Cross-sectional Perimeter Research Articles

Dimensional changes of the carpal tunnel and median nerve during manual mobilization of the carpal bones — Anatomical study

Study designCross-sectional study. BackgroundThe carpal tunnel is a clinically important fibro-osseous conduit for the median nerve and associated tendons. It is mechanically dynamic and therapeutic manual techniques that appear to move and change tunnel shape is part of clinical practice. ObjectivesTo measure changes in dimensions of the carpal tunnel and median nerve with manual mobilization of the carpal bones in cadavers. MethodsA total of 20 cryopreserved upper extremities from cadaveric specimens were used in the study. The wrist was cut using an anatomical saw at the level of the pisiform. Measurements of the cross-sectional area (CSA), anteroposterior diameter (APD), transverse diameter (TD), perimeter, flattening ratio and circularity of the carpal tunnel and of the median nerve, were taken, both in the anatomical position of the wrist and during the mobilization technique of the carpal bones. ResultsDuring the mobilization technique, the tunnel CSA (p < 0.011), APD (p < 0.001) and circularity (p < 0.001) significantly increased, while TD (p < 0.001), perimeter (p < 0.004) and flattening ratio (p < 0.001), decreased. The median nerve showed similar behavioral tendencies to the tunnel but only the CSA (p < 0.005), APD (p < 0.005) and flattening ratio (p < 0.004) of the nerve showed significant differences. ConclusionApplication of external manually applied compressive force across the wrist can increase the CSA of the carpal tunnel and the median nerve in cadavers. These results are consistent with other studies in which similar results were found non-invasively using ultrasound.

Core behavior and low-cycle fatigue estimation of the Perforated Core Buckling-Restrained Brace

The Perforated Core Buckling-Restrained Brace (PCBRB) is an all-steel BRB whose core has been split into two lateral bands connected by stabilizing bridges. The core, with a constant cross-section perimeter, can slide along the restrainer so that it can be inspected or replaced by simply removing a centering pin. We analyzed the behavior of two different Perforated Core (PC) geometries which we tested to failure with different load protocols of several maximum deformation amplitudes. The main difference between both geometries was the radius of the lateral band connections. The experimental results show how a low radius, despite offering a higher constant cross-section yielding length, leads to a lower dissipation capacity and to a closer distance between stabilizing bridges. The results also show a gradual drift of the internal and the external lateral band segments into permanent negative and positive elongations, respectively, which increases the minimum gap required between the core and the restrainer. We also analyzed the in-plane and the out-of-plane wavelength of the high-mode buckling of the PC and validated two wavelength prediction equations that would prevent the uncontrolled second-order deformations and the buckling failure of the PC. Finally, based on experimental data, we propose two low-cycle fatigue relationships for the PCBRB that would be valid for elastoplastic devices with uniform uniaxial strain distribution, such as BRBs and TADAS devices.

Late-emerging effects of perinatal undernutrition in neuronal limbic structures underlying the maternal response in the rat

Maternal care in the rat is an ancient behavioral response to specific multisensory inputs widely integrated in a complex forebrain, limbic and brain stem network to meet the basic needs of the young. Early undernutrition interferes with the morphofunctional organization of the brain, including maternal circuitry. The late-emerging effects of pre- and neonatal undernutrition on nest building and pup retrieval by lactating Wistar rats were correlated with dendritic arbor and perikaryon measurements (Golgi-Cox) in layer II pyramidal neurons of the anterior cingulate cortex, layer III pyramidal neurons of the medial prefrontal cortex and multipolar basolateral amygdala neurons examined on lactation days 4 and 12. In the underfed group, pregnant F0 dams received different percentages of a balanced diet. After birth, prenatally underfed (F1) pups continued the undernutrition by remaining with a nipple-ligated mother for 12 h. Weaning occurred at 25 days of age, and pups were subsequently provided an ad libitum diet. At 90 days of age, F1 dams were maternally tested. Early underfed dams showed significant reductions in nest building and prolonged retrieval latencies for grasping pups by inappropriate body areas. The behavioral alterations were concurrent with highly significant reductions in the somatic cross-sectional area and perimeter, spine density and dendritic crossings of cingulate cells and medial prefrontal cortical pyramids, as well as smaller effects on amygdala neurons. The anatomical findings suggest different postsynaptic organizations that may affect the neuronal excitability stages for the integration and encoding of cues triggering the altered maternal response components of early underfed dams.

