Magnetic properties of Fe5_5SiB2_2 and its alloys with P, S, and Co

Fe$_5$SiB$_2$ has been synthesized and magnetic measurements have been carried out, revealing that M$_{\text{sat}}$ = 0.92 MA/m at T = 300 K. The M vs T curve shows a broad peak around T = 160 K. The anisotropy constant, K$_1$, estimated at T = 300 K, is 0.25 MJ/m$^3$. Theoretical analysis of Fe$_5$SiB$_2$ system has been carried out and extended to the full range of Fe$_5$Si$_{1-x}$P$_x$B$_2$, Fe$_5$P$_{1-x}$S$_x$B$_2$, and (Fe$_{1-x}$Co$_x$)$_5$SiB$_2$ compositions. The electronic band structures have been calculated using the Full-Potential Local-Orbital Minimum-Basis Scheme (FPLO-14). The calculated total magnetic moments are 9.20, 9.15, 9.59 and 2.42$\mu_B$ per formula units of Fe$_5$SiB$_2$, Fe$_5$PB$_2$, Fe$_5$SB$_2$, and Co$_5$SiB$_2$, respectively. In agreement with experiment, magnetocrystalline anisotropy energies (MAE's) calculated for T = 0 K changes from a negative (easy-plane) anisotropy -0.28 MJ/m$^3$ for Fe$_5$SiB$_2$ to the positive (easy-axis) anisotropy 0.35 MJ/m$^3$ for Fe$_5$PB$_2$. Further increase of the number of p-electrons in Fe$_5$P$_{1-x}$S$_x$B$_2$ leads to an increase of MAE up to 0.77 MJ/m$^3$ for the hypothetical Fe$_5$P$_{0.4}$S$_{0.6}$B$_2$ composition. Volume variation and fixed spin moment calculations (FSM) performed for Fe$_5$SiB$_2$ show an inverse relation between MAE and magnetic moment in the region down to about 15\% reduction of the spin moment. The alloying of Fe$_5$SiB$_2$ with Co is proposed as a practical realization of magnetic moment reduction, which ought to increase MAE. MAE calculated in virtual crystal approximation (VCA) for a full range of (Fe$_{1-x}$Co$_x$)$_5$SiB$_2$ compositions reaches the maximum value of 1.16 MJ/m$^3$ at Co concentration x = 0.3, with the magnetic moment 7.75$\mu_B$ per formula unit. Thus, (Fe$_{0.7}$Co$_{0.3}$)$_5$SiB$_2$ is suggested as a candidate for a rare-earth free permanent magnet.Comment: 11 pages, 14 figure

Magnetic and mechanical effects of Mn substitutions in AlFe2B2

The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe2B2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe2B2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe2B2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe2B2. The Mn-Mn exchange interactions in AlMn2 B2 are found to be very small

A Condensation-Ordering Mechanism in Nanoparticle-Catalyzed Peptide Aggregation

Nanoparticles introduced in living cells are capable of strongly promoting the aggregation of peptides and proteins. We use here molecular dynamics simulations to characterise in detail the process by which nanoparticle surfaces catalyse the self- assembly of peptides into fibrillar structures. The simulation of a system of hundreds of peptides over the millisecond timescale enables us to show that the mechanism of aggregation involves a first phase in which small structurally disordered oligomers assemble onto the nanoparticle and a second phase in which they evolve into highly ordered beta-sheets as their size increases

Adipose stromal cells improve healing of vocal fold scar: Morphological and functional evidences

OBJECTIVES/HYPOTHESIS: Adipose derived stromal cells (ASCs) are abundant and easy to prepare. Such cells may be useful for treating severe vocal disturbance caused by acute vocal fold scars. STUDY DESIGN: Prospective animal experiments with controls. METHODS: Twenty New-Zealand white rabbits were used in the present study. We evaluated vocal fold healing, with or without injection of autologous ASCs, after acute scarring. A defined lesion was created and the ASCs were immediately injected. Vocal fold regeneration was evaluated histomorphometrically and via viscoelastic analysis using an electrodynamic shaker. RESULTS: Six weeks after ASC injection, vocal folds exhibited significantly less inflammation than control folds (P < 0.005). In addition, hypertrophy of the lamina propria and fibrosis were significantly reduced upon ASC injection (P < 0.02). The decrease in viscoelastic parameters was less important in the ASC injected group compared to the noninjected group (P = 0.08). CONCLUSION: Injection of autologous ASCs improved vocal fold healing in our preclinical model. Further studies are needed, but this method may be useful in humans. LEVEL OF EVIDENCE: NA. Laryngoscope, 126:E278-E285, 2016

