Fast radio bursts (FRBs) are millisecond-duration radio transients
of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star ...magnetospheres
or relativistic shocks far from the central energy source
. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters
or variable polarization angles in some other apparently one-off events
. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks.
Abstract
A quantum thermal machine is an open quantum system coupled to hot and cold thermal baths. Thus, its dynamics can be well understood using the concepts and tools from non-Hermitian quantum ...systems. A hallmark of non-Hermiticity is the existence of exceptional points where the eigenvalues of a non-Hermitian Hamiltonian or a Liouvillian superoperator and their associated eigenvectors coalesce. Here, we report the experimental realization of a single-ion heat engine and demonstrate the effect of Liouvillian exceptional points on the dynamics and the performance of a quantum heat engine. Our experiments have revealed that operating the engine in the exact- and broken-phases, separated by a Liouvillian exceptional point, respectively during the isochoric heating and cooling strokes of an Otto cycle produces more work and output power and achieves higher efficiency than executing the Otto cycle completely in the exact phase where the system has an oscillatory dynamics and higher coherence. This result opens interesting possibilities for the control of quantum heat engines and will be of interest to other research areas that are concerned with the role of coherence and exceptional points in quantum processes and in work extraction by thermal machines.
Glioblastomas represent the most aggressive glioma grade and are associated with a poor patient prognosis. The current standard of care, consisting of surgery, radiation and chemotherapy, only ...results in a median survival of 14 months, underscoring the importance of developing effective new therapeutic strategies. Among the challenges in treating glioblastomas are primary resistance and the rapid emergence of recurrent disease, which can result from tumor cell-intrinsic mechanisms in addition to tumor microenvironment (TME)-mediated extrinsic resistance. Using a PDGF-B-driven proneural glioma mouse model, we assessed a panel of tyrosine kinase inhibitors with different selectivity profiles. We found that PLX3397, an inhibitor of colony stimulating factor-1 receptor (CSF-1R), blocks glioma progression, markedly suppresses tumor cell proliferation and reduces tumor grade. By contrast, the multi-targeted tyrosine kinase inhibitors dovitinib and vatalanib, which directly target tumor cells, exert minimal anti-tumoral effects in vivo, despite killing glioma cells in vitro, suggesting a TME-mediated resistance mechanism may be involved. Interestingly, PLX3397 interferes with tumor-mediated education of macrophages and consequently restores the sensitivity of glioma cells to tyrosine kinase inhibitors in vivo in preclinical combination trials. Our findings thus demonstrate that microenvironmental alteration by CSF-1R blockade renders tumor cells more susceptible to receptor tyrosine kinase inhibition in a preclinical glioblastoma model, which may have important translational relevance.
We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band (g, r, i, z) light curves in the Pan-STARRS Medium Deep Fields. ...As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts of z 1 or z 0.3 that are relatively emission-line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN, we detect typical lags of several days in the rest frame between the g band and the riz bands. The detected lags are ∼2-3 times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC 5548 and microlensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from g − r to g − i and then to g − z is slower than predicted in the thin disk model, particularly for high-luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet Fe ii lines and Mg ii, which may point to changes in the accretion disk structure at higher metallicity.
Quantum gates induced by geometric phases are intrinsically robust against noise due to the global properties of their evolution paths. Compared to conventional nonadiabatic geometric quantum ...computation, the recently proposed nonadiabatic noncyclic geometric quantum computation (NNGQC) works in a faster fashion while still remaining the robust feature of the geometric operations. Here, we experimentally implement the NNGQC in a single trapped ultracold 40Ca+ ion to verify the noise-resilient and fast feature. By performing unitary operations under imperfect conditions, we witness the advantages of the NNGQC with measured fidelities by quantum process tomography in comparison to other two quantum gates by conventional nonadiabatic geometric quantum computation and by straightforward dynamical evolution. Our results provide the first evidence confirming the possibility of accelerated quantum information processing with limited systematic errors even in an imperfect situation.
