mM Of Cd Research Articles

A beam stop based correction procedure for high spatial frequency scatter in industrial cone-beam X-ray CT

In the energy range of industrial cone-beam CT (a 450kV X-ray tube is used), the detector scatter (veiling glare) turned out to be the most important source of secondary radiation for a digital imaging system working in the indirect conversion mode. It has been shown that the detector scatter drives the shape of the total image scatter. As a consequence, the latter may be characterized by an important high spatial frequency content questioning the hypothesis, frequently invoked in the scatter correction techniques, of a slowly varying scatter. We propose a beam stop array (BSA) based method for the evaluation/subtraction of the image scatter. The technique has the potential of simultaneously manage all sources of scattering radiation. It can be used in the high spatial frequency scatter case at the condition of opportunely selecting the BSA effective sampling step. It has been shown that the BSA approach can be also successfully combined with a beam hardening correction scheme based on the linearisation method. The work we present is supported by experimental measurements performed with two test objects at two different beam qualities: (i) 200kV+2.5mm of Cu and (ii) 400kV+4mm of Pb and 1mm of Cd. The detector scatter represents about 36% and 65% of the total white field image for the two investigated beam qualities, respectively.

Development of NIR Emitted CdTe Quantum Dots by Concentration Control Method

Recently, much research has been performed on quantum dots (QDs) due to the promising applications of LED, laser and bio-imaging. They can show the tunable fluorescent property between UV and IR via the control of particle size. Especially, near-infrared emission between 780-880 nm have attracted attention in bio-imaging area due to the deep penetration of emitted light and avoiding the window between the absorption band of hemoglobin and water. Until now, CdTe/CdSe core-shell type-II QDs, InAs/ZnSe, and InAsxP1-x/InP/ZnSe core-shell QDs were developed and applied for sentinel lymph node mapping as an example of a bio-imaging application. In particular, we are interested in CdTe QDs which have a smaller bandgap than the other IIVI QDs and which, therefore, can emit near-infrared light and provide high quantum efficiency. Bulk CdTe is a typical II-VI QDs with a bandgap of 824 nm, which becomes larger than that of bulk semiconductor with decreasing particle size. Several methods have been reported to tune the bandgap of CdTe QDs: 1) growth temperature and time control, 2) additional precursor injection and 3) chemical surface modification using different surfactants. In this paper, we present a new bandgap engineering method of CdTe QDs with controlling precursor concentration. A similar experiment has been conducted by Peng et al., but they studied sizeand shape-controlled QDs with surfactant change. The synthetic procedure used in the present study is similar to the method developed by Bawendi et al. for the production of CdSe QDs, using Cd(acac)2 and TOP-Te as cadmium and tellurium precursors, respectively. The mixture solution of cadmium and tellurium precursors was injected into the surfactant solution of TOP (trioctylphosphine), TOPO (trioctylphosphine oxide) and HDA (hexadecylamine) at 350 C and then cooled to room temperature. The concentration of precursors was controlled serially from one (9.64 mM of Cd) to six (57.84 mM of Cd). The detailed experimental procedures can be found in the Supporting Information. Scheme 1 depicts the bandgap variation versus size control, which were obtained from the emission peaks and TEM images, respectively. CdTe QDs with similar bandgap size to bulk semiconductors could be obtained by our method. Figure 1 shows that the CdTe QDs which were presented by the concentration control method were engineered to emit in the 670 to 800 nm range and that longer wavelength emission could be obtained at a high concentration than at a low concentration. A longer wavelength emission indicates larger particle size due to the Ostwald ripening in the high concentration. In other words, the monomers react very fast with each other and form nuclei when the precursors are injected at high temperature (350 C). The nuclei number in high concentration is larger than that in low concentration because of the high collision frequency in high concentration. Next, monomer depletion occurs very fast and the nuclei concentration decreases due to the Ostwald ripening which includes the decomposition of emission peaks move to a longer wavelength at high nuclei to monomer and re-growth in another nuclei. The monomer depletion and Ostwald ripening occur faster in high nuclei concentration. A few studies have reported on similar research about kinetics in QDs synthesis. Table 1 and Figure 2 show the emission peak positions and quantum yields (QYs) according to the concentration and molar ratio. The emission peaks appear in

