Presence Ofa Research Articles

Cationic-surfactant transfer facilitated by DNA adsorbed on a polarized1,2-dichloroethane/water interface

The voltammetric behaviour of high-molecular-weight DNA at a polarized1,2-dichloroethane/water (DCE/W) interface was investigated in the presence ofa cationic surfactant, dimethyldistearylammonium in DCE. A well-developedadsorption wave was obtained for salmon sperm DNA (purified) and herring spermDNA (commercial and purified). The peak current showed a Langmuir-typedependence on the DNA concentration. The half-peak width was relatively small(∼30 mV). To explain the voltammetric behaviour, a reaction model was proposed, in which thetransfer of surfactant ions from DCE to W is facilitated by DNA adsorbed on the DCE/Winterface. Theoretical simulation of the voltammetric wave was performed by assuming aFrumkin isotherm for the DNA–surfactant binding. When the interaction parameterg′ wasset to be 2, the theoretical value (38 mV) for the half-peak width was closest to the experimental value of∼30 mV.The g′ value of 2 suggested that there were strongly attractive interactions among the surfactantions on DNA.

Preparation of reactive surface-modified Ag nanoparticles and their assembly on a Sisurface via covalent bonds

Surface-modified Ag nanoparticles containingω-functionalized reactive groups were prepared via the reduction of aqueousAgNO3 in the presence ofa modifying agent, O,O′-di(10-undecene) dithiophosphinic acid (UDDPA). The resulting surface-modified Agnanoparticles were assembled on the surface of hydrogen-terminated Si(111) by a thermalhydrosilylation reaction. The morphologies and structures of the Ag nanoparticles and theirassembled film on the Si substrate were characterized by means of transmission electronmicroscopy (TEM), UV–visible absorption (UV–vis) spectroscopy, Fourier transformationinfrared (FTIR) spectroscopy, atomic force microscopy (AFM) and x-ray photoelectronspectroscopy (XPS). The friction and wear behavior of the assembled film of thesurface-modified Ag nanoparticles sliding against GCr15 steel (AISI52100) ina ball-on-plate configuration was evaluated using a UMT-2 friction and weartester. It was found that the surface-modified Ag nanoparticles had an averagediameter of about 10 nm. The surface-modified Ag nanoparticles had unsaturatedC = C functional groups sitting at the outermost surface and attached to the Si(111)surface via Si–C bonds. Moreover, the assembled film of the surface-modified Agnanoparticles showed good friction-reducing ability for sliding against the steelcounterpart at a small normal load and sliding velocity, but it had poor antiwearability and load-carrying capacity and was liable to lose lubricity under severesliding conditions, owing to a loss of structural integrity and consequent lubricationfailure.

Proteomic Identification of a Novel Anaplasma phagocytophilum DNA Binding Protein That Regulates a Putative Transcription Factor

Anaplasma phagocytophilum, the etiologic agent of human granulocytic anaplasmosis, is an obligatory intracellular bacterium. Little is known about the gene regulatory mechanisms for this bacterium. A gene encoding a putative transcription factor, tr1, upstream of three tandem genes encoding outer membrane proteins, including the major outer membrane protein P44, is driven by a strong promoter. In the present study, gel mobility shift assays revealed the presence of A. phagocytophilum proteins that interact with the promoter region of tr1. These proteins interacting with the tr1 promoter region were purified by biotin-labeled DNA affinity chromatography from a large amount of host cell-free bacteria. Mass spectrometry identified the major protein as an A. phagocytophilum 12.5-kDa hypothetical protein, which was named ApxR. In a DNase I protection assay, recombinant ApxR (rApxR) bound cooperatively to four 24- or 25-bp sites within 235 bp upstream of tr1: regions III and IV proximal to tr1 had higher affinity than regions I and II did. Deletion assays showed that regions III and IV were essential for rApxR binding, whereas regions I and II upstream of regions III and IV were not. The primary cis-acting region was region IV, since region IV alone was sufficient for rApxR to strongly transactivate the downstream gene in a lacZ reporter assay. Addition of regions I, II, and III did not enhance transactivation. These results show that ApxR is a novel transcriptional regulator that directly regulates tr1.

