Calculations of mass and moment of inertia for neutron stars

Masses and moments of inertia for slowly-rotating neutron stars are calculated from the Tolman-Oppenheimer-Volkoff equations and various equations of state for neutron-star matter. We have also obtained pressure and density as a function of the distance from the centre of the star. Generally, two different equations of state are applied for particle densities n > 0.47 fm^?3 and n < 0.47 fm^?3.The maximum mass is, in our calculations for all equations of state except for the unrealistic non-relativistic ideal Fermi gas, given by 1.50 M_⊙ < M < 1.82 M_⊙, which agrees very well with “experimental results”. Corresponding results for the maximum moment of inertia are 9.5 × 10⁴⁴ g · cm² < I < 1.58 × 10⁴⁵ g · cm², which also seem to agree very well with “experimental results”. The radius of the star corresponding to maximum mass and maximum moment of inertia is given by 8.2 km < R < 10.0 km, but a smaller central density ρ_c will give a larger radius.     

Atmospheric chemistry of C3-C6 cycloalkanecarbaldehydes

The rate coefficients for the gas phase reaction of NO3 and OH radicals with a series of cycloalkanecarbaldehydes have been measured in purified air at 298 +/- 2 K and 760 +/- 10 Torr by the relative rate method using a static reactor equipped with long-path Fourier transform infrared (FT-IR) detection. The values obtained for the OH radical reactions (in units of 10(-11) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 2.13 +/- 0.05; cyclobutanecarbaldehyde, 2.66 +/- 0.06; cyclopentanecarbaldehyde, 3.27 +/- 0.07; cyclohexanecarbaldehyde, 3.75 +/- 0.05. The values obtained for the NO3 radical reactions (in units of 10(-14) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 0.61 +/- 0.04; cyclobutanecarbaldehyde, 1.99 +/- 0.06; cyclopentanecarbaldehyde, 2.55 +/- 0.10; cyclohexanecarbaldehyde, 3.19 +/- 0.12. Furthermore, the reaction products with OH radicals have been investigated using long-path FT-IR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). The measured carbon balances were in the range 89-97%, and the identified products cover a wide spectrum of compounds including nitroperoxycarbonyl cycloalkanes, cycloketones, cycloalkyl nitrates, multifunctional compounds containing carbonyl, hydroxy, and nitrooxy functional groups, HCOOH, HCHO, CO, and CO2.     

Pre-equilibrium capillary zone electrophoresis or frontal analysis: advantages of plateau peak conditions in affinity capillary electrophoresis

The feasibility of using the affinity CE methodologies pre-equilibrium CZE and CE frontal analysis was tested on interaction systems exhibiting rapid on-and-off kinetics. Experimentally, the methodologies differ only with respect to the volume of sample introduced into the capillary. Pre-equilibrium CZE has been considered amendable to interactions with slow on-and-off kinetics only; however, it has recently been applied in studies of interactions with fast on-and-off kinetics. The effect of varying the sample volume introduced hydrodynamically into the capillary on the apparent degree of complexation was studied. For two different binding systems, the fraction of free analyte was found to be overestimated using pre-equilibrium CZE as compared to volumes providing plateau peak conditions as used with frontal analysis. Results indicate that frontal analysis conditions lead to more robust binding assays and thus more reliable data. The validity of data obtained by pre-equilibrium CZE may be low, thus the use of an experimental setup providing plateau peaks is highly recommended. It is suggested that the effect of altering the sample volume on the degree of binding should be investigated as part of method development and validation.     

Determination of octanol-water partition coefficients for carbonate esters and other small organic molecules by microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) was assessed as a tool for determination of octanol-water partition coefficients using 34 solutes encompassing 8 carbonate esters. It was confirmed that microemulsions containing 1.44-2.88% w/w SDS, 6.49% w/w 1-butanol, and 0.82% w/w n-heptane constitute a good model of octanol-water partitioning in the pH range of 1.4-7.4. Use of the migration index concept led to improved repeatability of the MEEKC method compared to the use of retention factors. Using a dynamical coating, a high electroosmotic flow at pH 1.4 and 4.75 was achieved expanding the practical pH working range of the MEEKC system. The correlation obtained between the migration index and log P was unaffected by pH indicating that the properties of the microemulsion droplets and, thus, partitioning are independent of pH. No evidence for congeneric behavior was found for the sample set comprising solutes with different hydrogen bonding properties suggesting that simple reference compounds can be used as calibrators. Lipophilicity estimates for the series of carbonate esters were obtained. The increase in lipophilicity with chain length was smaller than expected from the Hansch substituent constant, pi.     

