Is the pi-particle responsible for the 41 meV peak in YBa_2Cu_3O_7?

It is argued that there is no low-energy resonance associated with the pi-operators introduced by Demler and Zhang. This implies that the Hubbard model does not possess an approximate SO(5) symmetry generated by these operators. Recent finite-size studies are re-interpreted accordingly.Comment: 3 pages, latex (revtex

Uniformity in association schemes and coherent configurations: cometric Q-antipodal schemes and linked systems

Inspired by some intriguing examples, we study uniform association schemes and uniform coherent configurations, including cometric Q-antipodal association schemes. After a review of imprimitivity, we show that an imprimitive association scheme is uniform if and only if it is dismantlable, and we cast these schemes in the broader context of certain --- uniform --- coherent configurations. We also give a third characterization of uniform schemes in terms of the Krein parameters, and derive information on the primitive idempotents of such a scheme. In the second half of the paper, we apply these results to cometric association schemes. We show that each such scheme is uniform if and only if it is Q-antipodal, and derive results on the parameters of the subschemes and dismantled schemes of cometric Q-antipodal schemes. We revisit the correspondence between uniform indecomposable three-class schemes and linked systems of symmetric designs, and show that these are cometric Q-antipodal. We obtain a characterization of cometric Q-antipodal four-class schemes in terms of only a few parameters, and show that any strongly regular graph with a ("non-exceptional") strongly regular decomposition gives rise to such a scheme. Hemisystems in generalized quadrangles provide interesting examples of such decompositions. We finish with a short discussion of five-class schemes as well as a list of all feasible parameter sets for cometric Q-antipodal four-class schemes with at most six fibres and fibre size at most 2000, and describe the known examples. Most of these examples are related to groups, codes, and geometries.Comment: 42 pages, 1 figure, 1 table. Published version, minor revisions, April 201

Development of capillary based separation techniques for the separation of proteins equilibrated using hexapeptide ligand libraries

