Gain Slope Research Articles

The Correlation between Gain Slope, ASE Slope, and Second-Order Distortion of EDFAs in Directly Modulated AM-CATV Lightwave Systems

In the literature some disagreement and contradiction exist regarding the relationship between gain slope in EDFAs and the distortion this effect generates in analog multichannel CATV systems. We will try to identify these contradictions and consequently discuss the design criteria for an analog EDFA by showing that optimizing an EDFA for good gain slope can be done by sacrificing an insignificant amount of output power but enhancing the noise performance. The gain slope itself is measured with a new low-cost method: it will be shown from both theory and experiment that the ASE slope is a good approximation for the gain slope. We will finally demonstrate the predictive value of the gain-slope measurement by distortion measurement in a system evaluation.

4 Intrauterine growth retardation

IUGR puts the fetus at risk of stillbirth, perinatal morbidity and neonatal handicap, yet most instances of IUGR are not recognized. Progress has been made in recent years to monitor the high-risk fetus with intensive biometric and biophysical tests and to determine the appropriate time for intervention. These methods of surveillance are ineffective and inappropriate for population screening, and the main problem remains how to identify the at-risk fetus. Improvement of current performance requires the establishment of appropriate standards by which intrauterine growth can be assessed, and their introduction as part of well-organized screening programmes. We describe a computerized method of predicting the optimal weight for each pregnancy, which is individually adjusted for non-pathological variables such as maternal height, booking weight, ethnic group and parity. The optimal birthweight determines the expected slope or velocity of fetal weight gain. This individualized prediction improves the distinction between constitutional and pathological smallness. Furthermore, preterm weights are measured against a fetal weight norm rather than a birthweight standard that is derived from non-physiological preterm deliveries. The customized growth chart allows screening for growth retardation by determining the growth velocity through serial measurement and plotting of fundal height, backed up as necessary by ultrasound estimation of fetal weight and referral for more intensive surveillance as indicated.

Vertical vestibular input to and projections from the caudal parts of the vestibular nuclei of the decerebrate cat.

1. To investigate the type of vestibular signals that neurons in the caudal parts of the vestibular nuclei transmit to the cerebellum and spinal cord, we studied their responses to natural vestibular stimulation in vertical planes in decerebrate cats with the caudal cerebellum removed. Most neurons were in the caudal half of the descending vestibular nucleus, the remainder at corresponding levels of the medial nucleus or the medial-descending border. 2. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal tilts delivered at 0.05-1 Hz near the plane of body rotation that produced maximal modulation of the neuron's activity (response vector orientation). For most neurons the predominant vestibular input could be identified as coming from otolith organs (46%) or vertical semicircular canals (37%). Some neurons had otolith+canal convergence (9%) and others either had such converging input or some other form of central processing (8%). 3. Gain and phase of the responses of otolith neurons were comparable with values obtained in earlier studies on Deiters' nucleus and the rostral descending nucleus. Many canal neurons had a steeper gain slope and more advanced phase than observed previously for more rostral neurons. This may be due to more irregular afferent input to many neurons or to the absence of the vestibulocerebellum. 4. Response vector orientations of canal neurons were closely bunched near the planes of the ipsilateral vertical canals. The small number of contralaterally projecting vectors showed evidence of convergence between the two contralateral vertical canals. As is the case elsewhere in the vestibular nuclei, there was no evidence of convergence from bilateral vertical canals. Response vector orientations of otolith neurons were restricted to the roll quadrants; the majority pointed ipsilaterally. 5. Antidromic stimulation with an electrode in the restiform body or with several electrodes in the dorsal half of the white matter of the upper cervical cord was used to identify neurons projecting to the cerebellum and spinal cord, respectively. A substantial number of spontaneously firing neurons projected to the cerebellum, but there were few spontaneously active vestibulospinal neurons. The properties of the vestibular input to cerebellar-projecting neurons were the same as those of the population as a whole, but the effect of tilt on vestibulospinal neurons appeared weak or absent. 6. Many neurons were inhibited by stimulation of the restiform body. We suggest that this is mainly due to stimulation of the axons of vestibulocerebellar Purkinje cells. 7. Our results demonstrate a robust vertical vestibular input to the caudal parts of the vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic converting enzyme inhibition facilitates baroreceptor resetting to hypertensive levels.

