasmaspheric particles that would affect plasmaspheric material release to the Earth's magnetosphere and instabilities for exciting various waves.
Key Points
Interactions between ULF waves and cold electrons occur at L = 4–7 with dominant distributions in the dayside and a dawn‐dusk asymmetry
The event occurrence rates are increasing with larger AE, |SYMH|, and solar wind velocity
The resonant energy inferred from wave power and electron observations indicates that electrons at ones to hundreds of electron volts are affected by ULF waves
We present an analysis of “boomerang‐shaped” pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on 7 ...June 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90° pitch angle electrons, the phase change of the flux modulations across energy exceeds 180° and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock‐induced ULF waves interact with electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wavefield reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.
Key Points
Boomerang‐shaped pitch angle evolutions of relativistic electrons in Pc5 band is observed for the first time in the outer radiation belt
Electrons' drift resonating with azimuthally localized ULF waves can produce boomerang‐shaped pitch angle stripes
Nonlocal effects in drift‐resonant process on outer belt dynamics
Although the Earth's Van Allen radiation belts were discovered over 50 years ago, the dominant processes responsible for relativistic electron acceleration, transport and loss remain poorly ...understood. Here we show evidence for the action of coherent acceleration due to resonance with ultra-low frequency waves on a planetary scale. Data from the CRRES probe, and from the recently launched multi-satellite NASA Van Allen Probes mission, with supporting modelling, collectively show coherent ultra-low frequency interactions which high energy resolution data reveals are far more common than either previously thought or observed. The observed modulations and energy-dependent spatial structure indicate a mode of action analogous to a geophysical synchrotron; this new mode of response represents a significant shift in known Van Allen radiation belt dynamics and structure. These periodic collisionless betatron acceleration processes also have applications in understanding the dynamics of, and periodic electromagnetic emissions from, distant plasma-astrophysical systems.
Magnetic cavities (sometimes referred to as magnetic holes) at electron kinetic scale are thought to be one of the extremely small intermittent structures formed in magnetized turbulent plasmas, ...where the turbulence energy cascaded down to electron scale may finally be dissipated and consequently energize the electrons. However, the geometry and formation of these structures remain not definitively resolved. Here we discuss an electron scale magnetic cavity embedded in a proton scale magnetic cavity observed by the MMS spacecraft in the magnetosheath. By applying an innovative particle sounding technique, we directly depict the boundary of the electron scale magnetic cavity and uncover the geometry. We find that this structure is nearly circular with a radius of 10.0 km and its formation is due to the diamagnetic current. Investigation of the electron scale structure is only recently made possible by the high spatial and temporal resolution provided by MMS observations.
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