Synthesis and catalytic performance of CeOCl in Deacon reaction

Surface chlorinated CeO2 is an efficient material for HCl oxidation, which raises the question whether an oxychloride phase could be also active in the same reaction. CeOCl was synthesized by solid state reaction of cerium oxide with anhydrous cerium chloride and tested in HCl oxidation using various feed compositions at 703 K. X-ray diffraction of post-reaction samples revealed that CeOCl is unstable, in both oxygen-rich and -lean conditions. Applying oxygen over-stoichiometric feeds led to complete transformation of CeOCl into CeO2. Considerable HCl conversions were obtained only after this transformation, which confirms the essential role of bulk cerium oxide in this catalytic system

Loop and surface operators in N=2 gauge theory and Liouville modular geometry

Recently, a duality between Liouville theory and four dimensional N=2 gauge theory has been uncovered by some of the authors. We consider the role of extended objects in gauge theory, surface operators and line operators, under this correspondence. We map such objects to specific operators in Liouville theory. We employ this connection to compute the expectation value of general supersymmetric 't Hooft-Wilson line operators in a variety of N=2 gauge theories.Comment: 60 pages, 11 figures; v3: further minor corrections, published versio

In situ surface coverage analysis of RuO₂-catalysed HCl oxidation reveals the entropic origin of compensation in heterogeneous catalysis

In heterogeneous catalysis, rates with Arrhenius-like temperature dependence are ubiquitous. Compensation phenomena, which arise from the linear correlation between the apparent activation energy and the logarithm of the apparent pre-exponential factor, are also common. Here, we study the origin of compensation and find a similar dependence on the rate-limiting surface coverage term for each Arrhenius parameter. This result is derived from an experimental determination of the surface coverage of oxygen and chlorine species using temporal analysis of products and prompt gamma activation analysis during HCl oxidation to Cl2 on a RuO2 catalyst. It is also substantiated by theory. We find that compensation phenomena appear when the effect on the apparent activation energy caused by changes in surface coverage is balanced out by the entropic configuration contributions of the surface. This result sets a new paradigm in understanding the interplay of compensation effects with the kinetics of heterogeneously catalysed processes

Another derivation of the geometrical KPZ relations

We give a physicist's derivation of the geometrical (in the spirit of Duplantier-Sheffield) KPZ relations, via heat kernel methods. It gives a covariant way to define neighborhoods of fractals in 2d quantum gravity, and shows that these relations are in the realm of conformal field theory

Electrocatalytic Oxygen Evolution Reaction in Acidic Environments – Reaction Mechanisms and Catalysts

The low efficiency of the electrocatalytic oxidation of water to O2 (oxygen evolution reaction-OER) is considered as one of the major roadblocks for the storage of electricity from renewable sources in form of molecular fuels like H2 or hydrocarbons. Especially in acidic environments, compatible with the powerful proton exchange membrane (PEM), an earth-abundant OER catalyst that combines high activity and high stability is still unknown. Current PEM-compatible OER catalysts still rely mostly on Ir and/or Ru as active components, which are both very scarce elements of the platinum group. Hence, the Ir and/or Ru amount in OER catalysts has to be strictly minimized. Unfortunately, the OER mechanism, which is the most powerful tool for OER catalyst optimization, still remains unclear. In this review, we first summarize the current state of our understanding of the OER mechanism on PEM-compatible heterogeneous electrocatalysts, before we compare and contrast that to the OER mechanism on homogenous catalysts. Thereafter, an overview over monometallic OER catalysts is provided to obtain insights into structure-function relations followed by a review of current material optimization concepts and support materials. Moreover, missing links required to complete the mechanistic picture as well as the most promising material optimization concepts are pointed out

Cohort fertility patterns in the Nordic Countries

Previous analyses of period fertility suggest that the trends of the Nordic countries are sufficiently similar to speak of a common "Nordic fertility regime". We investigate whether this assumption can be corroborated by comparing cohort fertility patterns in the Nordic countries. We study cumulated and completed fertility of Nordic birth cohorts based on the childbearing histories of women born in 1935 and later derived from the population registers of Denmark, Finland, Norway, and Sweden. We further explore childbearing behaviour by womenâs educational attainment. The results show remarkable similarities in postponement and recuperation between the countries and very small differences in completed fertility across educational groups. Median childbearing age is about 2−3 years higher in the 1960−64 cohort than in the 1950−54 cohort, but the younger cohort recuperates the fertility level of the older cohort at ages 30 and above. A similar pattern of recuperation can be observed for highly educated women as compared to women with less education. An interesting finding is that of a positive relationship between educational level and the final number of children when women who become mothers at similar ages are compared. Country differences in fertility outcome are generally rather low. Childlessness is highest in Finland and lowest in Norway, and the educational differentials are largest in Norway. Despite such differences, the cohort analyses in many ways support the notion of a common Nordic fertility regime.Denmark, Finland, Norway, Sweden, cohort fertility

On the relation between quantum Liouville theory and the quantized Teichm"uller spaces

We review both the construction of conformal blocks in quantum Liouville theory and the quantization of Teichm\"uller spaces as developed by Kashaev, Checkov and Fock. In both cases one assigns to a Riemann surface a Hilbert space acted on by a representation of the mapping class group. According to a conjecture of H. Verlinde, the two are equivalent. We describe some key steps in the verification of this conjecture.Comment: Contribution to the proceedings of the 6th International Conference on CFTs and Integrable Models, Chernogolovka, Russia, September 2002; v2: Typos corrected, typographical change

Strings in AdS_3 and the SL(2,R) WZW Model. Part 3: Correlation Functions

We consider correlation functions for string theory on AdS_3. We analyze their singularities and we provide a physical interpretation for them. We explain which worldsheet correlation functions have a sensible physical interpretation in terms of the boundary theory. We consider the operator product expansion of the four point function and we find that it factorizes only if a certain condition is obeyed. We explain that this is the correct physical result. We compute correlation functions involving spectral flowed operators and we derive a constraint on the amount of winding violation.Comment: 87 pages, 7 figures; minor change

On the fundamental representation of Borcherds algebras with one imaginary simple root

Borcherds algebras represent a new class of Lie algebras which have almost all the properties that ordinary Kac-Moody algebras have, and the only major difference is that these generalized Kac-Moody algebras are allowed to have imaginary simple roots. The simplest nontrivial examples one can think of are those where one adds ``by hand'' one imaginary simple root to an ordinary Kac-Moody algebra. We study the fundamental representation of this class of examples and prove that an irreducible module is given by the full tensor algebra over some integrable highest weight module of the underlying Kac-Moody algebra. We also comment on possible realizations of these Lie algebras in physics as symmetry algebras in quantum field theory.Comment: 8 page

On supersymmetry breaking in string theory from gauge theory in a throat

We embed the supersymmetry breaking mechanism in N=1 SQCD of hep-th/0602239 in a smooth superstring theory using D-branes in the background R^4 \times SL(2)_{k=1}/U(1) which smoothly captures the throat region of an intersecting NS5-brane configuration. A controllable deformation of the supersymmetric branes gives rise to the mass deformation of the magnetic SQCD theory on the branes. The consequent instability on the open string worldsheet can be followed onto a stable non-supersymmetric configuration of D-branes which realize the metastable vacuum configuration in the field theory. The new brane configuration is shown to backreact onto the background such as to produce different boundary conditions for the string fields in the radial direction compared to the supersymmetric configuration. In the string theory, this is interpreted to mean that the supersymmetry breaking is explicit rather than spontaneous.Comment: 29 pages, harvmac, 8 figures; v2 typos corrected, reference adde