Intrinsic Pulsations Research Articles

The Mechanism of Resonant Amplification of One-Dimensional Detonation Propagating in a Non-Uniform Mixture

The propagation of detonation waves (i.e., supersonic combustion waves) in non-uniform gaseous mixtures has become a matter of interest over the past several years due to the development of rotating detonation engines. It was shown in a number of recent theoretical studies of one-dimensional pulsating detonation that perturbation of the parameters in front of the detonation wave can lead to a resonant amplification of intrinsic pulsations for a certain range of perturbation wavelengths. This work is dedicated to the clarification of the mechanism of this effect. One-dimensional reactive Euler equations with single-step Arrhenius kinetics were solved. Detonation propagation in a gas with sine waves in density was simulated in a shock-attached frame of reference. We carried out a series of simulations, varying the wavelength of the disturbances. We obtained a non-linear dependence of the amplitude of these pulsations on the wavelength of disturbances with resonant amplification for a certain range of wavelengths. The gain in velocity was about 25% of the Chapman–Jouguet velocity of the stable detonation wave. The effect is explained using the characteristic analysis in the x-t diagram. For the resonant case, we correlated the pulsation period with the time it takes for the C+ and C− characteristics to travel through the effective reaction zone. A similar pulsation mechanism is realized when a detonation wave propagates in a homogeneous medium.

Wavelet Transforms of Microlensing Data: Denoising, Extracting Intrinsic Pulsations, and Planetary Signals

Wavelets are waveform functions that describe transient and unstable variations, such as noise. In this work, we study the advantages of discrete and continuous wavelet transforms (DWTs and CWTs) of microlensing data to denoise them and extract their planetary signals and intrinsic pulsations hidden by noise. We first generate synthetic microlensing data and apply wavelet denoising to them. For these simulated microlensing data with ideally Gaussian noise based on the Optical Gravitational Lensing Experiment (OGLE) photometric accuracy, denoising with DWTs reduces standard deviations of data from real models by 0.044–0.048 mag. The efficiency to regenerate real models and planetary signals with denoised data strongly depends on the observing cadence and decreases from 37% to 0.01% with increasing cadence from 15 min to 6 hr. We then apply denoising on 100 microlensing events discovered by the OGLE group. On average, wavelet denoising for these data improves standard deviations and of data with respect to the best-fit models by 0.023 mag and 1.16, respectively. The best-performing wavelets (based on the highest signal-to-noise ratio’s peak (), the highest Pearson’s correlation, or the lowest root mean squared error for denoised data) are from the Symlet and Biorthogonal wavelet families in simulated and OGLE data, respectively. In some denoised data, intrinsic stellar pulsations or small planetary like deviations appear that were covered with noise in raw data. However, through DWT denoising rather flattened and wide planetary signals could be reconstructed rather than sharp signals. CWTs and 3D frequency–power–time maps could inform about the existence of sharp signals.

Discovery of four new EL CVn-type binaries in the Gaia eclipsing binaries

In this paper, we performed a search for EL CVn-type binaries based on the Gaia and TESS data. Through the combination of the Gaia DR3 eclipsing binary catalogue and the Gaia DR3 spectroscopic binary catalogue, we have identified 13 stars exhibiting EL CVn-like characteristics. Among these stars, nine have already been identified as EL CVn binaries, while the remaining four are newly discovered candidates. The photometric solutions and absolute parameters of the four binary systems were obtained by utilizing TESS photometry and orbital elements from Gaia DR3 spectroscopic binary catalogue. Light-curve modeling has revealed that all four binary systems with a detached configuration exhibit very low mass ratios, approximately q≃0.1. The derived physical parameters indicate that the four binary systems are highly probable candidates for being newly discovered EL CVn-type binaries. A preliminary frequency analysis was conducted on the residuals of the light curves, after the removal of binarity effects. The results suggest that the primary component star of TIC 100011519, TIC 219485855 and TIC 464641792 might be a δ Sct pulsator. However, TIC 399725538 does not exhibit any intrinsic pulsations.

