Pump Period Research Articles

Closed-Loop Insulin Pump Therapy in Young Type 1 Diabetic Children

Source: Ware J, Allen JM, Boughton CK, et al. Randomized trial of closed-loop control in very young children with type 1 diabetes. N Engl J Med. 2022;386:209-219; doi: 10.1056/NEJMoa2111673Investigators from multiple institutions conducted a crossover randomized trial to compare the effectiveness and safety of a closed-loop system (ie, artificial pancreas) to sensor-augmented insulin pump therapy in young children with type 1 diabetes. Participants were children 1-7 years old with a diagnosis of type 1 diabetes for at least 6 months, recruited from diabetes centers in 4 European countries. The closed-loop system consisted of a continuous glucose sensor and insulin pump connected to a smartphone app. The app included an algorithm that automatically adjusted insulin delivery based on real-time sensor glucose readings. With the sensor-augmented pump, insulin therapy was stopped if an algorithm predicted that sensor glucose levels were likely to drop below a specified threshold. Study children were randomized to receive 16 weeks of treatment with the closed loop system, followed by 16 weeks using the augmented-sensor pump, or vice versa. The primary outcome was percentage of time spent in the target glucose range (70 to 170 mg/dL) during each treatment period. Secondary outcomes included percentage of time spent in a hyperglycemic range (>180 mg/dL) and hypoglycemic range (<70 mg/dL) and mean glucose levels. These outcomes were based on readings from the glucose sensors. Glycated hemoglobin levels were measured at baseline and at the end of each treatment period. Differences in outcomes between the closed-loop and sensor-augmented pump treatment period were assessed with repeated-measures linear regression models. Data on adverse events also were collected.Data were analyzed on 74 children with a mean age of 5.6 ±1.6 years. The mean glycated hemoglobin level at baseline was 7.3 ±0.7%. The mean time spent in the target glucose range were 71.6 ±5.9% during the closed-loop period and 62.9 ±9.0% in the sensor-augmented pump period (adjusted difference, 8.7 percentage points; 95% CI, 7.4, 9.9; P <0.001). The median time spent at glucose level >180 mg/dL was significantly less during the closed-loop period than during the control period (22.9% vs 31.7%; adjusted difference, -8.5 percentage points; 95% CI, -.9.9, -7.1; P <0.001); mean sensor glucose levels (145 ±11.8 mg/dL and 158.1 ±18.5 mg/dL, respectively; P <0.001) and mean glycated hemoglobin levels (6.6 ±0.6% and 7.0 ±0.7%) were significantly lower during the closed-loop period than during treatment with the segmented-sensor pump. There was no difference between treatment periods for percentage of time with glucose <70 mg/dL (P = 0.74). One participant had a serious adverse event (severe hypoglycemia) during their closed-loop treatment period.The authors conclude that a closed-loop system improved glycemic control in young children with type 1 diabetes.Dr Fechner has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Type 1 diabetes is very difficult to manage in the young child. The therapeutic window for insulin is very narrow, with too much insulin resulting in hypoglycemia and too little insulin resulting in hyperglycemia. The last 5 years have seen tremendous advances in the technology available to children with type 1 diabetes. A 2019 study comparing the insulin pump to multiple daily injections showed that the insulin pump was superior to multiple daily injections. (See AAP Grand Rounds. 2019;42[1]:4.) Continuous glucose monitoring has decreased parental anxiety regarding risk of hypoglycemia and diabetic ketoacidosis;1 however, parents still are responsible for making insulin dose adjustments, and glycemic control overall is not improved.2 The results of a 2020 study of 6- to 13-year-olds with type 1 diabetes demonstrated that glucose levels were in the target range for a longer period of time in those randomized to a closed-loop system than those using a sensor-augmented pump. (See AAP Grand Rounds. 2020;44[6]:69.)3 The current researchers compared a hybrid closed-loop insulin delivery system to sensor-augmented pump therapy in younger children with type I diabetes.The strengths of the current study are the randomized, crossover design using the same algorithm with the closed-loop functionality either abled or disabled; each therapy was 16 weeks, which allowed a meaningful glycated hemoglobin to be obtained. There were no restrictions on previous episodes of hypoglycemia and diabetic ketoacidosis, and the study included a very young children with diabetes, who are more vulnerable to hypo- and hyperglycemia. Weaknesses of this study include underrepresentation of ethnic minorities and a patient population not representative of the typical type 1 diabetes population, as the average glycated hemoglobin level was 7.3% at baseline.4 Decreased patient compliance outside of the confines of a study may be reflected in poorer glucose control regardless of the insulin delivery system used.Hybrid closed-loop insulin therapy in young children with type 1 diabetes has the potential to significantly improve long-term outcomes through improved glycemic control.

