Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime
DEFF Research Database (Denmark)
Mics, Zoltán; D’Angio, Andrea; Jensen, Søren A.
2013-01-01
In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude...... model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find...... that the electron scattering time decreases from 320 to 60 fs, as the electron density changes from 1015 to 1019 cm−3....
Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J; Lopata, Kenneth
2016-09-07
Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.
Song, Sisi
2018-04-01
This paper concerns the three-dimensional nonhomogeneous incompressible magnetohydrodynamic equations with density-dependent viscosity and vacuum on Ω \\subset R^3. The domain Ω \\subset R^3 is a general connected smooth one, either bounded or unbounded. In particular, the initial density can have compact support when Ω is unbounded. First, we obtain the local existence and uniqueness of strong solution to the three-dimensional nonhomogeneous incompressible magnetohydrodynamic equations without any compatibility condition assumed on the initial data. Then, we also prove the continuous dependence of strong solution on the initial data under an additional compatibility condition.
He 2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study.
Vikas
2011-08-01
The He 2++ molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 10(9) G is investigated through a quantum fluid dynamics (QFD) and current-density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy density functional that depend not only on the electronic charge-density but also on the current density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 10(11) G. The TD behavior of the exchange- and correlation energy of the He 2++ is analyzed and compared with that obtained using a [B-TD-QFD-density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge-density alone. The CDFT based approach yields TD exchange- and correlation energy and TD electronic charge-density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He 2++ molecular ion is elucidated by treating electronic charge density as an electron-"fluid" in the terminology of QFD. Copyright © 2011 Wiley Periodicals, Inc.
Vikas, Hash(0x125f4490)
2011-02-01
Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.
International Nuclear Information System (INIS)
Vikas
2011-01-01
Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 10 11 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schroedinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >10 9 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >10 9 G, the conventional TD-DFT based approach differs 'dynamically' from the CDFT based approach under similar computational constraints. (author)
Probability densities in strong turbulence
Yakhot, Victor
2006-03-01
In this work we, using Mellin’s transform combined with the Gaussian large-scale boundary condition, calculate probability densities (PDFs) of velocity increments P(δu,r), velocity derivatives P(u,r) and the PDF of the fluctuating dissipation scales Q(η,Re), where Re is the large-scale Reynolds number. The resulting expressions strongly deviate from the Log-normal PDF P(δu,r) often quoted in the literature. It is shown that the probability density of the small-scale velocity fluctuations includes information about the large (integral) scale dynamics which is responsible for the deviation of P(δu,r) from P(δu,r). An expression for the function D(h) of the multifractal theory, free from spurious logarithms recently discussed in [U. Frisch, M. Martins Afonso, A. Mazzino, V. Yakhot, J. Fluid Mech. 542 (2005) 97] is also obtained.
Energy Technology Data Exchange (ETDEWEB)
Vikas [Quantum Chemistry Group, Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, 160014 Chandigrah (India)
2011-02-15
Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 10{sup 11} G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schroedinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >10{sup 9} G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >10{sup 9} G, the conventional TD-DFT based approach differs 'dynamically' from the CDFT based approach under similar computational constraints. (author)
Chu, Peng-Cheng; Li, Xiao-Hua; Ma, Hong-Yang; Wang, Bin; Dong, Yu-Min; Zhang, Xiao-Min
2018-03-01
We study the properties of strange quark matter (SQM) and quark stars (QSs) in strong magnetic fields within the extended confined isospin-density-dependent mass (CIDDM) model including the temperature dependence of the equivalent mass for quarks. The quark symmetry energy, quark symmetry free energy, and the equation of state (EOS) of SQM in constant magnetic fields at finite temperature are investigated, and it is found that including the temperature dependence in CIDDM model and considering strong magnetic fields can both significantly influence the properties of the SQM and the maximum mass of quark stars. Using the density-dependent magnetic field and assuming two extreme cases for the magnetic field orientation in QSs (the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial orientation), we analyze the mass-radius relations for different stages of the protoquark stars (PQSs) along the star evolution. Our results indicate that the maximum mass of magnetized PQSs may depend on not only the strength distribution and the orientation of the magnetic fields inside the PQSs, but also the heating process and the cooling process in the star evolution.
Why Density Dependent Propulsion?
Robertson, Glen A.
2011-01-01
In 2004 Khoury and Weltman produced a density dependent cosmology theory they call the Chameleon, as at its nature, it is hidden within known physics. The Chameleon theory has implications to dark matter/energy with universe acceleration properties, which implies a new force mechanism with ties to the far and local density environment. In this paper, the Chameleon Density Model is discussed in terms of propulsion toward new propellant-less engineering methods.
Strongly Interacting Matter at High Energy Density
International Nuclear Information System (INIS)
McLerran, L.
2008-01-01
This lecture concerns the properties of strongly interacting matter (which is described by Quantum Chromodynamics) at very high energy density. I review the properties of matter at high temperature, discussing the deconfinement phase transition. At high baryon density and low temperature, large N c arguments are developed which suggest that high baryonic density matter is a third form of matter, Quarkyonic Matter, that is distinct from confined hadronic matter and deconfined matter. I finally discuss the Color Glass Condensate which controls the high energy limit of QCD, and forms the low x part of a hadron wavefunction. The Glasma is introduced as matter formed by the Color Glass Condensate which eventually thermalizes into a Quark Gluon Plasma
density-dependent selection revisited
Indian Academy of Sciences (India)
Unknown
phila under density-dependent selection. In a Drosophila culture with very high larval density the environment deteriorates in two ways over time: food tends to run out, and toxic nitrogenous metabolic wastes tend to accumulate. There is, thus, selection favouring the ability to develop fast under crowded conditions, and also ...
Directory of Open Access Journals (Sweden)
Wei Li
2017-01-01
Full Text Available The major structural component of a blood clot is a meshwork of fibrin fibers. It has long been thought that the internal structure of fibrin fibers is homogeneous; that is, the protein density and the bond density between protofibrils are uniform and do not depend on fiber diameter. We performed experiments to investigate the internal structure of fibrin fibers. We formed fibrin fibers with fluorescently labeled fibrinogen and determined the light intensity of a fiber, I, as a function of fiber diameter, D. The intensity and, thus, the total number of fibrin molecules in a cross-section scaled as D1.4. This means that the protein density (fibrin per cross-sectional area, ρp, is not homogeneous but instead strongly decreases with fiber diameter as D-0.6. Thinner fibers are denser than thicker fibers. We also determined Young’s modulus, Y, as a function of fiber diameter. Y decreased strongly with increasing D; Y scaled as D-1.5. This implies that the bond density, ρb, also scales as D-1.5. Thinner fibers are stiffer than thicker fibers. Our data suggest that fibrin fibers have a dense, well-connected core and a sparse, loosely connected periphery. In contrast, electrospun fibrinogen fibers, used as a control, have a homogeneous cross-section.
A mechanistic analysis of density dependence in algal population dynamics
Directory of Open Access Journals (Sweden)
Adrian eBorlestean
2015-04-01
Full Text Available Population density regulation is a fundamental principle in ecology, but the specific process underlying functional expression of density dependence remains to be fully elucidated. One view contends that patterns of density dependence are largely fixed across a species irrespective of environmental conditions, whereas another is that the strength and expression of density dependence are fundamentally variable depending on the nature of exogenous or endogenous constraints acting on the population. We conducted a study investigating the expression of density dependence in Chlamydomonas spp. grown under a gradient from low to high nutrient density. We predicted that the relationship between per capita growth rate (pgr and population density would vary from concave up to concave down as nutrient density became less limiting and populations experienced weaker density regulation. Contrary to prediction, we found that the relationship between pgr and density became increasingly concave-up as nutrient levels increased. We also found that variation in pgr increased, and pgr levels reached higher maxima in nutrient-limited environments. Most likely, these results are attributable to population growth suppression in environments with high intraspecific competition due to limited nutrient resources. Our results suggest that density regulation is strongly variable depending on exogenous and endogenous processes acting on the population, implying that expression of density dependence depends extensively on local conditions. Additional experimental work should reveal the mechanisms influencing how the expression of density dependence varies across populations through space and time.
Strong coupling QCD at finite baryon-number density
International Nuclear Information System (INIS)
Karsch, F.; Muetter, K.H.
1989-01-01
We present a new representation of the partition function for strong-coupling QCD which is suitable also for finite baryon-number-density simulations. This enables us to study the phase structure in the canonical formulation (with fixed baryon number B) as well as the grand canonical one (with fixed chemical potential μ). We find a clear signal for a first-order chiral phase transition at μ c a=0.63. The critical baryon-number density n c a 3 =0.045 is only slightly higher than the density of nuclear matter. (orig.)
Density-dependent synthetic gauge fields using periodically modulated interactions
Greschner, Sebastian; Sun, G.; Poletti, D.; Santos, Luis
2014-01-01
We show that density-dependent synthetic gauge fields may be engineered by combining periodically modulated interactions and Raman-assisted hopping in spin-dependent optical lattices. These fields lead to a density-dependent shift of the momentum distribution, may induce superfluid-to-Mott insulator transitions, and strongly modify correlations in the superfluid regime. We show that the interplay between the created gauge field and the broken sublattice symmetry results, as well, in an intrig...
Density-dependent cladogenesis in birds.
Directory of Open Access Journals (Sweden)
Albert B Phillimore
2008-03-01
Full Text Available A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stronger slowdowns than small clades, even if the probability of speciation and extinction remains constant through time. This is a consequence of exponential growth: clades, which, by chance, diversify at above the average rate early in their history, will tend to be large. They will also tend to regress back to the average diversification rate later on, and therefore show a slowdown. We conducted a meta-analysis of the distribution of speciation events through time, focusing on sequence-based phylogenies for 45 clades of birds. Thirteen of the 23 clades (57% that include more than 20 species show significant slowdowns. The high frequency of slowdowns observed in large clades is even more extreme than expected under a purely stochastic constant-rate model, but is consistent with the adaptive radiation model. Taken together, our data strongly support a model of density-dependent speciation in birds, whereby speciation slows as ecological opportunities and geographical space place limits on clade growth.
Density-dependent feedbacks can mask environmental drivers of populations
DEFF Research Database (Denmark)
Dahlgren, Johan Petter
I present some results from studies identifying environmental drivers of vital rates and population dynamics when controlling for intraspecific density statistically or experimentally, show that density dependence can be strong even in populations of slow-growing species in stressful habitats, an...
and density-dependent quark mass model
Indian Academy of Sciences (India)
We report on the study of the mass–radius (–) relation and the radial oscillations of magnetized proto strange stars. For the quark matter we have employed the very recent modiﬁcation, the temperature- and density-dependent quark mass model of the well-known density-dependent quark mass model. We ﬁnd that the ...
Improving experimental phases for strong reflections prior to density modification
International Nuclear Information System (INIS)
Uervirojnangkoorn, Monarin; Hilgenfeld, Rolf; Terwilliger, Thomas C.; Read, Randy J.
2013-01-01
A genetic algorithm has been developed to optimize the phases of the strongest reflections in SIR/SAD data. This is shown to facilitate density modification and model building in several test cases. Experimental phasing of diffraction data from macromolecular crystals involves deriving phase probability distributions. These distributions are often bimodal, making their weighted average, the centroid phase, improbable, so that electron-density maps computed using centroid phases are often non-interpretable. Density modification brings in information about the characteristics of electron density in protein crystals. In successful cases, this allows a choice between the modes in the phase probability distributions, and the maps can cross the borderline between non-interpretable and interpretable. Based on the suggestions by Vekhter [Vekhter (2005 ▶), Acta Cryst. D61, 899–902], the impact of identifying optimized phases for a small number of strong reflections prior to the density-modification process was investigated while using the centroid phase as a starting point for the remaining reflections. A genetic algorithm was developed that optimizes the quality of such phases using the skewness of the density map as a target function. Phases optimized in this way are then used in density modification. In most of the tests, the resulting maps were of higher quality than maps generated from the original centroid phases. In one of the test cases, the new method sufficiently improved a marginal set of experimental SAD phases to enable successful map interpretation. A computer program, SISA, has been developed to apply this method for phase improvement in macromolecular crystallography
Roy, A. K.; Chu, Shih-I.
2002-05-01
We extend the quantum hydrodynamical (QFD) formulation of time-dependent density functional theory (TDDFT) to the study of multiphoton processes of many-electron atomic systems in intense laser fields (A. K. Roy and S. I. Chu, Phys. Rev. A (in press).). The QFD-TDDFT formulation results in a single generalized nonlinear Schrodinger equation (GNLSE) and includes the many-body effects through a local time-dependent exchange-correlation (xc) potential. The GNLSE is solved by the time- dependent generalized pseudospectral method (X. M. Tong and S.I. Chu, Chem. Phys. 217) (1997) 119. (X. Chu and S. I. Chu, Phys. Rev. A 63) (2001) 023411.. The procedure is applied to the study of multiphoton ionization (MPI) and high harmonic generation (HHG) of He and Ne in intense laser fields. Four different xc energy functionals are used in the study with an aim to explore the roles of exchange and correlation ovn MPI/HHG processes in details ^1.
Simulations of Turbulent Flows with Strong Shocks and Density Variations
Energy Technology Data Exchange (ETDEWEB)
Zhong, Xiaolin
2012-12-13
In this report, we present the research efforts made by our group at UCLA in the SciDAC project Simulations of turbulent flows with strong shocks and density variations. We use shock-fitting methodologies as an alternative to shock-capturing schemes for the problems where a well defined shock is present. In past five years, we have focused on development of high-order shock-fitting Navier-Stokes solvers for perfect gas flow and thermochemical non-equilibrium flow and simulation of shock-turbulence interaction physics for very strong shocks. Such simulation has not been possible before because the limitation of conventional shock capturing methods. The limitation of shock Mach number is removed by using our high-order shock-fitting scheme. With the help of DOE and TeraGrid/XSEDE super computing resources, we have obtained new results which show new trends of turbulence statistics behind the shock which were not known before. Moreover, we are also developing tools to consider multi-species non-equilibrium flows. The main results are in three areas: (1) development of high-order shock-fitting scheme for perfect gas flow, (2) Direct Numerical Simulation (DNS) of interaction of realistic turbulence with moderate to very strong shocks using super computing resources, and (3) development and implementation of models for computation of mutli-species non-quilibrium flows with shock-fitting codes.
Conspecific negative density dependence and forest diversity.
Johnson, Daniel J; Beaulieu, Wesley T; Bever, James D; Clay, Keith
2012-05-18
Conspecific negative density-dependent establishment, in which local abundance negatively affects establishment of conspecific seedlings through host-specific enemies, can influence species diversity of plant communities, but the generality of this process is not well understood. We tested the strength of density dependence using the United States Forest Service's Forest Inventory and Analysis database containing 151 species from more than 200,000 forest plots spanning 4,000,000 square kilometers. We found that most species experienced conspecific negative density dependence (CNDD), but there was little effect of heterospecific density. Additionally, abundant species exhibited weaker CNDD than rarer species, and species-rich regions exhibited stronger CNDD than species-poor regions. Collectively, our results provide evidence that CNDD is a pervasive mechanism driving diversity across a gradient from boreal to subtropical forests.
Bhattacharya, Abhishek; Dunson, David B
2012-08-01
This article considers a broad class of kernel mixture density models on compact metric spaces and manifolds. Following a Bayesian approach with a nonparametric prior on the location mixing distribution, sufficient conditions are obtained on the kernel, prior and the underlying space for strong posterior consistency at any continuous density. The prior is also allowed to depend on the sample size n and sufficient conditions are obtained for weak and strong consistency. These conditions are verified on compact Euclidean spaces using multivariate Gaussian kernels, on the hypersphere using a von Mises-Fisher kernel and on the planar shape space using complex Watson kernels.
Strongly interacting matter at high densities with a soliton model
Johnson, Charles Webster
1998-12-01
One of the major goals of modern nuclear physics is to explore the phase diagram of strongly interacting matter. The study of these 'extreme' conditions is the primary motivation for the construction of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory which will accelerate nuclei to a center of mass (c.m.) energy of about 200 GeV/nucleon. From a theoretical perspective, a test of quantum chromodynamics (QCD) requires the expansion of the conditions examined from one phase point to the entire phase diagram of strongly-interacting matter. In the present work we focus attention on what happens when the density is increased, at low excitation energies. Experimental results from the Brookhaven Alternating Gradient Synchrotron (AGS) indicate that this regime may be tested in the 'full stopping' (maximum energy deposition) scenario achieved at the AGS having a c.m. collision energy of about 2.5 GeV/nucleon for two equal- mass heavy nuclei. Since the solution of QCD on nuclear length-scales is computationally prohibitive even on today's most powerful computers, progress in the theoretical description of high densities has come through the application of models incorporating some of the essential features of the full theory. The simplest such model is the MIT bag model. We use a significantly more sophisticated model, a nonlocal confining soliton model developed in part at Kent. This model has proven its value in the calculation of the properties of individual mesons and nucleons. In the present application, the many-soliton problem is addressed with the same model. We describe nuclear matter as a lattice of solitons and apply the Wigner-Seitz approximation to the lattice. This means that we consider spherical cells with one soliton centered in each, corresponding to the average properties of the lattice. The average density is then varied by changing the size of the Wigner-Seitz cell. To arrive at a solution, we need to solve a coupled set of
Density-dependent changes in reproductive parameters and ...
African Journals Online (AJOL)
The correspondence between the temporal patterns in condition, reproductive parameters and population size are strongly suggestive of density-dependence, and indicate a compensatory response arising from reduced intraspecific competition. This is likely to have resulted from greater per capita food intake, improved ...
Density dependence of the nuclear energy-density functional
Papakonstantinou, Panagiota; Park, Tae-Sun; Lim, Yeunhwan; Hyun, Chang Ho
2018-01-01
Background: The explicit density dependence in the coupling coefficients entering the nonrelativistic nuclear energy-density functional (EDF) is understood to encode effects of three-nucleon forces and dynamical correlations. The necessity for the density-dependent coupling coefficients to assume the form of a preferably small fractional power of the density ρ is empirical and the power is often chosen arbitrarily. Consequently, precision-oriented parametrizations risk overfitting in the regime of saturation and extrapolations in dilute or dense matter may lose predictive power. Purpose: Beginning with the observation that the Fermi momentum kF, i.e., the cubic root of the density, is a key variable in the description of Fermi systems, we first wish to examine if a power hierarchy in a kF expansion can be inferred from the properties of homogeneous matter in a domain of densities, which is relevant for nuclear structure and neutron stars. For subsequent applications we want to determine a functional that is of good quality but not overtrained. Method: For the EDF, we fit systematically polynomial and other functions of ρ1 /3 to existing microscopic, variational calculations of the energy of symmetric and pure neutron matter (pseudodata) and analyze the behavior of the fits. We select a form and a set of parameters, which we found robust, and examine the parameters' naturalness and the quality of resulting extrapolations. Results: A statistical analysis confirms that low-order terms such as ρ1 /3 and ρ2 /3 are the most relevant ones in the nuclear EDF beyond lowest order. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one density-dependent term in nonrelativistic EDFs. The functional we propose easily accommodates known or adopted properties of nuclear matter near saturation. More importantly, upon extrapolation to dilute or asymmetric matter, it reproduces a range of existing microscopic
On the evolution of the density probability density function in strongly self-gravitating systems
International Nuclear Information System (INIS)
Girichidis, Philipp; Konstandin, Lukas; Klessen, Ralf S.; Whitworth, Anthony P.
2014-01-01
The time evolution of the probability density function (PDF) of the mass density is formulated and solved for systems in free-fall using a simple approximate function for the collapse of a sphere. We demonstrate that a pressure-free collapse results in a power-law tail on the high-density side of the PDF. The slope quickly asymptotes to the functional form P V (ρ)∝ρ –1.54 for the (volume-weighted) PDF and P M (ρ)∝ρ –0.54 for the corresponding mass-weighted distribution. From the simple approximation of the PDF we derive analytic descriptions for mass accretion, finding that dynamically quiet systems with narrow density PDFs lead to retarded star formation and low star formation rates (SFRs). Conversely, strong turbulent motions that broaden the PDF accelerate the collapse causing a bursting mode of star formation. Finally, we compare our theoretical work with observations. The measured SFRs are consistent with our model during the early phases of the collapse. Comparison of observed column density PDFs with those derived from our model suggests that observed star-forming cores are roughly in free-fall.
Role of density modulation in the spatially resolved dynamics of strongly confined liquids.
Saw, Shibu; Dasgupta, Chandan
2016-08-07
Confinement by walls usually produces a strong modulation in the density of dense liquids near the walls. Using molecular dynamics simulations, we examine the effects of the density modulation on the spatially resolved dynamics of a liquid confined between two parallel walls, using a resolution of a fraction of the interparticle distance in the liquid. The local dynamics is quantified by the relaxation time associated with the temporal autocorrelation function of the local density. We find that this local relaxation time varies in phase with the density modulation. The amplitude of the spatial modulation of the relaxation time can be quite large, depending on the characteristics of the wall and thermodynamic parameters of the liquid. To disentangle the effects of confinement and density modulation on the spatially resolved dynamics, we compare the dynamics of a confined liquid with that of an unconfined one in which a similar density modulation is induced by an external potential. We find several differences indicating that density modulation alone cannot account for all the features seen in the spatially resolved dynamics of confined liquids. We also examine how the dynamics near a wall depends on the separation between the two walls and show that the features seen in our simulations persist in the limit of large wall separation.
Response of a thin airfoil encountering strong density discontinuity
Energy Technology Data Exchange (ETDEWEB)
Marble, F.E. [California Inst. of Tech., Pasadena, CA (United States). Karman Lab. of Fluid Mechanics
1993-12-01
Airfoil theory for unsteady motion has been developed extensively assuming the undisturbed medium to be of uniform density, a restriction accurate for motion in the atmosphere. In some instances, notably for airfoil comprising fan, compressor and turbine blade rows, the undisturbed medium may carry density variations or ``spots``, resulting from non-uniformities in temperature or composition, of a size comparable to the blade chord. This condition exists for turbine blades, immediately downstream of the main burner of a gas turbine engine where the density fluctuations of the order of 50 percent may occur. Disturbances of a somewhat smaller magnitude arise from the ingestion of hot boundary layers into fans, and exhaust into hovercraft. Because these regions of non-uniform density convect with the moving medium, the airfoil experiences a time varying load and moment which the authors calculate.
Density dependence of clutch size: habitat heterogeneity or individual adjustment?
Both, C.
1998-01-01
1. Two hypotheses have been proposed to explain density- dependent patterns in reproduction. The habitat heterogeneity hypothesis (HHH) explains density-dependent reproduction at the population level from poorer quality territories in heterogeneous environments only being occupied at high densities.
Conspecific negative density dependence in American beech
Directory of Open Access Journals (Sweden)
Benjamin S. Ramage
2017-06-01
Full Text Available Background One of the most important drivers of forest biodiversity is conspecific negative density dependence (CNDD, a reduction in performance when conspecific densities are high. While the majority of CNDD research has focused on tropical forests, evidence is mounting that CNDD may also play an important role in temperate forests. To further explore the potential reach of this phenomenon, we investigated CNDD in American beech (Fagus grandifolia in a mature mid-Atlantic forest. Methods We used bivariate point pattern analyses to examine spatial relationships between large beech trees and conspecific saplings, and we also contrasted these patterns with comparable patterns for heterospecifics. In addition, to address the possibility of dispersal limitation and the associated effects on spatial patterns, we analyzed seedling density as a function of adult conspecific abundance. Results We found that beech saplings were more repelled from large conspecifics than large heterospecifics, despite the fact that beech seedling density was positively correlated with beech basal area. However, saplings of other canopy tree species were also repelled from adult beech trees, suggesting a general suppressive effect. Nonetheless, the discrepancy between beech seedling and sapling densities beneath adult conspecifics suggests that beech seedling survival rates were reduced in vicinity of conspecific adults. Conclusions Regardless of the extent to which beech inhibits heterospecific trees, a negative effect on conspecific recruits may be critical for biodiversity maintenance. Without this conspecific suppression, a dense layer of shade-tolerant beech saplings could form beneath adult beech trees. If this were to occur, beech would have a substantial head-start following canopy disturbance, and this late-successional species could potentially dominate a stand in perpetuity, through repeated disturbance cycles.
Density estimation in tiger populations: combining information for strong inference
Gopalaswamy, Arjun M.; Royle, J. Andrew; Delampady, Mohan; Nichols, James D.; Karanth, K. Ullas; Macdonald, David W.
2012-01-01
A productive way forward in studies of animal populations is to efficiently make use of all the information available, either as raw data or as published sources, on critical parameters of interest. In this study, we demonstrate two approaches to the use of multiple sources of information on a parameter of fundamental interest to ecologists: animal density. The first approach produces estimates simultaneously from two different sources of data. The second approach was developed for situations in which initial data collection and analysis are followed up by subsequent data collection and prior knowledge is updated with new data using a stepwise process. Both approaches are used to estimate density of a rare and elusive predator, the tiger, by combining photographic and fecal DNA spatial capture–recapture data. The model, which combined information, provided the most precise estimate of density (8.5 ± 1.95 tigers/100 km2 [posterior mean ± SD]) relative to a model that utilized only one data source (photographic, 12.02 ± 3.02 tigers/100 km2 and fecal DNA, 6.65 ± 2.37 tigers/100 km2). Our study demonstrates that, by accounting for multiple sources of available information, estimates of animal density can be significantly improved.
Strong density of a class of simple operators
International Nuclear Information System (INIS)
Somasundaram, S.; Mohammad, N.
1991-08-01
An algebra of simple operators has been shown to be strongly dense in the algebra of all bounded linear operators on function spaces of a compact (not necessarily abelian) group. Further, it is proved that the same result is also true for L 2 (G) if G is a locally compact (not necessarily compact) abelian group. (author). 6 refs
Invasions with density-dependent ecological parameters.
Balasuriya, Sanjeeva
2010-10-21
The speed and the minimum carrying capacity needed for a successful population expansion into new territory are addressed using a reaction-diffusion model. The model is able to encapsulate a rich collection of ecological behaviours, including the Allee effect, resource depletion due to consumption, dispersal adaptation due to population pressure, biological control agents, and a range of breeding suppression mechanisms such as embryonic diapause, delayed development and sperm storage. It is shown how many of these phenomena can be characterised as density-dependence in a few fundamental ecological parameters. With the help of a powerful mathematical technique recently developed by Balasuriya and Gottwald (J. Math. Biol. 61, pp. 377-399, 2010), explicit formulae for the effect on the speed and minimum carrying capacity are obtained. Copyright © 2010 Elsevier Ltd. All rights reserved.
Subramanian, K.; Mestel, L.
1993-12-01
A steady density wave in a disc-like galaxy could lead to a spiral form for the crucial α-effect term in standard dynamo theory. We had earlier studied this problem under the thin-disc approximation and by effecting an approximate separation of variables between the z-dependence and the r, φ-dependences of the magnetic field. We return to this problem by making an alternative approximation of our equations, which allows a better treatment of the case of strong departures from axisymmetry, albeit with a cruder treatment of the z-dependence. The numerical solution of the equations reveals, as in our earlier work, the existence of rapidly growing, global, bisymmetric magnetic modes, corotating with the density wave. The modes extend several kiloparsecs around the radius r_c_ where the wave corotates with the gas. The magnetic spiral is closely aligned with the density wave in regions where it has maximum strength; leading within r_c_ and trailing outside. These results are remarkably similar to that obtained in our earlier work, under a very different approximation scheme, encouraging belief in the robustness of the results obtained in both papers.
Wildlife disease elimination and density dependence
Potapov, A.
2012-05-16
Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent (DD) transmission, is ineffective for controlling diseases that are subject to frequency-dependent (FD) transmission. We investigate control for horizontally transmitted diseases with FD transmission where the control is via culling or harvest that is non-selective with respect to infection and the population can compensate through DD recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are FD. Eradication can be achieved under FD transmission when DD birth or recruitment induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination, and there is high enough transmission coefficient, application of both controls may be less efficient than vaccination alone. We illustrate the effects of these control approaches on disease prevalence for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment.
Time-dependent quantum fluid density functional theory of hydrogen ...
Indian Academy of Sciences (India)
dependent density; density functional theory; quantum fluid dynamics. ... (HHG) is also examined. The present approach goes beyond the linear response formalism and, in principle, calculates the TD electron density to all orders of change.
Screening in orbital-density-dependent functionals.
Colonna, Nicola; Nguyen, Ngoc Linh; Ferretti, Andrea; Marzari, Nicola
2018-03-01
Electronic-structure functionals that include screening effects, such as Hubbard or Koopmans' functionals, require to describe the response of a system to the fractional addition or removal of an electron from an orbital or a manifold. Here, we present a general method to incorporate screening based on linear-response theory, and we apply it to the case of the orbital-by-orbital screening of Koopmans' functionals. We illustrate the importance of such generalization when dealing with challenging systems containing orbitals with very different chemical character, also highlighting the simple dependence of the screening on the localization of the orbitals. We choose a set of 46 transition-metal complexes for which experimental data and accurate many-body perturbation theory calculations are available. When compared to experiment, results for ionization potentials show a very good performance with a mean absolute error of $~0.2$ eV, comparable to the most accurate many-body perturbation theory approaches. These results reiterate the role of Koopmans' compliant functionals as simple and accurate quasiparticle approximations to the exact spectral functional, bypassing diagrammatic expansions and relying only on the physics of the local density or generalized-gradient approximation.
Nuclear symmetry energy in density dependent hadronic models
International Nuclear Information System (INIS)
Haddad, S.
2008-12-01
The density dependence of the symmetry energy and the correlation between parameters of the symmetry energy and the neutron skin thickness in the nucleus 208 Pb are investigated in relativistic Hadronic models. The dependency of the symmetry energy on density is linear around saturation density. Correlation exists between the neutron skin thickness in the nucleus 208 Pb and the value of the nuclear symmetry energy at saturation density, but not with the slope of the symmetry energy at saturation density. (author)
Modelling interactions of toxicants and density dependence in wildlife populations
Schipper, Aafke M.; Hendriks, Harrie W.M.; Kauffman, Matthew J.; Hendriks, A. Jan; Huijbregts, Mark A.J.
2013-01-01
1. A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. 2. Here, we incorporated both density dependence and anthropogenic stressors in a stage-based matrix population model and parameterized it for a density-dependent population of peregrine falcons Falco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene (DDE) and polybrominated diphenyl ethers (PBDEs)]. Log-logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. 3. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant-induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. 4. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g−1 fresh weight for DDE and PBDEs, respectively. 5. Synthesis and applications. Our modelling results showed that particular life stages of a density-limited population may be relatively insensitive to
Vikas, Hash(0xb7f6e60)
2012-01-01
Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-density dependent vector exchange-correlation potential and energy density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0-1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the electronic charge-density alone. The current-density based approach yields exchange- and correlation energy as well as electronic charge-density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD electronic charge-density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating electronic charge-density as an `electron-fluid'. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the electronic charge-density distribution of the hydrogen molecule.
Adaptive density dependence of avian clutch size
Both, C.; Tinbergen, J.M.; Visser, M.E.
2000-01-01
In birds, the annual mean clutch size is often negatively correlated with population density. This relationship is at least in part due to adjustment by individuals. We investigated whether this response is adaptive in two ways. First we used an optimality model to predict how optimal clutch size
and density-dependent quark mass model
Indian Academy of Sciences (India)
V K Gupta et al gas of electrons and muons necessary to maintain charge neutrality. This strange quark matter (SQM) may in fact be the true ground state of matter [5–7]. ... Since a fair proportion of such dense proto stars are likely to be magnetized PSS, it would be interesting to study the effect of a strong magnetic field on ...
Density-dependent growth in invasive Lionfish (Pterois volitans.
Directory of Open Access Journals (Sweden)
Cassandra E Benkwitt
Full Text Available Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion.
Prevalence and strength of density-dependent tree recruitment
Kai Zhu; Christopher W. Woodall; Joao V.D. Monteiro; James S. Clark
2015-01-01
Density dependence could maintain diversity in forests, but studies continue to disagree on its role. Part of the disagreement results from the fact that different studies have evaluated different responses (survival, recruitment, or growth) of different stages (seeds, seedlings, or adults) to different inputs (density of seedlings, density or distance to adults). Most...
Density-dependent electron scattering in photoexcited GaAs
DEFF Research Database (Denmark)
Mics, Zoltán; D'Angio, Andrea; Jensen, Søren A.
2013-01-01
—In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...
Density dependence of clutch size : habitat heterogeneity or individual adjustment?
Both, Christiaan
1998-01-01
1. Two hypotheses have been proposed to explain density-dependent patterns in reproduction. The habitat heterogeneity hypothesis (HHH) explains density-dependent reproduction at the population level from poorer quality territories in hetero geneous environments only being occupied at high
Straw Formation and Enhanced Damping of Strong Density Waves in Saturn’s Rings
Stewart, Glen R.
2017-06-01
High resolution Cassini images of strong density waves in Saturn’s rings often show kilometer-scale structures in the wave troughs that are sometimes described as straw-like structures. These structures are likely formed by transient gravitational instabilities within the density wave and have the potential to greatly enhance the local viscous angular momentum transport and thereby limit the maximum amplitude of the density wave. A Hamiltonian theory for density waves has been developed that can describe the rate of local gravitational instabilities in the wave train. The Hamiltonian for single particle motion in the vicinity of an inner Lindblad resonance with a Saturnian satellite can be formulated such that the angle variable conjugate to the radial action is the resonant argument for the resonance. The density wave can then be derived using Hamiltonian perturbation methods to remove the satellite perturbation such that the transformed radial action and conjugate angles include the usual solution for self-gravitating density waves. Local gravitational instabilities in the density wave can now be formulated using a linearized collisionless Boltzmann equation that is expressed in terms of the transformed action-angle variables that contain the density wave solution. The gravitational potential of the linearized perturbation is found to be enhanced by a factor of ten or more in strong density waves, which likely explains the observation of kilometer-scale structures in these waves. The Hamiltonian formalism can also be used to derive an enhanced effective viscosity that results from these straw-like structures.
Zheng, Xiao; Yam, ChiYung; Wang, Fan; Chen, GuanHua
2011-08-28
We present the time-dependent holographic electron density theorem (TD-HEDT), which lays the foundation of time-dependent density-functional theory (TDDFT) for open electronic systems. For any finite electronic system, the TD-HEDT formally establishes a one-to-one correspondence between the electron density inside any finite subsystem and the time-dependent external potential. As a result, any electronic property of an open system in principle can be determined uniquely by the electron density function inside the open region. Implications of the TD-HEDT on the practicality of TDDFT are also discussed.
Deep Ocean Sound Propagation in Environments with Strong Range Dependence
2010-09-30
follow carbon dioxide uptake into the ocean from the atmosphere have been modeled to have a small but potentially detectable impact on ocean acoustic...to scattering). This work is being presented at the NPAL workshop. 8. Ambient noise level change due to ocean acidification A simplified model...range dependence. In addition, a study of oceanic acoustic response to acidification has been made. IMPACT/APPLICATIONS The research described
Study of nuclear level density parameter and its temperature dependence
International Nuclear Information System (INIS)
Nasrabadi, M. N.; Behkami, A. N.
2000-01-01
The nuclear level density ρ is the basic ingredient required for theoretical studies of nuclear reaction and structure. It describes the statistical nuclear properties and is expressed as a function of various constants of motion such as number of particles, excitation energy and angular momentum. In this work the energy and spin dependence of nuclear level density will be presented and discussed. In addition the level density parameter α will be extracted from this level density information, and its temperature and mass dependence will be obtained
Strong dependence of ultracold chemical rates on electric dipole moments
International Nuclear Information System (INIS)
Quemener, Goulven; Bohn, John L.
2010-01-01
We use the quantum threshold laws combined with a classical capture model to provide an analytical estimate of the chemical quenching cross sections and rate coefficients of two colliding particles at ultralow temperatures. We apply this quantum threshold model (QT model) to indistinguishable fermionic polar molecules in an electric field. At ultracold temperatures and in weak electric fields, the cross sections and rate coefficients depend only weakly on the electric dipole moment d induced by the electric field. In stronger electric fields, the quenching processes scale as d 4(L+(1/2)) where L>0 is the orbital angular-momentum quantum number between the two colliding particles. For p-wave collisions (L=1) of indistinguishable fermionic polar molecules at ultracold temperatures, the quenching rate thus scales as d 6 . We also apply this model to pure two-dimensional collisions and find that chemical rates vanish as d -4 for ultracold indistinguishable fermions. This model provides a quick and intuitive way to estimate chemical rate coefficients of reactions occuring with high probability.
Existence of a virtual cathode close to a strongly electron emissive wall in low density plasmas
Energy Technology Data Exchange (ETDEWEB)
Tierno, S. P., E-mail: sp.tierno@upm.es; Donoso, J. M.; Domenech-Garret, J. L.; Conde, L. [Department of Applied Physics, E.T.S.I. Aeronáutica y del Espacio. Universidad Politécnica de Madrid, 28040 Madrid (Spain)
2016-01-15
The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows a phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.
Existence of a virtual cathode close to a strongly electron emissive wall in low density plasmas
Tierno, S. P.; Donoso, J. M.; Domenech-Garret, J. L.; Conde, L.
2016-01-01
The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows a phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.
Estimating density dependence from time series of population age structure.
Lande, Russell; Engen, Steinar; Saether, Bernt-Erik; Coulson, Tim
2006-07-01
Population fluctuations are caused by demographic and environmental stochasticity, time lags due to life history, and density dependence. We model a general life history allowing density dependence within and among age or stage classes in a population undergoing small or moderate fluctuations around a stable equilibrium. We develop a method for estimating the overall strength of density dependence measured by the rate of return toward equilibrium, and we also consider a simplified population description and forecasting using the density-dependent reproductive value. This generality comes at the cost of requiring a time series of the population age or stage structure instead of a univariate time series of adult or total population size. The method is illustrated by analyzing the dynamics of a fully censused population of red deer (Cervus elaphus) based on annual fluctuations of age structure through 21 years.
Time dependent density functional calculation of plasmon response in clusters
Wang, Feng; Zhang, Feng-Shou; Eric, Suraud
2003-02-01
We have introduced a theoretical scheme for the efficient description of the optical response of a cluster based on the time-dependent density functional theory. The practical implementation is done by means of the fully fledged time-dependent local density approximation scheme, which is solved directly in the time domain without any linearization. As an example we consider the simple Na2 cluster and compute its surface plasmon photoabsorption cross section, which is in good agreement with the experiments.
Anthropogenically-Mediated Density Dependence in a Declining Farmland Bird.
Directory of Open Access Journals (Sweden)
Jenny C Dunn
Full Text Available Land management intrinsically influences the distribution of animals and can consequently alter the potential for density-dependent processes to act within populations. For declining species, high densities of breeding territories are typically considered to represent productive populations. However, as density-dependent effects of food limitation or predator pressure may occur (especially when species are dependent upon separate nesting and foraging habitats, high territory density may limit per-capita productivity. Here, we use a declining but widespread European farmland bird, the yellowhammer Emberiza citrinella L., as a model system to test whether higher territory densities result in lower fledging success, parental provisioning rates or nestling growth rates compared to lower densities. Organic landscapes held higher territory densities, but nests on organic farms fledged fewer nestlings, translating to a 5 times higher rate of population shrinkage on organic farms compared to conventional. In addition, when parental provisioning behaviour was not restricted by predation risk (i.e., at times of low corvid activity, nestling provisioning rates were higher at lower territory densities, resulting in a much greater increase in nestling mass in low density areas, suggesting that food limitation occurred at high densities. These findings in turn suggest an ecological trap, whereby preferred nesting habitat does not provide sufficient food for rearing nestlings at high population density, creating a population sink. Habitat management for farmland birds should focus not simply on creating a high nesting density, but also on ensuring heterogeneous habitats to provide food resources in close proximity to nesting birds, even if this occurs through potentially restricting overall nest density but increasing population-level breeding success.
Density functional theory for strongly-interacting electrons: Perspectives for Physics and Chemistry
Gori Giorgi, P.; Seidl, M.
2010-01-01
Improving the accuracy and thus broadening the applicability of electronic density functional theory (DFT) is crucial to many research areas, from material science, to theoretical chemistry, biophysics and biochemistry. In the last three years, the mathematical structure of the strong-interaction
Constraining the density dependence of the symmetry energy
International Nuclear Information System (INIS)
Lynch, W.G.; Zhang, Y.; Coupland, D.; Danielewicz, P; Famiano, M.; Li, Z.; Tsang, B.
2009-01-01
Full text: The density dependence of the symmetry energy plays an important role in nuclear masses, fission barriers, collective excitations, and neutron skin thicknesses of neutron-rich nuclei. It also governs many properties of the neutron stars such as their radii, the thickness of their inner crusts, phase transitions in the stellar interior, seismic activity, and cooling rates. Experiments are beginning to provide constraints on the density dependence of the symmetry energy at sub-saturation densities. This talk will review the measurements and some of the constraints that have been obtained so far. (author)
International Nuclear Information System (INIS)
Backes, Steffen
2017-04-01
The study of the electronic properties of correlated systems is a very diverse field and has lead to valuable insight into the physics of real materials. In these systems, the decisive factor that governs the physical properties is the ratio between the electronic kinetic energy, which promotes delocalization over the lattice, and the Coulomb interaction, which instead favours localized electronic states. Due to this competition, correlated electronic systems can show unique and interesting properties like the Metal-Insulator transition, diverse phase diagrams, strong temperature dependence and in general a high sensitivity to the environmental conditions. A theoretical description of these systems is not an easy task, since perturbative approaches that do not preserve the competition between the kinetic and interaction terms can only be applied in special limiting cases. One of the most famous approaches to obtain the electronic properties of a real material is the ab initio density functional theory (DFT) method. It allows one to obtain the ground state density of the system under investigation by mapping onto an effective non-interacting system that has to be found self-consistently. While being an exact theory, in practical implementations certain approximations have to be made to the exchange-correlation potential. The local density approximation (LDA), which approximates the exchange-correlation contribution to the total energy by that of a homogeneous electron gas with the corresponding density, has proven quite successful in many cases. Though, this approximation in general leads to an underestimation of electronic correlations and is not able to describe a metal-insulator transition due to electronic localization in the presence of strong Coulomb interaction. A different approach to the interacting electronic problem is the dynamical mean-field theory (DMFT), which is non-perturbative in the kinetic and interaction term but neglects all non
Energy Technology Data Exchange (ETDEWEB)
Backes, Steffen
2017-04-15
The study of the electronic properties of correlated systems is a very diverse field and has lead to valuable insight into the physics of real materials. In these systems, the decisive factor that governs the physical properties is the ratio between the electronic kinetic energy, which promotes delocalization over the lattice, and the Coulomb interaction, which instead favours localized electronic states. Due to this competition, correlated electronic systems can show unique and interesting properties like the Metal-Insulator transition, diverse phase diagrams, strong temperature dependence and in general a high sensitivity to the environmental conditions. A theoretical description of these systems is not an easy task, since perturbative approaches that do not preserve the competition between the kinetic and interaction terms can only be applied in special limiting cases. One of the most famous approaches to obtain the electronic properties of a real material is the ab initio density functional theory (DFT) method. It allows one to obtain the ground state density of the system under investigation by mapping onto an effective non-interacting system that has to be found self-consistently. While being an exact theory, in practical implementations certain approximations have to be made to the exchange-correlation potential. The local density approximation (LDA), which approximates the exchange-correlation contribution to the total energy by that of a homogeneous electron gas with the corresponding density, has proven quite successful in many cases. Though, this approximation in general leads to an underestimation of electronic correlations and is not able to describe a metal-insulator transition due to electronic localization in the presence of strong Coulomb interaction. A different approach to the interacting electronic problem is the dynamical mean-field theory (DMFT), which is non-perturbative in the kinetic and interaction term but neglects all non
Density-dependence as a size-independent regulatory mechanism
De Vladar, H.P.
2006-01-01
The growth function of populations is central in biomathematics. The main dogma is the existence of density-dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the Population. One important class of regulatory functions is the theta-logistic, which
Transverse momentum dependent quark densities from Lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Bernhard Musch,Philipp Hagler,John Negele,Andreas Schafer
2011-10-01
We study transverse momentum dependent parton distribution functions (TMDs) with non-local operators in lattice QCD, using MILC/LHPC lattices. We discuss the basic concepts of the method, including renormalization of the gauge link. Results obtained with a simplified operator geometry show visible dipole deformations of spin-dependent quark momentum densities.
Impact of density-dependent symmetry energy and Coulomb ...
Indian Academy of Sciences (India)
Research Articles Volume 82 Issue 3 March 2014 pp 515-527 ... In this paper, we study the time evolution, impact parameter, and excitation energy dependence of IMF production for the different forms of density-dependent symmetry ... School of Physics and Material Science, Thapar University, Patiala 147 004, India ...
Active Space Dependence in Multiconfiguration Pair-Density Functional Theory.
Sharma, Prachi; Truhlar, Donald G; Gagliardi, Laura
2018-02-13
In multiconfiguration pair-density functional theory (MC-PDFT), multiconfiguration self-consistent-field calculations and on-top density functionals are combined to describe both static and dynamic correlation. Here, we investigate how the MC-PDFT total energy and its components depend on the active space choice in the case of the H 2 and N 2 molecules. The active space dependence of the on-top pair density, the total density, the ratio of on-top pair density to half the square of the electron density, and the satisfaction of the virial theorem are also explored. We find that the density and on-top pair density do not change significantly with changes in the active space. However, the on-top ratio does change significantly with respect to active space change, and this affects the on-top energy. This study provides a foundation for designing on-top density functionals and automatizing the active space choice in MC-PDFT.
Transverse momentum dependent quark densities from Lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Bernhard Musch,Philipp Hagler,John Negele,Andreas Schafer
2011-02-01
We study transverse momentum dependent parton distribution functions (TMDs) with non-local operators in lattice QCD, using MILC/LHPC lattices. Results obtained with a simpli?ed operator geometry show visible dipole de- formations of spin-dependent quark momentum densities. We discuss the basic concepts of the method, including renormalization of the gauge link, and an ex- tension to a more elaborate operator geometry that would allow us to analyze process-dependent TMDs such as the Sivers-function.
Temperature Dependence Viscosity and Density of Different Biodiesel Blends
Directory of Open Access Journals (Sweden)
Vojtěch Kumbár
2015-01-01
Full Text Available The main goal of this paper is to assess the effect of rapeseed oil methyl ester (RME concentration in diesel fuel on its viscosity and density behaviour. The density and dynamic viscosity were observed at various mixing ratios of RME and diesel fuel. All measurements were performed at constant temperature of 40 °C. Increasing ratio of RME in diesel fuel was reflected in increased density value and dynamic viscosity of the blend. In case of pure RME, pure diesel fuel, and a blend of both (B30, temperature dependence of dynamic viscosity and density was examined. Temperature range in the experiment was −10 °C to 80 °C. Considerable temperature dependence of dynamic viscosity and density was found and demonstrated for all three samples. This finding is in accordance with theoretical assumptions and reference data. Mathematical models were developed and tested. Temperature dependence of dynamic viscosity was modeled using a polynomial 3rd polynomial degree. Correlation coefficients R −0.796, −0.948, and −0.974 between measured and calculated values were found. Temperature dependence of density was modeled using a 2nd polynomial degree. Correlation coefficients R −0.994, −0.979, and −0.976 between measured and calculated values were acquired. The proposed models can be used for flow behaviour prediction of RME, diesel fuel, and their blends.
Spin polarization in high density quark matter under a strong external magnetic field
DEFF Research Database (Denmark)
Tsue, Yasuhiko; Da Providência, João; Providência, Constança
2016-01-01
In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor-type interact......In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....
Parity dependence of level densities in 49V
International Nuclear Information System (INIS)
York, B.W.
1991-01-01
In this research, we have studied 48 Ti(p, p 1 ) and 48 (p, p 1 γ) in an effort to determine the dependence of level densities on parity in the compound nucleus 49 V. This nuclide was chosen because of the high level density of the 49 V system (leading to good statistical accuracy) and because the target is zero spin (making the assignment of J easier). 5 refs., 3 figs
Density dependence of orientational order in one-patch particles.
Iwashita, Yasutaka; Kimura, Yasuyuki
2017-07-26
Closely packed spherical patchy particles exhibit a range of orientationally ordered equilibrium structures depending on patch size and particle arrangement due to the existence of a sticky inter-patch interaction and rotational degrees of freedom. We experimentally study the packing density dependence of such ordering in particles with a thin deposited patch which imparts a shape anisotropy of a few percent in aspect ratio. These are confined between flat substrates with a chamber thickness of up to two particle layers. When the particles are tightly packed and almost in contact with each other, the anisotropic hard-body interaction dictates the orientational order. Thus, the order depends little on patch size, with rotational motion almost frozen. A small decrease in the density allows free rotational motion while translation is restricted to vibrational motion. This drastically changes the ordering mechanism, giving rise to a patch-size dependent equilibrium orientational order. Furthermore, within this density regime, we find yet another density-dependent transition within the tetragonal bilayer. This transition is reproduced by numerical simulation assuming no shape anisotropy, indicating that shape anisotropy is unnecessary for the transition and translational entropy significantly affects the equilibrium orientational order even in such a closely packed structure. Our study demonstrates the sensitivity of the ordering mechanism and the resulting order to the packing density, where the effect of such a tiny shape anisotropy is clearly observable owing to the patch opacity. The dependence of cluster structure in particle dispersions on patch size, confinement thickness and packing density is also reported.
Radial propagation in population dynamics with density-dependent diffusion
Ngamsaad, Waipot
2014-01-01
Population dynamics that evolve in a radial symmetric geometry are investigated. The nonlinear reaction-diffusion model, which depends on population density, is employed as the governing equation for this system. The approximate analytical solution to this equation is found. It shows that the population density evolves from the initial state and propagates in a traveling-wave-like manner for a long-time scale. If the distance is insufficiently long, the curvature has an ineluctable influence on the density profile and front speed. In comparison, the analytical solution is in agreement with the numerical solution.
Energy Technology Data Exchange (ETDEWEB)
Kapoor, Varun; Brics, Martins; Bauer, Dieter [Institut fuer Physik, Universitaet Rostock, 18051 Rostock (Germany)
2013-07-01
Autoionizing states are inaccessible to time-dependent density functional theory (TDDFT) using known, adiabatic Kohn-Sham (KS) potentials. We determine the exact KS potential for a numerically exactly solvable model Helium atom interacting with a laser field that is populating an autoionizing state. The exact single-particle density of the population in the autoionizing state corresponds to that of the energetically lowest quasi-stationary state in the exact KS potential. We describe how this exact potential controls the decay by a barrier whose height and width allows for the density to tunnel out and decay with the same rate as in the ab initio time-dependent Schroedinger calculation. However, devising a useful exchange-correlation potential that is capable of governing such a scenario in general and in more complex systems is hopeless. As an improvement over TDDFT, time-dependent reduced density matrix functional theory has been proposed. We are able to obtain for the above described autoionization process the exact time-dependent natural orbitals (i.e., the eigenfunctions of the exact, time-dependent one-body reduced density matrix) and study the potentials that appear in the equations of motion for the natural orbitals and the structure of the two-body density matrix expanded in them.
Strong composition-dependent disorder in InAs1-xNx alloys
International Nuclear Information System (INIS)
Benaissa, H.; Zaoui, A.; Ferhat, M.
2009-01-01
We investigate the main causes of disorder in the InAs 1-x N x alloys (x = 0, 0.03125, 0.0625, 0.09375, 0.125, 0.25, 0.5, 0.75, 0.875, 0.90625, 0.9375, 0.96875 and 1). The calculation is based on the density-functional theory in the local-density approximation. We use a plane wave-expansion non-norm conserving ab initio Vanderbilt pseudopotentials. To avoid the difficulty of considering the huge number of atomic configurations, we use an appropriate strategy in which we consider four configurations for a given composition where the N atoms are not randomly distributed. We mainly show that the band gap decreases (increases) rapidly with increasing (decreasing) compositions of N. As a consequence the optical band gap bowing is found to be strong and composition dependent. The obtained compounds, from these alloys, may change from semi-conducting to metal (passing to a negative bowing) and could be useful for device applications, especially at certain composition.
Cuticular antifungals in spiders: density- and condition dependence.
Directory of Open Access Journals (Sweden)
Daniel González-Tokman
Full Text Available Animals living in groups face a high risk of disease contagion. In many arthropod species, cuticular antimicrobials constitute the first protective barrier that prevents infections. Here we report that group-living spiders produce cuticular chemicals which inhibit fungal growth. Given that cuticular antifungals may be costly to produce, we explored whether they can be modulated according to the risk of contagion (i.e. under high densities. For this purpose, we quantified cuticular antifungal activity in the subsocial crab spider Diaea ergandros in both natural nests and experimentally manipulated nests of varying density. We quantified the body-condition of spiders to test whether antifungal activity is condition dependent, as well as the effect of spider density on body-condition. We predicted cuticular antifungal activity to increase and body-condition to decrease with high spider densities, and that antifungal activity would be inversely related to body-condition. Contrary to our predictions, antifungal activity was neither density- nor condition-dependent. However, body-condition decreased with density in natural nests, but increased in experimental nests. We suggest that pathogen pressure is so important in nature that it maintains high levels of cuticular antifungal activity in spiders, impacting negatively on individual energetic condition. Future studies should identify the chemical structure of the isolated antifungal compounds in order to understand the physiological basis of a trade-off between disease prevention and energetic condition caused by group living, and its consequences in the evolution of sociality in spiders.
Bulk viscosity of strange quark matter in density dependent quark ...
Indian Academy of Sciences (India)
Abstract. We have studied the bulk viscosity of strange quark matter in the density dependent quark mass model (DDQM) and compared results with calculations done earlier in the MIT bag model where u, d masses were neglected and first order interactions were taken into account. We find that at low temperatures and ...
Density-dependent growth and metamorphosis in the larval bronze ...
Indian Academy of Sciences (India)
Home; Journals; Journal of Biosciences; Volume 28; Issue 4. Density-dependent growth and metamorphosis in the larval bronze frog Rana temporalis is influenced by genetic relatedness of the cohort. S Girish S K Saidapur. Articles Volume 28 Issue 4 June 2003 pp 489-496 ...
Density-dependent growth and metamorphosis in the larval bronze ...
Indian Academy of Sciences (India)
Unknown
[Girish S and Saidapur S K 2002 Density-dependent growth and metamorphosis in the larval bronze frog Rana temporalis is influenced by genetic relatedness of the ... kin interaction during larval development in anurans seems to vary with the ... leaves were cut into small pieces of uniform size before boiling. Ten grams of ...
Time-dependent density functional theory for periodic systems
Kootstra, Freddie
2001-01-01
In this thesis the time-dependent version of density functional theory is described, which has been developed for crystalline non-metallic systems with periodicity in one to three dimensions. The application of this theory to the calculation of the optical reponse properties of a wide range of
Time-dependent quantum fluid density functional theory of hydrogen ...
Indian Academy of Sciences (India)
A time-dependent generalized non-linear Schrödinger equation (GNLSE) of motion was earlier derived in our laboratory by combining density functional theory and quantum fluid dynamics in threedimensional space. In continuation of the work reported previously, the GNLSE is applied to provide additional knowledge on ...
Evidence for density dependent population regulation in southern ...
African Journals Online (AJOL)
The means by which populations are regulated form a central theme in conservation biology, and much debate has revolved around density dependence as a mechanism driving population ... A significant increase in adult female survival was evident which is likely to have given rise to recent changes in population growth.
Evolution of density-dependent movement during experimental range expansions.
Fronhofer, E A; Gut, S; Altermatt, F
2017-12-01
Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. Although it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intrastrain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.
Density of biogas digestate depending on temperature and composition.
Gerber, Mandy; Schneider, Nico
2015-09-01
Density is one of the most important physical properties of biogas digestate to ensure an optimal dimensioning and a precise design of biogas plant components like stirring devices, pumps and heat exchangers. In this study the density of biogas digestates with different compositions was measured using pycnometers at ambient pressure in a temperature range from 293.15 to 313.15K. The biogas digestates were taken from semi-continuous experiments, in which the marine microalga Nannochloropsis salina, corn silage and a mixture of both were used as feedstocks. The results show an increase of density with increasing total solid content and a decrease with increasing temperature. Three equations to calculate the density of biogas digestate were set up depending on temperature as well as on the total solid content, organic composition and elemental composition, respectively. All correlations show a relative deviation below 1% compared to experimental data. Copyright © 2015. Published by Elsevier Ltd.
Model dependence of isospin sensitive observables at high densities
International Nuclear Information System (INIS)
Guo, Wen-Mei; Yong, Gao-Chan; Wang, Yongjia; Li, Qingfeng; Zhang, Hongfei; Zuo, Wei
2013-01-01
Within two different frameworks of isospin-dependent transport model, i.e., Boltzmann–Uehling–Uhlenbeck (IBUU04) and Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport models, sensitive probes of nuclear symmetry energy are simulated and compared. It is shown that neutron to proton ratio of free nucleons, π − /π + ratio as well as isospin-sensitive transverse and elliptic flows given by the two transport models with their “best settings”, all have obvious differences. Discrepancy of numerical value of isospin-sensitive n/p ratio of free nucleon from the two models mainly originates from different symmetry potentials used and discrepancies of numerical value of charged π − /π + ratio and isospin-sensitive flows mainly originate from different isospin-dependent nucleon–nucleon cross sections. These demonstrations call for more detailed studies on the model inputs (i.e., the density- and momentum-dependent symmetry potential and the isospin-dependent nucleon–nucleon cross section in medium) of isospin-dependent transport model used. The studies of model dependence of isospin sensitive observables can help nuclear physicists to pin down the density dependence of nuclear symmetry energy through comparison between experiments and theoretical simulations scientifically
DEFF Research Database (Denmark)
Fromager, Emmanuel; Jensen, Hans Jørgen Aagaard
2008-01-01
In many cases, density-functional theory (DFT) with current standard approximate functionals offers a relatively accurate and computationally cheap description of the short-range dynamic electron correlation effects. However, in general, standard DFT does not treat the dispersion interaction......-consistency problem" and provide computable orbital-based expressions for any order of perturbation, a general one-electron reduced-density-matrix-based formalism is proposed. Two applications of our general formalism are presented: The derivation of a hybrid second-order Møller-Plesset-DFT model and the formulation...
