7 research outputs found
Three-monotone spline approximation
AbstractFor rβ₯3, nβN and each 3-monotone continuous function f on [a,b] (i.e.,Β f is such that its third divided differences [x0,x1,x2,x3]f are nonnegative for all choices of distinct points x0,β¦,x3 in [a,b]), we construct a spline s of degree r and of minimal defect (i.e.,Β sβCrβ1[a,b]) with nβ1 equidistant knots in (a,b), which is also 3-monotone and satisfies βfβsβLβ[a,b]β€cΟ4(f,nβ1,[a,b])β, where Ο4(f,t,[a,b])β is the (usual) fourth modulus of smoothness of f in the uniform norm. This answers in the affirmative the question raised inΒ [8,Β RemarkΒ 3], which was the only remaining unproved Jackson-type estimate for uniform 3-monotone approximation by piecewise polynomial functions (ppfs) with uniformly spaced fixed knots.Moreover, we also prove a similar estimate in terms of the DitzianβTotik fourth modulus of smoothness for splines with Chebyshev knots, and show that these estimates are no longer valid in the case of 3-monotone spline approximation in the Lp norm with p<β. At the same time, positive results in the Lp case with p<β are still valid if one allows the knots of the approximating ppf to depend on f while still being controlled.These results confirm that 3-monotone approximation is the transition case between monotone and convex approximation (where most of the results are βpositiveβ) and k-monotone approximation with kβ₯4 (where just about everything is βnegativeβ)
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On concentrators and related approximation constants
Pippenger ([Pip77]) showed the existence of (6m; 4m; 3m; 6)-concentrator for each
positive integer m using a probabilistic method. We generalize his approach and prove existence
of (6m; 4m; 3m; 5:05)-concentrator (which is no longer regular, but has fewer edges). We apply
this result to improve the constant of approximation of almost additive set functions by additive
set functions from 44:5 (established by Kalton and Roberts in [KR83]) to 39. We show a more
direct connection of the latter problem to the Whitney type estimate for approximation of
continuous functions on a cube in Rd by linear functions, and improve the estimate of this
Whitney constant from 802 (proved by Brudnyi and Kalton in [BK00]) to 73
Π‘ΠΏΠ΅ΠΊΡΡΡ ΡΠΎΡΠΎ- ΠΈ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ Π»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΠΈ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² CdS[1-x]Se[x], Π΄ΠΈΡΠΏΠ΅ΡΠ³ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ Π² Π±ΠΎΡΠΎΡΠΈΠ»ΠΈΠΊΠ°ΡΠ½ΠΎΠΌ ΡΡΠ΅ΠΊΠ»Π΅
ΠΠΎΡΠ»ΡΠ΄ΠΆΠ΅Π½ΠΎ ΡΠΎΡΠΎΠ»ΡΠΌΡΠ½Π΅ΡΡΠ΅Π½ΡΡΡ (Π€Π) Ρ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΡΠΎΠ²Π°Π½Ρ Π»ΡΠΌΡΠ½Π΅ΡΡΠ΅Π½ΡΡΡ (Π’Π‘Π) Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ² CdS[1-x]Se[x] , Π²ΠΊΡΠ°ΠΏΠ»Π΅Π½ΠΈΡ
