High-frequency bubble layer scattering investigations require the measurement of the intensity of backscattered sound and the corresponding depth of the scatterers below the moving surface. ...Especially at high sea state conditions and high acoustic frequencies, bubbles acoustically mask the surface, i.e., the surface return cannot be detected. However, this environmental condition is the most interesting one in bubble scattering investigations and a reliable method is required to determine the range of the scatterers to the surface displacement. A method for the determination of the vertical profiling of acoustic scattering in the presence of bubbles at high sea state conditions is presented. It is based on the transmission of a low-frequency signal alternately to the high-frequency signal at which the scattering investigations are performed. The only information that is extracted from the low-frequency echo is the onset of the surface return. It is used to compute the true depth of scatterers at the high frequency. Experiments were conducted to determine the optimum low frequency at which the detection of the surface onset in the presence of a high bubble concentration is ensured. A screening ratio is defined to give a measure of the acoustic masking of the sea surface. It is depicted for an extreme wind condition (20 m/s) for the frequency range of 5-25 kHz and as a function of wind speed for 50 kHz measurements. Selected results of subsurface bubble scattering at 50 kHz from experiments under open sea conditions are presented for the wind speed regime from 9 to 22 m/s. Additionally, the two-frequency scatterometer is used to measure sea state characteristics simultaneously to the scattering investigations by remote sensing techniques.< >
The inverting pyramid Schwarz, Anita M; Arias, Omar S; Zviniene, Asta ...
2013., 2014, 2-24-2014, 2014-02-12
eBook, Book
Odprti dostop
Pension systems in Europe and Central Asia are facing unprecedented demographic change. While many of the countries in the region have undertaken reforms when the economy faces difficult times, these ...reforms are frequently reversed when the economy improves. The demographic challenges that the region faces require a sustained effort toward changing the pension system toward something which provides adequate and sustainable benefits. The book documents the increased generosity of pension systems in Europe from their initial inception, noting that the current expectations of the public are based on the most recent round of generosity. The book seeks to show a nontechnical audience that such generosity is neither based on customary practice nor affordable in the future. The increased generosity in the past was only possible because the demographic pyramid was expanding, but as it inverts with fewer young people and more elderly, that generosity will no longer be affordable. Returning to the pension system of the 1970's will go a long way toward providing adequate and sustainable benefits in the future. Moving to a more sustainable system will require reforms to labor markets, improvements in savings mechanisms, and may require additional public resources. The extent to which a country can undertake reforms in labor markets, savings, and public finances can influence the extent to which its pension system will have to change, with different solutions possible for different countries. But in all cases, the changes that need to be made have to be widely discussed and publicly accepted to prevent reversals. The book hopes to stimulate widespread public discussion of the issue to help countries make sustainable choices with gradual implementation, before they face such daunting challenges that they have to undertake sudden, harsh measures.
Results of the experiment SAXON Phase 2 which was conducted in November 1991 at the German Research Platform NORDSEE are presented. The experiment was designed to measure the acoustic and ...electromagnetic backscattering strength of the sea surface simultaneously and at the same sonar and radar wavelength. The grazing angle dependence was investigated at angles from 20/spl deg/ to 70/spl deg/. Backscattering from the same spot of the sea surface was measured at a grazing angle of 18/spl deg/ for both systems. The sonar frequencies were 50, 26.5, and 5 kHz corresponding to radar frequencies of 10, 5.3, and 1 GHz (X-, C-, and L-band), respectively. Data were collected at wind speeds ranging from 0 to 21 m/s. The results exhibit excellent correlation between sonar and radar backscattering in the low wind speed regime at all frequencies. At higher wind speeds, bubbles caused by breaking waves are the dominant acoustic backscattering mechanism at high sonar frequencies. In this case both systems no longer see the same scatterers and the correlation decreases. The parameter combinations of wind speed and sonar and radar frequency, for which the backscatter occurs from the sea surface only, are given for a grazing angle of 45.< >
Although many of the cellular and molecular mechanisms of angiogenesis have been intensely studied 1, little is known about the processes that underlie vascular anastomosis. We have generated ...transgenic fish lines expressing an EGFP-tagged version of the junctional protein zona occludens 1 (ZO1) to visualize individual cell behaviors that occur during vessel fusion and lumen formation in vivo. These life observations show that endothelial cells (ECs) use two distinct morphogenetic mechanisms, cell membrane invagination and cord hollowing to generate different types of vascular tubes. During initial steps of anastomosis, cell junctions that have formed at the initial site of cell contacts expand into rings, generating a cellular interface of apical membrane compartments, as defined by the localization of the apical marker podocalyxin-2 (Pdxl2). During the cord hollowing process, these apical membrane compartments are brought together via cell rearrangements and extensive junctional remodeling, resulting in lumen coalescence and formation of a multicellular tube. Vessel fusion by membrane invagination occurs adjacent to a preexisting lumen in a proximal to distal direction and is blood-flow dependent. Here, the invaginating inner cell membrane undergoes concomitant apicobasal polarization and the vascular lumen is formed by the extension of a transcellular lumen through the EC, which forms a unicellular or seamless tube.
