Bulk Displacement Research Articles

Rheological Compatibility of a Hardening Spacer Fluid and Oil-Based Drilling Fluid

Summary In the placement process of the cement slurry, treatment fluids such as the spacer are pumped ahead of the cementitious slurry to minimize the contamination of the slurry by drilling fluid and ensure superior bonding to the casing and formation. The spacer discussed in this work can harden with time and act as a settable spacer. This characteristic can be an advantage for well integrity if some spacer pockets are left in the annulus. Rheological compatibility of different mixtures of the spacer with oil-based drilling fluid (OBDF) has been studied using a rheometer, and the resulting R-factor, which indicates the degree of compatibility between fluids, has been calculated. An increase in the flow curve was observed for the mixture of the fluids. However, based on the R-index, these fluids are compatible with displacement in the wellbore. A nonionic surfactant, typically used in conventional spacers acting as an emulsifier and a water-wetting agent, was used in the hardening spacer design. The results show that the addition of OBDF to hardening spacer containing surfactant can increase viscoelasticity. Hardening spacer containing surfactant can successfully reverse the OBDF emulsion. By performing a small-scale mud displacement experiment, we observed that surfactant can improve the wall cleaning efficiency of the spacer while having minimal impact on the bulk displacement.

Molecular dynamics study of primary damage in the near-surface region in nickel

We carried out a large-scale molecular dynamics (MD) simulation to study displacement cascades in the near-surface region in pure nickel. These MD simulations were performed both in the bulk and near-surface regions with primary knock-on atom (PKA) energies of EPKA=1,5, or 10keV and at temperatures T=300,425, or 525K. In our study, the primary knock-on atom was taken to be created by a neutron knocking off a lattice atom. Accordingly, cascades were initiated by giving a lattice atom the appropriate velocity corresponding to the PKA energy. Assuming isotropic neutron fluence, the PKA was initiated in random directions (including toward and parallel to the free surface) in both bulk and near-surface simulations. This contrasts with previous studies in which the cascades were initiated by the projectiles directed toward the free surface to mimic ion irradiation. Therefore, for every (T,EPKA), near-surface cascade simulations were performed also as a function of PKA's initiation depth. Present results provide quantitative information about defect production and clustering in the primary damage state for near-surface and bulk displacement cascades. The effect of EPKA and T on the defect production (averaged over all PKA directions) is similar for both the near-surface and bulk cascades. In both cases, the defect production increases with EPKA, but the temperature has minimal effect. However, the production and clustering of vacancies are higher for near-surface cascades. In contrast, the production and clustering of self-interstitial atoms are lower and increase monotonically with depth. The decrease in the average number of vacancies and average vacancy cluster size with increasing depth is not monotonic.

Surface roughness measurement for the assessment of damage dynamics of existing and upgraded cube-armored breakwaters

Behavior of existing or upgraded rubble-mound breakwaters with non-conventional geometry, layering and surface porosity may be quite different from what predicted by state-of-art design approaches, and traditional techniques for damage estimation may be not sufficient. In the present work, a novel SfM-based technique for the analysis of damage mechanisms of cube-armored breakwaters is proposed, which is based on the evaluation of descriptors of the macro and micro-roughness of the armor layer. The first one represents the waviness of the armor slope, whereas the latter one is a proxy of the armor layer surface porosity. A systematic experimental investigation was performed, considering different upgrading options for a harbor rubble-mound breakwater with cube-shaped armor units, which involve, besides the rise of the wave wall, the addition of extra armor blocks similar or smaller than the existing ones. Damage measurements acquired through traditional laboratory techniques were combined with the armor surface roughness descriptors. The results of the novel analysis of the cube armor layer macro-roughness revealed that the processes which cause the displacement of the outer blocks are influenced by the level of waviness of the armor slope. Moreover, the quantitative analysis of the micro-roughness enabled the automated identification of four damage mechanisms experienced by the outer armor layer: (i) static equilibrium; (ii) incipient instability; (iii) bulk displacement; (iv) individual displacements. The use of the proposed roughness parameters makes simple and immediate the quantitative comparison between the performances of different upgrading solutions. • A novel SfM-based damage analysis technique for cube-armored breakwaters is proposed. • The armor layer surface is described through non-dimensional roughness descriptors. • Experimental data on upgraded structures are compared to the predictions of state-of-art. • The armor slope waviness significantly influences the stability of the upper layers. • Four damage mechanisms are identified as a function of a new roughness parameter.