Ρ Π±ΠΎΡΠΎΡΠΈΠ»ΡΠΊΠ°ΡΠ½Π΅ ΡΠΊΠ»ΠΎ. ΠΡΡΠΈΠΌΠ°Π½ΠΎ Π·Π°Π»Π΅ΠΆΠ½ΠΎΡΡΡ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½Π½Ρ ΡΠΌΡΠ³ ΠΏΡΠΈΠΊΡΠ°ΠΉΠΎΠ²ΠΎΡ ΡΠ° ΠΏΠΎΠ²'ΡΠ·Π°Π½ΠΎΡ Π· ΠΏΠΎΠ²Π΅ΡΡ
Π½Π΅Π²ΠΈΠΌΠΈ ΡΡΠ²Π½ΡΠΌΠΈ Π€Π Π²ΡΠ΄ Ρ
ΡΠΌΡΡΠ½ΠΎΠ³ΠΎ ΡΠΊΠ»Π°Π΄Ρ ΡΠ° ΡΠΎΠ·ΠΌΡΡΡ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ². ΠΠ±Π³ΠΎΠ²ΠΎΡΡΡΡΡΡΡ ΡΡΠ·Π½Π° ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ½Π° ΠΏΠΎΠ²Π΅Π΄ΡΠ½ΠΊΠ° Π±ΡΠ»ΡΡ Π²ΠΈΡΠΎΠΊΠΎΠ΅Π½Π΅ΡΠ³Π΅ΡΠΈΡΠ½ΠΎΡ ΡΠΌΡΠ³ΠΈ Π’Π‘Π (ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ ΠΏΡΠΈ 360-380 K, Π·Π°Π»Π΅ΠΆΠ½ΠΎ Π²ΡΠ΄ ΡΠΊΠ»Π°Π΄Ρ Ρ ΡΠΎΠ·ΠΌΡΡΡ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ²) Ρ Π½ΠΈΠ·ΡΠΊΠΎΠ΅Π½Π΅ΡΠ³Π΅ΡΠΈΡΠ½ΠΎΡ ΡΠΌΡΠ³ΠΈ (ΡΠΈΡΠΎΠΊΠΈΠΉ ΠΌΠ°ΠΊΡΠΈ-
ΠΌΡΠΌ Π² ΡΠ½ΡΠ΅ΡΠ²Π°Π»Ρ 350-450 K).ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Π° ΡΠΎΡΠΎΠ»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΡ (Π€Π) ΠΈ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Π½Π°Ρ Π»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΡ (Π’Π‘Π) Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² CdS[1-x]Se[x]x, Π΄ΠΈΡΠΏΠ΅ΡΠ³ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ
Π² Π±ΠΎΡΠΎΡΠΈΠ»ΠΈΠΊΠ°ΡΠ½ΠΎΠΌ ΡΡΠ΅ΠΊΠ»Π΅. ΠΠΎΠ»ΡΡΠ΅Π½Ρ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΡ ΠΏΠΎΠ»ΠΎΡ ΠΏΡΠΈΠΊΡΠ°Π΅Π²ΠΎΠΉ ΠΈ ΡΠ²ΡΠ·Π°Π½Π½ΠΎΠΉ Ρ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠ½ΡΠΌΠΈ ΡΡΠΎΠ²Π½ΡΠΌΠΈ Π€Π ΠΎΡ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΎΡΡΠ°Π²Π° ΠΈ ΡΠ°Π·ΠΌΠ΅ΡΠ° Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ². ΠΠ±ΡΡΠΆΠ΄Π°Π΅ΡΡΡ ΡΠ°Π·Π½ΠΎΠ΅ ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ½ΠΎΠ΅ ΠΏΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠ΅ Π±ΠΎΠ»Π΅Π΅ Π²ΡΡΠΎΠΊΠΎΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡ Π’Π‘Π (ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ ΠΏΡΠΈ 360-380 K Π² Π·Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡ ΡΠΎΡΡΠ°Π²Π° ΠΈ ΡΠ°Π·ΠΌΠ΅ΡΠ° Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ²) ΠΈ Π½ΠΈΠ·ΠΊΠΎΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡ (ΡΠΈΡΠΎΠΊΠΈΠΉ ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ Π² ΠΈΠ½ΡΠ΅ΡΠ²Π°Π»Π΅ 350-450 K).Photoluminescence (PL) and thermally stimulated luminescence (TSL) of CdS[1-x]Se[x] nanocrystals embedded in borosilicate glass are studied. The dependence of the spectral positions of the near-edge and surface-mediated PL bands on the nanocrystal composition and size is discussed. A different temperature behaviour
for the higher-energy TSL band (maximum at 360-380 K, dependent of the nanocrystal size and composition) and the lower-energy peak (broad maximum in the range 350-450 K) is discussed
Π‘ΠΏΠ΅ΠΊΡΡΡ ΡΠΎΡΠΎ- ΠΈ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ Π»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΠΈ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² CdS[1-x]Se[x], Π΄ΠΈΡΠΏΠ΅ΡΠ³ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ Π² Π±ΠΎΡΠΎΡΠΈΠ»ΠΈΠΊΠ°ΡΠ½ΠΎΠΌ ΡΡΠ΅ΠΊΠ»Π΅
