597 research outputs found
Commissioning of a Microdosimetric Device for Hadrontherapy
openRadiotherapy aims at maximising the dose delivered to the tumour whilst minimising that to the healthy
tissues. The absorbed dose, being an average quantity, doesnât consider the random nature of radiation
interactions. However, it is well acknowledged that biological effectiveness is related to the microscopic
distribution of absorbed energy rather than to its mean value. If the microscopic distribution is uniform
throughout the irradiated volume (for conventional photon-based radiotherapy), the absorbed dose is a
suitable parameter. For charged particles (e.g. protons, helium and carbon ions) ionizations are clustered
around the particle path and produce a not uniform pattern of energy deposition. In this case average
values do not accurately predict the biological effects.
In treatment planning systems (TPS) used in proton therapy it is currently assumed that the biological
effectiveness is constant, independent of the proton beam energy and penetration depth. However, the
scientific community is moving toward advanced protocols in which the change in biological effectiveness is
considered. In parallel, procedures for the quality assurance of the radiation quality (physical characteristics
of the radiation field correlated to the biological effectiveness) need to be developed. Microdosimetry is a
valuable technique, but commercial detectors for hadron-therapy applications are not currently available.
The engineering of advanced gas-based microdosimeters for the characterization of proton and carbon ion
beams is currently ongoing at Legnaro National Laboratories of INFN. This thesis focuses on the
characterization and optimization of new devices in gamma, neutron and therapeutic proton fields. The
response function will be studied for several operative conditions of the sensor, front-end electronics and
control/data acquisition system.Radiotherapy aims at maximising the dose delivered to the tumour whilst minimising that to the healthy
tissues. The absorbed dose, being an average quantity, doesnât consider the random nature of radiation
interactions. However, it is well acknowledged that biological effectiveness is related to the microscopic
distribution of absorbed energy rather than to its mean value. If the microscopic distribution is uniform
throughout the irradiated volume (for conventional photon-based radiotherapy), the absorbed dose is a
suitable parameter. For charged particles (e.g. protons, helium and carbon ions) ionizations are clustered
around the particle path and produce a not uniform pattern of energy deposition. In this case average
values do not accurately predict the biological effects.
In treatment planning systems (TPS) used in proton therapy it is currently assumed that the biological
effectiveness is constant, independent of the proton beam energy and penetration depth. However, the
scientific community is moving toward advanced protocols in which the change in biological effectiveness is
considered. In parallel, procedures for the quality assurance of the radiation quality (physical characteristics
of the radiation field correlated to the biological effectiveness) need to be developed. Microdosimetry is a
valuable technique, but commercial detectors for hadron-therapy applications are not currently available.
The engineering of advanced gas-based microdosimeters for the characterization of proton and carbon ion
beams is currently ongoing at Legnaro National Laboratories of INFN. This thesis focuses on the
characterization and optimization of new devices in gamma, neutron and therapeutic proton fields. The
response function will be studied for several operative conditions of the sensor, front-end electronics and
control/data acquisition system
From techno-scientific grammar to organizational syntax. New production insights on the nature of the firm
The paper aims at providing the conceptual building blocks of a theory of the firm which addresses its "ontological questions" (existence,boundaries and organization) by placing production at its core. We draw on engineering for a more accurate description of the production process itself, highlighting its inner complexity and potentially chaotic nature, and on computational linguistics for a production-based account of the nature of economic agents and of the mechanisms through which they build ordered production sets. In so doing, we give a "more appropriate" production basis to the crucial issues of how firm's boundaries are set, how its organisational structure is defined, and how it changes over time. In particular, we show how economic agents select some tasks to be performed internally, while leaving some other to external suppliers, on the basis of criteria based on both the different degrees of internal congruence of the tasks to be performed (i.e. the internal environment), and on the outer relationships carried out with other agents (i.e. the external environment)
State Space Modeling and Estimation of Flexible Structure Using the Theory of Functional Connections
