158 research outputs found
Finding a third archetypal technical system in architectural phenomenology
Within the scope of phenomenology and in order to understand architecture, the role of the technical system is as important as those of the purpose of the building or its form. Mass construction and skeletal construction relate to the architectural theory concepts stereotomy and tectonics respectively, which are suitable for describing the fundamental structural and constructive form of architecture. These two systems became established as man built his first shelters and, so far, represented opposite sides of the building industry’s possibilities. The development of new construction techniques and the relationship between research and technology have a great impact on architecture, although new processing methods and materials may not necessarily cause genuine tectonic changes. The technical dimension of architecture is analysed in this work describing how technical elements are built from materials, and then organised in systems. First, the paper examines the division of technical systems in two categories (massive systems and skeletal systems); then it studies timber’s modern production technologies and subsequently the paper critically analyses how these influence the architectural form. The paper concludes that a third archetypal technical system can be perceived with the assembly of surface elements, joining both the multifunctional aspect of the massive systems and the flexibility of the skeletal systems, this third category being fundamental in phenomenological terms
The structure of the nuclear stellar cluster of the Milky Way
We present high-resolution seeing limited and AO NIR imaging observations of
the stellar cluster within about one parsec of Sgr A*, the massive black hole
at the centre of the Milky Way. Stellar number counts and the diffuse
background light density were extracted from these observations in order to
examine the structure of the nuclear stellar cluster.Our findings are as
follows: (a) A broken-power law provides an excellent fit to the overall
structure of the GC nuclear cluster. The power-law slope of the cusp is
, the break radius is or
pc, and the cluster density decreases with a power-law index of
outside of . (b) Using the best velocity
dispersion measurements from the literature, we derive higher mass estimates
for the central parsec than assumed until now. The inferred density of the
cluster at the break radius is . This high density agrees well with the small extent and flat slope
of the cusp. Possibly, the mass of the stars makes up only about 50% of the
total cluster mass. (c) Possible indications of mass segregation in the cusp
are found (d) The cluster appears not entirely homogeneous. Several density
clumps are detected that are concentrated at projected distances of and
from Sgr A*.(e) There appears to exist an under-density of horizontal
branch/red clump stars near , or an over-density of stars of similar
brightness at and . (f) The extinction map in combination with
cometary-like features in an L'-band image may provide support for the
assumption of an outflow from Sgr A*.Comment: accepted for publication by A&A; please contact first author for
higher quality figure
Traces of past activity in the Galactic Centre
The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of
~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an
extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known
Eddington ratio BH. However, it was not always so; traces of "glorious" active
periods can be found in the surrounding medium. We review here our current view
of the X-ray emission from the Galactic Center (GC) and its environment, and
the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the
history of Sgr A*'s past activity and its impact on the surrounding medium. The
structure of the Central Molecular Zone (CMZ) has not changed significantly
since the last active phase of Sgr A*. This relic torus provides us with the
opportunity to image the structure of an AGN torus in exquisite detail.Comment: Invited refereed review. Chapter of the book: "Cosmic ray induced
phenomenology in star forming environments" (eds. Olaf Reimer and Diego F.
Torres
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
The frequency of metal enrichment of cool helium-atmosphere white dwarfs using the DESI early data release
There is an overwhelming evidence that white dwarfs host planetary systems; revealed by the presence, disruption, and accretion of planetary bodies. A lower limit on the frequency of white dwarfs that host planetary material has been estimated to be ≃ 25–50 per cent; inferred from the ongoing or recent accretion of metals on to both hydrogen-atmosphere and warm helium-atmosphere white dwarfs. Now with the unbiased sample of white dwarfs observed by the Dark Energy Spectroscopic Instrument (DESI) survey in their Early Data Release (EDR), we have determined the frequency of metal enrichment around cool-helium atmosphere white dwarfs as 21 ± 3 per cent using a sample of 234 systems. This value is in good agreement with values determined from previous studies. With the current samples we cannot distinguish whether the frequency of planetary accretion varies with system age or host-star mass, but the DESI data release 1 will contain roughly an order of magnitude more white dwarfs than DESI EDR and will allow these parameters to be investigated
Report of the Snowmass 2021 Topical Group on Lattice Gauge Theory
Lattice gauge theory continues to be a powerful theoretical and computational
approach to simulating strongly interacting quantum field theories, whose
applications permeate almost all disciplines of modern-day research in
High-Energy Physics. Whether it is to enable precision quark- and lepton-flavor
physics, to uncover signals of new physics in nucleons and nuclei, to elucidate
hadron structure and spectrum, to serve as a numerical laboratory to reach
beyond the Standard Model, or to invent and improve state-of-the-art
computational paradigms, the lattice-gauge-theory program is in a prime
position to impact the course of developments and enhance discovery potential
of a vibrant experimental program in High-Energy Physics over the coming
decade. This projection is based on abundant successful results that have
emerged using lattice gauge theory over the years: on continued improvement in
theoretical frameworks and algorithmic suits; on the forthcoming transition
into the exascale era of high-performance computing; and on a skillful,
dedicated, and organized community of lattice gauge theorists in the U.S. and
worldwide. The prospects of this effort in pushing the frontiers of research in
High-Energy Physics have recently been studied within the U.S. decadal Particle
Physics Planning Exercise (Snowmass 2021), and the conclusions are summarized
in this Topical Report.Comment: 57 pages, 1 figure. Submitted to the Proceedings of the US Community
Study on the Future of Particle Physics (Snowmass 2021). Topical Group Report
for TF05 - Lattice Gauge Theor
Preliminary Target Selection for the DESI Milky Way Survey (MWS)
International audienceThe DESI Milky Way Survey (MWS) will observe 8 million stars between mag, supplemented by observations of brighter targets under poor observing conditions. The survey will permit an accurate determination of stellar kinematics and population gradients; characterize diffuse substructure in the thick disk and stellar halo; enable the discovery of extremely metal-poor stars and other rare stellar types; and improve constraints on the Galaxy's 3D dark matter distribution from halo star kinematics. MWS will also enable a detailed characterization of the stellar populations within 100 pc of the Sun, including a complete census of white dwarfs. The target catalog from the preliminary selection described here is public
Lattice QCD and Particle Physics
Contribution from the USQCD Collaboration to the Proceedings of the US
Community Study on the Future of Particle Physics (Snowmass 2021).Comment: 27 pp. main text, 4 pp. appendices, 30 pp. reference
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