137,149 research outputs found
Oscillating supertubes and neutral rotating black hole microstates
No full textThe construction of neutral black hole microstates is an important problem, with implications for the information paradox. In this paper we conjecture a construction of non-supersymmetric supergravity solutions describing D-brane configurations which carry mass and angular momentum, but no other conserved charges. We first study a classical string solution which locally carries dipole winding and momentum charges in two compact directions, but globally carries no net winding or momentum charge. We investigate its backreaction in the D1-D5 duality frame, where this object becomes a supertube which locally carries oscillating dipole D1-D5 and NS1-NS5 charges, and again carries no net charge. In the limit of an infinite straight supertube, we find an exact supergravity solution describing this object. We conjecture that a similar construction may be carried out based on a class of two-charge non-supersymmetric D1-D5 solutions. These results are a step towards demonstrating how neutral black hole microstates may be constructed in string theory
Values congruence and commitment: throwing the role of psychological climate into the mix
No full textStudying the fit between employees and their organisations and the individual and organisational outcomes of this congruence has been an interesting topic for researchers over the past decades. However, the literature does not adequately address how this fit affects other organisational attitudes – in particular organisational commitment. In this study, a theory on the mechanism by which employees’ perception of person-organisation values fit impacts their affective organisational commitment and how this is impacted by their perceptions of the psychological climate is offered. Moreover, the study contributes to the literature through applying the Latent Congruence Model (LCM) developed by Cheung (2009a).Accordingly, all the hypotheses that pertain to values congruence, psychological climate and affective organisational commitment are simultaneously tested, controlling for the measurement errors. This SEM approach could be a useful analysis tool, especially as we know that, according to the simulation study of Cheung and Lau (2008), the bias in regression coefficients due to measurement error using path analysis may exceed 16% on average. Therefore, studying congruence under the frame of SEM in turn increases the accuracy and the significance of the congruence-related studies. The study was conducted in an Egyptian medium-sized textile organisation (N = 223). The results of the study supported the hypotheses that there would be positive relationships between affective organisational commitment and both perceived person-organisation values fit and psychological climate. Moreover, perceived person-organisation values fit demonstrated a positive impact on psychological climate. Importantly, psychological climate mediated the relationship between perceived person-organisation values fit and affective organisational commitment. The implications of these findings and directions for future research are discussed
Ultrasound-mediated transdermal drug delivery : mechanisms and applications
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1996.Includes bibliographical references (p. 73-81).Samir Mitragotri.Ph.D
Comments on black holes I: the possibility of complementarity
No full textWe comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who argue against black hole complementarity based on the claim that an infalling observer 'burns' as he approaches the horizon. We show that in fact measurements made by an infalling observer outside the horizon are statistically identical for the cases of vacuum at the horizon and radiation emerging from a stretched horizon. This forces us to follow the dynamics all the way to the horizon, where we need to know the details of Planck scale physics. We note that in string theory the fuzzball structure of microstates does not give any place to 'continue through' this Planck regime. AMPS argue that interactions near the horizon preclude traditional complementarity. But the conjecture of 'fuzzball complementarity' works in the opposite way: the infalling quantum is absorbed by the fuzzball surface, and it is the resulting dynamics that is conjectured to admit a complementary description
The role of technology and technology transfer in the strategy and structure of a multi-national engineering consulting firm from the developing countries
No full textThesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1991.Includes bibliographical references (leaves 110-113).by Samir Sawaya.M.S
The fuzzball nature of two-charge black hole microstates
No full textIt has been suggested by A. Sen that the entropy of two-charge supersymmetric bound states in string theory should be accounted for by adding the entropy of source-free horizonless supergravity solutions to the entropy associated with the horizons of small black holes. This would imply that the entropy arises differently depending on the duality frame: in the D1-D5 frame one would count source-free horizonless solutions, while in the NS1-P frame one would compute the area of a horizon. This might lead to the belief that the microstates are described by fuzzball solutions in the D1-D5 duality frame but by a black hole with a horizon in the latter. We argue that this is not the case, and that the microstates are fuzzballs in all duality frames. We observe that the scaling argument used by Sen fails to account for the entropy in the D1-P and other duality frames. We also note that the traditional extremal black hole solution is not a complete string background, since finite-action paths connect the exterior near-horizon extremal throat to the region inside the horizon, including the singularity. The singularity of the traditional black hole solution does not give a valid boundary condition for a fundamental string; correcting this condition by resolving the singularity modifies the black hole to a fuzzball with no horizon. We argue that for questions of counting states, the traditional black hole solution should be understood through its Euclidean continuation as a saddle point, and that the Lorentzian states being counted are fuzzballs in all duality frames.</p
Laboratory measurements of load-transfer in geosynthetic reinforced soils
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1996.Includes bibliographical references (p. 331-339).by Samir Chauhan.Ph.D
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Design and application of damped machine elements
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 165-168).by Samir A. Nayfeh.Ph.D
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