Surge Mode Research Articles

Model for Local Cavitation Instabilities in 2-Bladed Turbopump Inducers

Abstract Various local cavitation instabilities in turbopump inducers (e.g., alternate blade cavitation, super-synchronous rotating cavitation, etc.) have previously been experimentally identified. However, a model, which is capable of predicting such local instabilities is still lacking. Therefore, a new model, which models an N-bladed inducer as a system of N coupled mass- spring-damper systems, is presented to predict post-onset behavior of alternate blade cavitation instabilities. The model predicts alternate blade cavitation to occur. As the flow coefficient is decreased, the model predicts the magnitude of alternate blade cavitation to first increase and then decrease, and then finally vanish. If the flow coefficient is further decreased beyond the range of alternate blade cavitation, sudden increase in equilibrium incidence is predicted. All of these predictions agree with the previous experimental findings. Furthermore, simultaneous in-phase oscillations of the blade cavities are predicted during alternate blade cavitation. These in-phase oscillations of the cavities correspond to the surge mode oscillation, which had been previously mistakenly categorized as a global (system) instability. Finally, it is proposed that the above post-onset behaviors of alternate blade cavitations are general in two-bladed inducers, as long as the change in incidence on the following blade has a local minimum when it is expressed as a function of leading blade's incidence.

7940 Is Urocortin 2 A Mediator Of Stress-induced Suppression Of The Luteinizing Hormone Surge?

Abstract Disclosure: H.F. Bell: None. R.A. Carrasco: None. M.J. Kreisman: None. R.B. McCosh: None. K.M. Breen Church: None. Stress is thought to be a contributing factor to the reduction of reproductive function and infertility observed in many different species. Although this is a well-documented phenomenon, the neural mechanisms mediating the suppression of reproductive neuroendocrine activity in response to stress are not yet fully understood. The paraventricular nucleus (PVN) of the hypothalamus is an integral part of the neural response to stress. The PVN initiates activation of Corticotropin Releasing Hormone (CRH) neurons and, in addition to CRH, the PVN contains a population of neurons expressing Urocortin 2 (UCN2), a CRH-like family member, with high affinity for CRH receptor 2. In females, stress has been shown to inhibit both the pulse and surge modes of Luteinizing Hormone (LH) secretion. We have preliminary evidence that kisspeptin neurons, controlling either type of LH secretion, contain CRH receptor 2. In this study we tested the sufficiency of UCN2 to disrupt the estradiol-induced LH surge. Female mice were ovariectomized and given a high estradiol treatment to induce a circadian-timed LH surge. Two days later, UCN2 or Vehicle was administered into the lateral ventricle via ICV injection on the morning of the expected surge (10 AM). Blood and brains were collected in the evening (6 PM), at the time of the expected surge. Whole blood from the tail tip was measured by LH ELISA and a surge was defined as > 0.5 ng/mL. A majority of saline-treated animals expressed an LH surge (8 of 9 females). In contrast, 0% of UCN2-treated animals surged (n=7), suggesting that UCN2 impaired the positive feedback response to estradiol. Additionally, immunohistochemistry was performed to observe colocalization of c-Fos within Kisspeptin neurons in the rostral periventricular region of the third ventricle (RP3V) which are responsible for surge generation. Lower Kisspeptin/C-Fos co-expression in animals treated with UCN2 demonstrated the efficacy of UCN2 to impair estradiol-induced activation of RP3V Kisspeptin neurons which are critical for LH surge generation. These results support the hypothesis that UCN2 signaling plays a mediatory role in the stress-induced reduction of ovulatory function in the female mouse. Presentation: 6/1/2024

Analysis of Hydrodynamic Loads by a Vertical Hollow Cylindrical Structure in A Two-Layer Fluid of Finite Depth