Massive heartbeat stars from TESS

Context. Heartbeat stars are eccentric binaries that exhibit a characteristic shape of brightness changes close to the periastron passage, primarily caused by a variable tidal distortion of the components. Variable tidal potential can drive tidally excited oscillations (TEOs), which are usually gravity modes. Studies of heartbeat stars and TEOs open up new possibilities for probing the interiors of massive stars. There are only a few massive (masses of components ≳2 M⊙) systems of this type that are known thus far. Aims. Using TESS data from the first 16 sectors, we searched for new massive heartbeat stars and TEOs using a sample of over 300 eccentric spectroscopic binaries. Methods. We analysed 2 min and 30 min cadence TESS data. Then we fitted Kumar’s analytical model to the light curves of stars showing heartbeats and performed a times-series analysis of the residuals searching for TEOs and periodic intrinsic variability. Results. We found 20 massive heartbeat systems, of which 7 exhibit TEOs. The TEOs occur at harmonics of orbital frequencies in the range between 3 and 36, with the median value equal to 9, which is lower than those in known Kepler systems with TEOs. The most massive system in this sample is the quadruple star HD 5980, a member of the Small Magellanic Cloud. With a total mass of ∼150 M⊙ it is the most massive system showing a heartbeat. Six stars in the sample of the new heartbeat stars are eclipsing. A comparison of the parameters derived from fitting Kumar’s model and from light-curve modelling shows that Kumar’s model does not provide reliable parameters. In other words, the orbital parameters can be reliably derived from fitting heartbeat light curves only if the model includes all proximity effects. Finally, intrinsic pulsations of β Cep, SPB, δ Sct, and γ Dor-type were found in nine heartbeat systems. This opens an interesting possibility for studies of pulsation-binarity interaction and the co-existence of forced and self-excited oscillations.

Superviscous properties of the in vivo brain at large scales

There is growing awareness that brain mechanical properties are important for neural development and health. However, published values of brain stiffness differ by orders of magnitude between static measurements and in vivo magnetic resonance elastography (MRE), which covers a dynamic range over several frequency decades. We here show that there is no fundamental disparity between static mechanical tests and in vivo MRE when considering large-scale properties, which encompass the entire brain including fluid filled compartments. Using gradient echo real-time MRE, we investigated the viscoelastic dispersion of the human brain in, so far, unexplored dynamic ranges from intrinsic brain pulsations at 1 Hz to ultralow-frequency vibrations at 5, 6.25, 7.8 and 10 Hz to the normal frequency range of MRE of 40 Hz. Surprisingly, we observed variations in brain stiffness over more than two orders of magnitude, suggesting that the in vivo human brain is superviscous on large scales with very low shear modulus of 42±13 Pa and relatively high viscosity of 6.6±0.3 Pa∙s according to the two-parameter solid model. Our data shed light on the crucial role of fluid compartments including blood vessels and cerebrospinal fluid (CSF) for whole brain properties and provide, for the first time, an explanation for the variability of the mechanical brain responses to manual palpation, local indentation, and high-dynamic tissue stimulation as used in elastography.

Superviscous Properties of the In Vivo Brain at Large Scales

There is growing awareness that brain mechanical properties are important for neural development and health. Yet, published values of brain stiffness differ by orders of magnitude from ex vivo to in vivo, pointing to a general lack of understanding of the complex mechanical behavior of brain tissue. We here show that there is no fundamental disparity between ex vivo and in vivo data when considering large-scale properties of the entire brain. Using numerical simulations and novel real-time magnetic resonance elastography we investigated the viscoelastic dispersion of the human brain in, so far, unexplored dynamic ranges from intrinsic brain pulsations at 1Hz to externally induced harmonic vibrations at 40Hz. Surprisingly, we observed variations in brain stiffness over more than two orders of magnitude, suggesting that the in vivo human brain is superviscous on large scales with very low shear modulus of 42±13 Pa and relatively high viscosity of 6.6±0.3 Pa∙s according to the two-parameter solid model. Our data shed light on the crucial role of fluid compartments including blood vessels and cerebrospinal fluid (CSF) for whole brain properties and provide, for the first time, an explanation for the variability of the mechanical brain responses to manual palpation, local indentation, and high-dynamic tissue stimulation as used in elastography.

Stimulated Acoustic Light Scattering in the Externally Excited Optical Resonator

Dynamics of Stokes radiation generation in a nanodispersed medium within an optical resonator excited by external monochromatic radiation is investigated for the first time. Conversion of incident radiation results from ponderomotive buildup of intrinsic acoustic pulsations of the dispersed particles. It is assumed that the resonator mirrors reflect well the frequencies of the incident radiation and the first Stokes component.

