31 research outputs found
Knight Shift Anomalies in Heavy Electron Materials
We calculate non-linear Knight Shift vs. susceptibility anomalies
for Ce ions possessing local moments in metals. The ions are modeled with the
Anderson Hamiltonian and studied within the non-crossing approximation (NCA).
The non-linearity diminishes with decreasing Kondo temperature
and nuclear spin- local moment separation. Treating the Ce ions as an
incoherent array in CeSn, we find excellent agreement with the observed Sn
data.Comment: 4 pages, Revtex, 3 figures available upon request from
[email protected]
29-Si NMR and Hidden Order in URu2Si2
We present new 29-Si NMR spectra in URu2Si2 for varying temperature T, and
external field H. On lowering T, the systematics of the low-field lineshape and
width reveal an extra component (lambda) to the linewidth below T_N ~ 17 K not
observed previously. We find that lambda is magnetic-field independent and
dominates the low-field lineshape for all orientations of H with respect to the
tetragonal c axis. The behavior of lambda indicates a direct relationship
between the 29-Si spin and the transition at T_N, but it is inconsistent with a
coupling of the nuclei to static antiferromagnetic order/disorder of the U-spin
magnetization. This leads us to conjecture that lambda is due to a coupling of
29-Si to the system's hidden-order parameter. A possible coupling mechanism
involving charge degrees of freedom and indirect nuclear spin/spin interactions
is proposed. We also propose further experiments to test for the existence of
this coupling mechanism.Comment: 4 pages, 4 figures, submitted to PR
Itinerancy and Hidden Order in
We argue that key characteristics of the enigmatic transition at in indicate that the hidden order is a density wave formed within
a band of composite quasiparticles, whose detailed structure is determined by
local physics. We expand on our proposal (with J.A. Mydosh) of the hidden order
as incommnesurate orbital antiferromagnetism and present experimental
predictions to test our ideas. We then turn towards a microscopic description
of orbital antiferromagnetism, exploring possible particle-hole pairings within
the context of a simple one-band model. We end with a discussion of recent
high-field and thermal transport experiment, and discuss their implications for
the nature of the hidden order.Comment: 18 pages, 7 figures. v2 contains added referenc
Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}
Electrical resistivity , specific heat C, and magnetic susceptibility
measurements made on the filled skutterudite CeRu_4As_{12} reveal
non-Fermi liquid (NFL) T - dependences at low T, i.e., (T) T^{1.4}
and weak power law or logarithmic divergences in C(T)/T and (T).
Measurements also show that the T - dependence of the thermoelectric power S(T)
deviates from that seen in other Ce systems. The NFL behavior appears to be
associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than
a typical Kondo lattice scenario that would be appropriate for an integral Ce
valence of 3^+.Comment: 18 pages, 5 figure
Calculations of the Knight Shift Anomalies in Heavy Electron Materials
We have studied the Knight shift and magnetic susceptibility
of heavy electron materials, modeled by the infinite U Anderson model
with the NCA method. A systematic study of and for
different Kondo temperatures (which depends on the hybridization width
) shows a low temperature anomaly (nonlinear relation between and
) which increases as the Kondo temperature and distance
increase. We carried out an incoherent lattice sum by adding the of
a few hundred shells of rare earth atoms around a nucleus and compare the
numerically calculated results with the experimental results. For CeSn_3, which
is a concentrated heavy electron material, both the ^{119}Sn NMR Knight shift
and positive muon Knight shift are studied. Also, lattice coherence effects by
conduction electron scattering at every rare earth site are included using the
average-T matrix approximation. Also NMR Knight shifts for YbCuAl and the
proposed quadrupolar Kondo alloy Y_{0.8}U_{0.2}Pd_{3} are studied.Comment: 31 pages of RevTex, 22 Postscript figures, submmitted to PRB, some
figures are delete
Use of group records of feed intake to select for feed efficiency in rabbit
Models for genetic evaluation of feed efficiency (FE) for animals housed in groups when they are either fed ad libitum (F) or on restricted (R) feeding were implemented. Definitions of FE on F included group records of feed intake (¯FI_F) and individual records of growth rate (GF) and metabolic weight (MF). Growth rate (GR) as FE measurement on R was used.
