Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 53.515
Filtrar
1.
Ground Water ; 58(1): 35-45, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-30891740

RESUMO

Widely used numerical models of solute transport processes in subsurface aquifers are limited to nonlocally refined rectangular, or logically rectangular, structured grids. This presents an unsuitable option to efficient numerical simulations maintaining an acceptable level of accuracy. Optimal selection of locally refined cells for efficient solute transport models is challenging to the current generation of numerical models. We present a novel and relatively simple to implement algorithm addressing these shortcomings. This method operates in four steps involving travel times simulations, a grid coarsening stage followed by a selective local grid refinement based on a cell-wise indicator, and a final postprocessing step. The refinement index is the sum of weighted logarithmic distributions of scaled forward and backward travel times. We calculate representative flow and transport properties at the two scales of the composite grid with a flow-based upscaling technique. We present two test problems to demonstrate the performances of this new gridding algorithm. We obtain the most important speedups for composite grids generated with the highest indicator thresholds. When hydrodynamic dispersion effects increase, we obtain less important speedups. An important outcome of this work is that grid design depends on nature and strength of the underlying flow and solute transport processes. Therefore, we suggest developing solute transport workflows integrating this grid generation algorithm as an integral component to build comprehensive and efficient groundwater models.


Assuntos
Água Subterrânea , Movimentos da Água , Hidrodinâmica , Modelos Teóricos , Soluções
2.
Water Environ Res ; 92(1): 84-93, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31332878

RESUMO

Chromium (Cr(VI)) is highly toxic and carcinogenic. Cr(VI) water pollution has become more and more serious. This article reports on a study in which lotus seed pods (LSP), an agricultural waste product, was used to efficiently remove Cr(VI) from an aqueous solution, and the carbonization product of LSP after the removal of Cr(VI) (CPLSP) can be regarded as a resource containing Cr. Cr(VI) removed by LSP fits a pseudo-second-order model. pH levels greatly influence the amount of Cr removed. The maximum removal of Cr(VI) by LSP in aqueous solution was 153.85 mg/g. The possible removal mechanism is absorption, redox, and reabsorption based upon SEM/EDS, FT-IR, and XPS spectra results. The Cr content of CPLSP was 42.95% by ammonium persulfate oxidation titrimetric method. These results suggest that LSP can be an excellent, low cost, biomaterial for removing and enriching Cr(VI) from an aqueous solution. PRACTITIONER POINTS: Lotus seed pods are an efficient adsorbent for Cr(VI) from aqueous solutions. The Cr removal by lotus seed pods occurs via absorption, redox, and reabsorption. Cr can be captured after the pods are carbonized. Lotus seed pods can be applied to the removal and enrichment of Cr(VI) from waste water.


Assuntos
Lotus , Poluentes Químicos da Água , Purificação da Água , Adsorção , Cromo , Concentração de Íons de Hidrogênio , Cinética , Sementes , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier
3.
Food Chem ; 307: 125547, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31639582

RESUMO

Functional properties and antioxidant activity of soybean meal extracts obtained by conventional chemical method were compared to those obtained by using electro-activated solutions. The conventional extract obtained at pH8 had the highest WAC (400 ±â€¯7 g/100 g), while the lowest was that of samples extracted under pH3. Extract obtained using electro-activated solution Anolyte_300mA-30 min had WAC value (25 ±â€¯1 g/100 g). OAC was the highest for samples extracted under alkaline conditions whatever the extraction mode used with values of 5.50 ±â€¯0.54 to 6.85 ±â€¯0.62 mL/g. FC of the conventional extracts was higher compared to those extracted by electro-activation with maximal value of 52% for the conventional sample obtained at pH9, whereas the maximal FC of 28% was observed for the electro-activated sample obtained by using Anolyte_450mA-50 min. Electro-activated showed higher EP. Conventional extracts showed higher antioxidant activity (92.31 ±â€¯1.5%) than those obtained by electro-activation (47.46 ±â€¯0.94%).


