X-ray Populations in The Local Group: Insights with Hubble & Chandra

X-ray observations provide a unique perspective on the most energetic processes in the Universe. In particular, Low-mass X-ray binaries (LMXBs) found in globular clusters have been shown to depend on the mass, radius, and metallicity of the cluster. This thesis focuses on the impact environmental parameters have on X-ray sources and the underlying physical explanations for them. I studied the X-ray binary population in M31 using 1 Ms of Chandra ACIS data and 6-filter photometry from the Panchromatic Hubble Andromeda Treasury Survey. From a sample of 83 star clusters we found the brightest and most compact star clusters preferentially hosted an X-ray source. %A logistic regression analysis showed that the F475W magnitude had the strongest correlation followed by the effective radius, while the (F475W-F814W) colour, a probe of metallicity, was not statistically significant. An investigation of 1566 HII regions found that neither radius nor H-alpha luminosity was a predictor of an HII region hosting an X-ray source. I produced the most sensitive Chandra X-ray point source catalogue of M31, detecting \num\ X-ray sources in an area of ~0.6 degrees squared to a limiting unabsorbed 0.5-8.0 keV luminosity of 10E34 erg/s. The flatter completeness-corrected X-ray luminosity function of the bulge compared to the disk, consistent with previous work, indicated a lack of bright high-mass X-ray binaries in the disk and an aging population of LMXBs in the bulge. I also investigated the origin of the relationship between the metallicity of 109 Galactic globular clusters and LMXB formation by studying the number density of red giant branch (RGB) stars. Spearman and Kendall Rank tests between the RGB star density and metallicity [Fe/H] confirmed the data could not have been drawn from a random distribution

From a Misfire to an Open Future: Repetition, Performativity and the Promise of the Metaphor

This article deals with the notion of performativity through the work of J.L. Austin, Shoshana Felman, and, most significantly, Judith Butler. It examines the intertextual references of the work of the mentioned theorists mainly through the notion of promise which is used as an example, a metaphor, but also as an organizing principle of the performative logic of their texts

Mechanical properties and chemical stability of pivalolactone-based poly(ether ester)s

The processing, mechanical and chemical properties of poly(ether ester)s, prepared from pivalolactone (PVL), 1,4-butanediol (4G) and dimethyl terephthalate (DMT), were studied. The poly(ether ester)s could easily be processed by injection moulding, owing to their favourable rheological and thermal properties. The tensile response of a poly(ether ester) with a butylene terephthalate (4GT) content of 72 mol%, which exhibited the phenomena of necking and strain-hardening, was related to the morphology of these copolymers. The influence of the short 4G-PVL segments was reflected in a high Young's modulus and yield stress, and resulted in a tough behaviour for the poly(ether ester), with an ultimate elongation of 500%. The poly(ether ester)s were stable towards treatment at room temperature with water or weakly acidic or alkaline solutions. Conditioning at 90°C in water for 264 h resulted in a water uptake of 1 wt%, whereas the rate of hydrolysis was 0.0003 (expressed in An rel h-1) for the poly(ether ester) with a 4GT content of 72 mol%. Although a decay in the mechanical properties for the PVL-based poly(ether ester) after exposure to water at 90°C was observed, these materials were assumed to have a higher hydrolytical stability than other poly(ether ester)

Effect of methyl groups on the thermal properties of polyesters from methyl substituted 1,4-butanediols and 4,4'-biphenyldicarboxylic acid

Results are reported on the effect of lateral methyl groups on the thermal properties of a series of polyesters prepared from diethyl 4,4-biphenyldicarboxylate and various methyl substituted 1,4-butanediols. The diols were 1,4-butanediol; 2-methyl-1,4-butanediol; 2,2-dimethyl-1,4-butanediol; 2,3-dimethyl-1,4-butanediol; 2,2,3-trimethyl-1,4-butanediol; and 2,2,3,3-tetramethyl-1,4-butanediol. Apart from the tetramethyl derivatve, the transition temperatures of the methyl substituted polyesters were lower with respect of the unsubstituted polyester. On the basis of polarized photomicrographs, a smectic A mesophase was found for the unsubstituted polyester, whereas a nematic mesophase was observed for the 2-methyl substituted polyster. The 2,2-dimethyl, 2,3-dimethyl, and the 2,2,3-trimethyl substituted polyesters showed no liquid crystalline behavior. The 2,2,3,3-tetramethyl derivative displayed a birefringent melt phase although the DSC measurements were not unambiguous. A copolyester based on diethyl 4,4-biphenyldicarboxylate, 1,4-butanediol, and 2,2,3,3-tetramethyl-1,4-butanediol showed a broad nematic mesophase. Further evidence for the nematic mesophase of this copolyester and the 2-methyl substituted polyester was provided by dynamic rheological experiments. Based on thermogravimetric analysis, it was concluded that the thermal stability was affected only when four methyl side groups were present in the spacer

