The behaviour of ternary compounds InGaAs and GaAsN subjected to electron irradiation

This paper presents results of the effect of electron beam irradiation under UHV conditions on InGaAs/GaAs and GaAsN/GaAs systems using Auger electron spectroscopy (AES) and the electron energy loss spectroscopy (EELS) as surface analytical techniques. The ternary compounds In_0.53Ga_0.47As and In_0.2Ga_0.8As were irradiated by an electron beam under identical conditions (5 KeV; 10⁻³ A cm⁻²; for 60 min). The results showed that the compound In_0.53Ga_0.47As was stable under electron irradiation whereas changes in the Auger signal In-M₄₅N₄₅N₄₅ revealed that the electron beam had a significant effect on the compound In_0.2Ga_0.8As. GaAsN growth at 590 °C on GaAs is believed to produce a surface containing defects that is chemically unstable when bombarded by electrons. It was found that heating this compound at 730 °C stabilised the surface, protecting it from the effect of electron irradiation.     

Production of three anti-listerial peptides by Lactobacillus curvatus in MRS broth

Three novel bioactive peptides (BAP1–3) from Lactobacillus curvatus CWBI-B28 were isolated and purified using de Man, Rogosa and Sharp (MRS) broth by a three-step protein purification protocol including ammonium sulfate precipitation, hydrophobic C₁₈ Sep-Pak column and reverse-phase high performance liquid chromatography (RP-HPLC). This procedure allowed the recovery of chromatographically pure antimicrobial peptides with the yields of 19%, 10% and 15% of BAP1, BAP2 and BAP3, respectively. The respective apparent molecular masses as determined by tricine-SDS-polyacrilamide gel electrophoresis were 6365, 3426 and 3496. N-terminal amino acid sequencing of the BAPs and comparison of their sequences with those of international data bases indicated that BAP1 is more likely to be a casein-derived bioactive protein produced upon hydrolysis of the tryptone present in MRS broth by Lb. curvatus CWBI-B28 during active growth. However, the identity of BAP2 and BAP3 could not be determined with certainty; yet, they would be novel bacteriocins not fitting in any of the known classes of bacteriocins. Therefore, this strain would have the ability to produce intrinsic antimicrobial substances and also release bioprotective peptides from milk-proteins upon cultivation in milk or casein-containing food products due to its proteolytic activity. Thus, Lb. curratus CWBI-B28 possesses a good potential to be used in food preservation and safety.     

H∞ filtering of discrete-time switched singular systems with time-varying delays

In this article, the analysis and design problems of H_∞ filtering for a class of discrete-time switched singular systems with time-varying delay under an arbitrary switching signal are investigated. The main attention is focused on the design of a linear mode-dependent filter guaranteeing the regularity, causality, and asymptotic stability of the resulting filtering error system with a prescribed H_∞ performance bound. By using a multiple Lyapunov-Krasovskii functional, and utilizing the linearization technique, novel sufficient conditions for the solvability of H_∞ problem are derived in terms of linear matrix inequalities. Solving that, the desired filter gains can be determined. Any model transformation of system, which often leads the large computational burden is involved. The free weighting matrix technique is introduced to provide additional degree of freedom, which improves the conservativeness of the developed method. Finally, numerical examples are given to demonstrate the effectiveness and the merit of the proposed approach and to compare the obtained results with some previous works in the literature.     

Biocontrol of Listeria monocytogenes in a model cultured milk (lben) by in situ bacteriocin production from Lactococcus lactis ssp. lactis

Bacteriocin‐producing (Bac⁺) Lactococcus lactis ssp. lactis CCMM/IAV/BK1 isolated from traditional lben was used in the preparation of lben from pasteurized milk to assess its potential inhibitory activity against Listeria monocytogenes ATCC 7644. Production of bacteriocin (arbitrary units, AU) in MRS broth fortified with yeast extract (MRSY) in a fermentor under controlled and uncontrolled pH conditions was also investigated. This Bac⁺ strain yielded about 35 times more bacteriocin when the pH was maintained constant at 6.5 than under varying pH conditions. To test the effect of in situ bacteriocin production against L. monocytogenes, lben was made from cow's milk artificially contaminated with approximately 10⁷ cfu/mL and fermented with a mixed mesophilic starter culture consisting of the lactococcal Bac⁺ organism and Lc. lactis ssp. lactis biovar diacetylactis 66, a diacetyl‐producing strain, in a ratio of 1 : 1. Numbers of L. monocytogenes were monitored during fermentation and storage of lben at refrigeration temperature (c. 7°C) for up to 6 days. Performances of the Bac⁺ starter were compared to those of an isogenic Bac^? derivative strain obtained from the Bac⁺ starter by curing with ethidium bromide. The results showed that the amount of L. monocytogenes decreased to below the detectable level in a 1‐mL sample within 24 h of storage at 7°C in lben fermented with the Bac⁺ starter culture. On the contrary, L. monocytogenes survived for 6 days of storage at 7°C in lben made with the Bac^? starter. The Bac⁺ wild strain of the starter studied could be adequately used to produce lben or similar indigenous fermented milks of improved hygienic quality on an industrial scale. Alternatively, it could be used as an adjunct in minimally processed products or in products obtained from raw milk to add a safety factor.     