► In vivo confocal imaging of junctional remodeling during blood vessel fusion ► Different morphogenetic mechanisms lead to vascular tubes of different architectures ► Lumen coalescence is achieved by cell rearrangements generating multicellular tubes ► Unicellular tubes contain a transcellular lumen produced by membrane invagination
Organ formation and growth requires cells to organize into properly patterned three-dimensional architectures. Network formation within the vertebrate vascular system is driven by fusion events ...between nascent sprouts or between sprouts and pre-existing blood vessels. Here, we describe the cellular activities that occur during blood vessel anastomosis in the cranial vasculature of the zebrafish embryo. We show that the early steps of the fusion process involve endothelial cell recognition, de novo polarization of endothelial cells, and apical membrane invagination and fusion. These processes generate a unicellular tube, which is then transformed into a multicellular tube via cell rearrangements and cell splitting. This stereotypic series of morphogenetic events is typical for anastomosis in perfused sprouts. Vascular endothelial-cadherin plays an important role early in the anastomosis process and is required for filopodial tip cell interactions and efficient formation of a single contact site.
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•Vascular fusion requires cell contact, polarization, and apical membrane invagination•Unicellular tubes become multicellular via cell rearrangement and cell splitting•The anastomosis process of vascular fusion is conserved in various perfused vessels•VE-cadherin coordinates filopodial tip cell interactions to form a single contact
Network formation within the vertebrate vascular system is driven by fusion (anastomosis). Lenard et al. show that this fusion process involves endothelial cell recognition, de novo polarization, and apical membrane invagination and fusion, generating a unicellular tube that is then transformed into a multicellular tube via cell rearrangements and cell splitting.
Work with infectious Ebola viruses is restricted to biosafety level 4 (BSL4) laboratories, presenting a significant barrier for studying these viruses. Life cycle modeling systems, including ...minigenome systems and transcription- and replication-competent virus-like particle (trVLP) systems, allow modeling of the virus life cycle under BSL2 conditions; however, all current systems model only certain aspects of the virus life cycle, rely on plasmid-based viral protein expression, and have been used to model only single infectious cycles. We have developed a novel life cycle modeling system allowing continuous passaging of infectious trVLPs containing a tetracistronic minigenome that encodes a reporter and the viral proteins VP40, VP24, and GP1,2. This system is ideally suited for studying morphogenesis, budding, and entry, in addition to genome replication and transcription. Importantly, the specific infectivity of trVLPs in this system was ∼ 500-fold higher than that in previous systems. Using this system for functional studies of VP24, we showed that, contrary to previous reports, VP24 only very modestly inhibits genome replication and transcription when expressed in a regulated fashion, which we confirmed using infectious Ebola viruses. Interestingly, we also discovered a genome length-dependent effect of VP24 on particle infectivity, which was previously undetected due to the short length of monocistronic minigenomes and which is due at least partially to a previously unknown function of VP24 in RNA packaging. Based on our findings, we propose a model for the function of VP24 that reconciles all currently available data regarding the role of VP24 in nucleocapsid assembly as well as genome replication and transcription.
Ebola viruses cause severe hemorrhagic fevers in humans, with no countermeasures currently being available, and must be studied in maximum-containment laboratories. Only a few of these laboratories exist worldwide, limiting our ability to study Ebola viruses and develop countermeasures. Here we report the development of a novel reverse genetics-based system that allows the study of Ebola viruses without maximum-containment laboratories. We used this system to investigate the Ebola virus protein VP24, showing that, contrary to previous reports, it only modestly inhibits virus genome replication and transcription but is important for packaging of genomes into virus particles, which constitutes a previously unknown function of VP24 and a potential antiviral target. We further propose a comprehensive model for the function of VP24 in nucleocapsid assembly. Importantly, on the basis of this approach, it should easily be possible to develop similar experimental systems for other viruses that are currently restricted to maximum-containment laboratories.
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