Sequential piezoresponse force microscopy and the 'small-data' problem

The term big-data in the context of materials science not only stands for the volume, but also for the heterogeneous nature of the characterization data-sets. This is a common problem in combinatorial searches in materials science, as well as chemistry. However, these data-sets may well be 'small' in terms of limited step-size of the measurement variables. Due to this limitation, application of higher-order statistics is not effective, and the choice of a suitable unsupervised learning method is restricted to those utilizing lower-order statistics. As an interesting case study, we present here variable magnetic-field Piezoresponse Force Microscopy (PFM) study of composite multiferroics, where due to experimental limitations the magnetic field dependence of piezoresponse is registered with a coarse step-size. An efficient extraction of this dependence, which corresponds to the local magnetoelectric effect, forms the central problem of this work. We evaluate the performance of Principal Component Analysis (PCA) as a simple unsupervised learning technique, by pre-labeling possible patterns in the data using Density Based Clustering (DBSCAN). Based on this combinational analysis, we highlight how PCA using non-central second-moment can be useful in such cases for extracting information about the local material response and the corresponding spatial distribution

On the Influence of Ferroelectric Polarization States on the Magneto-electric Coupling in Two-phase Composites

Of particular attention in a variety of novel technical applications is the coupling between magnetic and electric field quantities. Materials that show magneto-electric (ME) coupling could enable new smart devices in the area of electric-field-controlled magnetic-data storage or highly sensitive magnetic-field sensors. In general, ME materials exhibit both a spontaneous magnetization and a spontaneous polarization. In this respect, they feature two ferroic states at the same time and are thus termed magneto-electric multiferroics. However, all natural and most of the synthesized ME multiferroics do not show an interaction between magnetization and electric polarization in the technically relevant temperature range. Thus, there is need for alternative realizations for ME coupling materials. A promising idea lies in the design and manufacturing of ME composites. These materials consist of a magnetostrictive and a piezoelectric phase and generate the ME coupling as a strain-induced product property. Since there exists a wealth of stable magnetostrictive and piezoelectric materials at ambient temperature, such composites yield the desired ME coupling also in a technically useful temperature range. In any case, the effective ME coupling is driven by microscopic interactions between the individual phases and thus highly depends on the microstructure of the composite. This calls for powerful homogenization methods that are able to predict the effective coupling for arbitrary microstructural morphologies. Motivated by that, we apply a two-scale computational homogenization framework for magneto-electro-mechanically coupled boundary value problems, which allows us to analyze the ME composite structures and calculate the effective ME-coefficient. Furthermore, by using a non-linear ferroelectric material model on the micro-level, we are able to simulate the polarization process of the ferroelectric phase. We show that this has a significant impact on the obtainable ME-coefficient

Doping of inorganic materials in microreactors – preparation of Zn doped Fe₃O₄ nanoparticles

Microreactor systems are now used more and more for the continuous production of metal nanoparticles and metal oxide nanoparticles owing to the controllability of the particle size, an important property in many applications. Here, for the first time, we used microreactors to prepare metal oxide nanoparticles with controlled and varying metal stoichiometry. We prepared and characterised Zn-substituted Fe₃O₄ nanoparticles with linear increase of Zn content (ZnxFe₃−xO₄ with 0 ≤ x ≤ 0.48), which causes linear increases in properties such as the saturation magnetization, relative to pure Fe₃O₄. The methodology is simple and low cost and has great potential to be adapted to the targeted doping of a vast array of other inorganic materials, allowing greater control on the chemical stoichiometry for nanoparticles prepared in microreactors

Simultaneous direct measurement of the electrocaloric and dielectric dynamics of ferroelectrics with microsecond temporal resolution

