298 research outputs found
Multipath variability due to the Gulf Stream
Also published as: Journal of the Acoustical Society of America 69 (1981): 982-988A phase-coded signal with 64-ms resolution was transmitted at 10-min intervals for a 19-day period over two
~300-km ranges. The acoustic source was moored at 2000-m depth northwest of Bermuda. One receiver was
moored at 2000-m depth to the northeast of the source and the other receiver was bottom mounted at ~1000-
m depth near Bermuda. The large (~0.6 s) travel time change at the Bermuda receiver is probably due in
large part to motion of the source mooring in the presence of currents. The multipath arrival pattern at the
moored receiver undergoes significant modification due to the presence of a southern meander of the Gulf
Stream which intersects this transmission path.Prepared for the Office of Naval Research under Contract
N00014-77-C-0196 and NORDA contract N00014-79-C-0071
Simulation and evaluation of the reactive virtual node layer
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 65-67).Developing software in a wireless, ad hoc environment is an intrinsically difficult problem. One way to mitigate it is to add an abstraction layer between the software and the individual mobile devices. This thesis describes one such abstraction, the Reactive Virtual Node (RVN) Layer [1, 2, 3, 4], as well as a new simulation framework written in Python. Additionally, this thesis uses the simulator to characterize an RVN-based routing service for multihop mobile ad hoc networks. The performance of the routing service is compared to the Ad hoc On-Demand Distance Vector routing protocol, as well as a greedy geographic routing protocol.by Mike Spindel.M.Eng
Novel Branches of (0,2) Theories
We show that recently proposed linear sigma models with torsion can be
obtained from unconventional branches of conventional gauge theories. This
observation puts models with log interactions on firm footing. If non-anomalous
multiplets are integrated out, the resulting low-energy theory involves log
interactions of neutral fields. For these cases, we find a sigma model geometry
which is both non-toric and includes brane sources. These are heterotic sigma
models with branes. Surprisingly, there are massive models with compact complex
non-Kahler target spaces, which include brane/anti-brane sources. The simplest
conformal models describe wrapped heterotic NS5-branes. We present examples of
both types.Comment: 36 pages, LaTeX, 2 figures; typo in Appendix fixed; references added
and additional minor change
About maximally localized states in quantum mechanics
We analyze the emergence of a minimal length for a large class of generalized
commutation relations, preserving commutation of the position operators and
translation invariance as well as rotation invariance (in dimension higher than
one). We show that the construction of the maximally localized states based on
squeezed states generally fails. Rather, one must resort to a constrained
variational principle.Comment: accepted for publication in PR
Sound channel propagation through eddies southeast of the Gulf Stream
Also published as: Journal of the Acoustical Society of America 68 (1980): 1750-1767Acoustical signals at 270 Hz from SOFAR floats drifting in the region southeast of the Gulf Stream were recorded during most of 1975 from a near axis sound channel hydrophone near Bermuda. The amplitude levels received exhibit a large increase (12â18 dB) commencing about 24 July, following a long period (March to July) of relatively lower peak level amplitudes. A major part of the increase can be attributed to the influence of a large cyclonic eddy (Gulf Stream ring) that passed slowly between the SOFAR floats and Bermuda. Such an eddy produces a large sound speed anomaly that extends to depths below the axis of the sound channel. On 24 July, two SOFAR floats were known to have approximately the same sound transmission path through the edge of the large eddy. The sound transmission peaks occur when no ocean eddy is between the SOFAR floats and the receiver. Their spacing shows they occur at regular refraction caustics in the sound channel. When the sound transmission path passes through an eddy, these transmission focal distances are shifted to greater range and the signal level may be greatly enhanced. The decrease of caustic peak intensities with range is 5 dB per double distance, and this agrees with theory. Several different levels of peak acoustic intensity occur and these result from two float depths and oceanic thermocline oscillations.Prepared for the Office of Naval Research under Contract
N00014-74-C-0262; NR 083-004·
An acoustic navigation system
This report describes a system for underwater acoustic
navigation developed, and in use, at the Woods Hole Oceanographic
Institution. It includes a brief discussion of the electronic
components, operation, mathematical analysis, and available computer
programs. There is a series of supplementary Technical Memoranda
containing more information on various aspects of the system. We believe that this kind of documentation is more
flexible and better meets the needs of potential users than including
all technical details in one large volume. These are not final or
definitive reports; acoustic navigation capabilities will continue
to evolve at W.H.O.I. for some time.
Acoustic navigation provides a method of tracking a ship, and an
underwater vehicle or instrument package (âfishâ), in the deep ocean.
Acoustic devices attached to the ship and fish measure the length of
time it takes a sound pulse to travel to acoustic transponders moored
on the ocean floor. If the transponder positions and the average
speed of sound are known, the ship or fish position can be found.Prepared for the Office of Naval Research
under Contracts N00014-71-C0284; NR 293-008
N00014-70-C0205; NR 263-103 and the National
Science Foundation/International Decade of
Ocean Exploration Grant GX-36024 and the
Applied Physics Laboratory of The Johns
Hopkins University Contract 372111
Mimimal Length Uncertainty Principle and the Transplanckian Problem of Black Hole Physics
The minimal length uncertainty principle of Kempf, Mangano and Mann (KMM), as
derived from a mutilated quantum commutator between coordinate and momentum, is
applied to describe the modes and wave packets of Hawking particles evaporated
from a black hole. The transplanckian problem is successfully confronted in
that the Hawking particle no longer hugs the horizon at arbitrarily close
distances. Rather the mode of Schwarzschild frequency deviates from
the conventional trajectory when the coordinate is given by in units of the non local distance legislated
into the uncertainty relation. Wave packets straddle the horizon and spread out
to fill the whole non local region. The charge carried by the packet (in the
sense of the amount of "stuff" carried by the Klein--Gordon field) is not
conserved in the non--local region and rapidly decreases to zero as time
decreases. Read in the forward temporal direction, the non--local region thus
is the seat of production of the Hawking particle and its partner. The KMM
model was inspired by string theory for which the mutilated commutator has been
proposed to describe an effective theory of high momentum scattering of zero
mass modes. It is here interpreted in terms of dissipation which gives rise to
the Hawking particle into a reservoir of other modes (of as yet unknown
origin). On this basis it is conjectured that the Bekenstein--Hawking entropy
finds its origin in the fluctuations of fields extending over the non local
region.Comment: 12 pages (LateX), 1 figur
Optimizing Two-Color Semiconductor Nanocrystal Immunoassays in Single Well Microtiter Plate Formats
The simultaneous detection of two analytes, chicken IgY (IgG) and Staphylococcal enterotoxin B (SEB), in the single well of a 96-well plate is demonstrated using luminescent semiconductor quantum dot nanocrystal (NC) tracers. The NC-labeled antibodies were prepared via sulfhydryl-reactive chemistry using a facile protocol that took <3 h. Dose response curves for each target were evaluated in a single immunoassay format and compared to Cy5, a fluorophore commonly used in fluorescent immunoassays, and found to be equivalent. Immunoassays were then performed in a duplex format, demonstrating multiplex detection in a single well with limits of detection equivalent to the single assay format: 9.8 ng/mL chicken IgG and 7.8 ng/mL SEB
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