Lateral Compressions Research Articles

Radiological characteristics and injury mechanism of Logsplitter injury: a descriptive and retrospective study

BackgroundLogsplitter Injury is a type of high-energy ankle fracture dislocation. The mechanism of injury has not been described in detail. A detailed understanding of the radiological features and pathological changes can further guide treatment.MethodsBetween April 2009 and December 2018, a retrospective analysis was conducted on 62 patients with Logsplitter injury. The study analysed the characteristics of fibular injury, tibial injury, syndesmosis injury, medial injury and lateral ligament injury on preoperative X-ray and CT scans. The incidence of the different injury types was summarised. The correlation between Logsplitter injuries and the mechanisms causing them were analysed using the Lauge-Hansen classification of ankle fractures.ResultsThe study provides data on the types of fractures observed. Of the total fractures, 98.4% were open fractures. The fibula injuries were classified as no fracture (1.6%), transverse or short oblique fractures (61.3%), butterfly fragments (25.8%), and comminuted fractures (11.3%). The tibial injuries included compression of lateral articular surfaces (38.7%) and posterior compressions (6.5%). Medial injuries, including medial malleolar fractures, accounted for 87.1%, and deltoid ligament rupture accounted for 12.9%. The study found that injuries to the syndesmosis consisted of simple ligament ruptures (11.3%), Tillaux fractures (8.1%), Volkmann fractures (43.5%), and Tillaux and Volkmann fractures (37.1%). In 12.9% of cases, there was a complete rupture of the lateral collateral ligament. Based on the Lauge-Hansen classification, 87.1% of injuries were pronation-abduction injuries, while 8.1% were pronation and external rotation injuries, and 1.6% were supination external rotation injuries. Furthermore, 3.2% of cases could not be classified.ConclusionThe pathoanatomic characteristics of Logsplitter injury are diverse, with some cases accompanied by collateral ligament injury. It is important to note that these evaluations are objective and based on current results. The most common injury mechanism is vertical violence combined with abduction, although in some cases, it may be a vertical combined external-rotation injury.Level of evidence(4) case series.Trial registrationThis study has been approved by the ethical research committee of the Honghui Hospital of Xi’an Jiaotong University, under the code: 202,003,002.

The anesthesiologist’s guide to swine trauma physiology research: a report of two decades of experience from the experimental traumatology laboratory

PurposeSwine are one of the major animal species used in translational research, with unique advantages given the similar anatomic and physiologic characteristics as man, but the investigator needs to be familiar with important differences. This article targets clinical anesthesiologists who are proficient in human monitoring. We summarize our experience during the last two decades, with the aim to facilitate for clinical and non-clinical researchers to improve in porcine research.MethodsThis was a retrospective review of 337 swine with a mean (SD) weight 60 (4.2) kg at the Experimental Traumatology laboratory at Södersjukhuset (Stockholm south general hospital) between 2003 and 2023, including laboratory parameters and six CT-angiography examinations.ResultsSwine may be ventilated through the snout using a size 2 neonatal mask. Intubate using a 35 cm miller laryngoscope and an intubating introducer. Swine are prone to alveolar atelectasis and often require alveolar recruitment. Insert PA-catheters through a cut-down technique in the internal jugular vein, and catheters in arteries and veins using combined cut-down and Seldinger techniques. Cardiopulmonary resuscitation is possible and lateral chest compressions are most effective. Swine are prone to lethal ventricular arrhythmias, which may be reversed by defibrillation. Most vital parameters are similar to man, with the exception of a higher core temperature, higher buffer bases and increased coagulation. Anesthesia methods are similar to man, but swine require five times the dose of ketamine.ConclusionSwine share anatomical and physiological features with man, which allows for seamless utilization of clinical monitoring equipment, medication, and physiological considerations.

A proof-of-concept study evaluating cardiac compression techniques for cardiopulmonary resuscitation in laying hens (Gallus gallus).