Assuntos
Antioxidantes/química , Soja/química , Elétrons , Refeições , Extratos Vegetais/química , Soluções
4.
Ecotoxicol Environ Saf ; 188: 109844, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-31727495

RESUMO

Aquatic bryophytes are widely used as indicators of water pollution with various substances, including metals. We present a first study concerning the feasibility of Monosoleum tenerum to remove potentially toxic metals Zn, Cu, Ni, Mn and Fe from water. The novel approach to study the bioaccumulation under controlled conditions and in vitro grown aquarium liverworts was applied. The plants were exposed to 1, 10 and 100 ppm multi-metal solution for 7 days and subsequently the metal content was determined in plant material and media to calculate the bioaccumulation factor (BAF). The study revealed various accumulation behavior (metal and dose dependent), which followed the order of Cu > Zn > Mn > Ni > Fe for 1 ppm; Zn > Cu > Mn > Fe > Ni for 10 ppm and Cu > Fe > Zn > Ni > Mn for 100 ppm solution. However, with increasing Cu, Mn and Ni concentration in the solution, BAF decreased. For Zn the highest BAF value (136) was obtained for the 10 ppm solution. Fe bioaccumulation increased with the increasing solution concentration. After 7 week exposure, the results indicated highest accumulation of Cu (3,25 mg) followed by Fe (1,8 mg) in the plant tissue for the 100 ppm solution. Overall, the bryophyte M. tenerum demonstrate high potential for the removal of toxic metals from the multi-metal solution via accumulation in plant tissue. The BAF values were proper to indicate the use of M. tenerum for phytofiltration of waste waters affected by Zn, Cu, Ni, Mn and Fe.


Assuntos
Hepatófitas/química , Metais Pesados/análise , Poluentes Químicos da Água/análise , Bioacumulação , Biodegradação Ambiental , Monitoramento Ambiental , Hepatófitas/crescimento & desenvolvimento , Hepatófitas/metabolismo , Modelos Teóricos , Soluções
5.
Chemosphere ; 238: 124432, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31421464

RESUMO

This study investigated the adsorption of tetracycline (TC) on biochar (BC) derived from waste Auricularia auricula dregs obtained at different pyrolysis temperatures. The characterization of BC and batch experiment results showed that BC prepared at a higher temperature was more suitable for removing TC, where the maximum adsorption capacities of BC samples prepared at 300 °C, 500 °C, and 700 °C were 7.22 mg/g, 9.90 mg/g, and 11.90 mg/g, respectively. A pseudo-first order kinetics model and Freundlich, Temkin, and Dubinin-Radushkevich isotherm models fitted well to the adsorption data. Liquid film diffusion was the rate-controlling step. In addition, π-π electron donor-acceptor interactions may have played a dominant role in the adsorption mechanism between the enone structure of TC and aromatic C of BC. These results may facilitate further investigations of the adsorption mechanism and optimization of the process.


Assuntos
Basidiomycota , Carvão Vegetal/química , Resíduos Industriais , Tetraciclina/química , Tetraciclina/isolamento & purificação , Água/química , Adsorção , Indústria Alimentícia , Temperatura Alta , Concentração de Íons de Hidrogênio , Cinética , Soluções , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
6.
Chemosphere ; 239: 124768, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31518917

RESUMO

There is a need for cheap but, efficient methods for the removal of precious metals from wastewaters, which are normally lost during mineral processing. Moreover, the disposal of yeast waste from brewing has been a problem in many parts of the world. In this study, the removal of Pt(IV) from aqueous solutions using the readily available bentonite clay functionalised with spent yeast from brewing was investigated. The maximum adsorption capacity of Pt(IV) with 100 mg yeast-functionalised bentonite at pH 2 within 90 min was 255 µg g-1 (98.5% efficiency) but, decreased as pH increased. The adsorption capacity of Pt(IV) was insignificantly (p > 0.05) affected by the presence of competing ions (Fe(III), Ca(II), Mg(II), K(I), Co(II), Ni(II), Hf(IV), Zn(II) and other platinum group metals (PGMs)). Moreover, most of these metals were significantly adsorbed along with Pt(IV). The indicative cost-benefit analysis showed that 1 kg of the yeast-functionalised bentonite can remove ∼700 g Pt(IV) in which a profit of more than USD20000 can be made. The bentonite functionalised with spent yeast from brewing has a potential to recover lost PGMs in wastewater. Since, this is a cheap process, the mining and other industries can make much profit from such recoveries.


