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1.
A comparative study on improved Arrhenius-type and artificial neural network models to predict high-temperature flow behaviors in 20MnNiMo alloy.
Quan, GZ, Yu, CT, Liu, YY, Xia, YF
TheScientificWorldJournal. 2014;:108492
Abstract
The stress-strain data of 20MnNiMo alloy were collected from a series of hot compressions on Gleeble-1500 thermal-mechanical simulator in the temperature range of 1173 ∼ 1473 K and strain rate range of 0.01 ∼ 10 s(-1). Based on the experimental data, the improved Arrhenius-type constitutive model and the artificial neural network (ANN) model were established to predict the high temperature flow stress of as-cast 20MnNiMo alloy. The accuracy and reliability of the improved Arrhenius-type model and the trained ANN model were further evaluated in terms of the correlation coefficient (R), the average absolute relative error (AARE), and the relative error (η). For the former, R and AARE were found to be 0.9954 and 5.26%, respectively, while, for the latter, 0.9997 and 1.02%, respectively. The relative errors (η) of the improved Arrhenius-type model and the ANN model were, respectively, in the range of -39.99% ∼ 35.05% and -3.77% ∼ 16.74%. As for the former, only 16.3% of the test data set possesses η-values within ± 1%, while, as for the latter, more than 79% possesses. The results indicate that the ANN model presents a higher predictable ability than the improved Arrhenius-type constitutive model.
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MRI of colorectal cancer liver metastases: comparison of orally administered manganese with intravenously administered gadobenate dimeglumine.
Brismar, TB, Kartalis, N, Kylander, C, Albiin, N
European radiology. 2012;(3):633-41
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Abstract
OBJECTIVES To compare the sensitivity of MRI to detect colorectal cancer liver metastases (CRLM) after ingestion of manganese-based contrast agent (CMC-001) with that of a comprehensive intravenous gadobenate dimeglumine protocol, and to assess the safety and acceptability of oral manganese. METHODS 20 patients suspected of having 1-6 CRLM were included prospectively in this randomised cross-over study. Liver MRI was performed with a one-week interval at 1.5 T and included T1-w VIBE and T2-HASTE, before and after administration of 1.6 g CMC-001 or 0.1 mmol/kg gadobenate dimeglumine. The metastasis-to-liver signal intensity (SI) ratio was calculated. Standard of reference was histopathology after surgery, or combination of other imaging studies and/or follow up. Adverse events (AE) and clinicolaboratory tests were monitored. RESULTS Of 44 metastases, 41 were detected after CMC-001 (93%) and 42 after gadobenate dimeglumine (95%). Fifteen false-positive lesions were found after CMC-001 and 2 after gadobenate dimeglumine. The metastasis-to-liver SI ratio was significantly higher after CMC-001 than after gadobenate dimeglumine (0.51 and 0.21 respectively, P < 0.0001). More AE occurred after manganese compared to gadobenate dimeglumine. CONCLUSIONS CMC-001 is as sensitive as an extensive intravenous gadobenate dimeglumine protocol in detecting CRLM. It was relatively well tolerated but had higher rates of gastrointestinal AE. KEY POINTS • Liver MRI after ingestion of manganese is highly sensitive for detecting metastases • High false-positive rate necessitates further evaluation, in some cases • The MR examination time is short • Oral ingestion of manganese seems safe and relatively well tolerated by patients • Manganese compounds may be useful for liver metastasis surveillance after colorectal cancer.
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Isotherm equilibria of Mn²⁺ biosorption in drinking water treatment by locally isolated Bacillus species and sewage activated sludge.
Hasan, HA, Abdullah, SR, Kofli, NT, Kamarudin, SK
Journal of environmental management. 2012;:34-43
Abstract
Manganese (Mn(2+)) is one of the inorganic contaminant that causes problem to water treatment and water distribution due to the accumulation on water piping systems. In this study, Bacillus sp. and sewage activated sludge (SAS) were investigated as biosorbents in laboratory-scale experiments. The study showed that Bacillus sp. was a more effective biosorbent than SAS. The experimental data were fitted to the Langmuir (Langmuir-1 & Langmuir-2), Freundlich, Temkin, Dubinin-Radushkevich (D-R) and Redlich-Peterson (R-P) isotherms to obtain the characteristic parameters of each model. Mn(2+) biosorption by Bacillus sp. was found to be significantly better fitted to the Langmuir-1 isotherm than the other isotherms, while the D-R isotherm was the best fit for SAS; i.e., the χ(2) value was smaller than that for the Freundlich, Temkin, and R-P isotherms. According to the evaluation using the Langmuir-1 isotherm, the maximum biosorption capacities of Mn(2+) onto Bacillus sp. and SAS were 43.5 mg Mn(2+)/g biomass and 12.7 mg Mn(2+)/g biomass, respectively. The data fitted using the D-R isotherm showed that the Mn(2+) biosorption processes by both Bacillus sp. and SAS occurred via the chemical ion-exchange mechanism between the functional groups and Mn(2+) ion.
