Recursos de colección

DSpace at MIT (103.835 recursos)

This site is a university repository providing access to the publication output of the institution. Registered users can set up email alerts to notify them of newly added relevant content. A certain level of encryption and security is embedded in the site which may cause some users accessibility problems.

MIT Open Access Articles

Mostrando recursos 26.041 - 26.060 de 29.488

  1. iSAM2: Incremental Smoothing and Mapping with Fluid Relinearization and Incremental Variable Reordering

    Kaess, Michael; Johannsson, Hordur; Roberts, Richard; Ila, Viorela; Leonard, John Joseph; Dellaert, Frank
    We present iSAM2, a fully incremental, graph-based version of incremental smoothing and mapping (iSAM). iSAM2 is based on a novel graphical model-based interpretation of incremental sparse matrix factorization methods, afforded by the recently introduced Bayes tree data structure. The original iSAM algorithm incrementally maintains the square root information matrix by applying matrix factorization updates. We analyze the matrix updates as simple editing operations on the Bayes tree and the conditional densities represented by its cliques. Based on that insight, we present a new method to incrementally change the variable ordering which has a large effect on efficiency. The efficiency and...

  2. Transcriptome response of high- and low-light-adapted Prochlorococcus strains to changing iron availability

    Thompson, Anne W.; Huang, Katherine H.; Saito, Mak A.; Chisholm, Sallie (Penny)
    Prochlorococcus contributes significantly to ocean primary productivity. The link between primary productivity and iron in specific ocean regions is well established and iron-limitation of Prochlorococcus cell division rates in these regions has been demonstrated. However, the extent of ecotypic variation in iron metabolism among Prochlorococcus and the molecular basis for differences is not understood. Here, we examine the growth and transcriptional response of Prochlorococcus strains, MED4 and MIT9313, to changing iron concentrations. During steady-state, MIT9313 sustains growth at an order-of-magnitude lower iron concentration than MED4. To explore this difference, we measured the whole-genome transcriptional response of each strain to abrupt iron starvation and rescue. Only four of the 1159...

  3. The Secular and Cyclic Determinants of Capitalization Rates: The Role of Property Fundamentals, Macroeconomic Factors, And Investor Sentiment

    Chervachidze, Serguei; Costello, James; Wheaton, William C.
    In this paper we revisit many studies that have attempted to explain the determinants of real estate capitalization rates. We introduce two new innovations. First we are able to identify two macroeconomic factors that greatly impact cap rates besides risk free treasury rates. These are the general corporate risk premium operating in the economy, and the amount of debt (liquidity) available. The addition of these factors greatly adds to the ability of previous models to explain the secular fall of cap rates in the last decade and the recent rise. In addition, we use innovative tests for “structural” shifts in...

  4. Contemporaneous Loan Stress and Termination Risk in the CMBS Pool: How "Ruthless" Is Default?

    Seslen, Tracey; Wheaton, William C.
    This study analyzes the impact of contemporaneous loan stress on the termination of loans in the commercial mortgage-backed securities pool from 1992 to 2004 using a novel measure, based on changes in net operating incomes and property values at the metropolitan statistical area-property-type-year level. Employing a semi-parametric competing risks model for a variety of specifications, we find that the probability of default is extremely low even at very high levels of stress, although the coefficient estimates of greatest interest are very statistically significant. These results suggest substantial lender forbearance and are consistent with previous research that models default as a...

  5. Low-noise Monte Carlo simulation of the variable hard sphere gas

    Radtke, Gregg A.; Hadjiconstantinou, Nicolas; Wagner, Wolfgang
    We present an efficient particle simulation method for the Boltzmann transport equation based on the low-variance deviational simulation Monte Carlo approach to the variable-hard-sphere gas. The proposed method exhibits drastically reduced statistical uncertainty for low-signal problems compared to standard particle methods such as the direct simulation Monte Carlo method. We show that by enforcing mass conservation, accurate simulations can be performed in the transition regime requiring as few as ten particles per cell, enabling efficient simulation of multidimensional problems at arbitrarily small deviation from equilibrium.

