662 research outputs found
Large-eddy simulations of stratified plane Couette flow using the anisotropic minimum-dissipation model
The anisotropic minimum-dissipation (AMD) model for large-eddy simulation (LES) has been recently developed, and here the model performance is examined in strat- ified plane Couette flow. To our knowledge this is the first use of the AMD model for resolved LES of stratified wall-bounded flow. A comparison with previously pub- lished direct numerical simulations (DNS) provides insight into model and grid re- quirements. Prandtl numbers of P r = 0.7 − 70 and a range of Richardson numbers show that the AMD LES performs well even with a strong stabilising buoyancy flux. We identify three new requirements for accurate LES of stratified wall-bounded flow. First, the LES must resolve the turbulent structures at the edge of the viscous sublayer in order to satisfy the Obukov length scale condition, L+s > 200. Other- wise the LES solution may laminarise where the DNS solution remains turbulent. Second, the LES must have enough vertical grid resolution within the viscous and diffusive sublayers to resolve the wall fluxes. Third, the grid must be reasonably isotropic (vertical-to-horizontal grid aspect ratio > 0.25) at the edge of the sublayer and through the turbulent interior for the AMD LES to correctly simulate the scalar flux. When these model requirements are fulfilled the AMD LES performs very well, producing vertical mean profiles, friction Reynolds number and Nusselt number con- sistent with DNS solutions at significantly higher grid resolution
HERschel Observations of Edge-on Spirals (HEROES). II: Tilted-ring modelling of the atomic gas disks
Context. Edge-on galaxies can offer important insights in galaxy evolution as
they are the only systems where the distribution of the different components
can be studied both radially and vertically. The HEROES project was designed to
investigate the interplay between the gas, dust, stars and dark matter (DM) in
a sample of 7 massive edge-on spiral galaxies.
Aims. In this second HEROES paper we present an analysis of the atomic gas
content of 6 out of 7 galaxies in our sample. The remaining galaxy was recently
analysed according to the same strategy. The primary aim of this work is to
constrain the surface density distribution, the rotation curve and the geometry
of the gas disks in a homogeneous way. In addition we identify peculiar
features and signs of recent interactions.
Methods. We construct detailed tilted-ring models of the atomic gas disks
based on new GMRT 21-cm observations of NGC 973 and UGC 4277 and re-reduced
archival HI data of NGC 5907, NGC 5529, IC 2531 and NGC 4217. Potential
degeneracies between different models are resolved by requiring a good
agreement with the data in various representations of the data cubes.
Results. From our modelling we find that all but one galaxy are warped along
the major axis. In addition, we identify warps along the line of sight in three
galaxies. A flaring gas layer is required to reproduce the data only for one
galaxy, but (moderate) flares cannot be ruled for the other galaxies either. A
coplanar ring-like structure is detected outside the main disk of NGC 4217,
which we suggest could be the remnant of a recent minor merger event. We also
find evidence for a radial inflow of 15 +- 5 km/s in the disk of NGC 5529,
which might be related to the ongoing interaction with two nearby companions.
(Abridged)Comment: 39 pages, 38 figures, Accepted for publication in Astronomy &
Astrophysic
The Herschel Virgo Cluster Survey XVI: a cluster inventory
Herschel FIR observations are used to construct Virgo cluster galaxy
luminosity functions and to show that the cluster lacks the very bright and the
numerous faint sources detected in field galaxy surveys. The far-infrared SEDs
are fitted to obtain dust masses and temperatures and the dust mass function.
The cluster is over dense in dust by about a factor of 100 compared to the
field. The same emissivity (beta) temperature relation applies for different
galaxies as that found for different regions of M31. We use optical and HI data
to show that Virgo is over dense in stars and atomic gas by about a factor of
100 and 20 respectively. Metallicity values are used to measure the mass of
metals in the gas phase. The mean metallicity is about 0.7 solar and 50% of the
metals are in the dust. For the cluster as a whole the mass density of stars in
galaxies is 8 times that of the gas and the gas mass density is 130 times that
of the metals. We use our data to consider the chemical evolution of the
individual galaxies, inferring that the measured variations in effective yield
are due to galaxies having different ages, being affected to varying degrees by
gas loss. Four galaxy scaling relations are considered: mass-metallicity,
mass-velocity, mass-star formation rate and mass-radius - we suggest that
initial galaxy mass is the prime driver of a galaxy's ultimate destiny.
Finally, we use X-ray observations and galaxy dynamics to assess the dark and
baryonic matter content compared to the cosmological model
A minimum-relaxation model for large eddy simulation
This paper is about a relaxation model for large-eddy simulation of turbulent flow that truncates the small scales of motion for which numerical resolution is not available by making sure that they do not get energy from the larger, resolved, eddies. The resolved scales are defined with the help of a box filter. The relaxation parameter is determined in such a way that the production of too small, box-fitting, scales is counteracted by the modeled dissipation. This dissipation-production balance is worked out with the help of Poincaré’s inequality, which results in a relaxation model that depends on the invariants of the velocity gradient. This model is discretized and equipped with a Schumann filter. It is successfully tested for isotropic turbulence as well as for turbulent channel flow
HERschel Observations of Edge-on Spirals (HEROES). I: Far-infrared morphology and dust mass determination
Context. Edge-on spiral galaxies with prominent dust lanes provide us with an
excellent opportunity to study the distribution and properties of the dust
within them. The HEROES project was set up to observe a sample of seven large
edge-on galaxies across various wavelengths for this investigation.
