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Temperature-dependent Raman spectra of K0.2Na0.8NbO3 ceramics

Lima, RJC; Paraguassu, W.; Freire, PTC; Sasaki, J. M.; Melo, FEA; Mendes, J.; Lanfredi, S.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 28-32
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We performed temperature-dependent Raman scattering studies on K0.2Na0.8NbO3 ceramics and compared the results with those for NaNbO3. The wavenumbers associated with NbO6 vibrations suggest the existence of two phase transitions, as occurs with pure NaNbO3 ceramics. Although the disorder on the Na/K site does not change either the room temperature phase of K0.2Na0.8NbO3 or the sequence of phase transitions compared with NaNbO3, it changes the temperature of the lowest phase transition and strongly modifies the temperature of the antiferroelectric --> new phase II phase transition. Additionally, the linewidth analysis shows that the orientational mechanism is the dominant contribution to linewidth, although the anharmonic contribution is increased, when compared with NaNbO3, owing to the random distribution of potassium in the sodium niobate matrix. Copyright (C) 2004 John Wiley Sons, Ltd.

Os grupos K0 topológico, algébrico e em álgebra de operadores

Weilandt, Taís Aguiar
Fonte: Universidade Federal de Santa Catarina Publicador: Universidade Federal de Santa Catarina
Tipo: Dissertação de Mestrado Formato: 163 p.| il.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Matemática Pura e Aplicada, Florianópolis, 2014.; Neste trabalho estudamos as K-teorias algébrica, topológica e de C-álgebras.Mostramos que se A é uma C-álgebra unital, então K0(A) é o mesmo (a menos de isomorfismo) na K-teoria algébrica e na K-teoria de C-álgebras. Além disso, considerando X um espaço topológico compacto Hausdorff, provamos o Teorema de Serre-Swan, isto é, que existe uma equivalência categórica entre a categoria dos C(X)-módulos projetivos finitamente gerados e a categoria dos fibrados vetoriais sobre X.
; Abstract : In this work we study algebraic and topological K-theory and the K-theory of C-algebras. We show that if A is a unital C-algebra then K0(A) is (up to isomorphism) the same in algebraic K-theory and in the K-Theory of C-Algebras. More over, we show the Serre-Swan theorem, which says that if Xis a compact Hausdorff space then there is a categorical equivalence between the category of finitely generated projective C(X)-modules and the category of vector bundles over X.

Implementation of a k/k0 method to identify long-range structure in transition states during conformational folding/unfolding of proteins

Pradeep, Lovy; Kurinov, Igor; Ealick, Steven E.; Scheraga, Harold A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/2007 Português
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A previously-introduced kinetic-rate constant (k/k0) method, where k and k0 are the folding (unfolding) rate constants in the mutant and the wild-type forms, respectively, of a protein, has been applied to obtain qualitative information about structure in the transition state (TS) ensemble of bovine pancreatic ribonuclease A (RNase A) which contains four native disulfide bonds. The method compares the folding (unfolding) kinetics of two versions of RNase A, with and without a covalent crosslink (in the form of a fifth disulfide bond); the method tests whether the crosslinked residues are associated in the folding (unfolding) transition state of the non-crosslinked version. To confirm that the fifth disulfide bond has not introduced a significant structural perturbation, we solved the crystal structure of the V43C-R85C mutant to 1.6 Å resolution. Our findings suggest that residues Val 43 and Arg 85 are not associated in the folding (unfolding) TS ensemble of RNase A, and also that Ala 4 and Val 118 may form non-native contacts in the folding (unfolding) TS ensemble.

K0.8Ag0.2Nb4O9AsO4

Ben Amor, Rym; Zid, Mohamed Faouzi; Driss, Ahmed
Fonte: International Union of Crystallography Publicador: International Union of Crystallography
Tipo: Artigo de Revista Científica
Publicado em 24/05/2008 Português
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The title compound, potassium silver tetra­niobium nona­oxide arsenate, K0.8Ag0.2Nb4O9AsO4, was prepared by a solid-state reaction at 1183 K. The structure consists of infinite (Nb2AsO14)n chains parallel to the b axis and cross-linked by corner sharing via pairs of edge-sharing octa­hedra. Each pair links together four infinite chains to form a three-dimensional framework. The K+ and Ag+ ions partially occupy several independent close positions in the inter­connected cavities delimited by the framework. K0.8Ag0.2Nb4O9AsO4 is likely to exhibit fast alkali-ion mobility and ion-exchange properties. The Wyckoff symbols of special positions are as follows: one Nb 8e, one Nb 8g, As 4c, two K 8f, one Ag 8f, one Ag 4c, one O 8g, one O 4c.

