1,562 research outputs found
Laboratory analysis of small strain moduli in compacted silts
Soil compaction quality control accounts for a significant portion of geotechnical practice. Often the performance of a roadway can be directly linked to the quality of the compacted subgrade. A poor subgrade can result in weak areas in the road causing excessive deflections at the surface, ultimately leading to a pot hole or uneven surface and an unpleasant ride for the travelers. Vehicles passing over a section of highway causes small strains in the founding soil. These strains accumulate over time. A better understanding of how the compacted soil responds at small strains could shed light on improving the quality of the soil in turn improving the quality of the roadway. In this study, the small strain moduli of compacted low plastic silt was investigated under varying moisture contents and dry densities. An ultrasonic pulse velocity testing system was used to determine the dynamic elastic moduli of the soil specimen. Detailed procedures on how to filter the ultrasonic pulse velocity results and determine wave arrival times were established. Trends in the dynamic elastic moduli versus dry density and moisture content were studied. A Briaud Compaction Device (BCD) was also used to determine the BCD Low- Strain Modulus. The BCD is a non-destructive test that can be used in both the laboratory and field as a means of quickly determining a modulus. The use of the BCD as a compaction quality control tool was investigated. BCD repeatability and the established trends suggest that the BCD could be benefit for compaction quality control. The BCD modulus was also compared to the dynamic elastic moduli producing trends with good correlation --Abstract, page iv
Constraints on (Omega_m,Omega_Lambda) using distributions of inclination angles for high redshift filaments
In this paper we present a scale free method to determine the cosmological
parameters (Omega_m, Omega_Lambda). The method is based on the requirement of
isotropy of the distribution of orientations of cosmological filaments. The
current structure formation paradigm predicts that the first structures to form
are voids and filaments, causing a web-like structure of the matter
distribution at high redshifts. Recent observational evidence suggests that the
threads, or filaments, of the cosmic web most easily are mapped in Ly-alpha
emission. We describe how such a 3D map can be used to constrain the
cosmological parameters in a way which, contrary to most other cosmological
tests, does not require the use of a standard rod or a standard candle. We
perform detailed simulations in order to define the optimal survey parameters
for the definition of an observing programme aimed to address this test, and to
investigate how statistical and observational errors will influence the
results. We conclude that observations should target filaments of comoving size
15-50 Mpc in the redshift range 2-4, and that each filament must be defined by
at least four Ly-alpha emitters. Detection of 20 filaments will be sufficient
to obtain a result, while 50 filaments will make it possible to place
significant new constraints on the values of Omega_m and Omega_Lambda permitted
by the current supernova observations. In a future paper we study how robust
these conclusions are to systematic velocities in the survey box.Comment: 8 pages, 6 figures, accepted for publication in A&
Modelling the variability of 1ES1218+30.4
The blazar 1ES1218+30.4 has been previously detected by the VERITAS and MAGIC
telescopes in the very high energies. The new detection of VERITAS from
December 2008 to April 2009 proves that 1ES1218+30.4 is not static, but shows
short-time variability. We show that the time variability may be explained in
the context of a self-consistent synchrotron-self Compton model, while the long
time observation do not necessarily require a time-resolved treatment. The
kinetic equations for electrons and photons in a plasma blob are solved
numerically including Fermi acceleration for electrons as well as synchrotron
radiation and Compton scattering. The light curve observed by VERITAS can be
reproduced in our model by assuming a changing level of electron injection
compared to the constant state of 1ES1218+30.4. The multiwavelength behaviour
during an outburst becomes comprehensible by the model. The long time
measurements of VERITAS are still explainable via a constant emission in the
SSC context, but the short outbursts each require a time-resolved treatment.Comment: 4 pages, 3 figures; accepted in A&A; AA/2010/1429
Ensemble versus individual system in quantum optics
Modern techniques allow experiments on a single atom or system, with new
phenomena and new challenges for the theoretician. We discuss what quantum
mechanics has to say about a single system. The quantum jump approach as well
