Investigating changes in productivity of an old growth Juniperus stand: A physiological and isotopic approach

Forest ecosystems play a central role in the global carbon cycle and are a major part of the terrestrial carbon sink. For more accurate predictions of terrestrial C sequestration models require a mechanistic understanding of how carbon cycling in trees and forests responds to atmospheric CO 2, temperature, and precipitation. With this comes a need for a greater understanding of the physiological mechanisms involved with changes in forest productivity as trees and forests age. This research used an old growth stand of Juniperus virginiana (Eastern red cedar) in the Central Appalachian Mountains of West Virginia to examine how carbon assimilation changes over time. This study had two components; the first examined of how tree age affects the physiological ecology of Juniperus virginiana in their native habitat; the second used the stable C isotopes in the annual growth rings to determine whether we could detect how climatic and environmental factors affected C assimilation and growth over the last century. The first component of this study provided little evidence that age strongly affects leaf photosynthesis or hydraulic conductivity. Current environmental conditions are far more indicative of physiological functioning than tree age. However, it may be that age-related changes in the physiology of J . virginiana occur earlier than the youngest ages of trees in this stand. The second component of this study found weak links between climate and tree productivity. Interestingly, a strong link between C i/Ca and deposition of both nitrogen and sulfur may be evidence that regulations put in place by congress have had noticeable effects on tree physiology. In an area of tree physiology that has focused primarily on the effect of rising CO 2 concentrations this link may lead to investigating other possible drivers of physiological change in trees

AC Magnetic Fields in the Vicinity of a Crack Calculated by Analytic and Numerical Methods

We report calculations of the impedance of a long solenoid which surrounds a cylinder of conducting material containing a radial surface crack. The calculation is accomplished by two independent methods. The first method expresses the field in the interior of the cracked cylinder as an infinite series of cylindrical Bessel functions. The coefficients in the series are determined in principle by boundary conditions; the most significant terms are calculated by solving the finite set of equations obtained by truncation of the series. The second method, applicable to any uniform geometric cross-section, obtains the impedance from the normal derivative of the field on the boundary of the conductor. This normal derivative satisfies a (boundary) Fredholm integral equation of the first kind; a solution is obtained by discretizing and solving the resulting linear system of algebraic equations. The impedance is calculated for a wide range of values of the ratios of crack depth-to-radius and radius-to-skin depth. The results are displayed in graphical form giving the fractional charges of the real and imaginary parts of the complex impedance induced by the presence of the crack

Frequency Dependence of Electric Current Perturbation Probe Response

The electric current perturbation (ECP) probe1–3 is similar to a conventional eddy current probe in that a coil, typically a cylindrical winding, is used to induce current in the test piece. The ECP probe differs in the use of a separate differential sensor coil, with axis parallel to the surface of the piece, and usually located just outside the induction coil winding. We have found that this sensor orientation tends to minimize probe-to-surface coupling and therefore minimizes liftoff noise

Sixteen-state magnetic memory based on the extraordinary Hall effect

We report on a proof-of-concept study of split-cell magnetic storage in which multi-bit magnetic memory cells are composed of several multilevel ferromagnetic dots with perpendicular magnetic anisotropy. Extraordinary Hall effect is used for reading the data. Feasibility of the approach is supported by realization of four-, eight- and sixteen- state cells

Statistical properties and statistical interaction for particles with spin: Hubbard model in one dimension and statistical spin liquid

We derive the statistical distribution functions for the Hubbard chain with infinite Coulomb repulsion among particles and for the statistical spin liquid with an arbitrary magnitude of the local interaction in momentum space. Haldane's statistical interaction is derived from an exact solution for each of the two models. In the case of the Hubbard chain the charge (holon) and the spin (spinon) excitations decouple completely and are shown to behave statistically as fermions and bosons, respectively. In both cases the statistical interaction must contain several components, a rule for the particles with the internal symmetry.Comment: (RevTex, 16 pages, improved version

Eddy-Current Detection Methods for Surface-Breaking Tight Cracks

The eddy-current (EC) NDE method has been in use for quite some time, and efforts have been made to make it a fully quantitative method. To evaluate impedance signals for a given EC inspection system, one has to characterize the system as a whole, including both probes and specimens. In particular, until probes are characterized, the electromagnetic fields cannot be calculated. Naturally, the amount of numerical computation becomes a serious issue during the course of development. It is necessary to choose probes carefully so as to maximize the flaw-characterization capability, while keeping numerical tasks within a reasonable size. Probes that are suitable for quantitative assessment are presumably different in nature from those with maximum detection capability. Among all kinds of existing probes, the simplest characterizable probe is the uniform-field-eddy-current (UFEC) probe. In fact, a series of studies, both theoretical and experimental, were devoted to demonstrating potential capabilities of UFEC probes [1–9]. The present theoretical work is another entry in this series. The numerical procedure developed in this work is limited to the case where cracks are tightly closed. The procedure is nevertheless capable, in principle, of dealing with an arbitrary range of frequencies

Reciprocity theorem in high-temperature superconductors

This article is devoted to the problem of the validity of the reciprocity theorem in high-temperature superconductors (HTSC). The violation of the reciprocity theorem in zero external magnetic fields has been studied. Experimental data obtained for two different superconducting materials: BiSrCaCuO and YBaCuO are presented. Results show that the basic form of the reciprocity theorem (without consideration of any additional anisotropy) is not valid near the critical temperature. We assume that the reciprocity theorem breaking is connected with the existence of an extraordinary transverse electric field originated from additional anisotropy and more general form of the reciprocity relations should be valid. However, the origin of this anisotropy is not clear yet. We suggest that the vortex-antivortex dynamics model taking into account vortex guiding can be responsible for the observed effect. Also the explanation based on weak P and T symmetry breaking in HTSC which is supported by the observation of the spontaneous magnetisation can not be excluded.Comment: 15 pages, 11 figure

Measuring thermoelectric transport properties of materials

In this review we discuss considerations regarding the common techniques used for measuring thermoelectric transport properties necessary for calculating the thermoelectric figure of merit, zT. Advice for improving the data quality in Seebeck coefficient, electrical resistivity, and thermal conductivity (from flash diffusivity and heat capacity) measurements are given together with methods for identifying possible erroneous data. Measurement of the Hall coefficient and calculation of the charge carrier concentration and mobility is also included due to its importance for understanding materials. It is not intended to be a complete record or comparison of all the different techniques employed in thermoelectrics. Rather, by providing an overview of common techniques and their inherent difficulties it is an aid to new researchers or students in the field. The focus is mainly on high temperature measurements but low temperature techniques are also briefly discussed