Making minimally invasive THR safe: conclusions from biomechanical simulation and analysis.

The use of smaller surgical incisions has become popularized for total hip arthroplasty (THR) because of the potential benefits of shorter recovery and improved cosmetic appearance. However, an increased incidence of serious complications has been reported. To minimize the risks of minimally invasive approaches to THR, we have developed an experimental approach which enables us to evaluate risk factors in these procedures through cadaveric simulations performed within the laboratory. During cadaveric hip replacement procedures performed via posterior and antero-lateral mini-incisions, pressures developed between the wound edges and the retractors were approximately double those recorded during conventional hip replacement using Charnley retractors (p < 0.01). In MIS procedures performed via the dual-incision approach, lack of direct visualisation of the proximal femur led to misalignment of broaches and implants with increased risk of cortical fracture during canal preparation and implant insertion. Cadaveric simulation of surgical procedures allows surgeons to measure variables affecting the technical success of surgery and to master new procedures without placing patients at risk.

Simulation of Drosophila circadian oscillations, mutations, and light responses by a model with VRI, PDP-1, and CLK.

A model of Drosophila circadian rhythm generation was developed to represent feedback loops based on transcriptional regulation of per, Clk (dclock), Pdp-1, and vri (vrille). The model postulates that histone acetylation kinetics make transcriptional activation a nonlinear function of [CLK]. Such a nonlinearity is essential to simulate robust circadian oscillations of transcription in our model and in previous models. Simulations suggest that two positive feedback loops involving Clk are not essential for oscillations, because oscillations of [PER] were preserved when Clk, vri, or Pdp-1 expression was fixed. However, eliminating positive feedback by fixing vri expression altered the oscillation period. Eliminating the negative feedback loop in which PER represses per expression abolished oscillations. Simulations of per or Clk null mutations, of per overexpression, and of vri, Clk, or Pdp-1 heterozygous null mutations altered model behavior in ways similar to experimental data. The model simulated a photic phase-response curve resembling experimental curves, and oscillations entrained to simulated light-dark cycles. Temperature compensation of oscillation period could be simulated if temperature elevation slowed PER nuclear entry or PER phosphorylation. The model makes experimental predictions, some of which could be tested in transgenic Drosophila.

Cellular dynamic simulator: an event driven molecular simulation environment for cellular physiology.

In this paper, we present the Cellular Dynamic Simulator (CDS) for simulating diffusion and chemical reactions within crowded molecular environments. CDS is based on a novel event driven algorithm specifically designed for precise calculation of the timing of collisions, reactions and other events for each individual molecule in the environment. Generic mesh based compartments allow the creation / importation of very simple or detailed cellular structures that exist in a 3D environment. Multiple levels of compartments and static obstacles can be used to create a dense environment to mimic cellular boundaries and the intracellular space. The CDS algorithm takes into account volume exclusion and molecular crowding that may impact signaling cascades in small sub-cellular compartments such as dendritic spines. With the CDS, we can simulate simple enzyme reactions; aggregation, channel transport, as well as highly complicated chemical reaction networks of both freely diffusing and membrane bound multi-protein complexes. Components of the CDS are generally defined such that the simulator can be applied to a wide range of environments in terms of scale and level of detail. Through an initialization GUI, a simple simulation environment can be created and populated within minutes yet is powerful enough to design complex 3D cellular architecture. The initialization tool allows visual confirmation of the environment construction prior to execution by the simulator. This paper describes the CDS algorithm, design implementation, and provides an overview of the types of features available and the utility of those features are highlighted in demonstrations.

Evaluating statistical methods used to estimate the number of postsynaptic receptors.

Calcium levels in spines play a significant role in determining the sign and magnitude of synaptic plasticity. The magnitude of calcium influx into spines is highly dependent on influx through N-methyl D-aspartate (NMDA) receptors, and therefore depends on the number of postsynaptic NMDA receptors in each spine. We have calculated previously how the number of postsynaptic NMDA receptors determines the mean and variance of calcium transients in the postsynaptic density, and how this alters the shape of plasticity curves. However, the number of postsynaptic NMDA receptors in the postsynaptic density is not well known. Anatomical methods for estimating the number of NMDA receptors produce estimates that are very different than those produced by physiological techniques. The physiological techniques are based on the statistics of synaptic transmission and it is difficult to experimentally estimate their precision. In this paper we use stochastic simulations in order to test the validity of a physiological estimation technique based on failure analysis. We find that the method is likely to underestimate the number of postsynaptic NMDA receptors, explain the source of the error, and re-derive a more precise estimation technique. We also show that the original failure analysis as well as our improved formulas are not robust to small estimation errors in key parameters.

