ECONOMIC AND ENVIRONMENTAL BENEFITS OF SOIL/WATER NITROGEN TESTING: THE CASE OF CENTRAL NEBRASKA

This research presents a competitive dynamic model to evaluate the economic and groundwater quality benefits resulting from the adoption of soil/water nitrogen testing. The model is applied to an irrigated corn production county in the Nebraska Mid-State area where the groundwater contamination level from nitrates is reported to be, on average, 18.7 parts per million (ppm). Adoption of nutrient management practices would result in increased economic benefits to farmers and reduced nitrate stocks in groundwater.Environmental Economics and Policy,

The malaria parasite cyclic GMP-dependent protein kinase plays a central role in blood-stage schizogony

A role for the Plasmodium falciparum cyclic GMP (cGMP)-dependent protein kinase (PfPKG) in gametogenesis in the malaria parasite was elucidated previously. In the present study we examined the role of PfPKG in the asexual blood-stage of the parasite life cycle, the stage that causes malaria pathology. A specific PKG inhibitor (compound 1, a trisubstituted pyrrole) prevented the progression of P. falciparum schizonts through to ring stages in erythrocyte invasion assays. Addition of compound 1 to ring-stage parasites allowed normal development up to 30 h postinvasion, and segmented schizonts were able to form. However, synchronized schizonts treated with compound 1 for ≥6 h became large and dysmorphic and were unable to rupture or liberate merozoites. To conclusively demonstrate that the effect of compound 1 on schizogony was due to its selective action on PfPKG, we utilized genetically manipulated P. falciparum parasites expressing a compound 1-insensitive PfPKG. The mutant parasites were able to complete schizogony in the presence of compound 1 but not in the presence of the broad-spectrum protein kinase inhibitor staurosporine. This shows that PfPKG is the primary target of compound 1 during schizogony and provides direct evidence of a role for PfPKG in this process. Discovery of essential roles for the P. falciparum PKG in both asexual and sexual development demonstrates that cGMP signaling is a key regulator of both of these crucial life cycle phases and defines this molecule as an exciting potential drug target for both therapeutic and transmission blocking action against malaria

Numerical evaluation of the flange thickness effect on the contact stress and prying action in T-Stub steel connection

Este artículo presenta un estudio numérico utilizando el programa ANSYS para análisis de conexiones de acero tipo «T» denominadas «T-Stub», en las cuales puede darse el fenómeno de acción de palanca. El efecto de apalancamiento en los tornillos de la placa ha sido estudiado antes, pero la localización de las fuerzas de palanca ha sido simplificada. El efecto del espesor de las placas de conexión «T-Stub» en las áreas de contacto entre ellas y un soporte rígido ha sido investigado en este artículo diferentemente de lo que se encuentra en la literatura técnica, en que dicho fenómeno es estudiado entre bases flexibles. La conexión ha sido discretizada con elemento de sólido 3D y elementos de interfaz. En los análisis realizados se adoptan diferentes espesores de la placa y tornillos de diámetros distintos en los cuales se ha aplicado una precarga. En este artículo se presenta una discusión sobre la magnitud de los esfuerzos en los tornillos y la extensión del área de contacto efectiva entre la placa y un soporte rígido.This paper presents a numerical study of «T-Stub» steel connections using FEM analyses. In such connections prying action phenomenon may take place. Prying action effect on the bolts has been studied before but the location of the prying action forces has always been simplified. The effect of the thickness of «T-Stub» flanges on contact areas between flanges and support base is investigated in this paper. A 3D finite element model is used and interface elements are employed for the investigation. Nonlinear FE analyses are undertaken on connection with different flange thickness and bolt preload with two bolts. Nonlinear gap elements are used as interfaces. Discussion and conclusions on contact areas and stresses, prying action distributions and resultant of loads on bolts in the «T-Stub» connections are presented.Peer Reviewe

Unidirectional Neuronal Cell growth and Differentiation on Aligned Polyhydroxyalkanoate Blend Microfibres with Varying Diameters

Polyhydroxyalkanoates (PHAs) are a family of prokaryotic-derived biodegradable and biocompatible natural polymers known to exhibit neuroregenerative properties. In this work, poly(3-hydroxybutyrate), P(3HB) and poly(3-hydroxyoctanoate), P(3HO), have been combined to form blend fibres for directional guidance of neuronal cell growth and differentiation. A 25:75 P(3HO)/P(3HB) blend (PHA blend) was used for the manufacturing of electrospun fibres as resorbable scaffolds to be used as internal guidance lumen structures in nerve conduits. The biocompatibility of these fibres was studied using neuronal and Schwann cells. Highly aligned and uniform fibres with varying diameters were fabricated by controlling electrospinning parameters. The resulting fibre diameters were 2.4 ± 0.3 µm, 3.7 ± 0.3 µm and 13.5 ± 2.3 µm for small, medium and large diameter fibres respectively. The cell response to these electrospun fibres was investigated with respect to growth and differentiation. Cell migration observed on the electrospun fibres showed topographical guidance in accordance with the direction of the fibres. The correlation between fibre diameter and neuronal growth under two conditions; individually and in co-culture with Schwann cells was evaluated. Results obtained from both assays revealed that all PHA blend fibre groups were able to support growth and guide aligned distribution of neuronal cells and there was a direct correlation between the fibre diameter and neuronal growth and differentiation. This work has led to the development of a family of unique biodegradable and highly biocompatible 3D substrates capable of guiding and facilitating the growth, proliferation and differentiation of neuronal cells as internal structures within nerve conduits

