The Asiago Supernova Catalogue- 10 years after

Ten years after the publication of the previous release, we present a new edition of the Asiago Supernova Catalogue updated to December 31, 1998 and containing data for 1447 supernovae and their parent galaxies\footnote{Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}. In addition to list the data for a large number of new SNe, we made an effort to search the literature for new information on past SNe as well. We also tried to update and homogenize the data for the parent galaxies. To allow a global view of the Catalogue, a few descriptive figures and a summary table is reported. The present Catalogue is intended as a large and modern database for statistical studies on the supernova phenomenon.Comment: 6 pages. To be published in A&A supplement. Enclosed as postscript files are the full lists in chronological (snean.ps) and R.A. (snear.ps) order (to be published only in electronic form.

Fast Scramblers Of Small Size

We investigate various geometrical aspects of the notion of `optical depth' in the thermal atmosphere of black hole horizons. Optical depth has been proposed as a measure of fast-crambling times in such black hole systems, and the associated optical metric suggests that classical chaos plays a leading role in the actual scrambling mechanism. We study the behavior of the optical depth with the size of the system and find that AdS/CFT phase transitions with topology change occur naturally as the scrambler becomes smaller than its thermal length. In the context of detailed AdS/CFT models based on D-branes, T-duality implies that small scramblers are described in terms of matrix quantum mechanics.Comment: 14 pages, 3 figures. Added reference

Structural Modification, Polymerization and Applications of Boron Difluoride Formazanates

This thesis describes the synthesis and characterization of a new family of fluorescent and redox-active BF2 complexes of formazanate [R1-N-N=C(R3)-N=N-R5]− ligands. The complexes were easily synthesized in two high-yielding steps, from inexpensive starting materials and readily purified by conventional methods. The properties of the resulting complexes can be tuned through structural variation – for example, appending electron donating or withdrawing substituents, or extending π conjugation. These methods of structural variation can bathochromically or hypsochromically shift the maximum absorption and emission wavelengths, vary the quantum yields, and allow for tuning of the reduction potentials. Using these methods, the properties of these complexes were optimized for use as fluorescence cell-imaging agents, and efficient electrochemiluminescence emitters. In order to expand the scope of this chemistry, copper-assisted azide-alkyne cycloaddition (CuAAC) chemistry was used to further modify the BF2 formazanate scaffold. Using this method, benzyl groups were appended to the BF2 complexes, which showed that the reaction proceeded cleanly, and that the resulting products had red-shifted wavelengths of maximum absorption and emission, and increased fluorescence quantum yields. Using the same strategy, a tetraethylene glycol based azide imparted water solubility, and the resulting complex was used in fluorescence cell-imaging experiments. Additionally, ferrocene moieties could be appended, which quenched the fluorescence of the resulting complex. Upon oxidation of the ferrocene groups, the fluorescence was regenerated allowing for these compounds to be used as redox sensors. Finally, CuAAC was used to synthesize copolymers of BF2 formazanate complexes and 9,9-dihexylfluorene. The resulting polymers had low band gaps (Eg = 1.67 eV) and good film-forming properties, paving the way for their use in organic photovoltaics. Finally, reaction of an o-phenol-substituted formazan with BF3•OEt2 and NEt3 resulted in a complex reaction mixture, which contained 5 BN heterocycles with unprecedented connectivity and interesting optical and electronic properties. Two of the most unique complexes were selected, and their chemical reduction products – a stable anion, radical anion and diradical dianion were studied in detail. Combined, this work has opened up an entirely new area of molecular materials with application in a variety of fields. This thesis describes the details of the work described above

The Distribution of High and Low Redshift Type Ia Supernovae

The distribution of high redshift Type Ia supernovae (SNe Ia) with respect to projected distance from the center of the host galaxy is studied and compared to the distribution of local SNe. The distribution of high-z SNe Ia is found to be similar to the local sample of SNe Ia discovered with CCDs, but different than the sample discovered photographically. This is shown to be due to the Shaw effect. These results have implications for the use of SNe Ia to determine cosmological parameters if the local sample of supernovae used to calibrate the light curve decline relationships is drawn from a sample discovered photographically. A K-S test shows that the probability that the high redshift SNe of the Supernova Cosmology Project are drawn from the same distribution as the low redshift calibrators of Riess et al. is 0.1%. This is a potential problem because photographically discovered SNe are preferentially discovered farther away from the galaxy nucleus, where SNe show a lower scatter in absolute magnitude, and are on average 0.3 magnitudes fainter than SNe located closer to the center of their host galaxy. This raises questions about whether or not the calibration SNe sample the full range of parameters potentially present in high redshift SNe Ia. The limited data available suggest that the calibration process is adequate; however, it would be preferable if high redshift SNe and the low redshift SNe used to calibrate them were drawn from the same sample, as subtle differences may be important. Data are also presented which suggest that the seeming anti-Malmquist trend noticed by Tammann et al.(1996, 1998) for SNe Ia in galaxies with Cepheid distances may be due to the location of the SNe in their host galaxies.Comment: 16 pages, 2 figures Accepted for publication in the Astrophysical Journa

