Pulsation Cycle Research Articles

AI canis minoris, a pulsating low-mass supergiant at an early transition phase from the AGB to the post-AGB stage of evolution

The U BV photometry and low-resolution spectroscopy for the semiregular variable AI CMi, a candidate for post-AGB objects, performed in 1996–2016 and 2000–2013, respectively, are presented. The star showed multiperiodic brightness variations with an amplitude up to $$1\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 5$$ in the V band, a significant (up to $$0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 4$$ ) bluing of the B − V and U − B colors as the star faded, and a change of its spectrum from G5 I to K3–5 I, depending on its brightness. A possible long-term fading of AI CMi below $$8\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 5$$ in the period from May 2013 to early 2015 is observed in the light curve. The colors in this episode did not change the pattern of their unusual behavior with brightness. The main feature of the spectrum for AI CMi is the appearance and strengthening of TiO absorption bands as its brightness declines, which are atypical in the spectra of ordinary G5–K3 supergiants. The bluing of the B − V and U − B colors is interpreted as the blanketing of stellar radiation predominantly in V (and to a lesser extent in B) by the TiO absorption bands whose intensity increases dramatically with decreasing brightness. Another cause of the bluing can be the scattering of stellar radiation by small dust particles in the gas–dust shell of AI CMi. The star’s continuum-normalized spectra over the period from 2000 to 2013 in the wavelength range 4200 to 7700 or 9200 A are presented. These were taken at different phases of the pulsation cycle and clearly demonstrate the behavior of the TiO absorption bands depending on the V magnitude and B − V color. The equivalent widths of individual TiO bands weremeasured, and their correlation with the photometric parameters of the star is shown. AI CMi belongs to the O-rich branch of AGB/post-AGB supergiants and has a luminosity of ~4000 L ⊙ at a distance of 1500 ± 700 pc. The mass of AI CMi is most likely small and close to the lower mass limit for post-AGB stars. The connection of the star’s pulsational activity and nonstationary wind with the formation of its molecular and dust shells is discussed briefly.

Heat Transfer in a Pulsed Fluidized Bed of Biomass Particles

Bed-to-surface heat transfer coefficients of various biomass particles were measured in a pulsed fluidized bed. Effects of flow rate, pulsation frequency, particle size distribution, fines, and vibration on heat transfer were investigated. Higher gas flow rates generally yielded higher heat transfer coefficients. Natural frequency was found to be optimum as it offered ample bed movement and internal solid circulation without too much inactivity between pulsation cycles. Heat transfer was also heavily influenced by the interaction between gas convective and particle convective heat transfer, which was verified by the proposed heat transfer model. Two mechanisms, one of which treated the flow-on and flow-off period within a pulsation cycle individually, the other utilized the actual bubble rise velocity obtained via high-speed imaging were identified to account for the significantly different flow behavior below and above natural frequency. Good agreement was observed between experimental data and modeled results.

An observational study of dust nucleation in Mira (o Ceti)

The formation of silicate dust in oxygen-rich envelopes of evolved stars is thought to be initiated by formation of seed particles that can withstand the high temperatures close to the stellar photosphere and act as condensation cores farther away from the star. Candidate species considered as first condensates are TiO and TiO$_2$. We aim to identify and characterize the circumstellar gas-phase chemistry of titanium that leads to the formation of solid titanium compounds in the envelope of $o$ Cet, the prototypical Mira, and seek an observational verification of whether titanium oxides play a major role in the onset of dust formation in M-type AGB stars. We present high angular-resolution ALMA observations at submillimeter (submm) wavelengths supplemented by APEX and Herschel spectra of the rotational features of TiO and TiO$_2$. In addition, circumstellar features of TiO and TiI are identified in optical spectra which cover multiple pulsation cycles of $o$ Cet. The submm ALMA data reveal TiO and TiO$_2$ bearing gas within the extended atmosphere of Mira. While TiO is traceable up to a radius (FWHM/2) of 4.0 R$_{\star}$, TiO$_2$ extends as far as 5.5 R$_{\star}$ and unlike TiO appears to be anisotropically distributed. Optical spectra display variable emission of TiI and TiO from inner parts of the extended atmosphere (<3 R$_{\star}$). Chemical models which include shocks are in general agreement with the observations of gas-phase titanium-bearing molecules. It is unlikely that substantial amounts of titanium is locked up in solids because the abundance of the gaseous titanium species is very high. In particular, formation of hot titanium-rich condensates is very improbable because we find no traces of their hot precursor species in the gas phase. It therefore appears unlikely that the formation of dust in Mira, and possibly other M-type AGB stars, is initiated by titanium oxides.

