133 research outputs found
A New Versatile System for Freeze-Substitution, Freeze-Drying and Low Temperature Embedding of Biological Specimens
A universal system for freeze-substitution (FS), freeze-drying (FD) and low temperature embedding (LTE) has been developed, suited to perform standardized procedures of cryoprocessing biological and medical specimens as well as systematic studies of dehydration and embedding at various low and high temperatures. In a 35 I Dewar vessel with 110 mm neck diameter an aluminum tube is mounted to the bottom of the liquid nitrogen (LN2x) reservoir and extends to the lower part of the cylindrical neck. At its top an aluminum plate serves as a contact surface for either the FS chamber or the FD chamber. FS and subsequent LTE are carried out in an environment of dry cold nitrogen gas provided by evaporating nitrogen from the dewar. Different capsules and moulds may be used for cryodehydration and LTE. FD of bulk specimens or cryosections takes place in an absolutely clean vacuum provided by a cryosorption pump integrated in the FD apparatus. Most of the Hp molecules from the frozen specimen are trapped by large cold surfaces inside the drying chamber. Due to the low LN2 consumption during FS or FD (3-4 l LN2/day) both procedures may be carried out for 8-10 days without refilling the dewar. A few representative results show that well frozen biological material is stabilized by prolonged FS or FD at temperatures of about -80°C without use of chemical fixatives like OsO4 in the substitution medium during FS or by OsO4 vapor fixation after FD
Investigations on the individual and maternal components of calving performance in cattle
International audienc
A protosolar nebula origin for the ices agglomerated by Comet 67P/Churyumov-Gerasimenko
The nature of the icy material accreted by comets during their formation in
the outer regions of the protosolar nebula is a major open question in
planetary science. Some scenarios of comet formation predict that these bodies
agglomerated from crystalline ices condensed in the protosolar nebula.
Concurrently, alternative scenarios suggest that comets accreted amorphous ice
originating from the interstellar cloud or from the very distant regions of the
protosolar nebula. On the basis of existing laboratory and modeling data, we
find that the N/CO and Ar/CO ratios measured in the coma of the Jupiter
family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the
European Space Agency's Rosetta spacecraft match those predicted for gases
trapped in clathrates. If these measurements are representative of the bulk
N/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the
ices accreted by the comet formed in the nebula and do not originate from the
interstellar medium, supporting the idea that the building blocks of outer
solar system bodies have been formed from clathrates and possibly from pure
crystalline ices. Moreover, because 67P/Churyumov-Gerasimenko is impoverished
in Ar and N, the volatile enrichments observed in Jupiter's atmosphere
cannot be explained solely via the accretion of building blocks with similar
compositions and require an additional delivery source. A potential source may
be the accretion of gas from the nebula that has been progressively enriched in
heavy elements due to photoevaporation.Comment: The Astrophysical Journal Letters, in pres
Immunohistochemical demonstration of cyclooxygenase-2 (COX-2) and prostaglandin receptors EP2 and FP expression in the bovine intercaruncular uterine wall around term
During parturition, uterine-derived prostaglandins (PG) play an outstanding role regarding the functional elimination of the corpus luteum and the promotion of uterine contraction. The rate-limiting enzyme cyclooxygenase-2 (COX-2), highly regulated in a cell-type and localization specific manner throughout pregnancy, is involved in uterine prostanoid production. Prostaglandins exert their effects via G-protein-coupled receptors. Distribution and cellular localization of these receptors are decisive factors for prostaglandin-mediated actions. Since both COX-2 and PG receptors have only been assessed during pregnancy in the cow, these parameters were localized immunohistochemically near term to evaluate their specific role at parturition. Thus, during two periods, segments of the intercaruncular uterine wall were collected from cows at slaughter being eight and nine months pregnant, from cattle during caesarean section, and after spontaneous calving. Results reveal that COX-2 was mainly localized in the cytoplasm of surface epithelial cells with a high expression in animals with induced parturition. The enzyme could also be found in lower concentrations within the glandular epithelium without any effect of gestational time or labour. In contrast to relaxant prostaglandin E receptor type 2 (EP2), not showing any change in all tissue layers observed, contractile prostaglandin F(2alpha) receptor (FP) was modulated during the peripartal period revealing a peak expression in animals with induced parturition. FP was localized in surface and glandular epithelial cells as well as in endometrial stroma and myometrial smooth muscle cells. Our study indicates that labour and induction of parturition may have an effect on amounts of immunohistochemically detectable COX-2 and FP. EP2 remains rather unchanged during the peripartal period. COX-2 and FP thus contribute via changes in amount and distribution to mechanisms associated with parturition
Organics in comet 67P â a first comparative analysis of mass spectra from ROSINAâDFMS, COSAC and Ptolemy
The ESA Rosetta spacecraft followed comet 67P at a close distance for more than 2 yr. In addition, it deployed the lander Philae on to the surface of the comet. The (surface) composition of the comet is of great interest to understand the origin and evolution of comets. By combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. We compare data from the double focusing mass spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission and previously published data from the two mass spectrometers COSAC (COmetary Sampling And Composition) and Ptolemy on the lander. The mass spectra of all three instruments show very similar patterns of mainly CHO-bearing molecules that sublimate at temperatures of 275 K. The DFMS data also show a great variety of CH-, CHN-, CHS-, CHO2- and CHNO-bearing saturated and unsaturated species. Methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured COSAC spectrum could not be confirmed. The presence of polyoxymethylene in the Ptolemy spectrum was found to be unlikely. However, the signature of the aromatic compound toluene was identified in DFMS and Ptolemy data. Comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67P, which is much more diverse than anticipated
First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko
International audienceContext: The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all.Aims: These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explainedMethods: The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals.Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230â500 m/s
Influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94765/1/jgra20796.pd
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