This paper aims to study the effect of surge radiation by a vertically hollow cylinder floating in a two-layer fluid of finite depth. Since most of the important characteristics of the oscillating water column are preserved by the hollow cylindrical structure, so the proposed device can be considered as an oscillating water column (OWC) which is one of the important wave energy device. In this two-layer fluid system, the upper layer is bounded above by a free surface and the lower layer is bounded below by a solid impermeable bottom, and the submerged hollow cylindrical structure allows it to oscillate in a surge mode of motion in the upper layer. On the assumption that wave amplitudes are small in comparison to wavelengths, hence the linear water wave theory is applied to formulate boundary value problems by dividing whole domain into 2 sub-domains. The formulated boundary value problems for surge radiated potentials in each sub-domain; we execute to obtain solutions in each sub-domain by using variable separation and matched eigenfunction expansion methods. With the help of obtained surge radiated potentials, we derive the radiation forces by the device in terms of added mass and damping coefficients. A set of influences of different parameters of the device on the added mass and damping coefficients are demonstrated in both surface and internal wave modes of motion. Hydrodynamic coefficients oscillate highly near a particular frequency, which leads to the resonance phenomena. In addition to that, the 3D plots of the free surface elevation in surface and internal wave modes are presented. A density ratio γ = 0.97 has a higher oscillation than a density ratio γ = 0.93, 0.95. High oscillations occur around a particular frequency ω = 3.83 due to the resonance phenomenon in which the waves incoming match with the natural motion of the object. HIGHLIGHTS A floating hollow vertical cylindrical structure is considered in a two-layer fluid system having finite depth The separation of variables and matched eigenfunction expansion methods are utilized to obtain the solutions to the boundary-value problems The diffracted velocity potentials under the surge mode of motion are evaluated in the identified regions The added mass, damping coefficients, free surface and interface elevations in surface and internal wave modes are evaluated with different set of parameters of the device A number of results are presented regarding the effect of parameters of the device on the added mass, damping coefficients, free surface and interface elevations It is observed that the density ratio of the two-layer fluid has significant effect on the added mass, damping coefficient and the elevations GRAPHICAL ABSTRACT

Wind tunnel hardware-in-the-loop experiments about the global response of a 15 MW floating wind turbine

This work describes a new wind tunnel hybrid experiment investigating the aerodynamics and the global response of a 15 MW floating wind turbine. The floater motion is realized with a 6-degrees-of-freedom robotic platform controlled with a hardware-in-the-loop system, in which aerodynamic forces developed by the turbine model are the input of a numerical simulation of the floater dynamics, hydrodynamic excitation, and mooring. It is shown that accuracy of the aerodynamic force feedback from the wind turbine is critical to reproduce the floating wind turbine motion, and measurement of aerodynamic loads is more uncertain in case of pitch motion that movement in the other directions. Free decay tests show that damping of platform surge, pitch, and yaw modes is increased with wind and operating wind turbine compared to the no wind case. The effect of aerodynamic loads on the platform response with stochastic waves is small in the wave frequency range, whereas response of the surge mode is increased with wind.

A review of the effect of fertility agents (Herbs and drugs) on the hypothalamus

The hypothalamus plays a central role in regulating fertility through its interactions with the hypothalamic-pituitary-gonadal (HPG) axis. This review provides a comprehensive analysis of the effects of fertility agents, including herbs and pharmaceutical drugs, on the hypothalamus and its role in fertility regulation. The hypothalamus directly influences the HPG axis by secreting GnRH, a hormone crucial for sexual development and ovulatory cycles. GnRH can be secreted in pulsatile or surge modes, with distinct implications for reproductive function. The HPG axis further regulates reproductive organs and hormonal production, affecting processes like oocyte maturation, ovulation, and steroid hormone synthesis. Herbal remedies have been used historically in various cultures to address fertility issues. Several plants, such as Withania somnifera, Punica granatum, Camellia sinensis, Matricaria chamomilla, Vitex agnus-castus, and Nigella sativa, have been studied for their potential to enhance fertility by modulating the HPG axis and influencing sex hormone levels. Pharmaceutical fertility drugs like clomiphene citrate and metformin also have a significant impact on the hypothalamus. Clomiphene citrate acts as a partial estrogen agonist in the hypothalamus, leading to increased gonadotropin-releasing hormone (GnRH) production and subsequent elevation of gonadotropin levels. Metformin, primarily used for diabetes management, can restore ovarian function in women with polycystic ovary syndrome (PCOS) and improve pregnancy outcomes. Understanding the intricate interactions between fertility agents and the hypothalamus is crucial for developing effective treatments for infertility and optimizing reproductive health.

