501 research outputs found
Modelling of root reinforcement and erosion control by ‘Veronese’ poplar on pastoral hill country in New Zealand
Background
The control of erosion processes is an important issue worldwide. In New Zealand, previous studies have shown the benefits of reforestation or bioengineering measures to control erosion. The impetus for this work focuses on linking recent research to the needs of practitioners by formulating quantitative guidelines for planning and evaluation of ground bioengineering stabilisation measures.
Methods
Two root distribution datasets of ‘Veronese’ poplar (Populus deltoides x nigra) were used to calibrate a root distribution model for application on single root systems and to interacting root systems at the hillslope scale. The root distribution model results were then used for slope stability calculations in order to quantitatively evaluate the mechanical stabilisation effects of spaced trees on pastoral hillslopes.
Results
This study shows that root distribution data are important inputs for quantifying root reinforcement at the hillslope scale, and that root distribution strongly depends on local environmental conditions and on the tree planting density. The results also show that the combination of soil mechanical properties (soil angle of internal friction and cohesion) and topographic conditions (slope inclination) are the major parameters to define how much root reinforcement is needed to stabilise a specific slope, and thus the spacing of the trees to achieve this.
Conclusions
For the worst scenarios, effective root reinforcement (>2 kPa) is reached for tree spacing ranging from 2500 stems per hectare (sph) for 0.1 m stem diameter at breast height (DBH) to 300 sph for 0.3 m stem DBH. In ideal growing conditions, tree spacing less than 100 sph is sufficient for stem DBH greater than 0.15 m. New quantitative information gained from this study can provide a basis for evaluating planting strategies using poplar trees for erosion control on pastoral hill country in New Zealand
Chaotic maps and flows: Exact Riemann-Siegel lookalike for spectral fluctuations
To treat the spectral statistics of quantum maps and flows that are fully
chaotic classically, we use the rigorous Riemann-Siegel lookalike available for
the spectral determinant of unitary time evolution operators . Concentrating
on dynamics without time reversal invariance we get the exact two-point
correlator of the spectral density for finite dimension of the matrix
representative of , as phenomenologically given by random matrix theory. In
the limit the correlator of the Gaussian unitary ensemble is
recovered. Previously conjectured cancellations of contributions of
pseudo-orbits with periods beyond half the Heisenberg time are shown to be
implied by the Riemann-Siegel lookalike
Two-Stage Priming of Allogeneic Natural Killer Cells for the Treatment of Patients with Acute Myeloid Leukemia: A Phase I Trial
Human Natural Killer (NK) cells require at least two signals to trigger tumor cell lysis. Absence of ligands providing either signal 1 or 2 provides NK resistance. We manufactured a lysate of a tumour cell line which provides signal 1 to resting NK cells without signal 2. The tumor-primed NK cells (TpNK) lyse NK resistant Acute Myeloid Leukemia (AML) blasts expressing signal 2 ligands. We conducted a clinical trial to determine the toxicity of TpNK cell infusions from haploidentical donors. 15 patients with high risk AML were screened, 13 enrolled and 7 patients treated. The remaining 6 either failed to respond to re-induction chemotherapy or the donor refused to undergo peripheral blood apheresis. The conditioning consisted of fludarabine and total body irradiation. This was the first UK trial of a cell therapy regulated as a medicine. The complexity of Good Clinical Practice compliance was underestimated and led to failures requiring retrospective independent data review. The lessons learned are an important aspect of this report. There was no evidence of infusional toxicity. Profound myelosuppression was seen in the majority (median neutrophil recovery day 55). At six months follow-up, three patients treated in Complete Remission (CR) remained in remission, one patient infused in Partial Remission had achieved CR1, two had relapsed and one had died. One year post-treatment one patient remained in CR. Four patients remained in CR after treatment for longer than their most recent previous CR. During the 2 year follow-up six of seven patients died; median overall survival was 400 days post infusion (range 141–910). This is the first clinical trial of an NK therapy in the absence of IL-2 or other cytokine support. The HLA-mismatched NK cells survived and expanded in vivo without on-going host immunosuppression and appeared to exert an anti-leukemia effect in 4/7 patients treated
Tunneling and the Band Structure of Chaotic Systems
We compute the dispersion laws of chaotic periodic systems using the
semiclassical periodic orbit theory to approximate the trace of the powers of
the evolution operator. Aside from the usual real trajectories, we also include
complex orbits. These turn out to be fundamental for a proper description of
the band structure since they incorporate conduction processes through
tunneling mechanisms. The results obtained, illustrated with the kicked-Harper
model, are in excellent agreement with numerical simulations, even in the
extreme quantum regime.Comment: 11 pages, Latex, figures on request to the author (to be sent by fax
Quantum Chaotic Dynamics and Random Polynomials
We investigate the distribution of roots of polynomials of high degree with
random coefficients which, among others, appear naturally in the context of
"quantum chaotic dynamics". It is shown that under quite general conditions
their roots tend to concentrate near the unit circle in the complex plane. In
order to further increase this tendency, we study in detail the particular case
of self-inversive random polynomials and show that for them a finite portion of
all roots lies exactly on the unit circle. Correlation functions of these roots
are also computed analytically, and compared to the correlations of eigenvalues
of random matrices. The problem of ergodicity of chaotic wave-functions is also
considered. For that purpose we introduce a family of random polynomials whose
roots spread uniformly over phase space. While these results are consistent
with random matrix theory predictions, they provide a new and different insight
into the problem of quantum ergodicity. Special attention is devoted all over
the paper to the role of symmetries in the distribution of roots of random
polynomials.Comment: 33 pages, Latex, 6 Figures not included (a copy of them can be
requested at [email protected]); to appear in Journal of Statistical
Physic
A Lovelock black hole bestiary
We revisit the study of (A)dS black holes in Lovelock theories. We present a
new tool that allows to attack this problem in full generality. In analyzing
maximally symmetric Lovelock black holes with non-planar horizon topologies
many distinctive and interesting features are observed. Among them, the
existence of maximally symmetric vacua do not supporting black holes in vast
regions of the space of gravitational couplings, multi-horizon black holes, and
branches of solutions that suggest the existence of a rich diagram of phase
transitions. The appearance of naked singularities seems unavoidable in some
cases, raising the question about the fate of the cosmic censorship conjecture
in these theories. There is a preferred branch of solutions for planar black
holes, as well as non-planar black holes with high enough mass or temperature.
