2,763 research outputs found
Rydberg excitation of a single trapped ion
We demonstrate excitation of a single trapped cold Ca ion to
Rydberg levels by laser radiation in the vacuum-ultraviolet at 122 nm
wavelength. Observed resonances are identified as 3dD to 51 F, 52 F
and 3dD to 64F. We model the lineshape and our results imply a
large state-dependent coupling to the trapping potential. Rydberg ions are of
great interest for future applications in quantum computing and simulation, in
which large dipolar interactions are combined with the superb experimental
control offered by Paul traps.Comment: 4 pages, 3 figure
Continuous Lyman-alpha generation by four-wave mixing in mercury for laser-cooling of antihydrogen
Cooling antihydrogen atoms is important for future experiments both to test
the fundamental CPT symmetry by high-resolution laser spectroscopy and also to
measure the gravitational acceleration of antimatter. Laser-cooling of
antihydrogen can be done on the strong 1S-2P transition at the wavelength of
Lyman-alpha (121.6nm). A continuous-wave laser at the Lyman-alpha wavelength
based on solid-state fundamental lasers is described. By using a two-photon and
a near one photon resonance a scan across the whole phasematching curve of the
four-wave mixing process is possible. Furthermore the influence of the beam
profile of one fundamental beam on the four-wave mixing process is studied.Comment: 4 pages, 4 figure
Greenhouse gas production in degrading ice-rich permafrost deposits in northeastern Siberia
Permafrost deposits have been a sink for atmospheric carbon for millennia. Thaw-erosional processes, however, can lead to rapid degradation of ice-rich permafrost and the release of substantial amounts of organic carbon (OC). The amount of the OC stored in these deposits and their potential to be microbially decomposed to the greenhouse gases carbon dioxide (CO2) and methane (CH4) depends on climatic and environmental conditions during deposition and the decomposition history before incorporation into the permafrost. Here, we examine potential greenhouse gas production in degrading ice-rich permafrost deposits from three locations in the northeast Siberian Laptev Sea region. The deposits span a period of about 55 kyr from the last glacial period and Holocene interglacial. Samples from all three locations were incubated under aerobic and anaerobic conditions for 134 days at 4 °C. Greenhouse gas production was generally higher in deposits from glacial periods, where 0.2–6.1% of the initially available OC was decomposed to CO2. In contrast, only 0.1–4.0% of initial OC were decomposed in permafrost deposits from the Holocene and the late glacial transition. Within the deposits from the Kargin interstadial period (Marine Isotope Stage 3), local depositional environments, especially soil moisture, also affected the preservation of OC. Sediments deposited under wet conditions contained more labile OC and thus produced more greenhouse gases than sediments deposited under drier conditions. To assess the greenhouse gas production potentials over longer periods, deposits from two locations were incubated for a total of 785 days. However, more than 50% of total CO2 production over 785 days occurred within the first 134 days under aerobic conditions while even 80% were produced over the same period under anaerobic conditions, which emphasizes the non-linearity of the OC decomposition processes. Methanogenesis was generally observed in active layer samples but only sporadically in permafrost samples and was several orders of magnitude smaller than CO2 production
Differential role of entorhinal and hippocampal nerve growth factor in short- and long-term memory modulation
Afghanistan - Primitive wellColorVolume 33, Page
High power, continuous-wave, single frequency fiber amplifier at 1091 nm and frequency doubling to 545.5 nm
We present a high power single-frequency ytterbium fiber amplifier system
with an output power of 30 W at 1091 nm. The amplifier system consists of two
stages, a preamplifier stage in which amplified spontaneous emission is
efficiently suppressed (>40 dB) and a high power amplifier with an efficiency
of 52 %. Two different approaches of frequency doubling are compared. We
achieve 8.6 W at 545.5 nm by single-pass frequency doubling in a MgO-doped
periodically poled stoichiometric LiTaO3 and up to 19.3 W at 545.5 nm by
frequency doubling with a lithium-triborate (LBO) crystal in an external
enhancement cavity
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
We report on further analysis of coherent microwave Cherenkov impulses
