9,008 research outputs found
Recommended from our members
Time-dependent simulations of large-scale quantum mechanical processes
Time dependent linear and nonlinear equations govern the evolution of an extensive set of physical systems and processes describing, to enumerate just a few, Bose-Einstein condensates; soliton propagation in optical and photonic band-gap fibers; quantum control of atomic and molecular collisions and reactions; highly-compressed liquids; and dense and ultracold plasmas. While the media vary substantially, the basic computational procedures have many common features. We focus on the nonlinear Schrodinger equation and discuss two powerful approaches to its propagation: the Arnoldi/Lanczos(AL)l and Real Space Product Formula(RSPF)2. Both provide efficient systematic approximations to the short-time exponential propagator that moves the solution between time steps. We implement the former in a discrete variable representation (DVR)3 both in spatial grid and finite element forms and the latter in a spatial mesh with a finite difference representation of the kinetic energy operator. Both approaches require O(N) operations to propagate the wavefunction between time steps and handle multidimensional systems. We shall also draw connections with Liouville formulations used in quantum molecular dynamics simulations of large collections of atoms and molecules. After briefly outlining these formulations, we shall discuss some of the varied applications
Iteration of Planar Amplitudes in Maximally Supersymmetric Yang-Mills Theory at Three Loops and Beyond
We compute the leading-color (planar) three-loop four-point amplitude of N=4
supersymmetric Yang-Mills theory in 4 - 2 epsilon dimensions, as a Laurent
expansion about epsilon = 0 including the finite terms. The amplitude was
constructed previously via the unitarity method, in terms of two Feynman loop
integrals, one of which has been evaluated already. Here we use the
Mellin-Barnes integration technique to evaluate the Laurent expansion of the
second integral. Strikingly, the amplitude is expressible, through the finite
terms, in terms of the corresponding one- and two-loop amplitudes, which
provides strong evidence for a previous conjecture that higher-loop planar N =
4 amplitudes have an iterative structure. The infrared singularities of the
amplitude agree with the predictions of Sterman and Tejeda-Yeomans based on
resummation. Based on the four-point result and the exponentiation of infrared
singularities, we give an exponentiated ansatz for the maximally
helicity-violating n-point amplitudes to all loop orders. The 1/epsilon^2 pole
in the four-point amplitude determines the soft, or cusp, anomalous dimension
at three loops in N = 4 supersymmetric Yang-Mills theory. The result confirms a
prediction by Kotikov, Lipatov, Onishchenko and Velizhanin, which utilizes the
leading-twist anomalous dimensions in QCD computed by Moch, Vermaseren and
Vogt. Following similar logic, we are able to predict a term in the three-loop
quark and gluon form factors in QCD.Comment: 54 pages, 7 figures. v2: Added references, a few additional words
about large spin limit of anomalous dimensions. v3: Expanded Sect. IV.A on
multiloop ansatz; remark that form-factor prediction is now confirmed by
other work; minor typos correcte
A commentary on key methodological developments related to nutritional life cycle assessment (nLCA) generated throughout a 6-year strategic scientific programme
Rothamsted Research (RRes) is the world's oldest agricultural research centre, notable for the development of the first synthetic fertilizer (superphosphate) and long-term farming experiments (LTEs) spanning over 170 years. In 2015, RRes recruited several life cycle assessment (LCA) experts and began adopting the method to utilize high resolution agronomical data covering livestock (primarily ruminants), grassland/forage productivity and quality, and arable systems established on its North Wyke Farm Platform (NWFP) and the LTEs. The NWFP is a UK ‘National Bioscience Research Infrastructure’ (NBRI) developed for informing and testing systems science utilising high-resolution data to determine whether it is possible to produce nutritious food sustainably. Thanks largely to the multidisciplinary knowledge at RRes, and its collaborators, its LCA Team has been at the forefront of methodological advances during a 6-year Institute Strategic Programme (ISP) ‘Soil-to-Nutrition’ (S2N). While S2N investigated the co-benefits and trade-offs of new mechanistic understanding of efficient nutrient use across scales from pot to landscape, this commentary specifically synthesizes progress in incorporating human nutrition in the context of environmental footprinting, known as ‘nutritional LCA’ (nLCA). We conclude our commentary with a brief discussion on future pathways of exploration and methodological developments covering various activities along entire agri-food supply-chains
