Acetylene-ammonia-18-crown-6 (1/2/1)

The title compound, C2H2·C12H24O6·2NH3, was formed by co-crystallization of 18-crown-6 and acetylene in liquid ammonia. The 18-crown-6 molecule has threefold rotoinversion symmetry. The acteylene molecule lies on the threefold axis and the whole molecule is generated by an inversion center. The two ammonia molecules are also located on the threefold axis and are related by inversion symmetry. In the crystal, the ammonia molecules are located below and above the crown ether plane and are connected by intermolecular N-H...O hydrogen bonds. The acetylene molecules are additionally linked by weak C-H...N interactions into chains that propagate in the direction of the crystallographic c axis. The 18-crown-6 molecule [occupancy ratio 0.830 (4):0.170 (4)] is disordered and was refined using a split model

A method of calculating the total flow from a given sea surface topography

Using a simple dynamical model of a wind-driven ocean circulation of the Stommel type, and an analytical basis developed to objectively analyze the sea surface height residuals from an altimeter and, in the process, to determine the total flow instead of just the near surface geostrophic component associated with the given sea surface topography. The method is based on first deriving the solution to the forced problem for a given wind stress required to develop a hypothetical true or perfect data field and to establishing the basis for the objective analysis. The stream function and the surface height field for the forced problem are developed in terms of certain characteristic functions with the same expansion coefficients for both fields. These characteristic functions are simply the solutions for a homogeneous elliptic equation for the stream function and the solutions of an inhomogeneous balance equation for the height field. For the objective analysis, using a sample of randomly selected height values from the true data field, the height field characteristic functions are used to fit the given topography in a least squares sense. The resulting expansion coefficients then permit the synthesis of the total flow field via the stream function characteristic modes and the solution is perfectly well behaved even along the equator. The method of solution is easily adaptable to realistic ocean basis by straight forward numerical methods. The analytical basis of the theory and the results for an ideal rectangular basin on a beta plane are described

Exchange rate pass-through and the role of international distribution channels

Manufacturers selling in foreign markets often do not completely pass on the effects of fluctuations in exchange rates to the prices of their products. Our paper addresses this puzzle and studies the effects of the international distribution channel on exchange rate pass-through. We develop an exchange rate pass-through model that takes into account the role of an intermediary between a domestic manufacturer and its consumers in a foreign market. We find that the magnitude of the pass-through depends on the presence of an incentive problem in the distribution channel. When there is no incentive problem, pass-through is complete; however, when there is an incentive problem, pass-through depends on various characteristics of the intermediary and the market setting. Our analysis underscores the importance of considering the role of international distribution channels and suggests directions for further work on exchange rate pass-through

Tidal estimation in the Atlantic and Indian Oceans, 3 deg x 3 deg solution

An estimation technique was developed to extrapolate tidal amplitudes and phases over entire ocean basins using existing gauge data and the altimetric measurements provided by satellite oceanography. The technique was previously tested. Some results obtained by using a 3 deg by 3 deg grid are presented. The functions used in the interpolation are the eigenfunctions of the velocity (Proudman functions) which are computed numerically from a knowledge of the basin's bottom topography, the horizontal plan form and the necessary boundary conditions. These functions are characteristic of the particular basin. The gravitational normal modes of the basin are computed as part of the investigation; they are used to obtain the theoretical forced solutions for the tidal constituents. The latter can provide the simulated data for the testing of the method and serve as a guide in choosing the most energetic functions for the interpolation

Structure determination techniques flex their muscles

A historical challenge: Gas-phase electron diffraction and single-crystal X-ray diffraction are both established techniques, but they were both pushed to their limits by the challenge posed by the highly flexible tetranitromethane molecule. New approaches had to be developed for the structure of the molecule to be elucidated

Fine tuning of crystal architecture by intermolecular interactions: synthon engineering

There has been a long time effort to influence or favourably fine tune structural properties by introduction of substituents or guest molecules of different sizes, shapes and chemical composition to consequently alter physico-chemical properties of the respective crystals. These attempts require the recognition, understanding and application of intermolecular interactions, crystallographic and, in case of occurrence, non-crystallographic symmetries. It brings us to the field of crystal engineering, which aims to produce new substances with required properties based on the knowledge of the structural properties of already characterised solids. A series of calixarene crystal structures are presented where the crystal packing is determined by spatial or by electrostatic effects. A series of laterally substituted calixarenes where both steric requirements and electrostatic forces play a role in the crystal architecture shows how the supramolecular synthon can be engineered

Analysis of high and selective uptake of CO2 in an oxamide-containing {Cu2(OOCR)4}-based metal-organic framework

The porous framework [Cu2(H2O)2L].4H2O.2DMA ((H¬4¬L = oxalylbis(azanediyl)diisophthalic acid; DMA = N,N-dimethylacetamide), denoted NOTT-125, is formed by connection of {Cu2(RCOO)4} paddlewheels with the isophthalate linkers in L4-. A single crystal structure determination reveals that NOTT-125 crystallises in monoclinic cell with a = 27.9161(6) Å, b = 18.6627(4) Å and c = 32.3643(8) Å, space group P2 (1)/c. The structure of this material shows fof topology, which can be viewed as the packing of two types of cages (Cage A and Cage B) in 3-dimensional space. Cage A is constructed by twelve {Cu2(OOCR)4} paddlewheels and six linkers to form an ellipsoid-shaped cavity approximately 24.0 Å along its long axis and 9.6 Å across the central diameter. Cage B consists of six {Cu2(OOCR)4} units and twelve linkers with a spherical diameter of 12.7 Å taking into account the van der Waals radii of the atoms. NOTT-125 incorporates oxamide functionality within the pore walls, and this, combined with high porosity in the desolvated NOTT-125a, is responsible for excellent CO2 uptake (40.1 wt% at 273 K and 1 bar) and selectivity for CO2 over CH4 or N2. Grand canonical Monte Carlo (GCMC) simulations show excellent agreement with the experimental gas isotherm data, and a computational study into the specific interactions and binding energies of both CO2 and CH4 with the linkers in NOTT-125 reveals a set of strong interactions between CO2 and the oxamide motif, which are not possible with a single amide

Fredholm determinant representation of the Painlev\'e II τ\tau-function

We formulate the generic $\tau$-function of the Painlev\'e II equation as a Fredholm determinant of an integrable (Its-Izergin-Korepin-Slavnov) operator. The $\tau$-function depends on the isomonodromic time $t$ and two Stokes' parameters, and the vanishing locus of the $\tau$-function, called the Malgrange divisor is determined by the zeros of the Fredholm determinant.Comment: 29 pages, 8 figures. V3: some signs correcte

Minimizing the Disruption of Traffic Flow of Automated Vehicles During Lane Changes

In intelligent transportation systems, most of the research work has focused on lane change assistant systems. No existing work considers minimizing the interruption of traffic flow by maximizing the number of lane changes while eliminating the collisions. In this thesis, we develop qualitative and quantitative approaches for minimizing the interruption of traffic flow for three lane scenarios and show that we can extend our approach to any random number of lanes. The algorithm we propose in this thesis is able to achieve the maximum number of lane changes provided that only one vehicle per group (novel concept which is described in this thesis) is allowed to change lanes at a time. Simulation results show that our approach provides much better performance when compared with different lane change algorithms without incurring large overhead, and is hence suitable for online use