3,943 research outputs found
Statistical uncertainty in quantum optical photodetection measurements
We present a complete statistical analysis of quantum optical measurement
schemes based on photodetection. Statistical distributions of quantum
observables determined from a finite number of experimental runs are
characterized with the help of the generating function, which we derive using
the exact statistical description of raw experimental outcomes. We use the
developed formalism to point out that the statistical uncertainty results in
substantial limitations of the determined information on the quantum state:
though a family of observables characterizing the quantum state can be safely
evaluated from experimental data, its further use to obtain the expectation
value of some operators generates exploding statistical errors. These issues
are discussed using the example of phase-insensitive measurements of a single
light mode. We study reconstruction of the photon number distribution from
photon counting and random phase homodyne detection. We show that utilization
of the reconstructed distribution to evaluate a simple well-behaved observable,
namely the parity operator, encounters difficulties due to accumulation of
statistical errors. As the parity operator yields the Wigner function at the
phase space origin, this example also demonstrates that transformation between
various experimentally determined representations of the quantum state is a
quite delicate matter.Comment: 18 pages REVTeX, 7 figures included using epsf. Few minor corrections
made, clarified conclusion
Maximum likelihood estimation of photon number distribution from homodyne statistics
We present a method for reconstructing the photon number distribution from
the homodyne statistics based on maximization of the likelihood function
derived from the exact statistical description of a homodyne experiment. This
method incorporates in a natural way the physical constraints on the
reconstructed quantities, and the compensation for the nonunit detection
efficiency.Comment: 3 pages REVTeX. Final version, to appear in Phys. Rev. A as a Brief
Repor
Light particle spectra from 35 MeV/nucleon 12C-induced reactions on 197Au
Energy spectra for p, d, t, 3He, 4He, and 6He from the reaction 12C+197Au at 35 MeV/nucleon are presented. A common intermediate rapidity source is identified using a moving source fit to the spectra that yields cross sections which are compared to analogous data at other bombarding energies and to several different models. The excitation function of the composite to proton ratios is compared with quantum statistical, hydrodynamic, and thermal models
Cinderella Strings
We investigate recent claims concerning a new class of cosmic string
solutions in the Weinberg-Salam model. They have the general form of previously
discussed semi-local and electroweak strings, but are modified by the presence
of a non-zero W-condensate in the core of the string. We explicitly construct
such solutions for arbitrary values of the winding number . We then prove
that they are gauge equivalent to bare electroweak strings with winding number
. We also develop new asymptotic expressions for large- strings.Comment: 11 pages, harvmac (b) and epsf (2 figures uuencoded
Balance of human choline kinase isoforms is critical for cell cycle regulation: Implications for the development of choline kinase-targeted cancer therapy.
The enzyme choline kinase (CK), which catalyzes the phosphorylation of choline to phosphorylcholine in the presence of ATP, has an essential role in the biosynthesis of phosphatidylcholine, the major constituent of all mammalian cell membranes. CK is encoded by two separate genes expressing the three isoforms CKα1, CKα2 and CKβ that are active as homodimeric or heterodimeric species. Metabolic changes observed in various cancer cell lines and tumors have been associated with differential and marked up-regulation of the CKα genes, and specific inhibition of CKα activity has been proposed as a potential anti-cancer strategy. As a result, less attention has been given to CKβ and its interaction with CKα. With the aim of profiling the intracellular roles of CKα and CKβ, we used RNA interference (RNAi) as a molecular approach to down-regulate the expression of CK in HeLa cells. Individual and simultaneous RNAi-based silencing of the CK α and β isoforms was achieved using different combinations of knockdown strategies. Efficient knockdown was confirmed by immunodetection using our isoform-specific antibodies and by quantitative real-time PCR. Our analyses of the phenotypic consequences of CK depletion showed the expected lethal effect of CKα knockdown. However, CKβ- and CKα + CKβ-silenced cells had no aberrant phenotype. Therefore, our results support the hypothesis that the balance of the α and β isoforms is critical for cancer cell survival. The suppression of the cancer cell killing effect of CKα silencing by simultaneous knockdown of both isoforms implies that a more effective CK-based anti-cancer strategy can be achieved by reducing cross-reactivity with CKβ
Measurement of complex fragments and clues to the entropy production from 42-137-MeV/nucleon Ar + Au
Intermediate-rapidity fragments with A=1-14 emitted from 42-137-MeV/nucleon Ar + Au have been measured. Evidence is presented that these fragments arise from a common moving source. Entropy values are extracted from the mass distributions by use of quantum statistical and Hauser-Feshbach theories. The extracted entropy values of S/A≈2-2.4 are much smaller than the values expected from measured deuteron-to-proton ratios, but are still considerably higher than theoretically predicted values
Sublinear Estimation of Weighted Matchings in Dynamic Data Streams
This paper presents an algorithm for estimating the weight of a maximum
weighted matching by augmenting any estimation routine for the size of an
unweighted matching. The algorithm is implementable in any streaming model
including dynamic graph streams. We also give the first constant estimation for
the maximum matching size in a dynamic graph stream for planar graphs (or any
graph with bounded arboricity) using space which also
extends to weighted matching. Using previous results by Kapralov, Khanna, and
Sudan (2014) we obtain a approximation for general graphs
using space in random order streams, respectively. In
addition, we give a space lower bound of for any
randomized algorithm estimating the size of a maximum matching up to a
factor for adversarial streams
Toward Design of Novel Materials for Organic Electronics
Materials for organic electronics are presently used in prominent applications, such as displays in mobile devices, while being intensely researched for other purposes, such as organic photovoltaics, large-area devices, and thin-film transistors. Many of the challenges to improve and optimize these applications are material related and there is a nearly infinite chemical space that needs to be explored to identify the most suitable material candidates. Established experimental approaches struggle with the size and complexity of this chemical space. Herein, the development of simulation methods is addressed, with a particular emphasis on predictive multiscale protocols, to complement experimental research in the identification of novel materials and illustrate the potential of these methods with a few prominent recent applications. Finally, the potential of machine learning and methods based on artificial intelligence is discussed to further accelerate the search for new materials
- …