Severe damage during the September 19, 1985 Mexican earthquake prompted a site visit by three cngincers and two seismologists representing the Canadian National Committee on Earthquake Engineering. This papcr includes background information on earthquake history of the region, details of the 1985 earthquake and its strong ground motion, subsoil conditions, and building code provisions. The team's observations of moderate damage in the epiccntral area are consistent with the relatively low near-field accelerations (15% g ) . In the damaged parts of Mexico City, soft soil conditions amplified the ground motion and resulted in almost pure harmonic motion with a period of about 2 s. These characteristics, together with the long duration and high accelerations (20% g ) caused severe damage to many structures, as is illustrated in the papcr. Lessons learned from the earthquake together with the Mexican emergency code changes are discussed.Trois inginieurs et deux sCismologues mandatts par Ic Comitt national Canadien dc gCnie parasismique sont all& examiner sur place les dommages importants causes le 19 septembre 1985 par lc tremblement de terre du Mexique. Cct articlc prCsente des informations sur I'historique des skismes ayant frappes cette region, le stisme de 1985 ct Ics vibrations fortes du sol, les conditions du sol sous-jacent, et les riglements du code du bit~ment. Les dommages modiris tcls qu'observts par I'Cquipe dans la region de I'tpicentre sont en accord avec les acctlCrations rclativement faibles mesurkes (15% g). Dans les quartiers de Mexico ayant subi des dommages, les sols meubles ont amplifit les vibrations en un mouvernent harmonique quasi parfait avec une periode d'environ 2 s. Ces caracttristiques, associCes 5 la longue durCe des vibrations ct des hautes accCltrations atteintes (20% g ) ont cause des dornmages irnportants i~ plusieurs Cdifices, comme I'illustre cet article. Lcs leqons tirtes de ce tremblement de terre ainsi que les changements d'urgence apportks au code mexicain du bitiment sont discutes.

The N-methyl-D-aspartate (NMDA) receptor has been widely implicated in numerous activity-dependent models of neural plasticity, learning, and memory. The formation of new synapses is a major assumption of the neural basis of learning. The current research was conducted to determine whether NMDA receptor activation could induce synaptic formation and, if so, whether this ability would mirror developmental changes in NMDA receptors. Rats at various developmental ages were given a single intraperitoneal injection of NMDA and sacrificed at various brief postinjection intervals (0.5-2 hr). The rats showed an age-dependent decline in the behavioral response to NMDA, as evidenced by reduced seizure activity and duration. Quantitative electron microscopic observations on the molecular layer of the occipital cortex, an area rich in NMDA receptors, revealed a transient increase in the length of postsynaptic thickenings in 17- and 35-day-old animals, appearing within 0.5 hr of injection. At 1 and 2 hr postinjection, an increase in synaptic density (number of synapses) was observed in 8-day-old animals. These results provide evidence that NMDA administration alone is capable of rapidly inducing alterations in synaptic structure and the formation of new synapses, underscoring the importance of the NMDA receptor in synaptogenesis and synaptic structural plasticity.

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Synopsis Rate of seepage and position of exit point of line of seepage are investigated for steady flow through homogeneous-isotropic dams with trapezoidal cross section. Rigorous analytical solutions are not at present available for dams of general trapezoidal shape. A tabulation of a available rigorous solutions is given in Fig. 2. Rigorous solutions for rate of seepage and position of the exit point of the line of seepage are evauated numerically and presented in graphical for the following cases: (a) dams with vertical entrance face and zero tailwater (Fig 3 and 5) (b) dams with horizontal discharge face and zero tailwater (Fig 4 and 6). An approximate solution is given for dams of general trapezoidal shape by combining the results of the above two cases. The accuracy of this solution is discussed. On a étudié le débit d'infiltration et la position des sorties des lignes d'infiltration dans le cas de l'écoulement constant au travers de barrages homogènes isotropes de section trapèzoidale. Il n'y a pas actuellement de solution analytique rigoureuse pour les barrages de forne trapèzoidale quelconque. On donne une table de solutions rigoureuses connues. en Fig. 2. On a évalué numériquement les solutions rigoureuses du débit d'infiltration et la position des sorties des lignes d'infiltration, et on présente les résultats sous forme graphique dans les cas suivants: (a) barrages à d'entrée verticale et en absence d'eau d'aval (Fig 3 et 5) (b) barrages à face de décharge verticale et en absence d'eau d'aval. On donne une solution approchée dans le cas des barrages à solution trapèzoidale quelconque en combinant les résultats des deux précédents.On discute de l'exactitude de la solution.

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