Pump Phase Research Articles

Mamyshev oscillation self-starting mode-locked fiber laser based on a self-feedback amplifying sub-cavity.

The Mamyshev oscillator (MO) boasts unparalleled modulation depth advantages in establishing mode-locking. However, this also significantly inhibits the self-starting of mode-locking. This Letter addresses the issue by constructing a self-feedback mechanism for regenerative oscillation. By amplifying noise cycles during the initial pumping phase to introduce periodic fluctuations in light intensity, we successfully achieve self-starting mode-locking at 1550 nm in an MO with a single gain arm structure at the pump power threshold of 76 mW. This self-starting mode-locking mechanism based on self-feedback sub-cavity amplification demonstrates excellent stability and repeatability in a single-arm MO structure. It provides what we believe to be a new approach for developing simple, reliable, and high repetition rate mode-locked lasers.

Exceptional points in the microcavity with phonon pump enhance the transparency and slow light

We theoretically investigated optomechanically induced transparency (OMIT) and slow light in a microcavity optomechanical system containing three nanoparticles, where the pump-probe field drives the cavity and a weak phonon pump drives the mechanical resonator. When the phonon pump frequency matches the pump-probe field frequency difference, adjusting the phonon pump's amplitude and phase can result in the transparency window exceeding unity. Tuning the relative positions of nanoparticles can periodically steer the system to exceptional points (EPs), further enhancing and modulating the transparency window. Furthermore, the phonon pump causes the phase dispersion at the transparency window to become highly steep, resulting in a large value and tunable group delay. Notably, when the system is at EPs, the slow light can be enhanced by approximately two times compared to when the system is not at EPs. Our research demonstrates a way to control optical transmission with potential applications in quantum communications and optical buffers.

Frequency stabilization of self-sustained oscillations in a sideband-driven electromechanical resonator

We present a method to stabilize the frequency of self-sustained vibrations in micromechanical and nanomechanical resonators. The method refers to a two-mode system with the vibrations at significantly different frequencies. The signal from one mode is used to control the other mode. In the experiment, self-sustained oscillations of micromechanical modes are excited by pumping at the blue-detuned sideband of the higher-frequency mode. Phase fluctuations of the two modes show near-perfect anticorrelation. They can be compensated in either of the modes by a stepwise change of the pump phase. The phase change of the controlled mode is proportional to the pump phase change, with the proportionality constant independent of the pump amplitude and frequency. This finding allows us to stabilize the phase of one mode against phase diffusion using the measured phase of the other mode. We demonstrate that phase fluctuations of either the high-frequency mode or the low-frequency mode can be significantly reduced. The results open new opportunities in generating stable vibrations in a broad frequency range via parametric down-conversion in nonlinear resonators. Published by the American Physical Society 2024

Magnon Supercurrent and the Phase Slippage in an Yttrium Iron Garnet Film

Exactly forty years ago, the spin superfluidity and Bose–Einstein condensation of magnons in superfluid antiferromagnetic 3He-B were discovered. In this work, the existence of spin superfluidity and phase slippage in an yttrium iron garnet film at room temperature is demonstrated using the optical Faraday effect. The s-patial distribution of the phase and amplitude of the spin precession under the conditions of magnon Bose‒Einstein condensation are studied by varying the pump phase difference between two strip lines exciting magnons.

Design and simulation optimization of phase-locked loop structure for phase-shifting power supply

A phase-locked loop (PLL) of a phase-shifting power supply for the power system is designed in this paper. Taking the industrial frequency current as the reference signal, the input and output characteristics of the phase-frequency detector with charge pump are analyzed. In addition, the transfer function of the PLL system is analyzed by combining the passive second-order low-pass filter and the voltage-controlled oscillator. As a result, the influence of parameters such as charge pump current, phase margin, and loop bandwidth on the performance of the PLL is investigated, and the optimal parameters of each section are obtained. The results show that the optimized PLL has a locking time of 0.75 s, a pull-out range of 63.16 Hz, and a locking range of 43.82 Hz, with high stability and noise immunity.