Laboratory Hydraulic Fracturing of Large-Scale Granite Characterized by Acoustic Emission Under Different Confining Conditions

Hydraulic fracturing (HF) technology is crucial to form connected fracture network within the low-permeability geothermal reservoir. However, the HF process and failure mechanism in this process are only partly understood. A series of true triaxial hydraulic fracturing tests on large-scale natural granite samples were conducted under different confining conditions, combining with acoustic emission monitoring to evaluate the initiation and propagation of hydraulic fractures. Results show that a main hydro-fracture was formed in three samples during the first fracturing process. Many AE events occurred during the first pump period. The proportion of tensile fractures during the hydraulic fracturing accounted for more than 85% of all fractures. The test results could provide a new understanding of the effect of HF under different stress conditions. And implied that field engineering should pay attention to the initial HF, which may determine the main fracture framework of the field at the first pump procedure.

Effects of remote ischemic postconditioning on HIF-1α and other markers in on-pump cardiac surgery.

There is a lack of data about the effects of remote ischemic postconditioning (RIPostC) on hypoxia-inducible factor-1α (HIF-1α) plasma levels after on-pump cardiac surgery (OPCS). This study aimed to measure the effects of RIPostC on postoperative HIF-1α plasma levels, cardiac markers and arterial oxygenation in patients undergoing OPCS. This single-centre randomized, double blind, controlled trial, enrolled 70 patients (35 control and 35 RIPostC). RIPostC was performed by 3 cycles (5min of ischemia followed by 5min of reperfusion) administered in upper arm immediately after the pump period. The primary outcome was to measure HIF-1α plasma levels: before surgery (T0), and 2h (T1), 8h (T2), 24h (T3), 36h (T4) and 48h (T5) after RIPostC. As secondary endpoint, Troponin T, CK-MB, CPK plasma levels and PaO2/FiO2 ratio were measured. HIF-1α plasma levels were increased at T1-T3 compared to T0 in both groups (P < 0.001). In the RIPostC group HIF-1α increased compared to the control group: differences between means (95% CI) were 0.034 (0.006-0.06) P = 0.019 at T1; 0.041 (0.013-0.069) P = 0.005 at T2; and 0.021 (0.001-0.042) P = 0.045 at T3. PaO2/FiO2 was higher in the RIPostC group than in the control group: at T3, T4 and T5. Moreover, Troponin T, CK-MB and CPK values decreased in the RIPostC group compared to the control group. HIF-1α plasma levels increased in control patients during for at least 36h after OPCS. RIPostC resulted in even higher HIF-1α levels during at least the first 24h and improved arterial oxygenation and cardiac markers.

