2,241 research outputs found
Noncontact modulation calorimetry of metallic liquids in low Earth orbit
Noncontact modulation calorimetry using electromagnetic heating and radiative heat loss under ultrahigh-vacuum conditions has been applied to levitated solid, liquid, and metastable liquid samples. This experiment requires a reduced gravity environment over an extended period of time and allows the measurement of several thermophysical properties, such as the enthalpy of fusion and crystallization, specific heat, total hemispherical emissivity, and effective thermal conductivity with high precision as a function of temperature. From the results on eutectic glass forming Zr-based alloys thermodynamic functions are obtained which describe the glass-forming ability of these alloys
New Insights into Cosmic Ray induced Biosignature Chemistry in Earth-like Atmospheres
With the recent discoveries of terrestrial planets around active M-dwarfs,
destruction processes masking the possible presence of life are receiving
increased attention in the exoplanet community. We investigate potential
biosignatures of planets having Earth-like (N-O) atmospheres orbiting
in the habitable zone of the M-dwarf star AD Leo. These are bombarded by high
energetic particles which can create showers of secondary particles at the
surface. We apply our cloud-free 1D climate-chemistry model to study the
influence of key particle shower parameters and chemical efficiencies of NOx
and HOx production from cosmic rays. We determine the effect of stellar
radiation and cosmic rays upon atmospheric composition, temperature, and
spectral appearance. Despite strong stratospheric O destruction by cosmic
rays, smog O can significantly build up in the lower atmosphere of our
modeled planet around AD Leo related to low stellar UVB. NO abundances
decrease with increasing flaring energies but a sink reaction for NO with
excited oxygen becomes weaker, stabilizing its abundance. CH is removed
mainly by Cl in the upper atmosphere for strong flaring cases and not via
hydroxyl as is otherwise usually the case. Cosmic rays weaken the role of
CH in heating the middle atmosphere so that HO absorption becomes more
important. We additionally underline the importance of HNO as a possible
marker for strong stellar particle showers. In a nutshell, uncertainty in NOx
and HOx production from cosmic rays significantly influences biosignature
abundances and spectral appearance.Comment: Manuscript version after addressing all referee comments. Published
in Ap
FlexRiLoG -- A SageMath Package for Motions of Graphs
In this paper we present the SageMath package FlexRiLoG (short for flexible
and rigid labelings of graphs). Based on recent results the software generates
motions of graphs using special edge colorings. The package computes and
illustrates the colorings and the motions. We present the structure and usage
of the package
Spin gating electrical current
We use an aluminium single electron transistor with a magnetic gate to
directly quantify the chemical potential anisotropy of GaMnAs materials.
Uniaxial and cubic contributions to the chemical potential anisotropy are
determined from field rotation experiments. In performing magnetic field sweeps
we observe additional isotropic magnetic field dependence of the chemical
potential which shows a non-monotonic behavior. The observed effects are
explained by calculations based on the kinetic
exchange model of ferromagnetism in GaMnAs. Our device inverts the conventional
approach for constructing spin transistors: instead of spin-transport
controlled by ordinary gates we spin-gate ordinary charge transport.Comment: 5 pages, 4 figure
Franck-Condon Physics in A Single Trapped Ion
We propose how to explore the Franck-Condon (FC) physics via a single ion
confined in a spin-dependent potential, formed by the combination of a Paul
trap and a magnetic field gradient. The correlation between electronic and
vibrational degrees of freedom, called as electron-vibron coupling, is induced
by a nonzero gradient. For a sufficiently strong electron-vibron coupling, the
FC blockade of low-lying vibronic transitions takes place. We analyze the
feasibility of observing the FC physics in a single trapped ion, and
demonstrate various potential applications of the ionic FC physics in quantum
state engineering and quantum information processing.Comment: 7 pages, 5 figure
Fast optical control of spin in semiconductor interfacial structures
We report on a picosecond-fast optical removal of spin polarization from a
self-confined photo-carrier system at an undoped GaAs/AlGaAs interface
possessing superior long-range and high-speed spin transport properties. We
employed a modified resonant spin amplification technique with unequal
intensities of subsequent pump pulses to experimentally distinguish the
evolution of spin populations originating from different excitation laser
pulses. We demonstrate that the density of spins, which is injected into the
system by means of the optical orientation, can be controlled by reducing the
electrostatic confinement of the system using an additional generation of
photocarriers. It is also shown that the disturbed confinement recovers within
hundreds of picoseconds after which spins can be again photo-injected into the
system
Thermodynamics of Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5 and Zr57Cu15.4Ni12.6Al10Nb5 bulk metallic glass forming alloys
The differences in the thermodynamic functions between the liquid and the crystalline states of three bulk metallic glass forming alloys, Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5, and Zr57Cu15.4Ni12.6Al10Nb5, were calculated. The heat capacity was measured in the crystalline solid, the amorphous solid, the supercooled liquid, and the equilibrium liquid. Using these heat capacity data and the heats of fusion of the alloys, the differences in the thermodynamic functions between the liquid and the crystalline states were determined. The Gibbs free energy difference between the liquid and the crystalline states gives a qualitative measure of the glass forming ability of these alloys. Using the derived entropy difference, the Kauzmann temperatures for these alloys were determined
Generation of entangled photons by trapped ions in microcavities under a magnetic field gradient
We propose a potential scheme to generate entangled photons by manipulating
trapped ions embedded in two-mode microcavities, respectively, assisted by a
magnetic field gradient. By means of the spin-spin coupling due to the magnetic
field gradient and the Coulomb repulsion between the ions, we show how to
efficiently generate entangled photons by detecting the internal states of the
trapped ions. We emphasize that our scheme is advantageous to create complete
sets of entangled multi-photon states. The requirement and the experimental
feasibility of our proposal are discussed in detail.Comment: 2 Tables, 2 Figures, To appear in Phys. Rev.
- …