Changes In Pulse Frequency Research Articles

Enhanced porphyrin-based hypoxia imaging by temporal oversampling of delayed fluorescence signal.

Protoporphyrin IX (PpIX) delayed fluorescence (DF) is inversely related to the oxygen present in tissues and has potential as a novel biomarker for surgical guidance and real-time tissue metabolism assessment. Despite the unique promise of this technique, its successful clinical translation is limited by the low intensity emitted. We developed a systematic study of ways to increase the PpIX DF signal through acquisition sampling changes, allowing optimized imaging at video rates. To accomplish signal increase, time-gating signal compression was achieved through changes in pulse frequency and power density, using sampling rates that are faster than the decay rate of the signal. The increased signal yield was tested and validated in vitro and then demonstrated in vivo, with comparison to settings that sample the full lifetime emission decay. Results in vitro and in vivo demonstrated that optimized timing could increase the detected intensity by a factor of 7. The images showed results that were superior than when sampling the full DF lifetime decay. The proposed timing optimization enhances PpIX-based DF real-time imaging of tissue hypoxia. By increasing sampling frequency and adjusting the acquisition gate and pulse width, the collected signal intensity improved sevenfold, demonstrated both in vitro and in vivo. The technique was shown to enable better visualization of small and anatomically challenging hypoxic structures. The improved target-to-background ratio and compatibility with pressure-enhanced sensing of tissue oxygen technique were demonstrated.

Structural and property regulation of double ceramic phase–reinforced AlCoCrFeNiTiZr–based high entropy alloy coatings by pulsed–wave lasers

In-situ synthesis ZrC and TiC reinforced AlCoCrFeNiTiZr–based high entropy alloy (HEA) coatings were successfully synthesized on R60702 using pulsed–laser cladding. The effects of pulse frequency (5, 50, 500, and 5000 Hz) on microstructure evolution, microhardness, wear resistance, and corrosion resistance were investigated. The results demonstrate that the HEA coatings consists of phases including BCC, HCP, and metal carbides (MC). The phase composition and proportion are influenced by changes in pulse frequency. At pulse frequencies of 5 and 50 Hz, the predominant MC phase is ZrC. As the pulse frequency increases, it transitions to a coexistence of ZrC + TiC before ultimately becoming predominantly TiC. Concurrently, the size of the ceramic phase and the proportion of the HCP phase initially decrease, then increase. A pulse frequency of 500 Hz yields optimizations in microhardness, wear resistance, and corrosion resistance. The favorable mechanical properties are attributed to the synergistic effect of solid solution strengthening, fine crystal strengthening, and ceramic phase strengthening. The optimal corrosion resistance is due to the formation of a stable passivation film while local corrosion and galvanic corrosion are weakened.

CHANGE OF PULSE FREQUENCY IN HORSES AS AN INDICATOR OF STRESS CAUSED BY LOADING INTO THE TRAILER

Transport and loading into a trailer is a potential source of stress for horses, which can consequently undermine the concept of animal welfare. The study aimed to determine the presence of stress reaction in horses during the loading into the trailer, expressed through a change in pulse frequency as an indicator of stress reaction. The study included 25 horses between the ages of 4 and 20. Heart rate verification was performed using a veterinary stethoscope with a double-sided membrane and controlled by a heart rate monitor. When the horses were resting in the stable (first measurement), a pulse frequency of 29 to 40 bpm was found. The second measurement was performed at the moment of loading when the horses stepped onto the loading platform of the trailer, and pulse frequency values from 42 to 72 bpm were found. The results of the t-test indicate that there is a statistically significant difference in the pulse frequency between the first and second measurements. The results of this study indicate that loading horses into the trailer can cause stress, which is manifested by an increase in pulse frequency. The tendency of horses to easily form habits allows their proper training to reduce the level of stress while loading into trailers, which would contribute to improving the well-being of horses, and at the same time contribute to reducing stress and the risk of injury to horses and staff.

