Inhibiting Left-Handed Wave Propagation by a Band Gap of Stacked Cut-Off Metallic Hole Arrays

In this letter, the behavior of a recently reported left-handed metamaterial working at millimeter-wave frequencies is analyzed. The metamaterial is built by the periodic stacking of metallic plates with sub-wavelength hole arrays that show extraordinary optical transmission. If the longitudinal period of the stacked structure is chosen adequately, it is possible to mold the electromagnetic wave propagation inside the structure from right-handed to left-handed. The transmission response of the fabricated prototype has been measured with a millimeter wave quasioptical vector network analyzer in the range between 40 GHz and 110 GHz confirming the possibility to tune the left-handed or right handed characteristics of the waves propagating there. These results can give rise to interesting applications such as novel lenses and other quasioptical structures     

Quasioptical Polarizer Based on Self-Complementary Sub-Wavelength Hole Arrays

In this letter, extraordinary transmission in sub-wavelength hole arrays is employed in combination with self-complementary Babinet concepts to design a novel class of quasioptical polarizer for millimeter wave frequencies. After a proper design, the device has been miniaturized in such a way that operation under Fresnel zone of a Gaussian beam has been demonstrated. Experimental validation opens up the way to new possibilities for polarizer design.     

Effect of heat treatment on the efficiency of Mg anodes

Commercial magnesium anodes were evaluated using ASTM G 97-89 for a standard test along with a technique of electrochemical impedance. Several heat treatments were performed, and the anodic efficiency was determined, showing an incremental increase of 10 to 12 % of the efficiency demonstrated by the nontreated commercial anodes (as-cast condition). The increase in efficiency was related to the microstructural characteristics. The appearance of second phase particles influenced the form of the corrosion process.     

Heterocyclic structures useful in medicinal chemistry: the case of pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide

Different aspects of a particular kind of heterocycle, namely pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide are discussed. These include synthesis, reactivity, tautomerism and acid-base properties, results of x-ray analysis and molecular orbital calcultations. Besides, some of the derivatives have shown interesting biological effects, among which are the diuretic properties which are also presented.     

Enhanced Gain by Double-Periodic Stacked Subwavelength Hole Array

Using a doubly periodicity structure the extraordinary transmission of subwavelength metallic hole arrays in the microwave range can be boosted. Stacking several of such plates a left-handed metamaterial can be obtained as it is shown by the computed dispersion diagrams as well as the amplitude and phase measurements. An effective refraction index along the propagation direction can be calculated, giving a negative magnitude between -1 and 0. This enhances the emission by a focused beam with narrow beamwidth. Several practical applications like novel antennas are envisaged.     

CO2 savings of ground source heat pump systems – A regional analysis

In the current study the savings of CO₂ emissions due to the use of ground source heat pump (GSHP) systems was investigated in comparison to conventional heating systems. Based on a subsidy program for GSHP systems in southwest Germany, the regional, average, and total CO₂ savings of 1105 installed GSHP systems were determined on a regional scale. The emitted CO₂ per kWh of heating demand for the studied scenario resulted in 149 g CO₂/kWh for GSHP using the German electricity mix and 65 g CO₂/kWh using the regional electricity mix, which results in CO₂ savings of 35% or 72%, respectively. Similar CO₂ avoidances of GSHP systems were found in American and European studies ranging between 15% and 77% strongly depending on the supplied energy for the heat pumps and the efficiency of installation. The resulting CO₂ savings for one installed GSHP unit in the present study therefore range between 1800 and 4000 kg per year. Nevertheless, the minimum average total annual CO₂ savings of all installed GSHP systems due to the subsidy program amounted to 2000 tons per year. The maximum regional avoided additional CO₂ emissions are primarily associated with the affluent suburbs of the most densely populated area in the region. In 2006 the total contribution of CO₂ savings due to GSHP systems in Germany was only about 3.4% of the total renewable energies. However, continuously rising numbers of installed GSHP units and the increasing use of renewable electricity demonstrate that there is a fine opportunity to substantially avoid additional CO₂ emissions associated with the provision of heating (and cooling) of buildings and other facilities.     

Characterization of surface cracks with Rayleigh waves: a numerical model

In the non-destructive testing of concrete structures, the use of Rayleigh waves shows some advantages to characterise surface cracks: easiness of excitation and recording, access to only one surface of the structure required, great spectral sensitivity to the propagation medium…. But the behaviour of Rayleigh waves on surface defects in concrete is difficult to perceive in the field, even if the dependence of the diffraction pattern on the crack's geometrical features is significant.A numerical model is adapted from earth physics in order to better understand the influence of the crack geometry on Rayleigh-wave propagation. This model, based on an indirect boundary element method, calculates the three-dimensional seismic response of two-dimensional structures. Synthetic seismograms are obtained for the propagation of a Rayleigh wave across various crack geometries. The variations of spectral ratios between the transmitted and incident waves are studied as a function of the crack depth. They are used to design an efficient procedure for the determination of crack depths.     

Effect of Cu additions over the lattice parameter and hardness of the NiAl intermetallic compound

A set of NiAl intermetallic alloys was prepared with several Cu additions, exploring the Ni-rich and the Al-rich side of the NiAl intermetallic compound. An abrupt increment in hardness was obtained in the Al-rich alloys, while the opposite occurs in the Ni-rich alloys. This may be due to the presence of β-phase (Ni,Cu) Al and γ′-phase (Ni,Cu)₃Al, in addition to the variation of the β-phase lattice parameter.