Multiconfiguration Pair-Density Functional Theory: A New Way To Treat Strongly Correlated Systems.
Gagliardi, Laura; Truhlar, Donald G; Li Manni, Giovanni; Carlson, Rebecca K; Hoyer, Chad E; Bao, Junwei Lucas
2017-01-17
The electronic energy of a system provides the Born-Oppenheimer potential energy for internuclear motion and thus determines molecular structure and spectra, bond energies, conformational energies, reaction barrier heights, and vibrational frequencies. The development of more efficient and more accurate ways to calculate the electronic energy of systems with inherently multiconfigurational electronic structure is essential for many applications, including transition metal and actinide chemistry, systems with partially broken bonds, many transition states, and most electronically excited states. Inherently multiconfigurational systems are called strongly correlated systems or multireference systems, where the latter name refers to the need for using more than one ("multiple") configuration state function to provide a good zero-order reference wave function. This Account describes multiconfiguration pair-density functional theory (MC-PDFT), which was developed as a way to combine the advantages of wave function theory (WFT) and density functional theory (DFT) to provide a better treatment of strongly correlated systems. First we review background material: the widely used Kohn-Sham DFT (which uses only a single Slater determinant as reference wave function), multiconfiguration WFT methods that treat inherently multiconfigurational systems based on an active space, and previous attempts to combine multiconfiguration WFT with DFT. Then we review the formulation of MC-PDFT. It is a generalization of Kohn-Sham DFT in that the electron kinetic energy and classical electrostatic energy are calculated from a reference wave function, while the rest of the energy is obtained from a density functional. However, there are two main differences with respent to Kohn-Sham DFT: (i) The reference wave function is multiconfigurational rather than being a single Slater determinant. (ii) The density functional is a function of the total density and the on-top pair density rather than
Density-waves instability and a skyrmion lattice on the surface of strong topological insulators
Baum, Yuval; Stern, Ady
2012-11-01
In this work we analyze the instability conditions for spin-density-wave (SDW) formation on the surface of strong topological insulators. We find that for a certain range of Fermi energies and strength of interactions the SDW state is favored compared to the unmagnetized and the uniform-magnetization states. We also find that the SDWs are of spiral nature and, for a certain range of parameters, a Skyrmion lattice may form on the surface. We show that this phase may have a nontrivial Chern number even in the absence of an external magnetic field.
Bogolubov–Hartree–Fock Theory for Strongly Interacting Fermions in the Low Density Limit
Energy Technology Data Exchange (ETDEWEB)
Bräunlich, Gerhard [Friedrich-Schiller-University Jena, Institute for Mathematics (Germany); Hainzl, Christian [University of Tübingen, Mathematical Institute (Germany); Seiringer, Robert, E-mail: robert.seiringer@ist.ac.at [Institute of Science and Technology Austria (Austria)
2016-06-15
We consider the Bogolubov–Hartree–Fock functional for a fermionic many-body system with two-body interactions. For suitable interaction potentials that have a strong enough attractive tail in order to allow for two-body bound states, but are otherwise sufficiently repulsive to guarantee stability of the system, we show that in the low-density limit the ground state of this model consists of a Bose–Einstein condensate of fermion pairs. The latter can be described by means of the Gross–Pitaevskii energy functional.
Energy density and energy flow of surface waves in a strongly magnetized graphene
Moradi, Afshin
2018-01-01
General expressions for the energy density and energy flow of plasmonic waves in a two-dimensional massless electron gas (as a simple model of graphene) are obtained by means of the linearized magneto-hydrodynamic model and classical electromagnetic theory when a strong external magnetic field perpendicular to the system is present. Also, analytical expressions for the energy velocity, wave polarization, wave impedance, transverse and longitudinal field strength functions, and attenuation length of surface magneto-plasmon-polariton waves are derived, and numerical results are prepared.
Legros, Mathieu; Lloyd, Alun L; Huang, Yunxin; Gould, Fred
2009-05-01
Density-dependent intraspecific competition has been considered an important determinant of the dynamics of larval stages of Aedes aegypti. A model was published in 1984 providing a mathematical description of this density dependence, based on field data, that has since been widely used. This description, however, is based on the strong assumption that all mortality is density-dependent. We re-examine the data without this premise and find a reduced importance of density dependence, as well as a different functional form. Based on these discrepancies, we emphasize that the characterization of density dependence in the larval stages of Ae. aegypti should be based on a more complete dataset, and we use artificially generated data to explore how such additional information could help developing a better description of this density dependence. We review other empirical studies on larval competition, discuss the need for further dedicated studies, and provide a few simple guidelines for the design of such studies.
Fermionic Statistics in the Strongly Correlated Limit of Density Functional Theory
2017-01-01
Exact pieces of information on the adiabatic connection integrand, Wλ[ρ], which allows evaluation of the exchange-correlation energy of Kohn–Sham density functional theory, can be extracted from the leading terms in the strong coupling limit (λ → ∞, where λ is the strength of the electron–electron interaction). In this work, we first compare the theoretical prediction for the two leading terms in the strong coupling limit with data obtained via numerical implementation of the exact Levy functional in the simple case of two electrons confined in one dimension, confirming the asymptotic exactness of these two terms. We then carry out a first study on the incorporation of the Fermionic statistics at large coupling λ, both numerical and theoretical, confirming that spin effects enter at orders ∼e–√λ. PMID:29111724
Lonely hearts or sex in the city? Density-dependent effects in mating systems.
Kokko, Hanna; Rankin, Daniel J
2006-02-28
Two very basic ideas in sexual selection are heavily influenced by numbers of potential mates: the evolution of anisogamy, leading to sex role differentiation, and the frequency dependence of reproductive success that tends to equalize primary sex ratios. However, being explicit about the numbers of potential mates is not typical to most evolutionary theory of sexual selection. Here, we argue that this may prevent us from finding the appropriate ecological equilibria that determine the evolutionary endpoints of selection. We review both theoretical and empirical advances on how population density may influence aspects of mating systems such as intrasexual competition, female choice or resistance, and parental care. Density can have strong effects on selective pressures, whether or not there is phenotypic plasticity in individual strategies with respect to density. Mating skew may either increase or decrease with density, which may be aided or counteracted by changes in female behaviour. Switchpoints between alternative mating strategies can be density dependent, and mate encounter rates may influence mate choice (including mutual mate choice), multiple mating, female resistance to male mating attempts, mate searching, mate guarding, parental care, and the probability of divorce. Considering density-dependent selection may be essential for understanding how populations can persist at all despite sexual conflict, but simple models seem to fail to predict the diversity of observed responses in nature. This highlights the importance of considering the interaction between mating systems and population dynamics, and we strongly encourage further work in this area.
Impact of density-dependent symmetry energy and Coulomb ...
Indian Academy of Sciences (India)
2014-03-07
Mar 7, 2014 ... ter in the events of big bang, supernova explosions, and in the interior of neutron stars. Therefore, it becomes possible to understand the thermodynamical properties of strongly interacting matter. In addition to the reaction conditions, the symmetry energy, i.e. the isospin-dependent part of nuclear equation ...
Angular momentum dependence of the nuclear level density parameter
International Nuclear Information System (INIS)
Aggarwal, Mamta; Kailas, S.
2010-01-01
Dependence of nuclear level density parameter on the angular momentum and temperature is investigated in a theoretical framework using the statistical theory of hot rotating nuclei. The structural effects are incorporated by including shell correction, shape, and deformation. The nuclei around Z≅50 with an excitation energy range of 30 to 40 MeV are considered. The calculations are in good agreement with the experimentally deduced inverse level density parameter values especially for 109 In, 113 Sb, 122 Te, 123 I, and 127 Cs nuclei.
Does density-dependent diversification mirror ecological competitive exclusion?
Directory of Open Access Journals (Sweden)
Melanie J Monroe
Full Text Available Density-dependence is a term used in ecology to describe processes such as birth and death rates that are regulated by the number of individuals in a population. Evolutionary biologists have borrowed the term to describe decreasing rates of species accumulation, suggesting that speciation and extinction rates depend on the total number of species in a clade. If this analogy with ecological density-dependence holds, diversification of clades is restricted because species compete for limited resources. We hypothesize that such competition should not only affect numbers of species, but also prevent species from being phenotypically similar. Here, we present a method to detect whether competitive interactions between species have ordered phenotypic traits on a phylogeny, assuming that competition prevents related species from having identical trait values. We use the method to analyze clades of birds and mammals, with body size as the phenotypic trait. We find no sign that competition has prevented species from having the same body size. Thus, since body size is a key ecological trait and competition does not seem to be responsible for differences in body size between species, we conclude that the diversification slowdown that is prevalent in these clades is unlikely due to the ecological interference implied by the term density dependence.
Simulating density-dependent flows using the lattice Boltzmann method
Bardsley, K. J.; Sukop, M. C.
2008-12-01
Seawater intrusion is a classic density-dependent problem in hydrogeology. It must be fully understood in order to be able to predict and prevent groundwater deterioration in coastal areas. All of the current programs used to study this issue are either finite difference or finite element methods. Density-dependent flow problems are exceptionally challenging for conventional numerical methods due to inherent non-linearity; definitive solutions are often elusive and a completely different modeling approach may be advantageous. The lattice Boltzmann method (LBM) represents such a numerical tool because it is not based on discretization of a series of differential equations. Instead, its foundation lies in the kinetic theory of gasses as proposed by Boltzmann. A key advantage of lattice Boltzmann method is that it has the ability to solve the Navier-Stokes equations in larger conduits and pores. Recent advances in lattice Boltzmann modeling permit simulation of large-scale density-dependent ground water flow and heat/solute transport. These simulations can be accomplished while retaining the advantages of 'regular' lattice Boltzmann methods, such as solute/heat transport at high Reynolds numbers. Hence it allows for eddy diffusion brought on by inertial components of flow at higher Reynolds numbers, which may occur in some coastal aquifers. This may prove to be an advantage for freshwater/seawater interface simulations especially given the highly macroporous nature of the aquifers underlying south Florida. Simulation of these phenomena is not possible with traditional Darcy's law-based groundwater models. Some geologists and engineers have been able to successfully apply LBM to fluid flow and contaminant transport problems. There are only a handful of scientists attempting to apply LBM to density-dependent flows in general; even fewer have considered seawater intrusion. We show how this method can be applied to density-dependent flows. We present two sets of results
Angular momentum dependence of the nuclear level density parameter
Directory of Open Access Journals (Sweden)
Gohil M.
2014-03-01
Full Text Available Neutron evaporation spectra alongwith γ-multiplicity has been measured from the 185Re* compound nucleus at the excitation energies ~27 and 37 MeV. Statistical model analysis of the experimental data has been carried out to extract the value of the inverse level density parameter k at different angular momentum regions (J corresponding to different γ-multiplicity. It is observed that, for the present system the value of k remains almost constant for different J. The present results on the angular momentum dependence of the nuclear level density (NLD parameter ã (=A/k, for nuclei with A ~180 is quite different from our earlier measurements in case of light and medium mass systems. The present analysis provides useful information to understand the angular momentum dependence of NLD at different nuclear mass regions.
Density-Dependent Phase Polyphenism in Nonmodel Locusts: A Minireview
Directory of Open Access Journals (Sweden)
Hojun Song
2011-01-01
Full Text Available Although the specific mechanisms of locust phase transformation are wellunderstood for model locust species such as the desert locust Schistocerca gregaria and the migratory locust Locusta migratoria, the expressions of density-dependent phase polyphenism in other nonmodel locust species are not wellknown. The present paper is an attempt to review and synthesize what we know about these nonmodel locusts. Based on all available data, I find that locust phase polyphenism is expressed in many different ways in different locust species and identify a pattern that locust species often belong to large taxonomic groups which contain mostly nonswarming grasshopper species. Although locust phase polyphenism has evolved multiple times within Acrididae, I argue that its evolution should be studied from a phylogenetic perspective because I find similar density-dependent phenotypic plasticity among closely related species. Finally, I emphasize the importance of comparative analyses in understanding the evolution of locust phase and propose a phylogeny-based research framework.
Model dependence in the density content of nuclear symmetry energy
International Nuclear Information System (INIS)
Mondal, C.; Agrawal, B.K.; Singh, S.K.; Patra, S.K.; Centelles, M.; Viñas, X.; Colò, G.; Roca-Maza, X.; Paar, N.
2014-01-01
Apart from very few light nuclei, all nuclear systems in nature, starting from tiny finite nuclei to huge astrophysical objects like neutron stars, are asymmetric. Densities of these systems vary over a wide range. So, accurate knowledge of symmetry energy over a wide range of density is very essential to understand several phenomena in finite nuclei as well as in neutron stars. We have shown using a representative set of systematically varied mean models that the correlation of symmetry energy slope parameter with the neutron skin thickness in 208 Pb nucleus has a noticeable amount of model dependence. The investigations in order to unveil the source of the model dependence in such correlations are underway
Wavelength dependence of light diffusion in strongly scattering macroporous gallium phosphide
Peeters, W.H.; Vellekoop, Ivo Micha; Mosk, Allard; Lagendijk, Aart
2008-01-01
We present time-resolved measurements of light transport through strongly scattering macroporous gallium phosphide at various vacuum wavelengths between 705 nm and 855 nm. Within this range the transport mean free path is strongly wavelength dependent, whereas the observed energy velocity is shown
Directory of Open Access Journals (Sweden)
Fatma Kaplan
2011-03-01
Full Text Available The ascarosides form a family of small molecules that have been isolated from cultures of the nematode Caenorhabditis elegans. They are often referred to as "dauer pheromones" because most of them induce formation of long-lived and highly stress resistant dauer larvae. More recent studies have shown that ascarosides serve additional functions as social signals and mating pheromones. Thus, ascarosides have multiple functions. Until now, it has been generally assumed that ascarosides are constitutively expressed during nematode development.Cultures of C. elegans were developmentally synchronized on controlled diets. Ascarosides released into the media, as well as stored internally, were quantified by LC/MS. We found that ascaroside biosynthesis and release were strongly dependent on developmental stage and diet. The male attracting pheromone was verified to be a blend of at least four ascarosides, and peak production of the two most potent mating pheromone components, ascr#3 and asc#8 immediately preceded or coincided with the temporal window for mating. The concentration of ascr#2 increased under starvation conditions and peaked during dauer formation, strongly supporting ascr#2 as the main population density signal (dauer pheromone. After dauer formation, ascaroside production largely ceased and dauer larvae did not release any ascarosides. These findings show that both total ascaroside production and the relative proportions of individual ascarosides strongly correlate with these compounds' stage-specific biological functions.Ascaroside expression changes with development and environmental conditions. This is consistent with multiple functions of these signaling molecules. Knowledge of such differential regulation will make it possible to associate ascaroside production to gene expression profiles (transcript, protein or enzyme activity and help to determine genetic pathways that control ascaroside biosynthesis. In conjunction with findings
Nuclear level density parameter 's dependence on angular momentum
International Nuclear Information System (INIS)
Aggarwal, Mamta; Kailas, S.
2009-01-01
Nuclear level densities represent a very important ingredient in the statistical Model calculations of nuclear reaction cross sections and help to understand the microscopic features of the excited nuclei. Most of the earlier experimental nuclear level density measurements are confined to low excitation energy and low spin region. A recent experimental investigation of nuclear level densities in high excitation energy and angular momentum domain with some interesting results on inverse level density parameter's dependence on angular momentum in the region around Z=50 has motivated us to study and analyse these experimental results in a microscopic theoretical framework. In the experiment, heavy ion fusion reactions are used to populate the excited and rotating nuclei and measured the α particle evaporation spectra in coincidence with ray multiplicity. Residual nuclei are in the range of Z R 48-55 with excitation energy range 30 to 40 MeV and angular momentum in 10 to 25. The inverse level density parameter K is found to be in the range of 9.0 - 10.5 with some exceptions
THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY
International Nuclear Information System (INIS)
Burkert, Andreas; Hartmann, Lee
2013-01-01
Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density Σ of Σ c ∼ 120 M ☉ pc –2 (A K ∼ 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area Σ SFR with increasing Σ, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of Σ SFR , approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of Σ SFR versus Σ in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A ∼ Σ –3 for low-mass regions and A ∼ Σ –1 for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse
Koons, David N; Colchero, Fernando; Hersey, Kent; Gimenez, Olivier
2015-06-01
Understanding the relative effects of climate, harvest, and density dependence on population dynamics is critical for guiding sound population management, especially for ungulates in arid and semiarid environments experiencing climate change. To address these issues for bison in southern Utah, USA, we applied a Bayesian state-space model to a 72-yr time series of abundance counts. While accounting for known harvest (as well as live removal) from the population, we found that the bison population in southern Utah exhibited a strong potential to grow from low density (β0 = 0.26; Bayesian credible interval based on 95% of the highest posterior density [BCI] = 0.19-0.33), and weak but statistically significant density dependence (β1 = -0.02, BCI = -0.04 to -0.004). Early spring temperatures also had strong positive effects on population growth (Pfat1 = 0.09, BCI = 0.04-0.14), much more so than precipitation and other temperature-related variables (model weight > three times more than that for other climate variables). Although we hypothesized that harvest is the primary driving force of bison population dynamics in southern Utah, our elasticity analysis indicated that changes in early spring temperature could have a greater relative effect on equilibrium abundance than either harvest or. the strength of density dependence. Our findings highlight the utility of incorporating elasticity analyses into state-space population models, and the need to include climatic processes in wildlife management policies and planning.
Yun, Li; Agrawal, Aneil F
2014-12-01
In what types of environments should we expect to find strong inbreeding depression? Previous studies indicate that inbreeding depression, δ, is positively correlated with the stressfulness of the environment in which it is measured. However, it remains unclear why stress, per se, should increase δ. To our knowledge, only "competitive stress" has a logical connection to δ. Through competition for resources, better quality (outbred) individuals make the environment worse for lower quality (inbred) individuals, accentuating the differences between them. For this reason, we expect inbreeding depression to be stronger in environments where the fitness of individuals is more sensitive to the presence of conspecifics (i.e., where fitness is more density dependent). Indeed, some studies suggest a role for competition within environments, but this idea has not been tested in the context of understanding variation in δ across environments. Using Drosophila melanogaster, we estimated δ for viability in 22 different environments. These environments were simultaneously characterized for (1) stressfulness and (2) density dependence. Although stress and density dependence are moderately correlated with each other, inbreeding depression is much more strongly correlated with density dependence. These results suggest that mean selection across the genome is stronger in environments where competition is intense, rather than in environments that are stressful for other reasons. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.
Zimmermann, Fabian; Ricard, Daniel; Heino, Mikko
2018-01-30
Population regulation is a central concept in ecology, yet in many cases its presence and the underlying mechanisms are difficult to demonstrate. The current paradigm maintains that marine fish populations are predominantly regulated by density-dependent recruitment. While it is known that density-dependent somatic growth can be present too, its general importance remains unknown and most practical applications neglect it. This study aimed to close this gap by for the first time quantifying and comparing density dependence in growth and recruitment over a large set of fish populations. We fitted density-dependent models to time-series data on population size, recruitment and age-specific weight from commercially exploited fish populations in the Northeast Atlantic Ocean and the Baltic Sea. Data were standardized to enable a direct comparison within and among populations, and estimated parameters were used to quantify the impact of density regulation on population biomass. Statistically significant density dependence in recruitment was detected in a large proportion of populations (70%), whereas for density dependence in somatic growth the prevalence of density dependence depended heavily on the method (26% and 69%). Despite age-dependent variability, the density dependence in recruitment was consistently stronger among age groups and between alternative approaches that use weight-at-age or weight increments to assess growth. Estimates of density-dependent reduction in biomass underlined these results: 97% of populations with statistically significant parameters for growth and recruitment showed a larger impact of density-dependent recruitment on population biomass. The results reaffirm the importance of density-dependent recruitment in marine fishes, yet they also show that density dependence in somatic growth is not uncommon. Furthermore, the results are important from an applied perspective because density dependence in somatic growth affects productivity and
Density and starting-energy dependent effective interaction
International Nuclear Information System (INIS)
Yamaguchi, Norio; Nagata, Sinobu; Kasuga, Teruo
1979-01-01
A new effective potential constructed from the reaction matrix calculation of nuclear matters is proposed, taking three-body effects into account. Starting from the two-body scattering equation for nuclear matters, an equation with averaged momentum is introduced as the definition of effective interaction. The parameters in the equation are the Fermi momentum and the starting energy. The nuclear density dependence and the starting energy dependence are independently treated in the potential. The effective interactions including three-body effects were calculated. The dependence on the starting energy is large. The effective interaction is more attractive in the triplet E state, and assures overall saturation without any artificial renormalization. The reaction matrix calculation can be well reproduced by the calculation with this effective potential. The results of calculation for the binding energy of He-4 and O-16 and the shell model matrix elements of O-16 are represented. (Kato, T.)
Pernal, Katarzyna
2012-05-14
Time-dependent density functional theory (TD-DFT) in the adiabatic formulation exhibits known failures when applied to predicting excitation energies. One of them is the lack of the doubly excited configurations. On the other hand, the time-dependent theory based on a one-electron reduced density matrix functional (time-dependent density matrix functional theory, TD-DMFT) has proven accurate in determining single and double excitations of H(2) molecule if the exact functional is employed in the adiabatic approximation. We propose a new approach for computing excited state energies that relies on functionals of electron density and one-electron reduced density matrix, where the latter is applied in the long-range region of electron-electron interactions. A similar approach has been recently successfully employed in predicting ground state potential energy curves of diatomic molecules even in the dissociation limit, where static correlation effects are dominating. In the paper, a time-dependent functional theory based on the range-separation of electronic interaction operator is rigorously formulated. To turn the approach into a practical scheme the adiabatic approximation is proposed for the short- and long-range components of the coupling matrix present in the linear response equations. In the end, the problem of finding excitation energies is turned into an eigenproblem for a symmetric matrix. Assignment of obtained excitations is discussed and it is shown how to identify double excitations from the analysis of approximate transition density matrix elements. The proposed method used with the short-range local density approximation (srLDA) and the long-range Buijse-Baerends density matrix functional (lrBB) is applied to H(2) molecule (at equilibrium geometry and in the dissociation limit) and to Be atom. The method accounts for double excitations in the investigated systems but, unfortunately, the accuracy of some of them is poor. The quality of the other
Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics
Lyskova, N.; Churazov, E.; Naab, T.
2018-04-01
We discuss constraints on the mass density distribution (parametrized as ρ ∝ r-γ) in early-type galaxies provided by strong lensing and stellar kinematics data. The constraints come from mass measurements at two `pinch' radii. One `pinch' radius r1 = 2.2REinst is defined such that the Einstein (i.e. aperture) mass can be converted into the spherical mass almost independently of the mass-model. Another `pinch' radius r2 = Ropt is chosen so that the dynamical mass, derived from the line-of-sight velocity dispersion, is least sensitive to the anisotropy of stellar orbits. We verified the performance of this approach on a sample of simulated elliptical galaxies and on a sample of 15 SLACS lens galaxies at 0.01 ≤ z ≤ 0.35, which have already been analysed in Barnabè et al. by the self-consistent joint lensing and kinematic code. For massive simulated galaxies, the density slope γ is recovered with an accuracy of ˜13 per cent, unless r1 and r2 happen to be close to each other. For SLACS galaxies, we found good overall agreement with the results of Barnabè et al. with a sample-averaged slope γ = 2.1 ± 0.05. Although the two-pinch-radii approach has larger statistical uncertainties, it is much simpler and uses only few arithmetic operations with directly observable quantities.
Maxwell Equation Violation by Density Dependent Magnetic Fields in Neutron Stars
Alloy, Marcelo D.; Menezes, Débora P.
We show that the widely used density dependent magnetic field prescriptions, necessary to account for the variation of the field intensity from the crust to the core of neutron stars violate one of the Maxwell equations. We estimate how strong the violation is when different equations of state are used and check for which cases the pathological problem can be cured. We then propose a simple solution that allows for the usual prescriptions to be used without violating a fundamental equation of physics.
Time-dependent density functional theory for many-electron systems interacting with cavity photons.
Tokatly, I V
2013-06-07
Time-dependent (current) density functional theory for many-electron systems strongly coupled to quantized electromagnetic modes of a microcavity is proposed. It is shown that the electron-photon wave function is a unique functional of the electronic (current) density and the expectation values of photonic coordinates. The Kohn-Sham system is constructed, which allows us to calculate the above basic variables by solving self-consistent equations for noninteracting particles. We suggest possible approximations for the exchange-correlation potentials and discuss implications of this approach for the theory of open quantum systems. In particular we show that it naturally leads to time-dependent density functional theory for systems coupled to the Caldeira-Leggett bath.
DEFF Research Database (Denmark)
Koons, David; Colchero, Fernando; Hersey, Kent
2015-01-01
Understanding the relative effects of climate, harvest, and density dependence on population dynamics is critical for guiding sound population management, especially for ungulates in arid and semi-arid environments experiencing climate change. To address these issues for bison in southern Utah, we...... spring temperature could have a greater ‘relative effect’ on equilibrium abundance than either harvest or the strength of density dependence. Our findings highlight the utility of incorporating elasticity analyses into state-space population models, and the need to include climatic processes in wildlife...... applied a Bayesian state-space model to a 72-year time series of abundance counts. While accounting for known harvest (as well as live removal) from the population, we found that the bison population in southern Utah exhibited strong potential to grow from low density (β0 = 0.26; Bayesian credible...
Increased transvascular low density lipoprotein transport in insulin dependent diabetes
DEFF Research Database (Denmark)
Kornerup, Karen; Nordestgaard, Børge Grønne; Feldt-Rasmussen, Bo
2003-01-01
for albumin were 6.8+/-2.5 and 5.4+/-2.0%/h (Paltered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, nephropathy, statin use, or different plasma insulin levels in diabetes patients. CONCLUSION: Transvascular LDL transport may...... accumulation and thus atherosclerosis. METHODS: We used an in vivo method for measurement of transvascular transport of low density lipoprotein (LDL) and applied it in 24 patients with insulin dependent diabetes mellitus (type 1) and in 30 healthy controls. LDL was individually sampled and autologous 131...
Time-dependent density-functional theory concepts and applications
Ullrich, Carsten A
2011-01-01
Time-dependent density-functional theory (TDDFT) describes the quantum dynamics of interacting electronic many-body systems formally exactly and in a practical and efficient manner. TDDFT has become the leading method for calculating excitation energies and optical properties of large molecules, with accuracies that rival traditional wave-function based methods, but at a fraction of the computational cost.This book is the first graduate-level text on the concepts and applications of TDDFT, including many examples and exercises, and extensive coverage of the literature. The book begins with a s
Limits for density dependent time inhomogeneous Markov processes.
Smith, Andrew G
2015-10-01
A new functional law of large numbers to approximate a time inhomogeneous Markov process that is only density dependent in the limit as an index parameter goes to infinity is developed. This extends previous results by other authors to a broader class of Markov processes while relaxing some of the conditions required for those results to hold. This result is applied to a stochastic metapopulation model that accounts for spatial structure as well as within patch dynamics with the novel addition of time dependent dynamics. The resulting nonautonomous differential equation is analysed to provide conditions for extinction and persistence for a number of examples. This condition shows that the migration of a species will positively impact the reproduction in less populated areas while negatively impacting densely populated areas. Crown Copyright © 2015. Published by Elsevier Inc. All rights reserved.
Berim, Gersh O.; Ruckenstein, Eli
2011-02-01
The dependence of the contact angles of nanodrops of Lennard-Jones type fluids in nanocavities on their sizes are calculated using a nonlocal density functional theory in a canonical ensemble. Cavities of various radii and depths, various temperatures, as well as various values of the energy parameter of the fluid-solid interactions were considered. It is argued that this dependence might affect strongly, for instance, the rate of heterogeneous nucleation on rough surfaces, which is usually calculated under the assumption of constant contact angle.
Mamo, Kiminad A.
2012-10-01
We study holographic RG flow of the shear viscosity tensor of anisotropic, strongly coupled {N}=4 super-Yang-Mills plasma by using its type IIB supergravity dual in anisotropic bulk spacetime. We find that the shear viscosity tensor has three independent components in the anisotropic bulk spacetime away from the boundary, and one of the components has a non-trivial RG flow while the other two have a trivial one. For the component of the shear viscosity tensor with non-trivial RG flow, we derive its RG flow equation, and solve the equation analytically to second order in the anisotropy parameter a. We derive the RG equation using the equation of motion, holographic Wilsonian RG method, and Kubo's formula. All methods give the same result. Solving the equation, we find that the ratio of the component of the shear viscosity tensor to entropy density η /s flows from above 1/{4π } the horizon (IR) to below 1/{4π } the boundary (UV) where it violates the holographic shear viscosity (Kovtun-Son-Starinets) bound and where it agrees with the other longitudinal component.
Density-dependence of functional spiking networks in vitro
Energy Technology Data Exchange (ETDEWEB)
Ham, Michael I [Los Alamos National Laboratory; Gintautuas, Vadas [Los Alamos National Laboratory; Rodriguez, Marko A [Los Alamos National Laboratory; Bettencourt, Luis M A [Los Alamos National Laboratory; Bennett, Ryan [UNIV OF NORTH TEXAS; Santa Maria, Cara L [UNIV OF NORTH TEXAS
2008-01-01
During development, the mammalian brain differentiates into specialized regions with unique functional abilities. While many factors contribute to this functional specialization, we explore the effect neuronal density can have on neuronal interactions. Two types of networks, dense (50,000 neurons and glia support cells) and sparse (12,000 neurons and glia support cells), are studied. A competitive first response model is applied to construct activation graphs that represent pairwise neuronal interactions. By observing the evolution of these graphs during development in vitro we observe that dense networks form activation connections earlier than sparse networks, and that link-!llltropy analysis of the resulting dense activation graphs reveals that balanced directional connections dominate. Information theoretic measures reveal in addition that early functional information interactions (of order 3) are synergetic in both dense and sparse networks. However, during development in vitro, such interactions become redundant in dense, but not sparse networks. Large values of activation graph link-entropy correlate strongly with redundant ensembles observed in the dense networks. Results demonstrate differences between dense and sparse networks in terms of informational groups, pairwise relationships, and activation graphs. These differences suggest that variations in cell density may result in different functional specialization of nervous system tissue also in vivo.
Asymptotic dependence of Gross–Tulub polaron ground-state energy in the strong coupling region
Directory of Open Access Journals (Sweden)
N.I. Kashirina
2017-12-01
Full Text Available The properties of translationally invariant polaron functional have been investigated in the region of strong and extremely strong coupling. It has been shown that the Gross–Tulub polaron functional obtained earlier using the methods of field theory was derived only for the region , where is the Fröhlich constant of the electron-phonon coupling. Various representations of exact and approximate polaron functionals have been considered. Asymptotic dependences of the polaron energy have been obtained using a functional extending the Gross–Tulub functional to the region of extremely strong coupling. The asymptotic dependence of polaron energies for an extremely strong coupling are (for the one-parameter variational function fk, and (for a two-parameter function . It has been shown that the virial theorem 1:3:4 holds for the two-parameter function . Minimization of the approximate functional obtained by expanding the exact Gross–Tulub functional in a series on leads to a quadratic dependence of the polaron energy. This approximation is justified for . For a two-parameter function , the corresponding dependence has the form . However, the use of approximate functionals, in contrast to the strict variational procedure, when the exact polaron functional varies, does not guarantee obtaining the upper limit for the polaron energy.
Energy Technology Data Exchange (ETDEWEB)
Finkbeiner, S. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Weber, J. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)
1995-01-15
The temperature dependence of the strong visible photoluminescence (550-850nm) is studied in differently prepared porous silicon samples. The variation in the photoluminescence intensity with temperature is a result of a decrease in the radiative decay time and an increase in the non-radiative recombination process with increasing temperatures. The strong visible photoluminescence is interpreted by a recombination of singlet and triplet excitons. The singlet-triplet splitting is comparable for all samples but depends on the detection wavelength and on sample preparation. We present similar data for the recombination process in siloxene which supports the model of a common origin of the strong visible photoluminescence in these very differently prepared samples. ((orig.))
Density dependence triggers runaway selection of reduced senescence.
Directory of Open Access Journals (Sweden)
Robert M Seymour
2007-12-01
Full Text Available In the presence of exogenous mortality risks, future reproduction by an individual is worth less than present reproduction to its fitness. Senescent aging thus results inevitably from transferring net fertility into younger ages. Some long-lived organisms appear to defy theory, however, presenting negligible senescence (e.g., hydra and extended lifespans (e.g., Bristlecone Pine. Here, we investigate the possibility that the onset of vitality loss can be delayed indefinitely, even accepting the abundant evidence that reproduction is intrinsically costly to survival. For an environment with constant hazard, we establish that natural selection itself contributes to increasing density-dependent recruitment losses. We then develop a generalized model of accelerating vitality loss for analyzing fitness optima as a tradeoff between compression and spread in the age profile of net fertility. Across a realistic spectrum of senescent age profiles, density regulation of recruitment can trigger runaway selection for ever-reducing senescence. This novel prediction applies without requirement for special life-history characteristics such as indeterminate somatic growth or increasing fecundity with age. The evolution of nonsenescence from senescence is robust to the presence of exogenous adult mortality, which tends instead to increase the age-independent component of vitality loss. We simulate examples of runaway selection leading to negligible senescence and even intrinsic immortality.
Changes in seasonal climate outpace compensatory density-dependence in eastern brook trout
Bassar, Ronald D.; Letcher, Benjamin H.; Nislow, Keith H.; Whiteley, Andrew R.
2016-01-01
Understanding how multiple extrinsic (density-independent) factors and intrinsic (density-dependent) mechanisms influence population dynamics has become increasingly urgent in the face of rapidly changing climates. It is particularly unclear how multiple extrinsic factors with contrasting effects among seasons are related to declines in population numbers and changes in mean body size and whether there is a strong role for density-dependence. The primary goal of this study was to identify the roles of seasonal variation in climate driven environmental direct effects (mean stream flow and temperature) versus density-dependence on population size and mean body size in eastern brook trout (Salvelinus fontinalis). We use data from a 10-year capture-mark-recapture study of eastern brook trout in four streams in Western Massachusetts, USA to parameterize a discrete-time population projection model. The model integrates matrix modeling techniques used to characterize discrete population structures (age, habitat type and season) with integral projection models (IPMs) that characterize demographic rates as continuous functions of organismal traits (in this case body size). Using both stochastic and deterministic analyses we show that decreases in population size are due to changes in stream flow and temperature and that these changes are larger than what can be compensated for through density-dependent responses. We also show that the declines are due mostly to increasing mean stream temperatures decreasing the survival of the youngest age class. In contrast, increases in mean body size over the same period are the result of indirect changes in density with a lesser direct role of climate-driven environmental change.
Exact-exchange time-dependent density-functional theory with the frequency-dependent kernel
International Nuclear Information System (INIS)
Shigeta, Yasuteru; Hirao, Kimihiko; Hirata, So
2006-01-01
The effects of the adiabatic approximation in time-dependent density-functional theory (TDDFT) on dynamic polarizabilities and van der Waals C 6 coefficients have been analyzed quantitatively. These effects are shown to be small in the off-resonance region of the perturbation frequencies by comparing the results from the exact-exchange TDDFT employing the optimized effective potentials and the corresponding frequency-dependent kernel [time-dependent optimized effective potentials (TDOEP)] and those from the frequency-independent kernel [adiabatic TDOEP (ATDOEP)]. The magnitude of the computed dynamic polarizabilities near the static limit is found to be in the order: time-dependent Hartree-Fock (TDHF)>ATDOEP>TDOEP, whereas that of C 6 is: TDHF>TDOEP>ATDOEP
Density dependence of SOL power width in ASDEX upgrade L-Mode
Directory of Open Access Journals (Sweden)
B. Sieglin
2017-08-01
A recent study [4] with an open divertor configuration found an asymmetry of the power fall-off length between inner and outer target with a smaller power fall-off length λq,i on the inner divertor target. Measurements with a closed divertor configuration find a similar asymmetry for low recycling divertor conditions. It is found, in the experiment, that the in/out asymmetry λq,i/λq,o is strongly increasing with increasing density. Most notably the heat flux density at the inner divertor target is reducing with increasing λq,i whilst the total power onto each divertor target stays constant. It is found that λq,o exhibits no significant density dependence for hydrogen and deuterium but increases with about the square root of the electron density for helium. The difference between H,D and He could be due to the different recycling behaviour in the divertor. These findings may help current modelling attempts to parametrize the density dependence of the widening of the power channel and thus allow for detailed comparison to both divertor effects like recycling or increased upstream SOL cross field transport.
International Nuclear Information System (INIS)
Jacobson, A.R.
1981-04-01
A laser diagnostic scheme is described which facilitates localization of density fluctuations along the line of sight. The method exploits both the generally observed anisotropy of density fluctuations in low-beta plasmas, as well as the twisting of the magnetic field which occurs across the minor diameter of reversed-field pinches, spheromaks, etc. Both interferometric and schlieren variations are discussed
International Nuclear Information System (INIS)
Koinov, Z.G.; Yanchev, I.Y.
1981-09-01
The density of states in heavily doped strongly compansated semiconductors in a strong magnetic field is calculated by using the path-integral method. The case is considered when correlation exists in the impurity positions owing to the Coulomb interactions between the charged donors and acceptors during the high-temperature preparation of the samples. The semiclassical formula is rederived and corrections to it due to the long-range character of the potential and its short-range fluctuations are obtained. The density of states in the tail is studied and analytical results are given in the classical and quantum cases. (author)
Female elk contacts are neither frequency nor density dependent
Cross, Paul C.; Creech, Tyler G.; Ebinger, Michael R.; Manlove, Kezia R.; Irvine, Kathryn M.; Henningsen, John C.; Rogerson, Jared D.; Scurlock, Brandon M.; Creely, Scott
2013-01-01
Identifying drivers of contact rates among individuals is critical to understanding disease dynamics and implementing targeted control measures. We studied the interaction patterns of 149 female elk (Cervus canadensis) distributed across five different regions of western Wyoming over three years, defining a contact as an approach within one body length (∼2 m). Using hierarchical models that account for correlations within individuals, pairs, and groups, we found that pairwise contact rates within a group declined by a factor of three as group sizes increased 33-fold. Per capita contact rates, however, increased with group size according to a power function, such that female elk contact rates fell in between the predictions of density- or frequency-dependent disease models. We found similar patterns for the duration of contacts. Our results suggest that larger elk groups are likely to play a disproportionate role in the disease dynamics of directly transmitted infections in elk. Supplemental feeding of elk had a limited impact on pairwise interaction rates and durations, but per capita rates were more than two times higher on feeding grounds. Our statistical approach decomposes the variation in contact rate into individual, dyadic, and environmental effects, and provides insight into factors that may be targeted by disease control programs. In particular, female elk contact patterns were driven more by environmental factors such as group size than by either individual or dyad effects.
On the penetration of a hot diapir through a strongly temperature-dependent viscosity medium
Daly, S. F.; Raefsky, A.
1985-01-01
The ascent of a hot spherical body through a fluid with a strongly temperature-dependent viscosity has been studied using an axisymmetric finite element method. Numerical solutions range over Peclet numbers of 0.1 - 1000 from constant viscosity up to viscosity variations of 100,000. Both rigid and stress-free boundary conditions were applied at the surface of the sphere. The dependence of drag on viscosity variation was shown to have no dependence on the stress boundary condition except for a Stokes flow scaling factor. A Nusselt number parameterization based on the stress-free constant viscosity functional dependence on the Peclet number scaled by a parameter depending on the viscosity structure fits both stress-free and rigid boundary condition data above viscosity variations of 100. The temperature scale height was determined as a function of sphere radius. For the simple physical model studied in this paper pre-heating is required to reduce the ambient viscosity of the country rock to less than 10 to the 22nd sq cm/s in order for a 10 km diapir to penetrate a distance of several radii.
Density-dependent growth of the polychaete Diopatra aciculata
Directory of Open Access Journals (Sweden)
Milada Safarik
2006-12-01
Full Text Available Effects of intraspecific density on growth of the tube-building polychaete Diopatra aciculata (Onuphidae were examined over a three-month period within a marine worm aquaculture facility. Three polychaete densities (500, 1000 and 2000 worms/m2 were represented within triplicate 0.30 m2 boxes containing late juvenile D. aciculata, sandy sediment and recirculating seawater. Daily food ration per worm was held constant across all density levels. Total length, weight and number of segments were recorded for 20 polychaetes randomly removed from each of nine treatment boxes at weeks 1, 7 and 14. Mean daily growth was higher during weeks 1-7 than during weeks 7-14 for all growth variables at each density level. Polychaetes at the highest density level exhibited lower rates of growth and more broken and/or regenerating posterior segments than those at low density. High D. aciculata density was also associated with reduced dissolved oxygen concentrations and high polychaete mortality (20%. At medium polychaete density (1000/m2, D. aciculata exhibited low levels of apparent stress and high biomass return per unit area, both of which are important considerations in the aquaculture rearing of this species. We suggest that further studies focus on age- and size-related factors contributing to density effects on polychaete growth.
Correlated electron dynamics and memory in time-dependent density functional theory
International Nuclear Information System (INIS)
Thiele, Mark
2009-01-01
Time-dependent density functional theory (TDDFT) is an exact reformulation of the time-dependent many-electron Schroedinger equation, where the problem of many interacting electrons is mapped onto the Kohn-Sham system of noninteracting particles which reproduces the exact electronic density. In the Kohn-Sham system all non-classical many-body effects are incorporated in the exchange-correlation potential which is in general unknown and needs to be approximated. It is the goal of this thesis to investigate the connection between memory effects and correlated electron dynamics in strong and weak fields. To this end one-dimensional two-electron singlet systems are studied. At the same time these systems include the onedimensional helium atom model, which is an established system to investigate the crucial effects of correlated electron dynamics in external fields. The studies presented in this thesis show that memory effects are negligible for typical strong field processes. Here the approximation of the spatial nonlocality is of primary importance. For the photoabsorption spectra on the other hand the neglect of memory effects leads to qualitative and quantitative errors, which are shown to be connected to transitions of double excitation character. To develop a better understanding of the conditions under which memory effects become important quantum fluid dynamics has been found to be especially suitable. It represents a further exact reformulation of the quantum mechanic many-body problem which is based on hydrodynamic quantities such as density and velocity. Memory effects are shown to be important whenever the velocity field develops strong gradients and dissipative effects contribute. (orig.)
Correlated electron dynamics and memory in time-dependent density functional theory
Energy Technology Data Exchange (ETDEWEB)
Thiele, Mark
2009-07-28
Time-dependent density functional theory (TDDFT) is an exact reformulation of the time-dependent many-electron Schroedinger equation, where the problem of many interacting electrons is mapped onto the Kohn-Sham system of noninteracting particles which reproduces the exact electronic density. In the Kohn-Sham system all non-classical many-body effects are incorporated in the exchange-correlation potential which is in general unknown and needs to be approximated. It is the goal of this thesis to investigate the connection between memory effects and correlated electron dynamics in strong and weak fields. To this end one-dimensional two-electron singlet systems are studied. At the same time these systems include the onedimensional helium atom model, which is an established system to investigate the crucial effects of correlated electron dynamics in external fields. The studies presented in this thesis show that memory effects are negligible for typical strong field processes. Here the approximation of the spatial nonlocality is of primary importance. For the photoabsorption spectra on the other hand the neglect of memory effects leads to qualitative and quantitative errors, which are shown to be connected to transitions of double excitation character. To develop a better understanding of the conditions under which memory effects become important quantum fluid dynamics has been found to be especially suitable. It represents a further exact reformulation of the quantum mechanic many-body problem which is based on hydrodynamic quantities such as density and velocity. Memory effects are shown to be important whenever the velocity field develops strong gradients and dissipative effects contribute. (orig.)
Zhang, Shuang; Yang, Jiong; Xu, Renjing; Wang, Fan; Li, Weifeng; Ghufran, Muhammad; Zhang, Yong-wei; Yu, Zongfu; Zhang, Gang; Qin, Qinghua; Lu, Yuerui
2014-01-01
Phosphorene is a new family member of two-dimensional materials. We observed strong and highly layer-dependent photoluminescence in few-layer phosphorene (2 to 5 layers). The results confirmed the theoretical prediction that few-layer phosphorene has a direct and layer-sensitive band gap. We also demonstrated that few-layer phosphorene is more sensitive to temperature modulation than graphene and MoS2 in Raman scattering. The anisotropic Raman response in few-layer phosphorene has enabled us ...
Sun, Jian
2012-02-21
A two-contact extraordinary magnetoresistance (EMR) device has been fabricated and characterized at various temperatures under magnetic fields applied in different directions. Large performance variations across the temperature range have been found, which are due to the strong dependence of the EMR effect on the mobility. The device shows the highest sensitivity of 562ω/T at 75 K with the field applied perpendicularly. Due to the overlap between the semiconductor and the metal shunt, the device is also sensitive to planar fields but with a lower sensitivity of about 20 to 25% of the one to perpendicular fields. © 2012 The Japan Society of Applied Physics.
Energy Technology Data Exchange (ETDEWEB)
Rose, Harvey [Los Alamos National Laboratory; Daughton, W [Los Alamos National Laboratory; Yin, L [Los Alamos National Laboratory
2009-01-01
The onset of Stimulated Raman scatter from an intense laser speckle is the simplest experimentally realizable laser-plasma-interaction environment. Despite this data and recent 3D particle simulations, the controlling mechanism at the onset of backscatter in the kinetic regime when strong electron trapping in the daughter Langmuir wave is a dominant nonlinearity is not understood. This paper explores the consequences of assuming that onset is controlled by large thermal fluctuations. A super exponential dependence of mean reflectivity on speckle intensity in the onset regime is predicted.
Continuous Dependence on the Density for Stratified Steady Water Waves
Chen, Robin Ming; Walsh, Samuel
2016-02-01
There are two distinct regimes commonly used to model traveling waves in stratified water: continuous stratification, where the density is smooth throughout the fluid, and layer-wise continuous stratification, where the fluid consists of multiple immiscible strata. The former is the more physically accurate description, but the latter is frequently more amenable to analysis and computation. By the conservation of mass, the density is constant along the streamlines of the flow; the stratification can therefore be specified by prescribing the value of the density on each streamline. We call this the streamline density function. Our main result states that, for every smoothly stratified periodic traveling wave in a certain small-amplitude regime, there is an L ∞ neighborhood of its streamline density function such that, for any piecewise smooth streamline density function in that neighborhood, there is a corresponding traveling wave solution. Moreover, the mapping from streamline density function to wave is Lipschitz continuous in a certain function space framework. As this neighborhood includes piecewise smooth densities with arbitrarily many jump discontinues, this theorem provides a rigorous justification for the ubiquitous practice of approximating a smoothly stratified wave by a layered one. We also discuss some applications of this result to the study of the qualitative features of such waves.
Dependence of Cardiac 11C-meta-Hydroxyephedrine Retention on Norepinephrine Transporter Density
Raffel, David M.; Chen, Wei; Sherman, Phillip S.; Gildersleeve, David L.; Jung, Yong-Woon
2006-01-01
The norepinephrine analog 11C-meta-hydroxyephedrine (HED) is used with PET to map the regional distribution of cardiac sympathetic neurons. HED is rapidly transported into sympathetic neurons by the norepinephrine transporter (NET) and stored in vesicles. Although much is known about the neuronal mechanisms of HED uptake and retention, there is little information about the functional relationship between HED retention and cardiac sympathetic nerve density. The goal of this study was to characterize the dependence of HED retention on nerve density in rats with graded levels of cardiac denervation induced chemically with the neurotoxin 6-hydroxydopamine (6-OHDA). Methods Thirty male Sprague–Dawley rats were divided into 6 groups, and each group was administered a different dose of 6-OHDA: 0 (controls), 7, 11, 15, 22, and 100 mg/kg intraperitoneally. One day after 6-OHDA injection, HED (3.7–8.3 MBq) was injected intravenously into each animal and HED concentrations in heart and blood at 30 min after injection were determined. Heart tissues were frozen and later processed by tissue homogenization and differential centrifugation into a membrane preparation for in vitro measurement of cardiac NET density. A saturation binding assay using 3H-mazindol as the radioligand was used to measure NET density (maximum number of binding sites [Bmax], fmol/mg protein) for each heart. Results In control animals, NET Bmax was 388 ± 23 fmol/mg protein and HED heart uptake (HU) at 30 min was 2.89% ± 0.35 %ID/g (%ID/g is percentage injected dose per gram tissue). The highest 6-OHDA dose of 100 mg/kg caused severe cardiac denervation, decreasing both NET Bmax and HED HU to 8% of their control values. Comparing values for all doses of 6-OHDA, HED retention had a strong linear correlation with NET density: HU = 0.0077Bmax − 0.028, r2 = 0.95. Conclusion HED retention is linearly dependent on NET density in rat hearts that have been chemically denervated with 6-OHDA, suggesting that
Density-dependent predation influences the evolution and behavior of masquerading prey
Skelhorn, John; Rowland, Hannah M.; Delf, Jon; Speed, Michael P.; Ruxton, Graeme D.
2011-01-01
Predation is a fundamental process in the interaction between species, and exerts strong selection pressure. Hence, anti-predatory traits have been intensively studied. Although it has long been speculated that individuals of some species gain protection from predators by sometimes almost-uncanny resemblances to uninteresting objects in the local environment (such as twigs or stones), demonstration of antipredatory benefits to such “masquerade” have only very recently been demonstrated, and the fundamental workings of this defensive strategy remain unclear. Here we use laboratory experiments with avian predators and twig-mimicking caterpillars as masqueraders to investigate (i) the evolutionary dynamics of masquerade; and (ii) the behavioral adaptations associated with masquerade. We show that the benefit of masquerade declines as the local density of masqueraders relative to their models (twigs, in our system) increases. This occurs through two separate mechanisms: increasing model density both decreased predators’ motivation to search for masqueraders, and made masqueraders more difficult to detect. We further demonstrated that masquerading organisms have evolved complex microhabitat selection strategies that allow them to best exploit the density-dependent properties of masquerade. Our results strongly suggest the existence of opportunity costs associated with masquerade. Careful evaluation of such costs will be vital to the development of a fuller understanding of both the distribution of masquerade across taxa and ecosystems, and the evolution of the life history strategies of masquerading prey. PMID:21464318
Wu, Shan; Burlingame, Quinn; Cheng, Zhao-Xi; Lin, Minren; Zhang, Q. M.
2014-12-01
Dielectric materials with high electric energy density and low loss are of great importance for applications in modern electronics and electrical systems. Strongly dipolar materials have the potential to reach relatively higher dielectric constants than the widely used non-polar or weakly dipolar polymers, as well as a much lower loss than that of nonlinear high K polymer dielectrics or polymer-ceramic composites. To realize the high energy density while maintaining the low dielectric loss, aromatic polythioureas and polyureas with high dipole moments, high dipole densities, tunable molecular structures and dielectric properties were investigated. High energy density (>24 J/cm3), high breakdown strength (>800 MV/m), and high charge-discharge efficiency (>90%) can be achieved in the new polymers. The molecular structure and film surface morphology were also studied; it is of great importance to optimize the fabrication process to make high-quality thin films.
Density-dependent vulnerability of forest ecosystems to drought
Bottero, Alessandra; D'Amato, Anthony W.; Palik, Brian J.; Bradford, John B.; Fraver, Shawn; Battaglia, Mike A.; Asherin, Lance A.
2017-01-01
1. Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a given area, is a primary driver of competitive intensity among trees, which influences tree growth and mortality. Manipulating tree population density may be a mechanism for moderating drought-induced stress and growth reductions, although the relationship between tree population density and tree drought vulnerability remains poorly quantified, especially across climatic gradients.2. In this study, we examined three long-term forest ecosystem experiments in two widely distributed North American pine species, ponderosa pine Pinus ponderosa (Lawson & C. Lawson) and red pine Pinus resinosa (Aiton), to better elucidate the relationship between tree population density, growth and drought. These experiments span a broad latitude and aridity range and include tree population density treatments that have been purposefully maintained for several decades. We investigated how tree population density influenced resistance (growth during drought) and resilience (growth after drought compared to pre-drought growth) of stand-level growth during and after documented drought events.3. Our results show that relative tree population density was negatively related to drought resistance and resilience, indicating that trees growing at lower densities were less vulnerable to drought. This result was apparent in all three forest ecosystems, and was consistent across species, stand age and drought intensity.4. Synthesis and applications. Our results highlighted that managing pine forest ecosystems at low tree population density represents a promising adaptive strategy for reducing the adverse impacts of drought on forest growth in coming decades
Strongly interacting bosons in a one-dimensional optical lattice at incommensurate densities
Lazarides, A.|info:eu-repo/dai/nl/315556668; Tieleman, O.|info:eu-repo/dai/nl/341386456; de Morais Smith, C.|info:eu-repo/dai/nl/304836346
2011-01-01
We investigate quantum phase transitions occurring in a system of strongly interacting ultracold bosons in a one-dimensional optical lattice. After discussing the commensurate-incommensurate transition, we focus on the phases appearing at an incommensurate filling. We find a rich phase diagram, with
Extension of SMAC scheme for variable density flows under strong temperature gradient
Anwer, S. F.; Khan, H. Naushad; Sanghi, S.; Ahmad, A.; Yahya, S. M.
2012-06-01
An extension of SMAC scheme is proposed for variable density flows under low Mach number approximation. The algorithm is based on a predictor-corrector time integration scheme that employs a projection method for the momentum equation. A constant-coefficient Poisson equation is solved for the pressure following both the predictor and corrector steps to satisfy the continuity equation at each time step. Spatial discretization is performed on a collocated grid system that offers computational simplicity and straight forward extension to curvilinear coordinate systems. To avoid the pressure odd-even decoupling that is typically encountered in such grids, a flux interpolation technique is introduced for the equations governing variable density flows. An important characteristic of the proposed algorithm is that it can be applied to flows in both open and closed domains. Its robustness and accuracy are illustrated with a non-isothermal, turbulent channel flow at temperature ratio of 1.01 and 2.
Strong anomaly, spectral-density sum rules, and broken (U(3) x U(3) symmetry
Energy Technology Data Exchange (ETDEWEB)
Debnath, S.; Bagchi, B.
1983-05-01
We obtain by making use of the anomaly term in the divergence of the flavor-singlet-axial-vector-current new spectral-function sum rules for the pseudoscalar density in a chiral SU()3) x SU(3) x U/sub 3/(1) framework. The positivity conditions on the spectral representations of the pseudoscalar densities lead to a new bound on the quark-condensate term <0Vertical Barq-barqVertical Bar0>< or =-(279 MeV)/sup 3/ (q = u, d, and s) corresponding bare-current-quark values of m/sub u/ = m/sub d/roughly-equal5 MeV and m/sub s/roughly-equal150 MeV.
Temperature Dependence Viscosity and Density of Different Biodiesel Blends
Vojtěch Kumbár; Antonín Skřivánek
2015-01-01
The main goal of this paper is to assess the effect of rapeseed oil methyl ester (RME) concentration in diesel fuel on its viscosity and density behaviour. The density and dynamic viscosity were observed at various mixing ratios of RME and diesel fuel. All measurements were performed at constant temperature of 40 °C. Increasing ratio of RME in diesel fuel was reflected in increased density value and dynamic viscosity of the blend. In case of pure RME, pure diesel fuel, and a blend of both (B3...
Energy Technology Data Exchange (ETDEWEB)
Nanda, Vikas; Kant, Niti, E-mail: nitikant@yahoo.com [Department of Physics, Lovely Professional University, G. T. Road, Phagwara, Punjab 144411 (India)
2014-07-15
The effect of plasma density ramp on self-focusing of cosh-Gaussian laser beam considering ponderomotive nonlinearity is analyzed using WKB and paraxial approximation. It is noticed that cosh-Gaussian laser beam focused earlier than Gaussian beam. The focusing and de-focusing nature of the cosh-Gaussian laser beam with decentered parameter, intensity parameter, magnetic field, and relative density parameter has been studied and strong self-focusing is reported. It is investigated that decentered parameter “b” plays a significant role for the self-focusing of the laser beam as for b=2.12, strong self-focusing is seen. Further, it is observed that extraordinary mode is more prominent toward self-focusing rather than ordinary mode of propagation. For b=2.12, with the increase in the value of magnetic field self-focusing effect, in case of extraordinary mode, becomes very strong under plasma density ramp. Present study may be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, and x-ray lasers. Moreover, plasma density ramp plays a vital role to enhance the self-focusing effect.
International Nuclear Information System (INIS)
Nanda, Vikas; Kant, Niti
2014-01-01
The effect of plasma density ramp on self-focusing of cosh-Gaussian laser beam considering ponderomotive nonlinearity is analyzed using WKB and paraxial approximation. It is noticed that cosh-Gaussian laser beam focused earlier than Gaussian beam. The focusing and de-focusing nature of the cosh-Gaussian laser beam with decentered parameter, intensity parameter, magnetic field, and relative density parameter has been studied and strong self-focusing is reported. It is investigated that decentered parameter “b” plays a significant role for the self-focusing of the laser beam as for b=2.12, strong self-focusing is seen. Further, it is observed that extraordinary mode is more prominent toward self-focusing rather than ordinary mode of propagation. For b=2.12, with the increase in the value of magnetic field self-focusing effect, in case of extraordinary mode, becomes very strong under plasma density ramp. Present study may be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, and x-ray lasers. Moreover, plasma density ramp plays a vital role to enhance the self-focusing effect
Isochoric heating and strong blast wave formation driven by fast electrons in solid-density targets
Santos, J. J.; Vauzour, B.; Touati, M.; Gremillet, L.; Feugeas, J.-L.; Ceccotti, T.; Bouillaud, R.; Deneuville, F.; Floquet, V.; Fourment, C.; Hadj-Bachir, M.; Hulin, S.; Morace, A.; Nicolaï, Ph; d'Oliveira, P.; Reau, F.; Samaké, A.; Tcherbakoff, O.; Tikhonchuk, V. T.; Veltcheva, M.; Batani, D.
