IGLIAS: A new experimental set-up for low temperature irradiation studies at large irradiation facilities.

We designed and built a mobile experimental set-up for studying the interaction of ion beams with solid samples in a wide temperature range from 9 to 300 K. It is either possible to mount up to three samples prepared ex situ or to prepare samples by condensation of molecules from gases or vapours onto IR or Visible-ultraviolet (Vis-UV) transparent windows. The physico-chemical evolution during irradiation can be followed in situ with different analysis techniques including Fourier transform infrared spectroscopy, Vis-UV, and quadrupole mass spectrometry.

Spatial distribution of FIR rotationally excited CH+ and OH emission lines in the Orion Bar PDR.

CONTEXT: The methylidyne cation (CH+) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500-1000 K) in photodissociation regions with high incident FUV radiation field. The excitation may also originate in dense gas (> 105 cm-3) followed by nonreactive collisions with H2, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH+ and OH correlate with the excited CO, a tracer of dense and warm gas, and formation pumping contributes to CH+ excitation. AIMS: Our goal is to examine the spatial distribution of the rotationally excited CH+ and OH emission lines in the Orion Bar in order to establish their physical origin and main formation and excitation mechanisms. METHODS: We present spatially sampled maps of the CH+ J=3-2 transition at 119.8 µm and the OH Λ-doublet at 84 µm in the Orion Bar over an area of 110″×110″ with Herschel (PACS). We compare the spatial distribution of these molecules with those of their chemical precursors, C+, O and H2, and tracers of warm and dense gas (high-J CO). We assess the spatial variation of CH+ J=2-1 velocity-resolved line profile at 1669 GHz with Herschel HIFI spectrometer observations. RESULTS: The OH and especially CH+ lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH+ and OH morphologies indicate that CH+ formation and excitation are strongly related to the observed vibrationally excited H2. This, together with the observed broad CH+ line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 µm emission coincides with a bright young object, proplyd 244-440, which shows that OH can be an excellent tracer of UV-irradiated dense gas. CONCLUSIONS: The spatial distribution of CH+ and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH+ J=3-2 excitation processes. The excitation of the OH Λ-doublet at 84 µm is mainly sensitive to the temperature and density.

Interstellar matrices: the chemical composition and evolution of interstellar ices as observed by ISO.

Matrix isolation techniques have been developed in the early sixties as a tool for studying the spectroscopic properties of out of equilibrium species (atoms, radicals, ions, reactive molecules), embedded in rare gas inert matrices at low temperatures. Cold interstellar grains surfaces are able to condense out gas phase molecules, routinely observed by radioastronomy. These grain 'mantles' can be considered as 'interstellar matrices'. However, these matrices are not clean and unreactive. They are made principally of dirty ices whose composition must be determined carefully to assess the importance of the solid state chemistry that takes place in the Interstellar Medium. Infrared spectroscopy, both in astronomy and in the laboratory, is the unique tool to determine the chemical composition of these ices. Astronomical spectra can directly be compared with laboratory ones obtained using classical matrix isolation techniques. Furthermore, dedicated experiments may be undertaken to further improve the understanding of the basic physico-chemical processes that take place in cosmic ices.

Windows through the dusty disks surrounding the youngest low-mass protostellar objects.

The formation and evolution of young low-mass stars are characterized by important processes of mass loss and accretion occurring in the innermost regions of their placentary circumstellar disks. Because of the large obscuration of these disks at optical and infrared wavelengths in the early protostellar stages (class 0 sources), they were previously detected only at radio wavelengths using interferometric techniques. We have detected with the Infrared Space Observatory the mid-infrared (mid-IR) emission associated with the class 0 protostar VLA1 in the HH1-HH2 region located in the Orion nebula. The emission arises in three wavelength windows (at 5. 3, 6.6, and 7.5 micrometers) where the absorption due to ices and silicates has a local minimum that exposes the central part of the young protostellar system to mid-IR investigations. The mid-IR emission arises from a central source with a diameter of 4 astronomical units at an averaged temperature of approximately 700 K, deeply embedded in a dense region with a visual extinction of 80 to 100 magnitudes.

A software for the description of workplaces in the PRS system.

Workplace description is an operation indispensable for the identification of professional risks and, in fulfillment of that objective, can best be accomplished by listing the constituent tasks associated with each job. This article presents a software in Visual-Basic to be run on a portable micro-computer, which facilitates this process according to these aims. The occupational physician and safety engineer can make good use of the exposure database resulting from the application of this program. Job histories are built automatically, while workers with similar exposures are grouped together and job-exposure matrices are elaborated. This information, computerized, sorted and re-assembled, can then be used effectively for studies in the field of occupational epidemiology.