Conservation of Transmission Phenotype of <I>Anaplasma marginale</I> (Rickettsiales: Anaplasmataceae) Strains Among <I>Dermacentor</I> and <I>Rhipicephalus</I> Ticks (Acari: Ixodidae)

Before the eradication of Boophilus ticks from the United States, Rhipicephalus (Boophilus) microplus (Canestrini) and Rhipicephalus (Boophilus) annulatus (Say) were important biological vectors of the cattle pathogen Anaplasma marginale Theiler. In the absence of Boophilus ticks, A. marginale continues to be transmitted by Dermacentor ticks. However, a few U.S. strains are not transmissible by Dermacentor andersoni Stiles, Dermacentor variabilis (Say), or both, raising the question of how these strains evolved and how they are maintained. We hypothesize that the U.S. non-Dermacentor-transmissible strains of A. marginale were formerly Boophilus-transmitted strains that have been maintained by a combination of persistent infection and mechanical transmission since the eradication of their biological vector from the United States. To test this hypothesis, we attempted to transmit a well-documented non-Dermacentor-transmissible A. marginale strain (Florida), by using D. andersoni and the two Boophilus species that formerly occurred in the United States. For comparison, we examined tick-borne transmission of a strain of A. marginale (Puerto Rico), which has previously been shown to be transmissible by both D. andersoni and B. microplus. All three species of tick transmitted the Puerto Rico strain, and immunohistochemical (IHC) analysis confirmed the presence ofA. marginale colonies in their salivary glands. All three tick species failed to transmit the Florida strain. Although both D. andersoni and B. microplus acquired transient midgut and salivary gland infections after acquisition feeding, we were unable to detect colonies of the Florida strain in the salivary glands with IHC. This demonstrates that the transmission phenotype ofA. marginale strains is conserved among tick species, and it suggests that the failure of the Florida strain to be transmitted by ticks is related to a general inability to efficiently invade or replicate in tick cells, rather than to a failure to invade or replicate in cells of a specific tick species.

Influence of Vitamin B 12 and Cocultures on the Growth of Dehalococcoides Isolates in Defined Medium

Bacteria belonging to the genus Dehalococcoides play a key role in the complete detoxification of chloroethenes as these organisms are the only microbes known to be capable of dechlorination beyond dichloroethenes to vinyl chloride (VC) and ethene. However, Dehalococcoides strains usually grow slowly with a doubling time of 1 to 2 days and have complex nutritional requirements. Here we describe the growth of Dehalococcoides ethenogenes 195 in a defined mineral salts medium, improved growth of strain 195 when the medium was amended with high concentrations of vitamin B(12), and a strategy for maintaining Dehalococcoides strains on lactate by growing them in consortia. Although strain 195 could grow in defined medium spiked with approximately 0.5 mM trichloroethene (TCE) and 0.001 mg/liter vitamin B(12), the TCE dechlorination and cellular growth rates doubled when the vitamin B(12) concentration was increased 25-fold to 0.025 mg/liter. In addition, the final ratios of ethene to VC increased when the higher vitamin concentration was used, which reflected the key role that cobalamin plays in dechlorination reactions. No further improvement in dechlorination or growth was observed when the vitamin B(12) concentration was increased to more than 0.025 mg/liter. In defined consortia containing strain 195 along with Desulfovibrio desulfuricans and/or Acetobacterium woodii and containing lactate as the electron donor, tetrachloroethene ( approximately 0.4 mM) was completely dechlorinated to VC and ethene and there was concomitant growth of Dehalococcoides cells. In the cultures that also contained D. desulfuricans and/or A. woodii, strain 195 cells grew to densities that were 1.5 times greater than the densities obtained when the isolate was grown alone. The ratio of ethene to VC was highest in the presence of A. woodii, an organism that generates cobalamin de novo during metabolism. These findings demonstrate that the growth of D. ethenogenes strain 195 in defined medium can be optimized by providing high concentrations of vitamin B(12) and that this strain can be grown to higher densities in cocultures with fermenters that convert lactate to generate the required hydrogen and acetate and that may enhance the availability of vitamin B(12).

