•Advanced computational methods are used to explain cleaning by cavitation bubbles.•Bubble growth produces suction forces on particles.•Bubble collapse generates reentrant jet and very strong shear ...right at the wall.•Bubble forces on particles depend on bubble strength and relative positions.•Dirt layer removal depends on relative bubble collapse energy and coating strength.
Surface cleaning using cavitation bubble dynamics is investigated numerically through modeling of bubble dynamics, dirt particle motion, and fluid material interaction. Three fluid dynamics models; a potential flow model, a viscous model, and a compressible model, are used to describe the flow field generated by the bubble all showing the strong effects bubble explosive growth and collapse have on a dirt particle and on a layer of material to remove. Bubble deformation and reentrant jet formation are seen to be responsible for generating concentrated pressures, shear, and lift forces on the dirt particle and high impulsive loads on a layer of material to remove. Bubble explosive growth is also an important mechanism for removal of dirt particles, since strong suction forces in addition to shear are generated around the explosively growing bubble and can exert strong forces lifting the particles from the surface to clean and sucking them toward the bubble. To model material failure and removal, a finite element structure code is used and enables simulation of full fluid–structure interaction and investigation of the effects of various parameters. High impulsive pressures are generated during bubble collapse due to the impact of the bubble reentrant jet on the material surface and the subsequent collapse of the resulting toroidal bubble. Pits and material removal develop on the material surface when the impulsive pressure is large enough to result in high equivalent stresses exceeding the material yield stress or its ultimate strain. Cleaning depends on parameters such as the relative size between the bubble at its maximum volume and the particle size, the bubble standoff distance from the particle and from the material wall, and the excitation pressure field driving the bubble dynamics. These effects are discussed in this contribution.
•The dynamics of a bubble cloud in an ultrasonic field near a wall is investigated.•Individual bubble dynamics and motion modeled using an Eulerian-Lagrangian approach.•Very high pressures can be ...generated at the wall due to collective bubble dynamics.•Highest pressures are generated when excitation is at bubble cloud resonance frequency.•The resonance driving frequency is a function of both bubble and cloud sizes.
The dynamics of a bubble cloud excited by a sinusoidal pressure field near a rigid wall is studied using a novel Eulerian/Lagrangian two-phase flow model. The effects of key parameters such as the amplitude and frequency of the excitation pressure, the cloud and bubble sizes, the void fraction, and the initial standoff distance on the bubbles’ collective behavior and the resulting pressure loads on the nearby wall are investigated. The study shows that nonlinear bubble cloud dynamics becomes more pronounced and results in higher pressure loading at the wall as the excitation pressure amplitude increases. The strongest collective bubble behavior occurs at a preferred resonance frequency. At this resonance frequency, pressure peaks orders of magnitudes higher than the excitation pressure result from the bubble interaction when the amplitude of the pressure excitation is high. The numerically obtained resonance frequency is significantly different from the reported natural frequency of a spherical cloud derived from linear theory, which assumes small amplitude oscillations in an unbounded medium. At high amplitudes of the excitation, the resonance frequency decreases almost linearly with the ratio of excitation pressure amplitude to ambient pressure until the ratio is larger than one.
Material pitting from cavitation has been used on and off as an indicator of the vague concept of ‘cavitation intensity’. Periodically, some researchers suggest the use of pitting tests as a means to ...provide quantitative measurements of the amplitude of the impulsive pressures in the cavitation field, especially when combined with Tabor׳s formula or with finite element computations with idealized synthetic loads. This paper examines the viability of such a suggested method using fully coupled bubble dynamics and material response, and strongly concludes that the method provides at best a qualitative assessment of the cavitation erosion potential. Peak pressures deduced from pit geometry are significantly lower than the ones actually applied. In addition the correspondence is highly dependent on the way the load is applied and different loading scenarios with the same amplitude of the cavitation impulsive pressure result in different pit aspect ratios.
•Cavitation pitting was modeled by coupling bubble and material dynamics.•Tabor relation was used to deduce stress from the computed pit geometries.•There is no one-to-one relationship between peak pressure and pit geometry.•Tabor deduced stress is an order of magnitude smaller than the imposed load.•Tabor deduced stress is close to the maximum equivalent stress in material.
► Pitting test results on three materials and various operating conditions are presented. ► Pitting rate follows an exponential law depending upon two parameters. ► Coverage time and characteristic ...pit diameter are the two key parameters. ► Scaling laws on pitting test data are discussed using these two parameters. ► Material and velocity effects on pitting rate are investigated.
