School of Physical and Mathematical Sciences

Permanent URI for this community

http://197.255.125.131:4000/handle/123456789/23032

Browse

Now showing 1 - 20 of 669

The endomorphism ring of pointed separable torsion-free Abelian groups
(Journal of Algebra, 1978-12) Webb, M.C.
This paper studies the endomorphism rings of separable torsion-free Abelian groups. Baer [l] defined an Abelian group to be separable if given any finite subset of the group there is a complctcly dccomposablc direct summand of the group containing that subset. The endomorphism rings of such groups have attracted the attention of several workers, notably that of Liebert [7] who characterized those rings isomorphic to the endomorphism ring of some separable Abelian p-group. Moreover, Baer [2] and Kaplansky [6] proved that if two torsion Abelian groups have isomorphic endomorphism rings, then the groups themselves are isomorphic. Results corresponding to these have been proven for homogeneous torsion- free Abelian groups, with Metelli and Salce [8] obtaining a characterization of the endomorphism rings of those groups and Hauptfleisch [5] showing that if two such groups have isomorphic endomorphism rings, then they are almost isomorphic. The meaning of “almost” becomes clear in Theorem 3, from which Hauptfleisch’s result follows as a corollary. We consider only torsion-free Abelian groups and any undefined concepts are standard ones from Fuchs [3]. We define a group to be pointed if the set of types of its rank-l summands contains a unique minimal type, when WC say that the group is pointed in that type. We say a group is idempointed if it is pointed in an idempotent type. Clearly homogeneous separable groups are pointed since all elements of the group have the same type and the group has at least one rank-l summand. We characterize the rings isomorphic to the endomorphism ring of some
Helly-type theorems about sets
(Discrete Mathematics, 1980-02) Fisk, S.; Abbw-Jackson, D.; Kleitman, D.
Suppose that G is a graph. A 1-factor is a set of edges of G such that every vertex of G meets exactly one of its edges. Suppose that we have a set Y of 1-factors of G such that any two 1-factors of Y have an edge in common. We investigate the following questions: 1. (1) How large may Y be? 2. (2) When is there necessarily an edge contained in all the members of Y? We answer these questions in the case that G is the complete graph on 2n vertices K2n or the complete bipartite graph Kn, n. In the next section we study the first question; the third section is devoted to the second. In the final section we show that B2(Kn,n) ≈ Kn,n and B2(K2n) ≈ K2n. We end with some unsolved problems. In the remainder of this section we identify the 1-factors of the two graphs, state our results, and recall the definitions of the space of colorings of G. B(G). (See [4]. © 1980.
Geochemistry of Lower Cretaceous sediments, Inner Zone of Southwest Japan: Constraints on provenance and tectonic environment
(Geochemical Journal, 2000-01) Asiedu, D.K.; Suzuki, S.; Nogami, K.; Shibata, T.
A geochemical study was carried out on Lower Cretaceous sedimentary rocks of the Wakino Subgroup, Kenseki Formation, and Sasayama Group, distributed in the Inner Zone of Southwest Japan. The chemical characteristics of the Lower Cretaceous sediments indicate that these rocks are immature first-order sediments derived from igneous and/or meta-igneous rocks of predominantly felsic composition. The sediments from the Kenseki Formation and the Sasayama Group, however, show high Cr and Ni abundances, suggesting a significant contribution of detritus from ultramafic rocks. Weathering at the source areas was moderate. The high Th/U ratios (mostly >3.8), negative Eu anomalies (Eu/Eu(*) between 0.67 and 0.93) and Th/Sc ratios (mostly between 0.5 and 1) of the Lower Cretaceous sediments suggest their derivation dominantly from an old upper crust with minor amounts of young arc-derived detritus. The major, trace and rare earth element compositions imply that deposition took place in an active continental margin environment. The small amounts of young arc-derived material in the sediments support the inference by other workers that arc magmatism was not so prominent in Southwest Japan during the early Cretaceous.
Provenance of sandstones from the Lower Cretaceous Sasayama Group, Inner Zone of Southwest Japan
(Sedimentary Geology, 2000-03) Asiedu, D.K.; Suzuki, S.; Shibata, T.
