Suppression of spin-density-wave transition and emergence of ferromagnetic ordering of Eu2+^{2+} moments in EuFe2−x_{2-x}Nix_{x}As2_{2}

We present a systematic study on the physical properties of EuFe$_{2-x}$Ni$_{x}$As$_{2}$ (0$\leq$\emph{x}$\leq$0.2) by electrical resistivity, magnetic susceptibility and thermopower measurements. The undoped compound EuFe$_{2}$As$_{2}$ undergoes a spin-density-wave (SDW) transition associated with Fe moments at 195 K, followed by antiferromagnetic (AFM) ordering of Eu$^{2+}$ moments at 20 K. Ni doping at the Fe site simultaneously suppresses the SDW transition and AFM ordering of Eu$^{2+}$ moments. For $x\geq$0.06, the magnetic ordering of Eu$^{2+}$ moments evolves from antiferromagnetic to ferromagnetic (FM). The SDW transition is completely suppressed for $x\geq$0.16, however, no superconducting transition was observed down to 2 K. The possible origins of the AFM-to-FM transition and the absence of superconductivity in EuFe$_{2-x}$Ni$_{x}$As$_{2}$ system are discussed.Comment: 5 pages, 5 figures, accepted for publication in PR

Superconductivity in SrNi2As2 Single Crystals

The electrical resistivity \rho(T) and heat capacity C(T) on single crystals of SrNi2As2 and EuNi2As2 are reported. While there is no evidence for a structural transition in either compound, SrNi2As2 is found to be a bulk superconductor at T_c=0.62 K with a Sommerfeld coefficient of \gamma= 8.7 mJ/mol K^2 and a small upper critical field H_{c2} \sim 200 Oe. No superconductivity was found in EuNi2As2 above 0.4 K, but anomalies in \rho and C reveal that magnetic order associated with the Eu^{2+} magnetic moments occurs at T_m = 14 K.Comment: 8 pages, 5 figure

Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2

The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase transition at 140 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (I4/mmm) to orthorhombic (Fmmm). 57Fe Moessbauer spectroscopy experiments show a single signal at room temperature and full hyperfine field splitting below the phase transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can serve as a new parent compound for oxygen-free iron arsenide superconductors.Comment: 4 pages, 6 figures, submitted to PR

PNR in 2011: Recalling Ten Years of Transatlantic Cooperation in PNR Information

In Fall 2011, U.S. and EU negotiators agreed on new parameters for the collection, processing, use, storage and crossborder transfer of Passenger Name Record (PNR) data. 2011 also marks the tenth anniversary of the September 11, 2001 terrorist attacks on the World Trade Center in New York City and the Pentagon in Washington D.C., which provides the historic reason for the cooperation in this area. These two events thus provide a timely basis and background against which to review the ten year history of the cooperation between the U.S. and the EU in PNR information management. This article maps the evolution of collaboration between the U.S. and the EU with respect to the PNR program by presenting the major dimensions involved. Moreover, it provides a comprehensive framework with a particular focus on the constant struggle for a consistent EU policy as well as the creation of the U.S.-EU Agreements in 2004 and 2007. It furthermore sketches major legal and political developments that have most likely had a significant impact on the negotiations and are, as a consequence, reflected in the concrete design of the new PNR Agreement. All this leads the author to the conclusion that—as thoroughly as it may have been designed and as complete as it may seem—the new PNR Agreement will not be the end of the transatlantic PNR saga, but rather the beginning of another intriguing chapter

PNR in 2011: Recalling Ten Years of Transatlantic Cooperation in PNR Information

In Fall 2011, U.S. and EU negotiators agreed on new parameters for the collection, processing, use, storage and crossborder transfer of Passenger Name Record (PNR) data. 2011 also marks the tenth anniversary of the September 11, 2001 terrorist attacks on the World Trade Center in New York City and the Pentagon in Washington D.C., which provides the historic reason for the cooperation in this area. These two events thus provide a timely basis and background against which to review the ten year history of the cooperation between the U.S. and the EU in PNR information management. This article maps the evolution of collaboration between the U.S. and the EU with respect to the PNR program by presenting the major dimensions involved. Moreover, it provides a comprehensive framework with a particular focus on the constant struggle for a consistent EU policy as well as the creation of the U.S.-EU Agreements in 2004 and 2007. It furthermore sketches major legal and political developments that have most likely had a significant impact on the negotiations and are, as a consequence, reflected in the concrete design of the new PNR Agreement. All this leads the author to the conclusion that—as thoroughly as it may have been designed and as complete as it may seem—the new PNR Agreement will not be the end of the transatlantic PNR saga, but rather the beginning of another intriguing chapter

Non-invasive quantification of exercise-induced changes in regional left ventricular function in normals and patients with one vessel coronary artery disease using radionuclide ventriculography

