135 research outputs found
Endocrine Disruptors and Leydig Cell Function
During the past decades, a large body of information concerning the effects of endocrine disrupting compounds (EDCs) on animals and humans has been accumulated. EDCs are of synthetic or natural origin and certain groups are known to disrupt the action of androgens and to impair the development of the male reproductive tract and external genitalia. The present overview describes the effects of the different classes of EDCs, such as pesticides, phthalates, dioxins, and phytoestrogens, including newly synthesized resveratrol analogs on steroidogenesis in Leydig cells. The potential impact of these compounds on androgen production by Leydig cells during fetal development and in the adult age is discussed. In addition, the possible role of EDCs in connection with the increasing frequency of abnormalities in reproductive development in animals and humans is discussed
Domain Dynamics in Piezoresponse Force Microscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure
Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is
studied using the combination of local hysteresis loop acquisition with
simultaneous domain imaging. The analytical theory for PFS signal from domain
of arbitrary cross-section is developed and used for the analysis of
experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest
formation of oblate domain at early stage of the domain nucleation and growth,
consistent with efficient screening of depolarization field within the
material. The fine structure of the hysteresis loop is shown to be related to
the observed jumps in the domain geometry during domain wall propagation
(nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.Comment: 17 pages, 3 figures, 2 Appendices, to be submmited to Appl. Phys.
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Domain wall conduction in multiaxial ferroelectrics
The conductance of domain wall structures consisting of either stripes or
cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed.
The effects of the domain size, wall tilt and curvature, on charge
accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory
for polarization combined with Poisson equation for charge distributions. Both
the classical ferroelectric parameters including expansion coefficients in
2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling,
inhomogeneous elastic strains and electrostriction are included in the present
analysis. Spatial distributions of the ionized donors, free electrons and holes
were found self-consistently using the effective mass approximation for the
respective densities of states. The proximity and size effect of the electron
and donor accumulation/depletion by thin stripe domains and cylindrical
nanodomains are revealed. In contrast to thick domain stripes and thicker
cylindrical domains, in which the carrier accumulation (and so the static
conductivity) sharply increases at the domain walls only, small nanodomains of
radius less then 5-10 correlation length appeared conducting across entire
cross-section. Implications of such conductive nanosized channels may be
promising for nanoelectronics.Comment: 39 pages, 11 figures, 3 tables, 4 appendice
Synthesis and luminescent properties of SrTiO₃:Pr³⁺ phosphors prepared by sol-gel method
New red SrTiO₃:Pr³⁺ phosphor for the field emission displays application was
prepared using the sol-gel method. The reaction between starting materials SrCl₂, Ti-(Oi-C₃H₇)₄
and PrCl₃ resulted in a mix of compounds transformed to single-phase
SrTiO₃:Pr after its annealing in air. Optimal technological conditions for preparation of
efficiently radiating SrTiO₃:Pr³⁺ phosphors were found. Both photoluminescence and
cathodoluminescence spectra showed the high intensity red peaks at the wavelength
λmax = 617 nm. The high luminance of 300 cd/m²
was obtained at the anode voltage of
10 kV
The Interaction of an 180 degree Ferroelectric Domain Wall with a Biased Scanning Probe Microscopy Tip: Effective Wall Geometry and Thermodynamics in Ginzburg-Landau-Devonshire Theory
The interaction of ferroelectric 180 degree domain wall with a strongly
inhomogeneous electric field of biased Scanning Probe Microscope tip is
analyzed within continuous Landau-Ginzburg-Devonshire theory. Equilibrium shape
of the initially flat domain wall boundary bends, attracts or repulses from the
probe apex, depending on the sign and value of the applied bias. For large
tip-wall separations, the probe-induced domain nucleation is possible. The
approximate analytical expressions for the polarization distribution are
derived using direct variational method. The expressions provide insight how
the equilibrium polarization distribution depends on the wall finite-width,
correlation and depolarization effects, electrostatic potential distribution of
the probe and ferroelectric material parameters.Comment: 37 pages, 9 figures, 4 Appendices, to be submitted to Phys. Rev.