Quantum quenches in driven-dissipative quadratic fermionic systems with parity-time symmetry

We study the quench dynamics of noninteracting fermionic quantum many-body systems that are subjected to Markovian drive and dissipation and are described by a quadratic Liouvillian which has parity-time (PT) symmetry. In recent work, we have shown that such systems relax locally to a maximum entropy ensemble that we have dubbed the PT-symmetric generalized Gibbs ensemble (PTGGE), in analogy to the generalized Gibbs ensemble that describes the steady state of isolated integrable quantum many-body systems after a quench. Here, using driven-dissipative versions of the Su-Schrieffer-Heeger (SSH) model and the Kitaev chain as paradigmatic model systems, we corroborate and substantially expand upon our previous results. In particular, we confirm the validity of a dissipative quasiparticle picture at finite dissipation by demonstrating light cone spreading of correlations and the linear growth and saturation to the PTGGE prediction of the quasiparticle-pair contribution to the subsystem entropy in the PT-symmetric phase. Further, we introduce the concept of directional pumping phases, which is related to the non-Hermitian topology of the Liouvillian and based upon qualitatively different dynamics of the dual string order parameter and the subsystem fermion parity in the SSH model and the Kitaev chain, respectively: depending on the postquench parameters, there can be pumping of string order and fermion parity through both ends of a subsystem corresponding to a finite segment of the one-dimensional lattice, through only one end, or there can be no pumping at all. We show that transitions between dynamical pumping phases give rise to a new and independent type of dynamical critical behavior of the rates of directional pumping, which are determined by the soft modes of the PTGGE. Published by the American Physical Society 2024

Značaj straina leve pretkomore u proceni srčane funkcije

Given the undeniable clinical and prognostic value, the function of the left atrium (LA) plays a leading role in the contemporary evaluation of cardiac diseases and is considered an essential morphological substrate for the development of cardiovascular diseases. It is sensitive to nervous, endocrine, and immunological stimuli. New evidence from the literature highlights the importance of fibrotic, electrical, and autonomic remodeling of the LA, introducing the concept of atrial cardiomyopathy, which is closely associated with atrial fibrillation and stroke. In the past, the diameter of the LA was the most important parameter for assessing its characteristics, but new information about the various roles of the LA has created the need for parameters that more precisely or thoroughly evaluate LA function. The function of the LA is complex, consisting of three phases: the reservoir phase (ventricular systole), the conduit phase (early diastole), and the pump phase (late diastole). The introduction of myocardial deformation analysis, or strain of the LA via speckle tracking, has achieved significant progress in detecting even subtle functional abnormalities before an increase in LA size. This method improves the diagnostic capabilities of standard echocardiographic examinations, and its diagnostic and prognostic value is sometimes comparable to more advanced and less accessible techniques such as cardiac magnetic resonance imaging and computed tomography.

Effects of 3D Concrete Printing Phases on the Mechanical Performance of Printable Strain-Hardening Cementitious Composites

Several studies have shown the potential of strain-hardening cementitious composites (SHCC) as a self-reinforcing printable mortar. However, papers published on the development of three-dimensional printable SHCC (3DP-SHCC) often report a discrepancy between the mechanical properties of the cast and printed specimens. This paper evaluates the effect of each successive phase of the printing process on the mechanical properties of the composite. To this end, materials were collected at three different stages in the printing process, i.e., after each of mixing, pumping, and extruding. The collected 3DP-SHCC materials were then cast in specimen moulds and their mechanical properties after curing were obtained. The resulting findings were juxtaposed with the mechanical properties of the specimens derived from a fully printed 3DP-SHCC element, and our findings indicate that while the density and the compressive strength are not significantly influenced by the printing process, the flexural and tensile strength, along with their associated deflection and strain, are strongly affected. Additionally, this research identifies the pumping phase as the primary phase influencing the mechanical properties during the printing process.

Mueller maneuver attenuates left atrial phasic volumes and myocardial strain in healthy younger adults.

