1,933 research outputs found
A Relational Theory of Authorship
No full textOver the years we have heard the debate as to whether authorship emanates solely from the individual or from the cultural context in which they inhabit. Writers such as Professors Woodmansee, Jaszi and Cohen have asserted a cultural theory of authorship. On one hand, there is the liberal philosophy of autonomous creativity evidenced in the notion of a "romantic author" (after the period known as romanticism). On the other hand we have more of a communitarian notion – that the author acts in a cultural context and authorship to some extent must be linked back to the social existence within which the author is situated.\ud
\ud
This article argues that for too long we have privileged the notion of the romantic author so much so that it is hard to argue for any other approach to copyright than one that focuses primarily on the author and their assignees such as publishers or associated commercialising agents such as recording companies. Furthermore it suggests that this approach fits awkwardly with the burgeoning networked society fuelled by the Internet to the point where it threatens innovation and the potential for productivity. To this end the article argues that we should more explicitly acknowledge the contribution of culture to authorship and more so the role of each and every individual in assisting and nurturing that authorship, as well as the contribution of users to creativity through consumptive, productive and transformative use of copyright works
Chancellor Konrad Adenauer: Convocation Speech
No full textRepository: Booth Family Center for Special Collections. For more information about this collection please email: [email protected] in Gaston Hall. Academic convocation and honorary degree ceremony in honor of West German Chancellor Konrad Adenauer. Begins with the reading of the University Charter by Secretary of the Corporation and Dean of the College of Arts and Sciences Brian A. McGrath, S.J. President Edward B. Bunn, S.J, then delivers a welcoming address in which he terms Adenauer a "symbol as well as a leader" of post-World War II German development. The honorary degree citation is read in Latin by the Graduate School Dean Gerard F. Yates, S.J. This is followed by Adenauer's address in German, then English, beginning around the 17 minute 45 mark, Adenauer concludes by announcing the setting up of a full scholarship to be awarded to a graduating Georgetown student for one year's study at any German University
Dimerization mechanisms of heterocyclic carbenes
No full textDavid C. Graham, Kingsley J. Cavell and Brian F. Yate
Increased stability of NO and NS heterocyclic carbenes?
No full textDensity functional theory has been used to investigate the effects of alkylation and oxidation on the stability of NO and NS heterocyclic carbenes. While O- and S-alkylation leads to a dramatic increase in stability with respect to dimerization, oxidation of the NS heterocyclic carbene to form the sulphoxide appears to have the opposite effect.David C. Graham and Brian F. Yate
GU Graduation Exercises June 7, 1953 Part 2 #68.
No full textRepository: Booth Family Center for Special Collections. For more information about this collection please email: [email protected] during the remarks of President Edward B. Bunn, S.J. This is followed by the reading of the Charter by Dean of the College of Arts and Sciences Brian A. McGrath, S.J., the presentation of the Medal of Merit to Charles M. Williams, C 1934, the reading of honorary degrees citations in Latin for Carlton Hayes, Francis C. Nash, and Frederick B. Sitterding, Jr., the presentation of candidates for degrees in course in Arts and Sciences by Dean Brian A. McGrath, S.J., in Graduate Studies by Dean Gerard F. Yates, S.J., in Medicine by Dean Paul A. McNally, S.J., in Law by Dean Hugh J. Fegan, S.J., in Dental Surgery by Dean C.V. Rault, in Foreign Service by Executive Assistant to the Regent Frank L. Fadner, S.J., and in Nursing by Dean Sister Angela Marie, S.C.N., and the presentation of candidates for commissions in the Officers Corps of the Armed Forces of the United States
Dimethylcuprate undergoes a dyotropic rearrangement