Cadmium–Induced Siderophore Production by a High Cd-Resistant Bacterial Strain Relieved Cd Toxicity in Plants Through Root Colonization

This study focuses on the isolation and characterization of a high cadmium (Cd)-resistant bacterial strain, and possible exploitation of its Cd-accumulation and Cd-induced siderophore production property to improve plant growth in cadmium-contaminated soil through root colonization. The bacterial strain could tolerate up to 8 mM of Cd and could accumulate Cd intracellularly. The strain showed Cd-induced siderophore production maximally at 1.75 mM of Cd concentration under culture condition. It stimulated the growth of mustard and pumpkin plants in Cd-added soil through its establishment in rhizosphere. Through biochemical characterization and 16S rDNA sequence analysis, the strain KUCd1, as the name given to it, was identified as a strain of Pseudomonas aeruginosa.

Polyamine metabolism in sunflower plants under long-term cadmium or copper stress

The effect of different doses of cadmium and copper was studied in relation to growth and polyamine (Pas) metabolism in shoots of sunflower plants. Cadmium accumulated to higher levels than copper and shoot length was reduced by 0.5 and 1 mM Cd, but only by 1 mM Cu. At 1 mM of Cd or Cu, Put content increased 270% and 160% with Cd2+ and Cu2+, respectively. Spermidine (Spd) was modified only by 1 mM Cd, while spermine (Spm) declined after seeds germinated, increasing thereafter but only with 1 mM Cd or Cu (273% over the controls for Cd and 230% for Cu at day 16). Both ADC and ODC activities were increased by 1 mM Cd, whereas 1 mM Cu enhanced ADC activity, but reduced ODC activity at every concentration used. The role of Pas as markers of Cd or Cu toxicity is discussed.

Relief of Arsenate Toxicity by Cd-Stimulated Phytochelatin Synthesis in the Green Alga Chlamydomonas reinhardtii

In most photosynthetic organisms, inorganic arsenic taken up into the cells inhibits photosynthesis and cellular growth. In a green alga, Chlamydomonas reinhardtii, 0.5 mM arsenate inhibited photosynthesis almost completely within 30 min. However, in cells acclimated with a sublethal concentration (0.05 to 0.1 mM) of Cd, the inhibition of photosynthesis at 30 min after the addition of arsenate was relieved by more than 50%. The concentrations of arsenic incorporated into the cells were not significantly different between the Cd-acclimated and the non-acclimated cells. The Cd-acclimated cells accumulated Cd and synthesized phytochelatin (PC) peptides, which are known to play an important role in detoxification of heavy metals in plants. By the addition of an inhibitor of glutathione (an intermediate in the PC biosynthetic pathway) biosynthesis, buthionine sulfoximine, cells lost not only Cd tolerance but also arsenate tolerance. These results suggest that glutathione and/or PCs synthesized in Cd-acclimated cells are involved in mechanisms of arsenate tolerance.

Tolerance to cadmium in Chlamydomonas sp. (Chlorophyta) strains isolated from an extreme acidic environment, the Tinto River (SW, Spain)