Experimental investigation of characteristics of instability evolution in a centrifugal compressor

The stable range of operation for the centrifugal compressor significantly influences the dynamic, economic, and environment-friendly characteristics of power systems. A deep understanding of the characteristics of instability evolution is necessary to improve the compressor stability. A centrifugal compressor equipped with a vaneless diffuser is experimentally investigated using high-response static-pressure measurements. The results obtained indicate that three typical rotational-speed ranges exist based on the different instability evolution characteristics, which reveals the various impeller–diffuser matching behaviors over the entire speed range. At low-speed ranges ((40%–75%)Nmax, Nmax is the maximum rotational speed), the compressor exhibits stable, Rotating Instability (RI), impeller stall (diffuser stall), and surge modes. The impeller stall mode is induced by RI and propagates downstream, resulting in the diffuser stall and compressor surge modes. In the medium-speed range ((75%–85%)Nmax), the compressor exhibits stable, diffuser stall, RI, and surge modes. In the high-speed range ((85%–100%)Nmax), the compressor exhibits stable, diffuser stall, and surge modes. The dominant instability position is shifted from the impeller to the diffuser as the rotational speed increases. Both the impeller and diffuser stall present an irregular sawtooth static-pressure wave and exhibit broadband frequency spectrum patterns.

Robust GABAergic Regulation of the GnRH Neuron Distal Dendron.

The amino acid transmitter γ-aminobutyric acid (GABA) is suspected to play an important role in regulating the activity of the gonadotropin-releasing hormone (GnRH) neurons controlling fertility. Rodent GnRH neurons have a novel dendritic compartment termed the "distal dendron" through which action potentials pass to the axon terminals and where inputs from the kisspeptin pulse generator drive pulsatile GnRH secretion. Combining Gnrh1-Cre mice with the Cre-dependent calcium sensor GCaMP6 and confocal imaging of acute brain slices, we examined whether GABA regulated intracellular calcium concentrations ([Ca2+]) in the GnRH neuron distal dendron. Short puffs of GABA on the dendron evoked either a monophasic sustained suppression of [Ca2+] or a biphasic acute elevation in [Ca2+] followed by the sustained suppression. Application of muscimol to the dendron replicated the acute elevation in [Ca2+] while baclofen generated the sustained suppression. Robust GABAB receptor-mediated inhibition was observed in 80% to 100% of dendrons recorded from females across the estrous cycle and from approximately 70% of dendrons in males. In contrast, the GABAA receptor-mediated excitation was rare in males and varied across the estrous cycle, being most prominent at proestrus. The activation of GABAB receptors potently suppressed the stimulatory effect of kisspeptin on the dendron. These observations demonstrate that the great majority of GnRH neuron distal dendrons are regulated by GABAergic inputs in a sex- and estrous cycle-dependent manner, with robust GABAB receptor-mediated inhibition being the primary mode of signaling. This provides a new, kisspeptin-independent, pathway for the regulation of pulsatile and surge modes of GnRH secretion in the rodent.

The potential impact of adverse aircraft-pilot couplings on the safety of tilt-rotor operations

