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We present an extensive new time series of spectroscopic data of the peculiar SN 1999aa in NGC 2595. Our data set includes 25 optical spectra between -11 and +58 days with respect to B-band maximum light, providing an unusually complete time history. The early spectra resemble those of an SN 1991T-like object but with a relatively strong Ca H and K absorption feature. The first clear sign of Si II lambda6355, characteristic of Type Ia supernovae, is found at day -7, and its velocity remains constant up to at least the first month after B-band maximum light. The transition to normal-looking spectra is found to occur earlier than in SN 1991T, suggesting SN 1999aa as a possible link between SN 1991T-like and Branch-normal supernovae. Comparing the observations with synthetic spectra, doubly ionized Fe, Si, and Ni are identified at early epochs. These are characteristic of SN 1991T-like objects. Furthermore, in the day -11 spectrum, evidence is found for an absorption feature that could be identified as high velocity C II lambda6580 or H alpha. At the same epoch C III lambda4648.8 at photospheric velocity is probably responsible for the absorption feature at 4500 8. High-velocity Ca is found around maximum light together with Si II and Fe II confined in a narrow velocity window. Implied constraints on supernovae progenitor systems and explosion hydrodynamic models are briefly discussed.

Twenty-five pairs of equine third metacarpals (McIII) were collected from horses of varying breeds and ranging in age from 1 d to 27 yr. Standard three-point bending tests were performed on the McIII to obtain comparative data on breaking load (BL), breaking strength (BS), and elasticity (E). Broken bones were reassembled and 2-cm sections cut from the bone 1 cm below the nutrient foramen and at the site of the break. Bone mineral content (BMC) and geometrical properties of these sections were determined. Maximum BMC (17.3 g/2 cm) was reached at 6.0 [+ or -] 1.8 yr of age. Horses in this study achieved 76% of maximum BMC by 1 yr of age. Maximum BL (1,888 kg) was reached at 4.6 [+ or -] 1.8 yr of age. The coefficient of determination ([r.sup.2]) between BMC and BL was .92 (P [is less than] .001). Breaking strength peaked at 2,272 kg/[cm.sup.2] at 6.3 [+ or -] 1.2 yr of age. The correlation between BS and BMC was .84 (P [is less than] .0001). At 1 yr of age BS was 1,919 kg/[cm.sup.2], or 85% of maximum BS. Elasticity increased linearly with log 10 age ([r.sup.2] = .91). The [r.sup.2] of BMC and E was .79 (P [is less than] .001). Area moment of inertia (I) of the cortex of the bone was best approximated by the area of an ellipse ([r.sup.2] = .91; P [is less than] .01). Results suggest that bone strength in horses peaks after most race horses have completed their careers.

Several first principles electronic structure calculations are conducted to explain the various effects of Y substitutions on the magnetism of the [Gd.sub.5][Ge.sub.4] compounds. The different specific crystallographic positions present in the alloys are also analyzed.

The single crystals of the antiferromagnetic compound U[Ni.sub.0.5][Sb.sub.2] ([T.sub.N] = 161 K) are studied by using measurements of magnetic susceptibility, specific heat and electrical resistivity at ambient pressure and resistivity under hydrostatic pressures. The effect of pressure is to raise [T.sub.N], while suppressing the amplitude of the small features in electrical resistivity versus temperature at lower temperatures and increasing the thermal hysteresis.