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Plasma desorption time-of-flight mass spectrometric elucidation of the mechanisms of adhesion enhancement between plasma-treated PEEK-carbon composite and an epoxyamine adhesive (1995)

Nsouli, B. ; Allali, H. ; Debre, O. ; [et al.]

New York, NY : Wiley-Blackwell

Rapid Communications in Mass Spectrometry 9 (1995), S. 1566-1571

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ISSN: 0951-4198

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Physics

Notes: Plasma desorption time-of-flight mass spectrometry (PD-TOFMS) using accelerated argon ions (9 MeV) has been successfully used for characterizing the surface modifications induced at the surface of poly(ether etherketone) (PEEK) by cold plasma treatments. While the intact polymer structure leads to the emission of negative ions from fragmentation of the repeat unit, the degradation of such a structure under plasma exposure gives rise to production of oxidized fragments. It is demonstrated that this production is highest for a plasma using a mixture of O2 and N2 (20:80), and that as a function of treatment duration, the rate of oxidation of the modified surface layer correlates with adhesive strength, at least in a first step. PD-TOFMS is used for analysis of the failure patterns of epoxyamine adhesive/PEEK/carbon composite in order to localize the fracture position. It is concluded that the increase of the cohesion of the interphase layer as a function of the plasma treatment duration leads to a shift from the interphase/PEEK interface to the bulk of the matrial.

Additional Material: 6 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/rcm.1290091520

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2

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Positron band structures for beryllium (1981)

Oriade, Joseph Oladipo

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 20 (1981), S. 891-896

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ISSN: 0020-7608

Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: We report on the band structure and wave functions of positrons, annihilating with electrons, from the thermalized state k+ = 0. We find that the bottom of the band to which the positron thermalizes in this metal is definitely nonambiguous. It is also found that even though the first few Bloch terms in the wave function can give the gross shape of the positron annihilation curve for this metal, the higher momentum components of high orders are definitely important if one is to assay the fine details of the curve.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/qua.560200412

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Assessment of IRI and IRI-Plas models over the African equatorial and low latitude region. (2016)

S. J. Adebiyi, I. A. Adimula, O. A. Oladipo, B. W. Joshua

Wiley

In: Journal of Geophysical Research JGR - Space Physics

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Publication Date: 2016-07-21

Description: A reliable ionospheric specification by empirical models is important to mitigate the effects of the ionosphere on the operations of satellite based positioning and navigation systems. This study evaluates the capability of the International Reference Ionosphere (IRI) and IRI extended to the plasmasphere (IRI-Plas) models in predicting the Total Electron Content (TEC) over stations located in the Southern hemisphere of the African equatorial and low latitude region. TEC derived from Global Positioning System (GPS) measurements were compared with TEC-predicted by both the IRI-Plas 2015 model and the three topside options of the IRI 2012 model [i.e. NeQuick (NeQ), IRI 2001 corrected factor (IRI-01 Corr) and the IRI 2001(IRI-01)]. Generally, the diurnal and the seasonal structures of modeled-TEC follow quite well with the observed-TEC in all the stations, although with some upward and downward offsets observed during the daytime and nighttime. The prediction errors of both models exhibit latitudinal variation and these showed seasonal trends. The values generally decrease with increase in latitude. The TEC data-model divergence of both models is most significant at stations in the equatorial region during the daytime and nighttime. Conversely, both models demonstrate most pronounced convergence during the nighttime at stations outside the equatorial region. The IRI-Plas model, in general, performed better in months and seasons when the three options of the IRI model underestimate TEC. Factors such as the height limitation of the IRI model, the inaccurate predictions of the bottomside and topside electron density profiles were used to explain the data-model discrepancies.

Print ISSN: 0148-0227

Topics: Geosciences , Physics

Published by Wiley on behalf of American Geophysical Union (AGU).

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Magnetic storm effects on the variation of TEC over Ilorin an equatorial station (2014)

J. O. Adeniyi, P. H. Doherty, A. O. Oladipo, O. Bolaji

Wiley

In: Radio Science

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Publication Date: 2014-10-25

Description: We have used Total Electron Content (TEC) derived from dual frequency GPS receivers to study magnetically quiet and storm time variations of the ionosphere at Ilorin(8.47°N, 4.68°E), an equatorial station in the Africa sector. Four years (2009-2012) data were used for the study. The result on the quiet-time variation of the ionosphere showed that diurnal variation of TEC is not symmetrical about noon. This is a departure from a typical Chapman variation. Daytime maximum occurred after local noon (13-16 LT) for all the seasons and at all solar activity levels considered. A significant effect of solar activity variation was observed on the seasonal trend in 2011. The tendency for magnetic storms to cause increases in TEC is much greater than those of decreases. Daytime maximum TEC usually occurred closer to the noon time during storm periods when compared to those of quiet periods. Maximum percent change in TEC on storm days varied from about 25 to 131 percent.

Print ISSN: 0048-6604

Electronic ISSN: 1944-799X

Topics: Geosciences , Physics

Published by Wiley on behalf of American Geophysical Union (AGU).