AbstractThis paper addresses the potential impact of adverse aircraft-pilot couplings on tiltrotor safety, when a pilot or autopilot attempts to constrain flight dynamics with strong control. The work builds on previously published research on the theory and application of constrained flight to fixed- and rotary-wing aircraft. Tiltrotor aircraft feature characteristics from both types of aircraft and how these determine behaviour in a unique manner is investigated using a FLIGHTLAB simulation model of the XV-15 aircraft. Two different scenarios are explored in detail, using linearised models that reflect the flight-physics of stability for small deviations from trim. First, the control of vertical flight path with longitudinal cyclic pitch and elevator, and the consequences for the stability of the aircraft surge mode and short-period pitch-heave mode. The classical surge-mode instability for flight at speeds below minimum power is shown to apply to the tiltrotor in helicopter mode but alleviated in conversion and airplane modes. The impact on the short–period mode is seen to be a trade-off between the stabilising pitch attitude and destabilising incidence (angle-of-attack) contributions to the flight-path angle. The second example concerns strong control of roll attitude in the presence of adverse aileron-yaw. Here, the yaw-sway motion can be driven unstable, a problem encountered on fixed-wing aircraft with weak weathercock stability, but rare in the rotorcraft world. For both examples, the loss of stability is expressed as the change in sign of effective damping or stiffness stability derivatives. The explanatory theory for these non-oscillatory or low-frequency aircraft-pilot couplings is presented, along with interpretations in terms of handling qualities criteria. The paper also addresses the question of how to translate the findings into a form of aeronautical knowledge useful for the pilot training community.

Prediction of centrifugal compressor instabilities for internal combustion engines operating cycle simulation

Centrifugal compressors, which serve the purpose of internal combustion engines (ICE) supercharging, have a region of unstable operation. The compressor instabilities can be distinguished as rotating stall, mild, or deep surge, depending on the compression system parameters. All these types of compressor operation should be avoided for engine durability and long service life. Therefore, it is important to provide fast, stable, and correct prediction of compressor instabilities at ICE operating cycle simulation. The experimental research was conducted for an aircraft engine compressor to measure compressor performance map in the region of unstable operation, which is usually never provided by the manufacturer, and to study the compression system operation in the mild and deep surge modes. A mathematical model was developed, based on the Moore-Greitzer approach together with the modified equation of the compressor outlet pipe airflow acceleration, and integrated into the Blitz-PRO service for ICE steady and transient operation simulation. It is shown that the suggested mathematical model correlates well with the experimental data for the compressor testbench case. The application of the developed mathematical model provides fast and stable calculations and prediction of the type of compression system instability.

Neuroendocrine control of gonadotropin-releasing hormone: Pulsatile and surge modes of secretion.

The concept that different systems control episodic and surge secretion of gonadotropin-releasing hormone (GnRH) was well established by the time that GnRH was identified and formed the framework for studies of the physiological roles of GnRH, and later kisspeptin. Here, we focus on recent studies identifying the neural mechanisms underlying these two modes of secretion, with an emphasis on their core components. There is now compelling data that kisspeptin neurons in the arcuate nucleus that also contain neurokinin B (NKB) and dynorphin (i.e., KNDy cells) and their projections to GnRH dendrons constitute the GnRH pulse generator in mice and rats. There is also strong evidence for a similar role for KNDy neurons in sheep and goats, and weaker data in monkeys and humans. However, whether KNDy neurons act on GnRH dendrons and/or GnRH soma and dendrites that are found in the mediobasal hypothalamus (MBH) of these species remains unclear. The core components of the GnRH/luteinising hormone surge consist of an endocrine signal that initiates the process and a neural trigger that drives GnRH secretion during the surge. In all spontaneous ovulators, the core endocrine signal is a rise in estradiol secretion from the maturing follicle(s), with the site of estrogen positive feedback being the rostral periventricular kisspeptin neurons in rodents and neurons in the MBH of sheep and primates. There is considerable species variations in the neural trigger, with three major classes. First, in reflex ovulators, this trigger is initiated by coitus and carried to the hypothalamus by neural or vascular pathways. Second, in rodents, there is a time of day signal that originates in the suprachiasmatic nucleus and activates rostral periventricular kisspeptin neurons and GnRH soma and dendrites. Finally, in sheep nitric oxide-producing neurons in the ventromedial nucleus, KNDy neurons and rostral kisspeptin neurons all appear to participate in driving GnRH release during the surge.