Respiratory-related brain pulsations are increased in epilepsy-a two-centre functional MRI study.

Resting-state functional MRI has shown potential for detecting changes in cerebral blood oxygen level-dependent signal in patients with epilepsy, even in the absence of epileptiform activity. Furthermore, it has been suggested that coefficient of variation mapping of fast functional MRI signal may provide a powerful tool for the identification of intrinsic brain pulsations in neurological diseases such as dementia, stroke and epilepsy. In this study, we used fast functional MRI sequence (magnetic resonance encephalography) to acquire ten whole-brain images per second. We used the functional MRI data to compare physiological brain pulsations between healthy controls (n = 102) and patients with epilepsy (n = 33) and furthermore to drug-naive seizure patients (n = 9). Analyses were performed by calculating coefficient of variation and spectral power in full band and filtered sub-bands. Brain pulsations in the respiratory-related frequency sub-band (0.11–0.51 Hz) were significantly (P < 0.05) increased in patients with epilepsy, with an increase in both signal variance and power. At the individual level, over 80% of medicated and drug-naive seizure patients exhibited areas of abnormal brain signal power that correlated well with the known clinical diagnosis, while none of the controls showed signs of abnormality with the same threshold. The differences were most apparent in the basal brain structures, respiratory centres of brain stem, midbrain and temporal lobes. Notably, full-band, very low frequency (0.01–0.1 Hz) and cardiovascular (0.8–1.76 Hz) brain pulses showed no differences between groups. This study extends and confirms our previous results of abnormal fast functional MRI signal variance in epilepsy patients. Only respiratory-related brain pulsations were clearly increased with no changes in either physiological cardiorespiratory rates or head motion between the subjects. The regional alterations in brain pulsations suggest that mechanisms driving the cerebrospinal fluid homeostasis may be altered in epilepsy. Magnetic resonance encephalography has both increased sensitivity and high specificity for detecting the increased brain pulsations, particularly in times when other tools for locating epileptogenic areas remain inconclusive.

Interaction of pressure waves with a bubble layer near free surface of a liquid

The radiation of pressure waves by a bubble layer near the free surface of a liquid excited by a high-intensity sound pulse has been studied. It was shown that the bubble layer exhibits the properties of a resonator with one partially transparent boundary. Bubbles on the boundary of the layer due to the interaction through the self-consistent field with the bubbles inside the layer perform collective pulsations. It was found that the emission spectrum of the layer is ruled. The lines of the emission spectrum of a layer have a regular composition and lie above the frequency of the intrinsic pulsations of bubbles.

Two new R CMa-type eclipsing binaries containing a possible low-mass Helium white dwarf precursor: KIC 7368103 and KIC 8823397

We report the discovery of two new R CMa-type eclipsing binaries, each consisting of a possible low-mass Helium white dwarf precursor. Based on the Kepler long-cadence photometry and the radial-velocity measurements given by Matson et al., we determined comprehensive photometric solutions and physical parameters of two binaries KIC 7368103 and KIC 8823397. Light-curve modelling reveals that they are both short-period detached system with very low mass ratios q ≃ 0.1. The derived physical parameters show that the two binary systems consist of an extremely low-mass (≃0.2 M|$\odot$|), oversized (>1 R|$\odot$|), and overluminous secondary component, accompanied by a less-evolved early A-type primary star. We therefore introduce KIC 7368103 and KIC 8823397 as two new R CMa-type binaries, which are probably evolving into EL CVn stars. After subtracting the synthetic eclipsing curve from the de-trended Kepler data, we carried out a preliminary frequency analysis of their light-curve residuals. KIC 7368103 was found to pulsate in 35 independent frequencies in the range from 14 to 31 d−1, which could be due to the intrinsic pulsations of the δ Sct-type primary star. However, no significant frequencies above the confidence level were detected in the binary KIC 8823397.

Altered physiological brain variation in drug-resistant epilepsy.

