Designing a licence plate for memorability

Good memorability of licence plates is important in those cases where licence plates are viewed for a brief period of time and the information is essential for police investigations. The purpose of the current study was to design a new Dutch licence plate that could be remembered well. A memory experiment was conducted, in which 16 different character arrangements were presented for both 450 and 550 ms to 48 participants with ages varying between 20 and 57 years. Participants had to rehearse the stimuli for 6 s, after which they had to be written down. Based on literature on short-term memory for serial order, character arrangements differed on three dimensions: 1) number of alternations between letters and digits; 2) letter to digit ratio; and 3) equality of group size. Results showed that number of alternations between characters of different categories affected memory performance the most. Letter to digit ratio and equality of group size affected memory performance to a lesser, but still significant, extent. A significant interaction between the latter two factors indicates that equal groups only lead to fewer memory errors when more than three letters are used. With three or fewer letters, group size is not a significant factor any more. Based on these results, a new licence plate for Dutch vehicles was recommended, which was subsequently adopted.     

A system to test the ground surface conditions of construction sites--for safe and efficient work without physical strain

Ground surface conditions on construction sites have an important influence on the health and safety of workers and their productivity. The development of an expert-based "working conditions evaluation" system is described, intended to assist site managers in recognising unsatisfactory ground conditions and remedying these. The system was evaluated in the period 2002-2003. The evaluation shows that companies recognize poor soil/ground conditions as problematic, but are not aware of the specific physical workload hazards. The developed methods allow assessment of the ground surface quality and selection of appropriate measures for improvement. However, barriers exist at present to wide implementation of the system across the industry. Most significant of these is that responsibility for a site's condition is not clearly located within contracting arrangements, nor is it a topic of serious negotiation.     

CYCLON: Inexpensive Membership Management for Unstructured P2P Overlays

Unstructured overlays form an important class of peer-to-peer networks, notably when content-based searching is at stake. The construction of these overlays, which is essentially a membership management issue, is crucial. Ideally, the resulting overlays should have low diameter and be resilient to massive node failures, which are both characteristic properties of random graphs. In addition, they should be able to deal with a high node churn (i.e., expect high-frequency membership changes). Inexpensive membership management while retaining random-graph properties is therefore important. In this paper, we describe a novel gossip-based membership management protocol that meets these requirements. Our protocol is shown to construct graphs that have low diameter, low clustering, highly symmetric node degrees, and that are highly resilient to massive node failures. Moreover, we show that the protocol is highly reactive to restoring randomness when a large number of nodes fail.Spyros Voulgaris is a PhD student in the Computer Systems department at the Vrije Universiteit Amsterdam. He received his MSc degree from the University of Michigan, Ann Arbor, and his BSc degree from the University of Patras, Greece. His research involves peer-to-peer systems, epidemic protocols, and ad-hoc networks. He is a scholarship recipient of the Greek State Scholarships Foundation (IKY) and the Alexander Onassis Foundation.Daniela Gavidia is a PhD student in the Computer Systems group at the Vrije Universiteit Amsterdam. She received her MSc degree from the Universiteit van Amsterdam. Her research interests include peer-to-peer systems and ad-hoc networks. Her recent work focuses on information dissemination in ad-hoc environments.Maarten van Steen is professor of Computer Science at the Vrije Universiteit Amsterdam. His research concentrates on large-scale distributed systems, notably content delivery networks and peer-to-peer systems. He is senior member of the IEEE and member of the ACM.     

Gold-enhanced biomolecular surface imaging of cells and tissue by SIMS and MALDI mass spectrometry

Surface metallization by plasma coating enhances desorption/ionization of membrane components such as lipids and sterols in imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) of tissues and cells. High-resolution images of cholesterol and other membrane components were obtained for neuroblastoma cells and revealed subcellular details (resolving power 1.5 mum). Alternatively, in matrix-enhanced SIMS, 2,5-dihydroxybenzoic acid electrosprayed on neuroblastoma cells allowed intact molecular ion imaging of phosphatidylcholine and sphingomyelin at the cellular level. Gold deposition on top of matrix-coated rat brain tissue sections strongly enhanced image quality and signal intensity in stigmatic matrix-assisted laser desorption/ionization imaging mass spectrometry. High-quality total ion count images were acquired, and the neuropeptide vasopressin was localized in the rat brain tissue section at the hypothalamic area around the third ventricle. Although the mechanism of signal enhancement by gold deposition is under debate, the results we have obtained for cells and tissue sections illustrate the potential of this sample preparation technique for biomolecular surface imaging by mass spectrometry.     

Measurement of T1 and T2 relaxation times of the pancreas at 7 T using a multi-transmit system

Objective

To determine T₁ and T₂ relaxation times of healthy pancreas parenchyma at 7 T using a multi-transmit system.

Materials and methods

Twenty-six healthy subjects were scanned with a 7 T MR system using eight parallel transceiver antennas, each with two additional receive loops. A Look-Locker sequence was used to obtain images for T₁ determination, while T₂ was obtained from spin-echo images and magnetic resonance spectroscopy measurements with different echo times. T₁ and T₂ times were calculated using a mono-exponential fit of the average magnitude signal from a region of interest in the pancreas and were tested for correlation with age.

