Biosilicification (chalcedony) in human cerebral cortex, hippocampus and cerebellum from aged patients

Aluminum and silicon have been observed to be present in the human degenerated brain and normal elderly brains by using a combination of scanning electron microscopy and X-ray spectrometry (EDS-SEM). Al and Si of electric organs were also reported - in electrocytes and cholinergic nerves - from living electric fish (family Rajidae). A biogenically produced crystalline mineral phase (i.e., chalcedony) has also been observed in electric organs by using a mineralogical microscope. Based on this evidence we decided to explore the presence of chalcedony (SiO(2)) in the human central nervous system (CNS). Sections from aged patients (mean, 81 years) were collected after autopsy and observed using a Leica DMLP mineralogical microscope. Chalcedony was detected in cerebral cortex and cerebellum. In plane-polarized light, chalcedony is rounded in shape, 12-20mum in size, translucent, with a low refraction index. The crossed-polarizer image shows first order birefringence color (grey-white) and radial extinction. Chalcedony was also detected in the hippocampus in large amounts and sizes (50-60mum). Chalcedony is a microcrystalline fibrous form of silica. It consists of nanoscale intergrowths of quartz and the optically length-slow fibrous silica polymorph moganite. Chalcedony precipitation occurs at a specific pH (7-8) and oxidation potential (Eh; 0.0 to -0.2) in geological environments. This observation supports the important role played by pH and Eh conditions in silica precipitation in elderly brains, as has also been reported in peripheral cholinergic nerves in electric organ from living electric fish. Carbonic anhydrases (CAs) (silicase) are involved in physiological pH regulation and may also be participating in the polymerization-depolymerization of chalcedony in the human brain. This is the first time a biogenically produced crystalline mineral phase (i.e., chalcedony) has been observed in the human CNS from aged patients.     

TDPAC studies on the sorption of Hf(IV) onto a silica surface

¹⁸¹Hf-PAC investigations were undertaken as a contribution to the understanding of the aquatic chemistry of the tetravalent elements. In solution, the growth of polymeric species with increasing pH was observed by PAC. For the sorption of Hf on silica surfaces we found a strong dependence of the PAC results on the pH value. The corresponding sites were assigned to surface complexation and surface precipitation, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quantum oscillations in p-type inversion layers of (111) and (100) silicon field effect transistors

For the first time Shubnikov-de Haas oscillations have been observed in p-type inversion layers of (111) and (100) silicon field effect transistors. For both orientations a single electric subband was found. The effective mass of the surface carriers was determined from the temperature dependence of the oscillations, for (111) surfaces as a function of the surface electric field. At low gate voltages spin splitting of the Landau levels was resolved.     

Enhanced light trapping for the silver nanoparticles embedded in the silica layer atop the silicon substrate

The optical properties of the structures with silver nanoparticles embedded in the silica layer atop the silicon substrate are simulated by the finite-difference time-domain method. The effects of nanoparticle size, period, silica layer thickness, and the angle of incidence of the illuminated light on optical transmissions are studied. It is found that there is the red-shift for the maximum of the total light transmitting into the silicon substrate as the silica layer thickness increases. The electric field intensity distributions and the average power densities for the structure with largest optical transmission is studied, and the strong electric field intensities are found in the silica regions surrounding to the silver nanoparticles, which can help the light energy going into the silicon substrate. By controlling the structure parameters, the optical transmissions of the structures with the silica layer can have higher optical transmissions than the cases without the silica layer. The silica layer plays the role as the graded refractive index layer between the air and the silicon substrate, and the light power from the incident wave can transmit into the silicon substrate with less optical reflections for choosing a suitable silica layer thickness. A guideline to design the structures with high optical transmissions for the solar spectra is given. This study cannot only be useful for the solar cells applications, but also other antireflection applications.     

