750 research outputs found
Controlled Nanoparticle Formation by Diffusion Limited Coalescence
Polymeric nanoparticles (NPs) have a great application potential in science
and technology. Their functionality strongly depends on their size. We present
a theory for the size of NPs formed by precipitation of polymers into a bad
solvent in the presence of a stabilizing surfactant. The analytical theory is
based upon diffusion-limited coalescence kinetics of the polymers.
Two relevant time scales, a mixing and a coalescence time, are identified and
their ratio is shown to determine the final NP diameter. The size is found to
scale in a universal manner and is predominantly sensitive to the mixing time
and the polymer concentration if the surfactant concentration is sufficiently
high. The model predictions are in good agreement with experimental data. Hence
the theory provides a solid framework for tailoring nanoparticles with a priori
determined size.Comment: 4 pages, 3 figure
The influence of motor activity on the development of cardiac arrhythmias during experimental emotional stress
Experimental emotional stress which can produce various disorders of cardiac rhythm: sinus tachycardia, atrial fibrillation, ventricular, extrasystoles and paroxysmal ventricular tachysystoles was studied. In these conditions the adrenalin content in the blood and myocardium is increased 3 to 4 times. It is found that moderate motor activity leads to a relative decrease of adrenalin in the myocardium and arrest of cardiac arrhythmias
A Selection Rule for Multiquark Decays
By assuming SU(6)_cs symmetry for pentaquark decays one finds a selection
rule, which strongly reduces the number of states able to decay into a baryon
and a meson final state and allows an intriguing identification for the Theta^+
particle recently discovered with the prediction of a narrow width.Comment: 10 pages, no figure
Phase behavior and structure formation of hairy-rod supramolecules
Phase behavior and microstructure formation of rod and coil molecules, which can associate to form hairy-rod polymeric supramolecules, are addressed theoretically. Association induces considerable compatibility enhancement between the rod and coil molecules and various microscopically ordered structures can appear in the compatibility region. The equilibria between microphase-separated states, the coil-rich isotropic liquid and the rod-rich nematic are discussed in detail. In the regime where hairy-rod supramolecules with a high grafting density appear as a result of the association, three phase diagram types are possible depending on the value of the association energy. In the low grafting density regime only the lamellar microstructure is proven to be stable
A Keck Survey of Gravitational Lens Systems: I. Spectroscopy of SBS 0909+532, HST 1411+5211, and CLASS B2319+051
We present new results from a continuing Keck program to study gravitational
lens systems. We have obtained redshifts for three lens systems, SBS 0909+532,
HST 1411+5211, and CLASS B2319+051. For all of these systems, either the source
or lens redshift (or both) has been previously unidentified. We find (z_l, z_s)
= (0.830, 1.377) for SBS 0909+532; (z_l, z_s) = (0.465, 2.811) for HST
1411+5211, although the source redshift is still tentative; and (z_l1, z_l2) =
(0.624, 0.588) for the two lensing galaxies in CLASS B2319+051. The background
radio source in B2319+051 has not been detected optically; its redshift is,
therefore, still unknown. We find that the spectral features of the central
lensing galaxy in all three systems are typical of an early-type galaxy. The
observed image splittings in SBS 0909+532 and HST 1411+5211 imply that the
masses within the Einstein ring radii of the lensing galaxies are 1.4 x 10^{11}
and 2.0 x 10^{11} h^{-1} M_sun, respectively. The resulting B band
mass-to-light ratio for HST 1411+5211 is 41.3 +/- 1.2 h (M/L)_sun, a factor of
5 times higher than the average early-type lensing galaxy. This large
mass-to-light is almost certainly the result of the additional mass
contribution from the cluster CL 3C295 at z = 0.46. For the lensing galaxy in
SBS 0909+532, we measure (M/L)_B = 4^{+11}_{-3} h (M/L)_sun where the large
errors are the result of significant uncertainty in the galaxy luminosity.
While we cannot measure directly the mass-to-light ratio of the lensing galaxy
in B2319+051, we estimate that (M/L)_B is between 3-7 h (M/L)_sun.Comment: Accepted for publication in Astronomical Journal. 21 pages, including
7 figure
Power Efficient, Low Noise 2-5 GHz Phase Locked Loop
A power and noise efficient solution for phase locked loop (PLL) is presented. A lock detector is implemented to deactivate the PLL components, except the voltage controlled oscil ator (VCO), in the locked state. Signals deactivating/activating the PLL are discussed on system level. The introduced technique significantly saves power and decreases PLL output jitter. As a result whole PLL power consumption and output noise decreased about 35-38% in expense of approximately 17% area overhead.Запропоновано рішення для системи фазового автопідстроювання частоти (ФАПЧ) з низьким енергоспоживанням та шумовими характеристиками. Сигнали активації та деактивації ФАПЛ розглянуті на системному рівні. Впроваджена техніка значно покращує енергозбереження та зменшує випадкові зміни фази. В результаті вдалося зменшити витрати енергії та фазовий шум приблизно на 35-38% при збільшенні площі робочої поверхні приблизно на 17%
The Heavy Photon Search beamline and its performance
The Heavy Photon Search (HPS) is an experiment to search for a hidden sector
photon, aka a heavy photon or dark photon, in fixed target electroproduction at
the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment
searches for the ee decay of the heavy photon with bump hunt and
detached vertex strategies using a compact, large acceptance forward
spectrometer, consisting of a silicon microstrip detector (SVT) for tracking
and vertexing, and a PbWO electromagnetic calorimeter for energy
measurement and fast triggering. To achieve large acceptance and good vertexing
resolution, the first layer of silicon detectors is placed just 10 cm
downstream of the target with the sensor edges only 500 m above and below
the beam. Placing the SVT in such close proximity to the beam puts stringent
requirements on the beam profile and beam position stability. As part of an
approved engineering run, HPS took data in 2015 and 2016 at 1.05 GeV and 2.3
GeV beam energies, respectively. This paper describes the beam line and its
performance during that data taking
How to measure the parity of the in collisions
Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which
observables can be used to determine the parity of the from the
reaction near its production threshold. In
particular, we show that the sign of the spin correlation coefficient
for small excess energies yields the negative of the parity of the .
The argument relies solely on the Pauli principle and parity conservation and
is therefore model--independent.Comment: References completed, discussion on possible influence of background
added; conclusions unchange
The proton and deuteron F_2 structure function at low Q^2
Measurements of the proton and deuteron structure functions are
presented. The data, taken at Jefferson Lab Hall C, span the four-momentum
transfer range GeV, and Bjorken values from 0.009 to
0.45, thus extending the knowledge of to low values of at low .
Next-to-next-to-leading order calculations using recent parton distribution
functions start to deviate from the data for GeV at the low and
high -values. Down to the lowest value of , the structure function is
in good agreement with a parameterization of based on data that have been
taken at much higher values of or much lower values of , and which is
constrained by data at the photon point. The ratio of the deuteron and proton
structure functions at low remains well described by a logarithmic
dependence on at low .Comment: 3 figures, submitted pape
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