Subjacent Structures Research Articles

Application of friction surfacing for solid state additive manufacturing of cylindrical shell structures

Solid-state additive manufacturing (AM) via friction stir based processes is gaining increased attention as these techniques are feasible for several similar and dissimilar material combinations and induce significantly lower energy input to the subjacent structure than fusion-based approaches as material melting is avoided. Available research concentrates on linear depositions; however, further development of these techniques towards application necessitates more complex deposition paths, e.g. curves and the crossing of edges of previously deposited layers. In this study, the solid-state layer deposition process of friction surfacing (FS) is investigated in terms of process behavior and appearance of the resulting deposit when curved deposition paths are applied. With advancing side on the curve's inner edge, material build-up occurs predominantly on this side of the layer, which results in a deposit of inhomogeneous thickness. This phenomenon is related to the FS process characteristic due to the superposition of rotational and travel movement on a curvature, and is more pronounced for curves with small radii. A further challenge exists for closed structures, where the deposition has to cross previously deposited layers. This can be successfully achieved by reducing the travel speed prior to passing the edge to provide sufficient plasticized material thickness below the stud tip. Overall, the study provides an understanding of the FS process behavior and process parameters for curved paths. Furthermore, recommendations for process control and path planning, e.g. for building closed cylindrical shell structures, are deduced.

Infarto cerebral e meningoencefalite trombótica em um bezerro devido a candidíase

ABSTRACT: We described a case of cerebral infarction and thrombotic meningoencephalitis due to candidiasis in a seven-month-old calf. The death occurred three days after the onset of apathy, fever, and the head’s lateral deviation to the left. Macroscopic changes in the brain consisted of asymmetry of telencephalic hemispheres; the right hemisphere was enlarged, causing cerebellar herniation. A focally extensive red area was observed on the surface of the right occipital lobe. At cross-sections of the fixed brain, the lesions revealed to be extensive, red-brown, soft or cavitated areas affecting the white and grey matter from the level of the thalamus to the cerebellum and compressing subjacent structures. Histologically, there was acute, coalescent, multifocal necrosupurative meningoencephalitis, associated with vasculitis, congestion, thrombosis, edema, infarction, and intralesional fungal hyphae. The diagnosis of cerebral infarction and thrombotic meningoencephalitis due to candidiasis was made by the pathological changes, the staining and morphological characteristics of the agent, and immunohistochemistry. The cerebral infarction and thrombotic meningoencephalitis in cattle can result from vascular lesions due to infection by Candida sp.; although uncommon, this case demonstrated that candidiasis should be part of a list of differential diagnoses of severe brain injuries in cattle.

"Honecker's Vassal" or a Prehistorian in the Service of Science? The Evaluation of Former East German Scholarship and the Concept of the Scholar in the Debate on Joachim Herrmann in Reunified Germany.

The evaluation and transformation process of the GDR research system in the wake of German reunification 1989/90 was immediately accompanied not only by debates within the scientific community, but also by an extensive discussion about the value and future perspectives of East German scholarship and its protagonists in the nationally circulated press. In 1990, the focus turned temporarily to the prominent East German prehistorian Joachim Herrmann after his election to the board of an international historical association. The article uses the example of Herrmann and the public discussion about him as a case study to examine the status of, and changes in, the authority of scholarship and the scholar in the context of the evaluation and restructuring of the East German research landscape in the early 1990s. A selection of press articles from nationwide German newspapers and newsmagazines, as well as archival letters exchanged between different participants in the debate serve as prisms carving out the central arguments and subjacent structures of the discussion. Therefore, Herrmann's case exposes generic characteristics of (different concepts of) scientific authority and the close connection between its negotiation and the search for identity in the newly reunited German academic sphere.