2017-10-01
We experimentally investigate the fast (metallic foils and subsequent high-pressure hydrodynamics induced by energetic electrons driven by high-intensity, high-contrast laser pulses. The early-time temperature profile inside the target is measured from the streaked optical pyrometry of the target rear side. This is further characterized from benchmarked simulations of the laser-target interaction and the fast electron transport. Despite a modest laser energy (laser-based platform dedicated to high-energy-density physics studies.
Kelley M. Stewart; R. Terry Bowyer; Brian L. Dick; Bruce K. Johnson; John G. Kie
2005-01-01
Density dependence plays a key role in life-history characteristics and population ecology of large, herbivorous mammals. We designed a manipulative experiment to test hypotheses relating effects of density-dependent mechanisms on physical condition and fecundity of North American elk (Cervus elaphus) by creating populations at low and high density...
Time-dependent quantum fluid density functional theory of hydrogen ...
Indian Academy of Sciences (India)
WINTEC
GNLSE) of motion was earlier derived in our laboratory by combining density functional theory and quantum fluid dynamics in three- dimensional space. In continuation of the work reported previously, the GNLSE is applied to provide addi-.
Farzanehpour, Mehdi; Tokatly, Ilya; Nano-Bio Spectroscopy Group; ETSF Scientific Development Centre Team
2015-03-01
We present a rigorous formulation of the time-dependent density functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v-representable. Spanish Ministry of Economy and Competitiveness (Grant No. FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (Grant No. IT578-13), COST Actions CM1204 (XLIC) and MP1306 (EUSpec).
Schuster, Andrea C; Herde, Antje; Mazzoni, Camila J; Eccard, Jana A; Sommer, Simone
2016-07-01
Strong spatiotemporal variation in population size often leads to reduced genetic diversity limiting the adaptive potential of individual populations. Key genes of adaptive variation are encoded by the immune genes of the major histocompatibility complex (MHC) playing an essential role in parasite resistance. How MHC variation persists in rodent populations that regularly experience population bottlenecks remains an important topic in evolutionary genetics. We analysed the consequences of strong population fluctuations on MHC class II DRB exon 2 diversity in two distant common vole (Microtus arvalis) populations in three consecutive years using a high-throughput sequencing approach. In 143 individuals, we detected 25 nucleotide alleles translating into 14 unique amino acid MHC alleles belonging to at least three loci. Thus, the overall allelic diversity and amino acid distance among the remaining MHC alleles, used as a surrogate for the range of pathogenic antigens that can be presented to T-cells, are still remarkably high. Both study populations did not show significant population differentiation between years, but significant differences were found between sites. We concluded that selection processes seem to be strong enough to maintain moderate levels of MHC diversity in our study populations outcompeting genetic drift, as the same MHC alleles were conserved between years. Differences in allele frequencies between populations might be the outcome of different local parasite pressures and/or genetic drift. Further understanding of how pathogens vary across space and time will be crucial to further elucidate the mechanisms maintaining MHC diversity in cyclic populations.
Comparative studies of density-functional approximations for light atoms in strong magnetic fields
Zhu, Wuming; Zhang, Liang; Trickey, S. B.
2014-08-01
For a wide range of magnetic fields, 0≤B≤2000 a.u., we present a systematic comparative study of the performance of different types of density-functional approximations in light atoms (2≤Z≤6). Local, generalized-gradient approximation (GGA; semilocal), and meta-GGA ground-state exchange-correlation (xc) functionals are compared on an equal footing with exact-exchange, Hartree-Fock (HF), and current-density-functional-theory (CDFT) approximations. Comparison also is made with published quantum Monte Carlo data. Though all approximations give qualitatively reasonable results, the exchange energies from local and GGA functionals are too negative for large B. Results from the Perdew-Burke-Ernzerhof ground-state GGA and Tao-Perdew-Staroverov-Scuseria (TPSS) ground-state meta-GGA functionals are very close. Because of confinement, self-interaction error in such functionals is more severe at large B than at B =0, hence self-interaction correction is crucial. Exact exchange combined with the TPSS correlation functional results in a self-interaction-free (xc) functional, from which we obtain atomic energies of comparable accuracy to those from correlated wave-function methods. Specifically for the B and C atoms, we provide beyond-HF energies in a wide range of B fields. Fully self-consistent CDFT calculations were done with the Vignale-Rasolt-Geldart (VRG) functional in conjunction with the PW92 xc functional. Current effects turn out to be small, and the vorticity variable in the VRG functional diverges in some low-density regions. This part of the study suggests that nonlocal, self-interaction-free functionals may be better than local approximations as a starting point for CDFT functional construction and that some basic variable other than the vorticity could be helpful in making CDFT calculations practical.
DEFF Research Database (Denmark)
van Gemert, Rob; Andersen, Ken Haste
2018-01-01
Currently applied fisheries models and stock assessments rely on the assumption that density-dependent regulation only affects processes early in life, as described by stock–recruitment relationships. However, many fish stocks also experience density-dependent processes late in life......, such as density-dependent adult growth. Theoretical studies have found that, for stocks which experience strong late-in-life density dependence, maximum sustainable yield (MSY) is obtained with a small fishery size-at-entry that also targets juveniles. This goes against common fisheries advice, which dictates...... that primarily adults should be fished. This study aims to examine whether the strength of density-dependent growth in actual fish stocks is sufficiently strong to reduce optimal fishery size-at-entry to below size-at-maturity. A size-structured model is fitted to three stocks that have shown indications of late-in-life...
Gmel, Gerhard; Holmes, John; Studer, Joseph
2015-06-29
There have been reviews on the association between density of alcohol outlets and harm including studies published up to December 2008. Since then the number of publications has increased dramatically. The study reviews the more recent studies with regard to their utility to inform policy. A systematic review found more than 160 relevant studies (published between January 2009 and October 2014). The review focused on: (i) outlet density and assaultive or intimate partner violence; (ii) studies including individual level data; or (iii) 'natural experiments'. Despite overall evidence for an association between density and harm, there is little evidence on causal direction (i.e. whether demand leads to more supply or increased availability increases alcohol use and harm). When outlet types (e.g. bars, supermarkets) are analysed separately, studies are too methodologically diverse and partly contradictory to permit firm conclusions besides those pertaining to high outlet densities in areas such as entertainment districts. Outlet density commonly had little effect on individual-level alcohol use, and the few 'natural experiments' on restricting densities showed little or no effects. Although outlet densities are likely to be positively related to alcohol use and harm, few policy recommendations can be given as effects vary across study areas, outlet types and outlet cluster size. Future studies should examine in detail outlet types, compare different outcomes associated with different strengths of association with alcohol, analyse non-linear effects and compare different methodologies. Purely aggregate-level studies examining total outlet density only should be abandoned. [Gmel G, Holmes J, Studer J. Are alcohol outlet densities strongly associated with alcohol-related outcomes? A critical review of recent evidence. Drug Alcohol Rev 2015]. © 2015 Australasian Professional Society on Alcohol and other Drugs.
Gary D. Grossman; Gary Sundin; Robert E. Ratajczak
2016-01-01
SummaryWe used long-term population data for rosyside dace (Clinostomus funduloides), a numerically dominant member of a stochastically organised fish assemblage, to evaluate the relative importance of density-dependent and density-independent processes to population...
DEFF Research Database (Denmark)
Johnsen, Kristinn; Yngvason, Jakob
1996-01-01
We report on a numerical study of the density matrix functional introduced by Lieb, Solovej, and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes exactly the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge Z...... and the electron number N tend to infinity with N/Z fixed, and the magnetic field B tends to infinity in such a way that B/Z4/3→∞. We have calculated electronic density profiles and ground-state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained...... by other methods. For iron at B=1012 G the ground-state energy differs by less than 2% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge...
Ang, Zoey Zy; Rawashdeh, Mohammad A; Heard, Rob; Brennan, Patrick C; Lee, Warwick; Lewis, Sarah J
2017-08-01
To investigate how breast screen readers classify normal screening cases using descriptors of normal mammographic features and to assess test cases for suitability for a single reading strategy. Fifteen breast screen readers interpreted a test set of 29 normal screening cases and classified them by firstly rating their perceived difficulty to reach a 'normal' decision, secondly identifying the cases' salient normal mammographic features and thirdly assessing the cases' suitability for a single reading strategy. The relationship between the perceived difficulty in making 'normal' decisions and the normal mammographic features was investigated. Regular ductal pattern (T b = -0.439, P = 0.001), uniform density (T b = -0.527, P normal' decisions. Cases with regular ductal pattern (T b = 0.447, P = 0.002), uniform density (T b = 0.550, P normal and hence their suitability for single reading. © 2017 The Royal Australian and New Zealand College of Radiologists.
Ouyang, Fang; Hui, Cang; Ge, Saiying; Men, Xin-Yuan; Zhao, Zi-Hua; Shi, Pei-Jian; Zhang, Yong-Sheng; Li, Bai-Lian
2014-09-01
Understanding drivers of population fluctuation, especially for agricultural pests, is central to the provision of agro-ecosystem services. Here, we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and, thus, the stable equilibrium of the pest population, often to a higher level, posing considerable risks to the provision of agro-ecosystem services and regional food security. Efficient and timely measures of pest management in the era of Anthropocene should target the strengthening and revival of weakening density dependence caused by climate change and human activities.
Quark mass density- and temperature- dependent model for bulk strange quark matter
al, Yun Zhang et.
2002-01-01
It is shown that the quark mass density-dependent model can not be used to explain the process of the quark deconfinement phase transition because the quark confinement is permanent in this model. A quark mass density- and temperature-dependent model in which the quark confinement is impermanent has been suggested. We argue that the vacuum energy density B is a function of temperature. The dynamical and thermodynamical properties of bulk strange quark matter for quark mass density- and temper...
Effects of density dependence in a temperate forest in northeastern China
Yao, Jie; Zhang, Xinna; Zhang, Chunyu; Zhao, Xiuhai; von Gadow, Klaus
2016-09-01
Negative density dependence may cause reduced clustering among individuals of the same species, and evidence is accumulating that conspecific density-dependent self-thinning is an important mechanism regulating the spatial structure of plant populations. This study evaluates that specific density dependence in three very large observational studies representing three successional stages in a temperate forest in northeastern China. The methods include standard spatial point pattern analysis and a heterogeneous Poisson process as the null model to eliminate the effects of habitat heterogeneity. The results show that most of the species exhibit conspecific density-dependent self-thinning. In the early successional stage 11 of the 16 species, in the intermediate successional stage 18 of the 21 species and in the old growth stage all 21 species exhibited density dependence after removing the effects of habitat heterogeneity. The prevalence of density dependence thus varies among the three successional stages and exhibits an increase with increasing successional stage. The proportion of species showing density dependence varied depending on whether habitat heterogeneity was removed or not. Furthermore, the strength of density dependence is closely related with species abundance. Abundant species with high conspecific aggregation tend to exhibit greater density dependence than rare species.
Density dependent atomic motion in a liquid alkali metal
International Nuclear Information System (INIS)
Pilgrim, W.-C.; Hosokawa, S.; Morkel, C.
2001-01-01
Inelastic X-ray and neutron scattering results obtained from liquid sodium and rubidium are presented. They cover the entire liquid range between melting and liquid vapour critical point. At high densities the dynamics of the liquid metal is characterized by collective excitations. The corresponding dispersion relations indicate the existence of surprisingly stable next neighbouring shells leading to an increase of the propagation speed for the collective modes. Below 2ρ crit. the dynamics changes from collective to localized indicating the existence of molecular aggregates. This interpretation is in accord with a simple model where the properties of a Rb- and a Rb 2 - lattice are calculated using density functional theory. (orig.)
Zhang, Shuang; Yang, Jiong; Xu, Renjing; Wang, Fan; Li, Weifeng; Ghufran, Muhammad; Zhang, Yong-Wei; Yu, Zongfu; Zhang, Gang; Qin, Qinghua; Lu, Yuerui
2014-09-23
Phosphorene is a new family member of two-dimensional materials. We observed strong and highly layer-dependent photoluminescence in few-layer phosphorene (two to five layers). The results confirmed the theoretical prediction that few-layer phosphorene has a direct and layer-sensitive band gap. We also demonstrated that few-layer phosphorene is more sensitive to temperature modulation than graphene and MoS2 in Raman scattering. The anisotropic Raman response in few-layer phosphorene has enabled us to use an optical method to quickly determine the crystalline orientation without tunneling electron microscopy or scanning tunneling microscopy. Our results provide much needed experimental information about the band structures and exciton nature in few-layer phosphorene.
Fast gain recovery rates with strong wavelength dependence in a non-linear SOA.
Cleary, Ciaran S; Power, Mark J; Schneider, Simon; Webb, Roderick P; Manning, Robert J
2010-12-06
We report remarkably fast and strongly wavelength-dependent gain recovery in a single SOA without the aid of an offset filter. Full gain recovery times as short as 9 ps were observed in pump-probe measurements when pumping to the blue wavelength side of a continuous wave probe, in contrast to times of 25 to 30 ps when pumping to the red wavelength side. Experimental and numerical analysis indicate that the long effective length and high gain led to deep saturation of the second half of the SOA by the probe. The consequent absorption of blue-shifted pump pulses in this region resulted in device dynamics analogous to those of the Turbo-Switch.
Strongly enhanced temperature dependence of the chemical potential in FeSe
Rhodes, L. C.; Watson, M. D.; Haghighirad, A. A.; Eschrig, M.; Kim, T. K.
2017-05-01
Employing a 10-orbital tight-binding model, we present a set of hopping parameters fitted directly to our latest high-resolution angle-resolved photoemission spectroscopy (ARPES) data for the high-temperature tetragonal phase of FeSe. Using these parameters, we predict a large 10 meV shift of the chemical potential as a function of temperature. To confirm this large temperature dependence, we performed ARPES experiments on FeSe and observed a ˜25 meV rigid shift to the chemical potential between 100 and 300 K. This strong shift has important implications for theoretical models of superconductivity and of nematic order in FeSe materials.
Lee-Yang-inspired functional with a density-dependent neutron-neutron scattering length
Grasso, M.; Lacroix, D.; Yang, C. J.
2017-05-01
Inspired by the low-density Lee-Yang expansion for the energy of a dilute Fermi gas of density ρ and momentum kF, we introduce here a Skyrme-type functional that contains only s -wave terms and provides, at the mean-field level, (i) a satisfactory equation of state for neutron matter from extremely low densities up to densities close to the equilibrium point, and (ii) a good-quality equation of state for symmetric matter at density scales around the saturation point. This is achieved by using a density-dependent neutron-neutron scattering length a (ρ ) which satisfies the low-density limit (for Fermi momenta going to zero) and has a density dependence tuned in such a way that the low-density constraint |a (ρ ) kF|≤1 is satisfied at all density scales.
Density dependence of relaxation dynamics in glass formers, and ...
Indian Academy of Sciences (India)
Anshul D S Parmar
Within the framework of the Adam-Gibbs relation, by employing density temperature scaling for the analysis, we find that softer particles make more fragile glasses, as deduced from dynamical quantities, which is found to be consistent with the Adam-Gibbs fragility. Keywords. Glass; fragility; supercooled liquids etc. 1.
Time-dependent quantum fluid density functional theory of hydrogen ...
Indian Academy of Sciences (India)
WINTEC
derived in our laboratory by combining density functional theory and quantum fluid dynamics in three- dimensional space. In continuation of the .... repulsion, electron-nuclear Coulomb attraction, ex- change and correlation interactions, ..... Eberly J H, Grobe R, Law C K and Su Q 1992 Adv. At. Mol. Opt. Phys. Suppl. 1 301. 8.
Bulk viscosity of strange quark matter in density dependent quark ...
Indian Academy of Sciences (India)
Results and discussion. In Ь3 we have derived analytic expression for the bulk viscosity of quark matter in the linear case: Ж М. 1 (eq. (27) for non-leptonic process and the corresponding equation with replaced by ' for the leptonic process.) For a given baryon density and temperature, the chemical potentials are evaluated ...
Observations of height-dependent pressure-perturbation structure of a strong mesoscale gravity wave
Starr, David O'C.; Korb, C. L.; Schwemmer, Geary K.; Weng, Chi Y.
1992-01-01
Airborne observations using a downward-looking, dual-frequency, near-infrared, differential absorption lidar system provide the first measurements of the height-dependent pressure-perturbation field associated with a strong mesoscale gravity wave. A pressure-perturbation amplitude of 3.5 mb was measured within the lowest 1.6 km of the atmosphere over a 52-km flight line. Corresponding vertical displacements of 250-500 m were inferred from lidar-observed displacement of aerosol layers. Accounting for probable wave orientation, a horizontal wavelength of about 40 km was estimated. Satellite observations reveal wave structure of a comparable scale in concurrent cirrus cloud fields over an extended area. Smaller-scale waves were also observed. Local meteorological soundings are analyzed to confirm the existence of a suitable wave duct. Potential wave-generation mechanisms are examined and discussed. The large pressure-perturbation wave is attributed to rapid amplification or possible wave breaking of a gravity wave as it propagated offshore and interacted with a very stable marine boundary layer capped by a strong shear layer.
DEFF Research Database (Denmark)
Refslund, Bjarke
2018-01-01
Based on case studies in a fish processing plant and a demolition company, this article shows how strong and institutionally embedded unions interact with migrant workers in a precarious labour market position in order to safeguard their working conditions and organise them. It shows how strong...... unions are in a good position to include migrant workers and thereby resist labour market segmentation. The strong Danish unions, faced with the serious challenges of intra-European labour migration, have increased their attention and resources devoted to organising migrant workers and including them...... in the IR-model. The dynamic relation between migrant workers and national unions in this high-density setting is discussed emphasising the need for building a trustful relation between the migrant workers and the unions in order to empower the migrants to better navigate in the national labour market...
International Nuclear Information System (INIS)
Sivasankaran, S.; Hoa, C.J.
2008-01-01
Natural convection of water near its density maximum in the presence of magnetic field in a cavity with temperature dependent properties is studied numerically. The viscosity and thermal conductivity of the water is varied with reference temperature and calculated by cubic polynomial. The finite volume method is used to solve the governing equations. The results are presented graphically in the form of streamlines, isotherms and velocity vectors and are discussed for various combinations of reference temperature parameter, Rayleigh number, density inversion parameter and Hartmann number. It is observed that flow and temperature field are affected significantly by changing the reference temperature parameter for temperature dependent thermal conductivity and both temperature dependent viscosity and thermal conductivity cases. There is no significant effect on fluid flow and temperature distributions for temperature dependent viscosity case when changing the values of reference temperature parameter. The average heat transfer rate considering temperature-dependent viscosity are higher than considering temperature-dependent thermal conductivity and both temperature-dependent viscosity and thermal conductivity. The average Nusselt number decreases with an increase of Hartmann number. It is observed that the density inversion of water leaves strong effects on fluid flow and heat transfer due to the formation of bi-cellular structure. The heat transfer rate behaves non-linearly with density inversion parameter. The direction of external magnetic field also affect the fluid flow and heat transfer. (authors)
Yeakel, Justin D; Gibert, Jean P; Gross, Thilo; Westley, Peter A H; Moore, Jonathan W
2018-05-19
The spatial dispersal of individuals plays an important role in the dynamics of populations, and is central to metapopulation theory. Dispersal provides connections within metapopulations, promoting demographic and evolutionary rescue, but may also introduce maladapted individuals, potentially lowering the fitness of recipient populations through introgression of heritable traits. To explore this dual nature of dispersal, we modify a well-established eco-evolutionary model of two locally adapted populations and their associated mean trait values, to examine recruiting salmon populations that are connected by density-dependent dispersal, consistent with collective migratory behaviour that promotes navigation. When the strength of collective behaviour is weak such that straying is effectively constant, we show that a low level of straying is associated with the highest gains in metapopulation robustness and that high straying serves to erode robustness. Moreover, we find that as the strength of collective behaviour increases, metapopulation robustness is enhanced, but this relationship depends on the rate at which individuals stray. Specifically, strong collective behaviour increases the presence of hidden low-density basins of attraction, which may serve to trap disturbed populations, and this is exacerbated by increased habitat heterogeneity. Taken as a whole, our findings suggest that density-dependent straying and collective migratory behaviour may help metapopulations, such as in salmon, thrive in dynamic landscapes. Given the pervasive eco-evolutionary impacts of dispersal on metapopulations, these findings have important ramifications for the conservation of salmon metapopulations facing both natural and anthropogenic contemporary disturbances.This article is part of the theme issue 'Collective movement ecology'. © 2018 The Authors.
White, J Wilson; Samhouri, Jameal F; Stier, Adrian C; Wormald, Clare L; Hamilton, Scott L; Sandin, Stuart A
2010-07-01
Coral and rocky reef fish populations are widely used as model systems for the experimental exploration of density-dependent vital rates, but patterns of density-dependent mortality in these systems are not yet fully understood. In particular, the paradigm for strong, directly density-dependent (DDD) postsettlement mortality stands in contrast to recent evidence for inversely density-dependent (IDD) mortality. We review the processes responsible for DDD and IDD per capita mortality in reef fishes, noting that the pattern observed depends on predator and prey behavior, the spatial configuration of the reef habitat, and the spatial and temporal scales of observation. Specifically, predators tend to produce DDD prey mortality at their characteristic spatial scale of foraging, but prey mortality is IDD at smaller spatial scales due to attack-abatement effects (e.g., risk dilution). As a result, DDD mortality may be more common than IDD mortality on patch reefs, which tend to constrain predator foraging to the same scale as prey aggregation, eliminating attack-abatement effects. Additionally, adjacent groups of prey on continuous reefs may share a subset of refuges, increasing per capita refuge availability and relaxing DDD mortality relative to prey on patch reefs, where the patch edge could prevent such refuge sharing. These hypotheses lead to a synthetic framework to predict expected mortality patterns for a variety of scenarios. For nonsocial, nonaggregating species and species that aggregate in order to take advantage of spatially clumped refuges, IDD mortality is possible but likely superseded by DDD refuge competition, especially on patch reefs. By contrast, for species that aggregate socially, mortality should be IDD at the scale of individual aggregations but DDD at larger scales. The results of nearly all prior reef fish studies fit within this framework, although additional work is needed to test many of the predicted outcomes. This synthesis reconciles some
Time-dependent density functional theory for multi-component systems
International Nuclear Information System (INIS)
Tiecheng Li; Peiqing Tong
1985-10-01
The Runge-Gross version of Hohenberg-Kohn-Sham's density functional theory is generalized to multi-component systems, both for arbitrary time-dependent pure states and for arbitrary time-dependent ensembles. (author)
Study of excitation energy dependence of nuclear level density parameter
International Nuclear Information System (INIS)
Mohanto, G.; Nayak, B.K.; Saxena, A.
2016-01-01
In the present study, we have populated CN by fusion reaction and excitation energy of the intermediate nuclei is determined after first chance α-emission to investigate excitation energy dependence of the NLD parameter. Evaporated neutron spectra were measured following alpha evaporation for obtaining NLD parameter for the reaction 11 B + 197 Au, populating CN 208 Po. This CN after evaporating an α-particle populates intermediate nucleus 204 Pb. The 204 Pb has magic number of Z=82. Our aim is to study the excitation energy dependence of NLD parameter for closed shell nuclei
Leicht-Young, S. A.; Latimer, A.M.; Silander, J.A.
2011-01-01
The neighborhood density of plants strongly affects their growth, reproduction, and survival. In most cases, high density increases competition and negatively affects a focal plant in predictable ways, leading to the self-thinning law. There are, however, situations in which high densities of plants facilitate focal plant performance, resulting in positive density dependence. Despite their importance in forest gap dynamics and distinctive growth form, there have been very few studies of the effect of density on lianas or vines. We grew an invasive (Celastrus orbiculatus) and a native (Celastrus scandens) liana species together in three different density treatments, while also manipulating the light and support availability. We found that across treatment conditions, C. orbiculatus always out-performed C. scandens, showing greater relative growth rate in height and diameter, greater biomass and higher survival. Both species responded similarly to the density treatments: with plants in high density not showing a decrease in relative height growth rate compared to medium density. Aboveground biomass for C. scandens was not affected by density, while for C. orbiculatus, the most massive plants were growing in medium density without support. More surprisingly, survival analysis indicated that the two species both had significantly lower mortality rates in the highest density treatment; this trend held true across the other treatments of light and supports. More generally, this study demonstrates that these lianas can escape the consequences of high density and thus the self-thinning law that affects self-supporting plants. This suggests a broader hypothesis about lianas in general: their greater flexibility in allocating growth resources allows them to grow taller and thinner without collapsing and thereby potentially escape shading and mortality even at high densities.
Lehtovaara, Lauri; Havu, Ville; Puska, Martti
2009-01-01
We present for static density functional theory and time-dependent density functional theory calculations an all-electron method which employs high-order hierarchical finite-element bases. Our mesh generation scheme, in which structured atomic meshes are merged to an unstructured molecular mesh, allows a highly nonuniform discretization of the space. Thus it is possible to represent the core and valence states using the same discretization scheme, i.e., no pseudopotentials or similar treatmen...
Tokatly, I. V.
2011-11-01
It is shown that the density-potential mapping and the V-representability problems in the time-dependent current density functional theory (TDCDFT) are reduced to the solution of a certain many-body nonlinear Schrödinger equation (NLSE). The derived NLSE for TDCDFT links the earlier NLSE-based formulations of the time-dependent deformation functional theory (TDDefFT) and the time-dependent density functional theory (TDDFT). We establish a close relation between the nonlinear many-body problems which control the existence of TDCDFT, TDDFT, and TDDefFT, and thus develop a unified point of view on the whole family of the TDDFT-type theories.
International Nuclear Information System (INIS)
Chen, Z; Kametani, F; Larbalestier, D C; Chen, Y; Xie, Y; Selvamanickam, V
2009-01-01
We have made extensive low temperature and high field evaluations of a recent 2.1 μm thick coated conductor (CC) grown by metal-organic chemical vapor deposition (MOCVD) with a view to its use for high field magnet applications, for which its very strong Hastelloy substrate makes it very suitable. This conductor contains dense three-dimensional (Y,Sm) 2 O 3 nanoprecipitates, which are self-aligned in planes tilted ∼7 deg. from the tape plane. Very strong vortex pinning is evidenced by high critical current density J c values of ∼3.1 MA cm -2 at 77 K and ∼43 MA cm -2 at 4.2 K, and by a strongly enhanced irreversibility field H irr , which reaches that of Nb 3 Sn (∼28 T at 1.5 K) at 60 K, even in the inferior direction of H parallel c axis. At 4.2 K, J c values are ∼15% of the depairing current density J d , much the highest of any superconductor suitable for magnet construction.
Energy Technology Data Exchange (ETDEWEB)
Chen, Z; Kametani, F; Larbalestier, D C [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States); Chen, Y; Xie, Y; Selvamanickam, V [SuperPower Incorporated, Schenectady, NY 12304 (United States)], E-mail: zhijun@asc.magnet.fsu.edu
2009-05-15
We have made extensive low temperature and high field evaluations of a recent 2.1 {mu}m thick coated conductor (CC) grown by metal-organic chemical vapor deposition (MOCVD) with a view to its use for high field magnet applications, for which its very strong Hastelloy substrate makes it very suitable. This conductor contains dense three-dimensional (Y,Sm){sub 2}O{sub 3} nanoprecipitates, which are self-aligned in planes tilted {approx}7 deg. from the tape plane. Very strong vortex pinning is evidenced by high critical current density J{sub c} values of {approx}3.1 MA cm{sup -2} at 77 K and {approx}43 MA cm{sup -2} at 4.2 K, and by a strongly enhanced irreversibility field H{sub irr}, which reaches that of Nb{sub 3}Sn ({approx}28 T at 1.5 K) at 60 K, even in the inferior direction of H parallel c axis. At 4.2 K, J{sub c} values are {approx}15% of the depairing current density J{sub d}, much the highest of any superconductor suitable for magnet construction.
Vuckovic, Stefan; Levy, Mel; Gori-Giorgi, Paola
2017-12-01
The augmented potential introduced by Levy and Zahariev [Phys. Rev. Lett. 113, 113002 (2014)] is shifted with respect to the standard exchange-correlation potential of the Kohn-Sham density functional theory by a density-dependent constant that makes the total energy become equal to the sum of the occupied orbital energies. In this work, we analyze several features of this approach, focusing on the limit of infinite coupling strength and studying the shift and the corresponding energy density at different correlation regimes. We present and discuss coordinate scaling properties of the augmented potential, study its connection to the response potential, and use the shift to analyze the classical jellium and uniform gas models. We also study other definitions of the energy densities in relation to the functional construction by local interpolations along the adiabatic connection. Our findings indicate that the energy density that is defined in terms of the electrostatic potential of the exchange-correlation hole is particularly well suited for this purpose.
Vuckovic, Stefan; Levy, Mel; Gori-Giorgi, Paola
2017-12-07
The augmented potential introduced by Levy and Zahariev [Phys. Rev. Lett. 113, 113002 (2014)] is shifted with respect to the standard exchange-correlation potential of the Kohn-Sham density functional theory by a density-dependent constant that makes the total energy become equal to the sum of the occupied orbital energies. In this work, we analyze several features of this approach, focusing on the limit of infinite coupling strength and studying the shift and the corresponding energy density at different correlation regimes. We present and discuss coordinate scaling properties of the augmented potential, study its connection to the response potential, and use the shift to analyze the classical jellium and uniform gas models. We also study other definitions of the energy densities in relation to the functional construction by local interpolations along the adiabatic connection. Our findings indicate that the energy density that is defined in terms of the electrostatic potential of the exchange-correlation hole is particularly well suited for this purpose.
Inelastic collisions and density-dependent excitation suppression in a 87Sr optical lattice clock
Bishof, M.; Martin, M. J.; Swallows, M. D.; Benko, C.; Lin, Y.; Quéméner, G.; Rey, A. M.; Ye, J.
2011-11-01
We observe two-body loss of 3P0 87Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 μK that are prepared either in a single nuclear-spin sublevel or with equal populations in two sublevels. The measured temperature and nuclear-spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the 1S0-3P0 transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system.
Energy Technology Data Exchange (ETDEWEB)
Bishof, M.; Martin, M. J.; Swallows, M. D.; Benko, C.; Lin, Y.; Quemener, G.; Rey, A. M.; Ye, J. [JILA, NIST and University of Colorado, Boulder, Colorado 80309-0440 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309-0390 (United States)
2011-11-15
We observe two-body loss of {sup 3} P{sub 0} {sup 87}Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 {mu}K that are prepared either in a single nuclear-spin sublevel or with equal populations in two sublevels. The measured temperature and nuclear-spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the {sup 1} S{sub 0}-{sup 3} P{sub 0} transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system.
Directory of Open Access Journals (Sweden)
Greta S Aeby
Full Text Available Growth anomalies (GAs are common, tumor-like diseases that can cause significant morbidity and decreased fecundity in the major Indo-Pacific reef-building coral genera, Acropora and Porites. GAs are unusually tractable for testing hypotheses about drivers of coral disease because of their pan-Pacific distributions, relatively high occurrence, and unambiguous ease of identification. We modeled multiple disease-environment associations that may underlie the prevalence of Acropora growth anomalies (AGA (n = 304 surveys and Porites growth anomalies (PGA (n = 602 surveys from across the Indo-Pacific. Nine predictor variables were modeled, including coral host abundance, human population size, and sea surface temperature and ultra-violet radiation anomalies. Prevalence of both AGAs and PGAs were strongly host density-dependent. PGAs additionally showed strong positive associations with human population size. Although this association has been widely posited, this is one of the first broad-scale studies unambiguously linking a coral disease with human population size. These results emphasize that individual coral diseases can show relatively distinct patterns of association with environmental predictors, even in similar diseases (growth anomalies found on different host genera (Acropora vs. Porites. As human densities and environmental degradation increase globally, the prevalence of coral diseases like PGAs could increase accordingly, halted only perhaps by declines in host density below thresholds required for disease establishment.
Aeby, Greta S; Williams, Gareth J; Franklin, Erik C; Haapkyla, Jessica; Harvell, C Drew; Neale, Stephen; Page, Cathie A; Raymundo, Laurie; Vargas-Ángel, Bernardo; Willis, Bette L; Work, Thierry M; Davy, Simon K
2011-02-18
Growth anomalies (GAs) are common, tumor-like diseases that can cause significant morbidity and decreased fecundity in the major Indo-Pacific reef-building coral genera, Acropora and Porites. GAs are unusually tractable for testing hypotheses about drivers of coral disease because of their pan-Pacific distributions, relatively high occurrence, and unambiguous ease of identification. We modeled multiple disease-environment associations that may underlie the prevalence of Acropora growth anomalies (AGA) (n = 304 surveys) and Porites growth anomalies (PGA) (n = 602 surveys) from across the Indo-Pacific. Nine predictor variables were modeled, including coral host abundance, human population size, and sea surface temperature and ultra-violet radiation anomalies. Prevalence of both AGAs and PGAs were strongly host density-dependent. PGAs additionally showed strong positive associations with human population size. Although this association has been widely posited, this is one of the first broad-scale studies unambiguously linking a coral disease with human population size. These results emphasize that individual coral diseases can show relatively distinct patterns of association with environmental predictors, even in similar diseases (growth anomalies) found on different host genera (Acropora vs. Porites). As human densities and environmental degradation increase globally, the prevalence of coral diseases like PGAs could increase accordingly, halted only perhaps by declines in host density below thresholds required for disease establishment.
Gor'kov, Lev P.
2012-04-01
We consider a single band of conduction electrons interacting with displacements of the transitional ions. In the classical regime strong enough coupling transforms the harmonic elastic energy for an ion to the one of the well with two deep minima, so that the system is described in terms of Ising spins. Intersite interactions order spins at lower temperatures. Extension to the quantum regime is discussed. Below the charge density wave (CDW) transition the energy spectrum of electrons remains metallic because the structural vector Q and the Fermi surface sizes are not related. Large values of the CDW gap seen in the tunneling experiments correspond to the energy of the minima in the electron-ion two-well complex. The gap is defined through the density of states inside the electronic bands below the CDW transition. We focus mainly on electronic properties of transition-metal dichalcogenides.
Farzanehpour, M.; Tokatly, I. V.
2014-11-01
We present a rigorous formulation of the time-dependent density-functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v representable.
Ghosh, Soumen; Cramer, Christopher J; Truhlar, Donald G; Gagliardi, Laura
2017-04-01
Predicting ground- and excited-state properties of open-shell organic molecules by electronic structure theory can be challenging because an accurate treatment has to correctly describe both static and dynamic electron correlation. Strongly correlated systems, i.e. , systems with near-degeneracy correlation effects, are particularly troublesome. Multiconfigurational wave function methods based on an active space are adequate in principle, but it is impractical to capture most of the dynamic correlation in these methods for systems characterized by many active electrons. We recently developed a new method called multiconfiguration pair-density functional theory (MC-PDFT), that combines the advantages of wave function theory and density functional theory to provide a more practical treatment of strongly correlated systems. Here we present calculations of the singlet-triplet gaps in oligoacenes ranging from naphthalene to dodecacene. Calculations were performed for unprecedently large orbitally optimized active spaces of 50 electrons in 50 orbitals, and we test a range of active spaces and active space partitions, including four kinds of frontier orbital partitions. We show that MC-PDFT can predict the singlet-triplet splittings for oligoacenes consistent with the best available and much more expensive methods, and indeed MC-PDFT may constitute the benchmark against which those other models should be compared, given the absence of experimental data.
Li, Jinhua; Ge, Kunpeng; Pan, Yongxin; Williams, Wyn; Liu, Qingsong; Qin, Huafeng
2013-10-01
Single-domain magnetite particles produced by magnetotactic bacteria (magnetosomes) and aligned in chains are of great interest in the biosciences and geosciences. Here, we investigated angular variation of magnetic properties of aligned Magnetospirillum magneticum AMB-1 cells, each of which contains one single fragmental chain of magnetosomes. With measurements at increasing angles from the chain direction, we observed that (i) the hysteresis loop gradually changes from nearly rectangular to a ramp-like shape (e.g., Bc and remanence decrease), (ii) the acquisition and demagnetization curves of IRM shift toward higher fields (e.g., Bcr increases), and (iii) the FORC diagram shifts toward higher coercivity fields (e.g., Bc,FORC increases). For low-temperature results, compared to unoriented samples, the samples containing aligned chains have a much lower remanence loss of field-cooled (δFC) and zero-field-cooled (δZFC) remanence upon warming through the Verwey transition, higher δ-ratio (δ = δFC/δZFC) for the measurement parallel to the chain direction, and lower δ-ratio, larger δFC and δZFC values for the perpendicular measurement. Micromagnetic simulations confirm the experimental observations and reveal that the magnetization reversal of magnetosome chain appears to be noncoherent at low angles and coherent at high angles. The simulations also demonstrate that the angular dependence of magnetic properties is related to the dispersion degree of individual chains, indicating that effects of anisotropy need to be accounted for when using rock magnetism to identify magnetosomes or magnetofossils once they have been preserved in aligned chains. Additionally, this study experimentally demonstrates an empirical correspondence of the parameter Bc,FORC to Bcr rather than Bc, at least for magnetite chains with strong shape anisotropy. This suggests FORC analysis is a good discriminant of magnetofossils in sediments and rocks.
Suppressing an anti-inflammatory cytokine reveals a strong age-dependent survival cost in mice.
Directory of Open Access Journals (Sweden)
Virginia Belloni
Full Text Available BACKGROUND: The central paradigm of ecological immunology postulates that selection acts on immunity as to minimize its cost/benefit ratio. Costs of immunity may arise because the energetic requirements of the immune response divert resources that are no longer available for other vital functions. In addition to these resource-based costs, mis-directed or over-reacting immune responses can be particularly harmful for the host. In spite of the potential importance of immunopathology, most studies dealing with the evolution of the immune response have neglected such non resource-based costs. To keep the immune response under control, hosts have evolved regulatory pathways that should be considered when studying the target of the selection pressures acting on immunity. Indeed, variation in regulation may strongly modulate the negative outcome of immune activation, with potentially important fitness consequences. METHODOLOGY/PRINCIPAL FINDINGS: Here, we experimentally assessed the survival costs of reduced immune regulation by inhibiting an anti-inflammatory cytokine (IL-10 with anti-IL-10 receptor antibodies (anti-IL-10R in mice that were either exposed to a mild inflammation or kept as control. The experiment was performed on young (3 months and old (15 months individuals, as to further assess the age-dependent cost of suppressing immune regulation. IL-10 inhibition induced high mortality in old mice exposed to the mild inflammatory insult, whereas no mortality was observed in young mice. However, young mice experienced a transitory lost in body mass when injected with the anti-IL-10R antibodies, showing that the treatment was to a lesser extent also costly for young individuals. CONCLUSIONS: These results suggest a major role of immune regulation that deserves attention when investigating the evolution of immunity, and indicate that the capacity to down-regulate the inflammatory response is crucial for late survival and longevity.
International Nuclear Information System (INIS)
Helbig, N.; Fuks, J.I.; Tokatly, I.V.; Appel, H.; Gross, E.K.U.; Rubio, A.
2011-01-01
Graphical abstract: We solve a 1D N-electron system, with N small, by mapping it onto an N-dimensional one-electron problem. We compare the exact solutions to the results from adiabatic density and density matrix functionals for different physical situations. Highlights: ► Static and dynamical correlations. ► Memory dependence of exchange-correlation functionals in TDDFT. ► Linear and non-linear response. ► Laser-induced population control. - Abstract: To address the impact of electron correlations in the linear and non-linear response regimes of interacting many-electron systems exposed to time-dependent external fields, we study one-dimensional (1D) systems where the interacting problem is solved exactly by exploiting the mapping of the 1D N-electron problem onto an N-dimensional single electron problem. We analyze the performance of the recently derived 1D local density approximation as well as the exact-exchange orbital functional for those systems. We show that the interaction with an external resonant laser field shows Rabi oscillations which are detuned due to the lack of memory in adiabatic approximations. To investigate situations where static correlations play a role, we consider the time-evolution of the natural occupation numbers associated to the reduced one-body density matrix. Those studies shed light on the non-locality and time-dependence of the exchange and correlation functionals in time-dependent density and density-matrix functional theories.
International Nuclear Information System (INIS)
Senda Ikuo.
1991-05-01
We propose dynamical models of hadrons, the nucleation model and the free-decay model, in which results of string model are used to represent interactions. The dynamical properties of hadrons, which are obtained by string model, are examined and their parameters are fitted by experimental data. The equilibrium properties of hadrons at high density are investigated by the nucleation model and we found a singular behaviour at energy density 3 ∼ 5 GeV/fm 3 , where hadrons coalesce to create highly excited states. We argue that this singular behaviour corresponds to the phase transition to quark-gluon plasma. The possibility to observe the production of high density strongly interacting matter at collider experiments are discussed using the free-decay model, which produces pion distributions as decay products of resonances. We show that our free-decay model recovers features of hadron distributions obtained in hadron collision experiments. Finally the perspectives and extensions are discussed. (author). 34 refs, 19 figs, 2 tabs
Dependency of irradiation damage density on tritium migration behaviors in Li2TiO3
International Nuclear Information System (INIS)
Kobayashi, Makoto; Toda, Kensuke; Oya, Yasuhisa; Okuno, Kenji
2014-01-01
Tritium migration behaviors in Li 2 TiO 3 with the increase of irradiation damage density were investigated by means of electron spin resonance and thermal desorption spectroscopy. The irradiation damages of F + -centers and O − -centers were formed by neutron irradiation, and their damage densities were increased with increasing neutron fluence. Tritium release temperature was clearly shifted toward higher temperature side with increasing neutron fluence, i.e. increasing damage density. The rate determining process for tritium release was also clearly changed depending on the damage density. Tritium release was mainly controlled by tritium diffusion process in crystalline grain of Li 2 TiO 3 at lower neutron fluence. The apparent tritium diffusivity was reduced as the damage density in Li 2 TiO 3 increased due to the introduction of tritium trapping/detrapping sites for diffusing tritium. Then, tritium trapping/detrapping processes began to control the overall tritium release with further damage introductions as the amount of tritium trapping sites increased enough to trap most of tritium in Li 2 TiO 3 . The effects of water vapor in purge gas on tritium release behaviors were also investigated. It was considered that hydrogen isotopes in purge gas would be dissociated and adsorbed on the surface of Li 2 TiO 3 . Then, hydrogen isotopes diffused inward Li 2 TiO 3 would occupy the tritium trapping sites before diffusing tritium reaches to these sites, promoting apparent tritium diffusion consequently. Kinetics analysis of tritium release for highly damaged Li 2 TiO 3 showed that the rate determining process of tritium release was the detrapping process of tritium formed as hydroxyl groups. The rate of tritium detrapping as hydroxyl groups was determined by the kinetic analysis, and was comparable to tritium release kinetics for Li 2 O, LiOH and Li 4 TiO 4 . The dangling oxygen atoms (O − -centers) formed by neutron irradiation would contribute strongly on the
Robinson, Orin J.; McGowan, Conor P.; Devers, Patrick K.
2017-01-01
Density dependence regulates populations of many species across all taxonomic groups. Understanding density dependence is vital for predicting the effects of climate, habitat loss and/or management actions on wild populations. Migratory species likely experience seasonal changes in the relative influence of density dependence on population processes such as survival and recruitment throughout the annual cycle. These effects must be accounted for when characterizing migratory populations via population models.To evaluate effects of density on seasonal survival and recruitment of a migratory species, we used an existing full annual cycle model framework for American black ducks Anas rubripes, and tested different density effects (including no effects) on survival and recruitment. We then used a Bayesian model weight updating routine to determine which population model best fit observed breeding population survey data between 1990 and 2014.The models that best fit the survey data suggested that survival and recruitment were affected by density dependence and that density effects were stronger on adult survival during the breeding season than during the non-breeding season.Analysis also suggests that regulation of survival and recruitment by density varied over time. Our results showed that different characterizations of density regulations changed every 8–12 years (three times in the 25-year period) for our population.Synthesis and applications. Using a full annual cycle, modelling framework and model weighting routine will be helpful in evaluating density dependence for migratory species in both the short and long term. We used this method to disentangle the seasonal effects of density on the continental American black duck population which will allow managers to better evaluate the effects of habitat loss and potential habitat management actions throughout the annual cycle. The method here may allow researchers to hone in on the proper form and/or strength of
Switching from negative to positive density-dependence among populations of a cobble beach plant.
Goldenheim, William M; Irving, Andrew D; Bertness, Mark D
2008-12-01
Interactions among species occur across a continuum from negative to positive and can have a critical role in shaping population and community dynamics. Growing evidence suggests that inter- and intra-specific interactions can vary in strength or even switch direction (i.e., negative to positive) depending on environmental conditions, consumer pressure, and also among life-history stages. We tested the hypothesis that seedlings and adults of the intertidal annual forb Suaeda linearis growing on New England shores exhibit positive density-dependence under physically stressful conditions high on the shore (i.e., greater temperatures, evaporative stress), but negative density-dependence under physically milder conditions low on the shore. Among experimental treatments of plant density (dense versus sparse) at each shore height, plant biomass, length, and number of leaves/branches were greater in dense stands high on the shore (positive density-dependence), but greater in sparse stands low on the shore (negative density-dependence). Such responses were consistent among life-history stages and generally consistent between sites. As a more direct measure of fitness, per capita seed production was also positively density-dependent high on the shore, but negatively density-dependent low on the shore. These results support the current theory predicting an increase in the frequency of positive interactions with increasing environmental stress and further emphasize the previously understated role of positive interactions in shaping and maintaining populations and communities.
Estimation of density-dependent mortality of juvenile bivalves in the Wadden Sea.
Directory of Open Access Journals (Sweden)
Henrike Andresen
Full Text Available We investigated density-dependent mortality within the early months of life of the bivalves Macoma balthica (Baltic tellin and Cerastoderma edule (common cockle in the Wadden Sea. Mortality is thought to be density-dependent in juvenile bivalves, because there is no proportional relationship between the size of the reproductive adult stocks and the numbers of recruits for both species. It is not known however, when exactly density dependence in the pre-recruitment phase occurs and how prevalent it is. The magnitude of recruitment determines year class strength in bivalves. Thus, understanding pre-recruit mortality will improve the understanding of population dynamics. We analyzed count data from three years of temporal sampling during the first months after bivalve settlement at ten transects in the Sylt-Rømø-Bay in the northern German Wadden Sea. Analyses of density dependence are sensitive to bias through measurement error. Measurement error was estimated by bootstrapping, and residual deviances were adjusted by adding process error. With simulations the effect of these two types of error on the estimate of the density-dependent mortality coefficient was investigated. In three out of eight time intervals density dependence was detected for M. balthica, and in zero out of six time intervals for C. edule. Biological or environmental stochastic processes dominated over density dependence at the investigated scale.
Nath, G.; Vishwakarma, J. P.
2016-06-01
The propagation of a strong spherical shock wave in a dusty gas with or without self-gravitational effects is investigated in the case of isothermal and adiabatic flows. The dusty gas is assumed to be a mixture of small solid particles and perfect gas. The equilibrium flow conditions are assumed to be maintained, and the density of the mixture is assumed to be varying and obeying an exponential law. Non-similarity solutions are obtained and the effects of variations of the mass concentration of solid particles in the mixture and the ratio of the density of solid particles to the initial density of the gas, and the presence of self-gravitational field on the flow variables are investigated at given times. Our analysis reveals that after inclusion of gravitational field effects surprisingly the shock strength increases and remarkable differences are found in the distribution of flow variables. An increase in time also, increases the shock strength. Further, it is investigated that the consideration of isothermal flow increases the shock strength, and removes the singularity in the density distribution. Also, the presence of gravitational field increases the compressibility of the medium, due to which it is compressed and therefore the distance between the inner contact surface and the shock surface is reduced. The shock waves in self-gravitating dusty gas can be important for description of shocks in supernova explosions, in the study of central part of star burst galaxies, star formation and shocks in stellar explosion, nuclear explosion, in industry, rupture of a pressurized vessel and explosion in the ionosphere. Other potential applications of this study include analysis of data from exploding wire experiments and cylindrically symmetric hypersonic flow problems associated with meteors or re-entry of vehicles etc. A comparison is made between the solutions in the cases of the gravitating and the non-gravitating media. The obtained solutions are applicable for
Probing the density dependence of the symmetry energy by nucleon flow
Fan, Xiao-Hua; Yong, Gao-Chan; Zuo, Wei
2018-03-01
In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, sensitive regions of some nucleon observables to the nuclear symmetry energy are studied. It is found that the symmetry-energy-sensitive observable n /p ratio in the 132Sn+124Sn reaction at 0.3 GeV/nucleon in fact just probes the density-dependent symmetry energy below the density of 1.5 ρ0 and effectively probes the density-dependent symmetry energy around or somewhat below the saturation density. Nucleon elliptic flow can probe the symmetry energy from the low-density region to the high-density region when changing the incident beam energies from 0.3 to 0.6 GeV/nucleon in the semi-central 132Sn+124Sn reaction. And nucleon transverse and elliptic flows in the semi-central 197Au+197Au reaction at 0.6 GeV/nucleon are more sensitive to the high-density behavior of the nuclear symmetry energy. One thus concludes that nucleon observables in the heavy reaction system and with higher incident beam energy are more suitable to be used to probe the high-density behavior of the symmetry energy. The present study may help one to get more specific information about the density-dependent symmetry energy from nucleon flow observable in heavy-ion collisions at intermediate energies.
Ouyang, Fang; Hui, Cang; Ge, Saiying; Men, Xin-Yuan; Zhao, Zi-Hua; Shi, Pei-Jian; Zhang, Yong-Sheng; Li, Bai-Lian
2014-01-01
Understanding drivers of population fluctuation, especially for agricultural pests, is central to the provision of agro-ecosystem services. Here, we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and, thus, the stable equilibrium of the pest population, often to a higher level, posing considerable risks to the provision of agro-ecosystem services and regional food security. Efficient and timely measures of pest management in the era of Anthropocene should target the strengthening and revival of weakening density dependence caused by climate change and human activities. PMID:25535553
2007 Time_Dependent Density-Functional Therory (July 15-20, 2007 Colby College, Maine)
Energy Technology Data Exchange (ETDEWEB)
Ullrich Carsten
2008-09-19
Time-dependent density-functional theory (TDDFT) provides an efficient, elegant, and formally exact way of describing the dynamics of interacting many-body quantum systems, circumventing the need for solving the full time-dependent Schroedinger equation. In the 20 years since it was first rigorously established in 1984, the field of TDDFT has made rapid and significant advances both formally as well as in terms of successful applications in chemistry, physics and materials science. Today, TDDFT has become the method of choice for calculating excitation energies of complex molecules, and is becoming increasingly popular for describing optical and spectroscopic properties of a variety of materials such as bulk solids, clusters and nanostructures. Other growing areas of applications of TDDFT are nonlinear dynamics of strongly excited electronic systems and molecular electronics. The purpose and scope of this Gordon Research Conference is to provide a platform for discussing the current state of the art of the rapidly progressing, highly interdisciplinary field of TDDFT, to identify and debate open questions, and to point out new promising research directions. The conference will bring together experts with a diverse background in chemistry, physics, and materials science.
Tanner, Jason E
2000-03-01
The influence of environmental variation on the demography of clonal organisms has been poorly studied. I utilise a matrix model of the population dynamics of the intertidal zoanthid Palythoa caesia to examine how density dependence and temporal variation in demographic rates interact in regulating population size. The model produces realistic simulations of population size, with erratic fluctuations between soft lower and upper boundaries of approximately 55 and 90% cover. Cover never exceeds the maximum possible of 100%, and the population never goes to extinction. A sensitivity analysis indicates that the model's behaviour is driven by density dependence in the fission of large colonies to produce intermediate sized colonies. Importantly, there is no density-dependent mortality in the model, and density dependence in recruitment, while present, is unimportant. Thus it appears that the main demographic processes which are considered to regulate population size in aclonal organisms may not be important for clonal species.
Ouma, B.O.; Amin, R.; Langevelde, van F.; Leader-Williams, N.
2010-01-01
Density-dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential.
Constraints on the density dependence of the symmetry energy from heavy-ion collisions
Tsang, M. B.; Chajecki, Z.; Coupland, D.; Danielewicz, P.; Famiano, F.; Hodges, R.; Kilburn, M.; Lu, F.; Lynch, W. G.; Winkelbauer, J.; Youngs, M.; Zhang, Y. X.
2011-04-01
Constraints on the equation of state (EoS) for symmetric matter (equal neutron and proton numbers) have been extracted from energetic collisions of heavy ions over a range of energies. Collisions of neutron-deficient and neutron-rich heavy ions now provide initial constraints on the EoS of neutron-rich matter at subsaturation densities from isospin diffusions and neutron proton ratios. This article reviews the experimental constraints on the density dependence of symmetry energy at subsaturation density.
DEFF Research Database (Denmark)
Leirs, Herwig; Steneth, Nils Chr.; Nichols, James D.
1997-01-01
no information on actual demographic rates(9,10). Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammute rat Mastomys natalensis (Smith, 1834), using statistical capture-recapture models, Both effects occur simultaneously, but we also demonstrate...
Explaining density-dependent regulation in earthworm populations using life-history analysis
Kammenga, J.E.; Spurgeon, D.J.; Svendsen, C.; Weeks, J.M.
2003-01-01
At present there is little knowledge about how density regulates population growth rate and to what extent this is determined by life-history patterns. We compared density dependent population consequences in the Nicholsonian sense based oil experimental observations and life-history modeling for
Directory of Open Access Journals (Sweden)
Rachael K Walsh
Full Text Available Aedes albopictus, a species known to transmit dengue and chikungunya viruses, is primarily a container-inhabiting mosquito. The potential for pathogen transmission by Ae. albopictus has increased our need to understand its ecology and population dynamics. Two parameters that we know little about are the impact of direct density-dependence and delayed density-dependence in the larval stage. The present study uses a manipulative experimental design, under field conditions, to understand the impact of delayed density dependence in a natural population of Ae. albopictus in Raleigh, North Carolina. Twenty liter buckets, divided in half prior to experimentation, placed in the field accumulated rainwater and detritus, providing oviposition and larval production sites for natural populations of Ae. albopictus. Two treatments, a larvae present and larvae absent treatment, were produced in each bucket. After five weeks all larvae were removed from both treatments and the buckets were covered with fine mesh cloth. Equal numbers of first instars were added to both treatments in every bucket. Pupae were collected daily and adults were frozen as they emerged. We found a significant impact of delayed density-dependence on larval survival, development time and adult body size in containers with high larval densities. Our results indicate that delayed density-dependence will have negative impacts on the mosquito population when larval densities are high enough to deplete accessible nutrients faster than the rate of natural food accumulation.
Dependence of the Spin Transfer Torque Switching Current Density on the Exchange Stiffness Constant
You, Chun-Yeol
2012-01-01
We investigate the dependence of the switching current density on the exchange stiffness constant in the spin transfer torque magnetic tunneling junction structure with micromagnetic simulations. Since the widely accepted analytic expression of the switching current density is based on the macro-spin model, there is no dependence of the exchange stiffness constant. When the switching is occurred, however, the spin configuration forms C-, S-type, or complicated domain structures. Since the spi...
Martinez, Jeannette C; Caprio, Michael A; Friedenberg, Nicholas A
2018-02-09
It has long been recognized that pest population dynamics can affect the durability of a pesticide, but dose remains the primary component of insect resistance management (IRM). For transgenic pesticidal traits such as Bt (Bacillus thuringiensis Berliner (Bacillales: Bacillaceae)), dose (measured as the mortality of susceptibles caused by a toxin) is a relatively fixed characteristic and often falls below the standard definition of high dose. Hence, it is important to understand how pest population dynamics modify durability and what targets they present for IRM. We used a deterministic model of a generic arthropod pest to examine how timing and strength of density dependence interacted with population growth rate and Bt mortality to affect time to resistance. As in previous studies, durability typically reached a minimum at intermediate doses. However, high population growth rates could eliminate benefits of high dose. The timing of density dependence had a more subtle effect. If density dependence operated simultaneously with Bt mortality, durability was insensitive to its strengths. However, if density dependence was driven by postselection densities, decreasing its strength could increase durability. The strength of density dependence could affect durability of both single traits and pyramids, but its influence depended on the timing of density dependence and size of the refuge. Our findings suggest the utility of a broader definition of high dose, one that incorporates population-dynamic context. That maximum growth rates and timing and strength of interactions causing density dependent mortality can all affect durability, also highlights the need for ecologically integrated approaches to IRM research. © The Author(s) 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
International Nuclear Information System (INIS)
Appel, H.
2007-05-01
In part I of this work we present a double-pole approximation (DPA) to the response equations of time-dependent density functional theory (TDDFT). The double-pole approximation provides an exact description of systems with two strongly coupled excitations which are isolated from the rest of the spectrum. In contrast to the traditional single-pole approximation of TDDFT the DPA also yields corrections to the Kohn-Sham oscillator strengths. We also demonstrate how to invert the double-pole solution which allows us to predict matrix elements of the exchange-correlation kernel f xc from experimental input. We attempt some first steps towards a time-dependent generalization of reduced density matrix functional theory (RDMFT). In part II we derive equations of motion for natural orbitals and occupation numbers. Using the equation of motion for the occupation numbers we show that an adiabatic extension of presently known ground-state functionals of static RDMFT always leads to occupation numbers which are constant in time. From the stationary conditions of the equations of motion for the N-body correlations (correlated parts of the N-body matrices) we derive a new class of ground-state functionals which can be used in static RDMFT. Applications are presented for a one-dimensional model system where the time-dependent many-body Schroedinger equation can be propagated numerically. We use optimal control theory to find optimized laser pulses for transitions in a model for atomic Helium. From the numerically exact correlated wavefunction we extract the exact time evolution of natural orbitals and occupation numbers for (i) laser-driven Helium and (ii) electron-ion scattering. Part III of this work considers time-dependent quantum transport within TDDFT. We present an algorithm for the calculation of extended eigenstates of single-particle Hamiltonians which is especially tailored to a finite-difference discretization of the Schroedinger equation. We consider the propagation
Energy Technology Data Exchange (ETDEWEB)
Appel, H.
