Search results for "Exponential decay"
showing 10 items of 67 documents
Refractive index controlled by film morphology and free carrier density in undoped ZnO through sol-pH variation
2018
Abstract Zinc oxide thin films, prepared by the sol-gel process, were deposited on glass substrate using spin coating technique. The sol-pH effect on the optical parameters was studied for alkaline sol. The surface roughness was investigated by atomic force microscopy (AFM) and varied from 20 to 40 nm. The optical transmission measurements were carried out to evaluate the behavior of the extinction coefficient and the refractive index. An exponential decay of the refractive index ‘n’ as a function of wavelength was observed. The refractive index increases slightly when the pH increases to pH = 9.5 where it reaches its maximum. Beyond this value, it decreases sharply. This behavior has been …
Memory effects and coverage dependence of surface diffusion in a model adsorption system
1999
We study the coverage dependence of surface diffusion coefficients for a strongly interacting adsorption system O/W(110) via Monte Carlo simulations of a lattice-gas model. In particular, we consider the nature and emergence of memory effects as contained in the corresponding correlation factors in tracer and collective diffusion. We show that memory effects can be very pronounced deep inside the ordered phases and in regions close to first and second order phase transition boundaries. Particular attention is paid to the details of the time dependence of memory effects. The memory effect in tracer diffusion is found to decay following a power law after an initial transient period. This beha…
Entanglement dynamics in superconducting qubits affected by local bistable impurities
2012
We study the entanglement dynamics for two independent superconducting qubits each affected by a bistable impurity generating random telegraph noise (RTN) at pure dephasing. The relevant parameter is the ratio $g$ between qubit-RTN coupling strength and RTN switching rate, that captures the physics of the crossover between Markovian and non-Markovian features of the dynamics. For identical qubit-RTN subsystems, a threshold value $g_\mathrm{th}$ of the crossover parameter separates exponential decay and onset of revivals; different qualitative behaviors also show up by changing the initial conditions of the RTN. We moreover show that, for different qubit-RTN subsystems, when both qubits are …
Temperature concepts for small, isolated systems: 1/t decay and radiative cooling
2003
We report on progress in our investigations of cluster cooling. The analysis of measurements is based on introduction of the microcanonical temperature and a statistical description of the decay of an ensemble with a broad distribution in temperature. The resulting time dependence of the decay rate is a power law close to t �1 , replaced by nearly exponential decay after a characteristic time for quenching by radiative cooling. We focus on results obtained for fullerenes, both anions and cations and recently also neutral C60.
Non-Bloch decay of transient nutations in S=1/2 systems: An experimental investigation.
1993
The decay of transient nutations has been experimentally investigated in S=1/2 spin systems at microwave frequency: E' centers in silica and [${\mathrm{AlO}}_{4}$${]}^{0}$ centers in quartz have been studied. We have found that the damping is well described by a single exponential decay function, as expected from a ${\mathit{T}}_{1}$-${\mathit{T}}_{2}$ model (Bloch model). However, the agreement is only qualitative. In fact the measured decay rate \ensuremath{\Gamma} is faster than expected and depends on the driving-field amplitude: it tends to the Bloch value ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{B}}$=1/2${\mathit{T}}_{2}$ in the low-power limit and becomes faster and faster on increas…
Polarizability of the neutron
1990
Abstract A first measurement of quasi-free Compton scattering by the neutron bound in the deuteron has yielded a value for the polarizability of the neutron of αn=(11.7 −11.7+4.3)×10 −4fm 3. This means that a finite value for the polarizability has been obtained, though the result is still consistent with zero. The π0 decay constant Fπ 0γγ and the pion nucleon coupling constant gNNπ have opposite signs.
Combined proton NMR wideline and NMR relaxometry to study SOM-water interactions of cation-treated soils
2013
Abstract Focusing on the idea that multivalent cations affect SOM matrix and surface, we treated peat and soil samples by solutions of NaCl, CaCl2 or AlCl3. Water binding was characterized with low field 1H-NMR-relaxometry (20 MHz) and 1H wideline NMR spectroscopy (400 MHz) and compared to contact angles. From 1H wideline, we distinguished mobile water and water involved in water molecule bridges (WaMB). Large part of cation bridges (CaB) between SOM functional groups are associated with WaMB. Unexpectedly, 1H NMRrelaxometry relaxation rates suggest that cross-linking in the Al-containing peat is not stronger than that by Ca. The relation between percentage of mobile water and WaMB water in…
Cracking behavior of zeolites with connected 12- and 10-member ring channels: The influence of pore structure on product distribution
1997
n-Heptane has been cracked on a CIT-1 zeolite which has connected 12- and 10-member ring (MR) channels, and its behavior was compared with that of MCM-22 with nonconnected 12- and 10-MR channels, and SSZ-24 and BETA with unidirectional and tridirectional 12-MR channels, respectively. The kinetic rate constant is highest for CIT-1, and the decay constant is lowest. From the selectivity point of view, its behavior can be better represented by a system with large cavities (the intersections between the 12- and 10-MR) connected by windows. This gives a behavior typical of that of large pore zeolites. CIT-1 produces a remarkably high selectivity toi-C4, and specially to isobutane. This zeolite s…
Luminescence of different modifications of crystalline silicon dioxide: Stishovite and coesite
2003
Abstract Luminescence of very small samples of single crystals of coesite and stishovite has been studied. The spectra were detected under ionizing radiation (X-ray and electron beam) and the decay kinetics of cathodoluminescence in the range of time from 10 ns to 3 ms was measured. The coesite luminescence possesses a broad band at 3 eV with exponential decay about 680 μs at 80 K. The nature of this luminescence was explained as a self-trapped exciton creation in tetrahedron framework. The stishovite luminescence possesses two bands—blue (2.8 eV) and UV (4.7 eV). The UV band intensity grows more than 20 times with irradiation dose from initial level. This shows that the corresponding lumin…
Correlation at low temperature I. Exponential decay
2003
Abstract The present paper generalizes the analysis in (Ann. H. Poincare 1 (2000) 59, Math. J. (AMS) 8 (1997) 123) of the correlations for a lattice system of real-valued spins at low temperature. The Gibbs measure is assumed to be generated by a fairly general Hamiltonian function with pair interaction. The novelty, as compared to [2,20], is that the single-site (self-) energies of the spins are not required to have only a single local minimum and no other extrema. Our derivation of exponential decay of correlations goes through the spectral analysis of a deformed Laplacian closely related to the Witten Laplacian studied in [2,20]. We prove that this Laplacian has a spectral gap above zero…