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Luping Shi

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cond-mat.mtrl-sci Machine Learning Neural and Evolutionary Computing Neurons and Cognition Robotics

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preprint2026arXiv

Joint sparse coding and temporal dynamics support context reconfiguration

Adaptive behavior requires the brain to transition between distinct contexts while maintaining representations of prior experience. The ability to reconfigure neural representations without erasing previously acquired knowledge is central to learning in dynamic environments, yet the neural mechanisms that support this balance remain unclear. Understanding these mechanisms is also critical for addressing catastrophic forgetting in artificial systems designed for lifelong learning. Here, we identify joint sparse coding and temporal dynamics in both the mouse medial prefrontal cortex (mPFC) and computational networks as mechanisms that help preserve prior representations during context transitions. Specifically, sparsity in context-dependent representations reduces cross-context interference, whereas temporal dynamics within the network activity further enhance context separability across time. Strikingly, networks endowed with both properties, such as spiking neural networks, exhibit improved retention during lifelong learning without auxiliary heuristics. These findings establish joint sparse coding and temporal dynamics as a core mechanism supporting flexible context reconfiguration in lifelong learning and, through their activity constraining nature, as an energy-efficient architectural principle for stable adaptation. Together, they provide a mechanistic framework for understanding how the brain preserves prior knowledge while flexibly adapting to new contexts.

preprint2026arXiv

Mind Dreamer: Untethering Imagination via Active Latent Intervention on Latent Manifolds

Model-Based Reinforcement Learning (MBRL) leverages latent imagination for sample efficiency, yet remains constrained by Historical Tethering: imagination is typically initialized from observed states. This creates a learning asymmetry, where the world model's manifold discovery outpaces the policy's sparse-reward optimization. We propose Mind Dreamer (MD), a framework that operationalizes Active Latent Intervention (ALI) to transcend Markovian continuity. MD reformulates discovery as the minimization of a global Relay Manifold Expected Free Energy (R-EFE); by sampling initial states from a learned generator $s_0 \sim p_{gen}(\cdot)$ rather than the historical buffer, MD utilizes an adversarial generator to synthesize non-continuous latent jumps to epistemic blind spots that are physically plausible yet cognitively challenging. To resolve the credit assignment paradox across these spatial ruptures, we derive the Relay Value Function (RVF) and Relay Uncertainty Function (RUF). These potentials treat synthesized anchors as counterfactual intermediary states, propagating pragmatic and epistemic value through a principled Bellman-style formulation. Notably, we prove that uncertainty propagation across discontinuities necessitates a quadratic discount $γ^2$, establishing a formal epistemic horizon. Theoretically, MD approximates a variance-minimizing importance sampler that expands the manifold's spectral gap, reducing the hitting time to critical bottleneck states. Empirically, MD achieves a 1.67$\times$ average speedup over DreamerV3 on DeepMind Control Suite, reaching 8.8$\times$ in sparse-reward tasks.

preprint2015arXiv

Single neutral substitutional 3d-transition metal in GeTe and GeSb2Te4 by the screened exchange functional

Fe doped GST has shown experimentally the ability to alter its magnetic properties by phase change. In this work, we use screened exchange hybrid functional to study the single neutral substitutional 3d transition metal (TM) in crystalline GeTe and GeSb2Te4. By curing the problem of local density functional (LDA) such as over delocalization of the 3d states, we find that Fe on Ge/Sb site has its majority d states fully occupied while its minority d states are empty, which is different than previous predicted electronic configuration by LDA. From early transition metal Cr to heavier Ni, the majority 3d states are gradually populated until fully occupied and then the minority 3d states begin to be filled. In order to study the magnetic contrast, we use lower symmetry crystalline GeTe and GeSb2Te4 as the amorphous phases, respectively, which has been proposed to model the medium range disordering. We find that only Co substitution in r-GeSb2Te4 and s-GeSb2Te4 shows magnetic contrast. The experimental magnetic contrast for Fe doped GST may be due to additional TM-TM interaction, which is not included in our model. It can also be possible that these lower symmetry crystalline models are not sufficient to characterize the magnetic properties of real 3d TM doped amorphous GST.

preprint2015arXiv

The electronic structures of TiO2/Ti4O7, Ta2O5/TaO2 interfaces and the interfacial effects of dopants

We study the electronic structures of TiO2/Ti4O7 and Ta2O5/TaO2 interfaces using the screened exchange (sX-LDA) functional. Both of these bilayer structures are useful infrastructures for high performance RRAMs. We find that the system Fermi energies of both interfaces are just above the conduction band edge of the corresponding stoichiometric oxides. According to the charge transition levels of the oxygen vacancies in Ta2O5 and TiO2, the oxygen vacancies are stabilized at the -2 charged state. We propose to introduce interfacial dopants to shift the system Fermi energies downward so that the +2 charged oxygen vacancy can be stable, which is important for the controlled switching under the electrical field. Several dipole models are presented to account for the ability of Fermi level shift due to the interfacial dopants.

preprint2015arXiv

The role of single oxygen or metal induced defect and correlated multiple defects in the formation of conducting filaments

We study the dependence of the formation energies of oxygen and metal induced defects in Ta2O5, TaO2, TaO, TiO2 and Ti4O7 on the chemical potential of electron and atomic constitutes. In the study of single defect, metal induced defects are found to be preferable to oxygen induced defects. This is against the experimental fact of the dominant role of oxygen induced defects in the RS process. A simple multiple defects picture without correlated atomic rearrangement does not cure this problem. The problem is resolved under the correlated multiple defect picture where the multiple defects result in correlated atomic rearrangement and the final products show certain atomic ordering.

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