Cavitation erosion during the incubation period was investigated via pitting tests conducted on three different materials: an Aluminum alloy, a Nickel Aluminum Bronze alloy and a Duplex Stainless Steel. Pitting tests were conducted in a cavitation tunnel in the velocity range 45–90m/s at a constant cavitation number. The test section was made of a straight nozzle 16mm in diameter discharged into the radial 2.5mm space between two flat walls. Cavitation appears in the form of a toroidal cavity attached to the nozzle exit and damage on the samples facing the nozzle is concentrated in a circular ring centered in the cavity closure region. The exposure time was adjusted to avoid pit overlapping. The material surface was examined using a conventional contact profilometer which allowed us to identify the pits, count them, and measure their main characteristics such as depth, surface area, and volume. From these the pitting rate, the coverage rate, and the depth of deformation rate were defined. Pits were classified according to their diameter. For all materials and operating conditions, pitting rate appears to follow an exponential law in relation to the pit diameter. This law depends upon two parameters only, which were identified as the coverage time τ (i.e. the time required for the surface to be covered by erosion pits) and a characteristic pit diameter δ, which corresponds to the pits whose contribution to the coverage process is the highest. Scaling laws for pitting were derived accounting for both material properties and flow velocity, and a procedure to make pitting test results non-dimensional is proposed. The influence of the material on pitting test results was analyzed. It is shown that the damage is not correlated in simple terms with the elastic limit determined from conventional tensile tests and it is conjectured that other parameters such as the strain rate might play a significant role and should be included in the analysis. The effect of flow velocity on both parameters τ and δ was analyzed and a classical power law was found for the influence of the flow velocity on pitting rate for all three materials. Finally, some analysis and discussion is given concerning distributions of pit volume and pit depth.
Background and purpose
Dementia in Parkinson's disease (PD) is common and disabling. Identification of modifiable risk factors for it is essential. Vascular risk factors (VRFs) may be associated with ...cognitive decline in early PD. Biomarkers that serve as surrogates of the long‐term effect of VRFs on PD are needed. To that end, we aimed to quantitate white matter hyperintensities (WMH) in early PD, measure associations with VRFs and examine relationships between WMH and longitudinal cognition.
Methods
Participants in the Parkinson's Progression Markers Initiative study (141 patients with PD, 63 healthy controls) with adequate baseline structural brain magnetic resonance imaging data were included. Hypertension and diabetes history, and body mass index were combined to create a vascular risk score. WMH were quantitated via automated methods. Cognition was assessed annually with a comprehensive test battery.
Results
In the PD group, vascular risk score was associated with WMH for total brain (β = 0.210; P = 0.021), total white matter (β = 0.214; P = 0.013), frontal (β = 0.220; P = 0.002) and temporal (β = 0.212; P = 0.002) regions. Annual rate of change in global cognition was greater in those with higher vascular risk score (β = −0.040; P = 0.007) and greater WMH (β = −0.029; P = 0.049). Higher temporal WMH burden was associated with great decline over time in verbal memory (β = −0.034; P = 0.031).
Conclusions
In early PD, modifiable VRFs are associated with WMH on brain magnetic resonance imaging. Temporal WMH burden predicts decline in verbal memory. WMH may serve as a surrogate marker for the effect of VRFs on cognitive abilities in PD.
Context.
Star-forming molecular clouds are characterised by the ubiquity of intertwined filaments. The filaments have been observed in both high- and low-mass star-forming regions, and they are ...thought to split into collections of sonic fibres. The locations where filaments converge are termed hubs, and these are associated with the young stellar clusters. However, the observations of filamentary structures within hubs at distances of 75–300 pc require a high angular resolution <2″ (~ 150–600 au) that limits the number of such studies conducted so far.
Aims.
The integral shaped filament (ISF) of the Orion A molecular cloud is noted for harbouring several hubs within which no filamentary structures have been observed so far. The goal of our study is to investigate the nature of the filamentary structures within one of these hubs, which is the chemically rich hub OMC-2 FIR 4, and to analyse their emission with high density and shock tracers.
Methods.
We observed the OMC-2 FIR 4 proto-cluster using Band 6 of the Atacama Large (sub-)Millimetre Array (ALMA) in Cycle 4 with an angular resolution of ~0.26″ (100 au). We analysed the spatial distribution of dust, the shock tracer SiO, and dense gas tracers (i.e., CH
3
OH, CS, and H
13
CN). We also studied the gas kinematics using SiO and CH
3
OH maps.
Results.
Our observations for the first time reveal interwoven filamentary structures within OMC-2 FIR 4 that are probed by several tracers. Each filamentary structure is characterised by a distinct velocity as seen from the emission peak of CH
3
OH lines. They also show transonic and supersonic motions. SiO is associated with filaments and also with multiple bow-shock features. The bow-shock features have sizes between ~500 and 2700 au and are likely produced by the outflow from HOPS-370. Their dynamical ages are <800 yr. In addition, for the first time, we reveal a highly collimated SiO jet (~1°) with a projected length of ~5200 au from the embedded protostar VLA 15.