Superconductivity in FeSe emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane. This phase may arise from orbital ordering, spin fluctuations or hidden magnetic ...quadrupolar order. Here we use inelastic neutron scattering on a mosaic of single crystals of FeSe, detwinned by mounting on a BaFe
As
substrate to demonstrate that spin excitations are most intense at the antiferromagnetic wave vectors Q
= (±1, 0) at low energies E = 6-11 meV in the normal state. This two-fold (C
) anisotropy is reduced at lower energies, 3-5 meV, indicating a gapped four-fold (C
) mode. In the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (E = 3.6 meV) at Q
with incommensurate scattering around 5-6 meV. Our results highlight the extreme electronic anisotropy of the nematic phase of FeSe and are consistent with a highly anisotropic superconducting gap driven by spin fluctuations.
The hierarchical equations of motion (HEOM), derived from the exact Feynman-Vernon path integral, is one of the most powerful numerical methods to simulate the dynamics of open quantum systems. Its ...applicability has so far been limited to specific forms of spectral reservoir distributions and relatively elevated temperatures. Here we solve this problem and introduce an effective treatment of quantum noise in frequency space by systematically clustering higher order Matsubara poles, equivalent to an optimized rational decomposition. This leads to an elegant extension of the HEOM to arbitrary temperatures and very general reservoirs in combination with efficiency, high accuracy, and long-time stability. Moreover, the technique can directly be implemented in other approaches such as Green's function, stochastic, and pseudomode formulations. As one highly nontrivial application, for the subohmic spin-boson model at vanishing temperature the Shiba relation is quantitatively verified which predicts the long-time decay of correlation functions.
Alginate, a group of polyuronic saccharides, has been widely used in both pharmaceutical and food industries due to its unique physicochemical properties as well as beneficial health effects. ...However, the potential applications of alginate are restricted because of its low water solubility and high solution viscosity when significant concentrations are needed, particularly in food products. Alginate oligosaccharides (AOS), oligomers containing 2 to 25 monomers, can be obtained via hydrolysis of glycosidic bonds, organic synthesis, or through biosynthesis. Generally, AOS have shorter chain lengths and thus improved water solubility when compared with higher molecular weight alginates of the same monomers. These oligosaccharides have attracted interest from both basic and applied researchers. AOS have unique bioactivity and can impart health benefits. They have shown immunomodulatory, antimicrobial, antioxidant, prebiotic, antihypertensive, antidiabetic, antitumor, anticoagulant, and other activities. As examples, they have been utilized as prebiotics, feed supplements for aquaculture, poultry, and swine, elicitors for plants and microorganisms, cryoprotectors for frozen foods, and postharvest treatments. This review comprehensively covers methods for AOS production from alginate, such as physical/chemical methods, enzymatic methods, fermentation, organic synthesis, and biosynthesis. Moreover, current progress in structural characterization, potential health benefits, and AOS metabolism after ingestion are summarized in this review. This review will discuss methods for producing and modified AOS with desirable structures that are suited for novel applications.
Amyotrophic lateral sclerosis (ALS) is a fatal degenerative motor neuron disorder. Ten percent of cases are inherited; most involve unidentified genes. We report here 13 mutations in the fused in ...sarcoma/translated in liposarcoma (FUS/TLS) gene on chromosome 16 that were specific for familial ALS. The FUS/TLS protein binds to RNA, functions in diverse processes, and is normally located predominantly in the nucleus. In contrast, the mutant forms of FUS/TLS accumulated in the cytoplasm of neurons, a pathology that is similar to that of the gene TAR DNA-binding protein 43 (TDP43), whose mutations also cause ALS. Neuronal cytoplasmic protein aggregation and defective RNA metabolism thus appear to be common pathogenic mechanisms involved in ALS and possibly in other neurodegenerative disorders.
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