IntroductionFunctional magnetic resonance imaging (fMRI) combined with simultaneous electroencephalography (EEG‐fMRI) has become a major tool in mapping epilepsy sources. In the absence of detectable epileptiform activity, the resting state fMRI may still detect changes in the blood oxygen level‐dependent signal, suggesting intrinsic alterations in the underlying brain physiology.MethodsIn this study, we used coefficient of variation (CV) of critically sampled 10 Hz ultra‐fast fMRI (magnetoencephalography, MREG) signal to compare physiological variance between healthy controls (n = 10) and patients (n = 10) with drug‐resistant epilepsy (DRE).ResultsWe showed highly significant voxel‐level (p < 0.01, TFCE‐corrected) increase in the physiological variance in DRE patients. At individual level, the elevations range over three standard deviations (σ) above the control mean (μ) CVMREG values solely in DRE patients, enabling patient‐specific mapping of elevated physiological variance. The most apparent differences in group‐level analysis are found on white matter, brainstem, and cerebellum. Respiratory (0.12–0.4 Hz) and very‐low‐frequency (VLF = 0.009–0.1 Hz) signal variances were most affected.ConclusionsThe CVMREG increase was not explained by head motion or physiological cardiorespiratory activity, that is, it seems to be linked to intrinsic physiological pulsations. We suggest that intrinsic brain pulsations play a role in DRE and that critically sampled fMRI may provide a powerful tool for their identification.

THE NATURE OF V392 ORI: A NEAR-CONTACT BINARY WITH AδSCUTI-TYPE COMPONENT

This study presents multi-color photometric observations of the short-period eclipsing binary V392 Ori. Taking into account the results obtained from the models and analyses of the BVRI light curves, the nature of the binary system as well as the light-curve variations were discussed. The distortions of the light curves were successfully synthesized with a cool-spot model. The photometric solutions indicated that V392 Ori is a semi-detached, near-contact system with the cooler secondary component filling and the primary nearly filling each of their Roche lobes. The mass ratio of the system is determined to be 0.247 ± 0.001, and the inclination is derived to be . Based on these results, the physical parameters of the components were estimated. The analysis indicates that the secular orbital period of the system is decreasing at a rate of −3.0 s per century, probably due to the nonconservative mass exchange and mass loss of the system, which could be the source of the long-term light-curve changes. By subtracting the theoretical light curves from the original observations, we remove the eclipse and proximity effects so as to investigate the short-term variations. Frequency analysis of the residual light reveals a periodicity of 35.5 minutes in all the BVRI bands. The nature of the intrinsic pulsations was discussed along with the evolution of the components. For the first time in the literature, we revealed that the primary component is a δ Scuti star. We thus list V392 Ori as a new candidate eclipsing binary with a δ Scuti component.

M dwarf search for pulsations within Kepler Guest Observer programme

We present the analysis of four M dwarf stars -plus one M giant that seeped past our selection criteria- observed in Cycle 3 of Kepler Guest Observer program (GO3) in a search for intrinsic pulsations. Stellar oscillations in M dwarfs were theoretically predicted by Rodr\'iguez-L\'opez et al. (2012) to be in the range ~20-40 min and ~4-8 h, depending on the age and the excitation mechanism. We requested Kepler short cadence observations to have an adequate sampling of the oscillations. The targets were chosen on the basis of detectable rotation in the initial Kepler results, biasing towards youth.The analysis reveals no oscillations attributable to pulsations at a detection limit of several parts per million, showing that either the driving mechanisms are not efficient in developing the oscillations to observable amplitudes, or that if pulsations are driven, the amplitudes are very low. The size of the sample, and the possibility that the instability strip is not pure, allowing the coexistence of pulsators and non-pulsators, prevent us from deriving definite conclusions. Inmediate plans include more M dwarfs photometric observations of similar precision with Kepler K2 mission and spectroscopic searches already underway within the Cool Tiny Beats Project (Anglada-Escud\'e et al. 2014, Berdi\~nas et al. 2014) with the high-resolution spectrographs HARPS and HARPS-N.

Three-dimensional dissipative optical solitons

Abstract A brief overview of recent theoretical results in the area of three-dimensional dissipative optical solitons is given. A systematic analysis demonstrates the existence and stability of both fundamental (spinless) and spinning three-dimensional dissipative solitons in both normal and anomalous group-velocity regimes. Direct numerical simulations of the evolution of stationary solitons of the three-dimensional cubic-quintic Ginzburg-Landau equation show full agreement with the predictions based on computation of the instability eigenvalues from the linearized equations for small perturbations. It is shown that the diffusivity in the transverse plane is necessary for the stability of vortex solitons against azimuthal perturbations, while fundamental (zero-vorticity) solitons may be stable in the absence of diffusivity. It has also been found that, at values of the nonlinear gain above the upper border of the soliton existence domain, the three-dimensional dissipative solitons either develop intrinsic pulsations or start to expand in the temporal (longitudinal) direction keeping their structure in the transverse spatial plane.

