214 research outputs found
Electron Energy-Loss Spectroscopy: A versatile tool for the investigations of plasmonic excitations
The inelastic scattering of electrons is one route to study the vibrational
and electronic properties of materials. Such experiments, also called electron
energy-loss spectroscopy, are particularly useful for the investigation of the
collective excitations in metals, the charge carrier plasmons. These plasmons
are characterized by a specific dispersion (energy-momentum relationship),
which contains information on the sometimes complex nature of the conduction
electrons in topical materials. In this review we highlight the improvements of
the electron energy-loss spectrometer in the last years, summarize current
possibilities with this technique, and give examples where the investigation of
the plasmon dispersion allows insight into the interplay of the conduction
electrons with other degrees of freedom
Assessment of Stress in Laboratory Beagle Dogs Constrained by a Pavlov Sling
The 3Rs - Replacement, Reduction and Refinement - have become increasingly
important in designing animal experiments. The Pavlov sling is thought to be a
non-invasive method to restrain dogs for examinations. The aim of our study
was to investigate whether laboratory Beagle dogs that had been trained to
tolerate restraint by a Pavlov sling are stressed by this procedure and,
furthermore, to analyze their behavior during this period. Five male and five
female Beagle dogs were used, each three years of age. Animals were restrained
in the Pavlov sling for 30 min on six days with an interval of at least two
days. The following behaviors were recorded every minute for each session:
postures of body, head, and ears, as well as state of eyes, tail, legs, and
mouth. Additionally, the animals were observed for the occurrence of
particular stress signs, including body shaking, sweating of the paws,
increased saliva production, piloerection, blinking of eyes, snout licking,
yawning, and panting. As an indicator for stress, salivary cortisol levels
were measured before, during, and after each session. Our results show that
for most behavioral parameters, e.g., body, leg, head, tail, and ear posture,
the frequency of changes between different behavior patterns, as well as
cortisol concentration, were not influenced by restraint in the Pavlov sling.
Therefore, the Pavlov sling does not seem to be perceived as a stressful
situation by the Beagle dogs. Our study demonstrates that under certain
conditions the use of the Pavlov sling in trained dogs can substitute for more
ordinary methods of immobilization, e.g., the use of narcotics
Evidence for an orbital dependent Mott transition in the ladders of (La,Ca)SrCuO derived by electron energy-loss spectroscopy
The knowledge of the charge carrier distribution among the different orbitals
of Cu and O is a precondition for the understanding of the physical properties
of various Cu-O frameworks. We employ electron energy-loss spectroscopy to
elucidate the charge carrier plasmon dispersion in (La,
Ca)SrCuO in dependency of as well as
temperature. We observe that the energy of the plasmon increases upon
increasing Ca content, which signals an internal charge redistribution between
the two Cu-O subsystems. Moreover, contrary to an uncorrelated model we come to
the conclusion that the holes transferred to the CuO ladders are mainly
located in the bonding and not in the anti-bonding band. This is caused by an
orbital dependent Mott transition
Time-reversal symmetry breaking versus superstructure
One of the mysteries of modern condenced-matter physics is the nature of the
pseudogap state of the superconducting cuprates. Kaminski et al.1 claimed to
have observed signatures of time-reversal symmetry breaking in the pseudogap
regime in underdoped Bi2Sr2CaCu2O8+d (Bi2212). Here we argue that the observed
dichroism is due to the 5x1 superstructure replica of the electronic bands and
therefore cannot be considered as evidence for the spontaneous time-reversal
symmetry breaking in cuprates.Comment: 5 pages, pd
Food Deprivation, Body Weight Loss and Anxiety-Related Behavior in Rats
In behavioral studies, food deprivation protocols are routinely used to
initiate or maintain motivational states that are required in a particular
test situation. However, there is limited evidence as to when food deprivation
compromises animal welfare. This study investigated the effects of different
lengths of food deprivation periods and restricted (fixed-time) feeding on