as the role of quantum trajectories are outlined and a rather sophisticated
example is given.Comment: Fundamental problems in quantum theory workshop, invited lecture. 11
pages Latex + 7 figures. To appear in Fortschr. d. Physi
Self-consistent Hartree-Fock approach to many-body localization
In this work, we develop a self-consistent Hartree-Fock approach to
theoretically study the far-from-equilibrium quantum dynamics of interacting
fermions, and apply this approach to explore the onset of many-body
localization (MBL) in these systems. We investigate the dynamics of a state
with a nonequilibrium density profile; we find that at weak disorder the
density profile equilibrates rapidly, whereas for strong disorder it remains
frozen on the accessible timescales. We analyze this behavior in terms of the
Hartree-Fock self-energy. At weak disorder the self-energy fluctuates strongly
and can be interpreted as a self-consistent noise process. By contrast, at
strong disorder the self-energy evolves with a few coherent oscillations which
cannot delocalize the system. Accordingly, the non-equilibrium site-resolved
spectral function shows a broad spectrum at weak disorder and sharp spikes at
strong disorder. Our Hartree-Fock theory incorporates spatial fluctuations and
rare-region effects. As a consequence, we find subdiffusive relaxation in
random systems; but, when the system is subjected to weak quasi-periodic
potentials, the subdiffusive response ceases to exist, as rare region effects
are absent in this case. This self-consistent Hartree-Fock approach can be
regarded as a relatively simple theory that captures much of the MBL
phenomenology.Comment: 11 pages, 10 figures, Added references and expanded discussion
Ultrasonic Pulse Velocity Tests on Compacted Soil
In This Paper, Results of a Series of Ultrasonic Pulse Velocity Tests on Compacted Soil Were Presented and Discussed. Ultrasonic Pulse Velocity Tests Provide Compression and Shear Wave Velocity Information that Can Be Used in Calculating Dynamic Elastic Moduli Such as Young\u27s Modulus and Shear Modulus. from the Test Results, Calculated Poisson\u27s Ratio Shows a Linear Relation with the Water Content in Compacted Soil, Which Leads to a Linear Trend in Both P and S Wave Velocity Against Water Content. Furthermore, Presenting Plots in Bulk Density Versus Wave Velocity Gives a Clearer Trend Than Dry Density Versus Wave Velocity. © 2009 ASCE
Novel Approaches for SER Spectroscopic Analysis of Protein Cofactors
Biomimetic systems employed for biotechnological applications i.e. as biosensors or bio fuel cells, require initial formation of conducting support/protein complexes with controlled properties. The specific interaction of the protein with the support determines important qualities of the device such as electrical communication, long-term stability and catalytic efficiency. In this respect the system parameters have to be chosen in a way that high protein loading on the support is achieved while protein denaturation upon adsorption is prevented. The conditions on the surface have to be adjusted in such a way that the desired surface reaction of the protein i.e. electron transfer to either the electrode or a second redox partner, is still guaranteed. Hence the choice of support, its functionlisation as well as the right adjustment of solution parameters play a crucial role in the rational design of these support/protein constructs
Calculating average surface enhancement factors of randomly nanostructured electrodes by a combination of SERS and impedance spectroscopy
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Polyhedron Ag nanostructures were created on top of a polished Au electrode via step-wise electrodeposition and tested as substrates for SERS spectroscopy. Average Raman enhancement factors were derived by combining SERS measurements with electrochemical impedance spectroscopy (EIS), which is able to determine the electroactive surface area of a randomly nanostructured surface. Depending on the deposition step an alternating increase and decrease of surface area was observed while the SERS intensity showed a clear maximum for the first deposition cycle. SEM pictures reveal the formation of Ag polyhedrons that are randomly dispersed on the Au surface. Furthermore the presence of a sub nanostructure on top of the polyhedron after the first deposition cycle is observed which becomes smoother after subsequent deposition cycles. Correlating the SEM pictures with SERS and EIS measurements it is concluded that the coral-like sub nanostructure is dominating the enhancement factor while the polyhedron structure itself only plays a minor role for electromagnetic field enhancement.DFG, EXC 314, Unifying Concepts in CatalysisDFG, GSC 1013, School of Analytical Sciences Adlershof (SALSA
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