10,967 research outputs found
Normal frames for non-Riemannian connections
The principal properties of geodesic normal coordinates are the vanishing of
the connection components and first derivatives of the metric components at
some point. It is well-known that these hold only at points where the
connection has vanishing torsion and non-metricity. However, it is shown that
normal frames, possessing the essential features of normal coordinates, can
still be constructed when the connection is non-Riemannian.Comment: 4 pages, plain TeX. To appear in Class. Quantum Gra
Nitrogen isotopes in chlorophyll and the origin of Eastern Mediterranean sapropels
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 February 1997The goals of this thesis were: (1) to establish methods for the determination of
nitrogen and carbon isotope ratios in marine particulate and sedimentary
chlorophyll derivatives; (2) to establish chlorophyll δ15N and δl3C as proxies for
the nitrogen and carbon isotopic composition of marine phytoplankton; and (3)
to use chlorophyll nitrogen isotopic ratios to understand the origin of Late
Quaternary Eastern Mediterranean sapropels.
Techniques are presented for the determination of chlorin nitrogen and carbon
isotopic ratios in marine particles and sediments with a precision greater than
0.15 per mil for both isotopes. The procedure can be performed in about 4 hours
for particulate and 8 hours for sediment samples, and relies on multiple
chromatographic purifications. About 20 g of a moderately organic-rich
sediment are required.
A technique is also presented for the determination of chlorin nitrogen and
carbon isotopic ratios by isotope-ratio monitoring gas chromatography-mass
spectrometry (irmGC-MS) by synthesizing bis-(tert.-butyldimethylsiloxy)Si(IV)
chlorin derivatives. However, yields for the 4-step synthesis were only about 5-6% and there was a net isotopic depletion of 1.2 (± 0.3) per mil in the derivative,
relative to the starting material.
These techniques are then used to show that the nitrogen isotopic difference
between chlorophyll and whole cells in six species of marine phytoplankton is
5.16 ± 2.40 per mil. For carbon, the isotopic difference between chlorophyll and
whole cells in five species of marine phytoplankton is -0.02 ± 2.12 per mil. A
model of the distribution of 15N in phytoplankton is constructed and it is
demonstrated that the interspecies variability observed for the nitrogen isotopic
difference between chlorophyll and whole cells can be attributed to differences in the partitioning of cellular nitrogen between non-protein biochemicals. In the
field, where mixed assemblages of phytoplankton prevail, the isotopic difference
beween chlorophyll and whole cells is expected to tend toward the average value
of 5.16 per mil.
Finally, the average nitrogen isotopic composition of chlorins from six Late
Quaternary Eastern Mediterranean sapropels (-5.01 + 0.38 per mil) was found to
be very similar to the δ15N of chlorophyll from the modem deep chlorophyll
maximum (-6.38 ± 1.80 per mil) in the Eastern Mediterranean. In addition,
sapropel photoautotrophic material, calculated from the chlorin δ15N, had the
same isotopic composition (0.15 per mil) as both bulk sapropel sediments (-0.08 ±
0.53 per mil) and deep water nitrate (-0.05 per mil). These data suggest (a) that
bottom waters were anoxic, (b) that organic matter burial efficiency was
enhanced, and (c) that oligotrophic conditions similar to today persisted, in the
Eastern Mediterranean during sapropel deposition. These results contradict
earlier interpretations of Late Quaternary bulk sedimentary δ15N in the Eastern
Mediterranean. The latter concluded that the pattern of high δ15N values in
intercalated marl oozes and low values in sapropels was the result of decreased
nutrient utilization, and hence, increased primary production, during sapropel
events. The low δ15N of deep water nitrate in the Eastern Mediterranean
suggests a significant source of new nitrogen from biological N2-fixation.
It is suggested that attempts to reconstruct the nitrogen isotopic composition of
marine organic matter in the past by measuring the δ15N of whole sediments
may be subject to misinterpretation due to the alteration of isotopic ratios during
diagenesis. The partial oxidation of marine organic matter can result in
significant isotopic enrichment of the preserved residual. The magnitude of this
enrichment appears to be large when bottom waters are well-oxygenated, and
small when bottom waters are anoxic. Environments where large temporal
reqox changes have occurred are expected to be the most problematic for the
interpretation of bulk sedimentary δ15N. In these environments, the diagenetic
signal can be at least as large as the primary isotopic signal being sought. The
Eastern Mediterranean Sea during the Late Quaternary appears to be one such
environment.Funding for this work came from an Office of Naval Research Graduate
Fellowship, the Woods Hole Oceanographic Institution Ocean Ventures Fund,
and a Petroleum Research Grant(# 30124-AC2)
No news for Kerr-Schild fields
Algebraically special fields with no gravitational radiation are described.