In this work, we present a novel method to model the dynamics of a continuous structure based on measurements taken at discrete points. The method is conceived to provide new instruments to address the problem of flexible dynamics modeling in a spacecraft, where an effective mathematical representation of the non-rigid behavior of the is of critical importance in the design of an effective and reliable attitude estimation and control system. Both the measurements and the model that describes the structure can be affected by uncertainty. The purpose of the developed method is to estimate the position and the velocity of any point of the physical domain relying on a limited number of measurements while filtering out the noise. To this aim, the well-assessed Kalman filter is used in synergy with the recently developed Theory of Functional Connections (TFC). This is a mathematical framework to perform functional interpolation with applications in many fields being currently discovered and investigated. Initially, an algorithm for the solution of the corresponding static problem was developed based on the TFC; the results of the tests were promising and the approach presented in this work constitutes an effort to extend the idea to the dynamic case. In the proposed method, the continuous structure is approximated by the TFC constrained expression, while the system state variables are defined as the coefficients used to represent the free function in a basis of orthogonal polynomials. This leads to a system that, despite being continuous and thus formed of an infinite number of material points, is modeled using a finite number of state variables allowing for the use of Kalman filter to deal with the uncertainties intrinsic in both the modeling and measurements. This is accomplished by exploiting the original structure model Differential Equation(s) to obtain a process model for the filter and using the constrained expression itself as the measurement model. Then the Kalman filter algorithm is applied and the a posteriori estimates of the state variables (that is the free function coefficients) can be used to build the TFC expression that approximates the instantaneous shape of the structure, thus enabling the evaluation of the displacement at any point of the domain. The power of the proposed method is twofold. First, an estimate of the displacements of all the points is obtained based on a limited number of noisy measurements. Second, the relation between discrete measurements and continuous displacement field always accounts for the real physics of the problem. In this paper, the theoretical developments of the proposed approach are shown along with the results of numerical simulations showing the effectiveness of the method in estimating the actual dynamics of a Euler-Bernoulli beam. The technique yielded good results both for the free response and in the case of a forcing input to the system
Probing the phase diagram of cuprates with YBaCuO thin films and nanowires
We have grown and characterized 30 nm thick YBaCuO
(YBCO) films, deposited by pulsed laser deposition on both MgO (110) and
SrTiO (001) substrates, which induce opposite strain to the superconducting
layer. By carefully tuning the in-situ post-annealing oxygen pressure, we
achieved, in a reproducible way, films at different oxygen doping, spanning
from the slightly overdoped down to the strongly underdoped region of the phase
diagram. The transport properties of the films, investigated through resistance
versus temperature measurements, are in perfect qualitative agreement with
single crystals. Starting from these films, we have also successfully
fabricated nanowires with widths down to 65 nm, at different oxygen doping. The
nanostructures exhibit characteristic temperatures (as the critical temperature
and the pseudogap temperature ) similar to those of the
as-grown films and carry critical current densities close to
the critical depairing value, limited by vortex entry. This implies that the
superconducting and the normal state properties of underdoped YBCO are
preserved in our films, and they can be studied as a function of the
dimensionality of the system, down to the nanoscale.Comment: 11 pages, 9 figures, submitted to Phys. Rev. Material
Ultra low noise YBCO nanoSQUIDs implementing nanowires
We present results on ultra low noise YBaCuO nano
Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such
devices, we implemented high quality YBCO nanowires, working as weak links
between two electrodes. We observe critical current modulation as a function of
an externally applied magnetic field in the full temperature range below the
transition temperature . The white flux noise below 1 at T = 8 K makes our nanoSQUIDs very attractive for
the detection of small spin systems.Comment: 11 pages, 4 figures, submitted to Appl. Phys. Lett. 25/01/201
Analysis of geometrical and topological attitude for proteinprotein interaction
Protein-protein interaction takes usually place on an extended area of the external molecules surfaces that are morphologically fitting. Geometric and topological congruence (i.e. concavity and convexity correspondences) is required to support the neighboring interaction of surface patches belonging to the two protein molecules. It is therefore important to adopt representations and data structures that can facilitate the analysis and the implementation of techniques for the evaluation of geometric and topological properties on extended surfaces. These areas of activity are usually roughly âplanarâ but with local concavity and complexity that must match each other for interacting. To this purpose we are suggesting a