emitted via the Askaryan mechanism from high-energy electromagnetic showers
produced at the Stanford Linear Accelerator Center (SLAC). In this report, the
time-domain based analysis of the measurements made with a broadband (nominally
1-18 GHz) log periodic dipole array antenna is described. The theory of a
transmit-receive antenna system based on time-dependent effective height
operator is summarized and applied to fully characterize the measurement
antenna system and to reconstruct the electric field induced via the Askaryan
process. The observed radiation intensity and phase as functions of frequency
were found to agree with expectations from 0.75-11.5 GHz within experimental
errors on the normalized electric field magnitude and the relative phase; 0.039
microV/MHz/TeV and 17 deg, respectively. This is the first time this agreement
has been observed over such a broad bandwidth, and the first measurement of the
relative phase variation of an Askaryan pulse. The importance of validation of
the Askaryan mechanism is significant since it is viewed as the most promising
way to detect cosmogenic neutrino fluxes at E > 10^15 eV.Comment: 10 pages, 9 figures, accepted by Phys. Rev.
Displacement field and elastic constants in non-ideal crystals
In this work a periodic crystal with point defects is described in the
framework of linear response theory for broken symmetry states using
correlation functions and Zwanzig-Mori equations. The main results are
microscopic expressions for the elastic constants and for the coarse-grained
density, point-defect density, and displacement field, which are valid in real
crystals, where vacancies and interstitials are present. The coarse-grained
density field differs from the small wave vector limit of the microscopic
density. In the long wavelength limit, we recover the phenomenological
description of elasticity theory including the defect density.Comment: Phys Rev. B, in print (2010
High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition
We have studied the electronic structure and charge ordering (Verwey)
transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the
enhanced probing depth and the use of different surface preparations we are
able to distinguish surface and volume effects in the spectra. The pseudogap
behavior of the intrinsic spectra and its temperature dependence give evidence
for the existence of strongly bound small polarons consistent with both dc and
optical conductivity. Together with other recent structural and theoretical
results our findings support a picture in which the Verwey transition contains
elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb
interaction
Results on Plasma Focusing of High Energy Density Electron and Positron Beams
We present results from the SLAC E-150 experiment on plasma focusing of high
energy density electron and, for the first time, positron beams. We also
discuss measurements on plasma lens-induced synchrotron radiation, longitudinal
dynamics of plasma focusing, and laser- and beam-plasma interactions.Comment: LINAC 2000 paper No. THC13, Monterey, CA. Aug.21-25,2000, 3 pages, 2
figure
Early Seizure Detection Based on Cardiac Autonomic Regulation Dynamics
Epilepsy is a neurological disorder that causes changes in the autonomic nervous system. Heart rate variability (HRV) reflects the regulation of cardiac activity and autonomic nervous system tone. The early detection of epileptic seizures could foster the use of new treatment approaches. This study presents a new methodology for the prediction of epileptic seizures using HRV signals. Eigendecomposition of HRV parameter covariance matrices was used to create an input for a support vector machine (SVM)-based classifier. We analyzed clinical data from 12 patients (9 female; 3 male; age 34.5 ± 7.5 years), involving 34 seizures and a total of 55.2 h of interictal electrocardiogram (ECG) recordings. Data from 123.6 h of ECG recordings from healthy subjects were used to test false positive rate per hour (FP/h) in a completely independent data set. Our methodological approach allowed the detection of impending seizures from 5 min to just before the onset of a clinical/electrical seizure with a sensitivity of 94.1%. The FP rate was 0.49 h−1 in the recordings from patients with epilepsy and 0.19 h−1 in the recordings from healthy subjects. Our results suggest that it is feasible to use the dynamics of HRV parameters for the early detection and, potentially, the prediction of epileptic seizures
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