In a 4-cell Caenorhabditis elegans embryo, two sister blastomeres called ABa and ABp are born with equivalent developmental potential, but eventually produce distinct patterns of cell fate. The different fates of ABa and ABp are specified at least in part by inductive interactions with neighboring blastomeres. Previous studies indicate that, at the 4-cell stage, a signal from the posterior-most...

We provide several non-approximability results for deterministic scheduling problems whose objective is to minimize the total job completion time. Unless P = NP, none of the problems under consideration can be approximated in polynomial time within arbitrarily good precision. Most of our results are derived by APX-hardness proofs. We show that, whereas scheduling on unrelated machines with unit...

Known results: • Generalizes Set Cover, (Non-Metric / Multi-level) Facility Location, Group Steiner Tree • Ω(log2− n)-hard (Halperin, Krauthgamer ’03) • |X| -apx in poly by sophisticated greedy algo (Zelikovsky ’97) • O(log |X|)-apx in nO(log |X|) time by more sophisticated greedy algo (Charikar, Chekuri, Cheung, Goel, Guha and Li ’99) • LP’s have integrality gap Ω( √ k) already for 5 layers; e...

For many classical planning domains, the computational complexity of non-optimal and optimal planning is known. However, little is known about the area in between the two extremes of finding some plan and finding optimal plans. In this contribution, we provide a complete classification of the propositional domains from the first four International Planning Competitions with respect to the appro...

Block Sorting is a well studied problem, motivated by its applications in Optical Character Recognition (OCR), and Computational Biology. Block Sorting has been shown to be NP-Hard, and two separate polynomial time 2-approximation algorithms have been designed for the problem. But questions like whether a better approximation algorithm can be designed, and whether the problem is APX-Hard have b...

We first prove the existence of natural Poly-APX-complete problems, for both standard and differential approximation paradigms, under already defined and studied suitable approximation preserving reductions. Next, we devise new approximation preserving reductions, called FT and DFT, respectively, and prove that, under these reductions, natural problems are PTAS-complete, always for both standar...

The sister blastomeres ABp and ABa are equipotent at the beginning of the 4-cell stage in C. elegans embryos, but soon become committed to different fates. We show that the glp-1 gene, a homolog of the Notch gene of Drosophila, functions in two distinct cell-cell interactions that specify the ABp and ABa fates. These interactions both require maternal expression of glp-1. We show that a second ...

Oxidative stress is a major threat for plants exposed to various environmental stresses. Previous studies found that transgenic potato plants expressing both copper zinc superoxide dismutase (CuZnSOD) and ascorbate peroxidase (APX) (referred to as SSA plants), or nucleoside diphosphate kinase 2 (NDPK2) (SN plants), showed enhanced tolerance to methyl viologen (MV)-induced oxidative stress and h...

Photosynthesis of leaf discs from transgenic tobacco plants (Nicotiana tabacum) that express a chimeric gene that encodes chloroplast-localized Cu/Zn superoxide dismutase (SOD+) was protected from oxidative stress caused by exposure to high light intensity and low temperature. Under the same conditions, leaf discs of plants that did not express the pea SOD isoform (SOD-) had substantially lower...