An investigation of the feasibility of utilizing GPS/TEC“signatures” for near-real time forecasting of auroral-Epropagation at high-HF and low-VHF frequencies

VHF propagation on ⩽5300 km polar paths has been documented during the maximum phase of sunspot cycle 19. Mode analysis on these polar paths has shown that auroral-E ionization (AEI) supported some modes. Electron densities and plasma frequencies which could support AEI modes at frequencies up to 46 MHz have also been measured. Long distance VHF propagation from AEI has also been reported by radio amateurs using frequencies in the 2 m band in a “sidescatter mode”. An AEI experiment has been in operation between Wales (Alaska) and Fairbanks (Alaska) where a 75-watt CW transmitter located in Wales transmits the Morse letter “R” every 5 s, and a receiver in Fairbanks detects the 25.5 MHz signal whenever AEI is present near the midpoint of the 960 km path. Another experiment is underway using a GPS total electron content (TEC) receiving station at Fairbanks also using AEI data from the Wales-Fairbanks experiment. From this, the authors examine 58 passes of GPS satellites whose E-layer penetration points lie close to the midpoint of the Wales-Fairbanks path and find that there is a threshold value of TEC above which auroral-E (AE) propagation occurs. They also find that AEI propagation is strongly correlated with large- and medium-scale E-region structures in TEC determined by the GPS measurements. When TEC ionospheric structures are not present near the Wales-Fairbanks path midpoint, no AEI signal is received. The authors tentatively conclude that the occurrence of these specific TEC signatures may be utilized as predictors of AEI forward propagation on paths within and parallel to the auroral oval     

Medium-frequency skywave propagation at high latitudes: results ofa five-year study

Skywave transmission from selected standard AM broadcasting stations in the northern tier of the contiguous United States, Alaska and Canada were monitored near Fairbanks, Alaska from late 1981 to 1987. The objective of this work was to better understand, among other things, the effect of latitude on MF skywave propagation. A modern stable and selective receiver was electronically scanned continuously through 12 preselected frequencies in a five-minute cycle including a calibration. Frequent aural monitoring insured that the correct frequencies were being monitored. The main antenna used during this program was a 106-ft (35-m) vertical with modified top-hat and a 30-radial ground system. The daily, seasonal, and magnetic storm-time behavior of signal strength from selected stations was monitored over one-half of sunspot cycle 21. The latitudinal location of the auroral oval in the E-region in respect to the ionospheric reflection points on the propagation paths created profound variations of signal strength. There was also a very wide variation in signal strengths on long north-south paths as a function of sunspot cycle. The results are briefly discussed     

Single-cell sphingosine kinase activity measurements in primary leukemia

Sphingosine kinase (SK) is a promising therapeutic target in a number of cancers, including leukemia. Traditionally, SK has been measured in bulk cell lysates, but this technique obscures the cellular heterogeneity present in this pathway. For this reason, SK activity was measured in single cells loaded with a fluorescent sphingosine reporter. An automated capillary electrophoresis (CE) system enabled rapid separation and quantification of the phosphorylated and nonphosphorylated sphingosine reporter in single cells. SK activity was measured in tissue-cultured cells derived from chronic myelogenous leukemia (K562), primary peripheral blood mononuclear cells (PBMCs) from three patients with different forms of leukemia, and enriched leukemic blasts from a patient with acute myeloid leukemia (AML). Significant intercellular heterogeneity existed in terms of the degree of reporter phosphorylation (as much as an order of magnitude difference), the amount of reporter uptake, and the metabolites formed. In K562 cells, the average amount of reporter converted to the phosphorylated form was 39?±?26 % per cell. Of the primary PBMCs analyzed, the average amount of phosphorylated reporter was 16?±?25 %, 11?±?26 %, and 13?±?23 % in a chronic myelogenous leukemia (CML) patient, an AML patient, and a B-cell acute lymphocytic leukemia (B-ALL) patient, respectively. These experiments demonstrated the challenge of studying samples comprised of multiple cell types, with tumor blasts present at 5 to 87 % of the cell population. When the leukemic blasts from a fourth patient with AML were enriched to 99 % of the cell population, 19?±?36 % of the loaded sphingosine was phosphorylated. Thus, the diversity in SK activity remained even in a nearly pure tumor sample. These enriched AML blasts loaded significantly less reporter (0.12?±?0.2 amol) relative to that loaded into the PBMCs in the other samples (≥1 amol). The variability in SK signaling may have important implications for SK inhibitors as therapeutics for leukemia and demonstrates the value of single-cell analysis in characterizing the nature of oncogenic signaling in cancer. Figure

Phosphorylation of a fluorescent sphingosine kinase reporter was used to measure single-cell SK activity in primary cells from leukemic patients. Peripheral blood mononuclear cells as well as enriched leukemic blasts were analyzed.     