Comparing the economic impacts of Asian integration by computational simulation analysis

The Geographical Simulation Model developed by IDE-JETRO (IDE-GSM) is a computer simulation model based on spatial economics. IDE-GSM enables us to predict the economic impacts of various trade and transport facilitation measures. Here, we mainly compare the prioritized projects of the Master Plan on ASEAN Connectivity (MPAC) and the Comprehensive Asia Development Plan (CADP). MPAC focus on specific hard or soft infrastructure projects that connect one ASEAN member state to another while the CADP emphasizes the importance of economic corridors or linkages between a large cluster and another cluster. As compared with MPAC projects, the simulation analysis shows that CADP projects have much larger positive impacts on ASEAN countries.

Simulation of a mechanical thrombectomy device based in the use of self-expandable stents for the blood clots extraction

Recently, we have presented some studies concerning the analysis, design and optimization of one experimental device developed in the UK - GPTAD - which has been designed to remove blood clots without the need to make contact with the clot itself, thereby potentially reducing the risk of problems such as downstream embolisation. Based on the idea of a modification of the previous device, in this work, we present a model based in the use of stents like the SolitaireTM FR, which is in contact with the clot itself. In the case of such devices, the stent is self-expandable and the extraction of the blood clot is faciliatated by the stent, which must be inside the clot. Such stents are generally inserted in position by using the guidewire inserted into the catheter. This type of modeling could potentially be useful in showing how the blood clot is moved by the various different forces involved. The modelling has been undertaken by analyzing the resistances, compliances and inertances effects. We model an artery and blood clot for range of forces for the guidewire. In each case we determine the interaction between blood clot, stent and artery.

Monte Carlo simulation of recrystallization

A Monte Carlo computer simulation technique, in which a continuum system is modeled employing a discrete lattice, has been applied to the problem of recrystallization. Primary recrystallization is modeled under conditions where the degree of stored energy is varied and nucleation occurs homogeneously (without regard for position in the microstructure). The nucleation rate is chosen as site saturated. Temporal evolution of the simulated microstructures is analyzed to provide the time dependence of the recrystallized volume fraction and grain sizes. The recrystallized volume fraction shows sigmoidal variations with time. The data are approximately fit by the Johnson-Mehl-Avrami equation with the expected exponents, however significant deviations are observed for both small and large recrystallized volume fractions. Under constant rate nucleation conditions, the propensity for irregular grain shapes is decreased and the density of two sided grains increases.

Crack mechanical failure in lithium niobate crystal under ion irradiation; novel simulation by extended finite elements

Swift heavy ion irradiation (ions with mass heavier than 15 and energy exceeding MeV/amu) transfer their energy mainly to the electronic system with small momentum transfer per collision. Therefore, they produce linear regions (columnar nano-tracks) around the straight ion trajectory, with marked modifications with respect to the virgin material, e.g., phase transition, amorphization, compaction, changes in physical or chemical properties. In the case of crystalline materials the most distinctive feature of swift heavy ion irradiation is the production of amorphous tracks embedded in the crystal. Lithium niobate is a relevant optical material that presents birefringence due to its anysotropic trigonal structure. The amorphous phase is certainly isotropic. In addition, its refractive index exhibits high contrast with those of the crystalline phase. This allows one to fabricate waveguides by swift ion irradiation with important technological relevance. From the mechanical point of view, the inclusion of an amorphous nano-track (with a density 15% lower than that of the crystal) leads to the generation of important stress/strain fields around the track. Eventually these fields are the origin of crack formation with fatal consequences for the integrity of the samples and the viability of the method for nano-track formation. For certain crystal cuts (X and Y), these fields are clearly anisotropic due to the crystal anisotropy. We have used finite element methods to calculate the stress/strain fields that appear around the ion-generated amorphous nano-tracks for a variety of ion energies and doses. A very remarkable feature for X cut-samples is that the maximum shear stress appears on preferential planes that form +/-45º with respect to the crystallographic planes. This leads to the generation of oriented surface cracks when the dose increases. The growth of the cracks along the anisotropic crystal has been studied by means of novel extended finite element methods, which include cracks as discontinuities. In this way we can study how the length and depth of a crack evolves as function of the ion dose. In this work we will show how the simulations compare with experiments and their application in materials modification by ion irradiation.