Molecular detection and diversity of novel diterpenoid dioxygenase DitA1 genes from proteobacterial strains and soil samples

Resin acids are tricyclic diterpenoids naturally synthesized by trees that are released from wood during pulping processes. Using a newly designed primer set, genes similar to that encoding the DitA1 catalytic alpha-subunit of the diterpenoid dioxygenase, a key enzyme in abietane resin acid degradation by Pseudomonas abietaniphila BKME-9, could be amplified from different Pseudomonas strains, whereas ditA1 gene sequence types representing distinct branches in the evolutionary tree were amplified from Burkholderia and Cupriavidus isolates. All isolates harbouring a ditA1-homologue were capable of growth on dehydroabietic acid as the sole source of carbon and energy and reverse transcription polymerase chain reaction analysis in three strains confirmed that ditA1 was expressed constitutively or in response to DhA, demonstrating its involvement in DhA-degradation. Evolutionary analyses indicate that gyrB (as a phylogenetic marker) and ditA1 genes have coevolved under purifying selection from their ancestral variants present in the most recent common ancestor of the genera Pseudomonas, Cupriavidus and Burkholderia. A polymerase chain reaction-single-strand conformation poylmorphism fingerprinting method was established to monitor the diversity of ditA1 genes in environmental samples. The molecular fingerprints indicated the presence ofa broad, previously unrecognized diversity of diterpenoid dioxygenase genes in soils, and suggest that other bacterial phyla may also harbour the genetic potential for DhA-degradation.

Factors influencing quality of health management information system (HMIS) data: The case of Kinondoni district in Dar es Salaam region, Tanzania

Objective: A study was done in Kinondoni Municipality, Tanzania, to assess quality of data collected through the HMIS and explore possible associated factors. Method: Using a structured questionnaire, health facility in-charges were interviewed. Attributes of data quality were recorded from health facility data using an observation schedule. A total of 69 health facilities were involved in the study including all (21) public health facilities and 25% (41/164) private facilities. Completion rate of health facility data was used as a proxy for measuring quality of data. Results: Although knowledge on HMIS basic concept was found to be associated with improved quality of data, training in HMIS did not seem to correspond with improved quality of data. Regardless of duration, supervision had no relationship with quality of data thus raising serious doubts on its quality. Presence of a focal person, responsible for day to day HMIS activities, had a positive influence on the quality of data where facilities with a focal person had a higher data completion rate (69.9%) compared to those without (44.7%). Accountability as measured by queries reportedly made by Municipal authorities on data inaccuracies was associated with better quality of data. However, queries on delay in sending report had no influence in quality of data. Conclusion: The study concludes that training, followed by supervision in HMIS, did not result into a significant improvement of the quality of HMIS. There is need to re-examine the current approaches used in training and supervision to focus on actual needs of health workers. As a long- term goal, creation of demand for processed data will serve to enhance ownership of the system by health workers, hence improve data quality

PCR-Based Detection ofAngiostrongylus cantonensisin Tissue and Mucus Secretions from Molluscan Hosts

Angiostrongylus cantonensis is a common cause of human eosinophilic meningitis. Recent outbreaks of this infection have shown that there is a need to determine the distribution of this nematode in the environment in order to control transmission. A. cantonensis is generally identified morphologically in the molluscan intermediate host by microscopic examination, which can be labor-intensive. The aim of this study was to develop a PCR-based method to detect A. cantonensis directly from molluscan tissue. A total of 34 Parmarion cf. martensi (Simroth) semislugs, 25 of which were naturally infected with A. cantonensis, were used to develop this assay. Tissue pieces (approximately 25 mg) were digested with pepsin-HCl to recover third-stage larvae for morphological identification or were used for DNA extraction. PCR primers were designed to amplify 1,134 bp from the Angiostrongylus 18S rRNA gene, and the amplicons produced were sequenced for identification at the species level. Both microscopy and the PCR-DNA sequencing analysis indicated that the same 25 semislugs were positive for A. cantonensis, showing that the two methods were equally sensitive and specific for this application. However, morphological detection requires access to living mollusks, whereas molecular analysis can also be performed with frozen tissue. The PCR-DNA sequencing method was further evaluated using tissue from Veronicella cubensis (Pfeiffer) slugs and mucus secretions from infected P. martensi. To our knowledge, this is the first use of a PCR-based method to confirm the presence of A. cantonensis in mollusks collected in the environment.

