Diffusion limit of langevin pdf models in weakly inhomogeneous turbulence

In this work, we discuss the modelling of transport in Langevin probability density function (PDF) models used to predict turbulent flows. Our focus is on the diffusion limit of these models, i.e. when advection and dissipation are the only active physical processes. In this limit, we show that Langevin PDF models allow for an asymptotic expansion in terms of the ratio of the integral length to the mean gradient length. The main contribution of this expansion yields an evolution of the turbulent kinetic energy equivalent to that given by a k-epsilon model. In particular, the transport of kinetic energy is given by a gradient diffusion term. Interestingly, the identification between PDF and k-epsilon models raises a number of questions concerning the way turbulent transport is closed in PDF models. In order to validate the asymptotic solution, several numerical simulations are performed.Dans cet article, nous abordons la question de la modélisation du transport turbulent dans les modèles de turbulence basés sur les fonctions de densité de probabilité (PDF). Nous étudions la limite diffusive de ces modèles obtenue lorsque l'advection et la dissipation sont les seuls processus physiques actifs. Dans cette limite, nous montrons que les modèles PDF donnent lieu à un développement asymptotique selon un petit paramètre correspondant au rapport de l'échelle intégrale sur l'échelle du gradient moyen. La contribution principale de ce développement s'identifie avec un modèle k-epsilon classique. En particulier, le transport de l'énergie turbulente est donné par une diffusion en premier gradient. L'identification entre modèle k-epsilon et modèle PDF permet de soulever un certain nombre de questions sur la manière dont le transport est modélisé dans les approches PDF. La solution asymptotique est validée par des simulations numériques réalisées à l'aide d'un code Monte Carlo mais aussi d'un code déterministe

Ancient Gold Mining at Ada Tepe, East Rhodopes, Bulgaria. Mineralogical Features of Au-Containing Fe-Oxides/Hydroxides from the Ada Tepe Gold Deposit. Their Significance in Clarifying the Ancient Gold Mining. Archaeologia Austriaca|Archaeologia Austriaca Band 100/2016|

Ada Tepe is the oldest known open-pit mine on the Balkan Peninsula for mining gold from host rocks. The mine probably started operation around 1500 BC and continued to function until the end of the 12th to the middle of the 11th century BC. The sedimentary and hydrothermally altered host rocks in the upper zone of Ada Tepe are usually of a grey or yellow colour or, in some places, yellow-brown. The rock pieces in the waste dumps are usually darker, with a red or red-brown coloration, which is obviously not connected to geological processes. It is suggested that the difference in colour between the host rocks and the fragments in the waste dumps are due to the phase transformation of minerals caused by the ancient miners using fire to fracture the host rocks in order to extract the gold ore. The majority of the analysed rock samples have a polyphase composition of goethite, hematite, schwertmannite, Au-Ag alloys, iron ochres, quartz and adularia. The phase diagnostics were performed by ore microscopy and powder X-ray diffraction (PXRD), morphological peculiarities were determined by scanning electron microscopy (SEM) while the thermal behaviour was investigated by differential thermal analysis and thermo gravimetric (DTA-TG) method. This paper will present the analytical results, which led to the conclusion that the difference in the coloration is due to the processes of transformation of nano-sized Fe3+ (oxy)hydroxides and (oxy)hydroxysulfate minerals caused by anthropogenic thermal processing

Crystal Structure of New Zinc-Hydroxy-Sulfate-Hydrate Zn₄(OH)₆SO₄·2–2.25H₂O

A theoretical model of the crystal structure of the newly obtained compound Zn4(OH)6SO4·2–2.25H2O based on the compilation of the crystal–chemical properties of two known zinc-hydroxy-sulfate phases—mineral namuwite and hemihydrate—is proposed. The single XRD data confirmed the model and determined the structure, with a trigonal symmetry SG of P-3, the unit cell with a = 8.3418(15) Å and c = 17.595(7) Å, and a cell volume of 1060.3(6) Å3, with Z = 2. The results show that the Zn4(OH)6SO4·2–2.5H2O crystal structure consists of an alternating paired octahedral–tetrahedral doubly decorated hydroxide layer with cationic vacancies and an aqueous interlayer

Structural Features and Thermal Behavior of Ion-Exchanged Clinoptilolite from Beli Plast Deposit (Bulgaria)