Challenges in research areas such as chemistry, medicine, environmental toxicology and biology require the analysis of complex samples. Fast analysis of these samples using separation techniques with spectrometric or spectroscopic detection is common. Most often, chromatographic separation techniques such as gas and liquid chromatography coupled to mass spectrometry are chosen. These techniques, however, often reach their limits when highly charged analytes are investigated. Here, electromigrative separation techniques with their orthogonal separation mechanism are an attractive alternative. A very promising electrophoretic separation technique, which is primarily used during this work, is capillary electrophoresis (CE). One of the greatest challenges using this technique lies in the separation of biological samples, since analytes such as polyamines, peptides and proteins interact with and adsorb on the surface of “bare fused silica”-capillaries which impairs reproducibility. Without efficient suppression of these interactions, separation efficiency and run-to-run reproducibility suffer. A good way to suppress these detrimental interactions of analytes with the capillary surface is to modify the surface using of dynamic, statically adsorbed or covalently bound capillary coatings. In this work, I present approaches for the reproducible separation of polyamines, peptides and proteins: 1) In Chapter 2, the use of poly ethylene oxide as dynamic coating in SDS-CE enables the size-based separation of proteins up to a weight of 100 kDa. Advantages of this technique over classic gelbased SDS-PAGE are separation times of about 20 min and direct quantification via on-line UVdetection without the need of preliminary labeling or subsequent dyeing. Separation times were reduced to 5 min by short-end-injection and modification of the aperture for UV-detection. The presented separation system offers outstanding matrix tolerance: even complex samples such as serum were successfully separated without additional processing. Increased separation performance and efficiency were aspired by the addition of alkanols to the BGE, variation of temperature and the use of enrichment plugs in the capillary. Therein, especially the use of 2- propanol in the BGE proves fruitful regarding separation efficiency in the mass range up to 40 kDa. In Chapter 3 I will interpret my results with an extensive literature search to show, that the observed increase in separation efficiency is linked to a change of the separation mechanism from Reptation- to Ogston-sieving. 2) In Chapter 4, I proudly present, that I achieved CE-separation with MS-hyphenation not only for small polyamines and peptides, but also of large, non-digested proteins. This was possible using a single capillary coating only based on N-acryloylamido ethoxyethanol (AAEE). This highly polar and covalently bound capillary coating offers enjoyably high reproducibly and stability, the latter enabling operating times of 100 h, even when complex samples such as human serum and polyamines in fish eggs were analyzed. In Chapter 5 a novel and parallelized approach for the synthesis of this capillary coating is presented. SEM-measurements of the capillary surface between reaction steps forced me to postulate a novel reaction-mechanism for the formation of the coated surface. Additionally, I present, that pre-conditioning of capillaries with hypercritical water can result in higher reproducibility of capillary-to-capillary performance and reduced synthesis time. In Chapter 6 I will show that the presented separation techniques are excellent for the separation and detection of proteins equilibrated using hexapeptide ligand libraries (HLL). A novel approach for the consecutive equilibration of small sample volumes, which enables a deep insight into the proteome, is critically discussed. Challenges intrinsic to the solid phase extraction of proteins using HLLs are traced back to irreversible binding sites on HLLs. To tackle this issue, different elution and pre-equilibration protocols are designed and investigated. To re-establish binding conditions in consecutive equilibration, which is consecutive equilibration, different protocols for the processing of eluates from HLLs using 10 kDa cut-off filters are presented. Aspects that critically impair yields and recovery rates come to the fore and improved protocols are presented. A further project focused on CE-MS-based pI-value determination of a hardly soluble, cyclic and antibiotic peptide (Chapter 7). Detection of this peptide was not possible using AAEE-coated capillaries. This problem was overcome by using non-coated capillaries and BGEs containing small amounts of citric acid, which functions not only as buffer but also as a dynamic capillary coating. To confirm the determined pI-vaues, a novel and time-saving approach for the sequential injection of amino acid reference substances was developed.Fragestellungen in der Chemie aber auch in vielen anderen Disziplinen wie der Medizin, Umwelttoxikologie und Biologie, erfordern die Untersuchung von teilweise sehr komplexen Stoffgemischen. Eine schnelle Untersuchung von komplexen Proben ist mittels Trenntechniken, gefolgt von spektroskopischer oder spektrometrischer Detektion möglich. Zu den am weitesten verbreiteten Techniken gehören hierbei chromatographische Methoden wie die Gas- und Flüssigchromatographie, häufig gekoppelt mit Massenspektrometrie. Geraten diese chromatographischen Techniken an ihre Grenzen, beispielsweise bei hoch geladenen Stoffen, so bietet sich der Einsatz von elektromigrativen Trenntechniken an, da diese einen orthogonalen Trennmechanismus besitzen. Die Kapillarelektrophorese (engl.: capillary electrophoresis, CE), mit welcher sich diese Arbeit befasst, zählt zu den elektromigrativen Trenntechniken. Eine große Herausforderung dieser Technik besteht u.a. in der geringen Reproduzierbarkeit bei der Analytik von Biomolekülen, welche sich auf die Verwendung von „bare fused silica“-Kapillaren und deren Wechselwirkung mit den Analyten zurückführen lässt. Wird diese Wechselwirkung nicht effizient unterdrückt, so sinkt die Trenneffizienz innerhalb und die Wiederholbarkeit zwischen Trennungen. Durch die Verwendung von dynamischen, statisch adsorbierten oder kovalent gebundenen Kapillarbeschichtungen kann diese Wechselwirkung effizient unterdrückt werden. In dieser Arbeit werden mehrere Möglichkeiten zur reproduzierbaren Trennung von Polyaminen, Peptiden und Proteinen vorgestellt: 1) In Kapitel 2 wird durch die Verwendung von Polyethylenoxid als dynamische Beschichtung und Siebmatrix in der SDS-CE die größenbasierte Trennung von Proteinen bis zu einer Masse von 100 kDa erreicht. Ein Vorteil gegenüber klassischen gelbasierten Verfahren wie SDS-PAGE ist hierbei, dass Proben innerhalb von 20 min getrennt und durch on-column UV-Detektion quantifiziert werden können, ohne vor- oder nachträgliches Anfärben oder Derivatisieren. Durch eine selbst entworfene Modifikation der Trennapparatur und Injektion vom kurzen Ende der Kapillare konnte diese Trennzeit für ein schnelles Screening auf 5 Minuten reduziert werden. Das vorgestellte Trennsystem zeichnet sich durch eine hohe Matrixtoleranz aus; selbst Proben wie menschliches Serum können ohne Aufarbeitung injiziert werden. Eine Verbesserung der Auflösung und Trenneffizienz wurde durch die Verwendung von verschiedenen Alkoholen im Hintergrundelektrolyten, die Variation der Trenntemperatur und die Etablierung von Anreicherungszonen in der Kapillare angestrebt. Hierbei zeigte vor allem die Verwendung von 2- Propanol im Hintergrundelektrolyten eine erhöhte Trenneffizienz im Massenbereich bis ca. 40 kDa. In Kapitel 3 wird anhand der eigenen Ergebnisse und durch ausführliche Literaturarbeit gezeigt, dass diese Verbesserung der Auflösung durch eine Verschiebung des Trennmechanismus von Reptation- zu Ogstonsieben ermöglicht wird. 2) Durch die Verwendung einer sehr polaren kovalenten Kapillarbeschichtung, dem NAcryloylamido- ethoxyethanol (AAEE), lässt sich die kapillarelektrophoretische Trennung von kleinen Polyaminen und Peptiden, aber auch großen und unverdauten Proteinen, bei gleichzeitiger massenspektrometrischer Detektion erreichen. Dies wird in Kapitel 4 vorgestellt. Erfreulich hohe Einsatzzeiten von ca. 100 h und gute Wiederholbarkeiten werden sogar bei der Untersuchung von menschlichem Serum oder Polyaminen in Fischeiern beobachtet. In Kapitel 5 werden ein neuer und ABSTRACT (DEUTSCH) 4 parallelisierter Ansatz zur Kapillarsynthese sowie ein koexistenter und durch SEM-Aufnahmen postulierter Reaktionsmechanismus vorgestellt. Zusätzlich wird ein Ansatz zur Vorbehandlung der Kapillaren durch die Verwendung von überkritischem Wasser vorgeschlagen, welcher ersten Versuchen nach zu einer höheren Reproduzierbarkeit der Beschichtung und einer beschleunigten Synthese führen kann. In Kapitel 6 werden die vorgestellten Analysetechniken werden für die Bestimmung von Proteinen in mittels Hexapeptidligandenbibliotheken angereicherten Proben verwendet. Ein Ansatz zur mehrfachen Anreicherung, der einen tiefen Blick ins Proteom erlauben soll, wird kritisch bewertet. Herausforderungen in der Festphasenanreicherung werden auf irreversible Bindungsstellen zurückgeführt. In diesem Zusammenhang werden verschiedene Elutions- und PreÄquilibrierungsprotokolle untersucht. Für die erfolgreiche Wiederbeladung, welche einen tieferen Blick ins Proteom erlaubt, werden verschiedene Protokolle zur Aufarbeitung des Eluats mittels 10 kDa-Cut-off-Filtern vorgestellt. Kritische Aspekte, welche die Ausbeuten beeinträchtigen, werden beleuchtet und Lösungswege aufgezeigt. In Kapitel 7 wird die MS-basierte pI-Wertbestimmung eines schwerlöslichen zyklischen Peptidantibiotikums vorgestellt. Dieses konnte mit AAEE-beschichteten Kapillaren nicht erfasst werden. Diese Herausforderung konnte durch die Verwendung unbeschichteter Kapillaren und geringen Mengen Zitronensäure im Hintergrundelektrolyt, welche als dynamische Beschichtung fungiert, umgangen werden. Zur Absicherung der bestimmten pI-Werte mit Aminosäurestandards wurde ein neuer und zeitsparender Ansatz der sequentiellen Injektion entwickelt