To determine in adult chickens which of 3 CPR techniques, sternal compressions (SC), SC with interposed caudal coelomic compressions (ICCC), or lateral compressions (LC), results in the highest mean systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) as measured directly from the carotid artery. Prospective, nonblinded, experimental crossover study. University teaching hospital laboratory. Ten retired laying hens. Birds were sedated, anesthetized, and placed in dorsal recumbency. A carotid artery catheter was placed to directly measure arterial pressure. Ventricular fibrillation was induced with direct cardiac stimulation using a 9-Volt battery. Each bird then received 2minutes of the 3 different cardiac compression techniques in a random order by 3 different compressors, with the compressor order also randomized. Birds were subsequently administered IV epinephrine, and transthoracic defibrillation was attempted. At the end of experimentation, each bird was euthanized, and simple gross necropsies were performed. Linear mixed models followed by pairwise paired t-tests were performed to evaluate differences in pressures generated by each technique. The primary study outcomes were SAP, DAP, and MAP over 2minutes of compressions for each compression technique. Pressures from ICCC (SAP: 27.6±5.3mmHg, DAP: 18.7±5.2mmHg, MAP: 21.7±5.2mmHg) were significantly higher than those from LC (SAP: 18.9±5.4mmHg, DAP: 11.6±4.1mmHg, MAP: 14.1±4.5mmHg). Pressures from SC (SAP: 24.5±6.4mmHg, DAP: 15.2±4.3mmHg, MAP: 18.3±5.0mmHg) were not significantly different from ICCC or LC. External compressions can generate detectable increases in arterial pressure in chickens with ventricular fibrillation. SC with ICCC generated significantly higher arterial pressures than LC. SC alone generated blood pressures that were not significantly different from those generated by SC with ICCC or LC.

Phase transitions of carbon nanotube bundles under non-proportional triaxial compressions

Lateral compressions of (n, n) and (n, 0) single-walled carbon nanotube (SWCNT) bundles are simulated by density functional theory. Feasible transition pathways are verified by the body-centered tetragonal C4 (bct-C4) phase from the (4, 4) bundle and the carbon-centered orthorhombic C8 (Cco-C8) phase from (6, 6) and (8, 8) bundles. Three new phases, the sp3-hybridized phases Cco-C16 from the (4, 0) bundle and Cco-C32 from the (8, 0) bundle, the hexagonal phase Hex-C24 composed of sp2- and sp3-hybridized carbons from the (6, 0) bundle, under non-proportional triaxial loading are predicted. Measured hardness values for Cco-C16/C32 exceed 40 GPa, indicating super-hardness. Electronic band structures of Cco-C16/C32 exhibit a 3.64 eV bandgap, while Hex-C24 exhibits metallic carbon properties. Our results provide the potential phase transition pathways of SWCNT bundles under non-proportional compression.

Rapid Exhumation Processes of the Gaoligong Mountain Range in the Southeastern Margin of the Qinghai–Tibet Plateau Since the Late Cenozoic

Three continent-scale ductile shear zones trending N-S are distributed in the southeast margin of the Qinghai–Tibet Plateau. Their tectonic deformation and exhumation histories are of great significance to understanding the orogenic processes within the continent and the growth as well as expansion mechanism of the plateau. The Gaoligong shear zone (GLGSZ) is the westernmost zone near the boundary of the Indian subduction plate and is less well studied than the Ailaoshan–Red River shear zone (ASRRSZ) in the east. In this study, low-temperature thermochronological methods including apatite (U-Th)/He (AHe), zircon (U-Th)/He (ZHe), and apatite fission track (AFT) were used to date the vertical profile samples from the Gaoligong Mountain to understand the exhumation processes that occurred in the late Cenozoic. Our results show that the GLGSZ has experienced two stages of rapid exhumation events since the late Cenozoic: in the middle Miocene (∼14.5 Ma) and early Pleistocene (∼2.9 Ma). Based on our data, we divided the late Cenozoic tectonic deformation and exhumation processes in the Gaoligong Mountain area into two stages: 1) From the middle to the late Miocene, large-scale regional dextral strike-slip movements and lateral compressions controlled the ductile shear zone and continuously denuded the mountain surface; 2) in the Pleistocene, rapid river erosion and undercutting caused by fluctuations of the monsoon system, together with the continuous activity of brittle faults, drove the latest rapid exhumations. A comparison of the thermochronological data of the different areas along the Gaoligong Mountain shows that the exhumation rate in its northern transect is significantly higher and the time of the onset of exhumation is earlier than that in the southern transect. These results indicate that the deformation processes began in the north and continued southwards and controlled the geomorphological characteristics of the Gaoligong Mountain, whose elevation is higher in the northern part than in the southern part.

