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Sustainability of brackishwater shrimp farming is of paramount importance for socio-economic development of southwest coastal Bangladesh. Here, shrimp farming is predominantly traditional, which is more vulnerable to climate change. Lack of understanding exists regarding the adaptation measures of local shrimp farmers in response to emerging impacts of changing climatic variables. This study provides the perceptions and adaptations of shrimp farmers in changing climatic context. A systematic random sampling method was employed to conduct a total of 240 questionnaire surveys and 60 key informant interviews from six sub-districts (Upazila) of southwest coastal Bangladesh to collect primary data. Changes in climate variables largely affect the shrimp yield by increasing frequency of shrimp disease, causing physical damage to farm structure and deteriorating quality of water. Shrimp farmers try to adapt to those changes in various ways, including increasing pond depth, exchanging tidal water, providing shade using aquatic plants, strengthening earthen dike and netting and fencing around the dike. Shrimp mixed cultivation is the most popular form of shrimp farming in the study area. More emphasis on implementing polyculture shrimp farming is necessary to improve climate change adaptation and to promote sustainability of this aquaculture practice in southwest coastal Bangladesh. [ABSTRACT FROM AUTHOR]

The heteroscedasticity consistent covariance matrix estimators are commonly used for the testing of regression coefficients when error terms of regression model are heteroscedastic. These estimators are based on the residuals obtained from the method of ordinary least squares and this method yields inefficient estimators in the presence of heteroscedasticity. It is usual practice to use estimated weighted least squares method or some adaptive methods to find efficient estimates of the regression parameters when the form of heteroscedasticity is unknown. But HCCM estimators are seldom derived from such efficient estimators for testing purposes in the available literature. The current article addresses the same concern and presents the weighted versions of HCCM estimators. Our numerical work uncovers the performance of these estimators and their finite sample properties in terms of interval estimation and null rejection rate. [ABSTRACT FROM AUTHOR]

The sorption behavior of 3.18×10 -6 mol l -1 solution of Tm(III) metal ions onto 7.25 mg l -1 of 1-(2-pyridylazo)-2-naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (?E ads ) and activation entropy (?S ads ) of the system were found to be 22.1±2.6 kJ mol -1 and 52.7±6.2 J mol -1 K -1 , respectively. The thermodynamic parameters such as enthalpy (?H), entropy (?S), and Gibbs free energy (?G) were calculated and interpreted. The positive value of ?H and negative value of ?G indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (?H diff ), entropy of adsorption (?S diff ) and adsorption free energy (?G ads ) at 313 K were determined and found to be 38±2 kJ mol -1 , 249±3 J mol -1 K -1 and –40.1±1.1 kJ mol -1 , respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy. [ABSTRACT FROM AUTHOR]

The adsorption studies of Eu(III) and Tm(III) was investigated on 4-(2-pyridylazo) resorcinol (PAR) loaded polyurethane foam (PUF). The sorption conditions were optimized with respect to pH, shaking time, and loading capacity. Kinetic of sorption of Eu(III) and Tm(III) were evaluated at different intervals of time. The diffusion coefficient of Eu(III) and Tm(III) are found to be 4.48 × 10−5 cm2 sec−1 and 7.81 × 10−5 cm2 sec−1. The Freundlich constant (1/n) are estimated to be 0.56 and 0.47 for Eu(III) and Tm(III), respectively, reflects a surface heterogeneity of the PUF. Langmuir isotherm gives a saturated capacity of 1.95 × 10−5 mol g−1 for Eu(III) and 1.01 × 10−4 mol g−1 for Tm(III), suggest a monolayer coverage of the surface. The Dubinin–Radushkevich (D–R) isotherm is applied and the sorption mean free energy (E) was calculated and was in the range 11–12 kJ mol−1 suggesting chemisorption involving chemical bonding is responsible for the adsorption process. The thermodynamics parameters such as enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) were calculated and interpreted. The large negative values of ΔH indicates that the adsorption of metal ions on PAR-loaded PUF is an exothermic process. A possible explanation of this exothermicity related to bonding has been given. The sorption is greatly affected in the presence of oxalate, citrate, tartrate, and phosphate. [ABSTRACT FROM AUTHOR]

