Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles

In the present work, we investigate the magnetic properties of ferrimagnetic and noninteracting maghemite (g-Fe2O3) hollow nanoparticles obtained by the Kirkendall effect. From the experimental characterization of their magnetic behavior, we find that polycrystalline hollow maghemite nanoparticles are characterized by low superparamagnetic-to-ferromagnetic transition temperatures, small magnetic moments, significant coercivities and irreversibility fields, and no magnetic saturation on external magnetic fields up to 5 T. These results are interpreted in terms of the microstructural parameters characterizing the maghemite shells by means of an atomistic Monte Carlo simulation of an individual spherical shell model. The model comprises strongly interacting crystallographic domains arranged in a spherical shell with random orientations and anisotropy axis. The Monte Carlo simulation allows discernment between the influence of the structure polycrystalline and its hollow geometry, while revealing the magnetic domain arrangement in the different temperature regimes.Comment: 26 pages, 8 figures. In press in Phys. Rev.

Molecular Imaging in TB: From the Bench to the Clinic

Despite all efforts, tuberculosis (TB) still constitutes a serious global health threat with 9.4 million new cases and 1.7 million deaths worldwide in 2009 (World Health Organisation,2010). Furthermore, an estimated one third of the worlds’ population is infected with the bacterium responsible, Mycobacterium tuberculosis. The main handicaps in fighting TB include a vaccine which works poorly in the most affected populations, and an arduous treatment regimen, involving a combination of several drugs taken over many months. This is further complicated by the emergence of multi-drug resistant (MDR) and extensively drug-resistant (XDR) M. tuberculosis strains, which require even longer treatment times with less well-tolerated drugs. Eradication of TB will require the development of new drugs and vaccines, alongside improved methods for diagnosis and monitoring treatment efficacy. With the vast burden of disease falling in resource poor settings, the challenge will also be to develop methodologies that can be deployed with minimal investment in infrastructure, maintenance and staff expertise. Recent decades have seen the emergence of the new discipline of molecular imaging. In essence, molecular imaging enables the non-invasive visualisation, characterisation, and quantification of biological processes taking place within intact living subjects, be it a mouse or man (Filippi & Rocca, 2011; Horky & Treves, 2011; Pysz et al., 2010; Sandhu et al., 2010). Imaging has long been applied to managing TB; simple chest x-rays have allowed clinicians to visualise TB in people for over a century (Singh & Nath, 1994). However, the new molecular imaging techniques are revolutionising medical research, with the potential to translate into significant changes in clinical practice. In this chapter we describe the new generation of imaging modalities and how these are being applied to eradicating TB, from the laboratory bench and in to the clinic

Vanadium redox flow batteries real-time State of Charge and State of Health estimation under electrolyte imbalance condition

This paper presents a novel observer architecture capable to estimate online the concentrations of the four vanadium species present in a vanadium redox flow battery (VRFB). The proposed architecture comprises three main stages: (1) a high-gain observer, to estimate the output voltage and its derivatives; (2) a dynamic inverter, to obtain a set of concentration candidate solutions; and (3) a static selector, to determine the actual concentrations. The methodology does not rely on the classic assumption of balanced electrolytes, thus significantly widening the application range in comparison with most of the literature previous studies. Furthermore, to perform the estimation, only a single voltage and current measurements are required, which eliminates the need of including complex and costly additional sensors. To validate the proposal, comprehensive simulation tests are conducted. These tests take into account typical side reactions that cause imbalance in VRFB systems, such as vanadium crossover and oxidation. The observer shows a remarkable performance when dealing with these realistic conditions, allowing to estimate with high accuracy and robustness the four vanadium concentrations, the State of Charge and the State of Health with a relative error below 2%.The project that gave rise to these results received the support of a fellowship from ”la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/DI21/11860023. This research was also supported by the Spanish Ministry of Science and Innovation, under the projects MAFALDA (PID2021-126001OB-C31) and MASHED (TED2021-129927B-I00). This work has been supported by the Spanish Ministry of Universities funded by the European Union - NextGenerationEU (2022UPC-MSC-93823).Peer ReviewedPostprint (published version

The Effects of the Peak-Peak Correlation on the Peak Model of Hierarchical Clustering

In two previous papers a semi-analytical model was presented for the hierarchical clustering of halos via gravitational instability from peaks in a random Gaussian field of density fluctuations. This model is better founded than the extended Press-Schechter model, which is known to agree with numerical simulations and to make similar predictions. The specific merger rate, however, shows a significant departure at intermediate captured masses. The origin of this was suspected as being the rather crude approximation used for the density of nested peaks. Here, we seek to verify this suspicion by implementing a more accurate expression for the latter quantity which accounts for the correlation among peaks. We confirm that the inclusion of the peak-peak correlation improves the specific merger rate, while the good behavior of the remaining quantities is preserved.Comment: ApJ accepted. 15 pages, including 4 figures. Also available at ftp://pcess1.am.ub.es/pub/ApJ/effectpp.ps.g

