Mean Flow Velocity Research Articles

Sedimentation of short-lived fluid-solid suspensions

In this study, we propose a particle sedimentation/aggradation law for homogeneous concentrated suspensions. This law, valid in the Stokes flow regime, can be used to describe the sedimentation process observed in short-lived rapid flows, developed at high Reynolds numbers, that can be described as low-viscosity quasi-parallel flows traveling at constant velocity and that progressively sediment during the dominant phase of transport to leave a triangular or trapezoidal deposit of constant slope. The particle aggradation velocity can thus be predicted from the product of the mean flow velocity and the deposit slope and turns out to be roughly similar to that measured from static suspensions of the same concentration, provided that the flow Reynolds number, based on the mean flow velocity, the fluid properties, and the particle size, remains inferior to a few hundred, such as the mixture agitation cannot disturb the sedimentation process. These important results provide the possibility of describing the depositional dynamics during the final stage of extreme events, as well as to infer the mixture rheology, from physical parameters that can be easily measured in the field.

Evaluation of an Unsteady Yaw, Gust, and Broadband Turbulence Generation System for Closed-Loop Automotive Wind Tunnels

<div>This study investigates the flow characteristics in the test section of a model-scale, three-quarters open-jet, closed-loop return wind tunnel equipped with a novel device featuring three subsystems to generate transient yaw, gusts, and turbulence. The effect of each subsystem on the resulting turbulent and unsteady flows is evaluated individually and simultaneously. It is demonstrated that this new turbulence generation system can generate yaw distributions with standard deviations ranging from 2.1° to 8.0°. This replicates a wide range of on-road yaw behavior. Additionally, the subsystems can activate transient yaw events and unsteady gusts. Frequency sweeping was demonstrated to fill a wide range of low-frequency spectra, which helps recreate the on-road flow spectra in wind tunnels. Unsteady gusts of more than 15% of the mean flow velocity were achieved. The active turbulence subsystem generates turbulence levels from a few percent, passively, to over 20% intensity levels actively, with tailorable levels depending on input parameters to the active grid. Combined, the subsystems were demonstrated to achieve a wide range of yaw distributions with different standard deviations and features of the on-road turbulence spectrum, from low-frequency events to broadband turbulence with significant inertial subrange within the model-scale wind tunnel.</div>

Feasibility of transcranial Doppler to evaluate vasculopathy among survivors of childhood brain tumors exposed to cranial radiation therapy.

The ability of transcranial Doppler (TCD) to detect asymptomatic cerebrovascular disease among childhood brain tumor survivors following exposure to cranial radiation therapy has not been established. Survivors of childhood brain tumors, more than 3years since diagnosis and exposed to greater than 30Gy cranial radiation, underwent a history and physical exam, laboratory biomarkers of cerebrovascular disease (cholesterol, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), high-sensitivity CRP, hemoglobin A1C, apoprotein A, and apoprotein B), and a TCD evaluation of their cerebral arteries. In all 165 cerebral arteries from 13 patients (medulloblastoma=10; germ cell tumor=3; females=5; mean age at diagnosis=8.0years; mean age at time of study=20.9years) were examined. Twenty-eight of 165 (17%) were considered abnormal by pre-specified criteria. Total 114 cerebral arteries from 13 patients were assessed for greater than 50% stenosis velocities. Arteries most likely to be considered abnormal included the distal bilateral vertebral arteries (right 38%, left 30%), basilar artery 30%, bilateral siphon internal carotid arteries (right 30%, left 23%), bilateral middle cerebral arteries (23% bilaterally), and bilateral anterior cerebral arteries (7% bilaterally). Two vessels had mean flow velocities consistent with 50% stenosis (1.8%). No vessels were found to have greater than 80% stenosis. TCD may be a useful and practical tool to examine asymptomatic cerebrovascular disease among childhood brain tumor survivors after exposure to cranial radiation therapy. Posterior circulation vessels appear to have the highest burden of disease in this group of brain tumor survivors, a majority of whom had medulloblastoma.

