The Two Fundamental H-Bond Types in Acid Salts Displayed in the Dimorphs of Potassium Hydrogen Tartronate

At ambient temperature the acid potassium salt of tartronic acid crystallizes in two forms. The a. form is monoclinic, space group P21/n with a= 7.356, b = 8.116, c = 9.197 A, fJ = 94.81° and Z = 4. The fJ form is also monclinic, space group P21/c with. a= 6.532, b = 9.248, c = 9.505, fJ = 99.74° and Z = 4. The a. and ~ structures were solved by Patterson and Fourier methods and refined to R = 0.047 with 1129 and 1204 observed diffractometer data respectively. The fundamental differences in structural aspects between the dimorphs of this acid salt are found in the H-bond schemes. In the a. form the carboxyl groups are coupled by A-type H bonds, in the ~ form by H bonds of the B type

Optimized Anisotropic Rotational Invariant Diffusion Scheme on Cone-Beam CT

Cone-beam computed tomography (CBCT) is an important image modality for dental surgery planning, with high resolution images at a relative low radiation dose. In these scans the mandibular canal is hardly visible, this is a problem for implant surgery planning. We use anisotropic diffusion filtering to remove noise and enhance the mandibular canal in CBCT scans. For the diffusion tensor we use hybrid diffusion with a continuous switch (HDCS), suitable for filtering both tubular as planar image structures. We focus in this paper on the diffusion discretization schemes. The standard scheme shows good isotropic filtering behavior but is not rotational invariant, the diffusion scheme of Weickert is rotational invariant but suffers from checkerboard artifacts. We introduce a new scheme, in which we numerically optimize the image derivatives. This scheme is rotational invariant and shows good isotropic filtering properties on both synthetic as real CBCT data

Segmentation of the mandibular canal in cone-beam CT data

Accurate information about the location of the mandibular canal is essential in case of dental implant surgery. The goal of our research is to find an automatic method which can segment the mandibular canal in Cone-beam CT (CBCT). \ud Mandibular canal segmentation methods in literature using a priori shape information are, the 2D active appearance model of Rueda et al., and 3D active shape model (ASM) of Kainmueller et al. The mean distance to manual annotation of the mandibular canal of the method of Kainmueller is around 1.1mm. The best method in literature is Kim et al. with an average distance of 0.7mm.\ud We develop and evaluate five methods for mandibular canal localization. The methods, Lukas Kanade tracking (LK), B-spline registration, demon registration, 3D active shape model (ASM), and active appearance model (AAM). The ASM and AAM need corresponding points between the mandibles in the training data. We develop and evaluate two methods to find corresponding points, minimum description length (MDL) and the second shape context (SC) based registration. To improve the quality of the CBCT scans we introduce a rotational invariant edge preserving optimized anisotropic diffusion filter.\ud We evaluate the performance on 13 CBCT scans. The registration methods have an average distance to expert annotation of the canal of more than 4mm, LK tracking a distance of 3mm, AAM and ASM a distance of respectively 2.0mm and 2.3mm. The MDL method does not improve point correspondences found by the SC method, and the pre-filtering with the introduced diffusion filter does not improve the ASM result. By using location based intensity weights we improve the AAM results, to an average distance of 1.88mm. The relatively large error is due to a low number of training datasets, and low CBCT scan quality

Optimising halting station of passenger railway lines

In many real life passenger railway networks, the types of stations and lines characterisethe halting stations of the train lines. Common types are Regional, Interregional or Intercity.This paper considers the problem of altering the halts of lines by both upgrading and downgrading stations, such that this results in less total travel time. We propose a combination of reduction methods, Lagrangian relaxation, and a problem-specific multiplier adjustment algorithm to solve the presented mixed integer linear programming formulation. A computational study of several real-life instances based on problem data of the Dutch passenger railway operator NS Reizigers is included.mathematical economics and econometrics ;

A branch-and-cut approach for solving line planning problems

An important strategic element in the planning process of a railway operator is the development of a line plan, i.e., a set of routes (paths) in a network of tracks, operated at a given hourly frequency. We consider a model formulation of the line planning problem where total operating costs are to be minimized. This model is solved with a branch-and-cut approach, for which we develop a variety of valid inequalities and reduction methods. A computational study of five real-life instances is included.operations research and management science;