746 research outputs found
A two-stage ceramic tile grout sealing process using a high power diode laser Part I: Grout development and materials characteristics
Work has been conducted using a 60 W-cw high power diode laser (HPDL) in order to determine the feasibility and characteristics of sealing the void between adjoining ceramic tiles with a specially developed grout material having an impermeable enamel surface glaze. A two-stage process has been developed using a new grout material which consists of two distinct components: an amalgamated compound substrate and a glazed enamel surface; the amalgamated compound seal providing a tough, heat resistant bulk substrate, whilst the enamel provides an impervious surface. HPDL processing has resulted in crack free seals produced in normal atmospheric conditions. The basic process phenomena are investigated and the laser effects in terms of seal morphology, composition and microstructure are presented. Also, the resultant heat affects are analysed and described, as well as the effects of the shield gases, O2 and Ar, during laser processing. Tiles were successfully sealed with power densities as low as 500 W/cm2 and at rates up to 600 mm/min. Contact angle measurements revealed that due to the wettability characteristics of the amalgamated oxide compound grout (AOCG), laser surface treatment was necessary in order to alter the surface from a polycrystalline to a semi-amorphous structure, thus allowing the enamel to adhere. Bonding of the enamel to the AOCG and the ceramic tiles was identified as being principally due to van der Waals forces, and on a very small scale, some of the base AOCG material dissolving into the glaze
Twisted speckle entities inside wavefront reversal mirrors
The previously unknown property of the optical speckle pattern reported. The
interference of a speckle with an oppositely moving phase-conjugated speckle
wave produces a randomly distributed ensemble of a twisted entities (ropes)
surrounding optical vortex lines. These entities appear in a wide range of
randomly chosen speckle parameters inside the phase-conjugating mirrors
regardless to an internal physical mechanism of the wavefront reversal. These
numerically generated interference patterns are relevant to a Brillouin -mirrors and to a four-wave mixing -mirrors based upon laser trapped
ultracold atomic cloud.Comment: 4 pages,3 figures, Accepted to Physical Review
КОМПЛЕКСНА ОЦІНКА ЯКОСТІ ВОДИ МАЛИХ РІЧОК НА ПРИКЛАДІ ЛІВИХ ПРИТОК РІЧКИ РОСЬ
The work deals with the problems of small rivers in Ukraine. The main objective is to develop the complex criteria for assessing the quality of river water. As a result of hydrochemical and hydrobiological studies the parameters of Rosava River (left tributary of the river Ros) water quality have been calculated. The main polluters of river water have been singled out and their dynamics has been analyzed. Comprehensive environmental index of this water is classified as "bad." The main causes of river pollution are: business activity in the basin, a large residential development on the banks and an increasing number of utility waste.Стаття присвячена проблемам малих річок України. Основна мета – розробка комплексних критеріїв оцінки якості річкової води. За результатами гідрохімічних та гідробіологічних досліджень розраховано параметри якості води річки Росава (ліва притока річки Рось). Виділено основні забруднювачі річкової води та проаналізовано їх динаміку. Показано, що за комплексним екологічним індексом ця вода належить до категорії «погана». Причинами забруднення річки Росава є діяльність підприємств у її басейні, значна житлова забудова на берегах та, відповідно, збільшення кількості житлово-комунальних стоків
Sum rules and electrodynamics of high-Tc cuprates in the pseudogap state
We explore connections between the electronic density of states (DOS) in a
conducting system and the frequency dependence of the scattering rate
inferred from infrared spectroscopy. We show that changes in
the DOS upon the development of energy gaps can be reliably tracked through the
examination of the spectra using the sum rules discussed in
the text. Applying this analysis to the charge dynamics in high- cuprates
we found radically different trends in the evolution of the DOS in the
pseudogap state and in the superconducting state.Comment: 4 pages, 3 figure
In-plane polarized collective modes in detwinned YBaCuO observed by spectral ellipsometry
The in-plane dielectric response of detwinned YBaCuO has
been studied by far-infared ellipsometry. A surprisingly lare number of
in-plane polarized modes are observed. Some of them correspond to pure phonon
modes. Others posses a large electronic contribution which strongly increases
in the superconducting state. The free carrier response and the collective
modes exhibit a pronounced a-b anisotropy. We discuss our results in terms of a
CDW state in the 1-d CuO chains and induced charge density fluctuations within
the 2-d CuO planes
Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor
The band structure of a prototypical dilute ferromagnetic semiconductor,
GaMnAs, is studied across the phase diagram via optical
spectroscopy. We prove that the Fermi energy () resides in a Mn induced
impurity band (IB). This conclusion is based upon careful analysis of the
frequency and temperature dependence of the optical conductivity
(). From our analysis of we infer
a large effective mass () of the carriers, supporting the view that
conduction occurs in an IB. Our results also provide useful insights into the
transport properties of Mn-doped GaAs.Comment: 4 pages, 4 figure
Determination of the electronic structure of bilayer graphene from infrared spectroscopy results
We present an experimental study of the infrared conductivity, transmission,
and reflection of a gated bilayer graphene and their theoretical analysis
within the Slonczewski-Weiss-McClure (SWMc) model. The infrared response is
shown to be governed by the interplay of the interband and the intraband
transitions among the four bands of the bilayer. The position of the main
conductivity peak at the charge neutrality point is determined by the
interlayer tunneling frequency. The shift of this peak as a function of the
gate voltage gives information about less known parameters of the SWMc model,
in particular, those responsible for the electron-hole and sublattice
asymmetries. These parameter values are shown to be consistent with recent
electronic structure calculations for the bilayer graphene and the SWMc
parameters commonly used for the bulk graphite.Comment: (v2) 11 pages, 7 figures; Important typo fixes and bibliography
addition
Searching for the Slater Transition in the Pyrochlore CdOsO with Infrared Spectroscopy
Infrared reflectance measurements were made on the single crystal pyrochlore
CdOsO in order to examine the transformations of the
electronic structure and crystal lattice across the boundary of the metal
insulator transition at . All predicted IR active phonons are
observed in the conductivity over all temperatures and the oscillator strength
is found to be temperature independent. These results indicate that charge
ordering plays only a minor role in the MIT and that the transition is strictly
electronic in nature. The conductivity shows the clear opening of a gap with
. The gap opens continuously, with a temperature
dependence similar to that of BCS superconductors, and the gap edge having a
distinct dependence. All of these
observables support the suggestion of a Slater transition in CdOsO.Comment: 4 pages, 4 figure
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