Transcranial doppler (TCD) in predicting outcomes following successful mechanical thrombectomy of large vessel occlusions in anterior circulation: a systematic review and meta-analysis

BackgroundTranscranial Doppler (TCD) is a non-invasive, bedside tool that allows for real-time monitoring of the patient’s hemodynamic status following mechanical thrombectomy (MT). This systematic review and meta-analysis aims to evaluate...

The novel and slowest arterial pressure waves: clinical implications in children with congenital heart disease following cardiovascular surgery.

Certain rhythmic arterial pressure waves in humans and animals have been noticed for over one century. We found the novel and slowest arterial pressure waves in children following surgical repair for CHD, and examined their characteristics and clinical implications. We enrolled 212 children with 22 types of CHD within postoperative 48 h. We monitored haemodynamics (blood pressure, cardiac cycle efficiency, dP/dTmax), cerebral (ScO2), and renal (SrO2) oxygen saturation every 6 s. Electroencephalogram was continuously monitored. Mean blood flow velocity (Vm) of the middle cerebral artery was measured at 24 h. We found the waves with a frequency of ∼ 90 s immediately following surgical repair in 46 patients in 12 types of CHD (21.7%), being most prevalent in patients with aortic arch abnormalities (Aorta Group, n = 24, 42.3%) or ventricular septal defect (Ventricular Septal Defect Group, n = 12, 23.5%). In Aorta and Ventricular Septal Defect Groups, the occurrence of the waves was associated with lower blood pressures, dP/dTmax, cardiac cycle efficiency, ScO2, SrO2, Vm, worse electroencephalogram background abnormalities, higher number of electroencephalogram sharp waves, and serum lactate (Ps <0.0001-0.07), and were accompanied with fluctuations of ScO2 and SrO2 in 80.6% and 69.6% of patients, respectively. The waves observed in children following cardiovascular surgery are the slowest ever reported, occurring most frequently in patients with aortic arch abnormalities or ventricular septal defect. While the occurrence of the waves was associated with statistically worse and fluctuated ScO2 and SrO2, worse systemic haemodynamics, and electroencephalogram abnormalities, at present these waves have no known clinical relevance.

Pelvic congestion syndrome analysis through quantitative 2-dimensional phase-contrast magnetic resonance imaging: A promising vision from an observational cohort study.

To examine the application of quantitative 2-dimensional phase-contrast magnetic resonance imaging (2D PC-MRI) for treating patients with pelvic congestion syndrome (PCS). We conducted a retrospective cross-sectional analysis by using quantitative 2D PC-MRI data enrolled between April 2017 and Sep 2023. In addition, 32 healthy female controls (HCs) were included. Most patients with PCS presented with chronic pelvic pain and more than half had extra-pelvic venous symptoms (80/81, 98% and 45/81, 56%, respectively). Quantitative 2D PC-MRI analyzed the 81 patients with PCS, 239 patients without PCS, and 32 HCs. The patients with PCS had higher stroke volume (SV), absolute SV (ASV), and mean flux (MF) in the calf region (interstitial pixel shift) than did the HCs. In the left gonadal vein, the patients with PCS had higher SV, backward flow volume (BFV), ASV, and MF and lower forward flow volume (FFV), stroke distance (SD), and mean velocity (MV) than did the HCs. However, the patients with PCS had lower SV, FFV, MF, SD, and MV in the great saphenous veins. Quantitative 2D PC-MRI analysis revealed that the PCS group had higher SV, FFV, BFV, ASV, and MF in the calf region than did the non-PCS group. The variables that most strongly differentiated the patients with PCS from the HCs were SV in the great saphenous veins, SD in the great saphenous veins and left gonadal vein, and MV in the great saphenous veins and left gonadal vein. Caudal flow in the left gonadal vein was identified in half of the patients with PCS (39/81, 48.1%); 14 of them received embolization for left gonadal vein. In additional to providing an objective 3-dimensional morphology of the pelvic veins and extra-pelvic leaks, quantitative 2D PC-MRI analysis reveals distinct hemodynamic profiles between patients with PCS, those without PCS, and HCs, especially in the gonadal veins and regional perfusion of the calves.

