76 research outputs found
La colonització del delta occidental del Llobregat (Gavà i Castelldefels) al segle XVIII: un fracàs econòmic i social
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Ultrafine particles produced by plasma enhanced chemical vapor deposition -from SiH4, CH4, NH3 and B2H6 gas mixtures- for nanostructured ceramics applications
[eng] Ultrafine particles of silicon and related binary and ternary alloys of
the Si-B-C-N system produced in our research group from silane,
methane, diborane, ammonia and nitrogen precursor gases by
plasma enhanced chemical vapor deposition at low pressure and
room temperature are reviewed. The in-situ techniques of plasma
analysis and surface characterization (quadrupolar mass spectrometry,
optical emission spectroscopy and ellipsometry) providing evidence
of powder formation and the polymerization reactions based
on the SinH2n- negative radicals electrically confined in the plasma
sheath are described. The square wave modulation (SQWM) of the
rf power is discussed as an efficient method of controlling the powder
particle production with low particle-size dispersion. The properties
of the powder particles determined by different structural
characterization techniques providing their size and distribution,
crystalline order and morphology, chemical composition and chemical
bond vibrational characteristics, are analyzed and discussed[cat] Hom presenta una revisió sobre les partÃcules ultrafines de silici i els
seus aliatges binaris i ternaris del sistema Si-B-C-N, produïdes en el
nostre grup de recerca a partir dels gasos precursors silà , metà , diborà ,
amonÃac i nitrogen, per dipòsit quÃmic en fase vapor (CVD) reforçat
per plasma, a baixa pressió i temperatura ambient. És descrita
també la utilització de tècniques in situ d'anà lisi per plasma i
de caracterització de superfÃcies (espectroscòpia de masses quadripolar,
espectroscòpia òptica d’emissió i el·lipsometria), que donaren
l’evidència de formació de partÃcules de pols i de reaccions
de polimerització basades en radicals negatius SinH2n– confinats
elèctricament en l’embolcall del plasma. La modulació d’ona quadrada
(SQWM) de la font de rf és estudiada com un eficient mètode
de control de la producció de partÃcules amb una petita dispersió
de llurs dimensions. Finalment, hom analitza i discuteix les propietats
de les partÃcules produïdes, determinades per diferents tècniques
de caracterització, que permeteren obtenir llurs dimensions
i distribució, ordre cristal·là i morfologia, composició quÃmica i les
caracterÃstiques vibracionals dels enllaços quÃmic
Si3N4 single-crystal nanowires grown from silicon micro and nanoparticles near the threshold of passive oxidation
A simple and most promising oxide-assisted catalyst-free method is used to
prepare silicon nitride nanowires that give rise to high yield in a short time.
After a brief analysis of the state of the art, we reveal the crucial role
played by the oxygen partial pressure: when oxygen partial pressure is slightly
below the threshold of passive oxidation, a high yield inhibiting the formation
of any silica layer covering the nanowires occurs and thanks to the synthesis
temperature one can control nanowire dimensions
Kinetic study of the oxide-assisted catalyst-free synthesis of silicon nitride nanowires
The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles
with N2 in the 1200-1440 C temperature range is reported. The nitridation
conditions are such that the reaction with nitrogen is favoured by the presence
of silicon oxide in the particles and by the active oxidation of silicon
without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on
the amount of silicon particles used in the experiments and that, in general,
the reaction slows down for greater amounts. This trend is explained by
particle stacking, which restricts the exchange of gases between the furnace
atmosphere and the atmosphere around the inner particles. In a first stage,
local oxygen partial pressure increases around the inner particles and inhibits
nitridation locally. If the amount of reactant Si nanoparticles is small
enough, this extrinsic effect is avoided and the intrinsic nitridation kinetics
can be measured. Experiments show that intrinsic kinetics does not depend on
temperature
Deposition and characterization of PECVD phosphorus doped silicon oxynitride layers for integrated optics applications
Phosphorus-doped silicon oxynitride layers have been deposited by a Plasma Enhanced Chemical Vapor Deposition process from , 2% and 5% gaseous mixtures. The flow rate was varied to investigate the effect of the dopant to the layer properties. As deposited and annealed (600, 800, 900 and 1000 °C) layers were characterized by Fourier transform infrared spectroscopy, Rutherford backscattering spectroscopy and spectroscopic ellipsometry. In this way the refractive index could be determined as well as the amount of hydrogen that is responsible for enhanced absorption in the 3rd telecommunication window around 1550 nm. The N-H bonds concentration was found to decrease with the phosphorus concentration. Furthermore the bonded hydrogen in the entire P-doped layers have been eliminated after annealing at 1000 °C, while undoped SiON layers require annealing at 1150 °C
