17,697 research outputs found
Development of improved single crystal gallium phosphide solar cells final report, jun. 12, 1963 - aug. 12, 1964
Single crystal gallium phosphide solar cell
A Robust AFPTAS for Online Bin Packing with Polynomial Migration
In this paper we develop general LP and ILP techniques to find an approximate
solution with improved objective value close to an existing solution. The task
of improving an approximate solution is closely related to a classical theorem
of Cook et al. in the sensitivity analysis for LPs and ILPs. This result is
often applied in designing robust algorithms for online problems. We apply our
new techniques to the online bin packing problem, where it is allowed to
reassign a certain number of items, measured by the migration factor. The
migration factor is defined by the total size of reassigned items divided by
the size of the arriving item. We obtain a robust asymptotic fully polynomial
time approximation scheme (AFPTAS) for the online bin packing problem with
migration factor bounded by a polynomial in . This answers
an open question stated by Epstein and Levin in the affirmative. As a byproduct
we prove an approximate variant of the sensitivity theorem by Cook at el. for
linear programs
Physical processes and zooplankton distribution in the Great South Channel : observational and numerical studies
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1995This thesis addresses the question, "How do small-scale physics and biology
combine to produce dense aggregations of certain species of zooplankton in the Great
South Channel (GSC) of the Gulf of Maine?" The thesis consists of three relatively
independent parts: an observational study made while following two right whales as
they fed on dense patches of the copepod Galanus finmarchicus in the northern GSC;
a detailed description of a tightly integrated set of biological and physical observations
made in the GSC by means of a new instrument, the Video Plankton Recorder (VPR);
and a two-dimensional Eulerian numerical model that simulates one way in which a
physical flow field, combined with a biological behavior pattern, may produce dense
plankton patches at a convergent front.
Part I: Data from a wide variety of instruments was combined to produce a coherent
picture of the physical and biological environment near two feeding right whales
observed in June, 1989. Instruments included a CTD (with transmissometer), a
MOCNESS net system, a 150-kHz ADCP, and a towed acoustic plankton profiler
operating at 120 and 200 kHz. Acoustic data were intercalibrated with net-tow
data and with "noise" in the transmissometer signal in order to estimate copepod
abundance in the plankton patches on which the whales were feeding. One of the
whales was observed to reverse course when copepod abundance dropped below about
1.5- 4.5 x 103 copepods/m3
, which is consistent with independent estimates of the
density of copepods necessary for a right whale to gain more energy from the prey it
ingests than it loses to the extra hydrodynamic drag it experiences while feeding.
Part II: The VPR is a towed underwater microscope designed to image plankton
non-invasively with sufficient resolution to obtain information on the spatial distribut
ion of organisms on scales ranging from millimeters to hundreds of kilometers. CTD
instrumentation mounted on the VPR makes it possible to correlate biological and
hydrographic data with great precision. This study reports data from one transect made across the GSC in May, 1992. The data show close correlations between hydrographic
features (such as fronts, plumes and water masses) and broad-scale plankton
distribution. In addition, it was possible to correlate the fine-scale (order tens of meters)
patchiness in plankton distribution with the local stability of the water column
(as indicated by gradient Richardson number). In one case, biological data provided
an aid in determining the origin of one of the observed water masses.
Part III: This chapter presents a two-dimensional Eulerian numerical model that
shows how depth-keeping swimming behavior on the part of an organism, combined
with a convergent flow field at a surface front , can create dense patches of the organism.
In this model a steady-state flow field and vertical diffusivity field are prescribed,
along with the initial distribution of the plankton. The plankton swim vertically with
speeds that depend only on depth, but the form of that depth-dependence may take
into account such factors as the vertical variation in light level or in the concentration
of some prey organism. An analysis of various nondimensional parameters associated
with the model illustrates the roles played in determining the final structure of the
patch by such factors as diffusion, water velocity and details of the animals' swimming
behavior. Output from the model is compared with data taken at a dense plankton
patch observed near a front in the northern Great South Channel in early June, 1989.My first three years in the Joint Program were paid for by the Office of
Naval Research under an ONR Fellowship. I would also like to acknowledge subsequent
support from the National Science Foundation under grant OCE 93-13671 and
the National Oceanic and Atmospheric Administration under grants NA36GP0374
and NA26GP0431
Recommended from our members
Exploring Black-Jewish Alliances In America And On College Campuses
Black and Jewish communities collaborated substantially from the late 1800s through the mid-1900s. These efforts helped progress educational, political and social equality for Blacks and Jews in America. However, political, racial and economic factors have strained community ties in recent decades.
College students at campuses nationwide have begun reviving Black-Jewish relations through joint programming and dialogue. Yale University, The University of Texas at Austin and Brandeis University each house unique models of Black-Jewish collaboration. One-on-one dialogue, coupled with an intentional shift in perspective, can help combat implicit and explicit racial biases in society. The practical and psychological benefits of forming Black-Jewish student alliances on campus far outweigh the time commitment and obstacles that may arise.Plan II Honors Progra
Recent developments in perturbation theory
Rayleigh-Schroeder perturbation theory - degenerate and non-degenerate states - quantum chemistry - other perturbation equation
Computer methods for the reduction, correlation and analysis of space battery test data, phase 2, part 1 Final report, 1 Nov. - 31 Dec. 1967
Computer methods for reduction, correlation, and analysis of space battery test dat
Williams v. State, 316 So. 2d 267 (Fla. 1975)
Criminal Law- GUILTY PLEAS- FACTUAL BASIS DETERMINATION NOT MANDATORY WHEN A COURT ACCEPTS A PLEA OF GUILTY OR NOLO CONTENDERE
Brillouin Cooling
We analyze how to exploit Brillouin scattering for the purpose of cooling
opto-mechanical devices and present a quantum-mechanical theory for Brillouin
cooling. Our analysis shows that significant cooling ratios can be obtained
with standard experimental parameters. A further improvement of cooling
efficiency is possible by increasing the dissipation of the optical anti-Stokes
resonance.Comment: 4 pages 3 figure
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