3,676 research outputs found
The origin of galaxy scaling laws in LCDM
It has long been recognized that tight relations link the mass, size, and
characteristic velocity of galaxies. These scaling laws reflect the way in
which baryons populate, cool, and settle at the center of their host dark
matter halos; the angular momentum they retain in the assembly process; as well
as the radial distribution and mass scalings of the dark matter halos. There
has been steady progress in our understanding of these processes in recent
years, mainly as sophisticated N-body and hydrodynamical simulation techniques
have enabled the numerical realization of galaxy models of ever increasing
complexity, realism, and appeal. These simulations have now clarified the
origin of these galaxy scaling laws in a universe dominated by cold dark
matter: these relations arise from the tight (but highly non-linear) relations
between (i) galaxy mass and halo mass, (ii) galaxy size and halo characteristic
radius; and (iii) from the self-similar mass nature of cold dark matter halo
mass profiles. The excellent agreement between simulated and observed galaxy
scaling laws is a resounding success for the LCDM cosmogony on the highly
non-linear scales of individual galaxies.Comment: Contribution to the Proceedings of the Simons Conference
"Illuminating Dark Matter", held in Kruen, Germany, in May 2018, eds. R.
Essig, K. Zurek, J. Fen
RAFCON: a Graphical Tool for Task Programming and Mission Control
There are many application fields for robotic systems including service
robotics, search and rescue missions, industry and space robotics. As the
scenarios in these areas grow more and more complex, there is a high demand for
powerful tools to efficiently program heterogeneous robotic systems. Therefore,
we created RAFCON, a graphical tool to develop robotic tasks and to be used for
mission control by remotely monitoring the execution of the tasks. To define
the tasks, we use state machines which support hierarchies and concurrency.
Together with a library concept, even complex scenarios can be handled
gracefully. RAFCON supports sophisticated debugging functionality and tightly
integrates error handling and recovery mechanisms. A GUI with a powerful state
machine editor makes intuitive, visual programming and fast prototyping
possible. We demonstrated the capabilities of our tool in the SpaceBotCamp
national robotic competition, in which our mobile robot solved all exploration
and assembly challenges fully autonomously. It is therefore also a promising
tool for various RoboCup leagues.Comment: 8 pages, 5 figure
The Imprint of Galaxy Formation on X-ray Clusters
It is widely believed that structure in the Universe evolves hierarchically,
as primordial density fluctuations, amplified by gravity, collapse and merge to
form progressively larger systems. The structure and evolution of X-ray
clusters, however, seems at odds with this hierarchical scenario for structure
formation. Poor clusters and groups, as well as most distant clusters detected
to date, are substantially fainter than expected from the tight relations
between luminosity, temperature and redshift predicted by these models. Here we
show that these discrepancies arise because, near the centre, the entropy of
the hot, diffuse intracluster medium (ICM) is higher tha possible if the ICM
is heated at modest redshift (z \ltsim 2) but prior to cluster collapse,
indicating that the formation of galaxies precedes that of clusters and that
most clusters have been assembled very recently.Comment: 5 pages, plus 2 postscript figures (one in colour), accepted for
publication in Natur
Galaxy clusters - Well of darkness
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62854/1/394122a0.pd
Recommended from our members
Wintertime Transport of Reactive Trace Gases From East Asia Into the Deep Tropics
THE EFFECTS OF OBSTACLE SHAPE AND VISCOSITY IN DEEP ROTATING FLOW OVER FINITE-HEIGHT TOPOGRAPHY
The limiting process introduced by Stewartson & Cheng (1979) is used to obtain solutions in the limit of vanishing Rossby number for deep rotating flows at arbitrary Reynolds number over cross-stream ridges of finite slope. Examination of inviscid solutions for infinite-depth flow shows strong dependence on obstacle shape of not only the magnitudes but also the positions of disturbances in the far field. In finite-depth flow there is present the Stewartson & Cheng inertial wave wake, which may be expressed as a sum of vertical modes whose amplitudes depend on the obstacle shape but are independent of distance downstream; the smoother the topography and the shallower the flow, the fewer the number of modes required to describe the motion. For abrupt topography the strength of the wake does not, however, decrease monoton- ically with decreasing container depth (or Rossby number). In very deep flows viscosity causes the wake to decay on a length scale of order the Reynolds number times the ridge width. In shallower flows, where only a few modes are present, the decay of the wake is more rapid. For Reynolds numbers and depths of the order of those in the experiments of Hide, Ibbetson & Lighthill (1968)) viscosity causes the disturbance to take on the appearance of a leaning column
Mirror Dark Matter
There appear to be three challenges that any theory of dark matter must face:
(i) why is of the same order as ? (ii) what
are the near solar mass objects () observed by the MACHO
microlensing project ? and (iii) understanding the shallow core density profile
of the halos of dwarf as well as low surface brightness galaxies. The popular
cold dark matter candidates, the SUSY LSP and the axion fail to meet these
challenges. We argue that in the mirror model suggested recently to explain the
neutrino anomalies, the mirror baryons being 15-20 times heavier than familiar
baryons, can play the role of the cold dark matter and provide reasonable
explanation of all three above properties without extra assumptions.Comment: Latex, 10 pages; Invited talk presented in PASCOS99 workshop, held in
Lake Tahoe, Dec. 1999 and DM2000 workshop held in Los Angeles, February, 200
On the use of surfaces of section in the Nâbody ring problem
In the Nâbody ring problem, we investigate the motion of a massless body interacting with N bodies of equal masses at the vertices of a regular polygon that rotates around a central mass. In this paper, we analyze the use of different surfaces of section in the numerical exploration of the escape in the Nâbody ring problem in order to get some conclusions about the geometry of the basins of escape in the corresponding configuration spaces
Neutralino dark matter vs galaxy formation
Neutralino dark matter may be incompatible with current cold dark matter
models with cuspy dark halos, because excessive synchrotron radiation may
originate from neutralino annihilations close to the black hole at the galactic
center.Comment: 6 pages, 3 figures, talk given at "Sources and detection of dark
matter in the Universe", Marina del Rey, CA, February 23-25, 200
Finding repeatable progressive pass clusters and application in international football
Progressive passing in football (soccer) is a key aspect in creating positive possession outcomes. Whilst this is well established, there is not a consistent way to describe the different types of progressive passes. We expand on the previous literature, providing a complete methodological approach to progressive pass clustering from selection of the number of clusters (k) to risk-reward profiling of these progressive pass types. In this paper the Separation and Concordance (SeCo) framework is utilised to provide a process to analyse k-means clustering solutions in a more repeatable way. The results demonstrate that we can find stable progressive pass clusters in International Football and their efficacy with progressive passes âMid Central to Mid Half Spaceâ in build-up and âMid Half Space to Final Centralâ into the final 3rd having the best balance between risk (turnover) and reward (shot created) in the subsequent possession. This allowed for opposition profiling of player and team patterns in different phases of play, with a case study presented for the teams in the Last 16 of the 2022 World Cup
- âŠ