Linear and nonlinear dynamics of pulsatile channel flow

The dynamics of small-amplitude perturbations, as well as the regime of fully developed nonlinear propagating waves, is investigated for pulsatile channel flows. The time-periodic base flows are known analytically and completely determined by the Reynolds number $Re$ (based on the mean flow rate), the Womersley number $Wo$ (a dimensionless expression of the frequency) and the flow-rate waveform. This paper considers pulsatile flows with a single oscillating component and hence only three non-dimensional control parameters are present. Linear stability characteristics are obtained both by Floquet analyses and by linearized direct numerical simulations. In particular, the long-term growth or decay rates and the intracyclic modulation amplitudes are systematically computed. At large frequencies (mainly $Wo\geqslant 14$), increasing the amplitude of the oscillating component is found to have a stabilizing effect, while it is destabilizing at lower frequencies; strongest destabilization is found for $Wo\simeq 7$. Whether stable or unstable, perturbations may undergo large-amplitude intracyclic modulations; these intracyclic modulation amplitudes reach huge values at low pulsation frequencies. For linearly unstable configurations, the resulting saturated fully developed finite-amplitude solutions are computed by direct numerical simulations of the complete Navier–Stokes equations. Essentially two types of nonlinear dynamics have been identified: ‘cruising’ regimes for which nonlinearities are sustained throughout the entire pulsation cycle and which may be interpreted as modulated Tollmien–Schlichting waves, and ‘ballistic’ regimes that are propelled into a nonlinear phase before subsiding again to small amplitudes within every pulsation cycle. Cruising regimes are found to prevail for weak base-flow pulsation amplitudes, while ballistic regimes are selected at larger pulsation amplitudes; at larger pulsation frequencies, however, the ballistic regime may be bypassed due to the stabilizing effect of the base-flow pulsating component. By investigating extended regions of a multi-dimensional parameter space and considering both two-dimensional and three-dimensional perturbations, the linear and nonlinear dynamics are systematically explored and characterized.

An investigation into inflection-point instability in the entrance region of a pulsating pipe flow.

This paper investigates the inflection-point instability that governs the flow disturbance initiated in the entrance region of a pulsating pipe flow. Under such a flow condition, the flow instability grows within a certain phase region in a pulsating cycle, during which the inflection point in the unsteady mean flow lifts away from the viscous effect-dominated region known as the Stokes layer. The characteristic frequency of the instability is found to be in agreement with that predicted by the mixing-layer model. In comparison with those cases not falling in this category, it is further verified that the flow phenomenon will take place only if the inflection point lifts away sufficiently from the Stokes layer.

Measurements of Turbulent Jet Mixing in a Turbulent Co-Flow Including the Influence of Periodic Forcing and Heating

In this work, the turbulent mixing of a confined coaxial jet in air is investigated by means of simultaneous particle image velocimetry and planar laser induced fluorescence of the acetone seeded flow injection. The jet is injected into a turbulent duct flow at atmospheric pressure through a 90 ∘ pipe bend. Measurements are conducted in a small scale windtunnel at constant mass flow rates and three modes of operation: isothermal steady jet injection at a Dean number of 20000 (Red=32000), pulsed isothermal injection at a Womersley number of 65 and steady injection at elevated jet temperatures of ΔT=50 K and ΔT=100 K. The experiment is aimed at providing statistically converged quantities of velocity, mass fraction, turbulent fluctuations and turbulent mass flux at several downstream locations. Stochastic error convergence over the number of samples is assessed within the outer turbulent shear layer. From 3000 samples the statistical error of time-averaged velocity and mass fraction is below 1 % while the error of Reynolds shear stress and turbulent mass flux components is in the of range 5-6 %. Profiles of axial velocity and turbulence intensity immediately downstream of the bend exit are in good agreement with hot-wire measurements from literature. During pulsed jet injection strong asymmetric growing of shear layer vortices lead to a skewed mass fraction profile in comparison with steady injection. Phase averaging of single shot PLIF-PIV measurements allows to track the asymmetric shear layer vortex evolvement and flow breakdown during a pulsation cycle with a resolution of 10∘. Steady injection with increased jet temperature supports mixing downstream from 6 nozzle diameters onward.

