15 research outputs found
Correlated conformation and charge transport in multiwall carbon nanotube - conducting polymer nanocomposites
The strikingly different charge transport behaviors in nanocomposites of
multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylene
dioxythiophene - polystyrene sulfonic acid (PEDOT-PSS) at low temperatures are
explained by probing their conformational properties using small angle X-ray
scattering (SAXS). The SAXS studies indicate assembly of elongated PEDOT-PSS
globules on the walls of nanotubes, coating them partially thereby limiting the
interaction between the nanotubes in the polymer matrix. This results in a
charge transport governed mainly by small polarons in the conducting polymer
despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge
carriers following 1D-VRH is evident which also gives rise to a positive
magnetoresistance (MR) with an enhanced localization length (~ 5 nm) due to the
presence of MWNTs. However, at T < 4 K, the observation of an unconventional
positive temperature coefficient of resistivity (TCR) is attributed to small
polaron tunnelling. The exceptionally large negative MR observed in this
temperature regime is conjectured to be due to the presence of quasi-1D MWNTs
that can aid in lowering the tunnelling barrier across the nanotube - polymer
boundary resulting in large delocalization.Comment: Accepted J. Phys.: Condens. Matte
Alarming carcinogenic and non-carcinogenic risk of heavy metals in Sabalan dam reservoir, Northwest of Iran
Abstract
This research aims to assess contamination status of water and sediment in Sabalan dam reservoir (SDR) and evaluate the impact of water withdrawal depths on the carcinogenic and non-carcinogenic risks of metals for exposed people. Results of metal pollution indices revealed some degree of pollution in water and sediment of the reservoir, especially associated with arsenic. Risk assessment of metals in water of the SDR for non-carcinogenic materials through different scenarios of water withdrawal depth revealed that consuming water from the depth of 10 m can be somewhat troublesome to human health. The carcinogenic risk of arsenic from depth of 10 m of the reservoir was about four times greater than that from water surface. Minimum carcinogenic risk of consuming water in the reservoir was found to be 1.69 × 10E-4, which is higher than the maximum limit proposed by the U.S. EPA, indicating the water consumption from the SDR can result in harmful effects on human health
Recent and future trends in sea surface temperature across the Persian Gulf and Gulf of Oman
Abstract
Climate change’s effect on sea surface temperature (SST) at the regional scale vary due to driving forces that include potential changes in ocean circulation and internal climate variability, ice cover, thermal stability, and ocean mixing layer depth. For a better understanding of future effects, it is important to analyze historical changes in SST at regional scales and test prediction techniques. In this study, the variation in SST across the Persian Gulf and Gulf of Oman (PG&GO) during the past four decades was analyzed and predicted to the end of 21st century using a proper orthogonal decomposition (POD) model. As input, daily optimum interpolation SST anomaly (DOISSTA) data, available from the National Oceanic and Atmospheric Administration of the United States, were used. Descriptive analyses and POD results demonstrated a gradually increasing trend in DOISSTA in the PG&GO over the past four decades. The spatial distribution of DOISSTA indicated: (1) that shallow parts of the Persian Gulf have experienced minimum and maximum values of DOISSTA and (2) high variability in DOISSTA in shallow parts of the Persian Gulf, including some parts of southern and northwestern coasts. Prediction of future SST using the POD model revealed the highest warming during summer in the entire PG&GO by 2100 and the lowest warming during fall and winter in the Persian Gulf and Gulf of Oman, respectively. The model indicated that monthly SST in the Persian Gulf may increase by up to 4.3 °C in August by the turn of the century. Similarly, mean annual changes in SST across the PG&GO may increase by about 2.2 °C by 2100
Effect of sonication time on the synthesis of the CdS nanoparticle based multiwall carbon nanotube – maleic anhydride – 1-octene nanocomposites
Effect of sonication time on the synthesis of the CdS nanoparticles within the matrix obtained through the covalent functionalization of multiwall carbon nanotube (MWCNT) with maleic anhydride (MA) - 1-octene copolymer was investigated. Cadmium chloride and thiourea were used as the raw materials. MWCNTs used for the matrix were synthesized by Catalytic Chemical Vapor Deposition using Fe-Co/Al2O3 as the catalyst. The obtained nanostructures were characterized by FTIR, XRD, Raman spectroscopy, TEM, SEM, TG and UV-Vis spectroscopy. Electrophysical properties of the polymer nanocomposites obtained using different periods of time for sonication were comparably investigated. The average CdS particle diameter was between 3.9-7.9nm as confirmed independently by TEM and XRD. UV-Vis spectroscopy revealed that the obtained nanostructures are appropriate base materials for making optical devices