W. A. Sibley

The International Panel on MS Diagnosis presents revised diagnostic criteria for multiple sclerosis (MS). The focus remains on the objective demonstration of dissemination of lesions in both time and space. Magnetic resonance imaging is integrated with dinical and other paraclinical diagnostic methods. The revised criteria facilitate the diagnosis of MS in patients with a variety of presentations, including "monosymptomatic" disease suggestive of MS, disease with a typical relapsing-remitting course, and disease with insidious progression, without clear attacks and remissions. Previously used terms such as "clinically definite" and "probable MS" are no longer recommended. The outcome of a diagnostic evaluation is either MS, "possible MS" (for those at risk for MS, but for whom diagnostic evaluation is equivocal), or "not MS."

Optical-absorption, -emission, and -excitation spectra are presented for ${\mathrm{Er}}^{3+}$ ions in fluorozirconate glass. Measured oscillator strengths of the transitions between $J$ manifolds at 300 and 15 K are compared with calculated electric and magnetic dipole oscillator strengths. Radiative rates for five luminescing states were calculated. The nonradiative rates from these excited states were determined by calculating the difference between the measured rates and the calculated radiative rates. The low-temperature nonradiative rates are in agreement with the phenomenological energy-gap law followed by rare-earth ions in a number of crystals and glasses. The temperature dependence of the lifetimes was analyzed using the Huang-Rhys theory of multiphonon emission. Values for the $^{4}I_{\frac{11}{2}}$ radiative and nonradiative rates obtained by the above methods are compared with those obtained applying the method Flaherty and DiBartolo used to study Mn${\mathrm{F}}_{2}$: ${\mathrm{Er}}^{3+}$. The multiphonon emission rates in fluorozirconate glass are much lower than the rates for the same levels of ${\mathrm{Er}}^{3+}$ in oxide glasses. Measurements of the bandwidths of the ground and excited states of ${\mathrm{Er}}^{3+}$ and the nearly exponential decay of the emissions indicate a relatively narrow distribution of site symmetries compared to oxide glasses.