Maximum Radial Expansion Research Articles

Ultra-fast mechanics and bioeffects of acoustic droplet vaporization in tissue-mimicking hydrogels

Acoustic droplet vaporization (ADV) enables phase-shift droplets to respond to focused ultrasound in a spatiotemporal manner, offering a versatile platform for theranostic applications. To better understand the ADV-inducedmechanics and resulting bioeffects in real-time, we integrated ultra-high-speed microscopy (up to 10 million frames per second), time-lapse confocal microscopy, and focused ultrasound. Three monodispersed phase-shift droplets—containing perfluoropentane (PFP), perfluorohexane (PFH), or perfluorooctane (PFO)—with an average diameter of ∼12 μm were studied in fibrin-based, tissue-mimicking hydrogels. To assess cellular bioeffects and mechanical changes resulting from ADV, we co-encapsulated fibroblasts and tracer particles within the hydrogel. Tracking the displacement of tracer particles during and after ADV indicated a hyper-local region of influence by an ADV-generated bubble, correlating inversely with the bulk boiling point of the phase-shift droplets. Additionally, cell membrane permeabilization significantly depended on the distance between the droplet and cell (d), decreasing rapidly with increasing d. We will discuss and compare ADV dynamics, including maximum radial expansion, expansion velocity, and induced radial strain, as well as the critical distance for cell membrane permeabilization in fibrin-based hydrogels containing three different phase-shift droplets. The findings here provide useful information to optimize ADV for more tailored theranostic applications.

Real-time spatiotemporal characterization of mechanics and sonoporation of acoustic droplet vaporization in acoustically responsive scaffolds.

Phase-shift droplets provide a flexible and dynamic platform for therapeutic and diagnostic applications of ultrasound. The spatiotemporal response of phase-shift droplets to focused ultrasound, via the mechanism termed acoustic droplet vaporization (ADV), can generate a range of bioeffects. Although ADV has been used widely in theranostic applications, ADV-induced bioeffects are understudied. Here, we integrated ultra-high-speed microscopy, confocal microscopy, and focused ultrasound for real-time visualization of ADV-induced mechanics and sonoporation in fibrin-based, tissue-mimicking hydrogels. Three monodispersed phase-shift droplets-containing perfluoropentane (PFP), perfluorohexane (PFH), or perfluorooctane (PFO)-with an average radius of ∼6 μm were studied. Fibroblasts and tracer particles, co-encapsulated within the hydrogel, were used to quantify sonoporation and mechanics resulting from ADV, respectively. The maximum radial expansion, expansion velocity, induced strain, and displacement of tracer particles were significantly higher in fibrin gels containing PFP droplets compared to PFH or PFO. Additionally, cell membrane permeabilization significantly depended on the distance between the droplet and cell (d), decreasing rapidly with increasing d. Significant membrane permeabilization occurred when d was smaller than the maximum radius of expansion. Both ultra-high-speed and confocal images indicate a hyper-local region of influence by an ADV bubble, which correlated inversely with the bulk boiling point of the phase-shift droplets. The findings provide insight into developing optimal approaches for therapeutic applications of ADV.

A systematic study of super-Eddington layers in the envelopes of massive stars

Context. The proximity to the Eddington luminosity has been attributed as the cause of several observed effects in massive stars. Computationally, if the luminosity carried through radiation exceeds the local Eddington luminosity in the low-density envelopes of massive stars, it can result in numerical difficulties, inhibiting further computation of stellar models. This problem is exacerbated by the fact that very few massive stars are observed beyond the Humphreys-Davidson limit, the same region in the Hertzsprung-Russell diagram where the aforementioned numerical issues relating to the Eddington luminosity occur in stellar models. Aims. One-dimensional stellar evolution codes have to use pragmatic solutions to evolve massive stars through this computationally difficult phase. In this work, we quantify the impact of these solutions on the evolutionary properties of massive stars. Methods. We used the stellar evolution code MESA with commonly used input parameters for massive stellar models to compute the evolution of stars in the initial mass range of 10–110 M⊙ at one-tenth of solar metallicity. Results. We find that numerical difficulties in stellar models with initial masses greater than or equal to 30 M⊙ cause these models to fail before the end of core helium burning. Recomputing these models using the same physical inputs but three different pragmatic solutions to treat the numerical instability, we find that the maximum radial expansion achieved by stars can vary by up to 2000 R⊙, while the remnant mass of the stars can vary by up to 14 M⊙ between the sets. These differences can have implications on studies such as binary population synthesis.