Investigation of Heat Transfer Surfaces for Space Power Systems

Heat exchangers used in the composition of large-capacity energy conversion systems for space applications must be able to operate at high temperatures (above 1000 K) and at high (several MPa) values of pressure difference between the “hot” and “cold” heat carrier/coolant channels. This is why especially demanding strength and stiffness requirements are posed to the heat-transfer matrix of these devices, a circumstance that precludes almost completely the use of well-known compact and light plate-and-fin devices with 50–100-μm-thick foil fins. The article presents the results from experimental investigations into the thermal and hydraulic characteristics of alternative versions of heat-transfer elements involving the use of different heat transfer enhancement methods. Experimental investigations of heat transfer and hydrodynamics were carried out for three types of heat-transfer surfaces: a tubular one composed of small-diameter (3 mm) thin-walled tubes deformed over the cross-section perimeter and length (twisted tubes), a plate one finned with pins having a diamond-shaped cross section (2 × 2 mm in cross section and 4 mm in height), and a plate one composed of thin-walled 0.2-mm-thick plates with the surface formed by oppositely directed truncated cones with saddle-like bridges (a biconvex stamped plate). After processing and analyzing the experimental data obtained for these heat-transfer surfaces, dimensionless dependences for the Nusselt number and the pressure-drop coefficient on the Reynolds number were constructed. The dimensionless formulas obtained for twisted tubes and for the pin-finned surface are compared with the well-known correlations. It is shown that the use of twisted tubes instead of round ones results in improving the heat transfer intensity by more than 20% with the hydrodynamic indicators worsened by 50%. The use of the pin-finned plate surface improves the heat transfer intensity by more than a factor of two as compared with using a staggered tube bundle.

Dimensional changes of the carpal tunnel and the median nerve during manual mobilization of the carpal bones

IntroductionThe carpal tunnel is a clinically important fibro-osseous conduit for the median nerve and associated tendons. It is mechanically dynamic, such that the dimensions of the tunnel and median nerve change with position, movement and application of externally applied force with mechanical devices. Therapeutic manual techniques that appear to move and change tunnel shape are part of clinical practice. The aim of this study was therefore to measure changes in dimensions of the carpal tunnel and median nerve with manual mobilization of the carpal bones. Material and methodsAn analytical descriptive study with 18 volunteer subjects and a total of 33 records was designed. Ultrasound measurements of the cross-sectional area (CSA), anteroposterior diameter (APD), transverse diameter (TD), perimeter, flattening ratio and circularity of the carpal tunnel and of the median nerve, were measured, both in the anatomical position of the wrist and during mobilization techniques of the carpal bones. ResultsDuring the mobilization technique, the tunnel (p = 0.003) CSA significantly increased. APD also increased significantly for the tunnel (<0.001) while TD decreased. The median nerve showed similar and significant (p < 0.001) changes than the tunnel. However, because several of the obtained differences where smaller than the SDD obtained in a previous study, these differences were considered as irrelevant. ConclusionsManual mobilization of the carpal bones produced significant changes in the dimensions of the carpal tunnel.

Non-exposed endoscopic wall-inversion surgery for gastrointestinal stromal tumor.

Laparoscopic and endoscopic cooperative surgery (LECS) is an accepted method of laparoscopic wedge resection, which is minimally invasive, for gastrointestinal stromal tumors (GISTs). We established a type of LECS achieving a full-thickness resection, non-exposed endoscopic wall-inversion surgery (NEWS), in an effort to prevent exposure of the peritoneal cavity to gastric intraluminal contents. We employed this surgical technique in 28 gastric GIST patients. We failed to complete NEWS in the initial two patients and in one patient with a large tumor (40 mm × 35 mm), but otherwise carried out the procedure successfully. Although a learning effect is speculated to occur, based on a decreasing trend in the operation time, the median operation time was 184 minutes showing that NEWS is still a time-consuming method. No significant differences were recognized in tumor size or location, except near the esophagogastric junction (EGJ), nor in the cross-sectional circumference. NEWS is feasible and appears to be a good option, especially for small GISTs with mucosal ulceration rendering full-thickness enucleation by opening of the gastric wall unfeasible.

