77 research outputs found
Grazing function g and collimation angular acceptance
The grazing function g is introducedâa synchrobetatron optical quantity that is analogous (and closely connected) to the Twiss and dispersion functions ÎČ, α, η, and ηâČ. It parametrizes the rate of change of total angle with respect to synchrotron amplitude for grazing particles, which just touch the surface of an aperture when their synchrotron and betatron oscillations are simultaneously (in time) at their extreme displacements. The grazing function can be important at collimators with limited acceptance angles. For example, it is important in both modes of crystal collimation operationâin channeling and in volume reflection. The grazing function is independent of the collimator typeâcrystal or amorphousâbut can depend strongly on its azimuthal location. The rigorous synchrobetatron condition g=0 is solved, by invoking the close connection between the grazing function and the slope of the normalized dispersion. Propagation of the grazing function is described, through drifts, dipoles, and quadrupoles. Analytic expressions are developed for g in perfectly matched periodic FODO cells, and in the presence of ÎČ or η error waves. These analytic approximations are shown to be, in general, in good agreement with realistic numerical examples. The grazing function is shown to scale linearly with FODO cell bend angle, but to be independent of FODO cell length. The ideal value is g=0 at the collimator, but finite nonzero values are acceptable. Practically achievable grazing functions are described and evaluated, for both amorphous and crystal primary collimators, at RHIC, the SPS (UA9), the Tevatron (T-980), and the LHC
Conceptual design of hollow electron lenses for beam halo control in the Large Hadron Collider
Collimation with hollow electron beams is a technique for halo control in
high-power hadron beams. It is based on an electron beam (possibly pulsed or
modulated in intensity) guided by strong axial magnetic fields which overlaps
with the circulating beam in a short section of the ring. The concept was
tested experimentally at the Fermilab Tevatron collider using a hollow electron
gun installed in one of the Tevatron electron lenses. Within the US LHC
Accelerator Research Program (LARP) and the European FP7 HiLumi LHC Design
Study, we are proposing a conceptual design for applying this technique to the
Large Hadron Collider at CERN. A prototype hollow electron gun for the LHC was
built and tested. The expected performance of the hollow electron beam
collimator was based on Tevatron experiments and on numerical tracking
simulations. Halo removal rates and enhancements of halo diffusivity were
estimated as a function of beam and lattice parameters. Proton beam core
lifetimes and emittance growth rates were checked to ensure that undesired
effects were suppressed. Hardware specifications were based on the Tevatron
devices and on preliminary engineering integration studies in the LHC machine.
Required resources and a possible timeline were also outlined, together with a
brief discussion of alternative halo-removal schemes and of other possible uses
of electron lenses to improve the performance of the LHC.Comment: 24 pages, 1 table, 10 figure
Use of Sheet Material for Rapid Prototyping of Cardiovascular Stents
Manufacturing of cardiovascular stents most commonly involve the use of tubular precursors and laser microcutting of the stent mesh, followed by chemical and electrochemical surface treatments. For mass manufacturing purposes, this production route is well-established, while for small batch or prototype production it proves to be cumbersome. Especially concerning newly developed alloys based, the production of microtubes is time consuming and highly costly. On the other hand, production of these new alloys in sheet metal form is a simpler approach, since the process uses non-dedicated tools and is easier as opposed to extrusion and tube drawing. Accordingly, in this work, the use of sheet material as precursor for rapid prototyping of cardiovascular stents is proposed. In particular, a ns-pulsed fiber laser is used for cutting permanent AISI 316L. Laser microcutting conditions are investigated in terms of generated spatter and kerf geometry. Chemical etching is employed to clean the dross generated around the cut kerf. A novel stent geometry allowing for transforming the sheet material to a tubular form is employed to produce prototype stents
Interplay between powder catchment efficiency and layer height in self-stabilized laser metal deposition
In laser metal deposition (LMD) the height of the deposited track can vary
within and between layers, causing significant deviations during the process
evolution. Previous works have shown that in certain conditions a
self-stabilizing mechanism occurs, maintaining a regular height growth and a
constant standoff distance between the part and the deposition nozzle. Here we
analyze the link between the powder catchment efficiency and the deposition
height stability. To this purpose, a monitoring system was developed to study
the deposition in different process conditions, using inline measurements of
the specimen weight in combination with the layer height information obtained
with coaxial optical triangulation. An analytical model was used to estimate
the deposition efficiency in real-time from the height monitoring and the
process parameters, which was verified by the direct mass measurements. The
results show that the track height stabilization is associated to a reduction
of the powder catchment efficiency, which is governed by the melt pool relative
position with respect to the powder cone and the laser beam. For a given set of
parameters, the standoff distance can be estimated to achieve the highest
powder catchment efficiency and a regular height through the build direction
Laser surface structuring of AZ31 Mg alloy for controlled wettability
Structured surfaces exhibit functional properties that can enhance the performance of a bioimplant in terms of biocompatibility, adhesion, or corrosion behavior. In order to tailor the surface property, chemical and physical methods can be used in a sequence of many steps. On the other hand, laser surface processing can provide a single step solution to achieve the designated surface function with the use of simpler equipment and high repeatability. This work provides the details on the surface structuring of AZ31, a biocompatible and biodegradable Mg alloy, by a single-step laser surface structuring based on remelting. The surfaces are characterized in terms of topography, chemistry, and physical integrity, as well as the effective change in the surface wetting behavior is demonstrated. The results imply a great potential in local or complete surface structuring of medical implants for functionalization by the flexible positioning of the laser beam
