Domain: Natural Science — Physics
Target concept: Polycrystalline ice under a microscope stage with slow heating under polarized light: grain boundary motion, grain growth, and progressive coarsening/fading of birefringence patterns (without a guaranteed complete disappearance).

Video generation prompt: Observe polycrystalline ice on a temperature-controlled microscope stage, gradually increase the temperature under cross-polarized light, and perform continuous recording.

Evaluation guide:
(i) Target concept: Solid-state microstructural evolution in polycrystalline ice under thermal activation, observed via polarized light microscopy.
Minimum mechanism: Ice remains solid throughout (no melting); rising temperature thermally activates grain-boundary migration (curvature-driven coarsening akin to Ostwald ripening, aided near 0°C by premelting/quasi-liquid layers at grain boundaries and junctions), so smaller grains shrink and larger grains grow at their expense. Because birefringent color under cross-polarized light comes from differences in crystallographic (c-axis) orientation between neighboring grains, eliminating boundaries and reducing the grain count coarsens and simplifies the birefringent pattern and weakens its overall color contrast; this does not require the remaining grains to become co-aligned, and full extinction to a perfectly isotropic (all-black) field is not guaranteed by grain growth alone.
(ii)Storyline: [Frame 0–3s] Fixed-view cross-polarized image shows a dark background and a polycrystalline ice sample with sharp, multicolored birefringent grains and clear boundaries. [Frame 3–6s] Boundaries visibly curve, translate, and retract; small grains shrink while large grains expand; birefringence remains strong. [Frame 6–9s] Boundary motion continues; grain count decreases; the birefringent pattern coarsens and its color contrast begins to fade. [Frame 9–10s] Background remains dark; only a few large grains with faint, muted birefringent color remain: the pattern is much simpler and dimmer than at the start, though still weakly birefringent. All transitions occur within the same fixed optical field, with no viewpoint change and no liquid phase.

Manual:
Experimental Procedure
1. Place polycrystalline ice sample on temperature-controlled microscope stage.
2. Engage cross-polarized light configuration (confirmed by dark background).
3. Gradually increase stage temperature while continuously recording.
Observation of Experimental Phenomena
- Initial: Distinct grain boundaries with strong birefringent color patterns.
- During heating: Grain boundaries move; adjacent grains coalesce; larger grains grow at expense of smaller ones.
- Final: The birefringent pattern coarsens into fewer, larger colored domains and its overall color contrast weakens noticeably, though full disappearance to a uniformly isotropic appearance is not guaranteed by grain growth alone.
Summary of Experimental Principles
Polycrystalline ice consists of many crystallites with random c-axis orientations. Under cross-polarized light, orientation-dependent birefringence produces colorful interference patterns. Heating provides energy for grain-boundary migration (solid-state diffusion, assisted near 0°C by premelting effects at boundaries and junctions), driving grain growth (Ostwald ripening). As boundaries are eliminated and the grain count drops, the birefringent pattern coarsens and its color contrast weakens, though this does not require the surviving grains to share a common orientation.

Prompt Grounding rubric:
level_1: No microscope stage is visible; no ice sample appears in view; no polarizer/analyzer configuration is evident (the image looks like ordinary bright-field or naked-eye lighting rather than a dark cross-polarized field); no temperature-control element (hot stage, heater coil, or controller readout) is shown; the clip does not depict a heating sequence at all.
level_2: A microscope stage and an ice-like sample are both present, but the cross-polarized configuration is not established (e.g., the background is bright or white rather than dark); the ice sample shows no internal grain structure (appears as a featureless white or grey block); there is no visible or implied heating element and no indication that temperature is being raised over the recording.
level_3: A temperature-controlled microscope stage is shown with a dark background confirming a cross-polarized configuration; the ice sample on the stage displays distinct, sharply bounded grains with birefringent multicolored patterns at the outset; however, only one of the three phenomena (grain-boundary motion, grain growth, or birefringence fading) is depicted anywhere in the clip, and the sample and stage remain visible throughout a single continuous view.
level_4: All required setup elements are present and correctly configured: a microscope stage with a visible thermal-control element (heater plate or a displayed temperature readout), a dark cross-polarized background maintained throughout, and a polycrystalline ice sample showing sharp grain boundaries and multicolored birefringence at the outset; at least two of the three phenomena (grain-boundary motion, grain growth, birefringence fading) are each visibly depicted at some point in the recording, clearly enough to identify without ambiguity, regardless of the order in which they appear.
level_5: Everything required at the 4-point level holds, and additionally: the thermal-control element is unambiguous (a visible heater coil or a temperature readout whose value visibly changes across the recording); the dark cross-polarized background is maintained with no interruption or brightening; and all three phenomena (grain-boundary motion, grain growth, and birefringence fading) are each clearly visible at some point during a single continuous fixed-view recording, with the ice sample and stage remaining the only subject in frame throughout.

