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61.
62.
Anna Vesterlund Annika Tovedal Ulrika Nygren Henrik Ramebäck 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):951-955
Chemical yield determination can be a limiting source to the combined standard uncertainty in measurements of radionuclides.
Therefore, the combined standard uncertainties in yield determination in the measurement of radioactive strontium using two
methods were evaluated. The two methods compared were the measurement of stable strontium by atomic absorption spectrometry
(AAS) and the gamma spectrometric measurement of 85Sr. The evaluation showed that using gamma spectrometry for yield determination can reduce the combined standard uncertainty
by a factor of three compared to AAS. The expanded uncertainties of AAS and gamma spectrometry were calculated to be 10% and
3.3% (k = 2), respectively. 相似文献
63.
Annika Günther 《Finite Fields and Their Applications》2009,15(4):517-533
For a module V over a finite semisimple algebra A we give the total number of self-dual codes in V. This enables us to obtain a mass formula for self-dual codes in permutation representations of finite groups over finite fields of coprime characteristic. 相似文献
64.
We consider a stochastic control problem over an infinite horizon where the state process is influenced by an unobservable
environment process. In particular, the Hidden-Markov-model and the Bayesian model are included. This model under partial
information is transformed into an equivalent one with complete information by using the well-known filter technique. In particular,
the optimal controls and the value functions of the original and the transformed problem are the same. An explicit representation
of the filter process which is a piecewise-deterministic process, is also given. Then we propose two solution techniques for
the transformed model. First, a generalized verification technique (with a generalized Hamilton–Jacobi–Bellman equation) is
formulated where the strict differentiability of the value function is weaken to local Lipschitz continuity. Second, we present
a discrete-time Markovian decision model by which we are able to compute an optimal control of our given problem. In this
context we are also able to state a general existence result for optimal controls. The power of both solution techniques is
finally demonstrated for a parallel queueing model with unknown service rates. In particular, the filter process is discussed
in detail, the value function is explicitly computed and the optimal control is completely characterized in the symmetric
case. 相似文献
65.
Calculations on Rydberg states are performed using quantum Monte Carlo methods. Excitation energies and singlet-triplet splittings are calculated for two model systems, the carbon atom (3P and 1P) and carbon monoxide ((1Sigma and 3Sigma). Kohn-Sham wave functions constructed from open-shell localized Hartree-Fock orbitals are used as trial and guide functions. The fixed-node diffusion quantum Monte Carlo (FN-DMC) method depends strongly on the wave function's nodal hypersurface. Nodal artefacts are investigated for the ground state of the carbon atom. Their effect on the FN-DMC results can be analyzed quantitatively. FN-DMC leads to accurate excitation energies but to less accurate singlet-triplet splittings. Variational Monte Carlo calculations are able to reproduce the experimental results for both the excitation energies and the singlet-triplet splittings. 相似文献
66.
Alemani M Peters MV Hecht S Rieder KH Moresco F Grill L 《Journal of the American Chemical Society》2006,128(45):14446-14447
The electric field applied between the tip of a scanning tunneling microscope and a metallic surface is shown to induce the reversible trans-cis isomerization of single azobenzene derivatives adsorbed on a Au(111) surface. The investigated molecule is symmetrically equipped with four tert-butyl groups, which decouple the azobenzene core from the metallic surface, facilitating the formation of highly ordered islands. Due to the spatial extension of the electric field, it is possible to switch many molecules within the same island simultaneously. 相似文献
67.
68.
Graf C Gao Q Schütz I Noufele CN Ruan W Posselt U Korotianskiy E Nordmeyer D Rancan F Hadam S Vogt A Lademann J Haucke V Rühl E 《Langmuir : the ACS journal of surfaces and colloids》2012,28(20):7598-7613
The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake. 相似文献
69.
In this paper, the strong approximation of a stochastic partial differential equation, whose differential operator is of advection-diffusion type and which is driven by a multiplicative, infinite dimensional, càdlàg, square integrable martingale, is presented. A finite dimensional projection of the infinite dimensional equation, for example a Galerkin projection, with nonequidistant time stepping is used. Error estimates for the discretized equation are derived in?L 2 and almost sure senses. Besides space and time discretizations, noise approximations are also provided, where the Milstein double stochastic integral is approximated in such a way that the overall complexity is not increased compared to an Euler?CMaruyama approximation. Finally, simulations complete the paper. 相似文献
70.
Gunnar Brinkmalm Erik Portelius Annika Öhrfelt Niklas Mattsson Rita Persson Mikael K. Gustavsson Charles H. Vite Johan Gobom Jan‐Eric Månsson Jonas Nilsson Adnan Halim Göran Larson Ulla Rüetschi Henrik Zetterberg Kaj Blennow Ann Brinkmalm 《Journal of mass spectrometry : JMS》2012,47(5):591-603
Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low‐energy collision‐induced dissociation tandem mass spectrometry (MS/MS), mainly long b‐fragments are observed, limiting the possibility to determine variations such as amino acid variants or post‐translational modifications (PTMs) within the N‐terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann–Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O‐glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top‐down MS‐based method. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献