Pulsatile flow in a compliant stenosed asymmetric model

Time-varying velocity field in an asymmetric constricted tube is experimentally studied using a two-dimensional particle image velocimetry system. The geometry resembles a vascular disease which is characterized by arterial narrowing due to plaque deposition. The present study compares the nature of flow patterns in rigid and compliant asymmetric constricted tubes for a range of dimensionless parameters appearing in a human artery. A blood analogue fluid is employed along with a pump that mimics cardioflow conditions. The peak Reynolds number range is Re ~ 300–800, while the Womersley number range considered in experiments is Wo ~ 6–8. These values are based on the peak velocity in a straight rigid tube connected to the model, over a pulsation frequency range of 1.2–2.4 Hz. The medial-plane velocity distribution is used to investigate the nature of flow patterns. Temporal distribution of stream traces and hemodynamic factors including WSS, TAWSS and OSI at important phases of the pulsation cycle are discussed. The flow patterns obtained from PIV are compared to a limited extent against numerical simulation. Results show that the region downstream of the constriction is characterized by a high-velocity jet at the throat, while a recirculation zone, attached to the wall, evolves in time. Compliant models reveal large flow disturbances upstream during the retrograde flow. Wall shear stress values are lower in a compliant model as compared to the rigid. Cross-plane flow structures normal to the main flow direction are visible at select phases of the cycle. Positive values of largest Lyapunov exponent are realized for wall movement and are indicative of chaotic motion transferred from the flow to the wall. These exponents increase with Reynolds number as well as compliance. Period doubling is observed in wall displacement of highly compliant models, indicating possible triggering of hemodynamic events in a real artery that may cause fissure in the plaque deposits.

Photometric and spectroscopic study of the supergiant with an infrared excess V1027 Cygni

We present the results of our $UBV$ and $JHKLM$-photometry for the semiregular pulsating variable V1027~Cyg, a supergiant with an infrared excess, over the period from 1991 to 2015. Our search for a periodicity in the $UBV$ brightness variations has led to several periods from $P=212^{d}$ to $P=320^{d}$ in different time intervals. We have found the period $P=237^{d}$ based on our infrared photometry. The variability amplitude, the light-curve shape, and the magnitude of V1027~Cyg at maximum light change noticeably from cycle to cycle. An ambiguous correlation of the $B-V$ and $U-B$ colors with the brightness has been revealed. The spectral energy distribution for V1027~Cyg from our photometry in the range 0.36 ($U$)-5.0 ($M$) $\mu$m corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range $\lambda$4400--9200 \AA\ were taken during 16 nights over the period 1995--2015. At the 1995 and 2011 photometric minima the star's spectrum exhibited molecular TiO bands whose intensity corresponded to spectral types M0--M1, while the photometric data point to a considerably earlier spectral type. We hypothesize that the TiO bands are formed in the upper layers of the extended stellar atmosphere. We have measured the equivalent widths of the strongest absorption lines, in particular, the infrared Ca~II triplet in the spectrum of V1027~Cyg. The calcium triplet (Ca T) with $W_{\lambda}(\mathrm{Ca~T})=20.3\pm1.8$ \AA\ as a luminosity indicator for supergiants places V1027 Cyg in the region of the brightest G--K supergiants. V1027 Cyg has been identified with the infrared source IRAS~20004+2955 and is currently believed to be a candidate for post-AGB stars. The evolutionary status of the star and its difference from other post-AGB objects are discussed.

The OmegaWhite survey for short-period variable stars – III: follow-up photometric and spectroscopic observations

We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-m and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 also with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find many of these variables have spectra which are consistent with being delta Scuti type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid' phenomena in a delta Scuti star, with OW J175848.21-271653.7 showing a pronounced 22% amplitude dip lasting 3 minutes during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.

