A study of the break-up characteristics of Chena River Basin using ERTS imagery

The author has identified the following significant results. The Chena River Basin was selected because of the availability of ground truth data for comparison. Very good agreement for snow distribution and rates of ablation was found between the ERTS-1 imagery, the snowmelt model, and field measurements. Monitoring snowmelt rates for relatively small basins appears to be practical. The main limitation of the ERTS-1 imagery is the interval of coverage. More frequent overflights providing coverage are needed for the study of transient hydrologic events. ERTS-1 data is most useful when used in conjunction with snowmelt prediction models and existing snow course data. These results should prove very useful in preliminary assessment of hydrologic conditions in ungaged watersheds and will provide a tool for month-to-month volume forecasting

Break-up characteristics of the Chena River watershed, central Alaska

The author has identified the following significant results. The snow melt for a small watershed (5130 sq km) in Central Alaska was successfully monitored with ERTS-1 imagery. Aerial photography was used as supporting data for periods without satellite coverage. Comparison both with actual measurements and with a computer model showed good agreement

Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring

The effects of electron-electron interaction of a two-electron nanoring on the energy levels and far-infrared (FIR) spectroscopy have been investigated based on a model calculation which is performed within the exactly numerical diagonalization. It is found that the interaction changes the energy spectra dramatically, and also shows significant influence on the FIR spectroscopy. The crossings between the lowest spin-singlet and triplet states induced by the coulomb interaction are clearly revealed. Our results are related to the experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223 (2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15

Order-disorder transition in nanoscopic semiconductor quantum rings

Using the path integral Monte Carlo technique we show that semiconductor quantum rings with up to six electrons exhibit a temperature, ring diameter, and particle number dependent transition between spin ordered and disordered Wigner crystals. Due to the small number of particles the transition extends over a broad temperature range and is clearly identifiable from the electron pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small systems see http://www.smallsystems.d

A possible cooling effect in high temperature superconductors

We show that an adiabatic increase of the supercurrent along a superconductor with lines of nodes of the order parameter on the Fermi surface can result in a cooling effect. The maximum cooling occurs if the supercurrent increases up to its critical value. The effect can also be observed in a mixed state of a bulk sample. An estimate of the energy dissipation shows that substantial cooling can be performed during a reasonable time even in the microkelvin regime.Comment: 5 pages, to appear in Phys. Rev.

Numerical heat transfer model of a traditional ice cellar with passive cooling methods