The left atrium (LA) is a key, but incompletely understood, modulator of left ventricular (LV) filling. Inspiratory negative intrathoracic pressure swings alter cardiac loading conditions, which may impact LA function. We studied acute effects of static inspiratory efforts on LA chamber function, LA myocardial strain, and LV diastolic filling. We included healthy adults (10 males/9 females, 24 ± 4 yr) and used Mueller maneuvers to reduce intrathoracic pressure to -30 cmH2O for 15 s. Over six repeated trials, we used echocardiography to acquire LA- and LV-focused two-dimensional (2-D) images, and mitral Doppler inflow and annular tissue velocity spectra. Images were analyzed for LA and LV chamber volumes, tissue relaxation velocities, transmitral filling velocities, and speckle tracking-derived LA longitudinal strain. Repeated measures were made at baseline, early Mueller, late Mueller, then early release, and late release. In the late Mueller compared with baseline, LV stroke volume decreased by -10 ± 4 mL (P < 0.05) and then returned to baseline upon release; this occurred with a -11 ± 9 mL (P < 0.05) end-diastolic volume reduction. Early diastolic LV filling was attenuated, reflected by decreased tissue relaxation velocity (-2 ± 2 cm/s, P < 0.05), E-wave filling velocity (-13 ± 14 cm/s, P < 0.05), and LA passive emptying volume (-5 ± 5 mL, P < 0.05), each returning to baseline with release. LA maximal volume decreased (-5 ± 5 mL, P < 0.05) during the Mueller maneuver, but increased relative to baseline following release (+4 ± 5 mL, P < 0.05), whereas LA peak positive longitudinal strain decreased (-6 ± 6%, P < 0.05) and then returned to baseline. Attenuated LA and in turn, LV filling may contribute to acute stroke volume reductions experienced during forceful inspiratory efforts.NEW & NOTEWORTHY In healthy younger adults, the Mueller maneuver transiently reduces left atrial filling and passive emptying during the reservoir and conduit phases, respectively. Corresponding reductions are seen in left atrial reservoir and conduit phase longitudinal myocardial strain and strain rate. However, left atrial pump phase active function and mechanics are largely preserved compared with baseline. Rapid changes in LA chamber volumes and myocardial strain with recurrent forceful inspiratory efforts and relaxation may reflect acute LA stress.

Effect of the structuration rate on dimensional stability and mechanical performance of 3D printed mortars

Digital concrete fabrication is a novel construction technique in which structural elements are built layer by layer without the use of formwork. This technology has introduced new challenges in materials engineering. More emphasis lies on the structuration behavior of cement-based materials. Concrete is designed to achieve adapted workability to flow during the pumping phase. It also requires proper build-up and stiffness to retain its shape after extrusion and sustain its own weight and, subsequently, the weight of successive layers. A high degree of structuration is recommended to ensure high printing quality. However, this may adversely affect the performance of the multi-layer printing process. In the present study, an experimental program was carried out to evaluate the impact of structuration rate on the dimensional stability and mechanical properties of the printed element at both early age and long term, respectively. Four different mixtures with various structuration rates were designed and printed. In the fresh state, variations in the layer’s height and width were recorded to evaluate the dimensional stability of the printed structure. On the other hand, several specimens were cut out of the freshly printed elements for mechanical tests. The compression and flexural tests were conducted after 7 and 28 days of moist-curing. The obtained results showed that there exists an optimum rate of structuration above which the quality of the bonding interface is compromised, generating losses in mechanical properties. Under this threshold, anisotropic behavior dominates, leading to low dimensional stability.

Universality class of the mode-locked glassy random laser

By means of enhanced Monte Carlo numerical simulations parallelized on GPUs we study the critical properties of the spin-glass-like model for the mode-locked glassy random laser, a 44-spin model with complex spins with a global spherical constraint and quenched random interactions. Implementing two different boundary conditions for the mode frequencies we identify the critical points and the critical indices of the random lasing phase transition with finite size scaling techniques. The outcome of the scaling analysis is that the mode-locked random laser universality class is compatible with a mean-field one, though different from the mean-field class of the Random Energy Model and of the glassy random laser in the narrow band approximation, that is, the fully connected version of the present model. The low temperature (high pumping) phase is finally characterized by means of the overlap distribution and evidence for the onset of replica symmetry breaking in the lasing regime is provided.

Accurate derivation of THG conversion efficiency in periodically poled nonlinear medium and optimizing conversion parameters

We have derived a novel equation to accurately predict the third harmonic generation (THG) conversion efficiency in hybrid periodically poled nonlinear medium. Our equation considers the general case that takes both depleted pump regime and phase mismatching cases, resulting in more precise predictions of efficiency. This level of accuracy is crucial for certain applications like high-power THG lasers. Moreover, accurate calculation of THG power density is essential to prevent exceeding the crystal damage threshold. We applied our equation on hybrid MgO:PPLN crystal to determine the optimal SHG region length corresponding to two different power densities, namely, 0.25 and 0.5MW/cm2. The effect of crystal temperature on efficiency was also studies. Furthermore, a comparison between the derived equation and the commonly used nondepleted pump regime equation was performed. We found that the latter equation is significantly less accurate, particularly at high power densities, with the efficiency of the depleted pump regime being 50.6% less than nondepleted one. To demonstrate the effectiveness of the equation, our results were compared with experimental data, and we observed a good agreement between them.