We investigated the acute and chronic effects of converting enzyme inhibitors (captopril or enalapril) and of angiotensin II receptor blockade (DuP 753) on rapid (30-minute) baroreceptor resetting elicited by a prompt and sustained hypertensive response provoked by aortic constriction. Pressure-nerve activity curves, pressure at 50% of maximal baroreceptor activity, baroreceptor gain (slope of the curve), and systolic threshold pressure for baroreceptor activation were determined as indexes of baroreceptor function. A slight fall in mean arterial pressure after acute treatment with the converting enzyme inhibitor or DuP 753 was accompanied by a partial leftward curve shift, which is associated with a partial threshold shift and increase in gain. A maintained hypertensive stimulus caused a partial rightward curve shift and partial (49% to 56%) threshold shift to hypertensive levels in both acutely treated and control rats. The hypertensive stimulus provoked a partial rightward curve shift and complete (88% to 94%) threshold shift to hypertensive levels in chronically treated rats. The effect of enalapril on baroreceptor function was unaltered by the bradykinin antagonist Hoe 140. These data demonstrate that chronic inhibition of converting enzyme or blockade of angiotensin II receptors facilitates rapid resetting of the baroreceptors to hypertensive levels caused by partial aortic constriction without a change in baroreceptor sensitivity.

A new type of waveguide ring cavity for resonator and filter applications

A new type of rectangular waveguide ring cavity has been developed for applications to resonators, filters, and multiplexers. The circuits have advantages of high Q and high power handling capability. H-plane and E-plane waveguide ring cavities have been investigated thoroughly in single-mode and dual-mode operations. For single-mode operation, regular resonant modes, split resonant modes, and forced resonant modes were explained by resonant mode charts of E-field points. Mechanically tuned and electronically tuned resonators built by adjusting the resonant modes between regular resonant modes and forced resonant modes have been demonstrated. For dual-mode operation, a dual-mode filter using a single H-plane ring cavity has been built with a bandwidth of 0.77%, a stopband attenuation of more than 40 dB, and a sharp gain slope transition. Another dual-mode filter which was formed by cascading two E-plane ring cavities has also been fabricated with a bandwidth of 1.12%, a stopband attenuation of 70 dB, a mode purity of 2 GHz at the center frequency of 26.82 GHz, and a sharp gain slope transition. >

Dynamic Neural Units with Applications to the Control of Unknown Nonlinear Systems

To emulate higher cognitive functions, such as sensory information processing and the attendant complexities of learning, memory storage, control, and vision, the biological neuron has to be modeled based upon feedback networks. The authors proposed such a neuronal model, called a “dynamic neural unit” DNU based upon the topology of a reverberating circuit in a neuronal pool of the central nervous system. The DNU architecture embodies delay elements, feedforward and feedback synaptic weights, and a nonlinear activation function. In this article, the concept of DNU is extended by incorporating both synaptic and somatic operations. The synaptic operation provides the optimum feed forward and feedback weights, while the somatic operation determines the optimum gain slope of the nonlinear activation function for a given task. The architectural details and the learning and adaptive algorithm to modify adjustable parameters, namely, feed forward and feedback synaptic weights, and slope of nonlinear function of the DNU are presented. The algorithm implementation of an isolated DNU is given. Considering DNU as the basic processing element, a three-stage dynamic neural network is developed. The effectiveness of the proposed dynamic neural network architecture as applied to the control of unknown nonlinear systems is discussed and extensive simulation results are presented.

Music signal time reverse effect apparatus

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Characterization of the baroreceptor heart rate reflex during development in spontaneously hypertensive rats.

