Thomas Greif

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We investigate the properties of the first galaxies at z & 10 with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds ≃ 10 K, and its ability to(More)
Probabilistic models with hidden variables such as probabilistic Latent Semantic Analysis (pLSA) and Latent Dirichlet Allocation (LDA) have recently become popular for solving several image content analysis tasks. In this work we will use a pLSA model to represent images for performing scene classification. We evaluate the influence of the type of local(More)
We perform three dimensional smoothed particle hydrodynamics (SPH) simulations in a realistic cosmological setting to investigate the expansion, feedback, and chemical enrichment properties of a 200 M⊙ pair-instability supernova (PISN) in the high-redshift universe. To this end, we use the entropy-conserving formulation of the cosmological simulation code(More)
The formation of the first galaxies is influenced by the radiative feedback from the first generations of stars. This feedback is manifested by the heating and ionization of the gas which lies within the H II regions surrounding the first stars, as well as by the photodissociation of hydrogen molecules within the larger Lyman-Werner (LW) bubbles that(More)
In our previous work [4] we have shown that the representation of images by the Latent Dirichlet Allocation (LDA) model combined with an appropriate similarity measure is suitable for performing large-scale image retrieval in a realworld database. The LDA model, however, relies on the assumption that all topics are independent of each other – something that(More)
We investigate the formation of metal-free, Population III (Pop III), stars within a minihalo at z ≃ 20 with a smoothed particle hydrodynamics (SPH) simulation, starting from cosmological initial conditions. Employing a hierarchical, zoom-in procedure, we achieve sufficient numerical resolution to follow the collapsing gas in the center of the minihalo up(More)
The very first stars to form in the universe heralded an end to the cosmic dark ages and introduced new physical processes that shaped early cosmic evolution. Until now, it was thought that these stars lived short, solitary lives, with only one extremely massive star, or possibly a very wide binary system, forming in each dark-matter minihalo. Here we(More)
The character of the first galaxies at redshifts z > ∼ 10 strongly depends on their level of pre-enrichment, which is in turn determined by the rate of primordial star formation prior to their assembly. In order for the first galaxies to remain metal-free, star formation in minihaloes must be highly suppressed, most likely by H2-dissociating LymanWerner(More)
We introduce a two–dimensional kinematic model for cyclic motions of humans, which is suitable for the use as temporal prior in any Bayesian tracking framework. This human motion model is solely based on simple kinematic properties: the joint accelerations. Distributions of joint accelerations subject to the cycle progress are learned from training data. We(More)
In this work we propose a novel approach to automatically detect a swimmer and estimate his/her pose continuously in order to derive an estimate of his/her stroke rate given that we observe the swimmer from the side. We divide a swimming cycle of each stroke into several intervals. Each interval represents a pose of the stroke. We use specifically trained(More)