1,033 research outputs found
Human-induced marine ecological degradation: micropaleontological perspectives
We analyzed published downcore microfossil records from 150 studies and reinterpreted them from an ecological degradation perspective to address the following critical but still imperfectly answered questions: (1) How is the timing of human-induced degradation of marine ecosystems different among regions? (2) What are the dominant causes of human-induced marine ecological degradation? (3) How can we better document natural variability and thereby avoid the problem of shifting baselines of comparison as degradation progresses over time? The results indicated that: (1) ecological degradation in marine systems began significantly earlier in Europe and North America ( approximately 1800s) compared with Asia (post-1900) due to earlier industrialization in European and North American countries, (2) ecological degradation accelerated globally in the late 20th century due to post-World War II economic growth, (3) recovery from the degraded state in late 20th century following various restoration efforts and environmental regulations occurred only in limited localities. Although complex in detail, typical signs of ecological degradation were diversity decline, dramatic changes in total abundance, decrease in benthic and/or sensitive species, and increase in planktic, resistant, toxic, and/or introduced species. The predominant cause of degradation detected in these microfossil records was nutrient enrichment and the resulting symptoms of eutrophication, including hypoxia. Other causes also played considerable roles in some areas, including severe metal pollution around mining sites, water acidification by acidic wastewater, and salinity changes from construction of causeways, dikes, and channels, deforestation, and land clearance. Microfossils enable reconstruction of the ecological history of the past 10(2)-10(3) years or even more, and, in conjunction with statistical modeling approaches using independent proxy records of climate and human-induced environmental changes, future research will enable workers to better address Shifting Baseline Syndrome and separate anthropogenic impacts from background natural variability.published_or_final_versio
Yukawa Couplings involving Excited Twisted Sector States for and Orbifolds
We study the Yukawa couplings among excited twist fields which might arise in
the low-energy effective field theory obtained by compactifying the heterotic
string on and orbifolds.Comment: SUSX--TH--93/12, 31 page
Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity
Magnetic fields generated by human and animal organs, such as the heart,
brain and nervous system carry information useful for biological and medical
purposes. These magnetic fields are most commonly detected using
cryogenically-cooled superconducting magnetometers. Here we present the frst
detection of action potentials from an animal nerve using an optical atomic
magnetometer. Using an optimal design we are able to achieve the sensitivity
dominated by the quantum shot noise of light and quantum projection noise of
atomic spins. Such sensitivity allows us to measure the nerve impulse with a
miniature room-temperature sensor which is a critical advantage for biomedical
applications. Positioning the sensor at a distance of a few millimeters from
the nerve, corresponding to the distance between the skin and nerves in
biological studies, we detect the magnetic field generated by an action
potential of a frog sciatic nerve. From the magnetic field measurements we
determine the activity of the nerve and the temporal shape of the nerve
impulse. This work opens new ways towards implementing optical magnetometers as
practical devices for medical diagnostics.Comment: Main text with figures, and methods and supplementary informatio
Twisted Sector Yukawa Couplings For The Orbifolds
The moduli dependent Yukawa couplings between twisted sectors of Coxeter orbifolds are studied.Comment: 40 pages, SUSX-TH-92/1
Ectopic A-lattice seams destabilize microtubules
Natural microtubules typically include one A-lattice seam within an otherwise helically symmetric B-lattice tube. It is currently unclear how A-lattice seams influence microtubule dynamic instability. Here we find that including extra A-lattice seams in GMPCPP microtubules, structural analogues of the GTP caps of dynamic microtubules, destabilizes them, enhancing their median shrinkage rate by >20-fold. Dynamic microtubules nucleated by seeds containing extra A-lattice seams have growth rates similar to microtubules nucleated by B-lattice seeds, yet have increased catastrophe frequencies at both ends. Furthermore, binding B-lattice GDP microtubules to a rigor kinesin surface stabilizes them against shrinkage, whereas microtubules with extra A-lattice seams are stabilized only slightly. Our data suggest that introducing extra A-lattice seams into dynamic microtubules destabilizes them by destabilizing their GTP caps. On this basis, we propose that the single A-lattice seam of natural B-lattice MTs may act as a trigger point, and potentially a regulation point, for catastrophe
Orbifold Models in M-Theory
Among orbifold compactifications of -theory, we examine
models containing the particle physics Standard Model in four-dimensional
spacetimes, which appear as fixed subspaces of the ten-dimensional spacetimes
at each end of the interval, , spanning the
dimension. Using the projection to break the gauge symmetry in each
of the four-planes and a limiting relation to corresponding heterotic string
compactifications, we discuss the restrictions on the possible resulting gauge
field and matter spectra. In particular, some of the states are non-local: they
connect two four-dimensional Worlds across the dimension.
We illustrate our programmable calculations of the matter field spectrum,
including the anomalous U(1) factor which satisfies a universal Green-Schwarz
relation, discuss a Dynkin diagram technique to showcase a model with
gauge symmetry, and discuss generalizations to
higher order orbifolds.Comment: 23 pages, 2 figures, 4 tables; LaTeX 3 time
Measurement of the electron transmission rate of the gating foil for the TPC of the ILC experiment
We have developed a gating foil for the time projection chamber envisaged as
a central tracker for the international linear collider experiment. It has a
structure similar to the Gas Electron Multiplier (GEM) with a higher optical
aperture ratio and functions as an ion gate without gas amplification. The
transmission rate for electrons was measured in a counting mode for a wide
range of the voltages applied across the foil using an Fe source and a
laser in the absence of a magnetic field. The blocking power of the foil
against positive ions was estimated from the electron transmissions.Comment: 25 pages containing 14 figures and 1 tabl
Discrete R-symmetries and Anomaly Universality in Heterotic Orbifolds
We study discrete R-symmetries, which appear in 4D low energy effective field
theory derived from hetetoric orbifold models. We derive the R-symmetries
directly from geometrical symmetries of orbifolds. In particular, we obtain the
corresponding R-charges by requiring that the couplings be invariant under
these symmetries. This allows for a more general treatment than the explicit
computations of correlation functions made previously by the authors, including
models with discrete Wilson lines, and orbifold symmetries beyond
plane-by-plane rotational invariance. Surprisingly, for the cases covered by
earlier explicit computations, the R-charges differ from the previous result.
We study the anomalies associated with these R-symmetries, and comment on the
results.Comment: 21 pages, 2 figures. Minor changes, typos corrected. Matches JHEP
published versio
Dynamic p-enrichment schemes for multicomponent reactive flows
We present a family of p-enrichment schemes. These schemes may be separated
into two basic classes: the first, called \emph{fixed tolerance schemes}, rely
on setting global scalar tolerances on the local regularity of the solution,
and the second, called \emph{dioristic schemes}, rely on time-evolving bounds
on the local variation in the solution. Each class of -enrichment scheme is
further divided into two basic types. The first type (the Type I schemes)
enrich along lines of maximal variation, striving to enhance stable solutions
in "areas of highest interest." The second type (the Type II schemes) enrich
along lines of maximal regularity in order to maximize the stability of the
enrichment process. Each of these schemes are tested over a pair of model
problems arising in coastal hydrology. The first is a contaminant transport
model, which addresses a declinature problem for a contaminant plume with
respect to a bay inlet setting. The second is a multicomponent chemically
reactive flow model of estuary eutrophication arising in the Gulf of Mexico.Comment: 29 pages, 7 figures, 3 table
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