4,315 research outputs found
Quantified Uncertainty in Thermodynamic Modeling for Materials Design
Phase fractions, compositions and energies of the stable phases as a function
of macroscopic composition, temperature, and pressure (X-T-P) are the principle
correlations needed for the design of new materials and improvement of existing
materials. They are the outcomes of thermodynamic modeling based on the
CALculation of PHAse Diagrams (CALPHAD) approach. The accuracy of CALPHAD
predictions vary widely in X-T-P space due to experimental error, model
inadequacy and unequal data coverage. In response, researchers have developed
frameworks to quantify the uncertainty of thermodynamic property model
parameters and propagate it to phase diagram predictions. In previous studies,
uncertainty was represented as intervals on phase boundaries (with respect to
composition) or invariant reactions (with respect to temperature) and was
unable to represent the uncertainty in eutectoid reactions or in the stability
of phase regions. In this work, we propose a suite of tools that leverages
samples from the multivariate model parameter distribution to represent
uncertainty in forms that surpass previous limitations and are well suited to
materials design. These representations include the distribution of phase
diagrams and their features, as well as the dependence of phase stability and
the distributions of phase fraction, composition activity and Gibbs energy on
X-T-P location - irrespective of the total number of components. Most
critically, the new methodology allows the material designer to interrogate a
certain composition and temperature domain and get in return the probability of
different phases to be stable, which can positively impact materials design
Quasi one dimensional He inside carbon nanotubes
We report results of diffusion Monte Carlo calculations for both He
absorbed in a narrow single walled carbon nanotube (R = 3.42 \AA) and strictly
one dimensional He. Inside the tube, the binding energy of liquid He is
approximately three times larger than on planar graphite. At low linear
densities, He in a nanotube is an experimental realization of a
one-dimensional quantum fluid. However, when the density increases the
structural and energetic properties of both systems differ. At high density, a
quasi-continuous liquid-solid phase transition is observed in both cases.Comment: 11 pages, 3ps figures, to appear in Phys. Rev. B (RC
Helium mixtures in nanotube bundles
An analogue to Raoult's law is determined for the case of a 3He-4He mixture
adsorbed in the interstitial channels of a bundle of carbon nanotubes. Unlike
the case of He mixtures in other environments, the ratio of the partial
pressures of the coexisting vapor is found to be a simple function of the ratio
of concentrations within the nanotube bundle.Comment: 3 pages, no figures, submitted to Phys. Rev. Let
Formation Time of a Fermion Pair Condensate
The formation time of a condensate of fermionic atom pairs close to a
Feshbach resonance was studied. This was done using a phase-shift method in
which the delayed response of the many-body system to a modulation of the
interaction strength was recorded. The observable was the fraction of condensed
molecules in the cloud after a rapid magnetic field ramp across the Feshbach
resonance. The measured response time was slow compared to the rapid ramp,
which provides final proof that the molecular condensates reflect the presence
of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure
Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance
We have observed Bose-Einstein condensation of pairs of fermionic atoms in an
ultracold ^6Li gas at magnetic fields above a Feshbach resonance, where no
stable ^6Li_2 molecules would exist in vacuum. We accurately determined the
position of the resonance to be 822+-3 G. Molecular Bose-Einstein condensates
were detected after a fast magnetic field ramp, which transferred pairs of
atoms at close distances into bound molecules. Condensate fractions as high as
80% were obtained. The large condensate fractions are interpreted in terms of
pre-existing molecules which are quasi-stable even above the two-body Feshbach
resonance due to the presence of the degenerate Fermi gas.Comment: submitted to PRL. v3: clarifying revisions, added referenc
Fifty-fold improvement in the number of quantum degenerate fermionic atoms
We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7
atoms, an improvement by a factor of fifty over all previous experiments with
degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic
Na-23 in the F=2, upper hyperfine ground state. We have also achieved
Bose-Einstein condensation of F=2 sodium atoms by direct evaporation
Characterisation and activity of mixed metal oxide catalysts for the gas-phase selective oxidation of toluene
Mixed metal bi-component oxide catalysts, including Fe/Mo, U/Mo, U/W, Fe/U, U/V and U/Sb have been prepared, characterised and evaluated for gas phase selective toluene oxidation. Selective toluene oxidation activity to form benzaldehyde was exhibited by Fe/Mo, U/Mo and U/W mixed oxide catalysts. The Fe/Mo catalyst produced the highest benzaldehyde yield. Catalysts that formed benzaldehyde also produced a range of by-products, these were other partial oxidation and coupling products, and preliminary studies of benzaldehyde oxidation suggests they were formed from secondary reactions of benzaldehyde. The Fe/U, Sb/U and U/V catalysts produced only total oxidation to carbon oxides. Catalysts were characterised by X-ray diffraction, laser Raman spectroscopy and temperature programmed reduction. Single molybdate phases were identified for the Fe/Mo and U/Mo catalysts, and a mixture of uranium molybdate and WO3 was identified for the U/W catalyst. Results suggest that the formation of a molybdate phase is important for the selective oxidation of toluene. In contrast, the U/Fe catalyst was a mixture of U3O8 and V2O5, whilst the Fe/U catalyst was comprised of highly dispersed iron oxide on UO3. The presence of U3O8 was responsible for toluene total oxidation. The U/Sb catalyst did not exhibit selective toluene oxidation, but previous studies have demonstrated that the catalyst exhibits high activity for selective propene oxidation. Similar behaviour has been observed for the other catalysts in this study, and it is apparent that catalysts that were selective for toluene oxidation were not selective for propene/propane oxidation and vice versa
Radio-Frequency Spectroscopy of Ultracold Fermions
Radio-frequency techniques were used to study ultracold fermions. We observed
the absence of mean-field "clock" shifts, the dominant source of systematic
error in current atomic clocks based on bosonic atoms. This is a direct
consequence of fermionic antisymmetry. Resonance shifts proportional to
interaction strengths were observed in a three-level system. However, in the
strongly interacting regime, these shifts became very small, reflecting the
quantum unitarity limit and many-body effects. This insight into an interacting
Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure
Kidney Transplantation and Diagnostic Imaging:The Early Days and Future Advancements of Transplant Surgery
The first steps for modern organ transplantation were taken by Emerich Ullmann (Vienne, Austria) in 1902, with a dog-to-dog kidney transplant, and ultimate success was achieved by Joseph Murray in 1954, with the Boston twin brothers. In the same time period, the ground-breaking work of Wilhelm C. Röntgen (1895) and Maria Sklodowska-Curie (1903), on X-rays and radioactivity, enabled the introduction of diagnostic imaging. In the years thereafter, kidney transplantation and diagnostic imaging followed a synergistic path for their development, with key discoveries in transplant rejection pathways, immunosuppressive therapies, and the integration of diagnostic imaging in transplant programs. The first image of a transplanted kidney, a urogram with intravenous contrast, was shown to the public in 1956, and the first recommendations for transplantation diagnostic imaging were published in 1958. Transplant surgeons were eager to use innovative diagnostic modalities, with renal scintigraphy in the 1960s, as well as ultrasound and computed tomography in the 1970s. The use of innovative diagnostic modalities has had a great impact on the reduction of post-operative complications in kidney transplantation, making it one of the key factors for successful transplantation. For the new generation of transplant surgeons, the historical alignment between transplant surgery and diagnostic imaging can be a motivator for future innovations
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