Lesional and Therapeutic Aspects of Tibial Plateau Fractures at the BSS University Hospital Center in Kati

Introduction: Tibial plateau fractures are solutions of continuity of the epiphyseal-metaphyseal block of the upper end of the tibia of which at least one line enters the joint. They threaten the stability and mobility of the knee and can compromise walking and standing. These fractures are on the increase, especially affecting young and active subjects. Orthopedic treatment is a rare indication apart from non-displaced or slightly displaced forms. Surgical treatment is required in displaced forms, particularly in depression fractures. The aim of this work was to report the lesional and therapeutic aspects of tibial plateau fractures in our department. Patients and Method: Patients and method: This was a retrospective study over 36 months from January 2019 to December 2021. Included in this study were patients treated for a tibial plateau fracture in our department and followed up for at least 10 months. The epidemiological and clinical data analyzed were age, sex, affected side, etiology, mechanism of injury, pathological anatomy and associated lesions. The fractures were classified according to the classification of Duparc and Ficat. The slightly or non-displaced forms were treated orthopedically while the displaced forms were treated surgically. The minimum follow-up was 10 months. The results were evaluated by the anatomical criteria according to Mazas and Duparc and functional according to Merle d’Aubigné. Results: The authors collected 71 cases of tibial plateau fractures. They accounted for 4.0% of all limb fractures, 5.8% of lower limb fractures and 33.8% of knee fractures in our service. The male sex was the most represented at 78.9% with a sex ratio of 3.7. The age group of [20 - 40] years was the most affected, i.e., 53.5%. The average age was 41 years with extremes of 17 and 82 years. The left side was affected (n = 47) and the right side (n = 24). Road traffic accident was the main cause. The mechanism of injury was mainly represented by lateral and sagittal compressions. Lateral unituberosity and bi-tuberosity fractures were the most frequent pathological types in our series, respectively 42.2% and 28.2%. The associated lesions were mainly represented by bone, ligament, skin and neurological lesions. The treatment was orthopedic in 52.1% and surgical in 47.9%. According to the functional criteria of PMA, our results were very good and good at 77.4%, Average at 14.1% and poor at 8.5%. Conclusion: It appears in this study that fractures of the tibial plateaus are frequent and serious because of their articular nature. Lateral and sagittal compressions are the most evoked injury mechanisms. Lateral unituberosity and bituberosity fractures are the most frequent pathological types. Functional and anatomical results are significantly better with surgical treatment.

Lesional and Therapeutic Aspects of Tibial Plateau Fractures at the BSS University Hospital Center in Kati