Molecular Analysis of the Subgingival Microbiota in Health and Disease

This investigation provides molecular analyses of the periodontal microbiota in health and disease. Subgingival samples from 47 volunteers with healthy gingivae or clinically diagnosed chronic periodontitis were characterized by PCR-denaturing gradient gel electrophoresis (DGGE) with primers specific for the V2-V3 region of the eubacterial 16S rRNA gene. A hierarchical dendrogram was constructed from band patterns. All unique PCR amplicons (DGGE bands) were sequenced for identity. Samples were also analyzed for the presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Tannerella forsythensis by multiplex PCR. Associations of patient age, gender, and smoking status together with the presence of each unique band and putative periodontal pathogens with disease were assessed by logistic regression. Periodontal pockets were colonized by complex eubacterial communities (10 to 40 distinct DGGE bands) with substantial individual variation in the community profile. Species diversity in health and disease was determined by the Shannon-Weaver index of diversity and compared by the Mann-Whitney U test. Sequence analyses of DGGE amplicons indicated the occurrence of many nontypical oral species and eubacteria previously associated with this environment. With the exception of T. forsythensis, the putative pathogens were not detected by DGGE. Multiplex PCR, however, detected T. forsythensis, A. actinomycetemcomitans, and P. gingivalis in 9% 16%, and 29% of the patients with disease, respectively. The presence of A. actinomycetemcomitans was significantly associated with disease (P < 0.01). Statistical analyses indicated that the presence of Treponema socranskii and Pseudomonas sp. was a significant predictor of disease (P < 0.05) and that there was no significant difference (P > 0.05) in terms of eubacterial species diversity between health and disease.

Panicum complanatum (Poaceae: Panicoideae: Paniceae), a New Species for Southeastern Brazil

A new species, Panicum complanatum from southeastern Brazil is described and illustrated, including a key to distinguish it from similar taxa. Panicum complanatum belongs to Panicum subg. Panicum and is characterized mainly by the presence of a regular row of flattened, long hairs at the ventral base of the upper lemma and palea.

AcinetobacterSkin Colonization of US Army Soldiers

To evaluate whether skin colonization with Acinetobacter calcoaceticus-baumannii complex exists in a population of healthy, nondeployed US Army soldiers and, if present, how it might relate to the infections seen in current war casualties. We sampled various skin sites of soldiers to test for the presence of A. calcoaceticus-baumannii complex and to establish the prevalence of colonization. We then used ribotyping and antimicrobial susceptibility profiles to compare the isolates we recovered with A. calcoaceticus-baumannii complex isolates from injured soldiers. Fort Sam Houston, Texas. A population of healthy, nondeployed US Army soldiers in training. A total of 17% of healthy soldiers were found to harbor A. calcoaceticus-baumannii complex. However, the strains differed from those recovered from injured soldiers. Skin carriage of A. calcoaceticus-baumannii complex exists among soldiers before deployment. However, the difference in the strains isolated from healthy soldiers, compared with the strains from injured soldiers, makes it difficult to identify skin colonization as the source of infection.

Magnetic properties of J–J–J′ quantum Heisenberg chains with spinS = 1/2,1, 3/2 and 2 in a magnetic field

By means of the density matrix renormalization group (DMRG) method, the magnetic properties of theJ–J–J ′ quantum Heisenbergchains with spin S = 1/2, 1, 3/2 and 2 in the ground states are investigated in the presence ofa magnetic field. Two different cases are considered. (a) WhenJ is antiferromagneticand J ′ is ferromagnetic (i.e. the AF–AF–F chain), the system is a ferrimagnet. Theplateaus of the magnetization are observed. It is found that the width of theplateaus decreases with increasing ferromagnetic coupling, and disappears whenJ ′/J passesa critical value. The saturated field is observed to be independent of the ferromagnetic coupling. (b) WhenJ is ferromagneticand J ′ is antiferromagnetic (i.e. the F–F–AF chain), the system becomes an antiferromagnet.The plateaus of the magnetization are also seen. The width of the plateausdecreases with decreasing antiferromagnetic coupling, and disappears whenJ ′/J passes a critical value. Though the ground state properties are quite different, themagnetization plateaus in both cases tend to disappear when the ferromagnetic couplingbecomes more dominant. Besides, no fundamental difference between the systems with spinhalf-integer and integer has been found.

Geodesics in conical manifolds

The aim of this paper is to extend the definition of geodesics to conical manifolds, defined as submanifolds of ${\mathbb R}^n$ with a finite number of singularities. We look for an approach suitable both for the local geodesic problem and for the calculus of variation in the large. We give a definition which links the local solutions of the Cauchy problem (1.1) with variational geodesics, i.e. critical points of the energy functional. We prove a deformation lemma (Theorem 2.2) which leads us to extend the Lusternik-Schnirelmann theory to conical manifolds, and to estimate the number of geodesics (Theorem 3.4 and Corollary 3.5). In Section 4, we provide some applications in which conical manifolds arise naturally: in particular, we focus on the brachistochrone problem for a frictionless particle moving in $S^n$ or in ${\mathbb R}^n$ in the presence of a potential $U(x)$ unbounded from below. We conclude with an appendix in which the main results are presented in a general framework.

