Realization of random-field dipolar Ising ferromagnetism in a molecular magnet

The longitudinal magnetic susceptibility of single crystals of the molecular magnet Mn$_{12}$-acetate obeys a Curie-Weiss law, indicating a transition to a ferromagnetic phase due to dipolar interactions. With increasing magnetic field applied transverse to the easy axis, the transition temperature decreases considerably more rapidly than predicted by mean field theory to a T=0 quantum critical point. Our results are consistent with an effective Hamiltonian for a random-field Ising ferromagnet in a transverse field, where the randomness is induced by an external field applied to Mn$_{12}$-acetate crystals that are known to have an intrinsic distribution of locally tilted magnetic easy axes.Comment: 4 pages, 4 figure

Alignment Of Magnetic Anisotropy Axes In Crystals Of Mn12 Acetate And Mn12-tBuAc Molecular Nanomagnets: Angle-Dependent Ac Susceptibility Study

We report the results of angular-dependent ac susceptibility experiments performed on two derivatives of Mn12 single-molecular magnets: the well-known Mn12 acetate, which contains disordered acetic acid molecules in interstitial sites of the crystal structure and Mn12-tBuAc, for which solvent molecules are very well ordered in the structure. Our results show (a) that the angular variation is very similar in the two compounds investigated and compatible with a maximum misalignment of the anisotropy axes of less than 3° and (b) that the tunneling rate is faster for the better ordered Mn12-tBuAc compound. These experiments question interstitial disorder as the dominant origin of the thermally activated tunneling phenomenon

Final results from the EU project AVATAR: aerodynamic modelling of 10 MW wind turbines

This paper presents final results from the EU project AVATAR in which aerodynamic models are improved and validated for wind turbines on a scale of 10 MW and more. Special attention is paid to the improvement of low fidelity engineering (BEM based) models with higher fidelity (CFD) models but also with intermediate fidelity free vortex wake (FVW) models. The latter methods were found to be a good basis for improvement of induction modelling in engineering methods amongst others for the prediction of yawed cases, which in AVATAR was found to be one of the most challenging subjects to model. FVW methods also helped to improve the prediction of tip losses. Aero-elastic calculations with BEM based and FVW based models showed that fatigue loads for normal production cases were over predicted with approximately 15% or even more. It should then be realised that the outcome of BEM based models does not only depend on the choice of engineering add-ons (as is often assumed) but it is also heavily dependent on the way the induced velocities are solved. To this end an annulus and element approach are discussed which are assessed with the aid of FVW methods. For the prediction of fatigue loads the so-called element approach is recommended but the derived yaw models rely on an annulus approach which pleads for a generalised solution method for the induced velocities

Effects Of Quantum Mechanics On The Deflagration Threshold In The Molecular Magnet Mn12 Acetate

We report experimental studies of the stability of a Mn12-Ac crystal against magnetic avalanches as a function of the magnitude and direction of the magnetic field, as well as a function of temperature. Strong evidence for quantum effects associated with this phenomenon is seen in the (Hz,Hx) metastability diagram. The data provide further support to the theory of magnetic deflagration

Crystal Lattice Desolvation Effects On The Magnetic Quantum Tunneling Of Single-Molecule Magnets

High-frequency electron paramagnetic resonance (HFEPR) and alternating current (ac) susceptibility measurements are reported for a new high-symmetry Mn12 complex, [Mn12O12(O2CCH3)16(CH3OH)4]⋅CH3OH. The results are compared to those of other high-symmetry spin S=10 Mn12 single-molecule magnets (SMMs), including the original acetate, [Mn12(O2CCH3)16(H2O)4]⋅2CH3CO2H⋅4H2O, and the [Mn12O12(O2CCH2Br)16(H2O)4]⋅4CH2Cl2 and [Mn12O12(O2CCH2But)16(CH3OH)4]⋅CH3OH complexes. These comparisons reveal important insights into the factors that influence the values of the effective barrier to magnetization reversal, Ueff, deduced on the basis of ac susceptibility measurements. In particular, we find that variations in Ueff can be correlated with the degree of disorder in a crystal which can be controlled by desolvating (drying) samples. This highlights the importance of careful sample handling when making measurements on SMM crystals containing volatile lattice solvents. The HFEPR data additionally provide spectroscopic evidence suggesting that the relatively weak disorder induced by desolvation influences the quantum tunneling interactions and that it is under-barrier tunneling that is responsible for a consistent reduction in Ueff that is found upon drying samples. Meanwhile, the axial anisotropy deduced from HFEPR is found to be virtually identical for all four Mn12 complexes, with no measurable reduction upon desolvation