Bathymetry and discharge estimation in large and data-scarce rivers using an entropy-based approach

ABSTRACT This study implements an entropy theory-based approach to infer bathymetry for 29 selected cross-sections along a 1740 km reach of the Congo River. A genetic algorithm optimization approach is used based on an analysis of near-surface velocity measurements to generate a random sample of 1000 bathymetry profiles from which the analysis is carried out. The resulting simulated bathymetry shows good agreement compared to the measurements obtained via Accoustic Doppler Current Profiler (ADCP), with a correlation that varies from 0.49 to 0.88. The bathymetry results are subsequently used to estimate the two-dimensional cross-sectional flow velocity distribution and, consequently, to calculate the river discharge. The mean errors observed for flow area, discharge, and mean velocity are found to be 2.7%, 1.3%, and 1%, respectively. This study demonstrates, for the first time, the successful application of an entropy-based approach to estimate bathymetry and discharge in large rivers and has significant implications for remote sensing applications.

Feasibility and effectiveness of a foam rolling intervention in pregnant women requiring bed rest for foetal protection: a randomised controlled trial

BackgroundBed rest during pregnancy can lead to reduced physical activity, impairing lower limb venous blood flow and increasing the risk of deep vein thrombosis (DVT) and muscle atrophy. We investigated the clinical efficacy of foam rolling intervention (FRI) in enhancing lower limb venous blood flow, mitigating the risk of DVT and muscle atrophy in pregnant women on bed rest.MethodsThis single-blind, randomised controlled trial enrolled 86 pregnant women with long-term bed rest for foetal protection (≥ 7 days), gestational age ≥ 20 weeks, and maternal age < 40 years. Participants were randomly assigned to a control or experimental group using a random number table. The control group received standard care, whereas the experimental group underwent FRI. Researchers and statisticians were aware of the treatment groups, however, the participants were blinded. Lower limb blood flow velocity, D-dimer levels, incidence of DVT, and the extent of lower limb muscle atrophy were assessed in both groups at baseline and post-intervention (day 7). To account for a 5% attrition rate and potential sampling error, the estimated sample size for each experimental and control group was 40.ResultsBefore the intervention, no significant differences were observed between the experimental and control groups in peak blood flow, mean flow velocity, D-dimer values, or leg circumference (P > 0.05), however, the peak blood velocities of the popliteal veins were significantly higher in the control group (P = 0.031). On the seventh day post-intervention, the experimental group had significantly higher mean and peak blood velocities in femoral and popliteal veins, significantly (P < 0.05), lower mean D-dimer levels (P = 0.035), and a significantly smaller reduction in thigh and calf circumference (P < 0.001). Consequently, the rate of thigh muscle atrophy was significantly slower in the experimental group (P = 0.011).ConclusionsFRI is an effective intervention for improving lower limb venous blood flow, mitigating the risk of DVT and muscle atrophy in pregnant women on bed rest.Trial registrationThis trial was retrospectively registered with the Chinese Clinical Trial Registry on June 18, 2024 (registration number: ChiCTR2400085770).

Optimizing Brain-Computer Interfaces for Methampetamine Use Disorder through Quantitative Electroencephalography (QEEG) and Transcranial Doppler Analysis: Article Review

A Brain-Computer Interface (BCI) is a system that allows a person to control external devices using only their brain activity. It works by translating brain signals into commands that can be understood by a computer. Several lines of evidence demonstrated the deleterious effect of methamphetamine (MA) on neurological and psychological functions. The use of amphetamines, such as MA, is associated with cerebrovascular complications such as cerebrovascular accidents (CVA) ,hemorrhage, hypoxic damage and vasculitis. Interestingly, while changes to cerebral blood flow (CBF) in response to acute amphetamine exposure have been reported. Transcranial Color Doppler (TCCD) is a non-invasive medical imaging technique that uses ultrasound waves to measure blood flow velocity in the major arteries of the brain, specifically within the circle of Willis. The research paper you referenced explores the use of TCCD as a potential measurement modality for BCIs. Quantitative electroencephalogram (qEEG) is a powerful tool for understanding brain function qEEG can reveal specific brain wave patterns associated with drug addiction, potentially providing insights into the neurobiological mechanisms underlying cravings, withdrawal symptoms, and relapse risk in Methamphetamine User Disorder (MUD). There is growing research interest in using Transcranial dopller as a measurement modality for BCIs.Here are some of the key considerations for using Transcranial doppler in BCIs: Mental Tasks, signal processing and classification, accuracy and reliability. Transcranial doppler provides information about blood flow in specific arteries but lacks detailed spatial information about brain activity. These patterns could vary depending on the type of drug, the severity of addiction, and individual differences. Transcranial doppler in measuring middle cerebral artery (MCA) blood flow velocity parameters (peak systolic velocity (PSV) and mean flow velocity (MFV)). qEEG can help researchers investigate the complex interplay between addiction and other brain disorders, like depression or anxiety. Characteristic qEEG in drugs addiction Increased Theta (4-8 Hz) and delta (1-4 Hz) brain waves are often associated with sleep and relaxation. However, research has shown that individuals with drug addiction may have increased theta and delta activity, particularly in the frontal and temporal regions of the brain. Altered Beta (13-30 Hz) brain waves are generally associated with wakefulness, alertness, and cognitive processing. Studies have observed both increases and decreases in beta activity in individuals with drug addiction, depending on the type of drug, the stage of addiction, and the specific brain regions being examined. The results of this research have important practical implications for building an diagnostic and functional assement with a better understanding of an using technology.

Investigation of the transportation characteristics of marine dredged-sediment in pipelines based on experimental pipeline models

Marine dredged-sediment(DS) is often transported through pipelines, where factors such as the solid volume concentration and transport rate can significantly influence the efficiency of the process. Inadequate selection of transport rates for a given solid volume concentration can lead to substantial energy losses. The pressure loss Δ P L or pressure loss gradient Δ P L / L are critical parameters for assessing energy loss during pipeline transport. In this study, large-scale indoor experiments on DS pipeline transport were conducted to investigate the effects of the cross-sectional mean flow velocity Vavg and solid concentration ϕ on the transport characteristics of DS. The results show that at higher solid volume concentrations, Δ P L / L increases rapidly with the square of Vavg and then plateaus, followed by a linear growth phase. In addition, a linear relationship is observed between lgf and lgVavg when the flow velocity is below critical velocity (Vavg ) critical ; above (Vavg ) critical , the friction factor f stabilizes at f 0 . Formulas for calculating (Vavg ) critical , f 0 and ϕ were developed. Additionally, a method for determining the optimal transport velocity of DS at varying volume concentrations was established, enabling the identification of the most efficient flow velocity for DS pipeline transportation across different concentrations. HIGHLIGHTS Pipeline model tests were conducted on marine dredged sediments. A formula for predicting pressure loss on the basis of solid concentration was derived. The impact of the solid concentration on the Darcy friction factor was determined. A method for determining the optimal transport velocity was established.

Alterations in Regional Brain Microcirculation in Patients with Sepsis: A Prospective Study Using Contrast-Enhanced Brain Ultrasound.

