Copper Complexation by Dissolved Organic Matter in arid Soils: A Voltametric Study

A voltammetric method was used to estimate the complexing capacity of water extracts from both desert soils sampled at the root zone of creosote and salt cedar plants, and in soils from interspace or background regions where no vegetative influence was apparent. The copper complexing capacity of water extracts of these desert soils was influenced by contact time and pH. In soils from the root zones of creosote and salt cedar plant, copper complexation capacities at pH 8 were from 5 µM to 60 µM after five min contact periods, while 18 h contact periods yielded copper complexation capacities of 40 µM–80 µM. Soils with no vegetative influence had copper complexing capacities of less the 2 µM. The copper complexing capacities of these soils are well correlated with the concentration of organic carbon in the water extract (r2 = 0.86). The abundance of soluble organic matter in the root zone of desert shrubs has the potential to control the solution speciation of Cu2+. The formation of soluble complexes should also have an important influence on the plant uptake and transport of copper, as well as other heavy metals in the root zones of desert shrubs and beyond

Phase Space Tomography of Classical and Nonclassical Vibrational States of Atoms in an Optical Lattice

Atoms trapped in optical lattice have long been a system of interest in the AMO community, and in recent years much study has been devoted to both short- and long-range coherence in this system, as well as to its possible applications to quantum information processing. Here we demonstrate for the first time complete determination of the quantum phase space distributions for an ensemble of $^{85}Rb$ atoms in such a lattice, including a negative Wigner function for atoms in an inverted state.Comment: Submitted to Journal of Optics B: Quantum and Semiclassical Optics. Special issue in connection with the 9th International Conference on Squeezed States and Uncertainty Relations, to be held in Besancon, France, on 2-6 May 200

Quantum Nonlocality in Two-Photon Experiments at Berkeley

We review some of our experiments performed over the past few years on two-photon interference. These include a test of Bell's inequalities, a study of the complementarity principle, an application of EPR correlations for dispersion-free time-measurements, and an experiment to demonstrate the superluminal nature of the tunneling process. The nonlocal character of the quantum world is brought out clearly by these experiments. As we explain, however, quantum nonlocality is not inconsistent with Einstein causality.Comment: 16 pages including 24 figure

Observation of high-order quantum resonances in the kicked rotor

Quantum resonances in the kicked rotor are characterized by a dramatically increased energy absorption rate, in stark contrast to the momentum localization generally observed. These resonances occur when the scaled Planck's constant hbar=(r/s)*4pi, for any integers r and s. However only the hbar=r*2pi resonances are easily observable. We have observed high-order quantum resonances (s>2) utilizing a sample of low temperature, non-condensed atoms and a pulsed optical standing wave. Resonances are observed for hbar=(r/16)*4pi r=2-6. Quantum numerical simulations suggest that our observation of high-order resonances indicates a larger coherence length than expected from an initially thermal atomic sample

Diagnostics and control of wavenumber stability and purity of tunable diode lasers relevant to their use as local oscillators in heterodyne systems

Initial operation of the tunable diode lasers (TDL) showed that it was not possible to adjust the wavenumber to one selected a priori in the TDL tuning range. During operation, the operating point would change by 0.1/cm over the longer term with even larger changes occurring during some thermal cycles. Most changes during thermal cycling required using lower temperatures and higher currents to reach the former wavenumber (when it could be reached). In many cases, an operating point could be selected by changing TDL current and temperature to give both the desired wavenumber and most of the power in a single mode. The selection procedure had to be used after each thermal cycling. Wavenumber nonlinearities of about 10% over a 0.5 cm tuning range were observed. Diagnostics of the single mode selected by a grating monochromator showed wavenumber fine structure under certain operating conditions. The characteristics due to the TDL environment included short term wavenumber stability, the instrument lineshape function, and intermediate term wavenumber stability

