Pairing mechanism in Fe pnictide superconductors

By applying an exact unitary transformation to a two-band hamiltonian which also includes the effects due to large pnictogen polarizabilities, we show that an attractive spin-mediated Hubbard term appears in the $d_{xz}$, $d_{yz}$ nearest-neighbour channel. This pairing mechanism implies a singlet superconducting order parameter in iron pnictides.Comment: 4 pages, 3 figure

Managing Capacity by Drift Control

We model the problem of managing capacity in a build-to-order environment as a Brownian drift control problem and seek a policy that minimizes the long-term average cost. We assume the controller can, at some cost, shift the processing rate among a finite set of alternatives by, for example, adding or removing staff, increasing or reducing the number of shifts or opening or closing production lines. The controller incurs a cost for capacity per unit time and a delay cost that reflects the opportunity cost of revenue waiting to be recognized or the customer service impacts of delaying delivery of orders. Furthermore he incurs a cost per unit to reject orders or idle resources as necessary to keep the workload of waiting orders within a prescribed range. We introduce a practical restriction on this problem, called the $Ss$-restricted Brownian control problem, and show how to model it via a structured linear program. We demonstrate that an optimal solution to the $Ss$-restricted problem can be found among a special class of policies called deterministic non-overlapping control band policies. These results exploit apparently new relationships between complementary dual solutions and relative value functions that allow us to obtain a lower bound on the average cost of any non-anticipating policy for the problem even without the $Ss$ restriction. Under mild assumptions on the cost parameters, we show that our linear programming approach is asymptotically optimal for the unrestricted Brownian control problem in the sense that by appropriately selecting the $Ss$-restricted problem, we can ensure its solution is within an arbitrary finite tolerance of a lower bound on the average cost of any non-anticipating policy for the unrestricted Brownian control problem

Endoskopska pretraga u bolesnika sa zadebljanjem stijenke kolona otkrivenim kompjutoriziranom tomografijom

Colorectal wall thickening is a condition which is occasionally encountered on computed tomography (CT) investigations. Malignancies and inflammatory bowel disease (IBD) may be the most common and most important pathologies in some cases. Our objective in this study was to evaluate colonoscopy results in patients with increased colorectal wall thickness identified on CT. Patients with colorectal wall thickening detected on abdominal CT taken for different indications in different healthcare facilities between October 2009 and March 2015 were evaluated. These patients were referred to gastroenterology department, received colonoscopy, and the results were compared retrospectively and statistically. A total of 132 patients having undergone colonoscopy for colonic wall thickening detected on CT were evaluated retrospectively. With the colonoscopies performed, malignancies were detected in 38 (28.8%), Crohn’s disease in two (1.5%), diverticulitis in 18 (13.6%) and colorectal polyp in 30 (22.7%) patients. Colonoscopy results were normal in 44 patients. All patients with colorectal malignancies were over 60 years of age, yielding a statistically significant figure (p=0.01). The mean hemoglobin level was 12.8 g/dL in patients with normal colonoscopy as compared with 9.5 g/dL in those with malignancies (p=0.001). On multivariate analysis, hemoglobin and age were the only significant variables to predict an abnormal result on endoscopy. Detecting colonic wall thickening on CT may indicate malignancy, especially in patients who are over 50 years of age and have hemoglobin values less than 10 g/dL.Zadebljanje stijenke kolona je stanje koje se ponekad vidi kod pretrage kompjutoriziranom tomografijom (computerized tomography, CT). Najčešće i najvažnije patologije u nekim slučajevima mogu biti maligne bolesti i upalne bolesti crijeva (inflammatory bowel disease, IBD). Cilj ovoga istraživanja bio je procijeniti rezultate kolonoskopije u bolesnika s povećanom debljinom kolorektalne stijenke utvrđenom na CT-u. Studija je obuhvatila bolesnike sa zadebljanjem kolorektalne stijenke otkrivenim na CT-u abdomena zbog različitih indikacija od listopada 2009. do ožujka 2015. godine. Ovi bolesnici su upućeni u kliniku za gastroenterologiju, napravljena im je kolonoskopija, a rezultati su retrospektivno statistički analizirani. Retrospektivno su analizirana 132 bolesnika podvrgnuta kolonoskopiji zbog zadebljanja stijenke kolona otkrivenog na CT-u. Na kolonoskopiji su otkrivene zloćudne promjene u 38 (28,8%), Crohnova bolest u dvoje (1,5%), divertikulitis u 18 (13,6%) i kolorektalni polip u 30 (22,7%) bolesnika. Rezultati kolonoskopije bili su normalni u 44 bolesnika. Svi bolesnici s kolorektalnim malignim promjenama bili su stariji od 60 godina, što je bilo statistički značajno (p=0,01). Srednja vrijednost hemoglobina bila je 12,8 g/dL u bolesnika s normalnim nalazom kolonoskopije u usporedbi s 9,5 g/dL u onih sa zloćudnim promjenama (p=0,001). Multivarijatna analiza pokazala je da su hemoglobin i dob jedine značajne varijable koje pretkazuju nenormalan endoskopski rezultat. Otkrivanje zadebljanja stijenke kolona na CT-u može ukazivati na malignitet, poglavito u bolesnika starijih od 50 godina s vrijednostima hemoglobina nižim od 10 g/dL

