Is string theory a theory of quantum gravity?

Some problems in finding a complete quantum theory incorporating gravity are discussed. One is that of giving a consistent unitary description of high-energy scattering. Another is that of giving a consistent quantum description of cosmology, with appropriate observables. While string theory addresses some problems of quantum gravity, its ability to resolve these remains unclear. Answers may require new mechanisms and constructs, whether within string theory, or in another framework.Comment: Invited contribution for "Forty Years of String Theory: Reflecting on the Foundations," a special issue of Found. Phys., ed. by G 't Hooft, E. Verlinde, D. Dieks, S. de Haro. 32 pages, 5 figs., harvmac. v2: final version to appear in journal (small revisions

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Aspects of the ecology of common wombats (Vombatus ursinus) at high density on pastoral land in Victoria

Free-living common wombats (Vombatus ursinus) living at high densities on pastoral land (1.9 wombats ha⁻¹) had most of their burrows (83%) confined to a 20-m-wide strip of remnant riparian vegetation adjacent to pasture (24 burrows ha⁻¹). The ratio of wombats to 'active' burrows (being used by wombats) was 1.0. Wombats shared burrows extensively, with a mean of 3.1 ± 0.3 (s.e.), range 2–9 wombats using each burrow (n = 37). The majority (70%) of occupied burrows contained several wombats independent of age, sex and stage of reproduction. On average, wombats used the same burrow for 3.8 consecutive nights before changing to another. Home ranges of wombats overlapped completely. Adult males had larger home ranges than females with young (7.3 ± 0.6, 6.1–8.3 ha, n = 3 versus 3.8 ± 0.5, 2.4–5.0 ha, n = 4, respectively). Distances travelled and the area used each night by wombats decreased in late winter and spring, when food was more abundant. Breeding occurred throughout the year but there was a cluster of births in summer. Lactation was associated with weight loss in females of several kilograms. Usually larger (30 kg) males that shared burrows or used burrows near (<300 m) to the burrows used by a female sired her young; however, occasionally wombats that used widely separated burrows (>700 m) bred. Adult males had a greater head length to weight ratio than adult females. Adult males generally emerged from their burrows shortly after dusk and 30 min before adult females. Ectoparasites such as ticks, mites, fleas and lice were common but the mite Sarcoptes scabiei was not found nor were there signs of sarcoptic mange in the population

Independent verification and validation of an industrial simulation model

The independent verification and validation (IV&V) of simulation models is largely restricted to applications in the military and public policy domains. There is little evidence of IV&V for industrial simulation models. This is largely because industrial simulations are normally of a much smaller scale and do not warrant a full IV&V. A procedure for IV&V of industrial simulation models is described that provides a viable alternative where the cost and time of IV&V must be contained. The procedure consists of the following activities: structured walkthrough, review of model assumptions, code examination, review of verification procedures, replications analysis, review of static analysis, review of output reporting, and investigation of results and experimentation. The IV&V of a Sellafield Limited supply chain model is described