Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime

We report on the magnetic and hyperthermia properties of iron nanoparticles synthesized by organometallic chemistry. They are 5.5 nm in diameter and display a saturation magnetization close to the bulk one. Magnetic properties are dominated by the contribution of aggregates of nanoparticles with respect to individual isolated nanoparticles. Alternative susceptibility measurements are been performed on a low interacting system obtained after eliminating the aggregates by centrifugation. A quantitative analysis using the Gittleman s model allow a determination of the effective anisotropy Keff = 1.3 * 10^5 J.m^{-3}, more than two times the magnetocristalline value of bulk iron. Hyperthermia measurements are performed on agglomerates of nanoparticles at a magnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximum measured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR) displays a square dependence with the magnetic field below 30 mT but deviates from this power law at higher value. SAR is linear with the applied frequency for mu_0H=19 mT. The deviations from the linear response theory are discussed. A refined estimation of the optimal size of iron nanoparticles for hyperthermia applications is provided using the determined effective anisotropy value

Phonon Mode Spectroscopy, Electron-Phonon Coupling and the Metal-Insulator Transition in Quasi-One-Dimensional M2Mo6Se6

We present electronic structure calculations, electrical resistivity data and the first specific heat measurements in the normal and superconducting states of quasi-one-dimensional M2Mo6Se6 (M = Tl, In, Rb). Rb2Mo6Se6 undergoes a metal-insulator transition at ~170K: electronic structure calculations indicate that this is likely to be driven by the formation of a dynamical charge density wave. However, Tl2Mo6Se6 and In2Mo6Se6 remain metallic down to low temperature, with superconducting transitions at Tc = 4.2K and 2.85K respectively. The absence of any metal-insulator transition in these materials is due to a larger in-plane bandwidth, leading to increased inter-chain hopping which suppresses the density wave instability. Electronic heat capacity data for the superconducting compounds reveal an exceptionally low density of states DEF = 0.055 states eV^-1 atom^-1, with BCS fits showing 2Delta/kBTc >= 5 for Tl2Mo6Se6 and 3.5 for In2Mo6Se6. Modelling the lattice specific heat with a set of Einstein modes, we obtain the approximate phonon density of states F(w). Deconvolving the resistivity for the two superconductors then yields their electron-phonon transport coupling function a^2F(w). In Tl2Mo6Se6 and In2Mo6Se6, F(w) is dominated by an optical "guest ion" mode at ~5meV and a set of acoustic modes from ~10-30meV. Rb2Mo6Se6 exhibits a similar spectrum; however, the optical phonon has a lower intensity and is shifted to ~8meV. Electrons in Tl2Mo6Se6 couple strongly to both sets of modes, whereas In2Mo6Se6 only displays significant coupling in the 10-18meV range. Although pairing is clearly not mediated by the guest ion phonon, we believe it has a beneficial effect on superconductivity in Tl2Mo6Se6, given its extraordinarily large coupling strength and higher Tc compared to In2Mo6Se6.Comment: 16 pages, 13 figure

Detectability of FSW defects with NDE methods

Peer reviewed: YesNRC publication: Ye

A severe case of pneumopathy in a duck breeder due to Chlamydia psittaci diagnosed by 16S rDNA sequencing

Introduction: Psittacosis is a zoonotic infectious disease contracted from birds and caused by Chlamydia psittaci, an obligate intracellular pathogen. In humans, the symptoms of the disease range from inapparent illness to systemic illness with severe pneumonia. Case presentation: A severe case of atypical pneumonia requiring extra‐corporeal membrane oxygenation in a duck breeder is described. Because of the critical urgency of the case described here, and without any clear identification of the pathogen during the first days of hospitalization, treatment had to be adjusted daily. While conventional clinical methods failed to identify the causative agent, C. psittaci was finally identified using broad‐range 16S rDNA PCR analysis performed on a sample of broncho‐alveolar fluid. Conclusion: Owing to the non‐specific clinical signs of psittacosis, early identification of cases of the disease remains a challenge. C. psittaci should be sought in patients presenting severe acute respiratory distress syndrome without any evidence of other infectious causes and especially when exposure to birds or bird products is reported. PCR is a very useful method to help identify fastidious organisms of this kind

Probabilistic chemotherapy in knee and hip replacement infection: the place of linezolid

Prosthetic joint infection (PJI) can occur with a wide range of microorganisms and clinical features. After replacement surgery of prosthetic joint, prescription of probabilistic broad-spectrum antimicrobial therapy is usual, while awaiting microbial culture results. The aim of our study was to describe the antibiotic susceptibility of microorganisms isolated from hip and knee PJI. The data were collected to determine the best alternative to the usual combination of piperacillin-tazobactam (TZP) or cefotaxime (CTX) and vancomycin (VAN). Based on a French prospective, multicenter study, we analyzed microbiological susceptibility to antibiotics of 183 strains isolated from patients with confirmed hip or knee PJI. In vitro susceptibility was evaluated: TZP+VAN, TZP+linezolid (LZD), CTX+VAN, and CTX+LZD. We also analyzed resistance to different antibiotics commonly used as oral alternatives. Among the 183 patients with PJI, 62 (34%) had a total knee prosthesis, and 121 (66%) a hip prosthesis. The main identified bacteria were Staphylococcus aureus (32.2% of isolates), coagulase-negative staphylococci (27.3%), Enterobacteriaceae (14.2%), and Streptococcus (13.7%). Infections were polymicrobial for 28 (15.3%) patients. All combinations were highly effective: CTX+VAN, CTX+LZD, TZP+VAN, and TZP+LZD (93.4%, 94%, 98.4%, and 98.9% of all cases respectively). Use of LZD instead of VAN in combination with a broad-spectrum beta-lactam covers almost all of the bacteria isolated in PJI. This association should be considered in probabilistic chemotherapy, as it is particularly easy to use (oral administration and no vancomycin monitoring)

Assessment of friction stir welds with nondestructive methods

Peer reviewed: YesNRC publication: Ye

Assessment of friction stir weld integrity for process control

Peer reviewed: YesNRC publication: Ye

Bridging Time Scales in Cellular Decision Making with a Stochastic Bistable Switch

Cellular transformations which involve a significant phenotypical change of the cell's state use bistable biochemical switches as underlying decision systems. In this work, we aim at linking cellular decisions taking place on a time scale of years to decades with the biochemical dynamics in signal transduction and gene regulation, occuring on a time scale of minutes to hours. We show that a stochastic bistable switch forms a viable biochemical mechanism to implement decision processes on long time scales. As a case study, the mechanism is applied to model the initiation of follicle growth in mammalian ovaries, where the physiological time scale of follicle pool depletion is on the order of the organism's lifespan. We construct a simple mathematical model for this process based on experimental evidence for the involved genetic mechanisms. Despite the underlying stochasticity, the proposed mechanism turns out to yield reliable behavior in large populations of cells subject to the considered decision process. Our model explains how the physiological time constant may emerge from the intrinsic stochasticity of the underlying gene regulatory network. Apart from ovarian follicles, the proposed mechanism may also be of relevance for other physiological systems where cells take binary decisions over a long time scale.Comment: 14 pages, 4 figure

Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes

We report on the magnetic hyperthermia properties of chemically synthesized ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the saturation magnetization of bulk iron. The specific absorption rate measured on 16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in other systems. A way to quantify the degree of optimization of any system with respect to hyperthermia applications is proposed. Applied here, this method shows that our nanoparticles are not fully optimized, probably due to the strong influence of magnetic interactions on their magnetic response. Once protected from oxidation and further optimized, such nano-objects could constitute efficient magnetic cores for biomedical applications requiring very large heating power