3,590 research outputs found

    Credit Line Availability and Utilization in REITs

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    Analysis of REIT credit line availability and use under normal conditions and during the recent financial crisis are provided. Descriptive statistics indicate REIT credit lines represent an important component of capital structure, credit line availability and utilization have increased substantially over the sample period, and REITs maintain precautionary liquidity via credit lines rather than holding cash. Multivariate results indicate that credit line availability is directly associated with cash flow uncertainty, dividend distributions, acquisitions, and capital market access and is inversely linked to the market-to-book ratio. Credit line use is unrelated to cash flow volatility and dividends, but is correlated with operating cash flow, acquisitions, and capital market access. Unlike with non-REITs, when setting credit limits lenders focus on dividends and not just operating cash flow. Despite finding that line availability is influenced by dividend payments, REITs do not systematically use lines to pay dividends implying that dividends are paid from operating cash flows.

    An evolutionary approach to the optimisation of autonomous pod distribution for application in an urban transportation service

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    For autonomous vehicles (AVs), which when deployed in urban areas are called “pods”, to be used as part of a commercially viable low-cost urban transport system, they will need to operate efficiently. Among ways to achieve efficiency, is to minimise time vehicles are not serving users. To reduce the amount of wasted time, this paper presents a novel approach for distribution of AVs within an urban environment. Our approach uses evolutionary computation, in the form of a genetic algorithm (GA), which is applied to a simulation of an intelligent transportation service, operating in the city of Coventry, UK. The goal of the GA is to optimise distribution of pods, to reduce the amount of user waiting time. To test the algorithm, real-world transport data was obtained for Coventry, which in turn was processed to generate user demand patterns. Results from the study showed a 30% increase in the number of successful journeys completed in a 24 hours, compared to a random distribution. The implications of these findings could yield significant benefits for fleet management companies. These include increases in profits per day, a decrease in capital cost, and better energy efficiency. The algorithm could also be adapted to any service offering pick up and drop of points, including package delivery and transportation of goods

    Ownership Structure, Property Performance, Multifamily Properties and REITs

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    This research extends literature that empirically evaluates the impact of ownership and management structure on property level performance. The results show that multifamily properties owned and managed by real estate investment trusts (REITs) generate higher effective rents at the property level than non-REIT-owned properties. After controlling for positive operating scale and brand effects, REIT property level performance is better than non-REIT property level performance in the market studied. The REIT structure represents diversified scale operators with property management skills. The results imply that the structure of property ownership can impact property performance.

    Direct synthesis of pyridine and pyrimidine derivatives

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.Vita.Includes bibliographical references.I. Synthesis of Substituted Pyridine Derivatives via the Ruthenium-Catalyzed Cycloisomerization of 3-Azadienynes. The two-step conversion of various N-vinyl and N-aryl amides to the corresponding substituted pyridines and quinolines, respectively, is described. The process involves the direct conversion of amides, including sensitive N-vinyl amides, to the corresponding trimethylsilyl alkynyl imines followed by a ruthenium-catalyzed protodesilylation and cycloisomerization. A wide range of new alkynyl imines are prepared and readily converted to the corresponding azaheterocycles. II. Single-Step Synthesis of Pyrimidine Derivatives. The single-step conversion of various N-vinyl and N-aryl amides to the corresponding pyrimidine and quinazoline derivatives, respectively, is described. The process involves amide activation with 2-chloropyridine and trifluoromethanesulfonic anhydride followed by nitrile addition into the reactive intermediate and cycloisomerization. In situ nitrile generation from primary amides allows for their use as nitrile surrogates. The use of this chemistry with sensitive N-vinyl amides and epimerizable substrates in addition to a wide range of functional groups is noteworthy. III. Direct Synthesis of Pyridine Derivatives. The single-step conversion of various N-vinyl and N-aryl amides to the corresponding pyridine and quinoline derivatives, respectively, is described. The process involves amide activation with trifluoromethanesulfonic anhydride in the presence of 2-chloropyridine followed by t-nucleophile addition to the activated intermediate and annulation. Compatibility of this chemistry with sensitive N-vinyl amides, epimerizable substrates, and a variety of functional groups is noteworthy.by Matthew D. Hill.Ph.D

    Solvent‐induced enantioselectivity reversal in a chiral metal organic framework

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    Solvent-induced enantioselectivity reversal is a rarely reported phenomenon in porous homochiral materials. Similar behavior has been studied in chiral high performance liquid chromatography, where minor modifications to the mobile phase can induce elution order reversal of two enantiomers on a chiral stationary phase column. We report the first instance of solvent-induced enantioselectivity reversal in a homochiral metal organic framework. Further, we highlight the complex enantioselectivity behavior of homochiral metal organic frameworks toward racemic mixtures in the presence of solvents through racemate-solvent enantioselectivity and loading experiments as well as enantiopure-solvent loading experiments. We hypothesize that this interesting selectivity reversal behavior is likely to be observed in other competitive adsorption, nonchiral selective processes involving a solvent