1. We have examined the baroreceptor-heart rate (HR) reflex in weight-matched conscious spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats during development. 2. Graded steady-state changes in mean arterial pressure (MAP) and the corresponding HR responses before and after vagal blockade with methylatropine were fitted to an S-shaped logistic function. 3. At 6 weeks of age, SHR had a 17% higher MAP than WKY and an increased baroreflex gain (slope) compared with WKY due to an increased curvature of the MAP-HR relationship. The HR range (the difference between the upper and lower HR plateaus) was similar in the two strains at this time. 4. From 9-14 weeks of age, the baroreflex gain progressively increased in WKY and decreased in SHR due to corresponding alterations in HR range. 5. By 20 weeks the baroreflex gain was 23% lower in SHR than WKY due to a 37% lower HR range. 6. There were no differences between the two strains in the sympathetic component of the baroreflex at any age, suggesting that the changes to baroreflex properties were confined to the cardiac vagus. 7. Pretreatment with enalapril from 4-9 weeks reduced the hypertension of SHR at 14 and 20 weeks by 38% and abolished all baroreceptor-HR reflex differences between the two strains. 8. These studies suggest that the major alteration to the baroreceptor-heart rate reflex in the SHR during development was a reduction in the maximum vagal capacity to respond to changes in blood pressure. This effect developed after the onset of hypertension and was prevented by antihypertensive treatment early in life. The lack of effect on the cardiac sympathetic component suggests that altered arterial baroreceptor afferents are not unlikely to be responsible.

A frequency domain approach to performance optimization of high-speed VLSI interconnects

An efficient method is presented for the computation of exact group delay, gain slope and their sensitivities with respect to design parameters in multiconductor transmission line networks. The group delay and gain slope sensitivities with respect to transmission line parameters are evaluated in terms of the second-order derivatives of the eigenvalues and eigenvectors of the propagation matrix. By combining this method with minimax optimization, a frequency-domain approach is developed to minimize transient delay and distortion in high-speed VLSI interconnects. Examples of interconnect optimization demonstrate simultaneous reductions of signal propagation delay, distortion, and crosstalk at several vital connection ports. Compared to direct time-domain optimization, the proposed approach is more than three times faster. The proposed technique is useful in optimal design of circuit interconnects for high-speed digital computers and communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Input-output relations of the feedback synapse between horizontal cells and cones in the tiger salamander retina.

1. The input-output relation of the feedback synapse between horizontal cells (HCs) and cones was studied by simultaneously recording the light responses of the HCs and of cones the outer segments of which were truncated off. 2. The postsynaptic light response of the truncated cone was depolarizing and free of direct influence of photocurrents. These postsynaptic light responses were graded and sustained; their waveform resembled that of the HC light responses. 3. Input-output relation of the HC-cone feedback synapse was obtained by plotting the simultaneous voltage points of the HC and truncated cone light responses. At the resting potential of the cone (-40 mV), the voltage gain of the feedback synapse was about -0.33 when VHC = -20 mV and it was about -0.03 when VHC = -60 mV. 4. At more hyperpolarized cone voltages, the feedback signals in cones became smaller, and they reversed at about -67 mV. The voltage gain of the feedback synapse at VHC = -20 mV was about -0.23, -0.18, -0.07, and +0.2 when Vcone = -44.5, -52.5, -65, and -77.5 mV, respectively. 5. Light hyperpolarized the HC, which resulted in a conductance change (delta Gs) in cones. The cone conductance decreased progressively as the HCs were increasingly hyperpolarized, and delta Gs reached a maximum value of 0.93 nS when the HCs were hyperpolarized from -20 to -52 mV. 6. The peak light responses of intact cones were plotted against the peak HC light responses. This gives the relationship between the pre- and postsynaptic voltages of the cone-HC (forward) and HC-cone (feedback) synapses at any given light intensity. Combining this relationship with the input-output relations obtained at various voltages of the truncated cones allows the input-output relation of the feedback synapse for light-evoked signals to be obtained. 7. The input-output relation of the feedback synapse for light-evoked signals was bell-shaped, because the feedback light responses were controlled by two opposing factors: as the light became brighter, the postsynaptic conductance change increased, but the driving force decreased. 8. For light-evoked signals, the slope gain (slope of the input-output relation) of the HC-cone feedback synapse was negative (varied from -0.33 to 0) when VHC lay between -20 and -52 mV; and it was positive (0 to +0.8) when VHC lay between -52 and -72 mV. 9.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid evaluation of electroless nickel plating rate on various catalytic metallic substrates using the coulostatic method with finite pulse width

