Soil acidity and the liming of Iowa soils

Whether or not their lands will give better crop yields if lime1 is applied has become a live question with Iowa farmers. They have written many letters of inquiry upon this point to the Iowa Agricultural Experiment Station and hundreds of soil samples have been analyzed to make satisfactory answer. To provide more complete information relative to this important question of soil acidity and the use of lime in Iowa, the agronomy section of the experiment station gathered many soil samples from well scattered localities in the principal soil areas. These were analyzed and the results are now presented and discussed in this bulletin. These analyses show that liming is likely to be profitable in the Mississippi loess, the Southern Iowa loess and the Iowan drift areas because those soils are very apt to be more or less acid; also, that the soils of the Wisconsin drift are only occasionally in need of liming, and those of the Missouri loess only very rarely

Nanopositioning of a diamond nanocrystal containing a single NV defect center

Precise control over the position of a single quantum object is important for many experiments in quantum science and nanotechnology. We report on a technique for high-accuracy positioning of individual diamond nanocrystals. The positioning is done with a home-built nanomanipulator under real-time scanning electron imaging, yielding an accuracy of a few nanometers. This technique is applied to pick up, move and position a single NV defect center contained in a diamond nanocrystal. We verify that the unique optical and spin properties of the NV center are conserved by the positioning process.Comment: 3 pages, 3 figures; high-resolution version available at http://www.ns.tudelft.nl/q

Robotic Mobility Diversity Algorithm with Continuous Search Space

Small scale fading makes the wireless channel gain vary significantly over small distances and in the context of classical communication systems it can be detrimental to performance. But in the context of mobile robot (MR) wireless communications, we can take advantage of the fading using a mobility diversity algorithm (MDA) to deliberately locate the MR at a point where the channel gain is high. There are two classes of MDAs. In the first class, the MR explores various points, stops at each one to collect channel measurements and then locates the best position to establish communications. In the second class the MR moves, without stopping, along a continuous path while collecting channel measurements and then stops at the end of the path. It determines the best point to establish communications. Until now, the shape of the continuous path for such MDAs has been arbitrarily selected and currently there is no method to optimize it. In this paper, we propose a method to optimize such a path. Simulation results show that such optimized paths provide the MDAs with an increased performance, enabling them to experience higher channel gains while using less mechanical energy for the MR motion

Deterministic nano-assembly of a coupled quantum emitter - photonic crystal cavity system

The interaction of a single quantum emitter with its environment is a central theme in quantum optics. When placed in highly confined optical fields, such as those created in optical cavities or plasmonic structures, the optical properties of the emitter can change drastically. In particular, photonic crystal (PC) cavities show high quality factors combined with an extremely small mode volume. Efficiently coupling a single quantum emitter to a PC cavity is challenging because of the required positioning accuracy. Here, we demonstrate deterministic coupling of single Nitrogen-Vacancy (NV) centers to high-quality gallium phosphide PC cavities, by deterministically positioning their 50 nm-sized host nanocrystals into the cavity mode maximum with few-nanometer accuracy. The coupling results in a 25-fold enhancement of NV center emission at the cavity wavelength. With this technique, the NV center photoluminescence spectrum can be reshaped allowing for efficient generation of coherent photons, providing new opportunities for quantum science.Comment: 13 pages, 4 figure

Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond

We investigate spin-dependent decay and intersystem crossing in the optical cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We use spin control and pulsed optical excitation to extract both the spin-resolved lifetimes of the excited states and the degree of optically-induced spin polarization. By optically exciting the centre with a series of picosecond pulses, we determine the spin-flip probabilities per optical cycle, as well as the spin-dependent probability for intersystem crossing. This information, together with the indepedently measured decay rate of singlet population provides a full description of spin dynamics in the optical cycle of NV centres. The temperature dependence of the singlet population decay rate provides information on the number of singlet states involved in the optical cycle.Comment: 11 pages, 5 figure

Consideraciones taxonómicas sobre Diatomeas epífitas del intermareal rocoso marplatense.I

Fourteen species and varieties of epiphytic diatom of intertidal seagras were studied using light and electron microscope for some of them. The ecological distribution of Navicula tripunctata (i\hiller) BOIYis extended to littoral environment. Licmophora juergensii Agardh, Nitzschia parvula mith and ,. marina Grunow are new records for Argentina.Catorce especies y valiedades de diatomeas epífitas de macroalgas intermarcales fueron estudiadas usando microscopio óptico y electrónico de barrido. La distribución ecológica de Navicula tripunctata (Müller) Bory es ampliada a ambientes marinos litorales. Licmophora juergensii Agardh, Nitzschia parvula Smith y marina Grunow son nuevas citas para Argentina

Tunable pseudo-magnetic fields for polaritons in strained metasurfaces

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this recordData availability: All relevant data are available from the corresponding authors upon reasonable request.Pseudo-magnetic fields generated in artificially strained lattices have enabled the emulation of exotic phenomena once thought to be exclusive to charged particles. However, to date, they have failed to emulate the tunability of real magnetic fields because they are determined solely by the engineered strain configuration, rendering them fixed by design. Here, we unveil a new universal mechanism to tune pseudo-magnetic fields for polaritons supported by a strained honeycomb metasurface composed of interacting dipole emitters/antennas. Without altering the strain configuration, we show that one can tune the pseudo-magnetic field strength by modifying the surrounding electromagnetic environment via an enclosing cavity waveguide, which modifies the nature of the dipole-dipole interactions. Remarkably, due to the competition between short-range Coulomb interactions and long-range photon-mediated interactions, the pseudo-magnetic field can be entirely switched off at a critical cavity width, without removing the strain. Consequently, by varying only the cavity width, we demonstrate a tunable Lorentz-like force that can be switched on/off and a collapse and revival of polariton Landau levels. Unlocking this tunable pseudo-magnetism poses new intriguing questions beyond the paradigm of conventional tight-binding physics.Engineering and Physical Sciences Research Council (EPSRC)Royal Societ