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Presents information on low-, medium- and high-frequency radiowave observations at very high latitudes. Analysis of frequency radio emissions; Information on Auroral hiss; Types of frequency radio emissions.

Presents the result of a study on the monitoring of solar low-frequency (LF)/medium-frequency (MF)/high-frequency (HF) radio emissions from remote sites in Antarctica. Existence of auroral-related LF/MF/HF radio emissions; Recording of individual spectra during quiet periods.

Auroral medium frequency burst (MFB) is a radio emission of natural auroral origin associated with substorm expansion phase and observable at ground level. The emission usually occurs at frequencies above 1500 kHz, but occasionally it extends to a sharp lower cutoff frequency at 1300-1500 kHz depending on the observing site, with a frequency gap below the cutoff and sporadic emission below the gap extending to frequencies as low as 1000 kHz. These low-frequency MFB components lie below the electron gyrofrequency and hence could represent either whistler or LO-modes. Recently, using crossed antennas and a two-channel receiver at Toolik Lake, Alaska, polarization of these low-frequency MFB components was measured for the first time and found to be left-hand. This observation eliminates whistler mode as a possibility and requires the low-frequency components be LO-mode in the ionosphere, which constrains their source location since it requires that the frequency exceeds the L-cutoff frequency. In these occasional events marked by a cutoff and low-frequency MFB components, the latter probably originate at high altitudes (>800 km) and reach the ground through extraordinary low-density polar cap ionosphere. [ABSTRACT FROM AUTHOR]

A second allogeneic stem cell transplantation (allo-SCT) is an option following relapse after an initial SCT for hematologic malignancies. Conditioning with intensity-modulated total marrow irradiation (IM-TMI) is feasible and shows promise in optimizing the therapeutic ratio. We report on clinical outcomes and to identify IM-TMI dose to the oral cavity that would be associated with lower incidence of mucositis to help guide planning. We conducted a retrospective analysis of patients undergoing second allo-SCT enrolled between Dec 2015 and Nov 2023 on a phase I dose-escalation trial of IM-TMI with fludarabine and melphalan. TMI doses were given twice daily, 1.5 Gy per fraction with total dose of 6, 9, or 12 Gy. The clinical target volume consisted of bones excluding mandible (except in 1 case), arms and lower extremities mid-femur down. We collected baseline patient and treatment characteristics and performed univariate analysis reported as mean (SD) or median [interquartile range]. Logistic regression (LR) was performed to evaluate potential predictors of oral mucositis incidence at 1 week following allo-SCT. Of 31 patients, 18 (58%) were male, predominantly white (83%), with median age of 49 [41, 64]. The mean BMI was 30.62 (22.33) and with a Karnofsky >90 (68%). Majority being treated for AML (74%). Most common disease status at time of 2nd allo-SCT included 1st relapse in 8 (26%) followed by 2nd complete remission in 5 (16.1%), and 3rd complete remission in 4 (13%). TMI dose of 9 Gy was delivered to 15 patients (48%), 12 Gy to 10 (32%), and 6 Gy to 5 (16%). The average dose to the oral cavity was 298.05 cGy (95.7), with the oral cavity receiving on average 32% of the prescribed dose. 16 patients (52%) experienced mucositis within a month following allo-SCT with IM-TMI; 14 occurred within 7 days, half grade 1 and grade 3 toxicities. Pearson correlation showed moderate association between oral cavity dose and mucositis grade at day 7 (r = 0.284). On LR analysis of predictors, the oral cavity mean dose (OR = 1.032) and age (OR = 0.878) were found to be significant predictors of mucositis incidence at day 7 (p = 0.04 and p = 0.03 respectively). In LR model with oral cavity mean dose and age categorized by the median value, an oral cavity mean dose greater than the median of 264.7 cGy was associated with an OR of 44.8 (p = 0.023). 5 of 31 patients (16%) had relapsed, 3 in the bone marrow and 2 with solid masses, at an average of 197 days (77.8) post allo-SCT. At a median follow up of 11 months, 11 patients (36%) were alive. Most common cause of death included persistence/progression of disease in 8 (40%) and infection in 9 patients (45%). Our study adds to the evolving literature on the integration of TMI into conditioning regimens for allo-SCT, specifically in the second transplant setting. Given that the oral cavity mean dose and age are significant predictors of mucositis incidence at day 7, caution must be applied in the delivery of TMI to the oral cavity, specifically in this population. [ABSTRACT FROM AUTHOR]

Compares electromagnetic noise detections in Antarctica. Number of noise spectra detected in observations; Power spectral density representation in volts; Sites with the least electromagnetic noise.