Effects of Second-Order Hydrodynamics on the Dynamic Responses and Fatigue Damage of a 15 MW Floating Offshore Wind Turbine

In order to investigate the effects of second-order hydrodynamic loads on a 15 MW floating offshore wind turbine (FOWT), this study employs a tool that integrates AQWA and OpenFAST to conduct fully coupled simulations of the FOWT subjected to wind and wave loadings. The load cases covering normal and extreme conditions are defined based on the met-ocean data observed at a specific site. The results indicate that the second-order wave excitations activate the surge mode of the platform. As a result, the surge motion is increased for each of the examined load case. In addition, the pitch, heave, and yaw motions are underestimated when neglecting the second-order hydrodynamics under the extreme condition. First-order wave excitation is the major contributor to the tower-base bending moments. The fatigue damage of the tower-base under the extreme condition is underestimated by 57.1% if the effect of second-order hydrodynamics is ignored. In addition, the accumulative fatigue damage over 25 years at the tower-base is overestimated by 16.92%. Therefore, it is suggested to consider the effects of second-order wave excitations of the floating platform for the design of the tower to reduce the cost of the FOWT.

The dendron and episodic neuropeptide release.

The unexpected observation that the long processes of gonadotrophin-releasing hormone (GnRH) neurons not only conducted action potentials, but also operated to integrate afferent information at their distal-most extent gave rise to the concept of a blended dendritic-axonal process termed the "dendron". The proximal dendrites of the GnRH neuron function in a conventional manner, receiving synaptic inputs and initiating action potentials that are critical for the surge mode of GnRH secretion. The distal dendrons are regulated by both classical synapses and volume transmission and likely operate using subthreshold electrotonic propagation into the nearby axon terminals in the median eminence. Evidence indicates that neural processing at the distal dendron is responsible for the pulsatile patterning of GnRH secretion. Although the dendron remains unique to the GnRH neuron, data show that it exists in both mice and rats and may be a common feature of mammalian species in which GnRH neuron cell bodies do not migrate into the basal hypothalamus. This review outlines the discovery and function of the dendron as a unique neuronal structure optimised to generate episodic neuronal output.

CENTRIFUGAL COMPRESSOR PERFORMANCE MAPS TREATMENT FOR INTERNAL COMBUSTION ENGINES OPERATING CYCLE SIMULATION

Simulation of the supercharged internal combustion engines operation cycle is impossible without correct estimation of the supercharger operating parameters. Standard approach is to use specially prepared performance maps of compressor and turbine of the turbocharger, which are based on the experimental (or manufacturer’s) raw data. Centrifugal compressor performance maps interpolation, extrapolation and treatment provides challenging requirements as it is important to get correct simulation under such special conditions as compressor choke, rotating stall and pumping surge. At the same time it’s important to obtain the fast and stable calculations of the engine’s operating cycle. Blitz-PRO – online internal combustion engines operating cycle simulation service – offers supercharger performance maps preprocessing and implementation. It provides three different modes of compressor surge consideration during calculations: 1) full-scale surge mode using Moore-Greitzer approach; 2) mild surge mode with flexible adjustment; 3) “stable” mode, when the surge is neglected and the compressor constant-speed lines are extended from the rotating stall point to the lower mass flow region with the hyperbolic equation. Using the MAN 8G70ME-E engine 12140 kW, 82 rpm operating point as an example, the calculation results are compared for three modes of compressor surge consideration. The “stable” mode provides the fastest and the most stable calculations, while the calculations under the full-scale surge mode could generate the numerical (nonphysical) instability of calculations, which are caused by the high sensitivity of the two-stroke engines to the gas exchange processes as it is shown. The mild surge mode provides fast and stable enough calculation with the surge consideration ability, which could be assumed as the best solution for the given example. The researcher should choose between provided three modes of the centrifugal compressor surge consideration according to the calculations tasks, preferring “stable” mode for initial model setup and mild surge mode for the surge probability check, while the accurate compressor surge simulation needs further development.

Protection of Centrifugal Compressor System

Surge and Choke phenomenon are the two unstable operating modes of a compression system. That surge mode occurs at mass flows below the so-called surge line, and the chock mode occurs at low pressure and high flow rate. These instability operation modes will reduce the compressor performance or even will be made damage to the compressor system [1-3]. There are many studies to prevent instability phenomenon by establishing control system to the ability to do that, but sometimes surge or chock phenomenon occurs although of this big effort. So, for this reason, the paper focus on the protection system, introduced to detect and prevent surge and shock stall occurrence to reduce damages possibility and keep the production at minimum losses. This can be achieved by setting the mass flow rate, pressure ratio, and operating speed in a predefined area. Depending on the data sets including measurements from compression systems of Sirt Oil Company, Libya, and performance characteristics curves and polynomial regression technique to define the operation area. The developed surge protection system was implemented on the Matlab Simulink program and presented in a simple form.

