Development of a nucleic acid lateral flow immunoassay for simultaneous detection of Listeria spp. and Listeriamonocytogenes in food

We present a new nucleic acid lateral flow immunoassay (NALFIA) for the assessment of listeria contamination. The detection procedure starts with enrichment of sample in Half Fraser broth (24 h). Following isolation of DNA, a duplex PCR is performed with two labelled primer sets, one generic and directed to a specific sequence of the gene encoding 16S rRNA from Listeria spp. and the other specific and directed to a part of the prfA gene encoding the central virulence gene regulator from the food pathogen Listeria monocytogenes (3.5 h). The PCR solution is directly added to the one-step assay device and the appearance of a grey/black line is indicative of the presence of specific amplicons (max 15 min). In all tests performed, the method correctly identified L. monocytogenes and strains of Listeria spp. PCR material of over 20 food samples was tested by NALFIA. The method proved to be useful for the detection of L. monocytogenes in different kinds of food sample

The interpretation of artifacts : a critique of Dennett's design stance

The Interpretation of Artifacts; A Critique of Dennett’s Design Stance Technological artifacts are a pervasive part of human life. They are, however, largely ignored in the analytic philosophical tradition, especially by philosophical naturalists. Being mind-dependent phenomena, tied up with human intentionality, analytic philosophers have largely found the topic unscientific, not objective, or simply trivial. An important exception is Daniel Dennett, who puts design at the heart of his naturalistic theory of mind

Nucleic Acid Lateral Flow Immunoassay for the Detection of Pathogenic Bacteria from Food

Nucleic acid lateral flow immunoassay (NALFIA) is a method combining molecular biological principle of detection with immunochemical principle of visualisation. Following isolation of DNA from the sample, a duplex PCR with two primer sets, of which one was labelled with biotin and the other with digoxigenin or fluorescein, respectively, was performed. The PCR solution and carbon particles conjugated with avidin are directly added to the nitrocellulose membrane with two test lines of immobilised antibodies specific for digoxigenin and fluorescein. The appearance of a black line indicates the presence of specific amplicon. We would like to present the NALFIA for the simultaneous detection of L. monocytogenes in particular and the genus Listeria in general, in food. Bacteria from the genus Listeria frequently contaminate a large variety of foods. Occurrence of Listeria strains in food may indicate errors in good hygienic and manufacturing practice, only L. monocytogenes is a significant human and animal pathogen responsible for the serious illness listeriosis. Conventional microbiological methods for L. monocytogenes detection are laborious and take several days to achieve a confirmed identification

Probing quantum-mechanical level repulsion in disordered systems by means of time-resolved selectively-excited resonance fluorescence

We argue that the time-resolved spectrum of selectively-excited resonance fluorescence at low temperature provides a tool for probing the quantum-mechanical level repulsion in the Lifshits tail of the electronic density of states in a wide variety of disordered materials. The technique, based on detecting the fast growth of a fluorescence peak that is red-shifted relative to the excitation frequency, is demonstrated explicitly by simulations on linear Frenkel exciton chains.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Short to long-range charge-transfer excitations in the zincbacteriochlorin-bacteriochlorin complex: a Bethe-Salpeter study

We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbacteriochlorin dyad, a paradigmatic photosynthetic complex. In great contrast with standard timedependent density functional theory calculations with (semi)local kernels, charge transfer excitations are correctly located above the intramolecular Q-bands transitions found to be in excellent agreement with experiment. Further, the asymptotic Coulomb behavior towards the true quasiparticle gap for charge transfer excitations at long distance is correctly reproduced, showing that the present scheme allows to study with the same accuracy intramolecular and charge transfer excitations at various spatial range and screening environment without any adjustable parameter.Comment: 5 pages, 2 figures, 1 tabl

Linear motor motion control using a learning feedforward controller

The design and realization of an online learning motion controller for a linear motor is presented, and its usefulness is evaluated. The controller consists of two components: (1) a model-based feedback component, and (2) a learning feedforward component. The feedback component is designed on the basis of a simple second-order linear model, which is known to have structural errors. In the design, an emphasis is placed on robustness. The learning feedforward component is a neural-network-based controller, comprised of a one-hidden-layer structure with second-order B-spline basis functions. Simulations and experimental evaluations show that, with little effort, a high-performance motion system can be obtained with this approach

Box traps on an atom chip for one-dimensional quantum gases

We present the implementation of tailored trapping potentials for ultracold gases on an atom chip. We realize highly elongated traps with box-like confinement along the long, axial direction combined with conventional harmonic confinement along the two radial directions. The design, fabrication and characterization of the atom chip and the box traps is described. We load ultracold ($\lesssim1 \mu$K) clouds of $^{87}$Rb in a box trap, and demonstrate Bose-gas focusing as a means to characterize these atomic clouds in arbitrarily shaped potentials. Our results show that box-like axial potentials on atom chips are very promising for studies of one-dimensional quantum gases.Comment: 9 pages 4 figure