Explaining the differences in massive star models from various simulations

ABSTRACT The evolution of massive stars is the basis of several astrophysical investigations, from predicting gravitational-wave event rates to studying star formation and stellar populations in clusters. However, uncertainties in massive star evolution present a significant challenge when accounting for these models’ behaviour in stellar population studies. In this work, we present a comparison between five published sets of stellar models from the BPASS (Binary Population and Spectral Synthesis), BoOST (Bonn Optimized Stellar Tracks), Geneva, MIST (MESA Isochrones and Stellar Tracks), and PARSEC (PAdova and TRieste Stellar Evolution Code) simulations at near-solar metallicity. The different sets of stellar models have been computed using slightly different physical inputs in terms of mass-loss rates and internal mixing properties. Moreover, these models also employ various pragmatic methods to overcome the numerical difficulties that arise due to the presence of density inversions in the outer layers of stars more massive than 40 M⊙. These density inversions result from the combination of inefficient convection in the low-density envelopes of massive stars and the excess of radiative luminosity to the Eddington luminosity. We find that the ionizing radiation released by the stellar populations can change by up to 18 per cent, the maximum radial expansion of a star can differ between 100 and 1600 R⊙, and the mass of the stellar remnant can vary up to 20 M⊙ between the five sets of simulations. We conclude that any attempts to explain observations that rely on the use of models of stars more massive than 40 M⊙ should be made with caution.

Preliminary Analysis of an Aged RPV Subjected to Station Blackout

Today, 46% of operating Nuclear Power Plants (NPP) have a lifetime between 31 and 40 years, while 19% have been in operation for more than 40 years. Long Term Operation (LTO) is an urgent requirement for all of the nuclear industry. The aim of this study is to assess the performance of a reactor pressure vessel (RPV) subjected to a station blackout (SBO) event. Alterations suffered by the material properties and creep at elevated temperatures are considered. In this study, coupling between MELCOR and Finite Element Method (FEM) codes is carried out. In the Finite Element (FE) model, the combined effects of ageing and creep are implemented through degraded material properties and a viscoplastic model. The reliability of the model is validated by comparing the FOREVER/C1 experimental results. The results show that the RPV lower head bends downwards with a maximum radial expansion of about 260 mm and RPV thermomechanical properties are reduced by more than 50% at high temperatures. The effects of ageing, creep and long heat-up strongly affect the resistance of the RPV system until the point of compromising it in the absence of/delayed emergency intervention. Aged RPV at end-of-life may collapse earlier, and in less time, with the same accidental conditions.

Nonlinear dynamics of a shell encapsulated microbubble near solid boundary in an ultrasonic field

Microbubbles have the potential to be used for diagnostic imaging and therapeutic delivery. However, the transition from microbubbles currently being used as ultrasound contrast agents to achieve its’ potentials in the biomedical field requires more in depth understanding. Of particular importance is the influence of microbubble encapsulation of a microbubble near a vessel wall on the dynamical behaviour as it stabilizes the bubble. However, many bubble studies do not consider shell encapsulation in their studies. In this work, the dynamics of an encapsulated microbubble near a boundary was studied by numerically solving the governing equations for microbubble oscillation. In order to elucidate the effects of a boundary to the non-linear microbubble oscillation the separation distances between microbubble will be varied along with the acoustic driving. The complex nonlinear vibration response was studied in terms of bifurcation diagrams and the maximum radial expansion. It was found that the increase in distance between the boundary and the encapsulated bubble will increase the oscillation amplitude. When the value of pressure amplitude increased the single bubble is more likely to exhibit the chaotic behaviour and maximum radius also increase as the inter wall-bubble distance is gradually increased. While, with higher driving frequency the maximum radial expansion decreases and suppress the chaotic behaviour.