The structural features and the thermal behavior of natural, Na-, Ca-, K-, Mg-, and Cd-exchanged clinoptilolite from the Beli Plast deposit (Bulgaria) were studied. Purified clinoptilolite sample was preliminary prepared and ion-exchanged at 100 °C for six days. DSC-TG analyses were performed for all studied forms. The effects in the DSC curves show differences with temperature due to release of weakly bound H2O molecules and strongly bound ones. The endotherm minima temperatures were between 78 and 115 °C decreasing in the sequence K- 2O molecules and the non-coordinating ones were determined by XRD structural refinement for all exchanged samples. The H2O molecules of the cation–hydrate complexes are released at higher temperatures than weakly bound ones and affected the DSC curves differently. The structural adjustments made by the Rietveld method, as well as the applied EDS analyzes for the chemical composition of the samples, allowed us to correlate these data to the thermal characteristics of the studied clinoptilolite samples

Lef1 restricts ectopic crypt formation and tumor cell growth in intestinal adenomas

Somatic mutations in APC or CTNNB1 genes lead to aberrant Wnt signaling and colorectal cancer (CRC) initiation and progression via-catenin-T cell factor/lymphoid enhancer binding factor TCF/LEF transcription factors. We found that Lef1 was expressed exclusively in Apc-mutant, Wnt ligand-independent tumors, but not in ligand-dependent, serrated tumors. To analyze Lef1 function in tumor development, we conditionally deleted Lef1 in intestinal stem cells of Apc(fl/fl) mice or broadly from the entire intestinal epithelium of Apc(fl/fl) or Apc(Min/+) mice. Loss of Lef1 markedly increased tumor initiation and tumor cell proliferation, reduced the expression of several Wnt antagonists, and increased Myc proto-oncogene expression and formation of ectopic crypts in Apc-mutant adenomas. Our results uncover a previously unknown negative feedback mechanism in CRC, in which ectopic Lef1 expression suppresses intestinal tumorigenesis by restricting adenoma cell dedifferentiation to a crypt-progenitor phenotype and by reducing the formation of cancer stem cell niches.Peer reviewe

Neuropilin-1 modulates vascular endothelial growth factor-induced poly(ADP-ribose)-polymerase leading to reduced cerebrovascular apoptosis

Cerebral ischemia is encompassed by cerebrovascular apoptosis, yet the mechanisms behind apoptosis regulation are not fully understood. We previously demonstrated inhibition of endothelial apoptosis by vascular endothelial growth factor (VEGF) through upregulation of poly(ADP-ribose)-polymerase (PARP) expression. However, PARP overactivation through oxidative stress can lead to necrosis. This study tested the hypothesis that neuropilin-1 (NP-1), an alternative VEGF receptor, regulates the response to cerebral ischemia by modulating PARP expression and, in turn, apoptosis inhibition by VEGF. In endothelial cell culture, NP-1 colocalized with VEGF receptor-2 (VEGFR-2) and acted as its coreceptor. This significantly enhanced VEGF-induced PARP mRNA and protein expression demonstrated by receptor-specific inhibitors and VEGF-A isoforms. NP-1 augmented the inhibitory effect of VEGF/VEGFR-2 interaction on apoptosis induced by adhesion inhibition through the αV-integrin inhibitor cRGDfV. NP-1/VEGFR-2 signal transduction involved JNK and Akt. In rat models of permanent and temporary middle cerebral artery occlusion, the ischemic cerebral hemispheres displayed endothelial and neuronal apoptosis next to increased endothelial NP-1 and VEGFR-2 expression compared to non-ischemic cerebral hemispheres, sham-operated or untreated controls. Increased vascular superoxide dismutase-1 and catalase expression as well as decreased glycogen reserves indicated oxidative stress in the ischemic brain. Of note, protein levels of intact PARP remained stable despite pro-apoptotic conditions through increased PARP mRNA production during cerebral ischemia. In conclusion, NP-1 is upregulated in conditions of imminent cerebrovascular apoptosis to reinforce apoptosis inhibition and modulate VEGF-dependent PARP expression and activation. We propose that NP-1 is a key modulator of VEGF maintaining cerebrovascular integrity during ischemia. Modulating the function of NP-1 to target PARP could help to prevent cellular damage in cerebrovascular disease

50 години Катедра „Социална медицина и организация на здравеопазването`

22 Май 201