HAWKS: Evolving Challenging Benchmark Sets for Cluster Analysis

Comprehensive benchmarking of clustering algorithms is rendered difficult by two key factors: (i) the elusiveness of a unique mathematical definition of this unsupervised learning approach and (ii) dependencies between the generating models or clustering criteria adopted by some clustering algorithms and indices for internal cluster validation. Consequently, there is no consensus regarding the best practice for rigorous benchmarking, and whether this is possible at all outside the context of a given application. Here, we argue that synthetic datasets must continue to play an important role in the evaluation of clustering algorithms, but that this necessitates constructing benchmarks that appropriately cover the diverse set of properties that impact clustering algorithm performance. Through our framework, HAWKS, we demonstrate the important role evolutionary algorithms play to support flexible generation of such benchmarks, allowing simple modification and extension. We illustrate two possible uses of our framework: (i) the evolution of benchmark data consistent with a set of hand-derived properties and (ii) the generation of datasets that tease out performance differences between a given pair of algorithms. Our work has implications for the design of clustering benchmarks that sufficiently challenge a broad range of algorithms, and for furthering insight into the strengths and weaknesses of specific approaches

Killing tensors in pp-wave spacetimes

The formal solution of the second order Killing tensor equations for the general pp-wave spacetime is given. The Killing tensor equations are integrated fully for some specific pp-wave spacetimes. In particular, the complete solution is given for the conformally flat plane wave spacetimes and we find that irreducible Killing tensors arise for specific classes. The maximum number of independent irreducible Killing tensors admitted by a conformally flat plane wave spacetime is shown to be six. It is shown that every pp-wave spacetime that admits an homothety will admit a Killing tensor of Koutras type and, with the exception of the singular scale-invariant plane wave spacetimes, this Killing tensor is irreducible.Comment: 18 page

Infrared Observations of Hot Gas and Cold Ice toward the Low Mass Protostar Elias 29

We have obtained the full 1-200 um spectrum of the low luminosity (36 Lsun) Class I protostar Elias 29 in the Rho Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of interstellar ice and the interrelationship of interstellar ice and hot core gases around low mass protostars. We see abundant hot CO and H2O gas, as well as the absorption bands of CO, CO2, H2O and ``6.85 um'' ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 with the conditions around several well studied luminous, high mass protostars. The high gas temperature and gas/solid ratios resemble those of relatively evolved high mass objects (e.g. GL 2591). However, none of the ice band profiles shows evidence for significant thermal processing, and in this respect Elias 29 resembles the least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude that the heating of the envelope of the low mass object Elias 29 is qualitatively different from that of high mass protostars. This is possibly related to a different density gradient of the envelope or shielding of the ices in a circumstellar disk. This result is important for our understanding of the evolution of interstellar ices, and their relation to cometary ices.Comment: 18 pages and 14 figures, accepted for publication in A&

Herschel evidence for disk flattening or gas depletion in transitional disks

Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [OI] 63 micron for 21 transitional disks. Our survey complements the larger Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by quadrupling the number of transitional disks observed with PACS at this wavelength. [OI] 63 micron traces material in the outer regions of the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [OI] 63 micron line luminosities two times fainter than their full disk counterparts. We self consistently determine various stellar properties (e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we find no correlations that can explain the lower [OI] 63 micron line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table

Visualization Tools for Visual Impact Assessments: A Study of Existing Technologies

In the last few decades, digital technology has dramatically altered how visual resource management and visual impact assessments (VIAs) are conducted. The recent emergence of low-cost immersive technology offers a suite of tools that could facilitate the VIA process. However, to date there is limited empirical evidence evaluating how these emerging technologies could influence VIA. The research presented here begins to fill this gap by comparing immersive virtual environments to existing 2D photo-based methods for assessing the visual impacts of development. 23 participants familiar with VIAs rated the visual qualities of different scenes presented as 360° images, Google Earth and 2D images. Results show a high similarity in perceived impacts between 2D images and Google Earth; 360° images were rated consistently lower. Overall, participants indicated that immersive visualization may have a role in VIAs, but it is critical these technologies be evaluated against on-site assessments before being adopted

Multimodal imaging of a vascularized idiopathic epiretinal membrane

PURPOSE: To report a case of vascularized idiopathic epiretinal membrane including the multimodal imaging. METHODS: Findings on clinical examination, color fundus photography, spectral-domain optical coherence tomography, optical coherence tomography angiography, and fluorescein angiography. RESULTS: Sixty-three-year-old woman with a previous rhegmatogenous retinal detachment (RRD) who presented with an asymptomatic idiopathic neovascular complex below an epiretinal membrane. It was assessed with fluorescein angiography, OCT and OCT-A. The vascularized ERM was already present previously to the retinal detachment. CONCLUSION: Our case report describes an example of idiopathic epiretinal membrane complicated by neovascularization; we hypothesized hypertension could be one of the factors in this case, as it may lead to decreased retinal perfusion and upregulation in vascular endothelial growth factor (VEGF). Multimodal imaging can help in detecting neovascularized ERM

Cob Development in Forage Maize: Influence of Harvest Date, Cultivar and Plastic Mulch

Forage maize grown for silage tends to be a compromise between reproductive and vegetative yield, and the cob component is the main driver of feeding value (Keane et al., 2003). Thus the aim is to produce a well-developed crop of high dry matter (DM) and starch content reflecting large cobs of well-filled grains rather than crops with low DM and starch contents reflecting poorly developed (immature) cob components at harvest. The use of plastic mulch can increase total DM yields with the increase in cob yield accounting for 75% of the total yield increase (Easson & Fearnehough, 1997). In this experiment the composition of cob components (i.e. rachis plus kernel) of two cultivars of different maturity under Irish conditions grown with or without plastic mulch were monitored between the harvest dates of 10 September to 9 November