15,454 research outputs found
The Value of Design-led Innovation in Chinese SMEs
Organised by: Cranfield UniversityThis paper focuses on understanding the role and use of design-led innovation in Chinese SMEs. The
insights were gained by undertaking a pilot study, based on an applied developmental research approach
involving participatory workshops, quantitative and qualitative positioning activities, in depth case studies
and an individual pilot project undertaken with SMEs in the Pearl River Delta [PRD] over an 18 month
period. It will discuss the findings, highlighting key areas of uncertainty that SMEs experience when
attempting to make the transition from OEM to OBM, and how the findings have contributed to the
development of a new design-led innovation framework.Mori Seiki – The Machine Tool Compan
Strengthening Data Security: an Holistic Approach
In the light of heightened concern around data security, this paper highlights some of the measures that can be used to develop and strengthen security in data archiving. The paper includes discussion of the different approaches that can be taken towards the construction of firm and resilient data and information security policies within the social science data archiving communities. While international standards can provide theoretical guidelines for the construction of such a policy, procedures need to be informed by more practical considerations. Attention is drawn to the necessity of following a holistic approach to data security, which includes the education of data creators in the reduction of disclosure risk, the integration of robust and appropriate data processing, handling and management procedures, the value of emerging technological solutions, the training of data users in data security, and the importance of management control, as well as the need to be informed by emerging government security and digital preservation standards
The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon
Spatial inhomogeneities in the spectral shape of the ultra-violet background
(UVB) at the tail-end of HeII reionisation are thought to be the primary cause
of the large fluctuations observed in the HeII to HI Ly-a forest optical depth
ratio, tau_HeII/tau_HI, at z~2-3. These spectral hardness fluctuations will
also influence the ionisation balance of intergalactic metals; we extract
realistic quasar absorption spectra from a large hydrodynamical simulation to
examine their impact on intergalactic SiIV and CIV absorbers. Using a variety
of toy UVB models, we find that while the predicted spatial inhomogeneities in
spectral hardness have a significant impact on tau_HeII/tau_HI, the longer mean
free path for photons with frequencies above and below the HeII ionisation edge
means these fluctuations have less effect on the SiIV and CIV ionisation
balance. Furthermore, UVB models which produce the largest fluctuations in
specific intensity at the HeII ionisation edge also have the softest ionising
spectra, and thus result in photo-ionisation rates which are too low to produce
significant fluctuations in the observed tau_SiIV/tau_CIV. Instead, we find
spatial variations in the IGM metallicity will dominate any scatter in
tau_SiIV/tau_CIV. Our results suggest that observational evidence for
homogeneity in the observed tau_SiIV/tau_CIV distribution does not rule out the
possibility of significant fluctuations in the UVB spectral shape at z~2-3. On
the other hand, the scatter in metallicity inferred from observations of
intergalactic CIV and SiIV absorption at z~2-3 using spatially uniform
ionisation corrections is likely intrinsic, and therefore provides a valuable
constraint on intergalactic metal enrichment scenarios at these redshifts.Comment: 13 pages, 7 figures, accepted to MNRA
The nature and evolution of the highly ionized near-zones in the absorption spectra of z~6 quasars
We use state-of-the-art hydrodynamical simulations combined with a 1D
radiative transfer code to assess the extent to which the highly ionized
regions observed close to z~6 quasars, which we refer to as near-zones, can
constrain the ionization state of the surrounding IGM. We find the appearance
in Lya absorption of a quasar HII ionization front expanding into a neutral IGM
can be very similar to a classical proximity zone, produced by the enhancement
in ionizing flux close to a quasar embedded in a highly ionized IGM. The
observed sizes of these highly ionized near-zones and their redshift evolution
can be reproduced for a wide range of IGM neutral hydrogen fractions for
plausible values of the luminosity and lifetime of the quasars. The observed
near-zone sizes at the highest observed redshifts are equally consistent with a
significantly neutral and a highly ionized surrounding IGM. Stronger
constraints on the IGM neutral hydrogen fraction can be obtained by considering
the relative size of the near-zones in the Lya and Lyb regions of a quasar
spectrum. A large sample of high quality quasar absorption spectra with
accurate determinations of near-zone sizes and their redshift evolution in both
the Lya and Lyb regions should confirm or exclude the possibility that the
Universe is predominantly neutral at the highest observed redshifts. The width
of the discrete absorption features in these near-zones will contain important
additional information on the ionization state and the previous thermal history
of the IGM at these redshifts.Comment: 25 pages, 11 figures, accepted for publication in MNRA
On the rapid demise of Lyman-alpha emitters at z>7 due to the increasing incidence of optically thick absorption systems
A variety of independent observational studies have now reported a
significant decline in the fraction of Lyman-break galaxies which exhibit Ly-a
emission over the redshift interval z=6-7. In combination with the strong
damping wing extending redward of Ly-a in the spectrum of the bright z=7.085
quasar ULAS 1120+0641, this has strengthened suggestions that the hydrogen in
the intergalactic medium (IGM) is still substantially neutral at z~7. Current
theoretical models imply HI fractions as large as 40-90 per cent may be
required to explain these data assuming there is no intrinsic evolution in the
Ly-a emitter population. We propose that such large neutral fractions are not
necessary. Based on a hydrodynamical simulation which reproduces the absorption
spectra of high-redshift (z~6-7) quasars, we demonstrate that the opacity of
the intervening IGM redward of rest-frame Ly-a can rise rapidly in average
regions of the Universe simply because of the increasing incidence of
absorption systems which are optically thick to Lyman continuum photons as the
tail-end of reionisation is approached. Our simulations suggest these data do
not require a large change in the IGM neutral fraction by several tens of per
cent from z=6-7, but may instead be indicative of the rapid decrease in the
typical mean free path for ionising photons expected during the final stages of
reionisation.Comment: 11 pages, 6 figures, accepted to MNRA
The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
We use a large set of hydrodynamical simulations, combined with measurements
of the Lyman alpha opacity of the IGM taken from the literature, to obtain
robust estimates for the photoionization rate per hydrogen atom at z=5 and 6.