The effects of selected concentrations of Cd on the growth and ultrastructure of three strains of Chlamydomonas sp. isolated from a highly acidic river, Río Tinto (SW Spain) were examined. The river is characterized by its extreme physico-chemical conditions in terms of low pH, mean 2.2 and high concentrations of heavy metals. Growth, Cd accumulation, chlorophyll a, influence of Fe in Cd toxicity and ultrastructural localization were determined. The strains were cultured in both, artificial chemically defined media as well as in natural water from the river. Since iron is the main component of the river water, the effect of different concentrations of this element in relation with Cd toxicity was also analysed. The three strains analysed showed comparable growth and ultrastructural changes. Cd concentration corresponding to 50% growth inhibition (EC 50) was 0.2 mM when cells were grown in artificial media. When cells were grown in natural water, no significant differences were found between the controls and the Cd supplemented media even at the highest concentration of 0.8 mM. At an inhibitory level of 0.1 mM of Cd, increasing the concentration of iron up to 90 or 180 mM resulted in a dramatic recovery in algal growth rates in artificial media, reaching normal growth curves. The accumulation of Cd depended on dose and time in the artificial media. The maximal accumulation of Cd was reached after 3 days for all Cd doses, and remained almost unchanged in the subsequent period of time. Chlorophyll a amount depended on dose but not on time in the artificial growth media. At the ultrastructural level, an increase in the periplasmalemmal space was observed due to the presence of a large number of vacuoles, together with a decrease in the relative volume of the nucleus when the cells were incubated in the presence of Cd. Pyrenoid and starch granules were observed and accumulation of spherical electron-dense bodies were also detected. X-ray spectra of these bodies for cells growing in artificial acid media showed intense C, O and Cd signals. In addition to these peaks, a strong Fe signal was also observed when cells were grown in natural acidic water.

Fitotoxidez de cádmio para Eucalyptus maculata e E. urophylla em solução nutritiva

Estudaram-se os efeitos de doses crescentes de Cd em solução nutritiva no crescimento e absorção mineral de mudas de Eucalyptus maculata e E. urophylla e respectivos sintomas de fitotoxidez em casa de vegetação. Mudas foram mantidas por cinco semanas em vasos contendo 2 L de solução nutritiva de Clark, adicionando-se 0, 45, 90, 135 e 180 miM de Cd fornecido como CdSO4. Após uma semana de exposição aos tratamentos, E. maculata exibiu pontuações avermelhadas nas nervuras, clorose internerval, necrose, murchamento das folhas e escurecimento das raízes. Além desses sintomas, E. urophylla apresentou morte das gemas apicais e acentuada queda de folhas. A dose crítica de Cd para reduzir em 10% a matéria seca da parte aérea foi baixa; 2,4 miM e 1,5 miM de Cd para E. maculata e E. urophylla, respectivamente. Os níveis críticos de toxidez na parte aérea foram de 14,5 mg kg-1 em E. maculata e 10,8 mg kg-1 de Cd em E. urophylla. Esses resultados indicaram que E. maculata é provavelmente menos sensível ao Cd do que E. urophylla. Foi também observado que o Cd reduziu a translocação de Cu em até 24 e 43% em E. maculata e E. urophylla, respectivamente. A translocação de Fe caiu de 36% em média, nas duas espécies no controle para apenas 12% com 180 miM Cd. A elevação nas doses de Cd reduziu os teores de Ca e Mg na parte aérea das espécies, atingindo-se teores de Mg abaixo da faixa considerada adequada em E. urophylla. Ficaram evidenciadas a fitotoxidez de Cd no Eucalyptus e a relação desta com a diminuição da translocação de Cu e Fe e com a diminuição dos teores foliares de Mg.

Cadmium accumulation and oxidative burst in garlic ( Allium sativum)

