1,703 research outputs found
Evidence of random magnetic anisotropy in ferrihydrite nanoparticles based on analysis of statistical distributions
We show that the magnetic anisotropy energy of antiferromagnetic ferrihydrite
depends on the square root of the nanoparticles volume, using a method based on
the analysis of statistical distributions. The size distribution was obtained
by transmission electron microscopy, and the anisotropy energy distributions
were obtained from ac magnetic susceptibility and magnetic relaxation. The
square root dependence corresponds to random local anisotropy, whose average is
given by its variance, and can be understood in terms of the recently proposed
single phase homogeneous structure of ferrihydrite.Comment: 6 pages, 2 figure
Mg2+-doped poly(ε-caprolactone)/siloxane biohybrids
Electrolytes based on a poly(ε-caprolactone) (PCL)/siloxane organic/inorganic host framework doped with magnesium triflate (Mg(CF3SO3)2) were synthesized by the sol-gel process. In the biohybrid matrix short PCL chains are covalently bonded via urethane linkages to the siliceous network. In this study the salt content of samples was identified using the conventional n notation, where n indicates the number of (C(=O)(CH2)5O) PCL repeat units per Mg2+ ion. Materials with compositions ranging from n=∞ to 2 were prepared. The only composition prepared that is not entirely amorphous is that with n = 1. Xerogels with n ≥ 7 are thermally stable up to up to at least 200 ºC. The most conducting ormolyte of the series is that with n = 26 (5.9x10-9 and 9.8x10-7 Scm-1 at 24 and 104 ºC, respectively).Fundação para a Ciência e Tecnologi
Structure, thermal properties, conductivity and electrochemical stability of di-urethanesil hybrids doped with LiCF3SO3
Variable chain length di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks were prepared by application of a sol-gel strategy. These materials, designated as di-urethanesils (represented as d-Ut(Y’), where Y’ indicates the average molecular weight of the polymer segment), were doped with lithium triflate (LiCF3SO3). The two host hybrid matrices used, d-Ut(300) and d-Ut(600), incorporate POE chains with approximately 6 and 13 (OCH2CH2) repeat units, respectively. All the samples studied, with compositions ∞ > n ≥ 1 (where n is the molar ratio of (OCH2CH2) repeat units per Li+),, are entirely amorphous. The di-urethanesils are thermally stable up to at least 200 ºC. At room temperature the conductivity maxima of the d-Ut(300)- and d-Ut(600)-based di-urethanesil families are located at n = 1 (approximately 2.0x10-6 and 7.4x10-5 Scm-1, respectively). At about 100 ºC, both these samples also exhibit the highest conductivity of the two electrolyte systems (approximately 1.6x10-4 and 1.0x10-3 Scm-1, respectively). The d-Ut(600)-based xerogel with n = 1 displays excellent redox stability.Fundação para a Ciência e a Tecnologia (FCT
Morphological and conductivity studies of di-ureasil xerogels containing lithium triflate
Sol–gel derived poly(oxyethylene)/siloxane hybrids doped with lithium triflate, LiCF3SO3, have been investigated. The host hybrid matrix of these materials, named di-ureasil and represented by U(600), is composed by a siliceous framework to which polyether chains containing 8.5 oxyethylene repeat units are covalently bonded through urea linkages. Xerogel samples U(600)nLiCF3SO3 with n (where n is the molar ratio of oxyethylene moieties per Li+ ion) between ∞ and 0.1 have been examined. X-ray diffraction and differential scanning calorimetry have provided conclusive evidence that the xerogels analyzed are entirely amorphous. The salt-rich material with n=1 exhibits the highest conductivity over the whole range of temperature analyzed (e.g. 4.3×10−6 and 2.0×10−4 Ω−1 cm−1, respectively, at 25 and 94 °C).Fundação para a Ciência e a Tecnologia (FCT
Short chain U(600) di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with lanthanum triflate salt
Promising La3+-doped electrolytes based on a hybrid poly(oxyethylene)/siliceous host matrix, U(600), have been produced. The organic and inorganic components of the hybrid structure are covalently bonded through urea linkages. The low molecular weight of the polyether segments of U(600) is thought to be responsible for the total amorphous character and high conductivity at room temperature (1.1×10−4 S cm−1) of these ormolytes.Fundação para a Ciência e a Tecnologia (FCT
Discovery of the acetyl cation, CH3CO+, in space and in the laboratory
Using the Yebes 40m and IRAM 30m radiotelescopes, we detected two series of
harmonically related lines in space that can be fitted to a symmetric rotor.
