1,417 research outputs found
A thermionic energy converter with a molybdenum-alumina cermet emitter
A study is made of the properties of cermets as electrode materials for thermionic energy converters. For thermodynamic reasons it is expected that all cermets composed of pure Mo and refractory oxides have the same bare work function. From data on the work function of Mo in an oxygen atmosphere this bare work function is estimated to be F=4.9 eV (at T=1400¿°C). Experimentally, the bare work function of Al2O3-Mo cermets was found to be F=4.5 eV, independent of the relative amounts of Al2O3 and Mo. The cesiated work function of the Al2O3-Mo cermets was found to be 0.15 eV lower than the cesiated work function of pure Mo. The bare work function of Mo3Al was found to be F=4.0 eV. The cesiated work function of Mo3Al at collector temperature conditions was 0.3 eV lower than the cesiated work function of pure Mo. The electrical power density of a diode with an Al2O3-Mo cermet emitter was 0.4 W/cm2 at 1300¿°C. The barrier index at this temperature was 2.36 V. The high barrier index is attributed to a high plasma voltage drop Vd=0.91 V
Precision cutting of glassy polymers: influence of aging on the cutting process
ABSTRACT This paper presents the results of an experimental study on the influence of aging on the cutting mechanics of glassy polymers. Polystyrene (PS), a glassy polymer, typically behaves brittle when subjected to a stress, it can be made ductile by rejuvenation. It was expected that PS would show a different cutting behaviour when it would be aged or rejuvenated. To investigate this two different molecular weight PS grades were used. Both aged and (mechanically) rejuvenated samples were made from each grade and cut. Cutting forces, chip morphology and surface quality were investigated. Although the chips showed no differences in brittleness and ductility, the measured cutting forces indicated that there is a difference between aged and rejuvenated PS. Also an interesting difference in cutting forces between the two PS grades was found. Investigation of the surface quality of the PS samples showed that the aged samples have smoother surfaces than the rejuvenated samples. It can be concluded that aging does have effect on the cutting mechanics and the obtained surface roughness
FSH isoform pattern in classic galactosemia
Female classic galactosemia patients suffer from primary ovarian insufficiency (POI). The cause for this long-term complication is not fully understood. One of the proposed mechanisms is that hypoglycosylation of complex molecules, a known secondary phenomenon of galactosemia, leads to FSH dysfunction. An earlier study showed less acidic isoforms of FSH in serum samples of two classic galactosemia patients compared to controls, indicating hypoglycosylation. In this study, FSH isoform patterns of five classic galactosemia patients with POI were compared to the pattern obtained in two patients with a primary glycosylation disorder (phosphomannomutase-2-deficient congenital disorders of glycosylation, PMM2-CDG) and POI, and in five postmenopausal women as controls. We used FPLC chromatofocussing with measurement of FSH concentration per fraction, and discovered that there were no significant differences between galactosemia patients, PMM2-CDG patients and postmenopausal controls. Our results do not support that FSH dysfunction due to a less acidic isoform pattern because of hypoglycosylation is a key mechanism of POI in this disease
The need for a new toxicity testing and risk analysis paradigm to implement REACH or any other large scale testing initiative
A thermionic energy converter with polycrystalline molybdenum electrodes
A research diode with polycrystalline molybdenum electrodes is described. Voltage-current characteristics are presented as a function of the cesium reservoir temperature. A power density of 4 W/cm2 is obtained at an emitter temperature of 1400¿°C. The influence of the temperatures of the emitter, collector, and cesium reservoir and of the interelectrode distance is experimentally investigated. Physical explanations for the various effects are given. The work function of the polycrystalline molybdenum emitter in a cesium atmosphere is evaluated as 2.5–2.7 eV depending on the reduced emitter temperature (i.e., the emitter temperature divided by the cesium reservoir temperature). A barrier index Vb =2.0 eV and a cesium plasma drop Vd =0.4 eV are found
Ground states and dynamics of population-imbalanced Fermi condensates in one dimension
By using the numerically exact density-matrix renormalization group (DMRG)
approach, we investigate the ground states of harmonically trapped
one-dimensional (1D) fermions with population imbalance and find that the
Larkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with
nonzero center-of-mass momentum, is realized for a wide range of parameters.
The phase diagram comprising the two phases of i) an LO state at the trap
center and a balanced condensate at the periphery and ii) an LO state at the
trap center and a pure majority component at the periphery, is obtained. The
reduced two-body density matrix indicates that most of the minority atoms
contribute to the LO-type quasi-condensate. With the time-dependent DMRG, we
also investigate the real-time dynamics of a system of 1D fermions in response
to a spin-flip excitation.Comment: 20 pages, 15 figures, accepted for publication in New Journal of
Physic
Imbalanced Superfluid Phase of a Trapped Fermi Gas in the BCS-BEC Crossover Regime
We theoretically investigate the ground state of trapped neutral fermions
with population imbalance in the BCS-BEC crossover regime. On the basis of the
single-channel Hamiltonian, we perform full numerical calculations of the
Bogoliubov-de Gennes equation coupled with the regularized gap and number
equations. The zero-temperature phase diagram in the crossover regime is
presented, where the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state
governs the weak-coupling BCS region of a resonance. It is found that the FFLO
oscillation vanishes in the BEC side, in which the system under population
imbalance turns into a phase separation (PS) between locally binding superfluid
and fully polarized spin domains. We also demonstrate numerical calculations
with a large particle number O(10^5), comparable to that observed in recent
experiments. The resulting density profile on a resonance yields the PS, which
is in good agreement with the recent experiments, while the FFLO modulation
exists in the pairing field. It is also proposed that the most favorable
location for the detection of the FFLO oscillation is in the vicinity of the
critical population imbalance in the weak coupling BCS regime, where the
oscillation periodicity becomes much larger than the interparticle spacing.
Finally, we analyze the radio-frequency (RF) spectroscopy in the imbalanced
system. The clear difference in the RF spectroscopy between BCS and BEC sides
reveals the structure of the pairing field and local ``magnetization''.Comment: 16 pages, 13 figures, replaced by the version to appear in J. Phys.
Soc. Jp
Finite temperature phase diagram of a polarised Fermi condensate
The two-component Fermi gas is the simplest fermion system displaying
superfluidity, and as such finds applications ranging from the theory of
superconductivity to QCD. Ultracold atomic gases provide an exceptionally clean
realization of this system, where the interatomic interaction and the atom
species population are both independent, tuneable parameters. This allows one
to investigate the Fermi gas with imbalanced spin populations, which had
previously been experimentally elusive, and this prospect has stimulated much
theoretical activity. Here we show that the finite temperature phase diagram
contains a region of phase separation between the superfluid and normal states
that touches the boundary of second-order superfluid transitions at a
tricritical point, reminiscent of the phase diagram of He-He mixtures.
A variation of interaction strength then results in a line of tricritical
points that terminates at zero temperature on the molecular Bose-Einstein
condensate (BEC) side. On this basis, we argue that tricritical points will
play an important role in the recent experiments on polarised atomic Fermi
gases.Comment: 6 pages, 4 figures. Manuscript extended and figures modified. For
final version, see Nature Physic
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