To quantitate changes in regional left ventricular function induced by ischemia or scar, rest and exercise equilibrium radionuclide studies of 26 patients with one vessel coronary artery disease and 12 normal individuals were analysed with a new method for regional ejection fraction determination. A computer algorithm provided observer-independent segmental analysis from a centre of gravity of the left ventricular activity at end-diastole (left anterior oblique projection). Special segments were assigned for anteroseptal, inferoapical and posterolateral areas corresponding to the three main coronary arteries. Reproducibility using an unchanged camera positioning was excellent even for 2 min acquisition studies (r=0.93) and still good after repositioning (r=0.80 to 0.87). In normal areas, regional ejection fraction increased or showed no change during exercise. In contrast, it decreased significantly in regions supplied by stenosed coronary arteries (ischemia) and remained depressed in scar zones. The method proved to be valid for regional changes induced by left anterior descending and left circumflex coronary obstructions, but less for right coronary artery lesions. Global ejection fraction reflected a sum of all regional changes implying that regional analysis should be more sensitive in detecting coronary artery diseas

Pressure induced superconductivity in CaFe2_2As2_2

CaFe$_2$As$_2$ has been found to be exceptionally sensitive to the application of hydrostatic pressure and superconductivity has been found to exist in a narrow pressure region that appears to be at the interface between two different phase transitions. The pressure - temperature ($P - T$) phase diagram of CaFe$_2$As$_2$ reveals that this stoichiometric, highly ordered, compound can be easily tuned to reveal all the salient features associated with FeAs-based superconductivity without introducing any disorder. Whereas at ambient pressure CaFe$_2$As$_2$ does not superconduct for $T > 1.8$ K and manifests a first order structural phase transition near $T \approx 170$ K, the application of $\sim 5$ kbar hydrostatic pressure fully suppresses the resistive signature of the structural phase transition and instead superconductivity is detected for $T < 12$ K. For $P \ge 5.5$ kbar a different transition is detected, one associated with a clear reduction in resistivity and for $P > 8.6$ kbar superconductivity is no longer detected. This higher pressure transition temperature increases rapidly with increasing pressure, exceeding 300 K by $P \sim 17$ kbar. The low temperature, superconducting dome is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity, and possibly the associated fluctuations, too dramatically

Strong coupling between Eu2+ spins and Fe2As2 layers in EuFe1.9Co0.1As2 observed with NMR

A combination of x-ray diffraction, magnetization, and 75As nuclear magnetic resonance (NMR) experiments were performed on single-crystal EuFe1.9Co0.1As2. The strength of the hyperfine interaction between the 75As nuclei and the Eu^(2+) 4f states suggests a strong coupling between the Eu^(2+) moments and the Fe1.9Co0.1As2 layers. Such a strong interlayer coupling may be due to an indirect exchange interaction between the localized Eu^(2+) 4f moments, mediated by the Fe 3d conduction electrons. Magnetic susceptibility as well as 75As-NMR measurements reveal a decrease of the SDW transition temperature to T_SDW = 120 K as a result of Co doping. A change of the slope in the temperature dependence of the NMR frequency of the 75As lower-satellite line was observed at 225 K. At the same temperature also a change of the satellite line shape was found. These changes of the NMR spectra may be caused by the formation of a nematic phase below 225 K in EuFe1.9Co0.1As2.Comment: 8 pages, 7 figure

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

Prolonged myocardial stunning after thrombolysis: can left ventricular function be assessed definitely at hospital discharge?

To assess whether myocardial dysfunction after acute reperfusion (‘stunning') may show delayed recovery, 33 patients of the European Cooperative Study (rtPA vs placebo) had radionuclide angiocardiography on day 9 and after 3-6 months. Sixteen patients (13 inferior, three anterior infarcts) had a normal left ventricular ejection fraction (LVEF) which remained unchanged (55.4 vs 53.9%). In contrast, LVEF of 17 patients (10 inferior, seven anterior infarcts) with depressed values on day 9 improved during follow-up from 38.8 to 45.2% (P<0.01). Improvement was only observed in patients with early reperfusion defined a priori as peak creatine kinase valuè ≤ 15 h of pain onset (from 40.9 to 49.3%; P<0.05) in contrast to patients without reperfusion (from 34.0 to 35.2%; ns). Accordingly, LVEF increased in patients with open infarct-related arteries at hospital discharge (n = 8; P = 0.053) but not with persistent occlusion (n = 7; P = 0.11). Thus, a depressed LVEF observed 9 days after reperfusion may show delayed recovery due to prolonged stunning. Therefore, after thrombolysis, left ventricular function may not be evaluated definitively at hospital discharge; results of such studies should be interpreted with cautio