Aims. Within this first paper, we present the Herschel observations and
perform a qualitative and quantitative analysis on them, and we derive some
global properties of the far infrared and submillimetre emission.
Methods. We determine horizontal and vertical profiles from the Herschel
observations of the galaxies in the sample and describe the morphology.
Modified black-body fits to the global fluxes, measured using aperture
photometry, result in dust temperatures and dust masses. The latter values are
compared to those that are derived from radiative transfer models taken from
the literature.
Results. On the whole, our Herschel flux measurements agree well with
archival values. We find that the exponential horizontal dust distribution
model often used in the literature generally provides a good description of the
observed horizontal profiles. Three out of the seven galaxies show signatures
of extended vertical emission at 100 and 160 {\mu}m at the 5{\sigma} level, but
in two of these it is probably due to deviations from an exactly edge-on
orientation. Only for NGC 4013, a galaxy in which vertically extended dust has
already been detected in optical images, we can detect vertically extended
dust, and the derived scaleheight agrees with the value estimated through
radiative transfer modelling. Our analysis hints at a correlation between the
dust scaleheight and its degree of clumpiness, which we infer from the
difference between the dust masses as calculated from modelling of optical data
and from fitting the spectral energy distribution of Herschel datapoints.Comment: 21 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
Blocking T cell co-stimulation in primary Sjögren's syndrome:rationale, clinical efficacy and modulation of peripheral and salivary gland biomarkers
There is accumulating evidence that patients with primary Sjögren's syndrome (pSS) display aberrant CD4+ T cell responses, both in the peripheral compartment and in the inflamed salivary glands. CD4+ T cell abnormalities are also critically associated with B cell hyper activation, one of the hallmarks of disease, which is linked with disease severity and evolution to lymphoma. T cell activation and the cross-talk between T and B cells are tightly regulated by the balance between co-stimulatory pathways, such as the interactions between CD80/CD86:CD28, CD40:CD40L and ICOS:ICOSL, and co-inhibitory signals, including the immunoregulatory CTLA-4 protein. Evidence from patients with pSS as well as data from animal models of the disease suggests that these pathways play a critical role in pSS pathogenesis and their targeting could be exploited for therapeutic purposes. In this review, we first summarise the evidence implicating aberrant T cell co-stimulation and co-inhibition in driving the disease before focusing on the results of recent randomised controlled trials (RCTs) with compounds able to block T cell co-stimulation and enhance T cell co-inhibition. Despite a clear biological effect on downstream B cell activation has been observed in patients treated with CTLA-4-Ig (abatacept) and with monoclonal antibodies targeting CD40 and ICOSL, the clinical efficacy of this approach has so far yielded mixed results; while the anti-CD40 monoclonal antibody iscalimab showed significant improvement in systemic disease activity compared to placebo, two large RCTs with abatacept and a phase IIa RCT with an anti-ICOSL monoclonal antibody (prezalumab) failed to reach their primary endpoints. Although the discrepancies between biological and clinical efficacy of targeting T cell co-stimulation on pSS remain unresolved, several factors including drug bioavailability and receptor occupancy, patient stratification based on T-cell related biomarkers and the choice of study outcome are likely to play an important role and form the basis for further work towards the quest for a disease-modifying biologic therapy in pSS
Blocking T cell co-stimulation in primary Sjögren's syndrome:rationale, clinical efficacy and modulation of peripheral and salivary gland biomarkers
There is accumulating evidence that patients with primary Sjögren's syndrome (pSS) display aberrant CD4+ T cell responses, both in the peripheral compartment and in the inflamed salivary glands. CD4+ T cell abnormalities are also critically associated with B cell hyper activation, one of the hallmarks of disease, which is linked with disease severity and evolution to lymphoma. T cell activation and the cross-talk between T and B cells are tightly regulated by the balance between co-stimulatory pathways, such as the interactions between CD80/CD86:CD28, CD40:CD40L and ICOS:ICOSL, and co-inhibitory signals, including the immunoregulatory CTLA-4 protein. Evidence from patients with pSS as well as data from animal models of the disease suggests that these pathways play a critical role in pSS pathogenesis and their targeting could be exploited for therapeutic purposes. In this review, we first summarise the evidence implicating aberrant T cell co-stimulation and co-inhibition in driving the disease before focusing on the results of recent randomised controlled trials (RCTs) with compounds able to block T cell co-stimulation and enhance T cell co-inhibition. Despite a clear biological effect on downstream B cell activation has been observed in patients treated with CTLA-4-Ig (abatacept) and with monoclonal antibodies targeting CD40 and ICOSL, the clinical efficacy of this approach has so far yielded mixed results; while the anti-CD40 monoclonal antibody iscalimab showed significant improvement in systemic disease activity compared to placebo, two large RCTs with abatacept and a phase IIa RCT with an anti-ICOSL monoclonal antibody (prezalumab) failed to reach their primary endpoints. Although the discrepancies between biological and clinical efficacy of targeting T cell co-stimulation on pSS remain unresolved, several factors including drug bioavailability and receptor occupancy, patient stratification based on T-cell related biomarkers and the choice of study outcome are likely to play an important role and form the basis for further work towards the quest for a disease-modifying biologic therapy in pSS
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