447 research outputs found
Evidence for differentiation in the iron-helicoidal-chain in GdFe(BO)
We report on a single-crystal X-ray structure study of
at room temperature and at T=90 K. At room temperature
crystallizes in a trigonal space group R32 (No. 155), the same as found for
other members of iron-borate family . At 90 K the
structure of has transformed to the space group
(No. 152). The low-temperature structure determination gives new
insight into the weakly first-order structural phase transition at 156 K and
into the related Raman phonon anomalies. The discovery of two inequivalent iron
chains in the low temperature structure provide new point of view on the
low-temperature magnetic properties.Comment: Subm. to Acta Cryst.
Resistivity of non-Fermi liquid U2Pt2In under pressure
Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by
means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa).
At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with
alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum
develops in rho(T). A study of the field dependence of the minimum confirms its
magnetic origin. The ratio c/a is proposed as the effective control parameter,
rather than the unit cell volume.Comment: 5 pages (incl. 2 figures), submitted to SCES'99, Nagan
Optically probing symmetry breaking in the chiral magnet Cu2OSeO3
We report on the linear optical properties of the chiral magnet Cu2OSeO3,
specifically associated with the absence of inversion symmetry, the chiral
crystallographic structure, and magnetic order. Through spectroscopic
ellipsometry, we observe local crystal-field excitations below the
charge-transfer gap. These crystal-field excitations are optically allowed due
to the lack of inversion symmetry at the Cu sites. Optical polarization
rotation measurements were used to study the structural chirality and magnetic
order. The temperature dependence of the natural optical rotation, originating
in the chiral crystal structure, provides evidence for a finite
magneto-electric effect in the helimagnetic phase. We find a large
magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the
helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the
ferrimagnetic phase. The large value of V can be explained by considering spin
cluster formation and the relative ease of domain reorientation in this
metamagnetic material. The magneto-optical activity allows us to map the
magnetic phase diagram, including the skyrmion lattice phase. In addition to
this, we probe and discuss the nature of the various magnetic phase transitions
in Cu2OSeO3.Comment: 9 pages, 10 figure
Swimming exercise enhances brain plasticity in fish
It is well-established that sustained exercise training can enhance brain plasticity and boost cognitive performance in mammals, but this phenomenon has not received much attention in fish. The aim of this study was to determine whether sustained swimming exercise can enhance brain plasticity in juvenile Atlantic salmon. Brain plasticity was assessed by both mapping the whole telencephalon transcriptome and conducting telencephalic region-specific microdissections on target genes. We found that 1772 transcripts were differentially expressed between the exercise and control groups. Gene ontology (GO) analysis identified 195 and 272 GO categories with a significant overrepresentation of up- or downregulated transcripts, respectively. A multitude of these GO categories was associated with neuronal excitability, neuronal signalling, cell proliferation and neurite outgrowth (i.e. cognition-related neuronal markers). Additionally, we found an increase in proliferating cell nuclear antigen (pcna) after both three and eight weeks of exercise in the equivalent to the hippocampus in fish. Furthermore, the expression of the neural plasticity markers synaptotagmin (syt) and brain-derived neurotrophic factor (bdnf) were also increased due to exercise in the equivalent to the lateral septum in fish. In conclusion, this is the first time that swimming exercise has been directly linked to increased telencephalic neurogenesis and neural plasticity in a teleost, and our results pave the way for future studies on exercise-induced neuroplasticity in fish.</p
Temporal progression in migratory status and sexual maturation in European silver eels during downstream migration
The onset of downstream migration of European eels is accompanied by a cessation of feeding and the start of sexual maturation which stresses the link between metabolism and sexual maturation, also suggesting an important role for exercise. Exercise has been tested with eels in swim tunnels and was found to stimulate the onset of sexual maturation. In this study, we have investigated the interplay between migration and maturation in the field during the downstream migration of female silver eels. Temporal changes in migratory status and sexual maturation among silver eels of the upstream Rhine River system over 3 months of the migration season (August, September and October) were determined in biometrical parameters, plasma 17β-estradiol and calcium levels, oocyte histology and gonadal fat levels. Furthermore, the ecological relevant parameters age as determined by otolithometry and health aspects indicated by haematocrit, haemoglobin and swim-bladder parasite load were measured. Silver eels were estimated to be 14 years old. A strong temporal progression in migratory stage was shown over the months of downstream migration. Catches probably represented a mix of reproductive migrants and feeding migrants of which the ratio increased over time. Furthermore, this study confirmed our hypothesis linking the migratory stage to early maturation as indicated by enlargement of the eyes, oocyte growth and fat deposition in the oocytes, exactly the same changes as found induced by exercise but not ruling out environmental influences. Migrants show extensive fat uptake by the oocytes, probably stimulated by the swimming exercise. In addition, at least 83% of the silver eels in this spawning run may have suffered from negative effects of swim-bladder parasites on their swimming performance
