117,477 research outputs found
Modified TiO2 particles differentially affect human skin fibroblasts exposed to UVA light.
No full textFree Radic Biol Med. 2010 Aug 1;49(3):408-15. Epub 2010 May 5.
Modified TiO(2) particles differentially affect human skin fibroblasts exposed to UVA light.
Tiano L, Armeni T, Venditti E, Barucca G, Mincarelli L, Damiani E.
Source
Dipartimento di Biochimica, Biologia e Genetica, , Università Politecnica delle Marche, I-60131 Ancona, Italy.
Abstract
Numerous sunscreens contain titanium dioxide (TiO(2)) because of its ability to reflect, scatter, and absorb UV radiation, thus preventing sunlight-related skin disorders. Since TiO(2) is well known to generate reactive oxygen species (ROS) under photoexcitation, it is chemically modified when used in sunscreens. In the present study, five modified TiO(2) particles, specifically developed and marketed for sunscreens, were tested using different in vitro models, including cultured human skin fibroblasts (HuDe), to investigate their possible photocatalytic effects following UVA exposure. The results obtained show that the type of modification and crystal form determine their ability to (a) induce photobleaching of the DPPH radical, (b) photodegrade deoxyribose, (c) reduce cell viability, (d) increase/decrease DNA damage, and (e) increase/decrease intracellular ROS. This research concludes that some modified TiO(2) particles still retain photocatalytic activity under the experimental conditions employed, especially those in which the anatase crystal form of TiO(2) is present. The penetration of TiO(2) nanosized particles into the viable epidermis of skin is still under debate; thus, the results presented here contribute to gaining further knowledge on the potential effects of TiO(2) particles at the cellular level, in the worst possible case that they do penetrate.
Copyright 2010 Elsevier Inc. All rights reserved.
PMID: 20450973 [PubMed - indexed for MEDLINE
Zn nanoparticle formation in FIB irradiated single crystal ZnO
No full textWe report on the formation of Zn nanoparticles induced by Ga+focused ion beam on single crystal ZnO. The irradiated materials have been studied as a function of the ion dose by means of atomic force microscopy, scanning electron microscopy, Raman spectroscopy and transmission electron microscopy, evidencing the presence of Zn nanoparticles with size of the order of 5â30 nm. The nanoparticles are found to be embedded in a shallow amorphous ZnO matrix few tens of nanometers thick. Results reveal that ion beam induced Zn clustering occurs producing crystalline particles with the same hexagonal lattice and orientation of the substrate, and could explain the alteration of optical and electrical properties found for FIB fabricated and processed ZnO based devices
On the thermal dynamic behaviour of the helium-cooled DEMO fusion reactor
No full textThe EU-DEMO conceptual design is being conducted among research institutions and universities from 26 countries of European Union, Switzerland and Ukraine. Its mission is to realise electricity from nuclear fusion reaction by 2050. As DEMO has been conceived to deliver net electricity to the grid, the choice of the Breeding Blanket (BB) coolant plays a pivotal role in the reactor design having a strong influence on plant operation, safety and maintenance. In particular, due to the pulsed nature of the heat source, the Primary Heat Transfer System (PHTS) becomes a very important actor of the Balance of Plant (BoP) together with the Power Conversion System (PCS). Moreover, aiming to mitigate the potential negative impact of plasma pulsing on BoP equipment, for the DEMO plant is also being investigated a "heat transfer chain" option which envisages an Intermediate Heat Transfer System (IHTS) equipped with an Energy Storage System (ESS) between PHTS and PCS. Within this framework, a preliminary study has been carried out to analyse the thermal dynamic behaviour of the IHTS system for the Helium-Cooled Pebble Bed (HCPB) BB concept during pulse/dwell transition which should be still considered as the normal operating mode of a fusion power plant. Starting from preliminary thermal-hydraulic calculations made in order to size the main BoP components, the global performances of DEMO BoP have been quantitatively assessed focusing the attention on the attitude of the whole IHTS to smooth the sudden power variations which come from the plasma. The paper describes criteria and rationale followed to develop a numerical model which manages to simulate simple transient scenarios of DEMO BoP. Results of numerical simulations are presented and critically discussed in order to point out the main issues that DEMO BoP has to overcome to achieve a viable electricity power output
Preliminary CAD implementation of EU-DEMO primary heat transfer systems for HCPB breeding blanket option
No full textCharacterization of magnetic IrMn/NiFe nanostructures
No full textIt is now largely demonstrated that magnetic systems structured on a nanometric length scale may exhibit peculiar magnetic properties, generally indicated as disordered magnetism effects, originating from the concomitant presence of topological disorder and competing magnetic interactions, as a consequence of the lack of structural periodicity. It is to be expected that this complex mix of magnetic effects play a relevant role also in the behavior of exchange coupled antiferromagnetic (AFM)/ferromagnetic (FM) systems, where the torque action exerted by the interfacial AFM spins on the FM ones brings about the insurgence of an unidirectional exchange anisotropy for the FM magnetization, and then the exchange bias (EB) effect.