The fates of massive stars: exploring uncertainties in stellar evolution with metisse

ABSTRACT In the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and dynamical systems of stars. Systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. We present a new approach to the commonly used single-star evolution (sse) fitting formulae, one that is more adaptable: method of interpolation for single star evolution (metisse). It makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. We have used metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), the bonn evolutionary code (bec), and the Cambridge stars code. metisse better reproduces stellar tracks computed using the stars code compared to sse, and is on average three times faster. Using stellar tracks computed with mesa and bec, we apply metisse to explore the differences in the remnant masses, the maximum radial expansion, and the main-sequence lifetime of massive stars. We find that different physical ingredients used in the evolution of stars, such as the treatment of radiation-dominated envelopes, can impact their evolutionary outcome. For stars in the mass range 9–100 M⊙, the predictions of remnant masses can vary by up to 20 M⊙, while the maximum radial expansion achieved by a star can differ by an order of magnitude between different stellar models.

Preliminary of finite element analysis (FEA) investigation on the stent expansion

The requirement of stent expansion is important to stent deployment on the inner of the defected blood vessel. This defected blood vessel decreases in lumen diameter size because of accumulation of fat or plaque and caused the reduction of blood flow and oxygen supply to overall body. According to clinical guidelines, blood vessel that blockage by 70% need to be stenting. Stent expand past it elastic limit and plastically deform until the targeted diameter is achieved. Explicit dynamics Finite Element Analysis (FEA) was used in this paper to analyse the stent expansion process. The knowledge of stent radial displacement could prevent the injury of inner surface of artery while understanding on longitudinal foreshortening that aided the stent placement on targeted artery location. The controlled variable was geometry, material and boundary condition of stent. The manipulated variable was the speed of pressure application. The outcomes of this stent expansion simulation are maximum radial expansion, the uniform of radial displacement and longitudinal foreshortening. This simulation results help to improve stent installation on human body for balloon expandable stent and increase the understanding of explicit dynamics structure simulation of finite element in biomedical application.

Waxy Soft White Wheat: Extrusion Characteristics and Thermal and Rheological Properties

Waxy wheat flour was analyzed for its thermal and rheological properties and was extruded to evaluate its potential for extruded products. Normal soft white wheat flour was analyzed with the same methods and same extrusion conditions to directly compare differences between the two types of flour. Through DSC analysis, waxy wheat flour was found to have a higher gelatinization peak temperature of 66.4°C than normal wheat at 64.0°C, although the transition required 2.00 J/g less energy. Rapid visco‐analysis indicated that the waxy wheat flour pasted much more quickly and at lower temperatures than the normal wheat flour. Preliminary extrusion experiments were conducted to determine the optimal screw profile for waxy wheat with respect to maximum radial expansion. The optimum screw profile was used for extrusion trials with varying flour moisture (15–25% wb) and extruder screw speed (200–400 rpm) while monitoring process conditions including back pressure and specific mechanical energy. Physical properties of the extrudates were then studied. The radial expansion ratios of the waxy wheat extrudates exceeded those of the normal wheat extrudates by nearly twice as much, and it was observed that the waxy wheat flour took less energy in the form of fewer shear screw elements to expand. The waxy wheat extrudates also exhibited significantly higher water solubility and less water absorption than the normal wheat extrudates owing to solubilizing of the extrudates. The results of our study indicate that waxy wheat flour may be a viable ingredient for creating direct expanded products with less energy.

