28,892 research outputs found
Testing high resolution SD ADC’s by using the noise transfer function
A new solution to improve the testability of high resolution SD Analogue to Digital Converters (SD ADC’s) using the quantizer input as test node is described. The theoretical basis for the technique is discussed and results from high level simulations for a 16 bit, 4th order, audio ADC are presented. The analysis demonstrates the potential to reduce the computational effort associated with test response analysis versus conventional techniques
Exactly-Solvable Models Derived from a Generalized Gaudin Algebra
We introduce a generalized Gaudin Lie algebra and a complete set of mutually
commuting quantum invariants allowing the derivation of several families of
exactly solvable Hamiltonians. Different Hamiltonians correspond to different
representations of the generators of the algebra. The derived exactly-solvable
generalized Gaudin models include the Bardeen-Cooper-Schrieffer,
Suhl-Matthias-Walker, the Lipkin-Meshkov-Glick, generalized Dicke, the Nuclear
Interacting Boson Model, a new exactly-solvable Kondo-like impurity model, and
many more that have not been exploited in the physics literature yet
Quons Restricted to the Antisymmetric Subspace: Formalism and Applications
In this work we develop a formalism to treat quons restricted to the
antisymmetric part of their many-body space. A model in which a system of
identical quons interact through a pairing force is then solved within this
restriction and the differences between our solution and the usual fermionic
model solution are then presented and discussed in detail. Possible connections
to physical systems are also considered.Comment: 12 pages, 3 figure
Changes in co-existence mechanisms along a long-term soil chronosequence revealed by functional trait diversity
1. Functional trait diversity can reveal mechanisms of species co-existence in plant communities. Few studies have tested whether functional diversity for foliar traits related to resource use strategy increases or decreases with declining soil phosphorus (P) in forest communities.
2. We quantified tree basal area and four foliar functional traits (i.e. nitrogen (N), phosphorus (P), thickness and tissue density) for all woody species along the c. 120 kyr Franz Josef soil chronosequence in cool temperate rainforest, where strong shifts occur in light and soil nutrient availability (i.e. total soil P declines from 805 to 100 mg g–1). We combined the abundance and trait data in functional diversity indices to quantify trait convergence and divergence, in an effort to determine whether mechanisms of co-existence change with soil fertility.
3. Relationships between species trait means and total soil N and P were examined using multiple regression, with and without weighting of species abundances. We used Rao’s quadratic entropy to quantify functional diversity at the plot scale, then compared this with random expectation, using a null model that randomizes abundances across species within plots. Taxonomic diversity was measured using Simpson’s Diversity. Relationships between functional and taxonomic diversity and total soil P were examined using jackknife linear regression.
4. Leaf N and P declined and leaf thickness and density increased monotonically with declining total soil P along the sequence; these relationships were unaffected by abundance-weighting of species in the analyses. Inclusion of total soil N did not improve predictions of trait means. All measures of diversity calculated from presence/absence data were unrelated to total soil N and P. There was no evidence for a relationship between Rao values using quantitative abundances and total soil P. However, there was a strongly positive relationship between Rao, expressed relative to random expectation, and total soil P, indicating trait convergence of dominant species as soil P declined.
5. Synthesis: Our results demonstrate that at high fertility dominant species differ in resource use strategy, but as soil fertility declines over the long-term, dominant species increasingly converge on a resource-retentive strategy. This suggests that differentiation in resource use strategy is required for co-existence at high fertility but not in low fertility ecosystems
Green cities and health: a question of scale?
<p><b>Background:</b> Cities are expanding and accommodating an increasing proportion of the world's population. It is important to identify features of urban form that promote the health of city dwellers. Access to green space has been associated with health benefits at both individual and neighbourhood level. We investigated whether a relationship between green space coverage and selected mortality rates exists at the city level in the USA.</p>
<p><b>Methods:</b> An ecological cross-sectional study. A detailed land use data set was used to quantify green space for the largest US cities (n=49, combined population of 43 million). Linear regression models were used to examine the association between city-level ‘greenness’ and city-level standardised rates of mortality from heart disease, diabetes, lung cancer, motor vehicle fatalities and all causes, after adjustment for confounders.</p>
<p><b>Results:</b> There was no association between greenness and mortality from heart disease, diabetes, lung cancer or automobile accidents. Mortality from all causes was significantly higher in greener cities.</p>
<p><b>Conclusions:</b> While considerable evidence suggests that access to green space yields health benefits, we found no such evidence at the scale of the American city. In the USA, greener cities tend also to be more sprawling and have higher levels of car dependency. Any benefits that the green space might offer seem easily eclipsed by these other conditions and the lifestyles that accompany them. The result merits further investigation as it has important implications for how we increase green space access in our cities.</p>
From one to Cooper pairs, step by step
We extend the one-pair Cooper configuration towards Bardeen-Cooper-Schrieffer
(BCS) model of superconductivity by adding one-by-one electron pairs to an
energy layer where a small attraction acts. To do it, we solve Richardson's
equations analytically in the dilute limit of pairs on the one-Cooper pair
scale. We find, through only keeping the first order term in this expansion,
that the correlated pair energy reads as the energy of isolated pairs
within a correction induced by the Pauli exclusion principle which
tends to decrease the average pair binding energy when the pair number
increases. Quite remarkably, extension of this first-order result to the dense
regime gives the BCS condensation energy exactly. This leads us to suggest a
different understanding of the BCS condensation energy with a pair number equal
to the number of pairs feeling the potential and an average pair binding energy
reduced by Pauli blocking to half the single Cooper pair energy - instead of
the more standard but far larger superconducting gap.Comment: 14 pages, 2 figure
ESTIMATING PRICE VARIABILITY IN AGRICULTURE: IMPLICATIONS FOR DECISION MAKERS
Using a stochastic version of the POLYSYS modeling framework, an examination of projected variability in agricultural prices, supply, demand, stocks, and incomes is conducted for corn, wheat, soybeans, and cotton during the 1998-2006 period. Increased planting flexibility introduced in the 1996 farm bill results in projections of significantly higher planted acreage variability compared to recent historical levels. Variability of ending stocks and stock-to-use ratios is projected to be higher for corn and soybeans and lower for wheat and cotton compared to the 1986-96 period. Significantly higher variability is projected for corn prices, with wheat and soybean prices also being more variable. No significant change in cotton price variability is projected.POLYSYS model, Price variability, Stochastic simulation, Crop Production/Industries,
Scheduling system upgrading & downbinning project at Qimonda Portugal, S.A.
Estágio realizado na Qimonda Portugal, S. A. orientado pelo Eng.º José Adriano MoreiraRelatório de estágio curricular da LGEI 2006/200
Lean Production and World Class Manufacturing: A Comparative Study of the Two Most Important Production Strategies of Recent Times
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