Stability of dissipative optical solitons in the three-dimensional cubic-quintic Ginzburg-Landau equation

We report results of a systematic analysis of the stability of dissipative optical solitons, with intrinsic vorticity $S=0$ and 1, in the three-dimensional complex Ginzburg-Landau equation with the cubic-quintic nonlinearity, which is a model of a dispersive optical medium with saturable self-focusing nonlinearity and bandwidth-limited nonlinear gain. The stability is investigated by means of computation of the instability growth rate for eigenmodes of small perturbations, and the results are verified against direct numerical simulations. We conclude that the presence of diffusivity in the transverse plane is necessary for the stability of vortex solitons (with $S=1$) against azimuthal perturbations, while zero-vorticity solitons may be stable in the absence of the diffusivity. On the other hand, the solitons with $S=0$ and $S=1$ have their stability regions at both anomalous and normal group-velocity dispersion, which is important to the experimental implementation. At values of the nonlinear gain above their existence region, the solitons either develop persistent intrinsic pulsations, or start expansion in the longitudinal direction, keeping their structure in the transverse plane.

Scaling laws for pulsed electrohydrodynamic drop formation

A pulsed electrohydrodynamic jet can produce on-demand drops much smaller than the delivery nozzle. This letter describes an experimentally validated model for electrically pulsed jets. Viscous drag in a thin nozzle limits the flow rate and leads to intrinsic pulsations of the cone jet. A scale analysis for intrinsic cone-jet pulsations is derived to establish the operating regime for drop deployment. The scaling laws are applicable to similar electrohydrodynamic processes in miniaturized electrospraying systems.

Ring melanoma of the ciliary body: report on twenty-three patients.

Ring melanoma of the ciliary body is a rare variant of uveal melanoma that has a poor prognosis. Only isolated cases have been reported in the literature. A retrospective review of the clinical features, management, histopathology, and prognosis of 23 consecutive patients with ring melanoma of the ciliary body was performed. Of 8,800 patients with uveal melanoma treated on the Oncology Service at Wills Eye Hospital over a 25-year period, only 23 patients (0.3%) were found to have ring melanoma of the ciliary body. The mean patient age was 59 years (median, 63 years; range, 8-81 years). The only visual symptom was blurred vision in 17 patients (74%), and the other six patients (26%) were asymptomatic. At the initial presentation elsewhere, melanoma was recognized in 13 cases (57%). In the remaining 10 cases (43%), the initial clinical diagnosis was glaucoma in three (13%), iris nevus in three (13%), cataract in two (9%), ciliary body detachment in one (4%), and iridocyclitis in one (4%). The patients were observed elsewhere for a mean of 3 months before the diagnosis of melanoma was suspected and referral to Oncology Service was made. On examination, the tumor involved a mean of eight clock hours of the ciliary body. Seven patients (30%) had complete circumferential (360 degrees) involvement of the ciliary body, and 16 (70%) had incomplete (180-360 degrees) ring involvement. The mean tumor thickness was 8 mm. Associated findings included neovascularization of the iris in one case (4%), shallow anterior chamber in 11 (48%), anterior chamber inflammation in five (22%), cataract in nine (39%), lens indentation in eight (35%), and lens subluxation in three (13%). A prominent episcleral (sentinel) vessel (17 cases, 74%), multilobulation of the mass (19 cases, 83%), blockage of light on transillumination (23 cases, 100%), and ultrasonographic hollowness with intrinsic pulsations (23 cases, 100%) were important features differentiating this tumor from simulating conditions. The tumor was managed with enucleation in all 23 patients. Histopathologic studies revealed epithelioid cell-type melanoma in two patients (9%), mixed cell-type in 17 (74%), and spindle cell-type in four (17%). Extraocular extension was present in eight patients (35%). Metastasis developed in 12 of 23 patients (52%) after a mean follow-up of 55 months. Ring melanoma of the ciliary body is a rare tumor that can remain hidden from ophthalmoscopic examination. Certain features, such as prominent episcleral sentinel vessels, multilobulation of the mass, light blockage on transillumination, and ultrasonographic hollowness with intrinsic vascular pulsations, suggest the diagnosis. The life prognosis is poor.