The coulostatic method using a finite pulse width was applied to measure the instantaneous plating rate i dep of nickel from a sodium citratesodium hypophosphite bath using four metallic substrates with different catalytic activities immersed in a stagnant electroless bath (pH 1 - 5.25, 65 - 90 °C). The electrodes tested were: (i) a preformed electroless Ni-P alloy on copper, (ii) copper (purity, 99.98%), (iii) palladium-activated copper and (iv) platinum (purity, 99.99%). The measured polarization resistance R p showed a reproducible inverse relation with i dep ( i dep = KR −1 p ). The proportionality constant K obtained from weight gain, polarization curves and coulostatic Tafel slope measurements agreed very well with catalytic substrates (i) and (iii). For systems using copper or platinum as substrates with low catalytic activity, i dep values resulting from the coulostatic method notably differ from those from polarization curves.

A pole‐zero pairing strategy for minimum‐gain‐sensitivity nth‐order biquadratic filter cascades

AbstractIn attempting to use the pole‐zero assignment for gain sensitivity minimization in biquadratic filter cascades, a new expression for the total gain error is derived. In this result the logarithmic gain slope appears as a weighting factor to a second term depending on the structure and the parameter or component inaccuracies. On the basis of this partitioning, a pairing method for minimum gain sensitivity is developed which uses the ‘modified bottleneck algorithm’. Additional investigations finally show that minimum gain sensitivity and optimum dynamic range lead to similar constraints which can be achieved simultaneously in most applications.

Accommodation characteristics before and after near work

Accommodation measurements on 32 young subjects using a polarised vernier optometer showed that the mean accommodation response/stimulus curve within an accommodative amplitude of 6.67 D followed a linear trend. Statistical analysis showed a significant link between the dark focus and optimum focus (accommodative response equals stimulus demand) but not between the dark focus and gain (slope). The distance refractive state shows a weak correlation with gain but not with the dark focus. These findings suggest that near vision adaptation results in dark focus adaptation which modifies closed-loop accommodation responses through its influence with the position of optimum focus.

Effects of altered CSF [H+] on ventilatory responses to exercise in the awake goat.

We investigated the effects of selective large changes in the acid-base environment of medullary chemoreceptors on the control of exercise hyperpnea in unanesthetized goats. Four intact and two carotid body-denervated goats underwent cisternal perfusion with mock cerebrospinal fluid (CSF) of markedly varying [HCO-3] (CSF [H+] = 21-95 neq/l; pH 7.68-7.02) until a new steady state of alveolar hypo- or hyperventilation was reached [arterial PCO2 (PaCO2) = 31-54 Torr]. Perfusion continued as the goats completed two levels of steady-state treadmill walking [2 to 4-fold increase in CO2 production (VCO2)]. With normal acid-base status in CSF, goats usually hyperventilated slightly from rest through exercise (-3 Torr PaCO2, rest to VCO2 = 1.1 l/min). Changing CSF perfusate [H+] changed the level of resting PaCO2 (+6 and -4 Torr), but with few exceptions, the regulation of PaCO2 during exercise (delta PaCO2/delta VCO2) remained similar regardless of the new ventilatory steady state imposed by changing CSF [H+]. Thus the gain (slope) of the ventilatory response to exercise (ratio of change in alveolar ventilation to change in VCO2) must have increased approximately 15% with decreased resting PaCO2 (acidic CSF) and decreased approximately 9% with increased resting PaCO2 (alkaline CSF). A similar effect of CSF [H+] on resting PaCO2 and on delta PaCO2/VCO2 during exercise also occurred in two carotid body-denervated goats. Our results show that alteration of the gain of the ventilatory response to exercise occurs on acute alterations in resting PaCO2 set point (via changing CSF [H+]) and that the primary stimuli to exercise hyperpnea can operate independently of central or peripheral chemoreception.

