Gulf stream: velocity fluctuations during the late cenozoic

Biostratigraphic analysis of seven piston cores from the southeastern Blake Plateau suggests that the upper Miocene to Recent sedimentary section at this location represents a history of deposition of calcareous ooze alternating with current-induced nondeposition or erosion. This record is primarily a result of long-term fluctuations in the velocity of the western boundary current or Gulf Stream, which sweeps the plateau. High-velocity phases of this current system, as signaled by hiatuses in the section, lie within the time limits 4.8 to 6.1, 3.9 to 4.4, 2.3 to 2.9, and 0 to 1.5 million years before present (B.P.). These time intervals are coeval with dated episodes of climatic decline and glaciation. The most intense acceleration of the Gulf Stream, as indicated by deep erosion of the Blake Plateau, occurred in the latest Miocene to earliest Pliocene (4.8 to 6.1 million years B.P.) in conjunction with a major expansion of the Antarctic ice cap. Subsequent accelerations of the Gulf Stream coincide with early Pliocene cooling in the Southern Hemisphere, worldwide expansion of high-altitude-high-latitude glaciers in the late Pliocene, and the classical glaciations of the Pleistocene. An additional, protracted increase in the average velocity of the Gulf Stream, which began in the late Miocene and culminated in the mid-Pliocene (about 3.8 million years B.P.), can be attributed to the gradual emergence of the Central American isthmus.     

Physics

From massive quarks deep in the hearts of atomic nuclei to the catastrophic collapse of giant stars in the farthest reaches of the universe, from the partial realization of Einstein's dream of a unified theory of the forces of nature to the most practical applications in technology, medicine, and throughout contemporary society, physics continues to have a profound impact on man's view of the universe and on the quality of life. The author argues that the past few years, in terms of new discoveries, new insight-and the new questions-have been among the most productive in the history of the field and puts into context his selection of some of the most important new developments in this fundamental science.     

Focus on polar research

A few of the scientific challenges of polar research are reviewed, with stress on the work being done by U.S. investigators. The accomplishments that have been made are impressive, but much remains to be done. An evaluation of future research goals and priorities in science per se and in the national interest is not attempted, but a research strategy for the future, presently planned by the National Research Council's Polar Research Board, should contribute to this end.     

The virus-vector relationship of the tomato leafcurl virus (TLCV) and its vector,Bemisia tabaci gennadius (Hemiptera: aleyrodidae)

Basic studies carried out in India showed that the incubation period of TLCV in plants varied from 8 days in August to 90 days in winter. The acquisition threshold for the whitefly,Bemisia tabaci Gen., was 31 min; it resulted in 3% transmission. An acquisition access of 24 h for a female whitefly on a TLCV source resulted in 30% transmission. A minimum feeding period of 32 min was required by a viruliferous whitefly to cause infection on tomato test plants; this gave 4% transmission. With inoculation access of 24 h on tomato test plants, the transmission rose to 24%. Starving the vector for 1 h pre-acquisition or 1 h pre-inoculation resulted in higher levels of transmission of TLCV: 36 and 40%, respectively, compared with 20% for non-starved whiteflies. Extending the fasting period beyond 1 h resulted in a reduced transmission level. The whiteflies could acquire the virus from the cotyledonary leaves of an infected tomato plant, with a resultant 28% transmission; but infection did not occur when the whiteflies had an inoculation access to such leaves. Higher transmission rates were obtained when the younger leaves on tomato plants were used for acquisition and inoculation. Transmission was 8 and 38% when five whiteflies per plant were allowed 24 h of acquisition access to 11- and 2-month-old virus sources, respectively. After an acquisition access of 24 h to a TLCV source, male and female whiteflies retained their infectivity for 5 and 53 days, respectively. Nymphs can acquire and transmit the virus. When ten whiteflies of each sex were given 24 h of acquisition and of inoculation access, the subsequent transmission rate of males and females was 56 and 86%, respectively. This virus is not transovarially transmitted. Whitefly colonies raised on brinjal were more efficient (70 and 84% transmission in two experiments) than those raised on chilli, cotton, cowpea, tobacco or tomato.     

A new pattern of morphofunctional relationship among cranial nerves: Evidence of anatomical and physiological connection between trigeminus and oculomotor nerves

It is shown that the cell bodies of the afferent fibres supplying the proprioceptivity to the extrinsic eye muscles are located within the semilunar ganglion. Furthermore, some Gasserian cells have central processes which enter the midbrain through the oculomotor nerve. Sensory ganglion cells, derived from the same strand of placodal cells forming the ophthalmic lobe, can be constantly detected within the oculomotor nerve of ox, monkey and man.

---

Kurzfassung Unsere Forschungen haben ergeben, dass sich die Zellkörper der fibrae afferentes, die dem äusserlichen Augenmuskeln die propriozeptive Sensibilität geben, im Ganglion des Gasser befinden. Ausserdem haben einige Zellen des Gasserschenganglion zentrale Verzweigungen die durch den Nervus oculomotorius in den Hirnstamm führen. Sensitive Ganglionzellen, die von der gleichen Reihe plakodischer Zellen stammen, und den lobus oftalmicus Gasseri formen, sind regelmassig im nervus oculomotorius des Rindes, des Affen und des Menschen zu finden.

---

Resume Nos recherches ont démontré que, chez le Mouton et le Porc, le ganglion de Gasser contient les corps cellulaires des fibres nerveuses desservant les fuseaux neuromusculaires des muscles extrinsèques de l'oeil. En outre, quelques cellules du ganglion de Gasser ont leurs prolongements centraux qui se portent au tronc cérébral en suivant à rebours les radicules du nerf oculomoteur. En fin, on a trouvé constamment des cellules ganglionnaires sensitives dans l'oculomoteur du Boeuf, du Singe et de l'Homme; ces cellules proviennent du même cordon de cellules placodiales qui forme le lobe ophthalmique du ganglion semilunaire.

---

Riassunto Le nostre ricerche hanno dimostrato che i corpi cellulari delle fibre nervose afferenti, che danno la sensibilità propriocettica al muscolo oculare estrinseco, si trovano nel ganglione di Gasser. Inoltre, alcune cellule del ganglione di Gasser hanno diramazioni centrali che portano al tronco cerebrale attraverso il nervo oculomotore. Infine, si sono costantemente incontrati nel nervo oculomotore del bovino, della scimmia e dell'uomo, cellule sensitive che provengono dallo stessotronco di cellule placodali che formano il lobo oftalmico.