Sinanköy (Lalapaşa-Edirne) ve Çevresinin Yapısal Jeomorfoloji Özelliklerinin Drenaj Sistemi Üzerindeki Etkileri

The main aim of this study is to determinate structural geomorphology features and research their effects on the drainage system. Firstly, 1/25.000 scale topographic map and 1/100.000 scale geological map were digitized on the Geographical Information Systems platform and a digital database was created. Structural features were examined; morphometric analyzes, lineament analyze and hydrological analyses were performed. In the field works; verification and correction of the GIS-based analyze results, measurements of structural features, photographing and mapping studies have been carried out. According to GIS-based analyze and measurement results; geological formations general strike is northwest-southeast, prevalent dip direction is southwest and dip angle values varying between 5-30°. Morphometric analyze results and field measurements, clearly defined the monoclinal structure geomorphology. It has been seen that “consequent” and “resequent “streams flow through northeast-southwest, parallel to the monoclinal structures’ natural slope direction, while “obsequent” and “subsequent” streams flow through west-east and northwest-southeast, deviating from the monoclinal structures natural slope direction. The evolutionary process of the drainage system has been affected by monoclinal structures’ geomorphologic, lithologic and stratigraphic characteristics. This influence also has controlled the exhumation of the subjacent structure, made the monoclinal structure landforms more evident. As a result of these processes, the drainage system gained a “trellis (orthogonal)” pattern that is compatible with the structure.

58-02: Initial evaluation of a novel Multi-Electrode Balloon Radio Frequency Ablation Catheter in Swine

Introduction: Isolation of pulmonary veins is efficacious in treating atrial fibrillation. Conventionally isolation is achieved with point-by-point radiofrequency ablation (RFA). However conventional RFA is time consuming, has limited efficacy, and is associated with a significant risk of complications. A range of multi-electrode catheters have been trialed, with variable success. To address these challenges, we developed a novel multi-electrode balloon catheter. This RF balloon catheter has multiple irrigated electrodes on the surface of a 28mm balloon. The catheter incorporates inter balloon cameras to provide real time images of electrode contact. A multi-channel generator delivers power to user-selected electrodes in unipolar or bipolar mode. Methods: Five Yorkshire pigs were treated with the novel balloon catheter. The catheter was delivered over the wire through a steerable sheath to the left atrium. Inter balloon imaging was used to confirm electrode position and contact. Electrodes were selected for bipolar ablation at the antrum of the targeted pulmonary vein. Following the procedures the pigs were sacrificed and the hearts and surrounding tissues examined. Cardiac tissue was then incubated in triphenyl tetrazolium chloride dye and examined. Results: In all five pigs the catheter could be delivered to the left atrium, and pulmonary vein ablation sets delivered. Pulmonary vein lesions were all transmural, 1–5mm in depth. No endocardial thrombus or complications were observed. Conclusion: Ablations using this novel multi-electrode balloon catheter provided continuous transmural lesions in the left atrium without thrombus nor injury to subjacent structures in this initial animal evaluation. The system provides a means of positioning, mapping, irrigating and creating multi-geometry lesions with a single catheter. The direct visualization within the balloon provides optimization of lesion placement. These initial results in swine suggest that this balloon catheter may be efficacious in ablation of atrial fibrillation, and warrant trials in humans.

Hemangiopericytoma: A Rare Case Report

Introduction: Hemangiopericytoma is a rare neoplasm that was first described by Stout and Murray in 1942 as a vascular tumor derived from the pericytes. They account for 2-3% of all soft tissue sarcomas in humans and they occur mainly in the musculoskeletal system. 15-30% of all hemangiopericytomas occur in the head and neck region. Only 5% are located in the sinonasal region, where they display a more benign behavior than in other parts of the body. Case Report: Herein, we are presenting an extremely rare case report of hemangiopericytoma in a 32 year old male patient with a brief overview regarding its epidemiology, macro- and microscopical characteristics, the clinico-pathological findings and the treatment of this extremely rare vascular neoplasm. Conclusion: Conclusion rests with the inclusion of the possibility of such rare vascular tumors in the possible differential diagnoses of the various peripheral soft tissue lesions. An early diagnosis thus helps in the effective management of such lesions without further bringing changes on the subjacent and adjacent structures and tissues including bone.

