An incomplete variant of Wilson's congruence

This article examines the nontrivial solutions of the congruence $$(p-1)\cdots(p-r) \equiv -1 \pmod p.$$ We discuss heuristics for the proportion of primes $p$ that have exactly $N$ solutions to this congruence. We supply numerical evidence in favour of these conjectures, and discuss the algorithms used in our calculations.Comment: 7 pages, 2 table

Social integration of macroparasites in ant societies: ultimate and proximate mechanisms

Ant colonies are commonly parasitized simultaneously by several species. While some parasites are recognized and attacked by their ant hosts, others have apparently cracked the ants’ recognition code and interact mainly peacefully with their hosts. Although such apparent differences in social integration among ant parasites have been described, the underlying mechanisms resulting in differential integration remain mostly unknown. Using Leptogenys army ants and their parasites, I studied ultimate mechanisms that might be responsible for differing integration levels by comparing the strength of host defence with the negative impact of parasites. In addition, I investigated proximate mechanisms of differing integration levels by evaluating the role of chemical deception by mimicry. The interactions of several parasitic beetle species with their Leptogenys hosts revealed that particular species fed on host larvae, while others did not. The hosts’ aggressiveness was enhanced towards brood-killing species, while non-predatory species received almost no aggression, resulting in social integration. Accordingly, the fitness costs of parasites likely influence the evolution of host defences against them in a multi-parasite situation. The role of chemical mimicry has been investigated in detail for two kleptoparasites, namely the silverfish Malayatelura ponerophila and the spider Gamasomorpha maschwitzi. By analyzing the transfer of a chemical label from the host ants to the parasites, I empirically demonstrated for the first time that ant parasites are able to acquire mimetic compounds from their host. Additional biosynthesis of mimetic compounds seems unlikely in both parasites, since the concentration of each cuticular hydrocarbon decreased in individuals that were isolated from the host. In addition, a high accuracy in chemical host resemblance was shown to be beneficial for the social integration of both parasites. Reduced accuracy in chemical host resemblance resulted either in aggressive host responses towards the silverfish or elevated host inspection behaviour towards the spider. The degree of dependency on chemical mimicry to achieve social integration differed considerably between the two parasites, however. Accordingly, the parasites’ level of social integration is affected by ultimate mechanisms such as the negative impact on the host as well as by proximate mechanisms such as the degree of accuracy in chemical host resemblance

Supramolecular chemical shift reagents inducing conformational transitions: NMR analysis of carbohydrate homooligomer mixtures

Supramolecular chemical shift reagents improve signal resolution for NMR analysis of homooligosaccharides by inducing conformational transitions upon binding.</p

Probing network dynamics in barrel cortex

Recent studies have demonstrated that a rat can be trained to behaviourally report the electrical stimulation of a single cortical neuron (Houweling and Brecht, 2008). Other studies have reported detection of the optogenetic stimulation of ~300 neurons (Huber et al., 2008). However, although the animal can detect the stimulation, it is unclear what effect this small perturbation is having on the network and to what degree this will alter the animal’s ability to perform a task. This thesis investigates the effect on both the local network and on behaviour of several magnitudes of neuronal perturbation, from a single spike to the excitation of several thousand neurons. Finding the limitations under which a network can function provides powerful insights into how neurons interact to form meaningful networks. I performed simultaneous intra- and multi-unit extracellular recordings from the rat barrel cortex. I introduced a single spike into the patched neuron, and monitored the evolution of network activity via the extracellular probe. I found that the introduction of a single spike in a neuron produces a detectable increase in firing rate in the local network. To extend the investigation, channelrhodopsin-2 (ChR2), a light-sensitive membrane protein, was electroporated under visual control into a small number (1 - 10) of layer 2/3 pyramidal cells in the somatosensory cortex of the adult mouse. After exciting the ChR2-positive neurons, the resulting network activity was measured both by cell-attached and whole-cell patch-clamp recordings from nearby neurons and by monitoring up to 50 nearby cells in different cortical layers using the multi-site silicon probe. I found that excitation of a small number of neurons caused an increase in the spike rate of the local network, which lasted up to 300 ms. On the next level, large-scale perturbations were introduced into the brain by the optogenetic excitation of several thousand neurons in the cortexof transgenic mice expressing ChR2 under the Thy1 promoter. A short (2-20 ms) pulse of blue light produced a strong initial response, measured in both the LFP and spiking activity across supragranular layers of the barrel cortex. This initial response was often followed by ~5 bursts of spikes which resulted in an oscillation in the LFP. This oscillation was found to be of similar frequency and time-scale to an oscillation recorded in the barrel cortex resulting from the deflection of a single whisker. After pharmacologically blocking activity in the thalamus, confirmed by loss of the whisker response, the light-induced oscillations disappeared, indicating that the thalamus is necessary for their propagation. Optogenetic stimulation was also able to generate oscillations in the awake animal. I investigated the effect of such a large perturbation on mice undergoing a simple whisker-deflection discrimination task. It was found that the performance of the mice initially dropped to chance level if a strong perturbation was delivered 100 ms before the sensory stimulation. If the strong perturbation was sustained for every trial, the performance of the mice did not improve. If the perturbing stimulation was removed and then introduced gradually, the animal was able to adapt to the stimulation and learn to perform the task despite the perturbation. In summary, small perturbations have a measurable effect on the local network, implying the use of a rate code for at least some brain states in the barrel cortex. A large perturbation produces a strong cortical response, which often leads to a strong oscillation. The same stimulus interferes with the behaviour of a mouse undergoing a simple task, and yet the mouse can learn to perform accurately despite the noise. Together, these findings suggest a coding regime with high degrees of redundancy and robustness. Although the cortical activity patterns are easily perturbed - even a single spike causes a temporary increase in firing rate - this disturbance does not have debilitating effects on the behaviour or the experience of the animal

