14,633 research outputs found
Sum rules for isospin centroids in pick-up reactions on general multishell target states
Sum Rules equations for pick-up reactions are presented for the first time
for the energy centroids of states both for the isospin T_< (\equiv T_0 - 1
\over 2) and T_> (\equiv T_0 + {1 \over 2}) of the final nucleus when a nucleon
is picked up from a general multishell target state with isospin T_0. These
equations contain two-body correlation terms, , which, at the present
moment, are difficult to handle analytically. These terms are managed by
combining these equations with the known stripping reactions equations. Sample
applications of these equations to experimental data are presented.Comment: 11 pages, LaTe
Study of effective interaction from single particle transfer reactions on f-p shell nuclei
The present study concentrates on the average effective two-body interaction
matrix elements being extracted, using sum-rule techniques, from transfer
reactions on target states having single orbital as well as two
orbitaloccupancy. This investigation deals with transfer reactions on f-p shell
nuclei involving (i) and transfer on target states using
Ca as inert core, and (ii) and transfer on states
using Ni as core.Comment: 12 pages, ptptex Subj-Classes: Nuclear Shell Structure
e-mail:[email protected]
Effective two-body interactions in the s-d shell nuclei from sum rules equations in tranfer reactions
Average effective two-body interaction matrix elements in the s-d shell have
been extracted, from data on experimentally measured isospin centroids, by
combining the recently derived new sum rules equations for pick-up reactions
with similar known equations for stripping reactions performed on general
multishell target states. Using this combination of stripping and pick-up
equations, the average effective matrix elements for the shells, 1d^2_5/2,
2s^2_1/2 and 1d^2_3/2 respectively have been obtained. A new feature of the
present work is that the restriction imposed in earlier works on target states,
that it be populated only by active neutrons has now been abandoned.Comment: 12 pages, RevTeX, e-mail: [email protected]
Kinetics of hexacelsian to celsian phase transformation in SrAl2Si2O8
The kinetics of hexacelsian to celsian phase transformation in SrAl2Si2O8 have been investigated. Phase pure hexacelsian was prepared by heat treatment of glass flakes at 990 C for 10 h. Bulk hexacelsian was isothermally heat treated at 1026, 1050, 1100, 1152, and 1200 C for various times. The amounts of monoclinic celsian formed were determined using quantitative X-ray diffraction. Values of reaction rate constant, k, at various temperatures were evaluated from the Avrami equation. The Avrami parameter was determined to be 1.1, suggesting a diffusionless, one-dimensional transformation mechanism. From the temperature dependence of k, the activation energy for this reaction was evaluated to be 527 plus or minus 50 kJ/mole (126 plus or minus 12 kcal/mole). This value is consistent with a mechanism involving the transformation of the layered hexacelsian structure to a three-dimensional network celsian structure which necessitates breaking of the strongest bonds, the Si-O bonds
Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices
Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples
Comments on 'Kinetic Study on the Hexacelsian-Celsian Phase Transformation'
A value of 20.1 +/- 4 kcal/mole for the activation energy (E) for the hexacelsian to celsian phase transformation in BaAl2Si2O8 was reported in an earlier work. In the present work, the earlier experimental data were reanalyzed and a much higher value of E was obtained. This revised E value is consistent with the transformation mechanism of a layered hexacelsian structure into a three-dimensional feldspar structure of celsian which would necessitate the breaking of the Si-O and/or the Al-O bonds
Sequential item pricing for unlimited supply
We investigate the extent to which price updates can increase the revenue of
a seller with little prior information on demand. We study prior-free revenue
maximization for a seller with unlimited supply of n item types facing m myopic
buyers present for k < log n days. For the static (k = 1) case, Balcan et al.
[2] show that one random item price (the same on each item) yields revenue
within a \Theta(log m + log n) factor of optimum and this factor is tight. We
define the hereditary maximizers property of buyer valuations (satisfied by any
multi-unit or gross substitutes valuation) that is sufficient for a significant
improvement of the approximation factor in the dynamic (k > 1) setting. Our
main result is a non-increasing, randomized, schedule of k equal item prices
with expected revenue within a O((log m + log n) / k) factor of optimum for
private valuations with hereditary maximizers. This factor is almost tight: we
show that any pricing scheme over k days has a revenue approximation factor of
at least (log m + log n) / (3k). We obtain analogous matching lower and upper
bounds of \Theta((log n) / k) if all valuations have the same maximum. We
expect our upper bound technique to be of broader interest; for example, it can
significantly improve the result of Akhlaghpour et al. [1]. We also initiate
the study of revenue maximization given allocative externalities (i.e.
influences) between buyers with combinatorial valuations. We provide a rather
general model of positive influence of others' ownership of items on a buyer's
valuation. For affine, submodular externalities and valuations with hereditary
maximizers we present an influence-and-exploit (Hartline et al. [13]) marketing
strategy based on our algorithm for private valuations. This strategy preserves
our approximation factor, despite an affine increase (due to externalities) in
the optimum revenue.Comment: 18 pages, 1 figur
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