A portable, programmable, multichannel stimulator with high compliance voltage for noninvasive neural stimulation of motor and sensory nerves in humans

Most neural stimulators do not have a high enough compliance voltage to pass current through the skin. The few stimulators that meet the high compliance voltage necessary for transcutaneous stimulation are typically large benchtop units that are not portable, and the stimulation waveforms cannot be readily customized. To address this, we present the design and validation of a portable, programmable, multichannel, noninvasive neural stimulator that can generate three custom bipolar waveforms at ± 150 V with microsecond temporal resolution. The design is low-cost, open-source, and validated on the benchtop and with a healthy population to demonstrate its functionality for sensory and motor stimulation. Sensory stimulation included electrocutaneous stimulation targeting cutaneous mechanoreceptors at the surface of the skin and transcutaneous nerve stimulation targeting the median nerve at the wrist. Both electrocutaneous stimulation on the hand and transcutaneous stimulation at the wrist can elicit isolated tactile percepts on the hand but changes in pulse frequency are more discriminable for electrocutaneous stimulation. Also, neuromuscular electrical stimulation of the flexor digiti profundus is evoked by applying electrical stimulation directly above the muscle in the forearm and to the median and ulnar nerves in the upper arm. Muscle and nerve stimulation evoked similar grip forces and force rise times, but nerve stimulation had a significantly slower fatigue rate. The development and validation of this noninvasive stimulator and direct comparison of common sensory and motor stimulation targets in a human population constitute an important step towards more widespread use and accessibility of neural stimulation for education and research.

Evidence for neutron star triaxial free precession in Her X-1 from Fermi/GBM pulse period measurements

ABSTRACT Her X-1/HZ Her is one of the best studied accreting X-ray pulsars. In addition to the pulsating and orbital periods, the X-ray and optical light curves of the source exhibit an almost periodic 35-d variability caused by a precessing accretion disc. The nature of the observed long-term stability of the 35-d cycle has been debatable. The X-ray pulse frequency of Her X-1 measured by the Fermi/GBM demonstrates periodical variations with X-ray flux at the main-on state of the source. We explain the observed periodic sub-microsecond pulse frequency changes by the free precession of a triaxial neutron star (NS) with parameters previously inferred from an independent analysis of the X-ray pulse evolution over the 35-d cycle. In the Fermi/GBM data, we identified several time intervals with a duration of half a year or longer where the NS precession period describing the pulse frequency variations does not change. We found that the NS precession period varies within one per cent in different intervals. Such variations in the free precession period on a year time-scale can be explained by $\lesssim 1{{\ \rm per\ cent}}$ changes in the fractional difference between the triaxial NS’s moments of inertia due to the accreted mass readjustment or variable internal coupling of the NS crust with the core.

Electrochemical behavior of Ti-6.5Al-2Zr-1Mo-1V alloy under rotating condition with periodically fluctuating current density

Titanium alloy plays a crucial role in the electrochemical field due to its excellent corrosion resistance. The passivation and dissolution behaviors of Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy in NaCl solution were studied by simulating the electrochemical machining process in a rotating condition, which made the anode in a state with alternating high and low current density. Electron probe micro analysis, ultra-depth microscope, scanning electron microscope, and X-ray photoelectron spectrometer were used to reveal the evolution of TA15 under fluctuating current density. The existence state of the passivation film on TA15 surface was closely related to the pulse frequency of the periodically fluctuating current density. At higher pulse frequency of 0.20 Hz, the material was hardly dissolved because passivation dominated the electrolysis behavior, while at lower pulse frequency of 0.01 Hz, the passivation and dissolution behaviors occurred alternately with the variation of the current density. Herein, the thickness of the passivation film was inversely proportional to the applied current density. Due to the different electrochemical characteristics of α phase and β phase, the surface of the TA15 changed from being smooth to porous after a period. In addition, the change of microstructure affected the content of O2– and exposed the suboxides of titanium. In a word, the change of pulse frequency and current density affected the electrochemical behavior of TA15, which was different from the conventional steady condition.