Presents observations on auroral radio emissions at the automatic geophysical observatory-P2 (AGO-P2) in Antarctica. Frequency emission ranges; Detection of an auroral roar event; Comparison with previous auroral observations.

Treatment resistance in T-cell acute lymphoblastic leukemia (T-ALL) is associated with phosphatase and tensin homolog (PTEN) deletions and resultant phosphatidylinositol 3′-kinase (PI3K)-AKT pathway activation, as well as MYC overexpression, and these pathways repress mitochondrial apoptosis in established T-lymphoblasts through poorly defined mechanisms. Normal T-cell progenitors are hypersensitive to mitochondrial apoptosis, a phenotype that is dependent on the expression of proapoptotic BIM. In a conditional zebrafish model, MYC downregulation induced BIM expression in T-lymphoblasts, an effect that was blunted by expression of constitutively active AKT. In human T-ALL cell lines and treatment-resistant patient samples, treatment with MYC or PI3K-AKT pathway inhibitors each induced BIM upregulation and apoptosis, indicating that BIM is repressed downstream of MYC and PI3K-AKT in high-risk T-ALL. Restoring BIM function in human T-ALL cells using a stapled peptide mimetic of the BIM BH3 domain had therapeutic activity, indicating that BIM repression is required for T-ALL viability. In the zebrafish model, where MYC downregulation induces T-ALL regression via mitochondrial apoptosis, T-ALL persisted despite MYC downregulation in 10% of bim wild-type zebrafish, 18% of bim heterozygotes and in 33% of bim homozygous mutants (P=0.017). We conclude that downregulation of BIM represents a key survival signal downstream of oncogenic MYC and PI3K-AKT signaling in treatment-resistant T-ALL. [ABSTRACT FROM AUTHOR]

Many phenomena in the high‐frequency pumped ionosphere exhibit dependence on the pump beam incident angle α. This motivates a systematic study of the α dependence of the stimulated electromagnetic emission (SEE), particularly near electron gyroharmonics. We report the first observations of stationary SEE spectra for α ranging from −28° (north) to 28° (south) at three receiving sites, for the pump frequency (f0) sweeping near the fourth gyroharmonic (4fc). The following is established: (i) For pumping near the magnetic zenith (α = 7°, 14°, 21°), when existent dynamic broad upshifted maximum in the SEE spectrum indicates that artificial ionization layers are excited, suppression of the downshifted maximum at f0 ≈ 4fс is weakest, and 4fс increases. (ii) Weaker similar effects occur for α = −14° (a condition called "mirror magnetic zenith"). (iii) For northern pump beam inclinations, the SEE intensity decreases (in comparison with southern inclinations and vertical), most strongly at the southernmost receiving site. Plain Language Summary: Many phenomena in the high‐frequency (HF)‐pumped upper ionosphere, such as artificial airglow, descending artificial ionization layers, pump‐induced plasma irregularities, and HF plasma modes, exhibit dependence on the pump beam incident angle with respect to the ionosphere. This motivates the systematic study of angle dependence of the stimulated electromagnetic emission (secondary radiation from the ionosphere) appearing due to plasma mode conversion into electromagnetic ones, particularly near electron gyroharmonics. We report the first observations of secondary radiation spectra as dependent on mismatch between the pump frequency and fourth gyroharmonic, for incident angle varying from −28° (north) to 28° (south) at different receiving sites. The results obtained indicate that the interaction between high‐power high‐frequency pump wave and plasma modes in the ionospheric plasma takes place in a wide range of pump beam inclination angles; the interaction is stronger for southern inclinations. Newly discovered emission peculiarities, such as the emission suppression decrease at the fourth gyroresonance and energy redistribution between different emission spectral components (both for pumping to the magnetic zenith, 14°, when artificial ionization occurs) and similar but weaker effects for "mirror magnetic zenith" (−14°), allow deeper understanding of the physical processes occurring in the HF‐pumped upper ionosphere. Key Points: Properties of the stimulated electromagnetic emission are studied for different pump wave beam inclinations near the fourth gyroharmonicFor pumping at magnetic zenith, a correlation between emission spectral lines and artificial ionization layers is obtainedFor northern pump beam inclinations, the emission intensity decreases, most strongly at the southernmost receiving site [ABSTRACT FROM AUTHOR]

We report on artificial descending plasma layers created in the ionosphere F region by high-power high-frequency (HF) radio waves from High-frequency Active Auroral Research Program at frequencies f0 near the fourth electron gyroharmonic 4fce. The data come from concurrent measurements of the secondary escaping radiation from the HF-pumped ionosphere, also known as stimulated electromagnetic emission, reflected probing signals at f0, and plasma line radar echoes. The artificial layers appeared only for injections along the magnetic field and f0 > 4fce at the nominal HF interaction altitude in the background ionosphere. Their average downward speed ~0.5 km/s holds until the terminal altitude where the local fourth gyroharmonic matches f0. The total descent increases with the nominal offset f0 - 4fce. [ABSTRACT FROM AUTHOR]

