1,255 research outputs found
Tunable Single-Walled Carbon Nanotube Fluorescence Emission Via Associated DNA Sequence
Single‑walled carbon nanotubes, or SWCNTs, are nanomaterials that possess unique characteristics, most importantly their differing structural arrangement in terms of chirality. Each single‑walled carbon nanotube exhibits a unique fluorescence spectra that is dependent upon its chirality. The association of single‑stranded DNA (ssDNA) with SWCNTs is monitored by near‑infrared fluorescence spectroscopy. The DNA:SWCNT hybrid exhibits fluorescence spectra dependence upon both the selected sequence and the selected chirality
Writing and Reading antiferromagnetic MnAu: N\'eel spin-orbit torques and large anisotropic magnetoresistance
Antiferromagnets are magnetically ordered materials which exhibit no net
moment and thus are insensitive to magnetic fields. Antiferromagnetic
spintronics aims to take advantage of this insensitivity for enhanced
stability, while at the same time active manipulation up to the natural THz
dynamic speeds of antiferromagnets is possible, thus combining exceptional
storage density and ultra-fast switching. However, the active manipulation and
read-out of the N\'eel vector (staggered moment) orientation is challenging.
Recent predictions have opened up a path based on a new spin-orbit torque,
which couples directly to the N\'eel order parameter. This N\'eel spin-orbit
torque was first experimentally demonstrated in a pioneering work using
semimetallic CuMnAs. Here we demonstrate for MnAu, a good conductor with a
high ordering temperature suitable for applications, reliable and reproducible
switching using current pulses and readout by magnetoresistance measurements.
The symmetry of the torques agrees with theoretical predictions and a large
read-out magnetoresistance effect of more than ~ is reproduced by
ab initio transport calculations.Comment: 5 pages, 4 figure
Climate and soil type together explain the distribution of microendemic species in a biodiversity hotspot
The grasshopper genus Caledonula, endemic to New Caledonia, was studied to understand the evolution of species distributions in relation to climate and soil types. Based on a comprehensive sampling of 80 locations throughout the island, the genus was represented by five species, four of which are new to science, of which three are described here. All the species have limited distributions in New Caledonia. Bioclimatic niche modelling shows that all the species were found in association with a wet climate and reduced seasonality, explaining their restriction to the southern half of the island. The results suggest that the genus was ancestrally constrained by seasonality. A molecular phylogeny was reconstructed using two mitochondrial and two nuclear markers. The partially resolved tree showed monophyly of the species found on metalliferous soils, and molecular dating indicated a rather recent origin for the genus. Adaptation to metalliferous soils is suggested by both morphological changes and radiation on these soils. The genus Caledonula is therefore a good model to understand the origin of microendemism in the context of recent and mixed influences of climate and soil type
Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)
We thank ORSAS (GS) and the EPSRC (DE and DMcK supported by project EP/E02971X/1, WYM supported by project EP/I031545/1) for funding.Examples of singly-metallated derivatives of 1,1[prime or minute]-bis(o-carborane) have been prepared and spectroscopically and structurally characterised. Metallation of [7-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-7,8-nido-C2B9H10]2- with a {Ru(p-cymene)}2+ fragment affords both the unisomerised species [1-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (2) and the isomerised [8-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-2-(p-cymene)-2,1,8-closo-RuC2B9H10] (3), and 2 is easily transformed into 3 with mild heating. Metallation with a preformed {CoCp}2+ fragment also affords a 3,1,2-MC2B9-1[prime or minute],2[prime or minute]-C2B10 product [1-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-3-Cp-3,1,2-closo-CoC2B9H10] (4), but if CoCl2/NaCp is used followed by oxidation the result is the 2,1,8-CoC2B9-1[prime or minute],2[prime or minute]-C2B10 species [8-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-2-Cp-2,1,8-closo-CoC2B9H10] (5). Compound 4 does not convert into 5 in refluxing toluene, but does do so if it is reduced and then reoxidised, perhaps highlighting the importance of the basicity of the metal fragment in the isomerisation of metallacarboranes. A computational study of 1,1[prime or minute]-bis(o-carborane) is in excellent agreement with a recently-determined precise crystallographic study and establishes that the {1[prime or minute],2[prime or minute]-closo-C2B10H11} fragment is electron-withdrawing compared to H.Publisher PDFPeer reviewe
A high-precision polarimeter
We have built a polarimeter in order to measure the electron beam
polarization in hall C at JLAB. Using a superconducting solenoid to drive the
pure-iron target foil into saturation, and a symmetrical setup to detect the
Moller electrons in coincidence, we achieve an accuracy of <1%. This sets a new
standard for Moller polarimeters.Comment: 17 pages, 9 figures, submitted to N.I.
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
Terahertz electromagnetic radiation is extremely useful for numerous
applications such as imaging and spectroscopy. Therefore, it is highly
desirable to have an efficient table-top emitter covering the 1-to-30-THz
window whilst being driven by a low-cost, low-power femtosecond laser
oscillator. So far, all solid-state emitters solely exploit physics related to
the electron charge and deliver emission spectra with substantial gaps. Here,
we take advantage of the electron spin to realize a conceptually new terahertz
source which relies on tailored fundamental spintronic and photonic phenomena
in magnetic metal multilayers: ultrafast photo-induced spin currents, the
inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an
analytical model, such spintronic route offers unique possibilities for
systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer
generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel
source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals
in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and
cost.Comment: 18 pages, 10 figure
Entropy production and fluctuation theorems under feedback control: the molecular refrigerator model revisited
We revisit the model of a Brownian particle in a heat bath submitted to an
actively controlled force proportional to the velocity that leads to thermal
noise reduction (cold damping). We investigate the influence of the continuous
feedback on the fluctuations of the total entropy production and show that the
explicit expression of the detailed fluctuation theorem involves different
dynamics and observables in the forward and backward processes. As an
illustration, we study the analytically solvable case of a harmonic oscillator
and calculate the characteristic function of the entropy production in a
nonequilibrium steady state. We then determine the corresponding large
deviation function which results from an unusual interplay between 'boundary'
and 'bulk' contributions.Comment: 16 pages, 5 figures. References 9,10,13,14,15 added. A few changes in
the text. Accepted for publication in J. Stat. Mec
y scaling in electron-nucleus scattering
Data on inclusive electron scattering from A = 4, 12, 27, 56, 197 nuclei at large momentum transfer are presented and analyzed in terms of y scaling. We find that the data do scale for y 1), and we study the convergence of the scaling function with the momentum transfer Q^2 and A
Elastic behavior in Contact Dynamics of rigid particles
The systematic errors due to the practical implementation of the Contact
Dynamics method for simulation of dense granular media are examined. It is
shown that, using the usual iterative solver to simulate a chain of rigid
particles, effective elasticity and sound propagation with a finite velocity
occur. The characteristics of these phenomena are investigated analytically and
numerically in order to assess the limits of applicability of this simulation
method and to compare it with soft particle molecular dynamics.Comment: submitted to PRE, 7 pages, 6 figure
Growth factors in multiple myeloma: a comprehensive analysis of their expression in tumor cells and bone marrow environment using Affymetrix microarrays
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