No abstract

Several inorganic materials are used to illustrate that bands in infrared emission spectra of solids change shape as the particle size of the sample is altered, and that the way in which a particular band changes depends upon the value of its absorption coefficient. The relationship found to exist between corresponding band shape changes in emission and reflection spectra indicates that Kirchoff's law holds to a first‐order approximation for particulate, or mat, surfaces. The implications of band shape changes are discussed in relation to remote compositional sensing, and it is pointed out as a consequence that the most obvious spectral features used for the identification of samples with polished surfaces are not necessarily the most useful for determining the composition of a target with a rough or mat surface.

A general theory is presented which segregates the rays composing the total reflectance from a mat surface according to their dependence on the intrinsic absorption coefficient. It is tested against experimental data obtained from samples of two materials (calcite and gypsum) which display a range of absorption band intensities over the 4-14-micro region. The ability of the theory to predict the different reflection behavior of bands of various intensities is demonstrated and considered important for explaining remote sensing data.

No abstract

Expression of the proendocrine gene neurogenin 3 (Ngn3) is required for the development of pancreatic islets. To better characterize the molecular events regulated by Ngn3 during development, we have determined the expression profiles of murine embryonic stem cells (mESCs) uniformly induced to overexpress Ngn3. An mESC line was created in order to induce Ngn3 by adding doxycycline to the culture medium. Genome-wide microarray analysis was performed to identify genes regulated by Ngn3 in a variety of contexts, including undifferentiated ESCs and differentiating embryoid bodies (EBs). Genes regulated by Ngn3 in a context-independent manner were identified and analyzed using systematic gene ontology tools. This analysis revealed Notch signaling as the most significantly regulated signaling pathway (p ‫؍‬ .009). This result is consistent with the hypothesis that Ngn3 expression makes the cell competent for Notch signaling to be activated and, conversely, more sensitive to Notch signaling inhibition. Indeed, EBs induced to express Ngn3 were significantly more sensitive to ␥-secretase inhibitormediated Notch signaling inhibition (p < .0001) when compared with uninduced EBs. Moreover, we find that Ngn3 induction in differentiating ESCs results in significant increases in insulin, glucagon, and somatostatin expression.