Effects of the separating shear layer on the reattachment flow structure Part 1: Pressure and turbulence quantities

The effect of the separating shear-layer thickness and shape on the structure of the flow in the reattachment region of a backward-facing step is examined using wall static-pressure profiles and turbulence data for a range of Reynolds number (800 < Re _H< 40,000) and upstream boundary-layer thickness (0 < δ/H < 2). The reattachment pressure and the peak pressure in the reattachment zone decrease in a continuous manner as the upstream boundary layer thickens. The thinnest boundary layers follow the correlation of Roshko and Lau. Using the pressure data, correlations are developed which can be used to predict the level of turbulent shear stress in the near-wall region at reattachment, a location in which experimental data are extremely difficult to obtain.     

Search for heavy particles decaying into electron-positron pairs in pp collisions

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.     

Towards a microchannel‐based X‐ray detector with two‐dimensional spatial and time resolution and high dynamic range

X‐ray detectors that combine two‐dimensional spatial resolution with a high time resolution are needed in numerous applications of synchrotron radiation. Most detectors with this combination of capabilities are based on semiconductor technology and are therefore limited in size. Furthermore, the time resolution is often realised through rapid time‐gating of the acquisition, followed by a slower readout. Here, a detector technology is realised based on relatively inexpensive microchannel plates that uses GHz waveform sampling for a millimeter‐scale spatial resolution and better than 100 ps time resolution. The technology is capable of continuous streaming of time‐ and location‐tagged events at rates greater than 10⁷ events per cm². Time‐gating can be used for improved dynamic range.     

Early Membrane Responses to Magnetic Particles are Predictors of Particle Uptake in Neural Stem Cells

Magnetic particles (MPs) offer several advantages for neural cell therapy, but limited particle uptake by neural cells is a barrier to translation. It is recently proved that tailoring particle physicochemical properties (by enhancing their iron content) dramatically improves uptake in neural stem cells (NSCs)—a major transplant population. High‐throughput screening of particles with varying physicochemical properties can therefore aid in identifying particles with optimal uptake features, but research is hampered by the lack of simple methodologies for studying neural cell membrane responses to nanoparticle platforms. A high‐resolution–high throughput method has been used to study early membrane responses of primary rodent NSCs to particles of variant magnetite loading, to attempt to correlate these responses with known particle internalization profiles. Membrane imaging is enhanced through sequential staining with osmium (O) and thiocarbohydrazide (T), a method termed OTOTO, combined with field‐emission scanning electron microscopy (FESEM). A five‐point classification system was used to systematically evaluate early MP‐induced membrane responses to particles possessing distinct physicochemical properties. Significantly different profiles of membrane activation were noted that correlate with particle uptake profiles. It is suggested that our method can serve as a valuable predictor of particle internalization in neural cells for diverse particle platforms.     

Non-linear Sagnac interferometry for pump-probe dispersion spectroscopy

We explore pump-probe non-linear Sagnac interferometry as a tool to measure the dispersive properties of a medium. We introduce the background theory, and show experimental spectra obtained on the D₂ transition with ⁸⁵Rb and ⁸⁷Rb. The measured dispersion spectra are in excellent agreement with the Kramers-Kronig relations. In addition, as both beams traverse identical optical paths, Sagnac interferometry is very robust against mechanical vibrationReceived: 5 June 2003, Published online: 16 September 2003PACS: 39.30. + w Spectroscopic techniques - 33.55.Ad Optical activity, optical rotation; circular dichroismG. Jundt: Present address: Institute of Quantum Electronics, Department of Physics, ETH Zürich, Hönggerberg 8093, Switzerland.     

Study of Zgamma events and limits on anomalous ZZgamma and Zgammagamma couplings in pp collisions at square root s = 1.96 TeV

We present a measurement of the Zgamma production cross section and limits on anomalous ZZgamma and Zgammagamma couplings for form-factor scales of lambda = 750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eegamma (mumugamma) final state using 320(290) pb(-1) of pp(-1) collisions at square root of s = 1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are /h(10,30)Z/ < 0.23, /h(20,40)Z/ < 0.020, /h(10,30)gamma/ < 0.23, and /h(20,40)gamma/ < 0.019 for lambda = 1000 GeV.     

Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS

Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.