Optical and Infrared Analysis of Type II SN 2006BC

We present nebular phase optical imaging and spectroscopy and near/mid-IR imaging of the Type II SN 2006bc. Observations reveal the central wavelength of the symmetric H$\alpha$ line profile to be red-shifted with respect to the host galaxy H$\alpha$ emission by day 325. Such an phenomenon has been argued to result from an asymmetric explosion in the iron-peak elements resulting in a larger mass of $^{56}$Ni and higher excitation of hydrogen on the far side of the SN explosion. We also observe a gradual blue-shifting of this H$\alpha$ peak which is indicative of dust formation in the ejecta. Although showing a normal peak brightness, V $\sim$ -17.2, for a core-collapse SN, 2006bc fades by $\sim$6 mag during the first 400 days suggesting either a relatively low $^{56}$Ni yield, an increase in extinction due to new dust, or both. A short duration flattening of the light curve is observed from day 416 to day 541 suggesting an optical light echo. Based on the narrow time window of this echo, we discuss implications on the location and geometry of the reflecting ISM. With our radiative transfer models, we find an upper limit of 2 x 10$^{-3}$ M$_{\odot}$ of dust around SN 2006bc. In the event that all of this dust were formed during the SN explosion, this quantity of dust is still several orders of magnitude lower than that needed to explain the large quantities of dust observed in the early universe.Comment: 6 pages, 10 figures, accepted for publication in Ap

The interface between the stellar wind and interstellar medium around R Cassiopeiae revealed by far-infrared imaging

The circumstellar dust shells of intermediate initial-mass (about 1 to 8 solar masses) evolved stars are generated by copious mass loss during the asymptotic giant branch phase. The density structure of their circumstellar shell is the direct evidence of mass loss processes, from which we can investigate the nature of mass loss. We used the AKARI Infrared Astronomy Satellite and the Spitzer Space Telescope to obtain the surface brightness maps of an evolved star R Cas at far-infrared wavelengths, since the temperature of dust decreases as the distance from the star increases and one needs to probe dust at lower temperatures, i.e., at longer wavelengths. The observed shell structure and the star's known proper motion suggest that the structure represents the interface regions between the dusty wind and the interstellar medium. The deconvolved structures are fitted with the analytic bow shock structure to determine the inclination angle of the bow shock cone. Our data show that (1) the bow shock cone of 1 - 5 x 10^-5 solar masses (dust mass) is inclined at 68 degrees with respect to the plane of the sky, and (2) the dust temperature in the bow shock cone is raised to more than 20 K by collisional shock interaction in addition to the ambient interstellar radiation field. By comparison between the apex vector of the bow shock and space motion vector of the star we infer that there is a flow of interstellar medium local to R Cas whose flow velocity is at least 55.6 km/s, consistent with an environment conducive to dust heating by shock interactions.Comment: 7 pages, 2 figures, accepted for publication in Astronomy and Astrophysic