A molecular dynamics study of swift heavy ion irradiation of amorphous silica: the role of thermal effects

Irradiation with swift heavy ions (SHI), roughly defined as those having atomic masses larger than 15 and energies exceeding 1 MeV/amu, may lead to significant modification of the irradiated material in a nanometric region around the (straight) ion trajectory (latent tracks). In the case of amorphous silica, SHI irradiation originates nano-tracks of higher density than the virgin material (densification). As a result, the refractive index is increased with respect to that of the surroundings. Moreover, track overlapping leads to continuous amorphous layers that present a significant contrast with respect to the pristine substrate. We have recently demonstrated that SHI irradiation produces a large number of point defects, easily detectable by a number of experimental techniques (work presented in the parallel conference ICDIM). The mechanisms of energy transfer from SHI to the target material have their origin in the high electronic excitation induced in the solid. A number of phenomenological approaches have been employed to describe these mechanisms: coulomb explosion, thermal spike, non-radiative exciton decay, bond weakening. However, a detailed microscopic description is missing due to the difficulty of modeling the time evolution of the electronic excitation. In this work we have employed molecular dynamics (MD) calculations to determine whether the irradiation effects are related to the thermal phenomena described by MD (in the ps domain) or to electronic phenomena (sub-ps domain), e.g., exciton localization. We have carried out simulations of up to 100 ps with large boxes (30x30x8 nm3) using a home-modified version of MDCASK that allows us to define a central hot cylinder (ion track) from which heat flows to the surrounding cold bath (unirradiated sample). We observed that once the cylinder has cooled down, the Si and O coordination numbers are 4 and 2, respectively, as in virgin silica. On the other hand, the density of the (cold) cylinder increases with respect to that of silica and, furthermore, the silica network ring size decreases. Both effects are in agreement with the observed densification. In conclusion, purely thermal effects do not explain the generation of point defects upon irradiation, but they do account for the silica densification.

Análisis paramétrico de transiciones a bocinas

Las transiciones en guía de onda son las estructuras utilizadas en microondas para transferir y adaptar la señal que viaja en un determinado sistema de transmisión (por ejemplo, un cable coaxial) a otro sistema de transmisión o a un sistema radiante (por ejemplo, una antena de bocina). Los dos sistemas de transmisión entre los que la transición adapta la señal pueden ser distintos o del mismo tipo pero con alguna de sus dimensiones diferente. Existen diferentes transiciones de guía de onda que dependiendo de su utilidad son diseñadas y construidas con diferentes secciones: circular, rectangular, elíptica o incluso combinaciones de éstas. No es necesario que la sección de la guía presente una forma geométrica conocida pero los estándares que se van a seguir hacen referencia en concreto a secciones rectangulares y circulares. En el trabajo que aquí se desarrolla se pretende optimizar por medio de simulaciones paramétricas una transición entre cable coaxial con conector tipo K y una guía de onda de sección circular que sigue el estándar presentado por Flann, Millitech y Antarfs para la banda WR34. La transición que va a ser objeto de este estudio se denomina transición tapered o transición conformada. Este tipo de transiciones se caracterizan por variar una de sus dimensiones progresivamente hasta llegar al tamaño definido en el estándar correspondiente. La manera de realizar la optimización de la transición se basará en el estudio del parámetro S11 que presente la estructura a lo largo de la banda de trabajo. Ya que se sigue el estándar WR34 la banda de trabajo que éste comprende va de 21,7 a 33 GHz. Se pretende conseguir que la respuesta del parámetro S11 se encuentre por debajo de -20 dB en la banda de WR34 como resultado del diseño para poder contar de esta manera con una buena adaptación. Finalmente se propondrá un criterio a seguir para optimizar este tipo de transiciones siguiendo el objetivo de mejor adaptación teniendo en cuenta el impacto de cada tramo sobre el rango de frecuencias en el que influye y se presentarán las características finales que presenta la transición bajo estudio. En este documento se introduce de manera breve la utilidad de los transformadores de impedancias lambda cuartos en líneas de transmisión, el estado del arte de las diferentes técnicas para su diseño, y la propuesta de diseño y caracterización objeto del presente trabajo. Posteriormente, se presenta el caso de estudio para el diseño de la transición para ser integrada a una bocina de choke. Luego, se introduce el marco teórico del trabajo presentando algunos ejemplos ilustrativos de tramos de guía de onda rectangular y guía de onda circular, introduciendo adaptadores de λ/4 en simulaciones. A continuación, se explica la implementación del modelo bajo estudio en CST (Computer Simulation Technology) Studio Suite. Finalmente se presenta la discusión de los resultados obtenidos, las conclusiones y líneas futuras de trabajo. ABSTRACT. Waveguide transitions are structures used in microwave in order to transfer and adapt the signal that travels from a certain transmission system (e.g. coaxial cable) to other transmission system or to a radiant system (e.g. horn antenna). Both transmission systems between which the transition adapts the signal can be different or from the same type, but with differences in some of their dimensions. There are different waveguide transitions that, depending on their utility, are designed and constructed in different sections: circular, rectangular, elliptic or combinations of the former. The section of the guide does not have to have a known geometric shape, although the standards to be followed in this thesis apply to rectangular and circular sections. In the work here presented, we aim to optimize by means of parametric simulations, a transition between a coaxial cable with a K-type connector and a waveguide with circular section following the standard presented by Flann, Millitech y Antarfs for the band WR34. The transition studied is called tapered transition, which is characterized by the progressive variation of its dimensions, until reaching the defined size of the corresponding standard. The way of optimizing the transition will be based in the study of the parameter S11 presented by the structure along the bandwidth. Since the standard used is the WR34, the bandwidth can be defined from 21.7 up to 33 GHz. It is aimed that the response of the S11 parameter be lower equal than -20dB in the frequency band under study according to the design in order to be well matched. Finally, a criterion to follow is proposed in order to optimize these transitions type, following the better-match objective. That will be done taking into account the impact of each section on the frequency range in which influences and the final characteristics of the studied transition will be presented. In this document, it is briefly introduced the utility of quarter-wave impedance transformers in transmission lines, the state-of-art of the different techniques for their design, and the proposal of design and characterization aimed with this work. Afterwards, the study case for the design of the transition to be integrated with a choke horn antenna will be presented. Later, the theoretical frame work is introduced, giving some illustrative examples of rectangular and circular waveguide sections, and also introducing λ/4 adaptors in the simulations. Subsequently, the implementation of the model under study in CST (Computer Simulation Technology) Studio Suite will be explained. Finally, the discussion of the results, conclusion and future lines of the work are presented.

