Parallel sequential Monte Carlo samplers and estimation of the number of states in a Hidden Markov Model

The majority of modelling and inference regarding Hidden Markov Models (HMMs) assumes that the number of underlying states is known a priori. However, this is often not the case and thus determining the appropriate number of underlying states for a HMM is of considerable interest. This paper proposes the use of a parallel sequential Monte Carlo samplers framework to approximate the posterior distribution of the number of states. This requires no additional computational effort if approximating parameter posteriors conditioned on the number of states is also necessary. The proposed strategy is evaluated on a comprehensive set of simulated data and shown to outperform the state of the art in this area: although the approach is simple, it provides good performance by fully exploiting the particular structure of the problem. An application to business cycle analysis is also presented.     

Determination of primary aromatic amine in quality control of X-ray contrast media by flow-injection analysis

An automated flow-injection method for determination of primary aromatic amines based on the Bratton-Marshall reaction is described. This method is used for analysis quality control of three different X-ray contrast media (Omnipaque, Imagopaque and Visipaque) which are viscous solutions. In flow-injection analysis, such samples cause refractive index effects and low. broad peaks due to prolonged residence time, these interferences are minimized by the use of a carrier solution (7 w/v % NaCl in 1 M HCl) with same refractive index as the samples, careful pH adjustment, use of knotted coils, and a specially designed detector. Validation of the method in the concentration range 4-40 microg ml(-1) (injected samples) shows a repeatability (n = 6) and day-to-day reproducibility (n = 9) of 0.4-9.2 and 2.3-17.5% RSD respectively. The accuracy is 81(near the lower limit of detection)-101%, with a limit of detection of 1 microg ml(-1). Linearity was shown in the concentration range tested. The method is well suited for in-process analysis, release control and stability testing of both drug substance and drug product. The cost of analysis is reduced compared to the manual method.     

Die Sattelkonformation der hydroporphinoiden Nickel(II)-Komplexe: Struktur,Ursprung und stereochemische Konsequenzen

The Saddle Conformation of Hydroporphinoid Nickel(II) Complexes: Structure, Origin, and Stereochemical Consequences Thirteen crystal structures document the general phenomenon of coordination-hole contraction in hexahydro- and tetrahydroporphinoid ligands of complexes with small metal ions such as low-spin Ni(II). The contraction is characterized by a deformation of the ligand system towards a saddle-shaped, ruffled conformation of approximate S₄ symmetry. The central metal ion is coplanar with the four coordinating N-centers whereas the four C(meso)-atoms are situated alternately above and below this coordination plane. Increasing steepness of the saddle (parameter d_m) is associated with decreasing metal-N distances. For metal pyrrocorphinates, d_m increases in the order Cu(II) < (pyridine) Co(II) < Ni(II), for Ni(II) complexes it does so in the order porphyrin < chlorin < bacteriochlorin < isobacteriochlorin < pyrrocorphin. In the saddle conformation of hydroporphinoid Ni(II) complexes, the hydropyrrole rings assume half-chair conformations whereby the individual half-chairs are conformationally constrained in such a way that the inclination of their peripheral single bond parallels the inclination of the ligand saddle (W-conformation of the ensemble of 5-membered ring half-chairs). There are only two such conformations available for a given complex; they interrelate by saddle inversion with concomitant inversion of the ensemble of half-chairs. The coordination-hole contraction of hydroporphinoid ligands is expected and observed experimentally to exert control on the stereochemistry and reactivity of the ligand periphery as well as on the axial electrophilicity of the central metal ion. Tetracoordinate nickel(II) pyrrocorphinates are found to favor the tctct configuration of substituents at the ligand periphery, nickel(II) isobacteriochlorinates the tct configuration, whereas nickel(II) bacteriochlorinates are expected to favor the ttt configuration. Relative rates and regioselectivities of autoxidation of nickel(II) pyrrocorphinates to corresponding bacterio-and isobacteriochlorinates depend on the configuration and conformation of the ligand periphery. The residual axial electrophilicity of the metal ion in tetracoordinate Ni(II) complexes of the octaethyl series appears to increase in the order chlorin < isobacteriochlorin ? bacteriochlorin < pyrrocorphin. All hydroporphinoid metal complexes used in the X-ray structure studies were prepared as part of exploring the porphyrinogen → pyrrocorphin tautomerization, a novel structural transformation of porphyrinogens.     

Clean-up of plasma extracts by gel permeation chromatography during analysis of isosorbide nitrates by capillary gas chromatography.

