Unconventional magnetism in all-carbon nanofoam

We report production of nanostructured carbon foam by a high-repetition-rate, high-power laser ablation of glassy carbon in Ar atmosphere. A combination of characterization techniques revealed that the system contains both sp2 and sp3 bonded carbon atoms. The material is a novel form of carbon in which graphite-like sheets fill space at very low density due to strong hyperbolic curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like behaviour up to 90 K, with a narrow hysteresis curve and a high saturation magnetization. Such magnetic properties are very unusual for a carbon allotrope. Detailed analysis excludes impurities as the origin of the magnetic signal. We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized due to the steric protection offered by the convoluted sheets.Comment: 14 pages, including 2 tables and 7 figs. Submitted to Phys Rev B 10 September 200

Study and Analysis of Supervised Vs Unsupervised Classification for Remote Sensing Images

Image classification is a procedure to automatically categorize all pixels in an image [9]. Image classification has emerged as a significant tool for investigating digital images [1].Image classification can be defined as the process of reducing an image to information classes. The categorization of image pixels is based on their digital numbers/grey values in one or more spectral bands. The main objective of image classification is to automatically categorize all pixels in a digital image into information classes or themes. The image classification tool for examination of the digital images. Classification is generally divided into two types as supervised classification and unsupervised classification [8]. This paper gives comparative study of Supervised & Unsupervised image classification

Situs inversus abdominalis and duodenal atresia. A case report and review of the literature

Fewer than 20 patients born with situs inversus and duodenal atresia have been reported in the literature. We present a patient with this condition. A newborn baby presented shortly after birth with persistent bilious vomiting. An abdominal radiograph showed a right-sided stomach bubble and a second bubble on the left - typical of duodenal atresia but with mirror image configuration. Laparotomy confirmed the diagnosis of situs inversus abdominalis, which was also demonstrated by contrast studies and ultrasound. Duodenoduodenostomy was performed and the patient discharged on day 8 postoperatively. Situs inversus is associated with other congenital malformations including splenic malformations, left-sided liver and cardiac abnormalities; it is rarely associated with duodenal atresia. Duodenal obstruction in the presence of situs inversus has been described, including obstruction due to a web, stenosis, pre-duodenal portal vein and complete atresia. The patient presented in this paper had a duodenal web in the second part of the duodenum. Before undertaking surgery it is important to establish the presence of associated gastrointestinal and cardiac abnormalities

Investigation of the structure of GexAsySe1−x−y glasses by x-ray photoelectron spectroscopy

We have measured and analyzed x-ray photoelectron spectra of a series of GexAsySe1−x−yglasses. The valence band spectra show that a number of Se-rich structures exist in the samples. After decomposing Ge, As, and Se3dspectra into several doublets and assigning them to the different local bond structures, it was found that, while GeSe₄/₂ tetrahedral, AsSe₃/₂ pyramidal, and Se trimers decrease in their integrated areas, most defect bonds increase with increasing mean coordination number. Moreover, while the appearance of Se trimers is reasonable in Se-rich samples, they never vanish, even in Se-poor samples. A possible mechanism to form Se trimers in Se-poor samples is discussed.This research was supported by Australian Research Council through its Centres of Excellence and Federation Fellow Programs

Sub-picosecond exchange-relaxation in the compensated ferrimagnet Mn2_2Rux_xGa

We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pulses are studied to reveal the roles played by the spin and intersublattice exchange. We find a two-step demagnetization process, similar to the well-established case of Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization rates. The behaviour is analysed using a four-temperature model, assigning different temperatures to the two manganese spin baths. Even in this strongly exchange-coupled system, the two spin reservoirs have considerably different behaviour. The half-metallic nature and strong exchange coupling of Mn$_2$Ru$_x$Ga lead to spin angular momentum conservation at much shorter time scales than found for Gd(FeCo)$_3$ which suggests that low-power, sub-picosecond switching of the net moment of Mn$_2$Ru$_x$Ga is possible.Comment: 5 pages, 3 figures, J. Phys.: Condens. Matter (2021

Subpicosecond laser ablation of dental enamel

Laser ablation of dental enamel with subpicosecond laser pulses has been studied over the intensity range of (0.1–1.4)×10¹⁴ W/cm² using 95 and 150 fs pulses at a pulse repetition rate of 1 kHz. The experimentally determined ablation threshold of 2.2±0.1 J/cm² was in good agreement with theoretical predictions based on an electrostaticablation model. The ablation rate increased linearly with the laser fluence for up to 15 times the ablation threshold. The absence of collateral damage was observed using optical and scanning electron microscopy. Pulpal temperature measurements showed an increase of about 10 °C during the 200 s course of ablation. However, air cooling at a rate of 5 l/min resulted in the intrapulpal temperature being maintained below the pulpal damage threshhold of 5.5 °C. The material removal rates for subpicosecond precision laser ablation of dental enamel are compared with other techniques

Spin relaxation of conduction electrons in bulk III-V semiconductors

Spin relaxation time of conduction electrons through the Elliot-Yafet, D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is calculated theoretically for bulk GaAs, GaSb, InAs and InSb of both $n$- and $p$-type. Relative importance of each spin relaxation mechanism is compared and the diagrams showing the dominant mechanism are constructed as a function of temperature and impurity concentrations. Our approach is based upon theoretical calculation of the momentum relaxation rate and allows understanding of the interplay between various factors affecting the spin relaxation over a broad range of temperature and impurity concentration.Comment: an error in earlier version correcte