The effect of the number of vessel grafts used in coronary artery bypass grafting surgery to short-term mortality

Purpose: The study aimed to share the short-term mortality rates of coronary artery bypass grafting (CABG) experience in a private hospital and to evaluate parameters affecting the clinical outputs following the CABG who were divided according to the number of vessel graft.&#x0D; Materials and Methods: The study is a longitudinal-term observational clinical study, with a patient follow-up period of 7 years in Turkey. We analyzed 3027 cases with outcomes and short-term mortality according to the number of vessel grafts that we used as 1 (n:608), 2-3 (n:1359), and four or more (n:1060) grafts.&#x0D; Results: The short-term mortality was found as 1.1% (36/3027) in all the patients. The male population was the highest in the group with the highest number of vascular grafts and its percentage to females was correlated with vessel grafts that we performed. Mean aortic cross-clamp time was 36.6±17.2 minutes, while bypass time was 66.4±21 minutes. The mean number of vessels revascularized was 3.17±0.9 (1-7). The amount of drainage was 419±286 ml. The period of intensive care was 1.2±1.1 days, while the hospital period was 5.2±1.5days. In comparison according to the number of vascular grafts, positive inotrope agent, drainage, blood supply, cross-clamp and pump period showed significant difference.&#x0D; Conclusion: The number of vessel grafts was related to clinical outputs of CABG operations and Our CABG in the private hospital reached the short-term mortality rates that were below the averages of Turkey and international operations.

Polder System to Handle Tidal Flood in Harbour Area (A Case Study in Tanjung Emas Harbour, Semarang, Indonesia)

Tanjung Emas harbour is one of strategic harbours in Indonesia, which is located in Semarang City. Several problems arise nowadays; the drainage channel capacity decreases due to lack of treatment, rainwater storage reduced, land subsidence and the rise of tide sea level. The flood control used is polder system that classified into several clusters. The research location is focused on the Cluster IV, which the right side of harbour area. According to the data, catchment area is 29.3 hectares, the lowest elevation area is in +0,5 m, the dike elevation is +2 m LWS. Then retention pond area prepared is 900 m2 (0.3% of CA), retention pond depth - 2m LWS. Based on simulation using 2×0.3 m3/sec pump and rainfall intensity return period of 25 years 303 mm, fluctuation in water retention pond can be maintained in +0,5 m water level. It is recommended to add 0.3 m3/sec alternative pump. A pump of 3×0.3 m3/sec needs to be prepared. Based on the simulation, by Polder system, the flood problem in harbour area can be solved.

3D printed selectable dilution mixer pumps.

In this paper, we demonstrate the ability to 3D print tightly integrated structures with active valves, pumps, and mixers, and we use our compact chip-to-chip interconnects [Gong et al., Lab Chip 18, 639-647 (2018)] to move bulky world-to-chip connections to separate interface chips for both post-print flushing and post-cure device operation. As example devices, we first examine 3D printed pumps, followed by two types of selectable ratio mixer pumps, a linear dilution mixer pump (LDMP) and a parallelized dilution mixer pump (PDMP), which occupy volumes of only and , respectively. The LDMP generates a selectable dilution ratio from a linear set of possibilities, while the PDMP generates a denser set of possible dilutions with a maximum dilution ratio of 1/16. The PDMP also incorporates a new 4-to-1 valve to simultaneously control 4 inlet channels. To characterize LDMP and PDMP operation and performance, we present a new, low-cost video method to directly measure the relative concentration of an absorptive dye on a pixel-by-pixel basis for each video frame. Using this method, we find that 6 periods of the active mixer that forms the core of the LDMP and PDMP are sufficient to fully mix the fluid, and that the generated concentrations track the designed dilution ratios as expected. The LDMP mixes 20 nl per 4.6 s mixer pump period, while the PDMP uses parallelized input pumps to process the same fluid volume with greater choice of dilution ratios in a 3.6 s period.

Development of a sensitive closed batch vessel hydride generation atomic absorption spectrometry method for the determination of cadmium in aqueous samples

ABSTRACTHydride generation atomic absorption spectrometry was used as a simple, sensitive, and economical method for the determination of cadmium at trace levels. This study includes a stepwise optimization of all parameters that have an impact on the production, transport, and atomization of cadmium hydride for rapid determination due to the unstable nature of the hydride produced. The cell temperature for atomization, pump period, and flow rate of carrier gas were varied, and the best conditions were defined to obtain lower detection limits. In addition, the acid and sodium borohydride concentrations were optimized since they directly affect the production of the cadmium hydride. Under optimum experimental conditions, the hydride generation efficiency was greatly enhanced to record optimized analytical signals. The accuracy of the method was determined by the analysis of a certified reference material, and the results were in good agreement with the certified value. A linear dynamic range for cadmium was observed from 0.10 to 2.0 µg/L. High sensitivity was obtained with a limit of detection of 0.029 µg/L.

