Heat capacity and phonon mean free path of wurtzite GaN

We report on lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range 20-300 K and by the adiabatic method in the range 5-70 K. We fit the experimental data using two temperatures model. The best fit with the accuracy of 3 % was obtained for the temperature independent Debye's temperature $\theta_{\rm D}=365$ {\rm K} and Einstein's temperature $\theta_{\rm E}=880$ {\rm K}. We relate these temperatures to the function of density of states. Using our results for heat conduction coefficient, we established in temperature range 10-100 K the explicit dependence of the phonon mean free path on temperature $\it{l}_{\rm ph}\propto T^{-2}$. Above 100 K, there is the evidence of contribution of the Umklapp processes which limit phonon free path at high temepratures. For phonons with energy $k_{\rm B}\times 300$ {\rm K} the mean free path is of the order 100 {\rm nm}Comment: 5 pages, 4 figure

2D and 3D cubic monocrystalline and polycrystalline materials: their stability and mechanical properties

We consider 2- and 3-dimensional cubic monocrystalline and polycrystalline materials. Expressions for Young's and shear moduli and Poisson's ratio are expressed in terms of eigenvalues of the stiffness tensor. Such a form is well suited for studying properties of these mechanical characteristics on sides of the stability triangles. For crystalline high-symmetry directions lines of vanishing Poisson's ratio are found. These lines demarcate regions of the stability triangle into areas of various auxeticity properties. The simplest model of polycrystalline 2D and 3D cubic materials is considered. In polycrystalline phases the region of complete auxetics is larger than for monocrystalline materials.Comment: 9 pages, 3 figures, in proceedings of the Tenth International School on Theoretical Physics, Symmetry and Structural Properties of Condensed Matter, Myczkowce 200

Elastic properties of cubic crystals: Every's versus Blackman's diagram

Blackman's diagram of two dimensionless ratios of elastic constants is frequently used to correlate elastic properties of cubic crystals with interatomic bondings. Every's diagram of a different set of two dimensionless variables was used by us for classification of various properties of such crystals. We compare these two ways of characterization of elastic properties of cubic materials and consider the description of various groups of materials, e.g. simple metals, oxides, and alkali halides. With exception of intermediate valent compounds, the correlation coefficients for Every's diagrams of various groups of materials are greater than for Blackaman's diagrams, revealing the existence of a linear relationship between two dimensionless Every's variables. Alignment of elements and compounds along lines of constant Poisson's ratio $\nu(,\textbf{m})$, ($\textbf{m}$ arbitrary perpendicular to ) is observed. Division of the stability region in Blackman's diagram into region of complete auxetics, auxetics and non-auxetics is introduced. Correlations of a scaling and an acoustic anisotropy parameter are considered.Comment: 8 pages, 9 figures, presented on The Ninth International School on Theoretical Physics "Symmetry and Structural Properties of Condensed Matter", 5 - 12 September 2007, Myczkowce, Polan

A First Step Towards Automatically Building Network Representations

To fully harness Grids, users or middlewares must have some knowledge on the topology of the platform interconnection network. As such knowledge is usually not available, one must uses tools which automatically build a topological network model through some measurements. In this article, we define a methodology to assess the quality of these network model building tools, and we apply this methodology to representatives of the main classes of model builders and to two new algorithms. We show that none of the main existing techniques build models that enable to accurately predict the running time of simple application kernels for actual platforms. However some of the new algorithms we propose give excellent results in a wide range of situations

Progenitor cells are responsible for formation of human prostate epithelium primary cultures

To analyze cell viability and morphology of primary cell cultures from CD133 immunolabeled and sorted cells from epithelium of patients suffering from benign prostate hyperplasia (BPH). Methods: Cells obtained from 5 patients were divided in two fractions. First fraction (CD133+/CD133–) was cultivated in DMEM with 10% FBS. Second fraction was mixed with CD133 microbeads and immunomagnetically divided into CD133+ and CD133– fractions. These cells were cultivated and followed-up for 2 weeks. Cells were stained for Annexin V FITC/propidium iodide. Results: Seventy CD133+/CD133– cultures, thirty-one of CD133+ and thirty-one of CD133– cells were established. There were 5-fold and 3-fold increase of CD133+/CD133- and CD133+ cell number after 2 weeks, respectively. CD133+/CD133– and CD133+ monolayers displayed epithelial-like morphology and cytokeratine expression. CD133– cultures collapsed. Cell viability within CD133+ and CD133– populations was 90.1 ± 6.3% and 24.3 ± 6.2%, respectively. Apoptotic index was 9.0 ± 6.1% and 28.5 ± 23.8% within CD133+ and CD133– cultures, respectively. Conclusions: CD133 separated human primary epithelial cell cultures displayed differences in morphology, viability and apoptosis occurrence. Immunomagnetic sorting can be recommended in each in vitro experiments with primary cell cultures in order to provide more objective results.Цель: оценить жизнеспособность и морфологию клеток первичных клеточных культур, полученных из меченных по CD133 и полученных с помощью клеточной сортировки клеток эпителия пациентов с доброкачественной гиперплазией предстательной железы (BPH). Методы: клетки, полученные от 5 пациентов, были разделены на 2 фракции. Первую фракцию (CD133+/CD133–) выращивали в DMEM с 10% FBS али с CD133 магнитными гранулами и с помощью магнита разделили клетки на CD133+- и CD133–-фракции. Далее клетки культивировали в течении 2 нед. Клетки окрашивали аннексиномV FITC/пропидий йодидом. Результаты: получено 70 CD133+/CD133- -культур клеток, 31 CD133+ и 31 CD133–. Через 2 нед культивирования отмечали 5-кратное и 3-кратное увеличение количества CD133+/CD133– и CD133+ клеток соответственно. CD133+/CD133- -и CD133+-клетки росли в монослое и имели морфологию эпителиальных клеток, экспрессировали цитокератин. CD133–-клетки не выжили. Выживаемость клеток в популяциях CD133+ и CD133– была 90,1 ± 6,3% и 24,3 ± 6,2% соответственно. Показатель апоптического индекса для культур CD133+ и CD133– был 9,0 ± 6,1% и 28,5 ± 23,8% соответственно. Выводы: показаны различия в морфологии, выживаемости клеток и частоте апоптоза для эпителиальных клеток, разделенных в зависимости от экспрессии CD133. Сортировка клеток с помощью иммуномагнитного разделения рекомендована для каждого in vitro эксперимента с использованием первичных клеточных культур для получения более объективных результатов