16,800 research outputs found

    Quantum Mechanics Lecture Notes. Selected Chapters

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    These are extended lecture notes of the quantum mechanics course which I am teaching in the Weizmann Institute of Science graduate physics program. They cover the topics listed below. The first four chapter are posted here. Their content is detailed on the next page. The other chapters are planned to be added in the coming months. 1. Motion in External Electromagnetic Field. Gauge Fields in Quantum Mechanics. 2. Quantum Mechanics of Electromagnetic Field 3. Photon-Matter Interactions 4. Quantization of the Schr\"odinger Field (The Second Quantization) 5. Open Systems. Density Matrix 6. Adiabatic Theory. The Berry Phase. The Born-Oppenheimer Approximation 7. Mean Field Approaches for Many Body Systems -- Fermions and Boson

    Calibration of the convective parameters in stellar pulsation hydrocodes

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    Despite the appearance of two- and three-dimensional models thanks to the rapid growth of computing performance, numerical hydrocodes used to model radial stellar pulsations still apply a one-dimensional stellar envelope model without any realistic atmosphere, in which a significant improvement was the inclusion of turbulent convection. However, turbulent convection is an inherently multi-dimensional physical process in the vicinity of the ionization zones that generate pulsation. The description of these processes in one dimension can only be approximated based on simplified theoretical considerations involving several undetermined dimensionless parameters. In this work, we confront two one-dimensional numerical codes, namely the Budapest-Florida code (BpF) and the MESA Radial Stellar Pulsations module (RSP), with radial velocity observations of several non-modulated RRab stars of the M3 globular cluster and specified the undetermined convective parameters by the measured data for both codes independently. Our determination shows that some of the parameters depend on the effective temperature, which dependence is established for the first time in this work, and we also found some degeneracy between the parameters. This procedure gives as by-product suggestions for parameters of the publicly available RSP code extensively used recently by researchers through the MESA package. This work is part of the preparatory work to establish a theoretical framework required to make progress based on the results of one-dimensional models to couple them with multi-dimensional ones for further detailed analysis of physical processes.Comment: Accepted in MNRAS, 19 pages, 14 figures, for associated mp4 video see https://konkoly.hu/KIK/data_en.html#P

    High-Frequency Gravitational Wave Detection via Optical Frequency Modulation

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    High-frequency gravitational waves can be detected by observing the frequency modulation they impart on photons. We discuss fundamental limitations to this method related to the fact that it is impossible to construct a perfectly rigid detector. We then propose several novel methods to search for O(MHz-GHz) gravitational waves based on the frequency modulation induced in the spectrum of an intense laser beam, by applying optical frequency demodulation techniques, or by using optical atomic clock technology. We find promising sensitivities across a broad frequency range.Comment: 11 pages, 3 figure

    SOFIA and ALMA Investigate Magnetic Fields and Gas Structures in Massive Star Formation: The Case of the Masquerading Monster in BYF 73