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Comparison of two adsorbents for the removal of pentavalent arsenic from aqueous solutions.
Li, Q, Xu, X, Cui, H, Pang, J, Wei, Z, Sun, Z, Zhai, J
Journal of environmental management. 2012;:98-106
Abstract
Two adsorbents, magnesia-loaded fly ash cenospheres (MGLC) and manganese-loaded fly ash cenospheres (MNLC), were prepared by wet impregnation of fly ash cenospheres with MgCl(2) solution or a mixed solution of MnCl(2) and KMnO(4), respectively. Their physicochemical properties were characterized by scanning electron microscopy, X-ray diffractometry, X-ray fluorescence spectrometry, and Fourier transform infrared spectrometry. Sorption experiments were conducted to examine the effects of adsorbent dosage, pH, time, temperature, ionic strength and competing anions on As(V) removal by MGLC and MNLC. Both MGLC and MNLC had greater pH buffering capacity and were less affected by changes in ionic strength. Competing anions (carbonate and dihydric phosphate) had a larger impact on As(V) removal by MNLC than by MGLC. Adsorption on MNLC reached equilibrium at 60 min, while adsorption on MGLC reached equilibrium at 120 min. The Langmuir adsorption isotherm was a good fit for the experimental data of As(V) adsorption on MGLC and MNLC, and the adsorption kinetics for both followed the pseudo-second-order rate equation. MGLC and MNLC had a larger removal capacity for As(V) than the cenospheres. Compared with MNLC, MGLC is a better absorbent.
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Oxidative degradation of azo dyes by manganese peroxidase under optimized conditions.
Mielgo, I, López, C, Moreira, MT, Feijoo, G, Lema, JM
Biotechnology progress. 2003;(2):325-31
Abstract
The application of enzyme-based systems in waste treatment is unusual, given that many drawbacks are derived from their use, including low efficiency, high costs and easy deactivation of the enzyme. The goal of this study is the development of a degradation system based on the use of the ligninolytic enzyme manganese peroxidase (MnP) for the degradation of azo dyes. The experimental work also includes the optimization of the process, with the objective of determining the influence of specific physicochemical factors, such as organic acids, H(2)O(2) addition, Mn(2+) concentration, pH, temperature, enzyme activity and dye concentration. A nearly total decolorization was possible at very low reaction times (10 min) and at high dye concentration (up to 1500 mg L(-)(1)). A specific oxidation capacity as high as 10 mg dye degraded per unit of MnP consumed was attained for a decolorization higher than 90%. Among all, the main factor affecting process efficiency was the strategy of H(2)O(2) addition. The continuous addition at a controlled flow permitted the progressive participation of H(2)O(2) in the catalytic cycle through a suitable regeneration of the oxidized form of the enzyme, which enhanced both the extent and the rate of decolorization. It was also found that, in this particular case, the presence of a chelating organic acid (e.g., malonic) was not required for an effective operation. Probably, Mn(3+) was chelated by the dye itself. The simplicity and high efficiency of the process open an interesting possibility of using of MnP for solving other environmental problems.
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Structural investigation of a high-affinity MnII binding site in the hammerhead ribozyme by EPR spectroscopy and DFT calculations. Effects of neomycin B on metal-ion binding.
Schiemann, O, Fritscher, J, Kisseleva, N, Sigurdsson, ST, Prisner, TF
Chembiochem : a European journal of chemical biology. 2003;(10):1057-65
Abstract
Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity Mn(II) binding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Ke of 4.4 microM in buffer solutions containing 1 M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant kappa of 0.7 MHz, an asymmetry parameter eta of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the Mn(II) ligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by Mn(II) in crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the Mn(II) site in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of kappa(14N)=+0.80 MHz, eta=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that Mn(II) is released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 microM) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry 1995, 34, 11 186).
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Coupled redox potentials in manganese and iron superoxide dismutases from reaction kinetics and density functional/electrostatics calculations.