Effects of packing structure on the optoelectronic and charge transport properties in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)

Spin-coated poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) films of different molecular weights (Mn= 9-255 kg/mol), both in the pristine and annealed state, were studied in an effort to elucidate changes in the polymer packing structure and the effects this structure has on the optoelectronic and charge transport properties of these films. A model based on quantum chemical calculations, wide-angle X-ray scattering, atomic force microscopy, Raman spectroscopy, photoluminescence, and electron mobility measurements was developed to describe the restructuring of the polymer film as a function of polymer chain length and annealing. In pristine high molecular weight films, the polymer chains exhibit a significant torsion angle between the F8 and BT units, and the BT units in neighboring chains are close to one another. Annealing films to sufficiently high transition temperatures allows the polymers to adopt a lower energy configuration in which the BT units in one polymer chain are adjacent to F8 units in a neighboring chain ("alternating structure"), and the torsion angle between F8 and BT units is reduced. This restructuring, dictated by the strong dipole on the BT unit, subsequently affects the efficiencies of interchain electron transfer and exciton migration. Films exhibiting the alternating structure show significantly lower electron mobilities than those of the pristine high molecular weight films, due to a decrease in the efficiency of interchain electron transport in this structure. In addition, interchain exciton migration to low energy weakly emissive states is also reduced for these alternating structure films, as observed in their photoluminescence spectra and efficiencies.     

An evaluation of solid-phase microextraction for analysis of volatile organic compounds in drinking water

Solid-phase microextraction (SPME) has been applied to the quantitative analysis of 60 volatile organic compounds (VOCs) in drinking water. Equilibration curves for the partitioning of the VOCs between the fiber coating and fortified water obtained at 20, 50, and 80 °C are found between the theoretical curves for completely agitated and non-agitated samples. Two important factors for the amount adsorbed by the SPME fiber coating are the extraction time and the fiber coating/water distribution coefficient, K_FW . Both depend on the sample temperature, but in a counteracting manner: Increasing the temperature shortened the equilibration times, especially for the heavier VOCs, but also lead to lower K_FW values, and consequently a lower sensitivity of the method. K_FW values are determined for 33 of the VOCs at 40, 60, and 80°C and the heats of adsorption,–ΔH, are calculated. The nature of the adsorption is found to be exothermic which explains the decreasing sensitivity of the method with increasing temperature. Detection limits were typically from 20 ng/l to 200 ng/l, except for the very light VOCs with which detection difficulties were encountered. For all of the VOCs the linear range extended from the lowest concentration at which they were actually detected to at least 5 mg/l. The precision, 3% average standard deviation when an internal standard was used, was satisfactory for most quantitative routine analysis. SPME was also applied to head-space (HS) analysis of drinking water through the coupled equilibrium between water/head-space/fiber coating. HS-SPME is demonstrated to have shorter equilibration times than SPME directly from the water and equal sensitivities, except for the very light VOCs. Water samples from a drinking water plant contaminated in the low μg/l range with 1,1,1-trichloroethane, trichloroethene and tetrachloroethene were analyzed. There seems to be a reasonable agreement between results obtained by SPME and purge & trap. It is concluded that SPME has a great potential for drinking water analysis.     

Stochastic boundary value problems: a white noise functional approach

Summary We give a program for solving stochastic boundary value problems involving functionals of (multiparameter) white noise. As an example we solve the stochastic Schrödinger equation {ie391-1} whereV is a positive, noisy potential. We represent the potentialV by a white noise functional and interpret the product of the two distribution valued processesV andu as a Wick productV u. Such an interpretation is in accordance with the usual interpretation of a white noise product in ordinary stochastic differential equations. The solutionu will not be a generalized white noise functional but can be represented as anL ¹ functional process.     

Thermogravimetric and dilatometric studies using Stepwise Isothermal Analysis and related techniques

The Stepwise Isothermal Analysis (SIA) technique, which was introduced by the author in the late seventies has proved to be very useful both in thermogravimetric and dilatometric studies. By this technique the heating and cooling programme is controlled by the rate of the reactions taking place in the sample, for instance thermal decompositions (TG) or sintering (dilatometry). By an advanced computer programme this control is achieved in the following way: The sample is heated at a constant heating rate until the reaction rate. i. e. the slope of the weight/length versus time curve, exceeds a preset limit at which point the heating is stopped. The reaction thereafter proceeds isothermally until the rate again becomes smaller than the limit where the heating is resumed. By this techniques the reactions thus characteristically take place in isothermal steps.This technique is especially useful in studies of thermal decompositions and it is believed that the decomposition températures determined by SIA is much more accurate than those determined by other techniques even for materials involving consecutive and close-lying reactions. One typical application of this technique is establishment of optimum conditions for removal of organic binders from ceramic powder compacts prepared for instance by dry pressing or injection moulding.The SIA technique is also very useful in kinetic studies and with the advanced computer systems available today rather sophisticated control and analysis of the data can be obtained. One example, which will also be discussed in the presentation, is a study of the decomposition of Ce-carbonate using first the standard technique described above by which the reaction mechanism could be established and then followed by the so-called Forced Stepwise Isothermal Analysis technique (FSIA) by which the activation energy could be obtained.Finally the SIA technique is also very useful in dilatometric sintering studies and to demonstrate this the result obtained both using SIA and the related constant shrinkage rate technique in a study of the initial sintering stage of CeO₂ will be presented.

