343 research outputs found
Cell transformation by light particles : review of available data
No full textData reported in the literature on neoplastic transformation induced in cultured cells by light charged particles are compared and analyzed as a function of LET and dose protraction. Light charged particles RBE for transformation is maximum between 75 and 120 keV/μm . The majority of the data suggest that RBE values for survival and transformation are of similar magnitude. Dose protraction effects on transformation induction depend on dose, dose rate and on radiation quality
Trajectory tracking in an underactuated, non-minimum phase two-link multibody system through model predictive control with embedded reference dynamics
No full textThis paper proposes a novel formulation of Model Predictive Control (MPC), based on linearized models, for tip trajectory tracking of time-varying references in an underactuated, non-minimum phase, two-link multibody system. Indeed, tip trajectory tracking in such systems is challenging due to the unstable internal dynamics. Additionally, when traditional MPC is used, the reference is usually tracked with delay, since MPC is intrinsically devoted to regulation or to step tracking. To overcome these issues, the proposed approach embeds an autonomous state-space model of the time-varying reference into the constrained optimization process of MPC. The controller is therefore named MPC with Embedded Reference Dynamics, MPC-ERD. By embedding the reference in the controller design, tracking with negligible error and delay is achieved, and no feedforward control is required, thus overcoming the difficulties in model inversion. The MPC-ERD is experimentally validated and the results are compared with those provided by standard MPC with embedded integrator (also including output error constraints). Besides inheriting the benefits of standard MPC, MPC-ERD ensures precise tracking of the tip time-varying reference, with negligible delay and error
Cross sections for rotational excitations of CH4, SiH4, GeH4, SnH4 and PbH4 by electron impact
No full textWe report differential and integral cross sections for rotational excitation of XH(4) molecules (X: C, Si, Ge, Sn, Pb) from 7.5-30 eV by electron impact. These cross sections were derived from fixed-nuclei scattering amplitudes (Bettega et al. 1995) obtained using the Schwinger Multichannel Method with Pseudopotentials (SMCPP) (Bettega et al. 1993). Our results represent the first rotational excitation cross sections for molecules as large as GeH4, SnH4 and PbH4 using entirely ab initio procedures. The cross sections for CH4 and SiH4 obtained with pseudopotentials are in very good agreement with all-electron calculations and with other theoretical results. A comparison between our calculated cross sections and experimental data for CH4 is in general encouraging, but some discrepancies remain. We found inelastic rotational cross sections and momentum transfer cross sections to be larger for SiH4, GeH4, SnH4 and PbH4 than for CH4. We could explain this feature.391596
GROWTH-KINETICS OF C3H10T1/2 CELLS EXPOSED TO LOW-LET RADIATION
No full textGrowth curves and size of the colonies of C3H10T1/2 cells exposed to low-LET radiation (31 MeV protons) were determined after 0, 1, 3, 5, and 7 Gy. The data show that: cell density at confluence was 3.3 x 10(4) cells/cm2; the initial division delay was very small; in the first 15 h the increase in the cell number was essentially the same at all doses; at 100 h the colony size distribution was very large, ranging from 0 to 7 generations, even within the control population. The temporal dependence of the growth properties of surviving and non-surviving cells was represented by the equation N = N0(Fe(a(t - dD] + (1 - F)ea/bD(1 - e - bD(1 - e - bD(t - dD]) where F is the surviving fraction, t the time of sampling, a the growth rate, d the division delay per unit dose, b the rate per unit of dose at which the non-surviving cells lose their ability to divide. The resulting values were: a = 0.029 +/- 0.002 h-1; b = 0.0041 +/- 0.0009 h-1 Gy-1 and d = 1 +/- 0.8 h Gy-1. It was found that growth curves are affected by non-surviving progeny up to 150, 200 and 250 h after irradiation at 3, 5 and 7 Gy, whereas at longer times the population consists essentially of progeny of surviving cells
Precise path following and trajectory tracking in cable-driven parallel robots through model predictive control with embedded reference dynamics
