Quantum phase transitions (QPTs) are usually associated with many-body systems in the thermodynamic limit when their ground states show abrupt changes at zero temperature with variation of a ...parameter in the Hamiltonian. Recently it has been realized that a QPT can also occur in a system composed of only a two-level atom and a single-mode bosonic field, described by the quantum Rabi model (QRM). Here we report an experimental demonstration of a QPT in the QRM using a
Yb
ion in a Paul trap. We measure the spin-up state population and the average phonon number of the ion as two order parameters and observe clear evidence of the phase transition via adiabatic tuning of the coupling between the ion and its spatial motion. An experimental probe of the phase transition in a fundamental quantum optics model without imposing the thermodynamic limit opens up a window for controlled study of QPTs and quantum critical phenomena.
The TET (ten-eleven translocation) family of α-ketoglutarate (α-KG)-dependent dioxygenases catalyzes the sequential oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), ...5-formylcytosine and 5-carboxylcytosine, leading to eventual DNA demethylation. The TET2 gene is a bona fide tumor suppressor frequently mutated in leukemia, and TET enzyme activity is inhibited in IDH1/2-mutated tumors by the oncometabolite 2-hydroxyglutarate, an antagonist of α-KG, linking 5mC oxidation to cancer development. We report here that the levels of 5hmC are dramatically reduced in human breast, liver, lung, pancreatic and prostate cancers when compared with the matched surrounding normal tissues. Associated with the 5hmC decrease is the substantial reduction of the expression of all three TET genes, revealing a possible mechanism for the reduced 5hmC in cancer cells. The decrease of 5hmC was also observed during tumor development in different genetically engineered mouse models. Together, our results identify 5hmC as a biomarker whose decrease is broadly and tightly associated with tumor development.
We present a three-dimensional (3D) extinction map of the southern sky. The map covers the SkyMapper Southern Survey (SMSS) area of ∼14,000 deg2 and has spatial resolutions between 6 9 and 27′. Based ...on the multi-band photometry of SMSS, the Two Micron All Sky Survey, the Wide-Field Infrared Survey Explorer Survey, and the Gaia mission, we have estimated values of the r-band extinction for ∼19 million stars with the spectral energy distribution analysis. Together with the distances calculated from the Gaia data release 2 (DR2) parallaxes, we have constructed a 3D extinction map of the southern sky. By combining our 3D extinction map with those from the literature, we present an all-sky 3D extinction map, and use it to explore the 3D distribution of the Galactic dust grains. We use two different models, one consisting of a single disk and another of two disks, to fit the 3D distribution of the Galactic dust grains. The data is better fitted by a two-disk model, yielding smaller values of the Bayesian Information Criterion. The best-fit model has scale heights of 73 and 225 pc for the "thin" and "thick" dust disks, respectively.
Self-assembly of rigid building blocks with explicit shape and symmetry is substantially influenced by the geometric factors and remains largely unexplored. We report the selective assembly behaviors ...of a class of precisely defined, nanosized giant tetrahedra constructed by placing different polyhedral oligomeric silsesquioxane (POSS) molecular nanoparticles at the vertices of a rigid tetrahedral framework. Designed symmetry breaking of these giant tetrahedra introduces precise positional interactions and results in diverse selectively assembled, highly ordered supramolecular lattices including a Frank-Kasper A15 phase, which resembles the essential structural features of certain metal alloys but at a larger length scale. These results demonstrate the power of persistent molecular geometry with balanced enthalpy and entropy in creating thermodynamically stable supramolecular lattices with properties distinct from those of other self-assembling soft materials.
In this letter, a compact ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna with lower wireless local area network (WLAN) coverage is proposed. The proposed MIMO antenna consists of ...two quasi-self-complementary monopoles, which are easy to achieve ultrawideband operation. By arranging two monopoles symmetrically, with their main radiation directions oppositely oriented, a UWB MIMO antenna with high isolation is proposed. This high isolation is achieved without using any other decoupling methods, which, totally, benefits from the monopoles' complementary and asymmetrical structures. The measured |S11| has the band of mainly covering 2.19-11.07 GHz except a little higher than -10 dB at 2.86-3.28 GHz, and with |S21| ≤ - 20 dB at most of the band. Since the proposed monopole has excellent inherent properties, a four-element UWB MIMO antenna with good isolation is also discussed.
Frank–Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up ...possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with “soft” spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.
How biomembranes are self‐organized to perform their functions remains a pivotal issue in biological and chemical science. Understanding the self‐assembly principles of lipid‐like molecules hence ...becomes crucial. Herein, we report the mesostructural evolution of amphiphilic sphere‐rod conjugates (giant lipids), and study the roles of geometric parameters (head–tail ratio and cross‐sectional area) during this course. As a prototype system, giant lipids resemble natural lipidic molecules by capturing their essential features. The self‐assembly behavior of two categories of giant lipids (I‐shape and T‐shape, a total of 8 molecules) is demonstrated. A rich variety of mesostructures is constructed in solution state and their molecular packing models are rationally understood. Giant lipids recast the phase behavior of natural lipids to a certain degree and the abundant self‐assembled morphologies reveal distinct physiochemical behaviors when geometric parameters deviate from natural analogues.
The bigger the better: Two categories of giant, lipid‐like amphiphilic molecules organize into various mesostructures, shedding new light on the underlying principles of lipid self‐assembly. The geometric parameters of these giant, lipid‐like molecules are modulated on a molecular level to understand the physiochemical driving forces behind their self‐assembly.
The natural resonance appears at 16
GHz for (Fe, Ni)/C nanocapsules with (Fe, Ni) alloys as cores and graphite as shells. Reflection loss (RL) exceeding −10
dB was obtained in the whole Ku-band ...(12.4–18
GHz) for an absorber thickness of 2.0
mm, while it exceeds −20
dB over the 13.6–16.6
GHz range. In addition, the bandwidth does not change dramatically for the thicknesses of 1.87–2.1
mm for the RL values exceeding −10
dB. The (Fe, Ni)/C nanocapsules with wide bandwidth absorption can be used as excellent electromagnetic-wave-absorption materials in the whole Ku-band.
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