93 research outputs found
Trajectory Prediction Learning using Deep Generative Models
No full textTrajectory prediction involves estimating an object's future path using its current state and historical data, with applications in autonomous vehicles, robotics, and human motion analysis. Deep learning methods trained on historical data have been applied to this task, but they struggle with complex spatial dependencies due to the intricate nature of trajectory data and dynamic environments. We introduce TrajLearn, a novel trajectory prediction model using generative models and higher-order mobility flow representations (hexagons). TrajLearn, given a trajectory's recent history and current state, predicts its next k steps. It employs a variant of beam search for exploring multiple paths, ensuring spatial continuity. Our experiments demonstrate that TrajLearn surpasses current leading methods and other baselines by about 60% on various real-world datasets. We also explore different prediction horizons (k values), perform resolution sensitivity analysis, and conduct an ablation study to evaluate the contributions of different model components
Deep Generative Models for Trajectory Prediction and Mobility Network Forecasting
No full textPredicting human mobility is essential for urban planning, traffic management, and epidemiology. This thesis tackles two intertwined challenges: accurately forecasting individual trajectories and inferring the resulting mobility network. First, we introduce TrajLearn, a Transformer‑based deep generative model that treats trajectories as token sequences and employs spatially constrained beam search to predict each individuals’s next k locations with high precision. Building on these forecasts, we present MobiNetForecast, which constructs and predicts the future topology of the mobility network by detecting when independently predicted trajectories intersect in space and time. Across large, real‑world datasets, our unified framework achieves up to 40% relative gains in trajectory accuracy and up to 100x improvement in contact prediction over state-of-the-art baselines. These results demonstrate that combining advanced sequence modeling with explicit contact inference offers a powerful, scalable solution for dynamic mobility network forecasting
Phosphorous Diffusion in N2+ -Implanted Germanium during Flash Lamp Annealing: Influence of Nitrogen on Ge Substrate Damage and Capping Layer Engineering
No full textIn this work we present a systematic study on post-implantation phosphorous diffusion control in Ge by co-implanted nitrogen in combination with various surface capping layers (Al2O3, SiO2 and Si3N4). Phosphorous has been implanted at low energy (11 keV) and high dose (1015 cm−2) in p-Ge (100) already implanted or not with low energy (10 keV−5 × 1014 cm−2) N2+. Flash Lamp Annealing (FLA) at 800–850°C for 20 ms in inert ambient has been used as post-implantation annealing scheme. In the absence of nitrogen, significant substrate damage and capping layer deterioration prevents a reliable comparison among the three capping materials. The presence of nitrogen in the Ge substrate, effectively suppresses the damage observed after the FLA. In this case, P diffusion is additionally retarded in the presence of Al2O3 as compared to SiO2 and Si3N4. The experimental results constitute a direct evidence of the action of the three capping layers as sinks for Ge vacancies with different interface recombination velocities. On the contrary, the nitrogen diffusion data suggest that interface recombination velocities of Ge interstitials are almost independent of the capping layer choice
GRAPHENE UNDER UNIAXIAL DEFORMATION: A RAMAN STUDY
No full textThe presented work summarizes various aspects of uniaxial deformation in monolayer graphene studied by means of Raman spectroscopy. Graphene flakes were subjected to tension - compression uniaxial loading using the cantilever beam technique. The evolution of the Raman single-resonance (G) and double-resonance (2D) bands was monitored at strain levels < 1%. The position of all peaks redshifts under tension and blueshifts under compression. The G peak splitting into two sub-bands (G(-) and G(+)) which is caused by symmetry lowering, is observed in both strain directions. The sub-bands' intensities are used to calculate the crystal lattice orientation of the measured graphene flakes with respect to the strain axis. The nature and splitting of the 2D band even in the unstrained flakes, when excited by the 785 nm (1.58 eV) laser line, is interpreted as the interplay between two distinct double resonance scattering processes
Temperature-induced valence transition and associated lattice collapse in samarium fulleride
No full textThe different degrees of freedom of a given system are usually independent of each other but can in some materials be strongly coupled, giving rise to phase equilibria sensitively susceptible to external perturbations. Such systems often exhibit unusual physical properties that are difficult to treat theoretically, as exemplified by strongly correlated electron systems such as intermediate-valence rare-earth heavy fermions and Kondo insulators, colossal magnetoresistive manganites and high-transition temperature (high-Tc) copper oxide superconductors. Metal fulleride salts1—metal intercalation compounds of C60—and materials based on rare-earth metals also exhibit strong electronic correlations. Rare-earth fullerides thus constitute a particularly intriguing system—they contain highly correlated cation (rare-earth) and anion (C60) sublattices. Here we show, using high-resolution synchrotron X-ray diffraction and magnetic susceptibility measurements, that cooling the rare-earth fulleride Sm2.75C60 induces an isosymmetric phase transition near 32 K, accompanied by a dramatic isotropic volume increase and a samarium valence transition from (2 + ) + to nearly 2 + . The negative thermal expansion—heating from 4.2 to 32 K leads to contraction rather than expansion—occurs at a rate about 40 times larger than in ternary metal oxides typically exhibiting such behaviour2. We attribute the large negative thermal expansion, unprecedented in fullerene or other molecular systems, to a quasi-continuous valence transition from Sm2+ towards the smaller Sm(2+)+, analogous to the valence or configuration transitions encountered in intermediate-valence Kondo insulators like SmS (ref. 3)
Novel Hybrid Materials Consisting of Regioregular Poly(3-octylthiophene)s Covalently Attached to Single-Wall Carbon Nanotubes
No full text
Phonon Properties of Multi-layered Graphene from Molecular Dynamics Simulations
No full textOral presentation for the "Nanoscale and Microscale Heat Transfer VII" conference (Girona, Spain)In this work, we have studied the phonon properties of multi-layered graphene of 1-5L and Bulk Graphite(BG) from the analysis of Molecular Dynamics (MD) simulations, by employing the k-space AutocorrelationSequence (k-VACS) method. From the atomic trajectories and positions obtained from MD we calculate theVelocity Autocorrelation Function of the atoms in the system, which is then Fourier Transformed (FT) toobtain the phonon Spectral Energy Density Z(k, ω) [1]. From this we extract the temperature-dependence ofthe energies ω k,j (T ) and lifetimes τ k,j (T ), as well as the Phonon Densities of States (PDOS), for temperaturesranging from 80 K to 1000 K (see Fig. 1). We then focus on the impact of the number of layers N on theenergies ω(T ) and lifetimes τ (T ) of Γ-point phonons, as well as the type of interlayer potential used. Forthe later we used comparatively the Kolmogorov-Crespi (KC) [2] and the Lennard-Jones (LJ) potentials.We have found that the number of layers N has little effect on the energies ω of the intra-layer (ZO andE 2g ) modes and greater effect on the inter-layer ones (Layer Shearing and Layer Breathing) modes, while τis more sensitive to N for all modes. The effect of N on the lifetimes was also found to be independent of thetype of potential used, as for both the KC and the LJ interlayer potential, the lifetime of the Raman-activeG phonon increases with the number of layers N . In Fig. 1 (left) we present for illustration the temperaturedependence of the G phonon lifetime τ G (T ) obtained from MD, compared with DFT calculations [6] andexperimental data [7]. In this work we present, to the best of our knowledge, several findings for the firsttime: the T-dependence of ω(T ) for the intralayer modes and the effect of N on the lifetime τ G (T ) of theRaman-active G phonon
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