High pressure synthesis of FePt nanoparticles with controlled morphology and Fe content

Magnetic nanoparticles (MNPs) are intensively researched due to their high potential in biomedicine, catalysis, and high density information storage. FePt NPs could be an alternative for commonly used magnetite NPs and the synthesis of FePt NPs is an active area of research. The challenge is to increase the Fe content and saturation magnetisation of FePt NPs so that they can be used in many practical applications. Fine tuning of synthetic methods is required in order to achieve the enhanced magnetic properties of FePt nanoparticles and novel methods are being sought. Herein, use of an autoclave is shown to increase the Fe content, crystallinity and the subsequent magnetic properties of FePt pseudo cube nanoparticles compared to those synthesised under atmospheric pressure. Decreasing the amount of oleic acid is also shown to increase the iron content and can lead to elongated FePt nanoparticles under normal pressure. Further application of nanoparticles synthesised in organic media often requires functionalisation or exchange of stabiliser chemicals. Greater demand for control over such functionalisation requires more information about nanoparticle–stabiliser chemical interactions. Infra-red studies indicate mono and bidentate coordination with oleic acid, however shifts of spectra show that the strength of the bidentate interactions weaken with increasing oleic acid amount

The Linear-Size Evolution of Classical Double Radio Sources

Recent investigations of how the median size of extragalactic radio sources change with redshift have produced inconsistent results. Eales compared the radio and optical properties of a bright 3C and faint 6C sample and concluded that $D\propto(1+z)^{-1.1\pm0.5}$ ($\Omega_0 = 0$), with $D$ being the median size of the radio sources at a given epoch and z the redshift. Oort, Katgert, and Windhorst, on the other hand, from a comparison of the properties of a number of radio samples, found much stronger evolution, with $D\propto(1+z)^{-3.3 \pm0.5}$. In this paper we attempt to resolve the difference. We have repeated the analysis of Eales using the virtually complete redshift information that now exists for the 6C sample. Confining our analysis to FR2 sources, which we argue is the best-understood class of radio sources and the least likely to be affected by selection effects, we find $D\propto(1+z)^{-1.2\pm0.5}$ ($\Omega_0 = 0$) and $D\propto(1+z)^{-1.7\pm0.4}$ ($\Omega_0 = 1$). Our complete redshift information allows us to gain insight into our result by plotting a radio luminosity-size (P-D) diagram for the 6C sample. The most obvious difference between the 3C and 6C P-D diagrams is the clump of sources in the 6C diagram at $D\sim 100 kpc, P_{151}\sim 5x10^{27} WHz^{-1}sr^{-1}$. These clump sources have similar sizes to the emission-line regions found around high-redshift radio galaxies, suggesting that the presence of dense line-emitting gas around high-redshift radio galaxies is responsible for the size evolution. We show that this explanation can quantitatively explain the observed size evolution, as long as there is either little X-ray emitting gas around these objects or, if there is, it is distributed in a similar way to the emission-line gas: highly anisotropic and inhomogeneous.Comment: compressed and uuencoded postscript file. 33 pages including 5 figures (441951 bytes). Accepted for publication in September Ap

Cluster, Classify, Regress: A General Method For Learning Discountinous Functions

This paper presents a method for solving the supervised learning problem in which the output is highly nonlinear and discontinuous. It is proposed to solve this problem in three stages: (i) cluster the pairs of input-output data points, resulting in a label for each point; (ii) classify the data, where the corresponding label is the output; and finally (iii) perform one separate regression for each class, where the training data corresponds to the subset of the original input-output pairs which have that label according to the classifier. It has not yet been proposed to combine these 3 fundamental building blocks of machine learning in this simple and powerful fashion. This can be viewed as a form of deep learning, where any of the intermediate layers can itself be deep. The utility and robustness of the methodology is illustrated on some toy problems, including one example problem arising from simulation of plasma fusion in a tokamak.Comment: 12 files,6 figure