Alterations in regional brain microcirculation have not been well studied in patients with sepsis. Regional brain microcirculation can be studied using contrast-enhanced brain ultrasound (CEUS) with microbubble administration. CEUS was used to assess alterations in regional brain microcirculation on 3 consecutive days in 58 patients with sepsis and within 24h of intensive care unit admission in 10 aged-matched nonseptic postoperative patients. Time-intensity perfusion curve variables (time-to-peak and peak intensity) were measured in different regions of interest of the brain parenchyma. The mean arterial pressure, cardiac index (using transthoracic echocardiography), global cerebral blood flow (using echo-color Doppler of the carotid and vertebral arteries), mean flow velocities of the middle cerebral arteries, and brain autoregulation (using transcranial echo-color Doppler) were measured simultaneously. The presence of structural brain injury in patients with sepsis was confirmed on computed tomography imaging, and encephalopathy, including coma and delirium, was evaluated using the Glasgow Coma Scale and the Confusion Assessment Method in the Intensive Care Unit. Of the 58 patients with sepsis, 42 (72%) developed acute encephalopathy and 11 (19%) had some form of structural brain injury. Brain autoregulation was impaired in 23 (40%) of the patients with sepsis. Brain microcirculation alterations were observed in the left lentiform nucleus and left white matter of the temporoparietal region of the middle cerebral artery in the sepsis nonsurvivors but not in the survivors or postoperative patients. The alterations were characterized by prolonged time-to-peak (p < 0.01) and decreased peak intensity (p < 0.01) on the time-intensity perfusion curve. Prolonged time-to-peak but not decreased peak intensity was independently associated with worse outcome (p = 0.03) but not with the development of encephalopathy (p = 0.77). Alterations in regional brain microcirculation are present in critically ill patients with sepsis and are associated with poor outcome. Trial registration Registered retrospectively on December 19, 2019.

Fluid–acoustic–structure resonance mechanism of a plane cascade via a low-speed wind tunnel test

Acoustic resonance is an important factor that contributes to aeroengine compressor failure. In this study, a plane cascade of compressor blades was designed to reproduce acoustic resonance via a low-speed wind tunnel test. A high-frequency hot-wire, microphone and strain gauge were used to synchronously measure the fluid, acoustic and structural parameters. We analysed the variation in the amplitude and frequency of the multi-field parameters with increasing mean flow velocity and explored the multi-field interaction mechanism that induces the acoustic resonance of the plane cascade. The plane cascade effectively reproduced the acoustic resonance phenomenon. The first-order acoustic-mode frequency of the plane cascade flow duct, second-order torsional vibration mode frequency of the blade and shedding mode frequency of the tip clearance leakage vortex were equal under acoustic resonance. The fluid, acoustic and structural fields showed a strong interaction effect, achieving the maximum blade vibration amplitude and causing fatigue cracks of torsional vibration at the blade root. The frequency lock-in region of the compressor plane cascade was divided into an ‘acoustic–structure’ interaction region, a ‘fluid–acoustic–structure’ interaction region and a first-order acoustic-mode dominant region with increasing mean flow velocity, which demonstrates an interesting phenomenon in which the fluid–acoustic–structure modes compete: acoustic mode &gt; blade vibration mode &gt; vortex shedding mode. The results demonstrate a unique approach to the study of acoustic resonance that provides insight into the acoustic resonance mechanism in a cascade of compressor blades.

Association between cerebral blood flow variation and cognitive decline in older patients undergoing hemodialysis.

The mechanism of cognitive impairment in hemodialysis patients is multifactorial. The relationship between cerebral blood flow and the decline of cognitive function is poorly understood. To investigate the association between cerebral blood flow variation and decline of cognitive function in older patients undergoing hemodialysis. In this prospective observational cohort study of 121 older patients undergoing hemodialysis, we used transcranial Doppler ultrasound (TCD) to measure cerebral arterial mean flow velocity (MFV) throughout dialysis, assessed cognitive function at baseline and 12-month follow-up, and then analyzed associations between MFV and changes on cognitive scores. TCD recordings demonstrated a significant reduction in MFV throughout dialysis, which were significantly correlated with cumulative ultrafiltration volume (rho 0.356, p < 0.001), ΔSBP (rho 0.251, p = 0.005), and ΔMAP (rho 0.194, p = 0.032). Compared with the baseline assessments, cognitive scores of participants at the 12-month follow-up were significantly worsened in global cognition (MOCA), some tests of memory (CFT-memory), executive function (TMT-B, SCWT-C, and SCWT-T), attention/processing speed (SDMT), and visuospatial function (CFT-copy) (p < 0.05). The worsening scores in global cognition (MOCA) (β = 0.066, 95% CI 0.018-0.113, p = 0.007) and some tests of memory (AVLT5) (β = 0.050, 95% CI 0.004-0.097, p = 0.035) and executive function (TMT-B, SCWT-C, SCWT-T) (β = 1.955, 95% CI 0.457-3.453, p = 0.011; β = 0.298, 95% CI 0.112-0.484, p = 0.002 and β = 1.371, 95% CI 0.429-2.303, p = 0.004, respectively) were significantly associated with the reduction of MFV. Hemodialysis may significantly reduce cerebral blood flow in older patients; Repetitive intradialytic decreases in CBF may be one of the mechanisms underlying the decline of cognitive function. https://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid=S000C5B5&selectaction=Edit&uid=U0003QEL&ts=4&cx=-djoi2.

