Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions

As a diagnostic of high-intensity laser interactions (> 10(19) W cm(-2)), the detection of radioactive isotopes is regularly used for the characterization of proton, neutron, ion, and photon beams. This involves sample removal from the interaction chamber and time consuming post shot analysis using NaI coincidence counting or Ge detectors. This letter describes the use of in situ detectors to measure laser-driven (p,n) reactions in Al-27 as an almost real-time diagnostic for proton acceleration. The produced Si-27 isotope decays with a 4.16 s half-life by the predominantly beta+ emission, producing a strong 511 keV annihilation peak. (c) 2006 American Institute of Physics.

The CMS experiment at the CERN LHC

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Crystallographic structure of Ti-6Al-4V, Ti-HP and Ti-CP under high-pressure

The phase stability of a commercial purity (Ti-CP), high purity (Ti-HP) and Ti-6Al-4V alloy were investigated in a diamond anvil cell up to 32 GPa and 298 K using a polychromatic X-ray beam. The Ti-CP and Ti-HP shown the same HCP (c/a∼0.632) to Hexagonal (c/a∼1.63) non reversible martensitic transition at about 9 GPa. The as received Ti-6Al-4V shows a very low relative volume fraction β-Ti / α-Ti. No phase changes were observed in the Ti-6Al-4V alloy in the pressure range of this study. The α phase of the Ti-6Al-4V shows monotonic volume cell pressure dependence. This volume change is reversible and non-hysteretic. The cell of the a phase recovered its original volume when the pressure was released. © 2010 IOP Publishing Ltd.

Identification of b-quark jets with the CMS experiment

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Recently, a new ternary phase was discovered in the Ti-Si-B system, located near the Ti6Si2B composition. The present study concerns the preparation of titanium alloys that contain such phase mixed with α-titanium and other intermetallic phases. High-purity powders were initially processed in a planetary ball-mill under argon atmosphere with Ti-18Si-6B and Ti-7.5Si-22.5B at. (%) initial compositions. Variation of parameters such as rotary speed, time, and ball diameters were adopted. The as-milled powders were pressureless sintered and hot pressed. Both the as-milled and sintered materials were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Sintered samples have presented equilibrium structures formed mainly by the α-Ti+Ti6Si2B+Ti5Si3+TiB phases. Silicon and boron peaks disappear throughout the milling processes, as observed in the powder diffraction data. Furthermore, an iron contamination of up to 10 at. (%) is measured by X-ray spectroscopy analysis on some regions of the sintered samples. Density, hardness and tribological results for these two compositions are also presented here.

Applications of High Speed Configurable Logic Devices in Modern Particle Physics Experiments

