Said Vuai - Academia.edu (original) (raw)

Papers by Said Vuai

This study was carried out to determine the chemical composition of cave water in Zanzibar Island... more This study was carried out to determine the chemical composition of cave water in Zanzibar Island, part of Tanzania. It was done by studying major cations (Ca, Mg, Na, K), and major anions (HCO3, SO4, Cl), in the water as indicators. Overall results indicated that, the cave water was influenced by marine and weathering contribution. However, weathering was more pronounced at Chomvi ndogo, Chomvi kubwa, and Miza wa Miza caves where it was more than 87% compared to Kilindi, Choweni and Makutani caves where it was less than 77%. Therefore marine contributed more in these last three caves. The trend for concentration contributed from marine water was similar to all sampling sites which was K<Ca<Mg<SO4<Na. The trend for weathering contribution was SO4< K Mg<Na<Ca at Chomvi ndogo, Chomvi kubwa and Miza wa Miza caves while at Kilindi, Choweni and Makutani caves the trend was Mg<K <SO4 <Na <Ca. These trends show that Na contributed more in marinogenic conten...

International Journal of Scientific & Technology Research, 2017

SSRN Electronic Journal, 2021

Chemical Geology, 2007

The chemical characteristics of freshwaters draining the silicate rocks in the northern part of O... more The chemical characteristics of freshwaters draining the silicate rocks in the northern part of Okinawa Island were studied to understand solute generation processes, and to determine rates of chemical weathering and CO 2 consumption. It was observed that the water chemistry is highly influenced by marine aerosols, contributing more than 60% of total solute. Significant positive correlations observed for chloride versus dissolved silica and chloride versus bicarbonate suggest a strong influence of evapotranspiration on the seasonality of solute concentration. It was also found that chemical weathering has been highly advanced in which the dominant kaolinite minerals are being gibbsitized. Carbonic acid was found to be the major chemical weathering agent, releasing greater than 80% of weathering-derived dissolved cations and silica while the remaining portion was attributed to weathering by sulfuric acid generated via oxidation of pyrite contained in the rocks. The flux of basic cations, weathering-derived silica and CO 2 consumption were relatively high due to favourable climatic condition, topography and high rate of mechanical erosion. Silicate weathering rates for basic cations were estimated to be 6.7-9.7 ton km − 2 y − 1. Carbon dioxide consumed by silicate weathering was 334-471 kmol km − 2 y − 1 which was slightly higher than that consumed by carbonate weathering. In general, divalent cations (Mg and Ca) and bicarbonate alkalinity derived from carbonate dissolution were higher than those from silicate weathering. As a consequence, the evolution of chemical species in the freshwaters of northern area of Okinawa Island to a large extent could be explained by mixing of two components, characterized by waters with Na + and Cl − as predominant species and waters enriched with Ca 2+ and HCO 3 − .

Designed Monomers and Polymers, 2021

ABSTRACT Endeavors have been made to construct new donor–acceptor (D-A) monomers utilizing 9 H-ca... more ABSTRACT Endeavors have been made to construct new donor–acceptor (D-A) monomers utilizing 9 H-carbazole (CB) as electron donors and different electron acceptors. All estimations were finished using DFT and TD-DFT, and B3LYP level with a 6–311 G basis set in the gas and chloroform solvent. The impacts of the distinctive acceptors on the geometry of molecules and optoelectronic properties of these D-A monomers were discussed to dissect the connection connecting the molecular structures and the optoelectronic properties. Likewise, the HOMO – LUMO energies, atomic orbital densities are calculated theoretically. Notwithstanding the charge transfer measure between the carbazole electron donor unit and the electron acceptor one is upheld by breaking down the optical spectra of the acquired monomers and the restriction of involved HOMO and LUMO. The outcomes show that the D-A monomers, CB-ODP, CB-TDP, and CB-SDP, are acceptable for optoelectronic applications in organic solar cells like BHJ.

International Journal of Photoenergy, Jan 8, 2019

This research work was conducted to investigate the structural, molecular, electronic, and photop... more This research work was conducted to investigate the structural, molecular, electronic, and photophysical parameters of the fluorescein dye derivatives using the density functional theory (DFT) and time dependent-density functional theory (TD-DFT) computations. The organic donor-π-acceptor dye used for dye-sensitized solar cells, based on 2-(3-hydroxy-6-oxo-6Hxanthene-9-yl)benzoic acid (fluorescein) and its five derivatives, was investigated. The derivatives were formed by attaching different donor groups at para position. The excited state energies, electron absorption spectra, and oscillator strengths (f) were calculated using TD-DFT/B3LYP/6-311G basis set calculations on fully DFT-optimized geometries. The HOMO orbital, LUMO orbital, and energy gap values show that fluorescein attached with thiophene (FST) compound has a smaller energy gap compared to others and the fluorescein attached with an amine (FSA) have a larger energy gap than all compounds. The increasing order of the energy gap between HOMO and LUMO for the fluorescein and its derivatives is FST < FSE < FSM < FS < FSO < FSA. In terms of electron injection efficiency, it was found that the FST has higher electron injection efficiency compared with other derivatives. In addition, light-harvesting efficiencies (LHEs) were calculated and the results showed that the FST has the highest LHE value. It is therefore suggested that FST has better properties for application in DSSC according to the result obtained.

