An extremely top-heavy initial mass function in the galactic center stellar disks

Composite armors, having two or more different materials, contain a ceramic layer in the front face and a metallic or polymer matrix composite as support on the back side backing. The function of the ceramic layer is to erode and break up the projectile and to increase the contact surface of the metallic plate by forming a hard cone. The role of the metallic backing layer is to absorb the kinetic energy of the projectile and support the fragmented ceramic. The most impportant advantage of these materials over monolithic metallic armors is to reduce the thickness by using the ceramic layer in front of the metallic layer. This provides reducing the weight of armor. In this study, experiments have been conducted to describe ballistic performance of polymer matrix composites having different geometrical shapes. To do these experiments, aramid and polyethilen composite specimens were first fabricated as laminates in different geometrical shapes. Then, these composite plates at charpy harms were investigeted in varios speed bullet to cover the impact damageKompozit zırhlar iki veya daha fazla farklı malzemeden oluşan, yüzeyde seramik katman ile arkada metal veya polimer matrisli kompozit destek içeren malzemelerdir. Seramik katmanın işlevi mermiyi aşındırma ve parçalamanın yanısıra sert koni oluşturarak metal katmanın temas yüzeyini artırmaktır. Metal destek katmanının görevi ise merminin kinetik enerjisini emmek ve darbe sonrası oluşacak seramik parçaları tutmaktır. Bu malzemelerin, tamamen metalik olan zırhlara göre en önemli avantajı, metalik katmandan önce seramik katmanın kullanılması yoluyla zırh kalınlığının, dolayısı ile zırhın ağırlığının azalmasını sağlamaktadır. Bu çalışmada değişik geometriye sahip, polimer matrisli kompozitlerin, balistik performansını ölçmek için deneyler yapılmıştır. Bunun için önce Aramid ve polietilen numuneler düz, iki değişik çapta silindirik ve küre plakalar halinde üretilmiştir. Bu kompozit plakalara atış poligonunda atışlar yapılmış ve oluşan darbe hasarları incelenmiştir

Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

Radioecological models for inland water systems

Following a nuclear accident, radioactivity may either be directly discharged into rivers, lakes and reservoirs or - after the re-mobilisation of dry and wet deposited material by rain events - may result in the contamination of surface water bodies. These so-called aquatic exposure pathways are still missing in the decision support system IMIS/PARK. Therefore, a study was launched to analyse aquatic and radioecological models with respect to their applicability for assessing the radiation exposure of the population. The computer codes should fulfil the following requirements: 1. to quantify the impact of radionuclides in water systems from direct deposition and via runoff, both dependent on time and space, 2. to forecast the activity concentration in water systems (rivers and lakes) and sediment, both dependent on time and space, and 3. to assess the time dependent activity concentration in fish. To that purpose, a literature survey was conducted to collect a list of all relevant computer models potentially suitable for these tasks. In addition, a detailed overview of the key physical process was provided, which should be considered in the models. Based on the three main processes, 9 codes were selected for the runoff from large watersheds, 19 codes for the river transport and 14 for lakes. (orig.)Nach einem kerntechnischen Unfall kann Radioaktivitaet direkt in stehende bzw. fliessende Gewaesser gelangen, oder aber auch durch atmosphaerischen Transport grossraeumig verteilt, auf dem Erdboden deponiert, durch Niederschlaege wieder remobilisiert und in Oberflaechenwasser transportiert werden. Diese sogenannten aquatischen Expositionspfade sind im Entscheidungshilfesystem IMIS/PARK bisher nicht explizit beruecksichtigt. Deshalb wurde eine Untersuchung mit der Zielsetzung durchgefuehrt, aquatische und radiooekologische Modelle hinsichtlich ihrer Eignung fuer eine zuverlaessige Abschaetzung der Strahlenexposition der Bevoelkerung zu analysieren. Mit Hilfe der Modelle soll es moeglich sein: - den Eintrag von Radionukliden in Gewaesser durch direkte Ablagerung und durch Runoff in Abhaengigkeit von der Zeit und vom Ort zu quantifizieren, - den Aktivitaetsverlauf im Wasser und im Sediment in Abhaengigkeit von der Zeit und vom Ort zu prognostizieren und - den zeitlichen Verlauf der Kontamination in Fischen abzuschaetzen. Zu diesem Zweck wurde eine Literaturrecherche durchgefuehrt, um alle relevanten Modelle zu identifizieren, die fuer die obige Problemstellung in Frage kommen koennten. Weiterhin wurden die wichtigsten physikalischen Prozesse beschrieben, die in einem geeigneten Computercode modelliert sein sollten. Entsprechend der drei identifizierten Hauptprozesse wurden 9 Computerprogramme im Bereich des Oberflaechenabflusses, 19 im Bereich des Transports in Fliessgewaessern und 14 bezueglich des Verhaltens von Radionukliden in Seen fuer die Untersuchungen ausgewaehlt. (orig.)SIGLEAvailable from TIB Hannover: ZA 5141(6089) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman