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Syftet med undersökningen är att ta reda på vad eleverna använder sig av för strategier när de löser textuppgifter i division. Fokus har varit på kommunikationsförmågan och dess betydelse för elevernas sätt att lösa textuppgifter. Intresset för området väcktes när jag var på min verksamhetsförlagda utbildning (VFU) där jag kunde se att elever hade svårigheter att veta vilken strategi de skulle använda sig av. Den kommunikativa förmågans betydelse för elevernas sätt att lösa textuppgifterna undersöks genom att eleverna löser uppgifterna i par. Resultatet av studien visar att eleverna använder sig av likartade strategier när de ska lösa textuppgifter inom division, dvs. rita, kort division och omvänd division m.fl. Eleverna hade om möjlighet getts använt sig av laborativt material. En annan aspekt som resultatet pekar på är att det finns många fördelar med att ge eleverna möjlighet att använda sig av den kommunikativa förmågan. Några fördelar är att eleverna kan delge varandra tankar, utveckla sina förmågor och lär sig föra matematiska resonemang.

L'objet de notre travail est l'édition critique, la traduction française et l'analyse mathématique du Liber mensurationum d'Abu Bakr, du Liber Saydi Abuothmi, du Liber Aderameti et du De superficierum divisionibus liber de Muhammad al-Baghdadi. Ces quatre textes de la tradition arabe traitent de deux chapitres de géométrie pratique: le mesurage et le découpage. Le mesurage a pour objet la détermination de grandeurs inconnues (longueurs, aires, volumes) à partir de grandeurs données. Le découpage consiste à diviser une figure géométrique en plusieurs parties selon des propriétés et des contraintes fixées a priori. Notre travail prend en compte certaines traditions mathématiques antérieures - mésopotamienne, grecque, latine de l'Antiquité tardive - en décrivant leurs activités de mesurage et de découpage. Nous complétons cette description avec une présentation des pratiques de l'Orient et de l'Occident musulmans. Ainsi, nous mettons en évidence certains éléments caractéristiques des pratiques de l'Occident musulman. Ceux-ci suggèreraient l'existence d'une tradition du mesurage et du découpage propre à cette région. Enfin, le corpus que nous présentons est un vecteur de la diffusion des pratiques de géométrie de la tradition arabe au monde latin. En effet, les quatre textes sont des traductions arabo-Iatines qui semblent avoir été réalisées en Andalus aux alentours du 12e siècle. À ce titre, leurs analyses nous permettent d'étudier un aspect de l'appropriation de la science arabe par les Latins. / The object of our work is the critical edition, the French translation and the mathematical analysis of the Liber mensurationum of Abu Bakr, of the Liber Saydi Abuothmi, of the Liber Aderameti and of the De superficierum divisionibus liber of Mulhammad al-Baghdadï. These four texts of the Arabian tradition are about two chapters of practical geometry : the measurement and the division of figures. The measurement has for object the determination of unknown quantities (lengths, areas, volumes) from quantities data. The division of figures consists in dividing a geometric figures in several parts according to properties and constraints fixed a priori. Our work takes in account sorne previous mathematical traditions - mesopotamian one, Greek and Latin of the late Antiquity - describing their activities of measurement and division of figures. We complete this description with a presentation of the practices of the muslim Orient and Occident. Thus, we put in evidence sorne characteristic elements of the practices of the Muslim west. These would suggest the existence of a tradition of the measurement and the division of figures to this region. Finally, the corpus that we present is a vector of the diffusion of the practices of geometry of the Arabian tradition in the Latin world. Indeed, the four texts are arabo-Latin translations that seem have been achieved in Andalus around the 12th century. Their analyses allow us to study an aspect of the appropriation of the Arabian science by the Latin.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2007. / Vita. / Includes bibliographical references. / The Escherichia coli AlkB protein is an exceptionally versatile DNA repair enzyme. Its expression is induced upon exposure to alkylating agents as part of the Ada-mediated adaptive response. This member of the ac-ketoglutarate/iron(II)-dependent dioxygenase family was originally discovered to reverse directly methylated lesions formed preferentially in single-stranded regions of DNA, such as 1-methyladenine and 3- methylcytosine. Repair proceeds via an oxidative demethylation pathway, in which the aberrant methyl group is hydroxylated and spontaneously lost as formaldehyde. Since these early studies, the list of lesions repaired by AlkB through this pathway has been extended to include 1-methylguanine, 3-methylthymine, 3-ethylcytosine, and 1-ethyladenine. Furthermore, the protein possesses a second, distinct chemical mechanism through which it can repair another class of lesions, the etheno-adducts formed by the reaction of DNA with metabolites of the carcinogen vinyl chloride or with breakdown products generated by lipid