Influence of Applied Frequency on Thermal Physical Properties of Coatings Prepared on Al and AlSi Alloys by Plasma Electrolytic Oxidation

In this study, plasma electrolytic oxidation (PEO) was performed on Al and AlSi substrates using a pulsed direct current (DC) power source. The coating process was carried out in a Na2SiO3 electrolyte with the systematic change of pulse frequency (50–1400 Hz). The surface characteristics of the coatings were examined using scanning electron microscopy (SEM). The phase structure was characterized using X-ray diffraction (XRD). A differential scanning calorimeter (DSC) and a laser flash apparatus (LFA) were employed to test heat capacity and heat conductivity, respectively. Results showed that as the discharge frequency increased, the thermal physical properties of Al-PEO and AlSi-PEO coatings changed in different ways. At a high frequency, Al-PEO coatings had low porosity and were closed-pore structured whereas AlSi-PEO coatings had high porosity and large-size open-pore structures could be observed on their surfaces due to concentrated discharges. Based on these findings, it was found that the thermal productivity of coatings is closely correlated with the open-/closed-pore structure instead of porosity. PEO coatings with low heat capacity or low heat conductivity could be obtained with a controlled frequency.

Influences of pulse frequency on formation and properties of composite anodic oxide films on Ti-10V-2Fe-3Al alloy

A thick composite anodic oxide film was fabricated in an environmentally friendly malic acid electrolyte containing PolyTetraFluoroEthylene (PTFE) nanoparticles on Ti-10V-2Fe-3Al alloys. The influence of pulse frequency on the morphology, microstructure and composition of composite anodic oxide films containing PTFE nanoparticles was investigated using Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM) and Raman spectroscopy. The tribological properties in terms of the friction coefficient, wear loss and morphology of worn surfaces were measured by ball-on-disc tests. The electrochemical property was evaluated by potentiodynamic polarization. The results indicated that the titanium dioxide of composite anodic oxide films transformed from anatase to rutile with the change of pulse frequency, which could result from the electrochemical dynamic equilibrium. The combination of PTFE nanoparticles and malic acid electrolyte molecules can influence the energy fluctuation of electrochemical equilibrium and formation of composite anodic oxide films. Moreover, composite anodic oxide films fabricated under the condition of 1.0–2.0 Hz exhibited the best wear resistance and corrosion property. The schematic diagram of the film formation and PTFE nanoparticles spreading process under different frequencies was elucidated.

Effect of Pulse Frequencies on Low Carbon Steel in 3.5 wt% NaCl Solution under Zero Charge Corrosion Protection

Zero charge corrosion protection (ZCCP) is an alternative to the existing cathodic protection methods. It applies a current/voltage pulse with a certain particular frequency to attain a potential of zero charge (Epzc) on the electrode-electrolyte interface. A study on the pulse frequencies of ZCCP system on low-carbon steel in 3.5 % NaCl Na solution was carried out for 14 days. The pulse frequencies are varied from 4, 20, 50 and 100 Hz. The ability of these frequencies in protecting samples is determined by means of corrosion rate based on weight loss analysis and surface morphology. Experimental observations indicate that low carbon steel corrosion protection is strongly influenced by changes in pulse frequency. Corrosion rates were found to gradually decrease as pulse frequency increased from 4, 20 to 50 Hz, nevertheless at higher frequencies (100 Hz), corrosion protection was observed to be less effective where the corrosion rate dramatically grew up. The surface morphology of the steel surface is smooth and protected at a pulse frequency of 50 Hz. This indicates that the current / voltage pulse of ZCCP system only requires 50 Hz which is equivalent to a standard AC power frequency applied in most countries including Malaysia.

Modification of TA15 alloy surface by high-pulse-frequency laser cleaning

The original morphology of the oxide layer and the surface of the titanium alloy has a significant impact on manufacturing and processing. The laser cleaning pulse frequency amplitude affects the single pulse energy. It will affect the original morphology of the surface and the compositional changes of the laser-generated oxide layer. This work aims to study the effect of pulse frequency on the surface morphology and the composition of laser-generated oxide layer of the TA15 alloy surface in laser cleaning. With normal pulse frequency (70 kHz), the surface roughness increased to micrometer order. The striation morphology was formed, accompanied by melting. With high pulse frequency (700 kHz), the surface roughness (Ra) decreased to submicrometer order. The striation morphology and the melting phenomenon weakened and disappeared. The change in pulse frequency results in different chemical bonds on the surface. With normal pulse frequency, the oxide layer forming on the surface was mainly composed of TiO2 and a small amount of TiO. With high pulse frequency, the oxide layer forming on the surface was mainly composed of TiO. After laser cleaning, the self-corrosion current of the sample decreased by orders of magnitude compared with that of untreated samples. The corrosion resistance increased as the pulse frequency increased. The self-corrosion potential increased with an increase in the TiO amount.