Several activities were conducted during my PhD activity. For the NEMO experiment a collaboration between the INFN/University groups of Catania and Bologna led to the development and production of a mixed signal acquisition board for the Nemo Km3 telescope. The research concerned the feasibility study for a different acquisition technique quite far from that adopted in the NEMO Phase 1 telescope. The DAQ board that we realized exploits the LIRA06 front-end chip for the analog acquisition of anodic an dynodic sources of a PMT (Photo-Multiplier Tube). The low-power analog acquisition allows to sample contemporaneously multiple channels of the PMT at different gain factors in order to increase the signal response linearity over a wider dynamic range. Also the auto triggering and self-event-classification features help to improve the acquisition performance and the knowledge on the neutrino event. A fully functional interface towards the first level data concentrator, the Floor Control Module, has been integrated as well on the board, and a specific firmware has been realized to comply with the present communication protocols. This stage of the project foresees the use of an FPGA, a high speed configurable device, to provide the board with a flexible digital logic control core. After the validation of the whole front-end architecture this feature would be probably integrated in a common mixed-signal ASIC (Application Specific Integrated Circuit). The volatile nature of the configuration memory of the FPGA implied the integration of a flash ISP (In System Programming) memory and a smart architecture for a safe remote reconfiguration of it. All the integrated features of the board have been tested. At the Catania laboratory the behavior of the LIRA chip has been investigated in the digital environment of the DAQ board and we succeeded in driving the acquisition with the FPGA. The PMT pulses generated with an arbitrary waveform generator were correctly triggered and acquired by the analog chip, and successively they were digitized by the on board ADC under the supervision of the FPGA. For the communication towards the data concentrator a test bench has been realized in Bologna where, thanks to a lending of the Roma University and INFN, a full readout chain equivalent to that present in the NEMO phase-1 was installed. These tests showed a good behavior of the digital electronic that was able to receive and to execute command imparted by the PC console and to answer back with a reply. The remotely configurable logic behaved well too and demonstrated, at least in principle, the validity of this technique. A new prototype board is now under development at the Catania laboratory as an evolution of the one described above. This board is going to be deployed within the NEMO Phase-2 tower in one of its floors dedicated to new front-end proposals. This board will integrate a new analog acquisition chip called SAS (Smart Auto-triggering Sampler) introducing thus a new analog front-end but inheriting most of the digital logic present in the current DAQ board discussed in this thesis. For what concern the activity on high-resolution vertex detectors, I worked within the SLIM5 collaboration for the characterization of a MAPS (Monolithic Active Pixel Sensor) device called APSEL-4D. The mentioned chip is a matrix of 4096 active pixel sensors with deep N-well implantations meant for charge collection and to shield the analog electronics from digital noise. The chip integrates the full-custom sensors matrix and the sparsifification/readout logic realized with standard-cells in STM CMOS technology 130 nm. For the chip characterization a test-beam has been set up on the 12 GeV PS (Proton Synchrotron) line facility at CERN of Geneva (CH). The collaboration prepared a silicon strip telescope and a DAQ system (hardware and software) for data acquisition and control of the telescope that allowed to store about 90 million events in 7 equivalent days of live-time of the beam. My activities concerned basically the realization of a firmware interface towards and from the MAPS chip in order to integrate it on the general DAQ system. Thereafter I worked on the DAQ software to implement on it a proper Slow Control interface of the APSEL4D. Several APSEL4D chips with different thinning have been tested during the test beam. Those with 100 and 300 um presented an overall efficiency of about 90% imparting a threshold of 450 electrons. The test-beam allowed to estimate also the resolution of the pixel sensor providing good results consistent with the pitch/sqrt(12) formula. The MAPS intrinsic resolution has been extracted from the width of the residual plot taking into account the multiple scattering effect.

Fabrication of high quality optical coherence tomography (OCT) calibration artefacts using femtosecond inscription

Optical coherence tomography (OCT) is a non-invasive three-dimensional imaging system that is capable of producing high resolution in-vivo images. OCT is approved for use in clinical trials in Japan, USA and Europe. For OCT to be used effectively in a clinical diagnosis, a method of standardisation is required to assess the performance across different systems. This standardisation can be implemented using highly accurate and reproducible artefacts for calibration at both installation and throughout the lifetime of a system. Femtosecond lasers can write highly reproducible and highly localised micro-structured calibration artefacts within a transparent media. We report on the fabrication of high quality OCT calibration artefacts in fused silica using a femtosecond laser. The calibration artefacts were written in fused silica due to its high purity and ability to withstand high energy femtosecond pulses. An Amplitude Systemes s-Pulse Yb:YAG femtosecond laser with an operating wavelength of 1026 nm was used to inscribe three dimensional patterns within the highly optically transmissive substrate. Four unique artefacts have been designed to measure a wide variety of parameters, including the points spread function (PSF), modulation transfer function (MTF), sensitivity, distortion and resolution - key parameters which define the performance of the OCT. The calibration artefacts have been characterised using an optical microscope and tested on a swept source OCT. The results demonstrate that the femtosecond laser inscribed artefacts have the potential of quantitatively and qualitatively validating the performance of any OCT system.