Fish under exercise
Improved knowledge on the swimming physiology of fish and its application to fisheries science and aquaculture (i.e., farming a fitter fish) is currently needed in the face of global environmental changes, high fishing pressures, increased aquaculture production as well as increased concern on fish well-being. Here, we review existing data on teleost fish that indicate that sustained exercise at optimal speeds enhances muscle growth and has consequences for flesh quality. Potential added benefits of sustained exercise may be delay of ovarian development and stimulation of immune status. Exercise could represent a natural, noninvasive, and economical approach to improve growth, flesh quality as well as welfare of aquacultured fish: a FitFish for a healthy consumer. All these issues are important for setting directions for policy decisions and future studies in this area. For this purpose, the FitFish workshop on the Swimming Physiology of Fish (http://www.ub.edu/fitfish2010) was organized to bring together a multidisciplinary group of scientists using exercise models, industrial partners, and policy makers. Sixteen international experts from Europe, North America, and Japan were invited to present their work and view on migration of fishes in their natural environment, beneficial effects of exercise, and applications for sustainable aquaculture. Eighty-eight participants from 19 different countries contributed through a poster session and round table discussion. Eight papers from invited speakers at the workshop have been contributed to this special issue on The Swimming Physiology of Fish
Visualizing the Formation of the Kondo Lattice and the Hidden Order in URu2Si2
Heavy electronic states originating from the f atomic orbitals underlie a
rich variety of quantum phases of matter. We use atomic scale imaging and
spectroscopy with the scanning tunneling microscope (STM) to examine the novel
electronic states that emerge from the uranium f states in URu2Si2. We find
that as the temperature is lowered, partial screening of the f electrons' spins
gives rise to a spatially modulated Kondo-Fano resonance that is maximal
between the surface U atoms. At T=17.5 K, URu2Si2 is known to undergo a 2nd
order phase transition from the Kondo lattice state into a phase with a hidden
order parameter. From tunneling spectroscopy, we identify a spatially
modulated, bias-asymmetric energy gap with a mean-field temperature dependence
that develops in the hidden order state. Spectroscopic imaging further reveals
a spatial correlation between the hidden order gap and the Kondo resonance,
suggesting that the two phenomena involve the same electronic states
Magnetic properties of the spin-1 chain compound NiClCHCHCHNH
We report experimental results of the static magnetization, ESR and NMR
spectroscopic measurements of the Ni-hybrid compound
NiClCHCHCHNH. In this material NiCl octahedra are
structurally arranged in chains along the crystallographic -axis. According
to the static susceptibility and ESR data Ni spins are isotropic
and are coupled antiferromagnetically (AFM) along the chain with the exchange
constant K. These are important prerequisites for the realization of
the so-called Haldane spin-1 chain with the spin-singlet ground state and a
quantum spin gap. However, experimental results evidence AFM order at K presumably due to small interchain couplings. Interestingly,
frequency-, magnetic field-, and temperature-dependent ESR measurements, as
well as the NMR data, reveal signatures which could presumably indicate an
inhomogeneous ground state of co-existent mesoscopically spatially separated
AFM ordered and spin-singlet state regions similar to the situation observed
before in some spin-diluted Haldane magnets
Mechanism of thermally activated c-axis dissipation in layered High-T superconductors at high fields
We propose a simple model which explains experimental behavior of -axis
resistivity in layered High-T superconductors at high fields in a limited
temperature range. It is generally accepted that the in-plane dissipation at
low temperatures is caused by small concentration of mobile pancake vortices
whose diffusive motion is thermally activated. We demonstrate that in such
situation a finite conductivity appears also in -direction due to the phase
slips between the planes caused by the mobile pancakes. The model gives
universal relation between the components of conductivity which is in good
agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure
Hidden Orbital Order in
When matter is cooled from high temperatures, collective instabilities
develop amongst its constituent particles that lead to new kinds of order. An
anomaly in the specific heat is a classic signature of this phenomenon. Usually
the associated order is easily identified, but sometimes its nature remains
elusive. The heavy fermion metal is one such example, where the
order responsible for the sharp specific heat anomaly at has
remained unidentified despite more than seventeen years of effort. In
, the coexistence of large electron-electron repulsion and
antiferromagnetic fluctuations in leads to an almost incompressible
heavy electron fluid, where anisotropically paired quasiparticle states are
energetically favored. In this paper we use these insights to develop a
detailed proposal for the hidden order in . We show that
incommensurate orbital antiferromagnetism, associated with circulating currents
between the uranium ions, can account for the local fields and entropy loss
observed at the transition; furthermore we make detailed predictions for
neutron scattering measurements
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