Increased Activity Tolerance based on Hemodynamic Status in Patients Coronary Heart Disease After Physical Rehabilitation of Phase I (Inpatient)

Coronary Heart Disease (CHD) is caused by atheroma/plaque attached to the endothelial lining of the coronary arteries which causes blockages in oxygen and nutrient distribution to the tissues. This condition causes CHD patients to experience deficits in functional capacities, such as self-care ability, incapacity for performing the activity of daily living and also social activities. This study aims to analyze activity tolerance based on hemodynamic status (respiration, blood pressure, pulse frequency, oxygen saturation) in CHD patients after phase 1 physical rehabilitation (inpatient). The research method is quasy experiment one group pre-post-test research method. The results of data analysis using the Friedman test found that there was a significant effect on respiration on days 2, 3, systolic blood pressure on days 1 and 3, no significant effect on diastolic blood pressure, significant changes in oxygen saturation on days 1, 2, and 3, changes in pulse frequency on days 1 and 3.

Gonadotrophic control of follicular development and function during the oestrous cycle of the ewe

Summary. In the adult non pregnant ewe the secretion of FSH is sufficient to ensure a continuous growth and development of antral follicles to 3–5 mm size at all times. Further development and increased secretion of oestradiol through the final 72 h to ovulation depends on adequate stimulation by LH. During anoestrus and the luteal phase of the cycle LH pulses occur too infrequently to stimulate sufficient oestradiol to evoke an LH surge. Moreover, during the luteal phase progesterone secreted by the corpus luteum not only reduces the frequency of LH pulses but also inhibits the ability of oestrogen to evoke an LH surge. At the time of luteal regression the frequency of LH pulses increases to at least one per hour due to the fall in progesterone secretion. This change in pulse frequency of LH is associated with a decrease in the secretion of FSH, probably because of a direct inhibitory action of oestrogen on the anterior pituitary gland. The dominant follicle is probably relatively independent of circulating levels of FSH due to the high concentration of oestradiol and FSH within the microenvironment of the follicular cavity.

Highly Catalytic Amorphous Ni–P Synthesized via Pulsed Electrodeposition

Ni–P coatings have attracted wide attention due to their good tribological properties, corrosion resistance, and high catalytic activity. The surface properties impact the overall catalytic performance of Ni–P as electrocatalysts. In this study, highly catalytic amorphous Ni–P electrodeposits are synthesized using pulsed electrodeposition technique. Pulse parameters show a significant effect on the morphology, crystallinity, and electro‐catalytic activity of the deposits. The Ni–P deposits are found to be amorphous up to the duty cycle of 50%, whereas higher duty cycles (toward direct current deposition) result in a transition to nanocrystalline structure. This is attributed to an indirect reduction process involving intermediate phosphine leading to co‐deposition of phosphorus and nickel. Change in pulse frequency results in significant variations in surface morphology. Methanol electro‐oxidation in alkaline environment is studied as a function of surface morphology for the amorphous Ni–P catalysts. Up to four‐fold increase in oxidation peak current is observed for nano‐morphologies with large electrochemical surface area synthesized at pulse frequency of 50 Hz. This demonstrates the potential of pulsed electrodeposition as a versatile toolbox for obtaining highly catalytic amorphous Ni–P as a potential substitute for expensive noble‐metals used in direct alcohol fuel cells.