We find the photoionization rate drops by a factor of two and four,
respectively, compared to our recent measurements at z = 2 - 4. The number of
ionizing photons emitted by known sources at z=5 and 6, based on an
extrapolation of source numbers below the detection limit and standard
assumptions for the relationship between the ionizing emissivity and observed
luminosity density at 1500 Angstroms, are in reasonable agreement with the
photoionization rates inferred from the Lyman alpha forest if the escape
fraction of ionizing photons from galaxies is large (>= 20 per cent). Claims to
the contrary may be attributed to the adoption of an unduly high value for the
clumping factor of ionized hydrogen. Using physically motivated assumptions for
the mean free path of ionizing photons our measurements of the photoionization
rate can be turned into an estimate of the ionizing emissivity. In comoving
units the inferred ionizing emissivity is nearly constant over the redshift
range 2-6 and corresponds to 1.5-3 photons emitted per hydrogen atom over a
time interval corresponding to the age of the Universe at z=6. This strongly
suggests that the epoch of reionization was photon-starved and extended.
[Abridged]Comment: 20 pages, 9 figures, accepted for publication in MNRA
Spectro-Perfectionism: An Algorithmic Framework for Photon Noise-Limited Extraction of Optical Fiber Spectroscopy
We describe a new algorithm for the "perfect" extraction of one-dimensional
spectra from two-dimensional (2D) digital images of optical fiber
spectrographs, based on accurate 2D forward modeling of the raw pixel data. The
algorithm is correct for arbitrarily complicated 2D point-spread functions
(PSFs), as compared to the traditional optimal extraction algorithm, which is
only correct for a limited class of separable PSFs. The algorithm results in
statistically independent extracted samples in the 1D spectrum, and preserves
the full native resolution of the 2D spectrograph without degradation. Both the
statistical errors and the 1D resolution of the extracted spectrum are
accurately determined, allowing a correct chi-squared comparison of any model
spectrum with the data. Using a model PSF similar to that found in the red
channel of the Sloan Digital Sky Survey spectrograph, we compare the
performance of our algorithm to that of cross-section based optimal extraction,
and also demonstrate that our method allows coaddition and foreground
estimation to be carried out as an integral part of the extraction step. This
work demonstrates the feasibility of current- and next-generation multi-fiber
spectrographs for faint galaxy surveys even in the presence of strong night-sky
foregrounds. We describe the handling of subtleties arising from fiber-to-fiber
crosstalk, discuss some of the likely challenges in deploying our method to the
analysis of a full-scale survey, and note that our algorithm could be
generalized into an optimal method for the rectification and combination of
astronomical imaging data.Comment: 9 pages, 4 figures, emulateapj; minor corrections and clarifications;
to be published in the PAS
New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization
We present new measurements of the intensity of the ionizing ultraviolet
background and the global emissivity of ionizing photons over 2 < z < 5. Our
results are based on a suite of updated measurements of physical properties of
the high-redshift intergalactic medium (IGM), including gas temperatures and
the opacity of the IGM to Ly-alpha and ionizing photons. Consistent with
previous works, we find a relatively flat hydrogen photoionization rate over 2
< z < 5, although our measurements are roughly a factor of two higher than the
2008 values of Faucher-Giguere et al., due primarily to our lower gas
temperatures. The ionizing emissivity we derive is also generally higher than
other recent estimates due to a combination of lower gas temperatures, higher
ionizing opacity, and an accounting of cosmological radiative transfer effects.
We find evidence that the emissivity increases from z~3 to 5, reaching ~5
ionizing photons per atom per gigayear at z=4.75 for realistic galaxy spectra.
We further find that galaxies must dominate the emissivity near 1 Ryd at z > 4,
and possibly at all redshifts z > 2.4. Our results suggest that the
globally-averaged ionizing "efficiency" of star-forming galaxies increases
substantially with redshift over 3.2 < z < 4.75. This trend is consistent with
the conclusion often drawn from reionization models that the ionizing
efficiency of galaxies must be higher during reionization in order for galaxies
to reionize the IGM by z=6. Our emissivity values at z~5 suggest that ionizing
photons may have been a factor of two more abundant during the final stages of
reionization than previously indicated. The evolution of the ionizing
emissivity over 2 < z < 5 suggests, moreover, that the steep decline in the
photoionization rate from z~5 to 6 may indicate a rapid evolution in the mean
free path at z > 5.Comment: 19 pages, 14 figures, MNRAS, in pres
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