Flux-based hierarchical organization of Escherichia coli’s metabolic network

Biological networks across scales exhibit hierarchical organization that may constrain network function. Yet, understanding how these hierarchies arise due to the operational constraint of the networks and whether they impose limits to molecular phenotypes remains elusive. Here we show that metabolic networks include a hierarchy of reactions based on a natural flux ordering that holds for every steady state. We find that the hierarchy of reactions is reflected in experimental measurements of transcript, protein and flux levels of Escherichia coli under various growth conditions as well as in the catalytic rate constants of the corresponding enzymes. Our findings point at resource partitioning and a fine-tuning of enzyme levels in E. coli to respect the constraints imposed by the network structure at steady state. Since reactions in upper layers of the hierarchy impose an upper bound on the flux of the reactions downstream, the hierarchical organization of metabolism due to the flux ordering has direct applications in metabolic engineering.

Membrane-less photoelectrochemical devices for H2O2 production: efficiency limit and operational constraint

A membrane-less design with 100% catalytic selectivity enables H2O2 accumulation at a maximum solar-to-H2O2 conversion efficiency of 20.0–27.5%.

Informal Firms and Financial Inclusion: Status and Determinants

Many firms in the developing world — including a majority of micro, small, and medium enterprises (MSMEs) — operate in the informal economy. The informal firms face a variety of constraints, making it harder for them to do business and grow. Lack of access to finance is often cited as the biggest operational constraint these firms face. This paper documents the use of finance and financing patterns of informal firms, highlights differences between use of finance by formal and informal firms, and identifies the most significant characteristics of informal firms that are associated with higher use of financial services.

Operational Constraints on Dimension of Space Imply both Spacetime and Timespace

Since polynomials of higher than fourth degree, which is the algebraic counterpart of generic geometric dimension, are insolvable in general, then presumably no more than just four mutually orthogonal geometric dimensions can be placed within a single geometric space if it is expected to be fully operational. Hence a hierarchical notion of dimension is needed in order to ensure that at least virtual orthogonality is respected, which in turn implies presence of certain hierarchically organized multispatial structures. It is shown that the operational constraint on physical spaces implies of necessity presence of both: 4-dimensional (4D) spacetime and a certain 4D timespace.

Numerical studies of infrared signature levels of complete aircraft

This paper begins with an outline of the procedure for predicting the infrared signature emissions from the airframe, engine casing, and the plume, and their attenuation by the intervening atmosphere. These emissions are contrasted against the background, to obtain the infrared signature levels. The infrared detector’s — noise equivalent flux density, is proposed as an operational constraint on the flight envelope. The shift of this newly imposed constraint on the flight envelope for several engine-operating conditions, and for turbojet and turbofan engines is studied. The signature levels from the casing and plume, of a turbofan and equivalent turbojet engine, are compared at different operating points on the flight envelope. Result in the form of a polar plot of infrared signature level variation with aspect is also examined for low flying missions. The results are analysed to direct stealth design and operation.