343 research outputs found
Singe ferroelectric and chiral magnetic domain of single-crystalline BiFeO in an electric field
We report polarized neutron scattering and piezoresponse force microscopy
studies of millimeter-sized single crystals of multiferroic BiFeO. The
crystals, grown below the Curie temperature, consist of a single ferroelectric
domain. Two unique electric polarization directions, as well as the populations
of equivalent spiral magnetic domains, can be switched reversibly by an
electric field. A ferroelectric monodomain with a single- single-helicity
spin spiral can be obtained. This level of control, so far unachievable in thin
films, makes single-crystal BiFeO a promising object for multiferroics
research.Comment: 4 figures in separate jpg file
Magnetoelectricity at room temperature in Bi0.9-xTbxLa0.1FeO3 system
Magnetoelectric compounds with the general formula, Bi0.9-xRxLa0.1FeO3 (R
=Gd, Tb, Dy, etc.), have been synthesized. These show the coexistence of
ferroelectricity and magnetism, possess high dielectric constant and exhibit
magnetoelectric coupling at room temperature. Such materials may be of great
significance in basic as well as applied research.Comment: 11 pages of text and figure
Electric-field switchable magnetization via the Dzyaloshinskii-Moriya interaction: FeTiO_3 versus BiFeO_3
In this article we review and discuss a mechanism for coupling between
electric polarization and magnetization that can ultimately lead to
electric-field switchable magnetization. The basic idea is that a ferroelectric
distortion in an antiferromagnetic material can "switch on" the
Dzyaloshinskii-Moriya interaction which leads to a canting of the
antiferromagnetic sublattice magnetizations, and thus to a net magnetization.
This magnetization M is coupled to the polarization P via a trilinear free
energy contribution of the form P(M x L), where L is the antiferromagnetic
order parameter. In particular, we discuss why such an invariant is present in
R3c FeTiO_3 but not in the isostructural multiferroic BiFeO_3. Finally, we
construct symmetry groups that in general allow for this kind of
ferroelectrically-induced weak ferromagnetism.Comment: 15 pages, 3 images, to appear in J. Phys: Condens. Matter Focus Issue
on Multiferroic
The HARPS search for southern extra-solar planets I. HD330075 b: a new 'hot Jupiter'
We report on the first extra-solar planet discovered with the brand new HARPS
instrument. The planet is a typical 'hot Jupiter' with m2sini = 0.62 MJup and
an orbital period of 3.39 days, but from the photometric follow-up of its
parent star HD330075 we can exclude the presence of a transit. The induced
radial-velocity variations exceed 100 m/s in semi-amplitude and are easily
detected by state-of-the-art spectro-velocimeters. Nevertheless, the faint
magnitude of the parent star (V = 9.36) benefits from the efficient instrument:
With HARPS less than 10 observing nights and 3 hours of total integration time
were needed to discover the planet and characterize its orbit. The orbital
parameters determined from the observations made during the first HARPS run in
July 2003 have been confirmed by 7 additional observations carried out in
February 2004. The bisector analysis and a photometric follow-up give no hint
for activity-induced radial-velocity variations, indicating that the velocity
curve is best explained by the presence of a low-mass companion to the star. In
this paper we present a set of 21 measurements of excellent quality with
weighted rms as low as 2.0 m/s. These measurements lead to a well defined orbit
and consequently to the precise orbital parameters determination of the
extra-solar planet HD330075b.Comment: 5 pages, 2 figures, accepted for publication by Astronomy and
Astrophysics, see also http://obswww.unige.ch/~udry/planet/planet.htm
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Influence of diabetes on ambulation and inflammation in men and women with symptomatic peripheral artery disease
