One of the greatest challenges in modern physics is to understand the behaviour of an ensemble of strongly interacting particles. A class of quantum many-body systems (such as neutron star matter and ...cold Fermi gases) share the same universal thermodynamic properties when interactions reach the maximum effective value allowed by quantum mechanics, the so-called unitary limit. This makes it possible in principle to simulate some astrophysical phenomena inside the highly controlled environment of an atomic physics laboratory. Previous work on the thermodynamics of a two-component Fermi gas led to thermodynamic quantities averaged over the trap, making comparisons with many-body theories developed for uniform gases difficult. Here we develop a general experimental method that yields the equation of state of a uniform gas, as well as enabling a detailed comparison with existing theories. The precision of our equation of state leads to new physical insights into the unitary gas. For the unpolarized gas, we show that the low-temperature thermodynamics of the strongly interacting normal phase is well described by Fermi liquid theory, and we localize the superfluid transition. For a spin-polarized system, our equation of state at zero temperature has a 2 per cent accuracy and extends work on the phase diagram to a new regime of precision. We show in particular that, despite strong interactions, the normal phase behaves as a mixture of two ideal gases: a Fermi gas of bare majority atoms and a non-interacting gas of dressed quasi-particles, the fermionic polarons.
CsV3 Sb5 is a newly discovered Z2 topological kagome metal showing the coexistence of a charge-density-wave (CDW)-like order at T* = 94 K and superconductivity (SC) at Tc = 2.5 K at ambient pressure. ...Here, we study the interplay between CDW and SC in CsV3 Sb5 via measurements of resistivity, dc and ac magnetic susceptibility under various pressures up to 6.6 GPa. We find that the CDW transition decreases with pressure and experience a subtle modification at Pc1 ≈ 0.6 – 0.9 GPa before it vanishes completely at Pc2 ≈ 2 GPa . Correspondingly, Tc(P) displays an unusual M -shaped double dome with two maxima around Pc1 and Pc2 , respectively, leading to a tripled enhancement of Tc to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range Pc1 ≤ P ≤ Pc2 as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around Pc1 has been discussed based on the band structure calculations. This work not only demonstrates the potential to raise Tc of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.
Spatial pattern information of carbon density in forest ecosystem including forest litter carbon (FLC) plays an important role in evaluating carbon sequestration potentials. The spatial variation of ...FLC density in the typical subtropical forests in southeastern China was investigated using Moran's I, geostatistics and a geographical information system (GIS). A total of 839 forest litter samples were collected based on a 12 km (south–north) × 6 km (east–west) grid system in Zhejiang province. Forest litter carbon density values were very variable, ranging from 10.2 kg ha−1 to 8841.3 kg ha−1, with an average of 1786.7 kg ha−1. The aboveground biomass had the strongest positive correlation with FLC density, followed by forest age and elevation. Global Moran's I revealed that FLC density had significant positive spatial autocorrelation. Clear spatial patterns were observed using local Moran's I. A spherical model was chosen to fit the experimental semivariogram. The moderate "nugget-to-sill" (0.536) value revealed that both natural and anthropogenic factors played a key role in spatial heterogeneity of FLC density. High FLC density values were mainly distributed in northwestern and western part of Zhejiang province, which were related to adopting long-term policy of forest conservation in these areas, while Hang-Jia-Hu (HJH) Plain, Jin-Qu (JQ) Basin and coastal areas had low FLC density due to low forest coverage and intensive management of economic forests. These spatial patterns were in line with the spatial-cluster map described by local Moran's I. Therefore, Moran's I, combined with geostatistics and GIS, could be used to study spatial patterns of environmental variables related to forest ecosystem.
We present an approach for compressing volumetric scalar fields using implicit neural representations. Our approach represents a scalar field as a learned function, wherein a neural network maps a ...point in the domain to an output scalar value. By setting the number of weights of the neural network to be smaller than the input size, we achieve compressed representations of scalar fields, thus framing compression as a type of function approximation. Combined with carefully quantizing network weights, we show that this approach yields highly compact representations that outperform state‐of‐the‐art volume compression approaches. The conceptual simplicity of our approach enables a number of benefits, such as support for time‐varying scalar fields, optimizing to preserve spatial gradients, and random‐access field evaluation. We study the impact of network design choices on compression performance, highlighting how simple network architectures are effective for a broad range of volumes.
Abstract
Reaching gigagauss magnetic fields opens new horizons both in atomic and plasma physics. At these magnetic field strengths, the electron cyclotron energy
ℏω
c
becomes comparable to the ...atomic binding energy (the Rydberg), and the cyclotron frequency
ω
c
approaches the plasma frequency at solid state densities that significantly modifies optical properties of the target. The generation of such strong quasistatic magnetic fields in laboratory remains a challenge. Using supercomputer simulations, we demonstrate how it can be achieved all-optically by irradiating a micro-channel target by a circularly polarized relativistic femtosecond laser. The laser pulse drives a strong electron vortex along the channel wall, inducing a megagauss longitudinal magnetic field in the channel by the Inverse Faraday Effect. This seed field is then amplified up to a gigagauss level and maintained on a sub-picosecond time scale by the synergistic effect of hydrodynamic flows and dynamos. Our scheme sets a possible platform for producing long living extreme magnetic fields in laboratories using readily available lasers. The concept might also be relevant for applications such as magneto-inertial fusion.