Introduction: Tibial plateau fractures are solutions of continuity of the epiphyseal-metaphyseal block of the upper end of the tibia of which at least one line enters the joint. They threaten the stability and mobility of the knee and can compromise walking and standing. These fractures are on the increase, especially affecting young and active subjects. Orthopedic treatment is a rare indication apart from non-displaced or slightly displaced forms. Surgical treatment is required in displaced forms, particularly in depression fractures. The aim of this work was to report the lesional and therapeutic aspects of tibial plateau fractures in our department. Patients and Method: Patients and method: This was a retrospective study over 36 months from January 2019 to December 2021. Included in this study were patients treated for a tibial plateau fracture in our department and followed up for at least 10 months. The epidemiological and clinical data analyzed were age, sex, affected side, etiology, mechanism of injury, pathological anatomy and associated lesions. The fractures were classified according to the classification of Duparc and Ficat. The slightly or non-displaced forms were treated orthopedically while the displaced forms were treated surgically. The minimum follow-up was 10 months. The results were evaluated by the anatomical criteria according to Mazas and Duparc and functional according to Merle d’Aubigné. Results: The authors collected 71 cases of tibial plateau fractures. They accounted for 4.0% of all limb fractures, 5.8% of lower limb fractures and 33.8% of knee fractures in our service. The male sex was the most represented at 78.9% with a sex ratio of 3.7. The age group of [20 - 40] years was the most affected, i.e., 53.5%. The average age was 41 years with extremes of 17 and 82 years. The left side was affected (n = 47) and the right side (n = 24). Road traffic accident was the main cause. The mechanism of injury was mainly represented by lateral and sagittal compressions. Lateral unituberosity and bi-tuberosity fractures were the most frequent pathological types in our series, respectively 42.2% and 28.2%. The associated lesions were mainly represented by bone, ligament, skin and neurological lesions. The treatment was orthopedic in 52.1% and surgical in 47.9%. According to the functional criteria of PMA, our results were very good and good at 77.4%, Average at 14.1% and poor at 8.5%. Conclusion: It appears in this study that fractures of the tibial plateaus are frequent and serious because of their articular nature. Lateral and sagittal compressions are the most evoked injury mechanisms. Lateral unituberosity and bituberosity fractures are the most frequent pathological types. Functional and anatomical results are significantly better with surgical treatment.

Open Kyphoplasty for Metastatic Spine Disease: A Retrospective Clinical Series

Symptomatic metastatic spine disease (MSD), is a challenging disease involving 3%-20% of patients with bone metastases. Different surgical options are available and must be tailored to the general and neurologic conditions of the patients. Open kyphoplasty (OKP) refers to decompressive hemilaminectomy, associated with a contralateral percutaneous kyphoplasty, and in some cases, to a posterior stabilization. The aim of the study was to critically review our experience during the last decade with OKP in patients with cancer. Fifty-three patients with cancer underwent OKP for symptomatic MSD. The Tokuhashi score and Spinal Instability Neoplastic Score were calculated for each patient. Length of hospital stay, perioperative complications, incidence of adjacent-level fractures, and median survival after surgery were evaluated. Karnofsky Performance Status, visual analog scale, and Dennis Pain Score were calculated preoperatively, postoperatively, and at last follow-up. Median Tokuhashi score and Spinal Instability Neoplastic Score were 10 and 10, respectively. The mean volume of filling material inserted was 3.6 mL. Median operative time was 180 minutes. Complications included 8 leakages (15%), 2 permanent motor deficits (3.8%), and 2 asymptomatic pulmonary embolisms (3.8%). Mean length of hospital stay was 7 days. A significant improvement was observed in Karnofsky Performance Status, visual analog scale score, and Dennis Pain Score (P < 0.0001). Median follow-up was 16 months and overall survival 22 months. OKP was an effective treatment of symptomatic MSDs in selected oncologic patients with low Tokuhashi scores. It relieved lateral epidural compressions, expanded indications of palliative surgery in patients who were not otherwise surgical candidates, and rapidly dealt with cement leakages.

Magnetotelluric Investigation of the Geo-Tectonic Stability of Campo-Ma’an Area in South Cameroon

The magnetotelluric prospection method has been widely used in Cameroon not only as a reconnaissance method for geophysical investigations but also to determine the nature of the subsurface and the structural settings of the various geological formations in the country that resulted from the global geo-tectonic movements. The present study is aimed at employing the magnetotelluric method to provide evidence on major tectonic dislocations which might have led to the presence of plutonic intrusions in the cratonic structure of the Ntem Complex as well as determining the nature of the contact between the sedimentary Campo Basin and the metamorphic cratonic Ntem Complex. The analyses and interpretations of iso-resistivity maps and geoelectric sections from magnetotelluric data has enabled us to show that tectonic forces at contact between the sedimentary Campo Basin and the metamorphic Ntem Complex were of three different categories: gravity gliding, magmatic upwelling and lateral compressions. The results of the action of these forces were the development of vertical and sub-vertical faulting systems at Craton-Sedimentary Basin contact and subsidence of overburden that appears to have also paved the way for the setting-up of the Ntem River bed and its flood plains. This river bed and its flood plains have been characterized as having a sedimentary deposit depth of 500 m and width of 20 km. Meanwhile, the deep-seated contact faulting systems within the two identified formations have varied fault magnitudes with a maximum of 60 km. The relatively high apparently resistivity values (up to1.0 kΩ•m) for the sedimentary and the very high values for the metamorphic formations (up to and above 10.0 kΩ•m) suggest that the whole area is at present relatively geo-tectonically stable.