Remarks on the exact energy functional for fermions: an analysis using the Löwdin partitioning technique

A comparison model based in the Löwdin partitioning technique is used to analyse the differences between the wave function and density functional models. This comparison model provides a tool, the Löwdin function f (E), to understand the structure of both theories and its discrepancies in terms of the subjacent mathematical structure and the necessary conditions of variationality required for the energy functional. It is argued that density functional theory (DFT) can be compared to the wave function theory (WFT) using the expressions of f (E) at E = 0. The WFT provides an explicit form of the exact energy functional for a fermion system from the full configuration interaction approach. The DFT can be seen as a special case of Löwdin function that does not satisfy all variational conditions on ρ(r) and also on the EXC[ρ] term. This analysis shows that ignoring the restrictions imposed by the spin and space symmetry requirements of the solutions when making a variational calculation implies that the correlations expressed by the ρ(r) function will be inconsistent with a γ1(r1; r′1) function derivable from a spin and space symmetry adapted wave function Ψ(r1s1, …, rnsn), even for a closed-shell system (i.e. an energy minimum that will exhibit the phenomenon of ‘overcorrelation’). The comparison scheme also provides a new insight on the variational requirements in order to achieve a consistent description of the molecular electronic structure of both ground and excited states. Some numerical results are reported.

Ultraviolet Light‐Induced Cyclobutane Pyrimidine Dimers in Rabbit Eyes

Sunlight exposure of the eye leads to pathologies including photokeratitis, cortical cataracts, pterygium, actinic conjunctivitis and age-related macular degeneration. It is well established that exposure to ultraviolet (UV) radiations leads to DNA damage, mainly cyclobutane pyrimidine dimers (CPDs). CPD formation is the principal factor involved in skin cancer. However, the exact mechanism by which sunlight induces ocular pathologies is not well understood. To shed light on this issue, we quantified the CPD formation onto DNA of rabbit ocular cells following UVB exposure. We found that CPDs were induced only in the structures of the ocular anterior chamber (cornea, iris and lens) and were more concentrated in the corneal epithelium. Residual UVB that pass through the cornea are completely absorbed by the anterior layers of the iris. CPDs were also detected in the central portion of the lens that is not protected by the iris (pupil). By determining the UV-induced DNA damage formation in eyes, we showed that anterior ocular structures are a reliable physical barrier that protects the subjacent structures from the toxic effects of UV. Although the corneal epithelium is the structure where most of the CPDs were detected, no cancer is related to solar exposure.

Illustrative Stream Surfaces

Stream surfaces are an intuitive approach to represent 3D vector fields. In many cases, however, they are challenging objects to visualize and to understand, due to a high degree of self-occlusion. Despite the need for adequate rendering methods, little work has been done so far in this important research area. In this paper, we present an illustrative rendering strategy for stream surfaces. In our approach, we apply various rendering techniques, which are inspired by the traditional flow illustrations drawn by Dallmann and Abraham \& Shaw in the early 1980s. Among these techniques are contour lines and halftoning to show the overall surface shape. Flow direction as well as singularities on the stream surface are depicted by illustrative surface streamlines. ;To go beyond reproducing static text book images, we provide several interaction features, such as movable cuts and slabs allowing an interactive exploration of the flow and insights into subjacent structures, e.g., the inner windings of vortex breakdown bubbles. These methods take only the parameterized stream surface as input, require no further preprocessing, and can be freely combined by the user. We explain the design, GPU-implementation, and combination of the different illustrative rendering and interaction methods and demonstrate the potential of our approach by applying it to stream surfaces from various flow simulations. ;