The statistically steady distributions P(log E) and Pe(log Ee) of waveform field E and envelope field Ee are studied for time-varying waves with stochastically driven amplitudes. The waves are represented in one dimension (1D) by a single mode or superposition of multiple independent modes, whose amplitudes follow stochastic differential equations. Both distributions at low fields follow power laws: P(log E)∝Ep and Pe(log Ee)∝Eeq with distinct exponents p and q. Transitions in both distributions are found between the single-mode and multimode cases, with the distributions in the latter essentially independent of the number N (provided N≥2) of modes. For N≥2, p≈+1.0, q≈+2.0, and both distributions agree quantitatively with independent analytic predictions. Applications to Langmuir waves observed in Earth’s polar cusp ionosphere show that both distributions for N≥2 agree quantitatively with the respective observations, suggesting that the Langmuir waves may be 1D and have a stochastic driver. [ABSTRACT FROM AUTHOR]

Coupling of the solar wind to the Earth magnetosphere/ionosphere is primarily through the high latitude regions, and there are distinct advantages in making remote sensing observations of these regions with a network of ground-based observatories over other techniques. The Antarctic continent is ideally situated for such a network, especially for optical studies, because the larger offset between geographic and geomagnetic poles in the south enables optical observations at a larger range of magnetic latitudes during the winter darkness. The greatest challenge for such ground-based observations is the generation of power and heat for a sizable ground station that can accommodate an optical imaging instrument. Under the sponsorship of the National Science Foundation, we have developed suitable automatic observing platforms, the Automatic Geophysical Observatories (AGOs) for a network of six autonomous stations on the Antarctic plateau. Each station housed a suite of science instruments including a dual wavelength intensified all-sky camera that records the auroral activity, an imaging riometer, fluxgate and search-coil magnetometers, and ELF/VLF and LM/MF/HF receivers. Originally these stations were powered by propane fuelled thermoelectric generators with the fuel delivered to the site each Antarctic summer. A by-product of this power generation was a large amount of useful heat, which was applied to maintain the operating temperature of the electronics in the stations. Although a reasonable degree of reliability was achieved with these stations, the high cost of the fuel air lift and some remaining technical issues necessitated the development of a different type of power unit. In the second phase of the project we have developed a power generation system using renewable energy that can operate automatically in the Antarctic winter. The most reliable power system consists of a type of wind turbine using a simple permanent magnet rotor and a new type of power control system with variable resistor shunts to regulate the power and dissipate the excess energy and at the same time provide heat for a temperature controlled environment for the instrument electronics and data system. We deployed such systems and demonstrated a high degree of reliability in several years of operation in spite of the relative unpredictability of the Antarctic environment. Sample data are shown to demonstrate that the AGOs provide key measurements, which would be impossible without the special technology developed for this type of observing platform. [ABSTRACT FROM AUTHOR]

Monthly averages of F-region cut-off frequency foF2 and peak height hmF2 data obtained during the solar maximum years 1978 and 2000 through the use of ionosondes located at equatorial and low latitude regions in Brazil are compared with the IRI representations. The equatorial stations are Fortaleza (3°53'S, 38°25'W), and Sa˜o Lui´s (2°20'S, 44°12'W), and the low latitude station was Cachoeira Paulista (22°41'S, 45°00'W). The ionosonde data analyzed here were taken at each 15 minutes, in the months of February, May, August and November, of 1978 and 2000. In a second part of this study, electron density profiles obtained by three rocket flights in the Brazilian equatorial region are also compared with the IRI representations. The rocket experiments were carried out on July 7, 1984, December 11, 1985 and October 14, 1994. The first and the second experiments were performed at the sub-equatorial station Natal (35°14'W, 5°55'S) and the third one at the equatorial station Alcaˆntara (2°19'S, 44°22W). The results clearly show that IRI significantly underestimates the equatorial hmF2 during the pre-midnight period. On the other hand, the IRI representation for hmF2 over off-equatorial station Cachoeira Paulista is in rather better agreement with the experimental density profile. The IRI representation of the foF2 parameter is in reasonable agreement with the data for both the equatorial region and Cachoeira Paulista, although the model appears to systematically overestimate foF2 in August for both 1978 and 2000. The rocket electron density profiles show that the highly variable height distribution of the electron density during ionospheric plasma bubble events may always prevent the correct representation of electron density profiles in the equatorial region during the occurrence of those events. [Copyright &y& Elsevier]