Data corresponded to 5,336 kits from a rabbit sire line, from 1,255 litters in 14 batches and 667 cages. A five-trait mixed model (also with metabolic weight on R, MR) was implemented including, for each trait, the systematic effects of batch, body weight at weaning, parity order and litter size; and the random effects of litter, additive genetic and individual. A Bayesian analysis was performed. Conditional traits such as ¯FI_F |M_F,G_F and G_F |M_F,¯FI_F were obtained from elements of additive genetics ( ( ¯FI_F |M_F,G_F )_g and ( G_F |M_F,¯FI_F )_g ) or phenotypic (( ¯FI_F |M_F,G_F )_p and ( G_F |M_F,¯FI_F )_p ) (co)variance matrices. In the first case, heritabilities were low (0.07 and 0.06 for ( ¯FI_F |M_F,G_F )_g and ( G_F |M_F,¯FI_F )_g, respectively) but null genetic correlation between the conditional and conditioning traits is guaranteed. In the second case, heritabilities were higher (0.22 and 0.16 for ( ¯FI_F |M_F,G_F )_p and ( G_F |M_F,¯FI_F )_p, respectively) but the genetic correlation between ( ¯FI_F |M_F,G_F )_p and G_F was moderate (0.58). Heritability of GR was low (0.08). This trait was negatively correlated with ( G_F |M_F,¯FI_F )_p and ( G_F |M_F,¯FI_F )_gof animals on F, which indicate a different genetic background. The correlation between GR and GF was also low to moderate (0.48) and the additive variance of GF was almost 4 times that of GR, suggesting the presence of a substantial genotype by feeding regimen interaction.info:eu-repo/semantics/acceptedVersio
Transcriptional responses underlying the hormetic and detrimental effects of the plant secondary metabolite gossypol on the generalist herbivore Helicoverpa armigera
<p>Abstract</p> <p>Background</p> <p>Hormesis is a biphasic biological response characterized by the stimulatory effect at relatively low amounts of chemical compounds which are otherwise detrimental at higher concentrations. A hormetic response in larval growth rates has been observed in cotton-feeding insects in response to increasing concentrations of gossypol, a toxic metabolite found in the pigment glands of some plants in the family Malvaceae. We investigated the developmental effect of gossypol in the cotton bollworm, <it>Helicoverpa armigera</it>, an important heliothine pest species, by exposing larvae to different doses of this metabolite in their diet. In addition, we sought to determine the underlying transcriptional responses to different gossypol doses.</p> <p>Results</p> <p>Larval weight gain, pupal weight and larval development time were measured in feeding experiments and a hormetic response was seen for the first two characters. On the basis of net larval weight gain responses to gossypol, three concentrations (0%, 0.016% and 0.16%) were selected for transcript profiling in the gut and the rest of the body in a two-color double reference design microarray experiment. Hormesis could be observed at the transcript level, since at the low gossypol dose, genes involved in energy acquisition such as β-fructofuranosidases were up-regulated in the gut, and genes involved in cell adhesion were down-regulated in the body. Genes with products predicted to be integral to the membrane or associated with the proteasome core complex were significantly affected by the detrimental dose treatment in the body. Oxidoreductase activity-related genes were observed to be significantly altered in both tissues at the highest gossypol dose.</p> <p>Conclusions</p> <p>This study represents the first transcriptional profiling approach investigating the effects of different concentrations of gossypol in a lepidopteran species. <it>H. armigera</it>'s transcriptional response to gossypol feeding is tissue- and dose-dependent and involves diverse detoxifying mechanisms not only to alleviate direct effects of gossypol but also indirect damage such as pH disturbance and oxygen radical formation. Genes discovered through this transcriptional approach may be additional candidates for understanding gossypol detoxification and coping with gossypol-induced stress. In a generalist herbivore that has evolved transcriptionally-regulated responses to a variety of different plant compounds, hormesis may be due to a lower induction threshold of growth-promoting, stress-coping responses and a higher induction threshold of detoxification pathways that are costly and cause collateral damage to the cell.</p