A contactless technique for direct time-resolved measurements of the full dynamics of the adiabatic temperature change in electrocaloric materials is introduced. The infrared radiation emitted by the electrocaloric sample is sensitively detected with $\mu$s time resolution and mK temperature resolution. We present time-resolved measurements of the electrocaloric effect up to kHz frequencies of the driving electric field and down to small field strengths. The simultaneous recording of transients for applied electric field and induced polarization gives a comprehensive view on the correlation of electrocaloric and ferroelectric properties. The technique can further be applied to the continuous measurement of fatigue for $> 10^6$ electric field cycles.Comment: 12 pages, 11 figure

Surgical treatment of pancreatic fistula after acute pancreatitis

Clinica I Chirurgie, Spitalul “Sf.Spiridon”, Departamentul de Chirurgie, Universitatea de Medicină şi Farmacie “Gr.T.Popa”, Iași, România, Al XII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova cu participare internațională 23-25 septembrie 2015Introducere: Fistula pancreatică este o complicație rară care apare în evoluția pancreatitei acute. Această complicație agravează evoluția bolii și este dificil de tratat, mai ales dacă are un debit important. Posibilitățile de tratament și momentul optim al intervenției chirurgicale rămân discutabile. Prezentare de caz: Pacient de 51 ani, sex masculin, consumător de alcool, se internează pentru dureri în etajul abdominal superior, grețuri, vărsături și meteorism. Se stabilește diagnosticul de pancreatită acută și se inițiază tratament conservator. La două săptămâni de la debut dezvoltă un abces subhepatic pentru care se intervine chirurgical. Începînd din ziua a 7-a postoperator pe tubul de dren subhepatic apare suc pancreatic cu un debit de 400-500 ml/zi. Explorările imagistice efectuate confirmă diagnosticul de fistulă pancreatică. După maturarea traectului fistulos se intervine chirurgical și se practică fistulojejunoanastomoză pe ansă în Y a la Roux. Evoluția postoperatorie a fost favorabilă. Pacientul se simte bine și nu are nici o acuză la 6 luni postoperator. Concluzie: Fistulo-jejunoanastomoza pe ansă Roux cu un traiect fistulos maturat este o soluție viabilă de tratament al fistulei pancreatice apărute în pancreatita acută.Introduction: Pancreatic fistula is a rare complication of acute pancreatitis, which seriously worsens the evolution and is a treatment challenge, especially when the output is high. The treatment options and timing are debatable. Case report: Male patient, 51, with a history of alcohol abuse, is admitted with pain in the upper abdomen, nausea, vomiting, abdominal distension, high amylasemia and lipasemia and the diagnosis of acute pancreatitis is established. After 2 weeks of treatment, a subhepatic abscess is surgically drained. Starting on the 7th postoperative day the subhepatic drainage tube produces 400-500 ml daily. Imaging explorations show a pancreatic fistula. After a delay for fistula maturation, Roux-en-Y fistula-jejunal anastomosis has been performed. Postoperative period was uneventful, with asymptomatic patient 6 months later. Conclusion: Roux-en-Y fistula-jejunal anastomosis of a mature pancreatic fistula is a valid approach in the management of high output pancreatic fistula after acute pancreatitis