Assuntos
Bentonita/química , Platina/isolamento & purificação , Saccharomyces cerevisiae/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Concentração de Íons de Hidrogênio , Resíduos Industriais , Metais/química , Soluções , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias , Água/química
7.
Chemosphere ; 239: 124763, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31526989

RESUMO

Nonredox metal ions have been widely recognized to be important in a wide range of biological and chemical oxidations as Lewis acids (LA). However, the role of LA in peroxymonosulfate (PMS) activation for wastewater treatment has not been considered until now. This study shows that oxidizing power of PMS can be promoted after binding nonredox metal ions such as Ca2+ as LA, leading to the easier reduction of the oxidant to radicals and substantial enhancement of dye degradation by employing manganese oxides OMS-2 as model catalysts. Increased with Lewis acidity of the metal ion, the rate of PMS decomposition enhanced linearly, while the dye degradation rate first increased and then declined due to the formation of a larger amount of dioxygen. The interactions between Ca2+ and PMS were further investigated by Raman, cyclic voltammetry and XPS; and the detailed mechanism of PMS activation was proposed. The performance of Ca2++OMS-2/PMS system under different conditions was also studied. The findings indicate the importance of LA in PMS activation reaction and their role must be considered in other transition metal oxides/PMS systems. It will be also helpful to design new and highly active catalysts for the reactions.


Assuntos
Ácidos de Lewis/química , Compostos de Manganês/química , Óxidos/química , Peróxidos/química , Poluentes Químicos da Água/química , Cálcio/química , Catálise , Corantes/química , Oxidantes/química , Oxirredução , Soluções , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química
8.
Biophys Chem ; 257: 106280, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31877450

RESUMO

High pressure acts as a mild and non-destructive activation mode for chemical reactions. However, in the context of organo-/biocatalysis, high pressure activation, has not been investigated systematically, although there are significant benefits such as rate acceleration, increased selectivity and the possibility of suppressing side product formation. The influence of hydrostatic pressure in solution on the catalytic performance of enzymes and small molecule organocatalysts such as amino acids, peptides, amines, cinchona alkaloids and thioureas is evaluated in this review, taking reactivity and selectivity as a probe to identify pressure effects on biomolecules.


Assuntos
Aminoácidos/química , Alcaloides de Cinchona/química , Peptídeos/química , Pressão , Catálise , Reação de Cicloadição , Enzimas/química , Enzimas/metabolismo , Soluções/química , Tioureia/análogos & derivados
9.
Chemosphere ; 238: 124646, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31473523

RESUMO

Humic substances (HS) in the aqueous solutions can be considered as colloidal particles formed by amphiphilic units. HS form micelles-like structures at concentrations close to 5 g/L. However colloidal behavior of HS at concentrations below 100 mg/L is unknown. Using radiotracer assay we have shown that in this concentration range HS form rare adsorption layers at the liquid/liquid interface and penetrate into the organic phase with the distribution ratio close to 10-3. We found that pH and HS molecular weight strongly influence on the distribution ratio but do not significantly change the adsorption. Furthermore, colloidal properties of HS are strongly depending on its origin: the highest surface activity was shown for HS separated from peat and the least was observed for HS separated from soils. We anticipate our assay to be a helpful tool for detailed analysis and modeling HS and humic-like materials colloidal behavior in the environment.


Assuntos
Substâncias Húmicas/análise , Soluções/química , Adsorção , Coloides , Concentração de Íons de Hidrogênio , Micelas , Peso Molecular , Solo , Trítio/análise
10.
Phys Chem Chem Phys ; 22(1): 212-222, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31799520

RESUMO

In this computational study, the intermolecular solute-solvent Nuclear Overhauser Effect (NOE) of the model protein ubiquitin in different chemical environments (free, bound to a partner protein and encapsulated) is investigated. Short-ranged NOE observables such as the NOE/ROE ratio reveal hydration phenomena on absolute timescales such as fast hydration sites and slow water clefts. We demonstrate the ability of solute-solvent NOE differences measured of the same protein in different chemical environments to reveal hydration changes on the relative timescale. The resulting NOE/ROE-surface maps are shown to be a central key for analyzing biologically relevant chemical influences such as complexation and confinement: the presence of a complexing macromolecule or a confining surface wall modulates the water mobility in the vicinity of the probe protein, hence revealing which residues of said protein are proximate to the foreign interface and which are chemically unaffected. This way, hydration phenomena can serve to indirectly map the precise influence (position) of other molecules or interfaces onto the protein surface. This proposed one-protein many-solvents approach may offer experimental benefits over classical one-protein other-protein pseudo-intermolecular transient NOEs. Furthermore, combined influences such as complexation and confinement may exert non-additive influences on the protein compared to a reference state. We offer a mathematical method to disentangle the influence of these two different chemical environments.