The tails in the Helix Nebula NGC 7293

We have examined a stream-source model for the production of the cometary tails observed in the Helix Nebula NGC 7293 in which a transonic or moderately supersonic stream of ionized gas overruns a source of ionized gas. Hydrodynamic calculations reveal velocity structures which are in good agreement with the observational data on tail velocities and are consistent with observations of the nebular structure. The results also are indicative of a stellar atmosphere origin for the cometary globules. Tail remnants persist for timescales long enough for their identification with faint striations visible in the nebula gas to be plausible.Comment: 7 pages, 6 figures, accepted for publication in A&

Interstellar abundances in the neutral and ionized gas of NGC604

We present FUSE spectra of the giant HII region NGC604 in the spiral galaxy M33. Chemical abundances are derived from far-UV absorption lines and are compared to those derived from optical emission lines. We derived the column densities of HI, NI, OI, SiII, PII, ArI, and FeII, fitting the line profiles with either a single component or several components. Our net results, assuming a single component, show that N, O, Si, and Ar are apparently underabundant in the neutral phase by a factor of 10 or more with respect to the ionized phase, while Fe is the same. However, we discuss the possibility that the absorption lines are made of individual unresolved components, and find that only PII, ArI, and FeII lines should not be affected by the presence of hidden saturated components, while NI, OI, and SiII might be much more affected. If N, O, and Si are actually underabundant in the neutral gas of NGC604 with respect to the ionized gas, this would confirm earlier results obtained for the blue compact dwarfs. However, a deeper analysis focused on P, Ar, and Fe mitigates the above conclusion and indicates that the neutral gas and ionized gas could have similar abundances.Comment: Accepted for publication in A&

Meixner class of non-commutative generalized stochastic processes with freely independent values I. A characterization

Let $T$ be an underlying space with a non-atomic measure $\sigma$ on it (e.g. $T=\mathbb R^d$ and $\sigma$ is the Lebesgue measure). We introduce and study a class of non-commutative generalized stochastic processes, indexed by points of $T$, with freely independent values. Such a process (field), $\omega=\omega(t)$, $t\in T$, is given a rigorous meaning through smearing out with test functions on $T$, with $\int_T \sigma(dt)f(t)\omega(t)$ being a (bounded) linear operator in a full Fock space. We define a set $\mathbf{CP}$ of all continuous polynomials of $\omega$, and then define a con-commutative $L^2$-space $L^2(\tau)$ by taking the closure of $\mathbf{CP}$ in the norm $\|P\|_{L^2(\tau)}:=\|P\Omega\|$, where $\Omega$ is the vacuum in the Fock space. Through procedure of orthogonalization of polynomials, we construct a unitary isomorphism between $L^2(\tau)$ and a (Fock-space-type) Hilbert space $\mathbb F=\mathbb R\oplus\bigoplus_{n=1}^\infty L^2(T^n,\gamma_n)$, with explicitly given measures $\gamma_n$. We identify the Meixner class as those processes for which the procedure of orthogonalization leaves the set $\mathbf {CP}$ invariant. (Note that, in the general case, the projection of a continuous monomial of oder $n$ onto the $n$-th chaos need not remain a continuous polynomial.) Each element of the Meixner class is characterized by two continuous functions $\lambda$ and $\eta\ge0$ on $T$, such that, in the $\mathbb F$ space, $\omega$ has representation \omega(t)=\di_t^\dag+\lambda(t)\di_t^\dag\di_t+\di_t+\eta(t)\di_t^\dag\di^2_t, where \di_t^\dag and \di_t are the usual creation and annihilation operators at point $t$

Time--delay autosynchronization of the spatio-temporal dynamics in resonant tunneling diodes

The double barrier resonant tunneling diode exhibits complex spatio-temporal patterns including low-dimensional chaos when operated in an active external circuit. We demonstrate how autosynchronization by time--delayed feedback control can be used to select and stabilize specific current density patterns in a noninvasive way. We compare the efficiency of different control schemes involving feedback in either local spatial or global degrees of freedom. The numerically obtained Floquet exponents are explained by analytical results from linear stability analysis.Comment: 10 pages, 16 figure