Dynamic atmospheres and winds of cool luminous giants

High spatial resolution techniques have given valuable insights into the mass loss mechanism of AGB stars, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust. Observations indicate that Al$_2$O$_3$ condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al$_2$O$_3$ grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. We have constructed a new generation of Dynamic Atmosphere & Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth & evaporation for both Al$_2$O$_3$ and Fe-free silicates (Mg$_2$SiO$_4$). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere & wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Condensation of Al$_2$O$_3$ at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. For solar abundances, radiation pressure due to Al$_2$O$_3$ is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al$_2$O$_3$ core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations.

Elastic-Plastic Thermomechanical Fatigue Analysis of Forging Dies

Abrasive wear and low cycle fatigue (LCF) have the greatest influence on the durability of dies. This paper presents a new criterion for estimation of the LCF of forging dies. The deformation model of Manson-Coffin is the classic model for the calculation of LCF. The pulsating cycle of loading dies and the phenomenon of cyclic thermal softening doesn’t provide implementation of the full Manson-Coffin’s model for the analysis of the tool life. At the same time the majority of researchers do not take into account the plastic strain component for estimation the fatigue durability of the dies and use only elastic component of the Manson-Coffin’s law or model of Basquin that is based on the analysis of the stress cycle. The present work uses the strain-kinetic criterion to analyze the durability of the dies that allows taking into account the elastic-plastic strain components and thermos-cyclic softening. During loading in bulk forging the first cycle is to be with plastic deformation while all remaining cycles would have to remain within the elastic limit due to metal hardening. Moreover it has been shown that cyclic softening effect may also be observed in the thermomechanical fatigue. This approach has been implemented for LCF simulation of the die in hot forging in FE program QForm by introducing a special subroutine. The comparison of results of the die fatigue failure simulation has shown good correspondence with practice.

Impact of the Automatic Control of a Coal Separation Process in a Jig on its Economic Efficiency

Abstract The beneficiation process of fine coal in jigs consists of two phases: stratification of coal grains in the bed according to their density and then splitting the stratified material into the product and the discharged refuse. At first, during subsequent water pulsations induced by opening and closing of air valves, the stratification of coal grains takes place due to varied velocity of their upward and downward movement. Grains of low density migrate to upper layers and grains of high density migrate to lower layers of the bed. The material travels horizontally on a screen along the jig compartment with the flow of water. The stratification of grains due to their density is not perfect, because the velocity of their upward and downward movement depends in part on their diameter, shape and the way in which the material loosens within a given pulsation cycle. The distribution of coal density fractions in the bed, characterized by the imperfection factor I, has been investigated by many researchers. The imperfection factor I is defined as the ratio of the probable error Ep and the separation density ρ50 (I = Ep/ρ50). The distribution of coal density fractions for an ideal and a real stratification process was compared. The maximum mass of the product of the desired quality (ash content) can be achieved for the ideal process when the imperfection I = 0. The stratified bed is then, in the end part of the jig, split into the product which overflows the end wall of the compartment and the refuse (or middlings) discharged through the bottom gate. The separation density (cut point) is established by the tonnage of the discharged bottom product (opening of the discharge gate). The separation density depends also on the tonnage of raw coal feeding the jig, and its washability characteristics. The impact of variations in the separation density on product parameters has been analysed. The mass of the product is always greater when the separation density is constant over a given period of time – even if in spite of its variations the process renders the same average ash content. Hence, the conclusion is to stabilise the separation density at the desired value as accurately as possible. The analysis was performed for raw coal washed in a three-product jig at the separation densities of 1.5 and 1.8 g/cm3. Percent contents (in brackets) of density fractions in raw coal were: &lt;1.35 g/cm3 (40%), 1.35–1.50 g/cm3 (12%), 1.50–1.65 g/cm3 (4%), 1.65–1.80 g/cm3 (4%), 1.80–1.95 g/cm3 (12%, &gt;1.95 g/cm3 (30%) (average ash in raw coal was 35.5%). In the analysis, an increase in the imperfection by 0.02 resulted in the decrease of the product tonnage by ΔQc = 1.0%. In this case, separation densities were set to ensure the same ash content in products (for I = 0 the change in tonnage was accepted at ΔQc = 0). The simulation analysis presented in the paper focused on the impact that fluctuations in separation density have on the economic effects of a jig operation. The influence of the separation density fluctuations on the product tonnage turned out to be nonlinear; for ±0.04 g/cm3 (control system with the radiometric density meter) the decrease in the product tonnage was ca. 0.5 % and for ±0.12 g/cm3 it was ca. 5.0% (control system with a float). The above results indicate that the operation of a refuse discharge system in a jig plays an important role in the final results of coal separation process defined in terms of tonnage and quality of the product.

