eBPF System Call Sensor

• The eBPF-based system call sensor is a kernel-level monitoring tool that leverages eBPF to capture and analyze system call events with minimal performance overhead.
• It employs dynamic tracing techniques to provide real-time detection of anomalies and to facilitate in-depth performance analysis in production environments.
• Practical implementations integrate this sensor with observability frameworks to enhance security visibility and resource utilization monitoring.

Diffusion-Augmented Contrastive Learning (DACL) is a hybrid representation learning framework designed to produce noise-invariant and discriminative embeddings for biosignals such as ECG by integrating latent-space diffusion processes with supervised contrastive objectives. The approach replaces hand-crafted or heuristic data augmentations with a learnable, manifold-respecting noising mechanism, and leverages a supervised contrastive loss to enforce both class separability and robustness to noise. The framework is motivated by the particular challenges of representation learning in physiological time series, where conventional augmentations fail to capture intrinsic variability or can destroy semantic content (Zewail, 24 Sep 2025).

1. Latent Manifold Construction via Scattering Transformer and VAE

DACL begins by constructing a smooth, information-preserving latent space tailored to the geometry of biosignals:

• Feature Backbone: Each raw ECG segment $x$ is transformed into a high-dimensional feature vector using a fixed, training-free Scattering Transformer (ST). The ST operator provides structured representations suitable for downstream compression.
• Variational Autoencoder Compression: A lightweight VAE $(E_\phi, D_\theta)$ is trained to encode the ST features. For an input $x$, the encoder yields a posterior $q_\phi(z_0|x)$ parameterized as a diagonal-covariance Gaussian with mean $\mu$ and variance $\sigma^2$. The VAE objective is

$$L_{\mathrm{VAE}} = \mathbb{E}_{q_\phi(z_0|x)}[ -\log p_\theta(x|z_0) ] + KL( q_\phi(z_0|x) \| p(z_0)), \quad p(z_0) = \mathcal{N}(0, I).$$

After optimization, the decoder $D_\theta$ is discarded, and the posterior mean $\mu(x)$ is retained as a "clean" latent code $z_0$. This ensures that subsequent augmentations operate on a semantically meaningful, low-dimensional manifold (Zewail, 24 Sep 2025).

2. Diffusion Forward Process as Principled Data Augmentation

The core innovation is the use of a diffusion process as a continuous, stochastic augmentation mechanism in latent space:

• Noise Schedule: A monotonically decreasing sequence $\alpha_1 > \alpha_2 > \cdots > \alpha_T$ governs the corruption dynamics, with cumulative product $\bar{\alpha}_t = \prod_{s=1}^t \alpha_s$.
• Noisy View Generation: For each sample, a timestep $t \sim \mathrm{Uniform}\{1,\dots,T\}$ and Gaussian noise $\epsilon \sim \mathcal{N}(0, I)$ are sampled. A noised latent $z_t$ is produced by

$$z_t = \sqrt{\bar{\alpha}_t}\, z_0 + \sqrt{1 - \bar{\alpha}_t} \, \epsilon.$$

This formulation ensures that augmentations are manifold-adaptive and allows the model to exploit a continuum of corruption levels from lightly- to heavily-noised views. These properties are unattainable with standard domain-agnostic noise injection or geometric data augmentations (Zewail, 24 Sep 2025).

3. Noise-Robust Representation Learning via Supervised Contrastive Objective

Robustness and discriminability are achieved through a supervised contrastive loss on synthetic noisy views:

• U-Net Encoding Architecture: Each $z_t$ and its associated timestep $t$ (sinusoidally embedded) are input to a small 1D U-Net, comprising down-sampling (Conv–GroupNorm–ReLU–downsample) and up-sampling (mirrored) components with skip connections. The network’s output is global-pooled to produce a $d$-dimensional embedding $h_t$.
• Multi-View Construction and Label Partitioning: For each instance and class, $K$ noisy views are generated at diverse timepoints $t$. For supervised contrastive learning, all views of the same class (at varying $t$) serve as positive pairs, and views from other classes constitute negatives.
• Supervised Contrastive Loss:

$$L_{SC} = - \sum_{i=1}^M \frac{1}{|P(i)|} \sum_{p \in P(i)} \log \left[ \frac{ \exp(h_i \cdot h_p / \tau) }{ \sum_{a \in A(i)} \exp(h_i \cdot h_a / \tau) } \right]$$

where $P(i)$ indexes all positive views (same class, different $t$), $A(i) = P(i) \cup N(i)$ is the aggregate set of positives and negatives, and $M$ is the total number of (sample, time) pairs. The temperature $\tau$ is a tunable hyperparameter. This loss enforces intra-class invariance across noise strengths and inter-class discrimination (Zewail, 24 Sep 2025).

