Buoyancy Instabilities in a Weakly Collisional Intracluster Medium

The intracluster medium of galaxy clusters is a weakly collisional, high-beta plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign, the magnetothermal instability (MTI) in the outskirts of non-isothermal clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena MHD code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e. Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We highlight the importance of the microscale instabilities that inevitably accompany and regulate the pressure anisotropies generated by the HBI and MTI. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few tens of kpc, conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically-aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during the formation of a cold filament produces accompanying hot filaments, which can be searched for in deep Chandra observations of nearby cool-core clusters. In the case of the MTI, anisotropic viscosity maintains the coherence of magnetic-field lines over larger distances than in the inviscid case, providing a natural lower limit for the scale on which the field can fluctuate freely. In the nonlinear state, the magnetic field exhibits a folded structure in which the field-line curvature and field strength are anti-correlated.Comment: 20 pages, 20 figures, submitted to ApJ; Abstract abridge

The Kinetics of the Formation of Aluminium Hydroxideby Seeding Sodium Aluminate Solutions with Hydrargillite Crystals IV. On the »Contact-intercrystallization«

It is shown that agglomeration of fine particles takes place in this system by the contact of crystallites. This mechanism is very quick and does not involve any measurable separation of a new solid phase from the solution. The name »contact-intercrystallization« is proposed. The most suitable way of evaluating the weight- size-distribution results is discussed. A method for distinguishing between various crystallization- mechanisms is proposed and some suggestions for practical application are given

Search of sub-parsec massive binary black holes through line diagnosis

We investigate on the spectral properties of an active black hole, member of a massive (10^7 - 10^9 Msun) sub-parsec black hole binary. We work under the hypothesis that the binary, surrounded by a circum-binary disc, has cleared a gap, and that accretion occurs onto the secondary black hole fed by material closer to the inner edge of the disc. Broad line emission clouds orbit around the active black hole and suffer erosion due to tidal truncation at the Roche Lobe surface, following gap opening and orbital decay. We consider three of the most prominent broad emission lines observed in the spectra of AGNs, i.e. CIV, MgII and H{\beta}, and compute the flux ratios between the lines of MgII and CIV (FMgII/FCIV) and those of MgII and H{\beta} (FMgII/FH{\beta}). We find that close black hole binaries have FMgII/FCIV up to one order of magnitude smaller than single black holes. By contrast FMgII/FH{\beta} may be significantly reduced only at the shortest separations. Peculiarly low values of line flux ratios together with large velocity offsets between the broad and narrow emission lines and/or periodic variability in the continuum (on timescales >= years) would identify genuine sub-pc binary candidates.Comment: 7 pages, 4 figures. Accepted for publication in MNRA

Experimental and numerical investigation of flow around a sphere with dimples for various flow regimes

Flow over a sphere is a typical bluff-body flow with many engineering applications. However, it has not been studied in depth, as compared to flow over a circular cylinder, because of the difficulties in the experimental set-up as well as in the computational approach for studying flow over a sphere. The main challenges are to understand the flow hydrodynamics and to clarify the flow pattern around a dimpled sphere because the flow pattern complying with the dimple structure on its surface is very complicated. In this paper experimental and numerical investigations of the fluid flow around a sphere with dimples, are represented. The sphere with dimples is placed in a quadratic cross section duct (measuring section) and numerical simulation results are obtained by solving RANS equations. Furthermore, experimental measurements are carried out using a Laser-Doppler Anemometer (LDA). Experimental and numerical results of flow velocity fields were compared for three different flow regimes (Re=8×103, 2×104 and 4×104). Numerical investigation was performed for wide range of Reynolds numbers (Re=270%106). The final purpose of this paper is experimental and numerical determination of velocity field, separation point, pressure and drag coefficient, the length of reverse flow region in the wake and RANS turbulent model which gives the best results for engineering practice

The supramolecular arrangement in the Ni(II) complexes of isothiosemicarbazide

The molecules of two complexes [Ni(ITSC)2(H2O)2](tere)·2H2O and [Ni(ITSC)2(NO3)2] (ITSC = S-methylisothiosemicarbazide; tere = terephthalate) tend to associate trough the hydrogen bonding interactions into the characteristic 2D blocks separated by the S-methyl moieties. The different coordination mode of the isothiosemicarbazide comparing to thiosemicarbazide (TSC) prevents the formation of the complementary hydrogen bonds with dicarboxylate important for selfassambly of TSC complexes, however in these ITSC the terephthalate anion has role in connection of the blocks and transformation of the 2D into the 3D supramolecular structure. The similar crystal arrangement is found in two earlier reported complexes of Ni(II) with ITSC.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Odgajivačka strategija u malim i zatvorenim populacijama domaćih životinja

