59 research outputs found
On the limited amplitude resolution of multipixel Geiger-mode APDs
The limited number of active pixels in a Geiger-mode Avalanche Photodiode
(G-APD) results not only in a non-linearity but also in an additional
fluctuation of its response. Both these effects are taken into account to
calculate the amplitude resolution of an ideal G-APD, which is shown to be
finite. As one of the consequences, the energy resolution of a scintillation
detector based on a G-APD is shown to be limited to some minimum value defined
by the number of pixels in the G-APD.Comment: 5 pages, 3 figure
Fast Neutron Detector for Fusion Reactor KSTAR Using Stilbene Scintillator
Various neutron diagnostic tools are used in fusion reactors to evaluate
different aspects of plasma performance, such as fusion power, power density,
ion temperature, fast ion energy, and their spatial distributions. The stilbene
scintillator has been proposed for use as a neutron diagnostic system to
measure the characteristics of neutrons from the Korea Superconducting Tokamak
Advanced Research (KSTAR) fusion reactor. Specially designed electronics are
necessary to measure fast neutron spectra with high radiation from a gamma-ray
background. The signals from neutrons and gamma-rays are discriminated by the
digital charge pulse shape discrimination (PSD) method, which uses total to
partial charge ratio analysis. The signals are digitized by a flash
analog-to-digital convertor (FADC). To evaluate the performance of the
fabricated stilbene neutron diagnostic system, the efficiency of 10 mm
soft-iron magnetic shielding and the detection efficiency of fast neutrons were
tested experimentally using a 252Cf neutron source. In the results, the
designed and fabricated stilbene neutron diagnostic system performed well in
discriminating neutrons from gamma-rays under the high magnetic field
conditions during KSTAR operation. Fast neutrons of 2.45 MeV were effectively
measured and evaluated during the 2011 KSTAR campaign.Comment: 15 pages, 14 figures, conferenc
High-precision determination of transition amplitudes of principal transitions in Cs from van der Waals coefficient C_6
A method for determination of atomic dipole matrix elements of principal
transitions from the value of dispersion coefficient C_6 of molecular
potentials correlating to two ground-state atoms is proposed. The method is
illustrated on atomic Cs using C_6 deduced from high-resolution Feshbach
spectroscopy. The following reduced matrix elements are determined < 6S_{1/2}
|| D || 6P_{1/2} > =4.5028(60) |e| a0 and
=6.3373(84) |e| a0 (a0= 0.529177 \times 10^{-8} cm.) These matrix elements are
consistent with the results of the most accurate direct lifetime measurements
and have a similar uncertainty. It is argued that the uncertainty can be
considerably reduced as the coefficient C_6 is constrained further.Comment: 4 pages; 3 fig
Quantum measurement problem and cluster separability
A modified Beltrametti-Cassinelli-Lahti model of measurement apparatus that
satisfies both the probability reproducibility condition and the
objectification requirement is constructed. Only measurements on microsystems
are considered. The cluster separability forms a basis for the first working
hypothesis: the current version of quantum mechanics leaves open what happens
to systems when they change their separation status. New rules that close this
gap can therefore be added without disturbing the logic of quantum mechanics.
The second working hypothesis is that registration apparatuses for microsystems
must contain detectors and that their readings are signals from detectors. This
implies that separation status of a microsystem changes during both preparation
and registration. A new rule that specifies what happens at these changes and
that guarantees the objectification is formulated and discussed. A part of our
result has certain similarity with 'collapse of the wave function'.Comment: 31 pages, no figure. Published versio
High-precision calculations of van der Waals coefficients for heteronuclear alkali-metal dimers
Van der Waals coefficients for the heteronuclear alkali-metal dimers of Li,
Na, K, Rb, Cs, and Fr are calculated using relativistic ab initio methods
augmented by high-precision experimental data. We argue that the uncertainties
in the coefficients are unlikely to exceed about 1%.Comment: 11 pages, 2 figs, graphicx.st
Impact of Gut Bacteria on the Infection and Transmission of Pathogenic Arboviruses by Biting Midges and Mosquitoes
Tripartite interactions among insect vectors, midgut bacteria, and viruses may determine the ability of insects to transmit pathogenic arboviruses. Here, we investigated the impact of gut bacteria on the susceptibility of Culicoides nubeculosus and Culicoides sonorensis biting midges for Schmallenberg virus, and of Aedes aegypti mosquitoes for Zika and chikungunya viruses. Gut bacteria were manipulated by treating the adult insects with antibiotics. The gut bacterial communities were investigated using Illumina MiSeq sequencing of 16S rRNA, and susceptibility to arbovirus infection was tested by feeding insects with an infectious blood meal. Antibiotic treatment led to changes in gut bacteria for all insects. Interestingly, the gut bacterial composition of untreated Ae. aegypti and C. nubeculosus showed Asaia as the dominant genus, which was drastically reduced after antibiotic treatment. Furthermore, antibiotic treatment resulted in relatively more Delftia bacteria in both biting midge species, but not in mosquitoes. Antibiotic treatment and subsequent changes in gut bacterial communities were associated with a significant, 1.8-fold increased infection rate of C. nubeculosus with Schmallenberg virus, but not for C. sonorensis. We did not find any changes in infection rates for Ae. aegypti mosquitoes with Zika or chikungunya virus. We conclude that resident gut bacteria may dampen arbovirus transmission in biting midges, but not so in mosquitoes. Use of antimicrobial compounds at livestock farms might therefore have an unexpected contradictory effect on the health of animals, by increasing the transmission of viral pathogens by biting midges.</p
Changes of separation status during registration and scattering
In our previous work, a new approach to the notorious problem of quantum
measurement was proposed. Existing treatments of the problem were incorrect
because they ignored the disturbance of measurement by identical particles and
standard quantum mechanics had to be modified to obey the cluster separability
principle. The key tool was the notion of separation status. Changes of
separation status occur during preparations, registrations and scattering on
macroscopic targets. Standard quantum mechanics does not provide any correct
rules that would govern these changes. This gives us the possibility to add new
rules to quantum mechanics that would satisfy the objectification requirement.
The method of the present paper is to start from the standard unitary evolution
and then introduce minimal corrections. Several representative examples of
registration and particle scattering on macroscopic targets are analysed case
by case in order to see their common features. The resulting general Rule of
Separation Status Changes is stated in the Conclusion.Comment: 30 pages, no figure, published versio
Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering
Spin asymmetries of semi-inclusive cross sections for the production of
positively and negatively charged hadrons have been measured in deep-inelastic
scattering of polarized positrons on polarized hydrogen and 3He targets, in the
kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark
distributions are extracted as a function of x for up $(u+u_bar) and down
(d+d_bar) flavors. The up quark polarization is positive and the down quark
polarization is negative in the measured range. The polarization of the sea is
compatible with zero. The first moments of the polarized quark distributions
are presented. The isospin non-singlet combination Delta_q_3 is consistent with
the prediction based on the Bjorken sum rule. The moments of the polarized
quark distributions are compared to predictions based on SU(3)_f flavor
symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version
contains tables of asymmetries and correlation matri
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