Non-Invasive Optical Characterization of Tissue Hemodynamics in Sickle Cell Patients Undergoing Treatment with Isoquercetin

Sickle Cell Disease (SCD) is an inherited hemoglobin disorder which causes a mutation in the β subunit of hemoglobin (HbA), thus producing hemoglobin S (HbS) (Williams and Thein, 2018). When HbS is deoxygenated, red blood cells (RBC) can polymerize, which promotes increased rigidity and microvascular occlusions. The presence of mutated HbS increases the likelihood of recurrent venous thromboembolism (VTE). There is an unmet need for real-time, non-invasive methods of assessing microvascular hemodynamics and endothelial dysfunction. Near-Infrared Spectroscopy (NIRS), is a non-invasive, optical technique which measures tissue absorption and scattering between 650-1100 nm in subcutaneous tissue. NIRS has the capability to quantitatively measure the concentration of oxy- and deoxy- hemoglobin as well as blood flow. To determine the sensitivity of NIRS to changes in hemodynamics in SCD patients, we evaluated a cohort of SCD patients undergoing treatment with Isoquercetin (IQ), a flavonoid antithrombotic agent, and correlated the findings with D-dimer, a marker for blood clot degradation. We recruited a sub-cohort of 17 of 46 patients participating in a randomized, double-blind, placebo-controlled trial of IQ and performed an optical hemodynamic assessment at baseline and 4 weeks post-treatment. We used the commercial, multi-modal NIRS device (MetaOx, ISS Inc) which combines frequency-domain NIRS (FD-NIRS) and diffuse correlation spectroscopy (DCS) to acquire optical markers of tissue composition and blood flow, respectively. NIRS testing included resting baseline measurements and a brachial cuff occlusion. As seen in Figure 1A, a blood pressure cuff was wrapped around the bicep and the NIRS probe was placed on the ipsilateral forearm muscle. The challenge consisted of a 3-minute baseline, 3-minute cuff occlusion at 200 mmHg, and a 3-minute recovery. The decay constant τc of the intensity autocorrelation function g2(τ), which is an indicator of the bulk displacement of scattering particles (i.e. RBCs) in the forearm, was fitted from the DCS data. We compared the mean τc during the last 30s of the occlusion to D-dimer levels for all 17 patients at baseline and at 4 weeks follow up. Following a data quality review, 8 patients had NIRS data for baseline and follow up visits. D-dimer levels were 1.875 mcg/mL ± 0.869 mcg/mL at baseline and 1.449 mcg/mL ± 0.874 mcg/mL at 4 weeks follow up. Among the 8 patients with good quality data, 5/8 showed an average decrease in τc by 0.424 ms at 4 weeks follow up and an average decrease in D-dimer levels by 0.768 mcg/mL. The patient in Figure 1B showed 42.0% decrease in τc and 46.6% decrease in D-dimer levels from baseline to 4 weeks follow up. 2/8 patients showed an increase in τc by an average of 0.139 ms and an average increase in D-dimer levels by 0.320 mcg/mL. 1/8 patient showed a decrease in the τc with no change in D-dimer levels. We found that 7/8 patients with baseline and follow up visits had matching trends between D-dimer levels and τc. As demonstrated, a larger τc signified less movement of scattering particles, such as RBCs, due to increased blood coagulation. The remaining 9/17 patients had data from one visit of acceptable quality and were excluded from this analysis. The results of this initial analysis demonstrate autocorrelation decay time could be a promising metric that is reflective of blood coagulation and rheology. While this analysis focused on the changes observed in optical blood flow markers, further work will be performed to both expand upon this analysis and to integrate the compositional data acquired from the FD-NIRS portion of the measurements. NIRS can potentially complement traditional blood biomarkers when assessing anti-thrombotic effects of SCD treatments, such as Isoquercetin. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Quantification of the heterogeneous effect of static and dynamic perivascular structures on patient-specific local aortic wall mechanics using inverse finite element modeling and DENSE MRI