body weight loss as well as anxiety-related and motivated behavior in 5–6
month old male and female Wistar rats. The observed body weight loss was not
influenced by sex and ranged between 4% (16 h deprivation) to approximately 9%
(fixed-time feeding). Despite significant body weight loss in all groups, the
motivation to eat under the aversive test conditions of the modified open
field test increased only after 48 h of food deprivation. Long-lasting effects
on anxiety as measured in the elevated plus maze test 24 h after refeeding
have not been observed, although fixed-time feeding could possibly lead to a
lasting anxiogenic effect in female rats. Overall, female rats showed a more
anxiolytic profile in both tests when compared to male rats. Despite these sex
differences, results suggest that food deprivation is not always paralleled by
an increased motivation to feed in a conflict situation. This is an important
finding as it highlights the need for tailored pilot experiments to evaluate
the impact of food deprivation protocols on animals in regard to the
principles of the 3Rs introduced by Russell and Burch. View Full-Tex
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Natural variation in physiological responses of tunisian hedysarum carnosum under iron deficiency
Iron (Fe) is an essential element for plant growth and development. The cultivation of leguminous plants has generated strong interest because of their growth even on poor soils. Calcareous and saline soils with poor mineral availability are wide-spread in Tunisia. In an attempt to select better forage crops adapted to Tunisian soils, we characterized Fe deficiency responses of three different isolates of Hedysarum carnosum, an endemic Tunisian extremophile species growing in native stands in salt and calcareous soil conditions. H. carnosum is a non-model crop. The three isolates, named according to their habitats Karkar, Thelja, and Douiret, differed in the expression of Fe deficiency symptoms like morphology, leaf chlorosis with compromised leaf chlorophyll content and photosynthetic capacity and leaf metal contents. Across these parameters Thelja was found to be tolerant, while Karkar and Douiret were susceptible to Fe deficiency stress. The three physiological and molecular indicators of the iron deficiency response in roots, Fe reductase activity, growth medium acidification and induction of the IRON-REGULATED TRANSPORTER1 homolog, indicated that all lines responded to -Fe, however, varied in the strength of the different responses. We conclude that the individual lines have distinct adaptation capacities to react to iron deficiency, presumably involving mechanisms of whole-plant iron homeostasis and internal metal distribution. The Fe deficiency tolerance of Thelja might be linked with adaptation to its natural habitat on calcareous soil
A Comparison of Stripe Modulations in LaBaCuO and LaNdSrCuO
We report combined soft and hard x-ray scattering studies of the electronic
and lattice modulations associated with stripe order in
LaBaCuO and LaNdSrCuO. We
find that the amplitude of both the electronic modulation of the hole density
and the strain modulation of the lattice is significantly larger in
LaBaCuO than in LaNdSrCuO
and is also better correlated. The in-plane correlation lengths are isotropic
in each case; for LaBaCuO, \AA\
whereas for LaNdSrCuOF,
\AA. We find that the modulations are temperature independent in
LaBaCuO in the low temperature tetragonal phase. In
contrast, in LaNdSrCuO, the amplitude grows
smoothly from zero, beginning 13 K below the LTT phase transition. We speculate
that the reduced average tilt angle in LaBaCuO results
in reduced charge localization and incoherent pinning, leading to the longer
correlation length and enhanced periodic modulation amplitude.Comment: 6 pages, 4 figure
Frenkel and charge transfer excitons in C60
We have studied the low energy electronic excitations of C60 using momentum
dependent electron energy-loss spectroscopy in transmission. The momentum
dependent intensity of the gap excitation allows the first direct experimental
determination of the energy of the 1Hg excitation and thus also of the total
width of the multiplet resulting from the gap transition. In addition, we could
elucidate the nature of the following excitations - as either Frenkel or charge
transfer excitons.Comment: RevTEX, 3 Figures, to appear in Phys. Rev.
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