2007-05-15
In part I of this work we present a double-pole approximation (DPA) to the response equations of time-dependent density functional theory (TDDFT). The double-pole approximation provides an exact description of systems with two strongly coupled excitations which are isolated from the rest of the spectrum. In contrast to the traditional single-pole approximation of TDDFT the DPA also yields corrections to the Kohn-Sham oscillator strengths. We also demonstrate how to invert the double-pole solution which allows us to predict matrix elements of the exchange-correlation kernel f{sub xc} from experimental input. We attempt some first steps towards a time-dependent generalization of reduced density matrix functional theory (RDMFT). In part II we derive equations of motion for natural orbitals and occupation numbers. Using the equation of motion for the occupation numbers we show that an adiabatic extension of presently known ground-state functionals of static RDMFT always leads to occupation numbers which are constant in time. From the stationary conditions of the equations of motion for the N-body correlations (correlated parts of the N-body matrices) we derive a new class of ground-state functionals which can be used in static RDMFT. Applications are presented for a one-dimensional model system where the time-dependent many-body Schroedinger equation can be propagated numerically. We use optimal control theory to find optimized laser pulses for transitions in a model for atomic Helium. From the numerically exact correlated wavefunction we extract the exact time evolution of natural orbitals and occupation numbers for (i) laser-driven Helium and (ii) electron-ion scattering. Part III of this work considers time-dependent quantum transport within TDDFT. We present an algorithm for the calculation of extended eigenstates of single-particle Hamiltonians which is especially tailored to a finite-difference discretization of the Schroedinger equation. We consider the
Floater dynamics can explain positive patterns of density-dependent fecundity in animal populations.
Penteriani, Vincenzo; Otalora, Fermín; Ferrer, Miguel
2006-11-01
After some 70 years of debate on density-dependent regulation of animal populations, there is still poor understanding of where spatial and temporal density dependence occurs. Clearly defining the portion of the population that shapes density-dependent patterns may help to solve some of the ambiguities that encircle density dependence and its patterns. In fact, individuals of the same species and population can show different dynamics and behaviors depending on their locations (e.g., breeding vs. dispersal areas). Considering this form of intrapopulation heterogeneity may improve our understanding of density dependence and population dynamics in general. We present the results of individual-based simulations on a metapopulation of the Spanish imperial eagle Aquila adalberti. Our results suggest that high rates of floater mortality within settlement areas can determine a shift in the classical relationship (from negative to positive) between the fecundity (i.e., fledglings per pair) and density (i.e., number of pairs) of the breeding population. Finally, we proved that different initial conditions affecting the breeder portion of the population can lead to the same values of fecundity. Our results can represent a starting point for new and more complex approaches studying the regulation of animal populations, where the forgotten and invisible component--the floater--is taken into account.
Csörgő, Miklós; Szyszkowicz, Barbara; Wang, Lihong
2006-01-01
In this paper we study strong approximations (invariance principles) of the sequential uniform and general Bahadur--Kiefer processes of long-range dependent sequences. We also investigate the strong and weak asymptotic behavior of the sequential Vervaat process, that is, the integrated sequential Bahadur--Kiefer process, properly normalized, as well as that of its deviation from its limiting process, the so-called Vervaat error process. It is well known that the Bahadur--Kiefer and the Vervaa...
Strong renormalization scheme dependence in τ-lepton decay: Fact or fiction?
International Nuclear Information System (INIS)
Chyla, J.
1995-01-01
The question of the renormalization scheme dependence of the τ semileptonic decay rate is examined in response to a recent criticism. Particular attention is payed to a distinction between a consistent quantitative description of this dependence and the actual selection of a subset of ''acceptable'' renormalization schemes. It is pointed out that this criticism is valid only within a particular definition of the ''strength'' of the renormalization scheme dependence and should not discourage further attempts to use the semileptonic τ decay rate for quantitative tests of perturbative QCD
Spin dynamics and spin-dependent recombination of a polaron pair under a strong ac drive
Malla, Rajesh K.; Raikh, M. E.
2017-08-01
We study theoretically the recombination within a pair of two polarons in magnetic field subject to a strong linearly polarized ac drive. Strong drive implies that the Zeeman frequencies of the pair partners are much smaller than the Rabi frequency, so that the rotating wave approximation does not apply. What makes the recombination dynamics nontrivial is that the partners recombine only when they form a singlet S . By admixing singlet to triplets, the drive induces the triplet recombination as well. We calculate the effective decay rate of all four spin modes. Our main finding is that, under the strong drive, the major contribution to the decay of the modes comes from short time intervals when the driving field passes through zero. When the recombination time in the absence of drive is short, fast recombination from S leads to anomalously slow recombination from the other spin states of the pair. We show that, with strong drive, this recombination becomes even slower. The corresponding decay rate falls off as a power law with the amplitude of the drive.
Yan, Chuan; Xu, Lei; Xu, Tongqin; Cao, Xiaoping; Wang, Fusheng; Wang, Shuqing; Hao, Shoushen; Yang, Hefang; Zhang, Zhibin
2013-03-01
Several studies show that climatic (extrinsic) factors can interact with density-dependent (intrinsic) factors to alter long-term population dynamics, yet there is a surprising lack of investigations of how anthropogenic disturbance modifies such dynamics. Such interactions could be especially important in agricultural systems subject to climate change. We investigated the effects of density dependence, climate, recurrent disturbance from flood irrigation and their interactions on the population dynamics of an important rodent pest, the Chinese striped hamster (Cricetulus barabensis), over 27 years in the croplands of the North China Plain. Strong density-dependent feedbacks occurred at both annual and seasonal scales. While warmer weather increased population sizes in nonbreeding seasons, this effect was counteracted by the negative effect of flood irrigation in breeding seasons. Precipitation showed significant positive effects in nonbreeding seasons, but negative effects in breeding seasons. There were important interactions between intrinsic dynamics, extrinsic dynamics and disturbance. Low temperature significantly increased the strength of density dependence in nonbreeding seasons, whereas intensification of flood irrigation area significantly increased the strength of density dependence but reduced the effect of summer precipitation in breeding seasons. Overall climate change is expected to increase population levels, but anthropogenic disturbance from flood irrigation will help prevent long-term population increases. The interactions between anthropogenic disturbance and both intrinsic and extrinsic (weather-driven) population dynamics caution that we need to consider anthropogenic disturbance as an integral component of population responses to climate change. © 2012 The Authors. Journal of Animal Ecology © 2012 British Ecological Society.
Ellipticity dependence of the near-threshold harmonics of H2 in an elliptical strong laser field.
Yang, Hua; Liu, Peng; Li, Ruxin; Xu, Zhizhan
2013-11-18
We study the ellipticity dependence of the near-threshold (NT) harmonics of pre-aligned H2 molecules using the time-dependent density functional theory. The anomalous maximum appearing at a non-zero ellipticity for the generated NT harmonics can be attributed to multiphoton effects of the orthogonally polarized component of the elliptical driving laser field. Our calculation also shows that the structure of the bound-state, such as molecular alignment and bond length, can be sensitively reflected on the ellipticity dependence of the near-threshold harmonics.
Excitation energy and angular momentum dependence of the nuclear level densities
International Nuclear Information System (INIS)
Razavi, R.; Kakavand, T.; Behkami, A. N.
2007-01-01
We have investigated the excitation energy (E) dependence of nuclear level density for Bethe formula and constant temperature model. The level density parameter aa nd the back shifted energy from the Bethe formula are obtained by fitting the complete level schemes. Also the level density parameters from the constant temperature model have been determined for several nuclei. we have shown that the microscopic theory provides more precise information on the nuclear level densities. On the other hand, the spin cut-off parameter and effective moment of inertia are determined by studying of the angular momentum (J) dependence of the nuclear level density, and effective moment of inertia is compared with rigid body value.
Density-dependent effects on hatching success of the olive ridley turtle, Lepidochelys olivacea.
Honarvar, Shaya; O'Connor, Michael P; Spotila, James R
2008-08-01
Historically, the olive ridley arribada at Playa Nancite, Costa Rica, was one of the largest olive ridley arribadas in the eastern Pacific with 70,000 nesting females in a year. Recently the Nancite arribada drastically declined. We hypothesized that the population decline at Playa Nancite could have been due to low hatching success as a result of the high density of nests on the beach, such that recruitment to the population was insufficient to balance losses. To test this hypothesis, we examined density-dependent effects on hatching success and their underlying mechanisms by experimentally manipulating nest densities in experimental plots on the nesting beach. We set up four nest-density treatments in five experimental blocks. We measured effects of density on hatching success, CO(2) and O(2) concentrations and temperature both within nests and in sand adjacent to nests frequently during incubation. Experimental nest densities affected hatching success with the highest density having the lowest hatching success. Higher nest density led to lower O(2) levels and higher CO(2) levels in the nest with greater changes in the latter part of the incubation. Highest temperatures occurred in high-density areas. Temperatures were lower in sand surrounding the nest than in the nest. Effects of density on temperature, CO(2) and O(2) were confirmed at a naturally high-density nesting beach, Playa La Flor, Nicaragua. Long-term failure in production of hatchlings due to historic high densities may have contributed to the decline of arribadas on Playa Nancite. Thus, density-dependent population control would have operated at the embryonic life stage in this population of olive ridley turtles.
Ecological drivers of guanaco recruitment: variable carrying capacity and density dependence.
Marino, Andrea; Pascual, Miguel; Baldi, Ricardo
2014-08-01
Ungulates living in predator-free reserves offer the opportunity to study the influence of food limitation on population dynamics without the potentially confounding effects of top-down regulation or livestock competition. We assessed the influence of relative forage availability and population density on guanaco recruitment in two predator-free reserves in eastern Patagonia, with contrasting scenarios of population density. We also explored the relative contribution of the observed recruitment to population growth using a deterministic linear model to test the assumption that the studied populations were closed units. The observed densities increased twice as fast as our theoretical populations, indicating that marked immigration has taken place during the recovery phase experienced by both populations, thus we rejected the closed-population assumption. Regarding the factors driving variation in recruitment, in the low- to medium-density setting, we found a positive linear relationship between recruitment and surrogates of annual primary production, whereas no density dependence was detected. In contrast, in the high-density scenario, both annual primary production and population density showed marked effects, indicating a positive relationship between recruitment and per capita food availability above a food-limitation threshold. Our results support the idea that environmental carrying capacity fluctuates in response to climatic variation, and that these fluctuations have relevant consequences for herbivore dynamics, such as amplifying density dependence in drier years. We conclude that including the coupling between environmental variability in resources and density dependence is crucial to model ungulate population dynamics; to overlook temporal changes in carrying capacity may even mask density dependence as well as other important processes.
Electron-nuclear coupling in time-dependent multicomponent density functional theory
Butriy, Olena O.
2008-01-01
In this thesis we developed the time-dependent version of the multicomponent density functional approach to treat time-dependent electron-nuclear systems. The method enables to describe the electron-nuclear coupling fully quantum mechanically. No Born-Oppenheimer approximation is involved in the
Time-dependent density-functional calculation of nuclear response functions
Nakatsukasa, Takashi
2017-01-01
Basic issues of the time-dependent density-functional theory are discussed, especially on the real-time calculation of the linear response functions. Some remarks on the derivation of the time-dependent Kohn-Sham equations and on the numerical methods are given.
Energy Technology Data Exchange (ETDEWEB)
Polat, Ozgur [ORNL; Sinclair IV, John W [ORNL; Zuev, Yuri L [ORNL; Thompson, James R [ORNL; Christen, David K [ORNL; Cook, Sylvester W [ORNL; Kumar, Dhananjay [ORNL; Chen, Y [SuperPower Incorporated, Schenectady, New York; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York
2011-01-01
The dependence of the critical current density Jc on temperature, magnetic field, and film thickness has been investigated in (Gd-Y)BaCu-oxide materials of 0.7, 1.4, and 2.8 m thickness. Generally, the Jc decreases with film thickness at investigated temperatures and magnetic fields. The nature and strength of the pinning centers for vortices have been identified through angular and temperature measurements, respectively. These films do not exhibit c-axis correlated vortex pinning, but do have correlated defects oriented near the ab-planes. For all film thicknesses studied, strong pinning dominates at most temperatures. The vortex dynamics were investigated through magnetic relaxation studies in the temperature range of 5 77 K in 1 T and 3 T applied magnetic fields, H || surface-normal. The creep rate S is thickness dependent at high temperatures, implying that the pinning energy is also thickness dependent. Maley analyses of the relaxation data show an inverse power law variation for the effective pinning energy Ueff ~ (J0/J) . Finally, the electric field-current density (E-J) characteristics were determined over a wide range of dissipation by combining experimental results from transport, swept field magnetometry (VSM), and Superconducting Quantum Interference Device (SQUID) magnetometry. We develop a self-consistent model of the combined experimental results, leading to an estimation of the critical current density Jc0(T) in the absence of flux creep.
Density dependence in a recovering osprey population: demographic and behavioural processes.
Bretagnolle, V; Mougeot, F; Thibault, J-C
2008-09-01
1. Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions.
SCHLATMANN, AR; HOEKSTRA, R; MORGENSTERN, R; OLSON, RE; PASCALE, J
1993-01-01
By analyzing spectra of emitted photons, we have studied state-selective electron capture in collisions of He2+ on aligned Na*(3p) atoms that span the ''velocity-matching'' energy between projectile and target electron. We find a strong dependence of the capture cross sections on the Na*(3p) orbital
Directory of Open Access Journals (Sweden)
Xiang Zeng
2016-06-01
Full Text Available Abstract We prove some almost sure central limit theorems for the maxima of strongly dependent nonstationary Gaussian vector sequences under some mild conditions. The results extend the ASCLT to nonstationary Gaussian vector sequences and give substantial improvements for the weight sequence obtained by Lin et al. (Comput. Math. Appl. 62(2:635-640, 2011.
Holanda, R. F. L.; Pereira, S. H.; Jain, Deepak
2017-11-01
In this work, by using strong gravitational lensing (SGL) observations along with Type Ia Supernovae (Union2.1) and gamma-ray burst data (GRBs), we propose a new method to study a possible redshift evolution of γ(z), the mass density power-law index of strong gravitational lensing systems. In this analysis, we assume the validity of cosmic distance duality relation and the flat universe. In order to explore the γ(z) behaviour, three different parametrizations are considered, namely: (P1) γ(zl) = γ0 + γ1zl; (P2) γ(zl) = γ0 + γ1zl/(1 + zl); and (P3) γ(zl) = γ0 + γ1ln (1 + zl), where zl corresponds to lens redshift. If γ0 = 2 and γ1 = 0, the singular isothermal sphere model is recovered. Our method is performed on SGL sub-samples defined by different lens redshifts and velocity dispersions. For the former case, the results are in full agreement with each other, while a 1σ tension between the sub-samples with low (≤250 km s-1) and high (>250 km s-1) velocity dispersions was obtained on the (γ0-γ1) plane. By considering the complete SGL sample, we obtain γ0 ≈ 2 and γ1 ≈ 0 within 1σ c.l. for all γ(z) parametrizations. However, we find the following best-fitting values of γ1: -0.085; -0.16; and -0.12 for P1, P2 and P3 parametrizations, respectively, suggesting a mild evolution for γ(z). By repeating the analysis with Type Ia Supernovae from Joint Light Analysis compilation, GRBs and SGL systems this mild evolution is reinforced.
Cubaynes, Sarah; MacNulty, Daniel R; Stahler, Daniel R; Quimby, Kira A; Smith, Douglas W; Coulson, Tim
2014-11-01
Understanding the population dynamics of top-predators is essential to assess their impact on ecosystems and to guide their management. Key to this understanding is identifying the mechanisms regulating vital rates. Determining the influence of density on survival is necessary to understand the extent to which human-caused mortality is compensatory or additive. In wolves (Canis lupus), empirical evidence for density-dependent survival is lacking. Dispersal is considered the principal way in which wolves adjust their numbers to prey supply or compensate for human exploitation. However, studies to date have primarily focused on exploited wolf populations, in which density-dependent mechanisms are likely weak due to artificially low wolf densities. Using 13 years of data on 280 collared wolves in Yellowstone National Park, we assessed the effect of wolf density, prey abundance and population structure, as well as winter severity, on age-specific survival in two areas (prey-rich vs. prey-poor) of the national park. We further analysed cause-specific mortality and explored the factors driving intraspecific aggression in the prey-rich northern area of the park. Overall, survival rates decreased during the study. In northern Yellowstone, density dependence regulated adult survival through an increase in intraspecific aggression, independent of prey availability. In the interior of the park, adult survival was less variable and density-independent, despite reduced prey availability. There was no effect of prey population structure in northern Yellowstone, or of winter severity in either area. Survival was similar among yearlings and adults, but lower for adults older than 6 years. Our results indicate that density-dependent intraspecific aggression is a major driver of adult wolf survival in northern Yellowstone, suggesting intrinsic density-dependent mechanisms have the potential to regulate wolf populations at high ungulate densities. When low prey availability or high
Hilal, Rifaat
2017-06-19
We aim at providing better insight into the parameters that govern the intramolecular charge transfer (ICT) and photo-injection processes in dyes for dye-sensitised solar cells (DSSC). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are utilized to study the geometry, electronic structure, electrostatic potential (ESP) and absorption spectrum, for a representative donor-π bridge-acceptor (D–π–A) dye for DSSC. The coplanar geometry of the dye (D1) facilitates strong conjugation and considerable delocalization originating the π CT interaction from donor to acceptor orbitals and the hyper-conjugative interactions involving Rydberg states. A model simulating the adsorption of the dye on the TiO surface is utilized to estimate binding energies. The effect of fluorine substituents in the π-spacer on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state lifetime, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.
International Nuclear Information System (INIS)
Yang Heping; Magilnick, Nathaniel; Xia Meng; Lu, Shelly C.
2008-01-01
Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen that exerts opposing effects depending on cell density. Glutathione (GSH) is the main non-protein thiol in mammalian cells that modulates growth and apoptosis. We previously showed that GSH level is inversely related to cell density of hepatocytes and is positively related to growth. Our current work examined whether HGF can modulate GSH synthesis in a cell density-dependent manner and how GSH in turn influence HGF's effects. We found HGF treatment of H4IIE cells increased cell GSH levels only under subconfluent density. The increase in cell GSH under low density was due to increased transcription of GSH synthetic enzymes. This correlated with increased protein levels and nuclear binding activities of c-Jun, c-Fos, p65, p50, Nrf1 and Nrf2 to the promoter region of these genes. HGF acts as a mitogen in H4IIE cells under low cell density and protects against tumor necrosis factor α (TNFα)-induced apoptosis by limiting JNK activation. However, HGF is pro-apoptotic under high cell density and exacerbates TNFα-induced apoptosis by potentiating JNK activation. The increase in cell GSH under low cell density allows HGF to exert its full mitogenic effect but is not necessary for its anti-apoptotic effect
Luo, Jun-Wei; Li, Shu-Shen; Zunger, Alex
2017-09-22
The electric field manipulation of the Rashba spin-orbit coupling effects provides a route to electrically control spins, constituting the foundation of the field of semiconductor spintronics. In general, the strength of the Rashba effects depends linearly on the applied electric field and is significant only for heavy-atom materials with large intrinsic spin-orbit interaction under high electric fields. Here, we illustrate in 1D semiconductor nanowires an anomalous field dependence of the hole (but not electron) Rashba effect (HRE). (i) At low fields, the strength of the HRE exhibits a steep increase with the field so that even low fields can be used for device switching. (ii) At higher fields, the HRE undergoes a rapid transition to saturation with a giant strength even for light-atom materials such as Si (exceeding 100 meV Å). (iii) The nanowire-size dependence of the saturation HRE is rather weak for light-atom Si, so size fluctuations would have a limited effect; this is a key requirement for scalability of Rashba-field-based spintronic devices. These three features offer Si nanowires as a promising platform for the realization of scalable complementary metal-oxide-semiconductor compatible spintronic devices.
Laser based imaging of time depending microscopic scenes with strong light emission
Hahlweg, Cornelius; Wilhelm, Eugen; Rothe, Hendrik
2011-10-01
Investigating volume scatterometry methods based on short range LIDAR devices for non-static objects we achieved interesting results aside the intended micro-LIDAR: the high speed camera recording of the illuminated scene of an exploding wire -intended for Doppler LIDAR tests - delivered a very effective method of observing details of objects with extremely strong light emission. As a side effect a schlieren movie is gathered without any special effort. The fact that microscopic features of short time processes with high emission and material flow might be imaged without endangering valuable equipment makes this technique at least as interesting as the intended one. So we decided to present our results - including latest video and photo material - instead of a more theoretical paper on our progress concerning the primary goal.
Amandeep, K.; Suneel, K.
2017-09-01
The present theoretical calculations have been performed within the framework of IQMD model to study a particular set of mass symmetric and asymmetric reactions (keeping total mass fixed) over a wide range of incident energies and colliding geometries. It has been observed that global as well as local nuclear stopping is influenced by the mass asymmetry of the reaction strongly. Influence of density-dependent symmetry energy has been observed in local nuclear stopping. Global stopping decreases with the increase in colliding geometry. Effect of colliding geometry on nuclear stopping is more at higher energies.
DEFF Research Database (Denmark)
Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.
2008-01-01
Time-dependent density functional theory (TD-DFT) and DFT-based multireference configuration interaction (DFT/MRCI) calculations are reported for a recently proposed benchmark set of 28 medium-sized organic molecules. Vertical excitation energies, oscillator strengths, and excited-state dipole...... moments are computed using the same geometries (MP2/6-31G*) and basis set (TZVP) as in our previous ab initio benchmark study on electronically excited states. The results from TD-DFT (with the functionals BP86, B3LYP, and BHLYP) and from DFT/MRCI are compared against the previous high-level ab initio...
Density dependence of the symmetry energy from neutron skin thickness in finite nuclei
International Nuclear Information System (INIS)
Vinas, X.; Centelles, M.; Roca-Maza, X.; Warda, M.
2014-01-01
The density dependence of the symmetry energy around saturation density, characterized by the slope parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate for L is obtained from experimental data on neutron skins extracted from antiprotonic atoms. We also discuss the ability of parity-violating elastic electron scattering to obtain information on the neutron skin thickness in 208 Pb and to constrain the density dependence of the nuclear symmetry energy. The size and shape of the neutron density distribution of 208 Pb predicted by mean-field models is briefly addressed. We conclude with a comparative overview of the L values predicted by several existing determinations. (orig.)
Romaniello, P; de Boeij, P L
2005-04-22
We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the zeroth-order regular approximation in the ground-state density-functional theory calculations, as well as in the time-dependent response calculations. The results for the dielectric function of gold calculated in the spectral range of 0-10 eV are compared with experimental data reported in literature and recent ellipsometric measurements. As well known, relativistic effects strongly influence the color of gold. We find that the onset of interband transitions is shifted from around 3.5 eV, obtained in a nonrelativistic calculation, to around 1.9 eV when relativity is included. With the inclusion of the scalar-relativistic effects there is an overall improvement of both real and imaginary parts of the dielectric function over the nonrelativistic ones. Nevertheless some important features in the absorption spectrum are not well reproduced, but can be explained in terms of spin-orbit coupling effects. The remaining deviations are attributed to the underestimation of the interband gap (5d-6sp band gap) in the local-density approximation and to the use of the adiabatic local-density approximation in the response calculation.
On Strong Positive Frequency Dependencies of Quality Factors in Local-Earthquake Seismic Studies
Morozov, Igor B.; Jhajhria, Atul; Deng, Wubing
2018-03-01
Many observations of seismic waves from local earthquakes are interpreted in terms of the frequency-dependent quality factor Q( f ) = Q0 f^{η } , where η is often close to or exceeds one. However, such steep positive frequency dependencies of Q require careful analysis with regard to their physical consistency. In particular, the case of η = 1 corresponds to frequency-independent (elastic) amplitude decays with time and consequently requires no Q-type attenuation mechanisms. For η > 1, several problems with physical meanings of such Q-factors occur. First, contrary to the key premise of seismic attenuation, high-frequency parts of the wavefield are enhanced with increasing propagation times relative to the low-frequency ones. Second, such attenuation cannot be implemented by mechanical models of wave-propagating media. Third, with η > 1, the velocity dispersion associated with such Q(f) occurs over unrealistically short frequency range and has an unexpected oscillatory shape. Cases η = 1 and η > 1 are usually attributed to scattering; however, this scattering must exhibit fortuitous tuning into the observation frequency band, which appears unlikely. The reason for the above problems is that the inferred Q values are affected by the conventional single-station measurement procedure. Both parameters Q 0 and are apparent, i.e., dependent on the selected parameterization and inversion method, and they should not be directly attributed to the subsurface. For η ≈ 1, parameter Q 0 actually describes the frequency-independent amplitude decay in access of some assumed geometric spreading t -α , where α is usually taken equal one. The case η > 1 is not allowed physically and could serve as an indicator of problematic interpretations. Although the case 0 < η < 1 is possible, its parameters Q 0 and may also be biased by the measurement procedure. To avoid such difficulties of Q-based approaches, we recommend measuring and interpreting the amplitude-decay rates
Local environment and density-dependent feedbacks determine population growth in a forest herb.
Dahlgren, Johan P; Ostergård, Hannah; Ehrlén, Johan
2014-12-01
Linking spatial variation in environmental factors to variation in demographic rates is essential for a mechanistic understanding of the dynamics of populations. However, we still know relatively little about such links, partly because feedbacks via intraspecific density make them difficult to observe in natural populations. We conducted a detailed field study and investigated simultaneous effects of environmental factors and the intraspecific density of individuals on the demography of the herb Lathyrus vernus. In regression models of vital rates we identified effects associated with spring shade on survival and growth, while density was negatively correlated with these vital rates. Density was also negatively correlated with average individual size in the study plots, which is consistent with self-thinning. In addition, average plant sizes were larger than predicted by density in plots that were less shaded by the tree canopy, indicating an environmentally determined carrying capacity. A size-structured integral projection model based on the vital rate regressions revealed that the identified effects of shade and density were strong enough to produce differences in stable population sizes similar to those observed in the field. The results illustrate how the local environment can determine dynamics of populations and that intraspecific density may have to be more carefully considered in studies of plant demography and population viability analyses of threatened species. We conclude that demographic approaches incorporating information about both density and key environmental factors are powerful tools for understanding the processes that interact to determine population dynamics and abundances.
Rüger, Robert; Niehaus, Thomas; van Lenthe, Erik; Heine, Thomas; Visscher, Lucas
2016-01-01
We report a time-dependent density functional based tight-binding (TD-DFTB) scheme for the calculation of UV/Vis spectra, explicitly taking into account the excitation of nuclear vibrations via the adiabatic Hessian Franck-Condon (AH|FC) method with a harmonic approximation for the nuclear wavefunction. The theory of vibrationally resolved UV/Vis spectroscopy is first summarized from the viewpoint of TD-DFTB. The method is benchmarked against time-dependent density functional theory (TD-DFT) ...
Energy Technology Data Exchange (ETDEWEB)
Al-Samman, T., E-mail: al-samman@imm.rwth-aachen.de [Institut fuer Metallkunde und Metallphysik, RWTH Aachen, Kopernikusstr. 14, D-52064 Aachen (Germany); Li, X. [Institut fuer Metallkunde und Metallphysik, RWTH Aachen, Kopernikusstr. 14, D-52064 Aachen (Germany); Chowdhury, S. Ghosh [CSIR National Metallurgical Laboratory, MST Division, Jamshedpur 831007 (India)
2010-06-15
Over recent years there have been a remarkable number of studies dealing with compression of magnesium. A literature search, however, shows a noticeably less number of papers concerned with tension and a very few papers comparing both modes, systematically, in one study. The current investigation reports the anisotropic deformation behavior and concomitant texture and microstructure evolution investigated in uniaxial tension and compression tests in two sample directions performed on an extruded commercial magnesium alloy AZ31 at different Z conditions. For specimens with the loading direction parallel to the extrusion axis, the tension-compression strength anisotropy was pronounced at high Z conditions. Loading at 45{sup o} from the extrusion axis yielded a tension-compression strength behavior that was close to isotropic. During tensile loading along the extrusion direction the extrusion texture resists twinning and favors prismatic slip (contrary to compression). This renders the shape change maximum in the basal plane and equal to zero along the c-axis, which resulted in the orientation of individual grains remaining virtually intact during all tension tests at different Z conditions. For the other investigated sample direction, straining was accommodated along the c-axis, which was associated with a lattice rotation, and thus, a change of crystal orientation. Uniaxial compression at a low Z condition (400 deg. C/10{sup -4} s{sup -1}) yielded a desired texture degeneration, which was explained on the basis of a more homogeneous partitioning of slip systems that reduces anisotropy and enhanced dynamic recrystallization (DRX), which counteracts the strong deformation texture. The critical strains for the nucleation of DRX in tensiled specimens at the highest investigated Z condition (200 deg. C/10{sup -2} s{sup -1}) were found to range between 4% and 5.6%.
Density-dependent light-assisted tunneling in fermionic optical lattices
Xu, Wenchao; Morong, William; Demarco, Brian
2016-05-01
Many recent theoretical proposals have discussed the possibility to realize density-dependent tunneling in optical lattices via external periodic driving. These methods enable the simulation of novel many-body quantum phases. Here we present experimental progress on realizing density-dependent tunneling for ultracold 40K atoms trapped in a cubic optical lattice via stimulated Raman transitions. After preparing a spin-polarized gas in the Mott insulator regime of the Hubbard model, a pair of Raman beams is applied to flip the spin of atoms. The Raman beams also introduce an effective density-dependent tunneling that can be tuned by the Raman frequency difference and Rabi rate. The Mott gap inferred from measurements of the fraction of atoms transferred between spin states as the Raman frequency difference is adjusted matches the prediction based on a tight-binding model. We also observe the interaction-dependent tunneling by measuring the fraction of doubly-occupied sites created by the Raman driving. This method allows the engineering of density-dependent tunneling and effective nearest-neighbor interactions in fermionic optical lattices. The authors acknowledge funding from the National Science Foundation (Grant No. PHY15-05468) and the Army Research Office (Grant No. W911NF-12-1-0462).
The role of weather and density dependence on population dynamics of Alpine-dwelling red deer.
Bonardi, Anna; Corlatti, Luca; Bragalanti, Natalia; Pedrotti, Luca
2017-01-01
The dynamics of red deer Cervus elaphus populations has been investigated across different environmental conditions, with the notable exception of the European Alps. Although the population dynamics of mountain-dwelling ungulates is typically influenced by the interaction between winter severity and density, the increase of temperatures and the reduction of snowpack occurring on the Alps since the 1980s may be expected to alter this pattern, especially in populations dwelling at medium - low elevations. Taking advantage of a 29-year time series of spring count data, we explored the role of weather stochasticity and density dependence on growth rate and vital rates (mortality and weaning success), and the density-dependent variation in body mass in a red deer population of the Italian Alps. The interaction between increasing values of density and snow depth exerted negative and positive effects on growth and mortality rates, respectively, while weaning success was negatively affected by increasing values of density, female-biased sex ratio and snow depth. Body mass of males and females of different age classes declined as population size increased. Our data support the role of winter severity and density dependence as key components of red deer population dynamics, and provide insight into the species' ecology on the European Alps. Despite the recent decline of snowpack on the Alpine Region, the negative impacts of winter severity and population abundance on growth rrate (possibly mediated by the density-dependent decline in body mass) confirms the importance of overwinter mortality in affecting the population dynamics of Alpine-dwelling red deer. © 2016 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.
Isoscalar giant resonances and Landau parameters with density-dependent effective interactions
International Nuclear Information System (INIS)
Kohno, Michio; Ando, Kazuhiko
1979-01-01
Discussion is given on the relations between the Landau parameters and the isoscalar giant (quadrupole- and monopole-) resonance energies by using general density-dependent interactions. In the limit of infinite nuclear matter, the isoscalar giant quadrupole energy is shown to depend not only on the effective mass but also on the Landau parameter F 2 . Collective energies of the isoscalar giant resonances are calculated for 16 O and 40 Ca with four different effective interactions, G-0, B1, SII and SV, by using the scaling- and constrained Hartree-Fock-methods. It is shown that the dependence of the collective energies on the effective interactions is essentially determined by the Landau parameters. The G-0 force is found to be most successful in reproducing the giant resonance energies. Validity of the RPA-moment theorems is examined for the case of local density-dependent interactions. (author)
Linear-response time-dependent density-functional theory with pairing fields.
Peng, Degao; van Aggelen, Helen; Yang, Yang; Yang, Weitao
2014-05-14
Recent development in particle-particle random phase approximation (pp-RPA) broadens the perspective on ground state correlation energies [H. van Aggelen, Y. Yang, and W. Yang, Phys. Rev. A 88, 030501 (2013), Y. Yang, H. van Aggelen, S. N. Steinmann, D. Peng, and W. Yang, J. Chem. Phys. 139, 174110 (2013); D. Peng, S. N. Steinmann, H. van Aggelen, and W. Yang, J. Chem. Phys. 139, 104112 (2013)] and N ± 2 excitation energies [Y. Yang, H. van Aggelen, and W. Yang, J. Chem. Phys. 139, 224105 (2013)]. So far Hartree-Fock and approximated density-functional orbitals have been utilized to evaluate the pp-RPA equation. In this paper, to further explore the fundamentals and the potential use of pairing matrix dependent functionals, we present the linear-response time-dependent density-functional theory with pairing fields with both adiabatic and frequency-dependent kernels. This theory is related to the density-functional theory and time-dependent density-functional theory for superconductors, but is applied to normal non-superconducting systems for our purpose. Due to the lack of the proof of the one-to-one mapping between the pairing matrix and the pairing field for time-dependent systems, the linear-response theory is established based on the representability assumption of the pairing matrix. The linear response theory justifies the use of approximated density-functionals in the pp-RPA equation. This work sets the fundamentals for future density-functional development to enhance the description of ground state correlation energies and N ± 2 excitation energies.
International Nuclear Information System (INIS)
Savel'ev, Sergey; Rakhmanov, A.L.; Nori, Franco
2006-01-01
Josephson plasma waves are scattered by the Josephson vortex lattice. This scattering results in a strong dependence, on the in-plane magnetic-field H ab , of the reflection and transmission of THz radiation propagating in layered superconductors. In particular, a tunable band-gap structure (THz photonic crystal) occurs in such a medium. These effects can be used, by varying H ab , for the selective frequency-filtering of THz radiation
International Nuclear Information System (INIS)
Eschner, Wolfgang; Schmidt, Matthias; Dietlein, Markus; Schicha, Harald
2008-01-01
Full text: Purpose: a) To evaluate the impact of the reduced life expectancy of patients (compared to a non-patient group with same age distribution) on their risk of developing cancer from the diagnostic use of radiation. b) To find an approximation to such reduction in risk which depends only on the patient's age, a, and his life expectancy, but is independent of the choice of values for the baseline risk of cancer incidence, m(a), and the enhanced relative risk ERR(a) from radiation exposure. Method: The lifetime attributable risk LAR (of a radiation-induced malignancy to manifest itself) is a function of age at exposure, e, and given by integrating over attained age, a, the product of ERR(a), baseline cancer risk m(a) and the relative probability of surviving to age a, S'(a,e). We define a 'prognosis-based LAR modifier' (PROLARM) as the ratio of risks for non-patient, LAR(a), and patient, LAR p (a), a dimensionless quantity that gives a measure of reduction of LAR due to the patient's prognosis. With the survival of the patient group, S p ' (a,e), and for any choice of fitted function for ERR(a) like those used in BEIR VII report, PROLARM ≥∫d'(a,e) da/∫S p '(a,e) da, i.e. the ratio of the survival integrals gives a lower (thus conservative) estimate of the reduction in risk. Results: The method was applied to n=4285 patients with metastatic breast cancer for whom survival as a function of age at metastasis was known. Figure shows that LAR is decreased significantly for all ages at exposure. At younger ages, this decrease is more pronounced (PROLARM ≥ 20 for e ≤ 65). Example: using ERR values of BEIR VII, the LAR due to 10 mSv effective dose at age a = 50 would drop from 1.2 E-3 for non-patient to 4.3E-5 for a patient, i.e. by a factor (PROLARM) of 29. Using only survival data, that factor is 27 (but no LAR can be computed). In other words: 10 mSv for a patient correspond risk-wise to 0.4 mSv for non-patient. The method can be applied to any pathology
Both, C.
2000-01-01
The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One
Both, C
The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One
Directory of Open Access Journals (Sweden)
Karsten Schönrogge
Full Text Available Revealing the interactions between alien species and native communities is central to understanding the ecological consequences of range expansion. Much has been learned through study of the communities developing around invading herbivorous insects. Much less, however, is known about the significance of such aliens for native vertebrate predators for which invaders may represent a novel food source. We quantified spatial patterns in native bird predation of invading gall-inducing Andricus wasps associated with introduced Turkey oak (Quercus cerris at eight sites across the UK. These gallwasps are available at high density before the emergence of caterpillars that are the principle spring food of native insectivorous birds. Native birds showed positive spatial density dependence in gall attack rates at two sites in southern England, foraging most extensively on trees with highest gall densities. In a subsequent study at one of these sites, positive spatial density dependence persisted through four of five sequential week-long periods of data collection. Both patterns imply that invading galls are a significant resource for at least some native bird populations. Density dependence was strongest in southern UK bird populations that have had longest exposure to the invading gallwasps. We hypothesise that this pattern results from the time taken for native bird populations to learn how to exploit this novel resource.
The importance of spatial models for estimating the strength of density dependence
DEFF Research Database (Denmark)
Thorson, James T.; Skaug, Hans J.; Kristensen, Kasper
2014-01-01
for an entire population. However, it is increasingly recognized that spatial heterogeneity in population densities has implications for population and community dynamics. We therefore adapt the Gompertz model to approximate local densities over continuous space instead of population-wide abundance...... the California Coast. In this case, the nonspatial model estimates implausible oscillatory dynamics on an annual time scale, while the spatial model estimates strong autocorrelation and is supported by model selection tools. We conclude by discussing the importance of improved data archiving techniques, so...
Local environment and density-dependent feedbacks determine population growth in a forest herb
DEFF Research Database (Denmark)
Dahlgren, Johan Petter; Östergård, Hannah; Ehrlén, Johan
2014-01-01
to observe in natural populations. We conducted a detailed field study and investigated simultaneous effects of environmental factors and the intraspecific density of individuals on the demography of the herb Lathyrus vernus. In regression models of vital rates we identified effects associated with spring...... that were less shaded by the tree canopy, indicating an environmentally determined carrying capacity. A size-structured integral projection model based on the vital rate regressions revealed that the identified effects of shade and density were strong enough to produce differences in stable population sizes...
Directory of Open Access Journals (Sweden)
Seth J Theuerkauf
Full Text Available Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders' density and the service(s of interest. We assessed the density-dependent effect of an invasive marsh grass, Phragmites australis, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR, USA. Plant species richness was equivalent among low, medium and high Phragmites density plots, and overall plant community composition did not vary significantly by Phragmites density. Shoreline change was most negative (landward retreat where Phragmites density was highest (-0.40 ± 0.19 m yr-1 vs. -0.31 ± 0.10 for low density Phragmites in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance where Phragmites density was highest (0.19 ± 0.05 m yr-1 vs. 0.12 ± 0.07 for low density Phragmites in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of Phragmites density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high Phragmites density plots (23.23 ± 2.0 kg C m-3 vs. 22.81 ± 3.8. In Kitty Hawk Woods, mean soil carbon content was greater in low Phragmites density plots (36.63 ± 10.22 kg C m-3 than those with medium (13.99 ± 1.23 kg C m-3 or high density (21.61 ± 4.53 kg C m-3, but differences were not significant. These findings suggest an overall neutral density-dependent effect of Phragmites on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species
Occurrence of Density-Dependent Height Repression within Jack Pine and Black Spruce Populations
Directory of Open Access Journals (Sweden)
Peter F. Newton
2015-07-01
Full Text Available The objective of this study was to investigate the occurrence of density-dependent height relationships in jack pine (Pinus banksiana Lamb. and black spruce (Picea mariana (Mill. B.S.P. populations. After assessing and ruling out the presence of consequential spatial correlation effects, the analysis consisted of analyzing the relationship between mean dominant height and initial planting density within 28 Nelder plots located in the central portion of the Canadian Boreal Forest Region. Employing remeasurement data obtained at periodic intervals (16, 20 and 40–41 years post-establishment across a stand density gradient ranging from a minimum of 1425 stems/ha to a maximum of 28,621 stems/ha, graphical and simple linear regression analyses were used to quantify the stand height–density relationship by species, plot and measurement year. The results indicated the presence of density-dependent effects on height development for both species: 65% of the 83 jack pine relationships and 89% of the 27 black spruce relationships had significant (p ≤ 0.05 and negative slope values. In regards to jack pine for which the data permitted, the occurrence and magnitude of the observed height repression effect increased over time. The asymptotic height repression effect for jack pine was 24% greater than that for black spruce. The results are discussed within the context of the applicability of the density-independent height growth assumption and potential implications for site quality estimation and thinning response modeling.
Temperature-dependent surface density of alkylthiol monolayers on gold nanocrystals
Liu, Xuepeng; Lu, Pin; Zhai, Hua; Wu, Yucheng
2018-03-01
Atomistic molecular dynamics (MD) simulations are performed to study the surface density of passivating monolayers of alkylthiol chains on gold nanocrystals at temperatures ranging from 1 to 800 K. The results show that the surface density of alkylthiol monolayer reaches a maximum value at near room temperature (200-300 K), while significantly decreases with increasing temperature in the higher temperature region (> 300 {{K}}), and slightly decreases with decreasing temperature at low temperature (< 200 {{K}}). We find that the temperature dependence of surface ligand density in the higher temperature region is attributed to the substantial ligand desorption induced by the thermal fluctuation, while that at low temperature results from the reduction in entropy caused by the change in the ordering of passivating monolayer. These results are expected helpful to understand the temperature-dependent surface coverage of gold nanocrystals.
Plant diversity increases with the strength of negative density dependence at the global scale
Joseph A. LaManna; Scott A. Mangan; Alfonso Alonso; Norman A. Bourg; Warren Y. Brockelman; Sarayudh Bunyavejchewin; Li-Wan Chang; Jyh-Min Chiang; George B. Chuyong; Keith Clay; Richard Condit; Susan Cordell; Stuart J. Davies; Tucker J. Furniss; Christian P. Giardina; I. A. U. Nimal Gunatilleke; C. V. Savitri Gunatilleke; Fangliang He; Robert W. Howe; Stephen P. Hubbell; Chang-Fu Hsieh; Faith M. Inman-Narahari; David Janík; Daniel J. Johnson; David Kenfack; Lisa Korte; Kamil Král; Andrew J. Larson; James A. Lutz; Sean M. McMahon; William J. McShea; Hervé R. Memiaghe; Anuttara Nathalang; Vojtech Novotny; Perry S. Ong; David A. Orwig; Rebecca Ostertag; Geoffrey G. Parker; Richard P. Phillips; Lawren Sack; I-Fang Sun; J. Sebastián Tello; Duncan W. Thomas; Benjamin L. Turner; Dilys M. Vela Díaz; Tomáš Vrška; George D. Weiblen; Amy Wolf; Sandra Yap; Jonathan A. Myers
2017-01-01
Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only...
Demonstrating the Temperature Dependence of Density via Construction of a Galilean Thermometer
Priest, Marie A.; Padgett, Lea W.; Padgett, Clifford W.
2011-01-01
A method for the construction of a Galilean thermometer out of common chemistry glassware is described. Students in a first-semester physical chemistry (thermodynamics) class can construct the Galilean thermometer as an investigation of the thermal expansivity of liquids and the temperature dependence of density. This is an excellent first…
Ruger, R.; Niehaus, T.; van Lenthe, E.; Heine, T.; Visscher, L.
2016-01-01
We report a time-dependent density functional based tight-binding (TD-DFTB) scheme for the calculation of UV/Vis spectra, explicitly taking into account the excitation of nuclear vibrations via the adiabatic Hessian Franck-Condon method with a harmonic approximation for the nu- clear wavefunction.
Directory of Open Access Journals (Sweden)
Wentao Wang
2012-01-01
Full Text Available This paper presents a new generalized Nicholson’s blowflies system with patch structure and nonlinear density-dependent mortality terms. Under appropriate conditions, we establish some criteria to guarantee the exponential extinction of this system. Moreover, we give two examples and numerical simulations to demonstrate our main results.
The Keldysh formalism applied to time-dependent current-density-functional theory
Gidopoulos, NI; Wilson, S
2003-01-01
In this work we demonstrate how to derive the Kohn-Sham equations of time-dependent current-density functional theory from a generating action functional defined on a Keldysh time contour. These Kohn-Sham equations contain an exchange-correlation contribution to the vector potential. For this
A spatial interpretation of the density dependence model in industrial demography
van Wissen, L
2004-01-01
In this paper the density dependence model, which was developed in organizational ecology, is compared to the economic-geographical notion of agglomeration economies. There is a basic resemblance: both involve some form of positive feedback between size of the population and growth. The paper
Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm
Jansen, Patrick A.; Visser, Marco D.; Wright, S. Joseph; Rutten, Gemma; Muller-Landau, Helene C.
Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a
BONE-DENSITY IN NON-INSULIN-DEPENDENT DIABETES-MELLITUS - THE ROTTERDAM STUDY
VANDAELE, PLA; STOLK, RP; BURGER, H; ALGRA, D; GROBBEE, DE; HOFMAN, A; BIRKENHAGER, JC; POLS, HAP
1995-01-01
Objective: To investigate the relation between noninsulin-dependent diabetes mellitus and bone mineral density at the lumbar spine and hip. Design: Population-based study with a cross-sectional survey, Setting: A district of Rotterdam, the Netherlands. Participants: 5931 residents (2481 men, 3450
The ideal free distribution as an evolutionarily stable state in density-dependent population games
Czech Academy of Sciences Publication Activity Database
Cressman, R.; Křivan, Vlastimil
2010-01-01
Roč. 119, č. 8 (2010), s. 1231-1242 ISSN 0030-1299 R&D Projects: GA AV ČR IAA100070601 Institutional research plan: CEZ:AV0Z50070508 Keywords : density-dependent population games Subject RIV: EH - Ecology, Behaviour Impact factor: 3.393, year: 2010
Brunel, T.P.A.
2015-01-01
This report presents a framework to model density dependent growth for the North East Atlantic mackerel. The model used is the classical von Bertalanffy equation, but modified so that growth is reduced when stock size increases. The model developed was able to reproduce quite closely the trends in
Density dependence of the symmetry energy from neutron skin thickness in finite nuclei
International Nuclear Information System (INIS)
Viñas, X.; Centelles, M.; Roca-Maza, X.; Warda, M.
2012-01-01
The density dependence of the symmetry energy, characterized by the parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate of L is obtained from experimental data of antiprotonic atoms. We also discuss the ability of parity violating electron scatering to obtain information about the neutron skin thickness in 208 Pb.
Czech Academy of Sciences Publication Activity Database
Keil, P.; Herben, Tomáš; Rosindell, J.; Storch, D.
2010-01-01
Roč. 265, č. 1 (2010), s. 68-86 ISSN 0022-5193 R&D Projects: GA MŠk LC06073 Institutional research plan: CEZ:AV0Z60050516 Keywords : Taylor´s power law * density dependence * pink noise Subject RIV: EF - Botanics Impact factor: 2.371, year: 2010
Density-dependent home-range size revealed by spatially explicit capture–recapture
Efford, M.G.; Dawson, Deanna K.; Jhala, Y.V.; Qureshi, Q.
2016-01-01
The size of animal home ranges often varies inversely with population density among populations of a species. This fact has implications for population monitoring using spatially explicit capture–recapture (SECR) models, in which both the scale of home-range movements σ and population density D usually appear as parameters, and both may vary among populations. It will often be appropriate to model a structural relationship between population-specific values of these parameters, rather than to assume independence. We suggest re-parameterizing the SECR model using kp = σp √Dp, where kp relates to the degree of overlap between home ranges and the subscript p distinguishes populations. We observe that kp is often nearly constant for populations spanning a range of densities. This justifies fitting a model in which the separate kp are replaced by the single parameter k and σp is a density-dependent derived parameter. Continuous density-dependent spatial variation in σ may also be modelled, using a scaled non-Euclidean distance between detectors and the locations of animals. We illustrate these methods with data from automatic photography of tigers (Panthera tigris) across India, in which the variation is among populations, from mist-netting of ovenbirds (Seiurus aurocapilla) in Maryland, USA, in which the variation is within a single population over time, and from live-trapping of brushtail possums (Trichosurus vulpecula) in New Zealand, modelling spatial variation within one population. Possible applications and limitations of the methods are discussed. A model in which kp is constant, while density varies, provides a parsimonious null model for SECR. The parameter k of the null model is a concise summary of the empirical relationship between home-range size and density that is useful in comparative studies. We expect deviations from this model, particularly the dependence of kp on covariates, to be biologically interesting.
Bhambure, Rahul; Gillespie, Christopher M.; Phillips, Michael; Graalfs, Heiner; Lenhoff, Abraham M.
2016-01-01
The ligand density critically affects the performance of ion-exchange resins in such measures as the adsorption capacity and transport characteristics. However, for tentacular and other polymer-modified exchangers, the mechanistic basis of the effect of ligand density on performance is not yet fully understood. In this study we map the ionic strength-dependent structural changes in tentacular cation exchangers with variable ligand densities as the basis for subsequent investigation of effects on functional properties. Inverse size-exclusion chromatography (ISEC), scanning electron microscopy (SEM) and small-angle x-ray scattering (SAXS) were used to assess the effect of ionic strength on the pore size and intraparticle architecture of resin variants with different ligand densities. Comparison of ISEC and cryo-SEM results shows a considerable reduction in average pore size with increasing ligand density; these methods also confirm an increase of average pore size at higher ionic strengths. SAXS analysis of ionic strength-dependent conformational changes in the grafted polyelectrolyte layer shows a characteristic ionomer peak at values of the scattering vector q (0.1 < q < 0.2 Å−1) that depend on the ligand density and the ionic strength of the solution. This peak attribution reflects nanoscale changes in the structure of the grafted polyelectrolyte chains that can in turn be responsible for observed pore-size changes in the tentacular resins. Finally, salt breakthrough experiments confirm a stronger Donnan exclusion effect on pore accessibility for small ions in the high ligand density variant. PMID:27544749
Density Dependence of Particle Transport in ECH Plasmas of the TJ-II Stellarator
Energy Technology Data Exchange (ETDEWEB)
Vargas, V. I.; Lopez-Bruna, D.; Guasp, J.; Herranz, J.; Estrada, T.; Medina, F.; Ochando, M.A.; Velasco, J.L.; Reynolds, J.M.; Ferreira, J.A.; Tafalla, D.; Castejon, F.; Salas, A.
2009-05-21
We present the experimental dependence of particle transport on average density in electron cyclotron heated (ECH) hydrogen plasmas of the TJ-II stellarator. The results are based on: (I) electron density and temperature data from Thomson Scattering and reflectometry diagnostics; (II) a transport model that reproduces the particle density profiles in steady state; and (III) Eirene, a code for neutrals transport that calculates the particle source in the plasma from the particle confinement time and the appropriate geometry of the machine/plasma. After estimating an effective particle diffusivity and the particle confinement time, a threshold density separating qualitatively and quantitatively different plasma transport regimes is found. The poor confinement times found below the threshold are coincident with the presence of ECH-induced fast electron losses and a positive radial electric field all over the plasma. (Author) 40 refs.
Is contextual-potentiated eating dependent on caloric density of food?
Directory of Open Access Journals (Sweden)
Fernando Fernández-Aranda
2009-01-01
Full Text Available One experiment tested whether a specific context could elicit eating in rats as a result of Pavlovian conditioning and whether this effect depended on the caloric density of food. Thirty two deprived rats experienced two contexts. They had access to food in context A, but no food was available in context B. During conditioning, half of the animals received high density caloric food (HD groups whereas the other half, low density caloric food (LD groups. Then, half of the rats in each type of food group was tested in context A and the other half in context B. The results demonstrated an effect of context conditioning only in HD groups. These findings suggest the relevance of both contextual conditioning and caloric density of food in eating behaviour. Implications for the aetiology of binge eating will be discussed.
Sensitivity and uncertainty analysis for functionals of the time-dependent nuclide density field
International Nuclear Information System (INIS)
Williams, M.L.; Weisbin, C.R.
1978-04-01
An approach to extend the present ORNL sensitivity program to include functionals of the time-dependent nuclide density field is developed. An adjoint equation for the nuclide field was derived previously by using generalized perturbation theory; the present derivation makes use of a variational principle and results in the same equation. The physical significance of this equation is discussed and compared to that of the time-dependent neutron adjoint equation. Computational requirements for determining sensitivity profiles and uncertainties for functionals of the time-dependent nuclide density vector are developed within the framework of the existing FORSS system; in this way the current capability is significantly extended. The development, testing, and use of an adjoint version of the ORIGEN isotope generation and depletion code are documented. Finally, a sample calculation is given which estimates the uncertainty in the plutonium inventory at shutdown of a PWR due to assumed uncertainties in uranium and plutonium cross sections. 8 figures, 4 tables
Dependences of Ultrasonic Parameters for Osteoporosis Diagnosis on Bone Mineral Density
International Nuclear Information System (INIS)
Hwang, Kyo Seung; Kim, Yoon Mi; Park, Jong Chan; Choi, Min Joo; Lee, Kang Il
2012-01-01
Quantitative ultrasound technologies for osteoporosis diagnosis measure ultrasonic parameters such as speed of sound(SOS) and normalized broadband ultrasound attenuation(nBUA) in the calcaneus (heel bone). In the present study, the dependences of SOS and nBUA on bone mineral density in the proximal femur with high risk of fracture were investigated by using 20 trabecular bone samples extracted from bovine femurs. SOS and nBUA in the femoral trabecular bone samples were measured by using a transverse transmission method with one matched pair of ultrasonic transducers with a center frequency of 1.0 MHz. SOS and nBUA measured in the 20 trabecular bone samples exhibited high Pearson's correlation coefficients (r) of r = 0.83 and 0.72 with apparent bone density, respectively. The multiple regression analysis with SOS and nBUA as independent variables and apparent bone density as a dependent variable showed that the correlation coefficient r = 0.85 of the multiple linear regression model was higher than those of the simple linear regression model with either parameter SOS or nBUA as an independent variable. These high linear correlations between the ultrasonic parameters and the bone density suggest that the ultrasonic parameters measured in the femur can be useful for predicting the femoral bone mineral density.
Quorum sensing and density-dependent dispersal in an aquatic model system.
Directory of Open Access Journals (Sweden)
Simon Fellous
Full Text Available Many organisms use cues to decide whether to disperse or not, especially those related to the composition of their environment. Dispersal hence sometimes depends on population density, which can be important for the dynamics and evolution of sub-divided populations. But very little is known about the factors that organisms use to inform their dispersal decision. We investigated the cues underlying density-dependent dispersal in inter-connected microcosms of the freshwater protozoan Paramecium caudatum. In two experiments, we manipulated (i the number of cells per microcosm and (ii the origin of their culture medium (supernatant from high- or low-density populations. We found a negative relationship between population density and rates of dispersal, suggesting the use of physical cues. There was no significant effect of culture medium origin on dispersal and thus no support for chemical cues usage. These results suggest that the perception of density - and as a result, the decision to disperse - in this organism can be based on physical factors. This type of quorum sensing may be an adaptation optimizing small scale monitoring of the environment and swarm formation in open water.
Dependences of Ultrasonic Parameters for Osteoporosis Diagnosis on Bone Mineral Density
Energy Technology Data Exchange (ETDEWEB)
Hwang, Kyo Seung; Kim, Yoon Mi; Park, Jong Chan; Choi, Min Joo; Lee, Kang Il [Department of Physics, Kangwon National University, Chuncheon (Korea, Republic of)
2012-10-15
Quantitative ultrasound technologies for osteoporosis diagnosis measure ultrasonic parameters such as speed of sound(SOS) and normalized broadband ultrasound attenuation(nBUA) in the calcaneus (heel bone). In the present study, the dependences of SOS and nBUA on bone mineral density in the proximal femur with high risk of fracture were investigated by using 20 trabecular bone samples extracted from bovine femurs. SOS and nBUA in the femoral trabecular bone samples were measured by using a transverse transmission method with one matched pair of ultrasonic transducers with a center frequency of 1.0 MHz. SOS and nBUA measured in the 20 trabecular bone samples exhibited high Pearson's correlation coefficients (r) of r = 0.83 and 0.72 with apparent bone density, respectively. The multiple regression analysis with SOS and nBUA as independent variables and apparent bone density as a dependent variable showed that the correlation coefficient r = 0.85 of the multiple linear regression model was higher than those of the simple linear regression model with either parameter SOS or nBUA as an independent variable. These high linear correlations between the ultrasonic parameters and the bone density suggest that the ultrasonic parameters measured in the femur can be useful for predicting the femoral bone mineral density.
A consumer-resource approach to the density-dependent population dynamics of mutualism
Holland, J. Nathaniel; DeAngelis, Donald L.
2010-01-01
Like predation and competition, mutualism is now recognized as a consumer resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant- mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.
A Holling Type II Pest and Natural Enemy Model with Density Dependent IPM Strategy
Directory of Open Access Journals (Sweden)
Xia Wang
2017-01-01
Full Text Available Resource limitations and density dependent releasing of natural enemies during the pest control and integrated pest management will undoubtedly result in nonlinear impulsive control. In order to investigate the effects of those nonlinear control strategies on the successful pest control, we have proposed a pest-natural enemy system concerning integrated pest management with density dependent instant killing rate and releasing rate. In particular, the releasing rate depicts how the number of natural enemy populations released was guided by their current density at the fixed moment. The threshold condition which ensures the existence and global stability of pest-free periodic solution has been discussed first, and the effects of key parameters on the threshold condition reveal that reducing the pulse period does not always benefit pest control; that is, frequent releasing of natural enemies may not be beneficial to the eradication of pests when the density dependent releasing method has been implemented. Moreover, the forward and backward bifurcations could occur once the pest-free periodic solution becomes unstable, and the system could exist with very complex dynamics. All those results confirm that the control actions should be carefully designed once the nonlinear impulsive control measures have been taken for pest management.
