331 research outputs found
Ten-year growth response of 45-year old Pinus banksiana Lamb. to urea fertilization and low thinning
The objectives of this investigation were 1) to examine
the duration and pattern of jack pine growth response to urea
fertilization and low thinning, and 2) to examine methods commonly
used in the measurement of fertilization and thinning trials in
jack pine.
The study area was located near Chapleau, Ontario in a
fire-originated jack pine stand. The stand was treated at age 45
with 336 kg urea-N/ha and a low thinning of 20 percent basal area
in a 2 X 2 factorial design with four replicates.
At stand age 55, 80 trees were felled for stem analysis,
representing 5 tree diameter classes within each stand treatment.
Volume increment, height increment, measures of form, and local
volume equations were determined from the stem analysis data. The
local volume equations were applied to diameter frequency distributions
at stand ages 45, 50, and 55 to calculate stand volumes at
these ages. A growth model was developed to characterize the
annual volume growth of individual trees. The model related the
annual volume growth of an individual tree to its volume, and the
stand volume. Aggregation of the annual volume increments of individual
trees allowed annual stand volume increments to be estimated.
Individual trees responded to fertilization with greater
10-year volume increment and merchantable height increment. On a
stand basis, fertilization resulted in about 20 m[superscript 3] ha[superscript 2] of additional gross volume growth during the ten-year response period,
This volume growth response was greatest in the third and fourth
years after fertilization. Fertilization appeared to have both a
direct effect and an indirect effect. Tlie direct effect was
growth response to the improved nitrogen status, and this effect
ceased 10 years after treatment. The indirect effect was greater
growth due to larger average tree size, and this effect was still
evident 10 years after treatment. Thinning had little effect beyond
salvaging potential mortality.
An examination of methods commonly used to estimate growth
responses to silvicultural treatments was made. The results suggest
that it is necessary to use treatment-specific and age-specific
local volume equations to accurately measure growth response
to fertilization
Levy distribution and long correlation times in supermarket sales
Sales data in a commodity market (supermarket sales to consumers) has been
analysed by studying the fluctuation spectrum and noise correlations. Three
related products (ketchup, mayonnaise and curry sauce) have been analysed. Most
noise in sales is caused by promotions, but here we focus on the fluctuations
in baseline sales. These characterise the dynamics of the market. Four hitherto
unnoticed effects have been found that are difficult to explain from simple
econometric models. These effects are: (1) the noise level in baseline sales is
much higher than can be expected for uncorrelated sales events; (2) weekly
baseline sales differences are distributed according to a broad non-Gaussian
function with fat tails; (3) these fluctuations follow a Levy distribution of
exponent alpha = 1.4, similar to financial exchange markets and in stock
markets; and (4) this noise is correlated over a period of 10 to 11 weeks, or
shows an apparent power law spectrum. The similarity to stock markets suggests
that models developed to describe these markets may be applied to describe the
collective behaviour of consumers.Comment: 19 pages, 7 figures, accepted for publication in Physica
Cells alter their tRNA abundance to selectively regulate protein synthesis during stress conditions
Decoding the information in mRNA during protein synthesis relies on tRNA adaptors, the abundance of which can affect the decoding rate and translation efficiency. To determine whether cells alter tRNA abundance to selectively regulate protein expression, we quantified changes in the abundance of individual tRNAs at different time points in response to diverse stress conditions in Saccharomyces cerevisiae. We found that the tRNA pool was dynamic and rearranged in a manner that facilitated selective translation of stress-related transcripts. Through genomic analysis of multiple data sets, stochastic simulations, and experiments with designed sequences of proteins with identical amino acids but altered codon usage, we showed that changes in tRNA abundance affected protein expression independently of factors such as mRNA abundance. We suggest that cells alter their tRNA abundance to selectively affect the translation rates of specific transcripts to increase the amounts of required proteins under diverse stress conditions
The Flavour Hierarchy and See-Saw Neutrinos from Bulk Masses in 5d Orbifold GUTs
In supersymmetric grand unified theories (GUTs) based on S^1/(Z_2 x Z'_2)
orbifold constructions in 5 dimensions, Standard Model (SM) matter and Higgs
fields can be realized in terms of 5d hypermultiplets. These hypermultiplets
can naturally have large bulk masses, leading to a localization of the zero
modes at one of the two branes or to an exponential suppression of the mass of
the lowest-lying non-zero mode. We demonstrate that these dynamical features
allow for the construction of an elegant 3-generation SU(5) model in 5
dimensions that explains all the hierarchies between fermion masses and CKM