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    We present SOFIA+ALMA continuum and spectral-line polarisation data on the massive molecular cloud BYF 73, revealing important details about the magnetic field morphology, gas structures, and energetics in this unusual massive star formation laboratory. The 154ÎŒ\mum HAWC+ polarisation map finds a highly organised magnetic field in the densest, inner 0.55×\times0.40 pc portion of the cloud, compared to an unremarkable morphology in the cloud's outer layers. The 3mm continuum ALMA polarisation data reveal several more structures in the inner domain, including a pc-long, ∌\sim500 M⊙_{\odot} "Streamer" around the central massive protostellar object MIR 2, with magnetic fields mostly parallel to the east-west Streamer but oriented north-south across MIR 2. The magnetic field orientation changes from mostly parallel to the column density structures to mostly perpendicular, at thresholds NcritN_{\rm crit} = 6.6×\times1026^{26} m−2^{-2}, ncritn_{\rm crit} = 2.5×\times1011^{11} m−3^{-3}, and BcritB_{\rm crit} = 42±\pm7 nT. ALMA also mapped Goldreich-Kylafis polarisation in 12^{12}CO across the cloud, which traces in both total intensity and polarised flux, a powerful bipolar outflow from MIR 2 that interacts strongly with the Streamer. The magnetic field is also strongly aligned along the outflow direction; energetically, it may dominate the outflow near MIR 2, comprising rare evidence for a magnetocentrifugal origin to such outflows. A portion of the Streamer may be in Keplerian rotation around MIR 2, implying a gravitating mass 1350±\pm50 M⊙_{\odot} for the protostar+disk+envelope; alternatively, these kinematics can be explained by gas in free fall towards a 950±\pm35 M⊙_{\odot} object. The high accretion rate onto MIR 2 apparently occurs through the Streamer/disk, and could account for ∌\sim33% of MIR 2's total luminosity via gravitational energy release.Comment: 33 pages, 32 figures, accepted by ApJ. Line-Integral Convolution (LIC) images and movie versions of Figures 3b, 7, and 29 are available at https://gemelli.spacescience.org/~pbarnes/research/champ/papers

    Stratosphere-Troposphere Coupling and Oceanic Feedbacks in an Aquaplanet Model

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    Since the 90’s, there have been many studies looking at the impact of stratospheric temperature perturbations (STP’s) on the troposphere below, and the mechanisms involved. However, it is not well-understood how these interactions might be modified by atmosphere-ocean coupling. This holds particular relevance to the study of e.g. ozone depletion/recovery in the Southern Ocean region. To investigate this, abrupt uniform, polar, and equatorial STP’s – corresponding to different types of forcings - were applied to the atmosphere of MITgcm in an aquaplanet, double-drake configuration. Each was conducted in three different versions of the model: atmosphere-only, atmosphere + slab-ocean, and fully-coupled atmosphere + ocean. In the atmosphere-only model, atmospheric responses similar to those of previous studies were recorded, underscoring their generic nature. In the coupled models, an initial weakening (~decades), and – in the fully coupled model - subsequent strengthening and poleward-shift (~centuries) of the underlying atmospheric response was produced, in polar/equatorial heating experiments. Uniform heating saw the latter process occur initially too. Sea surface temperature (SST) anomalies were found to drive these changes, with extratropical/tropical anomalies controlling the former/latter process. These were in turn attributable to changes in the zonal winds, causing anomalies in the turbulent and ocean heat fluxes, although uniform STP’s saw SST changes that were more controlled by large, near-uniform anomalous downwelling longwave fluxes. Our results highlight the importance of incorporating atmosphere-ocean coupling when studying the effects of STP’s, especially over longer timescales (&100 years). With respect to ozone depletion in the Southern Ocean, they suggest an amplified poleward jet shift which - as greenhouse gases continue to rise – may continue and amplify further into the 21st/22nd century.Open Acces

    The Adirondack Chronology

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    The Adirondack Chronology is intended to be a useful resource for researchers and others interested in the Adirondacks and Adirondack history.https://digitalworks.union.edu/arlpublications/1000/thumbnail.jp

    Physical phenomena controlling quiescent flame spread in porous wildland fuel beds

