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Papers by Mark David

Journal of Atmospheric and Solar Terrestrial Physics, Mar 1, 2002

This study revisits and attempts to quantify the effects of high-latitude electric field penetrat... more This study revisits and attempts to quantify the effects of high-latitude electric field penetration on the mid-latitude ionosphere. These penetration electric fields (PEFs) are strongest during geomagnetically dynamic and disturbed conditions. The consequences of PEFs arise principally from the induced vertical drift of the F-layer from the eastward electric field component. Both positive and negative storm phases are associated with the PEF. Although no readily available description of the PEF exists, observational and modeling results are combined to provide a crude model. The largest uncertainty arises from a lack of knowledge of whether PEFs are always short lived (less than 1h) or are a persisting feature of disturbed conditions. According to simulations with the Utah State University time dependent ionospheric model (TDIM), under Kp=3 conditions the PEF readily generates a factor of 2 increase in the pre-midnight ionosphere F-layer density (positive storm phase). For Kp=5 conditions this positive phase is further enhanced to produce almost an order of magnitude increase in F-region density. Negative storm phases, F-layer density decreases, are also present in the pre-dawn and pre-noon sectors. The pre-dawn negative storm phase can reach a factor of 10 for Kp=5 conditions while the pre-noon depletions are a few 10s of percent. These large density changes have operational impact on systems using coordinate registration based upon Global Positioning Satellite (GPS) measurements. GPS satellite-to-ground radio paths pass through the ionosphere at different angles relative to the zenith and hence have different propagation corrections dependent upon the paths total ionospheric electron content. Factors of 2 change in electron density corresponds to tens of centimeters to meters correction errors in coordinate registration position finding. Corrections this large are a potentially insurmountable obstacle for the GPS based wide area augmentation system (WAAS) designed to provide the airline industry over the USA position accuracy of only a few centimeters. Examples of mid-latitude ray tracing at 5 and 9MHz are used to demonstrate the frequency sensitivity and coordinate registration dependence upon these factors of 2 ionospheric density changes. Operational systems such as the over-the-horizon (OTH) radar is very sensitive to such dependences and hence upon the mid-latitude PEF.

Water Air Soil Pollut, 1986

Abstract. Solution chemistry was measured in two major inlets, lake water column, lake outlet, an... more Abstract. Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H +, sulfate-S, and A1 and smaller concentrations of ...

Water Air Soil Pollut, 1987

We compiled and summarized current literature on S input/output budgets for intensively studied s... more We compiled and summarized current literature on S input/output budgets for intensively studied sites and soil plots in the U.S. and Canada and found S retention to be related to both soil order and extent of the last glaciation (Wisconsinan). Zero net retention is associated with Spodosols and was found only at sites north of the limit of Wisconsinan glaciation. Sites south of the limit of glaciation appear to be retaining from 20 to 90% of incoming S. These findings support the hypothesis that there exist regional variations in S retention in North America. Such variations are important in determining and predicting effects of acidic deposition on surface water chemistry.

Geophysical Monograph Series, 2000

Lipids, 1989

Phospholipid content and fatty acid composition of human heart were determined on 36 biopsy speci... more Phospholipid content and fatty acid composition of human heart were determined on 36 biopsy specimens collected during open heart surgery. The main phospholipid classes, phosphatidylcholine (PC}, phosphatidylethanolamine {PE}, diphosphatidylglycerol {DPG}, and sphingomyelin (SPH} were separated by HPLC, quantified, and converted to fatty acid methyl esters which were chromatographed on capillary GLC columns. Sex and age (mainly 40-70} of patients had no significant influence on the relative distribution of phospholipid classes and only a slight effect on fatty acid composition. Incorporation of trans 18:1 in phospholipid classes was low. cis and trans octadecenoic isomers seemed to be selectively incorporated, the A9 and hll cis or trans isomers being predominant. Human and rat data were compared, and some species differences were noticed. In human PC, palmitic acid is higher and stearic acid much lower than in rat PC. Saturated dimethyl acetals (16:0 and 18:0} in PC and PE were greater for humans. Incorporation of 20:4 n-6 in human PE is higher than in rat PE. Lipids 21, 775-780 (1989}.

