Study of a high performance evaporative heat transfer surface

An evaporative surface is described for heat pipes and other two-phase heat transfer applications that consists of a hybrid composition of V-grooves and capillary wicking. Characteristics of the surface include both a high heat transfer coefficient and high heat flux capability relative to conventional open-faced screw thread surfaces. With a groove density of 12.6 cm/1 and ammonia working fluid, heat transfer coefficients in the range of 1 to 2 W/sq cm have been measured along with maximum heat flux densities in excess of 20 W/sq cm. A peak heat transfer coefficient in excess of 2.3 W/sq cm was measured with a 37.8 cm/1 hybrid surface

Mass-Enhanced Fermi Liquid Ground State in Na1.5_{1.5}Co2_2O4_4

Magnetic, transport, and specific heat measurements have been performed on layered metallic oxide Na$_{1.5}$Co$_2$O$_4$ as a function of temperature $T$. Below a characteristic temperature $T^*$=30$-$40 K, electrical resistivity shows a metallic conductivity with a $T^2$ behavior and magnetic susceptibility deviates from the Curie-Weiss behavior showing a broad peak at $\sim$14 K. The electronic specific heat coefficient $\gamma$ is $\sim$60 mJ/molK$^2$ at 2 K. No evidence for magnetic ordering is found. These behaviors suggest the formation of mass-enhanced Fermi liquid ground state analogous to that in $d$-electron heavy fermion compound LiV$_2$O$_4$.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B 69 (2004

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

A Measurement of Lifetime Difference in D0D^0 Meson Decays

We report a measurement of the $D^0$-$\bar{D}{}^0$ mixing parameter $y_{CP}$ using 23.4 fb$^{-1}$ of data collected near the $\Upsilon$(4S) resonance with the Belle detector at KEKB. $y_{CP}$ is measured from the lifetime difference of $D^0$ mesons decaying into the $K^-\pi^+$ state and the CP even eigenstate $K^-K^+$. We find $y_{CP}=(-0.5\pm 1.0{}^{+0.7}_{-0.8})\times10^{-2}$, where the first error is statistical and the second systematic, corresponding to a 95% confidence interval $-0.030 < y_{CP} < 0.020$.Comment: 10 pages, 3 figure

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

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.

Search for Charmless Two-body Baryonic Decays of B Mesons

We report the results of a search for the rare baryonic decays $B^0 \to p\bar{p}$, $\Lambda\bar{\Lambda}$, and $B^+ \to p\bar{\Lambda}$. The analysis is based on a data set of $31.7\times 10^6 B\bar{B}$ events collected by the Belle detector at the KEKB $e^+e^-$ collider. No statistically significant signals are found, and we set branching fraction upper limits ${\mathcal B}(B^0 \to p\bar{p}) < 1.2 \times 10^{-6}$, ${\mathcal B}(B^0 \to \Lambda\bar{\Lambda}) < 1.0 \times 10^{-6}$, and ${\mathcal B}(B^+ \to p\bar{\Lambda}) < 2.2 \times 10^{-6}$ at the 90% confidence level.Comment: 6 pages, 4 figures and 1 table. Submitted to Phys. Rev. D Rapid Communication