Home About us Contact
|
Home About us Contact | ||
|
|
||
Mechanical Work (mechanical + work)
Selected AbstractsPolymer/NiTi-composites: Fundamental Aspects, Processing and Properties,ADVANCED ENGINEERING MATERIALS, Issue 11 2005K. Neuking NiTi shape memory alloys can be used as actor materials and perform mechanical work; they can also be used for damping applications. In combination with polymers their functionality can be increased. Shape memory effects of NiTi alloys are associated with large strains and in a NiTi/polymer-composite, the polymer can accommodate these large strains without breaking. In a NiTi/polymer-composite the polymer can for example be used to store elastic energy, to provide corrosion resistance or to assist in a damping application. For all applications, a good bonding between the shape memory alloy and the polymer is required. The present paper considers fields of applications, processing and properties of NiTi/polymer-composites. [source] The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stentJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Tré R. Welch Abstract We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L -lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62°C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Modulation of cardiac ionic homeostasis by 3-iodothyronamineJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 9b 2009Sandra Ghelardoni Abstract 3-iodothyronamine (T1AM) is a novel endogenous relative of thyroid hormone, able to interact with trace amine-associated receptors, a class of plasma membrane G protein-coupled receptors, and to produce a negative inotropic and chronotropic effect. In the isolated rat heart 20,25 ,M T1AM decreased cardiac contractility, but oxygen consumption and glucose uptake were either unchanged or disproportionately high when compared to mechanical work. In adult rat cardiomyocytes acute exposure to 20 ,M T1AM decreased the amplitude and duration of the calcium transient. In patch clamped cardiomyocytes sarcolemmal calcium current density was unchanged while current facilitation by membrane depolarization was abolished consistent with reduced sarcoplasmic reticulum (SR) calcium release. In addition, T1AM decreased transient outward current (Ito) and IK1 background current. SR studies involving 20 ,M T1AM revealed a significant decrease in ryanodine binding due to reduced Bmax, no significant change in the rate constant of calcium-induced calcium release, a significant increase in calcium leak measured under conditions promoting channel closure, and no effect on oxalate-supported calcium uptake. Based on these observations we conclude T1AM affects calcium and potassium homeostasis and suggest its negative inotropic action is due to a diminished pool of SR calcium as a result of increased diastolic leak through the ryanodine receptor, while increased action potential duration is accounted for by inhibition of Ito and IK1 currents. [source] DATA ANALYSIS OF PENETROMETRIC FORCE/DISPLACEMENT CURVES FOR THE CHARACTERIZATION OF WHOLE APPLE FRUITSJOURNAL OF TEXTURE STUDIES, Issue 4 2005C. CAMPS ABSTRACT The objective of the present study was to compare two chemometric approaches for characterizing the rheological properties of fruits from puncture test force/displacement curves. The first approach (parameter approach) computed six texture parameters from the curves, which were supposed to be representative of skin hardness, fruit deformation before skin rupture, flesh firmness and mechanical work needed to penetrate the fruit. The second approach (whole curve approach) used the whole digitized curve (300 data points) in further data processing. Two experimental studies were compared: first, the variability of the rheological parameters of five apple cultivars; second, the rheological variability that was characterized as a function of storage conditions. For both approaches, factorial discriminant analysis was applied to discriminate the fruits based on the measured rheological properties. The qualitative groups in factorial discriminant analysis were either the apple cultivar or the storage conditions (days and temperatures of storage). The tests were carried out using cross-validation procedures, making it possible to compute the number of fruits correctly identified. Thus the percentage of correct identification was 92% and 87% for using the parameter and the whole curve approaches, respectively. The discrimination of storage duration was less accurate for both approaches giving about 50% correct identifications. Comparison of the percentage of correct classifications based on the whole curve and the parameter approaches showed that the six computed parameters gave a good summary of the information present in the curve. The whole curve approach showed that some additional information, not present in the six parameters, may be appropriate for a complete description of the fruit rheology. [source] Relation Between the Pacing Induced Sequence of Activation and Left Ventricular Pump Function in AnimalsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 4 2002FRITS W. PRINZEN PRINZEN, F.W., et al.: Relation Between the Pacing Induced Sequence of Activation and Left Ventricu-lar Pump Function in Animals. The main goal of this article was to review animal experimental work on the effect of asynchronous activation on ventricular pump function. During normal sinus rhythm and atrial pacing, the Purkinje system contributes significantly to the rapid electrical activation of the ventricles. In contrast, during ventricular pacing the impulse is almost exclusively conducted through the normal myocardium. As a consequence, electrical activation of the ventricles becomes asynchronous and has an abnormal sequence. The abnormal impulse conduction causes considerable disturbances to occur in regional systolic fiber shortening, mechanical work, blood flow, and oxygen consumption; low values occurring in early activated regions and values above normal being present in late activated regions. Many animal studies have now shown that the abnormal electrical activation, induced by ventricular pacing, leads to a depression of systolic and diastolic LV function. Pacing at the right ventricular apex (the conventional pacing site) reduces LV function more than pacing at the high ventricular septum or at LV sites. In canine hearts with experimental LBBB, LV pacing significantly improves LV pump function. Differences in LV pump function between (combinations of) pacing sites are poorly correlated with QRS duration. Therefore, the cause of the depression of LV function during abnormal electrical activation appears to be a combination of the asynchrony and the sequence of activation. These experimental findings justify continuing attention for optimizing the site(s) of ventricular pacing in