Double-pulse single-longitudinal-mode operation of injection-seeded laser using intracavity phase modulator

A single-longitudinal-mode (SLM) double-pulse injection-seeded neodymium-doped yttrium aluminium garnet (Nd:YAG) laser was established utilizing an RbTiOPO4 electro-optic crystal to modulate the optical path of the slave resonator for generating a resonance condition. The Q-switcher was fired twice during every pump period. This enabled the laser to emit a pair of SLM laser pulses with a time separation of 200 mu s. Each pulse had a pulse energy of 13 mJ at 50-Hz repetition rate, pulse duration of 20 +/- 0.5 ns, and linewidth of 30 +/- 0.3 MHz (within 2 min). The beam quality factor of M-2 was <1.22. A frequency jitter of 1.4 MHz was obtained within 2 min. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

System Performance Optimization of Frequency-Swept Pump-Based Rectangular Brillouin Optical Filter

In this paper, we realize a series of 2-GHz wide rectangular optical filters based on the stimulated Brillouin scattering (SBS) effect in optical fiber with a frequency-swept pump and gain feedback compensation scheme. The frequency sweep pump period is a key parameter to achieve acceptable signal performance in the frequency-swept pump based SBS gain filter. We evaluate the system performance of the signal, which is fed into the SBS filter based on frequency-swept pump with different sweep periods ranging from 0.1 to 100 μ s, in terms of eye diagrams and bit-error rate (BER) after 12.5 and 25 km of fiber transmission, respectively. Both 500-Mb/s and 1-Gb/s on-off-keying (OOK) signals are used for real-time signal quality evaluation. The optimum eye diagram and BER performance are achieved after 25 km transmission under a 1 μ s frequency sweep pump period, as well as after 12.5-km transmission under a 0.5 μ s sweep period. The experimental results show that the optimal frequency sweep pump period is always around 1/120 of the signal propagation time in the fiber for different transmission length, providing a guideline on the design of the frequency-swept pump based SBS gain filter and its applications.

Impact of dexmedetomidine on hemodynamic changes during and after coronary artery bypass grafting.

Objective:To determine the effect of dexmedetomidine (Dex) on hemodynamic changes during cardiopulmonary pump and postoperative period in coronary artery bypass grafting (CABG).Methods and Design:This study is designed as a double-blinded, randomized clinical trial.Setting:University hospital and single center.Participants:patients candidate for elective CABG.Intervention:Dex 0.5 μg/kg/h or placebo was infused from the initiation of anesthesia up to extubation in Intensive Care Unit (ICU).Measurements:Heart rate (HR) and blood pressure (BP), pain score, and total morphine dose requirement were monitored and compared during cardiac pump up to 12 h postoperative in ICU.Results:Mean arterial pressure was significantly higher in Dex group in postoperation period at 1 (P = 0.010) and 2 h (P = 0.002) compared to control group. HR was significantly lower in Dex group in postcardiopulmonary bypass (CPB) time at 0 h (P = 0.001), 1 h (P = 0.0016), and 2 h (P = 0.001), and then in postoperative period in ICU at 1 h (P = 0.025), 2 h (P = 0.0012), and 4 h (P = 0.0025) compared to control group. Postoperative pain score was significantly lower during 12 h after surgery.Conclusion:Dex could effectively blunt hemodynamic response to surgical stress, particularly during CPB pump and afterward. Infusion of Dex maintains BP at higher range and HR at lower range compared to placebo.