Presence of Actinobacillus actinomycetemcomitans on the community Periodontal Index (CPI) Teeth in Periodontally Healthy Individuals

The aim of this study was to compare the prevalence of Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) located at Community Periodontal Index (CPI) teeth versus randomly selected teeth to determine if the CPI teeth are representative of this bacteria subgingival colonization in periodontally healthy young individuals. Forty-four individuals between 18 and 27 years of age were included in the study (mean age 23.11 +/- 2.91 years). Pooled subgingival plaque samples were collected with paper points from the mesio-buccal aspect of the CPI teeth (10 teeth for adults and 6 teeth for persons under 20 years of age) and transported in reduced Ringer's solution to the culture medium. Sixty days following the first microbial analysis, new pooled microbial samples were obtained from the mesio-buccal aspect of 10 or 6 randomly selected teeth. The presence of A. actinomycetemcomitans was determined using a selective culture medium. Microbiological data were assessed by the Wilcoxon test (p < 0.05). A border line significance (p=0.51) was observed between CPI teeth and randomly selected teeth in terms of detecting the subgingival occurrence of A. actinomycetemcomitans. CPI teeth showed to be representative of A. actinomycetemcomitans subgingival colonization. Therefore, these results suggest that in periodontally healthy young individuals, CPI teeth could be an appropriate source of samples for the subginginval detection of this pathogen.

Neutrophil NADPH oxidase is reduced at the Anaplasma phagocytophilum phagosome.

The intracellular organism Anaplasma phagocytophilum causes human granulocytic ehrlichiosis and specifically infects and multiplies in neutrophilic granulocytes. Previous reports have suggested that, for its survival, this bacterium suppresses the neutrophil respiratory burst. To investigate the mechanism of survival, we first assessed the kinetics of A. phagocytophilum entry into neutrophils by using double-labeling confocal microscopy. At 30, 60, 120, and 240 min of incubation, 25, 50, 55, and 70% of neutrophils contained bacteria, respectively. The neutrophil respiratory burst in the presence of A. phagocytophilum was assessed by a kinetic cytochrome c assay and by measurement of oxygen consumption. Neutrophils in the presence of A. phagocytophilum did not produce a significant respiratory burst, but A. phagocytophilum did not inhibit the neutrophil respiratory burst when phorbol myristate acetate was added. Immunoelectron microscopy of neutrophils infected with A. phagocytophilum or Escherichia coli revealed that NADPH oxidase subunits gp91(phox) and p22(phox) were significantly reduced at the A. phagocytophilum phagosome after 1 and 4 h of incubation. In neutrophils incubated simultaneously with A. phagocytophilum and E. coli for 30, 60, and 90 min, gp91(phox) was present on 20, 14, and 10% of the A. phagocytophilum phagosomes, whereas p22(phox) was present in 11, 5, and 4% of the phagosomes, respectively. Similarly, on E. coli phagosomes, gp91(phox) was present in 62, 64, and 65%, whereas p22(phox) was detected in 54, 48, and 48%. We conclude that A. phagocytophilum does not suppress a global respiratory burst and that, under identical conditions in the same cells, A. phagocytophilum, but not E. coli, significantly reduces gp91(phox) and p22(phox) from its phagosome membrane.

Reinfection with Anaplasma phagocytophilum in BALB/c mice and cross-protection between two sympatric isolates.

Infection with Anaplasma phagocytophilum in white-footed mice results in partial protection against reinfection with the same agent. However, humans and domestic animals may be sequentially exposed to different isolates of the agent circulating in the same or adjacent foci. We investigated whether immune response to a tick-borne infection with A. phagocytophilum provides protection against homologous and heterologous challenges. BALB/c mice were infected with one of the two sympatric isolates of A. phagocytophilum via tick bite and challenged 16 weeks later by Ixodes scapularis nymphs infected with either the same or the alternative isolate. As controls, groups of infected mice were challenged by uninfected ticks to confirm an absence of reactivation of the original infection or groups of naive mice were fed upon by ticks from cohorts used for an infectious challenge. Xenodiagnostic I. scapularis larvae were fed upon each mouse at 14 and 21 days postchallenge (PCH) and tested for the presence of A. phagocytophilum as freshly molted nymphs. Blood samples for quantitative PCR were collected at 7, 14, 21, and 70 days PCH. Serum samples were collected weekly to monitor development of immune response. The proportion of infected animals, levels of bacteremia, and the prevalence of infection in xenodiagnostic ticks were higher in groups of control mice exposed to A. phagocytophilum for the first time than in mice reinfected with either homologous or heterologous isolates. The presence of antibodies against A. phagocytophilum did not protect mice from a challenge with either homologous or heterologous isolates, however the ensuing reinfection was significantly milder and of a shorter duration than the first infection with either isolate.

