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The masses of the exotic calcium isotopes 53 Ca and 54 Ca measured by a multi-reflection time-of-flight method confirm predictions of calculations including nuclear three-body interactions. Exotic calcium isotopes weighed The calcium atom provides an ideal system for the study of nuclear shell evolution, from the valley of stability to the limits of existence. Although predictions for the masses of the neutron-rich isotopes 51 Ca and 52 Ca have been tested by direct measurements, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Frank Wienholtz and colleagues report the mass determination of the exotic calcium isotopes 53 Ca and 54 Ca, using a multi-reflection time-of-flight mass spectrometer. The results provide key information for theoretical models and show that a description of extreme neutron-rich nuclei can be closely connected to a deeper understanding of nuclear forces. The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions 1 . Exceedingly neutron-rich nuclei become sensitive to new aspects of nuclear forces 2 . Calcium, with its doubly magic isotopes 40 Ca and 48 Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory 3 , 4 , 5 , 6 . Whereas predictions for the masses of 51 Ca and 52 Ca have been validated by direct measurements 4 , it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes 53 Ca and 54 Ca, using the multi-reflection time-of-flight mass spectrometer 7 of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics 8 .

The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of quantum chromodynamics. However, as these equations cannot be solved directly, nuclear interactions are described using simplified models, which are well constrained at typical inter-nucleon distances 1 – 5 but not at shorter distances. This limits our ability to describe high-density nuclear matter such as that in the cores of neutron stars 6 . Here we use high-energy electron scattering measurements that isolate nucleon pairs in short-distance, high-momentum configurations 7 – 9 , accessing a kinematical regime that has not been previously explored by experiments, corresponding to relative momenta between the pair above 400 megaelectronvolts per c ( c , speed of light in vacuum). As the relative momentum between two nucleons increases and their separation thereby decreases, we observe a transition from a spin-dependent tensor force to a predominantly spin-independent scalar force. These results demonstrate the usefulness of using such measurements to study the nuclear interaction at short distances and also support the use of point-like nucleon models with two- and three-body effective interactions to describe nuclear systems up to densities several times higher than the central density of the nucleus. High-energy electron scattering that can isolate pairs of nucleons in high-momentum configurations reveals a transition to spin-independent scalar forces at small separation distances, supporting the use of point-like nucleon models to describe dense nuclear systems.

PIEZO1 is a mechanosensitive channel that converts applied force into electrical signals. Partial molecular structures show that PIEZO1 is a bowl-shaped trimer with extended arms. Here we use cryo-electron microscopy to show that PIEZO1 adopts different degrees of curvature in lipid vesicles of different sizes. We also use high-speed atomic force microscopy to analyse the deformability of PIEZO1 under force in membranes on a mica surface, and show that PIEZO1 can be flattened reversibly into the membrane plane. By approximating the absolute force applied, we estimate a range of values for the mechanical spring constant of PIEZO1. Both methods of microscopy demonstrate that PIEZO1 can deform its shape towards a planar structure. This deformation could explain how lateral membrane tension can be converted into a conformation-dependent change in free energy to gate the PIEZO1 channel in response to mechanical perturbations. Cryo-electron microscopy and high-speed atomic force microscopy reveal that PIEZO1 can reversibly deform its shape towards a planar structure, which may explain how the PIEZO1 channel is gated in response to mechanical stimulation.

Coherent short-pulse laser excitation has been used to control the approximate energy and relative proximity of two valence electrons within the same alkaline-earth atom, thereby providing insight into the dynamical evolution of a three-body Coulomb system. Our time-domain experiments enable direct experimental study of the electron dynamics at the classical limit of a two-electron atom. As an example, we look at the mechanism of autoionization for one two-electron configuration class and find that the doubly excited atom decays through a single violent electron-electron collision rather than a gradual exchange of energy between the electrons.