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Large-scale Ionospheric Irregularities Occurrence at Ilorin, Nigeria (2014)

O.A. Oladipo, J.O. Adeniyi, A.O. Olawepo, P.H. Doherty

Wiley

In: Space Weather

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Publication Date: 2014-04-15

Description: Ionospheric irregularities are a regular occurrence at the equatorial latitude during the post sunset hours especially during high solar activity. These irregularities could pose serious challenges to satellite-based navigation and positioning applications by causing fading and degradation of trans-ionospheric signals passing through these irregularities. We have investigated large-scale ionospheric irregularities occurrence at Ilorin, Nigeria (Lat. = 8.48 °N, Long. = 4.67 °W, Dip = 4.1 °S), a station located within the equatorial region in the African sector. The index used in this study is the rate of change of TEC (ROT) derived from 30 seconds RINEX data obtained using a dual frequency GPS receiver (i.e. NovAtel GPStation-2). The study covers a period of four years (2009 to 2012). The results obtained showed that large-scale irregularities occur between March and November and are more pronounced between 1900 LT and 2400 LT. The irregularities were observed to show two peaks; one in March and the other in September. Solar activity trend was also observed. The irregularities level around the peaks seems to increase with solar activity. Although the study covered a period of four years, the period could be regarded as the increasing phase of the solar cycle 24.

Print ISSN: 1539-4964

Electronic ISSN: 1542-7390

Topics: Geosciences , Physics

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Paraoxonase 1 activity in subchronic low-level inorganic arsenic exposure through drinking water (2014)

Olusegun K. Afolabi, Adedoja D. Wusu, Olufunmilayo O. Ogunrinola, Esther O. Abam, David O. Babayemi, Oluwatosin A. Dosumu, Okechukwu B. Onunkwor, Elizabeth A. Balogun, Olusegun O. Odukoya, Oladipo Ademuyiwa

Wiley

In: Environmental Toxicology

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Publication Date: 2014-08-04

Description: ABSTRACT Epidemiological evidences indicate close association between inorganic arsenic exposure via drinking water and cardiovascular diseases. While the exact mechanism of this arsenic-mediated increase in cardiovascular risk factors remains enigmatic, epidemiological studies indicate a role for paraoxonase 1 (PON1) in cardiovascular diseases. To investigate the association between inorganic arsenic exposure and cardiovascular diseases, rats were exposed to sodium arsenite (trivalent; 50, 100, and 150 ppm As) and sodium arsenate (pentavalent; 100, 150, and 200 ppm As) in their drinking water for 12 weeks. PON1 activity towards paraoxon (PONase) and phenylacetate (AREase) in plasma, lipoproteins, hepatic, and brain microsomal fractions were determined. Inhibition of PONase and AREase in plasma and HDL characterized the effects of the two arsenicals. While the trivalent arsenite inhibited PONase by 33% (plasma) and 46% (HDL), respectively, the pentavalent arsenate inhibited the enzyme by 41 and 34%, respectively. AREase activity was inhibited by 52 and 48% by arsenite, whereas the inhibition amounted to 72 and 67%, respectively by arsenate. The pattern of inhibition in plasma and HDL indicates that arsenite induced a dose-dependent inhibition of PONase whereas arsenate induced a dose-dependent inhibition of AREase. In the VLDL + LDL, arsenate inhibited PONase and AREase while arsenite inhibited PONase. In the hepatic and brain microsomal fractions, only the PONase enzyme was inhibited by the two arsenicals. The inhibition was more pronounced in the hepatic microsomes where a 70% inhibition was observed at the highest dose of pentavalent arsenic. Microsomal cholesterol was increased by the two arsenicals resulting in increased cholesterol/phospholipid ratios. Our findings indicate that decreased PON1 activity observed in arsenic exposure may be an incipient biochemical event in the cardiovascular effects of arsenic. Modulation of PON1 activity by arsenic may also be mediated through changes in membrane fluidity brought about by changes in the concentration of cholesterol in the microsomes. © 2014 Wiley Periodicals, Inc. Environ Toxicol, 2014.

Print ISSN: 1520-4081

Electronic ISSN: 1522-7278

Topics: Energy, Environment Protection, Nuclear Power Engineering

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Ionospheric Scintillation Activity over Ilorin, Nigeria (2018)

O. A. Oladipo, J. O. Adeniyi, P. H. Doherty, S. M. Radicella, I. A. Adimula, A. O. Olawepo

Wiley

In: Space Weather

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Publication Date: 2018-01-24

Description: Scintillation of radio waves in the L-band frequency is a regular occurrence at the equatorial and auroral regions at night most especially during high solar activity periods. Scintillation is caused by plasma density irregularities and this could cause loss of lock of GNSS signals leading to impairment of the applications that rely on this system. A study on the occurrence of scintillation activity over Ilorin (latitude = 8.48 °N, longitude = 4.67 °W, Geomagnetic Latitude = 1.89 °S), Nigeria was done using S4 index data from NovAtel GPStation-2 receiver (2009 – 2012) and NovAtel GPStation-6 receiver (August 2013 – December 2016) which are both located at this station. The solar maximum period of the solar cycle 24 is located well within the period of this investigation; hence this study provides opportunity to see the occurrence pattern of scintillation during different seasons as well as the pattern from low solar activity to solar maximum. The results obtained showed that scintillation occurs between 21:00 LT and 04:00 LT at the peak of the occurrence in 2014. The time window of occurrence decreases with decrease in solar activity. Similarly, scintillation activity was observed to be more regular during high solar activity and it has two peaks of occurrence in March and October. A solar activity trend was observed in scintillation occurrence; scintillation activity increases with increase in the level of solar activity.

Print ISSN: 1539-4964

Electronic ISSN: 1542-7390

Topics: Geosciences , Physics

Published by Wiley on behalf of American Geophysical Union (AGU).

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