A fast algorithm for computing distance spectrum of convolutional codes

New rate-compatible convolutional (RCC) codes with high constraint lengths and a wide range of code rates are presented. These new codes originate from rate 1/4 optimum distance spectrum (ODS) convolutional parent encoders with constraint lengths 7-10. Low rate encoders (rates 115 down to 1/10) are found by a nested search, and high rate encoders (rates above 1/4) are found by rate-compatible puncturing. The new codes form rate-compatible code families more powerful and flexible than those previously presented. It is shown that these codes are almost as good as the existing optimum convolutional codes of the same fates. The effects of varying the design parameters of the rate-compatible punctured convolutional (RCPC) codes, i.e., the parent encoder rate, the puncturing period, and the constraint length, are also examined. The new codes are then applied to a multicode direct-sequence code-division multiple-access (DS-CDMA) system and are shown to provide good performance and rate-matching capabilities. The results, which are evaluated in terms of the efficiency for Gaussian and Rayleigh fading channels, show that the system efficiency increases with decreasing code rat

Cosmic Ray Diffusion in the Hamiltonian Guiding Center Approximation

Forå konstruere en metode tilå teste nøyaktigheten til den Hamiltonske føringssen- terapproksimasjonen undersøkes diffusjonskoeffisientene av kosmiske stråler propa- gert i et turbulent magnetisk felt. Målet er å reprodusere tidligere resultater for å forsikre at diffusjonssimuleringene kan benyttes til å sammenligne den Hamiltons- ke føringssenterapproksimasjonen opp mot det å løse Lorentz-ligningen direkte. Turbulensen simuleres som en hydrodynamisk turbulens som følger Kolmogorov’s energispektrum. For å simulere propagasjonen av kosmisk stråling ble en Runge- Kutta-integrator implementert for å løse Lorentz-ligningen. Isotropien av algorit- men som genererer det turbulente magnetfeltet verifiseres, og isotropien i feltet bevises gitt at korrekt sannsynlighetsfordeling for de tilfeldige fasene velges. Vi- dere vises den kvalitative atferden av diffsjonskoeffisientene å være i samsvar med tidligere resultater. Etter overgangen til det isotropiske regime finnes faktoren d 3 /d 1 til å være tilnærmet konstant ved d 3 /d 1 ∼ 10, som viser en signifikant aniso- tropisk atferd. Sammenligning av de gjennomsnittlige diffusjonskoeffisientene fra simuleringene opp mot de teoretiske verdiene viser at forskjellen er innen en faktor mellom 1.21 og 2.33. Diffusjonskoeffisienten vises å følge D(E) ∝ β som forventet, med β = 1/3 og β = 2 for the diffusive og det ballistiske regime respektivt. Videre vises det at overgangen mellom de to regimene starter ved høyere energi for de simulerte diffusjonskoeffisientene enn for de teoretiske koeffisientene. Hamiltonsk føringssenterteori anvendes på propageringen av kosmisk stråling gjennom forskjellige magnetiske felt, inklusive det uniforme feltet, spiralfelt med konstant og varierende feltstyrke, samt et uniformt felt i superposisjon med et turbulent felt. Målet er å teste under hvilke forhold føringssenterteorien kan brukes i stedet for å løse Lorentz-ligningen direkte, og fortsatt gi ekvivalente resultater. Videre testes det om føringssenterteorien øker effektiviteten i disse simuleringene. Det vises at føringssenterteorien reproduserer en tilsvarende bane til den pro- dusert av den eksakte løsningen, med unntak av drifteffekter påført av curlen til magnetfeltet, samt en akselerasjonseffekt påført av magnetfeltets gradient. Disse manglende effektene vises å komme av en feil i programmeringen av teorien. Resul- tatene peker mot at Hamiltonsk føringssenterteori, når den implementeres korrekt, vil simulere banene til kosmisk stråling gjennom det Galaktiske magnetfeltet med høy nøyaktighet. Simuleringene antyder også at føringssenterteorien vil være mer effektiv enn å løse Lorentz-ligningen direkte. Siden implementasjonen av føringssenterteorien ikke ble ferdigstilt inne tids- rammen av dette prosjektet, var det ikke mulig å implementere den i beregningene av diffusjonen av kosmisk stråling i det galaktiske magnetiske feltet.To provide a method of testing the accuracy of the Hamiltonian Guiding Center Approximation, the diffusion coefficients of cosmic rays propagating in a purely turbulent magnetic field is investigated. The goal is to reproduce earlier