Estudio acústico y electroacústico para la realización de un musical en el teatro Rialto de Madrid

El propósito de este Proyecto Fin de Carrera es el estudio acústico y electroacústico de la realización del musical “Hoy no me puedo levantar” en el Teatro Rialto de Madrid en 2005. En primer lugar, se realiza una breve introducción histórica, citando sus remodelaciones y comentando la situación actual del recinto. Posteriormente, es analizado el equipo de sonido empleado en el espectáculo a partir de cada uno de los distintos controles de sonido: FOH (Front of Hause), monitores y microfonía inalámbrica. De cada uno de ellos se explican sus principales funciones y los sistemas que los conforman. También se describe la utilización de las cabinas insonorizadas. A continuación, se detallan los sistemas electroacústicos (empleados en el diseño) de la sonorización de dicho musical, que se consideran divididos en las siguientes partes: sistema principal, refuerzos y retardos, efectos y monitores. Además, se detalla el software RMS (Remote Monitoring System), que aporta información del funcionamiento de estos sistemas en tiempo real. Seguidamente, se exponen el equipo, procedimiento y resultados de la medida in situ en el Teatro, aplicando la Norma UNE-EN ISO 3382-2/2008 para obtener el tiempo de reverberación y ruido de fondo. Con el objeto de inicializar la simulación por ordenador, primero se exportan los planos originales de AutoCAD a EASE 4.4, donde se finaliza el proceso de modelar el recinto. Posteriormente, se asignan materiales, áreas de audiencia, puntos de escucha y se ubican los sistemas electroacústicos. Se afina el tiempo de reverberación obtenido en la medida in situ mediante materiales de la base de datos del propio software. También se ajustan los sistemas electroacústicos en el recinto para obtener la ecualización empleada y los niveles de presión sonora directo y total para distintas frecuencias. Una vez finalizados los pasos anteriores, se procede a realizar estudios psicoacústicos para comprobar posibles ecos y el efecto precedencia (empleando retardos electrónicos o delays). Finalmente, se realizan estudios de inteligibilidad, en los que se justifica la Claridad de Voz (C50) y Claridad Musical (C80); el Índice de inteligibilidad del habla (SII), la Pérdida de articulación de consonantes (Alcons) y el Índice de transmisión del habla (STI). Por último se expone el presupuesto del proyecto y del alquiler del equipo de sonido del musical y se exponen las conclusiones del Proyecto Final de Carrera. ABSTRACT. The purpose of this Final Degree Project is the acoustic and electro-acoustic study of the musical “Hoy No Me Puedo Levantar” at Teatro Rialto in 2005 (Madrid, Spain). First of all, a brief review of its history is made, quoting its refurbishments and discussing the current situation of this enclosure. Later, the sound equipment of the show is analyzed through every different sound controls: FOH (Front Of House), monitors and wireless microphones. There is also an explanation about their principal functions and systems, as well as a description of the soundproof cabins. Then, the electro-acoustic systems are detailed and divided in the following parts: main system, boosters and delays, effects and monitors. The RMS software (Remote Monitoring System) is described too, since it gives relevant information of the systems operations in real time. Afterwards, equipment, procedures and results of the measurements are exposed, applying the UNE-EN ISO 3382-2/2008 regulation in order to obtain the reverberation time and background noise of the theatre. With the purpose of initialize the computer simulation, original plans are exported from AutoCad to EASE 4.4., where its modeling process is ended. Materials, audience areas, hearing points and electro-acoustic locations are assigned below. At the same time, reverberation time is tuned up using database materials of the software itself. Also, electro-acoustic systems of the enclosure are adjusted to get the equalization and pressure sound levels of the different frequencies. Once previous steps are finished, psycho-acoustic studies are made to check possible echoes and the precedence effect - using electronic delays -. Finally, intelligibility studies are detailed, where the Voice and Musical Clarities are justified: The Speech Intelligibility Index, the Loss of Consonants Articulation and the Talk Transmission Index. This Final Degree Project ends describing the budget and rent of the sound equipment and the final conclusions.