AbstractObjectiveTo determine whether diabetes and sex were factors associated with ambulatory function, endothelial cell inflammation, oxidative stress, and apoptosis, and with circulating biomarkers of inflammation and antioxidant capacity in patients with peripheral artery disease (PAD) and claudication.Materials/MethodsAmbulatory function of 180 symptomatic men and women with PAD was assessed during a graded maximal treadmill test, 6-minute walk test, and 4-meter walk test. Patients were further characterized on endothelial effects of circulating factors present in the sera using a cell culture-based bioassay on primary human arterial endothelial cells, and on circulating inflammatory and vascular biomarkers.ResultsMen and women with diabetes had greater prevalence (p = 0.007 and p = 0.015, respectively) of coronary artery disease (CAD) than patients without diabetes. To assure that this difference did not influence planned comparisons, the data set was stratified on CAD. Diabetic men with CAD had a lower peak walking time (PWT) during the treadmill test and a slower 4-meter gait speed compared to non-diabetic men with CAD (p < 0.05). Diabetic women with CAD had a lower PWT compared to their non-diabetic counterparts (p < 0.01). Additionally, diabetic men with CAD had higher pigment epithelium-derived factor (p < 0.05) than their non-diabetic counterparts, and diabetic women with CAD had higher leptin (p < 0.01) and interleukin-8 levels (p < 0.05).ConclusionsIn patients with PAD, diabetic men and women with CAD had more severe claudication than their non-diabetic counterparts, as measured by shorter PWT, and the men had further ambulatory impairment manifested by slower 4-meter gait speed. Furthermore, the diabetic patients with CAD had elevations in interleukin-8, leptin, and PEDF
Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets
A phenomenological theory of magnetic states in noncentrosymmetric tetragonal
antiferromagnets is developed, which has to include homogeneous and
inhomogeneous terms (Lifshitz-invariants) derived from Dzyaloshinskii-Moriya
couplings. Magnetic properties of this class of antiferromagnets with low
crystal symmetry are discussed in relation to its first known members, the
recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry
and magnetic ordering in these systems allow the simultaneous occurrence of
chiral inhomogeneous magnetic structures and weak ferromagnetism. New types of
incommensurate magnetic structures are possible, namely, chiral helices with
rotation of staggered magnetization and oscillations of the total
magnetization. Field-induced reorientation transitions into modulated states
have been studied and corresponding phase diagrams are constructed. Structures
of magnetic defects (domain-walls and vortices) are discussed. In particular,
vortices, i.e. localized non-singular line defects, are stabilized by the
inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric
antiferromagnets.Comment: 18 pages RevTeX4, 13 figure
Effect of sow age on the apparent total tract digestibility of nutrients in the diet
Abstract The objective of this research was to evaluate the effect of sow age on apparent total tract digestibility of nutrients and the concentration of metabolizable energy in the diet. The experiment was carried out on 20 gestating sows, divided into two groups: Group I -10 sows in first pregnancy (131 ± 4.5 kg) and Group II -10 sows in fourth pregnancy (225 ± 8.2 kg). Sows in the two groups were fed identical diets for sows during early pregnancy. The total collection of faeces began on day 30 of pregnancy and lasted eight days. Sows in the fourth pregnancy had greater digestibility coefficients of dry matter (4.1 percentage units), organic matter (3.4 percentage units), crude protein (5.5 percentage units) and crude fibre (6.2 percentage units) than sows in the first pregnancy. The total tract digestibility of ether extract, starch and sugars was not affected by pig age. The metabolizable energy, determined according to the content of digestible nutrients, in the sow diet in fourth pregnancy was 0.7 MJ/kg higher than in the diet of sows in their first pregnancy. Results of this research indicate that sow age should be considered when formulating diets during early pregnancy
The HARPS search for southern extrasolar planets. XXIII. 8 planetary companions to low-activity solar-type stars
In this paper, we present our HARPS radial-velocity data for eight
low-activity solar-type stars belonging to the HARPS volume-limited sample:
HD6718, HD8535, HD28254, HD290327, HD43197, HD44219, HD148156, and HD156411.
Keplerian fits to these data reveal the presence of low-mass companions around
these targets. With minimum masses ranging from 0.58 to 2.54 MJup, these
companions are in the planetary mass domain. The orbital periods of these
planets range from slightly less than one to almost seven years. The eight
orbits presented in this paper exhibit a wide variety of eccentricities: from
0.08 to above 0.8.Comment: 8 pages, 2 figures, accepted for publication in A&
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