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    Despite well-developed solid surface flame spread theories, we still lack a coherent theory to describe flame spread through porous wildland fuel beds. This porosity results in additional complexity, reducing the thermal conductivity of the fuel bed, but allowing in-bed radiative and convective heat transfer to occur. While previous studies have explored the effect of fuel bed structure on the overall fire behaviour, there remains a need for further investigation of the effect of fuel structure on the underlying physical phenomena controlling flame spread. Through an extensive series of laboratory-based experiments, this thesis provides detailed, physics-based insights for quiescent flame spread through natural porous beds, across a range of structural conditions. Measurements are presented for fuel beds representative of natural field conditions within an area of the fire-prone New Jersey Pinelands National Reserve, which compliment a related series of field experiments conducted as part of a wider research project. Additional systematic investigation across a wider range of fuel conditions identified independent effects of fuel loading and bulk density on the spread rate, flame height and heat release rate. However, neither fuel loading nor bulk density alone provided adequate prediction of the resulting fire behaviour. Drawing on existing structural descriptors (for both natural and engineered fuel beds) an alternative parameter ασΎ was proposed. This parameter (incorporating the fuel bed porosity (α), fuel element surface-to-volume ratio (σ), and the fuel bed height (ÎŽ)) was strongly correlated with the spread rate. One effect of the fuel bed structure is to influence the heat transfer mechanisms both above and within the porous fuel bed. Existing descriptions of radiation transport through porous fuel beds are often predicated on the assumption of an isotropic fuel bed. However, given their preferential angle of inclination, the pine needle beds in this study may not exhibit isotropic behaviour. Regardless, for the structural conditions investigated, horizontal heat transfer through the fuel bed was identified as the dominant heating mechanism within this quiescent flame spread scenario. However, the significance of heat transfer contributions from the above-bed flame generally increased with increasing ασΎ value of the fuel bed. Using direct measurements of the heat flux magnitude and effective heating distance, close agreement was observed between experimentally observed spread rates and a simple thermal model considering only radiative heat transfer through the fuel bed, particularly at lower values of ασΎ. Over-predictions occurred at higher ασΎ values, or where other heat transfer terms were incorporated, which may highlight the need to include additional heat loss terms. A significant effect of fuel structure on the primary flow regimes, both within and above these porous fuel beds, was also observed, with important implications for the heat transfer and oxygen supply within the fuel bed. Independent effects of fuel loading and bulk density on both the buoyant and buoyancy-driven entrainment flow were observed, with a complex feedback cycle occurring between Heat Release Rate (HRR) and combustion behaviour. Generally, increases in fuel loading resulted in increased HRR, and therefore increased buoyant flow velocity, along with an increase in the velocity of flow entrained towards the combustion region. The complex effects of fuel structure in both the flaming and smouldering combustion phases may necessitate modifications to other common modelling approaches. The widely used Rothermel model under-predicted spread rate for higher bulk density and lower ασΎ fuel beds. As previously suggested, an over-sensitivity to fuel bed height was observed, with experimental comparison indicating an under-prediction of reaction intensity at lower fuel heights. These findings have important implications particularly given the continuing widespread use of the Rothermel model, which continues to underpin elements of the BehavePlus fire modelling system and the US National Fire Danger Rating System. The physical insights, and modelling approaches, developed for this low-intensity, quiescent flame spread scenario, are applicable to common prescribed fire activities. It is hoped that this work (alongside complimentary laboratory and field experiments conducted by various authors as part of a wider multi-agency project (SERDP-RC2641)) will contribute to the emerging field of prescribed fire science, and help to address the pressing need for further development of fire prediction and modelling tools

    High intensity proton beam impact at 440 GeV/c on Mo and Cu coated CfC/graphite and SiC/SiC absorbers for beam intercepting devices