To investigate the temporal sequence of physiological reactions of garlic (Allium sativum) to cadmium (Cd) treatment, seedlings developed from cloves were grown in increasing concentrations of CdCl2, ranging from 1-10 mM, for up to 8 days in sand. Analysis of Cd uptake indicated that most Cd accumulated in roots, but some was also translocated and accumulated in leaves at longer exposure time (after 12h) and higher concentrations (5 and 10mM) of CdCl2. Changes in activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were characterized in leaves of garlic seedlings. Cd (5 and 10 mM) initially inhibited the activities of SOD and CAT but thereafter recovered or even increased compared with control plants. POD activities at 5 and 10 mM of Cd increased more than 3-4 times over control plants within 12 h and then dropped, but were still higher than controls at the end of the experiment. Otherwise lipid peroxidation enhanced with the increasing of incubation time and concentrations of external Cd. Leaves exposed to 1 mM CdCl2 showed a less pronounced response and only a small reduction in shoot growth. These results suggested that in leaves of garlic seedlings challenged by CdCl2 at higher concentrations, induction of these various enzymes is part of a general defense strategy to cope with overproduction of reactive oxygen. The possible mechanism of antioxidative enzymes changing before Cd accumulation in leaves of garlic seedlings is discussed.

Cationic Mixed Micelles in the Presence of β-Cyclodextrin: A Host–Guest Study

The conductances of trimethyltetradecylammonium bromide (TTAB)+triphenyltetradecylphosphonium bromide (TTPB) and TTAB+trimethylhexadecylammonium bromide (HTAB) over the entire mole fraction range of TTAB (αTTAB) were measured in water and in β-cyclodextrin+water (CD+W) mixtures at fixed 4 and 8 mM of CD at 30°C. The conductivity plots for both binary mixtures show a single break from which the mixed critical micelle concentration (cmc) and degree of micelle ionization (χ) were computed. From the slopes of the conductivity curves, the equivalent ionic conductivities of the monomeric (Λm), associated (Λass), and the micelle (Λmic) states were calculated and discussed with respect to the surfactant–CD complexation in the whole mole fraction range of both surfactant binary mixtures. The association constant (K) between the respective monomeric surfactant and CD cavity of fixed 4 mM CD was computed by considering 1:1 association from the surface tension measurements. A comparison among the K values for HTAB-CD, TTAB-CD, and TTPB-CD shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail. The nonideality in mixed micelle formation in pure water was evaluated by using the regular solution theory, and it was observed that both binary mixtures exhibit close to ideal behavior.

Feasability of using a graphite slowing-down-time spectrometer in the nondestructive assay of nuclear materials

A slowing-down-time spectrometer (SDTS), constructed for the study of nondestructive assay of fissile nuclear materials, is in its early stages of operation at the Nuclear Engineering Teaching Laboratory of the University of Texas at Austin. The spectrometer is made of a 101×105×122 cm 3 graphite rectangular parallelepiped and is based on injecting pulses of 14 MeV neutrons into the pile. The neutron source is a Texas Nuclear Corporation neutron generator that produces neutrons via the D–T reaction. Measurements and calculations have been conducted to study the time behavior of the neutrons and the assay capabilities of this spectrometer. A 3He detector covered with 0.8 mm of Cd was used to perform neutron die-away measurements in the graphite. A 4He detector was used to perform an assay of a fuel pin containing 13% by mass 239Pu. The calculations were made using the MCNP4B code, and a realistic 3-D mock-up of the experiment. Good agreement is found to exist between the measured time spectra and the ones predicted from the calculations. This included the experimental observation of a predicted rapid fall-off in the die-away spectrum due to the existence of the cadmium cover. Therefore, the time–energy coupling that is expected to hold in a SDTS is experimentally verified. In addition, the calculations and the measurements indicate that the interrogation of fissile materials is possible using a graphite SDTS. This is clear in the measured and calculated time signatures for the 239Pu sample, which include structure that reflects the two resonance groups and the 0.3 eV resonance peak observed in the 239Pu fission cross section.

Physiological and ultrastructural effects of cadmium on wheat (Triticum aestivum L.) leaves.