Thesis (M.S.) University of Alaska Fairbanks, 2011Permafrost ice cellars have been used for generations by Arctic communities for subsistence food storage. Many of these ice cellars have been recently reported to be difficult or impossible to maintain due to thawing and water accumulation inside the cellar. The thesis objective is to investigate the effectiveness of implementing passive techniques to lower the surrounding permafrost temperature, ideally to 0°F, the USDA recommended temperature, throughout the year. Numerical finite element modeling was used to investigate the effects on permafrost temperature with the addition of two-phase, closed thermosyphons and/or ground insulation. Thermosyphon condensers installed both above and below ground were studied. The numerical models were created using Comsol Multiphysics. The modeling results indicated that the addition of thermosyphons and insulation caused a decrease in permafrost temperatures surrounding the ice cellar, although the target temperature of 0°F could not be maintained throughout the year by any of the methods studied. Subsurface insulation decreased the amplitude between the minimum and maximum temperature of the cellar wall 4.5°C. Air thermosyphons decreased the average temperature 8.5°C, and with additional insulation, 90C. Ground thermosyphons were less effective, decreasing the average wall temperature 2.4°C. Additionally, thermosyphon performance was found to be rate-limited by conduction through permafrost.EPSCoR, The Center for Global Climate Change and ExxonMobil1. Introduction -- 1.1. Ice cellars -- 1.2. Cooling of permafrost -- 1.3. Objective and scope of thesis -- 2. Literature review -- 2.1. Ice cellars -- 2.2. Permafrost -- 2.2.1. Basics of permafrost -- 2.2.2. Northern Alaska permafrost conditions -- 2.2.3. Methods of cooling permafrost -- 2.2.4. Phase change material -- 2.3. Thermosyphons -- 2.3.1. Basics of thermosyphons -- 2.3.2. History of thermosyphons -- 2.3.3. Lab and test sites -- 2.3.4. Finite element modeling -- 2.4. Sub-surface insulation -- 2.4.1. Basics of insulation for permafrost preservation -- 2.4.2. Lab and test sites -- 2.4.3. Analytical and modeling solutions -- 3. Method of modeling and verification -- 3.1. Introduction -- 3.2. Methods -- 3.2.1. Volume fraction of water and ice -- 3.2.2. Latent heat effects -- 3.2.3. Sensible heat -- 3.2.4. Thermal conductivity -- 3.2.5. Density -- 3.2.6. Surface temperature (n-Factors) -- 3.2.7. Air-ground thermosyphons -- 3.2.8. Ground-ground thermosyphons -- 3.2.9. Model symmetry -- 3.3. Model verification -- 3.3.1. Stefan solution -- 3.3.2. Two dimensional base-case ice cellar verification -- 3.3.3. Three dimensional base ice cellar verification -- 4. Results and discussion -- 4.1. Introduction -- 4.2. Model parameters -- 4.2.1. Basic material properties -- 4.2.2. Constant model parameters -- 4.2.3. Barter Island climate averages -- 4.2.4. 2-D basic model geometric size -- 4.2.5. 3-D geometric size -- 4.2.6. Initial and boundary conditions -- 4.2.7. Mesh -- 4.3. Porosity study -- 4.3.1. Introduction -- 4.3.2. Effects -- 4.3.3. Conclusions -- 4.4. Subsurface insulation -- 4.4.1. Introduction -- 4.4.2. Effects -- 4.4.3. Conclusions -- 4.5. Heat transfer coefficient of air thermosyphons -- 4.5.1. Introduction -- 4.5.2. Effects -- 4.5.3. Conclusions -- 4.6. Air thermosyphon -- 4.6.1. Introduction -- 4.6.2. Effects -- 4.6.3. Conclusions -- 4.7. Air thermosyphons with sub-surface insulation -- 4.7.1. Introduction -- 4.7.2. Effects -- 4.7.3. Conclusions -- 4.8. Ground thermosyphon -- 4.8.1. Introduction -- 4.8.2. Effects -- 4.8.3. Conclusions -- 4.9. Comparison of different configurations -- 4.9.1. Air thermosyphons with and without insulation -- 4.9.2. Air and ground thermosyphons -- 4.9.3. Table of different configurations -- 5. Conclusions and future work -- 5.1. Conclusions -- 5.2. Future work --5.2.1. Natural convection -- 5.2.2. Governing equations for thermosyphons -- 5.2.3. Optimum radius for evaporator -- 5.2.4. Ground thermosyphons with insulation -- 5.2.5. Other considerations -- References

Solar radiation climatology of Alaska

Summary There are only six locations in Alaska for which global radiation data of more than a year in duration are available. This is an extremely sparse coverage for a state which covers 1.5Â10 6 km 2 and stretches over at least three climatic zones. Cloud observations are, however, available from 18 stations. We used fractional cloud cover and cloud type data to model the global radiation and thus obtain a more complete radiation coverage for Alaska. This extended data set allowed an analysis of geographic and seasonal trends. A simple 1-layer model based on Haurwitz's semiempirical approach, allowing for changes in cloud type and fractional coverage, was developed. The model predicts the annual global radiation¯uxes to within 2±11% of the observed values. Estimated monthly mean values gave an average accuracy within about 6% of the measurements. The estimates agree well with the observations during the ®rst four months of the year but less so for the last four. Changing surface albedo might explain this deviation. Previously, the 1993 National Solar Radiation Data Base (NSRDB) from the National Renewable Energy Laboratory (NREL) modeled global radiation data for 16 Alaskan stations. Although more complete and complex, the NREL model requires a larger number of input parameters, which are not available for Alaska. Hence, we believe that our model, which is based on cloud-radiation relationship and is speci®cally tuned to Alaskan conditions, produces better results for this region. Annual global solar radiation¯ux measurements are compared with results from global coverage models based on the International Satellite Cloud Climatology Project (ISCCP) data. Contour plots of seasonal and mean annual spatial distribution of global radiation for Alaska are presented and discussed in the context of their climatic and geographic settings

Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)

Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wave-like structure along the [110]-direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed in a x-ray diffraction analysis. The stabilization of the Fe3O4(001)-surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure

Inelastic light scattering and the excited states of many-electron quantum dots

A consistent calculation of resonant inelastic (Raman) scattering amplitudes for relatively large quantum dots, which takes account of valence-band mixing, discrete character of the spectrum in intermediate and final states, and interference effects, is presented. Raman peaks in charge and spin channels are compared with multipole strengths and with the density of energy levels in final states. A qualitative comparison with the available experimental results is given.Comment: 5 pages, accepted in J. Phys.: Condens. Matte