5,282 research outputs found
Gap-filling carbon dioxide, water, energy, and methane fluxes in challenging ecosystems - Comparing between methods, drivers, and gap-lengths
Eddy covariance serves as one the most effective techniques for long-term monitoring of ecosystem fluxes, however long-term data integrations rely on complete timeseries, meaning that any gaps due to missing data must be reliably filled. To date, many gap-filling approaches have been proposed and extensively evaluated for mature and/or less actively managed ecosystems. Random forest regression (RFR) has been shown to be stable and perform better in these systems than alternative approaches, particularly when filling longer gaps. However, the performance of RFR gap filling remains less certain in more challenging ecosystems, e.g., actively managed agri-ecosystems and following recent land-use change due to management disturbances, ecosystems with relatively low fluxes due to low signal to noise ratios, or for trace gases other than carbon dioxide (e.g., methane).
In an extension to earlier work on gap filling global carbon dioxide, water, and energy fluxes, we assess the RFR approach for gap filling methane fluxes globally. We then investigate a range of gap-filling methodologies for carbon dioxide, water, energy, and methane fluxes in challenging ecosystems, including European managed pastures, Southeast Asian converted peatlands, and North American drylands.
Our findings indicate that RFR is a competent alternative to existing research standard gap-filling algorithms. The marginal distribution sampling (MDS) is still suggested for filling short ( 30 days) gaps in carbon dioxide fluxes and also for gap filling other fluxes (e.g. sensible heat, latent energy and methane). In addition, using RFR with globally available reanalysis environmental drivers is effective when measured drivers are unavailable. Crucially, RFR was able to reliably fill cumulative fluxes for gaps > 3 moths and, unlike other common approaches, key environment-flux responses were preserved in the gap-filled data
Dynamical Electroweak Breaking and Latticized Extra Dimensions
Using gauge invariant effective Lagrangians in 1+3 dimensions describing the
Standard Model in 1+4 dimensions, we explore dynamical electroweak symmetry
breaking. The Top Quark Seesaw model arises naturally, as well as the full CKM
structure. We include a discussion of effects of warping, and indicate how
other dynamical schemes may also be realized.Comment: 30 pages, 12 figure
The structure of electroweak corrections due to extended gauge symmetries
This paper studies models with extended electroweak gauge sectors of the form
SU(2) x SU(2) x U(1) x [SU(2) or U(1)]. We establish the general behavior of
corrections to precision electroweak observables in this class of theories and
connect our results to previous work on specific models whose electroweak
sectors are special cases of our extended group.Comment: 18 pages, 2 figures; added a referenc
Finding Z' bosons coupled preferentially to the third family at CERN LEP and the Fermilab Tevatron
Z' bosons that couple preferentially to the third generation fermions can
arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1))
gauge groups. We show that existing limits on quark-lepton compositeness set by
the LEP and Tevatron experiments translate into lower bounds of order a few
hundred GeV on the masses of these Z' bosons. Resonances of this mass can be
directly produced at the Tevatron. Accordingly, we explore in detail the limits
that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We
also comment on the possibility of using hadronically-decaying taus to improve
the limits.Comment: LaTeX2e, 24 pages (including title page), 13 figures; version 2:
corrected typographical errors and bad figure placement; version 3: added
references and updated introduction; version 4: changes to compensate for old
latex version on arXiv server; version 5: additional references, and embedded
fonts in eps files for PRD; version 6: corrected some minor typos to address
PRD referee's comment
Beautiful Mirrors and Precision Electroweak Data
The Standard Model (SM) with a light Higgs boson provides a very good
description of the precision electroweak observable data coming from the LEP,
SLD and Tevatron experiments. Most of the observables, with the notable
exception of the forward-backward asymmetry of the bottom quark, point towards
a Higgs mass far below its current experimental bound. The disagreement, within
the SM, between the values for the weak mixing angle as obtained from the
measurement of the leptonic and hadronic asymmetries at lepton colliders, may
be taken to indicate new physics contributions to the precision electroweak
observables. In this article we investigate the possibility that the inclusion
of additional bottom-like quarks could help resolve this discrepancy. Two
inequivalent assignments for these new quarks are analysed. The resultant fits
to the electroweak data show a significant improvement when compared to that
obtained in the SM. While in one of the examples analyzed, the exotic quarks
are predicted to be light, with masses below 300 GeV, and the Higgs tends to be
heavy, in the second one the Higgs is predicted to be light, with a mass below
250 GeV, while the quarks tend to be heavy, with masses of about 800 GeV. The
collider signatures associated with the new exotic quarks, as well as the