The effects of a 7-day exposure of 3-day-old wheat plantsto increasing Cd concentrations are described, with special attention beinggiven to chloroplast ultrastructural changes, chlorophyll fluorescenceresponses, chlorophyll and nutrient concentration changes as well as growthchanges of the whole plant. The plants treated with 1 mM Cd showed symptomsof heavy metal toxicity. The root, shoot-leaf length and the root, shoot-leafbiomass progressively decreased with increasing Cd in nutrient solution andin 1 mM of Cd an almost complete inhibition of growth was found. Shoot-leafCd accumulation increased under Cd-treatments, while a Fe, Mg, Ca, and Kdecline in the above ground parts was observed. The growth reduction and theinhibition of chlorophyll content and photosynthesis observed in the upperplant parts seemed principally due to indirect Cd effects on the content ofessential nutrients. Cadmium treatment was shown to damage the structure ofchloroplasts, as manifested by the disturbed shape and the dilation of thethylakoid membranes. These ultrastructural changes suggest that Cd probablyinduced premature senescence.

Effect of cadmium and nickel on photosynthesis and the enzymes of the photosynthetic carbon reduction cycle in pigeonpea (Cajanus cajan L.)

The effect of Cd(2+) and Ni(2+) on the rate of photosynthesis and activities of key enzymes of the photosynthetic carbon reduction cycle was examined in leaves from pigeonpea (Cajanus cajan L., cv. UPAS-120) grown in nitrogen free sand culture. Two different concentrations of Cd(2+) and Ni(2+) were applied through the rooting medium at two growth stages. The application of Cd(2+) and Ni(2+) (0.5 and 1.0 mM) at an early vegetative stage (30 days after sowing) resulted in about 50% and 32% reduction in net photosynthesis, respectively. However, enzyme activities were decreased to different levels (2-61%) depending upon the enzyme and the concentration of the metal ion.These concentrations (0.5 and 1.0 mM of Cd(2+) and Ni(2+)) had no effect when applied at a later vegetative stage i.e. 70 days after sowing. However, when the concentration of Cd(2+) was increased to 10 mM, there was about an 86% reduction in the rate of photosynthesis but the enzyme activities were reduced by only about 40%. Although Ni(2+) reduced the photosynthetic rate by 65%, it had little effect on enzyme activities. The reduction in photosynthesis seems to occur indirectly through a decrease in chlorophyll content and stomatal conductance but not due to decreased enzyme activities. Oxygen evolution by leaf discs was inhibited by Cd(2+) and Ni(2+) in parallel with a reduction in photosynthesis. These data confirm the earlier reported effects of Cd(2+) and Ni(2+) on O2 evolution in isolated chloroplasts.

Nitrate assimilation in pea leaves in the presence of cadmium

Supply of 0.01 to 1.0 mM Cd acetates either to the intact seedlings or to the excised leaves of 15 dPisum sativum L. Cv. Bonvilla seedlings inhibitedin vivo nitrate reductase activity (NRA), total soluble protein, chlorophyll, and carotenoids. The inhibition was independent of metal concentrations. In excised leaf tissues, higher concentrations (0.5 to 1.0 mM) of Cd had no conspicuous effect on nitrate assimilation. When NRA was assayed byin vitro method, an increase of 12 to 45% was obtained with Cd in intact and excised leaves. It appears that NRA is more sensitive to Cd concentration than any other parameter examined.

Cadmium induced alterations in the intestinal absorption of glucose and fructose in a freshwater cat fish, Heteropneustes fossilis

The effect of four concentrations (1.0, 0.1, 0.01, and 0.001 mM) of Cd on the rate of absorption of two sugars, glucose and fructose by the intestine of the fresh water cat fish, Heteropneustes fossilis has been studied after 1 h at 23 °C. Intestinal glucose and fructose transport was also assessed in fish exposed to a sublettral concentration (0.0023 mM) of Cd in the ambient water for 15 and 30 days. Control fish showed no marked difference in the rates of absorption of glucose and fructose. All four concentrations of Cd decreased the rate of transport of glucose and fructose significantly. Among the two sugars, decrease in the rate of transport of fructose was more marked than glucose. In fish exposed to Cd in the ambient water, reduction of glucose and fructose absorption was greater after 30 days of exposure than after 15 days.