195 research outputs found
Association Behavior of Poly (methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in Aqueous Medium
ABA type tri-block amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique (ATRP) and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering (DLS) techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the close association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy (TEM). Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na+ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated.Singapore-MIT Alliance (SMA
Self-driven electron enrichment of ultrafine PdAu nanoparticles for electrochemical CO<sub>2</sub> reduction:High applicability of work function as an activity descriptor
Highly coupled metal/dopant-incorporated carbon dyads provide a possibility to modulate the electron density of metallic materials by forming a rectifying interface, thus showing an enhanced activity in electrochemical CO2 reduction reaction (ECRR). However, understanding the promotion effects of dopants for ECRR is limited to the prediction by theoretical interpretation and case-by-case studies. Herein, we report the direct experimental evidence that the work function, regulated by single structural factor-dopant contents, is significantly correlated to the ECRR reaction activity and kinetics. We prepared a series of PdAu/NxC electrocatalysts composed of ultrafine (∼5.7 nm) PdAu bimetallic nanoparticles and tailorable N-doped carbon supports. The wide range of the amount of N dopants allowed the modification of the band gap of the carbon easily. Using ultraviolet photoelectron spectroscopy (UPS) measurements, we demonstrate that the reactivity and kinetics trends of the PdAu/NxC in the ECRR can be intrinsically correlated with the work function of the catalysts. PdAu/N7.50C electrocatalyst with the highest N contents displays a 100% CO2-to-CO conversion and high conversion efficiency over a wide potential window, superior over other reported PdAu catalysts. This work provides a novel way to boost ECRR performance by deliberately lowering the work function of the metal/carbon electrocatalysts through the enhancement by dopants.</p
Bound state solutions of the Dirac-Rosen-Morse potential with spin and pseudospin symmetry
The energy spectra and the corresponding two- component spinor wavefunctions
of the Dirac equation for the Rosen-Morse potential with spin and pseudospin
symmetry are obtained. The wave ( state) solutions for this
problem are obtained by using the basic concept of the supersymmetric quantum
mechanics approach and function analysis (standard approach) in the
calculations. Under the spin symmetry and pseudospin symmetry, the energy
equation and the corresponding two-component spinor wavefunctions for this
potential and other special types of this potential are obtained. Extension of
this result to state is suggested.Comment: 18 page
The controlled teleportation of an arbitrary two-atom entangled state in driven cavity QED
In this paper, we propose a scheme for the controlled teleportation of an
arbitrary two-atom entangled state
in driven cavity QED.
An arbitrary two-atom entangled state can be teleported perfectly with the help
of the cooperation of the third side by constructing a three-atom GHZ entangled
state as the controlled channel. This scheme does not involve apparent (or
direct) Bell-state measurement and is insensitive to the cavity decay and the
thermal field. The probability of the success in our scheme is 1.0.Comment: 10 page
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
Search for the Lepton Flavor Violation Processes and
The lepton flavor violation processes and are
searched for using a sample of 5.8 events collected with
the BESII detector. Zero and one candidate events, consistent with the
estimated background, are observed in and
decays, respectively. Upper limits on the branching ratios are determined to be
and at the 90% confidence level (C.L.).Comment: 9 pages, 2 figure
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
Measurements of J/psi --> p \bar{p}
The process J/\psi --> p \bar{p} is studied using 57.7 X 10^6 J/\psi events
collected with the BESII detector at the Beijing Electron Positron Collider.
The branching ratio is determined to be Br(J/\psi --> p \bar{p})=(2.26 +- 0.01
+- 0.14) X 10^{-3}, and the angular distribution is well described by
\frac{dN}{d cos\theta_p}=1+\alpha\cos^2\theta_p with \alpha = 0.676 +- 0.036 +-
0.042, where \theta_p is the angle between the proton and beam directions. The
value of \alpha obtained is in good agreement with the predictions of
first-order QCD.Comment: 6 pages, 2 figures, RevTex4, Submitted to Phys.Lett.
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