Myocardial immune vulnerability unmasked after treatment with immune checkpoint inhibitors: a case report.

Laser powder bed fusion (LPBF) builds metal parts by scanning a focused laser over thin layers of powder, and it now serves the aerospace, energy, and biomedical sectors, where it enables part consolidation and design freedom beyond the reach of conventional manufacturing []. The laser melts a small pool that solidifies as the beam advances, and the depth of this pool determines whether successive layers fuse fully and whether the melt collapses into a keyhole, a deep vapor cavity that traps gas porosity and shortens fatigue life [,]. Reliable prediction of melt-pool depth is therefore a prerequisite for selecting process parameters and qualifying parts, and it remains a central modeling problem in metal additive manufacturing []. Two regimes govern the geometry of the pool. Below a threshold energy density, heat conduction sets the pool shape, and the depth and width grow together; above the threshold, the beam opens a vapor depression whose walls trap the beam through multiple reflections and drive the pool far deeper than conduction alone can account for. This is the keyhole regime [], and the variable that distinguishes it from the conduction regime is the absorbed energy density, expressed through the normalized enthalpy of King et al. [] and through closely related scaling parameters introduced by Fabbro [] and by Rubenchik et al. []. Analytical descriptions of the pool itself rest on a small set of closed-form solutions. The Rosenthal point source [] and its Gaussian-distributed extension by Eagar and Tsai [] remain the basis of most fast models, while finite-element practice more often uses a volumetric Gauss–Goldak source that deposits energy over a prescribed depth []. These solutions reproduce the lateral extent of the pool well and its penetration poorly, and the reason is structural: a surface source produces a near-semicircular conduction pool, so the depth-to-half-width ratio it can attain is bounded close to unity. That bound is itself the basis of the conventional geometric criterion, under which a cross-section is taken to be conduction-dominated below an aspect ratio of one and keyholing above it []. Identification of the transition has otherwise proceeded along two lines. Energy criteria place a threshold on the normalized enthalpy [] or on the related scaling groups [,], but the threshold is calibrated on measurements and shifts between datasets. Direct observation, by in situ X-ray imaging of the vapor depression or by operando absorptivity measurement [,], settles individual conditions but requires synchrotron or calorimetric access and therefore covers few parameter sets. Neither line answers the question a modeler actually faces, which is whether a given conduction model can reach a measured depth at all.