Impact of Manual Sustained Inflation vs Stepwise PEEP on Pulmonary and Cerebral Outcomes in Carotid Endarterectomy Patients.

BACKGROUND Recruitment maneuvers (RMs) are used to reduce pulmonary atelectasis in patients under general anesthesia, but they can lead to a decrease in cerebral hemodynamics. MATERIAL AND METHODS Thirty patients undergoing carotid endarterectomy were randomized to a manual sustained inflation (SI) group or a stepwise increase in PEEP (IP) group. During both RMs, the peak airway pressure (Ppeak) was maintained at 30 cmH₂O for 30 s. Electrical impedance tomography was used to evaluate pulmonary aeration changes. Mean velocity of blood flow in the middle cerebral artery (Vm) and cerebral oxygen saturation (rScO₂) was monitored intraoperatively. RESULTS IP improved lung aeration better at Ppeak=30 cmH₂O than SI (58.2±8.4% vs 46.0±8.3%, P=0.001) and this persisted until the end of surgery. Dorsal (dependent) ventilation 30 min after extubation in the SI group was lower than that before surgery (7.7±2.6% vs 9.9±3.8%, P=0.003). Vm and rScO₂ returned to baseline immediately after RM in the SI group, while it remained below baseline in the IP group (42.5±12.6 vs 50.9±18.8 cm/s, P<0.001 and 68.1±3.5% vs 70.6±3.7%, P=0.001). Heart rate declined significantly during RM only in the SI group (55.9±6.6 vs 52.2±6.9 bpm, P=0.008). CONCLUSIONS Compared with SI, IP performed better in improving lung aeration, with greater hemodynamic stability. IP resulted in slower recovery of cerebral blood flow and oxygenation.

Efficacy of butylphthalide in the treatment of patients with stroke attributed to intracranial arterial stenosis.

To explore the clinical efficacy of butylphthalide in treating patients with stroke attributed to intracranial artery stenosis (ICAS). In this retrospective study, records of 163 patients with stroke attributed to ICAS admitted to Jiaxing Second Hospital from January 2021 to January 2023 were retrospectively analyzed. Patients were divided into two groups based on the treatment received: control group (patients received routine treatment, n=55) and observation group (patients treated with butylphthalide on a routine basis, n=58). Changes in levels of cerebrovascular reactivity (CVR), breath-holding index (BHI), pulsatility index (PI), and middle cerebral artery mean flow velocity (Vm) between the two groups before and after treatment were compared. In addition, cognitive function, neurological function, and living ability were compared between the two groups before and after treatment, as well as the overall clinical efficacy of the treatment. The baseline data was comparable between the two groups (P>0.05). After the treatment, CVR, BHI, and Vm indicators in the observation group were significantly higher than those in the control group, while the levels of PI indexes were significantly lower than those in the control group (P<0.05). Montreal Cognitive Assessment (MoCA) and Barthel scale scores of the observation group were significantly higher compared to the control group, while the scores of National Institutes of Health Stroke Scale (NIHSS) were significantly lower (P<0.05). Butylphthalide in addition to routine treatment can effectively improve cerebrovascular reserve function, promote neurological and cognitive dysfunction recovery, and enhance daily living ability of patients with stroke caused by ICAS.