Assuntos
Ligases/química , Modelos Moleculares , Solventes/química , Ubiquitina/química , Água/química , Simulação por Computador , Soluções
11.
Water Sci Technol ; 80(6): 1053-1062, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31799949

RESUMO

Reactive Black 5 and Basic Blue 41 GRL dyeing solutions (dye-to-salt mixture in a 1:10 dye-to-salt mass ratio) were investigated as draw solutions (DS) in a forward osmosis (FO) system with a biomimetic membrane. Synthetic seawater (SSW) and textile wastewater (TWW1 and TWW2) were evaluated as feed solutions (FS) for water reclamation. Reactive Black 5 and Basic Blue 41 GRL were diluted from 0.02 M to concentrations of 0.002 and 0.004 M, respectively. With Reactive Black 5 as DS and SSW as FS, an initial flux of 20.24 L/m2 h and water recovery of 75% was achieved. Using TWW1 and TWW2, initial water fluxes of 19.51 and 13.43 L/m2 h were achieved, respectively, with a 30% water recovery. Using Basic Blue 41 GRL, initial water fluxes of 18.72, 15.13 and 13.42 L/m2 h were achieved with SSW, TWW1, and TWW2 as FS with water recoveries of 50%, 20% and 20%, respectively. The average reverse solute fluxes for Reactive Black 5 and Basic Blue 41 GRL were 0.06 to 0.34 g/m2 h, respectively. Diluted dyeing solutions were produced, with simultaneous water reclamation from SSW and TWW resulting in similar or higher water fluxes and lower reverse solute fluxes compared with other commercially available membranes.


Assuntos
Purificação da Água , Água , Membranas Artificiais , Osmose , Soluções , Águas Residuárias , Recursos Hídricos
12.
Water Sci Technol ; 80(6): 1205-1212, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31799964

RESUMO

Grape fruit (Citrus paradisi Macf.) peel (GP) was used as raw material to prepare two novel biosorbents: CaGP (Ca2+ type) and MgGP (Mg2+ type). Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms were used to characterize prepared adsorbents. Cd2+ biosorption by CaGP, MgGP and GP was investigated systematically by studying the effects of pH, biosorption time and initial concentration on the biosorption of Cd2+. The results showed that biosorption efficiencies of Cd2+ on CaGP and MgGP increased with increase in pH, and the highest removal of Cd2+ was occurred at pH 6.0. Meanwhile, Cd uptake capacity increased with contact time, and could reach equilibrium within 20 min. The rates of biosorption of Cd2+ on three prepared biosorbents were found to best-fit pseudo-second-order equation. Experimental isotherms were well fitted by Langmuir and Freundlich isotherms models. Moreover, according to the Langmuir equation, the maximum biosorption capacities (qm) of Cd2+ on CaGP and MgGP were found to be increased by 46.3% and 27.0%, respectively, compared with GP. The present study demonstrated that the waste grape fruit peel after simple Ca2+ or Mg2+ treatment could be used as a potential biosorbent for Cd2+, which indicated modified novel inactive/dead biological materials could remove Cd2+ from water.


Assuntos
Citrus paradisi , Poluentes Químicos da Água , Adsorção , Cádmio , Concentração de Íons de Hidrogênio , Cinética , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier , Água
13.
Water Sci Technol ; 80(7): 1226-1237, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31850874

RESUMO

We report the synthesis of hydroxyapatite (HAP) powder from waste mussel shells (decomposed to CaO) and phosphoric acid at room temperature without pH control. The powder synthesized was utilized for cadmium removal from aqueous solutions using the batch technique. The effects of solution pH, adsorbent dose; initial Cd2+ concentration, contact time, and temperatures were examined. Furthermore, the adsorption process revealed a pseudo-second-order reaction model and the Langmuir isotherm is the best-fit model to predict the experimental data and adsorption capacity was found to be 62.5 mg/g. Thermodynamic analysis revealed that because of the negative values of ΔGo and the positive value of ΔHo, the adsorption process was spontaneous and endothermic. Cadmium immobilization occurs through a two step mechanism: rapid ion exchange followed by partial dissolution of hydroxapatite and precipitation of cadmium containing hydroxyapatite.