Conclusions.
Our study unveiled the previously unresolved filamentary structures as well as the shocks within OMC-2 FIR 4. The kinematics of the filamentary structures might be altered by external and/or internal mechanisms such as the wind from H II regions, the precessing jet from the protostellar source HOPS-370, or the jet from VLA 15. While the complexity of the region, coupled with the limited number of molecular lines in our dataset, makes any clear association with these mechanisms challenging, our study shows that multi-scale observations of these regions are crucial for understanding the accretion processes and flow of material that shape star formation.
Context.
Class I protostars are a bridge between Class 0 protostars (≤10
5
yr old), and Class II (≥10
6
yr) protoplanetary disks. Recent studies show gaps and rings in the dust distribution of disks ...younger than 1 Myr, suggesting that planet formation may start already at the Class I stage. To understand what chemistry planets will inherit, it is crucial to characterize the chemistry of Class I sources and to investigate how chemical complexity evolves from Class 0 protostars to protoplanetary disks.
Aims.
There are two goals: (i) to perform a census of the molecular complexity in a sample of four Class I protostars, and (ii) to compare the data with the chemical compositions of earlier and later phases of the Sun-like star formation process.
Methods.
We performed IRAM-30 m observations at 1.3 mm towards four Class I objects (L1489-IRS, B5-IRS1, L1455-IRS1, and L1551-IRS5). The column densities of the detected species were derived assuming local thermodynamic equilibrium (LTE) or large velocity gradients (LVGs).
Results.
We detected 27 species: C-chains, N-bearing species, S-bearing species, Si-bearing species, deuterated molecules, and interstellar complex organic molecules (iCOMs; CH
3
OH, CH
3
CN, CH
3
CHO, and HCOOCH
3
). Among the members of the observed sample, L1551-IRS5 is the most chemically rich source. Different spectral profiles are observed: (i) narrow lines (~1 km s
−1
) towards all the sources, (ii) broader lines (~4 km s
−1
) towards L1551-IRS5, and (iii) line wings due to outflows (in B5-IRS1, L1455-IRS1, and L1551-IRS5). Narrow c-C
3
H
2
emission originates from the envelope with temperatures of 5–25 K and sizes of ~2′′−10′′. The iCOMs in L1551-IRS5 reveal the occurrence of hot corino chemistry, with CH
3
OH and CH
3
CN lines originating from a compact (~0.′′15) and warm (
T
> 50 K) region. Finally, OCS and H
2
S seem to probe the circumbinary disks in the L1455-IRS1 and L1551-IRS5 binary systems. The deuteration in terms of elemental D/H in the molecular envelopes is: ~10−70% (D
2
CO/H
2
CO), ~5−15% (HDCS/H
2
CS), and ~1−23% (CH
2
DOH/CH
3
OH). For the L1551-IRS5 hot corino we derive D/H ~2% (CH
2
DOH/CH
3
OH).
Conclusions.
Carbon chain chemistry in extended envelopes is revealed towards all the sources. In addition, B5-IRS1, L1455-IRS1, and L1551-IRS5 show a low-excitation methanol line that is narrow and centered at systemic velocity, suggesting an origin from an extended structure, plausibly UV-illuminated. The abundance ratios of CH
3
CN, CH
3
CHO, and HCOOCH
3
with respect to CH
3
OH measured towards the L1551-IRS5 hot corino are comparable to that estimated at earlier stages (prestellar cores, Class 0 protostars), and to that found in comets. The deuteration in our sample is also consistent with the values estimated for sources at earlier stages. These findings support the inheritance scenario from prestellar cores to the Class I phase when planets start forming.
Context.
Hot corinos are compact regions around solar-mass protostellar objects that are very rich in interstellar Complex Organic Molecules (iCOMs). How the abundance of these molecules is affected ...by the environmental physical conditions is still an open question. More specifically, addressing this point is key to understand our own chemical origins since the Solar System formed in a large cluster of low- to high-mass stars and was therefore subject to external heating and ultraviolet irradiation which may have shaped the chemistry of its early formation stages.
Aims.
The goal of this high resolution study is to determine the abundance ratios of iCOMs in HOPS-108, which is a Class 0 protostar and a hot corino candidate located in the nearest Solar System analogue, the protostellar cluster OMC-2 FIR 4, in Orion. We aim to compare the abundance ratios to those found in other hot corinos, which are all located in less crowded environments, in order to understand the impact of environmental conditions on hot corinos’ chemistry.
Methods.
We observed the OMC-2 FIR 4 proto-cluster using the Band 6 of the Atacama Large (sub-)Millimetre Array in Cycle 4 with an angular resolution of ~0.′′28 (110 au). We determined the abundances and temperature of the species using local thermodynamic equilibrium (LTE) and non-LTE analysis.
