Substitution effects on the temperature vs. magnetic-field phase diagrams of the quasi-1D effective Ising spin-1/2 chain system BaCo2_2V2_2O8_8

BaCo$_2$V$_2$O$_8$ is a one-dimensional antiferromagnetic spin-1/2 chain system with pronounced Ising anisotropy of the magnetic exchange. Due to finite interchain interactions long-range antiferromagnetic order develops below $T_{\rm N} \simeq 5.5$ K, which is accompanied by a structural distortion in order to lift magnetic frustration effects. The corresponding temperature $vs.$ magnetic-field phase diagram is highly anisotropic with respect to the magnetic-field direction and various details are still under vivid discussion. Here, we report the influence of several substitutions on the magnetic properties and the phase diagrams of BaCo$_2$V$_2$O$_8$. We investigate the substitution series Ba$_{\text{1-x}}$Sr$_{\text{x}}$Co$_{\text{2}}$V$_{\text{2}}$O$_{\text{8}}$ over the full range $0\le x \le 1$ as well as the influence of a partial substitution of the magnetic Co$^{2+}$ by small amounts of other magnetic transition metals or by non-magnetic magnesium. In all cases, the phase diagrams were obtained on single crystals from magnetization data and/or high-resolution studies of the thermal expansion and magnetostriction.Comment: 10 pages, 10 figure

Country clustering in comparative political economy

"In the comparative political economy of rich democracies there is a long tradition of classifying countries into one of a small number of categories based on their economic institutions and policies. The most recent of these is the Varieties of Capitalism project, which posits two major clusters of nations: coordinated and liberal market economies. This classification has generated controversy. We leverage recent advances in mixture model-based clustering to see what the data say on the matter. We find that there is considerable uncertainty around the number of clusters and, barring a few cases, which country should be placed in which cluster. Moreover, when viewed over time, both the number of clusters and country membership change considerably. As a result, arguments about who has the 'right' typology are misplaced. We urge caution in using these country classifications in structuring qualitative inquiry and discourage their usage as indicator variables in quantitative analysis, especially in the context of time-series cross-section data. We argue that the real value of both Esping-Andersen's work and the Varieties of Capitalism project consists of their theoretical contributions and heuristic classification of ideal types." (author's abstract)"In der vergleichenden Politischen Ökonomie reicher Demokratien gibt es eine lange Tradition, Länder aufgrund ihrer unterschiedlichen wirtschaftlichen Institutionen und Policies zu typologisieren. Die jüngste dieser Typologien - das 'Varieties-of-Capitalism'-Konzept - erfasst zwei Gruppen von Ländern: koordinierte und liberale Marktwirtschaften. Da diese Klassifizierung einige Kontroversen hervorgerufen hat, nutzen die Autoren neueste Fortschritte im 'mixture model-based clustering', um zu prüfen, welche Erkenntnisse die Daten zu diesem Problem liefern. Die Ergebnisse weisen eine beträchtliche Unsicherheit hinsichtlich der Anzahl der Cluster und, mit wenigen Ausnahmen, der Zuordnung der Länder zu Clustern auf. Betrachtet man größere Zeiträume, variieren darüber hinaus die Anzahl der Cluster und Ländermitgliedschaften erheblich. Als Folge dieser Befunde halten die Autoren Argumentationen über die 'richtige' Typologisierung für unangebracht und raten davon ab, diese Länderklassifizierungen zur Strukturierung qualitativer Studien heranzuziehen oder als Indikatorvariablen in quantitativen Analysen zu nutzen. Dies gilt insbesondere im Kontext von gepoolten Zeitreihen- und Querschnittsdaten. Sie argumentieren, dass der substanzielle Wert sowohl der Forschung von Esping-Andersen als auch des 'Varieties-of-Capitalism'-Ansatzes in den Beiträgen zur Theorie und den heuristischen Klassifizierungen von Idealtypen besteht." (Autorenreferat

Close the Deal and Deliver the System: Sales Training for IS Developers

The communication gap between IS developers and end users poses a key problem in IS development efforts. While a variety of tactics have been suggested to bring developers and users together to enhance communication and create a positive impact on system development efforts, the gap still remains. This paper proposes the implementation of an IS developer training program based on the fundamental principles of sales and sales training programs. The sales model is compared to models of change which closely represent the IS implementation process. Parallels are drawn between the roles of the IS developer and the sales agent, and the roles of the user and the sales customer. The sales training program is adapted to the environment of the IS developer, and recommendations are offered for the implementation of the program. Potential impacts of the training program for IS development efforts are also discussed

Sense of Community on Integrated Wilderness Trips: A Pilot Study

The purpose of this study was to examine sense of community on integrated wilderness trips. First, differences in perceived sense of community and perceived sense of group cohesion were analyzed from the viewpoint of the group as a whole to determine if there was any significant change over the course of a wilderness trip. Second, differences, if any, in perceived sense of community and perceived sense of group cohesion between people with disabilities and people without disabilities were determined

Production of Radiobromide: new Nickel Selenide target and optimized separation by dry distillation

Introduction Radioisotopes of bromine are of special interest for nuclear medical applications. The positron emitting isotopes 75Br (T½ = 1.6 h; β+ = 75.5 %) and 76Br (T½ = 16.2 h; β+ = 57 %) have suitable decay properties for molecular imaging with PET, while the Auger electron emitters 77Br (T½ = 57.0 h) and 80mBr (T½ = 4.4 h) as well as the β−-emitter 82Br (T½ = 35.3 h) are useful for internal radiotherapy. 77Br is additionally suited for SPECT. The isotopes 75Br, 76Br and 77Br are usually produced at a cyclotron either by 3He and α-particle induced reactions on natural arsenic or by proton and deuteron induced reactions on enriched selenium isotopes [1]. As target mate-rials for the latter two reactions, earlier ele-mental selenium [2] and selenides of Cu, Ag, Mn, Mo, Cr, Ti, Pb and Sn were investigated [cf. 3–7]. Besides several wet chemical separation techniques the dry distillation of bromine from the irradiated targets was investigated, too [cf. 2, 4, 5]. However, the method needs further development. Nickel selenide was investigated as a promising target to withstand high beam currents, and the dry distillation technique for the isolation of n.c.a. radiobromine from the target was optimized. Material and Methods Crystalline Nickel-(II) selenide (0.3–0.5 g) was melted into a 0.5 mm deep cavity of a 1 mm thick Ni plate covered with a Ni grid. NiSe has a melting point of 959 °C. For development of targeting and the chemical separation, natural target material was used. Irradiations of NiSe were usually performed with protons of 17 MeV using a slanting water cooled target holder at the cyclotron BC1710 [8]. For radiochemical studies a beam current of 3 µA and a beam time of about 1 h were appropriate. To separate the produced no-carrier-added (n.c.a.) radiobromine from the target material a dry distillation method was chosen. The apparatus was developed on the basis of a dry distillation method for iodine [cf. 9,10] and optimized to obtain the bromine as n.c.a. [*Br]bromide in a small volume of sodium hydroxide solution. Changing different components of the apparatus, the dead volume could be minimized and an almost constant argon flow as carrier medium was realized. Various capillaries of platinum, stainless steel and quartz glass with different diameters and lengths were tested to trap the radiobromine. Results and Conclusion Nickel selenide proved successful as target material for the production of radiobromine by proton irradiation with 17 MeV protons. The target was tested so far only at beam currents up to 10 µA, but further investigations are ongoing. The optimized dry distillation procedure allows trapping of 80–90 % of the produced radiobromine in a capillary. For this purpose quartz glass capillaries proved to be most suitable. After rinsing the capillary with 0.1 M NaOH solution the activity can be nearly completely obtained in less than 100 µL solution as [*Br]bromide immediately useable for radiosynthesis. So, the overall separation yield was estimated to 81 ± 5 %. The radionuclidic composition and activity of the separated radiobromide was measured by γ-ray spectrometry. Due to the use of natural selenium the determination of the isotopic purity was not meaningful, but it could be shown that the radiobromine was free from other radioisotopes co-produced in the target material and the backing. The radiochemical purity as well as the specific activity were determined by radio ionchromatography. Further experiments using NiSe produced from nickel and enriched selenium are to be per-formed. The isotopic purity of the produced respective radiobromide, the production yield at high beam currents and the reusability of the target material have to be studied

Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field

We report on magnetization, sound velocity, and magnetocaloric-effect measurements of the Ising-like spin-1/2 antiferromagnetic chain system BaCo$_2$V$_2$O$_8$ as a function of temperature down to 1.3 K and applied transverse magnetic field up to 60 T. While across the N\'{e}el temperature of $T_N\sim5$ K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity $v(B)$ and a clear minimum of temperature $T(B)$ at $B^{c,3D}_\perp=21.4$ T, indicating the suppression of the antiferromagnetic order. At higher fields, the $T(B)$ curve shows a broad minimum at $B^c_\perp = 40$ T, accompanied by a broad minimum in the sound velocity and a saturation-like magnetization. These features signal a quantum phase transition which is further characterized by the divergent behavior of the Gr\"{u}neisen parameter $\Gamma_B \propto (B-B^{c}_\perp)^{-1}$. By contrast, around the critical field, the Gr\"{u}neisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.Comment: Phys. Rev. Lett., to appea