13,397 research outputs found
An eco-solution for track & trace of goods and third party logistics
This paper presents a new economic cost-effective solution known as the Web and telephony based method for tracking and tracing of goods and small and medium sized third party logistic providers. Considering that these companies usually operate on very flat margins, a comparison is made of the available track and trace technologies like GPS, mobile phone approximated GPS and Java based cell tracking in terms of costs, operating risks, and other evaluation criteria
^25Mg NMR study of the MgB_2 superconductor
^25Mg NMR spectra and nuclear spin-lattice relaxation time, T_1, have been
measured in polycrystalline ^25MgB_2 with a superconducting transition
temperature T_c = 39.0 K in zero magnetic field. From the first order and
second order quadrupole perturbed NMR spectrum a quadrupole coupling frequency
nu_Q = 222(1.5) kHz is obtained. T_1T = 1090(50) sK and Knight shift K_c =
242(4) ppm are temperature independent in the normal conducting phase. The
^25Mg Korringa ratio equals to 0.95 which is very close to the ideal value of
unity for s-electrons. The comparison of the experimental nu_Q, T_1T, and K_c
with the corresponding values obtained by LDA calculations shows an excellent
agreement for all three quantities.Comment: 4 pages including 4 eps-figures, revtex
High-fidelity ion-trap quantum computing with hyperfine clock states
We propose the implementation of a geometric-phase gate on
magnetic-field-insensitive qubits with -dependent forces for
trapped ion quantum computing. The force is exerted by two laser beams in a
Raman configuration. Qubit-state dependency is achieved by a small frequency
detuning from the virtually-excited state. Ion species with excited states of
long radiative lifetimes are used to reduce the chance of a spontaneous photon
emission to less than 10 per gate-run. This eliminates the main source
of gate infidelity of previous implementations. With this scheme it seems
possible to reach the fault tolerant threshold.Comment: 4 pages, 1 figur
Photoinitiated processes in functionally diverse organic molecules elucidated by theoretical methods
In this thesis reaction mechanisms of organic compounds with applications in different areas, such as kinetic studies, labeling, and battery electrolytes, are investigated with theoretical methods from quantum chemistry, quantum dynamics, and molecular dynamics. The variety of the investigated molecules ranges from polycyclic hydrocarbons, dyes, electrolytes to precursors of reactive species. The work was performed either in close collaboration with experimentalists or based on experimental results and in this way allows an in-depth look at the occurring chemistry.
In the first part the concept of adapted reactive coordinates for reduced dimensional quantum dynamics is presented necessary for the studies in the following part. It relies on the Wilson G-matrix method as formulation of the kinetic part of the Hamiltonian and allows to include the relaxation of background coordinates besides the identified main reactive coordinates without optimizations for each grid point. The concept is shown for a photodissociation involving complex structural changes and the G-matrix elements and their influence on the dynamics are discussed.
In the second part the photoinitated bond cleavage reaction for diphenylmethyl chloride and diphenylmethyl bromide is studied. Based on the reactive coordinate system presented before, quantum dynamical simulations enlighten the path of the wave packet, which passes through two consecutive conical intersections—a three-state and a two-state one—as decisive elements for the product splitting. In the case of chlorine, the experimental signal is modeled from the simulated data to further prove the mechanism. For the bromine case, additionally non-adiabatic mixed quantum-classical dynamics is used to clarify the role of vibrations during the bond cleavage, which are responsible for small amplitude oscillations of the experimental signals. Throughout this part the “our own n-layered integrated molecular orbital and molecular mechanics” (ONIOM) method is used to reduce the involved computational cost.
The third part is dedicated to the photophysics of elongated π systems in organic molecules discussing two examples. The first one is the polycyclic hydrocarbon pyrene, the second one covalently linked constructs of DNA and the dye Cyanine 3. For pyrene, the ultrafast transition from the photo-accessible S2 state to the fluorescent S1 is simulated for the first time using two complementary dynamical methods. It is shown that both methods yield comparable results and demonstrate the strong coupling between the two states. The constructs in the second example are investigated experimentally and theoretically. Simulated spectra for a model system help attributing an occurring blue-shift to dimerization. Circular dichroism measurements and molecular dynamics simulations further characterize the formed dimers.
The last part comprises a joint experimental and theoretical study concerning the chemical stability of two electrolytes commonly used in lithium-ion batteries towards singlet oxygen. It is shown that singlet oxygen is reactive towards the electrolyte ethylene carbonate. Ab initio calculations suggest a concerted double hydrogen abstraction by the singlet oxygen as mechanism, which is not possible for the second electrolyte dimethyl carbonate. It is an example for the unusual reaction of an alkyl group with singlet oxygen and yields hydrogen peroxide. Ground state mixed quantum-classical dynamics verify the further decay of the reaction intermediate vinylene carbonate to carbon dioxide, which is found experimentally. The theoretically predicted intermediate formation of hydrogen peroxide is detected colorimetrically proving the reaction mechanism and its detrimental effect is investigated experimentally
Sammandrag från föredrag hållet av K. G. R005 Vid Scand-LAS symposium i Köpenhamn, 18—19/4 1977
No abstract availabl
Irreversible nucleation in molecular beam epitaxy: From theory to experiments
Recently, the nucleation rate on top of a terrace during the irreversible
growth of a crystal surface by MBE has been determined exactly. In this paper
we go beyond the standard model usually employed to study the nucleation
process, and we analyze the qualitative and quantitative consequences of two
important additional physical ingredients: the nonuniformity of the
Ehrlich-Schwoebel barrier at the step-edge, because of the existence of kinks,
and the steering effects, due to the interaction between the atoms of the flux
and the substrate. We apply our results to typical experiments of second layer
nucleation.Comment: 11 pages. Table I corrected and one appendix added. To be published
in Phys. Rev. B (scheduled issue: 15 February 2003
Theoretical calculations for solid oxygen under high pressure
The crystal structure of solid oxygen at low temperatures and at pressures up
to 7 GPa is studied by theoretical calculations. In the calculations, the
adiabatic potential of the crystal is approximated by a superposition of
pair-potentials between oxygen molecules calculated by an ab-initio method. The
monoclinic alpha structure is stable up to 6 GPa and calculated lattice
parameters agree well with experiments. The origin of a distortion and that of
an anisotropic lattice compressibility of the basal plane of alpha-O2 are
clearly demonstrated. In the pressure range from 6 to 7 GPa, two kinds of
structures are proposed by X-ray diffraction experiments: the alpha and
orthorhombic delta structures. It is found that the energy difference between
these structures becomes very small in this pressure range. The relation
between this trend and the incompatible results of X-ray diffraction
experiments is discussed.Comment: 12 pages, 6 figure
Weighted Bergman kernels and virtual Bergman kernels
We introduce the notion of "virtual Bergman kernel" and apply it to the
computation of the Bergman kernel of "domains inflated by Hermitian balls", in
particular when the base domain is a bounded symmetric domain.Comment: 12 pages. One-hour lecture for graduate students, SCV 2004, August
2004, Beijing, P.R. China. V2: typo correcte
Influence of adatom interactions on second layer nucleation
We develop a theory for the inclusion of adatom interactions in second layer
nucleation occurring in epitaxial growth. The interactions considered are due
to ring barriers between pairs of adatoms and binding energies of unstable
clusters. The theory is based on a master equation, which describes the time
development of microscopic states that are specified by cluster configurations
on top of an island. The transition rates are derived by scaling arguments and
tested against kinetic Monte-Carlo simulations. As an application we reanalyze
experiments to determine the step edge barrier for Ag/Pt(111).Comment: 4 pages, 4 figure
- …