Accurate micro-computed tomography imaging of pore spaces in collagen-based scaffold

In this work we have used X-ray micro-computed tomography (μCT) as a method to observe the morphology of 3D porous pure collagen and collagen-composite scaffolds useful in tissue engineering. Two aspects of visualizations were taken into consideration: improvement of the scan and investigation of its sensitivity to the scan parameters. Due to the low material density some parts of collagen scaffolds are invisible in a μCT scan. Therefore, here we present different contrast agents, which increase the contrast of the scanned biopolymeric sample for μCT visualization. The increase of contrast of collagenous scaffolds was performed with ceramic hydroxyapatite microparticles (HAp), silver ions (Ag⁺) and silver nanoparticles (Ag-NPs). Since a relatively small change in imaging parameters (e.g. in 3D volume rendering, threshold value and μCT acquisition conditions) leads to a completely different visualized pattern, we have optimized these parameters to obtain the most realistic picture for visual and qualitative evaluation of the biopolymeric scaffold. Moreover, scaffold images were stereoscopically visualized in order to better see the 3D biopolymer composite scaffold morphology. However, the optimized visualization has some discontinuities in zoomed view, which can be problematic for further analysis of interconnected pores by commonly used numerical methods. Therefore, we applied the locally adaptive method to solve discontinuities issue. The combination of contrast agent and imaging techniques presented in this paper help us to better understand the structure and morphology of the biopolymeric scaffold that is crucial in the design of new biomaterials useful in tissue engineering.     

Numerical simulation of the system “fixture–workpiece” for lever machining

In this article, the new configuration of fixture was proposed for ensuring the sufficient tool accessibility, which allows carrying out multiaxis machining of levers in one setup. The research based on numerical simulation was confirmed that the proposed fixture corresponds to all the accuracy parameters. Workpieces from steel, cast iron and aluminium alloy were investigated within the simulation. The values of displacements and stresses occurring during machining are less for proposed fixture in comparison with the existing fixtures that was confirmed by the deflected mode analysis. The modal analysis proved that the proposed fixture has much higher value of eigenfrequency than the other fixtures. To optimize the machining, the dependences for displacements and stresses on the cutting depth were determined. Oscillations of the system “fixture–workpiece” during machining were investigated for various manufacturing steps of levers machining of the fixtures from different fixture systems. The results of harmonic analysis showed that the dynamic stiffness of the proposed fixture was higher than that for the dedicated and modular fixtures. The oscillation amplitudes in the places of machined surfaces in the proposed fixture do not exceed the tolerance requirements for lever manufacturing.     

Fretting fatigue wear behavior of Y‐TZP dental ceramics processed by non‐conventional microwave sintering

The fretting wear behavior of self‐mated Y‐TZP dental materials obtained by nonconventional microwave and conventional sintering has been investigated. Two 3Y‐TZP materials, a widely utilized commercial dental ceramic (LAVA) and a lab‐prepared 3Y‐TZP powder based equivalent have been assessed. Relative density and mechanical properties as well as the grain size variations upon sintering have been evaluated. After exposure to selected gross slip regime fretting wear conditions, the wear tracks have been characterized allowing the measurement of the coefficient of friction, track profiles, and pit features. The results indicate that microwave sintering results in a similar fretting wear behavior as observed for conventional‐sintered 3Y‐TZP, as the measured volumetric wear loss is of a comparable order of magnitude. Regarding the influence of the grain size, the analysis revealed that a large grain size (>300 nm) results in an increased wear volume and that a higher resistance to fretting wear is constrained to a mid‐range particle size (100–250 nm). Since the fracture toughness of all investigated ceramic grades was comparable, the influence of the fracture toughness on fretting could not be assessed. Abrasive grooving, delamination, and microcracking have been identified as major wear mechanisms inside the wear tracks for both conventional‐ and microwave‐sintered 3Y‐TZP. In general, microwave sintering can provide 3Y‐TZP dental materials with a comparable fretting wear resistance as that observed for conventional sintering using lower dwell sintering temperatures and a shorter processing time.     

Transformations of structures: An algebraic approach

This paper introduces a new mathematical approach to transformations of structures, where the concept of structure is extremely general. Many structures and transformations that arise in biology as well as computer science are special cases of our concepts. A structure may be changed by finding an occurrence of a pattern and replacing it by another pattern as specified by a rule. To prove theorems about long sequences of applications of complicated rules, we need precise and tractable mathematical definitions of rules and how to apply them. This paper presents such definitions and three fundamental theorems, together with brief remarks on applications to control flow analysis, record handling, and evaluation of recursively defined functions. Unlike some previous efforts toward a rigorous theory of transformations of structures, this paper uses ideas and results from abstract algebra to minimize the need for elaborate constructions.A condensation of an earlier version of this paper was presented as [9] at the 7th Symposium on Mathematical Foundations of Computer Science, September 1978, Zakopane, Poland. Work by Ehrig was partially supported by IBM Germany and IBM World Trade Corp. Work by Rosen and Maggiolo-Schettini was partially supported by the Laboratorio di Cibernetica del C.N.R.     

