Spin excitations in a 4f-3d heterodimer on MgO

We report on the magnetic properties of HoCo dimers as a model system for the smallest intermetallic transition metal-lanthanide compound. The dimers are adsorbed on ultrathin MgO(100) films grown on Ag(100). New for $4f$ elements, we detect inelastic excitations with scanning tunneling microscopy and prove by their behaviour in applied magnetic field that they are spin-excitations. In combination with density functional theory and spin Hamiltonian analysis we determine the magnetic level distribution, as well as sign and magnitude of the exchange interaction between the two atoms. In contrast to typical $4f-3d$ bulk compounds, we find ferromagnetic coupling in the dimer

Quantifying residual hydrogen adsorption in low-temperature STMs

We report on low-temperature scanning tunneling microscopy observations demonstrating that individual Ti atoms on hexagonal boron nitride dissociate and adsorb hydrogen without measurable reaction barrier. The clean and hydrogenated states of the adatoms are clearly discerned by their apparent height and their differential conductance revealing the Kondo effect upon hydrogenation. Measurements at 50 K and 5 × 10−11 mbar indicate a sizable hydrogenation within only 1 h originating from the residual gas pressure, whereas measurements at 4.7 K can be carried out for days without H2 contamination problems. However, heating up a low-T STMto operate it at variable temperature results in very sudden hydrogenation at around 17 K that correlates with a sharp peak in the total chamber pressure. From a quantitative analysis we derive the desorption energies of H2 on the cryostat walls. We find evidence for hydrogen contamination also during Ti evaporation and propose a strategy on how to dose transition metal atoms in the cleanliest fashion. The present contribution raises awareness of hydrogenation under seemingly ideal ultra-high vacuum conditions, it quantifies the H2 uptake by isolated transition metal atoms and its thermal desorption from the gold plated cryostat walls

First operation and performance of a 200 lt double phase LAr LEM-TPC with a 40x76 cm^2 readout

In this paper we describe the design, construction, and operation of a first large area double-phase liquid argon Large Electron Multiplier Time Projection Chamber (LAr LEM-TPC). The detector has a maximum drift length of 60 cm and the readout consists of a $40\times 76$ cm$^2$ LEM and 2D projective anode to multiply and collect drifting charges. Scintillation light is detected by means of cryogenic PMTs positioned below the cathode. To record both charge and light signals, we have developed a compact acquisition system, which is scalable up to ton-scale detectors with thousands of charge readout channels. The acquisition system, as well as the design and the performance of custom-made charge sensitive preamplifiers, are described. The complete experimental setup has been operated for a first time during a period of four weeks at CERN in the cryostat of the ArDM experiment, which was equipped with liquid and gas argon purification systems. The detector, exposed to cosmic rays, recorded events with a single-channel signal-to-noise ratio in excess of 30 for minimum ionising particles. Cosmic muon tracks and their $\delta$-rays were used to assess the performance of the detector, and to estimate the liquid argon purity and the gain at different amplification fields.Comment: 23 pages, 21 figure

Intra-arterial vasodilators infusion for management of reversible cerebral vasoconstriction syndrome in a 12-year-old girl: A case report.

Reversible cerebral vasoconstriction syndrome (RCVS) is a vascular disease characterized by diffuse transient vasoconstriction and vasodilatation of the cerebral arteries. It is commonly associated with recurrent severe acute headaches with or without focal neurological deficits due to hemorrhages, infarcts, and even posterior reversible encephalopathy syndrome. The optimal management of acute neurologic deficits caused by RCVS is still uncertain. Calcium channel blockers (CCBs) such as nimodipine or verapamil have been reported to be effective in adult series. Intra-arterial injection of nimodipine, verapamil, and milrinone has recently been demonstrated to be safe and effective for treating severe segmental vasoconstriction in adults. CCBs are the most used treatment in the available pediatric literature. Intra-arterial vasodilators have been reported in some rare pediatric reports with more severe diseases, but their utility is still under investigation. We report a case of a 12-year-old girl who underwent a severe course of RCVS complicated by multiple cerebral infarcts, treated by several sessions of intra-arterial vasodilators infusion

Giant Liquid Argon Observatory for Proton Decay, Neutrino Astrophysics and CP-violation in the Lepton Sector (GLACIER)

GLACIER (Giant Liquid Argon Charge Imaging ExpeRiment) is a large underground observatory for proton decay search, neutrino astrophysics and CP-violation studies in the lepton sector. Possible underground sites are studied within the FP7 LAGUNA project (Europe) and along the JPARC neutrino beam in collaboration with KEK (Japan). The concept is scalable to very large masses.Comment: 4 pages, 1 figure, Contribution to the Workshop "European Strategy for Future Neutrino Physics", CERN, Oct. 200

Stable operation with gain of a double phase Liquid Argon LEM-TPC with a 1 mm thick segmented LEM

In this paper we present results from a test of a small Liquid Argon Large Electron Multiplier Time Projection Chamber (LAr LEM-TPC). This detector concept provides a 3D-tracking and calorimetric device capable of charge amplification, suited for next-generation neutrino detectors and possibly direct Dark Matter searches. During a test of a 3~lt chamber equipped with a 10$\times$10~cm$^2$ readout, cosmic muon data was recorded during three weeks of data taking. A maximum gain of 6.5 was achieved and the liquid argon was kept pure enough to ensure 20~cm drift (O(ppb)~O$_2$ equivalent).Comment: 7 pages, 6 figures, to appear in Proc. of 1st International Workshop towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba (Japan), March 201

Thermoacoustic tomography with detectors on an open curve: an efficient reconstruction algorithm

Practical applications of thermoacoustic tomography require numerical inversion of the spherical mean Radon transform with the centers of integration spheres occupying an open surface. Solution of this problem is needed (both in 2-D and 3-D) because frequently the region of interest cannot be completely surrounded by the detectors, as it happens, for example, in breast imaging. We present an efficient numerical algorithm for solving this problem in 2-D (similar methods are applicable in the 3-D case). Our method is based on the numerical approximation of plane waves by certain single layer potentials related to the acquisition geometry. After the densities of these potentials have been precomputed, each subsequent image reconstruction has the complexity of the regular filtration backprojection algorithm for the classical Radon transform. The peformance of the method is demonstrated in several numerical examples: one can see that the algorithm produces very accurate reconstructions if the data are accurate and sufficiently well sampled, on the other hand, it is sufficiently stable with respect to noise in the data

On the injectivity of the circular Radon transform arising in thermoacoustic tomography

The circular Radon transform integrates a function over the set of all spheres with a given set of centers. The problem of injectivity of this transform (as well as inversion formulas, range descriptions, etc.) arises in many fields from approximation theory to integral geometry, to inverse problems for PDEs, and recently to newly developing types of tomography. The article discusses known and provides new results that one can obtain by methods that essentially involve only the finite speed of propagation and domain dependence for the wave equation.Comment: To appear in Inverse Problem