Kobayashi Award 2019: The neuroendocrine regulation of the mammalian reproduction

Mammalian reproductive function is a complex system of many players orchestrated by the hypothalamus-pituitary–gonadal (HPG) axis. The hypothalamic gonadotropin-releasing hormone (GnRH) and the consequent pituitary gonadotropin release show two modes of secretory patterns, namely the surge and pulse modes. The surge mode is triggered by the positive feedback action of estrogen secreted from the mature ovarian follicle to induce ovulation in females of most mammalian species. The pulse mode of GnRH release is required for stimulating tonic gonadotropin secretion to drive folliculogenesis, spermatogenesis and steroidogenesis and is negatively fine-tuned by the sex steroids. Accumulating evidence suggests that hypothalamic kisspeptin neurons are the master regulator for animal reproduction to govern the HPG axis. Specifically, kisspeptin neurons located in the anterior hypothalamus, such as the anteroventral periventricular nucleus (AVPV) in rodents and preoptic nucleus (POA) in ruminants, primates and others, and the neurons located in the arcuate nucleus (ARC) in posterior hypothalamus in most mammals are considered to play a key role in generating the surge and pulse modes of GnRH release, respectively. The present article focuses on the role of AVPV (or POA) kisspeptin neurons as a center for GnRH surge generation and of the ARC kisspeptin neurons as a center for GnRH pulse generation to mediate estrogen positive and negative feedback mechanisms, respectively, and discusses how the estrogen epigenetically regulates kisspeptin gene expression in these two populations of neurons. This article also provides the mechanism how malnutrition and lactation suppress GnRH/gonadotropin pulses through an inhibition of the ARC kisspeptin neurons. Further, the article discusses the programming effect of estrogen on kisspeptin neurons in the developmental brain to uncover the mechanism underlying the sex difference in GnRH/gonadotropin release as well as an irreversible infertility induced by supra-physiological estrogen exposure in rodent models.

Different dendritic domains of the GnRH neuron underlie the pulse and surge modes of GnRH secretion in female mice.

The gonadotropin-releasing hormone (GnRH) neurons exhibit pulse and surge modes of activity to control fertility. They also exhibit an unusual bipolar morphology comprised of a classical soma-proximal dendritic zone and an elongated secretory process that can operate as both a dendrite and an axon, termed a 'dendron'. We show using expansion microscopy that the highest density of synaptic inputs to a GnRH neuron exists at its distal dendron. In vivo, selective chemogenetic inhibition of the GnRH neuron distal dendron abolishes the luteinizing hormone (LH) surge and markedly dampens LH pulses. In contrast, inhibitory chemogenetic and optogenetic strategies targeting the GnRH neuron soma-proximal dendritic zone abolish the LH surge but have no effect upon LH pulsatility. These observations indicate that electrical activity at the soma-proximal dendrites of the GnRH neuron is only essential for the LH surge while the distal dendron represents an autonomous zone where synaptic integration drives pulsatile GnRH secretion.

Experimental investigation on hybrid mooring systems for wave energy converters

Abstract This study presents a comprehensive experimental assessment of three hybrid mooring systems for a heaving-buoy wave energy converter. Free decay model tests are conducted to study the natural periods in heave, pitch and surge modes of the buoy when it is moored with different mooring configurations. A series of regular and irregular wave model tests are carried out to investigate the hydrodynamic responses of the point absorber as well as mooring dynamics. The effects of wave period, incident wave height and mooring configuration are evaluated. Besides, the influence of mooring configuration on buoy motion is discussed. To study the short term extreme dynamic tension, the traditional Weibull distribution, Weibull distribution based on tail data and peaks-over-threshold method are applied. The results showed that the Weibull distribution failed to present accurate extreme dynamic tension prediction when the snap events occur frequently, while the other two methods showed good performance despite of number of snap events. Based on the results of energy production performance and extreme dynamic tension, a novel mooring line design is suggested, which helps to reduce mooring dynamic tension.

