Search results for "BAND"
showing 10 items of 2610 documents
<title>Statistical bandwidth allocation for multiservice networks</title>
2002
Multiservice networks will carry di erent kinds of applications in the near future. Bandwidth requirements change rapidly, and the network resource management will play an important role to guarantee the use of the limited resources in the most eAEcient way. We approach the channel capacity allocation problem by developing an SLA (Service Level Agreement) based channel allocation method. In our model, the channel may be wired or wireless, so this method can be adapted in multi-technique networks. The algorithm allocates resources to several di erent service classes via several di erent capacity routes. Service provider perfroms optimization by allocating data rate in such a way that the sat…
On the statistical properties of the capacity of double Hoyt fading channels
2010
The statistical properties of the capacity of narrowband double Hoyt fading channels are studied. Toward this end, analytical expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the instantaneous channel capacity process are derived. Furthermore, for the characterization of the dynamical behavior of the time-varying channel capacity, expressions are provided for the level-crossing rate (LCR) and the average duration of fades (ADF). Since the double Rayleigh fading channel is a special case of the double Hoyt model, it is shown that the derived expressions can be reduced to the corresponding results already known for the capacity of the double…
Channel capacity of fading channels for differentially encoded transmission
1999
The capacity of flat fading channels when applying differential encoding with noncoherent reception and no channel state information available at the receiver is considered. Numerical results indicate the gains achievable by multiple symbol detection in the case of slowly time-varying channels and provide a comparison between schemes with different potential bandwidth efficiencies.
ChemInform Abstract: Metal-Metal Bonding and Metallic Behavior in Some ABO2 Delafossites.
2010
We present results of ab initio band structure calculations on some ABO2 delafossite oxides that have both the A and B sites occupied by transition metals. This class of materials includes insulators as well as some of the most conducting oxides. The calculations have been performed in order to understand the nature of the metallic and insulating states and the extensive metal−metal bonding displayed by these materials. The effect of polytypism on the electronic structure is examined. Among the interesting aspects of the electronic structure of these materials are the contributions from both A and B atoms to states near the Fermi energy and the highly disperse nature of bands derived from t…
Electrochromic absorbance changes in the chlorophyll-c-containing alga Pleurochloris meiringensis (Xanthophyceae)
1994
Flash-induced absorbance changes were measured in the Chl-c-containing alga Pleurochloris meiringensis (Xanthophyceae) between 430 and 570 nm. In addition to the bands originating from redox changes of cytochromes, three major positive and tow negative transient bands were observed both 0.7 and 20 ms after the exciting flash. These transient bands peaking at 520, 480 and 451 nm and 497 and 465 nm, respectively, could be assigned to an almost homogeneous shift of the absorbance bands with maxima at 506, 473 and 444 nm, respectively. The shape of the absorbance transients elicited from PS I or PS II was identical, and the two photosystems contributed nearly equally to the absorbance changes. …
Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2
2007
Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…
Ab initio modelling of the effects of varying Zr (Ti) concentrations on the atomic and electronic properties of stoichiometric PZT solid solutions
2017
Abstract Lead zirconate titanate Pb(ZrxTi1−x)O3 solid solution is considered as one of the most advanced ferroelectric and piezoelectric materials. Consequent variation of Zr (Ti) concentrations significantly affects the atomic and electronic properties of PZT structures. To perform ab initio modelling of different morphologies for lead zirconate titanate, we are using approach of hybrid density functional B3PW as implemented in CRYSTAL14 computer code. In this study, we are performing large-scale calculations of such PZT parameters as optimized lattice constants, atomic charges and bond populations, as well as band structure (e.g., band gap) and density of states.
Ab initio study of the electronic and atomic structure of the wolframite-type ZnWO4
2009
Abstract Ab initio quantum chemistry calculations of the structural and electronic properties of monoclinic wolframite-type ZnWO 4 crystal have been performed within the periodic linear combination of atomic orbitals (LCAO) method using six different Hamiltonians, based on density functional theory (DFT) and hybrid Hartree-Fock-DFT theory. The obtained results for optimized structural parameters, band gap and partial density of states are compared with available experimental data, and the best agreement is observed for hybrid Hamiltonians. The calculations show that zinc tungstate is a wide band gap material, with the direct gap about 4.6 eV, whose valence band has largely O 2p character, w…
Reactivity between molybdenum and TiO2(110) surfaces: evidence of a sub-monolayer mode and a multilayer mode
2005
Small amounts of molybdenum (from 0.03 to 1.3 eqML) were deposited on non-stoichiometric TiO 2 (1 1 0) surface. The deposits were investigated by means of LEED and X-ray/UV photoemission using synchrotron radiation. For the smallest coverage (<0.2 eqML), deposition leads to oxidation of molybdenum into species close to Mo 4+ .In such a case, states appearing in TiO 2 band gap are mainly due to reduced titanium. For higher coverages, metallic behaviour of molybdenum is observed. This phenomenon was explained, thanks to first principle calculations, as a decrease of the Mo-O interactions for the benefit of the Mo-Mo interactions as the surface molybdenum atom density increases.
Thermo‐optical investigations of NaNbO 3 thin films by spectral ellipsometry
2009
In this work a spectroscopic ellipsometry was applied to the thermo-optical investigations of sodium niobate NaNbO3 (NN) thin films at the wide temperature range of 5–820 K. The temperature dependence of complex refractive index dispersions and optical bang energy of the direct allowed electron transitions were evaluated. Additionally dynamic scans of the main ellipsometric angles at the several fixed wave lengths of 300, 400, 500 and 635 nm were performed to acquire more detailed temperature dependences of the refractive index and extinction coefficient. Pronounced minima/maxima and substantial jumps in the temperature dependence of complex refractive index and band gap energy were found a…