Towards time-dependent current-density-functional theory in the non-linear regime.
Escartín, J M; Vincendon, M; Romaniello, P; Dinh, P M; Reinhard, P-G; Suraud, E
2015-02-28
Time-Dependent Density-Functional Theory (TDDFT) is a well-established theoretical approach to describe and understand irradiation processes in clusters and molecules. However, within the so-called adiabatic local density approximation (ALDA) to the exchange-correlation (xc) potential, TDDFT can show insufficiencies, particularly in violently dynamical processes. This is because within ALDA the xc potential is instantaneous and is a local functional of the density, which means that this approximation neglects memory effects and long-range effects. A way to go beyond ALDA is to use Time-Dependent Current-Density-Functional Theory (TDCDFT), in which the basic quantity is the current density rather than the density as in TDDFT. This has been shown to offer an adequate account of dissipation in the linear domain when the Vignale-Kohn (VK) functional is used. Here, we go beyond the linear regime and we explore this formulation in the time domain. In this case, the equations become very involved making the computation out of reach; we hence propose an approximation to the VK functional which allows us to calculate the dynamics in real time and at the same time to keep most of the physics described by the VK functional. We apply this formulation to the calculation of the time-dependent dipole moment of Ca, Mg and Na2. Our results show trends similar to what was previously observed in model systems or within linear response. In the non-linear domain, our results show that relaxation times do not decrease with increasing deposited excitation energy, which sets some limitations to the practical use of TDCDFT in such a domain of excitations.
Tarjuelo, Rocío; Morales, Manuel B; Arroyo, Beatriz; Mañosa, Santiago; Bota, Gerard; Casas, Fabián; Traba, Juan
2017-11-01
Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard ( Tetrax tetrax ) and the great bustard ( Otis tarda ) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density-dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co-occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density-dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.
Towards time-dependent current-density-functional theory in the non-linear regime
Energy Technology Data Exchange (ETDEWEB)
Escartín, J. M. [Université de Toulouse, UPS, Laboratoire de Physique Théorique, IRSAMC, F-31062 Toulouse Cedex (France); CNRS, UMR5152, F-31062 Toulouse Cedex (France); Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Vincendon, M.; Dinh, P. M.; Suraud, E. [Université de Toulouse, UPS, Laboratoire de Physique Théorique, IRSAMC, F-31062 Toulouse Cedex (France); CNRS, UMR5152, F-31062 Toulouse Cedex (France); Romaniello, P. [Laboratoire de Physique Théorique, CNRS, IRSAMC, Université Toulouse III - Paul Sabatier and European Theoretical Spectroscopy Facility, 118 Route de Narbonne, 31062 Toulouse Cedex (France); Reinhard, P.-G. [Institut für Theoretische Physik, Universität Erlangen, Staudtstraße 7, D-91058 Erlangen (Germany)
2015-02-28
Time-Dependent Density-Functional Theory (TDDFT) is a well-established theoretical approach to describe and understand irradiation processes in clusters and molecules. However, within the so-called adiabatic local density approximation (ALDA) to the exchange-correlation (xc) potential, TDDFT can show insufficiencies, particularly in violently dynamical processes. This is because within ALDA the xc potential is instantaneous and is a local functional of the density, which means that this approximation neglects memory effects and long-range effects. A way to go beyond ALDA is to use Time-Dependent Current-Density-Functional Theory (TDCDFT), in which the basic quantity is the current density rather than the density as in TDDFT. This has been shown to offer an adequate account of dissipation in the linear domain when the Vignale-Kohn (VK) functional is used. Here, we go beyond the linear regime and we explore this formulation in the time domain. In this case, the equations become very involved making the computation out of reach; we hence propose an approximation to the VK functional which allows us to calculate the dynamics in real time and at the same time to keep most of the physics described by the VK functional. We apply this formulation to the calculation of the time-dependent dipole moment of Ca, Mg and Na{sub 2}. Our results show trends similar to what was previously observed in model systems or within linear response. In the non-linear domain, our results show that relaxation times do not decrease with increasing deposited excitation energy, which sets some limitations to the practical use of TDCDFT in such a domain of excitations.
DEFF Research Database (Denmark)
Gavnholt, Jeppe; Rubio, Angel; Olsen, Thomas
2009-01-01
Using time-evolution time-dependent density functional theory (TDDFT) within the adiabatic local-density approximation, we study the interactions between single electrons and molecular resonances at surfaces. Our system is a nitrogen molecule adsorbed on a ruthenium surface. The surface is modeled...... at two levels of approximation, first as a simple external potential and later as a 20-atom cluster. We perform a number of calculations on an electron hitting the adsorbed molecule from inside the surface and establish a picture, where the resonance is being probed by the hot electron. This enables us...
International Nuclear Information System (INIS)
George, S.M.; Harris, C.B.
1982-01-01
The dependence of inhomogeneous vibrational linewidth broadening on attractive forces form slowly varying local liquid number densities is examined. The recently developed Schweizer--Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths. The computed linewidths are compared to measured inhomogeneous broadening linewidths determined using picosecond vibrational dephasing experiments. There is a similarity between correlations of the Schweizer--Chandler and George--Auweter--Harris predicted inhomogeneous broadening linewidths and the measured inhomogeneous broadening linewidths. For the methyl stretches under investigation, this correspondence suggests that the width of the number density distribution in the liquid determines the relative inhomogeneous broadening magnitudes
Strange matter equation of state in the quark mass-density-dependent model
International Nuclear Information System (INIS)
Benvenuto, O.G.; Lugones, G.
1995-01-01
We study the properties and stability of strange matter at T=0 in the quark mass-density-dependent model for noninteracting quarks. We found a wide ''stability window'' for the values of the parameters (C,M s0 ) and the resulting equation of state at low densities is stiffer than that of the MIT bag model. At high densities it tends to the ultrarelativistic behavior expected because of the asymptotic freedom of quarks. The density of zero pressure is near the one predicted by the bag model and not shifted away as stated before; nevertheless, at these densities the velocity of sound is ∼50% larger in this model than in the bag model. We have integrated the equations of stellar structure for strange stars with the present equation of state. We found that the mass-radius relation is very much the same as in the bag model, although it extends to more massive objects, due to the stiffening of the equation of state at low densities
Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus.
Directory of Open Access Journals (Sweden)
Judit Vas
Full Text Available Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e., distance travelled, nearest and furthest neighbour distance and activity budgets (e.g., resting, feeding, social activities were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period. The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation.
Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus)
Vas, Judit; Andersen, Inger Lise
2015-01-01
Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus) in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e. distance travelled, nearest and furthest neighbour distance) and activity budgets (e.g. resting, feeding, social activities) were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period). The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation. PMID:26657240
Non-linear density-dependent effects of an intertidal ecosystem engineer.
Harley, Christopher D G; O'Riley, Jaclyn L
2011-06-01
Ecosystem engineering is an important process in a variety of ecosystems. However, the relationship between engineer density and engineering impact remains poorly understood. We used experiments and a mathematical model to examine the role of engineer density in a rocky intertidal community in northern California. In this system, the whelk Nucella ostrina preys on barnacles (Balanus glandula and Chthamalus dalli), leaving empty barnacle tests as a resource (favorable microhabitat) for other species. Field experiments demonstrated that N. ostrina predation increased the availability of empty tests of both barnacle species, reduced the density of the competitively dominant B. glandula, and indirectly increased the density of the competitively inferior C. dalli. Empty barnacle tests altered microhabitat humidity, but not temperature, and presumably provided a refuge from wave action. The herbivorous snail Littorina plena was positively associated with empty test availability in both observational comparisons and experimental manipulations of empty test availability, and L. plena density was elevated in areas with foraging N. ostrina. To explore the effects of variation in N. ostrina predation, we constructed a demographic matrix model for barnacles in which we varied predation intensity. The model predicted that number of available empty tests increases with predation intensity to a point, but declines when predation pressure was strong enough to severely reduce adult barnacle densities. The modeled number of available empty tests therefore peaked at an intermediate level of N. ostrina predation. Non-linear relationships between engineer density and engineer impact may be a generally important attribute of systems in which engineers influence the population dynamics of the species that they manipulate.
A density-dependent effective interaction for relativistic Hartree-Fock calculations
International Nuclear Information System (INIS)
Marcos, S.; Mathiot, J.F.; Lopez-Quelle, M.; Niembro, R.; Bernardos, P.
1996-01-01
We present a general method to derive density-dependent effective interactions to be used in the relativistic Hartree-Fock approximation. In the non-relativistic limit (i.e. at low density), this method is identical to the usual variational ansatz with a two-body correlation function whose range is used as a variational parameter. At normal nuclear matter density, it provides a useful prescription to fit relativistic Brueckner-Hartree-Fock calculations. It provides in particular a physical way to deal with the zero-range pieces of π and ρ interactions in the medium. We apply our method to infinite symmetric nuclear matter. This effective interaction is also particularly well suited for calculations in finite nuclei. (orig.)
Alam, N.; Pais, H.; Providência, C.; Agrawal, B. K.
2017-05-01
The spinodal instabilities in hot asymmetric nuclear matter and some important critical parameters derived thereof are studied by using six different families of relativistic mean-field models. The slopes of the symmetry energy coefficient vary over a wide range within each family. The critical densities and proton fractions are more sensitive to the symmetry energy slope parameter at temperatures much below its critical value (Tc˜14 -16 MeV ). The spread in the critical proton fraction at a given symmetry energy slope parameter is noticeably larger near Tc, indicating that the equation of state of warm asymmetric nuclear matter at subsaturation densities is not sufficiently constrained. The distillation effects are sensitive to the density dependence of the symmetry energy at low temperatures which tend to wash out with increasing temperature.
Density-dependent changes in effective area occupied for sea-bottom-associated marine fishes
DEFF Research Database (Denmark)
Thorson, James T.; Rindorf, Anna; Gao, Jin
2016-01-01
The spatial distribution of marine fishes can change for many reasons, including density-dependent distributional shifts. Previous studies show mixed support for either the proportional-density model (PDM; no relationship between abundance and area occupied, supported by ideal-free distribution...... marine regions, to determine whether the BM or PDM provides a better description for sea-bottom-associated fishes. We fit a spatio-temporal model and estimate changes in effective area occupied and abundance, and combine results to estimate the average abundance–area relationship as well as variability......-third of combinations (34.6%) are predicted to increase in area more than 1% for every 10% increase in abundance. We therefore infer that population density generally changes faster than effective area occupied during abundance changes. Gadiformes have the strongest estimated relationship (average 1.0% area increase...
Two-component hybrid time-dependent density functional theory within the Tamm-Dancoff approximation
Energy Technology Data Exchange (ETDEWEB)
Kühn, Michael [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Weigend, Florian, E-mail: florian.weigend@kit.edu [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Institut für Nanotechnologie, Karlsruher Institut für Technologie, Postfach 3640, 76021 Karlsruhe (Germany)
2015-01-21
We report the implementation of a two-component variant of time-dependent density functional theory (TDDFT) for hybrid functionals that accounts for spin-orbit effects within the Tamm-Dancoff approximation (TDA) for closed-shell systems. The influence of the admixture of Hartree-Fock exchange on excitation energies is investigated for several atoms and diatomic molecules by comparison to numbers for pure density functionals obtained previously [M. Kühn and F. Weigend, J. Chem. Theory Comput. 9, 5341 (2013)]. It is further related to changes upon switching to the local density approximation or using the full TDDFT formalism instead of TDA. Efficiency is demonstrated for a comparably large system, Ir(ppy){sub 3} (61 atoms, 1501 basis functions, lowest 10 excited states), which is a prototype molecule for organic light-emitting diodes, due to its “spin-forbidden” triplet-singlet transition.
Energy Technology Data Exchange (ETDEWEB)
Li, J. W., E-mail: li-jiwei@iapcm.ac.cn; He, X. T. [Key Lab of High Energy Density Physics Simulation, Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094 (China); Kang, W. [Key Lab of High Energy Density Physics Simulation, Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Li, J. H.; Zheng, W. D. [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094 (China)
2015-12-15
In order to reduce the effect of laser imprint in direct-drive ignition scheme a low-density foam buffered target has been proposed. This target is driven by a laser pulse with a low-intensity foot at the early stage of implosion, which heats the foam and elongates the thermal conduction zone between the laser absorption region and ablation front, increasing the thermal smoothing effect. In this paper, a relatively strong foot pulse is adopted to irradiate the critical-density foam buffered target. The stronger foot, near 1 × 10{sup 14 }W/cm{sup 2}, is able to drive a radiative shock in the low-density foam, which helps smooth the shock and further reduce the effect of laser imprint. The radiative shock also forms a double ablation front structure between the two ablation fronts to further stabilize the hydrodynamics, achieving the similar results to a target with a high-Z dopant in the ablator. 2D analysis shows that for the critical-density foam buffered target irradiated by the strong foot pulse, the laser imprint can be reduced due to the radiative shock in the foam and an increased thermal smoothing effect. It seems viable for the critical-density foam buffered target to be driven by a relatively strong foot pulse with the goal of reducing the laser imprint and achieving better implosion symmetry in the direct-drive laser fusion.
International Nuclear Information System (INIS)
Li, J. W.; He, X. T.; Kang, W.; Li, J. H.; Zheng, W. D.
2015-01-01
In order to reduce the effect of laser imprint in direct-drive ignition scheme a low-density foam buffered target has been proposed. This target is driven by a laser pulse with a low-intensity foot at the early stage of implosion, which heats the foam and elongates the thermal conduction zone between the laser absorption region and ablation front, increasing the thermal smoothing effect. In this paper, a relatively strong foot pulse is adopted to irradiate the critical-density foam buffered target. The stronger foot, near 1 × 10 14 W/cm 2 , is able to drive a radiative shock in the low-density foam, which helps smooth the shock and further reduce the effect of laser imprint. The radiative shock also forms a double ablation front structure between the two ablation fronts to further stabilize the hydrodynamics, achieving the similar results to a target with a high-Z dopant in the ablator. 2D analysis shows that for the critical-density foam buffered target irradiated by the strong foot pulse, the laser imprint can be reduced due to the radiative shock in the foam and an increased thermal smoothing effect. It seems viable for the critical-density foam buffered target to be driven by a relatively strong foot pulse with the goal of reducing the laser imprint and achieving better implosion symmetry in the direct-drive laser fusion
DEFF Research Database (Denmark)
Lacevic, N.; Starr, F. W.; Schrøder, Thomas
2003-01-01
Relaxation in supercooled liquids above their glass transition and below the onset temperature of "slow" dynamics involves the correlated motion of neighboring particles. This correlated motion results in the appearance of spatially heterogeneous dynamics or "dynamical heterogeneity." Traditional...... two-point time-dependent density correlation functions, while providing information about the transient "caging" of particles on cooling, are unable to provide sufficiently detailed information about correlated motion and dynamical heterogeneity. Here, we study a four-point, time-dependent density......-q behavior of S4(q,t) provides an estimate of the range of correlated particle motion. We find that xi4(t) has a maximum as a function of time t, and that the value of the maximum of xi4(t) increases steadily from less than one particle diameter to a value exceeding nine particle diameters in the temperature...
Remarks on time-dependent [current]-density functional theory for open quantum systems.
Yuen-Zhou, Joel; Aspuru-Guzik, Alán
2013-08-14
Time-dependent [current]-density functional theory for open quantum systems (OQS) has emerged as a formalism that can incorporate dissipative effects in the dynamics of many-body quantum systems. Here, we review and clarify some formal aspects of these theories that have been recently questioned in the literature. In particular, we provide theoretical support for the following conclusions: (1) contrary to what we and others had stated before, within the master equation framework, there is in fact a one-to-one mapping between vector potentials and current densities for fixed initial state, particle-particle interaction, and memory kernel; (2) regardless of the first conclusion, all of our recently suggested Kohn-Sham (KS) schemes to reproduce the current and particle densities of the original OQS, and in particular, the use of a KS closed driven system, remains formally valid; (3) the Lindblad master equation maintains the positivity of the density matrix regardless of the time-dependence of the Hamiltonian or the dissipation operators; (4) within the stochastic Schrödinger equation picture, a one-to-one mapping from stochastic vector potential to stochastic current density for individual trajectories has not been proven so far, except in the case where the vector potential is the same for every member of the ensemble, in which case, it reduces to the Lindblad master equation picture; (5) master equations may violate certain desired properties of the density matrix, such as positivity, but they remain as one of the most useful constructs to study OQS when the environment is not easily incorporated explicitly in the calculation. The conclusions support our previous work as formally rigorous, offer new insights into it, and provide a common ground to discuss related theories.
Dependence of critical current density on crystalline direction in thin YBCO films
DEFF Research Database (Denmark)
Paturi, P.; Peurla, M.; Raittila, J.
2005-01-01
The dependence of critical current density (J(c)) on the angle between the current direction and the (100) direction in the ab-plane of thin YBCO films deposited on (001)-SrTiO3 from natiocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from...... the nanocrystalline target it is found that J(c) does not depend on the angle whereas J(c) decreases with increasing angle in the films made from the microcrystalline target. The films were characterized by detailed X-ray diffraction measurements. The findings are explained in terms of a network of planar defects...
Parton densities in quantum chromodynamics. Gauge invariance, path-dependence, and Wilson lines
Energy Technology Data Exchange (ETDEWEB)
Cherednikov, Igor O. [Antwerpen Univ. (Belgium). Dept. Fysica; Veken, Frederik F. van der [CERN, Geneva (Switzerland)
2017-05-01
The purpose of this book is to give a systematic pedagogical exposition of the quantitative analysis of Wilson lines and gauge-invariant correlation functions in quantum chromodynamics. Using techniques from the previous volume (Wilson Lines in Quantum Field Theory, 2014), an ab initio methodology is developed and practical tools for its implementation are presented. Emphasis is put on the implications of gauge invariance and path-dependence properties of transverse-momentum dependent parton density functions. The latter are associated with the QCD factorization approach to semi-inclusive hadronic processes, studied at currently operating and planned experimental facilities.
Dependence of capacitance of metal-molten salt interface on local density profiles near electrode
International Nuclear Information System (INIS)
Ballone, P.; Pastore, G.; Tosi, M.P.; Painter, K.R.; Grout, P.J.; March, N.H.
1983-09-01
The mean spherical approximation applied to a metal-molten salt interface is generalized to take further account of the local density profiles near the electrode. The temperature dependence of the differential capacitance is shown to arise, in large measure from such local structure. However, the hard wall assumption for the electrode is retained and this must be kept in mind in comparing our model results with experiment. (author)
Optical properties of Al nanostructures from time dependent density functional theory
Mokkath, Junais Habeeb
2016-04-05
The optical properties of Al nanostructures are investigated by means of time dependent density functional theory, considering chains of varying length and ladders/stripes of varying aspect ratio. The absorption spectra show redshifting for increasing length and aspect ratio. For the chains the absorption is dominated by HOMO → LUMO transitions, whereas ladders and stripes reveal more complex spectra of plasmonic nature above a specific aspect ratio.
Directory of Open Access Journals (Sweden)
Brock M Huntsman
Full Text Available Density-dependent (DD and density-independent (DI habitat selection is strongly linked to a species' evolutionary history. Determining the relative importance of each is necessary because declining populations are not always the result of altered DI mechanisms but can often be the result of DD via a reduced carrying capacity. We developed spatially and temporally explicit models throughout the Chena River, Alaska to predict important DI mechanisms that influence Chinook salmon spawning success. We used resource-selection functions to predict suitable spawning habitat based on geomorphic characteristics, a semi-distributed water-and-energy balance hydrologic model to generate stream flow metrics, and modeled stream temperature as a function of climatic variables. Spawner counts were predicted throughout the core and periphery spawning sections of the Chena River from escapement estimates (DD and DI variables. Additionally, we used isodar analysis to identify whether spawners actively defend spawning habitat or follow an ideal free distribution along the riverscape. Aerial counts were best explained by escapement and reference to the core or periphery, while no models with DI variables were supported in the candidate set. Furthermore, isodar plots indicated habitat selection was best explained by ideal free distributions, although there was strong evidence for active defense of core spawning habitat. Our results are surprising, given salmon commonly defend spawning resources, and are likely due to competition occurring at finer spatial scales than addressed in this study.
Energy Technology Data Exchange (ETDEWEB)
Kaneda, Y.; Ejiri, J. [Obayashi Corp., Tokyo (Japan)
1996-10-01
This paper describes simulation results of strong acceleration motion with varying uncertain fault parameters mainly for a fault model of Hyogo-ken Nanbu earthquake. For the analysis, based on the fault parameters, the strong acceleration motion was simulated using the radiation patterns and the breaking time difference of composite faults as parameters. A statistic waveform composition method was used for the simulation. For the theoretical radiation patterns, directivity was emphasized which depended on the strike of faults, and the maximum acceleration was more than 220 gal. While, for the homogeneous radiation patterns, the maximum accelerations were isotopically distributed around the fault as a center. For variations in the maximum acceleration and the predominant frequency due to the breaking time difference of three faults, the response spectral value of maximum/minimum was about 1.7 times. From the viewpoint of seismic disaster prevention, underground structures including potential faults and non-arranging properties can be grasped using this simulation. Significance of the prediction of strong acceleration motion was also provided through this simulation using uncertain factors, such as breaking time of composite faults, as parameters. 4 refs., 4 figs., 1 tab.
An investigation on the bone density of patients with non-insulin-dependent diabetes mellitus
International Nuclear Information System (INIS)
Guo Yan; Huang Zhaomin; Meng Quanfei; Da Rengrong; Zhang Suidong; Weng Jianping
1999-01-01
Objective: To investigate the morbidity and pattern of osteoporosis in the patients with non-insulin-dependent diabetes mellitus (NIDDM). Methods: Bone density of lumbar vertebra, hip and whole body were measured in 48 patients with NIDDM and in 35 health people aged 30-35 years. All the patients were diagnosed by the standards introduced by the WHO committee in 1985. Outcome were measured by using t text, analysis of variance and coefficient of multiple correlation. Results: Bone density decreased in all the 48 patients with NIDDM, in which 25 (52.1%) patients were diagnosed as osteoporosis. In the patients with NIDDM and osteoporosis, there was a higher rate of the decrease of the bone density of hip (14.1% in male and 15.6% in female respectively) than that of lumbar vertebra. Conclusions: There is a higher morbidity of osteoporosis in the patients with NIDDM. The loss of the bone density might start at the hip. The bone mineral content of whole body lose markedly. And the longer the NIDDM and the menopause exist, the more obvious the decrease of the bone density is. The mechanism of the phenomena is considered as a result of not only the increased loss of calcium and absorption of the bone tissue induced by the secondary hyperparathyroidism, but also the decreased level of the serum insulin-like growth factor, which inhibits the bone formation
Density and temperature dependence of carrier dynamics in self-organized InGaAs quantum dots
International Nuclear Information System (INIS)
Norris, T B; Kim, K; Urayama, J; Wu, Z K; Singh, J; Bhattacharya, P K
2005-01-01
We have used two- and three-pulse femtosecond differential transmission spectroscopy to study the dependence of quantum dot carrier dynamics on temperature. At low temperatures and densities, the rates for relaxation between the quantum dot confined states and for capture from the barrier region into the various dot levels could be directly determined. For electron-hole pairs generated directly in the quantum dot excited state, relaxation is dominated by electron-hole scattering, and occurs on a 5 ps time scale. Capture times from the barrier into the quantum dot are of the order of 2 ps (into the excited state) and 10 ps (into the ground state). The phonon bottleneck was clearly observed in low-density capture experiments, and the conditions for its observation (namely, the suppression of electron-hole scattering for nongeminately captured electrons) were determined. As temperature increases beyond about 100 K, the dynamics become dominated by the re-emission of carriers from the lower dot levels, due to the large density of states in the wetting layer and barrier region. Measurements of the gain dynamics show fast (130 fs) gain recovery due to intradot carrier-carrier scattering, and picosecond-scale capture. Direct measurement of the transparency density versus temperature shows the dramatic effect of carrier re-emission for the quantum dots on thermally activated scattering. The carrier dynamics at elevated temperature are thus strongly dominated by the high density of the high energy continuum states relative to the dot confined levels. Deleterious hot carrier effects can be suppressed in quantum dot lasers by resonant tunnelling injection
Choo, Juanita; Carasco, Cecilia; Alvarez-Loayza, Patricia; Simpson, Beryl B; Economo, Evan P
2017-07-01
Natural enemies are known to be important in regulating plant populations and contributing to species coexistence (Janzen-Connell effects). The strength of Janzen-Connell effects (both distance- and density-effects) varies across species, but the life history traits that may mediate such a variation are not well understood. This study examined Janzen-Connell effects across the life stages (seed through adult stages) of two sympatric palm species with distinct phenologies and shade tolerances, two traits that may mediate the strength and timing of Janzen-Connell effects. Populations of two common palm species, Attalea phalerata and Astrocaryum murumuru , were studied in Manu National Park, Peru. Seed predation experiments were conducted to assess Janzen-Connell effects at the seed stage. In the post-seed stages, spatial point pattern analyses of the distributions of individuals and biomass were used to infer the strength of distance- and density-effects. Seed predation was both negative distance- and density-dependent consistent with the Janzen-Connell effects. However, only seedling recruitment for asynchronously fruiting Attalea phalerata was depressed near adults while recruitment remained high for synchronously fruiting Astrocaryum murumuru , consistent with weak distance-effects. Negative density-effects were strong in the early stages for shade-intolerant Attalea phalerata but weak or absent in shade-tolerant Astrocaryum murumuru. Distance- and density-effects varied among the life stages of the two palm species in a manner that corresponded to their contrasting phenology and shade tolerance. Generalizing such connections across many species would provide a route to understanding how trait-mediated Janzen-Connell effects scale up to whole communities of species. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com
Directory of Open Access Journals (Sweden)
D T Tyler Flockhart
Full Text Available A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.
Flockhart, D T Tyler; Martin, Tara G; Norris, D Ryan
2012-01-01
A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus) in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.
International Nuclear Information System (INIS)
1998-10-01
The topics discussed comprise the onset of instability in heated free jets and jets with density gradients, flow past heated/cooled boundaries, atmospheric shear flow, and mathematical modeling of laminar-turbulent transition phenomena. Three contributions have been input to INIS. (P.A.)
Pandey, Namita; Pal, Soumyadip; Sharma, Lokesh Kumar; Guleria, Randeep; Mohan, Anant; Srivastava, Tapasya
2017-01-01
Background: The 15q24-25 loci contain genes (CHRNA5 and CHRNA3) encoding nicotinic acetylcholine receptor subunits. We here determined for the first time the association of genetic variants rs16969968 and rs3743074 in CHRNA5 and CHRNA3, respectively, on nicotine dependence and lung cancer risk in a North Indian population by a case-control approach. Methods: Venous blood samples were obtained from 324 participants (108 lung cancer patients and 216 healthy individuals). DNA was extracted and PCR amplified with primers flanking the SNPs rs16969968 and rs3743074. Amplicons were subjected to sequencing and logistic regression was used to analyze association between variables. Results: The risk variant SNP rs16969968 in both heterozygous and homozygous forms appeared to exert a significant effect on nicotine dependence [GA (OR=2.77) and AA (OR=2.53)]. As expected, smoking was strongly associated with lung cancer (OR= 2.62). Risk allele rs16969968 in CHRNA5 also showed a significant association with increased lung cancer risk in our cohort, alone (OR= 4.99) and with smoking as a co-variable (OR= 4.28). Comparison of our analysis with other populations suggested that individuals with rs16969968 risk allele in the Indian population are more susceptible to lung cancer. Conclusion: Overall, the results strongly indicated that, in our cohort North Indian population, the genetic variant rs16969968, but not rs3743074, is significantly associated with both nicotine dependence and increased risk of lung cancer. While the results are significant, there is further need to increase the sample size and improve precision of our risk prediction. PMID:29172281
Ueda, Shigenori; Hamada, Ikutaro
2017-12-01
The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.
McLoughlin, Philip D; Lysak, Kenton; Debeffe, Lucie; Perry, Thomas; Hobson, Keith A
2016-08-01
Sea-to-land nutrient transfers can connect marine food webs to those on land, creating a dependence on marine webs by opportunistic species. We show how nitrogen, imported by gray seals, Halichoerus grypus, and traced through stable isotope (δ 15 N) measurements in marram grass, Ammophila breviligulata, significantly alters foraging behavior of a free-roaming megaherbivore (feral horses, Equus ferus caballus) on Sable Island, Canada. Values of δ 15 N correlated with protein content of marram and strongly related to pupping-seal densities, and positively influenced selective foraging by horses. The latter was density dependent, consistent with optimal foraging theory. We present the first demonstration of how sea-to-land nutrient transfers can affect the behavioral process of resource selection (resource use relative to availability) of terrestrial consumers. We hypothesize that persistence of horses on Sable Island is being facilitated by N subsidies. Our results have relevance to advancing theory on trophic dynamics in island biogeography and metaecosystem ecology. © 2016 by the Ecological Society of America.
Resampling method for applying density-dependent habitat selection theory to wildlife surveys.
Tardy, Olivia; Massé, Ariane; Pelletier, Fanie; Fortin, Daniel
2015-01-01
Isodar theory can be used to evaluate fitness consequences of density-dependent habitat selection by animals. A typical habitat isodar is a regression curve plotting competitor densities in two adjacent habitats when individual fitness is equal. Despite the increasing use of habitat isodars, their application remains largely limited to areas composed of pairs of adjacent habitats that are defined a priori. We developed a resampling method that uses data from wildlife surveys to build isodars in heterogeneous landscapes without having to predefine habitat types. The method consists in randomly placing blocks over the survey area and dividing those blocks in two adjacent sub-blocks of the same size. Animal abundance is then estimated within the two sub-blocks. This process is done 100 times. Different functional forms of isodars can be investigated by relating animal abundance and differences in habitat features between sub-blocks. We applied this method to abundance data of raccoons and striped skunks, two of the main hosts of rabies virus in North America. Habitat selection by raccoons and striped skunks depended on both conspecific abundance and the difference in landscape composition and structure between sub-blocks. When conspecific abundance was low, raccoons and striped skunks favored areas with relatively high proportions of forests and anthropogenic features, respectively. Under high conspecific abundance, however, both species preferred areas with rather large corn-forest edge densities and corn field proportions. Based on random sampling techniques, we provide a robust method that is applicable to a broad range of species, including medium- to large-sized mammals with high mobility. The method is sufficiently flexible to incorporate multiple environmental covariates that can reflect key requirements of the focal species. We thus illustrate how isodar theory can be used with wildlife surveys to assess density-dependent habitat selection over large
Stocking density affects the growth performance of broilers in a sex-dependent fashion.
Zuowei, S; Yan, L; Yuan, L; Jiao, H; Song, Z; Guo, Y; Lin, H
2011-07-01
The effects of stocking density, sex, and dietary ME concentration on live performance, footpad burns, and leg weakness of broilers were investigated. A total of 876 male and 1,020 female 1-d-old chicks were placed in 24 pens to simulate final stocking density treatments of 26 kg (LSD; 10 males or 12 females/m(2)) and 42 kg (HSD; 16 males or 18 females/m(2)) of BW/m(2) floor space. Two series of experimental diets with a 150 kcal/kg difference in ME concentration (2,800, 2,900, and 3,000 or 2,950, 3,050, and 3,150 kcal of ME/kg) were compared in a 3-phase feeding program. The HSD treatment significantly decreased BW gain and feed conversion ratio (FCR). The HSD chickens consumed less feed by 35 d of age; thereafter, the reverse was true. Male chickens had significantly higher feed intake (FI), BW gain, and FCR compared with females. A significant interaction was found of stocking density and age for FI, BW gain, and FCR. Compared with LSD treatment, HSD broilers had a higher FI and a lower FCR from 36 to 42 d of age. Stocking density, sex, and age had a significant interaction for BW gain and FCR. Female broilers had worse BW gain and FCR when stocked at high density from 36 to 42 d of age. Stocking density had no significant influence on breast, thigh, or abdominal fat yield. Female broilers had significantly higher breast yield and abdominal fat. Male broilers and HSD treatment had high footpad burn and gait scores. A low ME diet increased footpad burn score but had no effect on gait score. The result indicated that stocking density had a more severe effect on the growth of male broilers before 35 d of age. Female broilers need more space than males at similar BW per square meter near marketing age. The incidence and severity of leg weakness are associated with sex, diet, and stocking density. This result suggests that the deteriorated effect of high stocking density is sex and age dependent.
Hibbard, Bruce E; Meihls, Lisa N; Ellersieck, Mark R; Onstad, David W
2010-02-01
The percentage of viable eggs of the western corn rootworm, Diabrotica virgifera virgifera LeConte, which survived to the adult stage was evaluated for the effect of egg density in 2005 and 2007 in central Missouri. In 2005, each plot was 2.44 by 3.05 m and contained 64 maize (corn), Zea mays L., plants. In 2007, plots were 3.05 by 3.05 m and again contained 64 corn plants. Seven egg densities (2,400, 1,200, 600, 300, 100, 50, and 25 viable eggs per 30.5 cm) were evaluated with four to six replications in each year in a completely randomized design. In 2007 only, an additional row was infested near each plot to evaluate plant damage. In both years, there was no correlation of infestation level and percentage of emergence between infestation levels of 25-600 viable eggs per 30.5 cm, indicating that density-dependent mortality did not occur at these egg densities. In 2005, 8.04% of the viable eggs established on a corn plant and produced an adult at these lower infestation rates. In 2007, this value was 2.9%. Regardless of egg density, approximately 92-97% failed to establish and produce adults (density-independent mortality). In 2005 and in the combined analysis, as viable egg densities increased from 600 to 2400 per 30.5 cm there was a significant decrease in percentage of emergence. In a broken line analysis of the 2005 data, the point where density-dependent mortality began in the combined analysis was 851 eggs per 30.5 cm with a 95% confidence interval from 678 to 1024. That year density-dependent mortality was important at high infestations and killed 54.4% of those larvae that successfully established on a plant at the highest egg density. However, little or no density-dependent mortality occurred at infestation levels corn rootworm.
Pagán, Israel; Alonso-Blanco, Carlos; García-Arenal, Fernando
2009-07-01
Population density and costs of parasite infection may condition the capacity of organisms to grow, survive and reproduce, i.e. their competitive ability. In host-parasite systems there are different competitive interactions: among uninfected hosts, among infected hosts, and between uninfected and infected hosts. Consequently, parasite infection results in a direct cost, due to parasitism itself, and in an indirect cost, due to modification of the competitive ability of the infected host. Theory predicts that host fitness reduction will be higher under the combined effects of costs of parasitism and competition than under each factor separately. However, experimental support for this prediction is scarce, and derives mostly from animal-parasite systems. We have analysed the interaction between parasite infection and plant density using the plant-parasite system of Arabidopsis thaliana and the generalist virus Cucumber mosaic virus (CMV). Plants of three wild genotypes grown at different densities were infected by CMV at various prevalences, and the effects of infection on plant growth and reproduction were quantified. Results demonstrate that the combined effects of host density and parasite infection may result either in a reduction or in an increase of the competitive ability of the host. The two genotypes investing a higher proportion of resources to reproduction showed tolerance to the direct cost of infection, while the genotype investing a higher proportion of resources to growth showed tolerance to the indirect cost of infection. Our findings show that the outcome of the interaction between host density and parasitism depends on the host genotype, which determines the plasticity of life-history traits and consequently, the host capacity to develop different tolerance mechanisms to the direct or indirect costs of parasitism. These results indicate the high relevance of host density and parasitism in determining the competitive ability of a plant, and stress
Directory of Open Access Journals (Sweden)
Israel Pagán
2009-07-01
Full Text Available Population density and costs of parasite infection may condition the capacity of organisms to grow, survive and reproduce, i.e. their competitive ability. In host-parasite systems there are different competitive interactions: among uninfected hosts, among infected hosts, and between uninfected and infected hosts. Consequently, parasite infection results in a direct cost, due to parasitism itself, and in an indirect cost, due to modification of the competitive ability of the infected host. Theory predicts that host fitness reduction will be higher under the combined effects of costs of parasitism and competition than under each factor separately. However, experimental support for this prediction is scarce, and derives mostly from animal-parasite systems. We have analysed the interaction between parasite infection and plant density using the plant-parasite system of Arabidopsis thaliana and the generalist virus Cucumber mosaic virus (CMV. Plants of three wild genotypes grown at different densities were infected by CMV at various prevalences, and the effects of infection on plant growth and reproduction were quantified. Results demonstrate that the combined effects of host density and parasite infection may result either in a reduction or in an increase of the competitive ability of the host. The two genotypes investing a higher proportion of resources to reproduction showed tolerance to the direct cost of infection, while the genotype investing a higher proportion of resources to growth showed tolerance to the indirect cost of infection. Our findings show that the outcome of the interaction between host density and parasitism depends on the host genotype, which determines the plasticity of life-history traits and consequently, the host capacity to develop different tolerance mechanisms to the direct or indirect costs of parasitism. These results indicate the high relevance of host density and parasitism in determining the competitive ability of a
Density-dependent reduction and induction of milkweed cardenolides by a sucking insect herbivore.
Martel, John W; Malcolm, Stephen B
2004-03-01
The effect of aphid population size on host-plant chemical defense expression and the effect of plant defense on aphid population dynamics were investigated in a milkweed-specialist herbivore system. Density effects of the aposematic oleander aphid, Aphis nerii, on cardenolide expression were measured in two milkweed species, Asclepias curassavica and A. incarnata. These plants vary in constitutive chemical investment with high mean cardenolide concentration in A. curassavica and low to zero in A. incarnata. The second objective was to determine whether cardenolide expression in these two host plants impacts mean A. nerii colony biomass (mg) and density. Cardenolide concentration (microgram/g) of A. curassavica in both aphid-treated leaves and opposite, herbivore-free leaves decreased initially in comparison with aphid-free controls, and then increased significantly with A. nerii density. Thus, A. curassavica responds to aphid herbivory initially with density-dependent phytochemical reduction, followed by induction of cardenolides to concentrations above aphid-free controls. In addition, mean cardenolide concentration of aphid-treated leaves was significantly higher than that of opposite, herbivore-free leaves. Therefore, A. curassavica induction is strongest in herbivore-damage tissue. Conversely, A. incarnata exhibited no such chemical response to aphid herbivory. Furthermore, neither host plant responded chemically to herbivore feeding duration time (days) or to the interaction between herbivore initial density and feeding duration time. There were also no significant differences in mean colony biomass or population density of A. nerii reared on high cardenolide (A. curassavica) and low cardenolide (A. incarnata) hosts.
DEFF Research Database (Denmark)
Brandslund, Ivan; Nielsen, Aneta Aleksandra; Hyldtoft Petersen, Per
HbA1c as the diagnostic criterion for diabetes reduces incidence and prevalence of DM2 by 25% but strongly depending on analytical quality......HbA1c as the diagnostic criterion for diabetes reduces incidence and prevalence of DM2 by 25% but strongly depending on analytical quality...
Directory of Open Access Journals (Sweden)
Fengguo Liu
2018-03-01
Full Text Available Ionic liquids are considered environmentally friendly media for various industrial applications. Basic data on physicochemical properties are significant for a new material, in terms of developing its potential applications. In this work, 1-ethyl-3-methylimidazolium fluoride ([EMIm]F ionic liquid was synthesized via an anion metathesis process. Physical properties including the density, viscosity, electrical conductivity, and thermal stability of the product were measured. The results show that the density of [EMIm]F decreases linearly with temperature increases, while dynamic viscosity decreases rapidly below 320 K and the temperature dependence of electrical conductivity is in accordance with the VFT (Vogel–Fulcher–Tammann equation. The temperature dependence of the density, conductivity, and viscosity of [EMIm]F can be expressed via the following equations: ρ = 1.516 − 1.22 × 10−3 T, σm = 4417.1exp[−953.17/(T − 166.65] and η = 2.07 × 10−7exp(−5.39 × 104/T, respectively. [EMIm]F exhibited no clear melting point. However, its glass transition point and decomposition temperature are −71.3 °C and 135 °C, respectively.
Carleo, Giuseppe; Cevolani, Lorenzo; Sanchez-Palencia, Laurent; Holzmann, Markus
2017-07-01
We introduce the time-dependent variational Monte Carlo method for continuous-space Bose gases. Our approach is based on the systematic expansion of the many-body wave function in terms of multibody correlations and is essentially exact up to adaptive truncation. The method is benchmarked by comparison to an exact Bethe ansatz or existing numerical results for the integrable Lieb-Liniger model. We first show that the many-body wave function achieves high precision for ground-state properties, including energy and first-order as well as second-order correlation functions. Then, we study the out-of-equilibrium, unitary dynamics induced by a quantum quench in the interaction strength. Our time-dependent variational Monte Carlo results are benchmarked by comparison to exact Bethe ansatz results available for a small number of particles, and are also compared to quench action results available for noninteracting initial states. Moreover, our approach allows us to study large particle numbers and general quench protocols, previously inaccessible beyond the mean-field level. Our results suggest that it is possible to find correlated initial states for which the long-term dynamics of local density fluctuations is close to the predictions of a simple Boltzmann ensemble.
Noise-induced extinction for a ratio-dependent predator-prey model with strong Allee effect in prey
Mandal, Partha Sarathi
2018-04-01
In this paper, we study a stochastically forced ratio-dependent predator-prey model with strong Allee effect in prey population. In the deterministic case, we show that the model exhibits the stable interior equilibrium point or limit cycle corresponding to the co-existence of both species. We investigate a probabilistic mechanism of the noise-induced extinction in a zone of stable interior equilibrium point. Computational methods based on the stochastic sensitivity function technique are applied for the analysis of the dispersion of random states near stable interior equilibrium point. This method allows to construct a confidence domain and estimate the threshold value of the noise intensity for a transition from the coexistence to the extinction.
van Meer, R; Gritsenko, O V; Baerends, E J
2017-01-28
Straightforward interpretation of excitations is possible if they can be described as simple single orbital-to-orbital (or double, etc.) transitions. In linear response time-dependent density functional theory (LR-TDDFT), the (ground state) Kohn-Sham orbitals prove to be such an orbital basis. In contrast, in a basis of natural orbitals (NOs) or Hartree-Fock orbitals, excitations often employ many orbitals and are accordingly hard to characterize. We demonstrate that it is possible in these cases to transform to natural excitation orbitals (NEOs) which resemble very closely the KS orbitals and afford the same simple description of excitations. The desired transformation has been obtained by diagonalization of a submatrix in the equations of linear response time-dependent 1-particle reduced density matrix functional theory (LR-TDDMFT) for the NO transformation, and that of a submatrix in the linear response time-dependent Hartree-Fock (LR-TDHF) equations for the transformation of HF orbitals. The corresponding submatrix is already diagonal in the KS basis in the LR-TDDFT equations. While the orbital shapes of the NEOs afford the characterization of the excitations as (mostly) simple orbital-to-orbital transitions, the orbital energies provide a fair estimate of excitation energies.
Time-dependent current-density functional theory for generalized open quantum systems.
Yuen-Zhou, Joel; Rodríguez-Rosario, César; Aspuru-Guzik, Alán
2009-06-14
In this article, we prove the one-to-one correspondence between vector potentials and particle and current densities in the context of master equations with arbitrary memory kernels, therefore extending time-dependent current-density functional theory (TD-CDFT) to the domain of generalized many-body open quantum systems (OQS). We also analyse the issue of A-representability for the Kohn-Sham (KS) scheme proposed by D'Agosta and Di Ventra for Markovian OQS [Phys. Rev. Lett. 2007, 98, 226403] and discuss its domain of validity. We suggest ways to expand their scheme, but also propose a novel KS scheme where the auxiliary system is both closed and non-interacting. This scheme is tested numerically with a model system, and several considerations for the future development of functionals are indicated. Our results formalize the possibility of practising TD-CDFT in OQS, hence expanding the applicability of the theory to non-Hamiltonian evolutions.
Cui, Ganglong; Fang, Weihai; Yang, Weitao
2010-01-14
Time-dependent density functional theory (TDDFT) has broad application in the study of electronic response, excitation and transport. To extend such application to large and complex systems, we develop a reformulation of TDDFT equations in terms of non-orthogonal localized molecular orbitals (NOLMOs). NOLMO is the most localized representation of electronic degrees of freedom and has been used in ground state calculations. In atomic orbital (AO) representation, the sparsity of NOLMO is transferred to the coefficient matrix of molecular orbitals (MOs). Its novel use in TDDFT here leads to a very simple form of time propagation equations which can be solved with linear-scaling effort. We have tested the method for several long-chain saturated and conjugated molecular systems within the self-consistent charge density-functional tight-binding method (SCC-DFTB) and demonstrated its accuracy. This opens up pathways for TDDFT applications to large bio- and nano-systems.
Energy Technology Data Exchange (ETDEWEB)
Kao, C.H.; Tsou, C.T.; Chen, C.C.; Wang, S.J. (Taichung Veterans General Hospital, Taiwan (China))
1993-05-01
Bone mineral density (BMD) in 38 male patients with noninsulin-dependent diabetes mellitus (NIDDM) was measured by dual photon absorptiometry (DPA) using a M and SE Osteo Tech 300 scanner. The BMD of the second to fourth lumbar vertebrae was measured and the mean density was presented as g cm[sup -2]. The patients were distinguished according to the following three criteria: (1) blood sugar control was good or poor; (2) the duration of diabetes was long or short; (3) renal function was evaluated by effective renal plasma flow (ERPF) as good or poor. The results showed about half the cases of NIDDM had lower BMD. The patients with poor blood sugar control, longer disease duration and poor renal function had lower BMD. However, the difference between any two groups distinguished by the three criteria is not significant. We think that the causes of osteoporosis in patients with NIDDM may not be explained by only a single factor. (author).
International Nuclear Information System (INIS)
Kao, C.H.; Tsou, C.T.; Chen, C.C.; Wang, S.J.
1993-01-01
Bone mineral density (BMD) in 38 male patients with noninsulin-dependent diabetes mellitus (NIDDM) was measured by dual photon absorptiometry (DPA) using a M and SE Osteo Tech 300 scanner. The BMD of the second to fourth lumbar vertebrae was measured and the mean density was presented as g cm -2 . The patients were distinguished according to the following three criteria: (1) blood sugar control was good or poor; (2) the duration of diabetes was long or short; (3) renal function was evaluated by effective renal plasma flow (ERPF) as good or poor. The results showed about half the cases of NIDDM had lower BMD. The patients with poor blood sugar control, longer disease duration and poor renal function had lower BMD. However, the difference between any two groups distinguished by the three criteria is not significant. We think that the causes of osteoporosis in patients with NIDDM may not be explained by only a single factor. (author)
International Nuclear Information System (INIS)
Hong, Soon Cheol; Lee, Jae Il; Wu, Ruqian
2007-01-01
In order to investigate the magnetism of palladium nano-films, we performed first-principles calculations employing the highly precise full-potential linerized augmented plane-wave method based on density functional theory. The magnetism is investigated as a function of the thickness of the Pd thickness within a range of 1-21 monolayers. The magnetic stability of the Pd nano-films is calculated to depend delicately on its thickness. The ferromagnetic state is calculated to be stable for only some particular thicknesses of 1, 3, 9, and 15 layers. Invoking the ferromagnetism is not due to the localization at the surface but to the high density of states (DOS) at Fermi energy at the second layer from the surface
Effect of deformation and orientation on spin orbit density dependent nuclear potential
Mittal, Rajni; Kumar, Raj; Sharma, Manoj K.
2017-11-01
Role of deformation and orientation is investigated on spin-orbit density dependent part VJ of nuclear potential (VN=VP+VJ) obtained within semi-classical Thomas Fermi approach of Skyrme energy density formalism. Calculations are performed for 24-54Si+30Si reactions, with spherical target 30Si and projectiles 24-54Si having prolate and oblate shapes. The quadrupole deformation β2 is varying within range of 0.023 ≤ β2 ≤0.531 for prolate and -0.242 ≤ β2 ≤ -0.592 for oblate projectiles. The spin-orbit dependent potential gets influenced significantly with inclusion of deformation and orientation effect. The spin-orbit barrier and position gets significantly influenced by both the sign and magnitude of β2-deformation. Si-nuclei with β220. The possible role of spin-orbit potential on barrier characteristics such as barrier height, barrier curvature and on the fusion pocket is also probed. In reference to prolate and oblate systems, the angular dependence of spin-orbit potential is further studied on fusion cross-sections.
Size-dependent error of the density functional theory ionization potential in vacuum and solution
Energy Technology Data Exchange (ETDEWEB)
Sosa Vazquez, Xochitl A.; Isborn, Christine M., E-mail: cisborn@ucmerced.edu [Chemistry and Chemical Biology, School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343 (United States)
2015-12-28
Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potential for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. In vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.
Size-dependent Young’s modulus in ZnO nanowires with strong surface atomic bonds
Fan, Shiwen; Bi, Sheng; Li, Qikun; Guo, Qinglei; Liu, Junshan; Ouyang, Zhongliang; Jiang, Chengming; Song, Jinhui
2018-03-01
The mechanical properties of size-dependent nanowires are important in nano-electro-mechanical systems (NEMSs), and have attracted much research interest. Characterization of the size effect of nanowires in atmosphere directly to broaden their practical application instead of just in high vacuum situations, as reported previously, is desperately needed. In this study, we systematically studied the Young’s modulus of vertical ZnO nanowires in atmosphere. The diameters ranged from 48 nm to 239 nm with a resonance method using non-contact atomic force microscopy. The values of Young’s modulus in atmosphere present extremely strong increasing tendency with decreasing diameter of nanowire due to stronger surface atomic bonds compared with that in vacuum. A core-shell model for nanowires is proposed to explore the Young’s modulus enhancement in atmosphere, which is correlated with atoms of oxygen occurring near the nanowire surface. The modified model is more accurate for analyzing the mechanical behavior of nanowires in atmosphere compared with the model in vacuum. Furthermore, it is possible to use this characterization method to measure the size-related elastic properties of similar wire-sharp nanomaterials in atmosphere and estimate the corresponding mechanical behavior. The study of the size-dependent Young’s modulus in ZnO nanowires in atmosphere will improve the understanding of the mechanical properties of nanomaterials as well as providing guidance for applications in NEMSs, nanogenerators, biosensors and other related areas.
Bijleveld, Allert I; MacCurdy, Robert B; Chan, Ying-Chi; Penning, Emma; Gabrielson, Rich M; Cluderay, John; Spaulding, Eric L; Dekinga, Anne; Holthuijsen, Sander; ten Horn, Job; Brugge, Maarten; van Gils, Jan A; Winkler, David W; Piersma, Theunis
2016-04-13
Negative density-dependence is generally studied within a single trophic level, thereby neglecting its effect on higher trophic levels. The 'functional response' couples a predator's intake rate to prey density. Most widespread is a type II functional response, where intake rate increases asymptotically with prey density; this predicts the highest predator densities at the highest prey densities. In one of the most stringent tests of this generality to date, we measured density and quality of bivalve prey (edible cockles Cerastoderma edule) across 50 km² of mudflat, and simultaneously, with a novel time-of-arrival methodology, tracked their avian predators (red knots Calidris canutus). Because of negative density-dependence in the individual quality of cockles, the predicted energy intake rates of red knots declined at high prey densities (a type IV, rather than a type II functional response). Resource-selection modelling revealed that red knots indeed selected areas of intermediate cockle densities where energy intake rates were maximized given their phenotype-specific digestive constraints (as indicated by gizzard mass). Because negative density-dependence is common, we question the current consensus and suggest that predators commonly maximize their energy intake rates at intermediate prey densities. Prey density alone may thus poorly predict intake rates, carrying capacity and spatial distributions of predators. © 2016 The Author(s).
Time-Dependent Density Functional Theory for Open Systems and Its Applications.
Chen, Shuguang; Kwok, YanHo; Chen, GuanHua
2018-02-20
Photovoltaic devices, electrochemical cells, catalysis processes, light emitting diodes, scanning tunneling microscopes, molecular electronics, and related devices have one thing in common: open quantum systems where energy and matter are not conserved. Traditionally quantum chemistry is confined to isolated and closed systems, while quantum dissipation theory studies open quantum systems. The key quantity in quantum dissipation theory is the reduced system density matrix. As the reduced system density matrix is an O(M! × M!) matrix, where M is the number of the particles of the system of interest, quantum dissipation theory can only be employed to simulate systems of a few particles or degrees of freedom. It is thus important to combine quantum chemistry and quantum dissipation theory so that realistic open quantum systems can be simulated from first-principles. We have developed a first-principles method to simulate the dynamics of open electronic systems, the time-dependent density functional theory for open systems (TDDFT-OS). Instead of the reduced system density matrix, the key quantity is the reduced single-electron density matrix, which is an N × N matrix where N is the number of the atomic bases of the system of interest. As the dimension of the key quantity is drastically reduced, the TDDFT-OS can thus be used to simulate the dynamics of realistic open electronic systems and efficient numerical algorithms have been developed. As an application, we apply the method to study how quantum interference develops in a molecular transistor in time domain. We include electron-phonon interaction in our simulation and show that quantum interference in the given system is robust against nuclear vibration not only in the steady state but also in the transient dynamics. As another application, by combining TDDFT-OS with Ehrenfest dynamics, we study current-induced dissociation of water molecules under scanning tunneling microscopy and follow its time dependent
Critique of the foundations of time-dependent density-functional theory
International Nuclear Information System (INIS)
Schirmer, J.; Dreuw, A.
2007-01-01
The general expectation that, in principle, the time-dependent density-functional theory (TDDFT) is an exact formulation of the time evolution of an interacting N-electron system is critically reexamined. It is demonstrated that the previous TDDFT foundation, resting on four theorems by Runge and Gross (RG) [Phys. Rev. Lett. 52, 997 (1984)], is invalid because undefined phase factors corrupt the RG action integral functionals. Our finding confirms much of a previous analysis by van Leeuwen [Int. J. Mod. Phys. B 15, 1969 (2001)]. To analyze the RG theorems and other aspects of TDDFT, an utmost simplification of the Kohn-Sham (KS) concept has been introduced, in which the ground-state density is obtained from a single KS equation for one spatial (spinless) orbital. The time-dependent (TD) form of this radical Kohn-Sham (rKS) scheme, which has the same validity status as the ordinary KS version, has proved to be a valuable tool for analysis. The rKS concept is used to clarify also the alternative nonvariational formulation of TD KS theory. We argue that it is just a formal theory, allowing one to reproduce but not predict the time development of the exact density of the interacting N-electron system. Besides the issue of the formal exactness of TDDFT, it is shown that both the static and time-dependent KS linear response equations neglect the particle-particle (p-p) and hole-hole (h-h) matrix elements of the perturbing operator. For a local (multiplicative) operator this does not lead to a loss of information due to a remarkable general property of local operators. Accordingly, no logical inconsistency arises with respect to DFT, because DFT requires any external potential to be local. For a general nonlocal operator the error resulting from the neglected matrix elements is of second order in the electronic repulsion
Huntsman, Brock M.; Petty, J. Todd
2014-01-01
Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3–60 km2 and long-term average densities ranging from 0.335–0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for
Huntsman, Brock M; Petty, J Todd
2014-01-01
Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3-60 km(2) and long-term average densities ranging from 0.335-0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for
Directory of Open Access Journals (Sweden)
Brock M Huntsman
Full Text Available Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3-60 km(2 and long-term average densities ranging from 0.335-0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to
Time-dependent density functional theory for open quantum systems with unitary propagation.
Yuen-Zhou, Joel; Tempel, David G; Rodríguez-Rosario, César A; Aspuru-Guzik, Alán
2010-01-29
We extend the Runge-Gross theorem for a very general class of open quantum systems under weak assumptions about the nature of the bath and its coupling to the system. We show that for Kohn-Sham (KS) time-dependent density functional theory, it is possible to rigorously include the effects of the environment within a bath functional in the KS potential. A Markovian bath functional inspired by the theory of nonlinear Schrödinger equations is suggested, which can be readily implemented in currently existing real-time codes. Finally, calculations on a helium model system are presented.
Tao, Jianmin; Tretiak, Sergei; Zhu, Jian-Xin
2010-01-01
With technological advances, light-emitting conjugated oligomers and polymers have become competitive candidates in the commercial market of light-emitting diodes for display and other technologies, due to the ultralow cost, light weight, and flexibility. Prediction of excitation energies of these systems plays a crucial role in the understanding of their optical properties and device design. In this review article, we discuss the calculation of excitation energies with time-dependent density functional theory, which is one of the most successful methods in the investigation of the dynamical response of molecular systems to external perturbation, owing to its high computational efficiency.
Weed, Aaron S; Elkinton, Joseph S; Lany, Nina K
2016-12-01
Insect populations are affected by density-dependent and density-independent factors, and knowing how these factors affect long-term population growth is critical to pest management. In this study, we experimentally manipulated densities of the hemlock woolly adelgid on eastern and western hemlock trees in the western USA to evaluate the effects of density and host species on hemlock woolly adelgid crawler colonization. We then followed development of hemlock woolly adelgid on each hemlock species. Settlement of crawlers was strongly density-dependent and consistent between host species. In addition, a period of hot days that coincided with the settlement of hemlock woolly adelgid crawlers put our experimental and naturally occurring populations into diapause during April. Diapause resulted in one generation that yr in our experimental population. Analyses of long-term air temperature records indicated that diapause-inducing temperatures in April similar to those observed in our experiment have occurred rarely since 1909 and the frequency of these events has not changed over time. Prior work suggests that hemlock woolly adelgid completes two generations per yr in the western USA with a diapause occurring in the summer. This typical life history reflects the long-term influence of regional average seasonal temperature patterns on development and the timing of diapause-inducing temperatures. However, the timing of unseasonal weather, such as the hot days observed in our experiment, occasionally changes life history trajectories from this normal pattern. Our results show that density-dependent and density-independent factors have strong effects on generational mortality and life history of hemlock woolly adelgid that are important to its population dynamics and management. Published by Oxford University Press on behalf of Entomological Society of America 2016. This work is written by US Government employees and is in the public domain in the US.