Altered heart rate-arterial pressure relation during head-out water immersion in conscious dog.

The influence of head-out water immersion (WI) (37 degrees C) on baroreflex control of heart rate was studied in five trained, instrumented, conscious dogs. Arterial pressure was raised and lowered using occluder cuffs implanted around the aorta and inferior vena cava. Function curves relating transmural systolic arterial pressure (TSAP = systolic arterial pressure-pleural pressure) to heart rate (HR) were constructed to compare responses in air and during WI. The resting TSAP in air [142 +/- 8 mmHg (mean +/- SE) at 78 +/- 6 beats/min] increased significantly during WI (161 +/- 9 mmHg at 109 +/- 9 beats/min). During WI, the saturation TSAP at the bradycardia plateau of the relation increased significantly, by 19 mmHg, whereas the average gain (slope) of the relation decreased significantly, from -1.426 to -0.752 beats.min-1.mmHg-1. Therefore, WI elicits both a resetting and a decrease of the average gain of the TSAP-HR relation. The heart rate range increased during WI as well. After cholinergic blockade with atropine, WI did not elicit a resetting of the relation and the change in average gain was abolished. However, after beta 1-blockade with metoprolol, the resting TSAP increased significantly during WI and resetting persisted, but the decrease of average gain was abolished. Therefore, the alteration of the TSAP-HR relation in WI is achieved via a modulation of both adrenergic and cholinergic regulation of HR.

Operation of helium-filled proportional counter at low temperatures (4.2–295 K)

Following the previous work by our group, the operation of the helium-filled counter has been studied more in detail at liquid-helium (∼ 5 K), liquid-nitrogen (77 K) and room (295 K) temperatures. The collimated σ-ray beam from a 210Po source, which is installed inside the counter, has made it possible to measure the gas gain M from the ionization-chamber region with M = ∼1. The operation of the helium-filled counter is rather unstable at 77 and 295 K; when the applied voltage is increased, the gas gain steeply rises up to 10 3 and the pulse rise time becomes longer than 200 μm. On the other hand, the counter works stably at 5 K, although available gas gains are comparatively small, i.e., at most 170. The slope of gas gain at 5 K is more gentle than that at 77 or 295 K and the pulse rise time does not change (∼ 2 μs) so much in the wide range of applied voltage. Measured results for gas gain and pulse rise time are reported in this paper. The favourable operation at 5 K is not only due to the absence of impurity in helium gas but also to the suppression of electron emission from the cathode. This new feature of the proportional-counter operation at a very low temperature is also discussed from the standpoint of atomic processes in helium gas.

Fibronectin decreases pulmonary vascular permeability under baseline conditions and after administration of arachidonic acid in rabbit lungs

In blood- and plasma-free perfused isolated rabbit lungs, the influence of albumin and soluble fibronectin on vascular permeability was investigated. The lungs were perfused with Krebs Henseleit buffer containing no protein (KHB), containing 1 g/100 ml bovine albumin (KHAB) or containing albumin together with 100 pg/ml soluble fibronectin. The absence or presence of albumin had no influence on the perfusion pressure, the vascular compliance and the capillary filtration coefficient (CFC), determined by zero time extrapolation of the slope of weight gain which was induced by a sudden venous pressure elevation. Fibronectin caused a slight increase in pulmonary artery pressure, a slight decrease in vascular compliance and an approximately 50 % reduction of CFC. In a second set of experiments, KHAB-perfused lungs were stimulated by the administration of 100 μM arachidonic acid (AA) during the second hydrostatic challenge within a sequence of three venous pressure elevations. In the presence of indomethacin, which blocks any significant increase in pulmonary vascular pressure after AA application, this procedure caused an immediate gain in lung weight due to increased pulmonary vascular permeability, with > 10-fold increased CFC values subsequent to the AA application. In the presence of 100 μg/ml fibronectin, this AA-induced increase in CFC was mitigated to less than 20 % of the controls without the glycoprotein, with correspondingly severalfold reduced lung weight gain. In conclusion, the present study provides evidence for a direct influence of circulating soluble fibronectin on lung microvascular integrity and fluid balance under baseline conditions and after stimulation of the pulmonary AA cascade.

