Mixed land uses,land-use externalities,and residential property values: A reevaluation

Empirical evidence concerning the impact of neighborhood land-use externalities on residential property value is mixed. That is, no concensus has emerged in the literature as to whether locating non-residential land-use activities in residential neighborhoods can be expected to increase, decrease or leave unaltered surrounding property values. The purpose of this research was two-fold: 1) to construct a theoretical model of consumer behavior in which both the positive and negative effects of neighborhood land-use externalities are taken into account, and 2) to test this generalized model empirically, using hedonic pricing equations. The principal implication of the theoretical model is that the effect of non-residential activity on residential property values isa priori indeterminate, the outcome depending on the relative strength of the associated positive and negative external effects generated. The empirical test of the model was conducted for the city of Tucson, Arizona, where it is shown that over low ranges, increasing the amount of industrial, commercial, multifamily and public land-use activity in a neighborhood tended to increase surrounding residential property values. It is concluded that in locating future economic activity an optimal mix of landuse activities should be sought, not the regional separation of activities.     

Mechanisms affecting the infiltration and distribution of ethanol-blended gasoline in the vadose zone

One- and two-dimensional experiments were conducted to examine differences in the behavior of gasoline and gasohol (10% ethanol by volume) as they infiltrate through the unsaturated zone and spread at the capillary fringe. Ethanol in the spilled gasohol quickly partitions into the residual water in the vadose zone and is retained there as the gasoline continues to infiltrate. Under the conditions tested, over 99% of the ethanol was initially retained in the vadose zone. Depending on the volume of gasoline spilled and the depth to the water table, this causes an increase in the aqueous-phase saturation and relative permeability, thus allowing the ethanol-laden water to drain into the gasoline pool. Under the conditions tested, the presence of ethanol does not have a significant impact on the overall size or shape of the resulting gasoline pool at the capillary fringe. Residual gasoline saturations in the vadose zone were significantly reduced however because of reduced surface and interfacial tensions associated with high ethanol concentrations. The flux of ethanol in the effluent of the column ranged from 1.4 x 10(-4) to 4.5 x 10(-7) g/(cm2 min) with the LNAPL and from 6 x 10(-3) to 3.0 x 10(-4) g/(cm2 min) after water was introduced to simulate rain infiltration. The experimental results presented here illustrate that the dynamic effects of ethanol partitioning into the aqueous phase in the vadose zone create an initial condition that is significantly different than previously understood.     

Comparison of three techniques used to measure diffusive gas exchange from sheltered aquatic surfaces

Three approaches commonly used to quantify diffusive gas exchange across aquatic surfaces were compared in a densely treed, low-wind environment Diffusive surface fluxes of carbon dioxide (CO2) and methane (CH4) from a small boreal reservoir were estimated using (i) surface water concentrations, the thin boundary layer (TBL) equation, and gas transfer velocities (k) calculated using sulfur hexafluoride (SF6); (ii) surface water concentrations, the TBL equation, and k estimated from wind speed; and (iii) static floating chambers (FCs). Comparisons were made during three different approximately 10-day intervals (August 2000, June and September 2001). CO2 and CH4 fluxes estimated from SF6-derived k were on average 1-3 times greater than those determined from wind-estimated k Overall agreement between FC CO2 and CH4 flux estimates and those based on SF6 and wind speed derived kvalues was much weaker, with FC CO2 and CH4 flux estimates ranging from -9 to 23 times those based on SF6 and wind-estimated k values. Chamber deployment likely enhanced gas transfer through disturbance of the surface boundary layer, and results of this study suggest that caution must be exercised concerning the use of FCs on very still water surfaces. Furthermore, findings of this study contradict the common belief that use of wind speed to approximate k is inappropriate for small bodies of water characterized by low winds and surface obstructions.     

Design of phononic materials/structures for surface wave devices using topology optimization

We develop a topology optimization approach to design two- and three-dimensional phononic (elastic) materials, focusing primarily on surface wave filters and waveguides. These utilize propagation modes that transmit elastic waves where the energy is contained near a free surface of a material. The design of surface wave devices is particularly attractive given recent advances in nano- and micromanufacturing processes, such as thin-film deposition, etching, and lithography, which make it possible to precisely place thin film materials on a substrate with submicron feature resolution. We apply our topology optimization approach to a series of three problems where the layout of two materials (silicon and aluminum) is sought to achieve a prescribed objective: (1) a grating to filter bulk waves of a prescribed frequency in two and three dimensions, (2) a surface wave device that uses a patterned thin film to filter waves of a single or range of frequencies, and (3) a fully three-dimensional structure to guide a wave generated by a harmonic input on a free surface to a specified output port on the surface. From the first to the third example, the resulting topologies increase in sophistication. The results demonstrate the power and promise of our computational framework to design sophisticated surface wave devices.     

Factors Affecting the Collision of Aerosol Particles with Small Water Drops

The factors influencing the collision of aerosol particles with small water drops at low collision efficiencies are examined. The gravitational force and velocity slip of air on the drop surface are found to affect the collision efficiency in the range of values of 10^?4–^?2. The efficacies of the different computational models are compared for ratios of particle radius to drop radius of less than 0.1. The accuracy of the numerical scheme in the trajectory model can be verified by comparing the efficiencies obtained for submicrometer particles with the convective-diffusion model.     

A study of the homogeneous algorithm for dynamic economic dispatchwith network constraints and transmission losses

This paper presents a study of the homogeneous interior point (HIP) method for the economic dispatch problem that combines both independent blocks of constraints (generation demand balance, network flows) and coupling constraints (ramping) into a single optimization problem. By approximating the network constraints through the DC load flow, and the transmission losses through the B-matrix loss formula, the problem is reduced to a convex optimization problem that possesses nonlinear inequality constraints and free variables. The HIP algorithm is specialized in solving this problem, it yields either an approximate global optimum solution or detects possible infeasibility or unboundedness of the problem. The algorithm is tested on the IEEE 14, 30, 57, and 118 bus test systems dispatched over 10 half-hour intervals. The results show that the algorithm is practically efficient     

Recognizing whether sensors are on the same body

In an open mobile health (mHealth) sensing system, users will be able to seamlessly pair sensors with their cellphone and expect the system to just work. This ubiquity of sensors, however, creates the potential for users to accidentally wear sensors that are not paired with their own cellphone. Our method probabilistically detects this situation by finding correlations between embedded accelerometers in the cellphone and sensor. We evaluate our method over a dataset of seven individuals with sensors in various positions on their body and experimentally show that our method is capable of achieving an accuracy of 85%.     

Economics of vascular surgery

Vascular surgery is a relatively young specialty and its separation from general surgery has raised many questions about its cost and effectiveness. In this article the evidence for the treatment of common vascular conditions is evaluated. The reasons for conflicting results and opinions, together with possible solutions for the future, are also discussed.