On optimal cell planning: Case study for a DCS 1800 system

Micro and pico cell planning strategies are adopted in personal communication systems (PCS) in order to increase their capacity. The usage of the upper UHF band in combination with greater bandwidth is already proposed by telecom engineers in order to achieve the promised service quality and data rates. These strategies are characterized by an increased number of cells in specific geographical areas with the corresponding operating base transceiving stations (BTS) located at relatively low heights above the street level. In this case, the cell planning procedure in linear streets under line‐of‐sight (LOS) conditions needs further study concerning the technical characteristics of the PCS. In this paper, the propagation characteristics of a DCS 1800 system are investigated on a theoretical and experimental basis in a specific geographical area (center of Patras City in Northern Pelloponesse). An improved RF propagation model is proposed in order to determine the propagation path losses occurring under certain multipath fading conditions. Hence an optimum determination of a system's cellular area can be achieved. Copyright © 2001 John Wiley & Sons, Ltd.     

On the use of the BLYP functional for the DFT calculation of graphite–hydrogen systems

This letter focuses on a possible pitfall that can occur in the DFT calculation of graphite–hydrogen interactions under tokamaks conditions. Calculations based on the BLYP functional, in fact, result in a stable –C₂H₃ group that other functionals (OLYP, XLYP, PBE and BP) do not confirm.     

Transformation and Normal Vector Calculation of Parametrically Defined Surfaces Based on Dual Vectors and Screw Theory: Application to Phong's Shading Model

This paper presents a new approach for the transformation and normal vector calculation algorithms of parametrically defined surfaces via dual vectors and line transformations. The surface is defined via dual points, the transformation is performed by rotations and translations based on screw theory while normal vector calculation is utilized for shading based on Phong's illumination model. The main benefit of this approach lies into the compactness of the surface's representation since geometrical characteristics, such as tangent vectors, that are necessary for shading algorithms, are included within its definition. An extensive comparison is performed between the proposed approach and the traditional homogeneous model, presenting the merits of our approach. Analytical and experimental determination of the computational cost via computer implementation of 3D surface transformation and shading is presented. Point‐based methods for the representation, transformation and shading of parametrically defined surfaces are compared to the introduced line‐based methods (dual quaternions and dual orthogonal matrices). It is shown that the simplified rendering procedure of 3D objects, is considerably faster using screw theory over the traditional point‐based structures.     

Inverse Opal Scaffolds with Gradations in Mineral Content for Spatial Control of Osteogenesis

The design and fabrication of inverse opal scaffolds with gradations in mineral content to achieve spatial control of osteogenesis are described. The gradient in mineral content is established via the diffusion‐limited transport of hydroxyapatite nanoparticles in a closely packed lattice of gelatin microbeads. The mineral‐graded scaffold has an array of uniform pores and interconnected windows to facilitate efficient transport of nutrients and metabolic wastes, ensuring high cell viability. The graded distribution of mineral content can provide biochemical and mechanical cues for spatially regulating the osteogenic differentiation of adipose‐derived stromal cells. This new class of scaffolds holds promise for engineering the interfaces between mineralized and unmineralized tissues.     

Design and Fabrication of a Hierarchically Structured Scaffold for Tendon‐to‐Bone Repair

A hierarchically structured scaffold is designed and fabricated for facilitating tendon‐to‐bone repair. The scaffold is composed of three regions with distinct functions: (i) an array of channels to guide the in‐growth of cells and aligned deposition of collagen fibers, as well as integration of the scaffold with the tendon side, (ii) a region with a gradient in mineral composition to facilitate stress transfer between tendon and bone, and (iii) a mineralized inverse opal region to promote the integration of the scaffold with the underlying bone. Cell culture experiments confirm that adipose‐derived stromal cells are able to infiltrate and proliferate through the entire thickness of the scaffold without compromised cell viability. The seeded stem cells exhibit directed differentiation into tenocytes and osteoblasts along the mineral gradient as a response to the gradient in Young's modulus. This novel scaffold holds great promise to promote the formation of a functional tendon‐to‐bone attachment by offering a structurally and compositionally appropriate microenvironment for healing.     