No full textCable-driven parallel robots (CDPRs) are widely adopted in advanced manufacturing systems thanks to their large workspace, ease of construction, and low energy requirements. On the other hand, since the positivity of cable tensions must be ensured, their precise operation is not straightforward. An enhanced model predictive control (MPC) scheme is proposed in this paper for precise path following and trajectory tracking of time-varying references in CDPRs, as those usually required in high-performance manufacturing systems. Path following and trajectory tracking are challenging when references have fast dynamics; indeed, standard MPC formulations lead to good path following responses but, usually, bad performances in terms of trajectory tracking due to the presence of a tracking delay. To overcome this negative aspect, the reference dynamics is embedded into the constrained optimization process through an autonomous state-space approach by exploiting the dynamic mode decomposition (DMD) technique. The novel control approach is named MPC with embedded reference dynamics, MPC-ERD. A further novelty is that the operating limits of the motors in terms of torque and speed, described by their characteristic curve, are included into the controller design as time-varying constraints, together with additional cable tension constraints. The effectiveness of MPC-ERD is numerically validated through a cable-suspended parallel robot (CSPR), and the results are compared with those provided by both standard MPC with embedded integrator (i.e., the “velocity-form model”) and classic MPC without embedded integrator, confirming the superiority of MPC-ERD to ensure precise path and trajectory of the end-effector, with negligible delays and errors
Embedding reference dynamics in model predictive control for trajectory tracking of multi-input multi-output non-minimum phase underactuated multibody systems
No full textThis paper proposes a feedback control technique for path and trajectory tracking on multi-input, multi-output nonminimum phase underactuated multibody systems and applies it to a spatial gantry crane moving a double pendulum. The two links forming the double pendulum are connected in series and the desired output of the system is the tip of the second link. This output selection yields to a nonminimum phase system, which is a class of dynamical systems that are particularly challenging from the control design perspective. In this paper, an enhanced formulation of Model Predictive Control is proposed to solve the output trajectory tracking problem by embedding the dynamics of the spatial reference trajectory within the optimization process performed at each time step. The proposed control technique is formulated considering two different scenarios: the case of torque-controlled (i.e., current-controlled) actuators, and the case of position-controlled actuators. The latter is unusual in the field of MPC and is suitable for industrial applications where proprietary controllers are adopted. Numerical validations show negligible contour and tracking errors during the execution of the desired trajectories, with low computational effort
Using Pose-Dependent Model Predictive Control for Path Tracking with Bounded Tensions in a 3-DOF Spatial Cable Suspended Parallel Robot
No full textThis paper proposes the preliminary results on a novel control architecture based on model predictive control (MPC) for cable-driven parallel robots (CDPRs) and applies them to a three degrees of freedom (3-DOF) robot with a suspended configuration, leading to a cable-suspended parallel robot (CSPR). The goal of the control scheme is ensuring accurate path tracking of the reference end-effector path, while imposing a priori positive cable tensions. To handle the nonlinearities characterizing the dynamic model that governs this kind of multibody system and to keep the computational effort low, a position-dependent MPC algorithm with an embedded integrator is designed to compute the optimal cable tensions required to track the end-effector commanded path. Such tensions must belong to the feasible domain defined through a lower bound, which is slightly greater than zero, to ensure that cables pull the end-effector, and an upper bound, to represent the maximum stress that cables can withstand without breaking. The resulting controller is nonlinear, although it performs a local linearization in the prediction at each time step to reduce the computational effort. The optimal tensions are then transformed into the commanded motor torques through the inverse dynamic model of the servomotors driving the winches, since no force measurement is adopted in the controller implementation. The control architecture is designed and numerically validated through a spatial CSPR with lumped end-effector, and driven by three cables (i.e., with a non-redundant configuration). Four different paths are assumed to highlight various features of the proposed controller