    A Scenario-based Parametric Analysis of the Army Personnel-to-assignment Matching Problem

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    This study aims to compare linear programming and stable marriage approaches to the personnel assignment problem under conditions of uncertainty. Robust solutions should exhibit reduced variability of solutions in the presence of one or more additional constraints or problem perturbations added to some baseline problems.Several variations of each approach are compared with respect to solution speed, solution quality as measured by officer-to-assignment preferences and solution robustness as measured by the number of assignment changes required after inducing a set of representative perturbations or constraints to an assignment instance. These side constraints represent the realistic assignment categorical priorities and limitations encountered by army assignment managers who solve this problem semiannually, and thus the synthetic instances considered herein emulate typical problem instances

    Price Discovery and the Accuracy of Consolidated Data Feeds in the U.S. Equity Markets

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    Both the scientific community and the popular press have paid much attention to the speed of the Securities Information Processor, the data feed consolidating all trades and quotes across the US stock market. Rather than the speed of the Securities Information Processor, or SIP, we focus here on its accuracy. Relying on Trade and Quote data, we provide various measures of SIP latency relative to high-speed data feeds between exchanges, known as direct feeds. We use first differences to highlight not only the divergence between the direct feeds and the SIP, but also the fundamental inaccuracy of the SIP. We find that as many as 60 percent or more of trades are reported out of sequence for stocks with high trade volume, therefore skewing simple measures such as returns. While not yet definitive, this analysis supports our preliminary conclusion that the underlying infrastructure of the SIP is currently unable to keep pace with the trading activity in today's stock market.Comment: 18 pages, 20 figures, 2 table

    Application of the adjoint approach to optimise the initial conditions of a turbidity current with the AdjointTurbidity 1.0 model

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    Turbidity currents are one of the main drivers of sediment transport from the continental shelf to the deep ocean. The resulting sediment deposits can reach hundreds of kilometres into the ocean. Computer models that simulate turbidity currents and the resulting sediment deposit can help us to understand their general behaviour. However, in order to recreate real-world scenarios, the challenge is to find the turbidity current parameters that reproduce the observations of sediment deposits. This paper demonstrates a solution to the inverse sediment transportation problem: for a known sedimentary deposit, the developed model reconstructs details about the turbidity current that produced the deposit. The reconstruction is constrained here by a shallow water sediment-laden density current model, which is discretised by the finite-element method and an adaptive time-stepping scheme. The model is differentiated using the adjoint approach, and an efficient gradient-based optimisation method is applied to identify the turbidity parameters which minimise the misfit between the modelled and the observed field sediment deposits. The capabilities of this approach are demonstrated using measurements taken in the Miocene Marnoso-arenacea Formation (Italy). We find that whilst the model cannot match the deposit exactly due to limitations in the physical processes simulated, it provides valuable insights into the depositional processes and represents a significant advance in our toolset for interpreting turbidity current deposits

    Dual positive and negative regulation of GPCR signaling by GTP hydrolysis

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    G protein-coupled receptors (GPCRs) regulate a variety of intracellular pathways through their ability to promote the binding of GTP to heterotrimeric G proteins. Regulator of G protein signaling (RGS) proteins increase the intrinsic GTPase activity of G-subunits and are widely regarded as negative regulators of G protein signaling. Using yeast we demonstrate that GTP hydrolysis is not only required for desensitization, but is essential for achieving a high maximal (saturated level) response. Thus RGS-mediated GTP hydrolysis acts as both a negative (low stimulation) and positive (high stimulation) regulator of signaling. To account for this we generated a new kinetic model of the G protein cycle where GGTP enters an inactive GTP-bound state following effector activation. Furthermore, in vivo and in silico experimentation demonstrates that maximum signaling output first increases and then decreases with RGS concentration. This unimodal, non-monotone dependence on RGS concentration is novel. Analysis of the kinetic model has revealed a dynamic network motif that shows precisely how inclusion of the inactive GTP-bound state for the G produces this unimodal relationship

    Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition on Kuiper Belt and Oort Cloud Bodies

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    The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environments. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Interactions of surface irradiation, resultant chemical oxidation, and near-surface cryogenic fluid reservoirs have been proposed to account for Enceladus cryovolcanism and may have further applications to other icy irradiated bodies. The diversity of causative processes must be understood to account for observationally apparent diversities of the object surfaces