首尔大学

We consider the Vlasov-Poisson equation on R-n & times; R-n with n >= 3. We prove local well-posedness in H-s(R-n & times; R-n) with s > n/2-1/4, for initial distribution f(0) is an element of H-s(R-n & times; R-n) having compact support in v. In particular, data not belonging to L-p(R-n & times; R-n) for large p are allowed.

Tidal bores are common in tide-dominated estuaries, but their sedimentary products remain less well constrained than their hydrodynamics. This study examines the spatial transformation of tidal-bore hydrodynamics and associated flood-tide deposits across the inshore tidal flats of the Sittaung River estuary, Myanmar. Breaking bores approaching 1 m in height were directly observed along the main channel and lower sand flats, where bore passage was accompanied by abrupt water-level rise, strong flow acceleration, enhanced vertical motion, and high suspended-sediment concentrations. Bore height decreased landward within sandy blind tidal channels (BTCs). In BTC2, tidal bores less than 0.1 m high were directly observed, whereas at BTC1 a weak or cryptic bore-related hydraulic disturbance is inferred from the timing of water-level, velocity, and turbidity changes. Importantly, the strongest flood currents in the blind channels occurred after bore passage and were locally enhanced by channel geometry and scour-pool morphology. At BTC1, maximum turbidity preceded maximum local flood-current velocity by approximately 40–50 min, indicating that suspended-sediment concentration was not controlled solely by instantaneous local current speed and likely reflected a combination of local resuspension and landward sediment advection. The preserved bore-related flood-tide deposit commonly comprises an erosional base overlain by structureless to faintly laminated very fine sand, followed upward by more distinct parallel lamination and ripple cross-lamination. We interpret the basal structureless and lower faintly laminated interval as the portion most closely associated with bore passage and its immediate aftermath, whereas the overlying deposits primarily record the subsequent flood current. The complete succession is therefore regarded as a bore-related flood-tide deposit rather than a tidal-bore deposit sensu stricto. Spatial variability of these deposits reflects not only bore attenuation but also sediment advection, post-bore flow acceleration, local accommodation, scour-pool morphology, and subsequent ebb-tide reworking. High-elevation sand shoals are excluded from the bore-related facies succession and are interpreted primarily as river-flood deposits. These observations complement existing tidal-bore facies models by emphasizing the importance of blind-channel morphology and spatial separation between sediment entrainment, transport, and deposition in morphologically complex intertidal environments.

We prove local well-posedness and finite-time blow-up for a restricted fourth-order Prandtl equation posed on the half-line with clamped boundary conditions. The equation arises from a two-dimensional fourth-order Prandtl system via an ansatz reduction, and its nonlinearity involves a nonlocal integral term. To close a Duhamel fixed-point argument, we need uniform L^1 bounds for the associated half-line biharmonic heat kernel. We establish uniform L^1 estimates for the kernel and its derivatives, and we show that the semigroup preserves spatial regularity under appropriate compatibility conditions, using an alternative representation derived by integration by parts. These kernel estimates yield local existence and uniqueness for the restricted model and allow us to construct solutions that blow-up in finite time.

Background Subway stations are essential but demanding environments for older adults, yet how their experiences differ from those of younger users remains qualitatively underexplored. Prior work has examined older passengers in isolation, leaving it unclear which barriers are age-specific and which reflect universal design failures. Methods We compared 30 older adults (aged 65+) and 30 younger adults (aged 20–39) navigating a major multi-line transfer station in Seoul, South Korea. Non-participatory behavioral observation was paired with video-stimulated recall (VSR) interviews using first-person wearable camera footage. Thematic analysis was applied to 1,831 coded segments, with an exploratory gender comparison. Results Five discomfort themes were identified: Stairs, Escalator and Elevator, Signage, Crowding, and Station Infrastructure. Factors were universal when participant reach was comparable across groups and age-specific when one group's reach was at least twice the other's. Stair descent, elevator access, and handrail discomfort were older-adult-specific; being slowed by pedestrians ahead was younger-adult-specific; and stair ascent, crowding, and signage complexity were universal. Older adults generated 4.4 times as many high-level discomfort mentions, mainly in vertical circulation. Universal factors differed in meaning: crowding was a safety threat for older adults but a flow disruption for younger adults. Younger women had more high-level crowding mentions than older women. Conclusions The same station environment was associated with differing forms and levels of discomfort across groups; comparable participant reach did not imply comparable burden. Studying older adults alone risks conflating age-specific barriers with universal design failures. Inclusive station design should consider gender alongside age.