7,869 research outputs found
Gradient Photonic Materials Based on OneâDimensional Polymer Photonic Crystals
In nature, animals such as chameleons are wellâknown for the complex color patterns of their skin and the ability to adapt and change the color by manipulating sophisticated photonic crystal systems. Artificial gradient photonic materials are inspired by these color patterns. A concept for the preparation of such materials and their function as tunable mechanochromic materials is presented in this work. The system consists of a 1D polymer photonic crystal on a centimeter scale on top of an elastic poly(dimethylsiloxane) substrate with a gradient in stiffness. In the unstrained state, this system reveals a uniform red reflectance over the entire sample. Upon deformation, a gradient in local strain of the substrate is formed and transferred to the photonic crystal. Depending on the magnitude of this local strain, the thickness of the photonic crystal decreases continuously, resulting in a positionâdependent blue shift of the reflectance peak and hence the color in a rainbowâlike fashion. Using more sophisticated hardâsoftâhardâsoftâhard gradient elastomers enables the realization of stripeâlike reflectance patterns. Thus, this approach allows for the tunable formation of reflectance gradients and complex reflectance patterns. Envisioned applications are in the field of mechanochromic sensors, telemedicine, smart materials, and metamaterials
Exact Energy-Time Uncertainty Relation for Arrival Time by Absorption
We prove an uncertainty relation for energy and arrival time, where the
arrival of a particle at a detector is modeled by an absorbing term added to
the Hamiltonian. In this well-known scheme the probability for the particle's
arrival at the counter is identified with the loss of normalization for an
initial wave packet. Under the sole assumption that the absorbing term vanishes
on the initial wave function, we show that and , where denotes the mean
arrival time, and is the probability for the particle to be eventually
absorbed. Nearly minimal uncertainty can be achieved in a two-level system, and
we propose a trapped ion experiment to realize this situation.Comment: 8 pages, 2 figure
Observation of Feshbach resonances in an ultracold gas of Cr
We have observed Feshbach resonances in elastic collisions between ultracold
Cr atoms. This is the first observation of collisional Feshbach
resonances in an atomic species with more than one valence electron. The zero
nuclear spin of Cr and thus the absence of a Fermi-contact interaction
leads to regularly-spaced resonance sequences. By comparing resonance positions
with multi-channel scattering calculations we determine the s-wave scattering
length of the lowest potentials to be
\unit[112(14)]{a_0}, \unit[58(6)]{a_0} and -\unit[7(20)]{a_0} for S=6, 4,
and 2, respectively, where a_{0}=\unit[0.0529]{nm}.Comment: 4 pages, 2 figures, 1 tabl
Determination of the s-wave Scattering Length of Chromium
We have measured the deca-triplet s-wave scattering length of the bosonic
chromium isotopes Cr and Cr. From the time constants for
cross-dimensional thermalization in atomic samples we have determined the
magnitudes and ,
where . By measuring the rethermalization rate of Cr over a
wide temperature range and comparing the temperature dependence with the
effective-range theory and single-channel calculations, we have obtained strong
evidence that the sign of is positive. Rescaling our Cr
model potential to Cr strongly suggests that is positive,
too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and
Dipolar Relaxation in an ultra-cold Gas of magnetically trapped chromium atoms
We have investigated both theoretically and experimentally dipolar relaxation
in a gas of magnetically trapped chromium atoms. We have found that the large
magnetic moment of 6 results in an event rate coefficient for dipolar
relaxation processes of up to cms at a magnetic
field of 44 G. We present a theoretical model based on pure dipolar coupling,
which predicts dipolar relaxation rates in agreement with our experimental
observations. This very general approach can be applied to a large variety of
dipolar gases.Comment: 9 pages, 9 figure
Better Bell Inequality Violation by Collective Measurements
The standard Bell inequality experiments test for violation of local realism
by repeatedly making local measurements on individual copies of an entangled
quantum state. Here we investigate the possibility of increasing the violation
of a Bell inequality by making collective measurements. We show that
nonlocality of bipartite pure entangled states, quantified by their maximal
violation of the Bell-Clauser-Horne inequality, can always be enhanced by
collective measurements, even without communication between the parties. For
mixed states we also show that collective measurements can increase the
violation of Bell inequalities, although numerical evidence suggests that the
phenomenon is not common as it is for pure states.Comment: 7 pages, 4 figures and 1 table; references update
The NMDA antagonist dizocilpine (MK-801) reverses haloperidol-induced movement initiation deficits
The present study shows that systemic dopamine receptor blockade impaired movement initiation of rats, trained in a simple reaction time task for rapid initiation of locomotion in response to a combined optic/acoustic cue. Reaction time, movement time and the accelerative force were recorded for each initiation of locomotion. Results indicate a dose-related increase of reaction time following systemic administration of haloperidol (0.1, 0.15, 0.3 mg/kg i.p.). Measures derived from resulting force-time patterns showed a haloperidol-induced decrease (0.15 mg/kg i.p.) of the mean rate of force development, indicating a decreased initial acceleration. These effects were reversed by systemic co-administration of dizocilpine (MK-801) (0.08 mg/kg i.p.), a selective non-competitive N-methyl-d-aspartate (NMDA) antagonist. The haloperidol-induced movement initiation deficits in this task are in part comparable to akinesia seen in Parkinson's disease and their reversal by dizocilpine has implications for the treatment of this disease
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