No full textComparison of the gas-phase decomposition reactions of [CH<sub>3</sub>CuCH<sub>3</sub>]<sup>−</sup> and [CH<sub>3</sub>AgCH<sub>3</sub>]<sup>−</sup> reveals that [CH<sub>3</sub>CuCH<sub>3</sub>]<sup>−</sup> undergoes a competition between a dyotropic rearrangement and bond homolysis, whilst [CH<sub>3</sub>AgCH<sub>3</sub>]<sup>−</sup> only undergoes bond homolysis. Ab initio calculations reveal that the different behavior in [CH<sub>3</sub>AgCH<sub>3</sub>]<sup>−</sup> stems from both the lowering of the homolytic bond dissociation energy and an increase in dyotropic rearrangement activation energy
Two Spin-State Reactivity in the Activation and Cleavage of CO2by [ReO2]
No full textThe rhenium dioxide anion [ReO2](-) reacts with carbon dioxide in a linear ion trap mass spectrometer to produce [ReO3](-) corresponding to activation and cleavage of a C-O bond. Isotope labeling experiments using [(ReO2)-O-18](-) reveal that O-18/O-16 scrambling does not occur prior to cleavage of the C-O bond. Density functional theory calculations were performed to examine the mechanism for this oxygen atom abstraction reaction. Because the spins of the ground states are different for the reactant and product ions ((3)[ReO2](-) versus (1)[ReO3](-)), both reaction surfaces were examined in detail and multiple [O2Re-CO2](-) intermediates and transition structures were located and minimum energy crossing points were calculated. The computational energy results show that the intermediate [O2Re(eta(2)-C,O-CO2)](-) species most likely initiates C-O bond activation and cleavage. The stronger binding affinity of CO2 within this species and the greater instabilities of other [O2Re-CO2)](-) intermediates are significant enough that oxygen atom exchange is avoided
Ligand rotation in [Ar(R)N](3)M-N(2)-M'[N(R)Ar](3) (M, M' = Mo(II), Nb(III); R = (i)Pr and (t)Bu) dimers
No full textEarlier calculations on the model N2-bridged dimer (µ-N2)-{Mo[NH2]3}2 revealed that ligand rotation away from a trigonal arrangement around the metal centres was energetically favourable resulting in a reversal of the singlet and triplet energies such that the singlet state was stabilized 13 kJ mol–1 below the D3d triplet structure. These calculations, however, ignored the steric bulk of the amide ligands N(R)Ar (R =iPr and tBu, Ar = 3,5-C6H3Me2) which may prevent or limit the extent of ligand rotation. In order to investigate the consequences of steric crowding, density functional calculations using QM/MM techniques have been performed on the MoIIIMoIII and MoIIINbIII intermediate dimer complexes (µ-N2)-{Mo[N(R)Ar]3}2 and [Ar(R)N]3Mo-(µ-N2)-Nb[N(R)Ar]3 formed when three-coordinate Mo[N(R)Ar]3 and Nb[N(R)Ar]3 react with dinitrogen. The calculations indicate that ligand rotation away from a trigonal arrangement is energetically favourable for all of the ligands investigated and that the distortion is largely electronic in origin. However, the steric constraints of the bulky amide groups do play a role in determining the final orientation of the ligands, in particular, whether the ligands are rotated at one or both metal centres of the dimer. Analogous to the model system, QM/MM calculations predict a singlet ground state for the (µ-N2)-{Mo[N(R)Ar]3}2 dimers, a result which is seemingly at odds with the experimental triplet ground state found for the related (µ-N2)-{Mo[N(tBu)Ph]3}2 system. However, QM/MM calculations on the (µ-N2)-{Mo[N(tBu)Ph]3}2 dimer reveal that the singlet–triplet gap is nearly 20 kJ mol–1 smaller and therefore this complex is expected to exhibit very different magnetic behaviour to the (µ-N2)-{Mo[N(R)Ar]3}2 system.Gemma Christian, Robert Stranger, Brian F. Yates and David C. Graha
Theoretical approaches to estimating homolytic bond dissociation energies of organocopper and organosilver compounds
No full textAlthough organocopper and organosilver compounds are known to decompose by homolytic pathways among others, surprisingly little is known about their bond dissociation energies (BDEs). In order to address this deficiency, the performance of the DFT functionals BLYP, B3LYP, BP86, TPSSTPSS, BHandHLYP, M06L, M06, M06-2X, B97D, and PBEPBE, along with the double hybrids, mPW2-PLYP, B2-PLYP, and the ab initio methods, MP2 and CCSD(T), have been benchmarked against the thermochemistry for the M–C homolytic BDEs (<i>D</i><sub>0</sub>) of Cu–CH<sub>3</sub> and Ag–CH<sub>3</sub>, derived from guided ion beam experiments and CBS limit calculations (<i>D</i><sub>0</sub>(Cu–CH<sub>3</sub>) = 223 kJ·mol<sup>–1</sup>; <i>D</i><sub>0</sub>(Ag–CH<sub>3</sub>) = 169 kJ·mol<sup>–1</sup>). Of the tested methods, in terms of chemical accuracy, error margin, and computational expense, M06 and BLYP were found to perform