Structure and function of the cerebral organs in 'Paranemertes peregrina', 'Tetrastemma candidum' and 'Amphiporus lactifloreus' (Hoplonemertea : Monostilifera)

The histology and ultrastructure of the cerebral organs have been studied in three species of monostiliferous hoplonemertean: Paranemertes penegnina Coe, Amphiporus lactifloreus (Johnston) and Tetrastemma candidum (O.F. Muller). The role of the cerebral organs in osmoregulation and behaviour has been investigated in Paranemertes. Based on the information obtained, it is concluded that the cerebral organs in these species are chemoreceptors. The structure of the cerebral organs is essentially the same in the three species studied. The cerebral organs consist of two groups of sensory cells, two groups of gland cells, and two groups of endocytic/lysosomal cells (vesicular cells), as well as ciliated cells and support cells, surrounding a ciliated, blind-ending canal. The canal is functionally divided into two channels, designated the major and minor canals. According to the orientation of ciliary basal feet in cells of the canal epithelium, the minor canal is an incurrent channel, and the major canal is an excurrent channel. The organization of cell types with respect to the direction of flow in the canal is such that along the minor canal; Type A gland cell processes are upstream from Type 2 sensory cell dendrites, and Type 2 vesicular cells are downstream from the dendrites. Similarly, in the major canal. Type B gland cell processes are upstream, and Type 1 vesicular cells are downstream, from Type 1 sensory cell dendrites. Based on this organization, and on the interpretation of cellular fine structure in the cerebral organs, it is proposed that the function of gland cells is to secrete a mucous coating over the sensory epithelium, and the function of vesicular cells is to remove this coating from the canal as the mucus is carried downstream from the dendrites by ciliary action. In gland cells, the amount of secretion product present may be regulated by autophagic breakdown of secretion granules (crinophagy), according to a variable demand for secretion in the canal. Crinophagy contributes to the amount of vesicular material (degraded secretion product) present in the cerebral organs. Although the dendrites are not innervated, dendrite sensitivity may be modulated by variation of the rate of flow through the canal, and the rate of mucous turnover across the two sensory epithelia. An efferent nerve fibre is present among the ciliated cells of the minor canal. The fibre is rare and its synapse has not been observed. It is thought that the fibre innervates a few cells which act as pacemakers, their cilia mechanically entraining the beat frequency of other cilia, thus determining the rate of flow through the canal. There is no indication that vesicular material is disposed of outside the cerebral organs. In Paranemertes and Amphiporus, but not in Tetrastemma, the cephalic blood vessel lies adjacent to the posterior glandular part of the cerebral organ, however, this association is not reflected in the internal structure of the cerebral organs. It is, therefore, unlikely that the cerebral organs in these species have an endocrine function. The function of the cerebral organs in Paranemertes has been investigated by comparing the behaviour of intact worms with the behaviour of worms from which the cerebral organs have been surgically removed. Cerebral organ removal did not affect trail following behaviour, which is associated with homing, but it abolished the response of Paranemertes to prey trails. It is concluded that the cerebral organs of Paranemertes are chemoreceptors responsible for the detection of prey. The behavioural physiology of Paranemertes has been investigated, using extracellular suction electrodes to record from the lateral nerve cords and the cerebral organ nerves. The results indicate that the cerebral organs are sensitive to prey extract and distilled water, but not to mechanical, thermal or photic stimuli. The role of the cerebral organs of Paranemertes in salinity stress tolerance has been investigated by measuring the effect of cerebral organ removal on volume regulation, and by observing the effects of hypo-osmotic media on the cytology of the cerebral organs. Removal of the cerebral organs decreases volume regulatory capacity, however, a similar change is seen in sham-operated worms, indicating that the decreased capacity for regulation is due to the operation itself and not to interference with a physiological role of the cerebral organs. Cytological changes caused by exposure to dilute sea water are similar to those seen in worms fixed in hypo-osmotic fixative. It is unlikely, therefore, that these represent a co-ordinated response of the organs to salinity stress. No exchange of material between the cerebral organs and the vascular system was observed. It is concluded that in Paranemertes, the cerebral organs are not involved in osmoregulation

Efficiency of energy transfer in a light-harvesting system under quantum coherence

We investigate the role of quantum coherence in the efficiency of excitation transfer in a ring-hub arrangement of interacting two-level systems, mimicking a light-harvesting antenna connected to a reaction center as it is found in natural photosynthetic systems. By using a quantum jump approach, we demonstrate that in the presence of quantum coherent energy transfer and energetic disorder, the efficiency of excitation transfer from the antenna to the reaction center depends intimately on the quantum superposition properties of the initial state. In particular, we find that efficiency is sensitive to symmetric and asymmetric superposition of states in the basis of localized excitations, indicating that initial state properties can be used as a efficiency control parameter at low temperatures.Comment: Extended version of original paper. 7 pages, 2 figure