patients with normal and abnormal ventricular impulse conduction. [source] Industrial solidification processes in polybutene-1.POLYMER ENGINEERING & SCIENCE, Issue 1 2003Part II, influence of shear flow Following some early rudimentary results on shear-induced crystallization of polybutene-1 (1, 2), the present paper contains more detailed results. In the course of this work the origins of the highly oriented crystalline surface layers, as well known from injection molded samples, are more closely investigated. For the purpose, a special extrusion experiment is used, in which melts of various degrees of undercooling are moved through a duct of large aspect ratio. When, after the release of the pressure at the die entry, a quench of the duct to a temperature far below the melting point is delayed, a relaxation phenomenon is observed, in accordance with the experiences with i-PP. From these experiments one learns that the leading parameter of the process is something like the mechanical work done per unit volume, and that the relaxation time increases with decreasing temperature much faster than the viscosity of the melt. The results are qualitatively in excellent agreement with our previously obtained results for polypropylene. [source] Characterization of disk brake noise behavior via measurement of friction forcesPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Stefan Schlagner Squealing of disk brakes is a major problem in the field of vehicle design. It is commonly acknowledged, that this squeal is initiated by instability due to friction forces between the pads and the disk, leading to self excited vibrations. This work addresses the mechanical work of these friction forces in order to draw conclusions for the investigation of the noise behavior of disk brakes. Therefore a multi degree of freedom model is used to compare its stability behavior with the frictional work at the pads. The results obtained are applied to experiments in which, on the one hand brake pads with integrated piezoceramic actuators cause a broad band excitation and, on the other hand, dynamic pad velocities/accelerations and friction forces are measured. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Upper limb kinematics and the role of the wrist during stone tool productionAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010E.M. Williams Abstract Past studies have hypothesized that aspects of hominin upper limb morphology are linked to the ability to produce stone tools. However, we lack the data on upper limb motions needed to evaluate the biomechanical context of stone tool production. This study seeks to better understand the biomechanics of stone tool-making by investigating upper limb joint kinematics, focusing on the role of the wrist joint, during simple flake production. We test the hypotheses, based on studies of other upper limb activities (e.g., throwing), that upper limb movements will occur in a proximal-to-distal sequence, culminating in rapid wrist flexion just prior to strike. Data were captured from four amateur knappers during simple flake production using a VICON motion analysis system (50 Hz). Results show that subjects utilized a proximal-to-distal joint sequence and disassociated the shoulder joint from the elbow and wrist joints, suggesting a shared strategy employed in other contexts (e.g., throwing) to increase target accuracy. The knapping strategy included moving the wrist into peak extension (subject peak grand mean = 47.3°) at the beginning of the downswing phase, which facilitated rapid wrist flexion and accelerated the hammerstone toward the nodule. This sequence resulted in the production of significantly more mechanical work, and therefore greater strike forces, than would otherwise be produced. Together these results represent a strategy for increasing knapping efficiency in Homo sapiens and point to aspects of skeletal anatomy that might be examined to assess potential knapping ability and efficiency in fossil hominin taxa. Am J Phys Anthropol 143:134-145, 2010. © 2010 Wiley-Liss, Inc. [source] Untersuchung zur Lärmbelastung von Patienten und Pflegepersonal auf IntensivstationenBAUPHYSIK, Issue 4 2007Jörg Arnold Dipl.-Ing. Zur Untersuchung der Lärmbelastung auf Intensivstationen in Krankenhäusern wurden Schalldruckpegelmessungen sowohl in einem Patientenzimmer als auch in dem Foyer einer Intensivstation durchgeführt. Im Patientenzimmer wird eine hohe Lärmbelastung festgestellt. Zudem belegen die Messergebnisse, dass in jeder untersuchten Stunde Lärmereignisse auftraten, die leicht zum Aufwachen führen. Diese hohe Lärmdichte hat einen dramatischen Einfluss auf den Schlaf und damit auf die Erholung und Gesundung des Patienten. Es wurde eine für gesunde Patienten "sichere Aufwachschwelle" definiert, die auch in der Nacht im Mittel 5 mal je Stunde überschritten wird. Allerdings existieren in Deutschland bisher keine Grenzwerte zur Beurteilung der Lärmeinwirkung auf Patienten. Im Foyer ist in jeder untersuchten Schicht die geistige Arbeit des Pflegepersonals nach den Vorgaben der Richtlinie VDI 2058 deutlich beeinträchtigt und die zulässige Grenze für überwiegend mechanisierte Tätigkeiten wird fast erreicht. Nach dem aktuellen Arbeitsrecht sind allerdings alle Vorgaben eingehalten, da lediglich ein Grenzwert zum Schutz vor Lärmschwerhörigkeit angegeben wird. Das Ausmaß des Lärms und der dadurch verursachte Stress, sowohl für Patienten als auch für das Pflegepersonal, zeigen den dringenden Bedarf nach gesetzlichen Regelungen auch in Deutschland. Investigations on noise nuisance of patients and nursing staff. The aim of this study was to assess the exposure to noise in intensive care units. Therefore, sound pressure level measurements have been carried out in both the sickroom and the ward corridor. A high noise exposure in the sickroom was found. In addition the measurement results proves that sleep disturbing noise is occurring at all hours. This high noise density has a dramatic impact on the patients' convalescence and recovery process. One for healthy patients "certain wake-up threshold" was defined, which is exceeded 5 times per hour also in the night. There is no regulation by the German law regarding the patients' exposure to noise in hospitals. While in the ward corridor the intellectual work of the nursing staff according to VDI 2058 is disturbed significantly in every shift investigated, the permissible guideline limit for mechanical works in this specific working environment is almost achieved. But the guidelines of the current labour law are always complied with, because there is only one limit for protection against noise induced hearing loss. The magnitude of noise and stress caused thereby, for both the patients and the nursing staff, show the urgent need of specific regulations by German law. [source] | ||||||||||||||||