Search results

Filters

  • Journals
  • Authors
  • Keywords
  • Date
  • Type

Search results

Number of results: 74
items per page: 25 50 75
Sort by:

Abstract

Matrix metalloproteinases 2 and 9 (MMP2 and MMP9) are proteolytic enzymes involved with extracellular matrix degradation. They play a role in tumor invasion and metastases. Be- cause of their ability to degrade signaling molecules presented in extracellular matrix, MMPs contribute to tumor proliferation and apoptosis. The aim of this study was to evaluate expression of MMP2 (latent and both active and latent forms) and MMP9 (active, latent, active and latent forms) in different subtypes of canine lymphomas and their relationship with proliferative (mi- totic index and percentage of Ki67-positive cells) and apoptotic (apoptotic index) markers. Ex- pression of MMPs was assessed immunohistochemically using an immunoreactive score system. Expression of both MMPs was found in all 20 examined lymphomas belonging to six subtypes. Most cases showed a moderate level of all analyzed forms of MMP2 and MMP9. High expres- sion of MMPs was found in single cases. Except for a positive correlation between the active form of MMP9 and the mitotic index for all lymphoma cases, no other correlations between any remaining forms of MMPs and neither proliferative nor apoptotic markers were found, irrespec- tive of whether the analysis encompassed all cases or the most numerous lymphoma subtypes i.e. centroblastic and Burkitt-like. Our results were not able to clearly confirm the influence of MMPs on the proliferation and apoptotic activity of canine lymphoma cells. However, further studies examining MMPs activity by zymography, expression of their inhibitors and other factors in- volved in activation of cell proliferation and apoptosis inhibition are needed to clarify the role of MMPs, especially the active form of MMP9, in the behavior of canine lymphoma cells.
Go to article

Abstract

The petrographic composition of coal has a significant impact on its technological and sorption properties. That composition is most frequently determined by means of microscope quantitative analyses. Thus, aside from the purely scientific aspect, such measurements have an important practical application in the industrial usage of coal, as well as in issues related to the safety in underground mining facilities. The article discusses research aiming at analyzing the usefulness of selected parameters of a digital image description in the process of automatic identification of macerals of the inertinite group using neural networks. The description of the investigated images was based on statistical parameters determined on the basis of a histogram and co-occurrence matrix (Haralick parameters). Each of the studied macerals was described by means of a 20-element feature vector. An analysis of its principal components (PCA) was conducted, along with establishing the relationship between the number of the applied components and the effectiveness of the MLP network. Based on that, the optimum number of input variables for the investigated classification task was chosen, which resulted in reduction of the size of the network’s hidden layer. As part of the discussed research, the authors also analyzed the process of classification of macerals of the inertinite group using an algorithm based on a group of MLP networks, where each network possessed one output. As a result, average recognition effectiveness of 80.9% was obtained for a single MLP network, and of 93.6% for a group of neural networks. The obtained results indicate that it is possible to use the proposed methodology as a tool supporting microscopic analyses of coal.
Go to article

Abstract

The uncontrolled power flow in the AC power system caused by renewable energy sources (restless sources, distributed energy sources), dynamic loads, etc., is one of many causes of voltage perturbation, along with others, such as switching effects, faults, and adverse weather conditions. This paper presents a three-phase voltage and power flow controller, based on direct PWM AC/AC converters. The proposed solution is intended to protect sensitive loads against voltage fluctuation and problems with power flow control in an AC power system. In comparison to other solutions, such as DVR, UPFC, the presented solution is based on bipolar matrix choppers and operates without a DC energy storage unit or DC link. The proposed solution is able to compensate 50% voltage sags, in the case of three-phase symmetrical voltage perturbation, and single phase voltage interruptions. Additionally, by means of a voltage phase control with a range of #6;60◦ in each phase, it is possible to control the power flow in an AC power system. The paper presents an operational description, a theoretical analysis based on the averaged state space method and four terminal descriptions, and the experimental test results from a 1 kVA laboratory model operating under active load.
Go to article

Abstract

The investigation results of the mechanical reclamation of spent moulding sands from the Cordis technology are presented in the paper. The quality assessment of the obtained reclaim and the influence of the reclaim fraction in a matrix on the core sand strength is given. The reclaim quality assessment was performed on the basis of the determination of losses on ignition, Na2O content on reclaim grains and pH values. The reclaim constituted 100%, 75% and 50% of the core sand matrix, for which the bending strength was determined. The matrix reclamation treatment was performed in the experimental rotor reclaimer RD-6. Spent sands were applied in as-delivered condition and after the heating to a temperature of 140 o C. Shaped samples for strength tests were made by shooting and hardening of sands in the warmbox technology.
Go to article

