Thirty years of rotatable magnetrons

Rotating cylindrical magnetrons differ in design from the well known planar magnetrons. The cylindrical target rotates around a stationary magnet configuration which is essentially the same as the one for a rectangular planar magnetron. This target rotation results in some advantages such as a higher stability in reactive mode, a much larger material inventory, and suitability to be operated at higher power density. Besides these important technological advantages, this magnetron type also has some unique features related to its rotation and/or target design. The I/V characteristics are more sensitive to the background pressure, the critical reactive gas flow defining the switching between metallic mode and poisoned mode depends on the rotation speed, and negative ions are emitted from the racetrack in two beams. Due to the cylindrical design, angular resolved measurements are more easily investigated. This advantage is used to compare the target behavior in DC mode and HIPIMS.     

Thirty years of numerical flow simulation in hydraulic turbomachines

The application of computational fluid dynamics (CFD) in the design of water turbines and pumps started about 30 years ago. This paper reviews the main steps and breakthroughs in the methods that were made during this period, through the eyes of one particular water turbine company which spear-headed some of the first developments for practical applications. Practical examples are used to illustrate the developments of the tools from 1978 to 2008 and to give an overview of the complete revolution in hydraulic turbine design that has occurred over this time. Several periods with distinct levels of complexity, and hence accuracy of the physical models and of the simulation methods can be distinguished. The first steps coincided with the introduction of the Finite Element Method into CFD, and were characterized by simplified Quasi-3D Euler solutions and Fully 3D potential flow solutions. Over the years the complexity continuously increased in stages: via 3D Euler solutions, to steady RANS simulations of single blade passages using finite volume methods, extending to steady simulations of whole machines, until today unsteady RANS equations are solved with advanced turbulence models. The most active areas of research and development are now concerned with including the effects of 2-phase flows (free surface flow in Pelton turbines and cavitation) and fluid–structure interaction.     

Thirty years of safety climate research: Reflections and future directions

Looking back over 30 years of my own and other safety-climate scholars’ research, my primary reflection is that we have achieved an enormous task of validating safety climate as a robust leading indicator or predictor of safety outcomes across industries and countries. The time has therefore come for moving to the next phase of scientific inquiry in which constructs are being augmented by testing its relationships with antecedents, moderators and mediators, as well as relationships with other established constructs. Whereas there has been some significant progress in this direction over the last 30 years (e.g. leadership as a climate antecedent), much more work is required for augmenting safety climate theory. I hope this article will stimulate further work along these lines.     

A glimpse of quantum phenomena in optical lattices

Optical lattices in cold atomic systems offer an excellent setting for realizing quantum condensed matter phenomena. Here, a glimpse of such a setting is provided for the non-specialist. Some basic aspects of cold atomic gases and optical lattices are reviewed. Quantum many-body physics is explored in the case of interacting bosons on a lattice. Quantum behaviour in the presence of a potential landscape is examined for three different cases: a hexagonal lattice potential, a quasi-periodic potential and a disorder potential.     

Thirty years of Brazilian research in Antarctica: ups, downs and perspectives

The Antarctic continent is the most untouched region of the world but is also among the most vulnerable to global environmental change. Alterations to the Antarctic environment can have cascading effects many of which are unpredictable. Our objective was to investigate the contribution of Brazilian scientists to Antarctic research and to characterize the actions taken by the country to improve its scientific output and its international impact in this area. Scientific publications related to Antarctica, released from 1981 to 2011 were searched using three important science data bases. The data were used to determine the absolute increase and the relative growth rate of publications in order to characterize the contribution of Brazil to the world’s scientific understanding of Antarctica. The number of publications revealed an undersized contribution of the Brazilian science to the world’s publications about Antarctica. However, over the last 30 years there has been a substantial increase in the number of publications associated with governmental financial policies. As in other countries, Brazil’s most significant scientific contributions regarding the Antarctic continent are in the biological sciences. Therefore, public policies should maintain the current official support, while the research groups should pay attention to strategic scientific and technological areas still uncovered in the Antarctic research.     