In this work the EB properties of the IrMn/NiFe system in form of continuous film and of arrays of square dots with different size (1000, 500 and 300 nm), produced by e-beam lithography and dc-sputtering deposition, have been investigated. The stacking of the final samples was Si (substrate)/Cu[5 nm]/IrMn[10 nm]/NiFe[5 nm] (in square brackets the nominal thickness of each layer is reported). Structural investigations by TEM of the continuous IrMn/NiFe film indicate that the bulk of the AFM layer consists of nanograins with mean size ~ 10 nm, whereas the NiFe phase appears amorphous. In particular, the TEM analysis reveals the existence of a structurally disordered IrMn region (2-3 nm thick) at the interface between the FM phase and the bulk of the AFM layer. This finding, namely the evidence of structural disorder, strongly supports the spin-glass like magnetic character of the interfacial IrMn region, deduced by SQUID measurements on the continuous film, Figure 3. The existence of a low temperature frozen collective regime of the interfacial AFM spins and its break up above a critical temperature, that we have schematically settled at T = 100 K, determine the thermal evolution of the EB properties. In fact, below 100 K, the exchange coupling between IrMn and NiFe is ruled by magnetically correlated, frozen AFM spins, subjected to a strong effective local anisotropy, which results in high Hex (exchange field) and HC (coercivity) values. Above 100 K, the AFM/FM coupling is governed by a fraction of interfacial AFM spins, magnetically polarized by the AFM nanograins. Hence, Hex and HC decrease more and more with rising T, reflecting the progressive thermal instability of the AFM nanograins, assumed as essentially non-interacting. The spatial confinement, namely the passage from the continuous film to the dot structure, affects the exchange coupling mechanism when the dot size enters the sub-micron regime [1].
This research work has been carried out in the framework of the project FIRB 2010 “Tailoring the magnetic anisotropy of nanostructures for enhancing the magnetic stability of magnetoresistive devices”-NANOREST
References
1. F. Spizzo, E. Bonfiglioli, M. Tamisari, A. Gerardino, G. Barucca, A. Notargiacomo , F. Chinni, L. Del Bianco, “Magnetic exchange coupling in IrMn/NiFe nanostructures: from the continuous film to dot arrays”, Physical Review B, 91, pp.064410 1-9, 2015
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Enhancing the quality of metal powder feedstock for laser PBF through cross-contamination removal
No full textThe presence of impurities in metal powder feedstock for laser powder bed fusion (L-PBF) can strongly affect the mechanical properties of the sintered part. As a matter of fact, the contamination particles trapped in the uniform metal matrix of the raw material, act as a discontinuity and, therefore, as a site for fatigue crack nucleation and growth, leading to a dramatic reduction of the expected fatigue life. While cross-contamination detection is a key parameter to establish the quality level of the metal powder feedstock, its removal is crucial to ensure that the sintered parts will fulfil the service requirements. In this study, metal powder feedstock for laser PBF were intentionally contaminated, submitted to a removal process based on their magnetic properties, through suitably developed equipment. The contaminated and processed powders were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques
Laser Powder Bed Fusion: tailoring the microstructure of alloys for biomedical applications
No full textAdditive manufacturing (AM) is particularly attractive for biomedical applications, where complex geometries and a high degree of individualization are required. Laser powder bed fusion (LPBF) is an AM technology exploiting the action of a solid-state laser to locally melt a metal powder according to a computer aided design (CAD) model. In the present study, the EOS Cobalt Chrome SP2 (Co-Cr-Mo-W) and Ti64 (Ti6Al4V) powders were sintered by the system equipped with a Yb fiber laser. During LPBF, the Co-Cr-Mo-W metal powder undergoes total melting followed by rapid cooling, giving rise to athermal martensitic phase transformation from the high-temperature γ (fcc) phase to the low-temperature ε (hcp) phase. This produces an intricate network of thin ε-lamellae inside the γ phase matrix. After the firing cycle this structure is maintained, and a massive presence of coarse precipitates is also observed. Owing to the rapid cooling taking place during LPBF, in Ti6Al4V sintered samples only the acicular martensitic α' phase is present. The firing cycle induces the β phase formation at the α plate boundaries and this microstructure leads to reduced values of strength, with respect to those of the as-sintered samples. The highlighted behaviors show that by tuning the post-production heat treatments it is possible to tailor the microstructure and the mechanical properties
Glassy magnetic behavior and correlation length in nanogranular Fe-oxide and Au/Fe-oxide samples
No full textIn nanoscale magnetic systems, the possible coexistence of structural disorder and competing magnetic interactionsmay determine the appearance of a glassy magnetic behavior, implying the onset of a low-temperature disordered collective state of frozen magnetic moments. This phenomenology is the object of an intense research activity, stimulated by a fundamental scientific interest and by the need to clarify how disordered magnetism effects may affect the performance of magnetic devices (e.g., sensors and data storage media). We report the results of a magnetic study that aims to broaden the basic knowledge of glassy magnetic systems and concerns the comparison between two samples, prepared by a polyol method. The first can be described as a nanogranular spinel Fe-oxide phase composed of ultrafine nanocrystallites (size of the order of 1 nm); in the second, the Fe-oxide phase incorporated non-magnetic Au nanoparticles (10-20 nm in size). In both samples, the Fe-oxide phase exhibits a glassy magnetic behavior and the nanocrystallite moments undergo a very similar freezing process. However, in the frozen regime, the Au/Fe-oxide composite sample is magnetically softer. This effect is explained by considering that the Au nanoparticles constitute physical constraints that limit the length of magnetic correlation between the frozen Fe-oxide moments
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
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