Tunis University

About: Tunis University is a education organization based out in Tunis, Tunisia. It is known for research contribution in the topics: Population & Thin film. The organization has 11745 authors who have published 15400 publications receiving 154900 citations. The organization is also known as: University of Tunis & UT.

Structure and insertion properties of disordered and ordered LiNi0.5Mn1.5O4 spinels prepared by wet chemistry

Abstract: We present the synthesis, characterization, and electrode behavior of LiNi0.5Mn1.5O4 spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi0.5Mn1.5O4 appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel [Fd3m space group (SG)] and ordered spinel (P4132 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi0.5Mn1.5O4 powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d8 metal for Mn in LiNi0.5Mn1.5O4 oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi0.5Mn1.5O4 cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn2O4 and LiNi0.5Mn1.5O4 oxides are discussed.

Interactions of zinc and cadmium toxicity in their effects on growth and in antioxidative systems in tomato plants (Solarium lycopersicum)

Abstract: The interaction between zinc and cadmium was investigated in tomato plants (Solanum lycopersicum). Ten-day-old seedlings were treated with 10 micromol/L CdCl2 associated to different concentrations of ZnCl2 (10, 50, 100, and 150 micromol/L). Zn supply clearly reduced Cd accumulation in leaves and simultaneously increased Zn concentration. Cd induced oxidative stress in leaves as indicated by an increase in thiobarbituric acid-reactive substances (TBARS) level and chlorophyll breakdown. Furthermore, compared with control, Cd-treated plants had significantly higher activities of superoxide dismutase (SOD, EC 1.15.1.1), whereas, catalase (CAT, EC 1.111.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) activities were significantly suppressed by Cd addition. Zn supplementation, at low level, restored and enhanced the functional activity of these enzymes (SOD, CAT, APX and GR) as compared to Cd-alone-treated plants. The beneficial effect of adequate Zn level on Cd toxicity was confirmed by a significant decrease in TBARS level and restoration of chlorophyll content. However, when Zn was added at high level in combination with Cd there was an accumulation of oxidative stress, which was higher than that for Cd or excess Zn alone treatments. These results suggested that higher Zn concentrations and Cd are synergistic in their effect on plant growth parameters and oxidative stress.

Banking supervision and nonperforming loans: a cross‐country analysis

Abstract: Purpose – The purpose of this paper is to empirically analyse the cross‐countries determinants of nonperforming loans (NPLs), the potential impact of supervisory devices, and institutional environment on credit risk exposure.Design/methodology/approach – The paper employs aggregate banking, financial, economic, and legal environment data for a panel of 59 countries over the period 2002‐2006. It develops a comprehensive model to explain differences in the level of NPLs between countries. To assess the role of regulatory supervision on credit risk, the paper uses several interactions between institutional features and regulatory devices.Findings – The empirical results indicate that higher capital adequacy ratio (CAR) and prudent provisioning policy seems to reduce the level of problem loans. The paper also reports a desirable impact of private ownership, foreign participation, and bank concentration. However, the findings do not support the view that market discipline leads to better economic outcomes. All...