ALBERT

Notes: The overtone spectroscopy and intramolecular vibrational relaxation dynamics of CH chromophore in the fluoroform molecule is studied by a three-dimensional (3D) time-dependent wave-packet method, and the results are compared with the experiment and with those of a 2D (stretch–bend) wave-packet method. A third mode (CF symmetrical stretch) is included in order to explain the long time dynamics and the combination bands between the CF stretch fundamental and the Fermi polyad frequencies. The comparison with the 2D study is carried out by the use of a full set of dynamical and spectroscopic variables, based on the autocorrelation function of the bright states of each polyad. The spectroscopic variables then follow by Fourier transforming the autocorrelation function, while the dynamical ones emerge via survival probability in the frame of the dynamical statistical ensemble. These include several relaxation times and the number of cells and rates of phase–space exploration. The specific effect of the third mode is monitored by following the reduced dynamics of the system irrespective of the polyad stretch–bend dynamics, through population evolution. Dynamical results clearly reveal the third mode effects at very short and long times. In the last regime, we can observe a great span of different behaviors, depending on how the third mode excited states are involved. This richer variety of dynamical patterns cannot be observed in a two-mode model and justifies the present work. The spectroscopic results of both models are in good agreement with the experimental results. © 1997 American Institute of Physics.

Notes: Field studies were conducted in 1988 and 1989 to determine the phenology and growth of broomrape in sunflower as affected by crop sowing dates. The parasitic weed attachment was observed in sunflower plants with 6–7 leaves; later it was found throughout the vegetative and flowering period of the crop. O. cernua seedlings with shoot development extensive but subterranean were mainly observed at the early heading stage of sunflower. At this stage they were beginning to reduce sunflower plant growth as compared with non–parasitized plants. The emergence of broomrape began at the early flowering stage of the crop and was particularly abundant throughout this and the achene–filling stage. Generally, broomrape infection was much less at the first than at the second or third sunflower sowings, and caused less reduction in yield.The duration of the broomrape emergence period increased as sowing date was delayed. Since sunflower yield was higher at earlier sowing dates, early sowing may be recommended for sunflower crops in broomrape–infested areas under mild mediterranean climates. Effet de la date de semis sur les infections d'orobanche (Orobanche cernua Loefl.) en culture de tournesol (Helianthus annuus L.)Des études de plein champ ont été conduites en 1988 et 1989 pour déterminer comment la phénologie et la croissance des orobanches en culture de tournesol étaient affectées par les dates de semis de la culture. Le rattachement de 1'adventice parasite a été observeé chez les plantes de tournesol avec 6–7 feuilles; plus tard il était observé tout au long des périodes végétatives et de floraison de la culture.Des plantules d'O. cernua avec un développement de la tige important mais souterrain ont été principalement observées au stage bourgeon précoce du tournesol. A ce stade elles ont commencé & réquire la croissance du tournesol en comparaison avec des plantes non parasitées. La levée de 1'orobanche a commencé au début du stade de la floraison de la culture et a été particuliérement abondant pendant celle–ci et le stade remplissement des akénes. Généralement, l'infection d'orobanche a été beaucoup moins forte au premier qu'au second et troisiéme semis et a causé des baisses de rendement plus faibles.La durée de la période de levée des orobanches a augmenté quand le semis a été retardé. Puisque le rendement en tournesol a été plus élevé pour les dates de semis précoces, un semis précoce peut être recommandé pour le tournesol en zones infestées par les orobanches sous les climats méditerranéens. Die Bedeutung des Saattermins der Sonnenblume (Helianthus annuus L.) für den Befall mil der Sommerwurz (Orobanche cernua Loefl.) In Feldversuchen wurden 1988 und 1989 die PhÄnologie und das Wachstum der Sommerwurz in Sonnenblumenkulturen untersucht. Der Befall der Sonnenblumenpflanzen wurde im 6- bis 7-Blatt-Stadium festgestellt, aber auch später in der gesamten vegetativen und generativen Phase der Kulturpflanze. Keimpflanzen der Sommerwurz mit einer kräftigen, aber unterirdischen Sproßentwicklung wurden überwiegend im frühen Stadium der Blütenentwicklung der Sonnenblume beobachtet. In diesem Stadium begann die Wachstumshemmung der Sonnenblume. Zu Beginn der Blüte der Sonnenblume lief die Sommerwurz auf und war während dieses Entwicklungsstadiums und der folgenden Samenbildung besonders häufig anzutreffen. In der ersten Aussaat der Sonnenblume war der Befall allgemein geringer als in der zweiten oder dritten. Mit späterem Saattermin verlängerte sich die Keimungsperiode der Sommerwurz. Nachdem die Sonnenblume bei früherer Saat einem höheren Ertrag brachte, wird für mild-mediterrane Gebiete mit Befall von Sommerwurz eine frühe Aussaat empfohlen.

