Study of the earth's ionosphere by reception of radio waves from satellites

Thesis (M.A.)--Boston UniversityA study of ionospheric scintillations by the reception of signals from the Russian satellite 1962 Cosmos I was undertaken. The data were obtained at the Sagamore Hill Radio Observatory, Hamilton, Massachusetts, of the Air Force Cambridge Research Laboratories. The satellite transmitted at a frequency of 20 Mc/s and it was found possible to receive the first two harmonics at 40 Mc/s and 60 Me/s. A high percentage of scintillation was observed on all nighttime transits of the satellite. No marked variation of scintillation index with elevation angle was observed. The scintillation index varied with wavelength as lambda^(0.78) for magnetically quiet days and as lambda^(0.36) for magnetically disturbed days. A pronounced latitude dependence of scintillations was observed. The onset of scintillations occurred at a sub-ionospheric latitude (referred to a height of 300 km) of 35 degrees North for magnetically disturbed days. A zone of almost uniform scintillation exists beyond a latitude of 41 degrees North. On certain occasions the satellite passed through clouds of irregularities, the size of which were about 550 km. A model of the non-uniform distribution of irregularities in the ionosphere is proposed as a result of this study

Extreme Longitudinal Variability of Plasma Structuring in the Equatorial Ionosphere on a Magnetically Quiet Equinoctial Day

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22–23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American–Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground- and space-based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX, and a chain of GPS receivers are used in combination with the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) model to explore the relationship between the large-scale ionization distribution and small-scale irregularities at low latitudes in both the scintillating and nonscintillating longitude sectors. Our analysis shows that there are significant differences in the evolution of the ionization distributions during the evening hours, which are likely the result of differences in the daytime and postsunset vertical plasma drift in the two sectors. This study demonstrates the importance of USU-GAIM as a new tool for investigating longitudinal as well as day-to-day variability that is observed in the large-scale distribution of the ionosphere and how this relates to the occurrence of scintillation

Quark Mass Corrections to the Perturbative Thrust and its Effect on the determination of αs\alpha_s

We consider the effects of quark masses to the perturbative thrust in $e^+e^-$ annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of $\alpha_s$.Comment: Latex, 6 pages, 2 figures, minor change in text, added one referenc

1,3-Dipolar cycloadditions: Part III-Cycloaddition of C,N-diarylnitrones to N-cinnamoylpiperidines

105-11

A complex interplay between PGC-1 co-activators and mTORC1 regulates hematopoietic recovery following 5-fluorouracil treatment

In vitro stimulation of HSCs with growth factors generally leads to their depletion. Understanding the molecular mechanisms underlying expansion of HSCs in vivo following myeloablation could lead to successful expansion of HSCs ex vivo for therapeutic purposes. Current findings show that mTORC1 is activated in HSPCs following 5-fluorouracil treatment and that mTORC1 activation is dependent on mitochondrial ETC capacity of HSPCs. Moreover, expression of PGC-1 family members, proteins that regulate mitochondrial biogenesis, in HSPCs following 5-fluorouracil treatment changes; also, these proteins play a stage specific role in hematopoietic recovery. While PRC regulates HSCs' expansion during early recovery phase, PGC-1α regulates progenitor cell proliferation and recovery of hematopoiesis during later phase. During early recovery phase, PRC expression, mitochondrial activity and mTORC1 activation are relatively higher in PGC-1α−/− HSCs compared to WT HSCs, and PGC-1α−/− HSCs show greater expansion. Administration of rapamycin, but not NAC, during early recovery phase improves WT HSC numbers but decreases PGC-1α−/− HSC numbers. The current findings demonstrate that mTOR activation can increase HSC numbers provided that the energy demand created by mTOR activation is successfully met. Thus, critical tuning between mTORC1 activation and mitochondrial ETC capacity is crucial for HSC maintenance/expansion in response to mitogenic stimulation

Transforming growth factor-β1 modulates responses of CD34+ cord blood cells to stromal cell-derived factor-1/CXCL12

Disruption of stromal cell-derived factor-1 (SDF-1/CXCL12 [CXC chemokine ligand 12]) interaction leads to mobilization of stem/progenitor cells from bone marrow to circulation. However, prolonged exposure of CD34+ cells to SDF-1 desensitizes them to SDF-1. So how do cells remain responsive to SDF-1 in vivo when they are continuously exposed to SDF-1? We hypothesized that one or more mechanisms mediated by cytokines exist that could modulate SDF-1 responsiveness of CD34+ cells and the desensitization process. We considered transforming growth factor-β1 (TGF-β1) a possible candidate, since TGF-β1 has effects on CD34+ cells and is produced by stromal cells, which provide niches for maintenance and proliferation of stem/progenitor cells. TGF-β1 significantly restored SDF-1–induced chemotaxis and sustained adhesion responses in cord blood CD34+ cells preexposed to SDF-1. Effects of TGF-β1 were dependent on the dose and duration of TGF-β1 pretreatment. Phosphorylation of extracellular signal-regulated kinase 1 (Erk1)/Erk2 was implicated in TGF-β1 modulation of migratory and adhesion responses to SDF-1. Our results indicate that low levels of TGF-β1 can modulate SDF-1 responsiveness of CD34+ cells and thus may facilitate SDF-1–mediated retention and nurturing of stem/progenitor cells in bone marrow

Study of Field-Aligned Ionospheric E-Region Irregularities & Sporadic E at hf

70-75A continuous series of oblique backscatter observations at 19 MHz made at Plum Island, Massachusetts, (56° N invariant) over nearly half a solar cycle is utilized to derive the occurrence characteristics of aspect sensitive field-aligned irregularities in the E-Iayer and their association with ground backscattered echoes which are propagated via sporadic E(Es) reflection. Under quiet magnetic conditions, it is found that the field-aligned echo from E-Iayer heights [FAE (E)] displays a summer evening maximum in conjunction with the Es echo. A weak secondary maximum is observed in the winter with no detectable field-aligned structures being evident in the daytime Es. During disturbed magnetic conditions, the Es ground back-scattered echo is greatly suppressed together with a simultaneous increase of the FAE (E) which also appears in the day-time: no seasonal control is evident. These observations are discussed from the point of view of current plasma instability theories