X-Ray Diffraction Study of Boron Produced by Pyrolysis of Boron Tribromide

The goal of this research was to determine the composition of boron deposits produced by pyrolysis of boron tribromide, and to use the results to (a) determine the experimental conditions (reaction temperature, etc.) necessary to produce alpha-rhombohedral boron and (b) guide the development/refinement of the pyrolysis experiments such that large, high purity crystals of alpha-rhombohedral boron can be produced with consistency. Developing a method for producing large, high purity alpha-rhombohedral boron crystals is of interest because such crystals could potentially be used to achieve an alpha-rhombohedral boron based neutron detector design (a solid-state detector) that could serve as an alternative to existing neutron detector technologies. The supply of neutron detectors in the United States has been hampered for a number of years due to the current shortage of helium-3 (a gas used in many existing neutron detector technologies); the development of alternative neutron detector technology such as an alpha-rhombohedral boron based detector would help provide a more sustainable supply of neutron detectors in this country. In addition, the prospect/concept of an alpha-rhombohedral boron based neutron detector is attractive because it offers the possibility of achieving a design that is smaller, longer life, less power consuming, and potentially more sensitive than existing neutron detectors. The main difficulty associated with creating an alpha-rhombohedral boron based neutron detector is that producing large, high purity crystals of alpha-rhombohedral boron is extremely challenging. Past researchers have successfully made alpha-rhombohedral boron via a number of methods, but no one has developed a method for consistently producing large, high purity crystals. Alpha-rhombohedral boron is difficult to make because it is only stable at temperatures below around 1100-1200 °C, its formation is very sensitive to impurities, and the conditions necessary for its formation are not fully understood or agreed upon in the literature. In this research, the method of pyrolysis of boron tribromide (hydrogen reduction of boron tribromide) was used to deposit boron on a tantalum filament. The goal was to refine this method, or potentially use it in combination with a second method (amorphous boron crystallization), to the point where it is possible to grow large, high purity alpha-rhombohedral boron crystals with consistency. A pyrolysis apparatus was designed and built, and a number of trials were run to determine the conditions (reaction temperature, etc.) necessary for alpha-rhombohedral boron production. This work was focused on the x-ray diffraction analysis of the boron deposits; x-ray diffraction was performed on a number of samples to determine the types of boron (and other compounds) formed in each trial and to guide the choices of test conditions for subsequent trials. It was found that at low reaction temperatures (in the range of around 830-950 °C), amorphous boron was the primary form of boron produced. Reaction temperatures in the range of around 950-1000 °C yielded various combinations of crystalline boron and amorphous boron. In the first trial performed at a temperature of 950 °C, a mix of amorphous boron and alpha-rhombohedral boron was formed. Using a scanning electron microscope, it was possible to see small alpha-rhombohedral boron crystals (on the order of ~1 micron in size) embedded in the surface of the deposit. In subsequent trials carried out at reaction temperatures in the range of 950 °C – 1000 °C, it was found that various combinations of alpha-rhombohedral boron, beta-rhombohedral boron, and amorphous boron were produced; the results tended to be unpredictable (alpha-rhombohedral boron was not produced in every trial), and the factors leading to success/failure were difficult to pinpoint. These results illustrate how sensitive of a process producing alpha-rhombohedral boron can be, and indicate that further improvements to the test apparatus and test conditions (for example, higher purity/cleanliness) may be necessary to optimize the boron deposition. Although alpha-rhombohedral boron crystals of large size were not achieved, this research was successful in (a) developing a pyrolysis apparatus and test procedure that can serve as a platform for future testing, (b) determining reaction temperatures at which alpha-rhombohedral boron can form, and (c) developing a consistent process for analyzing the boron deposits and determining their composition. Further experimentation is necessary to achieve a pyrolysis apparatus and test procedure that can yield large alpha-rhombohedral boron crystals with consistency.