Decomposition of Algebraic Functions

AbstractFunctional decomposition—whether a functionf(x) can be written as a composition of functionsg(h(x)) in a non-trivial way—is an important primitive in symbolic computation systems. The problem of univariate polynomial decomposition was shown to have an efficient solution by Kozen and Landau (1989). Dickerson (1987) and Gathen (1990a) gave algorithms for certain multivariate cases. Zippel (1991) showed how to decompose rational functions. In this paper, we address the issue of decomposition of algebraic functions. We show that the problem is related to univariate resultants in algebraic function fields, and in fact can be reformulated as a problem ofresultant decomposition. We characterize all decompositions of a given algebraic function up to isomorphism, and give an exponential time algorithm for finding a non-trivial one if it exists. The algorithm involves genus calculations and constructing transcendental generators of fields of genus zero

New constraints on the expansion rate at redshift 2.3 from the Lyman-α\alpha forest

We measure the expansion rate of the Universe at redshift $z=2.3$ from the anisotropy of Lyman-$\alpha$ (Ly$\alpha$) forest correlations measured by the Sloan Digital Sky Survey (SDSS). Our result is the most precise from large-scale structure at $z>1$. In flat $\Lambda$CDM we determine the matter density to be $\Omega_\mathrm{m}=0.36^{+0.03}_{-0.04}$ from Ly$\alpha$ alone, a factor of two tighter than baryon acoustic oscillation results from the same data. Using a nucleosynthesis prior, we measure the Hubble constant to be $H_0=63.2\pm2.5$ km/s/Mpc. In combination with other SDSS tracers, we find $H_0=67.2\pm0.9$ km/s/Mpc and measure the dark energy equation-of-state parameter to be $w=-0.90\pm0.12$. Our work opens a new avenue for constraining cosmology at high redshift.Comment: Submitted to PR

Constraints on the Cosmic Expansion Rate at Redshift 2.3 from the Lyman-α Forest

We determine the product of the expansion rate and angular-diameter distance at redshift z ¼ 2.3 from the anisotropy of Lyman-α (Lyα) forest correlations measured by the Sloan Digital Sky Survey (SDSS). Our result is the most precise from large-scale structure at z > 1. Using the flat Λ cold dark matter model we determine the matter density to be Ωm ¼ 0.36þ0.03 −0.04 from Lyα alone. This is a factor of 2 tighter than baryon acoustic oscillation results from the same data due to our use of a wide range of scales (25 <r< 180 h−1 Mpc). Using a nucleosynthesis prior, we measure the Hubble constant to be H0 ¼ 63.2 2.5 km=s=Mpc. In combination with other SDSS tracers, we find H0 ¼ 67.2 0.9 km=s=Mpc and measure the dark energy equation-of-state parameter to be w ¼ −0.90 0.12. Our Letter opens a new avenue for constraining cosmology at high redshift

Improving forging outcomes of cast titanium aluminide alloy via cyclic induction heat treatment

The objective of this research was to improve the forging outcome of peritectic solidifying cast titanium aluminide (TiAl) 4822 alloy (Ti-48Al-2Nb-2Cr at.%) in hot isostatic pressed and homogenised (HH) condition using cyclic induction heat treatment (CHT). This study adds to research around CHT for TiAl alloys by applying industrially relevant induction heating to conduct five heating cycles at the single αphase temperatures (1370 °C) necessary for grain refinement. Two cooling rates were explored in each cycle, air cooling (ACCHT) and controlled furnace-like cooling (FCCHT), without returning to room temperature. Samples were assessed at each stage in terms of their morphologies, lamellar grain size and content, as well as phase and dynamic recrystallised fraction, and subsequent primary and secondary compression behaviour with uniaxial isothermal compression. The FCCHT process resulted in a homogeneously refined fully lamellar microstructure, and ACCHT, in a heterogeneous microstructure consisting of lamellar and feathery γ (γf) at differing fractions across the piece, depending on the cooling rate compared with HH. The results show that CHT improved forging outcomes for both compression stages investigated, resulting in uniform compression samples with higher volumes of dynamic recrystallised material compared with the instability seen with the compression of HH material

The Alcock–Paczyński effect from Lyman-α forest correlations: analysis validation with synthetic data

The three-dimensional distribution of the Ly α forest has been extensively used to constrain cosmology through measurements of the baryon acoustic oscillations (BAO) scale. However, more cosmological information could be extracted from the full shapes of the Ly α forest correlations through the Alcock–Paczyński (AP) effect. In this work, we prepare for a cosmological analysis of the full shape of the Ly α forest correlations by studying synthetic data of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). We use a set of 100 eBOSS synthetic data sets in order to validate such an analysis. These mocks undergo the same analysis process as the real data. We perform a full-shape analysis on the mean of the correlation functions measured from the 100 eBOSS realizations, and find that our model of the Ly α correlations performs well on current data sets. We show that we are able to obtain an unbiased full-shape measurement of DM/DH(zeff), where DM is the transverse comoving distance, DH is the Hubble distance, and zeff is the effective redshift of the measurement. We test the fit over a range of scales, and decide to use a minimum separation of rₘᵢₙ = 25 h−¹Mpc. We also study and discuss the impact of the main contaminants affecting Ly α forest correlations, and give recommendations on how to perform such analysis with real data. While the final eBOSS Ly α BAO analysis measured DM/DH(zeff = 2.33) with 4 per cent statistical precision, a full-shape fit of the same correlations could provide an ∼2 per cent measurement