Neural theory of association and concept-formation

The present paper looks for possible neural mechanism underlying such high-level brain functioning as association and concept-formation. Primitive neural models of association and concept-formation are presented, which will elucidate the distributed and multiply superposed manner of retaining knowledge in the brain. The models are subject to two rules of self-organization of synaptic weights, orthogonal and covariance learning. The convergence of self-organization is proved, and the characteristics of these learning rules are shown. The performances, especially the noise immunity, of the association net and concept-formation net are analyzed.This research was supported in part by a grant by the Sloan Foundation to the Center for Systems Neuroscience, University of Massachusetts     

Purification of CBS 819.72 α-amylase by aqueous two-phase systems: Modelling using Response Surface Methodology

The partition and purification of α-amylase from a culture supernatant of Aspergillus oryzae CBS 819.72 was made in aqueous two-phase system (ATPS). According to bibliography and preliminary studies, the factors polyethylene glycol (PEG) molecular weight (M_PEG) and concentration (C_PEG), buffer type (BU) and concentration (C_BU), temperature (T), salt nature (SALT) and concentration (C_SALT), bioligand (BL) and concentration (C_BL) and pH were investigated using a Plackett–Burman design to identify the factors affecting separation. Taking into consideration a simultaneous increase in enzyme recovery (R_Y) and purification factor (P_F), the best performance of the system was obtained at 4 °C and pH 6 using PEG 8000 g/mol, citrate buffer, KCl and sucrose. Experimental Box–Behnken design together with the Response Surface Methodology (RSM) have been used to find optimum C_PEG, C_Citrate and C_SALT. Quadratic models were predicted for P_F and R_Y in the top phase and a better compromise between these two parameters can be found by superimposing the contour plots of P_F and R_Y for 8% citrate. A region in the experimental space can be defined where the purification factor is always higher than 3 with yields exceeding 65%.     

Inoculum standardization for biodegradability tests

Summary To obtain standardized inoculum with constant characteristics for biodegradability test, Actizym powder was used instead of sludge. A predigestion and stabilization step were introduced to prepare “activated Actizym”, before inoculation and addition of test chemical. The inoculum obtained is similar to activated sludge in its microbiological and physical aspects. The reproducibility of the method was prooved and several controls were made using chemicals with different biodegradation rates.     

Chemical Composition and Cytotoxic Activity of Eucalyptus torquata Luehm. and Eucalyptus salmonophloia F. Muell. Trunk Bark Essential Oils against Human SW620 and MDA-MB-231 Cancer Cell Lines

In recent years, there has been a growing interest in the screening of natural active ingredients from Eucalyptus essential oils because of their evident importance in practical utility and their undeniable therapeutic properties. Based on this, the aim of the present study was to investigate the chemical profile of the essential oils of the trunk bark of Eucalyptus torquata Luehm. (ETEO), and E. salmonophloia F. Muell. (ESEO), growing in Tunisia. The in vitro cytotoxic properties of the extracted EOs were also evaluated against two human cancer cell lines: breast carcinoma cell lines MDA-MB-231 and colorectal cancer cell lines SW620. The analysis by gas chromatography coupled with mass spectrometry (GC/MS) led to the identification of 32 compounds from the ETEO, with the dominant constituents being the monoterpenes trans-myrtanol (73.4 %) and myrtenol (4.7 %), and the apocarotene (E)-β-ionone (3.9 %). In the case of ESEO, 29 compounds were identified with trans-myrtanol (25.0 %), decanoic acid (22.1 %), nonanoic acid (9.8 %), γ-elemene (6.5 %), γ-maaliene (5.5 %), and α-terpineol (5.3 %) as the main components. The cytotoxicity of EOs against the two chosen cell lines was tested using Crystal Violet Staining (CVS) assay and 5-fluorouracil as a reference drug. The two EOs exhibited a significant dose-dependent inhibition against the viability of the used cell lines. Their inhibitory effects were particularly observed towards SW620 colon carcinoma cells with IC₅₀ values of 26.71±1.22 and 22.21±0.85 μg/mL, respectively, indicating that both oils were more cytotoxic for SW620 cells compared to MDA-MB-231 one.     

Interspecific molecular variation of Tunisian complex Lolium perenne L. and Festuca arundinacea Schreb. based on the internal transcribed spacer locus (ITS)

To establish phylogenetic relationships and estimate the intra and interspecific divergence, the amplification and the sequencing of the internal transcribed spacers of ribosomal DNA (ITS = ITS1 + 5.8S + ITS2) were analyzed in Tunisian complex Lolium–Festuca DNA. These spacer regions have evolved mainly by point mutations. Results revealed a high level of polymorphism within studied species. Significant similarities were observed between these two species and showed the existence of an important phylogenetic relationship. Besides, this molecular approach has revealed two new clusterings, with a homologous ITS gene namely: Bromus hordeaceus and Hordeum murinum subsp. This could be explained by the conservation of an ancestral ITS gene in some fescue plants. Thus, Tunisian tall fescue and perennial ryegrass may derive from Bromus hordeaceus and Hordeum murinum subsp. Considerable morphology and bioclimatic distribution similarities were discovered in ITS sequences within the same species. This study can be of great help to identify suitable accessions that could be used in local fescue and ryegrass improvement program.