Leukemia, 1997

primary biliary cirrhosis, 6 rheumatoid arthritis, 7 autoimmune antibodies, providing a possible ... more primary biliary cirrhosis, 6 rheumatoid arthritis, 7 autoimmune antibodies, providing a possible mechanism for the autothyroiditis, 8,9 and systemic lupus erythematosus. 10 Kobayashi immune hemolytic anemia occurring during the course of Bet al 11 demonstrated the ability of transferring human chronic CLL. In order to confirm this hypothesis, we attempted to translymphocytic leukemia cells to SCID mice. Red cell autoantifer human B-CLL with AIHA to immunodeficient mice. Peripheral blood mononuclear cells (PBMC) from 11 B-CLL patients body production in the Hu-SCID by mononuclear cells from suffering from AIHA were transplanted into the peritoneal cava patient with ulcerative colitis and AIHA was observed by ity of lethally irradiated Balb/c mice reconstituted with SCID Yates et al. 12 In contrast PBMC from patients with AIHA failed bone marrow. Chimeric mice generated from PBMC of these to reconstitute SCID mice and to produce autoantibodies. 13 patients (in stage III-IV of the disease) exhibited an engraftment Recently, Lubin et al 14 described a new approach enabling profile with dominance of tumor cells and minuscule levels of engraftment of human PBMC in normal strains of mice or rats T cells. Eighty-five percent of the chimeric mice generated from 10 out of the 11 B-CLL patients with Coombs'-positive AIHA, following split-dose lethal irradiation. The recipients are produced human Ig with anti-human red cell specificity as initially converted into SCID-like animals by means of bone detected by indirect anti-globulin test. In addition, anti-red cell marrow transplantation from SCID donors and subsequently auto-antibodies were produced in 36% of chimeric mice generare infused with 50-100 × 10 6 human PBMC. These chimeric ated from PBMC of Coombs'-negative B-CLL. In contrast, conmice allow an effective and rapid engraftment of human cells, trol experiments in which splenic cells from idiopathic AIHA or enabling their functional study early after transplant. PBMC from normal donors were transplanted, failed to produce anti-RBC. This in vivo model further supports the relationship

Journal of Molecular and Cellular Cardiology, 1985

G. ROCQUELIN, L. GUENOT, E. JUSTRABO, A. GRYNBERO, M. DAVID. Fatty Acid Composition of Human Hear... more G. ROCQUELIN, L. GUENOT, E. JUSTRABO, A. GRYNBERO, M. DAVID. Fatty Acid Composition of Human Heart Phospholipids: Data from 53 Biopsy Specimens. Journal of Molecular and Cellular Cardiology (1985) 17, 769-773.

Journal of Geophysical Research, 2000

A global substorm electrodynamic model and a global ionospheric model were coupled in order to st... more A global substorm electrodynamic model and a global ionospheric model were coupled in order to study ionospheric dynamics during substorms, with the focus on small-scale substorm electrodynamic and plasma structures. The simulation results show that in the expansion phase, structured precipitation and channeled field-aligned currents quickly develop in the substorm onset region. The Hall and Pedersen conductance ratio in the region increases significantly, and the magnetospheric field-aligned currents are mainly closed by highly structured Hall currents. Correspondingly, the plasma in the ionosphere also undergoes significant changes during a substorm and is highly structured in both the horizontal and vertical directions. In the substorm onset region, there are spatially separated small-scale Ti and Te hot spots, downward E×B drifts, decreased total electron contents, and a lowered ionosphere. Also, there is a significant O+->NO+ conversion, leading to a great increase of NO+ and a lowering of the O+ peak height. These small-scale electrodynamic and plasma structures are very important for more realistically simulating the ionospheric dynamics during substorms. These results not only help to elucidate the multiscale ionospheric responses to substorms but also provide a theoretical guidance and cautions for the interpretation of various substorm observational data.

Journal of Geophysical Research, 2002

1] When plasma in the polar cap F region becomes highly structured, patches, irregularities, and ... more 1] When plasma in the polar cap F region becomes highly structured, patches, irregularities, and scintillations of HF signals may be observed. The topic of this paper is not the mechanism for structuring or distributing the plasma but rather the source of the plasma. By understanding the plasma source we gain insight into the specification and forecasting of ionospheric structures and irregularities as required for space weather applications. The two major sources of polar cap F region plasma are the solar EUV radiation and the auroral precipitation. The region over which solar EUV production occurs is readily modeled. In contrast, the auroral precipitation is not subject to diurnal or seasonal dependences in the same predictable manner; the auroral precipitation can almost be viewed as stochastic within certain geomagnetic coordinate constraints. In this study we use a physical model to separate the effects of solar EUV and auroral precipitation. We find that the auroral contribution does provide a far-from-negligible ''baseline'' level of polar cap F region plasma, upon which is superimposed the UT and seasonally dependent TOI. This baseline level of ionization is very difficult to predict or forecast since it is determined by plasma flux tube histories through extended regions of the auroral oval over several hours. This result raises the need for more advanced auroral precipitation modeling in order to obtain improved space weather specification. The inclusion of soft auroral precipitation is especially important since it can be a significant source of F region plasma.