Growth, Duplication and Lateral Mutual Compressive Deformation of Akouemma hemisphaeria on the Seafloor of Okondja Basin at 2.2 Ga (Gabon)

A colony of macro-fossils Akouemma hemisphaeria has been described in the Paleoproterozoic sedimentary basin of Okondja, Gabon. These fossils are classified into two groups according to their spheroidal or elongated forms. The spheroidal shapes are similar, have a tripartite structure with two hemispheres and a median disc and gradually pass to the elongated forms. These elongated forms have a pronounced bipartite tendency to two “hemispheres” separated by a median surface, and often have several ovoid “pieces” attached. The elongated specimens show both lateral growth marks and signs of fission. Growth marks are characterized by unidirectional homogeneous side elongations and lateral bud-like protuberances. The signs of fission are marked by circular furrows perpendicular to the direction of elongation, called “constriction furrows” with varying depths depending on the degree of fission of the specimen and internal vertical “division planes”. All of these ovoid and elongated specimens have undergone significant initial deformations due mainly to mutual lateral compressions in tabular beds. The Akouemma hemisphaeria macro-organisms, which were primitive probably sessile organisms, lived on the seafloor. They provide the oldest known record of macro-organisms on Earth having vegetative growth and asexual reproduction by budding, lateral elongation and fission. Their mutual lateral deformations would result from their growth.

ANN based investigations of reliabilities of the models for concrete under triaxial compression

Purpose A lot of triaxial compressive models for different concrete types and different concrete strength classes were proposed to be used in structural analyses. The existence of so many models creates conflicts and confusions during the selection of the models. In this study, reliability analyses were carried out to prevent such conflicts and confusions and to determine the most reliable model for normal- and high-strength concrete (NSC and HSC) under combined triaxial compressions. The paper aims to discuss these issues. Design/methodology/approach An analytical model was proposed to estimate the strength of NSC and HSC under different triaxial loadings. After verifying the validity of the model by making comparisons with the models in the literature, reliabilities of all models were investigated. The Monte Carlo simulation method was used in the reliability studies. Artificial experimental data required for the Monte Carlo simulation method were generated by using artificial neural networks. Findings The validity of the proposed model was verified. Reliability indexes of triaxial compressive models were obtained for the limit states, different concrete strengths and different lateral compressions. Finally, the reliability indexes were tabulated to be able to choose the best model for NSC and HSC under different triaxial compressions. Research limitations/implications Concrete compressive strength and lateral compression were taken as variables in the model. Practical implications The reliability indexes were tabulated to be able to choose the best model for NSC and HSC under different triaxial compressions. Originality/value A new analytical model was proposed to estimate the strength of NSC and HSC under different triaxial loadings. Reliability indexes of triaxial compressive models were obtained for the limit states, different concrete strengths and different lateral compressions. Artificial experimental data were obtained by using artificial neural networks. Four different artificial neural networks were developed to generate artificial experimental data. They can also be used in the estimations of the strength of NSC and HSC under different triaxial loadings.