Pressure-Dependent, Infrared-Emitting Phenomenon in Hypervelocity Impact

A series of hypervelocity impact experiments were conducted with variable target chamber atmospheric pressure ranging from 0.9 to 21.5 Torr. Using a two-stage light-gas gun, 5.7 mg nylon 6/6 right-cylinders were accelerated to speeds ranging between 6.0 and 6.3 km/s to impact 1.5 mm thick 6061-T6 aluminum plates. Full-field images of near-IR emission (0.9 to 1.7 μm) were measured using a high-speed spectrograph system with image exposure times of 1 μs. The radial expansion of an IR-emitting impact-generated phenomenon was observed to be dependent upon the ambient target chamber atmospheric pressures. Higher chamber pressures demonstrated lower radial expansions of the subsequently measured IR-emitting region uprange of the target. Dimensional analysis, originally presented by Taylor to describe the expansion of a hemispherical blast wave, is applied to describe the observed pressure-dependence of the IR-emitting cloud expansion. Experimental results are used to empirically determine two dimensionless constants for the analysis. The maximum radial expansion of the observed IR-emitting cloud is described by the Taylor blast-wave theory, with experimental results demonstrating the characteristic nonlinear dependence on atmospheric pressure. Furthermore, the edges of the measured IR-emitting clouds are observed to expand at extreme speeds ranging from approximately 13 to 39 km/s. In each experiment, impact ejecta and debris are simultaneously observed in the visible range using an ultrahigh-speed laser shadowgraph system. For the considered experiments, ejecta and debris speeds are measured between 0.6 and 5.1 km/s. Such a disparity in observed phenomena velocities suggests the IR-emitting cloud is a distinctly different phenomenon to both the uprange ejecta and downrange debris generated during a hypervelocity impact.

Comparing the Marmottant model for ultrasound contrast agents with experimental postexcitation signals.

When insonified with sufficiently large rarefactional pressures, single unconstrained ultrasound contrast agents undergo inertial collapse with postexcitation emissions. Experimental measurements of postexcitation signal data for Definity microbubbles are compared with the Marmottant theoretical model for large amplitude oscillations of ultrasound contrast agents (UCAs). After taking into account the insonifying pulse characteristics, microbubble properties, and size distribution of the population of UCAs, a good comparison between simulated results and experimental data is obtained by determining a threshold maximum radial expansion (Rmax) to indicate the onset of postexcitation activity. Though this threshold Rmax is found to vary depending on insonification frequency, the values obtained are well above the typical free bubble inertial cavitation threshold commonly chosen at 2R0. The close agreement between the experiment and models suggests that lipid shelled UCAs behave as unshelled bubbles during most of a large amplitude cavitation cycle, as proposed in the Marmottant equation. [NIH Grant No. R37EB002641.]

Thermal and Structural Analysis of Interaction Cavity and Its Effect on the Operating Mode Excitation for a 120 GHz, 1 MW Gyrotron

Thermal and structural analysis for a 120 GHz, 1 MW gyrotron interaction cavity and the effect of structural deformation on the operational mode excitation is presented. Finite element analysis codes ANSYS and COSMOS have been used for the thermal and structural simulation. The values of the water flow rate and the hydraulic diameter of the outer jacket have been optimized. The effect of the maximum radial expansion of the interaction cavity on eigenfrequency and mode excitation has also been analyzed. The change in eigenfrequency for the operating mode due to thermal expansion is 0.606 GHz. This value is very near the theoretically calculated value and under the tolerance limit of the maximum frequency deviation for the gyrotron operating mode.

Comparison between maximum radial expansion of ultrasound contrast agents and experimental postexcitation signal results

Experimental postexcitation signal data of collapsing Definity microbubbles are compared with the Marmottant theoretical model for large amplitude oscillations of ultrasound contrast agents (UCAs). After taking into account the insonifying pulse characteristics and size distribution of the population of UCAs, a good comparison between simulated results and previously measured experimental data is obtained by determining a threshold maximum radial expansion (Rmax) to indicate the onset of postexcitation. This threshold Rmax is found to range from 3.4 to 8.0 times the initial bubble radius, R0, depending on insonification frequency. These values are well above the typical free bubble inertial cavitation threshold commonly chosen at 2R0. The close agreement between the experiment and models suggests that lipid-shelled UCAs behave as unshelled bubbles during most of a large amplitude cavitation cycle, as proposed in the Marmottant equation.

