14,654 research outputs found
Method of measuring the thickness of radioactive thin films
Thickness monitor consists of proportional X-ray counter coupled to pulse counting system, copper filter over face of counter, rotatable collimator containing radioactive source, and rotatable shutter. Monitor can be used as integral part of neutron generator. It has been used to measure titanium tritide film thicknesses from 0.1 to 30 micrometers
Extracting joint weak values with local, single-particle measurements
Weak measurement is a new technique which allows one to describe the
evolution of postselected quantum systems. It appears to be useful for
resolving a variety of thorny quantum paradoxes, particularly when used to
study properties of pairs of particles. Unfortunately, such nonlocal or joint
observables often prove difficult to measure weakly in practice (for instance,
in optics -- a common testing ground for this technique -- strong photon-photon
interactions would be needed). Here we derive a general, experimentally
feasible, method for extracting these values from correlations between
single-particle observables.Comment: 6 page
Clock synchronization with dispersion cancellation
The dispersion cancellation feature of pulses which are entangled in
frequency is employed to synchronize clocks of distant parties. The proposed
protocol is insensitive to the pulse distortion caused by transit through a
dispersive medium. Since there is cancellation to all orders, also the effects
of slowly fluctuating dispersive media are compensated. The experimental setup
can be realized with currently available technology, at least for a proof of
principle.Comment: 4 pages, 3 figure
Identification of Decoherence-Free Subspaces Without Quantum Process Tomography
Characterizing a quantum process is the critical first step towards applying
such a process in a quantum information protocol. Full process characterization
is known to be extremely resource-intensive, motivating the search for more
efficient ways to extract salient information about the process. An example is
the identification of "decoherence-free subspaces", in which computation or
communications may be carried out, immune to the principal sources of
decoherence in the system. Here we propose and demonstrate a protocol which
enables one to directly identify a DFS without carrying out a full
reconstruction. Our protocol offers an up-to-quadratic speedup over standard
process tomography. In this paper, we experimentally identify the DFS of a
two-qubit process with 32 measurements rather than the usual 256, characterize
the robustness and efficiency of the protocol, and discuss its extension to
higher-dimensional systems.Comment: 6 pages, 5 figure
Quantum Nonlocality in Two-Photon Experiments at Berkeley
We review some of our experiments performed over the past few years on
two-photon interference. These include a test of Bell's inequalities, a study
of the complementarity principle, an application of EPR correlations for
dispersion-free time-measurements, and an experiment to demonstrate the
superluminal nature of the tunneling process. The nonlocal character of the
quantum world is brought out clearly by these experiments. As we explain,
however, quantum nonlocality is not inconsistent with Einstein causality.Comment: 16 pages including 24 figure
Oxalic, glyoxalic and pyruvic acids in eastern Pacific Ocean waters
A sensitive high performance liquid chromatographic (HPLC) technique has been used to determine the concentration and distribution of several α-keto acids and oxalic acid in seawater samples from a station (28°29′N, 128°38′W) in the eastern Pacific Ocean. Glyoxalic, pyruvic and oxalic acids were found to be present. Although the pyruvic acid profile at this station was in general featureless, the profiles for glyoxalic and oxalic acids showed variations which could be attributed to both primary production and heterotropic activity. Surface waters were found to have a combined concentration of glyoxalic and oxalic acids of ∼300 to 400 nm/liter which makes these two compounds some of the more abundant organic constituents of surface ocean waters
A preliminary longitudinal study of white matter alteration in cocaine use disorder subjects
Background Previous diffusion tensor imaging (DTI) studies have consistently shown that subjects with cocaine use disorder (CocUD) had altered white matter microstructure in the corpus callosum. It is believed that these alterations are due to preexisting factors, chronic cocaine use, or both. However, there is no published longitudinal DTI study on human cocaine users yet which could shed light on the relationship between cocaine use and DTI findings. Methods This study used a longitudinal design and DTI to test if the white matter microstructure shows quicker alteration in CocUD subjects than controls. DTI data were acquired from eleven CocUD subjects who participated a treatment study and eleven non-drug-using controls at baseline (Scan 1) and after ten weeks (Scan 2). The baseline fractional anisotropy (FA), a general measure of white matter microstucture, and the change in FA (ΔFA, equals Scan 1 FA minus Scan 2 FA) were both compared between groups. Results The two groups did not show a difference in FA at baseline. The CocUD subjects had significantly greater ΔFA than the controls in the left splenium of the corpus callosum. In CocUD subjects, greater ΔFA in this region was associated with shorter lifetime cocaine use and greater number of positive cocaine urine samples collected during the treatment. Conclusion The finding in the left splenium is consistent with previous animal studies and provide indirect evidence about the effects of chronic cocaine use on white matter alterations. The subject sample size is small, therefore the results should be treated as preliminary
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