Pattern of Extracranial Peripheral Aneurysm at a Referral Hospital in Kenya

Peripheral aneurysms are important because of concurrence with aortic ones and potential to thromboembolise or rapture. Their distribution shows population variations yet reports from Africa are scarce and altogether absent from Kenya. Objective To describe the pattern of peripheral aneurysms in a Kenyan national referral hospital. Patients and methods Records of in-patients with a diagnosis of peripheral aneurysms at Kenyatta National Hospital between January 1998 and December 2007 were analyzed for presentation, diagnostic method, risk factors, site, age and gender distribution. Only records containing all these data were included. Data were analyzed using SPSS version 13.0 and presented using tables, and bar charts. Results Ninety six cases involved the femoral (24%), common carotid (15.6%); brachial (12.5%); brachiocephalic (11.5%) and popliteal (10.4%) arteries. They presented with pulsatile mass (37.5%), painful swelling (22.9%) and pressure on subjacent structures (13.5%). Diagnosis was confirmed by Doppler ultrasound (37.5%), conventional angiography (30.2%) and plain ultrasound (14.6%). Mean age was 45.6 years (range 13 – 79 years); with 50% of them occurring in individuals aged 40 years and younger. Common risk factors were trauma (39.6%), hypertension (13.5%) and atherosclerosis (9.4%). Male:female ratio was: 15:1 for femoropopliteal, 5:1 for brachial; 1:1 for common carotid and 1:2.6 for brachiocephalic trunk. Conclusion Characteristics of peripheral aneurysms in the Kenyan study population vary from those of Caucasians. They are more widespread, trauma related, and occur in younger individuals. Prudent management of risk factors is recommended.

Electrical Conductivities and Critical Micelle Concentrations (Determined by the Local Polynomial Regression Method) of Imipramine and Clomipramine Hydrochlorides from (283 to 313) K

Electrical conductivity measurements for aqueous solutions of imipramine and clomipramine hydrochlorides have been carried out from (283 to 313) K. From these data, critical micelle concentrations (CMCs) have been obtained by application of the local polynomial regression method, which is based on a nonparametric estimation of the regression function. The method is extremely flexible because it does not impose any parametric model on the subjacent structure of the data but rather allows the data to speak for themselves. The variation of the CMC with temperature was a second-order polynomial, with different trends for imipramine (convex) and clomipramine (concave). This distinct behavior was analyzed by the effects of dehydration of the headgroups and thermal solubility of molecules.

A nonparametric approach to calculate critical micelle concentrations: the local polynomial regression method.

The application of a statistical method, the local polynomial regression method, (LPRM), based on a nonparametric estimation of the regression function to determine the critical micelle concentration (cmc) is presented. The method is extremely flexible because it does not impose any parametric model on the subjacent structure of the data but rather allows the data to speak for themselves. Good concordance of cmc values with those obtained by other methods was found for systems in which the variation of a measured physical property with concentration showed an abrupt change. When this variation was slow, discrepancies between the values obtained by LPRM and others methods were found.

Uterosacral Ligament

In Brief Objective To determine the optimal site in the uterosacral ligament for suspension of the vaginal vault with regard to adjacent anatomy and suspension strength. Methods Fifteen female cadavers were evaluated between December 1998 and September 1999. Eleven hemisected pelves were dissected to better define the uterosacral ligament and identify adjacent anatomy. Ureteral pressure profiles with and without relaxing incisions were done on four fresh specimens. Suture pullout strengths also were assessed in the uterosacral ligament. Results The uterosacral ligament was attached broadly to the first, second, and third sacral vertebrae, and variably to the fourth sacral vertebrae. The intermediate portion of the uterosacral ligament had fewer vital, subjacent structures. The mean ± standard deviation distance from ureter to uterosacral ligament was 0.9 ± 0.4, 2.3 ± 0.9, and 4.1 ± 0.6 cm in the cervical, intermediate, and sacral portions of the uterosacral ligament, respectively. The distance from the ischial spine to the ureter was 4.9 ± 2.0 cm. The ischial spine was consistently beneath the intermediate portion but variable in location beneath the breadth of the ligament. Uterosacral ligament tension was transmitted to the ureter, most notably near the cervix. The cervical and intermediate portions of the uterosacral ligament supported more than 17 kg of weight before failure. Conclusion Our findings suggest that the optimal site for fixation is the intermediate portion of the uterosacral ligament, 1 cm posterior to its most anterior palpable margin, with the ligament on tension. The intermediate portion of the uterosacral ligament is the optimal site for vaginal vault suspension based on protecting adjacent structures and uterosacral strength.