Heliyon, Nov 1, 2021

A series of six coumarin based dye derivatives were investigated and their geometry and optoelect... more A series of six coumarin based dye derivatives were investigated and their geometry and optoelectronic properties elucidated for suitability in dye-sensitized solar cells (DSSCs) using TD-DFT/B3LYP with 6-31G basis set. D-π-A schemes were developed by attaching various donors and acceptors to coumarin dye (CM) to calculate changes in their photovoltaic properties. D2-CM-A2 and D4-CM-A4 showed less dihedral angle because of the low steric effect between donor and connector. The D1-CM-A1 and D2-CM-A2 results of intramolecular charge transfer were higher because of low bond length and a strong group of electron donors. The results revealed that LUMO energies of D1-CM-A1, D2-CM-A2, D3-CM-A3 and D4-CM-A4 were higher than the conduction band edge of TiO2 electrode (−4.0 eV) suggesting that these dyes will inject the electrons into the conduction band of the semiconductor. In addition, the light harvest efficiency (LHE), open-circuit voltage (VOC) and band energy gap (Eg) values are calculated in the gas phase, as well as in the solvent phase. This study shows that D1-CM-D1 and D2-CM-A2 derivatives have better properties for application in the DSSCs.

Geologos, Dec 30, 2022

A geopark is a place where geological heritage is conserved and used sustainably to improve econo... more A geopark is a place where geological heritage is conserved and used sustainably to improve economic realities of residents (Mc Keever & Zouros, 2005). It is made up of several appealing and rare geological and palaeontological heritage sites that are particularly significant scientifically. Furthermore, geoparks may have ecological, archaeological, cultural and/or historical value (Eder & Patzak, 2004). Ngorongoro Lengai is the only area in Tanzania with UNESCO geopark status, from

Journal of Oceanography, Jun 1, 2005

Contamination of acidic red soil in the coastal areas of Okinawa Islands is a serious environment... more Contamination of acidic red soil in the coastal areas of Okinawa Islands is a serious environmental problem. This study was conducted to examine the effects of the salinity on pH and aluminum concentration when the acidic red soil interacts with seawater. Acidic red soil from Gushikawa recreation center was fractionated into bulk soil, coarse sand and silt + clay. Different weights of each fraction were equilibrated with seawater solutions. The pH and concentrations of Al 3+ , Na + , K + , Ca 2+ and Mg 2+ were then analyzed in the extracts. The results showed a decreasing trend of pH with increasing soil to solution ratio while the extracted Al 3+ revealed an increasing trend. The lowest pH values were 3.85, 4.06, 4.41, 4.66 and their corresponding highest Al 3+ concentrations were 2.50, 1.01, 0.062 and 0.036 mmolL-1 in the seawater extracts, one-tenth seawater extracts, one-hundredth seawater extracts and one-thousandth seawater solution extracts, respectively. Mostly, the concentrations of Na + , Ca 2+ , Mg 2+ and especially K + decreased with increasing soil weight in the high salinities but showed the opposite trend in the low salinity samples. Potassium concentration decreased by 39%, 53% and 40% in the seawater extracts, one-tenth and one-hundredth seawater extracts but increased by 200% in one-thousandth seawater extracts. The coincidence of the increase in Al 3+ and H + concentrations, and the decrease of Na + , K + , Ca 2+ and Mg 2+ concentrations in the solutions suggests ion exchange/adsorption, while the increased patterns, particularly at low salinity could be attributed to the dissolution of the species from the soils. which tends toward soil inflow to aquatic systems (Omija, 2000). The major mineral compositions of the red soils observed on a subtropical Island at Okinawa are mainly vermiculite, intergraded minerals, vermiculite/illite mixed layer, illite, kaolinite, and halloysite (Nurcholis et al., 1998). The dominant mineral compositions demonstrated in the Gushikawa recreation center (GRC) red soil are vermiculite-chlorite and kaolinite in the clay, quartz and muscovite in the silt and quartz in the fine sand (Vuai et al., 2003). Other minor mineral compositions in the soil include vermiculite/illite, goethite, feldspar, vermiculite and kaolinite. Tokashiki (1993) found that red soil, which is locally called Kunigami Mahji, covers about 55% of total area of Okinawa Islands (2250 km 2) and is characterized by low percentage base saturation, dominated by exchangeable aluminum. The red soil has low effective cation exchange capacity (<3 cmolkg-1) where Al is dominant (>50%) (Vuai, 2001). Using X-ray fluorescence, Yonaha (2002) examined the chemical compositions of