Tibial stress fractures are a common overuse injury resulting from the accumulation of bone microdamage due to repeated loading. Researchers and wearable device developers have sought to understand or predict stress fracture risks, and other injury risks, by monitoring the ground reaction force (GRF, the force between the foot and ground), or GRF correlates (e.g., tibial shock) captured via wearable sensors. Increases in GRF metrics are typically assumed to reflect increases in loading on internal biological structures (e.g., bones). The purpose of this study was to evaluate this assumption for running by testing if increases in GRF metrics were strongly correlated with increases in tibial compression force over a range of speeds and slopes. Ten healthy individuals performed running trials while we collected GRFs and kinematics. We assessed if commonly-used vertical GRF metrics (impact peak, loading rate, active peak, impulse) were strongly correlated with tibial load metrics (peak force, impulse). On average, increases in GRF metrics were not strongly correlated with increases in tibial load metrics. For instance, correlating GRF impact peak and loading rate with peak tibial load resulted in r = -0.29±0.37 and r = -0.20±0.35 (inter-subject mean and standard deviation), respectively. We observed high inter-subject variability in correlations, though most coefficients were negligible, weak or moderate. Seventy-six of the 80 subject-specific correlation coefficients computed indicated that higher GRF metrics were not strongly correlated with higher tibial forces. These results demonstrate that commonly-used GRF metrics can mislead our understanding of loading on internal structures, such as the tibia. Increases in GRF metrics should not be assumed to be an indicator of increases in tibial bone load or overuse injury risk during running. This has important implications for sports, wearable devices, and research on running-related injuries, affecting >50 scientific publications per year from 2015-2017.

The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.

AbstractIn an effort to find an effective interaction that can consistently be used for both the mean-field part and the residual part in beyond-mean-field theories, the properties of the Skyrme interactions as a residual interaction are investigated. The time-dependent density-matrix theory (TDDM) is used as a beyond-mean-field theory and the ground states of $^{16}$O and $^{40}$Ca are calculated using the five standard parametrizations of the Skyrme interaction, which differ in density and momentum dependence. It is found that the Skyrme interaction, which has strong density dependence and weak momentum dependence, induces substantial ground-state correlations comparable to the results of other theoretical calculations.

Self-massage tools such as foam rollers and massage balls are widely used in warm-ups and recovery, but their effects on dynamic strength tasks like squatting remain unclear. To compare the effects of a foam roller (FR), massage ball (MB), and vibrating massage ball (MBV) versus a control condition on squat load velocity profiles and associated electromyographic (EMG) activity in resistance-trained individuals. In this crossover study, fourteen experienced resistance-trained participants performed four experimental conditions: FR, MB, MBV, and control. After an initial session for incremental load testing and protocol familiarization, each participant performed eight back squats before and after each experimental session, while movement velocity, hip vertical displacement (range of motion), and EMG of the vastus lateralis and semimembranosus were recorded. MBV produced a significant increase in quadriceps EMG during the fastest repetition (β = 0.107; p = 0.003). In contrast, all interventions elicited a reduction in the second fastest repetition versus control (FR: β = -0.033, p = 0.005; MB: β = -0.025, p = 0.029; MBV: β = -0.036, p = 0.002). Moreover, both FR and MBV similarly decreased third fastest repetition and mean velocities relative to control (FR: third fastest repetition β = -0.025, p = 0.027; mean β = -0.046, p = 0.046; MBV: third fastest repetition β = -0.032, p = 0.005; mean velocity β = -0.031, p = 0.004). There were no significant changes in the hip vertical displacement. All self-massage conditions modestly impaired squat velocity, with the MB showing the least detrimental effect on performance.

The authors discuss the observation of strong correlation effects with cold atomic gases in the field of Bose-Einstein condensates.

The dense soup of matter in the core of neutron stars is hard to model, but particle-accelerator experiments in which energetic electrons scatter off atomic nuclei could help to explore this high-density regime. A test of effective nucleon–nucleon interactions at short separations.