Impact of the Covid-19 pandemic on education: experiences and feelings reported by primary school pupils from Greece and Turkey

Covid 19 pandemic had a huge impact upon life and the educational experience of students. One of the groups mostly affected from this pandemic is the school children. The sudden transition to distance education from traditional face-to-face education undoubtedly changed the implementation methods of the teaching programme in schools. The research study reported in this paper was carried out in Greece and Turkey. Responses were collected from primary school pupils who voluntarily and anonymously completed an online questionnaire with multiple choice questions. The latter were carefully worded in an appropriate and understandable way, using language suitable for primary school aged children. Comparisons between the responses from the two countries revealed similarities and differences. Through a comparative approach the research results are particularly scruitinised through the lenses of equal opportunities and social exclusion policies along with a cross cultural perspective, which is expected to have a useful impact during the post pandemic era. By sharing the collective knowledge and experience gained, we aspire to propose educational strategies for well-being and recovery, and overall educational process improvement

Spin Dynamics In Single-Molecule Magnets Combining Surface Acoustic Waves And High-Frequency Electron Paramagnetic Resonance

We report an experimental technique that integrates high-frequency surface acoustic waves (SAWs) with high-frequency electron paramagnetic resonance (HFEPR) spectroscopy in order to measure spin dynamics on fast time scales in single-molecule magnets. After the system is driven out of equilibrium by triggering magnetic avalanches, or simply by heating with short SAW pulses, the evolution of the spin populations within fixed energy levels is measured using HFEPR spectroscopy

Choledochoduodenal fistula presenting with pneumobilia in a patient with gallbladder cancer: a case report

<p>Abstract</p> <p>Introduction</p> <p>Spontaneous biliary tract fistulas are rare entities. Most of them are associated with long-standing gallstones (especially common bile duct stones, or recurrent biliary tract infections), some with more uncommon diseases such as gallbladder cancer. Some authors believe that back flow from fistulas predisposes patients to gallbladder cancer and some believe that cancer causes necrosis and fistula formation. Gallbladder cancer has a dismal prognosis and 85% of patients are dead within a year of diagnosis. A common complication of gallbladder cancer is obstruction of the common bile duct, which may produce multiple intra-hepatic abscesses in or near the tumor-laden gallbladder. Fistula formation may further complicate the clinical picture.</p> <p>Case presentation</p> <p>We present a case of choledochoduodenal fistula in a 60-year-old diabetic African-American woman with gallbladder cancer. The initial clinical presentation was confusing and complex. Our patient was also found to have a gallbladder fossa abscess that was drained percutaneously as another complicating factor relating to her cancer. She developed myocardial infarction, massive upper gastrointestinal bleeding and respiratory arrest during her stay in hospital. Computed tomography was very helpful in assessing our patient and we discuss how, in a patient with pneumobilia, it can be helpful for detecting fistula, air in bile ducts or to show contractions of the gallbladder.</p> <p>Conclusions</p> <p>We believe this case merits reporting as it shows an entity that is not frequently thought of, is hard to diagnose and can be fatal, as in our patient. Careful evaluation, and computed tomography studies and endoscopic retrograde cholangio-pancreatography are helpful in early diagnosis and finding better management options for these patients.</p