Kerr-Schild fields, which include as a concrete case the Kinnersley photon
rocket, form an important subclass of them.Comment: 4 pages, Revtex
The UN local communities and Indigenous peoples' platform: A traditional ecological knowledge-based evaluation
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2019 The Authors. WIREs Climate Change published by Wiley Periodicals, Inc.This review evaluates the potential of the proposed local communities and Indigenous peoples’ platform to effectively engage traditional ecological knowledge (TEK) for climate policy. Specifically, we assess the platform's potential to enable greater representation and participation of Indigenous peoples (IPs) within the United Nations Framework Convention on Climate Change (UNFCCC). An analytical
framework based on the extensive TEK and environmental management literature is developed, with a set of criteria identified against which to evaluate the platform. We find that although the process of designing the platform appears to be inclusive of Indigenous views, the structure itself does not recognize the roles that unequal power relations and colonialism play in marginalizing IPs. Limited attention
is paid to the institutional barriers within the UNFCCC and the drawbacks of pursuing knowledge “integration” as an end in itself. Based on this, recommendations for improving the platform structure are put forward including using a rights based framing, giving greater decision-making power to IPs, and developing mechanisms to ensure the holistic integrity of TEK and build the overall resilience of climate mitigation and adaptation systems.Ye
Position Sensing from Charge Dispersion in Micro-Pattern Gas Detectors with a Resistive Anode
Micro-pattern gas detectors, such as the Gas Electron Multiplier (GEM) and
the Micromegas need narrow high density anode readout elements to achieve good
spatial resolution. A high-density anode readout would require an unmanageable
number of electronics channels for certain potential micro-detector
applications such as the Time Projection Chamber. We describe below a new
technique to achieve good spatial resolution without increasing the electronics
channel count in a modified micro-detector outfitted with a high surface
resistivity anode readout structure. The concept and preliminary measurements
of spatial resolution from charge dispersion in a modified GEM detector with a
resistive anode are described below.Comment: 14 pages, 8 figures, submitted to Nucl. Inst. Meth; typo in eqn 4
corrected, fig 2 updated accordingl
On the resistivity at low temperatures in electron-doped cuprate superconductors
We measured the magnetoresistance as a function of temperature down to 20mK
and magnetic field for a set of underdoped PrCeCuO (x=0.12) thin films with
controlled oxygen content. This allows us to access the edge of the
superconducting dome on the underdoped side. The sheet resistance increases
with increasing oxygen content whereas the superconducting transition
temperature is steadily decreasing down to zero. Upon applying various magnetic
fields to suppress superconductivity we found that the sheet resistance
increases when the temperature is lowered. It saturates at very low
temperatures. These results, along with the magnetoresistance, cannot be
described in the context of zero temperature two dimensional
superconductor-to-insulator transition nor as a simple Kondo effect due to
scattering off spins in the copper-oxide planes. We conjecture that due to the
proximity to an antiferromagnetic phase magnetic droplets are induced. This
results in negative magnetoresistance and in an upturn in the resistivity.Comment: Accepted in Phys. Rev.
A Riemann-Hilbert Problem for an Energy Dependent Schr\"odinger Operator
\We consider an inverse scattering problem for Schr\"odinger operators with
energy dependent potentials. The inverse problem is formulated as a
Riemann-Hilbert problem on a Riemann surface. A vanishing lemma is proved for
two distinct symmetry classes. As an application we prove global existence
theorems for the two distinct systems of partial differential equations
for suitably restricted,
complementary classes of initial data
Spatial resolution of a GEM readout TPC using the charge dispersion signal
A large volume Time Projection Chamber (TPC) is being considered for the
central charged particle tracker for the detector for the proposed
International Linear Collider (ILC). To meet the ILC-TPC spatial resolution
challenge of ~100 microns with a manageable number of readout pads and channels
of electronics, Micro Pattern Gas Detectors (MPGD) are being developed which
could use pads comparable in width to the proportional-wire/cathode-pad TPC. We
have built a prototype GEM readout TPC with 2 mm x 6 mm pads using the new
concept of charge dispersion in MPGDs with a resistive anode. The dependence of
transverse resolution on the drift distance has been measured for small angle
tracks in cosmic ray tests without a magnetic field for Ar/CO2 (90:10). The
GEM-TPC resolution with charge dispersion readout is significantly better than
previous measurements carried out with conventional direct charge readout
techniques.Comment: 5 figures, 10 page
Chiral black hole in three-dimensional gravitational Chern-Simons
A chiral black hole can be defined from the three-dimensional pure
gravitational Chern-Simons action as an independent gravitational theory. The
third order derivative of the Cotton tensor gives a dimensional constant which
plays a role of the cosmological constant. The handedness of angular momentum
depends on the signature of the Chern-Simons coefficient. Even in the massless
black hole which corresponds to the static black hole, it has a nonvanishing
angular momentum. We also study statistical entropy and thermodynamic
stability.Comment: 6 pages, a reference added, minor changes to introductio
Permafrost - physical aspects and carbon cycling, databases and uncertainties
Permafrost is defined as ground that remains below 0°C for at least 2 consecutive years. About 24% of the northern hemisphere land area is underlain by permafrost. The thawing of permafrost has the potential to influence the climate system through the release of carbon (C) from northern high latitude terrestrial ecosystems, but there is substantial uncertainty about the sensitivity of the C cycle to thawing permafrost. Soil C can be mobilized from permafrost in response to changes in air temperature, directional changes in water balance, fire, thermokarst, and flooding. Observation networks need to be implemented to understand responses of
permafrost and C at a range of temporal and spatial scales. The understanding gained from these observation networks needs to be integrated into modeling frameworks capable of representing how the responses of permafrost C will influence the trajectory of climate in the future
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