Patterns of development of tachyphylaxis in patients with haemophilia and von Willebrand disease after repeated doses of desmopressin (DDAVP)
No full textWhen patients with mild haemophilia or von Willebrand disease (vWD) are repeatedly treated with desmopressin (DDAVP) at relatively short time intervals, some of them may become less responsive or unresponsive. The development of tachyphylaxis would limit the usefulness of DDAVP in clinical management of these patients. On the other hand, tachyphylaxis is not consistent, and its patterns of development are unknown. The aim of this study was to evaluate in controlled conditions the occurrence of tachyphylaxis by giving intravenous DDAVP (0.3 μg/kg) on four consecutive days to a selected group of patients with mild haemophilia A (n = 22) and type I vWD (n = 15). After each dose, we measured parameters known to change after DDAVP, i.e. factor VIII coagulant activity, bleeding time, von Willebrand factor antigen, ristocetin cofactor and tissue-type plasminogen activator antigen. We found that on average the responses obtained after the second dose of DDAVP were approximately 30% less than those obtained after the first, but were not further reduced after the third and fourth dose. At all time intervals after DDAVP, patients with vWD responded relatively better than patients with haemophilia, and there were fewer vWD patients who responded poorly or became unresponsive. In vWD patients there were no significant changes in the bleeding time responses and in blood pressure and heart rate. The clinical implications of these findings are that repeated doses of DDAVP can be given efficaciously to many patients (particularly to those with vWD), even though responses lower than those seen after the first dose should be expected
EARLY AND DELAYED REPRODUCTIVE DEATH IN HUMAN CELLS EXPOSED TO HIGH ENERGY IRON ION BEAMS
No full textThe aim of this research was to determine the biological effectiveness for early and delayed effects of high energy, high linear energy transfer (LET) charged particles. Survival and delayed reproductive death were measured in AG1522 human fibroblast cells exposed to Fe-ion beams of energies between 0.2 and 1 GeV/n, 0.97 GeV/n Ti-ion and 0.49 GcV/n Si-ion beams. The cells were irradiated at the HIMAC accelerator in Chiba, Japan (0.2 and 0.5 GeV/n Fe and 0.49 GeV/n Si) and at the NASA Space Radiation Laboratory in Brookhaven, USA (1 GeV/n Fe and 0.97 GeV/n Ti ions). The dose-effect curves were measured in the dose range between 0.25 and 2 Gy. For comparison cells were exposed to Co-60 gamma rays. Analysis of the dose-effect curves show that all the heavy ion beams induce inactivation and delayed reproductive death more effectively than 60 Co rays. The only exception is the 0.2 GeV/n Fe-ion beam at low doses. The progeny of the irradiated cells show delayed damage in the form of reproductive death with all the heavy ion beams with the 1 GeV/n Fe-ion beam being the most effective. The relative biological effectiveness at low doses of the iron beams is highest for LET values between 140 and 200 keV/mu m with values of 1.6 and 3 for early and delayed reproductive death, respectively. Analysis of the fluence-effect curves shows that the cross-sections for early and delayed inactivation increase with increasing LET up to 442 keV/mu m. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved
Model Inversion for Tip Control of Underactuated Non-minimum Phase Gantry Cranes with Small Inertia Ratio
No full textMotion planning in non-minimum phase underactuated multibody systems is challenging mainly due to the non-collocation of the control force with respect to desired output and due to the system flexibility. A motion planning method for non-minimum phase underactuated multibody systems based on the inverse dynamics is proposed in this paper. The approach is structured as follows. First, the system is partitioned into actuated and unactuated coordinates. Then, the desired output is described as a non-linear separable function of these coordinates. Since the system is non-minimum phase, output redefinition is exploited to virtually redefine the output displacement in order to stabilize the system internal dynamics. This enables the stable integration of the ODEs describing the evolution of the unactuated coordinates. Finally, the trajectory of the actuated coordinates is obtained through non-linear kinematic inversion. The method is then applied to the case of a spatial overhead crane moving a suspended load. The effectiveness of the method in tracking a spatial trajectory is demonstrated through numerical simulations
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