Development of oxidative sample preparation for the analysis of forensic soil samples with near‐IR Raman spectroscopy

Forensic soil samples have been traditionally analysed via examinations of colour, texture and mineral content by physical or chemical methods. These methods leave any organic or water‐soluble fractions unexamined. A range of analytical techniques have been applied in this area and these procedures have been reviewed recently. This study uses Raman Spectroscopy to assess both the mineralogical and the water‐soluble organic fractions in soil samples. Soil samples were collected from both urban and rural environments comprising the city of Bradford, England, and an arable farming district in Lincolnshire. This study demonstrates how, with the use of oxidative preparation methods, Raman spectroscopy can be used to successfully discriminate between soil types using mineralogy as well as the organic and water‐soluble fractions of soils. Copyright © 2011 John Wiley & Sons, Ltd.     

Auditory thresholds in a sound-producing electric fish (Pollimyrus): behavioral measurements of sensitivity to tones and click trains

In this report we present the first behavioral measurements of auditory sensitivity for Pollimyrus adspersus. Pollimyrus is an electric fish (Mormyridae) that uses both electric and acoustic signals for communication. Tone detection was assessed from the fish's electric organ discharge rate. Suprathreshold tones usually evoked an accelerated rate in naive animals. This response (rate modulation > or =25%) was maintained in a classical conditioning paradigm by presenting a weak electric current near the offset of 3.5-s tone bursts. An adaptive staircase procedure was used to find detection thresholds at frequencies between 100 and 1700 Hz. The mean audiogram from six individuals revealed high sensitivity in the 200-900 Hz range, with the best thresholds near 500 Hz (66.5+/-4.2 SE dB re: 1 microPa). Sensitivity declined slowly (about 20 dB/octave) above and below this sensitivity maximum. Sensitivity fell off rapidly above 1 kHz (about 60 dB/octave) and no responses were observed at 5 kHz. This behavioral sensitivity matched closely the spectral content of the sounds that this species produced during courtship. Experiments with click trains showed that sensitivity (about 83-dB peak) was independent of inter-click-interval, within the 10-100 ms range.     

A new analytical model of high voltage silicon on insulator （SOI） thin film devices

A new analytical model of high voltage silicon on insulator (SOI) thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate, with a threshold energy taken into account for electron multiplying. Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness, the proposed silicon critical electric field increases sharply with silicon film thickness decreasing especially in the case of thin films, and can come to 141V/μm at a film thickness of 0.1μm which is much larger than the normal value of about 30V/μm. From the proposed formula of silicon critical electric field, the expressions of dielectric layer electric field and vertical breakdown voltage (V_B,V) are obtained. Based on the model, an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage for SOI devices because of its high silicon critical electric field, and with a dielectric layer thickness of 2μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5μm, respectively. In addition, a relation between dielectric layer thickness and silicon film thickness is obtained, indicating a minimum vertical breakdown voltage that should be avoided when an SOI device is designed. 2D simulated results and some experimental results are in good agreement with analytical results.     

Instability of the distribution of atomic steps on Si(111) upon submonolayer gold adsorption at high temperatures

The gold adsorption effect on the distribution of monatomic steps on the (111) silicon surface is studied in situ by ultrahigh vacuum reflection electron microscopy at temperatures of 850–1260°C. A new effect of the instability of silicon surface morphology has been detected. This effect leads to the redistribution of regular steps (RSs) to step bunches (STs) and vice versa on a surface covered with a gold submonolayer. For the crystal heated by directly passing an electric current, the behavior of the RS ? SB morphological transitions on the silicon surface is investigated as a function of the gold coverage and the direction of the heating current. Thus, isothermal annealing at 900°C is accompanied by the following transitions on the silicon surface with predeposited 0.75 monolayer gold coverage: RS (0.72) ? SB (0.42) ? RS (0.24) ? SB (0.07) RS ? (0). The numbers given in parentheses are estimated values of the critical gold coverage measured in the monolayers at which the morphological transitions are observed. A change in the direction of the electric current used to heat the crystal leads to the reversible changes RS ? SB and SB ? RS at the same values of the critical gold coverage.     

