119 research outputs found
Sodium lactobionate sucrose solution for canine liver and kidney preservation.
With 24-hour preservation of canine liver, SLS solution showed inferior animal survival to UW solution. The lactobionate, raffinose, glutathione, and hydroxyethyl starch in UW solution have been shown to be important for liver preservation. However, our results suggest that sucrose should not be substituted for raffinose for the preservation of livers. In contrast to the liver, SLS solution performed the same or even better than UW solution for kidney preservation. The substitution of sucrose for raffinose, along with the addition of CPZ has either no effect or a slightly positive effect on kidney preservation. In conclusion, SLS solution may be a suitable solution for preserving canine kidneys, but is not suitable for liver preservation. These findings suggest that future development of preservation solutions should be focused on the needs of specific organs and not toward a generic, all encompassing preservation solution
The influence of charge and magnetic order on polaron and acoustic phonon dynamics in LuFe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e
Femtosecond optical pump-probe spectroscopy is used to reveal the influence of charge and magnetic order on polaron dynamics and coherent acoustic phonon oscillations in single crystals of charge-ordered, ferrimagnetic LuFe2O4. We experimentally observed the influence of magnetic order on polaron dynamics. We also observed a correlation between charge order and the amplitude of the acoustic phonon oscillations, due to photoinduced changes in the lattice constant that originate from the photoexcited electrons. This provides insight into the general behavior of coherent acoustic phonon oscillations in charge-ordered materials
Attosecond angular streaking and tunnelling time in atomic hydrogen
Tunnelling, one of the key features of quantum mechanics, ignited an ongoing
debate about the value, meaning and interpretation of 'tunnelling time'. Until
recently the debate was purely theoretical, with the process considered to be
instantaneous for all practical purposes. This changed with the development of
ultrafast lasers and in particular, the 'attoclock' technique that is used to
probe the attosecond dynamics of electrons. Although the initial attoclock
measurements hinted at instantaneous tunnelling, later experiments contradicted
those findings, claiming to have measured finite tunnelling times. In each case
these measurements were performed with multi-electron atoms. Atomic hydrogen
(H), the simplest atomic system with a single electron, can be 'exactly'
(subject only to numerical limitations) modelled using numerical solutions of
the 3D-TDSE with measured experimental parameters and acts as a convenient
benchmark for both accurate experimental measurements and calculations. Here we
report the first attoclock experiment performed on H and find that our
experimentally determined offset angles are in excellent agreement with
accurate 3D-TDSE simulations performed using our experimental pulse parameters.
The same simulations with a short-range Yukawa potential result in zero offset
angles for all intensities. We conclude that the offset angle measured in the
attoclock experiments originates entirely from electron scattering by the
long-range Coulomb potential with no contribution from tunnelling time delay.
That conclusion is supported by empirical observation that the electron offset
angles follow closely the simple formula for the deflection angle of electrons
undergoing classical Rutherford scattering by the Coulomb potential. Thus we
confirm that, in H, tunnelling is instantaneous (with an upperbound of 1.8 as)
within our experimental and numerical uncertainty.Comment: 7 figure
Structure and magnetism of new rare- earth-free intermetallic compounds: Fe3+xCo3âxTi2 (0 †x †3)
We report the fabrication of a set of new rare-earth-free magnetic compounds, which form the Fe3Co3Ti2-type hexagonal structure with P-6m2 symmetry. Neutron powder diffraction shows a significant Fe/Co anti-site mixing in the Fe3Co3Ti2 structure, which has a strong effect on the magnetocrystalline anisotropy as revealed by first-principle calculations. Increasing substitution of Fe atoms for Co in the Fe3Co3Ti2 lattice leads to the formation of Fe4Co2Ti2 , Fe5CoTi, and Fe6Ti2 with significantly improved permanent-magnet properties. A high magnetic anisotropy (13.0 Mergs/cm3) and sat- uration magnetic polarization (11.4 kG) are achieved at 10 K by altering the atomic arrangements and decreasing Fe/Co occupancy disorder
Magnetism of new metastable cobalt-nitride compounds