Limnology, Aug 1, 2003

Page 1. Limnology (2003) 4:63–71 © The Japanese Society of Limnology 2003 DOI 10.1007/s10201-003-... more Page 1. Limnology (2003) 4:63–71 © The Japanese Society of Limnology 2003 DOI 10.1007/s10201-003-0096-z RESEARCH PAPER Said Ali Vuai · Maki Ishiki · Akira Tokuyama Acidification of freshwaters by red soil in a subtropical silicate rock area, Okinawa, Japan ...

Geochemical Journal, 2003

The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H... more The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H 2 SO 4) in the soil. The acid reacts with soil minerals and dissolves aluminum and other acid-soluble metals. During rainfall, they are flushed and discharged into terrestrial and aquatic environments. The authors examined the chemical characteristics of the runoffs from ASS in Arashiyama and in Ooshitai, which are located in the northern part of Okinawa Island and evaluated their potential effects on surrounding environments. The results show that the runoffs were very acidic with pH range of 2.87 to 4.29, and minimum values were close to the pH values of the soils. The dominant species were SO 4 2-, Al 3+ , and Fe 2+ and they were well correlated with pH. The acidity of the runoffs caused dissolution of metals in the following order: Mn > Zn > Cu = Cd. The quality of runoffs was found to be poor and was mainly governed by the interaction of rain and soil. A comparison between the stream waters collected during rain event and on fine day showed a marked changes in stream water chemistry during rainfall as follows: alkalinity was reduced by 3.7 times, sulfate concentration was increased by 3 times whereas pH was decreased by 0.18 units. These changes are attributed to the contamination by runoff from ASS. Moreover brown flocky sediments were observed to have covered entire streambed at the discharging point. The chemical composition of the sediments shows that as those of runoffs, they were dominated by Fe, Al, and SO 4. These results indicate that the sediments were mainly formed as the results of mixing runoffs and stream water. ritic sediments are known as acid sulfate soils (Dent, 1986). The oxidation of pyrite produces high concentrations of ferrous ions, and sulfuric acid, which in turn attacks clay minerals and produces high concentrations of monomeric aluminum and other acid-soluble metals. Subsequent leaching of these toxic products into adjacent water bodies is rapidly increasing the stress on ecosystems. Drainage from acid sulfate soils has been associated with effects on plant growth (Moore and Patrick, 1991), acidification of water bodies (Sammut et al., 1996; Nguyen Thanh Tin

Atmospheric Research, 2011

Okinawa Island is located between mainland Japan to the northeast, Taiwan to the southwest and Ch... more Okinawa Island is located between mainland Japan to the northeast, Taiwan to the southwest and China to the west. In recent years, precipitation with relatively low pH has been observed in the island during winter seasons. This study was conducted to evaluate the potential sources and factors affecting distribution of trace metals in the atmosphere around the northern area of Okinawa Island. The results showed that the trace metal contamination was low comparable to rural areas of less industrialized countries. The annual average depositions were 6.0, 5.2, 4.4, 2.7 and 20.4 kg km − 2 y − 1 for Al, Fe, Mn, Cu, and Zn, respectively. The metals in the precipitation were mainly derived from the dissolution of wind-blown soil particles. The distribution of trace metals across the island showed the influence of road traffic as a source and cause of atmospheric pollution. Aluminium and Fe were found to be high closer to the main road and decreased further away from the road, while Zn and Cu were strongly correlated with average mean pH of precipitation. The variation of concentrations in the island was attributed to the distance from the main road, average rain pH at a particular sampling location and wind speed and direction. A strong correlation between lithological elements (Al and Fe) and anthropogenic elements (Zn and Cu) indicates that they were carried by the same particles and experienced similar scavenging mechanism during dissolution process.

