The Atomic and Molecular Content of Disks Around Very Low-mass Stars and Brown Dwarfs

There is growing observational evidence that disk evolution is stellar-mass dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from 8 very low-mass star and brown dwarf disks. We report the first detections of Ne+, H2, CO2, and tentative detections of H2O toward these faint and low-mass disks. Two of our [NeII] 12.81 micron emission lines likely trace the hot (>5,000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H2 S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [NeII] emission, in gas at about 600 K. We confirm the higher C2H2/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H2O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H2O lines trace warm > 600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks which may result from a more efficient formation of non-migrating icy planetesimals. A O/C=1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low-mass stars and brown dwarfs.Comment: Accepted to Ap

Pulsar Spin--Velocity Alignment: Further Results and Discussion

The reported alignment between the projected spin-axes and proper motion directions of pulsars is revisited in the light of new data from Jodrell Bank and Effelsberg. The present investigation uses 54 pulsars, the largest to date sample of pulsars with proper-motion and absolute polarisation, to study this effect. Our study has found strong evidence for pulsar spin-velocity alignment, excluding that those two vectors are completely uncorrelated, with >99% confidence. Although we cannot exclude the possibility of orthogonal spin-velocity configurations, comparison of the data with simulations shows that the scenario of aligned vectors is more likely than that of the orthogonal case. Moreover, we have determined the spread of velocities that a spin-aligned and spin-orthogonal distribution of kicks must have to produce the observed distribution of spin-velocity angle offsets. If the observed distribution of spin-velocity offset angles is the result of spin-aligned kicks, then we find that the distribution of kick-velocity directions must be broad with {\sigma}_v~30\degree if the orthogonal-kick scenario is assumed, then the velocity distribution is much narrower with {\sigma}_v<10\degree. Finally, in contrast to previous studies, we have performed robustness tests on our data, in order to determine whether our conclusions are the result of a statistical and/or systematic bias. The conclusion of a correlation between the spin and velocity vectors is independent of a bias introduced by subsets in the total sample. Moreover, we estimate that the observed alignment is robust to within 10% systematic uncertainties on the determination of the spin-axis direction from polarisation data.Comment: 20 pages, 7 figures, 1 Table, accepted in MNRA

Hypertext in the Semantic Web

The Semantic Web extends the current state of the Web with well-defined meaning. We advocate the use of ontological hypertext as an application of the Semantic Web to provide a principled and structured approach to navigating the resources on the Web. This paper demonstrates how we have applied this concept to two real-world scenarios

Hypertext in the Semantic Web

The Semantic Web extends the current state of the Web with well-defined meaning. We advocate the use of ontological hypertext as an application of the Semantic Web to provide a principled and structured approach to navigating the resources on the Web. This paper demonstrates how we have applied this concept to two real-world scenarios

Linking with Meaning: Ontological Hypertext for Scholars

The links in ontological hypermedia are defined according to the relationships between real-world objects. An ontology that models the significant objects in a scholar’s world can be used toward producing a consistently interlinked research literature. Currently the papers that are available online are mainly divided between subject- and publisher-specific archives, with little or no interoperability. This paper addresses the issue of ontological interlinking, presenting two experimental systems whose hypertext links embody ontologies based on the activities of researchers and scholars

Assessing the effects of radiotherapy on head and neck squamous cell carcinoma using microfluidic techniques