Abstract

We consider a four-level system with two subsystems coupled by weak interaction. The system is in thermal equilibrium. The thermodynamics of the system, namely internal energy, free energy, entropy and heat capacity, are evaluated using the canonical density matrix by two methods. First by Kronecker product method and later by treating the subsystems separately and then adding the evaluated thermodynamic properties of each subsystem. It is discovered that both methods yield the same result, the results obey the laws of thermodynamics and are the same as earlier obtained results. The results also show that each level of the subsystems introduces a new degree of freedom and increases the entropy of the entire system. We also found that the four-level system predicts a linear relationship between heat capacity and temperature at very low temperatures just as in metals. Our numerical results show the same trend.
Go to article

Abstract

The paper addresses the problem of constrained pole placement in discrete-time linear systems. The design conditions are outlined in terms of linear matrix inequalities for the Dstable ellipse region in the complex Z plain. In addition, it is demonstrated that the D-stable circle region formulation is the special case of by this way formulated and solved pole placement problem. The proposed principle is enhanced for discrete-lime linear systems with polytopic uncertainties.
Go to article

Abstract

This paper gives the simple algorithm for calculation of the degree and coefficients of the minimal polynomial for the complex matrix A = [aij]n x n .
Go to article

Abstract

This paper is devoted to measuring the continuous diagnosis capability of a system. A key metric and its calculation models are proposed enabling us to measure the continuous diagnosis capability of a system directly without establishing and searching the sequential fault tree (SFT) of the system. At first a description of a D matrix is given and its metric is defined to determine the weakness of a continuous diagnosis. Then based on the definition of a sequential fault combination, a sequential fault tree (SFT) is defined with its establishment process summarized. A key SFT metric is established to measure the continuous diagnosis capability of a system. Two basic types of dependency graphical models (DGMs) and one combination type of DGM are selected for characteristics analysis and establishment of metric calculation models. Finally, both the SFT searching method and direct calculation method are applied to two designs of one type of an auxiliary navigation equipment, which shows the high efficiency of the direct calculation method.
Go to article

Abstract

In the paper the parametric optimization problem for a linear system with two delays and a PD-controller is presented. In the parametric optimization problem the quadratic performance index is considered. The value of the quadratic index of quality is calculated due to the Lyapunov functional and is equal to the value of that functional for the initial function of the neutral system with two delays. The Lyapunov functional is determined by means of the Lyapunov matrix.
Go to article

Abstract

Austenitization is the first step of heat treatment preceding the isothermal quenching of ductile iron in austempered ductile iron (ADI) manufacturing. Usually, the starting material for the ADI production is ductile iron with more convenient pearlitic matrix. In this paper we present the results of research concerning the austenitizing of ductile iron with ferritic matrix, where all carbon dissolved in austenite must come from graphite nodules. The scope of research includedcarrying out the process of austenitization at 900o Cusing a variable times ranging from 5 to 240minutes,and then observations of the microstructure of the samples after different austenitizing times. These were supplemented with micro-hardness testing. The research showed that the process of saturating austenite with carbon is limited by the rate of dissolution of carbon from nodular graphite precipitates.
Go to article

Abstract

This paper discusses the mechanical properties of a material fabricated from commercially available metal powder mixtures designed for use as a metal matrix of diamond impregnated composites. The mixtures with the catalogue numbers CSA and CSA800 provided by a Chinese producer are suitable for experimental laboratory testing. The specimens were fabricated in a graphite mould using hot pressing. The material was tested for density, porosity, hardness, and tensile strength under static loading. A scanning electron microscope (SEM) was used to analyze the microstructure and cleavage fracture of broken specimens. It was essential to determine how the chemical composition and the fabrication process affected the microstructure and properties of the material. The properties of the sinters were compared with those of hot pressed specimens fabricated from sub-micron size cobalt powder (Cobalt SMS). Although the as-consolidated material is inferior to cobalt, it displays a favourable combination of hardness, yield strength and ductility, and seems to have a great potential for moderate and general purpose applications.
Go to article