Designed Monomers and Polymers, 2021

ABSTRACT In this research article, the new donor–acceptor (D–A) monomers developed using 4-methox... more ABSTRACT In this research article, the new donor–acceptor (D–A) monomers developed using 4-methoxy-9-methyl-9 H-carbazole (MMCB) as electron donors and various electron acceptors. DFT and TD-DFT methods at the level of B3LYP with a 6–311 G basis set in a gas and chloroform solvent were used to calculate electronic and optoelectronic properties. To dissect the relationship between the molecular and optoelectronic structures, the impacts of specific acceptors on the geometry of molecules and optoelectronic properties of these D–A monomers were discussed. The calculations are also carried out on HOMO–LUMO, atomic orbital densities. The calculated band gap E g of the monomers considered increases 3,6-MMCB-OCP ≈ 3,6-MMCB-BCO < 3,6-MMCB-SDP < 3,6-MMCB-SCP < 3,6-MMCB-TCP < 3,6-MMCB-TDP < 3,6-MMCB-BCS < 3,6-MMCB-BCT in both in the gas and solvent phases. Subsequently, the optoelectrical properties of E HOMO , E LUMO , E opt , and E B energies were critically updated. Compared to different monomers, the far lower E g of the 3,6-MMCB-OCP and 3,6-CB-BCO has shown optoelectronic applications in organic solar cells like BHJ.

The Scientific World Journal, Oct 28, 2022

Shifting sand (SS) is a single dune-shaped mass of black ash material moving across western Ngoro... more Shifting sand (SS) is a single dune-shaped mass of black ash material moving across western Ngorongoro in northern Tanzania. e moving sand has become an important tourist destination for several decades. Despite being part of the important geosites at the Ngorongoro Conservation Area, the nature, origin, and behaviors demonstrated by SS remain poorly understood. is work contributes toward understanding the nature and identi cation of the possible origin of the SS through the correlation of geochemical, mineralogical, and geomorphological data of ash material from four selected locations in the study area. To achieve this goal, elemental, mineralogical, and morphological characterization of ash samples was performed by energydispersive X-ray uorescence, polarized petrographic microscopy, automated sieve shaker, and binocular microscopy techniques, respectively. Correlation studies were based on magnesian-ferriferous associations, similarities in mineralogy, particle size, shape, and distribution patterns of ash materials, and weather data. ere are close similarities in the chemical compositions among ash samples of SS, Ootun area, and Oldoinyo Lengai. Augite and magnetite minerals appear only in samples of SS, Ootun area, and Oldoinyo Lengai, while hornblende appears only in the samples from the Ngorongoro crater. Oldoinyo Lengai rock petrography revealed signi cant amounts of augite minerals. Blocky and elongated-shaped ash particles dominate the samples from SS, Ootun area, and Oldoinyo Lengai. e particle size of ash materials decreases westwards across the study site. e distribution patterns of ash material align with the west-southwest wind direction. Based on these ndings, the study concludes that SS and Ootun ash could be tephra depositions resulting from past volcanic eruptions of Oldoinyo Lengai.

Geofluids, Sep 5, 2022

Oldoinyo Lengai has been a subject of international attention for geoscientists because of its un... more Oldoinyo Lengai has been a subject of international attention for geoscientists because of its uniqueness. The mountain is the world's only active natrocarbonatite volcano whose recent activities are well documented. However, little is known about its eruptive history during the Holocene. One way of uncovering past volcanic activities is through chronostratigraphic studies. A rare stratigraphic sequence in the Ootun area containing buried tephra beds and paleosols is presented in this article. The beds suggest that the nearby active Oldoinyo Lengai volcano experienced the main plume volcanism during the late Holocene. This work presents the lithology of the area, estimated deposition period, and elemental and mineralogical compositions of strata, and establishing similarities between ash properties and information from previously reported chemistry and eruptions of the Oldoinyo Lengai volcano. Energy dispersive X-ray fluorescence, X-ray diffractometry, and accelerated mass spectrometry techniques were used for elemental, mineralogical, and radiocarbon dating analyses. A 1.3-m vertical soil profile revealed three major strata: topsoil, tephra bed, and paleosols. The paleosols are presumed to have been topsoil of the Ootun area during the Holocene. Subsurface tephra layers were found to contain similar properties to the volcanic material of the Oldoinyo Lengai. Based on the experimental findings and literature data, the study reports the occurrence of two major plume eruption events from the Oldoinyo Lengai, which happened around the minimum (oldest) age of 490 ± 10 BC and 771 AD. This work is essentially important in demonstrating the relevance of the region's tephra chronostratigraphic studies by revealing the prospect of collecting additional scientific data on past geological processes and paleoenvironmental conditions of northern Tanzania.

… OF THE RYUKYUS, 2001

Title Particle size distribution, minerals and chemical composition of red soils from silicate ro... more Title Particle size distribution, minerals and chemical composition of red soils from silicate rock area of Central Okinawa Author(s) Vuai, Said Ali; Tokuyama, Akira; Tokashiki, Yoshihiro; Shimo, Moritaka ... 74 Said Ali Vuai, Akira Tokuyama, Yoshihiro Tokashiki, and Moritaka Shimo ...