Effects of Pressure Ratios of Axial Flow Compressors on the Deep Surge Frequencies Part II : Influences of Relative Locations of the Compressor

Macroscopic behaviors of the frequencies of deep-surges in systems of multi-stage compressors and flowpaths could be evaluated very roughly by a constant value of an effective reduced surge frequency fRsmeff, as described in Part I ofthe present study. However, some deviations from the rough average value could often appear, depending on the situations of the concerned systems. In the present study, the causes of the deviations are made clear by examinations on the numerical results. The deviations are concerned with the following three conditions; (1) a multi-stage compressor having a sufficiently high design pressure-ratio, (2) changes in the compressor speeds through near the design speed, and (3) a sufficiently short delivery plenum. In the situations affected by combined effects of the above three, the compressor could be located in a zone of the surge flow mode where the amplitude could vary noticeably in the axial direction. When the stall-responsible stages relocate from the front stages to the rear ones within the zone during the speed increase through near the design speed, the small difference in the relative location of the stall-responsible stages in the surge mode could sensitively affect the surge behaviors and lower the surge frequency. In the situations, incomplete stall recoveries, and sometimes subharmonic surges, tend to occur additionally, elongating the deep-surge periods and lowering the surge frequencies. It should be emphasized from the aspects of numerical-experimental observations that very local events as such could happen to have significant effects on the surge phenomena.

Time-varying linear quadratic Gaussian optimal control for three-degree-of-freedom wave energy converters

This paper presents a time-varying linear quadratic control for a three-degree-of-freedom (3-DoF) wave energy converter (WEC). The dynamic model for a heave-surge-pitch WEC has a linear coupling between pitch and surge modes, as well as a nonlinear coupling between the heave and pitch modes that affect the pitch motion. It is observed, however, that the heave motion is decoupled from the other two modes, and that the heave effect on the pitch motion can be recognized as a time-varying stiffness. Hence it is proposed in this paper to design a time-varying linear quadratic control for the coupled pitch-surge modes. The goal is to maximize the energy harvested over a receding time horizon. Prediction of the excitation forces is needed and is obtained based an estimate of the excitation force at the current time. The latter is obtained using an extended Kalman filter. The WEC motion is assumed constrained in this study. The results show that the energy harvested using this 3-DoF WEC is about three-fold higher than the energy extracted in heave mode, depending on the sea state. The paper also shows, with proper design of the control, it is possible to exploit this coupling to harvest more energy.

Kisspeptin: A Central Regulator of Reproduction in Mammals

The discovery of the role of kisspeptin neurons in the regulation of mammalian reproduction in 2003 was one of the biggest breakthroughs in reproductive endocrinology within the last few decades. Research during the past two decades since the discovery of kisspeptin has been unveiling the mechanism of how the hypothalamic kisspeptin neurons control reproductive functions through regulation of gonadotropin-releasing hormone (GnRH) secretion. This article aims to overview kisspeptin research, including the most recent studies from ours and other research groups, and to discuss the possibility of new strategies to control reproductive functions in farm animals. In the first section, we introduce the critical role of kisspeptin neurons in puberty onset and reproductive functions in mammals, including the regulation of two modes of GnRH/gonadotropin secretion, namely pulsatile and surge modes. The next section focuses more on the mechanism of how the kisspeptin neurons in the arcuate nucleus in the hypothalamus precisely controls GnRH pulse using other two neuropeptides, neurokinin B and dynorphin A. The article also discusses the mechanism suppressing reproductive function during lactation and other stress conditions through inhibition of kisspeptin neurons and consequent GnRH/gonadotropin secretion, to provide insights on the possibility of new strategies to control reproductive performance in domestic farm animals. Keywords Anteroventral Periventricular Nucleus, Arcuate Nucleus, Fertility, Gonadotropins, Pre-optic Area.