question of unification of couplings within these models and a possible
cosmological implication of the new physical degrees of freedom at the weak
scale are also discussed.Comment: 21 pages, 4 embedded postscript figures, LaTeX. Two minor corrections
performe
The balancing act between high electronic and low ionic transport influenced by perovskite grain boundaries
\ua9 2024 The Royal Society of Chemistry.A better understanding of the materials\u27 fundamental physical processes is necessary to push hybrid perovskite photovoltaic devices towards their theoretical limits. The role of the perovskite grain boundaries is essential to optimise the system thoroughly. The influence of the perovskite grain size and crystal orientation on physical properties and their resulting photovoltaic performance is examined. We develop a novel, straightforward synthesis approach that yields crystals of a similar size but allows the tuning of their orientation to either the (200) or (002) facet alignment parallel to the substrate by manipulating dimethyl sulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) ratios. This decouples crystal orientation from grain size, allowing the study of charge carrier mobility, found to be improved with larger grain sizes, highlighting the importance of minimising crystal disorder to achieve efficient devices. However, devices incorporating crystals with the (200) facet exhibit an s-shape in the current density-voltage curve when standard scan rates are used, which typically signals an energetic interfacial barrier. Using the drift-diffusion simulations, we attribute this to slower-moving ions (mobility of 0.37
7 10-10 cm2 V-1 s-1) in combination with a lower density of mobile ions. This counterintuitive result highlights that reducing ion migration does not necessarily minimise hysteresis
Effects of intersegmental transfers on target location by proteins
We study a model for a protein searching for a target, using facilitated
diffusion, on a DNA molecule confined in a finite volume. The model includes
three distinct pathways for facilitated diffusion: (a) sliding - in which the
protein diffuses along the contour of the DNA (b) jumping - where the protein
travels between two sites along the DNA by three-dimensional diffusion, and
finally (c) intersegmental transfer - which allows the protein to move from one
site to another by transiently binding both at the same time. The typical
search time is calculated using scaling arguments which are verified
numerically. Our results suggest that the inclusion of intersegmental transfer
(i) decreases the search time considerably (ii) makes the search time much more
robust to variations in the parameters of the model and (iii) that the optimal
search time occurs in a regime very different than that found for models which
ignore intersegmental transfers. The behavior we find is rich and shows
surprising dependencies, for example, on the DNA length.Comment: 40 pages, 14 figure
Scaling of the distribution of fluctuations of financial market indices
We study the distribution of fluctuations over a time scale (i.e.,
the returns) of the S&P 500 index by analyzing three distinct databases.
Database (i) contains approximately 1 million records sampled at 1 min
intervals for the 13-year period 1984-1996, database (ii) contains 8686 daily
records for the 35-year period 1962-1996, and database (iii) contains 852
monthly records for the 71-year period 1926-1996. We compute the probability
distributions of returns over a time scale , where varies
approximately over a factor of 10^4 - from 1 min up to more than 1 month. We
find that the distributions for 4 days (1560 mins) are
consistent with a power-law asymptotic behavior, characterized by an exponent
, well outside the stable L\'evy regime . To
test the robustness of the S&P result, we perform a parallel analysis on two
other financial market indices. Database (iv) contains 3560 daily records of
the NIKKEI index for the 14-year period 1984-97, and database (v) contains 4649
daily records of the Hang-Seng index for the 18-year period 1980-97. We find
estimates of consistent with those describing the distribution of S&P
500 daily-returns. One possible reason for the scaling of these distributions
is the long persistence of the autocorrelation function of the volatility. For
time scales longer than days, our results are
consistent with slow convergence to Gaussian behavior.Comment: 12 pages in multicol LaTeX format with 27 postscript figures
(Submitted to PRE May 20, 1999). See
http://polymer.bu.edu/~amaral/Professional.html for more of our work on this
are
Phenomenological constraints on SUSY SU(5) GUTs with non-universal gaugino masses
We study phenomenological aspects of supersymmetric SU(5) grand unified
theories with non-universal gaugino masses. For large tan beta, we investigate
constraints from the requirement of successful electroweak symmetry breaking,
the positivity of stau mass squared and the b to s gamma decay rate. In the
allowed region, the nature of the lightest supersymmetric particle is
determined. Examples of mass spectra are given. We also calculate loop
corrections to the bottom mass due to superpartners.Comment: 10 pages, 2 figures (8 eps files), uses REVTeX. Replaced to match the
version to be published in PRD: minor corrections and addition
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