This study was carried out to determine the chemical composition of cave water in Zanzibar Island... more This study was carried out to determine the chemical composition of cave water in Zanzibar Island, part of Tanzania. It was done by studying major cations (Ca, Mg, Na, K), and major anions (HCO3, SO4, Cl), in the water as indicators. Overall results indicated that, the cave water was influenced by marine and weathering contribution. However, weathering was more pronounced at Chomvi ndogo, Chomvi kubwa, and Miza wa Miza caves where it was more than 87% compared to Kilindi, Choweni and Makutani caves where it was less than 77%. Therefore marine contributed more in these last three caves. The trend for concentration contributed from marine water was similar to all sampling sites which was K<Ca<Mg<SO4<Na. The trend for weathering contribution was SO4< K Mg<Na<Ca at Chomvi ndogo, Chomvi kubwa and Miza wa Miza caves while at Kilindi, Choweni and Makutani caves the trend was Mg<K <SO4 <Na <Ca. These trends show that Na contributed more in marinogenic conten...

International Journal of Scientific & Technology Research, 2017

SSRN Electronic Journal, 2021

Chemical Geology, 2007

The chemical characteristics of freshwaters draining the silicate rocks in the northern part of O... more The chemical characteristics of freshwaters draining the silicate rocks in the northern part of Okinawa Island were studied to understand solute generation processes, and to determine rates of chemical weathering and CO 2 consumption. It was observed that the water chemistry is highly influenced by marine aerosols, contributing more than 60% of total solute. Significant positive correlations observed for chloride versus dissolved silica and chloride versus bicarbonate suggest a strong influence of evapotranspiration on the seasonality of solute concentration. It was also found that chemical weathering has been highly advanced in which the dominant kaolinite minerals are being gibbsitized. Carbonic acid was found to be the major chemical weathering agent, releasing greater than 80% of weathering-derived dissolved cations and silica while the remaining portion was attributed to weathering by sulfuric acid generated via oxidation of pyrite contained in the rocks. The flux of basic cations, weathering-derived silica and CO 2 consumption were relatively high due to favourable climatic condition, topography and high rate of mechanical erosion. Silicate weathering rates for basic cations were estimated to be 6.7-9.7 ton km − 2 y − 1. Carbon dioxide consumed by silicate weathering was 334-471 kmol km − 2 y − 1 which was slightly higher than that consumed by carbonate weathering. In general, divalent cations (Mg and Ca) and bicarbonate alkalinity derived from carbonate dissolution were higher than those from silicate weathering. As a consequence, the evolution of chemical species in the freshwaters of northern area of Okinawa Island to a large extent could be explained by mixing of two components, characterized by waters with Na + and Cl − as predominant species and waters enriched with Ca 2+ and HCO 3 − .

Designed Monomers and Polymers, 2021

ABSTRACT Endeavors have been made to construct new donor–acceptor (D-A) monomers utilizing 9 H-ca... more ABSTRACT Endeavors have been made to construct new donor–acceptor (D-A) monomers utilizing 9 H-carbazole (CB) as electron donors and different electron acceptors. All estimations were finished using DFT and TD-DFT, and B3LYP level with a 6–311 G basis set in the gas and chloroform solvent. The impacts of the distinctive acceptors on the geometry of molecules and optoelectronic properties of these D-A monomers were discussed to dissect the connection connecting the molecular structures and the optoelectronic properties. Likewise, the HOMO – LUMO energies, atomic orbital densities are calculated theoretically. Notwithstanding the charge transfer measure between the carbazole electron donor unit and the electron acceptor one is upheld by breaking down the optical spectra of the acquired monomers and the restriction of involved HOMO and LUMO. The outcomes show that the D-A monomers, CB-ODP, CB-TDP, and CB-SDP, are acceptable for optoelectronic applications in organic solar cells like BHJ.

International Journal of Photoenergy, Jan 8, 2019

This research work was conducted to investigate the structural, molecular, electronic, and photop... more This research work was conducted to investigate the structural, molecular, electronic, and photophysical parameters of the fluorescein dye derivatives using the density functional theory (DFT) and time dependent-density functional theory (TD-DFT) computations. The organic donor-π-acceptor dye used for dye-sensitized solar cells, based on 2-(3-hydroxy-6-oxo-6Hxanthene-9-yl)benzoic acid (fluorescein) and its five derivatives, was investigated. The derivatives were formed by attaching different donor groups at para position. The excited state energies, electron absorption spectra, and oscillator strengths (f) were calculated using TD-DFT/B3LYP/6-311G basis set calculations on fully DFT-optimized geometries. The HOMO orbital, LUMO orbital, and energy gap values show that fluorescein attached with thiophene (FST) compound has a smaller energy gap compared to others and the fluorescein attached with an amine (FSA) have a larger energy gap than all compounds. The increasing order of the energy gap between HOMO and LUMO for the fluorescein and its derivatives is FST < FSE < FSM < FS < FSO < FSA. In terms of electron injection efficiency, it was found that the FST has higher electron injection efficiency compared with other derivatives. In addition, light-harvesting efficiencies (LHEs) were calculated and the results showed that the FST has the highest LHE value. It is therefore suggested that FST has better properties for application in DSSC according to the result obtained.