Abstract

The stability of positive linear continuous-time and discrete-time systems is analyzed by the use of the decomposition of the state matrices into symmetrical and antisymmetrical parts. It is shown that: 1) The state Metzler matrix of positive continuous-time linear system is Hurwitz if and only if its symmetrical part is Hurwitz; 2) The state matrix of positive linear discrete-time system is Schur if and only if its symmetrical part is Hurwitz. These results are extended to inverse matrices of the state matrices of the positive linear systems.
Go to article

Abstract

We apply Bayesian inference to estimate transformation matrix that converts vector of industry outputs from NACE Rev. 1.1 to NACE Rev. 2 classification. In formal terms, the studied issue is a representative of the class of matrix balancing (updating, disaggregation) problems, often arising in the field of multi-sector economic modelling. These problems are characterised by availability of only partial, limited data and a strong role for prior assumptions, and are typically solved using bi-proportional balancing or cross-entropy minimisation methods. Building on Bayesian highest posterior density formulation for a similarly structured case, we extend the model with specification of prior information based on Dirichlet distribution, as well as employ MCMC sampling. The model features a specific likelihood, representing accounting restrictions in the form of an underdetermined system of equations. The primary contribution, compared to the alternative, widespread approaches, is in providing a clear account of uncertainty.
Go to article

Abstract

Light weight, low density with high mechanical properties and corrosion resistance, aluminum is the most important material and is commonly used for high performance applications such as aerospace, military and especially automotive industries. The researchers who participate in these industries are working hard to further decrease the weight of end products according to legal boundaries of greenhouse gases. A lot of research was undertaken to produce thin sectioned aluminum parts with improved mechanical properties. Several alloying element addition were investigated. Yet, nowadays aluminum has not met these expectations. Thus, composite materials, particularly metal matrix composites, have taken aluminum’s place due to the enhancement of mechanical properties of aluminum alloys by reinforcements. This paper deals with the overview of the reinforcements such as SiC, Al2O3 and graphene. Graphene has recently attracted many researcher due to its superior elastic modulus, high fatigue strength and low density. It is foreseen and predicted that graphene will replace and outperform carbon nanotubes (CNT) in near future.
Go to article

Abstract

The K4 graph and the inertia of the adjacency matrix for a connected planar graph. A substantial history exists about incorporating matrix analysis and graph theory into geography and the geospatial sciences. This study contributes to that literature, aiding in analyses of spatial relationships, especially in terms of spatial weights matrices. We focus on the n-by-n 0–1 binary adjacency matrix, whose rows and columns represent the nodes of a connected planar graph. The inertia of this matrix represents the number of positive (n+), negative (n−), and zero (n0) eigenvalues. Approximating the Jacobian term of spatial auto-normal models can benefit from calculating these matrix quantities. We establish restrictions for n- exploiting properties we uncover for the K4 graph.
Go to article

Abstract

In 1993 Engle and Kozicki proposed the notion of common features of which one example is a serial correlation common feature. We say that stationary, non-innovation processes exhibit common serial correlation when there exists at least one linear combination of them which is an innovation. Later on in 1993 Vahid and Engle combined the notions of cointegration among I(1) processes with common serial correlation within their first differences. It is commonly known that cointegrated time series have vector error correction (VEC) representation. The existence of common serial correlation leads to an additional reduced rank restriction imposed on the VEC model’s parameters. This type of restriction was later termed a strong form (SF) reduced rank structure, as opposed to a weak one introduced in 2006 by Hecq, Palm and Urbain. The main aim of the present paper is to construct the Bayesian vector error correction model with these additional strong form restrictions. The empirical validity of investigating both the short- and long-run co-movements between macroeconomic time series will be illustrated by the analysis of the price-wage nexus in the Polish economy.
Go to article

Abstract

A new method for computation of positive realizations of given transfer matrices of fractional linear continuous-time linear systems is proposed. Necessary and sufficient conditions for the existence of positive realizations of transfer matrices are given. A procedure for computation of the positive realizations is proposed and illustrated by examples.
Go to article

Abstract

In this paper, we present a synthesis of the parameters of the fiber Bragg grating (FBG) and the reconstruction of the distributed strain affecting the grating, performed by means of its reflection spectrum. For this purpose, we applied the transition matrix method and the Nelder-Mead nonlinear optimization method. Reconstruction results of the strain profile carried out on the basis of a simulated reflection spectrum as well as measured reflection spectrum of the FBG indicate good agreement with the original strain profile; the profile reconstruction errors are within the single digit percentage range. We can conclude that the Nelder-Mead optimization method combined with the transition matrix method can be used for distributed sensing problems.
Go to article