Exploratory use of ultrasound to determine whether demyelination following carpal tunnel syndrome co-exists with axonal degeneration.

Carpal tunnel syndrome (CTS) accompanied by secondary axonal degeneration cannot be clearly discriminated using the current cross-validated ultrasound severity classification system. This study aimed at exploring cut-off values of ultrasound parameters, including wrist cross-sectional area (W-CSA), wrist perimeter (W-P), ratio of cross-sectional area (R-CSA) and perimeter (R-P), changes of CSA and P from wrist to one third distal forearm (ΔCSA&ΔP) for differentiation. Seventy-three patients (13 male and 60 female) were assigned into group A (demyelination only, n = 40) and group B (demyelination with secondary axonal degeneration, n = 33) based on the outcomes of nerve conduction studies (NCS). Receiver Operative Characteristics (ROC) curves were plotted to obtain sensitivity, specificity, and accuracy of cut-off values for all the ultrasound parameters. The overall identified cut-off values (W-CSA 12.0 mm2, W-P 16.27 mm, R-CSA 1.85, R-P 1.48, ΔCSA 6.98 mm2, ΔP 5.77 mm) had good sensitivity (77.1–88.6%), fair specificity (40–62.2%) and fair-to-good accuracy (0.676–0.758). There were also significant differences in demographics (age and severity gradation, P < 0.001), NCS findings (wrist motor latency and conduction velocity, P < 0.0001; wrist motor amplitude, P < 0.05; distal sensory latency, P < 0.05; sensory amplitude, P < 0.001) and ultrasound measurements (W-CSA, W-P, R-CSA, R-P, ΔCSA&ΔP, P < 0.05) between groups. These findings suggest that ultrasound can be potentially used to differentiate demyelinating CTS with secondary axonal degeneration and provide better treatment guidance.

Early electrical field stimulation prevents the loss of spinal cord anterior horn motoneurons and muscle atrophy following spinal cord injury.

Our previous study revealed that early application of electrical field stimulation (EFS) with the anode at the lesion and the cathode distal to the lesion reduced injury potential, inhibited secondary injury and was neuroprotective in the dorsal corticospinal tract after spinal cord injury (SCI). The objective of this study was to further evaluate the effect of EFS on protection of anterior horn motoneurons and their target musculature after SCI and its mechanism. Rats were randomized into three equal groups. The EFS group received EFS for 30 minutes immediately after injury at T10. SCI group rats were only subjected to SCI and sham group rats were only subjected to laminectomy. Luxol fast blue staining demonstrated that spinal cord tissue in the injury center was better protected; cross-sectional area and perimeter of injured tissue were significantly smaller in the EFS group than in the SCI group. Immunofluorescence and transmission electron microscopy showed that the number of spinal cord anterior horn motoneurons was greater and the number of abnormal neurons reduced in the EFS group compared with the SCI group. Wet weight and cross-sectional area of vastus lateralis muscles were smaller in the SCI group to in the sham group. However, EFS improved muscle atrophy and behavioral examination showed that EFS significantly increased the angle in the inclined plane test and Tarlov's motor grading score. The above results confirm that early EFS can effectively impede spinal cord anterior horn motoneuron loss, promote motor function recovery and reduce muscle atrophy in rats after SCI.