  6. Patients providing the answers: narrowing the gap in data quality for emergency care

    Porter, Stephen Calder; Forbes, Peter; Manzi, Shannon; Kalish, Leslie A.
    Objective The authors examined the validity of documentation produced during paediatric emergency care to determine if a patient-driven health information technology called ParentLink produced higher-quality data than documentation completed by nurses and physicians. Design The authors analysed the quality of information across elements of allergies to medications and the history of present illness (HPI) collected during a quasi-experimental intervention study where control periods with usual care alternated with intervention periods when ParentLink was operational. Documentation by emergency department (ED) providers was abstracted and compared with information generated through ParentLink. The criterion standard for the history of allergies to medications was a...

  7. Long-term proton pump inhibitor administration, H pylori and gastric cancer: lessons from the gerbil

    Fox, James G.; Kuipers, Ernst J.
    The association between chronic active gastritis and pre-neoplastic conditions as well as invasive cancer of the stomach was established several decades ago. The risk of progression depended on the severity and distribution of gastritis, with cancer, in particular, occurring in subjects with pan-gastritis. Subsequently, Helicobacter pylori was recognised as the primary cause of chronic active gastritis, and it was demonstrated that the pattern of gastritis corresponded with the colonisation pattern of H pylori. We and others then showed both in animals and in humans that this pattern of colonisation and associated gastritis primarily depended on the level of acid output....

  8. Bacterial infection causes stress-induced memory dysfunction in mice

    Gareau, Melanie G.; Wine, Eytan; Rodrigues, David M.; Cho, Joon Ho; Whary, Mark T.; Philpott, Dana J.; MacQueen, Glenda; Sherman, Philip M.
    Background: The brain–gut axis is a key regulator of normal intestinal physiology; for example, psychological stress is linked to altered gut barrier function, development of food allergies and changes in behaviour. Whether intestinal events, such as enteric bacterial infections and bacterial colonisation, exert a reciprocal effect on stress-associated behaviour is not well established. Objective: To determine the effects of either acute enteric infection or absence of gut microbiota on behaviour, including anxiety and non-spatial memory formation. Methods: Behaviour was assessed following infection with the non-invasive enteric pathogen, Citrobacter rodentium in both C57BL/6 mice and germ-free Swiss-Webster mice, in the presence or absence...

  9. Mobile Phones and Outdoor Advertising: Measurable Advertising

    Quercia, Daniele; Di Lorenzo, Giusy; Calabrese, Francesco; Ratti, Carlo
    Television and newspapers sit at the top of many agency marketing plans, while outdoor advertising stays at the bottom. The reason for this is that it’s difficult to account for who views a billboard, so there is no way of consistently determining the effectiveness of outdoor advertising. As a result, agencies do not consider the medium and allocate their money elsewhere. To change this situation, one needs to create new credible audience measurements for the outdoor marketing industry. Here we propose a new way of performing audience measurements that combines mobile phone location estimations with information freely available on the Internet....

  10. Integrated Urban Sensing: A Geo-sensor Network for Public Health Monitoring and Beyond

    Resch, Bernd; Lipson, Sam; Bers, Josh; Ratti, Carlo; Mittlboeck, Manfred; Welsh, Matt; Britter, Rex E.; Blaschke, Thomas
    Pervasive environmental monitoring implies a wide range of technical, but also socio-political challenges, and this applies especially to the sensitive context of the city. In this paper, we elucidate issues for bringing out pervasive urban sensor networks and associated concerns relating to fine-grained information provision. We present the Common Scents project, which is based on the Live Geography approach, and show how it can overcome these challenges. As opposed to hitherto sensing networks, which are mostly built up in monolithic and closed systems, the Common Scents approach aims to establish an open, standards based and modular infrastructure. This ensures interoperability, portability and flexibility, which are crucial prerequisites for pervasive...