Limitations of high pressure sputtering for amorphous silicon deposition

Amorphous silicon thin films were deposited using the high pressure sputtering (HPS) technique to study the influence of deposition parameters on film composition, presence of impurities, atomic bonding characteristics and optical properties. An optical emission spectroscopy (OES) system has been used to identify the different species present in the plasma in order to obtain appropriate conditions to deposit high purity films. Composition measurements in agreement with the OES information showed impurities which critically depend on the deposition rate and on the gas pressure. We prove that films deposited at the highest RF power and 3.4 × 10^−2 mbar, exhibit properties as good as the ones of the films deposited by other more standard techniques.

Sphingosine-1-phosphate mediates proliferation maintaining the multipotency of human adult bone marrow and adipose tissue-derived stem cells

High renewal and maintenance of multipotency of human adult stem cells (hSCs), are a prerequisite for experimental analysis as well as for potential clinical usages. The most widely used strategy for hSC culture and proliferation is using serum. However, serum is poorly defined and has a considerable degree of inter-batch variation, which makes it difficult for large-scale mesenchymal stem cells (MSCs) expansion in homogeneous culture conditions. Moreover, it is often observed that cells grown in serum-containing media spontaneously differentiate into unknown and/or undesired phenotypes. Another way of maintaining hSC development is using cytokines and/or tissue-specific growth factors; this is a very expensive approach and can lead to early unwanted differentiation. In order to circumvent these issues, we investigated the role of sphingosine-1-phosphate (S1P), in the growth and multipotency maintenance of human bone marrow and adipose tissue-derived MSCs. We show that S1P induces growth, and in combination with reduced serum, or with the growth factors FGF and platelet-derived growth factor-AB, S1P has an enhancing effect on growth. We also show that the MSCs cultured in S1P-supplemented media are able to maintain their differentiation potential for at least as long as that for cells grown in the usual serum-containing media. This is shown by the ability of cells grown in S1P-containing media to be able to undergo osteogenic as well as adipogenic differentiation. This is of interest, since S1P is a relatively inexpensive natural product, which can be obtained in homogeneous high-purity batches: this will minimize costs and potentially reduce the unwanted side effects observed with serum. Taken together, S1P is able to induce proliferation while maintaining the multipotency of different human stem cells, suggesting a potential for S1P in developing serum-free or serum-reduced defined medium for adult stem cell cultures.

Intensity dependent residual amplitude modulation in electro-optic phase modulators

Residual amplitude modulation (RAM) mechanisms in electro-optic phase modulators are detrimental in applications that require high purity phase modulation of the incident laser beam. While the origins of RAMare not fully understood, measurements have revealed that it depends on the beam properties of the laser as well as the properties of the medium. Here we present experimental and theoretical results that demonstrate, for the first time, the dependence of RAM production in electro-optic phase modulators on beam intensity. The results show an order of magnitude increase in the level of RAM, around 10 dB, with a fifteenfold enhancement in the input intensity from 12 to 190 mW/mm 2. We show that this intensity dependent RAM is photorefractive in origin. © 2012 Optical Society of America.

