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Jumping of flea beetles onto inclined platforms
No full textThe flea beetle, Altica cirsicola, escapes predators by jumping and landing in a dense maze of leaves. How do they land on such varied surfaces? In this experimental study, we filmed the take-off, flight, and landing of flea beetles on a configurable angled platform. We report three in-flight behaviors: winged, wingless, and an intermediate winged mode. These modes significantly affected take-off speed, acceleration, and the duration that wings were deployed. When wings were closed, flea beetles rolled or pitched up to five times in the air. This work may help to understand how insects can jump and right themselves onto variable surfaces
Local Noether theorem for quantum lattice systems and topological invariants of gapped states
No full textWe study generalizations of the Berry phase for quantum lattice systems in arbitrary dimensions. For a smooth family of gapped ground states in d dimensions, we define a closed d + 2-form on the parameter space, which generalizes the curvature of the Berry connection. Its cohomology class is a topological invariant of the family. When the family is equivariant under the action of a compact Lie group G, topological invariants take values in the equivariant cohomology of the parameter space. These invariants unify and generalize the Hall conductance and the Thouless pump. A key role in these constructions is played by a certain differential graded Fréchet–Lie algebra attached to any quantum lattice system. As a by-product, we describe ambiguities in charge densities and conserved currents for arbitrary lattice systems with rapidly decaying interactions
Mechanism of a Luminescent Dicopper System That Facilitates Electrophotochemical Coupling of Benzyl Chlorides via a Strongly Reducing Excited State
No full textPhotochemical radical generation has become a modern staple in chemical synthesis and methodology. Herein, we detail the photochemistry of a highly reducing, highly luminescent dicopper system [Cu₂] (Eₒₓ* ≈ −2.7 V vs SCE; τₒ ≈ 10 μs) within the context of a model reaction: single-electron reduction of benzyl chlorides. The dicopper system is mechanistically well defined. As we show, it is the [Cu₂]* excited state that serves as the outer-sphere photoreductant of benzyl chloride substrates; the ground-state oxidized byproduct, [Cu₂]⁺, is electrochemically recycled, demonstrating a catalytic electrophotochemical C–C coupling process
The upper logarithmic density of monochromatic subset sums
No full textWe show that in any two-coloring of the positive integers there is a color for which the set of positive integers that can be represented as a sum of distinct elements with this color has upper logarithmic density at least (2 + √3)/4 and this is best possible. This answers a 40-year-old question of Erdős
xtusreg: Software for dynamic panel regression under irregular time spacing
No full textWe introduce a new command, xtusreg, that estimates parameters of fixed-effects dynamic panel regression models under unequal time spacing. After reviewing the method, we examine the finite-sample performance of the command using simulated data. We also illustrate the command with the National Longitudinal Survey Original Cohorts: Older Men, whose personal interviews took place in the unequally spaced years of 1966, 1967, 1969, 1971, 1976, 1981, and 1990. The methods underlying xtusreg are those discussed by Sasaki and Xin (2017, Journal of Econometrics 196: 320–330)
Håleniusite-(Ce), CeOF, the Ce Analogue of Håleniusite-(La) from the Água de Pau Volcano, Sãn Miguel Island, Azores District, Portugal
No full textHåleniusite-(Ce) (IMA2021-042), CeOF, is a new mineral discovered in ejectum from the Água de Pau volcano, Sãn Miguel Island, Azores District, Portugal. It occurs as opaque, cream-colored, fine-grained pseudomorphic replacements of hexagonal tablets of bastnäsite-(Ce). It is associated with astrophyllite and fluornatropyrochlore in a matrix composed mainly of albite, quartz, and aegirine. The mineral has a white streak and a calculated density of 5.890 g/cm³ for the empirical formula. The strongest powder diffraction lines are [d_(obs)Å(I_(obs))(hkl)]: 3.247(100)(111), 2.840(31)(200), 2.004(46)(220), and 1.705(42)(311). Electron probe microanalysis provided the empirical formula (Ce₀.₄₁La₀.₂₁Sm₀.₁₅Nd₀.₀₄Eu₀.₀₃Ca₀.₀₂Y₀.₀₂Dy₀.₀₂Gd₀.₀₁)_(Σ0.91)(O₀.₇₀F₀.₃₀)F₁.₀₀. Håleniusite-(Ce) has a fluorite-type structure, space group Fm3̅ m, with a = 5.6597(10) Å and V = 181.29(10) ų (Z = 4)
