We provide new non-approximability results for the restrictions of the Min Vertex Cover problem to bounded-degree, sparse and dense graphs. We show that, for a suuciently large B, the recent 16/15 lower bound proved by Bellare et al. 3] extends with negligible loss to graphs with bounded degree B. Then, we consider sparse graphs with no dense components (i.e. everywhere sparse graphs), and we s...

The Shortest Superstring Problem (SSP) consists, for a set of strings S = {s1, · · · , sn}, to find a minimum length string that contains all si, 1 ≤ i ≤ k, as substrings. This problem is proved to be NP-Complete and APX-hard. Guaranteed approximation algorithms have been proposed, the current best ratio being 2 11 23 , which has been achieved following a long and difficult quest. However, SSP ...

Changes in the activities of four enzymes involved in antioxidative plant defence against low temperature treatment were studied in winter wheat plants (Triticum aestivum L cv. Sadovo 1) grown on acid soil (pH 4.2, KCl) under controlled environmental conditions. To investigate the effect of molybdenum (Mo) deficiency on antioxidative defence of these plants, Mo was added to part of the plants a...

Biochemical changes in the plants of Pistia stratiotes L., a free floating macrophyte exposed to different concentrations of hexavalent chromium (0, 10, 40, 60, 80 and 160 microM) for 48, 96 and 144 h were studied. Chromium-induced oxidative stress in macrophyte was investigated using the multivariate modeling approaches. Cluster analysis rendered two fairly distinct clusters (roots and shoots)...

This study examined the effect of increasing chloroplastic superoxide dismutase (SOD), ascorbate peroxidase (APX), or glutathione reductase (GR) activity via plant transformation of cotton on the initial recovery of photosynthesis following exposures to 10 degrees C and high photon flux density (PFD). Growing wild-type or non-expressing segregate plants (controls) and transformants at two PFDs ...

Reactive oxygen species (ROS) are harmful to living organisms due to the potential oxidation of membranes, DNA, proteins, and carbohydrates. Freezing injury has been shown to involve the attack of ROS. Antioxidant enzymes can protect plant cells from oxidative stress imposed by freezing injury, therefore, cold acclimation may involve an increase in the expression of antioxidant enzymes. In this...

This study aimed to evaluate the effects of priming on seed germination under salt stress and gene expression in seeds and seedlings of P. angulata L. After priming for 10 days, seed germination was tested in plastic trays containing 15 ml of water (0 dS m-1 - control) or 15 ml of NaCl solution (2, 4, 6, 8, 10, 12, 14 and 16 dS m-1). Fresh and dry weight of shoots and roots of seedlings were ev...

PURPOSE (1) To use finite element (FE) modelling to estimate local iris stresses (i.e. internal forces) as a result of mechanical pupil expansion; and to (2) compare such stresses as generated from several commercially available expanders (Iris hooks, APX dilator and Malyugin ring) to determine which design and deployment method are most likely to cause iris damage. METHODS We used a biofidel...