Recent studies have highlighted the relevance of perivascular interactions on aortic wall mechanics. Most of the approaches assume static perivascular structures; however, the beating heart dynamically displaces the neighboring aorta. We develop a model to account for the effect of periaortic interactions due to static and dynamic structures by prescribing a moving elastic foundation boundary condition (EFBC) embedded into an inverse finite element algorithm using in vivo displacements from 2D displacement encoding with stimulated echoes (DENSE) MRI as target data. We applied this method at three different locations of interest, the distal aortic arch (DAA), descending thoracic aorta (DTA), and infrarenal abdominal aorta (IAA) for a total of 27 cases in healthy humans. The model reproduces the target diastole-to-systole deformation and bulk displacement of the aortic wall with median displacement errors below 0.5mm. The EFBC showed good agreement with the location of anatomical features and was consistent among individuals of similar characteristics. Results show that an energy source acting on the adventitia is required to reproduce the displacements measured at the vicinity of the heart, but not at the abdomen. The average adventitial load as a percentage of the luminal pulse-pressure was found to increase with age and to decrease along the descending aorta, from 61% at the DAA to 37% at the DTA, and 30% at the IAA. This approach offers a patient-specific method to estimate in vivo adventitial loads and aortic wall stiffness, which can bring a better understanding of normal and pathological in vivo aortic function.

358 An Anatomical Study of the Sylvian Fissure Using a Large Number of MRI Data Sets

Abstract Introduction Accurate manoeuvring of the Sylvian fissure borders to provide an optimal operating corridor is vital for minimising retraction. The anatomy of the fissure can pose technical challenges impacting the overall success of the procedure. Yaşargil previously proposed a classification distinguishing four anatomical variants correlating with surgical difficulty. We aim to utilise the open-source Human Connectome Project MRI data set to provide a computational classification of the fissure based on morphology. Method MR images of 2226 hemispheres were included in this study. Morphometrical parameters were designed and refined in MATLAB simulations. Combinations of parameters were analysed using K-Means Clustering. Results Following segmentation and removal of outliers, 1693 fissures remain for analysis. K-Means Clustering revealed three clusters with sulcal bulk displacement measure (deviation of the fissure towards the frontal or temporal lobe) and sulcal distance (width of the fissure) (silhouette score = 0.383). Conclusions Analysis of a large neuroimaging cohort suggested the existence of three weakly separated anatomical variants. We propose that looking at the quantitative scores rather than class allocation would be more informative for preoperative planning.

Hydrofracturing tests on granite samples using a true triaxial device equipped with acoustic emission sensors

We present a series of tests performed on granite samples using a true triaxial device designed and built at the Rock Mechanics Laboratory (University of A Coruña). The experiments were performed using cubic rock samples of 150 mm-edge, which were loaded to different stress conditions (σh < σh < σy < 45 MPa) on each loading axis. The device is based on a stiff steel frame that can be coupled to a servo-hydraulic testing machine that provides de vertical stress (av), while two high-pressure pumps are used to deliver the lateral stress (σh and ah). An additional high-pressure pump is used to inject the fluid (mineral oil) into the rock sample at a low constant-flow rate. The aluminium loading platens, which are bevelled at the edges to avoid interaction among adjacent faces, have holes and grooves to introduce acoustic emission sensors that allow the location of fracture propagation. The specimens were drilled using a 6 mm drill bit until reaching the geometrical centre. Then, a 1/8” (~3.18 mm) stainless steel tube is glued to the samples with epoxy. Strain measurements during the experiments were conducted using four strain gages attached to the orthogonal faces of the specimens. The system was further equipped with three LVDTs to account for the bulk displacement on each axis. Our results suggest a linear relationship between the breakdown pressure and the confining stress under hydrostatic conditions but no clear correlation in non-hydrostatic stress regime.

