ТЕХНОЛОГИИ ОПРЕДЕЛЕНИЯ МЕСТОПОЛОЖЕНИЯ АБОНЕНТОВ В СИСТЕМАХ СОТОВОЙ СВЯЗИ

Рассмотрены общие принципы определения местоположения мобильной станции, а так же наиболее распространённые методы и технологии

Calibration and evaluation of a motion measurement system for PET imaging studies

Positron Emission Tomography (PET) enables functional imaging of deep brain structures, but the bulk and weight of current systems preclude their use during many natural human activities, such as locomotion. The proposed long-term solution is to construct a robotic system that can support an imaging system surrounding the subject's head, and then move the system to accommodate natural motion. This requires a system to measure the motion of the head with respect to the imaging ring, for use by both the robotic system and the image reconstruction software. We report here the design, calibration, and experimental evaluation of a parallel string encoder mechanism for sensing this motion. Our results indicate that with kinematic calibration, the measurement system can achieve accuracy within 0.5mm, especially for small motions.Comment: arXiv admin note: text overlap with arXiv:2311.1786

Structure and dielectric response in the high TcT_c ferroelectric Bi(Zn,Ti)O3_3-PbTiO3_3 solid solutions

Theoretical {\em ab initio} and experimental methods were used to investigate the $x$Bi(Zn,Ti)O$_3$-(1-$x$)PbTiO$_3$ (BZT-PT) solid solution. We find that hybridization between Zn 4$p$ and O 2$p$ orbitals allows the formation of short, covalent Zn-O bonds, enabling favorable coupling between A-site and B-site displacements. This leads to large polarization, strong tetragonality and an elevated ferroelectric to paraelectric phase transition temperature. nhomogeneities in local structure near the 90$^\circ$ domain boundaries can be deduced from the asymetric peak broadening in the neutron and x-ray diffraction spectra. These extrinsic effects make the ferroelectric to paraelectric phase transition diffuse in BZT-PT solid solutions

Controlling crystal symmetries in phase-field crystal models

We investigate the possibility to control the symmetry of ordered states in phase-field crystal models by tuning nonlinear resonances. In two dimensions, we find that a state of square symmetry as well as coexistence between squares and hexagons can be easily obtained. In contrast, it is delicate to obtain coexistence of squares and liquid. We develop a general method for constructing free energy functionals that exhibit solid-liquid coexistence with desired crystal symmetries. As an example, we develop a free energy functional for square-liquid coexistence in two dimensions. A systematic analysis for determining the parameters of the necessary nonlinear terms is provided. The implications of our findings for simulations of materials with simple cubic symmetry are discussed.Comment: 19 pages, 6 figure

Mechanical loading impacts intramuscular drug transport : impact on local drug delivery

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2008.Includes bibliographical references (leaves 152-166).Controlled-release drug-delivery systems enable efficient and defined administration of therapeutic agents to target tissues. However, ultimate drug distribution and pharmacologic effect are determined by target tissue pharmacokinetics. In muscular tissues, complex architecture that is further augmented by dynamic motion and contraction can alter the pharmacokinetics and deposition of locally delivered macromolecules. We developed a system and applied a quantitative schema to investigate the impact of controlled mechanical loads applied to skeletal and cardiac muscle tissue on intramuscular transport of locally delivered drug. In a series of studies, we examined how the interaction between architectural configuration and functional mechanics alters the transport of drugs across both physicochemical and binding properties. We correlated these pharmacokinetic effects with characteristic parameters in the physiologic range of the tissue to derive mechanistic insight into the fundamental structural and dynamic elements that underlie these effects. While previous studies have revealed the unilateral scaling of substrate uptake with mechanical influences, we elucidated an architecturally defined pharmacokinetic setpoint whereby maximal drug penetration corresponds with optimal muscle function. Our findings elucidate basic biologic design in muscle that optimizes the interface between tissue and its physical environment. The unique insights from our investigations have broad impact on current understanding of the pharmacokinetic influences of biologic form and function, and elucidate new clinical strategies for controlled release and local delivery of a wide range of therapeutic compounds to mechanically active tissues.by Peter I-Kung Wu.Ph.D

Skeletal muscle biomechanics drives intramuscular transport of locally delivered drugs