Modal analysis and phase chemistry of sandstones of the Lower Cretaceous Sasayama Group, Southwest Japan, indicate that the detritus were derived from heterogeneous sources that include medium- to high-grade metamorphic, mafic-ultramafic, and acidic magmatic rocks. Garnet geochemistry suggests their derivation from epidote-amphibolite to granulite facies metamorphic rocks. Sphene and chlorite geochemistry suggests their derivation from mafic rocks. Chemical compositions of chromian spinel indicate input from Alpine-type peridotite. The chemistry of the chromian spinel further suggests that the Alpine-type peridotite source was most probably formed under an oceanic back-arc basin setting rather than mid-oceanic ridge setting. Chemical compositions of chromian magnetite indicate that the Alpine-type peridotite provenance was subjected to metamorphism of up to the lower amphibolite facies prior to erosion and transport. The metamorphic and granitic rocks of the Hida-Oki Terrane, ophiolitic rocks of the Sangun-Renge Terrane, and rhyolitic rocks from uncertain terrane (Akiyoshi?) are most probably the major source of detritus to the Sasayama basin. The basin is most likely a strike-slip basin that formed along the eastern margin of the Asian continent. (C) 2000 Elsevier Science B.V. All rights reserved.
Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, Japan
(Island Arc, 2000-03) Asiedu, D.K.; Suzuki, S.; Shibata, T.
The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high-grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote-amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle-derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted.
Production and characterization of titanium doped electrolytic manganese dioxide for use in rechargeable alkaline zinc/manganese dioxide batteries
(Journal of Power Sources, 2000-04) Nartey, V.K.; Binder, L.; Huber, A.
A preliminary screening test of some organo-titanium compounds was conducted. The aim was to find their chemical stability in the electrolyte used for manganese dioxide production. Titanium doped electrolytic manganese dioxide (Ti-EMD) samples were prepared using suitable organo-titanium compounds and a special fine-grained titanium dioxide. The Ti-EMD samples were characterized by conducting physical, chemical and electrochemical tests on them. Physical tests included: X-ray diffraction analysis and BET surface area determination. Chemical test conducted was the determination of titanium content of samples. The electrochemical characterization involved: cyclic voltammetry, galvanostatic discharge and application of sample in real cell situations. Doped samples performed well in comparison with TOSOH-Hellas GH-S (commercial battery grade electrolytic manganese dioxide).
Speciation of As(III) and As(V) in some Ghanaian gold tailings by a simple distillation method
(Water, Air, and Soil Pollution, 2000-09) Ahmad, K.; Carboo, D.
As(III) and As(V) in goldtailings and river-bed sediments from Obuasi were determined by distillation of arsenic as AsCl3. Results yielded 3750±426 mg kg-1 (45.2%) for As(V) and 3050±66 mg kg-1 (36.7%) for As(III) in the tailings. In the river-bed sediments, one spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 1447±51 mg kg-1 (100%), whilst a second spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 2976±51 mg kg-1 (100%). Using arsenic oxide standards, the recovery of As(III) and As(V) in the trioxide were 94.8 and 0.6% respectively. In a mixture of the two oxides, the recovery of As(III) was 87.6% with practically no interference from As(V). Total As content of the tailings was determined by neutron activation analysis (NAA) to be 8305±75 mg kg-1.As(III) and As(V) in gold tailings and river-bed sediments from Obuasi were determined by distillation of arsenic as AsCl3. Results yielded 3750±426 mg kg-1 (45.2%) for As(V) and 3050±66 mg kg-1 (36.7%) for As(III) in the tailings. In the river-bed sediments, one spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 1447±51 mg kg-1 (100%), whilst a second spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 2976±51 mg kg-1 (100%). Using arsenic oxide standards, the recovery of As(III) and As(V) in the trioxide were 94.8 and 0.6% respectively. In a mixture of the two oxides, the recovery of As(III) was 87.6% with practically no interference from As(V). Total As content of the tailings was determined by neutron activation analysis (NAA) to be 8305±75 mg kg-1.A simple distillation method based on the volatility of AsCl3 was used to examine the speciation of trivalent and pentavalent arsenic in mine tailings and river sediments at Obuasi, Ghana. Results showed that the sum of As(III) and As(V) concentrations in the tailings differed by 1495 mg/kg from the total As concentration of 8305 mg/kg. No As(III) was found in river-bed sediments because all As(III) had been converted to As(V).