An autoradiographic study comparing the interactions of 3 alpha-OH-5 alpha-pregnan-20-one, pregnenolone sulfate and pentobarbital with [3S]-TBPS binding sites and their modulation by GABA in different structures of the rat brain.

Using quantitative autoradiography, we have studied the distribution of the [35S]-TBPS binding sites of the GABA-A receptor complex in various structures of the rat brain. High densities of binding sites were observed in layer IV of the cerebral cortex, in the globus pallidus, and in the thalamus. Intermediate densities of binding sites were observed in superficial and deep layers of the cerebral cortex, in the dentate gyrus and in the hippocampus. For all of these structures, the interactions of 3 alpha-OH-5 alpha-pregnan-20-one (3 alpha 5 alpha P), pregnenolone sulfate (PS), and pentobarbital with [35S]-TBPS binding, in the presence or the absence of GABA were studied. In the absence of GABA, IC50 values for the inhibition of [35S]-TBPS binding were 10(-6) M for 3 alpha 5 alpha P and 10(-4) M for PS and pentobarbital in all of the brain regions studied. In the presence of GABA (5 x 10(-6) M), IC50 values were decreased by one order of magnitude for 3 alpha 5 alpha P, PS, and pentobarbital in all structures studied except layer IV of the cortex, where the IC50 value for PS was more markedly decreased (up to two orders of magnitude). By contrast, IC50 values for picrotoxin and TBPS to inhibit [35S]-TBPS binding were 10(-7) M and 10(-8) M, respectively, in the presence or absence of GABA.

Autoradiographic study of neurosteroid binding sites labelled with [35S]-TBPS in brain of different species.

Distribution of [35S]-TBPS binding sites was studied in various structures of brain in mouse and guinea pig and in cortex of monkey and in hippocampus of postmortem human brain. As it is observed for rat brain, high densities of [35S]-TBPS binding sites were found in layer IV of cortex in the four species, and in thalamus of mouse and guinea pig. Intermediate densities of binding sites were observed in superficial and deep layers of cortex in those four species and in hippocampus of mouse, guinea pig, and human. In all brain structures studied, 5 alpha 3 alpha P and picrotoxin produced a dose-dependent inhibition of [35S]-TBPS binding. No significant interregion or interspecies differences could not be detected for IC50 values of 5 alpha 3 alpha P or picrotoxin to inhibit [35S]-TBPS from its binding sites. In all regions studied, IC50 values were close to 1.5 x 10(-6) M for 5 alpha 3 alpha P and 2.3 x 10(-7) M for picrotoxin.

Inhibition by glucocorticoids of PGE2 and ACTH secretion induced by phorbol esters and EGF in rat pituitary cells.

In rat pituitary cells in primary culture glucocorticoids specifically inhibit PGE2 and ACTH secretions induced by TPA, a potent phorbol ester derivative (triamcinolone acetonide greater than dexamethasone greater than cortisol greater than or equal to corticosterone). However, while PGE2 secretion can be inhibited up to 80%, ACTH secretion can only be inhibited up to 40%. Similar inhibitory effects are observed with mepacrine, an inhibitor of phospholipase A2 (PLA2). Glucocorticoids having also been described as PLA2-inhibitors, their inhibitory effect on TPA-induced secretions could thus be related to their anti-PLA2 activity. Their inhibitory effect on PLA2 has been attributed to their ability to induce the synthesis of lipocortin, the activity of which could be regulated by activation of kinase C or EGF-receptor kinase. Since in our model, EGF-induced PGE2 secretion is also inhibited by dexamethasone, these results suggest that a lipocortin-like protein could be present in pituitary cells and involved in the effect of TPA and EGF on PGE2, and, at least partly, on ACTH release.

Role of calcium on TPA-induced secretion of ACTH and PGE2 by pituitary cells: effect of dexamethasone.

In pituitary cells in primary culture, ACTH and PGE2 secretions can be simultaneously stimulated by TPA, in the presence of Ca2+. However, whilst PGE2 secretion is under an absolute requirement for Ca2+, ACTH secretion is not. Both secretions are inhibited by dexamethasone but to various extents: PGE2 release is abolished in the presence of dexamethasone whilst only 35% of the TPA-induced ACTH release is sensitive to dexamethasone. Similar inhibitory effects are observed with mepacrine, a PLA2-inhibitor, suggesting that PLA2-activation could be related to these secretory process. Since PLA2-inhibition by dexamethasone is claimed to be mediated via lipocortin, these results suggest that a lipocortin-like protein is present in pituitary cells and could be involved in the TPA-induced secretions of PGE2 and ACTH.