Heavy thinning of ponderosa pine stands: an Arizona case study (Research Paper/RMRS–RP–22)

Growth and structural changes in a mosaic of even-aged ponderosa pine (Pinus ponderosa) stands were studied for 25 years to determine the long-term impacts of a heavy thinning treatment to a basal-area level of 25 ft2/acre. Basal area and volume growth of these stands has increased since thinning and likely will continue to increase as the residual trees increase in size. Furthermore, future stand integrity should be maintained at relatively low-density levels. It is unlikely, however, that timber production could be sustained at this level. A more plausible scenario is to manage the watershed for other resource values available from ponderosa pine stands

Universality, Scaling and Triviality in a Hierarchical Field Theory

Using polynomial truncations of the Fourier transform of the RG transformation of Dyson's hierarchical model, we show that it is possible to calculate very accurately the renormalized quantities in the symmetric phase. Numerical results regarding the corrections to the scaling laws, (i.e finite cut-off dependence) triviality, hyperscaling, universality and high-accuracy determinations of the critical exponents are discussed.Comment: LATTICE98(spin

Trends in Double Networks as Bioprintable and Injectable Hydrogel Scaffolds for Tissue Regeneration

Additive manufacturing and injection are essential tools in the rapidly developing field of personalized medicine and are particularly promising for applications in regenerative medicine. One of the biggest challenges in this vibrant research domain remains the processing of complex formulations with robust mechanical properties. Mimicking the native extracellular matrix associated with many tissues requires materials that have high degrees of functionality for performing the complex array of functions within the cellular environment. Furthermore, native tissues often possess outstanding mechanical properties, particularly in connective tissues. These exceptional mechanics are a challenge to emulate in their own right, especially considering the accompanying demands for additional functionality. Double-network hydrogels have emerged as strong candidates for tissue engineering because of the impressive mechanics and versatility in terms of chemical makeup. Combining advances in processing (i.e., additive manufacturing and injection) with dual-network hydrogel formulations has led to an impressive collection of results, making great strides toward systems capable of addressing the demanding environment surrounding tissues while being amenable to personalized fabrication techniques. This review provides a brief summary of the most contemporary trends collected from the literature describing dual-network hydrogels being demonstrated in additive manufacturing and injectable applications

Simulation and optimisation of terahertz emission from InGaAs and InP photoconductive switches

We simulate the terahertz emission from laterally-biased InGaAs and InP using a three-dimensional carrier dynamics model in order to optimise the semiconductor material. Incident pump-pulse parameters of current Ti:Sapphire and Er:fibre lasers are chosen, and the simulation models the semiconductor's bandstructure using parabolic Gamma, L and X valleys, and heavy holes. The emitted terahertz radiation is propagated within the semiconductor and into free space using a model based on the Drude-Lorentz dielectric function. As the InGaAs alloy approaches InAs an increase in the emitted power is observed, and this is attributed to a greater electron mobility. Additionally, low-temperature grown and ion-implanted InGaAs are modelled using a finite carrier trapping time. At sub-picosecond trapping times the terahertz bandwidth is found to increase significantly at the cost of a reduced emission power.Comment: 9 pages, 7 figure

An integral method for solving nonlinear eigenvalue problems

We propose a numerical method for computing all eigenvalues (and the corresponding eigenvectors) of a nonlinear holomorphic eigenvalue problem that lie within a given contour in the complex plane. The method uses complex integrals of the resolvent operator, applied to at least $k$ column vectors, where $k$ is the number of eigenvalues inside the contour. The theorem of Keldysh is employed to show that the original nonlinear eigenvalue problem reduces to a linear eigenvalue problem of dimension $k$. No initial approximations of eigenvalues and eigenvectors are needed. The method is particularly suitable for moderately large eigenvalue problems where $k$ is much smaller than the matrix dimension. We also give an extension of the method to the case where $k$ is larger than the matrix dimension. The quadrature errors caused by the trapezoid sum are discussed for the case of analytic closed contours. Using well known techniques it is shown that the error decays exponentially with an exponent given by the product of the number of quadrature points and the minimal distance of the eigenvalues to the contour

Classical Open String Models in 4-Dim Minkowski Spacetime

Classical bosonic open string models in fourdimensional Minkowski spacetime are discussed. A special attention is paid to the choice of edge conditions, which can follow consistently from the action principle. We consider lagrangians that can depend on second order derivatives of worldsheet coordinates. A revised interpretation of the variational problem for such theories is given. We derive a general form of a boundary term that can be added to the open string action to control edge conditions and modify conservation laws. An extended boundary problem for minimal surfaces is examined. Following the treatment of this model in the geometric approach, we obtain that classical open string states correspond to solutions of a complex Liouville equation. In contrast to the Nambu-Goto case, the Liouville potential is finite and constant at worldsheet boundaries. The phase part of the potential defines topological sectors of solutions.Comment: 25 pages, LaTeX, preprint TPJU-28-93 (the previous version was truncated by ftp...

