855 research outputs found
Battle over shipwrecks, treasure and history at the bottom of the sea
Thesis (S.M. in Science Writing)--Massachusetts Institute of Technology, Dept. of Comparative Media Studies, 2013."September 2013." Cataloged from PDF version of thesis.Includes bibliographical references (page 28).Though shipwrecks and treasure are deeply seductive to the public, the political, ethical, and scientific geography surrounding these sunken ships is not well publicized, except in cases involving large amounts of money. There is a battle for access rights to these objects with some claiming them as public historical commons, and others as commodity. Written for a popular audience, this thesis explores the history, technology and common sentiments surrounding shipwrecks from the people who have dedicated their lives to them: commercial firms (treasure hunters, salvors, etc.), academics (maritime archaeologists, conservators, educators, historians and cultural managers) and hobbyist SCUBA divers.by Leslie G. Baehr.S.M.in Science Writin
Age-related deficits in skeletal muscle recovery following disuse are associated with neuromuscular junction instability and ER stress, not impaired protein synthesis.
Age-related loss of muscle mass and strength can be accelerated by impaired recovery of muscle mass following a transient atrophic stimulus. The aim of this study was to identify the mechanisms underlying the attenuated recovery of muscle mass and strength in old rats following disuse-induced atrophy. Adult (9 month) and old (29 month) male F344BN rats underwent hindlimb unloading (HU) followed by reloading. HU induced significant atrophy of the hindlimb muscles in both adult (17-38%) and old (8-29%) rats, but only the adult rats exhibited full recovery of muscle mass and strength upon reloading. Upon reloading, total RNA and protein synthesis increased to a similar extent in adult and old muscles. At baseline and upon reloading, however, proteasome-mediated degradation was suppressed leading to an accumulation of ubiquitin-tagged proteins and p62. Further, ER stress, as measured by CHOP expression, was elevated at baseline and upon reloading in old rats. Analysis of mRNA expression revealed increases in HDAC4, Runx1, myogenin, Gadd45a, and the AChRs in old rats, suggesting neuromuscular junction instability/denervation. Collectively, our data suggests that with aging, impaired neuromuscular transmission and deficits in the proteostasis network contribute to defects in muscle fiber remodeling and functional recovery of muscle mass and strength
Soliton equations and the zero curvature condition in noncommutative geometry
Familiar nonlinear and in particular soliton equations arise as zero
curvature conditions for GL(1,R) connections with noncommutative differential
calculi. The Burgers equation is formulated in this way and the Cole-Hopf
transformation for it attains the interpretation of a transformation of the
connection to a pure gauge in this mathematical framework. The KdV, modified
KdV equation and the Miura transformation are obtained jointly in a similar
setting and a rather straightforward generalization leads to the KP and a
modified KP equation.
Furthermore, a differential calculus associated with the Boussinesq equation
is derived from the KP calculus.Comment: Latex, 10 page
Where Nanophotonics and Microfluidics Meet
A new generation of photonic devices has recently emerged that relies on using geometries of
sub-wavelength microstructures within a high refractive index contrast materials system. These
geometries are used to confine and manipulate light within very small volumes. High optical field
densities can be obtained within such structures, and these in turn can amplify optical
nonlinearities. Moreover, many of these structures, as for example photonic crystals and slotted
waveguides, can be engineered for the efficient localization of light within the low-index regions of
high index contrast microstructures. When such structures are back-filled nonlinear polymers or
liquids, devices can be tuned and novel phenomena can be observed. In particular, such devices
are very interesting when constructed from silicon on insulator (SOI) material in which the optical
waveguide also serves as a transparent electrical contact. Here we show examples of the design,
fabrication and testing of optical microstructures in which the electro-optic (χ2) and photorefractive
(χ3) nonlinearities are used for electro-optic tuning, frequency mixing, optical
rectification, and high-speed switching of light
Flow Phase Diagram for the Helium Superfluids
The flow phase diagram for He II and He-B is established and discussed
based on available experimental data and the theory of Volovik [JETP Letters
{\bf{78}} (2003) 553]. The effective temperature - dependent but scale -
independent Reynolds number , where
and are the mutual friction parameters and the superfluid Reynolds
number characterizing the circulation of the superfluid component in units of
the circulation quantum are used as the dynamic parameters. In particular, the
flow diagram allows identification of experimentally observed turbulent states
I and II in counterflowing He II with the turbulent regimes suggested by
Volovik.Comment: 2 figure
A new downscaling method for sub-grid turbulence modeling
In this
study we explore a new way to model sub-grid turbulence using particle
systems. The ability of particle systems to model small-scale turbulence is
evaluated using high-resolution numerical simulations. These high-resolution
data are averaged to produce a coarse-grid velocity field, which is then used
to drive a complete particle-system-based downscaling. Wind fluctuations and
turbulent kinetic energy are compared between the particle simulations and
the high-resolution simulation. Despite the simplicity of the physical model
used to drive the particles, the results show that the particle system is
able to represent the average field. It is shown that this system is able to
reproduce much finer turbulent structures than the numerical high-resolution
simulations. In addition, this study provides an estimate of the effective
spatial and temporal resolution of the numerical models. This highlights the
need for higher-resolution simulations in order to evaluate the very fine
turbulent structures predicted by the particle systems. Finally, a study of
the influence of the forcing scale on the particle system is presented
Algebraic description of spacetime foam
A mathematical formalism for treating spacetime topology as a quantum
observable is provided. We describe spacetime foam entirely in algebraic terms.
To implement the correspondence principle we express the classical spacetime
manifold of general relativity and the commutative coordinates of its events by
means of appropriate limit constructions.Comment: 34 pages, LaTeX2e, the section concerning classical spacetimes in the
limit essentially correcte
Dynamical Evolution in Noncommutative Discrete Phase Space and the Derivation of Classical Kinetic Equations
By considering a lattice model of extended phase space, and using techniques
of noncommutative differential geometry, we are led to: (a) the conception of
vector fields as generators of motion and transition probability distributions
on the lattice; (b) the emergence of the time direction on the basis of the
encoding of probabilities in the lattice structure; (c) the general
prescription for the observables' evolution in analogy with classical dynamics.
We show that, in the limit of a continuous description, these results lead to
the time evolution of observables in terms of (the adjoint of) generalized
Fokker-Planck equations having: (1) a diffusion coefficient given by the limit
of the correlation matrix of the lattice coordinates with respect to the
probability distribution associated with the generator of motion; (2) a drift
term given by the microscopic average of the dynamical equations in the present
context. These results are applied to 1D and 2D problems. Specifically, we
derive: (I) The equations of diffusion, Smoluchowski and Fokker-Planck in
velocity space, thus indicating the way random walk models are incorporated in
the present context; (II) Kramers' equation, by further assuming that, motion
is deterministic in coordinate spaceComment: LaTeX2e, 40 pages, 1 Postscript figure, uses package epsfi
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