Notes: The distribution in the spinal cord of the trigeminal primary projections in the frog Rana ridibunda was studied by means of the anterograde transport of horseradish peroxidase (HRP). Upon entering the medulla via the single trigeminal root, a conspicuous descending tract that reaches the cervical spinal cord segments is established. This projection arises in the ophthalmic (V1), maxillary (V2), and mandibular (V3) trigeminal nerve subdivisions. In the spinal cord, only a minor somatotopic arrangement of the trigeminal fibers was observed, with the fibers arising in V3 terminating somewhat more medially than those from V1 and V2. A dense projection to the medial aspect of the spinal cord, above the central canal, primarily involves V3. Each trigeminal branch sends projections at cervical levels to the contralateral dorsal field, and those from V2 are most abundant. Bilateral experiments with HRP application show convergence of primary trigeminal and spinal afferents within the dorsal field of the spinal cord.The pattern of arrangement of the trigeminal primary afferent fibers in the spinal cord of this frog largely resembles that of amniotes. However, the organization seems simpler and the slight somatotopic distribution of V1, V2, and V3 fibers is similar to the condition in other anamniotes. © 1993 Wiley-Liss, Inc.

Notes: Deep-level transient spectroscopy (DLTS) and constant-capacitance DLTS (CC-DLTS) techniques have been used to investigate selenium-related DX centers in AlGaAs alloys. The value of the thermal activation energy obtained by both techniques was the same (0.21 eV); however, experimental curves show some important differences. While CC-DLTS curves show only one peak, which reveals that there exists only one DX center in Se-doped AlGaAs, in DLTS curves it is possible to resolve up to two peaks lying at a lower temperature than the one observed by CC-DLTS. This disagreement may be due to the fact that DLTS measurements are strongly affected by refilling effects which occur in the edge zone of the space-charge region during capacitance transients performed at constant voltage. These effects accelerate the capacitance transients and can lead to too high thermal-emission rates. In contrast, these effects do not affect CC-DLTS curves, because in constant-capacitance voltage transients the edge of the space-charge region remains unchanged and refilling effects do not take place. These effects are rather important on DX levels because they exhibit thermally activated capture cross sections and very low ionization factors at the experimental temperatures and, therefore, capture processes are slow and their time constants can be similar to those of the emission processes.

Notes: The thermal lensing characteristics of several silicate, germanate, phosphate, and borate glasses were studied using a laser with a 7 ns pulse at 457 nm in a tight focus geometry. A geometric model was developed to describe the quadratic radial profile of the refractive index resulting from the laser-induced temperature profile. This model was utilized to interpret the effects of some of the relevant experimental parameters on the fluence transmission experiments. The influence of material properties such as different types of network former and modifier ions on the nonlinear optical properties of these materials were also studied. It was found that: (i) the greatest influence of the network modifier ions was due to their effect on the absorption coefficient of the glasses; (ii) in lead glasses, the thermo-optic coefficients dn/dT of the germanates and silicates with random network structures were greater than those of the borate and phosphate glasses with ring and chain structures; and (iii) the main contribution to the thermo-optic coefficient comes from the thermally induced changes in the electronic polarizability of the glass components. In these glasses, the oxygen polarizability provides the dominant contribution and is affected by the variations in the polarizing power (charge to radius-squared ratio) of the network former ions.

Notes: Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.