The search for new magnetic materials with high magnetization and magnetocrystalline anisotropy is important for a wide range of applications including information and energy processing. There is only a limited number of naturally occurring magnetic compounds that are suitable. This situation stimulates an exploration of new phases that occur far from thermal-equilibrium conditions, but their stabilization is generally inhibited due to high positive formation energies. Here a nanocluster-deposition method has enabled the discovery of a set of new non-equilibrium Co-N intermetallic compounds. The experimental search was assisted by computational methods including adaptive-genetic-algorithm and electronic- structure calculations. Conventional wisdom is that the interstitial or substitutional solubility of N in Co is much lower than that in Fe and that N in Co in equilibrium alloys does not produce materials with significant magnetization and anisotropy. By contrast, our experiments identify new Co-N compounds with favorable magnetic properties including hexagonal Co3N nanoparticles with a high saturation magnetic polarization (Js = 1.28 T or 12.8 kG) and an appreciable uniaxial magnetocrystalline anisotropy (K1 = 1.01 MJ/m3 or 10.1 Mergs/cm3). This research provides a pathway for uncovering new magnetic compounds with computational efficiency beyond the existing materials database, which is significant for future technologies
On the Structural Origin of the Single-ion Magnetic Anisotropy in LuFeO3
Electronic structures for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectra shape and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states has not changed, the spectra are sensitive to the changes in the local environments of the Fe3+ and Lu3+ sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe3+, which are non-zero and uneven. The single ion anisotropy on Fe3+ sites is found to originate from these uneven occupancies of the spin minority states via spin-orbit coupling in LuFeO3
Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3
The magnetic interactions between rare-earth and Fe ions in hexagonal rare-earth ferrites (h-RFeO3), may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate the interaction strength between the rare-earth and Fe ions as well as the magnetic moment of the rare-earth ions, element-specific magnetic characterization is needed. Using x-ray magnetic circular dichroism, we have studied the ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about 17 kOe. The magnetic moment of Yb is about 1.6ÎŒB at low temperature, significantly reduced compared with the 4.5 ÎŒB moment of a free Yb3+. In addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable enhancement compared with that in h-LuFeO3. These findings directly demonstrate that ferrimagnetic order exists in h-YbFeO3; they also account for the enhancement of magnetization and the reduction of coercivity in h-YbFeO3 compared with those in h-LuFeO3 at low temperature, suggesting an important role for the rare-earth ions in tuning the multiferroic properties of h-RFeO3
Nonvolatile voltage controlled molecular spinâstate switching for memory applications
Nonvolatile, molecular multiferroic devices have now been demonstrated, but it is worth giving some consideration to the issue of whether such devices could be a competitive alternative for solid-state nonvolatile memory. For the Fe (II) spin crossover complex [Fe{H2B(pz)2}2(bipy)], where pz = tris(pyrazol-1-yl)-borohydride and bipy = 2,20-bipyridine, voltage-controlled isothermal changes in the electronic structure and spin state have been demonstrated and are accompanied by changes in conductance. Higher conductance is seen with [Fe{H2B(pz)2}2(bipy)] in the high spin state, while lower conductance occurs for the low spin state. Plausibly, there is the potential here for low-cost molecular solid-state memory because the essential molecular thin films are easily fabricated. However, successful device fabrication does not mean a device that has a practical value. Here, we discuss the progress and challenges yet facing the fabrication of molecular multiferroic devices, which could be considered competitive to silicon
Discovering rare-earth-free magnetic materials through the development of a database
We develop an open-access database that provides a large array of datasets specialized for magnetic compounds as well as magnetic clusters. Our focus is on rare-earth-free magnets. Available datasets include (i) crystallography, (ii) thermodynamic properties, such as the formation energy, and (iii) magnetic properties that are essential for magnetic-material design. Our database features a large number of stable and metastable structures discovered through our adaptive genetic algorithm (AGA) searches. Many of these AGA structures have better magnetic properties when compared to those of the existing rare-earth-free magnets and the theoretical structures in other databases. Our database places particular emphasis on site-specific magnetic data, which are obtained by high-throughput first-principles calculations. Such site-resolved data are indispensable for machine-learning modeling. We illustrate how our data-intensive methods promote efficiency of the experimental discovery of new magnetic materials. Our database provides massive datasets that will facilitate an efficient computational screening, machine-learning-assisted design, and the experimental fabrication of new promising magnets
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