403 research outputs found
An experimental dynamic RAM video cache
As technological advances continue to be made, the demand for more efficient distributed multimedia systems is also affirmed. Current support for end-to-end QoS is still limited; consequently mechanisms are required to provide flexibility in resource loading. One such mechanism, caching, may be introduced both in the end-system and network to facilitate intelligent load balancing and resource management. We introduce new work at Lancaster University investigating the use of transparent network caches for MPEG-2. A novel architecture is proposed, based on router-oriented caching and the employment of large scale dynamic RAM as the sole caching medium. The architecture also proposes the use of the ISO/IEC standardised DSM-CC protocol as a basic control infrastructure and the caching of pre-built transport packets (UDP/IP) in the data plane. Finally, the work discussed is in its infancy and consequently focuses upon the design and implementation of the caching architecture rather than an investigation into performance gains, which we intend to make in a continuation of the work
Percepção de apoio social na adolescência: análise fatorial confirmatória da Escala Social Support Appraisals
de Mac Mahon Patrice, Say Léon, Waddington William Henri. Loi ouvrant au Ministre de l'Instruction publique et des Beaux-Arts, sur l'exercice 1876, un crédit supplémentaire de 90,126 fr. 39 c., applicable à des dépenses relatives à la détermination de la paralaxe du soleil. In: Bulletin administratif de l'instruction publique. Tome 20 n°404, 1877. pp. 201-202
Evidence for Large-Scale Structure at z=2.4 From Lyman-alpha Imaging
We present deep wide-field medium-band imaging in redshifted Lyman alpha of
fields surrounding HST detections of faint emitters, to characterize their
larger-scale environment. The radio galaxy 53W002 was previously found to be
part of a rich grouping at z=2.39, including 5 confirmed, compact, star-forming
objects. This is now shown to be part of a larger structure traced by bright
AGN, all contained within a projected span of 6.8 arcmin (3.2 Mpc). Of the 14
candidate emitters, six have been spectroscopically confirmed as active nuclei
in the range z=2.390 +/- 0.008. Various statistical tests give a significance
of 95-99% for the reality of this structure on the sky. This grouping is more
extended than a relaxed King model, at the 90% confidence level. Either this
configuration has yet to decouple fully from the Hubble expansion, or it
consists of subgroups which will themselves form a more compact, relaxed
structure. The redshift range for measured members is comparable to the Hubble
flow across the structure, which may imply that the structure is seen near
turnaround.
We surveyed two additional fields at z=2.4, and three contiguous fields at
z=2.6. Only a single candidate at z=2.4 was found, with six at z=2.6.
Comparison with the WFPC2 surveys suggests that the field-to-field contrast is
larger for brighter objects. From this survey alone, groupings such as the
53W002 "cluster" must have an area covering fraction <0.04 in this redshift
range.Comment: 28 pages including 8 figures, uses aaspp4.sty. Accepted for Dec. 1999
A
Active Nuclei and Star-Forming Objects at z>2: Metallicities, Winds, and Formation Histories
We present near-IR observations of AGN and star-forming objects in the field
of the radio galaxy 53W002 at z=2.39. The star-forming objects, of special
interest as candidate protogalactic objects, are uniformly very blue in
continuum slope, which fits with the strong Lyman alpha emission in indicating
metallicity less than half solar. They fall in a range of luminosity and
metallicity not populated by local objects. NICMOS spectroscopy detects [O III]
emission for two objects and sets interesting limits for the rest. These data
are satisfied by model stellar populations which have been forming stars for
the last 2-5 million years. We see no evidence for older populations, either in
broadband colors or as redder halos around the star-forming regions. These
results suggest that the compact star-forming objects we see at z=2.0-2.5 are
indeed early stages in the building of galaxies, rather than transient
star-forming events in larger systems. They also also permit an alternative
scheme, in which these low-mass systems are blowing winds rather than
self-enriching, and should fade rapidly with cosmic epoch. For the three
prominent AGN at z=2.39, emission-line ratios show metallicities just as high
as in nearby systems. The "ionization cones" appear in [O III] and H lines,
with continuum reflection in some cases as well. The contrast between the AGN
and fainter star-forming objects can be broadly accomodated in a hierarchical
formation picture, though there are still important unknowns as to the fate of
the star-forming objects.Comment: 9 JPEG figures; accepted by the Astronomical Journa
A Systematic Review of Anthropogenic Noise Impact on Avian Species
Purpose of review: This study aims to investigate anthropogenic noise impact on avian species by means of a systematic review of literature. Recent findings: Based on previous anthropogenic noise impact frameworks, it was possible to: clarify the impacts of noise on birds; optimise the existing frameworks with findings produced over 44 years; recategorise noise impacts into more appropriate categories, indicating which are the positive and negatives, as well as acute and chronic impacts caused by anthropogenic noise; provide a significant cluster model of anthropogenic noise impacts on avian species subdivided into impacts on ‘Behaviour’ and ‘Communication/Perception’ (Cluster 1) and ‘Physiology’ (Cluster 2); and show how avian hearing frequency range overlaps noise source frequency range. Summary: This research adopted the database of Peacock et al. [1, 2] regarding avian species due to its vast coverage across taxa. A systematic literature review of 50 peer-reviewed papers about anthropogenic noise impact on birds was undertaken. A Two-Step Cluster analysis was calculated, showing the data subdivided into two clusters. Cluster 1 (76.9%) showed behavioural responses mainly composed of negative and auditory perception and communication impacts, presenting positive or negative noise impacts. Cluster 2 (23.1%) mainly showed negative impacts on physiological outcomes caused by traffic, anthropogenic, and background noise
