276 research outputs found
Plume motion and large-scale circulation in a cylindrical Rayleigh-B\'enard cell
We used the time correlation of shadowgraph images to determine the angle
of the horizontal component of the plume velocity above (below) the
center of the bottom (top) plate of a cylindrical Rayleigh-B\'enard cell of
aspect ratio ( is the diameter and mm
the height) in the Rayleigh-number range for a Prandtl number . We expect that gives the
direction of the large-scale circulation. It oscillates time-periodically. Near
the top and bottom plates has the same frequency but is
anti-correlated.Comment: 4 pages, 6 figure
Biocultural diversity : a novel concept to assess human-nature interrelations, nature conservation and stewardship in cities
Biocultural diversity is an evolving perspective for studying the interrelatedness between people and their natural environment, not only in ecoregional hotspots and cultural landscapes, but also in urban green spaces. Developed in the 1990s in order to denote the diversity of life in all its manifestations. biological, cultural and linguistic. co-evolving within complex socio-ecological systems such as cities, biocultural diversity was identified in the GREEN SURGE project as a response to recent challenges cities face. Most important challenges are the loss of nature and degradation of ecosystems in and around cities as well as an alienation of urban residents from and loss of interaction with nature. The notion of biocultural diversity is dynamic in nature and takes local values and practices of relating to biodiversity of different cultural groups as a starting point for sustainable living with biodiversity. The issue is not only how to preserve or restore biocultural practices and values, but also how to modify, adapt and create biocultural diversity in ways that resonate with urban transformations. As future societies will largely diverge from today's societies, the cultural perspective on living with (urban) nature needs careful reconsideration. Biocultural diversity is not conceived as a definite concept providing prescriptions of what to see and study, but as a reflexive and sensitising concept that can be used to assess the different values and knowledge of people that reflect how they live with biodiversity. This short communication paper introduces a conceptual framework for studying the multi-dimensional features of biocultural diversity in cities along the three key dimensions of materialized, lived and stewardship, being departure points from which biocultural diversity can be studied.Peer reviewe
A Search for Wolf-Rayet Stars in the Small Magellanic Cloud
We conducted an extensive search for Wolf-Rayet stars (W-Rs) in the SMC,
using the same interference filter imaging techniques that have proved
successful in finding W-Rs in more distant members of the Local Group.
Photometry of some 1.6 million stellar images resulted in some 20 good
candidates, which we then examined spectroscopically. Two of these indeed
proved to be newly found W-Rs, bringing the total known in the SMC from 9 to
11. Other finds included previously unknown Of-type stars (one as early as
O5f?p)),the recovery of the Luminous Blue Variable S18, and the discovery of a
previously unknown SMC symbiotic star. More important, however, is the fact
that there does not exist a significant number of W-Rs waiting to be discovered
in the SMC. The number of W-Rs in the SMC is a factor of 3 lower than in the
LMC (per unit luminosity), and we argue this is the result of the SMC's low
metallicity on the evolution of the most massive stars.Comment: Accepted by Astrophysical Journal. Postscript version available via
ftp.lowell.edu/pub/massey/smcwr.ps.gz Revised version contains slightly
revised spectral types for the Of stars but is otherwise unchange
Dense Plasma Focus: physics and applications (radiation material science, single-shot disclosure of hidden illegal objects, radiation biology and medicine, etc.)
The paper presents some outcomes obtained during the year of 2013 of the activity in the frame of the International Atomic Energy Agency Co-ordinated research project "Investigations of Materials under High Repetition and Intense Fusion-Relevant Pulses". The main results are related to the effects created at the interaction of powerful pulses of different types of radiation (soft and hard X-rays, hot plasma and fast ion streams, neutrons, etc. generated in Dense Plasma Focus (DPF) facilities) with various materials including those that are counted as perspective ones for their use in future thermonuclear reactors. Besides we discuss phenomena observed at the irradiation of biological test objects. We examine possible applications of nanosecond powerful pulses of neutrons to the aims of nuclear medicine and for disclosure of hidden illegal objects. Special attention is devoted to discussions of a possibility to create extremely large and enormously diminutive DPF devices and probabilities of their use in energetics, medicine and modern electronics
Steps towards the hyperfine splitting measurement of the muonic hydrogen ground state: pulsed muon beam and detection system characterization
The high precision measurement of the hyperfine splitting of the
muonic-hydrogen atom ground state with pulsed and intense muon beam requires
careful technological choices both in the construction of a gas target and of
the detectors. In June 2014, the pressurized gas target of the FAMU experiment
was exposed to the low energy pulsed muon beam at the RIKEN RAL muon facility.
The objectives of the test were the characterization of the target, the
hodoscope and the X-ray detectors. The apparatus consisted of a beam hodoscope
and X-rays detectors made with high purity Germanium and Lanthanum Bromide
crystals. In this paper the experimental setup is described and the results of
the detector characterization are presented.Comment: 22 pages, 14 figures, published and open access on JINS
Quantitative analysis of WC stars: Constraints on neon abundances from ISO/SWS spectroscopy
Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11,
WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) -
using mid-infrared fine structure lines obtained with ISO/SWS. Stellar
parameters for each star are derived using a non-LTE model atmospheric code
(Hillier & Miller 1998) together with ultraviolet (IUE), optical (INT, AAT) and
infrared (UKIRT, ISO) spectroscopy. In the case of gamma Vel, we adopt results
from De Marco et al. (2000), who followed an identical approach.
