On the Enumeration of Minimal Covers and Minimal Forbidden Sets

An independence system is a family I of subsets of a ground set V with the property that any subset of any member of I also belongs to I. The inclusion-minimal sets not in I are called minimal covers. We prove several complexity results related to computation, enumeration, and counting of the minimal covers of an independence system. Our motivation to study these problems is their importance in the solution of resource-constrained scheduling problems. There the minimal covers correspond to minimal subsets of jobs that must not be scheduled simultaneously, so-called minimal forbidden sets. In this context, minimal covers are the minimal infeasible 0/1-solutions of a linear inequality system. We propose and analyze a simple backtracking algorithm that generates a complete representation of all minimal covers of the independence system induced by a linear inequality system. The practical performance of this algorithm is evaluated on the basis of instances from the project scheduling library PSPLIB.computer science applications;

PKA Phosphorylation of Src Mediates cAMP\u27s Inhibition of Cell Growth via Rap1

In fibrolast cells, cAMP antagonizes growth factor activation of ERKs and cell growth via PKA and the small P protein Rap1. We demonstrate here that PKA\u27s activation of Rap1 was mediated by the Rap1 guanine nucleotide exchange factor C3G, the adaptor Crk-L, the scaffold protein Cbl, and the tyrosine kinase Src. Src was required for cAMP activation of Rap1 and the inhibition of ERKs and cell growth. PKA activated Src both in vitro and in vivo by phosphorylation was required for cAMP\u27s activation of Src and Rap1, as well as cAMP\u27s inhibition of ERKs and cell proliferation. This study identifies an antiproliferative role for Src in the physiological regulation of cell growth by cAMP

B2-Adrenergic Receptor Activates Extracellular Signal-regulated Kinases (ERKs) via the Small G Protein Rap1 and the Serine/Threonine Kinase B-Raf

G protein-coupled receptors can induce cellular proliferation by stimulating the mitogen-activated protein (MAP) kinase cascade. Heterotrimeric G proteins are composed of both a and By subunits that can signal independently to diverse intracellular signaling pathways including those that activate MAP kinases. In this study, we examined the ability of isoproterenol, an agonist of the B2-adrenergic receptor (b2AR), to stimulate extracellular signal-regulated kinases (ERKs). Using HEK293 cells, which express endogenous b2AR, we show that isoproterenol stimulates ERKs via b2AR. This action of isoproterenol requires cAMP-dependent protein kinase and is insensitive to pertussis toxin, suggesting that Gas activation of cAMP-dependent protein kinase is required. Interestingly, b2AR activates both the small G proteins Rap1 and Ras, but only Rap1 is capable of coupling to Raf isoforms. b2AR inhibits the Ras-dependent activation of both Raf isoforms Raf-1 and B-Raf, whereas Rap1 activation by isoproterenol recruits and activates B-Raf. b2AR activation of ERKs is not blocked by expression of RasN17, an interfering mutant of Ras, but is blocked by expression of either RapN17 or Rap1GAP1, both of which interfere with Rap1 signaling. We propose that isoproterenol can activate ERKs via Rap1 and BRaf in these cells

The common feeder cockroach Blaptica dubia shows increased transmission distance based on mode of acquisition of environmental bacteria

Although some researchers claim that cockroaches are masters of disease transmission, these claims have little to no scientific support. Most studies concerning cockroaches as a vector of disease only focus on the bacteria found on the body surface, not on whether cockroaches have actually transferred pathogenic bacteria via surface contact. We set out to determine if cockroaches would act as a mechanical vector for the transfer of the opportunistic pathogen, E. coli. Roaches were contaminated with Green fluorescent protein expressing E. coli (GFP-E.coli) broth by either walking the roach through a broth culture or by complete immersion in the culture.. We then ran the roaches down a sterile agar track and measured the length of the glowing trail. Roaches were able to transmit E.coli, but only for a continuous distance of less than 50 cm, with the occasional sporadic colony growing after that. Roaches that were immersed in bacterial broth tracked the bacterium further than those that only walked through the solution. This suggests that while cockroaches are capable of acting as a mechanical vector, they are not capable of transporting transient flora over long distances. Future studies should explore this mechanism