Development of Local Feature Extraction and Reduction Schemes for Iris Biometrics

Iris is one of the most reliable biometric trait used for human recognition due to its stability and randomness. Typically, recognition concerns with the matching of the features extracted from the iris regions. A feature extraction method can be categorized as local or global, depending on the manner in which the features are extracted from an image. In case of global features fail to represent details of an image because, the computation is focused on the image as a whole. On the contrary, local features are more precise and capable of representing the details of an image as they are computed from specific regions of the image. In the conventional approaches, the local features consider corners as keypoints, that may not always be suitable for iris images. Salient regions are visually pre-attentive distinct portions in an image and are appropriate candidate for interest points. The thesis presents a salient keypoint detector called Salient Point of Interest using Entropy (SPIE). Entropy from local segments are used as the significant measure of saliency. In order to compute the entropy value of such portions, an entropy map is generated. Scale invariance property of the detector is achieved by constructing the scale-space for the input image. Generally local feature extraction methods suffer from high dimensionality. Thus, they are computationally expensive and unsuitable for real-time application. Some reduction techniques can be applied to decrease the feature size and increase the computational speed. In this thesis, feature reduction is achieved by decreasing the number of keypoints using density-based clustering. The proposed method reduces keypoints efficiently, by grouping all the closely placed keypoints into one. Each cluster is then represented by a keypoint with its scale and location, for which an algorithm is presented. The proposed schemes are validated through publicly available databases, which shows the superiority of the proposed ones over the existing state-of-the-art methods

Acquisition of chemical recognition cues facilitates integration into ant societies

<p>Abstract</p> <p>Background</p> <p>Social insects maintain the integrity of their societies by discriminating between colony members and foreigners through cuticular hydrocarbon (CHC) signatures. Nevertheless, parasites frequently get access to social resources, for example through mimicry of host CHCs among other mechanisms. The origin of mimetic compounds, however, remains unknown in the majority of studies (biosynthesis vs. acquisition). Additionally, direct evidence is scarce that chemical mimicry is indeed beneficial to the parasites (e.g., by improving social acceptance).</p> <p>Results</p> <p>In the present study we demonstrated that the kleptoparasitic silverfish <it>Malayatelura ponerophila </it>most likely acquires CHCs directly from its host ant <it>Leptogenys distinguenda </it>by evaluating the transfer of a stable-isotope label from the cuticle of workers to the silverfish. In a second experiment, we prevented CHC pilfering by separating silverfish from their host for six or nine days. Chemical host resemblance as well as aggressive rejection behaviour by host ants was then quantified for unmanipulated and previously separated individuals. Separated individuals showed reduced chemical host resemblance and they received significantly more aggressive rejection behaviour than unmanipulated individuals.</p> <p>Conclusion</p> <p>Our study clarifies the mechanism of chemical mimicry in a social insect parasite in great detail. It shows empirically for the first time that social insect parasites are able to acquire CHCs from their host. Furthermore, it demonstrates that the accuracy of chemical mimicry can be crucial for social insect parasites by enhancing social acceptance and, thus, allowing successful exploitation. We discuss the results in the light of coevolutionary arms races between parasites and hosts.</p

Effect of mutations in the β1-thyroid hormone receptor on the inhibition of T3 binding by desethylamiodarone

AbstractDesethylamiodarone (DEA) acts as a competitive inhibitor of triiodothyronine (T3) binding to the α1-thyroid hormone receptor (TRα1) but as a non-competitive inhibitor with respect to TRβ1. To gain insight into the position of the binding site of desethylamiodarone on TRβ1 we investigated the naturally occurring mutants Y321C, R429Q, P453A, P453T and the artificial mutants L421R and E457A in the ligand binding domain of human TRβ1. The IC50 values (in μM) of DEA for P453A (50±11) and P453T (55±16) mutant TRβ1 are not different from that for the wild type TRβ1 (56±15), but the IC50 values of R429Q (32±7; P<0.001) and E457A (17±3; P<0.001) are significantly lower than of the wild type. Scatchard plots and Langmuir analyses indicate a non-competitive nature of the inhibition by DEA of T3 binding to all four mutant TRβ1s tested. Mutants P453A and P453T do not influence overall electrostatic potential, and also do not influence the affinity for DEA compared to wild type. Mutant E457A causes a change from a negatively charged amino acid to a hydrophobic amino acid, enhancing the affinity for DEA. Mutant R429Q, located in helix 11, causes an electrostatic potential change from positive to uncharged, also resulting in greater affinity for DEA. We therefore postulate that amino acids R429 and E457 are at or close to the binding site for DEA, and that DEA does not bind in the T3 binding pocket itself, in line with the non-competitive nature of the inhibition of T3 binding to TRβ1 by DEA

Sensory cut-off point obtained from survival analysis statistics

In the present work we applied interval-censored survival analysis techniques to estimate sensory cut-off points based on consumer’s decision to accept or reject food products taking into account the inherent variability in sensory measurements. We compared the values obtained using this survival analysis methodology with those obtained by applying a previous regression based method. Cut-off point (COP) estimations were made for acid flavor in yogurt, strawberry flavor in a strawberry flavored drink and appearance quality index in broccoli. For two of these products the regression based cut-off points were unrealistic, and would lead to much too conservative COP’s, leading to unnecessary rejection of samples in quality control inspections or very short shelf-lives. For one of the products (strawberry flavored drink), the survival and regression-based COP’s were comparable. The survival analysis methodology is recommended for estimating sensory cut-off points in food products.Peer ReviewedPostprint (author’s final draft