Calculation of percolation thresholds in high dimensions for fcc, bcc, and diamond lattices

In a recent article, Galam and Mauger proposed an invariant for site and bond percolation thresholds, based on known values for twenty lattices (Eur. Phys. J. B 1 (1998) 255-258). Here we give a larger list of values for more than forty lattices in two to six dimensions. In this list are new results for fcc, bcc, and diamond lattices in 4, 5, and 6 dimensions. The list contains examples of lattices with equal site percolation thresholds, but different bond percolation thresholds. These and other examples show that there are deviations from the proposed invariant of up to 12% in two dimensions, increasing to 69% in higher dimensions.Comment: 12 pages, 3 figures (EPS), LaTe

Embracing the future: embedding digital repositories in the University of London

Digital repositories can help Higher Education Institutions (HEIs) to develop coherent and coordinated approaches to capture, identify, store and retrieve intellectual assets such as datasets, course material and research papers. With the advances of technology, an increasing number of Higher Education Institutions are implementing digital repositories. The leadership of these institutions, however, has been concerned about the awareness of and commitment to repositories, and their sustainability in the future. This study informs a consortium of thirteen London institutions with an assessment of current awareness and attitudes of stakeholders regarding digital repositories in three case study institutions. The report identifies drivers for, and barriers to, the embedding of digital repositories in institutional strategy. The findings therefore should be of use to decision-makers involved in the development of digital repositories. Our approach was entirely based on consultations with specific groups of stakeholders in three institutions through interviews with specific individuals. The research in this report was prepared for the SHERPA-LEAP Consortium and conducted by RAND Europe

On experimental procedures for entanglement verification

We give an overview of different types of entanglement that can be generated in experiments, as well as of various protocols that can be used to verify or quantify entanglement. We propose several criteria that, we argue, should be applied to experimental entanglement verification procedures. Explicit examples demonstrate that not following these criteria will tend to result in overestimating the amount of entanglement generated in an experiment or in infering entanglement when there is none. We distinguish protocols meant to refute or eliminate hidden-variable models from those meant to verify entanglement.Comment: 15 page

Gravitational instability and star formation in disk galaxies

We present a general star formation law where star formation rate depends upon efficiency $\alpha$, timescale $\tau$ of star formation, gas component $\sigma_{g}$ of surface mass density and a real exponent $n$. A given exponent $n$ determines $\tau$ which however yields the corresponding star formation rate. Current nominal Schmidt exponent $n_{s}$ for our model is $2<n_{s}<3$. Based on a gravitational instability parameter $Q_{A}$ and another dimensionless parameter $f_{P}\equiv (P/G\sigma_{c}^{2})^{1/2}$, where $P$ = pressure, $\sigma_{c}$ = column density of molecular clouds, we suggest a general equation for star formation rate which depends upon relative competence of the two parameters for various physical circumstances. We find that $Q_{A}$ emerges to be a better parameter for star formation scenario than Toomre Q-parameter. Star formation rate in the solar neighbourhood is found to be in good agreement with values inferred from previous studies. Under closed box approximation model, we obtain a relation between metallicity of gas and the efficiency of star formation. Our model calculations of metallicity in the solar neighbourhood agree with earlier estimates. We conclude that metallicity dispersion for stars of same age may result due to a change in efficiency through which different sample stars were processed. For no significant change of metallicity with age, we suggest that all sample stars were born with almost similar efficiency.Comment: 10 pages, 3 figures, submitted to MNRA

Development of clinical sign-based scoring system for assessment of omphalitis in neonatal calves

Omphalitis contributes significantly to morbidity and mortality in neonatal calves. Diagnosis of omphalitis is based on the local signs of inflammation—pain, swelling, local heat and purulent discharge. An abattoir trial identified an optimal, sign-based, scoring system for diagnosis of omphalitis. A sample of 187 calves aged between 7 and 15 days old were clinically examined for signs of umbilical inflammation and compared with postmortem examination of navels. On postmortem findings, 64 calves (34.2 per cent) had omphalitis. In the examined omphalitis cases, the most commonly affected umbilical structure was the urachus (78.1 per cent). Multivariable logistic regression revealed that thickening of the umbilical stump over 1.3?cm (P<0.001), discharge (P<0.001), raised local temperature (P=0.003) and the presence of umbilical hernia (P=0.024) were correlated and positive predictors of omphalitis. Discharge from the umbilical stump was associated with intra-abdominal inflammation (P=0.004). Assigning weights based on the multivariable logistic regression coefficients, a clinical scoring algorithm was developed. The cumulative score ranged from 0 to 9. Using this scoring system, calves were categorised as positive if their total score was =2. This scoring method had a sensitivity of 85.9 per cent, specificity of 74.8 per cent and correctly classified 78.6 per cent of all calves

Glass foam granulate as growing medium for tomato and cucumber

Glass foam granulate was evaluated for use as a horticultural rooting medium with laboratory tests and cultivation experiments. The laboratory tests included moisture characteristics, rehydration rate and pH buffering analyses. Cucumbers and later on tomatoes were propagated in rockwool propagation cubes and planted on slabs of Growstones™ glass foam granulate. They were compared with cucumber respectively tomatoes grown on rockwool slabs. Lab results show that the coarse nature of the glass foam granulate (0.5-5 cm) limits the maximum moisture content to 50%. The rehydration rate is very high, reaching more than 80% of container capacity in 5 min. The tested material initially reacts with water, raising the pH to over 10 pH units. Based on lab results a recipe for rinsing the material prior to cultivation was calculated. Cucumber cultivation results show an equal production to plants grown on rockwool. The first yield on glass foam granulate is 1-2 days earlier. The susceptibility to Pythium is significantly lower than on rockwool. The wax layer on cucumbers grown on glass foam granulate is perceptibly thicker as consequence of an elevated silicon level of 0.25 to 1.6 mmol L-1 in the slab solution. Tomatoes on glass foam granulate show smaller stem diameters and recovered faster from blossom end rot. Yield levels on glass foam granulate and rockwool are equal. In conclusion growing on glass foam granulate is equally productive as rockwool growing. The material is drier and thus less susceptible to Pythium and more generative in nature. Glass foam granulate can be irrigated with small and frequent irrigation cycles and the material must be rinsed with an acid solution before planting. Small amounts of silicon are released into the nutrient solution

The Way We Measure: Comparison of Methods to Derive Radial Surface Brightness Profiles

The breaks and truncations in the luminosity profile of face-on spiral galaxies offer valuable insights in their formation history. The traditional method of deriving the surface photometry profile for face-on galaxies is to use elliptical averaging. In this paper, we explore the question whether elliptical averaging is the best way to do this. We apply two additional surface photometry methods, one new: principle axis summation, and one old that has become seldom used: equivalent profiles. These are compared to elliptically averaged profiles using a set of 29 face-on galaxies. We find that the equivalent profiles match extremely well with elliptically averaged profiles, confirming the validity of using elliptical averaging. The principle axis summation offers a better comparison to edge-on galaxies.Comment: Accepted for publication by Monthly Notices of the R.A.S. A hi-res version is available at http://www.astro.rug.nl/~vdkruit/Petersetal-VI.pd