Reflex and mechanical contributions to head stabilization in alert cats.

Five alert cats were tested for their responses to rotation in a device that allowed rotation of the head on the trunk about a vertical axis passing through the C1-C2 vertebral joint. Electrodes were implanted to record the horizontal and vertical electrooculogram and electromyographic (EMG) activity of the dorsal neck muscles splenius, biventer cervicus, and complexus. Head rotation and torque acting on the head were recorded in the horizontal plane during rotations in the 0.05-5.0 Hz frequency range. Responses were interpreted with reference to a closed-loop dynamic model of the head-neck system. Whole-body rotation (WBR) with no neck movement elicited a vestibulocollic reflex (VCR). Neck muscle EMG lagged the sinusoidal platform rotation by approximately 120 degrees at low frequencies, which represents a 60 degrees lead relative to a perfectly compensatory 180 degrees lag. This phase lead was related to the cumulative eye position of the accompanying horizontal vestibular nystagmus as reported by Vidal et al. Horizontal head torque exhibited a similar low-frequency behavior. At high frequencies, EMG exhibited a progressively increasing phase lead and gain increase typical of a second-order lead system as described in decerebrate cats. Torque, however, showed much less lead and gain increase, presumably because of the low-pass filter properties of the process coupling muscle excitation to torque. Head torque did exhibit a steep increase in gain with frequency and a phase approaching that of platform acceleration at high frequencies when weights were attached to the head to increase its moment of inertia. The same +40 dB/decade gain slope and phase approaching 0 degree was observed during WBR rotation of the anesthetized cat in which head inertia is the only factor contributing to the torque. This dynamic behavior was predicted by the inertial component of the model. In the alert unweighted cat, the inertial torque was smaller than VCR-generated torque at frequencies below 4 Hz. Rotation of the neck with the head held fixed in space (HFS rotation) elicited a cervicocollic reflex (CCR). Neck EMG response was very similar to that observed during WBR, both in dynamic behavior and overall gain. Torque, however, was consistently greater than that generated by WBR and showed a steady increase of 8 dB/decade as frequency rose. The added torque can be attributed to the viscoelastic properties of neck muscles. Driven rotation of the head on the fixed body elicited torques that could be closely approximated by a vector sum of torques observed during WBR and HFS rotations.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic effects of chronic infusions of epinephrine and norepinephrine in rats

Chronic infusions of epinephrine, norepinephrine, or vehicle were performed in adult male rats by means of subcutaneous implanted osmotic minipumps (ALZET). The calculated dose was 180 ng/min during 7-8 days. Daily food intake and body weight were measured during this period and also 7 days before and 5 days after it. During the period of infusion, norepinephrine stopped body weight gain while epinephrine-infused rats gained weight at the same rate as controls. Once the infusion period was finished, epinephrine-infused rats gained more weight than controls, while norepinephrine-infused rats just returned to the slope of weight gain of the controls. In no group did food intake change. In a second experiment, similar infusions were carried out in other rats on the same schedule; body temperature, glycemia, and serum insulin and triiodothyronine were measured. Epinephrine infusion significantly elevated glycemia and triiodothyronine, whereas norepinephrine infusion increased temperature and serum insulin. The results obtained by chronic administration of the catecholamines support the concept of a disassociation of adrenomedullary and sympathetic nervous system metabolic effects.

Low-Noise Amplifiers for Terrestrial and Satellite Communication Systems

The paper presents design approach for realizing amplifiers for 1.7 to 2.1 GHz, 2.1 to 2.3 GHz, 2.3 to 2.5 GHz, 2.5 to 2.7 GHz frequency bands. An interstage matching network is designed by realizing a sloped insertion loss function, in order to compensate the gain slope of the two stages. The gain ripple and bandwidth perturbations due to the deviation from the exact insertion loss function is minimized using performance optimization. Two stage GaAs-FET amplifiers are realized using the above approach. This envisages the use of minimum variants for the production and have excellent reproducibility. Performance test results are also included for the developed amplifiers.