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Search Results: 1 - 10 of 209387 matches for " Bianca L; Bertsch "
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Curvas de absorción de nutrimentos para tres variedades de lirios (Lilium sp.) y afinamiento del programa de fertilización en una finca comercial en Heredia, Costa Rica
Barrantes-Infante,Bianca L; Bertsch,Floria;
Agronomía Costarricense , 2012,
Abstract: the fertilizer program was evaluated and optimized in a lily commercial farm, after the development of nutrient absorption curves in the varieties brunello, algarve and alma ata. the lily plants were separated into organs to evaluate the fresh and dry at 80oc weights, every 15 days, in 3 plants per variety. dry tissues underwent concentration analysis to obtain the nutrient absorption. based on nutrient absorption curves 5 fertilization treatments were designed: a treatment that consisted in the fertilization program of the commercial farm; the requirement treatment; which included only what the plant absorbs; an adjusted treatment, a treatment without any granular application; and the control. these treatments were applied to the siberia variety during the growing cycle. the absorption curves showed that most of the nutrients are provided by the bulb during the first 4 weeks of a total cycle of 12 to 14 weeks. the contents of n, p and k in the bulbs at the moment of planting ranged from 144-178, 19-28 and 160- 174 mg.bulb-1, respectively, while for a production of 66 (alma ata) and 72 (brunello and algarve) shoots.m-2 the aerial part of the plant consumed 15-18, 1.2-1.6 and 26.7-40.3 g.m-2, respectively. in all varieties, the highest absorption of n, p and k occurred at the end of the life cycle. the requirement treatment did not show significant differences from the treatment of the commercial farm, presenting the same level of production and quality; also, it produced the highest number of medium and large size plant with a commercial value. the requirement and adjusted treatments showed the highest number of large buttons (>5 cm). foliar applications of fertilizers proved to be important, mainly because the treatment without any granular fertilizer application had the highest percentage (56%) of bulbs and adventitious roots with the best appearance.
Spectral cutoffs in EGRET gamma-ray sources
O. Reimer,D. L. Bertsch
Physics , 2001,
Abstract: The EGRET instrument has measured detailed photon spectra between 30 MeV and 10 GeV, which are represented by means of single power-law fits for sources in the 3EG catalog. However, various sources show indications of spectral cutoffs at GeV energies, which are poorly represented by such simple fits. In the case of well exposed or bright EGRET sources, a description of spectral cutoffs with more complicated functional forms appears to be applicable. An application for such multicomponent fits should be seen in extrapolations beyond the energies accessible to EGRET, i.e. for detectability studies of low-threshold Imaging Atmospheric Cherenkov Telescopes (IACTs). In cases of unidentified gamma-ray sources positionally coincident with Supernova remnants, the spectral shape beyond power-law extrapolations might observationally explain why such prominent SNRs like gammaCygni, IC 443 and CTA1 have not been detected during several observation campaigns performed by IACTs over the last years.
LogN-LogS Studies of EGRET Sources
O. Reimer,D. L. Bertsch
Physics , 2001,
Abstract: A comprehensive investigation of logN-logS distributions of gamma-ray sources discovered by EGRET has been performed for subsequent use in population studies. Existing models explaining the spatial arrangement of unidentified sources do not compare against an observed logN-logS distribution. However, viable population models not only have to reproduce the logN-logS distribution for different source classes globally, they have to correspond to apparent differences among their spatial, spectral and variability characteristics. Furthermore, it needs to be understood in which way results from selections among the unidentified sources like "persistent" (Grenier 2000) or "steady" sources (Gehrels et al. 2000) are related to the overall picture regarding their logN-logS characteristics.
The Highest Energy Emission Detected by EGRET from Blazars
Brenda L. Dingus,David L. Bertsch
Physics , 2001, DOI: 10.1063/1.1419408
Abstract: Published EGRET spectra from blazars extend only to 10 GeV, yet EGRET has detected approximately 2000 gamma-rays above 10 GeV of which about half are at high Galactic latitude. We report a search of these high-energy gamma-rays for associations with the EGRET and TeV detected blazars. Because the point spread function of EGRET improves with energy, only ~2 gamma-rays are expected to be positionally coincident with the 80 blazars searched, yet 23 gamma-rays were observed. This collection of > 10 GeV sources should be of particular interest due to the improved sensitivity and lower energy thresholds of ground-based TeV observatories. One of the blazars, RGB0509+056, has the highest energy gamma-rays detected by EGRET from any blazar with 2 > 40 GeV, and is a BL Lac type blazar with unknown redshift.
Pairing in finite systems: beyond the HFB theory
L. M. Robledo,G. F. Bertsch
Physics , 2012,
Abstract: The Hartree-Fock-Bogoliubov approximation is very useful for treating both long- and short-range correlations in finite quantum fermion systems, but it must be extended in order to describe detailed spectroscopic properties. One problem is the symmetry-breaking character of the HFB approximation. We present a general and systematic way to restore symmetries and to extend the configuration space using pfaffian formulas for the many-body matrix elements. The advantage of those formulas is that the sign of the matrix elements is unambiguously determined. It is also helpful to extend the space of configurations by constraining the HFB solutions in some way. A powerful method for finding these constrained solutions is the gradient method, based on the generalized Thouless transformation. The gradient method also preserves the number parity of the Bogoliubov transformation, which facilitates the application of the theory to systems with odd particle number.
