Magnetic phase diagram of the Hubbard model

The competition between commensurate and incommensurate spin-density-wave phases in the infinite-dimensional single-band Hubbard model is examined with quantum Monte Carlo simulation and strong and weak coupling approximations. Quantum fluctuations modify the weak-coupling phase diagram by factors of order unity and produce remarkable agreement with the quantum Monte Carlo data, but strong-coupling theories (that map onto effective Falicov-Kimball models) display pathological behavior. The single-band model can be used to describe much of the experimental data in Cr and its dilute alloys with V and Mn.Comment: 12 pages plus 3 uuencoded postscript figures, ReVTe

Anisotropic random resistor networks: a model for piezoresistive response of thick-film resistors

A number of evidences suggests that thick-film resistors are close to a metal-insulator transition and that tunneling processes between metallic grains are the main source of resistance. We consider as a minimal model for description of transport properties in thick-film resistors a percolative resistor network, with conducting elements governed by tunneling. For both oriented and randomly oriented networks, we show that the piezoresistive response to an applied strain is model dependent when the system is far away from the percolation thresold, while in the critical region it acquires universal properties. In particular close to the metal-insulator transition, the piezoresistive anisotropy show a power law behavior. Within this region, there exists a simple and universal relation between the conductance and the piezoresistive anisotropy, which could be experimentally tested by common cantilever bar measurements of thick-film resistors.Comment: 7 pages, 2 eps figure

Associations Among Nitrogen Harvest Index and Other Traits Within Two Avena Species

The partitioning efficiency of nitrogen in crop plants is measured via nitrogen harvest index (NHI), which is the ratio of the weights of grain nitrogen to total plant nitrogen. To determine what associations, if any, exist between NHI and other plant traits for oats, 40 Avena sativa lines and 52 A. sterilis collections were studied. Significant variations occurred between and within species for NHI, groat yield (GTY), groat protein percentage (GTP), groat protein yield (GTPY), straw yield (SY), straw protein percentage (SP), total plant protein yield (TPPY), harvest index (HI), and vegetative growth rate (GR). Traits significantly associated with NHI within both Avena species were HI, GTY, GTPY, SP, and heading date (HD). Uptake and partitioning of nitrogen between grain and straw were not related in A. sativa, suggesting that these two phenomena were controlled by separate physiological mechanisms. Total dry matter accumulation and not protein percentage was the major factor influencing protein yields of both grain and straw. NHI was nor correlated with either GTY or GTP in A. sativa, suggesting that selecting for high NHI may break the inverse relationship between GTY and GTP within this species

Nitrogen Harvest Index Variation in Avena Sativa and A. Sterilis

Forty Avena sativa (L.) lines and 28 A. sterilis (L.) collections were evaluated in two nitrogen environments (i.e., low and high) for variation in nitrogen harvest index (NHI). Significant genetic variation for NHI occurred among entries within both species. NHI varied from 25 to 51%, with a mean of 42% for A. sterilis, and from 42 to 67%, with a mean of 59%, for A. sativa. Mean NHI was significantly lower in A. sterilis than in A. sativa. Some adapted entries with introgressed germplasm from A. sterilis had relatively high NHI\u27s, however. Plant traits that were associated with NHI were harvest index (HI), groat yield (GTY), groat protein yield (GTPY), heading date (HD), and straw protein percentage (SP). High nitrogen fertility caused a significant decrease in NHI and HI, significant increases in groat protein percentage (GTP), straw yield (SY), SP, straw protein yield (SPY), total plant protein yield (TPPY), and vegetative growth rate (GR), and no change in GTY and GTPY for A. sativa entries. High nitrogen increased GTP, SY, SP, SPY, TPPY, and GR and decreased NHI and HI in A. sterilis

Spin and charge excitations in incommensurate spin density waves

Collective excitations both for spin- and charge-channels are investigated in incommensurate spin density wave (or stripe) states on two-dimensional Hubbard model. By random phase approximation, the dynamical susceptibility \chi(q,\omega) is calculated for full range of (q,\omega) with including all higher harmonics components. An intricate landscape of the spectra in \chi(q,\omega) is obtained. We discuss the anisotropy of the dispersion cones for spin wave excitations, and for the phason excitation related to the motion of the stripe line. Inelastic neutron experiments on Cr and its alloys and stripe states of underdoped cuprates are proposed

Risk factors for feline infectious peritonitis in Australian cats

Objective: To determine whether patient signalment (age, breed, sex, and neuter status) are associated with naturally occurring feline infectious peritonitis (FIP) in cats in Australia. Design: A retrospective comparison of the signalment between cats with confirmed FIP and the general cat population. Results: The patient signalment of 382 FIP confirmed cases were compared with the Companion Animal Register of NSW and the general cat population of Sydney. Younger cats were significantly over-represented amongst FIP cases. Domestic crossbred, Persian, and Himalayan cats were significantly under-represented in the FIP cohort while several breeds were over-represented including British Shorthair, Devon Rex, and Abyssinian. A significantly higher proportion of male cats had FIP compared to female cats. Conclusion: This study provides further evidence that FIP is primarily a disease of young cats and that significant breed and sex predilections exist in Australia. This opens further avenues to investigate the role of genetic factors in FIP

Risk factors for feline infectious peritonitis in Australian cats

Objective: To determine whether patient signalment (age, breed, sex, and neuter status) are associated with naturally occurring feline infectious peritonitis (FIP) in cats in Australia. Design: A retrospective comparison of the signalment between cats with confirmed FIP and the general cat population. Results: The patient signalment of 382 FIP confirmed cases were compared with the Companion Animal Register of NSW and the general cat population of Sydney. Younger cats were significantly over-represented amongst FIP cases. Domestic crossbred, Persian, and Himalayan cats were significantly under-represented in the FIP cohort while several breeds were over-represented including British Shorthair, Devon Rex, and Abyssinian. A significantly higher proportion of male cats had FIP compared to female cats. Conclusion: This study provides further evidence that FIP is primarily a disease of young cats and that significant breed and sex predilections exist in Australia. This opens further avenues to investigate the role of genetic factors in FIP

Enhancement of the electronic contribution to the low temperature specific heat of Fe/Cr magnetic multilayer

We measured the low temperature specific heat of a sputtered $(Fe_{23\AA}/Cr_{12\AA})_{33}$ magnetic multilayer, as well as separate $1000\AA$ thick Fe and Cr films. Magnetoresistance and magnetization measurements on the multilayer demonstrated antiparallel coupling between the Fe layers. Using microcalorimeters made in our group, we measured the specific heat for $4<T<30 K$ and in magnetic fields up to $8 T$ for the multilayer. The low temperature electronic specific heat coefficient of the multilayer in the temperature range $4<T<14 K$ is $\gamma_{ML}=8.4 mJ/K^{2}g-at$. This is significantly larger than that measured for the Fe or Cr films (5.4 and $3.5 mJ/K^{2}mol$ respectively). No magnetic field dependence of $\gamma_{ML}$ was observed up to $8 T$. These results can be explained by a softening of the phonon modes observed in the same data and the presence of an Fe-Cr alloy phase at the interfaces.Comment: 20 pages, 5 figure