This work describes how gel permeation chromatography (GPC) can be used for sample clean-up to reduce the fouling of the column in an automated on-column injector. The analytes were isolated from plasma together with the internal standard (isomannide dinitrate) by liquid-liquid extraction on Extrelut silica columns. The extracts were evaporated and reconstituted in tetrahydrofuran for separation of the analytes from non-volatile plasma components by GPC on a styrene-divinylbenzene column with 100 A pore size. A programmable autosampler with an additional three-way valve was used for injection and fraction collection. The molecular weight fraction between 100 and 700 a.m.u. was collected and transferred to the on-column autosampler for capillary gas chromatography on a 30-m column butt-connected to a 0.2-m pre-column. The pre-column was replaced after 50 sample injections. When the GPC purification was excluded from the work-up procedure a deposit of non-volatile components was formed at the injection zone of the pre-column which resulted in excessive peak-tailing after only five or six injections of plasma extract. The limit of determination was 0.2 ng/ml plasma for isosorbide dinitrate and 0.4 ng/ml for the mononitrates.     

A suggested revised conformation of methylthionitrite as seen by its spectra and preliminary ab initio calculations

A proof has recently been given that gaseous methylthionitrite, CH₃SNO, occurs exclusively (or mainly) in its anti conformation [1]. The present paper claims that existing spectral evidence and ab initio calculations now performed suggest that gaseous methylthionitrite is mainly the syn conformer, the extra stability being of the order 1–2 kcal mol^?1. Methyl group rotation in the syn conformer is hindered by a three-fold barrier of height 689 cm^?1 while the methyl group rotation in the anti conformer is hardly hindered. The syn/anti energy difference and the barriers hindering methyl group rotation closely parallel the corresponding measured quantities in methylnitrite, CH₃ONO.     

Ab initio Hartree–Fock and configuration-interaction treatment of the interaction between two nickel atoms

The interaction between two nickel atoms in the configurations (3d)⁸(4s)² and (3d)⁹ (4s)¹ has been calculated using ab initio methods (Hartree–Fock and configuration interaction). The results of the calculations compare favorably with the optical spectrum. The discrepancy between the calculated and the experimental dissociation energy is discussed, and a new estimate of the dissociation energy is given. The configuration-interaction calculations show that the interaction between the two nickel atoms is of a very complex nature. In spite of this the binding can be interpreted in a simple way. The bond is minly due to the 4sσ_g molecular orbital while the 3d orbitals of the two nuclei are exchange coupled.     

Microwave drying of granules containing a moisture-sensitive drug: a promising alternative to fluid bed and hot air oven drying

The impact of microwave drying and binders (copolyvidone and povidone) on the degradation of acetylsalicylic acid (ASA) and physical properties of granules were compared with conventional drying methods. Moist granules containing ASA were prepared using a high shear granulator and dried with hot air oven, fluid bed or microwave (static or dynamic bed) dryers. Percent ASA degradation, size and size distribution, friability and flow properties of the granules were determined. Granules dried with the dynamic bed microwave dryer showed the least amount of ASA degradation, followed by fluid bed dryer, static bed microwave oven and hot air oven. The use of microwave drying with a static granular bed adversely affected ASA degradation and drying capability. Dynamic bed microwave dryer had the highest drying capability followed by fluid bed, static bed microwave dryer and conventional hot air oven. The intensity of microwave did not affect ASA degradation, size distribution, friability and flow properties of the granules. Mixing/agitating of granules during drying affected the granular physical properties studied. Copolyvidone resulted in lower amount of granular residual moisture content and ASA degradation on storage than povidone, especially for static bed microwave drying. In conclusion, microwave drying technology has been shown to be a promising alternative for drying granules containing a moisture-sensitive drug.     

Column selection and optimization for sulfur compound analyses by gas chromatography

The analysis of sulfur-containing compounds using fused silica capillary columns and the Sulfur Chemiluminescence Detector has been investigated. This combination of an inert chromatographic system and a high sensitivity, selective detector provides significant advantages for the analysis of low levels of sulfur compounds in complex matrices over existing techniques. Capillary columns coated with thick films (1–4 μm) of methyl silicone stationary phase permit separation of most sulfur containing compounds and, when used with sub-ambient column temperatures, these columns can be used for the separation of sulfur gases. The effects of stationary film thickness, column length, and internal diameter for the measurement of sulfur compounds in hydrocarbon matrices has been determined.     

Electronic structures of tetrahedral CrO 4 2− , VO 4 3− and TiCl4

The electronic structures of the tetrahedral systems CrO ₄ ^2– , VO ₄ ^3– and TiCl₄ are discussed on the basis of semiquantitative LCAO MO calculations.

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Zusammenfassung Die Elektronenstrukturen der Tetraedersysteme CrO ₄ ^2– , VO ₄ ^3– und TiCl₄ werden an Hand halbquantitativer LCAO-MO Rechnungen diskutiert.

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Résumé Discussion des structures électroniques des systèmes tétraédriques CrO ₄ ^2– , VO ₄ ^3– et TiCl₄ sur la base de calculs semi-quantitatifs LCAO MO.