2,370 research outputs found
Ab-initio calculations of the Optical band-gap of TiO2 thin films
Titanium dioxide has been extensively studied in recent decades for its
important photocatalytic application in environmental purification. The search
for a method to narrow the optical band-gap of TiO2 plays a key role for
enhancing its photocatalytic application. The optical band gap of epitaxial
rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on
sapphire and on SrTiO3 substrates was correlated to the lattice constants
estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for
bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of
3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the
optical band gap expansion for both phases, ab-initio calculations were
performed using the Vienna ab-initio software. The calculations for rutile as
well anatase show an almost linear increase of the band gap width with
decreasing volume or increasing lattice constant a. The calculated band gap
fits well with the experimental values. The conclusion from these calculations
is, in order to achieve a smaller band-gap for both, rutile or anatase, the
lattice constants c has to be compressed, and a has to be expanded.Comment: 4 pages, 4 figures, 1 tabl
Error-resistant Single Qubit Gates with Trapped Ions
Coherent operations constitutive for the implementation of single and
multi-qubit quantum gates with trapped ions are demonstrated that are robust
against variations in experimental parameters and intrinsically indeterministic
system parameters. In particular, pulses developed using optimal control theory
are demonstrated for the first time with trapped ions. Their performance as a
function of error parameters is systematically investigated and compared to
composite pulses.Comment: 5 pages 5 figure
Sedimentological studies of the "Ilha de Marchantaria" in the Solimões/Amazon River near Manaus
Sedimentological studies on the Ilha de Marchantaria an island in the Amazon river near Manaus reveal the existence of four different structural main units. A: Sandy channel bars consisting of giant ripples constitute deposits for the formation of islands or newly formed areas of the Varzea. B: Gradual accumulation on the channel bars leads to the formation of point bar ridges which consist chiefly of small-scale ripples. C: Between point bar ridges of different ages there exist swales. During rising water level the river water flows from the downward side into the swales where finegrained sediments are deposited. D: Permanent lakes are formed mainly in the centre of the islands. During low water periods the lakes may be cut of from the river. During high water periods when the whole island is flooded by the river, additional sedimentation takes place especially in the upstream area of the island. There is however, extensive erosion of the banks on the upstream side of the island. By erosion of the upstream end and sedimentation processes on the downstream end the island moves slowly downstream
Integrable dynamics of a discrete curve and the Ablowitz-Ladik hierarchy
We show that the following elementary geometric properties of the motion of a
discrete (i.e. piecewise linear) curve select the integrable dynamics of the
Ablowitz-Ladik hierarchy of evolution equations: i) the set of points
describing the discrete curve lie on the sphere S^3, ii) the distance between
any two subsequant points does not vary in time, iii) the dynamics does not
depend explicitly on the radius of the sphere. These results generalize to a
discrete context our previous work on continuous curves.Comment: LaTeX file, 14 pages + 4 figure
FlexRiLoG -- A SageMath Package for Motions of Graphs
In this paper we present the SageMath package FlexRiLoG (short for flexible
and rigid labelings of graphs). Based on recent results the software generates
motions of graphs using special edge colorings. The package computes and
illustrates the colorings and the motions. We present the structure and usage
of the package
Noncontact modulation calorimetry of metallic liquids in low Earth orbit
Noncontact modulation calorimetry using electromagnetic heating and radiative heat loss under ultrahigh-vacuum conditions has been applied to levitated solid, liquid, and metastable liquid samples. This experiment requires a reduced gravity environment over an extended period of time and allows the measurement of several thermophysical properties, such as the enthalpy of fusion and crystallization, specific heat, total hemispherical emissivity, and effective thermal conductivity with high precision as a function of temperature. From the results on eutectic glass forming Zr-based alloys thermodynamic functions are obtained which describe the glass-forming ability of these alloys
Individual addressing of trapped ions and coupling of motional and spin states using rf radiation
Individual electrodynamically trapped and laser cooled ions are addressed in
frequency space using radio-frequency radiation in the presence of a static
magnetic field gradient. In addition, an interaction between motional and spin
states induced by an rf field is demonstrated employing rf-optical double
resonance spectroscopy. These are two essential experimental steps towards
realizing a novel concept for implementing quantum simulations and quantum
computing with trapped ions.Comment: Replaced with published versio
Thermodynamics of Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5 and Zr57Cu15.4Ni12.6Al10Nb5 bulk metallic glass forming alloys
The differences in the thermodynamic functions between the liquid and the crystalline states of three bulk metallic glass forming alloys, Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5, and Zr57Cu15.4Ni12.6Al10Nb5, were calculated. The heat capacity was measured in the crystalline solid, the amorphous solid, the supercooled liquid, and the equilibrium liquid. Using these heat capacity data and the heats of fusion of the alloys, the differences in the thermodynamic functions between the liquid and the crystalline states were determined. The Gibbs free energy difference between the liquid and the crystalline states gives a qualitative measure of the glass forming ability of these alloys. Using the derived entropy difference, the Kauzmann temperatures for these alloys were determined
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