Our study clarifies the role of all branches of solutions, including
asymptotically dS black holes, and whether they should be considered when
studying these theories in the context of AdS/CFT.Comment: 40 pages, 16 figures; v2: references added and minor amendments; v3:
title changed to improve its accuracy and general reorganization of the
results to ameliorate their presentatio
Post-landslide soil and vegetation recovery in a dry, montane system is slow and patchy
Landslides are common disturbances in forests around the world, and a major threat to human
life and property. Landslides are likely to become more common in many areas as storms intensify. Forest
vegetation can improve hillslope stability via long, deep rooting across and through failure planes. In the
U.S. Rocky Mountains, landslides are infrequent but widespread when they do occur. They are also extremely
understudied, with little known about the basic vegetation recovery processes and rates of establishment
which restabilize hills. This study presents the first evaluation of post-landslide vegetation recovery
on forested landslides in the southern Rocky Mountains. Six years after a major landslide event, the surveyed
sites have very little regeneration in initiation zones, even when controlling for soil coverage. Soils
are shallower and less nitrogen rich in initiation zones as well. Rooting depth was similar between functional
groups regardless of position on the slide, but deep-rooting trees are much less common in initiation
zones. A lack of post-disturbance tree regeneration in these lower elevation, warm/dry settings, common
across a variety of disturbance types, suggests that complete tree restabilization of these hillslopes is likely
to be a slow or non-existent, especially as the climate warms. Replacement by grasses would protect
against shallow instabilities but not the deeper mass movement events which threaten life and property
Geometry of Polynomials and Root-Finding via Path-Lifting
Using the interplay between topological, combinatorial, and geometric
properties of polynomials and analytic results (primarily the covering
structure and distortion estimates), we analyze a path-lifting method for
finding approximate zeros, similar to those studied by Smale, Shub, Kim, and
others. Given any polynomial, this simple algorithm always converges to a root,
except on a finite set of initial points lying on a circle of a given radius.
Specifically, the algorithm we analyze consists of iterating where the form a decreasing sequence of
real numbers and is chosen on a circle containing all the roots. We show
that the number of iterates required to locate an approximate zero of a
polynomial depends only on (where is
the radius of convergence of the branch of taking to a root
) and the logarithm of the angle between and certain critical
values. Previous complexity results for related algorithms depend linearly on
the reciprocals of these angles. Note that the complexity of the algorithm does
not depend directly on the degree of , but only on the geometry of the
critical values.
Furthermore, for any polynomial with distinct roots, the average number
of steps required over all starting points taken on a circle containing all the
roots is bounded by a constant times the average of . The
average of over all polynomials with roots in the
unit disk is . This algorithm readily generalizes to
finding all roots of a polynomial (without deflation); doing so increases the
complexity by a factor of at most .Comment: 44 pages, 12 figure
An unusual CsrA family member operates in series with RsmA to amplify posttranscriptional responses in Pseudomonas aeruginosa
Members of the CsrA family of prokaryotic mRNA-binding proteins alter the translation and/or stability of transcripts needed for numerous global physiological processes. The previously described CsrA family member in Pseudomonas aeruginosa (RsmA) plays a central role in determining infection modality by reciprocally regulating processes associated with acute (type III secretion and motility) and chronic (type VI secretion and biofilm formation) infection. Here we describe a second, structurally distinct RsmA homolog in P. aeruginosa (RsmF) that has an overlapping yet unique regulatory role. RsmF deviates from the canonical 5 β-strand and carboxyl-terminal α-helix topology of all other CsrA proteins by having the α-helix internally positioned. Despite striking changes in topology, RsmF adopts a tertiary structure similar to other CsrA family members and binds a subset of RsmA mRNA targets, suggesting that RsmF activity is mediated through a conserved mechanism of RNA recognition. Whereas deletion of rsmF alone had little effect on RsmA-regulated processes, strains lacking both rsmA and rsmF exhibited enhanced RsmA phenotypes for markers of both type III and type VI secretion systems. In addition, simultaneous deletion of rsmA and rsmF resulted in superior biofilm formation relative to the wild-type or rsmA strains. We show that RsmF translation is derepressed in an rsmA mutant and demonstrate that RsmA specifically binds to rsmF mRNA in vitro, creating a global hierarchical regulatory cascade that operates at the posttranscriptional level
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