EFFECTS OF pH ON ELECTROFLOTATION OF SPHALERITE

Electroflotation studies on sphalerite fine particles, conducted under careful pH control using buffer electrolytes, reveal that for either H₂ or 0₂ electrolytic gases there exists an optimum pH range at which electroflotation is most effective. This can be explained by the observed dependence of electrolytic gas bubble size on the pH of the electrolyte.     

Blood lipids in metropolitan caracas school children. A preliminary report (author''s transl)

A study was made of EP recorded in the visual projection area of the cerebral cortex in children with normal sight and in those with disturbed refraction when presented with blank and checkered patterns, the dimensions of the chess squares equalling 10, 20, 40, 60 and 120 angular minutes. In children with normal sight the patterns were defocussed by eyeglass lenses of --1 to +/- 6 dioptries. The investigation revealed a different EP configuration on the presentation of blank and checkered patterns. There was a similarity between the EP change when a blank pattern was replaced by a checkered one, and when the checkered pattern was made sharper. It is assumed that these EP changes results from enhanced lateral inhibition due to the contrast boundaries of the checkered pattern, The experiments carried out on children with disturbed refraction indicated that the maximal EP amplitude corresponded to the optimal optic correction, which shows that theuse of EP is a promising cue in determing vision acuity.     

Dissociation of arousal and regulatory behaviors following lesions of the lateral hypothalamus.

Investigated the effect of lesions of the lateral hypothalamus on feeding and spontaneous locomotor activity in 3 experiments with a total of 110 male Sprague-Dawley rats. Lateral hypothalamic lesions produced aphagia and adipsia but did not prevent the increase in locomotor activity characteristic of starvation. In addition, both food deprivation and lateral hypothalamic self-starvation potentiated amphetamine-induced behavioral arousal. However, the lesions did abolish incentive-motivated activity to a stimulus signaling food. Results suggest a dissociation between the neural mechanisms mediating arousal and regulatory behaviors. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of thirst in the rat: Effects of hypertonic saline, polyethylene glycol, and vena cava ligation.

Describes 3 experiments in which over 465 Sprague-Dawley rats of various ages either (a) were injected with hypertonic sodium chloride solutions to produce intracellular dehydration, (b) were injected with polyethylene glycol to induce hypovolemia, or (c) underwent ligation of the inferior vena cava to stimulate the renin-angiotensin system. 16-day-old Ss drank like adults after injection of polyethylene glycol. Hypertonic saline injection did not elicit adultlike drinking until 30 days of age, and vena cava ligation did not produce adult levels of water consumption until 42 days postnatally. It is concluded that treatments which have been associated with different mechanisms of thirst, therefore, first become effective at different times during ontogeny. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Innovation in telecommunication and interfirm cooperative agreements

The purpose of this paper is to analyse the evolution towards the new paradigm of information and communication technology (ict) and its consequences in terms of strategies, in particular the development of cooperative agreements between telecommunication firms. To analyse the characteristics ofict paradigm we rely on some recent contributions in economics of technological change. We discuss in a second step the following proposition: an agreement is a flexible means to cope with increasing uncertainties and the durability of an agreement is conditioned by the search for a particular type of flexibility: dynamic and pro-active flexibility based on learning processes.     

Ontogeny of behavioral arousal: The role of environmental stimuli.

During the course of ontogenesis the developing rat has been reported to pass through a transient period of intense behavioral arousal which peaks at 15 days of age, a phenomenon that has been interpreted to reflect a sequential caudal to rostral development of excitatory and inhibitory systems in the mammalian brain. In the present 4 experiments with male and female Sprague-Dawley rats, it was shown that (a) this period of intense hyperactivity occurred only when the animal was tested alone in an unfamiliar environment, the degree of arousal was proportional to the dissimilarity between the home cage and the test environment, and isolation per se was insufficient to elicit the arousal response; (b) environmental temperature had a minimal influence on the degree of behavioral arousal in either familiar or unfamiliar environments; (c) unlearned responses to pheromonal or other naturally occurring nest odors did not suppress the high levels of locomotor activity evoked by unfamiliar environments in the 15-day-old rat pup; and (d) it is fear or distress evoked by the unfamiliar environment rather than curiosity that underlies this developmental phenomenon. It is concluded that the sequential increase and decrease in locomotor activity that occurs during ontogenesis cannot be used to support the principle of caudal to rostral development of excitatory and inhibitory centers in the CNS. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amplification of mode-locked semiconductor diode laser pulses in erbium-doped fibre amplifier

Amplification of picosecond pulses from an actively mode-locked semiconductor diode laser in an erbium-doped fibre amplifier pumped at 532 nm is demonstrated. Peak emission was centred on 1.536 mu m and a saturated amplifier gain of 13 dB yielded less than 10 ps pulses with a peak power of 0.58 W at 600 MHz. Optimisation of the mode-locked oscillator allowed amplified peak pulse powers greater than 3 W to be generated.<>     

Estimation of electrolytic hydrogen production potential in Venezuela from renewable energies

An initial estimation of the potential for hydrogen (H₂) production in Venezuela is made, obtained by water electrolysis using electricity from renewable sources, taking advantage of the great potential of the country for solar, wind and mini hydro energies. For the first two, its potential maps is obtained from insolation and wind speed maps, respectively, prepared from satellite data, and for mini-hydro, the potential is obtained from documentary information. To calculate the amount of H₂ to produce is used the Higher Heating Value, considering the electrolytic system overall efficiency of 75%, including power requirements of the electrolyzer, auxiliary equipment, and system losses. In addition, in the calculation of usable renewable potential are excluded land areas under special administration, marine, lake and urban areas, and other limitations are considered concerning energy conversion efficiencies and useful areas available for the location of the different renewable technologies.