Suzaku study of gas properties along filaments of A2744

Context: We present the results of Suzaku observations of a massive galaxy cluster A2744, which is an active merger at $z=0.308$. Aims: By using long X-ray observations of A2744, we aim to understand the growth of the cluster and the gas heating process through mass accretion along the surrounding filaments. Methods: We analyzed data from two-pointed Suzaku observations of A2744 to derive the temperature distribution out to the virial radius in three different directions. We also performed a deprojection analysis to study radial profiles of gas temperature, density, and entropy and compared the X-ray results with multi-wavelength data to investigate correlations with the surface density of galaxies and with radio relics. Results: The gas temperature was measured out to the virial radius $r_{200}$ in the north-east region and to about $1.5r_{200}$ in the north-west and south regions. The radial profile of the gas temperature is rather flat and the temperature is very high (even near $r_{200}$); it is comparable to the mean temperature of this cluster ($kT=9$ keV). These characteristics have not been reported in any other cluster. We find a hint of temperature jump in the northeast region whose location coincides with a large radio relic, indicating that the cluster experienced gas heating because of merger or mass accretion onto the main cluster. The temperature distribution is anisotropic and shows no clear positive correlation with the galaxy density, which suggests an inhomogeneous mass structure and a complex merger history in A2744.Comment: 8 pages, 8 figures, A&A accepte

ISTIHSAN (Telaah Sosiologi-Kultural Pemikiran Imam Hanafi)

Tulisan ini adalah upaya untuk mengeksplorasi pemikiran fikih Abu Hanifah dengan menggunakan kacamata sosiologis. Pemikiran seorang tokoh tidak lahir dengan sendirinya, tanpa peran serta kondisi social, politik dan budaya yang berkembang pada masa tokoh pemikir tersebut hidup. Karenanya, pemikiran Abu Hanifah tentang Istihsan juga tidak bisa dilepaskan dari kondisi dan struktur masyarakat Kufah, sebagai basis dan tempat tinggal Imam Abu Hanifa

On the spectroscopy of quantum dots in microcavities

At the occasion of the OECS conference in Madrid, we give a succinct account of some recent predictions in the spectroscopy of a quantum dot in a microcavity that remain to be observed experimentally, sometimes within the reach of the current state of the art.Comment: OECS11 Conference proceedings, in editor style. 4 pages, 1 figure. Animations provided separatel

Voltage-controlled Group Velocity of Edge Magnetoplasmon in the Quantum Hall Regime

We investigate the group velocity of edge magnetoplasmons (EMPs) in the quantum Hall regime by means of time-of-flight measurement. The EMPs are injected from an Ohmic contact by applying a voltage pulse, and detected at a quantum point contact by applying another voltage pulse to its gate. We find that the group velocity of the EMPs traveling along the edge channel defined by a metallic gate electrode strongly depends on the voltage applied to the gate. The observed variation of the velocity can be understood to reflect the degree of screening caused by the metallic gate, which damps the in-plane electric field and hence reduces the velocity. The degree of screening can be controlled by changing the distance between the gate and the edge channel with the gate voltage.Comment: 5 pages, 6 figures, to be published in Physical Review

X-Ray Study of the Outer Region of Abell 2142 with Suzaku

We observed outer regions of a bright cluster of galaxies A2142 with Suzaku. Temperature and brightness structures were measured out to the virial radius ($r_{200}$) with good sensitivity. We confirmed the temperature drop from 9 keV around the cluster center to about 3.5 keV at $r_{200}$, with the density profile well approximated by the $\beta$ model with $\beta = 0.85$. Within 0.4\r_{200}, the entropy profile agrees with $r^{1.1}$, as predicted by the accretion shock model. The entropy slope becomes flatter in the outer region and negative around $r_{200}$. These features suggest that the intracluster medium in the outer region is out of thermal equilibrium. Since the relaxation timescale of electron-ion Coulomb collision is expected to be longer than the elapsed time after shock heating at $r_{200}$, one plausible reason of the low entropy is the low electron temperature compared to that of ions. Other possible explanations would be gas clumpiness, turbulence and bulk motions of ICM\@. We also searched for a warm-hot intergalactic medium around $r_{200}$ and set an upper limit on the oxygen line intensity. Assuming a line-of-sight depth of 2 Mpc and oxygen abundance of 0.1 solar, the upper limit of an overdensity is calculated to be 280 or 380, depending on the foreground assumption.Comment: 14 pages, 8 figure

Synthesis, Characterization and Application of intermetallic Pd-X (Ga, Zn) Nanoparticles derived from ternary Hydrotalcite-like precursors

A novel, feasible synthesis approach for supported intermetallic Pd2Ga and PdZn nanoparticles derived from Hydrotalcite-like compounds (HTlc) is introduced. Ternary HTlc with the nominal composition (Pd2+,M2+)0.70(M3+)0.30(OH)2(CO3)0.15 ∙ m H2O are synthesized by pH-controlled co-precipitation. Mg2+/Ga3+ and Zn2+/Al3+ are chosen as M2+/M3+ combinations to permit formation of the nanocrystalline Pd2Ga and PdZn intermetallic compounds on a porous MgO/MgGa2O4 and ZnO/ZnAl2O4 support, respectively. In addition, a PdMgAl HTlc is prepared as monometallic Pd reference compound on a MgO/MgAl2O4 support. Incorporation of Pd2+ into the HT structure requires octahedral coordination, while Pd2+ ions prefer square planar coordination in aqueous solution. At the same substitution degree of M2+ by Pd2+, complete insertion is achieved for PdZnAl HT. In case of PdMgGa and PdMgAl HT a minor fraction is present as segregated Pd2+ on the external surface of the platelet-like particles with a local environment similar to PdO, i.e. in a square planar coordination. A limit of incorporation into the HT lattice exists at < 1 mol% for the Pd2+ containing precursors. Upon thermal decomposition in reductive atmosphere, intermetallic and metallic nanoparticles ranging from below 2 nm to 6 nm in size and exhibiting monomodal particle size distributions are formed. Alloying of Pd with Ga and Zn changes the crystal structure as well as the electronic structure and leads to the increased formation of isolated adsorption sites at the surface. Furthermore, dynamic surface changes of intermetallic Pd2Ga nanoparticles were noticed at longer exposure time to CO and higher CO coverage. This is attributed to the decomposition into metallic Pd and Ga2O3. The nanostructured Pd2Ga catalyst shows excellent performance in the selective semi-hydrogenation of acetylene similar to a bulk Pd2Ga model catalyst. In comparison to the elemental Pd catalyst the selectivity to ethylene is drastically improved by formation of Pd2Ga. Interestingly, the nanostructered catalyst slowly activates in the feed gas. The activation is triggered faster by a treatment in oxidative atmosphere. These dynamics of the Pd2Ga nanoparticles can be explained by the interplay of surface decomposition into Pd0 and Ga2O3 in oxygen and reversal of the strong-metal support interaction state leading to an increased activity. Furthermore, increased activities and selectivities in methanol steam reforming and methanol synthesis from CO2 are observed for the Pd2Ga and PdZn nanoparticles in contrast to the unmodified Pd particles. These structurally modified Pd catalysts exhibit a considerably lower selectivity to CO and enhanced formation of methanol compared to the monometallic Pd catalyst.Abstract i Zusammenfassung iii Danksagung v List of Figures x List of Tables xiv List of Abbreviations xv Chapter 1: Introduction and Overview 1 1.1. Intermetallic compounds 1 1.2. Motivation 2 1.3. Synthesis strategy for binary Pd-X intermetallic nanoparticles 3 1.4. Pd-Ga system 6 1.5. The Pd-Ga intermetallic compound Pd2Ga 7 1.6. Pd-Zn phase system 9 1.7. Pd-Ga IMCs as selective acetylene hydrogenation catalysts 10 1.8. Pd based IMCs in methanol synthesis and methanol steam reforming 13 1.9. Aims of this work and thesis structure 15 1.10. References 17 Chapter 2: Intermetallic Compound Pd2Ga as a Selective Catalyst for the Semi-Hydrogenation of Acetylene: From Model to High performance Catalyst 21 2.1 Introduction 22 2.2 Experimental Section 24 2.2.1 Synthesis Procedures 24 2.2.2 Characterization Techniques 24 2.2.3 Catalytic Measurements 25 2.3 Results and Discussion 27 2.4 Conclusion 34 2.5 References 36 Chapter 3: Dynamic Surface Processes of nanostructured Pd2Ga catalysts derived from ternary Hydrotalcite-like Precursors 38 3.1 Introduction 39 3.2 Experimental 40 3.2.1 Synthesis conditions 40 3.2.2 Characterization 41 3.2.3 Catalytic performance in the selective hydrogenation of acetylene 43 3.3 Results and Discussion 44 3.3.1 Structural and textural properties of the precursor material 44 3.3.2 Reduction and intermetallic phase formation 49 3.3.3 Structural properties of Pd2Ga nanoparticles 54 3.3.4 IR characterization of supported Pd2Ga nanoparticles during exposure to CO 58 3.3.5 Catalytic performance 62 3.4 Conclusions 69 3.5 References 71 Supplementary Information 73 Chapter 4: Methanol Synthesis and Methanol Steam Reforming of Supported Pd2Ga and PdZn Intermetallic Nanoparticles 79 4.1. Introduction 80 4.2 Experimental 81 4.2.1 Synthesis conditions 81 4.2.2 Characterization 82 4.2.3 Catalytic performance 84 4.2.3.1 Methanol synthesis from CO2 84 4.2.3.2 Methanol steam reforming 85 4.3 Results and discussion 86 4.3.1 Properties of the HTlc precursors 86 4.3.2 Reducibility of the HTlc precursors and IMC formation 88 4.3.2.1 TPR and MS measurements 88 4.3.2.2 XANES measurements 91 4.3.3 Properties of the ex-HTlc samples after reduction 93 4.4 Catalytic properties of the IMCs 97 4.4.1 Methanol synthesis from CO2 97 4.4.2 Steam reforming of methanol 100 4.5 Conclusion 102 4.6 References 103 Supplementary Information 105 Chapter 5: Final summary and conclusion 108 Appendix xvii Curriculum vitae xvii Publications xvii Oral presentations xviii Patent application xviii Poster presentations xi

Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures

We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with only two or three IJJs and the other is a stack of a few hundreds of IJJs on a narrow bridge structure. Experimental results of switching current distribution for the first switching events from zero-voltage state showed a good agreement with the conventional theory for a single Josephson junction, indicating that a crossover temperature from thermal activation to MQT regime for the former device structure was as high as that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high-$T_c$ cuprates, independent of device structures. The switching current distribution for the second switching events from the first resistive state, which were carefully distinguished from the first switchings, was also compared between two device structures. In spite of the difference in the heat transfer environment, the second switching events for both devices were found to show a similar temperature-independent behavior up to a much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of the self-heating owing to dissipative currents after the first switching. As possible candidates, the MQT process for the second switching and the effective increase of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.