The visible and near IR photoluminescent response of nc-Si:Er thin films produced by rfsputtering

In this contribution we present the visible and near IR photoluminescence (PL) analysis of Erdoped nanocrystalline silicon thin films produced by the rf magnetron sputtering method.Efficient photoluminescence was observed in these structures in both the visible and1.54 µm wavelength regions. We show the strong influence of the presence ofa nanocrystalline phase in films on their luminescence efficiency at1.54 µm, which has been studied for a series of specially prepared samples with differentcrystallinities, i.e. percentages and sizes of Si nanocrystals. The mechanism involved in thevisible photoluminescence of a highly crystalline nc-Si:H sample consisting of about 7 nmsilicon nanocrystals embedded in an amorphous matrix is discussed.

Resistenz in der antiretroviralen Therapie der HIV-Infektion*

@ Despite impressive success of highly active antiretroviral therapy, a durable control of viral replication cannot be achieved in a substantial proportion of HIV-infected patients. The most important reason is development of resistance, defined as capability of mutant virus to replicate in the presence ofa higher concentration of substance in comparison to wild-type virus. In the treated HIV-positive population resistance is prevalent in almost 50%, whereas in treatment-naives resistance can be found in 10-14%. For diagnosis, genotypic resistance tests (sequencing ofpol gene) and phenotypic resistance assays (susceptibility against antiretrovirals of an isolate in vitro) are available. A special problem is the interpretation of complex mutation patterns. Elaborate databases are implemented for this task. A number of clinical studies have demonstrated the value of resistance testing in the situation of virological failure. Resistance-guided salvage therapy was significantly more effective in these trials in comparison to former standard of care. This led to the recommendation of resistance testing in this clinical situation by German and international expert panels.

Detection of antibodies to Anaplasma phagocytophilum and Ehrlichia chaffeensis antigens in sera of Korean patients by western immunoblotting and indirect immunofluorescence assays.

Two hundred seventy one serum samples from South Korean patients were tested to detect antibodies against Anaplasma phagocytophilum (the human granulocytic ehrlichiosis agent) and Ehrlichia chaffeensis (the human monocytic ehrlichiosis agent) by indirect fluorescent-antibody assay (IFA) and the Western blot assay. These sera were collected from patients with symptoms of high fever. The rate of seropositivity for Orientia tsutsugamushi was 50.9% by IFA at the Public Health & Environmental Research Institute and National Institute of Health in South Korea. By IFA, 30 (11.1%) and 39 (14.4%) of the serum samples reacted with A. phagocytophilum and E. chaffeensis antigens, respectively. By the Western blot assays, 24 (8.9%) and 29 (10.7%) of the serum samples reacted with purified A. phagocytophilum and E. chaffeensis protein antigens, respectively. This report strengthens other evidence regarding the presence of A. phagocytophilum and E. chaffeensis infections in humans in South Korea.

Numerical and Physical Modelling of the Effect of a Dam on Powder Avalanche Motion: Comparison with Previous Approaches

As part of the European project CADZIE, the interactionbetween powder avalanches and dams has been studied. First, we simulated a powder avalancheusing a heavy salt solution in a water tank. These experiments showed that (1) the ratio betweenthe maximum velocity parallel to the slope and the front velocity is greater than 1 (up to 1.5),and that (2) the velocity normal to the slope can rise to 74% of the front velocity. The presence ofa dam leads to a reduction of front velocity. The ratio between the maximum horizontal velocityand the front velocity increases with the dam height and reaches a maximum value of 1.9. Aswe did not have access to the density distribution in our experimental set-up, we calibrateda numerical model thanks to the experiments and we deduced the dynamic pressure. Our resultsshowed that, for an avalanche without obstacle, AVAER (Rapin, 1995) and Beghin and Closet'shypothesis (1990) lead to an overestimation of the dynamic pressure in the lower partof the flow as well as in the upper part, and that the use of front velocity for estimating the lossof kinetic energy leads to an overestimation of the dam's effectiveness.