Lateral response of PET FRP-confined concrete

The passive confinement of externally wrapped fiber-reinforced polymer (FRP) composites can effectively restrain the unstable lateral expansion of confined concrete, hence results in significantly improved strength and ductility. Unlike uniform lateral expansion in circular columns, concrete expansion is highly variable around the cross-section perimeter in non-circular columns. In case of seismic retrofitting, where the ductility enhancement is of prime concern, bulging of concrete on flat sides and premature failure of FRP around the sharp corners usually limit the confinement effectiveness because of limited strain capacity of commonly used FRP composites. Most recently, new FRP composites and fiber ropes have been developed which possess large rupture strain (LRS) capacity. Concrete expansion under the restraining mechanism of such LRS materials’ confinement, particularly in non-circular columns, is hitherto unclear and should be investigated in detail for a reliable structural design. For this purpose, results of an experimental study on the lateral behavior of circular and non-circular concrete specimens confined by polyethylene terephthalate (PET) FRP, which possesses a LRS capacity, are presented and discussed in this paper. The parameters considered were the cross-sectional shape, the corner radius, and the number of FRP layers. Axial stress-lateral strain and lateral strain-axial strain relationships are presented to deeply understand the dilation of confined concrete. The experimental results showed remarkable influence of the considered parameters on the dilation of confined concrete. Different lateral expansions measured in different directions of non-circular specimens revealed important insights, which are responsible for the distribution of confining stress around the perimeter of such cross sections. In addition, predictions of lateral strain-axial strain response by some existing models were compared with the experimental results of PET FRP-confined circular specimens of this study. The comparison shows that these models were unable to predict well the lateral strain-axial strain response and need further modification.

Influence of Pore Characteristics on Electrochemical and Biological Behavior of Ti Foams

This study reports on titanium (Ti) foams produced using the powder metallurgy technique. During the investigation, the cross-sectional area and perimeter distributions of the pores within the foam were measured. Metallographic image processing analysis software combined with scanning electron microscopic images demonstrated that the pore size and circularity were affected by varying the volume percentage of the space-holder material. The corrosion resistance was investigated using electrochemical impedance spectroscopy and cyclic polarization tests. MG-63 osteoblast-like cells were used to study the biocompatibility and to evaluate the cell attachment, viability, and alkaline phosphatase activity. Analytical results indicated that 50 and 60 vol.% samples were suitable for biomedical applications. Because of the high degree of interconnectivity in the 60 and 70% porosity samples, the electrochemical parameters produced similar results. The corrosion rate of the porous samples showed that the amount of dissolved Ti was at an acceptable level that can be ejected by the body. Applying a fluoridated hydroxyapatite coating significantly increased the osteoblast cell functions on the porous surface.

Effects of electronic device overuse by university students in relation to clinical status and anatomical variations of the median nerve and transverse carpal ligament.

This study investigates the results of a questionnaire, provocative tests, and ultrasonographic measurements of carpal tunnel morphological parameters in intensive and nonintensive electronic device users. Forty-eight university students (equal numbers of intensive and nonintensive users, ≥5 h/day and <5 h/day of electronic device usage, respectively) were randomly selected after questionnaire responses were received and evaluated clinically and by ultrasonography. All participants were right-handed. Intensive users had significantly more positive results in Phalen's and Durkan's tests and reported more wrist/hand pain compared with nonintensive users (P < 0.05). Intensive users also had significantly larger median nerve cross-sectional areas, flattening ratios, and perimeters as well as greater bowing of the transverse carpal ligament compared with nonintensive users (P < 0.05). Overuse of electronic devices may adversely affect the median nerve within the carpal tunnel and the transverse carpal ligament, resulting in numbness, tingling, and pain in the hand. Caution may be warranted when using handheld electronic devices. Muscle Nerve 56: 873-880, 2017.

Liver morphometrics and metabolic blood profile across divergent phenotypes for feed efficiency in the bovine