results to assure the diffusion simulations can be used to compare the Hamiltonian guiding center theory to the direct solving of the Lorentz-equation. The turbulence is sim- ulated as a hydrodynamic turbulence following the Kolmogorov power spectrum. To simulate the cosmic ray propagation a step-size controlled Runge-Kutta algo- rithm is implemented to solve the Lorentz-equation. The isotropy of the algorithm generating the turbulent magnetic field is verified, and isotropy is proven given the correct choice of probability distribution for the random phases. Furthermore, the qualitative behavior of the diffusion coefficients is shown to be in accordance with previous results in both the isotropic and anisotropic regimes. After transitioning to the isotropic regime the factor d 3 /d 1 is found to be constant at d 3 /d 1 ∼ 10, which shows a significant amount of anisotropic behavior. Comparing the am- plitude of the average diffusion coefficients from the simulations with theoretical coefficients show that they are within a factor of 1.21 and 2.33. The scaling of the diffusion coefficient is found to follow the expected D(E) ∝ β when β = 1/3 and β = 2 for the diffusive and ballistic regimes respectively. The transition is shown to begin at a slightly higher energy for the simulated diffusion than for the theoretical diffusion. Hamiltonian guiding center theory is applied to the propagation of cosmic rays through different magnetic field models, including the uniform field, spiral fields with constant and non-constant field strengths, and a uniform field in superposition with a turbulent field. The aim is to test under which conditions the Hamiltonian guiding center theory can replace the direct solution of the Lorentz-equation and still provide equal results. Furthermore it is tested whether the guiding center theory is able to increase the efficiency of these simulations. It is shown that guiding center theory accurately reproduces the equivalent trajectory to that of the direct solution of the Lorentz-equation, exempt of a drift velocity caused by the curl of the magnetic field and an acceleration caused by the gradient of the magnetic field strength. The exemption of these effects are shown to be missing due to errors in the implementation. The presented results suggest that the Hamiltonian guiding center theory, when implemented correctly, will be able to accurately simulate the trajectories of cosmic rays through a Galactic magnetic field. The simulations using the guiding center theory also suggest the theory will be more efficient than directly solving the Lorentz-equation. As the guiding center theory implementation was not completed within the time frame of this project, it was not possible to implement it in the simulation of diffusion of cosmic rays in the Galactic magnetic field

Protein corona and nanoparticles: How can we investigate on?

Nanoparticles (NPs) represent one of the most promising tools for drug-targeting and drug-delivery. However, a deeper understanding of the complex dynamics that happen after their in vivo administration is required. Particularly, plasma proteins tend to associate to NPs, forming a new surface named the 'protein corona' (PC). This surface is the most exposed as the 'visible side' of NPs and therefore, can have a strong impact on NP biodistribution, targeting efficacy and also toxicity. The PC consists of two poorly delimited layers, known as 'hard corona' (HC) and 'soft corona' (SC), that are affected by the complexity of the environment and the formed protein-surface equilibrium during in vivo blood circulation. The HC corona is formed by proteins strongly associated to the NPs, while the SC is an outer layer consisting of loosely bound proteins. Several studies attempted to investigate the HC, which is easier to be isolated, but yielded poor reproducibility, due to varying experimental conditions. As a consequence, full mapping of the HC for different NPs is still lacking. Moreover, the current knowledge on the SC, which may play a major role in the 'first' interaction of NPs once in vivo, is very limited, mainly due to the difficulties in preserving it after purification. Therefore, multi-disciplinary approaches leading to the obtainment of a major number of information about the PC and its properties is strongly needed to fully understand its impact and to better support a more safety and conscious application of nanotechnology in medicine