VEGA/CHARA interferometric observations of Cepheids

The B-W method is used to determine the distance of Cepheids and consists in combining the angular size variations of the star, as derived from infrared surface-brightness relations or interferometry, with its linear size variation, as deduced from visible spectroscopy using the projection factor. While many Cepheids have been intensively observed by infrared beam combiners, only a few have been observed in the visible. This paper is part of a project to observe Cepheids in the visible with interferometry as a counterpart to infrared observations already in hand. Observations of delta Cep itself were secured with the VEGA/CHARA instrument over the full pulsation cycle of the star. These visible interferometric data are consistent in first approximation with a quasi-hydrostatic model of pulsation surrounded by a static circumstellar environment (CSE) with a size of theta_cse=8.9 +/- 3.0 mas and a relative flux contribution of f_cse=0.07+/-0.01. A model of visible nebula (a background source filling the field of view of the interferometer) with the same relative flux contribution is also consistent with our data at small spatial frequencies. However, in both cases, we find discrepancies in the squared visibilities at high spatial frequencies (maximum 2sigma) with two different regimes over the pulsation cycle of the star, phi=0.0-0.8 and phi=0.8-1.0. We provide several hypotheses to explain these discrepancies, but more observations and theoretical investigations are necessary before a firm conclusion can be drawn. For the first time we have been able to detect in the visible domain a resolved structure around delta~Cep. We have also shown that a simple model cannot explain the observations, and more work will be necessary in the future, both on observations and modelling.

Discovery of cycle-to-cycle modulated spectral line variability and velocity gradients in long-period Cepheids

This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of $\ell$ Carinae (P $\sim$ 35.5 d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via cross-correlation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, {\delta}v$_r$ (t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and depth all exhibit clear phase-dependent variability patterns that differ from one pulsation cycle to the next. Weak-line CCFs exhibit these effects more clearly than strong-line CCFs. BIS exhibits the most peculiar modulated variability and can be used to identify the presence of cycle-to-cycle modulated line profile variations. {\delta}v$_r$ (t) clearly exhibits cycle-to-cycle differences that correlate very closely with modulated BIS variability, suggesting perturbations of the atmospheric velocity field as the cause for modulated spectral line variability. These perturbations are most significant during contraction and are not in phase with the pulsation, transmitting information between consecutive pulsation cycles. This work shows RV curve modulation to be a consequence of atmospheric velocity gradient perturbations. Possible origins of these perturbations and their impact on Cepheid RV measurements as well as the projection factor used in Baade-Wesselink-type distance determinations are discussed.

Numerical investigation of air enclosed wave impacts in a depressurised tank

This paper presents a numerical investigation of a plunging wave impact event in a low-filling depressurised sloshing tank using a compressible multiphase flow model implemented in open-source CFD software. The main focus of this study is on the hydrodynamic loadings that impinge on the vertical wall of the tank. The detailed numerical solutions compare well with experimental results and confirm that an air trapped plunging wave impact causes the vertical wall to experience pulsating pressure loadings in which alternate positive and negative gauge pressures occur in sequence following the first applied pressure peak. The strongest pulsations of the pressure are found to be near the air pocket trapped by the water mass. The instantaneous pressure distribution along the vertical wall is nearly uniform in the area contained by the air pocket. The phases of pulsating pressures on the wall are in synchronisation with the expansion and contraction of the trapped air pocket. The pocket undergoes changes in shape, moves upwards with the water mass and eventually breaks up into small parts. A careful integration of the wall pressure reveals that the vertical structure as a whole experiences pulsating horizontal impact forces. It is found that the average period of pulsation cycles predicted in the present study is around 5–6ms, and the loading pulsations are quickly damped out in 0.1–0.2s. Further exploratory investigation of the fluid thermodynamics reveals that the temperature inside the trapped air pocket rises quickly for about 2ms synchronised with the pocket's first contraction, then the generated heat is rapidly transferred away in around 3ms.