Determination of Lead in Drinking and Wastewater by Hydride Generation Atomic Absorption Spectrometry

ABSTRACTThis work describes the optimization of hydride generation atomic absorption spectrometry for the determination of lead at trace concentrations. The parameters affecting the production, transport, and atomization of plumbane in a closed vessel were optimized. The concentrations of reagents affecting the generation of the lead hydride were also optimized to obtain high hydride generation efficiency. The atomization temperature, reaction period, pump speed, pump period, and flow rates of reducing agent and carrier gas were varied to maximize the sensitivity for lead. The accuracy of the method was evaluated by the analysis of certified reference materials. The method provided a linear dynamic range for lead from 2.0 to 40 µg/L with a limit of detection of 0.56 µg/L.

Single-frequency Q-switched double-pulse Nd:YAG laser

A laser diode dual-end-pumped injection-seeded single-frequency Q-switched double-pulse Nd:YAG laser is designed using a modified ramp-fire technique. The laser is capable of producing a pair of Q-switched single-frequency 1064 nm laser pulses in one pump period. Every pulse has an output energy of up to 10 mJ, width of nearly 20 ns, and interval of about 200 μs between two Q-switched pulses. The optical-to-optical efficiency of this laser is about 22.4% and its slope efficiency is 28%. A narrow spectrum linewidth of less than 28.6 MHz with a frequency of jitter around 1 MHz over 2 min may be obtained, and a beam quality of 1.23 in the horizontal direction and 1.31 in the vertical direction is detected.

Study of distributed erbium doped fiber amplifier

Basing on analyzing distributed erbium-doped fiber amplifier(d-EDFA) of evenly doped density along propagating direction, we put forward two sort d-EDFAs of slowly and linearly variously doped density along propagating direction: one-variation and two-variation d-EDFA. By using convective equations, we study the propagating properties of signal and noise in three sort d-EDFAs. Noise figure, signal-noise ratio, necessary pump and optimal pump period also are studied, under both transparent transmission and optimal doped density.

Remission of severe hypoglycemic incidents in young diabetic children treated with subcutaneous infusion

Conventional insulin therapy for diabetes mellitus can be inadequate for controlling glycemia in young patients in whom the risk of hypoglycemia is particularly high. A retrospective study comparing all the children under 6 years of age treated in our department by continuous subcutaneous insulin infusion (group P, n = 10, mean age: 3.7 years) to 17 children with conventional insulin therapy (group C, mean age: 5.1 years) was conducted during a mean period of 2 years. Mean insulin doses, HbAlc, pre-prandial and daily glycemic levels, measured at 0, 3, 6, 12, 18 and 24 months, did not differ significantly between both groups. Mean HbAlc levels remained < or = 8% in the two groups. There was no episode of severe hypoglycemia in group P vs ten episodes in group C (P < 0.05); this benefit was confirmed in those six children belonging to group P who had previously followed a conventional therapy: 11 episodes during the conventional period vs 0 episode during the pump period (P < 0.05). Nine out of ten families were very satisfied with the treatment by pump mainly because of a more comfortable life style and a reduction of parents' anxiety due to disappearance of severe hypoglycemias. The insulin pump therapy had some limits: cutaneous complications and technical ones were responsible for two keto-acidosis episodes (0.1 episode per year-patient) and a higher frequency of hospitalizations. In group C, hospitalizations were caused by severe hypoglycemias and unbalanced glycemic control. Insulin pump therapy could be indicated in young diabetic children at high risk of severe hypoglycemia under conditions of a specialized medical and educational supervision and knowledge of the limits of such a treatment.

