What is the Brillouin Zone of an Anisotropic Photonic Crystal?

The concept of the Brillouin zone (BZ) in relation to a photonic crystal fabricated in an optically anisotropic material is explored both experimentally and theoretically. In experiment, we used femtosecond laser pulses to excite THz polaritons and image their propagation in lithium niobate and lithium tantalate photonic crystal (PhC) slabs. We directly measured the dispersion relation inside PhCs and observed that the lowest bandgap expected to form at the BZ boundary forms inside the BZ in the anisotropic lithium niobate PhC. Our analysis shows that in an anisotropic material the BZ - defined as the Wigner-Seitz cell in the reciprocal lattice - is no longer bounded by Bragg planes and thus does not conform to the original definition of the BZ by Brillouin. We construct an alternative Brillouin zone defined by Bragg planes and show its utility in identifying features of the dispersion bands. We show that for an anisotropic 2D PhC without dispersion, the Bragg plane BZ can be constructed by applying the Wigner-Seitz method to a stretched or compressed reciprocal lattice. We also show that in the presence of the dispersion in the underlying material or in a slab waveguide, the Bragg planes are generally represented by curved surfaces rather than planes. The concept of constructing a BZ with Bragg planes should prove useful in understanding the formation of dispersion bands in anisotropic PhCs and in selectively tailoring their optical properties.Comment: 9 pages, 6 figure

THz generation using a reflective stair-step echelon

We present a novel method for THz generation in lithium niobate using a reflective stair-step echelon structure. The echelon produces a discretely tilted pulse front with less angular dispersion compared to a high groove-density grating. The THz output was characterized using both a 1-lens and 3-lens imaging system to set the tilt angle at room and cryogenic temperatures. Using broadband 800 nm pulses with a pulse energy of 0.95 mJ and a pulse duration of 70 fs (24 nm FWHM bandwidth, 39 fs transform limited width), we produced THz pulses with field strengths as high as 500 kV/cm and pulse energies as high as 3.1 $\mu$J. The highest conversion efficiency we obtained was 0.33%. In addition, we find that the echelon is easily implemented into an experimental setup for quick alignment and optimization.Comment: 19 pages, 4 figure

Testing alternative fuels, solar-thermal systems

The Terrestrial Energy Systems Technical Committee works to advance the application of engineering sciences and systems engineering to the production, storage, distribution and conservation of energy for terrestrial uses

Optimizing Lumber Production through Improved Accuracy of Side Clearance of Bandsaw Teeth and Quality Control Measures

As log costs increases as a result of increasing demand for wood products with a corresponding poor management of forest resource it has become more critical to obtain the maximum yield of useful product from each tree in order to sustain the wood industry. This work looks at the effect of the accuracy of side clearance of band saw teeth on the surface quality of sawn lumber as well as the level of adherence to quality standards when sawing Triplochiton scleroxylon (Wawa). The results obtained from the relationship between the accuracy of side clearance of band saw teeth and surface quality of sawn lumber indicates that there is a strong linear relationship between the two parameters. That is as the standard deviation of the side clearance of the band saw teeth decreases the surface quality of the sawn lumber becomes better. The correlation coefficient and coefficient of determination values for the two variables, that is, the accuracy of side clearance of the band saw teeth and the surface quality of the sawn lumber were -0.9042 and 0.8176 respectively. These values show that about 82% of the variations of the surface quality of the sawn lumber is influenced by the standard deviation of the side clearance of the band saw teeth. A graph of the relationship between the surface quality of the sawn lumber and standard deviation shows that on the average when the standard deviation of the side clearance of the band saw teeth is 0.225mm or low the surface quality of the sawn lumber produced could be qualitatively classified as good, very good or excellent. The result also indicated that the surface quality of the sawn lumber was excellent when the standard deviation of the side clearance of the band saw teeth was 0.07mm or low and was poor or very poor when the standard deviation of the side clearance was 0.252mm or more. A statistical control chart of sampled boards from the production process of the mill used for the study indicated that the mean thickness of the sawn boards was 42.42mm. The upper and lower control limits at 1.65 standard deviation were 44.08mm and 40.76mm respectively. The result indicates that about 15% of the total boards sampled were outside the control limits of the chart. The mean thickness of the sawn lumber at the mill for the study was 42.42mm as against nominal thickness of 41.00mm. This will result in a loss of about 3.46% timber for every board sawn and a subsequent loss of about 3.46m3 for every 100m3 of sawn lumber produced. African Journal of Educational Studies in Mathematics and Sciences Vol. 5 2007: pp. 1-

Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase

Ultrafast two-dimensional spectroscopy utilizes correlated multiple light-matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum. Its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. Here we report ultrafast two-dimensional terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by three terahertz field-dipole interactions. The nonlinear time-domain orientation signals are mapped into the frequency domain in two-dimensional rotational spectra which reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.Comment: 31 pages, 14 figure

Rapid and Precise Determination of Zero-Field Splittings by Terahertz Time-Domain Electron Paramagnetic Resonance Spectroscopy

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g-factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science.Comment: 36 pages, 30 figures, 1 tabl

Incidence of Blood and Meat Spots in Eggs from a Commercial Poultry Farm

A study was conducted in two phases simultaneously in a commercial poultry farm to ascertain whether egg weight, temperature variation in pens, and proximity of birds to a noise source had an influence on the incidence of blood and meat spots in chicken eggs. Phase one involved the random sampling of 60 eggs per week for 15 weeks, making a total of 900 eggs from the pens of a 50-week-old layer strain. Phase two determined the effect of noise from a 3.3 kW electrical gasoline generator on the incidence of blood and meat spots. It lasted for 14 weeks and involved the random sampling of 10 eggs per week directly from two pens (i.e., A & D). Pen A and D were 4.7 m and 68 m away from the noise source respectively. A Chi-square test was conducted to establish the relationship between the parameters, whilst a Cramer’s V test was used to determine the extent of association where differences were deemed significant (p<0.05). Out of the 1040 eggs collected, 63% of the eggs had spots (32% blood spots and 31% meat spots). No association was observed between the occurrence of spots and egg weight, temperature variation, and proximity of birds to a generator

Energy response of X-rays under high flux conditions using a thin APD for the energy range of 6–33 keV

This paper reports on the demonstration of a high-rate energy measurement technique using a thin depletion layer silicon avalanche photodiode (Si-APD). A dedicated amplitude-to-time converter is developed to realize simultaneous energy and timing measurement in a high rate condition. The energy response of the system is systematically studied by using monochromatic X-ray beam with an incident energy ranging from 6 to 33 keV. The obtained energy spectra contain clear peaks and tail distributions. The peak fraction monotonously decreases as the incident photon energy increases. This phenomenon can be explained by considering the distribution of the energy deposit in silicon, which is investigated by using a Monte Carlo simulation

Use of traditional serological methods and oral fluids to assess immunogenicity in children aged 2-16 years after successive annual vaccinations with LAIV.

BACKGROUND: The UK introduced quadrivalent live attenuated influenza vaccine (qLAIV) for children in 2013/2014. The impact of annual vaccination on effectiveness and immunogenicity is being assessed. METHOD: A phase III/IV open-label study of the immunogenicity of annual vaccination with qLAIV (Fluenz™) was conducted over three consecutive years (2014/15-2016/17) in 254, 249 and 162 children respectively. Serum responses to vaccine components were measured by Haemagglutination Inhibition (HAI) and anti-A(H1N1)pdm09 Neuraminidase (NAI) assays, stratified according to previous receipt of AS03B-adjuvanted A(H1N1)pdm09 pandemic vaccine in 2009/10. Antibody levels to the A(H1N1)pdm09 and H3N2 vaccine components in oral fluids (OF) were explored using an ELISA. FINDINGS: More paired pre- and post-vaccination oral fluids (96%) than paired sera (87%) were obtained. Geometric mean titre rises using HAI assays were limited, with maximum rises seen in year one for both influenza B strains when 39% and 43% of subjects seroconverted (95% confidence interval 33-46% and 36-50%, respectively) and year two for influenza H3N2, when 40% (33-46%) individuals seroconverted. Prior pandemic vaccine receipt resulted in higher pre- and post-vaccination A(H1N1)pdm09 HAI titres and lower pre-and post-vaccination NAI (N1 neuraminidase) titres in all three years. OF results were congruent with HAI results; assay specificity compared to HAI was 88.1 and 71.6 percent, and sensitivity was 86.4 and 74.8 percent respectively for A(H1N1)pdm09 and H3N2. CONCLUSION: In all three study years, vaccination with qLAIV resulted in poor antibody responses. However, OFs are an alternative specimen type that allows self sampling, can easily be obtained from children, and their analysis leads to similar conclusions as classic serology by HAI. Their suitability for seroprevalence studies should be investigated. We demonstrated a sustained effect from prior receipt of the AS03B-adjuvanted A(H1N1)pdm09 vaccine, even after repeat vaccination with qLAIV indicating that early exposure to influenza antigens has a significant long lasting effect