807 research outputs found
Effects of very high turbulence on convective heat transfer
The effects of high-intensity, large-scale turbulence on turbulent boundary-layer heat transfer are studied. Flow fields were produced with turbulence intensities up to 40% and length scales up to several times the boundary layer thickness. In addition, three different types of turbulence will be compared to see whether they have the same effect on the boundary layer. The three are: the far field of a free jet, flow downstream of a grid, and flow downstream of a simulated gas turbine combustor. Each turbulence field will be characterized by several measures: intensity (by component), scale, and spectrum. Heat transfer will be measured on a 2.5 m long, 0.5 m wide flat plate using the energy-balance technique. The same plate will be used in each of the four flow fields; a low-turbulence tunnel for baseline data, and the three flow situations mentioned
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Food System Transformation: Integrating a Political-Economy and Social-Ecological Approach to Regime Shifts.
Sustainably achieving the goal of global food security is one of the greatest challenges of the 21st century. The current food system is failing to meet the needs of people, and at the same time, is having far-reaching impacts on the environment and undermining human well-being in other important ways. It is increasingly apparent that a deep transformation in the way we produce and consume food is needed in order to ensure a more just and sustainable future. This paper uses the concept of regime shifts to understand key drivers and innovations underlying past disruptions in the food system and to explore how they may help us think about desirable future changes and how we might leverage them. We combine two perspectives on regime shifts-one derived from natural sciences and the other from social sciences-to propose an interpretation of food regimes that draws on innovation theory. We use this conceptualization to discuss three examples of innovations that we argue helped enable critical regime shifts in the global food system in the past: the Haber-Bosch process of nitrogen fixation, the rise of the supermarket, and the call for more transparency in the food system to reconnect consumers with their food. This paper concludes with an exploration of why this combination of conceptual understandings is important across the Global North/ Global South divide, and proposes a new sustainability regime where transformative change is spearheaded by a variety of social-ecological innovations
PF191012 Myszyniec - highest Orionid meteor ever recorded
On the night of Oct 18/19, 2012 at 00:23 UT a -14.7 mag Orionid fireball
occurred over northeastern Poland. The precise orbit and atmospheric trajectory
of the event is presented, based on the data collected by five video and one
photographic Polish Fireball Network (PFN) stations. The beginning height of
the meteor is 168.4 +\- 0.6 km which makes the PF191012 Myszyniec fireball the
highest ever observed, well documented meteor not belonging to the Leonid
shower. The ablation became the dominant source of light of the meteor at a
height of around 115 km. The thermalization of sputtered particles is suggested
to be the source of radiation above that value. The transition height of 115 km
is 10-15 km below the transition heights derived for Leonids and it might
suggest that the material of Leonids should be more fragile and have probably
smaller bulk density than in case of Orionids.Comment: 5 pages, 5 figures, accpeted for publication in Astronomy &
Astrophysic
A Magellan-IMACS-IFU Search for Dynamical Drivers of Nuclear Activity. I. Reduction Pipeline and Galaxy Catalog
Using the Inamori Magellan Areal Camera and Spectrograph (IMACS)
integral-field unit (IFU) on the 6.5m Magellan telescope, we have designed the
first statistically significant investigation of the two-dimensional
distribution and kinematics of ionized gas and stars in the central kiloparsec
regions of a well-matched sample of Seyfert and inactive control galaxies
selected from the Sloan Digital Sky Survey. The goals of the project are to use
the fine spatial sampling (0.2 arcsec/pixel) and large wavelength coverage
(4000-7000A) of the IMACS-IFU to search for dynamical triggers of nuclear
activity in the central region where active galactic nucleus (AGN) activity and
dynamical timescales become comparable, to identify and assess the impact of
AGN-driven outflows on the host galaxy and to provide a definitive sample of
local galaxy kinematics for comparison with future three-dimensional kinematic
studies of high-redshift systems. In this paper, we provide the first detailed
description of the procedure to reduce and calibrate data from the IMACS-IFU in
`long mode' to obtain two-dimensional maps of the distribution and kinematics
of ionized gas and stars. The sample selection criteria are presented,
observing strategy described and resulting maps of the sample galaxies
presented along with a description of the observed properties of each galaxy
and the overall observed properties of the sample.Comment: 62 pages. 41 figures. 5 tables. Accepted for publication in ApJS.