Using a sample of nearly 140,000 primary red-clump stars selected from the LAMOST and Gaia surveys, we have identified a large sample of "young" /Fe-enhanced stars with stellar ages younger than 6.0 ...Gyr and /Fe ratios greater than 0.15 dex. The stellar ages and /Fe ratios are measured from LAMOST spectra, using a machine-learning method trained with common stars in the LAMOST-APOGEE fields (for /Fe) and in the LAMOST-Kepler fields (for stellar age). The existence of these "young" /Fe-enhanced stars is not expected from the classical Galactic chemical evolution models. To explore their possible origins, we have analyzed the spatial distribution, and the chemical and kinematic properties of those stars and compared the results with those of the chemically thin and thick disk populations. We find that those "young" /Fe-enhanced stars have distributions in number density, metallicity, C/N abundance ratio, velocity dispersion, and orbital eccentricity that are essentially the same as those of the chemically thick disk population. Our results clearly show those so-called "young" /Fe-enhanced stars are not really young but genuinely old. Although other alternative explanations can not be fully ruled out, our results suggest that the most possible origin of these old stars is the result of stellar mergers or mass transfer.
Organ-on-a-chip platforms serve as cost-efficient testbeds for screening pharmaceutical agents, mimicking natural physiology, and studying disease. In the field of diabetes, the development of an ...islet-on-a-chip platform would have broad implications in understanding disease pathology and discovering potential therapies. Islet microphysiological systems are limited, however, by their poor cell survival and function in culture. A key factor that has been implicated in this decline is the disruption of islet-matrix interactions following isolation. Herein, we sought to recapitulate the in vivo peri-islet niche using decellularized extracellular matrix (ECM) hydrogels. Sourcing from porcine bladder, lung, and pancreas tissues, 3-D ECM hydrogels were generated, characterized, and validated using both rodent and human pancreatic islets. Optimized decellularization protocols resulted in hydrogels with distinctive viscoelastic properties that correlated to their matrix composition. The in situ 3-D encapsulation of human or rat islets within ECM hydrogels resulted in improved functional stability over standard culture conditions. Islet composition and morphology were also altered, with enhanced retention of islet-resident endothelial cells and the formation of cord-like structures or sprouts emerging from the islet spheroid. These supportive 3-D physiomimetic ECM hydrogels can be leveraged within microfluidic platforms for the long-term culture of islets.
Platelets are natural delivery vehicles within the blood, carrying and releasing their contents at sites of vasculature damage. Investigating the biology of platelets, and modifying them for new ...therapeutic uses, is limited by a lack of methods for efficiently transfecting these cells. The ability of four different classes of lipid nanoparticles (LNPs) to deliver mRNA to platelets was compared using confocal microscopy, flow cytometry and quantitative PCR. The amount of mRNA delivered, mechanism of uptake, and extent of platelet activation depended on the LNP formulation and platelet storage conditions. Cationic LNPs (cLNPs) delivered mRNA to the largest percentage of platelets but induced platelet activation. Ionizable cationic LNPs (icLNPs) delivered mRNA to fewer platelets and did not induce activation. Furthermore, mRNA delivered using icLNPs and cLNPs was stable in resting platelets and was released in platelet microparticles under specific conditions. The results demonstrate that mRNA can be delivered to platelets using cLNPs and icLNPs without impairing platelet aggregation or spreading. Optimizing the LNP formulations used here may lead to a transfection agent for platelets that allows for de novo synthesis of exogenous proteins in the future.
Crater Structure Behind Reconnection Front Huang, S. Y.; Xiong, Q. Y.; Yuan, Z. G. ...
Geophysical research letters,
16 March 2024, Letnik:
51, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Magnetic reconnection is the physical process that converts the energy from the fields to the plasmas in space, astrophysical and laboratory plasmas. The Reconnection front (RF) is the structure ...generated in the reconnection outflow region and participates in the energy release budget. Here, we first report a novel crater structure of magnetic field behind the RF, which is well supported by both the in‐situ observations from the Magnetospheric Multiscale mission and kinetic particle‐in‐cell simulations. The theoretical explanations from the simulations suggests that the formation of the crater structure is possibly due to that high‐speed outflow electron jet from inner electron diffusion region constantly strikes the RF. From another perspective, the crater structure is the continuous impact of the electron jet. Our results can establish a new understanding of the RF and energy conversion during magnetic reconnection.
Plain Language Summary
Magnetic reconnection is a natural process in space environments, astrophysical settings, and laboratories, where energy from magnetic fields is transformed into the energy of various particles. One crucial structure in this process is called the reconnection front (RF), which plays a big role in how energy is released. In our study, we have discovered something interesting: a unique crater‐like structure behind the RF. We found evidence for this in observations from the Magnetospheric Multiscale mission and computer simulations that study the behavior of particles in magnetic reconnection. Our simulations suggest that this crater shape happens because electrons have the high‐speed outflow and form current jets. It is like the electrons poured out from the inner electron diffusion region, hitting a speed bump. Another way to think about it is that this crater is formed by the continuous impact of fast‐outflowing electron jets. Understanding this crater structure helps us better grasp how the RF works and how energy changes during magnetic reconnection. Our research finds and tries to explain a new piece of the puzzle in understanding the mysteries of space and plasmas in the magnetic reconnection process.
Key Points
A novel crater structure is first verified behind the Reconnection front (RF) by both Magnetospheric Multiscale observations and particle‐in‐cell simulations
The formation of the crater structure appears to be associated with the high‐speed electron jets from inner electron diffusion region
A possible scenario that electron outflow constantly strikes the RF and then causes the formation of the crater structure
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