Time-dependent phenomena in plasma-assisted chemical vapor deposition of rugate optical films

The plasma-assisted chemical vapor deposition technique was used to produce thin-film structures with both sinusoidally and stepwise varying refractive-index profiles. The refractive index of the SiO(x)N(y) system used in the fabrication was found to be time dependent following a stepwise change in reactant gas flows or initiation of the plasma. This time dependence has been quantified using in situ ellipsometry and was found to have components with exponential and linear dependences. The time dependence of water vapor partial pressure in the system was identified as the cause of the linear dependence. Allowance for the time-dependent effects has improved the agreement between the calculated spectral response and the measured result for a broadband high-reflectance mirror consisting of an arithmetic progression of discrete layers.     

Transient optical phenomena in quartz fibers under high-power pulsed reactor irradiation

Measurements of the intensity of emission and induced optical absorption at 400–750 nm in KU-1 quartz fibers were performed under pulsed irradiation in a BARS-6 reactor (pulse duration, 80 μs; dose per pulse, up to 5×10¹² neutrons/cm² (E>0.2 MeV); dose rate, up to 10⁵ Gy/s). The nondelayed emission component is due to the Cerenkov radiation, the weak relaxation component has a relaxation time of ∼150±50 μs, and the radiation-induced optical absorption reaches a value of 2.5×10⁻⁴ cm⁻¹ (relaxation time, 600–1200 μs). A nonlinear dependence of the Cerenkov radiation on the dose rate and the presence of the relaxation emission component and the transient optical absorption may be associated with an optical inhomogeneity of glass induced by the high-power reactor irradiation.     

Orientation phenomena in chromophore DR1-containing polymer films and their non-linear optical response

The effectiveness of chromophore alignment in polymer films following corona poling can be assessed by the generated second harmonic signal. Optimization of the stability and strength of this nonlinear optical response may improve with a better understanding of the underlying principal order phenomena. Structural analysis by vibrational, optical, and ¹H NMR spectroscopy reveals side chain tacticity, aggregation effects, and changes in orientation as a function of temperature. Co-polymers with the functionalized chromophore Disperse Red 1 methacrylate (MDR1) were prepared for three different methacrylate types. High side chain polarity and short side chain length increase generally chromophore aggregation in films, whereas the very long poly-ether side chains in PMEO based co-polymers are wrapped separately around the DR1 entities. Side chain tacticity depends on space requirements, but also on the capacity of side groups to form OH-bridges. Side chain tacticity might present an additional parameter for the assessment of chromophore aggregation and poling induced alignments. Stepwise heating of co-polymer films causes an increase in the number of random over ordered side chain arrangements. Cross-linking by anhydride formation is observed after heating the methacrylic acid based co-polymer.     

Colors of the daytime overcast sky

Time-series measurements of daylight (skylight plus direct sunlight) spectra beneath overcast skies reveal an unexpectedly wide gamut of pastel colors. Analyses of these spectra indicate that at visible wavelengths, overcasts are far from spectrally neutral transmitters of the daylight incident on their tops. Colorimetric analyses show that overcasts make daylight bluer and that the amount of bluing increases with cloud optical depth. Simulations using the radiative-transfer model MODTRAN4 help explain the observed bluing: multiple scattering within optically thick clouds greatly enhances spectrally selective absorption by water droplets. However, other factors affecting overcast colors seen from below range from minimal (cloud-top heights) to moot (surface colors).     

Twilight and daytime colors of the clear sky

Digital image analysis of the cloudless sky's daytime and twilight chromaticities challenges some existing ideas about sky colors. First, although the observed colors of the clear daytime sky do lie near the blackbody locus, their meridional chromaticity curves may resemble it very little. Second, analyses of twilight colors show that their meridional chromaticity curves vary greatly, with some surprising consequences for their calorimetric gamuts.     