4. Robustness–Discrimination Tradeoff and Empirical Assessment

Learning in DACL is characterized by a dynamic tension:

• Noise Invariance: The architecture must “pull together” embeddings for all views $z_t$ across the full noise schedule. This forces the model to capture features that are robust to diffusion corruption, i.e., invariant content across $z_0, z_{t_1}, ..., z_{t_K}$ for a given sample.
• Class Separability: Simultaneously, the presence of negatives at all corruption levels prevents model collapse and ensures that discriminative, class-dependent features are preserved at every noise strength.
• Experimental Validation: On patient-split PhysioNet 2017 ECG (Normal vs. Abnormal), DACL achieves a frozen-encoder linear AUROC of 0.7815, outperforming both a supervised contrastive baseline with Gaussian augmentation (AUROC 0.6716) and a denoising autoencoder (AUROC 0.7532).
• Ablation: Diffusion Timestep: When stratifying positive views by noise level—“early” (light noise), “mid,” and “late” (heavy noise)—performance increases with heavier corruption. The harder the positive pair, the greater the achieved noise invariance and class discriminability; “late” yields highest AUROC (Zewail, 24 Sep 2025).

5. Practical Implementation and Extension Potential

• Training Sketch:

for each minibatch of N samples (x_i, y_i): z_{0,i} ← VAE_encoder(x_i) # freeze VAE for each i in batch: sample t_i ∼ Uniform[1…T], ϵ_i ∼ 𝒩(0,I) z_{t_i,i} ← sqrt{ᾱ_{t_i}} z_{0,i} + sqrt{1-ᾱ_{t_i}} ϵ_i h_{i} ← U-Net_Enc(z_{t_i,i}, t_i) compute L_SC over all (i,j) in batch using y update U-Net_Enc parameters

• Generality: The DACL protocol is immediately portable to other physiological signals (EEG, EMG, PPG) given suitable feature backbones. For non-biosignal domains with complex time-series or graph data, DACL can substitute hand-crafted augmentations with principled, learned manifold diffusion processes—particularly when augmentation heuristics are infeasible or unreliable.
• Prospective Enhancements: Possible research directions include adaptive timestep sampling (to focus contrastive learning on the most informative noise levels), end-to-end optimization of both VAE and contrastive encoder, and fusion of diffusion-based augmentations with traditional heuristics for richer positive sets (Zewail, 24 Sep 2025).

6. Comparative Placement and Impact

DACL advances contrastive representation learning for biosignals by tightly integrating generative modeling (via VAE and diffusion processes) with discriminative objectives (supervised contrastive loss):

• Principled Augmentation: Unlike random or ad hoc augmentations, the latent-space diffusion process remains on the learned statistical manifold, respects sample variability, and provides a controllable spectrum of augmentation strengths.
• Balancing Invariance and Discrimination: The supervised contrastive regime ensures an optimal tradeoff between robustness to noise and preservation of class information, which is empirically validated by performance trends at different points on the diffusion trajectory.
• Noise-Invariant Semantics: The model is compelled to learn semantic features that are stable not just under weak augmentations (which may be trivial), but across a broad range of manifest corruptions.
• Downstream Applicability: The attained embeddings are directly usable (via linear evaluation) for biomedical classification tasks exhibiting complex, real-world noise, and the architecture can be extended to domains with similar augmentation and invariance constraints (Zewail, 24 Sep 2025).

---

In summary, DACL exemplifies a new paradigm in representation learning for physiological and other complex time-series data by leveraging learned, diffusion-driven augmentations in conjunction with class-aware supervised contrastive objectives, thereby achieving robust, semantically meaningful, and noise-invariant embeddings (Zewail, 24 Sep 2025).