Massachusetts Institute of Technology

About: Massachusetts Institute of Technology is a education organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Population & Laser. The organization has 116795 authors who have published 268000 publications receiving 18272025 citations. The organization is also known as: MIT & M.I.T..

A line of sight approach to cosmic microwave background anisotropies

Abstract: We present a new method for calculating linear cosmic microwave background (CMB) anisotropy spectra based on integration over sources along the photon past light cone. In this approach the temperature anisotropy is written as a time integral over the product of a geometrical term and a source term. The geometrical term is given by radial eigenfunctions which do not depend on the particular cosmological model. The source term can be expressed in terms of photon, baryon and metric perturbations, all of which can be calculated using a small number of differential equations. This split clearly separates between the dynamical and geometrical effects on the CMB anisotropies. More importantly, it allows to significantly reduce the computational time compared to standard methods. This is achieved because the source term, which depends on the model and is generally the most time consuming part of calculation, is a slowly varying function of wavelength and needs to be evaluated only in a small number of points. The geometrical term, which oscillates much more rapidly than the source term, does not depend on the particular model and can be precomputed in advance. Standard methods that do not separate the two terms and require a much higher number of evaluations. The new method leads to about two orders of magnitude reduction in CPU time when compared to standard methods and typically requires a few minutes on a workstation for a single model. The method should be especially useful for accurate determinations of cosmological parameters from CMB anisotropy and polarization measurements that will become possible with the next generation of experiments. A programm implementing this method can be obtained from the authors.

Mll translocations specify a distinct gene expression profile, distinguishing a unique leukemia

Abstract: The present invention relates to the diagnosis of mixed lineage leukemia (MLL), acute lymphoblastic leukemia (ALL), and acute myellgenous leukemia (AML) according to the gene expression profile of a sample from an individual, as well as to methods of therapy and screening that utilize the genes indentified herein as targets.

CASE tools as organizational change: investigating incremental and radical changes in systems development

Abstract: This paper presents the findings of an empirical study into two organizations' experiences with the adoption and use of CASE tools over time. Using a grounded theory research approach, the study characterizes the organizations' experiences in terms of processes of incremental or radical organizational change. These findings are used to develop a theoretical framework for conceptualizing the organizational issues around the adoption and use of these tools-issues that have been largely missing from contemporary discussions of CASE tools. The paper thus has important implications for research and practice. Specifically, the framework and findings suggest that in order to account for the experiences and outcomes associated with CASE tools, researchers should consider the social context of systems development, the intentions and actions of key players, and the implementation process followed by the organization. Similarly, the paper suggests that practitioners will be better able to manage their organizations' experiences with CASE tools if they understand that such implementations involve a process of organizational change over time and not merely the installation of a new technology.

Economic Origins of Dictatorship and Democracy

Abstract: This book develops a framework for analyzing the creation and consolidation of democracy. Different social groups prefer different political institutions because of the way they allocate political power and resources. Thus democracy is preferred by the majority of citizens, but opposed by elites. Dictatorship nevertheless is not stable when citizens can threaten social disorder and revolution. In response, when the costs of repression are sufficiently high and promises of concessions are not credible, elites may be forced to create democracy. By democratizing, elites credibly transfer political power to the citizens, ensuring social stability. Democracy consolidates when elites do not have strong incentive to overthrow it. These processes depend on (1) the strength of civil society, (2) the structure of political institutions, (3) the nature of political and economic crises, (4) the level of economic inequality, (5) the structure of the economy, and (6) the form and extent of globalization.

Regulation of noise in the expression of a single gene

Abstract: Stochastic mechanisms are ubiquitous in biological systems. Biochemical reactions that involve small numbers of molecules are intrinsically noisy, being dominated by large concentration fluctuations 1‐3 . This intrinsic noise has been implicated in the random lysis/lysogeny decision of bacteriophage-λ 4 , in the loss of synchrony of circadian clocks 5,6 and in the decrease of precision of cell signals7. We sought to quantitatively investigate the extent to which the occurrence of molecular fluctuations within single cells (biochemical noise) could explain the variation of gene expression levels between cells in a genetically identical population (phenotypic noise). We have isolated the biochemical contribution to phenotypic noise from that of other noise sources by carrying out a series of differential measurements. We varied independently the rates of transcription and translation of a single fluorescent reporter gene in the chromosome of Bacillus subtilis, and we quantitatively measured the resulting changes in the phenotypic noise characteristics. We report that of these two parameters, increased translational efficiency is the predominant source of increased phenotypic noise. This effect is consistent with a stochastic model of gene expression in which proteins are produced in random and sharp bursts. Our results thus provide the first direct experimental evidence of the biochemical origin of phenotypic noise, demonstrating that the level of phenotypic variation in an isogenic population can be regulated by genetic parameters. We selected as our reporter system a single-copy chromosomal gene with an inducible promoter. As an estimated 50‐80% of bacterial genes are transcriptionally regulated 8 , this system typifies the majority of naturally occurring genes, allowing our results to be extended to natural systems. We incorporated a single copy of our reporter, the green fluorescent protein gene (gfp), into the chromosome of B. subtilis. We chose to integrate gfpinto the chromosome itself, rather than in the form of plasmids, as variation in plasmid copy number 9,10 can act as an additional and unwanted source of noise. Transcriptional efficiency was regulated by using an isopropyl-β-D-thiogalactopyranoside (IPTG)‐inducible promoter, Pspac, upstream of gfp, and varying the concentration of IPTG in the growth medium. Translational