This paper reviews the main characteristics of small and/or closed livestock populations. Although the emphasis during the realization of the genetic improvement in animal breeding is put on commercial breeding programmes, autochthonous breeds, races, strains, even herds of domestic animas, at the same time represent a potentially important segment for achieving the maintenance of the overall livestock production. These programmes are particularly important for the improvement of populations of animal genetic resources, as well as for the improvement of production in rural marginal areas. One of the main parameters for determining the size, and also the potential danger of a population is a so called effective size of the population (Ne). This parameter is determined according to the available number of male and female head of breeding stock in the population or in the herd and it varies under the influence of the sexes, changes in the size of the families, changes in the size of the population during time, as well as overlapping of the generations. Apart from the improvement of the economically important traits, the breeding programmes in small populations first of all must provide the increase of the effective size of the population aiming to limit or decrease the inbreeding, as well as the decrease of the variance in the size of the family. This is mainly achieved with so called "circular breeding plans" the sires being replaced by sons in the reproduction, and dams by daughters. The shortage of the generation interval by the change of the presence of some age categories i.e. larger number of young animals and animals that are at the peak of production comparing to a small number of older animals, can additionally influence on the genetic improvement of the traits.U radu su prikazane osnovne karakteristike malih i/ili zatvorenih populacija domaćih i gajenih životinja. Iako se akcenat prilikom realizacije genetskog unapređenja u stočarstvu stavlja na komercijalne odgajivačke programe, autohtone vrste, rase, sojevi, pa i zapati domaćih životinja, takođe predstavljaju potencijalno važan segment za dostizanje održivosti celokupne stočarske proizvodnje. Ovi programi su naročito značajni za unapređenje populacija animalnih genetskih resursa, kao i za unapređenje proizvodnje u ruralnim marginalnim oblastima. Jedan od osnovnih parametara za određivanje veličine, pa samim tim i potencijalne ugroženosti jedne populacije jeste tzv. efektivna veličina populacije (Ne). Ovaj parametar se određuje na osnovu raspoloživog broja priplodnjaka i plotkinja u populaciji ili zapatu i varira pod uticajem odnosa polova, promena u veličini familija, promena u veličini populacije tokom vremena, kao i preklapanja generacija. Pored unapređenja ekonomski važnih osobina, odgajivački programi u malim populacijama na prvom mestu moraju obezbediti povećanje efektivne veličine populacije sa ciljem ograničavanja ili smanjivanja inbreeding-a, kao i smanjivanja varijanse u veličini familije. To se uglavnom postiže tzv. "cirkularnim odgajivačkim planovima" u kojima očeve u reprodukciji zamenjuju sinovi, a majke kćeri. Skraćenje generacijskog intervala promenom zastupljenosti pojedinih starosnih kategorija u smislu veće zastupljenosti mladih grla i grla koja su u vrhu proizvodnje, a na račun starijih grla, može dodatno uticati na genetsko unapređenje osobina

Sporobolus pungens (Schreber) Kunth (Poaceae), rijetka i ugrožena psamofitska biljna vrsta u Hrvatskoj

Sporobolus pungens (Schreber) Kunth is rare and endangered psammophytic plant species, with four localities in Croatia known to date, all on the central and south Dalmatian islands. In October 2001 a new locality was found on the island of Mljet, in Blaca Bay seashore sands, as a part of the psammo-halophytic community Echinophoro-Elymetum farcti (Ammophilion).Sporobolus pungens (Schreber) Kunth, rijetka i ugrožena psamofitska biljna vrsta, dosad je bila poznata s četiri nalazišta u Hrvatskoj na srednjodalmatinskim i južnodalmatinskim otocima. U mjesecu listopadu 2001. nađeno je novo nalazište na otoku Mljetu, u uvali Blaca, na obalnim pijescima u sastavu psamohalofitske asocijacije Echinophoro-Elymetum farcti (Ammophilion)

Obtaining, characterization and optimization of hypolipidemic extracts of lemon balm (Melissa officinalis) and fenugreek (Trigonella foenum-graecum) using supercritical carbon dioxide