Heliyon, Nov 1, 2021

A series of six coumarin based dye derivatives were investigated and their geometry and optoelect... more A series of six coumarin based dye derivatives were investigated and their geometry and optoelectronic properties elucidated for suitability in dye-sensitized solar cells (DSSCs) using TD-DFT/B3LYP with 6-31G basis set. D-π-A schemes were developed by attaching various donors and acceptors to coumarin dye (CM) to calculate changes in their photovoltaic properties. D2-CM-A2 and D4-CM-A4 showed less dihedral angle because of the low steric effect between donor and connector. The D1-CM-A1 and D2-CM-A2 results of intramolecular charge transfer were higher because of low bond length and a strong group of electron donors. The results revealed that LUMO energies of D1-CM-A1, D2-CM-A2, D3-CM-A3 and D4-CM-A4 were higher than the conduction band edge of TiO2 electrode (−4.0 eV) suggesting that these dyes will inject the electrons into the conduction band of the semiconductor. In addition, the light harvest efficiency (LHE), open-circuit voltage (VOC) and band energy gap (Eg) values are calculated in the gas phase, as well as in the solvent phase. This study shows that D1-CM-D1 and D2-CM-A2 derivatives have better properties for application in the DSSCs.

Geologos, Dec 30, 2022

A geopark is a place where geological heritage is conserved and used sustainably to improve econo... more A geopark is a place where geological heritage is conserved and used sustainably to improve economic realities of residents (Mc Keever & Zouros, 2005). It is made up of several appealing and rare geological and palaeontological heritage sites that are particularly significant scientifically. Furthermore, geoparks may have ecological, archaeological, cultural and/or historical value (Eder & Patzak, 2004). Ngorongoro Lengai is the only area in Tanzania with UNESCO geopark status, from

Journal of Oceanography, Jun 1, 2005

Contamination of acidic red soil in the coastal areas of Okinawa Islands is a serious environment... more Contamination of acidic red soil in the coastal areas of Okinawa Islands is a serious environmental problem. This study was conducted to examine the effects of the salinity on pH and aluminum concentration when the acidic red soil interacts with seawater. Acidic red soil from Gushikawa recreation center was fractionated into bulk soil, coarse sand and silt + clay. Different weights of each fraction were equilibrated with seawater solutions. The pH and concentrations of Al 3+ , Na + , K + , Ca 2+ and Mg 2+ were then analyzed in the extracts. The results showed a decreasing trend of pH with increasing soil to solution ratio while the extracted Al 3+ revealed an increasing trend. The lowest pH values were 3.85, 4.06, 4.41, 4.66 and their corresponding highest Al 3+ concentrations were 2.50, 1.01, 0.062 and 0.036 mmolL-1 in the seawater extracts, one-tenth seawater extracts, one-hundredth seawater extracts and one-thousandth seawater solution extracts, respectively. Mostly, the concentrations of Na + , Ca 2+ , Mg 2+ and especially K + decreased with increasing soil weight in the high salinities but showed the opposite trend in the low salinity samples. Potassium concentration decreased by 39%, 53% and 40% in the seawater extracts, one-tenth and one-hundredth seawater extracts but increased by 200% in one-thousandth seawater extracts. The coincidence of the increase in Al 3+ and H + concentrations, and the decrease of Na + , K + , Ca 2+ and Mg 2+ concentrations in the solutions suggests ion exchange/adsorption, while the increased patterns, particularly at low salinity could be attributed to the dissolution of the species from the soils. which tends toward soil inflow to aquatic systems (Omija, 2000). The major mineral compositions of the red soils observed on a subtropical Island at Okinawa are mainly vermiculite, intergraded minerals, vermiculite/illite mixed layer, illite, kaolinite, and halloysite (Nurcholis et al., 1998). The dominant mineral compositions demonstrated in the Gushikawa recreation center (GRC) red soil are vermiculite-chlorite and kaolinite in the clay, quartz and muscovite in the silt and quartz in the fine sand (Vuai et al., 2003). Other minor mineral compositions in the soil include vermiculite/illite, goethite, feldspar, vermiculite and kaolinite. Tokashiki (1993) found that red soil, which is locally called Kunigami Mahji, covers about 55% of total area of Okinawa Islands (2250 km 2) and is characterized by low percentage base saturation, dominated by exchangeable aluminum. The red soil has low effective cation exchange capacity (<3 cmolkg-1) where Al is dominant (>50%) (Vuai, 2001). Using X-ray fluorescence, Yonaha (2002) examined the chemical compositions of

