Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.     

Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).     

Intraoperative contrast-enhanced MR-imaging as predictor of tissue damage during cryoablation of porcine liver

This study evaluate intraoperative Magnetic Resonance Imaging (MRI) as predictor of tissue damage following cryoablation of porcine liver with and without concomitant hepatic vascular inflow occlusion.Inflow occlusion was used during freezing in 6 of 12 pigs included. The volumes of the procedural ice-balls were estimated from MR images. Immediately after thawing contrast (MnDPDP) enhanced MRI was performed to estimate the volume of the cryolesion. Four days after ablation MRI was repeated of the in-vivo and the ex-vivo liver. Photography was performed of the sliced liver specimens to estimate the volumes of the lesions. The intraoperative volume of the cryolesion as shown by contrast enhanced MRI corresponded well to the ice-ball volume for lesions made without vascular occlusion (difference 0.3 +/- 0.9 cm(3), p = 0.239). For lesions made during occlusion the volume of the intraoperative cryolesion was larger than the corresponding ice-ball (difference 7.5 +/- 3.3 cm(3), p = 0.003). The volume of the cryolesions as estimated from histopathology four days after freezing and contrast enhanced MRI immediately after freezing corresponded well for lesions made with (difference -2.6 +/- 4.5 cm(3), p = 0.110) and without vascular occlusion (difference -0.5 +/- 2.3 cm(3), p = 0.695).Intraoperative MnDPDP-enhanced MRI of the cryolesion is predictive of the tissue damage induced during cryoablation of porcine liver. The procedural ice-ball is not, if induced during inflow occlusion.     

Instability of Interfaces in the Antiferromagnetic XXZ Chain at Zero Temperature

 For the antiferromagnetic, highly anisotropic XZ and XXZ quantum spin chains, we impose periodic boundary conditions on chains with an odd number of sites to force an interface (or kink) into the chain. We prove that the energy of the interface depends on the momentum of the state. This shows that at zero temperature the interface in such chains is not stable. This is in contrast to the ferromagnetic XXZ chain for which the existence of localized interface ground states has been proven for any amount of anisotropy in the Ising-like regime. Received: 15 August 2002 / Accepted: 8 January 2003 Published online: 14 April 2003 RID="⋆" ID="⋆" ? Copyright rests with the authors. Reproduction of the entire article for non-commercial purposes is permitted. Communicated by M. Aizenman     

Speech production in noise with and without hearing protection

People working in noisy environments often complain of difficulty communicating when they wear hearing protection. It was hypothesized that part of the workers' communication difficulties stem from changes in speech production that occur when hearing protectors are worn. To address this possibility, overall and one-third-octave-band SPL measurements were obtained for 16 men and 16 women as they produced connected speech while wearing foam, flange, or no earplugs (open ears) in quiet and in pink noise at 60, 70, 80, 90, and 100 dB SPL. The attenuation and the occlusion effect produced by the earplugs were measured. The Speech Intelligibility Index (SII) was also calculated for each condition. The talkers produced lower overall speech levels, speech-to-noise ratios, and SII values, and less high-frequency speech energy, when they wore earplugs compared with the open-ear condition. Small differences in the speech measures between the talkers wearing foam and flange earplugs were observed. Overall, the results of the study indicate that talkers wearing earplugs (and consequently their listeners) are at a disadvantage when communicating in noise.     

Synthesis of monodentate ferrocenylphosphines and their application to the palladium-catalyzed Suzuki reaction of aryl chlorides

Racemic and enantiopure ((p)()S)-1-bromo-2-methylferrocene 6 were synthesized in 4 steps from 2-(4,4-dimethyloxazolinyl)ferrocene and (S)-2-(4-methylethyloxazolinyl)ferrocene, respectively (46 and 81% overall yield). Bromolithium exchange and addition of ClPR(2) gave the corresponding racemic or enantiopure 2-methylferrocenyl phosphine ligands 2-MeFcPR(2) 11 (R = Ph), 12 (R = Cy), and 13 (R = (t)Bu) in 28-93% yield. Use of PCl(3) gave the C(3)-symmetric phosphine (2-MeFc)(3)P 5 from ((p)()S)-6(72% yield) but racemic 6 did not lead to the formation of triferrocenyl phosphines. Combination of 5 and Pd(2)(dba)(3) gave an active catalyst for the Suzuki reaction of aryl chlorides, for example, 4-chlorotoluene and phenylboronic acid reacted at only 60 degrees C in dioxane (86% yield). Other examples are reported together with the use of 12 in this same protocol. From the X-ray crystal structure of 5 the cone angle was determined as 211 degrees. With this, and the electronic character of 11, 12, and other phosphines (derived from nu(CO) of trans-[(R(3)P)(2)Rh(CO)Cl]), an analysis is made of the steric and electronic influences on ligand activity in the Suzuki reaction.     

Synthesis and characterization of luminescent osmium(II) carbonyl complexes based on chelating dibenzoylmethanate and halide ligands

Octahedral Os(II) complexes 1-5 with formula [Os(CO)3X(dbm)] are prepared through utilization of both solid-state pyrolysis and ligand exchange reactions. These complexes exhibit prominent 3pi-pi* phosphorescence with unusually long lifetimes (29-64 micros) and high quantum yields (0.08-0.13).     

Wavelength dependent photo-controlled differential release of compounds from solid phase resin

A method to effect photo-mediated differential release of bead-based compound libraries using a tuneable laser in combination with chromatically orthogonal photolabile linkers is described.     

Synthesis of HyBeacons and dual-labelled probes containing 2'-fluorescent groups for use in genetic analysis

An FMOC-protected 2'-hydroxyethyl uridine phosphoramidite has been used to synthesise fluorescein-labelled HyBeacon probes and "FAM-ROX" dual-labelled fluorogenic oligonucleotides.     

Furan-containing oligoaryl cyclophanene

[structure: see text] Furan-containing oligoaryl cyclophanene 1 and the corresponding cyclophane 2 were synthesized from propargylic dithioacetal 3. The electrochemical and photophysical properties and the fluxional behavior of these molecules have been examined. The emission of 1 appeared at 499 nm whereas that of 2 appeared at 389 nm.