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    The authors would like to acknowledge the support of CERN's Sources, Targets and Interactions (STI) Group, the Accelerator Consolidation Project at CERN, as well as M. Wendt and F. Caspers. This program is partially supported by JSPS KAKENHI Grant Number JP16H03994. This support is gratefully acknowledged. The research leading to these results has received funding from the transnational access activity ARIES which is co-funded by the European Union's Horizon 2020 Research and innovation programme under Grant Agreement no. 730871.Beam Intercepting Devices (BIDs) are essential protection elements for the operation of the Large Hadron Collider (LHC) complex. The LHC internal beam dump (LHC Target Dump Injection or LHC TDI) is the main protection BID of the LHC injection system; its main function is to protect LHC equipment in the event of a malfunction of the injection kicker magnets during beam transfer from the SPS to the LHC. Several issues with the TDI were encountered during LHC operation, most of them due to outgassing from its core components induced by electron cloud effects, which led to limitations of the injector intensity and hence had an impact onLHCavailability. The absorbing cores of the TDIs, and of beam intercepting devices in general, need to deal with high thermo-mechanical loads induced by the high intensity particle beams. In addition, devices such as the TDI—where the absorbing materials are installed close to the beam, are important contributors to the accelerator impedance budget. To reduce impedance, the absorbing materials that make up the core must be typically coated with high electrical conductivity metals. Beam impact testing of the coated absorbers is a crucial element of development work to ensure their correct operation. In the work covered by this paper, the behaviour of several metal-coated absorber materials was investigated when exposed to high intensity and high energy proton beams in the HiRadMat facility at CERN. Different coating configurations based on copper and molybdenum, and absorbing materials such as isostatic graphite, Carbon Fibre Composite (CfC) and Silicon Carbide reinforced with Silicon Carbide fibres (SiC-SiC), were tested in the facility to assess the TDI’s performance and to extract information for other BIDs using these materials. In addition to beam impact tests and an extensive Post Irradiation Examination (PIE) campaign to assess the performance of the coatings and the structural integrity of the substrates, extensive numerical simulations were carried out.CERN's Sources, Targets and Interactions (STI) GroupAccelerator Consolidation Project at CERNMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) JP16H03994transnational access activity ARIES - European Union 73087

    Science with Neutrino Telescopes in Spain

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    The authors gratefully acknowledge the funding support from the following Spanish programs: Ministerio de Ciencia, Innovacion, Investigacion y Universidades (MCIU): Programa Estatal de Generacion de Conocimiento (refs. PGC2018-096663-B-C41, -A-C42, -B-C43, -B-C44) (MCIU/FEDER); Generalitat Valenciana: Prometeo (PROMETEO/2020/019) and GenT (refs. CIDEGENT/2018/034, /2020/049, /2021/023); Junta de Andalucia (ref. A-FQM-053-UGR18).The primary scientific goal of neutrino telescopes is the detection and study of cosmic neutrino signals. However, the range of physics topics that these instruments can tackle is exceedingly wide and diverse. Neutrinos coming from outside the Earth, in association with othermessengers, can contribute to clarify the question of the mechanisms that power the astrophysical accelerators which are known to exist from the observation of high-energy cosmic and gamma rays. Cosmic neutrinos can also be used to bring relevant information about the nature of dark matter, to study the intrinsic properties of neutrinos and to look for physics beyond the Standard Model. Likewise, atmospheric neutrinos can be used to study an ample variety of particle physics issues, such as neutrino oscillation phenomena, the determination of the neutrino mass ordering, non-standard neutrino interactions, neutrino decays and a diversity of other physics topics. In this article, we review a selected number of these topics, chosen on the basis of their scientific relevance and the involvement in their study of the Spanish physics community working in the KM3NeT and ANTARES neutrino telescopes.Ministerio de Ciencia, Innovacion, Investigacion y Universidades (MCIU) PGC2018-096663-B-C41 A-C42 B-C43 B-C44MCIU/FEDERGeneralitat Valenciana PROMETEO/2020/019GenT CIDEGENT/2018/034 2020/049 2021/023Junta de Andalucia A-FQM-053-UGR1

