2,265 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
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
Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs
We investigate the detectability of atmospheric spectral features of
Earth-like planets in the habitable zone (HZ) around M dwarfs with the future
James Webb Space Telescope (JWST). We use a coupled 1D climate-chemistry-model
to simulate the influence of a range of observed and modelled M-dwarf spectra
on Earth-like planets. The simulated atmospheres served as input for the
calculation of the transmission spectra of the hypothetical planets, using a
line-by-line spectral radiative transfer model. To investigate the
spectroscopic detectability of absorption bands with JWST we further developed
a signal-to-noise ratio (S/N) model and applied it to our transmission spectra.
High abundances of CH and HO in the atmosphere of Earth-like planets
around mid to late M dwarfs increase the detectability of the corresponding
spectral features compared to early M-dwarf planets. Increased temperatures in
the middle atmosphere of mid- to late-type M-dwarf planets expand the
atmosphere and further increase the detectability of absorption bands. To
detect CH, HO, and CO in the atmosphere of an Earth-like planet
around a mid to late M dwarf observing only one transit with JWST could be
enough up to a distance of 4 pc and less than ten transits up to a distance of
10 pc. As a consequence of saturation limits of JWST and less pronounced
absorption bands, the detection of spectral features of hypothetical Earth-like
planets around most early M dwarfs would require more than ten transits. We
identify 276 existing M dwarfs (including GJ 1132, TRAPPIST-1, GJ 1214, and LHS
1140) around which atmospheric absorption features of hypothetical Earth-like
planets could be detected by co-adding just a few transits. We show that using
transmission spectroscopy, JWST could provide enough precision to be able to
partly characterise the atmosphere of Earth-like TESS planets around mid to
late M dwarfs.Comment: 18 pages, 10 figure
Low voltage control of ferromagnetism in a semiconductor p-n junction
The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.Comment: 11 pages, 4 figure
curled encodes the Drosophila homolog of the vertebrate circadian deadenylase nocturnin.
Absence of skew scattering in two-dimensional systems: Testing the origins of the anomalous Hall effect
We study the anomalous Hall conductivity in spin-polarized, asymmetrically
confined two-dimensional electron and hole systems, focusing on skew-scattering
contributions to the transport. We find that the skew scattering, principally
responsible for the extrinsic contribution to the anomalous Hall effect,
vanishes for the two-dimensional electron system if both chiral Rashba subbands
are partially occupied, and vanishes always for the two-dimensional hole gas
studied here, regardless of the band filling. Our prediction can be tested with
the proposed coplanar two-dimensional electron/hole gas device and can be used
as a benchmark to understand the crossover from the intrisic to the extrinsic
anomalous Hall effect.Comment: 4 pages, 2 figures include
Association of Botryosphaeriaceae grapevine trunk disease fungi with the reproductive structures of Vitis vinifera
Several species belonging to the Botryosphaeriaceae were isolated from grapevine (Vitis vinifera) tissue other than wood during a survey of two vineyards planted to cultivars ‘Chardonnay’ and ‘Shiraz’ in the Hunter Valley, New South Wales, Australia over the 2007/08 and 2008/09 growing seasons. A total of 188 isolates corresponding to nine different species of Diplodia, Dothiorella and Neofusicoccum anamorphs were isolated from dormant buds, flowers, pea-sized berries and mature berries prior to harvest in addition to 142 isolates from the trunks of the same vines. Furthermore, the occurrence of Dothiorella viticola, Diplodia mutila and Neofusicoccum australe is reported here for the first time from grapevines in the Hunter Valley. These findings may provide important information for the management and spread of Botryosphaeriaceae in vineyards where they are considered serious wood-invading pathogens. Botryosphaeriaceae are occasionally found on bunches, however, until now they have not directly been related to bunch rots. Control strategies for trunk diseases caused by Botryosphaeriaceae are currently limited to remedial surgery and wound protection. These strategies do not consider other grapevine tissue as potential inoculum sources for infection of Botryosphaeriaceae in the vineyard.
Edge spin accumulation in semiconductor two-dimensional hole gases
The controlled generation of localized spin densities is a key enabler of
semiconductor spintronics In this work, we study spin Hall effect induced edge
spin accumulation in a two-dimensional hole gas with strong spin orbit
interactions. We argue that it is an intrinsic property, in the sense that it
is independent of the strength of disorder scattering. We show numerically that
the spin polarization near the edge induced by this mechanism can be large, and
that it becomes larger and more strongly localized as the spin-orbit coupling
strength increases, and is independent of the width of the conducting strip
once this exceeds the elastic scattering mean-free-path. Our experiments in
two-dimensional hole gas microdevices confirm this remarkable spin Hall effect
phenomenology. Achieving comparable levels of spin polarization by external
magnetic fields would require laboratory equipment whose physical dimensions
and operating electrical currents are million times larger than those of our
spin Hall effect devices.Comment: 6 pages, 5 figure
Quantum Spin Hall Insulator State in HgTe Quantum Wells
Recent theory predicted that the Quantum Spin Hall Effect, a fundamentally
novel quantum state of matter that exists at zero external magnetic field, may
be realized in HgTe/(Hg,Cd)Te quantum wells. We have fabricated such sample
structures with low density and high mobility in which we can tune, through an
external gate voltage, the carrier conduction from n-type to the p-type,
passing through an insulating regime. For thin quantum wells with well width d
< 6.3 nm, the insulating regime shows the conventional behavior of vanishingly
small conductance at low temperature. However, for thicker quantum wells (d >
6.3 nm), the nominally insulating regime shows a plateau of residual
conductance close to 2e^2/h. The residual conductance is independent of the
sample width, indicating that it is caused by edge states. Furthermore, the
residual conductance is destroyed by a small external magnetic field. The
quantum phase transition at the critical thickness, d = 6.3 nm, is also
independently determined from the magnetic field induced insulator to metal
transition. These observations provide experimental evidence of the quantum
spin Hall effect.Comment: 16 pages, 5 figure
Quantum Zeno dynamics of a field in a cavity
We analyze the quantum Zeno dynamics that takes place when a field stored in
a cavity undergoes frequent interactions with atoms. We show that repeated
measurements or unitary operations performed on the atoms probing the field
state confine the evolution to tailored subspaces of the total Hilbert space.
This confinement leads to non-trivial field evolutions and to the generation of
interesting non-classical states, including mesoscopic field state
superpositions. We elucidate the main features of the quantum Zeno mechanism in
the context of a state-of-the-art cavity quantum electrodynamics experiment. A
plethora of effects is investigated, from state manipulations by phase space
tweezers to nearly arbitrary state synthesis. We analyze in details the
practical implementation of this dynamics and assess its robustness by
numerical simulations including realistic experimental imperfections. We
comment on the various perspectives opened by this proposal
- …