Agricultural pricing and environmental degradation

The link between agricultural pricing and land degradation is often difficult to analyze empirically. The authors'understanding of how agricultural supply responds to changing prices in developing countries is incomplete. Even more incomplete is the author's analysis of subsequent impacts on the resource base sustaining agricultural production. Yet available evidence suggests that some important effects do exist, and much further analysis of them is warranted. The social, economic, and environmental relationships that determine the often countervailing effects of price changes on land use and management are extremely complex. Not enough is known about: (1) farming systems in developing countries; (2) open-access use and common property resource rights; (3) land tenure regimes and security; (4) access to technology and other farming systems information; (5) the distribution of wealth and income; and (6) coping strategies for variable climatic, economic, and social conditions. All these factors influence how rural households respond to price changes in terms of managing land and natural resources, and often they may override the incentive effects of price changes. Changes in pricing policies will then be less effective in correcting resource degradation than other approaches to dealing with its underlying causes. Such approaches include providing better research and extension advice, improving property rights and management, and establishing more secure tenure or access rights. At the same time, it is wrong to assume that poor farmers - even those in resource-poor regions far from major markets - are totally isolated from agricultural markets. Virtually all subsistence households require some regular market income for cash purchases of agricultural inputs and basic necessities; many small farmers provide important cash and export crops. So changes in market prices often significantly affect the livelihoods of rural groups. Clearly, the economic incentives emerging from these impacts will affect farmers'decisions to invest in land management and improvements. Just because we do not always understand the economic and social factors determining these incentive effects does not mean they do not exist. Nor should the complexity of the links between price changes and resource management - which sometimes appear counterintuitive - deter further analysis of the role of agricultural pricing in land degradation.Environmental Economics&Policies,Crops&Crop Management Systems,Agricultural Knowledge&Information Systems,Economic Theory&Research,Agricultural Research

Dirac electrons in a Kronig-Penney potential: dispersion relation and transmission periodic in the strength of the barriers

The transmission T and conductance G through one or multiple one-dimensional, delta-function barriers of two-dimensional fermions with a linear energy spectrum are studied. T and G are periodic functions of the strength P of the delta-function barrier V(x,y) / hbar v_F = P delta(x). The dispersion relation of a Kronig-Penney (KP) model of a superlattice is also a periodic function of P and causes collimation of an incident electron beam for P = 2 pi n and n integer. For a KP superlattice with alternating sign of the height of the barriers the Dirac point becomes a Dirac line for P = (n + 1/2) pi.Comment: 5 pages, 6 figure

The importance of habitat quality for marine reserve fishery linkages

We model marine reserve - fishery linkages to evaluate the potential contribution of habitat-quality improvements inside a marine reserve to fish productivity and fishery catches. Data from Mombasa Marine National Park, Kenya, and the adjacent fishery are used. Marine reserves increase total fish biomass directly by providing refuge from exploitation and indirectly by improving fish habitat in the reserve. As natural mortality of the fish stock decreases in response to habitat enhancement in the reserve, catches increase by up to 2.6 tonnes (t).km(-2).year(-1) and total fish biomass by up to 36 t.km(-2). However, if habitat-quality improvement reduces the propensity of fish to move out of the reserve, catches may fall by up to 0.9 t.km(-2).year(-1). Our results indicate that habitat protection in reserves can underpin fish productivity and, depending on its effects on fish movements, augment catches

Experimental study of the effects of viscosity and viscoelasticity on a line vortex cavitation

This paper investigates the influence of viscosity and viscoelasticity on the structure of the flow in a line vortex in view of understanding their effects on cavitation inception. Experiments were conducted in a vortex chamber where the fluid injection speed and the liquid properties can be easily controlled. Measurements of the velocities, pressures, and thus the cavitation number were conducted using a PIV system, pressure gauges, and Pitot tubes. Experiments were performed using water, different dilute concentrations of polymer (POLYOX WSR 301) solutions, and solutions with different concentrations of corn syrup for a large range of Reynolds numbers. The measurements and observations showed that cavitation inception at the vortex center was delayed when polymer and corn syrup solutions are used as compared to the experiments in water. However, contrary to reported observations with tip vortices, here the large scale vortex was found to rotate faster in the polymer and corn syrup solutions. This did not match with our observations of cavitation inception delay in the case of polymers and the conventional thinking about the relationship between pressures and velocities in a vortex line. This may be due to the observations that the velocity fluctuations and the turbulent kinetic energy in the viscous core region increased significantly in the polymer and corn syrup solutions and could question the validity of a pressure computation based on a single vortex.http://deepblue.lib.umich.edu/bitstream/2027.42/84322/1/CAV2009-final152.pd

Methionine adenosyltransferases in liver cancer.

Methionine adenosyltransferases (MATs) are essential enzymes for life as they produce S-adenosylmethionine (SAMe), the biological methyl donor required for a plethora of reactions within the cell. Mammalian systems express two genes, MAT1A and MAT2A, which encode for MATα1 and MATα2, the catalytic subunits of the MAT isoenzymes, respectively. A third gene MAT2B, encodes a regulatory subunit known as MATβ which controls the activity of MATα2. MAT1A, which is mainly expressed in hepatocytes, maintains the differentiated state of these cells, whilst MAT2A and MAT2B are expressed in extrahepatic tissues as well as non-parenchymal cells of the liver (e.g., hepatic stellate and Kupffer cells). The biosynthesis of SAMe is impaired in patients with chronic liver disease and liver cancer due to decreased expression and inactivation of MATα1. A switch from MAT1A to MAT2A/MAT2B occurs in multiple liver diseases and during liver growth and dedifferentiation, but this change in the expression pattern of MATs results in reduced hepatic SAMe level. Decades of study have utilized the Mat1a-knockout (KO) mouse that spontaneously develops non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) to elucidate a variety of mechanisms by which MAT proteins dysregulation contributes to liver carcinogenesis. An increasing volume of work indicates that MATs have SAMe-independent functions, distinct interactomes and multiple subcellular localizations. Here we aim to provide an overview of MAT biology including genes, isoenzymes and their regulation to provide the context for understanding consequences of their dysregulation. We will highlight recent breakthroughs in the field and underscore the importance of MAT's in liver tumorigenesis as well as their potential as targets for cancer therapy

Water vapor radiometry research and development phase

This report describes the research and development phase for eight dual-channel water vapor radiometers constructed for the Crustal Dynamics Project at the Goddard Space Flight Center, Greenbelt, Maryland, and for the NASA Deep Space Network. These instruments were developed to demonstrate that the variable path delay imposed on microwave radio transmissions by atmospheric water vapor can be calibrated, particularly as this phenomenon affects very long baseline interferometry measurement systems. Water vapor radiometry technology can also be used in systems that involve moist air meteorology and propagation studies

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {\guillemotright}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.Comment: In press in J. Appl. Phy

Unbounded quantum backflow in two dimensions

Quantum backflow refers to the counterintuitive fact that the probability can flow in the direction opposite to the momentum of a quantum particle. This phenomenon has been seen to be small and fragile for one-dimensional systems, in which the maximal amount of backflow has been found to be bounded. Quantum backflow exhibits dramatically different features in two-dimensional systems that, contrary to the one-dimensional case, allow for degenerate energy eigenstates. Here we investigate the case of a charged particle that is confined to move on a finite disk punctured at the center and that is pierced through the center, and normally to the disk, by a magnetic flux line. We demonstrate that quantum backflow can be unbounded (in a certain sense), which makes this system a promising physical platform regarding the yet-to-be-performed experimental observation of this fundamental quantum phenomenon.Comment: 11 pages, 1 figur