105 research outputs found
Roche Lobe Shapes for testing MOND-like Modified Gravity
Dark Matter (DM) theories and mass-tracing-light theories like MOND are by
construction nearly degenerate on galactic scales, but not when it comes to the
predicted shapes of Roche Lobes of a two-body system (e.g., a globular cluster
orbiting a host galaxy). We show that the flattening of the Roche lobe is
sensitive to the function mu(g) in modification of the law of gravity. We
generalise the analytical results obtained in the deep-MOND limit by Zhao
(2005, astro-ph/0511713 and astro-ph/0512425), and consider a binary in the
framework of a MOND-like gravity modification function mu(g) or a general
non-Keplerian gravity g \propto R^-\zeta. We give analytical expressions for
the inner Lagrange point and Robe lobe axis ratios. The Roche lobe volume is
proven to scale linearly with the true mass ratio, which applies to any mu(g),
hence mass-tracing light models would overpredict the Roche lobe of a DM-poor
globular cluster in a DM-rich host galaxy, and underpredict the size of a
DM-richer dwarf satellite. The lobes are squashed with the flattening ~ 0.4 in
the strong gravity and ~ 0.6 in the weak gravity; a precise measurement of the
flattening could be used to verify the anisotropic dilation effect which is
generic to MOND-like gravity. We generalise these results for extended mass
distribution, and compare predicted Roche radii in different gravity theories
with limiting radii of observed globular clusters and dwarf galaxy satellites.Comment: 11p, 7 figs, accepted for Astronomy and Astrophysic
InstructSeq: Unifying Vision Tasks with Instruction-conditioned Multi-modal Sequence Generation
Empowering models to dynamically accomplish tasks specified through natural
language instructions represents a promising path toward more capable and
general artificial intelligence. In this work, we introduce InstructSeq, an
instruction-conditioned multi-modal modeling framework that unifies diverse
vision tasks through flexible natural language control and handling of both
visual and textual data. InstructSeq employs a multimodal transformer
architecture encompassing visual, language, and sequential modeling. We utilize
a visual encoder to extract image features and a text encoder to encode
instructions. An autoregressive transformer fuses the representations and
generates sequential task outputs. By training with LLM-generated natural
language instructions, InstructSeq acquires a strong comprehension of free-form
instructions for specifying visual tasks. This provides an intuitive interface
for directing capabilities using flexible natural instructions. Without any
task-specific tuning, InstructSeq achieves compelling performance on semantic
segmentation, referring expression segmentation/comprehension, and image
captioning. The flexible control and multi-task unification empower the model
with more human-like versatility and generalizability for computer vision. The
code will be released soon at https://github.com/rongyaofang/InstructSeq.Comment: 10 page
The Relaxin Gene Knockout Mouse: A Model of Progressive Scleroderma
Relaxin is a peptide hormone with anti-fibrotic properties. To investigate the long-term effects of relaxin deficiency on the ageing skin, we compared structural changes in the skin of ageing relaxin-deficient (RLX-/-) and normal (RLX+/+) mice, by biochemical, histological, and magnetic resonance imaging analyses. Skin biopsies from RLX+/+ and RLX-/- mice were obtained at different ages and analyzed for changes in collagen expression and distribution. We demonstrated an age-related progression of dermal fibrosis and thickening in male and female RLX-/- mice, associated with marked increases in types I and III collagen. The increased collagen was observed primarily in the dermis of RLX-/- mice by 1 mo of age, and eventually superseded the hypodermal layer. Additionally, fibroblasts from the dermis of RLX-/- mice were shown to produce increased collagen in vitro. Recombinant human gene-2 (H2) relaxin treatment of RLX-/- mice resulted in the complete reversal of dermal fibrosis, when applied to the early onset of disease, but was ineffective when applied to more established stages of dermal scarring. These combined findings demonstrate that relaxin provides a means to regulate excessive collagen deposition in disease states characterized by dermal fibrosis and with our previously published work demonstrate the relaxin-null mouse as a model of progressive scleroderma
Galaxy Bulges As Tests of CDM vs MOND in Strong Gravity
The tight correlation between galaxy bulges and their central black hole
masses likely emerges in a phase of rapid collapse and starburst at high
redshift, due to the balance of gravity on gas with the feedback force from
starbursts and the wind from the black hole; the average gravity on per unit
mass of gas is ~ 2 x 10^-10 m/sec^2 during the star burst phase. This level of
gravity could come from the real r^{-1} cusps of Cold Dark Matter (CDM) halos,
but the predicted gravity would have a large scatter due to dependence on
cosmological parameters and formation histories. Better agreement is found with
the gravity from the scalar field in some co-variant versions of MOND, which
can create the mirage of a Newtonian effective dark halo of density Pi r^{-1}
near the center, where the characteristic surface density Pi=130alpha^{-1} Msun
pc^{-2} and alpha is a fundamental constant of order unity fixed by the
Lagrangian of the co-variant theory if neglecting environmental effects.
We show with a toy analytical model and a hydrodynamical simulation that a
constant background gravity due to MOND/TeVeS scalar field implies a critical
pressure synchronizing starbursts and the formation of galaxy bulges and
ellipticals. A universal threshold for the formation of the brightest regions
of galaxies in a MONDian universe suggests that the central BHs, bulges and
ellipticals would respect tight correlations like the M_{bulge}-M_{BH}-sigma
relations. In general MOND tends to produce tight correlations in galaxy
properties because its effective halo has less freedom and scatter than CDM
halos.Comment: 30p, 6 figs, expanded. Accpeted for Ap
A proportional hazards model for time-to-event data with epidemiological bias
In hepatitis C virus (HCV) epidemiological studies, the estimation of progression to cirrhosis and prognostic effects of associated risk factors is of particular importance when projecting national disease burden. However, the progression estimates obtained from conventional methods could be distorted due to a referral bias (Fu et al., 2007). In recent years, several approaches have been developed to handle this epidemiological bias in analyzing time-to-event data. This paper proposes a new estimation approach for this problem under a semiparametric proportional hazards framework. The new method uses a martingale approach based on the mean rate function, rather than the traditional hazard rate function, and develops an iterative algorithm to estimate the Cox regression parameter and baseline hazard rate simultaneously. The consistency and asymptotic properties of the proposed estimators are derived theoretically and evaluated via simulation studies. The new method is also applied to a real HCV cohort study
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