Assuntos
Bivalves , Poluentes Químicos da Água , Adsorção , Animais , Cádmio , Durapatita , Concentração de Íons de Hidrogênio , Cinética , Soluções , Temperatura Ambiente , Termodinâmica
14.
Biophys Chem ; 254: 106265, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31669866

RESUMO

The impact of the differently hydrated non-electrolytes (protein structure destabilizers) on the fibrillation of hen egg white lysozyme (HEWL) was investigated. Two isomeric urea derivatives i.e. butylurea (BU) and N,N,N',N'-tetramethylurea (TMU) were chosen as a tested compounds. The obtained results show that butylurea exerts greater impact on HEWL and its fibrillation than tetramethylurea. Both substances decrease the time of induction of the fibrillation (lag time) but only BU increases the efficiency of amyloidogenesis. For the systems with equivalent reduction of the HEWL stability (250mM BU and 500mM TMU) the not-equivalent increase of the protein fibrillation was recorded (higher for BU). This fact suggests that specific interactions with protein, possibly water mediated, are responsible for the action of the tested substances.


Assuntos
Amiloide/química , Muramidase/química , Água/química , Animais , Galinhas , Dicroísmo Circular , Microscopia de Força Atômica , Muramidase/metabolismo , Estabilidade Proteica , Soluções/química , Ureia/química
15.
J Chem Theory Comput ; 15(12): 6968-6983, 2019 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-31714774

RESUMO

Intrinsically disordered proteins (IDPs) adopt heterogeneous conformational ensembles in solution. The properties of the conformational ensemble are dependent upon the solution conditions, including the presence of ions, temperature, and crowding, and often directly impact biological function. Many in vitro investigations focus on the properties of IDPs under dilute conditions, rather than the crowded environment found in vivo. Due to their heterogeneous nature, the study of IDPs under crowded conditions is challenging both experimentally and computationally. Despite this, such studies are worth pursuing due to the insight gained into biologically relevant phenomena. Here, we study the highly charged IDP Histatin 5 under self-crowded conditions in low and high salt conditions. A combination of small-angle X-ray scattering and different simulation models, spanning a range of computational complexity and detail, is used. Most models are found to have limited application when compared to results from experiments. The best performing model is the highly coarse-grained, bead-necklace model. This model shows that Histatin 5 has a conserved radius of gyration and a decreasing flexibility with increasing protein concentration. Due to its computational efficiency, we propose that it is a suitable model to study crowded IDP solutions, despite its simplicity.


Assuntos
Proteínas Intrinsicamente Desordenadas/química , Modelos Moleculares , Espalhamento a Baixo Ângulo , Difração de Raios X , Biologia Computacional , Soluções
16.
Water Sci Technol ; 80(5): 939-949, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31746801

RESUMO

This study aims to investigate the performance and mechanism of raw (R-ND) and saponin-modified nano diatomite (M-ND) in the removal of azithromycin from aqueous solutions. Adsorbent characterization was performed using X-ray fluorescence, Brunauer-Emmett-Teller (BET), scanning electron spectroscopy, dynamic light scattering and energy-dispersive X-ray analyses. It was shown that the specific surface area of R-ND was 119.5 m2/g, 14-fold higher than that for raw diatomite, and for M-ND it was 90.1 m2/g. Various adsorption conditions, i.e. adsorbent dosage, pH, initial concentration and contact time were investigated. According to the results, despite reducing the specific surface area by 25%, modification of nano diatomite by saponin markedly enhanced its performance in the removal of azithromycin. The maximum adsorption capacity of R-ND and M-ND in the removal of azithromycin was 68 and 91.7 mg/g, respectively. Fourier transform infrared spectroscopy results revealed that azithromycin was adsorbed by O-H groups on the diatomite surface. Weber-Morris intra-particle diffusion (IPD) model suggested that while IPD is not the rate-controlling step in high concentrations of azithromycin, it is the only step that controls the rate of adsorption in low concentrations. In comparison to R-ND, M-ND showed a higher efficiency in the removal of azithromycin and, therefore, it can be used as a promising low-cost adsorbent to remove azithromycin from aqueous solutions.