Multicore magnetic FePt nanoparticles: controlled formation and properties

Research on magnetic nanoparticles (NPs) has become one of the most active and exciting fields in materials science. The challenge is to produce magnetic NPs with high magnetic saturation without exceeding the super-paramagnetic limit so that they may be used as non-permanent magnets in biomedicine and catalysis. FePt offers enhanced saturation magnetisation properties compared to iron oxide, however synthetic methods require fine-tuning to achieve these superior properties. Multicore FePt NPs up to 44 nm in diameter and composed of Pt rich FePt nanocrystals within an iron rich FePt matrix not previously seen in the literature are presented here. The results indicate that coordination of Fe and Pt intermediates with oleic acid and oleylamine respectively hinders deposition of each respective metal in the growth of discrete and multicore NPs

A first sample of faint radio sources with virtually complete redshifts: I. Infrared images, the Hubble diagram, and the alignment effect

We have obtained redshifts and infrared images for a sample of faint B2/6C radio sources whose fluxes are about six times fainter than those of sources in the bright 3C sample. We now have unambiguous redshifts for 90% of the sources, making this the first faint radio sample with such complete redshift information. We find that the infrared Hubble diagrams (K versus z) of the 3C sample and the B2/6C sample are similar at a low redshift (z < 0.6), but by a redshift about 1 the 6C/B2 galaxies are on average about 0.6 mags fainter in the K-band than 3C galaxies at the same redshift. This suggests that the bright K-magnitudes of 3C galaxies at a redshift of about 1 are not the result of stellar evolution, but of a correlation between infrared and radio luminosity. We also find that the infrared stuctures of B2/6C galaxies at z=1 are less clearly aligned with their radio structures than 3C galaxies at this redshift, implying that the strength of the alignment effect depends on radio luminosity. Finally, above a redshift of 2 we find that the dispersion in the K-z relation of the B2/6C sample is about 2.7 times greater than that at low redshift, a result which is expected if at these redshifts we are beginning to penetrate into the epoch in which radio galaxies formed.Comment: 26 pages (TEX), 39 postscript figures (six of the larger figures can be obtained from ftp://ftp.astro.cf.ac.uk/pub/sae), 5 latex tables, to appear in MNRA

2020-2021 Supreme Court Preview: Notebook Cover Page

Our traditional notebook will not be available this year due to the virtual setting. However, we have compiled this virtual notebook to provide all participating in the Supreme Court Preview an opportunity to learn more about the upcoming docket and the issues facing the Court. We hope you enjoy the wealth of information available throughout this virtual notebook

Searching (the) FIRST radio arcs near ACO clusters

Gravitational lensing (GL) of distant radio sources by galaxy clusters should produce radio arc(let)s. We extracted radio sources from the FIRST survey near Abell cluster cores and found their radio position angles to be uniformly distributed with respect to the cluster centres. This result holds even when we restrict the sample to the richest or most centrally condensed clusters, and to sources with high S/N and large axial ratio. Our failure to detect GL with statistical methods may be due to poor cluster centre positions. We did not find convincing candidates for arcs either. Our result agrees with theoretical estimates predicting that surveys much deeper than FIRST are required to detect the effect. This is in apparent conflict with the detection of such an effect claimed by Bagchi & Kapahi (1995).Comment: 6 pages; 8 figures and 1 style file are included; to appear in Proc. "Observational Cosmology with the New Radio Surveys", eds. M. Bremer, N. Jackson & I. Perez-Fournon, Kluwer Acad. Pres

Unconventional field induced phases in a quantum magnet formed by free radical tetramers

We report experimental and theoretical studies on the magnetic and thermodynamic properties of NIT-2Py, a free radical-based organic magnet. From magnetization and specific heat measurements we establish the temperature versus magnetic field phase diagram which includes two Bose-Einstein condensates (BEC) and an infrequent half magnetization plateau. Calculations based on density functional theory demonstrates that magnetically this system can be mapped to a quasi-two-dimensional structure of weakly coupled tetramers. Density matrix renormalization group calculations show the unusual characteristics of the BECs where the spins forming the low-field condensate are different than those participating in the high-field one.Comment: 12 pages, 12 figure