141 research outputs found
Trajectory studies of Polar Statospheric Cloud Lidar Observations at Sodankyla (Finland) during SESAME: comparison with box model results of particle evolution
Polar statospheric clouds (PSC) were observed with the milti-wavelengh lidar of the MOANA project during SESAME. The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distributionof the droplets along the trajectory ewre calculated using micro-physical box model. Backscatter ratios ......Published165-1811.8. Osservazioni di geofisica ambientaleJCR Journalreserve
Microcin H47 System: An Escherichia coli Small Genomic Island with Novel Features
Genomic islands are DNA regions containing variable genetic information related to secondary metabolism. Frequently, they have the ability to excise from and integrate into replicons through site-specific recombination. Thus, they are usually flanked by short direct repeats that act as attachment sites, and contain genes for an integrase and an excisionase which carry out the genetic exchange. These mobility events would be at the basis of the horizontal transfer of genomic islands among bacteria
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The influence of the accessory genome on bacterial pathogen evolution
Bacterial pathogens exhibit significant variation in their genomic content of virulence factors. This reflects the abundance of strategies pathogens evolved to infect host organisms by suppressing host immunity. Molecular arms-races have been a strong driving force for the evolution of pathogenicity, with pathogens often encoding overlapping or redundant functions, such as type III protein secretion effectors and hosts encoding ever more sophisticated immune systems. The pathogens’ frequent exposure to other microbes, either in their host or in the environment, provides opportunities for the acquisition or interchange of mobile genetic elements. These DNA elements accessorise the core genome and can play major roles in shaping genome structure and altering the complement of virulence factors. Here, we review the different mobile genetic elements focusing on the more recent discoveries and highlighting their role in shaping bacterial pathogen evolution
Microlayers of solid particles observed by lidar at Sodankyla during SESAME
The physical condition of polar stratospheric aerosols is of great importance both for the modelling
of surface chemistry reactions and for the understanding of particle production and evaporation in the polar vortex. The particles can be either liquid, supercooled liquids or solid material at different
heights and temperatures. Since a solid particle can survive much longer when temperature rises above the freezing point, whereas liquid particles will evaporate quickly at temperatures above the
condensation temperature, the knowledge of the physical state is an important parameter to estimate the contribution to heterogenous chemistry of the different aerosol types observed.SubmittedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope
Lidar observations of liquid and solid PSC at Sodankyla
Polar stratospheric clouds (PSC) play a major role in the process of Artic and Antartic ozone depletion due to the surface provided for heterogeneus chemical reactions and the removal of NO2 from the gas phase. Therefore the phase, size and composition of PSC's should be known. The microphysical structure of the PSC's depends on the actual temperature and the corresponding; airmass thermal history. At temperatures below the ice frostpoint, PSC's of ice particles (Type II) are observed, while PSC's seen at temperatures above the frostpoint are classified as PSC Type Ia (anisotropic particles) and PSC Ib (spherical particles). PSC I were believed to consist of nitric acid trihydrate (NA'r). NAT should be stable some degrees above the ice frostpoint with a particle shape depending on the cooling rate [Toon et al., 1990]. However, the explanation of PSC based solely on the NAT-hypothesis can not explain a large amount of data [Toon and Tolbert, 1995]. The spherical shape of PSC Ib can be explained with a liquid supercooled ternary solution (STS) consisting of H2O, HNO3 and H2SO4. Scenarios for the formation of frozen background aerosol (sulfuric acid tetrahydrate, SAT) are now investigated. The described variance in shape and size of the PSC can be sensed by multispectral 2-polarization lidar, measuring range resolved scattering properties of atmospheric aerosols. Here the lidar observations of PSC's during the SESAME campaign are compared to the critical formation temperatures of the different PSC types.PublishedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope
Polar startospheric cloud observation at sodankyla (SF)
We present some preliminary results of MOANA (Measurements and modelling of Ozone and Aerosols in the Northern Atmosphere) multi-wavelength lidar system, which was operating at Sodankyla (SF) during SESAME. We observed various polar stratospheric cloud (PSC) episodes; in this work we report the measurements of January 12 (JI2) and January 19 (J19), 1995. The J12 PSC has a layered structure and two of the three particle layers show a depolarised backscattering signal. On the other hand the J19 PSC detected between 19 and 24km is likely composed of spherical (liquid) particles because no depolarization shows up. In the last case an analysis of the lidar backscattering at the different wavelengths allows to estimate the optical size distribution of the particles.PublishedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope
Results of a trajectory box model simulating the size distribution evolution of stratospheric particles (H2SO4/H2O and H2SO4/HNO3/H2O solutions). A case study during SESAME
A revised interpretation of ER-2 polar stratospheric cloud (PSC) observations during AASE I (1989) and MOE (1987) Tabazadeh et al., 1995) suggests a picture of the PSC formations which evidences the importance of the air mass thermal histories. A series of ER-2 measurements are consistent with the thennodynamical properties of the liquid H2SO4/HNO3/H20 solution particles, but the data collected in other flights are in agreement with the possible formation of amorphous solid solutions of HNO3 and H2O through a peculiar coolingiheating cycle below the solid sulfuric acid tetrahydrate (SAT) melting temperatures and above the water ice saturation temperatures (frost point). During this cycle the liquid H2SO4 stratospheric aerosols may undergo a phase transition to SAT particles, required for the growing of solid nitric acid hydrates. On the other hand Koop et al., (1995) report laboratory experiments which show that H2SO4/HNO3/H20 liquid particles never freeze under stratospheric conditions for temperatures higher than the frost point. despite the change in composition due to the HNO3 uptake when cooling. In addition, when solid particles are heated, they start to become liquid at the SAT melting point. Then the analysis of any PSC data should start from air mass trajectory studies, and some thermodynamical criteria could be used to infer the physical state (liquid or solid) of the sampled particles. We use a trajectory box model to study the microphysical properties of stratospheric clouds observed during SESAME by the MOANA (Measurements and modelling of Ozone and Aerosols in the Northern Atmosphere) lidar at Sodankyla (SF). Our models treats the gas to particle conversion of H2SO4, HNO3, H2O and the microphysics of Aitken particles (ATK), H2SO4/H20 (WS) and H2SO4/HNO3/H20 (WSN) solution droplets; H2SO4 -nH2O (SA) and HNO3 -nH20 (NA) solid hydrates particles are also taken into account. To analyze the MOANA observations, within a prescribed air mass thermal history, we adopt a simple criteria which states that the particles should be liquid just after having performed temperatures above the SAT melting point. while they are solid if the water ice saturation temperatures are reached. The model simulations along the air mass trajectories reaching the lidar site during the observations are in agreement with the aerosol size distribution optically retrieved by the MOANA multiwavelength lidar (Masci et al., .1995).PublishedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope
Polar Stratospheric Cloud Measurements by Multispectral Lidar at Sodankyla in Winter 1994/95
Polar stratospheric clouds (PSC) play a major role in the process of Arctic and Antarctic
ozone depletion due to heterogeneous chemical reactions responsible for chlorine acti-vation, and particle sedimentation redistributing nitrogen species in the stratosphere. Therefore the phase, size and the composition of PSCs should be known. PSC can be divided into PSC type I, observed at temperatures some degrees above the ice frostpoint, and PSC type II consisting of water ice particles occurring at temperatures below the frostpoint. PSC type I can be subdivided into aspherical (type Ia) and spherical (type Ib) particles. Measurements of gas phase HNO3 removal in presence of PSCs and labora¬tory studies led to the assumption that PSC type I consist of nitric acid trihydrate and theparticle shape depends on the cooling rate [1]. However the explanation ofPSC I based solely on the NAT-hypothesis can not explain a large amount of data [2], and other compositions like liquid supercooled ternary solu¬tions (STS) of H2O, HNO3 and H2SO 4 are discussed now [3]. Multiwavelength, 2-polarization lidar measurements give information about the size distribution, refractive index and physical state of the cloud particles.PublishedBerlin, Germany1.8. Osservazioni di geofisica ambientaleope
Chromosomal-level assembly of the Asian Seabass genome using long sequence reads and multi-layered scaffolding
We report here the ~670 Mb genome assembly of the Asian seabass (Lates calcarifer), a tropical marine teleost. We used long-read sequencing augmented by transcriptomics, optical and genetic mapping along with shared synteny from closely related fish species to derive a chromosome-level assembly with a contig N50 size over 1 Mb and scaffold N50 size over 25 Mb that span ~90% of the genome. The population structure of L. calcarifer species complex was analyzed by re-sequencing 61 individuals representing various regions across the species' native range. SNP analyses identified high levels of genetic diversity and confirmed earlier indications of a population stratification comprising three clades with signs of admixture apparent in the South-East Asian population. The quality of the Asian seabass genome assembly far exceeds that of any other fish species, and will serve as a new standard for fish genomics
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