Measurements of dielectrophoretic collection spectra of Escherichia coli and Staphylococcus aureus suspensions are used for obtaining dielectric characteristics of both types of bacteria. The experiments are interpreted using a numerical method that models the cells as compartmented spherical or rod-like particles. We show the usefulness of this simple method to extract significant information about the electrical properties of Gram-negative and -positive bacteria.

To determine why some pathways but not others produce sizable local field potentials (LFPs) and how far from the source can these be recorded, complementary experimental analyses and realistic modeling of specific brain structures are required. In the present study, we combined multiple in vivo linear recordings in rats and a tridimensional finite element model of the dentate gyrus, a curved structure displaying abnormally large positive LFPs. We demonstrate that the polarized dendritic arbour of granule cells (GCs), combined with the curved layered configuration of the population promote the spatial clustering of GC currents in the interposed hilus and project them through the open side at a distance from cell domains. LFPs grow up to 20 times larger than observed in synaptic sites. The dominant positive polarity of hilar LFPs was only produced by the synchronous activation of GCs in both blades by either somatic inhibition or dendritic excitation. Moreover, the corresponding anatomical pathways must project to both blades of the dentate gyrus as even a mild decrease in the spatial synchronization resulted in a dramatic reduction in LFP power in distant sites, yet not in the GC domains. It is concluded that the activation of layered structures may establish sharply delimited spatial domains where synaptic currents from one or another input appear to be segregated according to the topology of afferent pathways and the cytoarchitectonic features of the target population. These also determine preferred directions for volume conduction in the brain, of relevance for interpretation of surface EEG recordings.

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Progress in microelectrode-based technologies has facilitated the development of sophisticated methods for manipulating and separating cells, bacteria, and other bioparticles. For many of these various applications, the theoretical modeling of the electrical response of compartmentalized particles to an external field is important. In this paper we address the analysis of the interaction between cells immersed in rf fields. We use an integral formulation of the problem derived from a consideration of the charge densities induced at the interfaces of the particle compartments. The numerical solution by a boundary element technique allows characterization of their dielectric properties. Experimental validation of this theoretical model is obtained by investigating two effects: (1) The influence that dipolar "pearl chaining" has on the dielectrophoretic behavior of human T lymphocytes and (2) the frequency variation of the spin and orbital torques of approaching insulinoma beta-cells in a rotating field.

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The aim of this study was to perform a Rasch analysis on the 5-level ordinal scale version of the Locomotor Capabilities Index (LCI-5), in order to investigate rating scale quality and conduct reliability and validity assessments. A questionnaire was mailed to 144 subjects who had undergone lower limb amputation (LLA) in the previous five years and completed a rehabilitation and prosthetic training programme. A total of 123 persons (85%) responded to the questionnaire, a self-report assessment of prosthetic capability and performance which included the LCI-5, the Mobility Section of the Prosthesis Evaluation Questionnaire (PEQ-MS) and other variables associated to prosthetic wear and use. Following Rasch analysis and expert review, the LCI-5 response categories level 1 ('yes, if someone helps me') and 2 ('yes, if someone is near me') were combined into a single category and 4 items were deleted (due to misfitting). The remaining 10 items fitted the Rasch model (LCI10-4) and demonstrated good reliability (person separation reliability ¼ 0.94, item separation reliability ¼ 0.98) and internal construct validity. Moreover, the good correlation with the PEQ-MS (r s ¼ 0.77) and with prosthetic wear and use (r s range 0.34 -0.51) supported the convergent validity of the scale. In conclusion, Rasch analysis provided the rationale for improving the measurement qualities of the LCI-5, refining its rating scale (through category diagnostics), identifying those items most useful for measuring the intended construct (as per the indexes of unidimensionality and internal construct validity) and showing that one can place high confidence in the consistency of both the person-ability and item-difficulty estimates obtained (reliability).

This paper shows the importance of using a cell model with the proper geometry, orientation and internal structure to study possible cellular effects from direct radiofrequency exposure. For this purpose, the electric field intensity is calculated, using the finite element numerical technique, in single- and multilayer spherical, cylindrical and ellipsoidal mammalian cell models exposed to linearly polarized electromagnetic plane waves of frequencies 900 and 2450 MHz. An extensive analysis is performed on the influence that the cell geometry and orientation with respect to the external field have in the value of the electric field induced in the membrane and cytoplasm. We also show the significant role that the cytoplasmic and extracellular bound water layers play in determining the electric field intensity for the cylindrical and ellipsoidal cell models. Finally, a study of the mutual interactions between cells shows that polarizing effects between cells significantly modify the values of field intensity within the cell.

Station and link location, Circular line, Line designing, Degree of a node, 90B06, 90B80, 90C10, 90C35,