6,852 research outputs found
A new result on the Klein-Gordon equation in the background of a rotating black hole
This short paper should serve as basis for further analysis of a previously
found new symmetry of the solutions of the wave equation in the gravitational
field of a Kerr black hole. Its main new result is the proof of essential
self-adjointness of the spatial part of a reduced normalized wave operator of
the Kerr metric in a weighted L^2-space. As a consequence, it leads to a purely
operator theoretic proof of the well-posedness of the initial value problem of
the reduced Klein-Gordon equation in that field in that L^2-space and in this
way generalizes a corresponding result of Kay (1985) in the case of the
Schwarzschild black hole. It is believed that the employed methods are
applicable to other separable wave equations
Feynman versus Bakamjian-Thomas in Light Front Dynamics
We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body
systems with light front field theories that maintain closer contact with
Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations
and other kinematical quantities belonging to various composite subsystem
frames that correspond to different loop integrals. The BT formalism knows only
the rest frame of the whole composite system, where everything is evaluated.Comment: 5 page
Pressure-dependent optical investigations of -(BEDT-TTF)I: tuning charge order and narrow gap towards a Dirac semimetal
Infrared optical investigations of -(BEDT-TTF)I have been
performed in the spectral range from 80 to 8000~cm down to temperatures
as low as 10~K by applying hydrostatic pressure. In the metallic state, ~K, we observe a 50\% increase in the Drude contribution as well as the
mid-infrared band due to the growing intermolecular orbital overlap with
pressure up to 11~kbar. In the ordered state, , we extract how
the electronic charge per molecule varies with temperature and pressure:
Transport and optical studies demonstrate that charge order and metal-insulator
transition coincide and consistently yield a linear decrease of the transition
temperature by ~K/kbar. The charge disproportionation
diminishes by /kbar and the optical gap between
the bands decreases with pressure by -47~cm/kbar. In our high-pressure
and low-temperature experiments, we do observe contributions from the massive
charge carriers as well as from massless Dirac electrons to the low-frequency
optical conductivity, however, without being able to disentangle them
unambiguously.Comment: 13 pages, 17 figures, submitted to Phys. Rev.
Neutron Charge Radius: Relativistic Effects and the Foldy Term
The neutron charge radius is studied within a light-front model with
different spin coupling schemes and wave functions. The cancellation of the
contributions from the Foldy term and Dirac form factor to the neutron charge
form factor is verified for large nucleon sizes and it is independent of the
detailed form of quark spin coupling and wave function. For the physical
nucleon our results for the contribution of the Dirac form factor to the
neutron radius are insensitive to the form of the wave function while they
strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.
Doppler-tuned Bragg Spectroscopy of Excited Levels in He-Like Uranium: a discussion of the uncertainty contributions
We present the uncertainty discussion of a recent experiment performed at the
GSI storage ring ESR for the accurate energy measurement of the He-like uranium
1s2p3P2- 1s2s3S1 intra-shell transition. For this propose we used a Johann-type
Bragg spectrometer that enables to obtain a relative energy measurement between
the He-like uranium transition, about 4.51 keV, and a calibration x-ray source.
As reference, we used the Ka fluorescence lines of zinc and the Li-like uranium
1s22p2P3/2 - 1 s22s 2S1/2 intra-shell transition from fast ions stored in the
ESR. A comparison of the two different references, i.e., stationary and moving
x-ray source, and a discussion of the experimental uncertainties is presented
Doppler-tuned Bragg Spectroscopy of Excited Levels in He-Like Uranium: a discussion of the uncertainty contributions
We present the uncertainty discussion of a recent experiment performed at the
GSI storage ring ESR for the accurate energy measurement of the He-like uranium
1s2p3P2- 1s2s3S1 intra-shell transition. For this propose we used a Johann-type
Bragg spectrometer that enables to obtain a relative energy measurement between
the He-like uranium transition, about 4.51 keV, and a calibration x-ray source.
As reference, we used the Ka fluorescence lines of zinc and the Li-like uranium
1s22p2P3/2 - 1 s22s 2S1/2 intra-shell transition from fast ions stored in the
ESR. A comparison of the two different references, i.e., stationary and moving
x-ray source, and a discussion of the experimental uncertainties is presented
Experimental investigation of the asymmetric spectroscopic characteristics of electron- and hole-doped cuprates
Quasiparticle tunneling spectroscopic studies of electron- (n-type) and hole-doped (p-type) cuprates reveal that the pairing symmetry, pseudogap phenomenon and spatial homogeneity of the superconducting order parameter are all non-universal. We compare our studies of p-type YBa2Cu3O7-delta and n-type infinite-layer Sr(0.9)Ln(0.1)CuO(2) (Ln = La, Gd) systems with results from p-type Bi2Sr2CaCu2Ox and n-type one-layer Nd1.85Ce0.15CuO4 cuprates, and attribute various non-universal behavior to different competing orders in p-type and n-type cuprates
Doppler-tuned Bragg Spectroscopy of Excited Levels in He-Like Uranium: a discussion of the uncertainty contributions
We present the uncertainty discussion of a recent experiment performed at the
GSI storage ring ESR for the accurate energy measurement of the He-like uranium
1s2p3P2- 1s2s3S1 intra-shell transition. For this propose we used a Johann-type
Bragg spectrometer that enables to obtain a relative energy measurement between
the He-like uranium transition, about 4.51 keV, and a calibration x-ray source.
As reference, we used the Ka fluorescence lines of zinc and the Li-like uranium
1s22p2P3/2 - 1 s22s 2S1/2 intra-shell transition from fast ions stored in the
ESR. A comparison of the two different references, i.e., stationary and moving
x-ray source, and a discussion of the experimental uncertainties is presented
Medical Diagnostic Ultrasound
As early as 250 BCE, captains of ancient Greek ships would drop lead weights overboard to provide an estimate of water depth. They would count until those “sounders” produced an audible thud and in that way measure the propagation time of the falling weight. Even though the practice has given way to other technologies for sounding, one still hears the phrase “to sound something out.” In the 17th century, Isaac Newton became fascinated with sound propagation and was one of the first to describe relationships between the speed of sound and measurable properties of the propagation medium, such as density and pressure. Section 8 of Book 2 of the Principia, for example, is devoted to “the motion propagated through fluids” and includes the proposition that the sound speed is given by the square root of the ratio of the “elastic force” to the density of the medium
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