The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and
L1544. High level of theory ab initio calculations indicate that the best
possible candidate is the acetyl cation, CH3CO+, which is the most stable
product resulting from the protonation of ketene. We have produced this species
in the laboratory and observed its rotational transitions Ju = 10 up to Ju =
27. Hence, we report the discovery of CH3CO+ in space based on our
observations, theoretical calculations, and laboratory experiments. The derived
rotational and distortion constants allow us to predict the spectrum of CH3CO+
with high accuracy up to 500 GHz. We derive an abundance ratio
N(H2CCO)/N(CH3CO+) = 44. The high abundance of the protonated form of H2CCO is
due to the high proton affinity of the neutral species. The other isomer,
H2CCOH+, is found to be 178.9 kJ/mol above CH3CO+. The observed intensity ratio
between the K=0 and K=1 lines, 2.2, strongly suggests that the A and E symmetry
states have suffered interconversion processes due to collisions with H and/or
H2, or during their formation through the reaction of H3+ with H2CCO.Comment: Accepted for publication in A&A Letter
Short-chain di-ureasil ormolytes doped with potassium triflate: Phase diagram and conductivity behavior
Di-urea cross-linked poly(oxyethylene)/siloxane hybrids, synthesized by the sol-gel process and containing a wide concentration range of potassium triflate, KCF3SO3, have been analyzed by x-ray diffraction and differential scanning calorimetry. The pseudo-phase diagram proposed has been taken into account in the interpretation of the complex impedance measurements. The xerogels prepared are obtained as transparent, thin monoliths . At room temperature the highest conductivity found was 2 x 10-6Scm-1.Fundação para a Ciência e a Tecnologia (FCT
Galacturonosyltransferase 4 silencing alters pectin composition and carbon partitioning in tomato
Pectin is a main component of the plant cell wall and is the most complex family of polysaccharides in nature. Its composition is essential for the normal growth and morphology pattern, as demonstrated by pectin-defective mutant phenotypes. Besides this basic role in plant physiology, in tomato, pectin structure contributes to very important quality traits such as fruit firmness. Sixty-seven different enzymatic activities have been suggested to be required for pectin biosynthesis, but only a few genes have been identified and studied so far. This study characterized the tomato galacturonosyltransferase (GAUT) family and performed a detailed functional study of the GAUT4 gene. The tomato genome harbours all genes orthologous to those described previously in Arabidopsis thaliana, and a transcriptional profile revealed that the GAUT4 gene was expressed at higher levels in developing organs. GAUT4-silenced tomato plants exhibited an increment in vegetative biomass associated with palisade parenchyma enlargement. Silenced fruits showed an altered pectin composition and accumulated less starch along with a reduced amount of pectin, which coincided with an increase in firmness. Moreover, the harvest index was dramatically reduced as a consequence of the reduction in the fruit weight and number. Altogether, these results suggest that, beyond its role in pectin biosynthesis, GAUT4 interferes with carbon metabolism, partitioning, and allocation. Hence, this cell-wall-related gene seems to be key in determining plant growth and fruit production in tomato
Decoherence-protected quantum gates for a hybrid solid-state spin register
Protecting the dynamics of coupled quantum systems from decoherence by the
environment is a key challenge for solid-state quantum information processing.
An idle qubit can be efficiently insulated from the outside world via dynamical
decoupling, as has recently been demonstrated for individual solid-state
qubits. However, protection of qubit coherence during a multi-qubit gate poses
a non-trivial problem: in general the decoupling disrupts the inter-qubit
dynamics, and hence conflicts with gate operation. This problem is particularly
salient for hybrid systems, wherein different types of qubits evolve and
decohere at vastly different rates. Here we present the integration of
dynamical decoupling into quantum gates for a paradigmatic hybrid system, the
electron-nuclear spin register. Our design harnesses the internal resonance in
the coupled-spin system to resolve the conflict between gate operation and
decoupling. We experimentally demonstrate these gates on a two-qubit register
in diamond operating at room temperature. Quantum tomography reveals that the
qubits involved in the gate operation are protected as accurately as idle
qubits. We further illustrate the power of our design by executing Grover's
quantum search algorithm, achieving fidelities above 90% even though the
execution time exceeds the electron spin dephasing time by two orders of
magnitude. Our results directly enable decoherence-protected interface gates
between different types of promising solid-state qubits. Ultimately, quantum
gates with integrated decoupling may enable reaching the accuracy threshold for
fault-tolerant quantum information processing with solid-state devices.Comment: This is original submitted version of the paper. The revised and
finalized version is in print, and is subjected to the embargo and other
editorial restrictions of the Nature journa
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