Model-Based Control Design of Series Resonant Converter Based on the Discrete Time Domain Modelling Approach for DC Wind Turbine

This paper focuses on the modelling of the series resonant converter proposed as a DC/DC converter for DC wind turbines. The closed-loop control design based on the discrete time domain modelling technique for the converter (named SRC#) operated in continuous-conduction mode (CCM) is investigated. To facilitate dynamic analysis and design of control structure, the design process includes derivation of linearized state-space equations, design of closed-loop control structure, and design of gain scheduling controller. The analytical results of system are verified in z-domain by comparison of circuit simulator response (in PLECS™) to changes in pulse frequency and disturbances in input and output voltages and show a good agreement. Furthermore, the test results also give enough supporting arguments to proposed control design.

Progesterone-Mediated Inhibition of the GnRH Pulse Generator: Differential Sensitivity as a Function of Sleep Status.

During normal, early puberty, luteinizing hormone (LH) pulse frequency is low while awake but increases during sleep. Mechanisms underlying such changes are unclear, but a small study in early pubertal girls suggested that differential wake-sleep sensitivity to progesterone negative feedback plays a role. To test the hypothesis that progesterone acutely reduces waking LH pulse frequency more than sleep-associated pulse frequency in late pubertal girls. Randomized, placebo-controlled, double-blinded crossover study. Academic clinical research unit. Eleven normal, postmenarcheal girls, ages 12 to 15 years. Subjects completed two 18-hour admissions in separate menstrual cycles (cycle days 6 to 11). Frequent blood sampling for LH assessment was performed at 1800 to 1200 hours; sleep was encouraged at 2300 to 0700 hours. Either oral micronized progesterone (0.8 mg/kg/dose) or placebo was given at 0700, 1500, 2300, and 0700 hours, before and during the first admission. A second admission, performed at least 2 months later, was identical to the first except that placebo was exchanged for progesterone or vice versa (treatment crossover). LH pulse frequency during waking and sleeping hours. Progesterone reduced waking LH pulse frequency by 26% (P = 0.019), with no change observed during sleep (P = 0.314). The interaction between treatment condition (progesterone vs placebo) and sleep status (wake vs sleep) was highly significant (P = 0.007). In late pubertal girls, progesterone acutely reduced waking LH pulse frequency more than sleep-associated pulse frequency. Differential wake-sleep sensitivity to progesterone negative feedback may direct sleep-wake LH pulse frequency changes across puberty.

Neurokinin B Regulates Gonadotropin Secretion, Ovarian Follicle Growth, and the Timing of Ovulation in Healthy Women.

Context:Neurokinin B (NKB) is obligate for human puberty, but its role in adult female gonadotropin secretion and ovarian follicle growth is unknown.Objective:To investigate antagonism of NKB on pulsatile gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion and ovarian follicle development in healthy women.Design:Open investigation of the effects of a neurokinin-3 receptor (NK3R) antagonist (NK3Ra) vs a no-treatment control cycle.Setting:Clinical research facility.Patients or other participants:Healthy women with regular menses (n = 13).Intervention(s):NK3Ra MLE4901 40 mg taken orally twice daily from cycle day 5 to 6 for 7 days.Main outcome measure(s):LH secretion, ovarian follicle growth, and timing of ovulation.Results:NK3Ra administration reduced basal LH secretion without a change in pulse frequency and delayed the LH surge by 7 days, the duration of treatment [mean cycle day ± standard error of the mean (SEM), 22 ± 1 days vs 15 ± 1 days in control cycles; P = 0.0006]. Follicle growth (mean diameter at the end of administration of NK3Ra administration ± SEM, 9.3 ± 0.4 mm vs 15.1 ± 0.9 mm in control cycles; P < 0.0001) and rising estradiol concentrations (mean ± SEM, 166 ± 29 pmol/L vs 446 ± 86 pmol/L in control cycles; P < 0.0001) were prevented. After treatment, follicle development resumed and normal preovulatory follicle diameter and estradiol concentrations were demonstrated. Postovulatory progesterone rise was similarly delayed (peak cycle day, 30 ± 2 vs 22 ± 1; P = 0.002) and cycle length was prolonged (35 ± 1 days vs 29 ± 1 days in control cycles; P = 0.0003) but luteal progesterone excretion was unaffected by the NK3Ra (LH surge day +7 mean urinary progesterone levels ± SEM, 58 ± 10 pmol/mol vs 48±7 pmol/mol creatinine in control cycles; nonsignificant).Conclusion:These data demonstrate the involvement of NKB-NK3R signaling in the physiological regulation of GnRH/LH secretion, determining normal follicle development in women.