ISO/SWS datasets reveal the [NeIII] 15.5um line in each of our targets, while
[NeII] 12.8um, [SIV] 10.5um and [SIII] 18.7um are observed solely in gamma Vel.
Using a method updated from Barlow et al. (1988) to account for clumped winds,
we derive Ne/He=3-4x10^-3 by number, plus S/He=6x10^-5 for gamma Vel. Neon is
highly enriched, such that Ne/S in gamma Vel is eight times higher than cosmic
values. However, observed Ne/He ratios are a factor of two times lower than
predictions of current evolutionary models of massive stars. An imprecise
mass-loss and distance were responsible for the much greater discrepancy in
neon content identified by Barlow et al.
Our sample of WC5--8 stars span a narrow range in T* (=55--71kK), with no
trend towards higher temperature at earlier spectral type, supporting earlier
results for a larger sample by Koesterke & Hamann (1995). Stellar luminosities
range from 100,000 to 500,000 Lo, while 10^-5.1 < Mdot/(Mo/yr) < 10^-4.5,
adopting clumped winds, in which volume filling factors are 10%. In all cases,
wind performance numbers are less than 10, significantly lower than recent
estimates. Carbon abundances span 0.08 < C/He < 0.25 by number, while oxygen
abundances remain poorly constrained.Comment: 16 pages,7 figures accepted for MNRA
First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen
We report the first measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in a gaseous target, made of a H2/O2 mixture, exposed to a muon beam. This work sets constraints on theoretical models of muon transfer and is of fundamental importance for the measurement of the hyperfine splitting of muonic hydrogen ground state as proposed by the FAMU collaboration
First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen
We report the first measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in a gaseous target, made of a H2/O2 mixture, exposed to a muon beam. This work sets constraints on theoretical models of muon transfer and is of fundamental importance for the measurement of the hyperfine splitting of muonic hydrogen ground state as proposed by the FAMU collaboration
Spatially resolved STIS spectra of WR+OB binaries with colliding winds
We present spatially resolved spectra of the visual WR+OB massive binaries
WR86, WR146, and WR147, obtained with the Space Telescope Imaging Spectrograph
on board the Hubble Space Telescope. The systems are classified as follows:
WR86 = WC7 + B0 III, WR146 = WC6 + O8 I-IIf, WR147 = WN8 + O5-7 I-II(f). Both
WR146 and WR147 are known to have strong non-thermal radio emission arising in
a wind-wind collision shock zone between the WR and OB components. We find that
the spectra of their O companions show Halpha profiles in emission, indicative
of large mass-loss rates, and consistent with the colliding-wind model. Our
spectra indicate that the B component in WR86 has a low mass-loss rate, which
possibly explains the fact that WR86, despite being a long period WR+OB binary,
was not found to be a strong non-thermal radio emitter. Because of the small
mass-loss rate of the B star component in WR86, the wind collision region must
be closer to the B star and smaller in effective area, hence generating smaller
amounts of non-thermal radio emission. Absolute magnitudes for all the stars
are estimated based on the spectral types of the components (based on the
tables by Schmidt-Kaler for OB stars, and van der Hucht for WR stars), and
compared with actual, observed magnitude differences. While the derived
luminosities for the WC7 and B0 III stars in WR86 are consistent with the
observed magnitude difference, we find a discrepancy of at least 1.5 magnitudes
between the observed luminosities of the components in each of WR146 and WR147
and the absolute magnitudes expected from their spectral types. In both cases,
it looks as though either the WR components are about 2 magnitudes too bright
for their spectral types, or that the O components are about 2 magnitudes too
faint. We discuss possible explanations for this apparent discrepancy.Comment: Accepted for publication in the Astronomical Journa
Interacting Supernovae: Types IIn and Ibn
Supernovae (SNe) that show evidence of strong shock interaction between their
ejecta and pre-existing, slower circumstellar material (CSM) constitute an
interesting, diverse, and still poorly understood category of explosive
transients. The chief reason that they are extremely interesting is because
they tell us that in a subset of stellar deaths, the progenitor star may become
wildly unstable in the years, decades, or centuries before explosion. This is
something that has not been included in standard stellar evolution models, but
may significantly change the end product and yield of that evolution, and
complicates our attempts to map SNe to their progenitors. Another reason they
are interesting is because CSM interaction is an efficient engine for making
bright transients, allowing super-luminous transients to arise from normal SN
explosion energies, and allowing transients of normal SN luminosities to arise
from sub-energetic explosions or low radioactivity yield. CSM interaction
shrouds the fast ejecta in bright shock emission, obscuring our normal view of
the underlying explosion, and the radiation hydrodynamics of the interaction is
challenging to model. The CSM interaction may also be highly non-spherical,
perhaps linked to binary interaction in the progenitor system. In some cases,
these complications make it difficult to definitively tell the difference
between a core-collapse or thermonuclear explosion, or to discern between a
non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical
parameters of individual events and connections to possible progenitor stars
make this a rapidly evolving topic that continues to challenge paradigms of
stellar evolution.Comment: Final draft of a chapter in the "SN Handbook". Accepted. 25 pages, 3
fig
- …