  11. Nanometric self-assembling peptide layers maintain adult hepatocyte phenotype in sandwich cultures

    Wu, Jonathan; Mari-Buye, Nuria; Fernandez Muinos, Teresa; Borros, Salvador; Favia, Pietro; Semino, Carlos Eduardo
    Background: Isolated hepatocytes removed from their microenvironment soon lose their hepatospecific functions when cultured. Normally hepatocytes are commonly maintained under limited culture medium supply as well as scaffold thickness. Thus, the cells are forced into metabolic stress that degenerate liver specific functions. This study aims to improve hepatospecific activity by creating a platform based on classical collagen sandwich cultures. Results: The modified sandwich cultures replace collagen with self-assembling peptide, RAD16-I, combined with functional peptide motifs such as the integrin-binding sequence RGD and the laminin receptor binding sequence YIG to create a cell-instructive scaffold. In this work, we show that a...

  12. Introduction of customized inserts for streamlined assembly and optimization of BioBrick synthetic genetic circuits

    Norville, Julie E.; Derda, Ratmir; Gupta, Saurabh; Drinkwater, Kelly A.; Belcher, Angela M.; Leschziner, Andres E.; Knight, Thomas F., Jr.
    Background: BioBrick standard biological parts are designed to make biological systems easier to engineer (e.g. assemble, manipulate, and modify). There are over 5,000 parts available in the Registry of Standard Biological Parts that can be easily assembled into genetic circuits using a standard assembly technique. The standardization of the assembly technique has allowed for wide distribution to a large number of users -- the parts are reusable and interchangeable during the assembly process. The standard assembly process, however, has some limitations. In particular it does not allow for modification of already assembled biological circuits, addition of protein tags to pre-existing...

  13. Sparsification of RNA structure prediction including pseudoknots

    Mohl, Mathias; Salari, Raheleh; Will, Sebastian; Backofen, Rolf; Sahinalp, S. Cenk
    Abstract Background Although many RNA molecules contain pseudoknots, computational prediction of pseudoknotted RNA structure is still in its infancy due to high running time and space consumption implied by the dynamic programming formulations of the problem. Results In this paper, we introduce sparsification to significantly speedup the dynamic programming approaches for pseudoknotted RNA structure prediction, which also lower the space requirements. Although sparsification has been applied to a number of RNA-related structure prediction problems in the past few years, we provide the first application of sparsification to pseudoknotted RNA structure prediction specifically and to handling gapped fragments more generally -...

  14. The dynamic influence of the DRB1*1101 allele on the resistance of sheep to experimental Teladorsagia circumcincta infection

    Hassan, Musa A.; Good, Barbara; Hanrahan, James P.; Campion, Deirdre; Sayers, Gearoid; Mulcahy, Grace; Sweeney, Torres
    Suffolk sheep carrying the DRB1*1101 (previously referred to as-DRB1*0203 or G2) allele have been reported to show increased resistance to natural Teladorsagia circumcincta infection compared to non-carriers. The objective of this study was to compare the biochemical and physiological responses of DRB1*1101 carrier and non-carrier twin lambs to an experimental infection with 3 x 10 [superscript 4] L3 Teladorsagia circumcincta. The variables studied included worm burden, faecal egg count, abomasal mast cells, IgA, IgE, IgG1 plus IgG2 and haematological parameters at 0, 3, 7, 21 and 35 days post infection (dpi), and duodenal smooth muscle contractility at 0 and 35...

  15. Transcriptome sequencing and annotation of the microalgae Dunaliella tertiolecta: Pathway description and gene discovery for production of next-generation biofuels

    Rismani-Yazdi, Hamid; Haznedaroglu, Berat Z; Bibby, Kyle; Peccia, Jordan; Rismani-Yazdi, Hamid; Haznedaroglu, Berat Z.; Bibby, Kyle; Peccia, Jordan
    Background Biodiesel or ethanol derived from lipids or starch produced by microalgae may overcome many of the sustainability challenges previously ascribed to petroleum-based fuels and first generation plant-based biofuels. The paucity of microalgae genome sequences, however, limits gene-based biofuel feedstock optimization studies. Here we describe the sequencing and de novo transcriptome assembly for the non-model microalgae species, Dunaliella tertiolecta, and identify pathways and genes of importance related to biofuel production. Results Next generation DNA pyrosequencing technology applied to D. tertiolecta transcripts produced 1,363,336 high quality reads with an average length of 400 bases. Following quality and size trimming, ~ 45%...