Els papers de la Baronia d'Eramprunyà : aproximació a un fons patrimonial dispers en molts arxius
Determinació experimental del moment dìpolar magnètic: un mètode està tic i dos de dinà mics
NotÃcia de la Farga de Banyoles durant el segle XVI
La nostra aportació d'ara vol oferir una mica d'informació sobre aquests temps més reculats i foscos, a través de la documentació que hem trobat a l'Arxiu Històric Provincial de Girona (AHPG), on hem localitzat dos contractes d'arrendament referits a l'època en què la farga de Banyoles produïa claus i treballava el ferro
UV exposure causes energy trade-offs leading to increased chytrid fungus susceptibility in green tree frog larvae
Levels of ultraviolet (UV) radiation have increased in many parts of the world due to the anthropogenic destruction of the ozone layer. UV radiation is a potent immunosuppressant and can increase the susceptibility of animal hosts to pathogens. UV radiation can directly alter immune function via immunosuppression and photoimmunotolerance; however, UV may also influence pathogen defences by affecting the distribution of energy resources among competing physiological processes. Both defence against UV damage and repair of incurred damage, as well as the maintenance of immune defences and responding to an immune challenge, are energetically expensive. These competing demands for finite energy resources could trade off against one another, resulting in sub-optimal performance in one or both processes. We examined the potential for a disease-related energy trade-off in green tree frog (Litoria caerulea) larvae. Larvae were reared under high- or low-UV conditions for 12 weeks during which time we measured growth rates, metabolic rate and susceptibility to the amphibian fungal pathogen, Batrachochytrium dendrobatidis (Bd). We found that larvae exposed to high levels of UV radiation had higher rates of energy expenditure than those exposed to low UV levels; however, UV exposure did not affect growth rates or developmental timings. Larvae exposed to high UV radiation also experienced greater Bd infection rates and carried a higher infection burden than those not exposed to elevated UV radiation. We propose that the increased energetic costs of responding to UV radiation were traded off against immune defences to protect larval growth rates. These findings have important implications for the aetiology of some Bd-associated amphibian declines, particularly in montane environments where Bd infections are most severe and where UV levels are highest
Prognostic significance of metallothionein expression in renal cell carcinoma
BACKGROUND: Metallothionein (MT) protein expression deficiency has been implicated in carcinogenesis while MT over expression in tumors is indicative of tumor resistance to anti-cancer treatment. The purpose of the study was to examine the expression of MT expression in human renal cell carcinoma (RCC) and to correlate MT positivity, the pattern and extent of MT expression with tumor histologic cell type and nuclear grade, pathologic stage and patients' survival. PATIENTS AND METHODS: The immunohistochemical expression of MT was determined in 43 formalin-fixed and paraffin-embedded RCC specimens, using a mouse monoclonal antibody that reacts with both human MT-I and MT-II. Correlation was sought between immunohistochemical (MT positivity, intensity and extension of staining) and clinico-pathological data (histological cell type, tumor nuclear grade, pathologic stage and patients' survival). RESULTS: Positive MT staining was present in 21 cases (49%), being mild/moderate and intense in 8 and 13 cases, respectively. The pattern was cytoplasmic in 7 cases and was both cytoplasmic and nuclear in 14 cases. MT expression in a percentage of up to 25% of tumor cells (negative MT staining included) was observed in 31 cases, in a percentage 25–50% of tumor cells in 7 cases, and in a percentage of 50–75% of tumor cells in 5 cases. There was no significant correlation of MT intensity of staining to histological type, stage and patients' survival, while it was inversely correlated to higher tumor nuclear grade. MT extent of staining did not correlate with histological type, nuclear grade, and pathologic stage while a statistically significant association was found with patients' survival. CONCLUSIONS: The inverse correlation between MT staining intensity and tumor nuclear grade in RCC suggests a role of MT in tumor differentiation process. Since extent of MT expression is inversely correlated with survival it may be possibly used as a clinical prognostic parameter
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