Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering

We have measured the spin-dependent structure function $g_1^p$ in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range $0.003 < x < 0.7$ and $1 GeV^2 < Q^2 < 60 GeV^2$. A next-to-leading order QCD analysis is used to evolve the measured $g_1^p(x,Q^2)$ to a fixed $Q^2_0$. The first moment of $g_1^p$ at $Q^2_0 = 10 GeV^2$ is $\Gamma^p = 0.136\pm 0.013(stat.) \pm 0.009(syst.)\pm 0.005(evol.)$. This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge $a_0$ is found to be $0.28 \pm 0.16$. In the Adler-Bardeen factorization scheme, $\Delta g \simeq 2$ is required to bring $\Delta \Sigma$ in agreement with the Quark-Parton Model. A combined analysis of all available proton and deuteron data confirms the Bjorken sum rule.Comment: 33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical Review

Next-to-Leading Order QCD Analysis of Polarized Deep Inelastic Scattering Data

We present a Next-to-Leading order perturbative QCD analysis of world data on the spin dependent structure functions $g_1^p, g_1^n$, and $g_1^d$, including the new experimental information on the $Q^2$ dependence of $g_1^n$. Careful attention is paid to the experimental and theoretical uncertainties. The data constrain the first moments of the polarized valence quark distributions, but only qualitatively constrain the polarized sea quark and gluon distributions. The NLO results are used to determine the $Q^2$ dependence of the ratio $g_1/F_1$ and evolve the experimental data to a constant $Q^2 = 5 GeV^2$. We determine the first moments of the polarized structure functions of the proton and neutron and find agreement with the Bjorken sum rule.Comment: 21 pages, 4 figures; final version to be published in Phys. Lett. B. References updated. Uses elsart.cls version 1996/04/22, 2e-1.4

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Colh) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C10Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C10Br, a 'high temperature' glass transition, manifested by a Vogel-Fulcher-Tammann (VFT) type α2-process, was found at -31 °C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (α1) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as -100 °C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a 'hindered' polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails. © 2005 Elsevier B.V. All rights reserved.status: publishe

Multiple glass transitions in the plastic crystal phase of triphenylene derivates

The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Colh) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C10Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C10Br, a `high temperature¿ glass transition, manifested by a Vogel¿Fulcher¿Tammann (VFT) type ¿2-process, was found at ¿31 °C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (¿1) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as ¿100 °C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a `hindered¿ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails

Nickel hexacyanoferrate electrodes for high mono/divalent ion-selectivity in capacitive deionization

Selective ion removal has been a point of focus in capacitive deionization because of its industrial applications such as water purification, water softening, heavy metal separation and resource recovery. Conventionally, carbon is used as electrode material for selectivity. However, recent developments focus on intercalation materials such as Prussian Blue Analogues, due to their size-based preference towards cations. Selectivity of nickel hexacyanoferrate electrodes from a mixture of Na+, Mg2+, and Ca2+ ions was studied in this work. Here, a CDI cell with two identical NiHCF electrodes was operated in two desalination modes: (a) cyclic, in which ions are removed from and released into the same water reservoir and thus, the ion concentration remains the same after one cycle, and (b) continuous, in which ions are removed from one water reservoir and released back in a different reservoir. An average separation factor of ≈15 and 25, reflecting the selectivity of the electrodes, was obtained for Na+ over Ca2+ and Mg2+ from an equimolar solution of Na+, Ca2+ and Mg2+ in both, cyclic and continuous desalination. It was concluded that NiHCF, used in a symmetric CDI cell, is a promising material for highly selective removal of Na+ from a multivalent ion mixture.OLD ChemE/Organic Materials and Interface

Amine-terminated silicon nanoparticles: synthesis, optical properties and their use in bioimaging

Very stable and bright emitting amine-terminated Si nanoparticles (NPs) with different alkyl chain lengths between the Si core and amine end-group are synthesized. The obtained NPs have a spherical shape and homogeneous size distribution (1.57 ± 0.24 nm). Their emission can be tuned from the UV to the blue spectral region, in a controllable fashion, by only changing the alkyl spacer length. The emission quantum yields are 12% for all synthesized Si NPs. Excited state lifetimes are in the ns range and point to a direct band gap excitation. NH2-terminated Si NPs exhibit an exceptional stability over a wide pH range (1¿13) and high temperatures (120 °C). The diffusion coefficient of prepared Si NPs is determined by fluorescence correlation spectroscopy (FCS) to be 3.3 × 10-10 m2 s-1. The derived size of Si NPs from mobility corresponds to 1.4 nm which is in a good agreement with the size obtained by transmission electron microscopy (TEM). Prepared Si NPs are shown to be highly suitable for bioimaging studies as they are readily taken up by BV2 cells. Si NPs are located in the cells cytosol. Proliferation of stained BV2 cells is observed and showed that newly formed cells are also stained with Si NPs, indicating their minimal toxicity. By using Si NPs it is possible to stain multiple cell generations by only staining the mother cell

Photophysics of n-Butyl-Capped Silicon Nanoparticles

The photophysical properties are described of silicon nanoparticles protected with a shell of n-butyl chains, and with an asymmetric size distribution with a peak between 2 and 3 nm, and a tail extending up to 7 nm. The excited nanoparticles decay via multi-exponential luminescence on a time scale of a few nanoseconds. Longer-lived nonluminescent dark states were observed by nanosecond transient absorption spectroscopy. The average lifetime of the luminescent excited states increased somewhat with increasing wavelengths of excitation and emission. The nanosecond transient absorption spectra shifted to longer wavelengths with time. Probably, these observations are related to the size distribution of the particles: larger particles are excited at longer wavelength, emit at longer wavelength, and have longer-lived and red-shifted nanosecond transient absorption spectra. Two-photon excited luminescence showed broader emission spectra than one-photon excited luminescence at the same excitation energies. The two-photon cross-sections were found to be surprisingly small