Limnology, Aug 1, 2003

Page 1. Limnology (2003) 4:63–71 © The Japanese Society of Limnology 2003 DOI 10.1007/s10201-003-... more Page 1. Limnology (2003) 4:63–71 © The Japanese Society of Limnology 2003 DOI 10.1007/s10201-003-0096-z RESEARCH PAPER Said Ali Vuai · Maki Ishiki · Akira Tokuyama Acidification of freshwaters by red soil in a subtropical silicate rock area, Okinawa, Japan ...

Geochemical Journal, 2003

The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H... more The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H 2 SO 4) in the soil. The acid reacts with soil minerals and dissolves aluminum and other acid-soluble metals. During rainfall, they are flushed and discharged into terrestrial and aquatic environments. The authors examined the chemical characteristics of the runoffs from ASS in Arashiyama and in Ooshitai, which are located in the northern part of Okinawa Island and evaluated their potential effects on surrounding environments. The results show that the runoffs were very acidic with pH range of 2.87 to 4.29, and minimum values were close to the pH values of the soils. The dominant species were SO 4 2-, Al 3+ , and Fe 2+ and they were well correlated with pH. The acidity of the runoffs caused dissolution of metals in the following order: Mn > Zn > Cu = Cd. The quality of runoffs was found to be poor and was mainly governed by the interaction of rain and soil. A comparison between the stream waters collected during rain event and on fine day showed a marked changes in stream water chemistry during rainfall as follows: alkalinity was reduced by 3.7 times, sulfate concentration was increased by 3 times whereas pH was decreased by 0.18 units. These changes are attributed to the contamination by runoff from ASS. Moreover brown flocky sediments were observed to have covered entire streambed at the discharging point. The chemical composition of the sediments shows that as those of runoffs, they were dominated by Fe, Al, and SO 4. These results indicate that the sediments were mainly formed as the results of mixing runoffs and stream water. ritic sediments are known as acid sulfate soils (Dent, 1986). The oxidation of pyrite produces high concentrations of ferrous ions, and sulfuric acid, which in turn attacks clay minerals and produces high concentrations of monomeric aluminum and other acid-soluble metals. Subsequent leaching of these toxic products into adjacent water bodies is rapidly increasing the stress on ecosystems. Drainage from acid sulfate soils has been associated with effects on plant growth (Moore and Patrick, 1991), acidification of water bodies (Sammut et al., 1996; Nguyen Thanh Tin

Atmospheric Research, 2011

Okinawa Island is located between mainland Japan to the northeast, Taiwan to the southwest and Ch... more Okinawa Island is located between mainland Japan to the northeast, Taiwan to the southwest and China to the west. In recent years, precipitation with relatively low pH has been observed in the island during winter seasons. This study was conducted to evaluate the potential sources and factors affecting distribution of trace metals in the atmosphere around the northern area of Okinawa Island. The results showed that the trace metal contamination was low comparable to rural areas of less industrialized countries. The annual average depositions were 6.0, 5.2, 4.4, 2.7 and 20.4 kg km − 2 y − 1 for Al, Fe, Mn, Cu, and Zn, respectively. The metals in the precipitation were mainly derived from the dissolution of wind-blown soil particles. The distribution of trace metals across the island showed the influence of road traffic as a source and cause of atmospheric pollution. Aluminium and Fe were found to be high closer to the main road and decreased further away from the road, while Zn and Cu were strongly correlated with average mean pH of precipitation. The variation of concentrations in the island was attributed to the distance from the main road, average rain pH at a particular sampling location and wind speed and direction. A strong correlation between lithological elements (Al and Fe) and anthropogenic elements (Zn and Cu) indicates that they were carried by the same particles and experienced similar scavenging mechanism during dissolution process.