    The influence of complex volcanic vent morphology on eruption dynamics

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    VulkanausbrĂŒche gelten als eine der spektakulĂ€rsten Naturgewalten unserer Erde. Gleichzeitig stellen sie jedoch auch eine Gefahr fĂŒr die menschliche Gesundheit und Infrastruktur dar. Aufgrund ihrer Dynamik und ihres unberechenbaren Charakters geht von explosiven VulkanausbrĂŒchen eine besonders große GefĂ€hrdung des Menschen und seiner Umwelt aus. Im Zuge eines explosiven Ausbruchs werden heiße Gase und Pyroklasten in die AtmosphĂ€re ausgeworfen. Obwohl das Monitoring aktiver Vulkane in den letzten Jahren immer weiter verbessert wurde, ist es immer noch schwierig eine konkrete Vorhersage zu den AusbrĂŒchen zu erstellen. Aufgrund ihrer KomplexitĂ€t ist das Verhalten von Vulkanen nicht kalkulierbar. Bis heute ist weder eine Beobachtung, noch eine Messung der unterirdischen Rahmenbedingungen möglich, welche den Ausbruch steuern. Trotz dieser UnwĂ€gbarkeiten unterliegen VulkanausbrĂŒche dennoch physikalischen GesetzmĂ€ĂŸigkeiten, sodass die Möglichkeit besteht, die Prozesse im Untergrund eines Vulkans zu modellieren oder durch Experimente zu beschreiben. Aufgrund der KomplexitĂ€t der Wechselwirkungen innerhalb des Systems Vulkan ist es erforderlich Experimente zunehmend realistischer zu gestalten. Sobald das ausgeworfene Material aus dem Krater austritt können wir den Ausbruch visuell Beobachten. In diesem Bereich ist das Verhalten des Ausbruchs vollstĂ€ndig von den Prozessen im Untergrund und von der Geometrie des Kraters abhĂ€ngig. Im Vergleich zu den symmetrischen Kraterformen, welche in Experimenten und Modellen oft angenommen werden, sind die Krater in der Natur deutlich unregelmĂ€ĂŸiger geformt. Ihre Geometrien sind oft eingekerbt und haben eine schrĂ€ge OberflĂ€che. Zudem können sich die Kratergeometrien innerhalb kĂŒrzester Zeit verĂ€ndern. Um den Einfluss der Prozesse im Untergrund zu verstehen mĂŒssen wir zuerst den Einfluss der beobachtbaren Parameter (z. B. Kratergeometrie) ergrĂŒnden. Schlussendlich wird ein tiefergehendes VerstĂ€ndnis der Parameter, die VulkanausbrĂŒche steuern, zu einem Fortschritt und der Verbesserung der GefĂ€hrdungsanalysen fĂŒhren. Um dies zu erreichen, habe ich Beobachtungen aus Feldkampagnen und Laborexperimenten kombiniert. ZunĂ€chst habe ich die Geometrien von Vulkankratern erfasst und deren zeitliche Entwicklung dokumentiert. Dazu haben ich die Geometrie der Krater in der Kraterterrasse des Strombolis in einer hohen Auflösung vermessen und die jeweils zugehörigen Explosionen beobachtet. Dabei konnte ich feststellen, dass sowohl die IntensitĂ€t, als auch die Art und die Richtung der AusbrĂŒche durch FormverĂ€nderungen der OberflĂ€chentopografie beeinflusst werden. Mittels Drohneneinsatz habe ich innerhalb eines Zeitraums von neun Monaten (Mai 2019–Januar 2020) fĂŒnf topografische DatensĂ€tze erstellt. In diesem Zeitraum war es möglich „normale“ Strombolianische AktivitĂ€t, starke AusbrĂŒche und sogar zwei Paroxysmen zu beobachten (3. Juli und 28. August 2019), sodass es möglich war, die verschiedenen Ausbruchstypen mit den vorherrschenden Ablagerungs- und Abtragungsprozessen zu verknĂŒpfen. Zudem konnte ich die Anzahl der aktiven Krater, deren Positionen sowie deren Umgestaltung nachverfolgen. Da VerĂ€nderungen der Kratergeometrie und der Kraterposition auf eine Modifikation des Ausbruchsgeschehens hinweisen können, sind auch dies wichtige Faktoren fĂŒr eine GefĂ€hrdungsanalyse. Die aus den Feldforschungen gewonnenen Daten zeigen deutlich die KomplexitĂ€t, Vielseitigkeit und VariabilitĂ€t der Formen vulkanischer Krater in einer nie da gewesenen zeitlichen und rĂ€umlichen Auflösung. DarĂŒber hinaus haben die Beobachtungen der VulkanausbrĂŒche deutlich gemacht, wie stark die Beziehung zwischen dem Krater, der Kratergeometrie