A catalog of visual double and multiple stars with eclipsing components
A new catalog of visual double systems containing eclipsing binaries as one
component is presented. The main purpose of this catalog is to compile a
complete list of all known multiples of this variety, both for current analysis
and to highlight those in need of additional observations. All available
photometric and astrometric data were analyzed, resulting in new orbits for
eight systems and new times of minimum light for a number of the eclipsing
binaries. Some of the systems in the catalog have acceptable solutions for
their visual orbits, although in most cases their orbital periods are too long
for simultaneous analysis. Also included, however, are a number of systems
which currently lack an orbital solution but which may be suitable for
simultaneous analysis in the future.Comment: 15 pages, 8 figures, 4 tables, published in A
Nanoscale Electromechanics of Paraelectric Materials with Mobile Charges: Size effects and Nonlinearity of Electromechanical Response of SrTiO3 Films
Nanoscale enables a broad range of electromechanical coupling mechanisms that
are forbidden or negligible in the materials. We conduct a theoretical study of
the electromechanical response of thin paraelectric films with mobile vacancies
(or ions) paradigmatic for capacitor-type measurements in X-ray scattering,
piezoresponse force microscopy (PFM), and electrochemical strain microscopy
(ESM). Using quantum paraelectric SrTiO3 film as a model material with well
known electromechanical, electronic and electrochemical properties, we evaluate
the contributions of electrostriction, Maxwell stress, flexoelectric effect,
deformation potential and compositional Vegard strains caused by mobile
vacancies (or ions) and electrons to the electromechanical response. The local
electromechanical response manifests strong size effects, the scale of which is
determined by the ratio of the SrTiO3 film thickness and PFM/ESM tip size to
the carriers screening radius. Due to the strong dielectric nonlinearity effect
inherent in quantum paraelectrics, the dependence of the SrTiO3 film
electromechanical response on applied voltage demonstrates a pronounced
crossover from the linear to the quadratic law and then to the sub-linear law
with a factor of 2/3 under the voltage increase. The temperature dependence of
the electromechanical response as determined by the interplay between the
dielectric susceptibility and the screening radius is non-monotonic and has a
pronounced maxima, the position and width of which can be tuned by film
thickness. This study provides a comparative framework for analysis of
electromechanical coupling in the non-piezoelectric nanosystems.Comment: 50 pages, 10 figures, 3 appendices, to be submitted to Phys. Rev.
Effects of dietary phytoestrogens on plasma testosterone and triiodothyronine (T3) levels in male goat kids
<p>Abstract</p> <p>Background</p> <p>Exposure to xenoestrogens in humans and animals has gained increasing attention due to the effects of these compounds on reproduction. The present study was undertaken to investigate the influence of low-dose dietary phytoestrogen exposure, i.e. a mixture of genistein, daidzein, biochanin A and formononetin, on the establishment of testosterone production during puberty in male goat kids.</p> <p>Methods</p> <p>Goat kids at the age of 3 months received either a standard diet or a diet supplemented with phytoestrogens (3 - 4 mg/kg/day) for ~3 months. Plasma testosterone and total and free triiodothyronine (T<sub>3</sub>) concentrations were determined weekly. Testicular levels of testosterone and cAMP were measured at the end of the experiment. Repeated measurement analysis of variance using the MIXED procedure on the generated averages, according to the Statistical Analysis System program package (Release 6.12, 1996, SAS Institute Inc., Cary, NC, USA) was carried out.</p> <p>Results</p> <p>No significant difference in plasma testosterone concentration between the groups was detected during the first 7 weeks. However, at the age of 5 months (i.e. October 1, week 8) phytoestrogen-treated animals showed significantly higher testosterone concentrations than control animals (37.5 nmol/l vs 19.1 nmol/l). This elevation was preceded by a rise in plasma total T<sub>3 </sub>that occurred on September 17 (week 6). A slightly higher concentration of free T<sub>3 </sub>was detected in the phytoestrogen group at the same time point, but it was not until October 8 and 15 (week 9 and 10) that a significant difference was found between the groups. At the termination of the experiment, testicular cAMP levels were significantly lower in goats fed a phytoestrogen-supplemented diet. Phytoestrogen-fed animals also had lower plasma and testicular testosterone concentrations, but these differences were not statistically significant.</p> <p>Conclusion</p> <p>Our findings suggest that phytoestrogens can stimulate testosterone synthesis during puberty in male goats by increasing the secretion of T<sub>3</sub>; a hormone known to stimulate Leydig cell steroidogenesis. It is possible that feedback signalling underlies the tendency towards decreased steroid production at the end of the experiment.</p
Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects
Insect steroid hormones (ecdysteroids) are important for female reproduction in many insect species and are required for the initiation and coordination of vital developmental processes. Ecdysteroids are also important for adult male physiology and behavior, but their exact function and site of synthesis remains unclear, although previous studies suggest that the reproductive system may be their source. We have examined expression profiles of the ecdysteroidogenic Halloween genes, during development and in adults of the flour beetle Tribolium castaneum. Genes required for the biosynthesis of ecdysone (E), the precursor of the molting hormone 20-hydroxyecdysone (20E), are expressed in the tubular accessory glands (TAGs) of adult males. In contrast, expression of the gene encoding the enzyme mediating 20E synthesis was detected in the ovaries of females. Further, Spookiest (Spot), an enzyme presumably required for endowing tissues with competence to produce ecdysteroids, is male specific and predominantly expressed in the TAGs. We also show that prothoracicotropic hormone (PTTH), a regulator of E synthesis during larval development, regulates ecdysteroid levels in the adult stage in Drosophila melanogaster and the gene for its receptor Torso seems to be expressed specifically in the accessory glands of males. The composite results suggest strongly that the accessory glands of adult male insects are the main source of E, but not 20E. The finding of a possible male-specific source of E raises the possibility that E and 20E have sex-specific roles analogous to the vertebrate sex steroids, where males produce primarily testosterone, the precursor of estradiol. Furthermore this study provides the first evidence that PTTH regulates ecdysteroid synthesis in the adult stage and could explain the original finding that some adult insects are a rich source of PTTH
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