17,129 research outputs found
Theories of Technological Progress and the British Textile Industry from Kay to Cartwright
Editada en la Fundación Empresa PúblicaLa industria textil británica continúa en el centro del debate sobre la revolución industrial. Las innovaciones técnicas en el período produjeron una aceleración extraordinaria del crecimiento del output y una considerable reducción de los precios de los tejidos. En este trabajo presentamos un estudio de la comunidad de los inventores responsables de la transformación tecnológica, lo que nos permite alcanzar una serie de conclusiones nuevas sobre el ritmo y dirección de la actividad innovadora durante la revolución industrialThe cotton textile industry remains central to all accounts of the first industrial revolution. Innovations in this period precipitated an extraordinary acceleration in the growth of output and a steep decline in the cost of producing all varieties of cloth. In this paper we outline an explanation through an analysis of the community of inventors responsible for the technological transformation, which enables us to offer some generalizations of the pace and pattern of the inventive activity in this period.Publicad
Infrared Spectral Energy Distribution Model for Extremely Young Galaxies
The small grain sizes produced by Type II supernova (SN II) models in young,
metal-poor galaxies make the appearance of their infrared (IR) spectral energy
distribution (SED) quite different from that of nearby, older galaxies. To
study this effect, we have developed a model for the evolution of dust content
and the IR SED of low-metallicity, extremely young galaxies based on Hirashita
et al. (2002). We find that, even in the intense ultraviolet (UV) radiation
field of very young galaxies, small silicate grains are subject to stochastic
heating resulting in a broad temperature distribution and substantial MIR
continuum emission. Larger carbonaceous grains are in thermal equilibrium at T
\simeq 50 - 100K, and they also contribute to the MIR. We present the evolution
of SEDs and IR extinction of very young, low-metallicity galaxies. The IR
extinction curve is also shown. In the first few Myrs, the emission peaks at
\lambda \sim 30-50um at later times dust self-absorption decreases the apparent
grain temperatures, shifting the bulk of the emission into the submillimetre
band. We successfully apply the model to the IR SED of a low metallicity (1/41
Z_\odot) dwarf galaxy SBS0335-052. We find the SED, optical properties and
extinction of the star forming region to be consistent with a very young and
compact starburst. We also predict the SED of another extremely low-metallicity
galaxy, I Zw 18, for future observational tests. Some prospects for future
observations are discussed.Comment: MNRAS in press, pages, 6 figures, using mn2e.cls. Abstract abridge
Control of posture with FES systems
One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints
The HI content of extremely metal-deficient blue compact dwarf galaxies
We have obtained new HI observations with the 100m Green Bank Telescope (GBT)
for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf
(BCD) galaxies, selected from the Sloan Digital Sky Survey spectral data base
to be extremely metal-deficient (12+logO/H<7.6). Neutral hydrogen was detected
in 28 galaxies, a 97% detection rate. Combining the HI data with SDSS optical
spectra for the BCD sample and adding complementary galaxy samples from the
literature to extend the metallicity and mass ranges, we have studied how the
HI content of a galaxy varies with various global galaxian properties. There is
a clear trend of increasing gas mass fraction with decreasing metallicity, mass
and luminosity. We obtain the relation M(HI)/L(g)~L(g)^{-0.3}, in agreement
with previous studies based on samples with a smaller luminosity range. The
median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the
mean gas mass fraction is 0.90+/-0.15, with a lower limit of ~0.65. The HI
depletion time is independent of metallicity, with a large scatter around the
median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass
of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of
~0.2. About 65% of the BCDs in our sample have an effective yield larger than
the true yield, implying that the neutral gas envelope in BCDs is more
metal-deficient by a factor of 1.5-20, as compared to the ionized gas.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Glimmers: Resolving the Privacy/Trust Quagmire
Many successful services rely on trustworthy contributions from users. To
establish that trust, such services often require access to privacy-sensitive
information from users, thus creating a conflict between privacy and trust.
Although it is likely impractical to expect both absolute privacy and
trustworthiness at the same time, we argue that the current state of things,
where individual privacy is usually sacrificed at the altar of trustworthy
services, can be improved with a pragmatic , which allows
services to validate user contributions in a trustworthy way without forfeiting
user privacy. We describe how trustworthy hardware such as Intel's SGX can be
used client-side -- in contrast to much recent work exploring SGX in cloud
services -- to realize the Glimmer architecture, and demonstrate how this
realization is able to resolve the tension between privacy and trust in a
variety of cases
How does star formation proceed in the circumnuclear starburst ring of NGC 6951?