Computer simulations of enzyme catalysis: Finding out what has been optimized by evolution

The origin of the catalytic power of enzymes is discussed, paying attention to evolutionary constraints. It is pointed out that enzyme catalysis reflects energy contributions that cannot be determined uniquely by current experimental approaches without augmenting the analysis by computer simulation studies. The use of energy considerations and computer simulations allows one to exclude many of the popular proposals for the way enzymes work. It appears that the standard approaches used by organic chemists to catalyze reactions in solutions are not used by enzymes. This point is illustrated by considering the desolvation hypothesis and showing that it cannot account for a large increase in kcat relative to the corresponding kcage for the reference reaction in a solvent cage. The problems associated with other frequently invoked mechanisms also are outlined. Furthermore, it is pointed out that mutation studies are inconsistent with ground state destabilization mechanisms. After considering factors that were not optimized by evolution, we review computer simulation studies that reproduced the overall catalytic effect of different enzymes. These studies pointed toward electrostatic effects as the most important catalytic contributions. The nature of this electrostatic stabilization mechanism is far from being obvious because the electrostatic interaction between the reacting system and the surrounding area is similar in enzymes and in solution. However, the difference is that enzymes have a preorganized dipolar environment that does not have to pay the reorganization energy for stabilizing the relevant transition states. Apparently, the catalytic power of enzymes is stored in their folding energy in the form of the preorganized polar environment.

Computer-modeling origin of a simple genetic apparatus

This computer simulation is based on a model of the origin of life proposed by H. Kuhn and J. Waser, where the evolution of short molecular strands is assumed to take place in a distinct spatiotemporal structured environment. In their model, the prebiotic situation is strongly simplified to grasp essential features of the evolution of the genetic apparatus without attempts to trace the historic path. With the tool of computer implementation confining to principle aspects and focused on critical features of the model, a deeper understanding of the model's premises is achieved. Each generation consists of three steps: (i) construction of devices (entities exposed to selection) presently available; (ii) selection; and (iii) multiplication of the isolated strands (R oligomers) by complementary copying with occasional variation by copying mismatch. In the beginning, the devices are single strands with random sequences; later, increasingly complex aggregates of strands form devices such as a hairpin-assembler device which develop in favorable cases. A monomers interlink by binding to the hairpin-assembler device, and a translation machinery, called the hairpin-assembler-enzyme device, emerges, which translates the sequence of R1 and R2 monomers in the assembler strand to the sequence of A1 and A2 monomers in the A oligomer, working as an enzyme.

Modeling and validation of the thermal behavior of buildings for the development of demand response methods

The representation of the thermal behaviour of the building is achieved through a relatively simple dynamic model that takes into account the effects due to the thermal mass of the building components. The model of a intra-floor apartment has been built in the Matlab-Simulink environment and considers the heat transmission through the external envelope, wall and windows, the internal thermal masses, (i.e. furniture, internal wall and floor slabs) and the sun gain due to opaque and see-through surfaces of the external envelope. The simulations results for the entire year have been compared and the model validated, with the one obtained with the dynamic building simulation software Energyplus.

Graphical remote-access simulation system (GRASS), the communication and monitor components (GASP/GLASP).

"Supported in part by contract U.S. AEC AT(11-1)1469."