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The numerical solution of a possible inconsistent system oflinear inequalities in the l1 sense is considered. The non-differentiablel1 norm minimization problem is approximated by a piecewisequadratic Huber smooth function. A continuation algorithm isdesigned to find an l1 solution of the inequality system. Inthe case where the linear inequality system is consistent, asolution is obtained by solving any smoothed problem. Otherwise,the algorithm is shown to terminate in a finite number of iterations.We also consider an alternative smoothing scheme which sharessimilar properties with the first one, but results in an improvedcomputational performance of the continuation algorithm on inconsistentsystems. Numerical experiments are conducted to test the efficiencyof the algorithm. 相似文献
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Félix J Berisso MC Christian DC Gara A Gottschalk EE Gutiérrez G Hartouni EP Knapp BC Kreisler MN Lee S Markianos K Moreno G Reyes MA Sosa M Wang MH Wehmann A Wesson D 《Physical review letters》2002,88(6):061801
We report results from a study of Lambda(0) polarization in the exclusive reaction pp --> p(f)(Lambda0K+) at 800-GeV/c. We observe a dependence of the polarization on the Lambda0K+ invariant mass with large (+71%) positive polarization at small mass (1.63-GeV/c(2)) and large (-43%) negative polarization at large mass (2.75-GeV/c(2)). This observation confirms the result of the CERN ISR R608 experiment and extends the range over which the effect is observed. The strong dependence of the polarization on the Lambda0K+ invariant mass suggests that the origin of the polarization is closely related to the production dynamics of the diffractively produced Lambda0K+ system. 相似文献
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M. Gómez Berisso P. Pedrazzini J.G. Sereni O. Trovarelli C. Geibel F. Steglich 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):343-349
We present electrical resistivity and specific heat measurements of alloys on the Rh rich side of the phase diagram of the
Ce(Rh1-xPdx)2Si2 system. We compare these results with those obtained at intermediate and low Rh concentrations. The analysis of the concentration
and temperature dependence of the entropy and of the scaling behaviour of C
el
(
T
) and ρ(
T
) clearly confirm a separation of the magnetic phase diagram into two regions: the region x
≤0.3, showing a concentration independent characteristic temperature for the 4
f-electrons with T
0
≈ 45
K, while for x
> 0.3, T0 decreases to T
0
(
x
= 1) ≈ 15
K. At low Pd-content, TN decreases very rapidly from T
N
= 36
K in pure CeRh2Si2 to T
N
= 18
K at x
= 0.1. With higher Pd concentration TN stabilizes at T
N
≈ 15
K whereas the magnitude of the anomalies in C
el
(
T
) and in the susceptibility around TN are further reduced and disappear at x
≈ 0.3. This differs from the behavior found on the Pd-rich side, where TN decreases continuously to zero with increasing Rh content. The pronounced differences observed between both phase boundaries
and the drastic effect of doping on the Rh rich side suggest an itinerant character in CeRh2 Si2, in contrast with the localized character of CePd2Si2. Further evidence for the itinerant character of CeRh2Si2 is given by the ρ(
T
) dependence observed for x
≤0.3, which scales with ρ(
T
) of the prototype itinerant compound YCo2.
Received 31 December 2001 / Received in final form 6 July 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: berisso@cab.cnea.gov.ar 相似文献
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From the very beginning organic chemistry and total synthesis have been intimately joined. In fact, one of the first things that freshmen in organic chemistry learn is how to join two molecules together to obtain a more complex one. Of course they still have a long way to go to become fully mature synthetic chemists, but they must have the primary instinct to build molecules, as synthesis is the essence of organic chemistry. With the different points of view that actually coexist in the chemical community about the maturity of the science (art, or both) of organic synthesis, it is clear that nowadays we know how to make almost all of the most complex molecules ever isolated. The primary question is how easy is it to accomplish? For the readers of papers describing the total synthesis of either simple or complex molecules, it appears that the routes followed are, most of the time, smooth and free of troubles. The synthetic scheme written on paper is, apparently, done in the laboratory with few, if any, modifications and these, essentially, seem to be based on finding the optimal experimental conditions to effect the desired reaction. Failures in the planned synthetic scheme to achieve the goal, detours imposed by unexpected reactivity, or the absence of reactivity are almost never discussed, since they may diminish the value of the work reported. This review attempts to look at total synthesis from a different side; it will focus on troubles found during the synthetic work that cause detours from the original synthetic plan, or on the dead ends that eventually may force redesign. From there, the evolution from the original route to the final successful one that achieves the synthetic target will be presented. The syntheses discussed in this paper have been selected because they contain explicit information about the failures of the original synthetic plan, together with the evolution of the final route to the target molecule. Therefore, they contain a lot of useful negative information that may otherwise be lost. 相似文献