Reconfiguring, Replumbing, and Repurposing Hydraulic Structures - Responding to New Realities

We look into an ever-changing future filled with challenges to continue developing new water resources but with an increased emphasis on water conservation and preserving our natural environment. This is a different approach to that of the 20th century, where the emphasis was generally on development of water resources. As water engineers and managers facing an increasingly limited water supply, our challenge is to build, and in some cases change, infrastructure for a resilient future. The built infrastructure for water systems must protect life and provide a safe living environment, including an adequate supply and quality of fresh water. Skills and technologies adaptable to the new societal realities of the 21st century will be needed. This presentation will focus on the possibilities of reconfiguring, replumbing, and repurposing hydraulic structures even as we look to develop new water resources and face the growing water needs of an ever changing future. The paper is based on several case studies that concentrate on “Doing Things Differently.

Imaging of electron potential landscapes on Au(111)

The Hohenberg-Kohn theorem states that the ground state electron density completely determines the external potential acting on an electron system. Inspired by this fundamental theorem, we developed a novel approach to map directly the electron potential in surface systems: linear response theory applied to the total electron density as measured with scanning tunneling microscopy determines the external potential. Potential imaging is demonstrated for the s-p derived surface state on Au(111), where the "herringbone" reconstruction induces a periodic potential modulation, the details of which are revealed by our technique

Tsunami impacts on shallow groundwater and associated water supply on the East Coast of Sri Lanka: a post-tsunami well recovery support initiative and an assessment of groundwater salinity in three areas of Batticaloa and Ampara Districts

Groundwater, Aquifers, Salinity, Natural disasters, Water supply, Drinking water, Wells, Rehabilitation, Mosquitoes, Disease vectors, Environmental Economics and Policy, Health Economics and Policy, Resource /Energy Economics and Policy,

Molecular structure of nitrogen trichloride as determined by electron diffraction

Nitrogen trichloride was found to have a bond length of rg = 1.759 +/- 0.002 A and a Cl-N-Cl angle of 107.1 +/- 0.5[deg]. The bond angle is larger than that found in NF3, consistent with the (recently revised) trends displayed by the trihalides of phosphorus and arsenic, but much lower than the 120[deg] angle reported for the isoelectronic molecule N(SiH3)3. Moreover, a comparison between selected compounds reveals that the N-Cl bond length is appreciably greater, relatively, than the N-Si bond length. Accordingly, the bond angles and bond lengths suggest a greater reluctance of the nitrogen lone pairs to delocalize onto Cl than onto SiH3 groups. Mean amplitudes of vibration of NCl3 were derived both from the diffraction data and from recently published infrared and Raman frequencies. The values agree within the estimated uncertainties.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33551/1/0000052.pd

Noble metal surface states: deviations from parabolic dispersion

Dispersion relations of the s-p derived surface state on (111) surfaces of silver and copper have been measured using low-temperature scanning tunneling microscopy and spectroscopy. For silver as well as for copper we find a significant deviation from a parabolic dispersion characteristic of free-electron-like systems. A simple tight-binding model accounts for the trends in the measured dispersions. (C) 2000 Elsevier Science B.V. All rights reserved

Probing hot-electron dynamics at surfaces with a cold scanning tunneling microscope

We report on a novel approach to measure the phase relaxation length and femtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interference patterns in the local density of states for surface state electrons on Ag(111) and Cu(111). This decay is governed by inelastic; electron-electron scattering. We find a (E - E-F)(-2) energy dependence of the lifetimes for both Ag and Cu, and our values are comparable to the corresponding bulk electron lifetimes. This indicates that electron-electron interaction of hot surface state electrons with the Fermi sea is dominated by the underlying bulk electrons. [S0031-9007(99)09260-1]

Quantum coherence and lifetimes of surface-state electrons

We discuss a novel approach to measure the electron phase-relaxation length and femtosecond lifetimes at surfaces. It relies on the study of the spatial decay of quantum interference patterns in the local density of states (LDOS) with the STM. The method has been applied to s-p derived surface-state electrons on Cu(111) and Ag(111). The characteristic decay length of the LDOS oscillations is influenced by the finite lifetime, and thus reveals information about inelastic scattering in the two-dimensional (2D) electron gas. After an introduction in Section 1, we present a model describing the decay of Friedel oscillations off from straight steps in Section 2. Energy dependent lifetime measurements of hot electrons are presented in Section 3 and interpreted in terms of electron-electron scattering. The temperature dependent lifetime measurements of low-energy quasiparticles discussed in Section 4 give insight into the interaction of these 2D electrons with phonons. Our results on inelastic lifetimes are discussed in comparison with high-resolution angle-resolved photoemission and femtosecond two-photon photoemission measurements. (C) 2000 Elsevier Science B.V. All rights reserved

Thermal damping of quantum interference patterns of surface-state electrons

The temperature-dependent damping of quantum-mechanical interference patterns from surface-state electrons scattering off steps on Ag(111) and Cu(111) has been studied using scanning tunneling microscopy (STM) and spectroscopy in the temperature range 3,5-178 K. The thermal damping of the electron standing waves is described quantitatively within a simple plane-wave model accounting for thermal broadening due to the broadening of the Fermi-Dirac distributions of sample and tip, for beating effects between electrons with different kll vectors, and for inelastic collisions of the electrons, e.g., with phonons. Our measurements reveal that Fermi-Dirac broadening fully explains the observed damping for Ag and Cu. From the analysis of our data, lower limits of the phase-relaxation lengths at the Fermi energy EF Of the two-dimensional electron gas of L-phi(E-F)greater than or similar to 600 Angstrom at 3.5 K and greater than or similar to 250 Angstrom at 77 K for Ag(111), and of L-phi(E-F)greater than or similar to 660 Angstrom at 77 K and greater than or similar to 160 Angstrom at 178 K for Cu(111) are deduced. In contrast to integral measurements such as photoemission we measure L-phi close to EF and also locally. The latter eliminates residual line widths due to surface defect scattering found in the integrating techniques. Our STM results, therefore, currently provide a very good absolute estimate of L-phi and the inelastic lifetime tau=L-phi/v(F), respectively. Our values can be combined with photoemission results on dL(phi)/dT to derive the inelastic lifetime of surface state electrons at any T

Confinement of surface state electrons in Fabry-Perot resonators

Ag(111) surface state electrons have been confined in symmetric and asymmetric Fabry-Perot resonators formed by two atomically parallel step edges. The local density of states in the resonators has been measured by means of low-temperature scanning tunneling spectroscopy and can perfectly be explained with a simple Fabry-Perot-like model. The energy dependent reflection amplitudes and scattering phase shifts of the different kinds of Ag(111) step edges have been determined with high accuracy. The model character of the resonators opens up quantitative electron scattering experiments at test structures brought into the resonator