Boron Difluoride Formazanate Copolymers with 9,9-Di-n-hexylfluorene Prepared by Copper-Catalyzed Alkyne-Azide Cycloaddition Chemistry

The synthesis and characterization of copolymers based on boron difluoride formazanate (BF2L) and 9,9-di-n-hexylfluorene (hex2Fl) units are described. A series of model compounds [(BF2L)-(hex2Fl), (hex2Fl)-(BF2L)-(hex2Fl), and (BF2L)-(hex2Fl)-(BF2L)] were also studied in order to fully understand the spectroscopic properties of the title copolymer [(BF2L)-(hex2Fl)]n. The model compounds and copolymers, which were synthesized by copper catalyzed alkyne-azide cycloaddition chemistry, exhibited high molar absorptivities (25,700-54,900 M-1 cm-1), large Stokes shifts (123-143 nm, 3590-3880 cm-1), and tunable electrochemical behaviour (E°red1 ca. -0.75 V and E°red2 ca. -1.86 V vs. ferrocene/ferrocenium). The low-energy wavelength of maximum absorption and emission of the model compounds red-shifted relative to the BF2L repeating unit by ca. 30 nm per triazole ring formed, to maximum values of 557 nm and 700 nm in DMF, respectively. The low-energy absorption and emission properties of the copolymer were consistent with the model compound bearing two triazole rings [(hex2Fl)-(BF2L)-(hex2Fl)] and were not dependant on copolymer molecular weight. However, the title copolymers may show promise as a light-harvesting material based on their thin-film optical band gap of 1.67 eV

Tachyon condensation and off-shell gravity/gauge duality

We investigate quasilocal tachyon condensation by using gravity/gauge duality. In order to cure the IR divergence due to a tachyon, we introduce two regularization schemes: AdS space and a d=10 Schwarzschild black hole in a cavity. These provide stable canonical ensembles and thus are good candidates for the endpoint of tachyon condensation. Introducing the Cardy-Verlinde formula, we establish the on-shell gravity/gauge duality. We propose that the stringy geometry resulting from the off-shell tachyon dynamics matches onto the off-shell AdS black hole, where "off-shell" means non-equilibrium configuration. The instability induced by condensation of a tachyon behaves like an off-shell black hole and evolves toward a large stable black hole. The off-shell free energy and its derivative ($\beta$-function) are used to show the off-shell gravity/gauge duality for the process of tachyon condensation. Further, d=10 Schwarzschild black hole in a cavity is considered for the Hagedorn transition as a possible explanation of the tachyon condensation.Comment: 28 pages, 13 eps figures, version to appear in IJMP

Unitarity issue in BTZ black holes

We study the wave equation for a massive scalar in three-dimensional AdS-black hole spacetimes to understand the unitarity issues in a semiclassical way. Here we introduce four interesting spacetimes: the non-rotating BTZ black hole (NBTZ), pure AdS spacetime (PADS), massless BTZ black hole (MBTZ), and extremal BTZ black hole (EBTZ). Our method is based on the potential analysis and solving the wave equation to find the condition for the frequency $\omega$ exactly. In the NBTZ case, one finds the quasinormal (complex and discrete) modes which signals for a non-unitary evolution. Real and discrete modes are found for the PADS case, which means that it is unitary obviously. On the other hand, we find real and continuous modes for the two extremal black holes of MBTZ and EBTZ. It suggests that these could be candidates for the unitary system.Comment: 14 pages, contracted version to appear in MPL

Hagedorn Strings and Correspondence Principle in AdS(3)

Motivated by the possibility of formulating a strings/black hole correspondence in AdS space, we extract the Hagedorn behavior of thermal AdS_3 bosonic string from 1-loop partition function of SL(2,R) WZW model. We find that the Hagedorn temperature is monotonically increasing as the AdS radius shrinks, reaches a maximum of order of string scale set by the unitarity bound of the CFT for internal space. The resulting density of states near the Hagedorn temperature resembles the form as for strings in flat space and is dominated by the space-like long string configurations. We then argue a conjectured strings/black hole correspondence in AdS space by applying the Hagedorn thermodynamics. We find the size of the corresponding black hole is a function of the AdS radius. For large AdS radius a black hole far bigger than the string scale will form. On the contrary, when the AdS and string scales are comparable a string size black hole will form. We also examine strings on BTZ background obtained through SL(2,Z) transformation. We find a tachyonic divergence for a BTZ black hole of string scale size.Comment: 28 pages, 4 figures;v2 references added & appear on JHE