The effect of active immunization against adrenocorticotropic hormone on cortisol, beta-endorphin, vocalization, and growth in pigs
Because the poor growth performance of intensively housed pigs is associated with increased circulating glucocorticoid concentrations, we investigated the effects of glucocorticoid suppression by inducing a humoral immune response to ACTH on physiological and production variables in growing pigs. Grower pigs (28.6 0.9 kg) were immunized with amino acids 1 through 24 of ACTH conjugated to ovalbumin and suspended in diethylaminoethyl (DEAE) dextran-adjuvant or adjuvant alone (control) on d 1, 28, and 56. The ACTH-specific antibody titers generated suppressed increases in cortisol concentrations on d 63 in response to an acute stressor (P = 0.002; control = 71 +/- 8.2 ng/ mL; ACTH-immune = 43 +/- 4.9 ng/mL) without altering basal concentrations. Plasma beta-endorphin concentrations were also increased (P < 0.001) on d 63 (control = 18 +/- 2.1 ng/mL; ACTH-immune = 63 +/- 7.3 ng/mL), presumably because of a release from negative feedback on the expression of proopiomelanocortin in pituitary corticotropes. Immunization against ACTH did not alter ADG (P = 0.120; control = 1,077 25; ACTH-immune = 1,143 25 g) or ADFI (P = 0.64; control = 2,719 42; ACTH-immune = 2,749 42 g) and did not modify behavior (P = 0.681) assessed by measuring vocalization in response to acute restraint. In summary, suppression of stress-induced cortisol responses through ACTH immunization increased beta-endorphin concentrations, but it did not modify ADG, ADFI, or restraint vocalization score in growing pigs
Multi-wall carbon nanotubes as quantum dots
We have measured the differential conductance dI/dV of individual multi-wall
carbon nanotubes (MWNT) of different lengths. A cross-over from wire-like (long
tubes) to dot-like (short tubes) behavior is observed. dI/dV is dominated by
random conductance fluctuations (UCF) in long MWNT devices (L=2...7 ),
while Coulomb blockade and energy level quantization are observed in short ones
(L=300 nm). The electron levels of short MWNT dots are nearly four-fold
degenerate (including spin) and their evolution in magnetic field (Zeeman
splitting) agrees with a g-factor of 2. In zero magnetic field the sequential
filling of states evolves with spin S according to S=0 -> 1/2 -> 0... In
addition, a Kondo enhancement of the conductance is observed when the number of
electrons on the tube is odd.Comment: 10 pages, 4 figure
Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T
We have found weak long range antiferromagnetic order in the
quasi-two-dimensional insulating oxide which contains
Cr S=3/2 ions on a kagom\'{e} lattice. In a sample with 76%
occupancy of the chromium sites the ordered moment is 1.1(3) per
chromium ion which is only one third of the N\'{e}el value .
The magnetic unit cell equals the chemical unit cell, a situation which is
favored by inter-plane interactions. Gapless quantum spin-fluctuations
(T_NS(Q,\omega)$ in the ordered
phase.Comment: 18 pages, RevTex/Latex, with 6 figure
Anomalous dimension of the gluon operator in pure Yang-Mills theory
We present new one loop calculations that confirm the theorems of Joglekar
and Lee on the renormalization of composite operators. We do this by
considering physical matrix elements with the operators inserted at non-zero
momentum. The resulting IR singularities are regulated dimensionally. We show
that the physical matrix element of the BRST exact gauge variant operator which
appears in the energy- momentum tensor is zero. We then show that the physical
matrix elements of the classical energy-momentum tensor and the gauge invariant
twist two gluon operator are independent of the gauge fixing parameter. A
Sudakov factor appears in the latter cases. The universality of this factor and
the UV finiteness of the energy-momentum tensor provide another method of
finding the anomalous dimension of the gluon operator. We conjecture that this
method applies to higher loops and takes full advantage of the triangularity of
the mixing matrix.Comment: submitted to Phys. Rev. D, 18 pages LaTEX uses psfig and revtex
macros, figures appended as uuencoded Postscript file (complete Postsript
version including figures available via anonymous ftp from
ftp://max.physics.sunysb.edu/preprints/harris/paper.ps.Z), ITP-SB-94-3
8-hydroxy-2'-deoxyguanosine, a major mutagenic oxidative DNA lesion, and DNA strand breaks in nasal respiratory epithelium of children exposed to urban pollution.