best for homolytic dissociation of methylcopper and methylsilver, compared with the CBS limit gold standard. Thus the M06 functional was used to evaluate the M–C homolytic bond dissociation energies of Cu–R and Ag–R, R = Et, Pr, <i>i</i>Pr, <i>t</i>Bu, allyl, CH<sub>2</sub>Ph, and Ph. It was found that <i>D</i><sub>0</sub>(Ag–R) was always lower (∼50 kJ·mol<sup>–1</sup>) than that of <i>D</i><sub>0</sub>(Cu–R). The trends in BDE when changing the R ligand reflected the H–R bond energy trends for the alkyl ligands, while for R = allyl, CH<sub>2</sub>Ph, and Ph, some differences in bond energy trends arose. These trends in homolytic bond dissociation energy help rationalize the previously reported (Rijs, N. J.; O’Hair, R. A. J. <i>Organometallics</i><b>2010</b>, <i>29</i>, 2282–2291) fragmentation pathways of the organometallate anions, [CH<sub>3</sub>MR]<sup>−</sup>
Tissue engineering of a tracheal substitute
No full textLectin histochemistry and scanning electron microscopy (SEM) was used to assess the growth and characterise the differentiation of human respiratory epithelial cells (REC) cultured on two biomaterial scaffolds. The first scaffold, based on a hyaluronic acid derivative, was observed to be non-adhesive for REC. This lack of adhesion was found to be unrelated to the presence of the hyaluronic acid binding domain on the surface of isolated REC. The other scaffold, consisting of equine collagen, was observed to encourage REC spreading and adhesion. Positive Ulex Europaeus agglutinin (UEA) lectin staining of this preparation indicated the presence of ciliated REC on the scaffold surface. However, the marked decrease in peanut agglutinin (PNA) positive staining, relative to that of control cultures and native tissue, indicates a dedifferentiation of the secretory cells in monolayer. SEM analysis of REC cultured on the collagen scaffold confirmed the presence of ciliated cells thereby validating the UEA positive staining. The presence of both established and developing cilia was also verified. This indicates that collagen biomaterials are appropriate for the tissue engineering of REC. Furthermore, that UEA and PNA staining is a useful tool in the characterisation of cells cultured on biomaterials, therefore helpful in identifying biomaterials that are suitable for specific tissue engineering purposes.
The culture of REC at an air liquid interface (ALI) was investigated. Both conventional ALI inserts and the Biofleece scaffold were used. The cells grown the on conventional inserts became multilayered and showed some degree of ciliation after the period of ten days. The cells grown on the Biofleece scaffold became necrotic and died due to nutrient deprivation. The use of ALI culture techniques on scaffold materials needs to be adjusted to allow for sufficient nutrient supply to the cells.
The Biofleece scaffold was found to be suitable for the tissue engineering of cartilage in vitro. Constructs with a cartilage-like morphology were generated with the scaffold after two weeks in culture. The tissue-engineered cartilage was found to contain a higher number of cells and less extracellular matrix (ECM) than the native tissue controls. Suction seeding techniques were used to improve the distribution of cells within the scaffold and thereby increase the overall efficiency of cartilage tissue engineering within the scaffold. Alcian blue (AB) and Papanicolau (PN) stains of the tissue engineered cartilage described two distinct regions within the constructs, namely the developed cartilage-like region and the developing region. The latter is thought to be areas in which the cartilage cells are yet to fully remodel the scaffold material and deposit their own “native” ECM. However, the Biofleece scaffold material was observed to loose 40-50% of its initial volume during the tissue engineering process over a period of two weeks. Thus the degradation of the Biofleece scaffold exceeds the rate of maturation of the cartilage tissue within the scaffold. This rapid biodegradation is most likely a result of matrixmetalloproteinase (MMP), in particular collagenase, production by the maturing chondrocytes. This reduction in size means that the Biofleece scaffold is not an appropriate material for the tissue engineering of a trachea. The optimal biomaterial for the tissue engineering of a trachea would degrade at a rate equal too, or slower than, the time taken for the cells within the scaffold to mature into functional tissue.