The relation between accretion rate and jet power in X-ray luminous elliptical galaxies

Using Chandra X-ray observations of 9 nearby, X-ray luminous ellipticals with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi accretion rates calculated from the X-ray data and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, inferred from the energies and timescales required to inflate the cavities observed in the surrounding X-ray emitting gas, can be related to the accretion rates by a power law model. A significant fraction (2.2^{+1.0}_{-0.7} per cent, for P_jet=10^{43} erg/s) of the energy associated with the rest mass of material entering the accretion radius eventually emerges in the jets. The data also hint that this fraction may rise slightly with increasing jet power. Our results have significant implications for studies of accretion, jet formation and galaxy formation. The tight correlation between P_Bondi and P_jet suggests that the Bondi formulae provide a reasonable description of the accretion process, despite the likely presence of magnetic pressure and angular momentum in the accreting gas, and that the accretion flows are approximately stable over timescales of a few million years. Our results show that the black hole `engines' at the hearts of large elliptical galaxies and groups can feed back sufficient energy to stem cooling and star formation, leading naturally to the observed exponential cut off at the bright end of the galaxy luminosity function.Comment: Accepted for publication in MNRAS. 10 pages, 4 figures. Includes an enhanced statistical analysis and some additional data. Conclusions unchange

Pre-clinical evaluation of advanced nerve guide conduits using a novel 3D in vitro testing model

Autografts are the current gold standard for large peripheral nerve defects in clinics despite the frequentlyoccurring side effects like donor site morbidity. Hollow nerve guidance conduits (NGC) are proposed alternatives toautografts, but failed to bridge gaps exceeding 3 cm in humans. Internal NGC guidance cues like microfibresare believed to enhance hollow NGCs by giving additional physical support for directed regeneration of Schwann cellsand axons. In this study, we report a new 3D in vitro model that allows the evaluation of different intraluminal fibrescaffolds inside a complete NGC. The performance of electrospun polycaprolactone (PCL) microfibres inside 5 mmlong polyethylene glycol (PEG) conduits were investigated in neuronal cell and dorsal root ganglion (DRG) cultures invitro. Z-stack confocal microscopy revealed the aligned orientation of neuronal cells along the fibres throughout thewhole NGC length and depth. The number of living cells in the centre of the scaffold was not significantly different tothe tissue culture plastic (TCP) control. For ex vivo analysis, DRGs were placed on top of fibre-filled NGCs to simulatethe proximal nerve stump. In 21 days of culture, Schwann cells and axons infiltrated the conduits along the microfibreswith 2.2 ± 0.37 mm and 2.1 ± 0.33 mm, respectively. We conclude that this in vitro model can help define internal NGCscaffolds in the future by comparing different fibre materials, composites and dimensions in one setup prior to animaltesting

On the string interpretation of M(atrix) theory

It has been proposed recently that, in the framework of M(atrix) theory, N=8 supersymmetric U(N) Yang-Mills theory in 1+1 dimensions gives rise to type IIA long string configurations. We point out that the quantum moduli space of $SYM_{1+1}$ gives rise to two quantum numbers, which fit very well into the M(atrix) theory. The two quantum numbers become familiar if one switches to a IIB picture, where they represent configurations of D-strings and fundamental strings. We argue that, due to the SL(2,Z) symmetry, of the IIB theory, such quantum numbers must represent configurations that are present also in the IIA framework.Comment: 13 pages, Latex, more comment

Stability and Instability of Extreme Reissner-Nordstr\"om Black Hole Spacetimes for Linear Scalar Perturbations I

We study the problem of stability and instability of extreme Reissner-Nordstrom spacetimes for linear scalar perturbations. Specifically, we consider solutions to the linear wave equation on a suitable globally hyperbolic subset of such a spacetime, arising from regular initial data prescribed on a Cauchy hypersurface crossing the future event horizon. We obtain boundedness, decay and non-decay results. Our estimates hold up to and including the horizon. The fundamental new aspect of this problem is the degeneracy of the redshift on the event horizon. Several new analytical features of degenerate horizons are also presented.Comment: 37 pages, 11 figures; published version of results contained in the first part of arXiv:1006.0283, various new results adde