BackgroundFeed costs are a major expense in the production of beef cattle. Individual variation in the efficiency of feed utilization may be evident through feed efficiency-related phenotypes such as those related to major energetic sinks. Our objectives were to assess the relationships between feed efficiency with liver morphometry and metabolic blood profile in feedlot beef cattle.MethodsTwo populations (A = 112 and B = 45) of steers were tested for feed efficiency. Blood from the 12 most (efficient) and 12 least feed inefficient (inefficient) steers from population A was sampled hourly over the circadian period. Blood plasma samples were submitted for analysis on albumin, aspartate aminotransferase, γ-glutamyl transpeptidase urea, cholesterol, creatinine, alkaline phosphatase, creatine kinase, lipase, carbon dioxide, β-hydroxybutyrate, acetate and bile acids. Liver tissue was also harvested from 24 steers that were blood sampled from population A and the 10 steers with divergent feed efficiency in each tail of population B was sampled for microscopy at slaughter. Photomicroscopy images were taken using the portal triad and central vein as landmarks. Histological quantifications included cross-sectional hepatocyte perimeter and area, hepatocyte nuclear area and nuclei area as proportion of the hepatocyte area. The least square means comparison between efficient and inefficient steers for productive performance and liver morphometry and for blood analytes data were analyzed using general linear model and mixed model procedures of SAS, respectively.ResultsNo differences were observed for liver weight; however, efficient steers had larger hepatocyte (i.e. hepatocyte area at the porta triad 323.31 vs. 286.37 µm2) and nuclei dimensions at portal triad and central vein regions, compared with inefficient steers. The metabolic profile indicated efficient steers had lower albumin (36.18 vs. 37.65 g/l) and cholesterol (2.62 vs. 3.05 mmol/l) and higher creatinine (118.59 vs. 110.50 mmol/l) and carbon dioxide (24.36 vs. 23.65 mmol/l) than inefficient steers.ConclusionsImproved feed efficiency is associated with increased metabolism by the liver (enlarged hepatocytes and no difference on organ size), muscle (higher creatinine) and whole body (higher carbon dioxide); additionally, efficient steers had reduced bloodstream pools of albumin and cholesterol. These metabolic discrepancies between feed efficient and inefficient cattle may be determinants of productive performance.

Effect of prenatal exposure to alcohol on the development of brain vessels in human embryos and fetuses

IntroductionHuman embryos are most susceptible to exogenous effects during the first weeks of development.AimStudy the effects of prenatal alcohol intoxication on morphometric measures of developing vessels in the human embryonic and fetal cerebrum.MethodsEmbryos and fetuses (7–12 weeks): 23 obtained from alcoholic women with stage II alcoholism (the experimental group) and 30 from healthy women (the control group). The research involved electron microscopy, computer morphometry, parametric method of variational statistics and Scion software to determine mean vascular cross-sectional area, the relative cross-sectional area of vessels, the number of vessels per unit area, and the perimeter of vessels.ResultsFrom 10 weeks, vessels in the human brain start to differentiate into arteries and veins. At 12 weeks, capillary basal membranes were already clearly visible. We established a series of characteristics distinguishing brain tissues in the experimental group vs. that in controls: mean vessel cross-sectional areas and vessel perimeters were significantly reduced by 11 weeks vs. controls. The tendency persisted at 12 weeks. Relative vessel cross-sectional area in the experimental group was greater than in controls.ConclusionsMaternal alcoholization during pregnancy significantly influences the development of the cerebral circulatory system, manifesting mainly in changes in the vascularization of the growing brain.Disclosure of interestThe authors have not supplied their declaration of competing interest.

Crashworthiness analysis and optimization of fourier varying section tubes

Thin-walled structures are widely used as energy absorption devices for their proven advantages on lightweight and crashworthiness. However, a majority of studies have being focus on exploring separately the crashworthiness of the thin-walled structure with a specific geometric section, such as circular, square, hexagon, octagon etc., and little research has investigated the relationship of crashworthiness among thin-walled structures with different sections systematically. This paper utilizes Fourier series expansion to generate a series of novel sectional configurations, namely Fourier varying sectional tubes (FVSTs), to look into their advantages of crashworthiness, thereby developing some FVSTs with highest possible energy absorption capacity. Based on the validated finite element (FE) models, parametric analysis is conducted to investigate the effects of cross-sectional configuration, perimeter and thickness of FVSTs on collapse mode and energy absorption. The results showed that the collapse modes of FVSTs are fairly sensitive to cross-sectional configuration, perimeter and wall thickness. Of these FVSTs generated, the highest specific energy absorption (SEA) increases 77.54% by increasing perimeter and 69.73% by decreasing wall thickness. Finally, a discrete optimization based on the orthogonal arrays is conducted to obtain the optimal FVST for maximizing SEA under the constraint of the initial peak crushing force (IPCF). The optimized FVSTs are of superior crashworthiness and great potential as an energy absorber.