Atomic steps on the Si(111) surface during submonolayer gold adsorption

The effect of adsorption of submonolayer gold coatings on the Si(111) surface morphology in the temperature range 850–1260°C has been investigated by means in situ ultrahigh-vacuum reflection electron microscopy and ex situ atomic force microscopy. Reversible transformations of the silicon surface: from regular monoatomic steps to step bunches, depending on the gold coverage and direction of the electric current resistively heating the crystal, have been revealed. Stability of the regular distribution of monoatomic steps upon heating of the crystal by an alternating current is shown. The effect of an electric field applied to the sample on the diffusion of silicon and gold adatoms has been analyzed taking into account the effective adatom charge.     

Moganite in the Chalcedony Varieties of Continental Cherts (Miocene,Madrid Basin,Spain)

Varieties of chalcedony (calcedonite, quartzine, and lutecite) and other optical micro- and cryptocrystalline textures of quartz and opal from Miocene silcretes of the Madrid Basin were studied using a Thermo Fisher DXR Raman microscope. The microscope has a point-and-shoot Raman capability of 1 µm spatial resolution and was coupled with a standard optical microscope. Our results show that all the varieties of chalcedony can have a composite Raman spectrum of both quartz and moganite. The spectra are independent of the chalcedony origin by ageing, direct replacement, and cementation processes. Moganite was absent only in some calcedonite cements. The presence of moganite is independent of the surface sedimentary setting of the host rocks in which the silcretes are formed.     

Calculating specific absorbed fractions with standard Korean male adults

Based on data representing standard Korean male adults, a mathematical anthropomorphic phantom was developed to calculate the specific absorbed fraction for several organs. The results were then compared against values calculated with other phantoms (OTOKO of Japan, MIRD of the U.S. and GOLEM of Germany). We compared the specific absorbed fractions of six organs (the adrenals, kidneys, liver, lungs, pancreas and spleen) for two cases: when the source and target organs are the same, and when they are different. When both the source and target organs are the same the organ with the highest specific absorbed fraction regardless of energy level was found to be the adrenals in all phantoms. In comparing phantoms, the phantom developed on the basis of standard Koreans produced the highest specific absorbed fraction. Also, as a result of conducting an assessment by separating source organs from target organs, the phantom developed on the basis of standard Koreans displayed relatively high specific absorbed fractions although there were slight differences per organ.     

Evidences for Auger recombination in electron-hole droplets (silicon)

The microwave absorption technique was used to measure the transient free carrier density following an electric injection in silicon at 4°K. The experiment agrees with the idea that droplets are obtained by free carrier condensation directly, without a preliminary formation of free excitons.¹ An Auger recombination process in droplets explains the observed kinetics; parameters are measured.     

Muon spin resonance and repolarization in amorphous silicon monoxide (a-SiO)

Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu^* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature.     

硅基二氧化硅厚膜材料的快速生长

采用火焰水解法在Si片上快速淀积SiO₂厚膜材料,材料膜厚达到40μm以上,生长速率达8μm/min.然后将该材料分别在真空中/空气气氛中高温致密化处理,获得了各种形态的二氧化硅厚膜材料,包括平整度好、光滑透明的玻璃态SiO₂厚膜材料.并利用XRD、电子显微镜等仪器对SiO₂膜的表面和膜厚进行了测试分析.     

