Fabrication and Characterization of CuInS₂ and CuInSe₂ Light-Absorbing Thin Films for use in Solar Cells

Solar energy is free and globally abundant and harnessed cost-effectively, it has the potential to be the world’s main source of energy. CuInGa(S,Se)2 solar cells have a very high efficiency of 20 %. However, gallium is a rare and expensive element. We have decided to work on its alternative CuInSe2 (CISe) and CuInS2 (CIS) by removing gallium or both gallium and selenium. The p-type CISe or CIS light-absorbing semiconducting layer is crucial for this type of solar cell. Preparation methods for CIS and CISe films were developed to reduce the costs and enhance the photoelectrochemical efficiency. The first preparation method was a low-temperature, one-pot, solvothermal synthesis of CIS nanocrystals (NCs) using metal salts as precursors, which was optimized based on a photoelectrochemical (PEC) measurement. The resultant NCs were fully characterized in Chapter 2 by conventional analytical and physical methods such as XRD, EDX, SEM, XPS, and TEM. X-ray absorption near edge structure (XANES) was utilized to not only investigate the absence of secondary phases and oxidation states, but also to obtain information about the connectivity of the capping ligand, effects of composition on the electronic structure of the materials, and the position of the conduction band (Chapter 3). A linker molecule (3-mercaptopropyl) trimethoxysilane (MPTMS) was utilized to link the back contact to the CIS NCs. The monolayer, when tested with PEC measurements, produced a similar photocurrent density to much thicker films of CIS NCs. Polarization XANES was carried out to assess the CIS NC orientation (Chapter 4). NC films were cast in a variety of ways including spin-coating and drop-casting. The addition of the next layer, CdS, in the full device fabrication was also investigated. It was discovered that a low-temperature annealing process of the CIS/CdS bilayer followed by an additional CdS layer produced a significant photocurrent enhancement (Chapter 5). Also explored was the successive electrochemical deposition of copper and indium followed by selenization to form CISe. All films formed by these methods were fully characterized with respect to structure, composition, photoreactions, morphology, and optical properties as well as extended X-ray absorption fine structure (EXAFS) (Chapter 6

Recent La Plata basin drought conditions observed by satellite gravimetry

The Gravity Recovery and Climate Experiment (GRACE) provides quantitative measures of terrestrial water storage (TWS) change. GRACE data show a significant decrease in TWS in the lower (southern) La Plata river basin of South America over the period 2002-2009, consistent with recognized drought conditions in the region. GRACE data reveal a detailed picture of temporal and spatial evolution of this severe drought event, which suggests that the drought began in lower La Plata in around austral spring 2008 and then spread to the entire La Plata basin and peaked in austral fall 2009. During the peak, GRACE data show an average TWS deficit of ~12 cm (equivalent water layer thickness) below the 7 year mean, in a broad region in lower La Plata. GRACE measurements are consistent with accumulated precipitation data from satellite remote sensing and with vegetation index changes derived from Terra satellite observations. The Global Land Data Assimilation System model captures the drought event but underestimates its intensity. Limited available groundwater-level data in southern La Plata show significant groundwater depletion, which is likely associated with the drought in this region. GRAC-observed TWS change and precipitation anomalies in the studied region appear to closely correlate with the ENSO climate index, with dry and wet seasons corresponding to La Ni\~na and El Ni\~no events, respectively

Circulation of the North Atlantic Ocean from altimetry and the Gravity Recovery and Climate Experiment geoid

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C03005, doi:10.1029/2005JC003128.We discuss the ocean circulation derived from the temporally averaged sea surface height, which is referenced to the recently released geoid from the Gravity Recovery and Climate Experiment (GRACE) mission (GRACE Gravity Model 02 (GGM02)). The creation of a precise, independent geoid allows for the calculation of the reference gravitational potential undulation surface, which is associated with the resting ocean surface height. This reference height is then removed from the temporally averaged sea surface height, leaving the dynamic ocean topography. At its most basic level the dynamic ocean topography can be related to the ocean's surface circulation through geostrophy. This has previously been impracticable because of large uncertainties in previous estimates of the Earth's geoid. Prior geoids included the temporally averaged sea surface from altimeters as a proxy for the geoid and therefore were unsuitable for calculations of the ocean's circulation. Geoid undulations are calculated from the GRACE geoid and compared to those from the NASA Goddard Space Flight Center and National Imagery and Mapping Agency Joint Earth Geopotential Model (EGM96) geoid. Error estimates are made to assess the accuracy of the new geoid. The deep ocean pressure field is also estimated by combining the calculated dynamic ocean topography with hydrography. Finally, the derived circulation is compared to independent observations of the circulation from sea surface drifters and subsurface floats. It is shown that the GGM02 geoid is significantly more accurate for use in estimating the ocean's circulation.This work was supported by grants NNG04GE95G from the National Aeronautics and Space Administration and OCE 01-37122 from the National Science Foundation and the Young Investigator Program award N00014-03-1-0545 from the Office of Naval Research

Using discrete Darboux polynomials to detect and determine preserved measures and integrals of rational maps