Uterosacral ligament: description of anatomic relationships to optimize surgical safety

Objective: To determine the optimal site in the uterosacral ligament for suspension of the vaginal vault with regard to adjacent anatomy and suspension strength. Methods: Fifteen female cadavers were evaluated between December 1998 and September 1999. Eleven hemisected pelves were dissected to better define the uterosacral ligament and identify adjacent anatomy. Ureteral pressure profiles with and without relaxing incisions were done on four fresh specimens. Suture pullout strengths also were assessed in the uterosacral ligament. Results: The uterosacral ligament was attached broadly to the first, second, and third sacral vertebrae, and variably to the fourth sacral vertebrae. The intermediate portion of the uterosacral ligament had fewer vital, subjacent structures. The mean ± standard deviation distance from ureter to uterosacral ligament was 0.9 ± 0.4, 2.3 ± 0.9, and 4.1 ± 0.6 cm in the cervical, intermediate, and sacral portions of the uterosacral ligament, respectively. The distance from the ischial spine to the ureter was 4.9 ± 2.0 cm. The ischial spine was consistently beneath the intermediate portion but variable in location beneath the breadth of the ligament. Uterosacral ligament tension was transmitted to the ureter, most notably near the cervix. The cervical and intermediate portions of the uterosacral ligament supported more than 17 kg of weight before failure. Conclusion: Our findings suggest that the optimal site for fixation is the intermediate portion of the uterosacral ligament, 1 cm posterior to its most anterior palpable margin, with the ligament on tension.

French contributions to electron microscopic radioautography.

Radioautographic effects result from properties of ionizing radiations which act on a special photographic emulsion by leaving tracks in silver halide crystals. The phenomenon was observed in 1896 by Henri Becquerel [4] working at the Museum National d'Histoire Naturelle in Paris, by placing accidentally a crystal of uranium salt on a photographic plate protected from light. When he later developed the plate forgotten in a drawer, he was astonished to observe that the form of the uranium crystal was imprinted on the photographic emulsion. Becquerel gave first an erroneous interpretation of this unexpected phenomenon: he thought it was caused by some unknown radiations secondarily emitted by the phosphorescent property of this mineral. However, this impression could be reproduced when the crystal was left in a darkroom. Hence, he postulated that uranium itself was able to produce radiations which could not be detected by the eye but by photographic emulsion. His contribution to the discovery of the natural radioactivity was rewarded by a Nobel prize he shared with Made and Pierre Curie in 1903. In fact, Becquerel not only discovered radioactive radiations, but he invented simultaneously the principle of radioautography: the uranium crystal reproduced its outline by emitting radiations which were registered in the photographic emulsion. The principle of this method was applied 30 years later to detect the site of natural radioactive atoms in biological samples. In 1924, A Lacassagne and J Latt~s [39] at the Institut Curie imagined to place a photographic plate in contact with slices of organs previously embedded in paraffin blocks. When rabbits were given polonium, the radioactive radiations emitted, by polonium incorporated into the organs produced a blackening of the photographic plates. Thus the images provided a distribution of polonium in various tissues, but this technique did not allow to obtain a resolution at the cellular level and if one excepts radiotoxicological investigations, radioautographic applications of natural radioactivity were rather limited. A new impulse was given by the discovery of artificial radioactivity; FrEdEric and Irene Joliot-Curie, working at the Coll~ge de France, opened indeed new vistas to radioautography by extending the production of a great variety of radioactive isotopes which have been proved to be essential tools to put forth new concepts in physiology, pharmacology and medicine. As early as 1938, F Joliot, fascinated by the biological applications of this discovery, asked A Lacassagne to collaborate. The latter proposed CP Leblond, a young histologist educated at the FacultE catholique de mEdecine de Lille, to study the location of the 128I iodine isotope, produced by cyclotron, in the thyroid gland by radioautography [44]. This project was interrupted by World War II, but the idea remained in Leblond's mind. In 1943, he used another isotope of iodine and succeeded to obtain tracks in thyroid follicles [42]. It was necessary however to improve resolution. Leblond, now in Montreal, was conscious that a major pitfall was the distance between the radioactive source contained in tissue sections and the photographic emulsion used as detector of radiations. Moreover, a direct superimposition of the radioactive tracks and of the subjacent histological structures was required. With these goals in mind, BElanger and Leblond [5] devised in 1946 the so-called 'coating technique' of radioautography in which a gently-warm, liquid photographic emulsion is directly applied in close contact with the tissue sections. The thin film of coated emulsion adheres directly to the subjacent structures and reduces therefore the interspace between the radioactive source and the detector. After developing the radioautographs, the silver grains are visualized over the tissues or cells enclosing the radioactive tracer. Simultaneously, nuclear physicists devised new emulsions especially enriched in small-sized silver halide crystals, called 'nuclear emulsions'. A better knowledge of the interactions between nuclear emulsions and radiations permitted to obtain highsensitivity detection at minimum ionization (reviewed in [45]); a lowering of the detection threshold of beta-emitting isotopes was improved by activation procedures of the emulsion for light and for electron microscopy (reviewed in [52]). Since resolution, sensitivity and yield of the nuclear emulsion were also improving, the principle of the 'coating technique' could be adapted and applied to electron microscopic preparations.