Litwin, K. L.; Beyeler, J. D.; Polito, P. J.; Zygielbaum, B. R.; Sklar, L. S.; Collins, G. C.
2009-12-01
The tensile strength of ice bedrock on Titan should strongly influence the effectiveness of the erosional processes responsible for carving the extensive fluvial drainage networks and other surface features visible in images returned by the Cassini and Huygens probes. Recent measurements of the effect of temperature on the tensile strength of low-porosity, polycrystalline ice, without impurities, suggest that ice bedrock at the Titan surface temperature of 93 K may be as much as five times stronger than ice at terrestrial surface temperatures. However, ice bedrock on Titan and other outer solar system bodies may have significant porosity, and impurities such silicates or polymers are possible in such ices. In this laboratory investigation we are exploring the dependence of tensile strength on the density and concentration of impurities, for polycrystalline ice across a wide range of temperatures. We use the Brazilian tensile splitting test to measure strength, and control temperature with dry ice and liquid nitrogen. The 50 mm diameter ice cores are made from a log-normally distributed seed crystal mixture with a median size of 1.4 mm. To control ice density and porosity we vary the packing density of the seed grains in core molds and vary the degree of saturation of the matrix with added near-freezing distilled water. We also vary ice density by blending in a similarly-sized mixture of angular fragments of two types of impurities, a fine-grained volcanic rock and a polyethylene polymer. Because both types of impurities have greater tensile strength than ice at Earth surface temperatures, we expect higher concentrations of impurities to correlate with increased strength for ice-rock and ice-polymer mixtures. However, at the ultra-cold temperatures of the outer planets, we expect significant divergence in the temperature dependence of ice tensile strength for the various mixtures and resulting densities. These measurements will help constrain the range of possible
DEFF Research Database (Denmark)
Marchukov, O. V.; Eriksen, E. H.; Midtgaard, J. M.
2016-01-01
One-dimensional multi-component Fermi or Bose systems with strong zero-range interactions can be described in terms of local exchange coefficients and mapping the problem into a spin model is thus possible. For arbitrary external confining potentials the local exchanges are given by highly non...... to the computational complexity of the high-dimensional integrals involved. An approach using the local density approximation would therefore be a most welcome approximation due to its simplicity. Here we assess the accuracy of the local density approximation by going beyond the simple harmonic oscillator that has...... been the focus of previous studies and consider some double-wells of current experimental interest. We find that the local density approximation works quite well as long as the potentials resemble harmonic wells but break down for larger barriers. In order to explore the consequences of applying...
Redshift space correlations and scale-dependent stochastic biasing of density peaks
Desjacques, Vincent; Sheth, Ravi K.
2010-01-01
We calculate the redshift space correlation function and the power spectrum of density peaks of a Gaussian random field. Our derivation, which is valid on linear scales k≲0.1hMpc-1, is based on the peak biasing relation given by Desjacques [Phys. Rev. DPRVDAQ1550-7998, 78, 103503 (2008)10.1103/PhysRevD.78.103503]. In linear theory, the redshift space power spectrum is Ppks(k,μ)=exp(-f2σvel2k2μ2)[bpk(k)+bvel(k)fμ2]2Pδ(k), where μ is the angle with respect to the line of sight, σvel is the one-dimensional velocity dispersion, f is the growth rate, and bpk(k) and bvel(k) are k-dependent linear spatial and velocity bias factors. For peaks, the value of σvel depends upon the functional form of bvel. When the k dependence is absent from the square brackets and bvel is set to unity, the resulting expression is assumed to describe models where the bias is linear and deterministic, but the velocities are unbiased. The peak model is remarkable because it has unbiased velocities in this same sense—peak motions are driven by dark matter flows—but, in order to achieve this, bvel must be k dependent. We speculate that this is true in general: k dependence of the spatial bias will lead to k dependence of bvel even if the biased tracers flow with the dark matter. Because of the k dependence of the linear bias parameters, standard manipulations applied to the peak model will lead to k-dependent estimates of the growth factor that could erroneously be interpreted as a signature of modified dark energy or gravity. We use the Fisher formalism to show that the constraint on the growth rate f is degraded by a factor of 2 if one allows for a k-dependent velocity bias of the peak type. Our analysis also demonstrates that the Gaussian smoothing term is part and parcel of linear theory. We discuss a simple estimate of nonlinear evolution and illustrate the effect of the peak bias on the redshift space multipoles. For k≲0.1hMpc-1, the peak bias is deterministic but k
Parameter dependences of the separatrix density in nitrogen seeded ASDEX Upgrade H-mode discharges
Kallenbach, A.; Sun, H. J.; Eich, T.; Carralero, D.; Hobirk, J.; Scarabosio, A.; Siccinio, M.; ASDEX Upgrade Team; EUROfusion MST1 Team
2018-04-01
The upstream separatrix electron density is an important interface parameter for core performance and divertor power exhaust. It has been measured in ASDEX Upgrade H-mode discharges by means of Thomson scattering using a self-consistent estimate of the upstream electron temperature under the assumption of Spitzer-Härm electron conduction. Its dependence on various plasma parameters has been tested for different plasma conditions in H-mode. The leading parameter determining n e,sep was found to be the neutral divertor pressure, which can be considered as an engineering parameter since it is determined mainly by the gas puff rate and the pumping speed. The experimentally found parameter dependence of n e,sep, which is dominated by the divertor neutral pressure, could be approximately reconciled by 2-point modelling.
Hydrodynamic perspective on memory in time-dependent density-functional theory
Thiele, M.; Kümmel, S.
2009-05-01
The adiabatic approximation of time-dependent density-functional theory is studied in the context of nonlinear excitations of two-electron singlet systems. We compare the exact time evolution of these systems to the adiabatically exact one obtained from time-dependent Kohn-Sham calculations relying on the exact ground-state exchange-correlation potential. Thus, we can show under which conditions the adiabatic approximation breaks down and memory effects become important. The hydrodynamic formulation of quantum mechanics allows us to interpret these results and relate them to dissipative effects in the Kohn-Sham system. We show how the breakdown of the adiabatic approximation can be inferred from the rate of change of the ground-state noninteracting kinetic energy.
Hydrodynamic perspective on memory in time-dependent density-functional theory
International Nuclear Information System (INIS)
Thiele, M.; Kuemmel, S.
2009-01-01
The adiabatic approximation of time-dependent density-functional theory is studied in the context of nonlinear excitations of two-electron singlet systems. We compare the exact time evolution of these systems to the adiabatically exact one obtained from time-dependent Kohn-Sham calculations relying on the exact ground-state exchange-correlation potential. Thus, we can show under which conditions the adiabatic approximation breaks down and memory effects become important. The hydrodynamic formulation of quantum mechanics allows us to interpret these results and relate them to dissipative effects in the Kohn-Sham system. We show how the breakdown of the adiabatic approximation can be inferred from the rate of change of the ground-state noninteracting kinetic energy.
International Nuclear Information System (INIS)
Gregori, G.; Hansen, S.B.; Key, M.H.; King, J.; Mackinnon, A.J.; Park, H.; Patel, P.K.; Shepard, R.; Snavely, R.A.; Wilks, S.C.; Glenzer, S.H.
2005-01-01
We have measured high resolution copper Kα spectra from a picosecond high intensity laser produced plasma. By fitting the shape of the experimental spectra with a self-consistent-field model which includes all the relevant line shifts from multiply ionized atoms, we are able to infer time and spatially averaged electron temperatures (T e ) and ionization state (Z) in the foil. Our results show increasing values for T e and Z when the overall mass of the target is reduced. In particular, we measure temperatures in excess of 200 eV with Z ∼ 13-14. For these conditions the ion-ion coupling constant is Λ ii ∼ 8-9, thus suggesting the achievement of a strongly coupled plasma regime
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Mark C Ladd
2016-12-01
Full Text Available AbstractCoral restoration is gaining traction as a viable strategy to help restore degraded reefs. While the nascent field of coral restoration has rapidly progressed in the past decade, significant knowledge gaps remain regarding the drivers of restoration success that may impede our ability to effectively restore coral reef communities. Here, we conducted a field experiment to investigate the influence of coral density on the growth, habitat production, and survival of corals outplanted for restoration. We used nursery-raised colonies of Acropora cervicornis to experimentally establish populations of corals with either 3, 6, 12, or 24 corals within 4m2 plots, generating a gradient of coral densities ranging from 0.75 corals m-2 to 12 corals m-2. After 13 months we found that density had a significant effect on the growth, habitat production, and survivorship of restored corals. We found that coral survivorship increased as colony density decreased. Importantly, the signal of density dependent effects was context dependent. Our data suggest that positive density dependent effects influenced habitat production at densities of 3 corals m-2, but further increases in density resulted in negative density dependent effects with decreasing growth and survivorship of corals. These findings highlight the importance of density dependence for coral restoration planning and demonstrate the need to evaluate the influence of density for other coral species used for restoration. Further work focused on the mechanisms causing density dependence such as increased herbivory, rapid disease transmission, or altered predation rates are important next steps to advance our ability to effectively restore coral reefs.
Wavelet-based linear-response time-dependent density-functional theory
Natarajan, Bhaarathi; Genovese, Luigi; Casida, Mark E.; Deutsch, Thierry; Burchak, Olga N.; Philouze, Christian; Balakirev, Maxim Y.
2012-06-01
Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BIGDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program DEMON2K for the calculation of electronic absorption spectra of N2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BIGDFT than for DEMON2K. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BIGDFT, while all virtual orbitals are included in TD-DFT calculations in DEMON2K. As a reality check, we report the X-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidazo[1, 2-a]pyridin-3-amine.
A DENSITY DEPENDENCE FOR PROTOSTELLAR LUMINOSITY IN CLASS I SOURCES: COLLABORATIVE ACCRETION
Energy Technology Data Exchange (ETDEWEB)
Elmegreen, Bruce G. [IBM Research Division, T. J. Watson Research Center, Yorktown Hts., NY 10598 (United States); Hurst, Rachel [Scarsdale High School, 1057 White Plains Rd, Scarsdale, NY 10583 (United States); Koenig, Xavier, E-mail: bge@us.ibm.com [Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
2014-02-10
Class I protostars in three high-mass star-forming regions are found to have correlations among the local projected density of other Class I protostars, the summed flux from these other protostars, and the protostellar luminosity in the WISE 22 μm band. Brighter Class I sources form in higher-density and higher-flux regions, while low luminosity sources form anywhere. These correlations depend slightly on the number of neighbors considered (from 2 to 20) and could include a size-of-sample effect from the initial mass function (i.e., larger numbers include rarer and more massive stars). Luminosities seem to vary by neighborhood with nearby protostars having values proportional to each other and higher density regions having higher values. If Class I luminosity is partially related to the accretion rate, then this luminosity correlation is consistent with the competitive accretion model, although it is more collaborative than competitive. The correlation is also consistent with primordial mass segregation and could explain why the stellar initial mass function resembles the dense core mass function even when cores form multiple stars.
Thermodynamics predicts density-dependent energy use in organisms and ecological communities.
Yen, Jian D L; Paganin, David M; Thomson, James R; Mac Nally, Ralph
2015-04-01
Linking our knowledge of organisms to our knowledge of ecological communities and ecosystems is a key challenge for ecology. Individual size distributions (ISDs) link the size of individual organisms to the structure of ecological communities, so that studying ISDs might provide insight into how organism functioning affects ecosystems. Similarly shaped ISDs among ecosystems, coupled with allometric links between organism size and resource use, suggest the possibility of emergent resource-use patterns in ecological communities. We drew on thermodynamics to develop a maximization principle that predicted both organism and community energy use. These predictions highlighted the importance of density-dependent metabolic rates and were able to explain nonlinear relationships between community energy use and community biomass. We analyzed data on fish community energy use and biomass and found evidence of nonlinear scaling, which was predicted by the thermodynamic principle developed here and is not explained by other theories of ISDs. Detailed measurements of organism energy use will clarify the role of density dependence in driving metabolic rates and will further test our derived thermodynamic principle. Importantly, our study highlights the potential for fundamental links between ecology and thermodynamics.
Time-dependent density functional theory of open quantum systems in the linear-response regime.
Tempel, David G; Watson, Mark A; Olivares-Amaya, Roberto; Aspuru-Guzik, Alán
2011-02-21
Time-dependent density functional theory (TDDFT) has recently been extended to describe many-body open quantum systems evolving under nonunitary dynamics according to a quantum master equation. In the master equation approach, electronic excitation spectra are broadened and shifted due to relaxation and dephasing of the electronic degrees of freedom by the surrounding environment. In this paper, we develop a formulation of TDDFT linear-response theory (LR-TDDFT) for many-body electronic systems evolving under a master equation, yielding broadened excitation spectra. This is done by mapping an interacting open quantum system onto a noninteracting open Kohn-Sham system yielding the correct nonequilibrium density evolution. A pseudoeigenvalue equation analogous to the Casida equations of the usual LR-TDDFT is derived for the Redfield master equation, yielding complex energies and Lamb shifts. As a simple demonstration, we calculate the spectrum of a C(2 +) atom including natural linewidths, by treating the electromagnetic field vacuum as a photon bath. The performance of an adiabatic exchange-correlation kernel is analyzed and a first-order frequency-dependent correction to the bare Kohn-Sham linewidth based on the Görling-Levy perturbation theory is calculated.
A unified dislocation density-dependent physical-based constitutive model for cold metal forming
Schacht, K.; Motaman, A. H.; Prahl, U.; Bleck, W.
2017-10-01
Dislocation-density-dependent physical-based constitutive models of metal plasticity while are computationally efficient and history-dependent, can accurately account for varying process parameters such as strain, strain rate and temperature; different loading modes such as continuous deformation, creep and relaxation; microscopic metallurgical processes; and varying chemical composition within an alloy family. Since these models are founded on essential phenomena dominating the deformation, they have a larger range of usability and validity. Also, they are suitable for manufacturing chain simulations since they can efficiently compute the cumulative effect of the various manufacturing processes by following the material state through the entire manufacturing chain and also interpass periods and give a realistic prediction of the material behavior and final product properties. In the physical-based constitutive model of cold metal plasticity introduced in this study, physical processes influencing cold and warm plastic deformation in polycrystalline metals are described using physical/metallurgical internal variables such as dislocation density and effective grain size. The evolution of these internal variables are calculated using adequate equations that describe the physical processes dominating the material behavior during cold plastic deformation. For validation, the model is numerically implemented in general implicit isotropic elasto-viscoplasticity algorithm as a user-defined material subroutine (UMAT) in ABAQUS/Standard and used for finite element simulation of upsetting tests and a complete cold forging cycle of case hardenable MnCr steel family.
Colony Development and Density-Dependent Processes in Breeding Grey Herons
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Takeshi Shirai
2013-01-01
Full Text Available The density-dependent processes that limit the colony size of colonially breeding birds such as herons and egrets remain unclear, because it is difficult to monitor colonies from the first year of their establishment, and the most previous studies have considered mixed-species colonies. In the present study, single-species colonies of the Grey Heron (Ardea cinerea were observed from the first year of their establishment for 16 years in suburban Tokyo. Colony size increased after establishment, illustrating a saturation curve. The breeding duration (days from nest building to fledging by a pair increased, but the number of fledglings per nest decreased, with colony size. The reproductive season in each year began earlier, and there was greater variation in the timing of individual breeding when the colony size was larger. The prolonged duration until nestling feeding by early breeders of the colony suggests that herons at the beginning of the new breeding season exist in an unsteady state with one another, likely owing to interactions with immigrant individuals. Such density-dependent interference may affect reproductive success and limit the colony size of Grey Herons.
Herbivore-specific, density-dependent induction of plant volatiles: honest or "cry wolf" signals?
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Kaori Shiojiri
Full Text Available Plants release volatile chemicals upon attack by herbivorous arthropods. They do so commonly in a dose-dependent manner: the more herbivores, the more volatiles released. The volatiles attract predatory arthropods and the amount determines the probability of predator response. We show that seedlings of a cabbage variety (Brassica oleracea var. capitata, cv Shikidori also show such a response to the density of cabbage white (Pieris rapae larvae and attract more (naive parasitoids (Cotesia glomerata when there are more herbivores on the plant. However, when attacked by diamondback moth (Plutella xylostella larvae, seedlings of the same variety (cv Shikidori release volatiles, the total amount of which is high and constant and thus independent of caterpillar density, and naive parasitoids (Cotesia vestalis of diamondback moth larvae fail to discriminate herbivore-rich from herbivore-poor plants. In contrast, seedlings of another cabbage variety of B. oleracea (var. acephala: kale respond in a dose-dependent manner to the density of diamondback moth larvae and attract more parasitoids when there are more herbivores. Assuming these responses of the cabbage cultivars reflect behaviour of at least some genotypes of wild plants, we provide arguments why the behaviour of kale (B. oleracea var acephala is best interpreted as an honest signaling strategy and that of cabbage cv Shikidori (B. oleracea var capitata as a "cry wolf" signaling strategy, implying a conflict of interest between the plant and the enemies of its herbivores: the plant profits from being visited by the herbivore's enemies, but the latter would be better off by visiting other plants with more herbivores. If so, evolutionary theory on alarm signaling predicts consequences of major interest to students of plant protection, tritrophic systems and communication alike.
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Lizanne Janssens
Full Text Available Interactions between pollutants and suboptimal environmental conditions can have severe consequences for the toxicity of pollutants, yet are still poorly understood. To identify patterns across environmental conditions and across fitness-related variables we exposed Enallagma cyathigerum damselfly larvae to the pesticide chlorpyrifos at two food levels or at two temperatures and quantified four fitness-related variables (larval survival, development time, mass at emergence and adult cold resistance. Food level and temperature did not affect survival in the absence of the pesticide, yet the pesticide reduced survival only at the high temperature. Animals reacted to the pesticide by accelerating their development but only at the high food level and at the low temperature; at the low food level, however, pesticide exposure resulted in a slower development. Chlorpyrifos exposure resulted in smaller adults except in animals reared at the high food level. Animals reared at the low food level and at the low temperature had a higher cold resistance which was not affected by the pesticide. In summary our study highlight that combined effects of exposure to chlorpyrifos and the two environmental conditions (i were mostly interactive and sometimes even reversed in comparison with the effect of the environmental condition in isolation, (ii strongly differed depending on the fitness-related variable under study, (iii were not always predictable based on the effect of the environmental condition in isolation, and (iv bridged metamorphosis depending on which environmental condition was combined with the pesticide thereby potentially carrying over from aquatic to terrestrial ecosystems. These findings are relevant when extrapolating results of laboratory tests done under ideal environmental conditions to natural communities.
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Joy Ogbechi
2015-07-01
Full Text Available A well-known histopathological feature of diseased skin in Buruli ulcer (BU is coagulative necrosis caused by the Mycobacterium ulcerans macrolide exotoxin mycolactone. Since the underlying mechanism is not known, we have investigated the effect of mycolactone on endothelial cells, focussing on the expression of surface anticoagulant molecules involved in the protein C anticoagulant pathway. Congenital deficiencies in this natural anticoagulant pathway are known to induce thrombotic complications such as purpura fulimans and spontaneous necrosis. Mycolactone profoundly decreased thrombomodulin (TM expression on the surface of human dermal microvascular endothelial cells (HDMVEC at doses as low as 2 ng/ml and as early as 8 hrs after exposure. TM activates protein C by altering thrombin's substrate specificity, and exposure of HDMVEC to mycolactone for 24 hours resulted in an almost complete loss of the cells' ability to produce activated protein C. Loss of TM was shown to be due to a previously described mechanism involving mycolactone-dependent blockade of Sec61 translocation that results in proteasome-dependent degradation of newly synthesised ER-transiting proteins. Indeed, depletion from cells determined by live-cell imaging of cells stably expressing a recombinant TM-GFP fusion protein occurred at the known turnover rate. In order to determine the relevance of these findings to BU disease, immunohistochemistry of punch biopsies from 40 BU lesions (31 ulcers, nine plaques was performed. TM abundance was profoundly reduced in the subcutis of 78% of biopsies. Furthermore, it was confirmed that fibrin deposition is a common feature of BU lesions, particularly in the necrotic areas. These findings indicate that there is decreased ability to control thrombin generation in BU skin. Mycolactone's effects on normal endothelial cell function, including its ability to activate the protein C anticoagulant pathway are strongly associated with this
International Nuclear Information System (INIS)
Shen, Colin Y.; Evans, Thomas E.
2004-01-01
A non-hydrostatic density-stratified hydrodynamic model with a free surface has been developed from the vorticity equations rather than the usual momentum equations. This approach has enabled the model to be obtained in two different forms, weakly non-hydrostatic and fully non-hydrostatic, with the computationally efficient weakly non-hydrostatic form applicable to motions having horizontal scales greater than the local water depth. The hydrodynamic model in both its weakly and fully non-hydrostatic forms is validated numerically using exact nonlinear non-hydrostatic solutions given by the Dubriel-Jacotin-Long equation for periodic internal gravity waves, internal solitary waves, and flow over a ridge. The numerical code is developed based on a semi-Lagrangian scheme and higher order finite-difference spatial differentiation and interpolation. To demonstrate the applicability of the model to coastal ocean situations, the problem of tidal generation of internal solitary waves at a shelf-break is considered. Simulations carried out with the model obtain the evolution of solitary wave generation and propagation consistent with past results. Moreover, the weakly non-hydrostatic simulation is shown to compare favorably with the fully non-hydrostatic simulation. The capability of the present model to simulate efficiently relatively large scale non-hydrostatic motions suggests that the weakly non-hydrostatic form of the model may be suitable for application in a large-area domain while the computationally intensive fully non-hydrostatic form of the model may be used in an embedded sub-domain where higher resolution is needed
Time-dependent density functional theory with twist-averaged boundary conditions
Schuetrumpf, B.; Nazarewicz, W.; Reinhard, P.-G.
2016-05-01
Background: Time-dependent density functional theory is widely used to describe excitations of many-fermion systems. In its many applications, three-dimensional (3D) coordinate-space representation is used, and infinite-domain calculations are limited to a finite volume represented by a spatial box. For finite quantum systems (atoms, molecules, nuclei, hadrons), the commonly used periodic or reflecting boundary conditions introduce spurious quantization of the continuum states and artificial reflections from boundary; hence, an incorrect treatment of evaporated particles. Purpose: The finite-volume artifacts for finite systems can be practically cured by invoking an absorbing potential in a certain boundary region sufficiently far from the described system. However, such absorption cannot be applied in the calculations of infinite matter (crystal electrons, quantum fluids, neutron star crust), which suffer from unphysical effects stemming from a finite computational box used. Here, twist-averaged boundary conditions (TABC) have been used successfully to diminish the finite-volume effects. In this work, we extend TABC to time-dependent modes. Method: We use the 3D time-dependent density functional framework with the Skyrme energy density functional. The practical calculations are carried out for small- and large-amplitude electric dipole and quadrupole oscillations of 16O. We apply and compare three kinds of boundary conditions: periodic, absorbing, and twist-averaged. Results: Calculations employing absorbing boundary conditions (ABC) and TABC are superior to those based on periodic boundary conditions. For low-energy excitations, TABC and ABC variants yield very similar results. With only four twist phases per spatial direction in TABC, one obtains an excellent reduction of spurious fluctuations. In the nonlinear regime, one has to deal with evaporated particles. In TABC, the floating nucleon gas remains in the box; the amount of nucleons in the gas is found to be
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Hanna Björkelund
Full Text Available The interaction of the epidermal growth factor (EGF with its receptor (EGFR is known to be complex, and the common over-expression of EGF receptor family members in a multitude of tumors makes it important to decipher this interaction and the following signaling pathways. We have investigated the affinity and kinetics of (125I-EGF binding to EGFR in four human tumor cell lines, each using four culturing conditions, in real time by use of LigandTracer®.Highly repeatable and precise measurements show that the overall apparent affinity of the (125I-EGF - EGFR interaction is greatly dependent on cell line at normal culturing conditions, ranging from K(D ≈ 200 pM on SKBR3 cells to K(D≈8 nM on A431 cells. The (125I-EGF - EGFR binding curves (irrespective of cell line have strong signs of multiple simultaneous interactions. Furthermore, for the cell lines A431 and SKOV3, gefitinib treatment increases the (125I-EGF - EGFR affinity, in particular when the cells are starved. The (125I-EGF - EGFR interaction on cell line U343 is sensitive to starvation while as on SKBR3 it is insensitive to gefitinib and starvation.The intriguing pattern of the binding characteristics proves that the cellular context is important when deciphering how EGF interacts with EGFR. From a general perspective, care is advisable when generalizing ligand-receptor interaction results across multiple cell-lines.
Shen, Lu; Mickley, Loretta J.; Leibensperger, Eric M.; Li, Mingwei
2017-12-01
We find that summertime air quality in the eastern U.S. displays strong dependence on North Atlantic sea surface temperatures, resulting from large-scale ocean-atmosphere interactions. Using observations, reanalysis data sets, and climate model simulations, we further identify a multidecadal variability in surface air quality driven by the Atlantic Multidecadal Oscillation (AMO). In one-half cycle ( 35 years) of the AMO from cold to warm phase, summertime maximum daily 8 h ozone concentrations increase by 1-4 ppbv and PM2.5 concentrations increase by 0.3-1.0 μg m-3 over much of the east. These air quality changes are related to warmer, drier, and more stagnant weather in the AMO warm phase, together with anomalous circulation patterns at the surface and aloft. If the AMO shifts to the cold phase in future years, it could partly offset the climate penalty on U.S. air quality brought by global warming, an effect which should be considered in long-term air quality planning.
Jiang, Junjie; Song, Gaibei; Wang, Dongyang; Jin, Zuanming; Tian, Zhen; Lin, Xian; Han, Jiaguang; Ma, Guohong; Cao, Shixun; Cheng, Zhenxiang
2016-03-23
One of the biggest challenges in spintronics is finding how to switch the magnetization of a material. One way of the spin switching is the spin reorientation transition (SRT), a switching of macroscopic magnetization rotated by 90°. The macroscopic magnetization in a NdFeO3 single crystal rotates from Γ4 to Γ2 via Γ24 as the temperature is decreased from 170 to 100 K, while it can be switched back to Γ4 again by increasing the temperature. However, the precise roles of the magnetic-field induced SRT are still unclear. By using terahertz time-domain spectroscopy (THz-TDS), here, we show that the magnetic-field induced SRT between Γ4 and Γ2 is strongly anisotropic, depending on the direction of the applied magnetic field. Our experimental results are well interpreted by the anisotropy of rare-earth Nd(3+) ion. Furthermore, we find that the critical magnetic-field required for SRT can be modified by changing the temperature. Our study suggests that the anisotropic SRT in NdFeO3 single crystal provides a platform to facilitate the potential applications in robust spin memory devices.
International Nuclear Information System (INIS)
Roca-Maza, X.; Vinas, X.; Centelles, M.; Ring, P.; Schuck, P.
2011-01-01
Although ab initio calculations of relativistic Brueckner theory lead to large scalar isovector fields in nuclear matter, at present, successful versions of covariant density functional theory neglect the interactions in this channel. A new high-precision density functional DD-MEδ is presented which includes four mesons, σ, ω, δ, and ρ, with density-dependent meson-nucleon couplings. It is based to a large extent on microscopic ab initiocalculations in nuclear matter. Only four of its parameters are determined by adjusting to binding energies and charge radii of finite nuclei. The other parameters, in particular the density dependence of the meson-nucleon vertices, are adjusted to nonrelativistic and relativistic Brueckner calculations of symmetric and asymmetric nuclear matter. The isovector effective mass m p * -m n * derived from relativistic Brueckner theory is used to determine the coupling strength of the δ meson and its density dependence.
Sumi, Tomonari; Maruyama, Yutaka; Mitsutake, Ayori; Mochizuki, Kenji; Koga, Kenichiro
2018-02-05
Recently, we proposed a reference-modified density functional theory (RMDFT) to calculate solvation free energy (SFE), in which a hard-sphere fluid was introduced as the reference system instead of an ideal molecular gas. Through the RMDFT, using an optimal diameter for the hard-sphere reference system, the values of the SFE calculated at room temperature and normal pressure were in good agreement with those for more than 500 small organic molecules in water as determined by experiments. In this study, we present an application of the RMDFT for calculating the temperature and pressure dependences of the SFE for solute molecules in water. We demonstrate that the RMDFT has high predictive ability for the temperature and pressure dependences of the SFE for small solute molecules in water when the optimal reference hard-sphere diameter determined for each thermodynamic condition is used. We also apply the RMDFT to investigate the temperature and pressure dependences of the thermodynamic stability of an artificial small protein, chignolin, and discuss the mechanism of high-temperature and high-pressure unfolding of the protein. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Inflammation triggers emergency granulopoiesis through a density-dependent feedback mechanism.
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Derek W Cain
Full Text Available Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBPα. Inflammation, however, induces neutrophilia through a distinct pathway of "emergency" granulopoiesis that is dependent on C/EBPβ. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBPβ, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis.
Bruggeman, Jason E.; Swem, Ted; Andersen, David E.; Kennedy, Patricia L.; Nigro, Debora A.
2015-01-01
Intrinsic and extrinsic factors affect vital rates and population-level processes, and understanding these factors is paramount to devising successful management plans for wildlife species. For example, birds time migration in response, in part, to local and broadscale climate fluctuations to initiate breeding upon arrival to nesting territories, and prolonged inclement weather early in the breeding season can inhibit egg-laying and reduce productivity. Also, density-dependent regulation occurs in raptor populations, as territory size is related to resource availability. Arctic Peregrine Falcons (Falco peregrinus tundrius; hereafter Arctic peregrine) have a limited and northern breeding distribution, including the Colville River Special Area (CRSA) in the National Petroleum Reserve–Alaska, USA. We quantified influences of climate, topography, nest productivity, prey habitat, density dependence, and interspecific competition affecting Arctic peregrines in the CRSA by applying the Dail-Madsen model to estimate abundance and vital rates of adults on nesting cliffs from 1981 through 2002. Arctic peregrine abundance increased throughout the 1980s, which spanned the population's recovery from DDT-induced reproductive failure, until exhibiting a stationary trend in the 1990s. Apparent survival rate (i.e., emigration; death) was negatively correlated with the number of adult Arctic peregrines on the cliff the previous year, suggesting effects of density-dependent population regulation. Apparent survival and arrival rates (i.e., immigration; recruitment) were higher during years with earlier snowmelt and milder winters, and apparent survival was positively correlated with nesting season maximum daily temperature. Arrival rate was positively correlated with average Arctic peregrine productivity along a cliff segment from the previous year and initial abundance was positively correlated with cliff height. Higher cliffs with documented higher productivity (presumably
Impact of spin-orbit density dependent potential in heavy ion reactions forming Se nuclei
Energy Technology Data Exchange (ETDEWEB)
Rajni; Sharma, Ishita; Sharma, Manoj K. [Thapar University, School of Physics and Materials Science, Patiala (India); Jain, Deepika [Mata Gujri College, Department of Physics, Fatehgarh Sahib (India)
2017-10-15
The Skyrme energy density formalism is employed to explore the effect of spin-orbit interaction potential by considering a two nucleon transfer process via various entrance channels such as {sup 23}Na + {sup 49}V, {sup 25}Mg + {sup 47}Ti, {sup 27}Al + {sup 45}Sc, {sup 29}Si + {sup 43}Ca and {sup 31}P + {sup 41}K, all forming the same compound system {sup 72}Se*, using both spherical as well as quadrupole deformed (β{sub 2}) nuclei. For spherical nuclei, the spin-orbit density part V{sub J} of nuclear potential remains unaffected with the transfer of two nucleons from the target to the projectile, however, show notable variation in magnitude after inclusion of deformation effects. Likewise, deformations play an important role in the spin-orbit density independent part V{sub P}, as the fusion pocket start appears, which otherwise diminish for the spherical nuclei. Further, the effect of an increase in the N/Z ratio of Se is explored on V{sub J} as well as V{sub P} and results are compared with transfer channels. In addition to this, the role of double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}) with relative contribution of the isoscalar and isovector parts of spin-orbit strength is explored in view of SkI2, SkI3 and SkI4 Skyrme forces. Beside this, the decay path of {sup 72}Se* nucleus formed in {sup 27}Al + {sup 45}Sc reaction is investigated within the framework of dynamical cluster decay model (DCM), where the nuclear proximity potential is obtained by both Skyrme energy density formalism (SEDF) and proximity pocket formula. The fusion hindrance in the {sup 27}Al + {sup 45}Sc reaction is also addressed via the barrier lowering parameter ΔV{sub B}. Finally, the contribution of spin-orbit density dependent interaction potential is estimated for the {sup 27}Al + {sup 45}Sc reaction using single (W{sub 0} or W{sub 0}{sup '}) and double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}). (orig.)
International Nuclear Information System (INIS)
Solikhov, D.K.
2015-01-01
Present article is devoted to angular dependence of intensity of absent-minded radiation in approach of the strong dissipation of colliding ionic-sound waves. The operation angular dependence of dimensionless of intensity of absent-minded radiation in two-dimensional field of localisation of a wave of a rating in approach of the strong dissipation of passers is ionic-sound waves is viewed. (author)
Einum, Sigurd; Robertsen, Grethe; Fleming, Ian A
2008-01-01
Theory suggests an important role for population density in shaping adaptive landscapes through density-dependent selection. Here, we identify five methodological approaches for studying such selection, review the existing empirical evidence for it, and ask whether current declines in abundance can be expected to trigger evolutionary responses in salmonid fishes. Across taxa we find substantial amounts of evidence for population density influencing the location of adaptive peaks for a range o...
Einum, Sigurd; Robertsen, Grethe; Fleming, Ian A
2008-05-01
Theory suggests an important role for population density in shaping adaptive landscapes through density-dependent selection. Here, we identify five methodological approaches for studying such selection, review the existing empirical evidence for it, and ask whether current declines in abundance can be expected to trigger evolutionary responses in salmonid fishes. Across taxa we find substantial amounts of evidence for population density influencing the location of adaptive peaks for a range of traits, and, in the presence of frequency dependence, changing the shape of selection (stabilizing versus disruptive). For salmonids, biological and theoretical considerations suggest that the optimal value of a number of traits associated with juvenile competitive ability (e.g. egg size, timing of emergence from nests, dominance ability), may depend on population density. For adults, more direct experimental and comparative evidence suggest that secondary sexual traits can be subject to density-dependent selection. There is also evidence that density affects the frequency-dependent selection likely responsible for the expression of alternative male reproductive phenotypes in salmon. Less is known however about the role of density in maintaining genetic variation among juveniles. Further efforts are required to elucidate the indirect evolutionary effects of declining population abundances, both in salmonids and in other anthropogenically challenged organisms.
Global stability of a delayed SIR epidemic model with density dependent birth and death rates
Yoshida, Naoki; Hara, Tadayuki
2007-04-01
An SIR epidemic model with density dependent birth and death rates is formulated. In our model it is assumed that the total number of the population is governed by logistic equation. The transmission of infection is assumed to be of the standard form, namely proportional to I(t-h)/N(t-h) where N(t) is the total (variable) population size, I(t) is the size of the infective population and a time delay h is a fixed time during which the infectious agents develop in the vector. We consider transmission dynamics for the model. Stability of an endemic equilibrium is investigated. The stability result is stated in terms of a threshold parameter, that is, a basic reproduction number R0.
Self-consistent RPA and the time-dependent density matrix approach
Energy Technology Data Exchange (ETDEWEB)
Schuck, P. [Institut de Physique Nucleaire, Orsay (France); CNRS et Universite Joseph Fourier, Laboratoire de Physique et Modelisation des Milieux Condenses, Grenoble (France); Tohyama, M. [Kyorin University School of Medicine, Mitaka, Tokyo (Japan)
2016-10-15
The time-dependent density matrix (TDDM) or BBGKY (Bogoliubov, Born, Green, Kirkwood, Yvon) approach is decoupled and closed at the three-body level in finding a natural representation of the latter in terms of a quadratic form of two-body correlation functions. In the small amplitude limit an extended RPA coupled to an also extended second RPA is obtained. Since including two-body correlations means that the ground state cannot be a Hartree-Fock state, naturally the corresponding RPA is upgraded to Self-Consistent RPA (SCRPA) which was introduced independently earlier and which is built on a correlated ground state. SCRPA conserves all the properties of standard RPA. Applications to the exactly solvable Lipkin and the 1D Hubbard models show good performances of SCRPA and TDDM. (orig.)
Relativistic Hartree-Fock theory. Part I: density-dependent effective Lagrangians
Energy Technology Data Exchange (ETDEWEB)
LongWen Hui [School of Physics, Peking University, 100871 Beijing (China)]|[CNRS-IN2P3, UMR 8608, F-91406 Orsay Cedex (France)]|[Univ Paris-Sud, F-91405 Orsay (France); Giai, Nguyen Van [CNRS-IN2P3, UMR 8608, F-91406 Orsay Cedex (France)]|[Univ Paris-Sud, F-91405 Orsay (France); Meng, Jie [School of Physics, Peking University, 100871 Beijing (China)]|[Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing (China)]|[Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, 730000 Lanzhou (China)
2006-10-15
Effective Lagrangians suitable for a relativistic Hartree-Fock description of nuclear systems are presented. They include the 4 effective mesons {sigma}, {omega}, {rho} and {pi} with density-dependent meson-nucleon couplings. The criteria for determining the model parameters are the reproduction of the binding energies in a number of selected nuclei, and the bulk properties of nuclear matter (saturation point, compression modulus, symmetry energy). An excellent description of nuclear binding energies and radii is achieved for a range of nuclei encompassing light and heavy systems. The predictions of the present approach compare favorably with those of existing relativistic mean field models, with the advantage of incorporating the effects of pion-nucleon coupling. (authors)
Time-dependent density-functional theory in the projector augmented-wave method
DEFF Research Database (Denmark)
Walter, Michael; Häkkinen, Hannu; Lehtovaara, Lauri
2008-01-01
We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we fo...... surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear emission spectra using the time-propagation method....... found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born–Oppenheimer potential...
Density dependence of 2p-2h meson-exchange currents
Amaro, J. E.; Barbaro, M. B.; Caballero, J. A.; De Pace, A.; Donnelly, T. W.; Megias, G. D.; Ruiz Simo, I.
2017-06-01
We analyze the density dependence of the contribution of meson-exchange currents to the lepton-nucleus inclusive cross section in the two-particle two-hole channel. The model is based on the relativistic Fermi gas, where each nucleus is characterized by its Fermi momentum kF. We find that the 2p-2h nuclear response functions at their peaks scale as A kF2 for Fermi momentum going from 200 to 300 MeV/c and momentum transfer q from 2 kF to 2 GeV /c . This behavior is different from what is found for the quasielastic response, which scales as A /kF . Additionally, the deep scaling region is also discussed and there the usual scaling behavior is found to be preferable.
Plant diversity increases with the strength of negative density dependence at the global scale.
LaManna, Joseph A; Mangan, Scott A; Alonso, Alfonso; Bourg, Norman A; Brockelman, Warren Y; Bunyavejchewin, Sarayudh; Chang, Li-Wan; Chiang, Jyh-Min; Chuyong, George B; Clay, Keith; Condit, Richard; Cordell, Susan; Davies, Stuart J; Furniss, Tucker J; Giardina, Christian P; Gunatilleke, I A U Nimal; Gunatilleke, C V Savitri; He, Fangliang; Howe, Robert W; Hubbell, Stephen P; Hsieh, Chang-Fu; Inman-Narahari, Faith M; Janík, David; Johnson, Daniel J; Kenfack, David; Korte, Lisa; Král, Kamil; Larson, Andrew J; Lutz, James A; McMahon, Sean M; McShea, William J; Memiaghe, Hervé R; Nathalang, Anuttara; Novotny, Vojtech; Ong, Perry S; Orwig, David A; Ostertag, Rebecca; Parker, Geoffrey G; Phillips, Richard P; Sack, Lawren; Sun, I-Fang; Tello, J Sebastián; Thomas, Duncan W; Turner, Benjamin L; Vela Díaz, Dilys M; Vrška, Tomáš; Weiblen, George D; Wolf, Amy; Yap, Sandra; Myers, Jonathan A
2017-06-30
Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
Wavelet-based linear-response time-dependent density-functional theory
International Nuclear Information System (INIS)
Natarajan, Bhaarathi; Genovese, Luigi; Casida, Mark E.; Deutsch, Thierry; Burchak, Olga N.
2012-01-01
Highlights: ► We has been implemented LR-TD-DFT in the pseudopotential wavelet-based program. ► We have compared the results against all-electron Gaussian-type program. ► Orbital energies converges significantly faster for BigDFT than for DEMON2K. ► We report the X-ray crystal structure of the small organic molecule flugi6. ► Measured and calculated absorption spectrum of flugi6 is also reported. - Abstract: Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BIGDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program DEMON2K for the calculation of electronic absorption spectra of N 2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BIGDFT than for DEMON2K. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BIGDFT, while all virtual orbitals are included in TD-DFT calculations in DEMON2K. As a reality check, we report the X-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidazo[1, 2-a]pyridin-3-amine.
Role of prey and intraspecific density dependence on the population growth of an avian top predator
Fernandez-de-Simon, Javier; Díaz-Ruiz, Francisco; Cirilli, Francesca; Tortosa, Francisco S.; Villafuerte, Rafael; Ferreras, Pablo
2014-10-01
Exploring predator-prey systems in diverse ecosystems increases our knowledge about ecological processes. Predator population growth may be positive when conspecific density is low but predators also need areas with prey availability, associated with competition, which increases the risk of suffering losses but stabilises populations. We studied relationships between European rabbits Oryctolagus cuniculus (prey) and adult eagle owls Bubo bubo (predators) in south-western Europe. We assessed models explaining the predator population growth and stability. We estimated the abundance of rabbits and adult eagle owls during three years in eight localities of central-southern Spain. We explored models including rabbit and adult eagle owl abundance, accounting for yearly variations and including the locality as a random variable. We found that population growth of adult eagle owls was positive in situations with low conspecific abundance and tended to be negative but approaching equilibrium in situations of higher conspecific abundance. Population growth was also positively related to previous summer rabbit density when taking into account eagle owl conspecific abundance, possibly indicating that rabbits may support recruitment. Furthermore, abundance stability of adult eagle owls was positively related to previous winter-spring rabbit density, which could suggest predator population stabilisation through quick territory occupation in high-quality areas. These results exemplify the trade-off between prey availability and abundance of adult predators related to population growth and abundance stability in the eagle owl-rabbit system in south-western Europe. Despite rabbits have greatly declined during the last decades and eagle owls locally specialise on them, eagle owls currently have a favourable conservation status. As eagle owls are the only nocturnal raptor with such dependence on rabbits, this could point out that predators may overcome prey decreases in areas with
Directory of Open Access Journals (Sweden)
Ricardo E Gürtler
2009-05-01
Full Text Available Understanding the factors that affect the host-feeding preferences of triatomine bugs is crucial for estimating transmission risks and predicting the effects of control tactics targeting domestic animals. We tested whether Triatoma infestans bugs prefer to feed on dogs vs. chickens and on dogs vs. cats and whether vector density modified host choices and other vital rates under natural conditions.Two host choice experiments were conducted in small caged huts with two rooms between which bugs could move freely. Matched pairs of dog-chicken (six and dog-cat (three were assigned randomly to two levels of vector abundance and exposed to starved bugs during three nights. Bloodmeals from 1,160 bugs were tested by a direct enzyme-linked immunosorbent assay.Conditional logistic regression showed that dogs were highly preferred over chickens or cats and that vector density modified host-feeding choices. The relative risk of a bug being blood-engorged increased significantly when it fed only on dog rather than chicken or cat. Bugs achieved higher post-exposure weight at higher vector densities and successive occasions, more so if they fed on a dog rather than on a cat.Our findings strongly refute the hypothesis that T. infestans prefers to blood-feed on chickens rather than dogs. An increase in dog or cat availability or accessibility will increase the rate of bug feeding on them and exert strong non-linear effects on R(0. When combined with between-dog heterogeneities in exposure, infection, and infectiousness, the strong bug preference for dogs can be exploited to target dogs in general, and even the specific individuals that account for most of the risk, with topical lotions or insecticide-impregnated collars to turn them into baited lethal traps or use them as transmission or infestation sentinels based on their immune response to Trypanosoma cruzi or bug salivary antigens.
Ma, Songling; Hwang, Sungbo; Lee, Sehan; Acree, William E; No, Kyoung Tai
2018-03-30
To describe the physically realistic solvation free energy surface of a molecule in a solvent, a generalized version of the solvation free energy density (G-SFED) calculation method has been developed. In the G-SFED model, the contribution from the hydrogen bond (HB) between a solute and a solvent to the solvation free energy was calculated as the product of the acidity of the donor and the basicity of the acceptor of an HB pair. The acidity and basicity parameters of a solute were derived using the summation of acidities and basicities of the respective acidic and basic functional groups of the solute, and that of the solvent was experimentally determined. Although the contribution of HBs to the solvation free energy could be evenly distributed to grid points on the surface of a molecule, the G-SFED model was still inadequate to describe the angle dependency of the HB of a solute with a polarizable continuum solvent. To overcome this shortcoming of the G-SFED model, the contribution of HBs was formulated using the geometric parameters of the grid points described in the HB coordinate system of the solute. We propose an HB angle dependency incorporated into the G-SFED model, i.e., the G-SFED-HB model, where the angular-dependent acidity and basicity densities are defined and parametrized with experimental data. The G-SFED-HB model was then applied to calculate the solvation free energies of organic molecules in water, various alcohols and ethers, and the log P values of diverse organic molecules, including peptides and a protein. Both the G-SFED model and the G-SFED-HB model reproduced the experimental solvation free energies with similar accuracy, whereas the distributions of the SFED on the molecular surface calculated by the G-SFED and G-SFED-HB models were quite different, especially for molecules having HB donors or acceptors. Since the angle dependency of HBs was included in the G-SFED-HB model, the SFED distribution of the G-SFED-HB model is well described
Nagayama, Taisuke
2017-10-01
Model predictions for iron opacity are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones. The calculated iron opacities have narrower spectral lines, weaker quasi-continuum at short wavelength, and deeper opacity windows than the measurements. If correct, these measurements help resolve a decade old problem in solar physics. A key question is therefore: What is responsible for the model-data discrepancy? The answer is complex because the experiments are challenging and opacity theories depend on multiple entangled physical processes such as the influence of completeness and accuracy of atomic states, line broadening, contributions from myriad transitions from excited states, and multi-photon absorption processes. To help determine the cause of this discrepancy, a systematic study of opacity variation with temperature, density, and atomic number is underway. Measurements of chromium, iron, and nickel opacities have been performed at two different temperatures and densities. The collection of measured opacities provides constraints on hypotheses to explain the discrepancy. We will discuss implications of measured opacities, experimental errors, and possible opacity model refinements. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.
Georgiou, Katerina; Abramoff, Rose; Harte, John; Riley, William; Torn, Margaret
2017-04-01
Climatic, atmospheric, and land-use changes all have the potential to alter soil microbial activity via abiotic effects on soil or mediated by changes in plant inputs. Recently, many promising microbial models of soil organic carbon (SOC) decomposition have been proposed to advance understanding and prediction of climate and carbon (C) feedbacks. Most of these models, however, exhibit unrealistic oscillatory behavior and SOC insensitivity to long-term changes in C inputs. Here we diagnose the sources of instability in four models that span the range of complexity of these recent microbial models, by sequentially adding complexity to a simple model to include microbial physiology, a mineral sorption isotherm, and enzyme dynamics. We propose a formulation that introduces density-dependence of microbial turnover, which acts to limit population sizes and reduce oscillations. We compare these models to results from 24 long-term C-input field manipulations, including the Detritus Input and Removal Treatment (DIRT) experiments, to show that there are clear metrics that can be used to distinguish and validate the inherent dynamics of each model structure. We find that widely used first-order models and microbial models without density-dependence cannot readily capture the range of long-term responses observed across the DIRT experiments as a direct consequence of their model structures. The proposed formulation improves predictions of long-term C-input changes, and implies greater SOC storage associated with CO2-fertilization-driven increases in C inputs over the coming century compared to common microbial models. Finally, we discuss our findings in the context of improving microbial model behavior for inclusion in Earth System Models.
Time-dependent density functional methods for Raman spectra in open-shell systems.
Aquino, Fredy W; Schatz, George C
2014-01-16
We present an implementation of a time-dependent density functional theory (TD-DFT) linear response module in NWChem for unrestricted DFT calculations and apply it to the calculation of resonant Raman spectra in open-shell molecular systems using the short-time approximation. The new source code was validated and applied to simulate Raman spectra on several doublet organic radicals (e.g., benzyl, benzosemiquinone, TMPD, trans-stilbene anion and cation, and methyl viologen) and the metal complex copper phthalocyanine. We also introduce a divide-and-conquer approach for the evaluation of polarizabilities in relatively large systems (e.g., copper phthalocyanine). The implemented tool gives comparisons with experiment that are similar to what is commonly found for closed-shell systems, with good agreement for most features except for small frequency shifts, and occasionally large deviations for some modes that depend on the molecular system studied, experimental conditions not being accounted in the modeling such as solvation effects and extra solvent-based peaks, and approximations in the underlying theory. The approximations used in the quantum chemical modeling include (i) choice of exchange-correlation functional and basis set; (ii) harmonic approximation used in the frequency analysis to determine vibrational normal modes; and (iii) short-time approximation (omission of nuclear motion effects) used in calculating resonant Raman spectra.
Andrade, Xavier; Alberdi-Rodriguez, Joseba; Strubbe, David A; Oliveira, Micael J T; Nogueira, Fernando; Castro, Alberto; Muguerza, Javier; Arruabarrena, Agustin; Louie, Steven G; Aspuru-Guzik, Alán; Rubio, Angel; Marques, Miguel A L
2012-06-13
Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this paper we present the ongoing efforts to achieve the parallelization of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has great potential for execution in massively parallel systems such as modern supercomputers with thousands of processors and graphics processing units (GPUs). For harvesting the potential of conventional supercomputers, the main strategy is a multi-level parallelization scheme that combines the inherent scalability of real-time TDDFT with a real-space grid domain-partitioning approach. A scalable Poisson solver is critical for the efficiency of this scheme. For GPUs, we show how using blocks of Kohn-Sham states provides the required level of data parallelism and that this strategy is also applicable for code optimization on standard processors. Our results show that real-time TDDFT, as implemented in octopus, can be the method of choice for studying the excited states of large molecular systems in modern parallel architectures.
Oxidized low-density lipoproteins upregulate proline oxidase to initiate ROS-dependent autophagy.
Zabirnyk, Olga; Liu, Wei; Khalil, Shadi; Sharma, Anit; Phang, James M
2010-03-01
Epidemiological studies showed that high levels of oxidized low-density lipoproteins (oxLDLs) are associated with increased cancer risk. We examined the direct effect of physiologic concentrations oxLDL on cancer cells. OxLDLs were cytotoxic and activate both apoptosis and autophagy. OxLDLs have ligands for peroxisome proliferator-activated receptor gamma and upregulated proline oxidase (POX) through this nuclear receptor. We identified 7-ketocholesterol (7KC) as a main component responsible for the latter. To elucidate the role of POX in oxLDL-mediated cytotoxicity, we knocked down POX via small interfering RNA and found that this (i) further reduced viability of cancer cells treated with oxLDL; (ii) decreased oxLDL-associated reactive oxygen species generation; (iii) decreased autophagy measured via beclin-1 protein level and light-chain 3 protein (LC3)-I into LC3-II conversion. Using POX-expressing cell model, we established that single POX overexpression was sufficient to activate autophagy. Thus, it led to autophagosomes accumulation and increased conversion of LC3-I into LC3-II. Moreover, beclin-1 gene expression was directly dependent on POX catalytic activity, namely the generation of POX-dependent superoxide. We conclude that POX is critical in the cellular response to the noxious effects of oxLDL by activating protective autophagy.
Andrade, Xavier; Alberdi-Rodriguez, Joseba; Strubbe, David A.; Oliveira, Micael J. T.; Nogueira, Fernando; Castro, Alberto; Muguerza, Javier; Arruabarrena, Agustin; Louie, Steven G.; Aspuru-Guzik, Alán; Rubio, Angel; Marques, Miguel A. L.
2012-06-01
Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this paper we present the ongoing efforts to achieve the parallelization of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has great potential for execution in massively parallel systems such as modern supercomputers with thousands of processors and graphics processing units (GPUs). For harvesting the potential of conventional supercomputers, the main strategy is a multi-level parallelization scheme that combines the inherent scalability of real-time TDDFT with a real-space grid domain-partitioning approach. A scalable Poisson solver is critical for the efficiency of this scheme. For GPUs, we show how using blocks of Kohn-Sham states provides the required level of data parallelism and that this strategy is also applicable for code optimization on standard processors. Our results show that real-time TDDFT, as implemented in octopus, can be the method of choice for studying the excited states of large molecular systems in modern parallel architectures.
International Nuclear Information System (INIS)
Andrade, Xavier; Aspuru-Guzik, Alán; Alberdi-Rodriguez, Joseba; Rubio, Angel; Strubbe, David A; Louie, Steven G; Oliveira, Micael J T; Nogueira, Fernando; Castro, Alberto; Muguerza, Javier; Arruabarrena, Agustin; Marques, Miguel A L
2012-01-01
Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this paper we present the ongoing efforts to achieve the parallelization of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has great potential for execution in massively parallel systems such as modern supercomputers with thousands of processors and graphics processing units (GPUs). For harvesting the potential of conventional supercomputers, the main strategy is a multi-level parallelization scheme that combines the inherent scalability of real-time TDDFT with a real-space grid domain-partitioning approach. A scalable Poisson solver is critical for the efficiency of this scheme. For GPUs, we show how using blocks of Kohn-Sham states provides the required level of data parallelism and that this strategy is also applicable for code optimization on standard processors. Our results show that real-time TDDFT, as implemented in octopus, can be the method of choice for studying the excited states of large molecular systems in modern parallel architectures. (topical review)
Stochastic population growth in spatially heterogeneous environments: the density-dependent case.
Hening, Alexandru; Nguyen, Dang H; Yin, George
2018-02-01
This work is devoted to studying the dynamics of a structured population that is subject to the combined effects of environmental stochasticity, competition for resources, spatio-temporal heterogeneity and dispersal. The population is spread throughout n patches whose population abundances are modeled as the solutions of a system of nonlinear stochastic differential equations living on [Formula: see text]. We prove that r, the stochastic growth rate of the total population in the absence of competition, determines the long-term behaviour of the population. The parameter r can be expressed as the Lyapunov exponent of an associated linearized system of stochastic differential equations. Detailed analysis shows that if [Formula: see text], the population abundances converge polynomially fast to a unique invariant probability measure on [Formula: see text], while when [Formula: see text], the population abundances of the patches converge almost surely to 0 exponentially fast. This generalizes and extends the results of Evans et al. (J Math Biol 66(3):423-476, 2013) and proves one of their conjectures. Compared to recent developments, our model incorporates very general density-dependent growth rates and competition terms. Furthermore, we prove that persistence is robust to small, possibly density dependent, perturbations of the growth rates, dispersal matrix and covariance matrix of the environmental noise. We also show that the stochastic growth rate depends continuously on the coefficients. Our work allows the environmental noise driving our system to be degenerate. This is relevant from a biological point of view since, for example, the environments of the different patches can be perfectly correlated. We show how one can adapt the nondegenerate results to the degenerate setting. As an example we fully analyze the two-patch case, [Formula: see text], and show that the stochastic growth rate is a decreasing function of the dispersion rate. In particular, coupling two
Ross, Megan V.; Alisaukas, Ray T.; Douglas, David C.; Kellett, Dana K.
2017-01-01
A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992–2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May–30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment
Tenkès, Lucille-Marie; Hollerbach, Rainer; Kim, Eun-jin
2017-12-01
A probabilistic description is essential for understanding growth processes in non-stationary states. In this paper, we compute time-dependent probability density functions (PDFs) in order to investigate stochastic logistic and Gompertz models, which are two of the most popular growth models. We consider different types of short-correlated multiplicative and additive noise sources and compare the time-dependent PDFs in the two models, elucidating the effects of the additive and multiplicative noises on the form of PDFs. We demonstrate an interesting transition from a unimodal to a bimodal PDF as the multiplicative noise increases for a fixed value of the additive noise. A much weaker (leaky) attractor in the Gompertz model leads to a significant (singular) growth of the population of a very small size. We point out the limitation of using stationary PDFs, mean value and variance in understanding statistical properties of the growth in non-stationary states, highlighting the importance of time-dependent PDFs. We further compare these two models from the perspective of information change that occurs during the growth process. Specifically, we define an infinitesimal distance at any time by comparing two PDFs at times infinitesimally apart and sum these distances in time. The total distance along the trajectory quantifies the total number of different states that the system undergoes in time, and is called the information length. We show that the time-evolution of the two models become more similar when measured in units of the information length and point out the merit of using the information length in unifying and understanding the dynamic evolution of different growth processes.
Time-dependent density functional theory for nonlinear properties of open-shell systems.
Rinkevicius, Zilvinas; Jha, Prakash Chandra; Oprea, Corneliu I; Vahtras, Olav; Agren, Hans
2007-09-21
This paper presents response theory based on a spin-restricted Kohn-Sham formalism for computation of time-dependent and time-independent nonlinear properties of molecules with a high spin ground state. The developed approach is capable to handle arbitrary perturbations and constitutes an efficient procedure for evaluation of electric, magnetic, and mixed properties. Apart from presenting the derivation of the proposed approach, we show results from illustrating calculations of static and dynamic hyperpolarizabilities of small Si(3n+1)H(6n+3) (n=0,1,2) clusters which mimic Si(111) surfaces with dangling bond defects. The results indicate that the first hyperpolarizability tensor components of Si(3n+1)H(6n+3) have an ordering compatible with the measurements of second harmonic generation in SiO2/Si(111) interfaces and, therefore, support the hypothesis that silicon surface defects with dangling bonds are responsible for this phenomenon. The results exhibit a strong dependence on the quality of basis set and exchange-correlation functional, showing that an appropriate set of diffuse functions is required for reliable predictions of the first hyperpolarizability of open-shell compounds.