Mobile telephony access and usage in Africa

The study provides tools to identify policy interventions to improve ICT uptake and usage, and to define universal service obligations based on income and monthly usage costs. Results show what can be expected from lower access and usage costs in terms of market volume and new subscribers. Income is the main explanatory variable for usage. In terms of mobile expenditure, it is inelastic with respect to income. The share of mobile expenditure of individual income indicates that people with higher income spend a smaller proportion compared to those with lower income

Capabilities and limitations of a new thermal finite volume model for the evaluation of laser-induced thermo-mechanical retinal damage

Many experimental studies focus on the physical damage mechanisms of short-term exposure to laser radiation. In the nanosecond (ns) pulse range, damage in the Retinal Pigment Epithelium (RPE) will most likely occur at threshold levels due to bubble formation at the surface of the absorbing melanosome. The energy uptake of the melanosomes is one key aspect in modeling the bubble formation and damage thresholds. This work presents a thermal finite volume model for the investigation of rising temperatures and the temperature distribution of irradiated melanosomes. The model takes the different geometries and thermal properties of melanosomes into account, such as the heat capacity and thermal conductivity of the heterogeneous absorbing melanosomes and the surrounding tissue. This is the first time the size and shape variations on the melanosomes‘ thermal behavior are considered. The calculations illustrate the effect of the geometry on the maximum surface temperature of the irradiated melanosome and the impact on the bubble formation threshold. A comparison between the calculated bubble formation thresholds and the RPE cell damage thresholds within a pulse range of 3 to 5000 ns leads to a mean deviation of = 22 mJ ∕ cm2 with a standard deviation of = 21 mJ ∕ cm2. The best results are achieved between the simulation and RPE cell damage thresholds for pulse durations close to the thermal confinement time of individual melanosomes

Steering the Surprisingly Modular π-Acceptor Properties of N-Heterocyclic Carbenes: Implications for Gold Catalysis

Thumbnail image of graphical abstract Accept it! Although the π-acceptor properties of N-heterocyclic carbenes (NHCs) are often considered negligible, they can be enhanced to the extent that they start to dominate the catalytic behavior of gold–NHC complexes (see scheme). As it seems to be easier to tune the π acidity of NHCs than to alter their σ-donor properties, the general perception of this important class of ancillary ligands needs to be revised

Genetic and biochemical analyses of chromosome and plasmid gene homologues encoding ICL and ArCP domains in Vibrioanguillarum strain 775

Anguibactin, the siderophore produced by Vibrio anguillarum 775 is synthesized from 2,3-dihydroxybenzoic acid (DHBA), cysteine and hydroxyhistamine via a nonribosomal peptide synthetase (NRPS) mechanism. Most of the genes encoding anguibactin biosynthetic proteins are harbored by the pJM1 plasmid. In this work we report the identification of a homologue of the plasmid-encoded angB on the chromosome of strain 775. The product of both genes harbor an isochorismate lyase (ICL) domain that converts isochorismic acid to 2,3-dihydro-2,3-dihydroxybenzoic acid, one of the steps of DHBA synthesis. We show in this work that both ICL domains are functional in the production of DHBA in V. anguillarum as well as in E. coli. Substitution by alanine of the aspartic acid residue in the active site of both ICL domains completely abolishes their isochorismate lyase activity in vivo. The two proteins also carry an aryl carrier protein (ArCP) domain. In contrast with the ICL domains only the plasmid encoded ArCP can participate in anguibactin production as determined by complementation analyses and site-directed mutagenesis in the active site of the plasmid encoded protein, S248A. The site-directed mutants, D37A in the ICL domain and S248A in the ArCP domain of the plasmid encoded AngB were also tested in vitro and clearly show the importance of each residue for the domain function and that each domain operates independently.

Starting with Howard Gardner’s five minds, adding Elliott Jaques’s responsibility time span: implications for undergraduate management education

This article offers a perspective on management education derived from Howard Gardner’s five minds framework and Elliott Jaques’s responsibility time span. We describe the five minds (disciplined, synthesizing, creating, respectful, and ethical) and discuss some of the criticisms raised about Gardner’s approach. We introduce Jaques’s time span concept and suggest its applicability to the structuring of roles in a school of management. Putting Jacques together with Gardner allows us to explore questions about the five minds that could be addressed by deans, department chairs, and faculty members, each with a different responsibility time span