Effect of 5-hydroxytryptamine on the peripheral chemoreceptors in the rat

5-Hydroxytryptamine (5-HT), in the doses of 2-5 mug/kg injected into the carotid body area, produced a significant increase in the respiratory rate and carotid sinus nerve activity. Selective ablation of the ipsilateral carotid sinus nerve abolished the respiratory stimulation produced by the drug. On the other hand, the same doses of 5-HT injected into the ascending aorta did not produce stimulation of respiration when the carotid sinus nerves were sectioned. The activity of the aortic nerves did not increase after injecting the drug into the ascending aorta or at the root of the right subclavian artery. These results indicate that 5-HT stimulates the chemoreceptors in the carotid body of the rat. The lack of responses to the injections of the drug in the aortic or subclavian region was due to the absence of chemoreceptors in these regions of the rat.     

A Carrier-Based Unipolar PWM Current Controller That Minimizes the PWM-Cycle Average Current-Error Using Internal Feedback of the PWM Signals

A carrier-based unipolar pulsewidth modulation (PWM) current controller is described using a one-phase PWM rectifier bridge as a test circuit. The controller PWM signal generator uses a sawtooth carrier signal to obtain both synchronized PWM waveforms and a constant switching frequency. A current-error signal and an amplitude modulation depth signal are used to create the input reference signal to the PWM signal generator. The amplitude modulation depth signal is obtained from the PWM-cycle average of the PWM signal generator output signals. This internal feedback is illustrated using a second-order low pass Butterworth filter. With an appropriately designed low-pass filter, the current-error signal is forced to be centered on zero over a PWM cycle. The maximum peak-peak magnitude of the current-error signal is used as a design guideline for deciding an appropriate gain constant in the controller current feedback loop. The low pass filter design is examined to determine a suitable gain and 20-dB attenuation frequency to minimize the current-error signal. The steady-state and transient operation of the proposed current controller is compared with a proportional-integral controller and an average current-error controller. SPICE simulations and experimental results are used to demonstrate the characteristics of the controller.     

Interaction of L-glutamic acid with human T-lymphocytes

A specific interaction of [3H]Glu with T lymphocytes from the blood of healthy donors (Kd = 0.236 microM) was revealed and described. It was found that unlabeled quisqualate, a structural analogue of L-glutamic acid, and unlabeled dipeptides Ala-Glu, Glu-Ala, and Glu-Glu competitively inhibit the specific binding of [3H]Glu to T lymphocytes (with Ki 0.19, 2.4, 3.4, and 1.2 microM, respectively). Binding experiments with conjugates of labeled and unlabeled glutamic acid with dextran showed that the receptors of [3H]Glu are localized on the outer surface of the plasma membrane of T lymphocytes.     

Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Cu/SiO₂, Zn/SiO₂ and Cu-Zn/SiO₂ samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formula Zn_x-yCu_y(Zn_3-x–zCu_z–y▪_x)[Si₄O₁₀](OH)₂.nH₂O, where Zn_3-x-zCu_z-y– ions are located in octahedral sites, Zn_x-yCu_y–ions in the interlayer; ▪_x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates. Received: 7 November 2000 / Reviewed: 23 January 20001 / Accepted: 23 January 2001     

Modeling and analysis of communication systems based oncomputational methods for Markov chains

The authors describe a computational approach for modeling and analyzing modern communication systems based on numerical methods for Markov chains. Advanced direct and iterative procedures for the calculation of the stationary distribution of a homogeneous discrete- or continuous-time Markov chain with finite state space are presented. They are implemented in a convenient software tool called MACOM for interactive modeling and performance evaluation of communication systems. MACOM provides the user with a predefined markovian model world describing modern telecommunication networks with adaptive routing schemes and advanced congestion-control mechanisms. The versatility of these algorithms is illustrated by their application to Markovian queuing models derived from telecommunications networks