The co-culture of REC and chondrocytes was achieved through the use of matrigel as a basement membrane replacement (note that direct growth of REC on cartilage tissue has been observed to be difficult). The co-cultured constructs were not stable because the Biofleece scaffold degrades at a high rate in the presence of both cell types. The constructs were observed to shrink to approximately 35-30% of the original dimensions in a period of 3-7 days. The reason for this accelerated degradation is not known but is most likely the result of severe MMP production by the two cell types when in combination.
It was concluded that the characterisation procedures used in this study (histochemical staining, fluorescent staining and scanning electron microscopy) for both REC and chondrocyte tissue engineered constructs are appropriate for this and further studies. The chondrocyte seeding methodologies in particular are a useful tool for tissue engineering. This study succeeds in many ways to investigate the tissue engineering of a tracheal substitute by detailing how REC and chondrocytes can be cultured on biomaterials and assessed for tissue development. However, the study does not deliver such a viable substitute as an end product. The primary reason for this outcome is the rapid degradation of the Biofleece scaffold materialLectin Histochemie und Elektronenmikroskopie wurden benutzt, um das Wachstum von humanen respiratorischen Epithelzellen (RECs), welche auf zwei Biomaterialien kultiviert wurden, festzusetzen und ihren Differenzierungsgrad zu bestimmen. Das erste Trägermaterial, welches auf einem Hyaluronsäurederivat basiert, ließ keine Anheftung der RECs zu. Diese fehlende Anheftung ließ sich jedoch nicht zurückführen auf das Vorhandensein der Hyaluronsäure bindenden Domaine auf der Oberfläche isolierter RECs. Das andere Trägermaterial, aus Pferdekollagen hergestellt, zeigte dagegen eine verstärkte Teilungsaktivität und Anheftung der REC. Die positive Ulex Europaeus Agglutinin (UEA) Lectin Färbung dieser Proben ließ die Anwesenheit von mit Zilien versehenen RECs auf der Trägerstoffoberfläche vermuten. Darüber hinaus weist das im Vergleich zu Kontrollkulturen und nativem Gewebe deutliche Nachlassen der positiven Peanut Agglutinin–Färbereaktion auf eine Dedifferenzierung der sekretorischen Zellen in der Monolayer-Kultur hin. Die rasterelektronenmikroskopische Untersuchung der auf dem Kollagenbiomaterial kultivierten RECs bestätigte das Auftreten von Zellen mit Zilien und damit auch die Aussagekräftigkeit der positiven UEA–Färbung. Dies zeigt somit, dass Biomaterialien aus Kollagen für das Tissue Engineering von RECs geeignet sind und dass sowohl die UEA–als auch die PNA–Färbung geeignete Methoden zur Charakterisierung von Zellen darstellen, die auf Biomaterialien kultiviert wurden. Somit helfen sie bei der Identifizierung von Biomaterialien für bestimmte Einsatzgebiete im Tissue Engineering.
Des weiteren wurde die Kultivierung von RECs auf einem Air liquid interface (ALI) untersucht, wobei sowohl der konventionelle ALI–Einsatz als auch das Biovliesmaterial zum Einsatz kamen. Dabei wuchsen die Zellen auf dem konventionellen Einsatz in Multilayern und zeigten nach einem Zeitraum von 10 Tagen einen bestimmten Anteil an Ziliierung. Die Zellen auf dem Biovlies dagegen wurden nekrotisch und gingen schließlich an Nahrungsmangel ein. Deshalb muss der Einsatz von ALI–Kulturtechniken bei Trägermaterialien dementsprechend modifiziert werden, dass eine ausreichende Versorgung der Zellen mit Nährstoffen gewährleistet ist.
