811 research outputs found
Dust charge distribution in the interstellar medium
We investigate the equilibrium charge distribution of dust grains in the
interstellar medium (ISM). Our treatment accounts for collisional charging by
electrons and ions, photoelectric charging due to a background interstellar
radiation field, the collection of suprathermal cosmic ray electrons and
photoelectric emission due to a cosmic ray induced ultraviolet radiation field
within dense molecular clouds. We find that the charge equilibrium assumption
is valid throughout the multi-phase ISM conditions investigated here, and
should remain valid for simulations with resolutions down to AU scales. The
charge distribution of dust grains is size, composition, and ISM environment
dependent: local radiation field strength, , temperature, , and electron
number density, . The charge distribution is tightly correlated
with the `charging parameter', . In the molecular
medium, both carbonaceous and silicate grains have predominantly negative or
neutral charges with narrow distributions. In the cold neutral medium,
carbonaceous and silicate grains vary from negative and narrow distributions,
to predominantly positive and wide distributions depending on the magnitude of
the charging parameter. In the warm neutral medium, grains of all sizes are
positively charged with wide distributions. We derive revised parametric
expressions that can be used to recover the charge distribution function of
carbonaceous and silicate grains from 3.5 {\AA} to 0.25 m as a function of
the size, composition and ambient ISM parameters. Finally, we find that the
parametric equations can be used in environments other than Solar neighborhood
conditions, recovering the charge distribution function of dust grains in
photon dominated regions.Comment: 13 pages and 9 figures. Accepted for publication in MNRAS. Code
developed in this paper can be found: https://github.com/jcibanezm/DustCharg
Dust charge distribution in the interstellar medium
We investigate the equilibrium charge distribution of dust grains in the
interstellar medium (ISM). Our treatment accounts for collisional charging by
electrons and ions, photoelectric charging due to a background interstellar
radiation field, the collection of suprathermal cosmic ray electrons and
photoelectric emission due to a cosmic ray induced ultraviolet radiation field
within dense molecular clouds. We find that the charge equilibrium assumption
is valid throughout the multi-phase ISM conditions investigated here, and
should remain valid for simulations with resolutions down to AU scales. The
charge distribution of dust grains is size, composition, and ISM environment
dependent: local radiation field strength, , temperature, , and electron
number density, . The charge distribution is tightly correlated
with the `charging parameter', . In the molecular
medium, both carbonaceous and silicate grains have predominantly negative or
neutral charges with narrow distributions. In the cold neutral medium,
carbonaceous and silicate grains vary from negative and narrow distributions,
to predominantly positive and wide distributions depending on the magnitude of
the charging parameter. In the warm neutral medium, grains of all sizes are
positively charged with wide distributions. We derive revised parametric
expressions that can be used to recover the charge distribution function of
carbonaceous and silicate grains from 3.5 {\AA} to 0.25 m as a function of
the size, composition and ambient ISM parameters. Finally, we find that the
parametric equations can be used in environments other than Solar neighborhood
conditions, recovering the charge distribution function of dust grains in
photon dominated regions.Comment: 13 pages and 9 figures. Accepted for publication in MNRAS. Code
developed in this paper can be found: https://github.com/jcibanezm/DustCharg
Optical response of small silver clusters
The time-dependent local density approximation is applied to the optical
response of the silver clusters, Ag_2, Ag_3, Ag_8 and Ag_9^+. The calculation
includes all the electrons beyond the closed-shell Ag^{+11} ionic core, thus
including for the first time explicitly the filled d-shell in the response. The
excitation energy of the strong surface plasmon near 4 eV agrees well with
experiment. The theoretical transition strength is quenched by a factor of 4
with respect to the pure s-electron sum rule in Ag_8 due to the d-electrons. A
comparable amount of strength lies in complex states below 6 eV excitation. The
total below 6 eV, about 50% of the s sum rule, is consistent with published
experiments.Comment: 13 pages RevTex and 9 Postscript figure
Water formation on bare grains: When the chemistry on dust impacts interstellar gas
Context. Water together with O2 are important gas phase ingredients to cool
dense gas in order to form stars. On dust grains, H2 O is an important
constituent of the icy mantle in which a complex chemistry is taking place, as
revealed by hot core observations. The formation of water can occur on dust
grain surfaces, and can impact gas phase composition. Aims. The formation of
molecules such as OH, H2 O, HO2, H2 O2, as well as their deuterated forms and
O2 and O3 is studied in order to assess how the chemistry varies in different
astrophysical environments, and how the gas phase is affected by grain surface
chemistry. Methods. We use Monte Carlo simulations to follow the formation of
molecules on bare grains as well as the fraction of molecules released into the
gas phase. We consider a surface reaction network, based on gas phase
reactions, as well as UV photo-dissociation of the chemical species. Results.