Evaluation of CGP 39393 as the anticoagulant in cardiopulmonary bypass operation in a dog model

Recombinant desulphatohirudin HV1 (CGP 39393), a specific and potent peptidic inhibitor of thrombin, was evaluated as the sole anticoagulant in a dog model of cardiopulmonary bypass. CGP 39393 was administered as a bolus plus infusion for a 1-hour pump period at doses of 1.0 mg/kg + 0.75 mg·kg −1.h −1, 1.0 mg/kg + 1.50 mg · kg −1 · h −1, 1.0 mg/kg + 225 mg · kg −1 · h −1, or 1.0 mg/kg + 3.0 mg · kg −1 · h −1 (n = 5 per group). The lowest dose was ineffective, as a high degree of clot formation (314 ± 160 mg) occurred as determined by quantitation of protein deposits in the pump line filter. The three higher doses inhibited clot formation (35 to 44 mg) but did not reveal a dose-dependent effect ( p = 0.308 between groups). All four doses produced the same amount of postoperative blood loss (6.5 to 10 g/kg over 2 hours; p = 0.215 between groups) and no oozing of blood from cut tissues (sternum, muscle, skin) during or after operation. No adverse hemodynamic or hematologie effeds were observed. Animals were physiologically stable coming off pump, requiring minimal fluid replacement or other cardiovascular supportive measures. The chromogenic anti-lla assay could be used to monitor CGP 39393. Same activated partial thromboplastin time and all activated clotting time values were off scale on pump, but they fell immediately after cardiopulmonary bypass, typicalty reaching near-normal levels within 30 to 60 minutes. No reversal of CGP 39393 was used, as blood levels declined rapidly after cessation of the infusion. This stady in 2 dog model shows that CGP 39393 administered as a bolus plus infusion (minimum dose, 1.0 mg/kg + 1.50 mg · kg −1 · h −1) can be used safely and effectively during cardiopulmonary bypass for cardiac operation.

Theory of dynamical relaxation oscillations and frequency locking in a synchronously-pumped laser diode

It is shown that the rate equations for the plasma density and the light intensity, together with a delayed feedback of the light in the external resonator, can be used to describe the nonlinear dynamics of actively mode-locked laser diodes. In particular, the relaxation oscillations of the laser intensity and the plasma density around the stationary pulse solutions are calculated for a laser diode in a long resonator with a periodically pulsed pump current. For small negative detuning between the round-trip period and the pump period, slow dynamical relaxation oscillations that give rise to megahertz-sidemodes in the intensity correlation spectrum occur. For larger negative detuning the delayed feedback gives rise to a frequency locking between the light pulse frequency and the modulation frequency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Entrainment of the respiratory rhythm by periodic lung inflation during vagal cooling

the aim of this study was to determine whether pulmonary receptors other than slowly adapting stretch receptors are capable of entraining the respiratory rhythm when periodically stimulated during artificial ventilation. Experiments were performed on anaesthetised (urethane, 1.5 g/kg) and paralysed (pancuronium bromide, 0.1 mg/kg) rabbits. Vagi were cooled in order to block conduction in the myelinated fibres innervating slowly adapting receptors. The effectiveness of this cooling was assimilated to the absence of the Hering-Breuer inflation reflex and the presence of the deflation reflex. Our results indicate that under such conditions: (1) harmonic entrainment (one phrenic burst for one pump period) can be observed, (2) the range of harmonic entrainment is more limited when the vagi are cooled, and (3) during harmonic entrainment the inspiratory duration and phrenic activity are similar to what is observed at the same period with intact vagi, whereas vagal cooling modifies the phase difference between the phrenic burst and the pump. We have concluded that periodic input from rapidly adapting receptors and/or vagal C-fibres can entrain the respiratory rhythm as does input from slowly adapting receptors but with different patterns as evidenced by phase relationship.

Dependence of food intake on acute and chronic ventricular administration of insulin

Several lines of evidences indicate that insulin affords short- and long-term neuroendocrine signals to modulate ingestive behavior. To further study a possible role of insulin in the control of food intake, male Wistar rats were subjected to various intra-third cerebro-ventricular applications of saline and insulin. Infusion of 2.0 mIU/rat of insulin at 1100 and 1900 decreased food intake in a 23.5 hr test period. Infusion of 0.5 mIU/rat of insulin between 1100 and 1200 decreased nighttime food intake during the 1st and 2nd days. Infusion of 2.0 mIU/rat/24 hr of insulin from osmotic minipumps decreased nighttime food intake throughout the active pump period and the effect persisted into the post-pump period. The results support the notion that insulin is involved in the regulation of food intake in the rat.

