Computer Simulation of Ultrasonic Scattering and Texture in B-Mode Images

Diagnostic ultrasound has been widely used in clinical applications, such as soft tissue abnormality detection and blood flow detection. However, due to the complexity of ultrasonic wave propagation and scattering in biological tissues which generally involves wave reflection, refraction, scattering, absorption and other wave phenomena, it has always been a rather difficult task to interpret the wave mechanics through the received scattering signals

Fate of dissipative hierarchy of timescales in the presence of unitary dynamics

The generic behavior of purely dissipative open quantum many-body systems with local dissipation processes can be investigated using random matrix theory, revealing a hierarchy of decay timescales of observables organized by their complexity as shown in [Wang et al., $\href{https://link.aps.org/doi/10.1103/PhysRevLett.124.100604}{Phys. Rev. Lett. \textbf{124}, 100604 (2020)}]$. This hierarchy is reflected in distinct eigenvalue clusters of the Lindbladian. Here, we analyze how this spectrum evolves when unitary dynamics is present, both for the case of strongly and weakly dissipative dynamics. In the strongly dissipative case, the unitary dynamics can be treated perturbatively and it turns out that the locality of the Hamiltonian determines how susceptible the spectrum is to such a perturbation. For the physically most relevant case of (dissipative) two-body interactions, we find that the correction in the first order of the perturbation vanishes, leading to the relative robustness of the spectral features. For weak dissipation, the spectrum flows into clusters with well-separated eigenmodes, which we identify to be the local symmetries of the Hamiltonian

Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents

The timing of the origin and diversification of rodents remains controversial, due to conflicting results from molecular clocks and paleontological data. The fossil record tends to support an early Cenozoic origin of crown-group rodents. In contrast, most molecular studies place the origin and initial diversification of crown-Rodentia deep in the Cretaceous, although some molecular analyses have recovered estimated divergence times that are more compatible with the fossil record. Here we attempt to resolve this conflict by carrying out a molecular clock investigation based on a nine-gene sequence dataset and a novel set of seven fossil constraints, including two new rodent records (the earliest known representatives of Cardiocraniinae and Dipodinae). Our results indicate that rodents originated around 61.7–62.4 Ma, shortly after the Cretaceous/Paleogene (K/Pg) boundary, and diversified at the intraordinal level around 57.7–58.9 Ma. These estimates are broadly consistent with the paleontological record, but challenge previous molecular studies that place the origin and early diversification of rodents in the Cretaceous. This study demonstrates that, with reliable fossil constraints, the incompatibility between paleontological and molecular estimates of rodent divergence times can be eliminated using currently available tools and genetic markers. Similar conflicts between molecular and paleontological evidence bedevil attempts to establish the origination times of other placental groups. The example of the present study suggests that more reliable fossil calibration points may represent the key to resolving these controversies.Organismic and Evolutionary Biolog

Strong Pseudospin-Lattice Coupling in Sr3Ir2O7: Coherent Phonon Anomaly and Negative Thermal Expansion

The similarities to cuprates make iridates an interesting potential platform for investigating superconductivity. Equally attractive are their puzzling complex intrinsic interactions. Here, we report an ultrafast optical spectroscopy investigation of a coherent phonon mode in Sr3Ir2O7, a bilayer Ruddlesden-Popper perovskite iridate. An anomaly in the A1g optical phonon ({\nu} = 4.4 THz) is unambiguously observed below the N\'eel temperature (TN), which we attribute to pseudospin-lattice coupling (PLC). Significantly, we find that PLC is the dominant interaction at low temperature, and we directly measure the PLC coefficient to be {\lambda} = 150 +/- 20 cm-1, which is two orders of magnitude higher than that in manganites (< 2.4 cm-1) and comparable to that in CuO (50 cm-1, the strongest PLC or spin-lattice coupling (SLC) previously known). Moreover, we find that the strong PLC induces an anisotropic negative thermal expansion. Our findings highlight the key role of PLC in iridates and uncovers another intriguing similarity to cuprates

A pathogenic UFSP2 variant in an autosomal recessive form of pediatric neurodevelopmental anomalies and epilepsy