Evaluation of fibroin-based scaffolds for ocular tissue reconstruction

The epithelium of the corneolimbus contains stem cells for regenerating the corneal epithelium. Diseases and injuries affecting the limbus can lead to a condition known as limbal stem cell deficiency (LSCD), which results in loss of the corneal epithelium, and subsequent chronic inflammation and scarring of the ocular surface. Advances in the treatment of LSCD have been achieved through use of cultured human limbal epithelial (HLE) grafts to restore epithelial stem cells of the ocular surface. These epithelial grafts are usually produced by the ex vivo expansion of HLE cells on human donor amniotic membrane (AM), but this is not without limitations. Although AM is the most widely accepted substratum for HLE transplantation, donor variation, risk of disease transfer, and rising costs have led to the search for alternative biomaterials to improve the surgical outcome of LSCD. Recent studies have demonstrated that Bombyx mori silk fibroin (hereafter referred to as fibroin) membranes support the growth of primary HLE cells, and thus this thesis aims to explore the possibility of using fibroin as a biomaterial for ocular surface reconstruction. Optimistically, the grafted sheets of cultured epithelium would provide a replenishing source of epithelial progenitor cells for maintaining the corneal epithelium, however, the HLE cells lose their progenitor cell characteristics once removed from their niche. More severe ocular surface injuries, which result in stromal scarring, damage the epithelial stem cell niche, which subsequently leads to poor corneal re-epithelialisation post-grafting. An ideal solution to repairing the corneal limbus would therefore be to grow and transplant HLE cells on a biomaterial that also provides a means for replacing underlying stromal cells required to better simulate the normal stem cell niche. The recent discovery of limbal mesenchymal stromal cells (L-MSC) provides a possibility for stromal repair and regeneration, and therefore, this thesis presents the use of fibroin as a possible biomaterial to support a three dimensional tissue engineered corneolimbus with both an HLE and underlying L-MSC layer. Investigation into optimal scaffold design is necessary, including adequate separation of epithelial and stromal layers, as well as direct cell-cell contact. Firstly, the attachment, morphology and phenotype of HLE cells grown on fibroin were directly compared to that observed on donor AM, the current clinical standard substrate for HLE transplantation. The production, transparency, and permeability of fibroin membranes were also evaluated in this part of the study. Results revealed that fibroin membranes could be routinely produced using a custom-made film casting table and were found to be transparent and permeable. Attachment of HLE cells to fibroin after 4 hours in serum-free medium was similar to that supported by tissue culture plastic but approximately 6-fold less than that observed on AM. While HLE cultured on AM displayed superior stratification, epithelia constructed from HLE on fibroin maintained evidence of corneal phenotype (cytokeratin pair 3/12 expression; CK3/12) and displayed a comparable number and distribution of ÄNp63+ progenitor cells to that seen in cultures grown on AM. These results confirm the suitability of membranes constructed from silk fibroin as a possible substrate for HLE cultivation. One of the most important aspects in corneolimbal tissue engineering is to consider the reconstruction of the limbal stem cell niche to help form the natural limbus in situ. MSC with similar properties to bone marrow derived-MSC (BM-MSC) have recently been grown from the limbus of the human cornea. This thesis evaluated methods for culturing L-MSC and limbal keratocytes using various serum-free media. The phenotype of resulting cultures was examined using photography, flow cytometry for CD34 (keratocyte marker), CD45 (bone marrow-derived cell marker), CD73, CD90, CD105 (collectively MSC markers), CD141 (epithelial/vascular endothelial marker), and CD271 (neuronal marker), immunocytochemistry (alpha-smooth muscle actin; á-sma), differentiation assays (osteogenesis, adipogenesis and chrondrogenesis), and co-culture experiments with HLE cells. While all techniques supported to varying degrees establishment of keratocyte and L-MSC cultures, sustained growth and serial propagation was only achieved in serum-supplemented medium or the MesenCult-XF„¥ culture system (Stem Cell Technologies). Cultures established in MesenCult-XF„¥ grew faster than those grown in serum-supplemented medium and retained a more optimal MSC phenotype. L-MSC cultivated in MesenCult-XFR were also positive for CD141, rarely expressed £\-sma, and displayed multi-potency. L-MSC supported growth of HLE cells, with the largest epithelial islands being observed in the presence of L-MSC established in MesenCult-XF„¥ medium. All HLE cultures supported by L-MSC widely expressed the progenitor cell marker £GNp63, along with the corneal differentiation marker CK3/12. Our findings conclude that MesenCult-XFR is a superior culture system for L-MSC, but further studies are required to explore the significance of CD141 expression in these cells. Following on from the findings of the previous two parts, silk fibroin was tested as a novel dual-layer construct containing both an epithelium and underlying stroma for corneolimbal reconstruction. In this section, the growth and phenotype of HLE cells on non-porous versus porous fibroin membranes was compared. Furthermore, the growth of L-MSC in either serum-supplemented medium or the MesenCult-XFR culture system within fibroin fibrous mats was investigated. Lastly, the co-culture of HLE and L-MSC in serum-supplemented medium on and within fibroin dual-layer constructs was also examined. HLE on porous membranes displayed a flattened and squamous monolayer; in contrast, HLE on non-porous fibroin appeared cuboidal and stratified closer in appearance to a normal corneal epithelium. Both constructs maintained CK3/12 expression and distribution of £GNp63+ progenitor cells. Dual-layer fibroin scaffolds consisting of HLE cells and L-MSC maintained a similar phenotype as on the single layers alone. Overall, the present study proposed to create a three dimensional limbal tissue substitute of HLE cells and L-MSC together, ultimately for safe and beneficial transplantation back into the human eye. The results show that HLE and L-MSC can be cultivated separately and together whilst maintaining a clinically feasible phenotype containing a majority of progenitor cells. In addition, L-MSC were able to be cultivated routinely in the MesenCult-XF® culture system while maintaining a high purity for the MSC characteristic phenotype. However, as a serum-free culture medium was not found to sustain growth of both HLE and L-MSC, the combination scaffold was created in serum-supplemented medium, indicating that further refinement of this cultured limbal scaffold is required. This thesis has also demonstrated a potential novel marker for L-MSC, and has generated knowledge which may impact on the understanding of stromal-epithelial interactions. These results support the feasibility of a dual-layer tissue engineered corneolimbus constructed from silk fibroin, and warrant further studies into the potential benefits it offers to corneolimbal tissue regeneration. Further refinement of this technology should explore the potential benefits of using epithelial-stromal co-cultures with MesenCult-XF® derived L-MSC. Subsequent investigations into the effects of long-term culture on the phenotype and behaviour of the cells in the dual-layer scaffolds are also required. While this project demonstrated the feasibility in vitro for the production of a dual-layer tissue engineered corneolimbus, further studies are required to test the efficacy of the limbal scaffold in vivo. Future in vivo studies are essential to fully understand the integration and degradation of silk fibroin biomaterials in the cornea over time. Subsequent experiments should also investigate the use of both AM and silk fibroin with epithelial and stromal cell co-cultures in an animal model of LSCD. The outcomes of this project have provided a foundation for research into corneolimbal reconstruction using biomaterials and offer a stepping stone for future studies into corneolimbal tissue engineering.

