LEADERSHIP AND DECISION-MAKING AT A SMALL, SPECIALTY COLLEGE DURING ENROLLMENT DECLINE

Many less-selective, private colleges have experienced substantial enrollment declines, leading to financial instability. Colleges that are no longer able to operate independently will either close or be acquired by more stable institutions. This historical case study explored the leadership condition at a small, private, highly specialized college during a period of enrollment increase, followed by a rapid enrollment decline resulting in the college closing in 2022. Using semi-structured interviews and archival document analysis, this study considered how data were used to inform critical decisions, what decisions may have contributed to the institutional decline, and what actions leaders took in response to the decline. Five findings are presented, followed by a discussion of implications for similar institutions

A New Hydroxylated Nonaprenylhydroquinone from the Mediterranean Marine Sponge Sarcotragus spinosulus

Chemical investigation of the Mediterranean sponge Sarcotragus spinosulus led to the isolation of a new hydroxylated nonaprenylhydroquinone, along with two known metabolites, hepta- and octaprenylhydroquinones. The structure of the new metabolite was assigned by extensive 1D and 2D NMR analyses and MS studies. The antileukemic effect of the three compounds towards the chronic myelogenous leukemia (CML) cells line K562 was also evaluated

Reaction and transport processes in organometallic chemical vapor deposition

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999.Includes bibliographical references.Researchers have continued to explore light sources that are brighter, cheaper, more reliable, and emit light closer to natural sunlight than conventional incandescent and fluorescent lighting. The most recent advance in this direction is the fabrication of light emitting diodes (LEDs), and laser diodes that can emit in the short wavelength region of the visible spectrum (from green to violet). By using organometallic chemical vapor deposition (OMCVD) to fabricate thin films of the group III nitride materials (GaN, AIN, and InN), LEDs with lifetimes over 10,000 hours are now commercially available while rapid progress is being made towards a laser diode structure with a similar lifetime. These devices, coupled with the existing red, yellow, orange, and amber LEDs (based on AIInGaP, also grown by OMCVD) whose light-emission efficiency is already superior to incandescent lamps can lead to full color solid-sate light sources. OMCVD of AlGaInN involves complex chemistry and flow phenomena, which determine the quality of the deposited layers. Incorporation of significant concentrations of Al and In have proven difficult to achieve. The understanding of the dominant reaction pathways and their interaction with transport phenomena has been insufficient for design and optimization of nitride deposition processes. This thesis describes coupled finite element simulations of fluid flow, heat and mass transfer with emphasis on constructing kinetic mechanisms that incorporate all the chemistry information known by experimental studies and quantum chemistry calculations. A kinetic mechanism for GaN deposition is proposed. The model involves fast reaction between trimethylgallium and NH3 to form a Lewis type acid-base adduct which can dissociate or decompose at higher temperatures. The decomposition fragments can subsequently react to form dimer or trimer complexes in the gas phase containing multiple gallium-nitrogen bonds. Reaction rate parameters are obtained from quantum chemistry calculations in the literature and analysis of experimental data. The reaction mechanism is shown to be consistent with individual experimental observations, flow-tube decomposition studies, and growth rate temperature and pressure dependence in a horizontal OMCVD reactor as well as growth rate data in a close-spaced OMCVD reactor. The growth rate appears to be limited by GaN formation at low temperatures, mass transport at intermediate temperatures and GaN decomposition at temperatures higher than 1000°C. Dimer and trimer formation provide additional pathways of Ga supply to the surface at low temperatures and high pressures. In order to simulate nitride growth in a new OMCVD reactor with close-spaced-injector, a hierarchical simulation approach of fluid flow and mass transfer in such reactors was initially performed. Three-dimensional calculations establish that there is complete mixing in the gas phase, while the individual gas injectors dissipate within 5-8 mm from the reactor inlet under typical operating conditions. Two-dimensional parametric studies of growth rate and uniformity dependence on operating conditions and geometric factors were used to gain insight into the chamber performance. Regions of stagnation and rotating disk flows were delineated as a function of operating parameters. In the case of rotating disk flow, growth uniformity increases with pressure, contrary to the classical vertical rotating disk reactor response. A mechanism for AIN growth is also described. Formation of dimers and trimers in the gasphase is identified as the major pathway for decreased growth efficiency with decreasing pressure. An additional pathway involving nucleation and growth of oligomers from dimers and trimers, and ultimately particle formation, is consistent with decreased growth efficiency with increasing temperature. The kinetic model is consistent with experimental observations of temperature and pressure dependence of AIN growth rate in a horizontal hot-wall reactor and growth rate data for AlGaN in a close-spaced reactor. In agreement with experimental observations, the simulations predict AIN deposition in a close-spaced reactor under conditions that prohibit AIN growth in a horizontal reactor. Thin films of InxGalxN are used as the active region in the III-N devices. Thus, controlling the indium composition in a reproducible manner is imperative for III-N device fabrication. The solid indium mole fraction in InGaN is reported to independently depend on temperature, relative indium amount at the inlet, film growth rate, and carrier gas used. A simple trapping mechanism is proposed for InN growth in InGaN ternary alloys. In agreement with multiple experimental observations, the indium content appears to be controlled by competition between desorption kinetics and incorporation, the latter being determined by the GaN growth rate since InN is not stable under typical growth conditions. The effect of H2 carrier gas on indium mole fraction is also discussed. For laser diode fabrication in the III-Nitride system, selective area growth is used to deposit buffer layers with fewer dislocations. In addition to its recent use in the nitride system, selective area epitaxy has been pursued in OMCVD of III-V compound semiconductors in general. Quantitative understanding of selective epitaxy, in particular compositional variations arising in selective growth of ternary alloys such as InGaAs and InGaP that are currently not understood, is needed to realize advanced optoelectronic devices. A hierarchical modeling approach of selective area epitaxy is undertaken to identify the origins of growth rate enhancement and indium composition enrichment in the case of ternary InGa(As/P) growth. Simulations using the stagnant layer approach reveal that surface reaction rate differences give rise to the compositional modulation. A realistic fluid flow description in a vertical axisymmetric reactor is coupled with a simple kinetic mechanism for InGaAs/P deposition. Differences in homogeneous decomposition kinetics of In and Ga precursors give rise to different "effective" surface reaction rates that lead to the observed In-enrichment. The proposed model is in agreement with reports on the dependence of In-enrichment on operating parameters. Simulations show that, while the alloy deposition is limited by mass transport, differences in reaction rates are responsible for the composition variations in selective growth. Thus, the usefulness of reaction-transport models in elucidating the relative roles of different deposition pathways and gaining insight to the deposition process is demonstrated. Growth rate enhancement and In-enrichment model predictions are in excellent agreement with experimental data on lateral and axial dependence obtained in a horizontal reactor with a large masked area.by Theodoros Mihopoulos.Ph.D