solution different from the one of ligand-protein interaction in which are involved a pocket and a small molecule. The solution here suggested is based on the concavity tree representation. Starting from the convex hull of the protein molecule a recursive process leads to a series of concavity and meta-concavity that allows reaching
the detail level required. The consequence of the recursive process is obviously a hierarchical data structure (a tree) which at each level supports a complete description of a surface. Each node of the tree contains an array of features that support the geometrical, topological and biochemical properties of the correspondent surface patch
A non-parametric random effects model for the valuation of forest recreation services: An application to forest sites in Tuscany, Italy
This study assesses individualsâ preferences for the use of forest sites for recreational purposes by means of the Logit Mixed Logit (LMNL) model (Train, 2016). The appeal of the LML is that the analyst need not assume any specific functional form for the mixing distributions of random preferences. The empirical analysis generates a data-driven non-parametric representation of individualsâ preference heterogeneity. We apply this approach to data collected using an unlabeled discrete choice experiment, consisting of three recreational options, two of which are two hypothetical forest sites. Forest destinations are described by means of six attributes: forest type, sign-posting, hiking time, access to rivers or lakes, wildlife watching hides for visitors and cost of access. The empirical findings reveal that the signpost for each trail is the attribute for which respondents are on average willing to pay the most (6.565âŹ). Further evidence suggests that respondents have strong positive preferences for those forest sites that offer amenities such as wildlife watch hides and access to rivers or lakes. Finally, the histograms derived from the semi-parametric LML estimation reveal multimodality of random taste amongst respondents for different hypothetical forest site
A nonparametric random effects model for the valuation of forest recreation services: An application to forest sites in Tuscany, Italy
This study assesses individuals' preferences for the use of forest sites for recreational purposes by means of the logitâmixed logit (LML) model. The appeal of the LML is that the analyst does not need to assume any specific functional form for the mixing distributions of random preferences. The empirical analysis generates a dataâdriven nonparametric representation of individuals' preference heterogeneity. We apply this approach to data collected using an unlabelled discrete choice experiment (DCE), consisting of three recreational options, two of which are in two hypothetical forest sites. Forest destinations are described by means of six attributes: forest type, signposting, hiking time, access to rivers or lakes, wildlife watch hides for visitors and cost of access. The empirical findings reveal that the signpost for each trail is the attribute for which respondents are on average willing to pay the most (6.565âŹ). Further evidence suggests that respondents have strong positive preferences for those forest sites that offer amenities such as wildlife watch hides and access to rivers or lakes. Finally, the histograms derived from the semiâparametric LML estimation reveal multimodality of random taste amongst respondents for different hypothetical forest sites
Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
We present the fabrication and electrical transport characterization of underdoped YBa2Cu3O7-δnanowires. The nanowires have been realized without any protective capping layer and theyshow transport properties similar to those of the parent thin film, demonstrating that they havenot been damaged by the nanopatterning. The current-voltage characteristics of the underdopednanowires show large hysteretic voltage switching at the critical current, in contrast to theflux-flow like characteristics of optimally doped nanostructures, indicating the formation of aself-stabilizing hot spot. These results open up new possibilities for using the underdopednanowires as single photon detectors and for exploring the underdoped side of the YBa2Cu3O7-δphase diagram at the nanoscale
Mapping the Phase Diagram of a YBa2Cu3 O7-δ Nanowire Through Electromigration
We use electromigration (EM) to tune the oxygen content of YBa2Cu3O7-δ (YBCO) nanowires. During EM, the dopant oxygen atoms in the nanowire are moved under the combined effect of electrostatic force and Joule heating. The EM current can be tuned to either deplete or replenish nanowires with oxygen, allowing fine tuning of its hole-doping level. Electrical transport measurements and Kelvin probe microscopy corroborate good homogeneity of the doping level along the electromigrated nanowires. Thus, EM provides an effective method to study transport properties of YBCO in a wide doping range at the nanoscale in one and the same device
- âŚ