526 research outputs found
Microscopic model of diffusion limited aggregation and electrodeposition in the presence of levelling molecules
A microscopic model of the effect of unbinding in diffusion limited
aggregation based on a cellular automata approach is presented. The geometry
resembles electrochemical deposition - ``ions'' diffuse at random from the top
of a container until encountering a cluster in contact with the bottom, to
which they stick. The model exhibits dendritic (fractal) growth in the
diffusion limited case. The addition of a field eliminates the fractal nature
but the density remains low. The addition of molecules which unbind atoms from
the aggregate transforms the deposit to a 100% dense one (in 3D). The molecules
are remarkably adept at avoiding being trapped. This mimics the effect of
so-called ``leveller'' molecules which are used in electrochemical deposition
Spatial and Temporal Variation in Primary Productivity (NDVI) of Coastal Alaskan Tundra: Decreased Vegetation Growth Following Earlier Snowmelt
In the Arctic, earlier snowmelt and longer growing seasons due to warming have been hypothesized to increase vegetation productivity. Using the Normalized Difference Vegetation Index (NDVI) from both field and satellite measurements as an indicator of vegetation phenology and productivity, we monitored spatial and temporal patterns of vegetation growth for a coastal wet sedge tundra site near Barrow, Alaska over three growing seasons (2000-2002). Contrary to expectation, earlier snowmelt did not lead to increased productivity. Instead, productivity was associated primarily with precipitation and soil moisture, and secondarily with growing degree days, which, during this period, led to reduced growth in years with earlier snowmelt. Additional moisture effects on productivity and species distribution, operating over a longer time scale, were evident in spatial NDVI patterns associated with microtopography. Lower, wetter regions dominated by graminoids were more productive than higher, drier locations having a higher percentage of lichens and mosses, despite the earlier snowmelt at the more elevated sites. These results call into question the oft-stated hypothesis that earlier arctic growing seasons will lead to greater vegetation productivity. Rather, they agree with an emerging body of evidence from recent field studies indicating that early-season, local environmental conditions, notably moisture and temperature, are primary factors determining arctic vegetation productivity. For this coastal arctic site, early growing season conditions are strongly influenced by microtopography, hydrology, and regional sea ice dynamics, and may not be easily predicted from snowmelt date or seasonal average air temperatures alone. Our comparison of field to satellite NDVI also highlights the value of in-situ monitoring of actual vegetation responses using field optical sampling to obtain detailed information on surface conditions not possible from satellite observations alone
Biomarker Testing for People With Advanced Lung Cancer in England
Introduction: Optimal management of people with advanced NSCLC depends on accurate identification of predictive markers. Yet, real-world data in this setting are limited. We describe the impact, timeliness, and outcomes of molecular testing for patients with advanced NSCLC and good performance status in England. // Methods: In collaboration with Public Health England, patients with stages IIIB to IV NSCLC, with an Eastern Cooperative Oncology Group performance status of 0 to 2, in England, between June 2017 and December 2017, were identified. All English hospitals were invited to record information. // Results: A total of 60 of 142 invited hospitals in England participated in this study and submitted data on 1157 patients. During the study period, 83% of patients with advanced adenocarcinoma underwent molecular testing for three recommended predictive biomarkers (EGFR, ALK, and programmed death-ligand 1). A total of 80% of patients with nonsquamous carcinomas on whom biomarker testing was performed had adequate tissue for analysis on initial sampling. First-line treatment with a tyrosine kinase inhibitor was received by 71% of patients with adenocarcinoma and a sensitizing EGFR mutation and by 59% of those with an ALK translocation. Of patients with no driver mutation and a programmed death-ligand 1 expression of greater than or equal to 50%, 47% received immunotherapy. // Conclusions: We present a comprehensive data set for molecular testing in England. Although molecular testing is well established in England, timeliness and uptake of targeted therapies should be improved
2+1 flavor domain wall QCD on a (2 fm)^3 lattice: light meson spectroscopy with Ls = 16
We present results for light meson masses and pseudoscalar decay constants
from the first of a series of lattice calculations with 2+1 dynamical flavors
of domain wall fermions and the Iwasaki gauge action. The work reported here
was done at a fixed lattice spacing of about 0.12 fm on a 16^3\times32 lattice,
which amounts to a spatial volume of (2 fm)^3 in physical units. The number of
sites in the fifth dimension is 16, which gives m_{res} = 0.00308(4) in these
simulations. Three values of input light sea quark masses, m_l^{sea} \approx
0.85 m_s, 0.59 m_s and 0.33 m_s were used to allow for extrapolations to the
physical light quark limit, whilst the heavier sea quark mass was fixed to
approximately the physical strange quark mass m_s. The exact rational hybrid
Monte Carlo algorithm was used to evaluate the fractional powers of the fermion
determinants in the ensemble generation. We have found that f_\pi = 127(4) MeV,
f_K = 157(5) MeV and f_K/f_\pi = 1.24(2), where the errors are statistical
only, which are in good agreement with the experimental values.Comment: RBC and UKQCD Collaborations. 17 pages, 14 figures. Typeset with
ReVTEX4. v2: replaced with the version published in PRD with improved
introductio
Warming experiments elucidate the drivers of observed directional changes in tundra vegetation
Few studies have clearly linked long-term monitoring with insitu experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling insitu experiments with long-term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes
Acceleressence: Dark Energy from a Phase Transition at the Seesaw Scale
Simple models are constructed for "acceleressence" dark energy: the latent
heat of a phase transition occurring in a hidden sector governed by the seesaw
mass scale v^2/M_Pl, where v is the electroweak scale and M_Pl the
gravitational mass scale. In our models, the seesaw scale is stabilized by
supersymmetry, implying that the LHC must discover superpartners with a
spectrum that reflects a low scale of fundamental supersymmetry breaking.