Fish swim water bulk displacement visualization with digital holographic interferometry.

A collimated transmission beam interferometer is used to measure the water motion provoked by the fish swimming through it. An indirect measurement of the fish motion impact in the water contained in a home-type aquarium is detected. Measurements of the whole aquarium are possible due to a large diameter collimated laser beam in the interferometer's object arm. This beam goes through the aquarium, and any perturbation inside it deflects the collimated beam. The interferometer detects a phase difference, i.e., the beam through the disturbed water undergoes different optical paths. This optical phase change was first demonstrated by means of a simple test using spherical steel marbles placed in a cuvette. For this, the small water movements for a single steel marble are detected with the acquired optical phase. Next, the aquarium optical phase results show water movements according to the fishes' size and swimming speed. It is worth mentioning that no additives were added to the aquarium's fresh water during the tests, so the water was crystal clear.

DiSpect: Displacement spectrum imaging of flow and tissue perfusion using spin‐labeling and stimulated echoes

We propose a new method, displacement spectrum (DiSpect) imaging, for probing in vivo complex tissue dynamics such as motion, flow, diffusion, and perfusion. Based on stimulated echoes and image phase, our flexible approach enables observations of the spin dynamics over short (milliseconds) to long (seconds) evolution times. The DiSpect method is a Fourier-encoded variant of displacement encoding with stimulated echoes, which encodes bulk displacement of spins that occurs between tagging and imaging in the image phase. However, this method fails to capture partial volume effects as well as blood flow. The DiSpect variant mitigates this by performing multiple scans with increasing displacement-encoding steps. Fourier analysis can then resolve the multidimensional spectrum of displacements that spins exhibit over the mixing time. In addition, repeated imaging following tagging can capture dynamic displacement spectra with increasing mixing times. We demonstrate properties of DiSpect MRI using flow phantom experiments as well as in vivo brain scans. Specifically, the ability of DiSpect to perform retrospective vessel-selective perfusion imaging at multiple mixing times is highlighted. The DiSpect variant is a new tool in the arsenal of MRI techniques for probing complex tissue dynamics. The flexibility and the rich information it provides open the possibility of alternative ways to quantitatively measure numerous complex spin dynamics, such as flow and perfusion within a single exam.

Non-equilibrium thermodynamics approach to mass transport in sorptive dual continuum porous media: A theoretical foundation and numerical simulation

Modeling gas flow in sorptive porous materials (e.g. coal) offers significant challenges compared to that of non-sorptive porous media (e.g. conventional hydrocarbon reservoirs). Sorption processes in the matrix, gas flow in the fractures (cleats) and induced strains in the bulk of coal interact in a coupled manner, affecting the sorption, mechanical and hydraulic characteristics of the media. Despite extensive research on constitutive models that take into account the coupling processes in gas sorbing systems, these developed constitutive models are often phenomenological and thermodynamically inconsistent (violate thermodynamic laws). The models developed based on equilibrium thermodynamics on the other hand are unable to capture the time dependency of coupling processes. We, therefore, use the non-equilibrium thermodynamics along with continuum mechanics to derive a thermodynamically consistent formulation for the constitutive equations of mechanical, hydraulic and sorption processes in gas sorbing media considering the time dependency of the involved coupling processes. The model, also referred to as NETCoal in this study, considers changes in gas content in the tight coal matrix through sorption and diffusion processes along with gas leakage from the matrix into fractures (cleats) where Darcy type flow takes place. The model also accounts for the time dependency of coupling processes especially the volumetric strains induced by gas sorption and their overall effects on changes in the fracture aperture, hence in the bulk flow conductivity. The finite element method is then employed to discretize and solve the set of governing equations for the bulk displacement (and stress), the gas pressure in coal fractures and the gas content in the matrix. Simulation results are analyzed based on conceptualized cases with input data from a coal seam located in eastern Australia. We also present a parametric study to demonstrate the sensitivity of results to main coupling parameters.

Novel Surface Mechanomyography Sensor Assessment Of Hamstrings Contraction During A Neuromuscular Control Screening Task

PURPOSE: Hamstring strain is a common injury among athletes. Asymmetries in muscle balance and activation are potential injury risk factors. Surface mechanomyography (sMMG) sensors are wearable devices that when applied across a muscle group provide a novel measurement of physical muscle output during a contraction. The purpose of this study is to assess 1) the relationship of sMMG’s muscle bulk displacement measurement to force generation and 2) sMMG detection of hamstrings contraction timing compared to the clinical standard method of electromyography (EMG). METHODS: Healthy, active individuals (mean age= 30.0 ±10.77 y, n=9, 6 males, 3 females) underwent hamstrings neuromuscular control assessment with simultaneous recording of EMG and sMMG by sensors applied to the right hamstrings. Subjects performed a series of 3 resisted “make-test” isometric hamstring curls against a hand-held dynamometer (HHD). Raw sMMG data and 6th order Butterworth filter and TKEO processed EMG data were used in timing analyses. Paired T-tests and a Pearson correlation assessed relationships between measurement modalities. RESULTS: Peak hamstrings muscle bulk displacement detected by sMMG (mean= 4.02 ±1.04 mm) positively correlated with HHD maximum force generation (mean= 28.84 ±12.13 lb), r2= 0.850. There was no significant difference in the timing duration of muscle contraction between EMG (mean= 4.443 ±0.573 s) and sMMG (mean= 4.469 ±0.623 s), p= 0.279. CONCLUSIONS: Results are consistent with physiologic expectations that increased physical muscle bulk displacement during a contraction is associated with greater force. Similarity in time signatures with EMG support findings of successful sMMG detection of hamstrings contraction (Figure 1). The sMMG sensor may be helpful for assessing hamstrings muscle performance of both force output and timing as part of neuromuscular control screening for injury prevention, rehabilitation monitoring, or return-to-sport readiness.

Relationship of Surface Mechanomyography to Force Production in an Assessment of Gastrocnemius Muscle Contraction