In this Letter we propose a systematic approach for detecting and calculating preserved measures and integrals of a rational map. The approach is based on the use of cofactors and Discrete Darboux Polynomials and relies on the use of symbolic algebra tools. Given sufficient computing power, all rational preserved integrals can be found. We show, in two examples, how to use this method to detect and determine preserved measures and integrals of the considered rational maps.Comment: 8 pages, 1 Figur

Altimetric system: Earth observing system. Volume 2h: Panel report

A rationale and recommendations for planning, implementing, and operating an altimetric system aboard the Earth observing system (Eos) spacecraft is provided. In keeping with the recommendations of the Eos Science and Mission Requirements Working Group, a complete altimetric system is defined that is capable of perpetuating the data set to be derived from TOPEX/Poseidon, enabling key scientific questions to be addressed. Since the scientific utility and technical maturity of spaceborne radar altimeters is well documented, the discussion is limited to highlighting those Eos-specific considerations that materially impact upon radar altimetric measurements

Linear Darboux polynomials for Lotka-Volterra systems, trees and superintegrable families

We present a method to construct superintegrable $n$-component Lotka-Volterra systems with $3n-2$ parameters. We apply the method to Lotka-Volterra systems with $n$ components for $1 < n < 6$, and present several $n$-dimensional superintegrable families. The Lotka-Volterra systems are in one-to-one correspondence with trees on $n$ vertices.Comment: 14 pages, 4 figure

Report of the panel on geopotential fields: Gravity field, section 8

The objective of the Geopotential Panel was to develop a program of data acquisition and model development for the Earth's gravity and magnetic fields that meet the basic science requirements of the solid Earth and ocean studies. Presented here are the requirements for gravity information and models through the end of the century, the present status of our knowledge, data acquisition techniques, and an outline of a program to meet the requirements

Observation of charged nanograins at comet 67P/Churyumov‐Gerasimenko

Soon after the Rosetta Orbiter rendezvoused with comet 67P/Churyumov‐Gerasimenko at a solar distance of ~3.5 AU and began to fly in triangular‐shaped trajectories around it, the Ion and Electron Sensor detected negative particles at energies from about 100 eV/q to over 18 keV/q. The lower energy particles came from roughly the direction of the comet; the higher‐energy particles came from approximately the solar direction. These particles are interpreted as clusters of molecules, most likely water, which we refer to as nanograins because their inferred diameters are less than 100 nm. Acceleration of the grains away from the comet is through gas drag by the expanding cometary atmosphere, while acceleration back to the vicinity of the comet is caused partly by solar radiation pressure but mainly by the solar wind electric field. These observations represent the first measurements of energetic charged submicron‐sized dust or ice grains (nanograins) in a cometary environment.Key PointsFirst observation of charged nanograins from a cometNanograins are reflected by solar radiation pressure and accelerated by solar wind electric fieldsNanograins return to the vicinity of the comet after significant energizationPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113696/1/grl53313_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/113696/2/grl53313.pd

On the Lense-Thirring test with the Mars Global Surveyor in the gravitational field of Mars

I discuss some aspects of the recent test of frame-dragging performed by me by exploiting the Root-Mean-Square (RMS) orbit overlap differences of the out-of-plane component N of the orbit of the Mars Global Surveyor (MGS) spacecraft in the gravitational field of Mars. A linear fit of the full time series of the entire MGS data (4 February 1999-14 January 2005) yields a normalized slope 1.03 +/- 0.41 (with 95% confidence bounds). Other linear fits to different data sets confirm the agreement with general relativity. The huge systematic effects induced by the mismodeling in the martian gravitational field claimed by some authors are absent in the MGS out-of-plane record. The non-gravitational forces affect at the same level of the gravitomagnetic one the in-plane orbital components of MGS, not the out-of-plane one. Moreover, they experience high-frequency variations which does not matter in the present case in which secular effects are relevant.Comment: LaTex2e, 8 pages, no figures, no tables, 17 references. It refers to K. Krogh, Class. Quantum Grav., 24, 5709-5715, 2007 based on astro-ph/0701653. Final version to appear in CEJP (Central European Journal of Physics

IMAGE, the First of the NEW MIDEX Missions

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission will be the first of the new Mediumclass Explorer (MIDEX) missions to fly. Led by Southwest Research Institute with oversight from the Explorers Project Office at NASA GSFC, IMAGE is the first satellite mission dedicated to imaging the Earth\u27s magnetosphere. IMAGE will utilize a combination of ultraviolet and neutral atom imaging instruments plus an RF sounder to map and image the temporal and spatial features of the magnetosphere. The eight science sensors are mounted to a single deckplate. The deckplate is enveloped in an eight-sided spacecraft bus, 225 cm across the flats, developed by Lockheed Martin Missiles and Space Corporation. Constructed of laminated aluminum honeycomb panels, covered extensively by Gallium Arsenide solar cells, the spacecraft structure is designed to withstand the launch loads of a Delta 7326-9.5 ELV. Attitude control is via a single magnetic torque rod and passive nutation damper with aspect information provided by a star camera, sun sensor, and three-axis magnetometer. A single S-band transponder provides telemetry and command functionality. Interfaces between the self-contained payload and the spacecraft are limited to MIL-STD-1553 and power. This paper describes the IMAGE mission as well as the engineering details of the spacecraft