Newtonian gravity may be modified by effects arising from the exchange of
fields in the acceleressence sector whose Compton wavelengths are typically of
order the millimeter scale. There are two classes of models. In the first class
the universe is presently in a metastable vacuum and will continue to inflate
until tunneling processes eventually induce a first order transition. In the
simplest such model, the range of the new force is bounded to be larger than 25
microns in the absence of fine-tuning of parameters, and for couplings of order
unity it is expected to be \approx 100 microns. In the second class of models
thermal effects maintain the present vacuum energy of the universe, but on
further cooling, the universe will "soon" smoothly relax to a matter dominated
era. In this case, the range of the new force is also expected to be of order
the millimeter scale or larger, although its strength is uncertain. A firm
prediction of this class of models is the existence of additional energy
density in radiation at the eV era, which can potentially be probed in
precision measurements of the cosmic microwave background. An interesting
possibility is that the transition towards a matter dominated era has occurred
in the very recent past, with the consequence that the universe is currently
decelerating.Comment: 10 pages, references adde
Observation of Parity Nonconservation in Moller Scattering
We report a measurement of the parity-violating asymmetry in fixed target
electron-electron (Moller) scattering: A_PV = -175 +/- 30 (stat.) +/- 20
(syst.) parts per billion. This first direct observation of parity
nonconservation in Moller scattering leads to a measurement of the electron's
weak charge at low energy Q^e_W = -0.053 +/- 0.011. This is consistent with the
Standard Model expectation at the current level of precision:
sin^2\theta_W(M_Z)_MSbar = 0.2293 +/- 0.0024 (stat.) +/- 0.0016 (syst.) +/-
0.0006 (theory).Comment: Version 3 is the same as version 2. These versions contain minor text
changes from referee comments and a change in the extracted value of Q^e_W
and sin^2\theta_W due to a change in the theoretical calculation of the
bremsstrahulung correction (ref. 16
Precision Measurement of the Weak Mixing Angle in Moller Scattering
We report on a precision measurement of the parity-violating asymmetry in
fixed target electron-electron (Moller) scattering: A_PV = -131 +/- 14 (stat.)
+/- 10 (syst.) parts per billion, leading to the determination of the weak
mixing angle \sin^2\theta_W^eff = 0.2397 +/- 0.0010 (stat.) +/- 0.0008 (syst.),
evaluated at Q^2 = 0.026 GeV^2. Combining this result with the measurements of
\sin^2\theta_W^eff at the Z^0 pole, the running of the weak mixing angle is
observed with over 6 sigma significance. The measurement sets constraints on
new physics effects at the TeV scale.Comment: 4 pages, 2 postscript figues, submitted to Physical Review Letter
Jet Substructure at the Tevatron and LHC: New results, new tools, new benchmarks
In this report we review recent theoretical progress and the latest
experimental results in jet substructure from the Tevatron and the LHC. We
review the status of and outlook for calculation and simulation tools for
studying jet substructure. Following up on the report of the Boost 2010
workshop, we present a new set of benchmark comparisons of substructure
techniques, focusing on the set of variables and grooming methods that are
collectively known as "top taggers". To facilitate further exploration, we have
attempted to collect, harmonise, and publish software implementations of these
techniques.Comment: 53 pages, 17 figures. L. Asquith, S. Rappoccio, C. K. Vermilion,
editors; v2: minor edits from journal revision
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