Yan, Cui-ping; Zhang, Yong-qing; Zhang, Ding-yi; Dang, Jian-you
2008-08-01
In a field experiment with split-split plot design, the effects of sowing date and planting density on the grain's protein component and quality of strong gluten wheat cultivar Linyou 145 and medium gluten wheat cultivar Linyou 2018 were studied. The results showed that proper sowing date brought the highest protein content and yield in wheat grain. With sowing date postponed, the grain's gliadin and glutenin contents of Linyou 145 increased obviously, while those of Linyou 2018 changed little. The grain quality of Linyou 145 was more affected by sowing date, compared with that of Linyou 2018. When sowing at proper date, the grain's protein and glutenin contents had significant correlations with its wet gluten content, sedimentation value, dough stability time, softness, and evaluation value; while when the sowing date postponed, there existed a positive correlation between the contents of gliadin and wet gluten. The change of the proportions of different protein components in wheat grain induced by the variation of sowing date could be the main reason of the improvement in wheat grain quality. Within the test range (2.25 million - 3.75 million plants x hm(-2)) of planting density, the grain's protein content was less affected, but the grain quality of Linyou 145 was affected to a certain extent. Low planting density (2.25 million plants x hm(-2)) brought the best grain quality of Linyou 2018.
Pelzer, Kenley; Greenman, Loren; Gidofalvi, Gergely; Mazziotti, David A
2011-06-09
Polyaromatic hydrocarbons (PAHs) are a class of organic molecules with importance in several branches of science, including medicine, combustion chemistry, and materials science. The delocalized π-orbital systems in PAHs require highly accurate electronic structure methods to capture strong electron correlation. Treating correlation in PAHs has been challenging because (i) traditional wave function methods for strong correlation have not been applicable since they scale exponentially in the number of strongly correlated orbitals, and (ii) alternative methods such as the density-matrix renormalization group and variational two-electron reduced density matrix (2-RDM) methods have not been applied beyond linear acene chains. In this paper we extend the earlier results from active-space variational 2-RDM theory [Gidofalvi, G.; Mazziotti, D. A. J. Chem. Phys. 2008, 129, 134108] to the more general two-dimensional arrangement of rings--acene sheets--to study the relationship between geometry and electron correlation in PAHs. The acene-sheet calculations, if performed with conventional wave function methods, would require wave function expansions with as many as 1.5 × 10(17) configuration state functions. To measure electron correlation, we employ several RDM-based metrics: (i) natural-orbital occupation numbers, (ii) the 1-RDM von Neumann entropy, (iii) the correlation energy per carbon atom, and (iv) the squared Frobenius norm of the cumulant 2-RDM. The results confirm a trend of increasing polyradical character with increasing molecular size previously observed in linear PAHs and reveal a corresponding trend in two-dimensional (arch-shaped) PAHs. Furthermore, in PAHs of similar size they show significant variations in correlation with geometry. PAHs with the strictly linear geometry (chains) exhibit more electron correlation than PAHs with nonlinear geometries (sheets).
Accuracy of estimated geometric parameters of trees depending on the LIDAR data density
Hadas, Edyta; Estornell, Javier
2015-04-01
The estimation of dendrometric variables has become important for spatial planning and agriculture projects. Because classical field measurements are time consuming and inefficient, airborne LiDAR (Light Detection and Ranging) measurements are successfully used in this area. Point clouds acquired for relatively large areas allows to determine the structure of forestry and agriculture areas and geometrical parameters of individual trees. In this study two LiDAR datasets with different densities were used: sparse with average density of 0.5pt/m2 and the dense with density of 4pt/m2. 25 olive trees were selected and field measurements of tree height, crown bottom height, length of crown diameters and tree position were performed. To determine the tree geometric parameters from LiDAR data, two independent strategies were developed that utilize the ArcGIS, ENVI and FUSION software. Strategy a) was based on canopy surface model (CSM) slicing at 0.5m height and in strategy b) minimum bounding polygons as tree crown area were created around detected tree centroid. The individual steps were developed to be applied also in automatic processing. To assess the performance of each strategy with both point clouds, the differences between the measured and estimated geometric parameters of trees were analyzed. As expected, the tree height were underestimated for both strategies (RMSE=0.7m for dense dataset and RMSE=1.5m for sparse) and tree crown height were overestimated (RMSE=0.4m and RMSE=0.7m for dense and sparse dataset respectively). For dense dataset, strategy b) allows to determine more accurate crown diameters (RMSE=0.5m) than strategy a) (RMSE=0.8m), and for sparse dataset, only strategy a) occurs to be relevant (RMSE=1.0m). The accuracy of strategies were also examined for their dependency on tree size. For dense dataset, the larger the tree (height or crown longer diameter), the higher was the error of estimated tree height, and for sparse dataset, the larger the tree
Kishi, Ryohei; Nakano, Masayoshi
2011-04-21
A novel method for the calculation of the dynamic polarizability (α) of open-shell molecular systems is developed based on the quantum master equation combined with the broken-symmetry (BS) time-dependent density functional theory within the Tamm-Dancoff approximation, referred to as the BS-DFTQME method. We investigate the dynamic α density distribution obtained from BS-DFTQME calculations in order to analyze the spatial contributions of electrons to the field-induced polarization and clarify the contributions of the frontier orbital pair to α and its density. To demonstrate the performance of this method, we examine the real part of dynamic α of singlet 1,3-dipole systems having a variety of diradical characters (y). The frequency dispersion of α, in particular in the resonant region, is shown to strongly depend on the exchange-correlation functional as well as on the diradical character. Under sufficiently off-resonant condition, the dynamic α is found to decrease with increasing y and/or the fraction of Hartree-Fock exchange in the exchange-correlation functional, which enhances the spin polarization, due to the decrease in the delocalization effects of π-diradical electrons in the frontier orbital pair. The BS-DFTQME method with the BHandHLYP exchange-correlation functional also turns out to semiquantitatively reproduce the α spectra calculated by a strongly correlated ab initio molecular orbital method, i.e., the spin-unrestricted coupled-cluster singles and doubles.
Wave-vector-dependent electron-phonon coupling and the charge-density-wave transition in TbT e3
Maschek, M.; Rosenkranz, S.; Heid, R.; Said, A. H.; Giraldo-Gallo, P.; Fisher, I. R.; Weber, F.
2015-06-01
We present a high-energy-resolution inelastic x-ray scattering investigation of the soft phonon mode in the charge-density-wave (CDW) system TbT e3 . We analyze our data based on lattice dynamical calculations using density-functional-perturbation theory and find clear evidence that strongly momentum-dependent electron-phonon coupling defines the periodicity of the CDW superstructure: Our experiment reveals strong phonon softening and increased phonon linewidths over a large part in reciprocal space adjacent to the CDW ordering vector qCDW=(0 ,0 ,0.3 ) . Further, qCDW is clearly offset from the wave vector of (weak) Fermi surface nesting qFS=(0 ,0 ,0.25 ) , and our detailed analysis indicates that electron-phonon coupling is responsible for this shift. Hence, we can add TbT e3 , which was previously considered as a canonical CDW compound following the Peierls scenario, to the list of distinct charge-density-wave materials characterized by momentum-dependent electron-phonon coupling.
Wilmers, Christopher C; Post, Eric; Hastings, Alan
2007-05-01
While it is widely appreciated that climate can affect the population dynamics of various species, a mechanistic understanding of how climate interacts with life-history traits to influence population fluctuations requires development. Here we build a general density-dependent age-structured model that accounts for differential responses in life-history traits to increasing population density. We show that as the temporal frequency of favorable environmental conditions increases, population fluctuations also increase provided that unfavorable environmental conditions still occur. As good years accumulate and the number of individuals in a population increases, successive life-history traits become vulnerable to density dependence once a return to unfavorable conditions prevails. The stronger this ratcheting of density dependence in life-history traits by autocorrelated climatic conditions, the larger the population fluctuations become. Highly fecund species, and those in which density dependence occurs in juvenile and adult vital rates at similar densities, are most sensitive to increases in the frequency of favorable conditions. Understanding the influence of global warming on temporal correlation in regional environmental conditions will be important in identifying those species liable to exhibit increased population fluctuations that could lead to their extinction.
Directory of Open Access Journals (Sweden)
Rasmus Kaspersson
Full Text Available While the prevalence of density-dependence is well-established in population ecology, few field studies have investigated its underlying mechanisms and their relative population-level importance. Here, we address these issues, and more specifically, how differences in body-size influence population regulation. For this purpose, two experiments were performed in a small coastal stream on the Swedish west coast, using juvenile brown trout (Salmo trutta as a study species. We manipulated densities of large and small individuals, and observed effects on survival, migration, condition and individual growth rate in a target group of intermediate-sized individuals. The generality of the response was investigated by reducing population densities below and increasing above the natural levels (removing and adding large and small individuals. Reducing the density (relaxing the intensity of competition had no influence on the response variables, suggesting that stream productivity was not a limiting factor at natural population density. Addition of large individuals resulted in a negative density-dependent response, while no effect was detected when adding small individuals or when maintaining the natural population structure. We found that the density-dependent response was revealed as reduced growth rate rather than increased mortality and movement, an effect that may arise from exclusion to suboptimal habitats or increased stress levels among inferior individuals. Our findings confirm the notion of interference competition as the primary mode of competition in juvenile salmonids, and also show that the feedback-mechanisms of density-dependence are primarily acting when increasing densities above their natural levels.
Two-electron Rabi oscillations in real-time time-dependent density-functional theory.
Habenicht, Bradley F; Tani, Noriyuki P; Provorse, Makenzie R; Isborn, Christine M
2014-11-14
We investigate the Rabi oscillations of electrons excited by an applied electric field in several simple molecular systems using time-dependent configuration interaction (TDCI) and real-time time-dependent density-functional theory (RT-TDDFT) dynamics. While the TDCI simulations exhibit the expected single-electron Rabi oscillations at a single resonant electric field frequency, Rabi oscillations in the RT-TDDFT simulations are a two-electron process. The existence of two-electron Rabi oscillations is determined both by full population inversion between field-free molecular orbitals and the behavior of the instantaneous dipole moment during the simulations. Furthermore, the Rabi oscillations in RT-TDDFT are subject to an intensity threshold of the electric field, below which Rabi oscillations do not occur and above which the two-electron Rabi oscillations occur at a broad range of frequencies. It is also shown that at field intensities near the threshold intensity, the field frequency predicted to induce Rabi oscillations by linear response TDDFT only produces detuned Rabi oscillations. Instead, the field frequency that yields the full two-electron population inversion and Rabi oscillation behavior is shown to be the average of single-electron transition frequencies from the ground S0 state and the doubly-excited S2 state. The behavior of the two-electron Rabi oscillations is rationalized via two possible models. The first model is a multi-photon process that results from the electric field interacting with the three level system such that three level Rabi oscillations may occur. The second model suggests that the mean-field nature of RT-TDDFT induces paired electron propagation.
Horbowy, Jan
2017-01-01
Biomass reconstructions to pre-assessment periods for commercially important and exploitable fish species are important tools for understanding long-term processes and fluctuation on stock and ecosystem level. For some stocks only fisheries statistics and fishery dependent data are available, for periods before surveys were conducted. The methods for the backward extension of the analytical assessment of biomass for years for which only total catch volumes are available were developed and tested in this paper. Two of the approaches developed apply the concept of the surplus production rate (SPR), which is shown to be stock density dependent if stock dynamics is governed by classical stock-production models. The other approach used a modified form of the Schaefer production model that allows for backward biomass estimation. The performance of the methods was tested on the Arctic cod and North Sea herring stocks, for which analytical biomass estimates extend back to the late 1940s. Next, the methods were applied to extend biomass estimates of the North-east Atlantic mackerel from the 1970s (analytical biomass estimates available) to the 1950s, for which only total catch volumes were available. For comparison with other methods which employs a constant SPR estimated as an average of the observed values, was also applied. The analyses showed that the performance of the methods is stock and data specific; the methods that work well for one stock may fail for the others. The constant SPR method is not recommended in those cases when the SPR is relatively high and the catch volumes in the reconstructed period are low. PMID:29131850
Breed, Greg A; Don Bowen, W; Leonard, Marty L
2013-10-01
In populations of colony-breeding marine animals, foraging around colonies can lead to intraspecific competition. This competition affects individual foraging behavior and can cause density-dependent population growth. Where behavioral data are available, it may be possible to infer the mechanism of intraspecific competition. If these mechanics are understood, they can be used to predict the population-level functional response resulting from the competition. Using satellite relocation and dive data, we studied the use of space and foraging behavior of juvenile and adult gray seals (Halichoerus grypus) from a large (over 200,000) and growing population breeding at Sable Island, Nova Scotia (44.0 (o)N 60.0 (o)W). These data were first analyzed using a behaviorally switching state-space model to infer foraging areas followed by randomization analysis of foraging region overlap of competing age classes. Patterns of habitat use and behavioral time budgets indicate that young-of-year juveniles (YOY) were likely displaced from foraging areas near (intraspecific competition between adults and juveniles, resulting in the currently observed decelerating logistic population growth. Competition theory predicts that intraspecific competition resulting in a clear losing competitor should cause compensatory population regulation. This functional response produces a smooth logistic growth curve as carrying capacity is approached, and is consistent with census data collected from this population over the past 50 years. The competitive mechanism causing compensatory regulation likely stems from the capital-breeding life-history strategy employed by gray seals. This strategy decouples reproductive success from resources available around breeding colonies and prevents females from competing with each other while young are dependent.
Sapling growth rates reveal conspecific negative density dependence in a temperate forest.
Ramage, Benjamin S; Johnson, Daniel J; Gonzalez-Akre, Erika; McShea, William J; Anderson-Teixeira, Kristina J; Bourg, Norman A; Clay, Keith
2017-10-01
Local tree species diversity is maintained in part by conspecific negative density dependence (CNDD). This pervasive mechanism occurs in a variety of forms and ecosystems, but research to date has been heavily skewed toward tree seedling survival in tropical forests. To evaluate CNDD more broadly, we investigated how sapling growth rates were affected by conspecific adult neighbors in a fully mapped 25.6 ha temperate deciduous forest. We examined growth rates as a function of the local adult tree neighborhood (via spatial autoregressive modeling) and compared the spatial positioning of faster-growing and slower-growing saplings with respect to adult conspecific and heterospecific trees (via bivariate point pattern analysis). In addition, to determine whether CNDD-driven variation in growth rates leaves a corresponding spatial signal, we extended our point pattern analysis to a static, growth-independent comparison of saplings and the next larger size class. We found that negative conspecific effects on sapling growth were most prevalent. Five of the nine species that were sufficiently abundant for analysis exhibited CNDD, while only one species showed evidence of a positive conspecific effect, and one or two species, depending on the analysis, displayed heterospecific effects. There was general agreement between the autoregressive models and the point pattern analyses based on sapling growth rates, but point pattern analyses based on single-point-in-time size classes yielded results that differed markedly from the other two approaches. Our work adds to the growing body of evidence that CNDD is an important force in temperate forests, and demonstrates that this process extends to sapling growth rates. Further, our findings indicate that point pattern analyses based solely on size classes may fail to detect the process of interest (e.g., neighborhood-driven variation in growth rates), in part due to the confounding of tree size and age.
Directory of Open Access Journals (Sweden)
Jan Horbowy
Full Text Available Biomass reconstructions to pre-assessment periods for commercially important and exploitable fish species are important tools for understanding long-term processes and fluctuation on stock and ecosystem level. For some stocks only fisheries statistics and fishery dependent data are available, for periods before surveys were conducted. The methods for the backward extension of the analytical assessment of biomass for years for which only total catch volumes are available were developed and tested in this paper. Two of the approaches developed apply the concept of the surplus production rate (SPR, which is shown to be stock density dependent if stock dynamics is governed by classical stock-production models. The other approach used a modified form of the Schaefer production model that allows for backward biomass estimation. The performance of the methods was tested on the Arctic cod and North Sea herring stocks, for which analytical biomass estimates extend back to the late 1940s. Next, the methods were applied to extend biomass estimates of the North-east Atlantic mackerel from the 1970s (analytical biomass estimates available to the 1950s, for which only total catch volumes were available. For comparison with other methods which employs a constant SPR estimated as an average of the observed values, was also applied. The analyses showed that the performance of the methods is stock and data specific; the methods that work well for one stock may fail for the others. The constant SPR method is not recommended in those cases when the SPR is relatively high and the catch volumes in the reconstructed period are low.
Two-electron Rabi oscillations in real-time time-dependent density-functional theory
International Nuclear Information System (INIS)
Habenicht, Bradley F.; Tani, Noriyuki P.; Provorse, Makenzie R.; Isborn, Christine M.
2014-01-01
We investigate the Rabi oscillations of electrons excited by an applied electric field in several simple molecular systems using time-dependent configuration interaction (TDCI) and real-time time-dependent density-functional theory (RT-TDDFT) dynamics. While the TDCI simulations exhibit the expected single-electron Rabi oscillations at a single resonant electric field frequency, Rabi oscillations in the RT-TDDFT simulations are a two-electron process. The existence of two-electron Rabi oscillations is determined both by full population inversion between field-free molecular orbitals and the behavior of the instantaneous dipole moment during the simulations. Furthermore, the Rabi oscillations in RT-TDDFT are subject to an intensity threshold of the electric field, below which Rabi oscillations do not occur and above which the two-electron Rabi oscillations occur at a broad range of frequencies. It is also shown that at field intensities near the threshold intensity, the field frequency predicted to induce Rabi oscillations by linear response TDDFT only produces detuned Rabi oscillations. Instead, the field frequency that yields the full two-electron population inversion and Rabi oscillation behavior is shown to be the average of single-electron transition frequencies from the ground S 0 state and the doubly-excited S 2 state. The behavior of the two-electron Rabi oscillations is rationalized via two possible models. The first model is a multi-photon process that results from the electric field interacting with the three level system such that three level Rabi oscillations may occur. The second model suggests that the mean-field nature of RT-TDDFT induces paired electron propagation
Abrams, Peter A
2009-09-01
Consumer-resource models are used to deduce the functional form of density dependence in the consumer population. A general approach to determining the form of consumer density dependence is proposed; this involves determining the equilibrium (or average) population size for a series of different harvest rates. The relationship between a consumer's mortality and its equilibrium population size is explored for several one-consumer/one-resource models. The shape of density dependence in the resource and the shape of the numerical and functional responses all tend to be "inherited" by the consumer's density dependence. Consumer-resource models suggest that density dependence will very often have both concave and convex segments, something that is impossible under the commonly used theta-logistic model. A range of consumer-resource models predicts that consumer population size often declines at a decelerating rate with mortality at low mortality rates, is insensitive to or increases with mortality over a wide range of intermediate mortalities, and declines at a rapidly accelerating rate with increased mortality when mortality is high. This has important implications for management and conservation of natural populations.
Energy Technology Data Exchange (ETDEWEB)
Satija, Sushil K. (National Institute of Standards and Technology, Gaithersburg, MD); Mendez, Sergio (University of New Mexico, Albuquerque, NM); Balamurugan, Sreelatha S. (University of New Mexico, Albuquerque, NM); Balamurugan, Subramanian (University of New Mexico, Albuquerque, NM); Kent, Michael Stuart; Yim, Hyun; Lopez, Gabriel P. (University of New Mexico, Albuquerque, NM)
2003-07-01
1500 {angstrom}. More recently, Balamurugan et al. used surface plasmon resonance (SPR) to probe conformational changes in a PNIPAM brush grafted onto a gold layer by atom transfer radical polymerization (ATRP). For a sample with a dry film thickness of 517 {angstrom}, the SPR measurements indicated a significant contraction (extension of the layer with increasing/decreasing) temperature through the transition. Quantification of the change in profile characteristics was not reported, but it was noted that the change in the SPR signal occurred over a much broader range of temperature (15-35 C) than is typical of the transition for free chains in bulk solution. No systematic study of detailed PNIPAM chain conformations has yet been reported as a function of the two critical brush parameters, the surface density and molecular weight. A recent theoretical analysis by Baulin and Halperin has identified the surface density as a critical parameter demarcating different regimes of behavior. This arises from the concentration dependence of the Flory {chi} parameter as obtained from a recent phase behavior study of free chains in solution. Little attention has been paid to the surface density in previous experimental studies of grafted PNIPAM chains. We have begun a systematic study of the temperature-dependent conformational changes of PNIPAM grafted chains in water as a function of surface density and molecular weight using neutron reflection (NR). In previous work, we investigated the conformational changes of PNIPAM chains tethered to silicon oxide using two methods. The first was the 'grafting from' method in which N-isopropylacrylamide monomers were polymerized from the silicon surface with a chain transfer, free-radical technique. In the second method, preformed PNIPAM chains with carboxylic acid end groups associated with terminal hydroxyl groups of a mixed self-assembling monolayer. Detailed concentration profiles of the PNIPAM brushes were determined in D
Optical rotation calculated with time-dependent density functional theory: the OR45 benchmark.
Srebro, Monika; Govind, Niranjan; de Jong, Wibe A; Autschbach, Jochen
2011-10-13
Time-dependent density functional theory (TDDFT) computations are performed for 42 organic molecules and three transition metal complexes, with experimental molar optical rotations ranging from 2 to 2 × 10(4) deg cm(2) dmol(-1). The performances of the global hybrid functionals B3LYP, PBE0, and BHLYP, and of the range-separated functionals CAM-B3LYP and LC-PBE0 (the latter being fully long-range corrected), are investigated. The performance of different basis sets is studied. When compared to liquid-phase experimental data, the range-separated functionals do, on average, not perform better than B3LYP and PBE0. Median relative deviations between calculations and experiment range from 25 to 29%. A basis set recently proposed for optical rotation calculations (LPol-ds) on average does not give improved results compared to aug-cc-pVDZ in TDDFT calculations with B3LYP. Individual cases are discussed in some detail, among them norbornenone for which the LC-PBE0 functional produced an optical rotation that is close to available data from coupled-cluster calculations, but significantly smaller in magnitude than the liquid-phase experimental value. Range-separated functionals and BHLYP perform well for helicenes and helicene derivatives. Metal complexes pose a challenge to first-principles calculations of optical rotation.
Density-dependent hopping for ultracold atoms immersed in a Bose-Einstein-condensate vortex lattice
Chaviguri, R. H.; Comparin, T.; Di Liberto, M.; Caracanhas, M. A.
2018-02-01
Both mixtures of atomic Bose-Einstein condensates and systems with atoms trapped in optical lattices have been intensely explored theoretically, mainly due to the exceptional developments on the experimental side. We investigate the properties of ultracold atomic impurities (bosons) immersed in a vortex lattice of a second Bose-condensed species. In contrast to the static optical-lattice configuration, the vortex lattice presents intrinsic dynamics given by its Tkachenko modes. These excitations induce additional correlations between the impurities, which consist of a long-range attractive potential and a density-dependent hopping, described here in the framework of an extended Bose-Hubbard model. We compute the quantum phase diagram of the impurity species through a Gutzwiller ansatz and through the mean-field approach, and separately identify the effects of the two additional terms, i.e., the shift and the deformation of the Mott-insulator lobes. The long-range attraction, in particular, induces the existence of a triple point in the phase diagram, in agreement with previous quantum Monte Carlo calculations [Chaviguri et al., Phys. Rev. A 95, 053639 (2017), 10.1103/PhysRevA.95.053639].
Energy Technology Data Exchange (ETDEWEB)
Vecharynski, Eugene [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division; Brabec, Jiri [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division; Shao, Meiyue [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division; Govind, Niranjan [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab.; Yang, Chao [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division
2017-12-01
We present two efficient iterative algorithms for solving the linear response eigen- value problem arising from the time dependent density functional theory. Although the matrix to be diagonalized is nonsymmetric, it has a special structure that can be exploited to save both memory and floating point operations. In particular, the nonsymmetric eigenvalue problem can be transformed into a product eigenvalue problem that is self-adjoint with respect to a K-inner product. This product eigenvalue problem can be solved efficiently by a modified Davidson algorithm and a modified locally optimal block preconditioned conjugate gradient (LOBPCG) algorithm that make use of the K-inner product. The solution of the product eigenvalue problem yields one component of the eigenvector associated with the original eigenvalue problem. However, the other component of the eigenvector can be easily recovered in a postprocessing procedure. Therefore, the algorithms we present here are more efficient than existing algorithms that try to approximate both components of the eigenvectors simultaneously. The efficiency of the new algorithms is demonstrated by numerical examples.
Phase separation driven by density-dependent movement: A novel mechanism for ecological patterns.
Liu, Quan-Xing; Rietkerk, Max; Herman, Peter M J; Piersma, Theunis; Fryxell, John M; van de Koppel, Johan
2016-12-01
Many ecosystems develop strikingly regular spatial patterns because of small-scale interactions between organisms, a process generally referred to as spatial self-organization. Self-organized spatial patterns are important determinants of the functioning of ecosystems, promoting the growth and survival of the involved organisms, and affecting the capacity of the organisms to cope with changing environmental conditions. The predominant explanation for self-organized pattern formation is spatial heterogeneity in establishment, growth and mortality, resulting from the self-organization processes. A number of recent studies, however, have revealed that movement of organisms can be an important driving process creating extensive spatial patterning in many ecosystems. Here, we review studies that detail movement-based pattern formation in contrasting ecological settings. Our review highlights that a common principle, where movement of organisms is density-dependent, explains observed spatial regular patterns in all of these studies. This principle, well known to physics as the Cahn-Hilliard principle of phase separation, has so-far remained unrecognized as a general mechanism for self-organized complexity in ecology. Using the examples presented in this paper, we explain how this movement principle can be discerned in ecological settings, and clarify how to test this mechanism experimentally. Our study highlights that animal movement, both in isolation and in unison with other processes, is an important mechanism for regular pattern formation in ecosystems. Copyright Â© 2016 Elsevier B.V. All rights reserved.
DEFF Research Database (Denmark)
Jansen, Teunis; Burns, F.
2015-01-01
. The effect of adult density was minor, but increasing with age. The ontogenetic progression in density dependant regulation of growth appeared to reflect the spatial dynamics (migration patterns) in the feeding season. This is the first time growth patterns quantified in the adult mackerel population have......Density dependence of somatic growth has an important, but overlooked, impact on fisheries management advice. We therefore examined how growth relates to abundance in a case where growth has been observed to vary substantially in recent years, namely North East Atlantic mackerel, one of the most...... widespread and commercially important fish stocks in the North Atlantic. Growth of juvenile and early adult North East Atlantic mackerel was found to be decreasing since the late 1990s. Modelling showed that growth was related to density. Mean growth rate during the first year was tightly correlated...
Kocsmár, Éva; Szirtes, Ildikó; Kramer, Zsófia; Szijártó, Attila; Bene, László; Buzás, György Miklós; Kenessey, István; Bronsert, Peter; Csanadi, Agnes; Lutz, Lisa; Werner, Martin; Wellner, Ulrich Friedrich; Kiss, András; Schaff, Zsuzsa; Lotz, Gábor
2017-08-01
Conventional stainings (including H&E and special stains like Giemsa) are the most widely applied histopathologic detection methods of Helicobacter pylori (HP). We aimed to compare the diagnostic performance of Giemsa staining with immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH) on a monocentric cohort of 2896 gastric biopsies and relate results to histologic alterations in order to find such histopathologic subgroups in which these methods underperform. All cases were categorized regarding presence or absence of chronic gastritis, inflammatory activity, and mucosal structural alterations. Giemsa revealed 687 cases (23.7%), IHC 795 cases (27.5%), and FISH 788 cases (27.2%) as being HP positive. Giemsa showed significantly lower overall sensitivity (83.3%) compared to IHC (98.8%) and FISH (98.0%). Moreover, the sensitivity of Giemsa dramatically dropped to 33.6% in the nonactive cases. We found that sensitivity of Giemsa strongly depends on HP density and, accordingly, on the presence of activity. Structural alterations (intestinal metaplasia, atrophy, etc.) had only no or weak effect on sensitivity of the three stainings. Both IHC and FISH proved to be equally reliable HP detecting techniques whose diagnostic performance is minimally influenced by mucosal inflammatory and structural alterations contrary to conventional stainings. We highly recommend immunohistochemistry for clinically susceptible, nonactive chronic gastritis cases, if the conventional stain-based HP detection is negative. Moreover, we recommend to use IHC more widely as basic HP stain. Helicobacter pylori FISH technique is primarily recommended to determine bacterial clarithromycin resistance. Furthermore, it is another accurate diagnostic tool for HP. © 2017 John Wiley & Sons Ltd.
Density functional approximation for spin dependent quantum transport in magnetic nano structures
International Nuclear Information System (INIS)
Nyunt, Khine
2009-01-01
In quasi-classical theoretical framework, the transport of electrons and holes in semiconductor devices is treated with the Boltzmann transport equation or quantum-mechanical energy band theory - viz., the effective mass approximation and the random phase approximation. On the other hand, in the mesoscopic, nano electronic devices, for three- and lower- dimensional structures with nanometer scaling, the wave properties, spin, charge and the interactions between spin and charge of electrons are fully utilized, such as in artificial mini-Brillouin zones, quantum size effects, Coulomb blockade of single-electron tunneling and spin-polarized giant magnetoresistance tunneling. The complexity associated with the classical quantum-mechanical formalism in the study of transport in magnetic nano structures can be avoided by applying the so-called, Hohenberg-Kohns density functional theory. In particular, the N-electron problem is formulated as N one-electron equations where each electron interacts with all other electrons via an effective exchange-correlation potential. These interactions are augmented using the electron charge density. Plane wave sets and total energy pseudo-potential methods can be used self-consistently, to solve the Kohn-Sham one-electron equations. Because of the limitations of quasi-classical theory, it is more appropriate to treat the magneto-transport problem in nano structures by using quantum many-body theory. The starting point of the quantum transport theory is to take an external field as a perturbation for the many-particle system in equilibrium. This leads to a linear response and gives corresponding transport coefficients. One useful application of the Greens function techniques in quantum magneto-transport is to convert a homogeneous differential equation into an integral equation, viz., as in the time-dependent Schrodinger equation. We have applied to scattering of nano structural defects (impurities) in the electron gas (metal) as many
Kametani, F; Jiang, J; Scheuerlein, C; Malagoli, A; Di Michiel, M; Huang, Y; Miao, H; Parrell, J A; Hellstrom, E E; Larbalestier, D C
2011-01-01
Most studies of Bi2Sr2CaCu2Ox (Bi2212) show that the critical current density Jc is limited by the connectivity of the filaments, but what determines the connectivity is still elusive. Here we report on the role played by filament porosity in limiting Jc. By a microstructural investigation of wires quenched from the melt state, we find that porosity in the unreacted wire agglomerates into bubbles that segment the Bi2212 melt within the filaments into discrete sections. These bubbles do not disappear during subsequent processing because they are only partially filled by Bi2212 grains as the Bi2212 forms on cooling. Correlating the microstructure of quenched wires to their final, fully processed Jc values shows an inverse relation between Jc and bubble density. Bubbles are variable between conductors and perhaps from sample to sample, but they occur frequently and almost completely fill the filament diameter, so they exert a strongly variable but always negative effect on Jc. Bubbles reduce the continuous Bi221...
International Nuclear Information System (INIS)
Magli, R.; Fredrikze, H.; Barocchi, F.
1991-01-01
We present an analysis of the density dependence of the static structure factor in low density 36 Ar gas at T = 140 K, from which we derive the three-body contribution. Within the experimental accuracy, the three-body contribution in the linear density expansion for the Fourier transform of the direct correlation function C(k) agrees, for 3 -1 , with theoretical calculations based on a pair potential and the Axilrod-Teller three-body potential, eventually modified for short-range effects; for k -1 the neutron diffraction data show a behaviour significantly different with respect to the theoretical predictions
Haddad, S.
2017-11-01
The symmetry energy of a nucleus is determined in a local density approximation and integrating over the entire density distribution of the nucleus, calculated utilizing the relativistic density-dependent Thomas-Fermi approach. The symmetry energy is found to decrease with increasing neutron excess in the nucleus. The isovector coupling channel reduces the symmetry energy, and this effect increases with increased neutron excess. The isovector coupling channel increases the symmetry energy integral in ^{40}Ca and reduces it in ^{48}Ca, and the interplay between the isovector and the isoscalar channels of the nuclear force explains this isotope effect.
International Nuclear Information System (INIS)
Roman-Duval, Julia; Jackson, James; Federrath, Christoph; Klessen, Ralf S.; Brunt, Christopher; Heyer, Mark
2011-01-01
Turbulence plays a major role in the formation and evolution of molecular clouds. Observationally, turbulent velocities are convolved with the density of an observed region. To correct for this convolution, we investigate the relation between the turbulence spectrum of model clouds, and the statistics of their synthetic observations obtained from principal component analysis (PCA). We apply PCA to spectral maps generated from simulated density and velocity fields, obtained from hydrodynamic simulations of supersonic turbulence, and from fractional Brownian motion (fBm) fields with varying velocity, density spectra, and density dispersion. We examine the dependence of the slope of the PCA pseudo-structure function, α PCA , on intermittency, on the turbulence velocity (β v ) and density (β n ) spectral indexes, and on density dispersion. We find that PCA is insensitive to β n and to the log-density dispersion σ s , provided σ s ≤ 2. For σ s > 2, α PCA increases with σ s due to the intermittent sampling of the velocity field by the density field. The PCA calibration also depends on intermittency. We derive a PCA calibration based on fBm structures with σ s ≤ 2 and apply it to 367 13 CO spectral maps of molecular clouds in the Galactic Ring Survey. The average slope of the PCA structure function, (α PCA ) = 0.62 ± 0.2, is consistent with the hydrodynamic simulations and leads to a turbulence velocity exponent of (β v ) = 2.06 ± 0.6 for a non-intermittent, low density dispersion flow. Accounting for intermittency and density dispersion, the coincidence between the PCA slope of the GRS clouds and the hydrodynamic simulations suggests β v ≅ 1.9, consistent with both Burgers and compressible intermittent turbulence.
Ishimatsu, N; Takata, M; Nishibori, E; Sakata, M; Hayashi, J; Shirotani, I; Shimomura, O
2002-01-01
The physical properties relating to 4f electrons in cerium phosphide, especially the temperature dependence and the isomorphous transition that occurs at around 10 GPa, were studied by means of x-ray powder diffraction and charge density distribution maps derived by the maximum-entropy method. The compressibility of CeP was exactly determined using a helium pressure medium and the anomaly that indicated the isomorphous transition was observed in the compressibility. We also discuss the anisotropic charge density distribution of Ce ions and its temperature dependence.
Ellis, J D; Hepburn, H R; Ellis, A M; Elzen, P J
2003-08-01
Increasing small hive beetle (Aethina tumida Murray) density changes prison construction and guarding behaviour in European honeybees (Apis mellifera L.). These changes include more guard bees per imprisoned beetle and the construction of more beetle prisons at the higher beetle density. Despite this, the number of beetles per prison (inmate density) did not change. Beetles solicited food more actively at the higher density and at night. In response, guard bees increased their aggressive behaviour towards beetle prisoners but did not feed beetles more at the higher density. Only 5% of all beetles were found among the combs at the low density but this percentage increased five-fold at the higher one. Successful comb infiltration (and thus reproduction) by beetles is a possible explanation for the significant damage beetles cause to European honeybee colonies in the USA.
Truncation scheme of time-dependent density-matrix approach II
Energy Technology Data Exchange (ETDEWEB)
Tohyama, Mitsuru [Kyorin University School of Medicine, Mitaka, Tokyo (Japan); Schuck, Peter [Institut de Physique Nucleaire, IN2P3-CNRS, Universite Paris-Sud, Orsay (France); Laboratoire de Physique et de Modelisation des Milieux Condenses, CNRS et Universite Joseph Fourier, Grenoble (France)
2017-09-15
A truncation scheme of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy for reduced density matrices, where a three-body density matrix is approximated by two-body density matrices, is improved to take into account a normalization effect. The truncation scheme is tested for the Lipkin model. It is shown that the obtained results are in good agreement with the exact solutions. (orig.)
International Nuclear Information System (INIS)
Achterberg, O.; D'Agostini, G.; Apel, W.D.; Engler, J.; Fluegge, G.; Forstbauer, B.; Fries, D.C.; Fues, W.; Gamerdinger, K.; Henkes, T.; Hopp, G.; Krueger, M.; Kuester, H.; Mueller, H.; Randoll, H.; Schmidt, G.; Schneider, H.; Boer, W. de; Buschhorn, G.; Grindhammer, G.; Grosse-Wiesmann, P.; Gunderson, B.; Kiesling, C.; Kotthaus, R.; Kruse, U.; Lierl, H.; Lueers, D.; Oberlack, H.; Schacht, P.; Bonneaud, G.; Colas, P.; Cordier, A.; Davier, M.; Fournier, D.; Grivaz, J.F.; Haissinski, J.; Journe, V.; Laplanche, F.; Le Diberder, F.; Mallik, U.; Ros, E.; Veillet, J.J.; Behrend, H.J.; Fenner, H.; Schachter, M.J.; Schroeder, V.; Sindt, H.
1983-12-01
Hadronic events obtained with the CELLO detector at PETRA are compared with second order QCD predictions using different models for the fragmentation of quarks and gluons into hadrons. We find that the model dependence in the determination of the strong coupling constant persists when going from first to second order QCD calculations. (orig.)
Changes in density of aluminium, lead and zinc melts dependent on temperature
International Nuclear Information System (INIS)
Kazachkov, S.P.; Kochegura, N.M.; Markovskij, E.A.
1979-01-01
Density of aluminium, lead and zinc in various aggregate states has been studied in a wide temperature range. The density of the above metals was found to manifest temperature hysteresis after melting and cyclic change at the temperature of melting and crystallization. These phenomena are in agreement with the Stuart model of liquid state
Analysis of physical mechanisms underlying density-dependent transport in porous media
Landman, A.J.
2005-01-01
In this thesis, the interaction between (large) density gradients and flow and transport in porous media is studied. Large gradients in the density of groundwater exist for example near deep salt rock formations, which are considered as possible long-term storage sites for radioactive waste.
Wilderness experience quality: Effects of use density depend on how experience is conceived
David N. Cole; Troy E. Hall
2012-01-01
Different conceptions of experience and experience quality can explain ambiguous relationships among use density, crowding, experience and experience quality. We employed multiple methods to quantify experiential dimensions at a popular lake in the Alpine Lakes Wilderness, WA. Comparing weekdays to weekends, when use density is typically four times as high, we assessed...
Local environment and density-dependent feedbacks determine population growth in a forest herb
DEFF Research Database (Denmark)
Dahlgren, Johan Petter; Östergård, Hannah; Ehrlén, Johan
2014-01-01
Linking spatial variation in environmental factors to variation in demographic rates is essential for a mechanistic understanding of the dynamics of populations. However, we still know relatively little about such links, partly because feedbacks via intraspecific density make them difficult...... shade on survival and growth, while density was negatively correlated with these vital rates. Density was also negatively correlated with average individual size in the study plots, which is consistent with self-thinning. In addition, average plant sizes were larger than predicted by density in plots...... similar to those observed in the field. The results illustrate how the local environment can determine dynamics of populations and that intraspecific density may have to be more carefully considered in studies of plant demography and population viability analyses of threatened species. We conclude...
Directory of Open Access Journals (Sweden)
Sampa Banerjee
2017-06-01
Full Text Available Consequences of larval competition at the population level provide explanation for the differences in relative abundance of Aedes aegypti and Aedes albopictus in different geographical regions. The outcome of competition is assessed through the estimates of the life history traits as a response to varying density and resource available for larval development. In the present study, variations in the life history traits due to density-dependent intra- and inter- specific competition involving A. aegypti and A. albopictus were assessed following the minimalist model. The instar-I larvae (0-day old F2 generation of both Aedes species were reared to the adult stages using the initial rearing density of 1, 2, 4 and 6 (individuals/10ml in multiple replicates. The age at pupation, pupal weight, adult weight and adult wing length of the individuals were considered as the response variables and surrogates of estimating the competitive interactions. Density dependent variations in the competitive interactions were evident for both the mosquitoes with reference to the selected life history traits. In A. aegypti, the life history traits varied with the levels of competition, which was not observed for A. albopictus. Although the density levels considered in the present instance were lower than in earlier studies, the observations were similar, with A. albopictus being competitively superior. It appears that irrespective of the density levels, interspecific competition affects A. aegypti and thus may bear population level consequences and overall abundance in the areas where both species are present.
Roy, G; Bissonnette, L R
2001-09-20
Backscatter and depolarization lidar measurements from clouds and precipitation are reported as functions of the elevation angle of the pointing lidar direction. We recorded the data by scanning the lidar beam (Nd:YAG) at a constant angular speed of ~3.5 degrees /s while operating at a repetition rate of 10 Hz. We show that in rain there is an evident and at times spectacular dependence on the elevation angle. That dependence appears to be sensitive to raindrop size. We have developed a three-dimensional polarization-dependent ray-tracing algorithm to calculate the backscatter and the depolarization ratio by large nonspherical droplets. We have applied it to raindrop shapes derived from existing static and dynamic (oscillating) models. We show that many of the observed complex backscatter and depolarization features can be interpreted to a good extent by geometrical optics. These results suggest that there is a definite need for more extensive calculations of the scattering phase matrix elements for large deformed raindrops as functions of the direction of illumination. Obvious applications are retrieval of information on the liquid-solid phase of precipitation and on the size and the vibration state of raindrops.
Energy Technology Data Exchange (ETDEWEB)
Typel, S.; Wolter, H.H. [Sektion Physik, Univ. Muenchen, Garching (Germany)
1998-06-01
Nuclear matter and ground state properties for (proton and neutron) semi-closed shell nuclei are described in relativistic mean field theory with coupling constants which depend on the vector density. The parametrization of the density dependence for {sigma}-, {omega}- and {rho}-mesons is obtained by fitting to properties of nuclear matter and some finite nuclei. The equation of state for symmetric and asymmetric nuclear matter is discussed. Finite nuclei are described in Hartree approximation, including a charge and an improved center-of-mass correction. Pairing is considered in the BCS approximation. Special attention is directed to the predictions for properties at the neutron and proton driplines, e.g. for separation energies, spin-orbit splittings and density distributions. (orig.)
Yuan, Yi; Zhu, Zude; Shi, Jinfu; Zou, Zhiling; Yuan, Fei; Liu, Yijun; Lee, Tatia M. C.; Weng, Xuchu
2009-01-01
Numerous studies have documented cognitive impairments and hypoactivity in the prefrontal and anterior cingulate cortices in drug users. However, the relationships between opiate dependence and brain structure changes in heroin users are largely unknown. In the present study, we measured the density of gray matter (DGM) with voxel-based…
Czech Academy of Sciences Publication Activity Database
Vlasáková, Blanka
2015-01-01
Roč. 31, Part 1 (2015), s. 95-98 ISSN 0266-4674 R&D Projects: GA ČR GPP505/12/P039 Institutional support: RVO:67985939 Keywords : Clusia * ockroach * density dependence Subject RIV: EF - Botanics Impact factor: 0.975, year: 2015
Romaniello, P; de Boeij, PL
2005-01-01
We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the
Eijden, T.M. van; Ruijven, L.J. van; Giesen, E.B.W.
2004-01-01
Variation in the apparent stiffness of cancellous bone is generally ascribed to variation in cancellous structure and density, while the bone tissue stiffness is assumed to be constant. The purpose of the present study was to examine whether the bone tissue stiffness is dependent on the direction
Directory of Open Access Journals (Sweden)
Flávia Freitas Coelho
2005-09-01
Full Text Available Pistia stratiotes is an aquatic macrophyte that grows in temporary-ponds in the southern Pantanal, Brazil. It reproduces both sexually and asexually and is usually observed forming dense mats on the water surface, a condition favored by the plant’s vegetative reproduction coupled with an ability for rapid growth. In this study we examined the effect of densely crowded conditions on the production of reproductive and vegetative structures. In addition, we verified whether there is a trade-off between clonal growth and investment in sexual reproductive structures, and whether there is an allocation pattern with plant size. Individual plant biomass and the number of the rosettes producing sexual reproductive structures and vegetative growth structures both increased with density. Increase in plant size resulted in increased proportional allocation to sexual reproductive structures and vegetative growth structures. Allocation of biomass to reproduction did not occur at the expense of clonal growth. Thus, the density response appears as a increase of rosettes producing sexual reproductive structures and vegetative growth structures. Therefore, long leaves and stolons may be adaptive under densely crowded conditions where competition for light is intense. An important aspect in the study of trade-offs is the size-dependency of the allocation patterns .Usually, larger plants produce more biomass. Therefore, larger plants can allocate more biomass to both vegetative and sexual reproduction than smaller plants and thus show a positive correlation between both traits rather than the expected negative one. Rev. Biol. Trop. 53(3-4: 369-376. Epub 2005 Oct 3.Pistias strariotes es una macrófita acuática que crece en charcas estacionales en el Pantanal sureño de Brasil. Se reproduce tanto sexual como asexualmente y se obsrva generalmente que forma densas parches sobre la superficie del agua, una condicion que favorecida por la reproduccion vegetativa de la
Seed yield and protein content in sunflower depending on stand density
Directory of Open Access Journals (Sweden)
Balalić Igor M.
2016-01-01
Full Text Available The aim of this research was to investigate the effect of stand density on seed yield and protein content in sunflower hybrids. The field experiment was carried out at Rimski Šančevi location. Six NS sunflower hybrids were examined. Five hybrids are confectionery (NS Goliat, NS Slatki, NS Gricko, Vranac and Cepko, and one is used for bird food (NS-H-6485. The trial was arranged as randomized complete block design (RCBD with four replications. Sowing was done with six different densities (from 20,000 to 70,000 plants per hectare, with an increment of 10,000 plants per hectare. Analysis of variance (ANOVA showed that the effect of hybrid, stand density and hybrid × stand density interation were highly significant for seed yield and protein content. The highest seed yield, on the basis of average for all densities, was found in NS-H-6485 (4.77 t ha-1 and in NS Gricko (4.43 t ha-1. Average seed yield of hybrids significantly increased up to 50,000 plants per ha-1, when it reached the value of 4.50 t ha-1, and then decreased. Significantly higher protein content, taking into account all stand densities, showed hybrid Cepko (16.94%. Protein content, above the overall average value, was achieved in hybrid Vranac (16.11%. The highest protein content in the average for all six hybrids was at the lowest stand density (20,000 plants per ha-1, and then decreased up to higher densities. The results showed that stand density had significant effect on seed yield and protein content in sunflower hybrids. [Projekat Ministarstva nauke Republike Srbije, br. TR31025: The development of new cultivars and improving the technology of producing oil plant species for different purposes
The effects of density-dependent form factors for (e, e'p) reaction in quasi-elastic region
Energy Technology Data Exchange (ETDEWEB)
Kim, K.S. [Korea Aerospace University, School of Liberal Arts and Science, Goyang (Korea, Republic of); Cheoun, Myung-Ki [Soongsil University, Department of Physics, Seoul (Korea, Republic of); Kim, Hungchong [Kookmin University, Department of General Education, Seoul (Korea, Republic of); So, W.Y. [Kangwon National University at Dogye, Department of Radiological Science, Samcheok (Korea, Republic of)
2016-04-15
Within the framework of a relativistic single particle model, the effects of density-dependent electromagnetic form factors on the exclusive (e, e'p) reaction are investigated in the quasi-elastic region. The density-dependent electromagnetic form factors are generated from a quark-meson coupling model and used to calculate the cross sections in two different densities, either at the normal density of ρ{sub 0} ∝ 0.15 fm{sup -3} or at the lower density, 0.5ρ{sub 0}. Then these cross sections are analyzed in the two different kinematics: One is that the momentum of the outgoing nucleon is along the momentum transfer. The other is that the angle between the momentum of the outgoing nucleon and the momentum transfer is varied at fixed magnitude of the momentum of the outgoing nucleon. Our theoretical differential reduced cross sections are compared with the NIKHEF data for the {sup 208}Pb(e, e'p) reaction, which is related to the probability that a bound nucleon from a given orbit can be knocked-out of the nucleus. The effects of the density-dependent form factors increase the differential cross sections for both knocked-out proton and neutron by an amount of a few percent. Moreover they are shown to be almost the same within only a few percent, i.e., nearly independent of the shell location of knockout nucleons. These results are quite consistent with the characteristics of double magic nuclei which have relatively sharp smearing in the density distribution. (orig.)
Dadashev, R. Kh.; Dzhambulatov, R. S.; Mezhidov, V. Kh.; Elimkhanov, D. Z.
2018-05-01
Concentration dependences of the surface tension and density of solutions of three-component acetone-ethanol-water systems and the bounding binary systems at 273 K are studied. The molar volume, adsorption, and composition of surface layers are calculated. Experimental data and calculations show that three-component solutions are close to ideal ones. The surface tensions of these solutions are calculated using semi-empirical and theoretical equations. Theoretical equations qualitatively convey the concentration dependence of surface tension. A semi-empirical method based on the Köhler equation allows us to predict the concentration dependence of surface tension within the experimental error.
Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient
Hol, F.J.H.; Hubert, A.W.R.; Dekker, C.; Keymer Vergara, J.E.
2016-01-01
During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant
Carvalho, Luiz Sergio F; Martins, Naiara V; Moura, Filipe A; Cintra, Riobaldo M R; Almeida, Osorio L R; Quinaglia e Silva, Jose C; Sposito, Andrei C
2013-01-01
The decrease of insulin sensitivity (IS) during myocardial infarction (MI) is strongly associated with increased morbidity and mortality. Recent data suggest that in individuals under stable conditions, high-density lipoprotein (HDL) may improve IS. To date, the role of HDL in the modulation of IS in acute metabolic stress conditions such as MI remains unknown. To explore the association between plasma HDL-C and the change in IS during the acute phase of MI. Consecutive nondiabetic patients with ST-segment elevation MI (n = 22) underwent direct measurement of IS through the euglycemic hyperinsulinemic clamp on the first morning and on the fifth day after onset of MI. Patients were grouped according to HDL-C levels at admission above and below the median value (35 mg/dL). At admission, there was no significant difference in baseline IS index, clinical, anthropometric, or treatment characteristics between low and high HDL groups. Between admission and fifth day, there was a decrease of 8% in IS index in the low HDL group and an 11% increase in the high HDL group (P = .001 for intragroup and P = .012 for intergroup difference). This difference remained significant after we controlled for the sex, age, waist circumference, triglycerides, baseline IS index, and statin dose during hospitalization. This is the first study to provide evidence that plasma levels of HDL-C are strongly associated with the recovery rate of IS during the acute phase of MI. Copyright © 2013 National Lipid Association. Published by Elsevier Inc. All rights reserved.
Population density-dependent hair cortisol concentrations in rhesus monkeys (Macaca mulatta).
Dettmer, A M; Novak, M A; Meyer, J S; Suomi, S J
2014-04-01
Population density is known to influence acute measures of hypothalamic-pituitary-adrenal (HPA) axis activity in a variety of species, including fish, deer, birds, and humans. However, the effects of population density on levels of chronic stress are unknown. Given the fact that exposure to chronically elevated levels of circulating glucocorticoids results in a host of health disparities in animals and humans alike, it is important to understand how population density may impact chronic stress. We assessed hair cortisol concentrations (HCCs), which are reliable indicators of chronic HPA axis activity, in rhesus monkeys (Macaca mulatta) to determine the influence of population density on these values. In Experiment 1, we compared HCCs of monkeys living in high-density (HD; 1 monkey/0.87m(2)) and low-density (LD; 1 monkey/63.37m(2)) environments (N=236 hair samples) and found that HD monkeys exhibited higher hair cortisol across all age categories (infant, juvenile, young adult, adult, and aged) except infancy and aged (F(5)=4.240, p=0.001), for which differences were nearly significant. HD monkeys also received more severe fight wounds than LD monkeys (χ(2)=26.053, ppopulation levels across 5 years in the adult LD monkeys (N=155 hair samples) and found that increased population density was significantly positively correlated with HCCs in this semi-naturalistic population (r(s)=0.975, p=0.005). These are the first findings to demonstrate that increased population density is associated with increased chronic, endogenous glucocorticoid exposure in a nonhuman primate species. We discuss the implications of these findings with respect to laboratory research, population ecology, and human epidemiology. Published by Elsevier Ltd.
Niklasson, Anders M N; Weber, Valéry
2007-08-14
Linear scaling density matrix perturbation theory [A. M. N. Niklasson and M. Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is extended to basis-set-dependent quantum response calculations for a nonorthogonal basis set representation. The generalization is achieved by a perturbation-dependent congruence transform, derived from the factorization of the inverse overlap matrix, which transforms the generalized eigenvalue problem to an orthogonal, standard form. With this orthogonalization transform the basis-set-dependent perturbation in the overlap matrix is included in the orthogonalized Hamiltonian, which is expanded in orders of the perturbation. In this way density matrix perturbation theory developed for an orthogonal representation can be applied also to basis-set-dependent response calculations. The method offers an alternative to the previous solution of the basis-set-dependent response problem, based on a nonorthogonal generalization of the density matrix perturbation theory, where the calculations are performed within a purely nonorthogonal setting [A. M. N. Niklasson et al., J. Chem. Phys. 123, 44107 (2005)].
Egidi, Franco; Sun, Shichao; Goings, Joshua J; Scalmani, Giovanni; Frisch, Michael J; Li, Xiaosong
2017-06-13
We present a linear response formalism for the description of the electronic excitations of a noncollinear reference defined via Kohn-Sham spin density functional methods. A set of auxiliary variables, defined using the density and noncollinear magnetization density vector, allows the generalization of spin density functional kernels commonly used in collinear DFT to noncollinear cases, including local density, GGA, meta-GGA and hybrid functionals. Working equations and derivations of functional second derivatives with respect to the noncollinear density, required in the linear response noncollinear TDDFT formalism, are presented in this work. This formalism takes all components of the spin magnetization into account independent of the type of reference state (open or closed shell). As a result, the method introduced here is able to afford a nonzero local xc torque on the spin magnetization while still satisfying the zero-torque theorem globally. The formalism is applied to a few test cases using the variational exact-two-component reference including spin-orbit coupling to illustrate the capabilities of the method.
Dependence of intermittent density fluctuations on collisionality in TJ-K
Energy Technology Data Exchange (ETDEWEB)
Reuther, Kyle; Garland, Stephen; Ramisch, Mirko [Institut fuer Grenzflaechenverfahrenstechnikund Plasmatechnologie, Universitaet Stuttgart (Germany); Manz, Peter [Physik-Department E28, Technische Universitaet Muenchen, Garching (Germany)
2016-07-01
Particle and heat transport losses due to edge turbulence are well known phenomena commonly seen in toroidal magnetic confinement devices. Furthermore in the scrape-off layer (SOL), turbulent density fluctuations are often observed to be intermittent and dominate particle transport to the vessel walls. In the adiabatic limit (small collisionality), of the two-field Hasegawa-Wakatani model, simulated turbulent density fluctuations are observed to couple to potential fluctuations and exhibit Gaussian behavior. However, in the hydrodynamic limit (large collisionality) the density and potential decouple. As a result, the density becomes passively advected, evolves towards the vorticity, and exhibits intermittent behavior. The relationship between collisionality and intermittency is investigated experimentally at the stellarator TJ-K. To vary the plasma collisionality, which is related to electron density and temperature, parameters such as gas type, neutral gas pressure, magnetic field, and heating power are varied. Radial profiles of plasma density, temperature, floating potential, and vorticity are recorded via a scanning 7-tip Langmuir probe array. First results are presented.
DEFF Research Database (Denmark)
Yu, Yingpu; Scheel, Troels K.H.; Luna, Joseph M.
2017-01-01
Hepatitis C virus (HCV) requires the liver specific micro-RNA (miRNA), miR-122, to replicate. This was considered unique among RNA viruses until recent discoveries of HCV-related hepaciviruses prompting the question of a more general miR-122 dependence. Among hepaciviruses, the closest known HCV...... generated infectious NPHV/HCV chimeric viruses with the 5’ end of NPHV replacing orthologous HCV sequences. These chimeras were viable even in cells lacking miR-122, although miR-122 presence enhanced virus production. No other miRNAs bound this region. By random mutagenesis, we isolated HCV variants...... partially dependent on miR-122 as well as robustly replicating NPHV/HCV variants completely independent of any miRNAs. These miRNA independent variants even replicate and produce infectious particles in non-hepatic cells after exogenous delivery of apolipoprotein E (ApoE). Our findings suggest that miR-122...
Ke, Weiyao; Moreland, J. Scott; Bernhard, Jonah E.; Bass, Steffen A.
2017-10-01
We study the initial three-dimensional spatial configuration of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions using centrality and pseudorapidity-dependent measurements of the medium's charged particle density and two-particle correlations. A cumulant-generating function is first used to parametrize the rapidity dependence of local entropy deposition and extend arbitrary boost-invariant initial conditions to nonzero beam rapidities. The model is then compared to p +Pb and Pb + Pb charged-particle pseudorapidity densities and two-particle pseudorapidity correlations and systematically optimized using Bayesian parameter estimation to extract high-probability initial condition parameters. The optimized initial conditions are then compared to a number of experimental observables including the pseudorapidity-dependent anisotropic flows, event-plane decorrelations, and flow correlations. We find that the form of the initial local longitudinal entropy profile is well constrained by these experimental measurements.
Energy Technology Data Exchange (ETDEWEB)
Best, A.S.; Johst, K.; Muenkemueller, T.; Travis, J.M.J.
2007-09-15
Understanding the ability of species to shift their geographic range is of considerable importance given the current period of rapid climate change. Furthermore, a greater understanding of the spatial population dynamics underlying range shifting is required to complement the advances made in climate niche modelling. A simulation model is developed which incorporates three key features that have been largely overlooked in studies of range shifting dynamics: the form of intraspecific competition, density dependent dispersal and the transient dynamics of habitat patches. The results show that the exact shape of the response depends critically on both local and patch dynamics. Species whose intraspecific competition is contest based are more vulnerable than those whose competition is scramble based. Contesters are especially sensitive when combined with density dependent dispersal. Species living in patches whose carrying capacity grows slowly are also susceptible to rapid shifts of environmental conditions. A complementary analytic approach further highlights the importance of intraspecific competition. (au)
DEFF Research Database (Denmark)
Købmann, Brian Jensen; Westerhoff, H.V.; Snoep, J.L.