matrix elements in geometrical terms. Moreover, if U(1)_\chi (where SU(5) x
U(1)_\chi \subset SO(10)) is gauged in the bulk, but broken by the orbifold
action at the SM brane, the right-handed neutrino mass scale is naturally
suppressed relative to M_GUT. Together with our construction in the charged
fermion sector this leads, via the usual see-saw mechanism, to a realistic
light neutrino mass scale and large neutrino mixing angles.Comment: 10 pages LaTeX, 1 figure. Minor comments and reference added. Version
to be published in PL
Group-Theoretical Aspects of Orbifold and Conifold GUTs
Motivated by the simplicity and direct phenomenological applicability of
field-theoretic orbifold constructions in the context of grand unification, we
set out to survey the immensely rich group-theoretical possibilities open to
this type of model building. In particular, we show how every maximal-rank,
regular subgroup of a simple Lie group can be obtained by orbifolding and
determine under which conditions rank reduction is possible. We investigate how
standard model matter can arise from the higher-dimensional SUSY gauge
multiplet. New model building options arise if, giving up the global orbifold
construction, generic conical singularities and generic gauge twists associated
with these singularities are considered. Viewed from the purely field-theoretic
perspective, such models, which one might call conifold GUTs, require only a
very mild relaxation of the constraints of orbifold model building. Our most
interesting concrete examples include the breaking of E_7 to SU(5) and of E_8
to SU(4)xSU(2)xSU(2) (with extra factor groups), where three generations of
standard model matter come from the gauge sector and the families are
interrelated either by SU(3) R-symmetry or by an SU(3) flavour subgroup of the
original gauge group.Comment: references adde
A Shift Symmetry in the Higgs Sector: Experimental Hints and Stringy Realizations
We interpret reported hints of a Standard Model Higgs boson at ~ 125 GeV in
terms of high-scale supersymmetry breaking with a shift symmetry in the Higgs
sector. More specifically, the Higgs mass range suggested by recent LHC data
extrapolates, within the (non-supersymmetric) Standard Model, to a vanishing
quartic Higgs coupling at a UV scale between 10^6 and 10^18 GeV. Such a small
value of lambda can be understood in terms of models with high-scale SUSY
breaking if the Kahler potential possesses a shift symmetry, i.e., if it
depends on H_u and H_d only in the combination (H_u+\bar{H}_d). This symmetry
is known to arise rather naturally in certain heterotic compactifications. We
suggest that such a structure of the Higgs Kahler potential is common in a
wider class of string constructions, including intersecting D7- and D6-brane
models and their extensions to F-theory or M-theory. The latest LHC data may
thus be interpreted as hinting to a particular class of compactifications which
possess this shift symmetry.Comment: v2: References added. v3: References added, published versio
Homozygous MTAP deletion in primary human glioblastoma is not associated with elevation of methylthioadenosine.
Homozygous deletion of methylthioadenosine phosphorylase (MTAP) in cancers such as glioblastoma represents a potentially targetable vulnerability. Homozygous MTAP-deleted cell lines in culture show elevation of MTAP\u27s substrate metabolite, methylthioadenosine (MTA). High levels of MTA inhibit protein arginine methyltransferase 5 (PRMT5), which sensitizes MTAP-deleted cells to PRMT5 and methionine adenosyltransferase 2A (MAT2A) inhibition. While this concept has been extensively corroborated in vitro, the clinical relevance relies on exhibiting significant MTA accumulation in human glioblastoma. In this work, using comprehensive metabolomic profiling, we show that MTA secreted by MTAP-deleted cells in vitro results in high levels of extracellular MTA. We further demonstrate that homozygous MTAP-deleted primary glioblastoma tumors do not significantly accumulate MTA in vivo due to metabolism of MTA by MTAP-expressing stroma. These findings highlight metabolic discrepancies between in vitro models and primary human tumors that must be considered when developing strategies for precision therapies targeting glioblastoma with homozygous MTAP deletion
Effect of corticosteroid injection for trochanter pain syndrome: design of a randomised clinical trial in general practice
Background. Regional pain in the hip in adults is a common cause of a general practitioner visit. A considerable part of patients suffer from (greater) trochanteric pain syndrome or trochanteric bursitis. Local corticosteroid injections is one of the treatment options. Although clear evidence is lacking, small observational studies suggest that this treatment is effective in the short-term follow-up. So far, there are no randomised controlled trials available evaluating the efficacy of injection therapy. This study will investigate the efficacy of local corticosteroid injections in the trochanter syndrome in the general practice, using a randomised controlled trial design. The cost effectiveness of the corticosteroid injectio
Assessment of the ecological and economic benefits of environmental water in the Murray–Darling Basin : The final report to the Murray–Darling Basin Authority from the CSIRO Multiple Benefits of the Basin Plan Project
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