Concepts, terminology, and symbols are presented for specifying and relating directional variations in reflectance and emissivity of an opaque surface element. Their relationship to more familiar concepts, including those of perfectly diffuse and specular reflectance, is given, and they are applied to illustrative examples. It is shown that, when the usual reciprocity relationship holds, the reflectance for a ray incident on an opaque surface element is related by Kirchhoff's law to the emissivity of that element for a ray emitted along the same line in the opposite sense.

Directional Reflectance and Emissivity of an Opaque Surface

Commencally or potentially available selective and non-selective absorber surfaces for solar heat collectors are reviewed and the state-of-the-art of solar collector corrosion processes is outlined. The review of available published literature has indicated that a lack of quantitative information exists, relative to corrosion of collector surfaces. Available information (mostly qualitative) on durability aspects and corrosion of solar receiver surfaces is described to indicate potential corrosion problem areas and corrosion prevention possibilities. An outline of appropriate durability tests is presented.

Materials for photothermal solar energy conversion

Spectral reflectance properties of black chrome for use as a solar selective coating

Objectives: We assessed the knowledge and awareness of cervical cancer, HPV and HPV vaccine, and willingness and acceptability to vaccinate in sub-Saharan African (SSA) countries. We further identified countries that fulfill the two GAVI Alliance eligibility criteria to support nationwide HPV vaccination. Methods: We conducted a systematic review of peer-reviewed studies on the knowledge and awareness of cervical cancer, HPV and HPV vaccine, and willingness and acceptability to vaccinate. Trends in Diphtheria-tetanus-pertussis (DTP3) vaccine coverage in SSA countries from 1990–2011 were extracted from the World Health Organization database. Findings: The review revealed high levels of willingness and acceptability of HPV vaccine but low levels of knowledge and awareness of cervical cancer, HPV or HPV vaccine. We identified only six countries to have met the two GAVI Alliance requirements for supporting introduction of HPV vaccine: 1) the ability to deliver multi-dose vaccines for no less than 50% of the target vaccination cohort in an average size district, and 2) achieving over 70% coverage of DTP3 vaccine nationally. From 2008 through 2011 all SSA countries, with the exception of Mauritania and Nigeria, have reached or maintained DTP3 coverage at 70% or above. Conclusion: There is an urgent need for more education to inform the public about HPV, HPV vaccine, and cervical cancer, particularly to key demographics, (adolescents, parents and healthcare professionals), to leverage high levels of willingness and acceptability of HPV vaccine towards successful implementation of HPV vaccination programs. There is unpreparedness in most SSA countries to roll out national HPV vaccination as per the GAVI Alliance eligibility criteria for supporting

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Knowledge and awareness of HPV vaccine and acceptability to vaccinate in sub-Saharan Africa: a systematic review

The optical properties of bulk and thin‐film Zn3P2 have been measured at room temperature over the range 0.5–5.0 eV, with emphasis on the region of the interband absorption edge. The bulk absorption edge is found to be exponential in energy for values of absorption coefficient less than about 1500 cm−1. The thin‐film absorption edge, when freed of spurious absorptance due to scattering, is also found to be exponential over this range although shallower in slope. Analysis of the thin‐film data at higher values of absorption coefficient is inconclusive with respect to the nature of the edge. Nevertheless, indirect evidence suggests that the optical gap is probably direct and lies in the neighborhood of 1.6 eV. Measurements of refractive index in the near‐infrared yield n=3.3±0.1 in the long‐wavelength limit. The ultraviolet reflectivity spectrum is redetermined, and found to differ substantially from earlier reports. Results are discussed in terms of the Dow‐Redfield model of exponential absorption edges, t...

Optical properties of Zn3P2

An integrating sphere for determining spectral reflectance and transmittance as a function of angle of incidence and wavelength in the 0.33- to 2.5-μ region is described. Geometrical arrangement of sample, entrance port, and detector as well as directional characteristics of detector and sphere wall coating permit absolute or relative measurements to be made for a sample with an arbitrary reflection-distribution function.

Integrating Sphere for Imperfectly Diffuse Samples

Spectral and directional thermal radiation characteristics of selective sufaces for solar collectors

A heated cavity reflectometer modified for determining reflectance as a function of angle from the normal is described. Results for wavelengths between 1.5 and 25 microns are compared with theory and measurements made with a directional integrating sphere, a previously-described heated cavity instrument for normal measurements, and a total radiometer. Analysis and performance tests are presented to show consequences of modifications to the reference area, sample holder, and cavity.

D.K. Edwards

Papers

Integrating Sphere for Imperfectly Diffuse Samples

Spectral and directional thermal radiation characteristics of selective sufaces for solar collectors

Heated Cavity Reflectometer for Angular Reflectance Measurements