Finite Element Simulation and Analysis of Femoral Head Replacement

Although several years of research and experiment are dedicated to Total Hip Replacement (THR) of the conventional implant, there is yet no reliable answer for those patients who are very active and young. In this study, a modelling of the bone around two different types of implant has been carried out. Currently proposed design studied here, is the generic concept of stemless implant. The stemless implant reconstruction was compared to the conventional implant and also to the intact bone as control solution. A modelling approach with Finite Element (FE) method was adopted. A model of femur was developed and element optimisation was carried out to find the best mesh refinement. The models were divided into two regions from proximal head to 40 mm distance toward distal end (R1) and 40 mm distance from proximal head toward the distal end (R2). For two different loading conditions of bending and torsion, the models were solved by ANSYS software. The results were compared with those of the experimental literature for validation. The results of this study showed that the stem less implant had less deviation from the control sol ution of the bone in a l l reg ions and in both loading cond itions, com pa ring to the large d eviation of the stemmed i mplant fro m the intact bone. The stemless i mplant showed perfect fit to the control sol ution i n R2 region except for the 14 m m highest part of this reg ion where the ste m le ss i mplant showed strain red uction in the i nterface of the bone and the implant. This region wa s sub-trochanter and wa s concluded to practically be the weak point of this type of implant. Meanwhile, the stemless i mplant type had sign ificant changes in stress and strain d i stribution i n R1 reg io n . This region was the im plant region itself and it was concluded that a g reat amount of care m u st be taken for this region when designing such an i m plant. The results of this study ind icated that the stem less type of i m p lant could become a suitable alternative fo r conve ntional type of implant in hemia rthroplasties. However, the fixation of this type of i mplant and its effect on subtrochanter region m u st be con sidered for d esigning the fi nal prod uct. More comprehensive numerical investigations on specific designs, with more loading cond itions and contact algorithms inclusion, could be of major benefit to improve the fi nal o utcome of the design process

Cortical Control of the Fusimotor System in the Tenuissimus Muscle of the Cat

Cortical control of the sensory output of muscle spindles was studied in anaesthetized cats in two series of complementary experiments. Gamma motoneurone activity was monitored during electrical stimulation of the sensorimotor cortex: a) by recording from single primary and secondary sensory afferents from the tenuissimus and flexor digitorum longus muscles in dorsal root filaments and b) by visualizing directly the movements of intrafusal muscle fibres in exteriorised muscle spindles of the tenuissimus muscle. It was found that the state of anaesthesia was crucial in obtaining reproducible results and variation in the state of anaesthesia can alter the fusimotor effect from static to dynamic or even from excitation to inhibition. This is consistent with findings of Vedel and Mouillac-Baudevin (1970). The anaesthetic agent used was also important in determining the magnitude and type of the response to electrical stimulation. The initial burst of the primary afferent in response to passive stretch was by far greater with chloralose than with barbiturate anaesthesia in both tenuissimus and flexor digitorum longus muscles, suggesting that there may be a tonic low-level dynamic gamma excitation in chloralose anaesthesia. The state of the sensorimotor cortex is important too. Prevention of CO2 escape from the surface of the cortex in the present experiments by covering the cortex with 1 cm of mineral oil is thought to be the sole factor which made these results different from those obtained by Gladden and McWilliam (1977a,b). Other new findings were 1) the topographical mapping of the sensorimotor cortex in relation to the type of gamma motoneurones recruited, static or dynamic, and 2) evidence for independent cortical control of different types of static gamma motoneurones: 1) A "dynamic area" was identified from which dynamic effects were clearly elicited during stimulation. The boundaries were the cruciate sulcus (anteriorly), the ansate sulcus (posteriorly) and the sagital longitudinal fissure (medially). Laterally, the area extended half way to the postcruciate dimple. In addition from direct observation of intrafusal fibre movements it was clear that dynamic gamma motoneurones were never recruited alone. 2) Static effects were elicited following stimulation of a much wider area across the sensorimotor cortex, the postcruciate dimple being almost at the centre. The sensorimotor cortex was not only capable of controlling static gamma motoneurones independently from dynamic ones, but also capable of simultaneously inhibiting some, static gamma motoneurones and exciting others, lending support to the idea (Boyd, 1986) that there is more than one type of static gamma motoneurone

Cutting Conditions Optimisation of Titanium Metal Matrix Composites in Turning and Face Milling.