Effect of Positional Changes on Cerebral Perfusion in Parkinson's Disease Patients With Orthostatic Hypotension.

Orthostatic hypotension (OH) is one of the most common autonomic dysfunctions in Parkinson's disease (PD) patients. However, many patients with OH are asymptomatic. Conversely, orthostatic dizziness (OD) is not always associated with OH. We investigated the effects of positional changes on cerebral perfusion in patients with PD and OH. We enrolled 42 patients, comprising 31 PD patients and 11 healthy controls. All the subjects underwent the following clinical assessments: the OH questionnaire, head-up tilt test (HUTT) with transcranial Doppler (TCD), near-infrared spectroscopy, measurement of the change in oxygenated hemoglobin (ΔHboxy) during the squat-to-stand test (SST), measurement of the time derivative of total hemoglobin (DHbtot), and time taken to reach the peak (peak time [PT]) of DHbtot after restanding. The mean flow velocity change (ΔMFV) in the TCD during the HUTT failed to differentiate between the PD-OH(+) and PD-OH(-) groups. The change in oxygenated hemoglobin ΔHboxy was greater in the PD-OH(+) group, which persisted for 9 min until the end of the HUTT only in the left hemisphere. During SST, PT was significantly delayed in the left hemisphere in PD-OH(+) patients. Although TCD demonstrated no significant difference in ΔMFV, the parameters measured by near-infrared spectroscopy, such as ΔHboxy during HUTT and PT during the SST, significantly increased ΔHboxy or delayed PT in the left hemisphere of PD-OH(+). Positional changes have a detrimental effect on cerebral hemodynamics in patients with PD and OH, especially in the left hemisphere.

Modeling the impact of natural roughness of tension joints on heat transport

The understanding of heat transport in fractures is crucial for mining geothermal systems. Studies of heat transport in natural fractures at scales comprised between those of laboratory experiments and those of field tracer tests are seldom. To bridge the gap, a joint surface with characteristic plumose was scanned in the field using LiDAR technology. The scanned surface was used to build a numerical model of mode 1 fracture. Fluid flow and heat transport were modeled solving the steady-state Stokes equation and assuming Fourier transport, respectively. We considered three different fracture apertures and varied systematically roughness in order to investigate the impact of plumose on fluid and heat transport. The 3D velocity flow fields were characterized by mean hydraulic aperture and by statistics on the directional components of the velocity vector. The method of temporal moments was used to extract first and second moments from temperature breakthrough curves. Heat transport parameters (local and macroscopic) were calculated from first and second moments.We show that hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. The local variation of heat transport parameters is controlled by fracture roughness. For the macroscopic transport parameters, several transport regimes were identified. At low fracture aperture (i.e. 1 mm), conductive regime dominates heat transport in agreement with low Péclet numbers. In this case, fracture roughness affects the transport parameters via the loss of hydraulic aperture. With higher aperture (i.e. 3 mm) geometrical dispersion regime is dominant, roughness controlling the amplitude of transport parameters. At 5 mm aperture, transition from geometrical to Taylor dispersion occurs and the roughness tends to decrease dispersion and dispersivity according to the mean flow velocity.

The effects of acoustic disturbances and mechanical vibration on laminar premixed flames: A comparative study