und dem Auswurf von pyroklastischem Material ist. Diese Erkenntnis hat eine große Bedeutung fĂŒr die GefĂ€hrdungsanalyse, vor allem fĂŒr Gebiete, die potentiell durch vulkanische Bomben und pyroklastischem Fallout bedroht sind. Im Anschluss habe ich eine Reihe von Dekompressionsexperimenten mit Kratergeometrien durchgefĂŒhrt, welche auf den Beobachtungen am Stromboli aufbauen. Durch diese Experimente wurde der Zusammenhang zwischen Kratergeometrie und Ausbruchsdynamik bestĂ€tigt. Die verwendeten Geometrien haben eine geneigte OberflĂ€che mit einem Winkel von 5°, 15° und 30° und jeweils einer zylindrischen und einer trichterförmigen inneren Geometrie. Daraus ergeben sich sechs experimentelle Krater die mit folgenden experimentellen Bedingungen getestet wurden: Vier unterschiedliche StartdrĂŒcke (5, 8, 15 und 25 MPa) und zwei Gasvolumina (127.4cm3, 31.9cm3). Alle Experimente wurden bei Raumtemperatur und mit Argon durchgefĂŒhrt. Trotz des vertikalen Aufbaus konnte man auf beiden Seiten des Kraters unterschiedlich große Winkel des austretenden Gases beobachten. Weiterhin war der Gasstrahl geneigt. Die Richtung der Neigung wurde durch die innere Geometrie be- stimmt. Bei einer zylindrischen Geometrie neigte sich der Gasstrahl in die Einfallsrichtung der geneigten OberflĂ€che. Im Falle einer trichterförmigen inneren Geometrie neigt sich der Gasstrahl entgegen der Einfallsrichtung. Der Winkel des Gasaustritts war bei einer zylindrischen inneren Geometrie immer grĂ¶ĂŸer als bei der trichterförmigen Geometrie. Sowohl die Winkel des Gasaustritts als auch die Neigung des Gasstrahls zeigten eine starke Reaktion auf eine VerĂ€nderung der Druckbedingung und OberflĂ€chenneigung. Dabei zeigten sowohl der Austrittswinkel als auch die Neigung eine positive Korrelation mit dem Druck und der OberflĂ€chenneigung. Hohe Druckbedingungen haben außerdem dafĂŒr gesorgt, dass fĂŒr einen lĂ€ngeren Zeitraum ÜberdruckverhĂ€ltnisse am Kraterausgang herrschten. Ein höheres Gasvolumen hat grĂ¶ĂŸere Gasaustrittswinkel ermöglicht. Zuletzt habe ich die Dekompressionsexperimente durch den Einsatz von Partikeln ergĂ€nzt, um so den Auswurf von Gas und Partikeln wĂ€hrend eines explosiven Vulkanausbruchs nachzustellen. Dabei habe ich die beiden experimentellen Kratergeometrien aus den vorangegangenen Experimenten ausgewĂ€hlt, welche den stĂ€rksten Einfluss auf die Gasdynamik aufgezeigt haben. ZusĂ€tzlich habe ich eine dritte Kratergeometrie verwendet, die dem aktiven Krater S1 auf Stromboli nachempfunden ist. Die Geometrie entspricht der Kratergeometrie aus der Vermessung im Mai 2019. Die S1 Geometrie zeichnet sich durch einen asymmetrischen Öffnungswinkel aus (~10° auf einer Seite, ~40° auf der anderen Seite). ZusĂ€tzlich zu den drei Kratergeometrien wurden unterschiedliche Partikel verwendet (Schlacke und Bims), mit jeweils drei unterschiedlichen KorngrĂ¶ĂŸen (0.125–0.25, 0.5–1 und 1–2mm) und zwei Druckstufen (8 und 15MPa). Die Partikeldynamik, in der NĂ€he des experimentellen Kraters, wurde anhand der Winkel des Partikelauswurfs und der Geschwindigkeit der Partikel definiert und beschrieben. Dabei wurde festgestellt, dass die Geometrie des Kraters die Richtung und Neigung des Partikelauswurfswinkels und die Geschwindigkeit der Partikel bestimmt. Bei allen Kratergeometrien kam es zu einem asymmetrischen Partikelauswurf und im Falle von Bimspartikeln zudem zu einer ungleichmĂ€ĂŸigen Geschwindigkeitsverteilung. Die Kombination aus Daten aus Feldkampagnen, Experimenten mit Gas und Experimenten mit zusĂ€tzlichen Partikeln zeigte deutlich den starken Einfluss der Kratergeometrie auf Eruptionen. In der Natur, fĂŒhrt eine modifizierte Kratergeometrie zu einem verĂ€ndertem Auswurfsmuster der Pyroklasten. Im Labor haben komplexe Kratergeometrien zu geneigten Gasstrahlen, asymmetrischen Auswurfswinkeln von Gas- und Gaspartikeln und einer