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A<sc>bstract</sc> Electric fields can spontaneously decay via the Schwinger effect, the nucleation of a charged particle-anti particle pair separated by a critical distanced. What happens if the available distance is smaller thand? Previous work on this question has produced contradictory results. Here, we study the quantum evolution of electric fields when the field points in a compact direction with circumferenceL < dusing the massive Schwinger model, quantum electrodynamics in one space dimension with massive charged fermions. We uncover a new and previously unknown set of instantons that result in novel physics that disagrees with all previous estimates. In parameter regimes where the field value can be well-defined in the quantum theory, generic initial fieldsEare in factstable and do not decay, while initial values that are quantized in half-integer units of the chargeE= (k/2)gwithk∈ ℤoscillate in timefrom +(k/2)gto−(k/2)g, with exponentially small probability of ever taking any other value. We verify our results with four distinct techniques: numerically by measuring the decay directly in Lorentzian time on the lattice, numerically using the spectrum of the Hamiltonian, numerically and semi-analytically using the bosonized description of the Schwinger model, and analytically via our instanton estimate. 

MANA-2.0 is a scalable, future-proof design for transparent checkpointing of MPI-based computations. Its network transparency (“network-agnostic”) feature ensures that MANA-2.0 will provide a viable, efficient mechanism for trans-parently checkpointing MPI applications on current and future supercomputers. MANA-2.0 is an enhancement of previous work, the original MANA, which interposes MPI calls, and is a work in progress intended for production deployment. MANA-2.0 implements a series of new algorithms and features that improve MANA's scalability and reliability, enabling transparent checkpoint-restart over thousands of MPI processes. MANA-2.0 is being tested on today's Cori supercomputer at NERSC using Cray MPICH library over the Cray GNI network, but it is designed to work over any standard MPI running over an arbitrary network. Two widely-used HPC applications were selected to demonstrate the enhanced features of MANA-2.0: GROMACS, a molecular dynamics simulation code with frequent point-to-point communication, and VASP, a materials science code with frequent MPI collective communication. Perhaps the most important lesson to be learned from MANA-2.0 is a series of algorithms and data structures for library-based transformations that enable MPI-based computations over MANA-2.0 to reliably survive the checkpoint-restart transition. 

Paired measurements of¹⁴C/¹²C and²³⁰Th ages from two Hulu Cave stalagmites complete a precise record of atmospheric¹⁴C covering the full range of the¹⁴C dating method (~54,000 years). Over the last glacial period, atmospheric¹⁴C/¹²C ranges from values similar to modern values to values 1.70 times higher (42,000 to 39,000 years ago). The latter correspond to¹⁴C ages 5200 years less than calibrated ages and correlate with the Laschamp geomagnetic excursion followed by Heinrich Stadial 4. Millennial-scale variations are largely attributable to Earth’s magnetic field changes and in part to climate-related changes in the oceanic carbon cycle. A progressive shift to lower¹⁴C/¹²C values between 25,000 and 11,000 years ago is likely related, in part, to progressively increasing ocean ventilation rates.