51,197 research outputs found
Semiclassical approach to Bose-Einstein condensates in a triple well potential
We present a new approach for the analysis of Bose-Einstein condensates in a
few mode approximation. This method has already been used to successfully
analyze the vibrational modes in various molecular systems and offers a new
perspective on the dynamics in many particle bosonic systems. We discuss a
system consisting of a Bose-Einstein condensate in a triple well potential.
Such systems correspond to classical Hamiltonian systems with three degrees of
freedom. The semiclassical approach allows a simple visualization of the
eigenstates of the quantum system referring to the underlying classical
dynamics. From this classification we can read off the dynamical properties of
the eigenstates such as particle exchange between the wells and entanglement
without further calculations. In addition, this approach offers new insights
into the validity of the mean-field description of the many particle system by
the Gross-Pitaevskii equation, since we make use of exactly this correspondence
in our semiclassical analysis. We choose a three mode system in order to
visualize it easily and, moreover, to have a sufficiently interesting
structure, although the method can also be extended to higher dimensional
systems.Comment: 15 pages, 15 figure
Canonically Transformed Detectors Applied to the Classical Inverse Scattering Problem
The concept of measurement in classical scattering is interpreted as an
overlap of a particle packet with some area in phase space that describes the
detector. Considering that usually we record the passage of particles at some
point in space, a common detector is described e.g. for one-dimensional systems
as a narrow strip in phase space. We generalize this concept allowing this
strip to be transformed by some, possibly non-linear, canonical transformation,
introducing thus a canonically transformed detector. We show such detectors to
be useful in the context of the inverse scattering problem in situations where
recently discovered scattering echoes could not be seen without their help.
More relevant applications in quantum systems are suggested.Comment: 8 pages, 15 figures. Better figures can be found in the original
article, wich can be found in
http://www.sm.luth.se/~norbert/home_journal/electronic/v12s1.html Related
movies can be found in www.cicc.unam.mx/~mau
Measurements of a Quantum Dot with an Impedance-Matching On-Chip LC Resonator at GHz Frequencies
We report the realization of a bonded-bridge on-chip superconducting coil and
its use in impedance-matching a highly ohmic quantum dot (QD) to a
measurement setup. The coil, modeled as a lumped-element resonator, is
more compact and has a wider bandwidth than resonators based on coplanar
transmission lines (e.g. impedance transformers and stub tuners) at
potentially better signal-to-noise ratios. In particular for measurements of
radiation emitted by the device, such as shot noise, the 50 larger
bandwidth reduces the time to acquire the spectral density. The resonance
frequency, close to 3.25 GHz, is three times higher than that of the one
previously reported wire-bonded coil. As a proof of principle, we fabricated an
circuit that achieves impedance-matching to a load
and validate it with a load defined by a carbon nanotube QD of which we measure
the shot noise in the Coulomb blockade regime.Comment: 7 pages, 6 figure
Strong electron correlations in cobalt valence tautomers
We have examined cobalt based valence tautomer molecules such as
Co(SQ)(phen) using density functional theory (DFT) and variational
configuration interaction (VCI) approaches based upon a model Hamiltonian. Our
DFT results extend earlier work by finding a reduced total energy gap (order
0.6 eV) between high temperature and low temperature states when we fully relax
the coordinates (relative to experimental ones). Futhermore we demonstrate that
the charge transfer picture based upon formal valence arguments succeeds
qualitatively while failing quantitatively due to strong covalency between the
Co 3 orbitals and ligand orbitals. With the VCI approach, we argue that
the high temperature, high spin phase is strongly mixed valent, with about 30 %
admixture of Co(III) into the predominantly Co(II) ground state. We confirm
this mixed valence through a fit to the XANES spectra. Moreover, the strong
electron correlations of the mixed valent phase provide an energy lowering of
about 0.2-0.3 eV of the high temperature phase relative to the low temperature
one. Finally, we use the domain model to account for the extraordinarily large
entropy and enthalpy values associated with the transition.Comment: 10 pages, 4 figures, submitted to J. Chem. Phy
Quantum and classical echoes in scattering systems described by simple Smale horseshoes
We explore the quantum scattering of systems classically described by binary
and other low order Smale horseshoes, in a stage of development where the
stable island associated with the inner periodic orbit is large, but chaos
around this island is well developed. For short incoming pulses we find
periodic echoes modulating an exponential decay over many periods. The period
