Physical mechanism for a kinetic energy driven zero-bias anomaly in the Anderson-Hubbard model

The combined effects of strong disorder, strong correlations and hopping in the Anderson-Hubbard model have been shown to produce a zero bias anomaly which has an energy scale proportional to the hopping and minimal dependence on interaction strength, disorder strength and doping. Disorder-induced suppression of the density of states for a purely local interaction is inconsistent with both the Efros-Shklovskii Coulomb gap and the Altshuler-Aronov anomaly, and moreover the energy scale of this anomaly is inconsistent with the standard energy scales of both weak and strong coupling pictures. We demonstrate that a density of states anomaly with similar features arises in an ensemble of two-site systems, and we argue that the energy scale t emerges in strongly correlated systems with disorder due to the mixing of lower and upper Hubbard orbitals on neighboring sites.Comment: 4 pages, 3 figures; new version includes minor changes to figures and text to increase clarit

Temperature dependence of the zero-bias anomaly in the Anderson-Hubbard model: Insights from an ensemble of two-site systems

Motivated by experiments on doped transition metal oxides, this paper considers the interplay of interactions, disorder, kinetic energy and temperature in a simple system. An ensemble of two-site Anderson-Hubbard model systems has already been shown to display a zero-bias anomaly which shares features with that found in the two-dimensional Anderson-Hubbard model. Here the temperature dependence of the density of states of this ensemble is examined. In the atomic limit, there is no zero-bias anomaly at zero temperature, but one develops at small nonzero temperatures. With hopping, small temperatures augment the zero-temperature kinetic-energy-driven zero-bias anomaly, while at larger temperatures the anomaly is filled in.Comment: 8 pages, 3 figures; submitted to SCES 2010 conference proceeding

The effects of reinforcement interval on the acquisition of paired-associate responses

Effects of reinforcement interval on acquisition of paired-associate response

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy

Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful technique for extracting details of the momentum-resolved electronic band structure from inhomogeneities in the local density of states due to disorder-related quasiparticle scattering. To a large extent, current understanding of FTSTS is based on models of Friedel oscillations near isolated impurities. Here, a framework for understanding many-impurity effects is developed based on a systematic treatment of the variance Delta rho^2(q,omega) of the Fourier transformed local density of states rho(q,\omega). One important consequence of this work is a demonstration that the poor signal-to-noise ratio inherent in rho(q,omega) due to randomness in impurity positions can be eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show that an important bulk quantity, the mean-free-path, can be extracted from FTSTS experiments.Comment: 7 pages, 5 figures. A version of the paper with high resolution, colour figures is available at http://www.trentu.ca/physics/batkinson/FTSTS.ps.gz minor revisions in response to refree report + figure 5 is modifie

Yield and Value of Burley 21 Tobacco as Influenced by Nitrogen Nutrition, Suckering Practice, and Harvest Date

An experiment was conducted in the field during 1966 on Maury silt loam soil to obtain information of the effects of agronomic factors on yield and value of Burley 21 tobacco . Ammonium nitrate fertilizer at varying rates, and concentrated super-phosphate and potassium sulfate at constant rates , were broadcast and disked in after plowing and before transplanting. All plots received irrigation water (sprinkler system) to supplement rainfall when soil moisture dropped below 60% of available moisture-holding capacity. Sucker control practices utilized were (a) no topping - no suckering, (b) topping - no suckering, (c) topping - hand suckering, and (d) topping - MH-30. Half of the tobacco was harvested early (about 1 week prior to maturity) and half late (1 week past maturity) . However, N fertilizer at the 400 lb/ acre N rate delayed maturity about 2 weeks beyond that for tobacco treated at the 100 and 200 N rates . Thus all the early harvests were made 1 week prior to maturity, the 100- and 200-lb N treated plots 2 weeks later, and the 400-lb N plots 4 weeks after the early harvest

The Effect of Nitrogen Rate and Method of Sucker Control on Dry Matter Accumulation in Different Plant Parts of Burley 21 Tobacco

Earlier research has shown that higher leaf yields of burley tobacco result from topping and controlling sucker (axillary bud) growth. Suckering practices which provide the greatest degree of sucker control generally result in highest leaf yields . Chemically suckering with maleic hydrazide (MH-30) and other chemicals provides for a higher degree of control than most hand sucker ing practices although hand sucker ing at frequent intervals may produce leaf yields comparable to those from use of maleic hydrazide. High leaf yields resulting from a high degree of sucker control has been attributed to the elimination of the use of photosynthate to produce suckers

Effect of nonlocal interactions on the disorder-induced zero-bias anomaly in the Anderson-Hubbard model

To expand the framework available for interpreting experiments on disordered strongly correlated systems, and in particular to explore further the strong-coupling zero-bias anomaly found in the Anderson-Hubbard model, we ask how this anomaly responds to the addition of nonlocal electron-electron interactions. We use exact diagonalization to calculate the single-particle density of states of the extended Anderson-Hubbard model. We find that for weak nonlocal interactions the form of the zero-bias anomaly is qualitatively unchanged. The energy scale of the anomaly continues to be set by an effective hopping amplitude renormalized by the nonlocal interaction. At larger values of the nonlocal interaction strength, however, hopping ceases to be a relevant energy scale and higher energy features associated with charge correlations dominate the density of states.Comment: 9 pages, 7 figure

Uptake and Distribution of Mineral Elements by Burley 21 Tobacco as Influenced by Nitrogen Nutrition and Suckering Practice

Knowledge of nutrient content of tobacco and of removal of nutrients from soil is essential to developing sound fertilization practices for tobacco. Quantities of nutrient elements taken·up by tobacco vary widely. This is because of variations in variety, soil fertility level, fertilizer application, soil moisture, plant population, and other environmental and cultural factors . We conducted the present study to determine the effects of applied N and suckering practice on the content of mineral elements in certain plant parts of burley tobacco

What Happens to Fertilizer Nitrogen in the Soil?

What happens to the nitrogen a farmer applies as fertilizer each spring? First, let us consider the forms of nitrogen normally applied, and then attempt to trace what happens to the nitrogen once it is added to the soil. The average complete fertilizer contains approximately 70 percent of its nitrogen in the ammonium nitrogen form (NH4), about 10 percent in the urea form (this is quickly converted to ammonium nitrogen), and the remaining 20 percent in the nitrate nitrogen form (NO3)