P476 TOLERATED SUSTAINED VENTRICULAR FIBRILLATION IN LVAD RECIPIENT: THE WALKING DEAD

Abstract A 73–year–old man comes to the cardiac surgery clinic, due to the onset of an arrhythmic storm. In 1999, the patient was diagnosed with dilated cardiomyopathy with finding of a pathogenic mutation of the MYH7 gene by NGS panel analysis. Because of severely reduced systolic function despite OMT and left conduction delay, he underwent CRT–D implant in class IA. The patient‘s course was characterized by multiple exacerbations and a worsening course of ventricular dysfunction (EF 20%), such as to configure a picture of advanced heart failure, INTERMACS III (frequent flyer). Approximately 6 months later, the patient was admitted with signs of hypoperfusion refractory to inotrope therapy and significant congestion. In consideration of age, frailty and irreversible renal dysfunction, the patient was excluded from the transplant list. Therefore, he was a candidate for mechanical support as destination therapy, through the implantation of the Heart Mate III. At admission, the patient was monitored with evidence of ventricular fibrillation (image 1) and relative hemodynamic stability. The vital parameters reported a BP of 90/76 mmHg, FC not evaluable and SpO2 of 80%. For this reason, in anesthesiological assistance, asynchronous external defibrillation (200 J) was performed with restoration of the pacing rhythm. The monitoring of the LVAD showed a series of alerts: a reduction of the Pump Flow and phases of reduction of the Pulse Index (image 2). Event monitoring of the CRT–D revealed that the patient developed an arrhythmic storm, with appropriate but ineffective several shocks. The 8 shocks were followed by the interruption of the device therapies, but the patient, despite the ventricular fibrillation, had preserved perfusion. Medical therapy was optimized (mexiletine add–on) and CRT–D was rescheduled. Conclusions The presence of LVAD ensures a satisfactory cardiac output during arrhythmias that would lead to hemodynamic compromise. For this reason it is possible to identify patients who autonomously come to our observation in "cardiac arrest".

On the resilience of dual-waveguide parametric amplifiers to pump power and phase fluctuations

Parametric amplifiers based on coupled-core fibers and coupled integrated waveguides are promising devices for delivering broadband and flat gain spectrum with low noise figure in vital technological applications such as optical communications. To address potential practical issues that may arise in the experimental demonstration, in the present work, we derive analytical expressions for the impact of relative input pump phase and power fluctuations between two waveguides on pump waves stability. We, furthermore, evaluate, through numerical simulations, how the pump power oscillations between the two waveguides affect the amplifier spectrum, identifying optimal regimes of operation for coupled-core fibers and also for coupled integrated waveguides. Our findings hint at the resilience of these parametric amplifiers' architectures and at their possible practical implementation in realistic labs and real-world scenarios.

A Study on the Migration Rule and Flow Conductivity of Multi-particle Size Proppant in Shale Reservoir

To solve the problem that it is difficult to realize efficient prop of fracture network system in the volume fracturing process of shale reservoir, the migration and settlement mechanism of proppant in fractures is analyzed, the migration law of proppant under different particle size and different combination conditions is studied by using true three-dimensional simulation software, and the distribution of proppant concentration and fracture conductivity are simulated. On this basis, the applicability of proppant with different particle sizes under different fracture morphology is judged, and the combination of proppant particle sizes is optimized to maximize the full prop of the fracture network system, improve the conductivity of the fracture network system, and realize efficient fracturing stimulation of shale reservoirs. The research shows that when the fracture width is very small and the average fracture width is less than 1mm, it is difficult for medium/large size proppant to enter the fracture network and achieve effective fracturing prop. Therefore, it is recommended to use small/micro size proppant. Under the condition that the average fracture width is greater than 1mm and the proppant with large particle size can effectively enter the fracture, the combination of large size + medium size proppant particles settle quickly, and the porosity of the sand dike is large, which can reach a larger equilibrium height, increase the effective support width of the fracture, and improve the conductivity of the fracture network. The fracture conductivity is not only related to the proppant placement concentration, but also depends on the proppant placement structure in the fracture. After the fracture is effectively propped, further increasing the proppant concentration will block the fracture system and reduce the conductivity. Therefore, it is not suitable to pump small size proppant after pumping large/medium size proppant, so as to avoid unnecessary plugging to the proppant. Small size proppant is suitable for use in the early pumping phase.