ΠΠΎΡΠ»ΡΠ΄ΠΆΠ΅Π½ΠΎ ΡΠΎΡΠΎΠ»ΡΠΌΡΠ½Π΅ΡΡΠ΅Π½ΡΡΡ (Π€Π) Ρ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΡΠΎΠ²Π°Π½Ρ Π»ΡΠΌΡΠ½Π΅ΡΡΠ΅Π½ΡΡΡ (Π’Π‘Π) Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ² CdS[1-x]Se[x] , Π²ΠΊΡΠ°ΠΏΠ»Π΅Π½ΠΈΡ
Ρ Π±ΠΎΡΠΎΡΠΈΠ»ΡΠΊΠ°ΡΠ½Π΅ ΡΠΊΠ»ΠΎ. ΠΡΡΠΈΠΌΠ°Π½ΠΎ Π·Π°Π»Π΅ΠΆΠ½ΠΎΡΡΡ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½Π½Ρ ΡΠΌΡΠ³ ΠΏΡΠΈΠΊΡΠ°ΠΉΠΎΠ²ΠΎΡ ΡΠ° ΠΏΠΎΠ²'ΡΠ·Π°Π½ΠΎΡ Π· ΠΏΠΎΠ²Π΅ΡΡ
Π½Π΅Π²ΠΈΠΌΠΈ ΡΡΠ²Π½ΡΠΌΠΈ Π€Π Π²ΡΠ΄ Ρ
ΡΠΌΡΡΠ½ΠΎΠ³ΠΎ ΡΠΊΠ»Π°Π΄Ρ ΡΠ° ΡΠΎΠ·ΠΌΡΡΡ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ². ΠΠ±Π³ΠΎΠ²ΠΎΡΡΡΡΡΡΡ ΡΡΠ·Π½Π° ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ½Π° ΠΏΠΎΠ²Π΅Π΄ΡΠ½ΠΊΠ° Π±ΡΠ»ΡΡ Π²ΠΈΡΠΎΠΊΠΎΠ΅Π½Π΅ΡΠ³Π΅ΡΠΈΡΠ½ΠΎΡ ΡΠΌΡΠ³ΠΈ Π’Π‘Π (ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ ΠΏΡΠΈ 360-380 K, Π·Π°Π»Π΅ΠΆΠ½ΠΎ Π²ΡΠ΄ ΡΠΊΠ»Π°Π΄Ρ Ρ ΡΠΎΠ·ΠΌΡΡΡ Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»ΡΠ²) Ρ Π½ΠΈΠ·ΡΠΊΠΎΠ΅Π½Π΅ΡΠ³Π΅ΡΠΈΡΠ½ΠΎΡ ΡΠΌΡΠ³ΠΈ (ΡΠΈΡΠΎΠΊΠΈΠΉ ΠΌΠ°ΠΊΡΠΈ-
ΠΌΡΠΌ Π² ΡΠ½ΡΠ΅ΡΠ²Π°Π»Ρ 350-450 K).ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Π° ΡΠΎΡΠΎΠ»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΡ (Π€Π) ΠΈ ΡΠ΅ΡΠΌΠΎΡΡΠΈΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Π½Π°Ρ Π»ΡΠΌΠΈΠ½Π΅ΡΡΠ΅Π½ΡΠΈΡ (Π’Π‘Π) Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² CdS[1-x]Se[x]x, Π΄ΠΈΡΠΏΠ΅ΡΠ³ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ
Π² Π±ΠΎΡΠΎΡΠΈΠ»ΠΈΠΊΠ°ΡΠ½ΠΎΠΌ ΡΡΠ΅ΠΊΠ»Π΅. ΠΠΎΠ»ΡΡΠ΅Π½Ρ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΡ ΠΏΠΎΠ»ΠΎΡ ΠΏΡΠΈΠΊΡΠ°Π΅Π²ΠΎΠΉ ΠΈ ΡΠ²ΡΠ·Π°Π½Π½ΠΎΠΉ Ρ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠ½ΡΠΌΠΈ ΡΡΠΎΠ²Π½ΡΠΌΠΈ Π€Π ΠΎΡ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΎΡΡΠ°Π²Π° ΠΈ ΡΠ°Π·ΠΌΠ΅ΡΠ° Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ². ΠΠ±ΡΡΠΆΠ΄Π°Π΅ΡΡΡ ΡΠ°Π·Π½ΠΎΠ΅ ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ½ΠΎΠ΅ ΠΏΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠ΅ Π±ΠΎΠ»Π΅Π΅ Π²ΡΡΠΎΠΊΠΎΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡ Π’Π‘Π (ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ ΠΏΡΠΈ 360-380 K Π² Π·Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡ ΡΠΎΡΡΠ°Π²Π° ΠΈ ΡΠ°Π·ΠΌΠ΅ΡΠ° Π½Π°Π½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ²) ΠΈ Π½ΠΈΠ·ΠΊΠΎΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡ (ΡΠΈΡΠΎΠΊΠΈΠΉ ΠΌΠ°ΠΊΡΠΈΠΌΡΠΌ Π² ΠΈΠ½ΡΠ΅ΡΠ²Π°Π»Π΅ 350-450 K).Photoluminescence (PL) and thermally stimulated luminescence (TSL) of CdS[1-x]Se[x] nanocrystals embedded in borosilicate glass are studied. The dependence of the spectral positions of the near-edge and surface-mediated PL bands on the nanocrystal composition and size is discussed. A different temperature behaviour
for the higher-energy TSL band (maximum at 360-380 K, dependent of the nanocrystal size and composition) and the lower-energy peak (broad maximum in the range 350-450 K) is discussed