Dendritic growth and structure of undercooled nickel base alloys

The principal objectives of this overall investigation are to: study means for obtaining high undercooling in levitation melted droplets, and study structures produced upon the solidification of these undercooled specimens. Thermal measurements are made of the undercooling, and of the rapid recalescence, to develop an understanding of the solidification mechanism. Comparison of results is made with the modeling studies. Characterization and metallographic work is done to gain an understanding of the relationship between rapid solidification variables and the structures so produced. In ground based work to date, solidification of undercooled Ni-25 wt percent Sn alloy was observed by high-speed cinematography and the results compared with optical temperature measurements. Also in ground based work, high-speed optical temperature measurements were made of the solidification behavior of levitated metal samples within a transparent glass medium. Two undercooled Ni-Sn alloys were examined. Measurements were carried out on samples at undercoolings up to 330 K. Microstructures of samples produced in ground based work were determined by optical metallography and by SEM, and microsegregation by electron microprobe measurements. A series of flight tests were planned to conduct experiments similar to the ground based experiments. The Space Shuttle Columbia carried an alloy undercooled experiment in the STS 61-C mission in January 1986. A sample of Ni-32.5 wt percent Sn eutectic was melted and solidified under microgravity conditions

Solidification of undercooled liquids

During rapid solidification processing (RSP) the amount of liquid undercooling is an important factor in determining microstructural development by controlling phase selection during nucleation and morphological evolution during crystal growth. While undercooling is an inherent feature of many techniques of RSP, the deepest undercoolings and most controlled studies have been possible in carefully prepared fine droplet samples. From past work and recent advances in studies of nucleation kinetics it has become clear that the initiation of crystallization during RSP is governed usually by heterogeneous sites located at surfaces. With known nucleant sites, it has been possible to identify specific pathways of metastable phase formation and microstructural development in alloys. These advances have allowed for a clearer assessment of the interplay between undercooling, cooling rate and particle size statistics in structure formation. New approaches to the examination of growth processes have been developed to follow the thermal behavior and morphology in small samples in the period of rapid crystallization and recalescence. Based upon the new experimental information from these studies, useful models can be developed for the overall solidification process to include nucleation behavior, thermodynamic constraints, thermal history, growth kinetics, solute redistribution and resulting structures. From the refinement of knowledge concerning the underlying factors that govern RSP a basis is emerging for an effective alloy design and processing strategy

Solidification mechanism of highly undercooled metal alloys

Experiments were conducted on metal droplet undercooling, using Sn-25wt%Pb and Ni-34wt%Sn alloys. To achieve the high degree of undercooling, emulsification treatments were employed. Results show the fraction of supersaturated primary phase is a function of the amount of undercooling, as is the fineness of the structures. The solidification behavior of the tin-lead droplets during recalescence was analyzed using three different hypotheses; (1) solid forming throughout recalescence is of the maximum thermodynamically stable composition; (2) partitionless solidification below the T sub o temperature, and solid forming thereafter is of the maximum thermodynamically stable composition; and (3) partitionless solidification below the T sub o temperature with solid forming thereafter that is of the maximum thermodynamically metastable composition that is possible. The T sub o temperature is calculated from the equal molar free energies of the liquid solid using the regular solution approximation

Improvement of Production Rate of YBCO Coated Conductors Fabricated by TFA-MOD Method

AbstractThe metal-organic deposition (MOD) method using trifluoroacetate (TFA) salts is considered to be an effective method for inexpensively fabricating YBa2Cu3O7-y (YBCO) coated conductors with high critical current density property. The long-length TFA-MOD YBCO coated conductors have been fabricated by multi-turn reel-to-reel system. Increasing the thickness per single coating in the multi-turn reel-to-reel system is a cost-effective technique for fabrication of the precursor films in the calcination process since it reduces the number of coatings and shortens the processing time. In this work, we have developed a new starting solution consisting of non-fluorine salts of yttrium propionate and copper 2-ethylhexanoate with focusing on increasing the thickness per single coating for a high-rate fabrication of the YBCO coated conductors by the TFA-MOD method. The critical thickness per single coating of the precursor film fabricated from the new starting solution was improved to 0.44μm/coat. Furthermore, the addition of diacetoneacrylamide in the new starting solution increased the critical thickness per single coating to 0.79μm/coat. High critical current of 791 A/cm-width with high critical current density of 2.7 MA/cm2 was obtained using the new starting solution with diacetoneacrylamide at the thickness per single coating of 0.49μm/coat

New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field

The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of a parallel field, a new peak appears at finite frequency in the optical conductivity at the expense of suppression of c-axis condensate weight. We conclude that the dramatic change originates from different Josephson coupling strengths between bilayers with and without Josephson vortices. We find that the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under parallel magnetic field; this indicates that the condensate weight at \omega =0 is distributed to the intra-bilayer mode as well as to the new optical Josephson mode.Comment: 4 pages, 3 figure

Acquisition of loss of the wild-type NRAS locus with aggressive disease progression in a patient with juvenile myelomonocytic leukemia and a heterozygous NRAS mutation

ArticleHAEMATOLOGICA-THE HEMATOLOGY JOURNAL. 92(1-11): 1576-1578 (2007)journal articl

Is the drug-induced hypersensitivity syndrome (DIHS) due to human herpesvirus 6 infection or to allergy-mediated viral reactivation? Report of a case and literature review

<p>Abstract</p> <p>Background</p> <p>Drug-Induced Hypersensitivity Syndrome (DIHS) is a severe and rare systemic reaction triggered by a drug (usually an antiepileptic drug). We present a case of DISH and we review studies on the clinical features and treatment of DIHS, and on its pathogenesis in which two elements (Herpesvirus infection and the drug) interact with the immune system to trigger such a syndrome that can lead to death in about 20% of cases.</p> <p>Case presentation</p> <p>We report the case of a 26-year old woman with fever, systemic maculopapular rash, lymphadenopathy, hepatitis and eosinophilic leukocytosis. She had been treated with antibiotics that gave no benefit. She was taking escitalopram and lamotrigine for a bipolar disease 30 days before fever onset. Because the patient's general condition deteriorated, betamethasone and acyclovir were started. This treatment resulted in a mild improvement of symptoms. Steroids were rapidly tapered and this was followed with a relapse of fever and a worsening of laboratory parameters. Human herpesvirus 6 (HHV-6) DNA was positive as shown by PCR. Drug-Induced Hypersensitivity Syndrome (DIHS) was diagnosed. Symptoms regressed on prednisone (at a dose of 50 mg/die) that was tapered very slowly. The patient recovered completely.</p> <p>Conclusions</p> <p>The search for rare causes of fever led to complete resolution of a very difficult case. As DIHS is a rare disease the most relevant issue is to suspect and include it in differential diagnosis of fevers of unknown origin. Once diagnosed, the therapy is easy (steroidal administration) and often successful. However our case strongly confirms that attention should be paid on the steroidal tapering that should be very slow to avoid a relapse.</p

First isolation of Dysgonomonas mossii from intestinal juice of a patient with pancreatic cancer

ArticleARCHIVES OF MEDICAL RESEARCH. 37(7): 914-916 (2006)journal articl

In-plane thermal conductivity of large single crystals of Sm-substituted (Y1−x_{1-x}Smx_{x})Ba2_{2}Cu3_{3}O7−δ_{7-\delta}

We have investigated the in-plane thermal conductivity $\kappa_{ab}(T,H)$ of large single crystals of optimally oxygen-doped (Y$_{1-x}$,Sm$_{x}$)Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ ($x$=0, 0.1, 0.2 and 1.0) and YBa$_{2}$(Cu$_{1-y}$Zn$_{y}$)$_{3}$O$_{7-\delta}$($y$=0.0071) as functions of temperature and magnetic field (along the c axis). For comparison, the temperature dependence of $\kappa_{ab}$ for as-grown crystals with the corresponding compositions are presented. The nonlinear field dependence of $\kappa_{ab}$ for all crystals was observed at relatively low fields near a half of $T_{c}$. We make fits of the $\kappa(H)$ data to an electron contribution model, providing both the mean free path of quasiparticles $\ell_{0}$ and the electronic thermal conductivity $\kappa_{e}$, in the absence of field. The local lattice distortion due to the Sm substitution for Y suppresses both the phonon and electron contributions. On the other hand, the light Zn doping into the CuO $_{2}$ planes affects solely the electron component below $T_{c}$, resulting in a substantial decrease in $\ell_{0}$ .Comment: 7 pages,4 figures,1 tabl