商品包装设计中的图形研究

商品包装设计由造型、结构、文字、色彩、图形构成.     

Photoinduced nonlinear optical phenomena in Sb2Se3-BaCl2-SnCl2 glasses

Photoinduced nonlinear optical phenomena have been studied in amorphous Sb₂Te₃-CaCl₂-SnCl₂ glasses using photoinduced optical second harmonic generation (SHG). The photoinduced SHG signal was measured for double frequency of a CO₂ laser ( = 5.3 m) using a photoinducing CO laser ( = 5.5 m). We have found that the SHG signal intensity increases with increase of the CO laser photoinducing exposure and achieves its maximum value after 1.5 h. Absolute values of the SHG signals were more than one order in magnitude smaller comparing to a ₂₂₂ tensor component for the ZnSe single crystals. The SHG signal strongly increases if temperature decreases from 39 to 16 K. Femtosecond probe-pump measurements indicate existence of the SHG maximum at pump-probe time delay of about 43 ps. It is suggested that Sb-Se tetrahedra play a key role in the observed photoinduced nonlinear optical effects. Degree of noncentrosymmetry of corresponding bonds depends on time of the CO-laser illumination, temperature and mechanical stresses. Simultaneously, the investigated glasses can serve as promising materials for a femtosecond IR quantum electronics.     

Atmospheric ozone and colors of the Antarctic twilight sky

Zenith skylight is often distinctly blue during clear civil twilights, and much of this color is due to preferential absorption at longer wavelengths by ozone's Chappuis bands. Because stratospheric ozone is greatly depleted in the austral spring, such decreases could plausibly make Antarctic twilight colors less blue then, including at the zenith. So for several months in 2005, we took digital images of twilight zenith and antisolar skies at Antarctica's Georg von Neumayer Station. Our colorimetric analysis of these images shows only weak correlations between ozone concentration and twilight colors. We also used a spectroradiometer at a midlatitude site to measure zenith twilight spectra and colors. At both locations, spectral extinction by aerosols seems as important as ozone absorption in explaining colors seen throughout the twilight sky.     

Color and luminance asymmetries in the clear sky

A long-standing assumption about the clear sky is that its colors and luminances are distributed symmetrically about the principal plane. As useful as this approximation is, our digital-image analyses show that clear-sky color and luminance routinely depart perceptibly from exact symmetry. These analyses reconfirm our earlier measurements with narrow field-of-view spectroradiometers [J. Opt. Soc. Am. A 18, 1325 (2001)], and they do so with much higher temporal and angular resolution across the entire sky dome.     

Calibration and data elaboration procedure for sky irradiance measurements

The problems encountered in the elaboration of measurements of direct and sky diffuse solar irradiance are the following: (1) to carry out the calibration for the direct irradiance, which consists in determining the direct irradiance at the upper limit of the atmosphere; (2) to carry out the calibration for the diffuse irradiance, which consists in determining the solid viewing angle of the sky radiometer; (3) to determine the input parameters, namely, ground albedo, real and imaginary parts of the aerosol refractive index, and aerosol radius range; and (4) to determine from the optical data the columnar aerosol optical depth and volume radius distribution. With experimental data and numerical simulations a procedure is shown that enables one to carry out the two calibrations needed for the sky radiometer, to determine a best estimate of the input parameters, and, finally, to obtain the average features of the atmospheric aerosols. An interesting finding is that inversion of only data of diffuse irradiance yields the same accuracy of result as data of both diffuse and direct irradiance; in this case, only calibration of the solid viewing angle of the sky radiometer is needed, thus shortening the elaboration procedure. Measurements were carried out in the Western Mediterranean Sea (Italy), in Tokyo (Japan), and in Ushuaia (Tierra del Fuego, Argentina); data were elaborated with a new software package, the Skyrad code, based on an efficient radiative transfer scheme.