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Zusammenfassung Das vom Autor Ende der siebziger Jahre eingeführte Verfahren der Stufenweisen Isothermischen Analyse (SIA) erwies sich sowohl bei thermogravimetrischen als auch bei dilatometrischen Untersuchungen als sehr nutzvoll. Bei diesem Verfahren wir das Heiz- und Kühlprogramm durch die Geschwindigkeit der in der Probe ablaufenden Reaktion- z.B. der thermischen Zersetzung (TG) oder des Sintern (Dilatometrie) — gesteuert. Diese Steuerung wird durch ein Computerprogramm auf folgende Weise erreicht: Die Probe wird mit einer konstanten Aufheizgeschwindigkeit aufgeheizt, bis die Reaktionsgeschwindigkeit, d.h. der Anstieg der Gewichts/Längen — Zeitkurve, einen gewissen Grenzwert überschreitet, wodurch der Aufheizvorgang gestoppt wird. Die Reaktion wird anschlie\end isotherm fortgesetzt, bis die Geschwindigkeit wieder kleiner als der Grenzwert wird, zu diesem Zeitpunkt setzt die Aufheizung wieder ein. Durch dieses Verfahren erfolgt die Reaktion somit in isothermen Stufen.Dieses Verfahren ist besonders bei der Untersuchung von thermischen Zersetzungen nutzvoll und man nimmt an, da\ die mittels SIA ermittelte Zersetzungstemperatur wesentlich genauer ist als im Falle von anderen Verfahren, besonders bei Substanzen mit konsekutiven und nahe beieinanderliegenden Reaktionen. Eine typische Anwendung dieses Verfahrens ist die Ermittlung der Optimumbedingungen für die Entfernung organischer Bindemittel aus Keramikpulverpre\lingen, die z.B. durch Trockenpressen oder Spritzgie\en hergestellt wurden. Ein Anwendungsbeispiel dafür wird hier diskutiert.Auch bei kinetischen Untersuchungen ist das SIA Verfahren sehr nutzvoll und mit den heute erhältlichen Computersystemen ist eine anspruchsvollere überwachung und Analyse der Angaben ist möglich. Ein ebenfalls in vorliegender Arbeit diskutiertes Beispiel ist die Untersuchung der Zersetzung von Ceriumkarbonat, wobei zuerst die obenbeschriebene Standardmethode angewendet wird, wodurch der Reaktionsmechanismus abgeschätzt werden kann. Im Anschlu\ erfolgt eine sogenannte Erzwungene Stufenweise Isotherme Analyse (FSIA), wodurch die Aktivierungsenergie ermittelt werden kann.Letztendlich ist das SIA Verfahren auch bei dilatometrischen Sinteruntersuchungen sehr nutzbringend. Um dies darzustellen, wird bei einer Untersuchung des ursprünglichen Sinterzustandes von CeO₂, sowohl das durch SIA als auch das durch das Verfahren der konstanten Abschreckgeschwindigkeit≓ erhaltene Ergebnis dargestellt.

     

Synthesis of a hydroxyethylene isostere of the tripeptide Arg-Gly-Leu via a convergent acyl-like radical addition strategy

[reaction: see text] A hydroxyethylene isostere of the tripeptide Arg-Gly-Leu, representing an important fragment of a novel cyclic-peptide-based uPA inhibitor, was synthesized in few steps employing as the key step a samarium diiodide promoted coupling of either the 4-thiopyridyl ester of N(alpha)-Fmoc- or N(alpha)-Cbz-protected L-ornithine with the N-acryloyl derivative of L-leucine methyl ester. Epimerization under the coupling conditions at the chiral center in the alpha-position to the ketone was demonstrated not to take place. A stereoselective reduction of the Cbz-protected aminoketone obtained from this radical reaction was promoted by the same single-electron reducing agent in the presence of methanol providing the syn-amino alcohol with a diastereoselectivity of 85:15. With the use of lithium tri-tert-butoxyaluminum hydride in methanol, the corresponding anti-isomer was obtained almost exclusively. Subsequent elaboration of the ornithine moiety in the anti-isomer by introduction of the guanidine group followed by hydrolysis of the C-terminal ester bond and protection of the alcohol as its tert-butyldimethylsilyl ether provided the desired tripeptide mimic. The long reaction times required for the radical addition reactions with N(delta)-Boc-L-ornithine (up to 5 days) led to a short study where a series of 4-thiopyridyl esters of Cbz-protected amino acids were reacted with two acrylates. Whereas N(delta)-Boc-L-ornithine, alanine, phenylalanine, proline, and leucine all provided the aminoketone in 43-79% yield, valine only afforded traces of the coupling product.