asymmetrischen Verteilung der Geschwindigkeit von Partikeln gefĂŒhrt. Auf Basis dieser Beobachtungen komme ich zu dem Schluss, dass asymmetrische Vulkankrater eine asymmetrische Verteilung von pyroklastischem Auswurf hervorrufen. Das fĂŒhrt zu einer bevorzugten Richtung fĂŒr vulkanischen Fallout — und falls es zu einer kollabierenden AusbruchsĂ€ule kommt — zu einer bevorzugten Richtung fĂŒr pyroklastische Ströme. Der technische Fortschritt durch Drohnen, Photogrammmetrie und 3D Druck bietet einige Chancen fĂŒr die Vulkanologie. Luftaufnahmen durch Drohnen ermöglichen eine schnelle, gĂŒnstige und sichere Vermessung von Vulkankratern, auch in Zeiten erhöhter AktivitĂ€t. Zusammen mit Photogrammmetrie und 3D Druck lassen sich realitĂ€tsnahe Kratergeometrien erzeugen, fĂŒr zunehmend realistische skalierte Laborexperimente.Volcanic eruptions are among the most violent displays of the Earth’s natural forces and threaten human health and infrastructure. Explosive eruptions are hazardous due to their impulsive and dynamic nature, ejecting gas and pyroclasts at high velocity and temperature into the atmosphere. In recent years, monitoring efforts have increased, but forecasting eruptions is still challenging as volcanoes are complex systems with the potential for inherently unpredictable behaviours. To date, the underlying boundary conditions are beyond observation and quantification. Still, they are constrained by physical laws and can be described through models and experiments. The complexity and interdependency of the parameters governing the dynamics of volcanic eruptions ask for increasingly realistic experiments to investigate the sub-surface conditions driving volcanic eruptions. Above the vent, in the near-vent region, the dynamics of explosive eruptions can first be visually observed. The characteristics at this stage are purely the result of the underlying boundary conditions and the exit (vent) geometry. Volcanic vents are rarely the symmetric features that are often assumed in models and experiments. They often exhibit highly irregular shapes with notched or slanted rims that can be transient. To eventually understand the unobservable boundary conditions, it is necessary to initially gain knowledge about the effect of the observable factors (i.e. vent geometry). This knowledge will ultimately improve the understanding of the parameters affecting an explosive event to develop accurate probabilistic hazard maps. To this end, a combination of field observations and laboratory experiments was used. First, I characterised vent and crater shape changes at a frequently erupting volcano (Stromboli) to collect high-resolution geometric data of volcanic vents and observe the related explosion dynamics. As a result of topographic changes, variable eruption intensity, style and directionality could be detected. Five topographic data sets were acquired by unoccupied aerial vehicles (UAVs) over nine months (May 2019-January 2020). During this period, changes associated with "normal" Strombolian activity, "major explosions" and paroxysmal episodes (3 July and 28 August 2019) occurred. Hence, the topographic data made it possible to link the predominant constructive and destructive processes to these eruption styles. Furthermore, the number and position of active vents changed significantly, which is a critical parameter for hazard assessment as vent geometry and position can be linked to shifts in eruptive mechanisms. These field surveys highlight the geometric complexity and variability of volcanic vents at an unprecedented spatiotemporal resolution. Additionally, the observations of explosions suggested the paramount influence of crater and vent geometry on pyroclast ejection characteristics, a fact that has strong implications for areas potentially affected by bomb impact and pyroclastic fall