PURPOSEEfficient gastrocnemii force production is essential for performance of functional activities such as stair ascent/descent and athletic activities involving jumping or running. Appropriate neuromuscular control and timing of gastrocnemius contraction is also important for fatigue and injury prevention. Hand Held Dynamometry (HHD) is the clinical standard for assessing force production during a muscle contraction. However, HHD is unable to provide precise timing data on the muscle activation responsible for force generation or monitor fatigue during an activity. Surface mechanomyography (sMMG) sensors are novel wearable devices that can be applied across a muscle group to provide a measurement of physical muscle output during a contraction. The purpose of this study is 1) to assess the relationship of sMMG’s muscle bulk displacement measurement to force generation and 2) to confirm sMMG detection of gastrocnemius contraction compared to the clinical timing standard of electromyography (EMG).METHODSHealthy, athletic individuals (mean age= 32.56 ±10.57 y, n= 9, 7 males, 2 females) underwent a neuromuscular control assessment of the gastrocnemius. Subjects performed a series of 3 resisted “make‐test” isometric holds with the right leg supported on an exam table and the ankle plantar flexed at 90 degrees against a hand‐held dynamometer with simultaneous EMG and sMMG recording. The third trial was selected for analysis when available. EMG data was processed with a 6th order low‐pass Butterworth filter and a Teager‐Kaiser energy operator function. A threshold for detecting the time points of gastrocnemius activation and deactivation was set at 3 standard deviations of a resting calibration trial above the minimum value for each measurement modality. The relationship of sMMG signal output for physical muscle displacement was compared to muscle contraction force output via HHD and timing measured via EMG using paired T‐tests and a Pearson correlation.RESULTSPeak gastrocnemius muscle bulk displacement detected by sMMG (mean= 7.65 ±2.68 mm) positively correlated with maximum force generation detected by HHD during isometric contraction (mean= 58.43 ±13.12 lb), r2= 0.669. The duration of gastrocnemius muscle contraction during the isometric hold activity did not differ significantly between SMG (mean= 4.71 ±1.17 s) and EMG (mean= 4.53 ±1.17 s), p= 0.273.CONCLUSIONSCorrelation between HHD and sMMG support the findings that increased physical muscle bulk displacement of the gastrocnemius was associated with greater force production during a contraction. The similarity to EMG timing reinforces the ability of the sMMG sensor to consistently detect active gastrocnemius contraction without complex signal processing (Figure 1). sMMG sensors may be a useful measurement tool for assessment of gastrocnemius functional performance during neuromuscular control screenings for injury prevention and rehabilitation.Example comparison of signal output during a resisted isometric gastrocnemius hold between a hand‐held dynamometer [HHD, (A)], surface mechanomyography [sMMG, (B)], and electromyography [EMG, (C)]. Greenand redXs indicate calculated muscle activation and deactivation time points based on 3 standard deviations of a resting calibration trial above the minimum for each modality (Solonik et al., 2010).Figure 1

An equation for the isosbestic point wavelength in aqueous solutions of electrolytes

The existence of an isosbestic point in the OH bond vibration band of H2O molecules in solutions of strong electrolytes has been shown by many research groups but its physical meaning has been only recently read as the equilibrium point between two populations of water molecules where either water-ion or water-water interactions respectively prevail. Thus the isosbestic point provides useful information on the bulk displacement of water molecules in presence of solutes. Herein we show that the isosbestic point occurrence is correctly described by an equation describing the balance of the electrostatic forces. Furthermore, its wavelength is also related to the slope of the density vs. the solute concentration. These results support the view that the effect of the solute can be barely regulated within few hydration shells.

On the Performance of Time Domain Displacement Estimators for Magnetomotive Ultrasound Imaging.

In magnetomotive (MM) ultrasound (US) imaging, magnetic nanoparticles (NPs) are excited by an external magnetic field and the tracked motion of the surrounding tissue serves as a surrogate parameter for the NP concentration. MMUS procedures exhibit weak displacement contrasts due to small forces on the NPs. Consequently, precise US-based displacement estimation is crucial in terms of a sufficiently high contrast-to-noise ratio (CNR) in MMUS imaging. Conventional MMUS detection of the NPs is based on samplewise evaluation of the phase of the in-phase and quadrature (IQ) data, where a low signal-to-noise ratio (SNR) in the data leads to strong phase noise and, thus, to an increased variance of the displacement estimate. This paper examines the performance of two time-domain displacement estimators (DEs) for MMUS imaging, which differ from conventional MMUS techniques by incorporating data from an axial segment. The normalized cross correlation (NCC) estimator and a recursive Bayesian estimator, incorporating spatial information from neighboring segments, weighted by the local SNR, are adapted for the small MMUS displacement magnitudes. Numerical simulations of MM-induced, time-harmonic bulk and Gaussian-shaped displacement profiles show that the two time-domain estimators yield a reduced estimation error compared to the phase-shift-based estimator. Phantom experiments, using our recently proposed magnetic excitation setup, show a 1.9-fold and 3.4-fold increase of the CNR in the MMUS images for the NCC and Bayes estimator compared to the conventional method, while the amount of required data is reduced by a factor of 100.

Directional Water Collection in Nanopore Networks.