Characterization of inorganic coordination complexes by matrix-assisted laser desorption/ionization mass spectrometry

We report the direct laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis of four inorganic coordination complexes: monometallic [Ir(dpp)(2)Cl(2)](PF(6)), homonuclear trimetallic ([(bpy)(2)Ru(dpp)](2)RuCl(2))- (PF(6))(4), and heteronuclear [(tpy)Ru(tpp)Ru(tpp)RhCl(3)](PF(6))(4) and ([(bpy)(2)Ru(dpp)](2)IrCl(2))(PF(6))(5) (dpp = 2,3-bis-(2'-pyridyl)pyrazine, bpy = 2,2'-bipyridine, tpy = 2,2',6',2"-terpyradine, tpp = 2,3,5,6,-tetrakis-(2'-pyridyl)pyrazine). Spectral intensities and fragmentation patterns are compared and evaluated for instrument parameters, matrix selection, and matrix-to-analyte ratio. Direct LDI and MALDI mass spectra of the monometallic complex showed the same ion peaks and differed only in the relative peak intensities. Direct LDI of the trimetallic complexes produced only low-mass fragments containing one metal at most. MALDI spectra of the trimetallic complexes exhibited little fragmentation in the high-mass region (>1500 Da) and less fragmentation in the low-mass region compared to direct LDI. Significant fragments of the molecules were detected and identified, including ligand fragments, intermediate-mass fragments such as [Ru(tpy)](+), and molecular ions with varying degrees of PF(6)(-) loss ([M - n(PF(6))](+), where n = 1-3). A correlation exists between the solution-phase electrochemistry and the observed [M - n(PF(6))](+) series of peaks for the trimetallic complexes. Proper matrix selection for MALDI analysis was vital, as was an appropriate matrix-to-analyte ratio. The results demonstrate the applicability of MALDI-TOFMS for the structural characterization of labile inorganic coordination complexes.     

Auroral-E mode oblique HF propagation and its dependence on auroraloval position

The characteristics of 25.5 MHz one-hop mode propagation on a 950 km Alaskan path, over a one-year period shortly after sunspot maximum are presented as a function of the “planetary geomagnetic index-Kp”. The location of the E-region reflection point lies within the auroral oval for 3相似文献   

Work system change in technical organizations: problems andprospects for avoiding them

Flight controllers at the Johnson Space Center in Houston, Texas are developing a data system to use in support of Space Shuttle flights. The data system will significantly change the way the flight controllers do their jobs. The change is of interest to the engineering manager because it demonstrates how resistance to change can arise, even in highly technical organization, and illustrates useful strategies for overcoming this resistance. The authors focus on the changes brought about by the system, and how it is affecting the mechanical systems section, in particular     

Auroral and polar-cap ionospheric effects on radio propagation

Disturbances in the auroral and polar-cap ionosphere can have profound effects on radio signals traversing the high-latitude ionosphere (defined here as that latitudinal region poleward of approximately 55° corrected geomagnetic latitude). Some effects of the high-latitude ionosphere on polar radio paths were documented as early as the 1930s, but intensive investigations of this ionospheric global region started during the International Geophysical Year (IGY) 1957-1959. Starting in the mid-1960s it was realized that high-latitude ionospheric anomalies could affect radio signals from ELF through VHF on terrestrial and earth-space paths, especially during sunspot maximum, disturbed periods. A considerable effort has been made in the last two decades to model and predict the salient parameters of the auroral and polar-cap ionosphere. A somewhat lesser effort has been devoted to develop HF propagation programs which included high-latitude ionospheric effects. Salient past results are briefly reviewed, and developments in this field for the period 1970-91 are presented     

Transition management-a structured perspective

The various major models of transition management are presented and compared. They are organized into three distinct categories, based on their prescribed transition increment size, management structure, or method for influencing change in employees. Factors affecting the choice of a model are also provided. Through the careful selection of an appropriate method from each category, it is proposed that a hybrid transition structure has a better chance of success than the utilization of any one method