  16. Infrared thermometry study of nanofluid pool boiling phenomena

    Gerardi, Craig; Buongiorno, Jacopo; Hu, Lin-wen; McKrell, Thomas J.
    Abstract Infrared thermometry was used to obtain first-of-a-kind, time- and space-resolved data for pool boiling phenomena in water-based nanofluids with diamond and silica nanoparticles at low concentration (<0.1 vol.%). In addition to macroscopic parameters like the average heat transfer coefficient and critical heat flux [CHF] value, more fundamental parameters such as the bubble departure diameter and frequency, growth and wait times, and nucleation site density [NSD] were directly measured for a thin, resistively heated, indium-tin-oxide surface deposited onto a sapphire substrate. Consistent with other nanofluid studies, the nanoparticles caused deterioration in the nucleate boiling heat transfer (by as much as...

  17. Optimized design of a low-resistance electrical conductor for the multimegahertz range

    Kurs, Andre B.; Kesler, Morris; Johnson, Steven G.
    We propose a design for a conductive wire composed of several mutually insulated coaxial conducting shells. With the help of numerical optimization, it is possible to obtain electrical resistances significantly lower than those of a heavy-gauge copper wire or litz wire in the 2–20 MHz range. Moreover, much of the reduction in resistance can be achieved for just a few shells; in contrast, litz wire would need to contain ∼ 10[superscript 4] strands to perform comparably in this frequency range.

  18. An analytical inversion method for determining regional and global emissions of greenhouse gases: Sensitivity studies and application to halocarbons

    Stohl, A.; Seibert, P.; Arduini, J.; Eckhardt, S.; Fraser, P. J.; Greally, B. R.; Lunder, Chris R.; Maione, Michela; Muhle, Jens; O'Doherty, Simon; Prinn, Ronald G.; Reimann, S.; Saito, T.; Schmidbauer, N.; Simmonds, P. G.; Vollmer, M. K.; Weiss, R. F.; Yokouchi, Y.
    A new analytical inversion method has been developed to determine the regional and global emissions of long-lived atmospheric trace gases. It exploits in situ measurement data from three global networks and builds on backward simulations with a Lagrangian particle dispersion model. The emission information is extracted from the observed concentration increases over a baseline that is itself objectively determined by the inversion algorithm. The method was applied to two hydrofluorocarbons (HFC-134a, HFC-152a) and a hydrochlorofluorocarbon (HCFC-22) for the period January 2005 until March 2007. Detailed sensitivity studies with synthetic as well as with real measurement data were done to quantify...

  19. Shape and Biomechanical Characteristics of Human Red Blood Cells in Health and Disease

    Diez Silva, Monica; Dao, Ming; Han, Jongyoon; Lim, Chwee Teck; Suresh, Subra
    The biconcave shape and corresponding deformability of the human red blood cell (RBC) is an essential feature of its biological function. This feature of RBCs can be critically affected by genetic or acquired pathological conditions. In this review, we highlight new dynamic in vitro assays that explore various hereditary blood disorders and parasitic infectious diseases that cause disruption of RBC morphology and mechanics. In particular, recent advances in high-throughput microfluidic devices make it possible to sort/identify healthy and pathological human RBCs with different mechanobiological characteristics.

  20. Family, Ancestry and Self: What is the Moral Significance of Biological Ties

    Haslanger, Sally
    In a series of recent papers David Velleman has argued that it is morally wrong to bring a child into existence with the intention that the child will not have contact with one or both biological parents. (Velleman, 2005, 2008) Put another way, “other things being equal, children should be raised by their biological parents.” (Velleman, 2005 362fn 3) The primary targets of his argument are those who use anonymous donor egg or sperm to conceive a child. On his view, there is a significant value in being parented by and having ongoing contact with one’s biological relatives. “What is most troubling about gamete donation is...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.