There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 x 10 12 per cubic centimeter and could be preserved for more than 15 seconds. Three primary signatures of Bose-Einstein condensation were seen. (i) On top of a broad thermal velocity distribution, a narrow peak appeared that was centered at zero velocity. (ii) The fraction of the atoms that were in this low-velocity peak increased abruptly as the sample temperature was lowered. (iii) The peak exhibited a nonthermal, anisotropic velocity distribution expected of the minimum-energy quantum state of the magnetic trap in contrast to the isotropic, thermal velocity distribution observed in the broad uncondensed fraction.

/pdf/observation-of-bose-einstein-condensation-in-a-dilute-atomic-2wpb5ks2pi.pdf

Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor

The use of individual molecules as functional electronic devices was first proposed in the 1970s (ref 1) Since then, molecular electronics2,3 has attracted much interest, particularly because it could lead to conceptually new miniaturization strategies in the electronics and computer industry The realization of single-molecule devices has remained challenging, largely owing to difficulties in achieving electrical contact to individual molecules Recent advances in nanotechnology, however, have resulted in electrical measurements on single molecules4,5,6,7 Here we report the fabrication of a field-effect transistor—a three-terminal switching device—that consists of one semiconducting8,9,10 single-wall carbon nanotube11,12 connected to two metal electrodes By applying a voltage to a gate electrode, the nanotube can be switched from a conducting to an insulating state We have previously reported5 similar behaviour for a metallic single-wall carbon nanotube operated at extremely low temperatures The present device, in contrast, operates at room temperature, thereby meeting an important requirement for potential practical applications Electrical measurements on the nanotube transistor indicate that its operation characteristics can be qualitatively described by the semiclassical band-bending models currently used for traditional semiconductor devices The fabrication of the three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics

Room-temperature transistor based on a single carbon nanotube

The phenomenon of Bose-Einstein condensation of dilute gases in traps is reviewed from a theoretical perspective. Mean-field theory provides a framework to understand the main features of the condensation and the role of interactions between particles. Various properties of these systems are discussed, including the density profiles and the energy of the ground-state configurations, the collective oscillations and the dynamics of the expansion, the condensate fraction and the thermodynamic functions. The thermodynamic limit exhibits a scaling behavior in the relevant length and energy scales. Despite the dilute nature of the gases, interactions profoundly modify the static as well as the dynamic properties of the system; the predictions of mean-field theory are in excellent agreement with available experimental results. Effects of superfluidity including the existence of quantized vortices and the reduction of the moment of inertia are discussed, as well as the consequences of coherence such as the Josephson effect and interference phenomena. The review also assesses the accuracy and limitations of the mean-field approach.

https://arxiv.org/pdf/cond-mat/9806038.pdf

Theory of Bose-Einstein condensation in trapped gases

The molecular hydrogens (${\mathrm{H}}_{2}$, ${\mathrm{D}}_{2}$, HD, etc.) form the simplest of all molecular solids. The combination of the light mass, small moment of inertia, weak interactions, and the quasi-metastable ortho-para species result in a fascinating low-temperature behavior that can be understood to a large extent from considerations of first principles. After discussing single molecule properties and intermolecular interactions we discuss in detail the ortho-para properties, conversion and diffusion. This is followed by a description of the crystal structures and the orientational ordering phenomena. The thermodynamic properties are reviewed. The article is concluded with a discussion of the translational ground state of the solid and the effect of the large zero-point motion on the solid state properties. A large number of data are collected in tables and graphs to provide a reference source.

The solid molecular hydrogens in the condensed phase: Fundamentals and static properties

A semiempirical pair potential for molecular hydrogen and deuterium has been derived by fitting to solid state data. The potential is bounded to conform asymptotically to short‐ and long‐range theoretical results. In the solid, many‐body effects are accounted for by including a spherical form of the nonnegligible Axilrod–Muto–Teller three‐body forces. The potential can be used to successfully describe isotropic properties in the solid and gas phases.

The isotropic intermolecular potential for H2 and D2 in the solid and gas phases

In 1935, Wigner and Huntington predicted that molecular hydrogen would become an atomic metal at a pressure of 25 GPa. Eighty years and more than 400 GPa later, Dias and Silvera have finally produced metallic hydrogen at low temperature. The metallization occurred between 465 and nearly 500 GPa at 5.5 K. Spectroscopic measurements verified that hydrogen was in the atomic state. The observation completes an unexpectedly long quest to find the metallic hydrogen that Wigner and Huntington predicted so long ago.

Science , this issue p. [715][1]

 [1]: /lookup/doi/10.1126/science.aal1579

https://science.sciencemag.org/content/sci/355/6326/715.full.pdf

Observation of the Wigner-Huntington transition to metallic hydrogen

We have studied solid hydrogen under pressure at low temperatures. With increasing pressure we observe changes in the sample, going from transparent, to black, to a reflective metal, the latter studied at a pressure of 495 GPa. We have measured the reflectance as a function of wavelength in the visible spectrum finding values as high as 0.90 from the metallic hydrogen. We have fit the reflectance using a Drude free electron model to determine the plasma frequency of 30.1 eV at T= 5.5 K, with a corresponding electron carrier density of 6.7x1023 particles/cm3, consistent with theoretical estimates. The properties are those of a metal. Solid metallic hydrogen has been produced in the laboratory.

Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen

We reported the first observation of metallic hydrogen (MH) in the low temperature limit at a pressure of ~495 GPa in an article published in Science (1). This transition was first predicted by Wigner and Huntington (WE) over 80 years ago (2) at a pressure of ~25 GPa. In recent decades it became clear that the required pressure for metallization was far greater, in the 400-500 GPa range. Until now the observation of the WE transition in diamond anvil cells (DACs) has been prevented by one problem: the diamonds break before a sufficiently high pressure has been achieved. This has driven the high-pressure community to improve DACs and experimental methods to understand and overcome the conditions that limited the performance of diamonds and the pressure. In our experiment, with increasing pressure, we observed a clear transition from a transparent sample of solid molecular hydrogen to an opaque black sample to a shiny reflective sample of MH, as determined by reflectance measurements. There is no doubt that MH was produced at the highest pressures. Yet there have been criticisms concerning the pressure that was achieved, the possibility that the 50 nm alumina layer, deposited on diamonds to inhibit diffusion of hydrogen, might be transformed to a metal and be responsible for the reflectance, and analysis of the reflectance. Here we respond to the criticisms posted on the condensed matter arXiv by Loubeyre, Occelli, and Dumas (LOD)- arXiv:1702.07192, Eremets and Drozdov (ED)- arXiv:1702.05125, and Goncharov and Struzhkin (GS)- arXiv:1702.04246.

Isaac F. Silvera

Papers

The solid molecular hydrogens in the condensed phase: Fundamentals and static properties

The isotropic intermolecular potential for H2 and D2 in the solid and gas phases

Observation of the Wigner-Huntington transition to metallic hydrogen

Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen

Response to critiques on Observation of the Wigner-Huntington transition to metallic hydrogen