Detection and localization of selected acoustic events in acoustic field for smart surveillance applications

A method for automatic determination of position of chosen sound events such as speech signals and impulse sounds in 3-dimensional space is presented. The events are localized in the presence of sound reflections employing acoustic vector sensors. Human voice and impulsive sounds are detected using adaptive detectors based on modified peak-valley difference (PVD) parameter and sound pressure level. Localization based on signals from the multichannel acoustic vector probe is performed upon the detection. The described algorithms can be employed in surveillance systems to monitor behavior of public events participants. The results can be used to detect sound source position in real time or to calculate the spatial distribution of sound energy in the environment. Moreover, the spatial filtration can be performed to separate sounds arriving from a chosen direction.     

Multi-letter quantum finite automata: decidability of the equivalence and minimization of states

Multi-letter quantum finite automata (QFAs) can be thought of quantum variants of the one-way multi-head finite automata (Hromkovi?, Acta Informatica 19:377?C384, 1983). It has been shown that this new one-way QFAs (multi-letter QFAs) can accept with no error some regular languages, for example (a?+?b)*b, that are not acceptable by QFAs of Moore and Crutchfield (Theor Comput Sci 237:275?C306, 2000) as well as Kondacs and Watrous (66?C75, 1997; Observe that 1-letter QFAs are exactly measure-once QFAs (MO-1QFAs) of Moore and Crutchfield (Theor Comput Sci 237:275?C306, 2000)). In this paper, we study the decidability of the equivalence and minimization problems of multi-letter QFAs. Three new results presented in this paper are the following ones: (1) Given a k ₁-letter QFA ${{\mathcal A}_1}$ and a k ₂-letter QFA ${{\mathcal A}_2}$ over the same input alphabet ??, they are equivalent if and only if they are (n ² m ^k-1?m ^k-1?+?k)-equivalent, where m =?|??| is the cardinality of ??, k =?max(k ₁,k ₂), and n =?n ₁?+?n ₂, with n ₁ and n ₂ being numbers of states of ${{\mathcal A}_{1}}$ and ${{\mathcal A}_{2}}$ , respectively. When k =?1, this result implies the decidability of equivalence of measure-once QFAs (Moore and Crutchfield in Theor Comput Sci 237:275?C306, 2000). (It is worth mentioning that our technical method is essentially different from the previous ones used in the literature.) (2) A polynomial-time O(m ^2k-1 n ⁸?+?km ^k n ⁶) algorithm is designed to determine the equivalence of any two multi-letter QFAs (see Theorems 2 and 3; Observe that if a brute force algorithm to determine equivalence would be used, as suggested by the decidability outcome of the point (1), the worst case time complexity would be exponential). Observe also that time complexity is expressed here in terms of the number of states of the multi-letter QFAs and k can be seen as a constant. (3) It is shown that the states minimization problem of multi-letter QFAs is solvable in EXPSPACE. This implies also that the state minimization problem of MO-1QFAs (see Moore and Crutchfield in Theor Comput Sci 237:275?C306, 2000, page 304, Problem 5), an open problem stated in that paper, is also solvable in EXPSPACE.     

A differential double-coil inductive transducer for measuring electrical conductivity

A differential system of two double-coil inductive transducers for the contactless measurement of the electrical conductivity of conducting materials has been presented. The differential system can be employed in applications that require smaller measurement uncertainty than that provided by the single-transducer system. A mathematical model of the differential system is based on the model of a single double-coil inductive transducer; in this case, a so-called processing function is defined as a ratio of voltages at the measurement coil terminals with and without the test sample. The relative differential voltage of the differential system is derived as a difference of processing functions of two single transducers and depends on a relative difference between conductivities of the test and reference samples. The conductivity of the test sample is obtained either using precalculated graphs or by numerically processing the equation of the differential voltage. In order to verify the obtained theoretical results, experimental investigations have been carried out using a computer-controlled measurement system with the differential system of the transducers. The conductivity measurements have been carried out using samples made of aluminum rods. During the measurements, the temperature of the reference sample was equal to room temperature (20 degrees C), whereas the temperature of the test sample was changed in the range of 0-20 degrees C to obtain the conductivity variation. The obtained experimental results confirmed the accuracy of the theoretical model of the differential transducer.     

On Smart City and Safe City Concepts

Mobile Networks and Applications - With current environmental and social challenges in mind, we can say, that Smart Cities are becoming the need of modern society. Many cities in the world are...     

Note on generating fuzzy concept lattices via Galois connections

The aim of this paper is to compare an approach of creating fuzzy concept lattices proposed by Popescu with several other approaches. Particularly, we show that this approach is in some way equivalent to the approach of Kraj?i called generalized concept lattices. We also give a straightforward generalization of Popescu’s approach to non-homogeneous cases.