Paramagnetic effects of iron(III) species on nuclear magnetic relaxation of fluid protons in porous media

The (1)H NMR spin-lattice relaxation time, T(1), of saturated sands depended on the chemistry of the pore fluid, pore size distribution, and relaxivity of the surface. In the absence of paramagnetic impurities, surface relaxivities of quartz sand and silica gel samples of known porosity and surface area at any pH were lower than any previously reported values. Relaxation rate of the bulk pore fluid increased linearly with increasing Fe(III) concentration and varied with speciation of the ion. With only 0.01% of the silica surface sites occupied by sorbed Fe(III) ions, surface relaxivity increased by an order of magnitude. In addition, low concentrations of Fe(III)-bearing solid phases present as surface coatings or as separate mineral grains increased surface relaxation as much as two orders of magnitude. We believe that observations of relatively constant surface relaxivity in rocks by previous researchers were the result of consistently high surface concentrations of paramagnetic materials.     

Band gap tuning of defective silicon carbide nanotubes under external electric field: Density functional theory

We have theoretically investigated the effect of applying longitudinal and transverse electric field on silicon carbide nanotubes with different orientations of Stone Wales defects. We found that each type of Stone Wales defects maintained different formation energy. We have also successfully proved that the orientation of Stone Wales defects in silicon carbide nanotubes response quite differently upon applying external electric field, whereas, two important and interesting phenomena were observed. First, the semiconductor-metal phase transition occurred in silicon carbide nanotubes as well as the three types of Stone Wales defects. However, clear band gap variations were observed in all silicon carbide nanotubes under study. Second, the band gap variations in pristine silicon carbide nanotubes and nanotubes with different orientations of Stone Wales defects have the same trend, even though all silicon carbide nanotubes have clear band gap values under different strengths of the applied external electric field. However, band gap tuning under longitudinal electric field is less significant compared to band gap tuning under the transverse electric field.     

Kinetics of silicon precipitation in a directionally crystallized binary aluminum-silicon alloy

The precipitation of silicon atoms in aluminum in an Al-Si alloy has been studied using differential scanning calorimetry. The alloys containing 8, 13, and 15 wt % silicon were obtained by directional solidification of a ribbon pulled from the melt through a shaper by the Stepanov method at a rate of about 10³ μm/s. From the characteristics of the exothermic effects observed in the temperature range 430–650 K, it has been found that the precipitation process leading to the formation of the Guinier-Preston zones occurs with the effective activation energy of 75 kJ/mol, and its intensity decreases with increasing silicon content in the alloy from 8 wt % to the eutectic content. The effect correlates with a decrease in the volume fraction of dendrites of the primary α-Al crystals in the alloy. It can be assumed that the precipitation occurs in the dendrite primary crystals of the solid solution. Based on this assumption, it has been concluded that, during directional solidification of an aluminum-silicon alloy at a rate of 10³ μm/s, the metastable solid solution of silicon in aluminum, in which silicon atoms of the metallic lattice are transformed into clusters with covalent bonding forces, is formed during the dendrite growth of the primary crystals.     

Huge (but finite) time scales in slow relaxations: beyond simple aging

Experiments performed in the last years demonstrated slow relaxations and aging in the conductance of a large variety of materials. Here, we present experimental and theoretical results for conductance relaxation and aging for the case-study example of porous silicon. The relaxations are experimentally observed even at room temperature over time scales of hours, and when a strong electric field is applied for a time tw, the ensuing relaxation depends on tw. We derive a theoretical curve and show that all experimental data collapse onto it with a single time scale as a fitting parameter. This time scale is found to be of the order of thousands of seconds at room temperature. The generic theory suggested is not fine-tuned to porous silicon, and thus we believe the results should be universal, and the presented method should be applicable for many other systems manifesting memory and other glassy effects.     

Atomic structure of a (2 x 1) reconstructed NiSi2/Si(001) interface

Nickel disilicide/silicon (001) interfaces were investigated by aberration corrected scanning transmission electron microscopy (STEM). The atomic structure was derived directly from the high spatial resolution high angle annular dark field STEM images without recourse to image simulation. It comprises fivefold coordinated silicon and sevenfold coordinated nickel sites at the interface and shows a 2 x 1 reconstruction. The proposed structure has not been experimentally observed before but has been recently predicted theoretically by others to be energetically favored.