Three-Dimensional Reconstruction of Human Coronary and Peripheral Arteries From Images Recorded During Two-Dimensional Intravascular Ultrasound Examination

BACKGROUNDIntravascular ultrasound provides high-resolution images of vascular lumen, plaque, and subjacent structures in the vessel wall; current instrumentation, however, limits the operator to viewing a single, tomographic, two-dimensional image at any one time. Comparative analysis of serial two-dimensional images requires repeated review of the video playback recorded during the two-dimensional examination, followed by a mind's eye type of imagined reconstruction.METHODS AND RESULTSComputer-based, automated three-dimensional reconstruction was used to generate a tangible format with which to assess and compare a stacked series of two-dimensional images. Three-dimensional representations were prepared from sequential images obtained during intravascular ultrasound examination in 52 patients, 50 of whom were studied before and/or after percutaneous revascularization. Conventional two-dimensional ultrasound images were acquired by means of a systematic, timed pullback of the ultrasound catheter thro...

Large-magnitude Permian shortening and continental-margin tectonics in the southern Cordillera

The Last Chance allochthon, with displacement estimated to be 55 to 105 km and lateral extent possibly exceeding 300 km, was inferred to be Middle Triassic and thus kinematically distinct from a belt of Permian-Triassic deformation in the western Mojave Desert. Correlations of structures forming the Death Valley thrust belt, which includes the Last Chance allochthon, several subjacent structures, and their inferred lateral equivalents, suggest that prior to Tertiary extension, individual structures were laterally continuous for distances exceeding 150 km along strike, from the Nevada Test Site area southwest to the Darwin Plateau. Their inferred Mesozoic age and the presence of an Early Triassic overlap sequence on the Darwin Plateau precluded projection of these structures farther south, in spite of long-recognized strain compatibility problems associated with large displacement on thrusts that apparently terminated there without suitable accommodation structures, such as tear faults or lateral ramps. These problems may be resolved if the Last Chance allochthon is Permian, consistent with structural correlations, new isotopic data from post-tectonic stocks, and stratigraphic evidence. A large Permian turbidite basin near the Darwin Plateau can be interpreted as a marine foredeep resulting from emplacement of the 5-km-thick allochthon, rather than a local trough caused by transcurrent faulting during inferred Permian-Triassic continental truncation. I propose that anomalous eugeoclinal rocks in the western Mojave Desert have been emplaced against cratonic strata there by the Last Chance allochthon, which foreshortened an originally narrow continental margin.

Three-dimensional reconstruction of human coronary and peripheral arteries from images recorded during two-dimensional intravascular ultrasound examination.