We show that grain surface chemistry has a strong impact on gas phase
chemistry, and that this chemistry is very different for different dust grain
temperatures. Low temperatures favor hydrogenation, while higher temperatures
favor oxygenation. Also, UV photons dissociate the molecules on the surface,
that can reform subsequently. The formation-destruction cycle increases the
amount of species released into the gas phase. We also determine the time
scales to form ices in diffuse and dense clouds, and show that ices are formed
only in shielded environments, as supported by observations.Comment: Accepted in A&
Digital technologies, legal design and the future of the legal profession
Legal Technology – or “Legal Tech” – is disrupting the traditional operations and self-understanding of the legal profession. This chapter introduces the central claim of this book, namely that these developments are having and will continue to have a disruptive effect on the work of lawyers and that adapting to this new operating environment is crucial for legal professionals remaining relevant in an increasingly technology-driven world. This introductory chapter outlines some of the main features of this on-going transformation process, introduces some of the pressures it is creating for lawyers, and provides short summaries of the chapters that comprise this collection.fi=vertaisarvioitu|en=peerReviewed
Single-cell RNA-sequencing of herpes simplex virus 1-infected cells connects NRF2 activation to an antiviral program
Herpesvirus infection initiates a range of perturbations in the host cell, which remain poorly understood at the level of individual cells. Here, we quantify the transcriptome of single human primary fibroblasts during the first hours of lytic infection with HSV-1. By applying a generalizable analysis scheme, we define a precise temporal order of early viral gene expression and propose a set-wise emergence of viral genes. We identify host cell genes and pathways relevant for infection by combining three different computational approaches: gene and pathway overdispersion analysis, prediction of cell-state transition probabilities, as well as future cell states. One transcriptional program, which correlates with increased resistance to infection, implicates the transcription factor NRF2. Consequently, Bardoxolone methyl and Sulforaphane, two known NRF2 agonists, impair virus production, suggesting that NRF2 activation restricts viral infection. Our study provides insights into early stages of HSV-1 infection and serves as a general blueprint for the investigation of heterogeneous cell states in virus infection
Squeezed between shells? On the origin of the Lupus I molecular cloud. - II. APEX CO and GASS HI observations
Accepted for publication in a future issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Context. The Lupus I cloud is found between the Upper-Scorpius (USco) and the Upper-Centaurus-Lupus (UCL) sub-groups of the Scorpius-Centaurus OB-association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL. Aims. We investigate if the Lupus I molecular could have formed in a colliding flow, and in particular, how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. Methods. We performed APEX 13CO(2–1) and C 18O(2–1) line observations of three distinct parts of Lupus I that provide kinematic information on the cloud at high angular and spectral resolution. We compare those results to the atomic hydrogen data from the GASS H i survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. Results. We present evidence that the molecular gas of Lupus I is tightly linked to the atomic material of the USco shell. The CO emission in Lupus I is found mainly at velocities between vLSR = 3–6 km s−1 which is in the same range as the H i velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic H i shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The non-thermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario where Lupus I is located in the interaction zone between the USco shell and the UCL wind bubble. Conclusions. The kinematics observations are consistent with a scenario where the Lupus I cloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counter-pressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation.Peer reviewedFinal Accepted Versio