Laser micro-polishing of stainless steel for antibacterial surface applications
In this work laser micro polishing (LMP) of cold rolled 0.3 mm thick 304 stainless steel with a pulsed fibre laser is studied, for applications
where antibacterial properties are required. Due to its production method, the initial surface roughness of the tested material was considerably
low (Sa=85.3±2.8 ”m), rendering a demanding case for the laser polishing process. Accordingly, process feasibility under three different
atmospheric conditions, namely ambient, Ar and N2 atmosphere, was investigated. A large set of process parameter combinations was tested
and initial analysis was carried out to identify the polishing feasibility by inspection under an optical microscope. Once the feasibility window
was determined, a primary characterization was made on selected surfaces for roughness and waviness. Results show that in some process
conditions belonging to the explored feasibility range, surface roughness could be decreased by 50%
Patient-specific cardiovascular superelastic NiTi stents produced by laser powder bed fusion
To date, there is a general lack of customizability within the selection of endovascular devices for catheter-based vascular interventions. Laser powder bed fusion (LPBF) has been flexibly exploited to produce customized implants using conventional biomedical alloys for orthopedic and dental applications. Applying LPBF for cardiovascular applications, patient-specific stents can be produced with small struts (approximately 100-300 ”m), variable geometries, and clinically used metals capable of superelastic behaviour at body temperature (eg. equiatomic nickel-titanium alloys, NiTi). Additionally, the growing availability and use of patient-specific 3D models provides a unique opportunity to outline the necessary manufacturing process that would be required for customizable NiTi devices based on patient geometry. In order to fulfil the potential of the patient-specific superelastic stents, process and design know-how should be expanded to the novel material and fine details at the limits of conventional LPBF machines. In this work, a framework for developing a patient-specific superelastic NiTi stent produced by LPBF is demonstrated. At a proof-of-concept stage, the design procedures are shown in a geometry similar to the artery. The stents with 100 ”m nominal strut diameter are later produced with a Ni50.8Ti49.2 powder and heat treated. The results confirm the possibility of producing stents with a design suitable for highly complex patient-specific anatomies and having superelastic behavior at body temperature
Laser surface structuring affects polymer deposition, coating homogeneity, and degradation rate of Mg alloys
In the current work, a coating system consisted of a laser-structured surface, a thin layer primer and a polymeric coating to improve degradation behaviour of biocompatible and biodegradable Mg alloy is presented. The laser structuring allowed modification of surface topography as well as controlling the wettability of surface. The cellulose acetate primer provided protection from in-process degradation of samples during the successive layer-by-layer (LbL) coating process, where alternate layers of chitosan and carboxymethyl cellulose were applied. The results revealed that the laser structured surface plays an important role on the developed coating structure and final corrosion rate. Lowest corrosion rate among the coated samples (1.15 cm yr(-1)) was measured for the most hydrophilic laser-treated surface, corresponding to almost 16% reduction compared to the as-received samples
The âplacebo effectâ in the conservative treatment of plantar fasciitis: a systematic review and meta-analyses
Purpose: The study of the placebo effect is key to elucidate the âreal effectâ of conservative interventions for plantar fasciitis. The aim of this meta-analysis was to quantify the impact of placebo in the different conservative treatments of plantar fasciitis.
Methods: A systematic literature review was performed on double-blind placebo-controlled trials (RCTs) according to PRISMA guidelines on PubMed, Embase, and Web of Science. The meta-analysis primary outcome was the 0â10 pain variation after placebo treatments analyzed at 1 week, 1, 3, 6, and 12 months. The risk of bias was assessed using the RoB 2.0 tool, while the overall quality of evidence was graded according to the GRADE guidelines.
Results: The placebo effect for conservative treatments was studied in 42 double-blind RCTs on 1724 patients. The meta-analysis of VAS pain showed a statistically significant improvement after placebo administration of 2.13/10 points (P < 0.001), being highest at 12 months with 2.79/10 points (P < 0.001). The improvement of the placebo groups was higher in the extracorporeal shock wave therapy studies compared to the injection studies (2.59 vs 1.78; P = 0.05). Eight studies had a low risk of bias, 23 studies had âsome concerns,â and 4 studies had a high risk of bias. The GRADE evaluation showed an overall high quality of evidence.
Conclusion: This systematic review and meta-analysis demonstrated that the placebo effect represents an important component of all conservative approaches to treat plantar fasciitis. This effect is statistically and clinically significant, increases over time, and depends on the type of conservative treatment applied to address plantar fasciitis
Integrated Robot Motion and Process control for manufacturing reshaping
The future of metal manufacturing processes like laser cutting, welding, and additive manufacturing shall rely on intelligent systems spearheaded by Industry 4.0. Such a digital innovation is indeed driving machinery builders to a profound transformation. From custom machines designed and optimized for a specific process, the ambition is to exploit the openness and the large availability of industrial robots to increase flexibility and reconfigurability of multi processes implementations. The challenge is that machinery builders transform themselves into high-knowledge specialized process-driven robot integrators, able to optimize the robot motion with the process controller leveraging on intelligent sensing and cognition. The work describes the multi-annual collaboration of the BLM group and Politecnico di Milano, with the support of CNR, focused on the deployment of a complete working robotic workstation characterized by the full integration of the robot control and motion planning with manufacturing processes
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