Characterisation of Synthetic Multi-element Standards (SMELS) Used for the Validation of k0-NAA

VERMAERCKE Peter; ROBOUCH PIOTR; EGUSKIZA Mikel; DE CORTE F; KENNEDY G.; SMODIS B; MATSUE H; YONEZAWA F; LIN X; BLAAUW M; KUCERA J
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Articles in Journals Formato: Printed
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A synthetic multi-element standard material (SMELS) has been prepared for the validation of k0-standardised Neutron-Activation Analysis (k0-NAA). SMELS consists of three different materials in a polymer matrix spiked with different elements, so that each material can be used for an elemental analysis monitoring respectively short lived (SMELS Type I), medium (Type II) and long-lived (Type III) radionuclides. In previous studies the homogeneity and radiation stability of the material have been proven. The final step, discussed in this article, is the characterisation of the material in terms of the elemental content by neutron-activation analysis techniques.; JRC.D.4-Isotope measurements

K0-NAA for the Determination of Trace Elements in a Synthetic Material: a Collaborative Study

VERMAERCKE Peter; ROBOUCH Piotr
Fonte: Americal Institute of Physics (AIP) Publicador: Americal Institute of Physics (AIP)
Tipo: Contributions to Conferences Formato: Printed
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As part of an interlaboratory comparison in order to certify a synthetic material to be used for the validation of the proper implementation of k0-NAA a collaborative trial was organised. Based on this collaborative study, reproducibility relative standard deviations valued ranged typically from 2 to 5%. These values were compares with the Horwitz criterium leading to HORRAT values in most cases well below 1, although two exceeding 1, depending on the element to be determined. It could be concluded that k0-NAA is a very precise method, but that still some inconsistencies for certain elements remain.; JRC.D.8-Food safety and quality

Measurement of the Isotopic Composition of Germanium by k0-INAA and INAA

VERMAERCKE Peter; HULT Mikael; VERHEYEN L.; FARINA ARBOCCO F.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Contributions to Conferences Formato: Printed
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In experiments searching for neutrinoless double beta-decay high-purity Germanium detectors enriched in 76Ge will be used. Due to the nature of these experiments the isotopic composition of the enriched germanium is an important parameter. In order to determine the 76Ge/74Ge isotopic ratio in this new material, but also in natural and depleted samples, the feasibility of using k0- and relative standardisation neutron activation analysis for the determination of isotopic ratios was investigated. The paper will discuss the accuracy and the estimated uncertainty of both methods in general. It was found that both techniques are useful for the determination of isotopic ratios. The analysis also demonstrated that the k0-data forGe should be re-evaluated.; JRC.D.4-Nuclear physics

A novel route to produce a homogenous certified reference material for k0-neutron activation analysis: application to the certification of gold mass fraction in an Al-0.1% Au alloy

BACQUART THOMAS; LI Jihua; RIBEIRO GUEVARA Sergio; ARRIBÉRE M.a.; GERGANOVA TSVETELINA IVANOVA; STERCKX Marc; SCHUMACHER Peter; LINSINGER Thomas
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Articles in periodicals and books Formato: Online
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Reliable certified reference materials (CRM) are required for neutron dosimetry in k0-neutron activation analysis (k0-NAA). In the past, levitation melting was employed to produce highly homogeneous alloys used of the production of CRMs. This publication describes a novel and more efficient way of processing such alloys using the example of an Al-Au alloy, the evaluation of the efficacy with respect to achieving homogeneity and avoiding micro- and macroseggregation and the final certification of the Au mass fraction. First, Al-5 % Au alloy was melted by arc melting and then diluted into Al-0.1 % Au with high purity Al in a resistance furnace under the protection of high purity argon gas. The as-casted Al-0.1 % Au was then heat-treated at about 635 °C for 48 hours. No significant macroseggregation and no intermetallic phase (AuAl2) were observed in the heat-treated alloy. Using this approach, a new CRM for gold mass fraction in Al-0.1 % Au was produced in the form of wires and foils (ERM-EB530A, B and C). The relative uncertainty from gold inhomogeneity in the material was assessed using a randomised block design and inductively coupled plasma optical emission spectrometry (ICP-OES) and was found to be 0.3 %. The characterisation of the gold mass fraction was performed by an interlaboratory comparison of expert laboratories. Sixteen laboratories participated using instrumental neutron activation analysis (197Au(n...