Contribution to the study of marine resources: secondary metabolites from benthic organisms

Marine natural products (secondary metabolites) chemistry is a recent extension of natural products chemistry. The main targets of this research sector are the discovery (isolation and structural elucidation) of new chemical compounds, which come from marine organisms, the determination of their possible biological activities and their penetration in modern application areas. The above usually go with and are supported by the study and verifying of the ecological roles of the compounds. This Ph.D. dissertation falls in the scientific area of marine natural products, which is considered part of the broad area of natural resources. Three benthic organisms, common in Greek seas, were chosen according to certain criteria such as, the abundant population, the collection accessibility and the interesting chemical load. The selected organisms were the red alga Laurencia obtusa and the sponges Agelas oroides and Ircinia spinosula. L. obtusa’s organic extract, after processing, mainly by high pressure chromatographic techniques, provided a number of products, which were structurally elucidated based on their spectroscopic data. Five new and nine known secondary metabolites were isolated from the organism. The new products are the acetogenin cyclic ether Laurencienyne B and four oxygenated - halogenated diterpenes. Diterpenes Prevezol A, B and Prevezotriol A, are novel compounds (new carbon skeletons). The fourth diterpene has a Labdane type skeleton. The known metabolites that were isolated are four sesquiterpenes, one diterpene, three acetogenins and one alcohol. Chromatographic separations of a relatively non polar extract of A. oroides, provided four metabolites. Their structure confirmation was based on comparison between the experimental and bibliographic data. The products are three alkaloids - bromide pyrroles and a 4a-methylsterol. Using simple chromatographic techniques, two known, natural products, were isolated as main constituents from the sponge I. spinosula. These compounds belong to the class of polyprenylated hydroquinones, common molecules in genus Ircinia. The two metabolites were used for the synthesis of eleven derivatives, after modifications, through simple chemical reactions. All the compounds, natural and synthesized, were submitted to pharmacological evaluation, in order to, determine their structure – activity relationship. The results showed that the oxidation of the hydroquinones to quinones and the hydrogenation of the double bonds increase the biological activity of the molecules. The adequate quantities of the two sponge metabolites allowed us to undertake a study on the quantitative/qualitative variation of these constituents. The results showed a correlation between the contributions of the metabolites and physicochemical parameters of the ecosystem, such as the light intensity. The ecological roles of the natural products remain to be elucidated in future investigation.