Assuntos
Saponinas , Poluentes Químicos da Água , Adsorção , Azitromicina , Terra de Diatomáceas , Concentração de Íons de Hidrogênio , Cinética , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier
17.
Water Sci Technol ; 80(5): 989-997, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31746806

RESUMO

As a kind of earth-abundant and cheap natural clay mineral, palygorskite (Pal) was facilely modified by grafting with graphene oxide (GO) to fabricate GO/Pal composites for rapid removal of Pb(II) from aqueous solutions. The results of characterization confirmed that the GO/Pal composites were successfully grafted between GO sheets and Pal nanorods. The effects of pH, adsorbent dosage, adsorption time, initial Pb(II) concentration and temperature on the adsorption of Pb(II) onto the GO/Pal composites as adsorbents were systematically investigated. The maximum adsorption capacity over 106.6 mg/g was obtained within a short adsorption time of less than 1 h even at 298.15 K. The adsorption of Pb(II) was a fast process that more accurately followed the pseudo-second-order kinetic equation. This process also could be described better with the Langmuir equation model than the Freundlich model. The negative values of ΔG° and the positive values of ΔH° and ΔS° indicated that it was a spontaneous, endothermic and entropy-increasing adsorption process. Compared with pristine Pal and GO powders, such the GO/Pal composites as a cost-efficient and eco-friendly adsorbents could significantly improve the adsorption properties of Pb(II) and would have potential application in the industrial wastewater treatment for rapid removal of Pb(II).


Assuntos
Grafite , Poluentes Químicos da Água , Purificação da Água , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Chumbo , Compostos de Magnésio , Óxidos , Compostos de Silício , Soluções
18.
Environ Pollut ; 255(Pt 2): 113355, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31668956

RESUMO

Measurement of solute-transport parameters through soils for a wide range of solute- and soil-types is time-consuming, laborious, expensive and practically impossible. So, indirect methods for estimating the transport parameters by pedo-transfer functions are now advancing. This study developed and evaluated an Artificial Neural Network (ANN) model for estimating the transport velocity (V), dispersion coefficient (D) and retardation factor (R) of NaAsO2, Pb(NO3)2, Cd(NO3)2, C9H9N3O2 and CaCl2 from the basic soil properties. Breakthrough data of the solutes were measured in 14 agricultural soils of Bangladesh by time-domain reflectometry (TDR) in repacked soil columns under unsaturated steady-state water-flow conditions. The transport parameters of the chemicals were determined by analyzing the solute breakthrough data. Bulk density (γ), organic carbon (OC), clay (C) content, pH, median grain diameter (D50) and uniformity coefficient (Cu) of the soils were determined. An ANN model for V, D and R was developed by using data of eight soils, validated/tested with the data of five soils and verified with the data of one soil. Clay content and bulk density of the soils were the most sensitive input variables to the ANN model followed by other soil properties (OC, C, pH, D50 and Cu). The model reliably predicted V, D and R with relative root-mean-square error (RRMSE) of 0.028-0.363, mean error (ME) of - 0.00004 to 0.0005, bias error (BOE%) of 0-0.003 and modeling efficiency (EF) of >0.99. Thus, the ANN model can significantly enhance prediction of pollution transport through soils in terms of cost and effort.


Assuntos
Monitoramento Ambiental , Poluentes do Solo/análise , Agricultura , Bangladesh , Argila , Solo/química , Soluções
19.
J Chem Phys ; 151(16): 165101, 2019 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-31675878

RESUMO

As an extremely common structural motif, RNA hairpins with bulge loops [e.g., the human immunodeficiency virus type 1 (HIV-1) transactivation response (TAR) RNA] can play essential roles in normal cellular processes by binding to proteins and small ligands, which could be very dependent on their three-dimensional (3D) structures and stability. Although the structures and conformational dynamics of the HIV-1 TAR RNA have been extensively studied, there are few investigations on the thermodynamic stability of the TAR RNA, especially in ion solutions, and the existing studies also have some divergence on the unfolding process of the RNA. Here, we employed our previously developed coarse-grained model with implicit salt to predict the 3D structure, stability, and unfolding pathway for the HIV-1 TAR RNA over a wide range of ion concentrations. As compared with the extensive experimental/theoretical results, the present model can give reliable predictions on the 3D structure stability of the TAR RNA from the sequence. Based on the predictions, our further comprehensive analyses on the stability of the TAR RNA as well as its variants revealed that the unfolding pathway of an RNA hairpin with a bulge loop is mainly determined by the relative stability between different states (folded state, intermediate state, and unfolded state) and the strength of the coaxial stacking between two stems in folded structures, both of which can be apparently modulated by the ion concentrations as well as the sequences.


Assuntos
HIV-1/química , Conformação de Ácido Nucleico , RNA Viral/química , Íons/química , Modelos Moleculares , Soluções
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA