Localized Necking Research Articles

The effect of head and neck per-cooling on neuromuscular fatigue following exercise in the heat.

The effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON; 18 °C), hot (HOT; 35 °C), and HOT with head and neck cooling (HOTcooling). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOTcooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C; P < 0.05). Head and neck thermal sensation was similar in HOTcooling (4.2 ± 1.4) and CON (4.4 ± 0.9; P > 0.05) but lower than HOT (5.9 ± 1.5; P < 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P < 0.05). MVF and CAR were also lower in HOTcooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P > 0.05). Furthermore, they were greater in HOTcooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.

Abstract PR13: Comprehensive detection of ctDNA in localized head and neck cancer by genome- and methylome-based analysis

Abstract Head and neck squamous cell carcinoma (HNSCC) comprises 3% of all cancer cases worldwide. Despite intensive multimodal therapies, HNSCC patient outcomes remain heterogeneous with minimal improvements in survival. Utilization of fluid-based biomarkers for prognostication, risk stratification, and disease surveillance may improve patient outcomes by enabling more effective treatment decisions. Here, we describe the performance of comprehensive mutation and methylome analysis for highly sensitive detection of circulating tumor (ct)DNA in HNSCC plasma. To detect HNSCC-specific mutations and aberrant methylation in ctDNA, we conducted CAPP-Seq (CAncer Personalized Profiling by deep Sequencing) and cfMeDIP-seq (cell-free Methylated DNA ImmunoPrecipitation sequencing), respectively. For CAPP-Seq, we developed a HNSCC-specific hybrid capture panel and applied it to plasma DNA and peripheral blood leukocyte (PBL) genomic DNA from a cohort of HNSCC patients (n=32) and healthy controls (n=20). Single-nucleotide variants (SNVs) were identified by integrated digital error suppression (iDES). For cfMeDIP-seq, hypermethylated differentially methylated regions within regions of low PBL methylation were identified by DESeq2. A median of 3 mutations (range: 1-10) were detected by CAPP-Seq within plasma DNA of 20/32 (62.5%) HNSCC patients. Mean mutant allele frequency ranged from 0.1–5% (median: 0.92%) and correlated with tumor stage. Among these 20 patients, cfMeDIP-seq identified 860 DMRs that were enriched (hypermethylated) in HNSCC plasma DNA compared with healthy controls. These hypermethylated DMRs (hyper-DMRs) were over-represented by CpG islands and gene promoters and showed significant overlap with HNSCC-specific methylated regions in TCGA. When applied to all 32 HNSCC patients, hyper-DMR abundance was positively correlated with mutation-based ctDNA abundance (R=0.87; p=1e−16). Hyper-DMRs were capable of accurate discrimination of HNSCC patients and healthy controls (AUC=0.85). The median DNA fragment size within these hyperDMRs was lower in HNSCC patients compared to healthy controls—a characteristic of ctDNA described in previous studies—and correlated with both hyperDMR-based and mutation-based ctDNA abundance. We have conducted the first comparative analysis of genetic and epigenetic profiling approaches for ctDNA detection in HNSCC. Both CAPP-Seq and cfMeDIP-seq have the potential to detect ctDNA in patient plasma without prior knowledge of patient-specific tumor aberrations. With CAPP-seq, ctDNA was detectable at levels as low as 0.1%. Plasma methylome profiling using cfMeDIP-seq revealed hyper-DMRs with tumor-related features and that correlated with mutation-based ctDNA abundance. Future analysis will validate patient-specific mutations and methylation signals in tumor tissue and in longitudinally collected samples from this cohort. This abstract is also being presented as Poster B47. Citation Format: Justin M. Burgener, Jinfeng Zou, Zhen Zhao, Shu Y. Shen, Daniel D. De Carvalho, Scott V. Bratman. Comprehensive detection of ctDNA in localized head and neck cancer by genome- and methylome-based analysis [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr PR13.

An analytical model for necking strains in stretched plates under dynamic biaxial loading

A model for the prediction of localised necking in plates subjected to dynamic biaxial loading is presented. The proposed model extends the classic two-zone localisation analysis introduced by Marciniak and Kuczyński (1967) to include the contribution of inertia. Several examples of computations are presented to illustrate the influence of inertia, material rate-dependence and yield surface shape on plate necking under dynamic biaxial loading. It is found that inertia may significantly delay the occurrence of localised necking and increase the apparent ductility of the material. The results of the proposed model are compared to those of three-dimensional finite element simulations and a very good agreement is observed.

Formability prediction of substrate-supported metal layers using a non-associated plastic flow rule

When manufacturing flexible devices, it is quite common that localized necking appears due to the low ductility of the metal sheets used. To delay the inception of such localized necking, several industrial companies have proposed a promising technical solution based on the bonding of elastomer substrates to the metal sheets used in the manufacturing processes. In this context, the comprehensive numerical understanding of the impact of such substrate coating on the improvement of the ductility of elastomer-supported metal layers still remains a challenging goal. To achieve this goal, the bifurcation approach as well as the Marciniak and Kuczynski model are used to predict the occurrence of localized necking. The mechanical behavior of the metal layer is modeled by a non-associated anisotropic plasticity model. The adoption of non-associated plastic flow rule allows separating the description of the plastic potential from that of the yield function, which is essential to accurately model strong plastic anisotropy characterizing cold-rolled sheets. As to the elastomer substrate, its mechanical behavior is described by a neo-Hookean law. The paper presents a variety of numerical results relating to the prediction of plastic strain localization in both freestanding and elastomer-coated metal layers. The effects of the non-associativity of the plastic flow rule for the metal layer and the addition of an elastomer substrate on the predictions of localized necking are especially underlined. It is shown that the ductility limits predicted by the non-associated elasto-plastic model are lower than their counterparts determined by an associated plasticity model. It is also proven that adhering an elastomer layer to the metal layer can substantially delay the initiation of plastic strain localization.

Temporal and Spatial Detection of the Onset of Local Necking and Assessment of its Growth Behavior.

This study proposes a method for the temporal and spatial determination of the onset of local necking determined by means of a Nakajima test set-up for a DC04 deep drawing and a DP800 dual-phase steel, as well as an AA6014 aluminum alloy. Furthermore, the focus lies on the observation of the progress of the necking area and its transformation throughout the remainder of the forming process. The strain behavior is learned by a machine learning approach on the basis of the images when the process is close to material failure. These learned failure characteristics are transferred to new forming sequences, so that critical areas indicating material failure can be identified at an early stage, and consequently enable the determination of the beginning of necking and the analysis of the necking area. This improves understanding of the necking behavior and facilitates the determination of the evaluation area for strain paths. The growth behavior and traceability of the necking area is objectified by the proposed weakly supervised machine learning approach, thereby rendering a heuristic-based determination unnecessary. Furthermore, a simultaneous evaluation on image and pixel scale is provided that enables a distinct selection of the failure quantile of the probabilistic forming limit curve.

Use of localized necking and fracture as a failure criterion in ship collision analysis

This study explores the use of localized necking for failure modeling in maritime crash analysis, using large shell elements. The assumption that the failure of a large shell element occurs simultaneously with the onset of localized necking is revisited. This study particularly investigates the numerical implementation of the localized necking condition and its implications on the results of ship collision analysis involving not only plate rupture but also various failure mechanisms such as the crushing and tearing of web girders, stringers, and their intersections. Through a series of large-scale collision simulations, the effects of bending deformation on the initiation of necking, non-proportional loading paths, and ductile fractures not preceded by localized necking, are investigated. It is demonstrated that a localized necking-based fracture model provides a reasonable, relatively mesh-insensitive estimate of the onset of fracture in the outer hull panels; however, fracture propagation is very sensitive to the numerical implementation of the necking and fracture model, especially for the cases involving the crushing of web frames and stringers.

Microstructural Contributions of Different Polyolefins to the Deformation Mechanisms of Their Binary Blends.

The mixing of polymers, even structurally similar polyolefins, inevitably leads to blend systems with a phase-separated morphology. Fundamentally understanding the changes in mechanical properties and occurring deformation mechanisms of these immiscible polymer blends, is important with respect to potential mechanical recycling. This work focuses on the behavior of binary blends of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) under tensile deformation and their related changes in crystallinity and morphology. All of these polymers plastically deform by shear yielding. When unmixed, the high crystalline polyolefins HDPE and PP both exhibit a progressive necking phenomenon. LDPE initiates a local neck before material failure, while LLDPE is characterized by a uniform deformation as well as clear strain hardening. LLDPE/LDPE and LLDPE/PP combinations both exhibit a clear-cut matrix switchover. Polymer blends LLDPE/LDPE, LDPE/HDPE, and LDPE/PP show transition forms with features of composing materials. Combining PP in an HDPE matrix causes a radical switch to brittle behavior.

Mechanical response and microstructure evolution of commercially pure titanium subjected to repetitive bending under tension

The aim of this work was to study the cold formability of commercially pure Titanium alloy (Grade 2) by a testing methodology known as repetitive bending under tension (R-BUT). A dedicated test rig to perform the test was designed and fabricated to analyse the room temperature deformation behaviour of Ti-50A alloy sheet of 1.2 mm thickness. Samples from three different orientations were tested to investigate the effect of mechanical anisotropy on deformation behaviour. The results confirmed a significant increase in elongation to failure in samples subjected to R-BUT as compared to those subjected to standard tensile tests under similar conditions. This may be due to a delay in localised necking during R-BUT. Finite element analysis (FEA) suggested that a decrease in stress triaxiality in R-BUT could be the reason for enhanced formability of the materials compared to the conventional tension. Furthermore, electron backscatter diffraction (EBSD) study of the microstructure confirmed the development of highly strained regions that eventually lead to the formation of fine grains in the samples subjected to R-BUT. This could be due to a strain induced dynamic recovery process occurring during the test.

MicroRNA Expression Profiling of Cutaneous Squamous Cell Carcinomas Arising in Different Sites.

To examine the microRNA (miRNA) expression profile of cutaneous squamous cell carcinoma (cSCC) tumors from aggressive head and neck locations compared with nonaggressive anatomic sites and normal controls. Retrospective analysis of miRNA expression. Tertiary care center. Tissue samples were collected from 3 anatomic regions: aggressive head and neck sites (ie, ears/lip), nonaggressive locations (ie, extremities/trunk), and adjacent normal skin. RNA was isolated from tissue cores of 45 samples (18 aggressive sites, 15 nonaggressive sites, and 12 normal-adjacent skin). miRNA expression analysis was completed for approximately 800 miRNAs using the NanoString nCounter panel. Five candidate miRNAs were selected for validation. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed on the original samples plus 30 additional tissue samples (7 aggressive sites, 14 nonaggressive sites, and 9 normal-adjacent skin). Five candidate miRNAs with significant differences in miRNA expression (P < 0 ≤ .001) from discovery samples were selected: miR-21, miR-31, let-7g, miR-93, and miR-22. Relative expression for these miRNAs using qRT-PCR in the new sample set did not reveal any significant differences using 1-way analysis of variance. When sets were combined, miR-21 showed increased expression in aggressive tumors relative to nonaggressive tumors (P = .009), but no others reached statistical significance. cSCC behaves more aggressively when originating from specific anatomical subsites of the head and neck. Of 5 miRNAs evaluated, only miR-21 showed significantly higher expression in tumors from aggressive sites relative to nonaggressive sites. Larger sample sizes are needed to evaluate other miRNAs.

Examining Failure Behaviour of Commercially Pure Titanium During Tensile Deformation and Hole Expansion Test

Hole expansion ratio is a material parameter which defines the extent to which sheet metals are formed. Research has shown that, the stress state observed at the hole edge after hole expansion test is similar to those observed during conventional uniaxial tensile test. However, conventional tensile test methods are not efficient in evaluating material edge formability. This work utilised optical non-contact measuring techniques to examine failure behaviour during tensile test and hole expansion test of commercially pure titanium sheet, fabricated with either abrasive water jet cutting or electric discharge machining. The work found that, the deformation mode in conventional tensile testing are governed by localised necking and subsequently diffused necking prior to failure. Deformation mode observed in hole expansion test is characterised by localised necking with no visible occurrence of diffused necking prior to failure. The highest strains are concentrated at the hole edge during hole expansion test due to their sensitivity to the hole preparation method with accompanying multiple localised necking sites resulting in non-uniform deformation. Strains become concentrated in the bulk material microstructure rather than the machined edge during tensile testing resulting in single localised deformation site and a more homogenous deformation.

MON-530 Local Lymph Node Metastasis Is Less Common in RAS- Mutated Thyroid Cancer Compared to BRAFV600E- Mutated Thyroid Cancer

Introduction: Somatic mutations of RAS- and BRAFV600E- are the most common driver mutation in thyroid cancer (TC) and in the majority of cases, these are mutually exclusive1,2. Clinical characteristics of TC with either RAS or BRAFV600E mutation is not systemically studied. Methods: This is a retrospective study at the Ohio State University (OSU) from 1/2000 to 12/2018. Data were extracted from OSU Endocrine Neoplasia Repository (ENR). Medullary thyroid cancer was excluded. The treating physician determined patient management. Statistical analysis was performed with the chi-square test for categorical values and Mann-Whitney U test for continuous unpaired values. Two-sided P values of less than 0.05 were considered statistically significant. Results: Out of 320 patients, 152 patients had a positive mutational profile. Of these, 128 patients had a BRAFV600E mutation and 14 had a RAS mutation. Details of RAS mutation were as follows; NRASQ61K (n=2), NRASQ61R (n=1), HRASQ61R (n=1), HRASQ61K (n=1), NRAS without further details (n=9). Local lymph node metastasis was significantly less in RAS mutated cancer (58% vs 16%, p<0.05). Lymph node metastasis was limited to N1a in all RAS group, whereas 38% of BRAFV600E had N1b status. The number of positive lymph nodes were significantly fewer in the RAS group (mean 0.42 vs. 9.1, p=0.003). None of the patients in RAS group developed subsequent local neck recurrence, whereas 19% of BRAFV600E group developed a recurrence (p=0.05). Bone metastasis was more common in RAS compared to BRAFV600E group (21% vs 6%, p=0.04) but there were no differences in other distant metastases. Presence of extrathyroidal extension was significantly higher in BRAFV600E compared to RAS group (58 % vs 8%; p=0.04). Classic variant papillary thyroid cancer was the most common histologic diagnosis with both mutations, however, follicular-variant papillary thyroid cancer was more common in RAS than BRAFV600E group (29% vs 8%, p=0.04) and follicular thyroid cancer was only seen in the RAS group (25% vs 0%, p<0.05). There was no difference in gender, age at diagnosis, disease status after initial therapy, RAI treatment, RAI dosage, and mortality between the groups. Conclusion: Thyroid cancer associated with a RAS-mutation has less tendency to metastasize locally and has a higher incidence of bone metastasis compared to thyroid cancer with BRAFV600E-mutation. Individualized clinical follow up may be indicated depends on their mutational profile.

Sex-Specific Impact of Pain Severity, Insomnia, and Psychosocial Factors on Disability due to Spinal Degenerative Disease.

Purpose Pain experience due to spinal degenerative disease decreases activity of daily living and quality of life. The present cross-sectional study was aimed at examining the sex-specific impact of pain severity, psychosocial factors, and insomnia on the disability due to chronic pain arising from spinal degenerative disease. Methods In total, 111 outpatients with chronic spinal degenerative on initial diagnosis were analyzed. The definition of chronic spinal degenerative disease was (1) pain duration ≥3 months, (2) findings of nerve root compression on neurological examination and imaging, and (3) localized neck or lower back pain (not widespread, upper or lower limb pain). We used Numerical Rating Scale (NRS), Pain Disability Assessment Scale (PDAS), Hospital Anxiety and Depression Scale (HADS), Pain Catastrophizing Scale (PCS), and Athens Insomnia Scale (AIS) to assess patients. Univariate regression analysis was performed to investigate whether sex influences the PDAS score, and sex-stratified multivariate regression analysis was conducted to identify the variables associated with the PDAS score. Results Sex was identified as a predictor of the PDAS score (standardized coefficient (β) = 0.28; 95% confidence interval (CI), 0.10–0.46; p=0.003). In men, the AIS score was associated with PDAS (β = 0.36, 95% CI 0.09–0.63). Age (β = 0.31, 95% CI 0.06–0.55) and NRS (β = 0.40, 95% CI 0.14–0.67) were associated with PDAS in women. HADS-A, HADS-D, and PCS were not associated with PDAS in both sexes. Conclusion Insomnia was associated with disability in men, whereas aging and pain severity were associated with disability in women. Catastrophic thinking was not associated with disability in both sexes.

Influence of thickness reduction on forming limits of mild steel DC01

The Forming Limit Diagram (FLD) is an essential tool to assess sheet metal formability in sheet metal deep drawing. In FLDs/FLC (Forming Limit Curve) is representation of material formability limits at which material is not able to withstand higher deformation. In this work, different methodologies for FLC determination of mild steel DC01 are investigated. The Nakajima test is a well-known experiment for FLC determination but, however, contact conditions that can appear in the form of either friction or pressure may perturb the results. The former may cause the need for repetitions for different widths by altering the necking location, whereas the latter may be responsible for overestimation of the material formability. Another method for FLC determination without those effects is to use the cruciform specimen test under biaxial loading conditions. As the first step, Necking has to be induced at the center of cruciform specimen by thickness reduction or groove. Therefore, in this work, the cruciform geometry under biaxial loading is optimized using FEM through the comparative analysis. The goal of simulation was to induce the necking just in the thinner gauge, not adjacent zone. Thereupon, different loads on biaxial machine’s axes can provide different strain paths at the thinner gauge of the optimized specimen. After reviewing of various researches in connection with thickness reduction effect on sheet metal deformation, it was found that thickness reduction might not influence the material formability during uniaxial and plane strain tensions, but it was observed that there is gradual decrease of limit strains with decreasing the thickness for equi-biaxial tension.Manufacturing process like milling, cause small defects on material surface and local instability takes place at lower level of deformation. Besides, it was found that existence of through thickness normal stress leads to higher value of FLC. Deformation during Nakajima and cruciform experiments were captured by Digital Image Correlation (DIC) system. The execution and evaluation of those experiments are explained in detail and Time Dependent Method (TDM) was applied to detect the beginning time of instability. Experimental strain paths are compared with consideration of strain rates and, as it was expected, FLC from cruciform specimen is lower than Nakajima one, especially on the right hand side of FLD. The remarkable difference can be attributed to defects in the material and existence of through-thickness normal stress, which leads to overestimation of the material formability during Nakajima experiment.

Factors Affecting Surgical Margin Positivity after Radical Prostatectomy in the Turkish Population: A Multicenter Study of the Urooncology Association

Background: The prediction of positive surgical margins (SM) after radical prostatectomy (RP) is important for planning the surgical modality and adjuvant therapy in patients with prostate cancer (PCa). Objectives: To investigate factors affecting SM positivity in patients diagnosed with PCa who underwent RP using the PCa database of the Urooncology Association (Turkey). Methods: Patients who underwent RP due to clinically T1c–T3 PCa and who had detailed SM data for the RP specimen were included in the study. Pathological data of 12 core transrectal ultrasound prostate biopsies and RP were evaluated. Patients were divided into 2 groups (SM positive and SM negative) according to SM status after RP. Data were compared between the groups. Factors affecting SM positivity, the number of positive SM sites, and the location of positive SM were separately evaluated with regression models. Results: A total of 2,643 patients from 6 different centers (median age: 63 years) with a prostate-specific antigen (PSA) level of 7.3 ng/mL were investigated in the study. BMI, PSA, biopsy Gleason score (GS), and perineural invasion (PNI) were found to be independent predictive factors for SM positivity and the number of positive SM locations, respectively (p < 0.05). According to the positive SM location, PSA was found to be associated with positive SM in apex, anterior prostate, and bladder neck locations. Also, according to posterolateral SM status, PNI and nerve-sparing RP (nsRP) rates were 21.3 and 44% for patients with negative posterolateral SM, and rates were 35.4 and 50.6% for patients with positive posterolateral SM, respectively (p < 0.05). In patients who underwent nsRP, positive SM was present in 22.2% of patients who did not have PNI on prostate biopsy, whereas positive SM was present in 40.6% of patients with PNI (p < 0.001). Similarly, 10.9% of patients without PNI had positive posterolateral SM, whereas 17.3% of patients with PNI had positive posterolateral SM (p = 0.031). Conclusions: BMI, PSA, biopsy GS, and biopsy PNI positivity were found to be predictive factors affecting SM positivity. The most important factors affecting posterolateral positive SM were biopsy PNI and nsRP, indicating that the nsRP approach may cause positive SM in the posterolateral margin of the prostate (neurovascular bundle location) in patients with positive PNI on biopsy.

A new crystal plasticity constitutive model for simulating precipitation-hardenable aluminum alloys

Age hardened aluminum alloys have superior strengths compared to non-age hardenable alloys due to the growth of a secondary phase of precipitates. This work presents a new crystal plasticity numerical framework to simulate the mechanical properties of precipitation-hardened aluminum alloys. A precipitation hardening constitutive law is implemented into the crystal plasticity finite element method (CPFEM) to simulate the localized deformation behavior of a commercially available AA6060-T6 extrusion. Experimental characterization in the form of uniaxial tension and cyclic simple shear is performed on the alloy of interest to validate the formulation. The framework uses information obtained from transmission electron microscopy (TEM) on a similar alloy for the simulation of the precipitate hardening response. This information is incorporated into an elastic-viscoplastic homogenization scheme to predict the behavior of the precipitate directly. The model is shown to capture the stress-strain response, precipitate anisotropy, and the observed Bauschinger effect with good agreement. A series of parametric analyses are then performed to show the effects of precipitation on the bulk and localized necking response. It is observed that the precipitate configuration heavily influences the polycrystalline behavior, and the localized behavior is also affected in a rather complex way. The model captures the general reduction of anisotropy in age-hardened alloys and serves as a good physics-based foundation for future investigative studies.

Effect of superplastic deformation on microstructure evolution of 3207 duplex stainless steel

High temperature tensile, electron backscatter diffraction (EBSD) techniques and transmission electron microscope (TEM) were combined to perform a systematic investigation for superplastic deformation behavior, mechanism and microstructure evolution of 3207 duplex stainless steel. Excellent superplasticity of this alloy is indicated by the elongation indicates and the flow curves revealing four stages of deformation: elastic deformation stage, stable deformation stage, quasi-stable deformation stage and localized necking stage. Before the initial of quasi-stable deformation stage, several low angle boundaries (LAGBs) can be observed, indicating dislocation creep-controlled deformation is the dominant mechanism. In the middle and final of the quasi-stable deformation stage, LAGBs are found evolving into high angle boundaries (HAGBs) indicating the dominant deformation mechanism to be grain boundary sliding (GBS), leading to the weakened textures. In the localized necking stage, dislocations are found generated by the combination of cavities along grain boundaries, indicating the dominant deformation mechanism of GBS and an accommodation mechanism of conventional plastic deformation. The main softening mechanism responsible for the flow behaviors of the 3207 duplex stainless steel is identified as dynamic recrystallization (DRX), which completely neutralized the effect of work hardening at the quasi-stable deformation stage.

Bubble formation regimes in forced co-axial air-water jets

We report a detailed experimental characterization of the periodic bubbling regimes that take place in an axisymmetric air-water jet when the inner air stream is forced by periodic modulations of the pressure at the upstream air feeding chamber. When the forcing pressure amplitude is larger than a critical value, the bubble formation process is controlled by the forcing frequency, leading to the formation of nearly monodisperse bubbles whose volume is reduced as the forcing rate increases. We reveal the existence of two different breakup modes, M1 and M2, under effective forcing conditions. The bubble formation in mode M1 resembles the natural bubbling process, featuring an initial radial expansion of an air ligament attached to the injector, whose initial length is smaller than the wavelength of a small interfacial perturbation induced by the oscillating air flow rate. The expansion stage is followed by a ligament collapse stage, which begins with the formation of an incipient neck that propagates downstream while collapsing radially inwards, leading to the pinch-off of a new bubble. These two stages take place faster than in the unforced case due to the air flow modulation induced by the forcing system. The breakup mode M2 takes place with an intact ligament longer than one disturbance wavelength, whereby the interface already presents a local necking region at pinch-off, and leads to the formation of bubbles from the tip of an elongated air filament without an expansion stage. Scaling laws that provide closed expressions for the bubble volume, the intact ligament length, and the transition from the M1 breakup mode to the M2, as functions of the relevant governing parameters, are deduced from the experimental data. In particular, it has been found that the transition from mode M1 to mode M2 occurs at (StfΛWe)c=0.25 and that the intact ligament scales as li/ro∝Stf−1Λ1/5We1/4 within the breakup mode M1. Here ro is the radius of the gas stream, Λ the water-to-air velocity ratio, We the Weber number and Stf the dimensionless forcing frequency.