Diagnosis of gastric carcinoma by classification on feature projections

Cataloged from PDF version of article.A new classification algorithm, called benefit maximizing classifier on feature projections (BCFP), is developed and applied to the problem of diagnosis of gastric carcinoma. The domain contains records of patients with known diagnosis through gastroscopy results. Given a training set of such records, the BCFP classifier learns how to differentiate a new case in the domain. BCFP represents a concept in the form of feature projections on each feature dimension separately. Classification in the BCFP algorithm is based on a voting among the individual predictions made on each feature. In the gastric carcinoma domain, a lesion can be an indicator of one of nine different Levels of gastric carcinoma, from early to late stages. The benefit of correct classification of early levels is much more than that of late cases. Also, the costs of wrong classifications are not symmetric. In the training phase, the BCFP algorithm learns classification rules that maximize the benefit of classification. In the querying phase, using these rules, the BCFP algorithm tries to make a prediction maximizing the benefit. A genetic algorithm is applied to select the relevant features. The performance of the BCFP algorithm is evaluated in terms of accuracy and running time. The rules induced are verified by experts of the domain. (C) 2004 Elsevier B.V. All rights reserved

Enhanced thermoelectric properties of the Zintl phase BaGa_2Sb_2 via doping with Na or K

Na- or K-doped samples of Ba_(1−x)(Na, K)xGa_2Sb_2 were prepared by ball-milling followed by hot-pressing. The topological analysis of the electron density of BaGa_2Sb_2 implies a polar covalent nature of the Sb–Ga bonds in which the Sb atoms receive the electrons transferred from Ba rather than the Ga atoms. Successful doping of BaGa_2Sb_2 with Na or K was confirmed with combined microprobe and X-ray diffraction analysis. Alkali metal doping of BaGa_2Sb_2 increased the p-type charge carrier concentration to almost the predicted optimum values (∼10^(20) h^+ cm^(−3)) needed to achieve high thermoelectric performance. With increasing alkali metal concentration, electronic transport was shifted from non-degenerate semiconducting behaviour observed for BaGa_2Sb_2 to degenerate one for Na- or K-doped compounds. Overall, the thermoelectric figure of merit, zT, values reached up to ∼0.65 at 750 K, considerably higher than the undoped sample (zT ∼ 0.1 at 600 K), and a slight improvement relative to previously reported Zn-doped samples (∼0.6 at 800 K)

Thermoelectric Enhancement in BaGa_2Sb_2 by Zn Doping

The Zintl phase BaGa_2Sb_2 has a unique crystal structure in which large tunnels formed by ethane-like dimeric [Sb_3Ga−GaSb_3] units are filled with Ba atoms. BaGa_2Sb_2 was obtained in high purity from ball-milling followed by hot pressing. It shows semiconducting behavior, in agreement with the valence precise Zintl counting and band structure calculations, with a band gap ∼0.4 eV. The thermal conductivity of BaGa_2Sb_2 is found to be relatively low (0.95 W/K m at 550 K), which is an inherent property of compounds with complex crystal structures. As BaGa_2Sb_2 has a low carrier concentration (∼2 × 10^18 h^+/cm^3) at room temperature, the charge carrier tuning was performed by substituting trivalent Ga with divalent Zn. Zn-doped samples display heavily doped p-type semiconducting behavior with carrier concentrations in the range (5−8) × 10^19 h^+/cm^3. Correspondingly, the zT values were increased by a factor of 6 by doping compared to the undoped sample, reaching a value of ∼0.6 at 800 K. Zn-doped BaGa_2Sb_2 can thus be considered as a promising new thermoelectric material for intermediate-temperature applications

Strong coupling between magnetic and structural order parameters in SrFe2As2

X-ray and Neutron diffraction as well as muon spin relaxation and M\"ossbauer experiments performed on SrFe$_2$As$_2$ polycrystalls confirm a sharp first order transition at $T_0 = 205$,K corresponding to an orthorhombic phase distortion and to a columnar antiferromagnetic Fe ordering with a propagation vector (1,0,1), and a larger distortion and larger size of the ordered moment than reported for BaFe$_2$As$_2$. The structural and the magnetic order parameters present an remarkable similarity in their temperature dependence from $T_0$ down to low temperatures, showing that both phenomena are intimately connected. Accordingly, the size of the ordered Fe moments scale with the lattice distortion when going from SrFe$_2$As$_2$ to BaFe$_2$As$_2$. Full-potential band structure calculations confirm that the columnar magnetic order and the orthorhombic lattice distortion are intrinsically tied to each other.Comment: 10 pages, 4 figure

Magnetic and structural transitions in layered FeAs systems: AFe2As2 versus RFeAsO compounds

Resistivity, specific heat and magnetic susceptibility measurements performed on SrFe2As2 samples evidence a behavior very similar to that observed in LaFeAsO and BaFe2As2 with the difference that the formation of the SDW and the lattice deformation occur in a pronounced first order transition at T_0=205K. Comparing further data evidences that the Fe-magnetism is stronger in SrFe2As2 and in EuFe2As2 than in the other layered FeAs systems investigated up to now. Full potential LDA band structure calculations confirm the large similarity between the compounds, especially for the relevant low energy Fe 3d states. The relation between structural details and magnetic order is analyzed.Comment: 4 pages, 3 figure

Low-temperature synthesis of SmFeAsO0.7F0.3 wires with high transport critical current density

Ag-sheathed SmFeAsO0.7F0.3 (Sm-1111) superconducting wires were prepared by a one-step solid state reaction at temperatures as low as 850~900C, instead of commonly used temperatures of 1150~1250C. The X-ray diffraction pattern of the as-sintered samples is well indexed on the basis of tetragonal ZrCuSiAs-type structure. We characterized transport critical current density Jc of the SmFeAsO0.7F0.3 wires in increasing and subsequently decreasing fields, by a resistive four-probe method. A transport Jc as high as ~1300 A/cm^2 at 4.2 K and self field has been observed for the first time in Sm-1111 type polycrystalline superconductors. The Jc also shows a rapid depression in small applied fields as well as a magnetic-history dependence, indicating weak-linked grain boundaries. The low-temperature synthesis method can be very beneficial to fabricating the RE-1111 iron oxynictides in a convenient and safe way.Comment: 12 pages, 3 figure