Assessing liner performance using on-farm milk meters

The primary objective of this study was to quantify and compare the interactive effects of liner compression, milking vacuum level, and pulsation settings on average milk flow rates for liners representing the range of liner compression of commercial liners. A secondary objective was to evaluate a methodology for assessing liner performance that can be applied on commercial dairy farms. Eight different liner types were assessed using 9 different combinations of milking system vacuum and pulsation settings applied to a herd of 80 cows with vacuum and pulsation conditions changed daily for 36d using a central composite experimental design. Liner response surfaces were created for explanatory variables milking system vacuum (Vsystem) and pulsator ratio (PR) and response variable average milk flow rate (AMF=total yield/total cups-on time) expressed as a fraction of the within-cow average flow rate for all treatments (average milk flow rate fraction, AMFf). Response surfaces were also created for between-liner comparisons for standardized conditions of claw vacuum and milk ratio (fraction of pulsation cycle during which milk is flowing). The highest AMFf was observed at the highest levels of Vsystem, PR, and overpressure. All liners showed an increase in AMF as milking conditions were changed from low to high standardized conditions of claw vacuum and milk ratio. Differences in AMF between liners were smallest at the most gentle milking conditions (low Vsystem and low milk ratio), and these between-liner differences in AMF increased as liner overpressure increased. Differences were noted with vacuum drop between Vsystem and claw vacuum depending on the liner venting system, with short milk tube vented liners having the greater vacuum drop than mouthpiece chamber vented liners. The accuracy of liner performance assessment in commercial parlors fitted with milk meters can be improved by using a central composite experimental design with a repeated center point treatment, rotating different clusters to different stalls (milk meters), and adjusting performance estimates for similar claw vacuum and pulsation conditions.

Effect of pulsation rest phase duration on teat end congestion

The objective of this study was to quantify the effect of d-phase (rest phase) duration of pulsation on the teat canal cross-sectional area during the period of peak milk flow from bovine teats. A secondary objective was to test if the effect of d-phase duration on teat canal cross-sectional area was influenced by milking system vacuum level, milking phase (b-phase) duration, and liner overpressure. During the d-phase of the pulsation cycle, liner compression facilitates venous flow and removal of fluids accumulated in teat-end tissues. It was hypothesized that a short-duration d-phase would result in congestion of teat-end tissue and a corresponding reduction in the cross-sectional area of the teat canal. A quarter milking device, designed and built at the Milking Research and Instruction Laboratory at the University of Wisconsin–Madison, was used to implement an experiment to test this hypothesis. Pulsator rate and ratios were adjusted to achieve 7 levels of d-phase duration: 50, 100, 150, 175, 200, 250, and 300ms. These 7 d-phase durations were applied during one milking session and were repeated for 2 vacuum levels (40 and 50kPa), 2 milking phase durations (575 and 775ms), and 2 levels of liner overpressure (9.8 and 18kPa). We observed a significant reduction in the estimated cross-sectional area of the teat canal with d-phase durations of 50 and 100ms when compared with d-phase durations of 150, 175, 225, 250, and 300ms. No significant difference was found in the estimated cross-sectional area of the teat canal for d-phase durations from 150 to 300ms. No significant interaction was observed between the effect of d-phase and b-phase durations, vacuum level, or liner overpressure.