77Se NMR Evidence of Strongly Coupled Superconductivity in K0.8Fe2-xSe2

Ma, L.; He, J. B.; Wang, D. M.; Chen, G. F.; Yu, Weiqiang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/01/2011 Português
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We report the 77Se NMR Knight shift and spin-lattice relaxation studies on the superconducting state of the ternary iron selenide K0.8Fe2-xSe2 with Tc~30 K. Just below Tc, the Knight shift 77Kn shows an immediate drop, indicating a singlet pairing. The spin-lattice relaxation rate 1/77T1 decreases rapidly in the temperature range from TC to Tc/2, which can be fit with an isotropic gap of \Delta~3.8\pm 0.5 k_BTc. The Hebel-Slichter coherence peak is not observed. These data give bulk evidence for a strongly coupled superconductivity with isotropic gaps in K0.8Fe2-xSe2, which is similar to other iron-based high temperature superconductors. Below Tc/2, the spin-part of the Knight shift levels off to a constant value (~0.09%), and the spin-lattice relaxation follows a 1/T1 T^2 behavior, which are not well understood.; Comment: 4 pages, 3 figures

Search for the decay phi -> K0 K0bar gamma with the KLOE experiment

KLOE Collaboration; Ambrosino, F.; Antonelli, A.; Antonelli, M.; Archilli, F.; Beltrame, P.; Bencivenni, G.; Bertolucci, S.; Bini, C.; Bloise, C.; Bocchetta, S.; Bossi, F.; Branchini, P.; Capon, G.; Capussela, T.; Ceradini, F.; Ciambrone, P.; De Lucia, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We have searched for the decay phi -> K0 K0bar gamma, by detecting K_s pairs plus a photon and with the K_s-mesons decaying to pi^+ pi^-, in a sample of about 1.5x 10^9 phi-decays collected by the KLOE experiment at DAFNE. The reaction proceeds through the intermediate states f_0(980) gamma, a_0(980) gamma. We find five events with 3.2 events expected from background processes. We obtain the upper limit: BR (phi -> K0 K0bar gamma) < 1.9x10^-8 at 90% C.L. .; Comment: 11 pages, 8 figures, submitted to Physics Letters B

Upper fields and critical current density of K0.58Fe1.56Se2 single crystals grown by one step technique

Gao, Zhaoshun; Qi, Yanpeng; Wang, Lei; Yao, Chao; Wang, Dongliang; Zhang, Xianping; Ma, Yanwei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/03/2011 Português
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Single crystals of K0.58Fe1.56Se2 were successfully synthesized by a new single step process with the onset superconducting transition temperatures 31.9 K. The x-ray diffraction patterns suggest that they have high crystalline quality and c-axis orientation. A possible modulation structure of Fe-vacancy along c axis was observed. The upper critical field has been determined with the magnetic field along ab-plane and c-axis, yielding an anisotropy of about 3.3. It has also been shown that the critical current density of the K0.58Fe1.56Se2 is about 1.7x10^4 A/cm^2 at 5 K.; Comment: 14 pages, 6 figures. The damaged figures (fig.1 and fig.5) during the PDF file conversion were updated in the new version

Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T

Mun, E. D.; Altarawneh, M. M.; Mielke, C. H.; Zapf, V. S.; Hu, R.; Bud'ko, S. L.; Canfield, P. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are determined over a wide range of temperatures down to 1.5 K and magnetic fields up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for magnetic field applied along c-axis and ab-plane, respectively, were observed. Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K above 30 T. This leads to a non-monotonic temperature dependence of the anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~ 2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and (Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state and proximity to an insulating state, the Hc2(T) curves are remarkably similar.; Comment: slightly modified version, accepted to PRB, Rapid Communications

Quenching of superconductivity by Co doping in K0.8Fe2Se2

Zhou, Tingting; Chen, Xiaolong; Guo, Jiangang; Wang, Gang; Lai, Xiaofang; Wang, Shunchong; Jin, Shifeng; Zhu, Kaixing
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/02/2011 Português
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We synthesized a series of K0.8Fe2-xCoxSe2 samples with nominal compositions 0\leq x\leq 0.035 and investigated their physical properties. The results show that the superconductivity in K0.8Fe2-xCoxSe2 is quenched down to 5 K by 0.5 at. % Co doping, the fastest quenching rate ever-reported. The role played here by Co is in contrast with the one in FeAs based superconductors where Co usually induces superconductivity from parent compounds. Such a rapid quenching favors a localized 3d model against the itinerant one for iron pnictide superconductors.; Comment: 17 pages, 4 figures

Measurement of the branching fraction B(tau- --> K0 pi- nu) using the BaBar detector

Aubert, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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A preliminary measurement of the branching fraction B(tau- --> K0 pi- nu) is made using 384.6 fb-1 of e+e- collision data provided by the PEP-II collider, operating primarily at sqrt(s)=10.58 GeV, and recorded using the BaBar detector. From this we measure: B(tau- --> K0 pi- nu) = (0.840 +/- 0.004 (stat) +/- 0.023 (syst)) %. This result is the most precise measurement to date and is consistent with the world average.; Comment: 17 pages, 3 figures, submitted to ICHEP 2008

Observation of B+ -> p pbar pi+, B0 -> p pbar K0, and B+ -> p pbar K*+

Wang, M. -Z.; Collaboration, for the Belle
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We report the first observation of a b -> u type charmless baryonic B decay, B+ -> p pbar pi+, as well as b -> s type B0 -> p pbar K0 and B+ -> p pbar K*+ decays. The analysis is based on a 78fb^{-1} data sample recorded on the Upsilon(4S) resonance with the Belle detector at KEKB. We find BF(B+ -> p pbar pi+) = (3.06^{+0.73}_{-0.62} \pm 0.37)*10^{-6}, BF(B0 -> p pbar K0) =(1.88^{+0.77}_{-0.60} \pm 0.23)*10^{-6}, and BF(B+ -> p pbar K*+) = (10.3^{+3.6 + 1.3}_{-2.8 -1.7})*10^{-6}. We also update BF(B+ -> p pbar K+) = (5.66^{+0.67}_{-0.57} \pm 0.62)* 10^{-6}, and present an upper limit on BF(B0 -> p pbar K*0) at the 90% confidence level. A common feature of the observed decay modes is threshold peaking in baryon pair invariant mass.; Comment: 10 pages, 12 figure files

Upper critical fields and superconducting anisotropy of K0.70Fe1.55Se1.01S0.99 and K0.76Fe1.61Se0.96S1.04 single crystals

Lei, Hechang; Petrovic, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We have investigated temperature and angular dependence of resistivity of K0.70(7)Fe1.55(7)Se1.01(2)S0.99(2) and K0.76(5)Fe1.61(5)Se0.96(4)S1.04(5) single crystals. The upper critical fields Hc2(T) for both field directions decrease with the increase in S content. On the other hand, the angle-dependent magnetoresistivity for both compounds can be scaled onto one curve using the anisotropic Ginzburg-Landau theory. The obtained anisotropy of Hc2(T) increases with S content, implying that S doping might decrease the dimensionality of certain Fermi surface parts, leading to stronger two dimensional character.; Comment: 5 pages, 6 figures