Southwest metropolitan Mexico City children are repeatedly exposed to high levels of a complex mixture of air pollutants, including ozone, particulate matter, aldehydes, metals, and nitrogen oxides. We explored nasal cell 8-hydroxy-2'-deoxyguanosine (8-OHdG), a major mutagenic lesion producing G-->T transversion mutations, using an immunohistochemical method, and DNA single strand breaks (ssb) using the single cell gel electrophoresis assay as biomarkers of oxidant exposure. Nasal biopsies from the posterior inferior turbinate were examined in children in grades one through five, including 12 controls from a low-polluted coastal town and 87 Mexico City children. Each biopsy was divided for the 8-OHdG and DNA ssb assays. There was an age-dependent increase in the percentage of nasal cells with DNA tails > 10 microm in Mexico City children: 19 +/- 9% for control cells, and 43 +/- 4, 50 +/- 16, 56 +/- 17, 60 +/- 17 and 73 +/- 14%, respectively, for first through fifth graders (p < 0.05). Nasal ssb were significantly higher in fifth graders than in first graders (p < 0.05). Higher levels (2.3- to 3-fold) of specific nuclear staining for 8-OHdG were observed in exposed children as compared to controls (p < 0.05). These results suggest that DNA damage is present in nasal epithelial cells in Mexico City children. Persistent oxidative DNA damage may ultimately result in a selective growth of pr eneoplastic nasal initiated cells in this population and the potential for nasal neoplasms may increase with age. The combination of 8-OHdG and DNA ssb should be useful for monitoring oxidative damage in people exposed to polluted atmospheres
Phytoplankton blooms weakly influence the cloud forming ability of sea spray aerosol
After many field studies, the establishment of connections between marine microbiological processes, sea spray aerosol (SSA) composition, and cloud condensation nuclei (CCN) has remained an elusive challenge. In this study, we induced algae blooms to probe how complex changes in seawater composition impact the ability of nascent SSA to act as CCN, quantified by using the apparent hygroscopicity parameter (κapp). Throughout all blooms, κapp ranged between 0.7 and 1.4 (average 0.95 ± 0.15), consistent with laboratory investigations using algae‐produced organic matter, but differing from climate model parameterizations and in situ SSA generation studies. The size distribution of nascent SSA dictates that changes in κapp associated with biological processing induce less than 3% change in expected CCN concentrations for typical marine cloud supersaturations. The insignificant effect of hygroscopicity on CCN concentrations suggests that the SSA production flux and/or secondary aerosol chemistry may be more important factors linking ocean biogeochemistry and marine clouds.Key PointsChanges in seawater and sea spray composition did not strongly affect expected CCN concentrationsBlooms may impact clouds more strongly through changes in aerosol flux or secondary chemistryModel parameterizations likely overestimate changes in cloud nuclei due to primary marine organicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134444/1/grl54978_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134444/2/grl54978-sup-0001-supinfo.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134444/3/grl54978.pd
MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half-Wave Plate
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure
the E-mode polarization of the cosmic microwave background radiation (CMB).
MAXIPOL is the first bolometric CMB experiment to observe the sky using rapid
polarization modulation. To build MAXIPOL, the CMB temperature anisotropy
experiment MAXIMA was retrofitted with a rotating half-wave plate and a
stationary analyzer. We describe the instrument, the observations, the
calibration and the reduction of data collected with twelve polarimeters
operating at 140 GHz and with a FWHM beam size of 10 arcmin. We present maps of
the Q and U Stokes parameters of an 8 deg^2 region of the sky near the star
Beta Ursae Minoris. The power spectra computed from these maps give weak
evidence for an EE signal. The maximum-likelihood amplitude of
l(l+1)C^{EE}_{l}/(2 pi) is 55_{-45}^{+51} uK^2 (68%), and the likelihood
function is asymmetric and skewed positive such that with a uniform prior the
probability that the amplitude is positive is 96%. This result is consistent
with the expected concordance LCDM amplitude of 14 uK^2. The maximum likelihood
amplitudes for l(l+1)C^{BB}_{l}/(2 pi) and are
-31_{-19}^{+31} and 18_{-34}^{+27} uK^2 (68%), respectively, which are
consistent with zero. All of the results are for one bin in the range 151 < l <
693. Tests revealed no residual systematic errors in the time or map domain. A
comprehensive discussion of the analysis of the data is presented in a
companion paper.Comment: 19 pages, 11 figures, 2 tables, submitted to Ap
- …