Magnetoresistance and spin fluctuation resistivity of α-Mn thin films and their relationship to substrate temperatures
(Thin Solid Films, 2000-09) Boakye, F.; Nkum, R.K.; Adanu, K.G.
Electrical resistivity measurements in thermally evaporated α-Mn thin films have been carried out between 10 and 1.4 K using the van der Pauw four probe technique in magnetic fields up to 9 T. The results reveal a wide variation of the anomalous coefficient of T2 at low temperatures. This variation is found to be influenced by substrate temperatures. At high substrate temperatures (approximately 300 °C) a film whose residual resistivity in the expected range (0.10-0.85 μΩm) of bulk α-Mn is formed and its anomalously large coefficient of T2 at low temperatures is found to decrease appreciably with magnetic field. The magnitude of the resistivity at such low temperatures does not change for films coated on substrates held below 200 °C in fields up to 9 T. In such films the coefficient of T2 is negative and the magnitude of the coefficient of T2, (A) increases with decreasing substrate temperatures.
DL-Arginine monohydrate at 100 K
(Acta Crystallographica, Section C: Crystal Structure Communications, 2000-11) Kingsford-Adaboh, R.; Grosche, M.; Dittrich, B.; Luger, P.
In the title compound, C6H14N4O2·H2O, the α-amino group is neutral. The molecular side chain including the guanidinium group is not fully extended, having a near gauche-gauche conformation [χ3 = 59.0 (1)°; χ4 = 72.8 (1)°]. The network of hydrogen bonds stabilizing the crystal lattice includes those formed between the deprotonated and negatively charged α-carboxylate groups and the positively charged amino groups of the guanidinium group of neighbouring molecules. N-H···O double bond C and water-mediated N-H···O hydrogen bonds link individual molecules to produce pairs of spiral motifs laterally connected by N-H···O and C-H···O hydrogen bonds.
(E)- and (Z)-Foeniculin, Constituents of the Leaf Oil of a New Chemovariety of Clausena anisata
(Journal of Essential Oil Research, 2000-11) Garneau, F.-X.; Pichette, A.; Gagnon, H.; Jean, F.-I.; Addae-Mensah, I.; Osei-Safu, D.; Asomaning, W.A.; Oteng-Yeboah, A.; Moudachirou, M.; Koumaglo, K.H.
The leaf oils of Clausena anisata Hook. f. collected from Pokuase, Ghana, were found to contain (E)-foeniculin as a major constituent (>78%) in 17 of 19 samples. (E)-anethole was the major constituent of the two other samples (57% and 67%) with (E)-foeniculin as the second most important compound (38% and 29%). The identity of the new natural product (Z)-foeniculin, present in small amounts (0.2-1.4%), was based on a comparison of retention indices and mass spectra with those of a synthesized sample whose spectroscopic data, reported here for the first time, are in agreement with the proposed structure. Two other minor constituents were identified as the rarely encountered natural products dictagymnin (1-20%) and 4-(3-methyl-2-butenyl)oxybenzaldehyde (0-0.2%). © 2000, Taylor & Francis Group, LLC. All rights reserved.
Composotion and provenance of the upper Cretaceous to eocone sandstones in Central Palawan, Philippines: Constraints on the tectonic development of Palawan
(Island Arc, 2000-12) Suzuki, S.; Takemura, S.; Yumul, G.P.; David, S.D.; Asiedu, D.K.
Sandstones from the Upper Cretaceous to Eocene succession of Central Palawan are rich in quartz grains and acidic volcanic rock fragments. Potassium feldspar grains and granitic rock fragments are commonly observed. The moderate to high SiO2 and low FeO plus MgO contents of the sandstones support the proposal that clasts were derived from a continental source region. Southern China (Kwangtung and Fukien regions) is inferred to be the source area of the sandstones. The sedimentary facies of the Upper Cretaceous to Eocene succession consist of turbidite and sandstones, suggesting that they were deposited in the deep sea portions of submarine-fans and basin plains situated along a continental margin. These features indicate that the Upper Cretaceous to Eocene succession of the Central Palawan were derived and drifted from the southern margin of China. The tectonic history related to the formation of Palawan Island is also discussed.
The crystal structures of O,O-Dimethylalpinumisoflavone and 5-O-Methyl-4′-O-(3-methyl-but-2-en-1-yl)alpinumisoflavone
(Crystal Research and Technology, 2001-01) Kingsford-Adaboh, R.; Osei-Fosu, P.; Asomaning, W.A.; Weber, M.; Luger, P.