2002-01-01
Using molecular genetics we have introduced uncoupled ATPase activity in two different bacterial species, Escherichia coli and Lactococcus lactis, and determined the elasticities of the growth rate and glycolytic flux towards the intracellular [ATP]/[ADP] ratio. During balanced growth in batch...... cultures of E. coli the ATP demand was found to have almost full control on the glycolytic flux (FCC=0.96) and the flux could be stimulated by 70%. In contrast to this, in L. lactis the control by ATP demand on the glycolytic flux was close to zero. However, when we used non-growing cells of L. lactis...... (which have a low glycolytic flux) the ATP demand had a high flux control and the flux could be stimulated more than two fold. We suggest that the extent to which ATP demand controls the glycolytic flux depends on how much excess capacity of glycolysis is present in the cells....
International Nuclear Information System (INIS)
Kiesel, Maximilian Ludwig
2013-01-01
A general theory for all classes of unconventional superconductors is still one of the unsolved key issues in condensed-matter physics. Actually, it is not yet fully settled if there is a common underlying pairing mechanism. Instead, it might be possible that several distinct sources for unconventional (not phonon-mediated) superconductivity have to be considered, or an electron-phonon interaction is not negligible. The focus of this thesis is on the most probable mechanism for the formation of Cooper pairs in unconventional superconductors, namely a strictly electronic one where spin fluctuations are the mediators. Studying different superconductors in this thesis, the emphasis is put on material-independent features of the pairing mechanism. In addition, the investigation of the phase diagrams enables a view on the vicinity of superconductivity. Thus, it is possible to clarify which competing quantum fluctuations enhance or weaken the propensity for a superconducting state. The broad range of superconducting materials requires the use of more than one numerical technique to study an appropriate microscopic description. This is not a problem but a big advantage because this facilitates the approach-independent description of common underlying physics. For this evaluation, the strongly correlated cuprates are simulated with the variational cluster approach. Especially the question of a pairing glue is taken into consideration. Furthermore, it is possible to distinguish between retarded and non-retarded contributions to the gap function. The cuprates are confronted with the cobaltate Na x CoO 2 and graphene. These weakly correlated materials are investigated with the functional renormalization group (fRG) and reveal a comprehensive phase diagram, including a d+id-wave superconductivity, which breaks time-reversal symmetry. The corresponding gap function is nodeless, but for NaCoO, it features a doping-dependent anisotropy. In addition, some general considerations on
Energy Technology Data Exchange (ETDEWEB)
Kiesel, Maximilian Ludwig
2013-02-08
A general theory for all classes of unconventional superconductors is still one of the unsolved key issues in condensed-matter physics. Actually, it is not yet fully settled if there is a common underlying pairing mechanism. Instead, it might be possible that several distinct sources for unconventional (not phonon-mediated) superconductivity have to be considered, or an electron-phonon interaction is not negligible. The focus of this thesis is on the most probable mechanism for the formation of Cooper pairs in unconventional superconductors, namely a strictly electronic one where spin fluctuations are the mediators. Studying different superconductors in this thesis, the emphasis is put on material-independent features of the pairing mechanism. In addition, the investigation of the phase diagrams enables a view on the vicinity of superconductivity. Thus, it is possible to clarify which competing quantum fluctuations enhance or weaken the propensity for a superconducting state. The broad range of superconducting materials requires the use of more than one numerical technique to study an appropriate microscopic description. This is not a problem but a big advantage because this facilitates the approach-independent description of common underlying physics. For this evaluation, the strongly correlated cuprates are simulated with the variational cluster approach. Especially the question of a pairing glue is taken into consideration. Furthermore, it is possible to distinguish between retarded and non-retarded contributions to the gap function. The cuprates are confronted with the cobaltate Na{sub x}CoO{sub 2} and graphene. These weakly correlated materials are investigated with the functional renormalization group (fRG) and reveal a comprehensive phase diagram, including a d+id-wave superconductivity, which breaks time-reversal symmetry. The corresponding gap function is nodeless, but for NaCoO, it features a doping-dependent anisotropy. In addition, some general
Kananenka, Alexei A; Zgid, Dominika
2017-11-14
We present a rigorous framework which combines single-particle Green's function theory with density functional theory based on a separation of electron-electron interactions into short- and long-range components. Short-range contribution to the total energy and exchange-correlation potential is provided by a density functional approximation, while the long-range contribution is calculated using an explicit many-body Green's function method. Such a hybrid results in a nonlocal, dynamic, and orbital-dependent exchange-correlation functional of a single-particle Green's function. In particular, we present a range-separated hybrid functional called srSVWN5-lrGF2 which combines the local-density approximation and the second-order Green's function theory. We illustrate that similarly to density functional approximations, the new functional is weakly basis-set dependent. Furthermore, it offers an improved description of the short-range dynamic correlation. The many-body contribution to the functional mitigates the many-electron self-interaction error present in many density functional approximations and provides a better description of molecular properties. Additionally, we illustrate that the new functional can be used to scale down the self-energy and, therefore, introduce an additional sparsity to the self-energy matrix that in the future can be exploited in calculations for large molecules or periodic systems.
Energy Technology Data Exchange (ETDEWEB)
Brics, Martins; Kapoor, Varun; Bauer, Dieter [Institut fuer Physik, Universitaet Rostock, 18051 Rostock (Germany)
2013-07-01
Time-dependent density functional theory (TDDFT) with known and practicable exchange-correlation potentials does not capture highly correlated electron dynamics such as single-photon double ionization, autoionization, or nonsequential ionization. Time-dependent reduced density matrix functional theory (TDRDMFT) may remedy these problems. The key ingredients in TDRDMFT are the natural orbitals (NOs), i.e., the eigenfunctions of the one-body reduced density matrix (1-RDM), and the occupation numbers (OCs), i.e., the respective eigenvalues. The two-body reduced density matrix (2-RDM) is then expanded in NOs, and equations of motion for the NOs can be derived. If the expansion coefficients of the 2-RDM were known exactly, the problem at hand would be solved. In practice, approximations have to be made. We study the prospects of TDRDMFT following a top-down approach. We solve the exact two-electron time-dependent Schroedinger equation for a model Helium atom in intense laser fields in order to study highly correlated phenomena such as the population of autoionizing states or single-photon double ionization. From the exact wave function we calculate the exact NOs, OCs, the exact expansion coefficients of the 2-RDM, and the exact potentials in the equations of motion. In that way we can identify how many NOs and which level of approximations are necessary to capture such phenomena.
Surface density dependence of PCR amplicon hybridization on PNA/DNA probe layers
DEFF Research Database (Denmark)
Yao, Danfeng; Kim, Junyoung; Yu, Fang
2005-01-01
biotin/streptavidin interaction. Despite the neutral backbone of PNA, the hybridization reactions were strongly influenced by the variation of ionic strength. The association rates exhibited a monotonic decrease with ionic strength increase and the maximum hybridization signal was achieved...
International Nuclear Information System (INIS)
Mathew, D; Tanny, S; Parsai, E; Sperling, N
2015-01-01
Purpose: The current small field dosimetry formalism utilizes quality correction factors to compensate for the difference in detector response relative to dose deposited in water. The correction factors are defined on a machine-specific basis for each beam quality and detector combination. Some research has suggested that the correction factors may only be weakly dependent on machine-to-machine variations, allowing for determinations of class-specific correction factors for various accelerator models. This research examines the differences in small field correction factors for three detectors across two Varian Truebeam accelerators to determine the correction factor dependence on machine-specific characteristics. Methods: Output factors were measured on two Varian Truebeam accelerators for equivalently tuned 6 MV and 6 FFF beams. Measurements were obtained using a commercial plastic scintillation detector (PSD), two ion chambers, and a diode detector. Measurements were made at a depth of 10 cm with an SSD of 100 cm for jaw-defined field sizes ranging from 3×3 cm 2 to 0.6×0.6 cm 2 , normalized to values at 5×5cm 2 . Correction factors for each field on each machine were calculated as the ratio of the detector response to the PSD response. Percent change of correction factors for the chambers are presented relative to the primary machine. Results: The Exradin A26 demonstrates a difference of 9% for 6×6mm 2 fields in both the 6FFF and 6MV beams. The A16 chamber demonstrates a 5%, and 3% difference in 6FFF and 6MV fields at the same field size respectively. The Edge diode exhibits less than 1.5% difference across both evaluated energies. Field sizes larger than 1.4×1.4cm2 demonstrated less than 1% difference for all detectors. Conclusion: Preliminary results suggest that class-specific correction may not be appropriate for micro-ionization chamber. For diode systems, the correction factor was substantially similar and may be useful for class-specific reference
Antidot density dependence of magnetization reversal dynamics in ultrathin epitaxial Fe/GaAs(001)
International Nuclear Information System (INIS)
Moore, T A; Wastlbauer, G; Bland, J A C; Cambril, E; Natali, M; Decanini, D; Chen, Y
2004-01-01
Easy axis dynamic magneto-optic Kerr effect loops have been measured from ultrathin (2 nm) epitaxial Fe/GaAs(001) films patterned with arrays of 1 μm square antidots of different densities (antidot spacings 10-50 μm). The applied field was sinusoidal with frequency f = 0.01 Hz-2.3 kHz. A study of dynamic coercivity H c * as a function of f reveals an intermediate dynamic regime (20 Hz c * that is suppressed at high antidot density. The dip is attributed to timescale matching of the sweeping applied field with the domain wall propagation in the film. Suppression of the dip is explained by an increase of domain nucleation in the higher antidot density films in the intermediate dynamic regime. (letter to the editor)
Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient.
Hol, Felix J H; Hubert, Bert; Dekker, Cees; Keymer, Juan E
2016-01-01
During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant bacteria can, unexpectedly, colonize environments where a lethal concentration of the antibiotic kanamycin is present. Colonizing bacteria establish an adaptively resistant population, which remains viable for over 24 h while exposed to the antibiotic. Quantitative analysis of multiple colonization events shows that collectively swimming bacteria need to exceed a critical population density in order to successfully colonize the antibiotic landscape. After colonization, bacteria are not dormant but show both growth and swimming motility under antibiotic stress. Our results highlight the importance of motility and population density in facilitating adaptive resistance, and indicate that adaptive resistance may be a first step to the emergence of genetically encoded resistance in landscapes of antibiotic gradients.
Wierzcholski, Krzysztof
2014-01-01
The present paper is concerned with the calculation of the human hip joint parameters for periodic, stochastic unsteady, motion with asymmetric probability density function for gap height. The asymmetric density function indicates that the stochastic probabilities of gap height decreasing are different in comparison with the probabilities of the gap height increasing. The models of asymmetric density functions are considered on the grounds of experimental observations. Some methods are proposed for calculation of pressure distributions and load carrying capacities for unsteady stochastic conditions in a super thin layer of biological synovial fluid inside the slide biobearing gap limited by a spherical bone acetabulum. Numerical calculations are performed in Mathcad 12 Professional Program, by using the method of finite differences. This method assures stability of numerical solutions of partial differential equations and gives proper values of pressure and load carrying capacity forces occurring in human hip joints.
Kang, Guo-Jun; Song, Chao; Ren, Xue-Feng
2016-11-25
The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH₃-YD2 and TPhe-YD) were systematically investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO₂ cluster were fully investigated. From the analyses of natural bond orbital (NBO), extended charge decomposition analysis (ECDA), and electron density variations (Δρ) between the excited state and ground state, it was found that the introduction of N(CH₃)₂ and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT) character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH₃)₂ and 1,1,2-triphenylethene groups. NCH₃-YD2 with N(CH₃)₂ groups in the donor part is an effective way to improve the interactions between the dyes and TiO₂ surface, light having efficiency (LHE), and free energy change (ΔG inject ), which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs).
Directory of Open Access Journals (Sweden)
Guo-Jun Kang
2016-11-01
Full Text Available The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH3-YD2 and TPhe-YD were systematically investigated by density functional theory (DFT and time-dependent density functional theory (TD-DFT to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO2 cluster were fully investigated. From the analyses of natural bond orbital (NBO, extended charge decomposition analysis (ECDA, and electron density variations (Δρ between the excited state and ground state, it was found that the introduction of N(CH32 and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH32 and 1,1,2-triphenylethene groups. NCH3-YD2 with N(CH32 groups in the donor part is an effective way to improve the interactions between the dyes and TiO2 surface, light having efficiency (LHE, and free energy change (ΔGinject, which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs.
Zhan, Yihong; Cao, Zhenning; Bao, Ning; Li, Jianbo; Wang, Jun; Geng, Tao; Lin, Hao; Lu, Chang
2012-06-28
Conventional electroporation has been conducted by employing short direct current (dc) pulses for delivery of macromolecules such as DNA into cells. The use of alternating current (ac) field for electroporation has mostly been explored in the frequency range of 10kHz-1MHz. Based on Schwan equation, it was thought that with low ac frequencies (10Hz-10kHz), the transmembrane potential does not vary with the frequency. In this report, we utilized a flow-through electroporation technique that employed continuous 10Hz-10kHz ac field (based on either sine waves or square waves) for electroporation of cells with defined duration and intensity. Our results reveal that electropermeabilization becomes weaker with increased frequency in this range. In contrast, transfection efficiency with DNA reaches its maximum at medium frequencies (100-1000Hz) in the range. We postulate that the relationship between the transfection efficiency and the ac frequency is determined by combined effects from electrophoretic movement of DNA in the ac field, dependence of the DNA/membrane interaction on the ac frequency, and variation of transfection under different electropermeabilization intensities. The fact that ac electroporation in this frequency range yields high efficiency for transfection (up to ~71% for Chinese hamster ovary cells) and permeabilization suggests its potential for gene delivery. Copyright © 2012 Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Salam, A.; Akram, M.; Shahid, K.A.; Javed, M.; Zaidi, S.M.
1994-08-01
The relationship between green compressive strength and compacting pressure as well as green density has been investigated for uniaxially pressed aluminium powder compacts in the range 0 - 520 MPa. Two linear relationships occurred between compacting pressure and green compressive strength which corresponded to powder compaction stages II and III respectively, increase in strength being large during stage II and quite small in stage III with increasing pressure. On the basis of both, the experimental results and a previous model on cold compaction of powder particles, relationships between green compressive strength and green density and interparticle contact area of the compacts has been established. (author) 9 figs
International Nuclear Information System (INIS)
Shchepkin, Yu.G.; Slisenko, V.I.; Pavlenko, E.A.; Kostyuk, T.A.
2012-01-01
Research of neutron interactions with the matter under density interactions (DI) up to ∼10 9 cm -2 x s -1 , were provided with aim of revelation of possible dependence neutron cross section from DI. The method of research for revelation of such dependence was improved. It consists on transmission asymmetry (TA) of neutrons measurement through of samples pair from different matters. TA was revealed for all pairs containing 235 U, in particularly, for pair ( 235 U - Cd) TA consists of (2,541 ± 0,294) x 10 -4 that does not contradict to assumption of the cross section dependence from DI. It was defined that correlation related with fission of 235 U, and corresponding of relative change of the effective neutron cross section equals ∼2,6 x 10 -4 . Analysis shows that observed dependence may be treated as the result of secondary states composition of 235 U with anomaly great values of neutron cross section, yield, reduced of possibility radioactive transition and small energy, excited by fragment fission.
Energy Technology Data Exchange (ETDEWEB)
Pajęcka, Kamilla, E-mail: kpaj@novonordisk.com [Global Research, Novo Nordisk A/S, Måløv (Denmark); Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus (Denmark); Nielsen, Malik Nygaard [Global Research, Novo Nordisk A/S, Måløv (Denmark); Hansen, Troels Krarup [Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus (Denmark); Williams, Julie M. [Global Research, Novo Nordisk A/S, Måløv (Denmark)
2017-04-01
Background and aims: Nephropathy involves pathophysiological changes to the glomerulus. The primary glomerular endothelial cells (GEnCs) have emerged as an important tool for studying glomerulosclerotic mechanisms and in the screening process for drug-candidates. The success of the studies is dependent on the quality of the cell model. Therefore, we set out to establish an easy, reproducible model of the quiescent endothelial monolayer with the use of commercially available extracellular matrices (ECMs). Methods: Primary hGEnCs were seeded on various ECMs. Cell adhesion was monitored by an impedance sensing system. The localization of junctional proteins was assessed by immunofluorescence and the barrier function by passage of fluorescent dextrans and magnitude of VEGF response. Results: All ECM matrices except recombinant human laminin 111 (rhLN111) supported comparable cell proliferation. Culturing hGEnCs on rhLN521, rhLN511 or fibronectin resulted in a physiologically relevant barrier to 70 kDa dextrans which was 82% tighter than that formed on collagen type IV. Furthermore, only hGEnCs cultured on rhLN521 or rhLN511 showed plasma-membrane localized zonula occludens-1 and vascular endothelial cadherin indicative of proper tight and adherens junctions (AJ). Conclusion: We recommend culturing hGEnCs on the mature glomerular basement membrane laminin - rhLN521 – which, as the only commercially available ECM, promotes all of the characteristics of the quiescent hGEnC monolayer: cobblestone morphology, well-defined AJs and physiological perm-selectivity. - Highlights: • rhLN521, rhLN511 and hFN assure physiologically relevant permeability. • rhLN521 and rhLN511 ensure best cell morphology and adherens junction formation. • Collagen IV and I based coating results in disorganized hGEnC monolayer. • Physiologically relevant ECM may lead to down-regulation of self-produced matrices.
International Nuclear Information System (INIS)
Pajęcka, Kamilla; Nielsen, Malik Nygaard; Hansen, Troels Krarup; Williams, Julie M.
2017-01-01
Background and aims: Nephropathy involves pathophysiological changes to the glomerulus. The primary glomerular endothelial cells (GEnCs) have emerged as an important tool for studying glomerulosclerotic mechanisms and in the screening process for drug-candidates. The success of the studies is dependent on the quality of the cell model. Therefore, we set out to establish an easy, reproducible model of the quiescent endothelial monolayer with the use of commercially available extracellular matrices (ECMs). Methods: Primary hGEnCs were seeded on various ECMs. Cell adhesion was monitored by an impedance sensing system. The localization of junctional proteins was assessed by immunofluorescence and the barrier function by passage of fluorescent dextrans and magnitude of VEGF response. Results: All ECM matrices except recombinant human laminin 111 (rhLN111) supported comparable cell proliferation. Culturing hGEnCs on rhLN521, rhLN511 or fibronectin resulted in a physiologically relevant barrier to 70 kDa dextrans which was 82% tighter than that formed on collagen type IV. Furthermore, only hGEnCs cultured on rhLN521 or rhLN511 showed plasma-membrane localized zonula occludens-1 and vascular endothelial cadherin indicative of proper tight and adherens junctions (AJ). Conclusion: We recommend culturing hGEnCs on the mature glomerular basement membrane laminin - rhLN521 – which, as the only commercially available ECM, promotes all of the characteristics of the quiescent hGEnC monolayer: cobblestone morphology, well-defined AJs and physiological perm-selectivity. - Highlights: • rhLN521, rhLN511 and hFN assure physiologically relevant permeability. • rhLN521 and rhLN511 ensure best cell morphology and adherens junction formation. • Collagen IV and I based coating results in disorganized hGEnC monolayer. • Physiologically relevant ECM may lead to down-regulation of self-produced matrices.
Strongly correlating liquids and their isomorphs
Pedersen, Ulf R.; Gnan, Nicoletta; Bailey, Nicholas P.; Schröder, Thomas B.; Dyre, Jeppe C.
2010-01-01
This paper summarizes the properties of strongly correlating liquids, i.e., liquids with strong correlations between virial and potential energy equilibrium fluctuations at constant volume. We proceed to focus on the experimental predictions for strongly correlating glass-forming liquids. These predictions include i) density scaling, ii) isochronal superposition, iii) that there is a single function from which all frequency-dependent viscoelastic response functions may be calculated, iv) that...
As a result of the increased potential for disease transmission, insects are predicted to show an increased constitutive immunity when crowded. Nymphal Mormon crickets were collected in Montana and reared in the laboratory either solitarily or at densities similar to that experienced by Mormon cric...
Composition dependence of density of states in a-Se100−xSnx thin ...
Indian Academy of Sciences (India)
genide glassy semiconductors [5–15] and the results have been interpreted in terms of space charge limited conduction or Poole–Frenkel conduction. One of the most direct methods for the determination of the density of the localised states g0 in the mobility gap involves the measurements of SCLC, which can be easily ...
DEFF Research Database (Denmark)
Zubillaga, Maria; Skewes, Oscar; Soto, Nicolás
2014-01-01
on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km², with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting...
Age dependent mineral density in the bones of inhabitants of Karelia
Directory of Open Access Journals (Sweden)
I. G. Pashkova
2013-01-01
Full Text Available Analysis of the age changes of mineral density in the lumbar vertebrae was carried out in 929 people (740 women and 189 men at the age of 20 to 87 years, living in Karelia. Bone mineral density was evaluated by dual xray absorptiometry. In the women and in the men the spine bone mineralization peak was seen at the age of 22. The peak mineral density values were 5 % lower in the men and 1.6 % in the women in comparison with the data of the densitometer base. Considerable decrease of the bone mineral density in the vertebrae in the women began at the age of 41–45 years, and in the men – at the age of 51–55 years. Demineralization of the vertebrae in 75 year old women was 20 %, in the men it was 11.1 %, and in 81–87 year old women – 25.2 %.
The Potential Energy Density in Transverse String Waves Depends Critically on Longitudinal Motion
Rowland, David R.
2011-01-01
The question of the correct formula for the potential energy density in transverse waves on a taut string continues to attract attention (e.g. Burko 2010 "Eur. J. Phys." 31 L71), and at least three different formulae can be found in the literature, with the classic text by Morse and Feshbach ("Methods of Theoretical Physics" pp 126-127) stating…
Yamanaka, Takamitsu; Nakamoto, Yuki; Ahart, Muhtar; Mao, Ho-kwang
2018-04-01
Electron density distributions of PbTi O3 , BaTi O3 , and SrTi O3 were determined by synchrotron x-ray powder diffraction up to 55 GPa at 300 K and ab initio quantum chemical molecular orbital (MO) calculations, together with a combination of maximum entropy method calculations. The intensity profiles of Bragg peaks reveal split atoms in both ferroelectric PbTi O3 and BaTi O3 , reflecting the two possible positions occupied by the Ti atom. The experimentally obtained atomic structure factor was used for the determination of the deformation in electron density and the d-p-π hybridization between dx z (and dy z) of Ti and px (and py) of O in the Ti-O bond. Ab initio MO calculations proved the change of the molecular orbital coupling and of Mulliken charges with a structure transformation. The Mulliken charge of Ti in the Ti O6 octahedron increased in the ionicity with increasing pressure in the cubic phase. The bonding nature is changed with a decrease in the hybridization of the Ti-O bond and the localization of the electron density with increasing pressure. The hybridization decreases with pressure and disappears in the cubic paraelectric phase, which has a much more localized electron density distribution.
Lee, Jui-Huna; Wu, Chang-Fu; Hoek, Gerard; de Hoogh, Kees; Beelen, Rob; Brunekreef, Bert; Chan, Chang-Chuan
2015-05-01
Traffic intensity, length of road, and proximity to roads are the most common traffic indicators in the land use regression (LUR) models for particulate matter in ESCAPE study areas in Europe. This study explored what local variables can improve the performance of LUR models in an Asian metropolis with high densities of roads and strong activities of industry, commerce and construction. By following the ESCAPE procedure, we derived LUR models of PM₂.₅, PM₂.₅ absorbance, PM₁₀, and PMcoarse (PM₂.₅-₁₀) in Taipei. The overall annual average concentrations of PM₂.₅, PM₁₀, and PMcoarse were 26.0 ± 5.6, 48.6 ± 5.9, and 23.3 ± 3.1 μg/m(3), respectively, and the absorption coefficient of PM₂.₅ was 2.0 ± 0.4 × 10(-5)m(-1). Our LUR models yielded R(2) values of 95%, 96%, 87%, and 65% for PM₂.₅, PM₂.₅ absorbance, PM₁₀, and PMcoarse, respectively. PM₂.₅ levels were increased by local traffic variables, industrial, construction, and residential land-use variables and decreased by rivers; while PM₂.₅ absorbance levels were increased by local traffic variables, industrial, and commercial land-use variables in the models. PMcoarse levels were increased by elevated highways. Road area explained more variance than road length by increasing the incremental value of 27% and 6% adjusted R(2) for PM₂.₅ and PM₁₀ models, respectively. In the PM₂.₅ absorbance model, road area and transportation facility explain 29% more variance than road length. In the PMcoarse model, industrial and new local variables instead of road length improved the incremental value of adjusted R(2) from 39% to 60%. We concluded that road area can better explain the spatial distribution of PM₂.₅ and PM₂.₅ absorbance concentrations than road length. By incorporating road area and other new local variables, the performance of each PM LUR model was improved. The results suggest that road area is a better indicator of traffic intensity rather
Yields of ZP sweet maize hybrids in dependence on sowing densities
Directory of Open Access Journals (Sweden)
Srdić Jelena
2008-01-01
Full Text Available Sweet maize differs from maize of standard grain quality by many important traits that affect the ear appearance, and especially by traits controlling taste. The ear appearance trait encompasses the kernel row number, configuration, row pattern (direction and arrangement, seed set, kernel width and depth, ear shape and size. The quality of immature kernels is controlled by genes by which sweet maize differs from common maize. In order to obtain high-ranking and high-quality yields, it is necessary to provide the most suitable cropping practices for sweet maize hybrids developed at the Maize Research Institute, Zemun Polje. The adequate sowing density is one of more important elements of correct cropping practices. The objective of the present study was to determine the effect of four sowing densities in four ZP sweet maize hybrids of different FAO maturity groups on ear qualitative traits and yields obtained on chernozem type of soil in Zemun Polje. The observed traits of sweet maize (ear length, kernel row number, number of kernels per row, yield and shelling percentage significantly varied over years. The higher sowing density was the higher yield of sweet maize was, hence the highest ear yield of 9.67 t ha-1 , on the average for all four hybrids, was recorded at the highest sowing density of 70,000 plants ha-1. The highest yield was detected in the hybrid ZP 424su. The highest shelling percentage (67.81% was found in the hybrid ZP 521su at the sowing density of 60,000 plants ha-1. Generally, it can be stated that sweet maize hybrids of a shorter growing season (FAO 400 could be cultivated up to 70,000 plants ha-1, while those of a longer growing season (FAO 500 could be grown up to 60,000 plants ha-1. In such a way, the most favorable parameters of yields and the highest yields can be obtained.
Dependence of the outer density profiles of halos on their mass accretion rate
International Nuclear Information System (INIS)
Diemer, Benedikt; Kravtsov, Andrey V.
2014-01-01
We present a systematic study of the density profiles of ΛCDM halos, focusing on the outer regions, 0.1 < r/R vir < 9. We show that the median and mean profiles of halo samples of a given peak height exhibit significant deviations from the universal analytic profiles discussed previously in the literature, such as the Navarro-Frenk-White and Einasto profiles, at radii r ≳ 0.5R 200m . In particular, at these radii the logarithmic slope of the median density profiles of massive or rapidly accreting halos steepens more sharply than predicted. The steepest slope of the profiles occurs at r ≈ R 200m , and its absolute value increases with increasing peak height or mass accretion rate, reaching slopes of –4 and steeper. Importantly, we find that the outermost density profiles at r ≳ R 200m are remarkably self-similar when radii are rescaled by R 200m . This self-similarity indicates that radii defined with respect to the mean density are preferred for describing the structure and evolution of the outer profiles. However, the inner density profiles are most self-similar when radii are rescaled by R 200c . We propose a new fitting formula that describes the median and mean profiles of halo samples selected by their peak height or mass accretion rate with accuracy ≲ 10% at all radii, redshifts, and masses we studied, r ≲ 9R vir , 0 < z < 6, and M vir > 1.7 × 10 10 h –1 M ☉ . We discuss observational signatures of the profile features described above and show that the steepening of the outer profile should be detectable in future weak-lensing analyses of massive clusters. Such observations could be used to estimate the mass accretion rate of cluster halos.
Garland, N. A.; Boyle, G. J.; Cocks, D. G.; White, R. D.
2018-02-01
This study reviews the neutral density dependence of electron transport in gases and liquids and develops a method to determine the nonlinear medium density dependence of electron transport coefficients and scattering rates required for modeling transport in the vicinity of gas-liquid interfaces. The method has its foundations in Blanc’s law for gas-mixtures and adapts the theory of Garland et al (2017 Plasma Sources Sci. Technol. 26) to extract electron transport data across the gas-liquid transition region using known data from the gas and liquid phases only. The method is systematically benchmarked against multi-term Boltzmann equation solutions for Percus-Yevick model liquids. Application to atomic liquids highlights the utility and accuracy of the derived method.
Na, Bing; Lv, Ruihua; Xu, Wenfei; Yu, Pingsheng; Wang, Ke; Fu, Qiang
2007-11-22
Irradiation of ultrahigh molecular weight polyethylene (UHMWPE) with a dose of 150 kGy by an electron beam can effectively increase the entanglement density in the amorphous phase and has little influence on the properties of the crystalline phase, which provides examples to comparatively investigate the role of lamellar coupling and entanglement density in determining the strain-hardening effect in semicrystalline polymers. The strain-hardening modulus, deduced from the Haward plots of true stress-strain curves, is inversely temperature-dependent and has a sharp transition around 65 degrees C that corresponds to the mechanical alphaI-process of the crystalline phase for both nonirradiated and irradiated samples, irrespective of the entanglement density in the amorphous phase. Lamellar coupling takes more effect in determining the strain-hardening behavior before the mechanical alphaI-process is activated. With further increasing temperature, lamellar coupling becomes weaker and the role of the entangled amorphous phase is gradually presented. However, the same temperature dependence of the strain-hardening modulus in both nonirradiated and irradiated samples indicates that the strain-hardening behavior in semicrystalline polymer is mostly determined by lamellar coupling rather than by entanglement density.
Carty, G. J.; Hampshire, D. P.
2008-01-01
In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons alon...
International Nuclear Information System (INIS)
Schuetter, K.
1985-01-01
An instrument for measuring a time-differential disturbed angular correlation was developed. Using this instrument the disturbance of the spatial correlation of the γ-quanta of the 171-245 keV γ-γ-cascade in 111 Cd was examined in dependence of the density of the gaseous 111 InI-systems and the time difference between the emission of the both γ-quanta. (BBOE)
Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)
2002-01-01
We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.
Directory of Open Access Journals (Sweden)
A N Shriram
2014-01-01
Full Text Available Background & objectives: In India, diurnally sub periodic Wuchereria bancrofti transmitted by Downsiomyia nivea is prevalent only in the Nicobar district of Andaman and Nicobar Islands. The ongoing LF elimination programme aims at transmission interruption by bringing down the microfilarie (mf load in the community, which has implication on the parasite load in mosquito vector. Therefore, understanding density dependent constraints on transmission assumes significance from control perspective. The present study was undertaken in Teressa Island to understand the density dependent parasite mortality and survival probability of the parasite Do. nivea. Methods: The entomological data collected from Teressa Island, endemic for the diurnally sub periodic form of W. bancrofti were used to examine the parasite loss and its survival up to infectivity. Patterns of parasite distribution in Do. nivea were examined. Results: Distribution patterns of microfilariae were found to be over dispersed in Do. nivea. The later stages of the parasite in the vector were randomly distributed. Distribution pattern of various filarial larval stages suggested that the loss of parasites occurred as development progressed and was maximal between the first and second stages. Further, both the prevalence of infection and the degree of parasite aggregation in the vector population have fallen significantly with development of parasite stage. Interpretation & conclusions: Results indicate the operation of parasite density dependent mortality of vectors or parasite loss or combination of both. The present study with Aedes transmitted filariasis conducted before launching LF elimination programme in the study area indicates a comparable level of parasite regulation in the vector which has similar implications on the transmission threshold. Thus, the consideration of Aedes with Culex in deriving the critical level of antigen positive for making decisions on cessation of mass drug
Tempel, David G; Aspuru-Guzik, Alán
2012-01-01
We prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. The theorems of TDDFT applied to universal Hamiltonians imply that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. From a practical standpoint this opens the possibility of approximating observables of interest in quantum computations directly in terms of single-qubit quantities (i.e. as density functionals). Additionally, we also demonstrate that TDDFT provides an exact prescription for simulating universal Hamiltonians with other universal Hamiltonians that have different, and possibly easier-to-realize two-qubit interactions. This establishes the foundations of TDDFT for quantum computation and opens the possibility of developing density functionals for use in quantum algorithms.
Results of Current Density Distribution Mapping in PEM Fuel Cells Dependent on Operation Parameters
Directory of Open Access Journals (Sweden)
Zbigniew A. Styczynski
2013-07-01
Full Text Available This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC. While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence of various operation parameters, including multiple start-stop operation, at the anode, cathode and cooling locations on the distribution and long-term development of the current density. The system was operated for 500 h over two years with long periods of inactivity between measurements. The measurement results are evaluated and provide additional information on how to optimize the operation modes of fuel cells, including the start and stop of such systems as well as the water balance.
Oxidized low-density lipoproteins upregulate proline oxidase to initiate ROS-dependent autophagy
Zabirnyk, Olga; Liu, Wei; Khalil, Shadi; Sharma, Anit; Phang, James M.
2009-01-01
Epidemiological studies showed that high levels of oxidized low-density lipoproteins (oxLDLs) are associated with increased cancer risk. We examined the direct effect of physiologic concentrations oxLDL on cancer cells. OxLDLs were cytotoxic and activate both apoptosis and autophagy. OxLDLs have ligands for peroxisome proliferator-activated receptor gamma and upregulated proline oxidase (POX) through this nuclear receptor. We identified 7-ketocholesterol (7KC) as a main component responsible ...
Czech Academy of Sciences Publication Activity Database
Youssef, A.; Baničová, L.; Švindrych, Zdeněk; Janů, Zdeněk
2010-01-01
Roč. 118, č. 5 (2010), s. 1036-1037 ISSN 0587-4246. [Czech and Slovak Conference on Magnetism /14./. Košice, 06.07.2010-09.07.2010] R&D Projects: GA MŠk(CZ) ME10069 Institutional research plan: CEZ:AV0Z10100520 Keywords : superconductivity * critical state * Bean model * critical current density Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.467, year: 2010
International Nuclear Information System (INIS)
Nagadi, M.M.; Naqvi, A.A.
2007-01-01
Monte Carlo calculations were carried out to study the dependence of γ-ray yield on the bulk density and moisture content of a sample in a thermalneutron capture-based prompt gamma neutron activation analysis (PGNAA) setup. The results of the study showed a strong dependence of the γ-ray yield upon the sample bulk density. An order of magnitude increase in yield of 1.94 and 6.42 MeV prompt γ-rays from calcium in a Portland cement sample was observed for a corresponding order of magnitude increase in the sample bulk density. On the contrary the γ-ray yield has a weak dependence on sample moisture content and an increase of only 20% in yield of 1.94 and 6.42 MeV prompt γ-rays from calcium in the Portland cement sample was observed for an order of magnitude increase in the moisture content of the Portland cement sample. A similar effect of moisture content has been observed on the yield of 1.167 MeV prompt γ-rays from chlorine contaminants in Portland cement samples. For an order of magnitude increase in the moisture content of the sample, a 7 to 12% increase in the yield of the 1.167 MeV chlorine γ-ray was observed for the Portland cement samples containing 1 to 5 wt.% chlorine contaminants. This study has shown that effects of sample moisture content on prompt γ-ray yield from constituents of a Portland cement sample are insignificant in a thermal-neutrons capture-based PGNAA setup. (author)
Merluzzi, Andrew P; Dean, Douglas C; Adluru, Nagesh; Suryawanshi, Gaurav S; Okonkwo, Ozioma C; Oh, Jennifer M; Hermann, Bruce P; Sager, Mark A; Asthana, Sanjay; Zhang, Hui; Johnson, Sterling C; Alexander, Andrew L; Bendlin, Barbara B
2016-07-01
Human aging is accompanied by progressive changes in executive function and memory, but the biological mechanisms underlying these phenomena are not fully understood. Using neurite orientation dispersion and density imaging, we sought to examine the relationship between age, cellular microstructure, and neuropsychological scores in 116 late middle-aged, cognitively asymptomatic participants. Results revealed widespread increases in the volume fraction of isotropic diffusion and localized decreases in neurite density in frontal white matter regions with increasing age. In addition, several of these microstructural alterations were associated with poorer performance on tests of memory and executive function. These results suggest that neurite orientation dispersion and density imaging is capable of measuring age-related brain changes and the neural correlates of poorer performance on tests of cognitive functioning, largely in accordance with published histological findings and brain-imaging studies of people of this age range. Ultimately, this study sheds light on the processes underlying normal brain development in adulthood, knowledge that is critical for differentiating healthy aging from changes associated with dementia. Copyright © 2016 Elsevier Inc. All rights reserved.
Digital mammography screening: sensitivity of the programme dependent on breast density.
Weigel, Stefanie; Heindel, W; Heidrich, J; Hense, H-W; Heidinger, O
2017-07-01
To analyse the impact of breast density on the sensitivity of a population-based digital mammography screening programme (SP) as key evaluation parameter. 25,576 examinations were prospectively stratified from ACR category 1 to 4 for increments of 25 % density during independent double reading. SP was calculated as number of screen-detected cancers divided by the sum of screen-detected plus interval cancers (24-months period) per ACR category, related to the first reading (a), second reading (b) and highest stratification if discrepant (c). Chi-square tests were used for comparison. Overall sensitivity of the programme was 79.9 %. SP in ACR 4 (a: 50 %, b: 50 %, c: 50 %) was significantly lower than in ACR 3 (a: 72.9 %, b: 79.4 %, c: 80.7 %, p mammography screening with independent double reading leads to a high overall SP. In the small group of women with breast density classified as ACR 4 SP is significantly reduced compared to all other ACR categories. • Overall sensitivity of a population-based digital mammography screening programme (SP) was 79.9 %. • In women with ACR 1, 2, or 3, SP ranged between 72.9 %-100 %. • ACR 4 was rare in participants (<7 %) and SP was only 50 %. • SP in ACR 4 differed significantly from ACR 3 (p < 0.001).
Energy Technology Data Exchange (ETDEWEB)
Baczewski, Andrew David; Shulenburger, Luke; Desjarlais, Michael Paul; Magyar, Rudolph J.
2014-02-01
In recent years, DFT-MD has been shown to be a useful computational tool for exploring the properties of WDM. These calculations achieve excellent agreement with shock compression experiments, which probe the thermodynamic parameters of the Hugoniot state. New X-ray Thomson Scattering diagnostics promise to deliver independent measurements of electronic density and temperature, as well as structural information in shocked systems. However, they require the development of new levels of theory for computing the associated observables within a DFT framework. The experimentally observable x-ray scattering cross section is related to the electronic density-density response function, which is obtainable using TDDFT - a formally exact extension of conventional DFT that describes electron dynamics and excited states. In order to develop a capability for modeling XRTS data and, more generally, to establish a predictive capability for rst principles simulations of matter in extreme conditions, real-time TDDFT with Ehrenfest dynamics has been implemented in an existing PAW code for DFT-MD calculations. The purpose of this report is to record implementation details and benchmarks as the project advances from software development to delivering novel scienti c results. Results range from tests that establish the accuracy, e ciency, and scalability of our implementation, to calculations that are veri ed against accepted results in the literature. Aside from the primary XRTS goal, we identify other more general areas where this new capability will be useful, including stopping power calculations and electron-ion equilibration.
Responsivity Dependent Anodization Current Density of Nanoporous Silicon Based MSM Photodetector
Directory of Open Access Journals (Sweden)
Batool Eneaze B. Al-Jumaili
2016-01-01
Full Text Available Achieving a cheap and ultrafast metal-semiconductor-metal (MSM photodetector (PD for very high-speed communications is ever-demanding. We report the influence of anodization current density variation on the response of nanoporous silicon (NPSi based MSM PD with platinum (Pt contact electrodes. Such NPSi samples are grown from n-type Si (100 wafer using photoelectrochemical etching with three different anodization current densities. FESEM images of as-prepared samples revealed the existence of discrete pores with spherical and square-like shapes. XRD pattern displayed the growth of nanocrystals with (311 lattice orientation. The nanocrystallite sizes obtained using Scherrer formula are found to be between 20.8 nm and 28.6 nm. The observed rectifying behavior in the I-V characteristics is ascribed to the Pt/PSi/n-Si Schottky barrier formation, where the barrier height at the Pt/PSi interface is estimated to be 0.69 eV. Furthermore, this Pt/PSi/Pt MSM PD achieved maximum responsivity of 0.17 A/W and quantum efficiency as much as 39.3%. The photoresponse of this NPSi based MSM PD demonstrated excellent repeatability, fast response, and enhanced saturation current with increasing anodization current density.
Pastore, Mariachiara; Assfeld, Xavier; Mosconi, Edoardo; Monari, Antonio; Etienne, Thibaud
2017-07-14
We report a theoretical study on the analysis of the relaxed one-particle difference density matrix characterizing the passage from the ground to the excited state of a molecular system, as obtained from time-dependent density functional theory. In particular, this work aims at using the physics contained in the so-called Z-vector, which differentiates between unrelaxed and relaxed difference density matrices to analyze excited states' nature. For this purpose, we introduce novel quantum-mechanical quantities, based on the detachment/attachment methodology, for analysing the Z-vector transformation for different molecules and density functional theory functionals. A derivation pathway of these novel descriptors is reported, involving a numerical integration to be performed in the Euclidean space on the density functions. This topological analysis is then applied to two sets of chromophores, and the correlation between the level of theory and the behavior of our descriptors is properly rationalized. In particular, the effect of range-separation on the relaxation amplitude is discussed. The relaxation term is finally shown to be system-specific (for a given level of theory) and independent of the number of electrons (i.e., the relaxation amplitude is not simply the result of a collective phenomenon).
Energy Technology Data Exchange (ETDEWEB)
Rebolini, Elisa, E-mail: elisa.rebolini@kjemi.uio.no; Toulouse, Julien, E-mail: julien.toulouse@upmc.fr [Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, 4 place Jussieu, F-75005 Paris (France)
2016-03-07
We present a range-separated linear-response time-dependent density-functional theory (TDDFT) which combines a density-functional approximation for the short-range response kernel and a frequency-dependent second-order Bethe-Salpeter approximation for the long-range response kernel. This approach goes beyond the adiabatic approximation usually used in linear-response TDDFT and aims at improving the accuracy of calculations of electronic excitation energies of molecular systems. A detailed derivation of the frequency-dependent second-order Bethe-Salpeter correlation kernel is given using many-body Green-function theory. Preliminary tests of this range-separated TDDFT method are presented for the calculation of excitation energies of the He and Be atoms and small molecules (H{sub 2}, N{sub 2}, CO{sub 2}, H{sub 2}CO, and C{sub 2}H{sub 4}). The results suggest that the addition of the long-range second-order Bethe-Salpeter correlation kernel overall slightly improves the excitation energies.
Kerer, Manuela; Marksteiner, Josef; Hinterhuber, Hartmann; Kemmler, Georg; Bliem, Harald R; Weiss, Elisabeth M
2014-01-01
In Western cultures it has often been assumed that the experience of happy or sad emotions while listening to music is clearly correlated to the key (mode) and the tempo of the musical piece. Recent studies point towards more complex dependencies, but knowledge in this line of research is still very limited, especially regarding the experience of music for persons with memory-related disorders such as dementia. This pilot study explores the emotional content of music for patients with mild cognitive impairment (MCI) and early-stage Alzheimer's disease (AD) and compares them to healthy subjects. A new test was specifically designed for this study and presented to 10 patients with MCI diagnosis, 10 with AD diagnosis and 23 controls. The test comprised musical stimuli consisting of chords and short musical pieces in major and minor mode with variable note density (number of notes per second). In the current study no significant correlation between key and the attribution of 'happy' or 'sad' judgements to a musical piece could be found in all groups. Note density, however, was shown to exhibit a strong influence on happy/sad judgements in all groups. Our findings indicate that the note density of a musical piece is much more important for happy/sad judgements than the key. Furthermore, the diagnosis MCI and early AD had no influence on the attribution of emotional expressions to musical pieces, corroborating recent findings of spared memory for music in these patient groups.
Christmas, Kevin M; Bassingthwaighte, James B
2017-05-01
Solubilities of respiratory gasses in water, saline, and plasma decrease with rising temperatures and solute concentrations. Henry's Law, C = α·P, states that the equilibrium concentration of a dissolved gas is solubility times partial pressure. Solubilities in the water of a solution depend on temperature and the content of other solutes. Blood temperatures may differ more than 20°C between skin and heart, and an erythrocyte will undergo that range as blood circulates. The concentrations of O 2 and CO 2 are the driving forces for diffusion, exchanges, and for reactions. We provide an equation for O 2 and CO 2 solubilities, α, that allows for continuous changes in temperature, T, and solution density, ρ, in dynamically changing states:[Formula: see text]This two-exponential expression with a density scalar γ, and a density exponent β, accounts for solubility changes due to density changes of an aqueous solution. It fits experimental data on solubilities in water, saline, and plasma over temperatures from 20 to 40°C, and for plasma densities, ρ sol up to 1.020 g/ml with ~0.3% error. The amounts of additional bound O 2 (to Hb) and CO 2 (bicarbonate and carbamino) depend on the concentrations in the local water space and the reaction parameters. During exercise, solubility changes are large; both ρ sol and T change rapidly with spatial position and with time. In exercise hemoconcentration plasma, ρ sol exceeds 1.02, whereas T may range over 20°C. The six parameters for O 2 and the six for CO 2 are constants, so solubilities are calculable continuously as T and ρ sol change. NEW & NOTEWORTHY Solubilities for oxygen and carbon dioxide are dependent on the density of the solution, on temperature, and on the partial pressure. We provide a brief equation suitable for hand calculators or mathematical modeling, accounting for these factors over a wide range of temperatures and solution densities for use in rapidly changing conditions, such as extreme exercise or
Skone, Jonathan; Govoni, Marco; Galli, Giulia
Dielectric-dependent hybrid [DDH] functionals have recently been shown to yield highly accurate energy gaps and dielectric constants for a wide variety of solids, at a computational cost considerably less than standard GW calculations. The fraction of exact exchange included in the definition of DDH functionals depends (self-consistently) on the dielectric constant of the material. In the present talk we introduce a range-separated (RS) version of DDH functionals where short and long-range components are matched using material dependent, non-empirical parameters. Comparing with state of the art GW calculations and experiment, we show that such RS hybrids yield accurate electronic properties of both molecules and solids, including energy gaps, photoelectron spectra and absolute ionization potentials. This work was supported by NSF-CCI Grant Number NSF-CHE-0802907 and DOE-BES.
Abad, Sònia; Fole, Alberto; del Olmo, Nuria; Pubill, David; Pallàs, Mercè; Junyent, Fèlix; Camarasa, Jorge; Camins, Antonio; Escubedo, Elena
2014-03-01
Addictive drugs produce forms of structural plasticity in the nucleus accumbens and prefrontal cortex. The aim of this study was to investigate the impact of chronic MDMA exposure on pyramidal neurons in the CA1 region of hippocampus and drug-related spatial learning and memory changes. Adolescent rats were exposed to saline or MDMA in a regime that mimicked chronic administration. One week later, when acquisition or reference memory was evaluated in a standard Morris water maze (MWM), no differences were obtained between groups. However, MDMA-exposed animals performed better when the MWM was implemented under more difficult conditions. Animals of MDMA group were less anxious and were more prepared to take risks, as in the open field test they ventured more frequently into the central area. We have demonstrated that MDMA caused an increase in brain-derived neurotrophic factor (BDNF) expression. When spine density was evaluated, MDMA-treated rats presented a reduced density when compared with saline, but overall, training increased the total number of spines, concluding that in MDMA-group, training prevented a reduction in spine density or induced its recovery. This study provides support for the conclusion that binge administration of MDMA, known to be associated to neurotoxic damage of hippocampal serotonergic terminals, increases BDNF expression and stimulates synaptic plasticity when associated with training. In these conditions, adolescent rats perform better in a more difficult water maze task under restricted conditions of learning and memory. The effect on this task could be modulated by other behavioural changes provoked by MDMA.
Angular dependences of the luminescence and density of photon states in a chiral liquid crystal
International Nuclear Information System (INIS)
Umanskii, B A; Blinov, L M; Palto, S P
2013-01-01
Luminescence spectra of a laser dye-doped chiral liquid crystal have been studied in a wide range of angles (up to 60°) to the axis of its helical structure using a semicylindrical quartz prism, which made it possible to observe the shift and evolution of the photonic band gap in response to changes in angle. Using measured spectra and numerical simulation, we calculated the spectral distributions of the density of photon states in such a cholesteric crystal for polarised and unpolarised light, which characterise its structure as that of a chiral one-dimensional photonic crystal. (optics of liquid crystals)
Angular dependences of the luminescence and density of photon states in a chiral liquid crystal
Energy Technology Data Exchange (ETDEWEB)
Umanskii, B A; Blinov, L M; Palto, S P [A.V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, Moscow, Russian Federaion (Russian Federation)
2013-11-30
Luminescence spectra of a laser dye-doped chiral liquid crystal have been studied in a wide range of angles (up to 60°) to the axis of its helical structure using a semicylindrical quartz prism, which made it possible to observe the shift and evolution of the photonic band gap in response to changes in angle. Using measured spectra and numerical simulation, we calculated the spectral distributions of the density of photon states in such a cholesteric crystal for polarised and unpolarised light, which characterise its structure as that of a chiral one-dimensional photonic crystal. (optics of liquid crystals)
James A. Powell; Barbara J. Bentz
2014-01-01
For species with irruptive population behavior, dispersal is an important component of outbreak dynamics. We developed and parameterized a mechanistic model describing mountain pine beetle (Dendroctonus ponderosae Hopkins) population demographics and dispersal across a landscape. Model components include temperature-dependent phenology, host tree colonization...
Goldbogen, J A; Calambokidis, J; Oleson, E; Potvin, J; Pyenson, N D; Schorr, G; Shadwick, R E
2011-01-01
Lunge feeding by rorqual whales (Balaenopteridae) is associated with a high energetic cost that decreases diving capacity, thereby limiting access to dense prey patches at depth. Despite this cost, rorquals exhibit high rates of lipid deposition and extremely large maximum body size. To address this paradox, we integrated kinematic data from digital tags with unsteady hydrodynamic models to estimate the energy budget for lunges and foraging dives of blue whales (Balaenoptera musculus), the largest rorqual and living mammal. Our analysis suggests that, despite the large amount of mechanical work required to lunge feed, a large amount of prey and, therefore, energy is obtained during engulfment. Furthermore, we suggest that foraging efficiency for blue whales is significantly higher than for other marine mammals by nearly an order of magnitude, but only if lunges target extremely high densities of krill. The high predicted efficiency is attributed to the enhanced engulfment capacity, rapid filter rate and low mass-specific metabolic rate associated with large body size in blue whales. These results highlight the importance of high prey density, regardless of prey patch depth, for efficient bulk filter feeding in baleen whales and may explain some diel changes in foraging behavior in rorqual whales.
Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh; Nekrasov, Kirill A.; Kichigina, Natalia V.
2018-02-01
The structural, electronic, and vibrational properties of bulk platinum oxide (PtO) at compressive pressures in the interval from 0 GPa to 35 GPa are investigated using the density functional theory. The calculated electronic band structure of PtO shows poor metallicity at very low density of states on the Fermi level. However, the hybrid pseudopotential calculation yielded 0.78 eV and 1.30 eV direct band and indirect gap, respectively. Importantly, our results predict that PtO has a direct band gap within the framework of HSE06, and it prefers equally zero magnetic order at different pressures. In the Raman spectra, peaks are slightly shifted towards higher frequency with the decrease in pressure. We have also calculated the thermoelectric properties, namely the electronic thermal conductivity and electrical conductivity, with respect to temperature and thermodynamic properties such as entropy, specific heat at constant volume, enthalpy and Gibbs free energy with respect to pressure. The result shows that PtO is a promising candidate for use as a catalyst, in sensors, as a photo-cathode in water electrolysis, for thermal decomposition of inorganic salt and fuel cells.
A Density-Dependent Switch Drives Stochastic Clustering and Polarization of Signaling Molecules
Jilkine, Alexandra; Angenent, Sigurd B.; Wu, Lani F.; Altschuler, Steven J.
2011-01-01
Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered “off” state is desired? And, what limits the spread of clusters when an “on” state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the “neutral drift polarity model.” Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization. PMID:22102805
A density-dependent switch drives stochastic clustering and polarization of signaling molecules.
Directory of Open Access Journals (Sweden)
Alexandra Jilkine
2011-11-01
Full Text Available Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered "off" state is desired? And, what limits the spread of clusters when an "on" state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the "neutral drift polarity model." Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization.
Peng, Daoling; Li, Shaopeng; Peng, Liang; Gu, Feng Long; Yang, Weitao
2017-09-12
The time-dependent coupled perturbed Hartree-Fock/density-functional-theory (TDHF/TDDFT) approach has been reformulated based on nonorthogonal localized molecular orbitals (NOLMOs). Based on the NOLMO Fock equation, we have derived the corresponding NOLMO-TDHF/TDDFT equations up to the third order, and the formula for the frequency-dependent (hyper)polarizabilities has been given. Our approach has been applied to calculate both static and dynamic (hyper)polarizabilities of molecules varying from small molecules to large molecules. The NOLMO-TDHF/TDDFT approach can reproduce the reference canonical molecular orbital (CMO) results for all of our testing calculations. With the help of ongoing development of optimized local virtual molecular orbitals, the NOLMO-TDHF/TDDFT approach would be a very efficient method for large system calculations and tp achieve linear scaling.
Janesko, Benjamin G.
2018-02-01
Parameter-free atomistic simulations of entangled solid-state paramagnetic defects may aid in the rational design of devices for quantum information science. This work applies time-dependent density functional theory (TDDFT) embedded-cluster simulations to a prototype entangled-defect system, namely two adjacent singlet-coupled F color centers in lithium fluoride. TDDFT calculations accurately reproduce the experimental visible absorption of both isolated and coupled F centers. The most accurate results are obtained by combining spin symmetry breaking to simulate strong correlation, a large fraction of exact (Hartree-Fock-like) exchange to minimize the defect electrons' self-interaction error, and a standard semilocal approximation for dynamical correlations between the defect electrons and the surrounding ionic lattice. These results motivate application of two-reference correlated ab initio approximations to the M-center, and application of TDDFT in parameter-free simulations of more complex entangled paramagnetic defect architectures.
Hu, Zhongwei; Autschbach, Jochen; Jensen, Lasse
2014-09-28
Resonance hyper-Rayleigh scattering (HRS) of molecules and metal clusters have been simulated based on a time-dependent density functional theory approach. The resonance first-order hyperpolarizability (β) is obtained by implementing damped quadratic response theory using the (2n + 1) rule. To test this implementation, the prototypical dipolar molecule para-nitroaniline (p-NA) and the octupolar molecule crystal violet are used as benchmark systems. Moreover, small silver clusters Ag 8 and Ag 20 are tested with a focus on determining the two-photon resonant enhancement arising from the strong metal transition. Our results show that, on a per atom basis, the small silver clusters possess two-photon enhanced HRS comparable to that of larger nanoparticles. This finding indicates the potential interest of using small metal clusters for designing new nonlinear optical materials.
Electromotive force in strongly compressible magnetohydrodynamic turbulence
Yokoi, N.
2017-12-01
Variable density fluid turbulence is ubiquitous in geo-fluids, not to mention in astrophysics. Depending on the source of density variation, variable density fluid turbulence may be divided into two categories: the weak compressible (entropy mode) turbulence for slow flow and the strong compressible (acoustic mode) turbulence for fast flow. In the strong compressible turbulence, the pressure fluctuation induces a strong density fluctuation ρ ', which is represented by the density variance ( denotes the ensemble average). The turbulent effect on the large-scale magnetic-field B induction is represented by the turbulent electromotive force (EMF) (u': velocity fluctuation, b': magnetic-field fluctuation). In the usual treatment in the dynamo theory, the expression for the EMF has been obtained in the framework of incompressible or weak compressible turbulence, where only the variation of the mean density , if any, is taken into account. We see from the equation of the density fluctuation ρ', the density variance is generated by the large mean density variation ∂ coupled with the turbulent mass flux . This means that in the region where the mean density steeply changes, the density variance effect becomes relevant for the magnetic field evolution. This situation is typically the case for phenomena associated with shocks and compositional discontinuities. With the aid of the analytical theory of inhomogeneous compressible magnetohydrodynamic (MHD) turbulence, the expression for the turbulent electromotive force is investigated. It is shown that, among others, an obliqueness (misalignment) between the mean density gradient ∂ and the mean magnetic field B may contribute to the EMF as ≈χ B×∂ with the turbulent transport coefficient χ proportional to the density variance (χ ). This density variance effect is expected to strongly affect the EMF near the interface, and changes the transport properties of turbulence. In the case of an interface under the MHD slow
International Nuclear Information System (INIS)
Dokukin, E.B.; Kozlov, Zh.A.; Parfenov, V.A.; Puchkov, A.V.
1978-01-01
The experimental results on the relative-density temperature dependence of the Bose-condensate (BC) and on the mean kinetic energy per atom in a liquid hellium-4 are discussed. The investigation has been carried out by studying the spectra of inelastic neutron scattering at the momentum transfers k=12 - 14 A -1 at the temperatures of 1.2 -4.2 K. The experimental data have been analyzed by means of the two-gaussian and one-gaussian models. The BC relative density is estimated by the method of two-gaussian expansion of spectra of neutrons scattered by liquid helium. The temperature dependence has a singularity at T 0 . BC is observed at T 0 and none is observed at T>T 0 within the accuracy of an experiment and mathematical data processing. The BC relative density at T→0 makes up 0.022+-0.002, the temperature of the Bose condensation coinciding with that of the lambda-transition