Partial melt processing and electrical properties of Bi-Sr-Ca-Cu-o superconducting thick films on (100) MgO substrates

Superconducting thick films of Bi2Sr2CaCu2Oy (Bi-2212) on single-crystalline (100) MgO substrates have been prepared using a doctor-blade technique and a partial-melt process. It is found that the phase composition and the amount of Ag addition to the paste affect the structure and superconducting properties of the partially melted thick films. The optimum heat treatment schedule for obtaining high Jc has been determined for each paste. The heat treatment ensures attainment of high purity for the crystalline Bi-2212 phase and high orientation of Bi-2212 crystals, in which the c-axis is perpendicular to the substrate. The highest Tc, obtained by resistivity measurement, is 92.2 K. The best value for Jct (transport) of these thick films, measured at 77 K in self-field, is 8 × 10 3 Acm -2.

Manufacture of fine-grained Y2BaCuO5 powder by coprecipitation

Quantities of Y2BaCuO5 powder greater than 500g have been manufactured by a co-precipitation process. By suitable heat treatments, the particle size of these powders can be varied from 5µm to less than 500nm. Sub-micrometer size powders may, under some conditions, have a duller green colour which is attributed to <2% unreacted material. However, after re-grinding and re-firing of this powder, high-purity powders can be achieved without significant grain growth. Inductively coupled plasma (ICP) spectroscopy is used to measure the stoichiometry of the powders and X-ray diffraction is used to determine phase purity. In both cases, the bulk composition is consistent with Y2BaCuO5 and phase purity is considered better than 95%.