Selective vulnerability of tripartite synapses in Amyotrophic Lateral Sclerosis
Authors would like to acknowledge the following funders: Motor Neurone Disease (MND) Association UK (Miles/Apr18/863-791), the Euan MacDonald Centre and Chief Scientist Office, The European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (695568 SYNNOVATE), Simons Foundation Autism Research Initiative (529085), and the Wellcome Trust (Technology Development grant 202932).Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder. Separate lines of evidence suggest that synapses and astrocytes play a role in the pathological mechanisms underlying ALS. Given that astrocytes make specialised contacts with some synapses, called tripartite synapses, we hypothesise that tripartite synapses could act as the fulcrum of disease in ALS. To test this hypothesis, we have performed an extensive microscopy-based investigation of synapses and tripartite synapses in the spinal cord of ALS model mice and post-mortem human tissue from ALS cases. We reveal widescale synaptic changes at the early symptomatic stages of the SOD1G93a mouse model. Super-resolution microscopy reveals that large complex postsynaptic structures are lost in ALS mice. Most surprisingly, tripartite synapses are selectively lost, while non-tripartite synapses remain in equal number to healthy controls. Finally, we also observe a similar selective loss of tripartite synapses in human post-mortem ALS spinal cords. From these data we conclude that tripartite synaptopathy is a key hallmark of ALS.Publisher PDFPeer reviewe
Distinct Steps of Neural Induction Revealed by Asterix, Obelix and TrkC, Genes Induced by Different Signals from the Organizer
The amniote organizer (Hensen's node) can induce a complete nervous system when grafted into a peripheral region of a host embryo. Although BMP inhibition has been implicated in neural induction, non-neural cells cannot respond to BMP antagonists unless previously exposed to a node graft for at least 5 hours before BMP inhibitors. To define signals and responses during the first 5 hours of node signals, a differential screen was conducted. Here we describe three early response genes: two of them, Asterix and Obelix, encode previously undescribed proteins of unknown function but Obelix appears to be a nuclear RNA-binding protein. The third is TrkC, a neurotrophin receptor. All three genes are induced by a node graft within 4–5 hours but they differ in the extent to which they are inducible by FGF: FGF is both necessary and sufficient to induce Asterix, sufficient but not necessary to induce Obelix and neither sufficient nor necessary for induction of TrkC. These genes are also not induced by retinoic acid, Noggin, Chordin, Dkk1, Cerberus, HGF/SF, Somatostatin or ionomycin-mediated Calcium entry. Comparison of the expression and regulation of these genes with other early neural markers reveals three distinct “epochs”, or temporal waves, of gene expression accompanying neural induction by a grafted organizer, which are mirrored by specific stages of normal neural plate development. The results are consistent with neural induction being a cascade of responses elicited by different signals, culminating in the formation of a patterned nervous system
The thermodynamics of Pr55Gag-RNA interaction regulate the assembly of HIV
The interactions that occur during HIV Pr55Gag oligomerization and genomic RNA packagingare essential elements that facilitate HIV assembly. However, mechanistic details ofthese interactions are not clearly defined. Here, we overcome previous limitations in producinglarge quantities of full-length recombinant Pr55Gag that is required for isothermal titrationcalorimetry (ITC) studies, and we have revealed the thermodynamic properties of HIVassembly for the first time. Thermodynamic analysis showed that the binding between RNAand HIV Pr55Gag is an energetically favourable reaction (ΔG<0) that is further enhanced bythe oligomerization of Pr55Gag. The change in enthalpy (ΔH) widens sequentially from: (1)Pr55Gag-Psi RNA binding during HIV genome selection; to (2) Pr55Gag-Guanosine Uridine(GU)-containing RNA binding in cytoplasm/plasma membrane; and then to (3) Pr55Gag-Adenosine(A)-containing RNA binding in immature HIV. These data imply the stepwiseincrements of heat being released during HIV biogenesis may help to facilitate the processof viral assembly. By mimicking the interactions between A-containing RNA and oligomericPr55Gag in immature HIV, it was noted that a p6 domain truncated Pr50Gag Δp6 is less efficientthan full-length Pr55Gag in this thermodynamic process. These data suggest a potentialunknown role of p6 in Pr55Gag-Pr55Gag oligomerization and/or Pr55Gag-RNA interaction duringHIV assembly. Our data provide direct evidence on how nucleic acid sequences and theoligomeric state of Pr55Gag regulate HIV assembly
ISO Observations of the 53W002 Group at 6.7 microns: In Search of the Oldest Stellar Populations at z=2.4
We present a deep ISO observation at 6.7 microns of the 53W002 group of
galaxies and AGN at z=2.4. This approximately samples the emitted K band. The
faint, blue star-forming objects are not detected, as expected from their very
blue color across the emitted optical and UV. However, 53W002 itself is
detected at the 3-sigma level, with an emitted V-K color appropriate for a
population formed starting at z=3.6-7.0 with most likely value z=4.7. This fits
with shorter-wavelength data suggesting that the more massive members of this
group, which may all host AGN, began star formation earlier in deeper potential
wells than the compact Lyman-alpha emission objects. Two foreground galaxies
are detected, as well as several stars. One additional 6.7-micron source
closely coincides with an optically faint galaxy, potentially at z=2-3. The
overall source counts are consistent with other ISO deep fields.Comment: In press, PASP (August 2004
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