We investigate the use of Terahertz (THz) Time Domain Spectroscopy (TDS) as a tool for the measurement of the index dispersion of multi-walled carbon nanotubes (MWCNT) in polypropylene (PP) based ...composites. Samples containing 0.5% by volume concentration of non-functionalized and functionalized carbon nanotubes are prepared by melt compounding technology. Results indicate that the THz response of the investigated nanocomposites is strongly dependent on the kind of nanotube functionalization, which in turn impacts on the level of dispersion inside the polymer matrix. We show that specific dielectric parameters such as the refractive index and the absorption coefficient measured by THz spectroscopy can be both correlated to the index of dispersion as estimated using conventional optical microscopy.
We report on fs laser structuring and graphitization of diamond and experimental characterization of its THz response. A full characterization of graphitized, conductive layer generated by laser ...irradiation is carried out by performing scanning-electron microscopy, Raman spectroscopy and electrical measurements. The transmittance of the laser textured diamond samples, both with the graphitic overlayer and after selective oxidizing etching, is analyzed in the (0.25 ÷ 6.0) THz spectral range. A significant selective absorption of the graphitized overlayer towards polarized THz radiation is demonstrated, which is associated to the formation of graphitic laser induced periodic surface structures. This anisotropy allows conceiving compact passive metasurfaces based on conductive/dielectric patterns on the diamond plate surface for the development of robust, lightweight and broadband THz optical components.
•The effect of the LIPSS process on the surface chemical properties and consequently on SEY is investigated.•Femtosecond Laser-Induced Periodic Surface Structures (LIPSS) are used to reduce SEY in ...copper.•Copper treated with LIPSS shows a low surface debris density and is therefore less critical for ultra-high vacuum applications in particle accelerators.
The electron-cloud phenomenon is one cause of beam instabilities in high intensity positive particle accelerators. Among the proposed techniques to mitigate or control this detrimental effect, micro-/nano-geometrical modifications of vacuum chamber surfaces are promising to reduce the number of emitted secondary electrons. Femtosecond laser surface structuring readily allows the fabrication of Laser Induced Periodic Surface Structures (LIPSS) and is utilized in several fields, but has not yet been tested for secondary electron emission reduction. In this study, such treatment is carried out on copper samples using linearly and circularly polarized femtosecond laser pulses. The influence of the formed surface textures on the secondary electron yield (SEY) is studied. We investigate the morphological properties as well as the chemical composition by means of SEM, AFM, Raman and XPS analyses. Surface modification with linearly polarized light is more effective than using circularly polarized light, leading to a significant SEY reduction. Even though the SEY maximum is only reduced to a value of ~1.7 compared to standard laser-induced surface roughening approaches, the femtosecond-LIPSS process enables to limit material ablation as well as the production of undesired dust, and drastically reduces the number of redeposited nanoparticles at the surface, which are detrimental for applications in particle accelerators. Moreover, conditioning tests reveal that LIPSS processed Cu can reach SEY values below unity at electron irradiation doses above 10−3 C/mm2.
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Pendellösung effect in photonic crystals Savo, S; Di Gennaro, E; Miletto, C ...
Optics express,
2008-Jun-09, 2008-06-09, 20080609, Letnik:
16, Številka:
12
Journal Article
Recenzirano
Odprti dostop
At the exit surface of a photonic crystal, the intensity of the diffracted wave can be periodically modulated, showing a maximum in the "positive" (forward diffracted) or in the "negative" ...(diffracted) direction, depending on the slab thickness. This thickness dependence is a direct result of the so-called Pendell osung phenomenon, consisting of the periodic exchange inside the crystal of the energy between direct and diffracted beams. We report the experimental observation of this effect in the microwave region at about 14GHz by irradiating 2D photonic crystal slabs of different thickness and detecting the intensity distribution of the electromagnetic field at the exit surface and inside the crystal itself.
The term massive burns is used to indicate burns that cannot be covered by the patient's own skin by a single harvesting. Massiveburns therefore are a subclassification of major burns (i.e. burns > ...25% TBSA) and are typically managed in a tertiary burns centre.They have been variously defined as burns extending over more than 30%,1,2 35%,3 40%4 and 50%5,6 of the total body surface area(TBSA). As 20% of a patient's body surface area (such as the face, hand, feet and perineum) is not suited to provide donor sites, amaximum of 40% TBSA can be covered with the patient's own skin, and therefore it makes most sense to define a massive burn as aburn over 40% TBSA. Massive burns provide a number of treatment challenges. The large amounts of fluids required to resuscitate these patients puts them at risk for oedema formation in the tissues, burn bound progression and compartment syndromes. Although early total excision has been suggested as the standard-of-care in highincome environments, this is associated with a massive onslaught onto the patient's physiological reserves requiring resources that are scarce in middle- and low-income countries (LMICs). Many units under these circumstances practise a staged-excision approach, but this may be associated with a higher sepsis rate. When the patient survives the initial resuscitative stage, the question arises how to cover the burned areas. Although skin is often meshed to enlarge it, it should be appreciated that harvested skin undergoes primary contraction, decreasing its area by 10-20% in a split-thickness skin graft (SSG) and 40% in a full-thickness skin graft; the result is that a 1:3 mesh of an SSG only covers 1.8 x the original donor area. Larger expansion rates (1:4 and more) leave large interstitial areas that need to be covered by a temporary skin substitute, such as cadaver skin or a dermal substitute, to prevent them drying out, while the interstitial areas re-epithelialise. Principles for excision of massive burn wounds, such as early total excision versus staged excision, and the order of areas excised in each option are well covered elsewhere8 and will not be repeated here.
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