2,392 research outputs found
The impact of biofuel poplar cultivation on ground-level ozone and premature human mortality depends on cultivar selection and planting location
Isoprene and other volatile organic compounds emitted from vegetation play a key role in governing the formation of ground-level ozone. Emission rates of such compounds depend critically on the plant species. Future land use change, driven by the cultivation of biofuel feedstocks, will change the distribution of plant species and hence the magnitude and distribution of emissions. Here we use relationships between biomass yield and isoprene emissions derived from experimental data for 29 commercially available poplar hybrids to assess the impact that the large-scale cultivation of poplar for use as a biofuel feedstock will have on air quality in Europe. We show that the increases in ground-level ozone across Europe will increase the number of premature deaths attributable to ozone pollution each year by up to 6%. Substantial crop losses (up to ~9 Mt y-1 of wheat and maize) are also projected. We further demonstrate that these impacts are strongly dependent on the location of the poplar plantations, due to the prevailing meteorology, the population density and the dominant crop type of the region. Our findings indicate the need for a concerted and centralized decision-making process that considers all aspects of future land use change in Europe, and not just the effect on greenhouse gas emissions
Simulation of 3D Porous Media Flows with Application to Polymer Electrolyte Fuel Cells
A 3D lattice Boltzmann (LB) model with twenty-seven discrete velocities is presented and used for the simulation of three-dimensional porous media flows. Its accuracy in combination with the half-way bounce back boundary condition is assessed. Characteristic properties of the gas diffusion layers that are used in polymer electrolyte fuel cells can be determined with this model. Simulation in samples that have been obtained via X-ray tomographic microscopy, allows to estimate the values of permeability and relative effective diffusivity. Furthermore, the computational LB results are compared with the results of other numerical tools, as well as with experimental value
Dynamics of the Light-Cone Zero Modes: Theta Vacuum of the Massive Schwinger Model
The massive Schwinger model is quantized on the light cone with great care on
the bosonic zero modes by putting the system in a finite (light-cone) spatial
box. The zero mode of survives Dirac's procedure for the constrained
system as a dynamical degree of freedom. After regularization and quantization,
we show that the physical space condition is consistently imposed and relates
the fermion Fock states to the zero mode of the gauge field. The vacuum is
obtained by solving a Schr\"odinger equation in a periodic potential, so that
the theta is understood as the Bloch momentum. We also construct a one-meson
state in the fermion-antifermion sector and obtained the Schr\"odinger equation
for it.Comment: 23 pages, RevTex, no figure
Trends in alcohol use among Hawai‘i adolescents
It is important to review trends in youth alcohol use over time in order to effectively tailor prevention programs to address those trends. This article reviews data on alcohol use behaviors from the Centers for Disease Control and Prevention\u27s Youth Risk Behavior Survey in Hawai‘i from 1993 to 2007. Five alcohol use indicators were examined and stratified by grade level, from 9th grade through 12th grade. Significant drops in nearly all indicators are seen among 9th through 11th graders, but not among 12th graders. This suggests that Hawai‘i youth are responding well to anti-alcohol messaging as young teens, but a different approach may be needed to target older teens
RPA for Light-Front Hamiltonian Field Theory
A self-consistent random phase approximation (RPA) is proposed as an
effective Hamiltonian method in Light-Front Field Theory (LFFT). We apply the
general idea to the light-front massive Schwinger model to obtain a new bound
state equation and solve it numerically.Comment: A major revision in presentation, while the results essentially
unchanged. 2 figs. replaced, 1 fig. added, some parts of Sec. V moved to Sec.
IV, some wording changed, typos correcte
A New Method to Estimate the Noise in Financial Correlation Matrices
Financial correlation matrices measure the unsystematic correlations between
stocks. Such information is important for risk management. The correlation
matrices are known to be ``noise dressed''. We develop a new and alternative
method to estimate this noise. To this end, we simulate certain time series and
random matrices which can model financial correlations. With our approach,
different correlation structures buried under this noise can be detected.
Moreover, we introduce a measure for the relation between noise and
correlations. Our method is based on a power mapping which efficiently
suppresses the noise. Neither further data processing nor additional input is
needed.Comment: 25 pages, 8 figure
Radiosensitization of mammary carcinoma cells by telomere homolog oligonucleotide pretreatment
Introduction: Ionizing radiation (IR) is a widely used approach to cancer therapy, ranking second only to surgery in rate of utilization. Responses of cancer patients to radiotherapy depend in part on the intrinsic radiosensitivity of the tumor cells. Thus, promoting tumor cell sensitivity to IR could significantly enhance the treatment outcome and quality of life for patients. Methods: Mammary tumor cells were treated by a 16-base phosphodiester-linked oligonucleotide homologous to the telomere G-rich sequence TTAGGG (T-oligo: GGTTAGGTGTAGGTTT) or a control-oligo (the partial complement, TAACCCTAACCCTAAC) followed by IR. The inhibition of tumor cell growth in vitro was assessed by cell counting and clonogenic cell survival assay. The tumorigenesis of tumor cells after various treatments was measured by tumor growth in mice. The mechanism underlying the radiosensitization by T-oligo was explored by immunofluorescent determination of phosphorylated histone H2AX (H2AX) foci, -galactosidase staining, comet and Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assays. The efficacy of the combined treatment was assessed in a spontaneous murine mammary tumor model. Results: Pretreatment of tumor cells with T-oligo for 24 hours in vitro enhanced both senescence and apoptosis of irradiated tumor cells and reduced clonogenic potential. Radiosensitization by T-oligo was associated with increased formation and/or delayed resolution of H2AX DNA damage foci and fragmented DNA. T-oligo also caused radiosensitization in two in vivo mammary tumor models. Indeed, combined T-oligo and IR-treatment in vivo led to a substantial reduction in tumor growth. Of further significance, treatment with T-oligo and IR led to synergistic inhibition of the growth of spontaneous mammary carcinomas. Despite these profound antitumor properties, T-oligo and IR caused no detectable side effects under our experimental conditions. Conclusions: Pretreatment with T-oligo sensitizes mammary tumor cells to radiation in both in vitro and in vivo settings with minimal or no normal tissue side effects
Zero Mode and Symmetry Breaking on the Light Front
We study the zero mode and the spontaneous symmetry breaking on the light
front (LF). We use the discretized light-cone quantization (DLCQ) of
Maskawa-Yamawaki to treat the zero mode in a clean separation from all other
modes. It is then shown that the Nambu-Goldstone (NG) phase can be realized on
the trivial LF vacuum only when an explicit symmetry-breaking mass of the NG
boson is introduced. The NG-boson zero mode integrated over the LF
must exhibit singular behavior in the symmetric limit
, which implies that current conservation is violated at zero
mode, or equivalently the LF charge is not conserved even in the symmetric
limit. We demonstrate this peculiarity in a concrete model, the linear sigma
model, where the role of zero-mode constraint is clarified. We further compare
our result with the continuum theory. It is shown that in the continuum theory
it is difficult to remove the zero mode which is not a single mode with measure
zero but the accumulating point causing uncontrollable infrared singularity. A
possible way out within the continuum theory is also suggested based on the
`` theory''. We finally discuss another problem of the zero mode in the
continuum theory, i.e., no-go theorem of Nakanishi-Yamawaki on the
non-existence of LF quantum field theory within the framework of Wightman
axioms, which remains to be a challenge for DLCQ, `` theory'' or any other
framework of LF theory.Comment: 60 pages, the final section has been expanded. A few minor
corrections; version to be published in Phys. Rev.
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