RÉSUMÉ Il y a quelques décennies, les industries ont utilisé les composites à matrice métallique de titane (Ti-MMC) dans les valeurs limitées. Chacune des industries s'intéresse à la caractéristique particulière du Ti-MMC. Les constructeurs de voitures s'intéressent à la résistance à l'usure et à la fatigue de ce matériau dans la fabrication des composantes de moteur et de transmission pour ainsi diminuer le poids des véhicules. Les fournisseurs d'accessoires et de matériel médicaux utilisent le Ti-MMC vu sa grande rigidité spécifique et sa résistance en compression élevée. De plus, dans les domaines aéronautique et aérospatiale, les fabricants sont intéressés par le gain en légèreté de ce matériau. Mais il y a un problème avec le Ti-MMC, il a une faible usinabilité. Les aspects importants et acceptables pour l'usinage de pièces en industrie sont le coût de fabrication, de la finition de la surface et de la conformité au devis. Aussi, une dureté augmentée par les particules de céramique et une rigidité élevée du produit induisent un facteur de propagation élevée de fissures dans le corps du Ti-MMC. De plus, les particules fissurées ont tendance à éroder les arêtes des outils de coupe provoquant la dégradation de la finition de surface. Une très faible conductivité thermique, une haute résistance à la compression et une basse tendance à la déformation plastique devant l'arête de l’outil de coupe lors de son engagement avec ce matériau portent les contraintes mécaniques et thermiques à augmenter durant le processus d'usinage. Il n’y a que peu d’études sur le Ti-MMC, en particulier sur l'usinage de ce matériau. En général, les outils PCD sont connus comme étant les outils les plus performants lors de l'usinage du MMC, mais le coût de production est fortement affecté par le prix élevé de ces outils. Cette étude fait suite à des expériences réalisées sur l'effet de trois sortes d'outils (carbure revêtu, PCBN et PCD) sur le tournage et (carbure et d'outils PCD) sur le surfaçage du Ti-MMC. Sur les conséquences de la productivité, le taux d'usure des outils et la rugosité de surface de la pièce. Les conditions de coupe optimales sont déterminées pour chaque outil au tournage et au fraisage en bout du Ti-MMC. Les effets des paramètres de coupe sont extraits par analyse de variance. Pour l'optimisation du processus de tournage et de fraisage avec chaque outil, la méthode Taguchi est utilisée. De plus, les données de performance de ces outils lors de ces expériences sont analysées.----------ABSTRACT World leading manufacturing sectors, in particular aerospace and automotive industries wish to have lighter materials with better physical, mechanical and chemical properties than the prevalent hard to cut heavier materials. This has brought much attention to alternative materials such as metal matrix composite (MMC). MMCs are composed of non-metallic reinforcements (i.e. ceramic) in metal matrices which feature high toughness, wear and fatigue resistance and relatively light weight. One of the metallic composite with remarkable mechanical properties is titanium metal matrix composite (Ti-MMC). Ti-MMC has been successfully incorporated into numerous of products in various industrial sectors. Each industrial sector has an interest in particular characteristics of Ti-MMC. Automotive and aerospace industries are craving for high wear and fatigue resistant materials with low weight for delicate applications in engine and power train component. Medical components suppliers utilize Ti-MMC in pursuance of its great specific stiffness and elevated compressive strength. Despite having excellent features, various issues have emerged relate to the machining and machinability of Ti-MMCs. Due to the presence of hard and abrasive ceramic particles in metal matrices of Ti-MMCs, crack propagation appears on the Ti-MMC body. Furthermore, weak heat conductivity, low tendency to plastic deformation and high compressive resistance of the matrix exert large mechanical and thermal stresses to the cutting tool and the work-piece. This reveals that the principal machinability attributes of Ti-MMCs are rapid tool wear, low surface quality in Ti-MMC machined parts and excessive cost. According to the review of literature, there are few studies on the machining and machinability of Ti-MMCs. There is a lack of knowledge on appropriate setting levels of cutting process parameters for machining Ti-MMC, in particular milling and turning operations that deal with high material removal rate. The main objectives of this work are to study the cutting parameters governing the tool wear and surface quality (finish) when machining (milling and turning) Ti-MMCs, as well as cutting factors optimization using Taguchi method to better reach the optimum or near optimum surface finish, tool wear and productivity. To that end, comprehensive experimental studies are arranged in multi-level full factorial design and orthogonal array design of experiment

Ground-state properties of gapped graphene using the random phase approximation

We study the effect of band gap on the ground-state properties of Dirac electrons in a doped graphene within the random phase approximation at zero temperature. Band gap dependence of the exchange, correlation and ground-state energies and the compressibility are calculated. We additionally show that the conductance in the gapped graphene is smaller than gapless one. We also calculate the band gap dependence of charge compressibility and it decreases with increasing the band gap values.Comment: 11 pages, Final version. To appear in Phys. Rev.