Design and fabrication of drug‐eluting polymeric thin films for applications in ophthalmology

To study the development, characterisation, and drug release of one‐ and two‐layered thin films based on organic polymers [poly(D,L‐lactide‐co ‐glycolide) lactide:glycolide (65:35), poly(D,L‐lactide‐co ‐glycolide) lactide:glycolide (75:25), and polycaprolactone] and dexamethasone. To examine their applicability for intraocular lenses (IOLs) and function in intraocular drug delivery systems. Four series of thin films, single and double‐layer, were prepared by the spin‐coating method on a silicon substrate. The films were studied using atomic force microscopy and spectroscopic ellipsometry. The release rate of dexamethasone was studied for a period of ten weeks. Series A and C demonstrated the formation of large dexamethasone aggregates. The monolayer films of series C and D formed pores, in agreement with previous findings. The spectroscopic ellipsometry study demonstrated that the samples were transparent. The drug release study demonstrated that dexamethasone was released during the first 6 weeks at a desirable rate. The films exhibited properties suitable for use in intraocular drug delivery systems. The single‐layer thin films demonstrated a sufficient encapsulation of dexamethasone and appropriate release of the therapeutic substance. Further studies are necessary to investigate the possibility of developing the films directly on the surface of the IOL.Inspec keywords: eye, ellipsometry, spin coating, biomedical materials, polymer films, encapsulation, atomic force microscopy, drug delivery systems, aggregation, drugs, monolayers, ophthalmic lenses, polymer blendsOther keywords: IOL, intraocular drug delivery systems, spin‐coating method, atomic force microscopy, dexamethasone aggregates, monolayer films, organic polymers, spectroscopic ellipsometry, drug release, drug‐eluting polymeric thin films, ophthalmology, one‐layered thin films, two‐layered thin films, poly(D,L‐lactide‐co‐glycolide), polycaprolactone, intraocular lenses, dexamethasone release rate, dexamethasone encapsulation, time 6.0 week, Si     

State-complexity hierarchies of uniform languages of alphabet-size length

We study the state complexity of certain simple languages. If A$A$ is an alphabet of k$k$ letters, then a k$k$-language   is a nonempty set of words of length k$k$, that is, a uniform language of length k$k$. We show that the minimal state complexity of a k$k$-language is k+2$k+2$, and the maximal, (k^k−1−1)/(k−1)+2^k+1$(k^{k-1}-1)/(k-1)+2^k+1$. We prove constructively that, for every i$i$ between the minimal and maximal bounds, there is a language of state complexity i$i$. We introduce a class of automata accepting sets of words that are permutations of A$A$; these languages define a complete hierarchy of complexities between k²−k+3$k^2-k+3$ and 2^k+1$2^k+1$. The languages of another class of automata, based on k$k$-ary trees, define a complete hierarchy of complexities between 2^k+1$2^k+1$ and (k^k−1−1)/(k−1)+2^k+1$(k^{k-1}-1)/(k-1)+2^k+1$. This provides new examples of uniform languages of maximal complexity.     

A method for combining complementary techniques for document image segmentation

Image segmentation is a major task of handwritten document image processing. Many of the proposed techniques for image segmentation are complementary in the sense that each of them using a different approach can solve different difficult problems such as overlapping, touching components, influence of author or font style etc. In this paper, a combination method of different segmentation techniques is presented. Our goal is to exploit the segmentation results of complementary techniques and specific features of the initial image so as to generate improved segmentation results. Experimental results on line segmentation methods for handwritten documents demonstrate the effectiveness of the proposed combination method.     

Ab initio determination of the framework structure of the heavy-metal oxide Cs(x)Nb2.54W2.46O14 from 100 kV precession electron diffraction data

The present work deals with the ab initio determination of the heavy metal framework in Cs(x)(Nb, W)(5)O(14) from precession electron diffraction intensities. The target structure was first discovered by Lundberg and Sundberg [Ultramicroscopy 52 (1993) 429-435], who succeeded in deriving a tentative structural model from high-resolution electron microsopy (HREM) images. The metal framework of the compound was solved in this investigation via direct methods from hk0 precession electron diffraction intensities recorded with a Philips EM400 at 100 kV. A subsequent (kinematical) least-squares refinement with electron intensities yielded slightly improved co-ordinates for the 11 heavy atoms in the structure. Chemical analysis of several crystallites by EDX is in agreement with the formula Cs(0.44)Nb(2.54)W(2.46)O(14). Moreover, the structure was independently determined by Rietveld refinement from X-ray powder data obtained from a multi-phasic sample. The compound crystallises in the orthorhombic space group Pbam with refined lattice parameters a=27.145(2), b=21.603(2), and c=3.9463(3)A. Comparison of the framework structure from electron diffraction with the result from Rietveld refinement shows an average agreement for the heavy atoms within 0.09 A.