The sorption of iodine on polyurethane foam (PUF) has been investigated. The maximum sorption of 0.01 N of iodine solution on PUF was found to be >95% from 0.2 N HCl aqueous solution. The maximum equilibration was attained with 30 min agitation time. The iodine number was found to be 436±15 mg g-1. The average pore diameter of PUF was 8.3 nm and total surface area was 67 m2 g-1. The kinetic data indicates that the intraparticle diffusion rate of adsorption (Rd) and rate of mass action (k1) of iodine sorption on PUF were 0.48±0.03 mmole g-1 min-1/2 and 52±8 mmole g-1 min-1, respectively. The sorption data followed both Freundlich and Langmuir adsorption isotherms in the concentration range 0.03 N to 0.15 N of iodine. The Freundlich constants Cm=11.2±1.7 mmole g-1 and 1/n=0.57±0.05, and Langmuir constants M=4.9±0.6 mmole g-1 and b=12.9±1.3 L g-1 were established. The sorption free energy (E)=5.3±0.2 kJ mole-1 and loading capacity Xm=5.15±0.45 mmole g-1 were evaluated using D–R isotherm. The sorption energy reflects the physiosorption of iodine on PUF. The effect of temperature on the sorption yields the thermodynamic parameters ΔH=50±2 kJ mole-1 and ΔS=170±4 J mole-1 K-1. The Gibbs free energy (ΔG) ranges from 3.72 to -2.15 kJ mole-1, suggesting the endothermic nature of sorption of iodine, but is favorable at higher temperatures (>313K). The effect of different anions and cations on the sorption of iodine on PUF have been evaluated and discussed. [ABSTRACT FROM AUTHOR]

Sorption of cobalt(II)–thiocyanate complex onto polyurethane foam (PUF) has been investigated in detail with respect to the equilibrating time between Co(II)-thiocyanate complex in solution and foam, and concentrations of cobalt(II) and sorbent. The sorption was optimized with respect to the composition of electrolyte. Maximum sorption has been achieved from 0.1 M HCl solution containing 0.5 M SCN after 10 minutes of shaking time. The kinetics and thermodynamics of sorption are studied in detail. The kinetics follow a first-order rate equation with the rate constant, k, equal to 9.57 × 10-2 min.-1 The variation of equilibrium constant Kc with temperature (15–50°C) yields values of ΔH = -64 ± 4.6 kJ·mol-1, ΔS = -192.6 ± 15.6 J·mol-1·K-1, and ΔG = -8.71 kJ·mol-1 at 298 K. The sorption of Co(II)-thiocyanate onto PUF in the presence of common anions and cations has also been measured. The sorption data studied in the concentration range of Co(II) 1.12 × 10-4 to 1.20 × 10-3 M follow Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. Freundlich parameters 1/n = 0.35 ± 0.02 and A = 0.85 ± 0.2 mmol·g-1, Langmuir constants Q = (5.54 ± 0.12) × 10-5 mol·g-1 and b = (3.55 ± 0.74) × 104 dm3·mol-1 and D–R isotherms β = -0.002999 ± 0.000189 kJ2·mol-2, Cm = 10.66 ± 0.16 × 10-4 mol·g-1 and E = 12.9 ± 0.4 kJ·mol-1 have been evaluated. The possible sorption mechanism of cobalt–thiocyanate complex onto PUF is also discussed. [ABSTRACT FROM AUTHOR]

Mercury sulfide was prepared and characterized by measuring average pore size and surface area. The sorption of mercury onto mercury sulfide was investigated in detail with respect to sorptive medium, agitation time, sorbent and sorbate concentration, and temperature. The maximum sorption of mercury (>99.8) was achieved from 10-3 M hydrochloric acid solution using 50 mg mercury sulfide for 10 minutes. The sorption data of mercury followed the Langmuir isotherm over the entire concentration of mercury investigated whereas the Freundlich and Dubinin–Radushkevich isotherms were obeyed only up to low and moderate concentrations. Useful parameters like sorption capacity and energy have been evaluated using these isotherms. The variation of the equilibrium constant with temperature has the results ΔH=23.8 ± 3.2 kJ·mol-1, ΔS = 130 ± 10 J·mol-1, and ΔG = -13.5 ± 0.4 kJ·mol-1 at 298 K. Among the ions tested, tartrate, fluoride, and citrate increase the sorption whereas Cu(II), Ba(II), Zn(II), Ni(II), Fe(II), and Cr(III) reduce the sorption significantly. Except for Y(III) (∼91%), all the metal ions showed a lower affinity toward HgS, especially trivalent Ho, Fe, Sc, Tm, Ga, Dy, As, and Pr which showed sorption >1 and >10%. The mercury sulfide column can be used to separate Hg(II) from these trivalent metal ions. [ABSTRACT FROM AUTHOR]