The petrol extract of the rootbark of Milletia Thonningii obtained by column chromatography afforded sixteen different crystalline samples to be isolated. The crystal structures of two of these compounds, O,O-Dimethylalpinumisoflavone (I) and 5-O-Methyl-4′-O-(3-methyl-but-2-en-1-yl)alpinumisoflavone (II) are being reported here. (II) has two independent molecules in the asymmetric unit and differs from (I) in a longer side chain attached to C(15) of the phenyl ring. The structural features of the three molecules in the title compounds are reported and compared. The derivatives, being subject of this article are the first reported crystal structures where the isoflavone fragment is fused to a further six membered ring that results in a tricyclic ring system. The benzopyrone fragments are planar. The dihedral angles between the benzopyrone fragment and the phenyl ring being 55.38(6)° for (I) and 44.75(15)°/44.64(15)° for the respective independent molecules of (II) are within the range of values observed for similar structures.
Environmental isotopes (18O, 2H, and 87Sr/86Sr) as a tool in groundwater investigations in the Keta Basin, Ghana
(Hydrogeology Journal, 2001-04) Jørgensen, N.O.; Banoeng-Yakubo, B.K.
Analyses of environmental isotopes (18O, 2H, and 87Sr/86Sr) are applied to groundwater studies with emphasis on saline groundwater in aquifers in the Keta Basin, Ghana. The 87Sr/86Sr ratios of groundwater and surface water of the Keta Basin primarily reflect the geology and the mineralogical composition of the formations in the catchments and recharge areas. The isotopic compositions of 18O and 2H of deep groundwater have small variations and plot close to the global meteoric water line. Shallow groundwater and surface water have considerably larger variations in isotopic compositions, which reflect evaporation and preservation of seasonal fluctuations. A significant excess of chloride in shallow groundwater in comparison to the calculated evaporation loss is the result of a combination of evaporation and marine sources. Groundwaters from deep wells and dug wells in near-coastal aquifers are characterized by relatively high chloride contents, and the significance of marine influence is evidenced by well-defined mixing lines for strontium isotopes, and hydrogen and oxygen stable isotopes, with isotopic compositions of seawater as one end member. The results derived from environmental isotopes in this study demonstrate that a multi-isotope approach is a useful tool to identify the origin and sources of saline groundwater.
Differential thermopower of a CNT chiral carbon nanotube
(Journal of Physics Condensed Matter, 2001-05) Mensah, S.Y.; Allotey, F.K.A.; Mensah, N.G.; Nkrumah, G.
The differential thermopower of a chiral carbon nanotube (CNT) was calculated using a tractable analytical approach. We obtained an expression for the electrical conductivity σ and the thermopower α. The results were numerically analysed. We noted from the values of α that the material can behave as a semimetal, n-type semiconductor and a p-type semiconductor, depending on the parameters of the CNT. We propose the use of the CNT as a thermoelement.
Ground state energy of a polaron in a superlattice
(Superlattices and Microstructures, 2001-05) Mensah, S.Y.; Allotey, F.K.A.; Nkrumah, G.; Mensah, N.G.
The ground state energy of a polaron in a superlattice was calculated using the double-time Green functions. The effective mass of the polaron along the planes perpendicular to the superlattice axis was also calculated. The dependence of the ground state energy and the effective mass along the planes perpendicular to the superlattice axis on the electron-phonon coupling constant α and on the superlattice parameters (i.e. the superlattice period d and the bandwidth Δ) were studied. It was observed that if an infinite square-well potential is assumed, the ground state energy of the polaron decreases (i.e. becomes more negative) with increasing α and d, but increases with increasing Δ. For small values of α, the polaron ground state energy varies slowly with Δ, becoming approximately constant for large Δ. The effective mass along the planes perpendicular to the superlattice axis was found to be approximately equal to the mass of an electron for all typical values of α, d and Δ.
The anomalous low temperature resistivity and critical scattering of conduction electrons around the Néel point of α-Mn films containing dilute concentration of Ni
(Acta Materialia, 2001-06) Boakye, F.; Adanu, K.G.; Nkum, R.K.
Electrical resistivity measurements on thermally evaporated Mn100-xNix films (with x = 0.01, 0.02 and 0.05 at.% Ni) have been performed over the temperature range from 300 to 1.4 K using the van der Pauw four probe technique. The Néel point (TN) of the films determined using the model of Graig and Goldburg reveals a shift to upper values as the concentration of Ni is increased. Analysis of the resistivity data near the Néel points of these alloys gave critical exponents which are in moderate agreement with existing theories. The low temperature resistivity of the 0.02 and 0.05 at.% Ni in Mn specimens obeys a T2 law indicating a spin fluctuation scattering mechanism in these alloys. © 2001 Acta Materialia Inc.
Antiplasmodial activity of labdanes from Aframomum latifolium and Aframomum sceptrum
(Planta Medica, 2002-07) Duker-Eshun, G.; Jaroszewski, J.W.; Asomaning, W.A.; Oppong-Boachie, F.; Olsen, C.E.; Christensen, S.B.
Bioguided fractionation of extracts of Aframomum latifolium and A. sceptrum (Zingiberaceae) resulted in isolation of (+)-(S)-nerolidol and seven labdanes, coronarin B, galanal A and B, galanolactone, (E)-8β,17-epoxylabd-12-ene-15,16-dial, (+)-(E)-labda-8(17), 12-diene-15,16-dial and its diethyl acetal, the latter being presumably an isolation artefact. The labdanes show a modest in vitro activity against a chloroquine-sensitive Plasmodium falciparum strain.
Epithermal instrumental neutron activation analysis for the determination of gold and arsenic in Ghanaian gold tailings using conventional and anti-coincidence counting
(Journal of Radioanalytical and Nuclear Chemistry, 2003-01) Nyarko, B.J.B.; Serfor-Armah, Y.; Holzbecher, J.; Osae, E.K.; Akaho, E.H.K.; Carboo, D.; Chatt, A.
Epithermal instrumental neutron activation analysis (EINAA) together with both conventional and anti-coincidence counting techniques were used to analyze six different gold tailing samples from Ghana for Au and As. The method involves the use of the epi-cadmium site of the Dalhousie University Slowpoke-2 reactor facility for the irradiation of the samples. After irradiation, the samples were counted directly on the detectors. The identification and quantification of the elements were done using 411 keV photopeak of 198Au and both 559 keV and 657 keV photopeaks of 76As. The precision and accuracy of the method were evaluated-Values for Au in the samples ranged from 2.48 ppm and 6.76 ppm and for As between 1,550 ppm and 3,460 ppm. The values obtained using the two counting systems were in good agreement while the anti-coincidence counting system gave values of higher precision and accuracy. The detection limit for Au were 20 and 10 ppb for the conventional and anti-coincidence spectrometric systems, respectively, and 50 ppb for As in both cases. Details of the method and results are presented.
Compositional variations in manganese carbonate micronodules from the Lower Proterozoic Nsuta deposit, Ghana: Product of authigenic precipitation or post-formational diagenesis?
(Sedimentary Geology, 2003-01) Nyame, F.K.; Beukes, N.J.; Kase, K.; Yamamoto, M.
Detailed petrographic and microprobe studies of micronodules identified in the manganese carbonate orebody and adjacent Mn-rich rocks at the ∼ 2.2 Ga Nsuta deposit, Ghana, indicate distinct lithologic control on nodule structure and chemical composition. Nodules in the Mn-rich rocks adjacent to the manganese carbonate orebody conform with the well-banded nature of the rock and are distinctly zoned into alternating bands compositionally dominated by Mg kutnahorite and Mg-Ca rhodochrosite. Individual nodules are partially or completely cemented by thin dark silica and carbonates of Ca-Mg±Mn solid solution. Nodules in the orebody, on the contrary, are generally massive, homogeneous, consist predominantly of rhodochrosite and are only partially cemented by dark silica. Based on the stratigraphic relationship of the nodule-bearing rocks to the manganese carbonate orebody and the variations in texture and composition observed in the nodules, it would appear that the Mn carbonate nodules precipitated diagenetically in response to changing pore water chemistry and/or metal (Mn and Ca) supply. The overall mineralogical and geochemical features indicate, in addition, that the nodules may have preserved original carbonate compositions, both metastable and stable, during burial diagenesis and low-grade regional metamorphism. © 2002 Elsevier Science B.V. All rights reserved.
Giant electrical power factor in single-walled chiral carbon nanotube
(Superlattices and Microstructures, 2003-03) Mensah, S.Y.; Allotey, F.K.A.; Mensah, N.G.; Nkrumah, G.
The thermoelectrical properties of single walled chiral carbon nanotubes were studied. The use of semiclassical approach resulted in the prediction of electric power factor. The predicted electric power factor was then utilized in proposing the usage of carbon nanotubes as thermoelements for refrigeration.

Browse

Browsing School of Physical and Mathematical Sciences by Issue Date

Results Per Page

Sort Options