Soliton stabilization in microresonators with high order dispersion via pump phase modulation

We theoretically and numerically investigate the effects of third-order dispersion on microresonator solitons in anomalous dispersion with an extended normalized Lugiato–Lefever equation. The temporal position drift of solitons in the microresonator induced by the third-order dispersion is observed. The soliton temporal location stabilization is realized via pump phase modulation. Moreover, the final stable cavity soliton temporal position is deviated to the maxima of the pump phase modulation field profile which is the stable position of the solitons without high-order dispersion. We also study the effectiveness of the pump phase modulation in different modulation parameters. The research method sheds light on the cavity soliton stabilization, on-chip ultrashort pulse formation and optical information processing.

General solution of phase mismatched second harmonic conversion efficiency in periodically poled nonlinear medium

In this work we provide for the first time a novel and more accurate second harmonic generation (SHG) conversion efficiency equation for periodically poled nonlinear medium. We believe the equation derived in this work is more useful than equations reported in previous works which are limited because it is considering the case of either nondepleted pump regime or perfect phase matching. The equation derived in this work tackles the general case: depleted pump regime and phase mismatching which makes it important for theoretical – experimental study. We used MgO:PPLN crystal as an example to illustrate SHG conversion efficiency as function of crystal length, laser power density, crystal temperature and beam divergence. We included fundamental and second harmonic waves reflection at entrance and exit surfaces respectively and performed numerical solution using fifth-order Runge-Kutta method. The numerical results show excellent match with analytical results obtained from the derived formula. We compared our theoretical results with experimental results reported in the literature and the comparison shows a good match. Finally, we performed a comparison between depleted and nondepleted pump regime. The results show a difference of 20% between two efficiencies making nondepleted efficiency equation, which used in many theoretical – experimental comparisons, not accurate at high power densities.

Dead zone-less low power phase frequency detector, independent of duty cycle variations for charge pump phase locked loop

Dead zone-less low power phase frequency detector, independent of duty cycle variations for charge pump phase locked loop

Frequency Source Design of Fast Locking Laser Range Radar

Given the bad ranging precision in continuous wave laser range radar systems because of the large jitter of the main oscillator frequency source, this paper introduces the fast locking method, which is based on Field Programmable Gate Array (FPGA) and modified mixed Charge Pump Phase Locked Loop (CPPLL), effectively improving the locking time of PLL frequency source. The input frequency is generated by a temperature compensation quartz crystal oscillator with high stability frequency (TCXO). It improves the PLL performance using the two-order active filter, reduces the phase detector dead-banding, and improves the frequency stability through the buffer insertion in PFD. The traditional PLL was improved by using preset voltage mode, which improves the PLL lock time. Finally, it analyzes the influence of frequency stability on the ranging accuracy of laser radar. The test results show that PLL lock time is up to 1.6ms. It can be applied to continuous wave laser radar ranging systems.

Mechanical function of the left atrium within 28 days after restoration of sinus rhythm in patients with paroxysmal atrial fibrillation

Objective: Atrial fibrillation is a strong independent risk factor for cardioembolic stroke, with a significant impact on morbidity, mortality and healthcare costs. The aim of our study is to investigate left atrial mechanical function in healthy subjects and patients with atrial fibrillation paroxysms less than 48 hours with low risk of thromboembolic complications at 1 and 28 days after restoration of sinus rhythm. Methods: Thirty-six healthy controls and patients with paroxysms of non-valvular atrial fibrillation less than 48 hours (n=25) with low-risk CHA2DS2VASc score were included in the study. The mechanical function of the left atrium (LA) was investigated by the 2D speckle tracking program. Transthoracic echocardiography was performed on the 1st and 28th days after restoration of sinus rhythm by pharmacological cardioversion. Results: Despite the absence of differences in left ventricular systolic function and LA size between the groups, there was a significant decrease in LA deformation and strain rate on day 1 immediately after sinus rhythm recovery in the patients. In the pump phase, the decrease was about 3%, reservoir phase – 10%, and conduit phase – 7% compared to the control group. The strain rate also decreased in the patient group: -1.5 s-1 versus control: -2.14 s-1 (p&amp;lt;0.0001). On the 28th day after restoration of sinus rhythm, there were significant changes in reservoir and conduit functions in patients group in comparison with control group. Global longitudinal LA strain (reservoir phase) decreased to 7%, conduit phase decreased to 11% compared with the control group. In patients group we can see the dynamics during 28 days: pump phase and strain rate were significantly improved, however reservoir and conduit did not significantly change and were lower than in healthy. Conclusion: Mechanical function of the LA in patients with non-valvular atrial fibrillation and low risk of thromboembolic complications, studied with speckle tracking on the first day was significantly impaired compared with the control group (reservoir phase and strain rate). By day 28, mechanical function improved compared to day 1, but reservoir phase remained significantly lower than normal.