Compression Responses of Bio-Cellular Luffa Sponges

Crushing behaviors of luffa sponges were studied through mechanical experiments. Controlled by four-order hierarchical and anisotropic structures, luffa sponges exhibit anisotropic responses along axial, radial, and circumferential directions. The ultra-thin but stiff inner surface layer dominates the crushing behavior, endowing the axially compressed luffa cylinder with structural integrity, enhancing the elastic deformation and yielding strength. In radial, circumferential, and lateral compressions, after removing the inner surface layer, luffa sponges are compliant and have large quasi-linear deformation before densification, without a plateau characterized by yielding and deformation. Immersed into water, crushed luffa sponge cylinders recover their geometry completely. However, compression strength is only partially restored. Gradual damage of the inner surface layer in water immersing/drying cycles greatly weakens the compression strength. In the case of removal of the inner surface layer, crushed luffa sponge cylinders completely restore their quasi-linear deformation ability during the water immersing/drying cycles.

Organization of lipids in the tear film: a molecular-level view.

Biophysical properties of the tear film lipid layer are studied at the molecular level employing coarse grain molecular dynamics (MD) simulations with a realistic model of the human tear film. In this model, polar lipids are chosen to reflect the current knowledge on the lipidome of the tear film whereas typical Meibomian-origin lipids are included in the thick non-polar lipids subphase. Simulation conditions mimic those experienced by the real human tear film during blinks. Namely, thermodynamic equilibrium simulations at different lateral compressions are performed to model varying surface pressure, and the dynamics of the system during a blink is studied by non-equilibrium MD simulations. Polar lipids separate their non-polar counterparts from water by forming a monomolecular layer whereas the non-polar molecules establish a thick outermost lipid layer. Under lateral compression, the polar layer undulates and a sorting of polar lipids occurs. Moreover, formation of three-dimensional aggregates of polar lipids in both non-polar and water subphases is observed. We suggest that these three-dimensional structures are abundant under dynamic conditions caused by the action of eye lids and that they act as reservoirs of polar lipids, thus increasing stability of the tear film.

Dynamic Failure Surface of Concrete under Multiaxial Dynamic Loads

Study on the dynamic behavior of concrete is important, for the sake of seismic design and safety evaluation of mass concrete structures, such as concrete dams, nuclear reactors and so on. There have been a lot of uniaxial strength experiment data of concrete under dynamic loading, but multiaxial data is scarce, for the test of multiaxial strength of concrete under dynamic loading is difficult, while most mass structures work under multiaxial static and dynamic stress states. In this paper a three-dimension failure criterion of concrete under dynamic loading in octahedral stress space was proposed. Then the multixial strength tests of concrete under dynamic loading were carried out with concrete triaxial static and dynamic apparatus system. The selected loading paths consisted of uniaxial compression and tension, biaxial proportional loading compression, biaxial compression with one constant lateral compression and triaxial compression with two constant lateral compressions. In the test the strain rate range is 10-5~10-2/s. Based on the test data and the literature data, the characteristic of this failure surface is that it considered the influence of the strain rate and the angle of similarity; it is smooth, convex in meridian and deviatoric plane. The proposed model for nonlinear dynamic analysis and design of mass concrete structures under dynamic loading is useful.

Extreme bending of composite insulators on 750 kV compact transmission lines

In designing and constructing the first 750 kV double-circuit compact transmission line, much pioneering work is necessitated in the choice of tower, insulator strings and phase-to-phase spacers. In this paper the mechanical characteristics of three possible phase-to-phase composite spacers for such compact transmission lines are considered in respect of very large bending of the spacer. A large deflection theory is introduced to calculate the lateral deflections and longitudinal compressions caused by applied axial loads and these are compared with the results of tests on three spacers of different lengths and diameters. Agreement between calculation and test results was good and the necessity for the larger diameter demonstrated. No permanent damage due to the extreme bending was found and two of the spacer samples were found to be suitable for use in the compact transmission lines with a good safety margin in respect of such bending.

