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Determining paleomagnetic field intensity (paleointensity: PI) for lavas with high reliability and low measurement uncertainty is still difficult to achieve. Some of the factors on which the PI used methods depends are the non-ideal physical and magnetic characteristics of lava sample, grain size, cooling rate effect and thermal stability. Xitle volcano (SW Mexico City) is a good example to illustrate and discuss this problem because several previous PI studies that were carried out on its evolved flow units, have commonly resulted in different mean values with large dispersions. Indeed, 211 published PI data obtained by use of Thellier and microwave experiments gave a mean of 64. 1 μT with a standard deviation of 11. 0 μT. After a careful evaluation, we found that only 134 of these data can be considered reliable, as they meet a set of selection criteria designed in this study. These evaluated data gave an average mean …

Our knowledge of the Earth's magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data, which also includes the Americas. The present study reports 41 new palaeointensity data covering the past 3600 years which, together with 38 previously published data of similar quality, are used to construct a palaeointensity secular variation curve for Central Mexico. These new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in Mexico, which is of interest because of the many Holocene monogenetic volcanoes within the Trans-Mexican Volcanic Belt, and of its archaeological heritage. The most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 BCE, from about 45 to 65 μT. Other relative intensity highs of ≈45–55 μT …

We present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities (PI) from 33 volcanoes, sampled at 66 sites and covering the last 46 ka. Of these, 29 were radiocarbon-dated, 3 by thermo-luminescence, and one is of historical age (AD 1793). Rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content, and of pseudo single domain size. Paleodirections were determined using stepwise demagnetization protocols, and PI by the IZZI or Thellier-Coe protocols, and strict selection criteria were applied to ensure the reliability of the data. Previously published data were evaluated to fulfill similar quality criteria as our data, resulting in: 65 directional data point; 18 paleointensity entries from lavas; 59 archeointensities are found to be acceptable. All accepted data come from a region within an 860 km radius around Mexico City …

Copper nanoparticles were fabricated and deposited on a glass substrate by spark discharge of copper electrode under different
atmospheric conditions for SERS application. An interesting dependence of the deposition process and the formation of different
particle structures on the deposition atmospheres were observed. Static air atmosphere ensured the deposition of the Cu
particles on the glass surface by avoiding the repulsion between charged Cu particles and the surface of the glass through the
formation of CuO, which acts as a seed mediated for nanorods formation. The average diameter of the as-deposited Cu rods
was measured by the TEM to be 39 nm. Thermal annealing of the film up to 200 °C resulted in a reduction in the diameter
of the nanorods as well as an increase in the rod density. A water solution of dye molecule (crystal violet) with a concentration
of 1 × 10–6 to 1 × 10–9 M was dropped on the prepared Cu substrate. Raman signals from dye molecule were detected
and their intensities changed according to deposition time, post-annealing temperature and dye concentration. A significant
increase in the Raman scattering signal of a dye molecule was observed in the film fabricated at 30 min of deposition time
and post-annealed temperature of 200 °C for 1 h. This substrate provides a maximum SERS intensity with a detection limit
of 1 × 10–8 M, with an enhancement factor of 3.9 × 103. The SERS performance of the substrates was correlated well with
the change in their surface morphologies.

Nanostructured Au33Pd67
alloy films were fabricated on glass using one-step air
plasma DC magnetron sputtering. The films exhibited highly sensitive detection of
dye molecules (RhB and CV) by the surface-enhanced Raman scattering (SERS).
The synthesized films also showed good catalytic properties for the reduction in
4-nitrophenol at pH ≈ 9.8. Such unique characteristic of the films was linked to the
evolution of nanostructure, which can be controlled simply by the sputtering time.
At the shorter sputtering time (10 and 20 s), the film was composed of isolated particles.
By increasing the sputtering time (30 and 40 s), agglomeration of such nanoparticles
resulted in the formation of the partially connected island nanostructures
(about 38 nm) which can be confirmed by TEM and electrical resistivity measurement.
The detection limit of 1 × 10–12 M RhB and 1 × 10–8 M CV with an enhancement
factor of 7 × 107 and 3.3 × 104, respectively, was achieved over the film synthesized
at the sputtering time of 30 s. The high sensitivity of this film can be ascribed
to the strong electromagnetic field at the junction spots formed between the two
adjacent islands. Moreover, this film has a slightly lower SERS, and better catalytic
properties, in contrast to Au (30 s) film. Finally, the film providing efficient SERS
enhancement is not the most active catalyst. Unlike the SERS, the catalytic activity
depends highly on the amount of AuPd deposited.

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