oxidation. In this case, direct repair proceeds through epoxidation of the etheno bond, creating an intermediate that hydrolyzes to a glycol form and finally releases the two-carbon bridge as glyoxal, restoring the unadducted adenine or cytosine. Thus, the AlkB protein bridges the repair of alkylative lesions with those induced by oxidative stress and embodies the multi-faceted protection required to preserve genomic stability and coding information despite the constant threats to which organisms are exposed. / (cont.) Herein, we exploit and characterize a pair of E. coli strains differing only in AlkB status to demonstrate the ability of AlkB to repair the etheno-lesions, the structural analog 1,N6-ethanoadenine (EA), and 3-methyluracil in vivo. Additionally, we establish the ability of the EA "repair product" to form interstrand cross-links in certain sequence contexts of duplex DNA. We also show that although the adaptive response proteins repair lesions generated by oxidative stress, oxidative agents do not induce expression of the response. Finally, we establish that certain hypothesized substrates for AlkB are not in fact repaired by the enzyme, nor are they repaired by another adaptive response protein, AidB. This work extends the current knowledge regarding the amazing ability of AlkB to protect cellular nucleic acids from damage arising from a diverse array of both endogenous and exogenous sources. / by Lauren Elizabeth Frick. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, February 2008. / Includes bibliographical references (p. 213-231). / The combination of optical tweezers and single molecule fluorescence into an instrument capable of making combined, coincident measurements adds an observable dimension that allows for the examination of the localized effects of applied forces on biological systems. This technological advance had remained elusive due to the accelerated photobleaching of fluorophores in the presence of the high photon flux of the optical trap. This problem was circumvented by alternately modulating the trapping and fluorescence excitation laser beams, a technique named IOFF. Results show that our solution extends the longevity of Cy3 fluorophores by a factor of 20 without compromising the stiffness of the optical trap. This versatile arrangement can be extended to other fluorophores and was applied to unzip a 15 base pair region of dsDNA and to induce reversible conformational changes in a dsDNA hairpin labeled with a FRET pair. Next, this work developed an immobilization strategy and two single molecule assays for the CIpX ATPase, an enzyme capable of unfolding substrates that have been targeted for proteolytic degradation. In the first assay, which employs single molecule fluorescence, CIpX was found to unfold and translocate pre-engaged GFP substrates with a time constant of 22 s at saturating ATP concentrations, a rate that is 8-fold faster than bulk measurements clouded by binding and unbinding events. The second assay measured the strength of the ClpX-substrate interaction with optical tweezers. Results show that CIpX holds on to its substrates with forces on the order of 55 pN regardless of the nature and concentration of the nucleotide in solution. / (cont.) Finally, optical tweezers were used to characterize the rheological properties of methylcellulose and polarized cells, to quantify the mechanical properties of bacteriophage, and to measure the forces generated by a cellular actin spring. / by Ricardo R. Brau. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2007. / Includes bibliographical references (leaves 112-118). / Recognition of polymicrobial infections is becoming important for understanding differential host responses to environmental exposures, vaccines, as well as therapeutics. Citrobacter rodentium is a well-characterized model of infectious colitis with particular usefulness for modeling human diarrheal disease or inflammatory bowel disease. Infection with Helicobacter hepaticus is subclinical and persistent in C57BL/6 mice, but causes disease in susceptible strains and immunodeficient mice. To test the hypothesis that subclinical persistent infection modulates the host response to diarrheal disease a polymicrobial mouse model utilizing H. hepaticus and C. rodentium was developed and characterized. Concurrent infection has been shown to modulate disease outcome through several mechanisms including: cross-reactivity between viral antigens; shifting T cell response from Th1 to Th2 by helminth infection; and induction of regulatory T cells that suppress host response. In this new model of polymicrobial infection, a new paradigm in which persistent infection prolonged the course of acute colitis associated with a deviation from Thl-biased disease to Th17 was observed. / (cont.) In addition, Foxp3+naturally-occurring regulatory T cells (nTre,) were markedly increased during active colitis. The accumulation of nTreg was sustained when mice were persistently infected with H. hepaticus, indicating on-going active colitis. Although persistent infection was able to modulate host response, protective immunity to a subsequent C. rodentium infection was not compromised. Persistent infection also modulated host response to soluble antigen by preventing induction of oral tolerance to single bolus, but not to continuous, high-dose antigen feeding. Using H. hepaticus infection of C57BL/6 mice, models to investigate the immunomodulatory potential of persistent infection on immunogenic responses of protective immunity to enteric infection, host response to polymicrobial enteric infection, as well as tolerogenic responses to soluble antigen were developed. These models establish baselines for further investigation into the influences of persistent infection on host immune responses. / by Megan Earley McBee. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / This research examines the liability of storing CO2 in geological formations. There is a potential tortious and contractual liability exposure if stored CO2 is not fully contained by the geological formation. Using a combination of case study and survey methods, this research examines the risks confronted by CO2 storage, the legal and regulatory regimes governing these risks, and liability arrangements in other sectors where analogous risks have been confronted. Currently identifiable sources of liability include induced seismicity, groundwater contamination, harm to human health and the environment, property interests, and permanence. The risks of CO2 storage are analyzed in the context of several case studies: acid gas injection, natural gas storage, secondary oil recovery, and enhanced oil recovery. Methods for containing liability are considered in the context of regulatory analogs. This research finds that the current public and private mechanisms that would govern CO2 storage liability do not adequately address the issue. The analysis reveals six lessons learned: (1) the successful resolution of the CO2 liability issue will require combining our understanding of physical and regulatory analogs; (2) the prospect of CO2 storage liability will affect the implementation of predictive models and incentives to monitor leakage; (3) jurisdictional differences in liability exposure could affect where storage projects are eventually sited; (4) the development of liability rules is a function of an industry's emergence, but an industry's emergence, in turn, may affect the content of the liability rules; (5) regulatory compliance is not always a safe harbor for liability; and (6) statutes of limitation and repose mean that private liability is not necessarily "forever". A new liability arrangement is advocated where the current permitting regime is amended, long-term liability is managed by a governmental CO2 Storage Corporation with backing from an industry-financed CO2 Storage Fund, compensation for tortious liability occurs through an Office of Special Masters for CO2 Storage in the U.S. Federal Court of Claims, and the permanence issue is addressed on an annual ex post basis during the injection phase of CO2 storage operations and on an ex ante basis when sites are transferred to the CO2 Storage Corporation. / by Mark Anthony de Figueiredo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2007. / Leaf 187 blank. / Includes bibliographical references. / Gastric cancer is the second most common malignancy in the digestive system and the second leading cause of cancer-related death worldwide. Epidemiological data and experimental studies have identified several risk factors for gastric cancer, including Helicobacter pylori infection, low fruit and vegetable intake, N-nitrosoamine exposure, high salt diet, and smoking. Among these risk factors, H. pylori infection is the major cause of gastric cancer. Therefore, H. pylori has been classified as a type 1 (definite) carcinogen for gastric cancer by the World Health Organization (WHO) in 1994. H. pylori colonizes the human stomach and has been definitively linked to chronic gastritis. Infection in some: susceptible individuals results in serious gastric disease such as peptic ulcer or gastric cancer. The first aim of this thesis was to examine the role of different T cell subpopulations in H. pylori gastritis. Using a murine adoptive transfer model, adoptive transfer of wildtype (wt) effector T cells (TE) into H. pylori-infected lymphopenic Rag2-/- recipient mice resulted in H. pylori-associated corpus gastritis superimposed with non-specific gastroduodenitis. Cotransfer with TE and regulatory T cells (TR) from wt or IL10-/- mice reduced gastroduodenitis, but only wt TR cells reduced corpus gastritis. / (cont.) The second aim of this thesis was to evaluate the effect of vitamin C on H. pylori gastritis in vitamin C-deficient gulo-/- mice. It was found that a high vitamin C supplementation (3300 mg/L) in drinking water did not protect H. pylori gastritis, while a low vitamin C supplementation (33 mg/L) reduced the severity of H. pylori gastritis via an attenuated cellular immune response to H. pylori. The third aim of this thesis was to examine the role of DNA repair in H. pylori-associated gastric disease. We found that H. pylori-associated premalignant gastric atrophy was more severe in infected mice lacking DNA repair protein 3-alkyladenine DNA glycosylase or 06-methylguanine DNA methyltransferase in comparison to infected wt control mice. The forth aim of this thesis was to examine whether antimicrobial H. pylori eradication therapy could prevent gastric cancer development in INS-GAS mice, a model of gastric cancer. We found that antimicrobial H. pylori eradication therapy prevented the progression to gastric cancer in H. pylori-infected INS-GAS mice when treatment was instituted at an early stage of H. pylori infection. / (cont.) In conclusion, these studies provide further insight into the role of host immune responses in H. pylori pathogenesis. Additionally, information was garnered regarding the roles of vitamin C supplementation, DNA repair proteins, and H. pylori eradication therapy in H. pylori-associated gastric disease using genetically manipulated mice. / by Chung-Wei Lee. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2007. / "June 2007." / Includes bibliographical references (leaves 118-126). / Molecular springs have recently emerged as the basis for the fastest and most powerful movements at the cellular level in biology. The spasmoneme of the protozoan, Vorticella convallaria, is a model molecular spring, relying on energy stored in protein interactions to power contraction over a few hundred micrometers in a few milliseconds. While basic characteristics of Vorticella contraction are known, the underlying biochemical mechanism is unclear. The studies outlined here define and measure key parameters of spasmoneme performance which enable discrimination between proposed movement schemes and identification of new model parameters. Recent work has classified the spasmoneme as a power-limited machine (Upadhyaya, Baraban et al. 2007), where increases in viscous load correspond to decreases in velocity; in this work the maximum load at minimum velocity (the stall force), is measured. Work done by the stalk in contraction is shown to be dependent on its fractional change in length. This energy dependence arises from the basic underlying mechanism, and a major goal of this thesis was to characterize that mechanism by imaging the underlying structure. In the case of the Vorticella spasmoneme, imaging methods like birefringence imaging and electron microscopy, which do not require preexisting knowledge of protein identity, are particularly helpful. / (cont.) High-speed measurements of live Vorticella movements show the persistence of birefringence throughout the contraction-extension cycle. Orientation-independent measurements taken with an LC Pol-Scope show strong birefringence with slow axis parallel to the stalk long axis in both the extended and contracted states. Quantification of textural differences between the two states reveals slight structural disordering upon contraction. Transmission electron micrographs show a correlation between nanometer-scale filaments and the distribution of birefringence within the spasmoneme. As a whole these measurements indicate that any model of the contractile mechanism should consider the interactions of filamentous proteins at high concentrations which lead to longitudinal microscopic alignment in both the extended and contracted states. Implications of a proposed model are considered in the context of how they may be tested in vitro with purified constituent and homologous recombinant proteins, and how they can inform the development of biomimetic, nanoscale actuators. / by Danielle Cook France. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006. / MIT Science Library copy: printed in pages versus leaves. / Also issued in pages. / Includes bibliographical references (leaves 183-197). / The cardiac ventricular muscle cell (myocyte) is a key experimental system for exploring the mechanical properties of the diseased and healthy heart. The myocyte experimental model provides a higher level of physiological relevance than molecular or myofibril studies while avoiding problems inherent to multicellular preparations including heterogeneity of cell types and diffusion limited extracellular spaces. Millions of primary myocytes that remain viable for four to six hours can be readily isolated from animal models. However, the mechanical properties of only a few physically loaded myocytes can be explored in this time period using current, bulky and expensive instrumentation. In this thesis, a prototype instrument is described that is modular and inexpensive and could form the basis of an array of devices for probing the mechanical properties of single mammnalian myocytes in parallel. This would greatly increase the throughput of scientific experimentation and could be applied as a high content screening instrument in the pharmaceutical industry providing information at the level of a critical cellular phenotype, myocyte mechanical properties, for drug development and toxicology studies. / (cont.) The design, development and experimental verification of the modular instrument are presented here. The mathematical, mechanical and electrical characteristics of the novel force sensor and actuator system, Ho control implementation and data processing methodology are discussed. Finally, the functionality of the instrument is demonstrated by implementing novel methodologies for loading and attaching healthy, single mammalian ventricular myocytes to the force sensor and actuator and measuring their isometric twitch force and passive dynamic stiffness at varied sarcomere lengths. / by Michael G. Garcia-Webb. / Ph.D.