Scientific and Causal Correctness rubric:
level_1: No grain boundaries are ever visible in the ice sample, or birefringent color never appears at all; the sample looks uniformly white or grey, or is shown fully melted into liquid water from the start, so no solid-state grain evolution can be assessed.
level_2: Grain boundaries and birefringent color are visible, but they stay essentially static for the whole recording (no visible boundary motion, no change in grain count); or the birefringent color disappears in a single abrupt change rather than any progressive fading, with no preceding grain-boundary motion or grain growth shown.
level_3: Grain boundaries visibly move (curving, migrating, or retracting) and grain growth is evident (some grains visibly shrink or disappear while neighboring grains enlarge), and the birefringent pattern becomes visibly coarser or dimmer over the recording, but the order is wrong in at least one respect (e.g., the birefringent pattern changes before any boundary motion is shown, or grain count visibly drops before boundary motion begins).
level_4: Grain-boundary motion is shown starting first, grain growth (fewer, larger grains) follows as a visible consequence, and the birefringent pattern then visibly coarsens and dims as a result, in that order, with no reversal (grains do not re-subdivide, and birefringent color does not become sharper or more numerous again) and no liquid phase appearing at any point.
level_5: The causal chain from the 4-point level holds throughout the entire recording with no exceptions: wherever boundary motion is shown, the grain count has not yet dropped; wherever grain count visibly drops, boundary motion has already been shown at an earlier point; birefringent color only coarsens or dims after grain count has visibly dropped, and continues to do so without becoming brighter or more finely patterned again; the sample stays solid (no melting, no cracking, no liquid pooling) in every frame.

Spatiotemporal Consistency rubric:
level_1: The viewpoint or field of view abruptly changes (e.g., a sudden cut from a close-up of the grains to a wide microscope shot); the ice sample or its grain pattern vanishes and reappears, or jumps to a completely different grain arrangement between frames; the dark cross-polarized background suddenly switches to a bright field mid-recording; the stage or sample outline visibly warps or distorts between frames.
level_2: Grain boundaries appear and disappear intermittently without any visible motion connecting the two states; birefringent colors switch abruptly between unrelated hues (e.g., a grain jumps from magenta directly to yellow with no darkening or in-between transition) without any accompanying boundary movement; the stage or ice sample shifts or rotates within the frame for no apparent reason; the dark-field illumination appears to move or reverse partway through the recording.
level_3: The recording shows a brief, isolated hesitation in grain-boundary motion (a boundary appears to pause and then resume migrating) or a slight misalignment of the stage within the frame; the dark background shows a small, temporary change in brightness at one point in the clip; none of these issues involve the viewpoint changing, the sample structure breaking apart, or grains jumping to a new arrangement.
level_4: The viewpoint stays fixed for the entire recording; no grain boundary appears, disappears, or relocates without a continuous migration path connecting its start and end positions; the dark cross-polarized background never brightens or flickers; the birefringent pattern fades in a smooth, one-directional trend across the recording (it does not become more colorful or sharply patterned again after dimming); grain shrinkage and growth proceed as a gradual, continuous coarsening rather than sudden grain disappearance or appearance.
level_5: Everything required at the 4-point level holds, and additionally: every grain boundary's position changes smoothly frame to frame with no visible skipping or sudden repositioning; the birefringent pattern's dimming trend has no pauses, reversals, or flickers anywhere in the recording; grains merge or shrink through visibly continuous coalescence rather than any grain instantly vanishing or a new grain instantly appearing; focus, contrast, and the dark-field illumination look completely unchanged from the first frame to the last.