Purpose: Neurodevelopmental disabilities are common and genetically heterogeneous. We identified a homozygous variant in the gene encoding UFM1-specific peptidase 2 (UFSP2), which participates in the UFMylation pathway of protein modification. UFSP2 variants are implicated in autosomal dominant skeletal dysplasias, but not neurodevelopmental disorders. Homozygosity for the variant occurred in eight children from four South Asian families with neurodevelopmental delay and epilepsy. We describe the clinical consequences of this variant and its effect on UFMylation.Methods: Exome sequencing was used to detect potentially pathogenic variants and identify shared regions of homozygosity. Immunoblotting assessed protein expression and post-translational modifications in patient-derived fibroblasts.Results: The variant (c.344T\u3eA; p.V115E) is rare and alters a conserved residue in UFSP2. Immunoblotting in patient-derived fibroblasts revealed reduced UFSP2 abundance and increased abundance of UFMylated targets, indicating the variant may impair de-UFMylation rather than UFMylation. Reconstituting patient-derived fibroblasts with wild-type UFSP2 reduced UFMylation marks. Analysis of UFSP2\u27s structure indicated that variants observed in skeletal disorders localize to the catalytic domain, whereas V115 resides in an N-terminal domain possibly involved in substrate binding.Conclusion: Different UFSP2 variants cause markedly different diseases, with homozygosity for V115E causing a severe syndrome of neurodevelopmental disability and epilepsy

Enhanced Mid-depth Southward Transport in the Northeast Atlantic at the Last Glacial Maximum Despite a Weaker AMOC

While previous studies consistently suggest that North Atlantic Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than at pre-industrial, its strength is still controversial. Here, using a series of LGM experiments, we show that proxy records are consistent with a shallower and ∼50% weaker NADW, associated with a ∼3◦ equatorward shift of the sea ice edge and convection sites in the Norwegian Sea. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic, despite Antarctic Bottom Water transport being reduced by ∼40%. While the Deep Western Boundary Current in the northwest Atlantic weakens with NADW, the mid-depth southward flow on the east side of the north Mid-Atlantic Ridge strengthens, consistent with paleorecords. This northeast Atlantic intensification is due to a change in density gradients: a weaker AMOC reduces the transport of equatorial waters to the northeast Atlantic, thus weakening the North Atlantic zonal density gradient. The resultant globally weaker oceanic circulation at the LGM would have contributed to an increase in oceanic carbon content and thus a decrease in atmospheric CO2 concentration.This project was supported by the Australian Research Council. L. C. M., L. M., P. S., and J. Y. acknowledge funding from the Australian Research Council Grants DE150100107, DP180100048, DE150100223, FT140100993, FT180100606, and DP140101393. L. C. S. acknowledges support from NERC Grant NE/L006421/1

Monsoonal control on a delayed response of sedimentation to the 2008 Wenchuan earthquake

Infrequent extreme events such as large earthquakes pose hazards and have lasting impacts on landscapes and biogeochemical cycles. Sediments provide valuable records of past events, but unambiguously identifying event deposits is challenging because of nonlinear sediment transport processes and poor age control. Here, we have been able to directly track the propagation of a tectonic signal into stratigraphy using reservoir sediments from before and after the 2008 Wenchuan earthquake. Cycles in magnetic susceptibility allow us to define a precise annual chronology and identify the timing and nature of the earthquake’s sedimentary record. The grain size and Rb/Sr ratio of the sediments responded immediately to the earthquake. However, the changes were muted until 2 years after the event, when intense monsoonal runoff drove accumulation of coarser grains and lower Rb/Sr sediments. The delayed response provides insight into how climatic and tectonic agents interact to control sediment transfer and depositional processes.This work was funded by the 2nd Tibetan Plateau Scientific Expedition and Research (2019QZKK0707) and CAS programs (QYZDJ-SSW-DQC033, XDA2007010202, and 132B61KYSB20170008) grants to Z.J. and SKLLQG grant (SKLLQGPY1603) to F.Z

Random matrix theory for quantum and classical metastability in local Liouvillians

We consider the effects of strong dissipation in quantum systems with a notion of locality, which induces a hierarchy of many-body relaxation timescales as shown in [Phys. Rev. Lett. 124, 100604 (2020)]. If the strength of the dissipation varies strongly in the system, additional separations of timescales can emerge, inducing a manifold of metastable states, to which observables relax first, before relaxing to the steady state. Our simple model, involving one or two "good" qubits with dissipation reduced by a factor ? < 1 compared to the other "bad" qubits, confirms this picture and admits a perturbative treatment. Introduction-Quantum many-body systems are generically complex, and obtaining an analytic understanding of the position of all spectral resonances is often hopeless. It was realized early on [1-6] that this complexity is in fact so great that many statistical properties of the spectrum are identical with those of random matrices sampled from an ensemble determined by the symmetry of the system. These pioneering observations have been subsequently refined, resulting in cornerstones of our understanding of thermalization in unitary quantum many-body systems by virtue of the eigenstate thermalization hypothesis [7-14], only with exceptions in integrable [15-18], many-body localized [19-29], time-crystalline [30-32] or scarred and constrained systems [33-35]