3,701 research outputs found
Exact averages of central values of triple product L-functions
We obtain exact formulas for central values of triple product L-functions averaged over newforms of weight 2 and prime level. We apply these formulas to non-vanishing problems. This paper uses a period formula for the triple product L-function proved by Gross and Kudla
Permalloy-based carbon nanotube spin-valve
In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy,
forms contacts to carbon nanotubes (CNTs) that meet the requirements for the
injection and detection of spin-polarized currents in carbon-based spintronic
devices. We establish the material quality and magnetization properties of Py
strips in the shape of suitable electrical contacts and find a sharp
magnetization switching tunable by geometry in the anisotropic
magnetoresistance (AMR) of a single strip at cryogenic temperatures. In
addition, we show that Py contacts couple strongly to CNTs, comparable to Pd
contacts, thereby forming CNT quantum dots at low temperatures. These results
form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance
switchings in the tunneling magnetoresistance, which directly correspond to the
magnetization reversals in the individual contacts observed in AMR experiments.Comment: 3 page
Analysis of the electron transfer from Pheo− to QA in PS II membrane fragments from spinach by time resolved 325 nm absorption changes in the picosecond domain
AbstractAbsorption changes at 325 nm (ΔA325) induced by 15 ps laser flashes (λ = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (P I Q−A) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 × 1014 photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (ΔAclosed325) from those in open RCs (ΔAopen325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo− with a time constant of about 350 ± 100 ps
Exact semi-relativistic model for ionization of atomic hydrogen by electron impact
We present a semi-relativistic model for the description of the ionization
process of atomic hydrogen by electron impact in the first Born approximation
by using the Darwin wave function to describe the bound state of atomic
hydrogen and the Sommerfeld-Maue wave function to describe the ejected
electron. This model, accurate to first order in in the relativistic
correction, shows that, even at low kinetic energies of the incident electron,
spin effects are small but not negligible. These effects become noticeable with
increasing incident electron energies. All analytical calculations are exact
and our semi-relativistic results are compared with the results obtained in the
non relativistic Coulomb Born Approximation both for the coplanar asymmetric
and the binary coplanar geometries.Comment: 8 pages, 6 figures, Revte
Measurement of electron-hole friction in an n-doped GaAs/AlGaAs quantum well using optical transient grating spectroscopy
We use phase-resolved transient grating spectroscopy to measure the drift and
diffusion of electron-hole density waves in a semiconductor quantum well. The
unique aspects of this optical probe allow us to determine the frictional force
between a two-dimensional Fermi liquid of electrons and a dilute gas of holes.
Knowledge of electron-hole friction enables prediction of ambipolar dynamics in
high-mobility electron systems.Comment: to appear in PR
Thermal lensing-induced bifocusing of spatial solitons in Kerr-type optical media
Thermo-optical effects cause a bifocusing of incoming beams in optical media,
due to the birefringence created by a thermal lens that can resolve the
incoming beams into two-component signals of different polarizations. We
propose a non-perturbative theoretical description of the process of formation
of double-pulse solitons in Kerr optical media with a thermally-induced
birefringence, based on solving simultaneously the heat equation and the
propagation equation for a beam in a one-dimensional medium with uniform heat
flux load. By means of a non-isospectral Inverse Scattering Transform assuming
an initial solution with a pulse shape, a one-soliton solution to the wave
equation is obtained that represents a double-pulse beam which characteristic
properties depend strongly on the profile of heat spatial distribution.Comment: 5 pages, 2 figure
A light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions
We perform a gauge-transformation on the time-dependent Dirac equation
describing the evolution of an electron in a heavy-ion collision to remove the
explicit dependence on the long-range part of the interaction. We solve, in an
ultra-relativistic limit, the gauged-transformed Dirac equation using
light-front variables and a light-fronts representation, obtaining
non-perturbative results for the free pair-creation amplitudes in the collider
frame. Our result reproduces the result of second-order perturbation theory in
the small charge limit while non-perturbative effects arise for realistic
charges of the ions.Comment: 39 pages, Revtex, 7 figures, submitted to PR
Characterizing Quantum Microwave Radiation and its Entanglement with Superconducting Qubits using Linear Detectors
Recent progress in the development of superconducting circuits has enabled
the realization of interesting sources of nonclassical radiation at microwave
frequencies. Here, we discuss field quadrature detection schemes for the
experimental characterization of itinerant microwave photon fields and their
entanglement correlations with stationary qubits. In particular, we present
joint state tomography methods of a radiation field mode and a two-level
system. Including the case of finite quantum detection efficiency, we relate
measured photon field statistics to generalized quasi-probability distributions
and statistical moments for one-channel and two-channel detection. We also
present maximum-likelihood methods to reconstruct density matrices from
measured field quadrature histograms. Our theoretical investigations are
supported by the presentation of experimental data, for which microwave quantum
fields beyond the single-photon and Gaussian level have been prepared and
reconstructed.Comment: 14 pages, 5 figure
A Mechanical Mass Sensor with Yoctogram Resolution
Nanoelectromechanical systems (NEMS) have generated considerable interest as
inertial mass sensors. NEMS resonators have been used to weigh cells,
biomolecules, and gas molecules, creating many new possibilities for biological
and chemical analysis [1-4]. Recently, NEMS-based mass sensors have been
employed as a new tool in surface science in order to study e.g. the phase
transitions or the diffusion of adsorbed atoms on nanoscale objects [5-7]. A
key point in all these experiments is the ability to resolve small masses. Here
we report on mass sensing experiments with a resolution of 1.7 yg (1 yg =
10^-24 g), which corresponds to the mass of one proton, or one hydrogen atom.
The resonator is made of a ~150 nm long carbon nanotube resonator vibrating at
nearly 2 GHz. The unprecedented level of sensitivity allows us to detect
adsorption events of naphthalene molecules (C10H8) and to measure the binding
energy of a Xe atom on the nanotube surface (131 meV). These ultrasensitive
nanotube resonators offer new opportunities for mass spectrometry,
magnetometry, and adsorption experiments.Comment: submitted version of the manuscrip
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