Für das in vitro–Tissue Engineering von Knorpel erwies sich das Biovlies jedoch als geeignet. Mit ihm konnten nach zwei Wochen Kulturzeit Konstrukte mit einer knorpelähnlichen Morphologie erzeugt werden. Dabei zeigte sich, dass der Tissue Engineering–Knorpel eine höhere Zellzahl bei reduzierter extrazellulärer Matrix (ECM) aufwies als vergleichbares natives Kontrollgewebe. Dabei wurden Saugtechniken benutzt, um die Verteilung der Zellen im Trägerstoff zu verbessern. Die Alzian – Blau – Färbung (AB) und Papanicolau – Färbung (PN) zeigten bei dem Tissue Engineering–Knorpel zwei unterschiedliche Regionen innerhalb des Konstrukts, nämlich eine knorpelähnliche bereits entwickelte Region und eine sich entwickelnde Region. Bei letzterer dürfte es sich wohl um Gebiete handeln, in denen Zellen noch im Begriff sind, den Trägerstoff vollends umzubauen und ihre eigene „native“ ECM abzulagern. Nichtsdestoweniger büßte das Biovlies während des Tissue Engineering Prozesses über einen Zeitraum von zwei Wochen annähernd 40-50 % seines anfänglichen Volumens ein. Somit übersteigt das Ausmaß der Degradation des Biovlieses das des Heranreifens von Knorpelgewebe in dem Trägermaterial. Diese schnelle Biodegradation ist am ehesten das Ergebnis der Aktivität von Matrixmetalloproteinasen (MMP), insbesondere der Kollagenase, welche von reifenden Chondrozyten produziert wird. Diese Schrumpfung bedeutet also, dass das Biovlies kein geeignetes Material für das Tissue Engineering der Trachea darstellt. Denn ein optimales Biomaterial für das Tissue Engineering der Trachea sollte sich innerhalb derselben Zeit bzw. über einen längeren Zeitraum hinweg abbauen, als innerhalb desjenigen, den die sich in dem Trägermaterial befindlichen Zellen benötigen, um zu funktionalem Gewebe heranzureifen.
Durch den Einsatz von Matrigel als Ersatz für die Basalmembran konnte eine Kokultur aus RECs und Chondrozyten etabliert werden (wobei anzumerken ist, dass sich direktes Wachstum von RECs auf Knorpelgewebe als problematisch erweist). Die Konstrukte aus Kokulturen waren nicht stabil, da das Biovlies in Anwesenheit beider Zelltypen hochgradig abgebaut wird. Innerhalb von 3–7 Tagen schrumpften die Konstrukte auf ca. 35–50 % ihrer Ausgangsgröße zusammen. Der Grund für diesen beschleunigten Abbau ist unbekannt, jedoch ist am ehesten eine ausgeprägte Produktion von MMP durch die beiden Zellarten anzunehmen, sobald diese in Kombination vorliegen.
Insgesamt lässt sich sagen, dass die Methoden zur Zell- und Gewebecharakterisierung, welche in dieser Studie benutzt wurden (histochemische Färbungen, Fluoreszenzfärbung und Elektronenmikroskopie) sowohl für mit RECs als auch mit Chondrozyten hergestellte Konstrukte für die vorliegende Arbeit als auch zukünftige Studien als geeignet anzusehen sind. Diese Studie hat in vielerlei Hinsicht erfolgreich das Tissue Engineering einer Luftröhre untersuchen können, indem sie im Detail aufzeigt, wie RECs und Chondrozyten auf Biomaterialien kultiviert und für das Tissue Engineering eingesetzt werden können. Trotzdem kann diese Arbeit kein einsetzbares Ersatzmaterial als Endprodukt liefern. Der Hauptgrund für dieses Ergebnis ist in erster Linie in dem schnellen Abbau des Biovlieses als Trägermaterial zu sehen
- …