Effects of extrusion conditions on quality of cassava bran/cassava starch extrudates

SummaryBlends of cassava bran and cassava starch were processed in a single‐screw extruder. Response surface methodology was used to determine the effect of the concentration of cassava bran (10–50%), barrel temperature (150–210 °C), feed moisture (16–20%) and screw speed (120–180 r.p.m.) on the characteristics of the dried extrudates. All the independent variables were significant (P < 0.05) for radial expansion. The water absorption index (WAI) and water solubility index (WSI) were affected by bran level, screw speed and temperature, while only moisture and temperature influenced specific volume. The maximum radial expansion was found when all the independent variables were at their lowest levels. Lowest‐density extrudates (highest specific volume) were obtained at 16–18% moisture and 180–200 °C. An increase in bran level increased the WAI but decreased the WSI when the temperature was higher than 170 °C . Screw speed had a slight effect on those responses, decreasing water absorption and increasing water solubility when changed from 120 to 180 r.p.m.

Propagation velocities of gas rings in collisional ring galaxies

The propagation velocity of the first gas ring in collisional ring galaxies, i.e. the velocity at which the maximum in the radial gas density profile propagates radially in the galactic disk, is usually inferred from the radial expansion velocity of gas in the first ring. Our numerical hydrodynamics modeling of ring galaxy formation however shows that the maximum radial expansion velocity of gas in the first ring (vgas) is invariably below the propagation velocity of the first gas ring itself (). Modeling of the Cartwheel galaxy indicates that the outer ring is currently propagating at km s-1, while the maximum radial expansion velocity of gas in the outer ring is currently km s-1. The latter value is in marginal agreement with the measurements of Higdon ([CITE]) based on HI kinematics. Modeling of the radial color gradients of the Cartwheel ring galaxy also indicates that the outer ring is propagating at km s-1 for the adopted distance to the galaxy of 140 Mpc. On the other hand, the azimuthally averaged surface brightness profile of the Cartwheel's outer ring does not peak exterior to those in K- and B-bands, contrary to what would be expected for such a high propagation velocity. We show that a combined effect of 41° inclination, finite thickness, and warping of the Cartwheel's disk might be responsible for the lack of angular difference in the peak positions. Indeed, the radial surface brightness profiles obtained along the Cartwheel's major axis, where effects of inclination and finite thickness are minimized, do peak exterior to those at K- and B-bands. The angular difference in peak positions implies vring = 110 km s-1, which is in agreement with the model predictions. We briefly discuss the utility of radio continuum emission and spectral line equivalent widths for determining the propagation velocity of gas rings in collisional ring galaxies.

Stimulation of radial expansion in arabidopsis roots by inhibitors of actomyosin and vesicle secretion but not by various inhibitors of metabolism.

Plant morphogenesis depends on accurate control over growth anisotropy. To learn to what extent the control of growth anisotropy depends on cellular metabolism, we surveyed the response of growing roots to a range of inhibitors. Seedlings of Arabidopsis thaliana L. (Heynh), 7-8 d old, were transplanted onto plates containing an inhibitor, and elongation and radial expansion of roots were measured over the subsequent 2-d period. Fourteen inhibitors of diverse metabolic processes inhibited root elongation but failed to stimulate radial expansion. These inhibitors were aluminum sulfate, aphidicolin (DNA synthesis), caffeine (cell-plate formation), cisplatin (DNA synthesis), cycloheximide (protein synthesis), 3,4-dehydro-L-proline (proline hydroxylation), 6-dimethylaminopurine (protein kinases), dinitrophenol (mitochondrial ATP synthesis), galactose (UDP-glucose formation), Lovastatin, formerly mevinolin (isoprenoid formation), methionine sulfoximine (glutamine synthetase), methotrexate (folate metabolism), XRD-489 (synthesis of branched-chain amino acids), and high or low calcium treatments. These results show that various types of metabolic disruption, although inhibitory to elongation, do not reduce the high degree of anisotropic growth of the root. However, five chemicals did stimulate radial expansion; namely, the detergent, digitonin; two inhibitors of vesicle secretion, monensin and brefeldin A; and two inhibitors of actomyosin, cytochalasin B and butanedione monoxime. The maximum radial expansion induced by these compounds (except butanedione monoxime) was greater than that caused by ethylene, and the morphology of treated roots did not resemble that of roots treated with ethylene. These results indicate that vesicle secretion and actomyosin play a role in controlling anisotropic expansion.