Pivalolactone, 1 interchange reactions with polypivalolactone

Ester interchange, alcoholysis, and acidolysis of polypivalolactone (PPVL) were studied by melting PPVL with bisphenol diacetates, 1, 4-butanediol, or aromatic diacids. Interchange of PPVL with the diacetates and the diol occured readily, in particular in the presence of a titanium catalyst. Melting PPVL with 10 mol-% of bisphenol-Adiacetate in the presence of 0,5 wt.% tetrabutylorthotitanate resulted in an incorporation of 33% of the diacetate in the polymer chains, whereas the logarithmic viscosity number decreased by 81%. The ester interchange was suggested to proceed by an initial cleavage of ester bonds in the polymer chain of PPVL, resulting in the formation of shorter chains, followed by a reaction between the newly formed ester end-groups and initially present hydroxyl chain ends. The acidolysis of PPVL with the diacids proved to be less effective; in the case of the acidolysis of PPVL with 10 mol-% isophthalic acid, less than 1% of the diacid was incorporated in the polymer chains and a decrease in the logarithmic viscosity number of only 22% was found. Both the high stability of the ester bond in PPVL towards acids in general and the heterogeneity of these systems were supposed to cause the behaviour of PPVL with respect to acidolysis. The results concerning the interchange reactions with PPVL were compared with studies on other polyesters

Friction stir welding for marine applications : mechanical behaviour and microstructural characteristics of Al-Mg-Si-Cu plates

Friction stir welding is a multipurpose solid-state joining process mainly used for aluminium and steel plates and frames. Friction stir welded non-ferrous metallic alloys, similar or dissimilar, in particular aluminium alloys, provide opportunities for the improvement and developement of new product designs. This paper investigates the correlation between the mechanical behaviour and morphological structures of friction stir welded Al-Mg-Si(Cu) alloy plates in two temper conditions. Micro Vickers hardness and tensile tests were carried out. Additionally, morphology was investigated using optical microscopy and scanning electron microscopy. Samples subjected to the post weld heat treatment were shown to have the best properties owing to the formation of a significant number of hardening particles which, added to the nugget grain refinement, resulted in the increase of the material strength

Pivalolactone, 2. Copolyester synthesis via interchange reactions with polypivalolactone

The synthesis of copolyesters via interchange reactions of polypivalolactone (PPVL) with several compounds was studied. The synthetical procedures are two-stage melt processes: in the first stage ester bonds in the polymer chain are cleaved and new groups are incorporated in the polymer chain, while in the second step condensation of the end-groups formed occurs. For the synthesis of copolymers, three procedures were used, with tetrabutyl orthotitanate as a catalyst. PPVL was heated with equimolar mixtures of bisphenol-A diacetate (BPAac) and terephthalic acid (TA), but no copolymers were formed; instead, polycondensation of BPAac with TA occurred, leaving the PPVL unaffected. From PPVL and mixtures of BPAac and dimethyl terephthalate (DMT) polymers were obtained which contained a significant amount of copolymeric sequences. However, most of the polymeric chains consisted of PPVL and poly(bisphenol-A terephthalate) blocks. Random copolymers with thermal stability were obtained after heating PPVL with bisphenol-A polycarbonate and DMT. The latter process was studied in detail by IR, DSC, and solubility and selective degradation tests. Based on the results of these studies, the reactions occurring during the three procedures were discussed

Pivalolactone, 3. Reactive blending of polypivalolactone with polycarbonate

The occurrence of interchange reactions during heating of polypivalolactone (PPVL) with three polymers and their influence on the blend properties were studied. Physical blends of PPVL and bisphenol-A polycarbonate (PC) were found to be immiscible. By heating of PPVL/PC blends in the melt at 280°C, in diphenyl ether at 260°C and in a twin-screw extruder (TSE) at 280°C partial formation of copolymers was observed, provided that tetrabutyl orthotitanate (TnBT) was added. After heating of equimolar PPVL/PC blends in a TSE for 15 min, a PPVL-PC block copolymer could be isolated containing 25 mol-% pivalolactone (PVL) units. The results from thermal analyses indicated that PPVL/PC blends had become more miscible, due to the presence of copolymers formed by interchange reactions. After heating of equimolar mixtures of PPVL and a polyarylate (PAr) in a TSE for 15 min, PPVL-PAr copolymers with 5 mol-% PVL units could be isolated. Probably due to this low degree of interchange, no effect on the miscibility of the initially immiscible PPVL/PAr blends could be observed. PPVL/poly(butylene terephthalate) (PBT) blends, obtained after heating in a TSE, decomposed at a temperature between the melting temperatures of PPVL and PBT, indicating that interchange reactions may have occurred