Relaxation Processes in the Adsorption of Surface Layer Proteins to Lipid Membranes

The present work evaluates the kinetics of the interaction of S-layer protein from Lactobacillus brevis with lipid monolayers by measuring the changes in the surface pressure as a function of time for different lipid compositions and at different lateral compressions. At high surface pressures, or at high cholesterol ratios, in which membrane rigidity and surface polarity are increased, the kinetics can be described by a pure diffusional process. At low pressures or in the absence of cholesterol, the kinetics of protein interaction can be interpreted as a consequence of a relaxation process of the membrane structure coupled to diffusion. As the less packed monolayers are more hydrated, the relaxation processes at low initial surface pressures could be ascribed to changes in water organization in the membrane. These observations denote that kinetic insertion of proteins can be modulated by components that modify the hydration state of the interface.

선조질강 소재의 단조공정 측면에서의 특징

In this paper, plastic deformation behaviors of ESW105 and SCM435 steels are revealed by simulations and experiments. ESW105 is the special pre-heat-treated steel characterized by high initial yield strength and negligible strain- hardening behavior. The flow stresses of the two steels for large stain are calculated from tensile tests. Axial and lateral compressions of cylindrical bars are tested and simulated and the deformed shapes are compared to characterize the plastic deformation behaviors of the two materials. A forward extrusion process of a cylindrical bar is also simulated to reveal the difference. It has been shown that there are pretty much difference in plastic flow between ESW105 and SCM435 which causes from the difference in strain-hardening capability, implying that the experience-oriented design rules for common commercial materials may lead to failure in process design when the new material of ESW105 is applied without consideration of its plastic deformation behavior.

A stress interpretation scheme applied to lunar gravity and topography data

We present an approach of the inverse gravimetric problem that allows the gravity to be directly related to the deviatoric stresses without any rheological assumptions. In this approach a new set of parameters is considered: (1) the density variations over equipotential surfaces and the height of interfaces above the corresponding equipotential surfaces and (2) the stress difference. The method is applied to lunar topographic and gravimetric data that are interpreted in term of transversally isotropic deviatoric stress within the Moon. It also provides inference on density and crustal thickness variations. The estimated lateral variation in deviatoric stress is about 500 bars within the crust and upper mantle. In the crust, because of topography, the strongest stress differences take place on the far side, with large lateral compressions beneath the south pole–Aitken basin. Vertical compression under the mascons of the nearside is the main feature within the upper mantle.

Signal use by collared lizards, Crotaphytus collaris : the effects of familiarity and threat

Many lizard species use lateral compressions of the body during agonistic encounters. I investigated the signal value of the frequency at which these displays are presented and how that rate is affected by familiarity and threat. The response of resident collared lizards (Crotaphytus collaris) to tethered strangers, neighbors on the correct boundary, and neighbors displaced to the opposite boundary, was recorded by counting the number of lateral displays directed at the intruder and the number of subsequent acts of escalated aggression. There was no relationship between size asymmetry of the opponent and the rate of lateral display or aggression, nor was there a relationship between body size and the rate of lateral display or aggression. However, there was a high positive correlation between lateral display rate and aggression, suggesting that the rate of lateral displays is a conventional signal of motivation to attack. The highest rates of display and aggression were directed toward displaced neighbors, somewhat less toward strangers, and the least toward neighbors at the correct boundary. The ratio of aggressive acts to lateral displays followed the same pattern, presumably because the perceived threat to the resident decreases in the same order. Taken together these data suggest that collared lizards are able to assess the threat of an opponent and signal motivation to respond aggressively towards that opponent.

Annealed Polyelectrolyte Brushes under Normal and Lateral Compressions

We report here compression force measurements of diblock copolymers containing a short neutral hydrophobic sequence (polystyrene) and a long water-soluble weak polyelectrolyte sequence (poly(2-vinylpyridine)). This study focuses on the polyelectrolyte sequence and has been restricted to the case where the subphase is at pH 2. The lateral compressions were done using a Langmuir trough whereas the normal compressions were carried out with an atomic force microscope with a spherical particle attached to the tip. The thickness of the brush is considered as a function of the grafting density and is determined from the AFM force curves without reference to any theoretical model. At high grafting densities an “anomalous” behavior is observed, where the thickness of the brush decreases with increasing the grafting density. This is attributed to the annealed character of the polyelectrolyte.