579 research outputs found
Inert strength measurement on silica soaked at 250°C in liquid water and water vapour
The effect of water soaking and heat-treatment in saturated water vapour at
250°C for 192 h on the strength of silica glass is studied. Bending strength
meaurements in liquid nitrogen showed a clear increase of the inert strength
for heat-treated specimens over that of the untreated material. The increase
in strength is interpreted as the consequence of water diffusion into exposed
surfaces of the test specimen, which results in swelling of the glass and
shielding of cracks, present in the surface of the glass. Experimental results
are compared with theoretical predictions
Breakdown of the few-level approximation in collective systems
The validity of the few-level approximation in dipole-dipole interacting
collective systems is discussed. As example system, we study the archetype case
of two dipole-dipole interacting atoms, each modelled by two complete sets of
angular momentum multiplets. We establish the breakdown of the few-level
approximation by first proving the intuitive result that the dipole-dipole
induced energy shifts between collective two-atom states depend on the length
of the vector connecting the atoms, but not on its orientation, if complete and
degenerate multiplets are considered. A careful analysis of our findings
reveals that the simplification of the atomic level scheme by artificially
omitting Zeeman sublevels in a few-level approximation generally leads to
incorrect predictions. We find that this breakdown can be traced back to the
dipole-dipole coupling of transitions with orthogonal dipole moments. Our
interpretation enables us to identify special geometries in which partial
few-level approximations to two- or three-level systems are valid
Evaluation of crack-terminating angles in heat-treated silica DCDC-specimens
Cracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression, the crack front must retard and under residual tensile stresses advance, both compared with the crack contour in the absence of stresses. This effect can be used for an estimation of residual surface stresses in silica generated during the silica/water reaction and caused by volume swelling. A strong shielding stress intensity factor of about -2.5 MPa was found for DCDC specimen heat-treated for 192h at 250°C in water. This result is a clear indication for compressive stresses developing in the water diffusion zone at the surface
Coherent control in a decoherence-free subspace of a collective multi-level system
Decoherence-free subspaces (DFS) in systems of dipole-dipole interacting
multi-level atoms are investigated theoretically. It is shown that the
collective state space of two dipole-dipole interacting four-level atoms
contains a four-dimensional DFS. We describe a method that allows to populate
the antisymmetric states of the DFS by means of a laser field, without the need
of a field gradient between the two atoms. We identify these antisymmetric
states as long-lived entangled states. Further, we show that any single-qubit
operation between two states of the DFS can be induced by means of a microwave
field. Typical operation times of these qubit rotations can be significantly
shorter than for a nuclear spin system.Comment: 15 pages, 11 figure
An ultra-sensitive pulsed balanced homodyne detector: Application to time-domain quantum measurements
A pulsed balanced homodyne detector has been developed for precise
measurements of electric field quadratures of pulsed optical quantum states. A
high level of common mode suppression (> 85 dB) and low electronic noise (730
electrons per pulse) provide a signal to noise ratio of 14 dB for the
measurement of the quantum noise of individual pulses. Measurements at
repetition rates up to 1 MHz are possible. As a test, quantum tomography of the
coherent state is performed and the Wigner function and the density matrix are
reconstructed with a 99.5% fidelity. The detection system can also be used for
ultrasensitive balanced detection in cw mode, e.g. for weak absorption
measurements.Comment: 3 pages, submitted to Optics Letter
Peeling back the layers of crassulacean acid metabolism: functional differentiation between Kalanchoë fedtschenkoi epidermis and mesophyll proteomes
Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that offers the potential to engineer improved waterâuse efficiency (WUE) and drought resilience in C3 plants while sustaining productivity in the hotter and drier climates that are predicted for much of the world. CAM species show an inverted pattern of stomatal opening and closing across the diel cycle, which conserves water and provides a means of maintaining growth in hot, waterâlimited environments. Recent genome sequencing of the constitutive model CAM species KalanchoĂ« fedtschenkoi provides a platform for elucidating the ensemble of proteins that link photosynthetic metabolism with stomatal movement, and that protect CAM plants from harsh environmental conditions. We describe a largeâscale proteomics analysis to characterize and compare proteins, as well as diel changes in their abundance in guard cellâenriched epidermis and mesophyll cells from