Euclid preparation. XX. The Complete Calibration of the Color-Redshift Relation survey: LBT observations and data release
No full textThe Complete Calibration of the Color–Redshift Relation survey (C3R2) is a spectroscopic program designed to empirically calibrate the galaxy color–redshift relation to the Euclid depth (I_E = 24.5), a key ingredient for the success of Stage IV dark energy projects based on weak lensing cosmology. A spectroscopic calibration sample that is as representative as possible of the galaxies in the Euclid weak lensing sample is being collected, selecting galaxies from a self-organizing map (SOM) representation of the galaxy color space. Here, we present the results of a near-infrared H- and K-band spectroscopic campaign carried out using the LUCI instruments at the LBT. For a total of 251 galaxies, we present new highly reliable redshifts in the 1.3 ≤ z ≤ 1.7 and 2 ≤ z ≤ 2.7 ranges. The newly-determined redshifts populate 49 SOM cells that previously contained no spectroscopic measurements and almost twice the occupation numbers of an additional 153 SOM cells. A final optical ground-based observational effort is needed to calibrate the missing cells, in particular in the redshift range 1.7 ≤ z ≤ 2.7, which lack spectroscopic calibration. In the end, Euclid itself will deliver telluric-free near-IR spectra that can complete the calibration
Biocatalytic Carbene Transfer Using Diazirines
No full textBiocatalytic carbene transfer from diazo compounds is a versatile strategy in asymmetric synthesis. However, the limited pool of stable diazo compounds constrains the variety of accessible products. To overcome this restriction, we have engineered variants of Aeropyrum pernix protoglobin (ApePgb) that use diazirines as carbene precursors. While the enhanced stability of diazirines relative to their diazo isomers enables access to a diverse array of carbenes, they have previously resisted catalytic activation. Our engineered ApePgb variants represent the first example of catalysts for selective carbene transfer from these species at room temperature. The structure of an ApePgb variant, determined by microcrystal electron diffraction (MicroED), reveals that evolution has enhanced access to the heme active site to facilitate this new-to-nature catalysis. Using readily prepared aryl diazirines as model substrates, we demonstrate the application of these highly stable carbene precursors in biocatalytic cyclopropanation, N–H insertion, and Si–H insertion reactions
Strain-tuning of transport gaps and semiconductor-to-conductor phase transition in twinned graphene
No full textWe show, through the use of the Landauer-Büttiker (LB) formalism and a tight-binding (TB) model, that the transport gap of twinned graphene can be tuned through the application of a uniaxial strain in the direction normal to the twin band. Remarkably, we find that the transport gap E_(gap) bears a square-root dependence on the control parameter ϵₓ − ϵ꜀,, where ϵₓ is the applied uniaxial strain and ϵ꜀ ~ 19% is a critical strain. We interpret this dependence as evidence of criticality underlying a continuous phase transition, with ϵₓ − ϵ꜀ playing the role of control parameter and the transport gap E_(gap) playing the role of order parameter. For ϵₓ ϵ꜀ the transport gap closes to zero and the material becomes conductor, which evinces a semiconductor-to-conductor phase transition. The computed critical exponent of 1/2 places the transition in the meanfield universality class, which enables far-reaching analogies with other systems in the same class
Displacement-noise-free neutron interferometer for gravitational wave detection using a single Mach-Zehnder configuration
No full textThe improvement of sensitivity to gravitational waves (GWs) at lower frequencies is still challenging on account of displacement noise. One of the solutions is the neutron displacement-noise-free interferometer (DFI). We focus on a simplification of the detector configuration by taking advantage of the ability to adjust the neutron speed depending on the configuration. The new configuration consists of two beamsplitters and two mirrors, which constitute a single Mach-Zehnder interferometer (MZI). It is simpler than the configuration with two MZIs in previous research. All displacement noise of mirrors and beamsplitters can be canceled in the frequency domain. This cancellation can be explained intuitively using a phasor diagram