Multilayer modeling of porous grain surface chemistry I. The GRAINOBLE model
Mantles of iced water, mixed with CO, H2CO, and CH3OH are formed during the
so called prestellar core phase. In addition, radicals are also thought to be
formed on the grain surfaces, and to react to form complex organic molecules
later on, during the warm-up phase of the protostellar evolution. We aim to
study the formation of the grain mantles during the prestellar core phase and
the abundance of H2CO, CH3OH, and radicals trapped in them. We have developed a
macrosopic statistic multilayer model that follows the formation of grain
mantles with time and that includes two effects that may increase the number of
radicals trapped in the mantles: i) at each time of the mantle formation, only
the surface layer is chemically active rather than the entire bulk, and ii) the
porous structure of grains allows to trap reactive particles. The model
considers a network of H, O and CO forming neutral species such as water, CO,
formaldehyde, and methanol, plus several radicals. We run a large grid of
models to study the impact of the mantle multilayer nature and grain porous
structure. In addition, we explored the influence of the uncertainty of other
key parameters on the mantle composition. Our model predicts relatively large
abundances of radicals. In addition, the multilayer approach makes it possible
to follow the chemical differentiation within the grain mantle, showing that
the mantles are far from being uniform. For example, methanol is mostly present
in the outer layers of the mantles whereas CO and other reactive species are
trapped in the inner layers. The overall mantle composition depends on the
density and age of the prestellar core, and on some microscopic parameters.
Comparison with observations allows us to constrain the value of few parameters
and provide some indications on the physical conditions during the formation of
the ices.Comment: 20 pages and 19 figures. Accepted in Astronomy & Astrophysic
HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules II. The absorption line survey with the IRAM 30 m telescope
As a complement to the HyGAL Stratospheric Observatory for Infrared Astronomy
Legacy Program, we report the results of a ground-based absorption line survey
of simple molecules in diffuse and translucent Galactic clouds. Using the
Institut de Radioastronomie Millim\'etrique (IRAM) 30 m telescope, we surveyed
molecular lines in the 2 mm and 3 mm wavelength ranges toward 15 millimeter
continuum sources. These sources, which are all massive star-forming regions
located mainly in the first and second quadrants of the Milky Way, form the
subset of the HyGAL sample that can be observed by the IRAM 30 m telescope. We
detected HCO absorption lines toward 14 sightlines, toward which we
identified 78 foreground cloud components, as well as lines from HCN, HNC,
CH, and c-CH toward most sightlines. In addition, CS and HS
absorption lines are found toward at least half of the continuum sources.
Static Meudon photodissociation region (PDR) isobaric models that consider
ultraviolet-dominated chemistry were unable to reproduce the column densities
of all seven molecular species by just a factor of a few, except for HS.
The inclusion of other formation routes driven by turbulent dissipation could
possibly explain the observed high column densities of these species in diffuse
clouds. There is a tentative trend for HS and CS abundances relative to
H to be larger in diffuse clouds ((HS) and (CS) ) than in translucent clouds ((HS) and (CS) ) toward a small sample; however, a larger sample is required in order
to confirm this trend. The derived HS column densities are higher than the
values predicted from the isobaric PDR models, suggesting that chemical
desorption of HS from sulfur-containing ice mantles may play a role in
increasing the HS abundance.Comment: 41 pages, 25 figures, 10 tables, and 5 appendices. Accepted for
publication in A&
Immunotherapeutic targeting of membrane Hsp70-expressing tumors using recombinant human granzyme B
Background: We have previously reported that human recombinant granzyme B (grB) mediates apoptosis in membrane heat shock protein 70 (Hsp70)-positive tumor cells in a perforin-independent manner
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