3,710 research outputs found
Quantum-measurement backaction from a Bose-Einstein condensate coupled to a mechanical oscillator
We study theoretically the dynamics of a hybrid optomechanical system consisting of a macroscopic mechanical membrane magnetically coupled to a spinor Bose-Einstein condensate via a nanomagnet attached at the membrane center. We demonstrate that this coupling permits us to monitor indirectly the center-of-mass position of the membrane via measurements of the spin of the condensed atoms. These measurements normally induce a significant backaction on the membrane motion, which we quantify for the cases of thermal and coherent initial states of the membrane. We discuss the possibility of measuring this quantum backaction via repeated measurements. We also investigate the potential to generate nonclassical states of the membrane, in particular Schrödinger-cat states, via such repeated measurements
Application of Problem Based Learning and Mastery Learning to Multimedia Education
The current state of education and the workforce demands a special kind of learner capable of creativity, communicating effectively, analytical skill application, critical thinking, and problem solving. Whereas these skills are important, it is also a necessity for learners to be masters of the knowledge and skills that they have acquired. Traditional educational methods have proven to be somewhat ineffective in producing these results. Problem based learning has proven worthy in handling some of the load, however, mastery learning has been abandoned long ago for reasons in spite of its effectiveness. Through given examples and careful design, the educator will witness practical application of these models in tandem to create efficient, effective, and appealing instruction that suits the needs of education and the modern workforce
Quantum measurement backaction from a BEC coupled to a mechanical oscillator
We study theoretically the dynamics of a a hybrid optomechanical system
consisting of a macroscopic mechanical membrane magnetically coupled to a
spinor Bose-Einstein condensate via a nanomagnet attached at the membrane
center. We demonstrate that this coupling permits us to monitor indirectly the
center-of-mass position of the membrane via measurements of the spin of the
condensed atoms. These measurements normally induce a significant backaction on
the membrane motion, which we quantify for the cases of thermal and coherent
initial states of the membrane. We discuss the possibility of measuring that
quantum backaction via repeated measurements. We also investigate the potential
to generate non-classical states of the membrane, in particular Schrodinger cat
states, via such repeated measurements.Comment: 14 pages, 4 figures. Submitted to PR
Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
During the theoretical investigation of the ultimate sensitivity of
gravitational wave detectors through the 1970's and '80's, it was debated
whether quantum fluctuations of the light field used for detection, also known
as photon shot noise, would ultimately produce a force noise which would
disturb the detector and limit the sensitivity. Carlton Caves famously answered
this question with "They do." With this understanding came ideas how to avoid
this limitation by giving up complete knowledge of the detector's motion. In
these back-action evading (BAE) or quantum non-demolition (QND) schemes, one
manipulates the required quantum measurement back-action by placing it into a
component of the motion which is unobserved and dynamically isolated. Using a
superconducting, electro-mechanical device, we realize a sensitive measurement
of a single motional quadrature with imprecision below the zero-point
fluctuations of motion, detect both the classical and quantum measurement
back-action, and demonstrate BAE avoiding the quantum back-action from the
microwave photons by 9 dB. Further improvements of these techniques are
expected to provide a practical route to manipulate and prepare a squeezed
state of motion with mechanical fluctuations below the quantum zero-point
level, which is of interest both fundamentally and for the detection of very
weak forces
Nanometer-scale sharpness in corner-overgrown heterostructures
A corner-overgrown GaAs/AlGaAs heterostructure is investigated with
transmission and scanning transmission electron microscopy, demonstrating
self-limiting growth of an extremely sharp corner profile of 3.5 nm width. In
the AlGaAs layers we observe self-ordered diagonal stripes, precipitating
exactly at the corner, which are regions of increased Al content measured by an
XEDS analysis. A quantitative model for self-limited growth is adapted to the
present case of faceted MBE growth, and the corner sharpness is discussed in
relation to quantum confined structures. We note that MBE corner overgrowth
maintains nm-sharpness even after microns of growth, allowing the realization
of corner-shaped nanostructures.Comment: 4 pages, 3 figure
Neue Methoden zur Bekämpfung des Echten Mehltaus im Ökologischen Landbau
Blattoberflächen-modifizierende Salzapplikationen sollten als Bekämpfungsmittel gegen Echten Mehltau an Tomaten und Gurken getestet werden hinsichtlich folgender Eigenschaften:
- Wirkung verschiedener Salze
- Blattverträglichkeit
- Untersuchung der unterschiedlichen Wirkungsmechanismen mittels REM
- Übertragbarkeit in praxisnahe Versuche.
Die verschiedenen Salzlösungen und Kombinationen aus diesen Salzen unterschieden sich deutlich in ihrer Wirkung auf Gurkenmehltau. Die beste Wirkung ergab sich mit allenfalls geringer Schädigung des Blattes mit 0,1% MnCl2, 1 % Patentkali (K2SO4/MgSO4) und 1% Knöterichextrakt. MnCl2 liegt auf Grund seines niedrigen Deliqueszenzpunktes ständig gelöst auf der Blattoberfläche vor, wogegen sich Knöterichextrakt und Patentkali auf der Blattoberfläche in einer Art „Salzkriechen“ verteilen durch häufigen Wechsel zwischen Trocknen und Wiederverflüssigung. Salzschäden ließen sich verringern durch Zusatz von Netzmitteln zur Sprühlösung.
Rasterelektronische Visualisierung zeigte für alle untersuchten Lösungen einen direkt toxischen Effekt auf die Mehltausporen und ihre Hyphen in jeder Entwicklungsphase des Pilzes. Eine Verbesserung des Nährstoffstatus der Pflanzen scheidet als Wirkungsmechanismus aus, da alle Pflanzen optimal ernährt waren und die Behandlungen zu keinen signifikanten Veränderungen der Nährstoffgehalte in den Blättern führten.
Besonders chloridische Salze führten z.T. zu erheblicher Nekrotisierung der Blätter. Da diese Salzlösungen jedoch auch in geringer Konzentration in der Lage waren, die Ausbreitung des Echten Mehltau effektiv zu verhindern, sollten Möglichkeiten zur Mikrodosierung dieser Salze geprüft werden.
Extreme Witterungsbedingungen im Sommer 2003 führten dazu, dass Praxistests nicht ausgeführt oder normal beendet werden konnten. Es gilt jedoch als sicher, dass einige der untersuchten Salzmischungen in geringen Konzentrationen (zw. 0,1 und 1%) den Befall mit Echten Mehltaupilzen effektiv reduzieren können, ohne Blattoberflächen zu schädigen
Quantum Collective QCD String Dynamics
The string breaking model of particle production is extended in order to help
explain the transverse momentum distribution in elementary collisions. Inspired
by an idea of Bialas', we treat the string using a collective coordinate
approach. This leads to a chromo-electric field strength which fluctuates, and
in turn implies that quarks are produced according to a thermal distribution.Comment: 6 pages. Presented at SQM 2006. Submitted to J. Phys. G for
publication in proceedings. Vers. 2: Minor revisions; final hadron spectrum
calculation include
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Laser and electron deflection from transverse asymmetries in laser-plasma accelerators.
We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications
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