Fabrication and in situ compression testing of Mg micropillars with a nontrivial cross section: Influence of micropillar geometry on mechanical properties

Micropillars with a nontrivial cross-sectional shape but constant cross-sectional area were fabricated from a pure magnesium single crystal with (0001) orientation by a focused gallium ion beam using a modified annular milling method. The basic mechanical properties (compressive modulus, strength at different plastic strain levels and hardening exponent) of those structures were determined under compression by means of in situ nanoindentation in scanning electron microscope and correlated by the micropillar cross-sectional circumference. It was observed that the modulus and strength increased with increasing circumference. The values of the modulus for the complex cross sectional shapes are on average higher by 5%, and the yield strength, ranging between 274MPa and 342MPa, is on average higher by 20% relative to micropillars with a simple circular or polygonal cross section. Surprisingly, the hardening exponent remains nearly constant regardless of the micropillar cross section.

Evaluation the Venous Pressure of Deep Vein Thrombosis of Early Phase in Lower Extremity by Ultrasonic Imaging

Conventional ultrasound measures the diameter and the velocity of the vein to evaluate early venous tension changes in deep vein thrombosis (DVT) of lower extremity. The accuracy and repeatability of conventional measurement are poor, because diameter measurement of vein are susceptible to not only respiratory and extrusion of edema from soft tissue, but also affected by limit of sampling angle when measuring venous flow rate by the color box. By applying the ratio of common femoral vein and cross-sectional area/cross-sectional perimeter (A/C), DVT early vein tension change was evaluated. The cut-off value method and diagnostic value of the A/C preliminarily was discussed. This study by measuring the value of cross-sectional area, pipe perimeter and their ratio among groups evaluate the value of venous tension change and provide certain reference basis for early clinical intervention. Four-hundred and fifty orthopaedic patients (294 male V.S. 156 female) in our hospital were chosen to perform ultrasound examinations from June 2014 to April 2016, including 150 cases as normal control group, 150 cases as the flow reduced group, 150 cases as venous thrombosis group. Their average age was 36.8±11.0 years (8-67). Inclusion criteria includes that patients had no deep vein blood vessel diseases in lower extremity before. Cross-sectional area (A), cross-sectional perimeter value (C), the ratio of the two and the venous flow velocity of common femoral vein were measured and compared among groups. ROC curve was used to explore the diagnostic value of the A/C. The middle segment of the common femoral vein was selectecd as the measurement point where great saphenous vein enters. The standard of decreasing blood flow velocity was Vmean < 15 cm/s. Quantitative data using one-way ANOVA. P < 0.05 was considered to be statistically significant. For normal control group, the average value of cross-sectional area was 66.13±11.25mm2, the average value of cross-sectional perimeter was 28.84±5.14mm and the average value of A/C was 2.65±0.34. For flow reduced group, the average value of cross-sectional area was 94.82±12.57mm2, the average value of cross-sectional perimeter was 32.49±4.73mm and the average value of A/C was 3.26±0.27. For the venous thrombosis group, the average value of cross-sectional area was 151.63±17.41mm2, the average value of cross-sectional perimeter was 43.62±6.61mm and the average value of A/C was 3.94±0.53. There was significantly differences in the cross-sectional area between the normal control group and flow reduced group and venous thrombosis group (P<0.05). No significant statistical differences was found between flow reduced group and venous thrombosis group. With the development of venous thromboembolism disease gradually increase, A, C, and A/C were found to increase gradually and venous blood flow velocity gradually reduced. The cutoff point value of A/C was 2.91 to evaluate early vein tension change of DVT. The area under ROC curve of ratio of A/C was 0.891, sensitivity was 90.0%, specificity was 77.6%. A/C quantified the variation in vein tension which was used to be an abstract concept. The value of A/C was more stable than the venous diameter and showed relatively small disturbance when assessing the venous tension. We provide new thinking and reference for early intervention of clinical preventing DVT.