Han, WG, Lovell, T, Noodleman, L
Inorganic chemistry. 2002;(2):205-18
Abstract
A methodology for determining the coupled redox potentials (DeltaE(redox) degrees (coupled)) of manganese and iron superoxide dismutases (Mn(Fe)SODs), from the standard redox potential of reaction (O(2)(-) + 2H(+) + e(-) --> H(2)O(2)) and the experimental kinetic rate constants of Mn(Fe)SOD proteins, has been presented for the first time. A combined density functional (DF) and electrostatic protein/reaction field (DF/electrostatics) model has also been applied to seven protein structures, to study the structural, energetic, simple redox potential, pK(a), and coupled redox potential properties associated with each active site. The quantum cluster active site models, which include the metal, first shell ligands, represented by amino acid side chains and a solvent derived ligand, and the second shell H-bonding partners, were taken from the crystal structures, and geometry was optimized in four kinds of states: oxidized (III) and reduced (II) states with either a H(2)O molecule or a OH(-) group as the fifth coordinated ligand. We conclude from the calculations that the oxidized and reduced Mn(Fe)SODs are in the Mn(3+)(Fe(3+))(OH(-)) and Mn(2+)(Fe(2+))(H(2)O) forms, respectively; proton transfers will happen in both steps of the dismutation of superoxide anion (O(2)(-)), and the proton-transfer reactions will occur prior to or concerted with the electron transfer from O(2)(-) group to the Mn(3+)(Fe(3+))SOD metal center. The DeltaE(redox) degrees (coupled) of E. coli FeSOD calculated by the DF/electrostatics method is 0.16 V, which is very close to the experimental value of 0.25 V. The absolute values of DeltaE(redox) degrees (coupled) for T. thermophilus, human wild-type, and mutant Q143N MnSODs obtained from the DF/electrostatics method are -0.25, -0.29, and -0.11 V, which present the same trend and very similar relative values to those obtained from experimental kinetic rate constants (0.40, 0.32, and 0.59 V, respectively). The order DeltaE(redox) degrees (human wild-type) < DeltaE(redox) degrees (T. thermophilus) < DeltaE(redox) degrees (E. coli) < DeltaE(redox) degrees (Q143N) for MnSOD proteins is predicted by the DF/electrostatics calculations.
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A comparative study of manganese and lead levels in human umbilical cords and maternal blood from two urban centers exposed to different gasoline additives.
Smargiassi, A, Takser, L, Masse, A, Sergerie, M, Mergler, D, St-Amour, G, Blot, P, Hellier, G, Huel, G
The Science of the total environment. 2002;(1-3):157-64
Abstract
Manganese (Mn) and lead (Pb) are two neurotoxic chemicals and experimental evidence suggests that they can cross the placental barrier. Tetraethyl lead was still in use as an antiknock agent in Paris during the sampling period of the study, while it has been replaced by methylcyclopentadienyl manganese tricarbonyl (MMT) in Canada since 1977. By 1990, MMT was in 100% of gasoline in Canada. In a study of 160 pairs of mothers-neonates in Montreal and 206 pairs in Paris, we compared levels of Mn and Pb in the umbilical cord and in maternal blood. Neonates and mothers had significantly higher Pb levels in Paris where lead additives were still used in gasoline. Geometric mean maternal blood Pb levels were 5.4 microg/dl compared to 2.1 microg/dl in Montreal and cord blood Pb levels were 3.2 microg/dl in Parisian mothers compared to 1.7 microg/dl in Montreal. The prevalence of Paris Pb values superior to the 95th percentile of the Montreal distribution was highly elevated in all media studied. The prevalence of high Mn levels in umbilical cord blood was also significantly higher in Montreal. Surveillance programs are important to limit Pb overexposure and associated neurological effects in neonates where tetraethyl Pb is still in use as a gasoline additive. Since Mn is an essential element and dietary Mn intake may differ between Montreal and Paris, the difference observed with regard to high Mn values between Montreal and Paris cannot, at this time, be attributed to MMT in Montreal's gasoline. Further studies are needed to infer an association between Mn emissions from MMT and prenatal exposure to Mn.
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System design for in vivo neutron activation analysis measurements of manganese in the human brain: based on Monte Carlo modeling.
Arnold, ML, McNeill, FE, Prestwich, WV, Chettle, DR
Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine. 2000;(4-5):651-6
Abstract
Manganese is an essential nutrient required by the human body, but conversely, over exposure to the element may cause central nervous system damage. The technique of in vivo neutron activation analysis, using the McMaster KN-accelerator, is being investigated as a possible method of noninvasively determining manganese concentrations within the human body. Since the brain is the primary target of damage from exposure it would be the ideal site for measurements. Thus, Monte Carlo simulations have been undertaken to define the optimum experimental parameters for such a measurement, examining the use of possible moderator, reflector and collimator materials.