17,587 research outputs found
Bone substitute effect on vascularization and bone remodeling after application of phVEGF165 transfected BMSC
VEGF (vascular endothelial growth factor) promotes vascularization and remodeling of bone substitutes. The aim of this study was to examine the effect of distinct resorbable ceramic carriers on bone forming capacities of VEGF transfected bone marrow stromal cells (BMSC). A critical size defect of the radius in rabbits was filled either by a low surface scaffold called beta-TCP (tricalciumphsphate) or the high surface scaffold CDHA (calcium deficient hydroxy-apatite) loaded with autologous BMSC, which were either transfected with a control plasmid or a plasmid coding for phVEGF165. They were compared to unloaded scaffolds. Thus, six treatment groups (n = 6 in each group) were followed by X-ray over 16 weeks. After probe retrieval, the volume of new bone was measured by micro-CT scans and vascularization was assessed in histology. While only minor bone formation was found in both carriers when implanted alone, BMSC led to increased osteogenesis in both carriers. VEGF promoted vascularization of the scaffolds significantly in contrast to BMSC alone. Bone formation was increased in the beta-TCP group, whereas it was inhibited in the CDHA group that showed faster scaffold degradation. The results indicate that the interaction of VEGF transfected BMSC with resorbable ceramic carrier influences the ability to promote bone healing
Modelling the impact of treatment uncertainties in radiotherapy
Uncertainties are inevitably part of the radiotherapy process. Uncertainty in the dose deposited in the tumour exists due to organ motion, patient positioning errors, fluctuations in machine output, delineation of regions of interest, the modality of imaging used, and treatment planning algorithm assumptions among others; there is uncertainty in the dose required to eradicate a tumour due to interpatient variations in patient-specific variables such as their sensitivity to radiation; and there is uncertainty in the dose-volume restraints that limit dose to normal tissue.
This thesis involves three major streams of research including investigation of the actual dose delivered to target and normal tissue, the effect of dose uncertainty on radiobiological indices, and techniques to display the dose uncertainty in a treatment planning system. All of the analyses are performed with the dose distribution from a four-field box treatment using 6 MV photons. The treatment fields include uniform margins between the clinical target volume and planning target volume of 0.5 cm, 1.0 cm, and 1.5 cm. The major work is preceded by a thorough literature review on the size of setup and organ motion errors for various organs and setup techniques used in radiotherapy.
A Monte Carlo (MC) code was written to simulate both the treatment planning and delivery phases of the radiotherapy treatment. Using MC, the mean and the variation in treatment dose are calculated for both an individual patient and across a population of patients. In particular, the possible discrepancy in tumour position located from a single CT scan and the magnitude of reduction in dose variation following multiple CT scans is investigated. A novel convolution kernel to include multiple pretreatment CT scans in the calculation of mean treatment dose is derived. Variations in dose deposited to prostate and rectal wall are assessed for each of the margins and for various magnitudes of systematic and random error, and penumbra gradients.
The linear quadratic model is used to calculate prostate Tumour Control Probability (TCP) incorporating an actual (modelled) delivered prostate dose. The Kallman s-model is used to calculate the normal tissue complication probability (NTCP), incorporating actual (modelled) fraction dose in the deforming rectal wall. The impact of each treatment uncertainty on the variation in the radiobiological index is calculated for the margin sizes.Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2002
Symmetry Group and Group Representations Associated to the Thermodynamic Covariance Principle (TCP)
We describe the Lie group and the group representations associated to the
nonlinear Thermodynamic Coordinate Transformations (TCT). The TCT guarantee the
validity of the Thermodynamic Covariance Principle (TCP) : {\it The nonlinear
closure equations, i.e. the flux-force relations, everywhere and in particular
outside the Onsager region, must be covariant under TCT}. In other terms, the
fundamental laws of thermodynamics should be manifestly covariant under
transformations between the admissible thermodynamic forces, i.e. under TCT.
The TCP ensures the validity of the fundamental theorems for systems far from
equilibrium. The symmetry properties of a physical system are intimately
related to the conservation laws characterizing that system. Noether's theorem
gives a precise description of this relation. We derive the conserved
(thermodynamic) currents and, as an example of calculation, a simple system out
of equilibrium where the validity of TCP is imposed at the level of the kinetic
equations is also analyzed.Comment: 35 pages, 6 figure
A vehicle-to-infrastructure communication based algorithm for urban traffic control
We present in this paper a new algorithm for urban traffic light control with
mixed traffic (communicating and non communicating vehicles) and mixed
infrastructure (equipped and unequipped junctions). We call equipped junction
here a junction with a traffic light signal (TLS) controlled by a road side
unit (RSU). On such a junction, the RSU manifests its connectedness to equipped
vehicles by broadcasting its communication address and geographical
coordinates. The RSU builds a map of connected vehicles approaching and leaving
the junction. The algorithm allows the RSU to select a traffic phase, based on
the built map. The selected traffic phase is applied by the TLS; and both
equipped and unequipped vehicles must respect it. The traffic management is in
feedback on the traffic demand of communicating vehicles. We simulated the
vehicular traffic as well as the communications. The two simulations are
combined in a closed loop with visualization and monitoring interfaces. Several
indicators on vehicular traffic (mean travel time, ended vehicles) and IEEE
802.11p communication performances (end-to-end delay, throughput) are derived
and illustrated in three dimension maps. We then extended the traffic control
to a urban road network where we also varied the number of equipped junctions.
Other indicators are shown for road traffic performances in the road network
case, where high gains are experienced in the simulation results.Comment: 6 page
FAST TCP: Motivation, Architecture, Algorithms, Performance
We describe FAST TCP, a new TCP congestion control algorithm for high-speed long-latency networks, from design to implementation. We highlight the approach taken by FAST TCP to address the four difficulties which the current TCP implementation has at large windows. We describe the architecture and summarize some of the algorithms implemented in our prototype. We characterize its equilibrium and stability properties. We evaluate it experimentally in terms of throughput, fairness, stability, and responsiveness
Cooling neutron stars and superfluidity in their interiors
We study the heat capacity and neutrino emission reactions (direct and
modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of
nucleons) in matter of supranuclear density of the neutron star cores with
superfluid neutrons and protons. Various superfluidity types are analysed
(singlet-state pairing and two types of triplet-state pairing, without and with
nodes of the gap at a nucleon Fermi surface). The results are used for cooling
simulations of isolated neutron stars. Both, the standard cooling and the
cooling enhanced by the direct Urca process, are strongly affected by nucleon
superfluidity. Comparison of cooling theory of isolated neutron stars with
observations of their thermal radiation may give stringent constraints on the
critical temperatures of the neutron and proton superfluidities in the neutron
star cores.Comment: LaTeX, 85 pages, 23 figures, Physics - Uspekhi (accepted
Microfield Fluctuations and Spectral Line Shapes in Strongly Coupled Two-Component Plasmas
The spectral line shapes for hydrogen-like heavy ion emitters embedded in
strongly correlated two-component electron-ion plasmas are investigated with
numerical simulations. For that purpose the microfield fluctuations are
calculated by molecular dynamics simulations where short range quantum effects
are taken into account by using a regularized Coulomb potential for the
electron-ion interaction. The microfield fluctuations are used as input in a
numerical solution of the time-dependent Schroedinger equation for the
radiating electron. In distinction to the standard impact and quasistatic
approximations the method presented here allows to account for the correlations
between plasma ions and electrons. The shapes of the Ly-alpha line in Al are
investigated in the intermediate regime. The calculations are in good agreement
with experiments on the Ly-alpha line in laser generated plasmas.Comment: 5 figure
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