31P NMR spectroscopy and structural models of soil organic phosphorus under Eucalyptus

Nutrient Cycling in Agroecosystems - Organic phosphorus (Po) plays an important role in tropical forest nutrition on strongly-weathered soils. However, of its role in Eucalyptus nutrition little is...     

Biochemical and Biophysical Characterization of Recombinant Human 3-Phosphoglycerate Dehydrogenase

The human enzyme D-3-phosphoglycerate dehydrogenase (hPHGDH) catalyzes the reversible dehydrogenation of 3-phosphoglycerate (3PG) into 3-phosphohydroxypyruvate (PHP) using the NAD⁺/NADH redox cofactor, the first step in the phosphorylated pathway producing L-serine. We focused on the full-length enzyme that was produced in fairly large amounts in E. coli cells; the effect of pH, temperature and ligands on hPHGDH activity was studied. The forward reaction was investigated on 3PG and alternative carboxylic acids by employing two coupled assays, both removing the product PHP; 3PG was by far the best substrate in the forward direction. Both PHP and α-ketoglutarate were efficiently reduced by hPHGDH and NADH in the reverse direction, indicating substrate competition under physiological conditions. Notably, neither PHP nor L-serine inhibited hPHGDH, nor did glycine and D-serine, the coagonists of NMDA receptors related to L-serine metabolism. The investigation of NADH and phosphate binding highlights the presence in solution of different conformations and/or oligomeric states of the enzyme. Elucidating the biochemical properties of hPHGDH will enable the identification of novel approaches to modulate L-serine levels and thus to reduce cancer progression and treat neurological disorders.     

Use of linear programming to calculate dwell times for the design of petal tools

Two constraints in the design of a petal tool are, the angles that define it must all be positive, and wear must never be greater than the desired wear. The first constraint is equivalent to that of the positive dwell times of a small solid tool. In view of this foregoing, we present a design of petal tools that are used to generate conic surfaces from their nearest spheres and that correct the profile of a surface that is polished. We study optimal angular sizes of a petal tool, which are found after we use linear programming to calculate the optimal dwell times of a set of complete annular tools placed in different zones of the glass surface. We report numerical results of designed petal tools.     

Design of correlation filters for recognition of linearly distorted objects in linearly degraded scenes

Generalized correlation filters are proposed to improve recognition of a linearly distorted object embedded in a nonoverlapping background when the input scene is degraded with a linear system and additive noise. Several performance criteria defined for the nonoverlapping signal model are used for the design of filters. The derived filters take into account information about an object to be recognized, disjoint background, noise, and linear degradations of the target and the input scene. Computer simulation results obtained with the proposed filters are discussed and compared with those of various correlation filters in terms of discrimination capability, location errors, and tolerance to input noise.     

Device for rapid and agile measurement of diffusivity in micro- and nanochannels

The lack of a viable theory for describing diffusivity when fluids are confined at the micro- and nanoscale [Ladero et al. Chem. Eng. Sci.2007, 62, 666-678; Deen AIChE J.1987, 33, 1409-1425] has necessitated accurate measurement of diffusivity (D) [Jin and Chen Chromatographia2000, 52, 17-21; Nie et al. Science1994, 266, 1018-1021; Durand et al. Anal. Chem.2009, 81, 5407-5412], crucial for a host of micro- and nanofluidic technologies [Grattoni et al. Curr. Pharm. Biotechnol.2010, 11, 343-365]. We demonstrate a rapid and agile method for the direct measurement of diffusivity in a system possessing 10(4) to 10(5) precisely fabricated channels with characteristic sizes (β) ranging from micro- to nanometers. Custom chambers allowed us to measure the diffusivity in a closed unperturbed system using UV/vis spectroscopy. D was measured for rhodamine B (RhoB) in aqueous solution in channels of 200 and 1 μm, as well as 13 and 5.7 nm. The observed logarithmic scaling of diffusivity with β, in close agreement with prior experiments, but far from theoretical prediction, surprisingly highlights that diffusivity is significantly altered even at the microscale. Accurate measurement of D by reducing the size of the source reservoir by 3 orders of magnitude (from 150 μL to 910 nL) proves that a substantial reduction in measurement time (from 7 days to 40 min) can be achieved. Our design thus is ready for rapid translation into a standard analytical tool--useful for multiple applications.