Gas inflowing along stellar bars is often stalled at the location of
circumnuclear rings, that form an effective reservoir for massive star
formation and thus shape the central regions of galaxies. However, how exactly
star formation is proceeding within these circumnuclear starburst rings is
subject of debate. Two main scenarios for this process have been put forward:
In the first the onset of star formation is regulated by the total amount of
gas present in the ring with star forming starting once a mass threshold has
reached in a `random' position within the ring like `popcorn'. In the second
star formation preferentially takes place near the locations where the gas
enters the ring. This scenario has been dubbed `pearls-on-a-string'. Here we
combine new optical IFU data covering the full stellar bar with existing
multi-wavelength data to study in detail the 580 pc radius circumnuclear
starburst ring in the nearby spiral galaxy NGC 6951. Using HST archival data
together with Sauron and Oasis IFU data, we derive the ages and stellar masses
of star clusters as well as the total stellar content of the central region.
Adding information on the molecular gas distribution, stellar and gaseous
dynamics and extinction, we find that the circumnuclear ring in NGC 6951 is
~1-1.5 Gyr old and has been forming stars for most of that time. We see
evidence for preferred sites of star formation within the ring, consistent with
the `pearls-on-a-string' scenario, when focusing on the youngest stellar
populations. Due to the ring's longevity this signature is washed out when
older stellar populations are included in the analysis.Comment: accepted for publication in A&A, 15 page
Measuring categorisation in pre-school children: new toolkit, new insights
Introduction: whilst recent years have witnessed considerable research into infant categorisation, its development during the pre-school period has garnered far less interest and innovation.
Objective: this paper documents the development of a valid and reliable new toolkit for measuring categorisation in children, designed to allow fine-grained differentiation through four short tasks.
Methods: the paper outlines how a pilot study with 55 children reduced confounding variables, ruled out several explanations for performance variations and enabled procedural refinements. It then documents a study conducted with 190 children aged 30-60 months.
Results: this more sophisticated testing mechanism challenges previously accepted developmental norms and suggests both sex and socio-economic status (and their interaction) influence categorisational abilities in pre-schoolers.
Conclusion: the results indicate that preschool children’s ability to categorise varies markedly, with implications for their capacity to access formal education
Herschel observations of gamma-ray burst host galaxies: implications for the topology of the dusty interstellar medium
Long-duration gamma-ray bursts (GRBs) are indisputably related to star
formation, and their vast luminosity in gamma rays pin-points regions of star
formation independent of galaxy mass. As such, GRBs provide a unique tool for
studying star forming galaxies out to high-z independent of luminosity. Most of
our understanding of the properties of GRB hosts (GRBHs) comes from optical and
near-infrared (NIR) follow-up observations, and we therefore have relatively
little knowledge of the fraction of dust-enshrouded star formation that resides
within GRBHs. Currently ~20% of GRBs show evidence of significant amounts of
dust along the line of sight to the afterglow through the host galaxy, and
these GRBs tend to reside within redder and more massive galaxies than GRBs
with optically bright afterglows. In this paper we present Herschel
observations of five GRBHs with evidence of being dust-rich, targeted to
understand the dust attenuation properties within GRBs better. Despite the
sensitivity of our Herschel observations, only one galaxy in our sample was
detected (GRBH 070306), for which we measure a total star formation rate (SFR)
of ~100Mstar/yr, and which had a relatively high stellar mass
(log[Mstar]=10.34+0.09/-0.04). Nevertheless, when considering a larger sample
of GRBHs observed with Herschel, it is clear that stellar mass is not the only
factor contributing to a Herschel detection, and significant dust extinction
along the GRB sightline (A_{V,GRB}>1.5~mag) appears to be a considerably better
tracer of GRBHs with high dust mass. This suggests that the extinguishing dust
along the GRB line of sight lies predominantly within the host galaxy ISM, and
thus those GRBs with A_{V,GRB}>1~mag but with no host galaxy Herschel
detections are likely to have been predominantly extinguished by dust within an
intervening dense cloud.Comment: 14 pages, 7 figures. Accepted for publication in A&
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