Global systematics of octupole excitations in even-even nuclei
L. M. Robledo,G. F. Bertsch
Physics , 2011, DOI: 10.1103/PhysRevC.84.054302
Abstract: We present a computational methodology for a theory of the lowest octupole excitations applicable to all even-even nuclei beyond the lightest. The theory is the well-known generator-coordinate extension (GCM) of the Hartree-Fock-Bogoliubov self-consistent mean field theory (HFB). We use the discrete-basis Hill-Wheel method (HW) to compute the wave functions with an interaction from the Gogny family of Hamiltonians. Comparing to the compiled experimental data on octupole excitations, we find that the performance of the theory depends on the deformation characteristics of the nucleus. For nondeformed nuclei, the theory reproduces the energies to about 20 % apart from an overall scale factor of about 1.6. The performance is somewhat poorer for (quadrupole) deformed nuclei, and for both together the dispersion of the scaled energies about the experimental values is about 25 %. This compares favorably with the performance of similar theories of the quadrupole excitations. Nuclei having static octupole deformations in HFB form a special category. These nuclei have the smallest measured octupole excitation energies as well as the smallest predicted energies. However, in these cases the energies are seriously underpredicted by the theory. We find that a simple two-configuration approximation, the Minimization After Projection method, (MAP) is almost as accurate as the full HW treatment, provided that the octupole-deformed nuclei are omitted from the comparison. This article is accompanied by a tabulation of the predicted octupole excitations for 818 nuclei extending from dripline to dripline, computed with several variants of the Gogny interaction.
Symmetry restoration in Hartree-Fock-Bogoliubov based theories
G. F. Bertsch,L. M. Robledo
Physics , 2011, DOI: 10.1103/PhysRevLett.108.042505
Abstract: We present a pfaffian formula for projection and symmetry restoration for wave functions of the general Bogoliubov form, including quasiparticle excited states and linear combinations of them. This solves a long-standing problem in calculating states of good symmetry, arising from the sign ambiguity of the commonly used determinant formula. A simple example is given of projecting good particle number and angular momentum from a Bogoliubov wave function in the Fock space of a single j-shell.
Nuclear level statistics: extending the shell model theory to higher temperatures
Y. Alhassid,G. F. Bertsch,L. Fang
Physics , 2003, DOI: 10.1103/PhysRevC.68.044322
Abstract: The Shell Model Monte Carlo (SMMC) approach has been applied to calculate level densities and partition functions to temperatures up to ~ 1.5 - 2 MeV, with the maximal temperature limited by the size of the configuration space. Here we develop an extension of the theory that can be used to higher temperatures, taking into account the large configuration space that is needed. We first examine the configuration space limitation using an independent-particle model that includes both bound states and the continuum. The larger configuration space is then combined with the SMMC under the assumption that the effects on the partition function are factorizable. The method is demonstrated for nuclei in the iron region, extending the calculated partition functions and level densities up to T ~ 4 MeV. We find that the back-shifted Bethe formula has a much larger range of validity than was suspected from previous theory. The present theory also shows more clearly the effects of the pairing phase transition on the heat capacity.
Combinatorial level densities by the real-time method
G. F. Bertsch,L. M. Robledo
Physics , 2014, DOI: 10.1016/j.cpc.2014.08.012
Abstract: Levels densities of independent-particle Hamiltonians can be calculated easily by using the real-time representation of the evolution operator together with the fast Fourier transform. We describe the method and implement it with a set of Python programs. Examples are provided for the total and partial levels densities of a heavy deformed nucleus (Dy-164). The partial level densities that may be calculated are the projected ones on neutron number, proton number, azimuthal angular momentum, and parity.
Electromagnetic transition strengths in soft deformed nuclei
L. M. Robledo,G. F. Bertsch
Physics , 2012, DOI: 10.1103/PhysRevC.86.054306
Abstract: Spectroscopic observables such as electromagnetic transitions strengths can be related to the properties of the intrinsic mean-field wave function when the latter are strongly deformed, but the standard rotational formulas break down when the deformation decreases. Nevertheless there is a well-defined, non-zero, spherical limit that can be evaluated in terms of overlaps of mean-field intrinsic deformed wave functions. We examine the transition between the spherical limit and strongly deformed one for a range of nuclei comparing the two limiting formulas with exact projection results. We find a simple criterion for the validity of the rotational formula depending on $<\Delta \vec{J}^2>$, the mean square fluctuation in the angular momentum of the intrinsic state. We also propose an interpolation formula which describes the transition strengths over the entire range of deformations, reducing to the two simple expressions in the appropriate limits.
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