Discovery of a glitch in the accretion-powered pulsar SXP 1062

We present timing analysis of the accretion powered pulsar SXP 1062, based on the observations of \textit{Swift}, \textit{XMM-Newton} and \textit{Chandra} satellites covering a time span of about 2 years. We obtain a phase coherent timing solution which shows that SXP 1062 has been steadily spinning down with a rate $-\,4.29(7) \times 10^{-14}$ Hz s$^{-1}$ leading to a surface magnetic field estimate of about $1.5 \times 10^{14}$ G. We also resolve the binary orbital motion of the system from X-ray data which confirms an orbital period of 656(2) days. On MJD 56834.5, a sudden change in pulse frequency occurs with $\Delta\nu = 1.28(5) \times 10^{-6} $ Hz, which indicates a glitch event. The fractional size of the glitch is $\Delta \nu / \nu \! \sim \! 1.37(6) \times 10^{-3}$ and SXP 1062 continues to spin-down with a steady rate after the glitch. A short X-ray outburst 25 days prior to the glitch does not alter the spin-down of the source; therefore the glitch should be associated with the internal structure of the neutron star. While glitch events are common for isolated pulsars, the glitch of SXP 1062 is the first confirmation of the observability of this type of events among accretion powered pulsars. Furthermore, the value of the fractional change of pulse frequency ensures that we discover the largest glitch reported up to now.

The toadfish serotonin 2A (5-HT2A) receptor: molecular characterization and its potential role in urea excretion

Based on early pharmacological work, the serotonin 2A (5-HT2A) receptor subtype is believed to be involved in the regulation of toadfish pulsatile urea excretion. The goal of the following study was to characterize the toadfish 5-HT2A receptor at a molecular level, to determine the tissues in which this receptor is predominantly expressed and to further investigate the pharmacological specificity of toadfish pulsatile urea excretion by examining the effect of ketanserin, a 5-HT2A receptor antagonist, on resting rates of pulsatile urea excretion. The full-length toadfish 5-HT2A receptor encodes a 496 amino acid sequence and shares 57–80% sequence identity to 5-HT2A receptors of other organisms, with 100% conservation among important ligand-binding residues. Toadfish 5-HT2A receptor mRNA expression was highest in the swim bladder and gonad, followed by the whole brain. All other tissues tested (esophagus, stomach, anterior intestine, posterior intestine, rectum, liver, kidney, heart, muscle and gill) had mRNA expression levels that were significantly less than whole brain. Toadfish 5-HT2A receptor mRNA expression within the brain was highest in the hindbrain, telencephalon and midbrain/diencephalon regions. Treatment with the 5-HT2A receptor antagonist, ketanserin, resulted in a significant decrease in the pulsatile component of spontaneous urea excretion due to a reduction in urea pulse size with no significant change in pulse frequency. These results lend further support for the 5-HT2A receptor in the regulation of pulsatile urea excretion in toadfish.

Recent glitches detected in the Crab pulsar

From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches $\Delta\nu_{p}$ and $\Delta\dot{\nu}_{p}$ span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is $\sim$ 6.8 $\times 10^{-6}$ Hz, $\sim$ 3.5 times that of the glitch occured in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant $\sim$ 21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar.

A Dual Full-Bridge Resonant Class-E Bidirectional DC–DC Converter

A new bidirectional dc-dc converter composed of two class-E resonant converters is presented in this paper. Bidirectional power flow is controlled by transistor control pulse frequency changes, with a constant break between the succeeding pulses as in quasi-resonant converters. The boost or buck mode converter operation depends on the mutual relation between the control pulses of the transistor pairs which are located diagonally in the converter bridge. The advantages of the system involve are high operation frequency (200 and 450 kHz) and zero value of the transistor switching losses. This paper includes an analytical description that is useful for the converter design. The investigations are confirmed by PSpice simulations and an experiment of a laboratory model (1.6 kW).