Experimental Study on the Behavior of X-Section Pile Subjected to Cyclic Axial Load in Sand

X-section cast-in-place concrete pile is a new type of foundation reinforcement technique featured by the X-shaped cross-section. Compared with a traditional circular pile, an X-section pile with the same cross-sectional area has larger side resistance due to its larger cross-sectional perimeter. The behavior of static loaded X-section pile has been extensively reported, while little attention has been paid to the dynamic characteristics of X-section pile. This paper introduced a large-scale model test for an X-section pile and a circular pile with the same cross-sectional area subjected to cyclic axial load in sand. The experimental results demonstrated that cyclic axial load contributed to the degradation of shaft friction and pile head stiffness. The dynamic responses of X-section pile were determined by loading frequency and loading amplitude. Furthermore, comparative analysis between the X-section pile and the circular pile revealed that the X-section pile can improve the shaft friction and reduce the cumulative settlement under cyclic loading. Static load test was carried out prior to the vibration tests to investigate the ultimate bearing capacity of test piles. This study was expected to provide a reasonable reference for further studies on the dynamic responses of X-section piles in practical engineering.

Multipole analysis of the strain-mediated coupling between proteins adsorbed at tubular lipid membrane surface.

The tubular lipid membranes (TLMs) pulled out from vesicles are often used in in vitro studies of the interactions between curvature-inducing proteins and highly curved membranes. The protein molecules adsorbed at the membrane surface deform the TLM and couple with each other due to the induced strain. Here we propose an approach which models the single curvature-inducing protein action on the lipid bilayer by the multipole, the superposition of the point forces applied to the membrane in the region of the protein adsorption. We show that to be localized in the area of the protein size at the TLM surface, the force multipoles satisfying the mechanical equilibrium conditions should be composed of three or more point forces. The protein coupling energy mediated by the membrane strain is studied in detail. In the region of the tubular membrane stability the maximal distance between two neighboring interacting protein-induced force multipoles is estimated to be of the order of the TLM cross section perimeter. In the vicinity of the TLM instability in the region of the vanishing stretching force applied to the TLM, the interaction radius increases drastically. The high affinity of the single curvature-inducing protein molecule to the regions in the vicinity of the TLM ends is explained and related to the boundary conditions in the experimental set-ups. The reasons for the aggregate formation on the membrane surface are also discussed.

Force-distance curves on lubricant films: An approach to the characterization of the shape of the AFM tip

Force-distance curves have been acquired with an atomic force microscope on perfluorpolyether films. It is shown that curves acquired on films of different thickness, at different rates and with different dwell times can be overlapped by rescaling the time or distance axis. When the time or distance axis is rescaled, the force depends only on the surface tension of perfluorpolyether and on geometrical properties of the tip (aperture and perimeter of the tip at a given distance from the apex). Hence, curves acquired with the same tip overlap.By comparing curves acquired at different rates the dynamics of tip-wetting can be investigated. Furthermore, rescaled force-distance curves have been matched with the perimeter of cross sections of the tip, i.e. with the perimeter of the three-phase contact line. Such measurements pave the way for a non-destructive investigation of the tip shape.

Computation of Bending Stress in Pipes Using Weighted Hole-Drilling and DSPI Measurements

Pipelines usually operate under bending and axial stresses, caused by external loads, combined with residual stress distributions (manufacturing stresses), which affect the mechanical behavior of the pipe. Despite its semi-destructive nature, the hole drilling technique and digital speckle pattern interferometry (DSPI) can be applied to determine combined stresses along a cross-section. To achieve this, a set of equally-spaced angular points spread along the cross-section perimeter are measured. For non-uniform stress computations the hole drilling technique frequently gives a detailed stress distribution which is related to the external layer (1 mm) of the pipeline. In order to obtain a representative and unique value for the stress acting at each point, a novel approach can be used to evaluate a weighted average stress from each available stress distribution and to identify possible outlier measured points. In accordance with this approach, weighting coefficients are calculated using some particular features found in the residual stress profiles of pipelines. A reference bending test bench was used to evaluate the proposed methodology and it verified good agreement between the reference and computed stresses.