Microfluidic mixing using pulsating flows

Mixing of biological species in microfluidic channels is challenging since the mixing process is limited by the small mass diffusion coefficient of the species and by the dominance of viscous effects, captured by the low value of Reynolds number characteristic of laminar liquid flow in microchannels. This paper investigates the use of pulsating flows to enhance mixing in microflows. The dependence of the degree of mixing on various dimensionless groups is investigated. These dimensionless numbers are Strouhal number, pulse amplitude divided by base velocity, Reynolds number, location along the mixing channel normalized by the channel width, channel cross section aspect ratio, and phase difference between the inlet streams. The degree of mixing, observed to experience both spatial fluctuations down the mixing channel and temporal fluctuations over a pulsation cycle at the quasi-stationary state, is shown to be most sensitive to changes in pulsation amplitude and frequency. For a fixed pulsation amplitude and Reynolds number, the degree of mixing has a peak value for a certain Strouhal number above and below which the degree of mixing decreases. Increasing the pulsation amplitude improves mixing with the behavior becoming asymptotic at large pulsation amplitudes. The temporal fluctuations in the degree of mixing over a cycle at the quasi-stationary state decrease and the average degree of mixing increases downstream the mixing channel. The fluctuations are also smaller at higher values of the Strouhal number and are generally larger for larger pulsation amplitudes. This study also takes into account the rate of work input required to overcome viscous effects. While this power input is independent of the pulsation frequency, it exhibits a parabolic dependence on the pulsation amplitude. Finally, considering the dependence of the degree of mixing (mean and standard deviation), mixing length, and energy consumption on these dimensionless groups, examples of the trade-off that has to be made in choosing the operating conditions based on different constraints are presented.

Half a Century after the Outburst of the Symbiotic Nova V1016 Cyg

Abstract We present the results of our long-term UBV JHKLM photometry and spectroscopic monitoring of the symbiotic nova V1016 Cyg. After its outburst in 1964, the star showed fading in the U, B, V bands at a rate of about 0.03 mag per year. The behavior of the B − V and U − B color indices reflects variations of the emission lines, fading of the erupted component, weakening and reddening of the cool giant. Also, monotonic color and brightness variations in the infrared (IR) were observed at a scale of several thousand days. After 2004, the yearly mean IR brightness showed a decline and IR colors, reddening, due to the increase of the optical depth of the dust. The parameters of the cool star and of the dust envelope were estimated. The pulsation period of the Mira-type variable was refined, P = 465±5 days. The Mira’s photospheric temperature varied from 2100 to 2700 K in the pulsation cycle. The mass of the dust shell has grown twice during the recent decade, at a dust penetration rate of ∆M dust ~ 10−7 M ⊙/yr. Our spectroscopic monitoring of V1016 Cyg over 1995−2013 showed variations in the emission line strengths. The absolute fluxes of most lines decreased after 2000, whereas the relative intensities of [O III], [Ar III], [Fe VII], [Ca VII] lines with respect to Hβ are increasing after the possible minimum that could happen in the 1990s. An essential flux decline (approximately ten-fold between 1995 and 2013) in the Raman scattered O VI line at λ6825 shows the change of conditions in its formation zone, due to absorption of O VI 1032 Å quanta in the new dust shell of the cool component.

LX Cygni: A carbon star is born

Context: The Mira variable LX Cyg showed a dramatic increase of its pulsation period in the recent decades and appears to undergo an important transition in its evolution. Aims: We aim at investigating the spectral type evolution of this star over the recent decades as well as during one pulsation cycle in more detail and discuss it in connection with the period evolution. Methods: We present optical, near- and mid-IR low-resolution as well as optical high-resolution spectra to determine the current spectral type. The optical spectrum of LX Cyg has been followed for more than one pulsation cycle. Recent spectra are compared to archival spectra to trace the spectral type evolution and a Spitzer mid-IR spectrum is analysed for the presence of molecular and dust features. Furthermore, the current period is derived from AAVSO data. Results: It is found that the spectral type of LX Cyg changed from S to C sometime between 1975 and 2008. Currently, the spectral type C is stable during a pulsation cycle. It is shown that spectral features typical of C-type stars are present in its spectrum from ~0.5 to 14 $\mu{\rm{m}}$. An emission feature at 10.7 $\mu{\rm{m}}$ is attributed to SiC grains. The period of LX Cyg has increased from ~460 d to ~580 d within only 20 years, and is stable now. Conclusions: We conclude that the change in spectral type and the increase in pulsation period happened simultaneously and are causally connected. Both a recent thermal pulse (TP) and a simple surface temperature decrease appear unlikely to explain the observations. We therefore suggest that the underlying mechanism is related to a recent third dredge-up mixing event that brought up carbon from the interior of the star, i.e. that a genuine abundance change happened. We propose that LX Cyg is a rare transition type object that is uniquely suited to study the transformation from O- to C-rich stars in detail.