167 research outputs found
Phonon absorption-spectroscopy in the presence of strong elastic phonon scattering
In this work we show that in the presence of a strong phonon scattering background absorption structures can only be well resolved by reducing sample thickness to the phonon mean free path. This mean free path can be determined by analyzing the pulse shape of 285 GHz phonons. By reducing sample thickness to the appropriate value of 0,3mm the 21,2 cm -1 crystalline field transition in CaF 2:Er 3+ could be evaluated with the very high resolution of 5 GHz. In experiments performed on a 1mm thick LaF 3 Er 3+ sample we observed an absoption line at 14,2 cm -1 not visible in FIR absorption measurements
Phonon deficit effect and solid state refrigerators based on superconducting tunnel junctions
Thin film devices have the advantage of being extremely compact, operate in a
continuous mode, dissipate little power, and can easily be integrated in
cryogenic detectors. Motivated by such possibilities, we investigate the phonon
deficit effect in thin film (superconductor--insulator--superconductor)
and tunnel junctions. Under certain circumstances, the phonon absorption
spectra of such tunnel junctions have spectral windows of phonon
absorption/emission. We propose to use phonon filters to select the phonon
absorbtion windows and thus to enhance the cooling effect. Membranes attached
to such tunnel junctions can be cooled in this way more effectively. We discuss
a particular superlattice design of corresponding phonon filters.Comment: 8 pages 7 figure
Spectral dependence of the Kapitza resistance between O,5 K and 2,3 K
Summarizing, we observed strongly enhanced phonon transport from a real solid into 4 He starting at about 85 GHz which is independent of the He gas pressure up to liquid helium. With the isotope 3 He the onset frequency for enhanced phonon transport shifts to 100 GHz. The threshold frequencies are almost independent of the He temperature in the range between 0.5 K and 2.3 K. Only slight shifts to lower frequencies with decreasing He temperature have been observed. No significant influence of the generator material (Sn, Al, SiO) or the generator preparation on the onset frequency has been observed. Moreover at low temperatures and thin He films we observed an additional structure which might be interpreted as film thickness resonances in the He film layer on the generator
Enhancement of the Kapitza conductance at 0.32 meV phonon energy
Using quasimonochromatic relaxation phonons emitted by superconducting tunneling functions, the phonon transfer through real solid-liquid helium interfaces was tested. We found an enhancement of the energy transmission if the incident phonons exceed the threshold energy Eo = 0.32 meV. This sharp threshold energy shifts to 0.42 meV if the lighter isotope 3 He is used
Phonon Universal Transmission Fluctuations and Localization in Semiconductor Superlattices with a Controlled Degree of Order
We study both analytically and numerically phonon transmission fluctuations
and localization in partially ordered superlattices with correlations among
neighboring layers. In order to generate a sequence of layers with a varying
degree of order we employ a model proposed by Hendricks and Teller as well as
partially ordered versions of deterministic aperiodic superlattices. By
changing a parameter measuring the correlation among adjacent layers, the
Hendricks- Teller superlattice exhibits a transition from periodic ordering,
with alterna- ting layers, to the phase separated opposite limit; including
many intermediate arrangements and the completely random case. In the partially
ordered versions of deterministic superlattices, there is short-range order
(among any conse- cutive layers) and long range disorder, as in the N-state
Markov chains. The average and fluctuations in the transmission, the
backscattering rate, and the localization length in these multilayered systems
are calculated based on the superlattice structure factors we derive
analytically. The standard deviation of the transmission versus the average
transmission lies on a {\it universal\/} curve irrespective of the specific
type of disorder of the SL. We illustrate these general results by applying
them to several GaAs-AlAs superlattices for the proposed experimental
observation of phonon universal transmission fluctuations.Comment: 16-pages, Revte
Optogenetic Activation of A11 Region Increases Motor Activity
Limbic brain regions drive goal-directed behaviors. These behaviors often require dynamic motor responses, but the functional connectome of limbic structures in the diencephalon that control locomotion is not well known. The A11 region, within the posterior diencephalon has been postulated to contribute to motor function and control of pain. Here we show that the A11 region initiates movement. Photostimulation of channelrhodopsin 2 (ChR2) transfected neurons in A11 slice preparations showed that neurons could follow stimulation at frequencies of 20 Hz. Our data show that photostimulation of ChR2 transfected neurons in the A11 region enhances motor activity often leading to locomotion. Using vGluT2-reporter and vGAT-reporter mice we show that the A11 tyrosine hydroxylase positive (TH) dopaminergic neurons are vGluT2 and vGAT negative. We find that in addition to dopaminergic neurons within the A11 region, there is another neuronal subtype which expresses the monoenzymatic aromatic L-amino acid decarboxylase (AADC), but not TH, a key enzyme involved in the synthesis of catecholamines including dopamine. This monoaminergic-based motor circuit may be involved in the control of motor behavior as part of a broader diencephalic motor region
"Equine Asthmaâ â integrative biologic relevance of a recently proposed nomenclature
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