The energy conversion between the combustion process and acoustic waves is very complex in high-performance propulsion systems, which may trigger large-amplitude combustion instabilities, potentially leading to severe vibration or structural damage. Both acoustic disturbances and mechanical vibration are found to be able to cause the combustion instability, but their differences on the influence of laminar premixed flames are still unknown. In this paper, a premixed methane flame burner was disturbed by either a loudspeaker or an electromagnetic vibration exciter, and the effects of their forcing frequencies and amplitudes on the dynamic responses of the premixed methane flame were evaluated. Specifically, the unsteady heat release rate was measured by a photomultiplier tube, and the flame dynamic behaviors were captured by a high-speed camera with image intensifier. Furthermore, the acoustic disturbances upstream of the flame was measured by the two-microphone method, and the structure vibration was measured by an accelerometer. Then, the flame transfer functions were obtained at various equivalence ratios and mean flow velocities. The results demonstrated that the premixed flame exhibited obvious band-pass filtering characteristics when subjected to external forcing, whether through a loudspeaker or an electromagnetic vibration exciter. In addition, increasing either acoustic or structure excitation amplitude to a large extent can make the flame respond in a nonlinear manner. However, when the flame was subjected to mechanical vibration, the peak frequency corresponding to the maximum gain of the flame transfer function had minimal sensitivity to variations in equivalence ratios and mean flow velocities. In contrast, the acoustic disturbances were more likely to induce the nonlinear flame responses and flame front wrinkling.

Rationale and Design for the BLOCK-SAH Study (Pterygopalatine Fossa Block as an Opioid-Sparing Treatment for Acute Headache in Aneurysmal Subarachnoid Hemorrhage): A Phase II, Multicenter, Randomized, Double-Blinded, Placebo-Controlled Clinical Trial with a Sequential Parallel Comparison Design.

Acute post-subarachnoid hemorrhage (SAH) headaches are common and severe. Management strategies for post-SAH headaches are limited, with heavy reliance on opioids, and pain control is overall poor. Pterygopalatine fossa (PPF) nerve blocks have shown promising results in treatment of acute headache, including our preliminary and published experience with PPF-blocks for refractory post-SAH headache during hospitalization. The BLOCK-SAH trial was designed to assess the efficacy and safety of bilateral PPF-blocks in awake patients with severe headaches from aneurysmal SAH who require opioids for pain control and are able to verbalize pain scores. BLOCK-SAH is a phase II, multicenter, randomized, double-blinded, placebo-controlled clinical trial using the sequential parallel comparison design (SPCD), followed by an open-label phase. Across 12 sites in the United States, 195 eligible study participants will be randomized into three groups to receive bilateral active or placebo PPF-injections for 2 consecutive days with periprocedural monitoring of intracranial arterial mean flow velocities with transcranial Doppler, according to SPCD (group 1: active block followed by placebo; group 2: placebo followed by active block; group 3: placebo followed by placebo). PPF-injections will be delivered under ultrasound guidance and will comprise 5-mL injectates of 20mg of ropivacaine plus 4mg of dexamethasone (active PPF-block) or saline solution (placebo PPF-injection). The trial has a primary efficacy end point (oral morphine equivalent/day use within 24h after each PPF-injection), a primary safety end point (incidence of radiographic vasospasm at 48h from first PPF-injection), and a primary tolerability end point (rate of acceptance of second PPF-injection following the first PPF-injection). BLOCK-SAH will inform the design of a phase III trial to establish the efficacy of PPF-block, accounting for different headache phenotypes.

An adjoint Green’s function approach for thermoacoustic instabilities in a duct with mean flow

Thermoacoustic instabilities arise from the feedback between an acoustic field and the unsteady heat released in a burner, yielding self-sustained oscillations. A fundamental framework for modelling thermoacoustic instabilities in systems where a mean flow is present is introduced, based on the definition of the adjoint Green’s function which permits to convert the acoustic analogy equation into an integral equation. The adjoint Green’s problem produces sensitivity functions which quantify the response of the system to initial, boundary or other forcing terms. A simple one-dimensional system is examined; it includes a steady uniform mean flow and a nonlinear heat source with an amplitude-dependent time-delay heat release model. The versatility of the approach is demonstrated by applying it to two resonators characterized by different acoustic boundary conditions: a Rijke tube and a quarter-wave resonator. The control parameters are: heat source position, heater power and tube length. The results reveal that the proposed analytical framework successfully captures the limit cycles, triggering phenomena, hystereses, and Hopf bifurcations observed in experiments. We show that the mean flow velocity cannot be discarded in the study of such systems; by increasing it, a stabilization generally ensues, with a modification of the bistability characteristics of the system.