out. Secondly, I designed a series of shock-tube experiments incorporating the geometry elements observed at Stromboli to quantify the influence of vent geometry and several boundary conditions. These experiments validated the link between vent geometry and explosion dynamics that was observed in the field. The novel geometry element is an inclined exit plane of 5°, 15° and 30° slant angle combined with a cylindrical and diverging inner geometry resulting in six vent geometries. All experiments were conducted with gas-only (Argon) at room temperature, four different starting pressures (5, 8, 15, 25 MPa) and two reservoir volumes (127.4 cm3, 31.9 cm3). Despite the vertical setup, the slanted geometry yielded both a laterally variable gas spreading angle and an inclination of the jets. The inner geometry controlled the jet inclination towards the dip direction of the slanted exit plane (cylindrical) and against the dip direction of the slanted exit plane (diverging). Cylindrical vents produced larger gas spreading angles than diverging vents. Both gas spreading angle and jet inclination were highly sensitive to the experimental pressure and the slant angle. They had a positive correlation with maximum gas spreading angle and jet inclination. Additionally, the pressure was positively correlated with the maximum duration of underexpanded characteristics of the jet. The gas volume only showed a positive correlation with the maximum gas spreading angle. Thirdly, I added particles to the experiments to mimic the ejection of gas-particle jets during explosive volcanic eruptions. For this set of experiments, the two geometries with the 30° slant angle from the previous experimental series were used as they exhibited the strongest effect on the gas ejection dynamics. They were supplemented by a third vent that resembled the "real" geometry of Stromboli’s active S1 vent as it was mapped in May 2019 and fabricated by 3D printing. The S1’s geometry is characterised by a ~ 10° divergence on one side and a ~ 40° divergence on the other side. Besides three vent geometries, two types of particles (scoria and pumice), each with three different grain size distributions (0.125– 0.25, 0.5–1, 1–2 mm) and two starting pressures (8, 15 MPa) were used. The near-vent vent dynamics were characterised as a function of particle spreading angle and particle ejection velocity. The vent geometry governed the direction and the magnitude of particle spreading, and the velocity of particles. All geometries yielded asymmetric particle spreading as well as a non-uniform velocity distribution in experiments with pumice particles. The combination of field observations, gas-only and gas-particle experiments demonstrated the prime control exerted by vent geometry. In nature, a modification of the vent led to modified pyroclast ejection patterns. In the laboratory the complex geometries facilitated inclined gas jets, an asymmetric gas and particle spreading angle, and an asymmetric particle ejection velocity distribution. These findings suggest that the asymmetry of volcanic vents and/or craters can promote the asymmetric distribution of volcanic ejecta.Which, in turn, will lead to a preferred direction of volcanic fallout and — in case a column collapse occurs — to a preferred direction of the ensuing pyroclastic density currents. The availability of new technology like unoccupied aerial vehicles, photogrammetry and 3D printing provides several opportunities for the volcanological community. Aerial observations allow a fast, inexpensive and safe way to collect geometrical data of volcanic vents and craters, even in times of elevated volcanic activity. In combination with photogrammetry and 3D printing, "real" vents can be produced for increasingly realistic scaled laboratory experiments
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