Recurrent Variational Approach to the Two-Leg Hubbard Ladder

We applied the Recurrent Variational Approach to the two-leg Hubbard ladder. At half-filling, our variational Ansatz was a generalization of the resonating valence bond state. At finite doping, hole pairs were allowed to move in the resonating valence bond background. The results obtained by the Recurrent Variational Approach were compared with results from Density Matrix Renormalization Group.Comment: 10 pages, 14 Postscript figure

Activation and deactivation behavior of heteropoly acids as catalyst precursors

Activation and deactivation behavior of heteropoly acids as catalyst precursors O.Timpe, H. Noack, und G. Mestl§ Fitz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin Heteropoly acids (HPA) are important catalysts for selective partial oxidations due to their acid and redox active properties. Thee Keggin-type phosphorus molybdo acid H4[PMo12O40] is the basis for an industrially used catalyst in the methacrylic acid synthesis which contains vanadium too. The protons of the free HPA are partially exchanged by Cs+ ions. The insufficient stability of this class of substances does not allow their optimum use as catalysts. A continuous degradation of their catalytic properties and thus of the possible yields is observed under stationary reaction conditions. Due to their characteristic instability, it is unlikely that intact HPA´s are the active catalysts, although frequently stated in the literature. This correlates with the fact that the HPA has to be activated in the industrial application prior to the actual catalysis. The structural and chemical properties of the precursor-HPA are well characterized, correlate however only indirectly with the catalytic data. The oxides of the constituting transition metals are the final state of the HPA-decomposition, whose stoichiometry or degree of oxidation is determined by the surrounding atmosphere. The reaction pathway to these final decomposition products can be understood as a condensation process followed by complete structural reorganization. The loss of water occurs in two steps. The irreversible loss of structural water at elevated temperatures follows after the reversible loss of crystal water at temperatures below 400K. Oxygen defects are introduced into the Keggin anions with the loss of structural water. These defects are presumably the reason for the low reaction barriers of the subsequent structural reorganization of the defective Keggin anions. It could be shown by comparing thermogravimetric measurements of different molybdenum HPA, containing P as well as Si as the hetero atom, in different atmospheres that the reduction of the HPA occurs only after the loss of structural water. This reduction is the consequence of the loss of structural water because these HPA systems do not have a stability plateau after this step of water removal. Under oxidative conditions, the formation of MoO3 is observed after this step of loss of water. The comparison of HPA´s reveals a continuous mass loss of the P-containing samples after the loss of structural water under isothermal conditions in hydrogen atmosphere, which is qualitatively identified as the loss of P in form of reduced P-compounds, e.g. PH3. Directly after this mass loss, the TG curves show a step which is attributed to the reduction of the transition metal ions. The incorporation of V into the Keggin leads to an enhanced destabilizing effect in case of Si-HPA as compared to P-HPA. Investigations of the catalytic activity (TPRS) can be correlated with the TG data. After the loss of structural water, all investigated HPA are active for the partial oxidation reactions. This catalytic activity decreases with time on stream. Under catalytic conditions, the active fragments are not stable which were formed from the Keggin anions after loss of structural water. Total oxidation increases with the reactor temperature. In case of the Si-HPA, the total oxidation is the major reaction path already after the loss of structural water. It can be concluded from a comparison of the catalytic activities and selectivities of the different HPA that P stabilizes the fragments of the decomposed Keggins, which are characterized by a high degree of partial oxidation, in contrary to Si containing catalysts. Olefins react already at room temperature with the crystal water of the acidic HPA under water addition to alcohols. In this way the loss of water of the HPA samples is considerably increased and occurs already at room temperature. In contrast, HPA are not reduced by hydrogen at room temperature. The loss of structural water is shifted to lower temperatures in a similar way in presence of olefins. HPA preparations in which all protons of the HPA were exchanged by Cs+ ions exhibited an considerably enhanced stability toward reduction. These salts cannot desorb structural water. The decomposition and condensation of the Keggin anion fragments therefore is suppressed. Hence, these Cs salts are catalytically inactive for the partial oxidation. In contrast, more unstable tetraalkyl ammionum salts are catalytically active already at much lower temperatures which correlate with the redox potentials of the cations. It can be concluded that structural intact Keggin anions are catalytically inactive and have to be considered as the precursors of the actual active compounds

Pengaruh Persepsi Masyarakat Kecamatan Rantau Utara terhadap Minat Memilih Calon Kepala Daerah Independen pada Pilkada Kabupaten Labuhanbatu Tahun 2015

  The Regional Head Election of Labuhanbatu Regency is one of the forums for political participation for the public. The results of the independent candidate's vote in the Labuhanbatu Regency Election 2015 were able to compete with political party candidate. This phenomenon shows the public interest in choosing independent candidates. This research aims to determine how the effect of public perception on interest in choosing independent regional head candidate. Research method uses hypothesis test between X variable (perception) and Y variable (interest) and looks for the relationship between it. Population in research were voters in Rantau Utara District. Research used questionnaire distributed to 100 respondents who were selected through a sampling technique. Data analysis technique using cross tabulation, Pearson correlation and hypothesis test.   Keyword : Independent Candidate, Perception, Interest, Political Participatio

Gerakan Sosial-politik Teman Ahok Menjelang Pilkada DKI Jakarta Tahun 2017

  This research aims to know the form of Social-Politic Movement of Teman Ahok towards Province of Jakarta's Election in 2017. This research uses theoryl of New Social Movement by Nelson A. Pichardo and uses qualitative descriptive method. Sampling technique that is used is purposive sampling. This research shows that the form of Teman Ahok Social-Politic Movement are : first , Teman Ahok arranged a movement called Satu Juta KTP Untuk Ahok to support Ahok for Jakarta's Election in third quarter of 2015. Teman Ahok was collecting KTP of Jakarta's people and the target is finished.   Second, Teman Ahok uses Social Media to gained peoples who want Ahok to becoming Governor of Jakarta.  Third, Teman Ahok was connected with four political parties such as Golkar, Hanura, PSI, and Nasdem while collecting KTP in DKI Jakarta. Every political parties has their own agenda to supported Teman Ahok's movement.    Key Words : Jakarta, Election, Teman Ahok, New Social Movemen