Rapid computation of eddy current signals from narrow cracks

An existing boundary element method model for eddy current inspection of ideal or narrow cracks is revised. Using some lately devised concepts on efficiently and rapidly simulating canonical eddy current geometries, we show how this model can be made easier to implement and faster to calculate. The approach is largely based on a novel method for rapidly calculating the Green's function and reducing the matrix fill-time, and also on a similar method for rapidly computing the incident electric field. As a result, the model has been made an order of magnitude faster than the existing one without sacrificing accuracy. We pay attention to numerical analysis details and analyze issues that so far have not been clarified. The validity of our approach is also verified by the experiment. Although we have tested the model against published data, we have also produced our own precision measurements for surface and through-the-thickness slots in plates with the coils performing scans along and across the slots at various frequencies.     

Continuous electromagnetic radiation monitoring in the environment: analysis of the results in Greece

Non-ionising radiation-monitoring networks were initiated as a result of the public concerns about the potential health effects from telecommunication emissions. In the present study, the data acquired from such networks in Greece are used to assess the changes in the outdoor electromagnetic environment with respect to location and time. The study shows that there is a statistically significant difference between the urban (median electric field: 1.1 V m(-1)) and the rural (median electric field: 0.3 V m(-1)) installations of monitoring units and also shows that there is a median diurnal variation (daily maximum to minimum) of 20.2 and 33.8 % for the broadcasting and mobile telecommunication emissions, respectively. Moreover, there is a difference in the electric field between daytime and night, but not between morning and afternoon. The results are in line with previously published data from spot measurements, monitoring networks and personal exposimeter studies performed in several European countries.     

Adequately FRP confined reinforced concrete columns under axial compressive monotonic or cyclic loading

The study presents the experimental behavior of reinforced concrete square section specimens, externally confined by carbon or glass Fiber Reinforced Polymer (FRP) sheets. The columns are subjected to axial compressive monotonic or repeated load-unload cycles gradually increasing up to failure. The research focuses on columns with longitudinal bars which are critical to premature buckling while examining their effect on lower limit cases of strengthening through FRP confinement. Experiments include also plain concrete FRP confined columns and columns with bars adequately supported by transverse steel reinforcement for comparison. External FRP strengthening covers a wide range of volumetric mechanical FRP confinement ratios allowing comparative investigations. A significant variation in the behavior of FRP confined concrete comes up when bars are unstable, for a light external strengthening scheme as well as for monotonic or cyclic loading. The lower limits proposed by existing recommendations for adequate FRP confinement strengthening of columns are examined.     

Can the properties of carbon nanotubes influence their internalization by living cells?

Carbon nanotubes (CNTs) are widely used for biomedical applications as intracellular transporters of (bio)molecules, due to their high propensity to cross cell membranes. However, there is a clear discrepancy in the literature about their uptake mechanism, which should be related to the differences existing in the nanotube materials, as well as the experimental procedures. Despite the fact that there are some studies on the influence of the CNT surface chemistry, the role of the properties of non-functionalized CNTs in cellular uptake has not been much investigated to a great extent. In this work, different kinds of multi-wall CNTs (MWCNTs) are produced and fully characterized, in terms of diameter, length, metal impurity, carbon soot and surface chemistry. These MWCNT samples are tested in vitro, and the cellular uptake is indirectly evaluated by using standard fluorescent probes and confirmed by TEM images. Our assays demonstrate that nanotube length clearly influences their uptake and shorter (sub-1 μm) MWCNTs are easier to be internalized through an energy-independent pathway. The results of this investigation may be useful for the design of promising CNT-based vectors for cell therapy.     

Eddy-current interaction of a long coil with a slot in a conductive plate

We describe a truncated-domain method for calculating eddy currents in a plate with a long flaw. The plate is modeled as a conductive half-space and the flaw is a long slot with a rectangular cross section. A long two-dimensional (2-D) coil carrying an alternating current is aligned parallel to the slot. The coil impedance variation with frequency is determined for an arbitrary coil location. The electromagnetic field due to a long coil above a conductive half-space can be expressed as integrals of trigonometric functions. For a half-space with a long slot, however, additional boundary conditions must be satisfied at the slot walls. The truncated-domain method makes this possible by recasting the problem in a finite domain; as a result, the Fourier integral is replaced by a series. The domain can be made arbitrarily large, thereby yielding results that are numerically as close to the infinite domain solution as desired. We have used the truncated domain approach to study both eddy-current flaw interactions and edge effects in the limiting case of a very wide and deep slot. We confirmed the theoretical predictions by comparing them with results of a 2-D finite element calculation and of experiments.     

Overlapping B-trees: An implementation of a transaction time access method

A new variation of Overlapping B⁺-trees is presented, which provides efficient indexing of transaction time and keys in a two dimensional key-time space. Modification operations (i.e. insertions, deletions and updates) are allowed at the current version, whereas queries are allowed to any temporal version, i.e. either in the current or in past versions. Using this structure, snapshot and range-timeslice queries can be answered optimally. However, the fundamental objective of the proposed method is to deliver efficient performance in case of a general pure-key query (i.e. ‘history of a key’). The trade-off is a small increase in time cost for version operations and storage requirements.     

A Broadband Monitoring System for Electromagnetic-Radiation Assessment

A broadband monitoring system for measuring the total electric field radiated from broadcasting (radio, TV) and communications (mobile telephony, TETRA, WLAN) systems is presented. The system has been implemented for recording the field on a 24-hour basis. It has an omnidirectional sensor antenna and the appropriate electronic circuits. The heart of the system is a low-power, eight-bit RISC Microchip microcontroller, running at 10 MHz. Various digital and analog peripherals are connected to the microcontroller. The system can send the data to a personal computer through a USB interface, and can communicate through a GSM modem. Low cost and high reliability render the system inexpensive for the deployment of electromagnetic radiation-monitoring networks, and make it trustworthy for the public. Several tests of the sensor's pattern, the linearity of the response, and the frequency response have shown that the system can be successfully compared with commercially available systems.