Journal of Atmospheric and Solar-Terrestrial Physics, 2004

Sub-auroral polarization stream (SAPS) is the name given to an enhanced westward plasma flow in t... more Sub-auroral polarization stream (SAPS) is the name given to an enhanced westward plasma flow in the night-time mid-latitude ionosphere during geomagnetically disturbed conditions. A description of the SAPS electric field, based on observations from the Millstone Hill incoherent scatter radar, is used here to create a driver for the Utah State University time-dependent ionospheric model in order to assess the

Journal of Atmospheric and Solar-Terrestrial Physics, 2000

The 3-h K p index is widely used as a measure of geomagnetic activity for ionospheric studies. Sp... more The 3-h K p index is widely used as a measure of geomagnetic activity for ionospheric studies. Speci®cally, it is the planetary index used to determine the geomagnetic dependence of statistical auroral patterns and the convection electric ®eld for certain models. Its quasi anti-logarithm, the A p index, is similarly used in statistical models of the neutral atmosphere and neutral wind. Physics-based ionospheric models, such as the Utah State University (USU) Time-Dependent Ionospheric Model (TDIM), use these statistical models as magnetospheric and thermospheric inputs. However, the 3-h time interval between index computations is now considered a shortfall with regard to specifying and forecasting phenomena known to have faster time constants, e.g., auroral electrojet variations during a substorm. Therefore, these indices have been targeted for high-time resolution development; we have developed such indices in . We now use our 15-minute station``K-like'' index to determine the eect of introducing high-time resolution magnetic¯uctuations into the TDIM inputs. This study represented the highlatitude ionosphere by a grid of 1484 locations, and was carried out for a geomagnetic storm period during solar maximum and``simulated'' winter solstice conditions. We found that, for ®xed Interplanetary Magnetic Field (IMF) B y aB z ratio, driving the TDIM with our 15-minute``K-like'' index altered the average high-latitude N m F 2 value by as much as 8% (vs. the average N m F 2 obtained using a 3-h index to drive the TDIM). More signi®cantly, the standard deviation of the N m F 2 variations was up to 35%. Under some conditions, the average N m F 2 was changed by up to 30% with a standard deviation of over 60%. However, the eect of selecting dierent convection patterns that represented three southward IMF B z orientations led to larger eects. The high-latitude average N m F 2 changed by 10% or less, but the spread in the distribution always ranged from standard deviations of 29 to 68%. These results indicate that there is a substantial need to consider both short-term magnetic¯uctuations and inclusion of real-time IMF data in the inputs to ionospheric models. 7

Journal of Atmospheric and Solar-Terrestrial Physics, 2001

Neutral wind upwelling events are well documented in both the northern and southern high latitude... more Neutral wind upwelling events are well documented in both the northern and southern high latitude ionosphere. The vertical winds in the F-region frequently exceed 100 m=s, and winds in excess of 200 m=s have been observed. These upwelling events occur in a latitudinal band of 4 • -6 • width that extends in local time in the midnight-morning sector; this band always lies poleward of the auroral precipitation. Using the time dependent ionospheric model (TDIM), a series of sensitivity simulations are carried out, based on observational constraints provided by the spectacular upwelling event seen at both the Mawson and Davis stations in the Antarctic on 08 June 1997 . The model simulations indicate that the F-layer density at any given point may either increase or decrease during an upwelling event, depending upon the past history of the plasma ux tube. Because this past history of the F-layer convection is unknown for the speciÿc upwelling events a detailed case study cannot be undertaken. Instead a series of sensitivity simulations based upon a range of possible convection histories will be studied to determine the relative e ect of the upwelling. The absolute density is not dependent upon solar EUV production because of winter conditions, but is sensitive to the auroral electron precipitation. The best F-layer indicator of the upwelling is the height of the layer, hmF2. For upwelling events with vertical drifts of 100 m=s hmF2 can be increased by 100 km in 10 min. Upon leaving an upwelling region, the hmF2 almost as rapidly decreases to its normal height. Resulting from this lifting of the O + layer is the reduction in O + recombination and 630-nm emission; this latter consequence is observed as a standard feature of the upwelling events. In the topside ionosphere the electron density is responsive to the upwelling. The total electron content (TEC) is not, in general, sensitive to the uplifting events, however, low elevation slant path GPS TEC measurements might well detect the rapid uplifting of the F-layer.

International Journal of Cancer, 1984

The pathological features of 155 adult patients with soft-tissue sarcomas were studied retrospect... more The pathological features of 155 adult patients with soft-tissue sarcomas were studied retrospectively, in an attempt to set up a grading system for these tumors. As the first step, seven histological criteria (tumor differentiation, cellularity, importance of nuclear atypia, presence of malignant giant cells, mitosis count, pattern of tumor necrosis and presence of vascular emboli) were evaluated in a monofactorial analysis. Five of these (tumor differentiation, cellularity, mitosis count, tumor necrosis, and vascular emboli) were correlated with the advent of metastases and with survival. A multivariate analysis, using a Cox model, selected a minimal set of three factors (tumor differentiation, mitosis count, and tumor necrosis) the combination of which was necessary and sufficient to retain all the prognostic information. A grading system was elaborated, which turned out to be correlated with the advent of metastasis and with patients' survival. A second multivariate analysis introducing clinical prognostic features showed that the histological grade was the most important prognostic factor for soft-tissue sarcomas. Thus, this grading system appears to be highly interesting because of its prognostic value and the facility of its elaboration. However, its reproducibility should be tested.