Identifikacija neispravnih spojeva u gredama uz pomoć torzijskih vibracija

The determination of the shear dynamic modulus in wood product panels is of greater importance than its determination in wood beams. Yet with regards to the effect of defects on the obtained values of shear modulus, this factor is used to detect the defects and the degree of the defects. In this study, the effect of gluing defects in two joint shapes (scarf (45°) and finger joints (10 mm length and 3 mm pitch) were evaluated non-destructively using the torsional vibration method. Rectangular wood specimens with dimensions of 20 mm × 40 mm × 360 mm (R × T × L) were prepared from clear eastern beech. The joints were located at similar positions in the middle of the beams. The results showed that creating a healthy joint did not significantly change the values obtained for the shear modulus in either of the joint shapes. However, reducing the adhesion level in both types of joints caused a significant reduction in the shear modulus values. The results show that the changes in the dynamic shear modulus values in both joint types, as a result of changes in the glue coverage rating (fully, medium and low-glued joints) allows the detection of the defects as well as the degree of the defects.Određivanje dinamičkog modula smicanja u drvnim pločama važnije je od određivanja tog modula u drvenim gredama. Ipak, s obzirom na utjecaj grešaka na vrijednosti modula smicanja, određivanje tog faktora važno je za otkrivanje grešaka i njihova stupnja na drvnim proizvodima. U ovom je istraživanju metodom torzijskih vibracija nedestruktivno procijenjen utjecaj grešaka lijepljenja u dva oblika spoja: kosim sljubom (45°) i klinastim zupcima (duljine 10 mm i koraka 3 mm). Uzorci drva dimenzija 20 mm × 40 mm × 360 mm (R × T × L) izrađeni su od čiste bukovine, a spojevi su izvedeni na približno istim mjestima na sredini greda. Rezultati su pokazali da izrada zdravog spoja nije bitno promijenila vrijednosti modula smicanja ni za jedan od primijenjenih tipova spoja. Međutim, smanjenje razine adhezije u obje vrste spojeva uzrokovalo je znatno smanjenje vrijednosti modula smicanja. Rezultati pokazuju da promjene vrijednosti dinamičkog modula smicanja u oba tipa spoja kao rezultat promjene stupnja pokrivenosti ljepilom (potpuna, srednja i slaba pokrivenost) omogućuju otkrivanje grešaka lijepljenja, kao i stupnja grešaka drvnih spojeva

The effect of sublattice symmetry breaking on the electronic properties of a doped graphene

Motivated by a number of recent experimental studies, we have carried out the microscopic calculation of the quasiparticle self-energy and spectral function in a doped graphene when a symmetry breaking of the sublattices is occurred. Our systematic study is based on the many-body G$_0$W approach that is established on the random phase approximation and on graphene's massive Dirac equation continuum model. We report extensive calculations of both the real and imaginary parts of the quasiparticle self-energy in the presence of a gap opening. We also present results for spectral function, renormalized Fermi velocity and band gap renormalization of massive Dirac Fermions over a broad range of electron densities. We further show that the mass generating in graphene washes out the plasmaron peak in spectral weight.Comment: 22 Pages, 10 Figure

Pharmacological adherence with clinical guidelines: Acute coronary syndrome

Background and aims: The present time evidences show that adherence of clinical guideline by cardiologists in Acute Coronary Syndrome is sub optimal. The aim of this studywas to investigate the extent adherence by cardiologists from clinical guidelines in acute coronary syndrome on admission in hospitals in Isfahan. Methods: This cross sectional study was conducted on medical records of Acute Coronary Syndrome patients (unstable angina and myocardial infarction). The pharmacological adherence calculated from prescription of 4 recommended medications from clinical guidelines utilizing aspirin clopidogrel, beta blockers, statins, ACEI (angiotensin- converting enzyme inhibitor) or ARB (angiotensin II receptor blockers). Pharmacological adherence were divided into two groups of good-adherence equals or above %75 (4.3, 4.4) and poor- adherence below %75 (1.4, 2.4). Results: This research performed on 200 medical records of Acute Coronary Syndrome (ACS) patients. On admission%99, %80, %58 and %96.5 of patients received antiplatelet, beta blockers, ACEI/ARB and statins, respectively. In general, the extent of pharmacological adherence to updated clinical guidelines on admission was%58.5 which was poor. Conclusion: Poor adherence to updated clinical guidelines by cardiologists due to secondary prevention of ACS is very worrisome. It is necessary to investigate the reasons of non-adherence regarding aging society and the prevalence of cardiac disease