Abstract

The sound absorption property of polyurethane (PU) foams loaded with natural tea-leaf fibers and luffa cylindrica (LC) has been studied. The results show a significant improvement in the sound absorption property parallel to an increase in the amount of tea-leaf fibers (TLF). Using luffa-cylindrica as a filler material improves sound absorption properties of soft foam at all frequency ranges. Moreover, an increase in the thickness of the sample resulted in an improvement of the sound absorption property. It is pleasing to see that adding tea-leaf fibers and luffa-cylindrica to the polyurethane foam demonstrate a significant contribution to sound absorption properties of the material and it encourages using environmental friendly products as sound absorption material in further studies.
Go to article

Abstract

Porous materials are used in many vibro-acoustic applications. Different models describe their perfor- mance according to material’s intrinsic characteristics. In this paper, an evaluation of the effect of the porous and geometrical parameters of a liner on the acoustic power attenuation of an axisymmetric lined duct was performed using multimodal scattering matrix. The studied liner is composed by a porous ma- terial covered by a perforated plate. Empirical and phenomenal models are used to calculate the acoustic impedance of the studied liner. The later is used as an input to evaluate the duct attenuation. By varying the values of each parameter, its influence is observed, discussed and deduced
Go to article

Abstract

A hybrid method is presented for the integration of low-, mid-, and high-frequency driver filters in loud-speaker crossovers. The Pascal matrix is exploited to calculate denominators; the locations of minimum values in frequency magnitude responses are associated with the forms of numerators; the maximum values are used to compute gain factors. The forms of the resulting filters are based on the physical meanings of low-pass, band-pass, and high-pass filters, an intuitive idea which is easy to be understood. Moreover, each coefficient is believed to be simply calculated, an advantage which keeps the software-implemented crossover running smoothly even if crossover frequencies are being changed in real time. This characteristic allows users to efficiently adjust the bandwidths of the driver filters by subjective listening tests if objective measurements of loudspeaker parameters are unavailable. Instead of designing separate structures for a low-, mid-, and high-frequency driver filter, by using the proposed techniques we can implement one structure which merges three types of digital filters. Not only does the integration architecture operate with low computational cost, but its size is also compact. Design examples are included to illustrate the effectiveness of the presented methodology
Go to article

Abstract

A numerical method is developed for estimating the acoustic power of any baffled planar structure, which is vibrating with arbitrary surface velocity profile. It is well known that this parameter may be calculated with good accuracy using near field data, in terms of an impedance matrix, which is generated by the discretization of the vibrating surface into a number of elementary radiators. Thus, the sound pressure field on the structure surface can be determined by a combination of the matrix and the volume velocity vector. Then, the sound power can be estimated through integration of the acoustic intensity over a closed surface. On the other hand, few works exist in which the calculation is done in the far field from near field data by the use of radiation matrices, possibly because the numerical integration becomes complicated and expensive due to large variations of directivity of the source. In this work a different approach is used, based in the so-called Propagating Matrix, which is useful for calculating the sound pressure of an arbitrary number of points into free space, and it can be employed to estimate the sound power by integrating over a finite number of pressure points over a hemispherical surface surrounding the vibrating structure. Through numerical analysis, the advantages/disadvantages of the current method are investigated, when compared with numerical methods based on near field data. A flexible rectangular baffled panel is considered, where the normal velocity profile is previously calculated using a commercial finite element software. However, the method can easily be extended to any arbitrary shape. Good results are obtained in the low frequency range showing high computational performance of the method. Moreover, strategies are proposed to improve the performance of the method in terms of both computational cost and speed.
Go to article

Abstract

In this study, metal matrix composite materials containing melt-spun Al-20Si-5Fe alloys and boron carbide was produced by high energy ball milling and then hot pressing at 200 MPa pressure and 450°C. Mechanical and microstructural characterizations were performed by using an optical microscopy, X-Ray diffractometer, and dynamic microhardness tester. It was observed that boron carbide particles were homogenously distributed in the microstructure and values of microhardness and elastic modules were averagely 830 MPa and 42 GPa, respectively.
Go to article

This page uses 'cookies'. Learn more