Sintetski hipolipemici danas se sve više zamenjuju prirodnim hipolipemicima, usled utvrđenih nedostataka, nus-pojava i sporednih efekata sintetičkih lekova. Shodno tome, podstaknuta je povećana upotreba biljaka, odnosno njihovih aktivnih komponenata- sa hipolipemijskom aktivnošću. Zamena sintetskih jedinjenja prirodnim aktivnim komponentama usmerava istraživanja u pravcu ispitivanja različitih biljnih materijala i identifikovanja novih jedinjenja sa hipolipemijskim dejstvom koji se mogu iz njih izolovati. Zbog toga se veliki napori ulože u cilju dobijanja i izolovanja prirodnih hipolipemika, kao i za razvoj efikasnih i selektivnih tehnika ekstrakcije. Ekstrakciju konvencionalnim rastvaračima karakterišu niska selektivnost i visoke temperature, što može dovesti do degradacije željenih jedinjenja. Primenom natkritične ekstrakcije (NKE) koja se odvija na nižim temperaturama, sprečava se degradacija jedinjenja i dobija na kvalitetu ekstrakata shodno većoj koncentraciji komponenata sa željenim farmakološkim dejstvom. NKE je mnogo selektivnija od konvencionalnih načina ekstrakcije. Selektivnost prema pojedinim grupama jedinjenja se postiže podešavanjem uslova ekstrakcije (temperature i pritiska). Usled lake i potpune separacije natkritičnog fluida smanjenjem pritiska, ovaj vid ekstrakcije omogućava dobijanje ekstrakata bez tragova rastvarača (npr. za primenu u prehrambenoj, kozmetičkoj i farmaceutskoj industriji). Cilj ovog rada je bilo proučavanje frakcija ekstrakata matičnjaka (Melissae officinalis L., Lamiaceae) i grčkog semena (Trigonella foenum-graecum L., Fabaceae) bogatih supstancama sa hipolipemijskom aktivnosti, izolovanih primenom različitih metoda ekstrakcije, kao i optimizacija procesa njihovog dobijanja. Za dobijanje ekstrakata bogatih supstancama sa hipolipemijskim dejstvom, primenjena je subkritična (SKE) i NKE sa ugljenik (IV)-oksidom, hidrodestilacija i ekstrakcija etanolom. Na osnovu hemijskog profila dobijenih ekstrakata, identifikovane su supstance koje su u literaturi okarakterisane kao nosioci hipolipemijske aktivnosti i određivan je njihov sadržaj. Za identifikaciju i kvantifikaciju aktivnih komponenti u dobijenim ekstraktima korišćene su gasna hromatografija sa masenom spektrometrijom (GC/MS) i tečna hromatografije (HPLC). Cilj disertacije je bio ispitivanje kinetike izolacije ekstrakata bogatih komponenatama nosiocima hipolipemijskog dejstva, kao i analizi i optimizaciji različitih procesa ekstrakcije, pri čemu je glavni naglasak dat analizi kinetike procesa NKE, ispitivanjem uticaja variranja procesnih parametara (pritiska i temperature) subkritične i NKE i odgovarajućeg predtretmana biljnog materijala na prinos totalnog ekstrakta i u njemu sadržaj komponenata nosilaca hipolipemijskog dejstva...Synthetic hypolipemics nowdays have being replaced by natural ones due to the noticed deficiencies and side effects of synthetic drugs. Great effort is being devoted to the search for alternative and cheaper sources of natural hypolipemics, as well as to the development of efficient, selective and more convenient extraction techniques. Extraction with conventional solvents is characterized by poor selectivity and requires high temperatures, which could result in degradation of the desired compounds, and obtained extracts usually have solvent residues which is not convenient in medicinal use. Supercritical extraction (SCE) shows higher selectivity compared to conventional techniques of extraction. Selectivity of SCE towards some groups of compounds can be tuned by changing extraction conditions (pressure and temperature). According to easy and total separation of supercritical fluid from the extract achieved by lowering pressure, SCE presents type of extraction which allows obtaining extracts without residual solvents (for example for application in pharmaceutical, food and cosmetics industry). The aim of this study was the isolation of extracts of lemon balm (Melissae officinalis) and fenugreek (Trigonella foenum-graecum) rich in compounds that possess hypolipidemic activity according to literature data, using different extraction processes. The extracts rich in hypolipidemic substances were obtained by supercritical carbon dioxide extraction (SCE-CO2), hydrodistillation and ethanol extraction from plant material. Characterization and analysis of the obtained extracts as well as determination of contents of the components identified by the literature data as carriers of hypolipidemic activity, were performed . Identification and quantification of the active components in the extracts were performed using gas chromatography mass spectrometry (GC / MS) and liquid chromatography (HPLC). The research was based on the kinetic analysis and optimization of different extraction processes for obtaining extracts rich in components with hypolidemic activity. Kinetics of subcritical and supercritical extractions were analyzed, whereby, the influence of process parameters (pressure and temperature) as well as appropriate pretreatment of plant material on the yield of total extract and hypolipidemic compunds was examined..