Conditional probabilities in quantum theory, and the tunneling time controversy

It is argued that there is a sensible way to define conditional probabilities in quantum mechanics, assuming only Bayes's theorem and standard quantum theory. These probabilities are equivalent to the ``weak measurement'' predictions due to Aharonov {\it et al.}, and hence describe the outcomes of real measurements made on subensembles. In particular, this approach is used to address the question of the history of a particle which has tunnelled across a barrier. A {\it gedankenexperiment} is presented to demonstrate the physically testable implications of the results of these calculations, along with graphs of the time-evolution of the conditional probability distribution for a tunneling particle and for one undergoing allowed transmission. Numerical results are also presented for the effects of loss in a bandgap medium on transmission and on reflection, as a function of the position of the lossy region; such loss should provide a feasible, though indirect, test of the present conclusions. It is argued that the effects of loss on the pulse {\it delay time} are related to the imaginary value of the momentum of a tunneling particle, and it is suggested that this might help explain a small discrepancy in an earlier experiment.Comment: 11 pages, latex, 4 postscript figures separate (one w/ 3 parts

Clock synchronization with dispersion cancellation

The dispersion cancellation feature of pulses which are entangled in frequency is employed to synchronize clocks of distant parties. The proposed protocol is insensitive to the pulse distortion caused by transit through a dispersive medium. Since there is cancellation to all orders, also the effects of slowly fluctuating dispersive media are compensated. The experimental setup can be realized with currently available technology, at least for a proof of principle.Comment: 4 pages, 3 figure

The Vascular System of Xenotransplanted Tumors -Scanning Electron and Light Microscopic Studies-

A widely used model for investigating basic tumor characteristics and different treatment modalities preclinically is the immune-deficient, athymic nude mouse. This model offers many morphological parallelisms to the clinical situation. The aim of this study is to demonstrate the vascularization pattern of xenotransplanted human melanomas and sarcomas using different methods. Xenotransplanted tumors of 62 congenital thymusaplastic nude mice were examined ultrastructurally and topographically after corrosion cast and tissue preparation. Quantitative measurements of tumors injected with India ink were carried out to obtain comparable information on the vascular densities in the tumors. Quantitative measurements showed that there is no zonal, topographic arrangement of the vascular densities. Comparisons of the vascular densities in the centers of tumors with the densities in the periphery showed an extreme heterogeneity in tumor vessel distribution, which does not generally support the idea of a better vascularisation in the tumor periphery. Neither in the periphery nor in the center of the tumor regular vessels are to be seen consisting of intimal, medial and adventitial layers. Even the largest peripheral vessels, which often take a tortuous course, consist mainly of an endothelial layer and some perivascular connective tissue only. Areas with high vascular densities could be seen just beneath areas almost free of vessels. Besides endothelial-lined vessels numerous irregular, tumor cell-lined sinusoids are visible both in sarcomas and melanomas. The morphology of the vessels found scanning electron microscopically is generally in agreement with many features described transmission electron microscopically

Rank 3 permutation characters and maximal subgroups

In this paper we classify all maximal subgroups M of a nearly simple primitive rank 3 group G of type L=Omega_{2m+1}(3), m > 3; acting on an L-orbit E of non-singular points of the natural module for L such that 1_P^G <=1_M^G where P is a stabilizer of a point in E. This result has an application to the study of minimal genera of algebraic curves which admit group actions.Comment: 41 pages, to appear in Forum Mathematicu

Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence

Using a two-photon interference technique, we measure the delay for single-photon wavepackets to be transmitted through a multilayer dielectric mirror, which functions as a ``photonic bandgap'' medium. By varying the angle of incidence, we are able to confirm the behavior predicted by the group delay (stationary phase approximation), including a variation of the delay time from superluminal to subluminal as the band edge is tuned towards to the wavelength of our photons. The agreement with theory is better than 0.5 femtoseconds (less than one quarter of an optical period) except at large angles of incidence. The source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure