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Open Access Policy Deposits

This series is automatically populated with publications deposited by UC San Diego Department of Physics researchers in accordance with the University of California’s open access policies. For more information see Open Access Policy Deposits and the UC Publication Management System.

Zonal Flow and Self-regulating Mechanism in a Hydrodynamic Disk

(2025)

Abstract: This study addresses key aspects of momentum transport in hydrodynamic disks, which is critical for understanding zonal flow generation and turbulence in compressible hydrodynamic disks. We find that nonlinear momentum/density transport leads to the formation of zonal flows from the Rossby wave instability in disks. We analytically derive the generation and location of zonal flows and describe a modified Taylor identity applicable to compressible disk flows. We further present a self-regulation model, revealing a dynamic interplay between zonal flow and fluctuations driven by Rossby wave instability that regulates the nonlinear saturation state. This theoretical framework contributes insights into the dynamics of disks such as protoplanetary disks, shedding light on the intricate processes governing momentum/density transport and the emergence of zonal flows in the saturation of protoplanetary disks.

Cover page of High-Efficiency Continuous Spin-Conduction through NiO/Cu Bilayer Structure

High-Efficiency Continuous Spin-Conduction through NiO/Cu Bilayer Structure

(2025)

Materials that effectively separate charge and spin currents are key to advancing spin-orbit torque-based switching devices for nanomagnet memory. NiO, an insulating yet spin-conducting material, is essential in such systems. Interfacing NiO with a heavy metal like Pt, confines charge current to Pt while allowing spin current to pass through NiO into an adjacent NiFe layer. Introducing a spin-transparent Cu layer between NiO and Py prevents exchange interactions, transmits spin torque, and ensures a uniform magnetic environment at the Py interface, ensuring device reliability. To study spin-current conduction, we use dc bias-dependent spin-torque ferromagnetic resonance (ST-FMR) on nanobridges patterned from a Pt/NiO/Cu/NiFe stack with varying NiO thickness. Results show that a highly spin-transparent (93%) Cu spacer enables >40% spin-current transmission through defect-free NiO/Cu bilayers for NiO thicker than 1.5 nm. This stack demonstrates effective charge-spin separation and flexibility, with seamless spin-torque conversion from magnonic to electronic transport, enabling new spin-current-based device designs.

Cover page of Single-molecule measurements of bacteriophage lambda DNA packaging using purified terminase motor proteins and E. coli integration host factor.

Single-molecule measurements of bacteriophage lambda DNA packaging using purified terminase motor proteins and E. coli integration host factor.

(2025)

Biomotor-driven DNA packaging is a key step in the life cycle of many viruses. We previously developed single-molecule methods using optical tweezers to measure packaging dynamics of the bacteriophage lambda motor. The lambda system is more complex than others examined via single-molecule assays with respect to the packaging substrate and ancillary proteins required. Because of this, previous studies which efficiently detected packaging events used crude E. coli cell extracts containing host factors and the terminase packaging enzyme. However, use of extracts is suboptimal for biochemical manipulation and obfuscates interrogation of additional factors that affect the process. Here we describe an optical tweezers assay using purified lambda terminase holoenzyme. Packaging events are as efficient as with crude extracts, but only if purified E. coli integration host factor (IHF) is included in the motor assembly reactions. We find that the ATP-driven DNA translocation dynamics, motor force generation, and motor-DNA interactions without nucleotide are virtually identical to those measured with extracts. Thus, single-molecule packaging activity can be fully recapitulated in a minimal system containing only purified lambda procapsids, purified terminase, IHF, and ATP. This sets the stage for single-molecule studies to investigate additional phage proteins known to play essential roles in the packaging reaction.

Comparative studies of cross-phase dynamics in turbulent momentum flux and particle flux at the tokamak edge

(2025)

Abstract: Turbulent transport events, including turbulent transport flux of momentum (i.e., turbulent momentum flux or Reynolds stress) and turbulent transport flux of particle (i.e., turbulent particle flux), have important effects on the confinement performance of magnetic confinement fusion devices. Poloidal Reynolds stress is the ensemble average of the product of radial velocity fluctuations and poloidal velocity fluctuations, i.e., $$\langle {\widetilde{v}}_{r}{\widetilde{v}}_{\theta }\rangle$$ ⟨ v ~ r v ~ θ ⟩ . Turbulent particle flux is the ensemble average of the product of radial velocity fluctuations and density fluctuations, i.e., $$\langle \widetilde{n}{\widetilde{v}}_{r}\rangle$$ ⟨ n ~ v ~ r ⟩ . Changes in either amplitude of fluctuations or cross phase between fluctuations can cause changes in turbulent transport. In this paper, cross-phase dynamics in the Reynolds stress and turbulent particle flux at the tokamak edge are studied in detail. Reynolds stress and turbulent particle flux are, respectively, written as the product of fluctuation amplitudes and an average cross-phase factor. The mathematical expressions of the average cross-phase factors are derived. The average cross-phase factors and the power spectra of cross phase are obtained using experimental measurement data. It is found that the cross-phase dynamics in Reynolds stress and particle flux are very different. Reynolds stress is found to be more sensitive to cross phase than particle flux is. In the strong $$E\times B$$ E × B shear layer, spatial slips of cross phase lead to the obvious radial gradient of Reynolds stress. In the no/weak $$E\times B$$ E × B shear region, the cross phase in Reynolds stress tends to lock. Here, phase locking refers to that the power spectra of phase tend to distribute around a fixed phase which does not change with radial position, while phase slip means that the power spectra of cross phase tend to distribute around a phase that varies with radial position. Phase slip or locking mainly describes the central phase weighted by the power spectra, while the phase scattering mainly describes the dispersion of the power spectrum distribution of the phase. The increased scattering of cross phase, which indicates the power spectra distribution of the phase is more dispersed, contributes to the decreased Reynolds stress for higher collisionality. The cross phase in particle flux tends to lock in both strong and no/weak shear regions. The degree of scattering of cross phase in the particle flux does not change obviously as collisionality increases. For higher collisionality, it is the increased density fluctuation amplitude rather than cross-phase dynamics that leads to the increased particle flux. The underlying physical mechanism that causes Reynolds stress and particle flux to exhibit different phase dynamics is discussed.