Phase separation and stripe patterns in K0.8Fe1.6+xSe2 superconductors

Wang, Z. W.; Wang, Z.; Song, Y. J.; Ma, C.; Shi, H. L.; Chen, Z.; Tian, H. F.; Yang, H. X.; Chen, G. F.; Li, J. Q.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/04/2012 Português
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Structural investigations on the K0.8Fe1.6+xSe2 superconducting materials have revealed remarkable micro-stripes arising evidently from the phase separation. Two coexisted structural phases can be characterized by modulations of q1 = 1/5[a*+3b*], the antiferromagnetic phase K0.8Fe1.6Se2, and q2 = 1/2[a*+b*], the superconducting phase K0.75Fe2Se2, respectively. These stripe patterns likely result from the anisotropic assembly of superconducting particles along the [110] and [1-10] direction. In addition to the notable stripe structures, a nano-scale phase separation also appears in present superconducting system as clearly observed by high-resolution transmission electron microscopy. Certain notable experimental data obtained in this heterogenous system can be quantitatively explained by the percolation scenario.; Comment: 15 pages, 6 figures

Synthesis and physical properties of the new potassium iron selenide superconductor K0.80Fe1.76Se2

Hu, Rongwei; Mun, E. D.; Ryan, D. H.; Cho, K.; Kim, H.; Hodovanets, H.; Straszheim, W. E.; Tanatar, M. A.; Prozorov, R.; Rowan-Weetaluktuk, W. N.; Cadogan, J. M.; Altarawneh, M. M.; Mielke, C. H.; Zapf, V. S.; Bud'ko, S. L.; Canfield, P. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/01/2012 Português
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In this article we review our studies of the K0.80Fe1.76Se2 superconductor, with an attempt to elucidate the crystal growth details and basic physical properties over a wide range of temperatures and applied magnetic field, including anisotropic magnetic and electrical transport properties, thermodynamic, London penetration depth, magneto-optical imaging and Mossbauer measurements. We find that: (i) Single crystals of similar stoichiometry can be grown both by furnace-cooled and decanted methods; (ii) Single crystalline K0.80Fe1.76Se2 shows moderate anisotropy in both magnetic susceptibility and electrical resistivity and a small modulation of stoichiometry of the crystal, which gives rise to broadened transitions; (iii) The upper critical field, Hc2(T) is ~ 55 T at 2 K for H||c, manifesting a temperature dependent anisotropy that peaks near 3.6 at 27 K and drops to 2.5 by 18 K; (iv) Mossbauer measurements reveal that the iron sublattice in K0.80Fe1.76Se2 clearly exhibits magnetic order, probably of the first order, from well below Tc to its Neel temperature of Tn = 532 +/- 2 K. It is very important to note that, although, at first glance there is an apparent dilemma posed by these data: high Tc superconductivity in a near insulating...

The phi --> gamma K0 bar(K0) Decay

Oller, J. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/03/1998 Português
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The study of the process phi-->gamma K0 bar(K0) is calculated to be 5.10^(-8) in a scheme which takes into account the different isospin channels involved, I=0,1 with the resonant, f_0(980), a_0(980), and non resonant contributions.; Comment: 6 pages, 2 figures, LaTeX

Time-Dependent CP Asymmetries in b --> s qbar q Transitions and sin2phi1 in B0 --> J/psi K0 Decays with 386 Million BBbar Pairs

The Belle Collaboration; Abe, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/07/2005 Português
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We present measurements of time-dependent CP asymmetries in B0 --> phi(1020) K0, eta' K0, Ks Ks Ks, Ks pi0, f0(980) Ks, omega Ks and K+ K- Ks decays based on a sample of 386 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. These decays are dominated by the b --> s gluonic penguin transition and are sensitive to new CP-violating phases from physics beyond the standard model. One neutral B meson is fully reconstructed in one of the specified decay channels, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters sin2phi1^eff and {\cal A} for each of the decay modes are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. We also perform an improved measurement of CP asymmetries in B0 --> J/psi K0 decays using the same data sample. The same analysis procedure mentioned above yields sin2phi1 = +0.652 +/- 0.039(stat) +/- 0.020(syst), which serves as a reference point for the standard model, and {\cal A} = +0.010 +/- 0.026(stat) +/- 0.036(syst).; Comment: 36 pages, 17 figures, contributed to the XXII International Symposium on Lepton-Photon Interactions at High Energy (Lepton-Photon 2005)...