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaves 70-74).Introduction: Effective local drug delivery to contractile tissues such as skeletal muscle requires a thorough understanding of the impact of mechanical loads on intramuscular pharmacokinetics. Current preparations for studying skeletal muscle biomechanics typically use: mounting techniques that lead to mechanical disruption of the tissue, which can create drug transport artifacts. In order to accurately study mechanical influences on drug transport, experimental techniques and setups need to meet the particular design requirements of both biomechanical testing setups and local drug delivery preparations. Studies of intramuscular pharmacokinetics require anatomically physiologic and functionally viable conditions for accurate drug transport. In this study, we invent a method for the surgical isolation and mounting of whole skeletal muscles of small rodents that maintains the physiologic configuration of the tissue. We also invent a mounting assembly and dynamic loading system designed appropriately for in vitro drug transport studies. We present an effective protocol for tissue processing and visually quantifying intramuscular distribution of drug. With the primary objective of investigating muscle pharmacokinetics, we use these techniques in a study to elucidate the influence of mechanical loading on the intramuscular transport and distribution of locally delivered drug. Methods and Results: The dynamic loading system was characterized and used to investigate intramuscular transport of aqueous macromolecular drug. The loading system was designed to achieve a maximal force, velocity, and acceleration of up to 72N, 0.45m/s, and 8.5m/s2, respectively, for imposing cyclic strain on soleus muscle samples. Total compliance of the series assembly from the motor to muscle mounting blocks was less then 0.0057 ± 0.002mm/N.(cont.) Under proportional-integral-derivative (PID) control with a positional resolution of 20gpm, the loading system achieved a positional precision of +60gm or better for sinusoidal reference curves required in our studies. Tissue architectural and functional integrity as well as a technique for quantifying intramuscular fluorescent dextran were validated using the loading system. Histologic studies of rat soleus showed that interstitial porosity was consistent in tissues subjected to mechanical loading for 70 minutes, and changes in porosity were independent of the nature of imposed static (0-15% fixed strain) and cyclic (3Hz sinusoidal strain with amplitude of 2.5% oscillating about mean strains of 5-15%) loads. Permanent changes in architectural integrity depended only on the duration of time spent in vitro after isolation, in which porosity increased at the tissue edge from 11.1 + 3.3% to 21.0 + 6.1% over the course of a 70-minute incubation. The source solution used for local delivery of drug (dextran) preserved tissue functional viability, allowing muscle samples to maintain isometric twitch contractile activity at a rate of 3Hz for at least 1 hour. The active twitch force- length characteristic of soleus samples showed 0.24 + 0.06N at 0% strain, a maximum of 0.35 + 0.06N at 10% strain, and a decrease to 0.19 + 0.06N at 20% strain. Isometric twitch contractile force was at least 0.19N when measured every 15 minutes over a 2 hour period. Fractional volume of distribution for dextran was 84% of the bulk source concentration over the range of 0.1 M-lmM bulk concentrations, and demonstrated the non-binding properties of dextran. Fluorescence intensity of FITC-dextran equilibrated in soleus tissue exhibited a linear dependence on dextran concentration.(cont.) Dextran penetration and distribution in soleus muscles under either cyclic (3Hz, 0-20% peak-to- peak) or static (fixed at 0%) tensile strain for 80 minutes was quantified by fluorescent imaging. Penetration depth of 1mM 20kDa FITC-dextran at the planar surfaces of the soleus increased significantly from 0.52 + 0.09mm under static strain to 0.81 + 0.09mm under cyclic strain. Penetration at the curved margins of the soleus was significantly greater than at planar surfaces by a factor of 1.57 and 2.52 under static and cyclic strain, respectively. Penetration at curved surfaces increased to a greater extent, by a factor of 1.6, than at planar surfaces under cyclic strain. Discussion: This investigation demonstrated that dynamic, or cyclic, tensile strain impacts the penetration and distribution of aqueous drug in skeletal muscle. In the course of this study, we established an effective and robust experimental system and protocol for studying mechanical influences on intramuscular pharmacokinetics. The innovation of our surgical isolation and mounting technique allowed for the investigation of an isolated soleus muscle without disrupting the muscle, tendons, or physiologic bone attachments. The mounting device enabled muscles to be secured in a physiologic in situ configuration, to undergo more physiologically distributed tensile stresses and strains, and to be mechanically loaded while incubated in vitro in drug. Thus, the method and device eliminated the artificial tissue stresses typically introduced by current tissue handling techniques that could result in drug transport artifacts.(cont.) While effective as a standalone biomechanical testing preparation, characterization and validation of the dynamic loading system with a protocol for tissue processing and quantitative assessment of intramuscular fluorescent drug distribution demonstrated that it is a novel and robust preparation for investigating both tissue biomechanics and pharmacokinetics. With the finding from the present study that dynamic loading influences intramuscular drug transport in an architecturally dependent manner, we intend to investigate the isolated effects of different mechanical loading regimens on drug transport to establish a broader understanding of muscle pharmacokinetics. It is hoped that the insights from this work will guide the design and application of future local drug delivery strategies to mechanically active tissues.by Peter I-Kung Wu.S.M