Results

The age range of the included subjects was 21–72 years. Average T₁ and T₂ relaxation times in healthy pancreas were 896 ± 149 ms, and 26.7 ± 5.3 ms, respectively. No correlation with age was found.

Conclusion

T₁ and T₂ relaxation times of the healthy pancreas were reported for 7 T, which can be used for image acquisition optimization. No significant correlations were found between age and T₁ or T₂ relaxation times of the pancreas. Considering their low standard deviation and no observable age dependence, these values may be used as a baseline to study potentially pancreatic tissue affected by disease.

     

A note on large-scale logistic prediction: using an approximate graphical model to deal with collinearity and missing data

Large-scale prediction problems are often plagued by correlated predictor variables and missing observations. We consider prediction settings in which logistic regression models are used and propose a novel approach to make accurate predictions even when predictor variables are highly correlated and only partly observed. Our approach comprises three steps: first, to overcome the collinearity issue, we propose to model the joint distribution of the outcome variable and the predictor variables using the Ising network model. Second, to render the application of Ising networks feasible, we use a latent variable representation to apply a low-rank approximation to the network’s connectivity matrix. Finally, we propose an approximation to the latent variable distribution that is used in the representation to handle missing observations. We demonstrate our approach with numerical illustrations.

     

Same Neighbourhood … Different Views? A Confrontation of Internal and External Neighbourhood Reputations

Residents and non-residents are likely to think differently about a neighbourhood's reputation. Relatively little is known about the similarities and differences between these internal and external types of neighbourhood reputation or the relationship between reputations and ‘real’ or ‘objective’ neighbourhood characteristics. This paper addresses two points: first, the extent to which neighbourhood reputations differ between and within groups; second, the extent to which these neighbourhood reputations are associated with measured neighbourhood characteristics. Data from a specially designed survey carried out in 24 neighbourhoods in Utrecht, the fourth largest city in the Netherlands, are used. Analysis of the data showed that neighbourhood reputations are rated higher by residents and estate agents than by other city residents. Within the group of other city residents, differences were found in how neighbourhood reputations are rated by socio-economic status, ethnicity and educational background. Further, it was found that neighbourhood reputations are correlated with measured social characteristics of the neighbourhood, while physical and functional neighbourhood characteristics are of less importance.     

Jasmonic Acid and Herbivory Differentially Induce Carnivore-Attracting Plant Volatiles in Lima Bean Plants

Lima bean plants respond to feeding damage of two-spotted spider mites (Tetranychus urticae) with the emission of a complex blend of volatiles that are products of several different biosynthetic pathways. These volatiles attract the carnivorous mite Phytoseiulus persimilis, a specialist predator of the spider mites that exterminates entire prey populations, and thus the volatiles contribute indirectly to plant defense. The volatile blend constitutes information to the carnivores, and blend composition is an important factor in this. Jasmonic acid (JA) is involved in the signal transduction of this induced defense. Application of JA through the petiole of Lima bean plants induces a volatile blend that is similar, but not identical, to that emitted by spider mite-infested plants. The induced volatiles originate from the lipoxygenase pathway, the shikimic acid pathway, and the isoprenoid pathway. Among the induced bean plant volatiles are nitriles and oximes. Of a total of 61 components, 10 are emitted at significantly different rates. Among these are the terpene (E)-4,8-dimethyl-1,3,7-nonatriene and the phenolic methyl salicylate, two compounds that are known to attract P. persimilis. A crucial test for comparing the effect of spider mite damage and JA application on volatile induction is the response of P. persimilis. The carnivore is attracted by volatiles from JA-treated plants. Moreover, even treatment of Lima bean plants with methyl jasmonate vapor made the plants attractive to the carnivorous mites. However, the predators prefer the volatiles from spider-mite-infested Lima bean plants over those from JA-treated plants. Thus, chemical as well as behavioral analyses demonstrate that spider mite damage and JA treatment have similar, although not identical, effects on volatile induction in Lima bean plants.     

Directed evolution: From a staphylococcal lipase to a phospholipase

The lipase of Staphylococcus aureus (SAL) is able to degrade lipids and p‐nitrophenylesters but is not active on phospholipid substrates. Interestingly, the homologous lipase from Staphylococcus hyicus is highly active on phospholipids. In order to investigate the molecular basis for this difference in substrate specificity, phospholipase activity was introduced into SAL by directed evolution strategy. In this approach, sequential rounds of error‐prone PCR were performed in combination with a screening of the resulting mutant libraries. The screening was based on a high‐throughput plate assay and a subsequent chromogenic assay in 96‐well plate format to accurately determine the enzymatic activities in cell lysates of a selected number of clones. After 4 rounds of error‐prone PCR, two products were obtained, displaying a 7.8‐ and 9.2‐fold increase in absolute phospholipase activity and a 5.9‐ and 6.9‐fold increase in phospholipase/ lipase activity ratio. A final round of DNA shuffling with these two products and wildtype (WT)‐SAL was performed to combine beneficial mutations and to eliminate neutral or deleterious mutations. This procedure yielded a best variant containing 6 amino acid mutations displaying a 11.6‐fold increase in absolute phospholipase activity and a 11.5‐fold increase in phospholipase/lipase ratio as compared to the starting point. The character of the mutations and their possible effects on substrate specificity are discussed.