225 research outputs found
Peptide exchange on MHC-I by TAPBPR is driven by a negative allostery release cycle.
Chaperones TAPBPR and tapasin associate with class I major histocompatibility complexes (MHC-I) to promote optimization (editing) of peptide cargo. Here, we use solution NMR to investigate the mechanism of peptide exchange. We identify TAPBPR-induced conformational changes on conserved MHC-I molecular surfaces, consistent with our independently determined X-ray structure of the complex. Dynamics present in the empty MHC-I are stabilized by TAPBPR and become progressively dampened with increasing peptide occupancy. Incoming peptides are recognized according to the global stability of the final pMHC-I product and anneal in a native-like conformation to be edited by TAPBPR. Our results demonstrate an inverse relationship between MHC-I peptide occupancy and TAPBPR binding affinity, wherein the lifetime and structural features of transiently bound peptides control the regulation of a conformational switch located near the TAPBPR binding site, which triggers TAPBPR release. These results suggest a similar mechanism for the function of tapasin in the peptide-loading complex
Search for Charmless Two-body Baryonic Decays of B Mesons
We report the results of a search for the rare baryonic decays , , and . The analysis
is based on a data set of events collected by the
Belle detector at the KEKB collider. No statistically significant
signals are found, and we set branching fraction upper limits , , and at the 90% confidence level.Comment: 6 pages, 4 figures and 1 table. Submitted to Phys. Rev. D Rapid
Communication
Search for Direct CP Violation in B -> K pi Decays
We search for direct CP violation in flavor specific B -> K pi decays by
measuring the rate asymmetry between charge conjugate modes. The search is
performed on a data sample of 11.1 million B B bar events recorded on the
Upsilon(4S) resonance by the Belle experiment at KEKB. We measure 90%
confidence intervals in the partial rate asymmetry A_CP of -0.25 < A_CP(K-/+
pi+/-) < 0.37, -0.40 < A_CP(K-/+ pi^0) < 0.36, and -0.53 < A_CP(K^0 pi-/+) <
0.82. By combining the K-/+ pi+/- and K-/+ pi^0 final states, we conclude that
-0.22 < A_CP[K-/+(pi+/- + pi^0)] < 0.25 at the 90% confidence level.Comment: Submitted to PRD Rapid Communication
Precise Measurement of B Meson Lifetimes with Hadronic Decay Final States
The lifetimes of the B0bar and B- mesons are extracted from 29.1/fb of data
collected with the Belle detector at the KEK B-factory. A fit to the decay
length differences of neutral and charged B meson pairs, measured in events
where one of the B mesons is fully reconstructed in several hadronic modes,
yields tau_B0bar = 1.554 +/- 0.030(stat) +/- 0.019(syst) ps, tau_B- = 1.695 +/-
0.026(stat) +/- 0.015(syst) ps, and tau_B-/tau_B0bar = 1.091 +/- 0.023(stat)
+/- 0.014(syst).Comment: 10 pages, 2 figures, and 1 table. (To be) published in Phys. Rev.
Let
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
Measurement of Inclusive Production of Neutral Pions from Upsilon(4S) Decays
Using the Belle detector operating at the KEKB e+e- storage ring, we have
measured the mean multiplicity and the momentum spectrum of neutral pions from
the decays of the Upsilon(4S) resonance. We measure a mean of 4.70 +/- 0.04 +/-
0.22 neutral pions per Upsilon(4S) decay.Comment: 15 pages, 4 figs. Submitted to Phys.Rev.
Observation of Cabibbo suppressed decays at Belle
Cabibbo-suppressed decays using a 10.4 fb data
sample accumulated at the resonance with the Belle detector at
the KEKB storage ring. The high-momentum particle identification
system of Belle is used to isolate signals for , ,
and from the decay processes which
have much larger branching fractions. We report ratios of Cabibbo-suppressed to
Cabibbo-favored branching fractions of: ; ; ; and
. The first error is statistical and the second is systematic.
These are the first reported observations of the , and
decay processes.Comment: LaTeX, 12 pages, 2 figure
Measurement of B0d - B0d-bar mixing rate from the time evolution of dilepton events at the Upsilon(4S)
We report a determination of the B0d - B0d-bar mixing parameter Delta-m_d
based on the time evolution of dilepton yields in Upsilon(4S) decays. The
measurement is based on a 5.9 /fb data sample collected by the Belle detector
at KEKB. The proper-time difference distributions for same-sign and
opposite-sign dilepton events are simultaneously fitted to an expression
containing Delta-m_d as a free parameter. Using both muons and electrons, we
obtain Delta-m_d = 0.463 +- 0.008(stat.) +- 0.016(sys.) ps^{-1} This is the
first determination of Delta-m_d from time evolution measurements at the
Upsilon(4S). We also place limits on possible CPT violations.Comment: 12 pages, 2 figure
The use of MRI apparent diffusion coefficient (ADC) in monitoring the development of brain infarction
<p>Abstract</p> <p>Background</p> <p>To study the rules that apparent diffusion coefficient (ADC) changes with time and space in cerebral infarction, and to provide the evidence in defining the infarction stages.</p> <p>Methods</p> <p>117 work-ups in 98 patients with cerebral infarction (12 hyperacute, 43 acute, 29 subacute, 10 steady, and 23 chronic infarctions) were imaged with both conventional MRI and diffusion weighted imaging. The average ADC values, the relative ADC (rADC) values, and the ADC values or rADC values from the center to the periphery of the lesion were calculated.</p> <p>Results</p> <p>The average ADC values and the rADC values of hyperacute and acute infarction lesion depressed obviously. rADC values in hyperacute and acute stage was minimized, and increased progressively as time passed and appeared as "pseudonormal" values in approximately 8 to 14 days. Thereafter, rADC values became greater than normal in chronic stage. There was positive correlation between rADC values and time (P < 0.01). The ADC values and the rADC values in hyperacute and acute lesions had gradient signs that these lesions increased from the center to the periphery. The ADC values and the rADC values in subacute lesions had adverse gradient signs that these lesions decreased from the center to the periphery.</p> <p>Conclusion</p> <p>The ADC values of infarction lesions have evolution rules with time and space. The evolution rules with time and those in space can be helpful to decide the clinical stage, and to provide the evidence in guiding the treatment or judging the prognosis in infarction.</p
Measurement of the CP Violation Parameter sin(2phi_1) in B^0_d Meson Decays
We present a measurement of the Standard Model CP violation parameter
sin(2phi_1) based on a 10.5 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric e+e- collider. One
neutral B meson is reconstructed in the J/psi K_S, psi(2S) K_S, chi_{c1} K_S,
eta_c K_S, J/psi K_L or J/psi pi^0 CP-eigenstate decay channel and the flavor
of the accompanying B meson is identified from its charged particle decay
products. From the asymmetry in the distribution of the time interval between
the two B-meson decay points, we determine sin(2phi_1) = 0.58 +0.32-0.34 (stat)
+0.09-0.10 (syst).Comment: LaTex, 13 pages, 3 figures, submitted to P.R.
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