3,059 research outputs found
Interfacial adhesion: Theory and experiment
Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along wiith recommendations for future progress and needs
A Charge and Spin Readout Scheme For Single Self-Assembled Quantum Dots
We propose an all optical spin initialization and readout concept for single
self assembled quantum dots and demonstrate its feasibility. Our approach is
based on a gateable single dot photodiode structure that can be switched
between charge and readout mode. After optical electron generation and storage,
we propose to employ a spin-conditional absorption of a circularly polarized
light pulse tuned to the single negatively charged exciton transition to
convert the spin information of the resident electron to charge occupancy.
Switching the device to the charge readout mode then allows us to probe the
charge state of the quantum dot (1e, 2e) using non-resonant luminescence. The
spin orientation of the resident electron is then reflected by the
photoluminescence yield of doubly and singly charged transitions in the quantum
dot. To verify the feasibility of this spin readout concept, we have applied
time gated photoluminescence to confirm that selective optical charging and
efficient non perturbative measurement of the charge state can be performed on
the same dot. The results show that, by switching the electric field in the
vicinity of the quantum dot, the charging rate can be switched between a regime
of efficient electron generation and a readout regime, where the charge
occupancy and, therefore, the spin state of the dot can be tested via PL over
millisecond timescales, without altering it.Comment: 20 Pages, 6 Figures, submitted to Phys. Rev.
Concorde Noise-Induced Building Vibrations, Montgomery County, Maryland
A series of studies are reported to assess the noise induced building vibrations associated with Concorde operations. The levels of induced vibration and associated indoor/outdoor noise levels resulting from aircraft and nonaircraft events in selected homes, historic and other buildings near Dulles International Airport were recorded. The building response resulting from aircraft operations was found to be directly proportional to the overall sound pressure level and approximately independent of the aircraft type. The noise levels and, consequently, the response levels were observed to be higher for the Concorde operations than for the CTOL operations. Furthermore, the vibration could be closely reproduced by playing aircraft noise through a loudspeaker system located near the vibration measurement location. Nonaircraft events such as door closing were again observed to result in higher response levels than those induced by aircraft
Noise-Induced Building Vibrations Caused by Concorde and Conventional Aircraft Operations at Dulles and Kennedy International Airports
Outdoor and indoor noise levels resulting from aircraft flyovers and certain nonaircraft events were recorded, as were the associated vibration levels in the walls, windows, and floors at building test sites. In addition, limited subjective tests were conducted to examine the human detection and annoyance thresholds for building vibration and rattle caused by aircraft noise. Representative peak levels of aircraft noise-induced building vibrations are reported and comparisons are made with structural damage criteria and with vibration levels induced by common domestic events. In addition, results of a pilot study are reported which indicate the human detection threshold for noise-induced floor vibrations
New first integral for twisting type-N vacuum gravitational fields with two non-commuting Killing vectors
A new first integral for the equations corresponding to twisting type-N
vacuum gravitational fields with two non-commuting Killing vectors is
introduced. A new reduction of the problem to a complex second-order ordinary
differential equation is given. Alternatively, the mentioned first integral can
be used in order to provide a first integral of the second-order complex
equation introduced in a previous treatment of the problem.Comment: 7 pages, LaTeX, uses ioplppt.sty and iopl12.sty; to be published in
Class. Quantum Gra
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
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Deubiquitination of Dishevelled by Usp14 is required for Wnt signaling
Dishevelled (Dvl) is a key regulator of Wnt signaling both in the canonical and non-canonical pathways. Here we report the identification of a regulatory domain of ubiquitination (RDU) in the C-terminus of Dvl. Mutations in the RDU resulted in accumulation of polyubiquitinated forms of Dvl, which were mainly K63 linked. Small interfering RNA-based screening identified Usp14 as a mediator of Dvl deubiquitination. Genetic and chemical suppression of Usp14 activity caused an increase in Dvl polyubiquitination and significantly impaired downstream Wnt signaling. These data suggest that Usp14 functions as a positive regulator of the Wnt signaling pathway. Consistently, tissue microarray analysis of colon cancer revealed a strong correlation between the levels of Usp14 and β-catenin, which suggests an oncogenic role for Usp14 via enhancement of Wnt/β-catenin signaling
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
DECam integration tests on telescope simulator
The Dark Energy Survey (DES) is a next generation optical survey aimed at
measuring the expansion history of the universe using four probes: weak
gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and
Type Ia supernovae. To perform the survey, the DES Collaboration is building
the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera
which will be mounted at the Blanco 4-meter telescope at the Cerro Tololo
Inter- American Observatory. DES will survey 5000 square degrees of the
southern galactic cap in 5 filters (g, r, i, z, Y). DECam will be comprised of
74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k
x 2k CCDs for guiding and focus. Construction of DECam is nearing completion.
In order to verify that the camera meets technical specifications for DES and
to reduce the time required to commission the instrument, we have constructed a
full sized telescope simulator and performed full system testing and
integration prior to shipping. To complete this comprehensive test phase we
have simulated a DES observing run in which we have collected 4 nights worth of
data. We report on the results of these unique tests performed for the DECam
and its impact on the experiments progress.Comment: Proceedings of the 2nd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2011). To appear in Physics
Procedia. 8 pages, 3 figure
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