R. D. Strauss

Bio: R. D. Strauss is an academic researcher from Technische Universität München. The author has contributed to research in topics: Heliosphere & Cosmic ray. The author has an hindex of 22, co-authored 84 publications receiving 1562 citations. Previous affiliations of R. D. Strauss include North-West University & Ruhr University Bochum.

Modeling the modulation of galactic and jovian electrons by stochastic processes

Abstract: We present a newly developed numerical modulation model to study the transport of galactic and Jovian electrons in the heliosphere. The model employs stochastic differential equations (SDEs) to solve the corresponding transport equation in five dimensions (time, energy, and three spatial dimensions) which is difficult to accomplish with the numerical schemes used in finite difference models. Modeled energy spectra for galactic electrons are compared for the two drift cycles to observations at Earth. Energy spectra and radial intensity profiles of galactic and Jovian electrons are compared successfully to results from previous studies. In line with general drift considerations, it is found that most 100 MeV electrons observed at Earth enter the heliosphere near the equatorial regions in the A > 0 cycle, while they enter mainly over the polar regions in the A < 0 cycle. Our results indicate that 100 MeV electrons observed at Earth originate at the heliopause with ~600 MeV undergoing adiabatic cooling during their transport to Earth. The mean propagation time of these particles varies between ~180 and 300 days, depending on the drift cycle. For 10 MeV Jovian electrons observed at Earth, a mean propagation time of ~40 days is obtained. During this time, the azimuthal position of the Jovian magnetosphere varies by ~1°. At a 50 AU observational point, the mean propagation time of these electrons increases to ~370 days with an azimuthal position change of Jupiter of ~20°. The SDE approach is very effective in calculating these propagation times.

Modelling heliospheric current sheet drift in stochastic cosmic ray transport models

Abstract: Drifts are one of the major cosmic ray modulation mechanisms in the heliosphere. Three types of drifts occur in the background heliospheric magnetic field, namely curvature, gradient and current sheet drifts. The last component occurs because of the switch in magnetic field polarity across the heliospheric current sheet and is the main topic of study. We discuss and implement a new approach to model drifts in a numerical modulation model. The model employs stochastic differential equations to solve the relevant transport equation in five (three spatial, energy and time) dimensions. What is of interest is the fact that the model can handle current sheet tilt angles up to the theoretical maximum of α=90° and still remain numerically stable. We use the additional insights gained from the numerical model to investigate the effectiveness of drifts along the current sheet by examining the relationship between the current sheet path length and the cosmic ray propagation time. It is found that diffusion can disrupt the drift process very effectively, leading to diffusive short circuiting of the current sheet by the cosmic rays.

On cosmic ray modulation beyond the heliopause: where is the modulation boundary?

Abstract: Two of the paradigms in modeling the transport of galactic cosmic rays are that the modulation boundary is the heliopause and that the local interstellar spectra are identical to the galactic cosmic ray spectra. Here we demonstrate that the proton spectrum is already modulated due to an altered interstellar diffusion in the outer heliosheath as a consequence of the heliospheric "obstacle" in the interstellar flow. The main modulation effect however is adiabatic energy losses during a "confinement time" of cosmic rays inside the heliosphere.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Voyager 1 Observes Low-Energy Galactic Cosmic Rays in a Region Depleted of Heliospheric Ions

Abstract: On 25 August 2012, Voyager 1 was at 122 astronomical units when the steady intensity of low-energy ions it had observed for the previous 6 years suddenly dropped for a third time and soon completely disappeared as the ions streamed away into interstellar space. Although the magnetic field observations indicate that Voyager 1 remained inside the heliosphere, the intensity of cosmic ray nuclei from outside the heliosphere abruptly increased. We report the spectra of galactic cosmic rays down to ~3 × 10^6 electron volts per nucleon, revealing H and He energy spectra with broad peaks from 10 × 10^6 to 40 × 10^6 electron volts per nucleon and an increasing galactic cosmic-ray electron intensity down to ~10 × 10^6 electron volts.

DARWIN: towards the ultimate dark matter detector

Abstract: DARk matter WImp search with liquid xenoN (DARWIN(2)) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary g ...

PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions

Abstract: This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ∼1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z=0 and 4. The sample covers the stellar mass range log(M * /M e)=9.0-11.8, and SFRs relative to that on the MS, δMS=SFR/SFR (MS), from 10 −1.3 to 10 2.2. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t depl , defined as the ratio of molecular gas mass to SFR, scales as (1+z) −0.6 ×(δMS) −0.44 and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass μ gas depends on (* d +´´-) () () z M 1 M S 2.5 0.52 0.36 , which tracks the evolution of the specific SFR. The redshift dependence of μ gas requires a curvature term, as may the mass dependences of t depl and μ gas. We find no or only weak correlations of t depl and μ gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z.

Theoretical Challenges in Galaxy Formation

Abstract: Numerical simulations have become a major tool for understanding galaxy formation and evolution. Over the decades the field has made significant progress. It is now possible to simulate the formation of individual galaxies and galaxy populations from well-defined initial conditions with realistic abundances and global properties. An essential component of the calculation is to correctly estimate the inflow to and outflow from forming galaxies because observations indicating low formation efficiency and strong circumgalactic presence of gas are persuasive. Energetic “feedback” from massive stars and accreting supermassive black holes—generally unresolved in cosmological simulations—plays a major role in driving galactic outflows, which have been shown to regulate many aspects of galaxy evolution. A surprisingly large variety of plausible subresolution models succeeds in this exercise. They capture the essential characteristics of the problem, i.e., outflows regulating galactic gas flows, but their predicti...