Revealing the small post-necking elongation in twinning-induced plasticity steels

The mechanism of small post-necking elongation (PE) in twinning-induced plasticity (TWIP) steels has been investigated from a metallurgical and mechanical engineering perspective to understand and increase the PE. To achieve the above aims, seven TWIP steels with systematic variations in chemical composition, grain size, and pre-strain were prepared. The steels were then analyzed using tensile curves, electron backscatter diffraction techniques, numerical simulation, and a comparison study with other metals. The region of diffuse necking was not observed in C-added TWIP steels due to the negative strain rate sensitivity (m). The negative m value led to strain concentration at the narrow necking region, leading to localized necking and then shear cracks, resulting in the small PE. The dynamic strain aging (DSA) effect was closely related to the negative m value in TWIP steels. Therefore, the PE had a strong linear relationship with the onset strain of serration in the tensile curve. The texture development with an increased dislocation density by pre-strain can suppress the localized necking in TWIP steels, leading to an improvement in the PE. TWIP steel with a larger grain size had higher PE because the DSA was suppressed with increasing grain size.

High-Resolution Ultrasound of Small Clinically Relevant Nerves Running Across the Posterior Triangle of the Neck.

With the advent of high-frequency ultrasound (US) transducers, new perspectives have been opened in evaluating millimetric and submillimetric nerves that, despite their dimensions, can be considered relevant in clinical practice. In the posterior triangle of the neck, the suprascapular, long thoracic, phrenic, supraclavicular, great auricular, lesser occipital, and transverse cervical nerves are amenable to US examination and the object of special interest because they may be involved in many pathologic processes or have a value as targets of advanced therapeutic procedures. The correct identification of these nerves requires a deep knowledge of local neck anatomy and the use of a complex landmarks-based approach with US. This article describes the anatomy and US technique to examine small but clinically relevant nerves of the posterior triangle of the neck (excluding the brachial plexus), reviewing the main pathologic conditions in which they may be involved.

Cortical bone mapping improves finite element strain prediction accuracy at the proximal femur.

Despite evidence of the biomechanical role of cortical bone, current state of the art finite element models of the proximal femur built from clinical CT data lack a subject-specific representation of the bone cortex. Our main research hypothesis is that the subject-specific modelling of cortical bone layer from CT images, through a deconvolution procedure known as Cortical Bone Mapping (CBM, validated for cortical thickness and density estimates) can improve the accuracy of CT-based FE models of the proximal femur, currently limited by partial volume artefacts. Our secondary hypothesis is that a careful choice of cortical-specific density-elasticity relationship may improve model accuracy. We therefore: (i) implemented a procedure to include subject-specific CBM estimates of both cortical thickness and density in CT-based FE models. (ii) defined alternative models that included CBM estimates and featured a cortical-specific or an independently optimised density-elasticity relationship. (iii) tested our hypotheses in terms of elastic strain estimates and failure load and location prediction, by comparing with a published cohort of 14 femurs, where strain and strength in stance and fall loading configuration were experimentally measured, and estimated through reference FE models that did not explicitly model the cortical compartment. Our findings support the main hypothesis: an explicit modelling of the proximal femur cortical bone layer including CBM estimates of cortical bone thickness and density increased the FE strains prediction, mostly by reducing peak errors (average error reduced by 30%, maximum error and 95th percentile of error distribution halved) and especially when focusing on the femoral neck locations (all error metrics at least halved). We instead rejected the secondary hypothesis: changes in cortical density-elasticity relationship could not improve validation performances. From these improved baseline strain estimates, further work is needed to achieve accurate strength predictions, as models incorporating cortical thickness and density produced worse estimates of failure load and equivalent estimates of failure location when compared to reference models. In summary, we recommend including local estimates of cortical thickness and density in FE models to estimate bone strains in physiological conditions, and especially when designing exercise studies to promote bone strength.