leaves of K. fedtschenkoi. Proteins implicated in processes that encompass respiration, the transport of water and CO2, stomatal regulation, and CAM biochemistry are highlighted and discussed. Diel rescheduling of guard cell starch turnover in K. fedtschenkoi compared with that observed in Arabidopsis is reported and tissueâspecific localization in the epidermis and mesophyll of isozymes implicated in starch and malate turnover are discussed in line with the contrasting roles for these metabolites within the CAM mesophyll and stomatal complex. These data reveal the proteins and the biological processes enriched in each layer and provide key information for studies aiming to adapt plants to hot and dry environments by modifying leaf physiology for improved plant sustainability
Social Welfare and Collective Goods Coercion in Public Economics
This paper develops an expanded framework for social planning in which coercion stemming
from the provision of public goods is explicitly acknowledged. Key issues concern the precise
definition of coercion, its difference from redistribution, and its incorporation into social welfare optimization. The paper examines the implications for optimal policy, showing how the Samuelson condition, rules for optimal linear income taxation and commodity taxation, and for the marginal cost of public funds must be modified. In addition, the trade-off between social welfare and coercion is mapped under specific conditions and the implications of this trade-off for normative policy choice are considered
Spatial-temporally resolved high-frequency surface acoustic waves on silicon investigated by femtosecond spectroscopy
Various types of surface acoustic waves are generated by femtosecond pulses on bulk silicon with aluminium stripe transducers. Rayleigh and leaky longitudinal surface acoustic wave modes are detected in the time domain for various propagation distances. The modes are identified by measuring on various pitches and comparing the spectra with finite element calculations. The lifetimes of the modes are determined quantitatively by spatially separating pump and probe beam, showing a significant difference in the lifetimes of both modes. We were able to excite and measure Rayleigh modes with frequencies of up to 90âGHz using a 100ânm period grating.Fil: Schubert, Martin . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Grossmann, Martin . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Ristow, Oliver . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Hettich, Mike . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Bruchhausen, Axel Emerico. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Area de InvestigaciĂłn y Aplicaciones No Nucleares. Gerencia de FĂsica (Centro AtĂłmico Bariloche); Argentina. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Area de EnergĂa Nuclear. Instituto Balseiro; ArgentinaFil: Barretto, Elaine C. S. . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Scheer, Elke . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Gusev, Vitalyi . UniversitĂ© du Maine; Francia. Centre National de la Recherche Scientifique; FranciaFil: Dekorsy, Thomas . University of Konstanz. Department of Physics and Center for Applied Photonics; Alemani
Spectral structure and decompositions of optical states, and their applications
We discuss the spectral structure and decomposition of multi-photon states.
Ordinarily `multi-photon states' and `Fock states' are regarded as synonymous.
However, when the spectral degrees of freedom are included this is not the
case, and the class of `multi-photon' states is much broader than the class of
`Fock' states. We discuss the criteria for a state to be considered a Fock
state. We then address the decomposition of general multi-photon states into
bases of orthogonal eigenmodes, building on existing multi-mode theory, and
introduce an occupation number representation that provides an elegant
description of such states that in many situations simplifies calculations.
Finally we apply this technique to several example situations, which are highly
relevant for state of the art experiments. These include Hong-Ou-Mandel
interference, spectral filtering, finite bandwidth photo-detection, homodyne
detection and the conditional preparation of Schr\"odinger Kitten and Fock
states. Our techniques allow for very simple descriptions of each of these
examples.Comment: 12 page
Estimation of swelling stresses from crack-terminating angles
Cracks terminating at free surfaces are affected by local stresses in the surface region. The crack front retards under residual compressive stresses compared with the crack contour in the absence of stresses. This effect had been used in [1] for identifying compression in the surface of chemically toughened and ion-exchanged soda-lime glass surfaces. In [2] the same effect was proven for swelling stresses due to the silica/water reaction. In the present report, the stresses in the surface layers are predicted based on results for soda-lime glass. For silica heattreated in humid environments, compressive stresses in the order of about -130 MPa to -170 MPa are obtained
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