Respiratory oscillator entrainment by periodic vagal afferentes: an experimental test of a model.

This communication compares the well known phenomenon of respiratory driving by the respiratory pump through the Breuer Hering reflex with a model (Segundo, 1979) of a neuronal pacemaker (i.e. regularly firing) interactions via IPSP's. The assumption involves a linear dependence (“delay function”) of the postsynaptic interval lengthening (or “delay”) produced by the IPSP's on the position (or “phase”) with respect to the preceding spike of the latter's arrival. Cats anesthetized and paralized with gallamine were artificially ventilated using a computer driven respirator. The pump period and the respiratory period (identified by the phrenic discharge) corresponded to the model's presynaptic pacemaker interval and to that of the post synaptic one, respectively. The delay of the respiratory period by an inflation was related linearly and in increasing manner to the latter's phase with respect to the inspiration onset. In the steady state, plots of average respiratory period versus pump period consisted in a succession of broad “paradoxical” segments with positive slopes 3, 2, 1, 1/2, 1/3 in which respiration was locked with the pump as predicted by the model. The locked condition were less easy to reach when FACO2increased or when level of anaesthesia decreased. The limits of paradoxical segments were different when measured using pump periods that increased or using periods that decreased. There was therefore a hysteresis as if the delay function parameters changed, a behavior that was not part of the model that assumed fixed characteristics. These modifications were related to dependency of each cycle on the preceding one. The model proposed for simple neuronal pacemaker interactions can thus be applied satisfactorily to the drive of the complex respiratory neuronal oscillator by the respiratory pump through Breuer Hering reflex, providing nevertheless some additonal assumptions concerning respiratory cycle interdependency are introduced to account for the hysteresis phenomenon. The Breuer Hering reflex could be considered as the equivalent of IPSP acting on the central respiratory oscillator. FACO2increase and anesthesia level decrease produced the same effect as the addition of noise to the model's presynaptic pacemaker, thus leading to the hypothesis that they act by adding noise (e.g., randomly distributed excitatory input) at the level of Breuer Hering reflex inhibition.

Nonlinear theory of free-electron lasers and efficiency enhancement

The development of lasers in which the active medium is a relativistic stream of free electrons has recently evoked much interest. The potential advantages of such free-electron lasers include, among other things, continuous frequency tunability, very high operating power, and high efficiency. The free-electron laser (FEL) is characterized by a pump field, for example, a spatially periodic magnetic field which scatters from a relativistic-electron beam. The scattered radiation has a wavelength much smaller than the pump wavelength, depending on the electron-beam energy. The authors present a general self-consistent nonlinear theory of the FEL process. The nonlinear formulation of the temporal steady-state FEL problem results in a set of coupled differential equations governing the spatial evolution of the amplitudes and wavelength of the radiation and space-charge fields. These equations are readily solved numerically since the amplitude and wavelength vary on a spatial scale which is comparable to a growth length of the output radiation. A number of numerical and analytical illustrations are presented, ranging from the optical to the submillimeter-wavelength regime. Our nonlinear formulation in the linear regime is compared with linear theory, and agreement is found to be excellent. Analytical expressions for the saturated efficiency and radiation amplitude are alsomore » shown to be in very good agreement with our nonlinear numerical solutions. Efficiency curves are obtained for both the optical and submillimeter FEL examples with fixed magnetic-pump parameters. It is shown that these intrinsic efficiencies can be greatly enhanced by appropriately contouring the magnetic-pump period. In the case of the optical FEL, the theoretical single-pass efficiency can be made greater than 20% by appropriately decreasing the pump period and increasing the pump magnetic field.« less