The development of artificial nanosystems that mimic directional water-collecting ability of evolved biological surfaces is eagerly awaited. Here we report a new type of addressable water collection that is induced by coupling both vapor gradients, like a road drawn, and the temperature-tuned condensation in nanopores as step signals. What distinguishes the motion described here from the motions reported earlier is the fact that neither bulk liquid infiltration nor displacement of droplet is required. Instead, the motion results from a scanned water capture because of the temperature-dependent condensation command acting on the vapor pressure gradient track originated by a droplet without a bulk fluidic connection with a mesoporous film. This novel working principle demands only a small-range surface temperature control, which was entirely generated by a thermoelectric cell integrated to the mesoporous substrates. The strategy opens the route to achieving precise control over wetting location (from a few to hundreds of micrometers) and hence over the direction of water collected by these widely employed nanomaterials. Furthermore, as water is collected from condensation into the pores, the system naturally involves purification and subsequent delivery of clean water, which provides an added value to the proposed strategy.

Dynamic Gradients, Mobile Layers, Tg Shifts, Role of Vitrification Criterion, and Inhomogeneous Decoupling in Free-Standing Polymer Films

The force-level Elastically Collective Nonlinear Langevin Equation theory of activated relaxation in glass-forming free-standing thin films is re-visited to improve its treatment of collective elasticity effects. The naive cut off of the isotropic bulk displacement field approximation is improved to explicitly include spatial anisotropy with a modified boundary condition consistent with a step function liquid-vapor interface. The consequences of this improvement on dynamical predictions are quantitative but of significant magnitude and in the direction of further speeding up dynamics and further suppressing Tg. The theory is applied to thin films and also thick films to address new questions for three different polymers of different dynamic fragility. Variation of the vitrification time scale criterion over many orders of magnitude is found to have a minor effect on changes of the film-averaged Tg relative to its bulk value. The mobile layer length scale grows strongly with cooling and correlates in a nearly linear manner with the effective barrier deduced from the corresponding bulk isotropic liquid alpha relaxation time. The theory predicts a new type of spatially inhomogeneous "dynamic decoupling" corresponding to an effective factorization of the total barrier into its bulk temperature-dependent value multiplied by a function that only depends on location in the film. The effective decoupling exponent grows as the vapor surface is approached. Larger reductions of the absolute value of Tg shifts in thin polymer films are predicted for longer time vitrification criteria and more fragile polymers. Quantitative no-fit-parameter comparisons with experiment and simulation for film-thickness-dependent Tg shifts of PS and PC are in reasonable accord with the theory, including a nearly 100 K suppression of Tg in 4 nm PC films. Predictions are made for polyisobutylene thin films.

Cardiac-Related Spinal Cord Tissue Motion at the Foramen Magnum is Increased in Patients with Type I Chiari Malformation and Decreases Postdecompression Surgery

Type 1 Chiari malformation (CM-I) is a craniospinal disorder historically defined by cerebellar tonsillar position greater than 3-5 mm below the foramen magnum (FM). This definition has come under question because quantitative measurements of cerebellar herniation do not always correspond with symptom severity. Researchers have proposed several additional radiographic diagnostic criteria based on dynamic motion of fluids and/or tissues. The present study objective was to determine if cardiac-related craniocaudal spinal cord tissue displacement is an accurate indicator of the presence of CM-I and if tissue displacement is altered with decompression. A cohort of 20 symptomatic patients underwent decompression surgery. Fifteen healthy volunteers were recruited for comparison with the CM-I group. Axial phase-contrast magnetic resonance imaging (PC-MRI) measurements were collected before and after surgery at the FM with cranial-caudal velocity encoding and 20 frames per cardiac cycle with retrospective reconstruction. Spinal cord motion (SCM) at the FM was quantified based on the peak-to-peak integral of average spinal cord velocity. Tissue motion for the presurgical group was significantly greater than controls (P= 0.0009). Motiondecreased after surgery (P= 0.058) with an effect size of-0.151 mm and a standard error of 0.066 mm. Postoperatively, no statistical difference from controls in bulk displacement at the FM was found (P= 0.200) after post hoc testing using the Tukey adjustment for multiple comparisons. These results support SCM measurement by PC-MRI as a possible noninvasive radiographic diagnostic for CM-I. Dynamic measurement of SCM provides unique diagnostic information about CM-I alongside static quantification of tonsillar position and other intracranial morphometrics.

