Microcalorimetric measurements of the metabolic activity by bacteria and fungi in some Brazilian soils amended with different organic matter

The effect of bacterial and fungal activities on organic matter degradation in Brazilian soils was studied by a microcalorimetric method. Bacteria and fungi isolated from tropical soils and added to: Rhodic eutrudox (R), Typic eutrudox (V) and Quartzipsamment (Q) soils amended separately with moisture (control) (A) and 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 23 μg of trifluralin (T) were investigated. The number of colony forming units in soil suspension was quantified by microscopy and inoculated in respective soil. All processes were measured at intervals of 7 days over a period of 35 days. The exothermic thermal effect (μJ) per cm³ of bacteria or fungi per gram of dry soil, respectively, for each substrate was: [(9±1), (4±1)] RA; [(478±24), (105±5)] RE; [(121±6), (71±4)] RL; [(121±6), (71±4)] RH; [(8±1); (3±1)] RT; [(10±1), (9±1] VA; [(347±17), (261±13)] VE; [(71±4), (28±1)] VL; [(22±1), (33±2)] VH; [(7±1), (10±1)] VT; [(19±1), (12±1)] QA; [(1301±65), (46±2)] QE; [(89±4), (9±1)] QL; [(130±7), (11±1)] QH; [(32±2), (8±1)] QT. The calorimetric values are higher for bacteria than for fungi. In general, the results showed higher activities in the soil amended with cattle manure than with other additives.     

Underbody and ground effects on rotating disc flow: a global scale inviscid study

The flow induced by a finite disc rotating near horizontal ground is considered, including the effects of an underbody. This paper concentrates on determining the shape of the free layer beyond the rim of the disc which is horizontal in the absence of the underbody and ground but forced to deform to ensure that conditions across the layer are satisfied when the underbody or ground is added. The far-field behaviour, the inviscid flow produced by a nominally infinite disc near the ground and the global solution for small ground clearances are considered analytically, and the full problem is posed as an integral problem. This is then solved numerically and analytically. Results are presented for various heights of the disc above the ground and for discs with an axisymmetric underbody present. A universal form is found for the farfield shape (which is controlled by entrainment into the free layer) but both the underbody and the ground effects are found to increase very significantly for reduced clearances.     

共轴均匀带电薄圆盘间的相互作用力

本文利用静电场的高斯定律和环路定律巧妙地求出了均匀带电圆盘在空间任一点所产生的电场 ,进而计算出了共轴均匀带电薄圆盘之间的相互作用力     

高斯光束照射下的圆盘夫琅禾费衍射

推导了高斯光束照射圆孔或圆盘的衍射场普遍表达式，计算了半波带数接近于零的情况下上述衍射场的数据，进而分析了圆盘衍射场在艾里斑中增加一个暗环的原因。     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

碱性溶液中金电极上氧还原中间物研究

应用改进了的旋转全电极上的电势阶跃计时库仑法,分别测定了不同电极电势下氧还原过程中电极吸附中间物和溶解中间物氧化所需的电量,实验证明,在此过程中电极上确有吸附中间物存在,而且是电极电势的函数,但其分子属性尚需进一步鉴别。     

A game locating a needle in a circular haystack

A complete solution of the following Hider-Seeker zero-sum game is obtained. The hider hides a needle of lengtha, 0<a2, in the closed unit dise, and the seeker tries to locate it by shooting in a straight line across the disc. The payoff to the seeker is 1 if he hits the needle and 0 otherwise.     

Hydrodynamic voltammetry at the liquid|liquid interface: facilitated ion transfer and the rotating diffusion cell

A new approach to the voltammetric investigation of facilitated ion transfer processes is reported. The technique uses a rotating diffusion cell approach to induce laminar flow in the organic phase of a liquid|liquid electrochemical cell. The interface between two immiscible electrolyte solutions (ITIES) was stabilised against rotation with either γ-alumina or a track-etched polyester membrane. The resultant voltammetry is shown to be consistent with the Koutecký–Levich equation enabling kinetic parameters associated with facilitated transfer of sodium by dibenzo-18-crown-6 across the water|1,2-dichloroethane interface to be evaluated. In particular, the use of the more hydrophilic alumina membrane permits the uncertainties regarding the use of the membrane-stabilised ITIES, namely the interfacial position, to be eliminated.     

Kinetic parameters of the In(III)/In(I) electrode reaction in bromide medium

The electrode kinetic parameters of the In(III)/In(I) couple in acidic 4M bromide solution have been determined by means of the rotating disc electrode technique.

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Die elektrochemisch-kinetischen Parameter des In(III)/In(I)-Redoxsystems in Bromidlösung (Kurze Mitteilung)

Zusammenfassung Die elektrochemisch-kinetischen Parameter am In(III)/In(I)-Redoxsystem wurden in saurer 4-M-Bromidlösung mittels der rotierenden Scheibenelektrode bestimmt.

     

Removal of Mn(II) and Cd(II) from wastewaters by natural and modified clays

The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents, by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q ₀ parameter, which is related to the sorption capacity, corresponding to 6.3 mg g^{− 1} for K-10/Cd(II), 4.8 mg g^{− 1} for K-10/Mn(II), 11.2 mg g^{− 1} for NT-25/Cd(II) and 6.0 mg g^{− 1} for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction, a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L^{− 1} solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent.