Wreath operations in the group of automorphisms of the binary tree

AbstractA new operation called tree-wreathing is defined on groups of automorphisms of the binary tree. Given a countable residually finite 2-group H and a free abelian group K of finite rank r this operation produces uniformly copies of these as automorphism groups of the binary tree such that the group generated by them is an over-group of the restricted wreath product H≀K. Indeed, G contains a normal subgroup N which is an infinite direct sum of copies of the derived group H′ and the quotient group G/N is isomorphic to H≀K. The tree-wreathing construction preserves the properties of solvability, torsion-freeness and of having finite state (i.e., generated by finite automata). A faithful representation of any free metabelian group of finite rank is obtained as a finite-state group of automorphisms of the binary tree

A just-nonsolvable torsion-free group defined on the binary tree

AbstractA two-generator torsion-free subgroup of the group of finite-state automorphisms of the binary tree is constructed having the properties of being just-nonsolvable and residually “torsion-free solvable.” A presentation is produced for this subgroup in two generators and two relations together with their images under the iterated application of a certain simple substitution

Chiral Supersymmetric Gepner Model Orientifolds

We explicitly construct A-type orientifolds of supersymmetric Gepner models. In order to reduce the tadpole cancellation conditions to a treatable number we explicitly work out the generic form of the one-loop Klein bottle, annulus and Moebius strip amplitudes for simple current extensions of Gepner models. Equipped with these formulas, we discuss two examples in detail to provide evidence that in this setting certain features of the MSSM like unitary gauge groups with large enough rank, chirality and family replication can be achieved.Comment: 37 pages, TeX (harvmac), minor changes, typos corrected, to appear in JHE

Particle models from orientifolds at Gepner-orbifold points

We consider configurations of stacks of orientifold planes and D-branes wrapped on a non trivial internal space of the structure {(Gepner model)^{c=3n} x T^{2(3-n)}}/Z_N, for n=1,2,3. By performing simple moddings by discrete symmetries of Gepner models at orienti fold points, consistent with a Z_N orbifold action, we show that projection on D-brane configurations can be achieved, generically leading to chiral gauge theories. Either supersymmetric or non-supersymmetric (tachyon free) models can be obtained. We illustrate the procedure through some explicit examples.Comment: 36 pages, no figures Corrected sign of eq. 6.26 references added, minor correction

N=1 Type IIA brane configurations, Chirality and T-duality

We consider four-dimensional N=1 field theories realized by type IIA brane configurations of NS-branes and D4-branes, in the presence of orientifold six-planes and D6-branes. These configurations are known to present interesting effects associated to the appearance of chiral symmetries and chiral matter in the four-dimensional field theory. We center on models with one compact direction (elliptic models) and show that, under T-duality, the configurations are mapped to a set of type IIB D3-branes probing N=1 orientifolds of C^2/Z_N singularities. We explicitly construct these orientifolds, and show the field theories on the D3-brane probes indeed reproduces the field theories constructed using the IIA brane configurations. This T-duality map allows to understand the type IIB realization of several exotic brane dynamics effects on the type IIA side: Flavour doubling, the splitting of D6-branes and O6-planes in crossing a NS-brane and the effect of a non-zero type IIA cosmological constant turn out to have surprisingly standard type IIB counterparts.Comment: 39 pages, Latex, 7 eps figures. References adde

Effects of high pressure and temperature conditions on the chemical fate of flowback water related chemicals

Environmental risk assessment is generally based on atmospheric conditions for the modelling of chemical fate after entering the environment. However, during hydraulic fracturing, chemicals may be released deep underground. This study therefore focuses on the effects of high pressure and high temperature conditions on chemicals in flowback water to determine whether current environmental fate models need to be adapted in the context of downhole activities. Crushed shale and flowback water were mixed and exposed to different temperature (25–100 °C) and pressure (1–450 bar) conditions to investigate the effects they have on chemical fate. Samples were analysed using LC-HRMS based non-target screening. The results show that both high temperature and pressure conditions can impact the chemical fate of hydraulic fracturing related chemicals by increasing or decreasing concentrations via processes of transformation, sorption, degradation and/or dissolution. Furthermore, the degree and direction of change is chemical specific. The change is lower or equal to a factor of five, but for a few individual compounds the degree of change can exceed this factor of five. This suggests that environmental fate models based on surface conditions may be used for an approximation of chemical fate under downhole conditions by applying an additional factor of five to account for these uncertainties. More accurate insight into chemical fate under downhole conditions may be gained by studying a fluid of known chemical composition and an increased variability in temperature and pressure conditions including concentration, salinity and pH as variables.</p

On Susy Standard-like models from orbifolds of D=6 Gepner orientifolds

As a further elaboration of the proposal of Ref. [1] we address the construction of Standard-like models from configurations of stacks of orientifold planes and D-branes on an internal space with the structure ${(Gepner model)^{c=6} \times T^2}/Z_N$. As a first step, the construction of D=6 Type II B orientifolds on Gepner points, in the diagonal invariant case and for both, odd and even, affine levels is discussed. We build up the explicit expressions for B-type boundary states and crosscaps and obtain the amplitudes among them. From such amplitudes we read the corresponding spectra and the tadpole cancellation equations. Further compactification on a T^2 torus, by simultaneously orbifolding the Gepner and the torus internal sectors, is performed. The embedding of the orbifold action in the brane sector breaks the original gauge groups and leads to N=1 supersymmetric chiral spectra. Whenever even orbifold action on the torus is considered, new branes, with worldvolume transverse to torus coordinates, must be included. The detailed rules for obtaining the D=4 model spectra and tadpole equations are shown. As an illustration we present a 3 generations Left-Right symmetric model that can be further broken to a MSSM model.Comment: 40 pages, 2 figures, added references, table 3 correcte

Supersymmetric Orientifolds of Gepner Models

Supersymmetric orientifolds of four dimensional Gepner Models are constructed in a systematic way. For all levels of the Gepner model being odd the generic expression for both the A-type and the B-type Klein bottle amplitude is derived. The appearing massless tadpoles are canceled by introducing appropriate boundary states of Recknagel/Schomerus(RS). After determining the Moebius strip amplitude we extract general expressions for the tadpole cancellation conditions. We discuss the issue of chirality for such supersymmetric orientifold models and finally present a couple of examples in detail.Comment: 38 pages, TeX harvmac, ref. adde

Synthesis and post-synthetic modification of amine-, alkyne-, azide- and nitro-functionalized metal-organic frameworks based on DUT-5

Functionalized 4,4′-biphenyldicarboxylic acid molecules with additional amine, alkyne, azide or nitro groups were prepared and applied in the synthesis of novel metal-organic frameworks and mixed-linker metal-organic frameworks isoreticular to DUT-5. The properties of the frameworks could be tuned by varying the number of functional groups in the materials and the amine groups were employed in post-synthetic modification reactions without changing the framework structure or significantly decreasing the porosity of the materials. © The Royal Society of Chemistry 2015

Comparing conventional and green fracturing fluids by chemical characterisation and effect-based screening.

There is public and scientific concern about air, soil and water contamination and possible adverse environmental and human health effects as a result of hydraulic fracturing activities. The use of greener chemicals in fracturing fluid aims to mitigate these effects. This study compares fracturing fluids marketed as either ‘conventional’ or ‘green’, as assessed by their chemical composition and their toxicity in bioassays. Chemical composition was analysed via non-target screening using liquid chromatography - high resolution mass spectrometry, while toxicity was evaluated by the Ames fluctuation test to assess mutagenicity and CALUX reporter gene assays to determine specific toxicity. Overall, the results do not indicate that the ‘green’ fluids are less harmful than the ‘conventional’ ones. First, there is no clear indication that the selected green fluids contain chemicals present at lower concentrations than the selected conventional fluids. Second, the predicted environmental fate of the identified compounds does not seem to be clearly distinct between the ‘green’ and ‘conventional’ fluids, based on the available data for the top five chemicals based on signal intensity that were tentatively identified. Furthermore, Ames fluctuation test results indicate that the green fluids have a similar genotoxic potential than the conventional fluids. Results of the CALUX reporter gene assays add to the evidence that there is no clear difference between the green and conventional fluids. These results do not support the claim that currently available and tested green-labeled fracturing fluids are environmentally more friendly alternatives to conventional fracturing fluids