Towards precision constraints on gravity with the Effective Field Theory of Large-Scale Structure

We compare analytical computations with numerical simulations for dark-matter clustering, in general relativity and in the normal branch of DGP gravity (nDGP). Our analytical frameword is the Effective Field Theory of Large-Scale Structure (EFTofLSS), which we use to compute the one-loop dark-matter power spectrum, including the resummation of infrared bulk displacement effects. We compare this to a set of 20 COLA simulations at redshifts z = 0, z = 0.5, and z = 1, and fit the free parameter of the EFTofLSS, called the speed of sound, in both ΛCDM and nDGP at each redshift. At one-loop at z = 0, the reach of the EFTofLSS is kreach ≈ 0.14 Mpc−1 for both ΛCDM and nDGP. Along the way, we compare two different infrared resummation schemes and two different treatments of the time dependence of the perturbative expansion, concluding that they agree to approximately 1% over the scales of interest. Finally, we use the ratio of the COLA power spectra to make a precision measurement of the difference between the speeds of sound in ΛCDM and nDGP, and verify that this is proportional to the modification of the linear coupling constant of the Poisson equation.

Effect of void arrangement on ductile damage mechanisms in nodular graphite cast iron: In situ 3D measurements

The effect of the arrangement of two artificial voids on void growth and coalescence mechanisms is studied in flat specimens made of nodular graphite cast iron via in situ 3D laminography imaging and digital volume correlation for bulk displacement measurement. Two configurations of machined holes are studied (i) 90° with respect to the loading direction to mimic internal necking, and (ii) 45° to attempt to trigger a void sheeting mechanism between the artificial voids. The machined holes play the role of primary voids, the graphite nodules that of secondary voids. At a lower scale there is a smaller third population of voids. The 45° void orientation successfully causes a shear band between the primary voids. However, the growth and coalescence mechanisms of voids from graphite nodules are similar for the two configurations. Internal necking is found for nodules that are close to each other and void sheeting for large ferrite ligaments between nodules. Strain fields in the region between machined holes show necking for both cases as well as volume increase, i.e., positive trace of the strain tensor, confirmed by image analysis. The strain to failure in this inter-void region is evaluated in the bulk and also locally, between nodules and for different coalescence configurations. Similar levels are observed in both cases.

Bulk phase Behavior and displacement performance of CO2 foam induced by a combined foaming formulation

To overcome the viscous fingering and gravity segregation of CO2 flooding, a combined foaming formula (AOS/AVS/N70K-T) was proposed and compared with two well-known foaming formulas (i.e. AOS alone and AOS/HPAM). The assessment results indicated: 1) the proposed AOS/AVS/N70K-T noticeably balanced the foamability and foam stability in a reasonable manner (the foamability is larger than 500ml and the foam stability is greater than 2000s); 2) its apparent viscosity in high permeability rocks could increase by 36.3% compared to that in low permeability rocks; 3) the foam generated by direct injection mode endowed better blockage than the co-injection of the gas or solution, which could be validated by the investigations of the resistance factor (RF) and residual resistance factor (RRF); 4) the mobility reduction factor (MRF) of the AOS/AVS/N70K-T foam achieved the optimal value at an intermediate total gas/solution flow rate (with fixed gas/liquid ratio of 3:1), while its MRF dropped as gas flow rate rose. 5) The proposed formula displayed pronounced advantages over the other two foaming formulations in all of the respects mentioned above. Through the extensive studies, it is believed that the new formula combination might possess huge potential applications in CO2 Enhanced Oil Recovery (EOR).