is directly related to the development stage of the horseshoe. We exemplify our
studies with a one-dimensional system periodically kicked in time and we
mention possible experiments.Comment: 7 pages with 6 reduced quality figures! Please contact the authors
([email protected]) for an original good quality pre-prin
High electrochemical activity of the oxide phase in model ceria–Pt and ceria–Ni composite anodes
Fuel cells, and in particular solid-oxide fuel cells (SOFCs), enable high-efficiency conversion of chemical fuels into useful electrical energy and, as such, are expected to play a major role in a sustainable-energy future. A key step in the fuel-cell energy-conversion process is the electro-oxidation of the fuel at the anode. There has been increasing evidence in recent years that the presence of CeO_2-based oxides (ceria) in the anodes of SOFCs with oxygen-ion-conducting electrolytes significantly lowers the activation overpotential for hydrogen oxidation. Most of these studies, however, employ porous, composite electrode structures with ill-defined geometry and uncontrolled interfacial properties. Accordingly, the means by which electrocatalysis is enhanced has remained unclear. Here we demonstrate unambiguously, through the use of ceria–metal structures with well-defined geometries and interfaces, that the near-equilibrium H_2 oxidation reaction pathway is dominated by electrocatalysis at the oxide/gas interface with minimal contributions from the oxide/metal/gas triple-phase boundaries, even for structures with reaction-site densities approaching those of commercial SOFCs. This insight points towards ceria nanostructuring as a route to enhanced activity, rather than the traditional paradigm of metal-catalyst nanostructuring
Titanium and water-rich metamorphic olivine in high-pressure serpentinites from the Voltri Massif (Ligurian Alps, Italy): evidence for deep subduction of high-field strength and fluid-mobile elements
Titanium- and water-rich metamorphic olivine (Fo 86-88) is reported from partially dehydrated serpentinites from the Voltri complex, Ligurian Alps. The rocks are composed of mostly antigorite and olivine in addition to magnetite, chlorite, clinopyroxene and Ti-clinohumite. In situ secondary ion mass spectrometry (SIMS) data show that metamorphic olivine has very high and strongly correlated H2O (up to 0.7 wt%) and TiO2 contents (up to 0.85 wt%). Ti-rich olivine shows colourless to yellow pleochroism. Olivine associated with Ti-clinohumite contains low Ti, suggesting that Ti-rich olivine is not the breakdown product of Ti-clinohumite. Fourier transform infrared spectroscopy (FTIR) absorption spectra show peaks of serpentine, Ti-clinohumite and OH-related Si vacancies. Combining FTIR and SIMS data, we suggest the presence of clustered planar defects or nanoscale exsolutions of Ti-clinohumite in olivine. These defects or exsolutions contain more H2O (x similar to 0.1 in the formula 4Mg(2)SiO(4)center dot(1-x)Mg(OH, F)(2)center dot xTiO(2)) than Ti-clinohumite in the sample matrix (x = 0.34-0.46). In addition to TiO2 and H2O, secondary olivine contains significant Li (2-60 ppm), B (10-20 ppm), F (10-130 ppm) and Zr (0.9-2.1 ppm). It is enriched in B-11 (delta B-11 = +17 to +23 parts per thousand). Our data indicate that secondary olivine may play a significant role in transporting water, high-field strength and fluid-mobile elements into the deeper mantle as well as introduce significant B isotope anomalies. Release of hydrogen from H2O-rich olivine subducted into the deep mantle may result in strongly reduced mantle domains.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000043439/1SEQ:1PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000043439ADJUST_YN:YEMP_ID:A076886DEPT_CD:3345CITE_RATE:3.476FILENAME:de hoog et al-14-cmp-titanium- and water-ric.pdfDEPT_NM:지구환경과학부SCOPUS_YN:NCONFIRM:
Ionic and Electronic Conductivity of Nanostructured, Samaria-Doped Ceria
The ionic and electronic conductivities of samaria doped ceria electrolytes, Ce_(0.85)Sm_(0.15)O_(1.925−δ), with nanometric grain size have been evaluated. Nanostructured bulk specimens were obtained using a combination of high specific-surface-area starting materials and suitable sintering profiles under conventional, pressureless conditions. Bulk specimens with relatively high density (≥92% of theoretical density) and low medium grain size (as small as 33 nm) were achieved. Electrical A.C. impedance spectra were recorded over wide temperature (150 to 650°C) and oxygen partial pressure ranges (0.21 to 10^(−31) atm). Under all measurement conditions the total conductivity decreased monotonically with decreasing grain size. In both the electrolytic and mixed conducting regimes this behavior is attributed to the high number density of high resistance grain boundaries. The results suggest a possible variation in effective grain boundary width with grain size, as well as a possible variation in specific grain boundary resistance with decreasing oxygen partial pressure. No evidence appears for either enhanced reducibility or enhanced electronic conductivity upon nanostructuring
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