Leu-M

Anderson localization of waves in disordered media was originally predicted fifty years ago, in the context of transport of electrons in crystals. The phenomenon is much more general and has been observed in a variety of systems, including light waves. However, Anderson localization has not been observed directly for matter waves. Owing to the high degree of control over most of the system parameters (in particular the interaction strength), ultracold atoms offer opportunities for the study of disorder-induced localization. Here we use a non-interacting Bose-Einstein condensate to study Anderson localization. The experiment is performed with a one-dimensional quasi-periodic lattice-a system that features a crossover between extended and exponentially localized states, as in the case of purely random disorder in higher dimensions. Localization is clearly demonstrated through investigations of the transport properties and spatial and momentum distributions. We characterize the crossover, finding that the critical disorder strength scales with the tunnelling energy of the atoms in the lattice. This controllable system may be used to investigate the interplay of disorder and interaction (ref. 7 and references therein), and to explore exotic quantum phases.

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Anderson localization of a non-interacting Bose-Einstein condensate.

The importance of the Fano resonance concept is recognized across multiple fields of physics. In this Review, Fano resonance is explored in the context of optics, with particular emphasis on dielectric nanostructures and metasurfaces. Rapid progress in photonics and nanotechnology brings many examples of resonant optical phenomena associated with the physics of Fano resonances, with applications in optical switching and sensing. For successful design of photonic devices, it is important to gain deep insight into different resonant phenomena and understand their connection. Here, we review a broad range of resonant electromagnetic effects by using two effective coupled oscillators, including the Fano resonance, electromagnetically induced transparency, Kerker and Borrmann effects, and parity–time symmetry breaking. We discuss how to introduce the Fano parameter for describing a transition between two seemingly different spectroscopic signatures associated with asymmetric Fano and symmetric Lorentzian shapes. We also review the recent results on Fano resonances in dielectric nanostructures and metasurfaces.

Fano resonances in photonics

This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.

Ion mobility-mass spectrometry.

The syntheses of strongly anisotropic nanocrystals with one dimension much smaller than the two others, such as nanoplatelets, are still greatly underdeveloped. Here, we demonstrate the formation of atomically flat quasi-two-dimensional colloidal CdSe, CdS and CdTe nanoplatelets with well-defined thicknesses ranging from 4 to 11 monolayers. These nanoplatelets have the electronic properties of two-dimensional quantum wells formed by molecular beam epitaxy, and their thickness-dependent absorption and emission spectra are described very well within an eight-band Pidgeon-Brown model. They present an extremely narrow emission spectrum with full-width at half-maximum less than 40 meV at room temperature. The radiative fluorescent lifetime measured in CdSe nanoplatelets decreases with temperature, reaching 1 ns at 6 K, two orders of magnitude less than for spherical CdSe nanoparticles. This makes the nanoplatelets the fastest colloidal fluorescent emitters and strongly suggests that they show a giant oscillator strength transition.

Colloidal nanoplatelets with two-dimensional electronic structure

This paper studies the impact of ambiguity and ambiguity aversion on equilibrium asset prices and portfolio holdings in competitive financial markets. It argues that attitudes toward ambiguity are heterogeneous across the population, just as attitudes toward risk are heterogeneous across the population, but that heterogeneity of attitudes toward ambiguity has different implications than heterogeneity of attitudes toward risk. In particular, when some state probabilities are not known, agents who are sufficiently ambiguity averse find open sets of prices for which they refuse to hold an ambiguous portfolio. This suggests a different cross-section of portfolio choices, a wider range of state price/probability ratios and different rankings of state price/probability ratios than would be predicted if state probabilities were known. Experiments confirm all of these suggestions. Our findings contradict the claim that investors who have cognitive biases do not affect prices because they are infra-marginal: ambiguity averse investors have an indirect effect on prices because they change the per-capita amount of risk that is to be shared among the marginal investors. Our experimental data also suggest a positive correlation between risk aversion and ambiguity aversion that might explain the “value effect” in historical data.

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Theory and Experiment

Measurements of the Recombination of Electrons with H 3 O + · ( H 2 O ) n -Series Ions

Measurements of Recombination of Electrons with H3+ and H5+ Ions

Several ion–molecule reactions of ionospheric interest have been studied in a drift‐tube–mass‐spectrometer apparatus for ions of mean energy from thermal energies to ∼ 1 eV. The measured rate coefficients in cubic centimeters/second are N++O2: 5 × 10−10 from 0.039–0.9 eV; N2++O2: 6 × 10−11 at 0.039 eV, decreasing to ∼ 8 × 10−12 at 0.9 eV; O2++NO: 3 × 10−10 from 0.039–1.6 eV; O++CO2: 1 × 10−9 at 0.039 eV, decreasing to 5 × 10−10 cm3/sec at 1.3 eV. The relevance of the first three reactions for the Earth's ionosphere and of the last reaction for the Martian atmosphere is discussed briefly.

Ion–Molecule Reactions Involving N2+, N+, O2+, and O+ Ions from 300°K to ∼1 eV

The rate coefficients for the reactions of He+ ions with N2 and O2 have been measured in a drift tube–mass spectrometer from thermal energies (300°K) to ∼ 0.1 eV. In addition to reaction rate determinations by the usual product‐ion “arrival spectrum” method, a new technique involving “additional residence time” for the parent ion is described which is applicable even when parent and product ions have equal mobilities. The total rate coefficient (i.e., the sum of dissociative and the ordinary charge transfer) for He++N2 reaction was found to be (1.0 + 0.3, − 0.2) × 10−9 cm3/sec at 300°K, decreasing to ∼ 7 × 10−10 cm3/sec at 0.1 eV. The corresponding coefficient for the He++O2 reaction was measured to be (8.5 + 2.5, − 2.0) × 10−10 cm3/sec and to be independent of energy over the same range. The ratio of dissociative charge transfer (with N+ or O+, respectively, as reaction products) to ordinary charge transfer (with N2+ or O2+, respectively, as products) was found to be 0.55 / 0.45 for He++N2 and 0.8 / 0.2 ...

Rainer Johnsen

Papers

Theory and Experiment

Measurements of the Recombination of Electrons with H 3 O + · ( H 2 O ) n -Series Ions

Measurements of Recombination of Electrons with H3+ and H5+ Ions

Ion–Molecule Reactions Involving N2+, N+, O2+, and O+ Ions from 300°K to ∼1 eV

Ion–Molecule Reactions, He++O2 and He++N2, at Thermal Energies and Above