Intravascular ultrasound provides high-resolution images of vascular lumen, plaque, and subjacent structures in the vessel wall; current instrumentation, however, limits the operator to viewing a single, tomographic, two-dimensional image at any one time. Comparative analysis of serial two-dimensional images requires repeated review of the video playback recorded during the two-dimensional examination, followed by a "mind's eye" type of imagined reconstruction. Computer-based, automated three-dimensional reconstruction was used to generate a tangible format with which to assess and compare a "stacked" series of two-dimensional images. Three-dimensional representations were prepared from sequential images obtained during intravascular ultrasound examination in 52 patients, 50 of whom were studied before and/or after percutaneous revascularization. Conventional two-dimensional ultrasound images were acquired by means of a systematic, timed pullback of the ultrasound catheter through the respective vascular segments. Images were then assembled in automated fashion to create a three-dimensional depiction of the vessel lumen and wall. Computer-enhanced three-dimensional reconstructions were generated in both sagittal and cylindrical formats. The sagittal format resulted in a longitudinal profile similar to that obtained during angiographic examination; in contrast to angiography, however, the sagittal reconstruction offered 360 degrees of limitless orthogonal views of the plaque and arterial wall as well as the vascular lumen. The cylindrical format yielded a composite view of a given vascular segment, and a hemisected version of the cylindrical reconstruction enabled en face inspection of the reconstructed luminal surface. Sagittal reconstructions facilitated analysis of dissections and plaque fractures resulting from percutaneous revascularization, and the hemisected cylindrical reconstructions enhanced analysis of endovascular prostheses. This preliminary experience demonstrates that computer-based three-dimensional reconstruction may further augment the use of intravascular ultrasound in assessing vascular pathology and guiding interventional therapy.

Characteristics of seismic waves composing Hawaiian volcanic tremor and gas‐piston events observed by a near‐source array

A correlation method, specifically designed for describing the characteristics of a complex wave field, is applied to volcanic tremor and gas‐piston events recorded by a semicircular array of GEOS instruments set at the foot of the Puu Oo crater on the east rift of Kilauea volcano, Hawaii. The spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas‐piston events and tremor, and clearly depict dispersive waves propagating across the array from the direction of Puu Oo. The wave fields are composed of comparable amounts of Rayleigh and Love waves propagating with similar and extremely slow phase velocities ranging from 700 m/s at 2 Hz to 300 m/s at 8 Hz. The highly cracked solidified lava flow on which the array was deployed, and subjacent structure of alternating lava and ash layers formed during repeated eruptions of Puu Oo since 1983, appear to be responsible for the low velocities observed. The results from Puu Oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of Kilauea Iki. Rayleigh waves were not observed in Kilauea Iki, but well‐developed trains of Love waves were seen to propagate there with velocities twice as high as those observed near Puu Oo. These differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in Kilauea Iki, which may have lowered the phase velocity of Rayleigh waves more drastically than that of Love waves, resulting in severe scattering of the Rayleigh wave mode. On the other hand, the thin superficial pahoehoe flow under our array at Puu Oo may have favored the development of vertical columnar joints more extensively at this location than at Kilauea Iki, which may have reduced the shear moduli controlling the Love wave mode. The average phase velocities in the frequency band from 2 to 5 Hz found at Puu Oo are roughly similar to those determined for tremor at Klyuchevskoy volcano, Kamchatka, but the frequency dependence appears much stronger at Puu Oo.

Endothelial denudation and myointimal thickening in the rat carotid artery induced by the passage of bubbles

A new technique for the selective removal of endothelium in the rat carotid artery has been developed, and subsequent events in the vascular wall have been examined. To achieve de-endothelialization, more than 2,000 bubbles of nitrogen in phosphate-buffered saline are passed through a temporarily isolated segment of rat carotid over a period of 3 min. Bubbles are generated by a simple apparatus, consisting of a pressurized tilting chamber and catheter. Endothelium is removed while subendothelial basement membrane and other subjacent structures remain intact. Platelets attach to the denuded surface within minutes after re-establishment of blood flow. Myointimal thickening is found at 5 weeks and 4 months after de-endothelialization. The method is quite reliable and will facilitate further studies of reactions to carotid endothelial injury in young adult rats.