Porta hepatis: sonographic discrimination of bile ducts from arteries with pulsed Doppler with new anatomic criteria.

Duplex scanning of the porta hepatis was performed in 71 patients, and the identity of the common duct and hepatic artery were confirmed by characteristic pulsed Doppler signals or by tracing structures to known landmarks. In 59% of patients, the hepatic artery was as large or larger than the adjacent normal bile duct, suggesting that the two structures may occasionally be confused. Sonographic signs that help to confirm or support the differentiation of arteries from ducts include observation of intrinsic pulsations of arteries, indentation or displacement of structures by arteries, change in the caliber of bile ducts during real-time examination, and the orientation, contour, caliber, and curvature of the tubular structures of the porta hepatis. Simultaneous identification of the hepatic artery and extrahepatic bile duct using pulsed Doppler or these newly described anatomic criteria improves the diagnostic accuracy of sonography of the porta hepatis.

Asymptomatic Mediastinal Mass in a 49-Year-Old Man

History An asymptomatic 49-year-old man was referred because of an abnormal chest roentgenogram. Findings from physical examination were normal. Chest roentgenograms, tomogram, and esophagogram are presented (Fig 1 through 4). Diagnosis Bronchogenic cyst. An oval hemogeneous shadow to the left of the upper posterior mediastinum was found on the chest roentgenogram. Fluoroscopy and barium study showed this mass to be paraesophageal. 1 It moved with swallowing. No intrinsic pulsations were seen. Differential diagnosis included enteric cyst, bronchogenic cyst, esophageal tumor (eg, leiomyoma), substernal thyroid, lymph node enlargement, and vascular lesion. 2 Radioactive iodine scan showed no uptake in the mass, and the thyroid gland appeared normal. Thoracic aortography was also normal. At surgery, a 5-cm diameter cyst was found loosely attached posteriorly to the esophageal wall. It contained mucoid material. Histological sections of the wall showed ciliated pseudostratified columnar epithelium and underlying hyaline cartilage. Comment Bronchogenic cysts are developmental in

Congenital stenosis of the pulmonary artery branches: A classification, with postmortem findings in two cases

Stenosis of the pulmonary artery branches may be divided into the following: type I, single central stenosis; type II, bifurcation stenosis; type III, multiple, peripheral stenoses; and type III, combined central and peripheral stenoses. Well over half of the cases are accompanied, and thus frequently masked, by an associated cardiac defect. In these cases the first diagnosis of stenosis of the pulmonary artery branches is usually made either at surgery or in the catheter room, especially if selective angiocardiography is performed. The diagnosis of isolated stenosis of the pulmonary artery branches is to be considered in a patient with evidence of right ventricular preponderance and an atypical, frequently distant, holosystolic, or less often, quasicontinuous murmur in the second intercostal spaces well transmitted to the lungs. On the plain roentgenogram, the lung fields should be searched for vascular dilatations. Fluoroscopy with image amplification may reveal intrinsic pulsations separate from the hilar vessels. At catheterization, wide pulse pressure is noted in the main pulmonary artery; a pressure differential can be measured across the stenotic segments. Usually, confirmation of the diagnosis must await angiocardiography. Some patients apparently tolerale their disease well for years. In others, intimal fibrous proliferation and thrombosis may progressively narrow already stenotic vessels and lead to right ventricular failure. The dilated poststenotic, veinlike pulmonary arteries may become aneurysmal; troublesome, if not fatal, bleeding can follow. Endarteritis is an additional possible complication. In Case IV a reduction in diameter of the right pulmonary artery by two-thirds or more is illustrated which protects the vascular bed of the right lung from medial thickening and intimal proliferation present in the hypertensive vascular tree of the left lung. To date, surgical therapy has been directed to the removal of pulmonary artery ancurysms and to dilatation, widening or resection of the single central type of branch pulmonary artery stenosis. Knowledge of the natural history of isolated stenosis of the pulmonary artery branches and an understanding of the evolution of structural changes in these vessels is yet incomplete.