klaurent – Page 4 – Kavli Institute Pre-Print Publications

RAMSES-GPU: Cell-by-Cell Adaptive Mesh Refinement with Magneto-Hydrodynamics and Self-Gravity on Graphics Processing Units

Posted by klaurent July 22, 2026July 27, 2026Stanford, This Week: Astrophysics

Kavli Affiliate: Tom Abel | Summary:We present the implementation and optimization of the cosmological simulation code RAMSES on Graphics Processing Units (GPUs) using CUDA Fortran. This accelerated version ports the main computational routines, including hydrodynamics, particle dynamics, and self-gravity, to multi-GPU architectures. We detail our strategy for managing cell-by-cell Adaptive Mesh Refinement (AMR) on the […]

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Ferromagnetic transition in a chiral spin chain

Posted by klaurent July 22, 2026July 27, 2026This Week: Theoretical Physics, UCSB

Kavli Affiliate: Leon Balents | Summary:We study the zero-temperature properties of a spin-$1/2$ Heisenberg chain with an additional three-site chiral term of strength $g$. The model is known to be integrable and previous work using Bethe ansatz has identified a phase transition from the usual critical state for $g< g_c = 2/π$ to a chiral […]

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A dust-free hierarchically nested supermassive-star model for James Webb Space Telescope Little Red Dots

Posted by klaurent July 22, 2026July 27, 2026Peking, This Week: Astrophysics

Kavli Affiliate: Pau Amaro Seoane | Summary:Observations by the James Webb Space Telescope reveal a population of high-redshift objects, the little red dots. These sources exhibit optical reddening alongside blue ultraviolet continua, host broad Balmer lines indicative of active black holes, and lack detectable x-ray emission. Their cosmic abundance at early epochs exceeds standard Eddington-limited […]

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The High-Speed FPGA Readout System for the Advanced X-ray Imaging Satellite (AXIS)

Posted by klaurent July 22, 2026July 27, 2026MIT, This Week: Astrophysics

Kavli Affiliate: Marshall Bautz | Summary:The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class mission concept designed to deliver arcsecond spatial resolution, high-sensitivity spectral imaging across the 0.3-10 keV band. The X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing […]

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Fast, low-noise CCD systems for future strategic X-ray missions

Posted by klaurent July 22, 2026July 27, 2026MIT, This Week: Astrophysics

Kavli Affiliate: Marshall Bautz | Summary:Future strategic X-ray missions, such as those targeted by the Great Observatories Maturation Program (GOMaP), require fast, low-noise X-ray imaging spectrometers. To achieve the speed and noise capabilities required by such programs, our Stanford team, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing […]

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Height Dependent Phase Shifts of Wave Pulses in the Lower Solar Atmosphere Measured with SUNRISE III

Posted by klaurent July 22, 2026July 27, 2026Stanford, This Week: Astrophysics

Kavli Affiliate: Robert Cameron | Summary:We report on the measurement of the height-dependent time shifts of wave pulses in the lower solar atmosphere from high-resolution spectro-polarimetric observations obtained with the SUSI instrument on board the SUNRISE III balloon-borne solar observatory during its successful science flight in July 2024. The line-of-sight velocities derived from the line-core […]

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Ringing of the Reionization: A first direct measurement of the intergalactic pressure smoothing scale at redshift z>4.2 as imprinted onto small-scale peculiar velocities in the Lyman-alpha forest

Posted by klaurent July 22, 2026July 27, 2026Cambridge, This Week: Astrophysics

Kavli Affiliate: Martin Haehnelt | Summary:The epoch of reionization leaves detectable imprints in the thermal history of the Universe. In particular, the fast ionization fronts passing over cold gas in the cosmic web overpressurize the gas, leading to the well-established phenomenon of pressure smoothing due to the hydrodynamic response of the gas. Although the effect […]

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CATKit2-HCI: a collaborative framework for advancing high-contrast coronagraph testbeds

Posted by klaurent July 22, 2026July 27, 2026Caltech, This Week: Nanoscience

Kavli Affiliate: Dimitri Mawet| Summary:High-contrast exoplanet imaging requires dedicated laboratory testbeds for the development and validation of coronagraph architectures, wavefront sensing and control methods, calibration strategies, and system-level observing concepts. These testbeds often share similar software needs, yet many tools are developed independently at each institution. The CATKit2-High-Contrast-Imaging collaboration, or CATKit2-HCI, addresses this gap by […]

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RNDR noise modeling in first-generation Single electron Sensitive Readout (SiSeRO) devices

Posted by klaurent July 21, 2026July 27, 2026MIT, This Week: Astrophysics

Kavli Affiliate: Marshall Bautz | Summary:Flagship observatories require single-photon detectors with ultra-fast readout, sub-electron noise performance, and scalable large-format architectures. The X-ray Astronomy and Observational Cosmology group at Stanford, in collaboration with the MIT Kavli Institute and MIT Lincoln Laboratory, is developing readout technologies for next-generation detectors. Prototypes employing Single-electron Sensitive Readout (SiSeRO) amplifiers demonstrate […]

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Extreme Variability Reveals How the Eddington Ratio Regulates Coronal Power in Active Galactic Nuclei

Posted by klaurent July 21, 2026July 27, 2026Peking, This Week: Astrophysics

Kavli Affiliate: Luis Ho | Summary:The bolometric luminosity ($L_rm bol$) of active galactic nuclei (AGNs) is a key tracer of accretion physics, but its direct determination is often hindered by limited spectral coverage and contamination of the host galaxy. Bolometric corrections ($κ_λ = L_rm bol/L_λ$) offer a practical means of estimating $L_rm bol$, with the […]

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