Cloud microphysical effects of turbulent mixing and entrainment

Turbulent mixing and entrainment at the boundary of a cloud is studied by means of direct numerical simulations that couple the Eulerian description of the turbulent velocity and water vapor fields with a Lagrangian ensemble of cloud water droplets that can grow and shrink by condensation and evaporation, respectively. The focus is on detailed analysis of the relaxation process of the droplet ensemble during the entrainment of subsaturated air, in particular the dependence on turbulence time scales, droplet number density, initial droplet radius and particle inertia. We find that the droplet evolution during the entrainment process is captured best by a phase relaxation time that is based on the droplet number density with respect to the entire simulation domain and the initial droplet radius. Even under conditions favoring homogeneous mixing, the probability density function of supersaturation at droplet locations exhibits initially strong negative skewness, consistent with droplets near the cloud boundary being suddenly mixed into clear air, but rapidly approaches a narrower, symmetric shape. The droplet size distribution, which is initialized as perfectly monodisperse, broadens and also becomes somewhat negatively skewed. Particle inertia and gravitational settling lead to a more rapid initial evaporation, but ultimately only to slight depletion of both tails of the droplet size distribution. The Reynolds number dependence of the mixing process remained weak over the parameter range studied, most probably due to the fact that the inhomogeneous mixing regime could not be fully accessed when phase relaxation times based on global number density are considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in reduced quality), to appear in Theoretical Computational Fluid Dynamic

The UK risk assessment scheme for all non-native species

1. A pest risk assessment scheme, adapted from the EPPO (European and Mediterranean Plant Protection Organisation) scheme, was developed to assess the risks posed to UK species, habitats and ecosystems by non-native taxa. 2. The scheme provides a structured framework for evaluating the potential for non-native organisms, whether intentional or unintentional introductions, to enter, establish, spread and cause significant impacts in all or part of the UK. Specialist modules permit the relative importance of entry pathways, the vulnerability of receptors and the consequences of policies to be assessed and appropriate risk management options to be selected. Spreadsheets for summarising the level of risk and uncertainty, invasive attributes and economic impact were created. In addition, new methods for quantifying economic impact and summarising risk and uncertainty were explored. 3. Although designed for the UK, the scheme can readily be applied elsewhere

Residual cognitive deficits 50 years after lead poisoning during childhood

The long term neurobehavioural consequences of childhood lead poisoning are not known. In this study adult subjects with a documented history of lead poisoning before age 4 and matched controls were examined with an abbreviated battery of neuropsychological tests including measures of attention, reasoning, memory, motor speed, and current mood. The subjects exposed to lead were inferior to controls on almost all of the cognitive tasks. This pattern of widespread deficits resembles that found in children evaluated at the time of acute exposure to lead rather than the more circumscribed pattern typically seen in adults exposed to lead. Despite having completed as many years of schooling as controls, the subjects exposed to lead were lower in lifetime occupational status. Within the exposed group, performance on the neuropsychological battery and occupational status were related, consistent with the presumed impact of limitations in neuropsychological functioning on everyday life. The results suggest that many subjects exposed to lead suffered acute encephalopathy in childhood which resolved into a chronic subclinical encephalopathy with associated cognitive dysfunction still evident in adulthood. These findings lend support to efforts to limit exposure to lead in childhood

Assessing the potential demand for and effectiveness of integrating STI/HIV management services with Zimbabwe National Family Planning Council\u27s clinic-based family planning services

HIV/AIDS is a threat to individual lives and the national economies of many sub-Saharan African countries, despite efforts to contain its spread. The region also suffers from high levels of other reproductive tract infections (RTIs), some of which increase the risk of sexual transmission of HIV. The control of RTIs is therefore seen not only as an important reproductive health care strategy, but as a key strategy in reducing the spread of HIV/AIDS. Most national health care programs in the region are actively seeking cost-effective ways of implementing an RTI management program that would reduce and prevent RTIs and HIV. To date, most emphasis has been placed on managing RTI/HIV within high-risk groups, but many programs are now trying to reach a bigger proportion of the at-risk population through integrating RTI/HIV management services into existing maternal and child health/family planning (MCH/FP) programs. As noted in this baseline survey report, a variety of methods were used to collect and synthesize information that could be used in developing an appropriate and cost-effective approach to the integration of RTI/HIV within FP services