Staphylococcal enterotoxins and enterotoxin-like toxins with special reference to dairy products: An overview

Staphylococcal Enterotoxins (SEs) have been raising health concerns for food safety due to their association with staphylococcal foodborne poisoning (SFP). As superantigens, they also cause the life threatening toxic shock syndrome (TSS), the transmission of which via food cannot be ruled out despite the lack of epidemiological evidence. To date, at least 23 of these exotoxins are known and separated into SEs and Staphylococcal Enterotoxin-like (SEl) depending on whether or not they invoke emesis. This work presents an up-to-date overview on the presently known SEs/SEls from the perspective of their classification, pathogenesis, and genetic organisation. The incidence of these toxins in dairy products, the risk this poses to the public health, and possible control means are also reviewed.     

Behaviour of Listeria monocytogenes in raw sausages (merguez) in presence of a bacteriocin-producing lactococcal strain as a protective culture

The effectiveness of a bacteriocin produced by Lactococcus lactis subsp. lactis M in reducing population level and growth of Listeria monocytogenes ATCC 7644 in fermented merguez sausage was examined. Two different formulas (with or without added nitrites) were assayed and predetermined numbers of Listeria (ca 10⁶ cfu g⁻¹) were added to sausage mixture. The effect of in situ production of the bacteriocin by Lactococcus lactis M on Listeria monocytogenes ATCC 7644 during fermentation and storage of merguez sausages at room (ca 22 °C) or at refrigeration (ca 7 °C) temperature was tested. Results indicated that counts of Listeria monocytogenes were decreased during fermentation of merguez samples fermented with either the bacteriocin-producing Lactococcus lactis M (Bac⁺) or a nonbacteriocin-producing Lactococcus lactis J (Bac⁻). However, reduction in Listeria cfu's was greater in samples fermented with the Bac⁺ than in those fermented with the Bac⁻ starter. In merguez sausage made without nitrites addition, the Bac⁺ starter induced further decrease in Listeria counts by 1.5 log cycles compared with that induced by the Bac⁻ starter. While in merguez samples with added nitrites (0.4%), the effect of the bacteriocin produced in situ was less important than in those made without nitrites addition.     

Study by AES and EELS spectroscopies of antimony and phosphorus evaporated on massive indium and on cleaned InP

In this paper, we give some results related to interaction mechanism between the elements V such as antimony or phosphorus with the metal indium. We used both powerful spectroscopy methods the Auger electron spectroscopy (AES) and the electron energy loss spectroscopy (EELS) for which the spectra were recorded in direct mode N(E). The antimony was evaporated on pure In metal or on cleaned InP surface involving the In metal because of its cleaning by the argon ion bombardment at low energy 300 eV. The antimony flow composed of Sb₄ species arrived with a thermal energy on the In metal surface. Such an energy was sufficient to their diffusion into the In matrix because of the low melting point of In metal (123 °C). A nucleation phenomenon occurred between Sb₄ and the In metal to form small islands of antimony metal in bulk. Further antimony evaporation enabled to increase the size of these islands towards the surface. However, the antimony evaporated on cleaned InP reacted chemically with the In metal distributed on the InP surface to form a thin layer of InSb. The inner stoichiometric layers of InP and the size of Sb₄ species and also the stability of InP versus the temperature impeded the interdiffusion phenomenon of antimony to occur deeply into the InP matrix. The InSb layer played the role to stabilise the surface of the InP compound versus the heating at 450 °C and the electron irradiation of 4 KeV energy. But, the phosphorus evaporation on In metal or on cleaned InP led to form chemical bonds InP. The phosphorus flow included chemical species P and P₂ with a thermal energy able to stimulate the chemical reactivity process between indium and phosphorus to form the InP compound.     

Application of geothermal energy for heating and fresh water production in a brackish water greenhouse desalination unit: A case study from Algeria

The aim of this paper was to outline a proposed a new brackish water greenhouse desalination unit powered by geothermal energy for the development of arid and relatively cold regions, using Algeria as a case study. Countries which have abundant sea/brackish water resources and good geothermal conditions are ideal candidates for producing fresh water from sea/brackish water. The establishment of human habitats in these arid areas strongly depends on availability of fresh water. The main advantage of using geothermal energy to power brackish water greenhouse desalination units is that this renewable energy source can provide power 24 h a day. This resource is generally invariant with less intermittence problems compared to other renewable resources such as solar or wind energy. Geothermal resources can both be used to heat the greenhouses and to provide fresh water needed for irrigation of the crops cultivated inside the greenhouses. A review of the geothermal potential in the case study country is also outlined.