ObjectiveThe aim of this study was to investigate how HNSCC tissue biopsies maintained in a pseudo in vivo environment within a bespoke microfluidic device, respond to radiation treatment.Materials and Methods35 patients with HNSCC were recruited; in addition liver tissue from 5 Wistar rats was used. A glass microfluidic device was used to maintain the tissue biopsy samples in a viable state. Rat liver was used to optimise the methodology. HNSCC was obtained from patients with T1-T3 laryngeal or oropharyngeal SCC; N1-N2 metastatic cervical lymph nodes were also obtained. Irradiation consisted of single doses of between 2 Gy and 40 Gy and a fractionated course of 5x2 Gy. Cell death was assessed in the tissue effluent using the soluble markers LDH and cytochrome c, and in the tissue by immunohistochemical detection of cleaved cytokeratin18 (M30 antibody). Radiation-induced DNA strand breaks were detected using the TUNEL assay.ResultsA significant surge in LDH release was demonstrated in the rat liver after a single dose of 20 Gy; in HNSCC it was seen after 40 Gy, compared to the control. There was no significant difference in cytochrome c release after 5 Gy or 10 Gy. M30 demonstrated a dose-dependent increase in apoptotic index for a given increase in single dose radiation. There was a significant increase in apoptotic index between the non-irradiated HNSCC tissue and irradiated tissue and between the tissue irradiated with 1x2 Gy and 5x2 Gy. As with the apoptotic index, there was a significant increase in radiation-induced DNA breaks between the non-irradiated and the irradiated tissue and between the tissue irradiated with 1x2 Gy and 5x2 Gy.ConclusionThis microfluidic technique can be used to study the effects of radiation on HNSCC tissue. The device was capable of maintaining the HNSCC in a viable state, without it undergoing significant apoptosis or DNA damage and can be used to demonstrate the relationship between radiotherapy dose and radiation-induced cell death using tissue-based cell death markers.This study is a significant step towards achieving the ultimate goal of developing this device as a tool, capable of predicting a patient’s response to radiotherapy prior to the commencement of treatment

Digitometric Services for Open Archives Environments

We describe “digitometric” services and tools that add value to open-access eprint archives using the Open Archives Initiative (OAI) Protocol for Metadata Harvesting. Celestial is an OAI cache and gateway tool. Citebase Search enhances OAI-harvested metadata with linked references harvested from the full-text to provide a web service for citation navigation and research impact analysis. Digitometrics builds on data harvested using OAI to provide advanced visualisation and hypertext navigation for the research community. Together these services provide a modular, distributed architecture for building a “semantic web” for the research literature

A Younger Dryas plateau icefield in the Monadhliath, Scotland, and implications for regional palaeoclimate

A record of Younger Dryas glaciation in Scotland is well established. However, the role of the Monadhliath, a significant plateau area extending over 840 km2 in central Scotland, has never been investigated systematically. We present the first systematic glacial geomorphological mapping across the whole region, which has led to the identification of hitherto-unrecorded glacial and associated landforms. The spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield. In addition, a clear morphostratigraphical signature provides a strong indication that the icefield dates to the Younger Dryas (12.9–11.7 ka), which is supported by numerical ages in the southeast of the study area. Based on the geomorphological evidence and 2D glacier surface profile modelling, a 280 km2 icefield is reconstructed. A novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude (ELA) and palaeoprecipitation calculations, resulting in greater overall data confidence compared to traditional reconstruction methods. The ELA for the whole icefield is calculated to be 714 ± 25 m, whilst the ELAs of individual outlet glaciers range from 560 m in the west to 816 m in the east, demonstrating a significant W–E precipitation gradient across the region during the Younger Dryas. These ELAs compare well with those calculated for Younger Dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for Scotland during this time. Whilst the total amount of precipitation calculated from these ELAs is highly dependent on the method used, irrespective of this, the study suggests a more arid Younger Dryas climate in the region compared to the present day

Cultural evolution leads to vocal iconicity in an experimental iterated learning task

Experimental and cross-linguistic studies have shown that vocal iconicity is prevalent in words that carry meanings related to size and shape. Although these studies demonstrate the importance of vocal iconicity and reveal the cognitive biases underpinning it, there is less work demonstrating how these biases lead to the evolution of a sound symbolic lexicon in the first place. In this study, we show how words can be shaped by cognitive biases through cultural evolution. Using a simple experimental setup resembling the game telephone, we examined how a single word form changed as it was passed from one participant to the next by a process of immediate iterated learning. About 1,500 naïve participants were recruited online and divided into five condition groups. The participants in the control-group received no information about the meaning of the word they were about to hear, while the participants in the remaining four groups were informed that the word meant either big or small (with the meaning being presented in text), or round or pointy (with the meaning being presented as a picture). The first participant in a transmission chain was presented with a phonetically diverse word and asked to repeat it. Thereafter, the recording of the repeated word was played for the next participant in the same chain. The sounds of the audio recordings were then transcribed and categorized according to six binary sound parameters. By modelling the proportion of vowels or consonants for each sound parameter, the small-condition showed increases of front unrounded vowels and the pointy-condition increases of acute consonants. The results show that linguistic transmission is sufficient for vocal iconicity to emerge, which demonstrates the role non-arbitrary associations play in the evolution of language