How does negative triangularity mitigate ITG turbulence and transport?

(2025)

Abstract: Improved confinement in negative triangularity (NT) experiments is attributed to reduced fluxes driven by micro-turbulence. The physical mechanism of why thermal confinement improves in NT relative to PT is unknown. This study employs gyrokinetic flux tube simulations using the GENE code with local Miller equilibrium to elucidate the physical mechanisms behind the beneficial effects of NT flux surface shapes. The focus is on collisionless ion temperature gradient (ITG) driven turbulence with adiabatic electrons. The kinetic profiles are held fixed across a scan of triangularity values, thus enabling comparisons on a level playing field. The reduced linear growth rates for NT is shown to be due to a reduced eigenmode averaged magnetic drift frequency and a wider, stronger negative local magnetic shear region about the outboard mid-plane. The nonlinear heat flux is lower for NT than that for PT, due to reduced radial correlation length and increased correlation time ( τ c ) of fluctuations. These, in turn, are due to a comparatively higher level of self-generated zero-frequency E × B zonal shearing rate ω E in NT as compared to PT. Though the linear zonal potential residual is lower for NT, the nonlinearly generated E × B zonal shearing rate is higher for NT than for PT. This outcome is linked to the distinctive features of the radial wavenumber spectra of the zonal potential and the zonal shearing rate. The dimensionless parameter ω E τ c is suggested as a figure of merit. This is higher for NT than for PT. Thus, the reduced heat diffusivity for NT is linked to increased ω E τ c . Self-generated temperature corrugations (i.e. zonal temperature gradients) are much weaker than the background mean temperature gradient. Nevertheless, temperature corrugations are more pronounced in NT than in PT.

Cover page of Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at s NN = 5.02  TeV

Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at s NN = 5.02  TeV

(2025)

This Letter presents the first measurements of the groomed jet radius Rg and the jet girth g in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables Rg and g provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb−1 and 301 pb−1, respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum pTγ>100 GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum pTjet such that pTjet/pTγ>0.4. The measured Rg and g distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with pTjet/pTγ>0.8, i.e., those that closely balance the photon pTγ, are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with pTjet/pTγ>0.4 reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements.

Cover page of Constraints on the Higgs boson self-coupling from the combination of single and double Higgs boson production in proton-proton collisions at s = 13 TeV

Constraints on the Higgs boson self-coupling from the combination of single and double Higgs boson production in proton-proton collisions at s = 13 TeV

(2025)

The Higgs boson (H) trilinear self-coupling, λ3, is constrained via its measured properties and limits on the HH pair production using the proton-proton collision data collected by the CMS experiment at s=13TeV. The combination of event categories enriched in single-H and HH events is used to measure κλ, defined as the value of λ3 normalized to its standard model prediction, while simultaneously constraining the Higgs boson couplings to fermions and vector bosons. Values of κλ outside the interval −1.2<κλ<7.5 are excluded at 2σ confidence level, which is compatible with the expected range of −2.0<κλ<7.7 under the assumption that all other Higgs boson couplings are equal to their standard model predicted values. Relaxing the assumption on the Higgs couplings to fermions and vector bosons the observed (expected) κλ interval is constrained to be within −1.4<κλ<7.8 (−2.3<κλ<7.8) at 2σ confidence level.

Cover page of Measurement of inclusive and differential cross sections for W+W− production in proton-proton collisions at s = 13.6 TeV

Measurement of inclusive and differential cross sections for W+W− production in proton-proton collisions at s = 13.6 TeV

(2025)

Measurements at s=13.6TeV of the opposite-sign W boson pair production cross section in proton-proton collisions are presented. The data used in this study were collected with the CMS detector at the CERN LHC in 2022, and correspond to an integrated luminosity of 34.8fb−1. Events are selected by requiring one electron and one muon of opposite charge. A maximum likelihood fit is performed on signal- and background-enriched data categories defined by the flavor and charge of the leptons, the number of jets, and number of jets originating from b quarks. The overall sensitivity is significantly better than that of previous results with a similar integrated luminosity. The improvement comes from a more refined control of experimental uncertainties and an improved fit strategy. An inclusive W+W− production cross section of 125.7±5.6 pb is measured, in agreement with standard model predictions. Cross sections are also reported in a fiducial region close to that of the detector acceptance, both inclusively and differentially, as a function of the jet multiplicity in the event. For the first time in proton-proton collisions, WW events with zero, one, and at least two jets are studied simultaneously and compared with recent theoretical predictions.