High-resolution version available at:
http://www.astro.ljmu.ac.uk/~pbw/IMACS-IFU/IMACS-1-highRes.pd
Darboux points and integrability of homogeneous Hamiltonian systems with three and more degrees of freedom
We consider natural complex Hamiltonian systems with degrees of freedom
given by a Hamiltonian function which is a sum of the standard kinetic energy
and a homogeneous polynomial potential of degree . The well known
Morales-Ramis theorem gives the strongest known necessary conditions for the
Liouville integrability of such systems. It states that for each there
exists an explicitly known infinite set \scM_k\subset\Q such that if the
system is integrable, then all eigenvalues of the Hessian matrix V''(\vd)
calculated at a non-zero \vd\in\C^n satisfying V'(\vd)=\vd, belong to
\scM_k. The aim of this paper is, among others, to sharpen this result. Under
certain genericity assumption concerning we prove the following fact. For
each and there exists a finite set \scI_{n,k}\subset\scM_k such that
if the system is integrable, then all eigenvalues of the Hessian matrix
V''(\vd) belong to \scI_{n,k}. We give an algorithm which allows to find
sets \scI_{n,k}. We applied this results for the case and we found
all integrable potentials satisfying the genericity assumption. Among them
several are new and they are integrable in a highly non-trivial way. We found
three potentials for which the additional first integrals are of degree 4 and 6
with respect to the momenta.Comment: 54 pages, 1 figur
Magnetic Flux Expulsion in the Powerful Superbubble Explosions and the Alpha-Omega Dynamo
The possibility of the magnetic flux expulsion from the Galaxy in the
superbubble (SB) explosions, important for the Alpha-Omega dynamo, is
considered. Special emphasis is put on the investigation of the downsliding of
the matter from the top of the shell formed by the SB explosion which is able
to influence the kinematics of the shell. It is shown that either Galactic
gravity or the development of the Rayleigh-Taylor instabilities in the shell
limit the SB expansion, thus, making impossible magnetic flux expulsion. The
effect of the cosmic rays in the shell on the sliding is considered and it is
shown that it is negligible compared to Galactic gravity. Thus, the question of
possible mechanism of flux expulsion in the Alpha-Omega dynamo remains open.Comment: MNRAS, in press, 11 pages, 9 figure
Regular Orbits and Periodic Loops in Multiply-Barred Galactic Potentials
We show that non-chaotic multiply-periodic particle orbits can exist in a
galaxy-like potential where a small fast-tumbling nuclear bar is nested inside
a main bar which has a slower pattern speed. We introduce the concept of a
loop: a one-dimensional curve such that particles distributed along it at some
initial instant return to the same curve (as viewed in the rotating frame of
one of the bars) after the bars return to the same relative position. Just as
particles following regular orbits in a simply-barred potential are trapped
around closed periodic orbits, so regular orbits in a doubly-barred potential
oscillate about stable loops. We find both loops which remain aligned with the
inner bar and loops aligned with the outer bar: particles trapped around these
loops could form the building blocks for a long-lived, self-consistent,
doubly-barred galaxy. In a realistic doubly-barred galaxy potential, we
demonstrate the existence of stable loops which support the structure of the
inner bar. We use the epicyclic approximation to preview the pattern of gas
flow in a doubly-barred potential.Comment: 6 pages, 1 figure, submitted to ApJ Letter
CCD BV and 2MASS photometric study of the open cluster NGC 1513
We present CCD BV and JHK 2MASS photometric data for the open cluster
NGC 1513. We observed 609 stars in the direction of the cluster up to a
limiting magnitude of mag. The star count method shows that the
centre of the cluster lies at ,
and its angular size is arcmin.
The optical and near-infrared two-colour diagrams reveal the colour excesses in
the direction of the cluster as , and
mag. These results are consistent with normal
interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of
mag, which can be translated into a distance of
pc. Finally, using Padova isochrones we determined the metallicity
and age of the cluster as ( dex) and
, respectively.Comment: 15 pages, 12 figures and 4 tables, accepted for publication in
Astrophysics & Space Scienc
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