Designed Monomers and Polymers, 2021

ABSTRACT In this research article, the new donor–acceptor (D–A) monomers developed using 4-methox... more ABSTRACT In this research article, the new donor–acceptor (D–A) monomers developed using 4-methoxy-9-methyl-9 H-carbazole (MMCB) as electron donors and various electron acceptors. DFT and TD-DFT methods at the level of B3LYP with a 6–311 G basis set in a gas and chloroform solvent were used to calculate electronic and optoelectronic properties. To dissect the relationship between the molecular and optoelectronic structures, the impacts of specific acceptors on the geometry of molecules and optoelectronic properties of these D–A monomers were discussed. The calculations are also carried out on HOMO–LUMO, atomic orbital densities. The calculated band gap E g of the monomers considered increases 3,6-MMCB-OCP ≈ 3,6-MMCB-BCO < 3,6-MMCB-SDP < 3,6-MMCB-SCP < 3,6-MMCB-TCP < 3,6-MMCB-TDP < 3,6-MMCB-BCS < 3,6-MMCB-BCT in both in the gas and solvent phases. Subsequently, the optoelectrical properties of E HOMO , E LUMO , E opt , and E B energies were critically updated. Compared to different monomers, the far lower E g of the 3,6-MMCB-OCP and 3,6-CB-BCO has shown optoelectronic applications in organic solar cells like BHJ.

The Scientific World Journal, Oct 28, 2022

Shifting sand (SS) is a single dune-shaped mass of black ash material moving across western Ngoro... more Shifting sand (SS) is a single dune-shaped mass of black ash material moving across western Ngorongoro in northern Tanzania. e moving sand has become an important tourist destination for several decades. Despite being part of the important geosites at the Ngorongoro Conservation Area, the nature, origin, and behaviors demonstrated by SS remain poorly understood. is work contributes toward understanding the nature and identi cation of the possible origin of the SS through the correlation of geochemical, mineralogical, and geomorphological data of ash material from four selected locations in the study area. To achieve this goal, elemental, mineralogical, and morphological characterization of ash samples was performed by energydispersive X-ray uorescence, polarized petrographic microscopy, automated sieve shaker, and binocular microscopy techniques, respectively. Correlation studies were based on magnesian-ferriferous associations, similarities in mineralogy, particle size, shape, and distribution patterns of ash materials, and weather data. ere are close similarities in the chemical compositions among ash samples of SS, Ootun area, and Oldoinyo Lengai. Augite and magnetite minerals appear only in samples of SS, Ootun area, and Oldoinyo Lengai, while hornblende appears only in the samples from the Ngorongoro crater. Oldoinyo Lengai rock petrography revealed signi cant amounts of augite minerals. Blocky and elongated-shaped ash particles dominate the samples from SS, Ootun area, and Oldoinyo Lengai. e particle size of ash materials decreases westwards across the study site. e distribution patterns of ash material align with the west-southwest wind direction. Based on these ndings, the study concludes that SS and Ootun ash could be tephra depositions resulting from past volcanic eruptions of Oldoinyo Lengai.

Geofluids, Sep 5, 2022

Oldoinyo Lengai has been a subject of international attention for geoscientists because of its un... more Oldoinyo Lengai has been a subject of international attention for geoscientists because of its uniqueness. The mountain is the world's only active natrocarbonatite volcano whose recent activities are well documented. However, little is known about its eruptive history during the Holocene. One way of uncovering past volcanic activities is through chronostratigraphic studies. A rare stratigraphic sequence in the Ootun area containing buried tephra beds and paleosols is presented in this article. The beds suggest that the nearby active Oldoinyo Lengai volcano experienced the main plume volcanism during the late Holocene. This work presents the lithology of the area, estimated deposition period, and elemental and mineralogical compositions of strata, and establishing similarities between ash properties and information from previously reported chemistry and eruptions of the Oldoinyo Lengai volcano. Energy dispersive X-ray fluorescence, X-ray diffractometry, and accelerated mass spectrometry techniques were used for elemental, mineralogical, and radiocarbon dating analyses. A 1.3-m vertical soil profile revealed three major strata: topsoil, tephra bed, and paleosols. The paleosols are presumed to have been topsoil of the Ootun area during the Holocene. Subsurface tephra layers were found to contain similar properties to the volcanic material of the Oldoinyo Lengai. Based on the experimental findings and literature data, the study reports the occurrence of two major plume eruption events from the Oldoinyo Lengai, which happened around the minimum (oldest) age of 490 ± 10 BC and 771 AD. This work is essentially important in demonstrating the relevance of the region's tephra chronostratigraphic studies by revealing the prospect of collecting additional scientific data on past geological processes and paleoenvironmental conditions of northern Tanzania.

… OF THE RYUKYUS, 2001

Title Particle size distribution, minerals and chemical composition of red soils from silicate ro... more Title Particle size distribution, minerals and chemical composition of red soils from silicate rock area of Central Okinawa Author(s) Vuai, Said Ali; Tokuyama, Akira; Tokashiki, Yoshihiro; Shimo, Moritaka ... 74 Said Ali Vuai, Akira Tokuyama, Yoshihiro Tokashiki, and Moritaka Shimo ...