Results.
Our results reveal a rich organic chemistry towards HOPS-108, asserting that it is a hot corino where the following iCOMs are detected: CH
3
OH, HCOOCH
3
, CH
3
OCH
3
, CH
3
18
OH, CH
2
DOH, CH
3
COCH
3
, CH
3
CHO, CH
3
CN,
13
CH
3
CN, C
2
H
5
CN, and NH
2
CHO. Remarkably, we find a possible enhancement in the HCOOCH
3
abundance with respect to other known hot corinos. Indeed, the CH
3
OCH
3
/HCOOCH
3
abundance ratio in this source is ~0.2 and, within the uncertainties, it deviates from the known correlation marginally where CH
3
OCH
3
/HCOOCH
3
~1. A relatively low CH
2
DOH/CH
3
OH abundance ratio of ~0.02 is also obtained, which is in agreement with that found in another Orion source, HH212, suggesting a higher gas temperature during the early phases of ice mantle formation.
Conclusions.
The CH
3
OCH
3
/HCOOCH
3
and CH
2
DOH/CH
3
OH abundance ratios in HOPS-108 might result from different physical conditions in the Orion molecular complex compared to other regions. The former ratio cannot be reproduced with current chemical models, highlighting the importance of improving the chemical networks with theoretical calculations. More hot corinos located in heavily clustered regions such as Orion should be targeted in order to measure these ratios and evaluate whether they are an environmental product or whether HOPS-108 is an exceptional hot corino overall.
Introduction
Caregiver burden is high among caregivers of PD patients (CPD). Neuropsychiatric symptoms are leading contributors to CPD burden, but whether different symptoms differentially impact ...domains of caregiver burden is not known. Our objective was to examine which neuropsychiatric symptoms and demographic factors contribute to different domains of caregiver burden in PD.
Methods
This was a cross-sectional online survey study. Participants were recruited from the Fox Insight (FI) study and were eligible if they identified themselves as a CPD. The primary outcome was the Caregiver Burden Inventory (CBI) total score and its 5 sub-domain scores. The Neuropsychiatric Inventory Questionnaire (NPI-Q) assessed caregiver-reported neuropsychiatric symptoms in the care recipient. Multivariable linear regression models were used to characterize the associations between NPI-Q symptom severity scores and CBI scores. Covariates were caregiver age, sex, education, and caregiving duration.
Results
The sample consisted of 450 CPD, mean age 65.87 (SD 10.39) years, 74% females. After adjusting for covariates, CBI total score was predicted by NPI-Q total score (
β
= 1.96,
p
< 0.001); model adjusted
R
2
= 39.2%. Anxiety severity had the largest effect size standardized
β
(s
β
) = 0.224 on the time-dependency domain, which was also associated with female sex (s
β
= − 0.133) and age (s
β
= 0.088). Severity of disinhibition (s
β
= 0.218), agitation (s
β
= 0.199), and female sex (s
β
= 0.104) were associated with greater emotional burden.
Conclusion
Our findings indicate that demographic characteristics and specific neuropsychiatric symptoms contribute differentially to domains of caregiver burden. Tailored interventions to support CPD are needed.
Abstract Introduction Cognitive decline is common in Parkinson’s disease (PD), and identifying patients at highest risk for it is essential. We aimed to examine the effect of possible REM sleep ...behavior disorder (pRBD) on rate of cognitive decline in early PD, for both global cognition and in specific cognitive domains. Methods Parkinson’s Progression Markers Initiative (PPMI) is a multi-site, international study of PD patients untreated at enrollment. pRBD was assessed with the REM sleep behavior disorder questionnaire (RBDSQ). Global cognition was assessed at baseline and annually using the Montreal Cognitive Assessment (MoCA) and a cognitive battery. Linear mixed effects models were used to examine the relationship between pRBD (RBDSQ≥6) and rate of change in cognitive variables. Age, sex, years of education, and baseline motor and cognitive scores were included as covariates. Results The baseline sample consisted of 423 individuals with PD, mean age 61.7 years and 65.5% male. Data was available on 389, 366, and 196 participants at 1-year, 2-year, and 3-year follow-up respectively. Possible RBD occurred in 108 (25.5%) at baseline. In multivariate analyses, baseline RBD was associated with greater annual rate of decline in MoCA score (β=-0.34, 95%CI -0.54, -0.13, p<0.001), Symbol Digit Modalities Test (β=-0.69, 95%CI -1.3, -0.09, p=0.024), and Hopkins Verbal Learning Test-Revised, delayed free recall (β=-0.21, 95%CI -0.41, -0.013, p=0.037). Conclusions Possible RBD is common in early PD and predicts future cognitive decline, particularly in attention and memory domains.
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