Η χημεία των θαλάσσιων φυσικών προϊόντων - δευτερογενών μεταβολιτών - αποτελεί μία σύγχρονη προέκταση της χημείας φυσικών προϊόντων. Οι κύριοι στόχοι του ερευνητικού αυτού κλάδου είναι η ανακάλυψη (απομόνωση και δομική ταυτοποίηση) νέων χημικών ενώσεων που προέρχονται από θαλάσσιους οργανισμούς, τον εντοπισμό των πιθανών βιολογικών δράσεων τους και την ένταξή τους σε σύγχρονους χώρους εφαρμογής. Η πραγματοποίηση των παραπάνω, συνήθως συνοδεύεται και υποβοηθείται από την μελέτη και αποσαφήνιση του οικολογικού ρόλου των ενώσεων. Το αντικείμενο της διατριβής κινείται στην επιστημονική περιοχή των θαλάσσιων φυσικών προϊόντων, η οποία αποτελεί τμήμα του ευρύτερου χώρου των φυσικών πόρων και ειδικότερα αυτών του θαλάσσιου περιβάλλοντος. Με βάση ορισμένα κριτήρια επιλογής, όπως μεγάλοι πληθυσμοί, δυνατότητα και συνθήκες συλλογής, πλούσιο χημικό φορτίο, επιλέχθηκαν τρεις βενθικοί οργανισμοί, αρκετά κοινοί στις Ελληνικές θάλασσες και μελετήθηκαν ως προς τη χημεία των δευτερογενών μεταβολιτών τους. Οι οργανισμοί είναι το ροδοφύκος Laurencia obtusa και οι σπόγγοι Agelas oroides και Ircinia spinosula. Τα οργανικά εκχυλίσματα που προέκυψαν από την κατεργασία των οργανισμών, επεξεργάστηκαν με τεχνικές υγρής χρωματογραφίας, κυρίως υψηλής πίεσης, και απέδωσαν έναν αριθμό ουσιών, οι οποίες ταυτοποιήθηκαν δομικά μετά από φασματοσκοπική ανάλυση. Aπό το ροδοφύκος L. obtusa απομονώθηκαν συνολικά δεκατέσσερις δευτερογενείς μεταβολίτες, εκ’ των οποίων πέντε νέοι και εννέα γνωστοί. Τα νέα προϊόντα είναι ο κυκλικός αιθέρας ακετογενούς βιοσύνθεσης Λαυρενσιενίνη Β και τέσσερα οξυγονωμένα και αλογονωμένα διτερπένια. Τα διτερπένια Πρεβεζόλη A, B και Πρεβεζοτριόλη Α, αποτελούν πρωτότυπες δομές (νέοι ανθρακικοί σκελετοί). Το τέταρτο διτερπένιο ανήκει στην κατηγορία των Λαβδανίων. Παράλληλα απομονώθηκαν τέσσερα σεσκιτερπένια, ένα διτερπένιο, τρία προϊόντα ακετογενούς βιοσύνθεσης και μία αλκοόλη. Από τον σπόγγο A. oroides απομονώθηκαν τέσσερεις μεταβολίτες. Η ταυτοποίηση της δομής τους επιτεύχθηκε με φασματοσκοπική ανάλυση και αντιπαράθεση των φασματοσκοπικών δεδομένων με αυτά της βιβλιογραφίας. Οι χημικές ενώσεις που απομονώθηκαν από τον οργανισμό είναι τρία αλκαλοειδή - βρωμιομένα πυρρόλια και μία 4α-μεθυλοστερόλη. Από τον σπόγγο I. spinosula απομονώθηκαν και ταυτοποιήθηκαν δύο κύρια φυσικά προϊόντα, που ανήκουν στην κατηγορία των πολυπρενυλιομένων υδροκινονών. Οι μεταβολίτες αυτοί τροποποιήθηκαν δομικά, μέσω απλών χημικών αντιδράσεων αποδίδοντας έντεκα παράγωγα. Όλες οι ενώσεις, φυσικές και μη, μελετήθηκαν φαρμακολογικά, ώστε να προσδιοριστεί η σχέση δομής - δράσης. Τα αποτελέσματα δείχνουν ότι η οξείδωση των υδροκινονών σε κινόνες και η υδρογόνωση των διπλών δεσμών αυξάνει τη βιολογική δράση των μορίων. Η μελέτη της διακύμανσης των δύο υδροκινονών ανέδειξε την ποιοτική και ποσοτική συνιστώσες της. Τα αποτελέσματα δείχνουν την τάση εποχιακής διακύμανσης και εξάρτησης της βιοσύνθεσης των ενώσεων από φυσικοχημικές παραμέτρους

New brominated labdane diterpenes from the red alga Laurencia obtusa

Two labdane type brominated diterpenes (1 and 2) containing unprecedented eight- and seven-membered ether rings have been isolated from the organic extract of the red alga Laurencia obtusa, collected from Mitikas Bay in the Ionean Sea, Greece. The structures of the new natural products, as well as their relative stereochemistry, were established by means of spectral data analysis, including 2D NMR experiments