Management of gastrointestinal stromal tumours

First Surgical Clinic, Department of Surgery, University of Medicine and Pharmacy “Gr. T. Popa” Iasi, Romania, Al XI-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova și cea de-a XXXIII-a Reuniune a Chirurgilor din Moldova „Iacomi-Răzeșu” 27-30 septembrie 2011Tumorile stromale gastrointestinale (GIST) reprezintă cele mai frecvente tumori neepiteliale digestive (10%); ele constituie 3% din tumorile gastrointestinale. GIST-ul care originea în celulele Cajal și exprimă antigenul c-Kit. se localizează cel mai frecvent la nivelul stomacului (50-60%), urmat de intestinul subțire (30%), colon și ano-rect (5%). Metoda: am urmărit prospectiv 32 bolnavi cu GIST tratați în clinica noastră în perioada 2004-2011, confirmați imuno-histochimic. din acești 32 bolnavi, 8 au fost abordați laparoscopic. localizarea tumorilor a fost stomacul - 15, duodenul - 4, intestinul subțire-7, colonul-2 și rectul-4. Toți bolnavii au fost rezecați R0 cu excepția unui singur bolnav la care s-a practicat o rezecție anterioară de rect tip R1. Postoperator, 4 bolnavi au primit Imatinib. Toti bolnavii au fost urmăriți în medie 32 luni înregistrându-se 2 recidive după localizările rectale. Concluzie: diagnosticul preoperator de GIST poate fi bănuit prin metodele imagistice actuale (endoscopie, ecografie, CT, videocapsula). Multe GIST-uri gastrice pot fi rezecate laparoscopic dacă nu sunt localizate pe juxta orificială. și GIST-urile intestinului subțire pot fi rezecate prin abord miniminvaziv. Acest abord este fezabil în centre specializate și nu aduce riscuri suplimentare. Tipul rezecției potenșialul malign după indexul Fletcher sunt factorii cei mai importanți de prognostic. Tratamentul adjuvant este util în formele maligne, recidive, rezecții incomplete.A gastrointestinal stromal tumour (GIST) represents the most common non-epithelial tumour of the digestive tract (about 10%). It originates in the intestinal pacemaker cell (Cajal’s cells) and expresses cell/surface CD 117 also known as c-Kit antigen. GIST tumors develop most frequently in the stomach (about 50-60%), the small bowel (30%), and the colon and anorectum (5%). METHODS: We have prospectively recorded the clinical characteristics, type of surgery, pathological findings, adjuvant treatment, and recurrence of the 32 patients with confirmed GISTs admitted between 2004 and 2011. We present a series of eight consecutive patients with GIST treated with a minimal access approach. RESULTS: The location of the tumor was gastric 15, duodenal 4, small bowel 7, colon 2, and rectal 4. None of our patients had clinical, imagistic, or macroscopic metastases. All the patients had R0 resections, except a patient with local excision and another with R1 anterior resection for rectal GISTs. Postoperatively, 4 patients received Imatinib therapy. The mean follow-up period is 32 months (range 8-58 months); 2 recurrences, both after rectal GISTs. CONCLUSION: Preoperative diagnosis of GIST can be evoked today based on imaging data (endoscopy, ultrasound scan, and CT scan, video capsule, enteroscopy). Many gastric GISTs can be resected laparoscopically. Small bowel GISTs should more often be evaluated laparoscopically and, in many cases, laparoscopic resections or laparoscopic-assisted resections may provide efficient therapy with low morbidity and no compromise to oncology principles. Laparoscopic approach of GISTs are feasible and, in competent hands, bring no additional risks. Fletcher index is the most significant prognostic factor. Imatinib treatment may improve outcomes in incomplete resected or high-risk GISTs

Dilute Magnetism and Spin-Orbital Percolation Effects in Rh-doped Sr2IrO4

We have used a combination of resonant magnetic x-ray scattering (RMXS) and x-ray absorption spectroscopy (XAS) to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir(1-x)Rh(x)O4 (0.07 < x < 0.70). We show that Sr2Ir(1-x)Rh(x)O4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at x_c ~ 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. We propose that the magnetic phase diagram for this material can be understood in terms of a novel spin-orbital percolation picture.Comment: 9 pages, 7 figure

Dilute magnetism and spin-orbital percolation effects in Sr\u3csub\u3e2\u3c/sub\u3eIr\u3csub\u3e1−\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eRh\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

We have used a combination of resonant magnetic x-ray scattering and x-ray absorption spectroscopy to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir1−xRhxO4 (0.07 ≤ x ≤ 0.70). We show that Sr2Ir1−xRhxO4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at xc ∼ 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. We propose that the magnetic phase diagram for this material can be understood in terms of a novel spin-orbital percolation picture

The nature of iron-oxygen vacancy defect centers in PbTiO3

The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of 1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.